Magnetic properties and macroscopic heterogeneity of FeCoNbB Hitperms

NASA Astrophysics Data System (ADS)

Butvin, Pavol; Butvinová, Beata; Sitek, Jozef; Degmová, Jarmila; Vlasák, Gabriel; Švec, Peter; Janičkovič, Dušan

Nanocrystalline ribbons of Fe 81-xCo xNb 7B 12 (where x ranges from 0 to 40.5 at%) Hitperm alloys have been investigated as to their basic magnetic properties and the influence of the macroscopic heterogeneity. Different crystalline share at surfaces compared with the volume average is observed by conversion electron Mössbauer spectroscopy (CEMS) and Mössbauer spectroscopy (MS), respectively. This marks the presence of macroscopic heterogeneity in these Hitperms. The heterogeneity is generally more significant in Ar-annealed samples than in the vacuum-annealed ones. The characteristic slant hysteresis loops (hard-ribbon-axis) are seen as a rule with few exceptions. An inspection of hysteresis loop response of resin potted samples shows that the surfaces bi-axially squeeze the ribbon interior in heterogeneous Hitperms when the ribbons cool down after annealing. Certain compositions show macroscopic viscous flow prior to crystallization so the heterogeneity gets another chance to induce anisotropy during annealing. The induction attains 1.5 T but saturates poorly due to the heterogeneity and the ensuing anisotropy. Moreover the heterogeneity appears to hamper the crystallization within the ribbon interior. Unlike Finemets, the density of these Hitperms show no pronounced trend with annealing.

3D Rheological Modeling of NW Intraplate Europe, Deciphering Spatial Integrated strength patterns, Mechanical Strong Layering and EET

NASA Astrophysics Data System (ADS)

Beekman, F.; Hardebol, N.; Cloetingh, S.; Tesauro, M.

2006-12-01

Better understanding of 3D rheological heterogeneity of the European Lithosphere provide the key to tie the recorded intraplate deformation pattern to stress fields transmitted into plate interior from plate boundary forces. The first order strain patterns result from stresses transmitted through the European lithosphere that is marked by a patchwork of high strength variability from inherited structural and compositional heterogeneities and upper mantle thermal perturbations. As the lithospheric rheology depends primarily on its spatial structure, composition and thermal estate, the 3D strength model for the European lithosphere relies on a 3D compositional model that yields the compositional heterogeneities and an iteratively calculated thermal cube using Fouriers law for heat conduction. The accurate appraisal of spatial strength variability results from proper mapping and integration of the geophysical compositional and thermal input parameters. Therefore, much attention has been paid to a proper description of first order structural and tectonic features that facilitate compilation of the compositional and thermal input models. As such, the 3D strength model reflects the thermo-mechanical structure inherited from the Europeans polyphase deformation history. Major 3D spatial mechanical strength variability has been revealed. The East-European and Fennoscandian Craton to the NE exhibit high strength (30-50 1012 N/m) from low mantle temperatures and surface heatflow of 35-60 mW/m2 while central and western Europe reflect a polyphase Phanerozoic thermo- tectonic history. Here, regions with high rigidity are formed primarily by patches of thermally stabilized Variscan Massifs (e.g. Rhenish, Armorican, Bohemian, and Iberian Massif) with low heatflow and lithospheric thickness values (50-65 mW/m2; 110-150 km) yielding strengths of ~15-25 1012 N/m. In contrast, major axis of weakened lithosphere coincides with Cenozoic Rift System (e.g. Upper and Lower Rhine Grabens, Pannonian Basin and Massif Central) attributed to the presence of tomographically imaged plumes. This study has elucidated the memory of the present-days Europeans lithosphere induced by compositional and thermal heterogeneities. The resulting lateral strength variations has a clear signature of the pst lithospheres polyphase deformation and also entails active tectonics, tectonically induced topography and surface processes.

Profiling bacterial diversity in a limestone cave of the western Loess Plateau of China

PubMed Central

Wu, Yucheng; Tan, Liangcheng; Liu, Wuxing; Wang, Baozhan; Wang, Jianjun; Cai, Yanjun; Lin, Xiangui

2015-01-01

Bacteria and archaea sustain subsurface cave ecosystems by dominating primary production and fueling biogeochemical cyclings, despite the permanent darkness and shortage of nutrients. However, the heterogeneity and underlying mechanism of microbial diversity in caves, in particular those well connect to surface environment are largely unexplored. In this study, we examined the bacterial abundance and composition in Jinjia Cave, a small and shallow limestone cave located on the western Loess Plateau of China, by enumerating and pyrosequencing small subunit rRNA genes. The results clearly reveal the contrasting bacterial community compositions in relation to cave habitat types, i.e., rock wall deposit, aquatic sediment, and sinkhole soil, which are differentially connected to the surface environment. The deposits on the cave walls were dominated by putative cave-specific bacterial lineages within the γ-Proteobacteria or Actinobacteria that are routinely found on cave rocks around the world. In addition, sequence identity with known functional groups suggests enrichments of chemolithotrophic bacteria potentially involved in autotrophic C fixation and inorganic N transformation on rock surfaces. By contrast, bacterial communities in aquatic sediments were more closely related to those in the overlying soils. This is consistent with the similarity in elemental composition between the cave sediment and the overlying soil, implicating the influence of mineral chemistry on cave microhabitat and bacterial composition. These findings provide compelling molecular evidence of the bacterial community heterogeneity in an East Asian cave, which might be controlled by both subsurface and surface environments. PMID:25870592

Profiling bacterial diversity in a limestone cave of the western Loess Plateau of China.

PubMed

Wu, Yucheng; Tan, Liangcheng; Liu, Wuxing; Wang, Baozhan; Wang, Jianjun; Cai, Yanjun; Lin, Xiangui

2015-01-01

Bacteria and archaea sustain subsurface cave ecosystems by dominating primary production and fueling biogeochemical cyclings, despite the permanent darkness and shortage of nutrients. However, the heterogeneity and underlying mechanism of microbial diversity in caves, in particular those well connect to surface environment are largely unexplored. In this study, we examined the bacterial abundance and composition in Jinjia Cave, a small and shallow limestone cave located on the western Loess Plateau of China, by enumerating and pyrosequencing small subunit rRNA genes. The results clearly reveal the contrasting bacterial community compositions in relation to cave habitat types, i.e., rock wall deposit, aquatic sediment, and sinkhole soil, which are differentially connected to the surface environment. The deposits on the cave walls were dominated by putative cave-specific bacterial lineages within the γ-Proteobacteria or Actinobacteria that are routinely found on cave rocks around the world. In addition, sequence identity with known functional groups suggests enrichments of chemolithotrophic bacteria potentially involved in autotrophic C fixation and inorganic N transformation on rock surfaces. By contrast, bacterial communities in aquatic sediments were more closely related to those in the overlying soils. This is consistent with the similarity in elemental composition between the cave sediment and the overlying soil, implicating the influence of mineral chemistry on cave microhabitat and bacterial composition. These findings provide compelling molecular evidence of the bacterial community heterogeneity in an East Asian cave, which might be controlled by both subsurface and surface environments.

Relating Silica Scaling in Reverse Osmosis to Membrane Surface Properties.

PubMed

Tong, Tiezheng; Zhao, Song; Boo, Chanhee; Hashmi, Sara M; Elimelech, Menachem

2017-04-18

We investigated the relationship between membrane surface properties and silica scaling in reverse osmosis (RO). The effects of membrane hydrophilicity, free energy for heterogeneous nucleation, and surface charge on silica scaling were examined by comparing thin-film composite polyamide membranes grafted with a variety of polymers. Results show that the rate of silica scaling was independent of both membrane hydrophilicity and free energy for heterogeneous nucleation. In contrast, membrane surface charge demonstrated a strong correlation with the extent of silica scaling (R 2 > 0.95, p < 0.001). Positively charged membranes significantly facilitated silica scaling, whereas a more negative membrane surface charge led to reduced scaling. This observation suggests that deposition of negatively charged silica species on the membrane surface plays a critical role in silica scale formation. Our findings provide fundamental insights into the mechanisms governing silica scaling in reverse osmosis and highlight the potential of membrane surface modification as a strategy to reduce silica scaling.

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

Li, Lidong; Zhou, Lu; Ould-Chikh, Samy

Surface composition and structure are of vital importance for heterogeneous catalysts, especially for bimetallic catalysts, which often vary as a function of reaction conditions (known as surface segregation). The preparation of bimetallic catalysts with controlled metal surface composition and structure is very challenging. In this study, we synthesize a series of Ni/Pt bimetallic catalysts with controlled metal surface composition and structure using a method derived from surface organometallic chemistry. The evolution of the surface composition and structure of the obtained bimetallic catalysts under simulated reaction conditions is investigated by various techniques, which include CO-probe IR spectroscopy, high-angle annular dark-field scanningmore » transmission electron microscopy, energy-dispersive X-ray spectroscopy, extended X-ray absorption fine structure analysis, X-ray absorption near-edge structure analysis, XRD, and X-ray photoelectron spectroscopy. It is demonstrated that the structure of the bimetallic catalyst is evolved from Pt monolayer island-modified Ni nanoparticles to core–shell bimetallic nanoparticles composed of a Ni-rich core and a Ni/Pt alloy shell upon thermal treatment. As a result, these catalysts are active for the dry reforming of methane, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure.« less

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

Li, Lidong; Zhou, Lu; Ould-Chikh, Samy

The surface composition and structure are of vital importance for heterogeneous catalysts, especially for bimetallic catalysts, which often vary as a function of reaction conditions (known as surface segregation). The preparation of bimetallic catalysts with controlled metal surface composition and structure is very challenging. In this study, we synthesize a series of Ni/Pt bimetallic catalysts with controlled metal surface composition and structure using a method derived from surface organometallic chemistry. Moreover, the evolution of the surface composition and structure of the obtained bimetallic catalysts under simulated reaction conditions is investigated by various techniques, which include CO-probe IR spectroscopy, high-angle annularmore » dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, extended X-ray absorption fine structure analysis, X-ray absorption near-edge structure analysis, XRD, and X-ray photoelectron spectroscopy. It is demonstrated that the structure of the bimetallic catalyst is evolved from Pt monolayer island-modified Ni nanoparticles to core–shell bimetallic nanoparticles composed of a Ni-rich core and a Ni/Pt alloy shell upon thermal treatment. The catalysts are active for the dry reforming of methane, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure.« less

Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Hässig, M.; Altwegg, K.; Balsiger, H.; Bar-Nun, A.; Berthelier, J. J.; Bieler, A.; Bochsler, P.; Briois, C.; Calmonte, U.; Combi, M.; De Keyser, J.; Eberhardt, P.; Fiethe, B.; Fuselier, S. A.; Galand, M.; Gasc, S.; Gombosi, T. I.; Hansen, K. C.; Jäckel, A.; Keller, H. U.; Kopp, E.; Korth, A.; Kührt, E.; Le Roy, L.; Mall, U.; Marty, B.; Mousis, O.; Neefs, E.; Owen, T.; Rème, H.; Rubin, M.; Sémon, T.; Tornow, C.; Tzou, C.-Y.; Waite, J. H.; Wurz, P.

2015-01-01

Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well-sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: water, carbon monoxide, and carbon dioxide. These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface.

Experimental Constraints on the Chemical Differentiation of Mercurys Mantle

NASA Technical Reports Server (NTRS)

Boujibar, A.; Righter, K.; Pando, K.; Danielson, L.

2015-01-01

Mercury is known as being the most reduced terrestrial planet with the highest core/mantle ratio. Results from MESSENGER spacecraft have shown that its surface is FeO-poor (2-4 wt%) and S-rich (up to 6-7 wt%), which confirms the reducing nature of its silicate mantle. In addition several features suggest important melting stages of the Mercurian mantle: widespread volcanic deposits on its surface, a high crustal thickness (approximately 10% of the planet's volume) and chemical compositions of its surface suggesting several stages of differentiation and remelting processes. Therefore it is likely that igneous processes like magma ocean crystallization and continuous melting have induced chemical and mineralogical heterogeneities in the Mercurian mantle. The extent and nature of compositional variations produced by partial melting remains poorly constrained for the particular compositions of Mercury (very reducing conditions, low FeO-contents and high sulfur-contents). Melting experiments with bulk Mercury-analogue compositions are scarce and with poorly con-trolled starting compositions. Therefore additional experimental data are needed to better understand the differentiation processes that lead to the observed chemical compositions of Mercury's surface.

Chemical surface deposition of ultra-thin semiconductors

DOEpatents

McCandless, Brian E.; Shafarman, William N.

2003-03-25

A chemical surface deposition process for forming an ultra-thin semiconducting film of Group IIB-VIA compounds onto a substrate. This process eliminates particulates formed by homogeneous reactions in bath, dramatically increases the utilization of Group IIB species, and results in the formation of a dense, adherent film for thin film solar cells. The process involves applying a pre-mixed liquid coating composition containing Group IIB and Group VIA ionic species onto a preheated substrate. Heat from the substrate causes a heterogeneous reaction between the Group IIB and VIA ionic species of the liquid coating composition, thus forming a solid reaction product film on the substrate surface.

Immersion Freezing of Aluminas: The Effect of Crystallographic Properties on Ice Nucleation

NASA Astrophysics Data System (ADS)

King, M.; Chong, E.; Freedman, M. A.

2017-12-01

Atmospheric aerosol particles serve as the nuclei for heterogeneous ice nucleation, a process that allows for ice to form at higher temperatures and lower supersaturations with respect to ice. This process is essential to the formation of ice in cirrus clouds. Heterogeneous ice nucleation is affected by many factors including the composition, crystal structure, porosity, and surface area of the particles. However, these factors are not well understood and, as such, are difficult to account for in climate models. To test the effects of crystal structure on ice nucleation, a system of transition aluminas (Al2O3) that differ only in their crystal structure, despite being compositionally similar, were tested using immersion freezing. Particles were immersed in water and placed into a temperature controlled chamber. Freezing events were then recorded as the chamber was cooled to negative 30 °. Alpha-alumina, which is a member of the hexagonal crystal system, showed a significantly higher temperature at which all particles froze in comparison to other samples. This supports the hypothesis that, since a hexagonal crystal structure is the lowest energy state for ice, hexagonal surface structures would best facilitate ice nucleation. However, a similar sample of hexagonal chi-alumina did not show the same results. Further analysis of the samples will be done to characterize surface structures and composition. These conflicting data sets raise interesting questions about the effect of other surface features, such as surface area and porosity, on ice nucleation.

Lateral uniformity in chemical composition along a buried reaction front in polymers using off-specular reflectivity.

PubMed

Lavery, Kristopher A; Prabhu, Vivek M; Satija, Sushil; Wu, Wen-Li

2010-12-01

Off-specular neutron reflectometry was applied to characterize the form and amplitude of lateral compositional variations at a buried reaction-diffusion front. In this work, off-specular neutron measurements were first calibrated using off-specular x-ray reflectivity and atomic force microscopy via a roughened glass surface, both as a free surface and as a buried interface that was prepared by spin coating thin polymer films upon the glass surface. All three methods provided consistent roughness values despite the difference in their detection mechanism. Our neutron results demonstrated, for the first time, that the compositional heterogeneity at a buried reaction front can be measured; the model system used in this study mimics the deprotection reaction that occurs during the photolithographic process necessary for manufacturing integrated circuits.

Promoted Iron Nanocrystals Obtained via Ligand Exchange as Active and Selective Catalysts for Synthesis Gas Conversion

PubMed Central

2017-01-01

Colloidal synthesis routes have been recently used to fabricate heterogeneous catalysts with more controllable and homogeneous properties. Herein a method was developed to modify the surface composition of colloidal nanocrystal catalysts and to purposely introduce specific atoms via ligands and change the catalyst reactivity. Organic ligands adsorbed on the surface of iron oxide catalysts were exchanged with inorganic species such as Na2S, not only to provide an active surface but also to introduce controlled amounts of Na and S acting as promoters for the catalytic process. The catalyst composition was optimized for the Fischer–Tropsch direct conversion of synthesis gas into lower olefins. At industrially relevant conditions, these nanocrystal-based catalysts with controlled composition were more active, selective, and stable than catalysts with similar composition but synthesized using conventional methods, possibly due to their homogeneity of properties and synergic interaction of iron and promoters. PMID:28824820

Controlled surface segregation leads to efficient coke-resistant nickel/platinum bimetallic catalysts for the dry reforming of methane

DOE PAGES

Li, Lidong; Zhou, Lu; Ould-Chikh, Samy; ...

2015-02-03

Surface composition and structure are of vital importance for heterogeneous catalysts, especially for bimetallic catalysts, which often vary as a function of reaction conditions (known as surface segregation). The preparation of bimetallic catalysts with controlled metal surface composition and structure is very challenging. In this study, we synthesize a series of Ni/Pt bimetallic catalysts with controlled metal surface composition and structure using a method derived from surface organometallic chemistry. The evolution of the surface composition and structure of the obtained bimetallic catalysts under simulated reaction conditions is investigated by various techniques, which include CO-probe IR spectroscopy, high-angle annular dark-field scanningmore » transmission electron microscopy, energy-dispersive X-ray spectroscopy, extended X-ray absorption fine structure analysis, X-ray absorption near-edge structure analysis, XRD, and X-ray photoelectron spectroscopy. It is demonstrated that the structure of the bimetallic catalyst is evolved from Pt monolayer island-modified Ni nanoparticles to core–shell bimetallic nanoparticles composed of a Ni-rich core and a Ni/Pt alloy shell upon thermal treatment. As a result, these catalysts are active for the dry reforming of methane, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure.« less

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

Sherman, Andrew J

A heterogeneous body having ceramic rich cermet regions in a more ductile metal matrix. The heterogeneous bodies are formed by thermal spray operations on metal substrates. The thermal spray operations apply heat to a cermet powder and project it onto a solid substrate. The cermet powder is composed of complex composite particles in which a complex ceramic-metallic core particle is coated with a matrix precursor. The cermet regions are generally comprised of complex ceramic-metallic composites that correspond approximately to the core particles. The cermet regions are approximately lenticular shaped with an average width that is at least approximately twice themore » average thickness. The cermet regions are imbedded within the matrix phase and generally isolated from one another. They have obverse and reverse surfaces. The matrix phase is formed from the matrix precursor coating on the core particles. The amount of heat applied during the formation of the heterogeneous body is controlled so that the core particles soften but do not become so fluid that they disperse throughout the matrix phase. The force of the impact on the surface of the substrate tends to flatten them. The flattened cermet regions tend to be approximately aligned with one another in the body.« less

Quantifying forest vertical structure to determine bird habitat quality in the Greenbelt Corridor, Denton, TX

NASA Astrophysics Data System (ADS)

Matsubayashi, Shiho

This study presents the integration of light detection and range (LiDAR) and hyperspectral remote sensing to create a three-dimensional bird habitat map in the Greenbelt Corridor of the Elm Fork of the Trinity River. This map permits to examine the relationship between forest stand structure, landscape heterogeneity, and bird community composition. A biannual bird census was conducted at this site during the breeding seasons of 2009 and 2010. Census data combined with the three-dimensional map suggest that local breeding bird abundance, community structure, and spatial distribution patterns are highly influenced by vertical heterogeneity of vegetation surface. For local breeding birds, vertical heterogeneity of canopy surface within stands, connectivity to adjacent forest patches, largest forest patch index, and habitat (vegetation) types proved to be the most influential factors to determine bird community assemblages. Results also highlight the critical role of secondary forests to increase functional connectivity of forest patches. Overall, three-dimensional habitat descriptions derived from integrated LiDAR and hyperspectral data serve as a powerful bird conservation tool that shows how the distribution of bird species relates to forest composition and structure at various scales.

Beer-Lambert-Law Parametric Model of Reflectance Spectra for Dyed Fabrics

DTIC Science & Technology

2016-06-06

optical constants), phenomenological quantities and combinations of both [27,28,29]. For reflection from a dyed fabric of finite and nonuniform ...fabrics are characterized, inherently, by rough surfaces (thus diffuse reflectance), heterogeneous compositions, and nonuniform thicknesses. It follows

Effective Wettability of Heterogenous Fracture Surfaces Using the Lattice-Boltzmann Method

NASA Astrophysics Data System (ADS)

E Santos, J.; Prodanovic, M.; Landry, C. J.

2017-12-01

Fracture walls in the subsurface are often structured by minerals of different composition (potentially further altered in contact with fluids during hydrocarbon extraction or CO2 sequestration), this yields in a heterogeneous wettability of the surface in contact with the fluids. The focus of our work is to study how surfaces presenting different mineralogy and roughness affect multiphase flow in fractures. Using the Shan-Chen model of the lattice-Boltzmann method (LBM) we define fluid interaction and surface attraction parameters to simulate a system of a wetting and a non-wetting fluid. In this work, we use synthetically created fractures presenting different arrangements of wetting and non-wetting patches, and with or without roughness; representative of different mineralogy, similar workflow can be applied to fractures extracted from X-ray microtomography images of fractures porous media. The results from the LBM simulations provide an insight on how the distribution of mineralogy and surface roughness are related with the observed macroscopic contact angle. We present a comparison between the published analytical models, and our results based on surface areas, spatial distribution and local fracture aperture. The understanding of the variables that affect the contact angle is useful for the comprehension of multiphase processes in naturally fractured reservoirs like primary oil production, enhanced oil recovery and CO2 sequestration. The macroscopic contact angle analytical equations for heterogeneous surfaces with variable roughness are no longer valid in highly heterogeneous systems; we quantify the difference thus offering an alternative to analytical models.

The Pluto system: Initial results from its exploration by New Horizons

NASA Astrophysics Data System (ADS)

Stern, S. A.; Bagenal, F.; Ennico, K.; Gladstone, G. R.; Grundy, W. M.; McKinnon, W. B.; Moore, J. M.; Olkin, C. B.; Spencer, J. R.; Weaver, H. A.; Young, L. A.; Andert, T.; Andrews, J.; Banks, M.; Bauer, B.; Bauman, J.; Barnouin, O. S.; Bedini, P.; Beisser, K.; Beyer, R. A.; Bhaskaran, S.; Binzel, R. P.; Birath, E.; Bird, M.; Bogan, D. J.; Bowman, A.; Bray, V. J.; Brozovic, M.; Bryan, C.; Buckley, M. R.; Buie, M. W.; Buratti, B. J.; Bushman, S. S.; Calloway, A.; Carcich, B.; Cheng, A. F.; Conard, S.; Conrad, C. A.; Cook, J. C.; Cruikshank, D. P.; Custodio, O. S.; Dalle Ore, C. M.; Deboy, C.; Dischner, Z. J. B.; Dumont, P.; Earle, A. M.; Elliott, H. A.; Ercol, J.; Ernst, C. M.; Finley, T.; Flanigan, S. H.; Fountain, G.; Freeze, M. J.; Greathouse, T.; Green, J. L.; Guo, Y.; Hahn, M.; Hamilton, D. P.; Hamilton, S. A.; Hanley, J.; Harch, A.; Hart, H. M.; Hersman, C. B.; Hill, A.; Hill, M. E.; Hinson, D. P.; Holdridge, M. E.; Horanyi, M.; Howard, A. D.; Howett, C. J. A.; Jackman, C.; Jacobson, R. A.; Jennings, D. E.; Kammer, J. A.; Kang, H. K.; Kaufmann, D. E.; Kollmann, P.; Krimigis, S. M.; Kusnierkiewicz, D.; Lauer, T. R.; Lee, J. E.; Lindstrom, K. L.; Linscott, I. R.; Lisse, C. M.; Lunsford, A. W.; Mallder, V. A.; Martin, N.; McComas, D. J.; McNutt, R. L.; Mehoke, D.; Mehoke, T.; Melin, E. D.; Mutchler, M.; Nelson, D.; Nimmo, F.; Nunez, J. I.; Ocampo, A.; Owen, W. M.; Paetzold, M.; Page, B.; Parker, A. H.; Parker, J. W.; Pelletier, F.; Peterson, J.; Pinkine, N.; Piquette, M.; Porter, S. B.; Protopapa, S.; Redfern, J.; Reitsema, H. J.; Reuter, D. C.; Roberts, J. H.; Robbins, S. J.; Rogers, G.; Rose, D.; Runyon, K.; Retherford, K. D.; Ryschkewitsch, M. G.; Schenk, P.; Schindhelm, E.; Sepan, B.; Showalter, M. R.; Singer, K. N.; Soluri, M.; Stanbridge, D.; Steffl, A. J.; Strobel, D. F.; Stryk, T.; Summers, M. E.; Szalay, J. R.; Tapley, M.; Taylor, A.; Taylor, H.; Throop, H. B.; Tsang, C. C. C.; Tyler, G. L.; Umurhan, O. M.; Verbiscer, A. J.; Versteeg, M. H.; Vincent, M.; Webbert, R.; Weidner, S.; Weigle, G. E.; White, O. L.; Whittenburg, K.; Williams, B. G.; Williams, K.; Williams, S.; Woods, W. W.; Zangari, A. M.; Zirnstein, E.

2015-10-01

The Pluto system was recently explored by NASA’s New Horizons spacecraft, making closest approach on 14 July 2015. Pluto’s surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto’s atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto’s diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto’s large moon Charon displays tectonics and evidence for a heterogeneous crustal composition; its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected.

Oxalate enhanced degradation of Orange II in heterogeneous UV-Fenton system catalyzed by Fe3O4@γ-Fe2O3 composite.

PubMed

Dai, Huiwang; Xu, Shuying; Chen, Jianxin; Miao, Xiaozeng; Zhu, Jianxi

2018-05-01

Oxalate enhanced mechanism of Fe 3 O 4 @γ-Fe 2 O 3 was developed to provide novel insight into catalytic process regulation of iron oxide catalysts in heterogeneous UV-Fenton system. And the iron oxide composite of Fe 3 O 4 @γ-Fe 2 O 3 was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FTIR) spectroscopy and nitrogen adsorption-desorption isotherms. The results showed that large amount of iron could be leached from catalyst in the presence of oxalate, which promoted the homogeneous UV-Fenton reactions in solution. Orange II degradation could be significantly enhanced with the increase of the ratio of homogeneous UV-Fenton process to heterogeneous UV-Fenton process. The optimum concentration of oxalate determined by experiment was 0.5 mM in oxalate enhanced heterogeneous UV-Fenton system. On this condition, the pseudo-first-order rate constant value of Orange II degradation was 0.314 min -1 , which was 2.3 times as high as that in heterogeneous UV-Fenton system. The removal rates of color and TOC were 100% and 86.6% after 20 min and 120 min treatment, respectively. In addition, the iron ions in solution could be almost completely adsorbed back to the catalyst surface in later degradation stages of Orange II. During the recycle experiments, the results showed that the increase of pH in solution and the sorption of intermediates on the catalyst surface would hinder oxalate enhanced process and lead to a decrease of degradation rate of Orange II in oxalate enhanced heterogeneous UV-Fenton system. Copyright © 2018 Elsevier Ltd. All rights reserved.

Shallow to Deep Convection Transition over a Heterogeneous Land Surface Using the Land Model Coupled Large-Eddy Simulation

NASA Astrophysics Data System (ADS)

Lee, J.; Zhang, Y.; Klein, S. A.

2017-12-01

The triggering of the land breeze, and hence the development of deep convection over heterogeneous land should be understood as a consequence of the complex processes involving various factors from land surface and atmosphere simultaneously. That is a sub-grid scale process that many large-scale models have difficulty incorporating it into the parameterization scheme partly due to lack of our understanding. Thus, it is imperative that we approach the problem using a high-resolution modeling framework. In this study, we use SAM-SLM (Lee and Khairoutdinov, 2015), a large-eddy simulation model coupled to a land model, to explore the cloud effect such as cold pool, the cloud shading and the soil moisture memory on the land breeze structure and the further development of cloud and precipitation over a heterogeneous land surface. The atmospheric large scale forcing and the initial sounding are taken from the new composite case study of the fair-weather, non-precipitating shallow cumuli at ARM SGP (Zhang et al., 2017). We model the land surface as a chess board pattern with alternating leaf area index (LAI). The patch contrast of the LAI is adjusted to encompass the weak to strong heterogeneity amplitude. The surface sensible- and latent heat fluxes are computed according to the given LAI representing the differential surface heating over a heterogeneous land surface. Separate from the surface forcing imposed from the originally modeled surface, the cases that transition into the moist convection can induce another layer of the surface heterogeneity from the 1) radiation shading by clouds, 2) adjusted soil moisture pattern by the rain, 3) spreading cold pool. First, we assess and quantifies the individual cloud effect on the land breeze and the moist convection under the weak wind to simplify the feedback processes. And then, the same set of experiments is repeated under sheared background wind with low level jet, a typical summer time wind pattern at ARM SGP site, to account for more realistic situations. Our goal is to assist answering the question: "Do the sub-grid scale land surface heterogeneity matter for the weather and climate modeling?" This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS- 736011.

Areal-Averaged Spectral Surface Albedo in an Atlantic Coastal Area: Estimation from Ground-Based Transmission

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

Kassianov, Evgueni; Barnard, James; Flynn, Connor

Tower-based data combined with high-resolution satellite products have been used to produce surface albedo at various spatial scales over land. Because tower-based albedo data are available at only a few sites, surface albedos using these combined data are spatially limited. Moreover, tower-based albedo data are not representative of highly heterogeneous regions. To produce areal-averaged and spectrally-resolved surface albedo for regions with various degrees of surface heterogeneity, we have developed a transmission-based retrieval and demonstrated its feasibility for relatively homogeneous land surfaces. Here we demonstrate its feasibility for a highly heterogeneous coastal region. We use the atmospheric transmission measured during amore » 19-month period (June 2009 – December 2010) by a ground-based Multi-Filter Rotating Shadowband Radiometer (MFRSR) at five wavelengths (0.415, 0.5, 0.615, 0.673 and 0.87 µm) at the Department of Energy’s Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) site located on Graciosa Island. We compare the MFRSR-retrieved areal-averaged surface albedo with albedo derived from Moderate Resolution Imaging Spectroradiometer (MODIS) observations, and also a composite-based albedo. Lastly, we demonstrate that these three methods produce similar spectral signatures of surface albedo; however, the MFRSR-retrieved albedo, is higher on average (≤0.04) than the MODIS-based areal-averaged surface albedo and the largest difference occurs in winter.« less

Areal-Averaged Spectral Surface Albedo in an Atlantic Coastal Area: Estimation from Ground-Based Transmission

DOE PAGES

Kassianov, Evgueni; Barnard, James; Flynn, Connor; ...

2017-07-12

Tower-based data combined with high-resolution satellite products have been used to produce surface albedo at various spatial scales over land. Because tower-based albedo data are available at only a few sites, surface albedos using these combined data are spatially limited. Moreover, tower-based albedo data are not representative of highly heterogeneous regions. To produce areal-averaged and spectrally-resolved surface albedo for regions with various degrees of surface heterogeneity, we have developed a transmission-based retrieval and demonstrated its feasibility for relatively homogeneous land surfaces. Here we demonstrate its feasibility for a highly heterogeneous coastal region. We use the atmospheric transmission measured during amore » 19-month period (June 2009 – December 2010) by a ground-based Multi-Filter Rotating Shadowband Radiometer (MFRSR) at five wavelengths (0.415, 0.5, 0.615, 0.673 and 0.87 µm) at the Department of Energy’s Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) site located on Graciosa Island. We compare the MFRSR-retrieved areal-averaged surface albedo with albedo derived from Moderate Resolution Imaging Spectroradiometer (MODIS) observations, and also a composite-based albedo. Lastly, we demonstrate that these three methods produce similar spectral signatures of surface albedo; however, the MFRSR-retrieved albedo, is higher on average (≤0.04) than the MODIS-based areal-averaged surface albedo and the largest difference occurs in winter.« less

Mesoporous Colloidal Superparticles of Platinum-Group Nanocrystals with Surfactant-Free Surfaces and Enhanced Heterogeneous Catalysis

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

Hu, Yongxing; Liu, Yuzi; Sun, Yugang

2015-01-23

Synthesis of colloidal superparticles (CSPs) of nanocrystals, a class of assembled nanocrystals in the form of colloidal particles, has been emerging as a new frontier in the field of nanotechnology because of their potential novel properties originated from coupling of individual nanocrystals in CSPs. Here, a facile approach is reported for the controlled synthesis of mesoporous CSPs made of various platinum-group nanocrystals that exhibit high colloidal stability and ligand-free surfaces to significantly benefit their applications in solution-phase heterogeneous catalysis. The synthesis relies on self-limiting growth of composite particles through coprecipitation of both Pt-group nanocrystals (or their precursor compounds) and silvermore » halides on sacrificial substrates of colloidal silver particles. The intermediate silver halides in the composite particles play the critical role in limiting the continuous growth (and/or coalescence) of individual Pt-group nanocrystals and they can be selectively dissolved to create nanoscale pores in the resulting CSPs.« less

Heterogeneity and loss of soil nutrient elements under aeolian processes in the Otindag Desert, China

NASA Astrophysics Data System (ADS)

Li, Danfeng; Wang, Xunming; Lou, Junpeng; Liu, Wenbin; Li, Hui; Ma, Wenyong; Jiao, Linlin

2018-02-01

The heterogeneity of the composition of surface soils that are affected by aeolian processes plays important roles in ecological evolution and the occurrence of aeolian desertification in fragile ecological zones, but the associated mechanisms are poorly understood. Using field investigation, wind tunnel experiments, and particle size and element analyses, we discuss the variation in the nutrient elements of surface soils that forms in the presence of aeolian processes of four vegetation species (Caragana microphylla Lam, Artemisia frigida Willd. Sp. Pl., Leymus chinensis (Trin.) Tzvel. and Stipa grandis P. Smirn) growing in the Otindag Desert, China. These four vegetation communities correspond to increasing degrees of degradation. A total of 40 macro elements, trace elements, and oxides were measured in the surface soil and in wind-transported samples. The results showed that under the different degradation stages, the compositions and concentrations of nutrients in surface soils differed for the four vegetation species. Aeolian processes may cause higher heterogeneity and higher loss of soil nutrient elements for the communities of Artemisia frigida Willd. Sp. Pl., Leymus chinensis (Trin.) Tzvel, and Stipa grandis P. Smirn than for the Caragana microphylla Lam community. There was remarkable variation in the loss of nutrients under different aeolian transportation processes. Over the past several decades, the highest loss of soil elements occurred in the 1970s, whereas the loss from 2011 to the present was generally 4.0% of that in the 1970s. These results indicate that the evident decrease in nutrient loss has played an important role in the rehabilitation that has occurred in the region recently.

Cometary science. Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko.

PubMed

Hässig, M; Altwegg, K; Balsiger, H; Bar-Nun, A; Berthelier, J J; Bieler, A; Bochsler, P; Briois, C; Calmonte, U; Combi, M; De Keyser, J; Eberhardt, P; Fiethe, B; Fuselier, S A; Galand, M; Gasc, S; Gombosi, T I; Hansen, K C; Jäckel, A; Keller, H U; Kopp, E; Korth, A; Kührt, E; Le Roy, L; Mall, U; Marty, B; Mousis, O; Neefs, E; Owen, T; Rème, H; Rubin, M; Sémon, T; Tornow, C; Tzou, C-Y; Waite, J H; Wurz, P

2015-01-23

Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well-sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: water, carbon monoxide, and carbon dioxide. These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface. Copyright © 2015, American Association for the Advancement of Science.

On the design of composite protein-quantum dot biomaterials via self-assembly.

PubMed

Majithia, Ravish; Patterson, Jan; Bondos, Sarah E; Meissner, Kenith E

2011-10-10

Incorporation of nanoparticles during the hierarchical self-assembly of protein-based materials can impart function to the resulting composite materials. Herein we demonstrate that the structure and nanoparticle distribution of composite fibers are sensitive to the method of nanoparticle addition and the physicochemical properties of both the nanoparticle and the protein. Our model system consists of a recombinant enhanced green fluorescent protein-Ultrabithorax (EGFP-Ubx) fusion protein and luminescent CdSe-ZnS core-shell quantum dots (QDs), allowing us to optically assess the distribution of both the protein and nanoparticle components within the composite material. Although QDs favorably interact with EGFP-Ubx monomers, the relatively rough surface morphology of composite fibers suggests EGFP-Ubx-QD conjugates impact self-assembly. Indeed, QDs templated onto EGFP-Ubx film post-self-assembly can be subsequently drawn into smooth composite fibers. Additionally, the QD surface charge impacts QD distribution within the composite material, indicating that surface charge plays an important role in self-assembly. QDs with either positively or negatively charged coatings significantly enhance fiber extensibility. Conversely, QDs coated with hydrophobic moieties and suspended in toluene produce composite fibers with a heterogeneous distribution of QDs and severely altered fiber morphology, indicating that toluene severely disrupts Ubx self-assembly. Understanding factors that impact the protein-nanoparticle interaction enables manipulation of the structure and mechanical properties of composite materials. Since proteins interact with nanoparticle surface coatings, these results should be applicable to other types of nanoparticles with similar chemical groups on the surface.

The Pluto system: Initial results from its exploration by New Horizons.

PubMed

Stern, S A; Bagenal, F; Ennico, K; Gladstone, G R; Grundy, W M; McKinnon, W B; Moore, J M; Olkin, C B; Spencer, J R; Weaver, H A; Young, L A; Andert, T; Andrews, J; Banks, M; Bauer, B; Bauman, J; Barnouin, O S; Bedini, P; Beisser, K; Beyer, R A; Bhaskaran, S; Binzel, R P; Birath, E; Bird, M; Bogan, D J; Bowman, A; Bray, V J; Brozovic, M; Bryan, C; Buckley, M R; Buie, M W; Buratti, B J; Bushman, S S; Calloway, A; Carcich, B; Cheng, A F; Conard, S; Conrad, C A; Cook, J C; Cruikshank, D P; Custodio, O S; Dalle Ore, C M; Deboy, C; Dischner, Z J B; Dumont, P; Earle, A M; Elliott, H A; Ercol, J; Ernst, C M; Finley, T; Flanigan, S H; Fountain, G; Freeze, M J; Greathouse, T; Green, J L; Guo, Y; Hahn, M; Hamilton, D P; Hamilton, S A; Hanley, J; Harch, A; Hart, H M; Hersman, C B; Hill, A; Hill, M E; Hinson, D P; Holdridge, M E; Horanyi, M; Howard, A D; Howett, C J A; Jackman, C; Jacobson, R A; Jennings, D E; Kammer, J A; Kang, H K; Kaufmann, D E; Kollmann, P; Krimigis, S M; Kusnierkiewicz, D; Lauer, T R; Lee, J E; Lindstrom, K L; Linscott, I R; Lisse, C M; Lunsford, A W; Mallder, V A; Martin, N; McComas, D J; McNutt, R L; Mehoke, D; Mehoke, T; Melin, E D; Mutchler, M; Nelson, D; Nimmo, F; Nunez, J I; Ocampo, A; Owen, W M; Paetzold, M; Page, B; Parker, A H; Parker, J W; Pelletier, F; Peterson, J; Pinkine, N; Piquette, M; Porter, S B; Protopapa, S; Redfern, J; Reitsema, H J; Reuter, D C; Roberts, J H; Robbins, S J; Rogers, G; Rose, D; Runyon, K; Retherford, K D; Ryschkewitsch, M G; Schenk, P; Schindhelm, E; Sepan, B; Showalter, M R; Singer, K N; Soluri, M; Stanbridge, D; Steffl, A J; Strobel, D F; Stryk, T; Summers, M E; Szalay, J R; Tapley, M; Taylor, A; Taylor, H; Throop, H B; Tsang, C C C; Tyler, G L; Umurhan, O M; Verbiscer, A J; Versteeg, M H; Vincent, M; Webbert, R; Weidner, S; Weigle, G E; White, O L; Whittenburg, K; Williams, B G; Williams, K; Williams, S; Woods, W W; Zangari, A M; Zirnstein, E

2015-10-16

The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition; its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected. Copyright © 2015, American Association for the Advancement of Science.

Pinning of the Contact Line during Evaporation on Heterogeneous Surfaces: Slowdown or Temporary Immobilization? Insights from a Nanoscale Study.

PubMed

Zhang, Jianguo; Müller-Plathe, Florian; Leroy, Frédéric

2015-07-14

The question of the effect of surface heterogeneities on the evaporation of liquid droplets from solid surfaces is addressed through nonequilibrium molecular dynamics simulations. The mechanism behind contact line pinning which is still unclear is discussed in detail on the nanoscale. Model systems with the Lennard-Jones interaction potential were employed to study the evaporation of nanometer-sized cylindrical droplets from a flat surface. The heterogeneity of the surface was modeled through alternating stripes of equal width but two chemical types. The first type leads to a contact angle of 67°, and the other leads to a contact angle of 115°. The stripe width was varied between 2 and 20 liquid-particle diameters. On the surface with the narrowest stripes, evaporation occurred at constant contact angle as if the surface was homogeneous, with a value of the contact angle as predicted by the regular Cassie-Baxter equation. When the width was increased, the contact angle oscillated during evaporation between two boundaries whose values depend on the stripe width. The evaporation behavior was thus found to be a direct signature of the typical size of the surface heterogeneity domains. The contact angle both at equilibrium and during evaporation could be predicted from a local Cassie-Baxter equation in which the surface composition within a distance of seven fluid-particle diameters around the contact line was considered, confirming the local nature of the interactions that drive the wetting behavior of droplets. More importantly, we propose a nanoscale explanation of pinning during evaporation. Pinning should be interpreted as a drastic slowdown of the contact line dynamics rather than a complete immobilization of it during a transition between two contact angle boundaries.

Effect of the endcapping of reversed-phase high-performance liquid chromatography adsorbents on the adsorption isotherm

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

Gritti, Fabrice; Guiochon, Georges A

2005-09-01

The retention mechanisms of n-propylbenzoate, 4-t ert-butylphenol, and caffeine on the endcapped Symmetry-C{sub 18} and the non-endcapped Resolve-C{sub 18} are compared. The adsorption isotherms were measured by frontal analysis (FA), using as the mobile phase mixtures of methanol or acetonitrile and water of various compositions. The isotherm data were modeled and the adsorption energy distributions calculated. The surface heterogeneity increases faster with decreasing methanol concentration on the non-endcapped than on the endcapped adsorbent. For instance, for methanol concentrations exceeding 30% (v/v), the adsorption of caffeine is accounted for by assuming three and two different types of adsorption sites on Resolve-C{submore » 18} and Symmetry-C{sub 18}, respectively. This is explained by the effect of the mobile phase composition on the structure of the C{sub 18}-bonded layer. The bare surface of bonded silica appears more accessible to solute molecules at high water contents in the mobile phase. On the other hand, replacing methanol by a stronger organic modifier like acetonitrile dampens the differences between non-endcapped and endcapped stationary phase and decreases the degree of surface heterogeneity of the adsorbent. For instance, at acetonitrile concentrations exceeding 20%, the surface appears nearly homogeneous for the adsorption of caffeine.« less

Catalytic combustion of hydrogen-air mixtures in stagnation flows

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

Ikeda, H.; Libby, P.A.; Williams, F.A.

1993-04-01

The interaction between heterogeneous and homogeneous reactions arising when a mixture of hydrogen and air impinges on a platinum plate at elevated temperature is studied. A reasonably complete description of the kinetic mechanism for homogeneous reactions is employed along with a simplified model for heterogeneous reactions. Four regimes are identified depending on the temperature of the plate, on the rate of strain imposed on the flow adjacent to the plate and on the composition and temperature of the reactant stream: (1) surface reaction alone; (2) surface reaction inhibiting homogeneous reaction; (3) homogeneous reaction inhibiting surface reaction; and (4) homogeneous reactionmore » alone. These regimes are related to those found earlier for other chemical systems and form the basis of future experimental investigation of the chemical system considered in the present study.« less

Magnetodynamic properties of spatially distributed films based on a metal-dielectric composite

NASA Astrophysics Data System (ADS)

Tarasova, O. S.; Kalinin, Yu. E.; Sitnikov, A. V.; Yanchenko, L. I.

2017-09-01

The frequency dependences of the absorption coefficient of electromagnetic radiation and frequency dependences of the complex magnetic permeability of the fiberglass made of fiberglass cloth with a heterogeneous film deposited on the surface were investigated in the frequency range from 300 MHz to 10 GHz.

Surface studies of heterogeneous catalysts by time-of-flight secondary ion mass spectrometry.

PubMed

Grams, Jacek

2010-01-01

The aim of this paper was to present potentialities of time-of-flight secondary ion mass spectrometry (ToF- SIMS) in the studies of heterogeneous catalysts. The results of ToF-SIMS investigations of Co/Al2O3, Mo/Al2O3, Co-Mo/Al2O3, Au/Al2O3, Pt/TiO2 and Pd/TiO2 systems were described. It was demonstrated that, in this case, an application of ToF-SIMS makes possible the determination of surface composition of investigated catalysts (including an identification of surface contaminants), characterization of interactions between an active phase and support, estimation of active phase dispersion on the analyzed surface, comparison of the degree of metal oxidation after treatment of the catalyst in different conditions, investigation of catalyst deactivation processes (formation of new chemical compounds, adsorption of various impurities and poisons on the catalyst surface) and determination of organic precursors of catalysts.

C, N, and O Isotopic Heterogeneities in Low-density Supernova Graphite Grains from Orgueil

NASA Astrophysics Data System (ADS)

Groopman, Evan; Bernatowicz, Thomas; Zinner, Ernst

2012-07-01

We report on the results of NanoSIMS isotope imaging of low-density supernova graphite grains from the Orgueil meteorite. 70 nm thick microtomed sections of three supernova graphite grains were deposited on Si wafers and isotopically imaged in the NanoSIMS. These sections contain hotspots of excesses in 18O and 15N, which are spatially well correlated, and are likely carried by internal TiC subgrains. These hotspots are considerably more enriched in 18O and 15N than the host graphite grain. Correlations between 18O and 15N excesses indicate that the grains incorporated material from the He/C supernova zone. Isotope images of the surfaces of some grains show heterogeneities in their N and O isotope compositions, with extreme excesses in 15N and 18O. In the microtome sections, we also observe two types of heterogeneities in the grains' C isotopic compositions: smooth, radial gradients in 12C/13C, with this ratio trending toward solar with increasing radius; and highly anomalous pockets up to 2 μm in size with 12C/13C Gt solar that are located near the centers of the grain sections. Partial isotopic equilibration does not likely explain the C isotopic heterogeneities. These grains and their constituent parts probably formed in a stellar environment with changing isotopic composition.

The Impact of Organic Surfactants and Coatings in Regulating Heterogeneous N2O5 Reaction Kinetics on Nascent Marine Aerosol

NASA Astrophysics Data System (ADS)

Ryder, O. S.; Campbell, N.; Schill, S.; Pöhlker, C.; Andreae, M. O.; Bertram, T. H.

2013-12-01

The heterogeneous reaction of N2O5 on aerosol particles impacts both the lifetime of nitrogen oxides, and the production rate of chlorine radicals following the activation of particulate chloride to nitryl chloride in both coastal and continental regions. The extent to which N2O5 reactivity impacts oxidant loadings depends on the heterogeneous reaction rate, which is directly influenced by aerosol chemical composition, morphology, and physical phase state. In the marine environment, the chemical composition of aerosol particles produced via wave induced bubble bursting mechanisms varies greatly and is influenced by the composition of the sea surface microlayer . Here, we present direct measurements of N2O5 reaction kinetics determined using model sea-spray particles generated in a novel Marine Aerosol Reference Tank (MART), capable of generating accurate mimics of ambient sea spray particles, in a lab environment. Here, a synthetic sea salt ocean was sequentially doped with organic molecules chosen to mimic organic species present in natural sea water over the course of a phytoplankton bloom in the open ocean. These included sterol, galactose, lippolysaccharide, BSA protein, and 1,2-dipalmitoyl-sn-glycero-3-phosphate (DPPA). These observations permit discussion of the role of marine organics in regulating heterogeneous reaction kinetics, as well a re-evaluation of potential organic lab proxies for marine organics.

Surface Plasmon Resonance Evaluation of Colloidal Metal Aerogel Filters

NASA Technical Reports Server (NTRS)

Smith, David D.; Sibille, Laurent; Cronise, Raymond J.; Noever, David A.

1997-01-01

We have fabricated aerogels containing gold, silver, and platinum nanoparticles for gas catalysis applications. By applying the concept of an average or effective dielectric constant to the heterogeneous interlayer surrounding each particle, we extend the technique of immersion spectroscopy to porous or heterogeneous media. Specifically, we apply the predominant effective medium theories for the determination of the average fractional composition of each component in this inhomogeneous layer. Hence, the surface area of metal available for catalytic gas reaction is determined. The technique is satisfactory for statistically random metal particle distributions but needs further modification for aggregated or surfactant modified systems. Additionally, the kinetics suggest that collective particle interactions in coagulated clusters are perturbed during silica gelation resulting in a change in the aggregate geometry.

Heterogeneous reactions of chlorine nitrate and hydrogen chloride on type I polar stratospheric clouds

NASA Technical Reports Server (NTRS)

Leu, Ming-Taun; Moore, Steven B.; Keyser, Leon F.

1991-01-01

A fast-flow reactor coupled with a quadrupole mass spectrometer was used to study the heterogeneous reactions ClONO2 + HCl yields Cl2 + HNO3 (1) and ClONO2 + H2O yields HOCl + HNO3 (2) on vapor-deposited HNO3-H2O ice substrates. It was found that the sticking coefficient of HCl on these substrates was a strong function of the substrate composition, ranging from about 2 x 10 exp -5 at nitric acid trihydrate composition to 6 x 10 exp -3 at 45 wt pct HNO3. The HNO3-H2O ice substrates were found to have large internal surface areas, and corrections for gas-phase diffusion within the porous ices were applied to observed loss rates.

Surface design for controlled crystallization: the role of surface chemistry and nanoscale pores in heterogeneous nucleation.

PubMed

Diao, Ying; Myerson, Allan S; Hatton, T Alan; Trout, Bernhardt L

2011-05-03

Current industrial practice for control of primary nucleation (nucleation from a system without pre-existing crystalline matter) during crystallization from solution involves control of supersaturation generation, impurity levels, and solvent composition. Nucleation behavior remains largely unpredictable, however, due to the presence of container surfaces, dust, dirt, and other impurities that can provide heterogeneous nucleation sites, thus making the control and scale-up of processes that depend on primary nucleation difficult. To develop a basis for the rational design of surfaces to control nucleation during crystallization from solution, we studied the role of surface chemistry and morphology of various polymeric substrates on heterogeneous nucleation using aspirin as a model compound. Nucleation induction time statistics were utilized to investigate and quantify systematically the effectiveness of polymer substrates in inducing nucleation. The nucleation induction time study revealed that poly(4-acryloylmorpholine) and poly(2-carboxyethyl acrylate), each cross-linked by divinylbenzene, significantly lowered the nucleation induction time of aspirin while the other polymers were essentially inactive. In addition, we found the presence of nanoscopic pores on certain polymer surfaces led to order-of-magnitude faster aspirin nucleation rates when compared with surfaces without pores. We studied the preferred orientation of aspirin crystals on polymer films and found the nucleation-active polymer surfaces preferentially nucleated the polar facets of aspirin, guided by hydrogen bonds. A model based on interfacial free energies was also developed which predicted the same trend of polymer surface nucleation activities as indicated by the nucleation induction times.

Chemical analyses of micrometre-sized solids by a miniature laser ablation/ionisation mass spectrometer (LMS)

NASA Astrophysics Data System (ADS)

Tulej, Marek; Wiesendanger, Reto; Neuland, Maike; Meyer, Stefan; Wurz, Peter; Neubeck, Anna; Ivarsson, Magnus; Riedo, Valentine; Moreno-Garcia, Pavel; Riedo, Andreas; Knopp, Gregor

2017-04-01

Investigation of elemental and isotope compositions of planetary solids with high spatial resolution are of considerable interest to current space research. Planetary materials are typically highly heterogenous and such studies can deliver detailed chemical information of individual sample components with the sizes down to a few micrometres. The results of such investigations can yield mineralogical surface context including mineralogy of individual grains or the elemental composition of of other objects embedded in the sample surface such as micro-sized fossils. The identification of bio-relevant material can follow by the detection of bio-relevant elements and their isotope fractionation effects [1, 2]. For chemical analysis of heterogenous solid surfaces we have combined a miniature laser ablation mass spectrometer (LMS) (mass resolution (m/Dm) 400-600; dynamic range 105-108) with in situ microscope-camera system (spatial resolution ˜2um, depth 10 um). The microscope helps to find the micrometre-sized solids across the surface sample for the direct mass spectrometric analysis by the LMS instrument. The LMS instrument combines an fs-laser ion source and a miniature reflectron-type time-of-flight mass spectrometer. The mass spectrometric analysis of the selected on the sample surface objects followed after ablation, atomisation and ionisation of the sample by a focussed laser radiation (775 nm, 180 fs, 1 kHz; the spot size of ˜20 um) [4, 5, 6]. Mass spectra of almost all elements (isotopes) present in the investigated location are measured instantaneously. A number of heterogenous rock samples containing micrometre-sized fossils and mineralogical grains were investigated with high selectivity and sensitivity. Chemical analyses of filamentous structures observed in carbonate veins (in harzburgite) and amygdales in pillow basalt lava can be well characterised chemically yielding elemental and isotope composition of these objects [7, 8]. The investigation can be prepared with high selectivity since the host composition is typically readily different comparing to that of the analysed objects. In depth chemical analysis (chemical profiling) is found in particularly helpful allowing relatively easy isolation of the chemical composition of the host from the investigated objects [6]. Hence, both he chemical analysis of the environment and microstructures can be derived. Analysis of the isotope compositions can be measured with high level of confidence, nevertheless, presence of cluster of similar masses can make sometimes this analysis difficult. Based on this work, we are confident that similar studies can be conducted in situ planetary surfaces delivering important chemical context and evidences on bio-relevant processes. [1] Summons et al., Astrobiology, 11, 157, 2011. [2] Wurz et al., Sol. Sys. Res. 46, 408, 2012. [3] Riedo et al., J. Anal. Atom. Spectrom. 28, 1256, 2013. [4] Riedo et al., J. Mass Spectrom.48, 1, 2013. [5] Tulej et al., Geostand. Geoanal. Res., 38, 423, 2014. [6] Grimaudo et al., Anal. Chem. 87, 2041, 2015 [7] Tulej et al., Astrobiology, 15, 1, 2015. [8] Neubeck et al., Int. J. Astrobiology, 15, 133, 2016.

The Origin of the Compositional Diversity of Mercury's Surface Constrained From Experimental Melting of Enstatite Chondrites

NASA Technical Reports Server (NTRS)

Boujibar, A.; Righter, K.; Pando, K.; Danielson, L.

2015-01-01

Mercury is known as an endmember planet as it is the most reduced terrestrial planet with the highest core/mantle ratio. MESSENGER spacecraft has shown that its surface is FeO-poor (2-4 wt%) and Srich (up to 6-7 wt%), which confirms the reducing nature of its silicate mantle. Moreover, high resolution images revealed large volcanic plains and abundant pyroclastic deposits, suggesting important melting stages of the Mercurian mantle. This interpretation was confirmed by the high crustal thickness (up to 100 km) derived from Mercury's gravity field. This is also corroborated by a recent experimental result that showed that Mercurian partial melts are expected to be highly buoyant within the Mercurian mantle and could have risen from depths as high as the core-mantle boundary. In addition MESSENGER spacecraft provided relatively precise data on major elemental compositions of Mercury's surface. These results revealed important chemical and mineralogical heterogeneities that suggested several stages of differentiation and re-melting processes. However, the extent and nature of compositional variations produced by partial melting remains poorly constrained for the particular compositions of Mercury (very reducing conditions, low FeO-contents and high sulfur-contents). Therefore, in this study, we investigated the processes that lead to the various compositions of Mercury's surface. Melting experiments with bulk Mercury-analogue compositions were performed and compared to the compositions measured by MESSENGER.

Communicating why land surface heterogeneity matters

NASA Astrophysics Data System (ADS)

Tague, C.; Burke, W.; Bart, R. R.; Turpin, E.; Wood, T.; Gordon, D.

2017-12-01

As hydrologic scientists, we know that land surface heterogeneity can have nuanced and sometimes dramatic impacts on the water cycle. Land surface characteristics, including the structure and composition of vegetation and soil storage and drainage properties, alter how incoming precipitation is translated into streamflow and evapotranspiration. Land surface heterogeneity can explain why this partitioning of incoming precipitation cannot always be computed by a simple water budget calculation. We also know that land surface characteristics are dynamic - vegetation grows and changes with fire, disease and human actions and these changes will alter the partitioning of water - how much so, however depends itself on other site characteristics - soil water storage and the timing and magnitude of precipitation. This complex impact of space-time dynamics on the water cycle is something we need to effectively communicate to non-experts. For example, we may want to explain why sometimes forest management practices increase water availability but sometimes they don't - or why the impacts of urbanization or fire are location specific. If we do not communicate these dependencies we risk over-simplifying and eroding scientific credibility when observed effects don't match simple generalizations. On the other hand excessive detail can overwhelm and disengage audiences. So how do we help different communities public, private landowners, other scientists, NGOs, governments to better understand the role of space-time heterogeneity. To address this issue, we present some results from ongoing work that looks at the impact of fuel treatment of forest ecohydrology. This work stem from a collaboration between an ecohydrologic modeling team, social-scientists, a visual artist and compute graphics students. We use a coupled model, validated with field measurements, to show why spatial heterogeneity matters for understanding the impact of fuel treatments on the water cycle for the Sierra Critical Zone Observatory. We summarize current findings and present initial designs for translating these science based results into interactive visualization and conceptual art installations with the goal of better communicating the different components of landscape heterogeneity and why it matters

[Biliary calculi resistant to dissolution with bile acids: their heterogeneous composition and diversity of treatment response].

PubMed

Ruíz de Aguiar, A; Medina, J A; Garrido, G; Villacorta, J; Berenguer, J

1992-05-01

We have studied thirteen biliary stones resistant to biliary acids, using technical methods of stereomicroscopy, scanning electronic microscopy and EDX analyses. We have investigated changes on surface. Three biliary stones did not change and were considered resistant. Seven biliary stones appear partially dissolved and we observed many irregularities on surface and/or concentric dips in relation with cholesterol dissolution. In six cases, biliary pigment alternates with cholesterol. In three cases we observed a calcium carbonate coat on surface. One case included organic fibers. One biliary stone showed cholesterol with spherical bodies of calcium carbonate and pigment. It was a relapsed case of combined treatment. Three stones are composed of small black portions of polymerized calcium bilirubinate, rich in copper and iron. Our results demonstrate that biliary stones previously selected for treatment are a heterogeneous group. Because of this fact we get variable and unpredictable results.

Parameterization of N2O5 Reaction Probabilities on the Surface of Particles Containing Ammonium, Sulfate, and Nitrate

EPA Science Inventory

A comprehensive parameterization was developed for the heterogeneous reaction probability (γ) of N₂O₅ as a function of temperature, relative humidity, particle composition, and phase state, for use in advanced air quality models. The reaction probabilities o...

Cost minimization through optimized raw material quality composition

Treesearch

Urs Buehlmann; R. Edward Thomas; Xiaoqui Zuo

2011-01-01

Lumber, a heterogeneous, anisotropic material produced from sawing logs, contains a varying number of randomly dispersed, unusable areas (defects) distributed over each boards’ surface area. Each board's quality is determined by the frequency and distribution of these defects and the board's dimension. Typically, the industry classifies lumber into five...

Three-dimensional spectral analysis of compositional heterogeneity at Arruntia crater on (4) Vesta using Dawn FC

NASA Astrophysics Data System (ADS)

Thangjam, Guneshwar; Nathues, Andreas; Mengel, Kurt; Schäfer, Michael; Hoffmann, Martin; Cloutis, Edward A.; Mann, Paul; Müller, Christian; Platz, Thomas; Schäfer, Tanja

2016-03-01

We introduce an innovative three-dimensional spectral approach (three band parameter space with polyhedrons) that can be used for both qualitative and quantitative analyzes improving the characterization of surface compositional heterogeneity of (4) Vesta. It is an advanced and more robust methodology compared to the standard two-dimensional spectral approach (two band parameter space). The Dawn Framing Camera (FC) color data obtained during High Altitude Mapping Orbit (resolution ∼ 60 m/pixel) is used. The main focus is on the howardite-eucrite-diogenite (HED) lithologies containing carbonaceous chondritic material, olivine, and impact-melt. The archived spectra of HEDs and their mixtures, from RELAB, HOSERLab and USGS databases as well as our laboratory-measured spectra are used for this study. Three-dimensional convex polyhedrons are defined using computed band parameter values of laboratory spectra. Polyhedrons based on the parameters of Band Tilt (R0.92μm/R0.96μm), Mid Ratio ((R0.75μm/R0.83μm)/(R0.83μm/R0.92μm)) and reflectance at 0.55 μm (R0.55μm) are chosen for the present analysis. An algorithm in IDL programming language is employed to assign FC data points to the respective polyhedrons. The Arruntia region in the northern hemisphere of Vesta is selected for a case study because of its geological and mineralogical importance. We observe that this region is eucrite-dominated howarditic in composition. The extent of olivine-rich exposures within an area of 2.5 crater radii is ∼12% larger than the previous finding (Thangjam, G. et al. [2014]. Meteorit. Planet. Sci. 49, 1831-1850). Lithologies of nearly pure CM2-chondrite, olivine, glass, and diogenite are not found in this region. Although there are no unambiguous spectral features of impact melt, the investigation of morphological features using FC clear filter data from Low Altitude Mapping Orbit (resolution ∼ 18 m/pixel) suggests potential impact-melt features inside and outside of the crater. Our spectral approach can be extended to the entire Vestan surface to study the heterogeneous surface composition and its geology.

Olefin metathesis for effective polymer healing via dynamic exchange of strong carbon-carbon bonds

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

Guan, Zhibin; Lu, Yixuan

A method of preparing a malleable and/or self-healing polymeric or composite material is provided. The method includes providing a polymeric or composite material comprising at least one alkene-containing polymer, combining the polymer with at least one homogeneous or heterogeneous transition metal olefin metathesis catalyst to form a polymeric or composite material, and performing an olefin metathesis reaction on the polymer so as to form reversible carbon-carbon double bonds in the polymer. Also provided is a method of healing a fractured surface of a polymeric material. The method includes bringing a fractured surface of a first polymeric material into contact withmore » a second polymeric material, and performing an olefin metathesis reaction in the presence of a transition metal olefin metathesis catalyst such that the first polymeric material forms reversible carbon-carbon double bonds with the second polymeric material. Compositions comprising malleable and/or self-healing polymeric or composite material are also provided.« less

Heterogeneous Nucleation of Protein Crystals on Fluorinated Layered Silicate

PubMed Central

Ino, Keita; Udagawa, Itsumi; Iwabata, Kazuki; Takakusagi, Yoichi; Kubota, Munehiro; Kurosaka, Keiichi; Arai, Kazuhito; Seki, Yasutaka; Nogawa, Masaya; Tsunoda, Tatsuo; Mizukami, Fujio; Taguchi, Hayao; Sakaguchi, Kengo

2011-01-01

Here, we describe an improved system for protein crystallization based on heterogeneous nucleation using fluorinated layered silicate. In addition, we also investigated the mechanism of nucleation on the silicate surface. Crystallization of lysozyme using silicates with different chemical compositions indicated that fluorosilicates promoted nucleation whereas the silicates without fluorine did not. The use of synthesized saponites for lysozyme crystallization confirmed that the substitution of hydroxyl groups contained in the lamellae structure for fluorine atoms is responsible for the nucleation-inducing property of the nucleant. Crystallization of twelve proteins with a wide range of pI values revealed that the nucleation promoting effect of the saponites tended to increase with increased substitution rate. Furthermore, the saponite with the highest fluorine content promoted nucleation in all the test proteins regardless of their overall net charge. Adsorption experiments of proteins on the saponites confirmed that the density of adsorbed molecules increased according to the substitution rate, thereby explaining the heterogeneous nucleation on the silicate surface. PMID:21818343

Selective growth of n-type nanoparticles on p-type semiconductors for Z-scheme photocatalysis.

