Nitric oxide reduction in coal combustion: role of char surface complexes in heterogeneous reactions.

PubMed

Arenillas, Ana; Rubiera, Fernando; Pis, José J

2002-12-15

Nitrogen oxides are one of the major environmental problems arising from fossil fuel combustion. Coal char is relatively rich in nitrogen, and so this is an important source of nitrogen oxides during coal combustion. However, due to its carbonaceous nature, char can also reduce NO through heterogeneous reduction. The objectives of this work were on one hand to compare NO emissions from coal combustion in two different types of equipment and on the other hand to study the influence of char surface chemistry on NO reduction. A series of combustion tests were carried out in two different scale devices: a thermogravimetric analyzer coupled to a mass spectrometer and an FTIR (TG-MS-FTIR) and a fluidized bed reactor with an on line battery of analyzers. The TG-MS-FTIR system was also used to perform a specific study on NO heterogeneous reduction reactions using chars with different surface chemistry. According to the results obtained, it can be said that the TG-MS-FTIR system provides valuable information about NO heterogeneous reduction and it can give good trends of the behavior in other combustion equipments (i.e., fluidized bed combustors). It has been also pointed out that NO-char interaction depends to a large extent on temperature. In the low-temperature range (<800 degrees C), NO heterogeneous reduction seems to be controlled by the evolution of surface complexes. In the high-temperature range (>800 degrees C), a different mechanism is involved in NO heterogeneous reduction, the nature of the carbon matrix being a key factor.

Reduction of surface leakage current by surface passivation of CdZn Te and other materials using hyperthermal oxygen atoms

DOEpatents

Hoffbauer, Mark A.; Prettyman, Thomas H.

2001-01-01

Reduction of surface leakage current by surface passivation of Cd.sub.1-x Zn.sub.x Te and other materials using hyperthermal oxygen atoms. Surface effects are important in the performance of CdZnTe room-temperature radiation detectors used as spectrometers since the dark current is often dominated by surface leakage. A process using high-kinetic-energy, neutral oxygen atoms (.about.3 eV) to treat the surface of CdZnTe detectors at or near ambient temperatures is described. Improvements in detector performance include significantly reduced leakage current which results in lower detector noise and greater energy resolution for radiation measurements of gamma- and X-rays, thereby increasing the accuracy and sensitivity of measurements of radionuclides having complex gamma-ray spectra, including special nuclear materials.

The effect of water temperature and synoptic winds on the development of surface flows over narrow, elongated water bodies

NASA Technical Reports Server (NTRS)

Segal, M.; Pielke, R. A.

1985-01-01

Simulations of the thermally induced breeze involved with a relatively narrow, elongated water body is presented in conjunction with evaluations of sensible heat fluxes in a stable marine atmospheric surface layer. The effect of the water surface temperature and of the large-scale synoptic winds on the development of surface flows over the water is examined. As implied by the sensible heat flux patterns, the simulation results reveal the following trends: (1) when the synoptic flow is absent or light, the induced surface breeze is not affected noticeably by a reduction of the water surface temperature; and (2) for stronger synoptic flow, the resultant surface flow may be significantly affected by the water surface temperature.

Strain Evolution of Annealed Hydrogen-Implanted (0001) Sapphire

NASA Astrophysics Data System (ADS)

Wong, Christine Megan

Exfoliation is a technique used to remove a thin, uniform layer of material from the bulk that involves the annealing of hydrogen ion-implanted materials in order to initiate defect nucleation and growth leading to guided crack propagation. This study presents an investigation into the annealing process required to initiate blistering (an essential precursor to exfoliation) in (0001) sapphire implanted at room temperature with hydrogen ions. Triple axis x-ray diffraction was used to characterize the evolution of the implanted layer for single crystal (0001) sapphire substrates implanted at room temperature at 360 keV with either a 5x1016 cm -2 or 8x1016 cm-2 dose of hydrogen ions. A simulation of the ion distribution in TRIM estimated that the projected range and thickness of the implanted layer for both doses was approximately 2.2 mum. Following implantation, the implanted sapphire was annealed using a two-step annealing procedure. The first step was performed at a lower temperature, ideally to nucleate and coarsen defects. Temperatures investigated ranged from 550 - 650 °C. The second step was performed at a higher temperature (800 °C) to induce further defect coarsening and surface blistering. After all annealing steps, triple axis o/2theta and o scans were taken to observe any changes in the diffraction profile - namely, any reduction in the amplitude and shift in the location of the fringes associated with strain in the crystal - which would correlate with defect growth and nucleation. It was found that significant strain fringe reduction first occurred after annealing at 650 °C for 8 hours for both doses; however, it was not clear whether or not this strain reduction was due primarily to hydrogen diffusion or to recovery of other defects induced during the ion implantation. The o/2theta curves were then fit using Bede RADS in order to quantify the strain within the crystal and confirm the reduction of the strained layer within the crystal. Finally, Nomarski optical images of the sample surfaces were taken after each step to observe any visual changes or blistering that might have occurred. These optical images showed that the strain reduction observed using XRD did not correlate to blistering, as no blisters were observed in any of the optical images. Experimental results showed that at temperatures below 650 °C, no significant strain reduction occurs in hydrogen ion implanted (0001) sapphire. It has also been determined that for (0001) sapphire implanted at room temperature, it was not possible to produce surface blistering after a two-step annealing process at 650 °C and 800 °C, although significant strain reduction did occur, and ? scans showed peak broadening with subsequent annealing, indicating increasing mosaicity and potential defect nucleation. This was in contrast to previous findings that asserted that for sapphire annealed at 650 °C, surface blistering was observable. As previous findings were based on sapphire implanted at elevated temperatures, this may imply that the sapphire substrate reaches a higher temperature than expected during such implantation processes, which may account for the capability for surface blistering at a lower temperature. Conversely, for room temperature ion implantation, temperatures greater than 800 °C may be necessary to first nucleate hydrogen platelet defects and then produce surface blistering.

Ge quantum dot arrays grown by ultrahigh vacuum molecular-beam epitaxy on the Si(001) surface: nucleation, morphology, and CMOS compatibility.

PubMed

Yuryev, Vladimir A; Arapkina, Larisa V

2011-09-05

Issues of morphology, nucleation, and growth of Ge cluster arrays deposited by ultrahigh vacuum molecular beam epitaxy on the Si(001) surface are considered. Difference in nucleation of quantum dots during Ge deposition at low (≲600°C) and high (≳600°C) temperatures is studied by high resolution scanning tunneling microscopy. The atomic models of growth of both species of Ge huts--pyramids and wedges-- are proposed. The growth cycle of Ge QD arrays at low temperatures is explored. A problem of lowering of the array formation temperature is discussed with the focus on CMOS compatibility of the entire process; a special attention is paid upon approaches to reduction of treatment temperature during the Si(001) surface pre-growth cleaning, which is at once a key and the highest-temperature phase of the Ge/Si(001) quantum dot dense array formation process. The temperature of the Si clean surface preparation, the final high-temperature step of which is, as a rule, carried out directly in the MBE chamber just before the structure deposition, determines the compatibility of formation process of Ge-QD-array based devices with the CMOS manufacturing cycle. Silicon surface hydrogenation at the final stage of its wet chemical etching during the preliminary cleaning is proposed as a possible way of efficient reduction of the Si wafer pre-growth annealing temperature.

Use of a variable exposure photographic pyrometer to measure surface temperatures on a hemispherical-face model

NASA Technical Reports Server (NTRS)

Kantsios, A. G.; Henley, W. C., Jr.; Snow, W. L.

1982-01-01

The use of a photographic pyrometer for nonintrusive measurement of high temperature surfaces in a wind tunnel test is described. The advantages of the pyrometer for measuring surfaces whose unique shape makes use of thermocouples difficult are pointed out. The use of computer operated densitometers or optical processors for the data reduction is recommended.

Surface texturing of superconductors by controlled oxygen pressure

DOEpatents

Chen, N.; Goretta, K.C.; Dorris, S.E.

1999-01-05

A method of manufacture of a textured layer of a high temperature superconductor on a substrate is disclosed. The method involves providing an untextured high temperature superconductor material having a characteristic ambient pressure peritectic melting point, heating the superconductor to a temperature below the peritectic temperature, establishing a reduced pO{sub 2} atmosphere below ambient pressure causing reduction of the peritectic melting point to a reduced temperature which causes melting from an exposed surface of the superconductor and raising pressure of the reduced pO{sub 2} atmosphere to cause solidification of the molten superconductor in a textured surface layer. 8 figs.

Surface texturing of superconductors by controlled oxygen pressure

DOEpatents

Chen, Nan; Goretta, Kenneth C.; Dorris, Stephen E.

1999-01-01

A method of manufacture of a textured layer of a high temperature superconductor on a substrate. The method involves providing an untextured high temperature superconductor material having a characteristic ambient pressure peritectic melting point, heating the superconductor to a temperature below the peritectic temperature, establishing a reduced pO.sub.2 atmosphere below ambient pressure causing reduction of the peritectic melting point to a reduced temperature which causes melting from an exposed surface of the superconductor and raising pressure of the reduced pO.sub.2 atmosphere to cause solidification of the molten superconductor in a textured surface layer.

Temperature dependent surface modification of molybdenum due to low energy He+ ion irradiation

NASA Astrophysics Data System (ADS)

Tripathi, J. K.; Novakowski, T. J.; Joseph, G.; Linke, J.; Hassanein, A.

2015-09-01

In this paper, we report on the temperature dependent surface modifications in molybdenum (Mo) samples due to 100 eV He+ ion irradiation in extreme conditions as a potential candidate to plasma-facing components in fusion devices alternative to tungsten. The Mo samples were irradiated at normal incidence, using an ion fluence of 2.6 × 1024 ions m-2 (with a flux of 7.2 × 1020 ions m-2 s-1). Surface modifications have been studied using high-resolution field emission scanning electron-(SEM) and atomic force (AFM) microscopy. At 773 K target temperature homogeneous evolution of molybdenum nanograins on the entire Mo surface were observed. However, at 823 K target temperature appearance of nano-pores and pin-holes nearby the grain boundaries, and Mo fuzz in patches were observed. The fuzz density increases significantly with target temperatures and continued until 973 K. However, at target temperatures beyond 973 K, counterintuitively, a sequential reduction in the fuzz density has been seen till 1073 K temperatures. At 1173 K and above temperatures, only molybdenum nano structures were observed. Our temperature dependent studies confirm a clear temperature widow, 823-1073 K, for Mo fuzz formation. Ex-situ high resolution X-ray photoelectron spectroscopy studies on Mo fuzzy samples show the evidence of MoO3 3d doublets. This elucidates that almost all the Mo fuzz were oxidized during open air exposure and are thick enough as well. Likewise the microscopy studies, the optical reflectivity measurements also show a sequential reduction in the reflectivity values (i.e., enhancement in the fuzz density) up to 973 K and after then a sequential enhancement in the reflectivity values (i.e., reduction in the fuzz density) with target temperatures. This is in well agreement with microscopy studies where we observed clear temperature window for Mo fuzz growth.

Ge quantum dot arrays grown by ultrahigh vacuum molecular-beam epitaxy on the Si(001) surface: nucleation, morphology, and CMOS compatibility

PubMed Central

2011-01-01

Issues of morphology, nucleation, and growth of Ge cluster arrays deposited by ultrahigh vacuum molecular beam epitaxy on the Si(001) surface are considered. Difference in nucleation of quantum dots during Ge deposition at low (≲600°C) and high (≳600°C) temperatures is studied by high resolution scanning tunneling microscopy. The atomic models of growth of both species of Ge huts--pyramids and wedges-- are proposed. The growth cycle of Ge QD arrays at low temperatures is explored. A problem of lowering of the array formation temperature is discussed with the focus on CMOS compatibility of the entire process; a special attention is paid upon approaches to reduction of treatment temperature during the Si(001) surface pre-growth cleaning, which is at once a key and the highest-temperature phase of the Ge/Si(001) quantum dot dense array formation process. The temperature of the Si clean surface preparation, the final high-temperature step of which is, as a rule, carried out directly in the MBE chamber just before the structure deposition, determines the compatibility of formation process of Ge-QD-array based devices with the CMOS manufacturing cycle. Silicon surface hydrogenation at the final stage of its wet chemical etching during the preliminary cleaning is proposed as a possible way of efficient reduction of the Si wafer pre-growth annealing temperature. PMID:21892938

Determining the Effects of High Intensity Ultrasound on the Reduction of Microbes in Milk and Orange Juice Using Response Surface Methodology.

PubMed

Ganesan, Balasubramanian; Martini, Silvana; Solorio, Jonathan; Walsh, Marie K

2015-01-01

This study investigated the effects of high intensity ultrasound (temperature, amplitude, and time) on the inactivation of indigenous bacteria in pasteurized milk, Bacillus atrophaeus spores inoculated into sterile milk, and Saccharomyces cerevisiae inoculated into sterile orange juice using response surface methodology. The variables investigated were sonication temperature (range from 0 to 84°C), amplitude (range from 0 to 216 μm), and time (range from 0.17 to 5 min) on the response, log microbe reduction. Data were analyzed by statistical analysis system software and three models were developed, each for bacteria, spore, and yeast reduction. Regression analysis identified sonication temperature and amplitude to be significant variables on microbe reduction. Optimization of the inactivation of microbes was found to be at 84.8°C, 216 μm amplitude, and 5.8 min. In addition, the predicted log reductions of microbes at common processing conditions (72°C for 20 sec) using 216 μm amplitude were computed. The experimental responses for bacteria, spore, and yeast reductions fell within the predicted levels, confirming the accuracy of the models.

Determining the Effects of High Intensity Ultrasound on the Reduction of Microbes in Milk and Orange Juice Using Response Surface Methodology

PubMed Central

Martini, Silvana; Solorio, Jonathan; Walsh, Marie K.

2015-01-01

This study investigated the effects of high intensity ultrasound (temperature, amplitude, and time) on the inactivation of indigenous bacteria in pasteurized milk, Bacillus atrophaeus spores inoculated into sterile milk, and Saccharomyces cerevisiae inoculated into sterile orange juice using response surface methodology. The variables investigated were sonication temperature (range from 0 to 84°C), amplitude (range from 0 to 216 μm), and time (range from 0.17 to 5 min) on the response, log microbe reduction. Data were analyzed by statistical analysis system software and three models were developed, each for bacteria, spore, and yeast reduction. Regression analysis identified sonication temperature and amplitude to be significant variables on microbe reduction. Optimization of the inactivation of microbes was found to be at 84.8°C, 216 μm amplitude, and 5.8 min. In addition, the predicted log reductions of microbes at common processing conditions (72°C for 20 sec) using 216 μm amplitude were computed. The experimental responses for bacteria, spore, and yeast reductions fell within the predicted levels, confirming the accuracy of the models. PMID:26904659

Experimental and FDTD study of silicon surface morphology induced by femtosecond laser irradiation at a high substrate temperature.

PubMed

Deng, Guoliang; Feng, Guoying; Zhou, Shouhuan

2017-04-03

Substrate temperature is an important parameter for controlling the properties of femtosecond laser induced surface structures besides traditional ways. The morphology on silicon surface at different temperatures are studied experimentally. Compared to those formed at 300 K, smoother ripples, micro-grooves and nano/micro-holes are formed at 700 K. A two temperature model and FDTD method are used to discuss the temperature dependence of surface structures. The results show that the increased light absorption at elevated temperature leads to the reduction of surface roughness. The type-g feature in the FDTD-η map at 700 K, which corresponds to the energy deposition modulation parallel to the laser polarization with a periodicity bigger than the wavelength, is the origin of the formation of grooves. This work can benefit both surface structures based applications and the study of femtosecond laser-matter interactions.

Effect of surface modification on carbon nanotubes (CNTs) catalyzed nitrobenzene reduction by sulfide.

PubMed

Liu, Qi; Zhao, Han-Qing; Li, Lei; He, Pan-Pan; Wang, Yi-Xuan; Yang, Hou-Yun; Hu, Zhen-Hu; Mu, Yang

2018-06-04

Carbon nanotubes (CNTs) could be directly used as metal-free catalysts for the reduction of nitroaromatics by sulfide in water, but their catalytic ability need a further improvement. This study evaluated the feasibility of surface modification through thermal and radiation pretreatments to enhance catalytic activity of CNTs on nitrobenzene reduction by sulfide. The results show that thermal treatment could effectively improve the catalytic behaviors of CNTs for the reduction of nitrobenzene by sulfide, where the optimum annealing temperature was 400 °C. However, plasma radiation pretreatment didn't result in an obvious improvement of the CNTs catalytic activity. Moreover, the possible reasons have been explored and discussed in the study. Additionally, the impacts of various operational parameters on nitrobenzene reduction catalyzed by the CNTs after an optimized surface modification were also evaluated. It was found that the rate of nitrobenzene removal by sulfide was positively correlated with CNTs doses in a range of 0.3-300 mg L -1 ; the optimum pH was around 8.0; higher temperature and sulfide concentration facilitated the reaction; and the presence of humic acid exhibited a negative effect on nitrobenzene reduction. Copyright © 2018 Elsevier B.V. All rights reserved.

The Impact of Wet Soil and Canopy Temperatures on Daytime Boundary-Layer Growth.

NASA Astrophysics Data System (ADS)

Segal, M.; Garratt, J. R.; Kallos, G.; Pielke, R. A.

1989-12-01

The impact of very wet soil and canopy temperatures on the surface sensible heat flux, and on related daytime boundary-layer properties is evaluated. For very wet soils, two winter situations are considered, related to significant changes in soil surface temperature: (1) due to weather perturbations at a given location, and (2) due to the climatological north-south temperature gradient. Analyses and scaling of the various boundary-layer properties, and soil surface fluxes affecting the sensible beat flux, have been made; related evaluations show that changes in the sensible heat flux at a given location by a factor of 2 to 3 due to temperature changes related to weather perturbations is not uncommon. These changes result in significant alterations in the boundary-layer depth; in the atmospheric boundary-layer warming; and in the break-up time of the nocturnal surface temperature inversion. Investigation of the impact of the winter latitudinal temperature gradient on the above characteristics indicated that the relative increase in very wet soil sensible heat flux, due to the climatological reduction in the surface temperature in northern latitudes, moderates to some extent its reduction due to the corresponding decrease in solar radiation. Numerical model simulations confirmed these analytical evaluations.In addition, the impact of synoptic temperature perturbations during the transition seasons (fall and spring) on canopy sensible heal fluxes, and the related boundary-layer characteristics mentioned above, was evaluated. Analogous features to those found for very wet soil surfaces occurred also for the canopy situations. Likewise, evaluations were also carried out to explore the impact of high midlatitude foreste areas on the boundary-layer characteristics during the winter as compared to those during the summer. Similar impacts were found in both seasons, regardless of the substantial difference in the daily total solar radiation.

Effect of temperature on reduction of CaSO{sub 4} oxygen carrier in chemical-looping combustion of simulated coal gas in a fluidized bed reactor

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

Song, Q.L.; Xiao, R.; Deng, Z.Y.

2008-12-15

Chemical-looping combustion (CLC) is a promising combustion technology for gaseous and solid fuel with efficient use of energy and inherent separation of CO{sub 2}. The concept of a coal-fueled CLC system using, calcium sulfate (CaSO{sub 4}) as oxygen carrier is proposed in this study. Reduction tests of CaSO{sub 4} oxygen carrier with simulated coal gas were performed in a laboratory-scale fluidized bed reactor in the temperature range of 890-950{degree}C. A high concentration of CO{sub 2} was obtained at the initial reduction period. CaSO{sub 4} oxygen carrier exhibited high reactivity initially and decreased gradually at the late period of reduction. Themore » sulfur release during the reduction of CaSO{sub 4} as oxygen carrier was also observed and analyzed. H{sub 2} and CO{sub 2} conversions were greatly influenced by reduction temperature. The oxygen carrier conversion and mass-based reaction rates during the reduction at typical temperatures were compared. Higher temperatures would enhance reaction rates and result in high conversion of oxygen carrier. An XRD patterns study indicated that CaS was the dominant product of reduction and the variation of relative intensity with temperature is in agreement with the solid conversion. ESEM analysis indicated that the surface structure of oxygen carrier particles changed significantly from impervious to porous after reduction. EDS analysis also demonstrated the transfer of oxygen from the oxygen carrier to the fuel gas and a certain amount of sulfur loss and CaO formation on the surface at higher temperatures. The reduction kinetics of CaSO{sub 4} oxygen carrier was explored with the shrinking unreacted-core model. The apparent kinetic parameters were obtained, and the kinetic equation well predicted the experimental data. Finally, some basic considerations on the use of CaSO{sub 4} oxygen carrier in a CLC system for solid fuels were discussed.« less

In situ supported MnOx-CeOx on carbon nanotubes for the low-temperature selective catalytic reduction of NO with NH3

NASA Astrophysics Data System (ADS)

Zhang, Dengsong; Zhang, Lei; Shi, Liyi; Fang, Cheng; Li, Hongrui; Gao, Ruihua; Huang, Lei; Zhang, Jianping

2013-01-01

The MnOx and CeOx were in situ supported on carbon nanotubes (CNTs) by a poly(sodium 4-styrenesulfonate) assisted reflux route for the low-temperature selective catalytic reduction (SCR) of NO with NH3. X-Ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR) and NH3 temperature-programmed desorption (NH3-TPD) have been used to elucidate the structure and surface properties of the obtained catalysts. It was found that the in situ prepared catalyst exhibited the highest activity and the most extensive operating-temperature window, compared to the catalysts prepared by impregnation or mechanically mixed methods. The XRD and TEM results indicated that the manganese oxide and cerium oxide species had a good dispersion on the CNT surface. The XPS results demonstrated that the higher atomic concentration of Mn existed on the surface of CNTs and the more chemisorbed oxygen species exist. The H2-TPR results suggested that there was a strong interaction between the manganese oxide and cerium oxide on the surface of CNTs. The NH3-TPD results demonstrated that the catalysts presented a larger acid amount and stronger acid strength. In addition, the obtained catalysts exhibited much higher SO2-tolerance and improved the water-resistance as compared to that prepared by impregnation or mechanically mixed methods.The MnOx and CeOx were in situ supported on carbon nanotubes (CNTs) by a poly(sodium 4-styrenesulfonate) assisted reflux route for the low-temperature selective catalytic reduction (SCR) of NO with NH3. X-Ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR) and NH3 temperature-programmed desorption (NH3-TPD) have been used to elucidate the structure and surface properties of the obtained catalysts. It was found that the in situ prepared catalyst exhibited the highest activity and the most extensive operating-temperature window, compared to the catalysts prepared by impregnation or mechanically mixed methods. The XRD and TEM results indicated that the manganese oxide and cerium oxide species had a good dispersion on the CNT surface. The XPS results demonstrated that the higher atomic concentration of Mn existed on the surface of CNTs and the more chemisorbed oxygen species exist. The H2-TPR results suggested that there was a strong interaction between the manganese oxide and cerium oxide on the surface of CNTs. The NH3-TPD results demonstrated that the catalysts presented a larger acid amount and stronger acid strength. In addition, the obtained catalysts exhibited much higher SO2-tolerance and improved the water-resistance as compared to that prepared by impregnation or mechanically mixed methods. Electronic supplementary information (ESI) available: SEM images and EDS analysis, TEM images, and XPS spectrum of samples. See DOI: 10.1039/c2nr33006g

Natural printed silk substrate circuit fabricated via surface modification using one step thermal transfer and reduction graphene oxide

NASA Astrophysics Data System (ADS)

Cao, Jiliang; Huang, Zhan; Wang, Chaoxia

2018-05-01

Graphene conductive silk substrate is a preferred material because of its biocompatibility, flexibility and comfort. A flexible natural printed silk substrate circuit was fabricated by one step transfer of graphene oxide (GO) paste from transfer paper to the surface of silk fabric and reduction of the GO to reduced graphene oxide (RGO) using a simple hot press treatment. The GO paste was obtained through ultrasonic stirring exfoliation under low temperature, and presented excellent printing rheological properties at high concentration. The silk fabric was obtained a surface electric resistance as low as 12.15 KΩ cm-1, in the concentration of GO 50 g L-1 and hot press at 220 °C for 120 s. Though the whiteness and strength decreased with the increasing of hot press temperature and time slowly, the electric conductivity of RGO surface modification silk substrate improved obviously. The surface electric resistance of RGO/silk fabrics increased from 12.15 KΩ cm-1 to 18.05 KΩ cm-1, 28.54 KΩ cm-1 and 32.53 KΩ cm-1 after 10, 20 and 30 washing cycles, respectively. The results showed that the printed silk substrate circuit has excellent washability. This process requires no chemical reductant, and the reduction efficiency and reduction degree of GO is high. This time-effective and environmentally-friendly one step thermal transfer and reduction graphene oxide onto natural silk substrate method can be easily used to production of reduced graphene oxide (RGO) based flexible printed circuit.

Optimization of hot water treatment for removing microbial colonies on fresh blueberry surface.

PubMed

Kim, Tae Jo; Corbitt, Melody P; Silva, Juan L; Wang, Dja Shin; Jung, Yean-Sung; Spencer, Barbara

2011-08-01

Blueberries for the frozen market are washed but this process sometimes is not effective or further contaminates the berries. This study was designed to optimize conditions for hot water treatment (temperature, time, and antimicrobial concentration) to remove biofilm and decrease microbial load on blueberries. Scanning electron microscopy (SEM) image showed a well-developed microbial biofilm on blueberries dipped in room temperature water. The biofilm consisted of yeast and bacterial cells attached to the berry surface in the form of microcolonies, which produced exopolymer substances between or upon the cells. Berry exposure to 75 and 90 °C showed little to no microorganisms on the blueberry surface; however, the sensory quality (wax/bloom) of berries at those temperatures was unacceptable. Response surface plots showed that increasing temperature was a significant factor on reduction of aerobic plate counts (APCs) and yeast/mold counts (YMCs) while adding Boxyl® did not have significant effect on APC. Overlaid contour plots showed that treatments of 65 to 70 °C for 10 to 15 s showed maximum reductions of 1.5 and 2.0 log CFU/g on APCs and YMCs, respectively; with acceptable level of bloom/wax score on fresh blueberries. This study showed that SEM, response surface, and overlaid contour plots proved successful in arriving at optima to reduce microbial counts while maintaining bloom/wax on the surface of the blueberries. Since chemical sanitizing treatments such as chlorine showed ineffectiveness to reduce microorganisms loaded on berry surface (Beuchat and others 2001, Sapers 2001), hot water treatment on fresh blueberries could maximize microbial reduction with acceptable quality of fresh blueberries. © 2011 Institute of Food Technologists®

Probing the Active Surface Sites for CO Reduction on Oxide-Derived Copper Electrocatalysts

DOE PAGES

Verdaguer-Casadevall, Arnau; Li, Christina W.; Johansson, Tobias P.; ...

2015-07-30

CO electroreduction activity on oxide-derived Cu (OD-Cu) was found to correlate with metastable surface features that bind CO strongly. OD-Cu electrodes prepared by H 2 reduction of Cu 2O precursors reduce CO to acetate and ethanol with nearly 50% Faradaic efficiency at moderate overpotential. Temperature-programmed desorption of CO on OD-Cu revealed the presence of surface sites with strong CO binding that are distinct from the terraces and stepped sites found on polycrystalline Cu foil. After annealing at 350 °C, the surface-area corrected current density for CO reduction is 44-fold lower and the Faradaic efficiency is less than 5%. These changesmore » are accompanied by a reduction in the proportion of strong CO binding sites. Here, we propose that the active sites for CO reduction on OD-Cu surfaces are strong CO binding sites that are supported by grain boundaries. Uncovering these sites is a first step toward understanding the surface chemistry necessary for efficient CO electroreduction.« less

Effect of design factors on surface temperature and wear in disk brakes

NASA Technical Reports Server (NTRS)

Santini, J. J.; Kennedy, F. E.; Ling, F. F.

1976-01-01

The temperatures, friction, wear and contact conditions that occur in high energy disk brakes are studied. Surface and near surface temperatures were monitored at various locations in a caliper disk brake during drag type testing, with friction coefficient and wear rates also being determined. The recorded transient temperature distributions in the friction pads and infrared photographs of the rotor disk surface both showed that contact at the friction surface was not uniform, with contact areas constantly shifting due to nonuniform thermal expansion and wear. The effect of external cooling and of design modifications on friction, wear and temperatures was also investigated. It was found that significant decreases in surface temperature and in wear rate can be achieved without a reduction in friction either by slotting the contacting face of the brake pad or by modifying the design of the pad support to improve pad compliance. Both design changes result in more uniform contact conditions on the friction surface.

Determining Directional Emittance With An Infrared Imager

NASA Technical Reports Server (NTRS)

Daryabeigi, Kamran; Alderfer, David W.; Wright, Robert E., Jr.; Puram, Chith K.

1994-01-01

Directional emittances of flat specimen of smooth-surfaced, electrically nonconductive material at various temperatures computed from measurements taken by infrared radiometric imager operating in conjunction with simple ancillary equipment. Directional emittances useful in extracting detailed variations of surface temperatures from infrared images of curved, complexly shaped other specimens of same material. Advantages: simplification of measurement procedure and reduction of cost.

Surface charge sensing by altering the phase transition in VO2

NASA Astrophysics Data System (ADS)

Kumar, S.; Esfandyarpour, R.; Davis, R.; Nishi, Y.

2014-08-01

Detection of surface charges has various applications in medicine, electronics, biotechnology, etc. The source of surface charge induction may range from simple charge-polarized molecules like water to complicated proteins. It was recently discovered that surface charge accumulation can alter the temperature at which VO2 undergoes a Mott transition. Here, we deposited polar molecules onto the surface of two-terminal thin-film VO2 lateral devices and monitored the joule-heating-driven Mott transition, or conductance switching. We observed that the power required to induce the conductance switching reduced upon treatment with polar molecules and, using in-situ blackbody-emission direct measurement of local temperature, we show that this reduction in power was accompanied by reduction in the Mott transition temperature. Further evidence suggested that this effect has specificity to the nature of the species used to induce surface charges. Using x-ray absorption spectroscopy, we also show that there is no detectable change in oxidation state of vanadium or structural phase in the bulk of the 40 nm VO2 thin-film even as the phase transition temperature is reduced by up to 20 K by the polar molecules. The ability to alter the phase transition parameters by depositing polar molecules suggests a potential application in sensing surface charges of different origins and this set of results also highlights interesting aspects of the phase transition in VO2.

Effect of calcination temperature on the photocatalytic reduction and oxidation processes of hydrothermally synthesized titania nanotubes.

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

Viayan, B.; Dimitrijevic, N. M.; Rajh, T.

Titania nanotubes having diameters 8 to 12 nm and lengths of 50-300 nm were prepared using a hydrothermal method. Further, the titania nanotubes were calcined over the temperature range 200-800 C in order to enhance their photocatalytic properties by altering their morphology. The calcined titania nanotubes were characterized by using X-ray diffraction and surface area analysis and their morphological features were studied by scanning and transmission electron microscopy. Nanotubes calcined at 400 C showed the maximum extent of photocatalyitc reduction of carbon dioxide to methane, whereas samples calcined at 600 C produced maximum photocatalytic oxidation of acetaldehyde. Electron paramagnetic resonancemore » (EPR) spectroscopy was used to interrogate the effects of nanotube structure on the charge separation and trapping as a function of calcination temperature. EPR results indicated that undercoordinated titania sites are associated with maximum CO{sub 2} reduction occurring in nanotubes calcined at 400 C. Despite the collapse of the nantube structure to form nanorods and the concomitant loss of surface area, the enhanced charge separation associated with increased crystallinity promoted high rates of oxidation of acetaldehyde in titania materials calcined at 600 C. These results illustrate that calcination temperature allows us to tune the morphological and surface features of the titania nanostructures for particular photocatalytic reactions.« less

Estimation of Surface Heat Flux and Surface Temperature during Inverse Heat Conduction under Varying Spray Parameters and Sample Initial Temperature

PubMed Central

Aamir, Muhammad; Liao, Qiang; Zhu, Xun; Aqeel-ur-Rehman; Wang, Hong

2014-01-01

An experimental study was carried out to investigate the effects of inlet pressure, sample thickness, initial sample temperature, and temperature sensor location on the surface heat flux, surface temperature, and surface ultrafast cooling rate using stainless steel samples of diameter 27 mm and thickness (mm) 8.5, 13, 17.5, and 22, respectively. Inlet pressure was varied from 0.2 MPa to 1.8 MPa, while sample initial temperature varied from 600°C to 900°C. Beck's sequential function specification method was utilized to estimate surface heat flux and surface temperature. Inlet pressure has a positive effect on surface heat flux (SHF) within a critical value of pressure. Thickness of the sample affects the maximum achieved SHF negatively. Surface heat flux as high as 0.4024 MW/m2 was estimated for a thickness of 8.5 mm. Insulation effects of vapor film become apparent in the sample initial temperature range of 900°C causing reduction in surface heat flux and cooling rate of the sample. A sensor location near to quenched surface is found to be a better choice to visualize the effects of spray parameters on surface heat flux and surface temperature. Cooling rate showed a profound increase for an inlet pressure of 0.8 MPa. PMID:24977219

Satellite-derived, melt-season surface temperature of the Greenland Ice Sheet (2000-2005) and its relationship to mass balance

USGS Publications Warehouse

Hall, D.K.; Williams, R.S.; Casey, K.A.; DiGirolamo, N.E.; Wan, Z.

2006-01-01

Mean, clear-sky surface temperature of the Greenland Ice Sheet was measured for each melt season from 2000 to 2005 using Moderate-Resolution Imaging Spectroradiometer (MODIS)–derived land-surface temperature (LST) data-product maps. During the period of most-active melt, the mean, clear-sky surface temperature of the ice sheet was highest in 2002 (−8.29 ± 5.29°C) and 2005 (−8.29 ± 5.43°C), compared to a 6-year mean of −9.04 ± 5.59°C, in agreement with recent work by other investigators showing unusually extensive melt in 2002 and 2005. Surface-temperature variability shows a correspondence with the dry-snow facies of the ice sheet; a reduction in area of the dry-snow facies would indicate a more-negative mass balance. Surface-temperature variability generally increased during the study period and is most pronounced in the 2005 melt season; this is consistent with surface instability caused by air-temperature fluctuations.

Studies of oxidation and thermal reduction of the Cu(100) surface using a slow positron beam

NASA Astrophysics Data System (ADS)

Maddox, W. B.; Fazleev, N. G.; Nadesalingam, M. P.; Weiss, A. H.

2007-10-01

Positron probes of surfaces of oxides that play a fundamental role in modern science and technology are capable to non-destructively provide information that is both unique to the probe and complimentary to that extracted using other more standard techniques. We discuss recent progress in studies of oxidation and thermal reduction of the Cu(100) surface using positron-annihilation-induced Auger-electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 C. The intensity then decreases monotonically as the annealing temperature is increased to 600 C. Experimental PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and surface reconstruction. The effects of oxygen adsorption and defects on localization of the positron surface state wave function and positron annihilation characteristics are also analyzed. Possible explanations are provided for the observed behavior of the intensity of the positron annihilation induced Cu M2,3VV Auger peak with changes of the annealing temperature.

Modified Ni-Cu catalysts for ethanol steam reforming

NASA Astrophysics Data System (ADS)

Dan, M.; Mihet, M.; Almasan, V.; Borodi, G.; Katona, G.; Muresan, L.; Lazar, M. D.

2013-11-01

Three Ni-Cu catalysts, having different Cu content, supported on γ-alumina were synthesized by wet co-impregnation method, characterized and tested in the ethanol steam reforming (ESR) reaction. The catalysts were characterized for determination of: total surface area and porosity (N2 adsorption - desorption using BET and Dollimer Heal methods), Ni surface area (hydrogen chemisorption), crystallinity and Ni crystallites size (X-Ray Diffraction), type of catalytic active centers (Hydrogen Temperature Programmed Reduction). Total surface area and Ni crystallites size are not significantly influenced by the addition of Cu, while Ni surface area is drastically diminished by increasing of Cu concentration. Steam reforming experiments were performed at atmospheric pressure, temperature range 150-350°C, and ethanol - water molar ration of 1 at 30, using Ar as carrier gas. Ethanol conversion and hydrogen production increase by the addition of Cu. At 350°C there is a direct connection between hydrogen production and Cu concentration. Catalysts deactivation in 24h time on stream was studied by Transmission Electron Microscopy (TEM) and temperature-programmed reduction (TPR) on used catalysts. Coke deposition was observed at all studied temperatures; at 150°C amorphous carbon was evidenced, while at 350°C crystalline, filamentous carbon is formed.

Room temperature sterilization of surfaces and fabrics with a one atmosphere uniform glow discharge plasma.

PubMed

Kelly-Wintenberg, K; Montie, T C; Brickman, C; Roth, J R; Carr, A K; Sorge, K; Wadsworth, L C; Tsai, P P

1998-01-01

We report the results of an interdisciplinary collaboration formed to assess the sterilizing capabilities of the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP). This newly-invented source of glow discharge plasma (the fourth state of matter) is capable of operating at atmospheric pressure in air and other gases, and of providing antimicrobial active species to surfaces and workpieces at room temperature as judged by viable plate counts. OAUGDP exposures have reduced log numbers of bacteria, Staphylococcus aureus and Escherichia coli, and endospores from Bacillus stearothermophilus and Bacillus subtilis on seeded solid surfaces, fabrics, filter paper, and powdered culture media at room temperature. Initial experimental data showed a two-log10 CFU reduction of bacteria when 2 x 10(2) cells were seeded on filter paper. Results showed > or = 3 log10 CFU reduction when polypropylene samples seeded with E. coli (5 x 10(4)) were exposed, while a 30 s exposure time was required for similar killing with S. aureus-seeded polypropylene samples. The exposure times required to effect > or = 6 log10 CFU reduction of E. coli and S. aureus on polypropylene samples were no longer than 30 s. Experiments with seeded samples in sealed commercial sterilization bags showed little or no differences in exposure times compared to unwrapped samples. Plasma exposure times of less than 5 min generated > or = 5 log10 CFU reduction of commercially prepared Bacillus subtilis spores (1 x 10(5)); 7 min OAUGDP exposures were required to generate a > or = 3 log10 CFU reduction for Bacillus stearothermophilus spores. For all microorganisms tested, a biphasic curve was generated when the number of survivors vs time was plotted in dose-response cures. Several proposed mechanisms of killing at room temperature by the OAUGDP are discussed.

Ceria-based electrospun fibers for renewable fuel production via two-step thermal redox cycles for carbon dioxide splitting.

PubMed

Gibbons, William T; Venstrom, Luke J; De Smith, Robert M; Davidson, Jane H; Jackson, Gregory S

2014-07-21

Zirconium-doped ceria (Ce(1-x)Zr(x)O2) was synthesized through a controlled electrospinning process as a promising approach to cost-effective, sinter-resistant material structures for high-temperature, solar-driven thermochemical redox cycles. To approximate a two-step redox cycle for solar fuel production, fibrous Ce(1-x)Zr(x)O2 with relatively low levels of Zr-doping (0 < x < 0.1) were cycled in an infrared-imaging furnace with high-temperature (up to 1500 °C) partial reduction and lower-temperature (∼800 °C) reoxidation via CO2 splitting to produce CO. Increases in Zr content improve reducibility and sintering resistance, and, for x≤ 0.05, do not significantly slow reoxidation kinetics for CO production. Cycle stability of the fibrous Ce(1-x)Zr(x)O2 (with x = 0.025) was assessed for a range of conditions by measuring rates of O2 release during reduction and CO production during reoxidation and by assessing post-cycling fiber crystallite sizes and surface areas. Sintering increases with reduction temperature but occurs primarily along the fiber axes. Even after 108 redox cycles with reduction at 1400 °C and oxidation with CO2 at 800 °C, the fibers maintain their structure with surface areas of ∼0.3 m(2) g(-1), higher than those observed in the literature for other ceria-based structures operating at similarly high temperature conditions. Total CO production and peak production rate stabilize above 3.0 mL g(-1) and 13.0 mL min(-1) g(-1), respectively. The results show the potential for electrospun oxides as sinter-resistant material structures with adequate surface area to support rapid CO2 splitting in solar thermochemical redox cycles.

Delayed warming hiatus over the Tibetan Plateau

NASA Astrophysics Data System (ADS)

An, Wenling; Hou, Shugui; Hu, Yongyun; Wu, Shuangye

2017-03-01

A reduction in the warming rate for the global surface temperature since the late 1990s has attracted much attention and caused a great deal of controversy. During the same time period, however, most previous studies have reported enhanced warming over the Tibetan Plateau (TP). In this study we further examined the temperature trend of the TP and surrounding areas based on the homogenized temperature records for the period 1980-2014, we found that for the TP regions lower than 4000 m the warming rate has started to slow down since the late 1990s, a similar pattern consistent with the whole China and the global temperature trend. However, for the TP regions higher than 4000 m, this reduction in warming rate did not occur until the mid-2000s. This delayed warming hiatus could be related to changes in regional radiative, energy, and land surface processes in recent years.

Bi-induced band gap reduction in epitaxial InSbBi alloys

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

Rajpalke, M. K.; Linhart, W. M.; Yu, K. M.

2014-11-24

The properties of molecular beam epitaxy-grown InSb 1-x Bi x alloys are investigated. Rutherford backscattering spectrometry shows that the Bi content increases from 0.6% for growth at 350 °C to 2.4% at 200 °C. X-ray diffraction indicates Bi-induced lattice dilation and suggests a zinc-blende InBi lattice parameter of 6.626 Å. Scanning electron microscopy reveals surface InSbBi nanostructures on the InSbBi films for the lowest growth temperatures, Bi droplets at intermediate temperatures, and smooth surfaces for the highest temperature. The room temperature optical absorption edge was found to change from 172 meV (7.2 μm) for InSb to ~88 meV (14.1 μm)more » for InSb 0.976Bi 0.024, a reduction of ~35 meV/%Bi.« less

Advanced High Temperature Structural Seals

NASA Astrophysics Data System (ADS)

Newquist, Charles W.; Verzemnieks, Juris; Keller, Peter C.; Rorabaugh, Michael; Shorey, Mark

2002-10-01

This program addresses the development of high temperature structural seals for control surfaces for a new generation of small reusable launch vehicles. Successful development will contribute significantly to the mission goal of reducing launch cost for small, 200 to 300 pound payloads. Development of high temperature seals is mission enabling. For instance, ineffective control surface seals can result in high temperature (3100 F) flows in the elevon area exceeding structural material limits. Longer sealing life will allow use for many missions before replacement, contributing to the reduction of hardware, operation and launch costs.

Advanced High Temperature Structural Seals

NASA Technical Reports Server (NTRS)

Newquist, Charles W.; Verzemnieks, Juris; Keller, Peter C.; Rorabaugh, Michael; Shorey, Mark

2002-01-01

This program addresses the development of high temperature structural seals for control surfaces for a new generation of small reusable launch vehicles. Successful development will contribute significantly to the mission goal of reducing launch cost for small, 200 to 300 pound payloads. Development of high temperature seals is mission enabling. For instance, ineffective control surface seals can result in high temperature (3100 F) flows in the elevon area exceeding structural material limits. Longer sealing life will allow use for many missions before replacement, contributing to the reduction of hardware, operation and launch costs.

Transition of the Laminar Boundary Layer on a Delta Wing with 74 degree Sweep in Free Flight at Mach Numbers from 2.8 to 5.3

NASA Technical Reports Server (NTRS)

Chapman, Gary T.

1961-01-01

The tests were conducted at Mach numbers from 2.8 to 5.3, with model surface temperatures small compared to boundary-layer recovery temperature. The effects of Mach number, temperature ratio, unit Reynolds number, leading-edge diameter, and angle of attack were investigated in an exploratory fashion. The effect of heat-transfer condition (i.e., wall temperature to total temperature ratio) and Mach number can not be separated explicitly in free-flight tests. However, the data of the present report, as well as those of NACA TN 3473, were found to be more consistent when plotted versus temperature ratio. Decreasing temperature ratio increased the transition Reynolds number. The effect of unit Reynolds number was small as was the effect of leading-edge diameter within the range tested. At small values of angle of attack, transition moved forward on the windward surface and rearward on the leeward surface. This trend was reversed at high angles of attack (6 deg to 18 deg). Possible reasons for this are the reduction of crossflow on the windward side and the influence of the lifting vortices on the leeward surface. When the transition results on the 740 delta wing were compared to data at similar test conditions for an unswept leading edge, the results bore out the results of earlier research at nearly zero heat transfer; namely, sweep causes a large reduction in the transition Reynolds number.

Electronic properties and surface reactivity of SrO-terminated SrTiO3 and SrO-terminated iron-doped SrTiO3

PubMed Central

Staykov, Aleksandar; Tellez, Helena; Druce, John; Wu, Ji; Ishihara, Tatsumi; Kilner, John

2018-01-01

Abstract Surface reactivity and near-surface electronic properties of SrO-terminated SrTiO3 and iron doped SrTiO3 were studied with first principle methods. We have investigated the density of states (DOS) of bulk SrTiO3 and compared it to DOS of iron-doped SrTiO3 with different oxidation states of iron corresponding to varying oxygen vacancy content within the bulk material. The obtained bulk DOS was compared to near-surface DOS, i.e. surface states, for both SrO-terminated surface of SrTiO3 and iron-doped SrTiO3. Electron density plots and electron density distribution through the entire slab models were investigated in order to understand the origin of surface electrons that can participate in oxygen reduction reaction. Furthermore, we have compared oxygen reduction reactions at elevated temperatures for SrO surfaces with and without oxygen vacancies. Our calculations demonstrate that the conduction band, which is formed mainly by the d-states of Ti, and Fe-induced states within the band gap of SrTiO3, are accessible only on TiO2 terminated SrTiO3 surface while the SrO-terminated surface introduces a tunneling barrier for the electrons populating the conductance band. First principle molecular dynamics demonstrated that at elevated temperatures the surface oxygen vacancies are essential for the oxygen reduction reaction. PMID:29535797

Estimation of surface temperature in remote pollution measurement experiments

NASA Technical Reports Server (NTRS)

Gupta, S. K.; Tiwari, S. N.

1978-01-01

A simple algorithm has been developed for estimating the actual surface temperature by applying corrections to the effective brightness temperature measured by radiometers mounted on remote sensing platforms. Corrections to effective brightness temperature are computed using an accurate radiative transfer model for the 'basic atmosphere' and several modifications of this caused by deviations of the various atmospheric and surface parameters from their base model values. Model calculations are employed to establish simple analytical relations between the deviations of these parameters and the additional temperature corrections required to compensate for them. Effects of simultaneous variation of two parameters are also examined. Use of these analytical relations instead of detailed radiative transfer calculations for routine data analysis results in a severalfold reduction in computation costs.

Parasitic heat loss reduction in AMTEC cells by heat shield optimization

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

Borkowski, C.A.; Svedberg, R.C.; Hendricks, T.J.

1997-12-31

Alkali metal thermal to electric conversion (AMTEC) cell performance can be increased by the proper design of thermal radiative shielding internal to the AMTEC cell. These heat shields essentially lower the radiative heat transfer between the heat input zone of the cell and the heat rejection zone of the cell. In addition to lowering the radiative heat transfer between the heat input and heat rejection surfaces of the cell, the shields raise the AMTEC cell performance by increasing the temperature of the beta alumina solid electrolyte (BASE). This increase in temperature of the BASE tube allows the evaporator temperature tomore » be increased without sodium condensing within the BASE tubes. Experimental testing and theoretical analysis have been performed to compare the relative merits of two candidate heat shield packages: (1) chevron, and (2) cylindrical heat shields. These two heat shield packages were compared to each other and a baseline cell which had no heat shields installed. For the two heat shield packages, the reduction in total heat transfer is between 17--27% for the heat input surface temperature varying from 700 C, 750 C, and 800 C with the heat rejection surface temperature kept at 300 C.« less

The magnitude of tissue cooling during cryotherapy with varied types of compression.

PubMed

Tomchuk, David; Rubley, Mack D; Holcomb, William R; Guadagnoli, Mark; Tarno, Jason M

2010-01-01

Certified athletic trainers can choose different types of external compression (none, Flex-i-Wrap, and elastic wrap) when applying an ice bag to the body. However, which type facilitates the greatest magnitude of tissue cooling is unclear. To compare the effects of 2 common types of external compression on the magnitude of surface and intramuscular cooling during an ice-bag treatment. Randomized controlled trial. University research laboratory. Fourteen college students (10 women, 4 men; age = 22.4 +/- 1.8 years, height = 169.1 +/- 8.2 cm, mass = 73.3 +/- 18.5 kg, skinfold = 13.14 +/- 1.61 mm) with previous cryotherapy experience and a posterior lower leg skinfold equal to or less than 15 mm. On 3 different days separated by 24 to 48 hours, an ice bag was applied to the posterior lower leg surface of each participant for 30 minutes with no compression, with elastic wrap, or with Flex-i-Wrap. Posterior lower leg surface and intramuscular (2 cm) temperatures were recorded for 95 minutes. At 15 minutes, the elastic wrap produced greater surface temperature reduction than no compression (P = .03); this difference remained throughout the protocol (P range, .03 to .04). At 30 minutes, surface temperatures were 14.95 degrees C, 11.55 degrees C, and 9.49 degrees C when an ice bag was applied with no external compression, Flex-i-Wrap, and elastic wrap, respectively. Surface temperatures between Flex-i-Wrap and elastic wrap and between Flex-i-Wrap and no compression were never different. At 10 minutes, Flex-i-Wrap (P = .006) and elastic wrap (P < .001) produced greater intramuscular temperature reduction than no compression produced; these differences remained throughout the protocol. At 10 minutes, no compression, Flex-i-Wrap, and elastic wrap decreased intramuscular temperature by 1.34 degrees C, 2.46 degrees C, and 2.73 degrees C, respectively. At 25 minutes, elastic wrap (8.03 degrees C) produced greater temperature reduction than Flex-i-Wrap (6.65 degrees C) (P = .03) or no compression (4.63 degrees C) (P < .001 ). These differences remained throughout ice application and until 50 minutes after ice-bag removal. During an ice-bag application, external compression with elastic wrap was more effective than Flex-i-Wrap at reducing intramuscular tissue temperature. Elastic wraps should be used for acute injury care.

Lower-Conductivity Ceramic Materials for Thermal-Barrier Coatings

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Zhu, Dongming

2006-01-01

Doped pyrochlore oxides of a type described below are under consideration as alternative materials for high-temperature thermal-barrier coatings (TBCs). In comparison with partially-yttria-stabilized zirconia (YSZ), which is the state-of-the-art TBC material now in commercial use, these doped pyrochlore oxides exhibit lower thermal conductivities, which could be exploited to obtain the following advantages: For a given difference in temperature between an outer coating surface and the coating/substrate interface, the coating could be thinner. Reductions in coating thicknesses could translate to reductions in weight of hot-section components of turbine engines (e.g., combustor liners, blades, and vanes) to which TBCs are typically applied. For a given coating thickness, the difference in temperature between the outer coating surface and the coating/substrate interface could be greater. For turbine engines, this could translate to higher operating temperatures, with consequent increases in efficiency and reductions in polluting emissions. TBCs are needed because the temperatures in some turbine-engine hot sections exceed the maximum temperatures that the substrate materials (superalloys, Si-based ceramics, and others) can withstand. YSZ TBCs are applied to engine components as thin layers by plasma spraying or electron-beam physical vapor deposition. During operation at higher temperatures, YSZ layers undergo sintering, which increases their thermal conductivities and thereby renders them less effective as TBCs. Moreover, the sintered YSZ TBCs are less tolerant of stress and strain and, hence, are less durable.

Changes in the extremes of the climate simulated by CCC GCM2 under CO{sub 2} doubling

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

Zwiers, F.W.; Kharin, V.V.

Changes due to CO{sub 2} doubling in the extremes of the surface climate as simulated by the second-generation circulation model of the Canadian Centre for Climate Modelling and Analysis are studied in two 20-yr equilibrium simulations. Extreme values of screen temperature, precipitation, and near-surface wind in the control climate are compared to those estimated from 17 yr of the NCEP-NCAR reanalysis data and from some Canadian station data. The extremes of screen temperature are reasonably well reproduced in the control climate. Their changes under CO{sub 2} doubling can be connected with other physical changes such as surface albedo changes duemore » to the reduction of snow and sea ice cover as well as a decrease of soil moisture in the warmer world. The signal in the extremes of daily precipitation and near-surface wind speed due to CO{sub 2} doubling is less obvious. The precipitation extremes increase almost everywhere over the globe. The strongest change, over northwest India, is related to the intensification of the summer monsoon in this region in the warmer world. The modest reduction of wind extremes in the Tropics and middle latitudes is consistent with the reduction of the meridional temperature gradient in the 2{times}CO{sub 2} climate. The larger wind extremes occur in the areas where sea ice has retreated.« less

Effect of Pre-Irradiation Annealing and Laser Modification on the Formation of Radiation-Induced Surface Color Centers in Lithium Fluoride

NASA Astrophysics Data System (ADS)

Voitovich, A. P.; Kalinov, V. S.; Novikov, A. N.; Radkevich, A. V.; Runets, L. P.; Stupak, A. P.; Tarasenko, N. V.

2017-01-01

It is shown that surface color centers of the same type are formed in the surface layer and in regions with damaged crystal structure inside crystalline lithium fluoride after γ-irradiation. Results are presented from a study of the effect of pre-irradiation annealing on the efficiency with which surface centers are formed in lithium fluoride nanocrystals. Raising the temperature for pre-irradiation annealing from room temperature to 250°C leads to a substantial reduction in the efficiency with which these centers are created. Surface color centers are not detected after γ-irradiation for pre-irradiation annealing temperatures of 300°C and above. Adsorption of atmospheric gases on the crystal surface cannot be regarded as a necessary condition for the formation of radiation-induced surface centers.

Effect of foam on temperature prediction and heat recovery potential from biological wastewater treatment.

PubMed

Corbala-Robles, L; Volcke, E I P; Samijn, A; Ronsse, F; Pieters, J G

2016-05-15

Heat is an important resource in wastewater treatment plants (WWTPs) which can be recovered. A prerequisite to determine the theoretical heat recovery potential is an accurate heat balance model for temperature prediction. The insulating effect of foam present on the basin surface and its influence on temperature prediction were assessed in this study. Experiments were carried out to characterize the foam layer and its insulating properties. A refined dynamic temperature prediction model, taking into account the effect of foam, was set up. Simulation studies for a WWTP treating highly concentrated (manure) wastewater revealed that the foam layer had a significant effect on temperature prediction (3.8 ± 0.7 K over the year) and thus on the theoretical heat recovery potential (30% reduction when foam is not considered). Seasonal effects on the individual heat losses and heat gains were assessed. Additionally, the effects of the critical basin temperature above which heat is recovered, foam thickness, surface evaporation rate reduction and the non-absorbed solar radiation on the theoretical heat recovery potential were evaluated. Copyright © 2016 Elsevier Ltd. All rights reserved.

Wear reduction in ceramic bearings by surface generated pyrolytic carbon continuously replenished by ethylene gas

NASA Technical Reports Server (NTRS)

Lauer, J. L.; Davis, L. C.

1993-01-01

Sliding tests with a pin-on-disc tribometer and both sliding and rolling tests with a modified four-ball tester at bulk temperatures of about 500 C and contact pressures of about 2.2 GPa have demonstrated up to 80% reductions of friction and wear with silicon nitride surfaces when a stream of ethylene is directed into the conjunction region. The effects are even more pronounced when the ethylene is prenucleated by a flow over a coil of nichrome wire electrically heated to about 800 C and located about 30 cm upstream of the exit nozzle. Steel and Ni-plated steel are lubricated by this method even more efficiently at lower temperatures.

Advanced High Temperature Structural Seals

NASA Technical Reports Server (NTRS)

Newquist, Charles W.; Verzemnieks, Juris; Keller, Peter C.; Shorey, Mark W.; Steinetz, Bruce (Technical Monitor)

2000-01-01

This program addresses the development of high temperature structural seals for control surfaces for a new generation of small reusable launch vehicles. Successful development will contribute significantly to the mission goal of reducing launch cost for small, 200 to 300 lb payloads. Development of high temperature seals is mission enabling. For instance, ineffective control surface seals can result in high temperature (3100 F) flows in the elevon area exceeding structural material limits. Longer sealing life will allow use for many missions before replacement, contributing to the reduction of hardware, operation and launch costs. During the first phase of this program the existing launch vehicle control surface sealing concepts were reviewed, the aerothermal environment for a high temperature seal design was analyzed and a mock up of an arc-jet test fixture for evaluating seal concepts was fabricated.

Sustained drag reduction in a turbulent flow using a low-temperature Leidenfrost surface

PubMed Central

Saranadhi, Dhananjai; Chen, Dayong; Kleingartner, Justin A.; Srinivasan, Siddarth; Cohen, Robert E.; McKinley, Gareth H.

2016-01-01

Skin friction drag contributes a major portion of the total drag for small and large water vehicles at high Reynolds number (Re). One emerging approach to reducing drag is to use superhydrophobic surfaces to promote slip boundary conditions. However, the air layer or “plastron” trapped on submerged superhydrophobic surfaces often diminishes quickly under hydrostatic pressure and/or turbulent pressure fluctuations. We use active heating on a superhydrophobic surface to establish a stable vapor layer or “Leidenfrost” state at a relatively low superheat temperature. The continuous film of water vapor lubricates the interface, and the resulting slip boundary condition leads to skin friction drag reduction on the inner rotor of a custom Taylor-Couette apparatus. We find that skin friction can be reduced by 80 to 90% relative to an unheated superhydrophobic surface for Re in the range 26,100 ≤ Re ≤ 52,000. We derive a boundary layer and slip theory to describe the hydrodynamics in the system and show that the plastron thickness is h = 44 ± 11 μm, in agreement with expectations for a Leidenfrost surface. PMID:27757417

Thermal Instability of Fats Relative to Surface Wettability of Yellow Birchwood (Betula lutea)

Treesearch

Richard W. Hemingway

1969-01-01

The surface wettability and fats of yellow birchwood were examined in an attempt to illustrate how heat-induced changes in wood fats might be related to changes in surface wettability. A marked reduction of surface wettability accompanied heating of yellow birchwood. The degree of water repellency imparted to the wood was highly dependent upon heating temperature and...

The O2 reduction at the IFC modified O2 fuel cell electrode

NASA Technical Reports Server (NTRS)

Fielder, William L.; Singer, Joseph; Baldwin, Richard S.; Johnson, Richard E.

1992-01-01

The International Fuel Corporation (IFC) state of the art (SOA) O2 electrode (Au-10 percent Pt electrocatalyst by weight) is currently being used in the alkaline H2-O2 fuel cell in the NASA Space Shuttle. Recently, IFC modified O2 electrode, as a possible replacement for the SOA electrode. In the present study, O2 reduction data were obtained for the modified electrode at temperatures between 23.3 and 91.7 C. BET measurements gave an electrode BET surface area of about 2070 sq. cm/sq. cm of geometric surface area. The Tafel data could be fitted to two straight line regions. The slope for the lower region, designated as the 0.04 V/decade region, was temperature dependent, and the transfer coefficient was about 1.5. The 'apparent' energy of activation for this region was about 19 kcal/mol. An O2 reduction mechanism for this 0.04 region is presented. In the upper region, designated as the 0.08 V/decade region, diffusion may be the controlling process. Tafel data are presented to illustrate the increase in performance with increasing temperature.

Formation of nanocarbon spheres by thermal treatment of woody char from fast pyrolysis process

Treesearch

Qiangu Yan; Hossein Toghiani; Zhiyong Cai; Jilei Zhang

2014-01-01

Influences of thermal treatment conditions of temperature, reaction cycle and time, and purge gas type on nanocarbon formation over bio-chars from fast pyrolysis and effects of thermal reaction cycle and purge gas type on bio-char surface functional groups were investigated by temperature-programmed desorption (TPD) and temperature programmed reduction methods....

Tensile properties of candidate structural materials for high power spallation sources at high helium contents

NASA Astrophysics Data System (ADS)

Jung, P.; Henry, J.; Chen, J.

2005-08-01

Low activation 9%Cr martensitic steels EUROFER97, pure tantalum, and low carbon austenitic stainless steel 316L were homogeneously implanted with helium to concentrations up to 5000 appm at temperatures from 70 °C to 400 °C. The specimens were tensile tested at room temperature and at the respective implantation temperatures. In all materials the helium caused an increased in strength and reduction in ductility, with both changes being generally larger at lower implantation and testing temperatures. After implantation some work hardening was retained in 316L and in tantalum, while it almost completely disappeared in EUROFER97. After tensile testing, fracture surfaces were analysed by scanning electron microscopy (SEM). Implantation caused reduction of necking, but up to concentrations of 2500 appm He fracture surface still showed transgranular ductile appearance. Completely brittle intergranular fracture was observed in tantalum at 9000 appm He and is also expected for EUROFER97 at this concentration, according to previous results on similar 9%Cr steels.

Optimization of hetero-epitaxial growth for the threading dislocation density reduction of germanium epilayers

NASA Astrophysics Data System (ADS)

Chong, Haining; Wang, Zhewei; Chen, Chaonan; Xu, Zemin; Wu, Ke; Wu, Lan; Xu, Bo; Ye, Hui

2018-04-01

In order to suppress dislocation generation, we develop a "three-step growth" method to heteroepitaxy low dislocation density germanium (Ge) layers on silicon with the MBE process. The method is composed of 3 growth steps: low temperature (LT) seed layer, LT-HT intermediate layer as well as high temperature (HT) epilayer, successively. Threading dislocation density (TDD) of epitaxial Ge layers is measured as low as 1.4 × 106 cm-2 by optimizing the growth parameters. The results of Raman spectrum showed that the internal strain of heteroepitaxial Ge layers is tensile and homogeneous. During the growth of LT-HT intermediate layer, TDD reduction can be obtained by lowering the temperature ramping rate, and high rate deposition maintains smooth surface morphology in Ge epilayer. A mechanism based on thermodynamics is used to explain the TDD and surface morphological dependence on temperature ramping rate and deposition rate. Furthermore, we demonstrate that the Ge layer obtained can provide an excellent platform for III-V materials integrated on Si.

Evolution of catalytic activity of Au-Ag bimetallic nanoparticles on mesoporous support for CO oxidation.

PubMed

Wang, Ai-Qin; Chang, Chun-Ming; Mou, Chung-Yuan

2005-10-13

We report a novel Au-Ag alloy catalyst supported on mesoporous aluminosilicate Au-Ag@MCM prepared by a one-pot synthesis procedure, which is very active for low-temperature CO oxidation. The activity was highly dependent on the hydrogen pretreatment conditions. Reduction at 550-650 degrees C led to high activity at room temperature, whereas as-synthesized or calcined samples did not show any activity at the same temperature. Using various characterization techniques, such as XRD, UV-vis, XPS, and EXAFS, we elucidated the structure and surface composition change during calcination and the reduction process. The XRD patterns show that particle size increased only during the calcination process on those Ag-containing samples. XPS and EXAFS data demonstrate that calcination led to complete phase segregation of the Au-Ag alloy and the catalyst surface is greatly enriched with AgBr after the calcination process. However, subsequent reduction treatment removed Br- completely and the Au-Ag alloy was formed again. The surface composition of the reduced Au-Ag@MCM (nominal Au/Ag = 3/1) was more enriched with Ag, with the surface Au/Ag ratio being 0.75. ESR spectra show that superoxides are formed on the surface of the catalyst and its intensity change correlates well with the trend of catalytic activity. A DFT calculation shows that CO and O2 coadsorption on neighboring sites on the Au-Ag alloy was stronger than that on either Au or Ag. The strong synergism in the coadsorption of CO and O2 on the Au-Ag nanoparticle can thus explain the observed synergetic effect in catalysis.

Structural and electrochemical properties of nanostructured nickel silicides by reduction and silicification of high-surface-area nickel oxide

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

Chen, Xiao; Zhang, Bingsen; Li, Chuang

Graphical abstract: Nanostructured nickel silicides have been synthesized by reduction and silification of high-surface-area nickel oxide, and exhibited remarkably like-noble metal property, lower electric resistivity, and ferromagnetism at room temperature. Highlights: Black-Right-Pointing-Pointer NiSi{sub x} have been prepared by reduction and silification of high-surface-area NiO. Black-Right-Pointing-Pointer The structure of nickel silicides changed with increasing reaction temperature. Black-Right-Pointing-Pointer Si doping into nickel changed the magnetic properties of metallic nickel. Black-Right-Pointing-Pointer NiSi{sub x} have remarkably lower electric resistivity and like-noble metal property. -- Abstract: Nanostructured nickel silicides have been prepared by reduction and silicification of high-surface-area nickel oxide (145 m{sup 2} g{sup -1})more » produced via precipitation. The prepared materials were characterized by nitrogen adsorption, X-ray diffraction, thermal analysis, FT-IR spectroscopy, scanning electron microscopy, transmission electron microscopy, magnetic and electrochemical measurements. The nickel silicide formation involves the following sequence: NiO (cubic) {yields} Ni (cubic) {yields} Ni{sub 2}Si (orthorhombic) {yields} NiSi (orthorhombic) {yields} NiSi{sub 2} (cubic), with particles growing from 13.7 to 21.3 nm. The nickel silicides are ferromagnetic at room temperature, and their saturation magnetization values change drastically with the increase of Si content. Nickel silicides have remarkably low electrical resistivity and noble metal-like properties because of a constriction of the Ni d band and an increase of the electronic density of states. The results suggest that such silicides are promising candidates as inexpensive yet functional materials for applications in electrochemistry as well as catalysis.« less

Reduction of mixed Mn-Zr oxides: in situ XPS and XRD studies.

PubMed

Bulavchenko, O A; Vinokurov, Z S; Afonasenko, T N; Tsyrul'nikov, P G; Tsybulya, S V; Saraev, A A; Kaichev, V V

2015-09-21

A series of mixed Mn-Zr oxides with different molar ratios Mn/Zr (0.1-9) have been prepared by coprecipitation of manganese and zirconium nitrates and characterized by X-ray diffraction (XRD) and BET methods. It has been found that at concentrations of Mn below 30 at%, the samples are single-phase solid solutions (MnxZr1-xO2-δ) based on a ZrO2 structure. X-ray photoelectron spectroscopy (XPS) measurements showed that manganese in these solutions exists mainly in the Mn(4+) state on the surface. An increase in Mn content mostly leads to an increase in the number of Mn cations in the structure of solid solutions; however, a part of the manganese cations form Mn2O3 and Mn3O4 in the crystalline and amorphous states. The reduction of these oxides with hydrogen was studied by a temperature-programmed reduction technique, in situ XRD, and near ambient pressure XPS in the temperature range from 100 to 650 °C. It was shown that the reduction of the solid solutions MnxZr1-xO2-δ proceeds via two stages. During the first stage, at temperatures between 100 and 500 °C, the Mn cations incorporated into the solid solutions MnxZr1-xO2-δ undergo partial reduction. During the second stage, at temperatures between 500 and 700 °C, Mn cations segregate on the surface of the solid solution. In the samples with more than 30 at% Mn, the reduction of manganese oxides was observed: Mn2O3 → Mn3O4 → MnO.

Surface-Induced Near-Field Scaling in the Knudsen Layer of a Rarefied Gas

NASA Astrophysics Data System (ADS)

Gazizulin, R. R.; Maillet, O.; Zhou, X.; Cid, A. Maldonado; Bourgeois, O.; Collin, E.

2018-01-01

We report on experiments performed within the Knudsen boundary layer of a low-pressure gas. The noninvasive probe we use is a suspended nanoelectromechanical string, which interacts with He 4 gas at cryogenic temperatures. When the pressure P is decreased, a reduction of the damping force below molecular friction ∝P had been first reported in Phys. Rev. Lett. 113, 136101 (2014), 10.1103/PhysRevLett.113.136101 and never reproduced since. We demonstrate that this effect is independent of geometry, but dependent on temperature. Within the framework of kinetic theory, this reduction is interpreted as a rarefaction phenomenon, carried through the boundary layer by a deviation from the usual Maxwell-Boltzmann equilibrium distribution induced by surface scattering. Adsorbed atoms are shown to play a key role in the process, which explains why room temperature data fail to reproduce it.

Inactivation and UV Disinfection of Murine Norovirus with TiO2 under Various Environmental Conditions▿

PubMed Central

Lee, JungEun; Zoh, KyungDuk; Ko, GwangPyo

2008-01-01

We studied inactivation and UV disinfection of murine norovirus (MNV) as a surrogate for human norovirus. We investigated the effects of different surface characteristics, temperatures, and NaCl concentrations on MNV survival using both a plaque assay and a real-time TaqMan reverse transcription (RT)-PCR assay. MNV survived more than 40 days on diaper material, on gauze, and in a stool suspension. Compared to inactivation at lower temperatures (−20 and 4°C), inactivation of MNV was greater at higher temperatures (18 and 30°C). On the surface of both gauze and diaper material, there was a <2-log10 reduction in the amount of infectious MNV in 40 days after incubation at both −20 and 4°C, compared to a >5-log10 reduction after incubation at 30°C in 24 days. MNV survived better in a stool suspension than on the surface of gauze or diaper material. A higher salt concentration increased the rate of inactivation of MNV. In 72 h, <0.3-, 1.5-, and 2.5-log10 reductions in the amount of infectious MNV occurred in distilled water and 0.5 and 1 M NaCl, respectively. We observed only minor reductions in the numbers of viral RNA copies as quantified by real-time TaqMan RT-PCR regardless of the temperature, the salt concentration, or the suspending medium. We also evaluated UV disinfection of infectious MNV with and without TiO2. The amount of MNV was significantly reduced by 254-nm UV with and without TiO2. When 25 mJ/cm2 UV was used, 3.3- and 3.6-log10 reductions in the amounts of infectious MNV occurred with and without TiO2, respectively. Our results demonstrate that MNV can persist in various environmental conditions and can be efficiently controlled by UV disinfection. PMID:18245239

Reduction of precursors of chlorination by-products in drinking water using fluidized-bed biofilm reactor at low temperature.

PubMed

Xie, Shu-Guang; Wen, Dong-Hui; Shi, Dong-Wen; Tang, Xiao-Yan

2006-10-01

To investigate the reduction of chlorination by-products (CBPs) precursors using the fluidized-bed biofilm reactor (FBBR). Reduction of total organic carbon (TOC), ultraviolet absorbance (UV254), trihalomethane (THM) formation potential (THMFP), haloacetic acid (HAA) formation potential (HAAFP), and ammonia in FBBR were evaluated in detail. Results The reduction of TOC or UV254 was low, on average 12.6% and 4.7%, respectively, while the reduction of THMFP and HAAFP was significant. The reduction of ammonia was 30%-40% even below 3 degrees C, however, it could quickly rise to over 50% above 3degrees C. Conclusions The FBBR effectively reduces CBPs and ammonia in drinking water even at low temperature and seems to be a very promising and competitive drinking water reactor for polluted surface source waters, especially in China.

Effect of nano-scale morphology on micro-channel wall surface and electrical characterization in lead silicate glass micro-channel plate

NASA Astrophysics Data System (ADS)

Cai, Hua; Li, Fangjun; Xu, Yanglei; Bo, Tiezhu; Zhou, Dongzhan; Lian, Jiao; Li, Qing; Cao, Zhenbo; Xu, Tao; Wang, Caili; Liu, Hui; Li, Guoen; Jia, Jinsheng

2017-10-01

Micro-channel plate (MCP) is a two dimensional arrays of microscopic channel charge particle multiplier. Silicate composition and hydrogen reduction are keys to determine surface morphology of micro-channel wall in MCP. In this paper, lead silicate glass micro-channel plates in two different cesium contents (0at%, 0.5at%) and two different hydrogen reduction temperatures (400°C,450°C) were present. The nano-scale morphology, elements content and chemical states of microporous wall surface treated under different alkaline compositions and reduction conditions was investigated by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS), respectively. Meanwhile, the electrical characterizations of MCP, including the bulk resistance, electron gain and the density of dark current, were measured in a Vacuum Photoelectron Imaging Test Facility (VPIT).The results indicated that the granular phase occurred on the surface of microporous wall and diffuses in bulk glass is an aggregate of Pb atom derived from the reduction of Pb2+. In micro-channel plate, the electron gain and bulk resistance were mainly correlated to particle size and distribution, the density of dark current (DDC) went up with the increasing root-mean-square roughness (RMS) on the microporous wall surface. Adding cesiums improved the size of Pb atomic aggregation, lowered the relative concentration of [Pb] reduced from Pb2+ and decreased the total roughness of micro-channel wall surface, leading a higher bulk resistance, a lower electron gain and a less dark current. Increasing hydrogen reduction temperature also improved the size of Pb atomic aggregation, but enhanced the relative concentration of [Pb] and enlarged the total roughness of micro-channel wall surface, leading a higher bulk resistance, a lower electron gain and a larger dark current. The reasons for the difference of electrical characteristics were discussed.

Wind reduction by aerosol particles

NASA Astrophysics Data System (ADS)

Jacobson, Mark Z.; Kaufman, Yoram J.

2006-12-01

Aerosol particles are known to affect radiation, temperatures, stability, clouds, and precipitation, but their effects on spatially-distributed wind speed have not been examined to date. Here, it is found that aerosol particles, directly and through their enhancement of clouds, may reduce near-surface wind speeds below them by up to 8% locally. This reduction may explain a portion of observed ``disappearing winds'' in China, and it decreases the energy available for wind-turbine electricity. In California, slower winds reduce emissions of wind-driven soil dust and sea spray. Slower winds and cooler surface temperatures also reduce moisture advection and evaporation. These factors, along with the second indirect aerosol effect, may reduce California precipitation by 2-5%, contributing to a strain on water supply.

Effect of pretreatment on a platinized tin oxide catalyst used for low-temperature CO-oxidation

NASA Technical Reports Server (NTRS)

Drawdy, Jean E.; Hoflund, Gar B.; Gardner, Steven D.; Yngvadottir, Eva; Schryer, David R.

1990-01-01

A commercial platinized tin oxide catalyst used for low-temperature CO oxidation has been characterized using ion scattering spectroscopy (ISS), Auger electron spectroscopy (AES) and Electron Spectroscopy for Chemical Analysis (ESCA) before and after reduction in 40 Torr of CO for 1 hour at various temperatures from 75 to 175 C. The reduction results in loss of surface oxygen, formation of metallic tin, conversion of platinum oxides to Pt-O-Sn and Pt(OH)2 and a small amount of metallic Pt which alloys with the tin. These results should be useful in understanding how the pretreatment temperature affects the catalytic activity of platinized tin oxide toward CO oxidation.

XPS, AES and friction studies of single-crystal silicon carbide

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1982-01-01

The surface chemistry and friction behavior of a single crystal silicon carbide surface parallel to the 0001 plane in sliding contact with iron at various temperatures to 1500 C in a vacuum of 3 x 10 nPa are investigated using X-ray photoelectron and Auger electron spectroscopy. Results show that graphite and carbide-type carbon are seen primarily on the silicon carbide surface in addition to silicon at temperatures to 800 C by both types of spectroscopy. The coefficients of friction for iron sliding against a silicon carbide surface parallel to the 0001 plane surface are found to be high at temperatures up to 800 C, with the silicon and carbide-type carbon at maximum intensity in the X-ray photoelectron spectroscopy at 800 C. The concentration of the graphite increases rapidly on the surface as the temperature is increased above 800 C, while the concentrations of the carbide-type carbon and silicon decrease rapidly and this presence of graphite is accompanied by a significant decrease in friction. Preheating the surfaces to 1500 C also gives dramatically lower coefficients of friction when reheating in the sliding temperature range of from room temperature to 1200 C, with this reduction in friction due to the graphite layer on the silicon carbide surface.

Enhanced mechanical, thermal, and electric properties of graphene aerogels via supercritical ethanol drying and high-temperature thermal reduction.

PubMed

Cheng, Yehong; Zhou, Shanbao; Hu, Ping; Zhao, Guangdong; Li, Yongxia; Zhang, Xinghong; Han, Wenbo

2017-05-03

Graphene aerogels with high surface areas, ultra-low densities and thermal conductivities have been prepared to exploit their wide applications from pollution adsorption to energy storage, supercapacitor, and thermal insulation. However, the low mechanical properties, poor thermal stability and electric conductivity restrict these aerogels' applications. In this paper, we prepared mechanically strong graphene aerogels with large BET surface areas, low thermal conductivities, high thermal stability and electric conductivities via hydrothermal reduction and supercritical ethanol drying. Annealing at 1500 °C resulted in slightly increased thermal conductivity and further improvement in mechanical properties, oxidation temperature and electric conductivity of the graphene aerogel. The large BET surface areas, together with strong mechanical properties, low thermal conductivities, high thermal stability and electrical conductivities made these graphene aerogels feasible candidates for use in a number of fields covering from batteries to sensors, electrodes, lightweight conductor and insulation materials.

Effect of the Mn oxidation state and lattice oxygen in Mn-based TiO2 catalysts on the low-temperature selective catalytic reduction of NO by NH3.

PubMed

Lee, Sang Moon; Park, Kwang Hee; Kim, Sung Su; Kwon, Dong Wook; Hong, Sung Chang

2012-09-01

TiO2-supported manganese oxide catalysts formed using different calcination temperatures were prepared by using the wet-impregnation method and were investigated for their activity in the low-temperature selective catalytic reduction (SCR) of NO by NH3 with respect to the Mn valence and lattice oxygen behavior. The surface and bulk properties of these catalysts were examined using Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and temperature-programmed desorption (TPD). Catalysts prepared using lower calcination temperatures, which contained Mn4+ displayed high SCR activity at low temperatures and possessed several acid sites and active oxygen. The TPD analysis determined that the Brönsted and Lewis acid sites in the Mn/TiO2 catalysts were important for the low-temperature SCR at 80-160 and 200-350 degrees C, respectively. In addition, the available lattice oxygen was important for attaining high NO to NO2 oxidation at low temperatures. Recently, various Mn catalysts have been evaluated as SCR catalysts. However, there have been no studies on the relationship of adsorption and desorption properties and behavior of lattice oxygen according to the valence state for manganese oxides (MnO(x)). Therefore, in this study, the catalysts were prepared by the wet-impregnation method at different calcination temperatures in order to show the difference of manganese oxidation state. These catalysts were then characterized using various physicochemical techniques, including BET, XRD, TPR, and TPD, to understand the structure, oxidation state, redox properties, and adsorption and desorption properties of the Mn/TiO2 catalysts.

