Using Airborne Radar Stratigraphy to Model Surface Accumulation Anomaly and Basal Control over Deformed Basal Ice in Greenland

NASA Astrophysics Data System (ADS)

Das, I.; Bell, R. E.; Creyts, T. T.; Wolovick, M.

2013-12-01

Large deformed ice structures have been imaged at the base of northern Greenland ice sheet by IceBridge airborne radar. Numerous deformed structures lie along the base of both Petermann Glacier and Northeast Ice stream catchments covering 10-13% of the catchment area. These structures may be combinations of basal freeze-on and folded ice that overturns and inverts stratigraphy. In the interior, where the ice velocity is low, the radar imaged height of the deformed structures are frequently a significant fraction of the ice thickness. They are related to basal freeze on and stick-slip at the base of the ice sheet and may be triggered by subglacial water, sediments or local geological conditions. The larger ones (at times up to 700 m thick and 140 km long) perturb the ice stratigraphy and create prominent undulations on the ice surface and modify the local surface mass balance. Here, we investigate the relationship between the deformed structures and surface processes using shallow and deep ice radar stratigraphy. The surface undulations caused by the deformed structures modulate the pattern of local surface snow accumulation. Using normalized differences of several near-surface stratigraphic layers, we have calculated the accumulation anomaly over these deformed structures. The accumulation anomalies can be as high as 20% of the local surface accumulation over some of the larger surface depressions caused by these deformed structures. We observe distinct differences in the phases of the near-surface internal layers on the Petermann and Northeast catchments. These differences indicate that the deformed bodies over Petermann are controlled by conditions at the bed different from the Northeast Ice stream. The distinctly different near-surface stratigraphy over the deformed structures in the Petermann and Northeast catchments have opened up a number of questions including their formation and how they influence the ice dynamics, ice stratigraphy and surface mass balance. In this study we will model the different physical conditions at the bed and ice rheology from their distinct signatures in the near-surface strata. The results will identify the distinct mechanisms that form these bodies and their control over the surface morphology and snow accumulation.

Electrical Double Layer-Induced Ion Surface Accumulation for Ultrasensitive Refractive Index Sensing with Nanostructured Porous Silicon Interferometers.

PubMed

Mariani, Stefano; Strambini, Lucanos Marsilio; Barillaro, Giuseppe

2018-03-23

Herein, we provide the first experimental evidence on the use of electrical double layer (EDL)-induced accumulation of charged ions (using both Na + and K + ions in water as the model) onto a negatively charged nanostructured surface (e.g., thermally growth SiO 2 )-Ion Surface Accumulation, ISA-as a means of improving performance of nanostructured porous silicon (PSi) interferometers for optical refractometric applications. Nanostructured PSi interferometers are very promising optical platforms for refractive index sensing due to PSi huge specific surface (hundreds of m 2 per gram) and low preparation cost (less than $0.01 per 8 in. silicon wafer), though they have shown poor resolution ( R) and detection limit (DL) (on the order of 10 -4 -10 -5 RIU) compared to other plasmonic and photonic platforms ( R and DL on the order of 10 -7 -10 -8 RIU). This can be ascribed to both low sensitivity and high noise floor of PSi interferometers when bulk refractive index variation of the solution infiltrating the nanopores either approaches or is below 10 -4 RIU. Electrical double layer-induced ion surface accumulation (EDL-ISA) on oxidized PSi interferometers allows the interferometer output signal (spectral interferogram) to be impressively amplified at bulk refractive index variation below 10 -4 RIU, increasing, in turn, sensitivity up to 2 orders of magnitude and allowing reliable measurement of refractive index variations to be carried out with both DL and R of 10 -7 RIU. This represents a 250-fold-improvement (at least) with respect to the state-of-the-art literature on PSi refractometers and pushes PSi interferometer performance to that of state-of-the-art ultrasensitive photonics/plasmonics refractive index platforms.

A revised surface age for the North Polar Layered Deposits of Mars

USGS Publications Warehouse

Landis, Margaret E.; Byrne, Shane; Daubar, Ingrid J.; Herkenhoff, Kenneth E.; Dundas, Colin M.

2016-01-01

The North Polar Layered Deposits (NPLD) of Mars contain a complex stratigraphy that has been suggested to retain a record of past eccentricity- and obliquity-forced climate changes. The surface accumulation rate in the current climate can be constrained by the crater retention age. We scale NPLD crater diameters to account for icy target strength and compare surface age using a new production function for recent small impacts on Mars to the previously used model of Hartmann (2005). Our results indicate that ice is accumulating in these craters several times faster than previously thought, with a 100 m diameter crater being completely infilled within centuries. Craters appear to have a diameter-dependent lifetime, but the data also permit a complete resurfacing of the NPLD at ~1.5 ka.

SOFIA Science Imagery

NASA Image and Video Library

2017-09-14

SCI2017_0003: The column of material at and just below the surface of dwarf planet Ceres (box) – the top layer contains anhydrous (dry) pyroxene dust accumulated from space mixed in with native hydrous (wet) dust, carbonates, and water ice. (Bottom) Cross section of Ceres showing the surface layers that are the subject of this study plus a watery mantle and a rocky-metallic core. Credit: Pierre Vernazza, LAM–CNRS/AMU

Effect of greenhouse vegetable farming duration on Zinc accumulation in Northeast China

NASA Astrophysics Data System (ADS)

Wang, Jun; Yu, Peiying; Cui, Shuang; Chen, Xin; Shi, Yi

2018-02-01

Greenhouse vegetable production (GVP) has rapidly expanded, and reqiures more attention due to its heavy metal contamination. In this study, different cultivation greenhouses of 1, 2, 3, 5 and 13 years were selected to investigate the effects of GVP duration on Zn accumulation. The results revealed high Zn (total Zn and available Zn) accumulation in GVP surface layers (0-20 cm), and Zn contents in 0-20 cm soil layers were positively correlated with GVP duration (P<0.01). Zn accumulation was mainly attributed to manure fertilizer application due to higher concentrations of Zn in manures. For greenhouse sustainability, reduction of manure application and reasonable use of passivation materials may alleviate metal phytoavailability and the health risk.

Assessment of heavy metals contamination in surface layers of Roztocze National Park forest soils (SE Poland) by indices of pollution.

PubMed

Mazurek, Ryszard; Kowalska, Joanna; Gąsiorek, Michał; Zadrożny, Paweł; Józefowska, Agnieszka; Zaleski, Tomasz; Kępka, Wojciech; Tymczuk, Maryla; Orłowska, Kalina

2017-02-01

In most cases, in soils exposed to heavy metals accumulation, the highest content of heavy metals was noted in the surface layers of the soil profile. Accumulation of heavy metals may occur both as a result of natural processes as well as anthropogenic activities. The quality of the soil exposed to heavy metal contamination can be evaluated by indices of pollution. On the basis of determined heavy metals (Pb, Zn, Cu, Mn, Ni and Cr) in the soils of Roztocze National Park the following indices of pollution were calculated: Enrichment Factor (EF), Geoaccumulation Index (I geo ), Nemerow Pollution Index (PI Nemerow ) and Potential Ecological Risk (RI). Additionally, we introduced and calculated the Biogeochemical Index (BGI), which supports determination of the ability of the organic horizon to accumulate heavy metals. A tens of times higher content of Pb, Zn, Cu and Mn was found in the surface layers compared to their content in the parent material. This distribution of heavy metals in the studied soils was related to the influence of anthropogenic pollution (both local and distant sources of emission), as well as soil properties such as pH, organic carbon and total nitrogen content. Copyright © 2016 Elsevier Ltd. All rights reserved.

New insights into comparison between synthetic and practical municipal wastewater in cake layer characteristic analysis of membrane bioreactor.

PubMed

Zhou, Lijie; Zhuang, Wei-Qin; Wang, Xin; Yu, Ke; Yang, Shufang; Xia, Siqing

2017-11-01

In previous studies, cake layer analysis in membrane bioreactor (MBR) was both carried out with synthetic and practical municipal wastewater (SMW and PMW), leading to different results. This study aimed to identify the comparison between SMW and PMW in cake layer characteristic analysis of MBR. Two laboratory-scale anoxic/oxic MBRs were operated for over 90days with SMW and PMW, respectively. Results showed that PMW led to rough cake layer surface with particles, and the aggravation of cake layer formation with thinner and denser cake layer. Additionally, inorganic components, especially Si and Al, in PMW accumulated into cake layer and strengthened the cake layer structure, inducing severer biofouling. However, SMW promoted bacterial metabolism during cake layer formation, thus aggravated the accumulation of organic components into cake layer. Therefore, SMW highlighted the organic components in cake layer, but weakened the inorganic functions in practical MBR operation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Insights into accumulation variability over the last 2000 years at James Ross Island, Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Massam, A.; Mulvaney, R.; McConnell, J.; Abram, N.; Arienzo, M. M.; Whitehouse, P. L.

2016-12-01

The James Ross Island ice core, drilled to 364 m on the northern tip of the Antarctic Peninsula, preserves a climate record that spans beyond the Holocene period to the end of the last glacial maximum (LGM). Reanalysis of the ice core using high-resolution continuous flow analysis (CFA) highlighted errors in the identification of events of known age that had been used to constrain the earlier chronology. The new JRI2 chronology is annual layer counted to 300 years, with the remaining profile reconstructed using a new age-depth model that is tied to age horizons identified in the annual-layer counted WAIS Divide ice core record. An accurate age-depth profile requires reliable known-age horizons along the ice core profile. In addition, these allow us to determine a solution for the accumulation history and rate of compaction due to vertical strain. The accuracy of the known-age constraints used in JRI2 allows only a small uncertainty in the reconstruction of the most recent 2000 years of accumulation variability. Independently, the surface temperature profile has been estimated from the stable water isotope profile and calibrated to borehole temperature observations. We present the accumulation, vertical thinning and temperature history interpreted from the James Ross Island ice core for the most recent 2000 years. JRI2 reconstructions show accumulation variability on a decadal to centennial timescale up to 20% from the present-day mean annual accumulation rate of 0.63 m yr-1. Analysis of the accumulation profile for James Ross Island offers insight into the sensitivity of accumulation to a change in surface temperature, as well as the reliability of the assumed relationship between accumulation and surface temperature in climate reconstructions using stable water isotope proxies.

Consequences of plasma oxidation and vacuum annealing on the chemical properties and electron accumulation of In2O3 surfaces

NASA Astrophysics Data System (ADS)

Berthold, Theresa; Rombach, Julius; Stauden, Thomas; Polyakov, Vladimir; Cimalla, Volker; Krischok, Stefan; Bierwagen, Oliver; Himmerlich, Marcel

2016-12-01

The influence of oxygen plasma treatments on the surface chemistry and electronic properties of unintentionally doped and Mg-doped In2O3(111) films grown by plasma-assisted molecular beam epitaxy or metal-organic chemical vapor deposition is studied by photoelectron spectroscopy. We evaluate the impact of semiconductor processing technology relevant treatments by an inductively coupled oxygen plasma on the electronic surface properties. In order to determine the underlying reaction processes and chemical changes during film surface-oxygen plasma interaction and to identify reasons for the induced electron depletion, in situ characterization was performed implementing a dielectric barrier discharge oxygen plasma as well as vacuum annealing. The strong depletion of the initial surface electron accumulation layer is identified to be caused by adsorption of reactive oxygen species, which induce an electron transfer from the semiconductor to localized adsorbate states. The chemical modification is found to be restricted to the topmost surface and adsorbate layers. The change in band bending mainly depends on the amount of attached oxygen adatoms and the film bulk electron concentration as confirmed by calculations of the influence of surface state density on the electron concentration and band edge profile using coupled Schrödinger-Poisson calculations. During plasma oxidation, hydrocarbon surface impurities are effectively removed and surface defect states, attributed to oxygen vacancies, vanish. The recurring surface electron accumulation after subsequent vacuum annealing can be consequently explained by surface oxygen vacancies.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Chen; Metzler, Dominik; Oehrlein, Gottlieb S., E-mail: oehrlein@umd.edu

Angstrom-level plasma etching precision is required for semiconductor manufacturing of sub-10 nm critical dimension features. Atomic layer etching (ALE), achieved by a series of self-limited cycles, can precisely control etching depths by limiting the amount of chemical reactant available at the surface. Recently, SiO{sub 2} ALE has been achieved by deposition of a thin (several Angstroms) reactive fluorocarbon (FC) layer on the material surface using controlled FC precursor flow and subsequent low energy Ar{sup +} ion bombardment in a cyclic fashion. Low energy ion bombardment is used to remove the FC layer along with a limited amount of SiO{sub 2} frommore » the surface. In the present article, the authors describe controlled etching of Si{sub 3}N{sub 4} and SiO{sub 2} layers of one to several Angstroms using this cyclic ALE approach. Si{sub 3}N{sub 4} etching and etching selectivity of SiO{sub 2} over Si{sub 3}N{sub 4} were studied and evaluated with regard to the dependence on maximum ion energy, etching step length (ESL), FC surface coverage, and precursor selection. Surface chemistries of Si{sub 3}N{sub 4} were investigated by x-ray photoelectron spectroscopy (XPS) after vacuum transfer at each stage of the ALE process. Since Si{sub 3}N{sub 4} has a lower physical sputtering energy threshold than SiO{sub 2}, Si{sub 3}N{sub 4} physical sputtering can take place after removal of chemical etchant at the end of each cycle for relatively high ion energies. Si{sub 3}N{sub 4} to SiO{sub 2} ALE etching selectivity was observed for these FC depleted conditions. By optimization of the ALE process parameters, e.g., low ion energies, short ESLs, and/or high FC film deposition per cycle, highly selective SiO{sub 2} to Si{sub 3}N{sub 4} etching can be achieved for FC accumulation conditions, where FC can be selectively accumulated on Si{sub 3}N{sub 4} surfaces. This highly selective etching is explained by a lower carbon consumption of Si{sub 3}N{sub 4} as compared to SiO{sub 2}. The comparison of C{sub 4}F{sub 8} and CHF{sub 3} only showed a difference in etching selectivity for FC depleted conditions. For FC accumulation conditions, precursor chemistry has a weak impact on etching selectivity. Surface chemistry analysis shows that surface fluorination and FC reduction take place during a single ALE cycle for FC depleted conditions. A fluorine rich carbon layer was observed on the Si{sub 3}N{sub 4} surface after ALE processes for which FC accumulation takes place. The angle resolved-XPS thickness calculations confirmed the results of the ellipsometry measurements in all cases.« less

Surface origin and control of resonance Raman scattering and surface band gap in indium nitride

NASA Astrophysics Data System (ADS)

Alarcón-Lladó, Esther; Brazzini, Tommaso; Ager, Joel W.

2016-06-01

Resonance Raman scattering measurements were performed on indium nitride thin films under conditions where the surface electron concentration was controlled by an electrolyte gate. As the surface condition is tuned from electron depletion to accumulation, the spectral feature at the expected position of the (E 1, A 1) longitudinal optical (LO) near 590 cm-1 shifts to lower frequency. The shift is reversibly controlled with the applied gate potential, which clearly demonstrates the surface origin of this feature. The result is interpreted within the framework of a Martin double resonance, where the surface functions as a planar defect, allowing the scattering of long wavevector phonons. The allowed wavevector range, and hence the frequency, is modulated by the electron accumulation due to band gap narrowing. A surface band gap reduction of over 500 meV is estimated for the conditions of maximum electron accumulation. Under conditions of electron depletion, the full InN bandgap (E g  =  0.65 eV) is expected at the surface. The drastic change in the surface band gap is expected to influence the transport properties of devices which utilize the surface electron accumulation layer.

Looking Into and Through the Ross Ice Shelf - ROSETTA-ICE

NASA Astrophysics Data System (ADS)

Bell, R. E.

2015-12-01

Our current understanding of the structure and stability of the Ross Ice Shelf is based on satellite studies of the ice surface and the 1970's RIGGS program. The study of the flowlines evident in the MODIS imagery combined with surface geophysics has revealed a complex history with ice streams Mercer, Whillans and Kamb changing velocity over the past 1000 years. Here, we present preliminary IcePod and IceBridge radar data acquired in December 2014 and November 2013 across the Ross Ice Shelf that show clearly, for the first time, the structure of the ice shelf and provide insights into ice-ocean interaction. The three major layers of the ice shelf are (1) the continental meteoric ice layer), ice formed on the grounded ice sheet that entered the ice shelf where ice streams and outlet glaciers crossed the grounding line (2) the locally accumulating meteoric ice layer, ice and snow that forms from snowfall on the floating ice shelf and (3) a basal marine ice layer. The locally accumulating meteoric ice layer contains well-defined internal layers that are generally parallel to the ice surface and thickens away from the grounding line and reaches a maximum thickness of 220m along the line crossing Roosevelt Island. The continental meteoric layer is located below a broad irregular internal reflector, and is characterized by irregular internal layers. These internal layers are often folded, likely a result of deformation as the ice flowed across the grounding line. The basal marine ice layer, up to 50m thick, is best resolved in locations where basal crevasses are present, and appears to thicken along the flow at rates of decimeters per year. Each individual flowband of the ice shelf contains layers that are distinct in their structure. For example, the thickness of the locally accumulated layer is a function of both the time since crossing the grounding line and the thickness of the incoming ice. Features in the meteoric ice, such as distinct folds, can be traced between the two IceBridge lines located 47 km apart. The ROSETTA-ICE program will begin a systematic mapping of the Ross Ice Shelf and sub-ice topography using the IcePod system beginning in 2015. Together the new gravity-derived bathymetry and the mapping of the ice shelf structure will provide key insights into the stability of the ice shelf.

Junction characteristics of indium tin oxide/indium phosphide solar cells

NASA Astrophysics Data System (ADS)

Sheldon, P.; Ahrenkiel, R. K.; Hayes, R. E.; Russell, P. E.; Nottenburg, R. N.; Kazmerski, L. L.

Efficient indium tin oxide (ITO)/p-InP solar cells have been fabricated. Typical uncorrected efficiencies range from 9-12 percent at AM1 intensities. It is shown that deposition of ITO causes a semi-insulating layer at the InP surface as determined by C-V measurements. The thickness of this layer is approximately 750 A. We believe that this high resistivity region is due to surface accumulation of Fe at the ITO/InP interface.

Accumulation patterns around Dome C, East Antarctica, in the last 73 kyr

NASA Astrophysics Data System (ADS)

Cavitte, Marie G. P.; Parrenin, Frédéric; Ritz, Catherine; Young, Duncan A.; Van Liefferinge, Brice; Blankenship, Donald D.; Frezzotti, Massimo; Roberts, Jason L.

2018-04-01

We reconstruct the pattern of surface accumulation in the region around Dome C, East Antarctica, since the last glacial. We use a set of 18 isochrones spanning all observable depths of the ice column, interpreted from various ice-penetrating radar surveys and a 1-D ice flow model to invert for accumulation rates in the region. The shallowest four isochrones are then used to calculate paleoaccumulation rates between isochrone pairs using a 1-D assumption where horizontal advection is negligible in the time interval of each layer. We observe that the large-scale (100s km) surface accumulation gradient is spatially stable through the last 73 kyr, which reflects current modeled and observed precipitation gradients in the region. We also observe small-scale (10 s km) accumulation variations linked to snow redistribution at the surface, due to changes in its slope and curvature in the prevailing wind direction that remain spatially stationary since the last glacial.

Impact of micro-porous layer on liquid water distribution at the catalyst layer interface and cell performance in a polymer electrolyte membrane fuel cell

NASA Astrophysics Data System (ADS)

Tabe, Yutaka; Aoyama, Yusuke; Kadowaki, Kazumasa; Suzuki, Kengo; Chikahisa, Takemi

2015-08-01

In polymer electrolyte membrane fuel cells, a gas diffusion layer (GDL) with a micro-porous layer (MPL) gives better anti-flooding performance than GDLs without an MPL. To investigate the function and mechanism of the MPL to suppress water flooding, the liquid water distribution at the cathode catalyst layer (CL) surface are observed by a freezing method; in the method liquid water is immobilized in ice form by rapid freezing, followed by disassembling the cell for observations. The ice covered area is quantified by image processing and cells with and without an MPL are compared. The results show that the MPL suppresses water accumulation at the interface due to smaller pore size and finer contact with the CL, and this results in less water flooding. Investigation of ice formed after -10 °C cold start shutdowns and the temporary performance deterioration at ordinary temperatures also indicates a significant influence of the liquid water accumulating at the interface. The importance of the fine contact between CL and MPL, the relative absence of gaps, is demonstrated by a gas diffusion electrode (GDE) which is directly coated with catalyst ink on the surface of the MPL achieving finer contact of the layers.

Characteristics of ozone vertical profile observed in the boundary layer around Beijing in autumn.

PubMed

Ma, Zhiqiang; Zhang, Xiaoling; Xu, Jing; Zhao, Xiujuan; Meng, Wei

2011-01-01

In the autumn of 2008, the vertical profiles of ozone and meteorological parameters in the low troposphere (0-1000 m) were observed at two sites around Beijing, specifically urban Nanjiao and rural Shangdianzi. At night and early morning, the lower troposphere divided into two stratified layers due to temperature inversion. Ozone in the lower layer showed a large gradient due to the titration of NO. Air flow from the southwest brought ozone-rich air to Beijing, and the ozone profiles were marked by a continuous increase in the residual layer at night. The accumulated ozone in the upper layer played an important role in the next day's surface peak ozone concentration, and caused a rapid increase in surface ozone in the morning. Wind direction shear and wind speed shear exhibited different influences on ozone profiles and resulted in different surface ozone concentrations in Beijing.

Plastic deformation and wear process at a surface during unlubricated sliding

NASA Technical Reports Server (NTRS)

Yamamoto, T.; Buckley, D. H.

1982-01-01

The plastic deformation and wear of a 304 stainless steel surface sliding against an aluminum oxide rider with a spherical surface (the radius of curvature: 1.3 cm) were observed by using scanning electron and optical microscopes. Experiments were conducted in a vacuum of one million Pa and in an environment of fifty thousandth Pa of chlorine gas at 25 C. The load was 500 grams and the sliding velocity was 0.5 centimeter per second. The deformed surface layer which accumulates and develops successively is left behind the rider, and step shaped proturbances are developed even after single pass sliding under both environmental conditions. A fully developed surface layer is gradually torn off leaving a characteristic pattern. The mechanism for tearing away of the surface layer from the contact area and sliding track contour is explained assuming the simplified process of material removal based on the adhesion theory for the wear of materials.

Electrochemical Approach for Effective Antifouling and Antimicrobial Surfaces.

PubMed

Gaw, Sheng Long; Sarkar, Sujoy; Nir, Sivan; Schnell, Yafit; Mandler, Daniel; Xu, Zhichuan J; Lee, Pooi See; Reches, Meital

2017-08-09

Biofouling, the adsorption of organisms to a surface, is a major problem today in many areas of our lives. This includes: (i) health, as biofouling on medical device leads to hospital-acquired infections, (ii) water, since the accumulation of organisms on membranes and pipes in desalination systems harms the function of the system, and (iii) energy, due to the heavy load of the organic layer that accumulates on marine vessels and causes a larger consumption of fuel. This paper presents an effective electrochemical approach for generating antifouling and antimicrobial surfaces. Distinct from previously reported antifouling or antimicrobial electrochemical studies, we demonstrate the formation of a hydrogen gas bubble layer through the application of a low-voltage square-waveform pulses to the conductive surface. This electrochemically generated gas bubble layer serves as a separation barrier between the surroundings and the target surface where the adhesion of bacteria can be deterred. Our results indicate that this barrier could effectively reduce the adsorption of bacteria to the surface by 99.5%. We propose that the antimicrobial mechanism correlates with the fundamental of hydrogen evolution reaction (HER). HER leads to an arid environment that does not allow the existence of live bacteria. In addition, we show that this drought condition kills the preadhered bacteria on the surface due to water stress. This work serves as the basis for the exploration of future self-sustainable antifouling techniques such as incorporating it with photocatalytic and photoelectrochemical reactions.

Surface-atmosphere decoupling limits accumulation at Summit, Greenland.

PubMed

Berkelhammer, Max; Noone, David C; Steen-Larsen, Hans Christian; Bailey, Adriana; Cox, Christopher J; O'Neill, Michael S; Schneider, David; Steffen, Konrad; White, James W C

2016-04-01

Despite rapid melting in the coastal regions of the Greenland Ice Sheet, a significant area (~40%) of the ice sheet rarely experiences surface melting. In these regions, the controls on annual accumulation are poorly constrained owing to surface conditions (for example, surface clouds, blowing snow, and surface inversions), which render moisture flux estimates from myriad approaches (that is, eddy covariance, remote sensing, and direct observations) highly uncertain. Accumulation is partially determined by the temperature dependence of saturation vapor pressure, which influences the maximum humidity of air parcels reaching the ice sheet interior. However, independent proxies for surface temperature and accumulation from ice cores show that the response of accumulation to temperature is variable and not generally consistent with a purely thermodynamic control. Using three years of stable water vapor isotope profiles from a high altitude site on the Greenland Ice Sheet, we show that as the boundary layer becomes increasingly stable, a decoupling between the ice sheet and atmosphere occurs. The limited interaction between the ice sheet surface and free tropospheric air reduces the capacity for surface condensation to achieve the rate set by the humidity of the air parcels reaching interior Greenland. The isolation of the surface also acts to recycle sublimated moisture by recondensing it onto fog particles, which returns the moisture back to the surface through gravitational settling. The observations highlight a unique mechanism by which ice sheet mass is conserved, which has implications for understanding both past and future changes in accumulation rate and the isotopic signal in ice cores from Greenland.

Surface-atmosphere decoupling limits accumulation at Summit, Greenland

PubMed Central

Berkelhammer, Max; Noone, David C.; Steen-Larsen, Hans Christian; Bailey, Adriana; Cox, Christopher J.; O’Neill, Michael S.; Schneider, David; Steffen, Konrad; White, James W. C.

2016-01-01

Despite rapid melting in the coastal regions of the Greenland Ice Sheet, a significant area (~40%) of the ice sheet rarely experiences surface melting. In these regions, the controls on annual accumulation are poorly constrained owing to surface conditions (for example, surface clouds, blowing snow, and surface inversions), which render moisture flux estimates from myriad approaches (that is, eddy covariance, remote sensing, and direct observations) highly uncertain. Accumulation is partially determined by the temperature dependence of saturation vapor pressure, which influences the maximum humidity of air parcels reaching the ice sheet interior. However, independent proxies for surface temperature and accumulation from ice cores show that the response of accumulation to temperature is variable and not generally consistent with a purely thermodynamic control. Using three years of stable water vapor isotope profiles from a high altitude site on the Greenland Ice Sheet, we show that as the boundary layer becomes increasingly stable, a decoupling between the ice sheet and atmosphere occurs. The limited interaction between the ice sheet surface and free tropospheric air reduces the capacity for surface condensation to achieve the rate set by the humidity of the air parcels reaching interior Greenland. The isolation of the surface also acts to recycle sublimated moisture by recondensing it onto fog particles, which returns the moisture back to the surface through gravitational settling. The observations highlight a unique mechanism by which ice sheet mass is conserved, which has implications for understanding both past and future changes in accumulation rate and the isotopic signal in ice cores from Greenland. PMID:27386509

Tritium migration to the surfaces of Type 316 stainless steel; aluminum 6061; and oxygen-free, high-conductivity copper

DOE PAGES

Sharpe, M.; Shmayda, W. T.; Schroder, W. U.

2016-05-25

The migration of tritium to the surfaces of aluminum 6061, oxygen-free, high-conductivity copper (OFHC), and stainless-steel 316 from the bulk metal was studied using low-pressure Tonks–Langmuir argon plasma. The plasma is shown to be effective at removing tritium from metal surfaces in a controlled manner. Tritium is removed in decreasing quantities with successive plasma exposures, which suggests a depletion of the surface and near-surface tritium inventories. A diffusion model was developed to predict tritium migration from the bulk and its accumulation in the water layers present on the metal surface. The model reproduces the rate of tritium re-growth on themore » surface for all three metals and can be used to calculate the triton solubility in the water layers present on metal surfaces. The ratio of surface-to-bulk solubilities at the water-layer/bulk-metal interface uniquely determines the concentration ratio between these two media. Removing the tritium-rich water layers induces tritium to migrate from the bulk to the surface. Furthermore, this process is driven by a concentration gradient that develops in the bulk because of the perturbation on the surface.« less

The effect of fire and permafrost interactions on soil carbon accumulation in an upland black spruce ecosystem of interior Alaska: Implications for post-thaw carbon loss

USGS Publications Warehouse

O'Donnell, J. A.; Harden, J.W.; McGuire, A.D.; Kanevskiy, M.Z.; Jorgenson, M.T.; Xu, X.

2011-01-01

High-latitude regions store large amounts of organic carbon (OC) in active-layer soils and permafrost, accounting for nearly half of the global belowground OC pool. In the boreal region, recent warming has promoted changes in the fire regime, which may exacerbate rates of permafrost thaw and alter soil OC dynamics in both organic and mineral soil. We examined how interactions between fire and permafrost govern rates of soil OC accumulation in organic horizons, mineral soil of the active layer, and near-surface permafrost in a black spruce ecosystem of interior Alaska. To estimate OC accumulation rates, we used chronosequence, radiocarbon, and modeling approaches. We also developed a simple model to track long-term changes in soil OC stocks over past fire cycles and to evaluate the response of OC stocks to future changes in the fire regime. Our chronosequence and radiocarbon data indicate that OC turnover varies with soil depth, with fastest turnover occurring in shallow organic horizons (~60 years) and slowest turnover in near-surface permafrost (>3000 years). Modeling analysis indicates that OC accumulation in organic horizons was strongly governed by carbon losses via combustion and burial of charred remains in deep organic horizons. OC accumulation in mineral soil was influenced by active layer depth, which determined the proportion of mineral OC in a thawed or frozen state and thus, determined loss rates via decomposition. Our model results suggest that future changes in fire regime will result in substantial reductions in OC stocks, largely from the deep organic horizon. Additional OC losses will result from fire-induced thawing of near-surface permafrost. From these findings, we conclude that the vulnerability of deep OC stocks to future warming is closely linked to the sensitivity of permafrost to wildfire disturbance. ?? 2010 Blackwell Publishing Ltd.

Meltwater-induced changes in the structure and behavior of Greenland's firn

NASA Astrophysics Data System (ADS)

MacFerrin, M. J.; Machguth, H.; van As, D.; Charalampidis, C.; Heilig, A.; Vandecrux, B.; Stevens, C.; Abdalati, W.

2017-12-01

As surface melt increases across the Greenland ice sheet in a warming climate, Greenland's accumulation zone has absorbed a progressively greater volume of water. In low-accumulation regions lacking perennial aquifers, this meltwater has refrozen into subsurface ice, which is now fundamentally altering the structure of near-surface firn layers. Here we present an extensive collection of firn cores, in situ radar, NASA IceBridge radar, thermistor string measurements, in situ FirnCover compaction data and regional climate model results to illustrate several distinct ways that Greenland's percolation zone is being fundamentally altered by increasing surface melt. The bulk density of the top 20 meters' firn in the wet-snow facies has increased by up to 40% in the past 50 years, due primarily to an up to six-fold increase in firn ice content. Firn compaction rates have changed both in their annual magnitude and have been delayed in their seasonal phase by up to three months, driven primarily by an increased release of latent heat as water refreezes at depth. When firn exceeds a threshold of excess melt in which seasonal snow can no longer accommodate summer melt, individual refrozen ice layers at depth have annealed together to form low-permeability ice slabs (LPISs). These multi-meter thick layers of ice perched over porous firn block percolation to depth and increase the size of the runoff zone. LPISs are a type of "hybrid facies" capable both of running water off the surface, while continuing to slowly compact porous firn at depth. Currently LPISs cover approximately 5% of Greenland's current accumulation zone, but we project them to extend across 15-50% of the accumulation zone by 2100 under different forcing scenarios. These observed changes in the structure and behavior of Greenland's firn have serious implications for future runoff of the ice sheet. Additionally, they challenge modern assumptions which we use to quantify the mass balance of the Greenland ice sheet from airborne and space-borne measurements.

Recent accumulation rates of an Alpine glacier derived from repeated airborne GPR and firn cores

NASA Astrophysics Data System (ADS)

Sold, Leo; Huss, Matthias; Eichler, Anja; Schwikowski, Margit; Hoelzle, Martin

2014-05-01

The topmost areas of glaciers contain a valuable record of their past accumulation rates. The water equivalent of annual firn layers can be used to initiate or extend existing time series of local mass balance and, ultimately, to consolidate the knowledge on the response of glaciers to changing climatic conditions. Measurements of the thickness and density of firn layers typically involve drilling in remote areas and core analysis and are thus expensive in terms of time and effort. Here, we discuss measurements from 2012 on Findelengletscher, Switzerland, a large Alpine valley glacier, using two in-situ firn cores and airborne Ground-Penetrating Radar (GPR). The firn cores were analysed regarding their density, major ions and deuterium concentration. The ammonium (NH4+) concentration is known to show seasonality due to a higher source activity and pronounced vertical transportation in the atmosphere in summer. The deuterium concentration serves as a proxy for air temperature during precipitation formation. Together, they provide depth and dating of annual summer surfaces. GPR has previously been used for a non-destructive assessment of internal layers in snow, firn and ice. Signal reflections indicate changes in the dielectric properties of the material, e.g. density changes at former summer surfaces. Airborne surveys allow measurements to be taken in remote and inaccessible areas. However, to transfer information from the GPR pulse travel time to the depth domain, the dielectric permittivity of the material is required, that changes with density of the firn. We observed a good agreement of the GPR signal with pronounced changes in the density profile, ice layers and peak contents of major ions. This underlines the high potential of GPR for detecting firn layers. However, not all peak-densities and thick ice layers represent a former glacier summer surface but can also be due to melting and refreezing during winter. We show that up to four years of annual accumulation on Findelengletscher can be reconstructed from repeated GPR measurements alone. A simple transient spatial model for firn compaction is calibrated based on a comparison with GPR data of 2013 at positions were profiles intersect. Density and water equivalent of firn layers can then be extracted along the measured GPR profiles. However, if no in-situ information from firn cores is available, the dating of reflectors as former annual summer surfaces must be verified by external information such as modelled mass balance to avoid misinterpretations. We show that helicopter-borne GPR is an effective method to derive several years of past accumulation rates of mountain glaciers. It benefits but does not depend exclusively on the time-matched availability of firn cores when overlapping profiles are mapped in subsequent years.

Surface Nanocrystallization and Amorphization of Dual-Phase TC11 Titanium Alloys under Laser Induced Ultrahigh Strain-Rate Plastic Deformation

PubMed Central

Luo, Sihai; Zhou, Liucheng; Wang, Xuede; Cao, Xin; Nie, Xiangfan

2018-01-01

As an innovative surface technology for ultrahigh strain-rate plastic deformation, laser shock peening (LSP) was applied to the dual-phase TC11 titanium alloy to fabricate an amorphous and nanocrystalline surface layer at room temperature. X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy (HRTEM) were used to investigate the microstructural evolution, and the deformation mechanism was discussed. The results showed that a surface nanostructured surface layer was synthesized after LSP treatment with adequate laser parameters. Simultaneously, the behavior of dislocations was also studied for different laser parameters. The rapid slipping, accumulation, annihilation, and rearrangement of dislocations under the laser-induced shock waves contributed greatly to the surface nanocrystallization. In addition, a 10 nm-thick amorphous structure layer was found through HRTEM in the top surface and the formation mechanism was attributed to the local temperature rising to the melting point, followed by its subsequent fast cooling. PMID:29642379

Surface Nanocrystallization and Amorphization of Dual-Phase TC11 Titanium Alloys under Laser Induced Ultrahigh Strain-Rate Plastic Deformation.

PubMed

Luo, Sihai; Zhou, Liucheng; Wang, Xuede; Cao, Xin; Nie, Xiangfan; He, Weifeng

2018-04-06

As an innovative surface technology for ultrahigh strain-rate plastic deformation, laser shock peening (LSP) was applied to the dual-phase TC11 titanium alloy to fabricate an amorphous and nanocrystalline surface layer at room temperature. X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy (HRTEM) were used to investigate the microstructural evolution, and the deformation mechanism was discussed. The results showed that a surface nanostructured surface layer was synthesized after LSP treatment with adequate laser parameters. Simultaneously, the behavior of dislocations was also studied for different laser parameters. The rapid slipping, accumulation, annihilation, and rearrangement of dislocations under the laser-induced shock waves contributed greatly to the surface nanocrystallization. In addition, a 10 nm-thick amorphous structure layer was found through HRTEM in the top surface and the formation mechanism was attributed to the local temperature rising to the melting point, followed by its subsequent fast cooling.

Plastic deformation at surface during unlubricated sliding

NASA Technical Reports Server (NTRS)

Yamamoto, T.; Buckley, D. H.

1982-01-01

The plastic deformation and wear of 304 stainless-steel surface slid against an aluminum oxide rider were observed by using a scanning electron microscope and an optical microscope. Experiments were conducted in a vacuum of 0.000001 Pa and in an environment of 0.0005 Pa chlorine gas at 25 C. The load was 500 grams and the sliding velocity was 0.5 centimeter per second. The deformed surface layer which accumulates and develops successively is left behind the rider, and step-shaped protuberances are developed even after single pass sliding under both environmental conditions. A fully developed surface layer is gradually torn off leaving a characteristic pattern. These observations result from both adhesion and an adhesive wear mechanism.

Dust Accumulation on Mars

NASA Technical Reports Server (NTRS)

2005-01-01

Since landing on Mars a year ago, NASA's pair of six-wheeled geologists have been constantly exposed to martian winds and dust. As a result, the Spirit rover has gradually experienced a slight decline in power as a thin layer of dust has accumulated on the solar panels, blocking some of the sunlight that is converted to electricity. In this enlarged image of a postage-stamp-size (3-centimeter-square, 1.2-inch-square) portion of one of Spirit's solar panels, a fine layer of martian dust coats electrical connections and metal surfaces. Individual silt grains or clumps of dust are visible where sediment has accumulated in crevices between solar cells and circuits. The upper right half of the image shows the edge of one of the rover's solar cells. The lower left half shows electrical wires bonded with silicon adhesive to the underlying composite surface; the circular abrasions are the result of sanding by hand on Earth. The braided wire is connected to a thermocouple used to measure temperature based on electrical resistance. Spirit took this image with its microscopic imager on martian day, or sol, 350 (Dec. 26, 2004).

Early diagenesis and trace element accumulation in North American Arctic margin sediments

NASA Astrophysics Data System (ADS)

Kuzyk, Zou Zou A.; Gobeil, Charles; Goñi, Miguel A.; Macdonald, Robie W.

2017-04-01

Concentrations of redox-sensitive elements (S, Mn, Mo, U, Cd, Re) were analyzed in a set of 27 sediment cores collected along the North American Arctic margin (NAAM) from the North Bering Sea to Davis Strait via the Canadian Archipelago. Sedimentary distributions and accumulation rates of the elements were used to evaluate early diagenesis in sediments along this section and to estimate the importance of this margin as a sink for key elements in the polar and global oceans. Distributions of Mn, total S and reduced inorganic S demonstrated that diagenetic conditions and thus sedimentary carbon turnover in the NAAM is organized regionally: undetectable or very thin layers (<0.5 cm) of surface Mn enrichment occurred in the Bering-Chukchi shelves; thin layers (1-5 cm) of surface Mn enrichment occurred in Barrow Canyon and Lancaster Sound; and thick layers (5-20 cm) of surface Mn enrichment occurred in the Beaufort Shelf, Canadian Archipelago, and Davis Strait. Inventories of authigenic S below the Mn-rich layer decreased about fivefold from Bering-Chukchi shelf and Barrow Canyon to Lancaster Sound and more than ten-fold from Bering-Chukchi shelf to Beaufort Shelf, Canadian Archipelago and Davis Strait. The Mn, total S and reduced inorganic S distributions imply strong organic carbon (OC) flux and metabolism in the Bering-Chukchi shelves, lower aerobic OC metabolism in Barrow Canyon and Lancaster Sound, and deep O2 penetration and much lower OC metabolism in the Beaufort Shelf, Canadian Archipelago, and Davis Strait. Accumulation rates of authigenic S, Mo, Cd, Re, and U displayed marked spatial variability along the NAAM reflecting the range in sedimentary redox conditions. Strong relationships between the accumulation rates and vertical carbon flux, estimated from regional primary production values and water depth at the coring sites, indicate that the primary driver in the regional patterns is the supply of labile carbon to the seabed. Thus, high primary production combined with a shallow water column (average 64 m) leads to high rates of authigenic trace element accumulation in sediments from the Bering-Chukchi shelves. High to moderate primary production combined with deep water (average 610 m) leads to moderate rates of authigenic trace element accumulation in sediments from Lancaster Sound. Low to very low primary production combined with moderate water depths (average 380 m) leads to low rates of authigenic trace element accumulation in sediments in the Beaufort Shelf, Davis Strait and Canadian Archipelago. Authigenic Mo accumulation rates show a significant relationship with vascular plant input to the sediments, implying that terrestrial organic matter contributes significantly to metabolism in Arctic margin sediments. Our results suggest that the broad and shallow shelf of the Chukchi Sea, which has high productivity sustained by imported nutrients, contributes disproportionately to global biogeochemical cycles.

Regolith stratigraphy at the Chang'E-3 landing site as seen by lunar penetrating radar

NASA Astrophysics Data System (ADS)

Fa, Wenzhe; Zhu, Meng-Hua; Liu, Tiantian; Plescia, Jeffrey B.

2015-12-01

The Chang'E-3 lunar penetrating radar (LPR) observations at 500 MHz reveal four major stratigraphic zones from the surface to a depth of ~20 m along the survey line: a layered reworked zone (<1 m), an ejecta layer (~2-6 m), a paleoregolith layer (~4-11 m), and the underlying mare basalts. The reworked zone has two to five distinct layers and consists of surface regolith. The paleoregolith buried by the ejecta from a 500 m crater is relatively homogenous and contains only a few rocks. Population of buried rocks increases with depth to ~2 m at first, and then decreases with depth, representing a balance between initial deposition of the ejecta and later turnover of the regolith. Combining with the surface age, the LPR observations indicate a mean accumulation rate of about 5-10 m/Gyr for the surface regolith, which is at least 4-8 times larger than previous estimation.

Methanol adsorption and dissociation on LaMnO 3 and Sr doped LaMnO 3 (001) surfaces

DOE PAGES

Beste, Ariana

2017-06-20

Using density functional theory, we investigate in this paper methanol adsorption and dissociation on the MnO 2- and LaO-terminated LaMnO 3 (001) surface as a function of Sr dopant enrichment in and near the surface. In response to bulk cleavage, we find electron depletion of the negatively charged MnO 2 surface layer that is enhanced by Sr doping in the subsurface. In contrast, we observe electron accumulation in the positively charged LaO surface layer that is reduced by Sr doping in the surface layer. Methanol adsorbs dissociatively on the LaO termination of the LaMnO 3 (001) surface. Methanol adsorption onmore » the LaO termination is strongly preferred over adsorption on the MnO 2 termination. While moderate doping has a small influence on methanol adsorption and dissociation, when 100% of La is replaced by Sr in the surface or subsurface, the adsorption preference of methanol is reversed. Finally, if the surface is highly dopant enriched, methanol favours dissociative adsorption on the MnO 2-terminated surface.« less

Methanol adsorption and dissociation on LaMnO 3 and Sr doped LaMnO 3 (001) surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beste, Ariana

Using density functional theory, we investigate in this paper methanol adsorption and dissociation on the MnO 2- and LaO-terminated LaMnO 3 (001) surface as a function of Sr dopant enrichment in and near the surface. In response to bulk cleavage, we find electron depletion of the negatively charged MnO 2 surface layer that is enhanced by Sr doping in the subsurface. In contrast, we observe electron accumulation in the positively charged LaO surface layer that is reduced by Sr doping in the surface layer. Methanol adsorbs dissociatively on the LaO termination of the LaMnO 3 (001) surface. Methanol adsorption onmore » the LaO termination is strongly preferred over adsorption on the MnO 2 termination. While moderate doping has a small influence on methanol adsorption and dissociation, when 100% of La is replaced by Sr in the surface or subsurface, the adsorption preference of methanol is reversed. Finally, if the surface is highly dopant enriched, methanol favours dissociative adsorption on the MnO 2-terminated surface.« less

Self-organizing layers from complex molecular anions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warneke, Jonas; McBriarty, Martin E.; Riechers, Shawn L.

Ions are promising building blocks for tunable self-organizing materials with advanced technological applications. However, because of strong Coulomb attraction with counterions, the intrinsic properties of ions are difficult to exploit for preparation of bulk materials. Here, we report the precisely-controlled preparation of macroscopic surface layers by soft landing of mass selected complex anions which determine the self organization of the layers with their molecular properties. The family of halogenated dodecaborates [B12X12]2- (X = F, Cl, Br, I), in which the internal charge distribution between core and shell regions of the molecular ions systematically vary, was deposited on different self assembledmore » monolayer surfaces (SAMs) on gold at high coverage. Layers of anions were found to be stabilized by accumulation of neutral molecules. Different phases, self-organization mechanisms and optical properties were observed to depend upon the internal charge distribution of the deposited anions, the underlying surface and the coadsorbed molecules. This demonstrates rational control of the properties of anion based layers.« less

Controlling the Accumulation of Water at Oil-Solid Interfaces with Gradient Coating.

PubMed

Li, Yan; Yang, Qiaomu; Mei, Ran Andy; Cai, Meirong; Heng, Jerry Y Y; Yang, Zhongqiang

2017-07-13

In this work, we demonstrate a strategy to control the accumulation of water in the oil-solid interface using a gradient coating. Gradient chemistry on glass surface is created by vapor diffusion of organosilanes, leading to a range of contact angles from 110 to 20°. Hexadecane is placed on the gradient substrate as an oil layer, forming a "water/hexadecane/gradient solid substrate" sandwich structure. During incubation, water molecules spontaneously migrate through the micrometer-thick oil layer and result in the formation of micrometer-sized water droplets at the oil-solid interface. It turns out that water droplets at more hydrophobic regions tend to be closer to a regular spherical shape, which is attributed to their higher contact angle with the hydrophobic substrate. However, along the gradient from hydrophobic to hydrophilic, the water droplets gradually form more irregular shapes, as hydrophilic surfaces pin the edges of droplets to form a distorted morphology. It indicates that more hydrophilic surfaces containing more Si-OH groups lead to a higher electrostatic interaction with water and a higher growth rate of interfacial water droplets. This work provides further insights into the mechanism of spontaneous water accumulation at oil-solid interfaces and assists in the rational design for controlling such interfacial phenomenon.

Plastic deformation and wear process at a surface during unlubricated sliding

NASA Technical Reports Server (NTRS)

Yamamoto, T.; Buckley, D. H.

1983-01-01

The plastic deformation and wear of a 304 stainless steel surface sliding against an aluminum oxide rider with a spherical surface (the radius of curvature: 1.3 cm) were observed by using scanning electron and optical microscopes. Experiments were conducted in a vacuum of one million Pa and in an environment of fifty thousandth Pa of chlorine gas at 25 C. The load was 500 grams and the sliding velocity was 0.5 centimeter per second. The deformed surface layer which accumulates and develops successively is left behind the rider, and step shaped proturbances are developed even after single pass sliding under both environmental conditions. A fully developed surface layer is gradually torn off leaving a characteristic pattern. The mechanism for tearing away of the surface layer from the contact area and sliding track contour is explained assuming the simplified process of material removal based on the adhesion theory for the wear of materials. Previously announced in STAR as N82-32735

Unlocking annual firn layer water equivalents from ground-penetrating radar data on an Alpine glacier

NASA Astrophysics Data System (ADS)

Sold, L.; Huss, M.; Eichler, A.; Schwikowski, M.; Hoelzle, M.

2015-05-01

The spatial representation of accumulation measurements is a major limitation for current glacier mass balance monitoring approaches. Here, we present a method for estimating annual accumulation rates on a temperate Alpine glacier based on the interpretation of internal reflection horizons (IRHs) in helicopter-borne ground-penetrating radar (GPR) data. For each individual GPR measurement, the signal travel time is combined with a simple model for firn densification and refreezing of meltwater. The model is calibrated at locations where GPR repeat measurements are available in two subsequent years and the densification can be tracked over time. Two 10.5 m long firn cores provide a reference for the density and chronology of firn layers. Thereby, IRHs correspond to density maxima, but not exclusively to former summer glacier surfaces. Along GPR profile sections from across the accumulation area we obtain the water equivalent (w.e.) of several annual firn layers. Because deeper IRHs could be tracked over shorter distances, the total length of analysed profile sections varies from 7.3 km for the uppermost accumulation layer (2011) to 0.1 km for the deepest (i.e. oldest) layer (2006). According to model results, refreezing accounts for 10% of the density increase over time and depth, and for 2% of the water equivalent. The strongest limitation to our method is the dependence on layer chronology assumptions. We show that GPR can be used not only to complement existing mass balance monitoring programmes on temperate glaciers but also to retrospectively extend newly initiated time series.

Distribution and accumulation of mercury and copper in mangrove sediments in Shenzhen, the world's most rapid urbanized city.

PubMed

Li, Ruili; Xu, Hualin; Chai, Minwei; Qiu, Guo Yu

2016-02-01

To investigate the influence of mangrove forest on heavy metal accumulation and storage in intertidal sediments, core sediments from natural mangrove, restored mangrove, and adjacent mud flat spanning the intertidal zone along the south coastline of the most heavily urbanized Deep bay, Guangdong province, China were analyzed. The average concentrations of mercury (Hg) in surface sediments of natural mangrove and restored mangrove were 172 and 151 ng g(-1), whereas those of copper (Cu) were 75 and 50 μg g(-1), respectively. Compared to those from other typical mangrove wetlands of the world, the metal levels in Shenzhen were at median to high levels, which is consistent with the fact that Shenzhen is in high exploitation and its mangrove suffer intensive impact from human activities. Hg and Cu concentration profiles indicated a higher metal accumulation in surface layers of sediments, in agreement with enrichment of organic matter contents. Maximum concentration, enrichment factors, and excess (background-deducted) concentration inventories of metals (Hg and Cu) were substantially different between environments, decreasing from natural mangrove sediments to restored mangrove sediments to mud flat. Furthermore, metal inputs to Futian mangrove decreased in the order natural mangrove > restored mangrove > mud flat, indicating that mangrove facilitated the accumulation and storage of Hg and Cu in sediment layers.

Photo-induced persistent inversion of germanium in a 200-nm-deep surface region.

PubMed

Prokscha, T; Chow, K H; Stilp, E; Suter, A; Luetkens, H; Morenzoni, E; Nieuwenhuys, G J; Salman, Z; Scheuermann, R

2013-01-01

The controlled manipulation of the charge carrier concentration in nanometer thin layers is the basis of current semiconductor technology and of fundamental importance for device applications. Here we show that it is possible to induce a persistent inversion from n- to p-type in a 200-nm-thick surface layer of a germanium wafer by illumination with white and blue light. We induce the inversion with a half-life of ~12 hours at a temperature of 220 K which disappears above 280 K. The photo-induced inversion is absent for a sample with a 20-nm-thick gold capping layer providing a Schottky barrier at the interface. This indicates that charge accumulation at the surface is essential to explain the observed inversion. The contactless change of carrier concentration is potentially interesting for device applications in opto-electronics where the gate electrode and gate oxide could be replaced by the semiconductor surface.

Influence of charged defects on the interfacial bonding strength of tantalum- and silver-doped nanograined TiO2.

PubMed

Azadmanjiri, Jalal; Wang, James; Berndt, Christopher C; Kapoor, Ajay; Zhu, De Ming; Ang, Andrew S M; Srivastava, Vijay K

2017-05-17

A nano-grained layer including line defects was formed on the surface of a Ti alloy (Ti alloy , Ti-6Al-4V ELI). Then, the micro- and nano-grained Ti alloy with the formation of TiO 2 on its top surface was coated with a bioactive Ta layer with or without incorporating an antibacterial agent of Ag that was manufactured by magnetron sputtering. Subsequently, the influence of the charged defects (the defects that can be electrically charged on the surface) on the interfacial bonding strength and hardness of the surface system was studied via an electronic model. Thereby, material systems of (i) Ta coated micro-grained titanium alloy (Ta/MGTi alloy ), (ii) Ta coated nano-grained titanium alloy (Ta/NGTi alloy ), (iii) TaAg coated micro-grained titanium alloy (TaAg/MGTi alloy ) and (iv) TaAg coated nano-grained titanium alloy (TaAg/NGTi alloy ) were formed. X-ray photoelectron spectroscopy was used to probe the electronic structure of the micro- and nano-grained Ti alloy , and so-formed heterostructures. The thin film/substrate interfaces exhibited different satellite peak intensities. The satellite peak intensity may be related to the interfacial bonding strength and hardness of the surface system. The interfacial layer of TaAg/NGTi alloy exhibited the highest satellite intensity and maximum hardness value. The increased bonding strength and hardness in the TaAg/NGTi alloy arises due to the negative core charge of the dislocations and neighbor space charge accumulation, as well as electron accumulation in the created semiconductor phases of larger band gap at the interfacial layer. These two factors generate interfacial polarization and enhance the satellite intensity. Consequently, the interfacial bonding strength and hardness of the surface system are improved by the formation of mixed covalent-ionic bonding structures around the dislocation core area and the interfacial layer. The bonding strength relationship by in situ XPS on the metal/TiO 2 interfacial layer may be examined with other noble metals and applied in diverse fields.

Active Dust Mitigation Technology for Thermal Radiators for Lunar Exploration

NASA Technical Reports Server (NTRS)

Calle, C. I.; Buhler, C. R.; Hogue, M. D.; Johansen, M. R.; Hopkins, J. W.; Holloway, N. M. H.; Connell, J. W.; Chen, A.; Irwin, S. A.; Case, S. O.;

Influence of Near-Surface Severe Plastic Deformation of Mild Steel on the Inhibition Performance of Sodium Molybdate and 1H-Benzotriazole in Artificial Sea Water

NASA Astrophysics Data System (ADS)

Sabet Bokati, Kazem; Dehghanian, Changiz; Babaei, Mahdi

2018-02-01

The effects of near-surface severe plastic deformation (NS-SPD) on the inhibition performance of sodium molybdate (SM) and 1H-benzotriazole (BTA) for mild steel were investigated using weight loss, polarization and electrochemical impedance spectroscopy measurements. The crystal grain size of NS-SPD-processed surface was analyzed by x-ray diffractometry and field emission scanning electron microscopy. A deformed layer with thickness of 20 ± 5 µm was produced on mild steel surface after NS-SPD process due to accumulated strains. The NS-SPD process caused more effective adsorption of corrosion inhibitors due to the fabrication of a surface with a high density of preferential adsorption sites. However, the stability of protective layer was predominantly influenced by the effect of NS-SPD process on inhibition efficiency. The fairly good persistence of protective layer formed on the surface by SM-containing solution and also positive effect of NS-SPD process on adsorption of molybdate ions caused higher inhibition performance for sodium molybdate. However, NS-SPD process encouraged deterioration of protective layer formed on steel surface in the presence of BTA inhibitor. It was ascribed to partial coverage of surface, low stability of adsorbed layer and thus more adsorption of aggressive ions on unprotected area which was uncovered during immersion time.

Electron Transport in SrTio3 Accumulation Layers and Semiconductor Nanocrystal Films

NASA Astrophysics Data System (ADS)

Fu, Han

In this thesis, we study two subjects: SrTiO3 (STO) accumulation layers and films made of semiconductor nanocrystals (NCs), which are important for technological applications. We start from the low temperature conductivity of electron accumulation layers induced by the very strong electric field at the surface of STO sample. Due to the strongly nonlinear lattice dielectric response, the three-dimensional density of electrons n(z) in such a layer decays with the distance from the surface z very slowly as n(z) ≃ 1/z12/7 . We show that when the mobility is limited by the surface scattering the contribution of such a tail to the conductivity diverges at large z because of growing time electrons need to reach the surface. We explore truncation of this divergence by the finite sample width, by the bulk scattering rate, by the back gate voltage, or by the crossover to the bulk linear dielectric response with the dielectric constant kappa. As a result we arrive at the anomalously large mobility, which depends not only on the rate of the surface scattering, but also on the physics of truncation. Similar anomalous behavior is found for the Hall factor, the magnetoresistance, and the thermopower. For the second part, we extend to the cases of spherical and cylindrical geometries, and more complicated planar structures. For the planar case, we study overlapping accumulation layers in GdTiO3/STO/GdTiO 3 quantum wells and electron gases created by spill-out from NSTO (heavily n-type doped STO) layers into STO. Generalization of our approach to a spherical donor cluster creating a big Thomas-Fermi atom with electrons in STO brings us to the problem of supercharged nuclei. It is known that for an atom with nuclear charge Ze, where Z > 170, electrons collapse onto the nucleus resulting in a net charge Zn < Z. Here, instead of relativistic physics, the collapse is caused by the nonlinear dielectric response. Electrons collapse into the charged spherical donor cluster with radius R when its total charge number Z exceeds the critical value Zc ≃ R/a, where a is the lattice constant. The net charge eZ n grows with Z until Z exceeds Z*≃ (R/a)9/7. After this point, the charge number of the compact core Zn remains ≃ Z*, with the rest Z electrons forming a sparse Thomas-Fermi atom with it. We also study the case of long cylindrical clusters. In the third part, we look at the details of the surface scattering by roughness of accumulation layers. To connect with previous works on surface roughness scattering, we focus on conventional semiconductors with the linear dielectric response where accumulation layers with very large concentrations of electrons and many subbands filled became recently available due to ionic liquid and other new methods of gating. The low temperature mobility in such layers is limited by the surface roughness scattering. However theories of roughness scattering so far dealt only with the small-density single subband two-dimensional (2D) electron gas. Here we develop a theory of roughness scattering limited mobility for the multisubband large concentration case. We show that with growing 2D electron concentration N the surface dimensionless conductivity sigma/(2e2/h) first decreases as ≃ N-6/5 and then saturates as ˜ (LambdaaB/Delta 2) >> 1, where Lambda and Delta are the characteristic length and height of the surface roughness, aB is the effective Bohr radius. This means that in spite of the shrinkage of the 2D electron gas width and the related increase of the scattering rate, the 2D electron gas remains a good metal. Thus, there is no re-entrant metal-insulator transition at high concentrations conjectured by Das Sarma and Hwang [PRB 89, 121413 (2014)]. The expression of surface relaxation time can be generalized to the STO case where the dielectric response is nonlinear. We find that there is no reentrant metal-insulator transition, either, in STO accumulation layers at experimentally available large N.. Finally, we switch to the study of NC films. We focus on the variable-range hopping of electrons in semiconductor NC films below the critical doping concentration nc at which films become metallic. The hopping conductivity is then described by the Efros-Shklovskii law which depends on the localization length of electrons. We study how the localization length grows with the doping concentration n in the film of touching NCs. For that we calculate the electron transfer matrix element t(n) between neighboring NCs for two models when NCs touch by small facets or just one point. We study two sources of disorder: variations of NC diameters and random Coulomb potentials originating from random numbers of donors in NCs. We use the ratio of t(n) to the disorder-induced NC level dispersion to find the localization length of electrons due to the multi-step elastic co-tunneling process. We find three different phases at n < nc depending on the strength of disorder, the material, sizes of NCs and their facets: 1) "insulator" where the localization length of electrons increases monotonically with n and 2) "oscillating insulator" when the localization length (and the conductivity) oscillates with n from the insulator base and 3) "blinking metal" where the localization length periodically diverges. The first two phases were seen experimentally and we discuss how one can see the more exotic third one. In all three the localization length diverges at n = nc. This allows us to find nc..

Vertically resolved measurements of nighttime radical reservoirs in Los Angeles and their contribution to the urban radical budget.

PubMed

Young, Cora J; Washenfelder, Rebecca A; Roberts, James M; Mielke, Levi H; Osthoff, Hans D; Tsai, Catalina; Pikelnaya, Olga; Stutz, Jochen; Veres, Patrick R; Cochran, Anthony K; VandenBoer, Trevor C; Flynn, James; Grossberg, Nicole; Haman, Christine L; Lefer, Barry; Stark, Harald; Graus, Martin; de Gouw, Joost; Gilman, Jessica B; Kuster, William C; Brown, Steven S

2012-10-16

Photolabile nighttime radical reservoirs, such as nitrous acid (HONO) and nitryl chloride (ClNO(2)), contribute to the oxidizing potential of the atmosphere, particularly in early morning. We present the first vertically resolved measurements of ClNO(2), together with vertically resolved measurements of HONO. These measurements were acquired during the California Nexus (CalNex) campaign in the Los Angeles basin in spring 2010. Average profiles of ClNO(2) exhibited no significant dependence on height within the boundary layer and residual layer, although individual vertical profiles did show variability. By contrast, nitrous acid was strongly enhanced near the ground surface with much smaller concentrations aloft. These observations are consistent with a ClNO(2) source from aerosol uptake of N(2)O(5) throughout the boundary layer and a HONO source from dry deposition of NO(2) to the ground surface and subsequent chemical conversion. At ground level, daytime radical formation calculated from nighttime-accumulated HONO and ClNO(2) was approximately equal. Incorporating the different vertical distributions by integrating through the boundary and residual layers demonstrated that nighttime-accumulated ClNO(2) produced nine times as many radicals as nighttime-accumulated HONO. A comprehensive radical budget at ground level demonstrated that nighttime radical reservoirs accounted for 8% of total radicals formed and that they were the dominant radical source between sunrise and 09:00 Pacific daylight time (PDT). These data show that vertical gradients of radical precursors should be taken into account in radical budgets, particularly with respect to HONO.

Autonomous profiling float observations of the high biomass plume downstream of the Kerguelen plateau in the Southern Ocean

NASA Astrophysics Data System (ADS)

Grenier, M.; Della Penna, A.; Trull, T. W.

2014-12-01

Natural iron fertilisation from Southern Ocean islands results in high primary production and phytoplankton biomass accumulations readily visible in satellite ocean colour observations. These images reveal great spatial complexity with highly varying concentrations of chlorophyll, presumably reflecting both variations in iron supply and conditions favouring phytoplankton accumulation. To examine the second aspect, in particular the influences of variations in temperature and stratification, we deployed four autonomous profiling floats in the Antarctic Circumpolar Current near the Kerguelen plateau in the Indian sector of the Southern Ocean. Each "bio-profiler" measured more than 250 profiles of temperature (T), salinity (S), dissolved oxygen, chlorophyll fluorescence (Chl a), and particle backscatter in the top 300 m of the water column, sampling up to 5 profiles per day along meandering trajectories extending up to 1000 km. Comparison of surface Chl a estimates (top 50 m depth; analogous to values from satellite images) with total water column inventories revealed largely linear relationships, suggesting that dilution of chlorophyll by mixed layer depth variations plays only a minor role in the spatial distributions observed by satellite, and correspondingly that these images provide credible information on total and not just surface biomass accumulations. Regions of very high Chl a accumulation (1.5-10 μg L-1) were associated predominantly with a narrow T-S class of surface waters, which appears to derive from the northern Kerguelen plateau. In contrast, waters with only moderate Chl a enrichments (0.5-1.5 μg L-1) displayed no clear correlation with water properties, including no dependence on mixed layer depth, suggesting a diversity of sources of iron and/or its efficient dispersion across filaments of the plume. The lack of dependence on mixed layer depth also indicates a limited influence on production by light limitation. One float became trapped in a cyclonic eddy, allowing temporal evaluation of the water column in early autumn. During this period, decreasing surface Chl a inventories corresponded with decreases in oxygen inventories on sub-mixed layer density surfaces, consistent with significant export of organic matter and its respiration and storage as dissolved inorganic carbon in the ocean interior. These results are encouraging for the expanded use of autonomous observing platforms to study biogeochemical, carbon cycle, and ecological problems, although the complex blend of Lagrangian and Eulerian sampling achieved by the floats suggests that arrays rather than single floats will often be required.

Subsurface segregation of yttria in yttria stabilized zirconia

NASA Astrophysics Data System (ADS)

de Ridder, M.; van Welzenis, R. G.; van der Gon, A. W. Denier; Brongersma, H. H.; Wulff, S.; Chu, W.-F.; Weppner, W.

2002-09-01

The segregation behavior in 3 and 10 mol % polycrystalline yttria stabilized zirconia (YSZ), calcined at temperatures ranging from 300 to 1600 degC, is characterized using low-energy ion scattering (LEIS). In order to be able to separate the Y and Zr LEIS signals, YSZ samples have been prepared using isotopically enriched 94ZrO2 instead of natural zirconia. The samples are made via a special precipitation method at a low temperature. The segregation to the outermost surface layer is dominated by impurities. The increased impurity levels are restricted to this first layer, which underlines the importance of the use of LEIS for this study. For temperatures of 1000 degC and higher, the oxides of the impurities Na, Si, and Ca even cover the surface completely. The performance of a device like the solid oxide fuel cell which has an YSZ electrolyte and a working temperature around 1000 degC, will, therefore, be strongly hampered by these impurities. The reduction of impurities, to prevent accumulation at the surface, will only be effective if the total impurity bulk concentration can be reduced below the 10 ppm level. Due to the presence of the impurities, yttria cannot accumulate in the outermost layer. It does so, in contrast to the general belief, in the subsurface layer and to much higher concentrations than the values reported previously. The difference in the interfacial free energies of Y2O3 and ZrO2 is determined to be -21plus-or-minus3 kJ/mol.

[Effects of mulching management on biomass of Phyllostachys praecox and soil fertility].

PubMed

Zhai, Wan Lu; Yang, Chuan Bao; Zhang, Xiao Ping; Gao, Gui Bin; Zhong, Zhe Ke

2018-04-01

We analyzed the dynamics of stand growth and soil nutrient availability during the degradation processes of Phyllostachys praecox plantation, taking the advantage of bamboo forest stands with different mulching ages (0, 3, 6, 9 and 12 a). The results showed the aboveground and belowground biomass of bamboo forest reached the maximum value when they were covered by three years, which was significantly increased by 14.6% and 146.6% compared with the control. The soil nutrient content was affected by the mulching age and soil layer. Soil nutrients gradually accumulated in upper layer. Soil organic carbon and total nitrogen content were increased with the increases of coverage years. The soil total phosphorus content at different soil layers showed a trend of decreasing first and then increasing. It was the lowest level in the surface layer (0-20 cm) and the bottom (40-60 cm) in 6 years, and the subsurface (20-40 cm) soil reached the lowest level in three years. The total potassium content kept increasing in 0-20 cm soil layer, but decreased during the first three years of mulching and then increased in 20-60 cm soil layer. The comprehensive index of soil fertility quality was greatly improved after nine years mulching, with fertility of subsurface soil being better than that of surface and bottom soils. There was no relationship between the soil fertility index and biomass of different organs in bamboo in the different mulching ages. In the subsurface, however, nitrogen content was negatively related to leaf biomass and potassium was negatively correlated with the biomass of leaves and whip roots. Our results indicated that excessive accumulation of soil nutrients seriously inhibited the propagation and biomass accumulation of P. praecox after long-term mulching management and a large amount of fertilizer, which further aggravated the degradation of bamboo plantation.

Pluto: Fluidized Transport of Tholins by Heating of the Subsurface

NASA Technical Reports Server (NTRS)

Cruikshank, Dale P.; Spohrer, Steven; Grundy, William M.; Moore, Jeffrey M.; Umurhan, Orkan M.; White, Oliver L.; Beyer, Ross A.; Dalle Ore, Cristina M.; Stern, S. A.; Young, Leslie;

Estimating the Change of Groundwater Salinization in the Central North China Plain for Sustainable Groundwater Utilization

NASA Astrophysics Data System (ADS)

Zhan, Y.; He, X.; Zheng, C.; Guo, Z.

2017-12-01

Due to the growing demand of food supplies and limited freshwater resources, North China Plain (NCP) is highly dependent on the groundwater resources. Groundwater overdraft has made NCP a closed hydrologic basin, where the connection between surface and groundwater has been cut off, which can lead to salt accumulation in the groundwater system. Thus it is imperative to investigate the overall salt balance in the region for sustainable utilization of groundwater resources, as well as to better understand the salt accumulating processes caused by groundwater pumping and return flow. The central plain of NCP (excluding the piedmont plain and coastal plain) is selected in the present study, where the groundwater salt content is mainly controlled by precipitation, irrigation, groundwater pumping and rock-water interaction in vertical direction; therefore, a conceptual 1-D mixing model is developed for salt balance calculation, where the salt content is expressed by the concentration of Total Dissolved Solid (TDS) in groundwater. Geological structures and regional water balance data are obtained from numerical groundwater models previously developed in the area. The simulation starts in year 1900 with a 50-year time step and groundwater vertical flow velocity starting with 2 m/y. TDS concentration is then calculated through salt input and output in each layer, with consideration of soil salt accumulation, change of precipitation, rock-water interaction etc. The results suggest that in a closed hydrologic basin, groundwater pumping and return flow will gradually increase salt content in the groundwater body from upper layers to lower layers resulting from the flushing of salt accumulated in the top soil layer. After two time steps, the model is able to reproduce the observed TDS concentration in present time with reasonable accuracy; and after six time steps, which correspond to 300 years, the whole central plain of NCP will be under the influence of high salinity, which is around 2000 mg/L of TDS. The study also suggests that in order to predict the future change of salt content in groundwater in NCP more accurately, the mechanisms of how salinity accumulates in the surface soil is the most critical factor, which requires further research.

Suppression of surface charge accumulation on Al{sub 2}O{sub 3}-filled epoxy resin insulator under dc voltage by direct fluorination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Boya; Zhang, Guixin, E-mail: guixin@mail.tsinghua.edu.cn; Li, Chuanyang

2015-12-15

Surface charge accumulation on insulators under high dc voltage is a major factor that may lead to the reduction of insulation levels in gas insulated devices. In this paper, disc insulators made of Al{sub 2}O{sub 3}-filled epoxy resin were surface fluorinated using a F{sub 2}/N{sub 2} mixture (12.5% F{sub 2}) at 50 °C and 0.1 MPa for different durations of 15 min, 30 min and 60 min. A dc voltage was applied to the insulator for 30 min and the charge density on its surface was measured by an electrostatic probe. The results revealed significant lower surface charge densities on themore » fluorinated insulators in comparison with the original one. Surface conductivity measurements indicated a higher surface conductivity by over three orders of magnitude after fluorination, which would allow the charges to transfer along the surface and thus may suppress their accumulation. Further, attenuated total reflection infrared analysis and surface morphology observations of the samples revealed that the introduction of fluoride groups altered the surface physicochemical properties. These structure changes, especially the physical defects reduced the depth of charge traps in the surface layer, which was verified by the measurement of energy distributions of the electron and hole traps based on the isothermal current theory. The results in this paper demonstrate that fluorination can be a promising and effective method to suppress surface charge accumulation on epoxy insulators in gas insulated devices.« less

Influence of Persistent Wind Scour on the Surface Mass Balance of Antarctica

NASA Technical Reports Server (NTRS)

Das, Indrani; Bell, Robin E.; Scambos, Ted A.; Wolovick, Michael; Creyts, Timothy T.; Studinger, Michael; Fearson, Nicholas; Nicolas, Julien P.; Lenaerts, Jan T. M.; vandenBroeke, Michiel R.

2013-01-01

Accurate quantification of surface snow accumulation over Antarctica is a key constraint for estimates of the Antarctic mass balance, as well as climatic interpretations of ice-core records. Over Antarctica, near-surface winds accelerate down relatively steep surface slopes, eroding and sublimating the snow. This wind scour results in numerous localized regions (< or = 200 sq km) with reduced surface accumulation. Estimates of Antarctic surface mass balance rely on sparse point measurements or coarse atmospheric models that do not capture these local processes, and overestimate the net mass input in wind-scour zones. Here we combine airborne radar observations of unconformable stratigraphic layers with lidar-derived surface roughness measurements to identify extensive wind-scour zones over Dome A, in the interior of East Antarctica. The scour zones are persistent because they are controlled by bedrock topography. On the basis of our Dome A observations, we develop an empirical model to predict wind-scour zones across the Antarctic continent and find that these zones are predominantly located in East Antarctica. We estimate that approx. 2.7-6.6% of the surface area of Antarctica has persistent negative net accumulation due to wind scour, which suggests that, across the continent, the snow mass input is overestimated by 11-36.5 Gt /yr in present surface-mass-balance calculations.

Elevated CO2 facilitates C and N accumulation in a rice paddy ecosystem.

PubMed

Guo, Jia; Zhang, Mingqian; Wang, Xiaowen; Zhang, Weijian

2015-03-01

Elevated CO2 can stimulate wetland carbon (C) and nitrogen (N) exports through gaseous and dissolved pathways, however, the consequent influences on the C and N pools are still not fully known. Therefore, we set up a free-air CO2 enrichment experiment in a paddy field in Eastern China. After five year fumigation, we studied C and N in the plant-water-soil system. The results showed: (1) elevated CO2 stimulated rice aboveground biomass and N accumulations by 19.1% and 12.5%, respectively. (2) Elevated CO2 significantly increased paddy soil TOC and TN contents by 12.5% and 15.5%, respectively in the 0-15 cm layer, and 22.7% and 26.0% in the 15-30 cm soil layer. (3) Averaged across the rice growing period, elevated CO2 greatly increased TOC and TN contents in the surface water by 7.6% and 11.4%, respectively. (4) The TOC/TN ratio and natural δ15N value in the surface soil showed a decreasing trend under elevated CO2. The above results indicate that elevated CO2 can benefit C and N accumulation in paddy fields. Given the similarity between the paddies and natural wetlands, our results also suggest a great potential for long-term C and N accumulation in natural wetlands under future climate patterns. Copyright © 2015. Published by Elsevier B.V.

Impact of UV irradiation on multiwall carbon nanotubes in nanocomposites: formation of entangled surface layer and mechanisms of release resistance

PubMed Central

Nguyen, Tinh; Petersen, Elijah J.; Pellegrin, Bastien; Gorham, Justin M.; Lam, Thomas; Zhao, Minhua; Sung, Lipiin

2017-01-01

Multiwall carbon nanotubes (MWCNTs) are nanofillers used in consumer and structural polymeric products to enhance a variety of properties. Under weathering, the polymer matrix will degrade and the nanofillers may be released from the products potentially impacting ecological or human health. In this study, we investigated the degradation of a 0.72 % (by mass) MWCNT/amine-cured epoxy nanocomposite irradiated with high intensity ultraviolet (UV) light at various doses, the effects of UV exposure on the surface accumulation and potential release of MWCNTs, and possible mechanisms for the release resistance of the MWCNT surface layer formed on nanocomposites by UV irradiation. Irradiated samples were characterized for chemical degradation, mass loss, surface morphological changes, and MWCNT release using a variety of analytical techniques. Under 295 nm to 400 nm UV radiation up to a dose of 4865 MJ/m2, the nanocomposite matrix underwent photodegradation, resulting in formation of a dense, entangled MWCNT network structure on the surface. However, no MWCNT release was detected, even at very high UV doses, suggesting that the MWCNT surface layer formed from UV irradiation of polymer nanocomposites resist release. Four possible release resistance mechanisms of the UV-induced MWCNT surface layer are presented and discussed. PMID:28603293

Photoelectron spectroscopic and microspectroscopic probes of ferroelectrics

NASA Astrophysics Data System (ADS)

Tǎnase, Liviu C.; Abramiuc, Laura E.; Teodorescu, Cristian M.

2017-12-01

This contribution is a review of recent aspects connected with photoelectron spectroscopy of free ferroelectric surfaces, metals interfaced with these surfaces, graphene-like layers together with some exemplifications concerning molecular adsorption, dissociations and desorptions occurring from ferroelectrics. Standard photoelectron spectroscopy is used nowadays in correlation with other characterization techniques, such as piezoresponse force microscopy, high resolution transmission electron spectroscopy, and ferroelectric hysteresis cycles. In this work we will concentrate mainly on photoelectron spectroscopy and spectro-microscopy characterization of ferroelectric thin films, starting from atomically clean ferroelectric surfaces of lead zirco-titanate, then going towards heterostructures using this material in combination with graphene-like carbon layers or with metals. Concepts involving charge accumulation and depolarization near surface will be revisited by taking into account the newest findings in this area.

Defect-induced wetting on BaF 2(111) and CaF 2(111) at ambient conditions

NASA Astrophysics Data System (ADS)

Cardellach, M.; Verdaguer, A.; Fraxedas, J.

2011-12-01

The interaction of water with freshly cleaved (111) surfaces of isostructural BaF2 and CaF2 single crystals at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes and optical microscopy. Such surfaces exhibit contrasting behaviors for both materials: while on BaF2(111) two-dimensional water layers are formed after accumulation at step edges, CaF2(111) does not promote the formation of such layers. We attribute such opposed behavior to lattice match (mismatch) between hexagonal water ice and the hexagonal (111) surfaces of BaF2(CaF2). Optical microscope images reveal that this behavior also determines the way the surfaces become wetted at a macroscopic level.

Military Knowledge Handbook for Commanders (Selected Section)

DTIC Science & Technology

1988-03-28

8217 Accession For NTIS GRA&I DTIC TAB 0l Unannoun ed 0] ju,.it . " t ation Distri’muti on/ Availabilit %Codes Dist cSpeial GRAPHICS DISCLAIMER...cloud layers, the energy of ray radiation on the ground will increase due to reflection effect of the cloud layers. Water surface, ice, accumulated... water flow can direct the radioactive fallout into defense works and water sources to worsen contaminations; radioactive fallout can easily be retained in

Atmospheric boundary layer modification in the marginal ice zone

NASA Technical Reports Server (NTRS)

Bennett, Theodore J., Jr.; Hunkins, Kenneth

1986-01-01

A case study of the Andreas et al. (1984) data on atmospheric boundary layer modification in the marginal ice zone is made. The model is a two-dimensional, multilevel, linear model with turbulence, lateral and vertical advection, and radiation. Good agreement between observed and modeled temperature cross sections is obtained. In contrast to the hypothesis of Andreas et al., the air flow is found to be stable to secondary circulations. Adiabatic lifting and, at long fetches, cloud top longwave cooling, not an air-to-surface heat flux, dominate the cooling of the boundary layer. The accumulation with fetch over the ice of changes in the surface wind field is shown to have a large effect on estimates of the surface wind stress. It is speculated that the Andreas et al. estimates of the drag coefficient over the compact sea ice are too high.

Study of secondary-flow patterns in an annular cascade of turbine nozzle blades with vortex design

NASA Technical Reports Server (NTRS)

Rohlik, Harold E; Allen, Hubert W; Herzig, Howard Z

1953-01-01

In order to increase understanding of the origin of losses in a turbine, the secondary-flow components in the boundary layers and the blade wakes of an annular cascade of turbine nozzle blades (vortex design) was investigated. A detailed study was made of the total-pressure contours and, particularly, of the inner-wall loss cores downstream of the blades. The inner-wall loss core associated with a blade of the turbine-nozzle cascade is largely the accumulation of low-momentum fluids originating elsewhere in the cascade. This accumulation is effected by a secondary-flow mechanism which acts to transport the low-momentum fluids across the channels on the walls and radially in the blade wakes and boundary layers. The patterns of secondary flow were determined by use of hydrogen sulfide traces, paint, flow fences, and total pressure surveys. At one flow condition investigated, the radial transport of low-momentum fluid in the blade wake and on the suction surface near the trailing edge accounted for 65 percent of the loss core; 30 percent resulted from flow in the thickened boundary layer on the suction surface and 35 percent from flow in the blade wake.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kebede, Mulu A.; Bish, David L.; Losovyj, Yaroslav

Nitrous acid (HONO) accumulates in the nocturnal boundary layer where it is an important source of daytime hydroxyl radicals. Although there is clear evidence for the involvement of heterogeneous reactions of NO2 on surfaces as a source of HONO, mechanisms remain poorly understood. We used coated-wall flow tube measurements of NO2 reactivity on environmentally relevant surfaces [Fe (hydr)oxides, clay minerals, and soil from Arizona and the Saharan Desert] and detailed mineralogical characterization of substrates to show that reduction of NO2 by Fe-bearing minerals in soil can be a more important source of HONO than the putative NO2 hydrolysis mechanism. Themore » magnitude of NO2-to-HONO conversion depends on the amount of Fe2+ present in substrates and soil surface acidity. Studies examining the dependence of HONO flux on substrate pH revealed that HONO is formed at soil pH < 5 from the reaction between NO2 and Fe2+(aq) present in thin films of water coating the surface, whereas in the range of pH 5–8 HONO stems from reaction of NO2 with structural iron or surface complexed Fe2+ followed by protonation of nitrite via surface Fe-OH2+ groups. Reduction of NO2 on ubiquitous Fe-bearing minerals in soil may explain HONO accumulation in the nocturnal boundary layer and the enhanced [HONO]/[NO2] ratios observed during dust storms in urban areas.« less

Strain relaxation of thick (11–22) semipolar InGaN layer for long wavelength nitride-based device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jaehwan; Min, Daehong; Jang, Jongjin

2014-10-28

In this study, the properties of thick stress-relaxed (11–22) semipolar InGaN layers were investigated. Owing to the inclination of growth orientation, misfit dislocations (MDs) occurred at the heterointerface when the strain state of the (11–22) semipolar InGaN layers reached the critical point. We found that unlike InGaN layers based on polar and nonpolar growth orientations, the surface morphologies of the stress-relaxed (11–22) semipolar InGaN layers did not differ from each other and were similar to the morphology of the underlying GaN layer. In addition, misfit strain across the whole InGaN layer was gradually relaxed by MD formation at the heterointerface.more » To minimize the effect of surface roughness and defects in GaN layers on the InGaN layer, we conducted further investigation on a thick (11–22) semipolar InGaN layer grown on an epitaxial lateral overgrown GaN template. We found that the lateral indium composition across the whole stress-relaxed InGaN layer was almost uniform. Therefore, thick stress-relaxed (11–22) semipolar InGaN layers are suitable candidates for use as underlying layers in long-wavelength devices, as they can be used to control strain accumulation in the heterostructure active region without additional influence of surface roughness.« less

Surface electrons in inverted layers of p-HgCdTe

NASA Technical Reports Server (NTRS)

Schacham, Samuel E.; Finkman, Eliezer

1990-01-01

Anodic oxide passivation of p-type HgCdTe generates an inversion layer. Extremely high Hall mobility data for electrons in this layer indicated the presence of a two-dimensional electron gas. This is verified by use of the Shubnikov-de Haas effect from 1.45 to 4.15 K. Data are extracted utilizing a numerical second derivative of dc measurement. Three sub-bands are detected. Their relative occupancies are in excellent agreement with theory and with experimental results obtained on anodic oxide as accumulation layers of n-type HgCdTe. The effective mass derived is comparable to what was expected.

Fault creep and persistent asperities on the western section of the North Anatolian Fault, Turkey

NASA Astrophysics Data System (ADS)

Floyd, M.; Reilinger, R. E.; Ergintav, S.; Karabulut, H.; Vernant, P.; Konca, A. O.; Dogan, U.; Cetin, S.; Cakir, Z.; Mencin, D.; Bilham, R. G.; King, R. W.

2017-12-01

We interpret new geodetic and seismic observations along the western section of the North Anatolian Fault (NAF) in Turkey as evidence for persistent asperities on the fault surface. Analysis of geodetic and seismic observations of seven segments of the fault at different stages of the earthquake cycle suggest that areas of the fault surface that are accumulating strain (i.e. asperities) are deficient in interseismic seismicity and earthquake aftershocks compared to areas between asperities that are failing at least in part by fault creep. From west to east, these segments include the 2014 M6.9 Gokceada earthquake and 1912 M7.4 Ganos earthquake segments, the Sea of Marmara and Princes' Islands seismic "gaps", the 1999 M7.6/7.2 Izmit/Duzce earthquake segments, and the 1944 M7.4 Ismetpasa segment, which remains actively creeping. Aspects of each segment contribute to our interpretation of overall fault behavior. The most well-defined distribution of coseismic slip in relation to pre- and post-earthquake seismicity is for the 2014 Gokceada event. The most complete set of geodetic observations (pre-, co-, and short- and long-term post-seismic) come from the 1999 Izmit and Duzce events. Simple three-layer elastic models including a middle layer that is fully locked between earthquakes, and shallow and deeper layers that are allowed to creep, can account for these observations of the deformation cycle. Recent observations from InSAR, creepmeters and small-aperture GPS profiles indicate ongoing surface and shallow fault creep rates, as allowed by the upper layer of the three-layer model. Conceptually, creep in the deeper layer represents the deep healing of the fault following the earthquake. For the Izmit and Duzce earthquake segments, healing from prior earthquakes was complete before the 1999 sequence. More generally, the consistent pattern of strain accumulation along the full length of the NAF, including the long eastern segments that ruptured in major earthquakes in 1939, 1942 and 1943, suggests that deep fault healing is complete over time scales much shorter than the earthquake repeat time. Given their similarities, these results may be applicable and provide insights into the mechanics of strain accumulation and earthquake potential along other continental strike-slip faults such as the San Andreas Fault.

Ferroelectric polarization induces electric double layer bistability in electrolyte-gated field-effect transistors.

PubMed

Fabiano, Simone; Crispin, Xavier; Berggren, Magnus

2014-01-08

The dense surface charges expressed by a ferroelectric polymeric thin film induce ion displacement within a polyelectrolyte layer and vice versa. This is because the density of dipoles along the surface of the ferroelectric thin film and its polarization switching time matches that of the (Helmholtz) electric double layers formed at the ferroelectric/polyelectrolyte and polyelectrolyte/semiconductor interfaces. This combination of materials allows for introducing hysteresis effects in the capacitance of an electric double layer capacitor. The latter is advantageously used to control the charge accumulation in the semiconductor channel of an organic field-effect transistor. The resulting memory transistors can be written at a gate voltage of around 7 V and read out at a drain voltage as low as 50 mV. The technological implication of this large difference between write and read-out voltages lies in the non-destructive reading of this ferroelectric memory.

The formation mechanisms of surface nanocrystallites in β-type biomedical TiNbZrFe alloy by surface mechanical attrition treatment

NASA Astrophysics Data System (ADS)

Jin, Lei; Cui, Wenfang; Song, Xiu; Zhou, Lian

2015-08-01

A nanostructured surface layer was successfully performed on a biomedical β-type TiNbZrFe alloy by surface mechanical attrition treatment (SMAT). The results reveal that the surface layer along the depth from treated surface to strain-free matrix could be divided into an outer nanocrystalline layer (0-30 μm), a high-density dislocation region (30-200 μm) and an inner region with low-density dislocations and twins (200-700 μm) when the surface was treated for 60 min. The microhardness of the surface layer is enhanced and increases with increasing treatment time. Although the {1 1 2} <1 1 1> twin coordinates the deformations with dislocations, this coordination only occurs in the low strain area and cannot affect the nanocrystalline formation. The self-nanocrystallization of TiNbZrFe alloy is mainly attributed to dislocation movements. First, the dislocations start to move and easily form dislocation bands along certain crystal directions; then, multiple slips of dislocations gradually form dislocation tangles; after that, high-density dislocation tangles increases, which divides primary grains into many small domain areas. As high strain energies accumulate on the interfaces among these areas, the lattice rotation can be driven between the adjacent small domain areas, finally resulting in a large number of nanocrystalline regions with low or large angle grain boundaries.