PubMed

Miyauchi, Masahiro; Nukui, Yuuya; Atarashi, Daiki; Sakai, Etsuo

2013-10-09

Nanoparticles of an n-type WO3 semiconductor were segregated on the surface of p-type CaFe2O4 particles by a heterogeneous nucleation process under controlled hydrothermal conditions. By use of this approach, WO3 nanoparticles were selectively deposited on the surface of CaFe2O4, resulting in a significant increase in the photocatalytic reaction rate of the WO3/CaFe2O4 composite for the decomposition of gaseous acetaldehyde under visible-light irradiation. The high visible-light activity of the WO3/CaFe2O4 composite was due to efficient charge recombination through the junctions that formed between the two semiconductors.

Examining Model Atmospheric Particles Inside and Out

NASA Astrophysics Data System (ADS)

Wingen, L. M.; Zhao, Y.; Fairhurst, M. C.; Perraud, V. M.; Ezell, M. J.; Finlayson-Pitts, B. J.

2017-12-01

Atmospheric particles scatter incoming solar radiation and act as cloud condensation nuclei (CCN), thereby directly and indirectly affecting the earth's radiative balance and reducing visibility. These atmospheric particles may not be uniform in composition. Differences in the composition of a particle's outer surface from its core can arise during particle growth, (photo)chemical aging, and exchange of species with the gas phase. The nature of the surface on a molecular level is expected to impact growth mechanisms as well as their ability to act as CCN. Model laboratory particle systems are explored using direct analysis in real time-mass spectrometry (DART-MS), which is sensitive to surface composition, and contrasted with average composition measurements using high resolution, time-of-flight aerosol mass spectrometry (HR-ToF-AMS). Results include studies of the heterogeneous reactions of amines with solid dicarboxylic acid particles, which are shown to generate aminium dicarboxylate salts at the particle surface, leaving an unreacted core. Combination of both mass spectrometric techniques reveals a trend in reactivity of C3-C7 dicarboxylic acids with amines and allows calculation of the DART probe depth into the particles. The results of studies on additional model systems that are currently being explored will also be reported.

Constraining the Compositional Heterogeneity in CO-Dominated Comet C/2016 R2 (PanSTARRS)

NASA Astrophysics Data System (ADS)

McKay, Adam; Kelley, Michael; DiSanti, Michael; Womack, Maria; Wierzchos, Kacper; Biver, Nicolas; de Val-Borro, Miguel; Cordiner, Martin; Dello Russo, Neil; Feaga, Lori; Bauer, James; Cochran, Anita; Harrington Pinto, Olga

2018-05-01

Comets exhibit a primitive volatile composition, making them invaluable tools for understanding the formation of the Solar System. Constraining the compositional heterogeneity of cometary nuclei is vital for interpreting cometary composition in terms of the physical conditions operating in the protosolar disk at the time of planet formation. Some comets exhibit variability in observed coma composition over the course of their orbit. This could be indicative of a heterogeneous nucleus consisting of cometesimals formed in different parts of the protosolar nebula under differing conditions. Alternatively, the observed heterogeneity could be post-formation evolution. We propose to use Spitzer IRAC observations of CO2 in the atypically CO-rich comet C/2016 R2 (PanSTARRS) to better understand the compositional heterogeneity of cometary nuclei.

Condensation Dynamics on Mimicked Metal Matrix Hydrophobic Nanoparticle-Composites

NASA Astrophysics Data System (ADS)

Damle, Viraj; Sun, Xiaoda; Rykaczewski, Konrad

2014-11-01

Use of hydrophobic surfaces promotes condensation in the dropwise mode, which is significantly more efficient than the common filmwise mode. However, limited longevity of hydrophobic surface modifiers has prevented their wide spread use in industry. Recently, metal matrix composites (MMCs) having microscale hydrophobic heterogeneities dispersed in hydrophilic metal matrix have been proposed as durable and self-healing alternative to hydrophobic surface coatings interacting with deposited water droplets. While dispersion of hydrophobic microparticles in MMC is likely to lead to surface flooding during condensation, the effect of dispersion of hydrophobic nanoparticles (HNPs) with size comparable to water nuclei critical radii and spacing is not obvious. To this end, we fabricated highly ordered arrays of Teflon nanospheres on silicon substrates that mimic the top surface of the MMCs with dispersed HNPs. We used light and electron microscopy to observe breath figures resulting from condensation on these surfaces at varied degrees of subcooling. Here, we discuss the relation between the droplet size distribution, Teflon nanosphere diameter and spacing, and condensation mode. KR acknowledges startup funding from ASU.

Structure and chemical composition of layers adsorbed at interfaces with champagne.

PubMed

Aguié-Béghin, V; Adriaensen, Y; Péron, N; Valade, M; Rouxhet, P; Douillard, R

2009-11-11

The structure and the chemical composition of the layer adsorbed at interfaces involving champagne have been investigated using native champagne, as well as ultrafiltrate (UFch) and ultraconcentrate (UCch) obtained by ultrafiltration with a 10(4) nominal molar mass cutoff. The layer adsorbed at the air/liquid interface was examined by surface tension and ellipsometry kinetic measurements. Brewster angle microscopy demonstrated that the layer formed on polystyrene by adsorption or drop evaporation was heterogeneous, with a domain structure presenting similarities with the layer adsorbed at the air/liquid interface. The surface chemical composition of polystyrene with the adlayer was determined by X-ray photoelectron spectroscopy (XPS). The contribution of champagne constituents varied according to the liquid (native, UFch, and UCch) and to the procedure of adlayer formation (evaporation, adsorption, and adsorption + rinsing). However, their chemical composition was not significantly influenced either by ultrafiltration or by the procedure of deposition on polystyrene. Modeling this composition in terms of classes of model compounds gave approximately 35% (w/w) of proteins and 65% (w/w) of polysaccharides. In the adlayer, the carboxyl groups or esters represent about 18% of carbon due to nonpolypeptidic compounds, indicating the presence of either uronic acids in the complex structure of pectic polysaccharides or of polyphenolic esters. This structural and chemical information and its relationship with the experimental procedures indicate that proteins alone cannot be used as a realistic model for the macromolecules forming the adsorption layer of champagne. Polysaccharides, the other major macromolecular components of champagne wine, are assembled with proteins at the interfaces, in agreement with the heterogeneous character of the adsorbed layer at interfaces.

Progress in the Analysis of Complex Atmospheric Particles.

PubMed

Laskin, Alexander; Gilles, Mary K; Knopf, Daniel A; Wang, Bingbing; China, Swarup

2016-06-12

This article presents an overview of recent advances in field and laboratory studies of atmospheric particles formed in processes of environmental air-surface interactions. The overarching goal of these studies is to advance predictive understanding of atmospheric particle composition, particle chemistry during aging, and their environmental impacts. The diversity between chemical constituents and lateral heterogeneity within individual particles adds to the chemical complexity of particles and their surfaces. Once emitted, particles undergo transformation via atmospheric aging processes that further modify their complex composition. We highlight a range of modern analytical approaches that enable multimodal chemical characterization of particles with both molecular and lateral specificity. When combined, these approaches provide a comprehensive arsenal of tools for understanding the nature of particles at air-surface interactions and their reactivity and transformations with atmospheric aging. We discuss applications of these novel approaches in recent studies and highlight additional research areas to explore the environmental effects of air-surface interactions.

Scaling isotopic emissions and microbes across a permafrost thaw landscape

NASA Astrophysics Data System (ADS)

Varner, R. K.; Palace, M. W.; Saleska, S. R.; Bolduc, B.; Braswell, B. H., Jr.; Crill, P. M.; Chanton, J.; DelGreco, J.; Deng, J.; Frolking, S. E.; Herrick, C.; Hines, M. E.; Li, C.; McArthur, K. J.; McCalley, C. K.; Persson, A.; Roulet, N. T.; Torbick, N.; Tyson, G. W.; Rich, V. I.

2017-12-01

High latitude peatlands are a significant source of atmospheric methane. This source is spatially and temporally heterogeneous, resulting in a wide range of emission estimates for the atmospheric budget. Increasing atmospheric temperatures are causing degradation of underlying permafrost, creating changes in surface soil moisture, the surface and sub-surface hydrological patterns, vegetation and microbial communities, but the consequences to rates and magnitudes of methane production and emissions are poorly accounted for in global budgets. We combined field observations, multi-source remote sensing data and biogeochemical modeling to predict methane dynamics, including the fraction derived from hydrogenotrophic versus acetoclastic microbial methanogenesis across Stordalen mire, a heterogeneous discontinuous permafrost wetland located in northernmost Sweden. Using the field measurement validated Wetland-DNDC biogeochemical model, we estimated mire-wide CH4 and del13CH4 production and emissions for 2014 with input from field and unmanned aerial system (UAS) image derived vegetation maps, local climatology and water table from insitu and remotely sensed data. Model simulated methanogenic pathways correlate with sequence-based observations of methanogen community composition in samples collected from across the permafrost thaw landscape. This approach enables us to link below ground microbial community composition with emissions and indicates a potential for scaling across broad areas of the Arctic region.

Geographic patterns of fishes and jellyfish in Puget Sound surface waters

USGS Publications Warehouse

Rice, Casimir A.; Duda, Jeffrey J.; Greene, Correigh M.; Karr, James R.

2012-01-01

We explored patterns of small pelagic fish assemblages and biomass of gelatinous zooplankton (jellyfish) in surface waters across four oceanographic subbasins of greater Puget Sound. Our study is the first to collect data documenting biomass of small pelagic fishes and jellyfish throughout Puget Sound; sampling was conducted opportunistically as part of a juvenile salmon survey of daytime monthly surface trawls at 52 sites during May–August 2003. Biomass composition differed spatially and temporally, but spatial differences were more distinct. Fish dominated in the two northern basins of Puget Sound, whereas jellyfish dominated in the two southern basins. Absolute and relative abundance of jellyfish, hatchery Chinook salmon Oncorhynchus tshawytscha, and chum salmon O. keta decreased with increasing latitude, whereas the absolute and relative abundance of most fish species and the average fish species richness increased with latitude. The abiotic factors with the strongest relationship to biomass composition were latitude, water clarity, and sampling date. Further study is needed to understand the spatial and temporal heterogeneity in the taxonomic composition we observed in Puget Sound surface waters, especially as they relate to natural and anthropogenic influences.

Large heterogeneities in comet 67P as revealed by active pits from sinkhole collapse.

PubMed

Vincent, Jean-Baptiste; Bodewits, Dennis; Besse, Sébastien; Sierks, Holger; Barbieri, Cesare; Lamy, Philippe; Rodrigo, Rafael; Koschny, Detlef; Rickman, Hans; Keller, Horst Uwe; Agarwal, Jessica; A'Hearn, Michael F; Auger, Anne-Thérèse; Barucci, M Antonella; Bertaux, Jean-Loup; Bertini, Ivano; Capanna, Claire; Cremonese, Gabriele; Da Deppo, Vania; Davidsson, Björn; Debei, Stefano; De Cecco, Mariolino; El-Maarry, Mohamed Ramy; Ferri, Francesca; Fornasier, Sonia; Fulle, Marco; Gaskell, Robert; Giacomini, Lorenza; Groussin, Olivier; Guilbert-Lepoutre, Aurélie; Gutierrez-Marques, P; Gutiérrez, Pedro J; Güttler, Carsten; Hoekzema, Nick; Höfner, Sebastian; Hviid, Stubbe F; Ip, Wing-Huen; Jorda, Laurent; Knollenberg, Jörg; Kovacs, Gabor; Kramm, Rainer; Kührt, Ekkehard; Küppers, Michael; La Forgia, Fiorangela; Lara, Luisa M; Lazzarin, Monica; Lee, Vicky; Leyrat, Cédric; Lin, Zhong-Yi; Lopez Moreno, Josè J; Lowry, Stephen; Magrin, Sara; Maquet, Lucie; Marchi, Simone; Marzari, Francesco; Massironi, Matteo; Michalik, Harald; Moissl, Richard; Mottola, Stefano; Naletto, Giampiero; Oklay, Nilda; Pajola, Maurizio; Preusker, Frank; Scholten, Frank; Thomas, Nicolas; Toth, Imre; Tubiana, Cecilia

2015-07-02

Pits have been observed on many cometary nuclei mapped by spacecraft. It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact experiments and models cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts. Alternative mechanisms like explosive activity have been suggested, but the driving process remains unknown. Here we report that pits on comet 67P/Churyumov-Gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. We argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. Therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. The size and spatial distribution of pits imply that large heterogeneities exist in the physical, structural or compositional properties of the first few hundred metres below the current nucleus surface.

Constraining the physical properties of compositionally distinctive surfaces on Mars from overlapping THEMIS observations

NASA Astrophysics Data System (ADS)

Ahern, A.; Rogers, D.

2017-12-01

Better constraints on the physical properties (e.g. grain size, rock abundance, cohesion, porosity and amount of induration) of Martian surface materials can lead to greater understanding of outcrop origin (e.g. via sedimentary, effusive volcanic, pyroclastic processes). Many outcrop surfaces on Mars likely contain near-surface (<3 cm) vertical heterogeneity in physical properties due to thin sediment cover, induration, and physical weathering, that can obscure measurement of the bulk thermal conductivity of the outcrop materials just below. Fortunately, vertical heterogeneity within near-surface materials can result in unique, and possibly predictable, diurnal and seasonal temperature patterns. The KRC thermal model has been utilized in a number of previous studies to predict thermal inertia of surface materials on Mars. Here we use KRC to model surface temperatures from overlapping Mars Odyssey THEMIS surface temperature observations that span multiple seasons and local times, in order to constrain both the nature of vertical heterogeneity and the underlying outcrop thermal inertia for various spectrally distinctive outcrops on Mars. We utilize spectral observations from TES and CRISM to constrain the particle size of the uppermost surface. For this presentation, we will focus specifically on chloride-bearing units in Terra Sirenum and Meridiani Planum, as well as mafic and feldspathic bedrock locations with distinct spectral properties, yet uncertain origins, in Noachis Terra and Nili Fossae. We find that many of these surfaces exhibit variations in apparent thermal inertia with season and local time that are consistent with low thermal inertia materials overlying higher thermal inertia substrates. Work is ongoing to compare surface temperature measurements with modeled two-layer scenarios in order to constrain the top layer thickness and bottom layer thermal inertia. The information will be used to better interpret the origins of these distinctive outcrops.

Transport-induced shifts in condensate dew-point and composition in multicomponent systems with chemical reaction

NASA Technical Reports Server (NTRS)

Rosner, D. E.; Nagarajan, R.

1985-01-01

Partial heterogeneous condensation phenomena in multicomponent reacting systems are analyzed taking into consideration the chemical element transport phenomena. It is demonstrated that the dew-point surface temperature in chemically reactive systems is not a purely thermodynamic quantity, but is influenced by the multicomponent diffusion and Soret-mass diffusion phenomena. Several distinct dew-points are shown to exist in such systems and, as a result of transport constraints, the 'sharp' locus between two chemically distinct condensates is systematically moved to a difference mainstream composition.

Cold spraying of aluminum bronze on profiled submillimeter cermet structures formed by laser cladding

NASA Astrophysics Data System (ADS)

Ryashin, N. S.; Malikov, A. G.; Shikalov, V. S.; Gulyaev, I. P.; Kuchumov, B. M.; Klinkov, S. V.; Kosarev, V. F.; Orishich, A. M.

2017-10-01

The paper presents results of the cold spraying of aluminum bronze coatings on substrates profiled with WC/Ni tracks obtained by laser cladding. Reinforcing cermet frames shaped as grids with varied mesh sizes were clad on stainless steel substrates using a CO2 laser machine "Siberia" (ITAM SB RAS, Russia). As a result, surfaces/substrates with heterogeneous shape, composition, and mechanical properties were obtained. Aluminum bronze coatings were deposited from 5lF-NS powder (Oerlikon Metco, Switzerland) on those substrates using cold spraying equipment (ITAM SB RAS). Data of profiling, microstructure diagnostics, EDS analysis, and mechanical tests of obtained composites is reported. Surface relief of the sprayed coatings dependence on substrate structure has been demonstrated.

Developing a shale heterogeneity index to predict fracture response in the Mancos Shale

NASA Astrophysics Data System (ADS)

DeReuil, Aubry; Birgenheier, Lauren; McLennan, John

2017-04-01

The interplay between sedimentary heterogeneity and fracture propagation in mudstone is crucial to assess the potential of low permeability rocks as unconventional reservoirs. Previous experimental research has demonstrated a relationship between heterogeneity and fracture of brittle rocks, as discontinuities in a rock mass influence micromechanical processes such as microcracking and strain localization, which evolve into macroscopic fractures. Though numerous studies have observed heterogeneity influencing fracture development, fundamental understanding of the entire fracture process and the physical controls on this process is still lacking. This is partly due to difficulties in quantifying heterogeneity in fine-grained rocks. Our study tests the hypothesis that there is a correlation between sedimentary heterogeneity and the manner in which mudstone is fractured. An extensive range of heterogeneity related to complex sedimentology is represented by various samples from cored intervals of the Mancos Shale. Samples were categorized via facies analysis consisting of: visual core description, XRF and XRD analysis, SEM and thin section microscopy, and reservoir quality analysis that tested porosity, permeability, water saturation, and TOC. Systematic indirect tensile testing on a broad variety of facies has been performed, and uniaxial and triaxial compression testing is underway. A novel tool based on analytically derived and statistically proven relationships between sedimentary geologic and geomechanical heterogeneity is the ultimate result, referred to as the shale heterogeneity index. Preliminary conclusions from development of the shale heterogeneity index reveal that samples with compositionally distinct bedding withstand loading at higher stress values, while texturally and compositionally homogeneous, bedded samples fail at lower stress values. The highest tensile strength results from cemented Ca-enriched samples, medial to high strength samples have approximately equivalent proportions of Al-Ca-Si compositions, while Al-rich samples have consistently low strength. Moisture preserved samples fail on average at approximately 5 MPa lower than dry samples of similar facies. Additionally, moisture preserved samples fail in a step-like pattern when tested perpendicular to bedding. Tensile fractures are halted at heterogeneities and propagate parallel to bedding planes before developing a through-going failure plane, as opposed to the discrete, continuous fractures that crosscut dry samples. This result suggests that sedimentary heterogeneity plays a greater role in fracture propagation in moisture preserved samples, which are more indicative of in-situ reservoir conditions. Stress-strain curves will be further analyzed, including estimation of an energy released term based on post-failure response, and an estimation of volume of cracking measure on the physical fracture surface.

Spatially-Resolved Analyses of Aerodynamic Fallout from a Uranium-Fueled Nuclear Test

DOE PAGES

Lewis, L. A.; Knight, K. B.; Matzel, J. E.; ...

2015-07-28

The fiive silicate fallout glass spherules produced in a uranium-fueled, near-surface nuclear test were characterized by secondary ion mass spectrometry, electron probe microanalysis, autoradiography, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Several samples display compositional heterogeneity suggestive of incomplete mixing between major elements and natural U ( 238U/ 235U = 0.00725) and enriched U. Samples exhibit extreme spatial heterogeneity in U isotopic composition with 0.02 < 235U/ 238U < 11.84 among all five spherules and 0.02 < 235U/ 238U < 7.41 within a single spherule. Moreover, in two spherules, the 235U/ 238U ratio is correlated with changes in major elementmore » composition, suggesting the agglomeration of chemically and isotopically distinct molten precursors. Two samples are nearly homogenous with respect to major element and uranium isotopic composition, suggesting extensive mixing possibly due to experiencing higher temperatures or residing longer in the fireball. Linear correlations between 234U/ 238U, 235U/ 238U, and 236U/ 238U ratios are consistent with a two-component mixing model, which is used to illustrate the extent of mixing between natural and enriched U end members.« less

Magnetically separable maghemite/montmorillonite composite as an efficient heterogeneous Fenton-like catalyst for phenol degradation.

PubMed

Jin, Mingjie; Long, Mingce; Su, Hanrui; Pan, Yue; Zhang, Qiuzhuo; Wang, Juan; Zhou, Baoxue; Zhang, Yanwu

2017-01-01

To develop highly efficient and conveniently separable iron containing catalysts is crucial to remove recalcitrant organic pollutants in wastewater through a heterogeneous Fenton-like reaction. A maghemite/montmorillonite composite was synthesized by a coprecipitation and calcination method. The physiochemical properties of catalysts were characterized by XRD, TEM, nitrogen physisorption, thermogravimetric analysis/differential scanning calorimetry (TG/DSC), zeta potential, and magnetite susceptibility measurements. The influence of calcination temperatures and reaction parameters was investigated. The calcined composites retain magnetism because the presence of montmorillonite inhibited the growth of γ-Fe 2 O 3 nanoparticles, as well as their phase transition. The catalytic activities for phenol degradation were significantly enhanced by calcinations, which strengthen the interaction between iron oxides and aluminosilicate framework and result in more negatively charged surface. The composite (73 m 2 /g) calcined at 350 °C had the highest catalytic activities, with more than 99 % phenol reduction after only 35 min reaction at pH 3.6. Simultaneously, this catalyst exhibited high stability, low iron leaching, and magnetically separable ability for consecutive usage, making it promising for the removal of recalcitrant organic pollutants in wastewater.

Surfactant-assisted stabilization of Au colloids on solids for heterogeneous catalysis

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

Zhan, Wangcheng; Shu, Yuan; Sheng, Yujie

Here, the stabilization of surfactant-assisted synthesized colloidal noble metal nanoparticles (NPs, e.g., Au NPs) on solids is a promising strategy for preparing supported nanocatalysts for heterogeneous catalysis because of their uniform particle sizes, controllable shapes, and tunable compositions. However, the removal of surfactants to obtain clean surfaces for catalysis through traditional approaches (e.g., solvent extraction and thermal decomposition) can easily induce the sintering of NPs, greatly hampering their use in synthesis of novel catalysts. Herein, we demonstrate that such unwanted surfactants can be utilized to stabilize NPs on solids via a simple yet efficient thermal annealing strategy. After being annealedmore » in N 2 flow, the surface-bound surfactants are in situ carbonized as sacrificial architectures that form a conformal coating on NPs and assist in creating an enhanced metal-support interaction between NPs and substrate, thus slowing down the Ostwald ripening process during post-oxidative calcination to remove surface covers.« less

Surfactant-assisted stabilization of Au colloids on solids for heterogeneous catalysis

DOE PAGES

Zhan, Wangcheng; Shu, Yuan; Sheng, Yujie; ...

2017-03-22

Here, the stabilization of surfactant-assisted synthesized colloidal noble metal nanoparticles (NPs, e.g., Au NPs) on solids is a promising strategy for preparing supported nanocatalysts for heterogeneous catalysis because of their uniform particle sizes, controllable shapes, and tunable compositions. However, the removal of surfactants to obtain clean surfaces for catalysis through traditional approaches (e.g., solvent extraction and thermal decomposition) can easily induce the sintering of NPs, greatly hampering their use in synthesis of novel catalysts. Herein, we demonstrate that such unwanted surfactants can be utilized to stabilize NPs on solids via a simple yet efficient thermal annealing strategy. After being annealedmore » in N 2 flow, the surface-bound surfactants are in situ carbonized as sacrificial architectures that form a conformal coating on NPs and assist in creating an enhanced metal-support interaction between NPs and substrate, thus slowing down the Ostwald ripening process during post-oxidative calcination to remove surface covers.« less

Basin-scale heterogeneity in Antarctic precipitation and its impact on surface mass variability

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

Fyke, Jeremy; Lenaerts, Jan T. M.; Wang, Hailong

Annually averaged precipitation in the form of snow, the dominant term of the Antarctic Ice Sheet surface mass balance, displays large spatial and temporal variability. Here we present an analysis of spatial patterns of regional Antarctic precipitation variability and their impact on integrated Antarctic surface mass balance variability simulated as part of a preindustrial 1800-year global, fully coupled Community Earth System Model simulation. Correlation and composite analyses based on this output allow for a robust exploration of Antarctic precipitation variability. We identify statistically significant relationships between precipitation patterns across Antarctica that are corroborated by climate reanalyses, regional modeling and icemore » core records. These patterns are driven by variability in large-scale atmospheric moisture transport, which itself is characterized by decadal- to centennial-scale oscillations around the long-term mean. We suggest that this heterogeneity in Antarctic precipitation variability has a dampening effect on overall Antarctic surface mass balance variability, with implications for regulation of Antarctic-sourced sea level variability, detection of an emergent anthropogenic signal in Antarctic mass trends and identification of Antarctic mass loss accelerations.« less

Basin-scale heterogeneity in Antarctic precipitation and its impact on surface mass variability

DOE PAGES

Fyke, Jeremy; Lenaerts, Jan T. M.; Wang, Hailong

2017-11-15

Annually averaged precipitation in the form of snow, the dominant term of the Antarctic Ice Sheet surface mass balance, displays large spatial and temporal variability. Here we present an analysis of spatial patterns of regional Antarctic precipitation variability and their impact on integrated Antarctic surface mass balance variability simulated as part of a preindustrial 1800-year global, fully coupled Community Earth System Model simulation. Correlation and composite analyses based on this output allow for a robust exploration of Antarctic precipitation variability. We identify statistically significant relationships between precipitation patterns across Antarctica that are corroborated by climate reanalyses, regional modeling and icemore » core records. These patterns are driven by variability in large-scale atmospheric moisture transport, which itself is characterized by decadal- to centennial-scale oscillations around the long-term mean. We suggest that this heterogeneity in Antarctic precipitation variability has a dampening effect on overall Antarctic surface mass balance variability, with implications for regulation of Antarctic-sourced sea level variability, detection of an emergent anthropogenic signal in Antarctic mass trends and identification of Antarctic mass loss accelerations.« less

The Chemical Structure of the Hawaiian Mantle Plume

NASA Astrophysics Data System (ADS)

Ren, Z.; Hirano, N.; Hirata, T.; Takahashi, E.; Ingle, S.

2004-12-01

Numerous geochemical studies of Hawaiian basaltic lavas have shown that the Hawaiian mantle plume is isotopically heterogeneous. However, the distribution and scale of these heterogeneities remain unknown. This is essentially due to the complex interactions created by melting a heterogeneous source, subsequent aggregation of the melts on their way to the surface, and mixing that takes place in shallow magma chambers prior to eruption. In sum, the measured compositions of bulk lavas may represent only _eaverage_f compositions that do not fully reflect the complexity of either the mantle source heterogeneity and/or chemical structure. Melt inclusions, or samples of the local magma frozen in olivine phenocrysts during their formation, are better at recording the complex magmatic history than are the bulk samples. Here, we report major and trace element compositions of olivine-hosted melt inclusions from submarine Haleakala lavas that were collected by 2001-2002 JAMSTEC cruises measured by EPMA and LA-ICP-MS after homogenization at 1250° C, QFM for 20min. Melt inclusions from the submarine Hana Ridge (Haleakala volcano) show large ranges in CaO/Al2O3 (0.92-1.50), TiO2/Na2O (0.79-1.60) and Sr/Nb (14.56-36.60), Zr/Nb (6.48-16.95), ranging from Kilauea-like to Mauna Loa-like compositions within separately-sampled lavas as well as in a single host lava sample. Bulk rocks geochemistry shows that major element composition and trace element ratios such as Zr/Nb, Sr/Nb (Ren et al., 2004a, in press, J. Petrol.) together with Pb, Nd and Sr isotopic ratios (Ren et al., 2004b, submitted to J. Petrol.) of Haleakala shield volcano also display systematic compositional variation changing from a Kilauea-like in the submarine Hana Ridge (main shield stage) to Kilauea-Mauna Loa-like in the subaerial Honomanu stage (late shield stage, data from Chen and Frey, 1991). Some of the compositional variations in melt inclusions in single rocks are wider range than over-all variation observed in bulk rocks. It is important that both Kilauea-like and Mauna Loa-like compositions co-exist in melt inclusions in single submarine Hana Ridge rocks which are identified as Kilauea-like based on bulk geochemistry. These observations are inconsistent with the current interpretation that magma compositions are controlled by concentric zonation of the Hawaiian mantle plume (e.g. Kea component and Loa component), manifested as the Kea trend and the Loa trend volcanoes (e.g. Hauri, 1996; Lassiter et al., 1996). Our new data from olivine-hosted melt inclusions imply that the chemical structure of the Hawaiian mantle plume is significantly more complicated than previously modeled and the length-scale of chemical heterogeneity must be remarkably smaller than estimated based on bulk rock geochemistry.

Light-induced heterogeneous reactions of NO2 on indoor surfaces: How they affect the balance of nitrous acid

NASA Astrophysics Data System (ADS)

Gomez Alvarez, E.; Soergel, M.; Bassil, S.; Zetzsch, C.; Gligorovski, S.; Wortham, H.

2011-12-01

Nitrous acid (HONO) is an important indoor pollutant. The adverse health effects due to the formation of nitrosamines are well known. HONO acts as a nitrosating agent after wall reactions of HONO with nicotine [Sleiman et al., 2010]. Indoor air can be surprisingly rich in HONO (homes with fireplaces, stoves, gas heating and cooking) and also surfaces are abundant. High HONO concentrations have been measured in indoor environments, from the direct emissions and heterogeneous reactions of NO2 in darkness. However, the measured HONO concentrations do not correspond to the HONO levels determined by the models [Carslaw, 2007]. We have tested in a flow tube reactor on-line coupled to a NOx analyzer and a sensitive Long Path Absorption Photometry instrument, the behaviour of various indoor surfaces towards NO2 under simulated solar light irradiation (λ= 300-700 nm). Our study has allowed us to obtain a deeper knowledge on the mechanisms of heterogeneous formation of HONO, quantifying the dependence of HONO formation on behalf of NO2 concentration and relative humidity and the enhancement of HONO formation in the presence of light. Pyrex, acidic detergent, alkaline detergent, paint and lacquer were tested on behalf of their heterogeneous reactivity towards NO2 in the absence and in presence of light. The results obtained demonstrated that indoor surfaces are photo-chemically active under atmospherically relevant conditions. The strongly alkaline surfaces (such as certain types of detergent) show a strong long-term uptake capacity. However, other surfaces such as detergents with a more acidic character released HONO. In some cases such as paint and varnish, a strong HONO release with light was detected, which was significantly higher than that obtained over clean glass surfaces. Certain organics present on their composition could exert a photo-sensitizing effect that may explain their increased reactivity. Unfortunately, the final balance points towards an important net production of HONO from organics usually applied on different indoor surfaces that add to the very powerful HONO production simply due to heterogeneous reactivity on bare indoor surfaces. The results of this study add to the increasing concern over the reactivity in indoor environments and in particular from the point of view of HONO formation kinetics.

Progress in the Analysis of Complex Atmospheric Particles

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

Laskin, Alexander; Gilles, Mary K.; Knopf, Daniel A.

2016-06-16

This manuscript presents an overview on recent advances in field and laboratory studies of atmospheric particles formed in processes of environmental air-surfaces interactions. The overarching goal of these studies is to advance predictive understanding of atmospheric particle composition, particle chemistry during aging, and their environmental impacts. The diversity between chemical constituents and lateral heterogeneity within individual particles adds to the chemical complexity of particles and their surfaces. Once emitted, particles undergo transformation via atmospheric aging processes that further modify their complex composition. We highlight a range of modern analytical approaches that enable multi-modal chemical characterization of particles with both molecularmore » and lateral specificity. When combined, they provide a comprehensive arsenal of tools for understanding the nature of particles at air-surface interactions and their reactivity and transformations with atmospheric aging. We discuss applications of these novel approaches in recent studies and highlight additional research areas to explore environmental effects of air-surface interactions.« less

Progress in the analysis of complex atmospheric particles

DOE PAGES

Laskin, Alexander; Gilles, Mary K.; Knopf, Daniel A.; ...

2016-06-01

This study presents an overview of recent advances in field and laboratory studies of atmospheric particles formed in processes of environmental air-surface interactions. The overarching goal of these studies is to advance predictive understanding of atmospheric particle composition, particle chemistry during aging, and their environmental impacts. The diversity between chemical constituents and lateral heterogeneity within individual particles adds to the chemical complexity of particles and their surfaces. Once emitted, particles undergo transformation via atmospheric aging processes that further modify their complex composition. We highlight a range of modern analytical approaches that enable multimodal chemical characterization of particles with both molecularmore » and lateral specificity. When combined, these approaches provide a comprehensive arsenal of tools for understanding the nature of particles at air-surface interactions and their reactivity and transformations with atmospheric aging. We discuss applications of these novel approaches in recent studies and highlight additional research areas to explore the environmental effects of air-surface interactions.« less

Understanding and exploiting nanoscale surface heterogeneity for particle and cell manipulation

NASA Astrophysics Data System (ADS)

Kalasin, Surachate

This thesis explores the impact of surface heterogeneities on colloidal interactions and translates concepts to biointerfacial systems, for instance, microfluidic and biomedical devices. The thesis advances a model system, originally put forth by Kozlova: Tunable electrostatic surface heterogeneity is produced by adsorbing small amounts of cationic polyelectrolyte on a silica flat. The resulting positive electrostatic patches possess a density that is tuned from a saturated carpet down to average spacings on the order of a few hundred nanometers. At these length-scales, multiple adhesive elements (from tens to thousands) are present in the area of contact between a particle and a surface, a distinguishing feature of the thesis. Much of the literature addressing surface "heterogeneity" engineers surfaces with micron-scale features, almost always larger than the contact area between a particle and a second surface. With a nanoscale heterogeneity model, this thesis reports and quantitatively explains particle interaction behavior not typical of homogeneous interfaces. This includes (1) an adhesion threshold, a minimum average surface density of cationic patches needed for particle capture, (previously observed by Kozlova); (2) a crossover, from salt-destabilized to salt-stabilized interactions between heterogeneous surfaces with net-negative charge; (3) a shift of the adhesion threshold with shear, reducing adhesion; (4) a crossover from shear-enhanced to shear-hindered particle adhesion; (5) a range of surface compositions and processing parameters that sustain particle rolling; and (6) conditions where particles arrest immediately on contact. Through variations in ionic strength and particle size, the particle-surface contact area is systematically varied relative to the heterogeneity lengthscale. This provides a semi-quantitative explanation for the shifting of the adhesion threshold, in terms of the statistical probability of a particle being able to find a surface region sufficiently attractive for capture. Though neglecting hydrodynamics, the resulting (kappa-1a)1/2 power law scaling for the density of patches at the adhesion threshold roughly captures the general shape of the data. The study also reveals that at high ionic strength, particle-surface interactions are most influenced by the patchy surface heterogeneity; however, at low ionic strengths, the system becomes most sensitive to the average system properties. Thus for heterogeneous interfaces, the extent to which heterogeneity is influential depends on other factors (particle size, ionic strength). While this comprises a crossover from heterogeneity-dominated to mean field behavior, it is worth noting that even in the mean field regime, the spacing between patches always exceeds the Debye length, making the regions of different surface charge always distinct. Comparison with the simulations of Duffadar and Davis reveals that the criterion for particle capture is a nearly constant number of cationic patches per unit area of contact between a particle and a heterogeneous collector. The heterogeneous surface model displays a shear crossover seen with bacteria and other complex systems: At low shear, particle capture is enhanced, while at higher shears it is reduced. This behavior, sometimes rationalized in terms of the complex energy landscapes of biological bonds, is clearly explained in the heterogeneity model. For weakly adhesive systems engaging only a few adhesive elements or receptors, shear compromises the ability of a few bonds to capture particles. For more strongly adhesive systems, shear increases particle transport. The convolution of this competition leads to the non-monotonic effect of shear seen in biology. The complex variety of particle behaviors combined with the large number of independently variable parameters, each with different scaling of interfacial forces, necessitates a state-space approach to mapping regimes interactions and motion signatures. Following the approach taken by biophysicists for describing the interactions of leukocytes with the endothelial vasculature near an injury, the state spaces in this thesis map regimes of free particle motion, immediate firm arrest, and persistent rolling against macroscopic average patch density, Debye length, particle size, and shear rate. Surprisingly, the electrostatic heterogeneity state space resembles that for selectin-mediated leukocyte motion, and reasons are put forth. This finding is important because it demonstrates how synthetic nanoscale constructs can be exploited to achieve the selective cell capture mechanism previously attributed only to specialized cell adhesion molecules. This thesis initiates studies that extend these fundamental principles, developed for a tunable and well-characterized synthetic model to biological systems. For instance, it is demonstrated that general behaviors seen with the electrostatic model are observed when fibrinogen proteins are substituted for the electrostatic patches. This shows that the nature of the attractions is immaterial to adhesion, and that the effect of added salt primarily alters the range of the electrostatic repulsion and, correspondingly, the contact area. Also, studies with Staphylococcus aureus run parallel to those employing 1 mum silica spheres, further translating the concepts. Inaugural studies with mammalian cells, in the future work section, indicate that application of the surface heterogeneity approach to cell manipulation holds much future promise.

Surface compositional variation on the comet 67P/Churyumov-Gerasimenko by OSIRIS data

NASA Astrophysics Data System (ADS)

Barucci, M. A.; Fornasier, S.; Feller, C.; Perna, D.; Hasselmann, H.; Deshapriya, J. D. P.; Fulchignoni, M.; Besse, S.; Sierks, H.; Forgia, F.; Lazzarin, M.; Pommerol, A.; Oklay, N.; Lara, L.; Scholten, F.; Preusker, F.; Leyrat, C.; Pajola, M.; Osiris-Rosetta Team

2015-10-01

Since the Rosetta mission arrived at the comet 67P/Churyumov-Gerasimenko (67/P C-G) on July 2014, the comet nucleus has been mapped by both OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System, [1]) NAC (Narrow Angle Camera) and WAC (Wide Angle Camera) acquiring a huge quantity of surface's images at different wavelength bands, under variable illumination conditions and spatial resolution, and producing the most detailed maps at the highest spatial resolution of a comet nucleus surface.67/P C-G's nucleus shows an irregular bi-lobed shape of complex morphology with terrains showing intricate features [2, 3] and a heterogeneity surface at different scales.

Molecular catalysis science: Perspective on unifying the fields of catalysis.

PubMed

Ye, Rong; Hurlburt, Tyler J; Sabyrov, Kairat; Alayoglu, Selim; Somorjai, Gabor A

2016-05-10

Colloidal chemistry is used to control the size, shape, morphology, and composition of metal nanoparticles. Model catalysts as such are applied to catalytic transformations in the three types of catalysts: heterogeneous, homogeneous, and enzymatic. Real-time dynamics of oxidation state, coordination, and bonding of nanoparticle catalysts are put under the microscope using surface techniques such as sum-frequency generation vibrational spectroscopy and ambient pressure X-ray photoelectron spectroscopy under catalytically relevant conditions. It was demonstrated that catalytic behavior and trends are strongly tied to oxidation state, the coordination number and crystallographic orientation of metal sites, and bonding and orientation of surface adsorbates. It was also found that catalytic performance can be tuned by carefully designing and fabricating catalysts from the bottom up. Homogeneous and heterogeneous catalysts, and likely enzymes, behave similarly at the molecular level. Unifying the fields of catalysis is the key to achieving the goal of 100% selectivity in catalysis.

Molecular catalysis science: Perspective on unifying the fields of catalysis

PubMed Central

Ye, Rong; Hurlburt, Tyler J.; Sabyrov, Kairat; Alayoglu, Selim; Somorjai, Gabor A.

2016-01-01

Colloidal chemistry is used to control the size, shape, morphology, and composition of metal nanoparticles. Model catalysts as such are applied to catalytic transformations in the three types of catalysts: heterogeneous, homogeneous, and enzymatic. Real-time dynamics of oxidation state, coordination, and bonding of nanoparticle catalysts are put under the microscope using surface techniques such as sum-frequency generation vibrational spectroscopy and ambient pressure X-ray photoelectron spectroscopy under catalytically relevant conditions. It was demonstrated that catalytic behavior and trends are strongly tied to oxidation state, the coordination number and crystallographic orientation of metal sites, and bonding and orientation of surface adsorbates. It was also found that catalytic performance can be tuned by carefully designing and fabricating catalysts from the bottom up. Homogeneous and heterogeneous catalysts, and likely enzymes, behave similarly at the molecular level. Unifying the fields of catalysis is the key to achieving the goal of 100% selectivity in catalysis. PMID:27114536

Electroformation of Janus and patchy capsules

NASA Astrophysics Data System (ADS)

Rozynek, Zbigniew; Mikkelsen, Alexander; Dommersnes, Paul; Fossum, Jon Otto

2014-05-01

Janus and patchy particles have designed heterogeneous surfaces that consist of two or several patches with different materials properties. These particles are emerging as building blocks for a new class of soft matter and functional materials. Here we introduce a route for forming heterogeneous capsules by producing highly ordered jammed colloidal shells of various shapes with domains of controlled size and composition. These structures combine the functionalities offered by Janus or patchy particles, and those given by permeable shells such as colloidosomes. The simple assembly route involves the synergetic action of electro-hydrodynamic flow and electro-coalescence. We demonstrate that the method is robust and straightforwardly extendable to production of multi-patchy capsules. This forms a starting point for producing patchy colloidosomes with domains of anisotropic chemical surface properties, permeability or mixed liquid-solid phase domains, which could be exploited to produce functional emulsions, light and hollow supra-colloidosome structures, or scaffolds.

Synthesis of composite nanoparticles using co-precipitation of a magnetic iron-oxide shell onto core nanoparticles

NASA Astrophysics Data System (ADS)

Primc, Darinka; Belec, Blaž; Makovec, Darko

2016-03-01

Composite nanoparticles can be synthesized by coating a shell made of one material onto core nanoparticles made of another material. Here we report on a novel method for coating a magnetic iron oxide onto the surface of core nanoparticles in an aqueous suspension. The method is based on the heterogeneous nucleation of an initial product of Fe3+/Fe2+ co-precipitation on the core nanoparticles. The close control of the supersaturation of the precipitating species required for an exclusively heterogeneous nucleation and the growth of the shell were achieved by immobilizing the reactive Fe3+ ions in a nitrate complex with urea ([Fe((CO(NH2)2)6](NO3)3) and by using solid Mg(OH)2 as the precipitating reagent. The slow thermal decomposition of the complex at 60 °C homogeneously releases the reactive Fe3+ ions into the suspension of the core nanoparticles. The key stage of the process is the thermal hydrolysis of the released Fe3+ ions prior to the addition of Mg(OH)2. The thermal hydrolysis results in the formation of γ-FeOOH, exclusively at the surfaces of the core nanoparticles. After the addition of the solid hydroxide Mg(OH)2, the pH increases and at pH 5.7 the Fe2+ precipitates and reacts with the γ-FeOOH to form magnetic iron oxide with a spinel structure (spinel ferrite) at the surfaces of the core nanoparticles. The proposed low-temperature method for the synthesis of composite nanoparticles is capable of forming well-defined interfaces between the two components, important for the coupling of the different properties. The procedure is environmentally friendly, inexpensive, and appropriate for scaling up to mass production.

Impact-induced compositional variations on Mercury

NASA Astrophysics Data System (ADS)

Rivera-Valentin, E. G.; Barr, A. C.

2013-12-01

The surface of Mercury shows unexpected spectral variations spatially associated with crater and basin ejecta (the so-called 'low-reflectance material' or LRM; [1]). The low reflectance is suggested to be caused by a native darkening agent at depth that has been excavated and redeposited onto the surface [1]. Although LRM is generally associated with crater ejecta, it is not found within the ejecta blankets of many large impact craters, perhaps suggesting that the subsurface source is heterogeneous [2]. We have developed a 3-D Monte Carlo model of impact cratering, excavation, and ejecta blanket deposition. Our simulations of the effect of early impacts onto Mercury show that if the LRM originates from depth to cover ~15% of Mercury's surface [2], its source is ~30 km deep. Considering the estimated mercurian crustal thickness of 50 km [3] this implies the darkening agent is most probably located within a chemically distinct lower crust. Simulations show that repeated and overlapping impacts redistribute the darkening agent away from the basin source and create a weak association between crater size and LRM abundance. Thus subsurface heterogeneity is not required to produce the weak association between crater size and LRM abundance within crater ejecta; this is a natural consequence of overlapping impacts. Our results can elucidate the new high-resolution compositional mapping of Mercury's heavily cratered terrain and provide insight into subsurface composition. Acknowledgements: This work is supported by the Center for Lunar Origin and Evolution through the NASA Lunar Science Institute NNA09DB32A. References: [1] Denevi and Robinson, 2008, Icarus 197, 239-246. [2] Denevi et al., 2009, Science 324, 613-618. [3] Smith et al., 2012, Science 336, 214-217.

The dynamics of methane emissions in Alaskan peatlands at different trophic levels

NASA Astrophysics Data System (ADS)

Zhang, L.; Liu, X.; Langford, L.; Chanton, J.; Hines, M. E.

2016-12-01

One major uncertainty in estimating methane (CH4) emission from wetlands is extrapolating from highly heterogeneous and inadequately studied local sites to larger scales. The heterogeneity of peatlands comes from contrasting surface vegetation compositions within short distances that are usually associated with different nutrient sources and trophic status. Different microbial communities and metabolic pathways occur at different trophic levels. Stable isotope C ratios (δ13C) have been used as a robust tool to distinguish methanogenic pathways, but different sources of parent compounds (acetate and CO2) with unique δ13C signatures, and unresolved fractionation factors associated with different methanogens, add complexity. To better understand the relationships between trophic status, surface vegetation compositions and methanogenic pathways, 28 peatland sites were studied in Fairbanks and Anchorage, Alaska in the summer of 2015. These sites were ordinated using multiple factor analysis into 3 clusters based on pH, temp, CH4 and volatile fatty acids production rates, δ13C values, and surface vegetation composition. In the low-pH trophic cluster (pH 4.2), Sphagnum fuscum was the dominant species with specific sedges (Ledum decumbens), and primary fermentation rates was slow with no CH4 detected. In the intermediate trophic level (pH 5.3), in which Sphagnum magellanicum was largely present, both hydrogenotrophic (HM) and acetoclastic methanogenesis (AM) were very active. Syntrophy was present at certain sites, which may provide CO2 and acetate with unique δ13C for CH4 production. At the highest pH trophic cluster examined in this study (pH 5.8), Carex tenuiflora, Carex aquatilis, and Sphagnum Squarrosum dominated. CH4 production rates were higher than those in the intermediate cluster and the apparent fractionation factor a was lower.

Simultaneous Quantification of Temperature, Pyroxenite Abundance, and Upwelling Rates in the Iceland Mantle Source

NASA Astrophysics Data System (ADS)

Brown, E.; Lesher, C. E.

2014-12-01

The compositions and volumes of basalts erupted at the earth's surface are a function of mantle temperature, mantle composition, and the rate at which the mantle upwells through the melting zone. Thus, basaltic magmatism has long been used to probe the thermal and physiochemical state of the earth's mantle. Great insight has been gained into the mantle beneath the global spreading ridge system, where the mantle source is assumed to be homogeneous peridotite that upwells passively [1]. However, it is now recognized that many basalt source regions are lithologically heterogeneous (i.e. containing recycled lithospheric material ranging from harzburgite to pyroxenite) and upwell at rates in excess of those governed by plate separation. To account for these complexities, we have developed a forward melting model for lithologically heterogeneous mantle that incorporates thermodynamically and experimentally constrained melting functions for a range of peridotite and pyroxenite lithologies. The model is unique because it quantifies mantle upwelling rates based on the net buoyancy of the source, thus providing a means for linking basalt compositions/volumes to mantle flow while accounting for source heterogeneity. We apply the model to investigate the mantle properties governing magmatism along different rift segments in Iceland, where lithologic heterogeneity and variable upwelling rates have been inferred through geochemical means [2,3]. Using constraints from seismically determined crustal thicknesses and recent estimates of the proportion of pyroxenite-derived melt contributing to Icelandic basalt compositions [4,5], we show that mantle sources beneath Iceland have excess potential temperatures >85 °C, contain <7% pyroxenite, and maximum upwelling rates ~14 times the passive rate. Our modeling highlights the dominant role of elevated mantle temperature and enhanced upwelling for high productivity magmatism in Iceland, and a subordinate role for mantle heterogeneity, which is required to account for much of the observed chemical and isotopic diversity. [1] Langmuir et al, 1992, AGU Geophys. Mono. Ser. 71 [2] Chauvel & Hemond, 2000, G-cubed, v 1 [3] Kokfelt et al, 2003, EPSL, v 214 [4] Sobolev et al, 2007, Science, v 316 [5] Shorttle et al, 2014, EPSL, v 395

Structure and composition of insulin fibril surfaces probed by TERS

PubMed Central

Kurouski, Dmitry; Deckert-Gaudig, Tanja; Deckert, Volker; Lednev, Igor K.

2012-01-01

Amyloid fibrils associated with many neurodegenerative diseases are the most intriguing targets of modern structural biology. Significant knowledge has been accumulated about the morphology and fibril-core structure recently. However, no conventional methods could probe the fibril surface despite its significant role in the biological activity. Tip-enhanced Raman spectroscopy (TERS) offers a unique opportunity to characterize the surface structure of an individual fibril due to a high depth and lateral spatial resolution of the method in the nanometer range. Here, TERS is utilized for characterizing the secondary structure and amino acid residue composition of the surface of insulin fibrils. It was found that the surface is strongly heterogeneous and consists of clusters with various protein conformations. More than 30% of the fibril surface is dominated by β-sheet secondary structure, further developing Dobson’s model of amyloid fibrils (Jimenez et al. Proc. Natl. Acad. Sci. USA 2002). The propensity of various amino acids on the fibril surface and specific surface secondary structure elements were evaluated. β-sheet areas are rich in cysteine and aromatic amino acids, such as phenylalanine and tyrosine, whereas proline was found only in α-helical and unordered protein clusters. In addition, we showed that carboxyl, amino and imino groups are nearly equally distributed over β-sheet and α-helix/unordered regions. Overall, this study provides valuable new information about the structure and composition of the insulin fibril surface and demonstrates the power of TERS for fibril characterization. PMID:22813355

Chemical composition and heterogeneous reactivity of soot generated in the combustion of diesel and GTL (Gas-to-Liquid) fuels and amorphous carbon Printex U with NO2 and CF3COOH gases

NASA Astrophysics Data System (ADS)

Tapia, A.; Salgado, S.; Martín, P.; Villanueva, F.; García-Contreras, R.; Cabañas, B.

2018-03-01

The heterogeneous reactions of nitrogen dioxide (NO2) and trifluoroacetic acid (CF3COOH) with soot produced by diesel and GTL (gas-to-liquid) fuels were investigated using a Knudsen flow reactor with mass spectrometry as a detection system for gas phase species. Soot was generated with a 4 cylinder diesel engine working under steady-state like urban operation mode. Heterogeneous reaction of the mentioned gases with a commercial carbon, Printex U, used as reference, was also analyzed. The initial and the steady-state uptake coefficients, γ0 and γss, respectively, were measured indicating that GTL soot reacts faster than diesel soot and Printex U carbon for NO2 gas reactant. According to the number of reacted molecules on the surface, Printex U soot presents more reducing sites than diesel and GTL soot. Initial uptake coefficients for GTL and diesel soot for the reaction with CF3COOH gas reactant are very similar and no clear conclusions can be obtained related to the initial reactivity. The number of reacted molecules calculated for CF3COOH reactions shows values two orders of magnitude higher than the corresponding to NO2 reactions, indicating a greater presence of basic functionalities in the soot surfaces. More information of the surface composition has been obtained using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) before and after the reaction of soot samples with gas reactants. As conclusion, the interface of diesel and GTL soot before reaction mainly consists of polycyclic aromatic hydrocarbons (PAHs), nitro-compounds as well as ether functionalities. After reaction with gas reactant, it was observed that PAHs and nitro-compounds remain on the soot surface and new spectral bands such as carbonyl groups (carboxylic acids, aldehydes, esters and ketones) are observed. Physical properties of soot from both fuels studied such as BET surface isotherm and SEM analysis were also developed and related to the observed reactivity.

The Sources and Significance of Stratospheric Water Vapor: Mechanistic Studies from Equator to Pole

NASA Astrophysics Data System (ADS)

Smith, Jessica Birte

It is the future of the stratospheric ozone layer, which protects life at Earth's surface from harmful ultraviolet (UV) radiation, that is the focus of the present work. Fundamental changes in the composition and structure of the stratosphere in response to anthropogenic climate forcing may lead to catastrophic ozone loss under current, and even reduced, stratospheric halogen loading. In particular, the evolution toward a colder, wetter stratosphere, threatens to enhance the heterogeneous conversion of inorganic halogen from its reservoir species to its catalytically active forms, and thus promote in situ ozone loss. Water vapor concentrations control the availability of reactive surface area, which facilitates heterogeneous chemistry. Furthermore, the rates of the key heterogeneous processes are tightly controlled by the ambient humidity. Thus, credible predictions of UV dosage require a quantitative understanding of both the sensitivity of these chemical mechanisms to water vapor concentrations, and an elucidation of the processes controlling stratospheric water vapor concentrations. Toward this end, we present a set of four case studies utilizing high resolution in situ data acquired aboard NASA aircraft during upper atmospheric research missions over the past two decades. 1) We examine the broad scale humidity structure of the upper troposphere and lower stratosphere from the midlatitudes to the tropics, focusing on cirrus formation and dehydration at the cold-point tropical tropopause. The data show evidence for frequent supersaturation in clear air, and sustained supersaturation in the presence of cirrus. These results challenge the strict thermal control of the tropical tropopause. 2) We investigate the likelihood of cirrus-initiated activation of chlorine in the midlatitude lower stratosphere. At midlatitudes the transition from conditions near saturation below the local tropopause to undersaturated air above greatly reduces the probability of heterogeneous activation and in situ ozone loss in this region. 3) We probe the details of heterogeneous processing in the wintertime Arctic vortex, and find that in situ measurements of OH provide incontrovertible evidence for the heterogeneous reaction of HOCl with HCl. This reaction is critical to sustaining catalytically active chlorine and prolonging ozone loss in the springtime vortex. 4) We revisit the topic of midlatitude ozone loss with an emphasis upon the response of ozone in this region to changes in the chemical composition and thermal structure of the lower stratosphere induced by anthropogenic climate change. Specifically, we show evidence for episodic moisture plumes in the overworld stratosphere generated by the rapid evaporation of ice injected into this region by deep convection, and find that these high water vapor plumes have the potential to alter the humidity of the lower stratosphere, and drastically increase the rate of heterogeneous chemistry and in situ ozone loss, given sufficient reactive surface.

Small-scale spatial heterogeneity of ecosystem properties, microbial community composition and microbial activities in a temperate mountain forest soil.

PubMed

Štursová, Martina; Bárta, Jiří; Šantrůčková, Hana; Baldrian, Petr

2016-12-01

Forests are recognised as spatially heterogeneous ecosystems. However, knowledge of the small-scale spatial variation in microbial abundance, community composition and activity is limited. Here, we aimed to describe the heterogeneity of environmental properties, namely vegetation, soil chemical composition, fungal and bacterial abundance and community composition, and enzymatic activity, in the topsoil in a small area (36 m 2 ) of a highly heterogeneous regenerating temperate natural forest, and to explore the relationships among these variables. The results demonstrated a high level of spatial heterogeneity in all properties and revealed differences between litter and soil. Fungal communities had substantially higher beta-diversity than bacterial communities, which were more uniform and less spatially autocorrelated. In litter, fungal communities were affected by vegetation and appeared to be more involved in decomposition. In the soil, chemical composition affected both microbial abundance and the rates of decomposition, whereas the effect of vegetation was small. Importantly, decomposition appeared to be concentrated in hotspots with increased activity of multiple enzymes. Overall, forest topsoil should be considered a spatially heterogeneous environment in which the mean estimates of ecosystem-level processes and microbial community composition may confound the existence of highly specific microenvironments. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Probing functional groups at the gas-aerosol interface using heterogeneous titration reactions: a tool for predicting aerosol health effects?

PubMed

Setyan, Ari; Sauvain, Jean-Jacques; Guillemin, Michel; Riediker, Michael; Demirdjian, Benjamin; Rossi, Michel J

2010-12-17

The complex chemical and physical nature of combustion and secondary organic aerosols (SOAs) in general precludes the complete characterization of both bulk and interfacial components. The bulk composition reveals the history of the growth process and therefore the source region, whereas the interface controls--to a large extent--the interaction with gases, biological membranes, and solid supports. We summarize the development of a soft interrogation technique, using heterogeneous chemistry, for the interfacial functional groups of selected probe gases [N(CH(3))(3), NH(2)OH, CF(3)COOH, HCl, O(3), NO(2)] of different reactivity. The technique reveals the identity and density of surface functional groups. Examples include acidic and basic sites, olefinic and polycyclic aromatic hydrocarbon (PAH) sites, and partially and completely oxidized surface sites. We report on the surface composition and oxidation states of laboratory-generated aerosols and of aerosols sampled in several bus depots. In the latter case, the biomarker 8-hydroxy-2'-deoxyguanosine, signaling oxidative stress caused by aerosol exposure, was isolated. The increase in biomarker levels over a working day is correlated with the surface density N(i)(O3) of olefinic and/or PAH sites obtained from O(3) uptakes as well as with the initial uptake coefficient, γ(0), of five probe gases used in the field. This correlation with γ(0) suggests the idea of competing pathways occurring at the interface of the aerosol particles between the generation of reactive oxygen species (ROS) responsible for oxidative stress and cellular antioxidants.

NMR analysis of compositional heterogeneity in polysaccharides

USDA-ARS?s Scientific Manuscript database

Many copolysaccharides are compositionally heterogeneous, and the composition determined by the usual analytical or spectroscopic methods provides only an average value. For some polysaccharides, the NMR data contain copolymer sequence information, such as diad, triad, and tetrad sequence intensiti...

Synergistic effect among Cl2, SO2 and NO2 in their heterogeneous reactions on gamma-alumina

NASA Astrophysics Data System (ADS)

Huang, Zhenling; Zhang, Zhaohui; Kong, Weiheng; Feng, Shuo; Qiu, Ye; Tang, Siqun; Xia, Chuanqin; Ma, Lingling; Luo, Min; Xu, Diandou

2017-10-01

Severe haze in China has been a global concern in recent years. Most studies about the mechanism of haze formation mare only focused on the heterogeneous reactions of SO2 and NO2 on mineral aerosols. However, little is known about the role of molecular chlorine (Cl2) in those reactions. Here, we investigated the heterogeneous uptake of Cl2, SO2 and NO2 on γ-Al2O3 particles under different conditions using a quartz-based flow reactor. We found that the existence of γ-Al2O3 seed aerosols significantly promotes the formation of secondary chloride, sulfate and nitrate aerosols, and Cl2, NO2 and SO2 have synergistic effects when they react on γ-Al2O3 surface under humid condition. The results also shows that Cl2 can promote the formation of secondary sulfate and nitrate aerosols on γ-Al2O3 surface. Moreover, Cl2 is much easier to react with the surface of γ-Al2O3 and form secondary Cl- aerosol when comparing with NO2 and SO2, suggesting that Cl2 is of great importance in atmospheric chemistry, it has the potential to alter the surface properties (e.g., chemical composition and fraction) of mineral aerosol, enhance the production of secondary inorganic aerosols in the troposphere, and thus cause adverse effects on the climate and human health.

Treatment of wastewater containing Reactive Brilliant Blue KN-R using TiO2/BC composite as heterogeneous photocatalyst and adsorbent.

PubMed

Zhang, Shici; Lu, Xujie

2018-09-01

Heterogeneous photocatalysis namely titanium dioxide (TiO 2 ) supported on coconut shell biochar (BC) was synthesized by sol-gel method (calcined at 450 °C) in the paper, which was innovatively applied to the decolorization of Reactive Brilliant Blue KN-R. The transmission electron microscopy (TEM) and X-ray diffraction patterns (XRD) results demonstrated that anatase TiO 2 film was firmly immobilized on the surface and pores of BC. The photocatalysis tests under UV high pressure xenon lamp (300 W) showed highest decolorization efficiency occurred at strong acid and alkali conditions (pH = 1 and 11) reached as 99.71% and 96.99% respectively within 60 min. Therefore, the TiO 2 /BC composites demonstrated both photocatalytic and adsorption capacity on KN-R decolorized, and presented quite durable and reusable in regeneration cycles, indicating a widely application possibility in anthraquinones dyeing wastewater treatment. Copyright © 2018 Elsevier Ltd. All rights reserved.

Green's Function and Stress Fields in Stochastic Heterogeneous Continua

NASA Astrophysics Data System (ADS)

Negi, Vineet

Many engineering materials used today are heterogenous in composition e.g. Composites - Polymer Matrix Composites, Metal Matrix Composites. Even, conventional engineering materials - metals, plastics, alloys etc. - may develop heterogeneities, like inclusions and residual stresses, during the manufacturing process. Moreover, these materials may also have intrinsic heterogeneities at a nanoscale in the form of grain boundaries in metals, crystallinity in amorphous polymers etc. While, the homogenized constitutive models for these materials may be satisfactory at a macroscale, recent studies of phenomena like fatigue failure, void nucleation, size-dependent brittle-ductile transition in polymeric nanofibers reveal a major play of micro/nanoscale physics in these phenomena. At this scale, heterogeneities in a material may no longer be ignored. Thus, this demands a study into the effects of various material heterogeneities. In this work, spatial heterogeneities in two material properties - elastic modulus and yield stress - have been investigated separately. The heterogeneity in the elastic modulus is studied in the context of Green's function. The Stochastic Finite Element method is adopted to get the mean statistics of the Green's function defined on a stochastic heterogeneous 2D infinite space. A study of the elastic-plastic transition in a domain having stochastic heterogenous yield stress was done using Mont-Carlo methods. The statistics for various stress and strain fields during the transition were obtained. Further, the effects of size of the domain and the strain-hardening rate on the stress fields during the heterogeneous elastic-plastic transition were investigated. Finally, a case is made for the role of the heterogenous elastic-plastic transition in damage nucleation and growth.

Characterization and Distribution of Lunar Mare Basalt Types Using Remote Sensing Techniques. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Pieters, C.