Enhanced Hydrogen Transport over Palladium Ultrathin Films through Surface Nanostructure Engineering.

PubMed

Abate, Salvatore; Giorgianni, Gianfranco; Gentiluomo, Serena; Centi, Gabriele; Perathoner, Siglinda

2015-11-01

Palladium ultrathin films (around 2 μm) with different surface nanostructures are characterized by TEM, SEM, AFM, and temperature programmed reduction (TPR), and evaluated in terms of H2 permeability and H2-N2 separation. A change in the characteristics of Pd seeds by controlled oxidation-reduction treatments produces films with the same thickness, but different surface and bulk nanostructure. In particular, the films have finer and more homogeneous Pd grains, which results in lower surface roughness. Although all samples show high permeo-selectivity to H2 , the samples with finer grains exhibit enhanced permeance and lower activation energy for H2 transport. The analysis of the data suggests that grain boundaries between the Pd grains at the surface favor H2 transfer from surface to subsurface. Thus, the surface nanostructure plays a relevant role in enhancing the transport of H2 over the Pd ultrathin film, which is an important aspect to develop improved membranes that function at low temperatures and toward new integrated process architectures in H2 and syngas production with enhanced sustainability. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Studies Of Oxidation And Thermal Reduction Of The Cu(100) Surface Using Positron Annihilation Induced Auger Electron Spectroscopy

NASA Astrophysics Data System (ADS)

Fazleev, N. G.; Nadesalingam, M. P.; Maddox, W.; Weiss, A. H.

2011-06-01

Positron annihilation induced Auger electron spectroscopy (PAES) measurements from the surface of an oxidized Cu(100) single crystal show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 °C. The PAES intensity then decreases monotonically as the annealing temperature is increased to ˜550 °C. Experimental positron annihilation probabilities with Cu 3p and O 1s core electrons are estimated from the measured intensities of the positron annihilation induced Cu M2,3VV and O KLL Auger transitions. PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of the surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and various surface structures associated with low and high oxygen coverages. The variations in atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface are found to affect localization and spatial extent of the positron surface state wave function. The computed positron binding energy and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface. Theoretical positron annihilation probabilities with Cu 3p and O 1s core electrons computed for the oxidized Cu(100) surface are compared with experimental ones. The obtained results provide a demonstration of thermal reduction of the copper oxide surface after annealing at 300 °C followed by re-oxidation of the Cu(100) surface at higher annealing temperatures presumably due to diffusion of subsurface oxygen to the surface.

Studies Of Oxidation And Thermal Reduction Of The Cu(100) Surface Using Positron Annihilation Induced Auger Electron Spectroscopy

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

Fazleev, N. G.; Department of Physics, Kazan State University, Kazan 420008; Nadesalingam, M. P.

2011-06-01

Positron annihilation induced Auger electron spectroscopy (PAES) measurements from the surface of an oxidized Cu(100) single crystal show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 deg. C. The PAES intensity then decreases monotonically as the annealing temperature is increased to {approx}550 deg. C. Experimental positron annihilation probabilities with Cu 3p and O 1s core electrons are estimated from the measured intensities of the positron annihilation induced Cu M{sub 2,3}VV and O KLL Auger transitions. PAESmore » results are analyzed by performing calculations of positron surface states and annihilation probabilities of the surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and various surface structures associated with low and high oxygen coverages. The variations in atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface are found to affect localization and spatial extent of the positron surface state wave function. The computed positron binding energy and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface. Theoretical positron annihilation probabilities with Cu 3p and O 1s core electrons computed for the oxidized Cu(100) surface are compared with experimental ones. The obtained results provide a demonstration of thermal reduction of the copper oxide surface after annealing at 300 deg. C followed by re-oxidation of the Cu(100) surface at higher annealing temperatures presumably due to diffusion of subsurface oxygen to the surface.« less

Corneal surface temperature change as the mode of stimulation of the non-contact corneal aesthesiometer.

PubMed

Murphy, P J; Morgan, P B; Patel, S; Marshall, J

1999-05-01

The non-contact corneal aesthesiometer (NCCA) assesses corneal sensitivity by using a controlled pulse of air, directed at the corneal surface. The purpose of this paper was to investigate whether corneal surface temperature change was a component in the mode of stimulation. Thermocouple experiment: A simple model corneal surface was developed that was composed of a moistened circle of filter paper placed on a thermocouple and mounted on a glass slide. The temperature change produced by different stimulus pressures was measured for five different ambient temperatures. Thermal camera experiment: Using a thermal camera, the corneal surface temperature change was measured in nine young, healthy subjects after exposure to different stimulus air pulses. Pulse duration was set at 0.9 s but was varied in pressure from 0.5 to 3.5 millibars. Thermocouple experiment: An immediate drop in temperature was detected by the thermocouple as soon as the air flow was incident on the filter paper. A greater temperature change was produced by increasing the pressure of the incident air flow. A relationship was found and a calibration curve plotted. Thermal camera experiment: For each subject, a drop in surface temperature was detected at each stimulus pressure. Furthermore, as the stimulus pressure increased, the induced reduction in temperature also increased. A relationship was found and a calibration curve plotted. The NCCA air-pulse stimulus was capable of producing a localized temperature change on the corneal surface. The principal mode of corneal nerve stimulation, by the NCCA air pulse, was the rate of temperature change of the corneal surface.

Reduction effect of surface temperature of baked bricks with different pore shapes during absorption-evaporation test

NASA Astrophysics Data System (ADS)

Oguchi, Chiaki T.; Shinozuka, Katsumi

2017-04-01

To study the effect of decreasing in surface temperature of baked bricks with various pore shapes, the present study performed several experiments such as water absorbance test and heating test. For the preparation of experimental specimens, bricks with artificial spherical pores, artificial linear pores and non-additional artificial pores were made. The bricks were examined their properties of bulk density, Equotip hardness and absorbing properties by putting in the water. Wet bricks were also put in the incubator set at 50 °C, and monitored the increasing of surface temperature of each brick. Brick with linear pores shows higher water absorption rate in a short time than those with spherical pores. They evaporated moisture faster than those with a spherical pores. They kept the temperature by 11.7 °C lower than the setting temperature, whereas the bricks with a spherical pores kept the temperature by 10.5 °C . Bricks with linear pores has about 10% higher effectiveness of decreasing in surface temperature than those with spheroidal pores.

Mechanisms of metal sorption by biochars: Biochar characteristics and modifications.

PubMed

Li, Hongbo; Dong, Xiaoling; da Silva, Evandro B; de Oliveira, Letuzia M; Chen, Yanshan; Ma, Lena Q

2017-07-01

Biochar produced by thermal decomposition of biomass under oxygen-limited conditions has received increasing attention as a cost-effective sorbent to treat metal-contaminated waters. However, there is a lack of information on the roles of different sorption mechanisms for different metals and recent development of biochar modification to enhance metal sorption capacity, which is critical for biochar field application. This review summarizes the characteristics of biochar (e.g., surface area, porosity, pH, surface charge, functional groups, and mineral components) and main mechanisms governing sorption of As, Cr, Cd, Pb, and Hg by biochar. Biochar properties vary considerably with feedstock material and pyrolysis temperature, with high temperature producing biochars with higher surface area, porosity, pH, and mineral contents, but less functional groups. Different mechanisms dominate sorption of As (complexation and electrostatic interactions), Cr (electrostatic interactions, reduction, and complexation), Cd and Pb (complexation, cation exchange, and precipitation), and Hg (complexation and reduction). Besides sorption mechanisms, recent advance in modifying biochar by loading with minerals, reductants, organic functional groups, and nanoparticles, and activation with alkali solution to enhance metal sorption capacity is discussed. Future research needs for field application of biochar include competitive sorption mechanisms of co-existing metals, biochar reuse, and cost reduction of biochar production. Published by Elsevier Ltd.

Modeling of the oxygen reduction reaction for dense LSM thin films

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

Yang, Tao; Liu, Jian; Yu, Yang

In this study, the oxygen reduction reaction mechanism is investigated using numerical methods on a dense thin (La 1-xSr x) yMnO 3±δ film deposited on a YSZ substrate. This 1-D continuum model consists of defect chemistry and elementary oxygen reduction reaction steps coupled via reaction rates. The defect chemistry model contains eight species including cation vacancies on the A- and B-sites. The oxygen vacancy is calculated by solving species transportation equations in multiphysics simulations. Due to the simple geometry of a dense thin film, the oxygen reduction reaction was reduced to three elementary steps: surface adsorption and dissociation, incorporation onmore » the surface, and charge transfer across the LSM/YSZ interface. The numerical simulations allow for calculation of the temperature- and oxygen partial pressure-dependent properties of LSM. The parameters of the model are calibrated with experimental impedance data for various oxygen partial pressures at different temperatures. The results indicate that surface adsorption and dissociation is the rate-determining step in the ORR of LSM thin films. With the fine-tuned parameters, further quantitative analysis is performed. The activation energy of the oxygen exchange reaction and the dependence of oxygen non-stoichiometry on oxygen partial pressure are also calculated and verified using the literature results.« less

Modeling of the oxygen reduction reaction for dense LSM thin films

DOE PAGES

Yang, Tao; Liu, Jian; Yu, Yang; ...

2017-10-17

In this study, the oxygen reduction reaction mechanism is investigated using numerical methods on a dense thin (La 1-xSr x) yMnO 3±δ film deposited on a YSZ substrate. This 1-D continuum model consists of defect chemistry and elementary oxygen reduction reaction steps coupled via reaction rates. The defect chemistry model contains eight species including cation vacancies on the A- and B-sites. The oxygen vacancy is calculated by solving species transportation equations in multiphysics simulations. Due to the simple geometry of a dense thin film, the oxygen reduction reaction was reduced to three elementary steps: surface adsorption and dissociation, incorporation onmore » the surface, and charge transfer across the LSM/YSZ interface. The numerical simulations allow for calculation of the temperature- and oxygen partial pressure-dependent properties of LSM. The parameters of the model are calibrated with experimental impedance data for various oxygen partial pressures at different temperatures. The results indicate that surface adsorption and dissociation is the rate-determining step in the ORR of LSM thin films. With the fine-tuned parameters, further quantitative analysis is performed. The activation energy of the oxygen exchange reaction and the dependence of oxygen non-stoichiometry on oxygen partial pressure are also calculated and verified using the literature results.« less

Composite Structure Repair. Addendum

DTIC Science & Technology

1984-08-01

room temperature curing systems . For permanent repairs no reduction in " serciveability with regard to the maximum design temperature and the design...pressure for ply compaction and conformation of bonding surfaces. In certain instances, ambient temperature cure systems may be sufficient. - Noisture...than those placed on radomes. Some of ,the resins used for the repairs were ambient curing systems which also required no additional pressure for

Aerial thermography studies of power plant heated lakes

NASA Astrophysics Data System (ADS)

Villa-Aleman, Eliel; Garrett, Alfred J.; Kurzeja, Robert J.; Pendergast, Malcolm M.

2000-03-01

Remote sensing temperature measurements of water bodies is complicated by the temperature differences between the true surface or `skin' water and the bulk water below. Weather conditions control the reduction of the skin temperature relative to the bulk water temperature. Typical skin temperature depressions range from a few tenths of a degree Celsius to more than one degree. In this research project, the Savannah River Technology Center used aerial thermography and surface-based meteorological and water temperature measurements to study a power plant cooling lake in South Carolina. Skin and bulk water temperatures were measured simultaneously for imagery calibration and to product a database for modeling of skin temperature depressions as a function of weather and bulk water temperatures. This paper will present imagery that illustrates how the skin temperature depression was affected by different conditions in several locations on the lake and will present skin temperature modeling results.

Platinized tin oxide catalysts for CO2 lasers: Effects of pretreatment

NASA Technical Reports Server (NTRS)

Gardner, Steven D.; Hoflund, Gar B.; Schryer, David R.; Upchurch, Billy T.

1990-01-01

Platinized tin oxide surfaces used for low-temperature CO oxidation in CO2 lasers have been characterized before and after reduction in CO at 125 and 250 C using ion scattering spectroscopy (ISS) and X ray photoelectron spectroscopy (XPS). XPS indicates that the Pt is present initially as PtO2. Reduction at 125 C converts the PtO2 to Pt(OH)2 while reduction at 250 C converts the PtO2 to metallic Pt. ISS shows that the Pt in the outermost atomic layer of the catalyst is mostly covered by substrate species during the 250 C reduction. Both the ISS and XPS results are consistent with Pt/Sn alloy formation. The surface dehydration and migration of substrate species over surface Pt and Sn appear to explain why a CO pretreatment at 250 C produces inferior CO oxidation activities compared to a 125 C pretreatment.

Platinized tin oxide catalysts for CO2 lasers - Effects of pretreatment

NASA Technical Reports Server (NTRS)

Gardner, Steven D.; Hoflund, Gar B.; Schryer, David R.; Upchurch, Billy T.

1989-01-01

Platinized tin oxide surfaces used for low-temperature CO oxidation in CO2 lasers have been characterized before and after reduction in CO at 125 and 250 C using ion scattering spectroscopy (ISS) and X-ray photoelectron spectroscopy (XPS). XPS indicates that the Pt is present initially as Pto2. Reduction at 125 C converts the PtO2 to Pt(OH)2 while reduction at 250 C converts the PtO2 to metallic Pt. ISS shows that the Pt in the outermost atomic layer of the catalyst is mostly covered by substrate species during the 250 C reduction. Both the ISS and XPS results are consistent with Pt/Sn alloy formation. The surface dehydration and migration of substrate species over surface Pt and Sn appear to explain why a CO pretreatment at 250 C produces inferior CO oxidation activities compared to a 125 C pretreatment.

Satellite remotely-sensed land surface parameters and their climatic effects for three metropolitan regions

USGS Publications Warehouse

Xian, George

2008-01-01

By using both high-resolution orthoimagery and medium-resolution Landsat satellite imagery with other geospatial information, several land surface parameters including impervious surfaces and land surface temperatures for three geographically distinct urban areas in the United States – Seattle, Washington, Tampa Bay, Florida, and Las Vegas, Nevada, are obtained. Percent impervious surface is used to quantitatively define the spatial extent and development density of urban land use. Land surface temperatures were retrieved by using a single band algorithm that processes both thermal infrared satellite data and total atmospheric water vapor content. Land surface temperatures were analyzed for different land use and land cover categories in the three regions. The heterogeneity of urban land surface and associated spatial extents were shown to influence surface thermal conditions because of the removal of vegetative cover, the introduction of non-transpiring surfaces, and the reduction in evaporation over urban impervious surfaces. Fifty years of in situ climate data were integrated to assess regional climatic conditions. The spatial structure of surface heating influenced by landscape characteristics has a profound influence on regional climate conditions, especially through urban heat island effects.

Can Aerosol Offset Urban Heat Island Effect?

NASA Astrophysics Data System (ADS)

Jin, M. S.; Shepherd, J. M.

2009-12-01

The Urban Heat Island effect (UHI) refers to urban skin or air temperature exceeding the temperatures in surrounding non-urban regions. In a warming climate, the UHI may intensify extreme heat waves and consequently cause significant health and energy problems. Aerosols reduce surface insolation via the direct effect, namely, scattering and absorbing sunlight in the atmosphere. Combining the National Aeronautics and Space Administration (NASA) AERONET (AErosol RObotic NETwork) observations over large cities together with Weather Research and Forecasting Model (WRF) simulations, we find that the aerosol direct reduction of surface insolation range from 40-100 Wm-2, depending on seasonality and aerosol loads. As a result, surface skin temperature can be reduced by 1-2C while 2-m surface air temperature by 0.5-1C. This study suggests that the aerosol direct effect is a competing mechanism for the urban heat island effect (UHI). More importantly, both aerosol and urban land cover effects must be adequately represented in meteorological and climate modeling systems in order to properly characterize urban surface energy budgets and UHI.

Energy for biologic sulfate reduction in a hydrothermally formed ocean on Europa

NASA Astrophysics Data System (ADS)

Zolotov, Mikhail Y.; Shock, Everett L.

2003-04-01

Formation of a sulfate-bearing ocean on Jupiter's satellite Europa by quenched hydrothermal fluids provides a source of metabolic energy for low-temperature sulfate-reducing organisms that use dissolved H2 as an electron donor. Inhibition of thermodynamically favorable sulfate reduction in cooled hydrothermal fluids creates the potential for biologic reduction. Both high temperature and reduced conditions of ocean-forming hydrothermal solutions favor sulfate reduction in quenched fluids. The maximum amount of energy available to support autotrophic sulfate reduction is on the order of a few kilojoules per kilogram of water and is limited by the low abundances of either H2 or sulfate in ocean-forming fluids. Although this irreplaceable energy source might have supported early life on Europa, maintenance of biologic sulfate reduction throughout the ocean's history would require a supply of organic compounds from endogenic sources or from the satellite's surface.

KOH-activated multi-walled carbon nanotubes as platinum supports for oxygen reduction reaction

NASA Astrophysics Data System (ADS)

He, Chaoxiong; Song, Shuqin; Liu, Jinchao; Maragou, Vasiliki; Tsiakaras, Panagiotis

In the present investigation, multi-walled carbon nanotubes (MWCNTs) thermally treated by KOH were adopted as the platinum supporting material for the oxygen reduction reaction electrocatalysts. FTIR and Raman spectra were used to investigate the surface state of MWCNTs treated by KOH at different temperatures (700, 800, and 900 °C) and showed MWCNTs can be successfully functionalized. The structural properties of KOH-activated MWCNTs supported Pt were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and their electrochemical performance was evaluated by the aid of cyclic voltammetry (CV) and rotating disk electrode (RDE) voltammetry. According to the experimental findings of the present work, the surrface of MWCNTs can be successfully functionalized with oxygen-containing groups after activation by KOH, favoring the good dispersion of Pt nanoparticles with narrow size distribution. The as-prepared Pt catalysts supported on KOH treated MWCNTs at higher temperature, possess higher electrochemical surface area and exhibit desirable activity towards oxygen reduction reaction (ORR). More precisely, it has been found that the electrochemical active area of Pt/MWCNTs-900 is approximately two times higher than that of Pt/MWCNTs. It can be concluded that KOH activation is an effective way to decorate MWCNTs' surface with oxygen-containing groups and bigger surface area, which makes them more suitable as electrocatalyst support materials.

Laboratory Measured Emission Losses of Methyl Isothiocyanate at Pacific Northwest Soil Surface Fumigation Temperatures.

PubMed

Lu, Zhou; Hebert, Vincent R; Miller, Glenn C

2017-02-01

Temperature is a major environmental factor influencing land surface volatilization at the time of agricultural field fumigation. Cooler fumigation soil temperatures relevant to Pacific Northwest (PNW) application practices with metam sodium/potassium should result in appreciably reduced methyl isothiocyanate (MITC) emission rates, thus minimizing off target movement and bystander inhalation exposure. Herein, a series of laboratory controlled flow-through soil column assessments were performed evaluating MITC emissions over the range of cooler temperatures (2-13°C). Assessments were also conducted at the maximum allowed label application temperature of 32°C. All assessments were conducted at registration label-specified field moisture capacity, and no more than 50% cumulative MITC loss was observed over the 2-day post-fumigation timeframe. Three-fold reductions in MITC peak fluxes at cooler PNW application temperatures were observed compared to the label maximum temperature. This study supports current EPA metam sodium/potassium label language that indicates surface fumigations during warmer soil conditions should be discouraged.

The primary solar-type atmosphere surrounding the accreting Earth: H2O-induced high surface temperature.

NASA Astrophysics Data System (ADS)

Sasaki, S.

In the solar nebula, a growing planet attracts ambient gas to form a solar-type atmosphere. The structure of this H2-He atmosphere is calculated assuming the Earth was formed in the nebula. The blanketing effect of the atmosphere renders the planetary surface molten when the planetary mass exceeds 0.2 ME (ME being the present Earth's mass). Reduction of the surface melt by atmospheric H2 should add a large amount of H2O to the atmosphere: under the quartz-iron-fayalite oxygen buffer, partial pressure ratio P(H2O)/P(H2) becomes higher than 0.1. Enhancing opacity and gas mean molecular weight, the excess H2O raises the temperature and renders the atmosphere in convective equilibrium, while the dissociation of H2 suppresses the adiabatic temperature gradient. The surface temperature of the proto-Earth can be as high as 4700K when its mass is 1 ME. Such a high temperature may accelerate the evaporation of surface materials. A deep totally-molten magma ocean should exist in the accretion Earth.

Real-time first-principles simulations of thermionic emission from N-doped diamond surfaces

NASA Astrophysics Data System (ADS)

Shinozaki, Tomoki; Hagiwara, Satoshi; Morioka, Naoya; Kimura, Yuji; Watanabe, Kazuyuki

2018-06-01

We investigate thermionic emission from N-doped C(100) surfaces terminated with H or Li atoms using finite-temperature real-time density functional theory simulations. The current–temperature characteristics are found to follow the Richardson–Dushman (RD) equation, which was derived from a semiclassical theory. However, the Richardson constants are two orders of magnitude smaller than the ideal values from the RD theory. This considerable reduction is attributed primarily to the extremely low transmission probability of electrons from the surfaces toward the vacuum. The present method enables straightforward evaluation of the ideal efficiency of a thermionic energy converter.

Surface Chemistry of Perovskite-Type Electrodes During High Temperature CO2 Electrolysis Investigated by Operando Photoelectron Spectroscopy.

PubMed

Opitz, Alexander K; Nenning, Andreas; Rameshan, Christoph; Kubicek, Markus; Götsch, Thomas; Blume, Raoul; Hävecker, Michael; Knop-Gericke, Axel; Rupprechter, Günther; Klötzer, Bernhard; Fleig, Jürgen

2017-10-18

Any substantial move of energy sources from fossil fuels to renewable resources requires large scale storage of excess energy, for example, via power to fuel processes. In this respect electrochemical reduction of CO 2 may become very important, since it offers a method of sustainable CO production, which is a crucial prerequisite for synthesis of sustainable fuels. Carbon dioxide reduction in solid oxide electrolysis cells (SOECs) is particularly promising owing to the high operating temperature, which leads to both improved thermodynamics and fast kinetics. Additionally, compared to purely chemical CO formation on oxide catalysts, SOECs have the outstanding advantage that the catalytically active oxygen vacancies are continuously formed at the counter electrode, and move to the working electrode where they reactivate the oxide surface without the need of a preceding chemical (e.g., by H 2 ) or thermal reduction step. In the present work, the surface chemistry of (La,Sr)FeO 3-δ and (La,Sr)CrO 3-δ based perovskite-type electrodes was studied during electrochemical CO 2 reduction by means of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at SOEC operating temperatures. These measurements revealed the formation of a carbonate intermediate, which develops on the oxide surface only upon cathodic polarization (i.e., under sufficiently reducing conditions). The amount of this adsorbate increases with increasing oxygen vacancy concentration of the electrode material, thus suggesting vacant oxygen lattice sites as the predominant adsorption sites for carbon dioxide. The correlation of carbonate coverage and cathodic polarization indicates that an electron transfer is required to form the carbonate and thus to activate CO 2 on the oxide surface. The results also suggest that acceptor doped oxides with high electron concentration and high oxygen vacancy concentration may be particularly suited for CO 2 reduction. In contrast to water splitting, the CO 2 electrolysis reaction was not significantly affected by metallic particles, which were exsolved from the perovskite electrodes upon cathodic polarization. Carbon formation on the electrode surface was only observed under very strong cathodic conditions, and the carbon could be easily removed by retracting the applied voltage without damaging the electrode, which is particularly promising from an application point of view.

Surface Chemistry of Perovskite-Type Electrodes During High Temperature CO2 Electrolysis Investigated by Operando Photoelectron Spectroscopy

PubMed Central

2017-01-01

Any substantial move of energy sources from fossil fuels to renewable resources requires large scale storage of excess energy, for example, via power to fuel processes. In this respect electrochemical reduction of CO2 may become very important, since it offers a method of sustainable CO production, which is a crucial prerequisite for synthesis of sustainable fuels. Carbon dioxide reduction in solid oxide electrolysis cells (SOECs) is particularly promising owing to the high operating temperature, which leads to both improved thermodynamics and fast kinetics. Additionally, compared to purely chemical CO formation on oxide catalysts, SOECs have the outstanding advantage that the catalytically active oxygen vacancies are continuously formed at the counter electrode, and move to the working electrode where they reactivate the oxide surface without the need of a preceding chemical (e.g., by H2) or thermal reduction step. In the present work, the surface chemistry of (La,Sr)FeO3−δ and (La,Sr)CrO3−δ based perovskite-type electrodes was studied during electrochemical CO2 reduction by means of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at SOEC operating temperatures. These measurements revealed the formation of a carbonate intermediate, which develops on the oxide surface only upon cathodic polarization (i.e., under sufficiently reducing conditions). The amount of this adsorbate increases with increasing oxygen vacancy concentration of the electrode material, thus suggesting vacant oxygen lattice sites as the predominant adsorption sites for carbon dioxide. The correlation of carbonate coverage and cathodic polarization indicates that an electron transfer is required to form the carbonate and thus to activate CO2 on the oxide surface. The results also suggest that acceptor doped oxides with high electron concentration and high oxygen vacancy concentration may be particularly suited for CO2 reduction. In contrast to water splitting, the CO2 electrolysis reaction was not significantly affected by metallic particles, which were exsolved from the perovskite electrodes upon cathodic polarization. Carbon formation on the electrode surface was only observed under very strong cathodic conditions, and the carbon could be easily removed by retracting the applied voltage without damaging the electrode, which is particularly promising from an application point of view. PMID:28933825

Salinity surveys using an airborne microwave radiometer

NASA Technical Reports Server (NTRS)

Paris, J. F.; Droppleman, J. D.; Evans, D. E.

1972-01-01

The Barnes PRT-5 infrared radiometer and L-band channel of the multifrequency microwave radiometer are used to survey the distribution of surface water temperature and salinity. These remote sensors were flown repetitively in November 1971 over the outflow of the Mississippi River into the Gulf of Mexico. Data reduction parameters were determined through the use of flight data obtained over a known water area. With these parameters, the measured infrared and microwave radiances were analyzed in terms of the surface temperature and salinity.

Surface Selective Oxide Reduction During the Intercritical Annealing of Medium Mn Steel

NASA Astrophysics Data System (ADS)

Jo, Kyoung Rae; Cho, Lawrence; Oh, Jong Han; Kim, Myoung Soo; Kang, Ki Cheol; De Cooman, Bruno C.

2017-08-01

Third generation advanced high-strength steels achieve an excellent strength-ductility balance using a cost-effective alloy composition. During the continuous annealing of medium Mn steel, the formation of an external selective oxide layer of MnO has a negative impact on the coating quality after galvanizing. A procedure to reduce the selective oxide was therefore developed. It involves annealing in the temperature range of 1073 K to 1323 K (800 °C to 1050 °C) in a HNx gas atmosphere. Annealing at higher temperatures and the use of larger H2 volume fractions are shown to make the gas atmosphere reducing with respect to MnO. The reduction of the surface MnO layer was observed by SEM, GDOES, and cross-sectional TEM analysis.

Predicting East African spring droughts using Pacific and Indian Ocean sea surface temperature indices

USGS Publications Warehouse

Funk, Christopher C.; Hoell, Andrew; Shukla, Shraddhanand; Blade, Ileana; Liebmann, Brant; Roberts, Jason B.; Robertson, Franklin R.

2014-01-01

In southern Ethiopia, Eastern Kenya, and southern Somalia poor boreal spring rains in 1999, 2000, 2004, 2007, 2008, 2009 and 2011 contributed to severe food insecurity and high levels of malnutrition. Predicting rainfall deficits in this region on seasonal and decadal time frames can help decision makers support disaster risk reduction while guiding climate-smart adaptation and agricultural development. Building on recent research that links more frequent droughts to a stronger Walker Circulation, warming in the Indo-Pacific warm pool, and an increased western Pacific sea surface temperature (SST) gradient, we explore the dominant modes of East African rainfall variability, links between these modes and sea surface temperatures, and a simple index-based monitoring-prediction system suitable for drought early warning.

Leidenfrost vapour layer moderation of the drag crisis and trajectories of superhydrophobic and hydrophilic spheres falling in water.

PubMed

Vakarelski, Ivan U; Chan, Derek Y C; Thoroddsen, Sigurdur T

2014-08-21

We investigate the dynamic effects of a Leidenfrost vapour layer sustained on the surface of heated steel spheres during free fall in water. We find that a stable vapour layer sustained on the textured superhydrophobic surface of spheres falling through 95 °C water can reduce the hydrodynamic drag by up to 75% and stabilize the sphere trajectory for the Reynolds number between 10(4) and 10(6), spanning the drag crisis in the absence of the vapour layer. For hydrophilic spheres under the same conditions, the transition to drag reduction and trajectory stability occurs abruptly at a temperature different from the static Leidenfrost point. The observed drag reduction effects are attributed to the disruption of the viscous boundary layer by the vapour layer whose thickness depends on the water temperature. Both the drag reduction and the trajectory stabilization effects are expected to have significant implications for development of sustainable vapour layer based technologies.

Optimization of palm oil physical refining process for reduction of 3-monochloropropane-1,2-diol (3-MCPD) ester formation.

PubMed

Zulkurnain, Musfirah; Lai, Oi Ming; Tan, Soo Choon; Abdul Latip, Razam; Tan, Chin Ping

2013-04-03

The reduction of 3-monochloropropane-1,2-diol (3-MCPD) ester formation in refined palm oil was achieved by incorporation of additional processing steps in the physical refining process to remove chloroester precursors prior to the deodorization step. The modified refining process was optimized for the least 3-MCPD ester formation and acceptable refined palm oil quality using response surface methodology (RSM) with five processing parameters: water dosage, phosphoric acid dosage, degumming temperature, activated clay dosage, and deodorization temperature. The removal of chloroester precursors was largely accomplished by increasing the water dosage, while the reduction of 3-MCPD esters was a compromise in oxidative stability and color of the refined palm oil because some factors such as acid dosage, degumming temperature, and deodorization temperature showed contradictory effects. The optimization resulted in 87.2% reduction of 3-MCPD esters from 2.9 mg/kg in the conventional refining process to 0.4 mg/kg, with color and oil stability index values of 2.4 R and 14.3 h, respectively.

The effect of monomolecular surface films on the microwave brightness temperature of the sea surface

NASA Technical Reports Server (NTRS)

Alpers, W.; Blume, H.-J. C.; Garrett, W. D.; Huehnerfuss, H.

1982-01-01

It is pointed out that monomolecular surface films of biological origin are often encountered on the ocean surface, especially in coastal regions. The thicknesses of the monomolecular films are of the order of 3 x 10 to the -9th m. Huehnerfuss et al. (1978, 1981) have shown that monomolecular surface films damp surface waves quite strongly in the centimeter to decimeter wavelength regime. Other effects caused by films are related to the reduction of the gas exchange at the air-sea interface and the decrease of the wind stress. The present investigation is concerned with experiments which reveal an unexpectedly large response of the microwave brightness temperature to a monomolecular oleyl alcohol slick at 1.43 GHz. Brightness temperature is a function of the complex dielectric constant of thy upper layer of the ocean. During six overflights over an ocean area covered with an artificial monomolecular alcohol film, a large decrease of the brightness temperature at the L-band was measured, while at the S-band almost no decrease was observed.

Carbon and Mo transformations during the synthesis of mesoporous Mo2C/carbon catalysts by carbothermal hydrogen reduction

NASA Astrophysics Data System (ADS)

Wang, Haiyan; Liu, Shida; Liu, Bing; Montes, Vicente; Hill, Josephine M.; Smith, Kevin J.

2018-02-01

The synthesis of mesoporous Mo2C/carbon catalysts by carbothermal hydrogen reduction is reported. Petroleum coke (petcoke) was activated with KOH at 800 °C to obtain high surface area microporous activated petcoke (APC; 2000 m2/g). The APC was wet impregnated with ammonium heptamolybdate (AHM: 10 wt% Mo), dried and reduced in H2 at temperatures from 400 to 800 °C, to yield Mo2C/APC catalysts. Increased reduction temperature increased the Mo2C yield and the mesoporous volume of the Mo2C/APC. At a reduction temperature of 750 °C the mesopore volume of the catalyst doubled compared to the APC support and accounted for 37% of the total pore volume. Maintaining the final CHR temperature for 90 min further increased the Mo2C yield and mesoporosity of the catalyst. The role of Mo2C in the catalytic hydrogenation of the APC and mesopore generation is demonstrated. The activity of the Mo2C/carbon catalysts in the hydrodeoxygenation of 4-methyl phenol increased with increased CHR temperature and catalyst mesoporosity.

Decadal evolution of the surface energy budget during the fast warming and global warming hiatus periods in the ERA-interim

NASA Astrophysics Data System (ADS)

Hu, Xiaoming; Sejas, Sergio A.; Cai, Ming; Taylor, Patrick C.; Deng, Yi; Yang, Song

2018-05-01

The global-mean surface temperature has experienced a rapid warming from the 1980s to early-2000s but a muted warming since, referred to as the global warming hiatus in the literature. Decadal changes in deep ocean heat uptake are thought to primarily account for the rapid warming and subsequent slowdown. Here, we examine the role of ocean heat uptake in establishing the fast warming and warming hiatus periods in the ERA-Interim through a decomposition of the global-mean surface energy budget. We find the increase of carbon dioxide alone yields a nearly steady increase of the downward longwave radiation at the surface from the 1980s to the present, but neither accounts for the fast warming nor warming hiatus periods. During the global warming hiatus period, the transfer of latent heat energy from the ocean to atmosphere increases and the total downward radiative energy flux to the surface decreases due to a reduction of solar absorption caused primarily by an increase of clouds. The reduction of radiative energy into the ocean and the surface latent heat flux increase cause the ocean heat uptake to decrease and thus contribute to the slowdown of the global-mean surface warming. Our analysis also finds that in addition to a reduction of deep ocean heat uptake, the fast warming period is also driven by enhanced solar absorption due predominantly to a decrease of clouds and by enhanced longwave absorption mainly attributed to the air temperature feedback.

CO2 to methanol conversion using hydride terminated porous silicon nanoparticles.

PubMed

Dasog, M; Kraus, S; Sinelnikov, R; Veinot, J G C; Rieger, B

2017-03-09

Porous silicon nanoparticles (Si-NPs) prepared via magnesiothermic reduction were used to convert carbon dioxide (CO 2 ) into methanol. The hydride surface of the silicon nanoparticles acted as a CO 2 reducing reagent without any catalyst at temperatures above 100 °C. The Si nanoparticles were reused up to four times without significant loss in methanol yields. The reduction process was monitored using in situ FT-IR and the materials were characterized using SEM, TEM, NMR, XPS, and powder XRD techniques. The influence of reaction temperature, pressure, and Si-NP concentration on CO 2 reduction were also investigated. Finally, Si particles produced directly from sand were used to convert CO 2 to methanol.

Athermal design and analysis of glass-plastic hybrid lens

NASA Astrophysics Data System (ADS)

Yang, Jian; Cen, Zhaofeng; Li, Xiaotong

2018-01-01

With the rapid development of security market, the glass-plastic hybrid lens has gradually become a choice for the special requirements like high imaging quality in a wide temperature range and low cost. The reduction of spherical aberration is achieved by using aspherical surface instead of increasing the number of lenses. Obviously, plastic aspherical lens plays a great role in the cost reduction. However, the hybrid lens has a priority issue, which is the large thermal coefficient of expansion of plastic, causing focus shift and seriously affecting the imaging quality, so the hybrid lens is highly sensitive to the change of temperature. To ensure the system operates normally in a wide temperature range, it is necessary to eliminate the influence of temperature on the hybrid lens system. A practical design method named the Athermal Material Map is summarized and verified by an athermal design example according to the design index. It includes the distribution of optical power and selection of glass or plastic. The design result shows that the optical system has excellent imaging quality at a wide temperature range from -20 ° to 70 °. The method of athermal design in this paper has generality which could apply to optical system with plastic aspherical surface.

Drastic reduction in the growth temperature of graphene on copper via enhanced London dispersion force

PubMed Central

Choi, Jin-Ho; Li, Zhancheng; Cui, Ping; Fan, Xiaodong; Zhang, Hui; Zeng, Changgan; Zhang, Zhenyu

2013-01-01

London dispersion force is ubiquitous in nature, and is increasingly recognized to be an important factor in a variety of surface processes. Here we demonstrate unambiguously the decisive role of London dispersion force in non-equilibrium growth of ordered nanostructures on metal substrates using aromatic source molecules. Our first-principles based multi-scale modeling shows that a drastic reduction in the growth temperature, from ~1000°C to ~300°C, can be achieved in graphene growth on Cu(111) when the typical carbon source of methane is replaced by benzene or p-Terphenyl. The London dispersion force enhances their adsorption energies by about (0.5–1.8) eV, thereby preventing their easy desorption, facilitating dehydrogenation, and promoting graphene growth at much lower temperatures. These quantitative predictions are validated in our experimental tests, showing convincing demonstration of monolayer graphene growth using the p-Terphenyl source. The general trends established are also more broadly applicable in molecular synthesis of surface-based nanostructures. PMID:23722566

A New Method to Measure Temperature and Burner Pattern Factor Sensing for Active Engine Control

NASA Technical Reports Server (NTRS)

Ng, Daniel

1999-01-01

The determination of the temperatures of extended surfaces which exhibit non-uniform temperature variation is very important for a number of applications including the "Burner Pattern Factor" (BPF) of turbine engines. Exploratory work has shown that use of BPF to control engine functions can result in many benefits, among them reduction in engine weight, reduction in operating cost, increase in engine life, while attaining maximum engine efficiency. Advanced engines are expected to operate at very high temperature to achieve high efficiency. Brief exposure of engine components to higher than design temperatures due to non-uniformity in engine burner pattern can reduce engine life. The engine BPF is a measure of engine temperature uniformity. Attainment of maximum temperature uniformity and high temperatures is key to maximum efficiency and long life. A new approach to determine through the measurement of just one radiation spectrum by a multiwavelength pyrometer is possible. This paper discusses a new temperature sensing approach and its application to determine the BPF.

Impacts of aerosols on seasonal precipitation and snowpack in California based on convection-permitting WRF-Chem simulations

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

Wu, Longtao; Gu, Yu; Jiang, Jonathan H.

Here, a version of the WRF-Chem model with fully coupled aerosol–meteorology–snowpack is employed to investigate the impacts of various aerosol sources on precipitation and snowpack in California. In particular, the impacts of locally emitted anthropogenic and dust aerosols, and aerosols transported from outside California are studied. We differentiate three pathways of aerosol effects: aerosol–radiation interaction (ARI), aerosol–snow interaction (ASI), and aerosol–cloud interaction (ACI). The convection-permitting model simulations show that precipitation, snow water equivalent (SWE), and surface air temperature averaged over the whole domain (34–42° N, 117–124° W, not including ocean points) are reduced when aerosols are included, therefore reducing largemore » biases in these variables due to the absence of aerosol effects in the model. Aerosols affect California water resources through the warming of mountaintops and the reduction of precipitation; however, different aerosol sources play different roles in changing surface temperature, precipitation, and snowpack in California by means of various weights of the three pathways. ARI by all aerosols mainly cools the surface, leading to slightly increased SWE over the mountains. Locally emitted dust aerosols warm the surface of mountaintops through ASI, in which the reduced snow albedo associated with dusty snow leads to more surface absorption of solar radiation and reduced SWE. Transported aerosols and local anthropogenic aerosols play a dominant role in increasing nonprecipitating clouds but reducing precipitation through ACI, leading to reduced SWE and runoff on the Sierra Nevada, as well as the warming of mountaintops associated with decreased SWE and hence lower surface albedo. The average changes in surface temperature from October 2012 to June 2013 are about –0.19 and 0.22 K for the whole domain and over mountaintops, respectively. Overall, the averaged reduction during October to June is about 7 % for precipitation, 3 % for SWE, and 7 % for surface runoff for the whole domain, while the corresponding numbers are 12, 10, and 10 % for the mountaintops. The reduction in SWE is more significant in a dry year, with 9 % for the whole domain and 16 % for the mountaintops. The maximum reduction of ~20 % in precipitation occurs in May and is associated with the maximum aerosol loading, leading to the largest decrease in SWE and surface runoff over that period. It is also found that dust aerosols can cause early snowmelt on the mountaintops and reduced surface runoff after April.« less

Impacts of aerosols on seasonal precipitation and snowpack in California based on convection-permitting WRF-Chem simulations

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

Wu, Longtao; Gu, Yu; Jiang, Jonathan H.

A version of the WRF-Chem model with fully coupled aerosol–meteorology–snowpack is employed to investigate the impacts of various aerosol sources on precipitation and snowpack in California. In particular, the impacts of locally emitted anthropogenic and dust aerosols, and aerosols transported from outside California are studied. We differentiate three pathways of aerosol effects: aerosol–radiation interaction (ARI), aerosol–snow interaction (ASI), and aerosol–cloud interaction (ACI). The convection-permitting model simulations show that precipitation, snow water equivalent (SWE), and surface air temperature averaged over the whole domain (34–42° N, 117–124° W, not including ocean points) are reduced when aerosols are included, therefore reducing large biasesmore » in these variables due to the absence of aerosol effects in the model. Aerosols affect California water resources through the warming of mountaintops and the reduction of precipitation; however, different aerosol sources play different roles in changing surface temperature, precipitation, and snowpack in California by means of various weights of the three pathways. ARI by all aerosols mainly cools the surface, leading to slightly increased SWE over the mountains. Locally emitted dust aerosols warm the surface of mountaintops through ASI, in which the reduced snow albedo associated with dusty snow leads to more surface absorption of solar radiation and reduced SWE. Transported aerosols and local anthropogenic aerosols play a dominant role in increasing nonprecipitating clouds but reducing precipitation through ACI, leading to reduced SWE and runoff on the Sierra Nevada, as well as the warming of mountaintops associated with decreased SWE and hence lower surface albedo. The average changes in surface temperature from October 2012 to June 2013 are about -0.19 and 0.22 K for the whole domain and over mountaintops, respectively. Overall, the averaged reduction during October to June is about 7% for precipitation, 3% for SWE, and 7% for surface runoff for the whole domain, while the corresponding numbers are 12, 10, and 10% for the mountaintops. The reduction in SWE is more significant in a dry year, with 9% for the whole domain and 16% for the mountaintops. The maximum reduction of -20% in precipitation occurs in May and is associated with the maximum aerosol loading, leading to the largest decrease in SWE and surface runoff over that period. It is also found that dust aerosols can cause early snowmelt on the mountaintops and reduced surface runoff after April.« less

Impacts of aerosols on seasonal precipitation and snowpack in California based on convection-permitting WRF-Chem simulations

NASA Astrophysics Data System (ADS)

Wu, Longtao; Gu, Yu; Jiang, Jonathan H.; Su, Hui; Yu, Nanpeng; Zhao, Chun; Qian, Yun; Zhao, Bin; Liou, Kuo-Nan; Choi, Yong-Sang

2018-04-01

A version of the WRF-Chem model with fully coupled aerosol-meteorology-snowpack is employed to investigate the impacts of various aerosol sources on precipitation and snowpack in California. In particular, the impacts of locally emitted anthropogenic and dust aerosols, and aerosols transported from outside California are studied. We differentiate three pathways of aerosol effects: aerosol-radiation interaction (ARI), aerosol-snow interaction (ASI), and aerosol-cloud interaction (ACI). The convection-permitting model simulations show that precipitation, snow water equivalent (SWE), and surface air temperature averaged over the whole domain (34-42° N, 117-124° W, not including ocean points) are reduced when aerosols are included, therefore reducing large biases in these variables due to the absence of aerosol effects in the model. Aerosols affect California water resources through the warming of mountaintops and the reduction of precipitation; however, different aerosol sources play different roles in changing surface temperature, precipitation, and snowpack in California by means of various weights of the three pathways. ARI by all aerosols mainly cools the surface, leading to slightly increased SWE over the mountains. Locally emitted dust aerosols warm the surface of mountaintops through ASI, in which the reduced snow albedo associated with dusty snow leads to more surface absorption of solar radiation and reduced SWE. Transported aerosols and local anthropogenic aerosols play a dominant role in increasing nonprecipitating clouds but reducing precipitation through ACI, leading to reduced SWE and runoff on the Sierra Nevada, as well as the warming of mountaintops associated with decreased SWE and hence lower surface albedo. The average changes in surface temperature from October 2012 to June 2013 are about -0.19 and 0.22 K for the whole domain and over mountaintops, respectively. Overall, the averaged reduction during October to June is about 7 % for precipitation, 3 % for SWE, and 7 % for surface runoff for the whole domain, while the corresponding numbers are 12, 10, and 10 % for the mountaintops. The reduction in SWE is more significant in a dry year, with 9 % for the whole domain and 16 % for the mountaintops. The maximum reduction of ˜ 20 % in precipitation occurs in May and is associated with the maximum aerosol loading, leading to the largest decrease in SWE and surface runoff over that period. It is also found that dust aerosols can cause early snowmelt on the mountaintops and reduced surface runoff after April.

Impacts of aerosols on seasonal precipitation and snowpack in California based on convection-permitting WRF-Chem simulations

DOE PAGES

Wu, Longtao; Gu, Yu; Jiang, Jonathan H.; ...

2018-04-23

Here, a version of the WRF-Chem model with fully coupled aerosol–meteorology–snowpack is employed to investigate the impacts of various aerosol sources on precipitation and snowpack in California. In particular, the impacts of locally emitted anthropogenic and dust aerosols, and aerosols transported from outside California are studied. We differentiate three pathways of aerosol effects: aerosol–radiation interaction (ARI), aerosol–snow interaction (ASI), and aerosol–cloud interaction (ACI). The convection-permitting model simulations show that precipitation, snow water equivalent (SWE), and surface air temperature averaged over the whole domain (34–42° N, 117–124° W, not including ocean points) are reduced when aerosols are included, therefore reducing largemore » biases in these variables due to the absence of aerosol effects in the model. Aerosols affect California water resources through the warming of mountaintops and the reduction of precipitation; however, different aerosol sources play different roles in changing surface temperature, precipitation, and snowpack in California by means of various weights of the three pathways. ARI by all aerosols mainly cools the surface, leading to slightly increased SWE over the mountains. Locally emitted dust aerosols warm the surface of mountaintops through ASI, in which the reduced snow albedo associated with dusty snow leads to more surface absorption of solar radiation and reduced SWE. Transported aerosols and local anthropogenic aerosols play a dominant role in increasing nonprecipitating clouds but reducing precipitation through ACI, leading to reduced SWE and runoff on the Sierra Nevada, as well as the warming of mountaintops associated with decreased SWE and hence lower surface albedo. The average changes in surface temperature from October 2012 to June 2013 are about –0.19 and 0.22 K for the whole domain and over mountaintops, respectively. Overall, the averaged reduction during October to June is about 7 % for precipitation, 3 % for SWE, and 7 % for surface runoff for the whole domain, while the corresponding numbers are 12, 10, and 10 % for the mountaintops. The reduction in SWE is more significant in a dry year, with 9 % for the whole domain and 16 % for the mountaintops. The maximum reduction of ~20 % in precipitation occurs in May and is associated with the maximum aerosol loading, leading to the largest decrease in SWE and surface runoff over that period. It is also found that dust aerosols can cause early snowmelt on the mountaintops and reduced surface runoff after April.« less

Influence of the Latitudinal Temperature Gradient on Soil Dust Concentration and Deposition in Greenland

NASA Technical Reports Server (NTRS)

Tegen, Ina; Rind, David

2000-01-01

To investigate the effects of changes in the latitudinal temperature gradient and the global mean temperature on dust concentration in the Northern Hemisphere, experiments with the Goddard Institute for Space Studies General Circulation Model (GISS GCM) are performed. The dust concentration over Greenland is calculated from sources in central and eastern Asia, which are integrated on-line in the model. The results show that an increase in the latitudinal temperature gradient increases both the Asian dust source strength and the concentration over Greenland. The source increase is the result of increased surface winds, and to a minor extent, the increase in Greenland dust is also associated with increased northward transport. Cooling the climate in addition to this increased gradient leads to a decrease in precipitation scavenging, which helps produce a further (slight) increase in Greenland dust in this experiment. Reducing the latitudinal gradient reduces the surface wind and hence the dust source, with a subsequent reduction in Greenland dust concentrations. Warming the climate in addition to this reduced gradient leads to a further reduction in Greenland dust due to enhanced precipitation scavenging. These results can be used to evaluate the relationship of Greenland ice core temperature changes to changes in the latitudinal and global temperatures.

Studies of oxidation and thermal reduction of the Cu(100) surface using low energy positrons

NASA Astrophysics Data System (ADS)

Fazleev, N. G.; Maddox, W. B.; Weiss, A. H.

2010-03-01

Changes in the surface of an oxidized Cu(100) single crystal resulting from vacuum annealing have been investigated using positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 C. The intensity then decreases monotonically as the annealing temperature is increased to ˜600 C. In contrast, the O KLL PAES intensity is the lowest at 300 C and it starts to increase again as the temperature is increased further. PAES results are analyzed by performing calculations of positron surface states and annihilation characteristics taking into account the charge redistribution at the surface, surface reconstructions, and changes of electronic properties of the surfaces with adsorbed oxygen. Possible explanation is proposed for the observed behavior of the intensity of positron annihilation induced Cu M2,3VV and O KLL Auger peaks and probabilities of annihilation of surface trapped positrons with Cu 3p and O 1s core-level electrons with changes of the annealing temperature.

Thermal treatment induced modification of structural, surface and bulk magnetic properties of Fe61.5Co5Ni8Si13.5B9Nb3 metallic glass

NASA Astrophysics Data System (ADS)

Shah, M.; Satalkar, M.; Kane, S. N.; Ghodke, N. L.; Sinha, A. K.; Varga, L. K.; Teixeira, J. M.; Araujo, J. P.

2018-05-01

Effect of thermal annealing induced modification of structural, surface and bulk magnetic properties of Fe61.5Co5Ni8Si13.5B9Nb3 alloy is presented. The changes in properties were observed using synchrotron x-ray diffraction technique (SXRD), atomic force microscopy (AFM), magneto-optical kerr effect (MOKE) and bulk magnetic measurements. Significant variations on the both side of surface occur for the annealing temperature upto 500 °C promotes the surface crystallization. Surface roughness appears due to presence of nanocrystallization plays an important role in determining magnetic properties. Observed lower value of bulk coercivity Hc of 6.2 A/m annealed temperature at 450 °C/1 h ascribed to reduction of disorder as compared to the surface (both shiny and wheel side observed by MOKE measurement) whereas improvement of bulk saturation magnetization with annealing temperature indicates first near neighbor shell of Fe atoms are surrounded by Fe atoms. Evolution of coercivity of surface and bulk with annealing temperature has been presented in conjunction with the structural observations.

Ocean Warming, More than Acidification, Reduces Shell Strength in a Commercial Shellfish Species during Food Limitation

PubMed Central

Mackenzie, Clara L.; Ormondroyd, Graham A.; Curling, Simon F.; Ball, Richard J.; Whiteley, Nia M.; Malham, Shelagh K.

2014-01-01

Ocean surface pH levels are predicted to fall by 0.3–0.4 pH units by the end of the century and are likely to coincide with an increase in sea surface temperature of 2–4°C. The combined effect of ocean acidification and warming on the functional properties of bivalve shells is largely unknown and of growing concern as the shell provides protection from mechanical and environmental challenges. We examined the effects of near-future pH (ambient pH –0.4 pH units) and warming (ambient temperature +4°C) on the shells of the commercially important bivalve, Mytilus edulis when fed for a limited period (4–6 h day−1). After six months exposure, warming, but not acidification, significantly reduced shell strength determined as reductions in the maximum load endured by the shells. However, acidification resulted in a reduction in shell flex before failure. Reductions in shell strength with warming could not be explained by alterations in morphology, or shell composition but were accompanied by reductions in shell surface area, and by a fall in whole-body condition index. It appears that warming has an indirect effect on shell strength by re-allocating energy from shell formation to support temperature-related increases in maintenance costs, especially as food supply was limited and the mussels were probably relying on internal energy reserves. The maintenance of shell strength despite seawater acidification suggests that biomineralisation processes are unaffected by the associated changes in CaCO3 saturation levels. We conclude that under near-future climate change conditions, ocean warming will pose a greater risk to shell integrity in M. edulis than ocean acidification when food availability is limited. PMID:24489785

Ocean warming, more than acidification, reduces shell strength in a commercial shellfish species during food limitation.

PubMed

Mackenzie, Clara L; Ormondroyd, Graham A; Curling, Simon F; Ball, Richard J; Whiteley, Nia M; Malham, Shelagh K

2014-01-01

Ocean surface pH levels are predicted to fall by 0.3-0.4 pH units by the end of the century and are likely to coincide with an increase in sea surface temperature of 2-4 °C. The combined effect of ocean acidification and warming on the functional properties of bivalve shells is largely unknown and of growing concern as the shell provides protection from mechanical and environmental challenges. We examined the effects of near-future pH (ambient pH -0.4 pH units) and warming (ambient temperature +4 °C) on the shells of the commercially important bivalve, Mytilus edulis when fed for a limited period (4-6 h day(-1)). After six months exposure, warming, but not acidification, significantly reduced shell strength determined as reductions in the maximum load endured by the shells. However, acidification resulted in a reduction in shell flex before failure. Reductions in shell strength with warming could not be explained by alterations in morphology, or shell composition but were accompanied by reductions in shell surface area, and by a fall in whole-body condition index. It appears that warming has an indirect effect on shell strength by re-allocating energy from shell formation to support temperature-related increases in maintenance costs, especially as food supply was limited and the mussels were probably relying on internal energy reserves. The maintenance of shell strength despite seawater acidification suggests that biomineralisation processes are unaffected by the associated changes in CaCO3 saturation levels. We conclude that under near-future climate change conditions, ocean warming will pose a greater risk to shell integrity in M. edulis than ocean acidification when food availability is limited.

Water Drop Evaporation on Mushroom-like Superhydrophobic Surfaces: Temperature Effects.

PubMed

do Nascimento, Rodney Marcelo; Cottin-Bizonne, Cécile; Pirat, Christophe; Ramos, Stella M M

2016-03-01

We report on experiments of drop evaporation on heated superhydrophobic surfaces decorated with micrometer-sized mushroom-like pillars. We analyze the influence of two parameters on the evaporation dynamics: the solid-liquid fraction and the substrate temperature, ranging between 30 and 80 °C. In the different configurations investigated, the drop evaporation appears to be controlled by the contact line dynamics (pinned or moving). The experimental results show that (i) in the pinned regime, the depinning angles increase with decreasing contact fraction and the substrate heating promotes the contact line depinning and (ii) in the moving regime, the droplet motion is described by periodic stick-slip events and contact-angle oscillations. These features are highly smoothed at the highest temperatures, with two possible mechanisms suggested to explain such a behavior, a reduction in the elasticity of the triple line and a decrease in the depinning energy barriers. For all surfaces, the observed remarkable stability of the "fakir" state to the temperature is attributed to the re-entrant micropillar curvature that prevents surface imbibition.

Biogeochemistry of the coupled manganese-iron-sulfur cycles of intertidal surface sediments

NASA Astrophysics Data System (ADS)

Bosselmann, K.; Boettcher, M. E.; Billerbeck, M.; Walpersdorf, E.; Debeer, D.; Brumsack, H.-J.; Huettel, M.; Joergensen, B. B.

2003-04-01

The biogeochemistry of the coupled iron-manganese-sulfur-carbon cycles was studied in temperate intertidal surface sediments of the German Wadden Sea (North Sea). Coastal sampling sites include sand, mixed and mud flats with different organic matter and metal contents and permeability reflecting different hydrodynamic regimes. The field study focusses on the influence of temperature, organic matter load, and sediment types on the dynamics of biogeochemical reactions on different time scales (season, day-night, tidal cycles). One of the main interests was related to the cycling of metals (Mn, Fe) in relation to the activity of sulfate-reducing bacteria. Pore water profiles were investigated by sediment sectioning and high resolution gel sampling techniques. Microbial sulfate reduction rates were measured using radiolabeled sulfate with the whole core incubation technique and the spatial distribution of bacterial activity was visualised by using "2D-photoemulsion-monitoring technique". The biogeochemical sulfur cycle was additionally characterised by the stable isotope ratios (S,O) of different sulfur species (e.g., SO_4, AVS, pyrite). Element transfers (metals, nutrients) across the sediment-water interface were additionally quantified by the application of benthic flux chambers. Microbial sulfate reduction was generally highest in the suboxic zone of the surface sediments indicating its potential importance for the mobilization of iron and manganese. In organic matter poor permeable sediments tidal effects additionally influence the spatial and temporal distribution of dissolved redox-sensitive metals. In organic matter-rich silty and muddy sediments, temperature controlled the microbial sulfate reduction rates. Depth-integrated sulfate reduction rates in sandy sediments were much lower and controlled by both temperature and organic matter. Formation of anoxic sediment surfaces due to local enhanced organic matter load (so-called "black spots") may create windows of an increase flux of metals, nutrients and hydrogen sulfide. Acknowledgements: The study was supported by German Science Foundation within the DFG-research group "BioGeoChemistry of the Waddensea" and Max Planck Society.

Pressure-Sensitive Paint Measurements on Surfaces with Non-Uniform Temperature

NASA Technical Reports Server (NTRS)

Bencic, Timothy J.

1999-01-01

Pressure-sensitive paint (PSP) has become a useful tool to augment conventional pressure taps in measuring the surface pressure distribution of aerodynamic components in wind tunnel testing. While the PSP offers the advantage of a non-intrusive global mapping of the surface pressure, one prominent drawback to the accuracy of this technique is the inherent temperature sensitivity of the coating's luminescent intensity. A typical aerodynamic surface PSP test has relied on the coated surface to be both spatially and temporally isothermal, along with conventional instrumentation for an in situ calibration to generate the highest accuracy pressure mappings. In some tests however, spatial and temporal thermal gradients are generated by the nature of the test as in a blowing jet impinging on a surface. In these cases, the temperature variations on the painted surface must be accounted for in order to yield high accuracy and reliable data. A new temperature correction technique was developed at NASA Lewis to collapse a "family" of PSP calibration curves to a single intensity ratio versus pressure curve. This correction allows a streamlined procedure to be followed whether or not temperature information is used in the data reduction of the PSP. This paper explores the use of conventional instrumentation such as thermocouples and pressure taps along with temperature-sensitive paint (TSP) to correct for the thermal gradients that exist in aeropropulsion PSP tests. Temperature corrected PSP measurements for both a supersonic mixer ejector and jet cavity interaction tests are presented.

Skin Temperature Analysis and Bias Correction in a Coupled Land-Atmosphere Data Assimilation System

NASA Technical Reports Server (NTRS)

Bosilovich, Michael G.; Radakovich, Jon D.; daSilva, Arlindo; Todling, Ricardo; Verter, Frances

2006-01-01

In an initial investigation, remotely sensed surface temperature is assimilated into a coupled atmosphere/land global data assimilation system, with explicit accounting for biases in the model state. In this scheme, an incremental bias correction term is introduced in the model's surface energy budget. In its simplest form, the algorithm estimates and corrects a constant time mean bias for each gridpoint; additional benefits are attained with a refined version of the algorithm which allows for a correction of the mean diurnal cycle. The method is validated against the assimilated observations, as well as independent near-surface air temperature observations. In many regions, not accounting for the diurnal cycle of bias caused degradation of the diurnal amplitude of background model air temperature. Energy fluxes collected through the Coordinated Enhanced Observing Period (CEOP) are used to more closely inspect the surface energy budget. In general, sensible heat flux is improved with the surface temperature assimilation, and two stations show a reduction of bias by as much as 30 Wm(sup -2) Rondonia station in Amazonia, the Bowen ratio changes direction in an improvement related to the temperature assimilation. However, at many stations the monthly latent heat flux bias is slightly increased. These results show the impact of univariate assimilation of surface temperature observations on the surface energy budget, and suggest the need for multivariate land data assimilation. The results also show the need for independent validation data, especially flux stations in varied climate regimes.

Significant long-term reduction in n-channel MESFET subthreshold leakage using ammonium-sulfide surface treated gates

NASA Technical Reports Server (NTRS)

Neudeck, P. G.; Carpenter, M. S.; Melloch, Michael R.; Cooper, James A., Jr.

1991-01-01

Ammonium-sulfide (NH4)2S treated gates have been employed in the fabrication of GaAs MESFETs that exhibit a remarkable reduction in subthreshold leakage current. A greater than 100-fold reduction in drain current minimum is observed due to a decrease in Schottky gate leakage. The electrical characteristics have remained stable for over a year during undesiccated storage at room temperature, despite the absence of passivation layers.

Effect of Temperature and Graphite Immersion Method on Carbothermic Reduction of Fayalite Slag

NASA Astrophysics Data System (ADS)

Mitrašinović, Aleksandar

2017-09-01

In this work, graphite flakes were used to reduce fayalite slag originated from the pyrometallurgical copper extraction process. Experiments were conducted with a significantly different contact area between graphite and slag at two temperatures, 1300°C and 1400°C. The process was continuously monitored via the concentration change of CO and CO2 in off-gas. Reduction rate values in experiments where 150-micron-diameter graphite flakes were submerged into the slag and left to float slowly to the top are about four times higher compared with when graphite flakes were dispersed at the top surface of liquid slag. The activation energy for instigating reduction was 302.61 kJ mol-1 and 306.67 kJ mol-1 in the case where graphite flakes were submerged into the slag and dispersed at the surface, respectively. The reduction process is characterized by two distinctive periods: an initial steep increase in the concentration of CO and CO2 controlled by the Boudouard reaction and a subsequent slow decrease of CO and CO2 concentrations in the off-gas controlled by mass transfer of reducible oxides from bulk to the gas-slag interface.

The Work Softening by Deformation-Induced Disordering and Cold Rolling of 6.5 wt pct Si Steel Thin Sheets

NASA Astrophysics Data System (ADS)

Wang, Xianglong; Li, Haoze; Zhang, Weina; Liu, Zhenyu; Wang, Guodong; Luo, Zhonghan; Zhang, Fengquan

2016-09-01

As-cast strip of 6.5 wt pct Si steel was fabricated by twin-roll strip casting. After hot rolling at 1323 K (1050 °C), thin sheets with the thickness of 0.35 mm were produced by warm rolling at 373 K (100 °C) with rolling reductions of 15, 25, 35, 45, 55, and 65 pct. Influence of warm rolling reduction on ductility was investigated by room temperature bending test. The measurement of macro-hardness showed that "work softening" could begin when the warm rolling reduction exceeded 35 pct. The room temperature ductility of the thin sheets gradually increased with the increase of warm rolling reductions, and the plastic deformation during bending began to form when the warm rolling reduction was greater than 45 pct, the 65 pct rolled thin sheet exhibited the maximum plastic deformation of about 0.6 pct during bending at room temperature, with a few small dimples having been observed on the fracture surfaces. B2-ordered domains were formed in the 15, 25, 35, 45, and 55 pct rolled specimens, and their average size decreased with the increase of warm rolling reductions. By contrast, no B2-ordered domain could be found in the 65 pct rolled specimen. It had been observed that large-ordered domains could be split into several small parts by the slip of partial super-dislocations during warm rolling, which led to significant decrease of the order degree to cause the phenomenon of deformation-induced disordering. On the basis of these results, cold rolling schedule was developed to successfully fabricate 0.25-mm-thick sheets with good surface qualities and magnetic properties from warm rolled sheets.

Coupled Climate Model Simulations to Bracket the Impacts of Increasing Asian Aerosols Emissions and Aggressive Future Clean Air Policies

NASA Astrophysics Data System (ADS)

Dubey, M. K.; Zhang, Y.; Sun, S.; Olsen, S.; Dean, S.; Bleck, R.; Chylek, P.; Lohmann, U.

2007-12-01

We report ensemble simulations of the climatic impacts of changing anthropogenic aerosols (sulfate, organic and black carbon), which bracket two policy scenarios: increased emissions over China and India by a factor of three over current levels and a global reduction of aerosols by a factor of ten, using the NCAR-CCSM3 and NASA- GISS coupled ocean atmosphere models. Tripling the anthropogenic aerosols over China and India has a small cooling effect (about -0.12°C) on the global mean surface air temperature with a slight reduction in global mean precipitation by ~ -0.8%. On the other hand, global reduction of anthropogenic aerosols by a factor of ten would warm the global surface temperatures by 0.4 °C - 0.8 °C in less than 10 years after the reduction takes place as well as an increase in global precipitation by 3.0% - 3.3%. Comparisons of NCAR and NASA model simulations also suggest that the indirect effects of aerosols are about 1-2 times the direct effects of aerosols. Tripling Asian anthropogenic aerosols results in regional cooling and a reduction in precipitation primarily in Asia, with cooling (warming) also noted over the high latitudes of Northern (Southern) Hemisphere. Warming and increase in precipitation in the case of global reduction of aerosols are concentrated mainly over polluted land areas in both hemispheres. Tropical regions experience large changes in precipitation in both scenarios. We provide new insights into the climate model sensitivities of global mean temperatures and rainfall to aerosol forcing. Our results underscore the urgency of reducing greenhouse gas accumulation rates as the world reduces air pollution to improve human health and that potential increased Asian pollution, offsets only a small fraction of the warming by greenhouse gases.

Low-Temperature Desorption of N2O from NO on Rutile TiO2(110)-1x1

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

Kim, Boseong; Li, Zhenjun; Kay, Bruce D.

2014-05-08

We find that NO dosed on rutile TiO2(110)-1×1 at substrate temperatures as low as 50 K readily reacts to produce N2O which desorbs promptly from the surface leaving an oxygen adatom behind. The desorption rate of N2O reaches a maximum value after 1 – 2 sec at an NO flux of 1.2 ×1014 NO/cm2∙sec and then decreases rapidly as the initially clean, reduced TiO2(110) surface with ~5% oxygen vacancies (VO’s) becomes covered with oxygen adatoms and unreacted NO. The maximum desorption rate is also found to increase as the substrate temperature is raised up to about 100 K. Interestingly, themore » N2O desorption during the low-temperature (LT) NO dose is strongly suppressed when molecular oxygen is predosed, whereas it persists on the surface with VO’s passivated by surface hydroxyls. Our results show that the surface charge, not the VO sites, plays a dominant role in the LT N2O desorption induced by a facile NO reduction at such low temperatures.« less

Influence of temperature and organic load on chemical disinfection of Geobacillus steareothermophilus spores, a surrogate for Bacillus anthracis

PubMed Central

Guan, Jiewen; Chan, Maria; Brooks, Brian W.; Rohonczy, Liz

2013-01-01

This study evaluated the influence of temperature and organic load on the effectiveness of domestic bleach (DB), Surface Decontamination Foam (SDF), and Virkon in inactivating Geobacillus stearothermophilus spores, which are a surrogate for Bacillus anthracis spores. The spores were suspended in light or heavy organic preparations and the suspension was applied to stainless steel carrier disks. The dried spore inoculum was covered with the disinfectants and the disks were then incubated at various temperatures. At −20°C, the 3 disinfectants caused less than a 2.0 log10 reduction of spores in both organic preparations during a 24-h test period. At 4°C, the DB caused a 4.4 log10 reduction of spores in light organic preparations within 2 h, which was about 3 log10 higher than what was achieved with SDF or Virkon. In heavy organic preparations, after 24 h at 4°C the SDF had reduced the spore count by 4.5 log10, which was about 2 log10 higher than for DB or Virkon. In general, the disinfectants were most effective at 23°C but a 24-h contact time was required for SDF and Virkon to reduce spore counts in both organic preparations by at least 5.5 log10. Comparable disinfecting activity with DB only occurred with the light organic load. In summary, at temperatures as low as 4°C, DB was the most effective disinfectant, inactivating spores within 2 h on surfaces with a light organic load, whereas SDF produced the greatest reduction of spores within 24 h on surfaces with a heavy organic load. PMID:24082400

Extending the potential of evaporative cooling for heat-stress relief.

PubMed

Berman, A

2006-10-01

Factors were analyzed that limit the range of environmental conditions in which stress from heat may be relieved by evaporative cooling in shaded animals. Evaporative cooling reduces air temperature (Ta), but increases humidity. Equations were developed to predict Ta reduction as a function of ambient temperature and humidity and of humidity in cooled air. Predictions indicated that a reduction of Ta becomes marginal at humidities beyond 45%. A reduction of Ta lessens with rising ambient Ta. The impact of increasing humidity on respiratory heat loss (Hre) was estimated from existing data published on Holstein cattle. Respiratory heat loss is reduced by increased humidity up to 45%, but is not affected by higher humidity. Skin evaporative and sensible heat losses are determined not only by the humidity and temperature gradient, but also by air velocity close to the body surface. At higher Ta, the reduction in sensible heat loss is compensated for by an increased demand for Hre. High Hre may become a stressor when panting interferes with resting and rumination. Effects of temperature, humidity, air velocity, and body surface exposure to free air on Hre were estimated by a thermal balance model for lactating Holstein cows yielding 35 kg/d. The predictions of the simulations were supported by respiratory rate observations. The Hre was assumed to act as a stressor when exceeding 50% of the maximal capacity. When the full body surface was exposed to a 1.5 m/s air velocity, humidity (15 to 75%) had no significant predicted effect on Hre. For an air velocity of 0.3 m/s, Hre at 50% of the maximum rate was predicted at 34, 32.5, and 31.5 degrees C for relative humidities of 55, 65, and 75%, respectively. Similar results were predicted for an animal with two-thirds of its body surface exposed to 1.5 m/s air velocity. If air velocity was reduced for such animals to 0.3 m/s, the rise in Hre was expected to occur at approximately 25 degrees C and 50% relative humidity. Maximal rates of Hre were estimated at 27 to 30 degrees C when ambient humidity was 55% relative humidity and higher. High humidity may stress animals in evaporative cooling systems. Humidity stress may be prevented by a higher air velocity on the body surface of the animal, particularly in sheltered areas in which the exposed body surface is reduced, such as mangers and stalls. This may extend the use of evaporative cooling to less dry environments.

Dynamic investigation of the role of the surface sulfates in NO{sub x} reduction and SO{sub 2} oxidation over V{sub 2}O{sub 5}-WO{sub 3}/TiO{sub 2} catalysts

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

Orsenigo, C.; Lietti, L.; Tronconi, E.

1998-06-01

Transient experiments performed over synthesized and commercial V{sub 2}O{sub 5}-WO{sub 3}/TiO{sub 2} catalysts during catalyst conditioning and during step changes of the operating variables (SO{sub 2} inlet concentration and temperature) show that conditioning of the catalyst is required to attain significant and reproducible steady-state data in both the reduction of NO{sub x} and the oxidation of SO{sub 2}. The response time of conditioning for NO{sub x} reduction is of a few hours and that for SO{sub 2} oxidation is of several hours. Fourier transform infrared spectroscopy temperature programmed decomposition, and thermogravimetric measurements showed that catalyst conditioning is associated with amore » slow process of buildup of sulfates: the different characteristic conditioning times observed in the reduction of NO{sub x} and in the oxidation of SO{sub 2} suggest that the buildup of sulfates occurs first at the vanadyl sites and later on at the exposed titania surface. Formation of sulfates at or near the vanadyl sites increases the reactivity in the de-NO{sub x} reaction, possibly due to the increase in the Broensted and Lewis acidity of the catalyst, whereas the titania surface acts as SO{sub 3} acceptor and affects the outlet SO{sub 3} concentration during catalyst conditioning for the SO{sub 2} oxidation reaction. The response time to step changes in SO{sub 2} concentration and temperature is of a few hours in the case of SO{sub 2} oxidation and much shorter in the case of NO{sub x} reduction. The different time responses associated with conditioning and with step changes in the settings of the operating variables have been rationalized in terms of the different extent of perturbation of the sulfate coverage experienced by the catalyst.« less

Amazon Basin climate under global warming: the role of the sea surface temperature.

PubMed

Harris, Phil P; Huntingford, Chris; Cox, Peter M

2008-05-27

The Hadley Centre coupled climate-carbon cycle model (HadCM3LC) predicts loss of the Amazon rainforest in response to future anthropogenic greenhouse gas emissions. In this study, the atmospheric component of HadCM3LC is used to assess the role of simulated changes in mid-twenty-first century sea surface temperature (SST) in Amazon Basin climate change. When the full HadCM3LC SST anomalies (SSTAs) are used, the atmosphere model reproduces the Amazon Basin climate change exhibited by HadCM3LC, including much of the reduction in Amazon Basin rainfall. This rainfall change is shown to be the combined effect of SSTAs in both the tropical Atlantic and the Pacific, with roughly equal contributions from each basin. The greatest rainfall reduction occurs from May to October, outside of the mature South American monsoon (SAM) season. This dry season response is the combined effect of a more rapid warming of the tropical North Atlantic relative to the south, and warm SSTAs in the tropical east Pacific. Conversely, a weak enhancement of mature SAM season rainfall in response to Atlantic SST change is suppressed by the atmospheric response to Pacific SST. This net wet season response is sufficient to prevent dry season soil moisture deficits from being recharged through the SAM season, leading to a perennial soil moisture reduction and an associated 30% reduction in annual Amazon Basin net primary productivity (NPP). A further 23% NPP reduction occurs in response to a 3.5 degrees C warmer air temperature associated with a global mean SST warming.

Temperature Dependence of the Oxygen Reduction Mechanism in Nonaqueous Li–O 2 Batteries

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

Liu, Bin; Xu, Wu; Zheng, Jianming

The temperature dependence of the oxygen reduction mechanism in Li-O 2 batteries was investigated using carbon nanotube-based air electrodes and 1,2-dimethoxyethane-based electrolyte within a temperature range of 20C to 40C. It is found that the discharge capacity of the Li-O 2 batteries decreases from 7,492 mAh g -1 at 40C to 2,930 mAh g -1 at 0C. However, a sharp increase in capacity was found when the temperature was further decreased and a very high capacity of 17,716 mAh g -1 was observed at 20C at a current density of 0.1 mA cm-2. When the temperature increases from 20C tomore » 40C, the morphologies of the Li 2O 2 formed varied from ultra-small spherical particles to small flakes and then to large flake-stacked toroids. The lifetime of superoxide and the solution pathway play a dominate role on the battery capacity in the temperature range of -20C to 0C, but the electrochemical kinetics of oxygen reduction and the surface pathway dominate the discharge behavior in the temperature range of 0C to 40C. These findings provide fundamental understanding on the temperature dependence of oxygen reduction process in a Li-O 2 battery and will enable a more rational design of Li-O 2 batteries.« less

Biomimetic Superhydrophobic Hollowed-Out Pyramid Surface Based on Self-Assembly.

PubMed

Luo, Weipeng; Yu, Bin; Xiao, Dingbang; Zhang, Meng; Wu, Xuezhong; Li, Guoxi

2018-05-16

In this paper, we present a periodic hollowed-out pyramid microstructure with excellent superhydrophobicity. In our approach, T-topping pillars and capillary-induced self-assembly methods were combined with the photolithography process to fabricate a hollowed-out pyramid structure. First, a wideband ultraviolet source without a filter was used to fabricate the T-topping pillars during the exposure process; then, the evaporation-induced assembly collapsed the pillars and formed the hollowed-out pyramid structure. Scanning electron microscopy images showed the microstructures of the prepared surface. The contact angle of the surface was 154°. The surface showed excellent high temperature and ultraviolet irradiation tolerance, and the contact angle of the surface barely changed when the temperature dropped. This excellent environmental durability of our superhydrophobic surface has potential applications for self-cleaning and friction drag reduction under water.

Annealing effects on electron-beam evaporated Al 2O 3 films

NASA Astrophysics Data System (ADS)

Shuzhen, Shang; Lei, Chen; Haihong, Hou; Kui, Yi; Zhengxiu, Fan; Jianda, Shao

2005-04-01

The effects of post-deposited annealing on structure and optical properties of electron-beam evaporated Al 2O 3 single layers were investigated. The films were annealed in air for 1.5 h at different temperatures from 250 to 400 °C. The optical constants and cut-off wavelength were deduced. Microstructure of the samples was characterized by X-ray diffraction (XRD). Profile and surface roughness measurement instrument was used to determine the rms surface roughness. It was found that the cut-off wavelength shifted to short wavelength as the annealing temperature increased and the total optical loss decreased. The film structure remained amorphous even after annealing at 400 °C temperature and the samples annealed at higher temperature had the higher rms surface roughness. The decreasing total optical loss with annealing temperature was attributed to the reduction of absorption owing to oxidation of the film by annealing. Guidance to reduce the optical loss of excimer laser mirrors was given.

Evaluation of the Effect of Surface Finish on High-Cycle Fatigue of SLM-IN718

NASA Technical Reports Server (NTRS)

Lambert, D. M.

2016-01-01

The surface finish of parts produced by additive manufacturing processes is much rougher than the surface finish generated by machining processes, and a rougher surface can reduce the fatigue strength of a part. This paper discusses an effort to quantify that reduction of strength in high-cycle fatigue for selective laser melt (SLM) coupons. A high-cycle fatigue (HCF) knockdown factor was estimated for Inconel 718, manufactured with the SLM process. This factor is the percentage reduction from the maximum stress in fatigue for low-stress ground (LSG) specimens to the maximum stress of those left with the original surface condition at the same fatigue life. Specimens were provided by a number of vendors, free to use their "best practice"; only one heat treat condition was considered; and several test temperatures were characterized, including room temperature, 800F, 1000F, and 1200F. The 1000F data had a large variance, and was omitted from consideration in this document. A first method used linear approximations extracted from the graphs, and only where data was available for both. A recommended knockdown factor of the as-built surface condition (average roughness of approximately 245 micro-inches/inch) versus low-stress ground condition (roughness no more than 4 micro-inches/inch) was established at approximately 1/3 or 33%. This is to say that for the as-built surface condition, a maximum stress of 2/3 of the stress for LSG can be expected to produce a similar life in the as-built surface condition. In this first evaluation, the knockdown factor did not appear to be a function of temperature. A second approach, the "KP method", incorporated the surface finish measure into a new parameter termed the pseudo-stress intensity factor, Kp, which was formulated to be similar to the fracture mechanics stress intensity factor. Using Kp, the variance seemed to be reduced across all sources, and knockdown factors were estimated using Kp over the range where data occurred. A plot of the results suggests that the knockdown factor is a function of temperature, and that for low lives the knockdown might be lower than the knockdown observed above about one million cycles, where it tended to stabilize. This was not universal for all temperatures tested. The higher temperature tests are thought to be influenced by the test temperature, which perhaps continued the aging process. Further evaluation of the method is suggested.