Organic C and N stabilization in a forest soil: evidence from sequential density fractionation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sollins, P; Swanston, C; Kleber, M

2005-07-15

In mineral soil, organic matter (OM) accumulates mainly on and around surfaces of silt- and clay-size particles. When fractionated according to particle density, C and N concentration (per g fraction) and C/N of these soil organo-mineral particles decrease with increasing particle density across soils of widely divergent texture, mineralogy, location, and management. The variation in particle density is explained potentially by two factors: (1) a decrease in the mass ratio of organic to mineral phase of these particles, and (2) variations in density of the mineral phase. The first explanation implies that the thickness of the organic accumulations decreases withmore » increasing particle density. The decrease in C/N can be explained at least partially by especially stable sorption of cationic peptidic compounds (amine, amide, and pyrrole) directly to mineral surfaces, a phenomenon well documented both empirically and theoretically. These peptidic compounds, along with ligand-exchanged carboxylic compounds, could then form a stable inner organic layer onto which less polar organics could sorb more readily than onto the highly charged mineral surfaces (''onion'' layering model). To explore mechanisms underlying this trend in C concentration and C/N with particle density, we sequentially density fractionated an Oregon andic soil at 1.65, 1.85, 2.00, 2.28, and 2.55 g cm{sup -3} and analyzed the six fractions for measures of organic matter and mineral phase properties. All measures of OM composition showed either: (1) a monotonic change with density, or (2) a monotonic change across the lightest fractions, then little change over the heaviest fractions. Total C, N, and lignin phenol concentration all decreased monotonically with increasing density, and {sup 14}C mean residence time (MRT) increased with particle density from ca. 150 y to >980 y in the four organo-mineral fractions. In contrast, C/N, {sup 13}C and {sup 15}N concentration all showed the second pattern. All these data are consistent with a general pattern of an increase in extent of microbial processing with increasing organo-mineral particle density, and also with an ''onion'' layering model. X-ray diffraction before and after separation of magnetic materials showed that the sequential density fractionation isolated pools of differing mineralogy, with layer-silicate clays dominating in two of the intermediate fractions and primary minerals in the heaviest two fractions. There was no indication that these differences in mineralogy controlled the differences in density of the organo-mineral particles in this soil. Thus, our data are consistent with the hypothesis that variation in particle density reflects variation in thickness of the organic accumulations and with an ''onion'' layering model for organic matter accumulation on mineral surfaces. However, the mineralogy differences among fractions made it difficult to test either the layer-thickness or ''onion'' layering models with this soil. Although sequential density fractionation isolated pools of distinct mineralogy and organic-matter composition, more work will be needed to understand mechanisms relating the two factors.« less

Local Variability in Firn Layering and Compaction Rates Using GPR Data, Depth-Density Profiles, and In-Situ Reflectors in the Dry Snow Zone Near Summit Station, Greenland

NASA Astrophysics Data System (ADS)

Lines, A.; Elliott, J.; Ray, L.; Albert, M. R.

2017-12-01

Understanding the surface mass balance (SMB) of the Greenland ice sheet is critical to evaluating its response to a changing climate. A key factor in translating satellite and airborne elevation measurements of the ice sheet to SMB is understanding natural variability of firn layer depth and the relative compaction rate of these layers. A site near Summit Station, Greenland was chosen to investigate the variation in layering across a 100m by 100m grid using a 900 MHz and a 2.6 GHz ground penetrating radar (GPR) antenna. These radargrams were ground truthed by taking depth density profiles of five 2m snow pits and five 5m firn cores within the 100m by 100m grid. Combining these measurements with the accumulation data from the nearby ICECAPS weekly bamboo forest measurements, it's possible to see how the snow deposition from individual storm events can vary over a small area. Five metal reflectors were also placed on the surface of the snow in the bounds of the grid to serve as reference reflectors for similar measurements that will be taken in the 2018 field season at Summit Station. This will assist in understanding how one year of accumulation in the dry snow zone impacts compaction and how this rate can vary over a small area.

Kinetics of Accumulation of Damage in Surface Layers of Lithium-Containing Aluminum Alloys in Fatigue Tests with Rigid Loading Cycle and Corrosive Effect of Environment

NASA Astrophysics Data System (ADS)

Morozova, L. V.; Zhegina, I. P.; Grigorenko, V. B.; Fomina, M. A.

2017-07-01

High-resolution methods of metal physics research including electron, laser and optical microscopy are used to study the kinetics of the accumulation of slip lines and bands and the corrosion damage in the plastic zone of specimens of aluminum-lithium alloys 1441 and B-1469 in rigid-cycle fatigue tests under the joint action of applied stresses and corrosive environment. The strain parameters (the density of slip bands, the sizes of plastic zones near fracture, the surface roughness in singled-out zones) and the damage parameters (the sizes of pits and the pitting area) are evaluated.

The Role of Iron-Bearing Minerals in NO2 to HONO Conversion on Soil Surfaces.

PubMed

Kebede, Mulu A; Bish, David L; Losovyj, Yaroslav; Engelhard, Mark H; Raff, Jonathan D

2016-08-16

Nitrous acid (HONO) accumulates in the nocturnal boundary layer where it is an important source of daytime hydroxyl radicals. Although there is clear evidence for the involvement of heterogeneous reactions of NO2 on surfaces as a source of HONO, mechanisms remain poorly understood. We used coated-wall flow tube measurements of NO2 reactivity on environmentally relevant surfaces (Fe (hydr)oxides, clay minerals, and soil from Arizona and the Saharan Desert) and detailed mineralogical characterization of substrates to show that reduction of NO2 by Fe-bearing minerals in soil can be a more important source of HONO than the putative NO2 hydrolysis mechanism. The magnitude of NO2-to-HONO conversion depends on the amount of Fe(2+) present in substrates and soil surface acidity. Studies examining the dependence of HONO flux on substrate pH revealed that HONO is formed at soil pH < 5 from the reaction between NO2 and Fe(2+)(aq) present in thin films of water coating the surface, whereas in the range of pH 5-8 HONO stems from reaction of NO2 with structural iron or surface complexed Fe(2+) followed by protonation of nitrite via surface Fe-OH2(+) groups. Reduction of NO2 on ubiquitous Fe-bearing minerals in soil may explain HONO accumulation in the nocturnal boundary layer and the enhanced [HONO]/[NO2] ratios observed during dust storms in urban areas.

Raman study of bulk-heterojunction morphology in photoactive layers treated with solvent-vapor annealing

NASA Astrophysics Data System (ADS)

Onojima, Norio; Ishima, Yasuhisa; Izumi, Daisuke; Takahashi, Kazuyuki

2018-03-01

The effect of solvent-vapor annealing (SVA) on bulk-heterojunction morphology in photoactive layers composed of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was analyzed using Raman spectroscopy. We prepared the photoactive layers by electrostatic spray deposition (ESD) and fabricated organic photovoltaic devices with a conventional cell structure. Although postdeposition annealing can be omitted when the photoactive layer is deposited using ESD under dry condition, the surface is relatively rough owing to the existence of a number of droplet traces. The SVA treatment can eliminate such droplet traces, while excessive SVA resulted in a significant decrease in open-circuit voltage. The Raman study of the bulk-heterojunction morphology demonstrated the accumulation of P3HT molecules on the surface during SVA, which induced the recombination of photogenerated charges at the interface of the cathode/photoactive layer and thereby decreased the open-circuit voltage.

Observing the seasonal cycle of the upper ocean in the Ross Sea, Antarctica, with autonomous profiling floats

NASA Astrophysics Data System (ADS)

Porter, D. F.; Springer, S. R.; Padman, L.; Fricker, H. A.; Bell, R. E.

2017-12-01

The upper layers of the Southern Ocean where it meets the Antarctic ice sheet undergoes a large seasonal cycle controlled by surface radiation and by freshwater fluxes, both of which are strongly influenced by sea ice. In regions where seasonal sea ice and icebergs limit use of ice-tethered profilers and conventional moorings, autonomous profiling floats can sample the upper ocean. The deployment of seven Apex floats (by sea) and six ALAMO floats (by air) provides unique upper ocean hydrographic data in the Ross Sea close to the Ross Ice Shelf front. A novel choice of mission parameters - setting parking depth deeper than the seabed - limits their drift, allowing us to deploy the floats close to the ice shelf front, while sea ice avoidance algorithms allow the floats to to sample through winter under sea ice. Hydrographic profiles show the detailed development of the seasonal mixed layer close to the Ross front, and interannual variability of the seasonal mixed layer and deeper water masses on the central Ross Sea continental shelf. After the sea ice breakup in spring, a warm and fresh surface mixed layer develops, further warming and deepening throughout the summer. The mixed layer deepens, with maximum temperatures exceeding 0ºC in mid-February. By March, the surface energy budget becomes negative and sea ice begins to form, creating a cold, saline and dense surface layer. Once these processes overcome the stable summer stratification, convection erodes the surface mixed layer, mixing some heat downwards to deeper layers. There is considerable interannual variability in the evolution and strength of the surface mixed layer: summers with shorter ice-free periods result in a cooler and shallower surface mixed layer, which accumulates less heat than the summers with longer ice-free periods. Early ice breakup occurred in all floats in 2016/17 summer, enhancing the absorbed solar flux leading to a warmer surface mixed layer. Together, these unique measurements from autonomous profilers provide insight into the hydrographic state of the Ross Sea at the start of the spring period of sea-ice breakup, and how ocean mixing and sea ice interact to initiate the summer open-water season.

The Origin of Regional Dust Deposits on Mars

NASA Technical Reports Server (NTRS)

Christensen, P. R.

1985-01-01

Recently, additional evidence was derived from the Viking Infrared Thermal Mapper observations that allows a more complete model for the formation of Low Thermal inertia-high Albedo regions to be proposed. The first observation is that dust appears to be currently accumulating in the low thermal inertia regions. Following each global dust storm a thin layer of dust is deposited globally, as evidenced by an increase in surface albedo seen from orbit and from the Viking Lander sites. During the period following the storm, the bright dust fallout is subsequently removed from low albedo regions, as indicated by the post-storm darkening of these surfaces and by an increase in the atmospheric dust content over dark regions relative to the bright, low thermal inertia regions. Thus, the fine dust storm material is removed from dark regions but not from the bright regions, resulting in a net accumulation within the bright, low thermal inertia regions. Once deposition has begun, the covering of exposed rocks and sand and the accumulation of fine material on the surface make removal of material increasingly difficult, thereby enhancing the likelihood that material will accumulate within the low thermal inertia regions.

Impact of sludge layer geometry on the hydraulic performance of a waste stabilization pond.

PubMed

Ouedraogo, Faissal R; Zhang, Jie; Cornejo, Pablo K; Zhang, Qiong; Mihelcic, James R; Tejada-Martinez, Andres E

2016-08-01

Improving the hydraulic performance of waste stabilization ponds (WSPs) is an important management strategy to not only ensure protection of public health and the environment, but also to maximize the potential reuse of valuable resources found in the treated effluent. To reuse effluent from WSPs, a better understanding of the factors that impact the hydraulic performance of the system is needed. One major factor determining the hydraulic performance of a WSP is sludge accumulation, which alters the volume of the pond. In this study, computational fluid dynamics (CFD) analysis was applied to investigate the impact of sludge layer geometry on hydraulic performance of a facultative pond, typically used in many small communities throughout the developing world. Four waste stabilization pond cases with different sludge volumes and distributions were investigated. Results indicate that sludge distribution and volume have a significant impact on wastewater treatment efficiency and capacity. Although treatment capacity is reduced with accumulation of sludge, the latter may induce a baffling effect which causes the flow to behave closer to that of plug flow reactor and thus increase treatment efficiency. In addition to sludge accumulation and distribution, the impact of water surface level is also investigated through two additional cases. Findings show that an increase in water level while keeping a constant flow rate can result in a significant decrease in the hydraulic performance by reducing the sludge baffling effect, suggesting a careful monitoring of sludge accumulation and water surface level in WSP systems. Published by Elsevier Ltd.

Recent accumulation rates of an alpine glacier derived from firn cores and repeated helicopter-borne GPR

NASA Astrophysics Data System (ADS)

Sold, L.; Huss, M.; Eichler, A.; Schwikowski, M.; Hoelzle, M.

2014-08-01

The spatial representation of accumulation measurements is a major limitation for current glacier mass balance monitoring approaches. Here, we present a new method for estimating annual accumulation rates on a temperate alpine glacier based on the interpretation of internal reflection horizons (IRH) in helicopter-borne ground-penetrating radar (GPR) data. For each individual GPR measurement, the signal traveltime is combined with a simple model for firn densification and refreezing of meltwater. The model is calibrated at locations where GPR profiles intersect in two subsequent years and the densification can be tracked over time. Two 10.5 m long firn cores provide a reference for the density and chronology of firn layers. Thereby, IRH correspond to density maxima, but not exclusively to former summer glacier surfaces. From GPR profiles across the accumulation area, we obtain spatial distributions of water equivalent for at least four annual firn layers, reaching a mean density of 0.74 g cm-3. Refreezing accounts for 9% of the density increase over time and depth. The strongest limitation to our method is the dependence on layer chronology assumptions. The uncertainties inherent to the modelling approach itself are in the same order of conventional point measurements in snow pits. We show that GPR can be used to complement existing mass balance monitoring programs on temperate alpine glaciers, but also to retrospectively extend newly initiated time series.

[Dynamics of soil physical properties and biological soil crust during the vegetation restoration process of abandoned croplands in the Ordos Plateau, China].

PubMed

Cai, Wen Tao; Li, He Yi; Lai, Li Ming; Zhang, Xiao Long; Guan, Tian Yu; Zhou, Ji Hua; Jiang, Lian He; Zheng, Yuan Run

2017-03-18

A series of typical abandoned croplands in the regions of Ruanliang and Yingliang in the Ordos Plateau, China, were selected, and dynamics of the surface litter, biological soil crust and soil bulk density, soil texture, and soil moisture in different soil layers were investigated. The results showed that in the abandoned cropland in Ruanliang, the clay particle content and surface litter of the surface soil layer (0-10 cm) increased during the restoration process, while that of soil bulk density substantially decreased and soil water content slightly increased in the surface soil. In the medium soil layer (10-30 cm), the clay particle content increased and the soil water content slightly decreased. In the deep soil layer (30-50 cm), there was a relatively large variation in the physical properties. In the abandoned cropland in Yingliang, the coverage of litter and the coverage and thickness of the biological soil crust increased during the abandonment process. The surface soil bulk density, soil clay particle content and soil water content remained constant in 0-10 cm soil layer, while the physical properties varied substantially in 10-40 cm soil layer. The shallow distribution of the soil water content caused by the accumulation of the litter and clay particles on the soil surface might be the key reason of the replacement of the semi-shrub Artemisia ordosica community with a perennial grass community over the last 20 years of the abandoned cropland in Ruanliang. The relatively high soil water content in the shallow layer and the development of the biological soil crust might explain why the abandoned cropland in Yingliang was not invaded by the semi-shrub A. ordosica during the restoration process.

Laboratory Experiments Modelling Sediment Transport by River Plumes

NASA Astrophysics Data System (ADS)

Sutherland, Bruce; Gingras, Murray; Knudson, Calla; Steverango, Luke; Surma, Chris

2016-11-01

Through lock-release laboratory experiments, the transport of particles by hypopycnal (surface) currents is examined as they flow into a uniform-density and a two-layer ambient fluid. In most cases the tank is tilted so that the current flows over a slope representing an idealization of a sediment-bearing river flowing into the ocean and passing over the continental shelf. When passing into a uniform-density ambient, the hypopycnal current slows and stops as particles rain out, carrying some of the light interstitial fluid with them. Rather than settling on the bottom, in many cases the descending particles accumulate to form a hyperpycnal (turbidity) current that flows downslope. This current then slows and stops as particles both rain out to the bottom and also rise again to the surface, carried upward by the light interstitial fluid. For a hypopycnal current flowing into a two-layer fluid, the current slows as particles rain out and accumulate at the interface of the two-layer ambient. Eventually these particles penetrate through the interface and settle to the bottom with no apparent formation of a hyperpycnal current. Analyses are performed to characterize the speed of the currents and stopping distances as they depend upon experiment parameters. Natural Sciences and Engineering Research Council.

On the Development of Models for Height Profiles of the Wind Speed in the Atmospheric Surface Layer

NASA Astrophysics Data System (ADS)

Nikolaev, V. G.; Ganaga, S. V.; Kudryashov, Yu. I.; Nikolaev, V. V.

2018-03-01

The reliability of the known models of a height profile of the wind speed V( h) in the atmospheric boundary layer (ABL) and near-surface layer (NSL) is analyzed using the data of long-term ABL measurements accumulated in Russia in the state network of meteorological and aerological stations and the data of multilevel measurements at mast wind-measuring complexes. A new multilayer semiempirical model of V( h) is proposed which is based on aerodynamic and physical representations of the ABL vertical structure and relies on the hypothesis that wind-speed profiles providing the minimum wind friction on the ground and satisfying the conditions of profile smoothness are feasible in the ABL. This model ensures the best agreement with the data of meteorological, aerological, and mast wind measurements.

The Influence of Stellar Spin on Ignition of Thermonuclear Runaways

NASA Astrophysics Data System (ADS)

Galloway, Duncan K.; in ’t Zand, Jean J. M.; Chenevez, Jérôme; Keek, Laurens; Sanchez-Fernandez, Celia; Worpel, Hauke; Lampe, Nathanael; Kuulkers, Erik; Watts, Anna; Ootes, Laura; The MINBAR collaboration

2018-04-01

Runaway thermonuclear burning of a layer of accumulated fuel on the surface of a compact star provides a brief but intense display of stellar nuclear processes. For neutron stars accreting from a binary companion, these events manifest as thermonuclear (type-I) X-ray bursts, and recur on typical timescales of hours to days. We measured the burst rate as a function of accretion rate, from seven neutron stars with known spin rates, using a burst sample accumulated over several decades. At the highest accretion rates, the burst rate is lower for faster spinning stars. The observations imply that fast (>400 Hz) rotation encourages stabilization of nuclear burning, suggesting a dynamical dependence of nuclear ignition on the spin rate. This dependence is unexpected, because faster rotation entails less shear between the surrounding accretion disk and the star. Large-scale circulation in the fuel layer, leading to enhanced mixing of the burst ashes into the fuel layer, may explain this behavior; further numerical simulations are required to confirm this.

X-Ray-Based Imaging for Characterizing Heterogeneous Gas Diffusion Layers for Polymer Electrolyte Membrane Fuel Cells

NASA Astrophysics Data System (ADS)

George, Michael G.

Characterization of gas diffusion layers (GDLs) for polymer electrolyte membrane (PEM) fuel cells informs modeling studies and the manufacturers of next generation fuel cell materials. Identifying the physical properties related to the primary functions of the modern GDL (thermal, electrical, and mass transport) is necessary for understanding the impact of GDL design choices. X-ray micro-computed tomographic reconstructions of GDLs were studied to isolate GDL surface morphologies. Surface roughness was measured for a wide variety of samples and a sensitivity study highlighted the scale-dependence of surface roughness measurements. Furthermore, a spatially resolved distribution map of polytetrafluoroethylene (PTFE) in the microporous layer (MPL), critical for water management and mass transport, was identified and the existence of PTFE agglomerations was highlighted. Finally, the impact of accelerated degradation on GDL wettability and water transport increases in liquid water accumulation and oxygen mass transport resistance were quantified as a result of accelerated GDL degradation.

Experimental studies of MOS inversion and accumulation layers: Quantum mechanical effects and mobility

NASA Astrophysics Data System (ADS)

Chindalore, Gowrishankar L.

The development of fast, multi-functional, and energy efficient integrated circuits, is made possible by aggressively scaling the gate lengths of the MOS devices into the sub-quarter micron regime. However, with the increasing cost of fabrication, there is a strong need for the development of reliable and accurate device simulation capabilities. The development of the theoretical models for simulators is guided by extensive experimental data, which enable an experimental verification of the models, and lead to a better understanding of the underlying physics. This dissertation presents the methodology and the results for one such experimental effort, where two important physical effects in the inversion layer and the accumulation layer of a MOS device, namely, the quantum mechanical (QM) effects and the carrier mobility are investigated. Accordingly, this dissertation has been divided into two parts, with the first part discussing the increase in the threshold voltage and the accumulation electrical oxide thickness due to QM effects. The second part discusses the methodology and the experimental results for the extraction of the majority carrier mobilities in the accumulation layers of a MOSFET. The continued scaling of the MOS gate length requires decreased gate oxide thickness (tox) and increased channel doping (NB) in order to improve device performance while suppressing the short- channel effects. The combination of the two result in large enough transverse electric fields to cause significant quantization of the carriers in the potential well at the Si/SiO2 interface. Hence, compared to the classical calculations (where the QM effects are ignored), the QM effects are found to lead to an increase in the experimental threshold voltage by approximately 100mV, and an overestimation of the physical oxide thickness by approximately 3-4A, in MOSFET devices with a gate oxide thickness and the doping level anticipated for technologies with sub-quarter micron gate lengths. Thus, the experimental results indicate the need for using accurate QM models for simulating sub-quarter micron devices. Carrier mobility is a fundamental semiconductor device transport parameter that has been extensively characterized for both electrons and holes in the silicon bulk and MOS inversion layers. Accumulation layer mobility (μacc) has become increasingly important as the MOS devices have scaled to deep submicron gate lengths, and much effort has been required to achieve increased drive current. However, very little experimental data has been reported for carrier mobility in the MOS accumulation layers (Sun80, Man89). Hence, in this research work, the accumulation layer mobilities were extracted using buried-channel MOSFETs for both the electrons and holes, and for a wide range of doping levels at temperatures ranging from 25C to 150C. The experimental μacc is found to be greater than the corresponding bulk and the inversion layer mobilities, at low to moderate effective fields. However, at very high effective fields, where phonon and surface roughness scattering are dominant, the mobility behavior is found to be very similar to that of the inversion carriers. The extensive set of experimental data will enable the development of accurate local accumulation mobility models for inclusion in 2-D device simulators.

Effect of multilayer substrate configuration in horizontal subsurface flow constructed wetlands: assessment of treatment performance, biofilm development, and solids accumulation.

PubMed

Ding, Yanli; Lyu, Tao; Bai, Shaoyuan; Li, Zhenling; Ding, Haijing; You, Shaohong; Xie, Qinglin

2018-01-01

This study investigates the influence of multilayer substrate configuration in horizontal subsurface flow constructed wetlands (HSCWs) on their treatment performance, biofilm development, and solids accumulation. Three pilot-scale HSCWs were built to treat campus sewage and have been operational for 3 years. The HSCWs included monolayer (CW1), three-layer (CW3), and six-layer (CW6) substrate configurations with hydraulic conductivity of the substrate increasing from the surface to bottom in the multilayer CWs. It was demonstrated the pollutant removal performance after a 3-year operation improved in the multilayer HSCWs (49-80%) compared to the monolayer HSCW (29-41%). Simultaneously, the multilayer HSCWs exhibited significant features that prevented clogging compared to the monolayer configuration. The amount of accumulated solids was notably higher in the monolayer CW compared to multilayer CWs. Further, multilayer HSCWs could delay clogging by providing higher biofilm development for organics removal and consequently, lesser solids accumulations. Principal component analysis strongly supported the visualization of the performance patterns in the present study and showed that multilayer substrate configuration, season, and sampling locations significantly influenced biofilm growth and solids accumulation. Finally, the present study provided important information to support the improved multilayer configured HSCW implication in the future.

Anodic behavior of uranium in AlCl3-1-ethyl-3-methyl-imidazolium chloride ionic liquid

NASA Astrophysics Data System (ADS)

Jiang, Yidong; Luo, Lizhu; Wang, Shaofei; Bin, Ren; Zhang, Guikai; Wang, Xiaolin

2018-01-01

The oxidation state of metals unambiguously affects its anodic behavior in ionic liquid. We systematically investigated the anodic behavior of uranium with different surface oxidation states by electrochemical measurements, spectroscopic methods and surface analysis techniques. In the anodic process, metal uranium can be oxidized to U3+. The corresponding products accumulated on the metal/ILs interface will form a viscous layer. The anodic behavior of uranium is also strongly dependent upon the surface oxide states including thickness and homogeneity of the oxide film. With an increase in the thickness of oxide film, it will be breached at potentials in excess of a critical value. A uniform oxide on uranium surface can be breached evenly, and then the underlying metal starts to dissolve forming a viscous layer which can facilitate uniformly stripping of oxide, thus giving an oxide-free surface. Otherwise, a nonuniform oxide can result in a severe pitted surface with residue oxygen.

Soil carbon stocks and their rates of accumulation and loss in a boreal forest landscape

USGS Publications Warehouse

Rapalee, G.; Trumbore, S.E.; Davidson, E.A.; Harden, J.W.; Veldhuis, H.

1998-01-01

Boreal forests and wetlands are thought to be significant carbon sinks, and they could become net C sources as the Earth warms. Most of the C of boreal forest ecosystems is stored in the moss layer and in the soil. The objective of this study was to estimate soil C stocks (including moss layers) and rates of accumulation and loss for a 733 km2 area of the BOReal Ecosystem-Atmosphere Study site in northern Manitoba, using data from smaller-scale intensive field studies. A simple process-based model developed from measurements of soil C inventories and radiocarbon was used to relate soil C storage and dynamics to soil drainage and forest stand age. Soil C stocks covary with soil drainage class, with the largest C stocks occurring in poorly drained sites. Estimated rates of soil C accumulation or loss are sensitive to the estimated decomposition constants for the large pool of deep soil C, and improved understanding of deep soil C decomposition is needed. While the upper moss layers regrow and accumulate C after fires, the deep C dynamics vary across the landscape, from a small net sink to a significant source. Estimated net soil C accumulation, averaged for the entire 733 km2 area, was 20 g C m-2 yr-1 (28 g C m-2 yr-1 accumulation in surface mosses offset by 8 g C m-2 yr-1 lost from deep C pools) in a year with no fire. Most of the C accumulated in poorly and very poorly drained soils (peatlands and wetlands). Burning of the moss layer in only 1% of uplands would offset the C stored in the remaining 99% of the area. Significant interannual variability in C storage is expected because of the irregular occurrence of fire in space and time. The effects of climate change and management on fire frequency and on decomposition of immense deep soil C stocks are key to understanding future C budgets in boreal forests.

Soils of peatlands: histosols and gelisols

Treesearch

Randy Kolka; Scott D. Bridgham; Chien-Lu Ping

2016-01-01

Peatlands are a subset of wetlands that have accumulated significant amounts of soil organic matter. Soils of peatlands are colloquially known as peat, with mucks referring to peats that are decomposed to the point that the original plant remains are altered beyond recognition (Chapter 6, SSSA 2008). Generally, soils with a surface organic layer >40 cm thick...

Efficient identification of causal mutations through sequencing of bulked F2 from two allelic bloomless mutants

USDA-ARS?s Scientific Manuscript database

Sorghum (Sorghum bicolor Moench, L.) plant accumulates copious layers of epi-cuticular waxes (EW) on its aerial surfaces, more spectacular than most other crops. It provides a vapor barrier to reduce water loss and is considered as a major determinant of its superior drought tolerance. However, litt...

Monolithic in-based III-V compound semiconductor focal plane array cell with single stage CCD output

NASA Technical Reports Server (NTRS)

Fossum, Eric R. (Inventor); Cunningham, Thomas J. (Inventor); Krabach, Timothy N. (Inventor); Staller, Craig O. (Inventor)

1994-01-01

A monolithic semiconductor imager includes an indium-based III-V compound semiconductor monolithic active layer of a first conductivity type, an array of plural focal plane cells on the active layer, each of the focal plane cells including a photogate over a top surface of the active layer, a readout circuit dedicated to the focal plane cell including plural transistors formed monolithically with the monolithic active layer and a single-stage charge coupled device formed monolithically with the active layer between the photogate and the readout circuit for transferring photo-generated charge accumulated beneath the photogate during an integration period to the readout circuit. The photogate includes thin epitaxial semiconductor layer of a second conductivity type overlying the active layer and an aperture electrode overlying a peripheral portion of the thin epitaxial semiconductor layer, the aperture electrode being connectable to a photogate bias voltage.

The StreamCat Dataset: Accumulated Attributes for NHDPlusV2 Catchments (Version 2.1) for the Conterminous United States: Soil Erodibility (KFFACT)

EPA Pesticide Factsheets

This dataset represents the adjusted soil erodibility factor within individual, local NHDPlusV2 catchments and upstream, contributing watersheds. Attributes of the landscape layer were calculated for every local NHDPlusV2 catchment and accumulated to provide watershed-level metrics. (See Supplementary Info for Glossary of Terms) The STATSGO Layer table specifies two soil erodibility factors for each component layer, KFFACT and KFACT. The STATSGO documentation describes KFFACT as a soil erodibility factor which quanitifies the susceptibility of soil particles to detachment and movement by water. This factor is used in the Universal Soil Loss Equation to caluculate soil loss by water. KFACT is described as a soil erodibility factor which is adjusted for the effect of rock fragments. The average value of each of these soil erodibility factors was determined for the top (surface) layer for each map unit of each state.The base-flow index (BFI) grid for the conterminous United States was developed to estimate (1) BFI values for ungaged streams, and (2) ground-water recharge throughout the conterminous United States (see Data Source). Estimates of BFI values at ungaged streams and BFI-based ground-water recharge estimates are useful for interpreting relations between land use and water quality in surface and ground water. The soil erodibility factor was summarized by local catchment and by watershed to produce local catchment-level and watershed-level metri

Accumulation and persistence of chlorobiphenyls, organochlorine pesticides and faecal sterols at the Garroch Head sewage sludge disposal site, Firth of Clyde.

PubMed

Kelly, A G

1995-01-01

The sediment concentrations of organic carbon, faecal sterols, individual chlorobiphenyl congeners and organochlorine pesticides have been measured in seabed cores from the sewage sludge disposal area at Garroch Head in the Firth of Clyde. The measurements confirm the accumulative nature of the site with high levels of sedimentary faecal sterols (152 mg kg(-1) coprostanol). Levels of chlorobiphenyls, DDT compounds and dieldrin in surface sediment were elevated by factors of 12, 40 and 120, respectively, over those observed at a site remote from the effects of dumping. Total chlorobiphenyl levels of 515 microg kg(-1) Arochlor 1254 in surface sediment were comparable to levels found in other areas heavily contaminated with sewage sludge. The 20-cm depth of heavily sludge-contaminated sediment overlays a mixed sludge/basal sediment layer some 10 cm in depth. Levels of organochlorine contaminants were elevated to depths of 90 cm in the sediment, suggesting that the surface layer is a source of contaminants to the deeper sediment. Within the upper 15-20 cm sediment in the disposal area, chlorobiphenyls are conservative, the variation in their concentration with respect to depth being related to historical input. Lindane and possibly dieldrin, and hexachlorobenzene are not conservative. Faecal sterols are removed in sub-surface sediment, in contrast to conservative behaviour previously found at other sewage polluted sites.

Deep-Sea Carbonate Accumulation and Surface Ocean Saturation State in the Aftermath of the Cretaceous-Paleogene extinction

NASA Astrophysics Data System (ADS)

Pruss, S. B.; Higgins, J. A.; Bush, A. M.; Leckie, R. M.; Deeg, C.; Getzin, B. L.

2016-12-01

The role of the K-Pg extinction on biogeochemical cycling has been intensively studied in recent years. However, it remains unknown how extinctions in marine pelagic calcifiers impacted carbon cycling in the ocean. Low accumulation rates of microfossils in the aftermath of the extinction have been attributed to lowered production, which triggered a reduction in carbonate delivery to the seafloor. Interestingly, although microfossil abundance is lower and foraminifera are significantly smaller than in the latest Cretaceous, carbonate accumulated on the seafloor in the earliest Paleogene even in areas that should have been below the CCD. One such deep-water site in the South Pacific (U1370) was cored during IODP Expedition 329 in November 2010. We examined 16 samples from an anomalous carbonate layer provisionally assigned to lower Paleocene planktonic foraminiferal Zones P1a and P1b that preserves benthic and planktonic foraminifera. Carbon isotope values of the benthic species Nuttalies orealis range from 1.45 to 1.95‰ VPDB in the 16 samples. The planktonic species Parasubbotina pseudobulloides was only abundant enough for analysis in 4 samples, and these values range from 1.41 to 1.91‰ VPDB. We note, as others have, that no carbon isotope gradient existed between the benthic and planktonic foraminifera during the deposition of this carbonate layer, perhaps due to reduced primary production and/or export of organic carbon. The presence of this carbonate layer in the deep ocean and its preservation of a collapsed isotopic gradient are both consistent with a reduction in the surface-to-deep water gradient in carbonate saturation state during the unusual oceanographic conditions that followed the extinction. We speculate that this was associated with a sustained reduction in surface ocean saturation state with adverse consequences for neritic carbonate producers in the aftermath of the K-T extinction.

Concentration of Antifouling Biocides and Metals in Sediment Core Samples in the Northern Part of Hiroshima Bay

PubMed Central

Tsunemasa, Noritaka; Yamazaki, Hideo

2014-01-01

Accumulation of Ot alternative antifoulants in sediment is the focus of this research. Much research had been done on surface sediment, but in this report, the accumulation in the sediment core was studied. The Ot alternative antifoulants, Diuron, Sea-Nine211, and Irgarol 1051, and the latter’s degradation product, M1, were investigated in five samples from the northern part of Hiroshima Bay. Ot compounds (tributyltin (TBT) and triphenyltin (TPT)) were also investigated for comparison. In addition, metal (Pb, Cu, Zn, Fe and Mn) levels and chronology were measured to better understand what happens after accumulation on the sea floor. It was discovered that Ot alternative antifoulant accumulation characteristics in sediment were like Ot compounds, with the concentration in the sediment core being much higher than surface sediment. The concentration in sediment seems to have been affected by the regulation of Ot compounds in 1990, due to the concentration of Ot alternative antifoulants and Ot compounds at the survey point in front of the dock, showing an increase from almost the same layer after the regulation. PMID:24901529

Comparison of secondary flows and boundary-layer accumulations in several turbine nozzles

NASA Technical Reports Server (NTRS)

Kofskey, Milton G; Allen, Hubert W; Herzig, Howard Z

1953-01-01

An investigation was made of losses and secondary flows in three different turbine nozzle configurations in annular cascade. Appreciable outer shroud loss cores (passage vortices) were found to exist at the discharge of blades which had thickened suction surface boundary layers near the outer shroud. Blade designs having thinner boundary layers did not show such outer shroud loss cores, but indicated greater inward radial flow of low momentum air, in the wake loss is to this extent an indication of the presence or absence of radial flow. The blade wake was a combination of profile loss and low momentum air from the outer shroud, and the magnitude of the wake loss is to this extent an indication of the presence or absence of radial flow. At a high Mach number, shock-boundary-layer thickening on the blade suction surfaces provided an additional radial flow path for low momentum air, which resulted in large inner shroud loss regions accompanied by large deviations from design values of discharge angle. (author)

The Diamond Window with Boron-Doped Layers for the Output of Microwave Radiation at High Peak and Average Power Levels

NASA Astrophysics Data System (ADS)

Ivanov, O. A.; Kuzikov, S. V.; Vikharev, A. A.; Vikharev, A. L.; Lobaev, M. A.

2017-10-01

We propose a novel design of the barrier window for the output of microwave radiation at high peak and average power levels. A window based on a plate of polycrystalline CVD diamond with thin (nanometer-thick) boron-doped layers with increased conductivity is considered. Such a window, which retains the low radiation loss due to the small total thickness of the conductive layers and the high thermal conductivity inherent in diamond, prevents accumulation of a static charge on its surface, on the one hand, and allows one to produce a static electric field on the surface of the doped layer, which impedes the development of a multipactor discharge, on the other hand. In this case, a high level of the power of the transmitted radiation and a large passband width are ensured by choosing the configuration of the field in the form of a traveling wave inside the window.

Three-dimensional numerical simulation of water droplet emerging from a gas diffusion layer surface in micro-channels

NASA Astrophysics Data System (ADS)

Ding, Y.; Bi, H. T.; Wilkinson, D. P.

The dynamic formation of water droplets emerging from a gas diffusion layer (GDL) surface in micro-channels was simulated using the volume of fluid (VOF) method. The influence of GDL surface microstructure was investigated by changing the pore diameter and the number of pore openings on the GDL surface. Simulation results show that the microstructure of the GDL surface has a significant impact on the two-phase flow patterns in gas flow channels. For a non-uniform GDL surface, three stages were identified, namely emergence and merging on the GDL surface, accumulation on the channel sidewalls and detachment from the top wall. It was also found that if the pore size is small enough, the flow pattern in the channel does not change with further reduction in the pore diameter. However, the two-phase flow patterns change significantly with the wettability of the GDL surface and sidewalls, but remain the same when the liquid flow rate is reduced by two orders of magnitude from the reference case.

Electric Double Layer Composed of an Antagonistic Salt in an Aqueous Mixture: Local Charge Separation and Surface Phase Transition

NASA Astrophysics Data System (ADS)

Yabunaka, Shunsuke; Onuki, Akira

2017-09-01

We examine an electric double layer containing an antagonistic salt in an aqueous mixture, where the cations are small and hydrophilic but the anions are large and hydrophobic. In this situation, a strong coupling arises between the charge density and the solvent composition. As a result, the anions are trapped in an oil-rich adsorption layer on a hydrophobic wall. We then vary the surface charge density σ on the wall. For σ >0 the anions remain accumulated, but for σ <0 the cations are attracted to the wall with increasing |σ |. Furthermore, the electric potential drop Ψ (σ ) is nonmonotonic when the solvent interaction parameter χ (T ) exceeds a critical value χc determined by the composition and the ion density in the bulk. This leads to a first-order phase transition between two kinds of electric double layers with different σ and common Ψ . In equilibrium such two-layer regions can coexist. The steric effect due to finite ion sizes is crucial in these phenomena.

The meteorology and chemistry of high nitrogen oxide concentrations in the stable boundary layer at the South Pole

NASA Astrophysics Data System (ADS)

Neff, William; Crawford, Jim; Buhr, Marty; Nicovich, John; Chen, Gao; Davis, Douglas

2018-03-01

Four summer seasons of nitrogen oxide (NO) concentrations were obtained at the South Pole (SP) during the Sulfur Chemistry in the Antarctic Troposphere (ISCAT) program (1998 and 2000) and the Antarctic Tropospheric Chemistry Investigation (ANTCI) in (2003, 2005, 2006-2007). Together, analyses of the data collected from these studies provide insight into the large- to small-scale meteorology that sets the stage for extremes in NO and the significant variability that occurs day to day, within seasons, and year to year. In addition, these observations reveal the interplay between physical and chemical processes at work in the stable boundary layer of the high Antarctic plateau. We found a systematic evolution of the large-scale wind system over the ice sheet from winter to summer that controls the surface boundary layer and its effect on NO: initially in early spring (Days 280-310) the transport of warm air and clouds over West Antarctica dominates the environment over the SP; in late spring (Days 310-340), the winds at 300 hPa exhibit a bimodal behavior alternating between northwest and southeast quadrants, which is of significance to NO; in early summer (Days 340-375), the flow aloft is dominated by winds from the Weddell Sea; and finally, during late spring, winds aloft from the southeast are strongly associated with clear skies, shallow stable boundary layers, and light surface winds from the east - it is under these conditions that the highest NO occurs. Examination of the winds at 300 hPa from 1961 to 2013 shows that this seasonal pattern has not changed significantly, although the last twenty years have seen an increasing trend in easterly surface winds at the SP. What has also changed is the persistence of the ozone hole, often into early summer. With lower total ozone column density and higher sun elevation, the highest actinic flux responsible for the photolysis of snow nitrate now occurs in late spring under the shallow boundary layer conditions optimum for high accumulation of NO. This may occur via the non-linear HOX-NOx chemistry proposed after the first ISCAT field programs and NOx recycling to the surface where quantum yields may be large under the low-snow-accumulation regime of the Antarctic plateau. During the 2003 field program a sodar made direct measurements of the stable boundary layer depth (BLD), a key factor in explaining the chemistry of the high NO concentrations. Because direct measurements were not available in the other years, we developed an estimator for BLD using direct observations obtained in 2003 and step-wise linear regression with meteorological data from a 22 m tower (that was tested against independent data obtained in 1993). These data were then used with assumptions about the column abundance of NO to estimate surface fluxes of NOx. These results agreed in magnitude with results at Concordia Station and confirmed significant daily, intraseasonal and interannual variability in NO and its flux from the snow surface. Finally, we found that synoptic to mesoscale eddies governed the boundary layer circulation and accumulation pathways for NO at the SP rather than katabatic forcing. It was the small-scale features of the circulation including the transition from cloudy to clear conditions that set the stage for short-term extremes in NO, whereas larger-scale features were associated with more moderate concentrations.

Modeling of Ice Flow and Internal Layers Along a Flow Line Through Swiss Camp in West Greenland

NASA Technical Reports Server (NTRS)

Wang, W. L.; Zwally, H. Jay; Abdalati, W.; Luo, S.; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

An anisotropic ice flow line model is applied to a flow line through Swiss Camp (69.57 N, 49.28 W) in West Greenland to estimate the dates of internal layers detected by Radio-Echo Sounding measurements. The effect of an anisotropic ice fabric on ice flow is incorporated into the steady state flow line model. The stress-strain rate relationship for anisotropic ice is characterized by an enhancement factor based on the laboratory observations of ice deformation under combined compression and shear stresses. By using present-day data of accumulation rate, surface temperature, surface elevation and ice thickness along the flow line as model inputs, a very close agreement is found between the isochrones generated from the model and the observed internal layers with confirmed dates. The results indicate that this part of Greenland ice sheet is primarily in steady state.

Surface correlation effects in two-band strongly correlated slabs.

PubMed

Esfahani, D Nasr; Covaci, L; Peeters, F M

2014-02-19

Using an extension of the Gutzwiller approximation for an inhomogeneous system, we study the two-band Hubbard model with unequal band widths for a slab geometry. The aim is to investigate the mutual effect of individual bands on the spatial distribution of quasi-particle weight and charge density, especially near the surface of the slab. The main effect of the difference in band width is the presence of two different length scales corresponding to the quasi-particle profile of each band. This is enhanced in the vicinity of the critical interaction of the narrow band where an orbitally selective Mott transition occurs and a surface dead layer forms for the narrow band. For the doped case, two different regimes of charge transfer between the surface and the bulk of the slab are revealed. The charge transfer from surface/center to center/surface depends on both the doping level and the average relative charge accumulated in each band. Such effects could also be of importance when describing the accumulation of charges at the interface between structures made of multi-band strongly correlated materials.

Microstructures of tribologically modified surface layers in two-phase alloys

NASA Astrophysics Data System (ADS)

Figueroa, C. G.; Ortega, I.; Jacobo, V. H.; Ortiz, A.; Bravo, A. E.; Schouwenaars, R.

2014-08-01

When ductile alloys are subject to sliding wear, small increments of plastic strain accumulate into severe plastic deformation and mechanical alloying of the surface layer. The authors constructed a simple coaxial tribometer, which was used to study this phenomenon in wrought Al-Sn and cast Cu-Mg-Sn alloys. The first class of materials is ductile and consists of two immiscible phases. Tribological modification is observed in the form of a transition zone from virgin material to severely deformed grains. At the surface, mechanical mixing of both phases competes with diffusional unmixing. Vortex flow patterns are typically observed. The experimental Cu-Mg-Sn alloys are ductile for Mg-contents up to 2 wt% and consist of a- dendrites with a eutectic consisting of a brittle Cu2Mg-matrix with α-particles. In these, the observations are similar to the Al-Sn Alloys. Alloys with 5 wt% Mg are brittle due to the contiguity of the eutectic compound. Nonetheless, under sliding contact, this compound behaves in a ductile manner, showing mechanical mixing of a and Cu2Mg in the top layers and a remarkable transition from a eutectic to cellular microstructure just below, due to severe shear deformation. AFM-observations allow identifying the mechanically homogenized surface layers as a nanocrystalline material with a cell structure associated to the sliding direction.

Phenomenology of summer ozone episodes over the Madrid Metropolitan Area, central Spain

NASA Astrophysics Data System (ADS)

Querol, Xavier; Alastuey, Andrés; Gangoiti, Gotzon; Perez, Noemí; Lee, Hong K.; Eun, Heeram R.; Park, Yonghee; Mantilla, Enrique; Escudero, Miguel; Titos, Gloria; Alonso, Lucio; Temime-Roussel, Brice; Marchand, Nicolas; Moreta, Juan R.; Arantxa Revuelta, M.; Salvador, Pedro; Artíñano, Begoña; García dos Santos, Saúl; Anguas, Mónica; Notario, Alberto; Saiz-Lopez, Alfonso; Harrison, Roy M.; Millán, Millán; Ahn, Kang-Ho

2018-05-01

Various studies have reported that the photochemical nucleation of new ultrafine particles (UFPs) in urban environments within high insolation regions occurs simultaneously with high ground ozone (O3) levels. In this work, we evaluate the atmospheric dynamics leading to summer O3 episodes in the Madrid air basin (central Iberia) by means of measuring a 3-D distribution of concentrations for both pollutants. To this end, we obtained vertical profiles (up to 1200 m above ground level) using tethered balloons and miniaturised instrumentation at a suburban site located to the SW of the Madrid Metropolitan Area (MMA), the Majadahonda site (MJDH), in July 2016. Simultaneously, measurements of an extensive number of air quality and meteorological parameters were carried out at three supersites across the MMA. Furthermore, data from O3 soundings and daily radio soundings were also used to interpret atmospheric dynamics.The results demonstrate the concatenation of venting and accumulation episodes, with relative lows (venting) and peaks (accumulation) in O3 surface levels. Regardless of the episode type, the fumigation of high-altitude O3 (arising from a variety of origins) contributes the major proportion of surface O3 concentrations. Accumulation episodes are characterised by a relatively thinner planetary boundary layer (< 1500 m at midday, lower in altitude than the orographic features), light synoptic winds, and the development of mountain breezes along the slopes of the Guadarrama Mountain Range (located W and NW of the MMA, with a maximum elevation of > 2400 m a.s.l.). This orographic-meteorological setting causes the vertical recirculation of air masses and enrichment of O3 in the lower tropospheric layers. When the highly polluted urban plume from Madrid is affected by these dynamics, the highest Ox (O3+ NO2) concentrations are recorded in the MMA.Vertical O3 profiles during venting episodes, with strong synoptic winds and a deepening of the planetary boundary layer reaching > 2000 m a.s.l., were characterised by an upward gradient in O3 levels, whereas a reverse situation with O3 concentration maxima at lower levels was found during the accumulation episodes due to local and/or regional production. The two contributions to O3 surface levels (fumigation from high-altitude strata, a high O3 background, and/or regional production) require very different approaches for policy actions. In contrast to O3 vertical top-down transfer, UFPs are formed in the planetary boundary layer (PBL) and are transferred upwards progressively with the increase in PBL growth.

Modulation of the magnetic domain size induced by an electric field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ando, F.; Kakizakai, H.; Yamada, K.

2016-07-11

The electric field (EF) effect on the magnetic domain structure of a Pt/Co system was studied, where an EF was applied to the top surface of the Co layer. The width of the maze domain was significantly modified by the application of the EF at a temperature slightly below the Curie temperature. After a detailed analysis, a change in the microscopic exchange stiffness induced by the EF application was suggested to dominate the modulation of the domain width observed in the experiment. The accumulation of electrons at the surface of the Co layer resulted in an increase in the microscopicmore » exchange stiffness and the Curie temperature. The result was consistent with the recent theoretical prediction.« less

Experimental investigations of castellated monoblock structures in TEXTOR

NASA Astrophysics Data System (ADS)

Litnovsky, A.; Philipps, V.; Wienhold, P.; Sergienko, G.; Emmoth, B.; Rubel, M.; Breuer, U.; Wessel, E.

2005-03-01

To insure the thermo-mechanical durability of ITER it is planned to manufacture the castellated armour of the divertor i.e. to split the armour into cells [W. Daener et al., Fusion Eng. Des. 61&62 (2002) 61]. This will cause an increase of the surface area and may lead to carbon deposition and tritium accumulation in the gaps in between cells. To investigate the processes of deposition and fuel accumulation in gaps, a castellated test-limiter was exposed to the SOL plasma of TEXTOR. The geometry of castellation used was the same as proposed for the vertical divertor target in ITER [W. Daener et al., Fusion Eng. Des. 61&62 (2002) 61]. After exposure the limiter was investigated with various surface diagnostic techniques. Deposited layers containing carbon, hydrogen, deuterium and boron were found both on top plasma-facing surfaces and in the gaps. The amount of deuterium in the gaps was at least 30% of that found on the top surfaces.

Novel Transport Characterizations in Layered Two-Dimensional Materials and Bulk Chalcogenides

NASA Astrophysics Data System (ADS)

Pennypacker, Sam

We present a case study (September 20 - October 13, 2015) of synergistic, multi-instrument observations of aerosols, clouds and the marine boundary layer (MBL) at the Eastern North Atlantic (ENA) ARM site centered on a period of exceptionally low (20 - 50 cm-3) surface accumulation mode (0.1 - 1 mum) aerosol particle number concentrations. We divide the case study into three regimes (high, clean and ultra-clean) based on daily median number concentrations, and compare finer resolution (hourly or less) observations between these regimes. The analysis focuses on the possibility of using these ultra-clean events to study pristine conditions in the remote MBL, as well as examining evidence for a recently proposed conceptual model for the large-scale depletion of CCN-sized particles in post-frontal air masses. Relative to the high and clean regimes, the ultra-clean regime tends to exhibit significantly fewer particles between 0.1 and 0.4 mum in diameter and a relatively increased prevalence of larger accumulation mode particles. In addition, supermicron particles tend to dominate total scattering in the ultra-clean regime, and there is little evidence for absorbing aerosol. These observations are more in line with a heavily scavenged but natural marine aerosol population and minimal contribution from continental sources such as anthropogenic pollution, biomass burning or dust. The air masses with the consistently lowest accumulation mode aerosol number concentrations are largely dominated by heavily drizzling clouds with high liquid water path (LWP) cores, deep decoupled boundary layers, open cellular organization and notable surface forcing of sub-cloud turbulence, even at night. We end with a discussion of the implications of this work the second aerosol indirect effect and pristine conditions in the remote MBL.

Double-Layer Gadolinium Zirconate/Yttria-Stabilized Zirconia Thermal Barrier Coatings Deposited by the Solution Precursor Plasma Spray Process

NASA Astrophysics Data System (ADS)

Jiang, Chen; Jordan, Eric H.; Harris, Alan B.; Gell, Maurice; Roth, Jeffrey

2015-08-01

Advanced thermal barrier coatings (TBCs) with lower thermal conductivity, increased resistance to calcium-magnesium-aluminosilicate (CMAS), and improved high-temperature capability, compared to traditional yttria-stabilized zirconia (YSZ) TBCs, are essential to higher efficiency in next generation gas turbine engines. Double-layer rare-earth zirconate/YSZ TBCs are a promising solution. From a processing perspective, solution precursor plasma spray (SPPS) process with its unique and beneficial microstructural features can be an effective approach to obtaining the double-layer microstructure. Previously durable low-thermal-conductivity YSZ TBCs with optimized layered porosity, called the inter-pass boundaries (IPBs) were produced using the SPPS process. In this study, an SPPS gadolinium zirconate (GZO) protective surface layer was successfully added. These SPPS double-layer TBCs not only retained good cyclic durability and low thermal conductivity, but also demonstrated favorable phase stability and increased surface temperature capabilities. The CMAS resistance was evaluated with both accumulative and single applications of simulated CMAS in isothermal furnaces. The double-layer YSZ/GZO exhibited dramatic improvement in the single application, but not in the continuous one. In addition, to explore their potential application in integrated gasification combined cycle environments, double-layer TBCs were tested under high-temperature humidity and encouraging performance was recorded.

Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling

NASA Astrophysics Data System (ADS)

Heilig, Achim; Eisen, Olaf; MacFerrin, Michael; Tedesco, Marco; Fettweis, Xavier

2018-06-01

Increasing melt over the Greenland Ice Sheet (GrIS) recorded over the past several years has resulted in significant changes of the percolation regime of the ice sheet. It remains unclear whether Greenland's percolation zone will act as a meltwater buffer in the near future through gradually filling all pore space or if near-surface refreezing causes the formation of impermeable layers, which provoke lateral runoff. Homogeneous ice layers within perennial firn, as well as near-surface ice layers of several meter thickness have been observed in firn cores. Because firn coring is a destructive method, deriving stratigraphic changes in firn and allocation of summer melt events is challenging. To overcome this deficit and provide continuous data for model evaluations on snow and firn density, temporal changes in liquid water content and depths of water infiltration, we installed an upward-looking radar system (upGPR) 3.4 m below the snow surface in May 2016 close to Camp Raven (66.4779° N, 46.2856° W) at 2120 m a.s.l. The radar is capable of quasi-continuously monitoring changes in snow and firn stratigraphy, which occur above the antennas. For summer 2016, we observed four major melt events, which routed liquid water into various depths beneath the surface. The last event in mid-August resulted in the deepest percolation down to about 2.3 m beneath the surface. Comparisons with simulations from the regional climate model MAR are in very good agreement in terms of seasonal changes in accumulation and timing of onset of melt. However, neither bulk density of near-surface layers nor the amounts of liquid water and percolation depths predicted by MAR correspond with upGPR data. Radar data and records of a nearby thermistor string, in contrast, matched very well for both timing and depth of temperature changes and observed water percolations. All four melt events transferred a cumulative mass of 56 kg m-2 into firn beneath the summer surface of 2015. We find that continuous observations of liquid water content, percolation depths and rates for the seasonal mass fluxes are sufficiently accurate to provide valuable information for validation of model approaches and help to develop a better understanding of liquid water retention and percolation in perennial firn.

Improved fill factor in inverted planar perovskite solar cells with zirconium acetate as the hole-and-ion-blocking layer.

PubMed

Zhang, Xuewen; Liang, Chunjun; Sun, Mengjie; Zhang, Huimin; Ji, Chao; Guo, Zebang; Xu, Yajun; Sun, Fulin; Song, Qi; He, Zhiqun

2018-03-14

Planar perovskite solar cells (PSCs) have gained great interest due to their low-temperature solution preparation and simple process. In inverted planar PSCs, an additional buffer layer is usually needed on the top of the PCBM electron-transport layer (ETL) to enhance the device performance. In this work, we used a new buffer layer, zirconium acetate (Zr(Ac) 4 ). The inclusion of the Zr(Ac) 4 buffer layer leads to the increase of FF from ∼68% to ∼79% and PCE from ∼14% to ∼17% in the planar PSCs. The UPS measurement indicates that the Zr(Ac) 4 layer has a low HOMO level of -8.2 eV, indicating that the buffer layer can act as a hole-blocking layer. Surface morphology and surface chemistry investigations reveal that the elements I, MA and Pb can diffuse across the PCBM ETL, damaging the device performance. The covering Zr(Ac) 4 molecules fill in the pinholes of the PCBM layer and effectively block the ions/molecules of the perovskite from diffusion across the ETL. The resulting more robust PCBM/Zr(Ac) 4 ETL leads to weaker ionic charge accumulation and lower diode leakage current. The double role of hole-and-ion blocking of the Zr(Ac) 4 layer explains the improved FF and PCE in the PSCs.

Global Surface Dust Distribution Changes on Mars (MY24-33)

NASA Astrophysics Data System (ADS)

Piqueux, S.; Hayne, P. O.; Kleinboehl, A.; Edwards, C. S.; Elder, C. M.; Heavens, N. G.; Kass, D. M.; McCleese, D. J.; Schofield, J. T.; Shirley, J. H.; Smith, M. D.

2016-12-01

Telescopic and spacecraft observations document inter-annual and inter-seasonal changes of the Martian albedo that are interpreted to result from the redistribution of surface dust in response to atmospheric events such as global or regional dust storms, dust devil activity, or seasonal winds. Based on these observations and general circulation modeling, several authors have hypothesized that a necessary condition for global dust storm initiation and growth is the presence of strategically located surface dust reservoirs replenished during inter-storm periods. If this hypothesis is valid, the cyclical accumulation and removal of thermally thick (>50 μm) layers of dust at specific locations ought to produce a distinct temperature signature, since Martian dust exhibits extremely low thermal conductivity and thermal inertia values compared to sand, gravel, rocks, and bedrock. Characterizing dust movement using temperature data presents a major advantage over mapping relying solely on albedo changes: it yields dust layer thicknesses, whose spatial and temporal integration enables the derivation of surface dust fluxes. In this work, we use global (1° per pixel resolution) seasonal (10° Ls resolution, from MY24 to 33) maps of the Martian surface albedo, atmospheric dust opacity, and ground temperature (derived from TES, THEMIS, and MCS observations) to derive apparent variations of the thermal inertia, and thereby characterize surface changes consistent with the deposition or removal of dust. We show that changes in thermal inertia for some regions are consistent with dust accumulation; whereas others seem to lose dust. We compare these maps with published GCM dust lifting predictions, and with observations of past dust storm occurrence, thereby constraining the role of surface dust availability.

Planar edge Schottky barrier-tunneling transistors using epitaxial graphene/SiC junctions.

PubMed

Kunc, Jan; Hu, Yike; Palmer, James; Guo, Zelei; Hankinson, John; Gamal, Salah H; Berger, Claire; de Heer, Walt A

2014-09-10

A purely planar graphene/SiC field effect transistor is presented here. The horizontal current flow over one-dimensional tunneling barrier between planar graphene contact and coplanar two-dimensional SiC channel exhibits superior on/off ratio compared to conventional transistors employing vertical electron transport. Multilayer epitaxial graphene (MEG) grown on SiC(0001̅) was adopted as the transistor source and drain. The channel is formed by the accumulation layer at the interface of semi-insulating SiC and a surface silicate that forms after high vacuum high temperature annealing. Electronic bands between the graphene edge and SiC accumulation layer form a thin Schottky barrier, which is dominated by tunneling at low temperatures. A thermionic emission prevails over tunneling at high temperatures. We show that neglecting tunneling effectively causes the temperature dependence of the Schottky barrier height. The channel can support current densities up to 35 A/m.

Thin film surface treatments for lowering dust adhesion on Mars Rover calibration targets

NASA Astrophysics Data System (ADS)

Sabri, F.; Werhner, T.; Hoskins, J.; Schuerger, A. C.; Hobbs, A. M.; Barreto, J. A.; Britt, D.; Duran, R. A.

The current generation of calibration targets on Mars Rover serve as a color and radiometric reference for the panoramic camera. They consist of a transparent silicon-based polymer tinted with either color or grey-scale pigments and cast with a microscopically rough Lambertian surface for a diffuse reflectance pattern. This material has successfully withstood the harsh conditions existent on Mars. However, the inherent roughness of the Lambertian surface (relative to the particle size of the Martian airborne dust) and the tackiness of the polymer in the calibration targets has led to a serious dust accumulation problem. In this work, non-invasive thin film technology was successfully implemented in the design of future generation calibration targets leading to significant reduction of dust adhesion and capture. The new design consists of a μm-thick interfacial layer capped with a nm-thick optically transparent layer of pure metal. The combination of these two additional layers is effective in burying the relatively rough Lambertian surface while maintaining diffuse properties of the samples which is central to the correct operation as calibration targets. A set of these targets are scheduled for flight on the Mars Phoenix mission.

Characterization of structural response to hypersonic boundary-layer transition

DOE PAGES

Riley, Zachary B.; Deshmukh, Rohit; Miller, Brent A.; ...

2016-05-24

The inherent relationship between boundary-layer stability, aerodynamic heating, and surface conditions makes the potential for interaction between the structural response and boundary-layer transition an important and challenging area of study in high-speed flows. This paper phenomenologically explores this interaction using a fundamental two-dimensional aerothermoelastic model under the assumption of an aluminum panel with simple supports. Specifically, an existing model is extended to examine the impact of transition onset location, transition length, and transitional overshoot in heat flux and fluctuating pressure on the structural response of surface panels. Transitional flow conditions are found to yield significantly increased thermal gradients, and theymore » can result in higher maximum panel temperatures compared to turbulent flow. Results indicate that overshoot in heat flux and fluctuating pressure reduces the flutter onset time and increases the strain energy accumulated in the panel. Furthermore, overshoot occurring near the midchord can yield average temperatures and peak displacements exceeding those experienced by the panel subject to turbulent flow. Lastly, these results suggest that fully turbulent flow does not always conservatively predict the thermo-structural response of surface panels.« less

Miniregoliths. I - Dusty lunar rocks and lunar soil layers

NASA Technical Reports Server (NTRS)

Comstock, G. M.

1978-01-01

A detailed Monte-Carlo model for rock surface evolution shows that erosion processes alone cannot account for the shapes of the solar flare particle track profiles generally observed at depths of about 100 microns and less in rocks. The observed profiles are easily explained by a steady accumulation of fine dust at a rate of 0.3 to 3 mm per m.y., depending on the micrometeoroid impact rate which controls the dust cover and results in maximum dust thicknesses on the order of 100 microns to 1 mm. The commonly used lunar soil track parameters are derived in terms of parameters characterizing the exposure of soil grains in the few-millimeter-thick surface mixing and maturation zone which is one form of miniregolith. Correlation plots permit determining the degree of mixing in soil samples and the amount of processing (maturation) in surface miniregoliths. It is shown that the sampling process often artificially mixes together finer distinct layers, and that ancient miniregolith layers on the order of a millimeter thick are probably common in the lunar soil.

Snow control on active layer and permafrost in steep alpine rock walls (Aiguille du Midi, 3842 m a.s.l, Mont Blanc massif)

NASA Astrophysics Data System (ADS)

Magnin, Florence; Westermann, Sebastian; Pogliotti, Paolo; Ravanel, Ludovic; Deline, Philip

2016-04-01

Permafrost degradation through the thickening of the active layer and the rising temperature at depth is a crucial process of rock wall stability. The ongoing increase in rock falls observed during hot periods in mid-latitude mountain ranges is regarded as a result of permafrost degradation. However, the short-term thermal dynamics of alpine rock walls are misunderstood since they result of complex processes related to the interaction of local climate variables, heterogeneous snow cover and heat transfers. As a consequence steady-state and long-term changes that can be approached with simpler process mainly related to air temperature, solar radiations and heat conduction were the most common dynamics to be studied so far. The effect of snow on the bedrock surface temperature is increasingly investigated and has already been demonstrated to be an essential factor of permafrost distribution. Nevertheless, its effect on the year-to-year changes of the active layer thickness and of the permafrost temperature in steep alpine bedrock has not been investigated yet, partly due to the lack of appropriate data. We explore the role of snow accumulations on the active layer and permafrost thermal regime of steep rock walls of a high-elevated site, the Aiguille du Midi (AdM, 3842 m a.s.l, Mont Blanc massif, Western European Alps) by mean of a multi-methods approach. We first analyse six years of temperature records in three 10-m-deep boreholes. Then we describe the snow accumulation patterns on two rock faces by means of automatically processed camera records. Finally, sensitivity analyses of the active layer thickness and permafrost temperature towards timing and magnitude of snow accumulations are performed using the numerical permafrost model CryoGrid 3. The energy balance module is forced with local meteorological measurements on the AdM S face and validated with surface temperature measurements at the weather station location. The heat conduction scheme is calibrated with the temperature measurements in the S-exposed borehole. Results show that the snow may be responsible for permafrost presence while it is absent in the surrounding snow free bedrock. The long lasting of the snow at high elevation, where it can remain until the mid-summer has a delaying effect on the seasonal thaw, which contributes to the lowering of the active layer thickness.

Two Outer Membrane Proteins Contribute to Caulobacter crescentus Cellular Fitness by Preventing Intracellular S-Layer Protein Accumulation

DOE PAGES

Overton, K. Wesley; Park, Dan M.; Yung, Mimi C.; ...

2016-09-23

Surface layers, or S-layers, are two-dimensional protein arrays that form the outermost layer of many bacteria and archaea. They serve several functions, including physical protection of the cell from environmental threats. The high abundance of S-layer proteins necessitates a highly efficient export mechanism to transport the S-layer protein from the cytoplasm to the cell exterior.Caulobacter crescentusis unique in that it has two homologous, seemingly redundant outer membrane proteins, RsaF aand RsaF b, which together with other components form a type I protein translocation pathway for S-layer export. These proteins have homology toEscherichia coliTolC, the outer membrane channel of multidrug effluxmore » pumps. Here we provide evidence that, unlike TolC, RsaF aand RsaF bare not involved in either the maintenance of membrane stability or the active export of antimicrobial compounds. Rather, RsaF aand RsaF bare required to prevent intracellular accumulation and aggregation of the S-layer protein RsaA; deletion of RsaF aand RsaF bled to a general growth defect and lowered cellular fitness. Using Western blotting, transmission electron microscopy, and transcriptome sequencing (RNA-seq), we show that loss of both RsaF aand RsaF bled to accumulation of insoluble RsaA in the cytoplasm, which in turn caused upregulation of a number of genes involved in protein misfolding and degradation pathways. These findings provide new insight into the requirement for RsaF aand RsaF bin cellular fitness and tolerance to antimicrobial agents and further our understanding of the S-layer export mechanism on both the transcriptional and translational levels inC. crescentus. IMPORTANCEDecreased growth rate and reduced cell fitness are common side effects of protein production in overexpression systems. Inclusion bodies typically form inside the cell, largely due to a lack of sufficient export machinery to transport the overexpressed proteins to the extracellular environment. This phenomenon can conceivably also occur in natural systems. As one example of a system evolved to prevent intracellular protein accumulation, our study demonstrates thatCaulobacter crescentushas two homologous outer membrane transporter proteins that are involved in S-layer export. This is an interesting case study that demonstrates how bacteria can evolve redundancy to ensure adequate protein export functionality and maintain high cellular fitness. Moreover, we provide evidence that these two outer membrane proteins, although being the closestC. crescentushomologs to TolC inE. coli, do not process TolC functionality inC. crescentus.« less

Two Outer Membrane Proteins Contribute to Caulobacter crescentus Cellular Fitness by Preventing Intracellular S-Layer Protein Accumulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Overton, K. Wesley; Park, Dan M.; Yung, Mimi C.

ABSTRACT Surface layers, or S-layers, are two-dimensional protein arrays that form the outermost layer of many bacteria and archaea. They serve several functions, including physical protection of the cell from environmental threats. The high abundance of S-layer proteins necessitates a highly efficient export mechanism to transport the S-layer protein from the cytoplasm to the cell exterior.Caulobacter crescentusis unique in that it has two homologous, seemingly redundant outer membrane proteins, RsaF aand RsaF b, which together with other components form a type I protein translocation pathway for S-layer export. These proteins have homology toEscherichia coliTolC, the outer membrane channel of multidrugmore » efflux pumps. Here we provide evidence that, unlike TolC, RsaF aand RsaF bare not involved in either the maintenance of membrane stability or the active export of antimicrobial compounds. Rather, RsaF aand RsaF bare required to prevent intracellular accumulation and aggregation of the S-layer protein RsaA; deletion of RsaF aand RsaF bled to a general growth defect and lowered cellular fitness. Using Western blotting, transmission electron microscopy, and transcriptome sequencing (RNA-seq), we show that loss of both RsaF aand RsaF bled to accumulation of insoluble RsaA in the cytoplasm, which in turn caused upregulation of a number of genes involved in protein misfolding and degradation pathways. These findings provide new insight into the requirement for RsaF aand RsaF bin cellular fitness and tolerance to antimicrobial agents and further our understanding of the S-layer export mechanism on both the transcriptional and translational levels inC. crescentus. IMPORTANCEDecreased growth rate and reduced cell fitness are common side effects of protein production in overexpression systems. Inclusion bodies typically form inside the cell, largely due to a lack of sufficient export machinery to transport the overexpressed proteins to the extracellular environment. This phenomenon can conceivably also occur in natural systems. As one example of a system evolved to prevent intracellular protein accumulation, our study demonstrates thatCaulobacter crescentushas two homologous outer membrane transporter proteins that are involved in S-layer export. This is an interesting case study that demonstrates how bacteria can evolve redundancy to ensure adequate protein export functionality and maintain high cellular fitness. Moreover, we provide evidence that these two outer membrane proteins, although being the closestC. crescentushomologs to TolC inE. coli, do not process TolC functionality inC. crescentus.« less

Two Outer Membrane Proteins Contribute to Caulobacter crescentus Cellular Fitness by Preventing Intracellular S-Layer Protein Accumulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Overton, K. Wesley; Park, Dan M.; Yung, Mimi C.

Surface layers, or S-layers, are two-dimensional protein arrays that form the outermost layer of many bacteria and archaea. They serve several functions, including physical protection of the cell from environmental threats. The high abundance of S-layer proteins necessitates a highly efficient export mechanism to transport the S-layer protein from the cytoplasm to the cell exterior.Caulobacter crescentusis unique in that it has two homologous, seemingly redundant outer membrane proteins, RsaF aand RsaF b, which together with other components form a type I protein translocation pathway for S-layer export. These proteins have homology toEscherichia coliTolC, the outer membrane channel of multidrug effluxmore » pumps. Here we provide evidence that, unlike TolC, RsaF aand RsaF bare not involved in either the maintenance of membrane stability or the active export of antimicrobial compounds. Rather, RsaF aand RsaF bare required to prevent intracellular accumulation and aggregation of the S-layer protein RsaA; deletion of RsaF aand RsaF bled to a general growth defect and lowered cellular fitness. Using Western blotting, transmission electron microscopy, and transcriptome sequencing (RNA-seq), we show that loss of both RsaF aand RsaF bled to accumulation of insoluble RsaA in the cytoplasm, which in turn caused upregulation of a number of genes involved in protein misfolding and degradation pathways. These findings provide new insight into the requirement for RsaF aand RsaF bin cellular fitness and tolerance to antimicrobial agents and further our understanding of the S-layer export mechanism on both the transcriptional and translational levels inC. crescentus. IMPORTANCEDecreased growth rate and reduced cell fitness are common side effects of protein production in overexpression systems. Inclusion bodies typically form inside the cell, largely due to a lack of sufficient export machinery to transport the overexpressed proteins to the extracellular environment. This phenomenon can conceivably also occur in natural systems. As one example of a system evolved to prevent intracellular protein accumulation, our study demonstrates thatCaulobacter crescentushas two homologous outer membrane transporter proteins that are involved in S-layer export. This is an interesting case study that demonstrates how bacteria can evolve redundancy to ensure adequate protein export functionality and maintain high cellular fitness. Moreover, we provide evidence that these two outer membrane proteins, although being the closestC. crescentushomologs to TolC inE. coli, do not process TolC functionality inC. crescentus.« less

Surface desensitization of polarimetric waveguide interferometers

NASA Astrophysics Data System (ADS)

Worth, Colin

Non-specific binding of small molecules to the surface of waveguide biosensors presents a major obstacle to surface-sensing techniques that attempt to detect very low concentrations (<1 g/mm2) of large (500 nm to 3 mum) biological objects. Interferometric waveguide biosensors use the interaction of an evanescent light field outside of the guiding layer with a biological sample to detect a particular type of cell or bacteria at some distance from the sensor surface. In such experiments, binding of small proteins close to the surface can be a significant source of noise. It is possible to significantly improve the signal-to-noise ratio by varying the properties of the biosensor, in order to reduce or eliminate the biosensor's response to a thin protein layer at the waveguide surface, without significantly reducing the response to larger target particles. In many biosensing applications, specifically bound particles, such as bacteria, are much larger than non-specifically bound particles such as proteins. In addition, due to laminar flow conditions at the sensor surface, the latter smaller particles tend to accumulate on the sensor surface. By varying the waveguide parameters, it is possible to vary the sensitivity of the detector response as a function of sample distance from the detector, by changing the properties of the TE0 and TM0 guided modes. This results in a signal reduction of more than 85%, for thin (30 nm or less) layers adjacent to the waveguide surface.

Study of porous silicon optical waveguides impregnated with organic dyes

NASA Astrophysics Data System (ADS)

Pirasteh, P.; Charrier, J.; Dumeige, Y.; Chaillou, A.; Guendouz, M.; Haji, L.

2007-01-01

Planar waveguides were made using oxidised porous silicon layers. Then, they were impregnated with Congo Red or Disperse Red 1 dyes. Optical losses were investigated before and after impregnation. In our case, the losses of impregnated waveguides were always higher than those of non-impregnated ones. In order to achieve a better understanding of the origin of these losses, we not only studied the absorbance of solutions which would impregnate the porous layers but also the reflectance spectra of the obtained composite materials. According to the measurements, the increase in losses in the visible spectrum depends on the intrinsic absorption of the dye while in NIR, the increase would be due to an accumulation of dried dye on the surface of the waveguide which would give rise to the surface scattering losses.

Carbon-Nanotube-Based Electrochemical Double-Layer Capacitor Technologies for Spaceflight Applications

NASA Technical Reports Server (NTRS)

Arepalli, S.; Fireman, H.; Huffman, C.; Maloney, P.; Nikolaev, P.; Yowell, L.; Kim, K.; Kohl, P. A.; Higgins, C. D.; Turano, S. P.

2005-01-01

Electrochemical double-layer capacitors, or supercapacitors, have tremendous potential as high-power energy sources for use in low-weight hybrid systems for space exploration. Electrodes based on single-wall carbon nanotubes (SWCNTs) offer exceptional power and energy performance due to the high surface area, high conductivity, and the ability to functionalize the SWCNTs to optimize capacitor properties. This paper will report on the preparation of electrochemical capacitors incorporating SWCNT electrodes and their performance compared with existing commercial technology. Preliminary results indicate that substantial increases in power and energy density are possible. The effects of nanotube growth and processing methods on electrochemical capacitor performance is also presented. The compatibility of different SWCNTs and electrolytes was studied by varying the type of electrolyte ions that accumulate on the high-surface-area electrodes.

Dependence of the Carrier Transport Characteristics on the Buried Layer Thickness in Ambipolar Double-Layer Organic Field-Effect Transistors Investigated by Electrical and Optical Measurements

NASA Astrophysics Data System (ADS)

Zhang, Le; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa

2013-05-01

By using current-voltage (I-V) measurements and optical modulation spectroscopy, we investigated the dependence of the carrier behaviour on the film thickness of the buried pentacene layer in C60/pentacene ambipolar double-layer organic field-effect transistors (OFETs). It was found that the buried pentacene layer not only acted as a hole transport layer, but also accounted for the properties of the C60/pentacene interface. The hole and electron behaviour exhibited different thickness dependence on the buried pentacene layer, implying the presence of the spatially separated conduction paths. It was suggested that the injected holes transported along the pentacene/gate dielectric interface, which were little affected by the buried pentacene layer thickness or the upper C60 layer; while, the injected electrons accumulated at the C60/pentacene interface, which were sensitive to the interfacial conditions or the buried pentacene layer. Furthermore, it was suggested that the enhanced surface roughness of the buried pentacene layer was responsible for the observed electron behaviour, especially when dpent>10 nm.

On the Formation of Planetesimals: Radial Contraction of the Dust Layer Interacting with the Protoplanetary Disk Gas

NASA Astrophysics Data System (ADS)

Makalkin, A. B.; Artyushkova, M. E.

2017-11-01

Radial contraction of the dust layer in the midplane of a gas-dust protoplanetary disk that consists of large dust aggregates is modeled. Sizes of aggregates vary from centimeters to meters assuming the monodispersion of the layer. The highly nonlinear continuity equation for the solid phase of the dust layer is solved numerically. The purpose of the study is to identify the conditions under which the solid matter is accumulated in the layer, which contributes to the formation of planetesimals as a result of gravitational instability of the dust phase of the layer. We consider the collective interaction of the layer with the surrounding gas of the protoplanetary disk: shear stresses act on the gas in the dust layer that has a higher orbital velocity than the gas outside the layer, this leads to a loss of angular momentum and a radial drift of the layer. The stress magnitude is determined by the turbulent viscosity, which is represented as the sum of the α-viscosity associated with global turbulence in the disk and the viscosity associated with turbulence that is localized in a thin equatorial region comprising the dust layer and is caused by the Kelvin-Helmholtz instability. The evaporation of water ice and the continuity of the mass flux of the nonvolatile component on the ice line is also taken into account. It is shown that the accumulation of solid matter on either side of the ice line and in other regions of the disk is determined primarily by the ratio of the radii of dust aggregates on either side of the ice line. If after the ice evaporation the sizes (or density) of dust aggregates decrease by an order of magnitude or more, the density of the solid phase of the layer's matter in the annular zone adjacent to the ice line from the inside increases sharply. If, however, the sizes of the aggregates on the inner side of the ice line are only a few times smaller than behind the ice line, then in the same zone there is a deficit of mass at the place of the modern asteroid belt. We have obtained constraints on the parameters at which the layer compaction is possible: the global turbulence viscosity parameter (α < 10-5), the initial radial distribution of the surface density of the dust layer, and the distribution of the gas surface density in the disk. Restrictions on the surface density depend on the size of dust aggregates. It is shown that the timescale of radial contraction of a dust layer consisting of meter-sized bodies is two orders of magnitude and that of decimeter ones, an order of magnitude greater than the timescale of the radial drift of individual particles if there is no dust layer.

Accumulation and interparticle connections of triangular Ag-coated Au nanoprisms by oil-coating method for surface-enhanced Raman scattering applications

NASA Astrophysics Data System (ADS)

Noda, Yuta; Asaka, Toru; Fudouzi, Hiroshi; Hayakawa, Tomokatsu

2018-03-01

To examine the optical responses of surface-enhanced Raman scattering (SERS) for tuned plasmonic nanoparticles, triangular Ag-coated Au (Au@Ag) nanoprisms with different sizes were separately synthesized, which were well controlled in their size (edge-length) and localized surface plasmon resonance (LSPR) wavelength (69.0 ± 8.4 to 173.8 ± 25.6 nm in size and 662-943 nm in LSPR wavelength). The mechanism of Ag shell formation on the Au nanoprisms was also studied with scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS). The Au@Ag nanoprisms were immobilized by covering a colloidal solution containing the nanoprisms with silicone oil and evaporating the solvent in the oil (oil-coating method) so as to form a layer of accumulated plasmonic Au@Ag nanoprisms that had LSPR peak wavelengths tuned from 839 to 1182 nm. The accumulation conditions were analyzed by field-emission scanning electron microscopy (FE-SEM) and a Raman mapping technique. The Au@Ag nanoprisms under excitation at 632.8 nm exhibited higher SERS signals of rhodamine 6G, and SERS-mapped images of the novel immobilized films were obtained at different magnifications. It was concluded that accumulated Au@Ag nanoprisms undergoing tip-planar interconnections could produce enhanced local fields, resulting in higher SERS signals.

Characteristic of pollution with groundwater inflow (90)Sr natural waters and terrestrial ecosystems near a radioactive waste storage.

PubMed

Lavrentyeva, G V

2014-09-01

The studies were conducted in the territory contaminated by (90)Sr with groundwater inflow as a result of leakage from the near-surface trench-type radioactive waste storage. The vertical soil (90)Sr distribution up to the depth of 2-3 m is analyzed. The area of radioactive contamination to be calculated with a value which exceeds the minimum significant activity 1 kBq/kg for the tested soil layers: the contaminated area for the 0-5 cm soil layer amounted to 1800 ± 85 m(2), for the 5-10 cm soil layer amounted to 300 ± 12 m(2), for the 10-15 cm soil layer amounted to 180 ± 10 m(2). It is found that (90)Sr accumulation proceeds in a natural sorption geochemical barrier of the marshy terrace near flood plain. The exposure doses for terrestrial mollusks Bradybaena fruticum are presented. The excess (90)Sr interference level was registered both in the ground and surface water during winter and summer low-water periods and autumn heavy rains. Copyright © 2014 Elsevier Ltd. All rights reserved.

Self-assembly of DNA functionalized gold nanoparticles at the liquid-vapor interface

DOE PAGES

Zhang, Honghu; Wang, Wenjie; Hagen, Noah; ...

2016-05-30

Here, surface sensitive synchrotron X-ray scattering and spectroscopy are used to monitor and characterize the spontaneous formation of 2D Gibbs monolayers of thiolated single-stranded DNA-functionalized gold nanoparticles (ssDNAAuNPs) at the vapor–solution interface by manipulating salt concentrations. Grazing incidence small-angle X-ray scattering and X-ray refl ectivity show that the noncomplementary ssDNA-AuNPs dispersed in aqueous solution spontaneously accumulate at the vapor–liquid interface in the form of a single layer by increasing MgCl 2 or CaCl 2 concentrations. Furthermore, the monoparticle layer undergoes a transformation from short- to long-range (hexagonal) order above a threshold salt-concentration. Using various salts at similar ionic strength tomore » those of MgCl 2 or CaCl 2 such as, NaCl or LaCl 3, it is found that surface adsorbed NPs lack any order. X-ray fluorescence near total reflection of the same samples provides direct evidence of interfacial gold and more importantly a significant surface enrichment of the cations. Quantitative analysis reveals that divalent cations screen the charge of ssDNA, and that the hydrophobic hexyl-thiol group, commonly used to functionalize the ssDNA (for capping the AuNPs), is likely the driving force for the accumulation of the NPs at the interface.« less

Influence of Surface Sorption Processes on Spectral Induced Polarization Evaluated Using in-Situ Monitoring of a Na-22 Tracer

NASA Astrophysics Data System (ADS)

Hao, N.; Moysey, S. M.; Powell, B. A.; Ntarlagiannis, D.

2014-12-01

Spectral Induced Polarization (SIP) has been used to monitor subsurface biogeochemical processes in a variety of lab and field studies. However, there are several competing mechanisms that have been proposed to explain the SIP effect. This work targets the influence of ion sorption to mineral surfaces as a controlling factor on SIP utilizing a pH dependent surface adsorption experiment. In this experiment we use silica gel as an idealized medium where the number of available sites for cation sorption, which in this case is limited to Na+ and H+ ions, is influenced by changes in pH via protonation/deprotonation of silanol groups. The experiment uses 22Na as an in situ tracer as the radioactive decay of this nuclide can be continuously and non-invasively monitored using sensors placed outside of a column. The experiment was conducted by continuously pumping a 0.01M NaCl solution spiked with of 1μCi/L 22Na in to the column under three pH conditions (pH 5.0, 6.0 and 8.0). In the experiment, we observed an increasing number of gamma counts caused by the accumulation of sorbed 22Na in the column as we increased the pH from 5.0 to 6.5, and finally to 8.0. Simultaneously, we observed a linearly correlated (R2 = 0.99) rise in the imaginary conductivity response of the SIP measurements. Using the triple layer electrochemical polarization model for grain polarization to simulate our experimental SIP responses, we found that the estimated surface site density is within a factor of two of that estimated from the mass accumulation of sodium. Since the accumulation of sodium on the silica gel surface is responsible for both the increase in gamma radiation and the change in the electrical response, these observations support the theory that mobile ions in the Stern layer of mineral surfaces provide the primary control on SIP signals in silicate materials.

Low-temperature sol-gel oxide TFT with a fluoropolymer dielectric to enhance the effective mobility at low operation voltage

NASA Astrophysics Data System (ADS)

Yu, Shang-Yu; Wang, Kuan-Hsun; Zan, Hsiao-Wen; Soppera, Olivier

2017-06-01

In this article, we propose a solution-processed high-performance amorphous indium-zinc oxide (a-IZO) thin-film transistor (TFT) gated with a fluoropolymer dielectric. Compared with a conventional IZO TFT with a silicon nitride dielectric, a fluoropolymer dielectric effectively reduces the operation voltage to less than 3 V and greatly increases the effective mobility 40-fold. We suggest that the dipole layer formed at the dielectric surface facilitates electron accumulation and induces the electric double-layer effect. The dipole-induced hysteresis effect is also investigated.

Plastic accumulation in the Mediterranean sea.

PubMed

Cózar, Andrés; Sanz-Martín, Marina; Martí, Elisa; González-Gordillo, J Ignacio; Ubeda, Bárbara; Gálvez, José Á; Irigoien, Xabier; Duarte, Carlos M

2015-01-01

Concentrations of floating plastic were measured throughout the Mediterranean Sea to assess whether this basin can be regarded as a great accumulation region of plastic debris. We found that the average density of plastic (1 item per 4 m2), as well as its frequency of occurrence (100% of the sites sampled), are comparable to the accumulation zones described for the five subtropical ocean gyres. Plastic debris in the Mediterranean surface waters was dominated by millimeter-sized fragments, but showed a higher proportion of large plastic objects than that present in oceanic gyres, reflecting the closer connection with pollution sources. The accumulation of floating plastic in the Mediterranean Sea (between 1,000 and 3,000 tons) is likely related to the high human pressure together with the hydrodynamics of this semi-enclosed basin, with outflow mainly occurring through a deep water layer. Given the biological richness and concentration of economic activities in the Mediterranean Sea, the affects of plastic pollution on marine and human life are expected to be particularly frequent in this plastic accumulation region.

Antarctic Megadunes - Assessment of Topographic Form and Windward Progradation from ICESat Altimetry, 2003-2009

NASA Astrophysics Data System (ADS)

Shuman, C. A.; Scambos, T. A.; Fahnestock, M. A.; Suchdeo, V. P.

2011-12-01

More than 900,000 square kilometers of East Antarctica are covered by distinctive megadune features (Fahnestock et al., 2000, Courville et al., 2007) as first defined by Swithinbank (1988). These long, undulating, sinuous dunes are due to persistent gravity-driven katabatic winds and spatially variable accumulation. In the field, they have a distinctive morphology, but characterization of the evolution of these active landscape features requires detailed elevation data as well as radar backscatter and grain size information. In this study, we utilize NASA's ICESat laser altimetry data during 2003-2009 (corrected for intercampaign biases) in the vicinity of an NSF-OPP funded research site near 80.78°S, 124.5°E, occupied and instrumented during the 2002-2003 and 2003-2004 summer seasons with additional limited field observations from January 2011. Using remote sensing data sets and field observations, we can characterize these features including their extent, variability, and elevation change with time. Field measurements from ground penetrating radar, automatic weather stations, surface photos, snowpits, and shallow cores provide in situ and subsurface information on local dune structure. Based on these data, Antarctic megadunes can be characterized as linear strips of higher accumulation (~30 to 80 kg m-2 a-1 maximum, typically toward the lower part of the range) consisting of fine-grained, wind-packed snow, generally forming 2-8 meter high, 1-2 km wide ridges up to 100 km long and separated by 2-6 km of near-zero-accumulation wind glaze regions. Glaze surfaces overlie extremely metamorphosed firn composed of very coarse recrystallized grains with poorly expressed layering. Our study extends site-specific results summarized in Courville et al. (2007) across the megadune study area with co-located MODIS-based Mosaic of Antarctica (MOA) images and surface optical grain size (e.g. Scambos et al., 2007), calibrated SAR backscatter data from the Radarsat Antarctic Mapping Mission (RAMP; Jezek, 1999), and elevation profiles and derived elevation changes from ICESat. Megadunes form by windward accretion of snow from the blowing snow stream entrained in the katabatic layer (Frezzotti et al., 2002; Courville et al., 2007). Ground-penetrating radar profiles reveal that the accumulation rate and the surface profile shape are intimately related for megadunes, with peak accumulation at the maximum surface slope on the windward face. We infer from accumulation and slope data that active megadunes in the field study area should migrate to the windward at ~12.5 m a-1. This motion is somewhat offset in our study area by the GPS-measured ~4 m a-1 ice flow to the east at about 45 degrees to the mean wind azimuth. The region of maximum accumulation on the windward face should have a net thickening rate of up to 9 cm a-1 as the dune slowly shifts upwind (downwind areas should lower by somewhat smaller amounts). We detail ICESat elevation data across the study area for both accumulation and glaze areas of these dunes to attempt to document active migration.

The interdecadal worsening of weather conditions affecting aerosol pollution in the Beijing area in relation to climate warming

NASA Astrophysics Data System (ADS)

Zhang, Xiaoye; Zhong, Junting; Wang, Jizhi; Wang, Yaqiang; Liu, Yanju

2018-04-01

The weather conditions affecting aerosol pollution in Beijing and its vicinity (BIV) in wintertime have worsened in recent years, particularly after 2010. The relation between interdecadal changes in weather conditions and climate warming is uncertain. Here, we analyze long-term variations of an integrated pollution-linked meteorological index (which is approximately and linearly related to aerosol pollution), the extent of changes in vertical temperature differences in the boundary layer (BL) in BIV, and northerly surface winds from Lake Baikal during wintertime to evaluate the potential contribution of climate warming to changes in meteorological conditions directly related to aerosol pollution in this area; this is accomplished using NCEP reanalysis data, surface observations, and long-term vertical balloon sounding observations since 1960. The weather conditions affecting BIV aerosol pollution are found to have worsened since the 1960s as a whole. This worsening is more significant after 2010, with PM2.5 reaching unprecedented high levels in many cities in China, particularly in BIV. The decadal worsening of meteorological conditions in BIV can partly be attributed to climate warming, which is defined by more warming in the higher layers of the boundary layer (BL) than the lower layers. This worsening can also be influenced by the accumulation of aerosol pollution, to a certain extent (particularly after 2010), because the increase in aerosol pollution from the ground leads to surface cooling by aerosol-radiation interactions, which facilitates temperature inversions, increases moisture accumulations, and results in the extra deterioration of meteorological conditions. If analyzed as a linear trend, weather conditions have worsened by ˜ 4 % each year from 2010 to 2017. Given such a deterioration rate, the worsening of weather conditions may lead to a corresponding amplitude increase in PM2.5 in BIV during wintertime in the next 5 years (i.e., 2018 to 2022). More stringent emission reduction measures will need to be conducted by the government.

Predictive modeling of crystal accumulation in high-level waste glass melters processing radioactive waste

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matyáš, Josef; Gervasio, Vivianaluxa; Sannoh, Sulaiman E.