1977-01-01

The types of basal to be found on the moon were identified using reflectance spectra from a variety of lunar mare surfaces and craters as well as geochemical interpretations of laboratory measurements of reflectance from lunar, terrestrial, and meteoritic samples. Findings indicate that major basaltic units are not represented in lunar sample collections. The existence of late stage high titanium basalts is confirmed. All maria contain lateral variations of compositionally heterogenous basalts; some are vertically inhomogenous with distinctly different subsurface composition. Some basalt types are spectrally gradational, suggesting minor variations in composition. Mineral components of unsampled units can be defined if spectra are obtained with sufficient spectral coverage (.3 to 2.5 micron m) and spatial resolution (approximating .5 km).

Rational design of 3D inverse opal heterogeneous composite microspheres as excellent visible-light-induced NO2 sensors at room temperature.

PubMed

Wang, Tianshuang; Yu, Qi; Zhang, Sufang; Kou, Xueying; Sun, Peng; Lu, Geyu

2018-03-08

The lower gas sensitivity, humidity dependence of the gas sensing properties, and long recovery times of room-temperature gas sensors severely limit their applications. Herein, to address these issues, a series of 3D inverse opal (IO) In 2 O 3 -ZnO heterogeneous composite microspheres (HCMs) are fabricated by ultrasonic spray pyrolysis (USP) employing self-assembled sulfonated polystyrene (S-PS) spheres as a sacrificial template. The 3D IO In 2 O 3 -ZnO HCMs possess highly ordered 3D inverse opal structures and bimodal (meso-scale and macro-scale) pores, which can provide large accessible surface areas and rapid mass transfer, resulting in enhanced gas sensing characteristics. Furthermore, the 3D IO architecture and n-n heterojunctions can extend the photoabsorption range to the visible light area, effectively prolonging the lifetimes of photo-generated charge carriers, and can increase separation of visible light-generated charges. As a result, the as-prepared 3D IO In 2 O 3 -ZnO HCMs deliver excellent NO 2 sensing performance under visible light irradiation at room temperature, such as high sensitivity (R gas /R air = 54.3 to 5 ppm NO 2 ), low detection limit (250 ppb), fast recovery time (188 s), excellent selectivity and humidity independence. These enhanced photo-electronic gas sensing properties are attributed to the combination of highly ordered 3D IO microspheres and In 2 O 3 -ZnO heterogeneous composites.

Effective electromagnetic properties of microheterogeneous materials with surface phenomena

NASA Astrophysics Data System (ADS)

Levin, Valery; Markov, Mikhail; Mousatov, Aleksandr; Kazatchenko, Elena; Pervago, Evgeny

2017-10-01

In this paper, we present an approach to calculate the complex dielectric permittivity of a micro-heterogeneous medium composed of non-conductive solid inclusions embedded into the conductive liquid continuous host. To take into account the surface effects, we approximate the inclusion by a layered ellipsoid consisting of a dielectric core and an infinitesimally thin outer shell corresponding to an electrical double layer (EDL). To predict the effective complex dielectric permittivity of materials with a high concentration of inclusions, we have modified the Effective Field Method (EFM) for the layered ellipsoidal particles with complex electrical properties. We present the results of complex permittivity calculations for the composites with randomly and parallel oriented ellipsoidal inclusions. To analyze the influence of surface polarization, we have accomplished modeling in a wide frequency range for different existing physic-chemical models of double electrical layer. The results obtained show that the tensor of effective complex permittivity of a micro-heterogeneous medium with surface effects has complicate dependences on the component electrical properties, spatial material texture, and the inclusion shape (ellipsoid aspect ratio) and size. The dispersion of dielectric permittivity corresponds to the frequency dependence for individual inclusion of given size, and does not depend on the inclusion concentration.

Detection of oxygen isotopic anomaly in terrestrial atmospheric carbonates and its implications to Mars.

PubMed

Shaheen, R; Abramian, A; Horn, J; Dominguez, G; Sullivan, R; Thiemens, Mark H

2010-11-23

The debate of life on Mars centers around the source of the globular, micrometer-sized mineral carbonates in the ALH84001 meteorite; consequently, the identification of Martian processes that form carbonates is critical. This paper reports a previously undescribed carbonate formation process that occurs on Earth and, likely, on Mars. We identified micrometer-sized carbonates in terrestrial aerosols that possess excess (17)O (0.4-3.9‰). The unique O-isotopic composition mechanistically describes the atmospheric heterogeneous chemical reaction on aerosol surfaces. Concomitant laboratory experiments define the transfer of ozone isotopic anomaly to carbonates via hydrogen peroxide formation when O(3) reacts with surface adsorbed water. This previously unidentified chemical reaction scenario provides an explanation for production of the isotopically anomalous carbonates found in the SNC (shergottites, nakhlaites, chassignites) Martian meteorites and terrestrial atmospheric carbonates. The anomalous hydrogen peroxide formed on the aerosol surfaces may transfer its O-isotopic signature to the water reservoir, thus producing mass independently fractionated secondary mineral evaporites. The formation of peroxide via heterogeneous chemistry on aerosol surfaces also reveals a previously undescribed oxidative process of utility in understanding ozone and oxygen chemistry, both on Mars and Earth.

Detection of oxygen isotopic anomaly in terrestrial atmospheric carbonates and its implications to Mars

PubMed Central

Shaheen, R.; Abramian, A.; Horn, J.; Dominguez, G.; Sullivan, R.; Thiemens, Mark H.

2010-01-01

The debate of life on Mars centers around the source of the globular, micrometer-sized mineral carbonates in the ALH84001 meteorite; consequently, the identification of Martian processes that form carbonates is critical. This paper reports a previously undescribed carbonate formation process that occurs on Earth and, likely, on Mars. We identified micrometer-sized carbonates in terrestrial aerosols that possess excess 17O (0.4–3.9‰). The unique O-isotopic composition mechanistically describes the atmospheric heterogeneous chemical reaction on aerosol surfaces. Concomitant laboratory experiments define the transfer of ozone isotopic anomaly to carbonates via hydrogen peroxide formation when O3 reacts with surface adsorbed water. This previously unidentified chemical reaction scenario provides an explanation for production of the isotopically anomalous carbonates found in the SNC (shergottites, nakhlaites, chassignites) Martian meteorites and terrestrial atmospheric carbonates. The anomalous hydrogen peroxide formed on the aerosol surfaces may transfer its O-isotopic signature to the water reservoir, thus producing mass independently fractionated secondary mineral evaporites. The formation of peroxide via heterogeneous chemistry on aerosol surfaces also reveals a previously undescribed oxidative process of utility in understanding ozone and oxygen chemistry, both on Mars and Earth. PMID:21059939

Using Imaging Spectrometry measurements of Ecosystem Composition to constrain Regional Predictions of Carbon, Water and Energy Fluxes

NASA Astrophysics Data System (ADS)

Anderson, C.; Bond-Lamberty, B. P.; Huang, M.; Xu, Y.; Stegen, J.

2016-12-01

Ecosystem composition is a key attribute of terrestrial ecosystems, influencing the fluxes of carbon, water, and energy between the land surface and the atmosphere. The description of current ecosystem composition has traditionally come from relatively few ground-based inventories of the plant canopy, but are spatially limited and do not provide a comprehensive picture of ecosystem composition at regional or global scales. In this analysis, imaging spectrometry measurements, collected as part of the HyspIRI Preparatory Mission, are used to provide spatially-resolved estimates of plant functional type composition providing an important constraint on terrestrial biosphere model predictions of carbon, water and energy fluxes across the heterogeneous landscapes of the Californian Sierras. These landscapes include oak savannas, mid-elevation mixed pines, fir-cedar forests, and high elevation pines. Our results show that imaging spectrometry measurements can be successfully used to estimate regional-scale variation in ecosystem composition and resulting spatial heterogeneity in patterns of carbon, water and energy fluxes and ecosystem dynamics. Simulations at four flux tower sites within the study region yield patterns of seasonal and inter-annual variation in carbon and water fluxes that have comparable accuracy to simulations initialized from ground-based inventory measurements. Finally, results indicate that during the 2012-2015 Californian drought, regional net carbon fluxes fell by 84%, evaporation and transpiration fluxes fell by 53% and 33% respectively, and sensible heat increase by 51%. This study provides a framework for assimilating near-future global satellite imagery estimates of ecosystem composition with terrestrial biosphere models, constraining and improving their predictions of large-scale ecosystem dynamics and functioning.

Using Imaging Spectrometry measurements of Ecosystem Composition to constrain Regional Predictions of Carbon, Water and Energy Fluxes

NASA Astrophysics Data System (ADS)

Antonarakis, A. S.; Bogan, S.; Moorcroft, P. R.

2017-12-01

Ecosystem composition is a key attribute of terrestrial ecosystems, influencing the fluxes of carbon, water, and energy between the land surface and the atmosphere. The description of current ecosystem composition has traditionally come from relatively few ground-based inventories of the plant canopy, but are spatially limited and do not provide a comprehensive picture of ecosystem composition at regional or global scales. In this analysis, imaging spectrometry measurements, collected as part of the HyspIRI Preparatory Mission, are used to provide spatially-resolved estimates of plant functional type composition providing an important constraint on terrestrial biosphere model predictions of carbon, water and energy fluxes across the heterogeneous landscapes of the Californian Sierras. These landscapes include oak savannas, mid-elevation mixed pines, fir-cedar forests, and high elevation pines. Our results show that imaging spectrometry measurements can be successfully used to estimate regional-scale variation in ecosystem composition and resulting spatial heterogeneity in patterns of carbon, water and energy fluxes and ecosystem dynamics. Simulations at four flux tower sites within the study region yield patterns of seasonal and inter-annual variation in carbon and water fluxes that have comparable accuracy to simulations initialized from ground-based inventory measurements. Finally, results indicate that during the 2012-2015 Californian drought, regional net carbon fluxes fell by 84%, evaporation and transpiration fluxes fell by 53% and 33% respectively, and sensible heat increase by 51%. This study provides a framework for assimilating near-future global satellite imagery estimates of ecosystem composition with terrestrial biosphere models, constraining and improving their predictions of large-scale ecosystem dynamics and functioning.

Historical factors shaped species diversity and composition of Salix in eastern Asia.

PubMed

Wang, Qinggang; Su, Xiangyan; Shrestha, Nawal; Liu, Yunpeng; Wang, Siyang; Xu, Xiaoting; Wang, Zhiheng

2017-02-08

Ambient energy, niche conservatism, historical climate stability and habitat heterogeneity hypothesis have been proposed to explain the broad-scale species diversity patterns and species compositions, while their relative importance have been controversial. Here, we assessed the relative contributions of contemporary climate, historical climate changes and habitat heterogeneity in shaping Salix species diversity and species composition in whole eastern Asia as well as mountains and lowlands using linear regressions and distance-based redundancy analyses, respectively. Salix diversity was negatively related with mean annual temperature. Habitat heterogeneity was more important than contemporary climate in shaping Salix diversity patterns, and their relative contributions were different in mountains and lowlands. In contrast, the species composition was strongly influenced by contemporary climate and historical climate change than habitat heterogeneity, and their relative contributions were nearly the same both in mountains and lowlands. Our findings supported niche conservatism and habitat heterogeneity hypotheses, but did not support ambient energy and historical climate stability hypotheses. The diversity pattern and species composition of Salix could not be well-explained by any single hypothesis tested, suggesting that other factors such as disturbance history and diversification rate may be also important in shaping the diversity pattern and composition of Salix species.

Historical factors shaped species diversity and composition of Salix in eastern Asia

PubMed Central

Wang, Qinggang; Su, Xiangyan; Shrestha, Nawal; Liu, Yunpeng; Wang, Siyang; Xu, Xiaoting; Wang, Zhiheng

2017-01-01

Ambient energy, niche conservatism, historical climate stability and habitat heterogeneity hypothesis have been proposed to explain the broad-scale species diversity patterns and species compositions, while their relative importance have been controversial. Here, we assessed the relative contributions of contemporary climate, historical climate changes and habitat heterogeneity in shaping Salix species diversity and species composition in whole eastern Asia as well as mountains and lowlands using linear regressions and distance-based redundancy analyses, respectively. Salix diversity was negatively related with mean annual temperature. Habitat heterogeneity was more important than contemporary climate in shaping Salix diversity patterns, and their relative contributions were different in mountains and lowlands. In contrast, the species composition was strongly influenced by contemporary climate and historical climate change than habitat heterogeneity, and their relative contributions were nearly the same both in mountains and lowlands. Our findings supported niche conservatism and habitat heterogeneity hypotheses, but did not support ambient energy and historical climate stability hypotheses. The diversity pattern and species composition of Salix could not be well-explained by any single hypothesis tested, suggesting that other factors such as disturbance history and diversification rate may be also important in shaping the diversity pattern and composition of Salix species. PMID:28176816

Heterogeneous interaction of SiO2 with N2O5: aerosol flow tube and single particle optical levitation-Raman spectroscopy studies.

PubMed

Tang, M J; Camp, J C J; Rkiouak, L; McGregor, J; Watson, I M; Cox, R A; Kalberer, M; Ward, A D; Pope, F D

2014-09-25

Silica (SiO2) is an important mineral present in atmospheric mineral dust particles, and the heterogeneous reaction of N2O5 on atmospheric aerosol is one of the major pathways to remove nitrogen oxides from the atmosphere. The heterogeneous reaction of N2O5 with SiO2 has only been investigated by two studies previously, and the reported uptake coefficients differ by a factor of >10. In this work two complementary laboratory techniques were used to study the heterogeneous reaction of SiO2 particles with N2O5 at room temperature and at different relative humidities (RHs). The uptake coefficients of N2O5, γ(N2O5), were determined to be (7.2 ± 0.6) × 10(-3) (1σ) at 7% RH and (5.3 ± 0.8) × 10(-3) (1σ) at 40% RH for SiO2 particles, using the aerosol flow tube technique. We show that γ(N2O5) determined in this work can be reconciled with the two previous studies by accounting for the difference in geometric and BET derived aerosol surface areas. To probe the particle phase chemistry, individual micrometer sized SiO2 particles were optically levitated and exposed to a continuous flow of N2O5 at different RHs, and the composition of levitated particles was monitored online using Raman spectroscopy. This study represents the first investigation into the heterogeneous reactions of levitated individual SiO2 particles as a surrogate for mineral dust. Relative humidity was found to play a critical role: while no significant change of particle composition was observed by Raman spectroscopy during exposure to N2O5 at RH of <2%, increasing the RH led to the formation of nitrate species on the particle surface which could be completely removed after decreasing the RH back to <2%. This can be explained by the partitioning of HNO3 between the gas and adsorbed phases. The atmospheric implications of this work are discussed.

Fe3-xCuxO4 as highly active heterogeneous Fenton-like catalysts toward elemental mercury removal.

PubMed

Zhou, Changsong; Sun, Lushi; Zhang, Anchao; Wu, Xiaofeng; Ma, Chuan; Su, Sheng; Hu, Song; Xiang, Jun

2015-04-01

A series of novel spinel Fe3-xCuxO4 (0

Investigating melting induced mantle heterogeneities in plate driven mantle convection models

NASA Astrophysics Data System (ADS)

Price, M.; Davies, H.; Panton, J.

2017-12-01

Observations from geochemistry and seismology continue to suggest a range of complex heterogeneity in Earth's mantle. In the deep mantle, two large low velocity provinces (LLVPs) have been regularly observed in seismic studies, with their longevity, composition and density compared to the surrounding mantle debated. The cause of these observed LLVPs is equally uncertain, with previous studies advocating either thermal or thermo-chemical causes. There is also evidence that these structures could provide chemically distinct reservoirs within the mantle, with recent studies also suggesting there may be additional reservoirs in the mantle, such as bridgmanite-enriched ancient mantle structures (BEAMS). One way to test these hypotheses is using computational models of the mantle, with models that capture the full 3D system being both complex and computationally expensive. Here we present results from our global mantle model TERRA. Using our model, we can track compositional variations in the convecting mantle that are generated by self-consistent, evolving melting zones. Alongside the melting, we track trace elements and other volatiles which can be partitioned during melting events, and expelled and recycled at the surface. Utilising plate reconstruction models as a boundary condition, the models generate the tectonic features observed at Earth's surface, while also organising the lower mantle into recognisable degree-two structures. This results in our models generating basaltic `oceanic' crusts which are then brought into the mantle at tectonic boundaries, providing additional chemical heterogeneity in the mantle volume. Finally, by utilising thermodynamic lookup tables to convert the final outputs from the model to seismic structures, together with resolution filters for global tomography models, we are able to make direct comparisons between our results and observations. By varying the parameters of the model, we investigate a range of current hypotheses for heterogeneity in the mantle. Our work attempts to reconcile the many proposed current ideas for the deep mantle, giving additional insight from modelling on the latest observations from other Deep Earth disciplines.

Magnetically assisted slip casting of bioinspired heterogeneous composites

NASA Astrophysics Data System (ADS)

Le Ferrand, Hortense; Bouville, Florian; Niebel, Tobias P.; Studart, André R.

2015-11-01

Natural composites are often heterogeneous to fulfil functional demands. Manufacturing analogous materials remains difficult, however, owing to the lack of adequate and easily accessible processing tools. Here, we report an additive manufacturing platform able to fabricate complex-shaped parts exhibiting bioinspired heterogeneous microstructures with locally tunable texture, composition and properties, as well as unprecedentedly high volume fractions of inorganic phase (up to 100%). The technology combines an aqueous-based slip-casting process with magnetically directed particle assembly to create programmed microstructural designs using anisotropic stiff platelets in a ceramic, metal or polymer functional matrix. Using quantitative tools to control the casting kinetics and the temporal pattern of the applied magnetic fields, we demonstrate that this approach is robust and can be exploited to design and fabricate heterogeneous composites with thus far inaccessible microstructures. Proof-of-concept examples include bulk composites with periodic patterns of microreinforcement orientation, and tooth-like bilayer parts with intricate shapes exhibiting site-specific composition and texture.

Heterogeneous photo-Fenton decolorization of Orange II over Al-pillared Fe-smectite: response surface approach, degradation pathway, and toxicity evaluation.

PubMed

Li, Huiyuan; Li, Yanli; Xiang, Luojing; Huang, Qianqian; Qiu, Juanjuan; Zhang, Hui; Sivaiah, Matte Venkata; Baron, Fabien; Barrault, Joel; Petit, Sabine; Valange, Sabine

2015-04-28

A ferric smectite clay material was synthesized and further intercalated with Al2O3 pillars for the first time with the aim of evaluating its ability to be used as heterogeneous catalyst for the photo-Fenton decolorization of azo dye Orange II. UV irradiation was found to enhance the activity of the catalyst in the heterogeneous photo-Fenton process. Catalyst loading of 0.5g/L and hydrogen peroxide concentration of 13.5mM yielded a remarkable color removal, accompanied by excellent catalyst stability. The decolorization of Orange II followed the pseudo-first-order kinetics for initial dye concentrations from 20 to 160mg/L. The central composite design (CCD) based on the response surface methodology (RSM) was applied to evaluate the effects of several operating parameters, namely initial pH, catalyst loading and hydrogen peroxide concentration, on the decolorization efficiency. The RSM model was derived and the response surface plots were developed based on the results. Moreover, the main intermediate products were separated and identified using gas chromatography-mass spectrometry (GC-MS) and a possible degradation pathway was proposed accordingly. The acute toxicity experiments illustrated that the Daphniamagna immobilization rate continuously decreased during 150min reaction, indicating that the effluent was suitable for sequential biological treatment. Copyright © 2015 Elsevier B.V. All rights reserved.

Combined effects of landscape composition and heterogeneity on farmland avian diversity.

PubMed

Santana, Joana; Reino, Luís; Stoate, Chris; Moreira, Francisco; Ribeiro, Paulo F; Santos, José L; Rotenberry, John T; Beja, Pedro

2017-02-01

Conserving biodiversity on farmland is an essential element of worldwide efforts for reversing the global biodiversity decline. Common approaches involve improving the natural component of the landscape by increasing the amount of natural and seminatural habitats (e.g., hedgerows, woodlots, and ponds) or improving the production component of the landscape by increasing the amount of biodiversity-friendly crops. Because these approaches may negatively impact on economic output, it was suggested that an alternative might be to enhance the diversity (compositional heterogeneity) or the spatial complexity (configurational heterogeneity) of land cover types, without necessarily changing composition. Here, we develop a case study to evaluate these ideas, examining whether managing landscape composition or heterogeneity, or both, would be required to achieve conservation benefits on avian diversity in open Mediterranean farmland. We surveyed birds in farmland landscapes of southern Portugal, before (1995-1997) and after (2010-2012) the European Union's Common Agricultural Policy (CAP) reform of 2003, and related spatial and temporal variation in bird species richness to variables describing the composition, and the compositional and configurational heterogeneity, of the natural and production components of the landscape. We found that the composition of the production component had the strongest effects on avian diversity, with a particularly marked effect on the richness of farmland and steppe bird species. Composition of the natural component was also influential, mainly affecting the richness of woodland/shrubland species. Although there were some effects of compositional and configurational heterogeneity, these were much weaker and inconsistent than those of landscape composition. Overall, we suggest that conservation efforts in our area should focus primarily on the composition of the production component, by striving to maximize the prevalence of biodiversity-friendly crops. This recommendation probably applies to other areas such as ours, where a range of species of conservation concern is strongly associated with crop habitats.

Synthesis and adsorption properties of hollow tubular alumina fibers

NASA Astrophysics Data System (ADS)

Lozhkomoev, A. S.; Kazantsev, S. O.; Glazkova, E. A.

2017-12-01

In this study, composite glass fibers coated with alumina nanoplates and hollow tubular alumina fibers with a diameter of 400-500 nm are synthesized based on glass fiber templated hydrothermal strategy. Porous coatings on glass fibers and hollow fibers consist of cross-linked alumina nanoplates with the size of 100-200 nm and thickness of 2-5 nm. Their formation is attributed to the template-induced heterogeneous growth of alumina nanoplates on glass fibers of the B-06-F type. It is important that composite glass fibers and hollow tubular fibers have opposite surface charges and exhibit selective sorption characteristics towards anionic and cationic dyes.

Vanadium Pentoxide Nanobelt-Reduced Graphene Oxide Nanosheet Composites as High-Performance Pseudocapacitive Electrodes: ac Impedance Spectroscopy Data Modeling and Theoretical Calculations

PubMed Central

Gupta, Sanju; Aberg, Bryce; Carrizosa, Sara B.; Dimakis, Nicholas

2016-01-01

Graphene nanosheets and graphene nanoribbons, G combined with vanadium pentoxide (VO) nanobelts (VNBs) and VNBs forming GVNB composites with varying compositions were synthesized via a one-step low temperature facile hydrothermal decomposition method as high-performance electrochemical pseudocapacitive electrodes. VNBs from vanadium pentoxides (VO) are formed in the presence of graphene oxide (GO), a mild oxidant, which transforms into reduced GO (rGOHT), assisting in enhancing the electronic conductivity coupled with the mechanical robustness of VNBs. From electron microscopy, surface sensitive spectroscopy and other complementary structural characterization, hydrothermally-produced rGO nanosheets/nanoribbons are decorated with and inserted within the VNBs’ layered crystal structure, which further confirmed the enhanced electronic conductivity of VNBs. Following the electrochemical properties of GVNBs being investigated, the specific capacitance Csp is determined from cyclic voltammetry (CV) with a varying scan rate and galvanostatic charging-discharging (V–t) profiles with varying current density. The rGO-rich composite V1G3 (i.e., VO/GO = 1:3) showed superior specific capacitance followed by VO-rich composite V3G1 (VO/GO = 3:1), as compared to V1G1 (VO/GO = 1:1) composite, besides the constituents, i.e., rGO, rGOHT and VNBs. Composites V1G3 and V3G1 also showed excellent cyclic stability and a capacitance retention of >80% after 500 cycles at the highest specific current density. Furthermore, by performing extensive simulations and modeling of electrochemical impedance spectroscopy data, we determined various circuit parameters, including charge transfer and solution resistance, double layer and low frequency capacitance, Warburg impedance and the constant phase element. The detailed analyses provided greater insights into physical-chemical processes occurring at the electrode-electrolyte interface and highlighted the comparative performance of thin heterogeneous composite electrodes. We attribute the superior performance to the open graphene topological network being beneficial to available ion diffusion sites and the faster transport kinetics having a larger accessible geometric surface area and synergistic integration with optimal nanostructured VO loading. Computational simulations via periodic density functional theory (DFT) with and without V2O5 adatoms on graphene sheets are also performed. These calculations determine the total and partial electronic density of state (DOS) in the vicinity of the Fermi level (i.e., higher electroactive sites), in turn complementing the experimental results toward surface/interfacial charge transfer on heterogeneous electrodes. PMID:28773738

Measurement of the full-field polymerization shrinkage and depth of cure of dental composites using digital image correlation.

PubMed

Li, Jianying; Fok, Alex S L; Satterthwaite, Julian; Watts, David C

2009-05-01

The aim of this study was to measure the full-field polymerization shrinkage of dental composites using optical image correlation method. Bar specimens of cross-section 4mm x 2mm and length 10mm approximately were light cured with two irradiances, 450 mW/cm(2) and 180 mW/cm(2), respectively. The curing light was generated with Optilux 501 (Kerr) and the two different irradiances were achieved by adjusting the distance between the light tip and the specimen. A single-camera 2D measuring system was used to record the deformation of the composite specimen for 30 min at a frequency of 0.1 Hz. The specimen surface under observation was sprayed with paint to produce sufficient contrast to allow tracking of individual points on the surface. The curing light was applied to one end of the specimen for 40s during which the painted surface was fully covered. After curing, the cover was removed immediately so that deformation of the painted surface could be recorded by the camera. The images were then analyzed with specialist software and the volumetric shrinkage determined along the beam length. A typical shrinkage strain field obtained on a specimen surface was highly non-uniform, even at positions of constant distance from the irradiation surface, indicating possible heterogeneity in material composition and shrinkage behavior in the composite. The maximum volumetric shrinkage strain of approximately 1.5% occurred at a subsurface distance of about 1mm, instead of at the irradiation surface. After reaching its peak value, the shrinkage strain then gradually decreased with increasing distance along the beam length, before leveling off to a value of approximately 0.2% at a distance of 4-5mm. The maximum volumetric shrinkage obtained agreed well with the value of 1.6% reported by the manufacturer for the composite examined in this work. Using irradiance of 180 mW/cm(2) resulted in only slightly less polymerization shrinkage than using irradiance of 450 mW/cm(2). Compared to the other measurement methods, the image correlation method is capable of producing full-field information about the polymerization shrinkage behavior of dental composites.

Effect of boundary conditions on the numerical solutions of representative volume element problems for random heterogeneous composite microstructures

NASA Astrophysics Data System (ADS)

Cho, Yi Je; Lee, Wook Jin; Park, Yong Ho

2014-11-01

Aspects of numerical results from computational experiments on representative volume element (RVE) problems using finite element analyses are discussed. Two different boundary conditions (BCs) are examined and compared numerically for volume elements with different sizes, where tests have been performed on the uniaxial tensile deformation of random particle reinforced composites. Structural heterogeneities near model boundaries such as the free-edges of particle/matrix interfaces significantly influenced the overall numerical solutions, producing force and displacement fluctuations along the boundaries. Interestingly, this effect was shown to be limited to surface regions within a certain distance of the boundaries, while the interior of the model showed almost identical strain fields regardless of the applied BCs. Also, the thickness of the BC-affected regions remained constant with varying volume element sizes in the models. When the volume element size was large enough compared to the thickness of the BC-affected regions, the structural response of most of the model was found to be almost independent of the applied BC such that the apparent properties converged to the effective properties. Finally, the mechanism that leads a RVE model for random heterogeneous materials to be representative is discussed in terms of the size of the volume element and the thickness of the BC-affected region.

High-mass heterogeneous cluster formation by ion bombardment of the ternary alloy Au 7Cu 5Al 4

DOE PAGES

Zinovev, Alexander V.; King, Bruce V.; Veryovkin, Igor V.; ...

2016-02-04

The ternary alloy Au 7Cu 5Al 4 was irradiated with 0.1–10 keV Ar + and the surface composition analyzed using laser sputter neutral mass spectrometry. Ejected clusters containing up to seven atoms, with masses up to 2000 amu, were observed. By monitoring the signals from sputtered clusters, the surface composition of the alloy was seen to change with 100 eV Ar + dose, reaching equilibrium after 10 nm of the surface was eroded, in agreement with TRIDYN simulation and indicating that the changes were due to preferential sputtering of Al and Cu. Ejected gold containing clusters were found to increasemore » markedly in intensity while aluminum containing clusters decreased in intensity as a result of Ar sputtering. Such an effect was most pronounced for low energy (<1 keV) Ar + sputtering and was consistent with TRIDYN simulations of the depth profiling. As a result, the component sputter yields from the ternary alloy were consistent with previous binary alloy measurements but showed greater Cu surface concentrations than expected from TRIDYN simulations.« less

Heterogeneous Ice Nucleation Ability of NaCl and Sea Salt Aerosol Particles at Cirrus Temperatures

NASA Astrophysics Data System (ADS)

Wagner, Robert; Kaufmann, Julia; Möhler, Ottmar; Saathoff, Harald; Schnaiter, Martin; Ullrich, Romy; Leisner, Thomas

2018-03-01

In situ measurements of the composition of heterogeneous cirrus ice cloud residuals have indicated a substantial contribution of sea salt in sampling regions above the ocean. We have investigated the heterogeneous ice nucleation ability of sodium chloride (NaCl) and sea salt aerosol (SSA) particles at cirrus cloud temperatures between 235 and 200 K in the Aerosol Interaction and Dynamics in the Atmosphere aerosol and cloud chamber. Effloresced NaCl particles were found to act as ice nucleating particles in the deposition nucleation mode at temperatures below about 225 K, with freezing onsets in terms of the ice saturation ratio, Sice, between 1.28 and 1.40. Above 225 K, the crystalline NaCl particles deliquesced and nucleated ice homogeneously. The heterogeneous ice nucleation efficiency was rather similar for the two crystalline forms of NaCl (anhydrous NaCl and NaCl dihydrate). Mixed-phase (solid/liquid) SSA particles were found to act as ice nucleating particles in the immersion freezing mode at temperatures below about 220 K, with freezing onsets in terms of Sice between 1.24 and 1.42. Above 220 K, the SSA particles fully deliquesced and nucleated ice homogeneously. Ice nucleation active surface site densities of the SSA particles were found to be in the range between 1.0 · 1010 and 1.0 · 1011 m-2 at T < 220 K. These values are of the same order of magnitude as ice nucleation active surface site densities recently determined for desert dust, suggesting a potential contribution of SSA particles to low-temperature heterogeneous ice nucleation in the atmosphere.

Cooperative growth phenomena in silicon/germanium low-temperature epitaxy

NASA Astrophysics Data System (ADS)

Meyerson, Bernard S.; Uram, Kevin J.; LeGoues, Francoise K.

1988-12-01

A series of Si:Ge alloys and structures has been prepared by ultrahigh-vacuum chemical vapor deposition. Alloys of composition 0≤Ge/Si≤0.20 are readily deposited at T=550 °C. Commensurate, defect-free strained layers are deposited up to a critical thickness, whereupon the accumulated stress in the films is accommodated by the formation of dislocation networks in the substrate wafers. A cooperative growth phenomenon is observed where the addition of 10% germane to the gaseous deposition source accelerates silane's heterogeneous reaction rate by a factor of 25. A model is proposed where Ge acts as a desorption center for mobile hydrogen adatoms on the Si[100] surface, accelerating heterogeneous silane pyrolysis by the enhanced availability of chemisorption sites.

Noble Metal Immersion Spectroscopy of Silica Alcogels and Aerogels

NASA Technical Reports Server (NTRS)

Smith, David D.; Sibille, Laurent; Cronise, Raymond J.; Noever, David A.

1998-01-01

We have fabricated aerogels containing gold and silver nanoparticles for gas catalysis applications. By applying the concept of an average or effective dielectric constant to the heterogeneous interlayer surrounding each particle, we extend the technique of immersion spectroscopy to porous or heterogeneous media. Specifically, we apply the predominant effective medium theories for the determination of the average fractional composition of each component in this inhomogeneous layer. Hence, the surface area of metal available for catalytic gas reaction is determined. The technique is satisfactory for statistically random metal particle distributions but needs further modification for aggregated or surfactant modified systems. Additionally, the kinetics suggest that collective particle interactions in coagulated clusters are perturbed during silica gelation resulting in a change in the aggregate geometry.

Dehomogenized Elastic Properties of Heterogeneous Layered Materials in AFM Indentation Experiments.

PubMed

Lee, Jia-Jye; Rao, Satish; Kaushik, Gaurav; Azeloglu, Evren U; Costa, Kevin D

2018-06-05

Atomic force microscopy (AFM) is used to study mechanical properties of biological materials at submicron length scales. However, such samples are often structurally heterogeneous even at the local level, with different regions having distinct mechanical properties. Physical or chemical disruption can isolate individual structural elements but may alter the properties being measured. Therefore, to determine the micromechanical properties of intact heterogeneous multilayered samples indented by AFM, we propose the Hybrid Eshelby Decomposition (HED) analysis, which combines a modified homogenization theory and finite element modeling to extract layer-specific elastic moduli of composite structures from single indentations, utilizing knowledge of the component distribution to achieve solution uniqueness. Using finite element model-simulated indentation of layered samples with micron-scale thickness dimensions, biologically relevant elastic properties for incompressible soft tissues, and layer-specific heterogeneity of an order of magnitude or less, HED analysis recovered the prescribed modulus values typically within 10% error. Experimental validation using bilayer spin-coated polydimethylsiloxane samples also yielded self-consistent layer-specific modulus values whether arranged as stiff layer on soft substrate or soft layer on stiff substrate. We further examined a biophysical application by characterizing layer-specific microelastic properties of full-thickness mouse aortic wall tissue, demonstrating that the HED-extracted modulus of the tunica media was more than fivefold stiffer than the intima and not significantly different from direct indentation of exposed media tissue. Our results show that the elastic properties of surface and subsurface layers of microscale synthetic and biological samples can be simultaneously extracted from the composite material response to AFM indentation. HED analysis offers a robust approach to studying regional micromechanics of heterogeneous multilayered samples without destructively separating individual components before testing. Copyright © 2018 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Meander morphodynamics over self-formed floodplains: can the migration history affect the future morphology of the river?

NASA Astrophysics Data System (ADS)

Bogoni, M.; Lanzoni, S.; Putti, M.

2017-12-01

Floodplains, and rivers therein, constitute complex systems whose simulation involves modeling of hydrodynamic, morphodynamic, chemical, and biological processes which act over a wide range of time scales (from days to centuries) and affect each other. Self-formed floodplains are produced by the sedimentary processes associated with the migration of river bends and the formation of abandoned oxbow lakes consequent to the cutoff of mature meanders. The erosion and deposition processes at the banks lead to heterogeneities in the surface composition, thus the river may experience faster or slower migration rates depending on the spatial distribution of the erosional resistance. As a consequence, the past spatial configurations of the river (i.e. the migration history) play a key role in shaping the successive river paths.We recently published a paper addressing the modeling of meander morphodynamics over self-formed heterogeneous floodplain. Results show that the heterogeneity in floodplain composition associated with the formation of geomorphic units (i.e., scroll bars and oxbow lakes) and the choice of a reliable flow field model to drive channel migration are two fundamental ingredients for reproducing correctly the long-term morphodynamics of alluvial meanders. We compare numerically generated planforms obtained for different scenarios of floodplain heterogeneity to natural meandering paths, through half meander metrics and spatial distribution of channel curvatures. Statistical and spectral tools disclose the complexity embedded in meandering geometry and the crucial differences between apparently similar configurations.Floodplain heterogeneity affects both the temporal and spatial distributions of meander geometry, and eventually leads to a closer statistical similarity between simulated and natural planform shapes when scroll bars and oxbow lakes left behind are harder to erode than the surrounding floodplain.

Organic matter composition of soil macropore surfaces under different agricultural management practices

NASA Astrophysics Data System (ADS)

Glæsner, Nadia; Leue, Marin; Magid, Jacob; Gerke, Horst H.

2016-04-01

Understanding the heterogeneous nature of soil, i.e. properties and processes occurring specifically at local scales is essential for best managing our soil resources for agricultural production. Examination of intact soil structures in order to obtain an increased understanding of how soil systems operate from small to large scale represents a large gap within soil science research. Dissolved chemicals, nutrients and particles are transported through the disturbed plow layer of agricultural soil, where after flow through the lower soil layers occur by preferential flow via macropores. Rapid movement of water through macropores limit the contact between the preferentially moving water and the surrounding soil matrix, therefore contact and exchange of solutes in the water is largely restricted to the surface area of the macropores. Organomineral complex coated surfaces control sorption and exchange properties of solutes, as well as availability of essential nutrients to plant roots and to the preferentially flowing water. DRIFT (Diffuse Reflectance infrared Fourier Transform) Mapping has been developed to examine composition of organic matter coated macropores. In this study macropore surfaces structures will be determined for organic matter composition using DRIFT from a long-term field experiment on waste application to agricultural soil (CRUCIAL, close to Copenhagen, Denmark). Parcels with 5 treatments; accelerated household waste, accelerated sewage sludge, accelerated cattle manure, NPK and unfertilized, will be examined in order to study whether agricultural management have an impact on the organic matter composition of intact structures.

Reaction Heterogeneity in LiNi 0.8 Co 0.15 Al 0.05 O 2 Induced by Surface Layer

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

Grenier, Antonin; Liu, Hao; Wiaderek, Kamila M.

2017-08-15

Through operando synchrotron powder X-ray diffraction (XRD) analysis of layered transition metal oxide electrodes of composition LiNi0.8Co0.15Al0.05O2 (NCA), we decouple the intrinsic bulk reaction mechanism from surface-induced effects. For identically prepared and cycled electrodes stored in different environments, we demonstrate that the intrinsic bulk reaction for pristine NCA follows solid-solution mechanism, not a two-phase as suggested previously. By combining high resolution powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and surface sensitive X-ray photoelectron spectroscopy (XPS), we demonstrate that adventitious Li2CO3 forms on the electrode particle surface during exposure to air, through reaction with atmospheric CO2. This surfacemore » impedes ionic and electronic transport to the underlying electrode, with progressive erosion of this layer during cycling giving rise to different reaction states in particles with an intact vs an eroded Li2CO3 surface-coating. This reaction heterogeneity, with a bimodal distribution of reaction states, has previously been interpreted as a “two-phase” reaction mechanism for NCA, as an activation step that only occurs during the first cycle. Similar surface layers may impact the reaction mechanism observed in other electrode materials using bulk probes such as operando powder XRD.« less

Mineralogy of the Martian Surface: Crustal Composition to Surface Processes

NASA Technical Reports Server (NTRS)

Mustard, John F.

1997-01-01

The main results have been published in the refereed literature, and thus this report serves mainly to summarize the main findings and indicate where the detailed papers may be found. Reflectance spectroscopy has been an important tool for determining the mineralogic makeup of the near surface materials on Mars. Analysis of the spectral properties of the surface have demonstrated that these attributes are heterogeneous from the coarse spatial but high spectral resolution spectra obtained with telescopes to the high spatial but coarse spectral resolution Viking data (e.g. Arvidson et al., 1989; McEwen et al., 1989). Low albedo materials show strong evidence for the presence of igneous rock forming minerals while bright materials are generally interpreted as representing heavily altered crustal material. How these materials are physically and genetically related has important implications for understanding martian surface properties and processes, weathering histories and paths, and crustal composition. The goal of this research is to characterize the physical and chemical properties of low albedo materials on Mars and the relationship to intermediate and high albedo materials. Fundamental science questions to be pursued include: (1) the observed distributions of soil, rock, and dust a function of physical processes or weathering and (2) different stages of chemical and physical alteration fresh rock identified. These objectives will be addressed through detailed analyses and modelling of the ISM data from the Phobos-2 mission with corroborating evidence of surface composition and properties provided by data from the Viking mission.

Nanoparticles with tunable shape and composition fabricated by nanoimprint lithography.

PubMed

Alayo, Nerea; Conde-Rubio, Ana; Bausells, Joan; Borrisé, Xavier; Labarta, Amilcar; Batlle, Xavier; Pérez-Murano, Francesc

2015-11-06

Cone-like and empty cup-shaped nanoparticles of noble metals have been demonstrated to provide extraordinary optical properties for use as optical nanoanntenas or nanoresonators. However, their large-scale production is difficult via standard nanofabrication methods. We present a fabrication approach to achieve arrays of nanoparticles with tunable shape and composition by a combination of nanoimprint lithography, hard-mask definition and various forms of metal deposition. In particular, we have obtained arrays of empty cup-shaped Au nanoparticles showing an optical response with distinguishable features associated with the excitations of localized surface plasmons. Finally, this route avoids the most common drawbacks found in the fabrication of nanoparticles by conventional top-down methods, such as aspect ratio limitation, blurring, and low throughput, and it can be used to fabricate nanoparticles with heterogeneous composition.

Facile synthesis of three-dimensional diatomite/manganese silicate nanosheet composites for enhanced Fenton-like catalytic degradation of malachite green dye

NASA Astrophysics Data System (ADS)

Jiang, De Bin; Yuan, Yunsong; Zhao, Deqiang; Tao, Kaiming; Xu, Xuan; Zhang, Yu Xin

2018-05-01

In this work, we demonstrate a novel and simple approach for fabrication of the complex three-dimensional (3D) diatomite/manganese silicate nanosheet composite (DMSNs). The manganese silicate nanosheets are uniformly grown on the inner and outer surface of diatomite with controllable morphology using a hydrothermal method. Such structural features enlarged the specific surface area, resulting in more catalytic active sites. In the heterogeneous Fenton-like reaction, the DMSNs exhibited excellent catalytic capability for the degradation of malachite green (MG). Under optimum condition, 500 mg/L MG solution was nearly 93% decolorized at 70 min in the reaction. The presented results show an enhanced catalytic behavior of the DMSNs prepared by the low-cost natural diatomite material and simple controllable process, which indicates their potential for environmental remediation applications. [Figure not available: see fulltext.

Mineralogy of the Martian Surface: Crustal Composition to Surface Processes

NASA Technical Reports Server (NTRS)

Mustard, John F.

1999-01-01

Over the course of this award we have: 1) Completed and published the results of a study of the effects of hyperfine particles on reflectance spectra of olivine and quartz, which included the development of scattering codes. Research has also progressed in the analysis of the effects of fine particle sizes on clay spectra. 2) Completed the analysis of the mineralogy of dark regions, showed the insitu compositions are highly correlated to the SNC meteorites, and determined that the martian mantle was depleted in aluminum prior to 2-3 GA ago; Studies of the mineralogic heterogeneity of surficial materials on Mars have also been conducted. and 3) Performed initial work on the study of the physical and chemical processes likely to form and modify duricrust. This includes assessments of erosion rates, solubility and transport of iron in soil environments, and models of pedogenic crust formation.

Rotational spectral variations of asteroid (8) Flora Implications for the nature of the S-type asteroids and for the parent bodies of the ordinary chondrites

NASA Technical Reports Server (NTRS)

Gaffey, M. J.

1984-01-01

The surface material and the surface material heterogeneities of the asteroid Flora are characterized using the best available data sets and the most sophisticated interpretive calibrations. Five spectrally derived mineralogic and patrologic properties of the surface assemblage of Flora which are relevant to whether this body is a differentiated or undifferentiated object are considered: bulk mineralogy, mafic mineral assemblage, metallic phase, pyroxene composition and structural type, and mineralogic variation. All of these properties indicate that Flora is a differentiated body. Flora is probably the residual core of an intensely heated, thermally evolved, and magnetically differentiated planetesimal which was subsequently disrupted. The present surface sample layers formed at or near the core-mantle boundary in the parent body.

Unified Nusselt- and Sherwood-number correlations in axisymmetric finite-gap stagnation and rotating-disk flows

DOE PAGES

Coltrin, Michael E.; Kee, Robert J.

2016-06-18

This paper develops a unified analysis of stagnation flow heat and mass transport, considering both semi-infinite domains and finite gaps, with and without rotation of the stagnation surface. An important objective is to derive Nusselt- and Sherwood-number correlations that represent heat and mass transport at the stagnation surface. The approach is based on computationally solving the governing conservation equations in similarity form as a boundary-value problem. The formulation considers ideal gases and incompressible fluids. The correlated results depend on fluid properties in terms of Prandtl, Schmidt, and Damkohler numbers. Heterogeneous chemistry at the stagnation surface is represented as a singlemore » first-order reaction. A composite Reynolds number represents the combination of stagnation flows with and without stagnation-surface rotation.« less

Synergistic Enhancement of Electrocatalytic CO 2 Reduction with Gold Nanoparticles Embedded in Functional Graphene Nanoribbon Composite Electrodes

DOE PAGES

Rogers, Cameron; Perkins, Wade S.; Veber, Gregory; ...

2017-02-24

Regulating the complex environment accounting for the stability, selectivity, and activity of catalytic metal nanoparticle interfaces represents a challenge to heterogeneous catalyst design. Here in this paper, we demonstrate the intrinsic performance enhancement of a composite material composed of gold nanoparticles (AuNPs) embedded in a bottom-up synthesized graphene nanoribbon (GNR) matrix for the electrocatalytic reduction of CO 2. Electrochemical studies reveal that the structural and electronic properties of the GNR composite matrix increase the AuNP electrochemically active surface area (ECSA), lower the requisite CO 2 reduction overpotential by hundreds of millivolts (catalytic onset > -0.2 V versus reversible hydrogen electrodemore » (RHE)), increase the Faraday efficiency (>90%), markedly improve stability (catalytic performance sustained over >24 h), and increase the total catalytic output (>100-fold improvement over traditional amorphous carbon AuNP supports). The inherent structural and electronic tunability of bottom-up synthesized GNR-AuNP composites affords an unrivaled degree of control over the catalytic environment, providing a means for such profound effects as shifting the rate-determining step in the electrocatalytic reduction of CO 2 to CO, and thereby altering the electrocatalytic mechanism at the nanoparticle surface.« less

Interaction of Land Management Intensity and Micro-topography Controls on Geochemistry of Raindrop-Liberated/Mobilized Soil Particles

NASA Astrophysics Data System (ADS)

Hou, T.; Filley, T. R.; Berry, T.; Singh, S.; Hughes, M.; Tong, Y.; Papanicolaou, T.; Wacha, K.; Wilson, C. G.; Chaubey, I.

2017-12-01

The dynamics of raindrop-induced breakdown of soil aggregates, a critical factor in the initial process of surface erosion and lateral redistribution of soil, are strongly tied to land use intensity. What is unclear however is the relative control of rain and mechanical disturbance on the development of landscape-level heterogeneity in surface soil geochemistry. We used artificial rainfall simulated experiments including an aggregate stability test and time course rainfall-erosional test to evaluate the role of management intensity and micro-topography on the geochemistry of raindrop-liberated/mobilized particles from landscapes in southeastern Iowa. Comparing restored prairie, conservation tillage, and conventional tillage sites we found, and with a trend toward increasing tillage intensity, a decrease in aggregate stability and raindrop-liberated particles that were lower in organic carbon, nitrogen, and plant-derived biopolymers, while containing higher proportions of microbially-processed nitrogen than the raindrop stable aggregates. Time evolution of the geochemistry (e.g. elemental, stable isotope, and biopolymer composition) of transported soil particles exhibited distinct patterns based upon both position of the hillslope and oriented soil roughness. Additionally, in the restored prairie, raindrop liberated particles had identical geochemical composition to the raindrop stable aggregates. Our results demonstrate that agricultural sites under intensive tillage have not only a greater potential to liberate and mobilize soil particles during storms, but the mobilized particles will have a distinct chemical character based on tillage intensity, hillslope position and oriented roughness thus lead to a greater potential for landscape level heterogeneity in surface and buried soil chemistry upon mobilization and burial.

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.

One dimensional models of temperature and composition in the transition zone from a bayesian inversion of surface waves

NASA Astrophysics Data System (ADS)

Drilleau, M.; Beucler, E.; Mocquet, A.; Verhoeven, O.; Burgos, G.; Capdeville, Y.; Montagner, J.

2011-12-01

The transition zone plays a key role in the dynamics of the Earth's mantle, especially for the exchanges between the upper and the lower mantles. Phase transitions, convective motions, hot upwelling and/or cold downwelling materials may make the 400 to 1000 km depth range very anisotropic and heterogeneous, both thermally and chemically. A classical procedure to infer the thermal state and the composition is to interpret 3D velocity perturbation models in terms of temperature and mineralogical composition, with respect to a global 1D model. However, the strength of heterogeneity and anisotropy can be so high that the concept of a one-dimensional reference seismic model might be addressed for this depth range. Some recent studies prefer to directly invert seismic travel times and normal modes catalogues in terms of temperature and composition. Bayesian approach allows to go beyond the classical computation of the best fit model by providing a quantitative measure of model uncertainty. We implement a non linear inverse approach (Monte Carlo Markov Chains) to interpret seismic data in terms of temperature, anisotropy and composition. Two different data sets are used and compared : surface wave waveforms and phase velocities (fundamental mode and the first overtones). A guideline of this method is to let the resolution power of the data govern the spatial resolution of the model. Up to now, the model parameters are the temperature field and the mineralogical composition ; other important effects, such as macroscopic anisotropy, will be taken into account in the near future. In order to reduce the computing time of the Monte Carlo procedure, polynomial Bézier curves are used for the parameterization. This choice allows for smoothly varying models and first-order discontinuities. Our Bayesian algorithm is tested with standard circular synthetic experiments and with more realistic simulations including 3D wave propagation effects (SEM). The test results enhance the ability of this approach to match the three-component waveforms and address the question of the mean radial interpretation of a 3D model. The method is also tested using real datasets, such as along the Vanuatu-California path.

Absolute Molecular Orientation of Isopropanol at Ceria (100) Surfaces: Insight into Catalytic Selectivity from the Interfacial Structure

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

Doughty, Benjamin; Goverapet Srinivasan, Sriram; Bryantsev, Vyacheslav S.

The initial mechanistic steps underlying heterogeneous chemical catalysis can be described in a framework where the composition, structure, and orientation of molecules adsorbed to reactive interfaces are known. However, extracting this vital information is the limiting step in most cases due in part to challenges in probing the interfacial monolayer with enough chemical specificity to characterize the surface molecular constituents. These challenges are exacerbated at complex or spatially heterogeneous interfaces where competing processes and a distribution of local environments can uniquely drive chemistry. To address these limitations, this work presents a distinctive combination of materials synthesis, surface specific optical experiments,more » and theory to probe and understand molecular structure at catalytic interfaces. Specifically, isopropanol was adsorbed to surfaces of the model CeO 2 catalyst that were synthesized with only the (100) facet exposed. Vibrational sum-frequency generation was used to probe the molecular monolayer, and with the guidance of density functional theory calculations, was used to extract the structure and absolute molecular orientation of isopropanol at the CeO 2 (100) surface. Our results show that isopropanol is readily deprotonated at the surface, and through the measured absolute molecular orientation of isopropanol, we obtain new insight into the selectivity of the (100) surface to form propylene. Our findings reveal key insight into the chemical and physical phenomena taking place at pristine interfaces thereby pointing to intuitive structural arguments to describe catalytic selectivity in more complex systems.« less

Absolute Molecular Orientation of Isopropanol at Ceria (100) Surfaces: Insight into Catalytic Selectivity from the Interfacial Structure

DOE PAGES

Doughty, Benjamin; Goverapet Srinivasan, Sriram; Bryantsev, Vyacheslav S.; ...

2017-06-12

The initial mechanistic steps underlying heterogeneous chemical catalysis can be described in a framework where the composition, structure, and orientation of molecules adsorbed to reactive interfaces are known. However, extracting this vital information is the limiting step in most cases due in part to challenges in probing the interfacial monolayer with enough chemical specificity to characterize the surface molecular constituents. These challenges are exacerbated at complex or spatially heterogeneous interfaces where competing processes and a distribution of local environments can uniquely drive chemistry. To address these limitations, this work presents a distinctive combination of materials synthesis, surface specific optical experiments,more » and theory to probe and understand molecular structure at catalytic interfaces. Specifically, isopropanol was adsorbed to surfaces of the model CeO 2 catalyst that were synthesized with only the (100) facet exposed. Vibrational sum-frequency generation was used to probe the molecular monolayer, and with the guidance of density functional theory calculations, was used to extract the structure and absolute molecular orientation of isopropanol at the CeO 2 (100) surface. Our results show that isopropanol is readily deprotonated at the surface, and through the measured absolute molecular orientation of isopropanol, we obtain new insight into the selectivity of the (100) surface to form propylene. Our findings reveal key insight into the chemical and physical phenomena taking place at pristine interfaces thereby pointing to intuitive structural arguments to describe catalytic selectivity in more complex systems.« less

A study of fracture phenomena in fiber composite laminates. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Konish, H. J., Jr.

1973-01-01

The extension of linear elastic fracture mechanics from ostensibly homogeneous isotropic metallic alloys to heterogeneous anisotropic advanced fiber composites is considered. It is analytically demonstrated that the effects of material anisotropy do not alter the principal characteristics exhibited by a crack in an isotropic material. The heterogeneity of fiber composites is experimentally shown to have a negligible effect on the behavior of a sufficiently long crack. A method is proposed for predicting the fracture strengths of a large class of composite laminates; the values predicted by this method show good agreement with limited experimental data. The limits imposed by material heterogeneity are briefly discussed, and areas for further study are recommended.

Molecular- and nm-scale Investigation of the Structure and Compositional Heterogeneity of Naturally Occurring Ferrihydrite

NASA Astrophysics Data System (ADS)

Cismasu, C.; Michel, F. M.; Stebbins, J. F.; Tcaciuc, A. P.; Brown, G. E.

2008-12-01

Ferrihydrite is a hydrated Fe(III) nano-oxide that forms in vast quantities in contaminated acid mine drainage environments. As a result of its high surface area, ferrihydrite is an important environmental sorbent, and plays an essential role in the geochemical cycling of pollutant metal(loid)s in these settings. Despite its environmental relevance, this nanomineral remains one of the least understood environmental solids in terms of its structure (bulk and surface), compositional variations, and the factors affecting its reactivity. Under natural aqueous conditions, ferrihydrite often precipitates in the presence of several inorganic compounds such as aluminum, silica, arsenic, etc., or in the presence of organic matter. These impurities can affect the molecular-level structure of naturally occurring ferrihydrite, thus modifying fundamental properties that are directly correlated with solid-phase stability and surface reactivity. Currently there exists a significant gap in our understanding of the structure of synthetic vs. natural ferrihydrites, due to the inherent difficulties associated to the investigation of these poorly crystalline nanophases. In this study, we combined synchrotron- and laboratory-based techniques to characterize naturally occurring ferrihydrite from an acid mine drainage system situated at the New Idria mercury mine in California. We used high-energy X-ray total scattering and pair distribution function analysis to elucidate quantitative structural details of these samples. We have additionally used scanning transmission X-ray microscopy high resolution imaging (30 nm) to evaluate the spatial relationship of major elements Si, Al, and C within ferrihydrite. Al, Si and C K-edge near- edge X-ray absorption fine structure spectroscopy and 27Al nuclear magnetic resonance spectroscopy were used to obtain short-range structural information. By combining these techniques we attain the highest level of resolution permitted by current analytical methods to study such naturally occurring nanomaterials, both at the molecular- and nm-scale. This work provides structural information at the short-, medium- and long- range, as well as evidence of compositional heterogeneity, and mineral/organic matter associations.

Heterometallic metal-organic framework-templated synthesis of porous Co3O4/ZnO nanocage catalysts for the carbonylation of glycerol

NASA Astrophysics Data System (ADS)

Lü, Yinyun; Jiang, Yating; Zhou, Qi; Li, Yunmei; Chen, Luning; Kuang, Qin; Xie, Zhaoxiong; Zheng, Lansun

2017-12-01

The efficient synthesis of glycerol carbonate (GLC) has recently received great attention due to its significance in reducing excess glycerol in biodiesel production as well as its promising applications in several industrial fields. However, the achievement of high conversion and high selectivity of GLC from glycerol in heterogeneous catalytic processes remains a challenge due to the absence of high-performance solid catalysts. Herein, highly porous nanocage catalysts composed of well-mixed Co3O4 and ZnO nanocrystals were successfully fabricated via a facile heterometallic metal-organic framework (MOF)-templated synthetic route. Benefiting from a high porosity and the synergistic effect between Co3O4 and ZnO, the as-prepared composite catalysts exhibited a significantly enhanced production efficiency of GLC in the carbonylation reaction of glycerol with urea compared to the single-component counterparts. The yield of GLC over the Co50Zn50-350 catalyst reached 85.2%, with 93.3% conversion and near 91% GLC selectivity, and this catalytic performance was superior to that over most heterogeneous catalysts. More importantly, the proposed templated synthetic strategy of heterometallic MOFs facilitates the regulation of catalyst composition and surface structure and can therefore be potentially extended in the tailoring of other metal oxide composite catalysts.

Onset of solid state mantle convection and mixing during magma ocean solidification

NASA Astrophysics Data System (ADS)

Maurice, Maxime; Tosi, Nicola; Samuel, Henri; Plesa, Ana-Catalina; Hüttig, Christian; Breuer, Doris

2017-04-01

The fractional crystallization of a magma ocean can cause the formation of a compositional layering that can play a fundamental role for the subsequent long-term dynamics of the interior, for the evolution of geochemical reservoirs, and for surface tectonics. In order to assess to what extent primordial compositional heterogeneities generated by magma ocean solidification can be preserved, we investigate the solidification of a whole-mantle Martian magma ocean, and in particular the conditions that allow solid state convection to start mixing the mantle before solidification is completed. To this end, we performed 2-D numerical simulations in a cylindrical geometry. We treat the liquid magma ocean in a parametrized way while we self-consistently solve the conservation equations of thermochemical convection in the growing solid cumulates accounting for pressure-, temperature- and, where it applies, melt-dependent viscosity as well as parametrized yield stress to account for plastic yielding. By testing the effects of different cooling rates and convective vigor, we show that for a lifetime of the liquid magma ocean of 1 Myr or longer, the onset of solid state convection prior to complete mantle crystallization is likely and that a significant part of the compositional heterogeneities generated by fractionation can be erased by efficient mantle mixing.

Recent Advances in Inorganic Heterogeneous Electrocatalysts for Reduction of Carbon Dioxide.

PubMed

Zhu, Dong Dong; Liu, Jin Long; Qiao, Shi Zhang

2016-05-01

In view of the climate changes caused by the continuously rising levels of atmospheric CO2 , advanced technologies associated with CO2 conversion are highly desirable. In recent decades, electrochemical reduction of CO2 has been extensively studied since it can reduce CO2 to value-added chemicals and fuels. Considering the sluggish reaction kinetics of the CO2 molecule, efficient and robust electrocatalysts are required to promote this conversion reaction. Here, recent progress and opportunities in inorganic heterogeneous electrocatalysts for CO2 reduction are discussed, from the viewpoint of both experimental and computational aspects. Based on elemental composition, the inorganic catalysts presented here are classified into four groups: metals, transition-metal oxides, transition-metal chalcogenides, and carbon-based materials. However, despite encouraging accomplishments made in this area, substantial advances in CO2 electrolysis are still needed to meet the criteria for practical applications. Therefore, in the last part, several promising strategies, including surface engineering, chemical modification, nanostructured catalysts, and composite materials, are proposed to facilitate the future development of CO2 electroreduction. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Optimization of Buckypaper-enhanced Multifunctional Thermoplastic Composites

PubMed Central

Li, Zhongrui; Liang, Zhiyong

2017-01-01

A series of flattened-nanotube reinforced thermoplastic composites are sizably fabricated as a function of buckypaper loading. The effects of the volume fraction, nanotube alignment and length on the tensile performance of the composites are factored into a general expression. The incorporation of self-reinforcing polyphenylene resin (Parmax) into a highly aligned buckypaper frame at an optimal weight ratio boosts the tensile strength and Young’s modulus of the buckypaper/Parmax composite to 1145 MPa and 150 GPa, respectively, far exceeding those of Parmax and aligned buckypaper individually. The composite also exhibits improved thermal (>65 W/m-K) and electrical (~700 S/cm) conductivities, as well as high thermoelectric power (22 μV/K) at room temperature. Meanwhile, the composite displays a heterogeneously complex structure. The hexyl groups of Parmax noncovalently interact with the honeycomb structure of the flattened nanotube through π-stacking and CH-π interaction, correspondingly improving the dispersity of polymer on the nanotube surface and the interfacial stress transferring while the high alignment degrees of nanotube facilitate phonon and charge transport in the composites. PMID:28205637

A Chlorine-Centric Perspective on Fluid-Mediated Processes at Convergent Plate Boundaries

NASA Astrophysics Data System (ADS)

Selverstone, J.

2014-12-01

The release and migration of metamorphic fluids from subducting slabs into overlying mantle is widely recognized as a major mechanism in producing arc geochemical signatures and returning fluid-mobile elements to earth's crust and surface environments. Although the magnitudes of many geochemical fluxes are well constrained, the processes whereby mass transfer occurs in different portions of the subduction system are less well known. Chlorine stable isotopes provide a new perspective on some of these processes: Cl is hydrophilic, but decarbonation reactions favor Cl retention in minerals. Cl also shows less isotopic fractionation than other fluid-sensitive systems and may thus preserve evidence of specific fluid sources and/or fluid mixing events. Detailed studies of sedimentary sequences show that individual beds are isotopically homogeneous but large heterogeneities in δ37Cl exist across beds on a cm to m scale and vary as a function of depositional environment. Compositionally correlative medium-, high-, and ultrahigh-pressure metamorphic sequences in the Alps record decreases of 30-50% in Cl contents in the earliest stages of metamorphism, but little change thereafter. No statistically significant change in isotopic composition occurs during prograde metamorphism of individual horizons, and the same large degree of isotopic heterogeneity (up to 6‰) persists throughout the prograde devolatilization history of the rocks. Likewise, analysis of HP/UHP serpentinites and altered oceanic crust show that heterogeneous protolith compositions are preserved during transport to sub-arc depths, despite large-scale devolatilization. However, upward transport of rocks within the subduction channel results in highly localized interaction with isotopically distinct, Cl-bearing fluid packets. Overlying forearc wedge rocks also record heterogeneous and channelized interaction with distinct fluid components with different δ37Cl. Within-layer fluid compartmentalization during continuous devolatilization reactions must thus be reconciled with discontinuous, cross-layer fluid percolation out of the slab and into the wedge. The resulting implications of the chlorine data for recent mechanical models of slab-to-wedge fluid transport will be discussed.

In-situ study of the gas-phase composition and temperature of an intermediate-temperature solid oxide fuel cell anode surface fed by reformate natural gas

NASA Astrophysics Data System (ADS)

Santoni, F.; Silva Mosqueda, D. M.; Pumiglia, D.; Viceconti, E.; Conti, B.; Boigues Muñoz, C.; Bosio, B.; Ulgiati, S.; McPhail, S. J.