Influence of ground surface characteristics on the mean radiant temperature in urban areas.

PubMed

Lindberg, Fredrik; Onomura, Shiho; Grimmond, C S B

2016-09-01

The effect of variations in land cover on mean radiant temperature (T mrt ) is explored through a simple scheme developed within the radiation model SOLWEIG. Outgoing longwave radiation is parameterised using surface temperature observations on a grass and an asphalt surface, whereas outgoing shortwave radiation is modelled through variations in albedo for the different surfaces. The influence of ground surface materials on T mrt is small compared to the effects of shadowing. Nevertheless, altering ground surface materials could contribute to a reduction in T mrt to reduce the radiant load during heat-wave episodes in locations where shadowing is not an option. Evaluation of the new scheme suggests that despite its simplicity it can simulate the outgoing fluxes well, especially during sunny conditions. However, it underestimates at night and in shadowed locations. One grass surface used to develop the parameterisation, with very different characteristics compared to an evaluation grass site, caused T mrt to be underestimated. The implications of using high temporal resolution (e.g. 15 minutes) meteorological forcing data under partly cloudy conditions are demonstrated even for fairly proximal sites.

The Hydrological Impact of Geoengineering in the Geoengineering Model Intercomparison Project (GeoMIP)

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

Tilmes, S.; Fasullo, John; Lamarque, J.-F.

2013-10-14

Abstract: The hydrologic impact of enhancing Earth’s albedo due to solar radiation management (SRM) is investigated using simulations from 12 models contributing to the Geoengineering Model Intercomparison Project (GeoMIP). An artificial experiment is investigated, where global mean temperature is preserved at pre-industrial conditions, while atmospheric carbon dioxide concentrations are quadrupled. The associated reduction of downwelling surface solar radiation in a high CO2 environment leads to a reduction of global evaporation of 10% and 4% and precipitation of 6.1% and 6.3% over land and ocean, respectively. An initial reduction of latent heat flux at the surface is largely driven by reducedmore » evapotranspiration over land with instantly increasing CO2 concentrations in both experiments. A warming surface associated with the transient adjustment in the 4xCO2 experiment further generates an increase of global precipitation, with considerable regional changes, such as a significant precipitation reduction of 7% for the North American summer monsoon. Reduced global precipitation persists in the geoengineered experiment where temperatures are stabilized, with considerable regional rainfall deficits. Precipitation reductions that are consistent in sign across models are identified in the geoengineered experiment over monsoonal land regions of East Asia (6%), North America (7%), South America (6%) and South Africa (5%). In contrast to the 4xCO2 experiment, where the frequency of months with heavy precipitation intensity is increased by over 50%, it is reduced by up to 20% in the geoengineering scenario . The reduction in heavy precipitation is more pronounced over land than over the ocean, and accompanies a stronger reduction in evaporation over land. For northern mid-latitudes, maximum precipitation reduction over land ranges from 1 to 16% for individual models. For 45-65°N, the frequency of median to high intensity precipitation in summer is strongly reduced. These changes in precipitation in both total amount and frequency of extremes, point to a considerable weakening of the hydrological cycle in a geoengineered world.« less

Evaluation on the Nanoscale Zero Valent Iron Based Microbial Denitrification for Nitrate Removal from Groundwater

NASA Astrophysics Data System (ADS)

Peng, Lai; Liu, Yiwen; Gao, Shu-Hong; Chen, Xueming; Xin, Pei; Dai, Xiaohu; Ni, Bing-Jie

2015-07-01

Nanoscale zero valent iron (NZVI) based microbial denitrification has been demonstrated to be a promising technology for nitrate removal from groundwater. In this work, a mathematical model is developed to evaluate the performance of this new technology and to provide insights into the chemical and microbial interactions in the system in terms of nitrate reduction, ammonium accumulation and hydrogen turnover. The developed model integrates NZVI-based abiotic reduction of nitrate, NZVI corrosion for hydrogen production and hydrogen-based microbial denitrification and satisfactorily describes all of the nitrate and ammonium dynamics from two systems with highly different conditions. The high NZVI corrosion rate revealed by the model indicates the high reaction rate of NZVI with water due to their large specific surface area and high surface reactivity, leading to an effective microbial nitrate reduction by utilizing the produced hydrogen. The simulation results further suggest a NZVI dosing strategy (3-6 mmol/L in temperature range of 30-40 °C, 6-10 mmol/L in temperature range of 15-30 °C and 10-14 mmol/L in temperature range of 5-15 °C) during groundwater remediation to make sure a low ammonium yield and a high nitrogen removal efficiency.

Evaluation on the Nanoscale Zero Valent Iron Based Microbial Denitrification for Nitrate Removal from Groundwater

PubMed Central

Peng, Lai; Liu, Yiwen; Gao, Shu-Hong; Chen, Xueming; Xin, Pei; Dai, Xiaohu; Ni, Bing-Jie

2015-01-01

Nanoscale zero valent iron (NZVI) based microbial denitrification has been demonstrated to be a promising technology for nitrate removal from groundwater. In this work, a mathematical model is developed to evaluate the performance of this new technology and to provide insights into the chemical and microbial interactions in the system in terms of nitrate reduction, ammonium accumulation and hydrogen turnover. The developed model integrates NZVI-based abiotic reduction of nitrate, NZVI corrosion for hydrogen production and hydrogen-based microbial denitrification and satisfactorily describes all of the nitrate and ammonium dynamics from two systems with highly different conditions. The high NZVI corrosion rate revealed by the model indicates the high reaction rate of NZVI with water due to their large specific surface area and high surface reactivity, leading to an effective microbial nitrate reduction by utilizing the produced hydrogen. The simulation results further suggest a NZVI dosing strategy (3–6 mmol/L in temperature range of 30–40 °C, 6–10 mmol/L in temperature range of 15–30 °C and 10–14 mmol/L in temperature range of 5–15 °C) during groundwater remediation to make sure a low ammonium yield and a high nitrogen removal efficiency. PMID:26199053

Optimum deposition conditions of ultrasmooth silver nanolayers

PubMed Central

2014-01-01

Reduction of surface plasmon-polariton losses due to their scattering on metal surface roughness still remains a challenge in the fabrication of plasmonic devices for nanooptics. To achieve smooth silver films, we study the dependence of surface roughness on the evaporation temperature in a physical vapor deposition process. At the deposition temperature range 90 to 500 K, the mismatch of thermal expansion coefficients of Ag, Ge wetting layer, and sapphire substrate does not deteriorate the metal surface. To avoid ice crystal formation on substrates, the working temperature of the whole physical vapor deposition process should exceed that of the sublimation at the evaporation pressure range. At optimum room temperature, the root-mean-square (RMS) surface roughness was successfully reduced to 0.2 nm for a 10-nm Ag layer on sapphire substrate with a 1-nm germanium wetting interlayer. Silver layers of 10- and 30-nm thickness were examined using an atomic force microscope (AFM), X-ray reflectometry (XRR), and two-dimensional X-ray diffraction (XRD2). PACS 63.22.Np Layered systems; 68. Surfaces and interfaces; thin films and nanosystems (structure and nonelectronic properties); 81.07.-b Nanoscale materials and structures: fabrication and characterization PMID:24685115

Internal stress-induced melting below melting temperature at high-rate laser heating

NASA Astrophysics Data System (ADS)

Hwang, Yong Seok; Levitas, Valery I.

2014-06-01

In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67 K for a stress-free condition down to 898.1 K for uniaxial strain and to 920.8 K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamic equilibrium temperatures for the heating rate Q ≤1.51×1010K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1 K for Q = 1.51 × 1011 K/s and 936.9 K for Q = 1.46 × 1012 K/s.

On the Impact of Wind Farms on a Convective Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Lu, Hao; Porté-Agel, Fernando

2015-10-01

With the rapid growth in the number of wind turbines installed worldwide, a demand exists for a clear understanding of how wind farms modify land-atmosphere exchanges. Here, we conduct three-dimensional large-eddy simulations to investigate the impact of wind farms on a convective atmospheric boundary layer. Surface temperature and heat flux are determined using a surface thermal energy balance approach, coupled with the solution of a three-dimensional heat equation in the soil. We study several cases of aligned and staggered wind farms with different streamwise and spanwise spacings. The farms consist of Siemens SWT-2.3-93 wind turbines. Results reveal that, in the presence of wind turbines, the stability of the atmospheric boundary layer is modified, the boundary-layer height is increased, and the magnitude of the surface heat flux is slightly reduced. Results also show an increase in land-surface temperature, a slight reduction in the vertically-integrated temperature, and a heterogeneous spatial distribution of the surface heat flux.

PROCESS FOR PRODUCTION OF URANIUM

DOEpatents

Crawford, J.W.C.

1959-09-29

A process is described for the production of uranium by the autothermic reduction of an anhydrous uranium halide with an alkaline earth metal, preferably magnesium One feature is the initial reduction step which is brought about by locally bringing to reaction temperature a portion of a mixture of the reactants in an open reaction vessel having in contact with the mixture a lining of substantial thickness composed of calcium fluoride. The lining is prepared by coating the interior surface with a plastic mixture of calcium fluoride and water and subsequently heating the coating in situ until at last the exposed surface is substantially anhydrous.

Enhanced hydrothermal stability of Cu-ZSM-5 catalyst via surface modification in the selective catalytic reduction of NO with NH3

NASA Astrophysics Data System (ADS)

Zhang, Tao; Shi, Juan; Liu, Jian; Wang, Daxi; Zhao, Zhen; Cheng, Kai; Li, Jianmei

2016-07-01

The surface of Cu-ZSM-5 catalyst was modified by chemical liquid deposition (CLD) of tetraethoxysilane (TEOS) for enhancing its hydrothermal stability in the selective catalytic reduction of NO with NH3. After hydrothermal aging at 750 °C for 13 h, the catalytic performance of Cu-ZSM-5-Aged catalyst was significantly reduced for NO reduction in the entire temperature range, while that of Cu-ZSM-5-CLD-Aged catalyst was affected very little. The characterization results indicated that an inert silica layer was deposited on the surface of Cu-ZSM-5 and formed a protective layer, which prevents the detachment of Cu2+ from ZSM-5 ion-exchange positions and the dealumination of zeolite during the hydrothermal aging process. Based on the data it is hypothesized to be the primary reason for the high hydrothermal stability of Cu-ZSM-5-CLD catalyst.

Kinetics and mechanisms of iron sulfide reductions in hydrogen and in carbon monoxide

USGS Publications Warehouse

Wiltowski, T.; Hinckley, C.C.; Smith, Gerard V.; Nishizawa, T.; Saporoschenko, Mykola; Shiley, R.H.; Webster, J.R.

1987-01-01

The reduction of iron sulfides by hydrogen and by carbon monoxide has been studied using plug flow and thermogravimetric methods. The reactions were studied in the 523-723??K temperature range and were found to be first-order processes. Plug flow studies were used to correlate reaction rates between pyrite and the gases as a function of the surface area of the pyrite. The rate of H2S formation increases with the surface area of the pyrite sample. The results of thermogravimetric experiments indicate that the reactions consist of several steps. Rate constants for the pyrite reduction by H2 and by CO were obtained. The activation energies increased with degree of reduction. Values of Ea were 113.2 (step I) and 122.5 kJ/mole (step II) for pyrite reduction with CO and 99.4 (step I), 122.4 (step II), 125.2 (step III), and 142.6 kJ/mole (step IV) for pyrite reduction with hydrogen. ?? 1987.

Evidence and mechanism of Hurricane Fran-Induced ocean cooling in the Charleston Trough

NASA Astrophysics Data System (ADS)

Xie, Lian; Pietrafesa, L. J.; Bohm, E.; Zhang, C.; Li, X.

Evidence of enhanced sea surface cooling during and following the passage of Hurricane Fran in September 1996 over an oceanic depression located on the ocean margin offshore of Charleston, South Carolina (referred to as the Charleston Trough), [Pietrafesa, 1983] is documented. Approximately 4C° of sea surface temperature (SST) reduction within the Charleston Trough following the passage of Hurricane Fran was estimated based on SST imagery from Advanced Very High Resolution Radiometer (AVHRR) on the NOAA-14 polar orbiting satellite. Simulations using a three-dimensional coastal ocean model indicate that the largest SST reduction occurred within the Charleston Trough. This SST reduction can be explained by oceanic mixing due to storm-induced internal inertia-gravity waves.

Deleterious Thermal Effects due to Randomized Flow Paths in Pebble Bed, and Particle Bed Style Reactors

NASA Technical Reports Server (NTRS)

Moran, Robert P.

2013-01-01

Reactor fuel rod surface area that is perpendicular to coolant flow direction (+S) i.e. perpendicular to the P creates areas of coolant stagnation leading to increased coolant temperatures resulting in localized changes in fluid properties. Changes in coolant fluid properties caused by minor increases in temperature lead to localized reductions in coolant mass flow rates leading to localized thermal instabilities. Reductions in coolant mass flow rates result in further increases in local temperatures exacerbating changes to coolant fluid properties leading to localized thermal runaway. Unchecked localized thermal runaway leads to localized fuel melting. Reactor designs with randomized flow paths are vulnerable to localized thermal instabilities, localized thermal runaway, and localized fuel melting.

Vapor phase growth technique of III-V compounds utilizing a preheating step

NASA Technical Reports Server (NTRS)

Olsen, Gregory Hammond (Inventor); Zamerowski, Thomas Joseph (Inventor); Buiocchi, Charles Joseph (Inventor)

1978-01-01

In the vapor phase epitaxy fabrication of semiconductor devices and in particular semiconductor lasers, the deposition body on which a particular layer of the laser is to be grown is preheated to a temperature about 40.degree. to 60.degree. C. lower than the temperature at which deposition occurs. It has been discovered that by preheating at this lower temperature there is reduced thermal decomposition at the deposition surface, especially for semiconductor materials such as indium gallium phosphide and gallium arsenide phosphide. A reduction in thermal decomposition reduces imperfections in the deposition body in the vicinity of the deposition surface, thereby providing a device with higher efficiency and longer lifetime.

A significant reduction of ice adhesion on nanostructured surfaces that consist of an array of single-walled carbon nanotubes: A molecular dynamics simulation study

NASA Astrophysics Data System (ADS)

Bao, Luyao; Huang, Zhaoyuan; Priezjev, Nikolai V.; Chen, Shaoqiang; Luo, Kai; Hu, Haibao

2018-04-01

It is well recognized that excessive ice accumulation at low-temperature conditions can cause significant damage to civil infrastructure. The passive anti-icing surfaces provide a promising solution to suppress ice nucleation and enhance ice removal. However, despite extensive efforts, it remains a challenge to design anti-icing surfaces with low ice adhesion. Using all-atom molecular dynamics (MD) simulations, we show that surfaces with single-walled carbon nanotube array (CNTA) significantly reduce ice adhesion due to the extremely low solid areal fraction. It was found that the CNTA surface exhibits up to a 45% decrease in the ice adhesion strength in comparison with the atomically smooth graphene surface. The details of the ice detachment from the CNTA surface were examined for different water-carbon interaction energies and temperatures of the ice cube. Remarkably, the results of MD simulations demonstrate that the ice detaching strength depends linearly on the ratio of the ice-surface interaction energy and the ice temperature. These results open the possibility for designing novel robust surfaces with low ice adhesion for passive anti-icing applications.

Albedo as a modulator of climate response to tropical deforestation

NASA Technical Reports Server (NTRS)

Dirmeyer, Paul A.; Shukla, J.

1994-01-01

An atmospheric general circulation model with land surface properties represented by the simplified Simple Biosphere model is used to investigate the effects on local climate due to tropical deforestation for the Amazon basin. One control and three anomaly integrations of 4 years' duration are performed. In the anomaly integrations, rain forest in South America is replaced by degraded grassland. The anomaly integrations differ only in the optical properties of the grassland vegetation, with net surface albedos ranging from the same as to 0.09 lighter than that of rain forest. It is found that the change in climate, particularly rainfall, is strongly dependent on the change in surface albedo that accompanies deforestation. Replacement of forest by grass causes a reduction in transpiration and reduces frictional convergence by decreasing surface roughness. However, precipitation averaged over the deforested area is not necessarily reduced. Average precipitation decreases when the increase in albedo is greater than 0.03. If surface albedo is not increased appreciably as a result of deforestation, moisture flux convergence driven by the increase in surface temperature can offset the other effects, and average precipitation increases. As albedo is increased, surface temperature does not change, but surface latent and sensible heat flux decreases due to reduced radiational energy absorbed at the surface, resulting in a reduction in convection and precipitation. A change in the distribution of precipitation due to deforestation that appears to be independent of the albedo is observed.

Albedo as a modulator of climate response to tropical deforestation

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

Dirmeyer, P.A.; Shukla, J.

1994-10-01

An atmospheric general circulation model with land surface properties represented by the simplified Simple Biosphere model is used to investigate the effects on local climate due to tropical deforestation for the Amazon basin. One control and three anomaly integrations of 4 years` duration are performed. In the anomaly integrations, rain forest in South America is replaced by degraded grassland. The anomaly integrations differ only in the optical properties of the grassland vegetation, with net surface albedos ranging from the same as to 0.09 lighter than that of rain forest. It is found that the change in climate, particularly rainfall, ismore » strongly dependent on the change in surface albedo that accompanies deforestation. Replacement of forest by grass causes a reduction in transpiration and reduces frictional convergence by decreasing surface roughness. However, precipitation averaged over the deforested area is not necessarily reduced. Average precipitation decreases when the increase in albedo is greater than 0.03. If surface albedo is not increased appreciably as a result of deforestation, moisture flux convergence driven by the increase in surface temperature can offset the other effects, and average precipitation increases. As albedo is increased, surface temperature does not change, but surface latent and sensible heat flux decreases due to reduced radiational energy absorbed at the surface, resulting in a reduction in convection and precipitation. A change in the distribution of precipitation due to deforestation that appears to be independent of the albedo is observed.« less

An experimental investigation of temperature rise during compaction of pharmaceutical powders.

PubMed

Krok, Alexander; Mirtic, Andreja; Reynolds, Gavin K; Schiano, Serena; Roberts, Ron; Wu, Chuan-Yu

2016-11-20

During pharmaceutical powder compaction, temperature rise in the compressed powder can affect physiochemical properties of the powder, such as thermal degradation and change in crystallinity. Thus, it is of practical importance to understand the effect of process conditions and material properties on the thermal response of pharmaceutical formulations during compaction. The aim of this study was to examine the temperature rise of pharmaceutical powders during tableting, in particular, to explore how the temperature rise depends on material properties, compression speed and tablet shape. Three grades of microcrystalline cellulose (MCC) were considered: MCC Avicel pH 101, MCC Avicel pH 102 and MCC DG. These powders were compressed using a compaction simulator at various compaction speeds (10-500mm/s). Flat faced, shallow convex and normal convex tablets were produced and temperature distributions on the surface of theses tablets upon ejection were examined using an infrared thermoviewer. It was found that an increase in the compaction speed led to an increase in the average surface temperature. A higher surface temperature was induced when the powder was compressed into a tablet with larger surface curvature. This was primarily due to the increasing degree of powder deformation (i.e. the volume reduction) and the effect of interparticule/wall friction. Copyright © 2016 Elsevier B.V. All rights reserved.

The role of carbonaceous aerosols on short-term variations of precipitation over North Africa

DOE PAGES

Yoon, Jin -Ho; Rasch, Philip J.; Wang, Hailong; ...

2016-06-16

Northern Africa has been subject to extensive droughts in the late 20th century, which are frequently linked to changes in the Sea Surface Temperature (SST) in both the Atlantic and Indian Oceans. However, climate models forced by observed Sea Surface Temperatures have been unable to reproduce the magnitude of rainfall reduction over the last several decades. In this study, we propose that aerosol indirect effects (AIE) may be an important feedback mechanism to contribute this recent reduction. The climate model used here has a fully predictive aerosol life cycle. Results are presented for a set of sensitivity experiments designed tomore » distinguish the role of aerosol direct/semi-­direct and indirect effects on regional precipitation. Changes in cloud lifetime due to the presence of carbonaceous aerosols are proposed as a key mechanism to explain the reduced rainfall over the tropical and North Africa.« less

Evidence of enzymatic catalysis of oxygen reduction on stainless steels under marine biofilm.

PubMed

Faimali, Marco; Benedetti, Alessandro; Pavanello, Giovanni; Chelossi, Elisabetta; Wrubl, Federico; Mollica, Alfonso

2011-04-01

Cathodic current trends on stainless steel samples with different surface percentages covered by biofilm and potentiostatically polarized in natural seawater were studied under oxygen concentration changes, temperature increases, and additions of enzymic inhibitors to the solution. The results showed that on each surface fraction covered by biofilm the oxygen reduction kinetics resembled a reaction catalyzed by an immobilised enzyme with high oxygen affinity (apparent Michaelis-Menten dissociation constant close to K(O(2))(M)  ≈ 10 μM) and low activation energy (W ≈ 20 KJ mole(-1)). The proposed enzyme rapidly degraded when the temperature was increased above the ambient (half-life time of ∼1 day at 25°C, and of a few minutes at 50°C). Furthermore, when reversible enzymic inhibitors (eg sodium azide and cyanide) were added, the cathodic current induced by biofilm growth was inhibited.

Preliminary Report on Oak Ridge National Laboratory Testing of Drake/ACSS/MA2/E3X

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

Irminger, Philip; King, Daniel J.; Herron, Andrew N.

2016-01-01

A key to industry acceptance of a new technology is extensive validation in field trials. The Powerline Conductor Accelerated Test facility (PCAT) at Oak Ridge National Laboratory (ORNL) is specifically designed to evaluate the performance and reliability of a new conductor technology under real world conditions. The facility is set up to capture large amounts of data during testing. General Cable used the ORNL PCAT facility to validate the performance of TransPowr with E3X Technology a standard overhead conductor with an inorganic high emissivity, low absorptivity surface coating. Extensive testing has demonstrated a significant improvement in conductor performance across amore » wide range of operating temperatures, indicating that E3X Technology can provide a reduction in temperature, a reduction in sag, and an increase in ampacity when applied to the surface of any overhead conductor. This report provides initial results of that testing.« less

Natural manganese ore catalyst for low-temperature selective catalytic reduction of NO with NH3 in coke-oven flue gas.

PubMed

Zhu, Baozhong; Yin, Shoulai; Sun, Yunlan; Zhu, Zicheng; Li, Jiaxin

2017-11-01

Different types of manganese ore raw materials were prepared for use as catalysts, and the effects of different manganese ore raw materials and calcination temperature on the NO conversion were analyzed. The catalysts were characterized by XRF, XRD, BET, XPS, H 2 -TPR, NH 3 -TPD, and SEM techniques. The results showed that the NO conversion of calcined manganese ore with a Mn:Fe:Al:Si ratio of 1.51:1.26:0.34:1 at 450 °C reached 80% at 120 °C and 98% at 180~240 °C. The suitable proportions and better dispersibility of active ingredients, larger BET surface area, good reductibility, a lot of acid sites, contents of Mn 4+ and Fe 3+ , and surface-adsorbed oxygen played important roles in improving the NO conversion.

The role of carbonaceous aerosols on short-term variations of precipitation over North Africa

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

Yoon, Jin -Ho; Rasch, Philip J.; Wang, Hailong

Northern Africa has been subject to extensive droughts in the late 20th century, which are frequently linked to changes in the Sea Surface Temperature (SST) in both the Atlantic and Indian Oceans. However, climate models forced by observed Sea Surface Temperatures have been unable to reproduce the magnitude of rainfall reduction over the last several decades. In this study, we propose that aerosol indirect effects (AIE) may be an important feedback mechanism to contribute this recent reduction. The climate model used here has a fully predictive aerosol life cycle. Results are presented for a set of sensitivity experiments designed tomore » distinguish the role of aerosol direct/semi-­direct and indirect effects on regional precipitation. Changes in cloud lifetime due to the presence of carbonaceous aerosols are proposed as a key mechanism to explain the reduced rainfall over the tropical and North Africa.« less

In-Flight Validation of Mid and Thermal Infrared Remotely Sensed Data Using the Lake Tahoe and Salton Sea Automated Validation Sites

NASA Technical Reports Server (NTRS)

Hook, Simon J.

2008-01-01

The presentation includes an introduction, Lake Tahoe site layout and measurements, Salton Sea site layout and measurements, field instrument calibration and cross-calculations, data reduction methodology and error budgets, and example results for MODIS. Summary and conclusions are: 1) Lake Tahoe CA/NV automated validation site was established in 1999 to assess radiometric accuracy of satellite and airborne mid and thermal infrared data and products. Water surface temperatures range from 4-25C.2) Salton Sea CA automated validation site was established in 2008 to broaden range of available water surface temperatures and atmospheric water vapor test cases. Water surface temperatures range from 15-35C. 3) Sites provide all information necessary for validation every 2 mins (bulk temperature, skin temperature, air temperature, wind speed, wind direction, net radiation, relative humidity). 4) Sites have been used to validate mid and thermal infrared data and products from: ASTER, AATSR, ATSR2, MODIS-Terra, MODIS-Aqua, Landsat 5, Landsat 7, MTI, TES, MASTER, MAS. 5) Approximately 10 years of data available to help validate AVHRR.

In-vacuum scattered light reduction with black cupric oxide surfaces for sensitive fluorescence detection.

PubMed

Norrgard, E B; Sitaraman, N; Barry, J F; McCarron, D J; Steinecker, M H; DeMille, D

2016-05-01

We demonstrate a simple and easy method for producing low-reflectivity surfaces that are ultra-high vacuum compatible, may be baked to high temperatures, and are easily applied even on complex surface geometries. Black cupric oxide (CuO) surfaces are chemically grown in minutes on any copper surface, allowing for low-cost, rapid prototyping, and production. The reflective properties are measured to be comparable to commercially available products for creating optically black surfaces. We describe a vacuum apparatus which uses multiple blackened copper surfaces for sensitive, low-background detection of molecules using laser-induced fluorescence.

Facile Quantification and Identification Techniques for Reducing Gases over a Wide Concentration Range Using a MOS Sensor in Temperature-Cycled Operation.

PubMed

Schultealbert, Caroline; Baur, Tobias; Schütze, Andreas; Sauerwald, Tilman

2018-03-01

Dedicated methods for quantification and identification of reducing gases based on model-based temperature-cycled operation (TCO) using a single commercial MOS gas sensor are presented. During high temperature phases the sensor surface is highly oxidized, yielding a significant sensitivity increase after switching to lower temperatures (differential surface reduction, DSR). For low concentrations, the slope of the logarithmic conductance during this low-temperature phase is evaluated and can directly be used for quantification. For higher concentrations, the time constant for reaching a stable conductance during the same low-temperature phase is evaluated. Both signals represent the reaction rate of the reducing gas on the strongly oxidized surface at this low temperature and provide a linear calibration curve, which is exceptional for MOS sensors. By determining these reaction rates on different low-temperature plateaus and applying pattern recognition, the resulting footprint can be used for identification of different gases. All methods are tested over a wide concentration range from 10 ppb to 100 ppm (4 orders of magnitude) for four different reducing gases (CO, H₂, ammonia and benzene) using randomized gas exposures.

Facile Quantification and Identification Techniques for Reducing Gases over a Wide Concentration Range Using a MOS Sensor in Temperature-Cycled Operation

PubMed Central

Schultealbert, Caroline; Baur, Tobias; Schütze, Andreas; Sauerwald, Tilman

2018-01-01

Dedicated methods for quantification and identification of reducing gases based on model-based temperature-cycled operation (TCO) using a single commercial MOS gas sensor are presented. During high temperature phases the sensor surface is highly oxidized, yielding a significant sensitivity increase after switching to lower temperatures (differential surface reduction, DSR). For low concentrations, the slope of the logarithmic conductance during this low-temperature phase is evaluated and can directly be used for quantification. For higher concentrations, the time constant for reaching a stable conductance during the same low-temperature phase is evaluated. Both signals represent the reaction rate of the reducing gas on the strongly oxidized surface at this low temperature and provide a linear calibration curve, which is exceptional for MOS sensors. By determining these reaction rates on different low-temperature plateaus and applying pattern recognition, the resulting footprint can be used for identification of different gases. All methods are tested over a wide concentration range from 10 ppb to 100 ppm (4 orders of magnitude) for four different reducing gases (CO, H2, ammonia and benzene) using randomized gas exposures. PMID:29494545

Impact of the GeoMIP G1 sunshade geoengineering experiment on the Atlantic meridional overturning circulation

NASA Astrophysics Data System (ADS)

Hong, Yu; Moore, John C.; Jevrejeva, Svetlana; Ji, Duoying; Phipps, Steven J.; Lenton, Andrew; Tilmes, Simone; Watanabe, Shingo; Zhao, Liyun

2017-03-01

We analyze the multi-earth system model responses of ocean temperatures and the Atlantic Meridional Overturning Circulation (AMOC) under an idealized solar radiation management scenario (G1) from the Geoengineering Model Intercomparison Project. All models simulate warming of the northern North Atlantic relative to no geoengineering, despite geoengineering substantially offsetting the increases in mean global ocean temperatures. Increases in the temperature of the North Atlantic Ocean at the surface (˜0.25 K) and at a depth of 500 m (˜0.10 K) are mainly due to a 10 Wm-2 reduction of total heat flux from ocean to atmosphere. Although the AMOC is slightly reduced under the solar dimming scenario, G1, relative to piControl, it is about 37% stronger than under abrupt4 × CO2 . The reduction of the AMOC under G1 is mainly a response to the heat flux change at the northern North Atlantic rather than to changes in the water flux and the wind stress. The AMOC transfers heat from tropics to high latitudes, helping to warm the high latitudes, and its strength is maintained under solar dimming rather than weakened by greenhouse gas forcing acting alone. Hence the relative reduction in high latitude ocean temperatures provided by solar radiation geoengineering, would tend to be counteracted by the correspondingly active AMOC circulation which furthermore transports warm surface waters towards the Greenland ice sheet, warming Arctic sea ice and permafrost.

Regeneration and sulfur poisoning behavior of In/H-BEA catalyst for NOx reduction by CH4

NASA Astrophysics Data System (ADS)

Pan, Hua; Jian, Yanfei; Yu, Yanke; He, Chi; Shen, Zhenxing; Liu, Hongxia

2017-04-01

Sulfur poisoning and regeneration behavior of In/H-BEA catalyst were carried out in NOx reduction by CH4. In/H-BEA catalyst exhibited a poor resistance to sulfur dioxide after addition of 200 ppm SO2 and 10 vol.% H2O into NO reduction with CH4 at 450 °C for 45 h. Sulfur poisoning of In/H-BEA was attributed to the inhibition of NOx adsorption on Brønsted acid sites, suppression of reaction intermediates generation on the active sites, and the formation of surface sulfate species. The formation of surface sulfate reduced the availability of surface active sites, blocked the pore structure and decreased the surface area of catalyst. These changes in chemical and textural properties resulted in a severe loss in the activity of sulfated In/H-BEA catalyst for NO reduction with CH4. H2 reduction is a promising technology for regeneration of In/H-BEA deactivated by SO2 for removing NOx from lean-burn and diesel exhausts. Indium sulfate could be reduced by H2 to InO+ with In2O3 and In(OH)2+ as the intermediates. The optimal parameters of H2 reduction was regeneration temperature of 400 °C and regeneration time of 60 min which completely recovered the catalytic activity of In/H-BEA.

Fungistatic activity of heat-treated flaxseed determined by response surface methodology.

PubMed

Xu, Y; Hall, C; Wolf-Hall, C

2008-08-01

The objective of this study was to evaluate the effect of heat treatment on the fungistatic activity of flaxseed (Linum usitatissimum) in potato dextrose agar (PDA) medium and a fresh noodle system. The radial growth of Penicilliumn chrysogenum, Aspergillus flavus, and a Penicillium sp. isolated from moldy noodles, as well as the mold count of fresh noodle enriched with heat treated flaxseed, were used to assess antifungal activity. A central composite design in the response surface methodology was used to predict the effect of heating temperature and time on antifungal activity of flaxseed flour (FF). Statistical analysis determined that the linear terms of both variables (that is, heating temperature and time) and the quadratic terms of the heating temperature had significant (P<0.05) effects on the radial growth of all 3 test fungi and the mold count log-cycle reduction of fresh noodle. The interactions between the temperature and time were significant for all dependent variables (P<0.05). Significant reductions in antifungal activities were found when FF was subjected to high temperatures, regardless of heating time. In contrast, prolonging the heating time did not substantially affect the antifungal activities of FF at low temperature. However, 60% of the antifungal activity was retained after FF was heated at 100 degrees C for 15 min, which suggests a potential use of FF as an antifungal additive in food products subjected to low to mild heat treatments.

Saharan Dust Event Impacts on Cloud Formation and Radiation over Western Europe

NASA Technical Reports Server (NTRS)

Bangert, M.; Nenes, A.; Vogel, B.; Vogel, H.; Barahona, D.; Karydis, V. A.; Kumar, P.; Kottmeier, C.; Blahak, U.

2013-01-01

We investigated the impact of mineral dust particles on clouds, radiation and atmospheric state during a strong Saharan dust event over Europe in May 2008, applying a comprehensive online-coupled regional model framework that explicitly treats particle-microphysics and chemical composition. Sophisticated parameterizations for aerosol activation and ice nucleation, together with two-moment cloud microphysics are used to calculate the interaction of the different particles with clouds depending on their physical and chemical properties. The impact of dust on cloud droplet number concentration was found to be low, with just a slight increase in cloud droplet number concentration for both uncoated and coated dust. For temperatures lower than the level of homogeneous freezing, no significant impact of dust on the number and mass concentration of ice crystals was found, though the concentration of frozen dust particles reached up to 100 l-1 during the ice nucleation events. Mineral dust particles were found to have the largest impact on clouds in a temperature range between freezing level and the level of homogeneous freezing, where they determined the number concentration of ice crystals due to efficient heterogeneous freezing of the dust particles and modified the glaciation of mixed phase clouds. Our simulations show that during the dust events, ice crystals concentrations were increased twofold in this temperature range (compared to if dust interactions are neglected). This had a significant impact on the cloud optical properties, causing a reduction in the incoming short-wave radiation at the surface up to -75Wm-2. Including the direct interaction of dust with radiation caused an additional reduction in the incoming short-wave radiation by 40 to 80Wm-2, and the incoming long-wave radiation at the surface was increased significantly in the order of +10Wm-2. The strong radiative forcings associated with dust caused a reduction in surface temperature in the order of -0.2 to -0.5K for most parts of France, Germany, and Italy during the dust event. The maximum difference in surface temperature was found in the East of France, the Benelux, and Western Germany with up to -1 K. This magnitude of temperature change was sufficient to explain a systematic bias in numerical weather forecasts during the period of the dust event.

Oxidation/reduction reactions at the metal contact-TlBr interface: an x-ray photoelectron spectroscopy study

NASA Astrophysics Data System (ADS)

Nelson, A. J.; Swanberg, E. L.; Voss, L. F.; Graff, R. T.; Conway, A. M.; Nikolic, R. J.; Payne, S. A.; Kim, H.; Cirignano, L.; Shah, K.

2014-09-01

TlBr radiation detector operation degrades with time at room temperature and is thought to be due to electromigration of Tl and Br vacancies within the crystal as well as the metal contacts migrating into the TlBr crystal itself due to electrochemical reactions at the metal/TlBr interface. X-ray photoemission spectroscopy (XPS) was used to investigate the metal contact surface/interfacial structure on TlBr devices. Device-grade TlBr was polished and subjected to a 32% HCl etch to remove surface damage prior to Mo or Pt contact deposition. High-resolution photoemission measurements on the Tl 4f, Br 3d, Cl 2p, Mo 3d and Pt 4f core lines were used to evaluate surface chemistry and non-equilibrium interfacial diffusion. Results indicate that anion substitution at the TlBr surface due to the HCl etch forms TlBr1-xClx with consequent formation of a shallow heterojunction. In addition, a reduction of Tl1+ to Tl0 is observed at the metal contacts after device operation in both air and N2 at ambient temperature. Understanding contact/device degradation versus operating environment is useful for improving radiation detector performance.

A technique for measurement of instantaneous heat transfer in steady-flow ambient-temperature facilities

NASA Technical Reports Server (NTRS)

O'Brien, James E.

1990-01-01

An experimental technique is described for obtaining time-resolved heat flux measurements with high-frequency response (up to 100 kHz) in a steady-flow ambient-temperature facility. The heat transfer test object is preheated and suddenly injected into an established steady flow. Thin-film gages deposited on the test surface detect the unsteady substrate surface temperature. Analog circuitry designed for use in short-duration facilities and based on one-dimensional semiinfinite heat conduction is used to perform the temperature/heat flux transformation. A detailed description of substrate properties, instrumentation, experimental procedure, and data reduction is given, along with representative results obtained in the stagnation region of a circular cylinder subjected to a wake-dominated unsteady flow. An in-depth discussion of related work is also provided.

Origin and evolution of surface spin current in topological insulators

NASA Astrophysics Data System (ADS)

Dankert, André; Bhaskar, Priyamvada; Khokhriakov, Dmitrii; Rodrigues, Isabel H.; Karpiak, Bogdan; Kamalakar, M. Venkata; Charpentier, Sophie; Garate, Ion; Dash, Saroj P.

2018-03-01

The Dirac surface states of topological insulators offer a unique possibility for creating spin polarized charge currents due to the spin-momentum locking. Here we demonstrate that the control over the bulk and surface contribution is crucial to maximize the charge-to-spin conversion efficiency. We observe an enhancement of the spin signal due to surface-dominated spin polarization while freezing out the bulk conductivity in semiconducting Bi1.5Sb0.5Te1.7Se1.3 below 100 K . Detailed measurements up to room temperature exhibit a strong reduction of the magnetoresistance signal between 2 and100 K , which we attribute to the thermal excitation of bulk carriers and to the electron-phonon coupling in the surface states. The presence and dominance of this effect up to room temperature is promising for spintronic science and technology.

Drastic reduction of adsorption of CO and H2 on (111)-type Pd layers

NASA Technical Reports Server (NTRS)

Poppa, H.; Soria, F.

1983-01-01

Clean surfaces of (111)-type Pd layers, grown from the vapor phase on Mo(110) at room temperature, were used to study the adsorption of CO and H2 by temperature-programmed desorption, Auger electron spectroscopy, and low-energy electron diffraction. Mild annealing of the as-grown layers during a single desorption cycle (to about 600 K) drastically reduces the adsorption for both adsorbates. Low-dose argon-ion bombardment introduces surface imperfections which restore a high adsorption probability. The results are interpreted in terms of particular (111)-type surface structures that persist tp layer thicknesses of about four monolayers; the results raise questions with respect to the surface structure of supported thin epitaxial islands and particles of Pd and possibly also with respect to conventional methods of preparing bulk surfaces of Pd for adsorption studies.

Removal of hexavalent Cr by coconut coir and derived chars--the effect of surface functionality.

PubMed

Shen, Ying-Shuian; Wang, Shan-Li; Tzou, Yu-Min; Yan, Ya-Yi; Kuan, Wen-Hui

2012-01-01

The Cr(VI) removal by coconut coir (CC) and chars obtained at various pyrolysis temperatures were evaluated. Increasing the pyrolysis temperature resulted in an increased surface area of the chars, while the corresponding content of oxygen-containing functional groups of the chars decreased. The Cr(VI) removal by CC and CC-derived chars was primarily attributed to the reduction of Cr(VI) to Cr(III) by the materials and the extent and rate of the Cr(VI) reduction were determined by the oxygen-containing functional groups in the materials. The contribution of pure Cr(VI) adsorption to the overall Cr(VI) removal became relatively significant for the chars obtained at higher temperatures. Accordingly, to develop a cost-effective method for removing Cr(VI) from water, the original CC is more advantageous than the carbonaceous counterparts because no pyrolysis is required for the application and CC has a higher content of functional groups for reducing Cr(VI) to less toxic Cr(III). Copyright © 2011 Elsevier Ltd. All rights reserved.

Low-resistance gateless high electron mobility transistors using three-dimensional inverted pyramidal AlGaN/GaN surfaces

NASA Astrophysics Data System (ADS)

So, Hongyun; Senesky, Debbie G.

2016-01-01

In this letter, three-dimensional gateless AlGaN/GaN high electron mobility transistors (HEMTs) were demonstrated with 54% reduction in electrical resistance and 73% increase in surface area compared with conventional gateless HEMTs on planar substrates. Inverted pyramidal AlGaN/GaN surfaces were microfabricated using potassium hydroxide etched silicon with exposed (111) surfaces and metal-organic chemical vapor deposition of coherent AlGaN/GaN thin films. In addition, electrical characterization of the devices showed that a combination of series and parallel connections of the highly conductive two-dimensional electron gas along the pyramidal geometry resulted in a significant reduction in electrical resistance at both room and high temperatures (up to 300 °C). This three-dimensional HEMT architecture can be leveraged to realize low-power and reliable power electronics, as well as harsh environment sensors with increased surface area.

Can uncertainties in sea ice albedo reconcile patterns of data-model discord for the Pliocene and 20th/21st centuries?

USGS Publications Warehouse

Howell, Fergus W.; Haywood, Alan M.; Dolan, Aisling M.; Dowsett, Harry J.; Francis, Jane E; Hill, Daniel J.; Pickering, Steven J.; Pope, James O.; Salzmann, Ulrich; Wade, Bidget S

2014-01-01

General Circulation Model simulations of the mid-Pliocene warm period (mPWP, 3.264 to 3.025 Myr ago) currently underestimate the level of warming that proxy data suggest existed at high latitudes, with discrepancies of up to 11°C for sea surface temperature estimates and 17°C for surface air temperature estimates. Sea ice has a strong influence on high-latitude climates, partly due to the albedo feedback. We present results demonstrating the effects of reductions in minimum sea ice albedo limits in general circulation model simulations of the mPWP. While mean annual surface air temperature increases of up to 6°C are observed in the Arctic, the maximum decrease in model-data discrepancies is just 0.81°C. Mean annual sea surface temperatures increase by up to 2°C, with a maximum model-data discrepancy improvement of 1.31°C. It is also suggested that the simulation of observed 21st century sea ice decline could be influenced by the adjustment of the sea ice albedo parameterization.

Heat transfer from high-temperature surfaces to fluids II : correlation of heat-transfer and friction data for air flowing in inconel tube with rounded entrance

NASA Technical Reports Server (NTRS)

Lowdermilk, Warren H; Grele, Milton D

1949-01-01

A heat transfer investigation, which was an extension of a previously reported NACA investigation, was conducted with air flowing through an electrically heated inconel tube with a rounded entrance,an inside diameter of 0.402 inch, and a length of 24 inches over a range of conditions, which included Reynolds numbers up to 500,000, average surface temperatures up to 2050 degrees R, and heat-flux densities up to 150,000 Btu per hour per square foot. Conventional methods of correlating heat-transfer data wherein properties of the air were evaluated at the average bulk, film, and surface temperatures resulted in reductions of Nusselt number of about 38, 46, and 53 percent, respectively, for an increase in surface temperature from 605 degrees to 2050 degrees R at constant Reynolds number. A modified correlation method in which the properties of air were based on the surface temperature and the Reynolds number was modified by substituting the product of the density at the inside tube wall and the bulk velocity for the conventional mass flow per unit cross-sectional area, resulted in a satisfactory correlation of the data for the extended ranges of conditions investigated.

Application of ozonated dry ice (ALIGAL™ Blue Ice) for packaging and transport in the food industry.

PubMed

Fratamico, Pina M; Juneja, Vijay; Annous, Bassam A; Rasanayagam, Vasuhi; Sundar, M; Braithwaite, David; Fisher, Steven

2012-05-01

Dry ice is used by meat and poultry processors for temperature reduction during processing and for temperature maintenance during transportation. ALIGAL™ Blue Ice (ABI), which combines the antimicrobial effect of ozone (O(3)) along with the high cooling capacity of dry ice, was investigated for its effect on bacterial reduction in air, in liquid, and on food and glass surfaces. Through proprietary means, O(3) was introduced to produce dry ice pellets to a concentration of 20 parts per million (ppm) by total weight. The ABI sublimation rate was similar to that of dry ice pellets under identical conditions, and ABI was able to hold the O(3) concentration throughout the normal shelf life of the product. Challenge studies were performed using different microorganisms, including E. coli, Campylobacter jejuni, Salmonella, and Listeria, that are critical to food safety. ABI showed significant (P < 0.05) microbial reduction during bioaerosol contamination (up to 5-log reduction of E. coli and Listeria), on chicken breast (approximately 1.3-log reduction of C. jejuni), on contact surfaces (approximately 3.9 log reduction of C. jejuni), and in liquid (2-log reduction of C. jejuni). Considering the stability of O(3), ease of use, and antimicrobial efficacy against foodborne pathogens, our results suggest that ABI is a better alternative, especially for meat and poultry processors, as compared to dry ice. Further, ABI can potentially serve as an additional processing hurdle to guard against pathogens during processing, transportation, distribution, and/or storage. © 2012 Institute of Food Technologists®

Controlled, Stepwise Reduction and Band Gap Manipulation of Graphene Oxide.

PubMed

Mathkar, Akshay; Tozier, Dylan; Cox, Paris; Ong, Peijie; Galande, Charudatta; Balakrishnan, Kaushik; Leela Mohana Reddy, Arava; Ajayan, Pulickel M

2012-04-19

Graphene oxide (GO) has drawn tremendous interest as a tunable precursor in numerous areas, due to its readily manipulable surface. However, its inhomogeneous and nonstoichiometric structure makes achieving chemical control a major challenge. Here, we present a room-temperature based, controlled method for the stepwise reduction of GO, with evidence of sequential removal of each organic moiety. By analyzing signature infrared absorption frequencies, we identify the carbonyl group as the first to be reduced, while the tertiary alcohol takes the longest to be completely removed from the GO surface. Controlled reduction allows for progressive tuning of the optical gap from 3.5 eV down to 1 eV, while XPS spectra show a concurrent increase in the C/O ratio. This study is the first step toward selectively enhancing the chemical homogeneity of GO, thus providing greater control over its structure, and elucidating the order of removal of functional groups and hydrazine-vapor reduction.

Photo-illuminated diamond as a solid-state source of solvated electrons in water for nitrogen reduction.

PubMed

Zhu, Di; Zhang, Linghong; Ruther, Rose E; Hamers, Robert J

2013-09-01

The photocatalytic reduction of N₂ to NH₃ is typically hampered by poor binding of N₂ to catalytic materials and by the very high energy of the intermediates involved in this reaction. Solvated electrons directly introduced into the reactant solution can provide an alternative pathway to overcome such limitations. Here we demonstrate that illuminated hydrogen-terminated diamond yields facile electron emission into water, thus inducing reduction of N₂ to NH₃ at ambient temperature and pressure. Transient absorption measurements at 632 nm reveal the presence of solvated electrons adjacent to the diamond after photoexcitation. Experiments using inexpensive synthetic diamond samples and diamond powder show that photocatalytic activity is strongly dependent on the surface termination and correlates with the production of solvated electrons. The use of diamond to eject electrons into a reactant liquid represents a new paradigm for photocatalytic reduction, bringing electrons directly to reactants without requiring molecular adsorption to the surface.

America's Urban Forests: Keeping Our Cities Cool

NASA Technical Reports Server (NTRS)

Luvall, Jeffrey C.; Quattrochi, Dale A.

1997-01-01

The additional heating of the air over the city is the result of the replacement of naturally vegetated surfaces with those composed of asphalt, concrete, rooftops and other man-made materials. The temperatures of these artificial surfaces can be 20 to 40 C higher than vegetated surfaces. Materials such as asphalt store much of the sun's energy and remains hot long after sunset. This produces a dome of elevated air temperatures 5 to 8 C greater over the city, compared to the air temperatures over adjacent rural areas. This effect is called the "urban heat island". Tree canopies can reduce the urban heat island effect by dissipating the solar energy received by transpiring water from leaf surfaces which cools the air by taking "heat" from the air to evaporate the water and by shading surfaces like asphalt, roofs, and concrete parking lots which prevents initial heating and storage of heat. It is difficult to take enough temperature measurements over a large city area to characterize the surface temperature variability and quantify the temperature reduction effects of tree canopies. However, the use of remotely sensed thermal data from airborne scanners are ideal for the task. In a study funded by NASA, a series of flights over Huntsville AL were performed in September 1994 and over Atlanta in May 1997. In this article we will examine the techniques of analyzing remotely sensed data for measuring the effect of tree canopies in reducing the urban heat island effect.

Morphological variation of stimuli-responsive polypeptide at air-water interface

NASA Astrophysics Data System (ADS)

Shin, Sungchul; Ahn, Sungmin; Cheng, Jie; Chang, Hyejin; Jung, Dae-Hong; Hyun, Jinho

2016-12-01

The morphological variation of stimuli-responsive polypeptide molecules at the air-water interface as a function of temperature and compression was described. The surface pressure-area (π-A) isotherms of an elastin-like polypeptide (ELP) monolayer were obtained under variable external conditions, and Langmuir-Blodgett (LB) monolayers were deposited onto a mica substrate for characterization. As the compression of the ELP monolayer increased, the surface pressure increased gradually, indicating that the ELP monolayer could be prepared with high stability at the air-water interface. The temperature in the subphase of the ELP monolayer was critical in the preparation of LB monolayers. The change in temperature induced a shift in the π-A isotherms as well as a change in ELP secondary structures. Surprisingly, the compression of the ELP monolayer influenced the ELP secondary structure due to the reduction in the phase transition temperature with decreasing temperature. The change in the ELP secondary structure formed at the air-water interface was investigated by surface-enhanced Raman scattering. Moreover, the morphology of the ELP monolayer was subsequently imaged using atomic force microscopy. The temperature responsive behavior resulted in changes in surface morphology from relatively flat structures to rugged labyrinth structures, which suggested conformational changes in the ELP monolayers.

Surface atoms in Sc-O/W(1 0 0) system as Schottky emitter at high temperature

NASA Astrophysics Data System (ADS)

Tsujita, T.; Iida, S.; Nagatomi, T.; Takai, Y.

2003-12-01

The chemical bonding state of surface atoms in the Sc-O/W(1 0 0) system as a Schottky emitter was investigated at high temperature using a profile of Auger electron peaks to elucidate the mechanism of the marked reduction of the work function of the Sc-O/W(1 0 0) Schottky emitter. For this, Sc-deposited W(1 0 0), oxygen-exposed W(1 0 0) and Sc surfaces were prepared as reference surfaces. A comparison of the profiles of the Auger electron peaks from the Sc-O/W(1 0 0) surface with those from the reference surfaces has revealed that oxygen and Sc atoms on the Sc-O/W(1 0 0) surface form the Sc-O complexes at the operating temperature of the Sc-O/W(1 0 0) emitter of 1400 K. In addition, the ratio of the number of Sc atoms to that of oxygen atoms is estimated as 1:1 by the quantitative analysis of the AES peaks. The present results strongly suggest that the work function of the Sc-O/W(1 0 0) emitter is caused by the formation of Sc-O electric dipoles aligning into the p(2 × 1)-p(1 × 2) double-domain structure [Surf. Sci. 523 (2003) L37] on the Sc-O/W(1 0 0) surface at the operating temperature.

Is the boundary layer of an ionic liquid equally lubricating at higher temperature?

PubMed

Hjalmarsson, Nicklas; Atkin, Rob; Rutland, Mark W

2016-04-07

Atomic force microscopy has been used to study the effect of temperature on normal forces and friction for the room temperature ionic liquid (IL) ethylammonium nitrate (EAN), confined between mica and a silica colloid probe at 25 °C, 50 °C, and 80 °C. Force curves revealed a strong fluid dynamic influence at room temperature, which was greatly reduced at elevated temperatures due to the reduced liquid viscosity. A fluid dynamic analysis reveals that bulk viscosity is manifested at large separation but that EAN displays a nonzero slip, indicating a region of different viscosity near the surface. At high temperatures, the reduction in fluid dynamic force reveals step-like force curves, similar to those found at room temperature using much lower scan rates. The ionic liquid boundary layer remains adsorbed to the solid surface even at high temperature, which provides a mechanism for lubrication when fluid dynamic lubrication is strongly reduced. The friction data reveals a decrease in absolute friction force with increasing temperature, which is associated with increased thermal motion and reduced viscosity of the near surface layers but, consistent with the normal force data, boundary layer lubrication was unaffected. The implications for ILs as lubricants are discussed in terms of the behaviour of this well characterised system.

Demonstration of the Feasibility of High Temperature Bearing Lubrication From Carbonaceous Gases

NASA Technical Reports Server (NTRS)

Blanchet, Thierry A.; Sawyer, W. Gregory

1996-01-01

Research has been conducted on silicon nitride pin-on-disk sliding contacts at temperatures of up to 520 C, and four-ball rolling contacts with silicon nitride balls and 52100 steel or silicon nitride races at 590 C. These tests were conducted in a variety of gaseous environments in order to determine the effects of simulated engine exhaust gas on the carbonaceous gas decomposition lubrication scheme. In rolling tests with steel races and exhaust gas the wear track depth was roughly half that of tests run in nitrogen gas alone. The deposition of lubricous microcrystalline graphitic carbon on the rolling surfaces, generated from the carbon monoxide within the exhaust gas mixture, was verified by microfocused Raman spectroscopy. Ten-fold reductions in rolling wear could be achieved by the exhaust gas atmosphere in cases where water vapor was removed or not present. The exhaust gas mixture alone was not found to provide any lubricating effect on silicon nitride sliding contacts, where the rate of wear greatly exceeds the rate of carbon deposition. Directed admixture of acetylene (as low as 5% of the exhaust gas flow rates), has provided reductions in both wear volume and coefficient of friction by factors of 60X and 20X respectively for sliding contacts during the initial 80 m of sliding distance. Exhaust gas atmosphere with the acetylene admixture provided 65OX reductions in steady state wear rate compared to that measured for sliding contacts in dry N2. Such acetylene admixture also augments the ability of the exhaust gas atmosphere to lubricate high-temperature rolling contacts, with up to 25-fold reductions in wear track depth compared to those measured in the presence of N2 alone. In addition to providing some lubricating benefit itself, an important potential role of the exhaust gas from rich mixtures would be to shield bearings from 02. Such shielding enables surface deposition of lubricous pyrolytic carbon from the acetylene admixture, instead of combustion, rendering feasible the continuously replenished solid lubrication of high-temperature bearing surfaces.

A mechanism for inducing climatic variations through ozone destruction: Screening of galactic cosmic rays by solar and terrestrial magnetic fields

NASA Technical Reports Server (NTRS)

Chamberlain, J. W.

1976-01-01

A perturbation analysis, allowing for temperature and opacity feedbacks, is developed to calculate depletions in the O3 abundance and reductions of stratospheric solar heating that result from increases in NOx concentration. A pair of perturbation coefficients give the reduction in O3 and temperature through the stratosphere for a specified NOx increase. This type of analysis illustrates the tendency for various levels to self-heal when a perturbation occurs. Physical arguments indicate that the expected sign of the climatic effect is correct, with colder surface temperatures produced by reduced magnetic shielding. In addition, four qualitative reasons are suggested for thinking that significant ozone reductions by cosmic ray influxes will lead to an increased terrestrial albedo from stratospheric condensation. In this view, long-term (approximately 10,000 years) climatic changes have resulted from secular geomagnetic variations while shorter (approximately 100 years) excursions are related to changes in solar activity.

New Ni-based quaternary disk-shaped catalysts for low-temperature CO2 methanation: Fabrication, characterization, and performance.

PubMed

Moon, Dea Hyun; Lee, Sang Moon; Ahn, Jeong Yoon; Nguyen, Dinh Duc; Kim, Sung Su; Chang, Soon Woong

2018-07-15

Ni-based quaternary disk catalysts were manufactured for low-temperature CO 2 methanation reactions, and the reaction activity was examined with respect to the thermal treatment conditions. By applying varying reduction and combustion treatments, the same catalysts were compared, and the Ni oxidation conditions and physical features were confirmed through X-Ray diffraction, scanning electron microscopy, and energy dispersive X-ray analyses. In addition, oxygen adsorption/desorption changes were measured by temperature-programmed reduction after pre-treating with oxygen and hydrogen. The reduction treatment catalyst showed a conversion of 20% at 280 °C, and the 70% calcined catalyst did not form a NiO crystalloid. The activation of the catalyst increased because of NiO movement on the catalyst surface, which enabled easy transformation to metallic Ni. The prepared catalyst is a highly reactive, yet stable, candidate for practical catalytic CO 2 methanation. Copyright © 2018 Elsevier Ltd. All rights reserved.

Effect of Exposure on the Mechanical Properties of Gamma MET PX

NASA Technical Reports Server (NTRS)

Draper, S. L.; Lerch, B. A.; Locci, I. E.; Shazly, M.; Prakash, V.

2004-01-01

The effect of a service environment exposure on the mechanical properties of a high Nb content TiAl alloy, Gamma MET PX , was assessed. Gamma MET PX, like other TiAl alloys, experiences a reduction of ductility following high temperature exposure. Exposure in Ar, air, and high-purity oxygen all resulted in a loss of ductility with the ductility reduction increasing with oxygen content in the exposure atmosphere. Embrittling mechanisms, including bulk microstructural changes, moisture induced environmental embrittlement, and near surface effects were investigated. The embrittlement has been shown to be a near-surface effect, most likely due to the diffusion of oxygen into the alloy.

Forced heat loss from body surface reduces heat flow to body surface.

PubMed

Berman, A

2010-01-01

Heat stress is commonly relieved by forced evaporation from body surfaces. The mode of heat stress relief by heat extraction from the periphery is not clear, although it reduces rectal temperature. Radiant surface temperature (Ts) of the right half of the body surface was examined by thermovision in 4 lactating Holstein cows (30 kg of milk/d) during 7 repeated cycles of forced evaporation created by 30s of wetting followed by 4.5 min of forced airflow. Wetting was performed by an array of sprinklers (0.76 m(3)/h), and forced airflow (>3m/s velocity) over the right side of the body surface was produced by fans mounted at a height of 3m above the ground. Sprinkling wetted the hind legs, rump, and chest, but not the lower abdomen side, front legs, or neck. The animals were maintained in shade at an air temperature of 28 degrees C and relative humidity of 47%. Coat thickness was 1 to 2mm, so Ts closely represented skin temperature. Mean Ts of 5 x 20cm areas on the upper and lower hind and front legs, rump, chest, abdomen side, and neck were obtained by converting to temperature their respective gray intensity in single frames obtained at 10-s intervals. Little change occurred in Ts during the first wetting (0.1+/-0.6 degrees C), but it decreased rapidly thereafter (1.6+/-0.6 degrees C in the fifth wetting). The Ts also decreased, to a smaller extent, in areas that remained dry (0.7+/-1.0 degrees C). In all body sites, a plateau in Ts was reached by 2 min after wetting. The difference between dry and wet areas in the first cooling cycle was approximately 1.2 degrees C. The Ts of different body areas decreased during consecutive cooling cycles and reached a plateau by 3 cooling cycles in dry sites (front leg, neck, abdomen side), by 5 cooling cycles in the hind leg, and 7 cooling cycles in the rump and chest. The reduction in mean Ts produced by 7 cycles was 4.0 to 6.0 degrees C in wetted areas and 1.6 to 3.7 degrees C in sites that were not wetted. Initial rectal temperature was 38.9+/-0.1 degrees C; it remained unchanged during first 5 cooling cycles, decreased by 0.1 degrees C after 7 cooling cycles, and decreased to 38.4+/-0.06 degrees C after 8 to 10 cooling cycles, with no additional subsequent decrease. The concomitant reduction in Ts in dry and wet areas suggests an immediate vasoconstrictor response associated with heat extraction and later development of a cooler body shell. The reduction in rectal temperature represents a response involving transfer of heat from the body core to the body shell. This response mode requires consideration in settings of heat stress relief. Copyright 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Prominent metallic surface conduction and the singular magnetic response of topological Dirac fermion in three-dimensional topological insulator Bi1.5Sb0.5Te1.7Se1.3.

PubMed

Dutta, Prithwish; Pariari, Arnab; Mandal, Prabhat

2017-07-07

We report semiconductor to metal-like crossover in the temperature dependence of resistivity (ρ) due to the switching of charge transport from bulk to surface channel in three-dimensional topological insulator Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 . Unlike earlier studies, a much sharper drop in ρ(T) is observed below the crossover temperature due to the dominant surface conduction. Remarkably, the resistivity of the conducting surface channel follows a rarely observable T 2 dependence at low temperature, as predicted theoretically for a two-dimensional Fermi liquid system. The field dependence of magnetization shows a cusp-like paramagnetic peak in the susceptibility (χ) at zero field over the diamagnetic background. The peak is found to be robust against temperature and χ decays linearly with the field from its zero-field value. This unique behavior of the χ is associated with the spin-momentum locked topological surface state in Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 . The reconstruction of the surface state with time is clearly reflected through the reduction of the peak height with the age of the sample.

Assimilation of Freeze - Thaw Observations into the NASA Catchment Land Surface Model

NASA Technical Reports Server (NTRS)

Farhadi, Leila; Reichle, Rolf H.; DeLannoy, Gabrielle J. M.; Kimball, John S.

2014-01-01

The land surface freeze-thaw (F-T) state plays a key role in the hydrological and carbon cycles and thus affects water and energy exchanges and vegetation productivity at the land surface. In this study, we developed an F-T assimilation algorithm for the NASA Goddard Earth Observing System, version 5 (GEOS-5) modeling and assimilation framework. The algorithm includes a newly developed observation operator that diagnoses the landscape F-T state in the GEOS-5 Catchment land surface model. The F-T analysis is a rule-based approach that adjusts Catchment model state variables in response to binary F-T observations, while also considering forecast and observation errors. A regional observing system simulation experiment was conducted using synthetically generated F-T observations. The assimilation of perfect (error-free) F-T observations reduced the root-mean-square errors (RMSE) of surface temperature and soil temperature by 0.206 C and 0.061 C, respectively, when compared to model estimates (equivalent to a relative RMSE reduction of 6.7 percent and 3.1 percent, respectively). For a maximum classification error (CEmax) of 10 percent in the synthetic F-T observations, the F-T assimilation reduced the RMSE of surface temperature and soil temperature by 0.178 C and 0.036 C, respectively. For CEmax=20 percent, the F-T assimilation still reduces the RMSE of model surface temperature estimates by 0.149 C but yields no improvement over the model soil temperature estimates. The F-T assimilation scheme is being developed to exploit planned operational F-T products from the NASA Soil Moisture Active Passive (SMAP) mission.

The Recent Atlantic Cold Anomaly: Causes, Consequences, and Related Phenomena

NASA Astrophysics Data System (ADS)

Josey, Simon A.; Hirschi, Joel J.-M.; Sinha, Bablu; Duchez, Aurélie; Grist, Jeremy P.; Marsh, Robert

2018-01-01

Cold ocean temperature anomalies have been observed in the mid- to high-latitude North Atlantic on interannual to centennial timescales. Most notably, a large region of persistently low surface temperatures accompanied by a sharp reduction in ocean heat content was evident in the subpolar gyre from the winter of 2013-2014 to 2016, and the presence of this feature at a time of pervasive warming elsewhere has stimulated considerable debate. Here, we review the role of air-sea interaction and ocean processes in generating this cold anomaly and place it in a longer-term context. We also discuss the potential impacts of surface temperature anomalies for the atmosphere, including the North Atlantic Oscillation and European heat waves; contrast the behavior of the Atlantic with the extreme warm surface event that occurred in the North Pacific over a similar timescale; and consider the possibility that these events represent a response to a change in atmospheric planetary wave forcing.

Unraveling the oxygen vacancy structures at the reduced Ce O2(111 ) surface

NASA Astrophysics Data System (ADS)

Han, Zhong-Kang; Yang, Yi-Zhou; Zhu, Beien; Ganduglia-Pirovano, M. Verónica; Gao, Yi

2018-03-01

Oxygen vacancies at ceria (Ce O2 ) surfaces play an essential role in catalytic applications. However, during the past decade, the near-surface vacancy structures at Ce O2(111 ) have been questioned due to the contradictory results from experiments and theoretical simulations. Whether surface vacancies agglomerate, and which is the most stable vacancy structure for varying vacancy concentration and temperature, are being heatedly debated. By combining density functional theory calculations and Monte Carlo simulations, we proposed a unified model to explain all conflicting experimental observations and theoretical results. We find a novel trimeric vacancy structure which is more stable than any other one previously reported, which perfectly reproduces the characteristics of the double linear surface oxygen vacancy clusters observed by STM. Monte Carlo simulations show that at low temperature and low vacancy concentrations, vacancies prefer subsurface sites with a local (2 × 2) ordering, whereas mostly linear surface vacancy clusters do form with increased temperature and degree of reduction. These results well explain the disputes about the stable vacancy structure and surface vacancy clustering at Ce O2(111 ) , and provide a foundation for the understanding of the redox and catalytic chemistry of metal oxides.

Impact of Dust Radiative Forcing upon Climate. Chapter 13

NASA Technical Reports Server (NTRS)

Miller, Ronald L.; Knippertz, Peter; Perez Garcia-Pando, Carlos; Perlwitz, Jan P.; Tegan, Ina

2014-01-01

Dust aerosols perturb the atmospheric radiative flux at both solar and thermal wavelengths, altering the energy and water cycles. The climate adjusts by redistributing energy and moisture, so that local temperature perturbations, for example, depend upon the forcing over the entire extent of the perturbed circulation. Within regions frequently mixed by deep convection, including the deep tropics, dust particles perturb the surface air temperature primarily through radiative forcing at the top of the atmosphere (TOA). Many models predict that dust reduces global precipitation. This reduction is typically attributed to the decrease of surface evaporation in response to dimming of the surface. A counterexample is presented, where greater shortwave absorption by dust increases evaporation and precipitation despite greater dimming of the surface. This is attributed to the dependence of surface evaporation upon TOA forcing through its influence upon surface temperature and humidity. Perturbations by dust to the surface wind speed and vegetation (through precipitation anomalies) feed back upon the dust aerosol concentration. The current uncertainty of radiative forcing attributed to dust and the resulting range of climate perturbations calculated by models remain a useful test of our understanding of the mechanisms relating dust radiative forcing to the climate response.

Physicochemical properties influencing denitrification rate and microbial activity in denitrification bioreactors

NASA Astrophysics Data System (ADS)

Schmidt, C. A.

2012-12-01

The use of N-based fertilizer will need to increase to meet future demands, yet existing applications have been implicated as the main source of coastal eutrophication and hypoxic zones. Producing sufficient crops to feed a growing planet will require efficient production in combination with sustainable treatment solutions. The long-term success of denitrification bioreactors to effectively remove nitrate (NO¬3), indicates this technology is a feasible treatment option. Assessing and quantifying the media properties that affect NO¬3 removal rate and microbial activity can improve predictions on bioreactor performance. It was hypothesized that denitrification rates and microbial biomass would be correlated with total C, NO¬3 concentration, metrics of organic matter quality, media surface area and laboratory measures of potential denitrification rate. NO¬3 removal rates and microbial biomass were evaluated in mesocosms filled with different wood treatments and the unique influence of these predictor variables was determined using a multiple linear regression analysis. NO3 reduction rates were independent of NO¬3 concentration indicating zero order reaction kinetics. Temperature was strongly correlated with denitrification rate (r2=0.87; Q10=4.7), indicating the variability of bioreactor performance in differing climates. Fiber quality, and media surface area were strong (R>0.50), unique predictors of rates and microbial biomass, although C:N ratio and potential denitrification rate did not predict actual denitrification rate or microbial biomass. Utilizing a stepwise multiple linear regression, indicates that the denitrification rate can be effectively (r2=0.56;p<0.0001) predicted if the groundwater temperature, neutral detergent fiber and surface area alone are quantified. These results will assist with the widespread implementation of denitrification bioreactors to achieve significant N load reductions in large watersheds. The nitrate reduction rate as a function of groundwater temperature for all treatments. Correlations between nitrate reduction rate and properties of carbon media;

Energy Saving Melting and Revert Reduction Technology: Improved Die Casting Process to Preserve the Life of the Inserts

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

David Schwam, PI; Xuejun Zhu, Sr. Research Associate

2012-09-30

The goal of this project was to study the combined effects of die design, proper internal cooling and efficient die lubricants on die life. The project targeted improvements in die casting insert life by: Optomized Die Design for Reduced Surface Temperature: The life of die casting dies is significantly shorter when the die is exposed to elevated temperature for significant periods of time. Any die operated under conditions leading to surface temperature in excess of 1050oF undergoes structural changes that reduce its strength. Optimized die design can improve die life significantly. This improvement can be accomplished by means of coolingmore » lines, baffles and bubblers in the die. A key objective of the project was to establish criteria for the minimal distance of the cooling lines from the surface. This effort was supported with alloys and machining by BohlerUddeholm, Dunn Steel, HH Stark and Rex Buckeye. In plant testing and evaluation was conducted as in-kind cost share at St. Clair Die Casting. The Uddeholm Dievar steel evaluated in this program showed superior resistance to thermal fatigue resistance. Based on the experimental evidence, cooling lines could be placed as close as 0.5" from the surface. Die Life Extension by Optimized Die Lubrication: The life of die casting dies is affected by additions made to its surface with the proper lubricants. These lubricants will protect the surface from the considerable temperature peaks that occur when the molten melt enters the die. Dies will reach a significantly higher temperature without this lubricant being applied. The amount and type of the lubricant are critical variables in the die casting process. However, these lubricants must not corrode the die surface. This effort was supported with alloys and machining by BohlerUddeholm, Dunn Steel, HH Stark and Rex Buckeye. In plant testing and evaluation was conducted as in-kind cost share at St. Clair Die Casting. Chem- Trend participated in the program with die lubricants and technical support. Experiments conducted with these lubricants demonstrated good protection of the substrate steel. Graphite and boron nitride used as benchmarks are capable of completely eliminating soldering and washout. However, because of cost and environmental considerations these materials are not widely used in industry. The best water-based die lubricants evaluated in this program were capable of providing similar protection from soldering and washout. In addition to improved part quality and higher production rates, improving die casting processes to preserve the life of the inserts will result in energy savings and a reduction in environmental wastes. Improving die life by means of optimized cooling line placement, baffles and bubblers in the die will allow for reduced die temperatures during processing, saving energy associated with production. The utilization of optimized die lubricants will also reduce heat requirements in addition to reducing waste associated with soldering and washout. This new technology was predicted to result in an average energy savings of 1.1 trillion BTU's/year over a 10 year period. Current (2012) annual energy saving estimates, based on commercial introduction in 2010, a market penetration of 70% by 2020 is 1.26 trillion BTU's/year. Along with these energy savings, reduction of scrap and improvement in casting yield will result in a reduction of the environmental emissions associated with the melting and pouring of the metal which will be saved as a result of this technology. The average annual estimate of CO2 reduction per year through 2020 is 0.025 Million Metric Tons of Carbon Equivalent (MM TCE).« less

Effect of hot rolling on the structure and the mechanical properties of nitrogen-bearing austenitic-martensitic 14Kh15AN4M steel

NASA Astrophysics Data System (ADS)

Bannykh, O. A.; Betsofen, S. Ya.; Lukin, E. I.; Blinov, V. M.; Voznesenskaya, N. M.; Tonysheva, O. A.; Blinov, E. V.

2016-04-01

The effect of the rolling temperature and strain on the structure and the properties of corrosionresistant austenitic-martensitic 14Kh15AN4M steel is studied. The steel is shown to exhibit high ductility: upon rolling in the temperature range 700-1100°C at a reduction per pass up to 80%, wedge steel specimens are uniformly deformed along and across the rolling direction without cracking and other surface defects. Subsequent cold treatment and low-temperature tempering ensure a high hardness of the steel (50-56 HRC). Austenite mainly contributes to the hardening upon rolling in the temperature range 700-800°C at a reduction of 50-70%, and martensite makes the main contribution at higher temperatures and lower strains. Texture does not form under the chosen deformation conditions, which indicates dynamic recrystallization with the nucleation and growth of grains having no preferential orientation.

Numerical simulation of high-temperature thermal contact resistance and its reduction mechanism.

PubMed

Liu, Donghuan; Zhang, Jing

2018-01-01

High-temperature thermal contact resistance (TCR) plays an important role in heat-pipe-cooled thermal protection structures due to the existence of contact interface between the embedded heat pipe and the heat resistive structure, and the reduction mechanism of thermal contact resistance is of special interests in the design of such structures. The present paper proposed a finite element model of the high-temperature thermal contact resistance based on the multi-point contact model with the consideration of temperature-dependent material properties, heat radiation through the cavities at the interface and the effect of thermal interface material (TIM), and the geometry parameters of the finite element model are determined by simple surface roughness test and experimental data fitting. The experimental results of high-temperature thermal contact resistance between superalloy GH600 and C/C composite material are employed to validate the present finite element model. The effect of the crucial parameters on the thermal contact resistance with and without TIM are also investigated with the proposed finite element model.

Numerical simulation of high-temperature thermal contact resistance and its reduction mechanism

PubMed Central

Zhang, Jing

2018-01-01

High-temperature thermal contact resistance (TCR) plays an important role in heat-pipe-cooled thermal protection structures due to the existence of contact interface between the embedded heat pipe and the heat resistive structure, and the reduction mechanism of thermal contact resistance is of special interests in the design of such structures. The present paper proposed a finite element model of the high-temperature thermal contact resistance based on the multi-point contact model with the consideration of temperature-dependent material properties, heat radiation through the cavities at the interface and the effect of thermal interface material (TIM), and the geometry parameters of the finite element model are determined by simple surface roughness test and experimental data fitting. The experimental results of high-temperature thermal contact resistance between superalloy GH600 and C/C composite material are employed to validate the present finite element model. The effect of the crucial parameters on the thermal contact resistance with and without TIM are also investigated with the proposed finite element model. PMID:29547651

Protective coatings of metal surfaces by cold plasma treatment

NASA Technical Reports Server (NTRS)

Manory, R.; Grill, A.

1985-01-01

The cold plasma techniques for deposition of various types of protective coatings are reviewed. The main advantage of these techniques for deposition of ceramic films is the lower process temperature, which enables heat treating of the metal prior to deposition. In the field of surface hardening of steel, significant reduction of treatment time and energy consumption were obtained. A simple model for the plasma - surface reactions in a cold plasma system is presented, and the plasma deposition techniques are discussed in view of this model.

Tenacity of human norovirus and the surrogates feline calicivirus and murine norovirus during long-term storage on common nonporous food contact surfaces.

PubMed

Mormann, Sascha; Heißenberg, Cathrin; Pfannebecker, Jens; Becker, Barbara

2015-01-01

The transfer of human norovirus (hNV) to food via contaminated surfaces is highly probable during food production, processing, and preparation. In this study, the tenacity of hNV and its cultivable surrogates feline calicivirus (FCV) and murine norovirus (MNV) on two common nonporous surface materials at two storage temperatures was directly compared. Virus titer reduction on artificially inoculated stainless steel and plastic carriers was monitored for 70 days at room temperature and at 7°C. Viruses were recovered at various time points by elution. Genomes from intact capsids (hNV, FCV, and MNV) were quantified with real-time reverse transcription (RT) PCR, and infectivity (FCV and MNV) was assessed with plaque assay. RNase treatment before RNA extraction was used to eliminate exposed RNA and to assess capsid integrity. No significant differences in titer reduction were found between materials (stainless steel or plastic) with the plaque assay or the real-time quantitative RT-PCR. At room temperature, infectious FCV and MNV were detected for 7 days. Titers of intact hNV, FCV, and MNV capsids dropped gradually and were still detectable after 70 days with a loss of 3 to 4 log units. At 7°C, the viruses were considerably more stable than they were at room temperature. Although only MNV infectivity was unchanged after 70 days, the numbers of intact capsids (hNV, FCV, and MNV) were stable with less than a 1-log reduction. The results indicate that hNV persists on food contact surfaces and seems to remain infective for weeks. MNV appears to be more stable than FCV at 7°C, and thus is the most suitable surrogate for hNV under dry conditions. Although a perfect quantitative correlation between intact capsids and infective particles was not obtained, real-time quantitative RT-PCR provided qualitative data about hNV inactivation characteristics. The results of this comparative study might support future efforts in assessment of foodborne virus risk and food safety.

Optimization of palm fruit sterilization by microwave irradiation using response surface methodology

NASA Astrophysics Data System (ADS)

Sarah, M.; Madinah, I.; Salamah, S.

2018-02-01

This study reported optimization of palm fruit sterilization process by microwave irradiation. The results of fractional factorial experiments showed no significant external factors affecting temperature of microwave sterilization (MS). Response surface methodology (RSM) was employed and model equation of MS of palm fruit was built. Response surface plots and their corresponding contour plots were analyzed as well as solving model equation. The optimum process parameters for lipase reduction were obtained from MS of 1 kg palm fruit at microwave power of 486 Watt and heating time of 14 minutes. The experimental results showed reduction of lipase activity in the present work under MS treatment. The adequacy of the model equation for predicting the optimum response value was verified by validation data (P>0.15).

Integration of graphene onto silicon through electrochemical reduction of graphene oxide layers in non-aqueous medium

NASA Astrophysics Data System (ADS)

Marrani, Andrea Giacomo; Coico, Anna Chiara; Giacco, Daniela; Zanoni, Robertino; Scaramuzzo, Francesca Anna; Schrebler, Ricardo; Dini, Danilo; Bonomo, Matteo; Dalchiele, Enrique A.