The effectiveness of HLW vitrification is limited by precipitation/accumulation of spinel crystals [(Fe, Ni, Mn, Zn)(Fe, Cr)2O4] in the glass discharge riser of Joule-heated ceramic melters during idling. These crystals do not affect glass durability; however, if accumulated in thick layer, they can clog the melter and prevent discharge of molten glass into canisters. To address this problem, an empirical model was developed that can predict thicknesses of accumulated layers as a function of glass composition. This model predicts well the accumulation of single crystals and/or small-scale agglomerates, but, excessive agglomeration observed in high-Ni-Fe glass resulted in an under-prediction ofmore » accumulated layers, which gradually worsen over time as an increased number of agglomerates formed. Accumulation rate of ~53.8 ± 3.7 µm/h determined for this glass will result in ~26 mm thick layer in 20 days of melter idling.« less

Predictive modeling of crystal accumulation in high-level waste glass melters processing radioactive waste

NASA Astrophysics Data System (ADS)

Matyáš, Josef; Gervasio, Vivianaluxa; Sannoh, Sulaiman E.; Kruger, Albert A.

2017-11-01

The effectiveness of high-level waste vitrification at Hanford's Waste Treatment and Immobilization Plant may be limited by precipitation/accumulation of spinel crystals [(Fe, Ni, Mn, Zn)(Fe, Cr)2O4] in the glass discharge riser of Joule-heated ceramic melters during idling. These crystals do not affect glass durability; however, if accumulated in thick layers, they can clog the melter and prevent discharge of molten glass into canisters. To address this problem, an empirical model was developed that can predict thicknesses of accumulated layers as a function of glass composition. This model predicts well the accumulation of single crystals and/or small-scale agglomerates, but excessive agglomeration observed in high-Ni-Fe glass resulted in an underprediction of accumulated layers, which gradually worsened over time as an increased number of agglomerates formed. The accumulation rate of ∼53.8 ± 3.7 μm/h determined for this glass will result in a ∼26 mm-thick layer after 20 days of melter idling.

Optical and structural characteristics of high indium content InGaN/GaN multi-quantum wells with varying GaN cap layer thickness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, J.; Zhao, D. G., E-mail: dgzhao@red.semi.ac.cn; Jiang, D. S.

2015-02-07

The optical and structural properties of InGaN/GaN multi-quantum wells (MQWs) with different thicknesses of low temperature grown GaN cap layers are investigated. It is found that the MQW emission energy red-shifts and the peak intensity decreases with increasing GaN cap layer thickness, which may be partly caused by increased floating indium atoms accumulated at quantum well (QW) surface. They will result in the increased interface roughness, higher defect density, and even lead to a thermal degradation of QW layers. An extra growth interruption introduced before the growth of GaN cap layer can help with evaporating the floating indium atoms, andmore » therefore is an effective method to improve the optical properties of high indium content InGaN/GaN MQWs.« less

High temperature gas nitriding and tempering in 17Cr-1Ni-0.5C-0.4V steel

NASA Astrophysics Data System (ADS)

Kong, J. H.; Lee, D. J.; On, H. Y.; Park, S. J.; Kim, S. K.; Kang, C. Y.; Sung, J. H.; Lee, H. W.

2010-12-01

High temperature gas nitriding (HTGN) at 1050 °C and tempering of a 17Cr-1Ni-0.5C-0.4V (CNV) steel were experimentally investigated. The phases appearing in the surface layer of the HTGN-treated steel were martensite and austenite with mostly Cr2N precipitates that were formed by permeated nitrogen, and a small amount of Cr23C6 and VN precipitates. The reverse migration of carbon hindered the diffusion of nitrogen when nitrogen permeated from the surface to the interior, which resulted in the accumulation of nitrogen on the outermost surface. The strong affinity between nitrogen and chromium atoms induced the diffusion of chromium from the interior to the surface, leading to the substitution of Cr23C6 for Cr2N. After tempering the HTGN-treated steel at 500 °C, the dense precipitates of Cr2N and the increased martensite phase in the surface layer led to secondary hardening, which increased the hardness value up to 901 Hv.

Polyhydroxyalkanoate (PHA) Granules Have no Phospholipids.

PubMed

Bresan, Stephanie; Sznajder, Anna; Hauf, Waldemar; Forchhammer, Karl; Pfeiffer, Daniel; Jendrossek, Dieter

2016-05-25

Polyhydroxybutyrate (PHB) granules, also designated as carbonosomes, are supra-molecular complexes in prokaryotes consisting of a PHB polymer core and a surface layer of structural and functional proteins. The presence of suspected phospholipids in the surface layer is based on in vitro data of isolated PHB granules and is often shown in cartoons of the PHB granule structure in reviews on PHB metabolism. However, the in vivo presence of a phospholipid layer has never been demonstrated. We addressed this topic by the expression of fusion proteins of DsRed2EC and other fluorescent proteins with the phospholipid-binding domain (LactC2) of lactadherin in three model organisms. The fusion proteins specifically localized at the cell membrane of Ralstonia eutropha but did not co-localize with PHB granules. The same result was obtained for Pseudomonas putida, a species that accumulates another type of polyhydroxyalkanoate (PHA) granules related to PHB. Notably, DsRed2EC-LactC2 expressed in Magnetospirillum gryphiswaldense was detected at the position of membrane-enclosed magnetosome chains and at the cytoplasmic membrane but not at PHB granules. In conclusion, the carbonosomes of representatives of α-proteobacteria, β-proteobacteria and γ-proteobacteria have no phospholipids in vivo and we postulate that the PHB/PHA granule surface layers in natural producers generally are free of phospholipids and consist of proteins only.

Sedimentation, bioturbation, and sedimentary fabric evolution on a modern mesotidal mudflat: A multi-tracer study of processes, rates, and scales

NASA Astrophysics Data System (ADS)

Bentley, Samuel J.; Swales, Andrew; Pyenson, Benjamin; Dawe, Justin

2014-03-01

A study of muddy tidal-flat sedimentation and bioturbation was undertaken in the Waitetuna Arm of Raglan Harbor, New Zealand, to evaluate the physical and biological processes that control cycling of sediment between the intertidal seabed and sediment-water interface, and also the formation of tidal flat sedimentary fabric and fine-scale stratigraphy. Cores were collected along an intertidal transect, and analyzed for sedimentary fabric, 210Pb and 7Be radiochemical distributions, and grain size. At the same locations, a new approach for time-series core-X-radiography study was undertaken (spanning 191 days), using magnetite-rich sand as a tracer for sedimentation and bioturbation processes in shallow tidal flat sediments. Sedimentary fabric consists of a shallow stratified layer overlying a deeper zone of intensely bioturbated shelly mud. Bioadvection mixes the deeper zone and contributes fine sediment to the surface stratified layer, via biodeposition. Physical resuspension and deposition of surface muds by wave and tidal flow are also likely contributors to formation of the surficial stratified layer, but physical stratification is not observed below this depth. The deliberate tracer study allowed calculation of bioadvection rates that control strata formation, and can be used to model diagenetic processes. Results suggest that the upper ˜15 cm of seabed can be fully mixed over timescales <1.75 y. Such mixing will erase pre-existing sedimentary fabric and transport buried sediment and chemical compounds back to the tidal-flat surface. Shallow biodiffusion also exists, but produces much slower and shallower mass transport. Best fits for 210Pb profiles using a diagenetic bioadvection/sedimentation model and independently measured tiered bioadvection rates suggest that sediment accumulation rates (SARs) on the tidal flat are ˜0.25 cm/y, near the low end of contemporary New Zealand muddy intertidal SARs. Frequent deposition and erosion of the surface layer demonstrates that long-term sediment accumulation captures only a small fraction of sediment deposited at any one time. Model results also suggest that our magnetite tracer method may slightly underestimate short-term shallow mixing rates (demonstrated by 7Be profiles), and slightly overestimate longer-term, deeper bioturbation rates (demonstrated by 210Pb profiles).

Fractional laser-assisted delivery of methyl aminolevulinate: Impact of laser channel depth and incubation time.

PubMed

Haak, Christina S; Farinelli, William A; Tam, Joshua; Doukas, Apostolos G; Anderson, R Rox; Haedersdal, Merete

2012-12-01

Pretreatment of skin with ablative fractional lasers (AFXL) enhances the uptake of topical photosensitizers used in photodynamic therapy (PDT). Distribution of photosensitizer into skin layers may depend on depth of laser channels and incubation time. This study evaluates whether depth of intradermal laser channels and incubation time may affect AFXL-assisted delivery of methyl aminolevulinate (MAL). Yorkshire swine were treated with CO2 AFXL at energy levels of 37, 190, and 380 mJ/laser channel and subsequent application of MAL cream (Metvix) for 30, 60, 120, and 180 minutes incubation time. Fluorescence photography and fluorescence microscopy quantified MAL-induced porphyrin fluorescence (PpIX) at the skin surface and at five specific skin depths (120, 500, 1,000, 1,500, and 1,800 µm). Laser channels penetrated into superficial (∼300 µm), mid (∼1,400 µm), and deep dermis/upper subcutaneous fat layer (∼2,100 µm). Similar fluorescence intensities were induced at the skin surface and throughout skin layers independent of laser channel depth (180 minutes; P < 0.19). AFXL accelerated PpIX fluorescence from skin surface to deep dermis. After laser exposure and 60 minutes MAL incubation, surface fluorescence was significantly higher compared to intact, not laser-exposed skin at 180 minutes (AFXL-MAL 60 minutes vs. MAL 180 minutes, 69.16 a.u. vs. 23.49 a.u.; P < 0.01). Through all skin layers (120-1,800 µm), laser exposure and 120 minutes MAL incubation induced significantly higher fluorescence intensities in HF and dermis than non-laser exposed sites at 180 minutes (1,800 µm, AFXL-MAL 120 minutes vs. MAL 180 minutes, HF 14.76 a.u. vs. 6.69 a.u. and dermis 6.98 a.u. vs. 5.87 a.u.; P < 0.01). AFXL pretreatment accelerates PpIX accumulation, but intradermal depth of laser channels does not affect porphyrin accumulation. Further studies are required to examine these findings in clinical trials. Copyright © 2012 Wiley Periodicals, Inc.

Tropical warm pool rainfall variability and impact on upper ocean variability throughout the Madden-Julian oscillation

NASA Astrophysics Data System (ADS)

Thompson, Elizabeth J.

Heating and rain freshening often stabilize the upper tropical ocean, bringing the ocean mixed layer depth to the sea surface. Thin mixed layer depths concentrate subsequent fluxes of heat, momentum, and freshwater in a thin layer. Rapid heating and cooling of the tropical sea surface is important for controlling or triggering atmospheric convection. Ocean mixed layer depth and SST variability due to rainfall events have not been as comprehensively explored as the ocean's response to heating or momentum fluxes, but are very important to understand in the tropical warm pool where precipitation exceeds evaporation and many climate phenomena such as ENSO and the MJO (Madden Julian Oscillation) originate. The first part of the dissertation investigates tropical, oceanic convective and stratiform rainfall variability and determines how to most accurately estimate rainfall accumulation with radar from each rain type. The second, main part of the dissertation uses central Indian Ocean salinity and temperature microstructure measurements and surrounding radar-derived rainfall maps throughout two DYNAMO MJO events to determine the impact of precipitating systems on upper-ocean mixed layer depth and resulting SST variability. The ocean mixed layer was as shallow as 0-5 m during 528/1071 observation hours throughout 2 MJOs (54% of the data record). Out of 43 observation days, thirty-eight near-surface mixed layer depth events were attributed to freshwater stabilization, called rain-formed mixed layers (RFLs). Thirty other mixed layer stratification events were classified as diurnal warm layers (DWLs) due to stable temperature stratification by daytime heating. RFLs and DWLs were observed to interact in two ways: 1) RFLs fill preexisting DWLs and add to total near-surface mixed layer stratification, which occurred ten times; 2) RFLs last long enough to heat, creating a new DWL on top of the RFL, which happened nine times. These combination stratification events were responsible for the highest SST warming rates and some of the highest SSTs leading up to the most active precipitation and wind stage of the each MJO. DWLs without RFL interaction helped produce the highest SSTs in suppressed MJO conditions. As storm intensity, frequency, duration, and the ability of storms to maintain stratiform rain areas increased, RFLS became more common in the disturbed and active MJO phases. Along with the barrier layer, DWL and RFL stratification events helped suppress wind-mixing, cooling, and mixed layer deepening throughout the MJO. We hypothesize that both salinity and temperature stratification events, and their interactions, are important for controlling SST variability and therefore MJO initiation in the Indian Ocean. Most RFLs were caused by submesoscale and mesoscale convective systems with stratiform rain components and local rain accumulations above 10 mm but with winds mostly below 8 m s-1. We hypothesize that the stratiform rain components of storms helped stratify the ocean by providing weak but widespread, steady, long-lived freshwater fluxes. Although generally limited to rain rates ≤ 10 mm hr-1, it is demonstrated that stratiform rain can exert a strong buoyancy flux into the ocean, i.e. as high as maximum daytime solar heating. Storm morphology and the preexisting vertical structure of ocean stability were critical in determining ocean mixed layer depth variability in the presence of rain. Therefore, we suggest that high spatial and temporal resolution coupled ocean-atmosphere models that can parameterize or resolve storm morphology as well as ocean mixed layer and barrier layer evolution are needed to reproduce the diurnal and intraseasonal SST variability documented throughout the MJO.

Water ice is water ice: some applications and limitations of Earth analogues to Mars

NASA Astrophysics Data System (ADS)

Koutnik, M.; Pathare, A.; Waddington, E. D.; Winebrenner, D. P.

2017-12-01

Quantitative and qualitative analyses of ice on Mars have advanced with the acquisition of abundant topography, imagery, and radar data, which have enabled the planetary-science community to tackle sophisticated questions about the martian cryosphere. Over the past decades, many studies have applied knowledge of terrestrial ice-sheet and glacier flow to improve understanding of ice behavior on Mars. A key question for both planets is how we can robustly interpret past climate from glaciological and glacial geomorphological features. Doing this requires deciphering how the history of accumulation, ablation, dust/debris deposition, and flow led to the shape and internal structure of present-day ice. Terrestrial glaciology and glacial geomorphology provide physical relationships that can be extended across environmental conditions to characterize related processes that may act at different rates or on different timescales. However, there remain fundamental unknowns about martian ice rheology and history that often limit our ability to directly apply understanding of ice dynamics learned from Antarctica, Greenland, terrestrial glaciers, and laboratory ice experiments. But the field is rich with opportunity because the constitutive relationship for water ice depends on quantities that can typically be reasonably estimated; water ice is water ice. We reflect on progress to understand the history of the ice-rich North Polar Layered Deposits (NPLD) and of select mid-latitude Lobate Debris Aprons (LDAs), and the utility of terrestrial ice-sheet and glacier analogues for these problems. Our work on Earth and Mars has focused on constraining surface accumulation/ablation patterns and ice-flow histories from topography and radar observations. We present on the challenge of interpreting internal-layer shapes when both accumulation/ablation and ice-flow histories are unknown, and how this non-uniqueness can be broken only by making assumptions about one or the other. In particular, we discuss why internal layers alone are not a diagnostic test for ice flow. We also present progress in applying models of debris-covered glacier flow to LDAs where dynamic debris cover, ice flow, and accumulation/ablation act to shape the ice-mass surface.

Adsorption and electron-induced polymerization of methyl methacrylate on Ru(101xAF0)

NASA Astrophysics Data System (ADS)

Hedhili, M. N.; Yakshinskiy, B. V.; Wasielewski, R.; Ciszewski, A.; Madey, T. E.

2008-05-01

The adsorption and electron irradiation of methyl methacrylate (MMA) on a Ru(101¯0) surface have been studied using x-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), and low energy ion scattering. TPD analysis indicates that a monolayer of MMA chemisorbs and dissociates on the Ru(101¯0) surface. The reaction products observed upon heating include H2, CO, CO2, and a small amount of MMA. Physisorbed multilayers of MMA desorb at temperatures around 170K. Electron irradiation of physisorbed MMA at 140K leads to a modification of the MMA film: The XPS spectra show an increase in thermal stability of the film with retention of the MMA structure, and indicate that electron irradiation induces polymerization. An increase in the electron bombardment fluence induces a degradation of the formed polymerized species and leads to the accumulation of carbon on the Ru surface. These results are relevant to the accumulation of carbon on surfaces of Ru films that serve as capping layers on Mo /Si multilayer mirrors used in extreme ultraviolet lithography.

Dynamic perennial firn aquifer on an Arctic glacier

NASA Astrophysics Data System (ADS)

Christianson, Knut; Kohler, Jack; Alley, Richard B.; Nuth, Christopher; Pelt, Ward J. J.

2015-03-01

Ice-penetrating radar and GPS observations reveal a perennial firn aquifer (PFA) on a Svalbard ice field, similar to those recently discovered in southeastern Greenland. A bright, widespread radar reflector separates relatively dry and water-saturated firn. This surface, the phreatic firn water table, is deeper beneath local surface elevation maxima, shallower in surface lows, and steeper where the surface is steep. The reflector crosscuts snow stratigraphy; we use the apparent deflection of accumulation layers due to the higher dielectric permittivity below the water table to infer that the firn pore space becomes progressively more saturated as depth increases. Our observations indicate that PFAs respond rapidly (subannually) to surface forcing, and are capable of providing significant input to the englacial hydrology system.

High resolution, multi-2D seismic imaging of Solfatara crater (Campi Flegrei Caldera, southern Italy) from active seismic data

NASA Astrophysics Data System (ADS)

Gammaldi, S.; Amoroso, O.; D'Auria, L.; Zollo, A.

2018-05-01

A multi-2D imaging of the Solfatara Crater inside the Campi Flegrei Caldera, was obtained by the joint interpretation of geophysical evidences and the new active seismic dataset acquired during the RICEN experiment (EU project MEDSUV) in 2014. We used a total of 17,894 first P-wave arrival times manually picked on pre-processed waveforms, recorded along two 1D profiles criss-crossing the inner Solfatara crater, and performed a tomographic inversion based on a multi-scale strategy and a Bayesian estimation of velocity parameters. The resulting tomographic images provide evidence for a low velocity (500-1500 m/s) water saturated deeper layer at West near the outcropping evidence of the Fangaia, contrasted by a high velocity (2000-3200 m/s) layer correlated with a consolidated tephra deposit. The transition velocity range (1500-2000 m/s) layer suggests a possible presence of a gas-rich, accumulation volume. Thanks to the mutual P-wave velocity model, we infer a detailed image for the gas migration path to the Earth surface. The gasses coming from the deep hydrothermal plume accumulate in the central and most depressed area of the Solfatara being trapped by the meteoric water saturated layer. Therefore, the gasses are transmitted through the buried fault toward the east part of the crater, where the ring faults facilitate the release as confirmed by the fumaroles. Starting from the eastern surface evidence of the gas releasing in the Bocca Grande and Bocca Nuova fumaroles, and the presence of the central deeper plume we suggest a fault situated in the central part of the crater which seems to represent the main buried conduit among them plays a key role.

Periodic climate change on Mars: Review of evidence and effects on distribution of volatiles

USGS Publications Warehouse

Carr, M.H.

1982-01-01

The polar regions of Mars preserve, in both their layering and their topography, a record of recent climate changes. Because of the coincidence of the growth of the northern seasonal cap with global dust storms, dust may be currently accumulating on the northern cap, but conditions at the poles will alternate with the precessional cycle. Deposition is also modulated by changes in eccentricity and obliquity, which interact complexly, affecting initiation of global dust storms, the stability of volatiles at the surface, and global wind regimes. Formation of spiral valleys and low undulations on the surface of the layered deposits may result from prefential sublimation of volatiles on sunward-facing slopes and condensation on the adjacent flats, with the rates also modulated by astronomically caused insolation variations. Lack of impact craters on the surface and lack of interruption of the layers by impact scars suggest that the polar deposits are no more than a few million years old. Older deposits may have been periodically removed, as indicated by etch-pitted terrain at the south pole and by superposition relations around the periphery of the present layered deposits. Evidence of ancient periodic climate changes that occurred before formation of the present layered terrain is fragmentary but includes pedestal craters, parallel moraine-like ridges, and etched ground at high latitudes. Perturbation of the orbital motions also results in adsorption and desorption of volatiles in the regolith, which leads to variations in atmospheric pressure and partial dehydration of the equatorial near-surface materials. ?? 1982.

Insights into the effects of solvent properties in graphene based electric double-layer capacitors with organic electrolytes

NASA Astrophysics Data System (ADS)

Zhang, Shuo; Bo, Zheng; Yang, Huachao; Yang, Jinyuan; Duan, Liangping; Yan, Jianhua; Cen, Kefa

2016-12-01

Organic electrolytes are widely used in electric double-layer capacitors (EDLCs). In this work, the microstructure of planar graphene-based EDLCs with different organic solvents are investigated with molecular dynamics simulations. Results show that an increase of solvent polarity could weaken the accumulation of counter-ions nearby the electrode surface, due to the screen of electrode charges and relatively lower ionic desolvation. It thus suggests that solvents with low polarity could be preferable to yield high EDL capacitance. Meanwhile, the significant effects of the size and structure of solvent molecules are reflected by non-electrostatic molecule-electrode interactions, further influencing the adsorption of solvent molecules on electrode surface. Compared with dimethyl carbonate, γ-butyrolactone, and propylene carbonate, acetonitrile with relatively small-size and linear structure owns weak non-electrostatic interactions, which favors the easy re-orientation of solvent molecules. Moreover, the shift of solvent orientation in surface layer, from parallel orientation to perpendicular orientation relative to the electrode surface, deciphers the solvent twin-peak behavior near negative electrode. The as-obtained insights into the roles of solvent properties on the interplays among particles and electrodes elucidate the solvent influences on the microstructure and capacitive behavior of EDLCs using organic electrolytes.

Formation of Reversible Solid Electrolyte Interface on Graphite Surface from Concentrated Electrolytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Dongping; Tao, Jinhui; Yan, Pengfei

2017-02-10

Interfacial phenomena have always been key determinants for the performance of energy storage technologies. The solid electrolyte interfacial (SEI) layer, pervasive on the surfaces of battery electrodes for numerous chemical couples, directly affects the ion transport, charge transfer and lifespan of the entire energy system. Almost all SEI layers, however, are unstable resulting in the continuous consumption of the electrolyte. Typically, this leads to the accumulation of degradation products on/restructuring of the electrode surface and thus increased cell impedance, which largely limits the long-term operation of the electrochemical reactions. Herein, a completely new SEI formation mechanism has been discovered, inmore » which the electrolyte components reversibly self-assemble into a protective surface coating on a graphite electrode upon changing the potential. In contrast to the established wisdom regarding the necessity of employing the solvent ethylene carbonate (EC) to form a protective SEI layer on graphite, a wide range of EC-free electrolytes are demonstrated for the reversible intercalation/deintercalation of Li+ cations within a graphite lattice, thereby providing tremendous flexibility in electrolyte tailoring for battery couples. This novel finding is broadly applicable and provides guidance for how to control interfacial reactions through the relationship between ion aggregation and solvent decomposition at polarized interfaces.« less

Surface Area, and Oxidation Effects on Nitridation Kinetics of Silicon Powder Compacts

NASA Technical Reports Server (NTRS)

Bhatt, R. T.; Palczer, A. R.

1998-01-01

Commercially available silicon powders were wet-attrition-milled from 2 to 48 hr to achieve surface areas (SA's) ranging from 1.3 to 70 sq m/g. The surface area effects on the nitridation kinetics of silicon powder compacts were determined at 1250 or 1350 C for 4 hr. In addition, the influence of nitridation environment, and preoxidation on nitridation kinetics of a silicon powder of high surface area (approximately equals 63 sq m/g) was investigated. As the surface area increased, so did the percentage nitridation after 4 hr in N2 at 1250 or 1350 C. Silicon powders of high surface area (greater than 40 sq m/g) can be nitrided to greater than 70% at 1250 C in 4 hr. The nitridation kinetics of the high-surface-area powder compacts were significantly delayed by preoxidation treatment. Conversely, the nitridation environment had no significant influence on the nitridation kinetics of the same powder. Impurities present in the starting powder, and those accumulated during attrition milling, appeared to react with the silica layer on the surface of silicon particles to form a molten silicate layer, which provided a path for rapid diffusion of nitrogen and enhanced the nitridation kinetics of high surface area silicon powder.

Modeling concentric crater fill in Utopia Planitia, Mars, with an ice flow line model

NASA Astrophysics Data System (ADS)

Weitz, N.; Zanetti, M.; Osinski, G. R.; Fastook, J. L.

2018-07-01

Impact craters in the mid-latitudes of Mars are commonly filled to variable degrees with some combination of ice, dust, and rocky debris. Concentric surface features visible in these craters have been linked to debris transportation and glacial and periglacial processes. Concentric crater fill (CCF) observed today are interpreted to be the remains of repeated periods of accumulation and sublimation during the last tens to hundreds of million years. Previous work suggests that during phases of high obliquity, ice accumulates in crater interiors and begins to flow down steep crater slopes, slowly filling the crater. During times of low obliquity ice is protected from sublimation through a surface debris layer consisting of dust and rocky material. Here, we use an ice flow line model to understand the development of concentric crater fill. In a regional study of Utopia Planitia craters, we address questions about the influence of crater size on the CCF formation process, the time scales needed to fill an impact crater with ice, and explore commonly described flow features of CCF. We show that observed surface debris deposits as well as asymmetric flow features can be reproduced with the model. Using surface mass balance data from global climate models and a credible obliquity scenario, we find that craters less than 80 km in diameter can be entirely filled in less than 8 My, beginning as recently as 40 Ma ago. Uncertainties in input variables related to ice viscosity do not change the overall behavior of ice flow and the filling process. We model CCF for the Utopia Planitia region and find subtle trends for crater size versus fill level, crater size versus sublimation reduction by the surface debris layer, and crater floor elevation versus fill level.

Micro-NRA and micro-3HIXE with 3He microbeam on samples exposed in ASDEX Upgrade and Pilot-PSI machines

NASA Astrophysics Data System (ADS)

Kelemen, Mitja; Založnik, Anže; Vavpetič, Primož; Pečovnik, Matic; Pelicon, Primož; Hakola, Antti; Lahtinen, Aki; Karhunen, Juuso; Piip, Kaarel; Paris, Peeter; Laan, Matti; Krieger, Karl; Oberkofler, Martin; van der Meiden, Hennie; Markelj, Sabina

2017-08-01

Micro nuclear reaction analysis (micro-NRA) exploiting the nuclear reaction D(3He,p)4He was used for post-mortem analyses of special marker samples, exposed to deuterium plasma inside ASDEX Upgrade (AUG) tokamak and to the deuterium plasma jet in the Pilot-PSI linear plasma gun. Lateral concentration profiles of deuterium and erosion/deposition profiles of the marker materials were obtained by a combination of micro-NRA and particle induced X-ray emission by 3He beam (3HIXE). In the case of AUG samples, where 25 nm thick W marker layers had been deposited on unpolished and polished graphite substrates, the effect of surface roughness on local erosion and deposition was also investigated. The lateral distribution of W concentration showed that erosion is much more distinct in the case of polished samples and the resulting surface shows a ;leopard; skin pattern of W accumulated on carbon aggregates left on the surface from polishing. The Pilot-PSI samples indicated preferential accumulation of deuterium a few mm off from the centre of the region affected by the plasma beam. This is connected with the largest surface modifications while the thick deposited layers at the centre do not favour deuterium retention per se. The results were cross correlated with those obtained using laser-induced breakdown spectroscopy (LIBS). With its quantitative abilities, micro-NRA provided essential calibration data for in situ LIBS operation, as well as for complementary post mortem Secondary Ion Mass Spectroscopy (SIMS).

Predictive modeling of crystal accumulation in high-level waste glass melters processing radioactive waste

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matyáš, Josef; Gervasio, Vivianaluxa; Sannoh, Sulaiman E.

We present that the effectiveness of high-level waste vitrification at Hanford's Waste Treatment and Immobilization Plant may be limited by precipitation/accumulation of spinel crystals [(Fe, Ni, Mn, Zn)(Fe, Cr) 2O 4] in the glass discharge riser of Joule-heated ceramic melters during idling. These crystals do not affect glass durability; however, if accumulated in thick layers, they can clog the melter and prevent discharge of molten glass into canisters. To address this problem, an empirical model was developed that can predict thicknesses of accumulated layers as a function of glass composition. This model predicts well the accumulation of single crystals and/ormore » small-scale agglomerates, but excessive agglomeration observed in high-Ni-Fe glass resulted in an underprediction of accumulated layers, which gradually worsened over time as an increased number of agglomerates formed. In conclusion, the accumulation rate of ~53.8 ± 3.7 μm/h determined for this glass will result in a ~26 mm-thick layer after 20 days of melter idling.« less

Predictive modeling of crystal accumulation in high-level waste glass melters processing radioactive waste

DOE PAGES

Matyáš, Josef; Gervasio, Vivianaluxa; Sannoh, Sulaiman E.; ...

2017-08-30

We present that the effectiveness of high-level waste vitrification at Hanford's Waste Treatment and Immobilization Plant may be limited by precipitation/accumulation of spinel crystals [(Fe, Ni, Mn, Zn)(Fe, Cr) 2O 4] in the glass discharge riser of Joule-heated ceramic melters during idling. These crystals do not affect glass durability; however, if accumulated in thick layers, they can clog the melter and prevent discharge of molten glass into canisters. To address this problem, an empirical model was developed that can predict thicknesses of accumulated layers as a function of glass composition. This model predicts well the accumulation of single crystals and/ormore » small-scale agglomerates, but excessive agglomeration observed in high-Ni-Fe glass resulted in an underprediction of accumulated layers, which gradually worsened over time as an increased number of agglomerates formed. In conclusion, the accumulation rate of ~53.8 ± 3.7 μm/h determined for this glass will result in a ~26 mm-thick layer after 20 days of melter idling.« less

Feedback effects of boundary-layer meteorological factors on cumulative explosive growth of PM2.5 during winter heavy pollution episodes in Beijing from 2013 to 2016

NASA Astrophysics Data System (ADS)

Zhong, Junting; Zhang, Xiaoye; Dong, Yunsheng; Wang, Yaqiang; Liu, Cheng; Wang, Jizhi; Zhang, Yangmei; Che, Haochi

2018-01-01

In January 2013, February 2014, December 2015 and December 2016 to 10 January 2017, 12 persistent heavy aerosol pollution episodes (HPEs) occurred in Beijing, which received special attention from the public. During the HPEs, the precise cause of PM2.5 explosive growth (mass concentration at least doubled in several hours to 10 h) is uncertain. Here, we analyzed and estimated relative contributions of boundary-layer meteorological factors to such growth, using ground and vertical meteorological data. Beijing HPEs are generally characterized by the transport stage (TS), whose aerosol pollution formation is primarily caused by pollutants transported from the south of Beijing, and the cumulative stage (CS), in which the cumulative explosive growth of PM2.5 mass is dominated by stable atmospheric stratification characteristics of southerly slight or calm winds, near-ground anomalous inversion, and moisture accumulation. During the CSs, observed southerly weak winds facilitate local pollutant accumulation by minimizing horizontal pollutant diffusion. Established by TSs, elevated PM2.5 levels scatter more solar radiation back to space to reduce near-ground temperature, which very likely causes anomalous inversion. This surface cooling by PM2.5 decreases near-ground saturation vapor pressure and increases relative humidity significantly; the inversion subsequently reduces vertical turbulent diffusion and boundary-layer height to trap pollutants and accumulate water vapor. Appreciable near-ground moisture accumulation (relative humidity > 80 %) would further enhance aerosol hygroscopic growth and accelerate liquid-phase and heterogeneous reactions, in which incompletely quantified chemical mechanisms need more investigation. The positive meteorological feedback noted on PM2.5 mass explains over 70 % of cumulative explosive growth.

Characteristics of lead corrosion scales formed during drinking water distribution and their potential influence on the release of lead and other contaminants.

PubMed

Kim, Eun Jung; Herrera, Jose E

2010-08-15

Destabilization of the corrosion scale present in lead pipes used in drinking water distribution systems is currently considered a major problem for municipalities serviced in part by lead pipes. Although several lead corrosion strategies have been deployed with success, a clear understanding of the chemistry of corrosion products present in the scale is needed for an effective lead control. This contribution focuses on a comprehensive characterization of the layers present in the corrosion scale formed on the inner surfaces of lead pipes used in the drinking water distribution system of the City on London, ON, Canada. Solid corrosion products were characterized using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Toxic elements accumulated in the corrosion scale were also identified using inductively coupled plasma (ICP) spectrometry after acid digestion. Based on the XRD results, hydrocerussite was identified as the major lead crystalline corrosion phase in most of the pipes sampled, while cerussite was observed as the main crystalline component only in a few cases. Lead oxides including PbO(2) and Pb(3)O(4) were also observed in the inner layers of the corrosion scale. The presence of these highly oxidized lead species is rationalized in terms of the lead(II) carbonate phase transforming into lead(IV) oxide through an intermediate Pb(3)O(4) (2Pb(II)O x Pb(IV)O(2)) phase. In addition to lead corrosion products, an amorphous aluminosilicate phase was also identified in the corrosion scale. Its concentration is particularly high at the outer surface layers. Accumulation of toxic contaminants such as As, V, Sb, Cu, and Cr was observed in the corrosion scales, together with a strong correlation between arsenic accumulation and aluminum concentration.

Effects of Praxelis clematidea invasion on soil nitrogen fractions and transformation rates in a tropical savanna.

PubMed

Wei, Hui; Xu, Jialin; Quan, Guoming; Zhang, Jiaen; Qin, Zhong

2017-02-01

Plant invasion has been reported to affect a mass of soil ecological processes and functions, although invasion effects are often context-, species- and ecosystem- specific. This study was conducted to explore potential impacts of Praxelis clematidea invasion on contents of total and available soil nitrogen (N) and microbial N transformations in a tropical savanna. Soil samples were collected from the surface and sub-surface layers in plots with non-, slight, or severe P. clematidea invasion in Hainan Province of southern China, which remains less studied, and analyzed for contents of the total and available N fractions and microbial N transformations. Results showed that total N content significantly increased in the surface soil but trended to decrease in the sub-surface soil in the invaded plots relative to the non-invaded control. Slight invasion significantly increased soil alkali-hydrolysable N content in the two soil layers. Soil net N mineralization rate was not significantly changed in both the soil layers, although soil microbial biomass N was significantly higher in plots with severe invasion than the control. There was no significant difference in content of soil N fractions between plots with slight and severe invasion. Our results suggest that invasion of P. clematidea promotes soil N accumulation in the surface soil layer, which is associated with increased microbial biomass N. However, the invasion-induced ecological impacts did not increase with further invasion. Significantly higher microbial biomass N was maintained in plots with severe invasion, implying that severe P. clematidea invasion may accelerate nutrient cycling in invaded ecosystems.

On the Theory of Accumulation of Hydrocarbons in a Dome Used to Eliminate a Technogenic Spill at the Bottom of the Ocean

NASA Astrophysics Data System (ADS)

Gimaltdinov, I. K.; Kil'dibaeva, S. R.

2018-01-01

Consideration is given to the operation of a dome separator installed at the bottom of the World Ocean and intended to eliminate the effects of technogenic spill of hydrocarbons. It is assumed that oil and gas (methane) escape from the damaged well on the ocean floor. Under the conditions of stable existence of a hydrate, a hydration sheath is formed on the surface of methane bubbles. To collect the entering hydrocarbons, a dome from a soft polyurethane shell is installed above the spill site, inside which the hydrocarbons are accumulated. In the regime of steady-state operation of the dome, provision is made for pumping out of hydrocarbons for transportation and further utilization. In the work, temperature fields of the hydrocarbon layers accumulated in the dome are investigated.

Ions, metabolites, and cells: Water as a reporter of surface conditions during bacterial growth.

PubMed

Jarisz, Tasha A; Lane, Sarah; Gozdzialski, Lea; Hore, Dennis K

2018-06-14

Surface-specific nonlinear vibrational spectroscopy, combined with bulk solution measurements and imaging, is used to study the surface conditions during the growth of E. coli. As a result of the silica high surface charge density, the water structure at the silica-aqueous interface is known to be especially sensitive to pH and ionic strength, and surface concentration profiles develop that can be appreciably different from the bulk solution conditions. We illustrate that, in the presence of growing cells, a unique surface micro-environment is established as a result of metabolites accumulating on the silica surface. Even in the subsequent absence of the cells, this surface layer works to reduce the interfacial ionic strength as revealed by the enhanced signal from surface water molecules. In the presence of growing cells, an additional boost in surface water signal is attributed to a local pH that is higher than that of the bulk solution.

Ions, metabolites, and cells: Water as a reporter of surface conditions during bacterial growth

NASA Astrophysics Data System (ADS)

Jarisz, Tasha A.; Lane, Sarah; Gozdzialski, Lea; Hore, Dennis K.

2018-06-01

Surface-specific nonlinear vibrational spectroscopy, combined with bulk solution measurements and imaging, is used to study the surface conditions during the growth of E. coli. As a result of the silica high surface charge density, the water structure at the silica-aqueous interface is known to be especially sensitive to pH and ionic strength, and surface concentration profiles develop that can be appreciably different from the bulk solution conditions. We illustrate that, in the presence of growing cells, a unique surface micro-environment is established as a result of metabolites accumulating on the silica surface. Even in the subsequent absence of the cells, this surface layer works to reduce the interfacial ionic strength as revealed by the enhanced signal from surface water molecules. In the presence of growing cells, an additional boost in surface water signal is attributed to a local pH that is higher than that of the bulk solution.

Room temperature-synthesized vertically aligned InSb nanowires: electrical transport and field emission characteristics

PubMed Central

2013-01-01

Vertically aligned single-crystal InSb nanowires were synthesized via the electrochemical method at room temperature. The characteristics of Fourier transform infrared spectrum revealed that in the syntheses of InSb nanowires, energy bandgap shifts towards the short wavelength with the occurrence of an electron accumulation layer. The current–voltage curve, based on the metal–semiconductor–metal model, showed a high electron carrier concentration of 2.0 × 1017 cm−3 and a high electron mobility of 446.42 cm2 V−1 s−1. Additionally, the high carrier concentration of the InSb semiconductor with the surface accumulation layer induced a downward band bending effect that reduces the electron tunneling barrier. Consequently, the InSb nanowires exhibit significant field emission properties with an extremely low turn-on field of 1.84 V μm−1 and an estimative threshold field of 3.36 V μm−1. PMID:23399075

Purely electronic mechanism of electrolyte gating of indium tin oxide thin films

DOE PAGES

Leng, X.; Bozovic, I.; Bollinger, A. T.

2016-08-10

Epitaxial indium tin oxide films have been grown on both LaAlO 3 and yttria-stabilized zirconia substrates using RF magnetron sputtering. Electrolyte gating causes a large change in the film resistance that occurs immediately after the gate voltage is applied, and shows no hysteresis during the charging/discharging processes. When two devices are patterned next to one another and the first one gated through an electrolyte, the second one shows no changes in conductance, in contrast to what happens in materials (like tungsten oxide) susceptible to ionic electromigration and intercalation. These findings indicate that electrolyte gating in indium tin oxide triggers amore » pure electronic process (electron depletion or accumulation, depending on the polarity of the gate voltage), with no electrochemical reactions involved. Electron accumulation occurs in a very thin layer near the film surface, which becomes highly conductive. These results contribute to our understanding of the electrolyte gating mechanism in complex oxides and may be relevant for applications of electric double layer transistor devices.« less

Charge-Dissipative Electrical Cables

NASA Technical Reports Server (NTRS)

Kolasinski, John R.; Wollack, Edward J.

2004-01-01

Electrical cables that dissipate spurious static electric charges, in addition to performing their main functions of conducting signals, have been developed. These cables are intended for use in trapped-ion or ionizing-radiation environments, in which electric charges tend to accumulate within, and on the surfaces of, dielectric layers of cables. If the charging rate exceeds the dissipation rate, charges can accumulate in excessive amounts, giving rise to high-current discharges that can damage electronic circuitry and/or systems connected to it. The basic idea of design and operation of charge-dissipative electrical cables is to drain spurious charges to ground by use of lossy (slightly electrically conductive) dielectric layers, possibly in conjunction with drain wires and/or drain shields (see figure). In typical cases, the drain wires and/or drain shields could be electrically grounded via the connector assemblies at the ends of the cables, in any of the conventional techniques for grounding signal conductors and signal shields. In some cases, signal shields could double as drain shields.

Snow Densification and Recent Accumulation Along the iSTAR Traverse, Pine Island Glacier, Antarctica

NASA Astrophysics Data System (ADS)

Morris, E. M.; Mulvaney, R.; Arthern, R. J.; Davies, D.; Gurney, R. J.; Lambert, P.; De Rydt, J.; Smith, A. M.; Tuckwell, R. J.; Winstrup, M.

2017-12-01

Neutron probe measurements of snow density from 22 sites in the Pine Island Glacier basin have been used to determine mean annual accumulation using an automatic annual layer identification routine. A mean density profile which can be used to convert radar two-way travel times to depth has been derived, and the effect of annual fluctuations in density on estimates of the depth of radar reflectors is shown to be insignificant, except very near the surface. Vertical densification rates have been derived from the neutron probe density profiles and from deeper firn core density profiles available at 9 of the sites. These rates are consistent with the rates predicted by the Herron and Langway model for stage 1 densification (by grain-boundary sliding, grain growth and intracrystalline deformation) and stage 2 densification (predominantly by sintering), except in a transition zone extending from ≈8 to ≈13 m from the surface in which 10-14% of the compaction occurs. Profiles of volumetric strain rate at each site show that in this transition zone the rates are consistent with the Arthern densification model. Comparison of the vertical densification rates and volumetric strain rates indicates that the expected relation to mean annual accumulation breaks down at high accumulation rates even when corrections are made for horizontal ice velocity divergence.

Colloidal transport phenomena of milk components during convective droplet drying.

PubMed

Fu, Nan; Woo, Meng Wai; Chen, Xiao Dong

2011-10-15

Material segregation has been reported for industrial spray-dried milk powders, which indicates potential material migration during drying process. The relevant colloidal transport phenomenon and the underlying mechanism are still under debate. This study extended the glass-filament single droplet drying technique to observe not only the drying behaviour but also the dissolution behaviour of the correspondingly dried single particle. At progressively longer drying stage, a solvent droplet (water or ethanol) was attached to the semi-dried milk particle and the interaction between the solvent and the particle was video-recorded. Based on the different dissolution and wetting behaviours observed, material migration during milk drying was studied. Fresh skim milk and fresh whole milk were investigated using water and ethanol as solvents. Fat started to accumulate on the surface as soon as drying was started. At the initial stage of drying, the fat layer remained thin and the solubility of the semi-dried milk particle was much affected by lactose and protein present underneath the fat layer. Fat kept accumulating at the surface as drying progressed and the accumulation was completed by the middle stage of drying. The results from drying of model milk materials (pure sodium caseinate solution and lactose/sodium caseinate mixed solution) supported the colloidal transport phenomena observed for the milk drying. When mixed with lactose, sodium caseinate did not form an apparent solvent-resistant protein shell during drying. The extended technique of glass-filament single droplet approach provides a powerful tool in examining the solubility of individual particle after drying. Copyright © 2011 Elsevier B.V. All rights reserved.

Accumulation of radioactive corrosion products on steel surfaces of VVER type nuclear reactors. I. 110mAg

NASA Astrophysics Data System (ADS)

Hirschberg, Gábor; Baradlai, Pál; Varga, Kálmán; Myburg, Gerrit; Schunk, János; Tilky, Péter; Stoddart, Paul

Formation, presence and deposition of corrosion product radionuclides (such as 60Co, 51Cr, 54Mn, 59Fe and/or 110mAg) in the primary circuits of water-cooled nuclear reactors (PWRs) throw many obstacles in the way of normal operation. During the course of the work presented in this series, accumulations of such radionuclides have been studied at austenitic stainless steel type 08X18H10T (GOST 5632-61) surfaces (this austenitic stainless steel corresponds to AISI 321). Comparative experiments have been performed on magnetite-covered carbon steel (both materials are frequently used in some Soviet VVER type PWRs). For these laboratory-scale investigations a combination of the in situ radiotracer `thin gap' method and voltammetry is considered to be a powerful tool due to its high sensitivity towards the detection of the submonolayer coverages of corrosion product radionuclides. An independent technique (XPS) is also used to characterize the depth distribution and chemical state of various contaminants in the passive layer formed on austenitic stainless steel. In the first part of the series the accumulation of 110mAg has been investigated. Potential dependent sorption of Ag + ions (cementation) is found to be the predominant process on austenitic steel, while in the case of magnetite-covered carbon steel the silver species are mainly depleted in the form of Ag 2O. The XPS depth profile of Ag gives an evidence about the embedding of metallic silver into the entire passive layer of the austenitic stainless steel studied.

2D Effective Electron Mass at the Fermi Level in Accumulation and Inversion Layers of MOSFET Nano Devices.

PubMed

Singh, S L; Singh, S B; Ghatak, K P

2018-04-01

In this paper an attempt is made to study the 2D Fermi Level Mass (FLM) in accumulation and inversion layers of nano MOSFET devices made of nonlinear optical, III-V, ternary, Quaternary, II-VI, IV-VI, Ge and stressed materials by formulating 2D carrier dispersion laws on the basis of k → ⋅ p → ⋅ formalism and considering the energy band constants of a particular material. It is observed taking accumulation and inversion layers of Cd3As2, CdGeAs2, InSb, Hg1-xCdxTe and In1-xGaxAsyP1-y lattice matched to InP, CdS, GaSb and Ge as examples that the FLM depends on sub band index for nano MOSFET devices made of Cd3As2 and CdGeAs2 materials which is the characteristic features such 2D systems. Besides, the FLM depends on the scattering potential in all the cases and the same mass changes with increasing surface electric field. The FLM exists in the band gap which is impossible without heavy doping.

Characterizing near-surface firn from the scattered signal component of glacier surface reflections detected in airborne radio-echo sounding measurements

NASA Astrophysics Data System (ADS)

Rutishauser, A.; Grima, C.; Sharp, M. J.; Blankenship, D. D.; Young, D. A.; Cawkwell, F.; Dowdeswell, J. A.

2016-12-01

With recent summer warming, surface melt on Canadian Arctic ice caps has intensified and extended to higher elevations in ice cap accumulation areas. Consequently, more meltwater percolates into the near-surface firn, and refreezes as ice layers where firn temperatures are below freezing. This process can increase firn densification rates, causing a lowering of the glacier surface height even in the absence of mass changes. Thus, knowledge of spatio-temporal variations in the near-surface firn stratigraphy is important for interpreting altimetrically-derived estimates of ice cap mass balance. We investigate the use of the scattering signal component of glacier surface reflections in airborne radio-echo sounding (RES) measurements to characterize the near-surface firn stratigraphy. The scattering signal distribution over Devon Ice Cap is compared to firn stratigraphy derived from ground-based radar data. We identify three distinct firn facies zones at different elevation ranges. The scattered signal component changes significantly between the different firn facies zones: low scattering correlates to laterally homogeneous firn containing thin, flat and continuous ice layers at elevations above 1800 m and below 1200 m, where firn consists mainly of ice. Higher scattering values are found from 1200-1800 m where the firn contains discrete, undulating ice layers. No correlation was found between the scattering component and surface roughness. Modelled scattering values for the measured roughness were significantly less than the observed values, and did not reproduce their observed spatial distribution. This indicates that the scattering component is determined mainly by the structure of near-surface firn. Our results suggest that the scattering component of surface reflections from airborne RES measurements has potential for characterizing heterogeneity in the spatial structure of firn that is affected by melting and refreezing processes.

How Well do we Know Near-Surface Density When Determining Mass Balance by the Geodetic Method?

NASA Astrophysics Data System (ADS)

Kuhn, M. H.; Matzi, E.

2005-12-01

From a data set of firn pits in the accumulation area of Hintereisferner in the years 1964 - 2002 the behavior of density and water equivalent was analyzed with a view to estimating the potential errors in the application of the geodetic method. Since annual specific balance ranged from 100 to 3300 mm w.e. the profiles were scaled to total depth. For the uppermost 10% of the annual deposit at a typical location the 1964-2002 mean density would be 350 kg/m-3 with a standard deviation of 110 kg/m-3; for the 10% layer at the base of the annual snowpack the respective figures are 510 +- 30 kg/m-3. The normalized long term means of an ensemble of 9 pits ranged from 310 to 380 kg/m-3 in the top layer and from 510 to 540 kg/m-3 in the bottom layer. When one outlier is removed the the range in the bottom layer reduces to 525 to 540 kg/m-3. This small local variance encourages the use of the geodetic method. The comparison of elevation models of 1969 and 1997 yields a mass change that agrees very well with the results of the glaciological method provided the volume change is converted to mass with a density of 900 kg/m-3. While this may be true for the entire glacier on long terms, it will fail for individual years in the accumulation area. Possible errors are calculated from the data set emphasizing the role of year to year changes of specific balance and accumulation area ratio.

Queen Maud Land Traverses: Surface Glaciology (Invited)

NASA Astrophysics Data System (ADS)

Cameron, R. L.

2009-12-01

One of the main tasks of a glaciologist is to determine the mass budget of a glacier; and snow accumulation is the first part of the equation. To do this, a great number of snow pits must be dug to analyze the stratigraphy. A. P. Crary once said “to be a glaciologist one should first of all love to dig snow pits.” Seventy-five snow pits were dug on the SPQMLT traverses. Several experienced glaciologists had difficulty in interpreting the stratigraphic sequences in these pits. Irregular layering, caused by uneven deposition and subsequent erosion, suggested that some of the layers could be missing. However, the fallout of artificial radioactive nuclides released by the first large thermonuclear bomb test, on March 1, 1954, at Castle Bravo on Bikini Atoll, Marshall Islands, produced a datum horizon over the Antarctic ice sheet. This horizon is the summer of 1954-55 and provides the basis for measuring the average accumulation since 1955. Accumulation varied from 6.7 ± 0.2 g cm-2 yr-1 at South Pole Station to a low of 0.6 ± 0.2 g cm-2 yr-1 in a pit on the second leg of SPQMLT 2. The average accumulation along the entire traverse route was 3.7 g cm-2 yr-1. Temperatures at ten meters (considered an approximate mean annual air temperature) varied from -58.4 degrees Centigrade at Plateau Station (elevation 3620 meters) to -38 degrees Centigrade at the terminus of SPQMLT 3 (elevation 2310 meters). The condition of the ice sheet surface varied considerably. Some surface was quite hard and easy to traverse; while other areas that were smooth and soft were troublesome enough to bog down vehicles and sleds. Sastrugi were sporadic with some as high as a meter. A large crevasse field forced a slight change in course toward the end of the first leg of SPQMLT 2. There the ice thickness changed dramatically from 3060 meters to 1852 meters. At the time the geophysicist said, “The ‘bottom’ came up so fast I thought we would hit a nunatak.”

Progress of the LANL Low Temperature/Low Frequency Air Opacity Project - Optical Theory for HET-project: an update, April 2015

DOE Office of Scientific and Technical Information (OSTI.GOV)

Timmermans, Eddy Marcel Elvire; Nisoli, Cristiano; Mozyrsky, Dima

Light radiated from a hot, opaque thermal emitter originates mostly from near the surface at which the object becomes opaque (the surface of last scattering). To be specific, we define the “optical surface” as the surface at which the optical depth, as observed from a detector, takes on the value of 1. The optical depth along a line of sight depends on the wavelength dependent. Accumulating light in different spectral bands, spectral detector then records light from different surfaces, a structure that we can picture somewhat like the layers of an onion. The theoretical framework that predicts the emitted spectralmore » signal is radioactive transfer.« less

Orienting the Microstructure Evolution of Copper Phthalocyanine as an Anode Interlayer in Inverted Polymer Solar Cells for High Performance.

PubMed

Li, Zhiqi; Liu, Chunyu; Zhang, Xinyuan; Li, Shujun; Zhang, Xulin; Guo, Jiaxin; Guo, Wenbin; Zhang, Liu; Ruan, Shengping

2017-09-20

Recent advances in the interfacial modification of inverted-type polymer solar cells (PSCs) have resulted from controlling the surface energy of the cathode-modified layer (TiO 2 or ZnO) to enhance the short-circuit current (J sc ) or optimizing the contact morphology of the cathode (indium tin oxide or fluorine-doped tin oxide) and active layer to increase the fill factor. Herein, we report that the performance enhancement of PSCs is achieved by incorporating a donor macromolecule copper phthalocyanine (CuPc) as an anode modification layer. Using the approach based on orienting the microstructure evolution, uniformly dispersed island-shaped CuPc spot accumulations are built on the top of PTB7:PC 71 BM blend film, leading to an efficient spectral absorption and photogenerated exciton splitting. The best power conversion efficiency of PSCs is increased up to 9.726%. In addition to the enhanced light absorption, the tailored anode energy level alignment and optimized boundary morphology by incorporating the CuPc interlayer boost charge extraction efficiency and suppress the interfacial molecular recombination. These results demonstrate that surface morphology induction through molecular deposition is an effective method to improve the performance of PSCs, which reveals the potential implications of the interlayer between the organic active layer and the electrode buffer layer.

Complexation of Uranium by Cells and S-Layer Sheets of Bacillus sphaericus JG-A12

PubMed Central

Merroun, Mohamed L.; Raff, Johannes; Rossberg, André; Hennig, Christoph; Reich, Tobias; Selenska-Pobell, Sonja

2005-01-01

Bacillus sphaericus JG-A12 is a natural isolate recovered from a uranium mining waste pile near the town of Johanngeorgenstadt in Saxony, Germany. The cells of this strain are enveloped by a highly ordered crystalline proteinaceous surface layer (S-layer) possessing an ability to bind uranium and other heavy metals. Purified and recrystallized S-layer proteins were shown to be phosphorylated by phosphoprotein-specific staining, inductive coupled plasma mass spectrometry analysis, and a colorimetric method. We used extended X-ray absorption fine-structure (EXAFS) spectroscopy to determine the structural parameters of the uranium complexes formed by purified and recrystallized S-layer sheets of B. sphaericus JG-A12. In addition, we investigated the complexation of uranium by the vegetative bacterial cells. The EXAFS analysis demonstrated that in all samples studied, the U(VI) is coordinated to carboxyl groups in a bidentate fashion with an average distance between the U atom and the C atom of 2.88 ± 0.02 Å and to phosphate groups in a monodentate fashion with an average distance between the U atom and the P atom of 3.62 ± 0.02 Å. Transmission electron microscopy showed that the uranium accumulated by the cells of this strain is located in dense deposits at the cell surface. PMID:16151146

Electrical hysteresis in p-GaN metal-oxide-semiconductor capacitor with atomic-layer-deposited Al2O3 as gate dielectric

NASA Astrophysics Data System (ADS)

Zhang, Kexiong; Liao, Meiyong; Imura, Masataka; Nabatame, Toshihide; Ohi, Akihiko; Sumiya, Masatomo; Koide, Yasuo; Sang, Liwen

2016-12-01

The electrical hysteresis in current-voltage (I-V) and capacitance-voltage characteristics was observed in an atomic-layer-deposited Al2O3/p-GaN metal-oxide-semiconductor capacitor (PMOSCAP). The absolute minimum leakage currents of the PMOSCAP for forward and backward I-V scans occurred not at 0 V but at -4.4 and +4.4 V, respectively. A negative flat-band voltage shift of 5.5 V was acquired with a capacitance step from +4.4 to +6.1 V during the forward scan. Mg surface accumulation on p-GaN was demonstrated to induce an Mg-Ga-Al-O oxidized layer with a trap density on the order of 1013 cm-2. The electrical hysteresis is attributed to the hole trapping and detrapping process in the traps of the Mg-Ga-Al-O layer via the Poole-Frenkel mechanism.

Defects in Arsenic Implanted p + -n- and n + -p- Structures Based on MBE Grown CdHgTe Films

NASA Astrophysics Data System (ADS)

Izhnin, I. I.; Fitsych, E. I.; Voitsekhovskii, A. V.; Korotaev, A. G.; Mynbaev, K. D.; Varavin, V. S.; Dvoretsky, S. A.; Mikhailov, N. N.; Yakushev, M. V.; Bonchyk, A. Yu.; Savytskyy, H. V.; Świątek, Z.

2018-02-01

Complex studies of the defect structure of arsenic-implanted (with the energy of 190 keV) Cd x Hg 1-x Te ( x = 0.22) films grown by molecular-beam epitaxy are carried out. The investigations were performed using secondary-ion mass spectroscopy, transmission electron microscopy, optical reflection in the visible region of the spectrum, and electrical measurements. Radiation donor defects were studied in n +- p- and n +- n-structures obtained by implantation and formed on the basis of p-type and n-type materials, respectively, without activation annealing. It is shown that in the layer of the distribution of implanted ions, a layer of large extended defects with low density is formed in the near-surface region followed by a layer of smaller extended defects with larger density. A different character of accumulation of electrically active donor defects in the films with and without a protective graded-gap surface layer has been revealed. It is demonstrated that p +- n- structures are formed on the basis of n-type material upon activation of arsenic in the process of postimplantation thermal annealing with 100% activation of impurity and complete annihilation of radiation donor defects.

History and anatomy of subsurface ice on Mars

NASA Astrophysics Data System (ADS)

Schorghofer, Norbert; Forget, Francois

2012-08-01

Ice buried beneath a thin layer of soil has been revealed by neutron spectroscopy and explored by the Phoenix Mars Lander. It has also been exposed by recent impacts. This subsurface ice is thought to lose and gain volume in response to orbital variations (Milankovitch cycles). We use a powerful numerical model to follow the growth and retreat of near-surface ice as a result of regolith-atmosphere exchange continuously over millions of years. If a thick layer of almost pure ice has been deposited recently, it has not yet reached equilibrium with the atmospheric water vapor and may still remain as far equatorward as 43°N, where ice has been revealed by recent impacts. A potentially observable consequence is present-day humidity output from the still retreating ice. We also demonstrate that in a sublimation environment, subsurface pore ice can accumulate in two ways. The first mode, widely known, is the progressive filling of pores by ice over a range of depths. The second mode occurs on top of an already impermeable ice layer; subsequent ice accumulates in the form of pasted on horizontal layers such that beneath the ice table, the pores are completely full with ice. Most or all of the pore ice on Mars today may be of the second type. At the Phoenix landing site, where such a layer is also expected to exist above an underlying ice sheet, it may be extremely thin, due to exceptionally small variations in ice stability over time.

Hydrodynamical instabilities induced by atomic diffusion in F and A stars : Impact on the opacity profile and asteroseimic age determination

NASA Astrophysics Data System (ADS)

Deal, M.; Richard, O.; Vauclair, S.

2017-12-01

Atomic diffusion, including the effect of radiative accelerations on individual elements, leads to important variations of the chemical composition inside the stars. The accumulation in specific layers of the elements, which are the main contributors of the local opacity, leads to hydrodynamical instabilities that modify the internal stellar structure and surface abundances. The modification of the initial chemical composition has important effects on the internal stellar mixing and leads to different surface and internal abundances of the elements. These processes also modify the age determination by asteroseismology.

Polyhydroxyalkanoate (PHA) Granules Have no Phospholipids

PubMed Central

Bresan, Stephanie; Sznajder, Anna; Hauf, Waldemar; Forchhammer, Karl; Pfeiffer, Daniel; Jendrossek, Dieter

2016-01-01

Polyhydroxybutyrate (PHB) granules, also designated as carbonosomes, are supra-molecular complexes in prokaryotes consisting of a PHB polymer core and a surface layer of structural and functional proteins. The presence of suspected phospholipids in the surface layer is based on in vitro data of isolated PHB granules and is often shown in cartoons of the PHB granule structure in reviews on PHB metabolism. However, the in vivo presence of a phospholipid layer has never been demonstrated. We addressed this topic by the expression of fusion proteins of DsRed2EC and other fluorescent proteins with the phospholipid-binding domain (LactC2) of lactadherin in three model organisms. The fusion proteins specifically localized at the cell membrane of Ralstonia eutropha but did not co-localize with PHB granules. The same result was obtained for Pseudomonas putida, a species that accumulates another type of polyhydroxyalkanoate (PHA) granules related to PHB. Notably, DsRed2EC-LactC2 expressed in Magnetospirillum gryphiswaldense was detected at the position of membrane-enclosed magnetosome chains and at the cytoplasmic membrane but not at PHB granules. In conclusion, the carbonosomes of representatives of α-proteobacteria, β-proteobacteria and γ-proteobacteria have no phospholipids in vivo and we postulate that the PHB/PHA granule surface layers in natural producers generally are free of phospholipids and consist of proteins only. PMID:27222167

Biological and immunotoxicity evaluation of antimicrobial peptide-loaded coatings using a layer-by-layer process on titanium

PubMed Central

Shi, Jue; Liu, Yu; Wang, Ying; Zhang, Jing; Zhao, Shifang; Yang, Guoli

2015-01-01

The prevention and control of peri-implantitis is a challenge in dental implant surgery. Dental implants with sustained antimicrobial coating are an ideal way of preventing peri-implantitis. This study reports development of a non- immunotoxicity multilayered coating on a titanium surface that had sustained antimicrobial activity and limited early biofilm formation. In this study, the broad spectrum AMP, Tet213, was linked to collagen IV through sulfo-SMPB and has been renamed as AMPCol. The multilayer AMPCol coatings were assembled on smooth titanium surfaces using a LBL technique. Using XPS, AFM, contact angle analysis, and QCM, layer-by-layer accumulation of coating thickness was measured and increased surface wetting compared to controls was confirmed. Non-cytotoxicity to HaCaT and low erythrocyte hemolysis by the AMPCol coatings was observed. In vivo immunotoxicity assays showed IP administration of AMPCol did not effect serum immunoglobulin levels. This coating with controlled release of AMP decreased the growth of both a Gram-positive aerobe (Staphylococcus aureus) and a Gram-negative anaerobe (Porphyromonas gingivalis) up to one month. Early S. aureus biofilm formation was inhibited by the coating. The excellent long-term sustained antimicrobial activity of this multilayer coating is a potential method for preventing peri-implantitis through coated on the neck of implants before surgery. PMID:26548760

FTIR and SEM analysis applied in tissue engineering for root recovering surgery.

PubMed

Costa, Davidson Ribeiro; Nicolau, Renata Amadei; Costa, David Ribeiro; Raniero, Leandro José; Oliveira, Marco Antonio

2017-08-01

Gingival recession is defined by the displacement of the gingival margin in the apical direction, which overcomes the cementum enamel junction. The etiology of gingival retraction is related to tissue inflammation caused by the accumulation of biofilm, by trauma from brushing action. Aesthetic periodontal surgery aims to return the root coverage to aesthetic harmony, and reduce the risk of periodontal disease and caries. To assist in the root coverage process, the porcine collagen matrix (PCM) has been widely studied. The objectives of this study are to identify the types of collagen that make up the PCM and analyze their morphology. For this, five PCM fragments, 2 mm (thickness) × 2.6 mm (width), were analyzed with the aid of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The analysis by SEM showed that the PCM consists of two layers; the surface layer is compact, low porosity, and smooth surface, and a foamed underlying layer has high porosity. Through FTIR we identified that the surface and underlying layers are composed of collagen types I and III, respectively. This biomaterial is conducive to root coverage; it allows adsorption and cell proliferation following the matrix resorption and periodontal tissue neoformation. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1326-1329, 2017. © 2015 Wiley Periodicals, Inc.

Plastic Accumulation in the Mediterranean Sea

PubMed Central

Cózar, Andrés; Sanz-Martín, Marina; Martí, Elisa; González-Gordillo, J. Ignacio; Ubeda, Bárbara; Gálvez, José Á.; Irigoien, Xabier; Duarte, Carlos M.

2015-01-01

Concentrations of floating plastic were measured throughout the Mediterranean Sea to assess whether this basin can be regarded as a great accumulation region of plastic debris. We found that the average density of plastic (1 item per 4 m2), as well as its frequency of occurrence (100% of the sites sampled), are comparable to the accumulation zones described for the five subtropical ocean gyres. Plastic debris in the Mediterranean surface waters was dominated by millimeter-sized fragments, but showed a higher proportion of large plastic objects than that present in oceanic gyres, reflecting the closer connection with pollution sources. The accumulation of floating plastic in the Mediterranean Sea (between 1,000 and 3,000 tons) is likely related to the high human pressure together with the hydrodynamics of this semi-enclosed basin, with outflow mainly occurring through a deep water layer. Given the biological richness and concentration of economic activities in the Mediterranean Sea, the affects of plastic pollution on marine and human life are expected to be particularly frequent in this plastic accumulation region. PMID:25831129

Intrinsic two-dimensional states on the pristine surface of tellurium

NASA Astrophysics Data System (ADS)

Li, Pengke; Appelbaum, Ian

2018-05-01

Atomic chains configured in a helical geometry have fascinating properties, including phases hosting localized bound states in their electronic structure. We show how the zero-dimensional state—bound to the edge of a single one-dimensional helical chain of tellurium atoms—evolves into two-dimensional bands on the c -axis surface of the three-dimensional trigonal bulk. We give an effective Hamiltonian description of its dispersion in k space by exploiting confinement to a virtual bilayer, and elaborate on the diminished role of spin-orbit coupling. These intrinsic gap-penetrating surface bands were neglected in the interpretation of seminal experiments, where two-dimensional transport was otherwise attributed to extrinsic accumulation layers.

Sum-Frequency Generation Spectroscopy for Studying Organic Layers at Water-Air Interfaces: Microlayer Monitoring and Surface Reactivity

NASA Astrophysics Data System (ADS)

Laß, Kristian; Kleber, Joscha; Bange, Hermann; Friedrichs, Gernot

2015-04-01

The sea surface microlayer, according to commonly accepted terminology, comprises the topmost millimetre of the oceanic water column. It is often enriched with organic matter and is directly influenced by sunlight exposure and gas exchange with the atmosphere, hence making it a place for active biochemistry and photochemistry as well as for heterogeneous reactions. In addition, surface active material either is formed or accumulates directly at the air-water interface and gives rise to very thin layers, sometimes down to monomolecular thickness. This "sea surface nanolayer" determines the viscoelastic properties of the seawater surface and thus may impact the turbulent air-sea gas exchange rates. To this effect, this small scale layer presumably plays an important role for large scale changes of atmospheric trace gas concentrations (e.g., by modulating the ocean carbon sink characteristics) with possible implications for coupled climate models. To date, detailed knowledge about the composition, structure, and reactivity of the sea surface nanolayer is still scarce. Due to its small vertical dimension and the small amount of material, this surfactant layer is very difficult to separate and analyse. A way out is the application of second-order nonlinear optical methods, which make a direct surface-specific and background-free detection of this interfacial layer possible. In recent years, we have introduced the use of vibrational sum frequency generation (VSFG) spectroscopy to gain insight into natural and artificial organic monolayers at the air-water interface. In this contribution, the application of VSFG spectroscopy for the analysis of the sea surface nanolayer will be illustrated. Resulting spectra are interpreted in terms of layer composition and surfactant classes, in particular with respect to carbohydrate-containing molecules such as glycolipids. The partitioning of the detected surfactants into soluble and non-soluble ("wet" and "dry") surfactants will be discussed. Furthermore, the application of a combined VSFG/Langmuir trough experiment to investigate the reaction kinetics of heterogeneous oxidation processes will be highlighted. The ozonolysis of monolayers of unsaturated fatty acids serves as model system for natural aging processes of surfactant layers at the sea surface. Finally, a VSFG time series study of the sea surface nanolayer at a western Baltic Sea near-shore sampling station will be presented. The observed seasonality reveals a significant temporal shift with respect to the spring algal bloom showing that high organic material content in the microlayer does not necessarily correlate with high nanolayer abundance. This interesting finding and implications for the formation of surfactant material by degradation of biological material will be discussed briefly.

Hygrothermal analysis of surface layers of historical masonry

NASA Astrophysics Data System (ADS)

Kočí, Václav; Maděra, Jiří; Keppert, Martin; Černý, Robert

2017-11-01

The paper deals with the hygrothermal analysis of surface layers of historical masonry. Solid brick provided with a traditional and two modified lime-based plasters is studied. The heat and moisture transport in the envelope is induced by an exposure of the wall from the exterior side to dynamic climatic conditions of Olomouc, Czech Republic. The transport processes are described using diffusion type of mathematical model based on experimentally determined material properties. The computational results indicate that hygric transport and accumulation properties of exterior plasters affect the hygrothermal performance of the underlying solid brick in a very significant way, being able to regulate the amount of transported moisture. The modified lime plasters are not found generally superior to the traditional lime plasters in that respect. Therefore, their suitability for historical masonry should be assessed case by case, with a particular attention to the climatic conditions and to the properties of the load bearing structure.

Accumulation of polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs) in organic and mineral soil horizons from four U.S. remote forests.

PubMed

Obrist, Daniel; Zielinska, Barbara; Perlinger, Judith A

2015-09-01

We characterized distributions of 23 polycyclic aromatic hydrocarbons (Σ23PAH) and nine oxygenated PAHs (Σ9OPAH) in four remote forests. We observed highest Σ23PAH and Σ9OPAH concentrations in a coniferous forest in Florida, particularly in organic layers which we attributed to frequent prescribed burning. Across sites, Σ23PAH and Σ9OPAH concentrations strongly increased from surface to humidified organic layers (+1626%) where concentrations reached up to 584 ng g(-1). Concentrations in mineral soils were lower (average 37 ± 8 ng g(-1)); but when standardized per unit organic carbon (OC), PAH/OC and OPAH/OC ratios were at or above levels observed in organic layers. Accumulation in litter and soils (i.e., enrichment factors with depth) negatively correlated with octanol-water partition coefficients (Kow) and therefore was linked to water solubility of compounds. Concentrations of Σ9OPAHs ranged from 6 ± 6 ng g(-1) to 39 ± 25 ng g(-1) in organic layers, and from 3 ± 1 ng g(-1) to 11 ± 3 ng g(-1) in mineral soils, and were significantly and positively correlated to Σ23PAHs concentrations (r(2) of 0.90) across sites and horizons. While OPAH concentrations generally decreased from organic layers to mineral soil horizons, OPAH/OC ratios increased more strongly with depth compared to PAHs, in particular for anthrone, anthraquinone, fluorenone, and acenaphthenequinone. The strong vertical accumulation of OPAH relative to OC was exponentially and negatively correlated to C/N ratios (r(2)=0.67), a measure that often is used for tissue age. In fact, C/N ratios alone explained two-thirds of the variability in OPAH/OC ratios suggesting particularly high retention, sorption, and persistency of OPAHs in old, decomposed carbon fractions. Copyright © 2015 Elsevier Ltd. All rights reserved.

Modelling Internal Heterogeneities in Debris-Covered Glaciers: the Potential to Link Morphology and Climate

NASA Astrophysics Data System (ADS)

Stuurman, C. M.; Holt, J.; Levy, J.

2016-12-01

On Earth and Mars, debris-covered glaciers (DCGs) often exhibit arcuate ridges transverse to the flow direction. Additionally, there exists some evidence linking internal structure (which is controlled in part by climate) in DCGs with surface microtopography. A better understanding of the relationship between englacial debris bands, compressional stresses, and debris-covered glacier microtopography will augment understanding of formational environments and mechanisms for terrestrial and martian DCGs. In order to better understand relationships between DCG surface morphology and internal debris bands, we combine field observations with finite-element modeling techniques to relate internal structure of DCGs to their surface morphologies. A geophysical survey including time-domain electromagnetic and ground-penetrating radar techniques of the Galena Creek Rock Glacier, WY was conducted over two field seasons in 2015/2016. Geomorphic analysis by surface observation and photogrammetry, including examination of a cirque-based thermokarst, was used to guide and complement geophysical sounding methods. Very clean ice below a 1 m thick layer of debris was directly observed on the walls of a 40 m diameter thermokarst pond near the accumulation zone. An englacial debris band 0.7 m thick dipping 30o intersected the wall of the pond. Transverse ridges occur at varying ridge-to-ridge wavelengths at different locations on the glacier. The GPR data supports the idea that surface ridges correlate with the intersection of debris layers and the surface. Modelling evidence is consistent with the observation of ridges at debris-layer/surface intersections, with compressional stresses buckling ice up-stream of the debris band.

Inferring Firn Permeability from Pneumatic Testing: A Case Study on the Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Sommers, Aleah N.; Rajaram, Harihar; Weber, Eliezer P.; MacFerrin, Michael J.; Colgan, William T.; Stevens, C. Max

2017-03-01

Across the accumulation zone of the Greenland ice sheet, summer temperatures can be sufficiently warm to cause widespread melting, as was the case in July 2012 when the entire ice sheet experienced a brief episode of enhanced surface ablation. The resulting meltwater percolates into the firn and refreezes, to create ice lenses and layers within the firn column. This is an important process to consider when estimating the surface mass balance of the ice sheet. The rate of meltwater percolation depends on the permeability of the firn, a property that is not well constrained in the presence of refrozen ice layers and lenses. We present a novel, inexpensive method for measuring in-situ firn permeability using pneumatic testing, a well-established technique used in environmental engineering and hydrology. To illustrate the capabilities of this method, we estimate both horizontal and vertical permeability from pilot tests at six sites on the Greenland ice sheet: KAN-U, DYE-2, EKT, NASA-SE, Saddle, and EastGRIP. These sites cover a range of conditions from mostly dry firn (EastGRIP), to firn with several ice layers and lenses from refrozen meltwater (Saddle, NASA-SE, EKT), to firn with extensive ice layers (DYE-2 and KAN-U). The estimated permeability in firn without refrozen ice layers at EastGRIP agrees well with the range previously reported using an air permeameter to measure permeability through firn core samples at Summit, Greenland. At sites with ice lenses or layers, we find high degrees of anisotropy, with vertical permeability much lower than horizontal permeability. Pneumatic testing is a promising and low-cost technique for measuring firn permeability, particularly as meltwater production increases in the accumulation zone and ice layers and lenses from refrozen melt layers become more prevalent. In these initial proof-of-concept tests, the estimated permeabilities represent effective permeability at the meter scale. With appropriately higher vacuum pressures and more detailed monitoring, effective permeabilities over a larger scale may be quantified reliably, and multiple measurements during a season and across multiple years could improve understanding of the evolving firn structure and permeability. The technique is also suitable for broad application in Antarctica and other glaciers and ice caps.

Photoinduced Field-Effect Passivation from Negative Carrier Accumulation for High-Efficiency Silicon/Organic Heterojunction Solar Cells.

PubMed

Liu, Zhaolang; Yang, Zhenhai; Wu, Sudong; Zhu, Juye; Guo, Wei; Sheng, Jiang; Ye, Jichun; Cui, Yi

2017-12-26

Carrier recombination and light management of the dopant-free silicon/organic heterojunction solar cells (HSCs) based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are the critical factors in developing high-efficiency photovoltaic devices. However, the traditional passivation technologies can hardly provide efficient surface passivation on the front surface of Si. In this study, a photoinduced electric field was induced in a bilayer antireflective coating (ARC) of polydimethylsiloxane (PDMS) and titanium oxide (TiO 2 ) films, due to formation of an accumulation layer of negative carriers (O 2 - species) under UV (sunlight) illumination. This photoinduced field not only suppressed the silicon surface recombination but also enhanced the built-in potential of HSCs with 84 mV increment. In addition, this photoactive ARC also displayed the outstanding light-trapping capability. The front PEDOT:PSS/Si HSC with the saturated O 2 - received a champion PCE of 15.51% under AM 1.5 simulated sunlight illumination. It was clearly demonstrated that the photoinduced electric field was a simple, efficient, and low-cost method for the surface passivation and contributed to achieve a high efficiency when applied in the Si/PEDOT:PSS HSCs.

The history of hexachlorobenzene accumulation in Svalbard fjords.

PubMed

Pouch, A; Zaborska, A; Pazdro, K

2018-05-24

In the present study, we investigated the spatial and historical trends of hexachlorobenzene (HCB) contamination in dated sediments of three Svalbard fjords (Kongsfjorden, Hornsund, Adventfjorden) differing in environmental conditions and human impact. HCB concentrations ranging from below limit of quantification (6.86 pg/g d.w.) to 143.99 pg/g d.w. were measured. The highest concentrations were measured in two surface sediment layers of the core collected in Hornsund near the melting glacier. The lowest concentrations of HCB were measured in Adventfjorden, suggesting that local source of HCB is not significant and global transport processes are the major transport pathways. The history of HCB deposition did not fully reflect the history of HCB emission (largest in 1950s and 1960s). In case of several sediment cores, the HCB enrichment in surface (recent) sediments was noticed. This can indicate importance of secondary sources of HCB, e.g., the influx of HCB accumulated over decades on the surface of glaciers. Detected levels of HCB were generally low and did not exceed background concentration levels; thus, a negative effect on benthic organisms is not expected.

Processing of n+/p-/p+ strip detectors with atomic layer deposition (ALD) grown Al2O3 field insulator on magnetic Czochralski silicon (MCz-si) substrates

NASA Astrophysics Data System (ADS)

Härkönen, J.; Tuovinen, E.; Luukka, P.; Gädda, A.; Mäenpää, T.; Tuominen, E.; Arsenovich, T.; Junkes, A.; Wu, X.; Li, Z.

2016-08-01

Detectors manufactured on p-type silicon material are known to have significant advantages in very harsh radiation environment over n-type detectors, traditionally used in High Energy Physics experiments for particle tracking. In p-type (n+ segmentation on p substrate) position-sensitive strip detectors, however, the fixed oxide charge in the silicon dioxide is positive and, thus, causes electron accumulation at the Si/SiO2 interface. As a result, unless appropriate interstrip isolation is applied, the n-type strips are short-circuited. Widely adopted methods to terminate surface electron accumulation are segmented p-stop or p-spray field implantations. A different approach to overcome the near-surface electron accumulation at the interface of silicon dioxide and p-type silicon is to deposit a thin film field insulator with negative oxide charge. We have processed silicon strip detectors on p-type Magnetic Czochralski silicon (MCz-Si) substrates with aluminum oxide (Al2O3) thin film insulator, grown with Atomic Layer Deposition (ALD) method. The electrical characterization by current-voltage and capacitance-voltage measurement shows reliable performance of the aluminum oxide. The final proof of concept was obtained at the test beam with 200 GeV/c muons. For the non-irradiated detector the charge collection efficiency (CCE) was nearly 100% with a signal-to-noise ratio (S/N) of about 40, whereas for the 2×1015 neq/cm2 proton irradiated detector the CCE was 35%, when the sensor was biased at 500 V. These results are comparable with the results from p-type detectors with the p-spray and p-stop interstrip isolation techniques. In addition, interestingly, when the aluminum oxide was irradiated with Co-60 gamma-rays, an accumulation of negative fixed oxide charge in the oxide was observed.

An analysis of dynamical factors influencing 2013 giant jellyfish bloom near Qinhuangdao in the Bohai Sea, China∗

NASA Astrophysics Data System (ADS)

Wu, Lingjuan; Wang, Jia; Gao, Song; Zheng, Xiangrong; Huang, Rui

2017-02-01

The explosive growth of Nemopilema nomurai occurred near the coastal waters of Qinhuangdao in July 2013. However, it did not take place in 2012. In this paper, the dynamical factors of wind, ocean current and sea temperature on giant jellyfish bloom in 2013 is analyzed by a comprehensive investigation. The numerical experiments are based on a numerical trajectory model of the jellyfish particles, which are released into the waters from Feiyan Shoal to New Yellow River Mouth, where is speculated as the most likely remote source of Qinhuangdao jellyfish bloom. The results show that in surface layer the jellyfish drift is jointly driven by the surface wind and surface current. For example, in northeastern Bohai Bay, the giant jellyfish moved northwestward in surface layer with influence of the westward wind and current anomalies during the second half of May in 2013, then approached the south of Jingtang Port by early June, and accumulated near Qinhuangdao in early July. The 2012 scenario during the same period was quite different. The jellyfish particles influencing waters near Qinhuangdao decreased with depth and there was few (no) particles influencing Qinhuangdao in middle (bottom) layer because the anticyclonic residual circulation weakened with depth in Bohai Bay. Besides, in the potential source waters of jellyfish, sea temperature in 2012 was more suitable for jellyfish bloom than that in 2013 if there was adequate bait. Hence, the specified direction of wind and current pattern in the Bohai Sea in surface layer (especially in the northeastern Bohai Bay during the second half of May) was more important for jellyfish bloom near Qinhuangdao than the sea temperature in the potential source.

Modeled Seasonal Variations of Firn Density Induced by Steady State Surface Air Temperature Cycle

NASA Technical Reports Server (NTRS)

Jun, Li; Zwally, H. Jay; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

Seasonal variations of firn density in ice-sheet firn layers have been attributed to variations in deposition processes or other processes within the upper firn. A recent high-resolution (mm scale) density profile, measured along a 181 m core from Antarctica, showed small-scale density variations with a clear seasonal cycle that apparently was not-related to seasonal variations in deposition or known near-surface processes (Gerland and others 1999). A recent model of surface elevation changes (Zwally and Li, submitted) produced a seasonal variation in firn densification, and explained the seasonal surface elevation changes observed by satellite radar altimeters. In this study, we apply our 1-D time-dependent numerical model of firn densification that includes a temperature-dependent formulation of firn densification based on laboratory measurements of grain growth. The model is driven by a steady-state seasonal surface temperature and a constant accumulation rate appropriate for the measured Antarctic ice core. The modeled seasonal variations in firn density show that the layers of snow deposited during spring to mid-summer with the highest temperature history compress to the highest density, and the layers deposited during later summer to autumn with the lowest temperature history compress to the lowest density. The initial amplitude of the seasonal difference of about 0.13 reduces to about 0.09 in five years and asymptotically to 0.92 at depth, which is consistent with the core measurements.

Multi-Decadal Averages of Basal Melt for Ross Ice Shelf, Antarctica Using Airborne Observations

NASA Astrophysics Data System (ADS)

Das, I.; Bell, R. E.; Tinto, K. J.; Frearson, N.; Kingslake, J.; Padman, L.; Siddoway, C. S.; Fricker, H. A.

2017-12-01

Changes in ice shelf mass balance are key to the long term stability of the Antarctic Ice Sheet. Although the most extensive ice shelf mass loss currently is occurring in the Amundsen Sea sector of West Antarctica, many other ice shelves experience changes in thickness on time scales from annual to ice age cycles. Here, we focus on the Ross Ice Shelf. An 18-year record (1994-2012) of satellite radar altimetry shows substantial variability in Ross Ice Shelf height on interannual time scales, complicating detection of potential long-term climate-change signals in the mass budget of this ice shelf. Variability of radar signal penetration into the ice-shelf surface snow and firn layers further complicates assessment of mass changes. We investigate Ross Ice Shelf mass balance using aerogeophysical data from the ROSETTA-Ice surveys using IcePod. We use two ice-penetrating radars; a 2 GHz unit that images fine-structure in the upper 400 m of the ice surface and a 360 MHz radar to identify the ice shelf base. We have identified internal layers that are continuous along flow from the grounding line to the ice shelf front. Based on layer continuity, we conclude that these layers must be the horizons between the continental ice of the outlet glaciers and snow accumulation once the ice is afloat. We use the Lagrangian change in thickness of these layers, after correcting for strain rates derived using modern day InSAR velocities, to estimate multidecadal averaged basal melt rates. This method provides a novel way to quantify basal melt, avoiding the confounding impacts of spatial and short-timescale variability in surface accumulation and firn densification processes. Our estimates show elevated basal melt rates (> -1m/yr) around Byrd and Mullock glaciers within 100 km from the ice shelf front. We also compare modern InSAR velocity derived strain rates with estimates from the comprehensive ground-based RIGGS observations during 1973-1978 to estimate the potential magnitude of strain-driven thickness changes over four decades. Combining maps of basal melt rate with radar derived basal reflectivity, we identify regions that are undergoing melting and freezing and provide a comprehensive understanding of how ocean processes may be changing the base of Ross Ice Shelf in recent decades.

Low temperature self-cleaning properties of superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Wang, Fajun; Shen, Taohua; Li, Changquan; Li, Wen; Yan, Guilong

2014-10-01

Outdoor surfaces are usually dirty surfaces. Ice accretion on outdoor surfaces could lead to serious accidents. In the present work, the superhydrophobic surface based on 1H, 1H, 2H, 2H-Perfluorodecanethiol (PFDT) modified Ag/PDMS composite was prepared to investigate the anti-icing property and self-cleaning property at temperatures below freezing point. The superhydrophobic surface was deliberately polluted with activated carbon before testing. It was observed that water droplet picked up dusts on the cold superhydrophobic surface and took it away without freezing at a measuring temperature of -10 °C. While on a smooth PFDT surface and a rough surface base on Ag/PDMS composite without PFDT modification, water droplets accumulated and then froze quickly at the same temperature. However, at even lower temperature of -12 °C, the superhydrophobic surface could not prevent the surface water from icing. In addition, it was observed that the frost layer condensed from the moisture pay an important role in determining the low temperature self-cleaning properties of a superhydrophobic surface.

Atomic Oxygen Treatment Technique for Removal of Smoke Damage from Paintings

NASA Technical Reports Server (NTRS)

Rutledge, S. K.; Banks, B. A.

1997-01-01

Soot deposits that can accumulate on surfaces of a painting during a fire can be difficult to clean from some types of paintings without damaging the underlying paint layers. A non-contact technique has been developed which can remove the soot by allowing a gas containing atomic oxygen to flow over the surface and chemically react with the soot to form carbon monoxide and carbon dioxide. The reaction is limited to the surface, so the underlying paint is not touched. The process can be controlled so that the cleaning can be stopped once the paint surface is reached. This paper describes the smoke exposure and cleaning of untreated canvas, acrylic gesso, and sections of an oil painting using this technique. The samples were characterized by optical microscopy and reflectance spectroscopy.

Leaching of different elements from subbase layers of alternative aggregates in pavement constructions.

PubMed

Flyhammar, P; Bendz, D

2006-09-01

The objective of this study was to analyze the accumulated effects of leaching in two test roads were municipal solid waste incineration (MSWI) bottom ash and aggregate from a railway embankment, respectively, were used as subbase aggregates. Solid samples from the subbase and the subgrade were collected in trenches, which were excavated perpendicular to the road extension. The samples were analyzed with respect to pH, water content, electrical conductivity and extractable fractions of macro and trace constituents. To conclude, spatial distribution patterns of different constituents in subbase and subgrade layers confirms the existence of two major transport processes in a road with permeable shoulders: diffusion underneath surface asphalt layers driven by a concentration gradient directed horizontally towards the shoulder of the road where the dissolved elements are carried away by advection.

Mars Radiator Characterization Experimental Program

NASA Technical Reports Server (NTRS)

Witte, Larry C.; Hollingsworth, D. Keith

2004-01-01

Radiators are an enabling technology for the human exploration and development of the moon and Mars. As standard components of the heat rejection subsystem of space vehicles, radiators are used to reject waste heat to space and/or a planetary environment. They are typically large components of the thermal control system for a space vehicle or human habitation facility, and in some cases safety factors are used to oversize them when the operating environment cannot be fully characterized. Over-sizing can impose significant weight and size penalties that might be prohibitive for future missions. Radiator performance depends on the size of the radiator surface, its emittance and absorptance, the radiator temperature, the effective sky temperature surrounding the radiator, solar radiation and atmospheric irradiation levels, convection to or from the atmosphere (on Mars), and other conditions that could affect the nature of the radiator surface, such as dust accumulation. Most particularly, dust is expected to be a major contributor to the local environmental conditions on either the lunar or Martian surface. This conclusion regarding Mars is supported by measurements of dust accumulation on the Mars Sojourner Rover solar array during the Pathfinder mission. This Final Report describes a study of the effect of Martian dust accumulation on radiator performance. It is comprised of quantitative measurements of effective emittance for a range of dust accumulation levels on surfaces of known emittance under clean conditions. The test radiator coatings were Z-93P, NS-43G, and Silver Teflon (10 mil) film. The Martian dust simulant was Carbondale Red Clay. Results were obtained under vacuum conditions sufficient to reduce convection effects virtually to zero. The experiments required the development of a calorimetric apparatus that allows simultaneous measurements of the effective emittance for all the coatings at each set of experimental conditions. A method of adding dust to multiple radiator coupons was developed and shown to be capable of depositing dust on the surfaces with acceptable uniformity. In these experiments, the dust layer accumulates under earth gravity and in the presence of an earth atmosphere. An invention disclosure for the dust deposition apparatus is being filed through NASA and University of Houston.