2017-12-01

An innovative experimental setup is used for in-depth and in-operando characterization of solid oxide fuel cell anodic processes. This work focuses on the heterogeneous reactions taking place on a 121 cm2 anode-supported cell (ASC) running with a H2, CH4, CO2, CO and steam gas mixture as a fuel, using an operating temperature of 923 K. The results have been obtained by analyzing the gas composition and temperature profiles along the anode surface in different conditions: open circuit voltage (OCV) and under two different current densities, 165 mA cm-2 and 330 mA cm-2, corresponding to 27% and 54% of fuel utilization, respectively. The gas composition and temperature analysis results are consistent, allowing to monitor the evolution of the principal chemical and electrochemical reactions along the anode surface. A possible competition between CO2 and H2O in methane internal reforming is shown under OCV condition and low current density values, leading to two different types of methane reforming: Steam Reforming and Dry Reforming. Under a current load of 40 A, the dominance of exothermic reactions leads to a more marked increase of temperature in the portion of the cell close to the inlet revealing that current density is not uniform along the anode surface.

Charge heterogeneity of surfaces: mapping and effects on surface forces.

PubMed

Drelich, Jaroslaw; Wang, Yu U

2011-07-11

The DLVO theory treats the total interaction force between two surfaces in a liquid medium as an arithmetic sum of two components: Lifshitz-van der Waals and electric double layer forces. Despite the success of the DLVO model developed for homogeneous surfaces, a vast majority of surfaces of particles and materials in technological systems are of a heterogeneous nature with a mosaic structure composed of microscopic and sub-microscopic domains of different surface characteristics. In such systems, the heterogeneity of the surface can be more important than the average surface character. Attractions can be stronger, by orders of magnitude, than would be expected from the classical mean-field DLVO model when area-averaged surface charge or potential is employed. Heterogeneity also introduces anisotropy of interactions into colloidal systems, vastly ignored in the past. To detect surface heterogeneities, analytical tools which provide accurate and spatially resolved information about material surface chemistry and potential - particularly at microscopic and sub-microscopic resolutions - are needed. Atomic force microscopy (AFM) offers the opportunity to locally probe not only changes in material surface characteristic but also charges of heterogeneous surfaces through measurements of force-distance curves in electrolyte solutions. Both diffuse-layer charge densities and potentials can be calculated by fitting the experimental data with a DLVO theoretical model. The surface charge characteristics of the heterogeneous substrate as recorded by AFM allow the charge variation to be mapped. Based on the obtained information, computer modeling and simulation can be performed to study the interactions among an ensemble of heterogeneous particles and their collective motions. In this paper, the diffuse-layer charge mapping by the AFM technique is briefly reviewed, and a new Diffuse Interface Field Approach to colloid modeling and simulation is briefly discussed. Copyright © 2011 Elsevier B.V. All rights reserved.

Surface reactions of ethanol over UO 2(100) thin film

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

S. D. Senanayake; Mudiyanselage, K.; Burrell, A. K.

2015-10-08

The study of the reactions of oxygenates on well-defined oxide surfaces is important for the fundamental understanding of heterogeneous chemical pathways that are influenced by atomic geometry, electronic structure, and chemical composition. In this work, an ordered uranium oxide thin film surface terminated in the (100) orientation is prepared on a LaAlO 3 substrate and studied for its reactivity with a C-2 oxygenate, ethanol (CH 3CH 2OH). With the use of synchrotron X-ray photoelectron spectroscopy (XPS), we have probed the adsorption and desorption processes observed in the valence band, C 1s, O 1s, and U 4f to investigate the bondingmore » mode, surface composition, electronic structure, and probable chemical changes to the stoichiometric-UO 2(100) [smooth-UO 2(100)] and Ar +-sputtered UO 2(100) [rough-UO 2(100)] surfaces. Unlike UO 2(111) single crystal and UO 2 thin film, Ar-ion-sputtering of this UO 2(100) did not result in noticeable reduction of U cations. Upon ethanol adsorption (saturation occurred at 0.5 ML), only the ethoxy (CH 3CH 2O –) species is formed on smooth-UO 2(100) whereas initially formed ethoxy species are partially oxidized to surface acetate (CH3COO–) on the Ar +-sputtered UO 2(100) surface. Furthermore, all ethoxy and acetate species are removed from the surface between 600 and 700 K.« less

Coalescence-induced jumping of micro-droplets on heterogeneous superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Attarzadeh, Reza; Dolatabadi, Ali

2017-01-01

The phenomenon of droplets coalescence-induced self-propelled jumping on homogeneous and heterogeneous superhydrophobic surfaces was numerically modeled using the volume of fluid method coupled with a dynamic contact angle model. The heterogeneity of the surface was directly modeled as a series of micro-patterned pillars. To resolve the influence of air around a droplet and between the pillars, extensive simulations were performed for different droplet sizes on a textured surface. Parallel computations with the OpenMP algorithm were used to accelerate computation speed to meet the convergence criteria. The composition of the air-solid surface underneath the droplet facilitated capturing the transition from a no-slip/no-penetration to a partial-slip with penetration as the contact line at triple point started moving to the air pockets. The wettability effect from the nanoscopic roughness and the coating was included in the model by using the intrinsic contact angle obtained from a previously published study. As the coalescence started, the radial velocity of the coalescing liquid bridge was partially reverted to the upward direction due to the counter-action of the surface. However, we found that the velocity varied with the size of the droplets. A part of the droplet kinetic energy was dissipated as the merged droplet started penetrating into the cavities. This was due to a different area in contact between the liquid and solid and, consequently, a higher viscous dissipation rate in the system. We showed that the effect of surface roughness is strongly significant when the size of the micro-droplet is comparable with the size of the roughness features. In addition, the relevance of droplet size to surface roughness (critical relative roughness) was numerically quantified. We also found that regardless of the viscous cutoff radius, as the relative roughness approached the value of 44, the direct inclusion of surface topography was crucial in the modeling of the droplet-surface interaction. Finally, we validated our model against existing experimental data in the literature, verifying the effect of relative roughness on the jumping velocity of a merged droplet.

Electrokinetically driven microfluidic mixing with patchwise surface heterogeneity and AC applied electric field

NASA Astrophysics Data System (ADS)

Luo, Win-Jet; Yue, Cheng-Feng

2004-12-01

This paper investigates two-dimensional, time-dependent electroosmotic flows driven by an AC electric field via patchwise surface heterogeneities distributed along the microchannel walls. The time-dependent flow fields through the microchannel are simulated for various patchwise heterogeneous surface patterns using the backwards-Euler time stepping numerical method. Different heterogeneous surface patterns are found to create significantly different electrokinetic transport phenomena. It is shown that the presence of oppositely charged surface heterogeneities on the microchannel walls results in the formation of localized flow circulations within the bulk flow. These circulation regions grow and decay periodically in accordance with the applied periodic AC electric field intensity. The circulations provide an effective means of enhancing species mixing in the microchannel. A suitable design of the patchwise heterogeneous surface pattern permits the mixing channel length and the retention time required to attain a homogeneous solution to be reduced significantly.

Retrieval analysis of different orthodontic brackets: the applicability of electron microprobe techniques for determining material heterogeneities and corrosive potential

PubMed Central

HOLST, Alexandra Ioana; HOLST, Stefan; HIRSCHFELDER, Ursula; von SECKENDORFF, Volker

2012-01-01

Objective The objective of this study was to investigate the applicability of micro-analytical methods with high spatial resolution to the characterization of the composition and corrosion behavior of two bracket systems. Material and methods The surfaces of six nickel-free brackets and six nickel-containing brackets were examined for signs of corrosion and qualitative surface analysis using an electron probe microanalyzer (EPMA), prior to bonding to patient's tooth surfaces and four months after clinical use. The surfaces were characterized qualitatively by secondary electron (SE) images and back scattered electron (BSE) images in both compositional and topographical mode. Qualitative and quantitative wavelength-dispersive analyses were performed for different elements, and by utilizing qualitative analysis the relative concentration of selected elements was mapped two-dimensionally. The absolute concentration of the elements was determined in specially prepared brackets by quantitative analysis using pure element standards for calibration and calculating correction-factors (ZAF). Results Clear differences were observed between the different bracket types. The nickel-containing stainless steel brackets consist of two separate pieces joined by a brazing alloy. Compositional analysis revealed two different alloy compositions, and reaction zones on both sides of the brazing alloy. The nickel-free bracket was a single piece with only slight variation in element concentration, but had a significantly rougher surface. After clinical use, no corrosive phenomena were detectable with the methods applied. Traces of intraoral wear at the contact areas between the bracket slot and the arch wire were verified. Conclusion Electron probe microanalysis is a valuable tool for the characterization of element distribution and quantitative analysis for corrosion studies. PMID:23032212

Surface characterization of colloidal-sol gel derived biphasic HA/FA coatings.

PubMed

Cheng, Kui; Zhang, Sam; Weng, Wenjian

2007-10-01

Hydroxyapatite (HA) powders are ultrasonically dispersed in the precursor of fluoridated hydroxyapatite (FHA) or fluorapatite (FA) to form a "colloidal sol". HA/FA biphasic coatings are prepared on Ti6Al4V substrate via dip coating, 150 degrees C drying and 600 degrees C firing. The coatings show homogenous distribution of HA particles in the FA matrix. The relative phase proportion can be tailored by the amount of HA in the colloidal sol. The surfaces of the coatings consist of two kinds of distinct domains: HA and FA, resulting in a compositionally heterogeneous surface. The biphasic coating surface becomes increasingly rougher with HA powders, from around 200 nm of pure FA to 400-600 nm in Ra of biphasic coatings. The rougher biphasic HA/FA surfaces with chemically controllable domains will favor cell attachment, apatite layer deposition and necessary dissolution in clinical applications.

Mars

NASA Astrophysics Data System (ADS)

McSween, H. Y., Jr.; McLennan, S. M.

Of all the planets, Mars is the most Earthlike, inviting geochemical comparisons. Geochemical data for Mars are derived from spacecraft remote sensing, surface measurements and Martian meteorites. These analyses of exposed crustal materials enable estimates of bulk planet composition and inferences about its iron-rich mantle and core, as well as constraints on planetary differentiation and crust-mantle evolution. Mars probably had an early magma ocean, but there is no evidence for plate tectonics or crustal recycling any time in its history. The crust is basaltic in composition and lithologically heterogeneous, with radiometric crystallization ages ranging from ~4 billion years to within the last several hundred million years. Mantle sources for magmas vary considerably in incompatible element abundances. Although Mars is volatile element-rich, estimations of the amount of water delivered to the surface by volcanism are controversial. Low-temperature aqueous alteration affected the ancient Martian surface, producing clay minerals, sulfates, and other secondary minerals. Weathering and diagenetic trends are distinct from terrestrial chemical alteration, indicating different aqueous conditions. Organic matter has been found in Martian meteorites, but no geochemical signal of life has yet been discovered. Dynamic geochemical cycles for some volatile elements are revealed by stable isotope measurements. Long-term secular changes in chemical and mineralogical compositions of igneous rocks and sediments have been documented but are not well understood.

Elaboration of nano-structured grafted polymeric surface.

PubMed

Vrlinic, Tjasa; Debarnot, Dominique; Mozetic, Miran; Vesel, Alenka; Kovac, Janez; Coudreuse, Arnaud; Legeay, Gilbert; Poncin-Epaillard, Fabienne

2011-10-15

The surface grafting of multi-polymeric materials can be achieved by grafting as components such as polymers poly(N-isopropylacrylamide) and/or surfactant molecules (hexatrimethylammonium bromide, polyoxyethylene sorbitan monolaurate). The chosen grafting techniques, i.e. plasma activation followed by coating, allow a large spectrum of functional groups that can be inserted on the surface controlling the surface properties like adhesion, wettability and biocompatibility. The grafted polypropylene surfaces were characterized by contact angle analyses, XPS and AFM analyses. The influence of He plasma activation, of the coating parameters such as concentrations of the various reactive agents are discussed in terms of hydrophilic character, chemical composition and morphologic surface heterogeneity. The plasma pre-activation was shown inevitable for a permanent polymeric grafting. PNIPAM was grafted alone or with a mixture of the surfactant molecules. Depending on the individual proportion of each component, the grafted surfaces are shown homogeneous or composed of small domains of one component leading to a nano-structuration of the grafted surface. Copyright © 2011 Elsevier Inc. All rights reserved.

Experimental protocol for manipulating plant-induced soil heterogeneity.

PubMed

Brandt, Angela J; del Pino, Gaston A; Burns, Jean H

2014-03-13

Coexistence theory has often treated environmental heterogeneity as being independent of the community composition; however biotic feedbacks such as plant-soil feedbacks (PSF) have large effects on plant performance, and create environmental heterogeneity that depends on the community composition. Understanding the importance of PSF for plant community assembly necessitates understanding of the role of heterogeneity in PSF, in addition to mean PSF effects. Here, we describe a protocol for manipulating plant-induced soil heterogeneity. Two example experiments are presented: (1) a field experiment with a 6-patch grid of soils to measure plant population responses and (2) a greenhouse experiment with 2-patch soils to measure individual plant responses. Soils can be collected from the zone of root influence (soils from the rhizosphere and directly adjacent to the rhizosphere) of plants in the field from conspecific and heterospecific plant species. Replicate collections are used to avoid pseudoreplicating soil samples. These soils are then placed into separate patches for heterogeneous treatments or mixed for a homogenized treatment. Care should be taken to ensure that heterogeneous and homogenized treatments experience the same degree of soil disturbance. Plants can then be placed in these soil treatments to determine the effect of plant-induced soil heterogeneity on plant performance. We demonstrate that plant-induced heterogeneity results in different outcomes than predicted by traditional coexistence models, perhaps because of the dynamic nature of these feedbacks. Theory that incorporates environmental heterogeneity influenced by the assembling community and additional empirical work is needed to determine when heterogeneity intrinsic to the assembling community will result in different assembly outcomes compared with heterogeneity extrinsic to the community composition.

Different culture media affect growth characteristics, surface marker distribution and chondrogenic differentiation of human bone marrow-derived mesenchymal stromal cells.

PubMed

Hagmann, Sebastien; Moradi, Babak; Frank, Sebastian; Dreher, Thomas; Kämmerer, Peer Wolfgang; Richter, Wiltrud; Gotterbarm, Tobias

2013-07-30

Bone marrow-derived mesenchymal stromal cells (BM-MSCs) play an important role in modern tissue engineering, while distinct variations of culture media compositions and supplements have been reported. Because MSCs are heterogeneous regarding their regenerative potential and their surface markers, these parameters were compared in four widely used culture media compositions. MSCs were isolated from bone marrow and expanded in four established cell culture media. MSC yield/1000 MNCs, passage time and growth index were observed. In P4, typical MSC surface markers were analysed by fluorescence cytometry. Additionally, chondrogenic, adipogenic and osteogenic differentiation potential were evaluated. Growth index and P0 cell yield varied importantly between the media. The different expansion media had a significant influence on the expression of CD10, CD90, CD105, CD140b CD146 and STRO-1. While no significant differences were observed regarding osteogenic and adipogenic differentiation, chondrogenic differentiation was superior in medium A as reflected by GAG/DNA content. The choice of expansion medium can have a significant influence on growth, differentiation potential and surface marker expression of mesenchymal stromal cells, which is of fundamental importance for tissue engineering procedures.

Using confocal laser scanning microscopy to probe the milk fat globule membrane and associated proteins.

PubMed

Gallier, Sophie; Gragson, Derek; Jiménez-Flores, Rafael; Everett, David

2010-04-14

The bovine milk fat globule membrane (MFGM) is an important, biologically relevant membrane due to its functional and health properties. Its composition has been thoroughly studied, but its structure, especially the lateral organization of its components, still remains unclear. We have used confocal laser scanning microscopy (CLSM) to investigate the surface structure of the MFGM in globules with different degrees of processing using two types of fluorescently labeled phospholipid probes and a protein dye. Using this technique, we have observed heterogeneities in the distribution of MFGM lipids and proteins relating to the processing and size of the globules. The effect of pretreating the milk (centrifugation, pasteurization-homogenization and churning) was studied by double-staining the surface of the milk fat globules, followed by observation using CLSM, and by determining the phospholipid profile of raw milk, raw cream, processed milk and buttermilk powder. Our findings agree with other techniques by showing that the composition of the MFGM changes with processing through the loss of phospholipids and the adsorption of caseins and whey proteins onto the surface.

Compositions of Spherules and Rock Surfaces at Meridiani

NASA Technical Reports Server (NTRS)

Mittlefehldt, David W.; Jolliff, B. L.; Clark, B. C.; Gellert, R.

2007-01-01

The Alpha Particle X-ray Spectrometers (APXS) on the Mars Exploration Rovers (MER) have proven extremely valuable for analyzing rocks and soils on the surface of Mars. The precision of their compositional measurements has been shown to be phenomenal through analyses of the compositionally very uniform Meridiani soils. Through combined use of the rock abrasion tool (RAT) and the analytical instruments on the in-situ deployment device (IDD), analyses of the interiors of fine-grained and texturally uniform rocks with surfaces ground flat have been made under conditions that are nearly ideal for this mode of analysis. The APXS has also been used frequently to analyze materials whose characteristics, surface morphologies, and sample-detector geometries are less than ideal, but the analyses of which are nonetheless very useful for understanding the makeup of the target materials. Such targets include undisturbed rocks with irregular and sometimes coated surfaces and mixed targets such as soils that include fine-grained components as well as coarse grains and pieces of rocks. Such target materials include the well known hematite-rich concretions, referred to as blueberries because of their multispectral color, size, and mode of occurrence. In addition to non-ideal target geometry, such mixed materials also present a heterogeneous target in terms of density. These irregularities violate the assumptions commonly associated with analyses done in the laboratory to achieve the highest possible accuracy. Here we acknowledge the irregularities and we examine the inferences drawn from specific chemical trends obtained on imperfect targets in light of one of the potential pitfalls of natural materials on the surface of Mars, namely thin dust coatings.

Production and transformation of dissolved neutral sugars and amino acids by bacteria in seawater

NASA Astrophysics Data System (ADS)

Jørgensen, L.; Lechtenfeld, O. J.; Benner, R.; Middelboe, M.; Stedmon, C. A.

2014-10-01

Dissolved organic matter (DOM) in the ocean consists of a heterogeneous mixture of molecules, most of which are of unknown origin. Neutral sugars and amino acids are among the few recognizable biomolecules in DOM, and the molecular composition of these biomolecules is shaped primarily by biological production and degradation processes. This study provides insight into the bioavailability of biomolecules as well as the chemical composition of DOM produced by bacteria. The molecular compositions of combined neutral sugars and amino acids were investigated in DOM produced by bacteria and in DOM remaining after 32 days of bacterial degradation. Results from bioassay incubations with natural seawater (sampled from water masses originating from the surface waters of the Arctic Ocean and the North Atlantic Ocean) and artificial seawater indicate that the molecular compositions following bacterial degradation are not strongly influenced by the initial substrate or bacterial community. The molecular composition of neutral sugars released by bacteria was characterized by a high glucose content (47 mol %) and heterogeneous contributions from other neutral sugars (3-14 mol %). DOM remaining after bacterial degradation was characterized by a high galactose content (33 mol %), followed by glucose (22 mol %) and the remaining neutral sugars (7-11 mol %). The ratio of D-amino acids to L-amino acids increased during the experiments as a response to bacterial degradation, and after 32 days, the D/L ratios of aspartic acid, glutamic acid, serine and alanine reached around 0.79, 0.32, 0.30 and 0.51 in all treatments, respectively. The striking similarity in neutral sugar and amino acid compositions between natural (representing marine semi-labile and refractory DOM) and artificial (representing bacterially produced DOM) seawater samples, suggests that microbes transform bioavailable neutral sugars and amino acids into a common, more persistent form.

A parameterization of the heterogeneous hydrolysis of N2O5 for mass-based aerosol models: improvement of particulate nitrate prediction

NASA Astrophysics Data System (ADS)

Chen, Ying; Wolke, Ralf; Ran, Liang; Birmili, Wolfram; Spindler, Gerald; Schröder, Wolfram; Su, Hang; Cheng, Yafang; Tegen, Ina; Wiedensohler, Alfred

2018-01-01

The heterogeneous hydrolysis of N2O5 on the surface of deliquescent aerosol leads to HNO3 formation and acts as a major sink of NOx in the atmosphere during night-time. The reaction constant of this heterogeneous hydrolysis is determined by temperature (T), relative humidity (RH), aerosol particle composition, and the surface area concentration (S). However, these parameters were not comprehensively considered in the parameterization of the heterogeneous hydrolysis of N2O5 in previous mass-based 3-D aerosol modelling studies. In this investigation, we propose a sophisticated parameterization (NewN2O5) of N2O5 heterogeneous hydrolysis with respect to T, RH, aerosol particle compositions, and S based on laboratory experiments. We evaluated closure between NewN2O5 and a state-of-the-art parameterization based on a sectional aerosol treatment. The comparison showed a good linear relationship (R = 0.91) between these two parameterizations. NewN2O5 was incorporated into a 3-D fully online coupled model, COSMO-MUSCAT, with the mass-based aerosol treatment. As a case study, we used the data from the HOPE Melpitz campaign (10-25 September 2013) to validate model performance. Here, we investigated the improvement of nitrate prediction over western and central Europe. The modelled particulate nitrate mass concentrations ([NO3-]) were validated by filter measurements over Germany (Neuglobsow, Schmücke, Zingst, and Melpitz). The modelled [NO3-] was significantly overestimated for this period by a factor of 5-19, with the corrected NH3 emissions (reduced by 50 %) and the original parameterization of N2O5 heterogeneous hydrolysis. The NewN2O5 significantly reduces the overestimation of [NO3-] by ˜ 35 %. Particularly, the overestimation factor was reduced to approximately 1.4 in our case study (12, 17-18 and 25 September 2013) when [NO3-] was dominated by local chemical formations. In our case, the suppression of organic coating was negligible over western and central Europe, with an influence on [NO3-] of less than 2 % on average and 20 % at the most significant moment. To obtain a significant impact of the organic coating effect, N2O5, SOA, and NH3 need to be present when RH is high and T is low. However, those conditions were rarely fulfilled simultaneously over western and central Europe. Hence, the organic coating effect on the reaction probability of N2O5 may not be as significant as expected over western and central Europe.

Multiscale characteristics of mechanical and mineralogical heterogeneity using nanoindentation and Maps Mineralogy in Mancos Shale

NASA Astrophysics Data System (ADS)

Yoon, H.; Mook, W. M.; Dewers, T. A.

2017-12-01

Multiscale characteristics of textural and compositional (e.g., clay, cement, organics, etc.) heterogeneity profoundly influence the mechanical properties of shale. In particular, strongly anisotropic (i.e., laminated) heterogeneities are often observed to have a significant influence on hydrological and mechanical properties. In this work, we investigate a sample of the Cretaceous Mancos Shale to explore the importance of lamination, cements, organic content, and the spatial distribution of these characteristics. For compositional and structural characterization, the mineralogical distribution of thin core sample polished by ion-milling is analyzed using QEMSCAN® with MAPS MineralogyTM (developed by FEI Corporoation). Based on mineralogy and organic matter distribution, multi-scale nanoindentation testing was performed to directly link compositional heterogeneity to mechanical properties. With FIB-SEM (3D) and high-magnitude SEM (2D) images, key nanoindentation patterns are analyzed to evaluate elastic and plastic responses. Combined with MAPs Mineralogy data and fine-resolution BSE images, nanoindentation results are explained as a function of compositional and structural heterogeneity. Finite element modeling is used to quantitatively evaluate the link between the heterogeneity and mechanical behavior during nanoindentation. In addition, the spatial distribution of compositional heterogeneity, anisotropic bedding patterns, and mechanical anisotropy are employed as inputs for multiscale brittle fracture simulations using a phase field model. Comparison of experimental and numerical simulations reveal that proper incorporation of additional material information, such as bedding layer thickness and other geometrical attributes of the microstructures, may yield improvements on the numerical predictions of the mesoscale fracture patterns and hence the macroscopic effective toughness. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.

The petrogenesis of Gorgona komatiites, picrites and basalts: new field, petrographic and geochemical constraints

NASA Astrophysics Data System (ADS)

Kerr, A. C.; Marriner, G. F.; Arndt, N. T.; Tarney, J.; Nivia, A.; Saunders, A. D.; Duncan, R. A.

1996-04-01

Gorgona Island, Colombia is remarkable not only because it contains the only Phanerozoic komatiites, but also because it has mafic to ultramafic lavas with a wide range of compositions, from moderately enriched to extremely depleted (relative to Bulk Earth). The komatiite flows are, in many respects similar to Archaean komatiites; they formed from MgO-rich (18%) liquids and have upper spinifex zones and lower cumulate zones. The cumulate zones of Archaean komatiites contain many solid grains, in contrast more than 90% of the olivine in the Gorgona cumulates is highly skeletal. This combined with the fact that the Gorgona cumulate zones are thinner than those in Archaean komatiites, suggests that the komatiite magma became strongly superheated en route to the surface. The komatiites have trace element contents intermediate between those of the basalts and the ultramafic tuffs. Some basalts have isotope compositions indicative of long-term enrichment in incompatible elements, whereas other basalts and ultramafic volcanics have isotopic signatures that imply corresponding depletion. It is apparent that the plume source region of the Gorgona magmas was markedly heterogeneous, with at least two source components contributing to the observed variation in composition. This heterogeneity may have resulted from the incorporation of different components into the plume source, or it may be the result of complex melting and melt extraction processes during the ascent of a heterogeneous plume. Despite earlier suggestions that there may have been a significant age gap between depleted komatiite and basalt flows and the enriched basalts, new 40Ar- 39Ar dating of basalts and gabbros are more consistent with all being generated at 87 Ma during formation of the Caribbean/Colombian plateau, possibly at the Galapagos hotspot.

Bio-inspired heterogeneous composites for broadband vibration mitigation.

PubMed

Chen, Yanyu; Wang, Lifeng

2015-12-08

Structural biological materials have developed heterogeneous and hierarchical architectures that are responsible for the outstanding performance to provide protection against environmental threats including static and dynamic loading. Inspired by this observation, this research aims to develop new material and structural concepts for broadband vibration mitigation. The proposed composite materials possess a two-layered heterogeneous architecture where both layers consist of high-volume platelet-shape reinforcements and low-volume matrix, similar to the well-known "brick and mortar" microstructure of biological composites. Using finite element method, we numerically demonstrated that broadband wave attenuation zones can be achieved by tailoring the geometric features of the heterogeneous architecture. We reveal that the resulting broadband attenuation zones are gained by directly superimposing the attenuation zones in each constituent layer. This mechanism is further confirmed by the investigation into the phonon dispersion relation of each layer. Importantly, the broadband wave attenuation capability will be maintained when the mineral platelet orientation is locally manipulated, yet a contrast between the mineral platelet concentrations of the two constituent layers is essential. The findings of this work will provide new opportunities to design heterogeneous composites for broadband vibration mitigation and impact resistance under mechanically challenging environmental conditions.

Bio-inspired heterogeneous composites for broadband vibration mitigation

NASA Astrophysics Data System (ADS)

Chen, Yanyu; Wang, Lifeng

2015-12-01

Structural biological materials have developed heterogeneous and hierarchical architectures that are responsible for the outstanding performance to provide protection against environmental threats including static and dynamic loading. Inspired by this observation, this research aims to develop new material and structural concepts for broadband vibration mitigation. The proposed composite materials possess a two-layered heterogeneous architecture where both layers consist of high-volume platelet-shape reinforcements and low-volume matrix, similar to the well-known “brick and mortar” microstructure of biological composites. Using finite element method, we numerically demonstrated that broadband wave attenuation zones can be achieved by tailoring the geometric features of the heterogeneous architecture. We reveal that the resulting broadband attenuation zones are gained by directly superimposing the attenuation zones in each constituent layer. This mechanism is further confirmed by the investigation into the phonon dispersion relation of each layer. Importantly, the broadband wave attenuation capability will be maintained when the mineral platelet orientation is locally manipulated, yet a contrast between the mineral platelet concentrations of the two constituent layers is essential. The findings of this work will provide new opportunities to design heterogeneous composites for broadband vibration mitigation and impact resistance under mechanically challenging environmental conditions.

The evolution of Mercury's crust: a global perspective from MESSENGER.

PubMed

Denevi, Brett W; Robinson, Mark S; Solomon, Sean C; Murchie, Scott L; Blewett, David T; Domingue, Deborah L; McCoy, Timothy J; Ernst, Carolyn M; Head, James W; Watters, Thomas R; Chabot, Nancy L

2009-05-01

Mapping the distribution and extent of major terrain types on a planet's surface helps to constrain the origin and evolution of its crust. Together, MESSENGER and Mariner 10 observations of Mercury now provide a near-global look at the planet, revealing lateral and vertical heterogeneities in the color and thus composition of Mercury's crust. Smooth plains cover approximately 40% of the surface, and evidence for the volcanic origin of large expanses of plains suggests that a substantial portion of the crust originated volcanically. A low-reflectance, relatively blue component affects at least 15% of the surface and is concentrated in crater and basin ejecta. Its spectral characteristics and likely origin at depth are consistent with its apparent excavation from a lower crust or upper mantle enriched in iron- and titanium-bearing oxides.

Influence of Idealized Heterogeneity on Wet and Dry Planetary Boundary Layers Coupled to the Land Surface. 1; Instantaneous Fields and Statistics

NASA Technical Reports Server (NTRS)

Houser, Paul (Technical Monitor); Patton, Edward G.; Sullivan, Peter P.; Moeng, Chin-Hoh

2003-01-01

This is the first in a two-part series of manuscripts describing numerical experiments on the influence of 2-30 km striplike heterogeneity on wet and dry boundary layers coupled to the land surface. The strip-like heterogeneity is shown to dramatically alter the structure of the free-convective boundary layer by inducing significant organized circulations that modify turbulent statistics. The coupling with the land-surface modifies the circulations compared to previous studies using fixed surface forcing. Total boundary layer turbulence kinetic energy increases significantly for surface heterogeneity at scales between Lambda/z(sub i) = 4 and 9, however entrainment rates for all cases are largely unaffected by the strip-like heterogeneity.

Surface Coatings on Lunar Volcanic Glasses

NASA Technical Reports Server (NTRS)

Wentworth, Susan J.; McKay, D. S.; Thomas,-Keprta, K. L.; Clemett, S. J.

2007-01-01

We are undertaking a detailed study of surface deposits on lunar volcanic glass beads. These tiny deposits formed by vapor condensation during cooling of the gases that drove the fire fountain eruptions responsible for the formation of the beads. Volcanic glass beads are present in most lunar soil samples in the returned lunar collection. The mare-composition beads formed as a result of fire-fountaining approx.3.4-3.7 Ga ago, within the age range of large-scale mare volcanism. Some samples from the Apollo 15 and Apollo 17 landing sites are enriched in volcanic spherules. Three major types of volcanic glass bead have been identified: Apollo 15 green glass, Apollo 17 orange glass, and Apollo 17 "black" glass. The Apollo 15 green glass has a primitive composition with low Ti. The high-Ti compositions of the orange and black glasses are essentially identical to each other but the black glasses are opaque because of quench crystallization. A poorly understood feature common to the Apollo 15 and 17 volcanic glasses is the presence of small deposits of unusual materials on their exterior surfaces. For example, early studies indicated that the Apollo 17 orange glasses had surface enrichments of In, Cd, Zn, Ga, Ge, Au, and Na, and possible Pb- and Zn-sulfides, but it was not possible to characterize the surface features in detail. Technological advances now permit us to examine such features in detail. Preliminary FE-TEM/X-ray studies of ultramicrotome sections of Apollo 15 green glass indicate that the surface deposits are heterogeneous and layered, with an inner layer consisting of Fe with minor S and an outer layer of Fe and no S, and scattered Zn enrichments. Layering in surface deposits has not been identified previously; it will be key to defining the history of lunar fire fountaining.

Global variations in regolith properties on asteroid Vesta from Dawn's low-altitude mapping orbit

NASA Astrophysics Data System (ADS)

Denevi, Brett W.; Beck, Andrew W.; Coman, Ecaterina I.; Thomson, Bradley J.; Ammannito, Eleonora; Blewett, David T.; Sunshine, Jessica M.; de Sanctis, Maria Cristina; Li, Jian-Yang; Marchi, Simone; Mittlefehldt, David W.; Petro, Noah E.; Raymond, Carol A.; Russell, Christopher T.

2016-12-01

We investigate the depth, variability, and history of regolith on asteroid Vesta using data from the Dawn spacecraft. High-resolution (15-20 m pixel-1) Framing Camera images are used to assess the presence of morphologic indicators of a shallow regolith, including the presence of blocks in crater ejecta, spur-and-gully-type features in crater walls, and the retention of small (<300 m) impact craters. Such features reveal that the broad, regional heterogeneities observed on Vesta in terms of albedo and surface composition extend to the physical properties of the upper 1 km of the surface. Regions of thin regolith are found within the Rheasilvia basin and at equatorial latitudes from 0-90°E and 260-360°E. Craters in these areas that appear to excavate material from beneath the regolith have more diogenitic (Rheasilvia, 0-90°E) and cumulate eucrite (260-360°E) compositions. A region of especially thick regolith, where depths generally exceed 1 km, is found from 100-240°E and corresponds to heavily cratered, low-albedo surface with a basaltic eucrite composition enriched in carbonaceous chondrite material. The presence of a thick regolith in this area supports the idea that this is an ancient terrain that has accumulated a larger component of exogenic debris. We find evidence for the gardening of crater ejecta toward more howarditic compositions, consistent with regolith mixing being the dominant form of "weathering" on Vesta.

Chemical Evidence for Vertical Transport from Magma Chambers to the Surface During Mid-Ocean Ridge Volcanic Eruptions

NASA Astrophysics Data System (ADS)

Sinton, J. M.; Rubin, K. H.

2009-12-01

Many mid-ocean ridge eruptions show significant internal chemical heterogeneity; in general, the amount of chemical heterogeneity within eruptions scales with erupted volume. These variations reflect magmatic processes occurring in magma reservoirs prior to or possibly during eruption. For example, systematic variations in Mg# with along-axis distance in the early 90’s Aldo-Kihi (S. EPR near 17.5°S), 1996 N. Gorda, 1993 Co-Axial (Juan de Fuca Ridge), and 1991-2 and 2005-6 9°50’N EPR eruptions is unlikely to be related to fractionation during emplacement, and rather reflects variations in sub-axial magma reservoirs prior to eruption. Such variations are inconsistent with well-mixed sub-axial reservoirs and, in some cases, require relatively long-lived, systematic variations in reservoir temperatures along axis. Chemical heterogeneity within the Aldo-Kihi eruption preserves spatial variations in mantle-derived isotopic and trace element ratios with implications for the temporal and spatial scales of magma injections to the crust and along-axis mixing within shallow reservoirs. These spatial variations are difficult to reconcile with significant (> ~1 km) along-axis magma transport, as are striking correlations of chemical compositions with surface geological discontinuities or seismically imaged sub-axial magma chamber reflectors in the S. Hump (S. EPR), 9°50’N EPR, N. Gorda and 1975-1984 Krafla (N. Iceland) eruptive units. Rather, spatial correlations between surface lava compositions and sub-axial magma chamber properties or long-lived axial morphology suggest that most of the erupted magma was transported nearly vertically from the underlying reservoirs to the surface during these eruptions. In the case of the Krafla eruption, coincident deformation suggests a component of lateral melt migration at depth, despite chemical evidence for vertical transport of erupted lava from more than one chemical reservoir. In addition, along-ridge movement of earthquake epicenters during the 1992 Co-Axial and 1996 Gorda eruptions implies migration of stress release during these eruptions, even though vertical transport better explains chemical patterns. The nature of transport for most eruptions is unclear because of lack of systematic chemical patterns; this presentation emphasizes those cases where vertical transport appears to be required.

Using the heterogeneity distribution in Earth's mantle to study structure and flow

NASA Astrophysics Data System (ADS)

Rost, S.; Frost, D. A.; Bentham, H. L.

2016-12-01

The Earth's interior contains heterogeneities on many scale-lengths ranging from continent sized structures such as Large-Low Shear Velocity Provinces (LLSVPs) to grain-sized anomalies resolved using geochemistry. Sources of heterogeneity in Earth's mantle are for example the recycling of crustal material through the subduction process as well as partial melting and compositional variations. The subduction and recycling of oceanic crust throughout Earth's history leads to strong heterogeneities in the mantle that can be detected using seismology and geochemistry. Current models of mantle convection show that the subducted crustal material can be long-lived and is transported passively throughout the mantle by convective flows. Settling and entrainment is dependent on the density structure of the heterogeneity. Imaging heterogeneities throughout the mantle therefore allows imaging mantle flow especially in areas of inhibited flow due to e.g. viscosity changes or changes in composition or dynamics. The short-period seismic wavefield is dominated by scattered seismic energy partly originating from scattering at small-scale heterogeneities in Earth's mantle. Using specific raypath configurations we are able to sample different depths throughout Earth's mantle for the existence and properties of heterogeneities. These scattering probes show distinct variations in energy content with frequency indicating dominant heterogeneity length-scales in the mantle. We detect changes in heterogeneity structure both in lateral and radial directions. The radial heterogeneity structure requires changes in mantle structure at depths of 1000 km and 1800 to 2000 km that could indicate a change in viscosity structure in the mid mantle partly changing the flow of subducted crustal material into the deep mantle. Lateral changes in heterogeneity structure close to the core mantle boundary indicate lateral transport inhibited by the compositional anomalies of the LLSVPs.

Thermal inertia and surface heterogeneity on Mars

NASA Astrophysics Data System (ADS)

Putzig, Nathaniel E.

Thermal inertia derived from temperature observations is critical for understanding surface geology and assessing potential landing sites on Mars. Derivation methods generally assume uniform surface properties for any given observation. Consequently, horizontal heterogeneity and near-surface layering may yield apparent thermal inertia that varies with time of day and season. To evaluate the effects of horizontal heterogeneity, I modeled the thermal behavior of surfaces containing idealized material mixtures (dust, sand, duricrust, and rocks) and differing slope facets. These surfaces exhibit diurnal and seasonal variability in apparent thermal inertia of several 100 tiu, 1 even for components with moderately contrasting thermal properties. To isolate surface effects on the derived thermal inertia of Mars, I mapped inter- annual and seasonal changes in albedo and atmospheric dust opacity, accounting for their effects in a modified derivation algorithm. Global analysis of three Mars years of MGS-TES 2 data reveals diurnal and seasonal variations of ~200 tiu in the mid-latitudes and 600 tiu or greater in the polar regions. Correlation of TES results and modeled apparent thermal inertia of heterogeneous surfaces indicates pervasive surface heterogeneity on Mars. At TES resolution, the near-surface thermal response is broadly dominated by layering and is consistent with the presence of duricrusts over fines in the mid-latitudes and dry soils over ground ice in the polar regions. Horizontal surface mixtures also play a role and may dominate at higher resolution. In general, thermal inertia obtained from single observations or annually averaged maps may misrepresent surface properties. In lieu of a robust heterogeneous- surface derivation technique, repeat coverage can be used together with forward-modeling results to constrain the near-surface heterogeneity of Mars. 1 tiu == J m -2 K -1 s - 2 Mars Global Surveyor Thermal Emission Spectrometer

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

Miller, Thomas Martin; Patton, Bruce W.; Weber, Charles F.

The primary goal of this project is to evaluate x-ray spectra generated within a scanning electron microscope (SEM) to determine elemental composition of small samples. This will be accomplished by performing Monte Carlo simulations of the electron and photon interactions in the sample and in the x-ray detector. The elemental inventories will be determined by an inverse process that progressively reduces the difference between the measured and simulated x-ray spectra by iteratively adjusting composition and geometric variables in the computational model. The intended benefit of this work will be to develop a method to perform quantitative analysis on substandard samplesmore » (heterogeneous phases, rough surfaces, small sizes, etc.) without involving standard elemental samples or empirical matrix corrections (i.e., true standardless quantitative analysis).« less

The combustion of pure and composite propellants - The expansion and application of laminar flame theory to heterogeneous solid propellants.

NASA Technical Reports Server (NTRS)

Hertzberg, M.

1971-01-01

Development of a combustion theory based on the laminarized solutions to the energy and flow conservation equations, which is more realistic in recognizing the nature of the heating-rate problem and in obtaining a practical solution to estimating its magnitude. A new experimental approach is used for studying the combustion behavior of pure monopropellants and composite propellants which uses a laser beam to supply additional heat feedback to a burning surface. New experimental data are presented for the laser-induced combustion rate and ignition delay of pure ammonium perchlorate. The pure monopropellant theory is generalized to include such nonadiabatic effects, and the new experimental data are in good agreement with the nonadiabatic theory.-

Vacancy-mediated fcc/bcc phase separation in Fe1 -xNix ultrathin films

NASA Astrophysics Data System (ADS)

Menteş, T. O.; Stojić, N.; Vescovo, E.; Ablett, J. M.; Niño, M. A.; Locatelli, A.

2016-08-01

The phase separation occurring in Fe-Ni thin films near the Invar composition is studied by using high-resolution spectromicroscopy techniques and density functional theory calculations. Annealed at temperatures around 300 ∘C ,Fe0.70Ni0.30 films on W(110) break into micron-sized bcc and fcc domains with compositions in agreement with the bulk Fe-Ni phase diagram. Ni is found to be the diffusing species in forming the chemical heterogeneity. The experimentally determined energy barrier of 1.59 ±0.09 eV is identified as the vacancy formation energy via density functional theory calculations. Thus, the principal role of the surface in the phase separation process is attributed to vacancy creation without interstitials.

Linking potential heat source and sink to urban heat island: Heterogeneous effects of landscape pattern on land surface temperature.

PubMed

Li, Weifeng; Cao, Qiwen; Lang, Kun; Wu, Jiansheng

2017-05-15

Rapid urbanization has significantly contributed to the development of urban heat island (UHI). Regulating landscape composition and configuration would help mitigate the UHI in megacities. Taking Shenzhen, China, as a case study area, we defined heat source and heat sink and identified strong and weak sources as well as strong and weak sinks according to the natural and socioeconomic factors influencing land surface temperature (LST). Thus, the potential thermal contributions of heat source and heat sink patches were differentiated. Then, the heterogeneous effects of landscape pattern on LST were examined by using semiparametric geographically weighted regression (SGWR) models. The results showed that landscape composition has more significant effects on thermal environment than configuration. For a strong source, the percentage of patches has a positive impact on LST. Additionally, when mosaicked with some heat sink, even a small improvement in the degree of dispersion of a strong source helps to alleviate UHI. For a weak source, the percentage and density of patches have positive impacts on LST. For a strong sink, the percentage, density, and degree of aggregation of patches have negative impacts on LST. The effects of edge density and patch shape complexity vary spatially with the fragmentation of a strong sink. Similarly, the impacts of a weak sink are mainly exerted via the characteristics of percent, density, and shape complexity of patches. Copyright © 2017 Elsevier B.V. All rights reserved.

Characterization of the water chemistry, sediment (13)C and (18)O compositions of Kolleru Lake-a Ramsar wetland in Andhra Pradesh, India.

PubMed

Das Sharma, Subrata; Sujatha, D

2016-07-01

The chemistry of surface water sampled at different locations of the Kolleru Lake in Andhra Pradesh (India) show heterogeneous variability. The concentrations of dissolved sodium and chloride ions, total dissolved solids (TDS) together with high conductivity documented in water samples are indicative of mixing of saline seawater. This interpretation is further corroborated by enriched δ(18)O compositions of the carbonate fraction of the surface sediments collected at the same locations (as that of water) of the lake, and fairly good positive correlations of δ(18)O -Na(+) and δ(18)O-TDS. The saline water intrusion into the lake appears to be resulted due to its near stagnant to dry condition with reduced inflow and outflow. Such dry condition facilitated seawater intrusion into the lake due to several reasons: (i) proximity of lake to the sea (~35 km), (ii) overexploitation of fresh groundwater for agriculture as well as livestock farming, and (iii) incursion of tidal seawater (high sea waves) through Upputeru River, which is directly linked to the sea. We also document highly heterogeneous distribution of certain potentially toxic metal ions like chromium, copper, manganese, and zinc in the lake waters. Indiscriminate disposal of domestic and industrial effluents around the lake appears to be responsible for the presence of potentially toxic heavy metals. Based on these results, we finally suggest some measures for environmental rehabilitation of the lake and its surroundings.

Experimental studies of contact angle hysteresis phenomena on polymer surfaces – Toward the understanding and control of wettability for different applications.

PubMed

Grundke, K; Pöschel, K; Synytska, A; Frenzel, R; Drechsler, A; Nitschke, M; Cordeiro, A L; Uhlmann, P; Welzel, P B

2015-08-01

Contact angle hysteresis phenomena on polymer surfaces have been studied by contact angle measurements using sessile liquid droplets and captive air bubbles in conjunction with a drop shape method known as Axisymmetric Drop Shape Analysis - Profile (ADSA-P). In addition, commercially available sessile drop goniometer techniques were used. The polymer surfaces were characterized with respect to their surface structure (morphology, roughness, swelling) and surface chemistry (elemental surface composition, acid-base characteristics) by scanning electron microscopy (SEM), scanning force microscopy (SFM), ellipsometry, X-ray photoelectron spectroscopy (XPS) and streaming potential measurements. Heterogeneous polymer surfaces with controlled roughness and chemical composition were prepared by different routes using plasma etching and subsequent dip coating or grafting of polymer brushes, anodic oxidation of aluminium substrates coated with thin polymer films, deposition techniques to create regular patterned and rough fractal surfaces from core-shell particles, and block copolymers. To reveal the effects of swelling and reorientation at the solid/liquid interface contact angle hysteresis phenomena on polyimide surfaces, cellulose membranes, and thermo-responsive hydrogels have been studied. The effect of different solutes in the liquid (electrolytes, surfactants) and their impact on contact angle hysteresis were characterized for solid polymers without and with ionizable functional surface groups in aqueous electrolyte solutions of different ion concentrations and pH and for photoresist surfaces in cationic aqueous surfactant solutions. The work is an attempt toward the understanding of contact angle hysteresis phenomena on polymer surfaces aimed at the control of wettability for different applications. Copyright © 2014 Elsevier B.V. All rights reserved.

Biomimetic heterogeneous multiple ion channels: a honeycomb structure composite film generated by breath figures

NASA Astrophysics Data System (ADS)

Han, Keyu; Heng, Liping; Wen, Liping; Jiang, Lei

2016-06-01

We design a novel type of artificial multiple nanochannel system with remarkable ion rectification behavior via a facile breath figure (BF) method. Notably, even though the charge polarity in the channel wall reverses under different pH values, this nanofluidic device displays the same ionic rectification direction. Compared with traditional nanochannels, this composite multiple ion channel device can be more easily obtained and has directional ionic rectification advantages, which can be applied in many fields.We design a novel type of artificial multiple nanochannel system with remarkable ion rectification behavior via a facile breath figure (BF) method. Notably, even though the charge polarity in the channel wall reverses under different pH values, this nanofluidic device displays the same ionic rectification direction. Compared with traditional nanochannels, this composite multiple ion channel device can be more easily obtained and has directional ionic rectification advantages, which can be applied in many fields. Electronic supplementary information (ESI) available: Pore size distribution histograms of the AAO substrates; SEM images of the side view of pure AAO membranes and top view of the flat PI/AAO composite film; the current-time curves of the flat composite film; the current-voltage characteristics curves of pure AAO nanochannels with different mean pore diameters; CA of the two surfaces of the composite PI/AAO film, the structural formula of the polymer polyimide resin (PI), and solid surface zeta potential. See DOI: 10.1039/c6nr02506d

Mars and the remarkable Viking results

NASA Technical Reports Server (NTRS)

Soffen, G. A.

1978-01-01

It is pointed out that the Viking missions to Mars are the most extraordinary and complex remote effort ever performed by man. Factors which made the Viking results so remarkable are related to the technological engineering accomplishment, the voluminous scientific data about the planet, and the public interest. Quite surprisingly it was found that the Viking 1 landing site was very similar to the California desert. Attention is given to details of spacecraft landing on the Martian surface, aspects of landing site selection, the design and the operation of Lander instruments, the nine different investigations performed by the Lander, the significance of the pictures obtained of Mars, the remarkable heterogeneity of the planet, the extent and variety of volcanism, the presence of water in the solid and gaseous form on the Martian surface, the presence of water in the liquid phase at some time in the past, the two natural Martian satellites, the composition of the Martian polar caps and their changes during the seasons, the composition of the atmosphere, and the biological results, which remain ambiguous.

Geometric heterogeneity of the lattice and its effect on the kinetics phase transitions of surface reactions

NASA Astrophysics Data System (ADS)

Cortés, Joaquín.; Valencia, Eliana

1999-04-01

Two novel phenomena are discussed in this paper. The first one refers to the effect of the catalyst's surface heterogeneity on the smoothing of the first-order transition observed in the ( A+ B2) reaction (ZGB model). The second effect corresponds to obtaining information on the surface heterogeneity from the shape of the transition curve. Two types of heterogeneity were considered: the structure obtained by the random blocking of reactive sites, and the existence of a distribution in independent strips or terraces on the catalyst's surface.

Quasi-hexagonal Cu1.5Mn1.5O4 nanoplates decorated on hollow CuO by Kirkendall effect for enhancing lithium storage performance

NASA Astrophysics Data System (ADS)

Liu, Peng; Xia, Xifeng; Lei, Wu; Jiao, Xinyan; Lu, Lei; Ouyang, Yu; Hao, Qingli

2018-07-01

Constructing a hierarchical heterogeneous composite is deemed as an effective way to solve the current problems of metal oxides as lithium ion batteries' anodes. In this work, we simultaneously designed the heterogeneous component and structure of the novel hybrid based on Kirkendall effect. The composite was composed of quasi-hexagonal Cu1.5Mn1.5O4 nanoplates as a shell and CuO with voids as a core. The hybrids were characterized by using XRD, FTIR, TEM and SEM. It was found that the heating rate greatly influences the combination form of Cu1.5Mn1.5O4 and CuO. The quasi-hexagonal Cu1.5Mn1.5O4 nanoplates were assembled into branch-like shell decorated on the CuO surface under the low heating rate. However, the high heating rate led to a compact Cu1.5Mn1.5O4 shell, although the shell was also assembled by quasi-hexagonal nanoplates. The reasonable formation mechanism of the unique component and structure was proposed. Such a hybrid with the branch-like shell exhibited the best lithium storage performance. The improved electrochemical performance can be attributed to the unique component and structure. Typically, the inside voids can alleviate the volume change and the hierarchical shell can provide much contact and reaction sites. This work not only opens a new view in constructing heterogeneous hybrid with unique structure by Kirkendall effect, but also can be expanded for many other structure-based applications, such as energy storage, sensors, and heterogeneous catalysts.

Cassava/sugar palm fiber reinforced cassava starch hybrid composites: Physical, thermal and structural properties.

PubMed

Edhirej, Ahmed; Sapuan, S M; Jawaid, Mohammad; Zahari, Nur Ismarrubie

2017-08-01

A hybrid composite was prepared from cassava bagasse (CB) and sugar palm fiber (SPF) using casting technique with cassava starch (CS) as matrix and fructose as a plasticizer. Different loadings of SPF (2, 4, 6 and 8% w/w of dry starch) were added to the CS/CB composite film containing 6% CB. The addition of SPF significantly influenced the physical properties. It increased the thickness while decreasing the density, water content, water solubility and water absorption. However, no significant effect was noticed on the thermal properties of the hybrid composite film. The incorporation of SPF increased the relative crystallinity up to 47%, compared to 32% of the CS film. SEM micrographs indicated that the filler was incorporated in the matrix. The film with a higher concentration of SPF (CS-CB/SPF8) showed a more heterogeneous surface. It could be concluded that the incorporation of SPF led to changes in cassava starch film properties, potentially affecting the film performances. Copyright © 2017 Elsevier B.V. All rights reserved.

Two-Photon Laser-Induced Fluorescence O and N Atoms for the Study of Heterogeneous Catalysis in a Diffusion Reactor

NASA Technical Reports Server (NTRS)

Pallix, Joan B.; Copeland, Richard A.; Arnold, James O. (Technical Monitor)

1995-01-01

Advanced laser-based diagnostics have been developed to examine catalytic effects and atom/surface interactions on thermal protection materials. This study establishes the feasibility of using laser-induced fluorescence for detection of O and N atom loss in a diffusion tube to measure surface catalytic activity. The experimental apparatus is versatile in that it allows fluorescence detection to be used for measuring species selective recombination coefficients as well as diffusion tube and microwave discharge diagnostics. Many of the potential sources of error in measuring atom recombination coefficients by this method have been identified and taken into account. These include scattered light, detector saturation, sample surface cleanliness, reactor design, gas pressure and composition, and selectivity of the laser probe. Recombination coefficients and their associated errors are reported for N and O atoms on a quartz surface at room temperature.

The chemical composition and mineralogy of meteorites measured with very high spatial resolution by a laser mass spectrometer for in situ planetary research

NASA Astrophysics Data System (ADS)

Brigitte Neuland, Maike; Mezger, Klaus; Tulej, Marek; Frey, Samira; Riedo, Andreas; Wurz, Peter; Wiesendanger, Reto

2017-04-01

The knowledge of the chemical composition of moons, comets, asteroids or other planetary bodies is of particular importance for the investigation of the origin and evolution of the Solar System. High resolution in situ studies on planetary surfaces can yield important information on surface heterogeneity, basic grain mineralogy and chemical composition of surface and subsurface. In turn, these data are the basis for our understanding of the physical and chemical processes which led to the formation and alteration of planetary material [1]. We investigated samples of Allende and Sayh al Uhaymir with a highly miniaturised laser mass spectrometer (LMS), which has been designed and built for in situ space research [2,3]. Both meteorite samples were investigated with a spatial resolution of about 10μm in lateral direction. The high sensitivity and high dynamic range of the LMS allow for quantitative measurements of the abundances of the rock-forming and minor and trace elements with high accuracy [4]. From the data, the modal mineralogy of micrometre-sized chondrules can be inferred [5], conclusions about the condensation sequence of the material are possible and the sensitivity for radiogenic elements allows for dating analyses of the investigated material. We measured the composition of various chondrules in Allende, offering valuable clues about the condensation sequence of the different components of the meteorite. We explicitly investigated the chemical composition and heterogeneity of the Allende matrix with an accuracy that cannot be reached by the mechanical analysis methods that were and are widely used in meteoritic research. We demonstrate the capabilities for dating analyses with the LMS. By applying the U-Th-dating method, the age of the SaU169 sample could be determined. Our analyses show that the LMS would be a suitable instrument for high-quality quantitative chemical composition measurements on the surface of a celestial body like a planet, moon or asteroid. [1] Wurz, P., Whitby, J., Managadze, G. , "Laser Mass Spectrometry in Planetary Science", AIP Conf.Proc. CP1144(2009): 70-75. [2] Rohner, U., Whitby, J.A. and Wurz, P. "A miniature laser ablation time-of-flight mass spectrometer for in situ planetary exploration", Measurement Science and Technology 14 (2003): 2159-2164. [3] Riedo, A., Bieler, A., Neuland, M., Tulej, M. and Wurz, P., "Performance evaluation of a miniature laser ablation time-of-flight mass spectrometer designed for in situ investigations in planetary space research", Journal of Mass Spectrometry 48 (2013): 1 -15 [4] Neuland, M.B., Grimaudo, V., Mezger, K., Moreno-García, P., Riedo, A., Tulej, M. and Wurz, P., "Quantitative measurement of the chemical composition of geological standards with a miniature laser ablation/ionisation mass spectrometer designed for in situ application in space research", Meas. Sci. Technol. 27(2016), article ID:035904, 1 - 13. [5] Tulej, M., Neubeck, A., Ivarsson, M., Riedo, A., Neuland, M.B., Meyer, S. and Wurz, P., "Chemical composition of micrometer-sized filaments in an aragonite host by a miniature laser ablation/ionization mass spectrometer", Astrobiol., 15 (2015): 669 - 682.

Rotational Spectral Unmixing of Exoplanets: Degeneracies between Surface Colors and Geography

NASA Astrophysics Data System (ADS)

Fujii, Yuka; Lustig-Yaeger, Jacob; Cowan, Nicolas B.

2017-11-01

Unmixing the disk-integrated spectra of exoplanets provides hints about heterogeneous surfaces that we cannot directly resolve in the foreseeable future. It is particularly important for terrestrial planets with diverse surface compositions like Earth. Although previous work on unmixing the spectra of Earth from disk-integrated multi-band light curves appeared successful, we point out a mathematical degeneracy between the surface colors and their spatial distributions. Nevertheless, useful constraints on the spectral shape of individual surface types may be obtained from the premise that albedo is everywhere between 0 and 1. We demonstrate the degeneracy and the possible constraints using both mock data based on a toy model of Earth, as well as real observations of Earth. Despite the severe degeneracy, we are still able to recover an approximate albedo spectrum for an ocean. In general, we find that surfaces are easier to identify when they cover a large fraction of the planet and when their spectra approach zero or unity in certain bands.

Rotational Spectral Unmixing of Exoplanets: Degeneracies between Surface Colors and Geography

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

Fujii, Yuka; Lustig-Yaeger, Jacob; Cowan, Nicolas B., E-mail: yuka.fujii.ebihara@gmail.com

Unmixing the disk-integrated spectra of exoplanets provides hints about heterogeneous surfaces that we cannot directly resolve in the foreseeable future. It is particularly important for terrestrial planets with diverse surface compositions like Earth. Although previous work on unmixing the spectra of Earth from disk-integrated multi-band light curves appeared successful, we point out a mathematical degeneracy between the surface colors and their spatial distributions. Nevertheless, useful constraints on the spectral shape of individual surface types may be obtained from the premise that albedo is everywhere between 0 and 1. We demonstrate the degeneracy and the possible constraints using both mock datamore » based on a toy model of Earth, as well as real observations of Earth. Despite the severe degeneracy, we are still able to recover an approximate albedo spectrum for an ocean. In general, we find that surfaces are easier to identify when they cover a large fraction of the planet and when their spectra approach zero or unity in certain bands.« less

Rotational Spectral Unmixing of Exoplanets: Degeneracies Between Surface Colors and Geography

NASA Technical Reports Server (NTRS)

Fujii, Yuka; Lustig-Yaeger, Jacob; Cowan, Nicolas B.

2017-01-01

Unmixing the disk-integrated spectra of exoplanets provides hints about heterogeneous surfaces that we cannot directly resolve in the foreseeable future. It is particularly important for terrestrial planets with diverse surface compositions like Earth. Although previous work on unmixing the spectra of Earth from disk-integrated multi-band light curves appeared successful, we point out a mathematical degeneracy between the surface colors and their spatial distributions. Nevertheless, useful constraints on the spectral shape of individual surface types may be obtained from the premise that albedo is everywhere between 0 and 1. We demonstrate the degeneracy and the possible constraints using both mock data based on a toy model of Earth, as well as real observations of Earth. Despite the severe degeneracy, we are still able to recover an approximate albedo spectrum for an ocean. In general, we find that surfaces are easier to identify when they cover a large fraction of the planet and when their spectra approach zero or unity in certain bands.

Organizational heterogeneity of vertebrate genomes.

PubMed

Frenkel, Svetlana; Kirzhner, Valery; Korol, Abraham

2012-01-01

Genomes of higher eukaryotes are mosaics of segments with various structural, functional, and evolutionary properties. The availability of whole-genome sequences allows the investigation of their structure as "texts" using different statistical and computational methods. One such method, referred to as Compositional Spectra (CS) analysis, is based on scoring the occurrences of fixed-length oligonucleotides (k-mers) in the target DNA sequence. CS analysis allows generating species- or region-specific characteristics of the genome, regardless of their length and the presence of coding DNA. In this study, we consider the heterogeneity of vertebrate genomes as a joint effect of regional variation in sequence organization superimposed on the differences in nucleotide composition. We estimated compositional and organizational heterogeneity of genome and chromosome sequences separately and found that both heterogeneity types vary widely among genomes as well as among chromosomes in all investigated taxonomic groups. The high correspondence of heterogeneity scores obtained on three genome fractions, coding, repetitive, and the remaining part of the noncoding DNA (the genome dark matter--GDM) allows the assumption that CS-heterogeneity may have functional relevance to genome regulation. Of special interest for such interpretation is the fact that natural GDM sequences display the highest deviation from the corresponding reshuffled sequences.

Fast-degrading PLA/ORMOGLASS fibrous composite scaffold leads to a calcium-rich angiogenic environment

PubMed Central

Sachot, Nadège; Roguska, Agata; Planell, Josep Anton; Lewandowska, Malgorzata; Engel, Elisabeth; Castaño, Oscar

2017-01-01

The success of scaffold implantation in acellular tissue engineering approaches relies on the ability of the material to interact properly with the biological environment. This behavior mainly depends on the design of the graft surface and, more precisely, on its capacity to biodegrade in a well-defined manner (nature of ions released, surface-to-volume ratio, dissolution profile of this release, rate of material resorption, and preservation of mechanical properties). The assessment of the biological behavior of temporary templates is therefore very important in tissue engineering, especially for composites, which usually exhibit complicated degradation behavior. Here, blended polylactic acid (PLA) calcium phosphate ORMOGLASS (organically modified glass) nanofibrous mats have been incubated up to 4 weeks in physiological simulated conditions, and their morphological, topographical, and chemical changes have been investigated. The results showed that a significant loss of inorganic phase occurred at the beginning of the immersion and the ORMOGLASS maintained a stable composition afterward throughout the degradation period. As a whole, the nanostructured scaffolds underwent fast and heterogeneous degradation. This study reveals that an angiogenic calcium-rich environment can be achieved through fast-degrading ORMOGLASS/PLA blended fibers, which seems to be an excellent alternative for guided bone regeneration. PMID:28744124

The effects of dune slopes and material heterogeneity on the thermal behavior of dune fields in Mars' Southern Hemisphere

NASA Astrophysics Data System (ADS)

O'Shea, P. M.; Putzig, N. E.; Van Kooten, S.; Fenton, L. K.

2015-12-01

We analyzed the effects of slopes on the thermal properties of three dune fields in Mars' southern hemisphere. Although slope has important thermal effects, it is not the main driver of observed apparent thermal inertia (ATI) for these dunes. Comparing the ATI seasonal behavior as derived from Thermal Emission Spectrometer (TES) data with that modeled for compositional heterogeneities, we found that TES results correlate best with models of duricrust overlying and/or horizontally mixing with fines. We measured slopes and aspects in digital terrain models created from High Resolution Imaging Science Experiment (HiRISE) images of dunes within Proctor, Kaiser, and Wirtz craters. Using the MARSTHERM web toolset, we incorporated the slopes and aspects together with TES albedo, TES thermal inertia, surface pressure, and TES dust opacity, into models of seasonal ATI. Models that incorporate sub-pixel slopes show seasonal day and night ATI values that differ from the TES results by 0-300 J m-2 K-1 s-½. In addition, the models' day-night differences are opposite in sign from those of the TES results, indicating that factors other than slope are involved. We therefore compared the TES data to model results for a broad range of horizontally mixed and two-layered surfaces to seek other possible controls on the observed data, finding that a surface layer of higher thermal inertia is a likely contributor. However, it is clear from this study that the overall composition and morphology of the dune fields are more complex than currently available models allow. Future work will combine slopes with other model parameters such as multi-layered surfaces and lateral changes in layer thickness. Coupling these improvements with broader seasonal coverage from the Thermal Emission Imaging System (THEMIS) at more thermally favorable times of day would allow more accurate characterization of dune thermal behavior.