2018-07-01

Wafer-scale integration of reduced graphene oxide with H-terminated Si(1 1 1) surfaces has been accomplished by electrochemical reduction of a thin film of graphene oxide deposited onto Si by drop casting. Two reduction methods have been assayed and carried out in an acetonitrile solution. The initial deposit was subjected either to potential cycling in a 0.1 M TBAPF6/CH3CN solution at scan rates values of 20 mV s-1 and 50 mV s-1, or to a potentiostatic polarization at Eλ,c = -3 V for 450 s. The resulting interface has been characterized in its surface composition, morphology and electrochemical behavior by X-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy and electrochemical measurements. The results evidence that few-layer graphene deposits on H-Si(1 1 1) were obtained after reduction, and use of organic instead of aqueous medium led to a very limited surface oxidation of the Si substrate and a very low oxygen-to-carbon ratio. The described approach is fast, simple, economic, scalable and straightforward, as one reduction cycle is already effective in promoting the establishment of a graphene-Si interface. It avoids thermal treatments at high temperatures, use of aggressive chemicals and the presence of metal contaminants, and enables preservation of Si(1 1 1) surface from oxidation.

Cryotherapy-Induced Persistent Vasoconstriction After Cutaneous Cooling: Hysteresis Between Skin Temperature and Blood Perfusion.

PubMed

Khoshnevis, Sepideh; Craik, Natalie K; Matthew Brothers, R; Diller, Kenneth R

2016-03-01

The goal of this study was to investigate the persistence of cold-induced vasoconstriction following cessation of active skin-surface cooling. This study demonstrates a hysteresis effect that develops between skin temperature and blood perfusion during the cooling and subsequent rewarming period. An Arctic Ice cryotherapy unit (CTU) was applied to the knee region of six healthy subjects for 60 min of active cooling followed by 120 min of passive rewarming. Multiple laser Doppler flowmetry perfusion probes were used to measure skin blood flow (expressed as cutaneous vascular conductance (CVC)). Skin surface cooling produced a significant reduction in CVC (P < 0.001) that persisted throughout the duration of the rewarming period. In addition, there was a hysteresis effect between CVC and skin temperature during the cooling and subsequent rewarming cycle (P < 0.01). Mixed model regression (MMR) showed a significant difference in the slopes of the CVC-skin temperature curves during cooling and rewarming (P < 0.001). Piecewise regression was used to investigate the temperature thresholds for acceleration of CVC during the cooling and rewarming periods. The two thresholds were shown to be significantly different (P = 0.003). The results show that localized cooling causes significant vasoconstriction that continues beyond the active cooling period despite skin temperatures returning toward baseline values. The significant and persistent reduction in skin perfusion may contribute to nonfreezing cold injury (NFCI) associated with cryotherapy.

Cryotherapy-Induced Persistent Vasoconstriction After Cutaneous Cooling: Hysteresis Between Skin Temperature and Blood Perfusion

PubMed Central

Khoshnevis, Sepideh; Craik, Natalie K.; Matthew Brothers, R.; Diller, Kenneth R.

2016-01-01

The goal of this study was to investigate the persistence of cold-induced vasoconstriction following cessation of active skin-surface cooling. This study demonstrates a hysteresis effect that develops between skin temperature and blood perfusion during the cooling and subsequent rewarming period. An Arctic Ice cryotherapy unit (CTU) was applied to the knee region of six healthy subjects for 60 min of active cooling followed by 120 min of passive rewarming. Multiple laser Doppler flowmetry perfusion probes were used to measure skin blood flow (expressed as cutaneous vascular conductance (CVC)). Skin surface cooling produced a significant reduction in CVC (P < 0.001) that persisted throughout the duration of the rewarming period. In addition, there was a hysteresis effect between CVC and skin temperature during the cooling and subsequent rewarming cycle (P < 0.01). Mixed model regression (MMR) showed a significant difference in the slopes of the CVC–skin temperature curves during cooling and rewarming (P < 0.001). Piecewise regression was used to investigate the temperature thresholds for acceleration of CVC during the cooling and rewarming periods. The two thresholds were shown to be significantly different (P = 0.003). The results show that localized cooling causes significant vasoconstriction that continues beyond the active cooling period despite skin temperatures returning toward baseline values. The significant and persistent reduction in skin perfusion may contribute to nonfreezing cold injury (NFCI) associated with cryotherapy. PMID:26632263

Alternative Antimicrobial Commercial Egg Washing Procedures.

PubMed

Hudson, Lauren K; Harrison, Mark A; Berrang, Mark E; Jones, Deana R

2016-07-01

Commercial table eggs are washed prior to packaging. Standard wash procedures use an alkaline pH and warm water. If a cool water method could be developed that would still provide a microbiologically safe egg, the industry may save energy costs associated with water heating. Four wash procedures were evaluated for Salmonella reduction: pH 11 at 48.9°C (industry standard), pH 11 at ambient temperature (∼20°C), pH 6 at 48.9°C, and pH 6 at ambient temperature. Alkaline washes contained potassium hydroxide-based detergent, while pH 6 washes contained approximately 200 ppm of chlorine and a proprietary chlorine stabilizer (T-128). When eggs were inoculated by immersion in a cell suspension of Salmonella Enteritidis and Salmonella Typhimurium, all treatments resulted in a slight and similar reduction of Salmonella numbers (approximately 0.77 log CFU/ml of shell emulsion reduction). When eggs were inoculated by droplet on the shell surface, Salmonella counts were reduced by approximately 5 log CFU when washed with chlorine plus the chlorine stabilizer at both temperatures and with the alkaline wash at the high temperature. The reductions in Salmonella by these treatments were not significantly (P > 0.05) different from each other but were significantly (P < 0.05) more than the reduction observed for the 20°C alkaline treatment and 20°C control water treatments. Ambient temperature acidic washes reduced Salmonella contamination to the same degree as the standard pH 11 warm water wash and may be a viable option to reduce cost, increase shelf life, and slow pathogen growth in and on shell eggs.

Adsorption and desorption of hydrogen at nonpolar GaN (1 1 ¯ 00 ) surfaces: Kinetics and impact on surface vibrational and electronic properties

NASA Astrophysics Data System (ADS)

Lymperakis, L.; Neugebauer, J.; Himmerlich, M.; Krischok, S.; Rink, M.; Kröger, J.; Polyakov, V. M.

2017-05-01

The adsorption of hydrogen at nonpolar GaN (1 1 ¯00 ) surfaces and its impact on the electronic and vibrational properties is investigated using surface electron spectroscopy in combination with density functional theory (DFT) calculations. For the surface mediated dissociation of H2 and the subsequent adsorption of H, an energy barrier of 0.55 eV has to be overcome. The calculated kinetic surface phase diagram indicates that the reaction is kinetically hindered at low pressures and low temperatures. At higher temperatures ab initio thermodynamics show, that the H-free surface is energetically favored. To validate these theoretical predictions experiments at room temperature and under ultrahigh vacuum conditions were performed. They reveal that molecular hydrogen does not dissociatively adsorb at the GaN (1 1 ¯00 ) surface. Only activated atomic hydrogen atoms attach to the surface. At temperatures above 820 K, the attached hydrogen gets desorbed. The adsorbed hydrogen atoms saturate the dangling bonds of the gallium and nitrogen surface atoms and result in an inversion of the Ga-N surface dimer buckling. The signatures of the Ga-H and N-H vibrational modes on the H-covered surface have experimentally been identified and are in good agreement with the DFT calculations of the surface phonon modes. Both theory and experiment show that H adsorption results in a removal of occupied and unoccupied intragap electron states of the clean GaN (1 1 ¯00 ) surface and a reduction of the surface upward band bending by 0.4 eV. The latter mechanism largely reduces surface electron depletion.

On the nanostructuring and catalytic promotion of intermediate temperature solid oxide fuel cell (IT-SOFC) cathodes

NASA Astrophysics Data System (ADS)

Serra, José M.; Buchkremer, Hans-Peter

Solid oxide fuel cells (SOFCs) are highly efficient energy converters for both stationary and mobile purposes. However, their market introduction still demands the reduction of manufacture costs and one possible way to reach this goal is the decrease of the operating temperatures, which entails the improvement of the cathode electrocatalytic properties. An ideal cathode material may have mixed ionic and electronic conductivity as well as proper catalytic properties. Nanostructuring and catalytic promotion of mixed conducting perovskites (e.g. La 0.58Sr 0.4Fe 0.8Co 0.2O 3- δ) seem to be promising approaches to overcoming cathode polarization problems and are briefly illustrated here. The preparation of nanostructured cathodes with relatively high surface area and enough thermal stability enables to improve the oxygen exchange rate and therefore the overall SOFC performance. A similar effect was obtained by catalytic promoting the perovskite surface, allowing decoupling the catalytic and ionic-transport properties in the cathode design. Noble metal incorporation may improve the reversibility of the reduction cycles involved in the oxygen reduction. Under the cathode oxidizing conditions, Pd seems to be partially dissolved in the perovskite structure and as a result very well dispersed.

Enhanced thermoelectric performance in three-dimensional superlattice of topological insulator thin films

PubMed Central

2012-01-01

We show that certain three-dimensional (3D) superlattice nanostructure based on Bi2Te3 topological insulator thin films has better thermoelectric performance than two-dimensional (2D) thin films. The 3D superlattice shows a predicted peak value of ZT of approximately 6 for gapped surface states at room temperature and retains a high figure of merit ZT of approximately 2.5 for gapless surface states. In contrast, 2D thin films with gapless surface states show no advantage over bulk Bi2Te3. The enhancement of the thermoelectric performance originates from a combination of the reduction of lattice thermal conductivity by phonon-interface scattering, the high mobility of the topologically protected surface states, the enhancement of Seebeck coefficient, and the reduction of electron thermal conductivity by energy filtering. Our study shows that the nanostructure design of topological insulators provides a possible new way of ZT enhancement. PMID:23072433

Enhanced thermoelectric performance in three-dimensional superlattice of topological insulator thin films.

PubMed

Fan, Zheyong; Zheng, Jiansen; Wang, Hui-Qiong; Zheng, Jin-Cheng

2012-10-16

We show that certain three-dimensional (3D) superlattice nanostructure based on Bi2Te3 topological insulator thin films has better thermoelectric performance than two-dimensional (2D) thin films. The 3D superlattice shows a predicted peak value of ZT of approximately 6 for gapped surface states at room temperature and retains a high figure of merit ZT of approximately 2.5 for gapless surface states. In contrast, 2D thin films with gapless surface states show no advantage over bulk Bi2Te3. The enhancement of the thermoelectric performance originates from a combination of the reduction of lattice thermal conductivity by phonon-interface scattering, the high mobility of the topologically protected surface states, the enhancement of Seebeck coefficient, and the reduction of electron thermal conductivity by energy filtering. Our study shows that the nanostructure design of topological insulators provides a possible new way of ZT enhancement.

Can a reduction of solar irradiance counteract CO2-induced climate change? - Results from four Earth system models

NASA Astrophysics Data System (ADS)

Schmidt, H.; Alterskjær, K.; Karam, D. Bou; Boucher, O.; Jones, A.; Kristjansson, J. E.; Niemeier, U.; Schulz, M.; Aaheim, A.; Benduhn, F.; Lawrence, M.; Timmreck, C.

2012-01-01

In this study we compare the response of four state-of-the-art Earth system models to climate engineering under scenario G1 of the GeoMIP and IMPLICC model intercomparison projects. In G1, the radiative forcing from an instantaneous quadrupling of the CO2 concentration, starting from the preindustrial level, is balanced by a reduction of the solar constant. Model responses to the two counteracting forcings in G1 are compared to the preindustrial climate in terms of global means and regional patterns and their robustness. While the global mean surface air temperature in G1 remains almost unchanged, the meridional temperature gradient is reduced in all models compared to the control simulation. Another robust response is the global reduction of precipitation with strong effects in particular over North and South America and northern Eurasia. It is shown that this reduction is only partly compensated by a reduction in evaporation so that large continental regions are drier in the engineered climate. In comparison to the climate response to a quadrupling of CO2 alone the temperature responses are small in experiment G1. Precipitation responses are, however, of comparable magnitude but in many regions of opposite sign.

Effect of reductive treatments on Pt behavior and NOx storage in lean NOx trap catalysts

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

Wang, Xianqin; Kim, Do Heui; Kwak, Ja Hun

2011-10-01

Lean NOx trap (LNT) catalysts represent a promising approach to meet increasingly stringent NOx emission regulations on diesel and other lean-burn engines. Pt material properties, including dispersion and particle size, are known to be important factors in determining NOx uptake performance, since Pt provides active sites for NO oxidation to NO2 necessary for storing NOx as nitrates, and for the reduction of nitrates to N2. In this work, the physicochemical properties of Pt in Pt-BaO/Al2O3 LNT catalysts, such as the Pt accessible surface area and particle size, were investigated by using various tools, such as irreversible volumetric H2 chemisorption, highmore » resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD), following successive reductive treatments at elevated temperatures. NOx uptake activities were also measured to establish a relationship between the properties of Pt and NOx storage following identical high-temperature reductive treatments. We find that the reductive treatments of Pt-BaO/Al2O3 lean NOx trap catalysts at temperatures up to 500 ºC promote a significant increase in NOx uptake explained, in part, by an induced close interaction between Pt and BaO phases in the catalyst, thus enabling facilitation of the NOx storage process.« less

Vertical structure of recent Arctic warming.

PubMed

Graversen, Rune G; Mauritsen, Thorsten; Tjernström, Michael; Källén, Erland; Svensson, Gunilla

2008-01-03

Near-surface warming in the Arctic has been almost twice as large as the global average over recent decades-a phenomenon that is known as the 'Arctic amplification'. The underlying causes of this temperature amplification remain uncertain. The reduction in snow and ice cover that has occurred over recent decades may have played a role. Climate model experiments indicate that when global temperature rises, Arctic snow and ice cover retreats, causing excessive polar warming. Reduction of the snow and ice cover causes albedo changes, and increased refreezing of sea ice during the cold season and decreases in sea-ice thickness both increase heat flux from the ocean to the atmosphere. Changes in oceanic and atmospheric circulation, as well as cloud cover, have also been proposed to cause Arctic temperature amplification. Here we examine the vertical structure of temperature change in the Arctic during the late twentieth century using reanalysis data. We find evidence for temperature amplification well above the surface. Snow and ice feedbacks cannot be the main cause of the warming aloft during the greater part of the year, because these feedbacks are expected to primarily affect temperatures in the lowermost part of the atmosphere, resulting in a pattern of warming that we only observe in spring. A significant proportion of the observed temperature amplification must therefore be explained by mechanisms that induce warming above the lowermost part of the atmosphere. We regress the Arctic temperature field on the atmospheric energy transport into the Arctic and find that, in the summer half-year, a significant proportion of the vertical structure of warming can be explained by changes in this variable. We conclude that changes in atmospheric heat transport may be an important cause of the recent Arctic temperature amplification.

Surface Modification of Plastic Substrates Using Atomic Hydrogen

NASA Astrophysics Data System (ADS)

Heya, Akira; Matsuo, Naoto

The surface properties of a plastic substrate were changed by a novel surface treatment called atomic hydrogen annealing (AHA). In this method, a plastic substrate was exposed to atomic hydrogen generated by cracking of hydrogen molecules on heated tungsten wire. Surface roughness was increased and halogen elements (F and Cl) were selectively etched by AHA. In addition, plastic surface was reduced by AHA. The surface can be modified by the recombination reaction of atomic hydrogen, the reduction reaction and selective etching of halogen atom. It is concluded that this method is a promising technique for improvement of adhesion between inorganic films and plastic substrates at low temperatures.

Ultrathin Bi2WO6 nanosheet decorated with Pt nanoparticles for efficient formaldehyde removal at room temperature

NASA Astrophysics Data System (ADS)

Sun, Dong; Le, Yao; Jiang, Chuanjia; Cheng, Bei

2018-05-01

Two-dimensional (2D) ultrathin bismuth tungstate (Bi2WO6) nanosheets (BWO-NS) with a thickness of approximately 4.0 nm were synthesized by a one-step hydrothermal method, and decorated with platinum (Pt) nanoparticles (NPs) via an impregnation/borohydride-reduction approach. The as-prepared ultrathin Pt-BWO-NS exhibited superior catalytic activity for removing gaseous formaldehyde (HCHO) at ambient temperature, in comparison with bulk counterpart with Bi2WO6 sheet thickness of tens of nanometers. The ultrathin structure endowed the Pt-BWO-NS sample with larger specific surface area, which can provide abundant surface active sites for HCHO adsorption and facilitate the homogeneous dispersion of Pt NPs. X-ray photoelectron spectroscopy and hydrogen temperature-programmed reduction analyses revealed the interaction between the Bi2WO6 support and Pt species, which is crucial for activating surface oxygen atoms to participate in the catalytic HCHO oxidation process. By conducting in situ diffuse reflectance infrared Fourier transform spectroscopy under different atmospheres, i.e., gaseous HCHO in nitrogen or oxygen (O2), the reaction mechanism and the role of O2 were elucidated, with dioxymethylene, formate and linearly adsorbed carbon monoxide identified as the main reaction intermediates. This study may provide new enlightenment on fabricating novel 2D nanomaterials for efficient indoor air purification and potentially other environmental applications.

Study on aggregation behavior of Cytochrome C-conjugated silver nanoparticles using asymmetrical flow field-flow fractionation.

PubMed

Kim, Sun Tae; Lee, Yong-Ju; Hwang, Yu-Sik; Lee, Seungho

2015-01-01

In this study, 40 nm silver nanoparticles (AgNPs) were synthesized using the citrate reduction method and then the surface of AgNPs was modified by conjugating Cytochrome C (Cyto C) to improve stability and to enhance bioactivity and biocompatibility of AgNPs. It is known that Cyto C may undergo conformational changes under various conditions of pH, temperature, ionic strength, etc., resulting in aggregation of the particles. These parameters also affect the size and size distribution of Cyto C-conjugated AgNPs (Cyto C-AgNP). ζ-potential measurement revealed that the adsorption of Cyto C on the surface of AgNPs is saturated at the molar ratio [Cyto C]/[AgNPs] above about 300. Asymmetrical flow field-flow fractionation (AsFlFFF) analysis showed that hydrodynamic diameter of AgNPs increases by about 4 nm when the particle is saturated by Cyto C. The aggregation behavior of Cyto C-AgNP at various conditions of pH, temperature and ionic strength were investigated using AsFlFFF and UV-vis spectroscopy. It was found that the aggregation of Cyto C-AgNP increases with decreasing pH, increasing temperature and ionic strength due to denaturation of Cyto C on AgNPs and reduction in the thickness of electrostatic double layer on the surface of Cyto C-AgNP. Copyright © 2014 Elsevier B.V. All rights reserved.

Forests tend to cool the land surface in the temperate zone: An analysis of the mechanisms controlling radiometric surface temperature change in managed temperate ecosystems

NASA Astrophysics Data System (ADS)

Stoy, P. C.; Katul, G. G.; Juang, J.; Siqueira, M. B.; Novick, K. A.; Essery, R.; Dore, S.; Kolb, T. E.; Montes-Helu, M. C.; Scott, R. L.

2010-12-01

Vegetation is an important control on the surface energy balance and thereby surface temperature. Boreal forests and arctic shrubs are thought to warm the land surface by absorbing more radiation than the vegetation they replace. The surface temperatures of tropical forests tend to be cooler than deforested landscapes due to enhanced evapotranspiration. The effects of reforestation on surface temperature change in the temperate zone is less-certain, but recent modeling efforts suggest forests have a global warming effect. We quantified the mechanisms driving radiometric surface changes following landcover changes using paired ecosystem case studies from the Ameriflux database with energy balance models of varying complexity. Results confirm previous findings that deciduous and coniferous forests in the southeastern U.S. are ca. 1 °C cooler than an adjacent field on an annual basis because aerodynamic/ecophysiological cooling of 2-3 °C outweighs an albedo-related warming of <1 °C. A 50-70% reduction in the aerodynamic resistance to sensible and latent heat exchange in the forests dominated the cooling effect. A grassland ecosystem that succeeded a stand-replacing ponderosa pine fire was ca. 1 °C warmer than unburned stands because a 1.5 °C aerodynamic warming offset a slight surface cooling due to greater albedo and soil heat flux. An ecosystem dominated by mesquite shrub encroachment was nearly 2 °C warmer than a native grassland ecosystem as aerodynamic and albedo-related warming outweighed a small cooling effect due to changes in soil heat flux. The forested ecosystems in these case studies are documented to have higher carbon uptake than the non-forested systems. Results suggest that temperate forests tend to cool the land surface and suggest that previous model-based findings that forests warm the Earth’s surface globally should be reconsidered.Changes to radiometric surface temperature (K) following changes in vegetation using paired ecosystem case studies C4 grassland and shrub ecosystem surface temperatures were adjusted for differences in air temperature across sites.

In situ laser annealing system for real-time surface kinetic analysis

NASA Astrophysics Data System (ADS)

Wang, Q.; Sun, Y.-M.; Zhao, W.; Campagna, J.; White, J. M.

2002-11-01

For real-time analysis during thermal annealing, a continuous wave CO2 infrared laser was coupled to a surface analysis system equipped for x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). The laser beam was directed into the vacuum chamber through a ZnSe window to the back side of the sample. With 10 W laser output, the sample temperature reached 563 K. The chamber remained below 10-8 Torr during annealing and allowed XPS and ISS data to be gathered as a function of time at selected temperatures. As a test example, real time Cu2O reduction at 563 K was investigated.

Urban Soil: Assessing Ground Cover Impact on Surface Temperature and Thermal Comfort.

PubMed

Brandani, Giada; Napoli, Marco; Massetti, Luciano; Petralli, Martina; Orlandini, Simone

2016-01-01

The urban population growth, together with the contemporary deindustrialization of metropolitan areas, has resulted in a large amount of available land with new possible uses. It is well known that urban green areas provide several benefits in the surrounding environment, such as the improvement of thermal comfort conditions for the population during summer heat waves. The purpose of this study is to provide useful information on thermal regimes of urban soils to urban planners to be used during an urban transformation to mitigate surface temperatures and improve human thermal comfort. Field measurements of solar radiation, surface temperature (), air temperature (), relative humidity, and wind speed were collected on four types of urban soils and pavements in the city of Florence during summer 2014. Analysis of days under calm, clear-sky condition is reported. During daytime, sun-to-shadow differences for , apparent temperature index (ATI), and were significantly positive for all surfaces. Conversely, during nighttime, differences among all surfaces were significantly negative, whereas ATI showed significantly positive differences. Moreover, was significantly negative for grass and gravel. Relative to the shaded surfaces, was higher on white gravel and grass than gray sandstone and asphalt during nighttime, whereas gray sandstone was always the warmest surface during daytime. Conversely, no differences were found during nighttime for ATI and measured over surfaces that were exposed to sun during the day, whereas showed higher values on gravel than grass and asphalt during nighttime. An exposed surface warms less if its albedo is high, leading to a significant reduction of during daytime. These results underline the importance of considering the effects of surface characteristics on surface temperature and thermal comfort. This would be fundamental for addressing urban environment issues toward the heat island mitigation considering also the impact of urban renovation on microclimate. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Cube-textured nickel substrates for high-temperature superconductors

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

Specht, E.D.; Goyal, A.; Lee, D.F.

1998-02-01

The biaxial textures created in metals by rolling and annealing make them useful substrates for the growth of long lengths of biaxially textured material. The growth of overlayers such as high-temperature superconductors (HTS) require flat substrates with a single, sharp texture. A sharp cube texture is produced in high-purity Ni by rolling and annealing. The authors report the effect of rolling reduction and annealing conditions on the sharpness of the cube texture, the incidence of other orientations, the grain size, and the surface topography. A combination of high reduction, and high temperature annealing in a reducing atmosphere leads to >more » 99% cube texture, with mosaic of 9.0{degree} about the rolling direction (RD), 6.5{degree} about the transverse direction (TD), and 5.0{degree} about the normal direction (ND).« less

Dependence of trapped-flux-induced surface resistance of a large-grain Nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown through T c

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

Huang, Shichun; Kubo, Takayuki; Geng, R. L.

Recent studies by Romanenko et al. revealed that cooling down a superconducting cavity under a large spatial temperature gradient decreases the amount of trapped flux and leads to reduction of the residual surface resistance. In the present paper, the flux expulsion ratio and the trapped-flux-induced surface resistance of a large-grain cavity cooled down under a spatial temperature gradient up to 80K/m are studied under various applied magnetic fields from 5E-6 T to 2E-5 T. We show the flux expulsion ratio improves as the spatial temperature gradient increases, independent of the applied magnetic field: our results supports and enforces the previousmore » studies. We then analyze all RF measurement results obtained under different applied magnetic fields together by plotting the trapped- flux-induced surface resistance normalized by the applied magnetic field as a function of the spatial temperature gradient. All the data can be fitted by a single curve, which defines an empirical formula for the trapped- flux-induced surface resistance as a function of the spatial temperature gradient and applied magnetic field. The formula can fit not only the present results but also those obtained by Romanenko et al. previously. Furthermore, the sensitivity r fl of surface resistance from trapped magnetic flux of fine-grain and large-grain niobium cavities and the origin of dT/ds dependence of R fl/B a are also discussed.« less

Dependence of trapped-flux-induced surface resistance of a large-grain Nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown through T c

DOE PAGES

Huang, Shichun; Kubo, Takayuki; Geng, R. L.

2016-08-26

Recent studies by Romanenko et al. revealed that cooling down a superconducting cavity under a large spatial temperature gradient decreases the amount of trapped flux and leads to reduction of the residual surface resistance. In the present paper, the flux expulsion ratio and the trapped-flux-induced surface resistance of a large-grain cavity cooled down under a spatial temperature gradient up to 80K/m are studied under various applied magnetic fields from 5E-6 T to 2E-5 T. We show the flux expulsion ratio improves as the spatial temperature gradient increases, independent of the applied magnetic field: our results supports and enforces the previousmore » studies. We then analyze all RF measurement results obtained under different applied magnetic fields together by plotting the trapped- flux-induced surface resistance normalized by the applied magnetic field as a function of the spatial temperature gradient. All the data can be fitted by a single curve, which defines an empirical formula for the trapped- flux-induced surface resistance as a function of the spatial temperature gradient and applied magnetic field. The formula can fit not only the present results but also those obtained by Romanenko et al. previously. Furthermore, the sensitivity r fl of surface resistance from trapped magnetic flux of fine-grain and large-grain niobium cavities and the origin of dT/ds dependence of R fl/B a are also discussed.« less

Evaluation of new in vitro efficacy test for antimicrobial surface activity reflecting UK hospital conditions.

PubMed

Ojeil, M; Jermann, C; Holah, J; Denyer, S P; Maillard, J-Y

2013-12-01

Antimicrobial surfaces aim to reduce microbial bioburden and improve hygiene. The current antimicrobial surface efficacy test (ISO22196) is an initial screening test but its conditions, high temperature (37°C) and relative humidity (RH) (100%) bear little relationship to in-use conditions. To develop an antimicrobial surface efficacy test providing a realistic second-tier test, simulating in-use conditions. Surface relative humidity, temperature and soiling were measured over one year at a UK hospital, enabling realistic parameters to be set for our surface efficacy test. A nebulizer, connected to a cascade impactor, aerosolized and uniformly deposited a Staphylococcus aureus suspension over test copper alloys and control stainless steel surfaces. Bacteria were enumerated following nebulization, and after a range of contact times, under [20°C, 50% RH] and [20°C, 40% RH] parameters reflecting in-use conditions; [37°C, 100% RH] was employed to reflect conditions used in ISO22196. All copper alloys produced a >4 log10 reduction after 24h under all conditions tested. Copper alloys were more effective at [37°C, 100% RH] showing a >4 log10 reduction after 30 min than at in-use conditions [20°C, 50% RH and 20°C, 40% RH], for which 60 min was required to achieve the same level of kill, for most but not all alloys. The use of the nebulizer to deposit bacterial inocula on surfaces showed little variability in results. Our method was more discriminatory than the ISO22196 enabling distinction between the bactericidal surface activity, which allows for a more rigorous selection of antimicrobial surfaces for potential use in healthcare settings. Copyright © 2013 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.

Effect of Groove Surface Texture on Tribological Characteristics and Energy Consumption under High Temperature Friction.

PubMed

Wu, Wei; Chen, Guiming; Fan, Boxuan; Liu, Jianyou

2016-01-01

Energy consumption and tribological properties could be improved by proper design of surface texture in friction. However, some literature focused on investigating their performance under high temperature. In the study, different groove surface textures were fabricated on steels by a laser machine, and their tribological behaviors were experimentally studied with the employment of the friction and wear tester under distinct high temperature and other working conditions. The friction coefficient was recorded, and wear performance were characterized by double light interference microscope, scanning electron microscope (SEM) and x-ray energy dispersive spectrometry (EDS). Then, the performances of energy consumptions were carefully estimated. Results showed that friction coefficient, wear, and energy consumption could almost all be reduced by most textures under high temperature conditions, but to a different extent which depends on the experimental conditions and texture parameters. The main improvement mechanisms were analyzed, such as the hardness change, wear debris storage, thermal stress release and friction induced temperature reduction by the textures. Finally, a scattergram of the relatively reduced ratio of the energy consumption was drawn for different surface textures under four distinctive experimental conditions to illustrate the comprehensive energy consumption improving ability of textures, which was of benefit for the application of texture design.

Effect of Groove Surface Texture on Tribological Characteristics and Energy Consumption under High Temperature Friction

PubMed Central

Wu, Wei; Chen, Guiming; Fan, Boxuan; Liu, Jianyou

2016-01-01

Energy consumption and tribological properties could be improved by proper design of surface texture in friction. However, some literature focused on investigating their performance under high temperature. In the study, different groove surface textures were fabricated on steels by a laser machine, and their tribological behaviors were experimentally studied with the employment of the friction and wear tester under distinct high temperature and other working conditions. The friction coefficient was recorded, and wear performance were characterized by double light interference microscope, scanning electron microscope (SEM) and x-ray energy dispersive spectrometry (EDS). Then, the performances of energy consumptions were carefully estimated. Results showed that friction coefficient, wear, and energy consumption could almost all be reduced by most textures under high temperature conditions, but to a different extent which depends on the experimental conditions and texture parameters. The main improvement mechanisms were analyzed, such as the hardness change, wear debris storage, thermal stress release and friction induced temperature reduction by the textures. Finally, a scattergram of the relatively reduced ratio of the energy consumption was drawn for different surface textures under four distinctive experimental conditions to illustrate the comprehensive energy consumption improving ability of textures, which was of benefit for the application of texture design. PMID:27035658

INTEGRATED AND FIBER OPTICS: Investigation of the refractive index profile of inhomogeneous iron garnet films containing bismuth

NASA Astrophysics Data System (ADS)

Arzamastseva, G. V.; Kravchenko, V. B.; Filimonova, L. M.

1989-02-01

The refractive index n of quasihomogeneous iron garnet films with the composition (YGdYb)3 - xBixFe5 - yAlyO12 increased considerably as a result of reduction in the growth temperature Tg. This was attributed mainly by an increase in x and a reduction in y. The dependences n(Tg) were used to select the conditions for growth of inhomogeneous (across the thickness) films and to predict the refractive index profile n(z), where z was measured from the free surface along the normal to the film. The spectra of optical modes were analyzed in the WKB approximation and this yielded the n(z) profiles for films with a refractive index n decreasing monotonically from the free surface and for films with the symmetric profile n(z) (buried waveguides). The n(z) profiles were compared with the distributions of the compensation temperature Tc(z), and of x(z) and y(z) across the thickness.

Predictive Model of Supercooled Water Droplet Pinning/Repulsion Impacting a Superhydrophobic Surface: The Role of the Gas-Liquid Interface Temperature.

PubMed

Mohammadi, Morteza; Tembely, Moussa; Dolatabadi, Ali

2017-02-28

Dynamical analysis of an impacting liquid drop on superhydrophobic surfaces is mostly carried out by evaluating the droplet contact time and maximum spreading diameter. In this study, we present a general transient model of the droplet spreading diameter developed from the previously defined mass-spring model for bouncing drops. The effect of viscosity was also considered in the model by definition of a dash-pot term extracted from experiments on various viscous liquid droplets on a superhydrophobic surface. Furthermore, the resultant shear force of the stagnation air flow was also considered with the help of the classical Homann flow approach. It was clearly shown that the proposed model predicts the maximum spreading diameter and droplet contact time very well. On the other hand, where stagnation air flow is present in contradiction to the theoretical model, the droplet contact time was reduced as a function of both droplet Weber numbers and incoming air velocities. Indeed, the reduction in the droplet contact time (e.g., 35% at a droplet Weber number of up to 140) was justified by the presence of a formed thin air layer underneath the impacting drop on the superhydrophobic surface (i.e., full slip condition). Finally, the droplet wetting model was also further developed to account for low temperature through the incorporation of classical nucleation theory. Homogeneous ice nucleation was integrated into the model through the concept of the reduction of the supercooled water drop surface tension as a function of the gas-liquid interface temperature, which was directly correlated with the Nusselt number of incoming air flow. It was shown that the experimental results was qualitatively predicted by the proposed model under all supercooling conditions (i.e., from -10 to -30 °C).

Oxygen reduction on a Pt(111) catalyst in HT-PEM fuel cells by density functional theory

NASA Astrophysics Data System (ADS)

Sun, Hong; Li, Jie; Almheiri, Saif; Xiao, Jianyu

2017-08-01

The oxygen reduction reaction plays an important role in the performance of high-temperature proton exchange membrane (HT-PEM) fuel cells. In this study, a molecular dynamics model, which is based on the density functional theory and couples the system's energy, the exchange-correlation energy functional, the charge density distribution function, and the simplified Kohn-Sham equation, was developed to simulate the oxygen reduction reaction on a Pt(111) surface. Additionally, an electrochemical reaction system on the basis of a four-electron reaction mechanism was also developed for this simulation. The reaction path of the oxygen reduction reaction, the product structure of each reaction step and the system's energy were simulated. It is found that the first step reaction of the first hydrogen ion with the oxygen molecule is the controlling step of the overall reaction. Increasing the operating temperature speeds up the first step reaction rate and slightly decreases its reaction energy barrier. Our results provide insight into the working principles of HT-PEM fuel cells.

Inactivation of Burkholderia pseudomallei on environmental surfaces using spray-applied, common liquid disinfectants.

PubMed

Calfee, M W; Wendling, M

2015-11-01

Five commercially available liquid antimicrobials were evaluated for their ability to decontaminate common environmental surface materials, contaminated with Burkholderia pseudomallei, using a spray-based disinfectant delivery procedure. Tests were conducted at both an ambient temperature (c. 20°C) and a lower temperature (c. 12°C) condition. Nonporous materials (glass and aluminium) were more easily decontaminated than porous materials (wood, concrete and carpet). Citric acid (1%) demonstrated poor efficacy in all test conditions. Bleach (pH-adjusted), ethanol (70%), quaternary ammonium and PineSol®, demonstrated high (>6 log10 reduction) efficacies on glass and aluminium at both temperatures, but achieved varying results for wood, carpet and concrete. Temperature had minimal effect on decontamination efficacy during these tests. Much of the antimicrobial efficacy data for pathogenic micro-organisms are generated with testing that utilizes hard nonporous surface materials. These data are not directly translatable for decontaminant selection following an incident whereby complex and porous environmental surfaces are contaminated. This study presents efficacy data for spray-applied antimicrobial liquids, when used to decontaminate common environmental surfaces contaminated with Burkholderia pseudomallei. These data can help responders develop effective remediation strategies following an environmental contamination incident involving B. pseudomallei. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Thermal repellent properties of surface coating using silica

NASA Astrophysics Data System (ADS)

Lee, Y. Y.; Halim, M. S.; Aminudin, E.; Guntor, N. A.

2017-11-01

Extensive land development in urban areas is completely altering the surface profile of human living environment. As cities growing rapidly, impervious building and paved surfaces are replacing the natural landscape. In the developing countries with tropical climate, large masses of building elements, such as brick wall and concrete members, absorb and store large amount of heat, which in turn radiate back to the surrounding air during the night time. This bubble of heat is known as urban heat island (UHI). The use of high albedo urban surfaces is an inexpensive measure that can reduce surrounded temperature. Thus, the main focus of this study is to investigate the ability of silica, SiO2, with high albedo value, to be used as a thermal-repelled surface coating for brick wall. Three different silica coatings were used, namely silicone resin, silicone wax and rain repellent and one exterior commercial paint (jota shield paint) that commercially available in the market were applied on small-scale brick wall models. An uncoated sample also had been fabricated as a control sample for comparison. These models were placed at the outdoor space for solar exposure. Outdoor environment measurement was carried out where the ambient temperature, surface temperature, relative humidity and UV reflectance were recorded. The effect of different type of surface coating on temperature variation of the surface brick wall and the thermal performance of coatings as potential of heat reduction for brick wall have been studied. Based on the results, model with silicone resin achieved the lowest surface temperature which indicated that SiO2 can be potentially used to reduce heat absorption on the brick wall and further retains indoor passive thermal comfortability.

Determination of Ni Release in NiTi SMA with Surface Modification by Nitrogen Plasma Immersion Ion Implantation

NASA Astrophysics Data System (ADS)

de Camargo, Eliene Nogueira; Oliveira Lobo, Anderson; Silva, Maria Margareth Da; Ueda, Mario; Garcia, Edivaldo Egea; Pichon, Luc; Reuther, Helfried; Otubo, Jorge

2011-07-01

NiTi SMA is a promising material in the biomedical area due to its mechanical properties and biocompatibility. However, the nickel in the alloy may cause allergic and toxic reactions and thus limiting its applications. It was evaluated the influence of surface modification in NiTi SMA by nitrogen plasma immersion ion implantation (varying temperatures, and exposure time as follows: <250 °C/2 h, 290 °C/2 h, and 560 °C/1 h) in the amount of nickel released using immersion test in simulated body fluid. The depth of the nitrogen implanted layer increased as the implantation temperature increased resulting in the decrease of nickel release. The sample implanted in high implantation temperature presented 35% of nickel release reduction compared to reference sample.

Impacts of Climate Change on Surface Ozone and Intercontinental Ozone Pollution: A Multi-Model Study

NASA Technical Reports Server (NTRS)

Doherty, R. M.; Wild, O.; Shindell, D. T.; Zeng, G.; MacKenzie, I. A.; Collins, W. J.; Fiore, A. M.; Stevenson, D. S.; Dentener, F. J.; Schultz, M. G.;

Effects of the March 2015 solar eclipse on near-surface atmospheric electricity.

PubMed

Bennett, A J

2016-09-28

Measurements of atmospheric electrical and standard meteorological parameters were made at coastal and inland sites in southern England during the 20 March 2015 partial solar eclipse. Clear evidence of a reduction in air temperature resulting from the eclipse was found at both locations, despite one of them being overcast during the entire eclipse. The reduction in temperature was expected to affect the near-surface electric field (potential gradient (PG)) through a reduction in turbulent transfer of space charge. No such effect could be unambiguously confirmed, however, with variability in PG and air-Earth current during the eclipse being comparable to pre- and post-eclipse conditions. The already low solar radiation for this latitude, season and time of day was likely to have contributed to the reduced effect of the eclipse on atmospheric electricity through boundary layer stability. The absence of a reduction in mean PG shortly after time of maximum solar obscuration, as observed during eclipses at lower geomagnetic latitude, implied that there was no significant change in atmospheric ionization from cosmic rays above background variability. This finding was suggested to be due to the relative importance of cosmic rays of solar and galactic origin at geomagnetic mid-latitudes.This article is part of the themed issue 'Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse'. © 2016 The Author(s).

Partially oxidized iridium clusters within dendrimers: size-controlled synthesis and selective hydrogenation of 2-nitrobenzaldehyde

NASA Astrophysics Data System (ADS)

Higaki, Tatsuya; Kitazawa, Hirokazu; Yamazoe, Seiji; Tsukuda, Tatsuya

2016-06-01

Iridium clusters nominally composed of 15, 30 or 60 atoms were size-selectively synthesized within OH-terminated poly(amidoamine) dendrimers of generation 6. Spectroscopic characterization revealed that the Ir clusters were partially oxidized. All the Ir clusters efficiently converted 2-nitrobenzaldehyde to anthranil and 2-aminobenzaldehyde under atmospheric hydrogen at room temperature in toluene via selective hydrogenation of the NO2 group. The selectivity toward 2-aminobenzaldehyde over anthranil was improved with the reduction of the cluster size. The improved selectivity is ascribed to more efficient reduction than intramolecular heterocyclization of a hydroxylamine intermediate on smaller clusters that have a higher Ir(0)-phase population on the surface.Iridium clusters nominally composed of 15, 30 or 60 atoms were size-selectively synthesized within OH-terminated poly(amidoamine) dendrimers of generation 6. Spectroscopic characterization revealed that the Ir clusters were partially oxidized. All the Ir clusters efficiently converted 2-nitrobenzaldehyde to anthranil and 2-aminobenzaldehyde under atmospheric hydrogen at room temperature in toluene via selective hydrogenation of the NO2 group. The selectivity toward 2-aminobenzaldehyde over anthranil was improved with the reduction of the cluster size. The improved selectivity is ascribed to more efficient reduction than intramolecular heterocyclization of a hydroxylamine intermediate on smaller clusters that have a higher Ir(0)-phase population on the surface. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01460g

The rising greenhouse effect: experiments and observations in and around the Alps

NASA Astrophysics Data System (ADS)

Philipona, R.

2010-09-01

The rapid temperature increase of more than 1°C in central Europe over the last three decades is larger than expected from anthropogenic greenhouse warming. Surface radiation flux measurements in and around the Alps in fact confirm that not only thermal longwave radiation but also solar shortwave radiation increased since the 1980s. Surface energy budget analyses reveal the rising surface temperature to be well correlated with the radiative forcing, and also show an increase of the kinetic energy fluxes explaining the rise of atmospheric water vapor. Solar radiation mainly increased due to a strong decline of anthropogenic aerosols since mid of the 1980s. While anthropogenic aerosols were mainly accumulated in the boundary layer, this reduction let solar radiation to recover (solar brightening after several decades of solar dimming) mainly at low altitudes around the Alps. At high elevations in the Alps, solar forcing is much smaller and the respective temperature rise is also found to be smaller than in the lowlands. The fact that temperature increases less in the Alps than at low elevations is unexpected in the concept of greenhouse warming, but the radiation budget analyses clearly shows that in the plains solar forcing due to declining aerosols additionally increased surface temperature, whereas in the Alps temperature increased primarily due to greenhouse warming that is particularly manifested by a strong water vapor feedback.

Reduction mechanism of surface oxide films and characterization of formations on pulse electric-current sintered Al Mg alloy powders

NASA Astrophysics Data System (ADS)

Xie, Guoqiang; Ohashi, Osamu; Song, Minghui; Mitsuishi, Kazutaka; Furuya, Kazuo

2005-02-01

The microstructure of interfaces between powder particles in Al-Mg alloy specimens sintered by pulse electric-current sintering (PECS) process was characterized using high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS). The crystalline precipitates with nano-size in the interface were observed in all of Al-Mg alloy specimens. The composition was determined to be MgAl 2O 4 or MgO, or both of them, which depended on Mg content in alloy powder and sintering temperature. The precipitates were suggested to contribute to reduction reaction of Mg with oxide films originally covered at powder particles surface.

The impact of different cooling strategies on urban air temperatures: the cases of Campinas, Brazil and Mendoza, Argentina

NASA Astrophysics Data System (ADS)

Alchapar, Noelia Liliana; Pezzuto, Claudia Cotrim; Correa, Erica Norma; Chebel Labaki, Lucila

2017-10-01

This paper describes different ways of reducing urban air temperature and their results in two cities: Campinas, Brazil—a warm temperate climate with a dry winter and hot summer (Cwa), and Mendoza, Argentina—a desert climate with cold steppe (BWk). A high-resolution microclimate modeling system—ENVI-met 3.1—was used to evaluate the thermal performance of an urban canyon in each city. A total of 18 scenarios were simulated including changes in the surface albedo, vegetation percentage, and the H/W aspect ratio of the urban canyons. These results revealed the same trend in behavior for each of the combinations of strategies evaluated in both cities. Nevertheless, these strategies produce a greater temperature reduction in the warm temperate climate (Cwa). Increasing the vegetation percentage reduces air temperatures and mean radiant temperatures in all scenarios. In addition, there is a greater decrease of urban temperature with the vegetation increase when the H/W aspect ratio is lower. Also, applying low albedo on vertical surfaces and high albedo on horizontal surfaces is successful in reducing air temperatures without raising the mean radiant temperature. The best combination of strategies—60 % of vegetation, low albedos on walls and high albedos on pavements and roofs, and 1.5 H/W—could reduce air temperatures up to 6.4 °C in Campinas and 3.5 °C in Mendoza.

Reduction of the Livestock Ammonia Emission under the Changing Temperature during the Initial Manure Nitrogen Biomineralization

PubMed Central

Bagdonienė, Indrė; Baležentienė, Ligita

2013-01-01

Experimental data were applied for the modelling optimal cowshed temperature environment in laboratory test bench by a mass-flow method. The principal factor affecting exponent growth of ammonia emission was increasing air and manure surface temperature. With the manure temperature increasing from 4°C to 30°C, growth in the ammonia emission grew fourfold, that is, from 102 to 430 mg m−2h−1. Especial risk emerges when temperature exceeds 20°C: an increase in temperature of 1°C contributes to the intensity of ammonia emission by 17 mg m−2h−1. The temperatures of air and manure surface as well as those of its layers are important when analysing emission processes from manure. Indeed, it affects the processes occurring on the manure surface, namely, dehydration and crust formation. To reduce ammonia emission from cowshed, it is important to optimize the inner temperature control and to manage air circulation, especially at higher temperatures, preventing the warm ambient air from blowing direct to manure. Decrease in mean annual temperature of 1°C would reduce the annual ammonia emission by some 5.0%. The air temperature range varied between −15°C and 30°C in barns. The highest mean annual temperature (14.6°C) and ammonia emission (218 mg m−2h−1) were observed in the semideep cowshed. PMID:24453912

Temporal Changes in the Observed Relationship between Cloud Cover and Surface Air Temperature.

NASA Astrophysics Data System (ADS)

Sun, Bomin; Groisman, Pavel Ya.; Bradley, Raymond S.; Keimig, Frank T.

2000-12-01

The relationship between cloud cover and near-surface air temperature and its decadal changes are examined using the hourly synoptic data for the past four to six decades from five regions of the Northern Hemisphere: Canada, the United States, the former Soviet Union, China, and tropical islands of the western Pacific. The authors define the normalized cloud cover-surface air temperature relationship, NOCET or dT/dCL, as a temperature anomaly with a unit (one-tenth) deviation of total cloud cover from its average value. Then mean monthly NOCET time series (night- and daytime, separately) are area-averaged and parameterized as functions of surface air humidity and snow cover. The day- and nighttime NOCET variations are strongly anticorrelated with changes in surface humidity. Furthermore, the daytime NOCET changes are positively correlated to changes in snow cover extent. The regionally averaged nighttime NOCET varies from 0.05 K tenth1 in the wet Tropics to 1.0 K tenth1 at midlatitudes in winter. The daytime regional NOCET ranges from 0.4 K tenth1 in the Tropics to 0.7 K tenth1 at midlatitudes in winter.The authors found a general strengthening of a daytime surface cooling during the post-World War II period associated with cloud cover over the United States and China, but a minor reduction of this cooling in higher latitudes. Furthermore, since the 1970s, a prominent increase in atmospheric humidity has significantly weakened the effectiveness of the surface warming (best seen at nighttime) associated with cloud cover.The authors apportion the spatiotemporal field of interactions between total cloud cover and surface air temperature into a bivariate relationship (described by two equations, one for daytime and one for nighttime) with surface air humidity and snow cover and two constant factors. These factors are invariant in space and time domains. It is speculated that they may represent empirical estimates of the overall cloud cover effect on the surface air temperature.

Additional Term in the Webb-Pearman-Leuning Correction due to Surface Heating From an Open-Path Gas Analyzer

NASA Astrophysics Data System (ADS)

Burba, G. G.; Anderson, D. J.; Xu, L.; McDermitt, D. K.

2006-12-01

One laboratory and two field experiments were conducted between September 2005 and September 2006 to investigate the impact of an added heat flux in the sample path of the LI-7500 CO2/H2O gas analyzer caused by the difference in temperatures between the ambient air and the surface of the instrument. Contribution of heat dissipated from the internal instrument electronics toward the instrument surface was substantial, especially in cold conditions. In the environmental chamber, surface heating ranged from about 0 °C above ambient, at air temperatures above +40 °C, to about 7 °C, at an air temperature of -25 °C. In the field, daytime temperature differences were overall smaller than in the chamber due to convective cooling by the wind and some long-wave cooling, despite the added sunlight contribution. However, considerable temperature gradients (up to 2 °C per 1mm) were still observed over the lower window of the LI-7500, suggesting strong sensible heat fluxes above the instrument surface. The nighttime situation was different due to strong long-wave cooling of some parts of the instrument, partially (and sometimes, fully) offsetting effects of the electronics heating in the other parts. The concept of an added heat flux term in the Web-Pearman-Leuning correction is revisited, and effect of the instrument surface heating on the CO2 flux measurements is examined. The proposed concept is presented in detail, along with resulted corrections to the originally computed flux. Field data are examined separately for daytime and nighttime cases, and on hourly and seasonal time scales. Significant reduction in the apparent CO2 uptake during off-season periods was observed as a result of applying correction due to the added heat, while fluxes during the growing season have not been noticeably affected. The correction also resulted in the elimination of most of the wrong signs from the off-season open- path CO2 fluxes, in considerable reduction in variability of the data, elimination of the difference between measurements made with the LI-6262 and the LI-7500, and in a significant improvement in off-season integrations of CO2 exchange. A framework was created to develop a site-specific practical correction due to instrument surface heating. The concept may provide a basis for further research in the area of instrument temperature affecting the measurement of the open-path fluxes. Proposed correction may be useful for future CO2 flux research, and it can also be applied to pre-existing data today.

The salinity effect in a mixed layer ocean model

NASA Technical Reports Server (NTRS)

Miller, J. R.

1976-01-01

A model of the thermally mixed layer in the upper ocean as developed by Kraus and Turner and extended by Denman is further extended to investigate the effects of salinity. In the tropical and subtropical Atlantic Ocean rapid increases in salinity occur at the bottom of a uniformly mixed surface layer. The most significant effects produced by the inclusion of salinity are the reduction of the deepening rate and the corresponding change in the heating characteristics of the mixed layer. If the net surface heating is positive, but small, salinity effects must be included to determine whether the mixed layer temperature will increase or decrease. Precipitation over tropical oceans leads to the development of a shallow stable layer accompanied by a decrease in the temperature and salinity at the sea surface.

Electron scattering in graphene with adsorbed NaCl nanoparticles

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

Drabińska, Aneta, E-mail: Aneta.Drabinska@fuw.edu.pl; Kaźmierczak, Piotr; Bożek, Rafał

2015-01-07

In this work, the results of contactless magnetoconductance and Raman spectroscopy measurements performed for a graphene sample after its immersion in NaCl solution were presented. The properties of the immersed sample were compared with those of a non-immersed reference sample. Atomic force microscopy and electron spin resonance experiments confirmed the deposition of NaCl nanoparticles on the graphene surface. A weak localization signal observed using contactless magnetoconductance showed the reduction of the coherence length after NaCl treatment of graphene. Temperature dependence of the coherence length indicated a change from ballistic to diffusive regime in electron transport after NaCl treatment. The mainmore » inelastic scattering process was of the electron-electron type but the major reason for the reduction of the coherence length at low temperatures was additional, temperature independent, inelastic scattering. We associate it with spin flip scattering, caused by NaCl nanoparticles present on the graphene surface. Raman spectroscopy showed an increase in the D and D′ bands intensities for graphene after its immersion in NaCl solution. An analysis of the D, D′, and G bands intensities proved that this additional scattering is related to the decoration of vacancies and grain boundaries with NaCl nanoparticles, as well as generation of new on-site defects as a result of the decoration of the graphene surface with NaCl nanoparticles. The observed energy shifts of 2D and G bands indicated that NaCl deposition on the graphene surface did not change carrier concentration, but reduced compressive biaxial strain in the graphene layer.« less

Efficacy of Neutral Electrolyzed Water, Quaternary Ammonium and Lactic Acid-Based Solutions in Controlling Microbial Contamination of Food Cutting Boards Using a Manual Spraying Technique.

PubMed

Al-Qadiri, Hamzah M; Ovissipour, Mahmoudreza; Al-Alami, Nivin; Govindan, Byju N; Shiroodi, Setareh Ghorban; Rasco, Barbara

2016-05-01

Bactericidal activity of neutral electrolyzed water (NEW), quaternary ammonium (QUAT), and lactic acid-based solutions was investigated using a manual spraying technique against Salmonella Typhimurium, Escherichia coli O157:H7, Campylobacter jejuni, Listeria monocytogenes and Staphylococcus aureus that were inoculated onto the surface of scarred polypropylene and wooden food cutting boards. Antimicrobial activity was also examined when using cutting boards in preparation of raw chopped beef, chicken tenders or salmon fillets. Viable counts of survivors were determined as log10 CFU/100 cm(2) within 0 (untreated control), 1, 3, and 5 min of treatment at ambient temperature. Within the first minute of treatment, NEW and QUAT solutions caused more than 3 log10 bacterial reductions on polypropylene surfaces whereas less than 3 log10 reductions were achieved on wooden surfaces. After 5 min of treatment, more than 5 log10 reductions were achieved for all bacterial strains inoculated onto polypropylene surfaces. Using NEW and QUAT solutions within 5 min reduced Gram-negative bacteria by 4.58 to 4.85 log10 compared to more than 5 log10 reductions in Gram-positive bacteria inoculated onto wooden surfaces. Lactic acid treatment was significantly less effective (P < 0.05) compared to NEW and QUAT treatments. A decline in antimicrobial effectiveness was observed (0.5 to <2 log10 reductions were achieved within the first minute) when both cutting board types were used to prepare raw chopped beef, chicken tenders or salmon fillets. © 2016 Institute of Food Technologists®

Surfactant-assisted coal liquefaction

NASA Technical Reports Server (NTRS)

Hsu, G. C.

1977-01-01

Improved process of coal liquefaction utilizing nonaqueous surfactant has increased oil yield from 50 to about 80%. Asphaltene molecule formation of colloid particles is prevented by surfactant. Separated molecules present more surface area for hydrogenation reaction. Lower requirements for temperature, pressure, and hydrogen lead to reduction in capital and operation costs.

Lantana camara Linn leaf extract mediated green synthesis of gold nanoparticles and study of its catalytic activity

NASA Astrophysics Data System (ADS)

Dash, Shib Shankar; Bag, Braja Gopal; Hota, Poulami

2015-03-01

A facile one-step green synthesis of stable gold nanoparticles (AuNPs) has been described using chloroauric acid (HAuCl4) and the leaf extract of Lantana camara Linn (Verbenaceae family) at room temperature. The leaf extract enriched in various types of plant secondary metabolites is highly efficient for the reduction of chloroaurate ions into metallic gold and stabilizes the synthesized AuNPs without any additional stabilizing or capping agents. Detailed characterizations of the synthesized gold nanoparticles were carried out by surface plasmon resonance spectroscopy, transmission electron microscopy, dynamic light scattering, Zeta potential, X-ray diffraction and Fourier transform-infrared spectroscopy studies. The synthesized AuNPs have been utilized as a catalyst for the sodium borohydride reduction of 4-nitrophenol to 4-aminophenol in water at room temperature under mild reaction condition. The kinetics of the reduction reaction has been studied spectrophotometrically.

Experimental assessment of the performance of ablative heat shield materials from plasma wind tunnel testing

NASA Astrophysics Data System (ADS)

Löhle, S.; Hermann, T.; Zander, F.

2018-06-01

A method for assessing the performance of typical heat shield materials is presented in this paper. Three different material samples, the DLR material Zuram, the Airbus material Asterm and the carbon preform Calcarb were tested in the IRS plasma wind tunnel PWK1 at the same nominal condition. State of the art diagnostic tools, i.e., surface temperature with pyrometry and thermography and boundary layer optical emission spectroscopy were completed by photogrammetric surface recession measurements. These data allow the assessment of the net heat flux for each material. The analysis shows that the three materials each have a different effect on heat flux mitigation with ASTERM showing the largest reduction in surface heat flux. The effect of pyrolysis and blowing is clearly observed and the heat flux reduction can be determined from an energy balance.

Significant thermal conductivity reduction of silicon nanowire forests through discrete surface doping of germanium

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

Pan, Ying; Hong, Guo; Raja, Shyamprasad N.

2015-03-02

Silicon nanowires (SiNWs) are promising materials for the realization of highly-efficient and cost effective thermoelectric devices. Reduction of the thermal conductivity of such materials is a necessary and viable pathway to achieve sufficiently high thermoelectric efficiencies, which are inversely proportional to the thermal conductivity. In this article, vertically aligned forests of SiNW and germanium (Ge)-doped SiNW with diameters around 100 nm have been fabricated, and their thermal conductivity has been measured. The results show that discrete surface doping of Ge on SiNW arrays can lead to 23% reduction in thermal conductivity at room temperature compared to uncoated SiNWs. Such reduction canmore » be further enhanced to 44% following a thermal annealing step. By analyzing the binding energy changes of Ge-3d and Si-2p using X-ray photoelectron spectroscopy, we demonstrate that surface doped Ge interacts strongly with Si, enhancing phonon scattering at the Si-Ge interface as has also been shown in non-equilibrium molecular dynamics studies of single nanowires. Overall, our results suggest a viable pathway to improve the energy conversion efficiency of nanowire-forest thermoelectric nanomaterials.« less

Hydrothermal plume mapping as a prospecting tool for seafloor sulfide deposits: a case study at the Zouyu-1 and Zouyu-2 hydrothermal fields in the southern Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Tao, Chunhui; Chen, Sheng; Baker, Edward T.; Li, Huaiming; Liang, Jin; Liao, Shili; Chen, Yongshun John; Deng, Xianming; Zhang, Guoyin; Gu, Chunhua; Wu, Jialin

2017-06-01

Seafloor hydrothermal polymetallic sulfide deposits are a new type of resource, with great potential economic value and good prospect development. This paper discusses turbidity, oxidation-reduction potential, and temperature anomalies of hydrothermal plumes from the Zouyu-1 and Zouyu-2 hydrothermal fields on the southern Mid-Atlantic Ridge. We use the known location of these vent fields and plume data collected in multiple years (2009, 2011, 2013) to demonstrate how real-time plume exploration can be used to locate active vent fields, and thus associated sulfide deposits. Turbidity anomalies can be detected 10 s of km from an active source, but the location precision is no better than a few kilometers because fine-grained particles are quasi-conservative over periods of many days. Temperature and oxidation-reduction potential anomalies provide location precision of a few hundred meters. Temperature anomalies are generally weak and difficult to reliably detect, except by chance encounters of a buoyant plume. Oxidation-reduction potential is highly sensitive (nmol concentrations of reduced hydrothermal chemicals) to discharges of all temperatures and responds immediately to a plume encounter. Real-time surveys using continuous tows of turbidity and oxidation-reduction potential sensors offer the most efficient and precise surface ship exploration presently possible.

Relative sliding durability of two candidate high temperature oxide fiber seal materials

NASA Technical Reports Server (NTRS)

Dellacorte, Christopher; Steinetz, Bruce M.

1991-01-01

A test program to determine the relative sliding durability of two candidate ceramic fibers for high temperature sliding seal applications is described. Pin on disk tests were used to evaluate potential seal materials. Friction during the tests and fiber wear, indicated by the extent of fibers broken in a test bundle or yarn, was measured at the end of a test. In general, friction and wear increase with test temperature. This may be due to a reduction in fiber strength, a change in the surface chemistry at the fiber/counterface interface due to oxidation, adsorption and/or desorption of surface species and, to a lesser extent, an increase in counterface surface roughness due to oxidation at elevated temperatures. The relative fiber durability correlates with tensile strength indicating that tensile data, which is more readily available than sliding durability data, may be useful in predicting fiber wear behavior under various conditions. A simple model developed using dimensional analysis shows that the fiber durability is related to a dimensionless parameter which represents the ratio of the fiber strength to the fiber stresses imposed by sliding.

Impact of cycling at low temperatures on the safety behavior of 18650-type lithium ion cells: Combined study of mechanical and thermal abuse testing accompanied by post-mortem analysis

NASA Astrophysics Data System (ADS)

Friesen, Alex; Horsthemke, Fabian; Mönnighoff, Xaver; Brunklaus, Gunther; Krafft, Roman; Börner, Markus; Risthaus, Tim; Winter, Martin; Schappacher, Falko M.

2016-12-01

The impact of cycling at low temperatures on the thermal and mechanical abuse behavior of commercial 18650-type lithium ion cells was compared to fresh cells. Post-mortem analyses revealed a deposition of high surface area lithium (HSAL) metal on the graphite surface accompanied by severe electrolyte decomposition. Heat wait search (HWS) tests in an accelerating rate calorimeter (ARC) were performed to investigate the thermal abuse behavior of aged and fresh cells under quasi-adiabatic conditions, showing a strong shift of the onset temperature for exothermic reactions. HSAL deposition promotes the reduction of the carbonate based electrolyte due to the high reactivity of lithium metal with high surface area, leading to a thermally induced decomposition of the electrolyte to produce volatile gaseous products. Nail penetration tests showed a change in the thermal runaway (TR) behavior affected by the decomposition reaction. This study indicates a greater thermal hazard for LIB cells at higher SOC and experiencing aging at low temperature.

Heterogenous Material Integration and Band Engineering With Type II Superlattice

DTIC Science & Technology

2015-10-26

tunneling or surface effects. A careful variable area diode study is needed to investigate the effect of surfaces in this low temperature regime. In the mid...theoretically predicted advantages of T2SL over bulk MCT detectors, including lower tunneling currents [1] and suppressed Auger recombination rates [2...The tunneling currents are also reduced due to significant reduction in field drop. Thus the device can be made diffusion limited over wide range of

Rubber friction: The contribution from the area of real contact.

PubMed

Tiwari, A; Miyashita, N; Espallargas, N; Persson, B N J

2018-06-14

There are two contributions to the friction force when a rubber block is sliding on a hard and rough substrate surface, namely, a contribution F ad = τ f A from the area of real contact A and a viscoelastic contribution F visc from the pulsating forces exerted by the substrate asperities on the rubber block. Here we present experimental results obtained at different sliding speeds and temperatures, and we show that the temperature dependency of the shear stress τ f , for temperatures above the rubber glass transition temperature T g , is weaker than that of the bulk viscoelastic modulus. The physical origin of τ f for T > T g is discussed, and we propose that its temperature dependency is determined by the rubber molecule segment mobility at the sliding interface, which is higher than in the bulk because of increased free-volume effect due to the short-wavelength surface roughness. This is consistent with the often observed reduction in the glass transition temperature in nanometer-thick surface layers of glassy polymers. For temperatures T < T g , the shear stress τ f is nearly velocity independent and of similar magnitude as observed for glassy polymers such as PMMA or polyethylene. In this case, the rubber undergoes plastic deformations in the asperity contact regions and the contact area is determined by the rubber penetration hardness. For this case, we propose that the frictional shear stress is due to slip at the interface between the rubber and a transfer film adsorbed on the concrete surface.

Structural and surface properties of CuO-ZnO-Cr{sub 2}O{sub 3} catalysts and their relationship with selectivity to higher alcohol synthesis

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

Campos-Martin, J.M.; Fierro, J.L.G.; Guerrero-Ruiz, A.

1995-10-01

A series of copper-zinc-chromium catalysts of different compositions and calcination temperatures has been prepared, characterized by several techniques (BET specific surface area, XRD, gravimetric TPR, TPD-CO, and XPS), and tested under high alcohol synthesis (HAS) conditions. CO hydrogenation was carried out at reaction temperatures of 523-598 K and 50 bar total pressure. The influence of catalyst composition, calcination temperature, and surface characteristics on the HAS selectivity was studied. The optimum HAS yields were found in the low Cr content region, but chromium was needed. Although chromium oxide does not seem to be involved in the catalytic site, its presence inmore » the catalyst composition is essential, owing to the larger specific surfaces and catalyst stability obtained at the highest reaction temperatures. For low Cr content composition, the temperature-programmed reduction (TPR) profiles were shifted to higher temperatures and simultaneously larger CO{sub 2} amounts were found in the temperature-programmed desorption profiles of adsorbed CO (TPD-CO). Photoelectron spectra (XPS) revealed that the oxidation state of copper is Cu{sup 2+} in the calcined catalysts and Cu{sup O} in the reduced ones; Cu{sup +} was only stabilized in a CuCr{sub 2}O{sub 4} spinel in the Cr-rich catalysts. These features derived from catalyst characterization are discussed in the framework of the catalytic behaviour for HAS synthesis. 53 refs., 7 figs., 4 tabs.« less

Rubber friction: The contribution from the area of real contact

NASA Astrophysics Data System (ADS)

Tiwari, A.; Miyashita, N.; Espallargas, N.; Persson, B. N. J.

2018-06-01

There are two contributions to the friction force when a rubber block is sliding on a hard and rough substrate surface, namely, a contribution Fad = τf A from the area of real contact A and a viscoelastic contribution Fvisc from the pulsating forces exerted by the substrate asperities on the rubber block. Here we present experimental results obtained at different sliding speeds and temperatures, and we show that the temperature dependency of the shear stress τf, for temperatures above the rubber glass transition temperature Tg, is weaker than that of the bulk viscoelastic modulus. The physical origin of τf for T > Tg is discussed, and we propose that its temperature dependency is determined by the rubber molecule segment mobility at the sliding interface, which is higher than in the bulk because of increased free-volume effect due to the short-wavelength surface roughness. This is consistent with the often observed reduction in the glass transition temperature in nanometer-thick surface layers of glassy polymers. For temperatures T < Tg, the shear stress τf is nearly velocity independent and of similar magnitude as observed for glassy polymers such as PMMA or polyethylene. In this case, the rubber undergoes plastic deformations in the asperity contact regions and the contact area is determined by the rubber penetration hardness. For this case, we propose that the frictional shear stress is due to slip at the interface between the rubber and a transfer film adsorbed on the concrete surface.

Thermal Imaging of Body Surface Temperature Distribution in Women with Anorexia Nervosa.

PubMed

Chudecka, Monika; Lubkowska, Anna

2016-01-01

The drastic reduction in body weight observed in anorexia nervosa (AN) leads to various endocrine changes and consequently to disturbance in thermoregulation mechanisms and body temperature. Thermography allows for a noninvasive diagnosis of the distribution of skin surface temperatures, which is especially important for difficult patients such as women with AN, who are often very sensitive and difficult to treat. The main aim of this study was to measure the mean temperatures (Tmean ) of selected body areas in young women diagnosed with AN and identify those areas where the temperature differences were particularly significant between healthy women and them. Additionally, we determined the relationships between body mass index, body composition (especially subcutaneous and VFM) and the value of mean surface temperature (Tmean ) in AN woman. In the subjects with AN, Tmean of the abdomen, lower back and thighs were significantly higher than in the reference group, while Tmean of the hands were significantly lower. Among other things, analysis showed a significant negative correlation between Tmean of the abdomen, lower back and thighs, and the mass of subcutaneous and visceral fat. The lower Tmean of the hand was directly proportional to the reduced anthropomorphic parameters. The direct evaluation of body surface temperature distribution could provide clinical implications for the treatment of anorexic patients, including the potential use of thermotherapy in stimulating the circulatory system, especially in hypothermia, bradycardia and hypotension. Copyright © 2015 John Wiley & Sons, Ltd and Eating Disorders Association.

Influences of synthesis methods and modifier addition on the properties of Ni-based catalysts supported on reticulated ceramic foams

NASA Astrophysics Data System (ADS)

Nikolić, Vesna; Kamberović, Željko; Anđić, Zoran; Korać, Marija; Sokić, Miroslav; Maksimović, Vesna

2014-08-01

A method of synthesizing Ni-based catalysts supported on α-Al2O3-based foams was developed. The foams were impregnated with aqueous solutions of metal chlorides under an air atmosphere using an aerosol route. Separate procedures involved calcination to form oxides and drying to obtain chlorides on the foam surface. The synthesized samples were subsequently reduced with hydrogen. With respect to the Ni/Al2O3 catalysts, the chloride reduction route enabled the formation of a Ni coating without agglomerates or cracks. Further research included catalyst modification by the addition of Pd, Cu, and Fe. The influences of the additives on the degree of reduction and on the low-temperature reduction effectiveness (533 and 633 K) were examined and compared for the catalysts obtained from oxides and chlorides. Greater degrees of reduction were achieved with chlorides, whereas Pd was the most effective modifier among those investigated. The reduction process was nearly complete at 533 K in the sample that contained 0.1wt% Pd. A lower reduction temperature was utilized, and the calcination step was avoided, which may enhance the economical and technological aspects of the developed catalyst production method.

An anti-bacterial approach to nanoscale roughening of biomimetic rice-like pattern PP by thermal annealing

NASA Astrophysics Data System (ADS)

Jafari Nodoushan, Emad; Ebrahimi, Nadereh Golshan; Ayazi, Masoumeh

2017-11-01

In this paper, we introduced thermal annealing treatment as an effective way of increasing the nanoscale roughness of a semi-crystalline polymer surface. Annealing treatment applied to a biomimetic microscale pattern of rice leaf to achieve a superhydrophobic surface with a hierarchical roughness. Resulted surfaces was characterized by XRD, AFM and FE-SEM instruments and showed an increase of roughness and cristallinity within both time and temperature of treatment. These two parameters also impact on measured static contact angle up to 158°. Bacterial attachment potency has an inverse relationship with the similarity of surface pattern dimensions and bacterial size and due to that, thermal annealing could be an effective way to create anti-bacterial surface beyond its effect on water repellency. Point in case, the anti-bacterial properties of produced water-repellence surfaces of PP were measured and counted colonies of both gram-negative (E. coli) and gram-positive (S. aureus) bacteria reduced with the nature of PP and hierarchical pattern on that. Anti-bacterial characterization of the resulted surface reveals a stunning reduction in adhesion of gram-positive bacteria to the surface. S. aureus reduction rates equaled to 95% and 66% when compared to control blank plate and smooth surface of PP. Moreover, it also could affect the other type of bacteria, gram-negative (E. coli). In the latter case, adhesion reduction rates calculated 66% and 53% when against to the same controls, respectively.

The response of tropical cyclone activity to tropospheric aerosols, greenhouse gases and volcanic eruptions

NASA Astrophysics Data System (ADS)

Camargo, S. J.; Sobel, A. H.; Polvani, L. M.; Emanuel, K.; Previdi, M. J.

2017-12-01

Previous work has shown that aerosol cooling reduces tropical cyclone (TC) potential intensity (PI) more strongly than greenhouse gas warming increases it. This has the consequence that PI shows only small increases in simulations of the historical period despite considerable global warming over that period. We use CMIP5 models, as well as offline radiative kernels, to better understand this result. The outsize effect of aerosol forcing is a consequence of the fact that tropospheric aerosols act in the shortwave while greenhouse gases act in the longwave. Shortwave forcing has a greater impact on PI than does longwave, because of the differences in the response of the surface energy budget to the direct, temperature-independent component of the forcing. Shortwave forcing mainly drives the climate system in the surface, while greenhouse gases do so at the top of the atmosphere, so that net longwave flux associated with a temperature change can be small, especially at high temperature. Our kernel results also indicate that the temperature-dependent longwave feedback component is also greater by approximately a factor of two for the shortwave than the longwave forcing. Recent papers using observations and proxy reconstructions suggested a reduction of frequency, duration and intensity of Atlantic TCs in the years following volcanic eruptions. Observations show no significant reduction of TC activity in the first season after three large volcanic eruptions in the 20th Century, with the exception of the North Atlantic. The response to these volcanic eruptions cannot be separated from the coinciding El Niño events either in observations or in reanalysis. Both the NCAR Large Ensemble and CMIP5 models show a strong reduction in the PI following large volcanic eruptions. But, given that the models response to volcanic aerosols is known to be too strong, when a bias correction is considered, the PI signal after the volcanic eruptions becomes much smaller. Furthermore, there is no statistically significant reduction in TC activity for either the explicit synthetic downscaled CMIP5 storms following the volcanic eruptions. Therefore, there is little evidence of a global reduction of TC activity from direct volcanic aerosols.

Continued Development of a Global Heat Transfer Measurement System at AEDC Hypervelocity Wind Tunnel 9

NASA Technical Reports Server (NTRS)

Kurits, Inna; Lewis, M. J.; Hamner, M. P.; Norris, Joseph D.

2007-01-01

Heat transfer rates are an extremely important consideration in the design of hypersonic vehicles such as atmospheric reentry vehicles. This paper describes the development of a data reduction methodology to evaluate global heat transfer rates using surface temperature-time histories measured with the temperature sensitive paint (TSP) system at AEDC Hypervelocity Wind Tunnel 9. As a part of this development effort, a scale model of the NASA Crew Exploration Vehicle (CEV) was painted with TSP and multiple sequences of high resolution images were acquired during a five run test program. Heat transfer calculation from TSP data in Tunnel 9 is challenging due to relatively long run times, high Reynolds number environment and the desire to utilize typical stainless steel wind tunnel models used for force and moment testing. An approach to reduce TSP data into convective heat flux was developed, taking into consideration the conditions listed above. Surface temperatures from high quality quantitative global temperature maps acquired with the TSP system were then used as an input into the algorithm. Preliminary comparison of the heat flux calculated using the TSP surface temperature data with the value calculated using the standard thermocouple data is reported.

Surface properties and graphitization of polyacrylonitrile based fiber electrodes affecting the negative half-cell reaction in vanadium redox flow batteries

NASA Astrophysics Data System (ADS)

Langner, J.; Bruns, M.; Dixon, D.; Nefedov, A.; Wöll, Ch.; Scheiba, F.; Ehrenberg, H.; Roth, C.; Melke, J.

2016-07-01

Carbon felt electrodes for vanadium redox flow batteries are obtained by the graphitization of polyacrylonitrile based felts at different temperatures. Subsequently, the surface of the felts is modified via thermal oxidation at various temperatures. A single-cell experiment shows that the voltage efficiency is increased by this treatment. Electrode potentials measured with reference electrode setup show that this voltage efficiency increase is caused mainly by a reduction of the overpotential of the negative half-cell reaction. Consequently, this reaction is investigated further by cyclic voltammetry and the electrode activity is correlated with structural and surface chemical properties of the carbon fibers. By Raman, X-ray photoelectron and near edge X-ray absorption fine structure spectroscopy the role of edge sites and oxygen containing functional groups (OCFs) for the electrochemical activity are elucidated. A significant activity increase is observed in correlation with these two characteristics. The amount of OCFs is correlated with structural defects (e.g. edge sites) of the carbon fibers and therefore decreases with an increasing graphitization degree. Thus, for the same thermal oxidation temperature carbon fibers graphitized at a lower temperature show higher activities than those graphitized at a higher temperature.

Design, develop and test high temperature dynamic seals for the space shuttle's aerodynamic control surfaces

NASA Technical Reports Server (NTRS)

1973-01-01

A description is given of the design, development and testing of high temperature dynamic seals for the gaps between the structure and aerodynamic control surfaces on the space shuttle. These aerodynamic seals are required to prevent high temperature airflow from damaging thermally unprotected structures and components during entry. Two seal concepts evolved a curtain seal for the spanwise elevon cove gap, and a labyrinth seal for the area above the elevon, at the gap between the end of the elevon and the fuselage. On the basis of development testing, both seal concepts were shown to be feasible for controlling internal temperatures to 350 F or less when exposed to a typical space shuttle entry environment. The curtain seal concept demonstrated excellent test results and merits strong consideration for application on the space shuttle orbiter. The labyrinth seal concept, although demonstrating significant temperature reduction characteristics, may or may not be required on the Orbiter, depending on the actual design configuration and flight environment.

Adsorption and Reaction of Acetaldehyde on Shape-Controlled CeO2 Nanocrystals: Elucidation of Structure-function Relationships

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

Mann, Amanda K; Wu, Zili; Calaza, Florencia

2014-01-01

CeO2 cubes with {100} facets, octahedra with {111} facets, and wires with highly defective structures were utilized to probe the structure-dependent reactivity of acetaldehyde. Using temperature-programmed desorption (TPD), temperature-programmed surface reactions (TPSR), and in situ infrared spectroscopy it was found that acetaldehyde desorbs unreacted or undergoes reduction, coupling, or C-C bond scission reactions depending on the surface structure of CeO2. Room temperature FTIR indicates that acetaldehyde binds primarily as 1-acetaldehyde on the octahedra, in a variety of conformations on the cubes, including coupling products and acetate and enolate species, and primarily as coupling products on the wires. The percent consumptionmore » of acetaldehyde follows the order of wires > cubes > octahedra. All the nanoshapes produce the coupling product crotonaldehyde; however, the selectivity to produce ethanol follows the order wires cubes >> octahedra. The selectivity and other differences can be attributed to the variation in the basicity of the surfaces, defects densities, coordination numbers of surface atoms, and the reducibility of the nanoshapes.« less

Effect of Machining Parameters on Oxidation Behavior of Mild Steel

NASA Astrophysics Data System (ADS)

Majumdar, P.; Shekhar, S.; Mondal, K.

2015-01-01

This study aims to find out a correlation between machining parameters, resultant microstructure, and isothermal oxidation behavior of lathe-machined mild steel in the temperature range of 660-710 °C. The tool rake angles "α" used were +20°, 0°, and -20°, and cutting speeds used were 41, 232, and 541 mm/s. Under isothermal conditions, non-machined and machined mild steel samples follow parabolic oxidation kinetics with activation energy of 181 and ~400 kJ/mol, respectively. Exaggerated grain growth of the machined surface was observed, whereas, the center part of the machined sample showed minimal grain growth during oxidation at higher temperatures. Grain growth on the surface was attributed to the reduction of strain energy at high temperature oxidation, which was accumulated on the sub-region of the machined surface during machining. It was also observed that characteristic surface oxide controlled the oxidation behavior of the machined samples. This study clearly demonstrates the effect of equivalent strain, roughness, and grain size due to machining, and subsequent grain growth on the oxidation behavior of the mild steel.