Transient Proliferation of Proanthocyanidin-Accumulating Cells on the Epidermal Apex Contributes to Highly Aluminum-Resistant Root Elongation in Camphor Tree1[W

PubMed Central

Osawa, Hiroki; Endo, Izuki; Hara, Yukari; Matsushima, Yuki; Tange, Takeshi

2011-01-01

Aluminum (Al) is a harmful element that rapidly inhibits the elongation of plant roots in acidic soils. The release of organic anions explains Al resistance in annual crops, but the mechanisms that are responsible for superior Al resistance in some woody plants remain unclear. We examined cell properties at the surface layer of the root apex in the camphor tree (Cinnamomum camphora) to understand its high Al resistance mechanism. Exposure to 500 μm Al for 8 d, more than 20-fold higher concentration and longer duration than what soybean (Glycine max) can tolerate, only reduced root elongation in the camphor tree to 64% of the control despite the slight induction of citrate release. In addition, Al content in the root apices was maintained at low levels. Histochemical profiling revealed that proanthocyanidin (PA)-accumulating cells were present at the adjacent outer layer of epidermis cells at the root apex, having distinctive zones for cell division and the early phase of cell expansion. Then the PA cells were gradually detached off the root, leaving thin debris behind, and the root surface was replaced with the elongating epidermis cells at the 3- to 4-mm region behind the tip. Al did not affect the proliferation of PA cells or epidermis cells, except for the delay in the start of expansion and the accelerated detachment of the former. In soybean roots, the innermost lateral root cap cells were absent in both PA accumulation and active cell division and failed to protect the epidermal cell expansion at 25 μm Al. These results suggest that transient proliferation and detachment of PA cells may facilitate the expansion of epidermis cells away from Al during root elongation in camphor tree. PMID:21045123

Transient proliferation of proanthocyanidin-accumulating cells on the epidermal apex contributes to highly aluminum-resistant root elongation in camphor tree.

PubMed

Osawa, Hiroki; Endo, Izuki; Hara, Yukari; Matsushima, Yuki; Tange, Takeshi

2011-01-01

Aluminum (Al) is a harmful element that rapidly inhibits the elongation of plant roots in acidic soils. The release of organic anions explains Al resistance in annual crops, but the mechanisms that are responsible for superior Al resistance in some woody plants remain unclear. We examined cell properties at the surface layer of the root apex in the camphor tree (Cinnamomum camphora) to understand its high Al resistance mechanism. Exposure to 500 μm Al for 8 d, more than 20-fold higher concentration and longer duration than what soybean (Glycine max) can tolerate, only reduced root elongation in the camphor tree to 64% of the control despite the slight induction of citrate release. In addition, Al content in the root apices was maintained at low levels. Histochemical profiling revealed that proanthocyanidin (PA)-accumulating cells were present at the adjacent outer layer of epidermis cells at the root apex, having distinctive zones for cell division and the early phase of cell expansion. Then the PA cells were gradually detached off the root, leaving thin debris behind, and the root surface was replaced with the elongating epidermis cells at the 3- to 4-mm region behind the tip. Al did not affect the proliferation of PA cells or epidermis cells, except for the delay in the start of expansion and the accelerated detachment of the former. In soybean roots, the innermost lateral root cap cells were absent in both PA accumulation and active cell division and failed to protect the epidermal cell expansion at 25 μm Al. These results suggest that transient proliferation and detachment of PA cells may facilitate the expansion of epidermis cells away from Al during root elongation in camphor tree.

Anoxic monimolimnia: Nutrients devious feeders or bombs ready to explode?

NASA Astrophysics Data System (ADS)

Gianni, Areti; Zacharias, Ierotheos

2015-04-01

Coastal regions are under strong human influence and its environmental impact is reflected into their water quality. Oligotrophic estuaries and coastal systems have changed in mesotrophic and/or eutrophic, shown an increase in toxic algal blooms, hypoxic/anoxic events, and massive mortalities of many aquatic and benthic organisms. In strongly stratified and productive water basins, bottom water dissolved oxygen is depleted due to the excessive organic matter decomposition in these depths. Distribution and recycling of nutrients in their water column is inextricably dependent on oxygenation and redox conditions. Bottom water anoxia accelerates PO43-, NH4+ and H2S recycling and accumulation from organic matter decomposition. The anoxic, H2S, PO43- and NH4+ rich bottom water constitutes a toxic layer, threatening the balance of the entire ecosystem. In permanently stratified water basins, storm events could result in stratification destruction and water column total mixing. The turnover brings large amounts of H2S to the surface resulting in low levels of oxygen and massive fish kills. PO43- and NH4+ are released to the interface and surface waters promoting algal blooms. Μore organic matter is produced fueling anoxia. The arising question is, whether the balance of an anoxic water ecosystem is under the threat of its hypolimnetic nutrient and sulfide load, only in the case of storm events and water column total mixing. In polymictic water basins it is clear that the accumulated, in the bottom layer, nutrients will supply surface waters, after the pycnocline overturn. Besides this mechanism of basins' water quality degradation is nowadays recognized as one of the biggest obstacles in eutrophic environments management and restoration efforts. The role of internal load, in permanently stratified water basins, is not so clear. In the present study the impact of storm events on water column stability and bottom water anoxia of meromictic coastal basins, is investigated. The importance of internal load is emerged, presenting the disturbance on the main nutrients, dissolved oxygen, hydrogen sulfide and chlorophyll distribution, caused by the total water column mixing. Additionally, the relationship between temporal nutrients variations in surface layers, of permanent anoxic coastal basins with a) changes on the physicochemical characteristics of their water column, b) changes on the bottom water phosphorus and nitrogen concentration and c) their effect on the basin's primary productivity, is sought. In order to achieve the objectives of this study, two different sets of Aitoliko basin's (western Greece) data were used. The first one includes measurements of physicochemical parameters, nutrients, chlorophyll and hydrogen sulfide, four days after a storm event and the consequent anoxic crisis in Aitoliko basin on 4th of December 2008. The second one contains respective data obtained from a biennial (May 2006-May 2008) basin's monitoring. The changes in the physical, chemical and biological characteristics, of Aitoliko basin water column, after its total mixing, highlighted the importance of the accumulated nutrients and sulfides in the bottom layer. In addition, turned out that bottom layer can supply with nutrients the surface waters, even during periods of high water column stratification. Small scale, subtle, changes in physicochemical and hydrological basin's characteristics promoted this supply, affecting both quantitative and qualitative the ecosystem's primary productivity and shifting its quality character.

Measurements and Modeling of Turbulent Fluxes during Persistent Cold Air Pool Events in Salt Lake Valley, Utah

NASA Astrophysics Data System (ADS)

Ivey, C. E.; Sun, X.; Holmes, H.

2017-12-01

Land surface processes are important in meteorology and climate research since they control the partitioning of surface energy and water exchange at the earth's surface. The surface layer is coupled to the planetary boundary layer (PBL) by surface fluxes, which serve as sinks or sources of energy, moisture, momentum, and atmospheric pollutants. Quantifying the surface heat and momentum fluxes at the land-atmosphere interface, especially for different surface land cover types, is important because they can further influence the atmospheric dynamics, vertical mixing, and transport processes that impact local, regional, and global climate. A cold air pool (CAP) forms when a topographic depression (i.e., valley) fills with cold air, where the air in the stagnant layer is colder than the air aloft. Insufficient surface heating, which is not able to sufficiently erode the temperature inversion that forms during the nighttime stable boundary layer, can lead to the formation of persistent CAPs during wintertime. These persistent CAPs can last for days, or even weeks, and are associated with increased air pollution concentrations. Thus, realistic simulations of the land-atmosphere exchange are meaningful to achieve improved predictions of the accumulation, transport, and dispersion of air pollution concentrations. The focus of this presentation is on observations and modeling results using turbulence data collected in Salt Lake Valley, Utah during the 2010-2011 wintertime Persistent Cold Air Pool Study (PCAPS). Turbulent fluxes and the surface energy balance over seven land use types are quantified. The urban site has an energy balance ratio (EBR) larger than one (1.276). Negative Bowen ratio (-0.070) is found at the cropland site. In addition to turbulence observations, half-hourly WRF simulated net radiation, latent heat, sensible heat, ground heat fluxes during one persistent CAP event are evaluated using the PCAPS observations. The results show that sensible and latent heat fluxes during the CAP event are overestimated. The sensitivity of WRF results to large-scale forcing datasets, PBL schemes and land surface models (LSMs) are also investigated. The optimal WRF configuration for simulating surface turbulent fluxes and atmospheric mixing during CAP events is determined.

Is soil dressing a way once and for all in remediation of arsenic contaminated soils? A case study of arsenic re-accumulation in soils remediated by soil dressing in Hunan Province, China.

PubMed

Su, Shiming; Bai, Lingyu; Wei, Caibing; Gao, Xiang; Zhang, Tuo; Wang, Yanan; Li, Lianfang; Wang, Jinjin; Wu, Cuixia; Zeng, Xibai

2015-07-01

The investigation of arsenic (As) re-accumulation in an area previously remediated by soil dressing will help in sustainable controlling the risks of As to local ecosystems and should influence management decisions about remediation strategies. In this study, As content in an area remediated by soil dressing and the possible As accumulation risk in agricultural products were investigated. The results indicated that after 7 years of agricultural activities, the average As content (24.6 mg kg(-1)) in surface soil of the investigated area increased by 83.6% compared with that (13.4 mg kg(-1)) in clean soil. Of the surface soil samples (n = 88), 21.6% had As levels that exceeded the limits of the Environmental Quality Standard for Soils of China (GB 15618-1995) and 98.9% of the surface soil samples with As contents exceeding that in clean soil was observed. Soil dressing might be not a remediation method once and for all in some contaminated areas, even though no significant difference in available As content was found between clean (0.18 mg kg(-1)) and surface (0.22 mg kg(-1)) soils. The foreign As in surface soil of the investigated area mainly specifically sorbed with soil colloid or associated with hydrous oxides of Fe and Al, or existed in residual fraction. The upward movement of contaminated soil from the deeper layers and the atmospheric deposition of slag particles might be responsible for the re-accumulation of As in the investigated area. Decreases in soil pH in the investigated soils and the fact that no plant samples had As levels exceeding the limits of the National Food Safety Standards for Contaminants of China (GB 2762-2012) were also observed.

Patterns of Canopy and Surface Layer Consumption in a Boreal Forest Fire from Repeat Airborne Lidar

NASA Technical Reports Server (NTRS)

Alonzo, Michael; Morton, Douglas C.; Cook, Bruce D.; Andersen, Hans-Erik; Babcock, Chad; Pattison, Robert

2017-01-01

Fire in the boreal region is the dominant agent of forest disturbance with direct impacts on ecosystem structure, carbon cycling, and global climate. Global and biome-scale impacts are mediated by burn severity, measured as loss of forest canopy and consumption of the soil organic layer. To date, knowledge of the spatial variability in burn severity has been limited by sparse field sampling and moderate resolution satellite data. Here, we used pre- and post-fire airborne lidar data to directly estimate changes in canopy vertical structure and surface elevation for a 2005 boreal forest fire on Alaskas Kenai Peninsula. We found that both canopy and surface losses were strongly linked to pre-fire species composition and exhibited important fine-scale spatial variability at sub-30m resolution. The fractional reduction in canopy volume ranged from 0.61 in lowland black spruce stands to 0.27 in mixed white spruce and broad leaf forest. Residual structure largely reflects standing dead trees, highlighting the influence of pre-fire forest structure on delayed carbon losses from above ground biomass, post-fire albedo, and variability in understory light environments. Median loss of surface elevation was highest in lowland black spruce stands (0.18 m) but much lower in mixed stands (0.02 m), consistent with differences in pre-fire organic layer accumulation. Spatially continuous depth-of-burn estimates from repeat lidar measurements provide novel information to constrain carbon emissions from the surface organic layer and may inform related research on post-fire successional trajectories. Spectral measures of burn severity from Landsat were correlated with canopy (r = 0.76) and surface (r = -0.71) removal in black spruce stands but captured less of the spatial variability in fire effects for mixed stands (canopy r = 0.56, surface r = -0.26), underscoring the difficulty in capturing fire effects in heterogeneous boreal forest landscapes using proxy measures of burn severity from Landsat.

Patterns of canopy and surface layer consumption in a boreal forest fire from repeat airborne lidar

NASA Astrophysics Data System (ADS)

Alonzo, Michael; Morton, Douglas C.; Cook, Bruce D.; Andersen, Hans-Erik; Babcock, Chad; Pattison, Robert

2017-05-01

Fire in the boreal region is the dominant agent of forest disturbance with direct impacts on ecosystem structure, carbon cycling, and global climate. Global and biome-scale impacts are mediated by burn severity, measured as loss of forest canopy and consumption of the soil organic layer. To date, knowledge of the spatial variability in burn severity has been limited by sparse field sampling and moderate resolution satellite data. Here, we used pre- and post-fire airborne lidar data to directly estimate changes in canopy vertical structure and surface elevation for a 2005 boreal forest fire on Alaska’s Kenai Peninsula. We found that both canopy and surface losses were strongly linked to pre-fire species composition and exhibited important fine-scale spatial variability at sub-30 m resolution. The fractional reduction in canopy volume ranged from 0.61 in lowland black spruce stands to 0.27 in mixed white spruce and broadleaf forest. Residual structure largely reflects standing dead trees, highlighting the influence of pre-fire forest structure on delayed carbon losses from aboveground biomass, post-fire albedo, and variability in understory light environments. Median loss of surface elevation was highest in lowland black spruce stands (0.18 m) but much lower in mixed stands (0.02 m), consistent with differences in pre-fire organic layer accumulation. Spatially continuous depth-of-burn estimates from repeat lidar measurements provide novel information to constrain carbon emissions from the surface organic layer and may inform related research on post-fire successional trajectories. Spectral measures of burn severity from Landsat were correlated with canopy (r = 0.76) and surface (r = -0.71) removal in black spruce stands but captured less of the spatial variability in fire effects for mixed stands (canopy r = 0.56, surface r = -0.26), underscoring the difficulty in capturing fire effects in heterogeneous boreal forest landscapes using proxy measures of burn severity from Landsat.

Fibrin(ogen) mediates acute inflammatory responses to biomaterials

PubMed Central

1993-01-01

Although "biocompatible" polymeric elastomers are generally nontoxic, nonimmunogenic, and chemically inert, implants made of these materials may trigger acute and chronic inflammatory responses. Early interactions between implants and inflammatory cells are probably mediated by a layer of host proteins on the material surface. To evaluate the importance of this protein layer, we studied acute inflammatory responses of mice to samples of polyester terephthalate film (PET) that were implanted intraperitoneally for short periods. Material preincubated with albumin is "passivated," accumulating very few adherent neutrophils or macrophages, whereas uncoated or plasma- coated PET attracts large numbers of phagocytes. Neither IgG adsorption nor surface complement activation is necessary for this acute inflammation; phagocyte accumulation on uncoated implants is normal in hypogammaglobulinemic mice and in severely hypocomplementemic mice. Rather, spontaneous adsorption of fibrinogen appears to be critical: (a) PET coated with serum or hypofibrinogenemic plasma attracts as few phagocytes as does albumin-coated material; (b) in contrast, PET preincubated with serum or hypofibrinogenemic plasma containing physiologic amounts of fibrinogen elicits "normal" phagocyte recruitment; (c) most importantly, hypofibrinogenemic mice do not mount an inflammatory response to implanted PET unless the material is coated with fibrinogen or the animals are injected with fibrinogen before implantation. Thus, spontaneous adsorption of fibrinogen appears to initiate the acute inflammatory response to an implanted polymer, suggesting an interesting nexus between two major iatrogenic effects of biomaterials: clotting and inflammation. PMID:8245787

Can the soil fauna of boreal forests recover from lead-derived stress in a shooting range area?

PubMed

Selonen, Salla; Liiri, Mira; Setälä, Heikki

2014-04-01

The responses of soil faunal communities to lead (Pb) contamination in a shooting range area and the recovery of these fauna after range abandonment were studied by comparing the communities at an active shotgun shooting range, an abandoned shooting range, and a control site, locating in the same forest. Despite the similar overall Pb pellet load at the shooting ranges, reaching up to 4 kg m(-2), Pb concentrations in the top soil of the abandoned range has decreased due to the accumulation of detritus on the soil surface. As a consequence, soil animal communities were shown to recover from Pb-related disturbances by utilizing the less contaminated soil layer. Microarthropods showed the clearest signs of recovery, their numbers and community composition being close to those detected at the control site. However, in the deepest organic soil layer, the negative effects of Pb were more pronounced at the abandoned than at the active shooting range, which was detected as altered microarthropod and nematode community structures, reduced abundances of several microarthropod taxa, and the total absence of enchytraeid worms. Thus, although the accumulation of fresh litter on soil surface can promote the recovery of decomposer communities in the top soil, the gradual release of Pb from corroding pellets may pose a long-lasting risk for decomposer taxa deeper in the soil.

The importance of both geological and pedological processes in control of grain size and sedimentation rates in Peoria Loess

USGS Publications Warehouse

Wang, Hongfang; Mason, J.A.; Balsam, W.L.

2006-01-01

The loess-paleosol succession in the Peoria Loess in southern Illinois is characterized as alternating loess layers and weathering bands, known as paleosol A horizons. The fast loess accumulation during the late Wisconsin glaciation interacted with the incipient pedogenesis and caused unclear boundaries of loess-paleosol alternations in soil horizonation and mineralogy. Parameters of grain size distribution, sedimentation rate, matrix carbonate content and diffuse reflectance (i.e. soil colors and iron oxides) are used in this paper to discuss the geological and pedological influences for the Peoria Loess in Keller Farm section in southern Illinois. The multi-proxy analysis revealed that many paleosol A horizons, defined by the diffuse reflectance variability, contain finer-grained materials with a relatively higher sedimentation rate. It suggests that glaciofluvial sediments were available in the source areas for uploading eolian dust during the temporary ice sheet retreats. The denser vegetation and wetter surface soils on the loess deposit area could increase the dust trapping efficiency and caused a greater accumulation rate of loess deposits. The coarser-grained materials and slower sedimentation rate are often found in loess layers. It suggests that strong surface winds transported the coarser-grained materials from local dust sources and sparse vegetation and dry surface soils reduced the dust trapping efficiency during the ice sheet readvance. The strong interactions between the geological and pedological processes played an important role on the loess-paleosol alternations in southern Illinois during the late Wisconsin glaciation. ?? 2006 Elsevier B.V. All rights reserved.

Nafion induced surface confinement of oxygen in carbon-supported oxygen reduction catalysts

DOE PAGES

Chlistunoff, Jerzy; Sansinena, Jose -Maria

2016-11-17

We studied the surface confinement of oxygen inside layers of Nafion self-assembled on carbon-supported oxygen reduction reaction (ORR) catalysts. It is demonstrated that oxygen accumulates in the hydrophobic component of the polymer remaining in contact with the carbon surface. Furthermore, the amount of surface confined oxygen increases with the degree of carbon surface graphitization, which promotes the self-assembly of the polymer. Planar macrocyclic ORR catalysts possessing a delocalized system of π electrons such as Co and Fe porphyrins and phthalocyanines have virtually no effect on the surface confinement of oxygen, in accordance with their structural similarity to graphitic carbon surfacesmore » where they adsorb. Platinum particles in carbon-supported ORR catalysts with high metal contents (20%) disrupt the self-assembly of Nafion and virtually eliminate the oxygen confinement, but the phenomenon is still observed for low Pt loading (4.8%) catalysts.« less

Nafion induced surface confinement of oxygen in carbon-supported oxygen reduction catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chlistunoff, Jerzy; Sansinena, Jose -Maria

We studied the surface confinement of oxygen inside layers of Nafion self-assembled on carbon-supported oxygen reduction reaction (ORR) catalysts. It is demonstrated that oxygen accumulates in the hydrophobic component of the polymer remaining in contact with the carbon surface. Furthermore, the amount of surface confined oxygen increases with the degree of carbon surface graphitization, which promotes the self-assembly of the polymer. Planar macrocyclic ORR catalysts possessing a delocalized system of π electrons such as Co and Fe porphyrins and phthalocyanines have virtually no effect on the surface confinement of oxygen, in accordance with their structural similarity to graphitic carbon surfacesmore » where they adsorb. Platinum particles in carbon-supported ORR catalysts with high metal contents (20%) disrupt the self-assembly of Nafion and virtually eliminate the oxygen confinement, but the phenomenon is still observed for low Pt loading (4.8%) catalysts.« less

Dependence of LTX plasma performance on surface conditions as determined by in situ analysis of plasma facing components

NASA Astrophysics Data System (ADS)

Lucia, M.; Kaita, R.; Majeski, R.; Bedoya, F.; Allain, J. P.; Abrams, T.; Bell, R. E.; Boyle, D. P.; Jaworski, M. A.; Schmitt, J. C.

2015-08-01

The Materials Analysis and Particle Probe (MAPP) diagnostic has been implemented on the Lithium Tokamak Experiment (LTX) at PPPL, providing the first in situ X-ray photoelectron spectroscopy (XPS) surface characterization of tokamak plasma facing components (PFCs). MAPP samples were exposed to argon glow discharge conditioning (GDC), lithium evaporations, and hydrogen tokamak discharges inside LTX. Samples were analyzed with XPS, and alterations to surface conditions were correlated against observed LTX plasma performance changes. Argon GDC caused the accumulation of nm-scale metal oxide layers on the PFC surface, which appeared to bury surface carbon and oxygen contamination and thus improve plasma performance. Lithium evaporation led to the rapid formation of a lithium oxide (Li2O) surface; plasma performance was strongly improved for sufficiently thick evaporative coatings. Results indicate that a 5 h argon GDC or a 50 nm evaporative lithium coating will both significantly improve LTX plasma performance.

Copper Accumulation, Availability and Adsorption Capacity in Sandy Soils of Vineyards with Different Cultivation Duration

NASA Astrophysics Data System (ADS)

Mallmann, F. J. K.; Miotto, A.; Bender, M. A.; Gubiani, E.; Rheinheimer, D. D. S.; Kaminski, J.; Ceretta, C. A.; Šimůnek, J.

2015-12-01

Bordeaux mixture is a copper-based (Cu) fungicide and bactericide applied in vineyards to control plant diseases. Since it is applied several times per year, it accumulates in large quantities on plants and in soil. This study evaluates the Cu accumulation in, and desorption kinetics and adsorption capability of a sandy Ultisol in a natural field and in 3 vineyards for 5 (V1), 11 (V2), and 31 (V3) years in South of Brazil. Soil samples were collected in 8 depths (0-60 cm) of all four soil profiles, which all displayed similar soil properties. The following soil properties were measured: pH, organic matter (OM), soil bulk density, Cu total concentration, and Cu desorption and adsorption curves. A two first-order reactions model and the Langmuir isotherm were fitted to the desorption and adsorption curves, respectively. An increase in the total mass of Cu in the vineyards followed a linear regression curve, with an average annual increase of 7.15 kg ha-1. Cu accumulated down to a depth of 5, 20, and 30 cm in V1, V2 and V3, respectively, with the highest Cu content reaching 138.4 mg kg-1 in the 0-5 cm soil layer of V3. Cu desorption parameters showed a high correlation with its total concentration. Approximately 57 and 19% of total Cu were immediately and slowly available, respectively, indicating a high potential for plant absorption and/or downward movement. Cu concentrations extracted by EDTA from soil layers not affected by anthropogenic Cu inputs were very low. The maximum Cu adsorption capacity of the 0-5 and 5-10 cm soil layers increased with the vineyard age, reaching concentrations higher than 900 mg kg-1. This increase was highly related to OM and pH, which both increased with cultivation duration. Despite of low clay content of these soils, there is low risk of groundwater Cu contamination for actual conditions. However, high Cu concentrations in the surface layer of the long-term vineyards could cause toxicity problems for this and for companion crops.

MBE growth technology for high quality strained III-V layers

NASA Technical Reports Server (NTRS)

Grunthaner, Frank J. (Inventor); Liu, John K. (Inventor); Hancock, Bruce R. (Inventor)

1990-01-01

The III-V films are grown on large automatically perfect terraces of III-V substrates which have a different lattice constant, with temperature and Group III and V arrival rates chosen to give a Group III element stable surface. The growth is pulsed to inhibit Group III metal accumulation of low temperature, and to permit the film to relax to equilibrium. The method of the invention: (1) minimizes starting step density on sample surface; (2) deposits InAs and GaAs using an interrupted growth mode (0.25 to 2 monolayers at a time); (3) maintains the instantaneous surface stoichiometry during growth (As-stable for GaAs, In-stable for InAs); and (4) uses time-resolved RHEED to achieve aspects (1) through (3).

Electrical properties of double layer dielectric structures for space technology

NASA Astrophysics Data System (ADS)

Lian, Anqing

1993-04-01

Polymeric films such as polyimide (PI) and polyethylene terephthalate (PET) are used in space technology as thermal blankets. Thin SiO2 and SiN coatings plasma deposited onto PI and PET surfaces were proposed to protect the blanket materials against the space environment. The electrical properties of this kind of dual layer dielectric structure were investigated to understand the mechanisms for suppressing charge accumulation and flashover. Bulk and surface electrical conductivities of thin single-layer PI and PET samples and of the dual layer SiO2 and SiN combinations with PI and PET were measured in a range of applied electrical fields. The capacitance voltage (CV) technique was used for analyzing charge transport and distribution in the structures. The electric current in the bulk of the SiO2/PI and SiN/PI samples was found to depend on the polarity of the electric field. Other samples did not exhibit any such polarity effect. The polarity dependence is attributed to charge trapping at the PI/plasma deposit interface. The CV characteristics of the Al-PI-SiO2-Si structure confirm that charges which can modify the local electric field can be trapped near the interface. A model is proposed to interpret the properties of the currents in dual layer structures. This model can semi-quantitatively explain all the observed results.

Antimicrobial Properties of Diamond-Like Carbon/Silver Nanocomposite Thin Films Deposited on Textiles: Towards Smart Bandages

PubMed Central

Juknius, Tadas; Ružauskas, Modestas; Tamulevičius, Tomas; Šiugždinienė, Rita; Juknienė, Indrė; Vasiliauskas, Andrius; Jurkevičiūtė, Aušrinė; Tamulevičius, Sigitas

2016-01-01

In the current work, a new antibacterial bandage was proposed where diamond-like carbon with silver nanoparticle (DLC:Ag)-coated synthetic silk tissue was used as a building block. The DLC:Ag structure, the dimensions of nanoparticles, the silver concentration and the silver ion release were studied systematically employing scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic absorption spectroscopy, respectively. Antimicrobial properties were investigated using microbiological tests (disk diffusion method and spread-plate technique). The DLC:Ag layer was stabilized on the surface of the bandage using a thin layer of medical grade gelatin and cellulose. Four different strains of Staphylococcus aureus extracted from humans’ and animals’ infected wounds were used. It is demonstrated that the efficiency of the Ag+ ion release to the aqueous media can be increased by further RF oxygen plasma etching of the nanocomposite. It was obtained that the best antibacterial properties were demonstrated by the plasma-processed DLC:Ag layer having a 3.12 at % Ag surface concentration with the dominating linear dimensions of nanoparticles being 23.7 nm. An extra protective layer made from cellulose and gelatin with agar contributed to the accumulation and efficient release of silver ions to the aqueous media, increasing bandage antimicrobial efficiency up to 50% as compared to the single DLC:Ag layer on textile. PMID:28773494

Antimicrobial Properties of Diamond-Like Carbon/Silver Nanocomposite Thin Films Deposited on Textiles: Towards Smart Bandages.

PubMed

Juknius, Tadas; Ružauskas, Modestas; Tamulevičius, Tomas; Šiugždinienė, Rita; Juknienė, Indrė; Vasiliauskas, Andrius; Jurkevičiūtė, Aušrinė; Tamulevičius, Sigitas

2016-05-13

In the current work, a new antibacterial bandage was proposed where diamond-like carbon with silver nanoparticle (DLC:Ag)-coated synthetic silk tissue was used as a building block. The DLC:Ag structure, the dimensions of nanoparticles, the silver concentration and the silver ion release were studied systematically employing scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic absorption spectroscopy, respectively. Antimicrobial properties were investigated using microbiological tests (disk diffusion method and spread-plate technique). The DLC:Ag layer was stabilized on the surface of the bandage using a thin layer of medical grade gelatin and cellulose. Four different strains of Staphylococcus aureus extracted from humans' and animals' infected wounds were used. It is demonstrated that the efficiency of the Ag⁺ ion release to the aqueous media can be increased by further RF oxygen plasma etching of the nanocomposite. It was obtained that the best antibacterial properties were demonstrated by the plasma-processed DLC:Ag layer having a 3.12 at % Ag surface concentration with the dominating linear dimensions of nanoparticles being 23.7 nm. An extra protective layer made from cellulose and gelatin with agar contributed to the accumulation and efficient release of silver ions to the aqueous media, increasing bandage antimicrobial efficiency up to 50% as compared to the single DLC:Ag layer on textile.

Modification of Soil Temperature and Moisture Budgets by Snow Processes

NASA Astrophysics Data System (ADS)

Feng, X.; Houser, P.

2006-12-01

Snow cover significantly influences the land surface energy and surface moisture budgets. Snow thermally insulates the soil column from large and rapid temperature fluctuations, and snow melting provides an important source for surface runoff and soil moisture. Therefore, it is important to accurately understand and predict the energy and moisture exchange between surface and subsurface associated with snow accumulation and ablation. The objective of this study is to understand the impact of land surface model soil layering treatment on the realistic simulation of soil temperature and soil moisture. We seek to understand how many soil layers are required to fully take into account soil thermodynamic properties and hydrological process while also honoring efficient calculation and inexpensive computation? This work attempts to address this question using field measurements from the Cold Land Processes Field Experiment (CLPX). In addition, to gain a better understanding of surface heat and surface moisture transfer process between land surface and deep soil involved in snow processes, numerical simulations were performed at several Meso-Cell Study Areas (MSAs) of CLPX using the Center for Ocean-Land-Atmosphere (COLA) Simplified Version of the Simple Biosphere Model (SSiB). Measurements of soil temperature and soil moisture were analyzed at several CLPX sites with different vegetation and soil features. The monthly mean vertical profile of soil temperature during October 2002 to July 2003 at North Park Illinois River exhibits a large near surface variation (<5 cm), reveals a significant transition zone from 5 cm to 25 cm, and becomes uniform beyond 25cm. This result shows us that three soil layers are reasonable in solving the vertical variation of soil temperature at these study sites. With 6 soil layers, SSiB also captures the vertical variation of soil temperature during entire winter season, featuring with six soil layers, but the bare soil temperature is underestimated and root-zone soil temperature is overestimated during snow melting; which leads to overestimated temperature variations down to 20 cm. This is caused by extra heat loss from upper soil level and insufficient heat transport from the deep soil. Further work will need to verify if soil temperature displays similar vertical thermal structure for different vegetation and soil types during snow season. This study provides insight to the surface and subsurface thermodynamic and hydrological processes involved in snow modeling which is important for accurate snow simulation.

Preparation and evaluation of quercetin-loaded lecithin-chitosan nanoparticles for topical delivery.

PubMed

Tan, Qi; Liu, Weidong; Guo, Chenyu; Zhai, Guangxi

2011-01-01

The purpose of this study was to investigate lecithin-chitosan nanoparticles as a topical delivery system for quercetin. Tocopheryl propylene glycol succinate was chosen to be the surfactant for the nanosystem. The mean particle size of the nanoparticles was 95.3 nm, and the entrapment efficiency and drug loading for quercetin were 48.5% and 2.45%, respectively. Topical delivery in vitro and in vivo of the quercetin-loaded nanoparticles was evaluated using quercetin propylene glycol solution as the control. Compared with quercetin solution, the quercetin-loaded nanoparticles showed higher permeation ability, and significantly increased accumulation of quercetin in the skin, especially in the epidermis. Microstructure observation of the skin surface after administration indicated that the interaction between ingredients of the nanoparticles and the skin surface markedly changed the morphology of the stratum corneum and disrupted the corneocyte layers, thus facilitating the permeation and accumulation of quercetin in skin. Lecithin-chitosan nanoparticles are a promising carrier for topical delivery of quercetin.

Preparation and evaluation of quercetin-loaded lecithin-chitosan nanoparticles for topical delivery

PubMed Central

Tan, Qi; Liu, Weidong; Guo, Chenyu; Zhai, Guangxi

2011-01-01

Background The purpose of this study was to investigate lecithin-chitosan nanoparticles as a topical delivery system for quercetin. Methods Tocopheryl propylene glycol succinate was chosen to be the surfactant for the nanosystem. The mean particle size of the nanoparticles was 95.3 nm, and the entrapment efficiency and drug loading for quercetin were 48.5% and 2.45%, respectively. Topical delivery in vitro and in vivo of the quercetin-loaded nanoparticles was evaluated using quercetin propylene glycol solution as the control. Results Compared with quercetin solution, the quercetin-loaded nanoparticles showed higher permeation ability, and significantly increased accumulation of quercetin in the skin, especially in the epidermis. Microstructure observation of the skin surface after administration indicated that the interaction between ingredients of the nanoparticles and the skin surface markedly changed the morphology of the stratum corneum and disrupted the corneocyte layers, thus facilitating the permeation and accumulation of quercetin in skin. Conclusion Lecithin-chitosan nanoparticles are a promising carrier for topical delivery of quercetin. PMID:21904452

I-V curve hysteresis induced by gate-free charging of GaAs nanowires' surface oxide

NASA Astrophysics Data System (ADS)

Alekseev, P. A.; Geydt, P.; Dunaevskiy, M. S.; Lähderanta, E.; Haggrén, T.; Kakko, J.-P.; Lipsanen, H.

2017-09-01

The control of nanowire-based device performance requires knowledge about the transport of charge carriers and its limiting factors. We present the experimental and modeled results of a study of electrical properties of GaAs nanowires (NWs), considering their native oxide cover. Measurements of individual vertical NWs were performed by conductive atomic force microscopy (C-AFM). Experimental C-AFM observations with numerical simulations revealed the complex resistive behavior of NWs. A hysteresis of current-voltage characteristics of the p-doped NWs as-grown on substrates with different types of doping was registered. The emergence of hysteresis was explained by the trapping of majority carriers in the surface oxide layer near the reverse-biased barriers under the source-drain current. It was found that the accumulation of charge increases the current for highly doped p+-NWs on n+-substrates, while for moderately doped p-NWs on p+-substrates, charge accumulation decreases the current due to blocking of the conductive channel of NWs.

Suppression of Frost Nucleation Achieved Using the Nanoengineered Integral Humidity Sink Effect.

PubMed

Sun, Xiaoda; Rykaczewski, Konrad

2017-01-24

Inhibition of frost formation is important for increasing efficiency of refrigeration systems and heat exchangers, as well as for preventing the rapid icing over of water-repellant coatings that are designed to prevent accumulation of rime and glaze. From a thermodynamic point of view, this task can be achieved by either increasing hydrophobicity of the surface or decreasing the concentration of water vapor above it. The first approach has been studied in depth, but so far has not yielded a robust solution to the problem of frost formation. In this work, we systematically explore how frost growth can be inhibited by controlling water vapor concentration using bilayer coatings with a porous exterior covering a hygroscopic liquid-infused layer. We lay the theoretical foundation and provide experimental validation of the mass transport mechanism that governs the integral humidity sink effect based on this coating platform as well as reveal intriguing sizing effects about this system. We show that the concentration profile above periodically spaced pores is governed by the sink and source concentrations and two geometrical parameters: the nondimensional pore size and the ratio of the pore spacing to the boundary layer thickness. We demonstrate that when the ratio of the pore spacing to the boundary layer thickness vanishes, as for the nanoporous bilayer coatings, the entire surface concentration becomes uniform and equal to the concentration set by the hygroscopic liquid. In other words, the surface concentration becomes completely independent of the nanopore size. We identified the threshold geometrical parameters for this condition and show that it can lead to a 65 K decrease in the nucleation onset surface temperature below the dew point. With this fundamental insight, we use bilayer coatings to nanoengineer the integral humidity sink effect to provide extreme antifrosting performance with up to a 2 h delay in nucleation onset at 263 K. The nanoporous bilayer coatings can be designed to combine optimal antifrosting functionality with a superhydrophobic water repelling exterior to provide coatings that can robustly prevent frost, rime, and glaze accumulation. By minimizing the required amount of antifreeze, this anti-icing method can have minimal operational cost and environmental impact.

Response of Antarctic cryoconite microbial communities to light.

PubMed

Bagshaw, Elizabeth A; Wadham, Jemma L; Tranter, Martyn; Perkins, Rupert; Morgan, Alistair; Williamson, Christopher J; Fountain, Andrew G; Fitzsimons, Sean; Dubnick, Ashley

2016-06-01

Microbial communities on polar glacier surfaces are found dispersed on the ice surface, or concentrated in cryoconite holes and cryolakes, which are accumulations of debris covered by a layer of ice for some or all of the year. The ice lid limits the penetration of photosynthetically available radiation (PAR) to the sediment layer, since the ice attenuates up to 99% of incoming radiation. This suite of field and laboratory experiments demonstrates that PAR is an important control on primary production in cryoconite and cryolake ecosystems. Increased light intensity increased efficiency of primary production in controlled laboratory incubations of debris from the surface of Joyce Glacier, McMurdo Dry Valleys, Antarctica. However, when light intensity was increased to levels near that received on the ice surface, without the protection of an ice lid, efficiency decreased and measurements of photophysiology showed that the communities suffered light stress. The communities are therefore well adapted to low light levels. Comparison with Arctic cryoconite communities, which are typically not covered by an ice lid for the majority of the ablation season, showed that these organisms were also stressed by high light, so they must employ strategies to protect against photodamage. © FEMS 2016.

Rainfall Driven Sorting of Soils and Manure in Beef Feedlot Pens, Implications for Steroid Hormone Transport

NASA Astrophysics Data System (ADS)

Bryson, R.; Harter, T.

2009-12-01

Previous research has documented elevated estrogenic and androgenic activity in surface waters receiving cattle feedlot effluent, while current research shows that significant concentrations of hydrophobic steroid hormones are transported in the solid phase of feedlot pen surface runoff. Accumulated manure in beef feedlot pens includes organic matter ranging from colloidal particles to partially digested feed, forming a complex soil-manure conglomerate at the pen surface. We hypothesized that the transport of solid phase particles in rainfall runoff on beef feedlots would be influenced but not limited by shield layer development. Soils and manure at a beef feedlot were evaluated before and after rainfall-runoff events to determine changes in soil composition and structure. Runoff samples were also collected during an hour of runoff and analyzed for suspended solids. Results indicate that rainfall actively sorts the soil and manure components through raindrop impact, depression storage and runoff. However, transport of solid phase constituents was found to be elevated throughout the hydrograph. This suggests that the surface shield layer conceptualization applied to other soils should be modified before application to the soil-manure conglomerate found in beef feedlot pens.

Response of Antarctic cryoconite microbial communities to light

PubMed Central

Bagshaw, Elizabeth A.; Wadham, Jemma L.; Tranter, Martyn; Perkins, Rupert; Morgan, Alistair; Williamson, Christopher J.; Fountain, Andrew G.; Fitzsimons, Sean; Dubnick, Ashley

2016-01-01

Microbial communities on polar glacier surfaces are found dispersed on the ice surface, or concentrated in cryoconite holes and cryolakes, which are accumulations of debris covered by a layer of ice for some or all of the year. The ice lid limits the penetration of photosynthetically available radiation (PAR) to the sediment layer, since the ice attenuates up to 99% of incoming radiation. This suite of field and laboratory experiments demonstrates that PAR is an important control on primary production in cryoconite and cryolake ecosystems. Increased light intensity increased efficiency of primary production in controlled laboratory incubations of debris from the surface of Joyce Glacier, McMurdo Dry Valleys, Antarctica. However, when light intensity was increased to levels near that received on the ice surface, without the protection of an ice lid, efficiency decreased and measurements of photophysiology showed that the communities suffered light stress. The communities are therefore well adapted to low light levels. Comparison with Arctic cryoconite communities, which are typically not covered by an ice lid for the majority of the ablation season, showed that these organisms were also stressed by high light, so they must employ strategies to protect against photodamage. PMID:27095815

Behavior of implanted hydrogen in thermally stimulated blistering in silicon

NASA Astrophysics Data System (ADS)

Aleksandrov, P. A.; Baranova, E. K.; Baranova, I. V.; Budaragin, V. V.; Litvinov, V. L.

2003-11-01

The processes of accumulation of ion implanted hydrogen in blisters in silicon and its release during the thermal treatment from 350 to 1020degreesC have been studied by optical techniques. It was established that accumulation of gaseous hydrogen inside blisters takes place at temperatures lower than similar to450-500degreesC and is accompanied by the growth of blister thickness and deformation of their caps. At higher temperatures the gaseous hydrogen goes out of the cavities dissolving in silicon. Due to the internal pressure dropping the elastically deformed top layer partially relaxes and the blister thickness decreases. Etching of the surface layer reveals the agglomerations of small voids (<0.3 mm) located in the place of blisters approximately at their depth. Proceeding from the fact that the processes in blistering are similar to those in ion cut, the following conclusions with respect to the latter were drawn. The exfoliation processes themselves occur at temperatures lower than similar to500degreesC. The exfoliation efficiency particularly at the higher temperatures is essentially dependent on the heating rate.

[Effects of nitrogen application rate on light interception and dry matter distribution at diffe-rent layers in wheat canopy under supplemental irrigation based on measuring soil moisture.

PubMed

Zheng, Xue Jiao; Yu, Zhen Wen; Zhang, Yong Li; Shi, Yu

2018-02-01

With the large-spike wheat cultivar Shannong 23 as test material,a field experiment was conducted by increasing the relative soil moisture content to 70% and 65% at jointing and anthesis stages. Four nitrogen levels,0 (N 0 ), 180 (N 1 ), 240 (N 2 ) and 300 kg·hm -2 (N 3 ), were designed to examine the effects of nitrogen application rates on the interception of photosynthetic active radiation (PAR) and dry matter distribution of wheat at different canopy layers. The results showed that the total stem number of wheat population at anthesis stage, the leaf area index at 10, 20 and 30 days after anthesis, PAR capture ratio at upper and middle layers and total PAR capture ratio in wheat canopy on day 20 after anthesis of treatment N 2 were significantly higher than those in the treatments of both N 0 and N 1 . Those indexes showed no significant increase when the application rate increased to 300 kg·hm -2 (N 3 ). The vegetative organ dry matter accumulation of all layers at maturity stage of treatment N 2 were significantly higher than N 0 and N 1 . Compared with treatment N 0 and N 1 , N 2 increased the grain and total dry matter accumulation by 36.7% and 35.4%, 9.5% and 10.2%, respectively, but had no significant difference with treatment N 3 . The vegetative organ dry matter accumulation at all layers, grain and total dry matter accumulation were significantly and positively correlated with PAR capture ratio at upper and middle layers, and had no significant correlation with that at lower layer. The vegetative organ dry matter accumulation at all layers was significantly and positively correlated with grain dry matter accumulation. The application rate at 240 kg·hm -2 (N 2 ) would be the optimum treatment under the present experimental condition.

Impact of downward-mixing ozone on surface ozone accumulation in southern Taiwan.

PubMed

Lin, Ching-Ho

2008-04-01

The ozone that initially presents in the previous day's afternoon mixing layer can remain in the nighttime atmosphere and then be carried over to the next morning. Finally, this ozone can be brought to the ground by downward mixing as mixing depth increases during the daytime, thereby increasing surface ozone concentrations. Variation of ozone concentration during each of these periods is investigated in this work. First, ozone concentrations existing in the daily early morning atmosphere at the altitude range of the daily maximum mixing depth (residual ozone concentrations) were measured using tethered ozonesondes on 52 experimental days during 2004-2005 in southern Taiwan. Daily downward-mixing ozone concentrations were calculated by a box model coupling the measured daily residual ozone concentrations and daily mixing depth variations. The ozone concentrations upwind in the previous day's afternoon mixing layer were estimated by the combination of back air trajectory analysis and known previous day's surface ozone distributions. Additionally, the relationship between daily downward-mixing ozone concentration and daily photochemically produced ozone concentration was examined. The latter was calculated by removing the former from daily surface maximum ozone concentration. The measured daily residual ozone concentrations distributed at 12-74 parts per billion (ppb) with an average of 42 +/- 17 ppb are well correlated with the previous upwind ozone concentration (R2 = 0.54-0.65). Approximately 60% of the previous upwind ozone was estimated to be carried over to the next morning and became the observed residual ozone. The daily downward-mixing ozone contributes 48 +/- 18% of the daily surface maximum ozone concentration, indicating that the downward-mixing ozone is as important as daily photochemically produced ozone to daily surface maximum ozone accumulation. The daily downward-mixing ozone is poorly correlated with the daily photochemically produced ozone and contributes significantly to the daily variation of surface maximum ozone concentrations (R2 = 0.19). However, the contribution of downward-mixing ozone to daily ozone variation is not included in most existing statistical models developed for predicting daily ozone variation. Finally, daily surface maximum ozone concentration is positively correlated with daily afternoon mixing depth, attributable to the downward-mixing ozone.

Complementary microanalysis of Zn, Mn and Fe in the chelicera of spiders and scorpions using scanning MeV-ion and electron microprobes

NASA Astrophysics Data System (ADS)

Schofield, Robert; Lefevre, Harlan; Shaffer, Michael

1989-04-01

Energy-loss scanning transmission ion microscopy (ELSTIM or just STIM), PIXE and electron microprobe techniques are used to investigate certain minor element accumulations in a few spiders and scorpions. STIM and PIXE are used to survey the unsectioned specimens, while electron microprobe techniques are used for higher resolution investigations of several sections of the specimens. Concentration values measured using STIM and PIXE are found to be in satisfactory agreement with those measured using electron probe microanalysis. A garden spider Araneus diadematus is found to contain high concentrations of zinc in a thin layer near the surface of its fangs (reaching 23% of dry weight), and manganese in its marginal teeth (about 5% of dry weight). A wolf spider Alopecosa kochi is found to have similar concentrations of zinc in a layer near the surface of it's fang, and concentrations of manganese reaching 1.5% in a layer beneath the zinc containing layer. A scorpion Centruroides sp. is found to contain high concentrations of iron (reaching 8%) and zinc (reaching 24%) in the tips of teeth on the cheliceral fingers, and manganese (about 5%) in the stinger. The hypothesis that these elements simply harden the cuticle does not appear to explain their segregation patterns.

Polymeric capsule-cushioned leukocyte cell membrane vesicles as a biomimetic delivery platform

NASA Astrophysics Data System (ADS)

Gao, Changyong; Wu, Zhiguang; Lin, Zhihua; Lin, Xiankun; He, Qiang

2016-02-01

We report a biomimetic delivery of microsized capsule-cushioned leukocyte membrane vesicles (CLMVs) through the conversion of freshly reassembled leukocyte membrane vesicles (LMVs), including membrane lipids and membrane-bound proteins onto the surface of layer-by-layer assembled polymeric multilayer microcapsules. The leukocyte membrane coating was verified by using electron microscopy, a quartz crystal microbalance, dynamic light scattering, and confocal laser scanning microscopy. The resulting CLMVs have the ability to effectively evade clearance by the immune system and thus prolong the circulation time in mice. Moreover, we also show that the right-side-out leukocyte membrane coating can distinctly improve the accumulation of capsules in tumor sites through the molecular recognition of membrane-bound proteins of CLMVs with those of tumor cells in vitro and in vivo. The natural cell membrane camouflaged polymeric multilayer capsules with the immunosuppressive and tumor-recognition functionalities of natural leukocytes provide a new biomimetic delivery platform for disease therapy.We report a biomimetic delivery of microsized capsule-cushioned leukocyte membrane vesicles (CLMVs) through the conversion of freshly reassembled leukocyte membrane vesicles (LMVs), including membrane lipids and membrane-bound proteins onto the surface of layer-by-layer assembled polymeric multilayer microcapsules. The leukocyte membrane coating was verified by using electron microscopy, a quartz crystal microbalance, dynamic light scattering, and confocal laser scanning microscopy. The resulting CLMVs have the ability to effectively evade clearance by the immune system and thus prolong the circulation time in mice. Moreover, we also show that the right-side-out leukocyte membrane coating can distinctly improve the accumulation of capsules in tumor sites through the molecular recognition of membrane-bound proteins of CLMVs with those of tumor cells in vitro and in vivo. The natural cell membrane camouflaged polymeric multilayer capsules with the immunosuppressive and tumor-recognition functionalities of natural leukocytes provide a new biomimetic delivery platform for disease therapy. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08407e

Geo-electrical investigation of near surface conductive structures suitable for groundwater accumulation in a resistive crystalline basement environment: A case study of Isuada, southwestern Nigeria

NASA Astrophysics Data System (ADS)

Kayode, J. S.; Adelusi, A. O.; Nawawi, M. N. M.; Bawallah, M.; Olowolafe, T. S.

2016-07-01

This paper presents a geophysical surveying for groundwater identification in a resistive crystalline basement hard rock in Isuada area, Southwestern Nigeria. Very low frequency (VLF) electromagnetic and electrical resistivity geophysical techniques combined with well log were used to characterize the concealed near surface conductive structures suitable for groundwater accumulation. Prior to this work; little was known about the groundwater potential of this area. Qualitative and semi-quantitative interpretations of the data collected along eight traverses at 20 m spacing discovered conductive zones suspected to be fractures, faults, and cracks which were further mapped using Vertical Electrical Sounding (VES) technique. Forty VES stations were utilized using Schlumberger configurations with AB/2 varying from 1 to 100 m. Four layers i.e. the top soil, the weathered layer, the partially weathered/fractured basement and the fresh basement were delineated from the interpreted resistivity curves. The weathered layers constitute the major aquifer unit in the area and are characterized by moderately low resistivity values which ranged between about 52 Ωm and 270 Ωm while the thickness varied from 1 to 35 m. The depth to the basement and the permeable nature of the weathered layer obtained from both the borehole and the hand-dug wells was used to categorize the groundwater potential of the study area into high, medium and low ratings. The groundwater potential map revealed that about 45% of the study area falls within the low groundwater potential rating while about 10% constitutes the medium groundwater potential and the remaining 45% constitutes high groundwater potential. The low resistivity, thick overburden, and fractured bedrock constitute the aquifer units and the series of basement depressions identified from the geoelectric sections as potential conductive zones appropriate for groundwater development.

Dynamic changes in the distribution of minerals in relation to phytic acid accumulation during rice seed development.

PubMed

Iwai, Toru; Takahashi, Michiko; Oda, Koshiro; Terada, Yasuko; Yoshida, Kaoru T

2012-12-01

Phytic acid (inositol hexakisphosphate [InsP(6)]) is the storage compound of phosphorus in seeds. As phytic acid binds strongly to metallic cations, it also acts as a storage compound of metals. To understand the mechanisms underlying metal accumulation and localization in relation to phytic acid storage, we applied synchrotron-based x-ray microfluorescence imaging analysis to characterize the simultaneous subcellular distribution of some mineral elements (phosphorus, calcium, potassium, iron, zinc, and copper) in immature and mature rice (Oryza sativa) seeds. This fine-imaging method can reveal whether these elements colocalize. We also determined their accumulation patterns and the changes in phosphate and InsP(6) contents during seed development. While the InsP(6) content in the outer parts of seeds rapidly increased during seed development, the phosphate contents of both the outer and inner parts of seeds remained low. Phosphorus, calcium, potassium, and iron were most abundant in the aleurone layer, and they colocalized throughout seed development. Zinc was broadly distributed from the aleurone layer to the inner endosperm. Copper localized outside the aleurone layer and did not colocalize with phosphorus. From these results, we suggest that phosphorus translocated from source organs was immediately converted to InsP(6) and accumulated in aleurone layer cells and that calcium, potassium, and iron accumulated as phytic acid salt (phytate) in the aleurone layer, whereas zinc bound loosely to InsP(6) and accumulated not only in phytate but also in another storage form. Copper accumulated in the endosperm and may exhibit a storage form other than phytate.

Role of mariculture in the loading and speciation of mercury at the coast of the East China Sea.

PubMed

Liang, Peng; Gao, Xuefei; You, Qiongzhi; Zhang, Jin; Cao, Yucheng; Zhang, Chan; Wong, Ming-Hung; Wu, Sheng-Chun

2016-11-01

The effects of mariculture on mercury (Hg) contamination and speciation in water, sediment and cultured fish in a typical mariculture zone located in Xiangshan bay, Zhejiang province, east China, were studied. Water, sediment and fish samples were collected from mariculture sites (MS) and from corresponding reference sites (RS) 2500 m away from the MS. The THg concentration in overlying water in Xiangshan bay reached as high as 16.6 ± 19.5 ng L -1 , indicating that anthropogenic sources in this bay may contribution on Hg contamination in overlying water. Mariculture activities resulted in an increase in THg concentration in water from surface and bottom layers, which may be attributed to the discharge of domestic sewage and the accumulation of unconsumed fish feed and fish excreta in the benthic environment. Methylmercury (MeHg) concentrations in the bottom layer of overlying water and top surface layer of porewater underneath MS were higher than at RS, implying that mariculture activities promote Hg methylation in the interface between sediments and water. In addition, the concentrations of MeHg in sediment and porewater were significantly higher in summer than winter. It was observed that THg and MeHg contents in the muscle of blackhead seabream (Acanthopagrus schlegelii) (fed by the trash fish) were significantly higher (p < 0.001) than those in red snapper (Lutjanus campechanus) or perch (Perca fluviatilis) (fed by pellet fish feed). The THg and MeHg concentrations in the fish meat were closely related to the feeding mode, which indicate that fish feed rather than environmental media is the major pathway for Hg accumulation in fish muscle. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effect of the Graded-Gap Layer Composition on the Formation of n + -n - -p Structures in Boron-Implanted Heteroepitaxial Cd x Hg1- x Te Layers

NASA Astrophysics Data System (ADS)

Talipov, N. Kh.; Voitsekhovskii, А. V.; Grigor'ev, D. V.

2014-07-01

Processes of formation of n + -n--p-structures in boron-implanted heteroepitaxial (HEL) CdxHg1-xTe (CMT) layers of p-type grown by molecular beam epitaxy (HEL CMT MBE) with different compositions of the upper graded-gap layer are studied. It is shown that the surface composition (xs) of HEL CMT MBE significantly affects both the electrical parameters of the implanted layer and the spatial distribution of radiation defects of donor type. For HEL CMT MBE with the small surface composition xs = 0.22-0.33, it is found that the layer electron concentration (Ns) is decreased after saturation with accumulation of radiation defects, as the dose of B+ ions is increased in the range of D = 1ṡ1011-3ṡ1015 сm-2. An increase of the surface composition up to xs = 0.49-0.56 results in a significant decrease in Ns and a disappearance of the saturation of concentration in the whole dose range. The value of Ns monotonically increases with the energy (E) of boron ions and composition xs. It is found that for B+-ion energies E = 20-100 keV, the depth of the surface n + -layer increases with increasing energy and exceeds the total projected path of boron ions. However, in the energy range E = 100-150 keV, the depth of n+-layer stops increasing with the increase of the surface composition. The depth (dn) of a lightly doped n--layer monotonically decreases with increasing energy of boron ions in the entire range of E = 20-150 keV. With increasing dose (D) of B+ ions in the interval D = 1ṡ1014-1ṡ1015сm-2, deep n--layers with dn = 4-5 μm are formed only in the HEL CMT MBE with xs = 0.22-0.33. For the samples with xs = 0.49-0.56, the depth changes in the interval dn = 1.5-2.5 μm. At D ≤ 3ṡ1013сm-2, n + -n--p-structure is not formed for all surface compositions, if implantation is performed at room temperature. However, implantation at T = 130°C leads to the formation of a deep n--layer. Planar photodiodes with the n-p-junction area of A = 35×35 μm2 made on the basis of the boron implanted HEL CMT MBE with the surface compositions xs = 0.33-0.56 had high differential resistance Rd = 3ṡ106-107 Ω•cm2 and high product R0 Aeff = 9.0-20.7 Ω•cm2, where Aeff is the effective area of the charge carrier collecting. The values of Rd and R0 Aeff increased with increasing xs. It is found that the layer electron concentration in the boron implanted HEL CMT MBE with different surface compositions is increased, when exposed to normal conditions for a few years.

Investigating the influence of lithologic heterogeneity on gas hydrate formation and methane recycling at the base of the gas hydrate stability zone in channelized systems

NASA Astrophysics Data System (ADS)

Daigle, H.; Nole, M.; Cook, A.; Malinverno, A.

2017-12-01

In marine environments, gas hydrate preferentially accumulates in coarse-grained sediments. At the meso- to micro-scale, however, hydrate distribution in these coarse-grained units is often heterogeneous. We employ a methane hydrate reservoir simulator coupling heat and mass transfer as well as capillary effects to investigate how capillary controls on methane solubility affect gas and hydrate accumulations in reservoirs characterized by graded bedding and alternating sequences of coarse-grained sands and fine-grained silt and clay. Simulations bury a channelized reservoir unit encased in homogeneous, fine-grained material characterized by small pores (150 nm) and low permeability ( 1 md in the absence of hydrate). Pore sizes within each reservoir bed between vary between coarse sand and fine silt. Sands have a median pore size of 35 microns and a lognormal pore size distribution. We also investigate how the amount of labile organic carbon (LOC) affects hydrate growth due to microbial methanogenesis within the sediments. In a diffusion-dominated system, methane movies into reservoir layers along spatial gradients in dissolved methane concentration. Hydrate grows in such a way as to minimize these concentration gradients by accumulating slower in finer-grained reservoir layers and faster in coarser-grained layers. Channelized, fining-upwards sediment bodies accumulate hydrate first along their outer surfaces and thence inward from top to bottom. If LOC is present in thin beds within the channel, higher saturations of hydrate will be distributed more homogeneously throughout the unit. When buried beneath the GHSZ, gas recycling can occur only if enough hydrate is present to form a connected gas phase upon dissociation. Simulations indicate that this is difficult to achieve for diffusion-dominated systems, especially those with thick GHSZs and/or small amounts of LOC. However, capillary-driven fracturing behavior may be more prevalent in settings with thick GHSZs.

Investigating the influence of lithologic heterogeneity on gas hydrate formation and methane recycling at the base of the gas hydrate stability zone in channelized systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daigle, Hugh; Nole, Michael; Cook, Ann

In marine environments, gas hydrate preferentially accumulates in coarse-grained sediments. At the meso- to micro-scale, however, hydrate distribution in these coarse-grained units is often heterogeneous. We employ a methane hydrate reservoir simulator coupling heat and mass transfer as well as capillary effects to investigate how capillary controls on methane solubility affect gas and hydrate accumulations in reservoirs characterized by graded bedding and alternating sequences of coarse-grained sands and fine-grained silt and clay. Simulations bury a channelized reservoir unit encased in homogeneous, fine-grained material characterized by small pores (150 nm) and low permeability (~1 md in the absence of hydrate). Poremore » sizes within each reservoir bed between vary between coarse sand and fine silt. Sands have a median pore size of 35 microns and a lognormal pore size distribution. We also investigate how the amount of labile organic carbon (LOC) affects hydrate growth due to microbial methanogenesis within the sediments. In a diffusion-dominated system, methane movies into reservoir layers along spatial gradients in dissolved methane concentration. Hydrate grows in such a way as to minimize these concentration gradients by accumulating slower in finer-grained reservoir layers and faster in coarser-grained layers. Channelized, fining-upwards sediment bodies accumulate hydrate first along their outer surfaces and thence inward from top to bottom. If LOC is present in thin beds within the channel, higher saturations of hydrate will be distributed more homogeneously throughout the unit. When buried beneath the GHSZ, gas recycling can occur only if enough hydrate is present to form a connected gas phase upon dissociation. Simulations indicate that this is difficult to achieve for diffusion-dominated systems, especially those with thick GHSZs and/or small amounts of LOC. However, capillary-driven fracturing behavior may be more prevalent in settings with thick GHSZs.« less

Carbon-containing compounds on fusion-related surfaces: Thermal and ion-induced formation and erosion

NASA Astrophysics Data System (ADS)

Linsmeier, Christian

2004-12-01

The deposition of carbon on metals is the unavoidable consequence of the application of different wall materials in present and future fusion experiments like ITER. Presently used and prospected materials besides carbon (CFC materials in high heat load areas) are tungsten and beryllium. The simultaneous application of different materials leads to the formation of surface compounds due to the erosion, transport and re-deposition of material during plasma operations. The formation and erosion processes are governed by widely varying surface temperatures and kinetic energies as well as the spectrum of impinging particles from the plasma. The knowledge of the dependence on these parameters is crucial for the understanding and prediction of the compound formation on wall materials. The formation of surface layers is of great importance, since they not only determine erosion rates, but also influence the ability of the first wall for hydrogen isotope inventory accumulation and release. Surface compound formation, diffusion and erosion phenomena are studied under well-controlled ultra-high vacuum conditions using in-situ X-ray photoelectron spectroscopy (XPS) and ion beam analysis techniques available at a 3 MV tandem accelerator. XPS provides chemical information and allows distinguishing elemental and carbidic phases with high surface sensitivity. Accelerator-based spectroscopies provide quantitative compositional analysis and sensitivity for deuterium in the surface layers. Using these techniques, the formation of carbidic layers on metals is studied from room temperature up to 1700 K. The formation of an interfacial carbide of several monolayers thickness is not only observed for metals with exothermic carbide formation enthalpies, but also in the cases of Ni and Fe which form endothermic carbides. Additional carbon deposited at 300 K remains elemental. Depending on the substrate, carbon diffusion into the bulk starts at elevated temperatures together with additional carbide formation. Depending on the bond nature in the carbide (metallic in the transition metal carbides, ionic e.g. in Be2C), the surface carbide layer is dissolved upon further increased temperatures or remains stable. Carbide formation can also be initiated by ion bombardment, both of chemically inert noble gas ions or C+ or CO+ ions. In the latter case, a deposition-erosion equilibrium develops which leads to a ternary surface layer of constant thickness. A chemical erosion channel is also discussed for the enhanced erosion of thin carbon films on metals by deuterium ions.

How did nature engineer the highest surface lipid accumulation among plants? Exceptional expression of acyl-lipid-associated genes for the assembly of extracellular triacylglycerol by Bayberry ( Myrica pensylvanica ) fruits

DOE PAGES

Simpson, Jeffrey P.; Thrower, Nicholas; Ohlrogge, John B.

2016-02-09

Bayberry (Myrica pensylvanica) fruits are covered with a remarkably thick layer of crystalline wax consisting of triacylglycerol (TAG) and diacylglycerol (DAG) esterified exclusively with saturated fatty acids. As the only plant known to accumulate soluble glycerolipids as a major component of surface waxes, Bayberry represents a novel system to investigate neutral lipid biosynthesis and lipid secretion by vegetative plant cells. The assembly of Bayberry wax is distinct from conventional TAG and other surface waxes, and instead proceeds through a pathway related to cutin synthesis (Simpson and Ohlrogge, 2016). In this study, microscopic examination revealed that the fruit tissue that producesmore » and secretes wax (Bayberry knobs) is fully developed before wax accumulates and that wax is secreted to the surface without cell disruption. Comparison of transcript expression to genetically related tissues (Bayberry leaves, M. rubra fruits), cutin-rich tomato and cherry fruit epidermis, and to oil-rich mesocarp and seeds, revealed exceptionally high expression of 13 transcripts for acyl-lipid metabolism together with down-regulation of fatty acid oxidases and desaturases. The predicted protein sequences of the most highly expressed lipid-related enzyme-encoding transcripts in Bayberry knobs are 100% identical to the sequences from Bayberry leaves,which do not produce surface DAG or TAG. Together, these results indicate that TAG biosynthesis and secretion in Bayberry is achieved by both up and down-regulation of a small subset of genes related to the biosynthesis of cutin and saturated fatty acids, and also implies that modifications in gene expression, rather than evolution of new gene functions, was the major mechanism by which Bayberry evolved its specialized lipid metabolism.« less

Surface Melt and Firn Density Evolution in the Western Greenland Percolation Zone Over the Past 50 Years

NASA Astrophysics Data System (ADS)

Graeter, K.; Osterberg, E. C.; Hawley, R. L.; Thundercloud, Z. R.; Marshall, H. P.; Ferris, D. G.; Lewis, G.

2016-12-01

Predictions of the Greenland Ice Sheet's (GIS) contribution to sea-level rise in a warming climate depend on our ability to model the surface mass balance (SMB) processes occurring across the ice sheet. These processes are poorly constrained in the percolation zone, the region of the ice sheet where surface melt refreezes in the firn, thus preventing that melt from directly contributing to GIS mass loss. In this way, the percolation zone serves as a buffer to higher temperatures increasing mass loss. However, it is unknown how the percolation zone is evolving in a changing climate and to what extent the region will continue to serve as a buffer to future runoff. We collected seven shallow ( 22-30 m) firn cores from the Western Greenland percolation zone in May-June 2016 as part of the Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) project. Here we present data on melt layer stratigraphy, density, and annual accumulation for each core to determine: (1) the temporal and spatial accumulation and melt refreeze patterns in the percolation zone of W. Greenland over the past 40 - 55 years, and (2) the impacts of changing melt and refreeze patterns on the near-surface density profile of the percolation zone. Three of the GreenTrACS firn cores re-occupy firn core sites collected in the 1970's-1990's, allowing us to more accurately quantify the evolution of the percolation zone surface melt and firn density during the most recent decades of summertime warming. This work is the basis for broader investigations into how changes in W. Greenland summertime climate are impacting the SMB of the Greenland Ice Sheet.

Bauschinger Effect and Back Stress in Gradient Cu-Ge Alloy

NASA Astrophysics Data System (ADS)

Hu, Xianzhi; Jin, Shenbao; Zhou, Hao; Yin, Zhe; Yang, Jian; Gong, Yulan; Zhu, Yuntian; Sha, Gang; Zhu, Xinkun

2017-09-01

Using surface mechanical attrition treatment (SMAT), a gradient structure composed of two gradient structure (GS) layers and a coarse grain (CG) layer was generated from a Cu-5.7 wt pct Ge alloy, significantly improving the yield strength of the sample. Unloading-reloading tests showed an unusual Bauschinger effect in these GS samples. The back stresses caused by the accumulated geometrically necessary dislocations (GNDs) on the GS/CG border increased with increasing strain. As found by electron backscatter diffraction (EBSD), the GNDs are mainly distributed in the gradient structured layer, and the density of the GNDs increase with increasing SMAT time. The effect of the back stress increased with increasing SMAT processing time due to the increase in the strain gradient. The pronounced Bauschinger effect in a GS sample can improve the resistance to forward plastic flow and finally contributes to the high strength of GS samples.

Surface Reactivity Enhancement on a Pd/Bi2Te3 Heterostructure through Robust Topological Surface States

PubMed Central

He, Qing Lin; Lai, Ying Hoi; Lu, Yao; Law, Kam Tuen; Sou, Iam Keong

2013-01-01

We present a study of the surface reactivity of a Pd/Bi2Te3 thin film heterostructure. The topological surface states from Bi2Te3, being delocalized and robust owing to their topological natures, were found to act as an effective electron bath that significantly enhances the surface reactivity of palladium in the presence of two oxidizing agents, oxygen and tellurium respectively, which is consistent with a theoretical calculation. The surface reactivity of the adsorbed tellurium on this heterostructure is also intensified possibly benefitted from the effective transfer of the bath electrons. A partially inserted iron ferromagnetic layer at the interface of this heterostructure was found to play two competing roles arising from the higher-lying d-band center of the Pd/Fe bilayer and the interaction between the ferromagnetism and the surface spin texture of Bi2Te3 on the surface reactivity and their characteristics also demonstrate that the electron bath effect is long-lasting against accumulated thickness of adsorbates. PMID:23970163

A Mathematical Model of Melt Lake Development on an Ice Shelf

NASA Astrophysics Data System (ADS)

Buzzard, S. C.; Feltham, D. L.; Flocco, D.

2018-02-01

The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. Melt lakes have been implicated in ice shelf collapse; Antarctica's Larsen B Ice Shelf was observed to have a large amount of surface melt lakes present preceding its collapse in 2002. Such collapse can affect ocean circulation and temperature, cause habitat loss and contribute to sea level rise through the acceleration of tributary glaciers. We present a mathematical model of a surface melt lake on an idealized ice shelf. The model incorporates a calculation of the ice shelf surface energy balance, heat transfer through the firn, the production and percolation of meltwater into the firn, the formation of ice lenses, and the development and refreezing of surface melt lakes. The model is applied to the Larsen C Ice Shelf, where melt lakes have been observed. This region has warmed several times the global average over the last century and the Larsen C firn layer could become saturated with meltwater by the end of the century. When forced with weather station data, our model produces surface melting, meltwater accumulation, and melt lake development consistent with observations. We examine the sensitivity of lake formation to uncertain parameters and provide evidence of the importance of processes such as lateral meltwater transport. We conclude that melt lakes impact surface melt and firn density and warrant inclusion in dynamic-thermodynamic models of ice shelf evolution within climate models, of which our model could form the basis for the thermodynamic component.

Extracellular esterases of phylloplane yeast Pseudozyma antarctica induce defect on cuticle layer structure and water-holding ability of plant leaves.

PubMed

Ueda, Hirokazu; Mitsuhara, Ichiro; Tabata, Jun; Kugimiya, Soichi; Watanabe, Takashi; Suzuki, Ken; Yoshida, Shigenobu; Kitamoto, Hiroko

2015-08-01

Aerial plant surface (phylloplane) is a primary key habitat for many microorganisms but is generally recognized as limited in nutrient resources. Pseudozyma antarctica, a nonpathogenic yeast, is commonly isolated from plant surfaces and characterized as an esterase producer with fatty acid assimilation ability. In order to elucidate the biological functions of these esterases, culture filtrate with high esterase activity (crude enzyme) of P. antarctica was applied onto leaves of tomato and Arabidopsis. These leaves showed a wilty phenotype, which is typically associated with water deficiency. Furthermore, we confirmed that crude enzyme-treated detached leaves clearly lost their water-holding ability. In treated leaves of both plants, genes associated to abscisic acid (ABA; a plant stress hormone responding osmotic stress) were activated and accumulation of ABA was confirmed in tomato plants. Microscopic observation of treated leaf surfaces revealed that cuticle layer covering the aerial epidermis of leaves became thinner. A gas chromatography-mass spectrometry (GC-MS) analysis exhibited that fatty acids with 16 and 18 carbon chains were released in larger amounts from treated leaf surfaces, indicating that the crude enzyme has ability to degrade lipid components of cuticle layer. Among the three esterases detected in the crude enzyme, lipase A, lipase B, and P. antarctica esterase (PaE), an in vitro enzyme assay using para-nitrophenyl palmitate as substrate demonstrated that PaE was the most responsible for the degradation. These results suggest that PaE has a potential role in the extraction of fatty acids from plant surfaces, making them available for the growth of phylloplane yeasts.

[Calculation of environmental dredging depth of heavy sediments in Zhushan Bay of Taihu Lake metal polluted].

PubMed

Jiang, Xia; Wang, Wen-Wen; Wang, Shu-Hang; Jin, Xiang-Can

2012-04-01

Horizontal distribution of heavy metals in surface sediments of Zhushan Bay was investigated, and core sediment samples were collected in the representative area. Core sediments were divided into oxide layer (A), polluted layer (B), upper polluted transition layer(C1), lower polluted transition layer(C2) and normal mud layer(D) from top to bottom. The change of total contents of Cr, Ni, Cu, Zn, As, Cd, Hg, Pb and contents of biological available Cr, Ni, Cu, Zn, As, Cd, Pb with depths were analyzed. Ecological risk assessment of heavy metals in sediments was done by potential ecological risk index method. At last, environmental dredging depth was calculated. The results shows that the contents of Cr, Ni, Cu, Zn, As, Cd, Hg, Pb are 30.56-216.58, 24.07-59.95, 16.71-140.30, 84.31-193.43, 3.39-22.30, 0.37-1.59, 0.00-0.80 and 9.67-99.35 mg x kg(-1), respectively. The average concentrations of Cr, Ni, Cu, Zn, As, Cd, Hg, Pb are 79.74, 37.74, 44.83, 122.39, 10.39, 0.77, 0.14 and 40.08 mg x kg(-1), respectively. Heavy metals in the surface sediments of Zhushan Bay mainly distribute in the west bank and the estuaries of Taige canal, Yincun Port, and Huanshan River,and Cd pollution is relatively serious. There is an accumulative effect of heavy metals in Zhushan Bay, and the contents of biological available metals decrease with depths. Ecological risk grades of Cd in layer A and B are high, and the comprehensive potential ecological risk grades of each layer are in middle or low. The environmental dredging layers are A and B, and the average dredging depth is 0.39 m.

Fingering convection induced by atomic diffusion in stars: 3D numerical computations and applications to stellar models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zemskova, Varvara; Garaud, Pascale; Deal, Morgan

2014-11-10

Iron-rich layers are known to form in the stellar subsurface through a combination of gravitational settling and radiative levitation. Their presence, nature, and detailed structure can affect the excitation process of various stellar pulsation modes and must therefore be modeled carefully in order to better interpret Kepler asteroseismic data. In this paper, we study the interplay between atomic diffusion and fingering convection in A-type stars, as well as its role in the establishment and evolution of iron accumulation layers. To do so, we use a combination of three-dimensional idealized numerical simulations of fingering convection (which neglect radiative transfer and complexmore » opacity effects) and one-dimensional realistic stellar models. Using the three-dimensional simulations, we first validate the mixing prescription for fingering convection recently proposed by Brown et al. (within the scope of the aforementioned approximation) and identify what system parameters (total mass of iron, iron diffusivity, thermal diffusivity, etc.) play a role in the overall evolution of the layer. We then implement the Brown et al. prescription in the Toulouse-Geneva Evolution Code to study the evolution of the iron abundance profile beneath the stellar surface. We find, as first discussed by Théado et al., that when the concurrent settling of helium is ignored, this accumulation rapidly causes an inversion in the mean molecular weight profile, which then drives fingering convection. The latter mixes iron with the surrounding material very efficiently, and the resulting iron layer is very weak. However, taking helium settling into account partially stabilizes the iron profile against fingering convection, and a large iron overabundance can accumulate. The opacity also increases significantly as a result, and in some cases it ultimately triggers dynamical convection. The direct effects of radiative acceleration on the dynamics of fingering convection (especially in the nonlinear regime) remain to be added in the future to improve the quantitative predictions of the model.« less

The transitional depositional environment and sequence stratigraphy of Chasma Boreale

NASA Astrophysics Data System (ADS)

Brothers, S. C.; Kocurek, G.

2018-07-01

The depositional system within Chasma Boreale is unique in that it contains active aeolian environments, expressed as dune fields, and active cryosphere environments, present as layered ice deposits, as well as environments that transition between these. This work presents a new analysis of the Chasma Boreale sediment system that creates an interpretative framework addressing: (a) controls on the balance between aeolian and cryospheric processes in the modern depositional system, (b) the stratigraphic architecture of related sedimentary deposits, and (c) processes of sediment accumulation and preservation. Images from Context Camera (CTX; 6 m/pixel) are used to classify and map sedimentary environments, surfaces, and deposits on the reentrant floor, to refine the established geologic map of the reentrant, and to infer the stratigraphic record of the accumulation from Chasma Boreale's depositional system. A spectrum of sedimentary environments occurring between those dominated by aeolian and by cryospheric processes are identified. Through time, the boundaries of these sedimentary environments have shifted, resulting in complex lateral changes in the configuration of sedimentary environments on the reentrant's floor. Vertically, the stratigraphic record is characterized by the punctuation of sandy aeolian deposits by icy surfaces that indicate episodes of ice growth that preserve underlying deposits, resulting in accumulation. Stabilized icy surfaces occur at multiple vertical (temporal) scales and lateral extents, suggesting the influence of both regional climate change due to allogenic forcing, as well as autogenic dynamics within the transitional system. These observations demonstrate that the Chasma Boreale accumulation can be interpreted in an aeolian sequence stratigraphic framework. This work contributes the first detailed description of the processes forming polar aeolian sequences, with an emphasis on the competing and complementary dynamics between aeolian and cryospheric systems.

Stabilizing Effects of Bacterial Biofilms: EPS Penetration and Redistribution of Bed Stability Down the Sediment Profile

NASA Astrophysics Data System (ADS)

Chen, X. D.; Zhang, C. K.; Zhou, Z.; Gong, Z.; Zhou, J. J.; Tao, J. F.; Paterson, D. M.; Feng, Q.

2017-12-01

Biofilms, consisting of microorganisms and their secreted extracellular polymeric substances (EPSs), serve as "ecosystem engineers" stabilizing sedimentary environments. Natural sediment bed provides an excellent substratum for biofilm growth. The porous structure and rich nutrients allow the EPS matrix to spread deeper into the bed. A series of laboratory-controlled experiments were conducted to investigate sediment colonization of Bacillus subtilis and the penetration of EPS into the sediment bed with incubation time. In addition to EPS accumulation on the bed surface, EPS also penetrated downward. However, EPS distribution developed strong vertical heterogeneity with a much higher content in the surface layer than in the bottom layer. Scanning electron microscope images of vertical layers also displayed different micromorphological properties of sediment-EPS matrix. In addition, colloidal and bound EPSs exhibited distinctive distribution patterns. After the full incubation, the biosedimentary beds were eroded to test the variation of bed stability induced by biological effects. This research provides an important reference for the prediction of sediment transport and hence deepens the understanding of the biologically mediated sediment system and broadens the scope of the burgeoning research field of "biomorphodynamics."

Method of obtaining graphene and graphene-based electronic components and circuits with pencil directly on paper

NASA Astrophysics Data System (ADS)

Mailian, Aram; Mailian, Manvel; Shmavonyan, Gagik

2014-03-01

An easy method of obtaining graphene and graphene-based electronic components and circuits by drawing lines or repeatedly rubbing any type of graphite rod along the same path directly on paper and other insulating substrates is suggested. The structure containing rubbed-off layers behaves like a semiconducting material. The surface of the structure demonstrates ordered and oriented character containing few layer graphene. The carrier mobility is anisotropic through the thickness of the structure with the highest value of ~ 104 cm2/V .sec at the surface. Raman spectra of the structures in the near IR at excitation wavelength of 976 nm (1.27 eV) are registered. The observed phenomenon is universal, does not depend on the material of the substrate and could find a widespread application. For example, the junction between two rubbed off layers with different mobilities exhibits a non-Ohmic behavior. I-V characteristic of the junction is symmetrically curved with respect to 0 V. The greater is the difference between the carrier mobility, the higher is the curvature. The dynamic accumulation of the carriers in both sides of the junction creates a barrier responsible for non-Ohmic behavior.

Nanoscale deicing by molecular dynamics simulation.

PubMed

Xiao, Senbo; He, Jianying; Zhang, Zhiliang

2016-08-14

Deicing is important to human activities in low-temperature circumstances, and is critical for combating the damage caused by excessive accumulation of ice. The aim of creating anti-icing materials, surfaces and applications relies on the understanding of fundamental nanoscale ice adhesion mechanics. Here in this study, we employ all-atom modeling and molecular dynamics simulation to investigate ice adhesion. We apply force to detach and shear nano-sized ice cubes for probing the determinants of atomistic adhesion mechanics, and at the same time investigate the mechanical effect of a sandwiched aqueous water layer between ice and substrates. We observe that high interfacial energy restricts ice mobility and increases both ice detaching and shearing stresses. We quantify up to a 60% decrease in ice adhesion strength by an aqueous water layer, and provide atomistic details that support previous experimental studies. Our results contribute quantitative comparison of nanoscale adhesion strength of ice on hydrophobic and hydrophilic surfaces, and supply for the first time theoretical references for understanding the mechanics at the atomistic origins of macroscale ice adhesion.

Deposition of Fibrinogen on the Surface of in vitro Thrombi Prevents Platelet Adhesion

PubMed Central

Owaynat, Hadil; Yermolenko, Ivan S.; Turaga, Ramya; Lishko, Valeryi K.; Sheller, Michael R.; Ugarova, Tatiana P.

2015-01-01

The initial accumulation of platelets after vessel injury is followed by thrombin-mediated generation of fibrin which is deposited around the plug. While numerous in vitro studies have shown that fibrin is highly adhesive for platelets, the surface of experimental thrombi in vivo contains very few platelets suggesting the existence of natural anti-adhesive mechanisms protecting stabilized thrombi from platelet accumulation and continuous thrombus propagation. We previously showed that adsorption of fibrinogen on pure fibrin clots results in the formation of a nonadhesive matrix, highlighting a possible role of this process in surface-mediated control of thrombus growth. However, the deposition of fibrinogen on the surface of blood clots has not been examined. In this study, we investigated the presence of intact fibrinogen on the surface of fibrin-rich thrombi generated from flowing blood and determined whether deposited fibrinogen is nonadhesive for platelets. Stabilized fibrin-rich thrombi were generated using a flow chamber and the time that platelets spend on the surface of thrombi was determined by video recording. The presence of fibrinogen and fibrin on the surface of thrombi was analyzed by confocal microscopy using specific antibodies. Examination of the spatial distribution of two proteins revealed the presence of intact fibrinogen on the surface of stabilized thrombi. By manipulating the surface of thrombi to display either fibrin or intact fibrinogen, we found that platelets adhere to fibrin- but not to fibrinogen-coated thrombi. These results indicate that the fibrinogen matrix assembled on the outer layer of stabilized in vitro thrombi protects them from platelet adhesion. PMID:26482763

Deposition of fibrinogen on the surface of in vitro thrombi prevents platelet adhesion.

PubMed

Owaynat, Hadil; Yermolenko, Ivan S; Turaga, Ramya; Lishko, Valeryi K; Sheller, Michael R; Ugarova, Tatiana P

2015-12-01

The initial accumulation of platelets after vessel injury is followed by thrombin-mediated generation of fibrin which is deposited around the plug. While numerous in vitro studies have shown that fibrin is highly adhesive for platelets, the surface of experimental thrombi in vivo contains very few platelets suggesting the existence of natural anti-adhesive mechanisms protecting stabilized thrombi from platelet accumulation and continuous thrombus propagation. We previously showed that adsorption of fibrinogen on pure fibrin clots results in the formation of a nonadhesive matrix, highlighting a possible role of this process in surface-mediated control of thrombus growth. However, the deposition of fibrinogen on the surface of blood clots has not been examined. In this study, we investigated the presence of intact fibrinogen on the surface of fibrin-rich thrombi generated from flowing blood and determined whether deposited fibrinogen is nonadhesive for platelets. Stabilized fibrin-rich thrombi were generated using a flow chamber and the time that platelets spend on the surface of thrombi was determined by video recording. The presence of fibrinogen and fibrin on the surface of thrombi was analyzed by confocal microscopy using specific antibodies. Examination of the spatial distribution of two proteins revealed the presence of intact fibrinogen on the surface of stabilized thrombi. By manipulating the surface of thrombi to display either fibrin or intact fibrinogen, we found that platelets adhere to fibrin- but not to fibrinogen-coated thrombi. These results indicate that the fibrinogen matrix assembled on the outer layer of stabilized in vitro thrombi protects them from platelet adhesion. Copyright © 2015 Elsevier Ltd. All rights reserved.

Influence of pulse repetition rate on percussion drilling of Ti-based alloy by picosecond laser pulses

NASA Astrophysics Data System (ADS)

Kononenko, Taras V.; Freitag, Christian; Sovyk, Dmitry N.; Lukhter, Alexander B.; Skvortsov, Konstantin V.; Konov, Vitaly I.

2018-04-01

Percussion drilling of a Ti-based alloy with 8 ps laser pulses was investigated with emphasis on the influence of the pulse repetition rate (1-300 kHz) on the drilling process. Heat accumulation is found to be responsible for simultaneous significant rise of the average drilling rate, the occurrence of a rim around the hole entrance, as well as noticeable surface oxidation. This can be observed as soon as the repetition rate exceeds a certain critical value, which depends on the pulse energy applied. Dramatic rise of the recast layer thickness inside the growing hole was revealed for the limited range of the repetition rates around the lower boundary of the heat accumulation regime. Possible origins of this phenomenon are discussed.

Investigations into the climate of the South Pole

NASA Astrophysics Data System (ADS)

Town, Michael S.

Four investigations into the climate of the South Pole are presented. The general subjects of polar cloud cover, the surface energy balance in a stable boundary layer, subsurface energy transfer in snow, and modification of water stable isotopes in snow after deposition are investigated based on the historical data set from the South Pole. Clouds over the South Pole. A new, accurate cloud fraction time series is developed based on downwelling infrared radiation measurements taken at the South Pole. The results are compared to cloud fraction estimates from visual observations and satellite retrievals of cloud fraction. Visual observers are found to underestimate monthly mean cloud fraction by as much as 20% during the winter, and satellite retrievals of cloud fraction are not accurate for operational or climatic purposes. We find associations of monthly mean cloud fraction with other meteorological variables at the South Pole for use in testing models of polar weather and climate. Surface energy balance. A re-examination of the surface energy balance at the South Pole is motivated by large discrepancies in the literature. We are not able to find closure in the new surface energy balance, likely due to weaknesses in the turbulent heat flux parameterizations in extremely stable boundary layers. These results will be useful for constraining our understanding and parameterization of stable boundary layers. Subsurface energy transfer. A finite-volume model of the snow is used to simulate nine years of near-surface snow temperatures, heating rates, and vapor pressures at the South Pole. We generate statistics characterizing heat and vapor transfer in the snow on submonthly to interannual time scales. The variability of near-surface snow temperatures on submonthly time scales is large, and has potential implications for revising the interpretation of paleoclimate records of water stable isotopes in polar snow. Modification of water stable isotopes after deposition. The evolution of water stable isotopes in near-surface polar snow is simulated using a Rayleigh fractionation model including the processes of pore-space diffusion, forced ventilation, and intra-ice-grain diffusion. We find isotopic enrichment of winter snow during subsequent summers as enriched water vapor is forced into the snow and deposits as frost. This process depends on snow and atmospheric temperatures, surface wind speed, accumulation rate, and surface morphology. We further find that differential enrichment between the present day and the Last Glacial Maximum (LGM) may exaggerate the greenlandic glacial-interglacial temperature difference derived from water stable isotopes. In Antarctica, present-day post-depositional modification is likely equal to that of the LGM due to the compensating factors of lower temperatures and lower accumulation rate during the LGM.

Continuous and Episodic Modern Sediment Accumulation on Monterey Fan: Evidence from Ddt, 137Cs and Excess 210Pb

NASA Astrophysics Data System (ADS)

Gwiazda, R.; Paull, C. K.; Alexander, C. R.; Ussler, W.

2012-12-01

The mode and magnitude of fine-grained sediment accumulation on the Monterey Fan off the California central coast was investigated using pesticide concentrations and radioactive tracer profiles in sediment cores. DDT is a man-made pesticide that was used extensively in central California between 1945 and 1970. As such, its presence in marine sediments is a telltale sign of a modern sedimentation age. DDT and its metabolites, DDE and DDD, (collectively referred to as DDTr) were measured in fifty-five ~20cm-long sediment cores collected from the surface of the Monterey Fan up to 250 km to the south and 210 km to the west of the Monterey Canyon head, and in four transects across the Monterey Canyon channel at maximum water depths of 3160, 3380, 3580, and 3880 meters. Profiles of excess 210Pb (210Pbxs) and 137Cs were measured in 5 cores from the Fan to estimate recent sedimentation rates. Detectable levels of DDTr were observed in all but one of these cores, with DDTr concentrations characteristically highest at the surface and decreasing with depth. The area-normalized and depth-integrated DDTr content measured in all the cores in the Fan and in the deepest two channel transects was geographically fairly homogenous, with no statistical relationship between DDTr inventory and distance from the main channel crossing the Fan. The total sediment mass deposited on the Fan over the last 60 years, inferred from the total inventory of DDTr present in the area surveyed, is consistent with the amount of sediment delivered by the Salinas River over the same time period. 210Pbxs activities are fairly homogeneous within an uppermost layer of variable thickness (4.6-8cm) and decrease exponentially below it, but these exponential decreases are often interrupted by horizons with constant or increased 210Pbxs activity. Moreover, the coexistence of variable DDTr concentrations with homogeneous 210Pbxs activities in the top sediment indicates that the uniformity of 210Pbxs is not due primarily to bioturbation but rather the result of deposition of thick layers with constant 210Pbxs. These data indicate that fine-grained sedimentation on the Monterrey Fan appears to have a dual modality consisting of sustained slow accumulation at a modest rate during quiescent periods interrupted by episodes of rapid accumulation during discrete events. Median sedimentation rates during quiescent periods are 0.07 cm yr-1, but over the 110 year period of detectable 210Pbxs, which includes both slow continuous sedimentation and rapid accumulation events, the median overall sedimentation rate, calculated from the deepest detectable 210Pbxs samples, is 0.19 cm yr-1. On a per mass basis, sedimentation on the Fan has been equally divided between periods of continual slow accumulation and episodes of fast accumulation. The rapidly deposited layers on the Monterey Fan are inferred to result from the injection of fluvial sediments onto the Fan during episodic and exceptionally large floods of the Salinas River.