Giant calcite concretions in aeolian dune sandstones; sedimentological and architectural controls on diagenetic heterogeneity, mid-Cretaceous Iberian Desert System, Spain

NASA Astrophysics Data System (ADS)

Arribas, Maria Eugenia; Rodríguez-López, Juan Pedro; Meléndez, Nieves; Soria, Ana Rosa; de Boer, Poppe L.

2012-01-01

Aeolian dune sandstones of the Iberian erg system (Cretaceous, Spain) host giant calcite concretions that constitute heterogeneities of diagenetic origin within a potential aeolian reservoir. The giant calcite concretions developed in large-scale aeolian dune foresets, at the transition between aeolian dune toeset and damp interdune elements, and in medium-scale superimposed aeolian dune sets. The chemical composition of the giant concretions is very homogeneous. They formed during early burial by low Mg-calcite precipitation from meteoric pore waters. Carbonate components with yellow/orange luminescence form the nuclei of the poikilotopic calcite cement. These cements postdate earlier diagenetic features, characterized by early mechanical compaction, Fe-oxide cements and clay rims around windblown quartz grains resulting from the redistribution of aeolian dust over the grain surfaces. The intergranular volume (IGV) in friable aeolian sandstone ranges from 7.3 to 15.3%, whereas in cemented aeolian sandstone it is 18.6 to 25.3%. The giant-calcite concretions developed during early diagenesis under the influence of meteoric waters associated with the groundwater flow of the desert basin, although local (e.g. activity of fluid flow through extensional faults) and/or other regional controls (e.g. variations of the phreatic level associated with a variable water influx to the erg system and varying sea level) could have favoured the local development of giant-calcite concretions. The spatial distribution pattern of carbonate grains and the main bounding surfaces determined the spatial distribution of the concretions. In particular, the geometry of the giant calcite concretions is closely associated with main bounding aeolian surfaces. Thus, interdune, superimposition and reactivation surfaces exerted a control on the concretion geometries ranging from flat and tabular ones (e.g. bounded by interdunes) to wedge-shaped concretions at the dune foresets (e.g. bounded by superimposition and reactivation surfaces) determining the spatial distribution of the heterogeneities of diagenetic origin in the aeolian reservoir.

Crustal heterogeneity of the moon viewed from the Galileo SSI camera: Lunar sample calibrations and compositional implications

NASA Technical Reports Server (NTRS)

Pieters, Carle M.; Belton, M.; Becker, T.; Carr, M. H.; Chapmann, C.; Fanale, F. P.; Fischer, Erich M.; Gaddis, L.; Greeley, Ronald; Greenberg, R.

1991-01-01

Summaries are given of the spectral calibration, compositional parameters, nearside color, and limb and farside color of the Moon. The farside of the Moon, a large area of lunar crust, is dominated by heavily cratered terrain and basin deposits that represent the products of the first half billion years of crustal evolution. Continuing analysis of the returned lunar samples suggest a magma ocean and/or serial magmatism model for evolution of the primordial lunar crust. However, testing either hypothesis requires compositional information about the crustal stratigraphy and lateral heterogeneity. Resolution of this important planetary science issue is dependent on additional data. New Galileo multispectral images indicate previously unknown local and regional compositional diversity of the farside crust. Future analysis will focus on individual features and a more detailed assessment of crustal stratigraphy and heterogeneity.

Transient electroosmotic flow induced by AC electric field in micro-channel with patchwise surface heterogeneities.

PubMed

Luo, Win-Jet

2006-03-15

This paper investigates two-dimensional, time-dependent electroosmotic flow driven by an AC electric field via patchwise surface heterogeneities distributed along the micro-channel walls. The time-dependent flow fields through the micro-channel are simulated for various patchwise heterogeneous surface patterns using the backwards-Euler time stepping numerical method. Different heterogeneous surface patterns are found to create significantly different electrokinetic transport phenomena. The transient behavior characteristics of the generated electroosmotic flow are then discussed in terms of the influence of the patchwise surface heterogeneities, the direction of the applied AC electric field, and the velocity of the bulk flow. It is shown that the presence of oppositely charged surface heterogeneities on the micro-channel walls results in the formation of localized flow circulations within the bulk flow. These circulation regions grow and decay periodically in phase with the applied periodic AC electric field intensity. The location and rotational direction of the induced circulations are determined by the directions of the bulk flow velocity and the applied electric field.

Spatially resolved chemical imaging of individual atmospheric particles using nanoscale imaging mass spectrometry: insight into particle origin and chemistry

DOE PAGES

Ghosal, Sutapa; Weber, Peter K.; Laskin, Alexander

2014-01-14

Knowledge of the spatially resolved composition of atmospheric particles is essential for differentiating between their surface versus bulk chemistry and understanding particle reactivity and the potential environmental impact. Here, we demonstrate the application of nanometer-scale secondary ion mass spectrometry (CAMECA NanoSIMS 50 ion probe) for 3D chemical imaging of individual atmospheric particles without any sample pre-treatment, such as sectioning of particles. Use of NanoSIMS depth profile analysis enables elemental mapping of particles with nanometer spatial resolution over a broad range of particle sizes. We have used this technique to probe the spatially resolved composition of ambient particles collected during amore » field campaign in Mexico City. Particles collected during this campaign have been extensively characterized in the past using other particle analysis techniques and hence offer a unique opportunity for exploring the utility of depth-resolved chemical imaging in ambient particle research. The particles that we examined in our study include those collected during a pollution episode related to urban waste incineration as well as background particles from the same location before the episode. Particles from the pollution episode show substantial intra-particle compositional variability typical of particles resulting from multiple emission sources. In contrast, the background particles have relatively homogeneous compositions with enhanced presence of nitrogen, oxygen, and chlorine at the particle surface. We also observed the surface enhancement of nitrogen and oxygen species is consistent with the presence of surface nitrates resulting from gas–particle heterogeneous interactions and is indicative of atmospheric ageing of the particles. The results presented here illustrate 3D characterization of ambient particles for insight into their chemical history.« less

Spatially resolved chemical imaging of individual atmospheric particles using nanoscale imaging mass spectrometry: Insighs into particle origin and chemistry

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

Ghosal, Sutapa; Weber, Peter K.; Laskin, Alexander

2014-04-21

Knowledge of the spatially-resolved composition of atmospheric particles is essential for differentiating between their surface versus bulk chemistry, understanding particle reactivity and the potential environmental impact. We demonstrate the application of nanometer-scale secondary ion mass spectrometry (Cameca NanoSIMS 50 ion probe) for 3D chemical imaging of individual atmospheric particles without any sample pre-treatment, such as the sectioning of particles. Use of NanoSIMS depth profile analysis enables elemental mapping of particles with nanometer spatial resolution over a broad of range of particle sizes. We have used this technique to probe spatially resolved composition of ambient particles collected during a field campaignmore » in Mexico City. Particles collected during this campaign have been extensively characterized in the past using other particle analysis techniques and hence offer a unique opportunity for exploring the utility of depth resolved chemical imaging in ambient particle research. 1 Particles examined in this study include those collected during a pollution episode related to urban waste incineration as well as background particles from the same location prior to the episode. Particles from the pollution episode show substantial intra-particle compositional variability typical of particles resulting from multiple emission sources. In contrast, the background particles have relatively homogeneous compositions with enhanced presence of nitrogen, oxygen and chlorine at the particle surface. The observed surface enhancement of nitrogen and oxygen species is consistent with the presence of surface nitrates resulting from gas-particle heterogeneous interactions and is indicative of atmospheric ageing of the particles. The results presented here illustrate 3D characterization of ambient particles for insights into their chemical history.« less

Microwave-assisted solvothermal synthesis of novel hierarchical BiOI/rGO composites for efficient photocatalytic degardation of organic pollutants

NASA Astrophysics Data System (ADS)

Niu, Jinfen; Dai, Peixuan; Zhang, Qian; Yao, Binghua; Yu, Xiaojiao

2018-02-01

In the present paper, a novel composite of BiOI/rGO with excellent visible-light photocatalytic activity was successfully fabricated via very different simple, fast and mild rapid microwave hydrothermal method. The BiOI/rGO -1(BG-1) was donated as a simple chemical mechanical and the BiOI/rGO -2(BG-2) was donated as one-step rapid microwave hydrothermal method. The BG-1 were composed of the BiOI microspheres with a diameter of about 1 μm and mixed heterogeneously with graphene. While, the BG-2 were consist of the BiOI nanoplates with the thickness of approximately 20 nm dispersed heterogeneously on the surface of rGO. The degradation of 40 mg/L methylene blue (MB) and 20 mg/L levofloxacin (LEV) under visible light irradiation can reach about 11 and 3 times than that of P25, respectively. Furthermore, the reactive species of hole was determined to dominant the photodegradation process. The intensive photocatlytic could ascribe to more effective electron transportation and separations, this conclusion was different with other studies. A possible photocatalytic mechanism of BG-2 was also proposed.

Failure Rate of Direct High-Viscosity Glass-Ionomer Versus Hybrid Resin Composite Restorations in Posterior Permanent Teeth - a Systematic Review

PubMed Central

Mickenautsch, Steffen; Yengopal, Veerasamy

2015-01-01

Purpose Traditionally, resin composite restorations are claimed by reviews of the dental literature as being superior to glass-ionomer fillings in terms of restoration failures in posterior permanent teeth. The aim of this systematic review is to answer the clinical question, whether conventional high-viscosity glass-ionomer restorations, in patients with single and/or multi-surface cavities in posterior permanent teeth, have indeed a higher failure rate than direct hybrid resin composite restorations. Methods Eight databases were searched until December 02, 2013. Trials were assessed for bias risks, in-between datasets heterogeneity and statistical sample size power. Effects sizes were computed and statistically compared. A total of 55 citations were identified through systematic literature search. From these, 46 were excluded. No trials related to high-viscosity glass-ionomers versus resin composite restorations for direct head-to-head comparison were found. Three trials related to high-viscosity glass-ionomers versus amalgam and three trials related to resin composite versus amalgam restorations could be included for adjusted indirect comparison, only. Results The available evidence suggests no difference in the failure rates between both types of restoration beyond the play of chance, is limited by lack of head-to-head comparisons and an insufficient number of trials, as well as by high bias and in-between-dataset heterogeneity risk. The current clinical evidence needs to be regarded as too poor in order to justify superiority claims regarding the failure rates of both restoration types. Sufficiently large-sized, parallel-group, randomised control trials with high internal validity are needed, in order to justify any clinically meaningful judgment to this topic. PMID:26962372

Spatially-resolved studies on the role of defects and boundaries in electronic behavior of 2D materials

NASA Astrophysics Data System (ADS)

Hus, Saban M.; Li, An-Ping

2017-08-01

Two-dimensional (2D) materials are intrinsically heterogeneous. Both localized defects, such as vacancies and dopants, and mesoscopic boundaries, such as surfaces and interfaces, give rise to compositional or structural heterogeneities. The presence of defects and boundaries can break lattice symmetry, modify the energy landscape, and create quantum confinement, leading to fascinating electronic properties different from the ;ideal; 2D sheets. This review summarizes recent progress in understanding the roles of defects and boundaries in electronic, magnetic, thermoelectric, and transport properties of 2D layered materials. The focus is on the understanding of correlation of atomic-scale structural information with electronic functions by interrogating heterogeneities individually. The materials concerned are graphene, transition metal dichalcogenides (TMDs), hexagonal boron nitride (hBN), and topological insulators (TIs). The experimental investigations benefit from new methodologies and techniques in scanning tunneling microscopy (STM), including spin-polarized STM, scanning tunneling potentiometry (STP), scanning tunneling thermopower microscopy, and multi-probe STM. The experimental effort is complemented by the computational and theoretical approaches, capable of discriminating between closely competing states and achieving the length scales necessary to bridge across features such as local defects and complex heterostructures. The goal is to provide a general view of current understanding and challenges in studying the heterogeneities in 2D materials and to evaluate the potential of controlling and exploiting these heterogeneities for novel functionalities and electron devices.

Use of a cable-based system for observing the heterogeneity of vegetation communities in arctic tundra

NASA Astrophysics Data System (ADS)

Ahrends, H. E.; Oberbauer, S. F.; Tweedie, C.; Hollister, R. D.

2010-12-01

Knowledge of changing tundra vegetation and its response to climate variability is critical for understanding the land-atmosphere-interactions for the Arctic and the global system. However, vegetation characteristics, such as phenology, structure and species composition, are characterized by an extreme heterogeneity at a small scale. Manual observations of these variables are highly time-consuming, labor intensive, subjective, and disturbing to the vegetation. In contrast, recently developed robotic systems (networked infomechanical systems, NIMS) allow for performing non-intrusive spatially integrated measurements of vegetation communities. Within the ITEX (International Tundra Experiment) AON (Arctic Observation Network) project we installed a cable-based sensor system, running over a transect of approximately 50 m length and 2 m width, at two long-term arctic research sites in Alaska. The trolley was initially equipped with instruments recording the distance to vegetation canopy, up- and downwelling short- and longwave radiation, air and surface temperature and spectral reflection. We aim to study the thermal and spectral response of the vegetation communities over a wide range of ecosystem types. We expect that automated observations, covering the spatial heterogeneity of vegetation and surface characteristics, can give a deeper insight in ecosystem functioning and vegetation response to climate. The data can be used for scaling up vegetation characteristics derived from manual measurements and for linking them to aircraft and satellite data and to carbon, water and surface energy budgets measured at the ecosystem scale. Sampling errors due to cable sag are correctable and effects of wind-driven movements can be offset by repeat measurements. First hand-pulled test measurements during summer 2010 show strong heterogeneity of the observation parameters and a variable spectral and thermal response of the plants within the transects. Differences support the importance of our approach for upscaling purposes and for a comprehensive understanding of the arctic biome.

Internal and Surface Phenomena in Heterogenous Metal Combustion

NASA Technical Reports Server (NTRS)

Dreizin, Edward L.

1997-01-01

The phenomenon of gas dissolution in burning metals was observed in recent metal combustion studies, but it could not be adequately explained by the traditional metal combustion models. The research reported here addresses heterogeneous metal combustion with emphasis on the processes of oxygen penetration inside burning metal and its influence on the metal combustion rate, temperature history, and disruptive burning. The unique feature of this work is the combination of the microgravity environment with a novel micro-arc generator of monodispersed metal droplets, ensuring repeatable formation and ignition of uniform metal droplets with a controllable initial temperature and velocity. Burning droplet temperature is measured in real time with a three wavelength pyrometer. In addition, particles are rapidly quenched at different combustion times, cross-sectioned, and examined using SEM-based techniques to retrieve the internal composition history of burning metal particles. When the initial velocity of a spherical particle is nearly zero, the microgravity environment makes it possible to study the flame structure, the development of flame nonsymmetry, and correlation of the flame shape with the heterogeneous combustion processes.

Investigating the Impact of Surface Heterogeneity on the Convective Boundary Layer Over Urban Areas Through Coupled Large-Eddy Simulation and Remote Sensing

NASA Technical Reports Server (NTRS)

Dominguez, Anthony; Kleissl, Jan P.; Luvall, Jeffrey C.

2011-01-01

Large-eddy Simulation (LES) was used to study convective boundary layer (CBL) flow through suburban regions with both large and small scale heterogeneities in surface temperature. Constant remotely sensed surface temperatures were applied at the surface boundary at resolutions of 10 m, 90 m, 200 m, and 1 km. Increasing the surface resolution from 1 km to 200 m had the most significant impact on the mean and turbulent flow characteristics as the larger scale heterogeneities became resolved. While previous studies concluded that scales of heterogeneity much smaller than the CBL inversion height have little impact on the CBL characteristics, we found that further increasing the surface resolution (resolving smaller scale heterogeneities) results in an increase in mean surface heat flux, thermal blending height, and potential temperature profile. The results of this study will help to better inform sub-grid parameterization for meso-scale meteorological models. The simulation tool developed through this study (combining LES and high resolution remotely sensed surface conditions) is a significant step towards future studies on the micro-scale meteorology in urban areas.

Heterogeneous nucleation of ice on carbon surfaces.

PubMed

Lupi, Laura; Hudait, Arpa; Molinero, Valeria

2014-02-26

Atmospheric aerosols can promote the heterogeneous nucleation of ice, impacting the radiative properties of clouds and Earth's climate. The experimental investigation of heterogeneous freezing of water droplets by carbonaceous particles reveals widespread ice freezing temperatures. It is not known which structural and chemical characteristics of soot account for the variability in ice nucleation efficiency. Here we use molecular dynamics simulations to investigate the nucleation of ice from liquid water in contact with graphitic surfaces. We find that atomically flat carbon surfaces promote heterogeneous nucleation of ice, while molecularly rough surfaces with the same hydrophobicity do not. Graphitic surfaces and other surfaces that promote ice nucleation induce layering in the interfacial water, suggesting that the order imposed by the surface on liquid water may play an important role in the heterogeneous nucleation mechanism. We investigate a large set of graphitic surfaces of various dimensions and radii of curvature and find that variations in nanostructures alone could account for the spread in the freezing temperatures of ice on soot in experiments. We conclude that a characterization of the nanostructure of soot is needed to predict its ice nucleation efficiency.

Substrate-Based Noble-Metal Nanomaterials: Shape Engineering and Applications

NASA Astrophysics Data System (ADS)

Hajfathalian, Maryam

Nanostructures have potential for use in state-of-the-art applications such as sensing, imaging, therapeutics, drug delivery, and electronics. The ability to fabricate and engineer these nanoscale materials is essential for the continued development of such devices. Because the morphological features of nanomaterials play a key role in determining chemical and physical properties, there is great interest in developing and improving methods capable of controlling their size, shape, and composition. While noble nanoparticles have opened the door to promising applications in fields such as imaging, cancer targeting, photothermal treatment, drug delivery, catalysis and sensing, the synthetic processes required to form these nanoparticles on surfaces are not well-developed. Herein is a detailed account on efforts for adapting established solution-based seed-mediated synthetic protocols to structure in a substrate-based platform. These syntheses start by (i) defining heteroepitaxially oriented nanostructured seeds at site-specific locations using lithographic or directed-assembly techniques, and then (ii) transforming the seeds using either a solution or vapor phase processing route to activate kinetically- or thermodynamically-driven growth modes, to arrive at nanocrystals with complex and useful geometries. The first series of investigations highlight synthesis-routes based on heterogeneous nucleation, where templates serve as nucleation sites for metal atoms arriving in the vapor phase. In the first research direction, the vapor-phase heterogeneous nucleation of Ag on Au was carried out at high temperatures, where the Ag vapor was sourced from a sublimating foil onto adjacent Au templates. This process transformed both the composition and morphology of the initial Au Wulff-shaped nanocrystals to a homogeneous AuAg nanoprism. In the second case, the vapor-phase heterogeneous nucleation of Cu atoms on Au nanocrystal templates was investigated by placing a Cu foil next to Au templates and heating, which caused the Cu atoms from the foil to sublimate from the foil and heterogeneously nucleation on the surface of the immobilized Au seeds. This process caused the composition and morphology of the Au Wulff-shape to transform into a homogeneous AuCu nanotriangle. Lastly, we characterized the morphological features and composition, optical properties, and also the catalytic and photocatalytic performance toward hydrogenation of 4-nitrophenolate. The second series of investigations highlight synthetic routes utilizing competencies of substrate-based techniques with colloidal chemistry. We have demonstrated two substrate-based syntheses yielding bimetallic nanostructures where shape control was achieved through (i) facet-selective capping agents and (ii) additive and subtractive process. In the first case a citrate-based cubic structure has been synthesized in the presence or absence of ascorbic acid and the role of each has been considered in shape control. Reactions were carried out in which Ag+ ions were reduced onto substrate-immobilized Ag, Au, Pd, and Pt seeds. It was discovered that for syntheses lacking ascorbic acid, citrate acts as both the capping and the reducing agent, resulting in a robust nanocube growth mode; however, when ascorbic acid was included in these syntheses, then the growth mode reverted to one that advances the octahedral geometry. The conclusion of these results was that citrate, or one of its oxidation products, selectively caps (100) facets, but where this capability was compromised by ascorbic acid. In the second case, galvanic replacement reactions have been carried out on immobilized cubic and Wulff structures to create the substrate-based nanoshells and nanocages, where the prepositioned templates were chemically transformed into hollow structures. In this novel research, Wulff-shaped templates of Au, Pt, or Pd, formed through the dewetting of ultrathin films, were first transformed into core?shell structures through the reduction of Ag+ ions onto their surface and then further transformed through the galvanic replacement of Ag with Au. Detailed studies were provided highlighting discoveries related to (i) alloying, (ii) dealloying, (iii) hollowing, (iv) crystal structure and (vi) the localized surface plasmon resonance (LSPR). Overall, a series of synthetic strategies based on physical and chemical vapor deposition were devised and validated to achieve novel substrate- based nanomaterials with different shapes and compositions for a variety of applications such as sensing, plasmonics, catalysis, and photocatalysis. The novel research in this dissertation also takes advantage of competencies of substrate-based techniques with colloidal chemistry and, brings this rich and exciting chemistry and its associated functionalities to the substrate surface.

Nano-catalysts: Bridging the gap between homogeneous and heterogeneous catalysis

EPA Science Inventory

Functionalized nanoparticles have emerged as sustainable alternatives to conventional materials, as robust, high-surface-area heterogeneous catalyst supports. We envisioned a catalyst system, which can bridge the homogenous and heterogeneous system. Postsynthetic surface modifica...

Shaping electrocatalysis through tailored nanomaterials

DOE PAGES

Kang, Yijin; Yang, Peidong; Markovic, Nenad M.; ...

2016-09-21

Electrocatalysis is a subclass of heterogeneous catalysis that is aimed towards increase of the electrochemical reaction rates that are taking place at the surface of electrodes. Real-world electrocatalysts are usually based on precious metals in the form of nanoparticles due to their high surface-to-volume ratio, which enables better utilization of employed materials. Ability to tailor nanostructure of an electrocatalyst is critical in order to tune their electrocatalytic properties. Over the last decade, that has mainly been achieved through implementation of fundamental studies performed on well-defined extended surfaces with distinct single crystalline and polycrystalline structures. Based on these studies, it hasmore » been demonstrated that performance of an electrocatalyst could be significantly changed through the control of size, composition, morphology and architecture of employed nanomaterials. Here, this review outlines the following steps in the process of rational development of an efficient electrocatalyst: 1) electrochemical properties of well-defined surfaces, 2) synthesis and characterization of different classes of electrocatalysts, and 3) correlation between physical properties (size, shape, composition and morphology) and electrochemical behavior (adsorption, electrocatalytic activity and durability) of electrocatalyst. In addition, this is a brief summary of the novel research platforms in the development of functional nano materials for energy conversion and storage applications such as fuel cells electrolyzers and batteries.« less

Application of surface complexation models to anion adsorption by natural materials.

PubMed

Goldberg, Sabine

2014-10-01

Various chemical models of ion adsorption are presented and discussed. Chemical models, such as surface complexation models, provide a molecular description of anion adsorption reactions using an equilibrium approach. Two such models, the constant capacitance model and the triple layer model, are described in the present study. Characteristics common to all the surface complexation models are equilibrium constant expressions, mass and charge balances, and surface activity coefficient electrostatic potential terms. Methods for determining parameter values for surface site density, capacitances, and surface complexation constants also are discussed. Spectroscopic experimental methods of establishing ion adsorption mechanisms include vibrational spectroscopy, nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, X-ray absorption spectroscopy, and X-ray reflectivity. Experimental determinations of point of zero charge shifts and ionic strength dependence of adsorption results and molecular modeling calculations also can be used to deduce adsorption mechanisms. Applications of the surface complexation models to heterogeneous natural materials, such as soils, using the component additivity and the generalized composite approaches are described. Emphasis is on the generalized composite approach for predicting anion adsorption by soils. Continuing research is needed to develop consistent and realistic protocols for describing ion adsorption reactions on soil minerals and soils. The availability of standardized model parameter databases for use in chemical speciation-transport models is critical. Published 2014 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and as such, is in the public domain in the in the United States of America.

Subregional characterization of mesoscale eddies across the Brazil-Malvinas Confluence

NASA Astrophysics Data System (ADS)

Mason, Evan; Pascual, Ananda; Gaube, Peter; Ruiz, Simón; Pelegrí, Josep L.; Delepoulle, Antoine

2017-04-01

Horizontal and vertical motions associated with coherent mesoscale structures, including eddies and meanders, are responsible for significant global transports of many properties, including heat and mass. Mesoscale vertical fluxes also influence upper ocean biological productivity by mediating the supply of nutrients into the euphotic layer, with potential impacts on the global carbon cycle. The Brazil-Malvinas Confluence (BMC) is a western boundary current region in the South Atlantic with intense mesoscale activity. This region has an active role in the genesis and transformation of water masses and thus is a critical component of the Atlantic meridional overturning circulation. The collision between the Malvinas and Brazil Currents over the Patagonian shelf/slope creates an energetic front that translates offshore to form a vigorous eddy field. Recent improvements in gridded altimetric sea level anomaly fields allow us to track BMC mesoscale eddies with high spatial and temporal resolutions using an automated eddy tracker. We characterize the eddies across fourteen 5° × 5° subregions. Eddy-centric composites of tracers and geostrophic currents diagnosed from a global reanalysis of surface and in situ data reveal substantial subregional heterogeneity. The in situ data are also used to compute the evolving quasi-geostrophic vertical velocity (QG-ω) associated with each instantaneous eddy instance. The QG-ω eddy composites have the expected dipole patterns of alternating upwelling/downwelling, however, the magnitude and sign of azimuthally averaged vertical velocity varies among subregions. Maximum eddy values are found near fronts and sharp topographic gradients. In comparison with regional eddy composites, subregional composites provide refined information about mesoscale eddy heterogeneity.

Colloidal-based additive manufacturing of bio-inspired composites

NASA Astrophysics Data System (ADS)

Studart, Andre R.

Composite materials in nature exhibit heterogeneous architectures that are tuned to fulfill the functional demands of the surrounding environment. Examples range from the cellulose-based organic structure of plants to highly mineralized collagen-based skeletal parts like bone and teeth. Because they are often utilized to combine opposing properties such as strength and low-density or stiffness and wear resistance, the heterogeneous architecture of natural materials can potentially address several of the technical limitations of artificial homogeneous composites. However, current man-made manufacturing technologies do not allow for the level of composition and fiber orientation control found in natural heterogeneous systems. In this talk, I will present two additive manufacturing technologies recently developed in our group to build composites with exquisite architectures only rivaled by structures made by living organisms in nature. Since the proposed techniques utilize colloidal suspensions as feedstock, understanding the physics underlying the stability, assembly and rheology of the printing inks is key to predict and control the architecture of manufactured parts. Our results will show that additive manufacturing routes offer a new exciting pathway for the fabrication of biologically-inspired composite materials with unprecedented architectures and functionalities.

The 2014-15 eruption and the short-term geochemical evolution of the Fogo volcano (Cape Verde): Evidence for small-scale mantle heterogeneity

NASA Astrophysics Data System (ADS)

Mata, J.; Martins, S.; Mattielli, N.; Madeira, J.; Faria, B.; Ramalho, R. S.; Silva, P.; Moreira, M.; Caldeira, R.; Moreira, M.; Rodrigues, J.; Martins, L.

2017-09-01

Recurrent eruptions at very active ocean island volcanoes provide the ideal means to gain insight on the scale of spatial variations at the mantle source and on temporal changes of magma genesis and evolution processes. In 2014, after 19 years of quiescence, Fogo volcano (Cape Verde Archipelago) experienced a new eruption, with the vents located 200 m from those of the 1995 eruption, and less than 2000 m from those of the 1951 event. This offered a unique opportunity to investigate the existence of small-scale mantle heterogeneities and the short-term compositional evolution of magmas erupted by a very active oceanic volcano like Fogo. Here we present petrological and geochemical data from the early stages of the Fogo's most recent eruption - started on November 23, 2014 - and compare them with the signature of previous eruptions (particularly those of 1995 and 1951). The magmas erupted in 2014 are alkaline (up to 23.4% and 0.94% of normative ne and lc, respectively) with somewhat evolved compositions (Mg # < 56), ranging from tephrites to phonotephrites. The eruption of phonotephritic lavas preceded the effusion of tephritic ones. Lavas carried to the surface clinopyroxene and kaersutite phenocrysts and cognate megacrysts, which indicate that the main stages of magma evolution occurred in magma chambers most probably located at mantle depths (25.6 ± 5.5 km below sea level). This was followed by a shallower (< 1.5 km below sea level) and shorter (≈ 50 days) magma stagnation before the eruption. 2014 magmas have more unradiogenic Sr and more radiogenic Nd compositions than those of the previous 1951 and 1995 eruptions, which generally have less radiogenic Pb ratios. These isotopic differences - coming from quasi-coeval materials erupted almost in the same place - are remarkable and reflect the small-scale heterogeneity of the underlying mantle source. Moreover, they reflect the limited isotopic averaging of the source composition during partial melting events as well as the inefficient homogenization within the plumbing system when on route to the surface. The lid effect of an old and thick lithosphere is considered of utmost importance to the preservation of a significant part of source heterogeneity by erupted magmas. The decrease in the contribution of an enriched component to the Fogo magmas in the 2014 eruption marks a change on the volcano short-term evolution that was characterized by a progressive increase of the importance of such a component. Nb/U ratios of the 2014 lavas are similar, within 2σ, to the mean value of OIB, but significantly lower than those reported for the 1995 and 1951 eruptions. This is considered to reflect the lack of significant mixing of the 2014 magmas with lithospheric melts, as opposed to what is here hypothesised for the two previous eruptions.

Influence of Idealized Heterogeneity on Wet and Dry Planetary Boundary Layers Coupled to the Land Surface. 2; Phase-Averages

NASA Technical Reports Server (NTRS)

Houser, Paul (Technical Monitor); Patton, Edward G.; Sullivan, Peter P.; Moeng, Chin-Hoh

2003-01-01

We examine the influence of surface heterogeneity on boundary layers using a large-eddy simulation coupled to a land-surface model. Heterogeneity, imposed in strips varying from 2-30 km (1 less than lambda/z(sub i) less than 18), is found to dramatically alter the structure of the free convective boundary layer by inducing significant organized circulations. A conditional sampling technique, based on the scale of the surface heterogeneity (phase averaging), is used to identify and quantify the organized surface fluxes and motions in the atmospheric boundary layer. The impact of the organized motions on turbulent transport depends critically on the scale of the heterogeneity lambda, the boundary layer height zi and the initial moisture state of the boundary layer. Dynamical and scalar fields respond differently as the scale of the heterogeneity varies. Surface heterogeneity of scale 4 less than lamba/z(sub i) less than 9 induces the strongest organized flow fields (up, wp) while heterogeneity with smaller or larger lambda/z(sub i) induces little organized motion. However, the organized components of the scalar fields (virtual potential temperature and mixing ratio) grow continuously in magnitude and horizontal scale, as lambda/z(sub i) increases. For some cases, the organized motions can contribute nearly 100% of the total vertical moisture flux. Patch-induced fluxes are shown to dramatically impact point measurements that assume the time-average vertical velocity to be zero. The magnitude and sign of this impact depends on the location of the measurement within the region of heterogeneity.

Sea Spray Aerosol Structure and Composition Using Cryogenic Transmission Electron Microscopy

PubMed Central

2016-01-01

The composition and surface properties of atmospheric aerosol particles largely control their impact on climate by affecting their ability to uptake water, react heterogeneously, and nucleate ice in clouds. However, in the vacuum of a conventional electron microscope, the native surface and internal structure often undergo physicochemical rearrangement resulting in surfaces that are quite different from their atmospheric configurations. Herein, we report the development of cryogenic transmission electron microscopy where laboratory generated sea spray aerosol particles are flash frozen in their native state with iterative and controlled thermal and/or pressure exposures and then probed by electron microscopy. This unique approach allows for the detection of not only mixed salts, but also soft materials including whole hydrated bacteria, diatoms, virus particles, marine vesicles, as well as gel networks within hydrated salt droplets—all of which will have distinct biological, chemical, and physical processes. We anticipate this method will open up a new avenue of analysis for aerosol particles, not only for ocean-derived aerosols, but for those produced from other sources where there is interest in the transfer of organic or biological species from the biosphere to the atmosphere. PMID:26878061

Light changes the atmospheric reactivity of soot

PubMed Central

Monge, Maria Eugenia; D’Anna, Barbara; Mazri, Linda; Giroir-Fendler, Anne; Ammann, Markus; Donaldson, D. J.; George, Christian

2010-01-01

Soot particles produced by incomplete combustion processes are one of the major components of urban air pollution. Chemistry at their surfaces lead to the heterogeneous conversion of several key trace gases; for example NO2 interacts with soot and is converted into HONO, which rapidly photodissociates to form OH in the troposphere. In the dark, soot surfaces are rapidly deactivated under atmospheric conditions, leading to the current understanding that soot chemistry affects tropospheric chemical composition only in a minor way. We demonstrate here that the conversion of NO2 to HONO on soot particles is drastically enhanced in the presence of artificial solar radiation, and leads to persistent reactivity over long periods. Soot photochemistry may therefore be a key player in urban air pollution. PMID:20080580

Assessing the heterogeneity level in lipid nanoparticles for siRNA delivery: size-based separation, compositional heterogeneity, and impact on bioperformance.

PubMed

Zhang, Jingtao; Pei, Yi; Zhang, Hangchun; Wang, Lei; Arrington, Leticia; Zhang, Ye; Glass, Angela; Leone, Anthony M

2013-01-07

A primary consideration when developing lipid nanoparticle (LNP) based small interfering RNA (siRNA) therapeutics is formulation polydispersity or heterogeneity. The level of heterogeneity of physicochemical properties within a pharmaceutical batch could greatly affect the bioperformance, quality, and ability of a manufacturer to consistently control and reproduce the formulations. This article studied the heterogeneity in the size, composition, and in vitro performance of siRNA containing LNPs, by conducting preparative scale fractionation using a sephacryl S-1000 based size-exclusion chromatography (SEC) method. Eight LNPs with size in the range of 60-190 nm were first evaluated by the SEC method for size polydispersity characterization, and it was found that LNPs in the range of 60-150 nm could be well-resolved. Two LNPs (LNP A and LNP B) with similar bulk properties were fractionated, and fractions were studied in-depth for potential presence of polydispersity in size, composition, and in vitro silencing, as well as cytotoxicity. LNP A was deemed to be monodisperse following results of a semipreparative SEC fractionation that showed similar size, chemical composition, in vitro silencing activity, and cytotoxicity across the fractions. Therefore, LNP A represents a relatively homogeneous formulation and offers less of a challenge in its pharmaceutical development. In contrast, LNP B fractions were shown to be significantly more polydisperse in size distribution. Interestingly, LNP B SEC fractions also exhibited profound compositional variations (e.g., 5 fold difference in N/P ratio and 3 fold difference in lipid composition) along with up to 40 fold differences in the in vitro silencing activity. The impact of LNP size and formulation composition on in vitro performance is also discussed. The present results demonstrate the complexity and potential for presence of heterogeneity in LNP-based siRNA drug products. This underscores the need for tools that yield a detailed characterization of LNP formulations. This capability in tandem with the pursuit of improved formulation and process design can lead to more facile development of LNP-based siRNA pharmaceuticals of higher quality.

Basic surface-active properties in the homologous series of β-alkyl (C12H25/C18H37) polyethyleneoxy (n = 0-20) propionamides

PubMed Central

2013-01-01

Background Heterogeneous β-Alkyl (C12H25/C18H37) polyethyleneoxy (n = 0-20) propionamides [R(EO)nPD] represent new “hybrid” nonionic-ionic colloidal structures in the field of surface-active products (technical products). These “niche” compounds have three structural and compositional characteristics that also define their basic colloidal properties: mixture of R and PEO chain homologues; specific conformations due to the PEO chains; and the presence of side products from the addition of higher alcohols, polyethyleneglycols and traces of water to acrylamide. The proposed major objective of this paper is the basic informative colloidal characterization (functional classification, HLB balance, surface tension, critical micelle concentration) in direct correlation with the structural changes in the homologous series of LM(EO)nPD and CS(EO)nPD. The structures were obtained either indirectly by cyanoethylation followed by partial acid hydrolysis of the corresponding β-propionitriles, or directly by the nucleophilic addition under alkaline catalysis of linear higher alcohols C12H25/C14H29 (7/3) (LM) and C16H33/C18H37 (CS) as such and heterogeneous polyethoxylated (n = 3-20) to acrylamide monomer, through an adapted classic reaction scheme. Results In the series of basic colloidal characteristics investigated the structure-surface activity dependence is confirmed. Their indicative character for R(EO)nPD is based on the assumption that the structures studied are not unitary (heterogeneous) because: a) the hydrophobic chains C12H25/C18H37 have been grouped in two variants, C12H25/C14H29 (LM); C16H33/C18H37 (CS), each with an internal mass ratio of 7/3; b) the hydrophilic polyoxyethylene chains (n = 3-20) have polydisperse character; the meaning and value the oligomerization degree, n, is that of weighted average. In these conditions the surface tension increases proportionally with the oligomerization degree of the polyoxyethylene chain, while the critical micelle concentration decreases in the same homologous series as well as with the increase of the hydrophobic chain in the C12H25 to C18H37 series. A mechanism of micellization is proposed, consistent with the experimental data recorded and the hypotheses known from the consulted literature. Conclusions The idea of the obtaining and basic colloidal characterization of heterogeneous R(EO)nPD is justified. The knowledge and constructive approach of the heterogeneous character confirm the basic surface-active potential of R(EO)nPD, the structure-colloidal characteristics dependence and justifies further, more extensive research. PMID:23406530

Plant succession on gopher mounds in Western Cascade meadows: consequences for species diversity and heterogeneity

Treesearch

Chad C. Jones; Charles B. Halpern; Jessica Niederer

2008-01-01

Pocket gophers have the potential to alter the dynamics of grasslands by creating mounds that bury existing vegetation and locally reset succession. Gopher mounds may provide safe sites for less competitive species, potentially increasing both species diversity and vegetation heterogeneity (spatial variation in species composition). We compared species composition,...

Surface heterogeneity impacts on boundary layer dynamics via energy balance partitioning

USDA-ARS?s Scientific Manuscript database

The role of land-atmosphere interactions under heterogeneous surface conditions is investigated in order to identify mechanisms responsible for altering surface heat and moisture fluxes. Twelve coupled land surface – large eddy simulation scenarios with four different length scales of surface variab...

Vacancy-mediated fcc/bcc phase separation in Fe 1-xNi x ultrathin films

DOE PAGES

Mentes, T. O.; Stojic, N.; Vescovo, E.; ...

2016-08-01

The phase separation occurring in Fe-Ni thin lms near the Invar composition is studied by using high resolution spectromicroscopy techniques and density functional theory calculations. Annealed at temperatures around 300 C, Fe 0.70Ni 0.30 lms on W(110) break into micron-sized bcc and fcc domains with compositions in agreement with the bulk Fe-Ni phase diagram. Ni is found to be the di using species in forming the chemical heterogeneity. The experimentally-determined energy barrier of 1.59 0.09 eV is identi ed as the vacancy formation energy via density functional theory calculations. Thus, the principal role of the surface in the phase separationmore » process is attributed to vacancy creation without interstitials.« less

Out on a limb: Thermal microenvironments in the tropical forest canopy and their relevance to ants.

PubMed

Stark, Alyssa Y; Adams, Benjamin J; Fredley, Jennifer L; Yanoviak, Stephen P

2017-10-01

Small, cursorial ectotherms like ants often are immersed in the superheated air layers that develop millimeters above exposed, insolated surfaces (i.e., the thermal boundary layer). We quantified the thermal microenvironments around tree branches in the tropical rainforest canopy, and explored the effects of substrate color on the internal body temperature and species composition of arboreal ants. Branch temperatures during the day (09:00-16:00) were hottest (often > 50°C) and most variable on the upper surface, while the lowest and least variable temperatures occurred on the underside. Temperatures on black substrates declined with increasing distance above the surface in both the field and the laboratory. By contrast, a micro-scale temperature inversion occurred above white substrates. Wind events (ca. 2ms -1 ) eliminated these patterns. Internal temperatures of bodies of Cephalotes atratus workers experimentally heated in the laboratory were 6°C warmer on white vs. black substrates, and 6°C cooler than ambient in windy conditions. The composition of ant species foraging at baits differed between black-painted and unpainted tree branches, with a tendency for smaller ants to avoid the significantly hotter black surfaces. Collectively, these outcomes show that ants traversing canopy branches experience very heterogeneous thermal microenvironments that are partly influenced in predictable ways by branch surface coloration and breezy conditions. Copyright © 2017 Elsevier Ltd. All rights reserved.

Harnessing Big Data to Represent 30-meter Spatial Heterogeneity in Earth System Models

NASA Astrophysics Data System (ADS)

Chaney, N.; Shevliakova, E.; Malyshev, S.; Van Huijgevoort, M.; Milly, C.; Sulman, B. N.

2016-12-01

Terrestrial land surface processes play a critical role in the Earth system; they have a profound impact on the global climate, food and energy production, freshwater resources, and biodiversity. One of the most fascinating yet challenging aspects of characterizing terrestrial ecosystems is their field-scale (˜30 m) spatial heterogeneity. It has been observed repeatedly that the water, energy, and biogeochemical cycles at multiple temporal and spatial scales have deep ties to an ecosystem's spatial structure. Current Earth system models largely disregard this important relationship leading to an inadequate representation of ecosystem dynamics. In this presentation, we will show how existing global environmental datasets can be harnessed to explicitly represent field-scale spatial heterogeneity in Earth system models. For each macroscale grid cell, these environmental data are clustered according to their field-scale soil and topographic attributes to define unique sub-grid tiles. The state-of-the-art Geophysical Fluid Dynamics Laboratory (GFDL) land model is then used to simulate these tiles and their spatial interactions via the exchange of water, energy, and nutrients along explicit topographic gradients. Using historical simulations over the contiguous United States, we will show how a robust representation of field-scale spatial heterogeneity impacts modeled ecosystem dynamics including the water, energy, and biogeochemical cycles as well as vegetation composition and distribution.

a Study on the Physical and Chemical Properties of Stratospheric Aerosols.

NASA Astrophysics Data System (ADS)

Tabazadeh, Azadeh

The physical and chemical properties of stratospheric aerosols under background and perturbed conditions are discussed. First, a multi-component aerosol physical chemistry model was developed to study the composition and reactivity of stratospheric aerosols. The compositions are predicted from an equilibrium assumption between the condensed-and gas-phases, and they are calculated as a function of ambient temperature, relative humidity, and the total mass of nitric acid and sulfuric acid present per unit volume of air. The water and solute activity parameters in the aerosol model are derived from various laboratory sources, and the set of equilibrium equations are solved using a unique numerical scheme. The aerosol model is applied to study the formation of nitric acid-containing aerosols in the stratosphere. Also, the equilibrium compositions are used to estimate the extent of aqueous phase processing of chlorine species in the aerosol solutions. This processing can contribute to the depletion of the stratospheric ozone layer, especially after major volcanic eruptions where sulfate aerosols are more abundant. Second, a surface chemistry model was constructed that includes Langmuir trace-gas adsorption and desorption, Brunauer, Emmett and Teller adsorption of water vapor, surface poisoning, solvation and diffusion of molecules on the surface, chemical activation and reaction of adsorbates, and product desorption or reaction. This model is used to study the effects of relative humidity and other physical parameters on the efficiency of heterogeneous chemical processes which occur on the surfaces of solid polar stratospheric clouds. These heterogeneous chemical processes are responsible for the formation of the "ozone hole", can contribute to global ozone depletion, and may have tropospheric significance. Finally, a fluid dynamics and thermodynamics model of volcanic eruption columns was used to develop a scheme for predicting the extent of HCl removal from volcanic plumes. If most of the volcanically emitted chlorine stays in the upper atmosphere, the chlorine concentration in the stratosphere could increase by a factor of 2 to 10, leading to severe global ozone depletions. However, model results indicate that HCl is efficiently scavenged from volcanic plumes by supercooled water droplets, which form as the plume lofts and cools. HCl dissolution in these drops, followed by rainout, prevents substantial injections of chlorine into the stratosphere.

Influence of surface heterogeneity in electroosmotic flows—Implications in chromatography, fluid mixing, and chemical reactions in microdevices

NASA Astrophysics Data System (ADS)

Adrover, Alessandra; Giona, Massimiliano; Pagnanelli, Francesca; Toro, Luigi

2007-04-01

We analyze the influence of surface heterogeneity, inducing a random ζ-potential at the walls in electroosmotic incompressible flows. Specifically, we focus on how surface heterogeneity modifies the physico-chemical processes (transport, chemical reaction, mixing) occurring in microchannel and microreactors. While the macroscopic short-time features associated with solute transport (e.g. chromatographic patterns) do not depend significantly on ζ-potential heterogeneity, spatial randomness in the surface ζ-potential modifies the spectral properties of the advection-diffusion operator, determining different long-term properties of transport/reaction phenomena compared to the homogeneous case. Examples of physical relevance (chromatography, infinitely fast reactions) are addressed.

Stepping towards new parameterizations for non-canonical atmospheric surface-layer conditions

NASA Astrophysics Data System (ADS)

Calaf, M.; Margairaz, F.; Pardyjak, E.

2017-12-01

Representing land-atmosphere exchange processes as a lower boundary condition remains a challenge. This is partially a result of the fact that land-surface heterogeneity exists at all spatial scales and its variability does not "average" out with decreasing scales. Such variability need not rapidly blend away from the boundary thereby impacting the near-surface region of the atmosphere. Traditionally, momentum and energy fluxes linking the land surface to the flow in NWP models have been parameterized using atmospheric surface layer (ASL) similarity theory. There is ample evidence that such representation is acceptable for stationary and planar-homogeneous flows in the absence of subsidence. However, heterogeneity remains a ubiquitous feature eliciting appreciable deviations when using ASL similarity theory, especially in scalars such moisture and air temperature whose blending is less efficient when compared to momentum. The focus of this project is to quantify the effect of surface thermal heterogeneity with scales Ο(1/10) the height of the atmospheric boundary layer and characterized by uniform roughness. Such near-canonical cases describe inhomogeneous scalar transport in an otherwise planar homogeneous flow when thermal stratification is weak or absent. In this work we present a large-eddy simulation study that characterizes the effect of surface thermal heterogeneities on the atmospheric flow using the concept of dispersive fluxes. Results illustrate a regime in which the flow is mostly driven by the surface thermal heterogeneities, in which the contribution of the dispersive fluxes can account for up to 40% of the total sensible heat flux. Results also illustrate an alternative regime in which the effect of the surface thermal heterogeneities is quickly blended, and the dispersive fluxes provide instead a quantification of the flow spatial heterogeneities produced by coherent turbulent structures result of the surface shear stress. A threshold flow-dynamics parameter is introduced to differentiate dispersive fluxes driven by surface thermal heterogeneities from those induced by surface shear. We believe that results from this research are a first step in developing new parameterizations appropriate for non-canonical ASL conditions.

Field Observation of Heterogeneous Formation of Dicarboxylic acids, Keto-carboxylic acids, α-Dicarbonyls and Nitrate in Xi'an, China during Asian dust storm periods

NASA Astrophysics Data System (ADS)

Wang, G.; Wang, J.; Ren, Y.; Li, J.

2015-12-01

To understand the formation mechanism of secondary organic aerosols (SOA) on dust surfaces, this study investigated the concentrations and compositions of dicarboxylic acids (C2-C11), keto-carboxylic acids (C3-C7), α-dicarbonyls and inorganic ions in size-segregated aerosols (9-stages) collected in Xi'an, China during the nondust storm and dust storm periods of 2009 and 2011. During the events the ambient particulate dicarboxylic acids were 932-2240 ng m-3, which are comparable and even higher than those in nondust periods. Molecular compositions of the above SOA are similar to those in nondust periods with oxalic acid being the leading species. In the presence of the dust storms, all the above mentioned SOA species in Xi'an were predominantly enriched on the coarse particles (>2.1μm), and oxalic acid well correlated with NO3- (R2=0.72, p<0.001) rather than SO42-.This phenomenon differs greatly from the SOA in any other nondust period that is characterized by an enrichment of oxalic acid in fine particles and a strong correlation of oxalic acid with SO42-. Our results further demonstrate that NO3- in the dust periods in Xi'an was mostly derived from secondary oxidation, whereas SO42- during the events was largely derived from surface soil of Gobi deserts. We propose a formation pathway to explain these observations, in which nitric acid and/or nitrogen oxides react with dust to produce Ca(NO3)2 and form a liquid phase on the surface of dust aerosols via water vapor-absorption of Ca(NO3)2, followed by a partitioning of the gas-phase water-soluble organic precursors (e.g.,glyoxal and methylglyoxal) into the aqueous-phase and a subsequent oxidation into oxalic acid. To the best of our knowledge, we found for the first time the enrichment of glyoxal and methylglyoxal on dust surface. Our data suggest an important role of nitrate in the heterogeneous formation process of SOA on the surface of Asian dust.

Organic pi-stacking Semiconducting Material: Design, Synthesis and the Analysis of Structure and Properties

NASA Astrophysics Data System (ADS)

Wilkinson, Taylor Marie

Oil shales are naturally occurring heterogeneous composites with micro-scale, micro-structural variations. They may be found throughout the world, with large deposits located in the United States; shales are composed of organic matter known as kerogen, clays, calcite, quartz, and other minerals. Typically their microstructure consists of a composite network where the organic matter is housed in open and closed pores between different mineral phases that range in size from sub-micron to several microns. Currently, it is unknown how the micro-scale heterogeneity of the shale will impact hydraulic fracture, which is the key extraction technique used for these materials. In this thesis, high-resolution topographic and modulus maps were collected from oil shales with the use of new nanoindentation techniques in order to characterize the micro-scale, micro-structural variations that are typical for these materials. Dynamic modulus mapping allows for substantially higher spatial resolution of properties across grains and intragranular regions of kerogen than has previously been produced with standard quasistatic indentation methods. For accurate scanning, surface variations were minimized to maintain uniform contact of the tip and appropriate quasi-static and dynamic forces were used to maintain displacement amplitudes that avoid plastic deformation of the sample. Sample preparation to minimize surface roughness was completed with the use of focused ion beam milling, however, some variation was still noted. Due to the large changes in modulus values between the constituents of the shale, there were variations in the recorded displacement amplitude values as well. In order to distinguish biased data due to surface topography or a lack of displacement amplitude, filtering techniques were developed, optimization and implemented. Variations in surface topography, which resulted in the indenter tip not being able to accurately resolve surface features, and inadequate displacement amplitude values that prohibit differentiation between material changes and the noise floor of the machine, were removed. These filters resulted in a more valid interpretation of the micro-scale, micro-structural features and arrangement, as well as the mechanical properties, that are common to oil shales.

Mercury compositional units inferred by MDIS. A comparison with the geology in support to the BepiColombo mission

NASA Astrophysics Data System (ADS)

Zambon, Francesca; Carli, Cristian; Galluzzi, Valentina; Capaccioni, Fabrizio; Filacchione, Gianrico; Giacomini, Lorenza; Massirioni, Matteo; Palumbo, Pasquale

2016-04-01

Mercury has been explored by two spatial missions. Mariner 10 acquired 45% of the surface during three Hermean flybys in 1974, giving a first close view of the planet. The recent MESSENGER mission globally mapped the planet and contributed to understand many unsolved issues about Mercury (Solomon et al., 2007). Nevertheless, even after MESSENGER, Mercury surface composition remains still unclear, and the correlation between morphology and compositional heterogeneity is not yet well understood. Thanks to the Mercury Dual Imaging System (MDIS), onboard MESSENGER, a global coverage of Mercury surface with variable spatial resolution has been done. MDIS is equipped with a Narrow Angle Camera (NAC), dedicated to the high-resolution study of the surface morphology and a Wide Angle Camera (WAC) with 12 filters useful to investigate the surface composition (Hawkins et al., 2007). Several works were focused on the different terrains present on Mercury, in particular, Denevi et al. (2013) observes that ~27% of Hermean surface is covered by volcanic origin smooth plains. These plains show differences in composition associated to spectral slope variation. High-reflectance red plains (HRP), with spectral slope greater than the average and low-reflectance blue plains (LBP), with spectral slope lesser than the average has been identified. This spectral variations could be correlated with different chemical composition. The X-Ray Spectrometer (XRS) data show that HRP-type areas are associated with a low-Fe basalt-like composition, while the LBP are also Fe poor but are rich in Mg/Si and Ca/Si and with lower Al/Si and are interpreted as more ultramafic (Nittler et al., 2011; Weider et al., 2012; Denevi at al., 2013, Weider et al., 2014). In these work we produce high resolution multicolor mosaic to found a possible link between morphology and composition. The spectral properties have been used to define the principal units of Mercury's surface or to characterize other globally distributed distinct spectral units. Therefore, integrating the spectral variability to a well defined morpho-stratigraphic (photo-interpreted) map will permit to improve the geologic map itself, defining sub-units, and associating spectral properties to analogue deposits. We are working to produce quadrangles color mosaics and high resolution color mosaics of smaller areas to define color products (common planetary geologic map) and obtain an "advanced" geologic map. The mapping process permits integration of different geological surface information to better understand the planet crust formation and evolution. Merging data from different instruments provides additional information about lithological composition, contributing to the construction of a more complete geological map (e.g., Giacomini et al., 2012). These work has been done in support of the BepiColombo Mission, which has an innovative Spectrometer and Imagers Integrated Observatory SYStem (SIMBIO-SYS). SIMBIO-SYS is composed by three instruments, the visible-near-infrared imaging spectrometer (VIHI), the high-resolution imager (HRIC) and the stereo imaging system (STC) which will be albe to improve the knowledge of Mercury surface form the geological and compositional point of view. This research was supported by the Italian Space Agency (ASI) within the SIMBIOSYS project (ASI-INAF agreement no. I/022/10/0)

Coarse Scale In Situ Albedo Observations over Heterogeneous Land Surfaces and Validation Strategy

NASA Astrophysics Data System (ADS)

Xiao, Q.; Wu, X.; Wen, J.; BAI, J., Sr.

2017-12-01

To evaluate and improve the quality of coarse-pixel land surface albedo products, validation with ground measurements of albedo is crucial over the spatially and temporally heterogeneous land surface. The performance of albedo validation depends on the quality of ground-based albedo measurements at a corresponding coarse-pixel scale, which can be conceptualized as the "truth" value of albedo at coarse-pixel scale. The wireless sensor network (WSN) technology provides access to continuously observe on the large pixel scale. Taking the albedo products as an example, this paper was dedicated to the validation of coarse-scale albedo products over heterogeneous surfaces based on the WSN observed data, which is aiming at narrowing down the uncertainty of results caused by the spatial scaling mismatch between satellite and ground measurements over heterogeneous surfaces. The reference value of albedo at coarse-pixel scale can be obtained through an upscaling transform function based on all of the observations for that pixel. We will devote to further improve and develop new method that that are better able to account for the spatio-temporal characteristic of surface albedo in the future. Additionally, how to use the widely distributed single site measurements over the heterogeneous surfaces is also a question to be answered. Keywords: Remote sensing; Albedo; Validation; Wireless sensor network (WSN); Upscaling; Heterogeneous land surface; Albedo truth at coarse-pixel scale

Composition of Rheasilvia Basin on Asteroid Vesta

NASA Technical Reports Server (NTRS)

Ammannito, Eleonora; DeSanctis, Maria Christina; Capaccioni, Fabrizio; Capria, Maria Teresa; Combe, Jean Philippe; Frigeri, Alessandro; Jaumann, Ralf; Longobardo, Andrea; Marchi, Somone; McCord, Thomas B.;

Compression-induced crystallization of amorphous indomethacin in tablets: characterization of spatial heterogeneity by two-dimensional X-ray diffractometry.

PubMed

Thakral, Naveen K; Mohapatra, Sarat; Stephenson, Gregory A; Suryanarayanan, Raj

2015-01-05

Tablets of amorphous indomethacin were compressed at 10, 25, 50, or 100 MPa using either an unlubricated or a lubricated die and stored individually at 35 °C in sealed Mylar pouches. At selected time points, tablets were analyzed by two-dimensional X-ray diffractometry (2D-XRD), which enabled us to profile the extent of drug crystallization in tablets, in both the radial and axial directions. To evaluate the role of lubricant, magnesium stearate was used as "internal" and/or "external" lubricant. Indomethacin crystallization propensity increased as a function of compression pressure, with 100 MPa pressure causing crystallization immediately after compression (detected using synchrotron radiation). However, the drug crystallization was not uniform throughout the tablets. In unlubricated systems, pronounced crystallization at the radial surface could be attributed to die wall friction. The tablet core remained substantially amorphous, irrespective of the compression pressure. Lubrication of the die wall with magnesium stearate, as external lubricant, dramatically decreased drug crystallization at the radial surface. The spatial heterogeneity in drug crystallization, as a function of formulation composition and compression pressure, was systematically investigated. When formulating amorphous systems as tablets, the potential for compression induced crystallization warrants careful consideration. Very low levels of crystallization on the tablet surface, while profoundly affecting product performance (decrease in dissolution rate), may not be readily detected by conventional analytical techniques. Early detection of crystallization could be pivotal in the successful design of a dosage form where, in order to obtain the desired bioavailability, the drug may be in a high energy state. Specialized X-ray diffractometric techniques (2D; use of high intensity synchrotron radiation) enabled detection of very low levels of drug crystallization and revealed the heterogeneity in crystallization within the tablet.

Heterogeneous nucleation on rough surfaces: Generalized Gibbs' approach.

PubMed

Abyzov, Alexander S; Schmelzer, Jürn W P; Davydov, Leonid N

2017-12-07

Heterogeneous nucleation (condensation) of liquid droplets from vapor (gas) on a defective solid surface is considered. The vapor is described by the van der Waals equation of state. The dependence of nucleating droplet parameters on droplet size is accounted for within the generalized Gibbs approach. As a surface defect, a conic void is taken. This choice allows us to simplify the analysis and at the same time to follow the main aspects of the influence of the surface roughness on the nucleation process. Similar to condensation on ideal planar surfaces, the contact angle and catalytic factor for heterogeneous nucleation on a rough surface depend on the degree of vapor overcooling. In the case of droplet formation on a hydrophilic surface of a conic void, the nucleation rate considerably increases in comparison with the condensation on a planar interface. In fact, the presence of a defect on the hydrophilic surface leads to a considerable shift of the spinodal towards lower supersaturation in comparison with heterogeneous nucleation on a planar interface. With the decrease in the void cone angle, the heterogeneous spinodal approaches the binodal, and the region of metastability is diminished at the expense of the instability region.

Exploiting the flexibility and the polarization of ferroelectric perovskite surfaces to achieve efficient photochemistry and enantiospecificity

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

Rappe, Andrew

This research project explored the catalytic properties of complex surfaces of functional materials. The PI used first-principles density functional theory (DFT) calculations to explore a tightly integrated set of properties. The physical properties of complex functional materials that influence surface chemistry were explored, including bulk and surface electric dipoles, and surface conductivity. The energetic, compositional, electronic, and chemical properties of the surfaces of these materials were explored in detail, and connections between material properties and chemical reactivity were established. This project led to 28 publications, including Nat. Comm., JACS, 3 PRL, 7 PRB, 2 ACS Nano, 2 Nano Lett., 4more » JPCL, 2 JCP, Chem. Mater., ACS Appl. Mater. Interfaces, Phys. Rev. Appl., and a U.S. Patent on surface catalysts. The key accomplishments in this project involved work in six coordinated areas: pioneering ways to control bulk dipoles in order to dynamically affect catalysis, exploring novel ways of bringing charge to the surface for redox catalysis, nonstoichiometric surfaces offering new sites for heterogeneous catalysis, illustrating how surface catalysis responds to applied pressure, catalytic growth of carbon-based materials, and new computational methods allowing more accurate exploration of molecule-surface interactions« less

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

NASA Astrophysics Data System (ADS)

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

2015-04-01

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

Direct surface analysis coupled to high-resolution mass spectrometry reveals heterogeneous composition of the cuticle of Hibiscus trionum petals.

PubMed

Giorio, Chiara; Moyroud, Edwige; Glover, Beverley J; Skelton, Paul C; Kalberer, Markus

2015-10-06

Plant cuticle, which is the outermost layer covering the aerial parts of all plants including petals and leaves, can present a wide range of patterns that, combined with cell shape, can generate unique physical, mechanical, or optical properties. For example, arrays of regularly spaced nanoridges have been found on the dark (anthocyanin-rich) portion at the base of the petals of Hibiscus trionum. Those ridges act as a diffraction grating, producing an iridescent effect. Because the surface of the distal white region of the petals is smooth and noniridescent, a selective chemical characterization of the surface of the petals on different portions (i.e., ridged vs smooth) is needed to understand whether distinct cuticular patterns correlate with distinct chemical compositions of the cuticle. In the present study, a rapid screening method has been developed for the direct surface analysis of Hibiscus trionum petals using liquid extraction surface analysis (LESA) coupled with high-resolution mass spectrometry. The optimized method was used to characterize a wide range of plant metabolites and cuticle monomers on the upper (adaxial) surface of the petals on both the white/smooth and anthocyanic/ridged regions, and on the lower (abaxial) surface, which is entirely smooth. The main components detected on the surface of the petals are low-molecular-weight organic acids, sugars, and flavonoids. The ridged portion on the upper surface of the petal is enriched in long-chain fatty acids, which are constituents of the wax fraction of the cuticle. These compounds were not detected on the white/smooth region of the upper petal surface or on the smooth lower surface.

Composition of Junior Research Groups and Phd Completion Rate: Disciplinary Differences and Policy Implications

ERIC Educational Resources Information Center

Pull, Kerstin; Pferdmenges, Birgit; Backes-Gellner, Uschi

2016-01-01

This paper explores the link between the composition and the performance of junior research groups. The authors argue that the heterogeneity-performance link depends on the type of heterogeneity (cultural vs. study field) and on the disciplinary area. The authors test their hypotheses on a data set of 45 junior research groups and find a U-shaped…

Coupled factors influencing detachment of nano- and micro-sized particles from primary minima.