A new approach for crystallization of copper(ii) oxide hollow nanostructures with superior catalytic and magnetic response

NASA Astrophysics Data System (ADS)

Singh, Inderjeet; Landfester, Katharina; Chandra, Amreesh; Muñoz-Espí, Rafael

2015-11-01

We report the synthesis of copper(ii) oxide hollow nanostructures at ambient pressure and close to room temperature by applying the soft templating effect provided by the confinement of droplets in miniemulsion systems. Particle growth can be explained by considering a mechanism that involves both diffusion and reaction control. The catalytic reduction of p-nitrophenol in aqueous media is used as a model reaction to prove the catalytic activity of the materials: the synthesized hollow structures show nearly 100 times higher rate constants than solid CuO microspheres. The kinetic behavior and the order of the reduction reaction change due to the increase of the surface area of the hollow structures. The synthesis also leads to modification of physical properties such as magnetism.We report the synthesis of copper(ii) oxide hollow nanostructures at ambient pressure and close to room temperature by applying the soft templating effect provided by the confinement of droplets in miniemulsion systems. Particle growth can be explained by considering a mechanism that involves both diffusion and reaction control. The catalytic reduction of p-nitrophenol in aqueous media is used as a model reaction to prove the catalytic activity of the materials: the synthesized hollow structures show nearly 100 times higher rate constants than solid CuO microspheres. The kinetic behavior and the order of the reduction reaction change due to the increase of the surface area of the hollow structures. The synthesis also leads to modification of physical properties such as magnetism. Electronic supplementary information (ESI) available: Associated structural and morphological analysis, XPS characterization, BET surface area, catalytic measurements, recycle tests of the catalyst, and magnetic characterizations. See DOI: 10.1039/c5nr05579b

Role of Absolute Humidity in the Inactivation of Influenza Viruses on Stainless Steel Surfaces at Elevated Temperatures ▿

PubMed Central

McDevitt, James; Rudnick, Stephen; First, Melvin; Spengler, John

2010-01-01

Influenza virus has been found to persist in the environment for hours to days, allowing for secondary transmission of influenza via inanimate objects known as fomites. We evaluated the efficacy of heat and moisture for the decontamination of surfaces for the purpose of preventing of the spread of influenza. Aqueous suspensions of influenza A virus were deposited onto stainless steel coupons, allowed to dry under ambient conditions, and exposed to temperatures of 55°C, 60°C, or 65°C and relative humidity (RH) of 25%, 50%, or 75% for up to 1 h. Quantitative virus assays were performed on the solution used to wash the viruses from these coupons, and results were compared with the solution used to wash coupons treated similarly but left under ambient conditions. Inactivation of influenza virus on surfaces increased with increasing temperature, RH, and exposure time. Reductions of greater than 5 logs of influenza virus on surfaces were achieved at temperatures of 60 and 65°C, exposure times of 30 and 60 min, and RH of 50 and 75%. Our data also suggest that absolute humidity is a better predictor of surface inactivation than RH and allows the prediction of survival using two parameters rather than three. Modest amounts of heat and adequate moisture can provide effective disinfection of surfaces while not harming surfaces, electrical systems, or mechanical components, leaving no harmful residues behind after treatment and requiring a relatively short amount of time. PMID:20435770

Toward Stabilizing Co 3O 4 Nanoparticles as an Oxygen Reduction Reaction Catalyst for Intermediate-Temperature SOFCs

DOE PAGES

Ren, Yaoyu; Cheng, Yuan; Gorte, Raymond J.; ...

2017-04-05

The oxygen reduction reaction (ORR) activity of a series of composite cathodes consisting of a porous Gd 0.20Ce 0.80O 2-δ (GDC) scaffold infiltrated with Sr-, Co-, and Y-nitrate solutions has been systematically investigated in this study. The results show that such infiltrated cathodes if calcined at low temperatures such as 350°C exhibit low polarization resistance (RP) in the temperature range of 450–700°C, even though XRD analysis reveals that the calcined product is virtually a mixture of Co 3O 4 and SrCO 3. A further study by design-of-experiment suggests that the true ORR-active species is Co 3O 4, whereas SrCO 3more » serves as a sintering inhibitor to preserve the high surface area of Co 3O 4. The findings and understanding in this study present a new strategy for future development of active cathodes for intermediate-temperature solid oxide fuel cells (SOFCs).« less

Optimisation of low temperature extraction of banana juice using commercial pectinase.

PubMed

Sagu, Sorel Tchewonpi; Nso, Emmanuel Jong; Karmakar, Sankha; De, Sirshendu

2014-05-15

The objective of this work was to develop a process with optimum conditions for banana juice. The procedure involves hydrolyzing the banana pulp by commercial pectinase followed by cloth filtration. Response surface methodology with Doehlert design was utilised to optimize the process parameters. The temperature of incubation (30-60 °C), time of reaction (20-120 min) and concentration of pectinase (0.01-0.05% v/w) were the independent variables and viscosity, clarity, alcohol insoluble solids (AIS), total polyphenol and protein concentration were the responses. Total soluble sugar, pH, conductivity, calcium, sodium and potassium concentration in the juice were also evaluated. The results showed reduction of AIS and viscosity with reaction time and pectinase concentration and reduction of polyphenol and protein concentration with temperature. Using numerical optimization, the optimum conditions for the enzymatic extraction of banana juice were estimated. Depectinization kinetics was also studied at optimum temperature and variation of kinetic constants with enzyme dose was evaluated. Copyright © 2013 Elsevier Ltd. All rights reserved.

Toward Stabilizing Co 3O 4 Nanoparticles as an Oxygen Reduction Reaction Catalyst for Intermediate-Temperature SOFCs

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

Ren, Yaoyu; Cheng, Yuan; Gorte, Raymond J.

The oxygen reduction reaction (ORR) activity of a series of composite cathodes consisting of a porous Gd 0.20Ce 0.80O 2-δ (GDC) scaffold infiltrated with Sr-, Co-, and Y-nitrate solutions has been systematically investigated in this study. The results show that such infiltrated cathodes if calcined at low temperatures such as 350°C exhibit low polarization resistance (RP) in the temperature range of 450–700°C, even though XRD analysis reveals that the calcined product is virtually a mixture of Co 3O 4 and SrCO 3. A further study by design-of-experiment suggests that the true ORR-active species is Co 3O 4, whereas SrCO 3more » serves as a sintering inhibitor to preserve the high surface area of Co 3O 4. The findings and understanding in this study present a new strategy for future development of active cathodes for intermediate-temperature solid oxide fuel cells (SOFCs).« less

Internal stress-induced melting below melting temperature at high-rate laser heating

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

Hwang, Yong Seok, E-mail: yshwang@iastate.edu; Levitas, Valery I., E-mail: vlevitas@iastate.edu

In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67 K for a stress-free condition down to 898.1 K for uniaxial strain and to 920.8 K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamicmore » equilibrium temperatures for the heating rate Q≤1.51×10{sup 10}K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1 K for Q = 1.51 × 10{sup 11 }K/s and 936.9 K for Q = 1.46 × 10{sup 12 }K/s.« less

Structure refinement for tantalum nitrides nanocrystals with various morphologies

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

Liu, Lianyun; School of Science, Beijing Jiaotong University, 3 Shang Yuan Cun, Haidian District, Beijing 100044; Huang, Kai

2012-07-15

Graphical abstract: Tantalum nitrides nanocrystals with various phases and morphologies for the first time have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. Highlights: ► The spherical TaN, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. ► The crystal structures of different tantalum nitrides were determined by Rietveld refinement on the X-ray diffraction data and the examinations of electron microcopies. ► The specific surface area of the tantalum nitrides powders was around 10 m{supmore » 2} g{sup −1}. ► Tantalum nitrides powders could be suitable for capacitor with high specific capacitance. -- Abstract: Tantalum nitrides (TaN{sub x}) nanocrystals with different phase and morphology have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. The crystal structures of tantalum nitrides were determined by Rietveld refinement based on the X-ray diffraction data. The morphologies of various tantalum nitrides nanocrystals in high quality were analyzed through the electron microcopies examinations. The spherical TaN nanoparticles, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been selectively prepared at different annealing temperatures. In addition, the specific surface areas of the tantalum nitrides nanocrystals measured by BET method were around 9.87–11.64 m{sup 2} g{sup −1}, indicating that such nano-sized tantalum nitrides could be suitable for capacitor with high specific capacitance.« less

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

Ravikumar, Patta; Kisan, Bhagaban; Perumal, A., E-mail: perumal@iitg.ernet.in

We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO) band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinementmore » effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μ{sub B}/f.u. at 12 kOe applied field and coercivity of 170 Oe were obtained for 30 hours milled NiO powders at 600 rotation per minute milling speed. The change in the magnetic properties is also supported by the vibrational properties. Thermomagnetization measurements at high temperature reveal a well-defined magnetic phase transition at high temperature (T{sub C}) around 780 K due to induced ferromagnetic phase. Electron paramagnetic resonance (EPR) studies reveal a good agreement between the EPR results and magnetic properties. The observed results are described on the basis of crystallite size variation, defect density, large strain, oxidation/reduction of Ni and interaction between uncompensated surfaces and particle core with lattice expansion. The obtained results suggest that nanoscale NiO powders with high T{sub C} and moderate magnetic moment at room temperature with cubic structure would be useful to expedite for spintronic devices.« less

Enhancement of the killing effect of low-temperature plasma on Streptococcus mutans by combined treatment with gold nanoparticles.

PubMed

Park, Sang Rye; Lee, Hyun Wook; Hong, Jin Woo; Lee, Hae June; Kim, Ji Young; Choi, Byul Bo-Ra; Kim, Gyoo Cheon; Jeon, Young Chan

2014-08-08

Recently, non-thermal atmospheric pressure plasma sources have been used for biomedical applications such as sterilization, cancer treatment, blood coagulation, and wound healing. Gold nanoparticles (gNPs) have unique optical properties and are useful for biomedical applications. Although low-temperature plasma has been shown to be effective in killing oral bacteria on agar plates, its bactericidal effect is negligible on the tooth surface. Therefore, we used 30-nm gNPs to enhance the killing effect of low-temperature plasma on human teeth. We tested the sterilizing effect of low-temperature plasma on Streptococcus mutans (S. mutans) strains. The survival rate was assessed by bacterial viability stains and colony-forming unit counts. Low-temperature plasma treatment alone was effective in killing S. mutans on slide glasses, as shown by the 5-log decrease in viability. However, plasma treatment of bacteria spotted onto tooth surface exhibited a 3-log reduction in viability. After gNPs were added to S. mutans, plasma treatment caused a 5-log reduction in viability, while gNPs alone did not show any bactericidal effect. The morphological changes in S. mutans caused by plasma treatment were examined by transmission electron microscopy, which showed that plasma treatment only perforated the cell walls, while the combination treatment with plasma and gold nanoparticles caused significant cell rupture, causing loss of intracellular components from many cells. This study demonstrates that low-temperature plasma treatment is effective in killing S. mutans and that its killing effect is further enhanced when used in combination with gNPs.

Design and fabrication of a super alloy thermal protection system

NASA Technical Reports Server (NTRS)

Varisco, A.; Wolter, W.; Bell, P.

1978-01-01

A lightweight metallic TPS was designed, and two test articles were fabricated, one from Haynes 188 and one from Rene 41. A baseline TPS concept, selected at the beginning of the program, consisted of a Haynes 25 corrugation-stiffened beaded skin surface panel, a specially designed support system, and an insulation system. By optimizing the structure for the design loads and by chem-milling to remove material not needed, the mass of the baseline surface panel was reduced 25%, and the mass of the support structure was reduced 50%. The insulation system mass was reduced 40% by using two types of insulation, each suited to its temperature range, and by eliminating a foul bag which encapsulated the baseline insulation system. These reductions resulted in an overall 35% reduction in mass of the Haynes 188 panel from the baseline Haynes 25 design. Similar reductions were achieved with the Rene 41 system.

Hydrogen-induced morphotropic phase transformation of single-crystalline vanadium dioxide nanobeams.

PubMed

Hong, Woong-Ki; Park, Jong Bae; Yoon, Jongwon; Kim, Bong-Joong; Sohn, Jung Inn; Lee, Young Boo; Bae, Tae-Sung; Chang, Sung-Jin; Huh, Yun Suk; Son, Byoungchul; Stach, Eric A; Lee, Takhee; Welland, Mark E

2013-04-10

We report a morphotropic phase transformation in vanadium dioxide (VO2) nanobeams annealed in a high-pressure hydrogen gas, which leads to the stabilization of metallic phases. Structural analyses show that the annealed VO2 nanobeams are hexagonal-close-packed structures with roughened surfaces at room temperature, unlike as-grown VO2 nanobeams with the monoclinic structure and with clean surfaces. Quantitative chemical examination reveals that the hydrogen significantly reduces oxygen in the nanobeams with characteristic nonlinear reduction kinetics which depend on the annealing time. Surprisingly, the work function and the electrical resistance of the reduced nanobeams follow a similar trend to the compositional variation due mainly to the oxygen-deficiency-related defects formed at the roughened surfaces. The electronic transport characteristics indicate that the reduced nanobeams are metallic over a large range of temperatures (room temperature to 383 K). Our results demonstrate the interplay between oxygen deficiency and structural/electronic phase transitions, with implications for engineering electronic properties in vanadium oxide systems.

[Penetration of external thermal perturbations into homeothermic organisms, part I (author's transl)].

PubMed

Theves, B

1978-03-20

The general importance of the mean surface curvature for heat conduction problems is explained and a special symmetry with constant mean curvature on the isothermal surfaces is defined. The applicability for the body shapes of homeothermic organisms is demonstrated and the partial differential equation of heat conduction for this case is derived. The definition: heat release = real heat production + convective pseudoproduction eliminates the term of convective heat transfer through the blood stream and allows the reduction to a mere heat conduction problem. Formulas for the heat loss to the environment and for steady state temperature profiles are given. In case of sudden change of heat loss the partial differential equation is solved and a formula is derived, using dimensionless coordinates of time and distance. The mean surface curvature has strongest influence to the interior temperature field. The solution shows clearly the importance of thermal inertia of the homeothermic organism, for the external temperature wave penetrates into the body with a long phase displacement in time.

Decreasing cloud cover drives the recent mass loss on the Greenland Ice Sheet.

PubMed

Hofer, Stefan; Tedstone, Andrew J; Fettweis, Xavier; Bamber, Jonathan L

2017-06-01

The Greenland Ice Sheet (GrIS) has been losing mass at an accelerating rate since the mid-1990s. This has been due to both increased ice discharge into the ocean and melting at the surface, with the latter being the dominant contribution. This change in state has been attributed to rising temperatures and a decrease in surface albedo. We show, using satellite data and climate model output, that the abrupt reduction in surface mass balance since about 1995 can be attributed largely to a coincident trend of decreasing summer cloud cover enhancing the melt-albedo feedback. Satellite observations show that, from 1995 to 2009, summer cloud cover decreased by 0.9 ± 0.3% per year. Model output indicates that the GrIS summer melt increases by 27 ± 13 gigatons (Gt) per percent reduction in summer cloud cover, principally because of the impact of increased shortwave radiation over the low albedo ablation zone. The observed reduction in cloud cover is strongly correlated with a state shift in the North Atlantic Oscillation promoting anticyclonic conditions in summer and suggests that the enhanced surface mass loss from the GrIS is driven by synoptic-scale changes in Arctic-wide atmospheric circulation.

Performance of selective catalytic reduction of NO with NH3 over natural manganese ore catalysts at low temperature.

PubMed

Wang, Tao; Zhu, Chengzhu; Liu, Haibo; Xu, Yongpeng; Zou, Xuehua; Xu, Bin; Chen, Tianhu

2018-02-01

Natural manganese ore catalysts for selective catalytic reduction (SCR) of NO with NH 3 at low temperature in the presence and absence of SO 2 and H 2 O were systematically investigated. The physical and chemical properties of catalysts were characterized by X-ray diffraction, Brunauer-Emmett-Teller (BET) specific surface area, NH 3 temperature-programmed desorption (NH 3 -TPD) and NO-TPD methods. The results showed that natural manganese ore from Qingyang of Anhui Province had a good low-temperature activity and N 2 selectivity, and it could be a novel catalyst in terms of stability, good efficiency, good reusability and lower cost. The NO conversion exceeded 85% between 150°C and 300°C when the initial NO concentration was 1000 ppm. The activity was suppressed by adding H 2 O (10%) or SO 2 (100 or 200 ppm), respectively, and its activity could recover while the SO 2 supply is cut off. The simultaneous addition of H 2 O and SO 2 led to the increase of about 100% in SCR activity than bare addition of SO 2 . The formation of the amorphous MnO x , high concentration of lattice oxygen and surface-adsorbed oxygen groups and a lot of reducible species as well as adsorption of the reactants brought about excellent SCR performance and exhibited good SO 2 and H 2 O resistance.

Surface nanocrystalline and hardening effects of Ti-Al-V alloy by electropulsing ultrasonic shock

NASA Astrophysics Data System (ADS)

Ye, Xiaoxin

2015-04-01

The effect of electropulsing ultrasonic shock (EUS) on the surface hardening and microstructure of Ti6Al4V alloy was studied. It was found that electropulsing improved the microhardness dramatically both in the influential depth and maximum value, compared with the only ultrasonic-shocked sample. It's indicated that refined surface layer with nanocrystalline and improved microhardness were obtained on account of surface severe plastic deformation, dynamic recrystallization (DRX) and phase change, which was implemented at relative low temperature and high strain rate/capacity due to the coupling of the thermal and athermal effects of EUS. It's different from conventional experiments and theory. It's discussed that the positive contributions of EPT in the thermodynamics and kinetics of microstructure and properties change were attributed to the reduction of nucleation energy barrier and acceleration of atomic diffusion. Therefore, it's supposed that EUS is an energy-saving and high-efficiency method of surface treatment technique with the help of high-energy electropulses, which is promising in cost reduction of the surface engineering and energy management.

Dissecting the steps of CO2 reduction: 1. The interaction of CO and CO2 with γ-Al2O3: an in situ FTIR study

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

Szanyi, Janos; Kwak, Ja Hun

2014-08-07

The adsorption of CO2 and CO was investigated on a pure γ-Al2O3 support material that has been used for the preparation of Pd and Ru catalysts for the catalytic reduction of CO2. The adsorption of CO2 resulted in the formation of carbonates, bicarbonates and linearly adsorbed CO2 species. The amount and the nature of the adsorbed species were dependent on the annealing temperature of the alumina support. On γ-Al2O3 annealed at 473 K mostly bicarbonates formed, while no adsorbed CO2 was seen on this highly hydroxylated surface. With increasing calcinations temperature, i.e., increasing extent of dehydroxylation, the amounts of bothmore » surface nitrates and linear adsorbed CO2 increased, but still the most abundant surface species were bicarbonates. Surface carbonates and adsorbed CO2 can readily be removed from the alumina surface, while bicarbonates are stable to elevated temperatures. The interaction of CO with γ-Al2O3 is much weaker than that of CO2. At room temperatures CO adsorbs only on Lewis acid sites, and can be readily removed by evacuation. At 100 K CO can probe different defect sites on the alumina surface (both Lewis acid sites and surface hydroxyls). Under no conditions we have observed the formation of any carbonates or bicarbonates upon the interaction of CO with the pure alumina support. In co-adsorption experiments CO competes for adsorption sites with the linearly adsorbed CO2 on the 773 K-annealed γ-Al2O3 surface; but it does not result in the desorption of CO2, rather in the increase of weakly-held carbonate production. After the removal of adsorbed CO, CO2 moves back to its original adsorption sites, i.e., Lewis acidic Al3+ centers. The exposure of a CO2-saturated γ-Al2O3 to H2O did not affect any of the adsorbed surface species. The findings of this study will be used to rationalize the results of our ongoing in situ and in operando studies on the reduction of CO2 on supported Pd and Ru catalysts. Acknowledgements: We gratefully acknowledge the US Department of Energy Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences for the support of this work. The synthesis and catalyst pre-treatment portion of the work described in this manuscript was supported by a Laboratory Directed Research and Development (LDRD) project at the Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle Memorial Institute. J.H.K. also acknowledges the support of this work by the 2013 Research Fund of UNIST (Ulsan National Institute of Science and Technology, Ulsan, Korea).« less

Internal structural changes in keratin fibres resulting from combined hair waving and stress relaxation treatments: a Raman spectroscopic investigation.

PubMed

Kuzuhara, A

2016-04-01

The objective of our research was to investigate the influence of chemical treatments (reduction, stress relaxation and oxidation) on hair keratin fibres. The structure of cross-sections at various depths of virgin white human hair resulting from permanent waving treatments with stress relaxation process was directly analysed at a molecular level using Raman spectroscopy. In particular, the three disulphide (-SS-) conformations in human hair were compared by S-S band analysis. The gauche-gauche-gauche (GGG) and gauche-gauche-trans (GGT) contents of -SS- groups remarkably decreased, while the trans-gauche-trans (TGT) content was not changed by performing the reduction process with thioglycolic acid. In addition, the high-temperature stress relaxation process after reduction accelerated the disconnection of -SS- (GGG and GGT) groups in the human hair, while the low-temperature stress relaxation process after reduction accelerated the reconnection of -SS- (GGG and GGT) groups. Moreover, the S-O band intensity at 1042 cm(-1) , assigned to cysteic acid, existing in the cuticle region and the surface of the cortex region increased, while the GGG content significantly decreased by performing the oxidation process after the reduction and the high-temperature stress relaxation processes. The author concluded that the high-temperature relaxation process after reduction accelerated the disconnection of -SS- (GGG and GGT) groups, thereby leading to the remarkable local molecular disorganization (an increase in the cysteic acid content and a decrease in the GGG content) on the cuticle and cortex cells during the oxidation process. © 2015 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

Oxidation of Ti silicide surfaces

NASA Astrophysics Data System (ADS)

Cros, A.; Pirri, C.; Derrien, J.

1985-04-01

The oxidation of clean Ti suicide surface prepared under ultra high vacuum conditions, has been studied by ultraviolet and X-ray photo-emission spectroscopy techniques. At room temperature, the oxide overlayer is composed of both TiO 2 and SiO 2. An annealing at 400-600°C provokes the reduction of TiO 2 in the form of Ti suboxide while the liberated oxygen atoms bond to Si. This is not due to the presence of Si atoms and is rather an intrinsic property of native TiO 2. The simultaneous presence at high temperature of both SiO 2 and Ti suboxide is attributed to the existence of a rate limiting process due to diffusion barriers.

Development of the mechanical cryocooler system for the Sea Land Surface Temperature Radiometer

NASA Astrophysics Data System (ADS)

Camilletti, Adam; Burgess, Christopher; Donchev, Anton; Watson, Stuart; Weatherstone Akbar, Shane; Gamo-Albero, Victoria; Romero-Largacha, Victor; Caballero-Olmo, Gema

2014-11-01

The Sea Land Surface Temperature Radiometer is a dual view Earth observing instrument developed as part of the European Global Monitoring for Environment and Security programme. It is scheduled for launch on two satellites, Sentinel 3A and 3B in 2014. The instrument detectors are cooled to below 85 K by two split Stirling Cryocoolers running in hot redundancy. These coolers form part of a cryocooler system that includes a support structure and drive electronics. Aspects of the system design, including control and reduction of exported vibration are discussed; and results, including thermal performance and exported vibration from the Engineering Model Cryooler System test campaign are presented.

Drag reduction through self-texturing compliant bionic materials

PubMed Central

Liu, Eryong; Li, Longyang; Wang, Gang; Zeng, Zhixiang; Zhao, Wenjie; Xue, Qunji

2017-01-01

Compliant fish skin is effectively in reducing drag, thus the design and application of compliant bionic materials may be a good choice for drag reduction. Here we consider the drag reduction of compliant bionic materials. First, ZnO and PDMS mesh modified with n-octadecane were prepared, the drag reduction of self-texturing compliant n-octadecane were studied. The results show that the mesh modified by ZnO and PDMS possess excellent lipophilic and hydrophobic, thus n-octadecane at solid, semisolid and liquid state all have good adhesion with modified mesh. The states of n-octadecane changed with temperature, thus, the surface contact angle and adhesive force all varies obviously at different state. The contact angle decreases with temperature, the adhesive force shows a lower value at semisolid state. Furthermore, the drag testing results show that the compliant n-octadecane film is more effectively in drag reduction than superhydrophobic ZnO/PDMS film, indicating that the drag reduction mechanism of n-octadecane is significantly different with superhydrophobic film. Further research shows that the water flow leads to self-texturing of semisolid state n-octadecane, which is similar with compliant fish skin. Therefore, the compliant bionic materials of semisolid state n-octadecane with regular bulge plays a major role in the drag reduction. PMID:28053309

Drag reduction through self-texturing compliant bionic materials.

PubMed

Liu, Eryong; Li, Longyang; Wang, Gang; Zeng, Zhixiang; Zhao, Wenjie; Xue, Qunji

2017-01-05

Compliant fish skin is effectively in reducing drag, thus the design and application of compliant bionic materials may be a good choice for drag reduction. Here we consider the drag reduction of compliant bionic materials. First, ZnO and PDMS mesh modified with n-octadecane were prepared, the drag reduction of self-texturing compliant n-octadecane were studied. The results show that the mesh modified by ZnO and PDMS possess excellent lipophilic and hydrophobic, thus n-octadecane at solid, semisolid and liquid state all have good adhesion with modified mesh. The states of n-octadecane changed with temperature, thus, the surface contact angle and adhesive force all varies obviously at different state. The contact angle decreases with temperature, the adhesive force shows a lower value at semisolid state. Furthermore, the drag testing results show that the compliant n-octadecane film is more effectively in drag reduction than superhydrophobic ZnO/PDMS film, indicating that the drag reduction mechanism of n-octadecane is significantly different with superhydrophobic film. Further research shows that the water flow leads to self-texturing of semisolid state n-octadecane, which is similar with compliant fish skin. Therefore, the compliant bionic materials of semisolid state n-octadecane with regular bulge plays a major role in the drag reduction.

Drag reduction through self-texturing compliant bionic materials

NASA Astrophysics Data System (ADS)

Liu, Eryong; Li, Longyang; Wang, Gang; Zeng, Zhixiang; Zhao, Wenjie; Xue, Qunji

2017-01-01

Compliant fish skin is effectively in reducing drag, thus the design and application of compliant bionic materials may be a good choice for drag reduction. Here we consider the drag reduction of compliant bionic materials. First, ZnO and PDMS mesh modified with n-octadecane were prepared, the drag reduction of self-texturing compliant n-octadecane were studied. The results show that the mesh modified by ZnO and PDMS possess excellent lipophilic and hydrophobic, thus n-octadecane at solid, semisolid and liquid state all have good adhesion with modified mesh. The states of n-octadecane changed with temperature, thus, the surface contact angle and adhesive force all varies obviously at different state. The contact angle decreases with temperature, the adhesive force shows a lower value at semisolid state. Furthermore, the drag testing results show that the compliant n-octadecane film is more effectively in drag reduction than superhydrophobic ZnO/PDMS film, indicating that the drag reduction mechanism of n-octadecane is significantly different with superhydrophobic film. Further research shows that the water flow leads to self-texturing of semisolid state n-octadecane, which is similar with compliant fish skin. Therefore, the compliant bionic materials of semisolid state n-octadecane with regular bulge plays a major role in the drag reduction.

Radiant heat loss, an unexploited path for heat stress reduction in shaded cattle.

PubMed

Berman, A; Horovitz, T

2012-06-01

Reducing thermal radiation on shaded animals reduces heat stress independently of other means of stress relief. Radiant heat exchange was estimated as a function of climate, shade structure, and animal density. Body surface portion exposed to radiant sources in shaded environments was determined by geometrical relations to determine angles of view of radiation sources (roof underside, sky, sun-exposed ground, shaded ground) on the animal's surface. The relative representation of environment radiation sources on the body surface was determined. Animal thermal radiation balance was derived from radiant heat gained from radiation sources (including surrounding animals) and that lost from the animal surface. The animal environment was assumed to have different shade dimensions and temperatures. These were summed to the radiant heat balance of the cow. The data formed served to estimate the effect of changes in intensity of radiation sources, roof and shaded surface dimensions, and animal density on radiant heat balance (Rbal) of cattle. Roof height effect was expressed by effect of roof temperature on Rbal. Roof underside temperature (35 to 75°C) effect on Rbal was reduced by roof height. If roof height were 4m, an increase in its underside temperature from 35 to 75°C would increase mean Rbal from -63 to -2 W·m⁻², whereas if roof height were 10 m, Rbal would only increase from -99 to -88 W·m⁻². A hot ground temperature increase from 35 to 65°C reduced mean Rbal heat loss from -45 to 3 W·m⁻². Increasing the surface of the shaded area had only a minor effect on Rbal and on the effect of hot ground on Rbal. Increasing shade roof height reduced the effect of roof temperature on Rbal to minor levels when height was > 8m. Increasing the roof height from 4 to 10 m decreased Rbal from -32 to -94 W·m⁻². Increasing indirect radiation from 100 to 500 W·m⁻² was associated with an increase in Rbal from -135 to +23 W·m⁻². Their combined effects were lower Rbal with increasing roof height and a reduction in rate of decrease with increasing level of indirect radiation. Roof height as an Rbal attenuator declined with increasing indirect radiation level. The latter factor might be reduced by lowering roof surface radiation absorption and through roof heat transfer, as well as by use of shade structure elements to reduce indirect radiation in the shaded area. Radiant heat from the cow body surface may be reduced by lower cow density. Radiant heat attenuation may thus further elevate animal productivity in warm climates, with no associated operation costs. Copyright © 2012 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Microstructural changes and strain hardening effects in abrasive contacts at different relative velocities and temperatures

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

Rojacz, H., E-mail: rojacz@ac2t.at

2016-08-15

Strain hardening is commonly used to reach the full potential of materials and can be beneficial in tribological contacts. 2-body abrasive wear was simulated in a scratch test, aimed at strain hardening effects in various steels. Different working conditions were examined at various temperatures and velocities. Strain hardening effects and microstructural changes were analysed with high resolution scanning electron microscopy (HRSEM), electron backscatter diffraction (EBSD), micro hardness measurements and nanoindentation. Statistical analysing was performed quantifying the influence of different parameters on microstructures. Results show a crucial influence of temperature and velocity on the strain hardening in tribological contacts. Increased velocitymore » leads to higher deformed microstructures and higher increased surface hardness at a lower depth of the deformed zones at all materials investigated. An optimised surface hardness can be achieved knowing the influence of velocity (strain rate) and temperature for a “tailor-made” surface hardening in tribological systems aimed at increased wear resistance. - Highlights: •Hardening mechanisms and their intensity in tribological contacts are dependent on relative velocity and temperature. •Beneficial surface hardened zones are formed at certain running-in conditions; the scientific background is presented here. •Ferritic-pearlitic steels strain hardens via grain size reduction and decreasing interlamellar distances in pearlite. •Austenitic steels show excellent surface hardening (120% hardness increase) by twinning and martensitic transformation. •Ferritic steels with hard phases harden in the ferrite phase as per Hall-Petch equation and degree of deformation.« less

Surface Treatment on Physical Properties and Biocompatibility of Orthodontic Power Chains

PubMed Central

Cheng, H. C.; Chen, M. S.; Peng, B. Y.; Lin, W. T.; Wang, Y. H.

2017-01-01

The conventional orthodontic power chain, often composed of polymer materials, has drawbacks such as a reduction of elasticity owing to water absorption as well as surface discoloration and staining resulting from food or beverages consumed by the patient. The goal of this study was to develop a surface treatment (nanoimprinting) for orthodontic power chains and to alleviate their shortcomings. A concave template (anodic alumina) was manufactured by anodization process using pure aluminum substrate by employing the nanoimprinting process. Convex nanopillars were fabricated on the surface of orthodontic power chains, resulting in surface treatment. Distinct parameters of the nanoimprinting process (e.g., imprinting temperature, imprinting pressure, imprinting time, and demolding temperature) were used to fabricate nanopillars on the surface of orthodontic power chains. The results of this study showed that the contact angle of the power chains became larger after surface treatment. In addition, the power chains changed from hydrophilic to hydrophobic. The power chain before surface treatment without water absorption had a water absorption rate of approximately 4%, whereas a modified chain had a water absorption rate of approximately 2%–4%. Furthermore, the color adhesion of the orthodontic power chains after surface modification was less than that before surface modification. PMID:28540299

Efficacy of electrolysed oxidizing water in inactivating Vibrio parahaemolyticus on kitchen cutting boards and food contact surfaces.

PubMed

Chiu, T-H; Duan, J; Liu, C; Su, Y-C

2006-12-01

To determine the efficacy of electrolysed oxidizing (EO) water in inactivating Vibrio parahaemolyticus on kitchen cutting boards and food contact surfaces. Cutting boards (bamboo, wood and plastic) and food contact surfaces (stainless steel and glazed ceramic tile) were inoculated with V. parahaemolyticus. Viable cells of V. parahaemolyticus were detected on all cutting boards and food contact surfaces after 10 and 30 min, respectively, at room temperatures. Soaking inoculated food contact surfaces and cutting boards in distilled water for 1 and 3 min, respectively, resulted in various reductions of V. parahaemolyticus, but failed to remove the organism completely from surfaces. However, the treatment of EO water [pH 2.7, chlorine 40 ppm, oxidation-reduction potential 1151 mV] for 30, 45, and 60 s, completely inactivated V. parahaemolyticus on stainless steel, ceramic tile, and plastic cutting boards, respectively. EO water could be used as a disinfecting agent for inactivating V. parahaemolyticus on plastic and wood cutting boards and food contact surfaces. Rinsing the food contact surfaces with EO water or soaking cutting boards in EO water for up to 5 min could be a simple strategy to reduce cross-contamination of V. parahaemolyticus during food preparation.

Modified energetics and growth kinetics on H-terminated GaAs (110)

NASA Astrophysics Data System (ADS)

Galiana, B.; Benedicto, M.; Díez-Merino, L.; Lorbek, S.; Hlawacek, G.; Teichert, C.; Tejedor, P.

2013-10-01

Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As4, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å2 measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

Northwestern Pacific typhoon intensity controlled by changes in ocean temperatures.

PubMed

Mei, Wei; Xie, Shang-Ping; Primeau, François; McWilliams, James C; Pasquero, Claudia

2015-05-01

Dominant climatic factors controlling the lifetime peak intensity of typhoons are determined from six decades of Pacific typhoon data. We find that upper ocean temperatures in the low-latitude northwestern Pacific (LLNWP) and sea surface temperatures in the central equatorial Pacific control the seasonal average lifetime peak intensity by setting the rate and duration of typhoon intensification, respectively. An anomalously strong LLNWP upper ocean warming has favored increased intensification rates and led to unprecedentedly high average typhoon intensity during the recent global warming hiatus period, despite a reduction in intensification duration tied to the central equatorial Pacific surface cooling. Continued LLNWP upper ocean warming as predicted under a moderate [that is, Representative Concentration Pathway (RCP) 4.5] climate change scenario is expected to further increase the average typhoon intensity by an additional 14% by 2100.

Synthesis of Supported Pd 0 Nanoparticles from a Single-Site Pd 2+ Surface Complex by Alkene Reduction

DOE PAGES

Mouat, Aidan R.; Whitford, Cassandra L.; Chen, Bor-Rong; ...

2018-02-02

Here, a surface metal–organic complex, (-AlO x)Pd(acac) (acac = acetylacetonate), is prepared by chemically grafting the precursor Pd(acac) 2 onto γ-Al 2O 3 in toluene at 25 °C. The resulting surface complex is characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and dynamic nuclear polarization surface-enhanced solid-state nuclear magnetic resonance spectroscopy (DNP SENS). This surface complex is a precursor in the direct synthesis of size-controlled Pd nanoparticles under mild reductive conditions and in the absence of additional stabilizers or pretreatments. Indeed, upon exposure to gaseous ethylene or liquid 1-octene at 25more » °C, the Pd 2+ species is reduced to form Pd 0 nanoparticles with a mean diameter of 4.3 ± 0.6 nm, as determined by scanning transmission electron microscopy (STEM). These nanoparticles are catalytically relevant using the aerobic 1-phenylethanol oxidation as a probe reaction, with rates comparable to a conventional Pd/Al 2O 3 catalyst but without an induction period. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed reaction mass spectrometry (TPR-MS) reveal that the surface complex reduction with ethylene coproduces H 2, acetylene, and 1,3-butadiene. This process reasonably proceeds via an olefin activation/coordination/insertion pathway, followed by β-hydride elimination to generate free Pd 0. Lastly, the well-defined nature of the single-site supported Pd 2+ precursor provides direct mechanistic insights into this unusual and likely general reductive process.« less

Synthesis of Supported Pd 0 Nanoparticles from a Single-Site Pd 2+ Surface Complex by Alkene Reduction

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

Mouat, Aidan R.; Whitford, Cassandra L.; Chen, Bor-Rong

Here, a surface metal–organic complex, (-AlO x)Pd(acac) (acac = acetylacetonate), is prepared by chemically grafting the precursor Pd(acac) 2 onto γ-Al 2O 3 in toluene at 25 °C. The resulting surface complex is characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and dynamic nuclear polarization surface-enhanced solid-state nuclear magnetic resonance spectroscopy (DNP SENS). This surface complex is a precursor in the direct synthesis of size-controlled Pd nanoparticles under mild reductive conditions and in the absence of additional stabilizers or pretreatments. Indeed, upon exposure to gaseous ethylene or liquid 1-octene at 25more » °C, the Pd 2+ species is reduced to form Pd 0 nanoparticles with a mean diameter of 4.3 ± 0.6 nm, as determined by scanning transmission electron microscopy (STEM). These nanoparticles are catalytically relevant using the aerobic 1-phenylethanol oxidation as a probe reaction, with rates comparable to a conventional Pd/Al 2O 3 catalyst but without an induction period. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed reaction mass spectrometry (TPR-MS) reveal that the surface complex reduction with ethylene coproduces H 2, acetylene, and 1,3-butadiene. This process reasonably proceeds via an olefin activation/coordination/insertion pathway, followed by β-hydride elimination to generate free Pd 0. Lastly, the well-defined nature of the single-site supported Pd 2+ precursor provides direct mechanistic insights into this unusual and likely general reductive process.« less

Optimization of Bleaching Parameters in Refining Process of Kenaf Seed Oil with a Central Composite Design Model.

PubMed

Chew, Sook Chin; Tan, Chin Ping; Nyam, Kar Lin

2017-07-01

Kenaf seed oil has been suggested to be used as nutritious edible oil due to its unique fatty acid composition and nutritional value. The objective of this study was to optimize the bleaching parameters of the chemical refining process for kenaf seed oil, namely concentration of bleaching earth (0.5 to 2.5% w/w), temperature (30 to 110 °C) and time (5 to 65 min) based on the responses of total oxidation value (TOTOX) and color reduction using response surface methodology. The results indicated that the corresponding response surface models were highly statistical significant (P < 0.0001) and sufficient to describe and predict TOTOX value and color reduction with R 2 of 0.9713 and 0.9388, respectively. The optimal parameters in the bleaching stage of kenaf seed oil were: 1.5% w/w of the concentration of bleaching earth, temperature of 70 °C, and time of 40 min. These optimum parameters produced bleached kenaf seed oil with TOTOX value of 8.09 and color reduction of 32.95%. There were no significant differences (P > 0.05) between experimental and predicted values, indicating the adequacy of the fitted models. © 2017 Institute of Food Technologists®.

Reduction of Iron-Oxide-Carbon Composites: Part I. Estimation of the Rate Constants

NASA Astrophysics Data System (ADS)

Halder, S.; Fruehan, R. J.

2008-12-01

A new ironmaking concept using iron-oxide-carbon composite pellets has been proposed, which involves the combination of a rotary hearth furnace (RHF) and an iron bath smelter. This part of the research focuses on studying the two primary chemical kinetic steps. Efforts have been made to experimentally measure the kinetics of the carbon gasification by CO2 and wüstite reduction by CO by isolating them from the influence of heat- and mass-transport steps. A combined reaction model was used to interpret the experimental data and determine the rate constants. Results showed that the reduction is likely to be influenced by the chemical kinetics of both carbon oxidation and wüstite reduction at the temperatures of interest. Devolatilized wood-charcoal was observed to be a far more reactive form of carbon in comparison to coal-char. Sintering of the iron-oxide at the high temperatures of interest was found to exert a considerable influence on the reactivity of wüstite by virtue of altering the internal pore surface area available for the reaction. Sintering was found to be predominant for highly porous oxides and less of an influence on the denser ores. It was found using an indirect measurement technique that the rate constants for wüstite reduction were higher for the porous iron-oxide than dense hematite ore at higher temperatures (>1423 K). Such an indirect mode of measurement was used to minimize the influence of sintering of the porous oxide at these temperatures.

Nickel Nanocatalyst Ex-Solution from Ceria-Nickel Oxide Solid Solution for Low Temperature CO Oxidation.

PubMed

Singhania, Amit; Gupta, Shipra Mital

2018-07-01

In this work, in situ growth of Ni nanocatalysts to attach onto the ceria (CeO2) surface through direct Ni ex-solution from the NiO-CeO2 solid solution in a reducing atmosphere at high temperatures with an aim to improve the catalytic activity, and stability for low temperature carbon monoxide (CO) oxidation reaction have been reported. The NiO-CeO2 solid solutions were prepared by solution combustion method, and the results of XRD and RAMAN showed that doping of Ni increases the oxygen vacancies due to charge compensation. Ni is clearly visible in XRD and TEM of Ni ex-solved sample (R-UCe5Ni10) after reduction of NiO-CeO2 (UCe5Ni10) sample by 5% H2/Ar reduction at 1000 °C. TEM analysis revealed a size of 9.2 nm of Ni nanoparticle that is ex-solved on the surface CeO2. This ex-solved sample showed very high catalytic activity (T50 ~ 110 °C), and stability (100 h) for CO oxidation reaction as compared to prepared solid solution samples. This is due to the highly active metallic nano-phase which is ex-solved on the surface of CeO2 and strongly adherent to the support. The apparent activation energy Ni ex-solved sample is found out to be 48.4 kJ mol-1. Thus, the above Ni ex-solved sample shows a practical applicability for the CO reaction.

Miniature Convection Cooled Plug-type Heat Flux Gauges

NASA Technical Reports Server (NTRS)

Liebert, Curt H.

1994-01-01

Tests and analysis of a new miniature plug-type heat flux gauge configuration are described. This gauge can simultaneously measure heat flux on two opposed active surfaces when heat flux levels are equal to or greater than about 0.2 MW/m(sup 2). The performance of this dual active surface gauge was investigated over a wide transient and steady heat flux and temperature range. The tests were performed by radiatively heating the front surface with an argon arc lamp while the back surface was convection cooled with air. Accuracy is about +20 percent. The gauge is responsive to fast heat flux transients and is designed to withstand the high temperature (1300 K), high pressure (15 MPa), erosive and corrosive environments in modern engines. This gauge can be used to measure heat flux on the surfaces of internally cooled apparatus such as turbine blades and combustors used in jet propulsion systems and on the surfaces of hypersonic vehicles. Heat flux measurement accuracy is not compromised when design considerations call for various size gauges to be fabricated into alloys of various shapes and properties. Significant gauge temperature reductions (120 K), which can lead to potential gauge durability improvement, were obtained when the gauges were air-cooled by forced convection.

Growth and biofilm formation by Listeria monocytogenes in catfish mucus extract on four food-contact surfaces at 22°C and 10°C and their reduction by commercial disinfectants

USDA-ARS?s Scientific Manuscript database

The objective of this study was to determine the effect of strain and temperature on growth and biofilm formation by Listeria monocytogenes (Lm) in high and low concentrations of catfish mucus extract on different food-contact surfaces at 10°C and 22°C. The second objective of this study was to eval...

Exposure to elevated sea-surface temperatures below the bleaching threshold impairs coral recovery and regeneration following injury.

PubMed

Bonesso, Joshua Louis; Leggat, William; Ainsworth, Tracy Danielle

2017-01-01

Elevated sea surface temperatures (SSTs) are linked to an increase in the frequency and severity of bleaching events due to temperatures exceeding corals' upper thermal limits. The temperatures at which a breakdown of the coral- Symbiodinium endosymbiosis (coral bleaching) occurs are referred to as the upper thermal limits for the coral species. This breakdown of the endosymbiosis results in a reduction of corals' nutritional uptake, growth, and tissue integrity. Periods of elevated sea surface temperature, thermal stress and coral bleaching are also linked to increased disease susceptibility and an increased frequency of storms which cause injury and physical damage to corals. Herein we aimed to determine the capacity of corals to regenerate and recover from injuries (removal of apical tips) sustained during periods of elevated sea surface temperatures which result in coral stress responses, but which do not result in coral bleaching (i.e., sub-bleaching thermal stress events). In this study, exposure of the species Acropora aspera to an elevated SST of 32 °C (2 °C below the bleaching threshold, 34 °C) was found to result in reduced fluorescence of green fluorescent protein (GFP), reduced skeletal calcification and a lack of branch regrowth at the site of injury, compared to corals maintained under ambient SST conditions (26 °C). Corals maintained under normal, ambient, sea surface temperatures expressed high GFP fluorescence at the injury site, underwent a rapid regeneration of the coral branch apical tip within 12 days of sustaining injury, and showed extensive regrowth of the coral skeleton. Taken together, our results have demonstrated that periods of sustained increased sea surface temperatures, below the corals' bleaching threshold but above long-term summertime averages, impair coral recovery from damage, regardless of the onset or occurrence of coral bleaching.

Evidence of a reduction reaction of oxidized iron/cobalt by boron atoms diffused toward naturally oxidized surface of CoFeB layer during annealing

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

Sato, Soshi, E-mail: sato.soshi@cies.tohoku.ac.jp; Honjo, Hiroaki; Niwa, Masaaki

2015-04-06

We have investigated the redox reaction on the surface of Ta/CoFeB/MgO/CoFeB magnetic tunnel junction stack samples after annealing at 300, 350, and 400 °C for 1 h using angle-resolved X-ray photoelectron spectroscopy for precise analysis of the chemical bonding states. At a capping tantalum layer thickness of 1 nm, both the capping tantalum layer and the surface of the underneath CoFeB layer in the as-deposited stack sample were naturally oxidized. By comparison of the Co 2p and Fe 2p spectra among the as-deposited and annealed samples, reduction of the naturally oxidized cobalt and iron atoms occurred on the surface of the CoFeB layer.more » The reduction reaction was more significant at higher annealing temperature. Oxidized cobalt and iron were reduced by boron atoms that diffused toward the surface of the top CoFeB layer. A single CoFeB layer was prepared on SiO{sub 2}, and a confirmatory evidence of the redox reaction with boron diffusion was obtained by angle-resolved X-ray photoelectron spectroscopy analysis of the naturally oxidized surface of the CoFeB single layer after annealing. The redox reaction is theoretically reasonable based on the Ellingham diagram.« less

Photoactivity of N-doped ZnO nanoparticles in oxidative and reductive reactions

NASA Astrophysics Data System (ADS)

Oliveira, Jéssica A.; Nogueira, André E.; Gonçalves, Maria C. P.; Paris, Elaine C.; Ribeiro, Caue; Poirier, Gael Y.; Giraldi, Tania R.

2018-03-01

N-doped ZnO is a prospective material for photocatalytic reactions. However, only oxidative paths are well investigated in the literature. This paper describes a comparative study about ZnO and ZnO:N potential for oxidative and reductive reactions, probed by rhodamine B dye photodegradation and CO2 photoreduction. The materials were prepared by the polymeric precursor method, using urea as a nitrogen source, and different heat treatments were used to observe their effects on surface decontamination, crystallinity, particle sizes and shapes, and photocatalytic performance. ZnO and ZnO:N presented a wurtzite crystalline structure and nanometric-scale particles. Samples submitted to higher temperatures showed lower specific surface areas, but higher crystallinity and lower contents of species adsorbed on their surfaces. On the other hand, the photocatalysts annealed in shorter times presented smaller crystallite sizes and lower crystallinity. These factors influenced the photoactivity in both conditions, i.e., oxidation and reduction reactions, under the ultraviolet and visible light, indicating that structural factors influenced the adequate charge separation and consequent photocatalytic activity since the as-synthesized samples were versatile photocatalysts in both redox reactions.

Sintered wire cathode

DOEpatents

Falce, Louis R [San Jose, CA; Ives, R Lawrence [Saratoga, CA

2009-06-09

A porous cathode structure is fabricated from a plurality of wires which are placed in proximity to each other in elevated temperature and pressure for a sintering time. The sintering process produces the porous cathode structure which may be divided into a plurality of individual porous cathodes, one of which may be placed into a dispenser cathode support which includes a cavity for containing a work function reduction material such as BaO, CaO, and Al.sub.2O.sub.3. The work function reduction material migrates through the pores of the porous cathode from a work replenishment surface adjacent to the cavity of the dispenser cathode support to an emitting cathode surface, thereby providing a dispenser cathode which has a uniform work function and therefore a uniform electron emission.

Using Radiative Signatures to Diagnose the Cause of Warming Associated with the Californian Drought

NASA Astrophysics Data System (ADS)

Wolf, S.; Yin, D.; Roderick, M. L.

2016-12-01

California recently experienced among the worst droughts of the last century, with unprecedented precipitation deficits and record high temperatures. The dry conditions caused severe water shortages in one of the economically most important agricultural regions of the US, particularly in the Central Valley. It has been hypothesized that anthropogenic warming is increasing the likelihood of such extreme droughts in California, or more specifically, that these drought conditions are a consequence of warmer temperatures from the enhanced greenhouse effect. Process studies suggest, however, that increased temperatures during droughts are mostly a consequence of reduced evaporative cooling resulting from the reduction in precipitation. Here we use surface radiation components from NASA's Clouds and Earth's Radiant Energy Systems (CERES), climatic data and direct flux tower measurements to investigate the cause of warming associated with the recent Californian Drought. Based on radiative signatures and surface energy balance we show that the warmer temperatures were not associated with an enhanced greenhouse effect by anthropogenic warming. The radiative signature showed decreased longwave downward radiation during the water years 2013-2014 compared to the decadal mean of 2001-2012. Instead, increased solar downward radiation in combination with reduced evaporative cooling from water deficits enhanced surface temperatures and sensible heat transfer to the atmosphere. We conclude that the drought was not directly associated with warming by increased longwave downward radiation, and that there is no simple relation between warmer surface temperatures and drought.

Enhanced conductivity of tunnel junctions employing semimetallic nanoparticles through variation in growth temperature and deposition

NASA Astrophysics Data System (ADS)

Nair, Hari P.; Crook, Adam M.; Bank, Seth R.

2010-05-01

We report ErAs nanoparticle-enhanced tunnel junctions grown on GaAs with low specific resistances (<2×10-4 Ω cm-2), approximately tenfold lower than previous reports. A reduction in specific resistance was achieved by modifying the ErAs nanoparticle morphology through the molecular beam epitaxial growth conditions, particularly lower growth temperatures. A further investigation of the variation in tunnel junction resistance with the amount of ErAs deposited and growth temperature shows that nanoparticle surface coverage may not be the only factor determining tunnel junction resistance.

Electrochemical CO 2 reduction on Au surfaces: mechanistic aspects regarding the formation of major and minor products

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

Cave, Etosha R.; Montoya, Joseph H.; Kuhl, Kendra P.

In the future, industrial CO 2 electroreduction using renewable energy sources could be a sustainable means to convert CO 2 and water into commodity chemicals at room temperature and atmospheric pressure. This study focuses on the electrocatalytic reduction of CO 2 on polycrystalline Au surfaces, which have high activity and selectivity for CO evolution. Here, we explore the catalytic behavior of polycrystalline Au surfaces by coupling potentiostatic CO 2 electrolysis experiments in an aqueous bicarbonate solution with high sensitivity product detection methods. We observed the production of methanol, in addition to detecting the known products of CO 2 electroreduction onmore » Au: CO, H 2 and formate. We suggest a mechanism that explains Au's evolution of methanol. Specifically, the Au surface does not favor C-O scission, and thus is more selective towards methanol than methane. These insights could aid in the design of electrocatalysts that are selective for CO 2 electroreduction to oxygenates over hydrocarbons.« less

Electrochemical CO 2 reduction on Au surfaces: mechanistic aspects regarding the formation of major and minor products

DOE PAGES

Cave, Etosha R.; Montoya, Joseph H.; Kuhl, Kendra P.; ...

2017-01-06

In the future, industrial CO 2 electroreduction using renewable energy sources could be a sustainable means to convert CO 2 and water into commodity chemicals at room temperature and atmospheric pressure. This study focuses on the electrocatalytic reduction of CO 2 on polycrystalline Au surfaces, which have high activity and selectivity for CO evolution. Here, we explore the catalytic behavior of polycrystalline Au surfaces by coupling potentiostatic CO 2 electrolysis experiments in an aqueous bicarbonate solution with high sensitivity product detection methods. We observed the production of methanol, in addition to detecting the known products of CO 2 electroreduction onmore » Au: CO, H 2 and formate. We suggest a mechanism that explains Au's evolution of methanol. Specifically, the Au surface does not favor C-O scission, and thus is more selective towards methanol than methane. These insights could aid in the design of electrocatalysts that are selective for CO 2 electroreduction to oxygenates over hydrocarbons.« less

Heat Treatment of Tantalum and Niobium Powders Prepared by Magnesium-Thermic Reduction

NASA Astrophysics Data System (ADS)

Orlov, V. M.; Prokhorova, T. Yu.

2017-11-01

Changes in the specific surface area and porous structure of tantalum and niobium powders, which were prepared by magnesium-thermic reduction of Ta2O5, Mg4Ta2O9, and Mg4Nb2O9 oxide compounds and subjected to heat treatments at temperatures of 600-1500°C, have been studied. It is noted that, owing to the mesoporous structure of the magnesium-thermic powders, the decrease in the surface area during heat treatment, first of all, is related to a decrease in the amount of pores less than 10 nm in size. The heat treatment of a reacting mass is shown to allow us to correct the specific surface area of the powder without any increase in the oxygen content in it. Data on the effect of heat treatment conditions on the specific charge of capacitor anodes are reported.

A model for the catalytic reduction of NO with CO and N desorption

NASA Astrophysics Data System (ADS)

Díaz, J. J.; Buendía, G. M.

2018-02-01

In this work we have investigated by Monte Carlo simulations the dynamical behavior of a modified Yaldram-Khan (YK) model for the catalytic reduction of NO on a surface. Our model is simulated on a square lattice and includes the individual desorption of CO molecules and N atoms, processes associated with temperature effects. When CO desorption is added, strong fluctuations appear, which are associated with the spreading of N checkerboard structures on the surface. These structures take a long time to coalesce, allowing the existence of a unsteady but long lasting reactive state. N desorption also favors the reactivity of the system, this time by diminishing the size of the N structures and impeding their coalescence. The combined desorption of CO and N produces a reactive state as well, where reactive zones among N structures can take place on the surface.

Experimental assessment of the performance of ablative heat shield materials from plasma wind tunnel testing

NASA Astrophysics Data System (ADS)

Löhle, S.; Hermann, T.; Zander, F.

2017-12-01

A method for assessing the performance of typical heat shield materials is presented in this paper. Three different material samples, the DLR material uc(Zuram), the Airbus material uc(Asterm) and the carbon preform uc(Calcarb) were tested in the IRS plasma wind tunnel PWK1 at the same nominal condition. State of the art diagnostic tools, i.e., surface temperature with pyrometry and thermography and boundary layer optical emission spectroscopy were completed by photogrammetric surface recession measurements. These data allow the assessment of the net heat flux for each material. The analysis shows that the three materials each have a different effect on heat flux mitigation with ASTERM showing the largest reduction in surface heat flux. The effect of pyrolysis and blowing is clearly observed and the heat flux reduction can be determined from an energy balance.

Perioperative thermal insulation.

PubMed

Bräuer, Anselm; Perl, Thorsten; English, Michael J M; Quintel, Michael

2007-01-01

Perioperative hypothermia remains a common problem during anesthesia and surgery. Unfortunately, the implementation of new minimally invasive surgical procedures has not lead to a reduction of this problem. Heat losses from the skin can be reduced by thermal insulation to avoid perioperative hypothermia. However, only a small amount of information is available regarding the physical properties of insulating materials used in the Operating Room (OR). Therefore, several materials using validated manikins were tested. Heat loss from the surface of the manikin can be described as:"Q = h . DeltaT . A" where Q = heat flux, h = heat exchange coefficient, DeltaT = temperature gradient between the environment and surface, and A = covered area. Heat flux per unit area and surface temperature were measured with calibrated heat flux transducers. Environmental temperature was measured using a thermoanemometer. The temperature gradient between the surface and environment (DeltaT) was varied and "h" was determined by linear regression analysis as the slope of "DeltaT" versus heat flux per unit area. The reciprocal of the heat exchange coefficient defines the insulation. The insulation values of the materials varied between 0.01 Clo (plastic bag) to 2.79 Clo (2 layers of a hospital duvet). Given the range of insulating materials available for outdoor activities, significant improvement in insulation of patients in the OR is both possible and desirable.

Preparation of highly active manganese oxides supported on functionalized MWNTs for low temperature NOx reduction with NH3

NASA Astrophysics Data System (ADS)

Pourkhalil, Mahnaz; Moghaddam, Abdolsamad Zarringhalam; Rashidi, Alimorad; Towfighi, Jafar; Mortazavi, Yadollah

2013-08-01

Manganese oxide catalysts (MnOx) supported on functionalized multi-walled carbon nanotubes (FMWNTs) for low temperature selective catalytic reduction (LTSCR) of nitrogen oxides (NOx) with NH3 in the presence of excess O2 were prepared by the incipient wetness impregnation method. These catalysts were characterized by N2 adsorption, Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and H2-temperature programmed reduction (H2-TPR) methods. The effects of reaction temperature, MnOx loading, calcination temperature and calcination time were investigated. The presence of surface nitrate species under moderate calcination conditions may play a favorable role in the LTSCR of NOx with NH3. Under the reaction conditions of 200 °C, 1 bar, NO = NH3 = 900 ppm, O2 = 5 vol%, GHSV = 30,000 h-1 and 12 wt% MnOx, NOx conversion and N2 selectivity were 97% and 99.5%, respectively. The SCR activity was reduced in the presence of 100 ppm SO2 and 2.5 vol% H2O from 97% to 92% within 6 h at 200 °C, however such an effect was shown to be reversible by exposing the catalyst to a helium flow for 2 h at 350 °C due to thermal decomposition of ammonium sulphate salts.

Mechanisms of Ocean Heat Uptake

NASA Astrophysics Data System (ADS)

Garuba, Oluwayemi

An important parameter for the climate response to increased greenhouse gases or other radiative forcing is the speed at which heat anomalies propagate downward in the ocean. Ocean heat uptake occurs through passive advection/diffusion of surface heat anomalies and through the redistribution of existing temperature gradients due to circulation changes. Atlantic meridional overturning circulation (AMOC) weakens in a warming climate and this should slow the downward heat advection (compared to a case in which the circulation is unchanged). However, weakening AMOC also causes a deep warming through the redistributive effect, thus increasing the downward rate of heat propagation compared to unchanging circulation. Total heat uptake depends on the combined effect of these two mechanisms. Passive tracers in a perturbed CO2 quadrupling experiments are used to investigate the effect of passive advection and redistribution of temperature anomalies. A new passive tracer formulation is used to separate ocean heat uptake into contributions due to redistribution and passive advection-diffusion of surface heating during an ocean model experiment with abrupt increase in surface temperature. The spatial pattern and mechanisms of each component are examined. With further experiments, the effects of surface wind, salinity and temperature changes in changing circulation and the resulting effect on redistribution in the individual basins are isolated. Analysis of the passive advection and propagation path of the tracer show that the Southern ocean dominates heat uptake, largely through vertical and horizontal diffusion. Vertical diffusion transports the tracer across isopycnals down to about 1000m in 100 years in the Southern ocean. Advection is more important in the subtropical cells and in the Atlantic high latitudes, both with a short time scale of about 20 years. The shallow subtropical cells transport the tracer down to about 500m along isopycnal surfaces, below this vertical diffusion takes over transport in the tropics; in the Atlantic, the MOC transports heat as deep 2000m in about 30 years. Redistributive surface heat uptake alters the total amount surface heat uptake among the basins. Compared to the passive-only heat uptake, which is about the same among the basins, redistribution nearly doubles the surface heat input into the Atlantic but makes smaller increases in the Indian and Pacific oceans for a net global increase of about 25%, in the perturbation experiment with winds unchanged. The passive and redistributive heat uptake components are further distributed among the basins through the global conveyor belt. The Pacific gains twice the surface heat input into it through lateral transport from the other two basins, as a result, the Atlantic and Pacific gain similar amounts of heat even though surface heat input is in the Atlantic is much bigger. Of this heat transport, most of the passive component comes from the Indian and the redistributive component comes from the Atlantic. Different surface forcing perturbation gives different circulation change pattern and as a result yield different redistributive uptake. Ocean heat uptake is more sensitive to wind forcing perturbation than to thermohaline forcing perturbation. About 2% reduction in subtropical cells transport and southern ocean transport, in the wind-change perturbation experiment, resulted in about 10% reduction in the global ocean heat uptake of wind-unchanged experiment. The AMOC weakened by about 35% and resulted in a 25% increase in passive heat uptake in the wind-unchanged experiment. Surface winds weakening reduces heat uptake by warming the reservoir surface temperatures, while MOC weakening increases heat input by a cooling reservoir surface temperatures. Thermohaline forcing perturbation is combination of salinity and temperature perturbations, both weaken the AMOC, however, they have opposite redistributive effects. Ocean surface freshening gives positive redistributive effect, while surface temperature increase gives negative redistributive effect on heat uptake. The salinity effect dominates the redistributive effect for thermohaline perturbation.

Thermal lift generation and drag reduction in rarefied aerodynamics

NASA Astrophysics Data System (ADS)

Pekardan, Cem; Alexeenko, Alina

2016-11-01

With the advent of the new technologies in low pressure environments such as Hyperloop and helicopters designed for Martian applications, understanding the aerodynamic behavior of airfoils in rarefied environments are becoming more crucial. In this paper, verification of rarefied ES-BGK solver and ideas such as prediction of the thermally induced lift and drag reduction in rarefied aerodynamics are investigated. Validation of the rarefied ES-BGK solver with Runge-Kutta discontinous Galerkin method with experiments in transonic regime with a Reynolds number of 73 showed that ES-BGK solver is the most suitable solver in near slip transonic regime. For the quantification of lift generation, A NACA 0012 airfoil is studied with a high temperature surface on the bottom for the lift creation for different Knudsen numbers. It was seen that for lower velocities, continuum solver under predicts the lift generation when the Knudsen number is 0.00129 due to local velocity gradients reaching slip regime although lift coefficient is higher with the Boltzmann ES-BGK solutions. In the second part, the feasibility of using thermal transpiration for drag reduction is studied. Initial study in drag reduction includes an application of a thermal gradient at the upper surface of a NACA 0012 airfoil near trailing edge at a 12-degree angle of attack and 5 Pa pressure. It was seen that drag is reduced by 4 percent and vortex shedding frequency is reduced due to asymmetry introduced in the flow due to temperature gradient causing reverse flow due to thermal transpiration phenomena.

Comparative study of magnetic ordering in bulk and nanoparticles of Sm0.65Ca0.35MnO3: Magnetization and electron magnetic resonance measurements

NASA Astrophysics Data System (ADS)

Goveas, Lora Rita; Anuradha, K. N.; Bhagyashree, K. S.; Bhat, S. V.

2015-05-01

To explore the effect of size reduction to nanoscale on the hole doped Sm0.65Ca0.35MnO3 compound, dc magnetic measurements and electron magnetic resonance (EMR) were done on bulk and nanoparticle samples in the temperature range 10 ≤ T ≤ 300 K. Magnetization measurement showed that the bulk sample undergoes a charge ordering transition at 240 K and shows a mixed magnetic phase at low temperature. However, the nanosample underwent a ferromagnetic transition at 75 K, and the charge ordered state was destabilized on size reduction down to nanoscale. The low-temperature ferromagnetic component is found to be enhanced in nanoparticles as compared to their bulk counterpart. Interestingly around room temperature, bulk particles show higher magnetization where as at low temperature nanoparticles show higher magnetization. Ferromagnetism in the bulk is due to super exchange where as ferromagnetism in nanoparticles is due to uncompensated spins of the surface layer. Temperature variation of EMR parameters correlates well with the results of magnetic measurements. The magnetic behaviour of the nanoparticles is understood in terms of the core shell scenario.

Daily mean temperature estimate at the US SUFRAD stations as an average of the maximum and minimum temperatures

DOE PAGES

Chylek, Petr; Augustine, John A.; Klett, James D.; ...

2017-09-30

At thousands of stations worldwide, the mean daily surface air temperature is estimated as a mean of the daily maximum (T max) and minimum (T min) temperatures. In this paper, we use the NOAA Surface Radiation Budget Network (SURFRAD) of seven US stations with surface air temperature recorded each minute to assess the accuracy of the mean daily temperature estimate as an average of the daily maximum and minimum temperatures and to investigate how the accuracy of the estimate increases with an increasing number of daily temperature observations. We find the average difference between the estimate based on an averagemore » of the maximum and minimum temperatures and the average of 1440 1-min daily observations to be - 0.05 ± 1.56 °C, based on analyses of a sample of 238 days of temperature observations. Considering determination of the daily mean temperature based on 3, 4, 6, 12, or 24 daily temperature observations, we find that 2, 4, or 6 daily observations do not reduce significantly the uncertainty of the daily mean temperature. The bias reduction in a statistically significant manner (95% confidence level) occurs only with 12 or 24 daily observations. The daily mean temperature determination based on 24 hourly observations reduces the sample daily temperature uncertainty to - 0.01 ± 0.20 °C. Finally, estimating the parameters of population of all SURFRAD observations, the 95% confidence intervals based on 24 hourly measurements is from - 0.025 to 0.004 °C, compared to a confidence interval from - 0.15 to 0.05 °C based on the mean of T max and T min.« less

Daily mean temperature estimate at the US SUFRAD stations as an average of the maximum and minimum temperatures

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

Chylek, Petr; Augustine, John A.; Klett, James D.

At thousands of stations worldwide, the mean daily surface air temperature is estimated as a mean of the daily maximum (T max) and minimum (T min) temperatures. In this paper, we use the NOAA Surface Radiation Budget Network (SURFRAD) of seven US stations with surface air temperature recorded each minute to assess the accuracy of the mean daily temperature estimate as an average of the daily maximum and minimum temperatures and to investigate how the accuracy of the estimate increases with an increasing number of daily temperature observations. We find the average difference between the estimate based on an averagemore » of the maximum and minimum temperatures and the average of 1440 1-min daily observations to be - 0.05 ± 1.56 °C, based on analyses of a sample of 238 days of temperature observations. Considering determination of the daily mean temperature based on 3, 4, 6, 12, or 24 daily temperature observations, we find that 2, 4, or 6 daily observations do not reduce significantly the uncertainty of the daily mean temperature. The bias reduction in a statistically significant manner (95% confidence level) occurs only with 12 or 24 daily observations. The daily mean temperature determination based on 24 hourly observations reduces the sample daily temperature uncertainty to - 0.01 ± 0.20 °C. Finally, estimating the parameters of population of all SURFRAD observations, the 95% confidence intervals based on 24 hourly measurements is from - 0.025 to 0.004 °C, compared to a confidence interval from - 0.15 to 0.05 °C based on the mean of T max and T min.« less

Impacts of Aerosols on Seasonal Precipitation and Snowpack in California Based on Convection-Permitting WRF-Chem Simulations

NASA Astrophysics Data System (ADS)

Gu, Y.; Wu, L.; Jiang, J. H.; Su, H.; Yu, N.; Zhao, C.; Qian, Y.; Zhao, B.; Liou, K. N.; Choi, Y. S.

2017-12-01

A version of the WRF-Chem model with fully coupled aerosol-meteorology-snowpack is employed to investigate the impacts of various aerosol sources on precipitation and snowpack in California. In particular, the impacts of locally emitted anthropogenic and dust aerosols, and aerosols transported from outside of California are studied. We differentiate three pathways of aerosol effects including aerosol-radiation interaction (ARI), aerosol-snow interaction (ASI), and aerosol-cloud interaction (ACI). The convection-permitting model simulations show that precipitation, snow water equivalent (SWE), and surface air temperature averaged over the whole domain (34-42°N, 117-124°W, not including ocean points) are reduced when aerosols are included, therefore reducing the high model biases of these variables when aerosol effects are not considered. Aerosols affect California water resources through the warming of mountain tops and anomalously low precipitation, however, different aerosol sources play different roles in changing surface temperature, precipitation and snowpack in California by means of various weights of the three pathways. ARI by all aerosols mainly cools the surface, leading to slightly increased SWE over the mountains. Locally emitted dust aerosols warm the surface of mountain tops through ASI, in which the reduced snow albedo associated with dirty snow leads to more surface absorption of solar radiation and reduced SWE. Transported and local anthropogenic aerosols play a dominant role in increasing cloud water amount but reducing precipitation through ACI, leading to reduced SWE and runoff over the Sierra Nevada, as well as the warming of mountain tops associated with decreased SWE and hence lower surface albedo. The average changes in surface temperature from October to June are about -0.19 K and 0.22 K for the whole domain and over mountain tops, respectively. Overall, the averaged reduction during October to June is about 7% for precipitation, 3% for SWE, and 7% for surface runoff for the whole domain, while the corresponding numbers are 12%, 10%, and 10% for mountain tops. The reduction in SWE is more significant in a dry year, with 9% for the whole domain and 16% for mountain tops.

Superacid Passivation of Crystalline Silicon Surfaces.

PubMed

Bullock, James; Kiriya, Daisuke; Grant, Nicholas; Azcatl, Angelica; Hettick, Mark; Kho, Teng; Phang, Pheng; Sio, Hang C; Yan, Di; Macdonald, Daniel; Quevedo-Lopez, Manuel A; Wallace, Robert M; Cuevas, Andres; Javey, Ali

2016-09-14

The reduction of parasitic recombination processes commonly occurring within the silicon crystal and at its surfaces is of primary importance in crystalline silicon devices, particularly in photovoltaics. Here we explore a simple, room temperature treatment, involving a nonaqueous solution of the superacid bis(trifluoromethane)sulfonimide, to temporarily deactivate recombination centers at the surface. We show that this treatment leads to a significant enhancement in optoelectronic properties of the silicon wafer, attaining a level of surface passivation in line with state-of-the-art dielectric passivation films. Finally, we demonstrate its advantage as a bulk lifetime and process cleanliness monitor, establishing its compatibility with large area photoluminescence imaging in the process.

Reduction of chlorine radical chemical etching of GaN under simultaneous plasma-emitted photon irradiation

NASA Astrophysics Data System (ADS)

Liu, Zecheng; Imamura, Masato; Asano, Atsuki; Ishikawa, Kenji; Takeda, Keigo; Kondo, Hiroki; Oda, Osamu; Sekine, Makoto; Hori, Masaru

2017-08-01

Surface chemical reactions on the GaN surface with Cl radicals are thermally enhanced in the high-temperature Cl2 plasma etching of GaN, resulting in the formation of etch pits and thereby, a roughened surface. Simultaneous irradiation of ultraviolet (UV) photons in Cl2 plasma emissions with wavelengths of 258 and 306 nm reduces the surface chemical reactions because of the photodissociation of both Ga and N chlorides, which leads to a suppression of the increase in surface roughness. Compared with Si-related materials, we point out that photon-induced reactions should be taken into account during the plasma processing of wide-bandgap semiconductors.

A detailed study of Au-Ni bimetal synthesized by the phase separation mechanism for the cathode of low-temperature solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Yang, Tao; Rodrigues de Almeida, Carlos Manuel; Ramasamy, Devaraj; Almeida Loureiro, Francisco José

2014-12-01

A facile co-reduction and annealing synthesis route of nanospheric particles of Au-Ni bimetal with adjustable composition was developed. In a typical synthesis, a direct co-reduction of HAuCl4.4H2O and NiCl2 in aqueous solution was performed with the assistance of reductive NaBH4 and an anionic surfactant sodium dodecyl sulfate (SDS) functioned as the structure-directing agent. Ultrasonic mixing was used at the same time to control the size of the particles. The morphology, microstructure and the state of the surface atoms were analyzed in detail. These nanospheres showed enhanced electrocatalytic activity towards oxygen reduction reaction than that of pure Au nanoparticles, demonstrated in the low temperature SOFC as cathode. The maximum power density generated is 810 mW cm-2 at 550 °C. This is a promising route of taking advantages the Phase Separation Mechanism to greatly reduce the use of noble metals in the ORR field without sacrificing the electrocatalytic activity.

Structural and surface changes of cobalt modified manganese oxide during activation and ethanol steam reforming reaction

NASA Astrophysics Data System (ADS)

Gac, Wojciech; Greluk, Magdalena; Słowik, Grzegorz; Turczyniak-Surdacka, Sylwia

2018-05-01

Surface and structural changes of unmodified manganese and cobalt-manganese oxide during activation and ethanol steam reforming reaction conditions (ESR) were studied by means of X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction/oxidation (TPR/TPO) and transmission electron microscopy. It was shown that synthesis of cobalt manganese oxide by the redox precipitation method led to the formation of strongly dispersed cobalt ionic species within cryptomelane-based manganese oxide structure. Development of large cube-like MnO nanoparticles with spherical cobalt metallic crystallites decorated by manganese oxide on the high oxidation state and potassium species was observed during reduction. Cobalt manganese catalyst showed high initial activity and selectivity to H2 and CO2 in ethanol stem reforming reaction in the range of 390-480 °C. The drop of ethanol conversion and changes of selectivity with the time-on-stream were observed. An increase of reaction temperature led to intensification of deactivation phenomena. TEM studies evidenced coexistence of Co and CoOx nanoparticles formed under ethanol steam reforming conditions, partially covered by filamentous and encapsulating carbonaceous deposits.

Oxidation and thermal reduction of the Cu(1 0 0) surface as studied using positron annihilation induced Auger electron spectroscopy (PAES)

NASA Astrophysics Data System (ADS)

Fazleev, N. G.; Nadesalingam, M. P.; Maddox, W.; Mukherjee, S.; Rajeshwar, K.; Weiss, A. H.

2010-01-01

Changes in the surface of an oxidized Cu(1 0 0) single crystal resulting from vacuum annealing have been investigated using positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the annihilation induced Cu M 2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 °C. The intensity then decreases monotonically as the annealing temperature is increased to ˜600 °C. Experimental probabilities of annihilation of surface-trapped positrons with Cu 3p and O 1s core-level electrons are estimated from the measured intensities of the positron annihilation induced Cu M 2,3VV and O KLL Auger transitions. Experimental PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface, surface reconstructions, and electron-positron correlations effects. The effects of oxygen adsorption on localization of positron surface state wave function and annihilation characteristics are also analyzed. Possible explanation is proposed for the observed behavior of the intensity of positron annihilation induced Cu M 2,3VV and O KLL Auger peaks and probabilities of annihilation of surface-trapped positrons with Cu 3p and O 1s core-level electrons with changes of the annealing temperature.

The influence of metal-support interactions on the accurate determination of Ru dispersion for Ru/TiO{sub 2}

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

Komaya, Takashi; Bell, A.T.; Weng-Sieh, Zara

1994-09-01

Titania-supported Ru catalysts have been characterized by TEM, {sup 1}H NMR, and H{sub 2} chemisorption to determine the metal particle size, the fraction of the metal surface available for H{sub 2} chemisorption, and the H{sub 2} adsorption capacity of the catalyst, as functions of the reduction temperature. TEM micrographs show that as the reduction temperature rises from 573 to 773K, the average particle size of Ru remains the same but the surface of the particles is covered to an increasing extent by an amorphous layer of titania. Quantitative estimates of the fraction of the Ru particle surface available for H{submore » 2} chemisorption were obtained by {sup 1}H NMR. The NMR spectra also show that a fraction of the adsorbed H{sub 2} spills over onto the support and that as a consequence measurements of total H{sub 2} chemisorption overestimate the number of Ru sites available for H{sub 2} adsorption. The implications of these results for the correct calculation of Ru dispersion and the determination of turnover frequencies for reactions carried out over Ru/TiO{sub 2} are discussed. 16 refs., 5 figs., 1 tab.« less

Experimental and numerical investigations on the temperature distribution in PVD AlTiN coated and uncoated Al2O3/TiCN mixed ceramic cutting tools in hard turning of AISI 52100 steel

NASA Astrophysics Data System (ADS)

Sateesh Kumar, Ch; Patel, Saroj Kumar; Das, Anshuman

2018-03-01

Temperature generation in cutting tools is one of the major causes of tool failure especially during hard machining where machining forces are quite high resulting in elevated temperatures. Thus, the present work investigates the temperature generation during hard machining of AISI 52100 steel (62 HRC hardness) with uncoated and PVD AlTiN coated Al2O3/TiCN mixed ceramic cutting tools. The experiments were performed on a heavy duty lathe machine with both coated and uncoated cutting tools under dry cutting environment. The temperature of the cutting zone was measured using an infrared thermometer and a finite element model has been adopted to predict the temperature distribution in cutting tools during machining for comparative assessment with the measured temperature. The experimental and numerical results revealed a significant reduction of cutting zone temperature during machining with PVD AlTiN coated cutting tools when compared to uncoated cutting tools during each experimental run. The main reason for decrease in temperature for AlTiN coated tools is the lower coefficient of friction offered by the coating material which allows the free flow of the chips on the rake surface when compared with uncoated cutting tools. Further, the superior wear behaviour of AlTiN coating resulted in reduction of cutting temperature.