A uniform doping ultra-thin SOI LDMOS with accumulation-mode extended gate and back-side etching technology

NASA Astrophysics Data System (ADS)

Yan-Hui, Zhang; Jie, Wei; Chao, Yin; Qiao, Tan; Jian-Ping, Liu; Peng-Cheng, Li; Xiao-Rong, Luo

2016-02-01

A uniform doping ultra-thin silicon-on-insulator (SOI) lateral-double-diffused metal-oxide-semiconductor (LDMOS) with low specific on-resistance (Ron,sp) and high breakdown voltage (BV) is proposed and its mechanism is investigated. The proposed LDMOS features an accumulation-mode extended gate (AG) and back-side etching (BE). The extended gate consists of a P- region and two diodes in series. In the on-state with VGD > 0, an electron accumulation layer is formed along the drift region surface under the AG. It provides an ultra-low resistance current path along the whole drift region surface and thus the novel device obtains a low temperature distribution. The Ron,sp is nearly independent of the doping concentration of the drift region. In the off-state, the AG not only modulates the surface electric field distribution and improves the BV, but also brings in a charge compensation effect to further reduce the Ron,sp. Moreover, the BE avoids vertical premature breakdown to obtain high BV and allows a uniform doping in the drift region, which avoids the variable lateral doping (VLD) and the “hot-spot” caused by the VLD. Compared with the VLD SOI LDMOS, the proposed device simultaneously reduces the Ron,sp by 70.2% and increases the BV from 776 V to 818 V. Project supported by the National Natural Science Foundation of China (Grant Nos. 61176069 and 61376079).

IMPACT OF PARTICLE AGGLOMERATION ON ACCUMULATION RATES IN THE GLASS DISCHARGE RISER OF HLW MELTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matyas, Josef; Jansik, Danielle P.; Owen, Antionette T.

2013-08-05

The major factor limiting waste loading in continuous high-level radioactive waste (HLW) melters is an accumulation of particles in the glass discharge riser during a frequent and periodic idling of more than 20 days. An excessive accumulation can produce robust layers a few centimeters thick, which may clog the riser, preventing molten glass from being poured into canisters. Since the accumulation rate is driven by the size of particles we investigated with X-ray microtomography, scanning electron microscopy, and image analysis the impact of spinel forming components, noble metals, and alumina on the size, concentration, and spatial distribution of particles, andmore » on the accumulation rate. Increased concentrations of Fe and Ni in the baseline glass resulted in the formation of large agglomerates that grew over the time to an average size of ~185±155 µm, and produced >3 mm thick layer after 120 h at 850 °C. The noble metals decreased the particle size, and therefore significantly slowed down the accumulation rate. Addition of alumina resulted in the formation of a network of spinel dendrites which prevented accumulation of particles into compact layers.« less

Impact Of Particle Agglomeration On Accumulation Rates In The Glass Discharge Riser Of HLW Melter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kruger, A. A.; Rodriguez, C. A.; Matyas, J.

2012-11-12

The major factor limiting waste loading in continuous high-level radioactive waste (HLW) melters is an accumulation of particles in the glass discharge riser during a frequent and periodic idling of more than 20 days. An excessive accumulation can produce robust layers a few centimeters thick, which may clog the riser, preventing molten glass from being poured into canisters. Since the accumulation rate is driven by the size of particles we investigated with x-ray microtomography, scanning electron microscopy, and image analysis the impact of spinel forming components, noble metals, and alumina on the size, concentration, and spatial distribution of particles, andmore » on the accumulation rate. Increased concentrations of Fe and Ni in the baseline glass resulted in the formation of large agglomerates that grew over the time to an average size of ~185+-155 {mu}m, and produced >3 mm thick layer after 120 h at 850 deg C. The noble metals decreased the particle size, and therefore significantly slowed down the accumulation rate. Addition of alumina resulted in the formation of a network of spinel dendrites which prevented accumulation of particles into compact layers.« less

Measured Two-Dimensional Ice-Wedge Polygon Thermal and Active Layer Dynamics

NASA Astrophysics Data System (ADS)

Cable, W.; Romanovsky, V. E.; Busey, R.

2016-12-01

Ice-wedge polygons are perhaps the most dominant permafrost related features in the arctic landscape. The microtopography of these features, that includes rims, troughs, and high and low polygon centers, alters the local hydrology. During winter, wind redistribution of snow leads to an increased snowpack depth in the low areas, while the slightly higher areas often have very thin snow cover, leading to differences across the landscape in vegetation communities and soil moisture between higher and lower areas. To investigate the effect of microtopographic caused variation in surface conditions on the ground thermal regime, we established temperature transects, composed of five vertical array thermistor probes (VATP), across four different development stages of ice-wedge polygons near Barrow, Alaska. Each VATP had 16 thermistors from the surface to a depth of 1.5 m, for a total of 80 temperature measurements per polygon. We found snow cover, timing and depth, and active layer soil moisture to be major controlling factors in the observed thermal regimes. In troughs and in the centers of low-centered polygons, the combined effect of typically saturated soils and increased snow accumulation resulted in the highest mean annual ground temperatures (MAGT) and latest freezeback dates. While the centers of high-centered polygons, with thinner snow cover and a dryer active layer, had the lowest MAGT, earliest freezeback dates, and shallowest active layer. Refreezing of the active layer initiated at nearly the same time for all locations and polygons however, we found large differences in the proportion of downward versus upward freezing and the length of time required to complete the refreezing process between polygon types and locations. Using our four polygon stages as a space for time substitution, we conclude that ice-wedge degradation resulting in surface subsidence and trough deepening can lead to overall drying of the active layer and increased skewedness of snow distribution. Which in turn leads to shallower active layers, earlier freezeback dates, and lower MAGT. We also find that the large variation in active layer dynamics (active layer depth, downward vs upward freezing, and freezeback date) are important considerations to understanding and scaling biological processes occurring in these landscapes.

Prescribed fire experiences on crop residue removal for biomass exploitations. Application to the maritime pine forests in the Mediterranean Basin.

PubMed

Molina, Juan Ramón; García, Juan Pedro; Fernández, Juan José; Rodríguez Y Silva, Francisco

2018-01-15

Socioeconomic changes, climate change, rural migration and fire exclusion have led to a high woody biomass accumulation increasing potential wildfire severity. Mechanical thinning and prescribed burning practices are commonly used to prevent large fires. The purpose of this study was to assess burning treatment effectiveness following mechanical thinning from biomass harvesting. Prescribed burning to reduce residue removal could help mitigate fire behavior, mainly in strategic management or critical focal points. Field samplings were conducted before and immediately after burnings on different environmental scenarios where fuel load was classified by categories. Prescribed fires reduced available fuel in all fuel categories, mainly in surface litter layer. Total fuel load reduction ranged from 59.07% to 86.18%. In this sense, fuel reduction effects were more pronounced when burns were conducted fewer than 10% on surface litter moisture. The difference in fuel consumption among scenarios was higher for most all woody fuel components and decomposition litter layer than for surface litter layer. Managers can use this information to design technical prescription to achieve the targets while decomposed litter retention maintaining the soil properties and biodiversity. Understanding the most effective "burn window" should help better plan prescribed burning, both in term of fire behavior and fuel consumption, without altering ecosystem properties. Copyright © 2017 Elsevier B.V. All rights reserved.

Novel photoswitchable dielectric properties on nanomaterials of electronic core-shell γ-FeOx@Au@fullerosomes for GHz frequency applications.

PubMed

Wang, Min; Su, Chefu; Yu, Tzuyang; Tan, Loon-Seng; Hu, Bin; Urbas, Augustine; Chiang, Long Y

2016-03-28

We unexpectedly observed a large amplification of the dielectric properties associated with the photoswitching effect and the new unusual phenomenon of delayed photoinduced capacitor-like (i.e. electric polarization) behavior at the interface on samples of three-layered core-shell (γ-FeOx@AuNP)@[C60(>DPAF-C9)](n)2 nanoparticles (NPs) in frequencies of 0.5-4.0 GHz. The detected relative dielectric constant amplification was initiated upon switching off the light followed by relaxation to give an excellent recyclability. These NPs having e(-)-polarizable fullerosomic structures located at the outer layer were fabricated from highly magnetic core-shell γ-FeOx@AuNPs. Surface-stabilized 2 in a core-shell structure was found to be capable of photoinducing the surface plasmonic resonance (SPR) effect by white LED light. The accumulated SPR energy was subsequently transferred to the partially bilayered C60(>DPAF-C9) fullerosomic membrane layer in a near-field (∼1.5 nm) region without producing radiation heat. Since the monostatic SAR signal is dielectric property-dependent, we used these measurements to provide evidence of derived reflectivity changes on a surface coated with 2 at 0.5-4.0 GHz upon illumination of LED white light. We found that a high, >99%, efficiency of response amplification in image amplitude can be achieved.

Surfactant effect of gallium during molecular-beam epitaxy of GaN on AlN (0001)

NASA Astrophysics Data System (ADS)

Mula, Guido; Adelmann, C.; Moehl, S.; Oullier, J.; Daudin, B.

2001-11-01

We study the adsorption of Ga on (0001) GaN surfaces by reflection high-energy electron diffraction. It is shown that a dynamically stable Ga bilayer can be formed on the GaN surface for appropriate Ga fluxes and substrate temperatures. The influence of the presence of this Ga film on the growth mode of GaN on AlN(0001) by plasma-assisted molecular-beam epitaxy is studied. It is demonstrated that under nearly stoichiometric and N-rich conditions, the GaN layer relaxes elastically during the first stages of epitaxy. At high temperatures the growth follows a Stranski-Krastanov mode, whereas at lower temperatures kinetically formed flat platelets are observed. Under Ga-rich conditions-where a Ga bilayer is rapidly formed due to excess Ga accumulating on the surface-the growth follows a Frank-van der Merwe layer-by-layer mode at any growth temperature and no initial elastic relaxation occurs. Hence, it is concluded that excess Ga acts as a surfactant, effectively suppressing both Stranski-Krastanov islanding and platelet formation. It is further demonstrated that the Stranski-Krastanov transition is in competition with elastic relaxation by platelets, and it is only observed when relaxation by platelets is inefficient. As a result, a growth mode phase diagram is outlined for the growth of GaN on AlN(0001).

Recrystallization texture in nickel heavily deformed by accumulative roll bonding

NASA Astrophysics Data System (ADS)

Mishin, O. V.; Zhang, Y. B.; Godfrey, A.

2017-07-01

The recrystallization behavior of Ni processed by accumulative roll bonding to a total accumulated von Mises strain of 4.8 has been examined, and analyzed with respect to heterogeneity in the deformation microstructure. The regions near the bonding interface are found to be more refined and contain particle deformation zones around fragments of the steel wire brush used to prepare the surface for bonding. Sample-scale gradients are also observed, manifested as differences between the subsurface, intermediate and central layers, where the distributions of texture components are different. These heterogeneities affect the progress of recrystallization. While the subsurface and near-interface regions typically contain lower frequencies of cube-oriented grains than anywhere else in the sample, a strong cube texture forms in the sample during recrystallization, attributed to both a high nucleation rate and fast growth rate of cube-oriented grains. The observations highlight the sensitivity of recrystallization to heterogeneity in the deformation microstructure and demonstrate the importance of characterizing this heterogeneity over several length scales.

The relative contribution of near-bed vs. intragravel horizontal transport to fine sediment accumulation processes in river gravel beds

NASA Astrophysics Data System (ADS)

Casas-Mulet, Roser; Lakhanpal, Garima; Stewardson, Michael J.

2018-02-01

Understanding flow-sediment interactions is important for comprehending river functioning. Fine sediment accumulation processes, in particular, have key implications for ecosystem health. However, the amount of fines generated by intragravel flows and later accumulated in gravel streambeds may have been underestimated, as the hydraulic-related driving transport mechanisms in play are not clearly identified. Specifically, the relative contribution of fines from upper vs. lower sediment layers in gravel beds is not well understood. By recreating flooded and dewatered conditions in an experimental flume filled with natural sediment, we estimated such contributions by observing and collecting intragravel transported fines that were later accumulated into a void in the middle of the sediment matrix. Near-bed transport in the upper sediment layers (named Brinkman load) during flooded conditions accounted for most (90%) of the accumulated fines. Intragravel transport in the lower sediment layers (named Interstitial load) was the sole source of transport and accumulation during dewatered conditions with steeper hydraulic gradients. Interstitial load accounted for 10% of the total transport during flooded conditions. Although small, such estimations demonstrate that hydraulic-gradient transport in the lower sediment layers occurs in spite of the contradicting analytical assessments. We provide a case study to challenge the traditional approaches of assessing intragravel transport, and a useful framework to understand the origin and relative contribution of fine sediment accumulation in gravel beds. Such knowledge will be highly useful for the design of monitoring programs aiding river management, particularly in regulated rivers.

Greenland annual accumulation along the EGIG line, 1959-2004, from ASIRAS airborne radar and neutron-probe density measurements

NASA Astrophysics Data System (ADS)

Overly, Thomas B.; Hawley, Robert L.; Helm, Veit; Morris, Elizabeth M.; Chaudhary, Rohan N.

2016-08-01

We report annual snow accumulation rates from 1959 to 2004 along a 250 km segment of the Expéditions Glaciologiques Internationales au Groenland (EGIG) line across central Greenland using Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) radar layers and high resolution neutron-probe (NP) density profiles. ASIRAS-NP-derived accumulation rates are not statistically different (95 % confidence interval) from in situ EGIG accumulation measurements from 1985 to 2004. ASIRAS-NP-derived accumulation increases by 20 % below 3000 m elevation, and increases by 13 % above 3000 m elevation for the period 1995 to 2004 compared to 1985 to 1994. Three Regional Climate Models (PolarMM5, RACMO2.3, MAR) underestimate snow accumulation below 3000 m by 16-20 % compared to ASIRAS-NP from 1985 to 2004. We test radar-derived accumulation rates sensitivity to density using modeled density profiles in place of NP densities. ASIRAS radar layers combined with Herron and Langway (1980) model density profiles (ASIRAS-HL) produce accumulation rates within 3.5 % of ASIRAS-NP estimates in the dry snow region. We suggest using Herron and Langway (1980) density profiles to calibrate radar layers detected in dry snow regions of ice sheets lacking detailed in situ density measurements, such as those observed by the Operation IceBridge campaign.

Historical CO2 Records from the Law Dome DE08, DE08-2, and DSS Ice Cores (1006 A.D.-1978 A.D)

DOE Data Explorer

Etheridge, D. M. [Commonwealth Scientific and Industrial Research Organization (CSIRO), Aspendale, Australia; Barnola, J. M. [Laboratoire de Glaciologie et Géophysique de l'Environnement, Saint Martin d'Hères-Cedex, France; Morgan, V. I. [Antarctic CRC and Australian Antarctic Division, Hobart, Tasmania, Australia; Steele, L. P. [Commonwealth Scientific and Industrial Research Organization (CSIRO), Aspendale, Australia; Langenfelds, R. L. [Commonwealth Scientific and Industrial Research Organization (CSIRO), Aspendale, Australia; Francey, R. J. [Commonwealth Scientific and Industrial Research Organization (CSIRO), Aspendale, Australia; Martinez, Monica [Oak Ridge National Laboratory, Oak Ridge, TN (USA)

1998-01-01

The CO2 records presented here are derived from three ice cores obtained at Law Dome, East Antarctica from 1987 to 1993. The Law Dome site satisfies many of the desirable characteristics of an ideal ice core site for atmospheric CO2 reconstructions including negligible melting of the ice sheet surface, low concentrations of impurities, regular stratigraphic layering undisturbed at the surface by wind or at depth by ice flow, and high snow accumulation rate. Further details on the site, drilling, and cores are provided in Etheridge et al. (1996), Etheridge and Wookey (1989), and Morgan et al (1997).

Orbital observations of the lunar highlands on Apollo 16 and their interpretation

NASA Technical Reports Server (NTRS)

Mattingly, T. K.; El-Baz, F.

1973-01-01

From orbital altitudes, the lunar highlands display the same surface characteristics on both the far and near sides. Rugged terra and plains forming materials all appear as if dusted with a uniform mantle. No stratigraphy or evidence of layering are seen in highland craters, with the possible exception of South Ray Crater in the Descartes landing site area. Among the discussed small scale features of the lunar highlands are: fine lineaments, that appear to be real rather than artifacts of lighting, on both horizontal and inclined surfaces; ridge-like scarps that cut across highland topography; and benches that are believed to be high lava marks rather than talus accumulates.

The boron implantation in the varied zone MBE MCT epilayer

NASA Astrophysics Data System (ADS)

Voitsekhovskii, Alexander V.; Grigor'ev, Denis V.; Kokhanenko, Andrey P.; Korotaev, Alexander G.; Sidorov, Yuriy G.; Varavin, Vasiliy S.; Dvoretsky, Sergey A.; Mikhailov, Nicolay N.; Talipov, Niyaz Kh.

2005-09-01

In the paper experimental results on boron implantation of the CdxHg1-xTe epilayers with various composition near surface of the material are discussed. The electron concentration in the surface layer after irradiation vs irradiation dose and ion energy are investigated for range of doses 1011 - 3•1015 cm-2 and energies of 20 - 150 keV. Also the results of the electrical active defects distribution measurement, carried out by differential Hall method, after boron implantation are represented. Consideration of the received data shows, that composition gradient influence mainly on the various dynamics of accumulation of electric active radiation defects. The electric active defects distribution analysis shows, that the other factors are negligible.

Predicting Glucose Sensor Behavior in Blood Using Transport Modeling: Relative Impacts of Protein Biofouling and Cellular Metabolic Effects

PubMed Central

Novak, Matthew T.; Yuan, Fan; Reichert, William M.

2013-01-01

Background Tissue response to indwelling glucose sensors remains a confounding barrier to clinical application. While the effects of fully formed capsular tissue on sensor response have been studied, little has been done to understand how tissue interactions occurring before capsule formation hinder sensor performance. Upon insertion in subcutaneous tissue, the sensor is initially exposed to blood, blood borne constituents, and interstitial fluid. Using human whole blood as a simple ex vivo experimental system, the effects of protein accumulation at the sensor surface (biofouling effects) and cellular consumption of glucose in both the biofouling layer and in the bulk (metabolic effects) on sensor response were assessed. Methods Medtronic MiniMed SofSensor glucose sensors were incubated in whole blood, plasma-diluted whole blood, and cell-free platelet-poor plasma (PPP) to analyze the impact of different blood constituents on sensor function. Experimental conditions were then simulated using MATLAB to predict the relative impacts of biofouling and metabolic effects on the observed sensor responses. Results Protein biofouling in PPP in both the experiments and the simulations was found to have no interfering effect upon sensor response. Experimental results obtained with whole and dilute blood showed that the sensor response was markedly affected by blood borne glucose-consuming cells accumulated in the biofouling layer and in the surrounding bulk. Conclusions The physical barrier to glucose transport presented by protein biofouling does not hinder glucose movement to the sensor surface, and the consumption of glucose by inflammatory cells, and not erythrocytes, proximal to the sensor surface has a substantial effect on sensor response and may be the main culprit for anomalous sensor behavior immediately following implantation. PMID:24351181

Study of the water transportation characteristics of marsh saline soil in the Yellow River Delta.

PubMed

He, Fuhong; Pan, Yinghua; Tan, Lili; Zhang, Zhenhua; Li, Peng; Liu, Jia; Ji, Shuxin; Qin, Zhaohua; Shao, Hongbo; Song, Xueyan

2017-01-01

One-dimensional soil column water infiltration and capillary adsorption water tests were conducted in the laboratory to study the water transportation characteristics of marsh saline soil in the Yellow River Delta, providing a theoretical basis for the improvement, utilization and conservation of marsh saline soil. The results indicated the following: (1) For soils with different vegetation covers, the cumulative infiltration capacity increased with the depth of the soil layers. The initial infiltration rate of soils covered by Suaeda and Tamarix chinensis increased with depth of the soil layers, but that of bare soil decreased with soil depth. (2) The initial rate of capillary rise of soils with different vegetation covers showed an increasing trend from the surface toward the deeper layers, but this pattern with respect to soil depth was relatively weak. (3) The initial rates of capillary rise were lower than the initial infiltration rates, but infiltration rate decreased more rapidly than capillary water adsorption rate. (4) The two-parameter Kostiakov model can very well-simulate the changes in the infiltration and capillary rise rates of wetland saline soil. The model simulated the capillary rise rate better than it simulated the infiltration rate. (5) There were strong linear relationships between accumulative infiltration capacity, wetting front, accumulative capillary adsorbed water volume and capillary height. Copyright © 2016 Elsevier B.V. All rights reserved.

Methanol electro-oxidation on platinum modified tungsten carbides in direct methanol fuel cells: a DFT study.

PubMed

Sheng, Tian; Lin, Xiao; Chen, Zhao-Yang; Hu, P; Sun, Shi-Gang; Chu, You-Qun; Ma, Chun-An; Lin, Wen-Feng

2015-10-14

In exploration of low-cost electrocatalysts for direct methanol fuel cells (DMFCs), Pt modified tungsten carbide (WC) materials are found to be great potential candidates for decreasing Pt usage whilst exhibiting satisfactory reactivity. In this work, the mechanisms, onset potentials and activity for electrooxidation of methanol were studied on a series of Pt-modified WC catalysts where the bare W-terminated WC(0001) substrate was employed. In the surface energy calculations of a series of Pt-modified WC models, we found that the feasible structures are mono- and bi-layer Pt-modified WCs. The tri-layer Pt-modified WC model is not thermodynamically stable where the top layer Pt atoms tend to accumulate and form particles or clusters rather than being dispersed as a layer. We further calculated the mechanisms of methanol oxidation on the feasible models via methanol dehydrogenation to CO involving C-H and O-H bonds dissociating subsequently, and further CO oxidation with the C-O bond association. The onset potentials for the oxidation reactions over the Pt-modified WC catalysts were determined thermodynamically by water dissociation to surface OH* species. The activities of these Pt-modified WC catalysts were estimated from the calculated kinetic data. It has been found that the bi-layer Pt-modified WC catalysts may provide a good reactivity and an onset oxidation potential comparable to pure Pt and serve as promising electrocatalysts for DMFCs with a significant decrease in Pt usage.

Extraction of Ice Sheet Layers from Two Intersected Radar Echograms Near Neem Ice Core in Greenland

NASA Astrophysics Data System (ADS)

Xiong, S.; Muller, J.-P.

2016-06-01

Accumulation of snow and ice over time result in ice sheet layers. These can be remotely sensed where there is a contrast in electromagnetic properties, which reflect variations of the ice density, acidity and fabric orientation. Internal ice layers are assumed to be isochronous, deep beneath the ice surface, and parallel to the direction of ice flow. The distribution of internal layers is related to ice sheet dynamics, such as the basal melt rate, basal elevation variation and changes in ice flow mode, which are important parameters to model the ice sheet. Radar echo sounder is an effective instrument used to study the sedimentology of the Earth and planets. Ice Penetrating Radar (IPR) is specific kind of radar echo sounder, which extends studies of ice sheets from surface to subsurface to deep internal ice sheets depending on the frequency utilised. In this study, we examine a study site where folded ice occurs in the internal ice sheet south of the North Greenland Eemian ice drilling (NEEM) station, where two intersected radar echograms acquired by the Multi-channel Coherent Radar Depth Sounder (MCoRDS) employed in the NASA's Operation IceBridge (OIB) mission imaged this folded ice. We propose a slice processing flow based on a Radon Transform to trace and extract these two sets of curved ice sheet layers, which can then be viewed in 3-D, demonstrating the 3-D structure of the ice folds.

Modern Deposition Rates and Patterns of Carbon Burial in Southern Fiordland, New Zealand

NASA Astrophysics Data System (ADS)

Ramirez, M. T.; Allison, M. A.; Vetter, L.; Cui, X.; Bianchi, T. S.; Smith, R. W.; Savage, C.; Schüller, S.

2016-02-01

Fjords have been recognized as a hotspot of organic carbon burial, as they accumulate a disproportionate quantity of organic carbon given their areal extent in comparison to other marine settings. However, organic carbon is buried in context with other biogenic and mineral sediments, so localized sedimentation processes play a critical role in determining rates of organic carbon burial. Therefore, it is important to assess the local sources and processes responsible for depositing inorganic sediment as a control on the burial of organic carbon. Here we evaluate three fjords in southern New Zealand that are not glaciated, with a sedimentary system that is dominantly controlled by terrigenous input at fjord heads, reworking of sediments over fjord-mouth sills, and landslide events from the steep fjord walls. Sediment cores were collected throughout the three southernmost fjord systems of Fiordland, New Zealand, and analyzed to determine sedimentary fabric, mass accumulation rates, and organic carbon content. Sediment mass accumulation rates from 210Pb geochronology range up to 500 mg/cm2/yr in proximal and distal areas of the fjords, with lower rates (below 200 mg/cm2/yr) in medial reaches, where terrestrial and marine sediment input is minimal. X-radiographs and 210Pb downcore activity trends show evidence of both mass wasting and surface-sediment bioturbation operating throughout the fjords. Percent organic carbon displays a negative correlation with mass accumulation rate and thickness of the sediment surface mixed layer. Rates of organic carbon accumulation ranged from 3.97 to 21.59 mg/cm2/yr, with a mean of 13.41 mg/cm2/yr. Organic carbon accumulation rates are dependent on the sediment accumulation rate and the percent organic carbon of the sediment. Our results highlight the importance of spatial variability in sedimentation processes and rates within fjords when evaluating organic carbon burial in these systems.

ACR4, a putative receptor kinase gene of Arabidopsis thaliana, that is expressed in the outer cell layers of embryos and plants, is involved in proper embryogenesis.

PubMed

Tanaka, Hirokazu; Watanabe, Masaru; Watanabe, Daisuke; Tanaka, Toshihiro; Machida, Chiyoko; Machida, Yasunori

2002-04-01

The surfaces of higher plants are characterized by epidermis, which usually consists of a single layer of cells. The epidermis is derived from the outer cell layer of the embryo or protoderm, which arises as a result of periclinal cell division. After seed germination, most of the epidermal cells of the aerial parts of plants are derived from the outer cell layer of the shoot apical meristem (the L1 layer). Thus, knowledge of how the protoderm and/or L1 layer is established is fundamental to understanding the morphogenesis of higher plants. Here, we report the isolation of a gene encoding an Arabidopsis homologue (ACR4) of the maize putative receptor kinase CRINKLY4 (CR4), which is involved in epidermal differentiation. The domain organization of the predicted amino acid sequence of ACR4 is essentially identical to that of CR4. ACR4-GFP fusion protein localized to the cell surface when expressed in tobacco cell (BY-2) culture. ACR4 transcripts were detected in all the organs of the Arabidopsis plant. In developing embryos and shoot apices, ACR4 transcripts accumulated in protoderm and epidermis at relatively higher levels than in the inner tissues. Over-expression of antisense ACR4 in Arabidopsis plants resulted in malformation of embryos to varying degrees. These results suggest that ACR4 is, at a minimum, involved in the normal morphogenesis of embryos, most likely through properly differentiating protoderm cells.

Polychlorinated Biphenyls in a Temperate Alpine Glacier: 1. Effect of Percolating Meltwater on their Distribution in Glacier Ice.

PubMed

Pavlova, Pavlina Aneva; Jenk, Theo Manuel; Schmid, Peter; Bogdal, Christian; Steinlin, Christine; Schwikowski, Margit

2015-12-15

In Alpine regions, glaciers act as environmental archives and can accumulate significant amounts of atmospherically derived pollutants. Due to the current climate-warming-induced accelerated melting, these pollutants are being released at correspondingly higher rates. To examine the effect of melting on the redistribution of legacy pollutants in Alpine glaciers, we analyzed polychlorinated biphenyls in an ice core from the temperate Silvretta glacier, located in eastern Switzerland. This glacier is affected by surface melting in summer. As a result, liquid water percolates down and particles are enriched in the current annual surface layer. Dating the ice core was a challenge because meltwater percolation also affects the traditionally used parameters. Instead, we counted annual layers of particulate black carbon in the ice core, adding the years with negative glacier mass balance, that is, years with melting and subsequent loss of the entire annual snow accumulation. The analyzed samples cover the time period 1930-2011. The concentration of indicator PCBs (iPCBs) in the Silvretta ice core follows the emission history, peaking in the 1970s (2.5 ng/L). High PCB values in the 1990s and 1930s are attributed to meltwater-induced relocation within the glacier. The total iPCB load at the Silvretta ice core site is 5 ng/cm(2). A significant amount of the total PCB burden in the Silvretta glacier has been released to the environment.

Surface Crystallization of a MgO/Y2O3/SiO2/Al2O3/ZrO2 Glass: Growth of an Oriented β-Y2Si2O7 Layer and Epitaxial ZrO2

PubMed Central

Wisniewski, Wolfgang; Seidel, Sabrina; Patzig, Christian; Rüssel, Christian

2017-01-01

The crystallization behavior of a glass with the composition 54.7 SiO2·10.9 Al2O3·15.0 MgO·3.4 ZrO2·16.0 Y2O3 is studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD) and (scanning) transmission electron microscopy [(S)TEM] including energy-dispersive X-ray spectrometry (EDXS). This glass shows the sole surface crystallization of four different yttrium silicates of the composition Y2Si2O7 (YS). The almost simultaneous but independent nucleation of α-, β-, δ-, and ε-YS at the surface is followed by growth into the bulk, where ε-YS quickly dominates a first crystallized layer. An accumulation of Mg at the growth front probably triggers a secondary nucleation of β-YS, which forms a thin compact layer before fragmenting into a highly oriented layer of fine grained crystals occupying the remaining bulk. The residual glass between the YS growth structures allows the crystallization of indialite, yttrium stabilized ZrO2 (Y-ZrO2) and very probably μ-cordierite during cooling. Hence, this glass basically shows the inverted order of crystallization observed in other magnesium yttrium alumosilicate glasses containing less Y2O3. An epitaxial relationship between Y-ZrO2 and ε-YS is proven and multiple twinning relationships occur in the YS phases. PMID:28281661

Stability of the accumulation pattern around Dome C over the last glacial cycle

NASA Astrophysics Data System (ADS)

Cavitte, Marie; Parrenin, Frédéric; Ritz, Catherine; Blankenship, Donald; Young, Duncan; Frezzotti, Massimo; Roberts, Jason; van Ommen, Tas

2017-04-01

The "Candidate A" region, just to the south of Dome C, is one of the climate community's targets for retrieving "old ice", aiming for an ice core bottom age of 1.5 million-years. The region lies along the divide that separates the Byrd and Totten glacier catchments, and thus its position could be sensitive to differential behavior of those two systems. In the winter of 15/16, the University of Texas at Austin Institute for Geophysics (UTIG) collected a detailed airborne radar survey known as OIA (Old Ice A) (Young et al., in review). Seventeen internal radar reflections are mapped through this survey, encompassing both sides of the divide, spanning the last three glacial cycles, from 38 ka and 366 kyrs. Dates are obtained where the internal reflections intersect the EPICA Dome C ice core and the AICC20112 age-depth chronology can be transferred to each individual reflection. These internal reflections are easily traced in the OIA survey for several reasons: (1) Candidate A is a region of relatively stable ice, close to the ice divide, so very little horizontal flow has occurred and the radar reflections exhibit near-horizontal stratigraphy, (2) the gridded geometry of the survey design implies a high number of crossovers which allow regular checks on the accuracy of the reflection mapping, and supports the isochronal character of the reflections. Older airborne UTIG radar surveys in the region augment the dataset to provide constraints further away from the divide, and the same set of isochrones are traced throughout (previously published in Cavitte et al., 2016). We use a 1D inverse model (Parrenin et al., in prep) to reconstruct the patterns of paleo-accumulation through time all the way back to the penultimate interglacial (127 kyr). To do this, we first fit the isochrones' geometries and ages to invert for the steady-state accumulation rate, the basal melting rate and the p exponent in the Lliboutry flow formulation. We then reconstruct paleo-accumulation rates between each pair of isochrones by fitting the isochrone geometries exactly. Each "layer" therefore provides a map of the paleo-accumulation rate pattern for the time interval represented by the layer. We observe that the large-scale pattern of paleo-accumulation through the last 127 kyr has been consistent with today's: higher rates of accumulation to the NW of Dome C (i.e. nearer the coast) and lower rates with distance from the coast towards the SE. On smaller scales, we observe local accumulation highs, which correlate with local ice surface slope anomalies (usually reduced slopes) and remain stationary through time. We suggest that the stationary character of the paleo accumulation patterns, both regionally and locally, point to a relative stability of the ice sheet's surface geometry all the way back to the penultimate interglacial. This would imply a stable dome position throughout, and perhaps a balanced grounding line influence from the Byrd and Totten catchments.

Cellular and Pectin Dynamics during Abscission Zone Development and Ripe Fruit Abscission of the Monocot Oil Palm

PubMed Central

Roongsattham, Peerapat; Morcillo, Fabienne; Fooyontphanich, Kim; Jantasuriyarat, Chatchawan; Tragoonrung, Somvong; Amblard, Philippe; Collin, Myriam; Mouille, Gregory; Verdeil, Jean-Luc; Tranbarger, Timothy J.

2016-01-01

The oil palm (Elaeis guineensis Jacq.) fruit primary abscission zone (AZ) is a multi-cell layered boundary region between the pedicel (P) and mesocarp (M) tissues. To examine the cellular processes that occur during the development and function of the AZ cell layers, we employed multiple histological and immunohistochemical methods combined with confocal, electron and Fourier-transform infrared (FT-IR) microspectroscopy approaches. During early fruit development and differentiation of the AZ, the orientation of cell divisions in the AZ was periclinal compared with anticlinal divisions in the P and M. AZ cell wall width increased earlier during development suggesting cell wall assembly occurred more rapidly in the AZ than the adjacent P and M tissues. The developing fruit AZ contain numerous intra-AZ cell layer plasmodesmata (PD), but very few inter-AZ cell layer PD. In the AZ of ripening fruit, PD were less frequent, wider, and mainly intra-AZ cell layer localized. Furthermore, DAPI staining revealed nuclei are located adjacent to PD and are remarkably aligned within AZ layer cells, and remain aligned and intact after cell separation. The polarized accumulation of ribosomes, rough endoplasmic reticulum, mitochondria, and vesicles suggested active secretion at the tip of AZ cells occurred during development which may contribute to the striated cell wall patterns in the AZ cell layers. AZ cells accumulated intracellular pectin during development, which appear to be released and/or degraded during cell separation. The signal for the JIM5 epitope, that recognizes low methylesterified and un-methylesterified homogalacturonan (HG), increased in the AZ layer cell walls prior to separation and dramatically increased on the separated AZ cell surfaces. Finally, FT-IR microspectroscopy analysis indicated a decrease in methylesterified HG occurred in AZ cell walls during separation, which may partially explain an increase in the JIM5 epitope signal. The results obtained through a multi-imaging approach allow an integrated view of the dynamic developmental processes that occur in a multi-layered boundary AZ and provide evidence for distinct regulatory mechanisms that underlie oil palm fruit AZ development and function. PMID:27200017

Semiconductor light source with electrically tunable emission wavelength

DOEpatents

Belenky, Gregory [Port Jefferson, NY; Bruno, John D [Bowie, MD; Kisin, Mikhail V [Centereach, NY; Luryi, Serge [Setauket, NY; Shterengas, Leon [Centereach, NY; Suchalkin, Sergey [Centereach, NY; Tober, Richard L [Elkridge, MD

2011-01-25

A semiconductor light source comprises a substrate, lower and upper claddings, a waveguide region with imbedded active area, and electrical contacts to provide voltage necessary for the wavelength tuning. The active region includes single or several heterojunction periods sandwiched between charge accumulation layers. Each of the active region periods comprises higher and lower affinity semiconductor layers with type-II band alignment. The charge carrier accumulation in the charge accumulation layers results in electric field build-up and leads to the formation of generally triangular electron and hole potential wells in the higher and lower affinity layers. Nonequillibrium carriers can be created in the active region by means of electrical injection or optical pumping. The ground state energy in the triangular wells and the radiation wavelength can be tuned by changing the voltage drop across the active region.

Cell adhesion and proliferation on poly(tetrafluoroethylene) with plasma-metal and plasma-metal-carbon interfaces

NASA Astrophysics Data System (ADS)

Reznickova, Alena; Kvitek, Ondrej; Kolarova, Katerina; Smejkalova, Zuzana; Svorcik, Vaclav

2017-06-01

The aim of this article is to investigate the effect of the interface between plasma activated, gold and carbon coated poly(tetrafluoroethylene) (PTFE) on in vitro adhesion and spreading of mouse fibroblasts (L929). Surface properties of pristine and modified PTFE were studied by several experimental techniques. The thickness of a deposited gold film is an increasing function of the sputtering time, conversely thickness of carbon layer decreases with increasing distance between carbon source and the substrate. Because all the used surface modification techniques take place in inert Ar plasma, oxidized degradation products are formed on the PTFE surface, which affects wettability of the polymer surface. Cytocompatibility tests indicate that on samples with Au/C interface, the cells accumulate on the part of sample with evaporated carbon. Number of L929 cells proliferated on the studied samples is comparable to tissue culture polystyrene standard.

Charge reversal at a planar boundary between two dielectrics.

PubMed

Wang, Zhi-Yong

2016-01-01

Despite the ubiquitous character and relevance of the electric double layer in the entire realm of interface and colloid science, very little is known of the effect that surface heterogeneity exerts on the underlying mechanisms of ion adsorption. Herein, computer simulations offer a perspective that, in sharp contrast to the homogeneously charged surface, discrete groups promote multivalent counterion binding, leading to charge reversal but possibly having not a sign change of the electrophoretic mobility. Counterintuitively, the introduction of dielectric images yields a significantly greater accumulation of counterions, which further facilitates the magnitude of charge reversal. The reported results are very sensitive to both the degree of ion hydration and the representation of surface charges. Our findings shed light on the mechanism for charge reversal over a broad range of coupling regimes operating the adsorption of counterions through surface group bridging attraction with their own images and provide opportunities for experimental studies and theoretical development.

Charge reversal at a planar boundary between two dielectrics

NASA Astrophysics Data System (ADS)

Wang, Zhi-Yong

2016-01-01

Despite the ubiquitous character and relevance of the electric double layer in the entire realm of interface and colloid science, very little is known of the effect that surface heterogeneity exerts on the underlying mechanisms of ion adsorption. Herein, computer simulations offer a perspective that, in sharp contrast to the homogeneously charged surface, discrete groups promote multivalent counterion binding, leading to charge reversal but possibly having not a sign change of the electrophoretic mobility. Counterintuitively, the introduction of dielectric images yields a significantly greater accumulation of counterions, which further facilitates the magnitude of charge reversal. The reported results are very sensitive to both the degree of ion hydration and the representation of surface charges. Our findings shed light on the mechanism for charge reversal over a broad range of coupling regimes operating the adsorption of counterions through surface group bridging attraction with their own images and provide opportunities for experimental studies and theoretical development.

When sticky fluids don't stick: yield-stress fluid drops on heated surfaces

NASA Astrophysics Data System (ADS)

Blackwell, Brendan; Wu, Alex; Ewoldt, Randy

2016-11-01

Yield-stress fluids, including gels and pastes, are effectively fluid at high stress and solid at low stress. In liquid-solid impacts, these fluids can stick and accumulate where they impact; this sticky behavior motivates several applications of these rheologically-complex materials. Here we describe experiments with aqueous yield stress fluids that are more 'sticky' than water at room temperature (e.g. supporting larger coating thicknesses), but are less 'sticky' at higher temperatures. Specifically, we study the conditions for aqueous yield stress fluids to bounce and slide on heated surfaces when water sticks. Here we present high-speed imaging and color interferometry to observe the thickness of the vapor layer between the drop and the surface during both stick and non-stick events. We use these data to gain insight into the physics behind the phenomenon of the yield-stress fluids bouncing and sliding, rather than sticking, on hot surfaces.

Cavity formation and surface modeling of laser milling process under a thin-flowing water layer

NASA Astrophysics Data System (ADS)

Tangwarodomnukun, Viboon

2016-11-01

Laser milling process normally involves a number of laser scans over a workpiece to selectively remove the material and then to form cavities with shape and dimensions required. However, this process adversely causes a heat accumulation in work material, which can in turn damage the laser-milled area and vicinity in terms of recast deposition and change of material properties. Laser milling process performing in a thin-flowing water layer is a promising method that can overcome such damage. With the use of this technique, water can flush away the cut debris and at the same time cool the workpiece during the ablation. To understand the potential of this technique for milling application, the effects of process parameters on cavity dimensions and surface roughness were experimentally examined in this study. Titanium sheet was used as a workpiece to be milled by a nanosecond pulse laser under different water flow velocities. A smooth and uniform cut feature can be obtained when the metal was ablated under the high laser pulse frequency and high water flow velocity. Furthermore, a surface model based on the energy balance was developed in this study to predict the cavity profile and surface roughness. By comparing to the experiments, the predicted profiles had a good agreement with the measured ones.

A mechanism for comet surface collapse as observed by Rosetta on 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Prialnik, D.; Sierks, H.

2017-07-01

We explore a possible mechanism that may explain sudden depressions of surface areas on a comet nucleus, as suggested by observations of the Rosetta mission on comet 67P/Churyumov-Gerasimenko (hereafter, 67P/C-G). Assuming the area is covered by a thin, compact dust layer of low permeability to gas flow compared to deeper, porous layers, gas can accumulate below the surface when a surge of gas release from amorphous ice occurs upon crystallization. The gas pressure is found to exceed the hydrostatic pressure down to a depth of a few metres. The rapid build-up of pressure may weaken the already fragile, highly porous structure. Eventually, the high pressure gradient that arises drives the gas out and the pressure falls well below the hydrostatic pressure. The rapid pressure drop may result in collapse. Since the crystallization front lies at some depth below the surface, the location on the orbit when this phenomenon occurs is determined by the thermal lag, which, in turn, depends on the thermal conductivity. Numerical simulations show that mostly such activity occurs post-perihelion, but it may also occur pre-perihelion. When permeability is uniform, crystallization still causes increased gas production, but the gas pressure inside the nucleus remains below hydrostatic pressure.

Surface history of Mercury - Implications for terrestrial planets

NASA Technical Reports Server (NTRS)

Murray, B. C.; Strom, R. G.; Trask, N. J.; Gault, D. E.

1975-01-01

A plausible surface history of Mercury is presented which is suggested by Mariner 10 television pictures. Five periods are postulated which are delineated by successive variations in the modification of the surface by external and internal processes: accretion and differentiation, terminal heavy bombardment, formation of the Caloris basin, flooding of that basin and other areas, and light cratering accumulated on the smooth plains. Each period is described in detail; the overall history is compared with the surface histories of Venus, Mars, and the moon; and the implications of this history for earth are discussed. It is tentatively concluded that: Mercury is a differentiated planet most likely composed of a large iron core enclosed by a relatively thin silicate layer; heavy surface bombardment occurred about four billion years ago, which probably affected all the inner planets, and was followed by a period of volcanic activity; no surface modifications caused by tectonic, volcanic, or atmospheric processes took place after the volcanic period.

Holocene Accumulation and Ice Flow near the West Antarctic Ice Sheet Divide Ice Core Site

NASA Technical Reports Server (NTRS)

Koutnik, Michelle R.; Fudge, T.J.; Conway, Howard; Waddington, Edwin D.; Neumann, Thomas A.; Cuffey, Kurt M.; Buizert, Christo; Taylor, Kendrick C.

2016-01-01

The West Antarctic Ice Sheet Divide Core (WDC) provided a high-resolution climate record from near the Ross-Amundsen Divide in Central West Antarctica. In addition, radar-detected internal layers in the vicinity of the WDC site have been dated directly from the ice core to provide spatial variations in the age structure of the region. Using these two data sets together, we first infer a high-resolution Holocene accumulation-rate history from 9.2 thousand years of the ice-core timescale and then confirm that this climate history is consistent with internal layers upstream of the core site. Even though the WDC was drilled only 24 kilometers from the modern ice divide, advection of ice from upstream must be taken into account. We evaluate histories of accumulation rate by using a flowband model to generate internal layers that we compare to observed layers. Results show that the centennially averaged accumulation rate was over 20 percent lower than modern at 9.2 thousand years before present (B.P.), increased by 40 percent from 9.2 to 2.3 thousand years B.P., and decreased by at least 10 percent over the past 2 thousand years B.P. to the modern values; these Holocene accumulation-rate changes in Central West Antarctica are larger than changes inferred from East Antarctic ice-core records. Despite significant changes in accumulation rate, throughout the Holocene the regional accumulation pattern has likely remained similar to today, and the ice-divide position has likely remained on average within 5 kilometers of its modern position. Continent-scale ice-sheet models used for reconstructions of West Antarctic ice volume should incorporate this accumulation history.

Irradiation experiment on ZrC-coated fuel particles for high-temperature gas-cooled reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minato, Kazuo; Ogawa, Toru; Sawa, Kazuhiro

2000-06-01

The ZrC coating layer is a candidate to replace the SiC coating layer of the Triso-coated fuel particle. To compare the irradiation performance of the ZrC Triso-coated fuel particles with that of the normal Triso-coated fuel particles at high temperatures, a capsule irradiation experiment was performed, where both types of the coated fuel particles were irradiated under identical conditions. The burnup was 4.5% FIMA and the irradiation temperature was 1,400 to 1,650 C. The postirradiation measurement of the through-coating failure fractions of both types of coated fuel particles revealed better irradiation performance of the ZrC Triso-coated fuel particles. The opticalmore » microscopy and electron probe microanalysis on the polished cross section of the ZrC Triso-coated fuel particles revealed no interaction of palladium with the ZrC coating layer nor accumulation of palladium at the inner surface of the ZrC coating layer, whereas severe corrosion of the SiC coating layer was observed in the normal Triso-coated fuel particles. Although no corrosion of the ZrC coating layer was observed, additional evaluations need to be made of this layer's ability to satisfactorily retain the fission product palladium.« less

Transport and outflow to the North Atlantic in the lower marine troposphere during ICARTT 2004

NASA Astrophysics Data System (ADS)

Davis, S. R.; Talbot, R.; Mao, H.

2012-01-01

An analysis of pollution plumes emitted from sources in the Northeastern US was based on observations from the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) 2004 field campaign. Particular attention was given to the relation of these plumes to coastal transport patterns in lower tropospheric layers throughout the Gulf of Maine (GOM) and their contribution to large-scale pollution outflow from the North American continent. Using measurements obtained during a series of flights of the NOAA WP-3D and the NASA DC-8, a unique quasi-lagrangian case study was conducted for a freshly emitted plume emanating from the New York City source region in late July 2004. The initial development of this plume stemmed from the accumulation of boundary layer pollutants within a coastal residual layer where weak synoptic forcing triggered its advection by mean southwesterly flow. As the plume tracked into the GOM, analysis showed that the plume layer vertical structure evolved into an internal boundary layer form, with signatures of steep vertical gradients in temperature, moisture and wind speed often resulting in periodic turbulence. This structure remained well-defined during the plume study, allowing for the detachment of the plume layer from the surface and thus minimal deposition and plume-sea surface exchange. In contrast, lateral mixing with other low-level plumes was significant during its transit and facilitated in part by persistent shear driven turbulence which further contributed to the high spatial variability in trace gas mixing ratios. The impact of the plume inland was assessed using observations from the AIRMAP air quality network. This impact was noticeably detected as a contribution to poor surface ozone conditions and significant elevations of other major pollutants to levels equaling the highest observed that summer. Further contributions to larger-scale outflow across the North Atlantic was also observed and analyzed.

An Ideal Electrode Material, 3D Surface-Microporous Graphene for Supercapacitors with Ultrahigh Areal Capacitance

DOE PAGES

Chang, Liang; Stacchiola, Dario J.; Hu, Yun Hang

2017-07-03

The efficient charge accumulation of an ideal supercapacitor electrode requires abundant micropores and its fast electrolyte-ions transport prefers meso/macropores. But, current electrode materials cannot meet both requirements, resulting in poor performance. We creatively constructed three-dimensional cabbage-coral-like graphene as an ideal electrode material, in which meso/macro channels are formed by graphene walls and rich micropores are incorporated in the surface layer of the graphene walls. The unique 3D graphene material can achieve a high gravimetric capacitance of 200 F/g with aqueous electrolyte, 3 times larger than that of commercially used activated carbon (70.8 F/g). Furthermore, it can reach an ultrahigh arealmore » capacitance of 1.28 F/cm 2 and excellent rate capability (83.5% from 0.5 to 10 A/g) as well as high cycling stability (86.2% retention after 5000 cycles). The excellent electric double-layer performance of the 3D graphene electrode can be attributed to the fast electrolyte ion transport in the meso/macro channels and the rapid and reversible charge adsorption with negligible transport distance in the surface micropores.« less

Electron mobility in the inversion layers of fully depleted SOI films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaitseva, E. G., E-mail: ZaytsevaElza@yandex.ru; Naumova, O. V.; Fomin, B. I.

The dependences of the electron mobility μ{sub eff} in the inversion layers of fully depleted double–gate silicon-on-insulator (SOI) metal–oxide–semiconductor (MOS) transistors on the density N{sub e} of induced charge carriers and temperature T are investigated at different states of the SOI film (inversion–accumulation) from the side of one of the gates. It is shown that at a high density of induced charge carriers of N{sub e} > 6 × 10{sup 12} cm{sup –2} the μeff(T) dependences allow the components of mobility μ{sub eff} that are related to scattering at surface phonons and from the film/insulator surface roughness to be distinguished.more » The μ{sub eff}(N{sub e}) dependences can be approximated by the power functions μ{sub eff}(N{sub e}) ∝ N{sub e}{sup −n}. The exponents n in the dependences and the dominant mechanisms of scattering of electrons induced near the interface between the SOI film and buried oxide are determined for different N{sub e} ranges and film states from the surface side.« less

An Ideal Electrode Material, 3D Surface-Microporous Graphene for Supercapacitors with Ultrahigh Areal Capacitance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Liang; Stacchiola, Dario J.; Hu, Yun Hang

The efficient charge accumulation of an ideal supercapacitor electrode requires abundant micropores and its fast electrolyte-ions transport prefers meso/macropores. But, current electrode materials cannot meet both requirements, resulting in poor performance. We creatively constructed three-dimensional cabbage-coral-like graphene as an ideal electrode material, in which meso/macro channels are formed by graphene walls and rich micropores are incorporated in the surface layer of the graphene walls. The unique 3D graphene material can achieve a high gravimetric capacitance of 200 F/g with aqueous electrolyte, 3 times larger than that of commercially used activated carbon (70.8 F/g). Furthermore, it can reach an ultrahigh arealmore » capacitance of 1.28 F/cm 2 and excellent rate capability (83.5% from 0.5 to 10 A/g) as well as high cycling stability (86.2% retention after 5000 cycles). The excellent electric double-layer performance of the 3D graphene electrode can be attributed to the fast electrolyte ion transport in the meso/macro channels and the rapid and reversible charge adsorption with negligible transport distance in the surface micropores.« less

Ionic liquid gating on atomic layer deposition passivated GaN: Ultra-high electron density induced high drain current and low contact resistance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Hong; Du, Yuchen; Ye, Peide D., E-mail: yep@purdue.edu

2016-05-16

Herein, we report on achieving ultra-high electron density (exceeding 10{sup 14 }cm{sup −2}) in a GaN bulk material device by ionic liquid gating, through the application of atomic layer deposition (ALD) of Al{sub 2}O{sub 3} to passivate the GaN surface. Output characteristics demonstrate a maximum drain current of 1.47 A/mm, the highest reported among all bulk GaN field-effect transistors, with an on/off ratio of 10{sup 5} at room temperature. An ultra-high electron density exceeding 10{sup 14 }cm{sup −2} accumulated at the surface is confirmed via Hall-effect measurement and transfer length measurement. In addition to the ultra-high electron density, we also observe a reductionmore » of the contact resistance due to the narrowing of the Schottky barrier width on the contacts. Taking advantage of the ALD surface passivation and ionic liquid gating technique, this work provides a route to study the field-effect and carrier transport properties of conventional semiconductors in unprecedented ultra-high charge density regions.« less

Spatial-temporal dynamics of chemical composition of surface snow in East Antarctica along the Progress station-Vostok station transect

NASA Astrophysics Data System (ADS)

Khodzher, T. V.; Golobokova, L. P.; Osipov, E. Yu.; Shibaev, Yu. A.; Lipenkov, V. Ya.; Osipova, O. P.; Petit, J. R.

2014-05-01

In January of 2008, during the 53rd Russian Antarctic Expedition, surface snow samples were taken from 13 shallow (0.7 to 1.5 m depth) snow pits along the first tractor traverse from Progress to Vostok stations, East Antarctica. Sub-surface snow/firn layers are dated from 2.1 to 18 yr. The total length of the coast to inland traverse is more than 1280 km. Here we analysed spatial variability of concentrations of sulphate ions and elements and their fluxes in the snow deposited within the 2006-2008 time interval. Anions were analysed by high-performance liquid chromatography (HPLC), and the determination of selected metals, including Na, K, Mg, Ca and Al, was carried out by mass spectroscopy with atomization by induced coupled plasma (ICP-MS). Surface snow concentration records were examined for trends versus distance inland, elevation, accumulation rate and slope gradient. Na shows a significant positive correlation with accumulation rate, which decreases as distance from the sea and altitude increase. K, Ca and Mg concentrations do not show any significant relationship either with distance inland or with elevation. Maximal concentrations of these elements with a prominent Al peak are revealed in the middle part of the traverse (500-600 km from the coast). Analysis of element correlations and atmospheric circulation patterns allow us to suggest their terrestrial origin (e.g. aluminosilicates carried as a continental dust) from the Antarctic nunatak areas. Sulphate concentrations show no significant relationship with distance inland, elevation, slope gradient and accumulation rate. Non-sea salt secondary sulphate is the most important contribution to the total sulphate budget along the traverse. Sulphate of volcanic origin attributed to the Pinatubo eruption (1991) was revealed in the snow pit at 1276 km (depth 120-130 cm).

Study of the Effect of Nanoparticles and Surface Morphology on Reverse Osmosis and Nanofiltration Membrane Productivity

PubMed Central

Fang, Yuming; Duranceau, Steven J.

2013-01-01

To evaluate the significance of reverse osmosis (RO) and nanofiltration (NF) surface morphology on membrane performance, productivity experiments were conducted using flat-sheet membranes and three different nanoparticles, which included SiO2, TiO2 and CeO2. In this study, the productivity rate was markedly influenced by membrane surface morphology. Atomic force microscopy (AFM) analysis of membrane surfaces revealed that the higher productivity decline rates associated with polyamide RO membranes as compared to that of a cellulose acetate NF membrane was due to the inherent ridge-and-valley morphology of the active layer. The unique polyamide active layer morphology was directly related to the surface roughness, and was found to contribute to particle accumulation in the valleys causing a higher flux decline than in smoother membranes. Extended RO productivity experiments using laboratory grade water and diluted pretreated seawater were conducted to compare the effect that different nanoparticles had on membrane active layers. Membrane flux decline was not affected by particle type when the feed water was laboratory grade water. On the other hand, membrane productivity was affected by particle type when pretreated diluted seawater served as feed water. It was found that CeO2 addition resulted in the least observable flux decline, followed by SiO2 and TiO2. A productivity simulation was conducted by fitting the monitored flux data into a cake growth rate model, where the model was modified using a finite difference method to incorporate surface thickness variation into the analysis. The ratio of cake growth term (k1) and particle back diffusion term (k2) was compared in between different RO and NF membranes. Results indicated that k2 was less significant for surfaces that exhibited a higher roughness. It was concluded that the valley areas of thin-film membrane surfaces have the ability to capture particles, limiting particle back diffusion. PMID:24956946

Accumulation of phosphatidylcholine on gut mucosal surface is not dominated by electrostatic interactions.

PubMed

Korytowski, Agatha; Abuillan, Wasim; Amadei, Federico; Makky, Ali; Gumiero, Andrea; Sinning, Irmgard; Gauss, Annika; Stremmel, Wolfgang; Tanaka, Motomu

2017-05-01

The accumulation of phosphatidylcholine (PC) in the intestinal mucus layer is crucial for the protection of colon epithelia from the bacterial attack. It has been reported that the depletion of PC is a distinct feature of ulcerative colitis. Here we addressed the question how PC interacts with its binding proteins, the mucins, which may establish the hydrophobic barrier against colonic microbiota. In the first step, the interactions of dioleoylphosphatidylcholine (DOPC) with two mucin preparations from porcine stomach, have been studied using dynamic light scattering, zeta potential measurement, and Langmuir isotherms, suggesting that mucin binds to the surface of DOPC vesicles. The enthalpy of mucin-PC interaction could be determined by isothermal titration calorimetry. The high affinity to PC found for both mucin types seems reasonable, as they mainly consist of mucin 2, a major constituent of the flowing mucus. Moreover, by the systematic variation of net charges, we concluded that the zwitterionic DOPC has the strongest binding affinity that cannot be explained within the electrostatic interactions between charged molecules. Copyright © 2017 Elsevier B.V. All rights reserved.

Multi-year analysis of distributed glacier mass balance modelling and equilibrium line altitude on King George Island, Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Falk, Ulrike; López, Damián A.; Silva-Busso, Adrián

2018-04-01

The South Shetland Islands are located at the northern tip of the Antarctic Peninsula (AP). This region was subject to strong warming trends in the atmospheric surface layer. Surface air temperature increased about 3 K in 50 years, concurrent with retreating glacier fronts, an increase in melt areas, ice surface lowering and rapid break-up and disintegration of ice shelves. The positive trend in surface air temperature has currently come to a halt. Observed surface air temperature lapse rates show a high variability during winter months (standard deviations up to ±1.0 K (100 m)-1) and a distinct spatial heterogeneity reflecting the impact of synoptic weather patterns. The increased mesocyclonic activity during the wintertime over the past decades in the study area results in intensified advection of warm, moist air with high temperatures and rain and leads to melt conditions on the ice cap, fixating surface air temperatures to the melting point. Its impact on winter accumulation results in the observed negative mass balance estimates. Six years of continuous glaciological measurements on mass balance stake transects as well as 5 years of climatological data time series are presented and a spatially distributed glacier energy balance melt model adapted and run based on these multi-year data sets. The glaciological surface mass balance model is generally in good agreement with observations, except for atmospheric conditions promoting snow drift by high wind speeds, turbulence-driven snow deposition and snow layer erosion by rain. No drift in the difference between simulated mass balance and mass balance measurements can be seen over the course of the 5-year model run period. The winter accumulation does not suffice to compensate for the high variability in summer ablation. The results are analysed to assess changes in meltwater input to the coastal waters, specific glacier mass balance and the equilibrium line altitude (ELA). The Fourcade Glacier catchment drains into Potter cove, has an area of 23.6 km2 and is glacierized to 93.8 %. Annual discharge from Fourcade Glacier into Potter Cove is estimated to q ¯ = 25±6 hm3 yr-1 with the standard deviation of 8 % annotating the high interannual variability. The average ELA calculated from our own glaciological observations on Fourcade Glacier over the time period 2010 to 2015 amounts to 260±20 m. Published studies suggest rather stable conditions of slightly negative glacier mass balance until the mid-1980s with an ELA of approx. 150 m. The calculated accumulation area ratio suggests dramatic changes in the future extent of the inland ice cap for the South Shetland Islands.

Functionalized gold nanoparticles manifested as potent carriers for nucleolar targeting

NASA Astrophysics Data System (ADS)

Shahbazi, Reza; Ozcicek, Ilyas; Ozturk, Gurkan; Ulubayram, Kezban

2017-01-01

It is generally known that gold nanoparticles are localised in the cytoplasm and, if synthesised in small sizes or functionalized with specific proteins, they enter the cell nucleus. However, there is no report emphasising the importance of surface functionalization in their accumulation in the nucleolus. Here, for the first time in the literature, it is proposed that functionalization of gold nanoparticles with a thin layer of polyethyleneimine (PEI) spearheads them to the nucleolus of hard-to-transfect post-mitotic dorsal root ganglion neurones in a size-independent manner. As a potential for theranostic applications, it was found that functionalization with a thin layer of PEI affected the emission signal intensity of gold nanoparticles so that the cellular biodistribution of nanoparticles was visualised clearly under both confocal and two-photon microscopes.

The friction coefficient evolution of a MoS2/WC multi-layer coating system during sliding wear

NASA Astrophysics Data System (ADS)

Chan, T. Y.; Hu, Y.; Gharbi, Mohammad M.; Politis, D. J.; Wang, L.

2016-08-01

This paper discusses the evolution of friction coefficient for the multi-layered Molybdenum Disulphide (MoS2) and WC coated substrate during sliding against Aluminium AA 6082 material. A soft MoS2 coating was prepared over a hard WC coated G3500 cast iron tool substrate and underwent friction test using a pin-on-disc tribometer. The lifetime of the coating was reduced with increasing load while the Aluminium debris accumulated on the WC hard coating surfaces, accelerated the breakdown of the coatings. The lifetime of the coating was represented by the friction coefficient and the sliding distance before MoS2 coating breakdown and was found to be affected by the load applied and the wear mechanism.

Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14C "bomb pulse curve"

NASA Astrophysics Data System (ADS)

Shotyk, W.; Goodsite, M. E.; Roos-Barraclough, F.; Frei, R.; Heinemeier, J.; Asmund, G.; Lohse, C.; Hansen, T. S.

2003-11-01

Mercury concentrations are clearly elevated in the surface and sub-surface layers of peat cores collected from a minerotrophic ("groundwater-fed") fen in southern Greenland (GL) and an ombrotrophic ("rainwater-fed") bog in Denmark (DK). Using 14C to precisely date samples since ca. AD 1950 using the "atmospheric bomb pulse," the chronology of Hg accumulation in GL is remarkably similar to the bog in DK where Hg was supplied only by atmospheric deposition: this suggests not only that Hg has been supplied to the surface layers of the minerotrophic core (GL) primarily by atmospheric inputs, but also that the peat cores have preserved a consistent record of the changing rates of atmospheric Hg accumulation. The lowest Hg fluxes in the GL core (0.3 to 0.5 μg/m 2/yr) were found in peats dating from AD 550 to AD 975, compared to the maximum of 164 μg/m 2/yr in AD 1953. Atmospheric Hg accumulation rates have since declined, with the value for 1995 (14 μg/m 2/yr) comparable to the value for 1995 obtained by published studies of atmospheric transport modelling (12 μg/m 2/yr). The greatest rates of atmospheric Hg accumulation in the DK core are also found in the sample dating from AD 1953 and are comparable in magnitude (184 μg/m 2/yr) to the GL core; again, the fluxes have since gone into strong decline. The accumulation rates recorded by the peat core for AD 1994 (14 μg/m 2/yr) are also comparable to the value for 1995 obtained by atmospheric transport modelling (18 μg/m 2/yr). Comparing the Pb/Ti and As/Ti ratios of the DK samples with the corresponding crustal ratios (or "natural background values" for preanthropogenic peat) shows that the samples dating from 1953 also contain the maximum concentration of "excess" Pb and As. The synchroneity of the enrichments of all three elements (Hg, Pb, and As) suggests a common source, with coal-burning the most likely candidate. Independent support for this interpretation was obtained from the Pb isotope data ( 206Pb/ 207Pb = 1.1481 ± 0.0002 in the leached fraction and 1.1505 ± 0.0002 in the residual fraction) which is too radiogenic to be explained in terms of gasoline lead alone, but compares well with values for U.K. coals. In contrast, the lowest values for 206Pb/ 207Pb in the DK profile (1.1370 ± 0.0003 in the leached fraction and 1.1408 ± 0.0003 in the residual fraction) are found in the sample dating from AD 1979: this shows that the maximum contribution of leaded gasoline occurred approximately 25 yr after the zenith in total anthropogenic Pb deposition.

Effort towards symmetric removal and surface smoothening of 1.3-GHz niobium single-cell cavity in vertical electropolishing using a unique cathode

NASA Astrophysics Data System (ADS)

Chouhan, Vijay; Kato, Shigeki; Nii, Keisuke; Yamaguchi, Takanori; Sawabe, Motoaki; Hayano, Hitoshi; Ida, Yoshiaki

2017-08-01

A detailed study on vertical electropolishing (VEP) of a 1.3-GHz single-cell niobium coupon cavity, which contains six coupons and four viewports at different positions, is reported. The cavity was vertically electropolished using a conventional rod and three types of unique cathodes named as Ninja cathodes, which were designed to have four retractable blades made of either an insulator or a metal or a combination of both. This study reveals the effect of the cathodes and their rotation speed on uniformity in removal thickness and surface morphology at different positions inside the cavity. Removal thickness was measured at several positions of the cavity using an ultrasonic thickness gauge and the surface features of the coupons were examined by an optical microscope and a surface profiler. The Ninja cathode with partial metallic blades was found to be effective not only in reducing asymmetric removal, which is one of the major problems in VEP and might be caused by the accumulation of hydrogen (H2 ) gas bubbles on the top iris of the cavity, but also in yielding a smooth surface of the entire cavity. A higher rotation speed of the Ninja cathode prevents bubble accumulation on the upper iris, and might result in a viscous layer of similar thickness in the cavity cell. Moreover, a higher electric field at the equator owing to the proximity of partial metallic blades to the equator surface resulted in a smooth surface. The effects of H2 gas bubbles and stirring were also observed in lab EP experiments.

Small Volcano in Terra Cimmeria

NASA Technical Reports Server (NTRS)

2002-01-01

(Released 26 June 2002) The Science This positive relief feature (see MOLA context) in the ancient highlands of Mars appears to be a heavily eroded volcanic center. The top of this feature appears to be under attack by the erosive forces of the martian wind. Light-toned streaks are visible, trending northeast to southwest, and may be caused by scouring of the terrain, or they may be dune forms moving sand. The northeast portion of the caldera area looks as though a layer of material is being removed to expose a slightly lighter-toned surface underneath. The flanks of this feature are slightly less cratered than the surrounding terrain, which could be explained in two ways: 1) this feature may be younger than the surrounding area, and has had less time to accumulate meteorite impacts, or 2) the slopes that are observed today may be so heavily eroded that the original, cratered surfaces are now gone, exposing relatively uncratered rocks. Although most of Terra Cimmeria has low albedo, some eastern portions, such as shown in this image, demonstrate an overall lack of contrast that attests to the presence of a layer of dust mantling the surface. This dust, in part, is responsible for the muted appearance and infill of many of the craters at the northern and southern ends of this image The Story This flat-topped volcano pops out from the surface, the swirls of its ancient lava flows running down onto the ancient highlands of Mars. Its smooth top appears to be under attack by the erosive forces of the martian wind. How can you tell? Click on the image above for a close-up look. You'll see some light-toned streaks that run in a northeast-southwest direction. They are caused either by the scouring of the terrain or dunes of moving sand. Either way, the wind likely plays upon the volcano's surface. Look also for the subtle, nearly crescent shaped feature at the northeast portion of the volcano's cap. It looks as if a layer of material has been removed by the wind, exposing a slightly lighter-toned surface underneath. The sides of the volcano are less cratered than the rest of the terrain. Perhaps that means it is younger than the surrounding area and has had less time to accumulate meteorite impacts. On the other hand, perhaps erosion has scrubbed away the original cratered surfaces. It's a little hard to tell which possibility holds the key to the history of this area. Although most of Terra Cimmeria can look relatively darker (has a low albedo or low 'reflective power') than some other Martian areas, its eastern portions sometimes have an overall lack of contrast as seen in the above image. A layer of dust blankets the surface here, causing it to look muted. Many of the craters in the northern and southern ends of the image also seem subdued, as dust has partly filled in the stark holes they once created. The Cimmerians who give their name to this region were an ancient, little-known people of southern Russia mentioned in Assyrian inscriptions and by Homer.

Enhanced excitonic photoconductivity due to built-in internal electric field in TlGaSe{sub 2} layered semiconductor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seyidov, MirHasan Yu., E-mail: smirhasan@gyte.edu.tr; Suleymanov, Rauf A.; Institute of Physics Azerbaijan National Academy of Sciences, AZ-1143 Baku

2014-12-07

The strong enhancement, by several orders of magnitude, of the excitonic peak within the photoconductivity spectrum of TlGaSe{sub 2} semiconductor was observed. The samples were polarized in external dc electric field, which was applied prior to the measurements. Due to the accumulation of charges near the surface, an internal electric field was formed. Electron-hole pairs that were created after the absorption of light are fallen in and then separated by the built-in electric field, which prevents radiative recombination process.

Formation of the Martian Polar Layered Terrains: Quantifying Polar Water Ice and Dust Surface Deposition during Current and Past Orbital Epochs with the NASA Ames GCM

NASA Astrophysics Data System (ADS)

Emmett, Jeremy; Murphy, Jim

2016-10-01

Structural and compositional variability in the layering sequences comprising Mars' polar layered terrains (PLT's) is likely explained by orbital-forced climatic variations in the sedimentary cycles of water ice and dust from which they formed [1]. The PLT's therefore contain a direct, extensive record of the recent climate history of Mars encoded in their structure and stratigraphy, but deciphering this record requires understanding the depositional history of their dust and water ice constituents. 3D Mars atmosphere modeling enables direct simulation of atmospheric dynamics, aerosol transport and quantification of surface accumulation for a range of past and present orbital configurations. By quantifying the net yearly polar deposition rates of water ice and dust under Mars' current and past orbital configurations characteristic of the last several millions of years, and integrating these into the present with a time-stepping model, the formation history of the north and south PLT's will be investigated, further constraining their age and composition, and, if reproducible, revealing the processes responsible for prominent features and stratigraphy observed within the deposits. Simulating the formation of the deposits by quantifying net deposition rates during past orbital epochs and integrating these into the present, effectively 'rebuilding' the terrains, could aid in understanding deeper stratigraphic trends, correlating between geographically-separated deposits, explaining the presence and shapes of large-scale polar features, and correlating stratigraphy with geological time. Quantification of the magnitude and geographical distribution of surface aerosol accumulation will build on the work of previous GCM-based investigations [3]. Construction and analysis of hypothetical stratigraphic sequences in the PLT's will draw from previous climate-controlled stratigraphy methodologies [2,4], but will utilize GCM-derived net deposition rates to model orbital influences on sedimentation and erosion.[1] Milkovich S.M. and Head J. W. (2005) JGR, 110. [2] Laskar J.B. and Mustard J.F. (2002) Nature, 419, 375-377 [3] Newman C.E. et al. (2005) Icarus, 174, 135-160. [4] Hvidberg C.S. et al. (2012) Icarus, 221, 405-419.

Nanoscale Seebeck effect at hot metal nanostructures

NASA Astrophysics Data System (ADS)

Ly, Aboubakry; Majee, Arghya; Würger, Alois

2018-02-01

We theoretically study the electrolyte Seebeck effect in the vicinity of a heated metal nanostructure, such as the cap of an active Janus colloid in an electrolyte, or gold-coated interfaces in optofluidic devices. The thermocharge accumulated at the surface varies with the local temperature, thus modulating the diffuse part of the electric double layer. On a conducting surface with non-uniform temperature, the isopotential condition imposes a significant polarization charge within the metal. Surprisingly, this does not affect the slip velocity, which takes the same value on insulating and conducting surfaces. Our results for specific-ion effects agree qualitatively with recent observations for Janus colloids in different electrolyte solutions. Comparing the thermal, hydrodynamic, and ion diffusion time scales, we expect a rich transient behavior at the onset of thermally powered swimming, extending to microseconds after switching on the heating.

Dynamics of near-surface electric discharges and mechanisms of their interaction with the airflow

NASA Astrophysics Data System (ADS)

Leonov, Sergey B.; Adamovich, Igor V.; Soloviev, Victor R.

2016-12-01

The main focus of the review is on dynamics and kinetics of near-surface discharge plasmas, such as surface dielectric barrier discharges sustained by AC and repetitively pulsed waveforms, pulsed DC discharges, and quasi-DC discharges, generated in quiescent air and in the airflow. A number of technical issues related to plasma flow control applications are discussed in detail, including discharge development via surface ionization waves, charge transport and accumulation on dielectric surface, discharge contraction, different types of flow perturbations generated by surface discharges, and effect of high-speed flow on discharge dynamics. In the first part of the manuscript, plasma morphology and results of electrical and optical emission spectroscopy measurements are discussed. Particular attention is paid to dynamics of surface charge accumulation and dissipation, both in diffuse discharges and during development of ionization instabilities resulting in discharge contraction. Contraction leads to significant increase of both the surface area of charge accumulation and the energy coupled to the plasma. The use of alternating polarity pulse waveforms accelerates contraction of surface dielectric barrier discharges and formation of filamentary plasmas. The second part discusses the interaction of discharge plasmas with quiescent air and the external airflow. Four major types of flow perturbations have been identified: (1) low-speed near-surface jets generated by electrohydrodynamic interaction (ion wind); (2) spanwise and streamwise vortices formed by both electrohydrodynamic and thermal effects; (3) weak shock waves produced by rapid heating in pulsed discharges on sub-microsecond time scale; and (4) near-surface localized stochastic perturbations, on sub-millisecond time, detected only recently. The mechanism of plasma-flow interaction remains not fully understood, especially in filamentary surface dielectric barrier discharges. Localized quasi-DC surface discharges sustained in a high-speed flow are discussed in the third part of the review. Although dynamics of this type of the discharge is highly transient, due to its strong interaction with the flow, the resultant flow structure is stationary, including the oblique shock and the flow separation region downstream of the discharge. The oblique shock is attached to a time-averaged, wedge-shaped, near-wall plasma layer, with the shock angle controlled by the discharge power, which makes possible changing the flow structure and parameters in a controlled way. Finally, unresolved and open-ended issues are discussed in the summary.

Experimental Study of the Morphology and Dynamics of Gas-Laden Layers Under the Anodes in an Air-Water Model of Aluminum Reduction Cells

NASA Astrophysics Data System (ADS)

Vékony, Klára; Kiss, László I.

2012-10-01

The bubble layer formed under an anode and the bubble-induced flow play a significant role in the aluminum electrolysis process. The bubbles covering the anode bottom reduce the efficient surface that can carry current. In our experiments, we filmed and studied the bubble layer under the anode in a real-size air-water electrolysis cell model. Three different flow regimes were found depending on the gas generation rate. The covering factor was found to be proportional to the gas generation rate and inversely proportional to the angle of inclination. A correlation between the average height of the entire bubble layer and the position under the anode was determined. From this correlation and the measured contact sizes, the volume of the accumulated gas was calculated. The sweeping effect of large bubbles was observed. Moreover, the small bubbles under the inner edge of the anode were observed to move backward as a result of the escape of huge gas pockets, which means large momentum transport occurs in the bath.

Improvement in performance and reliability with CF4 plasma pretreatment on the buffer oxide layer for low-temperature polysilicon thin-film transistor

NASA Astrophysics Data System (ADS)

Fan, Ching-Lin; Lin, Yi-Yan; Yang, Chun-Chieh

2012-03-01

This study applies CF4 plasma pretreatment to a buffer oxide layer to improve the performance of low-temperature polysilicon thin-film transistors (LTPS TFTs). Results show that the fluorine atoms piled up at the interface between the bulk channel and buffer oxide layer and accumulated in the bulk channel. The reduction of the trap states density by fluorine passivation can improve the electrical characteristics of the LTPS TFTs. It is found that the threshold voltage reduced from 4.32 to 3.03 V and the field-effect mobility increased from 29.71 to 45.65 cm2 V-1 S-1. In addition, the on current degradation and threshold voltage shift after stressing were significantly improved about 31% and 70%, respectively. We believe that the proposed CF4 plasma pretreatment on the buffer oxide layer can passivate the trap states and avoid the plasma induced damage on the polysilicon channel surface, resulting in the improvement in performance and reliability for LTPS-TFT mass production application on AMOLED displays with critical reliability requirement.

Structure of Subsurface Sediments in the Scan Basin (Scotia Sea)

NASA Astrophysics Data System (ADS)

Schreider, Al. A.; Schreider, A. A.; Sazhneva, A. E.; Galindo-Zaldivar, J.; Ruano, P.; Maldonado, A.; Martos-Martin, Y.; Lobo, F.

2018-01-01

The structure of sediments in the Scotia Sea is used as a basis for reconstructing the geological history of its bottom in the Late Quaternary. The Scan Basin is one of the main elements of the topography of the southern Scotia Sea. Its formation played a considerable role in the fragmentation of the continent, which included the Bruce and Discovery banks. The main parameters of the sediment layer in the Scan Basin have been reconstructed by the present time, but its top part has not been studied. In this work, we analyze the first data obtained on the R/V Gesperidas with the use of a TOPAS PS 18/40 high-resolution seismic profilograph in 2012. Three layers in the subsurface sediments on the bottom of the Scan Basin were specified for the first time. The mean periods of their deposition in the Late Quaternary were determined as 115000 years for the first, 76000 years for the second, and 59 000 years for the third layer from the surface of the bottom. The duration of the total accumulation period of the three layers is about 250000 years.

A study on a instability slope in Taiwan subjected to rainfalls

NASA Astrophysics Data System (ADS)

Hsiao, D. H.; Hsieh, C. S.; Yeh, L. C.; Lin, D. Y.; T-A Phan, V.

2018-04-01

After the long-term monitoring on the Chaishan area in Taiwan from 2005 to 2012 by Kaohsiung City Government, the obtained results showed that annual lateral displacements in the region are about 7-8cm to the Taiwan Strait. The geological surface profiles of Chaishan area are in sequence weathered limestone, clay layer, limestone and mudstone layer, respectively. Thus the frictional resistance between weathered soils and rock layer could decrease after infiltration of rainwater due to impervious to water of the lowest mudstone layer. Typhoon invades often Taiwan each year, resulting in rainfall infiltration and rising groundwater level, as well as increased pore water pressure within the soil mass, causing the earth movements in some parts of Chaishan, especially in the Temple A (Shan Hai Temple) accompanied with cracking phenomenon. In this paper, limit equilibrium (LE) and finite element method (FEM) are used for slope analysis, in which the slope is considered as unsaturated soil. Results showed groundwater amounts are easy to accumulate and increasing pore water pressure give resulting in decreased safety factor. Both of groundwater level and rain durations were also considered in this study.

Modeling forest development after fire disturbance: Climate, soil organic layer, and nitrogen jointly affect forest canopy species and long-term ecosystem carbon accumulation in the North American boreal forest

NASA Astrophysics Data System (ADS)

Trugman, A. T.; Fenton, N.; Bergeron, Y.; Xu, X.; Welp, L.; Medvigy, D.

2015-12-01

Soil organic layer dynamics strongly affect boreal forest development after fire. Field studies show that soil organic layer thickness exerts a species-specific control on propagule establishment in the North American boreal forest. On organic soils thicker than a few centimeters, all propagules are less able to recruit, but broadleaf trees recruit less effectively than needleleaf trees. In turn, forest growth controls organic layer accumulation through modulating litter input and litter quality. These dynamics have not been fully incorporated into models, but may be essential for accurate projections of ecosystem carbon storage. Here, we develop a data-constrained model for understanding boreal forest development after fire. We update the ED2 model to include new aspen and black spruce species-types, species-specific propagule survivorship dependent on soil organic layer depth, species-specific litter decay rates, dynamically accumulating moss and soil organic layers, and nitrogen fixation by cyanobacteria associated with moss. The model is validated against diverse observations ranging from monthly to centennial timescales and spanning a climate gradient in Alaska, central Canada, and Quebec. We then quantify differences in forest development that result from changes in organic layer accumulation, temperature, and nitrogen. We find that (1) the model accurately reproduces a range of observations throughout the North American boreal forest; (2) the presence of a thick organic layer results in decreased decomposition and decreased aboveground productivity, effects that can increase or decrease ecosystem carbon uptake depending on location-specific attributes; (3) with a mean warming of 4°C, some forests switch from undergoing succession to needleleaf forests to recruiting multiple cohorts of broadleaf trees, decreasing ecosystem accumulation by ~30% after 300 years; (4) the availability of nitrogen regulates successional dynamics such than broadleaf species are less able to compete with needleleaf trees under low nitrogen regimes. We conclude that a joint regulation between the soil organic layer, temperature, and nitrogen will likely play an important role in influencing boreal forests development after fire in future climates, and should be represented in models.

Temporal and spatial variability of the sediment grain-size distribution on the Eel shelf: The flood layer of 1995

USGS Publications Warehouse

Drake, D.E.

1999-01-01

Sediment grain-size characteristics observed on the Eel shelf have been analyzed using a wet-sieving technique that minimizes breakage of aggregates. At several sites on the 70-m isobath north of the river, where a 1995 flood layer attained a maximum thickness of about 9 cm, replicate box cores were collected on seven cruises during February 1995 to January 1997. These samples provide a unique opportunity to follow the evolution of a flood layer over a two-year period as it was modified and gradually buried. One month after the flood, a layer of tan-colored, high-porosity sediment with up to 96% of its particles in the size range of 0-20 ??m had accumulated on the central part of the shelf, 7-30 km north of the river and principally between the 50-m and 90-m isobaths. Substantial coarsening of this layer occurred between February 1995 and May 1995, particularly along the southern and the landward edge of the deposit in water depths of <70 m. The early stage of coarsening was probably caused by physical reworking of the surface 0.5-cm of the deposit and by addition of new sediment from shallower regions of the shelf. Temporal changes in inventories of several grain-size fractions show that physical processes continued to add coarse sediment to the flood layer after May 1995, but the large increases in thickness of the surface mixed layer could only be attributed to bioturbation by a recovering, or seasonally fluctuating, benthic community. The 1995 flood layer has evolved from exhibiting limited variability and normal grading (i:e., upward fining) to a layer that (1) shows significant spatial variability on scales from centimeters to 10's of meters, (2) is substantially coarser owing to additions of sediment from the inner shelf, (3) is inversely graded (i.e., coarsens upward), and (4) is intensely bioturbated to depths of 4-5 cm.

Layered storage of biogenic methane-enriched gas bubbles in peat: A lumped capacitance model controlled by soil structure

NASA Astrophysics Data System (ADS)

Chen, X.; Comas, X.; Binley, A. M.; Slater, L. D.

2017-12-01

Methane can accumulate in the gaseous phase in peats, and enter the atmosphere as gas bubbles with a mass flux higher than that via diffusion and plant-mediated pathways. A complete understanding of the mechanisms regulating bubble storage in peats remains incomplete. We developed a layered model to quantify the storage of gas bubbles over a peat column based on a general lumped capacitance model. This conceptual model was applied to explain the effects of peat structure on bubble storage at different depths observed in a laboratory experiment. A peat monolith was collected from the Everglades, a subtropical wetland located in Florida (USA), and kept submerged in a cuboid chamber over 102 days until gas bubble saturation was achieved. Time-lapse ground-penetrating radar (GPR) was used to estimate changes in gas content of each layer and the corresponding average dimensions of stored gas bubbles. The results highlight a hotspot layer of bubble accumulation at depths between 5 and 10 cm below the monolith surface. Bubbles in this shallow hotspot layer were larger relative to those in deeper layers, whilst the degree of decomposition of the upper layers was generally smaller than that of the lower layers based on von Post humification tests. X-ray Computer tomography (CT) was applied to resin-impregnated peat sections from different depths and the results showed that a higher porosity promotes bubbles storage. The stored gas bubbles were released by changing water levels and the air CH4 concentrations above the peat monolith were measured using a flow-through chamber system to confirm the high CH4 concentration in the stored bubbles. Our findings suggest that bubble capacitance is related to the difference in size between gas bubbles and peat pores. This work has implications for better understanding how changes in water table elevation associated with climate change and sea level rise (particularly for freshwater wetlands near coastal areas like the Everglades) may potentially alter bubble sizes, thus bubble storage in peats.

Arctic Circle Traverse 2010 (ACT-10): South East Greenland snow accumulation variability from firn coring and ice sounding radar

NASA Astrophysics Data System (ADS)

Forster, R. R.; Miege, C.; Box, J. E.; McConnell, J.; Spikes, V. B.; Burgess, E. W.

2010-12-01

The Greenland Ice Sheet plays an important role in Earth’s climate system evolution. The snow accumulation rate is the largest single mass budget term. With only 14% of the ice sheet area, Southeast Greenland contains the highest accumulation rates, accounting for one third of the total snow accumulation and annual variability. The high accumulation rates have made the region less desirable for long climate record ice cores and therefore, contain relatively very few in situ measurements to constrain the ice sheet mass budget. We present annual snow accumulation rates from the Arctic Circle Traverse 2010 (ACT-10). During April and May 2010 we acquired three 50 m firn cores connected by surface-based 400 MHz ground penetrating radar (GPR) in Southeast Greenland. The traverse repeated and extended the original Arctic Circle Traverse in 2004 (Spikes et al., 2004). Dating is achieved using geochemical analysis of the cores to identify isochronal layers detected by the GPR yielding annual accumulation estimates along the traverse between the core sites. The 300 km ACT-10 GPR snowmobile traverse extended the ACT-04 path 80 km to the lowest elevation core site at 1776 m. Meanwhile, airborne radars, operating as part of NASA’s Operation IceBridge also acquired data over the full length of the ACT-10 path, simultaneously with a portion of the traverse and within days for the remaining segments. The IceBridge and ACT-10 data are to be combined in a calibration effort such that snow accumulation rates may be mapped elsewhere in Greenland and even in Antarctica.