PubMed

Shen, Chongyang; Lazouskaya, Volha; Jin, Yan; Li, Baoguo; Ma, Zhiqiang; Zheng, Wenjuan; Huang, Yuanfang

2012-06-01

This study examined the detachments of nano- and micro-sized colloids from primary minima in the presence of cation exchange by laboratory column experiments. Colloids were initially deposited in columns packed with glass beads at 0.2 M CaCl(2) in the primary minima of Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energies. Then, the columns were flushed with NaCl solutions with different ionic strengths (i.e., 0.001, 0.01, 0.1 and 0.2 M). Detachments were observed at all ionic strengths and were particularly significant for the nanoparticle. The detachments increased with increasing electrolyte concentration for the nanoparticle whereas increased from 0.001 M to 0.01 M and decreased with further increasing electrolyte concentration for the micro-sized colloid. The observations were attributed to coupled influence of cation exchange, short-range repulsion, surface roughness, surface charge heterogeneity, and deposition in the secondary minima. The detachments of colloids from primary minima challenge the common belief that colloid interaction in primary minimum is irreversible and resistant to disturbance in solution ionic strength and composition. Although the significance of surface roughness, surface charge heterogeneity, and secondary minima on colloid deposition has been widely recognized, our study implies that they also play important roles in colloid detachment. Whereas colloid detachment is frequently associated with decrease of ionic strength, our results show that increase of ionic strength can also cause detachment due to influence of cation exchange. Copyright © 2012 Elsevier B.V. All rights reserved.

A method for rapid quantitative assessment of biofilms with biomolecular staining and image analysis.

PubMed

Larimer, Curtis; Winder, Eric; Jeters, Robert; Prowant, Matthew; Nettleship, Ian; Addleman, Raymond Shane; Bonheyo, George T

2016-01-01

The accumulation of bacteria in surface-attached biofilms can be detrimental to human health, dental hygiene, and many industrial processes. Natural biofilms are soft and often transparent, and they have heterogeneous biological composition and structure over micro- and macroscales. As a result, it is challenging to quantify the spatial distribution and overall intensity of biofilms. In this work, a new method was developed to enhance the visibility and quantification of bacterial biofilms. First, broad-spectrum biomolecular staining was used to enhance the visibility of the cells, nucleic acids, and proteins that make up biofilms. Then, an image analysis algorithm was developed to objectively and quantitatively measure biofilm accumulation from digital photographs and results were compared to independent measurements of cell density. This new method was used to quantify the growth intensity of Pseudomonas putida biofilms as they grew over time. This method is simple and fast, and can quantify biofilm growth over a large area with approximately the same precision as the more laborious cell counting method. Stained and processed images facilitate assessment of spatial heterogeneity of a biofilm across a surface. This new approach to biofilm analysis could be applied in studies of natural, industrial, and environmental biofilms.

Earthquake prediction using extinct monogenetic volcanoes: A possible new research strategy

NASA Astrophysics Data System (ADS)

Szakács, Alexandru

2011-04-01

Volcanoes are extremely effective transmitters of matter, energy and information from the deep Earth towards its surface. Their capacities as information carriers are far to be fully exploited so far. Volcanic conduits can be viewed in general as rod-like or sheet-like vertical features with relatively homogenous composition and structure crosscutting geological structures of far more complexity and compositional heterogeneity. Information-carrying signals such as earthquake precursor signals originating deep below the Earth surface are transmitted with much less loss of information through homogenous vertically extended structures than through the horizontally segmented heterogeneous lithosphere or crust. Volcanic conduits can thus be viewed as upside-down "antennas" or waveguides which can be used as privileged pathways of any possible earthquake precursor signal. In particular, conduits of monogenetic volcanoes are promising transmitters of deep Earth information to be received and decoded at surface monitoring stations because the expected more homogenous nature of their rock-fill as compared to polygenetic volcanoes. Among monogenetic volcanoes those with dominantly effusive activity appear as the best candidates for privileged earthquake monitoring sites. In more details, effusive monogenetic volcanic conduits filled with rocks of primitive parental magma composition indicating direct ascent from sub-lithospheric magma-generating areas are the most suitable. Further selection criteria may include age of the volcanism considered and the presence of mantle xenoliths in surface volcanic products indicating direct and straightforward link between the deep lithospheric mantle and surface through the conduit. Innovative earthquake prediction research strategies can be based and developed on these grounds by considering conduits of selected extinct monogenetic volcanoes and deep trans-crustal fractures as privileged emplacement sites of seismic monitoring stations using an assemblage of physical, chemical and biological sensors devised to detect precursory signals. Earthquake prediction systems can be built up based on the concept of a signal emission-transmission-reception system, in which volcanic conduits and/or deep fractures play the role of the most effective signal transmission paths through the lithosphere. Unique "precursory fingerprints" of individual seismic structures are expected to be pointed out as an outcome of target-oriented strategic prediction research. Intelligent pattern-recognition systems are to be included for evaluation of the signal assemblages recorded by complex sensor arrays. Such strategies are expected however to be limited to intermediate-depth and deep seismic structures. Due to its particular features and geotectonic setting, the Vrancea seismic structure in Romania appears to be an excellent experimental target for prediction research.

Homogeneous and Heterogeneous (Fex, Cr1-x)(OH)3 Precipitation: Implications for Cr Sequestration

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

Dai, Chong; Zuo, Xiaobing; Cao, B

2016-02-16

The formation of (Fe, Cr)(OH)3 nanoparticles determines the fate of aqueous Cr in many aquatic environments. Using small angle X-ray scattering, precipitation rates of (Fe, Cr)(OH)3 nanoparticles in solution and on quartz were quantified from 0.1 mM Fe(III) solutions containing 0 – 0.25 mM Cr(III) at pH = 3.7 ± 0.2. Concentration ratio of aqueous Cr(III)/Fe(III) controlled the chemical composition (x) of (Fex, Cr1-x)(OH)3 precipitates, solutions’ supersaturation with respect to precipitates, and the surface charge of quartz. Therefore, aqueous Cr(III)/Fe(III) ratio affected homogeneous (in solution) and heterogeneous (on quartz) precipitation rates of (Fex, Cr1-x)(OH)3 through different mechanisms. The sequestration mechanismsmore » of Cr(III) in precipitates were also investigated. In solutions with high aqueous Cr(III)/Fe(III) ratios, surface enrichment of Cr(III) on the precipitates occurred, resulting in slower particle growth in solution. From solutions with 0 – 0.1 mM Cr(III), the particles on quartz grew from 2 to 4 nm within 1 h. Interestingly, from solution with 0.25 mM Cr(III), particles of two distinct sizes (2 and 6 nm) formed on quartz, and their sizes remained unchanged throughout the reaction. Our study provided new insights on homogeneous and heterogeneous precipitation of (Fex, Cr1-x)(OH)3 nanoparticles, which can help determine the fate of Cr in aquatic environments.« less

Effects of the duration and inorganic nitrogen composition of a nutrient-rich patch on soil exploration by the roots of Lolium perenne in a heterogeneous environment.

PubMed

Nakamura, Ryoji; Kachi, N; Suzuki, J-I

2010-05-01

We investigated the growth of and soil exploration by Lolium perenne under a heterogeneous environment before its roots reached a nutrient-rich patch. Temporal changes in the distribution of inorganic nitrogen, i.e., NO(3)(-)-N and NH(4)(+)-N, in the heterogeneous environment during the experimental period were also examined. The results showed that roots randomly explored soil, irrespective of the patchy distribution of inorganic nitrogen and differences in the chemical composition of inorganic nitrogen distribution between heterogeneous and homogeneous environments. We have also elucidated the potential effects of patch duration and inorganic nitrogen distribution on soil exploration by roots and thus on plant growth.

Interphase and particle dispersion correlations in polymer nanocomposites

NASA Astrophysics Data System (ADS)

Senses, Erkan

Particle dispersion in polymer matrices is a major parameter governing the mechanical performance of polymer nanocomposites. Controlling particle dispersion and understanding aging of composites under large shear and temperature variations determine the processing conditions and lifetime of composites which are very important for diverse applications in biomedicine, highly reinforced materials and more importantly for the polymer composites with adaptive mechanical responses. This thesis investigates the role of interphase layers between particles and polymer matrices in two bulk systems where particle dispersion is altered upon deformation in repulsive composites, and good-dispersion of particles is retained after multiple oscillatory shearing and aging cycles in attractive composites. We demonstrate that chain desorption and re-adsorption processes in attractive composites under shear can effectively enhance the bulk microscopic mechanical properties, and long chains of adsorbed layers lead to a denser entangled interphase layer. We further designed experiments where particles are physically adsorbed with bimodal lengths of homopolymer chains to underpin the entanglement effect in interphases. Bimodal adsorbed chains are shown to improve the interfacial strength and used to modulate the elastic properties of composites without changing the particle loading, dispersion state or polymer conformation. Finally, the role of dynamic asymmetry (different mobilities in polymer blends) and chemical heterogeneity in the interphase layer are explored in systems of poly(methyl methacrylate) adsorbed silica nanoparticles dispersed in poly(ethylene oxide) matrix. Such nanocomposites are shown to exhibit unique thermal-stiffening behavior at temperatures above glass transitions of both polymers. These interesting findings suggest that the mobility of the surface-bound polymer is essential for reinforcement in polymer nanocomposites, contrary to existing glassy layer theories for polymers on attractive particle surfaces. The shown thermally-induced stiffening behavior is reversible and makes this interfacial mechanism highly attractive in developing new active, remotely controllable engineered materials from non-responsive components.

The role of phonological alternation in speech production: evidence from Mandarin tone sandhi

PubMed Central

Politzer-Ahles, Stephen; Zhang, Jie

2014-01-01

We investigate the role of phonological alternation during speech production in Mandarin using implicit priming, a paradigm in which participants respond faster to words in sets that are phonologically homogeneous than in sets that are phonologically heterogeneous. We test whether priming is obtained when words in a set share the same tones at the underlying level but have different tones at the surface level-i.e., when the set includes a word that undergoes a phonological alternation which changes the tone. Sets that are heterogeneous at the surface level (in which the heterogeneity is due to a phonological operation) failed to elicit priming, as did sets that are heterogeneous at the underlying and surface levels (in which the heterogeneity is due to the lexical representations). This finding suggests that the phonological alternation was computed before the initiation of articulation, offering evidence that the progression from underlying phonological representations to articulatory execution may be mediated online by phonological input-to-output mapping. Furthermore, sets of words that are heterogeneous only at the surface level showed a different trend than sets of words that are heterogeneous at both levels, suggesting that both the surface and underlying levels of representation play a role during speech production. PMID:24967001

Heterogeneous nucleation of polymorphs on polymer surfaces: polymer-molecule interactions using a heterogeneous dielectric solvation model.

PubMed

Wahlberg, Nanna; Madsen, Anders Ø; Mikkelsen, Kurt V

2018-06-09

We have investigated the mechanism of the nucleation of acetaminophen on poly(methyl-methacrylate) and poly(vinyl-acetate) utilizing a combination of quantum mechanical computations and electrostatic models. We have used a heterogeneous dielectric solvation model to determine the stability of different orientations of acetaminophen on polymer surfaces. We find that for the nucleation of acetaminophen on the polymer surfaces in vacuum, the most stable orientation is a flat orientation. For the nucleation process in solution where acetaminophen and the polymer surface are surrounded by a solvent, we find that the heterogeneous dielectric solvation model predicts that a sideways orientation is the most stable orientation.

Effects of Fine-Scale Landscape Variability on Satellite-Derived Land Surface Temperature Products Over Sparse Vegetation Canopies

NASA Astrophysics Data System (ADS)

Powell, R. L.; Goulden, M.; Peterson, S.; Roberts, D. A.; Still, C. J.

2015-12-01

Temperature is a primary environmental control on biological systems and processes at a range of spatial and temporal scales, from controlling biochemical processes such as photosynthesis to influencing continental-scale species distribution. The Landsat satellite series provides a long record (since the mid-1980s) of relatively high spatial resolution thermal infrared (TIR) imagery, from which we derive land surface temperature (LST) grids. Here, we investigate fine spatial resolution factors that influence Landsat-derived LST over a spectrally and spatially heterogeneous landscape. We focus on paired sites (inside/outside a 1994 fire scar) within a pinyon-juniper scrubland in Southern California. The sites have nearly identical micro-meteorology and vegetation species composition, but distinctly different vegetation abundance and structure. The tower at the unburned site includes a number of in-situ imaging tools to quantify vegetation properties, including a thermal camera on a pan-tilt mount, allowing hourly characterization of landscape component temperatures (e.g., sunlit canopy, bare soil, leaf litter). We use these in-situ measurements to assess the impact of fine-scale landscape heterogeneity on estimates of LST, including sensitivity to (i) the relative abundance of component materials, (ii) directional effects due to solar and viewing geometry, (iii) duration of sunlit exposure for each compositional type, and (iv) air temperature. To scale these properties to Landsat spatial resolution (~100-m), we characterize the sub-pixel composition of landscape components (in addition to shade) by applying spectral mixture analysis (SMA) to the Landsat Operational Land Imager (OLI) spectral bands and test the sensitivity of the relationships established with the in-situ data at this coarser scale. The effects of vegetation abundance and cover height versus other controls on satellite-derived estimates of LST will be assessed by comparing estimates at the burned vs. unburned sites across multiple seasons (~30 dates).

Record of archaeal activity at the serpentinite-hosted Lost City Hydrothermal Field.

PubMed

Méhay, S; Früh-Green, G L; Lang, S Q; Bernasconi, S M; Brazelton, W J; Schrenk, M O; Schaeffer, P; Adam, P

2013-11-01

Samples of young, outer surfaces of brucite-carbonate deposits from the ultramafic-hosted Lost City hydrothermal field were analyzed for DNA and lipid biomarker distributions and for carbon and hydrogen stable isotope compositions of the lipids. Methane-cycling archaeal communities, notably the Lost City Methanosarcinales (LCMS) phylotype, are specifically addressed. Lost City is unlike all other hydrothermal systems known to date and is characterized by metal- and CO2 -poor, high pH fluids with high H2 and CH4 contents resulting from serpentinization processes at depth. The archaeal fraction of the microbial community varies widely within the Lost City chimneys, from 1-81% and covaries with concentrations of hydrogen within the fluids. Archaeal lipids include isoprenoid glycerol di- and tetraethers and C25 and C30 isoprenoid hydrocarbons (pentamethylicosane derivatives - PMIs - and squalenoids). In particular, unsaturated PMIs and squalenoids, attributed to the LCMS archaea, were identified for the first time in the carbonate deposits at Lost City and probably record processes exclusively occurring at the surface of the chimneys. The carbon isotope compositions of PMIs and squalenoids are remarkably heterogeneous across samples and show highly (13) C-enriched signatures reaching δ(13) C values of up to +24.6‰. Unlike other environments in which similar structural and isotopic lipid heterogeneity has been observed and attributed to diversity in the archaeal assemblage, the lipids here appear to be synthesized solely by the LCMS. Some of the variations in lipid isotope signatures may, in part, be due to unusual isotopic fractionation during biosynthesis under extreme conditions. However, we argue that the diversity in archaeal abundances, lipid structure and carbon isotope composition rather reflects the ability of the LCMS archaeal biofilms to adapt to chemical gradients in the hydrothermal chimneys and possibly to perform either methanotrophy or methanogenesis using dissolved inorganic carbon, methane or formate as a function of the prevailing environmental conditions. © 2013 John Wiley & Sons Ltd.

Tracking Transport and Transformation of Aerosols using C and O-triple Isotopic Composition of Carbonates: CSI La Jolla

NASA Astrophysics Data System (ADS)

Thiemens, M. H.; Shaheen, R.; Chong, K.; Hill, A.; Wong, J.; Zhang, Z.; Dominguez, G.

2012-12-01

Aerosols affect climate in numerous ways, including change in the earth's energy balance by absorbing and scattering solar radiations, alteration of the hydrological cycle by serving as cloud condensation nuclei, change in biogeochemical cycles by providing nutrients. Another significant process is the effect on the chemical composition of the atmosphere by providing surfaces for heterogeneous chemical reactions. Fine particles of aerodynamic diameter less than 2.5μm (PM2.5) also impinge upon human health by admission to the respiratory system causing a range of cardiopulmonary diseases. Both climate and public health aspects depend on their physical and chemical properties, therefore, understanding physico-chemical and photochemical transformations on aerosol surfaces is important for predicting their effects on climate change, atmospheric chemistry and human health. Here we present initial findings on the processes occurring on aerosol surfaces using isotopes to delineate day and night time chemistry, thus resolving photochemistry effects, and to identify their sources by way of the carbon isotopes. Aerosols were collected on filter papers for 12h during the day and at night time from June-Dec. 2011in La Jolla, CA., using high volume, multi stage cascade impactors. CO2 released after treating these filter papers with 100% phosphoric acid at 27oC was collected, purified chromatographically and analyzed for both C and O isotopes. Our data indicate that both C and O isotopes can be used to distinguish between heterogeneous and photochemical transformations. Aerosol carbonates collected during the day time were depleted in δ13Cday = -23 to -28‰ and δ18Oday = +3 to +10‰ and were isotopically distinct from the carbonates collected at night time δ13Cnight = 0 to -12‰, δ18Onightnight = +23 to +32‰. Higher chloride concentration in the samples collected at night time indicated the transport of marine air masses whereas higher nitrate and sulfate concentration indicated urban air pollution in the samples collected during the day time. To further constraint the origin of air masses being collected at La Jolla, Ca, NOAA Hysplit back trajectories were analyzed for 24 and 48h at three different altitudes (500m, 1000m, <1500m). Our analysis found dominance of urban air masses from Los Angeles and San Diego area during the day time whereas aerosols collected at night time had a significant component of marine air masses and some contribution from San Diego areas at our sampling site, as expected. To further understand the role of ozone in heterogeneous and photochemical transformation, oxygen triple isotopic composition of the carbonates will be measured. Scanning electron microscopy will also be used to characterize the physical and chemical features of the aerosols. The comprehensive approach will facilitate to define changes in surface chemistry of the aerosols occuring during their transport and aging.

Chapman Conference on the Hydrologic Aspects of Global Climate Change, Lake Chelan, WA, June 12-14, 1990, Selected Papers

NASA Technical Reports Server (NTRS)

Lettenmaier, Dennis P. (Editor); Rind, D. (Editor)

1992-01-01

The present conference on the hydrological aspects of global climate change discusses land-surface schemes for future climate models, modeling of the land-surface boundary in climate models as a composite of independent vegetation, a land-surface hydrology parameterizaton with subgrid variability for general circulation models, and conceptual aspects of a statistical-dynamical approach to represent landscape subgrid-scale heterogeneities in atmospheric models. Attention is given to the impact of global warming on river runoff, the influence of atmospheric moisture transport on the fresh water balance of the Atlantic drainage basin, a comparison of observations and model simulations of tropospheric water vapor, and the use of weather types to disaggregate the prediction of general circulation models. Topics addressed include the potential response of an Arctic watershed during a period of global warming and the sensitivity of groundwater recharge estimates to climate variability and change.

In situ observation of the impact of surface oxidation on the crystallization mechanism of GeTe phase-change thin films by scanning transmission electron microscopy

NASA Astrophysics Data System (ADS)

Berthier, R.; Bernier, N.; Cooper, D.; Sabbione, C.; Hippert, F.; Noé, P.

2017-09-01

The crystallization mechanisms of prototypical GeTe phase-change material thin films have been investigated by in situ scanning transmission electron microscopy annealing experiments. A novel sample preparation method has been developed to improve sample quality and stability during in situ annealing, enabling quantitative analysis and live recording of phase change events. Results show that for an uncapped 100 nm thick GeTe layer, exposure to air after fabrication leads to composition changes which promote heterogeneous nucleation at the oxidized surface. We also demonstrate that protecting the GeTe layer with a 10 nm SiN capping layer prevents nucleation at the surface and allows volume nucleation at a temperature 50 °C higher than the onset of crystallization in the oxidized sample. Our results have important implications regarding the integration of these materials in confined memory cells.

Heterogeneity in fire severity within early season and late season prescribed burns in a mixed-conifer forest

USGS Publications Warehouse

Knapp, E.E.; Keeley, J.E.

2006-01-01

Structural heterogeneity in forests of the Sierra Nevada was historically produced through variation in fire regimes and local environmental factors. The amount of heterogeneity that prescription burning can achieve might now be more limited owing to high fuel loads and increased fuel continuity. Topography, woody fuel loading, and vegetative composition were quantified in plots within replicated early and late season burn units. Two indices of fire severity were evaluated in the same plots after the burns. Scorch height ranged from 2.8 to 25.4 m in early season plots and 3.1 to 38.5 m in late season plots, whereas percentage of ground surface burned ranged from 24 to 96% in early season plots and from 47 to 100% in late season plots. Scorch height was greatest in areas with steeper slopes, higher basal area of live trees, high percentage of basal area composed of pine, and more small woody fuel. Percentage of area burned was greatest in areas with less bare ground and rock cover (more fuel continuity), steeper slopes, and units burned in the fall (lower fuel moisture). Thus topographic and biotic factors still contribute to the abundant heterogeneity in fire severity with prescribed burning, even under the current high fuel loading conditions. Burning areas with high fuel loads in early season when fuels are moister may lead to patterns of heterogeneity in fire effects that more closely approximate the expected patchiness of historical fires.

Raman spectroscopic investigations on natural samples from the Integrated Ocean Drilling Program (IODP) Expedition 311: indications for heterogeneous compositions in hydrate crystals.

PubMed

Schicks, J M; Ziemann, M A; Lu, H; Ripmeester, J A

2010-12-01

Natural gas hydrates usually are found in the form of structure I, encasing predominantly methane in the hydrate lattices as guest molecules, sometimes also minor amount of higher hydrocarbons, CO2 or H2S. Raman spectroscopy is an approved tool to determine the composition of the hydrate phase. Thus, in this study Raman spectroscopic analyses have been applied to hydrate samples obtained from Integrated Ocean Drilling Program (IODP) Expedition 311 in two different approaches: studying the samples randomly taken from the hydrate core, and--as a new application--mapping small areas on the surface of clear hydrate crystals. The results obtained imply that the gas composition of hydrate, in terms of relative concentrations of CH4 and H2S, is not homogeneous over a core or even within a crystal. The mapping method yielded results with very high lateral resolution, indicating the coexistence of different phases with the same structure but different compositions within a hydrate crystal. Copyright © 2010 Elsevier B.V. All rights reserved.

High-Fidelity Microstructural Characterization and Performance Modeling of Aluminized Composite Propellant

DOE PAGES

Kosiba, Graham D.; Wixom, Ryan R.; Oehlschlaeger, Matthew A.

2017-10-27

Image processing and stereological techniques were used to characterize the heterogeneity of composite propellant and inform a predictive burn rate model. Composite propellant samples made up of ammonium perchlorate (AP), hydroxyl-terminated polybutadiene (HTPB), and aluminum (Al) were faced with an ion mill and imaged with a scanning electron microscope (SEM) and x-ray tomography (micro-CT). Properties of both the bulk and individual components of the composite propellant were determined from a variety of image processing tools. An algebraic model, based on the improved Beckstead-Derr-Price model developed by Cohen and Strand, was used to predict the steady-state burning of the aluminized compositemore » propellant. In the presented model the presence of aluminum particles within the propellant was introduced. The thermal effects of aluminum particles are accounted for at the solid-gas propellant surface interface and aluminum combustion is considered in the gas phase using a single global reaction. In conclusion, properties derived from image processing were used directly as model inputs, leading to a sample-specific predictive combustion model.« less

High-Fidelity Microstructural Characterization and Performance Modeling of Aluminized Composite Propellant

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

Kosiba, Graham D.; Wixom, Ryan R.; Oehlschlaeger, Matthew A.

Image processing and stereological techniques were used to characterize the heterogeneity of composite propellant and inform a predictive burn rate model. Composite propellant samples made up of ammonium perchlorate (AP), hydroxyl-terminated polybutadiene (HTPB), and aluminum (Al) were faced with an ion mill and imaged with a scanning electron microscope (SEM) and x-ray tomography (micro-CT). Properties of both the bulk and individual components of the composite propellant were determined from a variety of image processing tools. An algebraic model, based on the improved Beckstead-Derr-Price model developed by Cohen and Strand, was used to predict the steady-state burning of the aluminized compositemore » propellant. In the presented model the presence of aluminum particles within the propellant was introduced. The thermal effects of aluminum particles are accounted for at the solid-gas propellant surface interface and aluminum combustion is considered in the gas phase using a single global reaction. In conclusion, properties derived from image processing were used directly as model inputs, leading to a sample-specific predictive combustion model.« less

Characteristics of biochar: Microchemical properties

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

Amonette, James E.; Joseph, Stephen

2009-03-13

Biochars, being derived from a variety of biological feedstocks that have been thermally degraded under a range of conditions, exhibit a correspondingly large range in composition and chemistry. Due in part to the somewhat chaotic nature of the thermal process itself, this chemical heterogeneity extends to the microscopic scale even within a single biochar. Thus, in the strictest sense, each biochar made under a particular feedstock/process combination presents a unique mixture of phases and microenvironments that gives rise to a unique set of chemical properties. In some respects, the chemical complexity of biochars rivals that of incipient soils. In thismore » chapter we focus on the chemical complexity of biochar as manifested primarily at a microscopic and molecular scale. We start by describing the biochar-formation process and how this influences the composition and nature of the solid phases, entrained oils, and their organization at the microscopic level. We then proceed to discuss the range of surface chemistries exhibited by biochars in terms of functional groups and electrochemical properties. We conclude with a discussion of the influence of these properties on the sorption of aqueous species at biochar surfaces.« less

Graphitic design: prospects of graphene-based nanocomposites for solar energy conversion, storage, and sensing.

PubMed

Lightcap, Ian V; Kamat, Prashant V

2013-10-15

Graphene not only possesses interesting electrochemical behavior but also has a remarkable surface area and mechanical strength and is naturally abundant, all advantageous properties for the design of tailored composite materials. Graphene-semiconductor or -metal nanoparticle composites have the potential to function as efficient, multifunctional materials for energy conversion and storage. These next-generation composite systems could possess the capability to integrate conversion and storage of solar energy, detection, and selective destruction of trace environmental contaminants or achieve single-substrate, multistep heterogeneous catalysis. These advanced materials may soon become a reality, based on encouraging results in the key areas of energy conversion and sensing using graphene oxide as a support structure. Through recent advances, chemists can now integrate such processes on a single substrate while using synthetic designs that combine simplicity with a high degree of structural and composition selectivity. This progress represents the beginning of a transformative movement leveraging the advancements of single-purpose chemistry toward the creation of composites designed to address whole-process applications. The promising field of graphene nanocomposites for sensing and energy applications is based on fundamental studies that explain the electronic interactions between semiconductor or metal nanoparticles and graphene. In particular, reduced graphene oxide is a suitable composite substrate because of its two-dimensional structure, outstanding surface area, and electrical conductivity. In this Account, we describe common assembly methods for graphene composite materials and examine key studies that characterize its excited state interactions. We also discuss strategies to develop graphene composites and control electron capture and transport through the 2D carbon network. In addition, we provide a brief overview of advances in sensing, energy conversion, and storage applications that incorporate graphene-based composites. With these results in mind, we can envision a new class of semiconductor- or metal-graphene composites sensibly tailored to address the pressing need for advanced energy conversion and storage devices.

Post-processing of metal matrix composites by friction stir processing

NASA Astrophysics Data System (ADS)

Sharma, Vipin; Singla, Yogesh; Gupta, Yashpal; Raghuwanshi, Jitendra

2018-05-01

In metal matrix composites non-uniform distribution of reinforcement particles resulted in adverse affect on the mechanical properties. It is of great interest to explore post-processing techniques that can eliminate particle distribution heterogeneity. Friction stir processing is a relatively newer technique used for post-processing of metal matrix composites to improve homogeneity in particles distribution. In friction stir processing, synergistic effect of stirring, extrusion and forging resulted in refinement of grains, reduction of reinforcement particles size, uniformity in particles distribution, reduction in microstructural heterogeneity and elimination of defects.

Origin and Role of Recycled Crust in Flood Basalt Magmatism: Case Study of the Central East Greenland Rifted Margin

NASA Astrophysics Data System (ADS)

Brown, E.; Lesher, C. E.

2015-12-01

Continental flood basalts (CFB) are extreme manifestations of mantle melting derived from chemically/isotopically heterogeneous mantle. Much of this heterogeneity comes from lithospheric material recycled into the convecting mantle by a range of mechanisms (e.g. subduction, delamination). The abundance and petrogenetic origins of these lithologies thus provide important constraints on the geodynamical origins of CFB magmatism, and the timescales of lithospheric recycling in the mantle. Basalt geochemistry has long been used to constrain the compositions and mean ages of recycled lithologies in the mantle. Typically, this work assumes the isotopic compositions of the basalts are the same as their mantle source(s). However, because basalts are mixtures of melts derived from different sources (having different fusibilities) generated over ranges of P and T, their isotopic compositions only indirectly represent the isotopic compositions of their mantle sources[1]. Thus, relating basalts compositions to mantle source compositions requires information about the melting process itself. To investigate the nature of lithologic source heterogeneity while accounting for the effects of melting during CFB magmatism, we utilize the REEBOX PRO forward melting model[2], which simulates adiabatic decompression melting in lithologically heterogeneous mantle. We apply the model to constrain the origins and abundance of mantle heterogeneity associated with Paleogene flood basalts erupted during the rift-to-drift transition of Pangea breakup along the Central East Greenland rifted margin of the North Atlantic igneous province. We show that these basalts were derived by melting of a hot, lithologically heterogeneous source containing depleted, subduction-modified lithospheric mantle, and <10% recycled oceanic crust. The Paleozoic mean age we calculate for this recycled crust is consistent with an origin in the region's prior subduction history, and with estimates for the mean age of recycled crust in the modern Iceland plume[3]. These results suggest that this lithospheric material was not recycled into the lower mantle before becoming entrained in the Iceland plume. [1] Rudge et al. (2013). GCA, 114, p112-143; [2] Brown & Lesher (2014). Nat. Geo., 7, p820-824; [3] Thirlwall et al. (2004). GCA, 68, p361-386

Global Variations in Regolith Properties on Asteroid Vesta from Dawn's Low-Altitude Mapping Orbit

NASA Technical Reports Server (NTRS)

Denevi, Brett W.; Beck, Andrew W.; Coman, Ecaterina; Thomson, Bradley J.; Ammannito, Eleonora; Blewett, David T.; Sunshine, Jessica M.; De Sanctis, Maria Cristina; Li, Jian-Yang; Marchi, Simone;

The Athabasca Granulite Terrane and Evidence for Dynamic Behavior of Lower Continental Crust

NASA Astrophysics Data System (ADS)

Dumond, Gregory; Williams, Michael L.; Regan, Sean P.

2018-05-01

Deeply exhumed granulite terranes have long been considered nonrepresentative of lower continental crust largely because their bulk compositions do not match the lower crustal xenolith record. A paradigm shift in our understanding of deep crust has since occurred with new evidence for a more felsic and compositionally heterogeneous lower crust than previously recognized. The >20,000-km2 Athabasca granulite terrane locally provides a >700-Myr-old window into this type of lower crust, prior to being exhumed and uplifted to the surface between 1.9 and 1.7 Ga. We review over 20 years of research on this terrane with an emphasis on what these findings may tell us about the origin and behavior of lower continental crust, in general, in addition to placing constraints on the tectonic evolution of the western Canadian Shield between 2.6 and 1.7 Ga. The results reveal a dynamic lower continental crust that evolved compositionally and rheologically with time.

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

Hammond, Glenn Edward; Yang, Xiaofan; Song, Xuehang

The groundwater-surface water interaction zone (GSIZ) plays an important role in riverine and watershed ecosystems as the exchange of waters of variable composition and temperature (hydrologic exchange flows) stimulate microbial activity and associated biogeochemical reactions. Variable temporal and spatial scales of hydrologic exchange flows, heterogeneity of the subsurface environment, and complexity of biogeochemical reaction networks in the GSIZ present challenges to incorporation of fundamental process representations and model parameterization across a range of spatial scales (e.g. from pore-scale to field scale). This paper presents a novel hybrid multiscale simulation approach that couples hydrologic-biogeochemical (HBGC) processes between two distinct length scalesmore » of interest.« less

Surface Chemistry in Heterogeneous Catalysis: An Emerging Discipline.

ERIC Educational Resources Information Center

White, J. M.; Campbell, Charles T.

1980-01-01

Provides background data on surface chemistry as an emerging discipline. Highlights the important role which surfaces play in catalysis by focusing on the catalyzed oxidation of carbon monoxide. Provides a demonstration of how surfaces exert their influences in heterogeneous phenomena and illustrates how experimental problems in this field are…

Predicting Catalytic Activity of Nanoparticles by a DFT-Aided Machine-Learning Algorithm.

PubMed

Jinnouchi, Ryosuke; Asahi, Ryoji

2017-09-07

Catalytic activities are often dominated by a few specific surface sites, and designing active sites is the key to realize high-performance heterogeneous catalysts. The great triumphs of modern surface science lead to reproduce catalytic reaction rates by modeling the arrangement of surface atoms with well-defined single-crystal surfaces. However, this method has limitations in the case for highly inhomogeneous atomic configurations such as on alloy nanoparticles with atomic-scale defects, where the arrangement cannot be decomposed into single crystals. Here, we propose a universal machine-learning scheme using a local similarity kernel, which allows interrogation of catalytic activities based on local atomic configurations. We then apply it to direct NO decomposition on RhAu alloy nanoparticles. The proposed method can efficiently predict energetics of catalytic reactions on nanoparticles using DFT data on single crystals, and its combination with kinetic analysis can provide detailed information on structures of active sites and size- and composition-dependent catalytic activities.

Spatial variability in plant species composition and peatland carbon exchange

NASA Astrophysics Data System (ADS)

Goud, E.; Moore, T. R.; Roulet, N. T.

2015-12-01

Plant species shifts in response to global change will have significant impacts on ecosystem carbon (C) exchange and storage arising from changes in hydrology. Spatial variation in peatland C fluxes have largely been attributed to the spatial distribution of microhabitats that arise from variation in surface topography and water table depth, but little is known about how plant species composition impacts peatland C cycling or how these impacts will be influenced by changing environmental conditions. We quantified the effect of species composition and environmental variables on carbon dioxide (CO2) and methane (CH4) fluxes over 2 years in a temperate peatland for four plant communities situated along a water table gradient from ombrotrophic bog to beaver pond. We hypothesized that (i) spatial heterogeneity in species composition would drive predictable spatial heterogeneity in C fluxes due to variation in plant traits and ecological tolerances, and (ii) increases in peat temperature would increase C fluxes. Species had different effects on C fluxes primarily due to differences in leaf traits. Differences in ecological tolerances among communities resulted in different rates of CO2 exchange in response to changes in water table depth. There was an overall reduction in ecosystem respiration (ER), gross primary productivity (GPP) and CH4 flux in response to colder peat temperatures in the second year, and the additive effects of a deeper water table in the bog margin and pond sites further reduced flux rates in these areas. These results demonstrate that different plant species can increase or decrease the flux of C into and out of peatlands based on differences in leaf traits and ecological tolerances, and that CO2 and CH4 fluxes are sensitive to changes in soil temperature, especially when coupled with changes in moisture availability.

Large-scale Generation of Patterned Bubble Arrays on Printed Bi-functional Boiling Surfaces

NASA Astrophysics Data System (ADS)

Choi, Chang-Ho; David, Michele; Gao, Zhongwei; Chang, Alvin; Allen, Marshall; Wang, Hailei; Chang, Chih-Hung

2016-04-01

Bubble nucleation control, growth and departure dynamics is important in understanding boiling phenomena and enhancing nucleate boiling heat transfer performance. We report a novel bi-functional heterogeneous surface structure that is capable of tuning bubble nucleation, growth and departure dynamics. For the fabrication of the surface, hydrophobic polymer dot arrays are first printed on a substrate, followed by hydrophilic ZnO nanostructure deposition via microreactor-assisted nanomaterial deposition (MAND) processing. Wettability contrast between the hydrophobic polymer dot arrays and aqueous ZnO solution allows for the fabrication of heterogeneous surfaces with distinct wettability regions. Heterogeneous surfaces with various configurations were fabricated and their bubble dynamics were examined at elevated heat flux, revealing various nucleate boiling phenomena. In particular, aligned and patterned bubbles with a tunable departure frequency and diameter were demonstrated in a boiling experiment for the first time. Taking advantage of our fabrication method, a 6 inch wafer size heterogeneous surface was prepared. Pool boiling experiments were also performed to demonstrate a heat flux enhancement up to 3X at the same surface superheat using bi-functional surfaces, compared to a bare stainless steel surface.

Interrogating Surface Functional Group Heterogeneity of Activated Thermoplastics Using Super-Resolution Fluorescence Microscopy.

PubMed

ONeil, Colleen E; Jackson, Joshua M; Shim, Sang-Hee; Soper, Steven A

2016-04-05

We present a novel approach for characterizing surfaces utilizing super-resolution fluorescence microscopy with subdiffraction limit spatial resolution. Thermoplastic surfaces were activated by UV/O3 or O2 plasma treatment under various conditions to generate pendant surface-confined carboxylic acids (-COOH). These surface functional groups were then labeled with a photoswitchable dye and interrogated using single-molecule, localization-based, super-resolution fluorescence microscopy to elucidate the surface heterogeneity of these functional groups across the activated surface. Data indicated nonuniform distributions of these functional groups for both COC and PMMA thermoplastics with the degree of heterogeneity being dose dependent. In addition, COC demonstrated relative higher surface density of functional groups compared to PMMA for both UV/O3 and O2 plasma treatment. The spatial distribution of -COOH groups secured from super-resolution imaging were used to simulate nonuniform patterns of electroosmotic flow in thermoplastic nanochannels. Simulations were compared to single-particle tracking of fluorescent nanoparticles within thermoplastic nanoslits to demonstrate the effects of surface functional group heterogeneity on the electrokinetic transport process.

Modeling of nanoscale liquid mixture transport by density functional hydrodynamics

NASA Astrophysics Data System (ADS)

Dinariev, Oleg Yu.; Evseev, Nikolay V.

2017-06-01

Modeling of multiphase compositional hydrodynamics at nanoscale is performed by means of density functional hydrodynamics (DFH). DFH is the method based on density functional theory and continuum mechanics. This method has been developed by the authors over 20 years and used for modeling in various multiphase hydrodynamic applications. In this paper, DFH was further extended to encompass phenomena inherent in liquids at nanoscale. The new DFH extension is based on the introduction of external potentials for chemical components. These potentials are localized in the vicinity of solid surfaces and take account of the van der Waals forces. A set of numerical examples, including disjoining pressure, film precursors, anomalous rheology, liquid in contact with heterogeneous surface, capillary condensation, and forward and reverse osmosis, is presented to demonstrate modeling capabilities.

Preparation of transition metal composite graphite felt cathode for efficient heterogeneous electro-Fenton process.

PubMed

Liang, Liang; Yu, Fangke; An, Yiran; Liu, Mengmeng; Zhou, Minghua

2017-01-01

A composite graphite felt (GF) modified with transition metal was fabricated and used as cathode in heterogeneous electro-Fenton (EF) for methyl orange (MO) degradation. Characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), the morphology and surface physicochemical properties of the cathodes after modification were observed considerably changed. After loading metals, the current response became higher, the accumulation of H 2 O 2 and the degradation efficiency of MO were improved. Under the same conditions, GF-Co had the highest catalytic activity for electro-reduction of O 2 to H 2 O 2 and MO degradation. At pH 3, 99 % of MO degradation efficiency was obtained using GF-Co after 120 min treatment and even at initial pH 9, 82 % of that was obtained. TOC removal efficiency reached 93.8 % using GF-Co at pH 3 after 120 min treatment while that was 12.3 % using GF. After ten-time runs, the mineralization ratio of the GF-Co was still 89.5 %, suggesting that GF-Co was very promising for wastewater treatment. The addition of isopropanol proved that · OH played an important role in degradation of MO.

Variation in coastal Antarctic microbial community composition at sub-mesoscale: spatial distance or environmental filtering?

PubMed

Moreno-Pino, Mario; De la Iglesia, Rodrigo; Valdivia, Nelson; Henríquez-Castilo, Carlos; Galán, Alexander; Díez, Beatriz; Trefault, Nicole

2016-07-01

Spatial environmental heterogeneity influences diversity of organisms at different scales. Environmental filtering suggests that local environmental conditions provide habitat-specific scenarios for niche requirements, ultimately determining the composition of local communities. In this work, we analyze the spatial variation of microbial communities across environmental gradients of sea surface temperature, salinity and photosynthetically active radiation and spatial distance in Fildes Bay, King George Island, Antarctica. We hypothesize that environmental filters are the main control of the spatial variation of these communities. Thus, strong relationships between community composition and environmental variation and weak relationships between community composition and spatial distance are expected. Combining physical characterization of the water column, cell counts by flow cytometry, small ribosomal subunit genes fingerprinting and next generation sequencing, we contrast the abundance and composition of photosynthetic eukaryotes and heterotrophic bacterial local communities at a submesoscale. Our results indicate that the strength of the environmental controls differed markedly between eukaryotes and bacterial communities. Whereas eukaryotic photosynthetic assemblages responded weakly to environmental variability, bacteria respond promptly to fine-scale environmental changes in this polar marine system. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Bioinspired Hierarchical Nanofibrous Silver-Nanoparticle/Anatase-Rutile-Titania Composite as an Anode Material for Lithium-Ion Batteries.

PubMed

Luo, Yan; Li, Jiao; Huang, Jianguo

2016-11-29

A new bioinspired hierarchical nanofibrous silver-nanoparticle/anatase-rutile-titania (Ag-NP/A-R-titania) composite was fabricated by employing a natural cellulose substance (e.g., commercial laboratory cellulose filter paper) as the structural scaffold template, which was composed of anatase-phase titania (A-titania) nanotubes with rutile-phase titania (R-titania) nanoneedles grown on the surfaces and further silver nanoparticles (AgNPs) immobilized thereon. As it was employed as an anode material for lithium-ion batteries (LIBs), high reversible capacity, enhanced rate performance, and excellent cycling stability were achieved as compared with those of the corresponding cellulose-substance-derived nanotubular A-titania, R-titania, heterogeneous anatase/rutile titania (A-R-titania) composite, and commercial P25 powder. This benefited from its unique porous cross-linked three-dimensional structure inherited from the initial cellulose substance scaffold, which enhances the sufficient electrode/electrolyte contact, relieves the severe volume change upon cycling, and improves the amount of lithium-ion storage; moreover, the high loading content of the silver component in the composite improves the electrical conductivity of the electrode. The structural integrity of the composite was maintained upon long-term charge/discharge cycling, indicating its significant stability.

Immersion Condensation on Oil-Infused Heterogeneous Surfaces for Enhanced Heat Transfer

PubMed Central

Xiao, Rong; Miljkovic, Nenad; Enright, Ryan; Wang, Evelyn N.

2013-01-01

Enhancing condensation heat transfer is important for broad applications from power generation to water harvesting systems. Significant efforts have focused on easy removal of the condensate, yet the other desired properties of low contact angles and high nucleation densities for high heat transfer performance have been typically neglected. In this work, we demonstrate immersion condensation on oil-infused micro and nanostructured surfaces with heterogeneous coatings, where water droplets nucleate immersed within the oil. The combination of surface energy heterogeneity, reduced oil-water interfacial energy, and surface structuring enabled drastically increased nucleation densities while maintaining easy condensate removal and low contact angles. Accordingly, on oil-infused heterogeneous nanostructured copper oxide surfaces, we demonstrated approximately 100% increase in heat transfer coefficient compared to state-of-the-art dropwise condensation surfaces in the presence of non-condensable gases. This work offers a distinct approach utilizing surface chemistry and structuring together with liquid-infusion for enhanced condensation heat transfer. PMID:23759735

Operando characterization of catalysts through use of a portable microreactor

DOE PAGES

Zhao, Shen; Li, Yuanyuan; Stavitski, Eli; ...

2015-10-09

To provide new understandings of the mechanisms of catalytic reactions, improved methods are needed than can monitor changes in the electronic, structural and chemical properties of catalysts, doing so in the operando conditions in which catalysts work. We describe here a microreactor-based approach that integrates the capabilities of advanced x-ray, electron, optical and gas-phase compositional analysis techniques in operando conditions. For several exemplary catalytic systems, we demonstrate how this approach enables characterization of three major factors contributing to structure-property correlations evidenced in heterogeneously catalyzed reactions, namely: the atomic structure and elemental compositions of nanocatalysts; the physiochemical properties of the supportmore » and catalyst-support interfaces; and the gas and surface-phase chemistry occurring under operando conditions. We highlight the generality of the approach as well as outline opportunities for future developments.« less

Soil Components in Heterogeneous Impact Glass in Martian Meteorite EETA79001

NASA Technical Reports Server (NTRS)

Schrader, C. M.; Cohen, B. A.; Donovan, J. J.; Vicenzi, E. P.

2010-01-01

Martian soil composition can illuminate past and ongoing near-surface processes such as impact gardening [2] and hydrothermal and volcanic activity [3,4]. Though the Mars Exploration Rovers (MER) have analyzed the major-element composition of Martian soils, no soil samples have been returned to Earth for detailed chemical analysis. Rao et al. [1] suggested that Martian meteorite EETA79001 contains melted Martian soil in its impact glass (Lithology C) based on sulfur enrichment of Lithology C relative to the meteorite s basaltic lithologies (A and B) [1,2]. If true, it may be possible to extract detailed soil chemical analyses using this meteoritic sample. We conducted high-resolution (0.3 m/pixel) element mapping of Lithology C in thin section EETA79001,18 by energy dispersive spectrometry (EDS). We use these data for principal component analysis (PCA).

Systematics of the CHON and other light-element particle populations in Comet Halley

NASA Technical Reports Server (NTRS)

Clark, Benton; Mason, Larry W.; Kissel, Jochen

1986-01-01

Based on chemical signatures measured by the PIA experiment during the Giotto flyby of comet Halley, particle classifications were designated. In addition to silicate-like grains and particles of mixed (cosmic) composition, there appear to be several light-element rich populations, including the CHON, (H,C), (H,C,O), and (H,C,N) particle types. These compositional classes are further distinguished by differences in mass distributions, a density indicator, and variations in relative abundance within the coma. These particle populations are evidence for chemical heterogeneity in the surface of the cometary nucleus. Particles found mainly in the inner coma may be volatile icy grains. Most of the N of the comet may be found in up to three different populations of grains; one or more of these may be responsible for the observation of cyanojets.

Facile solid-state synthesis of highly dispersed Cu nanospheres anchored on coal-based activated carbons as an efficient heterogeneous catalyst for the reduction of 4-nitrophenol

NASA Astrophysics Data System (ADS)

Wang, Shan; Gao, Shasha; Tang, Yakun; Wang, Lei; Jia, Dianzeng; Liu, Lang

2018-04-01

Coal-based activated carbons (AC) were acted as the support, Cu/AC catalysts were synthesized by a facile solid-state reaction combined with subsequent heat treatment. In Cu/AC composites, highly dispersed Cu nanospheres were anchored on AC. The catalytic activity for 4-nitrophenol (4-NP) was investigated, the effects of activation temperature and copper loading on the catalytic performance were studied. The catalysts exhibited very high catalytic activity and moderate chemical stability due to the unique characteristics of the particle-assembled nanostructures, the high surface area and the porous structure of coal-based AC and the good dispersion of metal particles. Design and preparation of non-noble metal composite catalysts provide a new direction for improving the added value of coal.

Microchemical and Structural Evidence for Space Weathering in Soils from Asteroid Itokawa

NASA Technical Reports Server (NTRS)

Thompson, M. S.; Christoffersen, R.; Zega, T. J.

2013-01-01

The chemistry, microstructure and optical properties of grains on the surfaces of airless bodies are continu-ously modified due to their interactions predominantly with solar energetic ions and micrometeorite impacts. Collectively known as space weathering, this phenomenon results in a discrepancy between remotely sensed spectra from asteroids and those ac-quired directly from meteorites. The return of pristine samples from the asteroid Itokawa provides insight into surface processes on airless bodies and will help in correlating remote sensing data with laboratory analysis of meteorites. Samples and Methods: We examined Itokawa samples RA-QD02-0042-01 and RA-QD-02-0042-02, ultramicrotomed sec-tions of a singular grain prepared by the Hayabusa sample cura-tion team. We analyzed these slices using a 200 keV JEOL 2010F transmission electron microscope (TEM) at Arizona State Uni-versity and a 200 keV JEOL 2500SE TEM at NASA JSC. Both field emission TEMs are equipped with energy-dispersive X-ray spectrometers (EDS) and scanning TEM (STEM) detectors. Results and Discussion: TEM observations reveal that the sectioned grain predominantly consists of a single crystal of low-Ca orthopyroxene, with subsidiary smaller regions of olivine, Fe-Ni sulfide, and Fe-Ni metal. EDS-spectrum imaging and high-resolution TEM (HRTEM) show local, nanocrystalline regions of the outermost 2 to 5 nm of the pyroxene are composed of an Fe-Mg-S-rich and Si- and O-depleted layer that is underlain by a 2- to 5-nm thick amorphous zone enriched in Si. These layers occur in multiple microtome slices and have uniform thicknesses. We also observe localized 'islands' of material on the surface of the pyroxene which HRTEM imaging indicates are amorphous and EDS measurements show are compositionally heterogeneous. A 10- to 60-nm thick partially amorphous zone occurs below the compositionally distinct rim. While this this zone is associated with the compositionally heterogeneous outer layer, it also occurs as a local stand-alone feature on the exterior rim of the grain. Ar-eas of the pyroxene grain rim also exhibit a vesicular texture. The TEM data indicate a complex history of space weather-ing for samples RA-QD02-0042-01 and -02. The outermost layer of nanocrystalline material with varied composition is consistent with previously suggested [3-4] chemical and structural pro-cessing by solar wind ions, with a possible additional role for im-pact vapor deposition [3-4]. The amorphous and compositionally distinct islands on the surface of this grain, similar to lunar glasses, suggest formation through vapor deposition via micrometeor-ite impact events. In comparison, the amorphization and vesicula-tion textures are likely a product of radiation damage from the solar wind. The depth and degree of amorphization, in conjunction with model calculations, will help provide an upper limit on exposure time for these particles.

Heterogeneous Ice Nucleation: Interplay of Surface Properties and Their Impact on Water Orientations.

PubMed

Glatz, Brittany; Sarupria, Sapna

2018-01-23

Ice is ubiquitous in nature, and heterogeneous ice nucleation is the most common pathway of ice formation. How surface properties affect the propensity to observe ice nucleation on that surface remains an open question. We present results of molecular dynamics studies of heterogeneous ice nucleation on model surfaces. The models surfaces considered emulate the chemistry of kaolinite, an abundant component of mineral dust. We investigate the interplay of surface lattice and hydrogen bonding properties in affecting ice nucleation. We find that lattice matching and hydrogen bonding are necessary but not sufficient conditions for observing ice nucleation at these surfaces. We correlate this behavior to the orientations sampled by the metastable supercooled water in contact with the surfaces. We find that ice is observed in cases where water molecules not only sample orientations favorable for bilayer formation but also do not sample unfavorable orientations. This distribution depends on both surface-water and water-water interactions and can change with subtle modifications to the surface properties. Our results provide insights into the diverse behavior of ice nucleation observed at different surfaces and highlight the complexity in elucidating heterogeneous ice nucleation.

Rapid Passage of a Small-Scale Mantle Heterogeneity Through the Melting Regions of Kilauea and Mauna Loa Volcanoes

NASA Astrophysics Data System (ADS)

Pietruszka, A. J.; Marske, J. P.; Weis, D.; Garcia, M. O.; Rhodes, J. M.

2006-12-01

There are few quantitative estimates for the size, shape, and distribution of small-scale compositional heterogeneities within the Hawaiian mantle plume. The chemistry of recent lavas from the two most active Hawaiian volcanoes, Kilauea and Mauna Loa, provide a snapshot of the heterogeneous structure of the plume beneath Hawaii. We present Pb and Sr isotope ratios of two suites of young prehistoric lavas from these volcanoes: (1) Kilauea lavas from AD 1000 to 1500, and (2) 14C-dated Mauna Loa flows from ~2,650- 140 years BP. Prior to this study, the Pb and Sr isotope ratios of lavas from these volcanoes were thought to be completely distinct (e.g., Abouchami et al., 2005). However, these prehistoric Kilauea and Mauna Loa lavas display a systematic isotopic fluctuation, and the Kilauea lavas (in particular) span the Pb and Sr isotopic divide that was previously thought to exist between these two volcanoes. For a brief period from AD 250 to 1500, the Pb and Sr isotope ratios of Kilauea and Mauna Loa lavas departed from values typical for each volcano's historical period, moved towards a common isotopic composition, and subsequently, returned to more typical values. This transient magmatic event was probably caused by the rapid passage of a small-scale compositional heterogeneity though the melting regions of these volcanoes. The heterogeneity is thought to be either a single body that extends between the summits of both Kilauea and Mauna Loa (~35 km long) or the ubiquitous plume matrix itself. The time scale of this event (centuries) is much shorter than previously noted for variations in the isotopic composition of Hawaiian lavas due to the upwelling of heterogeneities within the plume (thousands to tens of thousands of years; Blichert-Toft et al., 2003; Kurz et al., 2004). Calculations based on the duration of the isotopic excursion suggest a maximum thickness for the melting region (and thus, the heterogeneity) of only ~5-10 km.

Prediction of Nanoparticle and Colloid Attachment on Unfavorable Mineral Surfaces Using Representative Discrete Heterogeneity.

PubMed

Trauscht, Jacob; Pazmino, Eddy; Johnson, William P

2015-09-01

Despite several decades of research there currently exists no mechanistic theory to predict colloid attachment in porous media under environmental conditions where colloid-collector repulsion exists (unfavorable conditions for attachment). It has long been inferred that nano- to microscale surface heterogeneity (herein called discrete heterogeneity) drives colloid attachment under unfavorable conditions. Incorporating discrete heterogeneity into colloid-collector interaction calculations in particle trajectory simulations predicts colloid attachment under unfavorable conditions. As yet, discrete heterogeneity cannot be independently measured by spectroscopic or other approaches in ways directly relevant to colloid-surface interaction. This, combined with the fact that a given discrete heterogeneity representation will interact differently with differently sized colloids as well as different ionic strengths for a given sized colloid, suggests a strategy to back out representative discrete heterogeneity by a comparison of simulations to experiments performed across a range of colloid size, solution IS, and fluid velocity. This has recently been performed for interaction of carboxylate-modified polystyrene latex (CML) microsphere attachment to soda lime glass at pH 6.7 with NaCl electrolyte. However, extension to other surfaces, pH values, and electrolytes is needed. For this reason, the attachment of CML (0.25, 1.1, and 2.0 μm diameters) from aqueous suspension onto a variety of unfavorable mineral surfaces (soda lime glass, muscovite, and albite) was examined for pH values of 6.7 and 8.0), fluid velocities (1.71 × 10(-3) and 5.94 × 10(-3) m s(-1)), IS (6.0 and 20 mM), and electrolytes (NaCl, CaSO4, and multivalent mixtures). The resulting representative heterogeneities (heterodomain size and surface coverage, where heterodomain refers to nano- to microscale attractive domains) yielded colloid attachment predictions that were compared to predictions from existing applicable semiempirical expressions in order to examine the strengths and weaknesses of the discrete heterogeneity approach and opportunities for improvement.

Heterogeneity and anisotropy in the lithospheric mantle

NASA Astrophysics Data System (ADS)

Tommasi, Andréa; Vauchez, Alain

2015-10-01

The lithospheric mantle is intrinsically heterogeneous and anisotropic. These two properties govern the repartition of deformation, controlling intraplate strain localization and development of new plate boundaries. Geophysical and geological observations provide clues on the types, ranges, and characteristic length scales of heterogeneity and anisotropy in the lithospheric mantle. Seismic tomography points to variations in geothermal gradient and hence in rheological behavior at scales of hundreds of km. Seismic anisotropy data substantiate anisotropic physical properties consistent at scales of tens to hundreds of km. Receiver functions imply lateral and vertical heterogeneity at scales < 10 km, which might record gradients in composition or anisotropy. Observations on naturally deformed peridotites establish that compositional heterogeneity and Crystal Preferred Orientations (CPOs) are ubiquitous from the mm to the km scales. These data allow discussing the processes that produce/destroy heterogeneity and anisotropy and constraining the time scales over which they are active. This analysis highlights: (i) the role of deformation and reactive percolation of melts and fluids in producing compositional and structural heterogeneity and the feedbacks between these processes, (ii) the weak mechanical effect of mineralogical variations, and (iii) the low volumes of fine-grained microstructures and difficulty to preserve them. In contrast, olivine CPO and the resulting anisotropy of mechanical and thermal properties are only modified by deformation. Based on this analysis, we propose that strain localization at the plate scale is, at first order, controlled by large-scale variations in thermal structure and in CPO-induced anisotropy. In cold parts of the lithospheric mantle, grain size reduction may contribute to strain localization, but the low volume of fine-grained domains limits this effect.

The mystery of membrane organization: composition, regulation and physiological relevance of lipid rafts

PubMed Central

Sezgin, Erdinc; Levental, Ilya; Mayor, Satyajit; Eggeling, Christian

2017-01-01

Cellular plasma membranes are laterally heterogeneous, featuring a variety of distinct subcompartments that differ in their biophysical properties and composition. A large body of research has focused on understanding the basis for this heterogeneity and its physiological relevance. The membrane raft hypothesis formalized a physicochemical principle for a subtype of such lateral membrane heterogeneity, wherein the preferential associations of cholesterol and saturated lipids drives the formation of relatively packed (ordered) membrane domains that selectively recruit certain lipids and proteins. Recent years have yielded new insights into this concept and its in vivo relevance, primarily owing to the development of biochemical and biophysical technologies. PMID:28356571

Spatial, seasonal, and source variability in the stable oxygen and hydrogen isotopic composition of tap waters throughout the USA

USGS Publications Warehouse

Landwehr, Jurate M.; Coplen, Tyler B.; Stewart, David W.

2013-01-01

To assess spatial, seasonal, and source variability in stable isotopic composition of human drinking waters throughout the entire USA, we have constructed a database of δ18O and δ2H of US tap waters. An additional purpose was to create a publicly available dataset useful for evaluating the forensic applicability of these isotopes for human tissue source geolocation. Samples were obtained at 349 sites, from diverse population centres, grouped by surface hydrologic units for regional comparisons. Samples were taken concurrently during two contrasting seasons, summer and winter. Source supply (surface, groundwater, mixed, and cistern) and system (public and private) types were noted. The isotopic composition of tap waters exhibits large spatial and regional variation within each season as well as significant at-site differences between seasons at many locations, consistent with patterns found in environmental (river and precipitation) waters deriving from hydrologic processes influenced by geographic factors. However, anthropogenic factors, such as the population of a tap’s surrounding community and local availability from diverse sources, also influence the isotopic composition of tap waters. Even within a locale as small as a single metropolitan area, tap waters with greatly differing isotopic compositions can be found, so that tap water within a region may not exhibit the spatial or temporal coherence predicted for environmental water. Such heterogeneities can be confounding factors when attempting forensic inference of source water location, and they underscore the necessity of measurements, not just predictions, with which to characterize the isotopic composition of regional tap waters. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Chemical trends in ocean islands explained by plume–slab interaction

NASA Astrophysics Data System (ADS)

Dannberg, Juliane; Gassmöller, Rene

2018-04-01

Earth's surface shows many features, of which the genesis can be understood only through their connection with processes in Earth's deep interior. Recent studies indicate that spatial geochemical patterns at oceanic islands correspond to structures in the lowermost mantle inferred from seismic tomographic models. This suggests that hot, buoyant upwellings can carry chemical heterogeneities from the deep lower mantle toward the surface, providing a window to the composition of the lowermost mantle. The exact nature of this link between surface and deep Earth remains debated and poorly understood. Using computational models, we show that subducted slabs interacting with dense thermochemical piles can trigger the ascent of hot plumes that inherit chemical gradients present in the lowermost mantle. We identify two key factors controlling this process: (i) If slabs induce strong lower-mantle flow toward the edges of these piles where plumes rise, the pile-facing side of the plume preferentially samples material originating from the pile, and bilaterally asymmetric chemical zoning develops. (ii) The composition of the melt produced reflects this bilateral zoning if the overlying plate moves roughly perpendicular to the chemical gradient in the plume conduit. Our results explain some of the observed geochemical trends of oceanic islands and provide insights into how these trends may originate.

Analysis of Electrokinetic Mixing Using AC Electric Field and Patchwise Surface Heterogeneities

NASA Astrophysics Data System (ADS)

Luo, Win-Jet; Yarn, Kao-Feng; Hsu, Shou-Ping

2007-04-01

In this paper, the authors investigate the use of an applied AC electric field and microchannel surface heterogeneities to carry out the microfluidic mixing of two-dimensional, time-dependent electroosmotic flows. The time-dependent flow fields within the microchannel are simulated using the backwards-Euler time-stepping numerical method. The mixing efficiencies obtained in microchannels with two different patchwise surface heterogeneity patterns are investigated. In general, the results show that the application of an AC electric field significantly reduces the required mixing length compared with the use of a DC electric field. Furthermore, the presence of oppositely charged surface heterogeneities on the microchannel walls results in the formation of localized flow circulation regions within the bulk flow. These circulation regions grow and decay periodically in accordance with the periodic variation of the AC electric field intensity and provide an effective means of enhancing species mixing in the microchannel. Consequently, the use of an AC electric field together with patchwise surface heterogeneities permits a significant reduction in both the mixing channel length and the retention time required to attain a homogeneous solution.

Characterizing heterogeneous dynamics at hydrated electrode surfaces.

PubMed

Willard, Adam P; Limmer, David T; Madden, Paul A; Chandler, David

2013-05-14

In models of Pt 111 and Pt 100 surfaces in water, motions of molecules in the first hydration layer are spatially and temporally correlated. To interpret these collective motions, we apply quantitative measures of dynamic heterogeneity that are standard tools for considering glassy systems. Specifically, we carry out an analysis in terms of mobility fields and distributions of persistence times and exchange times. In so doing, we show that dynamics in these systems is facilitated by transient disorder in frustrated two-dimensional hydrogen bonding networks. The frustration is the result of unfavorable geometry imposed by strong metal-water bonding. The geometry depends upon the structure of the underlying metal surface. Dynamic heterogeneity of water on the Pt 111 surface is therefore qualitatively different than that for water on the Pt 100 surface. In both cases, statistics of this ad-layer dynamic heterogeneity responds asymmetrically to applied voltage.

Characterizing heterogeneous dynamics at hydrated electrode surfaces

NASA Astrophysics Data System (ADS)

Willard, Adam P.; Limmer, David T.; Madden, Paul A.; Chandler, David

2013-05-01

In models of Pt 111 and Pt 100 surfaces in water, motions of molecules in the first hydration layer are spatially and temporally correlated. To interpret these collective motions, we apply quantitative measures of dynamic heterogeneity that are standard tools for considering glassy systems. Specifically, we carry out an analysis in terms of mobility fields and distributions of persistence times and exchange times. In so doing, we show that dynamics in these systems is facilitated by transient disorder in frustrated two-dimensional hydrogen bonding networks. The frustration is the result of unfavorable geometry imposed by strong metal-water bonding. The geometry depends upon the structure of the underlying metal surface. Dynamic heterogeneity of water on the Pt 111 surface is therefore qualitatively different than that for water on the Pt 100 surface. In both cases, statistics of this ad-layer dynamic heterogeneity responds asymmetrically to applied voltage.