Reduction of Trapped-Ion Anomalous Heating by in situ Surface Plasma Cleaning

DTIC Science & Technology

2015-04-29

the trap chip temperature. To load ions, we initially cool 88Sr atoms into a remotely-located magneto - optical trap (MOT), then use a resonant push beam... trap heating rates [10]. Furthermore, some previous experiments have shown an improvement in the heating rates of surface-electrode ion traps after...rate when the trap chip is held at 4 K is not significantly improved by the plasma cleaning. While the observed frequency scaling is not the same in

Precursor-Surface Reactions in Plasma Deposition of Silicon Thin Films

NASA Astrophysics Data System (ADS)

Bakos, Tamas

2005-03-01

Device-quality hydrogenated amorphous silicon (a-Si:H) thin films are usually grown by plasma deposition under conditions where the SiH3 radical is the dominant deposition precursor. In this presentation, we report results of first-principles density functional theory calculations on the interactions of the SiH3 radical with the crystalline Si(100)-(2x1):H surface in conjunction with molecular-dynamics simulations of a-Si:H thin film growth by SiH3 radicals, which elucidate the pathways and energetics of surface reactions that govern important film properties. In particular, we show that an SiH3 radical can insert into strained surface Si-Si dimer bonds, abstract surface H through an Eley-Rideal mechanism, and passivate surface dangling bonds; these reactions follow exothermic and barrierless pathways that lead to a temperature-independent growth rate in agreement with experimental measurements. We also identify a thermally activated surface H abstraction process, in which the SiH3 radical diffuses through overcoordinated surface Si atoms until it encounters a favorable site for H abstraction; the diffusion and H-abstraction steps have commensurate activation barriers. This mechanism explains partly the reduction of the film H content at elevated substrate temperatures.

Study of Sea Surface Temperatures changes due to tropical cyclone fanoos in the southwest Bay of Bengal using satellite and argo observations

NASA Astrophysics Data System (ADS)

Krishna Kailasam, Muni

Sea surface temperature (SST) plays an important role in the studies of global climate system and as a boundary condition for operational numerical forecasts. Estimation of SST has tra-ditionally been performed with satellite based sensors operating in the infrared (IR) portion of the electromagnetic spectrum, where the ocean emissivity is close to unity. The National Oceanic and Atmospheric Administration (NOAA) satellite series, the GOES Imagers on the Geostationary Operational Environmental Satellites, the Along Track Scanning Radiometer (ATSR) on the European Remote Sensing satellites and the Moderate Resolution Imaging Spectroradiometer (MODIS) on the NASA EOS platform are successful examples of IR sen-sors currently used for operational SST retrievals. Significant progress in SST retrieval from remote sensing data came with the introduction of a new low-frequency channel (10.7 GHz) on microwave (MW) sensors. The anthropogenic effects over a period of time resulted in increase of infrared absorbers such as greenhouse gases and absorbing aerosol would produce increase of both daytime maximum and nighttime minimum temperatures. In contrast, the increases of visible reflectors such as sulfate aerosols and low cloud amount would result in a decrease of the daytime maximum temperature. Solar radiation, wind stress and vertical mixing are known to be the three major factors impacting the SST seasonal variations. In the present study, impact of absorbing aerosols on the sea surface temperature (SST) over Bay of Bengal (BoB) region was investigated. Increased aerosol loading over BoB was observed due to advection of aerosols from continental region consisting of absorbing particles primarily from dust and biomass burning. This increased loading over BoB resulted in reduction of surface reaching solar radiation. Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) de-rived SST over BoB showed negative correlation with OMI-Aerosol Index (AI) (R = 0.87) and Terra/Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) AOD550 (R = 0.77) suggesting reduction in SST due to absorption of incoming solar radiation by aerosols.

Stress studies in EFG

NASA Technical Reports Server (NTRS)

1983-01-01

Stress distributions were calculated for a creep law to predict a rate of plastic deformation. The expected reduction in stresses is obtained. Improved schemes for calculating growth system temperature distributions were evaluated. Temperature field modeling examined the possibility of using horizontal temperature gradients to influence stress distribution in ribbon. The defect structure of 10 cm wide ribbon grown in the cartridge system was examined. A new feature is identified from an examination of cross sectional micrographs. It consists of high density dislocation bands extending through the ribbon thickness. A four point bending apparatus was constructed for high temperature study of the creep response of silicon, to be used to generate defects for comparison with as grown defects in ribbon. The feasibility of laser interferometric techniques for sheet residual stress distribution measurement is examined. The mathematical formalism for calculating residual stress from changes in surface topology caused by an applied stress in a rectangular specimen was developed, and the system for laser interferometric measurement to obtain surface topology data was tested on CZ silicon.

Hydrogenation Reactions of CO and CO2: New Insights through In Situ X-ray Spectroscopy and Chemical Transient Kinetics Experiments on Cobalt Catalysts

NASA Astrophysics Data System (ADS)

Ralston, Walter Thomas

The catalytic hydrogenations of CO and CO2 to more useful chemicals is not only beneficial in producing more valuable products and reducing dependence on fossil fuels, but present a scientific challenge in how to control the selectivity of these reactions. Using colloidal chemistry techniques, a high level of control over the synthesis of nanomaterials can be achieved, and by exploiting this fact a simple model system can be realized to understand the reaction of CO and CO2 on a molecular level. Specifically, this dissertation focuses on understanding cobalt materials for the conversion of CO and CO2 into more useful, valuable chemicals. Colloidally prepared cobalt nanoparticles with a narrow size distribution were supported in mesoporous SiO2 and TiO2 to study the effect of the support on the Co catalyzed hydrogenation of CO and CO2. The 10nm Co/SiO2 and Co/TiO2 catalysts were tested for CO and CO2 hydrogenation at 5 bar with a ratio to hydrogen of 1:2 and 1:3, respectively. In addition, the effect of Co oxidation state was studied by using different reduction pretreatment temperatures (250°C and 450°C). The results showed that for both hydrogenation reactions, Co/TiO2 had a high activity at both reduction temperatures compared to Co/SiO2. However, unlike Co/SiO2 which showed higher activity after 450°C reduction, Co/TiO2 had a higher activity after reduction at 250°C. Through synchrotron x-ray spectroscopy, it was concluded that the TiO2 was wetting the Co particle at higher reduction temperatures and dewetting at lower reduction temperatures. In addition to the wetting, CoO was observed to be the surface species on Co/TiO2 catalyst after reduction at low temperatures, which catalyzed both CO and CO2 hydrogenation reactions with higher activity than the Co metal obtained after reduction at 450°C. Classical steady-state measurements are limited in so much as they are often unable to provide information on individual reaction steps in complex reaction pathways. To attempt to circumvent this, a chemical transient kinetics (CTK) reactor was designed and built. Verification of the reactor was performed by evaluating a catalyst from the literature and confirming the results. A CoMgO catalyst was used to accomplish this, and our original findings show that at short time scales steric hindrances at the surface may push the product distribution towards olefinic rather than branched compounds. Continuing work on the CTK, two distinct particle sizes of Co nanoparticles were synthesized and tested under atmospheric conditions (H2:CO = 2:1) on the transient reactor. 4.3 nm Co and 9.5 nm Co were supported on MCF-17 to study the previously observed size effect, where Co nanoparticles lose activity at smaller sizes. It was found that indeed, the 4.3 nm Co are less active because they contain less CO dissociation sites, which are necessary for populating the surface with carbon monomers and spurring subsequent chain growth. The specific CO dissociation site was identified as the Co (221) step, of which larger Co particles have more and smaller Co particles have less. To investigate the nature of the MnO / Co3O4 interface, an in situ study using synchrotron radiation was undertaken. A sample of 6nm MnO nanoparticles loaded on mesoporous Co3O4 was studied with ambient pressure x-ray photoelectron spectroscopy, soft x-ray absorption spectroscopy at the Mn and Co L edges, and scanning transmission x-ray microscopy. X-ray measurements show that under reducing conditions of CO + H2, the MnO nanoparticles wet the Co surface until it is completely covered by a layer of MnO. Through the combination of techniques, it is shown that the system is catalytic active at the low pressures studied, and that the nature of the interface between MnO and Co3O4 is highly dependent on the temperature and gaseous environment it is prepared in. (Abstract shortened by ProQuest.).

Terrestrial cooling in Northern Europe during the eocene-oligocene transition.

PubMed

Hren, Michael T; Sheldon, Nathan D; Grimes, Stephen T; Collinson, Margaret E; Hooker, Jerry J; Bugler, Melanie; Lohmann, Kyger C

2013-05-07

Geochemical and modeling studies suggest that the transition from the "greenhouse" state of the Late Eocene to the "icehouse" conditions of the Oligocene 34-33.5 Ma was triggered by a reduction of atmospheric pCO2 that enabled the rapid buildup of a permanent ice sheet on the Antarctic continent. Marine records show that the drop in pCO2 during this interval was accompanied by a significant decline in high-latitude sea surface and deep ocean temperature and enhanced seasonality in middle and high latitudes. However, terrestrial records of this climate transition show heterogeneous responses to changing pCO2 and ocean temperatures, with some records showing a significant time lag in the temperature response to declining pCO2. We measured the Δ47 of aragonite shells of the freshwater gastropod Viviparus lentus from the Solent Group, Hampshire Basin, United Kingdom, to reconstruct terrestrial temperature and hydrologic change in the North Atlantic region during the Eocene-Oligocene transition. Our data show a decrease in growing-season surface water temperatures (~10 °C) during the Eocene-Oligocene transition, corresponding to an average decrease in mean annual air temperature of ~4-6 °C from the Late Eocene to Early Oligocene. The magnitude of cooling is similar to observed decreases in North Atlantic sea surface temperature over this interval and occurs during major glacial expansion. This suggests a close linkage between atmospheric carbon dioxide concentrations, Northern Hemisphere temperature, and expansion of the Antarctic ice sheets.

The Effect of High Temperature Corrosion on Mechanical Behavior of a GAMMA-TiAl Alloy

NASA Astrophysics Data System (ADS)

Zhao, Wenyue; Ma, Yue; Gong, Shengkai

The mechanical properties of Ti-48Al-2Cr-2Nb alloy were discussed after the high temperature corrosion tests carried out with salt mixture of 75wt. % Na2SO4 and 25wt. % NaCl at 800°C. The microstructure of the alloy after corrosion was observed by SEM and the fracture behavior of the corroded and uncorroded alloys was investigated by means of the three-point bending tests. It has been shown that the corrosion path was mainly along the lamellar structure and rough surface with a large number of corrosion pits formed during the high temperature corrosion. The experimental results also indicated that the bearing capacity of bending fracture descended evidently due to the molten salt corrosion at high temperature, which only had remarkable effects on the surface state of the alloy. The microcracks inside the alloy always propagated along the phase interfaces and grain boundaries while the corrosion pits on salt-deposited surface became the main crack initiation location in corroded alloy. The stress concentration caused by corrosion was considered as the essential reason of the property reduction, which decreased the energy barrier of crack nucleation and shortened the incubation period.

Thermal Management Techniques for Oil-Free Turbomachinery Systems

NASA Technical Reports Server (NTRS)

Radil, Kevin; DellaCorte, Chris; Zeszotek, Michelle

2006-01-01

Tests were performed to evaluate three different methods of utilizing air to provide thermal management control for compliant journal foil air bearings. The effectiveness of the methods was based on bearing bulk temperature and axial thermal gradient reductions during air delivery. The first method utilized direct impingement of air on the inner surface of a hollow test journal during operation. The second, less indirect method achieved heat removal by blowing air inside the test journal to simulate air flowing axially through a hollow, rotating shaft. The third method emulated the most common approach to removing heat by forcing air axially through the bearing s support structure. Internal bearing temperatures were measured with three, type K thermocouples embedded in the bearing that measured general internal temperatures and axial thermal gradients. Testing was performed in a 1 atm, 260 C ambient environment with the bearing operating at 60 krpm and supporting a load of 222 N. Air volumetric flows of 0.06, 0.11, and 0.17 cubic meters per minute at approximately 150 to 200 C were used. The tests indicate that all three methods provide thermal management but at different levels of effectiveness. Axial cooling of the bearing support structure had a greater effect on bulk temperature for each air flow and demonstrated that the thermal gradients could be influenced by the directionality of the air flow. Direct air impingement on the journal's inside surface provided uniform reductions in both bulk temperature and thermal gradients. Similar to the direct method, indirect journal cooling had a uniform cooling effect on both bulk temperatures and thermal gradients but was the least effective of the three methods.

Experimental Investigation of Jet Impingement Heat Transfer Using Thermochromic Liquid Crystals

NASA Technical Reports Server (NTRS)

Dempsey, Brian Paul

1997-01-01

Jet impingement cooling of a hypersonic airfoil leading edge is experimentally investigated using thermochromic liquid crystals (TLCS) to measure surface temperature. The experiment uses computer data acquisition with digital imaging of the TLCs to determine heat transfer coefficients during a transient experiment. The data reduction relies on analysis of a coupled transient conduction - convection heat transfer problem that characterizes the experiment. The recovery temperature of the jet is accounted for by running two experiments with different heating rates, thereby generating a second equation that is used to solve for the recovery temperature. The resulting solution requires a complicated numerical iteration that is handled by a computer. Because the computational data reduction method is complex, special attention is paid to error assessment. The error analysis considers random and systematic errors generated by the instrumentation along with errors generated by the approximate nature of the numerical methods. Results of the error analysis show that the experimentally determined heat transfer coefficients are accurate to within 15%. The error analysis also shows that the recovery temperature data may be in error by more than 50%. The results show that the recovery temperature data is only reliable when the recovery temperature of the jet is greater than 5 C, i.e. the jet velocity is in excess of 100 m/s. Parameters that were investigated include nozzle width, distance from the nozzle exit to the airfoil surface, and jet velocity. Heat transfer data is presented in graphical and tabular forms. An engineering analysis of hypersonic airfoil leading edge cooling is performed using the results from these experiments. Several suggestions for the improvement of the experimental technique are discussed.

Marine Cloud Brightening: regional applications to the weakening of hurricanes and reduction in coral bleaching

NASA Astrophysics Data System (ADS)

Gadian, A.; Hauser, R.; Kleypas, J. A.; Latham, J.; Parkes, B.; Salter, S.

2013-12-01

This study examines the potential to cool ocean surface waters in regions of hurricane genesis and early development. This would be achieved by seeding, with copious quantities of seawater cloud condensation nuclei (CCN), low-level maritime stratocumulus clouds covering these regions or those at the source of incoming currents. Higher cloud droplet density would increase these clouds' reflectivity to incoming sunlight, and possibly their longevity. This approach is a more localized application of the Marine Cloud Brightening (MCB) geoengineering technique promoting global cooling. By utilizing a climate ocean/atmosphere coupled model, HadGEM1, and by judicious seeding of maritime stratocumulus clouds, we demonstrate that we may be able to significantly reduce sea surface temperatures (SSTs) in hurricane development regions. Thus artificial seeding may reduce hurricane intensity; but how well the magnitude of this effect is yet to be determined. Increases in coral bleaching events over the last few decades have been largely caused by rising SSTs, and continued warming is expected to cause even greater increases through this century. Using thr same Global Climate Model to examine the potential of MCB to cool oceanic surface waters in three coral reef provinces. Our simulations indicate that under doubled CO2 conditions, the substantial increases in coral bleaching conditions from current values in three reef regions (Caribbean, French Polynesia, and the Great Barrier Reef) were eliminated when MCB was applied, which reduced the SSTs at these sites roughly to their original values. In this study we also illustrate how even regional application of MCB can affect the planetary meridional heat flux and the reduction in poleward heat transfer. (a) Change in annual average sea surface temperature, Celsius, between the 2xCO2 and CONTROL simulations. (b) Change in annual average sea surface temperature, Celsius, between the CONTROL and 2xCO2+MCB simulations. The dashed black boxes in both panels represent the three coral reef regions. In the Southern north Atlantic, the warmer SSTs in (a) is reduced to the current "control" temperatures, weakening hurricane formation.

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

Tang, Guoping; Zheng, Jianqiu; Xu, Xiaofeng

Soil organic carbon turnover to CO 2 and CH 4 is sensitive to soil redox potential and pH conditions. But, land surface models do not consider redox and pH in the aqueous phase explicitly, thereby limiting their use for making predictions in anoxic environments. Using recent data from incubations of Arctic soils, we extend the Community Land Model with coupled carbon and nitrogen (CLM-CN) decomposition cascade to include simple organic substrate turnover, fermentation, Fe(III) reduction, and methanogenesis reactions, and assess the efficacy of various temperature and pH response functions. Incorporating the Windermere Humic Aqueous Model (WHAM) enables us to approximatelymore » describe the observed pH evolution without additional parameterization. Though Fe(III) reduction is normally assumed to compete with methanogenesis, the model predicts that Fe(III) reduction raises the pH from acidic to neutral, thereby reducing environmental stress to methanogens and accelerating methane production when substrates are not limiting. Furthermore, the equilibrium speciation predicts a substantial increase in CO 2 solubility as pH increases, and taking into account CO 2 adsorption to surface sites of metal oxides further decreases the predicted headspace gas-phase fraction at low pH. Without adequate representation of these speciation reactions, as well as the impacts of pH, temperature, and pressure, the CO 2 production from closed microcosms can be substantially underestimated based on headspace CO 2 measurements only. Our results demonstrate the efficacy of geochemical models for simulating soil biogeochemistry and provide predictive understanding and mechanistic representations that can be incorporated into land surface models to improve climate predictions.« less

Biogeochemical modeling of CO2 and CH4 production in anoxic Arctic soil microcosms

NASA Astrophysics Data System (ADS)

Tang, Guoping; Zheng, Jianqiu; Xu, Xiaofeng; Yang, Ziming; Graham, David E.; Gu, Baohua; Painter, Scott L.; Thornton, Peter E.

2016-09-01

Soil organic carbon turnover to CO2 and CH4 is sensitive to soil redox potential and pH conditions. However, land surface models do not consider redox and pH in the aqueous phase explicitly, thereby limiting their use for making predictions in anoxic environments. Using recent data from incubations of Arctic soils, we extend the Community Land Model with coupled carbon and nitrogen (CLM-CN) decomposition cascade to include simple organic substrate turnover, fermentation, Fe(III) reduction, and methanogenesis reactions, and assess the efficacy of various temperature and pH response functions. Incorporating the Windermere Humic Aqueous Model (WHAM) enables us to approximately describe the observed pH evolution without additional parameterization. Although Fe(III) reduction is normally assumed to compete with methanogenesis, the model predicts that Fe(III) reduction raises the pH from acidic to neutral, thereby reducing environmental stress to methanogens and accelerating methane production when substrates are not limiting. The equilibrium speciation predicts a substantial increase in CO2 solubility as pH increases, and taking into account CO2 adsorption to surface sites of metal oxides further decreases the predicted headspace gas-phase fraction at low pH. Without adequate representation of these speciation reactions, as well as the impacts of pH, temperature, and pressure, the CO2 production from closed microcosms can be substantially underestimated based on headspace CO2 measurements only. Our results demonstrate the efficacy of geochemical models for simulating soil biogeochemistry and provide predictive understanding and mechanistic representations that can be incorporated into land surface models to improve climate predictions.

Study on factors affecting the droplet temperature in plasma MIG welding process

NASA Astrophysics Data System (ADS)

Mamat, Sarizam Bin; Tashiro, Shinichi; Tanaka, Manabu; Yusoff, Mahani

2018-04-01

In the present study, the mechanism to control droplet temperature in the plasma MIG welding was discussed based on the measurements of the droplet temperature for a wide range of MIG currents with different plasma electrode diameters. The measurements of the droplet temperatures were conducted using a two color temperature measurement method. The droplet temperatures in the plasma MIG welding were then compared with those in the conventional MIG welding. As a result, the droplet temperature in the plasma MIG welding was found to be reduced in comparison with the conventional MIG welding under the same MIG current. Especially when the small plasma electrode diameter was used, the decrease in the droplet temperature reached maximally 500 K. Also, for a particular WFS, the droplet temperatures in the plasma MIG welding were lower than those in the conventional MIG welding. It is suggested that the use of plasma contributes to reducing the local heat input into the base metal by the droplet. The presence of the plasma surrounding the wire is considered to increase the electron density in its vicinity, resulting in the arc attachment expanding upwards along the wire surface to disperse the MIG current. This dispersion of MIG current causes a decrease in current density on the droplet surface, lowering the droplet temperature. Furthermore, dispersed MIG current also weakens the electromagnetic pinch force acting on the neck of the wire above the droplet. This leads to a larger droplet diameter with increased surface area through lower frequency of droplet detachment to decrease the MIG current density on the droplet surface, as compared to the conventional MIG welding at the same MIG current. Thus, the lower droplet temperature is caused by the reduction of heat flux into the droplet. Consequently, the mechanism to control droplet temperature in the plasma MIG welding was clarified.

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

Jadeja, K.A.; Patel, K.M.; Tanna, R.L., E-mail: kumarpal@ipr.res.in

Low temperature glow discharge wall conditioning (GDC) using H{sub 2} gas is effective in reduction of oxygen and carbon (low-Z) contain impurities on near surface region of vessel wall. The high retention of hydrogen in vessel wall/components due to long operation of H{sub 2} GDC increases hydrogen out-gassing during tokamak operation and affects the production of high temperature plasma. The hydrogen retention can be reduced using inert gas GDC by sputter cleaning for short duration. But in that case the out-gassing rate of inert gas increases, that again impairs the plasma performance. To overcome above problems, the GDC with hydrogen-inertmore » gas mixture can be used for better removal of C and O surface contaminants and low hydrogen retention in surface. In ADITYA tokamak, H{sub 2}-GDC is carried out regularly after plasma operation, while the GDC with argon-hydrogen (Ar-H{sub 2}) mixture has been experimentally tested to observe the reduction of oxygen and carbon impurities along with low hydrogen retention. In Ar-H{sub 2} GDC, the reason being the formation of ArH{sup +} hydride ions, which has quite long life and more energy compared to H{sub 2}{sup +} ions formed in H{sub 2} GDC for breaking the bond of wall molecules. A systematic comparative study of H{sub 2} GDC and Ar-H{sub 2} Mixture GDC by changing the mixture ratio has been carried out in ADITYA tokamak. The relative levels of oxygen and carbon contain impurities have been measured using residual gas analyzer in both GDC's. We have observed a substantial reduction in oxygen and carbon impurities with a significant improvement in wall condition with Ar-H{sub 2} GDC compared to the H{sub 2} GDC. The effect of wall conditioning by Ar-H{sub 2} GDC on the performance of high temperature plasma operation will be presented in this paper. (author)« less

Preparation, characterization and dissolution of passive oxide film on the 400 series stainless steel surfaces

NASA Astrophysics Data System (ADS)

Sathyaseelan, V. S.; Rufus, A. L.; Chandramohan, P.; Subramanian, H.; Velmurugan, S.

2015-12-01

Full system decontamination of Primary Heat Transport (PHT) system of Pressurised Heavy Water Reactors (PHWRs) resulted in low decontamination factors (DF) on stainless steel (SS) surfaces. Hence, studies were carried out with 403 SS and 410 SS that are the material of construction of "End-Fitting body" and "End-Fitting Liner tubes". Three formulations were evaluated for the dissolution of passive films formed over these alloys viz., i) Two-step process consisting of oxidation and reduction reactions, ii) Dilute Chemical Decontamination (DCD) and iii) High Temperature Process. The two-step and high temperature processes could dissolve the oxide completely while the DCD process could remove only 60%. Various techniques like XRD, Raman spectroscopy and SEM-EDX were used for assessing the dissolution process. The two-step process is time consuming, laborious while the high temperature process is less time consuming and is recommended for SS decontamination.

High temperature superconductor analog electronics for millimeter-wavelength communications

NASA Technical Reports Server (NTRS)

Romanofsky, R. R.; Bhasin, K. B.

1991-01-01

The performance of high temperature superconductor (HTS) passive microwave circuits up to X-band was encouraging when compared to their metallic counterparts. The extremely low surface resistance of HTS films up to about 10 GHz enables a reduction in loss by as much as 100 times compared to copper when both materials are kept at about 77 K. However, a superconductor's surface resistance varies in proportion to the frequency squared. Consequently, the potential benefit of HTS materials to millimeter-wave communications requires careful analysis. A simple ring resonator was used to evaluate microstrip losses at Ka-band. Additional promising components were investigated such as antennas and phase shifters. Prospects for HTS to favorable impact millimeter-wave communications systems are discussed.

Impacts of stratospheric sulfate geoengineering on tropospheric ozone

NASA Astrophysics Data System (ADS)

Xia, Lili; Nowack, Peer J.; Tilmes, Simone; Robock, Alan

2017-10-01

A range of solar radiation management (SRM) techniques has been proposed to counter anthropogenic climate change. Here, we examine the potential effects of stratospheric sulfate aerosols and solar insolation reduction on tropospheric ozone and ozone at Earth's surface. Ozone is a key air pollutant, which can produce respiratory diseases and crop damage. Using a version of the Community Earth System Model from the National Center for Atmospheric Research that includes comprehensive tropospheric and stratospheric chemistry, we model both stratospheric sulfur injection and solar irradiance reduction schemes, with the aim of achieving equal levels of surface cooling relative to the Representative Concentration Pathway 6.0 scenario. This allows us to compare the impacts of sulfate aerosols and solar dimming on atmospheric ozone concentrations. Despite nearly identical global mean surface temperatures for the two SRM approaches, solar insolation reduction increases global average surface ozone concentrations, while sulfate injection decreases it. A fundamental difference between the two geoengineering schemes is the importance of heterogeneous reactions in the photochemical ozone balance with larger stratospheric sulfate abundance, resulting in increased ozone depletion in mid- and high latitudes. This reduces the net transport of stratospheric ozone into the troposphere and thus is a key driver of the overall decrease in surface ozone. At the same time, the change in stratospheric ozone alters the tropospheric photochemical environment due to enhanced ultraviolet radiation. A shared factor among both SRM scenarios is decreased chemical ozone loss due to reduced tropospheric humidity. Under insolation reduction, this is the dominant factor giving rise to the global surface ozone increase. Regionally, both surface ozone increases and decreases are found for both scenarios; that is, SRM would affect regions of the world differently in terms of air pollution. In conclusion, surface ozone and tropospheric chemistry would likely be affected by SRM, but the overall effect is strongly dependent on the SRM scheme. Due to the health and economic impacts of surface ozone, all these impacts should be taken into account in evaluations of possible consequences of SRM.

New operation strategy for driving the selectivity of NO x reduction to N 2, NH 3 or N 2O during lean/rich cycling of a lean NO x trap catalyst

DOE PAGES

Mráček, David; Koci, Petr; Choi, Jae -Soon; ...

2015-09-08

Periodical regeneration of NO x storage catalyst (also known as lean NO x trap) by short rich pulses of CO, H 2 and hydrocarbons is necessary for the reduction of nitrogen oxides adsorbed on the catalyst surface. Ideally, the stored NO x is converted into N 2, but N 2O and NH 3 by-products can be formed as well, particularly at low-intermediate temperatures. The N 2 and N 2O products are formed concurrently in two peaks. The primary peaks appear immediately after the rich-phase inception, and tail off with the breakthrough of the reductant front accompanied by NH 3 product.more » In addition, the secondary N 2 and N 2O peaks then appear at the rich-to-lean transition as a result of reactions between surface-deposited reductants/intermediates (CO, HC, NH 3, — NCO) and residual stored NO x under increasingly lean conditions.« less

Effect of temperature and sunlight on the stability of human adenoviruses and MS2 as fecal contaminants on fresh produce surfaces.

PubMed

Carratalà, Anna; Rodriguez-Manzano, Jesús; Hundesa, Ayalkibet; Rusiñol, Marta; Fresno, Sandra; Cook, Nigel; Girones, Rosina

2013-06-17

Determining the stability, or persistence in an infectious state, of foodborne viral pathogens attached to surfaces of soft fruits and salad vegetables is essential to underpin risk assessment studies in food safety. Here, we evaluate the effect of temperature and sunlight on the stability of infectious human adenoviruses type 2 and MS2 bacteriophages on lettuce and strawberry surfaces as representative fresh products. Human adenoviruses have been selected because of their double role as viral pathogens and viral indicators of human fecal contamination. Stability assays were performed with artificially contaminated fresh samples kept in the dark or under sunlight exposure at 4 and 30°C over 24h. The results indicate that temperature is the major factor affecting HAdV stability in fresh produce surfaces, effecting decay between 3 and 4 log after 24h at 30°C. The inactivation times to achieve a reduction between 1 and 4-log are calculated for each experimental condition. This work provides useful information to be considered for improving food safety regarding the transmission of foodborne viruses through supply chains. Copyright © 2013 Elsevier B.V. All rights reserved.

Effective micro-spray cooling for light-emitting diode with graphene nanoporous layers

NASA Astrophysics Data System (ADS)

Keong Lay, Kok; Yew Cheong, Brian Mun; Li Tong, Wei; Tan, Ming Kwang; Hung, Yew Mun

2017-04-01

A graphene nanoplatelet (GNP) coating is utilized as a functionalized surface in enhancing the evaporation rate of micro-spray cooling for light-emitting diodes (LEDs). In micro-spray cooling, water is atomized into micro-sized droplets to reduce the surface energy and to increase the surface area for evaporation. The GNP coating facilitates the effective filmwise evaporation through the attribute of fast water permeation. The oxygenated functional groups of GNPs provide the driving force that initiates the intercalation of water molecules through the carbon nanostructure. The water molecules slip through the frictionless passages between the hydrophobic carbon walls, resulting an effective filmwise evaporation. The enhancement of evaporation leads to an enormous temperature reduction of 61.3 °C. The performance of the LED is greatly enhanced: a maximum increase in illuminance of 25% and an extension of power rating from 9 W to 12 W can be achieved. With the application of GNP coating, the high-temperature region is eliminated while maintaining the LED surface temperature for optimal operation. This study paves the way for employing the effective hybrid spray-evaporation-nanostructure technique in the development of a compact, low-power-consumption cooling system.

Reduction of structural defects in thick 4H-SiC epitaxial layers grown on 4° off-axis substrates

NASA Astrophysics Data System (ADS)

Yazdanfar, M.; Ivanov, I. G.; Pedersen, H.; Kordina, O.; Janzén, E.

2013-06-01

By carefully controlling the surface chemistry of the chemical vapor deposition process for silicon carbide (SiC), 100 μm thick epitaxial layers with excellent morphology were grown on 4° off-axis SiC substrates at growth rates exceeding 100 μm/h. In order to reduce the formation of step bunching and structural defects, mainly triangular defects, the effect of varying parameters such as growth temperature, C/Si ratio, Cl/Si ratio, Si/H2 ratio, and in situ pre-growth surface etching time are studied. It was found that an in-situ pre growth etch at growth temperature and pressure using 0.6% HCl in hydrogen for 12 min reduced the structural defects by etching preferentially on surface damages of the substrate surface. By then applying a slightly lower growth temperature of 1575 °C, a C/Si ratio of 0.8, and a Cl/Si ratio of 5, 100 μm thick, step-bunch free epitaxial layer with a minimum triangular defect density and excellent morphology could be grown, thus enabling SiC power device structures to be grown on 4° off axis SiC substrates.

Photoemission stability of negative electron affinity GaN photocathode

NASA Astrophysics Data System (ADS)

Zhang, Junju; Wang, Xiaohui; Yang, Wenzheng; Tang, Weidong; Fu, Xiaoqian; Li, Biao; Chang, Benkang

2012-11-01

The stability for reflection-mode GaN photocathode has been investigated by monitoring the photocurrent and the spectral response at room temperature. We watch that the photocurrent of the cathode decays with time in the vacuum system, and compare the spectral response curves after activation and after degradation. The photocurrent decay mechanism for reflection-mode NEA GaN photocathode was studied by the surface model ?GaN (Mg) :Cs ?:O-Cs. The reduction of the effective dipole quantity, which is caused by harmful gases, is the key factor of the photocurrent reduction.

Adhesion of in situ precipitated calcium carbonate in the presence and absence of magnetic field in quiescent conditions on different solid surfaces.

PubMed

Chibowski, Emil; Hołysz, Lucyna; Szcześ, Aleksandra

2003-11-01

Deposition of in situ precipitated calcium carbonate from Na(2)CO(3) and CaCl2 solutions on different substrates, i.e. stainless steel, copper, aluminium, and glass, was investigated at different temperatures, 20 degrees C, 40 degrees C, 60 degrees C and 80 degrees C, both in the absence and presence of S-S 0.1T magnetic field (MF). It was found that in quiescent conditions during 2h the amounts deposited firmly on the surfaces decreased with increasing temperature. If MF was present the deposition was reduced at all temperatures, and depended on the nature of the substrate. The largest MF effect was found on glass at 60 degrees C, which amounted 50% reduction of the deposit. However, at 80 degrees C no deposition was found in the presence of MF on aluminium surface. At this temperature the reproducibility of the experiments was poor, and an additional effect due to the metal surface corrosion (especially that of aluminium and copper) may be thought in alkaline environment of the experiments (pH ca. 10). Based on optical microscope photographs, it was concluded that the amounts of crystallographic forms of CaCO3 depended on the nature of substrate on which the precipitation and then the adhesion took place. To some extent the ratios of CaCO3 forms precipitated were different in the bulk phase than on the substrate surfaces at the same temperature, and this conclusion was based on the X-ray diffractograms. Some possible mechanisms causing MF effects are discussed.

The effects of internal heating and large scale climate variations on tectonic bi-stability in terrestrial planets

NASA Astrophysics Data System (ADS)

Weller, M. B.; Lenardic, A.; O'Neill, C.

2015-06-01

We use 3D mantle convection and planetary tectonics models to explore the links between tectonic regimes and the level of internal heating within the mantle of a planet (a proxy for thermal age), planetary surface temperature, and lithosphere strength. At both high and low values of internal heating, for moderate to high lithospheric yield strength, hot and cold stagnant-lid (single plate planet) states prevail. For intermediate values of internal heating, multiple stable tectonic states can exist. In these regions of parameter space, the specific evolutionary path of the system has a dominant role in determining its tectonic state. For low to moderate lithospheric yield strength, mobile-lid behavior (a plate tectonic-like mode of convection) is attainable for high degrees of internal heating (i.e., early in a planet's thermal evolution). However, this state is sensitive to climate driven changes in surface temperatures. Relatively small increases in surface temperature can be sufficient to usher in a transition from a mobile- to a stagnant-lid regime. Once a stagnant-lid mode is initiated, a return to mobile-lid is not attainable by a reduction of surface temperatures alone. For lower levels of internal heating, the tectonic regime becomes less sensitive to surface temperature changes. Collectively our results indicate that terrestrial planets can alternate between multiple tectonic states over giga-year timescales. Within parameter space regions that allow for bi-stable behavior, any model-based prediction as to the current mode of tectonics is inherently non-unique in the absence of constraints on the geologic and climatic histories of a planet.

Measurement of UO2 surface oxidation using grazing-incidence x-ray diffraction: Implications for nuclear forensics

NASA Astrophysics Data System (ADS)

Tracy, Cameron L.; Chen, Chien-Hung; Park, Sulgiye; Davisson, M. Lee; Ewing, Rodney C.

2018-04-01

Nuclear forensics involves determination of the origin and history of interdicted nuclear materials based on the detection of signatures associated with their production and trafficking. The surface oxidation undergone by UO2 when exposed to air is a potential signature of its atmospheric exposure during handling and transport. To assess the sensitivity of this oxidation to atmospheric parameters, surface sensitive grazing-incidence x-ray diffraction (GIXRD) measurements were performed on UO2 samples exposed to air of varying relative humidity (34%, 56%, and 95% RH) and temperature (room temperature, 50 °C, and 100 °C). Near-surface unit cell contraction was observed following exposure, indicating oxidation of the surface and accompanying reduction of the uranium cation ionic radii. The extent of unit cell contraction provides a measure of the extent of oxidation, allowing for comparison of the effects of various exposure conditions. No clear influence of relative humidity on the extent of oxidation was observed, with samples exhibiting similar degrees of unit cell contraction at all relative humidities investigated. In contrast, the thickness of the oxidized layers increased substantially with increasing temperature, such that differences on the order of 10 °C yielded readily observable crystallographic signatures of the exposure conditions.

Optimization of heat and relative humidity conditions to reduce Escherichia coli O157:H7 contamination and maximize the germination of radish seeds.

PubMed

Song, M K; Kim, H W; Rhee, M S

2016-06-01

We previously reported that a combination of heat and relative humidity (RH) had a marked bactericidal effect on Escherichia coli O157:H7 on radish seeds. Here, response surface methodology with a Box-Behnken design was used to build a model to predict reductions in E. coli O157:H7 populations based on three independent variables: heating temperature (55 °C, 60 °C, or 65 °C), RH (40%, 60%, and 80%), and holding time (8, 15, or 22 h). Optimum treatment conditions were selected using a desirability function. The predictive model for microbial reduction had a high regression coefficient (R(2) = 0.97), and the accuracy of the model was verified using validation data (R(2) = 0.95). Among the three variables examined, heating temperature (P < 0.0001) and RH (P = 0.004) were the most significant in terms of bacterial reduction and seed germination, respectively. The optimum conditions for microbial reduction (6.6 log reduction) determined by ridge analysis were as follows: 64.5 °C and 63.2% RH for 17.7 h. However, when both microbial reduction and germination rate were taken into consideration, the desirability function yielded optimal conditions of 65 °C and 40% RH for 8 h (6.6 log reduction in the bacterial population; 94.4% of seeds germinated). This study provides comprehensive data that improve our understanding of the effects of heating temperature, RH, and holding time on the E. coli O157:H7 population on radish seeds. Radish seeds can be exposed to these conditions before sprouting, which greatly increases the microbiological safety of the products. Copyright © 2015 Elsevier Ltd. All rights reserved.

Fractography of the high temperature hydrogen attack of a medium carbon steel

NASA Technical Reports Server (NTRS)

Melson, H. G.; Moorhead, R. D.

1975-01-01

Microscopic fracture processes were studied which are associated with hydrogen attack of a medium carbon steel in a well-controlled, high-temperature, high-purity hydrogen environment. Exposure to a hydrogen pressure and temperature of 3.5 MN/m2 and 575 C was found to degrade room temperature tensile properties with increasing exposure time. After 408 hr, yield and ultimate strengths were reduced by more than 40 percent and elongation was reduced to less than 2 percent. Initial fissure formation was found to be associated with manganese rich particles, most probably manganese oxide, aligned in the microstructure during the rolling operation. Fissure growth was found to be associated with a reduction in carbide content of the microstructure and was inhibited by the depletion of carbon. The interior surfaces of sectioned fissures or bubbles exhibit both primary and secondary cracking by intergranular separation. The grain surfaces were rough and rounded, suggesting a diffusion-associated separation process. Specimens that failed at room temperature after exposure to hydrogen were found to exhibit mixed mode fracture having varying amounts of intergranular separation, dimple formation, and cleavage, depending on exposure time.

Spatially distinct effects of preceding precipitation on heat stress over Eastern China

NASA Astrophysics Data System (ADS)

Tang, Q.; Liu, X.; Zhang, X.; Groisman, P. Y.; Sun, S.; Lu, H.; Li, Z.

2017-12-01

In many terrestrial regions, higher than usual surface temperatures are associated with (or even are induced by) surface moisture deficits. When in the warm season temperatures become anomalously high, their extreme values affect human beings causing heat stress. Besides increased temperature, rising humidity may also have substantial implications for human body thermal comfort. However, effects of surface moisture on heat stress, when considering both temperature and humidity, are less known. In this study, the relationship between the number of hot days in July as indicated by the wet-bulb globe temperature (WBGT) and preceding 3-month precipitation was assessed over Eastern China. It is found that the probability of occurrence of the above-the-average number of hot days exceeds 0.7 after preceding precipitation deficit in northeastern China, but is less than 0.3 in southeastern China. Generally, over Eastern China, precipitation in preceding months is negatively correlated with temperature and positively correlated with specific humidity in July. The combined effects generate a spatially distinct pattern: precipitation deficits in preceding months enhance heat stress in northeastern China while in southern China these deficits are associated with reduction of heat stress. In the south, abundant preceding precipitation tends to increase atmospheric humidity that is instrumental for increase of heat stress. These results contribute predictive information about the probability of mid-summer heat stress in Eastern China a few weeks ahead of its occurrence.

Rapidly reversible redox transformation in nanophase manganese oxides at room temperature triggered by changes in hydration

PubMed Central

Birkner, Nancy; Navrotsky, Alexandra

2014-01-01

Chemisorption of water onto anhydrous nanophase manganese oxide surfaces promotes rapidly reversible redox phase changes as confirmed by calorimetry, X-ray diffraction, and titration for manganese average oxidation state. Surface reduction of bixbyite (Mn2O3) to hausmannite (Mn3O4) occurs in nanoparticles under conditions where no such reactions are seen or expected on grounds of bulk thermodynamics in coarse-grained materials. Additionally, transformation does not occur on nanosurfaces passivated by at least 2% coverage of what is likely an amorphous manganese oxide layer. The transformation is due to thermodynamic control arising from differences in surface energies of the two phases (Mn2O3 and Mn3O4) under wet and dry conditions. Such reversible and rapid transformation near room temperature may affect the behavior of manganese oxides in technological applications and in geologic and environmental settings. PMID:24733903

Rapidly reversible redox transformation in nanophase manganese oxides at room temperature triggered by changes in hydration.

PubMed

Birkner, Nancy; Navrotsky, Alexandra

2014-04-29

Chemisorption of water onto anhydrous nanophase manganese oxide surfaces promotes rapidly reversible redox phase changes as confirmed by calorimetry, X-ray diffraction, and titration for manganese average oxidation state. Surface reduction of bixbyite (Mn2O3) to hausmannite (Mn3O4) occurs in nanoparticles under conditions where no such reactions are seen or expected on grounds of bulk thermodynamics in coarse-grained materials. Additionally, transformation does not occur on nanosurfaces passivated by at least 2% coverage of what is likely an amorphous manganese oxide layer. The transformation is due to thermodynamic control arising from differences in surface energies of the two phases (Mn2O3 and Mn3O4) under wet and dry conditions. Such reversible and rapid transformation near room temperature may affect the behavior of manganese oxides in technological applications and in geologic and environmental settings.

Regional climate impacts of a possible future grand solar minimum.

PubMed

Ineson, Sarah; Maycock, Amanda C; Gray, Lesley J; Scaife, Adam A; Dunstone, Nick J; Harder, Jerald W; Knight, Jeff R; Lockwood, Mike; Manners, James C; Wood, Richard A

2015-06-23

Any reduction in global mean near-surface temperature due to a future decline in solar activity is likely to be a small fraction of projected anthropogenic warming. However, variability in ultraviolet solar irradiance is linked to modulation of the Arctic and North Atlantic Oscillations, suggesting the potential for larger regional surface climate effects. Here, we explore possible impacts through two experiments designed to bracket uncertainty in ultraviolet irradiance in a scenario in which future solar activity decreases to Maunder Minimum-like conditions by 2050. Both experiments show regional structure in the wintertime response, resembling the North Atlantic Oscillation, with enhanced relative cooling over northern Eurasia and the eastern United States. For a high-end decline in solar ultraviolet irradiance, the impact on winter northern European surface temperatures over the late twenty-first century could be a significant fraction of the difference in climate change between plausible AR5 scenarios of greenhouse gas concentrations.

The Sensitivity of U.S. Surface Ozone Formation to NOx, and VOCs as Viewed from Space

NASA Technical Reports Server (NTRS)

Duncan, Bryan N.; Yoshida, Yasuko; Sillman, Sanford; Retscher, Christian; Pickering, Kenneth E.; Martin, Randall V.; Celarier, Edward A.

2009-01-01

We investigated variations in the sensitivity of surface ozone formation in summer to precursor species concentrations of volatile organic compounds (VOCs) and nitrogen oxides (NO(x)) as inferred from the ratio of tropospheric columns of formaldehyde and nitrogen dioxide from the Aura Ozone Monitoring Instrument (OMI). The data indicate that ozone formation became: 1. more sensitive to NO(x) over most of the U.S, from 2005 to 2007 because of substantial decreases in NO(x) emissions primarily from stationary sources, and 2. more sensitive to NO(x) with increasing temperature, in part because emissions of highly reactive, biogenic isoprene increase with temperature, thus increasing the total VOC reactivity. Based on our interpretation of the data, current strategies implemented to reduce unhealthy levels of surface ozone should focus more on reducing NO(x) emissions, except in some downtown areas which have historically benefited from reductions in VOC emissions.

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

Gu, K. X.; Wang, J. J.; Yuan, Z.

The effect of cryogenic treatment on the plastic property of Ti-6Al-4V plate was studied in the present work. After cryogenic treatment, the low temperature temper at 180 ▭ was conducted in one of the groups and the results were compared with that of the untreated and cryotreated ones. The SLX series program controlled cryogenic equipment was used for the cryogenic treatment. The tensile tests were conducted by universal tensile testing machine and parameters of elongation and area reduction were used to evaluate plastic property. The scanning electron microscope was used to study the morphology of microstructure and fracture surface. Themore » results show that after cryogenic treatment alone the elongation increased 10.6% and the area reduction increased 13.5% while the strength reduced to a small extent. Cryogenic treatment followed with low temperature temper increased the elongation and area reduction just by the extent of 4.7% and 9.5%. It means that the additional low temperature temper after cryogenic is not beneficial to the tensile properties of Ti-6Al-4V alloy. The examination of microstructure by scanning electron microscopy revealed that cryogenic treatment reduced the content of β phase particles which is the main reason for the improvement in plasticity.« less

Solar irradiance reduction to counteract radiative forcing from a quadrupling of CO2: climate responses simulated by four earth system models

NASA Astrophysics Data System (ADS)

Schmidt, H.; Alterskjær, K.; Karam, D. Bou; Boucher, O.; Jones, A.; Kristjánsson, J. E.; Niemeier, U.; Schulz, M.; Aaheim, A.; Benduhn, F.; Lawrence, M.; Timmreck, C.

2012-06-01

In this study we compare the response of four state-of-the-art Earth system models to climate engineering under scenario G1 of two model intercomparison projects: GeoMIP (Geoengineering Model Intercomparison Project) and IMPLICC (EU project "Implications and risks of engineering solar radiation to limit climate change"). In G1, the radiative forcing from an instantaneous quadrupling of the CO2 concentration, starting from the preindustrial level, is balanced by a reduction of the solar constant. Model responses to the two counteracting forcings in G1 are compared to the preindustrial climate in terms of global means and regional patterns and their robustness. While the global mean surface air temperature in G1 remains almost unchanged compared to the control simulation, the meridional temperature gradient is reduced in all models. Another robust response is the global reduction of precipitation with strong effects in particular over North and South America and northern Eurasia. In comparison to the climate response to a quadrupling of CO2 alone, the temperature responses are small in experiment G1. Precipitation responses are, however, in many regions of comparable magnitude but globally of opposite sign.

Analog VLSI system for active drag reduction

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

Gupta, B.; Goodman, R.; Jiang, F.

1996-10-01

In today`s cost-conscious air transportation industry, fuel costs are a substantial economic concern. Drag reduction is an important way to reduce costs. Even a 5% reduction in drag translates into estimated savings of millions of dollars in fuel costs. Drawing inspiration from the structure of shark skin, the authors are building a system to reduce drag along a surface. Our analog VLSI system interfaces with microfabricated, constant-temperature shear stress sensors. It detects regions of high shear stress and outputs a control signal to activate a microactuator. We are in the process of verifying the actual drag reduction by controlling microactuatorsmore » in wind tunnel experiments. We are encouraged that an approach similar to one that biology employs provides a very useful contribution to the problem of drag reduction. 9 refs., 21 figs.« less

Effects of electrolyzed oxidizing water on reducing Listeria monocytogenes contamination on seafood processing surfaces.

PubMed

Liu, Chengchu; Duan, Jingyun; Su, Yi-Cheng

2006-02-15

The effects of electrolyzed oxidizing (EO) water on reducing Listeria monocytogenes contamination on seafood processing surfaces were studied. Chips (5 x 5 cm(2)) of stainless steel sheet (SS), ceramic tile (CT), and floor tile (FT) with and without crabmeat residue on the surface were inoculated with L. monocytogenes and soaked in tap or EO water for 5 min. Viable cells of L. monocytogenes were detected on all chip surfaces with or without crabmeat residue after being held at room temperature for 1 h. Soaking contaminated chips in tap water resulted in small-degree reductions of the organism (0.40-0.66 log cfu/chip on clean surfaces and 0.78-1.33 log cfu/chip on dirty surfaces). Treatments of EO water significantly (p<0.05) reduced L. monocytogenes on clean surfaces (3.73 log on SS, 4.24 log on CT, and 5.12 log on FT). Presence of crabmeat residue on chip surfaces reduced the effectiveness of EO water on inactivating Listeria cells. However, treatments of EO water also resulted in significant reductions of L. monocytogenes on dirty surfaces (2.33 log on SS and CT and 1.52 log on FT) when compared with tap water treatments. The antimicrobial activity of EO water was positively correlated with its chlorine content. High oxidation-reduction potential (ORP) of EO water also contributed significantly to its antimicrobial activity against L. monocytogenes. EO water was more effective than chlorine water on inactivating L. monocytogenes on surfaces and could be used as a chlorine alternative for sanitation purpose. Application of EO water following a thorough cleaning process could greatly reduce L. monocytogenes contamination in seafood processing environments.

Instream habitat restoration and stream temperature reduction in a whirling disease-positive Spring Creek in the Blackfoot River Basin, Montana

USGS Publications Warehouse

Pierce, Ron; Podner, Craig; Marczak, Laurie B; Jones, Leslie A.

2014-01-01

Anthropogenic warming of stream temperature and the presence of exotic diseases such as whirling disease are both contemporary threats to coldwater salmonids across western North America. We examined stream temperature reduction over a 15-year prerestoration and postrestoration period and the severity of Myxobolus cerebralisinfection (agent of whirling disease) over a 7-year prerestoration and postrestoration period in Kleinschmidt Creek, a fully reconstructed spring creek in the Blackfoot River basin of western Montana. Stream restoration increased channel length by 36% and reduced the wetted surface area by 69% by narrowing and renaturalizing the channel. Following channel restoration, average maximum daily summer stream temperatures decreased from 15.7°C to 12.5°C, average daily temperature decreased from 11.2°C to 10.0°C, and the range of daily temperatures narrowed by 3.3°C. Despite large changes in channel morphology and reductions in summer stream temperature, the prevalence and severity of M. cerebralis infection for hatchery Rainbow Trout Oncorhynchus mykiss remained high (98–100% test fish with grade > 3 infection) versus minimal for hatchery Brown Trout Salmo trutta (2% of test fish with grade-1 infection). This study shows channel renaturalization can reduce summer stream temperatures in small low-elevation, groundwater-dominated streams in the Blackfoot basin to levels more suitable to native trout. However, because of continuous high infections associated with groundwater-dominated systems, the restoration of Kleinschmidt Creek favors brown trout Salmo trutta given their innate resistance to the parasite and the higher relative susceptibility of other salmonids.

Decreasing cloud cover drives the recent mass loss on the Greenland Ice Sheet

PubMed Central

Hofer, Stefan; Tedstone, Andrew J.; Fettweis, Xavier; Bamber, Jonathan L.

2017-01-01

The Greenland Ice Sheet (GrIS) has been losing mass at an accelerating rate since the mid-1990s. This has been due to both increased ice discharge into the ocean and melting at the surface, with the latter being the dominant contribution. This change in state has been attributed to rising temperatures and a decrease in surface albedo. We show, using satellite data and climate model output, that the abrupt reduction in surface mass balance since about 1995 can be attributed largely to a coincident trend of decreasing summer cloud cover enhancing the melt-albedo feedback. Satellite observations show that, from 1995 to 2009, summer cloud cover decreased by 0.9 ± 0.3% per year. Model output indicates that the GrIS summer melt increases by 27 ± 13 gigatons (Gt) per percent reduction in summer cloud cover, principally because of the impact of increased shortwave radiation over the low albedo ablation zone. The observed reduction in cloud cover is strongly correlated with a state shift in the North Atlantic Oscillation promoting anticyclonic conditions in summer and suggests that the enhanced surface mass loss from the GrIS is driven by synoptic-scale changes in Arctic-wide atmospheric circulation. PMID:28782014

Solar Eclipse Effect on Shelter Air Temperature

NASA Technical Reports Server (NTRS)

Segal, M.; Turner, R. W.; Prusa, J.; Bitzer, R. J.; Finley, S. V.

1996-01-01

Decreases in shelter temperature during eclipse events were quantified on the basis of observations, numerical model simulations, and complementary conceptual evaluations. Observations for the annular eclipse on 10 May 1994 over the United States are presented, and these provide insights into the temporal and spatial changes in the shelter temperature. The observations indicated near-surface temperature drops of as much as 6 C. Numerical model simulations for this eclipse event, which provide a complementary evaluation of the spatial and temporal patterns of the temperature drops, predict similar decreases. Interrelationships between the temperature drop, degree of solar irradiance reduction, and timing of the peak eclipse are also evaluated for late spring, summer, and winter sun conditions. These simulations suggest that for total eclipses the drops in shelter temperature in midlatitudes can be as high as 7 C for a spring morning eclipse.

Ni-O4 species anchored on N-doped graphene-based materials as molecular entities and electrocatalytic performances for oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Jang, Dawoon; Lee, Seungjun; Shin, Yunseok; Ohn, Saerom; Park, Sunghee; Lim, Donggyu; Park, Gilsoo; Park, Sungjin

2017-12-01

The generation of molecular active species on the surface of nano-materials has become promising routes to produce efficient electrocatalysts. Development of cost-effective catalysts with high performances for oxygen reduction reaction (ORR) is an important challenge for fuel cell and metal-air battery applications. In this work, we report a novel hybrid produced by room-temperature solution processes using Ni-based organometallic molecules and N-doped graphene-based materials. Chemical and structural characterizations reveal that Ni-containing species are well-dispersed on the surface of graphene network as molecular entity. The hybrid shows excellent electrocatalytic performances for ORR in basic medium with an onset potential of 0.87 V (vs. RHE), superior durability and good methanol tolerance.

Surface nanocrystalline and hardening effects of Ti-Al-V alloy by electropulsing ultrasonic shock

NASA Astrophysics Data System (ADS)

Ye, Xiaoxin; Tang, Guoyi

2015-03-01

The effect of electropulsing ultrasonic shock (EUS) on the surface hardening and microstructure of Ti6Al4V alloy was studied. It was found that electropulsing improved the microhardness dramatically both in the influential depth and maximum value, compared with the only ultrasonic-shocked sample. It's indicated that refined surface layer with nanocrystalline and improved microhardness were obtained on account of surface severe plastic deformation, dynamic recrystallization (DRX) and phase change, which was implemented at relative low temperature and high strain rate/capacity due to the coupling of the thermal and athermal effects of EUS. It's different from conventional experiments and theory. It's discussed that the positive contributions of EPT in the thermodynamics and kinetics of microstructure and properties change were attributed to the reduction of nucleation energy barrier and acceleration of atomic diffusion. Therefore, it's supposed that EUS is an energy-saving and high-efficiency method of surface treatment technique with the help of high-energy electropulses, which is promising in cost reduction of the surface engineering and energy management. The work is supported by National Natural Science Foundation of China (No. 50571048) and Shenzhen science and technology research funding project of China (No. SGLH20121008144756946).

Warm Arctic-cold Siberia: comparing the recent and the early 20th-century Arctic warmings

NASA Astrophysics Data System (ADS)

Wegmann, Martin; Orsolini, Yvan; Zolina, Olga

2018-02-01

The Warm Arctic-cold Siberia surface temperature pattern during recent boreal winter is suggested to be triggered by the ongoing decrease of Arctic autumn sea ice concentration and has been observed together with an increase in mid-latitude extreme events and a meridionalization of tropospheric circulation. However, the exact mechanism behind this dipole temperature pattern is still under debate, since model experiments with reduced sea ice show conflicting results. We use the early twentieth-century Arctic warming (ETCAW) as a case study to investigate the link between September sea ice in the Barents-Kara Sea (BKS) and the Siberian temperature evolution. Analyzing a variety of long-term climate reanalyses, we find that the overall winter temperature and heat flux trend occurs with the reduction of September BKS sea ice. Tropospheric conditions show a strengthened atmospheric blocking over the BKS, strengthening the advection of cold air from the Arctic to central Siberia on its eastern flank, together with a reduction of warm air advection by the westerlies. This setup is valid for both the ETCAW and the current Arctic warming period.

Solar Arrays for Low-Irradiance Low-Temperature and High-Radiation Environments

NASA Technical Reports Server (NTRS)

Boca, Andreea (Principal Investigator); Stella, Paul; Kerestes, Christopher; Sharps, Paul

2017-01-01

This is the Base Period final report DRAFT for the JPL task 'Solar Arrays for Low-Irradiance Low-Temperature and High-Radiation Environments', under Task Plan 77-16518 TA # 21, for NASA's Extreme Environments Solar Power (EESP) project. This report covers the Base period of performance, 7/18/2016 through 5/2/2017.The goal of this project is to develop an ultra-high efficiency lightweight scalable solar array technology for low irradiance, low temperature and high-radiation (LILT/Rad) environments. The benefit this technology will bring to flight systems is a greater than 20 reduction in solar array surface area, and a six-fold reduction in solar array mass and volume. The EESP project objectives are summarized in the 'NRA Goal' column of Table 1. Throughout this report, low irradiance low temperature (LILT) refers to 5AU -125 C test conditions; beginning of life (BOL) refers to the cell state prior to radiation exposure; and end of life (EOL) refers to the test article condition after exposure to a radiation dose of 4e15 1MeV e(-)/cm(exp 2).

Effects of soot-induced snow albedo change on snowpack and hydrological cycle in western U.S. based on WRF chemistry and regional climate simulations

NASA Astrophysics Data System (ADS)

Qian, Y.; Gustafson, W. I.; Leung, R.; Ghan, S. J.

2008-12-01

Radiative forcing induced by soot on snow is an important anthropogenic forcing affecting the global climate. In this study we simulated the deposition of soot aerosol on snow and the resulting impact on snowpack and the hydrological cycle in the western United States. A yearlong simulation was performed using the chemistry version of the Weather Research and Forecasting model (WRF-Chem) to determine the soot deposition, followed by three simulations using WRF in meteorology-only mode, with and without the soot-induced snow albedo perturbations. The chemistry simulation shows large spatial variability in soot deposition that reflects the localized emissions and the influence of the complex terrain. The soot-induced snow albedo perturbations increase the surface net solar radiation flux during late winter to early spring, increase the surface air temperature, and reduce the snow accumulation and spring snowmelt. These effects are stronger over the central Rockies and southern Alberta, where soot deposition and snowpack overlap the most. The indirect forcing of soot accelerates snowmelt and alters stream flows, including a trend toward earlier melt dates in the western United States. The soot-induced albedo reduction initiates a positive feedback process whereby dirty snow absorbs more solar radiation, heating the surface and warming the air. This warming causes reduced snow depth and fraction, which further reduces the regional surface albedo for the snow covered regions. For a doubled snow albedo perturbation, the change to surface energy and temperature is around 50-80%, however, snowpack reduction is nonlinearly accelerated.

Effects of soot-induced snow albedo change on snowpack and hydrological cycle in western United States based on Weather Research and Forecasting chemistry and regional climate simulations

NASA Astrophysics Data System (ADS)

Qian, Yun; Gustafson, William I.; Leung, L. Ruby; Ghan, Steven J.

2009-02-01

Radiative forcing induced by soot on snow is an important anthropogenic forcing affecting the global climate. In this study we simulated the deposition of soot aerosol on snow and the resulting impact on snowpack and the hydrological cycle in the western United States. A year-long simulation was performed using the chemistry version of the Weather Research and Forecasting model (WRF-Chem) to determine the soot deposition, followed by three simulations using WRF in meteorology-only mode, with and without the soot-induced snow albedo perturbations. The chemistry simulation shows large spatial variability in soot deposition that reflects the localized emissions and the influence of the complex terrain. The soot-induced snow albedo perturbations increase the surface net solar radiation flux during late winter to early spring, increase the surface air temperature, and reduce the snow accumulation and spring snowmelt. These effects are stronger over the central Rockies and southern Alberta, where soot deposition and snowpack overlap the most. The indirect forcing of soot accelerates snowmelt and alters stream flows, including a trend toward earlier melt dates in the western United States. The soot-induced albedo reduction initiates a positive feedback process whereby dirty snow absorbs more solar radiation, heating the surface and warming the air. This warming causes reduced snow depth and fraction, which further reduces the regional surface albedo for the snow-covered regions. For a doubled snow albedo perturbation, the change to surface energy and temperature is around 50-80%; however, snowpack reduction is nonlinearly accelerated.

Surface spin-glass, large surface anisotropy, and depression of magnetocaloric effect in La0.8Ca0.2MnO3 nanoparticles

NASA Astrophysics Data System (ADS)

Xi, S. B.; Lu, W. J.; Wu, H. Y.; Tong, P.; Sun, Y. P.

2012-12-01

The surface magnetic behavior of La0.8Ca0.2MnO3 nanoparticles was investigated. We observed irreversibility in high magnetic field. The surface spin-glass behavior as well as the high-field irreversibility is suppressed by increasing particle size while the freezing temperature TF does not change with particle size. The enhanced coercivity has been observed in the particles and we attributed it to the large surface anisotropy. We have disclosed a clear relationship between the particle size, the thickness of the shell, and the saturation magnetization of the particles. The large reduction of the saturation magnetization of the samples is found to be induced by the increase of nonmagnetic surface large since the thickness of the spin-disordered surface layer increases with a decrease in the particle size. Due to the reduction of the magnetization, the magnetocaloric effect (MCE) has been reduced by the decreased particle size since the nonmagnetic surface contributes little to the MCE. Based on the core-shell structure, large relative cooling powers RCP(s) of 180 J/kg and 471 J/kg were predicted for a field change of 2.0 T and 4.5 T, respectively, in the small particles with thin spin-glass layer.

An energetic perspective on hydrological cycle changes in the Geoengineering Model Intercomparison Project

NASA Astrophysics Data System (ADS)

Kravitz, Ben; Rasch, Philip J.; Forster, Piers M.; Andrews, Timothy; Cole, Jason N. S.; Irvine, Peter J.; Ji, Duoying; Kristjánsson, Jón Egill; Moore, John C.; Muri, Helene; Niemeier, Ulrike; Robock, Alan; Singh, Balwinder; Tilmes, Simone; Watanabe, Shingo; Yoon, Jin-Ho

2013-12-01

of surface and atmospheric energy budget responses to CO2 and solar forcings can be used to reveal mechanisms of change in the hydrological cycle. We apply this energetic perspective to output from 11 fully coupled atmosphere-ocean general circulation models simulating experiment G1 of the Geoengineering Model Intercomparison Project (GeoMIP), which achieves top-of-atmosphere energy balance between an abrupt quadrupling of CO2 from preindustrial levels (abrupt4xCO2) and uniform solar irradiance reduction. We divide the climate system response into a rapid adjustment, in which climate response is due to adjustment of the atmosphere and land surface on short time scales, and a feedback response, in which the climate response is predominantly due to feedback related to global mean temperature changes. Global mean temperature change is small in G1, so the feedback response is also small. G1 shows a smaller magnitude of land sensible heat flux rapid adjustment than in abrupt4xCO2 and a larger magnitude of latent heat flux adjustment, indicating a greater reduction of evaporation and less land temperature increase than abrupt4xCO2. The sum of surface flux changes in G1 is small, indicating little ocean heat uptake. Using an energetic perspective to assess precipitation changes, abrupt4xCO2 shows decreased mean evaporative moisture flux and increased moisture convergence, particularly over land. However, most changes in precipitation in G1 are in mean evaporative flux, suggesting that changes in mean circulation are small.

Nested high-resolution modeling of the impact of urbanization on regional climate in three vast urban agglomerations in China

NASA Astrophysics Data System (ADS)

Wang, Jun; Feng, Jinming; Yan, Zhongwei; Hu, Yonghong; Jia, Gensuo

2012-11-01

In this paper, the Weather Research and Forecasting Model, coupled to the Urban Canopy Model, is employed to simulate the impact of urbanization on the regional climate over three vast city agglomerations in China. Based on high-resolution land use and land cover data, two scenarios are designed to represent the nonurban and current urban land use distributions. By comparing the results of two nested, high-resolution numerical experiments, the spatial and temporal changes on surface air temperature, heat stress index, surface energy budget, and precipitation due to urbanization are analyzed and quantified. Urban expansion increases the surface air temperature in urban areas by about 1°C, and this climatic forcing of urbanization on temperature is more pronounced in summer and nighttime than other seasons and daytime. The heat stress intensity, which reflects the combined effects of temperature and humidity, is enhanced by about 0.5 units in urban areas. The regional incoming solar radiation increases after urban expansion, which may be caused by the reduction of cloud fraction. The increased temperature and roughness of the urban surface lead to enhanced convergence. Meanwhile, the planetary boundary layer is deepened, and water vapor is mixed more evenly in the lower atmosphere. The deficit of water vapor leads to less convective available potential energy and more convective inhibition energy. Finally, these combined effects may reduce the rainfall amount over urban areas, mainly in summer, and change the regional precipitation pattern to a certain extent.

Nested High Resolution Modeling of the Impact of Urbanization on Regional Climate in Three Vast Urban Agglomerations in China

NASA Astrophysics Data System (ADS)

Wang, Jun; Feng, Jinming; Yan, Zhongwei; Hu, Yonghong; Jia, Gensuo

2013-04-01

In this paper, the Weather Research and Forecasting (WRF) model coupled to the Urban Canopy Model (UCM) is employed to simulate the impact of urbanization on the regional climate over three vast city agglomerations in China. Based on high resolution land use and land cover data, two scenarios are designed to represent the non-urban and current urban land use distributions. By comparing the results of two nested, high resolution numerical experiments, the spatial and temporal changes on surface air temperature, heat stress index, surface energy budget and precipitation due to urbanization are analyzed and quantified. Urban expansion increases the surface air temperature in urban areas by about 1? and this climatic forcing of urbanization on temperature is more pronounced in summer and nighttime than other seasons and daytime. The heat stress intensity, which reflects the combined effects of temperature and humidity, is enhanced by about 0.5 units in urban areas. The regional incoming solar radiation increases after urban expansion, which may be caused by the reduction of cloud fraction. The increased temperature and roughness of the urban surface lead to enhanced convergence. Meanwhile, the planetary boundary layer is deepened and water vapor is mixed more evenly in the lower atmosphere. The deficit of water vapor leads to less convective available potential energy and more convective inhibition energy. Finally, these combined effects may reduce the rainfall amount over urban area mainly in summer and change the regional precipitation pattern to a certain extent.

Theory of activated glassy relaxation, mobility gradients, surface diffusion, and vitrification in free standing thin films

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

Mirigian, Stephen, E-mail: kschweiz@illinois.edu, E-mail: smirigian@gmail.com; Schweizer, Kenneth S., E-mail: kschweiz@illinois.edu, E-mail: smirigian@gmail.com

2015-12-28

We have constructed a quantitative, force level, statistical mechanical theory for how confinement in free standing thin films introduces a spatial mobility gradient of the alpha relaxation time as a function of temperature, film thickness, and location in the film. The crucial idea is that relaxation speeds up due to the reduction of both near-surface barriers associated with the loss of neighbors in the local cage and the spatial cutoff and dynamical softening near the vapor interface of the spatially longer range collective elasticity cost for large amplitude hopping. These two effects are fundamentally coupled. Quantitative predictions are made formore » how an apparent glass temperature depends on the film thickness and experimental probe technique, the emergence of a two-step decay and mobile layers in time domain measurements, signatures of confinement in frequency-domain dielectric loss experiments, the dependence of film-averaged relaxation times and dynamic fragility on temperature and film thickness, surface diffusion, and the relationship between kinetic experiments and pseudo-thermodynamic measurements such as ellipsometry.« less

On the Regulation of the Pacific Warm Pool Temperature

NASA Technical Reports Server (NTRS)

Chou, Ming-Dah; Chou, Sue-Hsien; Chan, Pui-King; Lau, William K. M. (Technical Monitor)

2002-01-01

In the tropical western Pacific, regions of the highest sea surface temperature (SST) and the largest cloud cover are found to have the largest surface heating, primarily due to the weak evaporative cooling associated with weak winds. This situation is in variance with the suggestions that the temperature in the Pacific warm pool is regulated either by the reduced solar heating due to an enhanced cloudiness or by the enhanced evaporative cooling due to an elevated SST. It is clear that an enhanced surface heating in an enhanced convection region is not sustainable and must be interrupted by variations in large-scale atmospheric circulation. As the deep convective regions shift away from regions of high SST due primarily to seasonal variation and secondarily to interannual variation of the large-scale atmospheric and oceanic circulation, both trade wind and evaporative cooling in the high SST region increase, leading to a reduction in SST. We conclude that the evaporative cooling associated with the seasonal and interannual variations of trade winds in the primary factor that prevent the warm pool SST from increasing to a value much higher than what is observed.

Development and Testing of High Surface Area Iridium Anodes for Molten Oxide Electrolysis

NASA Technical Reports Server (NTRS)

Shchetkovskiy, Anatoliy; McKechnie, Timothy; Sadoway, Donald R.; Paramore, James; Melendez, Orlando; Curreri, Peter A.

2010-01-01

Processing of lunar regolith into oxygen for habitat and propulsion is needed to support future space missions. Direct electrochemical reduction of molten regolith is an attractive method of processing, because no additional chemical reagents are needed. The electrochemical processing of molten oxides requires high surface area, inert anodes. Such electrodes need to be structurally robust at elevated temperatures (1400-1600?C), be resistant to thermal shock, have good electrical conductivity, be resistant to attack by molten oxide (silicate), be electrochemically stable and support high current density. Iridium with its high melting point, good oxidation resistance, superior high temperature strength and ductility is the most promising candidate for anodes in high temperature electrochemical processes. Several innovative concepts for manufacturing such anodes by electrodeposition of iridium from molten salt electrolyte (EL-Form? process) were evaluated. Iridium electrodeposition to form of complex shape components and coating was investigated. Iridium coated graphite, porous iridium structure and solid iridium anodes were fabricated. Testing of electroformed iridium anodes shows no visible degradation. The result of development, manufacturing and testing of high surface, inert iridium anodes will be presented.

Development and Testing of High Surface Area Iridium Anodes for Molten Oxide Electrolysis

NASA Technical Reports Server (NTRS)

Shchetkovskiy, Anatoliy; McKechnie, Timothy; Sadoway, Donald R.; Paramore, James; Melendez, Orlando; Curreri, Peter A.

2010-01-01

Processing of lunar regolith into oxygen for habitat and propulsion is needed to support future space missions. Direct electrochemical reduction of molten regolith is an attractive method of processing, because no additional chemical reagents are needed. The electrochemical processing of molten oxides requires high surface area, inert anodes. Such electrodes need to be structurally robust at elevated temperatures (1400-1600 C), be resistant to thermal shock, have good electrical conductivity, be resistant to attack by molten oxide (silicate), be electrochemically stable and support high current density. Iridium with its high melting point, good oxidation resistance, superior high temperature strength and ductility is the most promising candidate for anodes in high temperature electrochemical processes. Several innovative concepts for manufacturing such anodes by electrodeposition of iridium from molten salt electrolyte (EL-Form process) were evaluated. Iridium electrodeposition to form of complex shape components and coating was investigated. Iridium coated graphite, porous iridium structure and solid iridium anodes were fabricated. Testing of electroformed iridium anodes shows no visible degradation. The result of development, manufacturing and testing of high surface, inert iridium anodes will be presented.

Neighborhood Landscape Spatial Patterns and Land Surface Temperature: An Empirical Study on Single-Family Residential Areas in Austin, Texas.

PubMed

Kim, Jun-Hyun; Gu, Donghwan; Sohn, Wonmin; Kil, Sung-Ho; Kim, Hwanyong; Lee, Dong-Kun

2016-09-02

Rapid urbanization has accelerated land use and land cover changes, and generated the urban heat island effect (UHI). Previous studies have reported positive effects of neighborhood landscapes on mitigating urban surface temperatures. However, the influence of neighborhood landscape spatial patterns on enhancing cooling effects has not yet been fully investigated. The main objective of this study was to assess the relationships between neighborhood landscape spatial patterns and land surface temperatures (LST) by using multi-regression models considering spatial autocorrelation issues. To measure the influence of neighborhood landscape spatial patterns on LST, this study analyzed neighborhood environments of 15,862 single-family houses in Austin, Texas, USA. Using aerial photos, geographic information systems (GIS), and remote sensing, FRAGSTATS was employed to calculate values of several landscape indices used to measure neighborhood landscape spatial patterns. After controlling for the spatial autocorrelation effect, results showed that larger and better-connected landscape spatial patterns were positively correlated with lower LST values in neighborhoods, while more fragmented and isolated neighborhood landscape patterns were negatively related to the reduction of LST.

Theory of activated glassy relaxation, mobility gradients, surface diffusion, and vitrification in free standing thin films.

PubMed

Mirigian, Stephen; Schweizer, Kenneth S

2015-12-28

We have constructed a quantitative, force level, statistical mechanical theory for how confinement in free standing thin films introduces a spatial mobility gradient of the alpha relaxation time as a function of temperature, film thickness, and location in the film. The crucial idea is that relaxation speeds up due to the reduction of both near-surface barriers associated with the loss of neighbors in the local cage and the spatial cutoff and dynamical softening near the vapor interface of the spatially longer range collective elasticity cost for large amplitude hopping. These two effects are fundamentally coupled. Quantitative predictions are made for how an apparent glass temperature depends on the film thickness and experimental probe technique, the emergence of a two-step decay and mobile layers in time domain measurements, signatures of confinement in frequency-domain dielectric loss experiments, the dependence of film-averaged relaxation times and dynamic fragility on temperature and film thickness, surface diffusion, and the relationship between kinetic experiments and pseudo-thermodynamic measurements such as ellipsometry.

Neighborhood Landscape Spatial Patterns and Land Surface Temperature: An Empirical Study on Single-Family Residential Areas in Austin, Texas

PubMed Central

Kim, Jun-Hyun; Gu, Donghwan; Sohn, Wonmin; Kil, Sung-Ho; Kim, Hwanyong; Lee, Dong-Kun

2016-01-01

Rapid urbanization has accelerated land use and land cover changes, and generated the urban heat island effect (UHI). Previous studies have reported positive effects of neighborhood landscapes on mitigating urban surface temperatures. However, the influence of neighborhood landscape spatial patterns on enhancing cooling effects has not yet been fully investigated. The main objective of this study was to assess the relationships between neighborhood landscape spatial patterns and land surface temperatures (LST) by using multi-regression models considering spatial autocorrelation issues. To measure the influence of neighborhood landscape spatial patterns on LST, this study analyzed neighborhood environments of 15,862 single-family houses in Austin, Texas, USA. Using aerial photos, geographic information systems (GIS), and remote sensing, FRAGSTATS was employed to calculate values of several landscape indices used to measure neighborhood landscape spatial patterns. After controlling for the spatial autocorrelation effect, results showed that larger and better-connected landscape spatial patterns were positively correlated with lower LST values in neighborhoods, while more fragmented and isolated neighborhood landscape patterns were negatively related to the reduction of LST. PMID:27598186

Mesoporous Germanium Anode Materials for Lithium-Ion Battery with Exceptional Cycling Stability in Wide Temperature Range.

PubMed

Choi, Sinho; Cho, Yoon-Gyo; Kim, Jieun; Choi, Nam-Soon; Song, Hyun-Kon; Wang, Guoxiu; Park, Soojin

2017-04-01

Porous structured materials have unique architectures and are promising for lithium-ion batteries to enhance performances. In particular, mesoporous materials have many advantages including a high surface area and large void spaces which can increase reactivity and accessibility of lithium ions. This study reports a synthesis of newly developed mesoporous germanium (Ge) particles prepared by a zincothermic reduction at a mild temperature for high performance lithium-ion batteries which can operate in a wide temperature range. The optimized Ge battery anodes with the mesoporous structure exhibit outstanding electrochemical properties in a wide temperature ranging from -20 to 60 °C. Ge anodes exhibit a stable cycling retention at various temperatures (capacity retention of 99% after 100 cycles at 25 °C, 84% after 300 cycles at 60 °C, and 50% after 50 cycles at -20 °C). Furthermore, full cells consisting of the mesoporous Ge anode and an LiFePO 4 cathode show an excellent cyclability at -20 and 25 °C. Mesoporous Ge materials synthesized by the zincothermic reduction can be potentially applied as high performance anode materials for practical lithium-ion batteries. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Extremely Warm Early Winter 2000 in Europe: What is the Forcing

NASA Technical Reports Server (NTRS)

Otterman, J.; Angell, J. K.; Atlas, R.; Ardizzone, J.; Demaree, G.; Jusem, J. C.; Koslowsky, D.; Terry, J.; Einaudi, Franco (Technical Monitor)

2001-01-01

High variability characterizes the winter climate of central Europe: interannual fluctuations in the surface-air temperature as large as 18 C over large areas are fairly common. The extraordinary early-winter 2000 in Europe appears to be a departure to an unprecedented extreme of the existing climate patterns. Such anomalous events affect agriculture, forestry, fuel consumption, etc., and thus deserve in-depth analysis. Our analysis indicates that the high anomalies of the surface-air temperature are predominantly due to the southwesterly flow from the eastern North Atlantic, with a weak contribution by southerly flow from the western Mediterranean. Backward trajectories based on the SSM/I and NCEP Reanalysis datasets traced from west-central Europe indicate that the warm air masses flowing into Europe originate in the southern North Atlantic, where the surface-air temperatures exceed by 15c or more the climatic norms in Europe for late-November or early-December. Because such large ocean-to-continent temperature differences characterize the winter conditions, we refer to this episode which started in late November as occurring in the early winter. In this season, with the sun low over the horizon in Europe, absorption of insolation by the surface has little significance. The effect of cloudiness, a corollary to the low-level maritime-air advection, is a warming by a reduction of heat loss (greenhouse effect). In contrast, in the summer, clouds, by reducing absorption of insolation, produce a cooling, effect at the surface.

Impacts of snow darkening by absorbing aerosols on South Asian monsoon

NASA Astrophysics Data System (ADS)

Kim, K. M.; Lau, W. K. M.; Kim, M. K.; Sang, J.; Yasunari, T. J.; Koster, R. D.