Soils of the Eastern mountainsides of the southern Sikhote-Alin (on the example of Lazovsky nature reserve, Russia)

NASA Astrophysics Data System (ADS)

Tregubova, Valentina; Semal, Victoria; Nesterova, Olga; Yaroslavtsev, Alexis

2017-04-01

The most common soils of the southern Far East are Brownzems under Russian classification (Cambisols), which are the zonal ones, emerging on the steep slopes and tops of hills, on high river terraces under broad-leaved and cedar-broad-leaved forests. Those soils formed due to two processes: organic matter metamorphism and clayization by siallite, leading to the formation of clay-metamorphic horizon Bw. The main morphological features of Cambisols are not deep soil profile (50 - 70 cm), weak horizons differentiation, with lots of cobble. Chemically those soils are low saturated, even in the humus horizon. Distribution of total absorbed bases is mostly accumulative, which is related to the distribution of humus in these soils, and the predominant type of clay fraction distribution of. The only exception are Humic Cambisols and Humic Cambisols Calcic which were formed on redeposited products of limestone rock weathering. Fine-grained deposits are mainly loams with a low content of silt. Silt distribution has an accumulative character with a gradual decrease in the content of silt down from the top of the profile. Layer of fresh leaf fall is very common for the Humic Cambisols surfaces, and under it there is the litter of plant residues with different degrees of decomposition. Accumulative humus horizon is dark gray with brownish tint, thin, from 10 to 15 cm in depth, loose, crumbly, highly penetrated by roots, with a strong granular structure, with aggregates tightly attached to the root hairs, sandy loam or sandy clay loam. The middle horizon is brown, yellowish-brown, divided into sub-horizons, with different color intensity, density, soil texture and amount of cobble. Dystric Cambisols are acidic or strongly acidic with low saturation of soil absorbing complex. Due to amount and distribution of organic matter these soils can be divided into two groups. The first group is soils with accumulative humus distribution: with a low depth humus-accumulative horizon (11 - 12 cm) and high content of organic matter (23 - 26 %); humus in the upper horizons mainly consists of humic acids, while in lower horizons it is with higher ratio of fulvic acids. The second group is soils with a gradual humus distribution along the profile and with a smaller amount of organic matter in the upper horizon (9 - 13 %) and with no differentiation in humus composition. Folic Cambisols are formed on the watershed surfaces, on the steep slopes under pine and oak trees. Under thin litter horizon these soils have organic-accumulative horizon of well decomposed organic matter, but in contrast with Dystric Cambisols it doesn't have strong granular structure. At the bottom the organic horizon is humic-impregnated or has clear streaks of humus. Humic Cambisols are formed in the lower parts of slopes, on steep slopes and high river terraces under pine and deciduous forests. All this soils have humified litter horizon, which is up to 7 cm in depth, weak differentiation of the soil profile, deep humus-accumulative horizon (18 - 31 cm) with dark gray, almost black color, with strong granular structure and loam or clay loam texture. Soil acidity is determined by the lithogenic basis. Base saturation is quite high (77 - 90%) in mineral horizons and is up to 70 % in organic and accumulative ones. There is a high amount of humus on the entire profile (5 - 16 %), which consists of humic acids in the upper half of the profile and of fulvates at the bottom. Humic Cambisols Gleyic are located in the lower parts of gentle slopes under mixed forest. Due to higher moisture at the lower parts of slopes this soils have signs of weak gley process in dense subsoil horizons in the form of small light grey spots. Humic Leptosols are weakly developed soils formed on rocky hills, boulders, rocky outcrops, under thick moss layer, under which is a layer of weathered gravel rock. Humic Cambisols (Calcic) are formed on the surface sediments of limestone. They have a deep soil profile, up to 40 cm and it's humus-accumulative horizon is dark gray or black, gradually passing into soil-forming rock. Bw horizon, typical for Cambisols, is weak.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishi, Shohei; Taguchi, Dai; Manaka, Takaaki

By using electric-field-induced optical second-harmonic generation measurement coupled with the conventional current-voltage (I-V) measurement, we studied the carrier transport of organic double-layer diodes with a Au/pentacene/fluorine polymer (FP)/indium zinc oxide (IZO) structure. The rectifying I-V characteristics were converted into the I-E characteristics of the FP and pentacene layers. Results suggest a model in which Schottky-type electron injection from the IZO electrode to the FP layer governs the forward electrical conduction (V > 0), where the space charge electric field produced in the FP layer by accumulated holes at the pentacene/FP interface makes a significant contribution. On the other hand, Schottky-type injection bymore » accumulated interface electrons from the pentacene layer to the FP layer governs the backward electrical conduction (V < 0). The electroluminescence generated from the pentacene layer in the region V > 0 verifies the electron transport across the FP layer, and supports the above suggested model.« less

Modeling contamination migration on the Chandra X-Ray Observatory

NASA Technical Reports Server (NTRS)

O'Dell, Stephen L.; Swartz, Douglas A.; Anderson, Scot K.; Chen, Kenny C.; Giordano, Rino J.; Knollenberg, Perry J.; Morris, Peter A.; Plucinsky, Paul P.; Tice, Neil W.; Tran, Hien

2005-01-01

During its first 5 years of operation, the cold (-60 C) optical blocking filter of the Advanced CCD Imaging Spectrometer (ACIS), on board the Chandra X-ray Observatory, has accumulated a contaminating layer that attenuates the low-energy x rays. To assist in assessing the likelihood of successfully baking off the contaminant, members of the Chandra Team developed contamination-migration simulation software. The simulation follows deposition onto and (temperature-dependent) vaporization from surfaces comprising a geometrical model of the Observatory. A separate thermal analysis, augmented by on-board temperature monitoring, provides temperatures for each surface of the same geometrical model. This paper describes the physical basis for the simulations, the methodologies, and the predicted migration of the contaminant for various bake-out scenarios and assumptions.

Mapping Surface Temperatures on a Debris-Covered Glacier with an Unmanned Aerial Vehicle

NASA Astrophysics Data System (ADS)

Kraaijenbrink, Philip D. A.; Shea, Joseph M.; Litt, Maxime; Steiner, Jakob F.; Treichler, Désirée; Koch, Inka; Immerzeel, Walter W.

2018-05-01

A mantel of debris cover often accumulates across the surface of glaciers in active mountain ranges with exceptionally steep terrain, such as the Andes, Himalaya and New Zealand Alps. Such a supraglacial debris layer has a major influence on a glacier's surface energy budget, enhancing radiation absorption and melt when the layer is thin, but insulating the ice when thicker than a few cm. Information on spatially distributed debris surface temperature has the potential to provide insight into the properties of the debris, its effects on the ice below and its influence on the near-surface boundary layer. Here, we deploy an unmanned aerial vehicle (UAV) equipped with a thermal infrared sensor on three separate missions over one day to map changing surface temperatures across the debris-covered Lirung Glacier in the Central Himalaya. We present a methodology to georeference and process the acquired thermal imagery, and correct for emissivity and sensor bias. Derived UAV surface temperatures are compared with distributed simultaneous in situ temperature measurements as well as with Landsat 8 thermal satellite imagery. Results show that the UAV-derived surface temperatures vary greatly both spatially and temporally, with -1.4±1.8, 11.0 ±5.2 and 15.3±4.7 °C for the three flights (mean±sd), respectively. The range in surface temperatures over the glacier during the morning is very large with almost 50 °C. Ground-based measurements are generally in agreement with the UAV imagery, but considerable deviations are present that are likely due to differences in measurement technique and approach, and validation is difficult as a result. The difference in spatial and temporal variability captured by the UAV as compared with much coarser satellite imagery is striking and it shows that satellite derived temperature maps should be interpreted with care. We conclude that UAVs provide a suitable means to acquire surface temperature maps of debris-covered glacier surfaces at high spatial and temporal resolution, but that there are caveats with regard to absolute temperature measurement.

Computation on free gas seepage and associated seabed pockmark formation

NASA Astrophysics Data System (ADS)

Su, Z.; Cathles, Lawrence M.; Chen, D. F.; Wu, N. Y.

2010-03-01

Seabed pockmarks formed by seepage of subsurface fluids are very commonly located in areas where gas is present in near-surface sediments. Especially, they are widely observed on the seafloor at hydrate regions around the world. In this paper we consider that capillary sealing is the crucial mechanism for gas entrapment, gas escape, and pockmark formation. In the hydrate system, free gas is trapped beneath the hydrate layer. The gas overpressure increases as the gas accumulates beneath the hydrate. the hydrate layer is a capillary seal. Capillary seals have the property that they fail completely when the gas pressure reaches the point that they are invaded by gas. The release of gas is thus episodic and sudden. We imagine in our model that when it occurs the venting gas will push the overlying water upward at increasingly higher velocities as the gas pipe approaches the seafloor. As the water velocity increases, the near surface sediments will become quick at a depth that is a function of the thickness of free gas column under the hydrate seal and the depth of hydrate seal, leaving a pockmark on the seafloor. The model shows that at least a 22-m-thick free gas layer beneath the hydrate at Blake Ridge is needed to form the 4-m-deep pockmark at the seabed.

Why is there net surface heating over the Antarctic Circumpolar Current?

NASA Astrophysics Data System (ADS)

Czaja, Arnaud; Marshall, John

2015-05-01

Using a combination of atmospheric reanalysis data, climate model outputs and a simple model, key mechanisms controlling net surface heating over the Southern Ocean are identified. All data sources used suggest that, in a streamline-averaged view, net surface heating over the Antarctic Circumpolar Current (ACC) is a result of net accumulation of solar radiation rather than a result of heat gain through turbulent fluxes (the latter systematically cool the upper ocean). It is proposed that the fraction of this net radiative heat gain realized as net ACC heating is set by two factors. First, the sea surface temperature at the southern edge of the ACC. Second, the relative strength of the negative heatflux feedbacks associated with evaporation at the sea surface and advection of heat by the residual flow in the oceanic mixed layer. A large advective feedback and a weak evaporative feedback maximize net ACC heating. It is shown that the present Southern Ocean and its circumpolar current are in this heating regime.

Ultrastructure of the embryonic snake skin and putative role of histidine in the differentiation of the shedding complex.

PubMed

Alibardi, Lorenzo

2002-02-01

The morphogenesis and ultrastructure of the epidermis of snake embryos were studied at progressive stages of development through hatching to determine the time and modality of differentiation of the shedding complex. Scales form as symmetric epidermal bumps that become slanted and eventually very overlapped. During the asymmetrization of the bumps, the basal cells of the forming outer surface of the scale become columnar, as in an epidermal placode, and accumulate glycogen. Small dermal condensations are sometimes seen and probably represent primordia of the axial dense dermis of the growing tip of scales. Deep, dense, and superficial loose dermal regions are formed when the epidermis is bilayered (periderm and basal epidermis) and undifferentiated. Glycogen and lipids decrease from basal cells to differentiating suprabasal cells. On the outer scale surface, beneath the peridermis, a layer containing dense granules and sparse 25-30-nm thick coarse filaments is formed. The underlying clear layer does not contain keratohyalin-like granules but has a rich cytoskeleton of intermediate filaments. Small denticles are formed and they interdigitate with the oberhautchen spinulae formed underneath. On the inner scale surface the clear layer contains dense granules, coarse filaments, and does not form denticles with the aspinulated oberhautchen. On the inner side surface the oberhautchen only forms occasional spinulae. The sloughing of the periderm and embryonic epidermis takes place in ovo 5-6 days before hatching. There follow beta-, mesos-, and alpha-layers, not yet mature before hatching. No resting period is present but a new generation is immediately produced so that at 6-10 h posthatching an inner generation and a new shedding complex are forming beneath the outer generation. The first shedding complex differentiates 10-11 days before hatching. In hatchlings 6-10 h old, tritiated histidine is taken up in the epidermis 4 h after injection and is found mainly in the shedding complex, especially in the apposed membranes of the clear layer and oberhautchen cells. This indicates that a histidine-rich protein is produced in preparation for shedding, as previously seen in lizard epidermis. The second shedding (first posthatching) takes place at 7-9 days posthatching. It is suggested that the shedding complex in lepidosaurian reptiles has evolved after the production of a histidine-rich protein and of a beta-keratin layer beneath the former alpha-layer. Copyright 2002 Wiley-Liss, Inc.

Effects of hydraulic retention time and bioflocculant addition on membrane fouling in a sponge-submerged membrane bioreactor.

PubMed

Deng, Lijuan; Guo, Wenshan; Ngo, Huu Hao; Du, Bing; Wei, Qin; Tran, Ngoc Han; Nguyen, Nguyen Cong; Chen, Shiao-Shing; Li, Jianxin

2016-06-01

The characteristics of activated sludge and membrane fouling were evaluated in a sponge-submerged membrane bioreactor (SSMBR) at different hydraulic retention times (HRTs) (6.67, 5.33 and 4.00h). At shorter HRT, more obvious membrane fouling was caused by exacerbated cake layer formation and aggravated pore blocking. Activated sludge possessed more extracellular polymeric substances (EPS) due to excessive growth of biomass and lower protein to polysaccharide ratio in soluble microbial products (SMP). The cake layer resistance was aggravated by increased sludge viscosity together with the accumulated EPS and biopolymer clusters (BPC) on membrane surface. However, SMP showed marginal effect on membrane fouling when SSMBRs were operated at all HRTs. The SSMBR with Gemfloc® addition at the optimum HRT of 6.67h demonstrated superior sludge characteristics such as larger floc size, less SMP in mixed liquor with higher protein/polysaccharide ratio, less SMP and BPC in cake layer, thereby further preventing membrane fouling. Copyright © 2016 Elsevier Ltd. All rights reserved.

Interpreting Electromagnetic Reflections In Glaciology

NASA Astrophysics Data System (ADS)

Eisen, O.; Nixdorf, U.; Wilhelms, F.; Steinhage, D.; Miller, H.

Electromagnetic reflection (EMR) measurements are active remote sensing methods that have become a major tool for glaciological investigations. Although the basic pro- cesses are well understood, the unambiguous interpretation of EMR data, especially internal layering, still requires further information. The Antacrtic ice sheet provides a unique setting for investigating the relation between physical­chemical properties of ice and EMR data. Cold ice, smooth surface topography, and low accumulation facilitates matters to use low energy ground penetrating radar (GPR) devices to pene- trate several tens to hundreds of meters of ice, covering several thousands of years of snow deposition history. Thus, sufficient internal layers, primarily of volcanic origin, are recorded to enable studies on a local and regional scale. Based on dated ice core records, GPR measurements at various frequencies, and airborne radio-echo sound- ing (RES) from Dronning Maud Land (DML), Antarctica, combined with numerical modeling techniques, we investigate the influence of internal layering characteristics and properties of the propagating electromagnetic wave on EMR data.

Microstructure and mechanical properties of Al/Cu/Mg laminated composite sheets produced by the ARB proces

NASA Astrophysics Data System (ADS)

Rahmatabadi, Davood; Tayyebi, Moslem; Hashemi, Ramin; Faraji, Ghader

2018-05-01

In the present study, an Al/Cu/Mg multi-layered composite was produced by accumulative roll bonding (ARB) through seven passes, and its microstructure and mechanical properties were evaluated. The microstructure investigations show that plastic instability occurred in both the copper and magnesium reinforcements in the primary sandwich. In addition, a composite with a perfectly uniform distribution of copper and magnesium reinforcing layers was produced during the last pass. By increasing the number of ARB cycles, the microhardness of the layers including aluminum, copper, and magnesium was significantly increased. The ultimate tensile strength of the sandwich was enhanced continually and reached a maximum value of 355.5 MPa. This strength value was about 3.2, 2, and 2.1 times higher than the initial strength values for the aluminum, copper, and magnesium sheets, respectively. Investigation of tensile fracture surfaces during the ARB process indicated that the fracture mechanism changed to shear ductile at the seventh pass.

[Impact of short-term grazing disturbance on nitrogen accumulation of biological soil crusts in the hilly Loess Plateau region, China].

PubMed

Wang, Shan Shan; Zhao, Yun Ge; Shi, Ya Fang; Gao, Li Qian; Yang, Qiao Yun

2017-12-01

The variations of total nitrogen, available nitrogen and microbial biomass nitrogen caused by simulated grazing disturbance were investigated in the sixth and twelfth months by using field survey combined with laboratory analysis in order to reveal the sensitivity of nitrogen content in biocrustal soils to disturbance in the hilly Loess Plateau region. The results showed that nitrogen contents in biocrustal soil were sensitive to disturbance. Total nitrogen and available nitrogen in the biocrustal layers were decreased by 0.17-0.39 g·kg -1 and 1.78-5.65 mg·kg -1 during the first half-year compared to the undisturbed treatment, and they were found respectively decreased by 0.13-0.40 g·kg -1 and 11.45-32.68 mg·kg -1 one year later since disturbance. The content of microbial biomass nitrogen in the biocrustal layer was reduced by 69.99-330.97 mg·kg -1 , whereas the content was increased by 25.51-352.17 mg·kg -1 in soil of 0-2 cm layer. The induction of nitrogen accumulation depended on the intensity of disturbance. Slight variation was observed in the nitrogen accumulation in biocrustal layer under 20% and 30% disturbance, while significant reduction was found in the 40% and 50% disturbance. Significant reduction was detected only in nitrogen accumulation in the biocrustal layers, whereas no significant influence was found in the top 5 cm soil layer.

Development of dental composites with reactive fillers that promote precipitation of antibacterial-hydroxyapatite layers.

PubMed

Aljabo, Anas; Abou Neel, Ensanya A; Knowles, Jonathan C; Young, Anne M

2016-03-01

The study aim was to develop light-curable, high strength dental composites that would release calcium phosphate and chlorhexidine (CHX) but additionally promote surface hydroxyapatite/CHX co-precipitation in simulated body fluid (SBF). 80 wt.% urethane dimethacrylate based liquid was mixed with glass fillers containing 10 wt.% CHX and 0, 10, 20 or 40 wt.% reactive mono- and tricalcium phosphate (CaP). Surface hydroxyapatite layer thickness/coverage from SEM images, Ca/Si ratio from EDX and hydroxyapatite Raman peak intensities were all proportional to both time in SBF and CaP wt.% in the filler. Hydroxyapatite was, however, difficult to detect by XRD until 4 weeks. XRD peak width and SEM images suggested this was due to the very small size (~10 nm) of the hydroxyapatite crystallites. Precipitate mass at 12 weeks was 22 wt.% of the sample CaP total mass irrespective of CaP wt.% and up to 7 wt.% of the specimen. Early diffusion controlled CHX release, assessed by UV spectrometry, was proportional to CaP and twice as fast in water compared with SBF. After 1 week, CHX continued to diffuse into water but in SBF, became entrapped within the precipitating hydroxyapatite layer. At 12 weeks CHX formed 5 to 15% of the HA layer with 10 to 40 wt.% CaP respectively. Despite linear decline of strength and modulus in 4 weeks from 160 to 101 MPa and 4 to 2.4 GPa, respectively, upon raising CaP content, all values were still within the range expected for commercial composites. The high strength, hydroxyapatite precipitation and surface antibacterial accumulation should reduce tooth restoration failure due to fracture, aid demineralised dentine repair and prevent subsurface carious disease respectively. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

Optimization of Photovoltaic Performance Through the Integration of Electrodynamic Dust Shield Layers

NASA Technical Reports Server (NTRS)

Nason, Steven; Davis, Kris; Hickman, Nicoleta; McFall, Judith; Arens, Ellen; Calle, Carlos

2009-01-01

The viability of photovoltaics on the Lunar and Martian surfaces may be determined by their ability to withstand significant degradation in the Lunar and Martian environments. One of the greatest threats is posed by fine dust particles which are continually blown about the surfaces. In an effort to determine the extent of the threat, and to investigate some abatement strategies, a series of experiments were conducted outdoors and in the Moon and Mars environmental chamber at the Florida Solar Energy Center. Electrodynamic dust shield prototypes based on the electric curtain concept have been developed by our collaborators at the Kennedy Space Center [1]. These thin film layers can remove dust from surfaces and prevent dust accumulation. Several types of dust shields were designed, built and tested under high vacuum conditions and simulated lunar gravity to validate the technology for lunar exploration applications. Gallium arsenide, single crystal and polycrystalline silicon photovoltaic integrated devices were designed, built and tested under Moon and Mars environmental conditions as well as under ambient conditions. Photovoltaic efficiency measurements were performed on each individual cell with the following configurations; without an encapsulation layer, with a glass covering, and with various thin film dust shields. It was found that the PV efficiency of the hybrid systems was unaffected by these various thin film dust shields, proving that the optical transmission of light through the device is virtually uninhibited by these layers. The future goal of this project is to incorporate a photovoltaic cell as the power source for the electrodynamic dust shield system, and experimentally show the effective removal of dust obstructing any light incident on the cell, thus insuring power production is maximized over time.

Boosting surface charge-transfer doping efficiency and robustness of diamond with WO3 and ReO3

NASA Astrophysics Data System (ADS)

Tordjman, Moshe; Weinfeld, Kamira; Kalish, Rafi

2017-09-01

An advanced charge-transfer yield is demonstrated by employing single monolayers of transition-metal oxides—tungsten trioxide (WO3) and rhenium trioxide (ReO3)—deposited on the hydrogenated diamond surface, resulting in improved p-type sheet conductivity and thermal stability. Surface conductivities, as determined by Hall effect measurements as a function of temperature for WO3, yield a record sheet hole carrier concentration value of up to 2.52 × 1014 cm-2 at room temperature for only a few monolayers of coverage. Transfer doping with ReO3 exhibits a consistent narrow sheet carrier concentration value of around 3 × 1013 cm-2, exhibiting a thermal stability of up to 450 °C. This enhanced conductivity and temperature robustness exceed those reported for previously exposed surface electron acceptor materials used so far on a diamond surface. X-ray photoelectron spectroscopy measurements of the C1s core level shift as a function of WO3 and ReO3 layer thicknesses are used to determine the respective increase in surface band bending of the accumulation layers, leading to a different sub-surface two-dimensional hole gas formation efficiency in both cases. This substantial difference in charge-exchange efficiency is unexpected since both surface acceptors have very close work functions. Consequently, these results lead us to consider additional factors influencing the transfer doping mechanism. Transfer doping with WO3 reveals the highest yet reported transfer doping efficiency per minimal surface acceptor coverage. This improved surface conductivity performance and thermal stability will promote the realization of 2D diamond-based electronic devices facing process fabrication challenges.

Formation and dynamics of a chemically stratified layer below the Earth's CMB

NASA Astrophysics Data System (ADS)

Bouffard, M.; Labrosse, S.; Choblet, G.; Aubert, J.; Fournier, A.

2017-12-01

Seismological and magnetic observations are compatible with the presence of a stratified layer below the Earth's CMB (Lay and Young, 1990; Tanaka, 2007; Gubbins, 2007; Helffrich and Kaneshima, 2010; Lesur et al., 2015) and the existence of such a layer has also been predicted by several theoretical arguments listed below. The proposed thickness varies from 60 km to several hundreds of kilometers across the literature, but is usually close to 100 km. The layer may be thermally stratified if the CMB heat flow is subadiabatic (Gubbins et al., 1982; Labrosse et al., 1997; Lister and Buffett, 1998; Labrosse, 2015) but the possibility of a stratification of chemical origin has also been evoked. Various mechanisms have been proposed for the formation of a chemically stratified layer and include barodiffusion i.e. diffusion of light elements against the pressure gradient (Fearn and Loper, 1981; Braginsky, 2006; Gubbins and Davies, 2013), chemical plumes and blobs that would be able to reach the CMB where they would accumulate (Loper, 1989; Braginsky, 1994; Moffatt and Loper, 1994; Loper, 2007) or ascending droplets in a Fe-S system kept from mixing by surface tension (Franck, 1982). Layering may also be present if immiscible liquids evolve as the composition changes due to inner core growth (Helffrich and Kaneshima, 2004). To finish, Buffett and Seagle (2010) also studied the possibility that light elements be dissolved from the mantle into the core, forming a lighter layer that could grow by diffusion over long time scales. So far, no numerical simulation of core dynamics has been able to validate any of these potential mechanisms and produce a chemically stratified layer in a self-consistent manner. Using a particle-in-cell method newly implemented in the code PARODY (E. Dormy, J. Aubert) allowing to perform simulations of thermochemical convection in the infinite Lewis number limit (neglecting the compositional diffusivity), I will show that a chemically stratified layer systematically forms in simulations via the accumulation of undiffused plumes and blobs that reach the top boundary. I will discuss the dynamics of such a layer and will present scaling laws of its thickness as a function of the control parameters. Extrapolation to the terrestrial case and the potential implications for core dynamics will also be discussed.

Pollution of intensively managed greenhouse soils by nutrients and heavy metals in the Yellow River Irrigation Region, Northwest China.

PubMed

Kong, Xiaole; Cao, Jing; Tang, Rangyun; Zhang, Shengqiang; Dong, Fang

2014-11-01

The present study aimed to assess the potential ecological risk of heavy metals and nutrient accumulation in polytunnel greenhouse soils in the Yellow River irrigation region (YRIR), Northwest China, and to identify the potential sources of these heavy metals using principal component analysis. Contents of available nitrogen (AN), phosphorus (AP), and potassium (AK) in the surface polytunnel greenhouse soils (0-20 cm) varied from 13.42 to 486.78, from 39.10 to 566.97, and from 21.64 to 1,156.40 mg kg(-1), respectively, as well as AP, soil organic matter (SOM) and AK contents tended to increase significantly at the 0-20- and 20-40-cm soil layers. Heavy metal accumulations occurred in the polytunnel greenhouse soils as compared to arable soils, especially at a depth of 20 cm where Cd, Zn and Cu contents were significantly higher than arable soil. Cd and As were found to be the two main polluting elements in the greenhouse soils because their contents exceeded the thresholds established for greenhouse vegetable production HJ333-2006 in China and the background of Gansu province. It has been shown that Cd, Cu, Pb and Zn at the 0-20-cm soil layer were derived mainly from agricultural production activities, whereas contents of Cr and Ni at the same soil layer were determined by 'natural' factors and As originated from natural sources, deposition and irrigation water.

How did nature engineer the highest surface lipid accumulation among plants? Exceptional expression of acyl-lipid-associated genes for the assembly of extracellular triacylglycerol by Bayberry (Myrica pensylvanica) fruits.

PubMed

Simpson, Jeffrey P; Thrower, Nicholas; Ohlrogge, John B

2016-09-01

Bayberry (Myrica pensylvanica) fruits are covered with a remarkably thick layer of crystalline wax consisting of triacylglycerol (TAG) and diacylglycerol (DAG) esterified exclusively with saturated fatty acids. As the only plant known to accumulate soluble glycerolipids as a major component of surface waxes, Bayberry represents a novel system to investigate neutral lipid biosynthesis and lipid secretion by vegetative plant cells. The assembly of Bayberry wax is distinct from conventional TAG and other surface waxes, and instead proceeds through a pathway related to cutin synthesis (Simpson and Ohlrogge, 2016). In this study, microscopic examination revealed that the fruit tissue that produces and secretes wax (Bayberry knobs) is fully developed before wax accumulates and that wax is secreted to the surface without cell disruption. Comparison of transcript expression to genetically related tissues (Bayberry leaves, M. rubra fruits), cutin-rich tomato and cherry fruit epidermis, and to oil-rich mesocarp and seeds, revealed exceptionally high expression of 13 transcripts for acyl-lipid metabolism together with down-regulation of fatty acid oxidases and desaturases. The predicted protein sequences of the most highly expressed lipid-related enzyme-encoding transcripts in Bayberry knobs are 100% identical to the sequences from Bayberry leaves, which do not produce surface DAG or TAG. Together, these results indicate that TAG biosynthesis and secretion in Bayberry is achieved by both up and down-regulation of a small subset of genes related to the biosynthesis of cutin and saturated fatty acids, and also implies that modifications in gene expression, rather than evolution of new gene functions, was the major mechanism by which Bayberry evolved its specialized lipid metabolism. This article is part of a Special Issue entitled: Plant Lipid Biology edited by Kent D. Chapman and Ivo Feussner. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Surface polishing of niobium for superconducting radio frequency (SRF) cavity applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Liang

2014-08-01

Niobium cavities are important components in modern particle accelerators based on superconducting radio frequency (SRF) technology. The interior of SRF cavities are cleaned and polished in order to produce high accelerating field and low power dissipation on the cavity wall. Current polishing methods, buffered chemical polishing (BCP) and electro-polishing (EP), have their advantages and limitations. We seek to improve current methods and explore laser polishing (LP) as a greener alternative of chemical methods. The topography and removal rate of BCP at different conditions (duration, temperature, sample orientation, flow rate) was studied with optical microscopy, scanning electron microscopy (SEM), and electronmore » backscatter diffraction (EBSD). Differential etching on different crystal orientations is the main contributor to fine grain niobium BCP topography, with gas evolution playing a secondary role. The surface of single crystal and bi-crystal niobium is smooth even after heavy BCP. The topography of fine grain niobium depends on total removal. The removal rate increases with temperature and surface acid flow rate within the rage of 0~20 °C, with chemical reaction being the possible dominate rate control mechanism. Surface flow helps to regulate temperature and avoid gas accumulation on the surface. The effect of surface flow rate on niobium EP was studied with optical microscopy, atomic force microscopy (AFM), and power spectral density (PSD) analysis. Within the range of 0~3.7 cm/s, no significant difference was found on the removal rate and the macro roughness. Possible improvement on the micro roughness with increased surface flow rate was observed. The effect of fluence and pulse accumulation on niobium topography during LP was studied with optical microscopy, SEM, AFM, and PSD analysis. Polishing on micro scale was achieved within fluence range of 0.57~0.90 J/cm2, with pulse accumulation adjusted accordingly. Larger area treatment was proved possible by overlapping laser tracks at proper ratio. Comparison of topography and PSD indicates that LP smooths the surface in a way similar to EP. The optimized LP parameters were applied to different types of niobium surfaces representing different stages in cavity fabrication. LP reduces the sharpness on rough surfaces effectively, while doing no harm to smooth surfaces. Secondary ion mass spectrometer (SIMS) analysis showed that LP reduces the oxide layer slightly and no contamination occurred from LP. EBSD showed no significant change on crystal structure after LP.« less

Crystal accumulation in the Hanford Waste Treatment Plant high level waste melter. Preliminary settling and resuspension testing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fox, K. M.; Fowley, M. D.; Miller, D. H.

2016-05-01

The full-scale, room-temperature Hanford Tank Waste Treatment and Immobilization Plant (WTP) High-Level Waste (HLW) melter riser test system was successfully operated with silicone oil and magnetite particles at a loading of 0.1 vol %. Design and construction of the system and instrumentation, and the selection and preparation of simulant materials, are briefly reviewed. Three experiments were completed. A prototypic pour rate was maintained, based on the volumetric flow rate. Settling and accumulation of magnetite particles were observed at the bottom of the riser and along the bottom of the throat after each experiment. The height of the accumulated layer atmore » the bottom of the riser, after the first pouring experiment, approximated the expected level given the solids loading of 0.1 vol %. More detailed observations of particle resuspension and settling were made during and after the third pouring experiment. The accumulated layer of particles at the bottom of the riser appeared to be unaffected after a pouring cycle of approximately 15 minutes at the prototypic flow rate. The accumulated layer of particles along the bottom of the throat was somewhat reduced after the same pouring cycle. Review of the time-lapse recording showed that some of the settling particles flow from the riser into the throat. This may result in a thicker than expected settled layer in the throat.« less

High capacitance density MIS capacitor using Si nanowires by MACE and ALD alumina dielectric

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leontis, I.; Nassiopoulou, A. G., E-mail: A.Nassiopoulou@inn.demokritos.gr; Botzakaki, M. A.

2016-06-28

High capacitance density three-dimensional (3D) metal-insulator-semiconductor (MIS) capacitors using Si nanowires (SiNWs) by metal-assisted chemical etching and atomic-layer-deposited alumina dielectric film were fabricated and electrically characterized. A chemical treatment was used to remove structural defects from the nanowire surface, in order to reduce the density of interface traps at the Al{sub 2}O{sub 3}/SiNW interface. SiNWs with two different lengths, namely, 1.3 μm and 2.4 μm, were studied. A four-fold capacitance density increase compared to a planar reference capacitor was achieved with the 1.3 μm SiNWs. In the case of the 2.4 μm SiNWs this increase was ×7, reaching a value of 4.1 μF/cm{sup 2}. Capacitance-voltagemore » (C-V) measurements revealed that, following a two-cycle chemical treatment, frequency dispersion at accumulation regime and flat-band voltage shift disappeared in the case of the 1.3 μm SiNWs, which is indicative of effective removal of structural defects at the SiNW surface. In the case of the 2.4 μm SiNWs, frequency dispersion at accumulation persisted even after the two-step chemical treatment. This is attributed to a porous Si layer at the SiNW tops, which is not effectively removed by the chemical treatment. The electrical losses of MIS capacitors in both cases of SiNW lengths were studied and will be discussed.« less

High-speed imaging of the transient ice accretion process on a NACA 0012 airfoil

NASA Astrophysics Data System (ADS)

Waldman, Rye; Hu, Hui

2014-11-01

Ice accretion on aircraft wings poses a performance and safety threat as aircraft encounter supercooled droplets suspended in the cloud layer. The details of the ice accretion depend on the atmospheric conditions and the fight parameters. We present the measurement results of the experiments conducted in the Iowa State icing wind tunnel on a NACA 0012 airfoil to study the transient ice accretion process under varying icing conditions. The icing process on the wing consists of a complex interaction of water deposition, surface water transport, and freezing. The aerodynamics affects the water deposition, the heat and mass transport, and ice accumulation; meanwhile, the accumulating ice also affects the aerodynamics. High-speed video of the unsteady icing accretion process was acquired under controlled environmental conditions to quantitatively measure the transient water run back, rivulet formation, and accumulated ice growth, and the experiments show how varying the environmental conditions modifies the ice accretion process. Funding support from the Iowa Energy Center with Grant No. 14-008-OG and National Science Foundation (NSF) with Grant No. CBET-1064196 and CBET-1438099 is gratefully acknowledged.

New Martian climate constraints from radar reflectivity within the north polar layered deposits

NASA Astrophysics Data System (ADS)

Lalich, D. E.; Holt, J. W.

2017-01-01

The north polar layered deposits (NPLD) of Mars represent a global climate record reaching back millions of years, potentially recorded in visible layers and radar reflectors. However, little is known of the specific link between those layers, reflectors, and the global climate. To test the hypothesis that reflectors are caused by thick and indurated layers known as "marker beds," the reflectivity of three reflectors was measured, mapped, and compared to a reflectivity model. The measured reflectivities match the model and show a strong sensitivity to layer thickness, implying that radar reflectivity may be used as a proxy for short-term accumulation patterns and that regional climate plays a strong role in layer thickness variations. Comparisons to an orbitally forced NPLD accumulation model show a strong correlation with predicted marker bed formation, but dust content is higher than expected, implying a stronger role for dust in Mars polar climate than previously thought.

Surface charge accumulation of solid insulator under nanosecond pulse in vacuum: 3D distribution features and mechanism

NASA Astrophysics Data System (ADS)

Qi, Bo; Gao, Chunjia; Sun, Zelai; Li, Chengrong

2017-11-01

Surface charge accumulation can incur changes in electric field distribution, involved in the electron propagation process, and result in a significant decrease in the surface flashover voltage. The existing 2D surface charge measurement fails to meet the actual needs in real engineering applications that usually adopt the 45° conical frustum insulators. The present research developed a novel 3D measurement platform to capture surface charge distribution on solid insulation under nanosecond pulse in a vacuum. The results indicate that all surface charges are positive under a positive pulse and negative under a negative pulse. Surface charges tend to accumulate more near the upper electrode. Surface charge density increases significantly with the increase in pulse counts and amplitudes. Accumulation of surface charge results in a certain decrease of flashover voltage. Taking consideration of the secondary electron emission for the surface charge accumulation, four materials were obtained to demonstrate the effects on surface charge. Combining the effect incurred by secondary electron emission and the weighty action taken by surface charge accumulation on the flashover phenomena, the discharge mechanism along the insulator surface under nanosecond pulse voltage was proposed.

Sedimentology, petrography and early diagenesis of a travertine-colluvium succession from Chusang (southern Tibet)

NASA Astrophysics Data System (ADS)

Wang, Zhijun; Meyer, Michael C.; Hoffmann, Dirk L.

2016-08-01

The Chusang travertine is situated in southern Tibet at an altitude of ~ 4200 m asl. in a cold-arid, periglacial environment and is characterized by interbedding of hydrothermal carbonate with colluvium. Here we present sedimentological and petrographical data to elucidate the depositional environment and sedimentary processes responsible for hydrothermal carbonate precipitation and early diagenetic alteration as well as clastic sediment accumulation and provide initial 230Th/U ages to constrain the time-depth of this travertine-colluvium succession. Three main travertine lithofacies have been identified: 1) a dense laminated lithofacies, 2) a porous layered lithofacies and 3) an intraclastic lithofacies that results from erosion of pre-existing hot spring carbonate. The colluvium is composed of cohesive debris flow layers that derived from mass-wasting events from the adjacent hillslopes. Micro-fabric analyses suggest that dense laminated travertine forms via rapid calcite precipitation from hot spring water seasonally subjected to severe winter cooling, while porous layered travertine results from seasonal dilution of hot spring water with rain water during the summer monsoon months, which in turn stimulates biological productivity and gives rise to a porous summer layer. Early diagenesis in the form of recrystallization and extensive formation of pore cements is common in the Chusang travertine, but never eradicates the original crystal fabrics completely. The sedimentary architecture of the deposit is conditioned by (i) the gently dipping (~ 10°) pre-existing terrain on which hot spring water is discharged from multiple travertine mounds causing laterally extensive travertine sheets to precipitate, and (ii) the adjacent much steeper (up to 30°) periglacial hillslopes that are the source area of repeated debris flows that accumulate on the travertine surface. The resulting travertine-colluvium succession has a total thickness of ~ 24 m and 230Th/U dating suggests that the base of this succession has a minimum age of ~ 486 ka, while the upper part (top-most ~ 8 m) of the succession started accumulating in the earliest Holocene. We hypothesize that hot spring activity (and thus travertine precipitation) and the occurrence of debris flow events has a climatic nexus, i.e. are both triggered by phases of enhanced Indian summer monsoon.

PEDOT:PSS as multi-functional composite material for enhanced Li-air-battery air electrodes.

PubMed

Yoon, Dae Ho; Yoon, Seon Hye; Ryu, Kwang-Sun; Park, Yong Joon

2016-01-27

We propose PSS as a multi-functional composite material for an enhanced Li-air-battery air electrode. The PSS layer was coated on the surface of carbon (graphene) using simple method. A electrode containing PSS-coated graphene (PEDOT electrode) could be prepared without binder (such as PVDF) because of high adhesion of PSS. PEDOT electrode presented considerable discharge and charge capacity at all current densities. These results shows that PSS acts as a redox reaction matrix and conducting binder in the air electrode. Moreover, after cycling, the accumulation of reaction products due to side reaction in the electrode was significantly reduced through the use of PSS. This implies that PSS coating layer can suppress the undesirable side reactions between the carbon and electrolyte (and/or Li2O2), which causes enhanced Li-air cell cyclic performance.

Quantitative analysis of optical and recombination losses in Cu(In,Ga)Se{sub 2} thin-film solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kosyachenko, L. A., E-mail: lakos@chv.ukrpack.net; Lytvynenko, V. Yu.; Maslyanchuk, O. L.

2016-04-15

Optical and recombination losses in a Cu(In,Ga)Se{sub 2} thin-film solar cell with a band gap of 1.36–1.38 eV are theoretically analyzed. The optical transmittance of the ZnO and CdS layers through which the radiation penetrates into the absorbing layer is determined. Using optical constants, the optical loss caused by reflection at the interfaces (7.5%) and absorption in the ZnO and CdS layers (10.2%) are found. To calculate the recombination loss, the spectral distribution of the quantum efficiency of CdS/CuIn{sub 1–x}Ga{sub x}Se{sub 2} is investigated. It is demonstrated that, taking the drift and diffusion components of recombination at the front andmore » rear surfaces of the absorber into account, the quantum efficiency spectra of the investigated solar cell can be analytically described in detail. The real parameters of the solar cell are determined by comparing the calculated results and experimental data. In addition, the losses caused by the recombination of photogenerated carriers at the front and rear surfaces of the absorbing layer (1.8% and <0.1%, respectively), at its neutral part (7.6%), and in the space-charge region of the p–n heterojunction (1.0%) are determined. A correction to the parameters of Cu(In,Ga)Se{sub 2} is proposed, which enhances the charge-accumulation efficiency.« less

Analysis of Strong Wintertime Ozone Events in an Area of Extensive Oil and Gas Extraction

NASA Astrophysics Data System (ADS)

Rappenglück, Bernhard; Ackermann, Luis; Alvarez, Sergio; Golovko, Julia; Buhr, Martin; Field, Robert; Soltis, Jeff; Montague, Derek C.; Hauze, Bill; Scott, Adamson; Risch, Dan; Wilkerson, George; Bush, David; Stoeckenius, Till; Keslar, Cara

2015-04-01

During recent years, elevated ozone (O3) values have been observed repeatedly in the Upper Green River Basin (UGRB), Wyoming during wintertime. This paper presents an analysis of high ozone days in late winter 2011 (1-hour average up to 166 ppbv). Intensive Observational Periods (IOPs) were performed which included comprehensive surface and boundary layer measurements. Low windspeeds in combination with low mixing layer heights (~50 m agl) are essential for accumulation of pollutants. Air masses contain substantial amounts of reactive nitrogen (NOx) and non-methane hydrocarbons (NMHC) emitted from fossil fuel exploration activities in the Pinedale Anticline. On IOP days in the morning hours reactive nitrogen (up to 69%), then aromatics and alkanes (each ~10-15%; mostly ethane and propane) are major contributors to the hydroxyl (OH) reactivity. This time frame largely coincides with lowest NMHC/NOx ratios (~50), reflecting a relatively low NMHC mixture, and a change from a NOx-limited regime towards a NMHC limited regime. OH production on IOP days is mainly due to nitrous acid (HONO). On a 24-hr basis and as determined for a measurement height of 1.80 m above the surface HONO photolysis on IOP days can contribute ~83% to OH production on average, followed by alkene ozonolysis (~9%). Photolysis by ozone and HCHO photolysis contributes about 4% each to hydroxyl formation. High HONO levels (maximum hourly median on IOP days: 1,096 pptv) are favored by a combination of shallow boundary layer conditions and enhanced photolysis rates due to the high albedo of the snow surface. HONO is most likely formed through (i) abundant nitric acid (HNO3) produced in atmospheric oxidation of NOx, deposited onto the snow surface and undergoing photo-enhanced heterogeneous conversion to HONO and (ii) combustion related emission of HONO. HONO production is confined to the lowermost 10 m of the boundary layer. HONO, serves as the most important precursor for OH, strongly enhanced due to the high albedo of the snow cover.

The StreamCat Dataset: Accumulated Attributes for NHDPlusV2 Catchments (Version 2.1) for the Conterminous United States: Base Flow Index

EPA Pesticide Factsheets

This dataset represents the base flow index values within individual, local NHDPlusV2 catchments and upstream, contributing watersheds. Attributes of the landscape layer were calculated for every local NHDPlusV2 catchment and accumulated to provide watershed-level metrics. (See Supplementary Info for Glossary of Terms) The base-flow index (BFI) grid for the conterminous United States was developed to estimate (1) BFI values for ungaged streams, and (2) ground-water recharge throughout the conterminous United States (see Source_Information). Estimates of BFI values at ungaged streams and BFI-based ground-water recharge estimates are useful for interpreting relations between land use and water quality in surface and ground water. The bfi (%) was summarized by local catchment and by watershed to produce local catchment-level and watershed-level metrics as a continuous data type (see Data Structure and Attribute Information for a description).

How does the ice sheet surface mass balance relate to snowfall? Insights from a ground-based precipitation radar in East Antarctica

NASA Astrophysics Data System (ADS)

Souverijns, Niels; Gossart, Alexandra; Gorodetskaya, Irina V.; Lhermitte, Stef; Mangold, Alexander; Laffineur, Quentin; Delcloo, Andy; van Lipzig, Nicole P. M.

2018-06-01

Local surface mass balance (SMB) measurements are crucial for understanding changes in the total mass of the Antarctic Ice Sheet, including its contribution to sea level rise. Despite continuous attempts to decipher mechanisms controlling the local and regional SMB, a clear understanding of the separate components is still lacking, while snowfall measurements are almost absent. In this study, the different terms of the SMB are quantified at the Princess Elisabeth (PE) station in Dronning Maud Land, East Antarctica. Furthermore, the relationship between snowfall and accumulation at the surface is investigated. To achieve this, a unique collocated set of ground-based and in situ remote sensing instrumentation (Micro Rain Radar, ceilometer, automatic weather station, among others) was set up and operated for a time period of 37 months. Snowfall originates mainly from moist and warm air advected from lower latitudes associated with cyclone activity. However, snowfall events are not always associated with accumulation. During 38 % of the observed snowfall cases, the freshly fallen snow is ablated by the wind during the course of the event. Generally, snow storms of longer duration and larger spatial extent have a higher chance of resulting in accumulation on a local scale, while shorter events usually result in ablation (on average 17 and 12 h respectively). A large part of the accumulation at the station takes place when preceding snowfall events were occurring in synoptic upstream areas. This fresh snow is easily picked up and transported in shallow drifting snow layers over tens of kilometres, even when wind speeds are relatively low ( < 7 ms-1). Ablation events are mainly related to katabatic winds originating from the Antarctic plateau and the mountain ranges in the south. These dry winds are able to remove snow and lead to a decrease in the local SMB. This work highlights that the local SMB is strongly influenced by synoptic upstream conditions.

Cadmium removal from urban stormwater runoff via bioretention technology and effluent risk assessment for discharge to surface water.

PubMed

Wang, Jianlong; Zhang, Pingping; Yang, Liqiong; Huang, Tao

2016-01-01

Bioretention technology, a low-impact development stormwater management measure, was evaluated for its ability to remove heavy metals (specifically cadmium, Cd) from urban stormwater runoff. Fine sand, zeolite, sand and quartz sand were selected as composite bioretention media. The effects of these materials on the removal efficiency, chemical forms, and accumulation and migration characteristics of Cd were examined in laboratory scale bioretention columns. Heretofore, few studies have examined the removal of Cd by bioretention. A five-step sequential extraction method, a single-contamination index method, and an empirical migration equation were used in the experiments. The average Cd removal efficiency of quartz sand approached 99%, and removal by the other media all exceeded 90%. The media types markedly affected the forms of Cd found in the columns as well as its vertical migration rate. The Cd accumulated in the four media was mainly in residual form; moreover, accumulation of Cd occurred mainly in the surface layer of the bioretention column. The migration depth of Cd in the four media increased with elapsed time, in the following sequence: zeolite>quartz sand>fine sand>sand. In contrast, the migration rate decreased with elapsed time, and the migration rate of Cd was lowest in sand (0.015 m per annum over the first ten years). The comprehensive risk index analysis indicated that the risk arising from Cd discharge to surface water was "intermediate", and that the degree of risk was lowest in sand, then quartz sand, zeolite, and fine sand in sequence. These results indicate that the adsorption and accumulation of Cd in the four media are more significant than the migration of Cd. In addition, the results of Cd risk assessment for the effluent indicate that each of the four media can serve as long-term adsorption material in a bioretention facility for purifying stormwater runoff. Copyright © 2016 Elsevier B.V. All rights reserved.

Anomalous X-Ray Reflectivity Characterization of Ion Distribution at Biomimetic Membranes

NASA Astrophysics Data System (ADS)

Vaknin, David; Krüger, Peter; Lösche, Mathias

2003-05-01

Anomalous x-ray reflectivity measurements provides detailed information on ion binding to biomembrane surfaces. Using a monochromatic beam tuned to various x-ray energies at the Argonne National Laboratory Advanced Photon Source and utilizing a newly commissioned x-ray liquid surfaces reflectometer, measurements at and away from ion absorption edges allow determination of the distribution of these ions as they accumulate near lipid membranes. As a model, the interaction of Ba2+ ions with DMPA- (1,2-dimyristoyl-sn-glycero-3-phosphatidic acid) monolayers at the aqueous surface is studied. We find an unexpectedly large concentration of barium at the interface, ≈1.5 per DMPA-, forming a Stern layer of bound ions and a cloud of less densely bound ions near the lipid headgroups. This result can be understood only if one assumes that bound cations are partially speciated, e.g., as BaOH+.

Ion irradiation damage in ilmenite at 100 K

USGS Publications Warehouse

Mitchell, J.N.; Yu, N.; Devanathan, R.; Sickafus, K.E.; Nastasi, M.A.; Nord, G.L.

1997-01-01

A natural single crystal of ilmenite (FeTiO3) was irradiated at 100 K with 200 keV Ar2+. Rutherford backscattering spectroscopy and ion channeling with 2 MeV He+ ions were used to monitor damage accumulation in the surface region of the implanted crystal. At an irradiation fluence of 1 ?? 1015 Ar2+/cm2, considerable near-surface He+ ion dechanneling was observed, to the extent that ion yield from a portion of the aligned crystal spectrum reached the yield level of a random spectrum. This observation suggests that the near-surface region of the crystal was amorphized by the implantation. Cross-sectional transmission electron microscopy and electron diffraction on this sample confirmed the presence of a 150 nm thick amorphous layer. These results are compared to similar investigations on geikielite (MgTiO3) and spinel (MgAl2O4) to explore factors that may influence radiation damage response in oxides.

Dynamics of Permafrost Associated Methane Hydrate in Response to Climate Change

NASA Astrophysics Data System (ADS)

You, K.; Flemings, P. B.

2014-12-01

The formation and melting of methane hydrate and ice are intertwined in permafrost regions. A shortage of methane supply leads to formation of hydrate only at depth, below the base of permafrost. We consider a system with the ground surface initially at 0 oC with neither ice nor hydrate present. We abruptly decrease the temperature from 0 to -10 oC to simulate the effect of marine regression/ global cooling. A low methane supply rate of 0.005 kg m-2 yr-1 from depth leads to distinct ice and hydrate layers: a 100 m continuous hydrate layer is present beneath 850 m at 80 k.y.. However, a high methane supply rate of 0.1 kg m-2 yr-1 leads to 50 m ice-bonded methane hydrate at the base of permafrost, and the hydrate layer distributes between the depth of 350 and 700 m at 80 k.y.. We apply our model to illuminate future melting of hydrate at Mallik, a known Arctic hydrate accumulation. We assume a 600 m thick ice saturated (average 90%) layer extending downward from the ground surface. We increase the surface temperature linearly from -6 to 0 oC for 300 yr and then keep the surface temperature at 0 oC to reflect future climate warming caused by doubling of CO2. Hydrate melting is initiated at the base of the hydrate layer after 15 k.y.. Methane gas starts to vent to the atmosphere at 38 k.y. with an average flux of ~ 0.35 g m-2 yr-1. If the 600 m thick average ice saturation is decreased to half (45%) (or to zero), methane gas starts to vent to the atmosphere at 29 k.y. (or at 20 k.y.) with the same average flux. These results are found by a newly-developed fully-coupled multiphase multicomponent fluid flow and heat transport model. Our thermodynamic equilibrium-based model emphasizes the role of salinity in both ice and hydrate dynamics.

Thickness dependence and the role of spin transfer torque in nonlinear giant magnetoresistance of permalloy dual spin valves

NASA Astrophysics Data System (ADS)

Banerjee, N.; Aziz, A.; Ali, M.; Robinson, J. W. A.; Hickey, B. J.; Blamire, M. G.

2010-12-01

The recent discovery of nonlinear current-dependent magnetoresistance in dual spin valve devices [A. Aziz, O. P. Wessely, M. Ali, D. M. Edwards, C. H. Marrows, B. J. Hickey, and M. G. Blamire, Phys. Rev. Lett. 103, 237203 (2009)10.1103/PhysRevLett.103.237203] opens up the possibility for distinct physics which extends the standard model of giant magnetoresistance. When the outer ferromagnetic layers of a dual spin valve are antiparallel, the resulting accumulation of spin in the middle ferromagnetic layer strongly modifies its bulk and interfacial spin asymmetry and resistance. Here, we report experimental evidence of the role of bulk spin accumulation in this nonlinear effect and show that interfacial spin accumulation alone cannot account for the observed dependence of the effect on the thickness of the middle ferromagnetic layer. It is also shown that spin torque acting on the middle ferromagnetic layer combined with the nonlinear effect might be useful in understanding the dynamical features associated with the nonlinear behavior.

[Effects of nitrogen application level on soil nitrate accumulation and ammonia volatilization in high-yielding wheat field].

PubMed

Wang, Dong; Yu, Zhenwen; Yu, Wenming; Shi, Yu; Zhou, Zhongxin

2006-09-01

The study showed that during the period from sowing to pre-wintering, the soil nitrate in high-yielding wheat field moved down to deeper layers, and accumulated in the layers below 140 cm. An application rate of 96-168 kg N x hm(-2) increased the nitrate content in 0-60 cm soil layer and the wheat grain yield and its protein content, and decreased the proportion of apparent N loss to applied N and the ammonia volatilization loss from basal nitrogen. Applying 240 kg N x hm(-2) promoted the downward movement of soil nitrate and its accumulation in deeper layers, increased the proportion of apparent N loss to applied N and the ammonia volatilization loss from basal nitrogen, had no significant effect on the protein content of wheat grain, but decreased the grain yield. The appropriate application rate of nitrogen on high-yielding wheat field was 132-204 kg N x hm(-2).

Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization

USGS Publications Warehouse

Mark Torre Jorgenson,; Mikhail Kanevskiy,; Yuri Shur,; Natalia Moskalenko,; Dana Brown,; Wickland, Kimberly P.; Striegl, Robert G.; Koch, Joshua C.

2015-01-01

Ground ice is abundant in the upper permafrost throughout the Arctic and fundamentally affects terrain responses to climate warming. Ice wedges, which form near the surface and are the dominant type of massive ice in the Arctic, are particularly vulnerable to warming. Yet processes controlling ice wedge degradation and stabilization are poorly understood. Here we quantified ice wedge volume and degradation rates, compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. Mean ice wedge volume in the top 3 m of permafrost was 21%. Imagery from 1949 to 2012 showed thermokarst extent (area of water-filled troughs) was relatively small from 1949 (0.9%) to 1988 (1.5%), abruptly increased by 2004 (6.3%) and increased slightly by 2012 (7.5%). Mean annual surface temperatures varied by 4.9°C among degradation and stabilization stages and by 9.9°C from polygon center to deep lake bottom. Mean thicknesses of the active layer, ice-poor transient layer, ice-rich intermediate layer, thermokarst cave ice, and wedge ice varied substantially among stages. In early stages, thaw settlement caused water to impound in thermokarst troughs, creating positive feedbacks that increased net radiation, soil heat flux, and soil temperatures. Plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface, thus reducing surface water depth and soil temperatures in later stages. The ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change.

Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization

NASA Astrophysics Data System (ADS)

Jorgenson, M. T.; Kanevskiy, M.; Shur, Y.; Moskalenko, N.; Brown, D. R. N.; Wickland, K.; Striegl, R.; Koch, J.

2015-11-01

Ground ice is abundant in the upper permafrost throughout the Arctic and fundamentally affects terrain responses to climate warming. Ice wedges, which form near the surface and are the dominant type of massive ice in the Arctic, are particularly vulnerable to warming. Yet processes controlling ice wedge degradation and stabilization are poorly understood. Here we quantified ice wedge volume and degradation rates, compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. Mean ice wedge volume in the top 3 m of permafrost was 21%. Imagery from 1949 to 2012 showed thermokarst extent (area of water-filled troughs) was relatively small from 1949 (0.9%) to 1988 (1.5%), abruptly increased by 2004 (6.3%) and increased slightly by 2012 (7.5%). Mean annual surface temperatures varied by 4.9°C among degradation and stabilization stages and by 9.9°C from polygon center to deep lake bottom. Mean thicknesses of the active layer, ice-poor transient layer, ice-rich intermediate layer, thermokarst cave ice, and wedge ice varied substantially among stages. In early stages, thaw settlement caused water to impound in thermokarst troughs, creating positive feedbacks that increased net radiation, soil heat flux, and soil temperatures. Plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface, thus reducing surface water depth and soil temperatures in later stages. The ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change.

Evaluating the Governing Factors of Variability in Nocturnal Boundary Layer Height Based on Elastic Lidar in Wuhan.

PubMed

Wang, Wei; Mao, Feiyue; Gong, Wei; Pan, Zengxin; Du, Lin

2016-11-01

The atmospheric boundary layer (ABL), an atmospheric region near the Earth's surface, is affected by surface forcing and is important for studying air quality, climate, and weather forecasts. In this study, long-term urban nocturnal boundary layers (NBLs) were estimated by an elastic backscatter light detection and ranging (LiDAR) with various methods in Wuhan (30.5° N, 114.4° E), a city in Central China. This study aims to explore two ABL research topics: (1) the relationship between NBL height (NBLH) and near-surface parameters (e.g., sensible heat flux, temperature, wind speed, and relative humidity) to elucidate meteorological processes governing NBL variability; and (2) the influence of NBLH variations in surface particulate matter (PM) in Wuhan. We analyzed the nocturnal ABL-dilution/ABL-accumulation effect on surface particle concentration by using a typical case. A long-term analysis was then performed from 5 December 2012-17 June 2016. Results reveal that the seasonal averages of nocturnal (from 20:00 to 05:00 next day, Chinese standard time) NBLHs are 386 ± 161 m in spring, 473 ± 154 m in summer, 383 ± 137 m in autumn, and 309 ± 94 m in winter. The seasonal variations in NBLH, AOD, and PM 2.5 display a deep (shallow) seasonal mean NBL, consistent with a small (larger) seasonal mean PM 2.5 near the surface. Seasonal variability of NBLH is partly linearly correlated with sensible heat flux at the surface (R = 0.72). Linear regression analyses between NBLH and other parameters show the following: (1) the positive correlation (R = 0.68) between NBLH and surface temperature indicates high (low) NBLH corresponding to warm (cool) conditions; (2) the slight positive correlation (R = 0.52) between NBLH and surface relative humidity in Wuhan; and (3) the weak positive correlation (R = 0.38) between NBLH and wind speed inside the NBL may imply that the latter is not an important direct driver that governs the seasonal variability of NBLH.

Soil Surface Organic Layers in Alaska's Arctic Foothills: Development, Distribution and Microclimatic Feedbacks

NASA Astrophysics Data System (ADS)

Baughman, C. A.; Mann, D. H.; Verbyla, D.; Valentine, D.; Kunz, M. L.; Heiser, P. A.

2013-12-01

Accumulated organic matter at the ground surface plays an important role in arctic ecosystems. These soil surface organic layers (SSOLs) influence temperature, moisture, and chemistry in the underlying mineral soil and, on a global basis, comprise enormous stores of labile carbon. Understanding the dynamics of SSOLs is prerequisite to modeling the responses of arctic ecosystem processes to climate changes. Here, we ask three questions regarding SSOLs in the Arctic Foothills in northern Alaska: 1) What environmental factors control their spatial distribution? 2) How long do they take to form? 3) What is the relationship between SSOL thickness and mineral soil temperature through the growing season? The best topographically-controlled predictors of SSOL thickness and spatial distribution are duration of sunlight during the growing-season, upslope drainage area, slope gradient, and elevation. SSOLs begin to form within several decades following disturbance but require 500-700 years to reach equilibrium states. Once formed, mature SSOLs lower peak growing-season temperature and mean annual temperature in the underlying mineral horizon by 8° and 3° C respectively, which reduces available growing degree days within the upper mineral soil by nearly 80%. How ongoing climate change in northern Alaska will affect the region's SSOLs is an open and potentially crucial question.

Response of the Shockley surface state to an external electrical field: A density-functional theory study of Cu(111)

NASA Astrophysics Data System (ADS)

Berland, K.; Einstein, T. L.; Hyldgaard, P.

2012-01-01

The response of the Cu(111) Shockley surface state to an external electrical field is characterized by combining a density-functional theory calculation for a slab geometry with an analysis of the Kohn-Sham wave functions. Our analysis is facilitated by a decoupling of the Kohn-Sham states via a rotation in Hilbert space. We find that the surface state displays isotropic dispersion, quadratic until the Fermi wave vector but with a significant quartic contribution beyond. We calculate the shift in energetic position and effective mass of the surface state for an electrical field perpendicular to the Cu(111) surface; the response is linear over a broad range of field strengths. We find that charge transfer occurs beyond the outermost copper atoms and that accumulation of electrons is responsible for a quarter of the screening of the electrical field. This allows us to provide well converged determinations of the field-induced changes in the surface state for a moderate number of layers in the slab geometry.

Secondary Flows and Boundary-Layer Accumulations in Turbine Nozzles

NASA Technical Reports Server (NTRS)

Rohlik, Harold E; Kofskey, Milton G; Allen, Hubert W; Herzig, Howard Z

1954-01-01

An investigation of secondary-flow loss patterns originating in three sets of turbine nozzle blade passages was conducted by means of flow-visualization studies and detailed flow measurements. For all cases, high loss values were measured in the fluid downstream of the corners formed by the suction surfaces of the blades and the shrouds, and these losses were accompanied by discharge-angle deviations from design values. Despite the size of the loss regions and angle gradients, over-all mass-average blade efficiencies were of the order of 0.99 and 0.98 and, therefore, are not a good index of blade performance.

In situ coagulation versus pre-coagulation for gravity-driven membrane bioreactor during decentralized sewage treatment: Permeability stabilization, fouling layer formation and biological activity.

PubMed

Ding, An; Wang, Jinlong; Lin, Dachao; Tang, Xiaobin; Cheng, Xiaoxiang; Li, Guibai; Ren, Nanqi; Liang, Heng

2017-12-01

Gravity-driven membrane filtration systems are promising for decentralized sewage treatment due to their low energy consumption and low maintenance. However, the low stable permeability/flux is currently limiting their wider application. With the ultimate goal of increasing permeability, the aim of this study was to evaluate the effect of coagulation (in situ coagulation and pre-coagulation) on the performance of a gravity-driven membrane bioreactor (GDMBR) during treatment of synthetic sewage. Results show that in situ coagulation significantly increased permeability (more than two-fold); however, no stabilization of permeability occurred over the whole operation, when non-coagulated and pre-coagulated reactors were compared. The high permeability observed was attributed to the accumulated aluminium floc in the reactor, which prevented formation of fluorescent microbial metabolites (aromatic and tryptophan proteins, as well as fulvic acids), and further avoided membrane pore blocking. In addition, the surface porosity of the fouling layer was improved (from 11.2% to 32.4% for non-coagulated and in situ coagulated reactors). The unstable permeability was possibly associated with lower biological processes within the fouling layer. These might include lower adenosine triphosphate (ATP) content and lower fluorescent metabolites from the extracellular polymeric substances (EPS) caused by the accumulated Al (compared with the control). On the other hand, pre-coagulation improved the level of stable permeability compared with the control (80 versus 40 L/m 2 h bar), mainly because pre-coagulation decreased the EPS content and also maintained high ATP content of the fouling layer. In addition, both coagulation processes reduced the total filtration resistance, mainly the hydraulically reversible resistance and cake layer resistance, which could lower the cleaning frequency. Overall, coagulation could greatly increase the removal efficiency and improve the GDMBR permeability, which would make the process suitable for decentralized wastewater treatment. Copyright © 2017 Elsevier Ltd. All rights reserved.

Dating of 30m ice cores drilled by Japanese Antarctic Research Expedition and environmental change study

NASA Astrophysics Data System (ADS)

Motoyama, H.; Suzuki, T.; Fukui, K.; Ohno, H.; Hoshina, Y.; Hirabayashi, M.; Fujita, S.

2017-12-01

1. Introduction It is possible to reveal the past climate and environmental change from the ice core drilled in polar ice sheet and glaciers. The 54th Japanese Antarctic Research Expedition conducted several shallow core drillings up to 30 m depth in the inland and coastal areas of the East Antarctic ice sheet. Ice core sample was cut out at a thickness of about 5 cm in the cold room of the National Institute of Polar Research, and analyzed ion, water isotope, dust and so one. We also conducted dielectric profile measurement (DEP measurement). The age as a key layer of large-scale volcanic explosion was based on Sigl et al. (Nature Climate Change, 2014). 2. Inland ice core Ice cores were collected at the NDF site (77°47'14"S, 39°03'34"E, 3754 m.a.s.l.) and S80 site (80°00'00"S, 40°30'04"E, 3622 m.a.s.l.). Dating of ice core was done as follows. Calculate water equivalent from core density. Accumulate water equivalent from the surface. Approximate the relation of depth - cumulative water equivalent by a quartic equation. We determined the key layer with nssSO42 - peak corresponding to several large volcanic explosions. The accumulation rate was kept constant between the key layers. As a result, NDF was estimated to be around 1360 AD and S80 was estimated to be around 1400 AD in the deepest ice core. 3. Coastal ice core An ice core was collected at coastal H15 sites (69°04'10"S, 40°44'51"E, 1030 m.a.s.l.). Dating of ice core was done as follows. Calculate water equivalent from ice core density. Accumulate water equivalent from the surface. Approximate the relation of depth - cumulative water equivalent by a quartic equation. Basically we decided to summer (December) and winter (June) due to the seasonal change of the water isotope (δD or δ18O). In addition to the seasonal change of isotope, confirm the following. Maximum of SO42- / Na +, which is earlier in time than the maximum of water isotope. Maximum of MSA at about the same time as the maximum of the water isotope. Na+ is maximal immediately after the local maximum of the water isotope. The deepest age was estimated to be around 1940 AD. 4. Example of results In the inland area, the annual average surface mass balance decreased from 1450 to 1850 AD, but it has increased since 1850 AD. The annual mass balance of coastal H15 is consistent with the result of snow stake measurement.

A model experiment of liquefaction and fluid transport: quantifying the effect of permeability discontinuity

NASA Astrophysics Data System (ADS)

Yasuda, N.; Sumita, I.

2013-12-01

Model experiments of liquefaction of a water-saturated sand (quick sand) is commonly conducted in class and in public. Various phenomena caused by liquefaction are reproduced within a closed bottle containing push-pins (Nohguchi, 2004). Experiments for tilted and layered case have also been conducted (Peacock, 2006). However quantitative measurements of liquid transport in these experiments have rarely been made. Here we show that such measurements are possible by analyzing the video images taken during such experiments. In addition, we show that a simple physical model is capable of explaining the time scales needed to expel the interstitial liquid. An experimental cell (cross section 22.0 mm x 99.4 mm, height 107.6 mm) is filled with a granular matter and water. The lower 33.0 mm consists of a two-layered granular medium, the upper layer consists of fine particles and the lower layer consists of coarse particles, with particle sizes of 0.05 mm and 0.2 mm, respectively. Since permeability depends on the square of the particle size, the upper layer becomes a low-permeability layer. We liquefy the cell by an impulsive vibration and study how the liquid migrates afterwards. We also vary the particle size combinations (upper layer: 0.05-0.15 mm, lower layer: 0.15-0.6 mm) and the thickness ratio of the 2 layers, and study how the time scale of the liquid migration depends on these changeable parameters. In a two-layered medium, we find that the pore water which originated from the bottom layer temporary accumulates at the interface of the two layers, and then ascends through the upper layer in the form of horizontal sheet or vertical channels. We find that these two different discharge styles are controlled by the permeability ratio of the two layers. We study the temporal change of the thicknesses of the two layers and find that there are three stages; 1: the slope of the upper surface is leveled by the impulse, 2: the pore water is discharged from the bottom layer and accumulates at the interface, after which it migrates upwards, 3: water discharge ends, and particles settle. We measured the relaxation time needed for the discharge and compaction to end. Because low-permeability layer inhibits pore water from rising, longer time is needed for a two-layer case compared to the one-layer case. When the particle size of the upper layer is about 1/3 or smaller than that of the lower layer, relaxation time becomes independent of the bottom particle size. We modeled the relaxation time by introducing the effective permeability of two-layered medium, and find that it explains the measurements well. References Nohguchi, Y., 2004, ICTAM04 Proceedings, Warsaw, Poland. Peacock, D. C. P., 2006, J. Geosci.Ed, 54, 550

Spatiotemporal analysis of black spruce forest soils and implications for the fate of C

USGS Publications Warehouse

Harden, Jennifer W.; Manies, Kristen L.; O'Donnell, Jonathan; Johnson, Kristofer; Frolking, Steve; Fan, Zhaosheng

2012-01-01

Post-fire storage of carbon (C) in organic-soil horizons was measured in one Canadian and three Alaskan chronosequences in black spruce forests, together spanning stand ages of nearly 200 yrs. We used a simple mass balance model to derive estimates of inputs, losses, and accumulation rates of C on timescales of years to centuries. The model performed well for the surface and total organic soil layers and presented questions for resolving the dynamics of deeper organic soils. C accumulation in all study areas is on the order of 20–40 gC/m2/yr for stand ages up to ∼200 yrs. Much larger fluxes, both positive and negative, are detected using incremental changes in soil C stocks and by other studies using eddy covariance methods for CO2. This difference suggests that over the course of stand replacement, about 80% of all net primary production (NPP) is returned to the atmosphere within a fire cycle, while about 20% of NPP enters the organic soil layers and becomes available for stabilization or loss via decomposition, leaching, or combustion. Shifts toward more frequent and more severe burning and degradation of deep organic horizons would likely result in an acceleration of the carbon cycle, with greater CO2 emissions from these systems overall.

Time-Varying Upper-Plate Deformation during the Megathrust Subduction Earthquake Cycle

NASA Astrophysics Data System (ADS)

Furlong, Kevin P.; Govers, Rob; Herman, Matthew

2015-04-01

Over the past several decades of the WEGENER era, our abilities to observe and image the deformational behavior of the upper plate in megathrust subduction zones has dramatically improved. Several intriguing inferences can be made from these observations including apparent lateral variations in locking along subduction zones, which differs from interseismic to coseismic periods; the significant magnitude of post-earthquake deformation (e.g. following the 20U14 Mw Iquique, Chile earthquake, observed on-land GPS post-EQ displacements are comparable to the co-seismic displacements); and incompatibilities between rates of slip deficit accumulation and resulting earthquake co-seismic slip (e.g. pre-Tohoku, inferred rates of slip deficit accumulation on the megathrust significantly exceed slip amounts for the ~ 1000 year recurrence.) Modeling capabilities have grown from fitting simple elastic accumulation/rebound curves to sparse data to having spatially dense continuous time series that allow us to infer details of plate boundary coupling, rheology-driven transient deformation, and partitioning among inter-earthquake and co-seismic displacements. In this research we utilize a 2D numerical modeling to explore the time-varying deformational behavior of subduction zones during the earthquake cycle with an emphasis on upper-plate and plate interface behavior. We have used a simplified model configuration to isolate fundamental processes associated with the earthquake cycle, rather than attempting to fit details of specific megathrust zones. Using a simple subduction geometry, but realistic rheologic layering we are evaluating the time-varying displacement and stress response through a multi-earthquake cycle history. We use a simple model configuration - an elastic subducting slab, an elastic upper plate (shallower than 40 km), and a visco-elastic upper plate (deeper than 40 km). This configuration leads to an upper plate that acts as a deforming elastic beam at inter-earthquake loading times and rates with a viscously relaxed regime at depths greater than 40 km. Analyses of our preliminary model results lead to the following: 1. Co-seismic stress transfer from the unloading elastic layer (shallow) into an elastically loading visco-elastic layer (deeper) - extends ~ 100 km inboard of locked zone. This stress transfer affects both coseismic and post-seismic surface displacements. 2. Post-seismic response of upper plate involves seaward motion for initial 10-20 years (~ 2 Maxwell times) after EQ. This occurs in spite of there being no slip on locked plate boundary - i.e. this is not plate boundary after-slip but rather is a consequence of stress relaxation in co-seismically loaded visco-elastic layer. However standard inversions of the surface displacement field would indicate significant after-slip along the locked plate interface. 3. By approximately 80 years (8 Maxwell times) system has returned to simple linear displacement pattern - the expected behavior for a shortening elastic beam. Prior to that time, the surface (observable) displacement pattern changes substantially over time and would result in an apparent temporal variation in coupling - from near-zero coupling to fully locked over ~ 80 years post-earthquake. These preliminary results indicate that care is needed in interpreting observed surface displacement fields from GPS, InSAR, etc. during the interseismic period. temporal variations in crustal deformation observed in regions such as the recent Tohoku, Maule, and Iquique megathrust events which are ascribed to fault plane after-slip may in fact reflect processes associated with re-equilibration of the visco-elastic subduction system.

A Coupled Ice-Atmosphere-Dust Model for a Neoproterozoic "Mudball Earth"

NASA Astrophysics Data System (ADS)

Goodman, J. C.; Strom, D.

2010-12-01

The Neoproterozoic "Snowball Earth" glaciations remain a subject of intense debate. While many have used field data to argue for either a totally or partially ice-covered Earth, fewer efforts have been made to establish the basic physical climate state and internal dynamics of these alternatives. Description of feedbacks is especially important: how does a globally ice-covered Earth reinforce itself as a stable climate system, and/or sow the seeds for its own destruction? In previous work, we investigated the flow properties of thick floating global ice sheets, and found that flow from pole to equator tends to eliminate regions of thin ice in the tropics. We briefly mentioned that ice flow and sublimation could lead to a "lag deposit" of dust on top of the tropical ice. The consequences of this were explored in detail by Dorian Abbott and others, who found that the accumulation of dust atop tropical ice causes a strong warming effect, which strongly promotes deglaciation of a Snowball climate. However, Abbott et al specified a dust layer ab initio in their GCM simulations, leaving aside the processes which produce it. Here, we present the results of our efforts to add dust processes to an earlier coupled atmosphere/ocean/ice model originally developed by David Pollard and Jim Kasting. Their model includes energy balance equations for the atmosphere and an ice mechanics model for glacial flow. To this we have added variables tracking the fraction of dust incorporated into snow and ice; the transport and accumulation of this dust through ice flow; the effects of dust on albedo and penetration of sunlight into the ice; restriction of evaporation from dust-covered surfaces; and density and buoyancy effects of dusty ice. Dust is added to the surface globally at a fixed rate, and is removed by meltwater runoff. We find that ice in tropical regions of net evaporation quickly develops a surface dust layer which drastically lowers its albedo. This dust layer develops rapidly (1000-10,000 years), and remains relatively thin (mm to cm). Its albedo effect is not strong enough to cause deglaciation on its own, but does warm the planet to near the melting point: modest amounts of CO2 are enough to cause total deglaciation. Our results show that the "mudball Earth" is a remarkably stable climate system. Drastic changes in forcing, such as varying the rate of dust accumulation by a factor of 100, have little effect on the climate, due to a strong feedback control. With summertime temperatures just below melting, adding more dust to lower the planetary albedo warms the Earth, causing summertime melting which washes away the additional dust, maintaining status quo. Dust layer thickness is controlled by a related hydrological feedback: if the dust becomes thick enough to prevent evaporation in the tropics, then less snow falls at midlatitudes. Thus, midlatitude snow cover becomes dustier and darker, warming the planet, which again melts some ice to eliminate excess dust. Future work with this model will consider the patchiness of thin dust cover on an ice surface, and will also look at the consequences of large instantaneous dust sources such as asteroid/comet impacts or large volcanic eruptions.

A possible climate signal in the surface morphology and internal structure of Galena Creek Rock Glacier, Wyoming

NASA Astrophysics Data System (ADS)

Petersen, Eric; Holt, John; Levy, Joseph; Stuurman, Cassie; Nerozzi, Stefano; Cardenas, Benjamin; Pharr, James; Aylward, Dan; Schmidt, Logan; Hoey, William; Prem, Parvathy; Rambo, Jackie; Lim, YeJin; Maharaj, Kian

2016-04-01

Galena Creek Rock Glacier (GCRG) has been shown in previous studies to be a debris-covered glacier (e.g. Ackert, Jr., 1998), and is thus a target of interest as a record of climate and an element of the mountain hydrological system. The goal of this study was to investigate possible relationships between surface morphology and internal structure and composition of GCRG. This was achieved using ground-penetrating radar (GPR), time-domain electromagnetic sounding (TEM), and photogrammetry to produce digital terrain models (DTMs). We acquired 6 longitudinal GPR surveys at 50 and 100 MHz, 2 common midpoint GPR surveys, and 28 TEM soundings on GCRG from the head to the toe, and ground-based photogrammetry data were collected to produce a DTM of its cirque at 10 cm resolution. TEM soundings locally constrained the bulk thickness of GCRG to 26-75 meters. Common midpoint and hyperbola analyses of GPR surveys produced dielectric constants in the near subsurface of 4 in the upper glacier to 5-9 in the middle and lower glacier. These are consistent with clean ice and a mélange of rock with air and/or ice, respectively. GPR revealed a pervasive shallow reflector at 1-2.5m depth that we interpret to be the interface between the surface debris layer and glacier ice. There is increased structure and clutter in the GPR data beneath this interface as one moves down glacier. Observations were additionally made of a 40m wide, 4-5m deep circular thermokarst pond located on upper GCRG in the cirque. The walls of the pond revealed a cross-section of the top several meters of GCRG's interior: a dry surface layer of rocky debris 1-1.5m thick overlying pure glacier ice. An englacial debris band was also observed, roughly 50 cm thick and presenting at an apparent up-glacier dip of ~30 degrees, intersecting the surface near a subtle ridge resolved in the photogrammetry DTM. A GPR transect conducted near the pond over 6 similar ridges imaged 6 corresponding up-glacier dipping reflectors that intersected the surface at 15-35 degrees at each ridge. Each of these reflectors is interpreted to be a debris band similar to the one observed in the thermokarst pond. These debris bands are hypothesized to represent climatic "tree rings:" they are formed in interglacial periods as rockfall accumulates and preserves underlying ice and then buried by subsequent ice deposition in the accumulation zone during positive mass balance periods. The up-glacier dip is the 2D expression of "nested spoons" morphology, expected from glacier flow. The potential connections between surface ridge morphology, englacial debris bands, and regional climate-driven ice accumulation make GCRG a prime candidate for further investigation.

Mechanical and Functional Properties of Nickel Titanium Adhesively Bonded Joints

NASA Astrophysics Data System (ADS)

Niccoli, F.; Alfano, M.; Bruno, L.; Furgiuele, F.; Maletta, C.

2014-07-01

In this study, adhesive joints made up of commercial NiTi sheets with shape memory capabilities are analyzed. Suitable surface pre-treatments, i.e., degreasing, sandblasting, and chemical etching, are preliminary compared in terms of surface roughness, surface energy, and substrate thinning. Results indicate that chemical etching induces marked substrate thinning without substantial gains in terms of surface roughness and free energy. Therefore, adhesive joints with degreased and sandblasted substrates are prepared and tested under both static and cyclic conditions, and damage development within the adhesive layer is monitored in situ using a CCD camera. Sandblasted specimens have a significantly higher mechanical static strength with respect to degreased ones, although they essentially fail in similar fashion, i.e., formation of microcracks followed by decohesion along the adhesive/substrate interface. In addition, the joints show a good functional response with almost complete shape memory recovery after thermo-mechanical cycling, i.e., a small accumulation of residual deformations occurs. The present results show that adhesive bonding is a viable joining technique for NiTi alloys.

Bioinspired Surfaces with Superwettability for Anti-Icing and Ice-Phobic Application: Concept, Mechanism, and Design.

PubMed

Zhang, Songnan; Huang, Jianying; Cheng, Yan; Yang, Hui; Chen, Zhong; Lai, Yuekun

2017-12-01

Ice accumulation poses a series of severe issues in daily life. Inspired by the nature, superwettability surfaces have attracted great interests from fundamental research to anti-icing and ice-phobic applications. Here, recently published literature about the mechanism of ice prevention is reviewed, with a focus on the anti-icing and ice-phobic mechanisms, encompassing the behavior of condensate microdrops on the surface, wetting, ice nucleation, and freezing. Then, a detailed account of the innovative fabrication and fundamental research of anti-icing materials with special wettability is summarized with a focus on recent progresses including low-surface energy coatings and liquid-infused layered coatings. Finally, special attention is paid to a discussion about advantages and disadvantages of the technologies, as well as factors that affect the anti-icing and ice-phobic efficiency. Outlooks and the challenges for future development of the anti-icing and ice-phobic technology are presented and discussed. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Questioning the Sedimentary Paradigm for Granites

NASA Astrophysics Data System (ADS)

Glazner, A. F.; Bartley, J. M.; Coleman, D. S.; Boudreau, A.; Walker, J. D.

2007-12-01

A critical question regarding volcano-pluton links is whether plutons are samples of magma that passed through on its way to eruption, or residues left behind after volcanic rocks were extracted. A persistent theme of recent work on granites sensu lato is that many are sedimentary accumulations of crystals that lost significant volumes of magmatic liquid. This view is based on observations of structures that clearly seem to reflect deposition on a magma chamber floor (e.g., flows of chilled mafic magma into silicic magma) and on the inference that many other structures, such as modal layering, truncated layering, and crystal accumulations, reflect crystal sedimentation on such chamber floors. There are significant physical and geochemical reasons to question this view, based on observations in the Sierra Nevada of California and similar results from other batholiths. First, few granites show the enrichments in Ba, Sr, and relative Eu that feldspar accumulation should produce. Second, sedimentary features such as graded bedding and cross-bedding form in highly turbulent flows, but turbulence is unachievable in viscous silicic liquids, where velocities on the order of 104 m/s would be required to induce turbulence in a liquid with η=104 Pa s. Third, tabular modally layered domains commonly cut surrounding modal layering on both sides, and orientations of modal layering and of the troughs of "ladder dikes" commonly scatter widely within hectare-sized areas; it is difficult to reconcile these features with gravity-driven settling. Fourth, accumulations of K-feldspar megacrysts are typically inferred to be depositional, but this is precluded by crystallization of most K- feldspar after rheologic lock-up occurs. Finally, accumulations of K-feldspar and hornblende are typically packed too tightly to be depositional. With analogy to layered mafic intrusions, many features attributed to crystal sedimentation in granites may be better explained by crystal aging and other in situ chemical processes. In particular, many of these features may record pore-melt flow paths rather than depositional processes.

Bacterial and fungal biofilm formation on anodized titanium alloys with fluorine.

PubMed

Perez-Jorge, Concepcion; Arenas, Maria-Angeles; Conde, Ana; Hernández-Lopez, Juan-Manuel; de Damborenea, Juan-Jose; Fisher, Steve; Hunt, Alessandra M Agostinho; Esteban, Jaime; James, Garth

2017-01-01

Orthopaedic device-related infections are closely linked to biofilm formation on the surfaces of these devices. Several modified titanium (Ti-6Al-4V) surfaces doped with fluorine were studied in order to evaluate the influence of these modifications on biofilm formation by Gram-positive and Gram-negative bacteria as well as a yeast. The biofilm studies were performed according to the standard test method approved by ASTM (Designation: E2196-12) using the Rotating Disk Reactor. Four types of Ti-6Al-4V samples were tested; chemically polished (CP), two types of nanostructures containing fluorine, nanoporous (NP) and nanotubular (NT), and non-nanostructured fluorine containing samples (fluoride barrier layers, FBL). Different species of Gram-positive cocci, (Staphylococcus aureus and epidermidis), Gram-negative rods (Escherichia coli, Pseudomonas aeruginosa), and a yeast (Candida albicans) were studied. For one of the Gram-positive (S. epidermidis) and one of the Gram-negative (E. coli) species a statistically-significant decrease in biofilm accumulation for NP and NT samples was found when compared with the biofilm accumulation on CP samples. The results suggest an effect of the modified materials on the biofilm formation.

A quantitative model and the experimental evaluation of the liquid fuel layer for the downward flame spread of XPS foam.

PubMed

Luo, Shengfeng; Xie, Qiyuan; Tang, Xinyi; Qiu, Rong; Yang, Yun

2017-05-05

The objective of this work is to investigate the distinctive mechanisms of downward flame spread for XPS foam. It was physically considered as a moving down of narrow pool fire instead of downward surface flame spread for normal solids. A method was developed to quantitatively analyze the accumulated liquid fuel based on the experimental measurement of locations of flame tips and burning rates. The results surprisingly showed that about 80% of the generated hot liquid fuel remained in the pool fire during a certain period. Most of the consumed solid XPS foam didn't really burn away but transformed as the liquid fuel in the downward moving pool fire, which might be an important promotion for the fast fire development. The results also indicated that the dripping propensity of the hot liquid fuel depends on the total amount of the hot liquid accumulated in the pool fire. The leading point of the flame front curve might be the breach of the accumulated hot liquid fuel if it is enough for dripping. Finally, it is suggested that horizontal noncombustible barriers for preventing the accumulation and dripping of liquid fuel are helpful for vertical confining of XPS fire. Copyright © 2017 Elsevier B.V. All rights reserved.

A low-frequency noise model with carrier generation-recombination process for pentacene organic thin-film transistor

NASA Astrophysics Data System (ADS)

Han, C. Y.; Qian, L. X.; Leung, C. H.; Che, C. M.; Lai, P. T.

2013-07-01

By including the generation-recombination process of charge carriers in conduction channel, a model for low-frequency noise in pentacene organic thin-film transistors (OTFTs) is proposed. In this model, the slope and magnitude of power spectral density for low-frequency noise are related to the traps in the gate dielectric and accumulation layer of the OTFT for the first time. The model can well fit the measured low-frequency noise data of pentacene OTFTs with HfO2 or HfLaO gate dielectric, which validates this model, thus providing an estimate on the densities of traps in the gate dielectric and accumulation layer. It is revealed that the traps in the accumulation layer are much more than those in the gate dielectric, and so dominate the low-frequency noise of pentacene OTFTs.

Modeling Peat Ages Using 7Be Data to Account for Downwash of 210Pb

NASA Astrophysics Data System (ADS)

Manies, K.; Fuller, C.; Jones, M.

2016-12-01

In order to determine the amount of peat, and thus carbon, which has accumulated since the last thaw event, we are interested in dating the surface layers of boreal thermokarst bogs. However, there can often be a mismatch by several decades between dates obtained using 210Pb, 14C, or 137Cs. We found that 210Pb-based dates were almost always younger than 14C-based dates. One of the limitations often cited regarding the use of 210Pb dating for peatlands is the potential for this radionuclide to be transported down the soil profile, biasing the mean accumulation rate (MAR) towards higher values which, in turn, results in younger ages at a specific horizon. 7Be, which has similar depositional behaviors as 210Pb but a much shorter half-life (53.22 days), can be used to help determine if there is movement of 210Pb through surface layers and the depths to which 210Pb-bearing particles are transported (over the mean life of 7Be). These data can then be used in new models, such as the Linked Radionuclide aCcumulation model (LRC; Landis et al., 2016, http://dx.doi.org/10.1016/ j.gca.2016.02.2013), which account for 210Pb downwash when calculating soil horizon ages. To this end, we measured 7Be within a bog four times over the growing season. 7Be was found to 4 cm in May, reached its maximum depth of penetration in July (7 cm), and then receded again to 4 cm. The maximum integrated 7Be activity was also found in July. This pattern is similar to other studies which found 7Be deposition decreased over the rainy season. Next, we will calculate peat ages with models that include downwash of 210Pb, the depths of which will be based on the penetration depth of 7Be. These ages will be compared to 210Pb ages obtained with both the Constant Rate of Supply (CRS) and Constant Flux - Constant Sedimentation (CF:CS) models and to 137Cs- and 14C-derived ages. We anticipate that dates based on models that include some transport of 210Pb into the soil profile will provide more accurate peat formation dates and allow for more accurate carbon accumulation rates.

A Computational Study of Vocal Fold Dehydration During Phonation.

PubMed

Wu, Liang; Zhang, Zhaoyan

2017-12-01

While vocal fold dehydration is often considered an important factor contributing to vocal fatigue, it still remains unclear whether vocal fold vibration alone is able to induce severe dehydration that has a noticeable effect on phonation and perceived vocal effort. A three-dimensional model was developed to investigate vocal fold systemic dehydration and surface dehydration during phonation. Based on the linear poroelastic theory, the model considered water resupply from blood vessels through the lateral boundary, water movement within the vocal folds, water exchange between the vocal folds and the surface liquid layer through the epithelium, and surface fluid accumulation and discharge to the glottal airway. Parametric studies were conducted to investigate water loss within the vocal folds and from the surface after a 5-min sustained phonation under different permeability and vibration conditions. The results showed that the dehydration generally increased with increasing vibration amplitude, increasing epithelial permeability, and reduced water resupply. With adequate water resupply, a large-amplitude vibration can induce an overall systemic dehydration as high as 3%. The distribution of water loss within the vocal folds was non-uniform, and a local dehydration higher than 5% was observed even under conditions of a low overall systemic dehydration (<1%). Such high level of water loss may severely affect tissue properties, muscular functions, and phonations characteristics. In contrast, water loss of the surface liquid layer was generally an order of magnitude higher than water loss inside the vocal folds, indicating that the surface dehydration level is likely not a good indicator of the systemic dehydration.

Advanced capabilities and applications of a sputter-RBS system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brijs, B.; Deleu, J.; Beyer, G.

1999-06-10

In previous experiments, sputter-RBS{sup 1} has proven to be an ideal tool to study the interaction of low energy ions. This contribution employs the same methodology to identify surface contamination induced during sputtering and to the determine absolute sputter yields. In the first experiment ERDA analysis was used to study the evolution of Hydrogen contamination during sputter-RBS experiments. Since the determination of Hydrogen concentration in very thin near surface layers is frequently limited by the presence of a strong surface peak of Hydrogen originating from adsorbed contamination of the residual vacuum, removal of this contamination would increase the sensitivity formore » Hydrogen detection in the near sub surface drastically. Therefore low energy (12 keV) Argon sputtering was used to remove the Hydrogen surface peak. However enhanced Hydrogen adsorption was observed related to the Ar dose. This experiment shows that severe vacuum conditions and the use of high current densities/sputter yields are a prerequisite for an efficient detection of Hydrogen in the near surface layers. In the second experiment, an attempt was made to determine the sputter yield of Cu during low energy (12 keV) Oxygen bombardment. In order to determine the accumulated dose of the low energy ion beam, a separate Faraday cup in combination with a remote controlled current have been added to the existing sputter-RBS set-up. Alternating sputtering and RBS analysis seem to be an adequate tool for the determination of the absolute sputter yield of Cu and this as well in the as under steady state conditions.« less

Improving the Representation of Snow Crystal Properties Within a Single-Moment Microphysics Scheme

NASA Technical Reports Server (NTRS)

Molthan, Andrew L.; Petersen, Walter A.; Case, Jonathan L.; Dembek, S. R.