Lattice Boltzmann Simulation of Electroosmotic Micromixing by Heterogeneous Surface Charge

NASA Astrophysics Data System (ADS)

Tang, G. H.; Wang, F. F.; Tao, W. Q.

Microelectroosmotic flow is usually restricted to low Reynolds number regime, and mixing in these microfluidic systems becomes problematic due to the negligible inertial effects. To gain an improved understanding of mixing enhancement in microchannels patterned with heterogeneous surface charge, the lattice Boltzmann method has been employed to obtain the electric potential distribution in the electrolyte, the flow field, and the species concentration distribution, respectively. The simulation results show that heterogeneous surfaces can significantly disturb the streamlines leading to apparently substantial improvements in mixing. However, the introduction of such a feature can reduce the mass flow rate in the channel. The reduction in flow rate effectively prolongs the available mixing time when the flow passes through the channel and the observed mixing enhancement by heterogeneous surfaces partly results from longer mixing time.

The composition of heterogeneous control laws

NASA Technical Reports Server (NTRS)

Kuipers, Benjamin; Astrom, Karl

1991-01-01

The fuzzy control literature and industrial practice provide certain nonlinear methods for combining heterogeneous control laws, but these methods have been very difficult to analyze theoretically. An alternate formulation and extension of this approach is presented that has several practical and theoretical benefits. An example of heterogeneous control is given and two alternate analysis methods are presented.

Size scales over which ordinary chondrites and their parent asteroids are homogeneous in oxidation state and oxygen-isotopic composition

NASA Astrophysics Data System (ADS)

Rubin, Alan E.; Ziegler, Karen; Young, Edward D.

2008-02-01

Literature data demonstrate that on a global, asteroid-wide scale (plausibly on the order of 100 km), ordinary chondrites (OC) have heterogeneous oxidation states and O-isotopic compositions (represented, respectively, by the mean olivine Fa and bulk Δ 17O compositions of equilibrated samples). Samples analyzed here include: (a) two H5 chondrite Antarctic finds (ALHA79046 and TIL 82415) that have the same cosmic-ray exposure age (7.6 Ma) and were probably within ˜1 km of each other when they were excavated from the H-chondrite parent body, (b) different individual stones from the Holbrook L/LL6 fall that were probably within ˜1 m of each other when their parent meteoroid penetrated the Earth's atmosphere, and (c) drill cores from a large slab of the Estacado H6 find located within a few tens of centimeters of each other. Our results indicate that OC are heterogeneous in their bulk oxidation state and O-isotopic composition on 100-km-size scales, but homogeneous on meter-, decimeter- and centimeter-size scales. (On kilometer size scales, oxidation state is heterogeneous, but O isotopes appear to be homogeneous.) The asteroid-wide heterogeneity in oxidation state and O-isotopic composition was inherited from the solar nebula. The homogeneity on small size scales was probably caused in part by fluid-assisted metamorphism and mainly by impact-gardening processes (which are most effective at mixing target materials on scales of ⩽1 m).

Nano- to Formation-Scale Estimates of Mineral-Specific Reactive Surface Area

NASA Astrophysics Data System (ADS)

Cole, D. R.; Swift, A.; Sheets, J.; Anovitz, L. M.

2017-12-01

Predictions of changes in fluid composition, coupled with the evolution of the solid matrix, include the generation and testing of reactive transport models. However, translating a heterogeneous natural system into physical and chemical model parameters, including the critical but poorly-constrained metric of fluid-accessible surface area, continues to challenge Earth scientists. Studies of carbon storage capacity, permeability, rock strain due to mineral dissolution and precipitation, or the prediction of rock evolution through diagenesis and weathering each consider macroscale outcomes of processes that often are critically impacted by rock surface geometry at the nanoscale. The approach taken here is to consider the whole vertical extent of a saline reservoir and then to address two questions. First, what is the accessible surface area for each major mineral, and for all adjacent pore sizes from <2 nm on up, within each major lithofacies in that formation? Second, with the formation thus divided into units of analysis, parameterized, and placed into geologic context, what constraints can be placed on reactive surface area as a function of mineral composition? A complex sandstone covering a substantial fraction of the quartz-K-feldspar-illite ternary is selected and mineral-specific surface area quantified using neutron scattering, nitrogen and mercury porosimetry, multi-signal high-resolution mineral mapping, and other techniques. For neutron scattering, scale-specific pore geometries enable more accurate translation of volume into surface area. By applying this workflow to all end-member lithologies of this reservoir formation, equations and maps of surface area as a function of position on a quartz-feldspar-clay ternary plot are developed for each major mineral. Results from this work therefore advance our ability to parameterize models not just for the particular formation studied, but for similar geologic units as well.

Lipid Clustering Correlates with Membrane Curvature as Revealed by Molecular Simulations of Complex Lipid Bilayers

PubMed Central

Koldsø, Heidi; Shorthouse, David; Hélie, Jean; Sansom, Mark S. P.

2014-01-01

Cell membranes are complex multicomponent systems, which are highly heterogeneous in the lipid distribution and composition. To date, most molecular simulations have focussed on relatively simple lipid compositions, helping to inform our understanding of in vitro experimental studies. Here we describe on simulations of complex asymmetric plasma membrane model, which contains seven different lipids species including the glycolipid GM3 in the outer leaflet and the anionic lipid, phosphatidylinositol 4,5-bisphophate (PIP2), in the inner leaflet. Plasma membrane models consisting of 1500 lipids and resembling the in vivo composition were constructed and simulations were run for 5 µs. In these simulations the most striking feature was the formation of nano-clusters of GM3 within the outer leaflet. In simulations of protein interactions within a plasma membrane model, GM3, PIP2, and cholesterol all formed favorable interactions with the model α-helical protein. A larger scale simulation of a model plasma membrane containing 6000 lipid molecules revealed correlations between curvature of the bilayer surface and clustering of lipid molecules. In particular, the concave (when viewed from the extracellular side) regions of the bilayer surface were locally enriched in GM3. In summary, these simulations explore the nanoscale dynamics of model bilayers which mimic the in vivo lipid composition of mammalian plasma membranes, revealing emergent nanoscale membrane organization which may be coupled both to fluctuations in local membrane geometry and to interactions with proteins. PMID:25340788

Lipid clustering correlates with membrane curvature as revealed by molecular simulations of complex lipid bilayers.

PubMed

Koldsø, Heidi; Shorthouse, David; Hélie, Jean; Sansom, Mark S P

2014-10-01

Cell membranes are complex multicomponent systems, which are highly heterogeneous in the lipid distribution and composition. To date, most molecular simulations have focussed on relatively simple lipid compositions, helping to inform our understanding of in vitro experimental studies. Here we describe on simulations of complex asymmetric plasma membrane model, which contains seven different lipids species including the glycolipid GM3 in the outer leaflet and the anionic lipid, phosphatidylinositol 4,5-bisphophate (PIP2), in the inner leaflet. Plasma membrane models consisting of 1500 lipids and resembling the in vivo composition were constructed and simulations were run for 5 µs. In these simulations the most striking feature was the formation of nano-clusters of GM3 within the outer leaflet. In simulations of protein interactions within a plasma membrane model, GM3, PIP2, and cholesterol all formed favorable interactions with the model α-helical protein. A larger scale simulation of a model plasma membrane containing 6000 lipid molecules revealed correlations between curvature of the bilayer surface and clustering of lipid molecules. In particular, the concave (when viewed from the extracellular side) regions of the bilayer surface were locally enriched in GM3. In summary, these simulations explore the nanoscale dynamics of model bilayers which mimic the in vivo lipid composition of mammalian plasma membranes, revealing emergent nanoscale membrane organization which may be coupled both to fluctuations in local membrane geometry and to interactions with proteins.

Heterogeneity of chemokine cell-surface receptor expression in triple-negative breast cancer

PubMed Central

Norton, Kerri-Ann; Popel, Aleksander S; Pandey, Niranjan B

2015-01-01

Introduction: Tumor heterogeneity is a well-established concept in cancer research. In this paper, we examine an additional type of tumor cell heterogeneity - tumor cell-surface receptor heterogeneity. Methods: We use flow cytometry to measure the frequency and numbers of cell-surface receptors on triple negative breast cancer cell lines. Results: We find two distinct populations of human triple-negative breast cancer cells MDA-MB-231 when they are grown in culture, one with low surface levels of various chemokine receptors and a second with much higher levels. The population with high surface levels of these receptors is increased in the more metastatic MDA-MB-231-luc-d3h2ln cell line. Conclusion: We hypothesize that this high cell-surface receptor population is involved in metastasis. We find that the receptor high populations can be modulated by tumor conditioned media and IL6 treatment indicating that the tumor microenvironment is important for the maintenance and sizes of these populations. PMID:26101698

Reactions at surfaces in the atmosphere: integration of experiments and theory as necessary (but not necessarily sufficient) for predicting the physical chemistry of aerosols.

PubMed

Finlayson-Pitts, Barbara J

2009-09-28

While particles have significant deleterious impacts on human health, visibility and climate, quantitative understanding of their formation, composition and fates remains problematic. Indeed, in many cases, even qualitative understanding is lacking. One area of particular uncertainty is the nature of particle surfaces and how this determines interactions with gases in the atmosphere, including water, which is important for cloud formation and properties. The focus in this Perspective article is on some chemistry relevant to airborne particles and especially to reactions occurring on their surfaces. The intent is not to provide a comprehensive review, but rather to highlight a few selected examples of interface chemistry involving inorganic and organic species that may be important in the lower atmosphere. This includes sea salt chemistry, nitrate and nitrite ion photochemistry, organics on surfaces and heterogeneous reactions of oxides of nitrogen on proxies for airborne mineral dust and boundary layer surfaces. Emphasis is on the molecular level understanding that can only be gained by fully integrating experiment and theory to elucidate these complex systems.

Contribution of Microchemical Surface Analysis of Archaeological Artefacts

NASA Astrophysics Data System (ADS)

Mousser, H.; Madani, A.; Amri, R.; Mousser, A.; Darchen, A.

2009-11-01

Museum CIRTA of the town of Constantine has a collection of more than 35000 coins and statuettes going back to Numide, Roman, Republican, Vandal and Byzantine times and is struck in the name of the cities, of the kingdoms and the empires. Surface analysis of these coins gives information about the chemical composition and leads to recommendations for restoration and preservations. This work is a contribution of microchemical surface study of coin with the effigy of the Numide King Massinissa (Constantine between 3rd and 2nd century before Jesus Christ). The photographic and scanning electron microscopy coupled with energy dispersive spectrometry (SEM + EDS) and diffraction of X-ray (DRX) was used. The optic microscopy (OMP) and SEM pictures of coins showed heterogeneous surface. Scanning electron microscopy coupled with energy dispersive spectrometry identified three basic metals copper (46.06%), antimony (17.74%) and lead (12.06%), (Weight Percentage). The DRX identifies stages (copper and lead) and their crystalline oxides Bindheimite (Pb2Sb2O7) and Bystromite (MgSb2O6) on the coin's surface.

Novel amphiphilic poly(dimethylsiloxane) based polyurethane networks tethered with carboxybetaine and their combined antibacterial and anti-adhesive property

NASA Astrophysics Data System (ADS)

Jiang, Jingxian; Fu, Yuchen; Zhang, Qinghua; Zhan, Xiaoli; Chen, Fengqiu

2017-08-01

The traditional nonfouling materials are powerless against bacterial cells attachment, while the hydrophobic bactericidal surfaces always suffer from nonspecific protein adsorption and dead bacterial cells accumulation. Here, amphiphilic polyurethane (PU) networks modified with poly(dimethylsiloxane) (PDMS) and cationic carboxybetaine diol through simple crosslinking reaction were developed, which had an antibacterial efficiency of 97.7%. Thereafter, the hydrolysis of carboxybetaine ester into zwitterionic groups brought about anti-adhesive properties against bacteria and proteins. The surface chemical composition and wettability performance of the PU network surfaces were investigated by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and contact angle analysis. The surface distribution of PDMS and zwitterionic segments produced an obvious amphiphilic heterogeneous surface, which was demonstrated by atomic force microscopy (AFM). Enzyme-linked immunosorbent assays (ELISA) were used to test the nonspecific protein adsorption behaviors. With the advantages of the transition from excellent bactericidal performance to anti-adhesion and the combination of fouling resistance and fouling release property, the designed PDMS-based amphiphilic PU network shows great application potential in biomedical devices and marine facilities.

Heterogeneous Catalysis: On Bathroom Mirrors and Boiling Stones

ERIC Educational Resources Information Center

Philipse, Albert P.

2011-01-01

Though heterogeneous nucleation of liquid droplets on a smooth surface (such as a bathroom mirror) is a classical topic in nucleation theory, it is not well-known that this topic is actually a pedagogical example of heterogeneous catalysis: the one and only effect of the surface is to lower the activation Gibbs energy of droplet formation. In…

Fine and Coarse-Scale Patterns of Vegetation Diversity on Reclaimed Surface Mine-land Over a 40-Year Chronosequence.

PubMed

Bohrer, Stefanie L; Limb, Ryan F; Daigh, Aaron L; Volk, Jay M; Wick, Abbey F

2017-03-01

Rangelands are described as heterogeneous, due to patterning in species assemblages and productivity that arise from species dispersal and interactions with environmental gradients and disturbances across multiple scales. The objectives of rangeland reclamation are typically vegetation establishment, plant community productivity, and soil stability. However, while fine-scale diversity is often promoted through species-rich seed mixes, landscape heterogeneity and coarse-scale diversity are largely overlooked. Our objectives were to evaluate fine and coarse-scale vegetation patterns across a 40-year reclamation chronosequence on reclaimed surface coalmine lands. We hypothesized that both α-diversity and β-diversity would increase and community patch size and species dissimilarity to reference sites would decrease on independent sites over 40 years. Plant communities were surveyed on 19 post-coalmine reclaimed sites and four intact native reference sites in central North Dakota mixed-grass prairie. Our results showed no differences in α or β-diversity and plant community patch size over the 40-year chronosequence. However, both α-diversity and β-diversity on reclaimed sites was similar to reference sites. Native species establishment was limited due to the presence of non-native species such as Kentucky bluegrass (Poa pratensis) on both the reclaimed and reference sites. Species composition was different between reclaimed and reference sites and community dissimilarity increased on reclaimed sites over the 40-year chronosequence. Plant communities resulting from reclamation followed non-equilibrium succession, even with consistent seeds mixes established across all reclaimed years. This suggests post-reclamation management strategies influence species composition outcomes and land management strategies applied uniformly may not increase landscape-level diversity.

Microwave absorption properties of polypyrrole-SrFe12O19-TiO2-epoxy resin nanocomposites: Optimization using response surface methodology

NASA Astrophysics Data System (ADS)

Seyed Dorraji, M. S.; Rasoulifard, M. H.; Amani-Ghadim, A. R.; Khodabandeloo, M. H.; Felekari, M.; Khoshrou, M. R.; hajimiri, I.

2016-10-01

At a few works are discussed about formation of heterogeneous composites with different distribution of particle shape and size that are used for electromagnetic absorption purposes. In this study a novel heterogeneous nanocpmposites is investigated. The nanocomposite has been successfully prepared based on epoxy resin including various nano-metal oxides (TiO2, SrFe12O19) and polypyrrole (PPy) by sol-gel and the solution chemistry method, respectively. The performance of prepared nanocomposite in absorption of microwave in X-band range was investigated and transmission line method by X-band waveguide straight was used to measure EM parameters of nanocomposites. The Response surface methodology (RSM) with central composite design (CCD) was utilized to study the effects of the wt.% TiO2 in SrFe12O19, wt.% Tio2-SrFe12O19 in PPy and wt.% TiO2-SrFe12O19-PPy in epoxy resin, on the microwave absorption properties with the absorber thickness of only 2 mm. The proposed quadratic model was in accordance with the experimental results with correlation coefficient of 96.5%. The optimum condition for maximum microwave absorption efficiency were wt.% TiO2 in SrFe12O19 of 70, wt.% TiO2-SrFe12O19 in PPy of 10 and wt.% TiO2-SrFe12O19-PPy in epoxy of 25. The sample prepared in optimal conditions indicated reflection loss of -15 dB corresponding to 97% absorption, at the range of 9.2-10.8 GHz.

Large-scale Generation of Patterned Bubble Arrays on Printed Bi-functional Boiling Surfaces

PubMed Central

Choi, Chang-Ho; David, Michele; Gao, Zhongwei; Chang, Alvin; Allen, Marshall; Wang, Hailei; Chang, Chih-hung

2016-01-01

Bubble nucleation control, growth and departure dynamics is important in understanding boiling phenomena and enhancing nucleate boiling heat transfer performance. We report a novel bi-functional heterogeneous surface structure that is capable of tuning bubble nucleation, growth and departure dynamics. For the fabrication of the surface, hydrophobic polymer dot arrays are first printed on a substrate, followed by hydrophilic ZnO nanostructure deposition via microreactor-assisted nanomaterial deposition (MAND) processing. Wettability contrast between the hydrophobic polymer dot arrays and aqueous ZnO solution allows for the fabrication of heterogeneous surfaces with distinct wettability regions. Heterogeneous surfaces with various configurations were fabricated and their bubble dynamics were examined at elevated heat flux, revealing various nucleate boiling phenomena. In particular, aligned and patterned bubbles with a tunable departure frequency and diameter were demonstrated in a boiling experiment for the first time. Taking advantage of our fabrication method, a 6 inch wafer size heterogeneous surface was prepared. Pool boiling experiments were also performed to demonstrate a heat flux enhancement up to 3X at the same surface superheat using bi-functional surfaces, compared to a bare stainless steel surface. PMID:27034255

Characterisation of ground motion recording stations in the Groningen gas field

NASA Astrophysics Data System (ADS)

Noorlandt, Rik; Kruiver, Pauline P.; de Kleine, Marco P. E.; Karaoulis, Marios; de Lange, Ger; Di Matteo, Antonio; von Ketelhodt, Julius; Ruigrok, Elmer; Edwards, Benjamin; Rodriguez-Marek, Adrian; Bommer, Julian J.; van Elk, Jan; Doornhof, Dirk

2018-05-01

The seismic hazard and risk analysis for the onshore Groningen gas field requires information about local soil properties, in particular shear-wave velocity ( V S). A fieldwork campaign was conducted at 18 surface accelerograph stations of the monitoring network. The subsurface in the region consists of unconsolidated sediments and is heterogeneous in composition and properties. A range of different methods was applied to acquire in situ V S values to a target depth of at least 30 m. The techniques include seismic cone penetration tests (SCPT) with varying source offsets, multichannel analysis of surface waves (MASW) on Rayleigh waves with different processing approaches, microtremor array, cross-hole tomography and suspension P-S logging. The offset SCPT, cross-hole tomography and common midpoint cross-correlation (CMPcc) processing of MASW data all revealed lateral variations on length scales of several to tens of metres in this geological setting. SCPTs resulted in very detailed V S profiles with depth, but represent point measurements in a heterogeneous environment. The MASW results represent V S information on a larger spatial scale and smooth some of the heterogeneity encountered at the sites. The combination of MASW and SCPT proved to be a powerful and cost-effective approach in determining representative V S profiles at the accelerograph station sites. The measured V S profiles correspond well with the modelled profiles and they significantly enhance the ground motion model derivation. The similarity between the theoretical transfer function from the V S profile and the observed amplification from vertical array stations is also excellent.

Characterisation of ground motion recording stations in the Groningen gas field

NASA Astrophysics Data System (ADS)

Noorlandt, Rik; Kruiver, Pauline P.; de Kleine, Marco P. E.; Karaoulis, Marios; de Lange, Ger; Di Matteo, Antonio; von Ketelhodt, Julius; Ruigrok, Elmer; Edwards, Benjamin; Rodriguez-Marek, Adrian; Bommer, Julian J.; van Elk, Jan; Doornhof, Dirk

2018-01-01

The seismic hazard and risk analysis for the onshore Groningen gas field requires information about local soil properties, in particular shear-wave velocity (V S). A fieldwork campaign was conducted at 18 surface accelerograph stations of the monitoring network. The subsurface in the region consists of unconsolidated sediments and is heterogeneous in composition and properties. A range of different methods was applied to acquire in situ V S values to a target depth of at least 30 m. The techniques include seismic cone penetration tests (SCPT) with varying source offsets, multichannel analysis of surface waves (MASW) on Rayleigh waves with different processing approaches, microtremor array, cross-hole tomography and suspension P-S logging. The offset SCPT, cross-hole tomography and common midpoint cross-correlation (CMPcc) processing of MASW data all revealed lateral variations on length scales of several to tens of metres in this geological setting. SCPTs resulted in very detailed V S profiles with depth, but represent point measurements in a heterogeneous environment. The MASW results represent V S information on a larger spatial scale and smooth some of the heterogeneity encountered at the sites. The combination of MASW and SCPT proved to be a powerful and cost-effective approach in determining representative V S profiles at the accelerograph station sites. The measured V S profiles correspond well with the modelled profiles and they significantly enhance the ground motion model derivation. The similarity between the theoretical transfer function from the V S profile and the observed amplification from vertical array stations is also excellent.

Transient Creep of a Composite Lower Crust. 1; Constitutive Theory

NASA Technical Reports Server (NTRS)

Ivins, Erik R.; Sammis, Charles G.

1996-01-01

A composite model is proposed to describe the time-dependent response of the Earth's lower crust. The motivation for such it model is twofold: First, new observations of widespread postseismic deformation indicate that the deep continental crust responds viscoelastically, having both long-and short-term decay times. Second, by any number of observationally based rationales, the lower crust is compositionally and structurally heterogeneous over many length scales. For heterogeneities that have much smaller characteristic lengths than the minimum deformation wavelength of interest, the aggregate rheology can be described by composite media theory. For wavelengths of the order of the thickness of the lower crust (approx. = 25-40 km) and larger, composite theory may be applied to heterogeneities that are smaller than about several hundred meters, or equivalent to the vertical extent of a thick lower crustal mylonitic shear zone. The composite media theory developed here is constructed using both Eshelhy-Mori-Tanaka theory for aligned generalized spheroidal inclusions and a generalized self-consistent method. The inclusions and matrix are considered to be Maxwellian viscoelastic: a rheology that is consistent with past homogeneous models of postseismic stress relaxation. The composite theory presented here introduces a transient response to a suddenly imposed stress field which does not appear in homogeneous Maxwell models. Analytic expressions for the amplitude and duration of the transient and for the effective long-and short-term viscosities of the composite are given which describe the sensitivity to inclusion concentration (phi), to shape, and to ratio of inclusion-to-matrix viscosity (R).

Degradation of chlorinated organic solvents in aqueous percarbonate system using zeolite supported nano zero valent iron (Z-nZVI) composite.

PubMed

Danish, Muhammad; Gu, Xiaogang; Lu, Shuguang; Naqvi, Muhammad

2016-07-01

Chlorinated organic solvents (COSs) are extensively detected in contaminated soil and groundwater that pose long-term threats to human life and environment. In order to degrade COSs effectively, a novel catalytic composite of natural zeolite-supported nano zero valent iron (Z-nZVI) was synthesized in this study. The performance of Z-nZVI-catalyzed sodium percarbonate (SPC) in a heterogeneous Fenton-like system was investigated for the degradation of COSs such as 1,1,1-trichloroethane (1,1,1-TCA) and trichloroethylene (TCE). The surface characteristics and morphology of the Z-nZVI composite were tested using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Total pore volume, specific surface area, and pore size of the natural zeolite and the Z-nZVI composite were measured using Brunauer-Emmett-Teller (BET) method. SEM and TEM analysis showed significant elimination of aggregation and well dispersion of iron nano particles on the framework of natural zeolite. The BET N2 measurement analysis indicated that the surface area of the Z-nZVI composite was 72.3 m(2)/g, much larger than that of the natural zeolite (0.61 m(2)/g). For the contaminant analysis, the samples were extracted with n-hexane and analyzed through gas chromatograph. The degradation of 1,1,1-TCA and TCE in the Z-nZVI-catalyzed percarbonate system were 48 and 39 % respectively, while strong augmentation was observed up to 83 and 99 %, respectively, by adding the reducing agent (RA), hydroxyl amine (NH2OH•HCl). Probe tests validated the presence of OH(●) and O2 (●-) which were responsible for 1,1,1-TCA and TCE degradation, whereas both free radicals were strengthened with the addition of RA. In conclusion, the Z-nZVI/SPC oxidation with reducing agent shows potential technique for degradation of groundwater contaminated by 1,1,1-TCA and TCE.

An LES study on the spatial variability impact of surface sensible heat flux (SHF) on the convective boundary layer (CBL)

NASA Astrophysics Data System (ADS)

Kang, S. L.; Chun, J.; Kumar, A.

2015-12-01

We study the spatial variability impact of surface sensible heat flux (SHF) on the convective boundary layer (CBL), using the Weather Research and Forecasting (WRF) model in large eddy simulation (LES) mode. In order to investigate the response of the CBL to multi-scale feature of the surface SHF field over a local area of several tens of kilometers or smaller, an analytic surface SHF map is crated as a function of the chosen feature. The spatial variation in the SHF map is prescribed with a two-dimensional analytical perturbation field, which is generated by using the inverse transform technique of the Fourier series whose coefficients are controlled, of which spectrum to have a particular slope in the chosen range of wavelength. Then, the CBL responses to various SHF heterogeneities are summarized as a function of the spectral slope, in terms of mean structure, turbulence statistics and cross-scale processes. The range of feasible SHF heterogeneities is obtained from the SHF maps produced by a land surface model (LSM) of the WRF system. The LSM-derived SHF maps are a function of geographical data on various resolutions. Based on the numerical experiment results with the surface heterogeneities in the range, we will discuss the uncertainty in the SHF heterogeneity and its impact on the atmosphere in a numerical model. Also we will present the range of spatial scale of the surface SHF heterogeneity that significantly influence on the whole CBL. Lastly, we will report the test result of the hypothesis that the spatial variability of SHF is more representative of surface thermal heterogeneity than is the latent heat flux over the local area of several tens of kilometers or smaller.

Monsoon Circulations and Tropical Heterogeneous Chlorine Chemistry in the Stratosphere

NASA Astrophysics Data System (ADS)

Kinnison, Doug; Solomon, Susan; Garcia, Rolando; Bandoro, Justin; Wilka, Catherine; Neeley, Ryan, III; Schmidt, Anja; Barnes, John; Vernier, Jean-Paul; Höpfner, Michael; Mills, Michael

2017-04-01

Heterogeneous chlorine chemistry on and in liquid polar stratospheric particles is thought to play a significant role in polar and subpolar ozone depletion. Previous studies have not provided evidence for heterogeneous chlorine chemistry occurring in the tropical stratosphere. Using the current best understanding of liquid stratospheric particle chemistry in a state-of-the-art numerical model, we examine whether such processes should be expected to affect tropical composition, particularly at and slightly above the cold tropical tropopause, in association with the Asian and North American summer (June-July-August) monsoons. The Specified Dynamics version of the Community Earth System Model version 1 (CESM1) Whole Atmosphere Community Climate Model (WACCM) is used in this study. This model is nudged to externally specified dynamical fields for temperature, zonal and meridional winds, and surface pressure fields from the NASA Modern Era Retrospective Analysis for Research and Applications (MERRA). Model simulations suggest that transport processes associated with the summer monsoons bring increased abundances of hydrochloric acid (HCl) into contact with liquid sulfate aerosols in the cold tropical lowermost stratosphere, leading to heterogeneous chemical activation of chlorine species. The calculations indicate that the spatial and seasonal distributions of chlorine monoxide (ClO) and chlorine nitrate (ClONO2) near the monsoon regions of the northern hemisphere tropical and subtropical lowermost stratosphere could provide indicators of heterogeneous chlorine processing. In the model, these processes impact the local ozone budget and decrease ozone abundances, implying a chemical contribution to longer-term northern tropical ozone profile changes at 16-19 km.

Chemical and physical characterization of fertile soil-derived ice residuals from the Fifth International Ice Nucleation workshop in November 2014 (FIN-1)

NASA Astrophysics Data System (ADS)

Hiranuma, Naruki; Möhler, Ottmar; Kulkarni, Gourihar; Laskin, Alexander; Zelenyuk, Alla

2017-04-01

The climate impact of ice-nucleating particles (INPs) derived from fertile soils on global scale has been recently accented by their diversity and efficient freezing ability. However, their representation in atmospheric models is limited in part due to our incomplete knowledge of fertile soil composition, abundance and associated sensitivity to heterogeneous ice nucleation. To fill given knowledge gap, we have investigated a unique/rich set of ice crystal residual samples derived from a variety of fertile soil samples obtained through our participation in the Fifth International Ice Nucleation workshop (FIN-1). FIN-1 was held at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) facility at Karlsruhe Institute of Technology (KIT), which is the world's foremost facility for studying ice clouds in a controlled setting, in November 2014 to comprehensively study the heterogeneous ice formation in the atmosphere with collaboration among 10 international groups that were funded through European consortium, NSF and USDOE agencies. Here, we will present the nanoscale surface morphology and elemental/molecular composition of ice crystal residuals as well as that of total aerosol samples from the FIN-1 activity to identify and classify any specific mineral and organic inclusions that may have promoted nucleation of ice. Comparing total aerosols to residuals will shed light on the composition and abundance of certain particle types in INPs. Acknowledgements: The valuable contributions of the INUIT (Ice Nuclei Research Unit) collaborators, the FIN organizers, their institutions and the FIN-1 Workshop science team are gratefully acknowledged.

Heterogeneity of Microbiota Dysbiosis in Chronic Rhinosinusitis: Potential Clinical Implications and Microbial Community Mechanisms Contributing to Sinonasal Inflammation.

PubMed

Lee, Keehoon; Pletcher, Steven D; Lynch, Susan V; Goldberg, Andrew N; Cope, Emily K

2018-01-01

Recent studies leveraging next-generation sequencing and functional approaches to understand the human microbiota have demonstrated the presence of diverse, niche-specific microbial communities at nearly every mucosal surface. These microbes contribute to the development and function of physiologic and immunological features that are key to host health status. Not surprisingly, several chronic inflammatory diseases have been attributed to dysbiosis of microbiota composition or function, including chronic rhinosinusitis (CRS). CRS is a heterogeneous disease characterized by inflammation of the sinonasal cavity and mucosal microbiota dysbiosis. Inflammatory phenotypes and bacterial community compositions vary considerably across individuals with CRS, complicating current studies that seek to address causality of a dysbiotic microbiome as a driver or initiator of persistent sinonasal inflammation. Murine models have provided some experimental evidence that alterations in local microbial communities and microbially-produced metabolites influence health status. In this perspective, we will discuss the clinical implications of distinct microbial compositions and community-level functions in CRS and how mucosal microbiota relate to the diverse inflammatory endotypes that are frequently observed. We will also describe specific microbial interactions that can deterministically shape the pattern of co-colonizers and the resulting metabolic products that drive or exacerbate host inflammation. These findings are discussed in the context of CRS-associated inflammation and in other chronic inflammatory diseases that share features observed in CRS. An improved understanding of CRS patient stratification offers the opportunity to personalize therapeutic regimens and to design novel treatments aimed at manipulation of the disease-associated microbiota to restore sinus health.

Membrane adhesion and the formation of heterogeneities: biology, biophysics, and biotechnology.

PubMed

Gordon, V D; O'Halloran, T J; Shindell, O

2015-06-28

Membrane adhesion is essential to many vital biological processes. Sites of membrane adhesion are often associated with heterogeneities in the lipid and protein composition of the membrane. These heterogeneities are thought to play functional roles by facilitating interactions between proteins. However, the causal links between membrane adhesion and membrane heterogeneities are not known. Here we survey the state of the field and indicate what we think are understudied areas ripe for development.

Roughness Versus Charge Contributions to Representative Discrete Heterogeneity Underlying Mechanistic Prediction of Colloid Attachment, Detachment and Breakthrough-Elution Behavior Under Environmental Conditions.

NASA Astrophysics Data System (ADS)

Johnson, William; Farnsworth, Anna; Vanness, Kurt; Hilpert, Markus

2017-04-01

The key element of a mechanistic theory to predict colloid attachment in porous media under environmental conditions where colloid-collector repulsion exists (unfavorable conditions for attachment) is representation of the nano-scale surface heterogeneity (herein called discrete heterogeneity) that drives colloid attachment under unfavorable conditions. The observed modes of colloid attachment under unfavorable conditions emerge from simulations that incorporate discrete heterogeneity. Quantitative prediction of attachment (and detachment) requires capturing the sizes, spatial frequencies, and other properties of roughness asperities and charge heterodomains in discrete heterogeneity representations of different surfaces. The fact that a given discrete heterogeneity representation will interact differently with different-sized colloids as well as different ionic strengths for a given sized colloid allows backing out representative discrete heterogeneity via comparison of simulations to experiments performed across a range of colloid size, solution IS, and fluid velocity. This has been achieved on unfavorable smooth surfaces yielding quantitative prediction of attachment, and qualitative prediction of detachment in response to ionic strength or flow perturbations. Extending this treatment to rough surfaces, and representing the contributions of nanoscale roughness as well as charge heterogeneity is a focus of this talk. Another focus of this talk is the upscaling the pore scale simulations to produce contrasting breakthrough-elution behaviors at the continuum (column) scale that are observed, for example, for different-sized colloids, or same-sized colloids under different ionic strength conditions. The outcome of mechanistic pore scale simulations incorporating discrete heterogeneity and subsequent upscaling is that temporal processes such as blocking and ripening will emerge organically from these simulations, since these processes fundamentally stem from the limited sites available for attachment as represented in discrete heterogeneity.

Super-Resolution Microscopy Unveils Dynamic Heterogeneities in Nanoparticle Protein Corona.

PubMed

Feiner-Gracia, Natalia; Beck, Michaela; Pujals, Sílvia; Tosi, Sébastien; Mandal, Tamoghna; Buske, Christian; Linden, Mika; Albertazzi, Lorenzo

2017-11-01

The adsorption of serum proteins, leading to the formation of a biomolecular corona, is a key determinant of the biological identity of nanoparticles in vivo. Therefore, gaining knowledge on the formation, composition, and temporal evolution of the corona is of utmost importance for the development of nanoparticle-based therapies. Here, it is shown that the use of super-resolution optical microscopy enables the imaging of the protein corona on mesoporous silica nanoparticles with single protein sensitivity. Particle-by-particle quantification reveals a significant heterogeneity in protein absorption under native conditions. Moreover, the diversity of the corona evolves over time depending on the surface chemistry and degradability of the particles. This paper investigates the consequences of protein adsorption for specific cell targeting by antibody-functionalized nanoparticles providing a detailed understanding of corona-activity relations. The methodology is widely applicable to a variety of nanostructures and complements the existing ensemble approaches for protein corona study. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Measurements of spatially resolved velocity variations in shock compressed heterogeneous materials using a line-imaging velocity interferometer

NASA Astrophysics Data System (ADS)

Trott, Wayne M.; Knudson, Marcus D.; Chhabildas, Lalit C.; Asay, James R.

2000-04-01

Relatively straightforward changes in the design of a conventional optically recording velocity interferometer system (ORVIS) can be used to produce a line-imaging instrument that allows adjustment of spatial resolution over a wide range. As a result, line-imaging ORVIS can be tailored to various specific applications involving dynamic deformation of heterogeneous materials as required by their characteristic length scales (ranging from a few μm for ferroelectric ceramics to a few mm for concrete). A line-imaging system has been successfully interfaced to a compressed gas gun driver and fielded on numerous tests in combination with simultaneous dual delay-leg, "push-pull" VISAR measurements. These tests include shock loading of glass-reinforced polyester composites, foam reverberation experiments (measurements at the free surface of a thin aluminum plate impacted by foam), and measurements of dispersive velocity in a shock-loaded explosive simulant (sugar). Results are presented that illustrate the capability for recording detailed spatially resolved material response.

Rapid passage of a small-scale mantle heterogeneity through the melting regions of Kilauea and Mauna Loa Volcanoes

NASA Astrophysics Data System (ADS)

Marske, Jared P.; Pietruszka, Aaron J.; Weis, Dominique; Garcia, Michael O.; Rhodes, J. Michael

2007-07-01

Recent Kilauea and Mauna Loa lavas provide a snapshot of the size, shape, and distribution of compositional heterogeneities within the Hawaiian mantle plume. Here we present a study of the Pb, Sr, and Nd isotope ratios of two suites of young prehistoric lavas from these volcanoes: (1) Kilauea summit lavas erupted from AD 900 to 1400, and (2) 14C-dated Mauna Loa flows erupted from ˜ 2580-140 yr before present (relative to AD 1950). These lavas display systematic isotopic fluctuations, and the Kilauea lavas span the Pb isotopic divide that was previously thought to exist between these two volcanoes. For a brief period from AD 250 to 1400, the 206Pb/ 204Pb and 87Sr/ 86Sr isotope ratios and ɛNd values of Kilauea and Mauna Loa lavas departed from values typical for each volcano (based on historical and other young prehistoric lavas), moved towards an intermediate composition, and subsequently returned to typical values. This is the only known period in the eruptive history of these volcanoes when such a simultaneous convergence of Pb, Sr, and Nd isotope ratios has occurred. The common isotopic composition of lavas erupted from both Kilauea and Mauna Loa during this transient magmatic event was probably caused by the rapid passage of a small-scale compositional heterogeneity through the melting regions of both volcanoes. This heterogeneity is thought to have been either a single body (˜ 35 km long based on the distance between the summits of these volcanoes) or the plume matrix itself (which would be expected to be present beneath both volcanoes). The time scale of this event (centuries) is much shorter than previously noted for variations in the isotopic composition of Hawaiian lavas due to the upwelling of heterogeneities within the plume (thousands to tens of thousands of years). Calculations based on the timing of the isotopic convergence suggest a maximum thickness for the melting region (and thus, the heterogeneity) of ˜ 5-10 km. The small size of the heterogeneity indicates that melt can be extracted from small regions within the Hawaiian plume with minimal subsequent chemical modification (beyond the effects of crystal fractionation). This would be most effective if melt transport in the mantle beneath Hawaiian shield volcanoes occurs mostly in chemically isolated channels.

Metal oxides, clay minerals and charcoal determine the composition of microbial communities in matured artificial soils and their response to phenanthrene.

PubMed

Babin, Doreen; Ding, Guo-Chun; Pronk, Geertje Johanna; Heister, Katja; Kögel-Knabner, Ingrid; Smalla, Kornelia

2013-10-01

Microbial communities in soil reside in a highly heterogeneous habitat where diverse mineral surfaces, complex organic matter and microorganisms interact with each other. This study aimed to elucidate the long-term effect of the soil mineral composition and charcoal on the microbial community composition established in matured artificial soils and their response to phenanthrene. One year after adding sterile manure to different artificial soils and inoculating microorganisms from a Cambisol, the matured soils were spiked with phenanthrene or not and incubated for another 70 days. 16S rRNA gene and internal transcribed spacer fragments amplified from total community DNA were analyzed by denaturing gradient gel electrophoresis. Metal oxides and clay minerals and to a lesser extent charcoal influenced the microbial community composition. Changes in the bacterial community composition in response to phenanthrene differed depending on the mineral composition and presence of charcoal, while no shifts in the fungal community composition were observed. The abundance of ring-hydroxylating dioxygenase genes was increased in phenanthrene-spiked soils except for charcoal-containing soils. Here we show that the formation of biogeochemical interfaces in soil is an ongoing process and that different properties present in artificial soils influenced the bacterial response to the phenanthrene spike. © 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

The Extraterrestrial Materials Simulation Laboratory

NASA Technical Reports Server (NTRS)

Green, J. R.

2001-01-01

In contrast to fly-by and orbital missions, in situ missions face an incredible array of challenges in near-target navigation, landing site selection, descent, landing, science operations, sample collection and handling, drilling, anchoring, subsurface descent, communications, and contamination. The wide range of materials characteristics and environments threaten mission safety and success. For example, many physical properties are poorly characterized, including strength, composition, heterogeneity, phase change, texture, thermal properties, terrain features, atmospheric interaction, and stratigraphy. Examples of the range of materials properties include, for example: (1) Comets, with a possible compressive strength ranging from a light fluff to harder than concrete: 10(exp 2) to 10 (exp 8) Pa; (2) Europa, including a possible phase change at the surface, unknown strength and terrain roughness; and (3) Titan, with a completely unknown surface and possible liquid ocean. Additional information is contained in the original extended abstract.

Planetary Accretion, Oxygen Isotopes and the Central Limit Theorem

NASA Technical Reports Server (NTRS)

Nuth, Joseph A., III; Hill, Hugh G. M.; Vondrak, Richard R. (Technical Monitor)

2001-01-01

The accumulation of presolar dust into increasingly larger aggregates (CAIs and Chondrules, Asteroids, Planets) should result in a very drastic reduction in the numerical spread in oxygen isotopic composition between bodies of similar size, in accord with the Central Limit Theorem. Observed variations in oxygen isotopic composition are many orders of magnitude larger than would be predicted by a simple, random accumulation model that begins in a well-mixed nebula - no matter which size-scale objects are used as the beginning or end points of the calculation. This discrepancy implies either that some as yet unspecified process acted on the solids in the Solar Nebula to increase the spread in oxygen isotopic composition during each and every stage of accumulation or that the nebula was heterogeneous and maintained this heterogeneity throughout most of nebular history. Large-scale nebular heterogeneity would have significant consequences for many areas of cosmochemistry, including the application of some well-known isotopic systems to the dating of nebular events or the prediction of bulk compositions of planetary bodies on the basis of a uniform cosmic abundance.

Synthesis of low-size flower-like AlOOH structures

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

Bakina, Olga V., E-mail: ovbakina@ispms.tsc.ru, E-mail: eagl@ispms.tsc.ru; Glazkova, Elena A., E-mail: ovbakina@ispms.tsc.ru, E-mail: eagl@ispms.tsc.ru; Lozhkomoev, Aleksandr S., E-mail: asl@ispms.tsc.ru

Al/Cu, Al/Zn, and Al/Fe bimetallic nanoparticles have been obtained using the method of simultaneous electrical explosion of metal pairs in an argon atmosphere. The nanoparticles are chemically active and interact with water at 60°C forming flower-like hierarchical porous structures with a high specific surface area. As the Al/Cu nanopowder is oxidized with water, flower-like pseudoboehmite composite structures are formed with the size of under 1.0 μm; structurally heterogeneous electron-dense spherical inclusions of unreacted metal copper and intermetallides are identified inside them. Al/Fe product transformations are presented by the flower-like pseudoboehmite surrounded by lamellar structures enriched with ferric oxides. Al/Zn nanoparticlesmore » react with water, forming the flower-like pseudoboehmite and mainly hexagonal zinc oxide laminae. The composite particles obtained can be used as antibacterial agents in manufacturing medical supplies.« less

Cytoplasmic Dynein Regulation by Subunit Heterogeneity and Its Role in Apical Transport

PubMed Central

Tai, Andrew W.; Chuang, Jen-Zen; Sung, Ching-Hwa

2001-01-01

Despite the existence of multiple subunit isoforms for the microtubule motor cytoplasmic dynein, it has not yet been directly shown that dynein complexes with different compositions exhibit different properties. The 14-kD dynein light chain Tctex-1, but not its homologue RP3, binds directly to rhodopsin's cytoplasmic COOH-terminal tail, which encodes an apical targeting determinant in polarized epithelial Madin-Darby canine kidney (MDCK) cells. We demonstrate that Tctex-1 and RP3 compete for binding to dynein intermediate chain and that overexpressed RP3 displaces endogenous Tctex-1 from dynein complexes in MDCK cells. Furthermore, replacement of Tctex-1 by RP3 selectively disrupts the translocation of rhodopsin to the MDCK apical surface. These results directly show that cytoplasmic dynein function can be regulated by its subunit composition and that cytoplasmic dynein is essential for at least one mode of apical transport in polarized epithelia. PMID:11425878

Analysis of Košice Meteorite by Mössbauer Spectroscopy

NASA Astrophysics Data System (ADS)

Sitek, Jozef; Dekan, Július; Sedlačková, Katarína

2016-07-01

The 57Fe Mössbauer spectroscopy method was used to investigate iron-containing compounds in town Košice meteorite fallen on the territory of Slovakia in February 2010. The results showed that the Mössbauer spectra consisted of magnetic and non-magnetic components related to different iron-bearing phases. The non-magnetic phase includes olivine, pyroxene and traces of Fe3+ phase and the magnetic component comprises troilite (FeS) and iron-rich Fe-Ni alloy with hyperfine magnetic field typical for kamacite. Samples from meteorite were obtained in powder from different depths to inspect its heterogeneous composition. The content of kamacite increases to the detriment of troilite from the surface toward the centre of the sample. Measurements at liquid nitrogen temperature confirmed phase composition of investigated meteorite. Main constituent elements of studied samples were also determined by X-ray fluorescence analysis.

Microbial Functional Potential and Community Composition in Permafrost-Affected Soils of the NW Canadian Arctic

PubMed Central

Frank-Fahle, Béatrice A.; Yergeau, Étienne; Greer, Charles W.; Lantuit, Hugues; Wagner, Dirk

2014-01-01

Permafrost-affected soils are among the most obvious ecosystems in which current microbial controls on organic matter decomposition are changing as a result of global warming. Warmer conditions in polygonal tundra will lead to a deepening of the seasonal active layer, provoking changes in microbial processes and possibly resulting in exacerbated carbon degradation under increasing anoxic conditions. To identify current microbial assemblages in carbon rich, water saturated permafrost environments, four polygonal tundra sites were investigated on Herschel Island and the Yukon Coast, Western Canadian Arctic. Ion Torrent sequencing of bacterial and archaeal 16S rRNA amplicons revealed the presence of all major microbial soil groups and indicated a local, vertical heterogeneity of the polygonal tundra soil community with increasing depth. Microbial diversity was found to be highest in the surface layers, decreasing towards the permafrost table. Quantitative PCR analysis of functional genes involved in carbon and nitrogen-cycling revealed a high functional potential in the surface layers, decreasing with increasing active layer depth. We observed that soil properties driving microbial diversity and functional potential varied in each study site. These results highlight the small-scale heterogeneity of geomorphologically comparable sites, greatly restricting generalizations about the fate of permafrost-affected environments in a warming Arctic. PMID:24416279

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

Bonamici, Chloë E.; Kinman, William S.; Fournelle, John H.

Reprocessed earth material is a glassy nuclear fallout debris from near-surface nuclear tests. A geochemical approach to analysis of glassy fallout is uniquely suited to determine the means of reprocessing and shed light on the mechanisms of fallout formation. An improved understanding of fallout formation is of interest both for its potential to guide post-detonation nuclear forensic investigations and in the context of possible affinities between glassy debris and other glasses generated by high-energy natural events, such as meteorite impacts and lightning strikes. Our study presents a large major-element compositional dataset for glasses within aerodynamic fallout from the Trinity nuclearmore » test (“trinitite”) and a geochemically based analysis of the glass compositional trends. Silica-rich and alkali-rich trinitite glasses show compositions and textures consistent with formation through melting of individual mineral grains—quartz and alkali feldspar, respectively—from the test-site sediment. Furthermore, the volumetrically dominant glass phase—called the CaMgFe glass—shows extreme major-element compositional variability. Compositional trends in the CaMgFe glass are most consistent with formation through volatility-controlled condensation from compositionally heterogeneous plasma. Radioactivity occurs only in CaMgFe glass, indicating that co-condensation of evaporated bulk ground material and trace device material was the main mechanism of radioisotope incorporation into trinitite. CaMgFe trinitite glasses overlap compositionally with basalts, rhyolites, fulgurites, tektites, and microtektites but display greater compositional diversity than all of these naturally formed glasses. Indeed, the most refractory CaMgFe glasses compositionally resemble early solar system condensates—specifically, CAIs.« less

Science and Reconnaissance from the Europa Clipper Mission Concept: Exploring Europa's Habitability

NASA Astrophysics Data System (ADS)

Senske, D.; Pappalardo, R. T.; Prockter, L. M.; Paczkowski, B.; Vance, S.; Goldstein, B.; Magner, T. J.; Cooke, B.

2014-12-01

Europa is a prime candidate to search for a present-day habitable environment in our solar system. As such, NASA has engaged a Science Definition Team (SDT) to define a strategy to advance our scientific understanding of this icy world with the goal: Explore Europa to investigate its habitability. A mission architecture is defined where a spacecraft in Jupiter orbit would make many close flybys of Europa, concentrating on remote sensing to explore the moon. The spacecraft trajectory would permit ~45 flybys at a variety of latitudes and longitudes, enabling globally distributed regional coverage of Europa's surface. This concept is known as the Europa Clipper. The SDT recommended three science objectives for the Europa Clipper: Ice Shell and Ocean--Characterize the ice shell and any subsurface water, including their heterogeneity, ocean properties, and the nature of surface-ice-ocean exchange; Composition--Understand the habitability of Europa's ocean through composition and chemistry; Geology--Understand the formation of surface features, including sites of recent or current activity, and characterize high science interest localities. The SDT also considered implications of the recent HST detection of plumes at Europa. To feed forward to potential future exploration that could be enabled by a lander, it was deemed that the Clipper should provide the capability to perform reconnaissance. In consultation with NASA Headquarters, the SDT developed a reconnaissance goal: Characterize Scientifically Compelling Sites, and Hazards, for a Potential Future Landed Mission to Europa. This leads to two objectives: Site Safety--Assess the distribution of surface hazards, the load-bearing capacity of the surface, the structure of the subsurface, and the regolith thickness; Science Value--Assess the composition of surface materials, the geologic context of the surface, the potential for geological activity, the proximity of near surface water, and the potential for active upwelling of ocean material. The Clipper concept provides an efficient means to explore Europa and investigate its habitability. Development of the mission concept is ongoing with current studies focusing on spacecraft design trades and refinements, launch vehicle options (EELV and SLS), and power source (MMRTG and solar), to name a few.

An upscaled rate law for magnesite dissolution in heterogeneous porous media

NASA Astrophysics Data System (ADS)

Wen, Hang; Li, Li

2017-08-01

Spatial heterogeneity in natural subsurface systems governs water fluxes and residence time in reactive zones and therefore determines effective rates of mineral dissolution. Extensive studies have documented mineral dissolution rates in natural systems, although a general rate law has remain elusive. Here we fill this gap by answering two questions: (1) how and to what extent does spatial heterogeneity affect water residence time and effectively-dissolving surface area? (2) what is the upscaled rate law that quantifies effective dissolution rates in natural, heterogeneous media? With data constraints from experimental work, 240 Monte-Carlo numerical experiments of magnesite dissolution within quartz matrix were run with spatial distributions characterized by a range of permeability variance σ2lnκ (0.5-6.0) and correlation length (2-50 cm). Although the total surface area and global residence time (τa) are the same in all experiments, the water fluxes through reactive magnesite zones varies between 0.7 and 72.8% of the total water fluxes. Highly heterogeneous media with large σ2lnκ and long λ divert water mostly into non-reactive preferential flow paths, therefore bypassing and minimizing flow in low permeability magnesite zones. As a result, the water residence time in magnesite zones (i.e., reactive residence time τa,r) is long and magnesite dissolution quickly reaches local equilibrium, which leads to small effective surface area and low dissolution rates. Magnesite dissolution rates in heterogeneous media vary from 2.7 to 100% of the rates in the equivalent homogeneous media, with effectively-dissolving surface area varying from 0.18 to 6.83 m2 (out of 51.71 m2 total magnesite surface area). Based on 240 numerical experiments and 45 column experiments, a general upscaled rate law in heterogeneous media, RMgCO3,ht =kAe,hm(1 - exp(-τa/τa,r))α, was derived to quantify effective dissolution rates. The dissolution rates in heterogeneous media are a function of the rate constants k being those measured under well-mixed conditions, effective surface area in equivalent homogeneous media Ae,hm, and the heterogeneity factor (1 - exp(-τa/τa,r))α. The heterogeneity factor quantify heterogeneity effects and depends on the relative magnitude of global residence time (τa) and reactive residence time (τa,r), as well as the shape factor α(= 5 σlnκ2) of the gamma distribution for reactive residence times. Exponential forms of rate laws have been used at the micro-scale describing direct interactions among water and mineral surface, and at the catchment scale describing weathering rates and concentration-discharge relationships. These observations highlight the key role of mineral-water contact time in determining dissolution rates at different scales. This work also emphasizes the importance of critical interfaces between reactive and non-reactive zones as determined by the details of spatial patterns and effective surface area as a scaling factor that quantifies dissolution rates in heterogeneous media across scales.

ZIF-8 derived hexagonal-like α-Fe2O3/ZnO/Au nanoplates with tunable surface heterostructures for superior ethanol gas-sensing performance

NASA Astrophysics Data System (ADS)

Chen, Ying; Li, Hui; Ma, Qian; Che, Quande; Wang, Junpeng; Wang, Gang; Yang, Ping

2018-05-01

A series of hexagonal-like α-Fe2O3/ZnO/Au nanoplate heterostructures with tunable morphologies and superior ethanol gas-sensing performance were successfully synthesized via the facile multi-step reaction processes. Hexagonal-like α-Fe2O3 nanoplates with uniform size around 150 nm are employed as new sensor substrates for loading the well-distributed ZnO and Au nanoparticles with adjustable size distribution on the different surfaces. Brunauer-EmmeQ-Teller (BET) surface areas of α-Fe2O3 and α-Fe2O3/ZnO samples are evaluated to be 37.94 and 61.27 m2/g, respectively, while α-Fe2O3/ZnO/Au composites present the highest value of 79.08 m2/g. These α-Fe2O3-based functional materials can exhibit outstanding sensing properties to ethanol. When the ethanol concentration is 100 ppm, the response value of α-Fe2O3/ZnO/Au composites can reach up to 170, which is 14.6 and 80.3 times higher than that of α-Fe2O3/ZnO and pure α-Fe2O3, respectively. The recycling stability and long-time effectiveness can be availably maintained within 30 days, as well as the response and recovery times are shortened to 4 and 5 s, respectively. Significantly, the response value of α-Fe2O3/ZnO/Au composite is still up to 63 at an operating temperature of 280 °C even though the ethanol concentration decreases to 10 ppm. The enhanced gas sensing mechanism would be focused on the synergistic effects of phase compositions, surface heterogeneous structures, large specific surface area, and the selective depositions of Au nanoparticles in α-Fe2O3/ZnO/Au sensors. The synergistic effect of different surface heterostructures referring to α-Fe2O3/Au and α-Fe2O3/ZnO/Au and their novel electron transport processes on the surfaces are first investigated and discussed in details. It is expected that hexagonal-like α-Fe2O3/ZnO/Au nanoplate heterostructures with excellent sensing performance can be the promising highly-sensitive materials in the actual application for monitoring and detecting ethanol.

Polyacrylic acid grafted kaolinite via a facile ‘grafting to’ approach based on heterogeneous esterification and its adsorption for Cu2+

NASA Astrophysics Data System (ADS)

Zhao, Ping; Zhou, Qi; Yan, Chunjie; Luo, Wenjun

2017-03-01

Kaolinite (KLN) was successfully decorated by polyacrylic acid (PAA) brushes via a facile ‘one-step’ manner in this study. This process was achieved by heterogeneous esterification between carboxyl on the PAA chains and hydroxyl on the KLN in the presence of Al3+ as catalyst. The prepared composite (denoted as PAA-g-KLN) was characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction pattern (XRD), Field emission scanning electron microscopy (FE-SEM) and thermogravimetry (TG) to confirm the successful grafting of PAA brushes on the surface of KLN. Subsequently, the PAA-g-KLN was used as adsorbent for the removal of Cu2+ from wastewater. Due to the introduction of abundant and highly accessible carboxyl groups on the surface of kaolinite, PAA-g-KLN exhibited an enhanced adsorption performance than raw kaolinite, which could be up to 32.45 mg·g-1 at 45 °C with a fast adsorption kinetic. Theoretical models analysis revealed that Langmuir isotherm model and the pseudo second-order model were more suitable for well elucidation of the experimental data. In addition, the regeneration experiment showed that the PAA-g-KLN could still keep a satisfactory adsorption capacity (>65%) by being reused for 6 consecutive cycles. The study provides an easy and rapid method for surface polyelectrolyte modification on inorganic mineral as a promising adsorbent to remove Cu2+ from aqueous solution.

Shallow-to-Deep Convection Transition over Land: Atmospheric and surface controls inferred from long-term ground-based observations

NASA Astrophysics Data System (ADS)

Zhang, Y.; Klein, S. A.

2016-12-01

Warm-season decade-long observations are used to investigate mechanisms controlling the transition from shallow to deep convection over land. The data are from the DOE Atmospheric Radiation Measurement Climate Research Facility Southern Great Plains site. The study focuses on two questions: 1) what environmental parameters differ between the two convective regimes: fair-weather shallow cumulus versus late-afternoon deep convection, especially in the late morning a few hours before deep convection begins? And 2) Do convective regimes such as fair-weather shallow cumulus and late-afternoon deep convection have any preferences over soil moisture conditions (dry or wet) and soil moisture heterogeneities? It is found that a more humid environment immediately above the boundary layer is present before the start of late afternoon heavy precipitation events. Greater boundary layer inhomogeneity in moist static energy, temperature, moisture, and horizontal wind before precipitation begins is correlated to larger rain rates at the initial stage of precipitation. Late-afternoon deep convection tends to prefer drier soil conditions with larger surface heterogeneity. This observational study helps our understanding of convective responses to different environmental factors especially surface versus atmospheric controls. This work leads to the establishment of composite cases of different continental convective regimes for large-eddy simulations and single-column tests of climate model parameterizations. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-698972

The Modelling Analysis of the Response of Convective Transport of Energy and Water to Multiscale Surface Heterogeneity over Tibetan Plateau

NASA Astrophysics Data System (ADS)

SUN, G.; Hu, Z.; Ma, Y.; Ma, W.

2017-12-01

The land-atmospheric interactions over a heterogeneous surface is a tricky issue for accurately understanding the energy-water exchanges between land surface and atmosphere. We investigate the vertical transport of energy and water over a heterogeneous land surface in Tibetan Plateau during the evolution of the convective boundary layer using large eddy simulation (WRF_LES). The surface heterogeneity is created according to remote sensing images from high spatial resolution LandSat ETM+ images. The PBL characteristics over a heterogeneous surface are analyzed in terms of secondary circulations under different background wind conditions based on the horizontal and vertical distribution and evolution of wind. The characteristics of vertical transport of energy and heat over a heterogeneous surface are analyzed in terms of the horizontal distribution as well as temporal evolution of sensible and latent heat fluxes at different heights under different wind conditions on basis of the simulated results from WRF_LES. The characteristics of the heat and water transported into the free atmosphere from surface are also analyzed and quantified according to the simulated results from WRF_LES. The convective transport of energy and water are analyzed according to horizontal and vertical distributions of potential temperature and vapor under different background wind conditions. With the analysis based on the WRF_LES simulation, the performance of PBL schemes of mesoscale simulation (WRF_meso) is evaluated. The comparison between horizontal distribution of vertical fluxes and domain-averaged vertical fluxes of the energy and water in the free atmosphere is used to evaluate the performance of PBL schemes of WRF_meso in the simulation of vertical exchange of energy and water. This is an important variable because only the energy and water transported into free atmosphere is able to influence the regional and even global climate. This work would will be of great significance not only for understanding the land atmosphere interactions over a heterogeneous surface by evaluating and improving the performance PBL schemes in WRF-meso, but also for the understanding the profound effect of Tibetan Plateau on the regional and global climate.

The genesis solar-wind sample return mission

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

Wiens, Roger C

2009-01-01

The compositions of the Earth's crust and mantle, and those of the Moon and Mars, are relatively well known both isotopically and elementally. The same is true of our knowledge of the asteroid belt composition, based on meteorite analyses. Remote measurements of Venus, the Jovian atmosphere, and the outer planet moons, have provided some estimates of their compositions. The Sun constitutes a large majority, > 99%, of all the matter in the solar system. The elemental composition of the photosphere, the visible 'surface' of the Sun, is constrained by absorption lines produced by particles above the surface. Abundances for manymore » elements are reported to the {+-}10 or 20% accuracy level. However, the abundances of other important elements, such as neon, cannot be determined in this way due to a relative lack of atomic states at low excitation energies. Additionally and most importantly, the isotopic composition of the Sun cannot be determined astronomically except for a few species which form molecules above sunspots, and estimates derived from these sources lack the accuracy desired for comparison with meteoritic and planetary surface samples measured on the Earth. The solar wind spreads a sample of solar particles throughout the heliosphere, though the sample is very rarified: collecting a nanogram of oxygen, the third most abundant element, in a square centimeter cross section at the Earth's distance from the Sun takes five years. Nevertheless, foil collectors exposed to the solar wind for periods of hours on the surface of the Moon during the Apollo missions were used to determine the helium and neon solar-wind compositions sufficiently to show that the Earth's atmospheric neon was significantly evolved relative to the Sun. Spacecraft instruments developed subsequently have provided many insights into the composition of the solar wind, mostly in terms of elemental composition. These instruments have the advantage of observing a number of parameters simultaneously, including charge state distributions, velocities, and densities, all of which have been instrumental in characterizing the nature of the solar wind. However, these instruments have lacked the ability to make large dynamic range measurements of adjacent isotopes (i.e., {sup 17}O/{sup 16}O {approx} 2500) or provide the permil (tenths of percent) accuracy desirable for comparison with geochemical isotopic measurements. An accurate knowledge of the solar and solar-wind compositions helps to answer important questions across a number of disciplines. It aids in understanding the acceleration mechanisms of the solar wind, gives an improved picture of the charged particle environment near the photosphere, it constrains processes within the Sun over its history, and it provides a database by which to compare differences among planetary systems with the solar system's starting composition, providing key information on planetary evolution. For example, precise knowledge of solar isotopic and elemental compositions of volatile species in the Sun provides a baseline for models of atmospheric evolution over time for Earth, Venus, and Mars. Additionally, volatile and chemically active elements such as C, H, O, N, and S can tell us about processes active during the evolution of the solar nebula. A classic example of this is the oxygen isotope system. In the 1970s it was determined that the oxygen isotopic ratio in refractory inclusions in primitive meteorites was enriched {approx}4% in {sup 16}O relative to the average terrestrial, lunar, and thermally processed meteorite materials. In addition, all processed solar-system materials appeared to each have a unique oxygen isotopic composition (except the Moon and Earth, which are thought to be formed from the same materials), though differences are in the fraction of a percent range, much smaller than the refractory material {sup 16}O enrichment. Several theories were developed over the years to account for the oxygen isotope heterogeneity, each theory predicting a different solar isotopic composition and each invoking a different early solar-system process to produce the heterogeneity. Other volatiles such as C, N, and H may also have experienced similar effects, but with only two isotopes it is often impossible to distinguish with these elements between mass-dependent fractionation and other effects such as mixing or mass-independent fractionation. Table 1 provides a summary of the major measurement objectives of the Genesis mission. Determining the solar oxygen isotopic composition is at the top of the list. Volatile element and isotope ratios constitute six of the top seven priorities. A number of disciplines stand to gain from information from the Genesis mission, as will be discussed later. Based on the Apollo solar-wind foil experiment, the Genesis mission was designed to capture solar wind over orders of magnitude longer duration and in a potentially much cleaner environment than the lunar surface.« less

Functional polyaniline/multiwalled carbon nanotube composite as an efficient adsorbent material for removing pharmaceuticals from aqueous media.