2016-12-01

Seasonal heating over the Tibetan Plateau is a main driver of the onset of the South Asian Monsoon. Aerosols can play an important role in pre- and early monsoon seasonal heating process over the Tibetan Plateau by increasing atmospheric heating in the northern India, and by heating of the surface of the Tibetan Plateau and Himalayan slopes, via reduction of albedo of the snow surface through surface deposition - the so call snow-darkening effect (SDE). To examine the impact of SDE on weather and climate during late spring and early summer, two sets of NASA/GEOS-5 model simulations with and without SDE are conducted. Results show that SDE-induced surface heating accelerates snow melts and increases surface temperature over 4K in the entire Tibetan Plateau regions during boreal summer. Warmer Tibetan Plateau further accelerates seasonal warming in the upper troposphere and increases the north-south temperature gradient between the Tibetan Plateau and the equatorial Indian Ocean. This reversal of the north-south temperature gradient is a primary cause of the onset of the South Asian monsoon. SDE-induced increase of the meridional temperature gradient drives meridional circulation and enhanced upper tropospheric easterlies and lower tropospheric westerlies, and intensifies monsoon circulation and rainfall. This pattern enhances the EHP-like circulation anomalies induced by atmospheric heating of absorbing aerosols over the northern India. SDE-induced change in the India subcontinent differs that in Eurasia. SDE-induced land-atmospheric interactions in two regions will be also compared.

Investigation of TiN thin film oxidation depending on the substrate temperature at vacuum break

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

Piallat, Fabien, E-mail: fabien.piallat@gmail.com; CEA, LETI, Campus Minatec, F-38054 Grenoble; LTM-CNRS, 17 rue des Martyrs, 38054 Grenoble

2016-09-15

Due to the reduction of the thickness of the layers used in the advanced technology nodes, there is a growing importance of the surface phenomena in the definition of the general properties of the materials. One of the least controlled and understood phenomenon is the oxidation of metals after deposition, at the vacuum break. In this study, the influence of the sample temperature at vacuum break on the oxidation level of TiN deposited by metalorganic chemical vapor deposition is investigated. TiN resistivity appears to be lower for samples which underwent vacuum break at high temperature. Using X-ray photoelectron spectrometry analysis,more » this change is correlated to the higher oxidation of the TiN layer. Moreover, angle resolved XPS analysis reveals that higher is the temperature at the vacuum break, higher is the surface oxidation of the sample. This surface oxidation is in turn limiting the diffusion of oxygen in the volume of the layer. Additionally, evolution of TiN layers resistivity was monitored in time and it shows that resistivity increases until a plateau is reached after about 10 days, with the lowest temperature at vacuum break resulting in the highest increase, i.e., the resistivity of the sample released to atmosphere at high temperature increased by a factor 1.7 whereas the resistivity of the sample cooled down under vacuum temperature increased by a factor 2.7.« less

Contributions of internal climate variability to mitigation of projected future regional sea level rise

NASA Astrophysics Data System (ADS)

Hu, A.; Bates, S. C.

2017-12-01

Observations indicate that the global mean surface temperature is rising, so does the global mean sea level. Sea level rise (SLR) can impose significant impacts on island and coastal communities, especially when SLR is compounded with storm surges. Here, via analyzing results from two sets of ensemble simulations from the Community Earth System Model version 1, we investigate how the potential SLR benefits through mitigating the future emission scenarios from business as usual to a mild-mitigation over the 21st Century would be affected by internal climate variability. Results show that there is almost no SLR benefit in the near term due to the large SLR variability due to the internal ocean dynamics. However, toward the end of the 21st century, the SLR benefit can be as much as a 26±1% reduction of the global mean SLR due to seawater thermal expansion. Regionally, the benefits from this mitigation for both near and long terms are heterogeneous. They vary from just a 11±5% SLR reduction in Melbourne, Australia to a 35±6% reduction in London. The processes contributing to these regional differences are the coupling of the wind-driven ocean circulation with the decadal scale sea surface temperature mode in the Pacific and Southern Oceans, and the changes of the thermohaline circulation and the mid-latitude air-sea coupling in the Atlantic.

Leaching under Oxygen Pressure with Carbonate Solution Reduction by Hydrogen; LIXIVIATION OXYDANTE DES PECHBLENDES ET PRECIPITATION DE L'URANIUM PAR L'HYDROGENE. APPLICATION AUX MINERAIS PAUVRES FRANCAIS

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

Balaceanu, J.C.; Coussemant, F.; Mouret, P.

1959-10-31

A study was made of the basic characteristics of the leaching with carbonate solution under oxygen pressure and of the catalytic hydrogen reduction of low-grade French ores. Pure U/sub 3/O/sub 8/ was used in the investigations on leaching. The effects of oxygen pressure, temperature, initial surface of the oxide, surfuce during the course of the reaction, and concentration of the carbonate solution were determined. It was shown that the heterogeneous reactions involve a constant surface and two steps. A pilot plant experiment was made on a number of low-grade French ores. With ores the leaching is not sensitive to oxygenmore » pressure. Dilute solutions of sodium uranyl carbonate are obtained from the leaching. The uranium can be precipitated as an oxide of a lower valent state by catalytic reduction with hydrogen. The study of this step was made on pure solutions of sodium uranyl carbonate in the presence of nickel and platinum catalysts. The reaction is strongly modified by the presence of even low concentrations of sodium bicarbonate. The reaction velocity increases with hydrogen pressure up to 5 atm, but then becomes independent of the pressure. The precipitation is accelerated by an increase in temperature. (J.S.R.)« less

Increased importance of methane reduction for a 1.5 degree target

NASA Astrophysics Data System (ADS)

Collins, William J.; Webber, Christopher P.; Cox, Peter M.; Huntingford, Chris; Lowe, Jason; Sitch, Stephen; Chadburn, Sarah E.; Comyn-Platt, Edward; Harper, Anna B.; Hayman, Garry; Powell, Tom

2018-04-01

To understand the importance of methane on the levels of carbon emission reductions required to achieve temperature goals, a processed-based approach is necessary rather than reliance on the transient climate response to emissions. We show that plausible levels of methane (CH4) mitigation can make a substantial difference to the feasibility of achieving the Paris climate targets through increasing the allowable carbon emissions. This benefit is enhanced by the indirect effects of CH4 on ozone (O3). Here the differing effects of CH4 and CO2 on land carbon storage, including the effects of surface O3, lead to an additional increase in the allowable carbon emissions with CH4 mitigation. We find a simple robust relationship between the change in the 2100 CH4 concentration and the extra allowable cumulative carbon emissions between now and 2100 (0.27 ± 0.05 GtC per ppb CH4). This relationship is independent of modelled climate sensitivity and precise temperature target, although later mitigation of CH4 reduces its value and thus methane reduction effectiveness. Up to 12% of this increase in allowable emissions is due to the effect of surface ozone. We conclude early mitigation of CH4 emissions would significantly increase the feasibility of stabilising global warming below 1.5 °C, alongside having co-benefits for human and ecosystem health.

A Thermochromic Superhydrophobic Surface

PubMed Central

Cataldi, Pietro; Bayer, Ilker S.; Cingolani, Roberto; Marras, Sergio; Chellali, Ryad; Athanassiou, Athanassia

2016-01-01

Highly enhanced solid-state thermochromism is observed in regioregular poly(3-hexylthiophene), P3HT, when deposited on a superhydrophobic polymer-SiO2 nanocomposite coating. The conformal P3HT coating on the nanocomposite surface does not alter or reduce superhydrophicity while maintaining its reversible enhanced thermochromism. The polymeric matrix of the superhydrophobic surface is comprised of a blend of poly(vinylidene fluoride-co-hexafluoropropylene) copolymer and an acrylic adhesive. Based on detailed X-ray diffraction measurements, this long-lasting, repeatable and hysteresis-free thermochromic effect is attributed to the enhancement of the Bragg peak associated with the d-spacing of interchain directional packing (100) which remains unaltered during several heating-cooling cycles. We propose that the superhydrophobic surface confines π–π interchain stacking in P3HT with uniform d-spacing into its nanostructured texture resulting in better packing and reduction in face-on orientation. The rapid response of the system to sudden temperature changes is also demonstrated by water droplet impact and bounce back on heated surfaces. This effect can be exploited for embedded thin film temperature sensors for metal coatings. PMID:27301422

Isothermal Oxidation of Magnetite to Hematite in Air and Cyclic Reduction/Oxidation Under Carbon Looping Combustion Conditions

NASA Astrophysics Data System (ADS)

Simmonds, Tegan; Hayes, Peter C.

2017-12-01

In the carbon looping combustion process the oxygen carrier is regenerated through oxidation in air; this process has been simulated by the oxidation of dense synthetic magnetite for selected temperatures and times. The oxidation of magnetite in air is shown to occur through the formation of dense hematite layers on the particle surface. This dense hematite forms through lath type shear transformations or solid-state diffusion through the product layer. Cyclic reduction in CO-CO2/oxidation in air of hematite single crystals has been carried out under controlled laboratory conditions at 1173 K (900 °C). It has been shown that the initial reduction step is critical to determining the product microstructure, which consists of gas pore dendrites in the magnetite matrix with blocky hematite formed on the pore surfaces. The progressive growth of the magnetite layer with the application of subsequent cycles appears to continue until no original hematite remains, after which physical disintegration of the particles takes place.

The role of iron-oxide aerosols and sunlight in the atmospheric reduction of Hg(II) species: A DFT+ U study

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

Tacey, Sean A.; Szilvasi, Tibor; Xu, Lang

Experimental and field measurements have shown that, in the presence of both iron-containing aerosols and sunlight, oxidized mercury species such as HgCl 2 and HgBr 2 undergo reduction to elemental mercury (Hg°), which remains in the atmosphere longer than oxidized mercury species due to its higher volatility. We performed density functional theory (DFT, PW91+U) calculations to elucidate the reduction mechanism for atmospheric HgCl 2 and HgBr 2 to Hg° on several iron-oxide aerosol surfaces relevant in the troposphere. On the OH-Fe-R-terminated α-Fe 2O 3(0001) surface, predicted to be most prevalent under ambient conditions, we show that: (1) the first Hg-Xmore » bond is broken via either thermal or photolytic activation depending on the ambient temperature; (2) photons with an energy of 2.69 eV (461 nm) are required to break the second Hg-X bond; and (3) a photo-induced surface-to-adsorbate charge-transfer process can promote Hg° desorption with an excitation energy of 2.59 eV (479 nm). All the calculated excitation energies are below the threshold value of 3.9 eV (320 nm) for photons in the troposphere, suggesting that sunlight can facilitate mercury reduction on iron-oxide aerosol surfaces. In contrast, the gas-phase reduction of HgCl 2 (HgBr 2) involves photoexcitation requiring an energy of 4.98 (4.45) eV (249 (279) nm); therefore, the energy range of sunlight is not suitable for gas-phase reduction. Our computational results provide the first evidence on the detailed mechanism for the combined role of aerosols and photons in the reduction of HgCl 2 and HgBr 2. In conclusion, our methodology can be adapted to study other photochemical heterogeneous processes in the atmosphere.« less

The role of iron-oxide aerosols and sunlight in the atmospheric reduction of Hg(II) species: A DFT+ U study

DOE PAGES

Tacey, Sean A.; Szilvasi, Tibor; Xu, Lang; ...

2018-04-22

Experimental and field measurements have shown that, in the presence of both iron-containing aerosols and sunlight, oxidized mercury species such as HgCl 2 and HgBr 2 undergo reduction to elemental mercury (Hg°), which remains in the atmosphere longer than oxidized mercury species due to its higher volatility. We performed density functional theory (DFT, PW91+U) calculations to elucidate the reduction mechanism for atmospheric HgCl 2 and HgBr 2 to Hg° on several iron-oxide aerosol surfaces relevant in the troposphere. On the OH-Fe-R-terminated α-Fe 2O 3(0001) surface, predicted to be most prevalent under ambient conditions, we show that: (1) the first Hg-Xmore » bond is broken via either thermal or photolytic activation depending on the ambient temperature; (2) photons with an energy of 2.69 eV (461 nm) are required to break the second Hg-X bond; and (3) a photo-induced surface-to-adsorbate charge-transfer process can promote Hg° desorption with an excitation energy of 2.59 eV (479 nm). All the calculated excitation energies are below the threshold value of 3.9 eV (320 nm) for photons in the troposphere, suggesting that sunlight can facilitate mercury reduction on iron-oxide aerosol surfaces. In contrast, the gas-phase reduction of HgCl 2 (HgBr 2) involves photoexcitation requiring an energy of 4.98 (4.45) eV (249 (279) nm); therefore, the energy range of sunlight is not suitable for gas-phase reduction. Our computational results provide the first evidence on the detailed mechanism for the combined role of aerosols and photons in the reduction of HgCl 2 and HgBr 2. In conclusion, our methodology can be adapted to study other photochemical heterogeneous processes in the atmosphere.« less

Supporting palladium metal on gold nanoparticles improves its catalysis for nitrite reduction

NASA Astrophysics Data System (ADS)

Qian, Huifeng; Zhao, Zhun; Velazquez, Juan C.; Pretzer, Lori A.; Heck, Kimberly N.; Wong, Michael S.

2013-12-01

Nitrate (NO3-) and nitrite (NO2-) anions are often found in groundwater and surface water as contaminants globally, especially in agricultural areas due to nitrate-rich fertilizer use. One popular approach to studying the removal of nitrite/nitrate from water has been their degradation to dinitrogen via Pd-based reduction catalysis. However, little progress has been made towards understanding how the catalyst structure can improve activity. Focusing on the catalytic reduction of nitrite in this study, we report that Au NPs supporting Pd metal ("Pd-on-Au NPs") show catalytic activity that varies with volcano-shape dependence on Pd surface coverage. At room temperature, in CO2-buffered water, and under H2 headspace, the NPs were maximally active at a Pd surface coverage of 80%, with a first-order rate constant (kcat = 576 L gPd-1 min-1) that was 15x and 7.5x higher than monometallic Pd NPs (~4 nm; 40 L gPd-1 min-1) and Pd/Al2O3 (1 wt% Pd; 76 L gPd-1 min-1), respectively. Accounting only for surface Pd atoms, these NPs (576 L gsurface-Pd-1 min-1) were 3.6x and 1.6x higher than monometallic Pd NPs (160 L gsurface-Pd-1 min-1) and Pd/Al2O3 (361 L gsurface-Pd-1 min-1). These NPs retained ~98% of catalytic activity at a chloride concentration of 1 mM, whereas Pd/Al2O3 lost ~50%. The Pd-on-Au nanostructure is a promising approach to improve the catalytic reduction process for nitrite and, with further development, also for nitrate anions.Nitrate (NO3-) and nitrite (NO2-) anions are often found in groundwater and surface water as contaminants globally, especially in agricultural areas due to nitrate-rich fertilizer use. One popular approach to studying the removal of nitrite/nitrate from water has been their degradation to dinitrogen via Pd-based reduction catalysis. However, little progress has been made towards understanding how the catalyst structure can improve activity. Focusing on the catalytic reduction of nitrite in this study, we report that Au NPs supporting Pd metal ("Pd-on-Au NPs") show catalytic activity that varies with volcano-shape dependence on Pd surface coverage. At room temperature, in CO2-buffered water, and under H2 headspace, the NPs were maximally active at a Pd surface coverage of 80%, with a first-order rate constant (kcat = 576 L gPd-1 min-1) that was 15x and 7.5x higher than monometallic Pd NPs (~4 nm; 40 L gPd-1 min-1) and Pd/Al2O3 (1 wt% Pd; 76 L gPd-1 min-1), respectively. Accounting only for surface Pd atoms, these NPs (576 L gsurface-Pd-1 min-1) were 3.6x and 1.6x higher than monometallic Pd NPs (160 L gsurface-Pd-1 min-1) and Pd/Al2O3 (361 L gsurface-Pd-1 min-1). These NPs retained ~98% of catalytic activity at a chloride concentration of 1 mM, whereas Pd/Al2O3 lost ~50%. The Pd-on-Au nanostructure is a promising approach to improve the catalytic reduction process for nitrite and, with further development, also for nitrate anions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr04540d

Changes in properties of starch isolated from whole rice grains with brown, black, and red pericarp after storage at different temperatures.

PubMed

Ziegler, Valmor; Ferreira, Cristiano Dietrich; Goebel, Jorge Tiago Schwanz; El Halal, Shanise Lisie Mello; Santetti, Gabriela Soster; Gutkoski, Luiz Carlos; Zavareze, Elessandra da Rosa; Elias, Moacir Cardoso

2017-02-01

The aim of this study was to evaluate the physicochemical, morphological, crystallinity, thermal, and pasting properties of starches isolated from rice grains with brown, black, and red pericarp. Starch was isolated from the rice grains at initial storage time, and after 6months of storage at different storage temperatures (16, 24, 32 and 40°C). Starch isolated from the grains stored for 6months at 40°C showed darker coloration, surface deformation of granules, and a significant reduction in the extraction yield, final viscosity, enthalpy, and crystallinity, independent of the grain pericarp coloration. The time and storage temperature not influence the swelling power and solubility of starch isolated from grains with brown pericarp, while for the grains with black and red pericarp there was reduction in swelling power and solubility of starches isolated of grains stored at 40°C. Grains stored at 16°C showed minimum changes in starch properties. Copyright © 2016 Elsevier Ltd. All rights reserved.

Interdigitated Pt-GaN Schottky interfaces for high-temperature soot-particulate sensing

NASA Astrophysics Data System (ADS)

So, Hongyun; Hou, Minmin; Jain, Sambhav R.; Lim, Jongwoo; Senesky, Debbie G.

2016-04-01

A microscale soot-particulate sensor using interdigitated platinum-gallium nitride (Pt-GaN) Schottky interfaces was developed to monitor fine soot particles within high-temperature environments (e.g., combustion exhausts and flues). Upon exposure to soot particles (30 to 50 nm in diameter) from an experimental chimney, an increased current (∼43.6%) is observed through the back-to-back Schottky contact to n-type GaN. This is attributed to a reduction in the effective Schottky barrier height (SBH) of ∼10 meV due to the electric field from the charged soot particles in the depletion region and exposed GaN surface. Furthermore, the microfabricated sensor was shown to recover sensitivity and regenerate the sensing response (∼11 meV SBH reduction) after exposure to temperature as high as 550 °C. This study supports the feasibility of a simple and reliable soot sensor to meet the increasing market demand for particulate matter sensing in harsh environments.

Metal-support interactions during the adsorption of CO on thin layers and islands of epitaxial palladium

NASA Technical Reports Server (NTRS)

Park, C.; Poppa, H.; Soria, F.

1984-01-01

Islands and continuous layers of palladium were grown in an ultrahigh vacuum on substrates of Mo(110)c(14 x 7)-O, designated MoO(x), and of clean Mo(110). It was found that as-deposited islands and layers exhibited bulk palladium adsorption properties for CO when deposited at room temperature and for palladium thicknesses in excess of about 3 monolayers. CO adsorption was drastically reduced, however, on annealing. For islands, annealing temperatures of as low as 400 K led to some reduction in CO adsorption whereas more severe reductions were found to occur at 600 K for islands and at 800 K for continuous multilayers. The deactivation depended on the palladium thickness, the substrate species and the extent of thermal treatments. Auger electron spectroscopy, temperature-programmed desorption and Delta-Phi measurements were combined to interpret the deactivation behavior in terms of substrate-support interactions involving the diffusion of substrate species towards the palladium surface.

Effect of high-temperature on the swellable organically-modified silica (SOMS) and its application to gas-phase hydrodechlorination of trichloroethylene

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

Sohn, Hyuntae; Celik, Gokhan; Gunduz, Seval

Pd catalysts supported on swellable organically-modified silica (SOMS) and high-temperature-treated swellable organically-modified silica (H-SOMS) were characterized and tested for gas-phase hydrodechlorination (HDC) of trichloroethylene (TCE) conditions. The high-temperature treatment on SOMS resulted in an increase in surface area and pore diameter as well as significant improvement of Pd dispersion on H-SOMS with smaller Pd particle sizes compared to the Pd/SOMS catalyst. Although the high-temperature treatment led to some alteration of the SOMS polysiloxane network, the hydrophobicity and organic vapor adsorption characteristics of SOMS were preserved. The reduction and oxidation characteristics of Pd on SOMS and HSOMS were investigated in situmore » using XANES technique. It was found that the Pd sites in the pores of SOMS was accessible to small molecules such as H 2, facilitating the reduction of PdO x, whereas oxidation of metallic Pd was limited even at higher temperatures when O 2 was used. This effect was only observed over Pd/SOMS catalyst. For Pd/H-SOMS, because the pores were more widely open than Pd/SOMS, both reduction and oxidation of Pd were observed. Finally, the catalytic activity of Pd/H-SOMS for gas-phase HDC of TCE was significantly better than Pd/SOMS. When water was added to the reactant stream (TCE + H 2O), both Pd/SOMS and Pd/H-SOMS maintained its catalytic performances due to hydrophobic property of the supports.« less

In situ X-ray diffraction study of reduction processes of Fe{sub 3}O{sub 4}- and Fe{sub 1-x}O-based ammonia-synthesis catalysts

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

Zheng Yifan, E-mail: zhengyifan@zjut.edu.c; Catalysis Institute, Zhejiang University of Technology, Hangzhou 310014; Liu Huazhang

2009-09-15

The temperature-programmed reduction process of two types of industrial ammonia-synthesis catalysts, A110 and ZA-5, which are, respectively, based on Fe{sub 3}O{sub 4} and Fe{sub 1-x}O precursors, were studied by in situ X-ray power diffraction (XRD). It has been found that the ZA-5 has lower reduction temperature and faster reduction rate, and its active phase alpha-Fe possesses a higher value of lattice microstrain than A110. The simulation based on Rietveld refinement has also shown that the shape of alpha-Fe grain of ZA-5 has a mixed shape of cube and sphere with more exposing (111) and (211) planes, while that of A110more » looks like a concave cube with more exposing (110) planes. Based on the results obtained, a growth model of alpha-Fe during the reduction of Fe{sub 3}O{sub 4}- and Fe{sub 1-x}O-based ammonia-synthesis catalysts is proposed, and the origins for the activity difference has been also discussed. - Graphical Abstract: A proposed growth model of active phase alpha-Fe during reduction. Due to H{sub 2} diffusing easily into the pores, reduction starts on outside and inside surface simultaneously to form 'microcrystalline film', and the particles shrink during reduction which results in breaking of the aggregated oxide particle.« less

Eastern Pacific cooling and Atlantic overturning circulation during the last deglaciation.

PubMed

Kienast, Markus; Kienast, Stephanie S; Calvert, Stephen E; Eglinton, Timothy I; Mollenhauer, Gesine; François, Roger; Mix, Alan C

2006-10-19

Surface ocean conditions in the equatorial Pacific Ocean could hold the clue to whether millennial-scale global climate change during glacial times was initiated through tropical ocean-atmosphere feedbacks or by changes in the Atlantic thermohaline circulation. North Atlantic cold periods during Heinrich events and millennial-scale cold events (stadials) have been linked with climatic changes in the tropical Atlantic Ocean and South America, as well as the Indian and East Asian monsoon systems, but not with tropical Pacific sea surface temperatures. Here we present a high-resolution record of sea surface temperatures in the eastern tropical Pacific derived from alkenone unsaturation measurements. Our data show a temperature drop of approximately 1 degrees C, synchronous (within dating uncertainties) with the shutdown of the Atlantic meridional overturning circulation during Heinrich event 1, and a smaller temperature drop of approximately 0.5 degrees C synchronous with the smaller reduction in the overturning circulation during the Younger Dryas event. Both cold events coincide with maxima in surface ocean productivity as inferred from 230Th-normalized carbon burial fluxes, suggesting increased upwelling at the time. From the concurrence of equatorial Pacific cooling with the two North Atlantic cold periods during deglaciation, we conclude that these millennial-scale climate changes were probably driven by a reorganization of the oceans' thermohaline circulation, although possibly amplified by tropical ocean-atmosphere interaction as suggested before.

Manganese Oxide Nanoarray-Based Monolithic Catalysts: Tunable Morphology and High Efficiency for CO Oxidation

DOE PAGES

Chen, Sheng-Yu; Song, Wenqiao; Lin, Hui-Jan; ...

2016-03-08

In this work, a generic one-pot hydrothermal synthesis route has been successfully designed and utilized to in situ grow uniform manganese oxide nanorods and nanowires onto the cordierite honeycomb monolithic substrates, forming a series of nanoarray-based monolithic catalysts. During the synthesis process, three types of potassium salt oxidants have been used with different reduction potentials, i.e., K 2Cr 2O 7, KClO 3, and K 2S 2O 8, denoted as HM-DCM, HM-PCR, and HM-PSF, respectively. The different reduction potentials of the manganese source (Mn 2+) and oxidants induced the formation of manganese oxide nanoarrays with different morphology, surface area, and reactivitymore » of carbon monoxide (CO) oxidation. K 2Cr 2O 7 and KClO 3 can induce sharp and long nanowires with slow growth rates due to their low reduction potentials. In comparison, the nanoarrays of HM-PSF presented shorter nanorods but displayed an efficient 90% CO oxidation conversion at 200 °C (T90) without noble-metal loading. Reducibility tests for the three monolithic catalysts by hydrogen temperature-programmed reduction revealed an activation energy order of HM-PSF > HM-DCM > HM-PCR for CO oxidation. The characterizations of oxygen temperature-programmed desorption and X-ray photoelectron spectroscopy indicated the abundant surface-adsorbed oxygen and lattice oxygen contributing to the superior reactivity of HM-PSF. Finally, the straightforward synthetic process showed a scalable, low-cost, and template-free method to fabricate manganese oxide nanoarray monolithic catalysts for exhaust treatment.« less

Surface-enhanced Raman scattering studies of the reduction of p-nitroaniline catalyzed by a nanonized Ag porous-glass hybrid composite.

PubMed

Huang, Genin Gary; Sou, Nga-Lai; Hung, Mei-Jou

2016-09-05

Nanonized noble metal composites have been known for their excellent catalytic properties. However, the mechanism and intermediates formed on the surfaces of nanocatalysts during catalysis are speculated with mostly insufficient evidence. In this study, to obtain further understanding of the roles of noble metal nanocatalysts in a catalytic reaction, surface-enhanced Raman scattering (SERS) was used to monitor the surfaces of silver (Ag) nanocatalysts. Furthermore, UV-Vis spectrometry was used to trace the concentration variations of reactants and products in bulk solutions, thereby correlating the variations of the Ag nanocatalyst surfaces with those in the bulk solutions. Nanonized Ag porous-glass hybrid composites were prepared by reducing naked Ag nanoparticles on porous-glass filter plates and were used as catalysts for nitroanilines reduction. The complete process was monitored using SERS and UV-Vis spectrometry simultaneously. The results indicated that the reactant and product molecules adsorbed on the Ag nanocatalysts can reach equilibrium, and the equilibrium is affected by the reaction conditions, including reducing agent concentration, pH of the reaction system, and temperature. In addition, the reduction of reactants in the bulk solutions is also related to the behavior of Ag nanocatalyst surfaces. Furthermore, Ag nanocatalysts can act as electron relays even if their surfaces are occupied by reactants and products. Analyzing the collected SERS and UV-Vis spectra can provide a new insight into Ag nanoparticle catalysis, and the role of Ag nanocatalysts can be further comprehended. Copyright © 2016 Elsevier B.V. All rights reserved.

Results of the Mariner 6 and 7 Mars occultation experiments

NASA Technical Reports Server (NTRS)

Hogan, J. S.; Stewart, R. W.; Rasool, S. I.; Russell, L. H.

1972-01-01

Final profiles of temperature, pressure, and electron density on Mars were obtained for the Mariner 6 and 7 entry and exit cases, and results are presented for both the lower atmosphere and ionosphere. The results of an analysis of the systematic and formal errors introduced at each stage of the data-reduction process are also included. At all four occulation points, the lapse rate of temperature was subdadiabatic up to altitudes in excess of 20 km. A pronounced temperature inversion was present above the surface at the Mariner 6 exit point. All four profiles exhibit a sharp, superadiabatic drop in temperature at high altitudes, with temperatures falling below the frost point of CO2. These results give a strong indication of frozen CO2 in the middle atmosphere of Mars.

Air cooling of disk of a solid integrally cast turbine rotor for an automotive gas turbine

NASA Technical Reports Server (NTRS)

Gladden, H. J.

1977-01-01

A thermal analysis is made of surface cooling of a solid, integrally cast turbine rotor disk for an automotive gas turbine engine. Air purge and impingement cooling schemes are considered and compared with an uncooled reference case. Substantial reductions in blade temperature are predicted with each of the cooling schemes studied. It is shown that air cooling can result in a substantial gain in the stress-rupture life of the blade. Alternatively, increases in the turbine inlet temperature are possible.

Dental health assessed after interproximal enamel reduction: caries risk in posterior teeth.

PubMed

Zachrisson, Björn U; Minster, Line; Ogaard, Bjørn; Birkhed, Dowen

2011-01-01

We investigated whether careful interdental enamel reduction (using extrafine diamond disks with air cooling, followed by contouring with triangular diamond burs and polishing) leads to increased caries risk in premolars and first molars. Our subjects were 43 consecutive patients from 19 to 71 years of age who had received mesiodistal enamel reduction of anterior and posterior teeth 4 to 6 years previously. Dental caries were assessed on standardized bite-wing radiographs according to a 5-grade scale and with a fine-tip explorer catch. The incidence of interproximal caries was compared between reproximated and unground contralateral surfaces in the same patient. Patients were asked about their toothbrushing habits, use of dental floss and toothpicks, and regular fluoride supplementation after the orthodontic appliances were removed. The overall clinical impression generally showed healthy dentitions with excellent occlusion. Only 7 (2.5%) new caries lesions (all grade 1) were found among 278 reproximated mesial or distal surfaces, in 3 patients. Among 84 contralateral unground reference tooth surfaces, 2 lesions (2.4%) were seen. On nonpaired premolars and molars that had not been ground, 23 surfaces had to be referred for caries treatment (grade 3 or occlusal caries). Eleven of these occurred in 1 patient. None of the 43 patients reported increased sensitivity to temperature variations. Interdental enamel reduction with this protocol did not result in increased caries risk in posterior teeth. We found no evidence that proper mesiodistal enamel reduction within recognized limits and in appropriate situations will cause harm to the teeth and supporting structures. Copyright © 2011 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

Mechanism of H adatoms improving the O2 reduction reaction on the Zn-modified anatase TiO2 (101) surface studied by first principles calculation.

PubMed

Liu, Liangliang; Li, Chongyang; Jiang, Man; Li, Xiaodong; Huang, Xiaowei; Wang, Zhu; Jia, Yu

2018-06-05

First principles calculations were performed to cast insight into the mechanism of the improvement of O2 reduction reaction (ORR) activity by Zn and H interstitials on the anatase TiO2 (101) surface. For the Zn-modified anatase TiO2 (101) surface, both surface and subsurface Zn interstitials could contribute to O2 adsorption and dissociation, but the dissociation barriers of O2 molecules are still too high, which limits the ORR activity. After a H adatom is introduced onto the Zn-modified anatase TiO2 (101) surface, the highest energy barriers are greatly reduced compared with those of the Zn-modified surface. Meanwhile, it is observed that the dissociation barriers decrease almost linearly with the increase of the charge difference of adsorption O2 between initial and transition state configurations. Specifically, subsurface Zn and surface H interstitials facilitate O2 dissociation and subsequent oxidation reactions, and further frequency analysis shows that these dissociation processes are frequent even at the room temperature of 300 K. In a word, this work provides a theoretical support to design a high ORR activity catalyst of the TiO2 nanocrystal comparable to precious Pt catalysts.

Single-Crystal Antimonene Films Prepared by Molecular Beam Epitaxy: Selective Growth and Contact Resistance Reduction of the 2D Material Heterostructure.

PubMed

Chen, Hsuan-An; Sun, Hsu; Wu, Chong-Rong; Wang, Yu-Xuan; Lee, Po-Hsiang; Pao, Chun-Wei; Lin, Shih-Yen

2018-05-02

Single-crystal antimonene flakes are observed on sapphire substrates after the postgrowth annealing procedure of amorphous antimony (Sb) droplets prepared by using molecular beam epitaxy at room temperature. The large wetting angles of the antimonene flakes to the sapphire substrate suggest that an alternate substrate should be adopted to obtain a continuous antimonene film. By using a bilayer MoS 2 /sapphire sample as the new substrate, a continuous and single-crystal antimonene film is obtained at a low growth temperature of 200 °C. The results are consistent with the theoretical prediction of the lower interface energy between antimonene and MoS 2 . The different interface energies of antimonene between sapphire and MoS 2 surfaces lead to the selective growth of antimonene only atop MoS 2 surfaces on a prepatterned MoS 2 /sapphire substrate. With similar sheet resistance to graphene, it is possible to use antimonene as the contact metal of 2D material devices. Compared with Au/Ti electrodes, a specific contact resistance reduction up to 3 orders of magnitude is observed by using the multilayer antimonene as the contact metal to MoS 2 . The lower contact resistance, the lower growth temperature, and the preferential growth to other 2D materials have made antimonene a promising candidate as the contact metal for 2D material devices.

The black rock series supported SCR catalyst for NO x removal.

PubMed

Xie, Bin; Luo, Hang; Tang, Qing; Du, Jun; Liu, Zuohua; Tao, Changyuan

2017-09-01

Black rock series (BRS) is of great potential for their plenty of valued oxides which include vanadium, iron, alumina and silica oxides, etc. BRS was used for directly preparing of selective catalytic reduction (SCR) catalyst by modifying its surface texture with SiO 2 -TiO 2 sols and regulating its catalytic active constituents with V 2 O 5 and MoO 3 . Consequently, 90% NO removal ratio was obtained within 300-400 °C over the BRS-based catalyst. The structure and properties of the BRS-based catalyst were characterized by the techniques of N 2 adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), H 2 -temperature programmed reduction (H 2 -TPR), and NH 3 -temperature programmed desorption (NH 3 -TPD). The results revealed that the BRS-based catalyst possesses favorable properties for NO x removal, including highly dispersed active components, abundant surface-adsorbed oxygen O α , well redox property, and numerous Brønsted acid sites. Particularly, the BRS-based catalyst exhibited considerable anti-poisoning performance compared with commercial TiO 2 -based catalyst. The former catalyst shows a NO conversion surpassing 80% from 300 to 400 °C for potassium poisoning, and a durability of SO 2 and H 2 O exceeding 85% at temperatures from 300 to 450 °C.

Terrestrial cooling in Northern Europe during the Eocene–Oligocene transition

PubMed Central

Hren, Michael T.; Sheldon, Nathan D.; Grimes, Stephen T.; Collinson, Margaret E.; Hooker, Jerry J.; Bugler, Melanie; Lohmann, Kyger C.

2013-01-01

Geochemical and modeling studies suggest that the transition from the “greenhouse” state of the Late Eocene to the “icehouse” conditions of the Oligocene 34–33.5 Ma was triggered by a reduction of atmospheric pCO2 that enabled the rapid buildup of a permanent ice sheet on the Antarctic continent. Marine records show that the drop in pCO2 during this interval was accompanied by a significant decline in high-latitude sea surface and deep ocean temperature and enhanced seasonality in middle and high latitudes. However, terrestrial records of this climate transition show heterogeneous responses to changing pCO2 and ocean temperatures, with some records showing a significant time lag in the temperature response to declining pCO2. We measured the Δ47 of aragonite shells of the freshwater gastropod Viviparus lentus from the Solent Group, Hampshire Basin, United Kingdom, to reconstruct terrestrial temperature and hydrologic change in the North Atlantic region during the Eocene–Oligocene transition. Our data show a decrease in growing-season surface water temperatures (∼10 °C) during the Eocene–Oligocene transition, corresponding to an average decrease in mean annual air temperature of ∼4–6 °C from the Late Eocene to Early Oligocene. The magnitude of cooling is similar to observed decreases in North Atlantic sea surface temperature over this interval and occurs during major glacial expansion. This suggests a close linkage between atmospheric carbon dioxide concentrations, Northern Hemisphere temperature, and expansion of the Antarctic ice sheets. PMID:23610424

In situ transmission electron microscopic observations of redox cycling of a Ni-ScSZ cermet fuel cell anode.

PubMed

Matsuda, Junko; Kawasaki, Tatsuya; Futamura, Shotaro; Kawabata, Tsutomu; Taniguchi, Shunsuke; Sasaki, Kazunari

2018-05-19

In situ transmission electron microscopy (TEM) observations of a Ni(O)-Sc2O3-stabilized ZrO2 (ScSZ; 10 mol% Sc2O3, 1 mol% CeO2, 89 mol% ZrO2) anode in a solid oxide fuel cell (SOFC) have been performed at high temperatures under a hydrogen/oxygen gas atmosphere using an environmental transmission electron microscope (ETEM); the specimens were removed from cross-sections of the real SOFC by focused ion beam milling and lifting. When heating the NiO-ScSZ anode under a hydrogen atmosphere of 3 mbar in ETEM, nano-pores were formed at the grain boundaries and on the surface of NiO particles at around 400°C due to the volume shrinkage accompanying the reduction of NiO to Ni. Moreover, densification of Ni occurred when increasing the temperature from 600 to 700°C. High-magnification TEM images obtained in the early stages of NiO reduction revealed that the (111) planes of Ni grew almost parallel to the (111) planes of NiO. In the case of heating Ni-ScSZ under an oxygen atmosphere of 3 mbar in ETEM, oxidation of Ni starting from the surface of the particles occurred above 300°C. All Ni particles became polycrystalline NiO after the temperature was increased to 800°C. Volume expansion/contraction by mass transfer to the outside/inside of the Ni particles in the anode during repeated oxidation/reduction seems to result in the agglomeration of Ni catalysts during long-term SOFC operation. We emphasize that our in situ TEM observations will be applied to observe electrochemical reactions in SOFCs under applied electric fields.

Dissecting the steps of CO2 reduction: 2. The interaction of CO and CO2 with Pd/γ-Al2O3: an in situ FTIR study

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

Szanyi, Janos; Kwak, Ja Hun

2014-08-07

Alumina supported Pd catalysts with metal loadings of 0.5, 2.5 and 10 wt% were investigated by in situ FTIR spectroscopy in order to understand the nature of adsorbed species formed during their exposure to CO2 and CO. Exposing the annealed samples to CO2 at 295 K resulted in the formation of alumina support-bound surface species only: linear adsorbed CO2, bidentate carbonates and bicarbonates. Room temperature exposure of all three samples to CO produced IR features characteristic of both ionic and metallic Pd, as well as bands we observed upon CO2 adsorption (alumina support-bound species). Low temperature (100 K) adsorption ofmore » CO on the three samples provided information about the state of Pd after oxidation and reduction. Oxidized samples contained exclusively ionic Pd, while mostly metallic Pd was present in the reduced samples. Subsequent annealing of the CO-saturated samples revealed the facile (low temperature) reduction of PdOx species by adsorbed CO. This process was evidenced by the variations in IR bands characteristic of ionic and metallic Pd-bound CO, as well as by the appearance of IR bands associated with CO2 adsorption as a function of annealing temperature. Samples containing oxidized Pd species (oxidized, annealed or reduced) always produced CO2 upon their exposure to CO, while CO2-related surface entities were observed on samples having only fully reduced (metallic) Pd. Acknowledgements: The catalyst preparation was supported by a Laboratory Directed Research and Development (LDRD) project. This work was supported by the US Department of Energy Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy. JHK also acknowledges the support of this work by the 2013 Research Fund of UNIST (Ulsan National Institute of Science and Technology, Ulsan, Korea).« less

Evaluation of Contrail Reduction Strategies Based on Environmental and Operational Costs

NASA Technical Reports Server (NTRS)

Chen, Neil Y.; Sridhar, Banavar; Ng, Hok K.; Li, Jinhua

2013-01-01

This paper evaluates a set of contrail reduction strategies based on environmental and operational costs. A linear climate model was first used to convert climate effects of carbon dioxide emissions and aircraft contrails to changes in Absolute Global Temperature Potential, a metric that measures the mean surface temperature change due to aircraft emissions and persistent contrail formations. The concept of social cost of carbon and the carbon auction price from recent California's cap-and-trade system were then used to relate the carbon dioxide emissions and contrail formations to an environmental cost index. The strategy for contrail reduction is based on minimizing contrail formations by altering the aircraft's cruising altitude. The strategy uses a user-defined factor to trade off between contrail reduction and additional fuel burn and carbon dioxide emissions. A higher value of tradeoff factor results in more contrail reduction but also more fuel burn and carbon emissions. The strategy is considered favorable when the net environmental cost benefit exceeds the operational cost. The results show how the net environmental benefit varies with different decision-making time-horizon and different carbon cost. The cost models provide a guidance to select the trade-off factor that will result in the most net environmental benefit.

CuO based catalysts on modified acidic silica supports tested in the de-NOx reduction.

PubMed

Bennici, Simona; Gervasini, Antonella; Lazzarin, Marta; Ragaini, Vittorio

2005-03-01

A series of dispersed CuO catalysts supported on modified silica supports with Al2O3 (SA), TiO2 (ST), and ZrO2 (SZ) were prepared optimising the adsorption method of copper deposition assisted by ultrasound treatment, already reported in a previous paper (S. Bennici, A. Gervasini, V. Ragaini, Ultrason. Sonochem. 10 (2003) 61). The obtained catalysts were characterized in their bulk (atomic absorption, X-ray diffraction, temperature programmed reduction) and surface (N2 adsorption, X-ray photoelectron spectroscopy, scanning electron microscopy) properties. The morphology of the finished materials was not deeply modified compared with that of the relevant supports. The employed complemented techniques evidenced a well dispersed CuO phase with a copper-support interaction on the most acidic supports (SA and SZ). The catalyst performances were studied in the reaction of selective catalytic reduction of NOx with ethene in oxidizing atmosphere in a flow apparatus under variable times (0.360-0.072 s) and temperatures (200-450 degrees C). The catalysts prepared on the most acidic supports (SA and SZ) were the most active and selective towards N2 formation. They showed a particular interesting activity in the reaction of NO2 reduction besides that of NO reduction.

Titan probe technology assessment and technology development plan study

NASA Technical Reports Server (NTRS)

Castro, A. J.

1980-01-01

The need for technology advances to accomplish the Titan probe mission was determined by defining mission conditions and requirements and evaluating the technology impact on the baseline probe configuration. Mission characteristics found to be technology drivers include (1) ten years dormant life in space vacuum; (2) unknown surface conditions, various sample materials, and a surface temperature; and (3) mission constraints of the Saturn Orbiter Dual Probe mission regarding weight allocation. The following areas were identified for further development: surface sample acquisition system; battery powered system; nonmetallic materials; magnetic bubble memory devices, and the landing system. Preentry science, reliability, and weight reduction and redundancy must also be considered.

Bi flux-dependent MBE growth of GaSbBi alloys

DOE PAGES

Rajpalke, M. K.; Linhart, W. M.; Yu, K. M.; ...

2015-03-05

The incorporation of Bi in GaSb 1-xBi x alloys grown by molecular beam epitaxy is investigated as a function of Bi flux at fixed growth temperature (275 °C) and growth rate (1 μm h⁻¹). The Bi content is found to vary proportionally with Bi flux with Bi contents, as measured by Rutherford backscattering, in the range 0 < x ≤ 4.5%. The GaSbBi samples grown at the lowest Bi fluxes have smooth surfaces free of metallic droplets. The higher Bi flux samples have surface Bi droplets. The room temperature band gap of the GaSbBi epitaxial layers determined from optical absorptionmore » decreases linearly with increasing Bi content with a reduction of ~32 meV/%Bi.« less

Impact of thermal radiation on MHD slip flow of a ferrofluid over a non-isothermal wedge

NASA Astrophysics Data System (ADS)

Rashad, A. M.

2017-01-01

This article is concerned with the problem of magnetohydrodynamic (MHD) mixed convection flow of Cobalt-kerosene ferrofluid adjacent a non-isothermal wedge under the influence of thermal radiation and partial slip. Such type of problems are posed by electric generators and biomedical enforcement. The governing equations are solved using the Thomas algorithm with finite-difference type and solutions for a wide range of magnet parameter are presented. It is found that local Nusselt number manifests a considerable diminishing for magnetic parameter and magnifies intensively in case of slip factor, thermal radiation and surface temperature parameters. Further, the skin friction coefficient visualizes a sufficient enhancement for the parameters thermal radiation, surface temperature and magnetic field, but a huge reduction is recorded by promoting the slip factor.

Change of Cu+ species and synergistic effect of copper and cerium during reduction-oxidation treatment for preferential CO oxidation

NASA Astrophysics Data System (ADS)

Zhang, Hao; Zhao, Xiaozhou; Wang, Shuang; Zeng, Shanghong; Su, Haiquan

2018-05-01

The CuO-CeO2@SiO2 catalyst with flower-sphere morphology was prepared by the impregnation method and then experienced the reduction-oxidation treatment at different temperatures. The multi-technique characterization shows that the reduction-oxidation treatment can remodel CuO, improve textural and surface properties and change Cu+ content and synergistic effect of copper and cerium. The importance of this work lies in the fact that the decrease of Cu+ content and synergistic effect of copper and cerium that occurs in the reduction-oxidation process results in the decrease of catalytic activity over the CuO-CeO2@SiO2 catalyst for preferential CO oxidation. The process of reaction in rich-hydrogen streams is equivalent to a reduction procedure which decreases Cu+ content and synergistic effect of copper and cerium.

Nanoscale Fe/Ag particles activated persulfate: optimization using response surface methodology.

PubMed

Silveira, Jefferson E; Barreto-Rodrigues, Marcio; Cardoso, Tais O; Pliego, Gema; Munoz, Macarena; Zazo, Juan A; Casas, José A

2017-05-01

This work studied the bimetallic nanoparticles Fe-Ag (nZVI-Ag) activated persulfate (PS) in aqueous solution using response surface methodology. The Box-Behnken design (BBD) was employed to optimize three parameters (nZVI-Ag dose, reaction temperature, and PS concentration) using 4-chlorophenol (4-CP) as the target pollutant. The synthesis of nZVI-Ag particles was carried out through a reduction of FeCl 2 with NaBH 4 followed by reductive deposition of Ag. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface area. The BBD was considered a satisfactory model to optimize the process. Confirmatory tests were carried out using predicted and experimental values under the optimal conditions (50 mg L -1 nZVI-Ag, 21 mM PS at 57 °C) and the complete removal of 4-CP achieved experimentally was successfully predicted by the model, whereas the mineralization degree predicted (90%) was slightly overestimated against the measured data (83%).

Direct measurements and analysis of skin friction and cooling downstream of multiple flush-slot injection into a turbulent Mach 6 boundary layer

NASA Technical Reports Server (NTRS)

Howard, F. G.; Strokowski, A. J.

1978-01-01

Experiments were conducted to determine the reduction in surface skin friction and the effectiveness of surface cooling downstream of one to four successive flush slots injecting cold air at an angle of 10 deg into a turbulent Mach 6 boundary layer. Data were obtained by direct measurement of surface shear and equilibrium temperatures, respectively. Increasing the number of slots decreased the skin friction, but the incremental improvement in skin-friction reduction decreased as the number of slots was increased. Cooling effectiveness was found to improve, for a given total mass injection, as the number of slots was increased from one to four. Comparison with previously reported step-slot data, however, indicated that step slots with tangential injection are more effective for both reducing skin friction and cooling than the present flush-slot configuration. Finite-difference predictions are in reasonable agreement with skin-friction data and with boundary-layer profile data.

The evaluation of the micro-tracks and micro-dimples on the tribological characteristics of thrust ball bearings.

PubMed

Amanov, Auezhan; Pyoun, Young-Shik; Cho, In-Shik; Lee, Chang-Soon; Park, In-Gyu

2011-01-01

One of the primary remedies for tribological problems is surface modification. The reduction of the friction between the ball and the raceway of bearings is a very important goal of the development of bearing technology. A low friction has a positive effect in terms of the extension of the fatigue life, avoidance of a temperature rise, and prevention of premature failure of bearings. Therefore, this research sought to investigate the effects of micro-tracks and micro-dimples on the tribological characteristics at the contact point between the ball and the raceway of thrust ball bearings (TBBs). The ultrasonic nanocrystal surface modification (UNSM) technology was applied using different intervals (feed rates) to the TBB raceway surface to create micro-tracks and micro-dimples. The friction coefficient after UNSM at 50 microm intervals showed marked sensitivity and a significant reduction of 30%. In this study, the results showed that more micro-dimples yield a lower friction coefficient.

Decontamination of Streptococci biofilms and Bacillus cereus spores on plastic surfaces with DC and pulsed corona discharges

NASA Astrophysics Data System (ADS)

Koval'ová, Zuzana; Tarabová, Kataŕna; Hensel, Karol; Machala, Zdenko

2013-02-01

Cold air plasmas of DC and pulsed corona discharges: positive streamers and negative Trichel pulses were used for bio-decontamination of Streptococci biofilm and Bacillus cereus spores on polypropylene plastic surfaces. The reduction of bacterial population (evaluated as log10) in the biofilm on plastic surfaces treated by DC corona reached 2.4 logs with 10 min treatment time and 3.3 logs with 2 min treatment time with water spraying. The enhancement of plasma biocidal effects on the biofilm by electro-spraying of water through a hollow needle high-voltage electrode was investigated. No significant polarity effect was found with DC corona. Pulsed corona was demonstrated slightly more bactericidal for spores, especially in the negative polarity where the bacterial population reduction reached up to 2.2 logs at 10 min exposure time. Contribution to the Topical Issue "13th International Symposium on High Pressure Low Temperature Plasma Chemistry (Hakone XIII)", Edited by Nicolas Gherardi, Henryca Danuta Stryczewska and Yvan Ségui.

Dynamics of ice nucleation on water repellent surfaces.

PubMed

Alizadeh, Azar; Yamada, Masako; Li, Ri; Shang, Wen; Otta, Shourya; Zhong, Sheng; Ge, Liehui; Dhinojwala, Ali; Conway, Ken R; Bahadur, Vaibhav; Vinciquerra, A Joseph; Stephens, Brian; Blohm, Margaret L

2012-02-14

Prevention of ice accretion and adhesion on surfaces is relevant to many applications, leading to improved operation safety, increased energy efficiency, and cost reduction. Development of passive nonicing coatings is highly desirable, since current antiicing strategies are energy and cost intensive. Superhydrophobicity has been proposed as a lead passive nonicing strategy, yet the exact mechanism of delayed icing on these surfaces is not clearly understood. In this work, we present an in-depth analysis of ice formation dynamics upon water droplet impact on surfaces with different wettabilities. We experimentally demonstrate that ice nucleation under low-humidity conditions can be delayed through control of surface chemistry and texture. Combining infrared (IR) thermometry and high-speed photography, we observe that the reduction of water-surface contact area on superhydrophobic surfaces plays a dual role in delaying nucleation: first by reducing heat transfer and second by reducing the probability of heterogeneous nucleation at the water-substrate interface. This work also includes an analysis (based on classical nucleation theory) to estimate various homogeneous and heterogeneous nucleation rates in icing situations. The key finding is that ice nucleation delay on superhydrophobic surfaces is more prominent at moderate degrees of supercooling, while closer to the homogeneous nucleation temperature, bulk and air-water interface nucleation effects become equally important. The study presented here offers a comprehensive perspective on the efficacy of textured surfaces for nonicing applications.

Dual gas-diffusion membrane- and mediatorless dihydrogen/air-breathing biofuel cell operating at room temperature

NASA Astrophysics Data System (ADS)

Xia, Hong-qi; So, Keisei; Kitazumi, Yuki; Shirai, Osamu; Nishikawa, Koji; Higuchi, Yoshiki; Kano, Kenji

2016-12-01

A membraneless direct electron transfer (DET)-type dihydrogen (H2)/air-breathing biofuel cell without any mediator was constructed wherein bilirubin oxidase from Myrothecium verrucaria (BOD) and membrane-bound [NiFe] hydrogenase from Desulfovibrio vulgaris Miyazaki F (MBH) were used as biocatalysts for the cathode and the anode, respectively, and Ketjen black-modified water proof carbon paper (KB/WPCC) was used as an electrode material. The KB/WPCC surface was modified with 2-aminobenzoic acid and p-phenylenediamine, respectively, to face the positively charged electron-accepting site of BOD and the negatively charged electron-donating site of MBH to the electrode surface. A gas-diffusion system was employed for the electrodes to realize high-speed substrate supply. As result, great improvement in the current density of O2 reduction with BOD and H2 reduction with MBH were realized at negatively and postively charged surfaces, respectively. Gas diffusion system also suppressed the oxidative inactivation of MBH at high electrode potentials. Finally, based on the improved bioanode and biocathode, a dual gas-diffusion membrane- and mediatorless H2/air-breathing biofuel cell was constructed. The maximum power density reached 6.1 mW cm-2 (at 0.72 V), and the open circuit voltage was 1.12 V using 1 atm of H2 gas as a fuel at room temperature and under passive and quiescent conditions.

RCCM2-BATS model over tropical South America: Applications to tropical deforestation

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

Hahmann, A.N.; Dickinson, R.E.

A multiyear simulation of the global climate uses a revised version of the National Center for Atmospheric Research (NCAR) Community Climate Model Version 2 (CCM2) coupled to the Biosphere-Atmosphere Transfer Scheme (BATS). It is compared with global and rain gauge precipitation climatologies to evaluate precipitation fields and European Centre for Medium-Range Forecasts analyses to evaluate the atmospheric circulation. The near-surface climate is compared with data from Amazonian field campaigns. The model simulation of the South American climate agrees closely with the observational record and is much improved from past simulations with previous versions of the NCAR Community Climate model overmore » this portion of the Tropics. The model is then used to study the local and regional response to tropical deforestation over Amazonia. In addition to the standard deforestation forcing, consisting mainly of increased albedo and decreased roughness length, two additional sensitivity experiments were conducted to assess the individual contributions from these forcings to the deforestation changes. The standard deforestation simulation shows slight increases in annually averaged surface temperature (+1{degrees}C) and reductions in annually averaged precipitation and evaporation (-363 and -149 mm yr{sup -1}, respectively). As expected, increases in surface albedo over Amazonia produce a reduction in net downward solar radiation at the surface and consequently a reduction in net surface radiation and surface latent heat flux. The roughness decrease, on the other hand, reduces the surface latent heat fluxes through decreases in the surface drag coefficient. The regional changes in moisture convergence and precipitation during the Amazonian wet season display a shift in the area of maximum precipitation rather than an overall decrease over the deforested area. 45 refs., 16 figs., 4 tabs.« less

Influence of air-sea coupling on Indian Ocean tropical cyclones

NASA Astrophysics Data System (ADS)

Lengaigne, Matthieu; Neetu, S.; Samson, Guillaume; Vialard, Jérôme; Krishnamohan, K. S.; Masson, Sébastien; Jullien, Swen; Suresh, I.; Menkes, Christophe E.

2018-02-01

This paper assesses the impact of air-sea coupling on Indian Ocean tropical cyclones (TCs) by comparing a 20-year long simulation of a ¼° regional coupled ocean-atmosphere model with a twin experiment, where the atmospheric component is forced by sea surface temperature from the coupled simulation. The coupled simulation reproduces the observed spatio-temporal TCs distribution and TC-induced surface cooling reasonably well, but overestimates the number of TCs. Air-sea coupling does not affect the cyclogenesis spatial distribution but reduces the number of TCs by 20% and yields a better-resolved bimodal seasonal distribution in the northern hemisphere. Coupling also affects intensity distribution, inducing a four-fold decrease in the proportion of intense TCs (Cat-2 and stronger). Air-sea coupling damps TCs growth through a reduction of inner-core upward enthalpy fluxes due to the TC-induced cooling. This reduction is particularly large for the most intense TCs of the northern Indian Ocean (up to 250 W m-2), due to higher ambient surface temperatures and larger TC-induced cooling there. The negative feedback of air-sea coupling on strongest TCs is mainly associated with slow-moving storms, which spend more time over the cold wake they induce. Sensitivity experiments using a different convective parameterization yield qualitatively similar results, with a larger ( 65%) reduction in the number of TCs. Because of their relatively coarse resolution (¼°), both set of experiments however fail to reproduce the most intense observed TCs. Further studies with finer resolution models in the Bay of Bengal will be needed to assess the expectedly large impact of air-sea coupling on those intense and deadly TCs.

A modeling study of the effects of aerosols on clouds and precipitation over East Asia

NASA Astrophysics Data System (ADS)

Liu, Xiaodong; Xie, Xiaoning; Yin, Zhi-Yong; Liu, Changhai; Gettelman, Andrew

2011-12-01

The National Center for Atmospheric Research Community Atmosphere Model (version 3.5) coupled with the Morrison-Gettelman two-moment cloud microphysics scheme is employed to simulate the aerosol effects on clouds and precipitation in two numerical experiments, one representing present-day conditions (year 2000) and the other the pre-industrial conditions (year 1750) over East Asia by considering both direct and indirect aerosol effects. To isolate the aerosol effects, we used the same set of boundary conditions and only altered the aerosol emissions in both experiments. The simulated results show that the cloud microphysical properties are markedly affected by the increase in aerosols, especially for the column cloud droplet number concentration (DNC), liquid water path (LWP), and the cloud droplet effective radius (DER). With increased aerosols, DNC and LWP have been increased by 137% and 28%, respectively, while DER is reduced by 20%. Precipitation rates in East Asia and East China are reduced by 5.8% and 13%, respectively, by both the aerosol's second indirect effect and the radiative forcing that enhanced atmospheric stability associated with the aerosol direct and first indirect effects. The significant reduction in summer precipitation in East Asia is also consistent with the weakening of the East Asian summer monsoon, resulting from the decreasing thermodynamic contrast between the Asian landmass and the surrounding oceans induced by the aerosol's radiative effects. The increase in aerosols reduces the surface net shortwave radiative flux over the East Asia landmass, which leads to the reduction of the land surface temperature. With minimal changes in the sea surface temperature, hence, the weakening of the East Asian summer monsoon further enhances the reduction of summer precipitation over East Asia.

Biogeochemical modeling of CO 2 and CH 4 production in anoxic Arctic soil microcosms

DOE PAGES

Tang, Guoping; Zheng, Jianqiu; Xu, Xiaofeng; ...

2016-09-12

Soil organic carbon turnover to CO 2 and CH 4 is sensitive to soil redox potential and pH conditions. But, land surface models do not consider redox and pH in the aqueous phase explicitly, thereby limiting their use for making predictions in anoxic environments. Using recent data from incubations of Arctic soils, we extend the Community Land Model with coupled carbon and nitrogen (CLM-CN) decomposition cascade to include simple organic substrate turnover, fermentation, Fe(III) reduction, and methanogenesis reactions, and assess the efficacy of various temperature and pH response functions. Incorporating the Windermere Humic Aqueous Model (WHAM) enables us to approximatelymore » describe the observed pH evolution without additional parameterization. Though Fe(III) reduction is normally assumed to compete with methanogenesis, the model predicts that Fe(III) reduction raises the pH from acidic to neutral, thereby reducing environmental stress to methanogens and accelerating methane production when substrates are not limiting. Furthermore, the equilibrium speciation predicts a substantial increase in CO 2 solubility as pH increases, and taking into account CO 2 adsorption to surface sites of metal oxides further decreases the predicted headspace gas-phase fraction at low pH. Without adequate representation of these speciation reactions, as well as the impacts of pH, temperature, and pressure, the CO 2 production from closed microcosms can be substantially underestimated based on headspace CO 2 measurements only. Our results demonstrate the efficacy of geochemical models for simulating soil biogeochemistry and provide predictive understanding and mechanistic representations that can be incorporated into land surface models to improve climate predictions.« less

The effect of future reduction in aerosol emissions on climate extremes in China

NASA Astrophysics Data System (ADS)

Wang, Zhili; Lin, Lei; Yang, Meilin; Xu, Yangyang

2016-11-01

This study investigates the effect of reduced aerosol emissions on projected temperature and precipitation extremes in China during 2031-2050 and 2081-2100 relative to present-day conditions using the daily data output from the Community Earth System Model ensemble simulations under the Representative Concentration Pathway (RCP) 8.5 with an applied aerosol reduction and RCP8.5 with fixed 2005 aerosol emissions (RCP8.5_FixA) scenarios. The reduced aerosol emissions of RCP8.5 magnify the warming effect due to greenhouse gases (GHG) and lead to significant increases in temperature extremes, such as the maximum of daily maximum temperature (TXx), minimum of daily minimum temperature (TNn), and tropical nights (TR), and precipitation extremes, such as the maximum 5-day precipitation amount, number of heavy precipitation days, and annual total precipitation from days ˃95th percentile, in China. The projected TXx, TNn, and TR averaged over China increase by 1.2 ± 0.2 °C (4.4 ± 0.2 °C), 1.3 ± 0.2 °C (4.8 ± 0.2 °C), and 8.2 ± 1.2 (30.9 ± 1.4) days, respectively, during 2031-2050 (2081-2100) under the RCP8.5_FixA scenario, whereas the corresponding values are 1.6 ± 0.1 °C (5.3 ± 0.2 °C), 1.8 ± 0.2 °C (5.6 ± 0.2 °C), and 11.9 ± 0.9 (38.4 ± 1.0) days under the RCP8.5 scenario. Nationally averaged increases in all of those extreme precipitation indices above due to the aerosol reduction account for more than 30 % of the extreme precipitation increases under the RCP8.5 scenario. Moreover, the aerosol reduction leads to decreases in frost days and consecutive dry days averaged over China. There are great regional differences in changes of climate extremes caused by the aerosol reduction. When normalized by global mean surface temperature changes, aerosols have larger effects on temperature and precipitation extremes over China than GHG.

The influence of Ag content and annealing time on structural and optical properties of SGS antimony-germanate glass doped with Er3+ ions

NASA Astrophysics Data System (ADS)

Zmojda, J.; Kochanowicz, M.; Miluski, P.; Baranowska, A.; Basa, A.; Jadach, R.; Sitarz, M.; Dorosz, D.

2018-05-01

A series of erbium doped SGS antimony-germanate glass embedding silver (Ag0) nanoparticles have been synthesized by a one-step melt-quench thermochemical reduction technique. The effect of NPs concentration and annealing time on the structural and photoluminescent (PL) properties were investigated. The Raman spectra as a function of temperature measured in-situ allow to determine the structural changes in vicinity of Ag+ ions and confirmed thermochemical reduction of Ag+ ions by Sb3+ ions. The surface plasmon resonance absorption band was evidenced near 450 nm. The impact of local field effect generated by Ag0 nanoparticles (NPs) and energy transfer from surface of silver NPs to trivalent erbium ions on near-infrared and up-conversion luminescence was described in terms of enhancement and quench phenomena.

Dynamic processes occurring at the Cr IIIaq-manganite (γ-MnOOH) interface: simultaneous adsorption, microprecipitation, oxidation/reduction, and dissolution

NASA Astrophysics Data System (ADS)

Weaver, Robert M.; Hochella, Michael F.; Ilton, Eugene S.

2002-12-01

The complex interaction between Cr IIIaq and manganite (γ-MnOOH) was systematically studied at room temperature over a pH range of 3 to 6, and within a concentration range of 10 -4 to 10 -2 M CrOH 2+aq. Solution compositional changes during batch reactions were characterized by inductively coupled plasma spectroscopy and ultraviolet-visible spectrophotometry. The manganites were characterized before and after reaction with X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), high-resolution field-emission SEM, and energy-dispersive spectroscopy analysis. Fluid-cell atomic force microscopy was used to follow these metal-mineral interactions in situ. The reactions are characterized by (1) sorption of Cr III and the surface-catalyzed microprecipitation of Cr III-hydroxy hydrate on manganite surfaces, (2) the acidic dissolution of the manganite, and (3) the simultaneous reductive dissolution of manganite coupled with the oxidation of Cr IIIaq to highly toxic Cr VIaq. Cr III-hydroxy hydrate was shown to precipitate on the manganite surface while still undersaturated in bulk solution. The rate of manganite dissolution increased with decreasing pH due both to acid-promoted and Mn-reduction-promoted dissolution. Cr oxidation also increased in the lower pH range, this as a result of its direct redox coupling with Mn reduction. Neither Mn II nor Cr VI were ever detected on manganite surfaces, even at the maximum rate of their generation. At the highest pHs of this study, Cr IIIaq was effectively removed from solution to form Cr III-hydroxy hydrate on manganite surfaces and in the bulk solution, and manganite dissolution and Cr VIaq generation were minimized. All interface reactions described above were heterogeneous across the manganite surfaces. This heterogeneity is a direct result of the heterogeneous semiconducting nature of natural manganite crystals and is also an expression of the proximity effect, whereby redox processes on semiconducting surfaces are not limited to next nearest neighbor sites.

Watershed management to support coral reef recovery and resiliency

Treesearch

Lisa Vandiver; Tom Moore; Sean Griffin; Michael Nemeth; Rob Ferguson

2016-01-01

Coral reef habitats in the Caribbean region have experienced significant reductions in abundance over the past several decades. These declines are due to both global stressors, such as increases in sea surface temperatures and ocean acidification, and localized stressors, such as land-based sources of pollution (LBSPs). Climate change has led to increased occurrence ...

Ion temperature gradient driven transport in tokamaks with square shaping

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

Joiner, N.; Dorland, W.

2010-06-15

Advanced tokamak schemes which may offer significant improvement to plasma confinement on the usual large aspect ratio Dee-shaped flux surface configuration are of great interest to the fusion community. One possibility is to introduce square shaping to the flux surfaces. The gyrokinetic code GS2[Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1996)] is used to study linear stability and the resulting nonlinear thermal transport of the ion temperature gradient driven (ITG) mode in tokamak equilibria with square shaping. The maximum linear growth rate of ITG modes is increased by negative squareness (diamond shaping) and reduced by positive values (square shaping).more » The dependence of thermal transport produced by saturated ITG instabilities on squareness is not as clear. The overall trend follows that of the linear instability, heat and particle fluxes increase with negative squareness and decrease with positive squareness. This is contradictory to recent experimental results [Holcomb et al., Phys. Plasmas 16, 056116 (2009)] which show a reduction in transport with negative squareness. This may be reconciled as a reduction in transport (consistent with the experiment) is observed at small negative values of the squareness parameter.« less

Method of producing silicon. [gas phase reactor multiple injector liquid feed system

NASA Technical Reports Server (NTRS)

Wolf, C. B.; Meyer, T. N. (Inventor)

1980-01-01

A liquid reactant injector assembly suited for the injection of liquid reactant into a high temperature metal reductant vapor and carrier gas stream for the production of metal is presented. The assembly is especially adapted for the continuous production of high purity silicon by the reduction of SiCl4 with sodium. The assembly includes a refractory-lined, hollow metal shell having ten equally-spaced, concentric, radially directed ports provided in the shell and wall. A hydraulic, atomizing type spray nozzle is mounted in each of the ports recessed from the inner wall surface.

Fundamental Studies on High Temperature Deformation Recrystallization, and Grain Growth of Two-Phase Materials.

DTIC Science & Technology

1988-01-01

gm (17 ml) Benzalkonium . Chloride (50%) 35 ml Ethanol The Ti-V alloys were etched with the following etchant for 6 to 10 seconds. 4 mlHN03 conc. 2 ml...60 % reduction in area was given for all the alloys. This work was found to be sufficient to recrystallize all of the alloys within 6 hours at 9730 K...condition of net reduction in surfaces 17 °.4- *. *¢ ’ N N-, . ’ . . ’,, . , . . .,...’,’." ,,_...,. ,...’.’.’, ...-.......-.. : ’If LS becomes b2 .(db]/d1

Microstructure and dry-sliding wear properties of DC plasma nitrided 17-4 PH stainless steel

NASA Astrophysics Data System (ADS)

Li, Gui-jiang; Wang, Jun; Li, Cong; Peng, Qian; Gao, Jian; Shen, Bao-luo

2008-05-01

An attempt that the precipitation hardening steel 17-4PH was conducted by DC plasma nitriding (DCPN) is made to develop a kind of candidate material for nuclear reactor. Nitriding process performed at temperature ⩽ 400 °C takes effect on creation of the layers composed of S-phase (expanded austenite) and αN‧ (expanded martensite). Up to the temperature of 420 °C, the S-phase peaks disappear due to the transformation occurrence (S-phase → αN‧ + CrN). For the samples nitrided at temperature ⩾ 450 °C, no evidence of αN‧ is found owing to a precipitation (αN‧ → α +CrN) taking place. For the 480 °C/4 h treated sample, it is the surface microhardness that plays the lead role in the wear rate reduction but the surface roughness; while for the 400 °C/4 h treated sample, it is both of the surface roughness and the S-phase formation. Dry sliding wear of the untreated 17-4PH is mainly characterized by strong adhesion, abrasion and oxidation mechanism. Samples nitrided at 400 °C which is dominated by slight abrasion and plastic deformation exhibit the best dry sliding wear resistance compared to the samples nitrided at other temperatures.

Spatially distinct effects of preceding precipitation on heat stress over eastern China

NASA Astrophysics Data System (ADS)

Liu, Xingcai; Tang, Qiuhong; Zhang, Xuejun; Groisman, Pavel; Sun, Siao; Lu, Hui; Li, Zhe

2017-11-01

In many terrestrial regions, higher than usual surface temperatures are associated with (or are even induced by) surface moisture deficits. When in the warm season temperatures become anomalously high, their extreme values affect human beings causing heat stress. Besides increased temperature, rising humidity may also have substantial implications for bodily thermal comfort. However, the effects of surface moisture on heat stress, when considering both temperature and humidity, are less known. In this study, the relationship between the number of hot days in July as indicated by the wet-bulb globe temperature and the preceding three months of precipitation was assessed over eastern China. It is found that the probability of occurrence of above the average number of hot days exceeds 0.7 after a preceding precipitation deficit in northeastern China, but is less than 0.3 in southeastern China. Generally, over eastern China, the precipitation in the preceding months is negatively correlated with temperature and positively correlated with specific humidity in July. The combined effects generate a spatially distinct pattern: precipitation deficits in preceding months enhance heat stress in northeastern China while in southern China these deficits are associated with reduction of heat stress. In the south, abundant preceding precipitation tends to increase atmospheric humidity that is instrumental for the increase of heat stress. These results contribute predictive information about the probability of mid-summer heat stress in eastern China a few weeks ahead of its occurrence.

Understanding Automotive Exhaust Catalysts Using a Surface Science Approach: Model NOx Storage Materials

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

Szanyi, Janos; Yi, Cheol-Woo W.; Mudiyanselage, Kumudu K.

2013-11-01

The structure-reactivity relationships of model BaO-based NOx storage/reduction catalysts were investigated under well controlled experimental conditions using surface science analysis techniques. The reactivity of BaO toward NO2, CO2, and H2O was studied as a function of BaO layer thickness [0\\hBaO\\30 monolayer (ML)], sample temperature, reactant partial pressure, and the nature of the substrate the NOx storage material was deposited onto. Most of the efforts focused on understanding the mechanism of NO2 storage either on pure BaO, or on BaO exposed to CO2 or H2O prior to NO2 exposure. The interaction of NO2 with a pure BaO film results in themore » initial formation of nitrite/nitrate ion pairs by a cooperative adsorption mechanism predicted by prior theoretical calculations. The nitrites are then further oxidized to nitrates to produce a fully nitrated surface. The mechanism of NO2 uptake on thin BaO films (\\4 ML), BaO clusters (\\1 ML) and mixed BaO/Al2O3 layers are fundamentally different: in these systems initially nitrites are formed only, and then converted to nitrates at longer NO2 exposure times. These results clarify the contradicting mechanisms presented in prior studies in the literature. After the formation of a nitrate layer the further conversion of the underlying BaO is slow, and strongly depends on both the sample temperature and the NO2 partial pressure. At 300 K sample temperature amorphous Ba(NO3)2 forms that then can be converted to crystalline nitrates at elevated temperatures. The reaction between BaO and H2O is facile, a series of Ba(OH)2 phases form under the temperature and H2O partial pressure regimes studied. Both amorphous and crystalline Ba(OH)2 phases react with NO2, and initially form nitrites only that can be converted to nitrates. The NO2 adsorption capacities of BaO and Ba(OH)2 are identical, i.e., both of these phases can completely be converted to Ba(NO3)2. In contrast, the interaction of CO2 with pure BaO results in the formation of a BaCO3 layer that prevents to complete carbonation of the entire BaO film under the experimental conditions applied in these studies. However, these ‘‘carbonated’’ BaO layers readily react with NO2, and at elevated sample temperature even the carbonate layer is converted to nitrates. The importance of the metal oxide/metal interface in the chemistry on NOx storage-reduction catalysts was studied on BaO(\\1 ML)/Pt(111) reverse model catalysts. In comparison to the clean Pt(111), new oxygen adsorption phases were identified on the BaO/Pt(111) surface that can be associated with oxygen atoms strongly adsorbed on Pt atoms at the peripheries of BaO particles. A simple kinetic model developed helped explain the observed thermal desorption results. The role of the oxide/metal interface in the reduction of Ba(NO3)2 was also substantiated in experiments where Ba(NO3)2/O/Pt(111) samples were exposed to CO at elevated sample temperature. The catalytic decomposition of the nitrate phase occurred as soon as metal sites opened up by the removal of interfacial oxygen via CO oxidation from the O/Pt(111) surface. The temperature for catalytic nitrate reduction was found to be significantly lower than the onset temperature of thermal nitrate decomposition. We gratefully acknowledge the US Department of Energy (DOE), Office of Science, Division of Chemical Sciences, Geosciences, and Biosciences for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national user facility sponsored by the DOE Office of Biological and Environmental Research and located at the Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle under contract number DE-AC05-76RL01830.« less

Detailed modeling of electron emission for transpiration cooling of hypersonic vehicles

NASA Astrophysics Data System (ADS)

Hanquist, Kyle M.; Hara, Kentaro; Boyd, Iain D.

2017-02-01

Electron transpiration cooling (ETC) is a recently proposed approach to manage the high heating loads experienced at the sharp leading edges of hypersonic vehicles. Computational fluid dynamics (CFD) can be used to investigate the feasibility of ETC in a hypersonic environment. A modeling approach is presented for ETC, which includes developing the boundary conditions for electron emission from the surface, accounting for the space-charge limit effects of the near-wall plasma sheath. The space-charge limit models are assessed using 1D direct-kinetic plasma sheath simulations, taking into account the thermionically emitted electrons from the surface. The simulations agree well with the space-charge limit theory proposed by Takamura et al. for emitted electrons with a finite temperature, especially at low values of wall bias, which validates the use of the theoretical model for the hypersonic CFD code. The CFD code with the analytical sheath models is then used for a test case typical of a leading edge radius in a hypersonic flight environment. The CFD results show that ETC can lower the surface temperature of sharp leading edges of hypersonic vehicles, especially at higher velocities, due to the increase in ionized species enabling higher electron heat extraction from the surface. The CFD results also show that space-charge limit effects can limit the ETC reduction of surface temperatures, in comparison to thermionic emission assuming no effects of the electric field within the sheath.

Remarkable support effect on the reactivity of Pt/In2O3/MOx catalysts for methanol steam reforming

NASA Astrophysics Data System (ADS)

Liu, Xin; Men, Yong; Wang, Jinguo; He, Rong; Wang, Yuanqiang

2017-10-01

Effects of supports over Pt/In2O3/MOx catalysts with extremely low loading of Pt (1 wt%) and In2O3 loadings (3 wt%) are investigated for the hydrogen production of methanol steam reforming (MSR) in the temperature range of 250-400 °C. Under practical conditions without the pre-reduction, the 1Pt/3In2O3/CeO2 catalyst shows the highly efficient catalytic performance, achieving almost complete methanol conversion (98.7%) and very low CO selectivity of 2.6% at 325 °C. The supported Pt/In2O3 catalysts are characterized by means of Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), high-resolution transmission microscopy (HRTEM), temperature programmed reduction with hydrogen (H2-TPR), CO pulse chemisorption, temperature programmed desorption of methanol and water (CH3OH-TPD and H2O-TPD). These demonstrate that the nature of catalyst support of Pt/In2O3/MOx plays crucial roles in the Pt dispersion associated by the strong interaction among Pt, In2O3 and supporting materials and the surface redox properties at low temperature, and thus affects their capability to activate the reactants and determines the catalytic activity of methanol steam reforming. The superior 1Pt/3In2O3/CeO2 catalyst, exhibiting a remarkable reactivity and stability for 32 h on stream, demonstrates its potential for efficient hydrogen production of methanol steam reforming in mobile and de-centralized H2-fueled PEMFC systems.

Solid oxide fuel cell cathode infiltrate particle size control and oxygen surface exchange resistance determination

NASA Astrophysics Data System (ADS)

Burye, Theodore E.

Over the past decade, nano-sized Mixed Ionic Electronic Conducting (MIEC) -- micro-sized Ionic Conducting (IC) composite cathodes produced by the infiltration method have received much attention in the literature due to their low polarization resistance (RP) at intermediate (500-700°C) operating temperatures. Small infiltrated MIEC oxide nano-particle size and low intrinsic MIEC oxygen surface exchange resistance (Rs) have been two critical factors allowing these Nano-Micro-Composite Cathodes (NMCCs) to achieve high performance and/or low temperature operation. Unfortunately, previous studies have not found a reliable method to control or reduce infiltrated nano-particle size. In addition, controversy exists on the best MIEC infiltrate composition because: 1) Rs measurements on infiltrated MIEC particles are presently unavailable in the literature, and 2) bulk and thin film Rs measurements on nominally identical MIEC compositions often vary by up to 3 orders of magnitude. Here, two processing techniques, precursor nitrate solution desiccation and ceria oxide pre-infiltration, were developed to systematically produce a reduction in the average La0.6Sr0.4Co0.8Fe 0.2O3-delta (LSCF) infiltrated nano-particle size from 50 nm to 22 nm. This particle size reduction reduced the SOFC operating temperature, (defined as the temperature where RP=0.1 Ocm 2) from 650°C to 540°C. In addition, Rs values for infiltrated MIEC particles were determined for the first time through finite element modeling calculations on 3D Focused Ion Beam-Scanning Electron Microscope (FIB-SEM) reconstructions of electrochemically characterized infiltrated electrodes.

Mitigating Climate Change with Ocean Pipes: Influencing Land Temperature and Hydrology and Termination Overshoot Risk

NASA Astrophysics Data System (ADS)

Kwiatkowski, L.; Caldeira, K.; Ricke, K.