2010-01-01

As computational resources continue their expansion, weather forecast models are transitioning to the use of parameterizations that predict the evolution of hydrometeors and their microphysical processes, rather than estimating the bulk effects of clouds and precipitation that occur on a sub-grid scale. These parameterizations are referred to as single-moment, bulk water microphysics schemes, as they predict the total water mass among hydrometeors in a limited number of classes. Although the development of single moment microphysics schemes have often been driven by the need to predict the structure of convective storms, they may also provide value in predicting accumulations of snowfall. Predicting the accumulation of snowfall presents unique challenges to forecasters and microphysics schemes. In cases where surface temperatures are near freezing, accumulated depth often depends upon the snowfall rate and the ability to overcome an initial warm layer. Precipitation efficiency relates to the dominant ice crystal habit, as dendrites and plates have relatively large surface areas for the accretion of cloud water and ice, but are only favored within a narrow range of ice supersaturation and temperature. Forecast models and their parameterizations must accurately represent the characteristics of snow crystal populations, such as their size distribution, bulk density and fall speed. These properties relate to the vertical distribution of ice within simulated clouds, the temperature profile through latent heat release, and the eventual precipitation rate measured at the surface. The NASA Goddard, single-moment microphysics scheme is available to the operational forecast community as an option within the Weather Research and Forecasting (WRF) model. The NASA Goddard scheme predicts the occurrence of up to six classes of water mass: vapor, cloud ice, cloud water, rain, snow and either graupel or hail.

Multiple layers of temporal and spatial control regulate accumulation of the fruiting body-specific protein APP in Sordaria macrospora and Neurospora crassa.

PubMed

Nowrousian, Minou; Piotrowski, Markus; Kück, Ulrich

2007-07-01

During fungal fruiting body development, specialized cell types differentiate from vegetative mycelium. We have isolated a protein from the ascomycete Sordaria macrospora that is not present during vegetative growth but accumulates in perithecia. The protein was sequenced by mass spectrometry and the corresponding gene was termed app (abundant perithecial protein). app transcript occurs only after the onset of sexual development; however, the formation of ascospores is not a prerequisite for APP accumulation. The transcript of the Neurospora crassa ortholog is present prior to fertilization, but the protein accumulates only after fertilization. In crosses of N. crassa Deltaapp strains with the wild type, APP accumulates when the wild type serves as female parent, but not in the reciprocal cross; thus, the presence of a functional female app allele is necessary and sufficient for APP accumulation. These findings highlight multiple layers of temporal and spatial control of gene expression during fungal development.

Direct single-layered fabrication of 3D concavo convex patterns in nano-stereolithography

NASA Astrophysics Data System (ADS)

Lim, T. W.; Park, S. H.; Yang, D. Y.; Kong, H. J.; Lee, K. S.

2006-09-01

A nano-surfacing process (NSP) is proposed to directly fabricate three-dimensional (3D) concavo convex-shaped microstructures such as micro-lens arrays using two-photon polymerization (TPP), a promising technique for fabricating arbitrary 3D highly functional micro-devices. In TPP, commonly utilized methods for fabricating complex 3D microstructures to date are based on a layer-by-layer accumulating technique employing two-dimensional sliced data derived from 3D computer-aided design data. As such, this approach requires much time and effort for precise fabrication. In this work, a novel single-layer exposure method is proposed in order to improve the fabricating efficiency for 3D concavo convex-shaped microstructures. In the NSP, 3D microstructures are divided into 13 sub-regions horizontally with consideration of the heights. Those sub-regions are then expressed as 13 characteristic colors, after which a multi-voxel matrix (MVM) is composed with the characteristic colors. Voxels with various heights and diameters are generated to construct 3D structures using a MVM scanning method. Some 3D concavo convex-shaped microstructures were fabricated to estimate the usefulness of the NSP, and the results show that it readily enables the fabrication of single-layered 3D microstructures.

1/12-scale physical modeling experiments in support of tank 241-SY- 101 hydrogen mitigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fort, J.A.; Bamberger, J.A.; Bates, J.M.

1993-01-01

Hanford tank 241-SY-101 is a 75-ft-dia double-shell tank that contains approximately 1.1 M gal of radioactive fuel reprocessing waste. Core samples have shown that the tank contents are separated into two main layers, a article laden supernatant liquid at the top of the tank and a more dense slurry on the bottom. Two additional layers may be present, one being a potentially thick sludge lying beneath the slurry at the bottom of the tank and the other being the crust that has formed on the surface of the supernatant liquid. The supernatant is more commonly referred to as the convectivemore » layer and the slurry as the non-convective layer. Accumulation of gas (partly hydrogen) in the non-convective layer is suspected to be the key mechanism behind the gas burp phenomena, and several mitigation schemes are being developed to encourage a more uniform gas release rate (Benegas 1992). To support the full-scale hydraulic mitigation test, scaled experiments were performed to satisfy two objectives: 1. provide an experimental database for numerical- model validation; 2. establish operating parameter values required to mobilize the settled solids and maintain the solids in suspension.« less

1/12-scale physical modeling experiments in support of tank 241-SY- 101 hydrogen mitigation. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fort, J.A.; Bamberger, J.A.; Bates, J.M.

1993-01-01

Hanford tank 241-SY-101 is a 75-ft-dia double-shell tank that contains approximately 1.1 M gal of radioactive fuel reprocessing waste. Core samples have shown that the tank contents are separated into two main layers, a article laden supernatant liquid at the top of the tank and a more dense slurry on the bottom. Two additional layers may be present, one being a potentially thick sludge lying beneath the slurry at the bottom of the tank and the other being the crust that has formed on the surface of the supernatant liquid. The supernatant is more commonly referred to as the convectivemore » layer and the slurry as the non-convective layer. Accumulation of gas (partly hydrogen) in the non-convective layer is suspected to be the key mechanism behind the gas burp phenomena, and several mitigation schemes are being developed to encourage a more uniform gas release rate (Benegas 1992). To support the full-scale hydraulic mitigation test, scaled experiments were performed to satisfy two objectives: 1. provide an experimental database for numerical- model validation; 2. establish operating parameter values required to mobilize the settled solids and maintain the solids in suspension.« less

Chemical and isotopic evolution of a layered eastern U.S. snowpack and its relation to stream-water composition

USGS Publications Warehouse

Shanley, J.B.; Kendall, C.; Albert, M.R.; Hardy, J.P.

1995-01-01

The chemical, isotopic, and morphologic evolution of a layered snowpack was investigated during the winter of 1993-94 at Sleepers River Research Watershed in Danville, Vermont. The snowpack was monitored at two small basins: a forested basin at 525 m elevation, and an agricultural basin at 292 m elevation. At each site, the snowpack morphology was characterized and individual layers were sampled seven times during the season. Nitrate and 8d18O profiles in the snowpack remained relatively stable until peak accumulation in mid-March, except near the snow surface, where rain-on-snow events caused water and nitrate movement down to impeding ice layers. Subsequently, water and nitrate moved more readily through the ripening snowpack. As the snowpack evolved, combined processes of preferential ion elution, isotopic fractionation, and infiltration of isotopically heavy rainfall caused the pack to become depleted in solutes and isotopically enriched. The release of nitrate and isotopically depleted water was reflected in patterns of nitrate concentrations and ??18O of meltwater and stream water. Results supported data from the previous year which suggested that streamflow in the forested basin during snowmelt was dominated by groundwater discharge.

Comparison of stable boundary layer depth estimation from sodar and profile mast.

NASA Astrophysics Data System (ADS)

Dieudonne, Elsa; Anderson, Philip

2015-04-01

The depth of the atmospheric turbulent mixing layer next to the earths surface, hz, is a key parameter in analysis and modeling of the interaction of the atmosphere with the surface. The transfer of momentum, heat, moisture and trace gases are to a large extent governed by this depth, which to a first approximation acts as a finite reservoir to these quantities. Correct estimates of the evolution of hz assists the would allow accurate prognosis of the near-surface accumulation of these variables, that is, wind speed, temperature, humidity and tracer concentration. Measuring hz however is not simple, especially where stable stratification acts to reduce internal mixing, and indeed, it is not clear whether hz is similar for momentum, heat and tracer. Two methods are compared here, to assess their similarity: firstly using acoustic back-scatter is used as an indicator of turbulent strength, the upper limit implying a change to laminar flow and the top of the boundary layer. Secondly, turbulence kinetic energy profiles, TKE(z), are extrapolated to estimate z for TKE(z) = 0, again implying laminar flow. Both techniques have the implied benefit of being able to run continually (via sodar and turbulence mast respectively) with the prospect of continual, autonomous data analysis generating time series of hz. This report examines monostatic sodar echo and sonic anemometer-derived turbulence profile data from Halley Station on the Brunt Ice Shelf Antarctica, during the austral winter of 2003. We report that the two techniques frequently show significant disagreement in estimated depth, and still require manual intervention, but further progress is possible.

A model for thin layer formation by delayed particle settling at sharp density gradients

NASA Astrophysics Data System (ADS)

Prairie, Jennifer C.; White, Brian L.

2017-02-01

Thin layers - regions where plankton or particles accumulate vertically on scales of a few meters or less - are common in coastal waters, and have important implications for both trophic dynamics and carbon cycling. These features can form by a variety of biological and physical mechanisms, including localized growth, shear-thinning, and directed swimming. An additional mechanism may result in the formation of thin layers of marine aggregates, which have been shown to decrease their settling velocity when passing through sharp density gradients, a behavior termed delayed settling. Here, we apply a simple vertical advection-diffusion model to predict the properties of aggregate thin layers formed by this process. We assume a constant vertical flux of particles from the surface, which is parameterized by observations from laboratory experiments with marine aggregates. The formation, maintenance, and shape of the layers are described in relation to non-dimensional numbers that depend on environmental conditions and particle settling properties. In particular, model results demonstrate layer intensity and sharpness both increase with higher Péclet number (Pe), that is, under conditions with weaker mixing relative to layer formation. Similarly, more intense and sharper layers are found when the delayed settling behavior of aggregates is characterized by a lower velocity minimum. The model also predicts layers that are vertically asymmetric and highly "peaky" when compared with a Gaussian distribution, features often seen in thin layers in natural environments. Lastly, by comparing model predictions with observations of thin layers in the field, we are able to gain some insight into the applicability of delayed settling as a thin layer formation mechanism in different environmental conditions.

Substrate porosity enhances chondrocyte attachment, spreading, and cartilage tissue formation in vitro.

PubMed

Spiteri, C G; Pilliar, R M; Kandel, R A

2006-09-15

Tissue engineering is being explored as a new approach to treat damaged cartilage. As the biomaterial used may influence tissue formation, the effects of substrate geometry on chondrocyte behavior in vitro were examined. Articular chondrocytes were isolated and cultured on the surface of smooth, rough, porous-coated, and fully porous Ti-6Al-4V substrates. The percentage of chondrocytes that attached to each substrate at 24 h was determined. After 24 and 72 h, chondrocytes were visualized by scanning electron microscopy and cell areas were measured. Collagen and proteoglycan accumulation within the first 24 h was determined by incorporation with [3H]-proline and [35S]-SO4, respectively. Chondrocyte attachment as well as matrix accumulation was enhanced as substrate surface area increased. Cell areas on the fully porous substrate were over four times greater than on any other substrate by 72 h in culture. After 8 weeks in culture, a continuous layer of cartilaginous tissue formed only on the surface of the fully porous substrate. This suggests that fully porous Ti-6Al-4V substrates provide the conditions that favor cartilage tissue formation by influencing cell attachment and extent of cell spreading. Understanding how substrate porosity influences chondrocyte behavior may help identify methods to further enhance cartilage tissue formation in vitro. 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006.

Solar cell modules with improved backskin and methods for forming same

DOEpatents

Hanoka, Jack I.

1998-04-21

A laminated solar cell module with a backskin layer that reduces the materials and labor required during the manufacturing process. The solar cell module includes a rigid front support layer formed of light transmitting material having first and second surfaces. A transparent encapsulant layer has a first surface disposed adjacent the second surface of the front support layer. A plurality of interconnected solar cells have a first surface disposed adjacent a second surface of the transparent encapsulant layer. The backskin layer is formed of a thermoplastic olefin, which includes first ionomer, a second ionomer, glass fiber, and carbon black. A first surface of the backskin layer is disposed adjacent a second surface of the interconnected solar cells. The transparent encapsulant layer and the backskin layer, in combination, encapsulate the interconnected solar cells. An end portion of the backskin layer can be wrapped around the edge of the module for contacting the first surface of the front support layer to form an edge seal. A laminated solar cell module with a backskin layer that reduces the materials and labor required during the manufacturing process. The solar cell module includes a rigid front support layer formed of light transmitting material having first and second surfaces. A transparent encapsulant layer has a first surface disposed adjacent the second surface of the front support layer. A plurality of interconnected solar cells have a first surface disposed adjacent a second surface of the transparent encapsulant layer. The backskin layer is formed of a thermoplastic olefin, which includes first ionomer, a second ionomer, glass fiber, and carbon black. A first surface of the backskin layer is disposed adjacent a second surface of the interconnected solar cells. The transparent encapsulant layer and the backskin layer, in combination, encapsulate the interconnected solar cells. An end portion of the backskin layer can be wrapped around the edge of the module for contacting the first surface of the front support layer to form an edge seal.

Aerosol-Monsoon Interaction, maintenance and variability of the Asian Tropopause Aerosol Layer (ATAL)

NASA Astrophysics Data System (ADS)

Yuan, C.; Lau, W. K. M.; Li, Z.

2016-12-01

In recent years, the discovery of the Asian Tropopause Aerosol Layer (ATAL) from NASA satellite observations has sparked much interests in research on its composition, origin and relationships to the transport processes of atmospheric constituents in the upper troposphere and lower stratosphere (UTLS) and the variability of the Asian Monsoon Anticyclone (AMA). In this paper, based on analysis of MERRA2 reanalysis data, we present results showing that: 1) water vapor, aerosols and chemical gases (BC, OC, dust and CO) originated for the earth surface contribute significantly to the composition of the ATAL during the Asian summer monsoon, 2) one of the major pathways is via the strong large-scale vertical motion, and convective ascent over the Northern Himalayan Foothills during the peak phase of the Indian monsoon, 3) once transported into the UTLS , atmospheric constituents are capped by the Tropopuase inversion Layer (TIL) and advected around within and in the vicinity of the AMA forming the ATAL, 4) the ATAL is modulated by UTLS transport processes which undergo intrinsic monsoon intraseasonal oscillations with 20-30 day quasi-periodicity, coupled to lower tropospheric monsoon dynamics and diabatic heating processes, 5) the pre-monsoon accumulation of absorbing aerosols (BC, OC and dust) over the Indo-Gangetic Plain is more than likely to play an important role in enhancing the UTLS transport of atmospheric constituents from the earth surface to the ATAL.

PEDOT:PSS as multi-functional composite material for enhanced Li-air-battery air electrodes

PubMed Central

Yoon, Dae Ho; Yoon, Seon Hye; Ryu, Kwang-Sun; Park, Yong Joon

2016-01-01

We propose PEDOT:PSS as a multi-functional composite material for an enhanced Li-air-battery air electrode. The PEDOT:PSS layer was coated on the surface of carbon (graphene) using simple method. A electrode containing PEDOT:PSS-coated graphene (PEDOT electrode) could be prepared without binder (such as PVDF) because of high adhesion of PEDOT:PSS. PEDOT electrode presented considerable discharge and charge capacity at all current densities. These results shows that PEDOT:PSS acts as a redox reaction matrix and conducting binder in the air electrode. Moreover, after cycling, the accumulation of reaction products due to side reaction in the electrode was significantly reduced through the use of PEDOT:PSS. This implies that PEDOT:PSS coating layer can suppress the undesirable side reactions between the carbon and electrolyte (and/or Li2O2), which causes enhanced Li-air cell cyclic performance. PMID:26813852

Investigation of Various Active Layers for Their Performance on Organic Solar Cells.

PubMed

Huang, Pao-Hsun; Wang, Yeong-Her; Ke, Jhong-Ciao; Huang, Chien-Jung

2016-08-09

The theoretical mechanism of open-circuit voltages (V OC ) in OSCs based on various small molecule organic materials is studied. The structure under investigation is simple planar heterojunction (PHJ) by thermal vacuum evaporation deposition. The various wide band gaps of small molecule organic materials are used to enhance the power conversion efficiency (PCE). The donor materials used in the device include: Alpha-sexithiophene (α-6T), Copper(II) phthalocyanine (CuPc), boron subnaphthalocyanine chloride (SubNc) and boron Subphthalocyanine chloride (SubPc). It is combined with fullerene or SubPc acceptor material to obtain a comprehensive understanding of the charge transport behavior. It is found that the V OC of the device is largely limited by charge transport. This was associated with the space charge effects and hole accumulation. These results are attributed to the improvement of surface roughness and work function after molybdenum trioxide (MoO₃) is inserted as an anode buffer layer.

Molecular Simulations of Graphene-Based Electric Double-Layer Capacitors

NASA Astrophysics Data System (ADS)

Kalluri, Raja K.; Konatham, Deepthi; Striolo, Alberto

2011-03-01

Towards deploying renewable energy sources it is crucial to develop efficient and cost-effective technologies to store electricity. Traditional batteries are plagued by a number of practical problems that at present limit their widespread applicability. One possible solution is represented by electric double-layer capacitors (EDLCs). To deploy EDLCs at the large scale it is necessary to better understand how electrolytes pack and diffuse within narrow charged pores. We present here simulation results for the concentrated aqueous solutions of NaCl, CsCl, and NaI confined within charged graphene-based porous materials. We discuss how the structure of confined water, the salt concentration, the ions size, and the surface charge density determine the accumulation of electrolytes within the porous network. Our results, compared to data available for bulk systems, are critical for relating macroscopic observations to molecular-level properties of the confined working fluids. Research supported by the Department of Energy.

Online measurement of bead geometry in GMAW-based additive manufacturing using passive vision

NASA Astrophysics Data System (ADS)

Xiong, Jun; Zhang, Guangjun

2013-11-01

Additive manufacturing based on gas metal arc welding is an advanced technique for depositing fully dense components with low cost. Despite this fact, techniques to achieve accurate control and automation of the process have not yet been perfectly developed. The online measurement of the deposited bead geometry is a key problem for reliable control. In this work a passive vision-sensing system, comprising two cameras and composite filtering techniques, was proposed for real-time detection of the bead height and width through deposition of thin walls. The nozzle to the top surface distance was monitored for eliminating accumulated height errors during the multi-layer deposition process. Various image processing algorithms were applied and discussed for extracting feature parameters. A calibration procedure was presented for the monitoring system. Validation experiments confirmed the effectiveness of the online measurement system for bead geometry in layered additive manufacturing.

Mobility balance in the light-emitting layer governs the polaron accumulation and operational stability of organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Kim, Jae-Min; Lee, Chang-Heon; Kim, Jang-Joo

2017-11-01

Organic light-emitting diode (OLED) displays are lighter and more flexible, have a wider color gamut, and consume less power than conventional displays. Stable materials and the structural design of the device are important for OLED longevity. Control of charge transport and accumulation in the device is particularly important because the interaction of excitons and polarons results in material degradation. This research investigated the charge dynamics of OLEDs experimentally and by drift-diffusion modeling. Parallel capacitance-voltage measurements of devices provided knowledge of charge behavior at different driving voltages. A comparison of exciplex-forming co-host and single host structures established that the mobility balance in the emitting layers determined the amount of accumulated polarons in those layers. Consequently, an exciplex-forming co-host provides a superior structure in terms of device lifetime and efficiency because of its well-balanced mobility. Minimizing polaron accumulation is key to achieving long OLED device lifetimes. This is a crucial aspect of device physics that must be considered in the device design structure.

Changes in vegetation, peat properties and peat accumulation in Swedish peatlands as revealed by archive data.

NASA Astrophysics Data System (ADS)

Schoning, Kristian; Sohlenius, Gustav

2016-04-01

In this investigation we have studied patterns in peat accumulation and changes in mire status since the early 1900s for two areas in Sweden. In the early 1900s the Geological Survey of Sweden collected a vast amount of peat and peatland data, including information on vegetation and land-use. We have used this archive data to evaluate changes in mire vegetation, mire wetness and surface peat properties, rates of peat accumulation, succession in young wetlands and the effects of cultivation on peatlands. In total 156 mires in an uplift area of eastern middle Sweden were included in the data-set, including both pristine mires and peatlands used for agricultural purposes. In this area new peatlands have continuously been formed during the past 7 000 years making it possible to evaluate changes in peat accumulation over time. The other study area is situated in the south Swedish Uplands where we have revisited some larger bogs. The results from our investigation show that many of the peatlands have underwent major changes since the early 1900s. In most of the small peatlands we have found important changes in vegetation where mire vegetation has been replaced by nutrient demanding and/or dry species flora while the tree stand on large mires in south Sweden have increased. In some mires humification has increased in the uppermost peat-layers and the mire surface have become drier compared to the early 1900s. In eastern middle Sweden there are indications that the peat accumulation is lower 0,5 mm/year in older peatlands compared with younger ones 1,2 mm/year, although the mire vegetation in the older peatlands is dominated by sphagnum. The peat depth of the cultivated mires in this area shows a mean decrease of 40 cm since the early 1900s.

Historical occurrences of polybrominated diphenyl ethers and polychlorinated biphenyls in Manila Bay, Philippines, and in the upper Gulf of Thailand.

PubMed

Kwan, Charita S; Takada, Hideshige; Boonyatumanond, Ruchaya; Kato, Yoshihisa; Mizukawa, Kaoruko; Ito, Maki; Dung, Le Quang; Zakaria, Mohamad Pauzi; Santiago, Evangeline C

2014-02-01

Historical trends of the accumulation of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in a typical tropical Asian environment were investigated using radio-dated sediment cores from Manila Bay, the Philippines and from the upper Gulf of Thailand. Vertical profiles indicated earlier usage of PCBs than of PBDEs which coincided with their industrial production. The increasing concentrations of total PBDEs and PCBs toward the surface suggested an increased consumption of PBDEs; and possible leakage of PCBs from old machineries into the aquatic environment in recent years. Current input of PCBs to the catchment of Manila Bay was supported by the analyses of air samples and plastic resin pellets. The vertical profiles of total PBDEs in the cores (i.e., rapidly increasing concentrations corresponding to the mid-1980s until mid-1990s, followed by a decrease until the early 2000s, and increasing again toward the surface) likely corresponded to the rapid economic growth in Asia in the 1990s, the Asian financial crisis in 1997, and the economic recovery since early 2000s. BDE-209 was predominant especially on the surface layers. BDEs 47 and 99 generally decreased toward the surface, reflecting the phase-out of the technical penta-PBDE products and the regulation by the Stockholm Convention in recent years. Increasing ratios of BDE-202/209, 206/209, 207/209 and decreasing % of BDE-209 down the core layers may provide evidence for the anaerobic debromination of BDE-209 in the sediment cores. Inventories in ng/cm(2) of total PCBs were higher than total PBDEs (92 vs. 34 and 47 vs. 11 in the Philippines; 47 vs. 33 in Thailand). However, the doubling times indicated faster accumulation of total PBDEs (6-7 years) and BDE-209 (6-7.5 years) than of PCBs (8-11 years). Furthermore, the temporal increase in BDE-209 was comparable to or faster than those reported in other water bodies around the world. © 2013.

Tunnel barrier schottky

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chu, Rongming; Cao, Yu; Li, Zijian

2018-02-20

A diode includes: a semiconductor substrate; a cathode metal layer contacting a bottom of the substrate; a semiconductor drift layer on the substrate; a graded aluminum gallium nitride (AlGaN) semiconductor barrier layer on the drift layer and having a larger bandgap than the drift layer, the barrier layer having a top surface and a bottom surface between the drift layer and the top surface, the barrier layer having an increasing aluminum composition from the bottom surface to the top surface; and an anode metal layer directly contacting the top surface of the barrier layer.

Leaching behavior of veterinary antibiotics in animal manure-applied soils.

PubMed

Pan, Min; Chu, L M

2017-02-01

Agricultural fields worldwide are being contaminated by the escalating application of veterinary antibiotics (VAs) via animal manure and biosolids applied as fertilizers or of wastewater for irrigation, resulting in soil degradation and damage to the health of terrestrial environments. This paper describes a series of column studies investigating the leaching behavior of five VAs, tetracycline (TC), sulfamethazine (SMZ), norfloxacin (NOR), erythromycin (ERY) and chloramphenicol (CAP), under different simulated rainfall conditions that could occur in agricultural environments. Our aim was to explore the effects of acid rain and torrential rain on the leaching of different VAs and to determine their leaching behaviors along the soil profile. The results showed that acid rain accelerated the accumulation of VAs from animal manure in surface soil while long rainfall durations promoted the downward migration of VAs in soil. Under acid rain conditions, a higher concentration of VAs remained in the animal manure. More VAs were eluted to deeper soil layers and the leachate under extreme rainfall conditions. The leachability of VAs was higher in sandy soil than in clay or loamy soil. SMZ and ERY posed a higher risk to deeper soil layers and groundwater, while NOR and TC tended to persist in surface soil, which can be explained by their different physicochemical properties in soil. Moreover, the general trends from two model assessments and soil column measurements appeared to be in agreement. SMZ had a high leachability, while NOR tended to accumulate in soils. This study provided vital insight into the persistence mechanisms of VAs in terrestrial environments and their potential risks to soils and groundwater. Copyright © 2016 Elsevier B.V. All rights reserved.

Mechanism of Surface Alkylation of a Gold Aerogel with Tetra-n-butylstannane-d36: Identification of Byproducts.

PubMed

Benkovičová, Monika; Wen, Dan; Plutnar, Jan; Čížková, Martina; Eychmüller, Alexander; Michl, Josef

2017-05-18

The formation of self-assembled monolayers on surfaces is often likely to be accompanied by the formation of byproducts, whose identification holds clues to the reaction mechanism but is difficult due to the minute amounts produced. We now report a successful identification of self-assembly byproducts using gold aerogel with a large specific surface area, a procedure likely to be applicable generally. Like a thin gold layer on a flat substrate, the aerogel surface is alkylated with n-butyl-d 9 groups upon treatment with a solution of tetra-n-butylstannane-d 36 under ambient conditions. The reaction byproducts accumulate in the mother liquor in amounts sufficient for GC-MS analysis. In chloroform solvent, they are butene-d 8 , butane-d 10 , octane-d 18 , and tributylchlorostannane-d 27 . In hexane, they are the same except that tributylchlorostannane-d 27 is replaced with hexabutyldistannane-d 54 . The results are compatible with an initial homolytic dissociation of a C-Sn bond on the gold surface, followed by known radical processes.

Electric breakdowns of the "plasma capacitors" occurs on insulation coating of the ISS surface

NASA Astrophysics Data System (ADS)

Homin, Taras; Korsun, Anatolii

High electric fields and currents are occurred in the spacecrafts plasma environment by onboard electric generators. Thus the high voltage solar array (SA) of the American segment of International Space Station (ISS) generates potential 160 V. Its negative pole is shorted to the frames of all the ISS segments. There is electric current between the SA and the frame through the plasma environment, i.e. electric discharge occurs. As a result a potential drop exists between the frames of all the ISS segments and the environmental plasma [1], which is cathode drop potential varphi _{c} defined. When ISS orbiting, the φc varies greatly in the range 0-100 V. A large area of the ISS frames and SA surface is coated with a thin dielectric film. Because of cathode drop potential the frame surfaces accumulate ion charges and the SA surfaces accumulate electron charges. These surfaces become plasma capacitors, which accumulate much charge and energy. Micrometeorite impacts or buildup of potential drop in excess of breakdown threshold varphi_{b} (varphi _{c} > varphi _{b} = 60 V) may cause breakdowns of these capacitors. Following a breakdown, the charge collected at the surfaces disperses and transforms into a layer of dense plasma [2]. This plasma environment of the spacecraft produces great pulsed electric fields E at the frame surfaces as well as heavy currents between construction elements which in turn induce great magnetic fields H. Therefore the conductive frame and the environmental plasma is plasma inductors. We have calculated that the densities of these pulsing and high-frequency fields E and H generated in the plasma environment of the spacecraft may exceed values hazardous to human. Besides, these fields must induce large electromagnetic impulses in the space-suit and in the power supply and control circuits of onboard systems. During astronaut’s space-suit activity, these fields will penetrate the space-suit and the human body with possible hazardous effects. These effects need to be studied, and appropriate remedies are to be developed. References 1. Mikatarian, R., et al., «Electrical Charging of the International Space Station», AIAA Paper No. 2003-1079, 41th. Aerospace Sciences Meeting and Exhibit, January 2003. 2. A.G. Korsun, «Electric discharge processes intensification mechanisms on International Space Station surface». Astronautics and rocket production, 1, 2011 (in Russian).

Dissected Mantle Terrain on Mars: Formation Mechanisms and the Implications for Mid- latitude Near-surface Ground Ice

NASA Astrophysics Data System (ADS)

Searls, M. L.; Mellon, M. T.

2008-12-01

Determining the present and past distribution of surface and subsurface ice on Mars is critical for understanding the volatile inventory and climatic history of the planet. An analysis of a latitude-dependent layer of surface material known as the dissected mantle terrain can provide valuable insight into the distribution of ice in the recent past. The dissected mantle terrain is a surface unit that occurs globally in the mid-latitude of Mars. This unit is characterized by a smooth mantle of uniform thickness and albedo that is draped over the existing topography. This smooth mantle is disaggregated and dissected in places resulting in a hummocky pitted appearance. We propose that the mid-latitude dissected terrain results from collapse of a dusty mantle into the void left from desiccation of an underlying ice-rich (pure or dirty ice) layer. During period(s) of high obliquity, it is possible for ice to become stable at lower latitudes. Due to lack of direct solar insolation, surface ice deposits will preferentially accumulate on pole-ward facing slopes first. A mantle of dust and dirt is then deposited on top of these ice-rich deposits. As the climate changes, desiccation of the now buried ice leads to collapse of the overlying dusty layer resulting in a hummocky pitted appearance. This theory is supported by the pole-ward preference for the dissection pits as well an increase in dissection with increasing latitude. A study of the global distribution of the mid-latitude dissected terrain can provide invaluable clues towards unlocking the distribution of ice in the recent past. An analysis of HiRISE images and MOLA data indicate that the distribution of dissection pits varies from one region to the next. Knowing the distribution of ice in conjunction with ice stability modeling can provide a global view of the climate and orbital history of Mars at the time these features formed.

Countermeasures to Microbiofouling in Simulated Ocean Thermal Energy Conversion Heat Exchangers with Surface and Deep Ocean Waters in Hawaii

PubMed Central

Berger, Leslie Ralph; Berger, Joyce A.

1986-01-01

Countermeasures to biofouling in simulated ocean thermal energy conversion heat exchangers have been studied in single-pass flow systems, using cold deep and warm surface ocean waters off the island of Hawaii. Manual brushing of the loops after free fouling periods removed most of the biofouling material. However, over a 2-year period a tenacious film formed. Daily free passage of sponge rubber balls through the tubing only removed the loose surface biofouling layer and was inadequate as a countermeasure in both titanium and aluminum alloy tubes. Chlorination at 0.05, 0.07, and 0.10 mg liter-1 for 1 h day-1 lowered biofouling rates. Only at 0.10 mg liter-1 was chlorine adequate over a 1-year period to keep film formation and heat transfer resistance from rising above the maximum tolerated values. Lower chlorination regimens led to the buildup of uneven or patchy films which produced increased flow turbulence. The result was lower heat transfer resistance values which did not correlate with the amount of biofouling. Surfaces which were let foul and then treated with intermittent or continuous chlorination at 0.10 mg of chlorine or less per liter were only partially or unevenly cleaned, although heat transfer measurements did not indicate that fact. It took continuous chlorination at 0.25 mg liter-1 to bring the heat transfer resistance to zero and eliminate the fouling layer. Biofouling in deep cold seawater was much slower than in the warm surface waters. Tubing in one stainless-steel loop had a barely detectable fouling layer after 1 year in flow. With aluminum alloys sufficient corrosion and biofouling material accumulated to require that some fouling coutermeasure be used in long-term operation of an ocean thermal energy conversion plant. Images PMID:16347076

The effect of solvent polarity on the accumulation of leachables from pharmaceutical product containers.

PubMed

Jenke, Dennis; Odufu, Alex; Poss, Mitchell

2006-02-01

Material/water equilibrium interaction constants (E(b)) were determined for 12 organic model solutes and a plastic material used in pharmaceutical product containers (non-PVC polyolefin). An excellent correlation was obtained between the measured interaction constants and the organic solute's octanol/water partition coefficient. The effect of solvent polarity on E(b) was assessed by examining the interaction between the plastic and selected model solutes in binary ethanol/water mixtures. In general, logE(b) could be linearily related to the polarity of the ethanol/water mixture. This information, coupled with the interaction model, was used to estimate the levels to which container leachables could accumulate in contacted solutions. Such estimates were made for six known leachables of the polyolefin material and compared to the leachable's measured accumulation levels in binary ethanol/water systems. In general, the accumulation level of the leachables increased with increasing solution polarity. For most of the leachables, the measured accumulation level was less than the calculated levels, suggesting that equilibrium was not achieved in the leaching portion of this study. This lack of equilibrium is attributable to the layered structure of the material studied, as such layering retards the migration of the leachables that are derived from the material's non-solution contact layers.

Methane oxidation in Saanich Inlet during summer stratification

NASA Technical Reports Server (NTRS)

Ward, B. B.; Kilpatrick, K. A.; Wopat, A. E.; Minnich, E. C.; Lidstrom, M. E.

1989-01-01

Saanich Inlet, British Columbia, an fjord on the southeast coast of Vancouver Island, typically stratifies in summer, leading to the formation of an oxic-anoxic interface in the water column and accumulation of methane in the deep water. The results of methane concentration measurements in the water column of the inlet at various times throughout the summer months in 1983 are presented. Methane gradients and calculated diffusive fluxes across the oxic-anoxic interface increased as the summer progressed. Methane distribution and consumption in Saanich Inlet were studied in more detail during August 1986. At this time, a typical summer stratification with an oxic-anoxic interface around 140 m was present. At the interface, steep gradients in nutrient concentrations, bacterial abundance and methane concentration were observed. Methane oxidation was detected in the aerobic surface waters and in the anaerobic deep layer, but highest rates occurred in a narrow layer at the oxic-anoxic interface. Estimated methane oxidation rates were suffcient to consume 100 percent of the methane provided by diffusive flux from the anoxic layer. Methane oxidation is thus a mechanism whereby atmospheric flux from anoxic waters is minimized.

Influence of atomic layer deposition valve temperature on ZrN plasma enhanced atomic layer deposition growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muneshwar, Triratna, E-mail: muneshwa@ualberta.ca; Cadien, Ken

2015-11-15

Atomic layer deposition (ALD) relies on a sequence of self-limiting surface reactions for thin film growth. The effect of non-ALD side reactions, from insufficient purging between pulses and from precursor self-decomposition, on film growth is well known. In this article, precursor condensation within an ALD valve is described, and the effect of the continuous precursor source from condensate evaporation on ALD growth is discussed. The influence of the ALD valve temperature on growth and electrical resistivity of ZrN plasma enhanced ALD (PEALD) films is reported. Increasing ALD valve temperature from 75 to 95 °C, with other process parameters being identical, decreasedmore » both the growth per cycle and electrical resistivity (ρ) of ZrN PEALD films from 0.10 to 0.07 nm/cycle and from 560 to 350 μΩ cm, respectively. Our results show that the non-ALD growth resulting from condensate accumulation is eliminated at valve temperatures close to the pressure corrected boiling point of precursor.« less

Complexation-Based Detection of Nickel(II) at a Graphene-Chelate Probe in the Presence of Cobalt and Zinc by Adsorptive Stripping Voltammetry

PubMed Central

Pokpas, Keagan; Jahed, Nazeem; Baker, Priscilla G.

2017-01-01

The adsorptive stripping voltammetric detection of nickel and cobalt in water samples at metal film electrodes has been extensively studied. In this work, a novel, environmentally friendly, metal-free electrochemical probe was constructed for the ultra-trace determination of Ni2+ in water samples by Adsorptive Cathodic Stripping Voltammetry (AdCSV). The electrochemical platform is based on the adsorptive accumulation of Ni2+ ions directly onto a glassy carbon electrode (GCE) modified with dimethylglyoxime (DMG) as chelating agent and a Nafion-graphene (NGr) nanocomposite to enhance electrode sensitivity. The nafion-graphene dimethylglyoxime modified glassy carbon electrode (NGr-DMG-GCE) shows superior detection capabilities as a result of the improved surface-area-to-volume ratio and enhanced electron transfer kinetics following the incorporation of single layer graphene, while limiting the toxic effects of the sensor by removal of the more common mercury, bismuth and lead films. Furthermore, for the first time the NGr-DMG-GCE, in the presence of common interfering metal ions of Co2+ and Zn2+ demonstrates good selectivity and preferential binding towards the detection of Ni2+ in water samples. Structural and morphological characterisation of the synthesised single layer graphene sheets was conducted by Raman spectrometry, HRTEM and HRSEM analysis. The instrumental parameters associated with the electrochemical response, including accumulation potential and accumulation time were investigated and optimised in addition to the influence of DMG and graphene concentrations. The NGr-DMG-GCE demonstrated well resolved, reproducible peaks, with RSD (%) below 5% and a detection limit of 1.5 µg L−1 for Ni2+ reduction at an accumulation time of 120 s. The prepared electrochemical sensor exhibited good detection and quantitation towards Ni2+ detection in tap water samples, well below 0.1 mg L−1 set by the WHO and EPA standards. This is comparable to the South African drinking water guidelines of 0.15 mg L−1. PMID:28757588

Distribution of inorganic and organic nutrients in the South Pacific Ocean - evidence for long-term accumulation of organic matter in nitrogen-depleted waters

NASA Astrophysics Data System (ADS)

Raimbault, P.; Garcia, N.; Cerutti, F.

2007-08-01

The BIOSOPE cruise of the RV Atalante was devoted to study the biogeochemical properties in the South Pacific between the Marquesas Islands (141° W-8° S) and the Chilean upwelling (73° W-34° S). The 8000 km cruise had the opportunity to encounter different trophic situations, and especially strong oligotrophic conditions in the Central South Pacific Gyre (SPG, between 123° W and 101° W). In this isolated region, nitrate was undetectable between surface and 160-180 m, while regenerated nitrogen (nitrite and ammonium) only revealed some traces (<20 nmoles l-1), even in the subsurface maximum. Integrated nitrate over the photic layer, which reached 165 m, was close to zero. In spite of this severe nitrogen-depletion, phosphate was always present at significant concentrations (≍0.1 μmoles l-1), while silicate maintained at low but classical oceanic levels (≍1 μmoles l-1). In contrast, the Marquesas region (MAR) at west and Chilean upwelling (UPW) at east were characterized by large nutrient contents one hundred to one thousand fold higher than in the SPG. Distribution of surface chlorophyll concentration reflected this gradient of nitrate availability. The lowest value (0.023 nmoles l-1) was measured in the centre of the SPG, where integrated chlorophyll over the photic layer was very weak (≍10 mg m-2), since a great part (up to 50%) of the deep chlorophyll maximum (DCM) was located below the 1% light. But, because of the relative high concentration encountered in the DCM (0.2 μg l-1), chlorophyll a content over the photic layer varied much less (by a factor 2 to 5) than the nitrate content. In contrast to chlorophyll a, integrated content of particulate organic matter (POM) remained more or less constant along the investigated area (500 mmoles m-2, 60 mmoles m-2 and 3.5 mmoles m-2 for particulate organic carbon, particulate organic nitrogen and particulate organic phosphorus, respectively), except in the upwelling where values were two fold higher. Extensive comparison has shown that glass fiber GF/F filters efficiency collected particulate chlorophyll, while a significant fraction of POM (up to 50%) passed trough this filter and was retained by 0.2 μm Teflon membrane. The most striking feature was the large accumulation of dissolved organic matter (DOM) in the SPG relative to surrounding waters, especially dissolved organic carbon (DOC) where concentrations were at levels rarely measured in oceanic waters (>100 μmoles l-1). Due to this large pool of DOM over the whole photic layer of the SPG, integrated values followed an opposite geographical pattern than this of inorganic nutrients with a large accumulation within the centre of the SPG. While suspended particulate matter in the mixed layer had C/N ratio largely conform to Redfield stoichiometry (C/N≍6.6), marked deviations were observed in this excess DOM (C/N≍16 to 23). The existence of C-rich dissolved organic matter is recognized as a feature typical of oligotrophic waters, requiring the over consumption of carbon. Thus, in spite of strong nitrate-depletion leading to low chlorophyll biomass, the closed ecosystem of the SPG can produce a large amount of carbon. The implications of this finding are discussed, the conclusion being that, due to the lack of seasonal vertical mixing and weak lateral advection, the dissolved organic carbon biologically produced can be accumulated and stored in the photic layer for a very long period.

Morphological evolution in a strained-heteroepitaxial solid droplet on a rigid substrate: Dynamical simulations

NASA Astrophysics Data System (ADS)

Ogurtani, Tarik Omer; Celik, Aytac; Oren, Ersin Emre

2010-09-01

A systematic study based on the self-consistent dynamical simulations is presented for the spontaneous evolution of an isolated thin solid droplet (bump) on a rigid substrate, which is driven by the surface drift diffusion induced by the capillary and mismatch stresses. In this study, we mainly focused on the development kinetics of the "Stranski-Krastanow" island type morphology, initiated by the nucleation route rather than the surface roughening scheme. The physicomathematical model, which bases on the irreversible thermodynamics treatment of surfaces and interfaces with singularities [T. O. Ogurtani, J. Chem. Phys. 124, 144706 (2006)], furnishes us to have autocontrol on the otherwise free-motion of the triple junction contour line between the substrate and the droplet without presuming any equilibrium dihedral contract (wetting) angles at the edges. During the development of the bell-shaped Stranski-Krastanow island through the mass accumulation at the central region of the droplet via surface drift diffusion with and/or without growth, the formation of an extremely thin wetting layer is observed. This wetting layer has a thickness of a fraction of a nanometer and covers not only the initial computation domain but also its further extension beyond the original boundaries. We also observed the formation of the multiple islands separated by shallow wetting layers above a certain threshold level of the mismatch strain and/or the size (i.e., volume) of the droplets. This threshold level depends on the initial physicochemical data and the aspect ratio (i.e., shape) of the original droplets. During the course of the simulations, we continuously tracked both the morphology (i.e., the peak height, the extension of the wetting layer beyond the domain boundaries, and the triple junction contact angle) and energetic (the global Helmholtz free energy changes associated with the total strain and surface energy variations) in the system. We observed that the morphology related quantities are reaching certain saturation limits or plateaus, when the growth mode is turned-off. On the other hand, the global Helmholtz free energy showed a steady decrease in time even though the total surface free energy of the droplet reaches a stationary value as expected a priori. Based on these observations and according to the accepted irreversible thermodynamic terminology as coined by celebrated Prigogine, we state that the Stranski-Krastanow type island morphologies are genuine stationary nonequilibrium states.

Vibrational sum-frequency generation spectroscopy of lipid bilayers at repetition rates up to 100 kHz

NASA Astrophysics Data System (ADS)

Yesudas, Freeda; Mero, Mark; Kneipp, Janina; Heiner, Zsuzsanna

2018-03-01

Broadband vibrational sum-frequency generation (BB-VSFG) spectroscopy has become a well-established surface analytical tool capable of identifying the orientation and structure of molecular layers. A straightforward way to boost the sensitivity of the technique could be to increase the laser repetition rate beyond that of standard BB-VSFG spectrometers, which rely on Ti:sapphire lasers operating at repetition rates of 1-5 kHz. Nevertheless, possible thermally induced artifacts in the vibrational spectra due to higher laser average powers are unexplored. Here, we discuss laser power induced temperature accumulation effects that distort the BB-VSFG spectra of 1,2-diacyl-sn-glycero-3-phosphocholine at an interface between two transparent phases at repetition rates of 5, 10, 50, and 100 kHz at constant pulse energy. No heat-induced distortions were found in the spectra, suggesting that the increase in the laser repetition rate provides a feasible route to an improved signal-to-noise ratio or shorter data acquisition times in BB-VSFG spectroscopy for thin films on transparent substrates. The results have implications for future BB-VSFG spectrometers pushing the detection limit for molecular layers with low surface coverage.

Evidence for propagation of cold-adapted yeast in an ice core from a Siberian Altai glacier

NASA Astrophysics Data System (ADS)

Uetake, Jun; Kohshima, Shiro; Nakazawa, Fumio; Takeuchi, Nozomu; Fujita, Koji; Miyake, Takayuki; Narita, Hideki; Aizen, Vladimir; Nakawo, Masayoshi

2011-03-01

Cold environments, including glacier ice and snow, are known habitats for cold-adapted microorganisms. We investigated the potential for cold-adapted yeast to have propagated in the snow of the high-altitude Belukha glacier. We detected the presence of highly concentrated yeast (over 104 cells mL-1) in samples of both an ice core and firn snow. Increasing yeast cell concentrations in the same snow layer from July 2002 to July 2003 suggests that the yeast cells propagated in the glacier snow. A cold-adapted Rhodotorula sp. was isolated from the snow layer and found to be related to psychrophilic yeast previously found in other glacial environments (based on the D1/D2 26S rRNA domains). 26S rRNA clonal analysis directly amplified from meltwater within the ice core also revealed the presence of genus Rhodotorula. Analyses of the ice core showed that all peaks in yeast concentration corresponded to the peaks in indices of surface melting. These results support the hypothesis that occasional surface melting in an accumulation area is one of the major factors influencing cold-adapted yeast propagation.

Enhanced electron mobility at the two-dimensional metallic surface of BaSnO3 electric-double-layer transistor at low temperatures

NASA Astrophysics Data System (ADS)

Fujiwara, Kohei; Nishihara, Kazuki; Shiogai, Junichi; Tsukazaki, Atsushi

2017-05-01

Wide-bandgap oxides exhibiting high electron mobility hold promise for the development of useful electronic and optoelectronic devices as well as for basic research on two-dimensional electron transport phenomena. A perovskite-type tin oxide, BaSnO3, is currently one of such targets owing to distinctly high mobility at room temperature. The challenge to overcome towards the use of BaSnO3 thin films in applications is suppression of dislocation scattering, which is one of the dominant scattering origins for electron transport. Here, we show that the mobility of the BaSnO3 electric-double-layer transistor reaches 300 cm2 V-1 s-1 at 50 K. The improved mobility indicates that charged dislocation scattering is effectively screened by electrostatically doped high-density charge carriers. We also observed metallic conduction persisting down to 2 K, which is attributed to the transition to the degenerate semiconductor. The experimental verification of bulk-level mobility at the densely accumulated surface sheds more light on the importance of suppression of dislocation scattering by interface engineering in doped BaSnO3 thin films for transparent electrode applications.

Adhesion and migration of CHO cells on micropatterned single layer graphene

NASA Astrophysics Data System (ADS)

Keshavan, S.; Oropesa-Nuñez, R.; Diaspro, A.; Canale, C.; Dante, S.

2017-06-01

Cell patterning technology on single layer graphene (SLG) is a fairly new field that can find applications in tissue engineering and biomaterial/biosensors development. Recently, we have developed a simple and effective approach for the fabrication of patterned SLG substrates by laser micromachining, and we have successfully applied it for the obtainment of geometrically ordered neural networks. Here, we exploit the same approach to investigate the generalization of the cell response to the surface cues of the fabricated substrates and, contextually, to quantify cell adhesion on the different areas of the patterns. To attain this goal, we tested Chinese hamster ovary (CHO) cells on PDL-coated micropatterned SLG substrates and quantified the adhesion by using single cell force spectroscopy (SCFS). Our results indicate higher cell adhesion on PDL-SLG, and, consequently, an initial CHO cell accumulation on the graphene areas, confirming the neuronal behaviour observed previously; interestingly, at later time point in culture, cell migration was observed towards the adjacent SLG ablated regions, which resulted more favourable for cell proliferation. Therefore, our findings indicate that the mechanism of interaction with the surface cues offered by the micropatterned substrates is strictly cell-type dependent.

Spatio-Temporal Variability of Recent Snow Accumulation Across the West Antarctic Ice Sheet Divide Using Ultra-High Frequency Radar and Shallow Firn Cores

NASA Astrophysics Data System (ADS)

Keeler, D. G.; Rupper, S.; Forster, R. R.; Miège, C.; Brewer, S.; Koenig, L.

2017-12-01

The West Antarctic Ice Sheet (WAIS) could be a substantial source of future sea level rise, with 3+ meters of potential increase stored in the ice sheet. Adequate predictions of WAIS contributions, however, depend on well-constrained surface mass balance estimates for the region. Given the sparsity of available data, such estimates are tenuous. Although new data are periodically added, further research (both to collect more data and better utilize existing data) is critical to addressing these issues. Here we present accumulation data from 9 shallow firn cores and 600 km of Ku band radar traces collected as part of the Satellite Era Antarctic Traverse (SEAT) 2011/2012 field season. Using these data, combined with similar data collected during the SEAT 2010/2011 field season, we investigate the spatial variability in accumulation across the WAIS Divide and surrounding regions. We utilize seismic interpretation and 3D visualization tools to investigate the extent and variations of laterally continuous internal horizons in the radar profiles, and compare the results to nearby firn cores. Previous results show that clearly visible, laterally continuous horizons in radar returns in this area do not always represent annual accumulation isochrones, but can instead represent multi-year or sub-annual events. The automated application of Bayesian inference techniques to averaged estimates of multiple adjacent radar traces, however, can estimate annually-resolved independent age-depth scales for these radar data. We use these same automated techniques on firn core isotopic records to infer past snow accumulation rates, allowing a direct comparison with the radar-derived results. Age-depth scales based on manual annual-layer counting of geochemical and isotopic species from these same cores provide validation for the automated approaches. Such techniques could theoretically be applied to additional radar/core data sets in polar regions (e.g. Operation IceBridge), thereby increasing the number of high resolution accumulation records available in these data-sparse regions. An increased understanding of the variability in magnitude and past rates of surface mass balance can provide better constraints on sea level projections and more precise context for present-day and future observations in these regions.

Engineered cartilage using primary chondrocytes cultured in a porous cartilage-derived matrix

PubMed Central

Cheng, Nai-Chen; Estes, Bradley T; Young, Tai-Horng; Guilak, Farshid

2011-01-01

Aim To investigate the cell growth, matrix accumulation and mechanical properties of neocartilage formed by human or porcine articular chondrocytes on a porous, porcine cartilage-derived matrix (CDM) for use in cartilage tissue engineering. Materials & methods We examined the physical properties, cell infiltration and matrix accumulation in different formulations of CDM and selected a CDM made of homogenized cartilage slurry as an appropriate scaffold for long-term culture of human and porcine articular chondrocytes. Results The CDM scaffold supported growth and proliferation of both human and porcine chondrocytes. Histology and immunohistochemistry showed abundant cartilage-specific macromolecule deposition at day 28. Human chondrocytes migrated throughout the CDM, showing a relatively homogeneous distribution of new tissue accumulation, whereas porcine chondrocytes tended to form a proteoglycan-rich layer primarily on the surfaces of the scaffold. Human chondrocyte-seeded scaffolds had a significantly lower aggregate modulus and hydraulic permeability at day 28. Conclusions These data show that a scaffold derived from native porcine articular cartilage can support neocartilage formation in the absence of exogenous growth factors. The overall characteristics and properties of the constructs depend on factors such as the concentration of CDM used, the porosity of the scaffold, and the species of chondrocytes. PMID:21175289

The Dye Sensitized Photoelectrosynthesis Cell (DSPEC) for Solar Water Splitting and CO2 Reduction

NASA Astrophysics Data System (ADS)

Meyer, Thomas; Alibabaei, Leila; Sherman, Benjamin; Sheridan, Matthew; Ashford, Dennis; Lapides, Alex; Brennaman, Kyle; Nayak, Animesh; Roy, Subhangi; Wee, Kyung-Ryang; Gish, Melissa; Meyer, Jerry; Papanikolas, John

The dye-sensitized photoelectrosynthesis cell (DSPEC) integrates molecular level light absorption and catalysis with the bandgap properties of stable oxide materials such as TiO2 and NiO. Excitation of surface-bound chromophores leads to excited state formation and rapid electron or hole injection into the conduction or valence bands of n or p-type oxides. Addition of thin layers of TiO2 or NiO on the surfaces of mesoscopic, nanoparticle films of semiconductor or transparent conducting oxides to give core/shell structures provides a basis for accumulating multiple redox equivalents at catalysts for water oxidation or CO2 reduction. UNC EFRC Center for Solar Fuels, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001011.

Easy synthesis of hierarchical carbon spheres with superior capacitive performance in supercapacitors.

PubMed

Huang, Xinhua; Kim, Seok; Heo, Min Seon; Kim, Ji Eun; Suh, Hongsuk; Kim, Il

2013-10-01

An easy template-free approach to the fabrication of pure carbon microspheres has been achieved via direct pyrolysis of as-prepared polyaromatic hydrocarbons including polynaphthalene and polypyrene. The polyaromatics were synthesized from aromatic hydrocarbons (AHCs) using anhydrous zinc chloride as the Friedel-Crafts catalyst and chloromethyl methyl ether as a cross-linker. The experimental results show that the methylene bridges between phenyl rings generate a hierarchical porous polyaromatic precursor to form three-dimensionally (3D) interconnected micro-, meso-, and macroporous networks during carbonization. These hierarchical porous carbon aggregates of spherical carbon spheres exhibit faster ion transport/diffusion behavior and increased surface area usage in electric double-layer capacitors. Furthermore, micropores are present in the 3D interconnected network inside the cross-linked AHC-based carbon microspheres, thus imparting an exceptionally large, electrochemically accessible surface area for charge accumulation.

A subsurface depocenter in the South Polar Layered Deposits of Mars

NASA Astrophysics Data System (ADS)

Whitten, J. L.; Campbell, B. A.; Morgan, G. A.

2017-08-01

The South Polar Layered Deposits (SPLD) are one of the largest water ice reservoirs on Mars, and their accumulation is driven by variations in the climate primarily controlled by orbital forcings. Patterns of subsurface layering in the SPLD provide important information about past atmospheric dust content, periods of substantial erosion, and variations in local or regional deposition. Here we analyze the SPLD using SHAllow RADar (SHARAD) sounder data to gain a unique perspective on the interior structure of the deposits and to determine what subsurface layers indicate about the preserved climate history. SHARAD data reveal a major deviation from the gently domical layering typical of the SPLD: a subsurface elongate dome. The dome most likely formed due to variations in the accumulation of ice and snow across the cap, with a higher rate occurring in this region over a prolonged period. This SPLD depositional center provides an important marker of south polar climate patterns.

Spatial variation in below ground carbon cycling in a pristine peatland, driven by present and past vegetation

NASA Astrophysics Data System (ADS)

Mathijssen, Paul; Knorr, Klaus-Holger; Gałka, Mariusz; Borken, Werner

2017-04-01

Peat carbon cycling is controlled by both large scale factors, such as climate and hydrological setting, and small scale factors, such as microtopography, vegetation, litter quality, and rooting depth. These small scale factors commonly vary within peatlands, causing variation in the carbon balance at different locations within the same site. Understanding the relationship between small scale carbon cycling and vegetation helps us to assess the variation of carbon dynamics of peatlands, because vegetation composition acts as an integrator of factors such as microtopography, hydrology, and nutrient level. Variation in vegetation illustrates spatial variation of these underlying factors. Furthermore, the presence of certain plant species affects carbon cycling directly through litter quality or aeration through root tissues. In order to understand these within-site variations in terms of carbon cycling, we investigated carbon accumulation, decomposition, and biogeochemistry of pore waters along a transect of peat cores with changing vegetation and water levels in an ombrotrophic peatland in southern Patagonia. The transect ran from a Sphagnum magellanicum dominated spot with relatively high water table, to intermediately wet spots with mixed Sphagnum/shrubs vegetation, or dominated by Cyperaceae, eventually to a more elevated and drier spot dominated by cushion plants (mainly Astelia pumila). There were large differences in peat accumulation rates and peat densities, with faster peat growth and lower densities under Sphagnum, but overall carbon accumulation rates were quite similar in the various microenvironments. At most plots C/N ratios decreased with depth, concurrent with increasing humification index derived from FT-IR spectra. But under cushion plants this relation was opposite: more humification with depth, but also C/N ratios increases. This reflected the differing source material at depth under the cushion plants, and that the cushion plant peat layers were formed on top of Sphagnum peat. The divergent source material throughout a peat core makes it difficult to use C/N ratios to indicate peat decomposition rates. Although the low peat density and higher C/N ratios indicate that overall carbon turnover is slow at Sphagnum plots, pore water methane concentrations were elevated. At cushion plant plots, however, higher redox potentials exist until greater depths due to aerenchymous roots, inhibiting methane production and release. Our results demonstrate that large variation exists within pristine bogs, in terms of decomposition patterns, organic matter quality, and carbon turnover pathways, corresponding to variation in surface moisture levels and vegetation. Furthermore, variation in carbon cycling properties are maintained in buried peat layers and reflect more the organic material of that layer, than the current surface carbon dynamics.

Experimental and Theoretical Investigations of Glass Surface Charging Phenomena

NASA Astrophysics Data System (ADS)

Agnello, Gabriel

Charging behavior of multi-component display-type (i.e. low alkali) glass surfaces has been studied using a combination of experimental and theoretical methods. Data obtained by way of a Rolling Sphere Test (RST), streaming/zeta potential and surface energy measurements from commercially available display glass surfaces (Corning EAGLE XGRTM and Lotus(TM) XT) suggest that charge accumulation is highly dependent on surface treatment (chemical and/or physical modification) and measurement environment, presumably through reactionary mechanisms at the surface with atmospheric moisture. It has been hypothesized that water dissociation, along with the corresponding hydroxylation of the glass surface, are important processes related to charging in glass-metal contact systems. Classical Molecular Dynamics (MD) simulations, in conjunction with various laboratory based measurements (RST, a newly developed ElectroStatic Gauge (ESG) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS)) on simpler Calcium AluminoSilicate (CAS) glass surfaces were used to further explore these phenomena. Analysis of simulated high-silica content (≥50%) (CAS) glass structures suggest that controlled variation of bulk chemistry can directly affect surface defect concentrations, such as non-bridging oxygen (NBO), which can be suitable high-energy sites for hydrolysis-type reactions to occur. Calculated NBO surface concentrations correlate well with charge based measurements on laboratory fabricated CAS surfaces. The data suggest that a directional/polar shift in contact-charge transfer occurs at low silica content (≤50%) where the highest concentrations of NBOs are observed. Surface charging sensitivity with respect to NBO concentration decreases as the relative humidity of the measurement environment increases; which should be expected as the highly reactive sites are progressively covered by liquid water layers. DRIFTS analysis of CAS powders expand on this analysis showing a gradual increase in molecular water absorption at the surface in samples containing ≥60% silica, and an abrupt decrease in those with ≤60% silica. This behavior is very likely related to the aforementioned charge polarity shift (negative (-) to positive (+)) in low silica containing glasses, leading to the conclusion that structural defect mediated charge accumulation and/or transfer are likely to be important mechanisms related to the contact charging of glass surfaces.

Tensile behavior and flow stress anisotropy of accumulative roll bonded Cu-Nb nanolaminates

DOE PAGES

Nizolek, Thomas; Beyerlein, Irene J.; Mara, Nathan A.; ...

2016-02-01

The flow stress, ductility, and in-plane anisotropy are evaluated for bulk accumulative roll bonded copper-niobium nanolaminates with layer thicknesses ranging from 1.8 μm to 15 nm. Uniaxial tensile tests conducted parallel to the rolling direction and transverse direction demonstrate that ductility generally decreases with decreasing layer thickness; however, at 30 nm, both high strengths (1200 MPa) and significant ductility (8%) are achieved. The yield strength increases monotonically with decreasing layer thickness, consistent with the Hall-Petch relationship, and significant in-plane flow stress anisotropy is observed. As a result, Taylor polycrystal modeling is used to demonstrate that crystallographic texture is responsible formore » the in-plane anisotropy and that the effects of texture dominate even at nanoscale layer thicknesses.« less

Can the Solid State Greenhouse Effect Produce ~100 Year Cycles in the Mars South Polar Residual CO2 Ice Cap?

NASA Astrophysics Data System (ADS)

Line, M. R.; Ingersoll, A. P.

2010-12-01

Malin et al. (2001) reported that the south perennial cap consists of quasi-circular pits ~8 meters deep, with a flat surface in between. The walls of the pits are retreating at a rate of 1 to 3 meters per year. Byrne and Ingersoll (2003a, 2003b) showed evidence that the floors of the pits are water ice and the upper layer is CO2. This layer will be gone in a few Martian centuries, if the observations are taken at face value. This raises some difficult questions: How likely is it that mankind would be witnessing the final few hundred years of the residual CO2 frost on Mars? Can one imagine extreme weather events that could recharge the residual CO2 frost once it is gone? Both seem unlikely, and we propose a different mechanism. Kieffer et al. (2000) showed that sunlight can penetrate several meters through the seasonal CO2 frost, where it warms the surface below. We have observational evidence that the same is happening in the perennial CO2 frost. Further, we have a model that shows how this "solid-state greenhouse" can lead to cyclic behavior, in which layers of CO2 build up on a water ice substrate, are heated internally by sunlight and lose mass from within. Eventually the layer becomes too weak to support itself, and it collapses to form pits. Then a new CO2 layer accumulates and the process repeats. Our study addresses fundamental questions of long-term stability of the Martian polar caps and how the caps control the atmospheric pressure. Instead of invoking extreme climate events to explain the data, we propose that processes within the frost itself can lead to cyclic growth and collapse of the pits. Our model implies that there is no long-term change in the ~8 meter layer of CO2 and no extreme weather events to make it change.

Do Skeletal Density Changes Within the Tissue Layer of Corals Affect Paleoclimate Reconstructions?

NASA Astrophysics Data System (ADS)

Griffiths, J. S.; DeLong, K. L.; Quinn, T.; Taylor, F. W.; Kilbourne, K. H.; Wagner, A. J.

2016-02-01

Sea surface temperature (SST) reconstructions from coral geochemistry provide information on past climate variability; however, not all coral studies agree on a common calibration slope. Therefore, understanding the impacts of coral skeletal growth on strontium-to-calcium ratios (Sr/Ca) and oxygen isotopic ratios (δ18O) is necessary to ensure accurate calibrations. The study of Gagan et al. (2012) suggests that for the Pacific coral genera Porites, SST calibrations for coral Sr/Ca and δ18O need to be adjusted to account for skeletal density changes in the tissue layer, which may attenuate the seasonal cycle in coral geochemistry. We attempt to duplicate those results and density patterns in several Porites lutea colonies from two locations, yet our results do not show an increase in density in the tissue layer. Another study with Montastraea faveolata reveals reduced seasonality in coral Sr/Ca compared to slower-growing Siderastrea siderea in close proximity and same water depth, suggesting the faster growing M. faveolata geochemistry may be attenuated. By measuring skeletal density changes by micromilling a standard volume throughout the tissue layer and immediately below, we find no pattern of skeletal accumulation in the tissue layer of multiple colonies of M. faveolata and S. siderea from different locations. We conclude that these species lay down all of their skeletal material at the skeleton surface, thus skeletal density changes in the tissue layer do not account for reduced seasonality. We propose that time averaging occurs in M. faveolata as a result of the coral polyp's deep calyces mixing time intervals in the adjacent thecal wall in which micromilling for geochemical analysis produces a sample area that contains several growth increments. Our results show that skeletal density growth effects cannot be applied to all coral genera and paves the way for new research on calyx depth as an alternative explanation for differences in coral calibration slopes.

Transfer of radio-cesium from forest soil to woodchips using fungal activities

NASA Astrophysics Data System (ADS)

Kaneko, Nobuhiro; Huang, Yao; Tanaka, Yoichiro; Fujiwara, Yoshihiro; Sasaki, Michiko; Toda, Hiroto; Takahashi, Terumasa; Kobayashi, Tatsuaki; Harada, Naoki; Nonaka, Masahiro

2014-05-01

Raido-cesium released to terrestrial ecosystems by nuclear accidents is know to accumulate forest soil and organic layer on the soil. Forests in Japan are not exceptions. Practically it is impossible to decontaminate large area of forests. However, there is a strong demand from local people, who has been using secondary forests (Satoyama) around croplands in hilly areas, to decontaminate radio-cesium, because those people used to collect wild mushrooms and edible plants, and there are active cultures of mushrooms using logs and sawdusts. These natural resource uses consist substantial part of their economical activities, Therefore it is needed to decontaminate some selected part of forests in Japan to local economy. Clear cutting and scraping surface soil and organic matter are common methods of decontamination. However the efficiency of decontamination is up to 30% reduction of aerial radiation, and the cost to preserve contaminated debris is not affordable. In this study we used wood chips as a growth media for saprotrophic fungi which are known to accumulate redio-cesium. There are many studies indicated that mushrooms accumulated redio-cesium from forest soil and organic layer. It is not practical to collect mushrooms to decontaminate redio-cesium, because biomass of mushrooms are not enough to collect total contaminants. Mushrooms are only minor part of saprotrophic fungi. Fungal biomass in forest soil is about 1% of dead organic matter on forest floor. Our previous study to observe Cs accumulation to decomposing leaf litter indicated 18% absorption of total soil radio-Cs to litter during one year field incubation (Kaneko et al., 2013), and Cs concentration was proportional to fungal biomass on litter. This result indicated that fungi transferred radio-cesium around newly supplied leaf litter free of contamination. Therefore effective decontamination will be possible if we can provide large amount of growth media for saprotrophic fungi, and the media can be removed from forests with fungal bodies. We covered forest floor using wood chips, and observed Cs accumulation, and found that up to 50% of soil radio-cesium was transferred from soil to wood chips after 6-month of field incubation. Therefore this method is effective to decontaminate forest using ecological process. Kaneko N, Huang Y, Nakamori T, Tanaka Y, Nonaka M. Radio-cesium accumulation during decomposition of leaf litter in a deciduous forest after the Fukushima NPP accident. Geophysical Research Abstracts. 2013;15(EGU2013):7809.

Systems and methods for advanced ultra-high-performance InP solar cells

DOEpatents

Wanlass, Mark

2017-03-07

Systems and Methods for Advanced Ultra-High-Performance InP Solar Cells are provided. In one embodiment, an InP photovoltaic device comprises: a p-n junction absorber layer comprising at least one InP layer; a front surface confinement layer; and a back surface confinement layer; wherein either the front surface confinement layer or the back surface confinement layer forms part of a High-Low (HL) doping architecture; and wherein either the front surface confinement layer or the back surface confinement layer forms part of a heterointerface system architecture.

Method of making photovoltaic cell

DOEpatents

Cruz-Campa, Jose Luis; Zhou, Xiaowang; Zubia, David

2017-06-20

A photovoltaic solar cell comprises a nano-patterned substrate layer. A plurality of nano-windows are etched into an intermediate substrate layer to form the nano-patterned substrate layer. The nano-patterned substrate layer is positioned between an n-type semiconductor layer composed of an n-type semiconductor material and a p-type semiconductor layer composed of a p-type semiconductor material. Semiconductor material accumulates in the plurality of nano-windows, causing a plurality of heterojunctions to form between the n-type semiconductor layer and the p-type semiconductor layer.

Auger electron intensity variations in oxygen-exposed large grain polycrystalline silver

NASA Technical Reports Server (NTRS)

Lee, W. S.; Outlaw, R. A.; Hoflund, G. B.; Davidson, M. R.

1989-01-01

Auger electron spectroscopic studies of the grains in oxygen-charged polycrystal-line silver show significant intensity variations as a function of crystallographic orientation. These intensity variations were observed by studies of the Auger images and line scans of the different grains (randomly selected) for each silver transition energy. The results can be attributed to the diffraction of the ejected Auger electrons and interpreted by corresponding changes in the electron mean-free path for inelastic scattering and by oxygen atom accumulation in the subsurface. The subsurface (second layer) octahedral sites increased in size because of surface relaxation and serve as a stable reservoir for the dissolved oxygen.

Floating basaltic lava balloons - constrains on the eruptive process based on morphologic parameters

NASA Astrophysics Data System (ADS)

Pacheco, J. M.; Zanon, V.; Kueppers, U.

2011-12-01

The 1998-2001 submarine Serreta eruption brought to science a new challenge. This eruption took place offshore of Terceira Island (Azores), on the so-called Serreta Submarine Ridge, corresponding to a basaltic fissure zone with alkaline volcanism, within a tectonic setting controlled by an hyper-slow spreading rift (the Terceira Rift). The inferred eruptive centers are alignment along a NE-SW direction over an area with depths ranging from 300 to more than 1000 meters. The most remarkable products of this eruption, were large basaltic balloons observed floating at the sea surface. Those balloons, designated as Lava Balloons, are spherical to ellipsoidal structures, ranging from 0.4 up to about 3 m in length, consisting of a thin lava shell enveloping a closed hollow interior, normally formed by a single large vesicle, or a few large convoluted vesicles, that grants an overall density below water density. The cross section of the lava shell usually ranges between 3 and 8 cm and has a distinct layered structure, with different layers defined by different vesicularity, bubble number density and crystal content. The outermost layer is characterized by very small vesicles and high bubble number density whereas the innermost layer has larger vesicles, lower bubble number density and higher crystal content. These observations indicate that the rapidly quenched outer layer preserved the original small vesicles present on the magma at the time of the balloon's formation while the inner layer continued to evolve, producing higher crystal content and allowing time for the expansion of vesicles inward and their efficient coalescence. The outer surface of the balloons exhibits patches of very smooth glassy surface and areas with striation and grooves resulting from small scale fluidal deformation. These surface textures are interpreted as the result of the extrusion process and were produced in a similar manner to the striation found on subaerial toothpaste lavas. Such characteristics are indicative that the outer surface of the balloon quenched as it was being extruded and preserved the scars of a squeeze-up process. On this outer surface, several superficial expansion cracks reveal that after its generation the balloon endured some expansion before reaching the sea surface, most likely due to hydrostatic decompression during its rise. The entire shell of the balloons shows bends and folds resulting from large ductile deformations, also suggesting an origin as an effusive process of squeezing-up a large vesicle through a fissure in a thin lava crust, similarly to the extrusion of a gas filled lava toe. Actually, the volume of the lava shell is not enough to produce all the gas in the balloons interior. More likely, at an earlier stage, degassing of magma as an open system allowed gas to segregate and accumulate to form large vesicles. The development of very large vesicles would be favored by a ponding system such as a lava lake.

Bimetallic alloy electrocatalysts with multilayered platinum-skin surfaces

DOEpatents

Stamenkovic, Vojislav R.; Wang, Chao; Markovic, Nenad M.

2016-01-26

Compositions and methods of preparing a bimetallic alloy having enhanced electrocatalytic properties are provided. The composition comprises a PtNi substrate having a surface layer, a near-surface layer, and an inner layer, where the surface layer comprises a nickel-depleted composition, such that the surface layer comprises a platinum skin having at least one atomic layer of platinum.

Applicability of Unmanned Aerial Vehicles in Research on Aeolian Processes

NASA Astrophysics Data System (ADS)

Algimantas, Česnulevičius; Artūras, Bautrėnas; Linas, Bevainis; Donatas, Ovodas; Kęstutis, Papšys

2018-02-01

Surface dynamics and instabilities are characteristic of aeolian formation. The method of surface comparison is regarded as the most appropriate one for evaluation of the intensity of aeolian processes and the amount of transported sand. The data for surface comparison can be collected by topographic survey measurements and using unmanned aerial vehicles. Time cost for relief microform fixation and measurement executing topographic survey are very high. The method of unmanned aircraft aerial photographs fixation also encounters difficulties because there are no stable clear objects and contours that enable to link aerial photographs, to determine the boundaries of captured territory and to ensure the accuracy of surface measurements. Creation of stationary anchor points is irrational due to intense sand accumulation and deflation in different climate seasons. In September 2015 and in April 2016 the combined methodology was applied for evaluation of intensity of aeolian processes in the Curonian Spit. Temporary signs (marks) were installed on the surface, coordinates of the marks were fixed using GPS and then flight of unmanned aircraft was conducted. The fixed coordinates of marks ensure the accuracy of measuring aerial imagery and the ability to calculate the possible corrections. This method was used to track and measure very small (micro-rank) relief forms (5-10 cm height and 10-20 cm length). Using this method morphometric indicators of micro-terraces caused by sand dunes pressure to gytia layer were measured in a non-contact way. An additional advantage of the method is the ability to accurately link the repeated measurements. The comparison of 3D terrain models showed sand deflation and accumulation areas and quantitative changes in the terrain very clearly.

Modelling hazardous surface hoar layers in the mountain snowpack over space and time

NASA Astrophysics Data System (ADS)

Horton, Simon Earl

Surface hoar layers are a common failure layer in hazardous snow slab avalanches. Surface hoar crystals (frost) initially form on the surface of the snow, and once buried can remain a persistent weak layer for weeks or months. Avalanche forecasters have difficulty tracking the spatial distribution and mechanical properties of these layers in mountainous terrain. This thesis presents numerical models and remote sensing methods to track the distribution and properties of surface hoar layers over space and time. The formation of surface hoar was modelled with meteorological data by calculating the downward flux of water vapour from the atmospheric boundary layer. The timing of surface hoar formation and the modelled crystal size was verified at snow study sites throughout western Canada. The major surface hoar layers over several winters were predicted with fair success. Surface hoar formation was modelled over various spatial scales using meteorological data from weather forecast models. The largest surface hoar crystals formed in regions and elevation bands with clear skies, warm and humid air, cold snow surfaces, and light winds. Field surveys measured similar regional-scale patterns in surface hoar distribution. Surface hoar formation patterns on different slope aspects were observed, but were not modelled reliably. Mechanical field tests on buried surface hoar layers found layers increased in shear strength over time, but had persistent high propensity for fracture propagation. Layers with large crystals and layers overlying hard melt-freeze crusts showed greater signs of instability. Buried surface hoar layers were simulated with the snow cover model SNOWPACK and verified with avalanche observations, finding most hazardous surface hoar layers were identified with a structural stability index. Finally, the optical properties of surface hoar crystals were measured in the field with spectral instruments. Large plate-shaped crystals were less reflective at shortwave infrared wavelengths than other common surface snow grains. The methods presented in this thesis were developed into operational products that model hazardous surface hoar layers in western Canada. Further research and refinements could improve avalanche forecasts in regions prone to hazardous surface hoar layers.

Thermal Alternating Polymer Nanocomposite (TAPNC) Coating Designed to Prevent Aerodynamic Insect Fouling

PubMed Central

Bayer, Ilker S.; Krishnan, K. Ghokulla; Robison, Robert; Loth, Eric; Berry, Douglas H.; Farrell, Thomas E.; Crouch, Jeffrey D.

2016-01-01

Insect residue adhesion to moving surfaces such as turbine blades and aircraft not only causes surface contamination problems but also increases drag on these surfaces. Insect fouling during takeoff, climb and landing can result in increased drag and fuel consumption for aircraft with laminar-flow surfaces. Hence, certain topographical and chemical features of non-wettable surfaces need to be designed properly for preventing insect residue accumulation on surfaces. In this work, we developed a superhydrophobic coating that is able to maintain negligible levels of insect residue after 100 high speed (50 m/s) insect impact events produced in a wind tunnel. The coating comprises alternating layers of a hydrophobic, perfluorinated acrylic copolymer and hydrophobic surface functional silicon dioxide nanoparticles that are infused into one another by successive thermal treatments. The design of this coating was achieved as a result of various experiments conducted in the wind tunnel by using a series of superhydrophobic surfaces made by the combination of the same polymer and nanoparticles in the form of nanocomposites with varying surface texture and self-cleaning hydrophobicity properties. Moreover, the coating demonstrated acceptable levels of wear abrasion and substrate adhesion resistance against pencil hardness, dry/wet scribed tape peel adhesion and 17.5 kPa Taber linear abraser tests. PMID:27924913

Thermal Alternating Polymer Nanocomposite (TAPNC) Coating Designed to Prevent Aerodynamic Insect Fouling.

PubMed

Bayer, Ilker S; Krishnan, K Ghokulla; Robison, Robert; Loth, Eric; Berry, Douglas H; Farrell, Thomas E; Crouch, Jeffrey D

2016-12-07

Insect residue adhesion to moving surfaces such as turbine blades and aircraft not only causes surface contamination problems but also increases drag on these surfaces. Insect fouling during takeoff, climb and landing can result in increased drag and fuel consumption for aircraft with laminar-flow surfaces. Hence, certain topographical and chemical features of non-wettable surfaces need to be designed properly for preventing insect residue accumulation on surfaces. In this work, we developed a superhydrophobic coating that is able to maintain negligible levels of insect residue after 100 high speed (50 m/s) insect impact events produced in a wind tunnel. The coating comprises alternating layers of a hydrophobic, perfluorinated acrylic copolymer and hydrophobic surface functional silicon dioxide nanoparticles that are infused into one another by successive thermal treatments. The design of this coating was achieved as a result of various experiments conducted in the wind tunnel by using a series of superhydrophobic surfaces made by the combination of the same polymer and nanoparticles in the form of nanocomposites with varying surface texture and self-cleaning hydrophobicity properties. Moreover, the coating demonstrated acceptable levels of wear abrasion and substrate adhesion resistance against pencil hardness, dry/wet scribed tape peel adhesion and 17.5 kPa Taber linear abraser tests.

Thermal Alternating Polymer Nanocomposite (TAPNC) Coating Designed to Prevent Aerodynamic Insect Fouling

NASA Astrophysics Data System (ADS)

Bayer, Ilker S.; Krishnan, K. Ghokulla; Robison, Robert; Loth, Eric; Berry, Douglas H.; Farrell, Thomas E.; Crouch, Jeffrey D.

2016-12-01

Insect residue adhesion to moving surfaces such as turbine blades and aircraft not only causes surface contamination problems but also increases drag on these surfaces. Insect fouling during takeoff, climb and landing can result in increased drag and fuel consumption for aircraft with laminar-flow surfaces. Hence, certain topographical and chemical features of non-wettable surfaces need to be designed properly for preventing insect residue accumulation on surfaces. In this work, we developed a superhydrophobic coating that is able to maintain negligible levels of insect residue after 100 high speed (50 m/s) insect impact events produced in a wind tunnel. The coating comprises alternating layers of a hydrophobic, perfluorinated acrylic copolymer and hydrophobic surface functional silicon dioxide nanoparticles that are infused into one another by successive thermal treatments. The design of this coating was achieved as a result of various experiments conducted in the wind tunnel by using a series of superhydrophobic surfaces made by the combination of the same polymer and nanoparticles in the form of nanocomposites with varying surface texture and self-cleaning hydrophobicity properties. Moreover, the coating demonstrated acceptable levels of wear abrasion and substrate adhesion resistance against pencil hardness, dry/wet scribed tape peel adhesion and 17.5 kPa Taber linear abraser tests.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simpson, Jeffrey P.; Thrower, Nicholas; Ohlrogge, John B.

Bayberry (Myrica pensylvanica) fruits are covered with a remarkably thick layer of crystalline wax consisting of triacylglycerol (TAG) and diacylglycerol (DAG) esterified exclusively with saturated fatty acids. As the only plant known to accumulate soluble glycerolipids as a major component of surface waxes, Bayberry represents a novel system to investigate neutral lipid biosynthesis and lipid secretion by vegetative plant cells. The assembly of Bayberry wax is distinct from conventional TAG and other surface waxes, and instead proceeds through a pathway related to cutin synthesis (Simpson and Ohlrogge, 2016). In this study, microscopic examination revealed that the fruit tissue that producesmore » and secretes wax (Bayberry knobs) is fully developed before wax accumulates and that wax is secreted to the surface without cell disruption. Comparison of transcript expression to genetically related tissues (Bayberry leaves, M. rubra fruits), cutin-rich tomato and cherry fruit epidermis, and to oil-rich mesocarp and seeds, revealed exceptionally high expression of 13 transcripts for acyl-lipid metabolism together with down-regulation of fatty acid oxidases and desaturases. The predicted protein sequences of the most highly expressed lipid-related enzyme-encoding transcripts in Bayberry knobs are 100% identical to the sequences from Bayberry leaves,which do not produce surface DAG or TAG. Together, these results indicate that TAG biosynthesis and secretion in Bayberry is achieved by both up and down-regulation of a small subset of genes related to the biosynthesis of cutin and saturated fatty acids, and also implies that modifications in gene expression, rather than evolution of new gene functions, was the major mechanism by which Bayberry evolved its specialized lipid metabolism.« less

Concentrations of metals associated with mining waste in sediments, biofilm, benthic macroinvertebrates, and fish from the Coeur d'Alene River Basin, Idaho

USGS Publications Warehouse

Farag, A.M.; Woodward, D.F.; Goldstein, J.N.; Brumbaugh, W.; Meyer, J.S.

1998-01-01

Arsenic, Cd, Cu, Pb, Hg, and Zn were measured in sediments, biofilm, benthic macroinvertebrates, and fish from the Coeur d'Alene (CDA) River to characterize the pathway of metals transfer between these components. Metals enter the CDA Basin via tributaries where mining activities have occurred. In general, the ranking of food-web components from the greatest to smallest concentrations of metals was as follows: biofilm (the layer of abiotic and biotic material on rock surfaces) and sediments > invertebrates > whole fish. Elevated Pb was documented in invertebrates, and elevated Cd and Zn were documented in sediment and biofilm approximately 80 km downstream to the Spokane River. The accumulation of metals in invertebrates was dependent on functional feeding group and shredders-scrapers that feed on biofilm accumulated the largest concentrations of metals. Although the absolute concentrations of metals were the largest in biofilm and sediments, the metals have accumulated in fish approximately 50 km downstream from Kellogg, near the town of Harrison. While metals do not biomagnify between trophic levels, the metals in the CDA Basin are bioavailable and do biotransfer. Trout less than 100 mm long feed exclusively on small invertebrates, and small invertebrates accumulate greater concentrations of metals than large invertebrates. Therefore, early-lifestage fish may be exposed to a larger dose of metals than adults.

Late-Holocene climate evolution at the WAIS Divide site, West Antarctica: Bubble number-density estimates

USGS Publications Warehouse

Fegyveresi, John M.; Alley, R.B.; Spencer, M.K.; Fitzpatrick, J.J.; Steig, E.J.; White, J.W.C.; McConnell, J.R.; Taylor, K.C.

2011-01-01

A surface cooling of ???1.7??C occurred over the ???two millennia prior to ???1700 CE at the West Antarctic ice sheet (WAIS) Divide site, based on trends in observed bubble number-density of samples from the WDC06A ice core, and on an independently constructed accumulation-rate history using annual-layer dating corrected for density variations and thinning from ice flow. Density increase and grain growth in polar firn are both controlled by temperature and accumulation rate, and the integrated effects are recorded in the number-density of bubbles as the firn changes to ice. Numberdensity is conserved in bubbly ice following pore close-off, allowing reconstruction of either paleotemperature or paleo-accumulation rate if the other is known. A quantitative late-Holocene paleoclimate reconstruction is presented for West Antarctica using data obtained from the WAIS Divide WDC06A ice core and a steady-state bubble number-density model. The resultant temperature history agrees closely with independent reconstructions based on stable-isotopic ratios of ice. The ???1.7??C cooling trend observed is consistent with a decrease in Antarctic summer duration from changing orbital obliquity, although it remains possible that elevation change at the site contributed part of the signal. Accumulation rate and temperature dropped together, broadly consistent with control by saturation vapor pressure.

Possible Mud Cracks Preserved in Martian Rock

NASA Image and Video Library

2017-01-17

The network of cracks in this Martian rock slab called "Old Soaker" may have formed from the drying of a mud layer more than 3 billion years ago. The view spans about 4 feet (1.2 meters) left-to-right and combines three images taken by the Mars Hand Lens Imager (MAHLI) camera on the arm of NASA's Curiosity Mars rover. Mud cracks would be evidence of a time when dry intervals interrupted wetter periods that supported lakes in the area. Curiosity has found evidence of ancient lakes in older, lower-lying rock layers and also in younger mudstone that is above Old Soaker. MAHLI was positioned about 3 feet (90 centimeters) above the surface when it took the component images on Dec. 31, 2016, during the 1,566th Martian day, or sol, of Curiosity's work on Mars. This observation was planned as part of assessing a hypothesis that the target preserves evidence of drying mud. The location is within an exposure of Murray formation mudstone on lower Mount Sharp inside Gale Crater. The slab bears a network of four- and five-sided polygons about half an inch to 1 inch (1 to 2 centimeters) across, which matches the pattern commonly formed when a thin layer of mud dries. Some edges of the polygons are ridges of material the same color as the surrounding rock. This could result from a three-step process after cracks form due to drying: Wind-blown sediments accumulate in the open cracks. Later, these sediments and the dried mud become rock under the pressure of multiple younger layers that accumulate on top of them. Most recently, after the overlying layers were eroded away by wind, the vein-filling material resists erosion better than the once-muddy material, so the pattern that began as cracks appears as ridges. Note that some of the cracks contain material much brighter than the surrounding rock. These are mineral veins. Curiosity has found such bright veins of calcium sulfate in many rock layers the rover has investigated. These veins form from circulation of mineral-laden groundwater through underground cracks. Rover-team scientists suggest that a likely scenario for the history of Old Soaker is more than one generation of fracturing: mud cracks first, with sediment accumulating in them, then a later episode of underground fracturing and vein forming. The target rock's name comes from the name of an island off the coast of Maine. The names informally assigned by the rover team to features in the area of lower Mount Sharp that includes this slab are from a list of islands, hills and other sites in or near Maine's Bar Harbor. http://photojournal.jpl.nasa.gov/catalog/PIA21261

Characterization of Titanium Oxide Layers Formation Produced by Nanosecond Laser Coloration

NASA Astrophysics Data System (ADS)

Brihmat-Hamadi, F.; Amara, E. H.; Kellou, H.

2017-06-01

Laser marking technique is used to produce colors on titanium while scanning a metallic sample under normal atmospheric conditions. To proceed with different operating conditions related to the laser beam, the parameters of a Q-switched diode-pumped Nd:YAG ( λ = 532 nm) laser, with a pulse duration of τ = 5 ns, are varied. The effect on the resulting mark quality is the aim of the present study which is developed to determine the influence of the operating parameters ( i.e., pulse frequency, beam scanning speed, and pumping intensity) and furthermore their combination, such as the accumulated fluences and the overlapping rate of laser impacts. From the obtained experimental results, it is noted that the accumulated fluences and the scanning speed are the most influential operating parameters during laser marking, since they have a strong effect on the surface roughness and reflectance, and the occurrence of many oxide phases such as TiO, Ti2O3, TiO2 ( γ- phase, anatase, and rutile).

Efficiency of Tungsten Dust Collection of Different Types of Dust Particles by Electrostatic Probe

NASA Astrophysics Data System (ADS)

Begrambekov, L. B.; Voityuk, A. N.; Zakharov, A. M.; Bidlevich, O. A.; Vechshev, E. A.; Shigin, P. A.; Vayakis, J.; Walsh, M.

2017-12-01

Formation of dust particles and clusters is observed in almost every modern thermonuclear facility. Accumulation of dust in the next generation thermonuclear installations can dramatically affect the plasma parameters and lead to the accumulation of unacceptably large amounts of tritium. Experiments on collection of dust particles by a model of electrostatic probe developed for collection of metallic dust at ITER are described in the article. Experiments on the generation of tungsten dust consisting of flakes formed during the destruction of tungsten layers formed on the walls of the plasma chamber sputtered from the surface of the tungsten target by plasma ions were conducted. The nature of dust degassing at elevated temperatures and the behavior of dust in an electric field were studied. The results obtained are compared with the results of the experiments with dust consisting of crystal particles of simple geometric shapes. The effectiveness of collection of both types of dust using the model of an electrostatic probe is determined.

Magnon diffusion theory for the spin Seebeck effect in ferromagnetic and antiferromagnetic insulators

NASA Astrophysics Data System (ADS)

Rezende, Sergio M.; Azevedo, Antonio; Rodríguez-Suárez, Roberto L.

2018-05-01

In magnetic insulators, spin currents are carried by the elementary excitations of the magnetization: spin waves or magnons. In simple ferromagnetic insulators there is only one magnon mode, while in two-sublattice antiferromagnetic insulators (AFIs) there are two modes, which carry spin currents in opposite directions. Here we present a theory for the diffusive magnonic spin current generated in a magnetic insulator layer by a thermal gradient in the spin Seebeck effect. We show that the formulations describing magnonic perturbation using a position-dependent chemical potential and those using a magnon accumulation are completely equivalent. Then we develop a drift–diffusion formulation for magnonic spin transport treating the magnon accumulation governed by the Boltzmann transport and diffusion equations and considering the full boundary conditions at the surfaces and interfaces of an AFI/normal metal bilayer. The theory is applied to the ferrimagnetic yttrium iron garnet and to the AFIs MnF2 and NiO, providing good quantitative agreement with experimental data.