2014-12-01

With increasing risk of dangerous climate change geoengineering solutions to Earth's climate problems have attracted much attention. One proposed geoengineering approach considers the use of ocean pipes as a means to increase ocean carbon uptake and the storage of thermal energy in the deep ocean. We use a latest generation Earth System Model (ESM) to perform simulations of idealised extreme implementations of ocean pipes. In our simulations, downward transport of thermal energy by ocean pipes strongly cools the near surface atmosphere - by up to 11°C on a global mean. The ocean pipes cause net thermal energy to be transported from the terrestrial environment to the deep ocean while increasing the global net transport of water to land. By cooling the ocean surface more than the land, ocean pipes tend to promote a monsoonal-type circulation, resulting in increased water vapour transport to land. Throughout their implementation, ocean pipes prevent energy from escaping to space, increasing the amount of energy stored in Earth's climate system despite reductions in surface temperature. As a consequence, our results indicate that an abrupt termination of ocean pipes could cause dramatic increases in surface temperatures beyond that which would have been obtained had ocean pipes not been implemented.

Climatic Effects of Medium-Sized Asteroid Impacts on Land

NASA Astrophysics Data System (ADS)

Bardeen, C.; Garcia, R. R.; Toon, O. B.; Otto-Bliesner, B. L.; Wolf, E. T.

2015-12-01

Using the Community Earth System Model (CESM), a three-dimensional coupled climate model with interactive chemistry, we have simulated the climate response to a medium-sized (1 km) asteroid impact on the land. An impact of this size would cause local fires and may also generate submicron dust particles. Dust aerosols are injected into the upper atmosphere where they persist for ~3 years. Soot aerosols from fires are injected into the troposphere and absorb solar radiation heating the air which helps loft the soot into the stratosphere where it persists for ~10 years. Initially, these aerosols cause a heating of over 240 K in the stratosphere and up to a 70% reduction in downwelling solar radiation at the surface. Global average surface temperature cools by as much as -8.5 K, ocean temperature cools by -4.5 K, precipitation is reduced by 50%, and the ozone column is reduced by 55%. The surface UV Index exceeds 20 in the tropics for several years. These changes represent a significant hazard to life on a global scale. These results extend the work of Pierazzo et al. (2010), also using CESM, which found a significant impact on stratospheric ozone, but little change in surface temperature or precipitation, from a 1 km asteroid impact in the ocean.

Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering

DOE PAGES

Tolstova, Yulia; Omelchenko, Stefan T.; Shing, Amanda M.; ...

2016-03-17

The crystallographic orientation of a metal affects its surface energy and structure, and has profound implications for surface chemical reactions and interface engineering, which are important in areas ranging from optoelectronic device fabrication to catalysis. However, it can be very difficult and expensive to manufacture, orient, and cut single crystal metals along different crystallographic orientations, especially in the case of precious metals. One approach is to grow thin metal films epitaxially on dielectric substrates. In this work, we report on growth of Pt and Au films on MgO single crystal substrates of (100) and (110) surface orientation for use asmore » epitaxial templates for thin film photovoltaic devices. We develop bias-assisted sputtering for deposition of oriented Pt and Au films with sub-nanometer roughness. We show that biasing the substrate decreases the substrate temperature necessary to achieve epitaxial orientation, with temperature reduction from 600 to 350 °C for Au, and from 750 to 550 °C for Pt, without use of transition metal seed layers. Additionally, this temperature can be further reduced by reducing the growth rate. Biased deposition with varying substrate bias power and working pressure also enables control of the film morphology and surface roughness.« less

Carbon-doped boron nitride nanosheet as a promising catalyst for N2O reduction by CO or SO2 molecule: A comparative DFT study

NASA Astrophysics Data System (ADS)

Esrafili, Mehdi D.; Saeidi, Nasibeh

2018-06-01

We report for the first time, the catalytic activity of the experimentally available carbon-doped boron nitride nanosheet (C-BNNS) towards the reduction of N2O in the presence of CO or SO2 molecule. According to our density functional theory calculations, C-doping can introduce high spin density into BN monolayer which is mainly localized over the C and its neighboring N atoms. The Hirshfeld charge density analysis reveals that the electron-rich C-BNNS acts as an electron donating support to activate N2O molecule which is an important step in the reduction of N2O. The N2O reduction reaction starts with the dissociative adsorption of N2O over the C-BNNS surface, yielding the N2 molecule and an activated oxygen moiety (Oads) adsorbed over the C atom. The reaction then proceeds via the elimination of Oads by a CO or SO2 molecule. The obtained low activation energies clearly indicate that the metal-free C-BNNS surface can be regarded as a highly active catalyst for the reduction of N2O. The results of this study may open new avenues in searching low cost and highly active BN-based catalysts for low temperature reduction of N2O.

Acoustically enhanced boiling heat transfer on a heated surface containing open microchannels

NASA Astrophysics Data System (ADS)

Boziuk, Thomas R.; Smith, Marc K.; Glezer, Ari

2011-11-01

Acoustic actuation is used to enhance boiling heat transfer on a submerged heated surface containing an array of open microchannels by controlling the formation and evolution of vapor bubbles and inhibiting the instability that leads to film boiling at the critical heat flux. The effect of actuation at millimeter and micrometer scales is investigated with emphasis on the behavior of bubble nucleation, growth, contact-line motion, condensation, and detachment. The results show that microchannels control the location of boiling and reduce the mean surface superheat. In addition, acoustic actuation increases the heat flux at a given surface temperature and leads to a significant increase in the critical heat flux, a reduction of the vapor mass above the surface, and the breakup of low-frequency vapor slug formation. Supported by ONR.

Studies on Various Functional Properties of Titania Thin Film Developed on Glazed Ceramic Wall Tiles

NASA Astrophysics Data System (ADS)

Anil, Asha; Darshana R, Bangoria; Misra, S. N.

A sol-gel based TiO2 thin film was applied on glazed wall tiles for studying its various functional properties. Thin film was deposited by spin coating on the substrate and subjected to curing at different temperatures such as 600°C, 650, 700°C, 750°C and 800°C with 10 minutes soaking. The gel powder was characterized by FTIR, DTA/TG and XRD. Microstructure of thin film was analyzed by FESEM and EDX. Surface properties of the coatings such as gloss, colour difference, stain resistance, mineral hardness and wettability were extensively studied. The antibacterial activity of the surface of coated substrate against E. coli was also examined. The durability of the coated substrate in comparison to the uncoated was tested against alkali in accordance with ISO: 10545 (Part 13):1995 standard. FESEM images showed that thin films are dense and homogeneous. Coated substrates after firing results in lustre with high gloss, which increased from 330 to 420 GU as the curing temperature increases compared to that of uncoated one (72 GU). Coated substrate cured at 800°C shows higher mineral hardness (5 Mohs’) compared to uncoated one (4 Mohs’) and films cured at all temperatures showed stain resistance. The experimental results showed that the resistance towards alkali attack increase with increase in curing temperature and alkali resistance of sample cured at 800 °C was found to be superior compared to uncoated substrate. Contact angle of water on coated surface of substrates decreased with increase in temperature. Bacterial reduction percentages of the coated surface was 97% for sample cured at 700°C and it decreased from 97% to 87% as the curing temperature increased to 800 °C when treated with E. coli bacteria.

Transient climate simulation from the Maunder Minimum to present day using prescribed changes in GHG, total/spectral solar irradiance and ozone

NASA Astrophysics Data System (ADS)

Spangehl, Thomas; Cubasch, Ulrich; Schimanke, Semjon

A fully coupled AO-GCM including representation of the middle atmosphere is used for tran-sient simulation of climate from 1630 to 2000 AD. For better representation of changes in the UV/visible part of the solar spectrum an improved short-wave radiation scheme is implemented. The model is driven by changes in GHG concentrations, solar activity and volcanic eruptions. Solar variability is introduced via changes in total/spectral solar irradiance (TSI/SSI) and pre-scribed changes in stratospheric ozone. The secular trend in TSI is in the range of 0.1 percent increase from Maunder Minimum to present-day. Volcanic eruptions are represented via abrupt reduction in TSI. With the applied forcings the model does not simulate a clear reduction of the annual Northern Hemisphere (NH) mean near surface temperature during Maunder Minimum. By contrast the Dalton Minimum is characterized by distinct cooling and there is a significant raise of NH mean near surface temperature until the end of the 20th century. Focusing on the North Atlantic/European region the winter mean near surface temperature change pat-tern from Late Maunder Minimum (1675-1715) to present-day (1960-1990) reveals maximum warming over north-eastern Europe and cooling over the western North Atlantic with maxi-mum cooling west of Greenland. These changes can partly be explained by a shift of the NAO towards a more positive phase. The simulated changes in tropospheric circulation are discussed with special emphasize on the role of the solar forcing. Besides the stratospheric solar forcing which may affect NAO variability via downward propagation of the solar signal from the strato-sphere to the troposphere the magnitude of the secular trend in TSI might play a role. For the period from Maunder Minimum to present-day the simulation shows less near surface temper-ature increase especially over arctic regions when compared to simulations performed with the same model including the standard radiation scheme but applying larger TSI variations. The associated changes in lower tropospheric baroclinicity are more favourable for synoptic scale wave activity over the North Atlantic and might thereby contribute to strengthening of the NAO.

Investigation of multi-scale flash-weakening of rock surfaces during high speed slip

NASA Astrophysics Data System (ADS)

Barbery, M. R.; Saber, O.; Chester, F. M.; Chester, J. S.

2017-12-01

A significant reduction in the coefficient of friction of rock can occur if sliding velocity approaches seismic rates as a consequence of weakening of microscopic sliding contacts by flash heating. Using a high-acceleration and -speed biaxial apparatus equipped with a high-speed Infra-Red (IR) camera to capture thermographs of the sliding surface, we have documented the heterogeneous distribution of temperature on flash-heated decimetric surfaces characterized by linear arrays of high-temperature, mm-size spots, and streaks. Numerical models that are informed by the character of flash heated surfaces and that consider the coupling of changes in temperature and changes in the friction of contacts, supports the hypothesis that independent mechanisms of flash weakening operate at different contact scales. Here, we report on new experiments that provide additional constraints on the life-times and rest-times of populations of millimeter-scale contacts. Rock friction experiments conducted on Westerly granite samples in a double-direct shear configuration achieve velocity steps from 1 mm/s to 900 mm/s at 100g accelerations over 2 mm of displacement with normal stresses of 22-36 MPa and 30 mm of displacement during sustained high-speed sliding. Sliding surfaces are machined to roughness similar to natural fault surfaces and that allow us to control the characteristics of millimeter-scale contact populations. Thermographs of the sliding surface show temperatures up to 200 C on millimeter-scale contacts, in agreement with 1-D heat conduction model estimates of 180 C. Preliminary comparison of thermal modeling results and experiment observations demonstrate that we can distinguish the different life-times and rest-times of contacts in thermographs and the corresponding frictional weakening behaviors. Continued work on machined surfaces that lead to different contact population characteristics will be used to test the multi-scale and multi-mechanism hypothesis for flash weakening during seismic slip on rough fault surfaces.

Modelling and simulation of effect of ultrasonic vibrations on machining of Ti6Al4V.

PubMed

Patil, Sandip; Joshi, Shashikant; Tewari, Asim; Joshi, Suhas S

2014-02-01

The titanium alloys cause high machining heat generation and consequent rapid wear of cutting tool edges during machining. The ultrasonic assisted turning (UAT) has been found to be very effective in machining of various materials; especially in the machining of "difficult-to-cut" material like Ti6Al4V. The present work is a comprehensive study involving 2D FE transient simulation of UAT in DEFORM framework and their experimental characterization. The simulation shows that UAT reduces the stress level on cutting tool during machining as compared to that of in continuous turning (CT) barring the penetration stage, wherein both tools are subjected to identical stress levels. There is a 40-45% reduction in cutting forces and about 48% reduction in cutting temperature in UAT over that of in CT. However, the reduction magnitude reduces with an increase in the cutting speed. The experimental analysis of UAT process shows that the surface roughness in UAT is lower than in CT, and the UATed surfaces have matte finish as against the glossy finish on the CTed surfaces. Microstructural observations of the chips and machined surfaces in both processes reveal that the intensity of thermal softening and shear band formation is reduced in UAT over that of in CT. Copyright © 2013 Elsevier B.V. All rights reserved.

Bombardment-induced segregation and redistribution

NASA Astrophysics Data System (ADS)

Lam, N. Q.; Wiedersich, H.

During ion bombardment, a number of processes can alter the compositional distribution and microstructure in near-surface regions of alloys. The relative importance of each process depends principally on the target composition, temperature, and ion characteristics. In addition to displacement mixing leading to a randomization of atomic locations, and preferential loss of alloying elements by sputtering, which are dominant at relatively low temperatures, several thermally-activated processes, including radiation-enhanced diffusion, radiation-induced segregation and Gibbsian adsorption, also play important roles. At elevated temperatures, nonequilibrium point defects induced by ion impacts become mobile and tend to anneal out by recombination and diffusion to extended sinks, such as dislocations, grain boundaries and free surfaces. The high defect concentrations, far exceeding the thermodynamic equilibrium values, can enhance diffusion-controlled processes, while persistent defect fluxes, originating from the spatial non-uniformity in defect production and annihilation, give rise to local redistribution of alloy constituents because of radiation-induced segregation. Moreover, when the alloy is maintained at high temperature, Gibbsian adsorption, driven by the reduction in free energy of the system, occurs even without irradiation; it involves a compositional perturbation in a few atom layers near the alloy surface. The combination of these processes leads to the complex development of a compositionally-modified layer in the subsurface region. Considerable progress has been made recently in identifying and understanding the relative contributions from the individual processes under various irradiation conditions. In the present paper, selected examples of these different phenomena and their synergistic effects on the evolution of the near-surface compositions of alloys during sputtering and ion implantation at elevated temperatures are discussed.

First principles investigation of heterogeneous catalysis on metal oxide surfaces

NASA Astrophysics Data System (ADS)

Ghoussoub, Mireille

Metal oxides possess unique electronic and structural properties that render them highly favourable for applications in heterogeneous catalysis. In this study, computational atomistic modelling based on Density Functional Theory was used to investigate the reduction of carbon dioxide over hydroxylated indium oxide nanoparticles, as well at the activation of methane over oxygen-covered bimetallic surfaces. The first study employed metadynamics-biased ab initio molecular dynamics to obtain the free energy surface of the various reaction steps at finite temperature. In the second study, the nudged elastic band method was used to probe the C-H activation mechanisms for different surface configurations. In both cases, activation energies, reaction energies, transition state structures, and charge analysis results are used to explain the underlying mechanistic pathways.

The Effect of Soil Temperature Seasonality on Climate Reconstructions from Paleosols

NASA Astrophysics Data System (ADS)

Gallagher, T. M.; Hren, M. T.; Sheldon, N. D.

2017-12-01

Accurate continental temperature reconstructions provide important constraints on climate sensitivity to changes in atmospheric pCO2, the timing and rates of tectonic uplift, and the driving mechanisms and feedbacks associated with major climate events. Temperature seasonality is an important variable to consider, because not only does it exert a strong control on the biosphere, but it can obfuscate changes in mean annual air temperature (MAAT) in the geologic record. In order to better understand the effect temperature seasonality has on paleosol temperature proxies, soil temperature data was compiled from over 200 stations that comprise the NCDC Soil Climate Analysis Network. Observed soil temperature variations were then compared to predicted soil temperature values based on normal seasonal air temperature trends. Approximately one quarter of sites record less temperature variation than predicted. This reduction in soil temperature seasonality is a result of warmer than predicted cold-season temperatures, driven by cold-season processes such as snow cover insulation. The reduction in soil temperature seasonality explains why pedo-transfer functions to break down below MAAT values of 6-8 °C. Greater than predicted soil temperature seasonality is observed at nearly half of the sites, driven primarily by direct heating of the soil surface by solar radiation. Deviations larger than 2 °C are not common until mean annual precipitation falls below 300 mm, suggesting that complications introduced by ground heating are primarily restricted to paleosols that formed in more arid environments. Clumped isotope measurements of pedogenic carbonate and bulk paleosol elemental data from a stacked series of paleosols spanning the Eocene-Oligocene in Northeastern Spain are also examined to demonstrate how the documented seasonal trends in modern soils can help inform paleo-applications.

Reduced deuterium retention in simultaneously damaged and annealed tungsten

NASA Astrophysics Data System (ADS)

Simmonds, M. J.; Wang, Y. Q.; Barton, J. L.; Baldwin, M. J.; Yu, J. H.; Doerner, R. P.; Tynan, G. R.

2017-10-01

Deuterium (D) retention in polycrystalline tungsten (W) with copper (Cu) ion damage concurrently produced at elevated surface temperature is investigated. An in situ heated stage held W samples at a controlled temperature up to 1243 K, which were subjected to displacement damage produced by 3.4 MeV Cu ions. D retention is subsequently explored by exposure of the W samples held at 383 K to a D2 plasma ion fluence of 1024 D+/m2. Nuclear reaction analysis (NRA), utilizing the D(3He,p)4He nuclear reaction, is used to probe the D concentration in the near surface up to 6 μm. Thermal desorption spectroscopy (TDS) is used to measure outgassed HD and D2 molecules to determine the bulk D concentration. Both NRA and TDS measure a significant reduction in D retention for samples damaged at elevated temperature. TDS quantitatively shows that the lowest energy trap remains largely unaffected while higher energy traps, induced by Cu ions, are annealed and approach intrinsic concentrations as the temperature during ion damage approaches 1243 K. Analysis of TDS data yields an activation energy of (0.10 ± 0.02) eV for recovery of ion-damage induced traps at elevated temperature.

Size effect on the structural, magnetic, and magnetotransport properties of electron doped manganite La0.15Ca0.85MnO3

NASA Astrophysics Data System (ADS)

Thomas, Rini; Das, Gangadhar; Mondal, Rajib; Pradheesh, R.; Mahato, R. N.; Geetha Kumary, T.; Nirmala, R.; Morozkin, A. V.; Lamsal, J.; Yelon, W. B.; Nigam, A. K.; Malik, S. K.

2012-04-01

Nanocrystalline La0.15Ca0.85MnO3 samples of various grain sizes ranging from ˜17 to 42 nm have been prepared by sol-gel technique. Phase purity and composition were verified by room temperature x-ray diffraction and SEM-EDAX analysis. The bulk La0.15Ca0.85MnO3 is known to order antiferromagnetically around 170 K and to undergo a simultaneous crystal structural transition. DC magnetization measurements on 17 nm size La0.15Ca0.85MnO3 show a peak at ˜130 K (TN) in zero-field-cooled (ZFC) state. Field-cooled magnetization bifurcates from ZFC data around 200 K hinting a weak ferromagnetic component near room temperature due to surface moments of the nanoparticle sample. Low temperature powder neutron diffraction experiments reveal that the incomplete structural transition from room temperature orthorhombic to low temperature orthorhombic-monoclinic state also occurs in the nanoparticle sample as in the bulk. Magnetization in the ordered state decreases as particle size increases, thus indicating the reduction of the competing ferromagnetic surface moments.

Comparison of preparation methods for ceria catalyst and the effect of surface and bulk sulfates on its activity toward NH3-SCR.

PubMed

Chang, Huazhen; Ma, Lei; Yang, Shijian; Li, Junhua; Chen, Liang; Wang, Wei; Hao, Jiming

2013-11-15

A series of CeO2 catalysts prepared with sulfate (S) and nitrate (N) precursors by hydrothermal (H) and precipitation (P) methods were investigated in selective catalytic reduction of NOx by NH3 (NH3-SCR). The catalytic activity of CeO2 was significantly affected by the preparation methods and the precursor type. CeO2-SH, which was prepared by hydrothermal method with cerium (IV) sulfate as a precursor, showed excellent SCR activity and high N2 selectivity in the temperature range of 230-450 °C. Based on the results obtained by temperature-programmed reduction (H2-TPR), transmission infrared spectra (IR) and thermal gravimetric analysis (TGA), the excellent performance of CeO2-SH was correlated with the surface sulfate species formed in the hydrothermal reaction. These results indicated that sulfate species bind with Ce(4+) on the CeO2-SH catalyst, and the specific sulfate species, such as Ce(SO4)2 or CeOSO4, were formed. The adsorption of NH3 was promoted by these sulfate species, and the probability of immediate oxidation of NH3 to N2O on Ce(4+) was reduced. Accordingly, the selective oxidation of NH3 was enhanced, which contributed to the high N2 selectivity in the SCR reaction. However, the location of sulfate on the CeO2-SP catalyst was different. Plenty of sulfate species were likely deposited on CeO2-SP surface, covering the active sites for NO oxidation, which resulted in poor SCR activity in the test temperature range. Moreover, the resistance to alkali metals, such as Na and K, was improved over the CeO2-SH catalyst. Copyright © 2013 Elsevier B.V. All rights reserved.

Transient climate and ambient health impacts due to national solid fuel cookstove emissions

PubMed Central

Lacey, Forrest G.; Henze, Daven K.; Lee, Colin J.; van Donkelaar, Aaron; Martin, Randall V.

2017-01-01

Residential solid fuel use contributes to degraded indoor and ambient air quality and may affect global surface temperature. However, the potential for national-scale cookstove intervention programs to mitigate the latter issues is not yet well known, owing to the spatial heterogeneity of aerosol emissions and impacts, along with coemitted species. Here we use a combination of atmospheric modeling, remote sensing, and adjoint sensitivity analysis to individually evaluate consequences of a 20-y linear phase-out of cookstove emissions in each country with greater than 5% of the population using solid fuel for cooking. Emissions reductions in China, India, and Ethiopia contribute to the largest global surface temperature change in 2050 [combined impact of −37 mK (11 mK to −85 mK)], whereas interventions in countries less commonly targeted for cookstove mitigation such as Azerbaijan, Ukraine, and Kazakhstan have the largest per cookstove climate benefits. Abatement in China, India, and Bangladesh contributes to the largest reduction of premature deaths from ambient air pollution, preventing 198,000 (102,000–204,000) of the 260,000 (137,000–268,000) global annual avoided deaths in 2050, whereas again emissions in Ukraine and Azerbaijan have the largest per cookstove impacts, along with Romania. Global cookstove emissions abatement results in an average surface temperature cooling of −77 mK (20 mK to −278 mK) in 2050, which increases to −118 mK (−11 mK to −335 mK) by 2100 due to delayed CO2 response. Health impacts owing to changes in ambient particulate matter with an aerodynamic diameter of 2.5 μm or less (PM2.5) amount to ∼22.5 million premature deaths prevented between 2000 and 2100. PMID:28115698

Thermal Performance of Precast Concrete Sandwich Panel (PCSP) Design for Sustainable Built Environment

NASA Astrophysics Data System (ADS)

Ern, Peniel Ang Soon; Ling, Lim Mei; Kasim, Narimah; Hamid, Zuhairi Abd; Masrom, Md Asrul Nasid Bin

2017-10-01

Malaysia’s awareness of performance criteria in construction industry towards a sustainable built environment with the use of precast concrete sandwich panel (PCSP) system is applied in the building’s wall to study the structural behaviour. However, very limited studies are conducted on the thermal insulation of exterior and interior panels in PCSP design. In hot countries such as Malaysia, proper designs of panel are important to obtain better thermal insulation for building. This study is based on thermal performance of precast concrete sandwich panel design for sustainable built environment in Malaysia. In this research, three full specimens, which are control specimen (C), foamed concrete (FC) panels and concrete panels with added palm oil fuel ash (FC+ POFA), where FC and FC+POFA sandwiched with gypsum board (G) were produced to investigate their thermal performance. Temperature difference of exterior and interior surface of specimen was used as indicators of thermal-insulating performance of PCSP design. Heat transfer test by halogen lamp was carried out on three specimens where the exterior surface of specimens was exposed to the halogen lamp. The temperature reading of exterior and interior surface for three specimens were recorded with the help of thermocouple. Other factors also studied the workability, compressive strength and axial compressive strength of the specimens. This study has shown that FC + POFA specimen has the strength nearer to normal specimen (C + FC specimen). Meanwhile, the heat transfer results show that the FC+POFA has better thermal insulation performance compared to C and FC specimens with the highest temperature difference, 3.4°C compared to other specimens. The results from this research are useful to be implemented in construction due to its benefits such as reduction of energy consumption in air-conditioning, reduction of construction periods and eco-friendly materials.

Synthesis and Characterization of Highly Crystalline Graphene Aerogels

DOE PAGES

Worsley, Marcus A.; Pham, Thang T.; Yan, Aiming; ...

2014-10-06

Aerogels are used in a broad range of scientific and industrial applications due to their large surface areas, ultrafine pore sizes, and extremely low densities. Recently, a large number of reports have described graphene aerogels based on the reduction of graphene oxide (GO). Though these GO-based aerogels represent a considerable advance relative to traditional carbon aerogels, they remain significantly inferior to individual graphene sheets due to their poor crystallinity. Here, we report a straightforward method to synthesize highly crystalline GO-based graphene aerogels via high-temperature processing common in commercial graphite production. The crystallization of the graphene aerogels versus annealing temperature ismore » characterized using Raman and X-ray absorption spectroscopy, X-ray diffraction, and electron microscopy. Nitrogen porosimetry shows that the highly crystalline graphene macrostructure maintains a high surface area and ultrafine pore size. Because of their enhanced crystallinity, these graphene aerogels exhibit a ~200 °C improvement in oxidation temperature and an order of magnitude increase in electrical conductivity.« less

On the Mechanism of In Nanoparticle Formation by Exposing ITO Thin Films to Hydrogen Plasmas.

PubMed

Fan, Zheng; Maurice, Jean-Luc; Chen, Wanghua; Guilet, Stéphane; Cambril, Edmond; Lafosse, Xavier; Couraud, Laurent; Merghem, Kamel; Yu, Linwei; Bouchoule, Sophie; Roca I Cabarrocas, Pere

2017-10-31

We present our systematic work on the in situ generation of In nanoparticles (NPs) from the reduction of ITO thin films by hydrogen (H 2 ) plasma exposure. In contrast to NP deposition from the vapor phase (i.e., evaporation), the ITO surface can be considered to be a solid reservoir of In atoms thanks to H 2 plasma reduction. On one hand, below the In melting temperature, solid In NP formation is governed by the island-growth mode, which is a self-limiting process because the H 2 plasma/ITO interaction will be gradually eliminated by the growing In NPs that cover the ITO surface. On the other hand, we show that above the melting temperature In droplets prefer to grow along the grain boundaries on the ITO surface and dramatic coalescence occurs when the growing NPs connect with each other. This growth-connection-coalescence behavior is even strengthened on In/ITO bilayers, where In particles larger than 10 μm can be formed, which are made of evaporated In atoms and in situ released ones. Thanks to this understanding, we manage to disperse dense evaporated In NPs under H 2 plasma exposure when inserting an ITO layer between them and substrate like c-Si wafer or glass by modifying the substrate surface chemistry. Further studies are needed for more precise control of this self-assembling method. We expect that our findings are not limited to ITO thin films but could be applicable to various metal NPs generation from the corresponding metal oxide thin films.

Redox thermodynamics of the native and alkaline forms of eukaryotic and bacterial class I cytochromes c.

PubMed

Battistuzzi, G; Borsari, M; Sola, M; Francia, F

1997-12-23

The reduction potentials of beef heart cytochrome c and cytochromes c2 from Rhodopseudomonas palustris, Rhodobacter sphaeroides, and Rhodobacter capsulatus were measured through direct electrochemistry at a surface-modified gold electrode as a function of temperature in nonisothermal experiments carried out at neutral and alkaline pH values. The thermodynamic parameters for protein reduction (DeltaS degrees rc and DeltaH degrees rc) were determined for the native and alkaline conformers. Enthalpy and entropy terms underlying species-dependent differences in E degrees and pH- and temperature-induced E degrees changes for a given cytochrome were analyzed. The difference of about +0.1 V in E degrees between cytochromes c2 and the eukaryotic species can be separated into an enthalpic term (-DeltaDeltaH degrees rc/F) of +0.130 V and an entropic term (TDeltaDeltaS degrees rc/F) of -0.040 V. Hence, the higher potential of the bacterial species appears to be determined entirely by a greater enthalpic stabilization of the reduced state. Analogously, the much lower potential of the alkaline conformer(s) as compared to the native species is by far enthalpic in origin for both protein families, and is largely determined by the substitution of Met for Lys in axial heme ligation. Instead, the biphasic E degrees /temperature profile for the native cytochromes is due to a difference in reduction entropy between the conformers at low and high temperatures. Temperature-dependent 1H NMR experiments suggest that the temperature-induced transition also involves a change in orientation of the axial methionine ligand with respect to the heme plane.

Stagnation region gas film cooling: Effects of dimensionless coolant temperature

NASA Technical Reports Server (NTRS)

Bonnice, M. A.; Lecuyer, M. R.

1983-01-01

An experimental investigation was conducted to mode the film cooling performance for a turbine vane leading edge using the stagnation region of a cylinder in cross flow. Experiments were conducted with a single row of spanwise angled (25 deg) coolant holes for a range of the coolant blowing ratio and dimensionless coolant temperature with free stream-to-wall temperature ratio approximately 1.7 and Re sub D = 90000. the cylindrical test surface was instrumented with miniature heat flux gages and wall thermocouples to determine the percentage reduction in the Stanton number as a function of the distance downstream from injection (x/d sub 0) and the location between adjacent holes (z/S). Data from local heat flux measurements are presented for injection from a single row located at 5 deg, 22.9 deg, 40.8 deg, from stagnation using a hole spacing ratio of S/d = 5. The film coolant was injected with T sub c T sub w with a dimensionless coolant temperature in the range 1.18 or equal to theta sub c or equal to 1.56. The data for local Stanton Number Reduction (SNR) showed a significant increase in SNR as theta sub c was increased above 1.0.

Survival of norovirus surrogate on various food-contact surfaces.

PubMed

Kim, An-Na; Park, Shin Young; Bae, San-Cheong; Oh, Mi-Hwa; Ha, Sang-Do

2014-09-01

Norovirus (NoV) is an environmental threat to humans, which spreads easily from one infected person to another, causing foodborne and waterborne diseases. Therefore, precautions against NoV infection are important in the preparation of food. The aim of this study was to investigate the survival of murine norovirus (MNV), as a NoV surrogate, on six different food-contact surfaces: ceramic, wood, rubber, glass, stainless steel, and plastic. We inoculated 10(5) PFU of MNV onto the six different surface coupons that were then kept at room temperature for 28 days. On the food-contact surfaces, the greatest reduction in MNV was 2.28 log10 PFU/coupon, observed on stainless steel, while the lowest MNV reduction was 1.29 log10 PFU/coupon, observed on wood. The rank order of MNV reduction, from highest to lowest, was stainless steel, plastic, rubber, glass, ceramic, and wood. The values of d R (time required to reduce the virus by 90%) on survival plots of MNV determined by a modified Weibull model were 277.60 h (R(2) = 0.99) on ceramic, 492.59 h (R(2) = 0.98) on wood, 173.56 h on rubber (R(2) = 0.98), 97.18 h (R(2) = 0.94) on glass, 91.76 h (R(2) = 0.97) on stainless steel, and 137.74 h (R(2) = 0.97) on plastic. The infectivity of MNV on all food-contact surfaces remained after 28 days. These results show that MNV persists in an infective state on various food-contact surfaces for long periods. This study may provide valuable information for the control of NoV on various food-contact surfaces, in order to prevent foodborne disease.

Global Model of Time-Modulated Electronegative Discharges for Neutral Radical and Electron Temperature Control

NASA Astrophysics Data System (ADS)

Kim, Sungjin; Lieberman, M. A.; Lichtenberg, A. J.

2003-10-01

Control and reduction of neutral radical flux/ion flux ratio and electron temperature Te is required for next generation etching in the microelectronics industry. We investigate time-modulated power for these purposes using a volume-averaged (global) oxygen discharge model, We consider pressures of 10-50 mTorr and plasma densities of 10^10-10^11 cm-3. In this regime, the discharge is found to be weakly electronegative. The modulation period and the duty ratio (on-time/period) are varied to determine the optimum conditions for reduction of FR= O-atom flux/ion flux and T_e. Two chambers with different height/diameter ratios (<< 1, and unity) are examined to determine the influence of the surface-area/volume ratio. At a fixed duty ratio, both FR and Te are found to have minimum values as the pulse period is varied, with the minimum value decreasing as the duty ratio decreases. Significant reductions in FR and Te are found. Support provided by Lam Research, NSF Grant ECS-0139956, California industries, and UC-SMART Contract SM99-10051.

Highly-basic large-pore zeolite catalysts for NOx reduction at low temperatures

DOEpatents

Penetrante, Bernardino M.; Brusasco, Raymond M.; Merritt, Bernard T.; Vogtlin, George E.

2004-02-03

A high-surface-area (greater than 600 m2/g), large-pore (pore size diameter greater than 6.5 angstroms), basic zeolite having a structure such as an alkali metal cation-exchanged Y-zeolite is employed to convert NO.sub.x contained in an oxygen-rich engine exhaust to N.sub.2 and O.sub.2. Preferably, the invention relates to a two-stage method and apparatus for NO.sub.x reduction in an oxygen-rich engine exhaust such as diesel engine exhaust that includes a plasma oxidative stage and a selective reduction stage. The first stage employs a non-thermal plasma treatment of NO.sub.x gases in an oxygen-rich exhaust and is intended to convert NO to NO.sub.2 in the presence of O.sub.2 and added hydrocarbons. The second stage employs a lean-NO.sub.x catalyst including the basic zeolite at relatively low temperatures to convert such NO.sub.2 to environmentally benign gases that include N.sub.2, CO.sub.2, and H.sub.2 O.

Excimer laser assisted very fast exfoliation and reduction of graphite oxide at room temperature under air ambient for Supercapacitors electrode

NASA Astrophysics Data System (ADS)

Malek Hosseini, S. M. B.; Baizaee, S. M.; Naderi, Hamid Reza; Dare Kordi, Ali

2018-01-01

Excimer laser was used for reduction and exfoliation of graphite oxide (GO) at room temperature under air ambient. The prepared excimer laser reduced graphite oxide (XLRGO) is characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), nitrogen adsorption/desorption (BET method), X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and UV-vis absorption techniques for surface, structural functional groups and band gap analysis. Electrochemical properties are investigated using cyclic voltammetry, galvanostatic charge-discharge, electrochemical impedance spectroscopy (EIS) and continues cyclic voltammetry (CCV) in 0.5 M Na2SO4 as electrolyte. Electrochemical investigations revealed that XLRGO electrode has enhanced supercapacitive performance including specific capacitance of 299 F/g at a scan rate of 2 mV/s. Furthermore, CCV measurement showed that XLRGO electrode kept 97.8% of its initial capacitance/capacity after 4000 cycles. The obtained results from electrochemical investigations confirm that the reduction of GO by using an excimer laser produces high-quality graphene for supercapacitor applications without the need for additional operations.

Rapid room-temperature synthesis of nanocrystalline spinels as oxygen reduction and evolution electrocatalysts.

PubMed

Cheng, Fangyi; Shen, Jian; Peng, Bo; Pan, Yuede; Tao, Zhanliang; Chen, Jun

2011-01-01

Spinels can serve as alternative low-cost bifunctional electrocatalysts for oxygen reduction/evolution reactions (ORR/OER), which are the key barriers in various electrochemical devices such as metal-air batteries, fuel cells and electrolysers. However, conventional ceramic synthesis of crystalline spinels requires an elevated temperature, complicated procedures and prolonged heating time, and the resulting product exhibits limited electrocatalytic performance. It has been challenging to develop energy-saving, facile and rapid synthetic methodologies for highly active spinels. In this Article, we report the synthesis of nanocrystalline M(x)Mn(3-x)O(4) (M = divalent metals) spinels under ambient conditions and their electrocatalytic application. We show rapid and selective formation of tetragonal or cubic M(x)Mn(3-x)O(4) from the reduction of amorphous MnO(2) in aqueous M(2+) solution. The prepared Co(x)Mn(3-x)O(4) nanoparticles manifest considerable catalytic activity towards the ORR/OER as a result of their high surface areas and abundant defects. The newly discovered phase-dependent electrocatalytic ORR/OER characteristics of Co-Mn-O spinels are also interpreted by experiment and first-principle theoretical studies.

Effect of pH and pulsed electric field process parameters on the aflatoxin reduction in model system using response surface methodology: Effect of pH and PEF on Aflatoxin Reduction.

PubMed

Vijayalakshmi, Subramanian; Nadanasabhapathi, Shanmugam; Kumar, Ranganathan; Sunny Kumar, S

2018-03-01

The presence of aflatoxin, a carcinogenic and toxigenic secondary metabolite produced by Aspergillus species, in food matrix has been a major worldwide problem for years now. Food processing methods such as roasting, extrusion, etc. have been employed for effective destruction of aflatoxins, which are known for their thermo-stable nature. The high temperature treatment, adversely affects the nutritive and other quality attributes of the food, leading to the necessity of application of non-thermal processing techniques such as ultrasonication, gamma irradiation, high pressure processing, pulsed electric field (PEF), etc. The present study was focused on analysing the efficacy of the PEF process in the reduction of the toxin content, which was subsequently quantified using HPLC. The process parameters of different pH model system (potato dextrose agar) artificially spiked with aflatoxin mix standard was optimized using the response surface methodology. The optimization of PEF process effects on the responses aflatoxin B1 and total aflatoxin reduction (%) by pH (4-10), pulse width (10-26 µs) and output voltage (20-65%), fitted 2FI model and quadratic model respectively. The response surface plots obtained for the processes were of saddle point type, with the absence of minimum or maximum response at the centre point. The implemented numerical optimization showed that the predicted and actual values were similar, proving the adequacy of the fitted models and also proved the possible application of PEF in toxin reduction.

Surface decoration through electrostatic interaction leading to enhanced reactivity: Low temperature synthesis of nanostructured chromium borides (CrB and CrB{sub 2})

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

Menaka,; Kumar, Bharat; Kumar, Sandeep

The present study describes a novel low temperature route at ambient pressure for the synthesis of nanocrystalline chromium borides (CrB and CrB{sub 2}) without using any flux or additives. The favorable and intimate mixing of nanoparticles of chromium acetate (Cr source) and boron forms an active chromium–boron precursor which decomposes at much lower temperature (400 °C) to form CrB (which is ∼1000 °C less than the known ambient pressure synthesis). The chromium acetate nanoparticles (∼5 nm) decorate the larger boron particles (150–200 nm) due to electrostatic interactions resulting from opposing surface charges of boron (zeta potential:+48.101 mV) and chromium acetatemore » (zeta potential:−4.021 mV) in ethanolic medium and is evident in the TEM micrographs. The above method leads to the formation of pure CrB film like structure at 400 °C and nanospheres (40–60 nm) at 600 °C. Also, chromium diboride (CrB{sub 2}) nanoparticles (25 nm) could be obtained at 1000 °C. - Graphical abstract: Variation of surface charge of reactants, precursor and the products, chromium borides (CrB and CrB{sub 2}). Highlights: ► Novel borothermal reduction process for synthesis of chromium boride. ► Significant lowering of reaction temperature to obtain nanocrystalline chromium boride. ► Enhanced reactivity due to appropriate surface interactions.« less

Low cost, surfactant-less, one pot synthesis of Cu 2O nano-octahedra at room temperature

NASA Astrophysics Data System (ADS)

Ahmed, Asar; Gajbhiye, Namdeo S.; Joshi, Amish G.

2011-08-01

Cu 2O octahedra were successfully synthesized via a novel wet-chemical method using D-glucose and hydrazine as reducing agent at room temperature without the presence of any other surfactant. Presence of D-glucose was important for the stabilization of the evolved copper octahedra and also for facilitating the reduction of the Cu(II) ions. The existence of glucose moieties on the surface as capping agent was confirmed by the FT-IR spectra while there was presence of excess oxygen atoms on the surface leading to the formation of a thin CuO layer at the octahedra surface, as confirmed by the XPS study, probably promoted by the capping glucose. Effect of NaOH concentration on the reaction and the formation of octahedra was also studied. The formation mechanism of obtained Cu 2O octahedra has been discussed. These octahedra were then studied for their photocatalytic properties in degradation of organic dyes, rhodamine B and methyl orange.

Ambipolar surface state thermoelectric power of topological insulator Bi2Se3.

PubMed

Kim, Dohun; Syers, Paul; Butch, Nicholas P; Paglione, Johnpierre; Fuhrer, Michael S

2014-01-01

We measure gate-tuned thermoelectric power of mechanically exfoliated Bi2Se3 thin films in the topological insulator regime. The sign of the thermoelectric power changes across the charge neutrality point as the majority carrier type switches from electron to hole, consistent with the ambipolar electric field effect observed in conductivity and Hall effect measurements. Near the charge neutrality point and at low temperatures, the gate-dependent thermoelectric power follows the semiclassical Mott relation using the expected surface state density of states but is larger than expected at high electron doping, possibly reflecting a large density of states in the bulk gap. The thermoelectric power factor shows significant enhancement near the electron-hole puddle carrier density ∼0.5 × 10(12) cm(-2) per surface at all temperatures. Together with the expected reduction of lattice thermal conductivity in low-dimensional structures, the results demonstrate that nanostructuring and Fermi level tuning of three-dimensional topological insulators can be promising routes to realize efficient thermoelectric devices.

Measurement and modeling of surface temperature dynamics of the NSTX liquid lithium divertor

NASA Astrophysics Data System (ADS)

McLean, A. G.; Gan, K. F.; Ahn, J.-W.; Gray, T. K.; Maingi, R.; Abrams, T.; Jaworski, M. A.; Kaita, R.; Kugel, H. W.; Nygren, R. E.; Skinner, C. H.; Soukhanovskii, V. A.

2013-07-01

Dual-band infrared (IR) measurements of the National Spherical Torus eXperiment (NSTX) Liquid Lithium Divertor (LLD) are reported that demonstrate liquid Li is more effective at removing plasma heat flux than Li-conditioned graphite. Extended dwell of the outer strike point (OSP) on the LLD caused an incrementally larger area to be heated above the Li melting point through the discharge leading to enhanced D retention and plasma confinement. Measurement of Tsurface near the OSP demonstrates a significant reduction of the LLD surface temperature compared to that of Li-coated graphite at the same major radius. Modeling of these data with a 2-D simulation of the LLD structure in the DFLUX code suggests that the structure of the LLD was successful at handling up to q⊥,peak = 5 MW/m2 inter-ELM and up to 10 MW/m2 during ELMs from its plasma-facing surface as intended, and provide an innovative method for inferring the Li layer thickness.

Ceria nanoclusters on graphene/Ru(0001): A new model catalyst system

DOE PAGES

Novotny, Z.; Netzer, F. P.; Dohnalek, Z.

2016-03-22

In this study, the growth of ceria nanoclusters on single-layer graphene on Ru(0001) has been examined, with a view towards fabricating a stable system for model catalysis studies. The surface morphology and cluster distribution as a function of oxide coverage and substrate temperature has been monitored by scanning tunneling microscopy (STM), whereas the chemical composition of the cluster deposits has been determined by Auger electron spectroscopy (AES). The ceria nanoparticles are of the CeO 2(111)-type and are anchored at the intrinsic defects of the graphene surface, resulting in a variation of the cluster densities across the macroscopic sample surface. Themore » ceria clusters on graphene display a remarkable stability against reduction in ultrahigh vacuum up to 900 K, but some sintering of clusters is observed for temperatures > 450 K. The evolution of the cluster size distribution suggests that the sintering proceeds via a Smoluchowski ripening mechanism, i.e. diffusion and aggregation of entire clusters.« less

The Impact of Transported Pollution on Arctic Climate

NASA Astrophysics Data System (ADS)

Quinn, P.; Stohl, A.; Arneth, A.; Berntsen, T.; Burkhart, J. F.; Flanner, M. G.; Kupiainen, K.; Shepherd, M.; Shevchenko, V. P.; Skov, H.; Vestreng, V.

2011-12-01

Arctic temperatures have increased at almost twice the global average rate over the past 100 years. Warming in the Arctic has been accompanied by an earlier onset of spring melt, a lengthening of the melt season, changes in the mass balance of the Greenland ice sheet, and a decrease in sea ice extent. Short-lived, climate warming pollutants such as black carbon (BC) have recently gained attention as a target for immediate mitigation of Arctic warming in addition to reductions in long lived greenhouse gases. Model calculations indicate that BC increases surface temperatures within the Arctic primarily through deposition on snow and ice surfaces with a resulting decrease in surface albedo and increase in absorbed solar radiation. In 2009, the Arctic Monitoring and Assessment Program (AMAP) established an Expert Group on BC with the goal of identifying source regions and energy sectors that have the largest impact on Arctic climate. Here we present the results of this work and investigate links between mid-latitude pollutants and Arctic climate.

Strong localization induced anomalous temperature dependence exciton emission above 300 K from SnO{sub 2} quantum dots

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

Pan, S. S., E-mail: sspan@issp.ac.cn, E-mail: ghli@issp.ac.cn; Li, F. D.; Liu, Q. W.

2015-05-07

SnO{sub 2} quantum dots (QDs) are potential materials for deep ultraviolet (DUV) light emitting devices. In this study, we report the temperature and excitation power-dependent exciton luminescence from SnO{sub 2} QDs. The exciton emission exhibits anomalous blue shift, accompanied with band width reduction with increasing temperature and excitation power above 300 K. The anomalous temperature dependences of the peak energy and band width are well interpreted by the strongly localized carrier thermal hopping process and Gaussian shape of band tails states, respectively. The localized wells and band tails at conduction minimum are considered to be induced by the surface oxygen defectsmore » and local potential fluctuation in SnO{sub 2} QDs.« less

Tunable optical response of bowtie nanoantenna arrays on thermoplastic substrates

NASA Astrophysics Data System (ADS)

Sharac, N.; Sharma, H.; Veysi, M.; Sanderson, R. N.; Khine, M.; Capolino, F.; Ragan, R.

2016-03-01

Thermally responsive polymers present an interesting avenue for tuning the optical properties of nanomaterials on their surfaces by varying their periodicity and shape using facile processing methods. Gold bowtie nanoantenna arrays are fabricated using nanosphere lithography on prestressed polyolefin (PO), a thermoplastic polymer, and optical properties are investigated via a combination of spectroscopy and electromagnetic simulations to correlate shape evolution with optical response. Geometric features of bowtie nanoantennas evolve by annealing at temperatures between 105 °C and 135 °C by releasing the degree of prestress in PO. Due to the higher modulus of Au versus PO, compressive stress occurs on Au bowtie regions on PO, which leads to surface buckling at the two highest annealing temperatures; regions with a 5 nm gap between bowtie nanoantennas are observed and the average reduction is 75%. Reflectance spectroscopy and full-wave electromagnetic simulations both demonstrate the ability to tune the plasmon resonance wavelength with a window of approximately 90 nm in the range of annealing temperatures investigated. Surface-enhanced Raman scattering measurements demonstrate that maximum enhancement is observed as the excitation wavelength approaches the plasmon resonance of Au bowtie nanoantennas. Both the size and morphology tunability offered by PO allows for customizing optical response.

Microstructure Characterization and Corrosion Properties of Nitrocarburized AISI 4140 Low Alloy Steel

NASA Astrophysics Data System (ADS)

Fattah, M.; Mahboubi, F.

2012-04-01

Plasma nitrocarburizing treatments of AISI 4140 low alloy steel have been carried out in a gas mixture of 85% N2-12% H2-3% CO2. All treatments were performed for 5 h at a chamber pressure of 4 mbar. Different treatment temperatures varying from 520 to 620 °C have been used to investigate the effect of treatment temperature on the corrosion and hardness properties and also microstructure of the plasma nitrocarburized steel. Scanning electron and optical microscopy, x-ray diffraction, microhardness measurement, and potentiodynamic polarization technique in 3.5% NaCl solution were used to study the treated surfaces. The results revealed that plasma nitrocarburizing at temperatures below 570 °C can readily produce a monophase ɛ compound layer. The compound layer formed at 620 °C is composed of two sub-layers and is supported by an austenite zone followed by the diffusion layer. The thickest diffusion layer was related to the sample treated at 620 °C. Microhardness results showed a reduction of surface hardness with increasing the treatment temperature from 520 to 620 °C. It has also been found that with increasing treatment temperature from 520 to 545 °C the corrosion resistance increases up to a maximum and then decreases with further increasing treatment temperature from 545 to 620 °C.

Ammonia-treated phosphate glasses useful for sealing to metals metals

DOEpatents

Brow, Richard K.; Day, Delbert E.

1991-01-01

A method of improving surface-dependent properties of phosphate glass such as durability and wear resistance without significantly affecting its thermal expansion coefficient is provided which comprises annealing the glass in a dry ammonia atmosphere at temperatures approximating the transition temperature of the glass. The ammonia annealing treatment of the present invention is carried out for a time sufficient to allow incorporation of a thin layer of nitrogen into the surface of the phosphate glass, and the treatment improves the durability of the glass without the reduction in the thermal expansion coefficient that has restricted the effectiveness of prior ammonia treatments. The improved phosphate glass resulting from this method is superior in wear resistance, yet maintains suitable thermal expansion properties so that it may be used effectively in a variety of applications requiring hermetic glass-metal seals.

Ammonia-treated phosphate glasses useful for sealing to metals

DOEpatents

Brow, R.K.; Day, D.E.

1991-09-03

A method of improving surface-dependent properties of phosphate glass such as durability and wear resistance without significantly affecting its thermal expansion coefficient is provided which comprises annealing the glass in a dry ammonia atmosphere at temperatures approximating the transition temperature of the glass. The ammonia annealing treatment of the present invention is carried out for a time sufficient to allow incorporation of a thin layer of nitrogen into the surface of the phosphate glass, and the treatment improves the durability of the glass without the reduction in the thermal expansion coefficient that has restricted the effectiveness of prior ammonia treatments. The improved phosphate glass resulting from this method is superior in wear resistance, yet maintains suitable thermal expansion properties so that it may be used effectively in a variety of applications requiring hermetic glass-metal seals.

Reduction of the low-temperature bulk gap in samarium hexaboride under high magnetic fields

DOE PAGES

Wolgast, S.; Jaime, Marcelo; Balakirev, Fedor Fedorovich; ...

2017-06-13

SmB 6 exhibits a small (15–20 meV) band gap at low temperatures due to hybridized d and f electrons, a tiny (3 meV) transport activation energy E A above 4 K, and surface states accessible to transport below 2 K. We study its magnetoresistance in 60-T pulsed fields between 1.5 and 4 K. The response of the nearly T independent surface states (which show no Shubnikov–de Haas oscillations) is distinct from that of the activated bulk. E A shrinks by 50% under fields up to 60 T. Data up to 93 T suggest that this trend continues beyond 100 T,more » in contrast to previous explanations. It rules out emerging theories to explain observed exotic magnetic quantum oscillations.« less

Synthesis of porous nanocrystalline NiO with hexagonal sheet-like morphology by homogeneous precipitation method

NASA Astrophysics Data System (ADS)

Sharma, Ravi Kant; Ghose, Ranjana

2015-04-01

Porous nanocrystalline NiO has been synthesized by a simple homogeneous precipitation method in short time at low calcination temperature without using any surfactant, chelating or gelating agents. The porous nanocrystalline NiO with a hexagonal sheet-like morphology were obtained by calcination of Ni(OH)2 nanoflakes at 500 °C. The calcination temperature strongly influences the morphology, crystallite size, specific surface area, pore volume and optical band gap of the samples. The samples were characterized using powder X-ray diffraction, thermal gravimetric analysis, FT-IR spectroscopy, UV-Visible diffuse reflectance spectroscopy, surface area measurements, field emission scanning electron microscopy coupled with energy dispersive X-ray analysis and transmission electron microscopy. The chemical activity of the samples was tested by catalytic reduction of 4-nitrophenol with NaBH4.

High-Temperature Smart Structures for Engine Noise Reduction and Performance Enhancement

NASA Technical Reports Server (NTRS)

Quackenbush, Todd R.; McKillip, Robert M., Jr.

2011-01-01

One of key NASA goals is to develop and integrate noise reduction technology to enable unrestricted air transportation service to all communities. One of the technical priorities of this activity has been to account for and reduce noise via propulsion/airframe interactions, identifying advanced concepts to be integrated with the airframe to mitigate these noise-producing mechanisms. An adaptive geometry chevron using embedded smart structures technology offers the possibility of maximizing engine performance while retaining and possibly enhancing the favorable noise characteristics of current designs. New high-temperature shape memory alloy (HTSMA) materials technology enables the devices to operate in both low-temperature (fan) and high-temperature (core) exhaust flows. Chevron-equipped engines have demonstrated reduced noise in testing and operational use. It is desirable to have the noise benefits of chevrons in takeoff/landing conditions, but have them deployed into a minimum drag position for cruise flight. The central feature of the innovation was building on rapidly maturing HTSMA technology to implement a next-generation aircraft noise mitigation system centered on adaptive chevron flow control surfaces. In general, SMA-actuated devices have the potential to enhance the demonstrated noise reduction effectiveness of chevron systems while eliminating the associated performance penalty. The use of structurally integrated smart devices will minimize the mechanical and subsystem complexity of this implementation. The central innovations of the effort entail the modification of prior chevron designs to include a small cut that relaxes structural stiffness without compromising the desired flow characteristics over the surface; the reorientation of SMA actuation devices to apply forces to deflect the chevron tip, exploiting this relaxed stiffness; and the use of high-temperature SMA (HTSMA) materials to enable operation in the demanding core chevron environment. The overall conclusion of these design studies was that the cut chevron concept is a critical enabling step in bringing the variable geometry core chevron within reach. The presence of the cut may be aerodynamically undesirable in some respects, but it is present only when the chevron is not immersed in the core jet exhaust. When deployed, the gap closes as the chevron tip enters the high-speed, high-temperature core stream. Aeroacoustic testing and flow visualization support the contention that this cut is inconsequential to chevron performance.

Influence of thermal stratification and slip conditions on stagnation point flow towards variable thicked Riga plate

NASA Astrophysics Data System (ADS)

Anjum, A.; Mir, N. A.; Farooq, M.; Khan, M. Ijaz; Hayat, T.

2018-06-01

This article addresses thermally stratified stagnation point flow of viscous fluid induced by a non-linear variable thicked Riga plate. Velocity and thermal slip effects are incorporated to disclose the flow analysis. Solar thermal radiation phenomenon is implemented to address the characteristics of heat transfer. Variations of different physical parameters on the horizontal velocity and temperature distributions are described through graphs. Graphical interpretations of skin friction coefficient (drag force at the surface) and Nusselt number (rate of heat transfer) are also addressed. Modified Hartman number and thermal stratification parameter result in reduction of temperature distribution.

The Selective Epitaxy of Silicon at Low Temperatures.

NASA Astrophysics Data System (ADS)

Lou, Jen-Chung

1991-01-01

This dissertation has developed a process for the selective epitaxial growth (SEG) of silicon at low temperatures using a dichlorosilane-hydrogen mixture in a hot-wall low pressure chemical vapor deposition (LPCVD) reactor. Some basic issues concerning the quality of epilayers --substrate preparation, ex-situ and in-situ cleaning, and deposition cycle, have been studied. We find it necessary to use a plasma etch to open epitaxial windows for the SEG of Si. A cycled plasma etch, a thin sacrificial oxide growth, and an oxide etching step can completely remove plasma-etch-induced surface damage and contaminants, which result in high quality epilayers. A practical wafer cleaning step is developed for low temperature Si epitaxial growth. An ex-situ HF vapor treatment can completely remove chemical oxide from the silicon surface and retard the reoxidation of the silicon surface. An in-situ low-concentration DCS cycle can aid in decomposition of surface oxide during a 900 ^circC H_2 prebake step. An HF vapor treatment combined with a low-concentration of DCS cycle consistently achieves defect-free epilayers at 850^circC and lower temperatures. We also show that a BF_sp{2}{+ } or F^+ ion implantation is a potential ex-situ wafer cleaning process for SEG of Si at low temperatures. The mechanism for the formation of surface features on Si epilayers is also discussed. Based on O ^+ ion implantation, we showed that the oxygen incorporation in silicon epilayers suppresses the Si growth rate. Therefore, we attribute the formation of surface features to the local reduction of the Si growth rate due to the dissolution of oxide islands at the epi/substrate interface. Finally, with this developed process for the SEG of silicon, defect-free overgrown epilayers are also obtained. This achievement demonstrates the feasibility for the future silicon-on-oxide (SOI) manufacturing technology.

The role of clouds in early Pliocene warmth

NASA Astrophysics Data System (ADS)

Burls, N.; Fedorov, A. V.

2013-12-01

The climate of the early Pliocene (4-5 million years ago) presents a challenging puzzle to climate scientists - although the Earth experienced atmospheric CO2 concentrations similar to the elevated levels seen today, many climate characteristics in both low to high latitudes were very different. In particular, a salient feature of the modern climate, the pronounced cold tongues on the eastern sides of the Pacific and Atlantic equatorial basins, were much weaker. At the same time the ocean meridional (equator-to-pole) temperature gradient was also reduced. However, state-of-the-art coupled general circulation models forced with elevated CO2 concentrations and reconstructed Pliocene boundary conditions fail to capture the full extent of warming in the equatorial cold tongues and high-latitude regions relative to present-day conditions, and hence the corresponding reduction in meridional and zonal sea surface temperature gradients suggested by paleoclimatic evidence (as reviewed by Fedorov et al., 2013, Nature 496). A number of physical processes unresolved or underestimated by these models have been proposed as a contributing factor or a potential driving force resulting in these differences. Amongst the proposed hypotheses is the idea that different cloud properties might be the key to the Pliocene puzzle. In this study we demonstrate how a modified spatial distribution in cloud albedo could have been responsible for sustaining Pliocene climate. In particular, we show that a reduction in the meridional gradient in cloud albedo can sustain reduced meridional and zonal gradients in sea surface temperature, an expanded warm pool in the ocean, weaker Hadley and Walker circulations in the atmosphere, and amplified high-latitude warming. Having conducted a range of modified cloud albedo experiments, we arrive at our Pliocene simulation, which shows an excellent agreement with proxy sea surface temperature data from the major equatorial and coastal upwelling regions, the tropical warm pool, and the mid- and high- latitudes. A good agreement is also achieved with available subsurface temperature data. Within this simulated early Pliocene state, we explore the major climatic features such as ENSO and the Atlantic meridional overturning circulation (AMOC).

Adsorption of Poly(ethylene oxide)-Poly(lactide) Copolymers. Effects of Composition and Degradation.

PubMed

Muller, Dries; Carlsson, Fredrik; Malmsten, Martin

2001-04-01

The effect of chemical degradation of two diblock copolymers of poly(ethylene oxide) (E) and poly(lactide) (L), E(39)L(5) and E(39)L(20), on their adsorption at silica and methylated silica was investigated with in situ ellipsometry. Steric stablization of polystyrene dispersions was investigated in relation to degradation. Hydrolysis of the poly(lactide) block of the copolymers was followed at different temperatures and pH by using HPLC to measure the occurrence of lactic acid in solution. The block copolymers were quite stable in pH-unadjusted solution at low temperature, whereas degradation was facilitated by increasing temperature or lowering of the pH. Lower degradation rates of E(39)L(20) where observed at low temperature in comparison with those of E(39)L(5), whereas the degradation rates of the copolymers were quantitatively similar at high temperature. The adsorption of the copolymers at methylated silica substrates decreased with increasing degree of degradation due to the reduction in the ability of hydrophobic block to anchor the copolymer layer at the surface. At silica the adsorption initially increased with increasing degradation, particularly for E(39)L(20) due to deposition of aggregates onto the surface. After extensive degradation the adsorption of the copolymers at both silica and methylated silica resembled that of the corresponding poly(ethylene oxide) homopolymer. Overall, it was found that the eventual reduction in adsorption occurred at a lower degree of degradation for E(39)L(5) than for E(39)L(20). Mean-field calculations showed a reduced anchoring for the block copolymers with decreasing poly(lactide) block length at hydrophobic surfaces. In accordance with this finding, it was observed that polystyrene dispersions were stabilized by E(39)L(20) or E(39)L(5) in a way that depended on both the lactide block length and the degree of degradation. Upon degradation of the hydrophobic block, stabilization of the polystyrene dispersions was maintained initially, but eventually degradation resulted in destabilization. The average residual copolymer concentration required for stabilization of the polystyrene dispersions was much higher than the corresponding concentration of intact copolymer required for stabilization. Copyright 2001 Academic Press.

Reduction and Analysis of Phosphor Thermography Data With the IHEAT Software Package

NASA Technical Reports Server (NTRS)

Merski, N. Ronald

1998-01-01

Detailed aeroheating information is critical to the successful design of a thermal protection system (TPS) for an aerospace vehicle. This report describes NASA Langley Research Center's (LaRC) two-color relative-intensity phosphor thermography method and the IHEAT software package which is used for the efficient data reduction and analysis of the phosphor image data. Development of theory is provided for a new weighted two-color relative-intensity fluorescence theory for quantitatively determining surface temperatures on hypersonic wind tunnel models; an improved application of the one-dimensional conduction theory for use in determining global heating mappings; and extrapolation of wind tunnel data to flight surface temperatures. The phosphor methodology at LaRC is presented including descriptions of phosphor model fabrication, test facilities and phosphor video acquisition systems. A discussion of the calibration procedures, data reduction and data analysis is given. Estimates of the total uncertainties (with a 95% confidence level) associated with the phosphor technique are shown to be approximately 8 to 10 percent in the Langley's 31-Inch Mach 10 Tunnel and 7 to 10 percent in the 20-Inch Mach 6 Tunnel. A comparison with thin-film measurements using two-inch radius hemispheres shows the phosphor data to be within 7 percent of thin-film measurements and to agree even better with predictions via a LATCH computational fluid dynamics solution (CFD). Good agreement between phosphor data and LAURA CFD computations on the forebody of a vertical takeoff/vertical lander configuration at four angles of attack is also shown. In addition, a comparison is given between Mach 6 phosphor data and laminar and turbulent solutions generated using the LAURA, GASP and LATCH CFD codes. Finally, the extrapolation method developed in this report is applied to the X-34 configuration with good agreement between the phosphor extrapolation and LAURA flight surface temperature predictions. The phosphor process outlined in the paper is believed to provide the aerothermodynamic community with a valuable capability for rapidly obtaining (4 to 5 weeks) detailed heating information needed in TPS design.

Effect of Fermi surface nesting on resonant spin excitations in Ba{<_1-x}K{<_x}Fe{<_2}As{<_2}.

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

Castellan, J.-P.; Rosenkranz, S.; Goremychkin, E.A.

2011-01-01

We report inelastic neutron scattering measurements of the resonant spin excitations in Ba{sub 1-x}K{sub x}Fe{sub 2}As{sub 2} over a broad range of electron band filling. The fall in the superconducting transition temperature with hole doping coincides with the magnetic excitations splitting into two incommensurate peaks because of the growing mismatch in the hole and electron Fermi surface volumes, as confirmed by a tight-binding model with s{sub {+-}}-symmetry pairing. The reduction in Fermi surface nesting is accompanied by a collapse of the resonance binding energy and its spectral weight, caused by the weakening of electron-electron correlations.

Modelling of aflatoxin G1 reduction by kefir grain using response surface methodology.

PubMed

Ansari, Farzaneh; Khodaiyan, Faramarz; Rezaei, Karamatollah; Rahmani, Anosheh

2015-01-01

Aflatoxin G1 (AFG1) is one of the main toxic contaminants in pistachio nuts and causes potential health hazards. Hence, AFG1 reduction is one of the main concerns in food safety. Kefir-grains contain symbiotic association of microorganisms well known for their aflatoxin decontamination effects. In this study, a central composite design (CCD) using response surface methodology (RSM) was applied to develop a model in order to predict AFG1 reduction in pistachio nuts by kefir-grain (already heated at 70 and 110°C). The independent variables were: toxin concentration (X1: 5, 10, 15, 20 and 25 ng/g), kefir-grain level (X2: 5, 10, 20, 10 and 25%), contact time (X3: 0, 2, 4, 6 and 8 h), and incubation temperature (X4: 20, 30, 40, 50 and 60°C). There was a significant reduction in AFG1 (p < 0.05) when pre-heat-treated kefir-grain used. The variables including X1, X3 and the interactions between X2-X4 as well as X3-X4 have significant effects on AFG1 reduction. The model provided a good prediction of AFG1 reduction under the assay conditions. Optimization was used to enhance the efficiency of kefir-grain on AFG1 reduction. The optimum conditions for the highest AFG1 reduction (96.8%) were predicted by the model as follows: toxin concentration = 20 ng/g, kefir-grain level = 10%, contact time = 6 h, and incubation temperature = 30°C which validated practically in six replications.

Methanol synthesis on ZnO(0001{sup ¯}). IV. Reaction mechanisms and electronic structure

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

Frenzel, Johannes, E-mail: johannes.frenzel@theochem.rub.de; Marx, Dominik

2014-09-28

Methanol synthesis from CO and H{sub 2} over ZnO, which requires high temperatures and high pressures giving rise to a complex interplay of physical and chemical processes over this heterogeneous catalyst surface, is investigated using ab initio simulations. The redox properties of the surrounding gas phase are known to directly impact on the catalyst properties and thus, set the overall catalytic reactivity of this easily reducible oxide material. In Paper III of our series [J. Kiss, J. Frenzel, N. N. Nair, B. Meyer, and D. Marx, J. Chem. Phys. 134, 064710 (2011)] we have qualitatively shown that for the partiallymore » hydroxylated and defective ZnO(0001{sup ¯}) surface there exists an intricate network of surface chemical reactions. In the present study, we employ advanced molecular dynamics techniques to resolve in detail this reaction network in terms of elementary steps on the defective surface, which is in stepwise equilibrium with the gas phase. The two individual reduction steps were investigated by ab initio metadynamics sampling of free energy landscapes in three-dimensional reaction subspaces. By also sampling adsorption and desorption processes and thus molecular species that are in the gas phase but close to the surface, our approach successfully generated several alternative pathways of methanol synthesis. The obtained results suggest an Eley-Rideal mechanism for both reduction steps, thus involving “near-surface” molecules from the gas phase, to give methanol preferentially over a strongly reduced catalyst surface, while important side reactions are of Langmuir-Hinshelwood type. Catalyst re-reduction by H{sub 2} stemming from the gas phase is a crucial process after each reduction step in order to maintain the catalyst's activity toward methanol formation and to close the catalytic cycle in some reaction channels. Furthermore, the role of oxygen vacancies, side reactions, and spectator species is investigated and mechanistic details are discussed based on extensive electronic structure analysis.« less

Aerosol reductions could dominate regional climate responses in low GHG emission scenarios

NASA Astrophysics Data System (ADS)

Samset, B. H.; Sand, M.; Smith, C. J.; Bauer, S.; Forster, P.; Fuglestvedt, J. S.; Osprey, S. M.; Schleussner, C. F.

2017-12-01

Limiting global warming to current political goals requires strong, rapid mitigation of anthropogenic greenhouse gas (GHG) emissions. Concurrently, emissions of anthropogenic aerosols will decline sharply, due to co-emission with greenhouse gases, and future measures to improve air quality. As the net climate effect of GHG and aerosol emissions over the industrial era is poorly constrained, predicting the impact of strong aerosol emission reductions remains challenging. Here we investigate the isolated and compound climate impacts from removing present day anthropogenic emissions of black carbon (BC), organic carbon (OC) and SO2, and moderate, near term GHG dominated global warming, using four coupled climate models. As the dominating effect of aerosol emission reduction is a removal of cooling from sulphur, the resulting climate impacts amplify those of GHG induced warming. BC emissions contribute little to reducing surface warming, but have stronger regional impacts. For the major aerosol emission regions, extreme weather indices are more sensitive to aerosol removal than to GHG increases, per degree of surface warming. East Asia in particular stands out, mainly due to the high present regional aerosol emissions. We show how present climate models indicate that future regional climate change will depend strongly on changes in loading and distribution of aerosols in the atmosphere, in addition to surface temperature change.

Oxidation and reduction under cover: Chemistry at the confined space between ultra-thin nanoporous silicates and Ru(0001)

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

J. Anibal Boscoboinik; Zhong, Jian -Qiang; Kestell, John

2016-03-23

The oxidation and reduction of Ru(0001) surfaces at the confined space between two-dimensional nanoporous silica frameworks and Ru(0001) have been investigated using synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS). The porous nature of the frameworks and the weak interaction between the silica and the ruthenium substrate allow oxygen and hydrogen molecules to go through the nanopores and react with the metal at the interface between the silica framework and the metal surface. In this work, three types of two-dimensional silica frameworks have been used to study their influence in the oxidation and reduction of the ruthenium surface at elevated pressuresmore » and temperatures. These frameworks are bilayer silica (0.5 nm thick), bilayer aluminosilicate (0.5 nm thick), and zeolite MFI nanosheets (3 nm thick). It is found that the silica frameworks stay essentially intact under these conditions, but they strongly affect the oxidation of ruthenium, with the 0.5 nm thick aluminosilicate bilayer completely inhibiting the oxidation. Furthermore, the latter is believed to be related to the lower chemisorbed oxygen content arising from electrostatic interactions between the negatively charged aluminosilicate framework and the Ru(0001) substrate.« less

Enhancement of the electrooxidation of ethanol on Pt-Sn-P/C catalysts prepared by chemical deposition process

NASA Astrophysics Data System (ADS)

Xue, Xinzhong; Ge, Junjie; Tian, Tian; Liu, Changpeng; Xing, Wei; Lu, Tianhong

In this paper, five Pt 3Sn 1/C catalysts have been prepared using three different methods. It was found that phosphorus deposited on the surface of carbon with Pt and Sn when sodium hypophosphite was used as reducing agent by optimization of synthetic conditions such as pH in the synthetic solution and temperature. The deposition of phosphorus should be effective on the size reduction and markedly reduces PtSn nanoparticle size, and raise electrochemical active surface (EAS) area of catalyst and improve the catalytic performance. TEM images show PtSnP nanoparticles are highly dispersed on the carbon surface with average diameters of 2 nm. The optimum composition is Pt 3Sn 1P 2/C (note PtSn/C-3) catalyst in my work. With this composition, it shows very high activity for the electrooxidation of ethanol and exhibit enhanced performance compared with other two Pt 3Sn 1/C catalysts that prepared using ethylene glycol reduction method (note PtSn/C-EG) and borohydride reduction method (note PtSn/-B). The maximum power densities of direct ethanol fuel cell (DEFC) were 61 mW cm -2 that is 150 and 170% higher than that of the PtSn/C-EG and PtSn/C-B catalyst.

Aerosol contribution to the rapid warming of near-term climate under RCP 2.6

NASA Astrophysics Data System (ADS)

Chalmers, N.; Highwood, E. J.; Hawkins, E.; Sutton, R.; Wilcox, L. J.

2012-09-01

The importance of aerosol emissions for near term climate projections is investigated by analysing simulations with the HadGEM2-ES model under two different emissions scenarios: RCP2.6 and RCP4.5. It is shown that the near term warming projected under RCP2.6 is greater than under RCP4.5, even though the greenhouse gas forcing is lower. Rapid and substantial reductions in sulphate aerosol emissions due to a reduction of coal burning in RCP2.6 lead to a reduction in the negative shortwave forcing due to aerosol direct and indirect effects. Indirect effects play an important role over the northern hemisphere oceans, especially the subtropical northeastern Pacific where an anomaly of 5-10 Wm-2 develops. The pattern of surface temperature change is consistent with the expected response to this surface radiation anomaly, whilst also exhibiting features that reflect redistribution of energy, and feedbacks, within the climate system. These results demonstrate the importance of aerosol emissions as a key source of uncertainty in near term projections of global and regional climate.

Arctic spring ozone reduction associated with projected sea ice loss

NASA Astrophysics Data System (ADS)

Deser, C.; Sun, L.; Tomas, R. A.; Polvani, L. M.

2013-12-01

The impact of Arctic sea ice loss on the stratosphere is investigated using the Whole-Atmosphere Community Climate Model (WACCM), by prescribing the sea ice in the late 20th century and late 21st century, respectively. The localized Sea Surface Temperature (SST) change associated with sea ice melt is also included in the future run. Overall, the model simulates a negative annular-mode response in the winter and spring. In the stratosphere, polar vortex strengthens from February to April, peaking in March. Consistent with it, there is an anomalous cooling in the high-latitude stratosphere, and polar cap ozone reduction is up to 20 DU. Since the difference between these two runs lies only in the sea ice and localized SST in the Arctic, the stratospheric circulation and ozone changes can be attributed to the surface forcing. Eliassen-Palm analysis reveals that the upward propagation of planetary waves is suppressed in the spring as a consequence of sea ice loss. The reduction in propagation causes less wave dissipation and thus less zonal wind deceleration in the extratropical stratosphere.

a Novel Catalyst for Reductive Dechlorination of Chlorobenzene in Subcritical Water:. Bifunctional Fe/ZrO2

NASA Astrophysics Data System (ADS)

Wei, Guang-Tao; Wei, Chao-Hai; He, Feng-Mei; Wu, Chao-Fei

Bifunctional Fe/ZrO2 was prepared by mechanical mixing method, and its bifunctional effect on reductive dechlorination of chlorobenzene in subcritical water was studied. Dechlorination efficiency increased with increasing iron content in catalyst and catalyst amount. Dechlorination efficiency slowed when the iron content in catalyst reached 30%; bifunctional catalyst of Fe/ZrO2 was more efficient in dechlorination of chlorobenzene than Fe alone. Catalyst of Fe (30%)/ZrO2 was characterized by means of X-ray diffraction (XRD), H2 temperature programmed desorption (H2-TPD), and N2 adsorption. The possible mechanism of dechlorination in subcritical water by this bifunctional catalyst was proposed. H+ produced in the water dissociation formed the highly reactive spillover hydrogen on the surface of catalyst, and then reacted with chlorobenzene adsorbed on the catalyst surface by ZrO2 to form benzene and chloride ions.

Biopolymer coated gold nanocrystals prepared using the green chemistry approach and their shape-dependent catalytic and surface-enhanced Raman scattering properties.

PubMed

Chou, Chih-Wei; Hsieh, Hui-Hsuan; Hseu, You-Cheng; Chen, Ko-Shao; Wang, Gou-Jen; Chang, Hsien-Chang; Pan, Yong-Li; Wei, Yi-Syuan; Chang, Ko Hsin; Harn, Yeu-Wei

2013-07-21

This study deals with the preparation of multi-shaped nanoscale gold crystals under synthetically simple, green, and efficient conditions using a seed-mediated growth approach in the presence of hyaluronic acid (HA). These highly biocompatible multi-shaped gold nanocrystals were examined to evaluate their catalytic and surface enhanced Raman scattering (SERS) properties. The results show that the size and shape of the nanocrystals are mainly correlated to the amount of seed, seed size, HA concentration, and reaction temperature. Gold seeds accelerate the reduction of the gold precursor to form gold nanocrystals using HA. The HA serves as a reducing agent and a growth template for the reduction of Au(III) and nanocrystal stabilization. The multi-shaped gold nanocrystals showed superior catalytic properties and higher SERS performance. The simple, green approach efficiently controls the nanocrystals and creates many opportunities for future applications.

Decreased calcification in the Southern Ocean over the satellite record

NASA Astrophysics Data System (ADS)

Freeman, Natalie M.; Lovenduski, Nicole S.

2015-03-01

Widespread ocean acidification is occurring as the ocean absorbs anthropogenic carbon dioxide from the atmosphere, threatening marine ecosystems, particularly the calcifying plankton that provide the base of the marine food chain and play a key role within the global carbon cycle. We use satellite estimates of particulate inorganic carbon (PIC), surface chlorophyll, and sea surface temperature to provide a first estimate of changing calcification rates throughout the Southern Ocean. From 1998 to 2014 we observe a 4% basin-wide reduction in summer calcification, with ˜9% reductions in large regions (˜1 × 106 km2) of the Pacific and Indian sectors. Southern Ocean trends are spatially heterogeneous and primarily driven by changes in PIC concentration (suspended calcite), which has declined by ˜24% in these regions. The observed decline in Southern Ocean calcification and PIC is suggestive of large-scale changes in the carbon cycle and provides insight into organism vulnerability in a changing environment.

Passivation effect on optical and electrical properties of molecular beam epitaxy-grown HgCdTe/CdTe/Si layers

NASA Astrophysics Data System (ADS)

Kiran, Rajni; Mallick, Shubhrangshu; Hahn, Suk-Ryong; Lee, T. S.; Sivananthan, Sivalingam; Ghosh, Siddhartha; Wijewarnasuriya, P. S.

2006-06-01

The effects of passivation with two different passivants, ZnS and CdTe, and two different passivation techniques, physical vapor deposition (PVD) and molecular beam epitaxy (MBE), were quantified in terms of the minority carrier lifetime and extracted surface recombination velocity on both MBE-grown medium-wavelength ir (MWIR) and long-wavelength ir HgCdTe samples. A gradual increment of the minority carrier lifetime was reported as the passivation technique was changed from PVD ZnS to PVD CdTe, and finally to MBE CdTe, especially at low temperatures. A corresponding reduction in the extracted surface recombination velocity in the same order was also reported for the first time. Initial data on the 1/ f noise values of as-grown MWIR samples showed a reduction of two orders of noise power after 1200-Å ZnS deposition.

Stabilizing nanostructured solid oxide fuel cell cathode with atomic layer deposition.

PubMed

Gong, Yunhui; Palacio, Diego; Song, Xueyan; Patel, Rajankumar L; Liang, Xinhua; Zhao, Xuan; Goodenough, John B; Huang, Kevin

2013-09-11

We demonstrate that the highly active but unstable nanostructured intermediate-temperature solid oxide fuel cell cathode, La0.6Sr0.4CoO3-δ (LSCo), can retain its high oxygen reduction reaction (ORR) activity with exceptional stability for 4000 h at 700 °C by overcoating its surfaces with a conformal layer of nanoscale ZrO2 films through atomic layer deposition (ALD). The benefits from the presence of the nanoscale ALD-ZrO2 overcoats are remarkable: a factor of 19 and 18 reduction in polarization area-specific resistance and degradation rate over the pristine sample, respectively. The unique multifunctionality of the ALD-derived nanoscaled ZrO2 overcoats, that is, possessing porosity for O2 access to LSCo, conducting both electrons and oxide-ions, confining thermal growth of LSCo nanoparticles, and suppressing surface Sr-segregation is deemed the key enabler for the observed stable and active nanostructured cathode.