Bioinspired Antifreeze Secreting Frost-Responsive Pagophobic Coatings

NASA Astrophysics Data System (ADS)

Sun, Xiaoda; Damle, Viraj; Rykaczewski, Konrad

2014-11-01

Prevention of ice and frost accumulation is of interest to transportation, power generation, and agriculture industries. Superhydrophobic and lubricant impregnated pagophobic coatings have been proposed, however, they both fail in frosting conditions. Inspired by functional liquid secretion in natural systems, such as toxin secretion by poison dart frost in response to predator presence, we developed frost-responsive antifreeze secreting pagophobic coatings. These are bi-layered coatings with an inner superhydrophilic ``dermis'' infused with antifreeze and an outer permeable superhydrophobic ``epidermis.'' The superhydrophobic epidermis separates the antifreeze from the environment and prevents ice accumulation by repelling impinging water droplets. In frosting conditions, the antifreeze is secreted from the dermis through pores in the epidermis either due to contact with condensed droplets or temporary switch of the epidermis wettability from hydrophobic to hydrophilic caused by surface icing. Here we demonstrate superior performance of this multifunctional coating in simulated frosting, freezing mist/fog, and freezing spray/rain conditions. KR acknowledges startup funding from ASU.

Environmental risks associated with unconventional gas extraction: an Australian perspective

NASA Astrophysics Data System (ADS)

Mallants, Dirk; Bekele, Elise; Schmidt, Wolfgang; Miotlinski, Konrad; Gerke Gerke, Kirill

2015-04-01

Coal seam gas is naturally occurring methane gas (CH4) formed by the degradation of organic material in coal seam layers over geological times, typically over several millions of years. Unlike conventional gas resources, which occur as discrete accumulations in traps formed by folds and other structures in sedimentary layers, coal seam gas is generally trapped in low permeable rock by adsorption of the gas molecules within the rock formation and cannot migrate to a trap and form a conventional gas deposit. Extraction of coal seam gas requires producers to de pressurise the coal measures by abstracting large amounts of groundwater through pumping. For coal measures that have too low permeabilities for gas extraction to be economical, mechanical and chemical techniques are required to increase permeability and thus gas yield. One such technique is hydraulic fracturing (HF). Hydraulic fracturing increases the rate and total amount of gas extracted from coal seam gas reservoirs. The process of hydraulic fracturing involves injecting large volumes of hydraulic fracturing fluids under high pressure into the coal seam layers to open up (i.e. fracture) the gas-containing coal layers, thus facilitating extraction of methane gas through pumping. After a hydraulic fracturing operation has been completed in a coal seam gas well, the fracturing fluid pressure is lowered and a significant proportion of the injected fluid returns to the surface as "flowback" water via coal seam gas wells. Flowback water is fluid that returns to the surface after hydraulic fracturing has occurred but before the well is put into production; whereas produced water is fluid from the coal measure that is pumped to the surface after the well is in production. This paper summarises available literature data from Australian coal seam gas practices on i) spills from hydraulic fracturing-related fluids used during coal seam gas drilling and hydraulic fracturing operations, ii) leaks to soil and shallow groundwater of flowback water and produced water from surface impoundments, iii) risks from well integrity failure, and iv) increased gas in water bores.

Detailed studies of a high-capacity electrode material for rechargeable batteries, Li2MnO3-LiCo(1/3)Ni(1/3)Mn(1/3)O2.

PubMed

Yabuuchi, Naoaki; Yoshii, Kazuhiro; Myung, Seung-Taek; Nakai, Izumi; Komaba, Shinichi

2011-03-30

Lithium-excess manganese layered oxides, which are commonly described by the chemical formula zLi(2)MnO(3)-(1-z)LiMeO(2) (Me = Co, Ni, Mn, etc.), are of great importance as positive electrode materials for rechargeable lithium batteries. In this Article, Li(x)Co(0.13)Ni(0.13)Mn(0.54)O(2-δ) samples are prepared from Li(1.2)Ni(0.13)Co(0.13)Mn(0.54)O(2) (or 0.5Li(2)MnO(3)-0.5LiCo(1/3)Ni(1/3)Mn(1/3)O(2)) by an electrochemical oxidation/reduction process in an electrochemical cell to study a reaction mechanism in detail before and after charging across a voltage plateau at 4.5 V vs Li/Li(+). Changes of the bulk and surface structures are examined by synchrotron X-ray diffraction (SXRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (SIMS). SXRD data show that simultaneous oxygen and lithium removal at the voltage plateau upon initial charge causes the structural rearrangement, including a cation migration process from metal to lithium layers, which is also supported by XAS. This is consistent with the mechanism proposed in the literature related to the Li-excess manganese layered oxides. Oxygen removal associated with the initial charge on the high voltage plateau causes oxygen molecule generation in the electrochemical cells. The oxygen molecules in the cell are electrochemically reduced in the subsequent discharge below 3.0 V, leading to the extra capacity. Surface analysis confirms the formation of the oxygen containing species, such as lithium carbonate, which accumulates on the electrode surface. The oxygen containing species are electrochemically decomposed upon second charge above 4.0 V. The results suggest that, in addition to the conventional transition metal redox reactions, at least some of the reversible capacity for the Li-excess manganese layered oxides originates from the electrochemical redox reaction of the oxygen molecules at the electrode surface.

Minimizing residues and strain in 2D materials transferred from PDMS.

PubMed

Jain, Achint; Bharadwaj, Palash; Heeg, Sebastian; Parzefall, Markus; Taniguchi, Takashi; Watanabe, Kenji; Novotny, Lukas

2018-06-29

Integrating layered two-dimensional (2D) materials into 3D heterostructures offers opportunities for novel material functionalities and applications in electronics and photonics. In order to build the highest quality heterostructures, it is crucial to preserve the cleanliness and morphology of 2D material surfaces that come in contact with polymers such as PDMS during transfer. Here we report that substantial residues and up to ∼0.22% compressive strain can be present in monolayer MoS 2 transferred using PDMS. We show that a UV-ozone pre-cleaning of the PDMS surface before exfoliation significantly reduces organic residues on transferred MoS 2 flakes. An additional 200 ◦ C vacuum anneal after transfer efficiently removes interfacial bubbles and wrinkles as well as accumulated strain, thereby restoring the surface morphology of transferred flakes to their native state. Our recipe is important for building clean heterostructures of 2D materials and increasing the reproducibility and reliability of devices based on them.

Minimizing residues and strain in 2D materials transferred from PDMS

NASA Astrophysics Data System (ADS)

Jain, Achint; Bharadwaj, Palash; Heeg, Sebastian; Parzefall, Markus; Taniguchi, Takashi; Watanabe, Kenji; Novotny, Lukas

2018-06-01

Integrating layered two-dimensional (2D) materials into 3D heterostructures offers opportunities for novel material functionalities and applications in electronics and photonics. In order to build the highest quality heterostructures, it is crucial to preserve the cleanliness and morphology of 2D material surfaces that come in contact with polymers such as PDMS during transfer. Here we report that substantial residues and up to ∼0.22% compressive strain can be present in monolayer MoS2 transferred using PDMS. We show that a UV-ozone pre-cleaning of the PDMS surface before exfoliation significantly reduces organic residues on transferred MoS2 flakes. An additional 200 ◦C vacuum anneal after transfer efficiently removes interfacial bubbles and wrinkles as well as accumulated strain, thereby restoring the surface morphology of transferred flakes to their native state. Our recipe is important for building clean heterostructures of 2D materials and increasing the reproducibility and reliability of devices based on them.

Relationship between boundary layer heights and growth rates with ground-level ozone in Houston, Texas

NASA Astrophysics Data System (ADS)

Haman, C. L.; Couzo, E.; Flynn, J. H.; Vizuete, W.; Heffron, B.; Lefer, B. L.

2014-05-01

Measurements and predictions of ambient ozone (O3), planetary boundary layer (PBL) height, the surface energy budget, wind speed, and other meteorological parameters were made near downtown Houston, Texas, and were used to investigate meteorological controls on elevated levels of ground-level O3. Days during the study period (1 April 2009 to 31 December 2010 for measurements and 15 April 2009 to 17 October 2009 for modeled) were classified into low (LO3) and high ozone (HO3) days. The majority of observed high HO3 days occurred in a postfrontal environment. Observations showed there is not a significant difference in daily maximum PBL heights on HO3 and LO3 days. Modeling results showed large differences between maximum PBL heights on HO3 and LO3 days. Nighttime and early morning observed and modeled PBL heights are consistently lower on HO3 days than on LO3 days. The observed spring LO3 days had the most rapid early morning PBL growth (~350 m h-1) while the fall HO3 group had the slowest (~200 m h-1). The predicted maximum average hourly morning PBL growth rates were greater on HO3 (624 m h-1) days than LO3 days (361 m h-1). Observed turbulent mixing parameters were up to 2-3 times weaker on HO3 days, which indicate large-scale subsidence associated with high-pressure systems (leading to clear skies and weak winds) substantially suppresses mixing. Lower surface layer ventilation coefficients were present in the morning on HO3 days in the spring and fall, which promotes the accumulation of O3 precursors near the surface.

Hierarchical adaptive nanostructured PVD coatings for extreme tribological applications: the quest for nonequilibrium states and emergent behavior.

PubMed

Fox-Rabinovich, German S; Yamamoto, Kenji; Beake, Ben D; Gershman, Iosif S; Kovalev, Anatoly I; Veldhuis, Stephen C; Aguirre, Myriam H; Dosbaeva, Goulnara; Endrino, Jose L

2012-08-01

Adaptive wear-resistant coatings produced by physical vapor deposition (PVD) are a relatively new generation of coatings which are attracting attention in the development of nanostructured materials for extreme tribological applications. An excellent example of such extreme operating conditions is high performance machining of hard-to-cut materials. The adaptive characteristics of such coatings develop fully during interaction with the severe environment. Modern adaptive coatings could be regarded as hierarchical surface-engineered nanostructural materials. They exhibit dynamic hierarchy on two major structural scales: (a) nanoscale surface layers of protective tribofilms generated during friction and (b) an underlying nano/microscaled layer. The tribofilms are responsible for some critical nanoscale effects that strongly impact the wear resistance of adaptive coatings. A new direction in nanomaterial research is discussed: compositional and microstructural optimization of the dynamically regenerating nanoscaled tribofilms on the surface of the adaptive coatings during friction. In this review we demonstrate the correlation between the microstructure, physical, chemical and micromechanical properties of hard coatings in their dynamic interaction (adaptation) with environment and the involvement of complex natural processes associated with self-organization during friction. Major physical, chemical and mechanical characteristics of the adaptive coating, which play a significant role in its operating properties, such as enhanced mass transfer, and the ability of the layer to provide dissipation and accumulation of frictional energy during operation are presented as well. Strategies for adaptive nanostructural coating design that enhance beneficial natural processes are outlined. The coatings exhibit emergent behavior during operation when their improved features work as a whole. In this way, as higher-ordered systems, they achieve multifunctionality and high wear resistance under extreme tribological conditions.

Hierarchical adaptive nanostructured PVD coatings for extreme tribological applications: the quest for nonequilibrium states and emergent behavior

PubMed Central

Fox-Rabinovich, German S; Yamamoto, Kenji; Beake, Ben D; Gershman, Iosif S; Kovalev, Anatoly I; Veldhuis, Stephen C; Aguirre, Myriam H.; Dosbaeva, Goulnara; Endrino, Jose L

2012-01-01

Adaptive wear-resistant coatings produced by physical vapor deposition (PVD) are a relatively new generation of coatings which are attracting attention in the development of nanostructured materials for extreme tribological applications. An excellent example of such extreme operating conditions is high performance machining of hard-to-cut materials. The adaptive characteristics of such coatings develop fully during interaction with the severe environment. Modern adaptive coatings could be regarded as hierarchical surface-engineered nanostructural materials. They exhibit dynamic hierarchy on two major structural scales: (a) nanoscale surface layers of protective tribofilms generated during friction and (b) an underlying nano/microscaled layer. The tribofilms are responsible for some critical nanoscale effects that strongly impact the wear resistance of adaptive coatings. A new direction in nanomaterial research is discussed: compositional and microstructural optimization of the dynamically regenerating nanoscaled tribofilms on the surface of the adaptive coatings during friction. In this review we demonstrate the correlation between the microstructure, physical, chemical and micromechanical properties of hard coatings in their dynamic interaction (adaptation) with environment and the involvement of complex natural processes associated with self-organization during friction. Major physical, chemical and mechanical characteristics of the adaptive coating, which play a significant role in its operating properties, such as enhanced mass transfer, and the ability of the layer to provide dissipation and accumulation of frictional energy during operation are presented as well. Strategies for adaptive nanostructural coating design that enhance beneficial natural processes are outlined. The coatings exhibit emergent behavior during operation when their improved features work as a whole. In this way, as higher-ordered systems, they achieve multifunctionality and high wear resistance under extreme tribological conditions. PMID:27877499

In Situ, High-Resolution Profiles of Labile Metals in Sediments of Lake Taihu

PubMed Central

Wang, Dan; Gong, Mengdan; Li, Yangyang; Xu, Lv; Wang, Yan; Jing, Rui; Ding, Shiming; Zhang, Chaosheng

2016-01-01

Characterizing labile metal distribution and biogeochemical behavior in sediments is crucial for understanding their contamination characteristics in lakes, for which in situ, high-resolution data is scare. The diffusive gradient in thin films (DGT) technique was used in-situ at five sites across Lake Taihu in the Yangtze River delta in China to characterize the distribution and mobility of eight labile metals (Fe, Mn, Zn, Ni, Cu, Pb, Co and Cd) in sediments at a 3 mm spatial resolution. The results showed a great spatial heterogeneity in the distributions of redox-sensitive labile Fe, Mn and Co in sediments, while other metals had much less marked structure, except for downward decreases of labile Pb, Ni, Zn and Cu in the surface sediment layers. Similar distributions were found between labile Mn and Co and among labile Ni, Cu and Zn, reflecting a close link between their geochemical behaviors. The relative mobility, defined as the ratio of metals accumulated by DGT to the total contents in a volume of sediments with a thickness of 10 mm close to the surface of DGT probe, was the greatest for Mn and Cd, followed by Zn, Ni, Cu and Co, while Pb and Fe had the lowest mobility; this order generally agreed with that defined by the modified BCR approach. Further analyses showed that the downward increases of pH values in surface sediment layer may decrease the lability of Pb, Ni, Zn and Cu as detected by DGT, while the remobilization of redox-insensitive metals in deep sediment layer may relate to Mn cycling through sulphide coprecipitation, reflected by several corresponding minima between these metals and Mn. These in situ data provided the possibility for a deep insight into the mechanisms involved in the remobilization of metals in freshwater sediments. PMID:27608033

Protecting the surface of a light absorber in a photoanode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Shu; Lewis, Nathan S.

A photoanode includes a passivation layer on a light absorber. The passivation layer is more resistant to corrosion than the light absorber. The photoanode includes a surface modifying layer that is location on the passivation layer such that the passivation layer is between the light absorber and the surface modifying layer. The surface modifying layer reduces a resistance of the passivation layer to conduction of holes out of the passivation layer.

Suppression on allotropic transformation of Sn planar anode with enhanced electrochemical performance

NASA Astrophysics Data System (ADS)

Wang, Peng; Hu, Junhua; Cao, Guoqin; Zhang, Shilin; Zhang, Peng; Liang, Changhao; Wang, Zhuo; Shao, Guosheng

2018-03-01

Different configurations of Sn and C films were deposited and used as a planar anode for Li ion battery. The interplay of carbon layer with Sn as supporting and buffering, respectively, was revealed. The suppression on the allotropic transformation to α phase by a carbon layer results in a significantly improved capacity retention rate, which also avoids the crack of Sn film. As expected, a conductive carbon layer improves rating performance. However, a supporting carbon layer (SC) just contributes to the charge transfer process. A DFT approach was used to assess the allotropic transformation process. An additional barrier (∼0.86 eV) exits on the α-β diagram, which is responsible for the irreversibility of α phase back to β phase. An enhanced persistence of β phase in Sn/C anode contributes to cycling performance. A Li rich condition contributes to the stabilization of β-Sn, which is thermodynamically favored. A nano buffering carbon (BC) layer can evidently alleviate the side reaction on Sn surface, which in turn promotes the diffusion of Li ions in electrode and generates a Li rich condition. The direct contact of Sn with electrolyte leads to serious accumulation of α-Sn during cycling and results in a poor cycling performance. By the synergistic effect of BC and SC, a sandwich C/Sn/C structure demonstrates an enchantment in electrochemical behavior.

Semiconductor/dielectric interface engineering and characterization

NASA Astrophysics Data System (ADS)

Lucero, Antonio T.

The focus of this dissertation is the application and characterization of several, novel interface passivation techniques for III-V semiconductors, and the development of an in-situ electrical characterization. Two different interface passivation techniques were evaluated. The first is interface nitridation using a nitrogen radical plasma source. The nitrogen radical plasma generator is a unique system which is capable of producing a large flux of N-radicals free of energetic ions. This was applied to Si and the surface was studied using x-ray photoelectron spectroscopy (XPS). Ultra-thin nitride layers could be formed from 200-400° C. Metal-oxide-semiconductor capacitors (MOSCAPs) were fabricated using this passivation technique. Interface nitridation was able to reduce leakage current and improve the equivalent oxide thickness of the devices. The second passivation technique studied is the atomic layer deposition (ALD) diethylzinc (DEZ)/water treatment of sulfur treated InGaAs and GaSb. On InGaAs this passivation technique is able to chemically reduce higher oxidation states on the surface, and the process results in the deposition of a ZnS/ZnO interface passivation layer, as determined by XPS. Capacitance-voltage (C-V) measurements of MOSCAPs made on p-InGaAs reveal a large reduction in accumulation dispersion and a reduction in the density of interfacial traps. The same technique was applied to GaSb and the process was studied in an in-situ half-cycle XPS experiment. DEZ/H2O is able to remove all Sb-S from the surface, forming a stable ZnS passivation layer. This passivation layer is resistant to further reoxidation during dielectric deposition. The final part of this dissertation is the design and construction of an ultra-high vacuum cluster tool for in-situ electrical characterization. The system consists of three deposition chambers coupled to an electrical probe station. With this setup, devices can be processed and subsequently electrically characterized without exposing the sample to air. This is the first time that such a system has been reported. A special air-gap C-V probe will allow top gated measurements to be made, allowing semiconductor-dielectric interfaces to be studied during device processing.

Historic CH4 Records from Antarctic and Greenland Ice Cores, Antarctic Firn Data, and Archived Air Samples from Cape Grim, Tasmania

DOE Data Explorer

Etheridge, D. M. [Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia; Steele, L. P. [Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia; Francey, R. J. [Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia; Langenfelds, R. L. [Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia

2002-01-01

The Antarctic CH4 records presented here are derived from three ice cores obtained at Law Dome, East Antarctica (66°44'S, 112°50'E, 1390 meters above mean sea level). Law Dome has many qualities of an ideal ice core site for the reconstruction of past concentrations of atmospheric gases; these qualities include: negligible melting of the ice sheet surface, low concentrations of impurities, regular stratigraphic layering undisturbed by wind stress at the surface or differential ice flow at depth, and a high snow accumulation rate. Further details on the site, drilling, and cores are provided by Etheridge et al. (1998), Etheridge et al. (1996), Etheridge and Wookey (1989), and Morgan et al. (1997). The two Greenland ice cores are from the Summit region (72°34' N, 37°37' W, 3200 meters above mean sea level). Lower snow accumulation rate there results in lower air-age resolution, and measurements presented here cover only the pre-industrial period (until 1885). More details about these measurements are presented in Etheridge et al. (1998). Additionally, this site contains firn data from Core DE08-2, and archived air samples from Cape Grim, Tasmania, for comparison.

Potential for a large earthquake near Los Angeles inferred from the 2014 La Habra earthquake.

PubMed

Donnellan, Andrea; Grant Ludwig, Lisa; Parker, Jay W; Rundle, John B; Wang, Jun; Pierce, Marlon; Blewitt, Geoffrey; Hensley, Scott

2015-09-01

Tectonic motion across the Los Angeles region is distributed across an intricate network of strike-slip and thrust faults that will be released in destructive earthquakes similar to or larger than the 1933  M 6.4 Long Beach and 1994  M 6.7 Northridge events. Here we show that Los Angeles regional thrust, strike-slip, and oblique faults are connected and move concurrently with measurable surface deformation, even in moderate magnitude earthquakes, as part of a fault system that accommodates north-south shortening and westerly tectonic escape of northern Los Angeles. The 28 March 2014 M 5.1 La Habra earthquake occurred on a northeast striking, northwest dipping left-lateral oblique thrust fault northeast of Los Angeles. We present crustal deformation observation spanning the earthquake showing that concurrent deformation occurred on several structures in the shallow crust. The seismic moment of the earthquake is 82% of the total geodetic moment released. Slip within the unconsolidated upper sedimentary layer may reflect shallow release of accumulated strain on still-locked deeper structures. A future M 6.1-6.3 earthquake would account for the accumulated strain. Such an event could occur on any one or several of these faults, which may not have been identified by geologic surface mapping.

Potential for a large earthquake near Los Angeles inferred from the 2014 La Habra earthquake

PubMed Central

Grant Ludwig, Lisa; Parker, Jay W.; Rundle, John B.; Wang, Jun; Pierce, Marlon; Blewitt, Geoffrey; Hensley, Scott

2015-01-01

Abstract Tectonic motion across the Los Angeles region is distributed across an intricate network of strike‐slip and thrust faults that will be released in destructive earthquakes similar to or larger than the 1933 M6.4 Long Beach and 1994 M6.7 Northridge events. Here we show that Los Angeles regional thrust, strike‐slip, and oblique faults are connected and move concurrently with measurable surface deformation, even in moderate magnitude earthquakes, as part of a fault system that accommodates north‐south shortening and westerly tectonic escape of northern Los Angeles. The 28 March 2014 M5.1 La Habra earthquake occurred on a northeast striking, northwest dipping left‐lateral oblique thrust fault northeast of Los Angeles. We present crustal deformation observation spanning the earthquake showing that concurrent deformation occurred on several structures in the shallow crust. The seismic moment of the earthquake is 82% of the total geodetic moment released. Slip within the unconsolidated upper sedimentary layer may reflect shallow release of accumulated strain on still‐locked deeper structures. A future M6.1–6.3 earthquake would account for the accumulated strain. Such an event could occur on any one or several of these faults, which may not have been identified by geologic surface mapping. PMID:27981074

Meteorological conditions during a severe, prolonged regional heavy air pollution episode in eastern China from December 2016 to January 2017

NASA Astrophysics Data System (ADS)

Deng, Xueliang; Cao, Weihua; Huo, Yanfeng; Yang, Guanying; Yu, Caixia; He, Dongyan; Deng, Weitao; Fu, Wei; Ding, Heming; Zhai, Jing; Cheng, Long; Zhao, Xuhui

2018-03-01

A severe, prolonged and harmful regional heavy air pollution episode occurred in eastern China from December 2016 to January 2017. In this paper, the pollutant characteristics and the meteorological formation mechanism of this pollution event, including climate anomalies, surface weather conditions, planetary boundary layer structure and large-scale circulation features, were analysed based on observational pollution data, surface meteorological data, sounding data and ERA-Interim reanalysis data. The results are as follows. (1) Five pollution stages were identified in eastern China. The two most severe episodes occurred from December 27, 2016 to January 4, 2017 and from January 8 to 12 2017. During these two pollution episodes, fine mode particles were major contributors, and hourly PM2.5 concentrations often exceeded 150 μg/m3, reaching a maximum of 333 μg/m3 at Fuyang station. Gaseous pollutants were transformed into secondary aerosols through heterogeneous reactions on the surface of PM2.5. (2) Compared with the same period over the years 2000-2016, 2017 presented meteorological field climate anomalies in conjunction with unfavourable surface conditions (weak winds, high relative humidity, fewer hours of sunshine, high cloud cover) and adverse atmospheric circulation (weak East Asian winter monsoon and an abnormal geopotential height of 500 hPa), which caused poorer visibility in 2017 than in the other analysed years. (3) During the development of heavy pollution event, unfavourable surface weather conditions, including poorer visibility, weaker pressure, higher relative humidity, lower wind speed with unfavourable wind direction and less precipitation suppressed the horizontal diffusion ability of air pollutants. Furthermore, the unfavourable structure of the atmospheric boundary layer was the key cause of the rapid PM2.5 increase. The deep, strong temperature inversion layer and weak vertical wind velocity could have suppressed vertical motion and enhanced the stability of the near-surface atmosphere, causing the air pollutants to accumulate at low levels and exacerbating the air pollution problem. Finally, a persistent stagnant weather system with a weak geopotential height field of 1000 hPa and warm air advection at 850 hPa was the main feature of atmospheric circulation associated with the heavy pollution.

Frequency dispersion analysis of thin dielectric MOS capacitor in a five-element model

NASA Astrophysics Data System (ADS)

Zhang, Xizhen; Zhang, Sujuan; Zhu, Huichao; Pan, Xiuyu; Cheng, Chuanhui; Yu, Tao; Li, Xiangping; Cheng, Yi; Xing, Guichao; Zhang, Daming; Luo, Xixian; Chen, Baojiu

2018-02-01

An Al/ZrO2/IL/n-Si (IL: interface layer) MOS capacitor has been fabricated by metal organic decomposition of ZrO2 and thermal deposition Al. We have measured parallel capacitance (C m) and parallel resistance (R m) versus bias voltage curves (C m, R m-V) at different AC signal frequency (f), and C m, R m-f curves at different bias voltage. The curves of C m, R m-f measurements show obvious frequency dispersion in the range of 100 kHz-2 MHz. The energy band profile shows that a large voltage is applied on the ZrO2 layer and IL at accumulation, which suggests possible dielectric polarization processes by some traps in ZrO2 and IL. C m, R m-f data are used for frequency dispersion analysis. To exclude external frequency dispersion, we have extracted the parameters of C (real MOS capacitance), R p (parallel resistance), C IL (IL capacitance), R IL (IL resistance) and R s (Si resistance) in a five-element model by using a three-frequency method. We have analyzed intrinsic frequency dispersion of C, R p, C IL, R IL and R s by studying the dielectric characteristics and Si surface layer characteristics. At accumulation, the dispersion of C and R p is attributed to dielectric polarization such as dipolar orientation and oxide traps. The serious dispersion of C IL and R IL are relative to other dielectric polarization, such as border traps and fixed oxide traps. The dispersion of R s is mainly attributed to contact capacitance (C c) and contact resistance (R c). At depletion and inversion, the frequency dispersion of C, R p, C IL, R IL, and R s are mainly attributed to the depletion layer capacitance (C D). The interface trap capacitance (C it) and interface trap resistance (R it) are not dominant for the dispersion of C, R p, C IL, R IL, and R s.

Controls on the distributions of organic carbon and nitrogen in the eastern Pacific Ocean

NASA Astrophysics Data System (ADS)

Hansell, Dennis A.; Waterhouse, Tye Y.

1997-05-01

Measurements of total organic carbon (TOC) and nitrogen (TON) were made on the WOCE P18 line (from 67°S to 23°N along 103°/110°W). There was an accumulation of TOC on the equator and in the oligotrophic waters north and south of the equator. The concentrations of TOC were well correlated with temperature, indicating an important physical control on its distribution. The boundary separating shallow, TOC-rich water from deep, TOC-poor water overlaid the main thermocline. This observation suggests that water column stability or residence time imparted by the main thermocline is a primary determinant of TOC accumulation. Elevated TON concentrations were found in all surface waters, with the lowest values found in the region of 20-35°S. Net TON drawdown in the South Pacific subtropical gyre, likely due to biological utilization and vertical export of the nitrogen, was initiated with depletion of equatorially upwelled nitrate. The degree to which inorganic nitrogen was limiting in the surface layer south of the equator served to control the concentrations of TON. Such controls were not exerted on organic carbon, as reflected by increasing C:N ratios of organic matter as TON was removed. Unlike the findings in the South Pacific, TON concentrations in oligotrophic waters north of the equator were frequently higher than on the equator. Such accumulations are hypothesized to be maintained from nitrogen fixation, nitrogen input due to vertical migration of autotrophs or diffusive flux of inorganic nitrogen into the euphotic zone across the relatively shallow nitracline.

Hydrodynamic size-dependent cellular uptake of aqueous QDs probed by fluorescence correlation spectroscopy.

PubMed

Dong, Chaoqing; Irudayaraj, Joseph

2012-10-11

Aqueous quantum dots (QDs) directly synthesized with various thiol ligands have been investigated as imaging probes in living cells. However, the effect of the surface chemistry of these ligands on QDs' cellular uptakes and their intracellular fate remains poorly understood. In this work, four CdTe QDs were directly synthesized under aqueous conditions using four different thiols as stabilizers and their interactions with cells were investigated. Fluorescence correlation spectroscopy (FCS), X-ray photoelectron spectroscopy (XPS), and zeta potential measurements on QDs primarily show that the surface structure of these QDs is highly dependent on the thiol ligands used in the preparation of QDs' precursors, including its layer thicknesses, densities, and surface charges. Subsequently, FCS integrated with the maximum-entropy-method-based FCS (MEMFCS) was used to investigate the concentration distribution and dynamics of these QDs in living A-427 cells. Our findings indicate that QDs' surface characteristics affect cell membrane adsorption and subsequent internalization. More critically, we show that the cellular uptake of aqueous QDs is dependent on their hydrodynamic diameter and might have the potential to escape trapped environments to accumulate in the cytoplasm.

Surface modification and deuterium retention in reduced-activation steels exposed to low-energy, high-flux pure and helium-seeded deuterium plasmas

NASA Astrophysics Data System (ADS)

Alimov, V. Kh; Ogorodnikova, O. V.; Hatano, Y.; Gasparyan, YuM.; Efimov, V. S.; Mayer, M.; Zhou, Z.; Oyaizu, M.; Isobe, K.; Nakamura, H.; Hayashi, T.

2018-04-01

Surface topography of and deuterium (D) retention in reduced activation ferritic-martensitic Eurofer'97 and ferritic oxide dispersion strengthening ODS-16Cr steels have been studied after exposure at 600 K to low-energy (70 and 200 eV), high-flux (∼1022 D/m2s) pure D and D-10%He plasmas with D fluence of 2 × 1025 D/m2. The methods used were scanning electron microscopy, energy-scanning D(3He,p)4He nuclear reaction, and thermal desorption spectroscopy. As a result of the plasma exposures, nano-sized structures are formed on the steel surfaces. After exposure to pure D plasmas, a significant fraction of D is accumulated in the bulk, at depths larger than 8 μm. After exposures to D-He plasmas, D is retained mainly in the near-surface layers. In spite of the fact that the He fluence was lower than the D fluence, the He retention in the steels is one order of magnitude higher than the D retention.

Generation of Subsurface Voids, Incubation Effect, and Formation of Nanoparticles in Short Pulse Laser Interactions with Bulk Metal Targets in Liquid: Molecular Dynamics Study

PubMed Central

2017-01-01

The ability of short pulse laser ablation in liquids to produce clean colloidal nanoparticles and unusual surface morphology has been employed in a broad range of practical applications. In this paper, we report the results of large-scale molecular dynamics simulations aimed at revealing the key processes that control the surface morphology and nanoparticle size distributions by pulsed laser ablation in liquids. The simulations of bulk Ag targets irradiated in water are performed with an advanced computational model combining a coarse-grained representation of liquid environment and an atomistic description of laser interaction with metal targets. For the irradiation conditions that correspond to the spallation regime in vacuum, the simulations predict that the water environment can prevent the complete separation of the spalled layer from the target, leading to the formation of large subsurface voids stabilized by rapid cooling and solidification. The subsequent irradiation of the laser-modified surface is found to result in a more efficient ablation and nanoparticle generation, thus suggesting the possibility of the incubation effect in multipulse laser ablation in liquids. The simulations performed at higher laser fluences that correspond to the phase explosion regime in vacuum reveal the accumulation of the ablation plume at the interface with the water environment and the formation of a hot metal layer. The water in contact with the metal layer is brought to the supercritical state and provides an environment suitable for nucleation and growth of small metal nanoparticles from metal atoms emitted from the hot metal layer. The metal layer itself has limited stability and can readily disintegrate into large (tens of nanometers) nanoparticles. The layer disintegration is facilitated by the Rayleigh–Taylor instability of the interface between the higher density metal layer decelerated by the pressure from the lighter supercritical water. The nanoparticles emerging from the layer disintegration are rapidly cooled and solidified due to the interaction with water environment, with a cooling rate of ∼2 × 1012 K/s observed in the simulations. The computational prediction of two distinct mechanisms of nanoparticle formation yielding nanoparticles with different characteristic sizes provides a plausible explanation for the experimental observations of bimodal nanoparticle size distributions in laser ablation in liquids. The ultrahigh cooling and solidification rates suggest the possibility for generation of nanoparticles featuring metastable phases and highly nonequilibrium structures. PMID:28798858

Nacre-Templated Synthesis of Highly Dispersible Carbon Nanomeshes for Layered Membranes with High-Flux Filtration and Sensing Properties.

PubMed

Kong, Meng; Li, Mingjie; Shang, Ruoxu; Wu, Jingyu; Yan, Peisong; Xu, Dongmei; Li, Chaoxu

2018-01-24

Marine shells not only represent a rapidly accumulating type of fishery wastes but also offer a unique sort of hybrid nanomaterials produced greenly and massively in nature. The elaborate "brick and mortar" structures of nacre enabled the synthesis of carbon nanomeshes with <1 nm thickness, hierarchical porosity, and high specific surface area through pyrolysis, in which two-dimensional (2D) organic layers served as the carbonaceous precursor and aragonite platelets as the hard template. Mineral bridges within 2D organic layers templated the formation of mesh pores of 20-70 nm. In contrast to other hydrophobic carbon nanomaterials, these carbon nanomeshes showed super dispersibility in diverse solvents and thus processability for membranes through filtration, patterning, spray-coating, and ink-writing. The carbon membranes with layered structures were capable of serving not only for high-flux filtration and continuous flow absorption but also for electrochemical and strain sensing with high sensitivity. Thus, utilization of marine shells, on one hand, relieves the environmental concern of shellfish waste, on the other hand, offers a facile, green, low-cost, and massive approach to synthesize unique carbon nanomeshes alternative to graphene nanomeshes and applicable in environmental adsorption, filtration, wearable sensors, and flexible microelectronics.

Transfer characteristics and low-frequency noise in single- and multi-layer MoS{sub 2} field-effect transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Deepak; Theiss Research, Inc., La Jolla, California 92037; Department of Electrical and Computer Engineering, George Mason University, Fairfax, Virginia 22030

Leveraging nanoscale field-effect transistors (FETs) in integrated circuits depends heavily on its transfer characteristics and low-frequency noise (LFN) properties. Here, we report the transfer characteristics and LFN in FETs fabricated with molybdenum disulfide (MoS{sub 2}) with different layer (L) counts. 4L to 6L devices showed highest I{sub ON}-I{sub OFF} ratio (≈10{sup 8}) whereas LFN was maximum for 1L device with normalized power spectral density (PSD) ≈1.5 × 10{sup −5 }Hz{sup −1}. For devices with L ≈ 6, PSD was minimum (≈2 × 10{sup −8 }Hz{sup −1}). Further, LFN for single and few layer devices satisfied carrier number fluctuation (CNF) model in both weak andmore » strong accumulation regimes while thicker devices followed Hooge's mobility fluctuation model in the weak accumulation regime and CNF model in strong accumulation regime, respectively. Transfer-characteristics and LFN experimental data are explained with the help of model incorporating Thomas-Fermi charge screening and inter-layer resistance coupling.« less

Fluvial landscapes evolution in the Gangkou River basin of southern Taiwan: Evidence from the sediment cores

NASA Astrophysics Data System (ADS)

Chen, Jia-Hong; Chyi, Shyh-Jeng; Yen, Jiun-Yee; Lin, Li-Hung; Yen, I.-Chin; Yu, Neng-Ti; Ho, Lih-Der; Jen, Chia-Hung

2017-04-01

The Gangkou River basin is the largest basin in the eastern Hengchun Peninsula of Taiwan. Its main river length is 31km and the basin area is 102sq. km. The width of the active channel is relatively narrow, but the valley from the middle to downstream is remarkably wide, indicating a feature of underfit stream. We drilled two sediment cores in the downstream area, including a 30m core (core-A) from a higher terrace, which is 14m above mean sea level, and a 20m core (core-B) from a lower terrace, which is 4m above mean sea level. Most of the sediments in the core-A are mud, which represents the flood plain facies, and 14C dates in the core-A range from 11ka to 7ka BP. Furthermore, the sediment layers reveal signals of marine events at the core depths of 5m to 11m by X-ray fluorescence. In the core-B, there is an erosional surface at the core depth of 5m. The age of the fluvial gravel layer above the erosional surface is about 0.4ka BP, and the mud layer top the surface is about 8.5ka BP. The preliminary results show that (1) as the tectonic uplift rate induced by the marine terraces around the basin is 1.0 to 2.5 mm/yr, and the accumulation rate of the mud layer in the basin is 6.7 to 8.7 mm/yr, the sediments infilling (more than 30-meters-thick) in the downstream area of the basin should be the results of the lower tectonic uplifting and the higher post-glacial sea level rise and; (2) the marine sediment layer with 14C dates of 7.5ka to 8.5ka BP is very likely the remain of the maximum flooding surface (MFS) in the early Holocene. These results indicate that the fluvial landscapes evolution of the basin was controlled by the sea-level; (3) the erosional surface in the core-B indicates the Gangkou River continuously erode the infilling sediments from 7ka to 0.4ka BP. Previous studies show that the sea-level around Taiwan gradually declined from its high stand since 6ka, we proposed that the continuous erosion was probably the results of tectonic uplifting and eustatic sea-level fall.

An overlapping region between the two terminal folding units of the outer surface protein A (OspA) controls its folding behavior.

PubMed

Makabe, Koki; Nakamura, Takashi; Dhar, Debanjan; Ikura, Teikichi; Koide, Shohei; Kuwajima, Kunihiro

2018-04-27

Although many naturally occurring proteins consist of multiple domains, most studies on protein folding to date deal with single-domain proteins or isolated domains of multi-domain proteins. Studies of multi-domain protein folding are required for further advancing our understanding of protein folding mechanisms. Borrelia outer surface protein A (OspA) is a β-rich two-domain protein, in which two globular domains are connected by a rigid and stable single-layer β-sheet. Thus, OspA is particularly suited as a model system for studying the interplays of domains in protein folding. Here, we studied the equilibria and kinetics of the urea-induced folding-unfolding reactions of OspA probed with tryptophan fluorescence and ultraviolet circular dichroism. Global analysis of the experimental data revealed compelling lines of evidence for accumulation of an on-pathway intermediate during kinetic refolding and for the identity between the kinetic intermediate and a previously described equilibrium unfolding intermediate. The results suggest that the intermediate has the fully native structure in the N-terminal domain and the single layer β-sheet, with the C-terminal domain still unfolded. The observation of the productive on-pathway folding intermediate clearly indicates substantial interactions between the two domains mediated by the single-layer β-sheet. We propose that a rigid and stable intervening region between two domains creates an overlap between two folding units and can energetically couple their folding reactions. Copyright © 2018. Published by Elsevier Ltd.

Real-time observation of Cu2ZnSn(S,Se)4 solar cell absorber layer formation from nanoparticle precursors.

PubMed

Mainz, Roland; Walker, Bryce C; Schmidt, Sebastian S; Zander, Ole; Weber, Alfons; Rodriguez-Alvarez, Humberto; Just, Justus; Klaus, Manuela; Agrawal, Rakesh; Unold, Thomas

2013-11-07

The selenization of Cu-Zn-Sn-S nanocrystals is a promising route for the fabrication of low-cost thin film solar cells. However, the reaction pathway of this process is not completely understood. Here, the evolution of phase formation, grain size, and elemental distributions is investigated during the selenization of Cu-Zn-Sn-S nanoparticle precursor thin films by synchrotron-based in situ energy-dispersive X-ray diffraction and fluorescence analysis as well as by ex situ electron microscopy. The precursor films are heated in a closed volume inside a vacuum chamber in the presence of selenium vapor while diffraction and fluorescence signals are recorded. The presented results reveal that during the selenization the cations diffuse to the surface to form large grains on top of the nanoparticle layer and the selenization of the film takes place through two simultaneous reactions: (1) a direct and fast formation of large grained selenides, starting with copper selenide which is subsequently transformed into Cu2ZnSnSe4; and (2) a slower selenization of the remaining nanoparticles. As a consequence of the initial formation of copper selenides at the surface, the subsequent formation of CZTSe starts under Cu-rich conditions despite an overall Cu-poor composition of the film. The implications of this process path for the film quality are discussed. Additionally, the proposed growth model provides an explanation for the previously observed accumulation of carbon from the nanoparticle precursor beneath the large grained layer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Zongyuan; Duchon, Tomas; Wang, Huanru

Ambient-Pressure X-ray Photoelectron Spectroscopy (AP-XPS) and Infrared Reflection Absorption Spectroscopy (AP-IRRAS) have been used to elucidate the active sites and mechanistic steps associated with the ethanol steam reforming reaction (ESR) over Ni–CeO 2(111) model catalysts. Our results reveal that surface layers of the ceria substrate are both highly reduced and hydroxylated under reaction conditions while the small supported Ni nanoparticles are present as Ni 0/NixC. A multifunctional, synergistic role is highlighted in which Ni, CeO x and the interface provide an ensemble effect in the active chemistry that leads to H 2. Ni 0 is the active phase leading tomore » both C–C and C–H bond cleavage in ethanol and it is also responsible for carbon accumulation. On the other hand, CeO x is important for the deprotonation of ethanol/water to ethoxy and OH intermediates. The active state of CeO x is a Ce 3+(OH) x compound that results from extensive reduction by ethanol and the efficient dissociation of water. Additionally, we gain an important insight into the stability and selectivity of the catalyst by its effective water dissociation, where the accumulation of surface carbon can be mitigated by the increased presence of surface OH groups. As a result, the co-existence and cooperative interplay of Ni 0 and Ce 3+(OH) x through a metal–support interaction facilitate oxygen transfer, activation of ethanol/water as well as the removal of coke.« less

30 CFR 75.1709 - Accumulations of methane and coal dust on surface coal-handling facilities.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Accumulations of methane and coal dust on... Miscellaneous § 75.1709 Accumulations of methane and coal dust on surface coal-handling facilities. [Statutory Provisions] Adequate measures shall be taken to prevent methane and coal dust from accumulating in excessive...

Elucidating effects of atmospheric deposition and peat decomposition processes on mercury accumulation rates in a northern Minnesota peatland over last 10,000 cal years

NASA Astrophysics Data System (ADS)

Nater, E. A.; Furman, O.; Toner, B. M.; Sebestyen, S. D.; Tfaily, M. M.; Chanton, J.; Fissore, C.; McFarlane, K. J.; Hanson, P. J.; Iversen, C. M.; Kolka, R. K.

2014-12-01

Climate change has the potential to affect mercury (Hg), sulfur (S) and carbon (C) stores and cycling in northern peatland ecosystems (NPEs). SPRUCE (Spruce and Peatland Responses Under Climate and Environmental change) is an interdisciplinary study of the effects of elevated temperature and CO2 enrichment on NPEs. Peat cores (0-3.0 m) were collected from 16 large plots located on the S1 peatland (an ombrotrophic bog treed with Picea mariana and Larix laricina) in August, 2012 for baseline characterization before the experiment begins. Peat samples were analyzed at depth increments for total Hg, bulk density, humification indices, and elemental composition. Net Hg accumulation rates over the last 10,000 years were derived from Hg concentrations and peat accumulation rates based on peat depth chronology established using 14C and 13C dating of peat cores. Historic Hg deposition rates are being modeled from pre-industrial deposition rates in S1 scaled by regional lake sediment records. Effects of peatland processes and factors (hydrology, decomposition, redox chemistry, vegetative changes, microtopography) on the biogeochemistry of Hg, S, and other elements are being assessed by comparing observed elemental depth profiles with accumulation profiles predicted solely from atmospheric deposition. We are using principal component analyses and cluster analyses to elucidate relationships between humification indices, peat physical properties, and inorganic and organic geochemistry data to interpret the main processes controlling net Hg accumulation and elemental concentrations in surface and subsurface peat layers. These findings are critical to predicting how climate change will affect future accumulation of Hg as well as existing Hg stores in NPE, and for providing reference baselines for SPRUCE future investigations.

Spin transport and spin accumulation signals in Si studied in tunnel junctions with a Fe/Mg ferromagnetic multilayer and an amorphous SiOxNy tunnel barrier

NASA Astrophysics Data System (ADS)

Nakane, Ryosho; Hada, Takato; Sato, Shoichi; Tanaka, Masaaki

2018-04-01

We studied the spin accumulation signals in phosphorus-doped n+-Si (8 × 1019 cm-3) by measuring the spin transport in three-terminal vertical devices with Fe(3 nm)/Mg(0 and 1 nm)/SiOxNy(1 nm)/n+-Si(001) tunnel junctions, where the amorphous SiOxNy layer was formed by oxnitridation of the Si substrate with radio frequency plasma. Obvious spin accumulation signals were observed at 4-300 K in the spin extraction geometry when the thickness of the Mg insertion layer was 1 nm. We found that by inserting a thin (1 nm) Mg layer, intermixing of Fe and SiOxNy is suppressed, leading to the appearance of the spin accumulation signals, and this result is consistent with the dead layer model recently proposed by our group [S. Sato et al., Appl. Phys. Lett. 107, 032407 (2015)]. We obtained relatively high spin polarization (PS) of electrons tunneling through the junction and long spin lifetime (τS): PS = 16% and τS = 5.6 ns at 4 K and PS = 7.5% and τS = 2.7 ns at 300 K. Tunnel junctions with an amorphous SiOxNy tunnel barrier are very promising for Si-based spintronic devices, since they can be formed by the method compatible with the silicon complementary metal-oxide-semiconductor technology.

Photovoltaic cell with nano-patterned substrate

DOEpatents

Cruz-Campa, Jose Luis; Zhou, Xiaowang; Zubia, David

2016-10-18

A photovoltaic solar cell comprises a nano-patterned substrate layer. A plurality of nano-windows are etched into an intermediate substrate layer to form the nano-patterned substrate layer. The nano-patterned substrate layer is positioned between an n-type semiconductor layer composed of an n-type semiconductor material and a p-type semiconductor layer composed of a p-type semiconductor material. Semiconductor material accumulates in the plurality of nano-windows, causing a plurality of heterojunctions to form between the n-type semiconductor layer and the p-type semiconductor layer.

Laser ablation ICP-MS analysis of the radial distribution of lead in the femur of Alligator mississippiensis.

PubMed

Seltzer, Michael D; Lance, Valentine A; Elsey, Ruth M

2006-06-15

A laser ablation ICP-MS technique has been used to examine the radial distribution of lead in transverse sections of alligator femur. Annual bone growth in the femur results in the deposition of incremental layers of calcified tissue at the periphery of existing bone. Patterns of lead concentration within these layers provide a record of time-dependent accumulation from which exposure history can potentially be deduced. Femur specimens obtained from captive-reared alligators exhibited levels of lead accumulation that were entirely consistent with previously documented clinical signs of lead intoxication. In contrast, femurs obtained from wild alligators contained only minor amounts of lead that were likely accumulated as a result of incidental exposure.

Influence from Surrounding Land on the Turbulence Measurements Above a Lake

NASA Astrophysics Data System (ADS)

Sahlée, Erik; Rutgersson, Anna; Podgrajsek, Eva; Bergström, Hans

2014-02-01

Turbulence measurements taken at a Swedish lake are analyzed. Although the measurements took place over a relatively large lake with several km of undisturbed fetch, the turbulence structure was found to be highly influenced by the surrounding land during daytime. Variance spectra of both horizontal velocity and scalars during both unstable and stable stratification displayed a low frequency peak. The energy at lower frequencies showed a daily variation, increasing in the morning and decreasing in the afternoon. This behaviour is explained by spectral lag, where the low frequency energy due to large eddies that originate from the convective boundary layer above the surrounding land. When the air is advected over the lake the small eddies rapidly equilibrate with the new surface forcing. However, the large eddies remain for an appreciable distance and influence the turbulence in the developing lake boundary layer. The variances of the horizontal velocity and scalars are increased by these large eddies, while the turbulent fluxes are mainly unaffected. The drag coefficient, Stanton number and Dalton number used to parametrize the momentum flux, heat flux and latent heat flux respectively all compare well with current parametrizations developed for open sea conditions. The diurnal cycle of the partial pressure of methane, pCH4, observed at this site is closely related to the diurnal cycle of the lake-air methane flux. An idealized two-dimensional model simulation of the boundary layer at a lake site indicates that the strong response of pCH4 to the surface methane flux is due to the shallow internal boundary layer that develops above the lake, allowing methane to accumulate in a relatively small volume.

Past and Future Stability of Deep Peatland Carbon Stocks: Assessing the Nature and Fate of Carbon in a Northern Minnesota Ombrotrophic Peatland (Invited)

NASA Astrophysics Data System (ADS)

Hanson, P. J.; Chanton, J.; Iversen, C. M.; McFarlane, K. J.; Tfaily, M. M.; Xu, X.

2013-12-01

An ombrotrophic Picea-Sphagnum peatland located on the Marcell Experimental Forest in northern Minnesota is being prepared for experimental manipulations to evaluate carbon cycle responses to warming and elevated CO2. Pretreatment characterization of the peatland, which has a mean peat depth of ~3 meters, showed that belowground carbon (C) stocks were greater than 2200 MgC ha-1. This is easily 10× greater than the combined above- and belowground C stocks found in typical eastern deciduous forests. Carbon has accumulated under saturated, cool to cold conditions since the last glaciers receded some 10,000 years ago. Mean bulk-14C assessments show a modern C signature and decadal turnover time for peat in the raised hummock topography, as well as in the oxic acrotelm layer which extends to a depth of 30-cm below hollow microtopography. Deeper peat layers (below 30-cm depth) have C ages ranging from 1000- to 2000 years for relatively shallow layers, to between 7000 and 8000 years at 2.5 m depth. In contrast, the 14C signatures of dissolved inorganic C (DIC) and dissolved organic C (DOC), which reflect the substrates consumed by microbes, were relatively modern, even at depths of up to 2 meters. The modern 14C signatures indicate that microbial respiration at depth is fueled by surface inputs of DOC. Furthermore, the contrast in δ14C between solid-phase peat and DOC at deeper peat depths will allow researchers to quantify the effects of warming and elevated CO2 on the fate of peat stored in this ombrotrophic peatland for millennia. It is unclear whether C accumulation in peatlands will continue under warmer conditions associated with atmospheric and climatic change. Modeled projections for net peat C turnover throughout the peat profile will be discussed in the context of the planned warming manipulations. Initial hypotheses suggest that peat accumulation may be sustained for low levels of warming, but shift to a pattern of net carbon release as both CO2 and CH4 for warmer future climates.

Accumulation and chemical fractionation of heavy metals in andisols after a different, 6-year fertilization management.

PubMed

Zhao, Bingzi; Maeda, Morihiro; Zhang, Jiabao; Zhu, Anning; Ozaki, Yasuo

2006-03-01

Andisols are widespread in Japan and have some special properties such as high anion exchange capacity, low bulk density, and high organic matter content, which might influence the accumulation or chemical fractionation of heavy metals. However, few such data exist in Japanese andisols. The primary objective of this study was to investigate the distribution and chemical fractions of Cu, Zn, Ni, and Cr in the soil profiles and subsequently to assess their potential environmental hazard. Soil samples were taken from a field experiment conducted on Japanese andisols, which had received either swine compost or chemical fertilizers for 6 years. Concentrations of Cu, Zn, Ni, and Cr were determined for all of the obtained extract solutions by ICP-AES. Considerably higher total concentrations of Cu and Zn were observed in the top 20 cm layer of the compost-amended soil, relative to the unfertilized soil, while chemical fertilizers had little effect. Application of the swine compost increased the concentrations of Cu and Zn, but not Ni and Cr, in all fractions in the top 20 cm layer. The greatest increase in the organically bound fraction (OM) Cu and dilute acid-exchangeable fraction (DAEXCH) Zn was observed. This suggests that Cu and Zn are potentially bioavailable and mobile in the andisol profiles after 6-year consecutive applications of the swine compost. On the other hand, distribution of Cu, Zn, Ni and Cr among various soil fractions was generally unaffected by chemical fertilizers. We observed that 6-year consecutive applications of the swine compost led to an increase in total metals of Cu and Zn, as well as their all-chemical fractions, in the top 20 cm soil layers. Potential hazard of heavy metals, especially of Cu and Zn, as a result of the use of swine compost on andisols, must be taken into account. The long-term effect of the accumulation of heavy metals, particularly Cu and Zn, in various plant tissues and soils, as well as their potential risk to surface water via runoff and groundwater via leaching, needs to be carefully considered. Further investigations in the long-term experiments are therefore necessary.

Can we Ecohydrologically Rehabilitate Disturbed Peatlands? From "Wetlands of Mass Decomposition" to "Yes We Can"

NASA Astrophysics Data System (ADS)

Waddington, J. M.; Cagampan, J.; Lucchese, M.; Thompson, D. K.; Duval, T. P.

2009-05-01

The natural carbon storage function of peatland ecosystems can be severely affected by human and natural disturbances such as drainage, peat extraction, drought and wildfire. Cutover peatands, for example, become a large and persistent source of atmospheric CO2 following peat extraction. The recovery (rehabilitation, re- establishment, restoration) of disturbed peatlands to a net carbon sink depends to a large extent on the rate of recovery of the surface peat layer referred to as the acrotelm. The acrotelm serves to stabilize water table variation providing ideal conditions for vegetation re-establishment, particularly peat forming Sphagnum moss. Here we present results from several ecosystem-scale field experiments where we examined the change in hydrophysical properties of peat following peat extraction and subsequent restoration and discuss how this affects peatland-atmosphere CO2. We found that moisture retention properties of a new peat layer at a restored peatland were distinct from near- by natural and naturally regenerated sites. Despite considerable biomass accumulation and increase in peat thickness, the new peat layer differed with respect to its moisture retention properties, an indication that factors other than growth have an impact on the restoration of the returning moss layer. Similarly in an acrotelm transplant experiment we determined that the restored peatland experienced high variability in volumetric moisture content (VMC) in the capitula zone (upper 2 cm) where large diurnal changes in VMC (~30%) were observed, suggesting possible disturbance to the peat matrix structure during the extraction-restoration process. However, soil - water retention analysis and physical peat properties (porosity and bulk density) suggest that no significant differences existed between the natural and restored sites. A simple hydrologic model demonstrated that the new peat layer will become an acrotelm in ~20 years when ~20 cm of peat has accumulated, an approach which may aid in designing a long-term sampling strategy for assessing the long- term effects of restoration of disturbed peatlands on peatland hydrology and ecology. Applications of these findings to a new research collaboration on the effects of wildfire on peatland ecohydrology will be discussed.

Sedimentary laminations in the Isheyevo (CH/CBb) carbonaceous chondrite formed by gentle impact-plume sweep-up

NASA Astrophysics Data System (ADS)

Garvie, Laurence A. J.; Knauth, L. Paul; Morris, Melissa A.

2017-08-01

Prominent macroscopic sedimentary laminations, consisting of mm- to cm-thick alternating well-sorted but poorly mixed silicate and metal-rich layers cut by faults and downward penetrating load structures, are prevalent in the Isheyevo (CH/CBb) carbonaceous chondrite. The load structures give the up direction of this sedimentary rock that accumulated from in-falling metal- and silicate-rich grains under near vacuum conditions onto the surface of an accreting planetesimal. The Isheyevo meteorite is the end result of a combination of events and processes that we suggest was initiated by the glancing blow impact of two planetesimals. The smaller impactor was disrupted forming an impact plume downrange of the impact. The components within the plume were aerodynamically size sorted by the nebular gas and swept up by the impacted planetesimal before turbulent mixing within the plume could blur the effects of the sorting. This plume would have contained a range of materials including elementally zoned Fe-Ni metal grains that condensed in the plume to disrupted unaltered material from the crust of the impactor, such as the hydrated matrix lumps. The juxtaposition of hydrated matrix lumps, some of which have not been heated above 150 °C, together with components that formed above 1000 °C, is compelling evidence that they were swept up together. Sweep-up would have occurred as the rotating impactor moved through the plume producing layers of material: the Isheyevo sample thus represents material accumulated while that part of the rotating planetesimal moved into the plume. Vibrations from subsequent impacts helped to form the load structures and induced weak grading within the layers via kinetic sieving. Following sweep-up, the particles were compacted under low static temperatures as evidenced by the preservation of elementally zoned Fe-Ni metal grains with preserved martensite α2 cores, distinct metal-metal grain boundaries, and metal-deformation microstructures. This meteorite provides evidence of gentle layer-by-layer accretion in the early Solar System, and also extends the terrestrial sedimentary source-to-sink paradigm to a near vacuum environment where neither fluvial nor aeolian processes operate.

Recent Rise in West Greenland Surface Melt and Firn Density Driven by North Atlantic SSTs and Blocking Events

NASA Astrophysics Data System (ADS)

Osterberg, E. C.; Graeter, K.; Hawley, R. L.; Marshall, H. P.; Ferris, D. G.; Lewis, G.; Birkel, S. D.; Meehan, T.; McCarthy, F.

2017-12-01

The Greenland Ice Sheet (GrIS) has been losing mass since at least the early 2000s, mostly due to enhanced surface melt. Approximately 40% of the surface melt currently generated on the GrIS percolates into the snow/firn and refreezes, where it has no immediate impact on GrIS mass balance or sea-level rise. However, in situ observations of surface melt are sparse, and thus it remains unclear how melt water percolation and refreezing are modifying the GrIS percolation zone under recent warming. In addition, understanding the climatic drivers behind the recent increase in melt is critical for accurately predicting future GrIS surface melt rates and contributions to sea-level rise. Here we show that there have been significant increases in melt refreeze and firn density over the past 30-50 years along a 250 km-long region of the Western Greenland percolation zone (2137 - 2218 m elevation). We collected seven shallow firn cores as part of the 2016 Greenland Traverse for Accumulation and Climate Studies (GreenTrACS), analyzed each for melt layer stratigraphy and density, and developed timescales for each based on annual layer counting of seasonal chemical oscillations (e.g. δ18O, dust, and biogenic sulfur). The cores indicate that refrozen melt layers have increased 2- to 9-fold since 1970, with statistically significant (p < 0.05) linear trends at the five southernmost core sites. Comparisons of two GreenTrACS cores to co-located PARCA cores collected in 1998 reveal significant (p < 0.05) increases in density averaged over the top 10 m of firn ranging from 32-42 kg/m3. Recent density increases closely correspond with the locations of refrozen melt water. We use output from the MARv3.7 Regional Climate Model to assess climatic forcing of surface melt at GreenTrACS sites, and find significant summer-to-summer correlations between melt generation and the frequency of blocking high pressure centers over Greenland (represented by the Greenland Blocking Index; GBI), and with North Atlantic sea surface temperatures (represented by the Atlantic Multidecadal Oscillation; AMO). Thus, future surface melt rates in Western Greenland depend on the complex evolution of the GBI and AMO under anthropogenic forcing, both of which remain poorly constrained in 21st century model projections.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Foltz, Gregory R.; Balaguru, Karthik; Leung, Lai-Yung R.

The impact of tropical cyclones on surface chlorophyll concentration is assessed in the western subtropical North Atlantic Ocean during 1998–2011. Previous studies in this area focused on individual cyclones and gave mixed results regarding the importance of tropical cyclone-induced mixing for changes in surface chlorophyll. Using a more integrated and comprehensive approach that includes quantification of cyclone-induced changes in mixed layer depth, here it is shown that accumulated cyclone energy explains 22% of the interannual variability in seasonally-averaged (June–November) chlorophyll concentration in the western subtropical North Atlantic, after removing the influence of the North Atlantic Oscillation (NAO). The variance explainedmore » by tropical cyclones is thus about 70% of that explained by the NAO, which has well-known impacts in this region. It is therefore likely that tropical cyclones contribute significantly to interannual variations of primary productivity in the western subtropical North Atlantic during the hurricane season.« less

Notes on a Mesodinium rubrum red tide in San Francisco Bay (California, USA)

USGS Publications Warehouse

Cloern, James E.; Cole, Brian E.; Hager, Stephen W.

1994-01-01

Discrete red patches of water were observed in South San Francisco Bay (USA) on 30 April 1993, and examination of live samples showed that this red tide was caused by surface accumulations of the pigmented ciliate Mesodinium rubrum . Vertical profiles showed strong salinity and temperature stratification in the upper 5 m, peak chlorophyll fluorescence in the upper meter, and differences in the small-scale density structure and fluorescence distribution among red patches. Events preceding this Mesodinium red tide included: (i) heavy precipitation and run-off, allowing for strong salinity stratification; (ii) a spring diatom bloom where the chlorophyll a concentration reached 50 mg m −3 ; (ii) depletions of dissolved inorganic N and Si in the photic zone; and (iv) several days of rapid warming and stabilization of the upper surface layer. These conditions may be general prerequisites for M.rubrum blooms in temperate estuaries.

Research on stratified evolution of composite materials under four-point bending loading

NASA Astrophysics Data System (ADS)

Hao, M. J.; You, Q. J.; Zheng, J. C.; Yue, Z.; Xie, Z. P.

2017-12-01

In order to explore the effect of stratified evolution and delamination on the load capacity and service life of the composite materials under the four-point bending loading, the artificial tectonic defects of the different positions were set up. The four-point bending test was carried out, and the whole process was recorded by acoustic emission, and the damage degree of the composite layer was judged by the impact accumulation of the specimen - time-amplitude history chart, load-time-relative energy history chart, acoustic emission impact signal positioning map. The results show that the stratified defects near the surface of the specimen accelerate the process of material failure and expansion. The location of the delamination defects changes the bending performance of the composites to a great extent. The closer the stratification defects are to the surface of the specimen, the greater the damage, the worse the service capacity of the specimen.

Analysis of Ti valence states in resistive switching regions of a rutile TiO2‑ x four-terminal memristive device

NASA Astrophysics Data System (ADS)

Yamaguchi, Kengo; Takeuchi, Shotaro; Tohei, Tetsuya; Ikarashi, Nobuyuki; Sakai, Akira

2018-06-01

We have performed Ti valence state analysis of our four-terminal rutile TiO2‑ x single-crystal memristors using scanning transmission electron microscopy–electron energy loss spectroscopy (STEM–EELS). Analysis of Ti-L2,3 edge EELS spectra revealed that the electrocolored region formed by the application of voltage includes a valence state reflecting highly reduced TiO2‑ x due to the accumulation of oxygen vacancies. Such a valence state mainly exists within ∼50 nm from the crystal surface and extends along specific crystal directions. These electrically reduced surface layers are considered to directly contribute to the resistive switching (RS) in the four-terminal device. The present results add new insights into the microscopic mechanisms of the RS phenomena and should contribute to further development and improvements of TiO2‑ x based memristive devices.

The Effect of the Thickness of the Sensitive Layer on the Performance of the Accumulating NOx Sensor

PubMed Central

Groß, Andrea; Richter, Miriam; Kubinski, David J.; Visser, Jacobus H.; Moos, Ralf

2012-01-01

A novel and promising method to measure low levels of NOx utilizes the accumulating sensor principle. During an integration cycle, incoming NOx molecules are stored in a sensitive layer based on an automotive lean NOx trap (LNT) material that changes its electrical resistivity proportional to the amount of stored NOx, making the sensor suitable for long-term detection of low levels of NOx. In this study, the influence of the thickness of the sensitive layer, prepared by multiple screen-printing, is investigated. All samples show good accumulating sensing properties for both NO and NO2. In accordance to a simplified model, the base resistance of the sensitive layer and the sensitivity to NOx decrease with increasing thickness. Contrarily, the sensor response time increases. The linear measurement range of all samples ends at a sensor response of about 30% resulting in an increase of the linearly detectable amount with the thickness. Hence, the variation of the thickness of the sensitive layer is a powerful tool to adapt the linear measurement range (proportional to the thickness) as well as the sensitivity (proportional to the inverse thickness) to the application requirements. Calculations combining the sensor model with the measurement results indicate that for operation in the linear range, about 3% of the LNT material is converted to nitrate.

Advanced processing methods to introduce and preserve dipole orientation in organic electro-optic materials for next generation photonic devices

NASA Astrophysics Data System (ADS)

Huang, Su

Organic electro-optic (E-O) materials have attracted considerable research attention in the past 20 years due to their rising potentials in a lot of novel photonic applications, such as high-speed telecommunication, terahertz generation and ultra-fast optical interconnections. Chapter 2 of this dissertation focuses on a barrier layer approach to improve the poling efficiency of electro-optic polymers. First of all, high conduction current from excessive charge injection is identified as a fundamental challenge of effective poling. After analyzing the conduction mechanism, we introduce a sol-gel derived thin titanium dioxide (TiO2) layer that can significantly block excessive charge injection and reduce the leakage current during high field poling. Ultralarge E-O coefficients, up to 160-350 pm/V at 1310 nm have been achieved by poling with such a barrier, which are 26%-40% higher than the results poled without such a TiO2 layer. This enhancement is explained by the suppressed charge injection and space charge accumulation by the insertion of the high injection barrier from the TiO2 barrier layer. In Chapter 3, the impact of the inserted barrier layer on the temporal alignment stability of E-O polymers is discussed. Considerable stability enhancement is confirmed using both standard 500-hour temporal alignment stability test at 85 °C and thermally stimulated discharge method. We suggest that the enhancement comes from improved stability of the screening charge. During poling the additional barrier layer helps to lower the injection and thus the space charge accumulation. And this reduced space charge accumulation further helps to replace the space charge part in the total formulation of screening charge with more stable interface trapped charge. We thus expand this knowledge to a group of other materials that can also block excessive charge injection and suppressed space charge accumulation, including dielectric polymers polyvinyl alcohol (PVA), poly(4-vinylphenol) (PVP) and TOPAS as well as ferroelectric polymer poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE), 65/35 copolymer), which differ largely from the others in dielectric constant, conductivity and surface properties. The only common feature of them is that they all lowered the charge injection and leakage current for 1-2 orders during poling. On every buffer layer we tried, similar trend of stability enhancement is found. These results suggest that the observed temporal stability enhancement is indeed an effect from the abovementioned mechanism. Chapter 4 focuses on the development of an innovative new poling method, which utilizes pyroelectric effect instead of external power sources to overcome the limitations of conventional contact poling and corona poling. With careful theory assisted design, we developed a reliable protocol to efficiently introduce dipole orientation in organic E-O materials by heating and cooling them with detachable pyroelectric crystals. This new method can potentially improve the process adaptability of organic E-O materials in a variety of photonic devices. Large Pockels coefficients (up to 81 pm/V at 1.3 micron) have been successfully achieved in thin films poled using this method. The effective fields in these experiments are estimated to be around 0.5 to 0.9 MV/cm, which agree well with the electrostatics analysis using an idealized model. The same method is directly applied to surface modified hybrid polymer silicon slot waveguide ring-resonator modulators devices. A 25 pm/V tunability of resonance peak wavelength shift has been realized, which was higher than any reported results in similar devices. Chapter 5 discusses about the possible application of the pyroelectric poling in a multi-stack waveguide device architecture. A long-existing challenge to pole E-O polymer based photonic devices is how to effectively drop the poling voltage to the core layer, which is usually sandwiched between two dielectric claddings. In the past, this was done by using relatively conductive claddings, which on the other hand can bring larger optical loss and dielectric loss to the waveguide. Thus careful engineering compromise must be made between better poling efficiency and lower loss. Pyroelectric poling as discussed in Chapter 4 opens up new possibilities. In this chapter, it is demonstrated that E-O polymer films can be poled even with 3 orders thicker dielectric layer in circuit using pyroelectric poling. The theoretical analysis matches well with the experimental results. (Abstract shortened by UMI.).

Using nuclear magnetic resonance and transient electromagnetics to characterise water distribution beneath an ice covered volcanic crater: the case of Sherman Crater Mt. Baker Washington.

USGS Publications Warehouse

Irons, Trevor P.; Martin, Kathryn; Finn, Carol A.; Bloss, Benjamin; Horton, Robert J.

2014-01-01

Surface and laboratory Nuclear Magnetic Resonance (NMR) measurements combined with transient electromagnetic (TEM) data are powerful tools for subsurface water detection. Surface NMR (sNMR) and TEM soundings, laboratory NMR, complex resistivity, and X-Ray Diffraction (XRD) analysis were all conducted to characterise the distribution of water within Sherman Crater on Mt. Baker, WA. Clay rich rocks, particularly if water saturated, can weaken volcanoes, thereby increasing the potential for catastrophic sector collapses that can lead to far-travelled, destructive debris flows. Detecting the presence and volume of shallow groundwater is critical for evaluating these landslide hazards. The TEM data identified a low resistivity layer (<10 ohm-m), under 60 m of glacial ice related to water saturated clays. The TEM struggles to resolve the presence or absence of a plausible thin layer of bulk liquid water on top of the clay. The sNMR measurements did not produce any observable signal, indicating the lack of substantial accumulated bulk water below the ice. Laboratory analysis on a sample from the crater wall that likely represented the clays beneath the ice confirmed that the controlling factor for the lack of sNMR signal was the fine-grained nature of the media. The laboratory measurements further indicated that small pores in clays detected by the XRD contain as much as 50% water, establishing an upper bound on the water content in the clay layer. Forward modelling of geologic scenarios revealed that bulk water layers as thin as ½ m between the ice and clay layer would have been detectable using sNMR. The instrumentation conditions which would allow for sNMR detection of the clay layer are investigated. Using current instrumentation the combined analysis of the TEM and sNMR data allow for valuable characterisation of the groundwater system in the crater. The sNMR is able to reduce the uncertainty of the TEM in regards to the presence of a bulk water layer, a valuable piece of information in hazard assessment.

MEMS based pyroelectric thermal energy harvester

DOEpatents

Hunter, Scott R; Datskos, Panagiotis G

2013-08-27

A pyroelectric thermal energy harvesting apparatus for generating an electric current includes a cantilevered layered pyroelectric capacitor extending between a first surface and a second surface, where the first surface includes a temperature difference from the second surface. The layered pyroelectric capacitor includes a conductive, bimetal top electrode layer, an intermediate pyroelectric dielectric layer and a conductive bottom electrode layer. In addition, a pair of proof masses is affixed at a distal end of the layered pyroelectric capacitor to face the first surface and the second surface, wherein the proof masses oscillate between the first surface and the second surface such that a pyroelectric current is generated in the pyroelectric capacitor due to temperature cycling when the proof masses alternately contact the first surface and the second surface.

Methylmercury Mass Budgets and Distribution Characteristics in the Western Pacific Ocean.

PubMed

Kim, Hyunji; Soerensen, Anne L; Hur, Jin; Heimbürger, Lars-Eric; Hahm, Doshik; Rhee, Tae Siek; Noh, Seam; Han, Seunghee

2017-02-07

Methylmercury (MeHg) accumulation in marine organisms poses serious ecosystem and human health risk, yet the sources of MeHg in the surface and subsurface ocean remain uncertain. Here, we report the first MeHg mass budgets for the Western Pacific Ocean estimated based on cruise observations. We found the major net source of MeHg in surface water to be vertical diffusion from the subsurface layer (1.8-12 nmol m -2  yr -1 ). A higher upward diffusion in the North Pacific (12 nmol m -2  yr -1 ) than in the Equatorial Pacific (1.8-5.7 nmol m -2  yr -1 ) caused elevated surface MeHg concentrations observed in the North Pacific. We furthermore found that the slope of the linear regression line for MeHg versus apparent oxygen utilization in the Equatorial Pacific was about 2-fold higher than that in the North Pacific. We suggest this could be explained by redistribution of surface water in the tropical convergence-divergence zone, supporting active organic carbon decomposition in the Equatorial Pacific Ocean. On the basis of this study, we predict oceanic regions with high organic carbon remineralization to have enhanced MeHg concentrations in both surface and subsurface waters.

Wintertime vertical variations in particulate matter (PM) and precursor concentrations in the San Joaquin Valley during the California Regional Coarse PM/Fine PM Air Quality Study.

PubMed

Brown, Steven G; Roberts, Paul T; McCarthy, Michael C; Lurmann, Frederick W; Hyslop, Nicole P

2006-09-01

Air quality monitoring was conducted at a rural site with a tower in the middle of California's San Joaquin Valley (SJV) and at elevated sites in the foothills and mountains surrounding the SJV for the California Regional PM10/ PM2.5 Air Quality Study. Measurements at the surface and n a tower at 90 m were collected in Angiola, CA, from December 2000 through February 2001 and included hourly black carbon (BC), particle counts from optical particle counters, nitric oxide, ozone, temperature, relative humidity, wind speed, and direction. Boundary site measurements were made primarily using 24-hr integrated particulate matter (PM) samples. These measurements were used to understand the vertical variations of PM and PM precursors, the effect of stratification in the winter on concentrations and chemistry aloft and at the surface, and the impact of aloft-versus-surface transport on PM concentrations. Vertical variations of concentrations differed among individual species. The stratification may be important to atmospheric chemistry processes, particularly nighttime nitrate formation aloft, because NO2 appeared to be oxidized by ozone in the stratified aloft layer. Additionally, increases in accumulation-mode particle concentrations in the aloft layer during a fine PM (PM2.5) episode corresponded with increases in aloft nitrate, demonstrating the likelihood of an aloft nighttime nitrate formation mechanism. Evidence of local transport at the surface and regional transport aloft was found; transport processes also varied among the species. The distribution of BC appeared to be regional, and BC was often uniformly mixed vertically. Overall, the combination of time-resolved tower and surface measurements provided important insight into PM stratification, formation, and transport.

Changes in the firn structure of the western Greenland Ice Sheet caused by recent warming

DOE PAGES

de la Peña, S.; Howat, I. M.; Nienow, P. W.; ...

2015-06-11

Atmospheric warming over the Greenland Ice Sheet during the last 2 decades has increased the amount of surface meltwater production, resulting in the migration of melt and percolation regimes to higher altitudes and an increase in the amount of ice content from refrozen meltwater found in the firn above the superimposed ice zone. Here we present field and airborne radar observations of buried ice layers within the near-surface (0–20 m) firn in western Greenland, obtained from campaigns between 1998 and 2014. We find a sharp increase in firn-ice content in the form of thick widespread layers in the percolation zone,more » which decreases the capacity of the firn to store meltwater. The estimated total annual ice content retained in the near-surface firn in areas with positive surface mass balance west of the ice divide in Greenland reached a maximum of 74 ± 25 Gt in 2012, when compared to the 1958–1999 average of 13 ± 2 Gt, while the percolation zone area more than doubled between 2003 and 2012. Increased melt and column densification resulted in surface lowering averaging -0.80 ± 0.39 m yr -1 between 1800 and 2800 m in the accumulation zone of western Greenland. Since 2007, modeled annual melt and refreezing rates in the percolation zone at elevations below 2100 m surpass the annual snowfall from the previous year, implying that mass gain in the region is retained after melt in the form of refrozen meltwater. Furthermore, if current melt trends over high elevation regions continue, subsequent changes in firn structure will have implications for the hydrology of the ice sheet and related abrupt seasonal densification could become increasingly significant for altimetry-derived ice sheet mass balance estimates.« less

Lactobacillus acidophilus CP23 with weak immunomodulatory activity lacks anchoring structure for surface layer protein.

PubMed

Yanagihara, Sae; Kato, Shinji; Ashida, Nobuhisa; Yamamoto, Naoyuki

2015-05-01

To determine the reason for the low levels of Surface layer protein A (SlpA) on CP23 cells, which might play a crucial role in the immunomodulatory effect of Lactobacillus acidophilus, the DNA sequence of the slpA gene of CP23 and L-92 strains, including the upstream region, were analyzed. Unexpectedly, there was no significant difference in the predicted amino acid sequence of the C-terminus needed for cell anchoring, and only an additional Ala-Val-Ala sequence inserted in the N-terminal region of the mature CP23 protein. Therefore, anchoring of SlpA on the cell wall of CP23 and L-92 was evaluated by a reconstitution assay, which showed that SlpA released by LiCl treatment from both CP23 and L-92 was successfully anchored on LiCl-treated L-92 cells, but not on LiCl-treated CP23 cells. Moreover, quantitative analysis of SlpA protein in the culture medium of CP23 and L-92 by ELISA revealed higher levels of SlpA secretion in CP23 cells than in L-92 cells. Collectively, these results suggest that the lower levels of SlpA on the surface of CP23 cells might be caused by less cell wall capacity for SlpA anchoring, leading to an accumulation of SlpA in the culture medium of CP23 cells. The present study supports the importance of cell surface structure of L. acidophilus L-92 for SlpA anchoring on the cell surface needed for immunomodulatory effect. Copyright © 2014 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, B.; Valdes, P.J.

The U.K. University Global Atmospheric Modeling Programme GCM is used to investigate whether the growth of Northern Hemisphere ice sheets could have been initiated by changes of orbital parameters and sea surface temperatures. Two different orbital configurations, corresponding to the present day and 115 kyr BP are used. The reduced summer solar insolation in the Northern Hemisphere results in a decrease of the surface temperature by 4{degrees} to 10{degrees}C in the northern continents and to perennial snow in some high-latitude regions. Therefore, the model results support the hypothesis that a deficit of summer insolation can create conditions favorable for initiationmore » of ice sheet growth in the Northern Hemisphere. A decreased sea surface temperature northward of 65{degrees}N during the Northern Hemisphere summer may contribute to the maintenance of ice sheets. A simple mixed-layer ocean model coupled to the GCM indicates that the changes of sea surface temperature and extension of sea ice due to insolation changes play an important role in inception of the Fennoscandian, Laurentide, and Cordilleran ice sheets. The model results suggest that the regions of greatest sensitivity for ice initiation are the Canadian Archipelago, Baffin Island, Tibetan Plateau, Scandinavia, Siberia, Alaska, and Keewatin, where changing orbital parameters to 115 kyr BP results in the snow cover remaining throughout the warmer summer, leading to long-term snow accumulation. The model results are in general agreement with geological evidence and are the first time that a GCM coupled with a mixed layer ocean has reproduced the inception of the Northern Hemisphere ice sheets. 69 refs., 21 figs., 3 tabs.« less

Carbon, nitrogen, and phosphorus accumulation in floodplains of Atlantic Coastal Plain rivers, USA

USGS Publications Warehouse

Noe, G.B.; Hupp, C.R.

2005-01-01

Net nutrient accumulation rates were measured in riverine floodplains of the Atlantic Coastal Plain in Virginia, Maryland, and Delaware, USA. The floodplains were located in watersheds with different land use and included two sites on the Chickahominy River (urban), one site on the Mattaponi River (forested), and five sites on the Pocomoke River (agricultural). The Pocomoke River floodplains lie along reaches with natural hydrogeomorphology and on reaches with restricted flooding due to channelization and levees. A network of feldspar clay marker horizons was placed on the sediment surface of each floodplain site 3-6 years prior to sampling. Sediment cores were collected from the material deposited over the feldspar clay pads. This overlying sediment was separated from the clay layer and then dried, weighed, and analyzed for its total carbon (C), nitrogen (N), and phosphorus (P) content. Mean C accumulation rates ranged from 61 to 212 g??m-2??yr-1, N accumulation rates ranged from 3.5 to 13.4 g??m -2??yr-1, and P accumulation rates ranged from 0.2 to 4.1 g??m-2??yr-1 among the eight floodplains. Patterns of intersite variation in mineral sediment and P accumulation rates were similar to each other, as was variation in organic sediment and C and N accumulation rates. The greatest sediment and C, N, and P accumulation rates were observed on Chickahominy River floodplains downstream from the growing metropolitan area of Richmond, Virginia. Nutrient accumulation rates were lowest on Pocomoke River floodplains that have been hydraulically disconnected from the main channel by channelization and levees. Sediment P concentrations and P accumulation rates were much greater on the hydraulically connected floodplain immediately downstream of the limit of channelization and dense chicken agriculture of the upper Pocomoke River watershed. These findings indicate that (1) watershed land use has a large effect on sediment and nutrient retention in floodplains, and (2) limiting the hydraulic connectivity between river channels and floodplains minimizes material retention by floodplains in fluvial hydroscapes. ?? 2005 by the Ecological Society of America.

Layered Mantling Deposits in the Northern Mid-Latitudes

NASA Image and Video Library

2017-02-22

Ice-rich mantling deposits accumulate from the atmosphere in the Martian mid-latitudes in cycles during periods of high obliquity (axial tilt), as recently as several million years ago. These deposits accumulate over cycles in layers, and here in the southern mid-latitudes, where the deposits have mostly eroded away due to warmer temperatures, small patches of the remnant layered deposits can still be observed. The map is projected here at a scale of 25 centimeters (9.8 inches) per pixel. [The original image scale is 29.5 centimeters (11.6 inches) per pixel (with 1 x 1 binning); objects on the order of 89 centimeters (35 inches) across are resolved.] North is up. http://photojournal.jpl.nasa.gov/catalog/PIA21462

Thermal actuation of extinguishing systems

NASA Astrophysics Data System (ADS)

Evans, D. D.

1984-03-01

A brief review of the Response Time Index (RTI) method of characterizing the thermal response of commercial sprinklers and heat detectors is presented. Measured ceiling layer flow temperature and velocity histories from a bedroom fire test are used to illustrate the use of RTI in calculating sprinkler operation times. In small enclosure fires, a quiescent warm gas layer confined by the room walls may accumulate below the ceiling before sprinkler operation. The effects of this warm gas layer on the fire plume and ceiling jet flows are accounted for by substitution of an equivalent point source fire. Encouraging agreement was found between measured ceiling jet temperatures from steady fires in a laboratory scale cylindrical enclosure put into dimensionless form based on parameters of the substitute fire source, and existing empirical correlations from fire tests in large enclosures in which a quiescent warm upper gas layer does not accumulate.

Soil organic carbon and nitrogen accumulation on coal mine spoils reclaimed with maritime pine (Pinus pinaster Aiton) in Agacli-Istanbul.

PubMed

Sever, Hakan; Makineci, Ender

2009-08-01

Mining operations on open coal mines in Agacli-Istanbul have resulted in the destruction of vast amounts of land. To rehabilitate these degraded lands, plantations on this area began in 1988. Twelve tree species were planted, however, the most planted tree species was maritime pine (Pinus pinaster Aiton). This study performed on 14 sample plots randomly selected in maritime pine plantations on coal mine soil/spoils in 2005. Soil samples were taken from eight different soil layers (0-1, 1-3, 3-5, 5-10, 10-20, 20-30, 30-40 and 40-50 cm) into the soil profile. On soil samples; fine soil fraction (<2 mm), soil acidity (pH), organic carbon (C(org)) and total nitrogen (N(t)) contents were investigated, and results were compared statistically among soil layers. As a result, 17 years after plantations, total forest floor accumulation determined as 17,973.20 kg ha(-1). Total nitrogen and organic matter amounts of forest floor were 113.90 and 14,640.92 kg ha(-1) respectively. Among soil layers, the highest levels of organic carbon (1.77%) and total nitrogen (0.096%) and the lowest pH value (pH 5.38) were found in 0-1 cm soil layer, and the variation differs significantly among soil layers. Both organic carbon and total nitrogen content decreased, pH values increased from 0-1 to 5-10 cm layer. In conclusion, according to results obtained maritime pine plantations on coal mine spoils; slow accumulation and decomposition of forest floor undergo simultaneously. Depending on these changes organic carbon and total nitrogen contents increased in upper layer of soil/spoil.

Enhancement of superconducting transition temperature in FeSe electric-double-layer transistor with multivalent ionic liquids

NASA Astrophysics Data System (ADS)

Miyakawa, Tomoki; Shiogai, Junichi; Shimizu, Sunao; Matsumoto, Michio; Ito, Yukihiro; Harada, Takayuki; Fujiwara, Kohei; Nojima, Tsutomu; Itoh, Yoshimitsu; Aida, Takuzo; Iwasa, Yoshihiro; Tsukazaki, Atsushi

2018-03-01

We report on an enhancement of the superconducting transition temperature (Tc) of the FeSe-based electric-double-layer transistor (FeSe-EDLT) by applying the multivalent oligomeric ionic liquids (ILs). The IL composed of dimeric cation (divalent IL) enables a large amount of charge accumulation on the surface of the FeSe ultrathin film, resulting in inducing electron-rich conduction even in a rather thick 10 nm FeSe channel. The onset Tc in FeSe-EDLT with the divalent IL is enhanced to be approaching about 50 K at the thin limit, which is about 7 K higher than that in EDLT with conventional monovalent ILs. The enhancement of Tc is a pronounced effect of the application of the divalent IL, in addition to the large capacitance, supposing preferable interface formation of ILs driven by geometric and/or Coulombic effect. The present finding strongly indicates that multivalent ILs are powerful tools for controlling and improving physical properties of materials.

Effects of aleurone layer on rice cooking: A histological investigation.

PubMed

Wu, Jianyong; Chen, Jun; Liu, Wei; Liu, Chengmei; Zhong, Yejun; Luo, Dawen; Li, Zhongqiang; Guo, Xiaojuan

2016-01-15

Understanding how aleurone layer (AL) affects rice cooking behaviour is important for rice processing. Individual effects of AL on rice cooking behaviour were evaluated and histological characters of AL before and after cooking were investigated. AL slightly affected rice cooking quality (optimum cooking time, water absorption, volume expansion ratio and total solids loss) while remarkably affected rice texture (hardness and adhesiveness) and peak viscosity. Histological investigation showed that channels were formed in AL during cooking. The channels facilitated the penetration of water, which could explain why AL exhibited slight effects on rice cooking quality. In addition, thick cell walls and thermally stable aleurone grains were widely distributed in AL. Leached components accumulated on them and formed a reinforced coated film on rice surface during cooking, which may be a possible mechanism accounting for the remarkable effect of AL on rice texture. Histological characters of AL are closely related with rice cooking behaviour. Copyright © 2014 Elsevier Ltd. All rights reserved.

Some constraints on the thermal history of the lunar magma ocean

NASA Technical Reports Server (NTRS)

Herbert, F.; Drake, M. J.; Sonett, C. P.; Wiskerchen, M. J.

1977-01-01

If the accumulating evidence is accepted that the outer portion of the moon was molten for 100-200 million years, it is clear that a permanent insulating surface layer existed over nearly all of that epoch. Considerations of crustal stability against break-up and foundering lead to the view that this insulating blanket must have been an early-forming plagioclase-rich layer light enough to float on the hot magma. It is found that radiometric age-dating evidence implies a fairly specific history for the solidification of the lunar magma ocean. The possibility is anticipated that geochronological and petrological constraints will be sufficient to narrow the range of allowed geophysical and geochemical models. It is hoped that such a study will make it possible to deduce the original depth, and hence, the composition of the lunar magma ocean. If the moon accreted homogeneously, the composition of the magma ocean will also be that of the whole moon, and hence such models should allow estimation of the bulk lunar composition.

Accumulation of neurocan, a brain chondroitin sulfate proteoglycan, in association with the retinal vasculature in RCS rats.

PubMed

Zhang, Yiqin; Rauch, Uwe; Perez, Maria-Thereza R

2003-03-01

To examine whether and how the retinal distribution of the chondroitin sulfate proteoglycan neurocan is affected after photoreceptor cell loss and whether it correlates with the multiple secondary cellular changes that accompany the photoreceptor degeneration. Retinas from normal rats (Sprague-Dawley; postnatal days [P]0-P70), RCS rats with dystrophic retinas (P0-P300), RCS-rdy(+) congenic rats with nondystrophic retinas (P0-202), and rhodopsin mutant rats, P23H (P0-P257) and S334ter (P0-P220), were processed for immunohistochemistry using a polyclonal antibody to rat neurocan. The overall distribution of neurocan was similar in all retinas examined. Neurocan immunostaining was detected over the nerve fiber layer, the plexiform layers, the photoreceptor outer segments region, and the ciliary epithelium. With age, labeling throughout the plexiform layers decreased continuously. In RCS rats however, conspicuous labeling was also seen in association with retinal vessels, from P15 onward. Accumulation of neurocan in association with the retinal vasculature does not correlate with photoreceptor cell loss, because it was not observed in the rhodopsin mutant rats. During the earliest stages of the disease, accumulation of debris in the subretinal space in RCS rats may be sufficient per se to initiate a cascade of metabolic changes that result in accumulation of neurocan. With time, the neurocan accumulated perivascularly may, by interaction with other matrix molecules, modulate at least some of the vascular alterations observed in this animal model.