PubMed

Dutra, Flávia Viana Avelar; Pires, Bruna Carneiro; Nascimento, Tienne Aparecida; Borges, Keyller Bastos

2018-09-01

The composite polyaniline/multiwalled carbon nanotube (PAni/MWCNT, 1:0.1 w/w) was developed with the intention of binding the adsorbent properties of two materials and using it to adsorb pharmaceuticals from aqueous media. PAni/MWCNT was characterized by scanning electron microscopy, thermogravimetry, infrared spectroscopy, pH at the point of zero charge, and the effect on the surface wettability of the material. As proof of concept, adsorption studies were carried out using meloxicam (MLX) as the pharmaceutical and it was evaluated as a function of pH, temperature, ionic strength, contact time and variation in concentration. Kinetics and isothermal models were applied to evaluate the mechanism of the adsorption process. The best MLX adsorption result was at pH 2 with 6 min of contact with PAni/MWCNT. The kinetics models that fitted the experimental data were pseudo-second order and Elovich and the kinetics model was the dual-site Langmuir-Freundlich. Both models suggest that the adsorption occurs by the chemical nature of the surface and in the pores of the energetically heterogeneous composite. The PAni/MWCNT presented an adsorption capacity of 221.2 mg g -1 , a very good value when compared with the literature and can be used to remove pharmaceuticals from aqueous environments. Copyright © 2018 Elsevier Ltd. All rights reserved.

Rb-Sr and Sm-Nd Ages of Zagami DML and SR Isotopic Heterogeneity in Zagami

NASA Technical Reports Server (NTRS)

Nyquist, L.aurenceE.; Shih, C.-Y.; Reese, Y. D.

2010-01-01

Zagami contains lithologic heterogeneity suggesting that it did not form in a homogeneous, thick lava flow [1]. We have previously investigated the Sr and Nd isotopic systematics of Coarse-Grained (CG) and Fine-Grained (FG) lithologies described by [2]. Both appear to belong to Normal Zagami (NZ) [1,3], but their initial Sr-isotopic compositions differ [4,5]. Here we report new analyses of the Dark Mottled Lithology (DML, [3]) that show its age and initial Sr and Nd isotopic compositions to be identical within error limits with those of CG, but Sr initial isotopic compositions differ from those of FG.

Bayesian inversion analysis of nonlinear dynamics in surface heterogeneous reactions.

PubMed

Omori, Toshiaki; Kuwatani, Tatsu; Okamoto, Atsushi; Hukushima, Koji

2016-09-01

It is essential to extract nonlinear dynamics from time-series data as an inverse problem in natural sciences. We propose a Bayesian statistical framework for extracting nonlinear dynamics of surface heterogeneous reactions from sparse and noisy observable data. Surface heterogeneous reactions are chemical reactions with conjugation of multiple phases, and they have the intrinsic nonlinearity of their dynamics caused by the effect of surface-area between different phases. We adapt a belief propagation method and an expectation-maximization (EM) algorithm to partial observation problem, in order to simultaneously estimate the time course of hidden variables and the kinetic parameters underlying dynamics. The proposed belief propagation method is performed by using sequential Monte Carlo algorithm in order to estimate nonlinear dynamical system. Using our proposed method, we show that the rate constants of dissolution and precipitation reactions, which are typical examples of surface heterogeneous reactions, as well as the temporal changes of solid reactants and products, were successfully estimated only from the observable temporal changes in the concentration of the dissolved intermediate product.

Membrane adhesion and the formation of heterogeneities: biology, biophysics, and biotechnology

PubMed Central

Gordon, V. D.; O’Halloran, T.J.; Shindell, O.

2015-01-01

Membrane adhesion is essential to many vital biological processes. Sites of membrane adhesion are often associated with heterogeneities in the lipid and protein composition of the membrane. These heterogeneities are thought to play functional roles by facilitating interactions between proteins. However, the causal links between membrane adhesion and membrane heterogeneities are not known. Here we survey the state of the field and indicate what we think are understudied areas ripe for development. PMID:25866854

Subseafloor processes in mid-ocean ridge hydrothennal systems

NASA Astrophysics Data System (ADS)

Alt, Jeffrey C.

Convective circulation of seawater through oceanic crust at mid-ocean ridges (MOR) and on ridge flanks has wide-ranging effects on heat transport, the chemical and isotopic compositions of ocean crust and seawater, mineralization of the crust, and on the physical properties of oceanic basement. Submarine hydrothermal systems remove about 30% of the heat lost from oceanic crust [Selater et al., 1981; Stein and Stein, 1994], and chemical and isotopic exchange between seawater and basement rocks exerts important controls on the composition of seawater [Edmond et al., 1979a; Thompson, 1983]. The composition of altered crust is also changed and, when subducted, this altered crust can contribute to chemical and isotopic heterogeneities in the mantle [Zindler and Hart, 1986] and may affect the compositions of volcanic rocks in island arcs [Perfit et al., 1980; Tatsumi, 1989]. Mineralization of ocean crust occurs where metals, leached from large volumes of altered crust at depth, are concentrated at or near the surface by hydrothermal circulation [Hannington, 1995]. Hydrothermal alteration of magnetic minerals may affect the source of marine magnetic anomalies [Pariso and Johnson, 1991], and the formation of secondary minerals influences the density, porosity, and seismic velocity structure of the crust [Wilkens et al., 1991; Jacobson, 1992].

Characterizing physical properties and heterogeneous chemistry of single particles in air using optical trapping-Raman spectroscopy

NASA Astrophysics Data System (ADS)

Gong, Z.; Wang, C.; Pan, Y. L.; Videen, G.

2017-12-01

Heterogeneous reactions of solid particles in a gaseous environment are of increasing interest; however, most of the heterogeneous chemistry studies of airborne solids were conducted on particle ensembles. A close examination on the heterogeneous chemistry between single particles and gaseous-environment species is the key to elucidate the fundamental mechanisms of hydroscopic growth, cloud nuclei condensation, secondary aerosol formation, etc., and reduce the uncertainty of models in radiative forcing, climate change, and atmospheric chemistry. We demonstrate an optical trapping-Raman spectroscopy (OT-RS) system to study the heterogeneous chemistry of the solid particles in air at single-particle level. Compared to other single-particle techniques, optical trapping offers a non-invasive, flexible, and stable method to isolate single solid particle from substrates. Benefited from two counter-propagating hollow beams, the optical trapping configuration is adaptive to trap a variety of particles with different materials from inorganic substitution (carbon nanotubes, silica, etc.) to organic, dye-doped polymers and bioaerosols (spores, pollen, etc.), with different optical properties from transparent to strongly absorbing, with different sizes from sub-micrometers to tens of microns, or with distinct morphologies from loosely packed nanotubes to microspheres and irregular pollen grains. The particles in the optical trap may stay unchanged, surface degraded, or optically fragmented according to different laser intensity, and their physical and chemical properties are characterized by the Raman spectra and imaging system simultaneously. The Raman spectra is able to distinguish the chemical compositions of different particles, while the synchronized imaging system can resolve their physical properties (sizes, shapes, morphologies, etc.). The temporal behavior of the trapped particles also can be monitored by the OT-RS system at an indefinite time with a resolution from 10 ms to 5 min, which can be further applied to monitor the dynamics of heterogeneous reactions. The OT-RS system provides a flexible method to characterize and monitor the physical properties and heterogeneous chemistry of optically trapped solid particles in gaseous environment at single-particle level.

AMS+ALS: Kinetic and Product Studies of the Heterogeneous Oxidation of Organic Aerosol at the Advanced Light Source

NASA Astrophysics Data System (ADS)

Kroll, J. H.; Wilson, K. R.; Kessler, S. H.; Browne, E. C.; Nah, T.; Smith, J.; Worsnop, D. R.

2014-12-01

The atmospheric oxidation of condensed-phase organic species can have a major influence on the composition, properties, and impacts of organic aerosol (OA); however the rates and products of such "aging" reactions are poorly constrained. Here we describe a series of laboratory experiments aimed at better understanding one class of aging reactions, the heterogeneous oxidation of OA by gas-phase oxidants. Central to these experiments is the availability of vacuum ultraviolet (VUV) light at the Chemical Dynamics Beamline of the Advanced Light Source at LBNL, which enables the implementation of VUV photoionization aerosol mass spectrometry. This technique allows for the real-time, speciated measurement of OA composition, yielding molecular information that is highly complementary to ensemble data from electron-impact ionization. OA composition is measured with both ionization schemes as a function of oxidant exposure within a flow reactor, providing detailed information on the kinetics and products of heterogeneous oxidation over multiple generations of oxidation. Specific topics investigated include the branching between functionalization and fragmentation of OA components, the formation of secondary organic aerosol from photolytically-generated radical species, and the heterogeneous aging of soot-associated organic species.

Higher-level phylogeny of paraneopteran insects inferred from mitochondrial genome sequences

PubMed Central

Li, Hu; Shao, Renfu; Song, Nan; Song, Fan; Jiang, Pei; Li, Zhihong; Cai, Wanzhi

2015-01-01

Mitochondrial (mt) genome data have been proven to be informative for animal phylogenetic studies but may also suffer from systematic errors, due to the effects of accelerated substitution rate and compositional heterogeneity. We analyzed the mt genomes of 25 insect species from the four paraneopteran orders, aiming to better understand how accelerated substitution rate and compositional heterogeneity affect the inferences of the higher-level phylogeny of this diverse group of hemimetabolous insects. We found substantial heterogeneity in base composition and contrasting rates in nucleotide substitution among these paraneopteran insects, which complicate the inference of higher-level phylogeny. The phylogenies inferred with concatenated sequences of mt genes using maximum likelihood and Bayesian methods and homogeneous models failed to recover Psocodea and Hemiptera as monophyletic groups but grouped, instead, the taxa that had accelerated substitution rates together, including Sternorrhyncha (a suborder of Hemiptera), Thysanoptera, Phthiraptera and Liposcelididae (a family of Psocoptera). Bayesian inference with nucleotide sequences and heterogeneous models (CAT and CAT + GTR), however, recovered Psocodea, Thysanoptera and Hemiptera each as a monophyletic group. Within Psocodea, Liposcelididae is more closely related to Phthiraptera than to other species of Psocoptera. Furthermore, Thysanoptera was recovered as the sister group to Hemiptera. PMID:25704094

CT Identification and Fractal Characterization of 3-D Propagation and Distribution of Hydrofracturing Cracks in Low-Permeability Heterogeneous Rocks

NASA Astrophysics Data System (ADS)

Liu, Peng; Ju, Yang; Gao, Feng; Ranjith, Pathegama G.; Zhang, Qianbing

2018-03-01

Understanding and characterization of the three-dimensional (3-D) propagation and distribution of hydrofracturing cracks in heterogeneous rock are key for enhancing the stimulation of low-permeability petroleum reservoirs. In this study, we investigated the propagation and distribution characteristics of hydrofracturing cracks, by conducting true triaxial hydrofracturing tests and computed tomography on artificial heterogeneous rock specimens. Silica sand, Portland cement, and aedelforsite were mixed to create artificial heterogeneous rock specimens using the data of mineral compositions, coarse gravel distribution, and mechanical properties that were measured from the natural heterogeneous glutenite cores. To probe the effects of material heterogeneity on hydrofracturing cracks, the artificial homogenous specimens were created using the identical matrix compositions of the heterogeneous rock specimens and then fractured for comparison. The effects of horizontal geostress ratio on the 3-D growth and distribution of cracks during hydrofracturing were examined. A fractal-based method was proposed to characterize the complexity of fractures and the efficiency of hydrofracturing stimulation of heterogeneous media. The material heterogeneity and horizontal geostress ratio were found to significantly influence the 3-D morphology, growth, and distribution of hydrofracturing cracks. A horizontal geostress ratio of 1.7 appears to be the upper limit for the occurrence of multiple cracks, and higher ratios cause a single crack perpendicular to the minimum horizontal geostress component. The fracturing efficiency is associated with not only the fractured volume but also the complexity of the crack network.

Heterogeneity of activated carbons in adsorption of aniline from aqueous solutions

NASA Astrophysics Data System (ADS)

Podkościelny, P.; László, K.

2007-08-01

The heterogeneity of activated carbons (ACs) prepared from different precursors is investigated on the basis of adsorption isotherms of aniline from dilute aqueous solutions at various pH values. The APET carbon prepared from polyethyleneterephthalate (PET), as well as, commercial ACP carbon prepared from peat were used. Besides, to investigate the influence of carbon surface chemistry, the adsorption was studied on modified carbons based on ACP carbon. Its various oxygen surface groups were changed by both nitric acid and thermal treatments. The Dubinin-Astakhov (DA) equation and Langmuir-Freundlich (LF) one have been used to model the phenomenon of aniline adsorption from aqueous solutions on heterogeneous carbon surfaces. Adsorption-energy distribution (AED) functions have been calculated by using an algorithm based on a regularization method. Analysis of these functions for activated carbons studied provides important comparative information about their surface heterogeneity.

Heterogeneity in fire severity with early season and late season prescribed burns in a mixed conifer forest

Treesearch

Eric E. Knapp; Jon E. Keeley

2006-01-01

Structural heterogeneity in forests of the Sierra Nevada was historically produced through variation in fire regimes and local environmental factors. The amount of heterogeneity that prescription burning can achieve might now be more limited owing to high fuel loads and increased fuel continuity. Topography, woody fuel loading, and vegetative composition were...

Sea spray aerosol structure and composition using cryogenic transmission electron microscopy

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

Patterson, Joseph P.; Collins, Douglas B.; Michaud, Jennifer M.

The surface properties of atmospheric aerosol particles largely control their impact on climate by affecting their ability to uptake water, react heterogeneously, and nucleate ice in clouds. However, in the vacuum of a conventional electron microscope, the native surface structure often undergoes chemical rearrangement resulting in surfaces that are quite different from their atmospheric configurations. Herein, we report the development of a cryo-TEM approach where sea spray aerosol particles are flash frozen in their native state and then probed by electron microscopy. This unique approach allows for the detection of not only mixed salts, but also soft materials including wholemore » hydrated bacteria, diatoms, virus particles, marine vesicles, as well as gel networks within hydrated salt droplets. As a result, we anticipate this method will open up a new avenue of analysis for aerosol particles, not only for ocean-derived aerosols, but for those produced from other sources where there is interest in the transfer of organic or biological species from the biosphere to the atmosphere.« less

Hydrologic pathways and chemical composition of runoff during snowmelt in Loch Vale Watershed, Rocky Mountain National Park, Colorado, USA

USGS Publications Warehouse

Denning, A. Scott; Baron, Jill S.; Mast, M. Alisa; Arthur, Mary

1991-01-01

Intensive sampling of a stream draining an alpine-subalpine basin revealed that depressions in pH and acid neutralizing capacity (ANC) of surface water at the beginning of the spring snowmelt in 1987 and 1988 were not accompanied by increases in strong acid anions, and that surface waters did not become acidic (ANC<0). Samples of meltwater collected at the base of the snowpack in 1987 were acidic and exhibited distinct ‘pulses’ of nitrate and sulfate. Solutions collected with lysimeters in forest soils adjacent to the stream revealed high levels of dissolved organic carbon (DOC) and total Al. Peaks in concentration of DOC, Al, and nutrient species in the stream samples indicate a flush of soil solution into the surface water at the beginning of the melt. Infiltration of meltwater into soils and spatial heterogeneity in the timing of melting across the basin prevented stream and lake waters from becoming acidic.

Modeling Pressure-Driven Transport of Proteins through a Nanochannel

PubMed Central

Carr, Rogan; Comer, Jeffrey; Ginsberg, Mark D.; Aksimentiev, Aleksei

2012-01-01

Reducing the size of a nanofluidic channel not only creates new opportunities for high-precision manipulation of biological macromolecules, but also makes the performance of the entire nanofluidic system more susceptible to undesirable interactions between the transported biomolecules and the walls of the channel. In this manuscript, we report molecular dynamics simulations of a pressure-driven flow through a silica nanochannel that characterized, with atomic resolution, adsorption of a model protein to its surface. Although the simulated adsorption of the proteins was found to be nonspecific, it had a dramatic effect on the rate of the protein transport. To determine the relative strength of the protein–silica interactions in different adsorbed states, we simulated flow-induced desorption of the proteins from the silica surface. Our analysis of the protein conformations in the adsorbed states did not reveal any simple dependence of the adsorption strength on the size and composition of the protein–silica contact, suggesting that the heterogeneity of the silica surface may be a important factor. PMID:22611338

Sea spray aerosol structure and composition using cryogenic transmission electron microscopy

DOE PAGES

Patterson, Joseph P.; Collins, Douglas B.; Michaud, Jennifer M.; ...

2016-01-15

The surface properties of atmospheric aerosol particles largely control their impact on climate by affecting their ability to uptake water, react heterogeneously, and nucleate ice in clouds. However, in the vacuum of a conventional electron microscope, the native surface structure often undergoes chemical rearrangement resulting in surfaces that are quite different from their atmospheric configurations. Herein, we report the development of a cryo-TEM approach where sea spray aerosol particles are flash frozen in their native state and then probed by electron microscopy. This unique approach allows for the detection of not only mixed salts, but also soft materials including wholemore » hydrated bacteria, diatoms, virus particles, marine vesicles, as well as gel networks within hydrated salt droplets. As a result, we anticipate this method will open up a new avenue of analysis for aerosol particles, not only for ocean-derived aerosols, but for those produced from other sources where there is interest in the transfer of organic or biological species from the biosphere to the atmosphere.« less

Representation of vegetation by continental data sets derived from NOAA-AVHRR data

NASA Technical Reports Server (NTRS)

Justice, C. O.; Townshend, J. R. G.; Kalb, V. L.

1991-01-01

Images of the normalized difference vegetation index (NDVI) are examined with specific attention given to the effect of spatial scales on the understanding of surface phenomena. A scale variance analysis is conducted on NDVI annual and seasonal images of Africa taken from 1987 NOAA-AVHRR data at spatial scales ranging from 8-512 km. The scales at which spatial variation takes place are determined and the relative magnitude of the variations are considered. Substantial differences are demonstrated, notably an increase in spatial variation with coarsening spatial resolution. Different responses in scale variance as a function of spatial resolution are noted in an analysis of maximum value composites for February and September; the difference is most marked in areas with very seasonal vegetation. The spatial variation at different scales is attributed to different factors, and methods involving the averaging of areas of transition and surface heterogeneity can oversimplify surface conditions. The spatial characteristics and the temporal variability of areas should be considered to accurately apply satellite data to global models.

Fabrication of ZnAl mixed metal-oxides/RGO nanohybrid composites with enhanced photocatalytic activity under visible light

NASA Astrophysics Data System (ADS)

Ni, Jie; Xue, Jinjuan; Shen, Jing; He, Guangyu; Chen, Haiqun

2018-05-01

The ZnAl mixed metal-oxides (MMOs)/graphene nanocomposites were successfully fabricated by a facile hydrothermal method combined with a calcination process. The thermal treatment enables simultaneously the formation of ZnO/ZnAl2O4 heterogeneous structure, which are uniformly decorated on the surface of graphene, accompanying with the reduction of graphene oxide. The as-prepared heterostructure photocatalysts were well characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectroscopy (DRS) to conduct investigations into the phase structures, microstructure and optical capability. The ZnAl MMO/RGO20 composite displayed favorable adsorption property and photo-degradation efficiency for Ciprofloxacin (CIP) aqueous solution under visible light. The photo-degradation efficiency of the as-prepared ZnAl MMO/RGO20 was 3.0 and even 4.6 times higher than that of ZnAl MMO and pure ZnAl LDH, respectively. The improvement of photocatalytic performance is ascribed to the synergistic effect of heterogeneous structure coupled with graphene, which realizes efficient charge separation efficiency, enlarged visible light adsorption range, and chemical stability of hybrid nanocomposite. The results of EIS, PL and photocurrent response also explained the best performance of ZnAl MMO/RGO20 nanocomposite. Besides, the mechanism of ZnAl MMO/RGO20 photocatalytic system was proposed and analyzed in detail.

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

Wang, Bingbing; Knopf, Daniel A.; China, Swarup

Heterogeneous ice nucleation is a physical chemistry process of critical relevance to a range of topics in the fundamental and the applied sciences and technologies. Heterogeneous ice nucleation remains insufficiently understood. This is in part due to the lack of experimental methods capable of in situ visualization of ice formation over nucleating substrates with microscopically characterized morphology and composition. We present development, validation and first applications of a novel electron microscopy platform allowing observation of individual ice nucleation events at temperature and relative humidity (RH) relevant for ice formation in a broad range of environmental and applied technology processes. Themore » approach utilizes a custom-built ice nucleation cell, interfaced with an Environmental Scanning Electron Microscope (IN-ESEM system). The IN-ESEM system allows dynamic observations of individual ice formation events over particles of atmospheric relevance and determination of the ice nucleation mechanisms. Additional IN-ESEM experiments allow examination of the location of ice formation on the surface of individual particles and micro-spectroscopy analysis of the ice nucleating particles (INPs). This includes elemental composition detected by the energy dispersed analysis of X-rays (EDX), speciation of the organic content in particles using scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS), and Helium ion microscopy (HeIM). The capabilities of the IN-ESEM experimental platform are demonstrated first on laboratory standards and then by chemical imaging of INPs using a complex sample of ambient particles.« less

Interdisciplinary scientist participation in the Phobos mission

NASA Technical Reports Server (NTRS)

1992-01-01

Data was acquired from VSK (2 wide-angle visible-NIR TV cameras at 0.4 to 0.6 micrometers and 0.8 to 1.1 micrometers, and a narrow-angle TV camera), KRFM (10-band UV-visible spectrometer at 0.3 to 0.6 micrometers and a 6-band radiometer at 5-50 micrometers), and ISM (a 128-channel NIR imaging spectrometer at 0.8 to 3 micrometers). These data provided improved mapping coverage of Phobos; improved mass, shape, and volume determinations, with the density shown to be lower than that of all known meteorites, suggesting a porous interior; evidence for a physically, spectrally and possibly compositionally heterogeneous surface; and proof that the spectral properties do not closely resemble those of unaltered carbonaceous chondrites, but show more resemblance to the spectra of altered mafic material. For Mars, the data show that the underlying rock type can be distinguished through the global dust cover; that the spectral properties and possibly composition vary laterally between and within the geologic provinces; that the surface physical properties vary laterally, and in many cases, the boundaries coincide with those of the geologic units; and the acquired data also demonstrate the value of reflectance spectroscopy and radiometry to the study of Martian geology.

It's a Sooty Problem: Black Carbon and Aerosols from Space

NASA Technical Reports Server (NTRS)

Kaufman, Yoram J.

2005-01-01

Our knowledge of atmospheric aerosols (smoke, pollution, dust or sea salt particles, small enough to be suspended in the air), their evolution, composition, variability in space and time and interaction with solar radiation, clouds and precipitation is lacking despite decades of research. Just recently we recognized that understanding the global aerosol system is fundamental for progress in climate change and hydrological cycle research. While a single instrument was used to demonstrate 50 yrs ago that the global CO2 levels are rising, posing thread to our climate, we need an may of satellites, surface networks of radiometers, elaborated laboratory and field experiments coupled with chemical transport models to understand the global aerosol system. This complexity of the aerosol problem results from their short lifetime (1 week), variability of the chemical composition and complex chemical and physical processes in the atmosphere. The result is a heterogeneous distribution of aerosol and their properties. The new generation of satellites and surface networks of radiometers provides exciting opportunities to measure the aerosol properties and their interaction with clouds and climate. However farther development in the satellite capability, aerosol chemical models and climate models is needed to fully decipher the aerosol secrets with accuracy required to predict future climates.

Metal Nanoparticle Aerogel Composites

NASA Technical Reports Server (NTRS)

Smith, David D.; Sibille, Laurent; Ignont, Erica; Snow, Lanee; Rose, M. Franklin (Technical Monitor)

2000-01-01

We have fabricated sol-gels containing gold and silver nanoparticles. Formation of an aerogel produces a blue shift in the surface plasmon resonance as a result of the decrease in the dielectric constant of the matrix upon supercritical extraction of the solvent. However, as a result of chemical interface damping this blue shift does not obey effective medium theories. Annealing the samples in a reducing atmosphere at 400 C eliminates this discrepancy and results in narrowing and further blue shifting of the plasmon resonance. Metal particle aggregation also results in a deviation from the predictions of effective medium theories, but can be controlled through careful handling and by avoiding the use of alcohol. By applying effective medium theories to the heterogeneous interlayer surrounding each metal particle, we extend the technique of immersion spectroscopy to inhomogeneous materials characterized by spatially dependent dielectric constants, such as aerogels. We demonstrate that the shift in the surface plasmon wavelength provides the average fractional composition of each component (air and silica) in this inhomogeneous layer, i.e. the porosity of the aerogel or equivalently, for these materials, the catalytic dispersion. Additionally, the kinetics suggest that collective particle interactions in coagulated metal clusters are perturbed during silica gelation resulting in a change in the aggregate geometry.

Parameter studies on the energy balance closure problem using large-eddy simulation

NASA Astrophysics Data System (ADS)

De Roo, Frederik; Banerjee, Tirtha; Mauder, Matthias

2017-04-01

The imbalance of the surface energy budget in eddy-covariance measurements is still a pending problem. A possible cause is the presence of land surface heterogeneity. Heterogeneities of the boundary layer scale or larger are most effective in influencing the boundary layer turbulence, and large-eddy simulations have shown that secondary circulations within the boundary layer can affect the surface energy budget. However, the precise influence of the surface characteristics on the energy imbalance and its partitioning is still unknown. To investigate the influence of surface variables on all the components of the flux budget under convective conditions, we set up a systematic parameter study by means of large-eddy simulation. For the study we use a virtual control volume approach, and we focus on idealized heterogeneity by considering spatially variable surface fluxes. The surface fluxes vary locally in intensity and these patches have different length scales. The main focus lies on heterogeneities of length scales of the kilometer scale and one decade smaller. For each simulation, virtual measurement towers are positioned at functionally different positions. We discriminate between the locally homogeneous towers, located within land use patches, with respect to the more heterogeneous towers, and find, among others, that the flux-divergence and the advection are strongly linearly related within each class. Furthermore, we seek correlators for the energy balance ratio and the energy residual in the simulations. Besides the expected correlation with measurable atmospheric quantities such as the friction velocity, boundary-layer depth and temperature and moisture gradients, we have also found an unexpected correlation with the temperature difference between sonic temperature and surface temperature. In additional simulations with a large number of virtual towers, we investigate higher order correlations, which can be linked to secondary circulations. In a companion presentation (EGU2017-2130) these correlations are investigated and confirmed with the help of micrometeorological measurements from the TERENO sites where the effects of landscape scale surface heterogeneities are deemed to be important.

Low temperature synthesis of polyaniline-crystalline TiO2-halloysite composite nanotubes with enhanced visible light photocatalytic activity.

PubMed

Li, Cuiping; Wang, Jie; Guo, Hong; Ding, Shujiang

2015-11-15

A series of one-dimensional polyaniline-crystalline TiO2-halloysite composite nanotubes with different mass ratio of polyaniline to TiO2 are facilely prepared by employing the low-temperature synthesis of crystalline TiO2 on halloysite nanotubes. The halloysite nanotubes can adsorb TiO2/polyaniline precursors and induce TiO2 nanocrystals/polyaniline to grow on the support in situ simultaneously. By simply adjusting the acidity of reaction system, PANI-crystalline TiO2-HA composite nanotubes composed of anatase, a mixed phase TiO2 and different PANI redox state are obtained. The XRD and UV-vis results show that the surface polyaniline sensitization has no effect on the crystalline structure of halloysite and TiO2 and the light response of TiO2 is extended to visible-light regions. Photocatalysis test results reveal the photocatalytic activity will be affected by the pH value and the volume ratio of ANI to TTIP. The highest photocatalytic activity is achieved with the composite photocatalysts prepared at pH 0.5 and 1% volume ratio of ANI and TTIP owing to the sensitizing effect of polyaniline and the charge transfer from the photoexcited PANI sensitizer to TiO2. Moreover, the PANI-TiO2-HA composite nanotubes synthesized by one-step at pH 0.5 with 1% volume ratio of ANI to TTIP exhibit higher visible light photocatalytic activity than those synthesized by the two-step. Heterogeneous PANI-TiO2-HA composite nanotubes prepared at pH 0.5 exhibit a higher degradation activity than that prepared at pH 1.5. The redoped experiment proves that the PANI redox state plays the main contribution to the enhanced visible light catalytic degradation efficiency of PANI-TiO2-HA prepared at pH 0.5. Furthermore, the heterogeneous PANI-crystalline TiO2-HA nanotubes have good photocatalytic stability and can be reused four times with only gradual loss of activity under visible light irradiation. Copyright © 2015 Elsevier Inc. All rights reserved.

High resolution analysis of trace elements in corals by laser ablation ICP-MS

NASA Astrophysics Data System (ADS)

Sinclair, Daniel J.; Kinsley, Leslie P. J.; McCulloch, Malcolm T.

1998-06-01

A method has been developed using laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) for rapid high resolution analysis of B, Mg, Sr, Ba, and U in corals. Corals represent a challenge for a microbeam technique due to their compositional and structural heterogeneity, their nonsilicate matrix, and their unusual range of trace element compositions relative to available standards. The method employs an argon-fluoride excimer laser (λ = 193 nm), masked to produce a beam 600 μm wide by 20 μm across to average ablation sampling over a range of structural features. Coral sections are scanned at a constant rate beneath the laser to produce a continuous sampling of the coral surface. Sensitivity drift is controlled by careful preconditioning of the ICP-MS to carbonate material, and standardisation is carried out by bracketing each traverse down the coral sample by analyses of a CaSiO 3 glass synthesised from coral powder. The method demonstrates excellent reproducibility of both the shape and magnitude of coralline trace element profiles, with typical precisions of between 1.0 and 3.7% based on analysis of the synthetic standard. Accuracy varies between 3.8% for B and 31% for U. Discrepancies are attributed to heterogeneities in the synthetic standard, and matrix differences between the silicate standard and carbonate sample. The method is demonstrated by analysis of a coral collected from Australia's Great Barrier Reef near a weather station recording in-situ sea-surface-temperature (SST). The elements B, Mg, Sr, and U show seasonal compositional cycles, and tentative calibrations against SST have been derived. Using independent ICP-MS solution estimates of the coral composition to correct for standardisation uncertainties, the following calibrations have been derived: B/Ca (μmol/mol)= 1000 (±20)- 20.6 (±0.8)× SSTMg/Ca (mmol/mol)= 0.0 (±0.3)+ 0.16 (±0.01)× SSTSr/Ca (mmol/mol)= 10.8 (±0.1)- 0.070 (±0.004)× SSTU/Ca (μmol/mol)= 2.24 (±0.07)- 0.046 (±0.003)× SSTl These calibrations agree with literature within experimental errors, except for Mg which displays a 35% greater temperature dependence than reported previously. None of the elements in the coral appear to be sensitive to decreases in salinity associated with heavy rainfall in the summer of 1991/1992.

Mesoarchean melting and Neoarchean to Paleoproterozoic metasomatism during the formation of the cratonic mantle keel beneath West Greenland

NASA Astrophysics Data System (ADS)

van Acken, D.; Luguet, A.; Pearson, D. G.; Nowell, G. M.; Fonseca, R. O. C.; Nagel, T. J.; Schulz, T.

2017-04-01

Highly siderophile element (HSE) concentration and 187Os/188Os isotopic heterogeneity has been observed on various scales in the Earth's mantle. Interaction of residual mantle peridotite with infiltrating melts has been suggested to overprint primary bulk rock HSE signatures originating from partial melting, contributing to the heterogeneity seen in the global peridotite database. Here we present a detailed study of harzburgitic xenolith 474527 from the Kangerlussuaq suite, West Greenland, coupling the Re-Os isotope geochemistry with petrography of both base metal sulfides (BMS) and silicates to assess the impact of overprint induced by melt-rock reaction on the Re-Os isotope system. Garnet harzburgite sample 474527 shows considerable heterogeneity in the composition of its major phases, most notably olivine and Cr-rich garnet, suggesting formation through multiple stages of partial melting and subsequent metasomatic events. The major BMS phases show a fairly homogeneous pentlandite-rich composition typical for BMS formed via metasomatic reaction, whereas the 187Os/188Os compositions determined for 17 of these BMS are extremely heterogeneous ranging between 0.1037 and 0.1981. Analyses by LA-ICP-MS reveal at least two populations of BMS grains characterized by contrasting HSE patterns. One type of pattern is strongly enriched in the more compatible HSE Os, Ir, and Ru over the typically incompatible Pt, Pd, and Re, while the other type shows moderate enrichment of the more incompatible HSE and has overall lower compatible HSE/incompatible HSE composition. The small-scale heterogeneity observed in these BMS highlights the need for caution when utilizing the Re-Os system to date mantle events, as even depleted harzburgite samples such as 474527 are likely to have experienced a complex history of metasomatic overprinting, with uncertain effects on the HSE.

Geochemical evidence for groundwater behavior in an unconfined aquifer, south Florida

NASA Astrophysics Data System (ADS)

Meyers, Jayson B.; Swart, Peter K.; Meyers', Janet L.

1993-07-01

Five well sites have been investigated along an east-west transect across the surfical aquifer system (SAS) of south Florida. Differences between rainfall during wet seasons (June-October) and evaporation during dry seasons (November-May) give surface waters of this region isotopically light ( δ 18O -22‰ and δ D -7.6‰ ) and heavy ( δ 18O +4.2‰ ) compositions, respectively. Surface waters and shallow groundwaters are enriched in 18O and D to the west, which is consistent with westward decrease in equal excess of rainfall. In the shallow portion of the SAS (less than 20 m, Biscayne sub-aquifer) heterogeneous stable isotopic compositions occur over short spans of time (less than 90 days), reflecting seasonal changes in the isotopic composition of recharge and rapid flushing. Homogeneous stable isotopic compositions occur below the Biscayne sub-aquifer, marking the zone of delayed circulation. Surface evaporation calculated from a stable isotope evaporation model agrees with previously published estimates of 75-95% by physical evaporation measurements and water budget calculations. This model contains many parameters that are assumed to be mean values, but short-term variability in some of these parameters may make this model unsuitable for the application of yearly mean values. For the Everglades, changes in the isotopic composition of atmospheric vapor during the dry season may cause the model to yield anomalous results when annual mean values are used. Chloride-enriched waters (more than 280 mg 1 -1) form a plume emanating from the bottom central portion of the transect. Elevated chloride concentration and light stable isotopic composition ( δ 18O ≈ -2‰ , δ D ≈ -8‰ ) suggest this plume is probably caused not by salinity of residual seawater in the aquifer, but by leakage from the minor artesian water-bearing zone of the Floridan aquifer system. Stable isotope values from Floridan aquifer groundwater plot close to the meteoric water line, in the same area as Everglades rainfall. These Floridan waters are interpreted to have originated in central Florida some 25 000-132 000 years ago, indicating that meteoric conditions in the Florida peninsula have changed little since late Pleistocene time.

Chemical Heterogeneity on Mercury's Surface Revealed by the MESSENGER X-ray Spectrometer

NASA Technical Reports Server (NTRS)

Weider, Shoshana Z.; Nittler, Larry R.; Starr, Richard D.; McCoy, Timothy J.; Stockstill-Cahill, Karen R.; Byrne, Paul K.; Denevi, Brett W.; Head, James W.; Solomon, Sean C.

2012-01-01

We present the analysis of 205 spatially resolved measurements of the surfacecomposition of Mercury from MESSENGERs X-Ray Spectrometer. The surfacefootprints of these measurements are categorized according to geological terrain. Northernsmooth plains deposits and the plains interior to the Caloris basin differ compositionallyfrom older terrain on Mercury. The older terrain generally has higher MgSi, SSi, andCaSi ratios, and a lower AlSi ratio than the smooth plains. Mercurys surface mineralogyis likely dominated by high-Mg mafic minerals (e.g., enstatite), plagioclase feldspar, andlesser amounts of Ca, Mg, andor Fe sulfides (e.g., oldhamite). The compositionaldifference between the volcanic smooth plains and the older terrain reflects differentabundances of these minerals and points to the crystallization of the smooth plains from amore chemically evolved magma source. High-degree partial melts of enstatite chondritematerial provide a generally good compositional and mineralogical match for much ofthe surface of Mercury. An exception is Fe, for which the low surface abundance onMercury is still higher than that of melts from enstatite chondrites and may indicate anexogenous contribution from meteoroid impacts.

Equivalent Aqueous Phase Modulation of Domain Segregation in Myelin Monolayers and Bilayer Vesicles

PubMed Central

Oliveira, Rafael G.; Schneck, Emanuel; Funari, Sergio S.; Tanaka, Motomu; Maggio, Bruno

2010-01-01

Purified myelin can be spread as monomolecular films at the air/aqueous interface. These films were visualized by fluorescence and Brewster angle microscopy, showing phase coexistence at low and medium surface pressures (<20–30 mN/m). Beyond this threshold, the film becomes homogeneous or not, depending on the aqueous subphase composition. Pure water as well as sucrose, glycerol, dimethylsulfoxide, and dimethylformamide solutions (20% in water) produced monolayers that become homogeneous at high surface pressures; on the other hand, the presence of salts (NaCl, CaCl2) in Ringer's and physiological solution leads to phase domain microheterogeneity over the whole compression isotherm. These results show that surface heterogeneity is favored by the ionic milieu. The modulation of the phase-mixing behavior in monolayers is paralleled by the behavior of multilamellar vesicles as determined by small-angle and wide-angle x-ray scattering. The correspondence of the behavior of monolayers and multilayers is achieved only at high surface pressures near the equilibrium adsorption surface pressure; at lower surface pressures, the correspondence breaks down. The equilibrium surface tension on all subphases corresponds to that of the air/alkane interface (27 mN/m), independently on the surface tension of the clean subphase. PMID:20816062

Petrophysical constraints on the seismic properties of the Kaapvaal craton mantle root

NASA Astrophysics Data System (ADS)

Baptiste, V.; Tommasi, A.

2013-07-01

We calculated the seismic properties of 47 mantle xenoliths from 9 kimberlitic pipes in the Kaapvaal craton based on their modal composition, the crystal preferred orientations (CPO) of olivine, ortho- and clinopyroxene, and garnet, the Fe content of olivine, and the pressures and temperatures at which the rocks were equilibrated. These data allow constraining the variation of seismic anisotropy and velocities with depth. The fastest P wave and fast split shear wave (S1) polarization direction is always close to olivine [100] maximum. Changes in olivine CPO symmetry result in minor variations in the seismic anisotropy patterns. Seismic anisotropy is higher for high olivine contents and stronger CPO. Maximum P waves azimuthal anisotropy (AVp) ranges between 2.5 and 10.2% and S waves polarization anisotropy (AVs) between 2.7 and 8%. Seismic properties averaged in 20 km thick intervals depth are, however, very homogeneous. Based on these data, we predict the anisotropy that would be measured by SKS, Rayleigh (SV) and Love (SH) waves for 5 end-member orientations of the foliation and lineation. Comparison to seismic anisotropy data in the Kaapvaal shows that the coherent fast directions, but low delay times imaged by SKS studies and the low azimuthal anisotropy and SH faster than SV measured using surface waves may only be consistently explained by dipping foliations and lineations. The strong compositional heterogeneity of the Kaapvaal peridotite xenoliths results in up to 3% variation in density and in up to 2.3% of variation Vp, Vs and the Vp/Vs ratio. Fe depletion by melt extraction increases Vp and Vs, but decreases the Vp/Vs ratio and density. Orthopyroxene enrichment decreases the density and Vp, but increases Vs, strongly reducing the Vp/Vs ratio. Garnet enrichment increases the density, and in a lesser manner Vp and the Vp/Vs ratio, but it has little to no effect on Vs. These compositionally-induced variations are slightly higher than the velocity perturbations imaged by body-wave tomography, but cannot explain the strong velocity anomalies reported by surface wave studies. Comparison of density and seismic velocity profiles calculated using the xenoliths' compositions and equilibrium conditions to seismological data in the Kaapvaal highlights that: (i) the thickness of the craton is underestimated in some seismic studies and reaches at least 180 km, (ii) the deep sheared peridotites represent very local modifications caused and oversampled by kimberlites, and (iii) seismological models probably underestimate the compositional heterogeneity in the Kaapvaal mantle root, which occurs at a scale much smaller than the one that may be sampled seismologically.

Microstructure-Property Correlation in Magnesium-based Hydrogen Storage Systems: The Case for Ball-milled Magnesium Hydride Powder and Magnesium-based Multilayered Composites

NASA Astrophysics Data System (ADS)

Danaie, Mohsen

The main focus of this thesis is the characterization of defects and microstructure in high-energy ball milled magnesium hydride powder and magnesium-based multilayered composites. Enhancement in kinetics of hydrogen cycling in magnesium can be achieved by applying severe plastic deformation. A literature survey reveals that, due to extreme instability of alpha-MgH 2 in transmission electron microscope (TEM), the physical parameters that researchers have studied are limited to particle size and grain size. By utilizing a cryogenic TEM sample holder, we extended the stability time of the hydride phase during TEM characterization. Milling for only 30 minutes resulted in a significant enhancement in desorption kinetics. A subsequent annealing cycle under pressurized hydrogen reverted the kinetics to its initial sluggish state. Cryo-TEM analysis of the milled hydride revealed that mechanical milling induces deformation twinning in the hydride microstructure. Milling did not alter the thermodynamics of desorption. Twins can enhance the kinetics by acting as preferential locations for the heterogeneous nucleation of metallic magnesium. We also looked at the phase transformation characteristics of desorption in MgH2. By using energy-filtered TEM, we investigated the morphology of the phases in a partially desorbed state. Our observations prove that desorption phase transformation in MgH2 is of "nucleation and growth" type, with a substantial energy barrier for nucleation. This is contrary to the generally assumed "core-shell" structure in most of the simulation models for this system. We also tested the hydrogen storage cycling behavior of bulk centimeter-scale Mg-Ti and Mg-SS multilayer composites synthesized by accumulative roll-bonding. Addition of either phase (Ti or SS) allows the reversible hydrogen sorption at 350°C, whereas identically roll-bonded pure magnesium cannot be absorbed. In the composites the first cycle of absorption (also called "activation") kinetics improve with increased number of fold and roll (FR) operations. With increasing FR operations the distribution of the Ti phase is progressively refined, and the shape of the absorption curve no longer remains sigmoidal. Up to a point, increasing the loading amount of the second phase also accelerates the kinetics. Microscopy analysis performed on 1--2 wt.% hydrogen absorbed composites demonstrates that MgH 2 formed exclusively on various heterogeneous nucleation sites. During activation, MgH2 nucleation occurred at the Mg-hard phase interfaces. On the subsequent absorption cycles, heterogeneous nucleation primarily occurred in the vicinity of "internal" free surfaces such as cracks.

Distribution, Community Composition, and Potential Metabolic Activity of Bacterioplankton in an Urbanized Mediterranean Sea Coastal Zone.

PubMed

Richa, Kumari; Balestra, Cecilia; Piredda, Roberta; Benes, Vladimir; Borra, Marco; Passarelli, Augusto; Margiotta, Francesca; Saggiomo, Maria; Biffali, Elio; Sanges, Remo; Scanlan, David J; Casotti, Raffaella

2017-09-01

Bacterioplankton are fundamental components of marine ecosystems and influence the entire biosphere by contributing to the global biogeochemical cycles of key elements. Yet, there is a significant gap in knowledge about their diversity and specific activities, as well as environmental factors that shape their community composition and function. Here, the distribution and diversity of surface bacterioplankton along the coastline of the Gulf of Naples (GON; Italy) were investigated using flow cytometry coupled with high-throughput sequencing of the 16S rRNA gene. Heterotrophic bacteria numerically dominated the bacterioplankton and comprised mainly Alphaproteobacteria , Gammaproteobacteria , and Bacteroidetes Distinct communities occupied river-influenced, coastal, and offshore sites, as indicated by Bray-Curtis dissimilarity, distance metric (UniFrac), linear discriminant analysis effect size (LEfSe), and multivariate analyses. The heterogeneity in diversity and community composition was mainly due to salinity and changes in environmental conditions across sites, as defined by nutrient and chlorophyll a concentrations. Bacterioplankton communities were composed of a few dominant taxa and a large proportion (92%) of rare taxa (here defined as operational taxonomic units [OTUs] accounting for <0.1% of the total sequence abundance), the majority of which were unique to each site. The relationship between 16S rRNA and the 16S rRNA gene, i.e., between potential metabolic activity and abundance, was positive for the whole community. However, analysis of individual OTUs revealed high rRNA-to-rRNA gene ratios for most (71.6% ± 16.7%) of the rare taxa, suggesting that these low-abundance organisms were potentially active and hence might be playing an important role in ecosystem diversity and functioning in the GON. IMPORTANCE The study of bacterioplankton in coastal zones is of critical importance, considering that these areas are highly productive and anthropogenically impacted. Their richness and evenness, as well as their potential activity, are very important to assess ecosystem health and functioning. Here, we investigated bacterial distribution, community composition, and potential metabolic activity in the GON, which is an ideal test site due to its heterogeneous environment characterized by a complex hydrodynamics and terrestrial inputs of varied quantities and quality. Our study demonstrates that bacterioplankton communities in this region are highly diverse and strongly regulated by a combination of different environmental factors leading to their heterogeneous distribution, with the rare taxa contributing to a major proportion of diversity and shifts in community composition and potentially holding a key role in ecosystem functioning. Copyright © 2017 American Society for Microbiology.

Distribution, Community Composition, and Potential Metabolic Activity of Bacterioplankton in an Urbanized Mediterranean Sea Coastal Zone

PubMed Central

Richa, Kumari; Balestra, Cecilia; Piredda, Roberta; Benes, Vladimir; Borra, Marco; Passarelli, Augusto; Margiotta, Francesca; Saggiomo, Maria; Biffali, Elio; Sanges, Remo; Scanlan, David J.

2017-01-01

ABSTRACT Bacterioplankton are fundamental components of marine ecosystems and influence the entire biosphere by contributing to the global biogeochemical cycles of key elements. Yet, there is a significant gap in knowledge about their diversity and specific activities, as well as environmental factors that shape their community composition and function. Here, the distribution and diversity of surface bacterioplankton along the coastline of the Gulf of Naples (GON; Italy) were investigated using flow cytometry coupled with high-throughput sequencing of the 16S rRNA gene. Heterotrophic bacteria numerically dominated the bacterioplankton and comprised mainly Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes. Distinct communities occupied river-influenced, coastal, and offshore sites, as indicated by Bray-Curtis dissimilarity, distance metric (UniFrac), linear discriminant analysis effect size (LEfSe), and multivariate analyses. The heterogeneity in diversity and community composition was mainly due to salinity and changes in environmental conditions across sites, as defined by nutrient and chlorophyll a concentrations. Bacterioplankton communities were composed of a few dominant taxa and a large proportion (92%) of rare taxa (here defined as operational taxonomic units [OTUs] accounting for <0.1% of the total sequence abundance), the majority of which were unique to each site. The relationship between 16S rRNA and the 16S rRNA gene, i.e., between potential metabolic activity and abundance, was positive for the whole community. However, analysis of individual OTUs revealed high rRNA-to-rRNA gene ratios for most (71.6% ± 16.7%) of the rare taxa, suggesting that these low-abundance organisms were potentially active and hence might be playing an important role in ecosystem diversity and functioning in the GON. IMPORTANCE The study of bacterioplankton in coastal zones is of critical importance, considering that these areas are highly productive and anthropogenically impacted. Their richness and evenness, as well as their potential activity, are very important to assess ecosystem health and functioning. Here, we investigated bacterial distribution, community composition, and potential metabolic activity in the GON, which is an ideal test site due to its heterogeneous environment characterized by a complex hydrodynamics and terrestrial inputs of varied quantities and quality. Our study demonstrates that bacterioplankton communities in this region are highly diverse and strongly regulated by a combination of different environmental factors leading to their heterogeneous distribution, with the rare taxa contributing to a major proportion of diversity and shifts in community composition and potentially holding a key role in ecosystem functioning. PMID:28667110

A Parameterization for Land-Atmosphere-Cloud Exchange (PLACE): Documentation and Testing of a Detailed Process Model of the Partly Cloudy Boundary Layer over Heterogeneous Land.

NASA Astrophysics Data System (ADS)

Wetzel, Peter J.; Boone, Aaron

1995-07-01

This paper presents a general description of, and demonstrates the capabilities of, the Parameterization for Land-Atmosphere-Cloud Exchange (PLACE). The PLACE model is a detailed process model of the partly cloudy atmospheric boundary layer and underlying heterogeneous land surfaces. In its development, particular attention has been given to three of the model's subprocesses: the prediction of boundary layer cloud amount, the treatment of surface and soil subgrid heterogeneity, and the liquid water budget. The model includes a three-parameter nonprecipitating cumulus model that feeds back to the surface and boundary layer through radiative effects. Surface heterogeneity in the PLACE model is treated both statistically and by resolving explicit subgrid patches. The model maintains a vertical column of liquid water that is divided into seven reservoirs, from the surface interception store down to bedrock.Five single-day demonstration cases are presented, in which the PLACE model was initialized, run, and compared to field observations from four diverse sites. The model is shown to predict cloud amount well in these while predicting the surface fluxes with similar accuracy. A slight tendency to underpredict boundary layer depth is noted in all cases.Sensitivity tests were also run using anemometer-level forcing provided by the Project for Inter-comparison of Land-surface Parameterization Schemes (PILPS). The purpose is to demonstrate the relative impact of heterogeneity of surface parameters on the predicted annual mean surface fluxes. Significant sensitivity to subgrid variability of certain parameters is demonstrated, particularly to parameters related to soil moisture. A major result is that the PLACE-computed impact of total (homogeneous) deforestation of a rain forest is comparable in magnitude to the effect of imposing heterogeneity of certain surface variables, and is similarly comparable to the overall variance among the other PILPS participant models. Were this result to be bourne out by further analysis, it would suggest that today's average land surface parameterization has little credibility when applied to discriminating the local impacts of any plausible future climate change.

Estimating and validating surface energy fluxes at field scale over a heterogeneous land surfaces based on two-source energy balance model (TSEB)

USDA-ARS?s Scientific Manuscript database

Accurate estimation of surface energy fluxes at field scale over large areas has the potential to improve agricultural water management in arid and semiarid watersheds. Remote sensing may be the only viable approach for mapping fluxes over heterogeneous landscapes. The Two-Source Energy Balance mode...

The impacts of pore-scale physical and chemical heterogeneities on the transport of radionuclide-carrying colloids

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

Wu, Ning

Independent of the methods of nuclear waste disposal, the degradation of packaging materials could lead to mobilization and transport of radionuclides into the geosphere. This process can be significantly accelerated due to the association of radionuclides with the backfill materials or mobile colloids in groundwater. The transport of these colloids is complicated by the inherent coupling of physical and chemical heterogeneities (e.g., pore space geometry, grain size, charge heterogeneity, and surface hydrophobicity) in natural porous media that can exist on the length scale of a few grains. In addition, natural colloids themselves are often heterogeneous in their surface properties (e.g.,more » clay platelets possess opposite charges on the surface and along the rim). Both physical and chemical heterogeneities influence the transport and retention of radionuclides under various groundwater conditions. However, the precise mechanisms how these coupled heterogeneities influence colloidal transport are largely elusive. This knowledge gap is a major source of uncertainty in developing accurate models to represent the transport process and to predict distribution of radionuclides in the geosphere.« less

Methods and compositions for chromosome-specific staining

DOEpatents

Gray, Joe W.; Pinkel, Daniel

2003-07-22

Methods and compositions for chromosome-specific staining are provided. Compositions comprise heterogenous mixtures of labeled nucleic acid fragments having substantially complementary base sequences to unique sequence regions of the chromosomal DNA for which their associated staining reagent is specific. Methods include methods for making the chromosome-specific staining compositions of the invention, and methods for applying the staining compositions to chromosomes.

HETEROGENEOUS SOOT NANOSTRUCTURE IN ATMOSPHERIC AND COMBUSTION SOURCE AEROSOLS

EPA Science Inventory

Microscopic images of soot emissions from wildfire and a wide range of anthropogenic combustion sources show that the nanostructures of individual particles in these emissions are predominantly heterogeneous, decidedly influenced by the fuel composition and by the particular comb...

Shape-engineering substrate-based plasmonic nanomaterials

NASA Astrophysics Data System (ADS)

Gilroy, Kyle D.

The advancement of next generation technologies is reliant on our ability to engineer matter at the nanoscale. Since the morphological features of nanomaterials dictate their chemical and physical properties, a significant effort has been put forth to develop syntheses aimed at fine tuning their size, shape and composition. This massive effort has resulted in a maturing colloidal chemistry containing an extensive collection of morphologies with compositions nearly spanning the entire transition of the periodic table. While colloidal nanoparticles have opened the door to promising applications in fields such as cancer theranostics, drug delivery, catalysis and sensing; the synthetic protocols for the placement of nanomaterials on surfaces, a requisite for chip-based devices, are ill-developed. This dissertation serves to address this limitation by highlighting a series of syntheses related to the design of substrate-based nanoparticles whose size, shape and composition are controllably engineered to a desired endpoint. The experimental methods are based on a template-mediated approach which sees chemical modifications made to prepositioned thermally assembled metal nanostructures which are well bonded to a sapphire substrate. The first series of investigations will highlight synthetic routes utilizing galvanic replacement reactions, where the prepositioned templates are chemically transformed into hollow nanoshells. Detailed studies are provided highlighting discoveries related to (i) hollowing, (ii) defect transfer, (iii) strain induction, (iv) interdiffusion, (v) crystal structure and (vi) the localized surface plasmon resonance (LSPR). The second series of investigations, based on heterogeneous nucleation, have Au templates serve as nucleation sites for metal atoms arriving in either the solution- or vapor phase. The solution-phase heterogeneous nucleation of Ag on Au reveals that chemical kinetics (injection rate & precursor concentration) can be used to control the nature of how Ag atoms grow on the Au template. It was discovered that (i) slow kinetics leads to an anisotropic growth mode (heterodimeric structures), (ii) fast kinetics causes a very uniform deposition (Au-Ag coreshell morphology, or Au Ag) and (iii) medium kinetics produces structures with an intermediate morphology (truncated octahedron). In the second case, where the nucleation event is carried out at high temperatures, the Ag vapor is sourced from a sublimating foil onto adjacent Au templates. This process drives the composition and morphology from a Au Wulff-shape to a homogeneous Au-Ag nanoprism. By tracking over time the (i) morphological features, (ii) LSPR and (iii) composition; insights into the fundamental atomic scale growth mechanisms are elucidated. Overall, substrate-based template-mediated syntheses have proven to be an effective route for directing growth pathways toward a desired endpoint giving rise to an impressive new group of complex substrate-based nanostructures with asymmetric, core-shell and hollowed morphologies. While this dissertation is focused heavily on the development of synthetic procedures aimed at generating substrate-based plasmonic nanomaterials, the last chapter will serve to highlight a series of on-going studies aimed at defining these nanomaterials as highly effective heterogeneous catalysts. Several examples are shown including (i) nanoparticle films synthesize via sputter deposition, (ii) mechanically induced nanotexturing of bulk copper foils, (iii) ultra-small AuPd nanoparticles synthesized via pulse laser, (iv) substrate-based AuCu nanoprisms and (v) the Wulff in a Cage Morphology.

Transport of Cryptosporidium parvum Oocysts in Charge Heterogeneous Porous Media: Microfluidics Experiment and Numerical Simulation

NASA Astrophysics Data System (ADS)

Liu, Y.; Meng, X.; Guo, Z.; Zhang, C.; Nguyen, T. H.; Hu, D.; Ji, J.; Yang, X.

2017-12-01

Colloidal attachment on charge heterogeneous grains has significant environmental implications for transport of hazardous colloids, such as pathogens, in the aquifer, where iron, manganese, and aluminium oxide minerals are the major source of surface charge heterogeneity of the aquifer grains. A patchwise surface charge model is often used to describe the surface charge heterogeneity of the grains. In the patchwise model, the colloidal attachment efficiency is linearly correlated with the fraction of the favorable patches (θ=λ(θf - θu)+θu). However, our previous microfluidic study showed that the attachment efficiency of oocysts of Cryptosporidium parvum, a waterborne protozoan parasite, was not linear correlated with the fraction of the favorable patches (λ). In this study, we developed a pore scale model to simulate colloidal transport and attachment on charge heterogeneous grains. The flow field was simulated using the LBM method and colloidal transport and attachment were simulated using the Lagrange particle tracking method. The pore scale model was calibrated with experimental results of colloidal and oocyst transport in microfluidic devices and was then used to simulate oocyst transport in charge heterogeneous porous media under a variety of environmental relative conditions, i.e. the fraction of favorable patchwise, ionic strength, and pH. The results of the pore scale simulations were used to evaluate the effect of surface charge heterogeneity on upscaling of oocyst transport from pore to continuum scale and to develop an applicable correlation between colloidal attachment efficiency and the fraction of the favorable patches.

Essential elucidation for preparation of supported nickel phosphide upon nickel phosphate precursor

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

Liu, Xuguang, E-mail: liuxuguang@qust.edu.cn; Xu, Lei; Zhang, Baoquan

2014-04-01

Preparation of supported nickel phosphide (Ni{sub 2}P) depends on nickel phosphate precursor, generally related to its chemical composition and supports. Study of this dependence is essential and meaningful for the preparation of supported Ni{sub 2}P with excellent catalytic activity. The chemical nature of nickel phosphate precursor is revealed by Raman and UV–vis spectra. It is found that initial P/Ni mole ratio ≥0.8 prohibits the Ni-O-Ni bridge bonding (i.e., nickel oxide). This chemical bonding will not result in Ni{sub 2}P structure, verified by XRD characterization results. The alumina (namely, γ-Al{sub 2}O{sub 3}, θ-Al{sub 2}O{sub 3}, or α-Al{sub 2}O{sub 3}) with distinctmore » physiochemical properties also results in diverse chemical nature of nickel phosphate, and then different nickel phosphides. The influence of alumina support on producing Ni{sub 2}P was explained by the theory of surface energy heterogeneity, calculated by the NLDFT method based on N{sub 2}-sorption isotherm. The uniform surface energy of α-Al{sub 2}O{sub 3} results only in the nickel phosphosate precursor and thus the Ni{sub 2}P phase. - Graphical abstract: Surface energy heterogeneity in alumina (namely α-Al{sub 2}O{sub 3}, θ-Al{sub 2}O{sub 3}, and γ-Al{sub 2}O{sub 3}) supported multi-oxidic precursors with different reducibilities and thus diverse nickel phosphides (i.e., Ni{sub 3}P, Ni{sub 12}P{sub 5}, Ni{sub 2}P). - Highlights: • Preparing pure Ni{sub 2}P. • Elucidating nickel phosphate precursor. • Associating with surface energy.« less

Solution properties and spectroscopic characterization of polymeric precursors to SiNCB and BN ceramic materials

NASA Astrophysics Data System (ADS)

Cortez, E.; Remsen, E.; Chlanda, V.; Wideman, T.; Zank, G.; Carrol, P.; Sneddon, L.

1998-06-01

Boron Nitride, BN, and composite SiNCB ceramic fibers are important structural materials because of their excellent thermal and oxidative stabilities. Consequently, polymeric materials as precursors to ceramic composites are receiving increasing attention. Characterization of these materials requires the ability to evaluate simultaneous molecular weight and compositional heterogeneity within the polymer. Size exclusion chromatography equipped with viscometric and refractive index detection as well as coupled to a LC-transform device for infrared absorption analysis has been employed to examine these heterogeneities. Using these combined approaches, the solution properties and the relative amounts of individual functional groups distributed through the molecular weight distribution of SiNCB and BN polymeric precursors were characterized.

Micromechanics Based Failure Analysis of Heterogeneous Materials

NASA Astrophysics Data System (ADS)

Sertse, Hamsasew M.

In recent decades, heterogeneous materials are extensively used in various industries such as aerospace, defense, automotive and others due to their desirable specific properties and excellent capability of accumulating damage. Despite their wide use, there are numerous challenges associated with the application of these materials. One of the main challenges is lack of accurate tools to predict the initiation, progression and final failure of these materials under various thermomechanical loading conditions. Although failure is usually treated at the macro and meso-scale level, the initiation and growth of failure is a complex phenomena across multiple scales. The objective of this work is to enable the mechanics of structure genome (MSG) and its companion code SwiftComp to analyze the initial failure (also called static failure), progressive failure, and fatigue failure of heterogeneous materials using micromechanics approach. The initial failure is evaluated at each numerical integration point using pointwise and nonlocal approach for each constituent of the heterogeneous materials. The effects of imperfect interfaces among constituents of heterogeneous materials are also investigated using a linear traction-displacement model. Moreover, the progressive and fatigue damage analyses are conducted using continuum damage mechanics (CDM) approach. The various failure criteria are also applied at a material point to analyze progressive damage in each constituent. The constitutive equation of a damaged material is formulated based on a consistent irreversible thermodynamics approach. The overall tangent modulus of uncoupled elastoplastic damage for negligible back stress effect is derived. The initiation of plasticity and damage in each constituent is evaluated at each numerical integration point using a nonlocal approach. The accumulated plastic strain and anisotropic damage evolution variables are iteratively solved using an incremental algorithm. The damage analyses are performed for both brittle failure/high cycle fatigue (HCF) for negligible plastic strain and ductile failure/low cycle fatigue (LCF) for large plastic strain. The proposed approach is incorporated in SwiftComp and used to predict the initial failure envelope, stress-strain curve for various loading conditions, and fatigue life of heterogeneous materials. The combined effects of strain hardening and progressive fatigue damage on the effective properties of heterogeneous materials are also studied. The capability of the current approach is validated using several representative examples of heterogeneous materials including binary composites, continuous fiber-reinforced composites, particle-reinforced composites, discontinuous fiber-reinforced composites, and woven composites. The predictions of MSG are also compared with the predictions obtained using various micromechanics approaches such as Generalized Methods of Cells (GMC), Mori-Tanaka (MT), and Double Inclusions (DI) and Representative Volume Element (RVE) Analysis (called as 3-dimensional finite element analysis (3D FEA) in this document). This study demonstrates that a micromechanics based failure analysis has a great potential to rigorously and more accurately analyze initiation and progression of damage in heterogeneous materials. However, this approach requires material properties specific to damage analysis, which are needed to be independently calibrated for each constituent.

Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) with Raman Imaging Applied to Lunar Meteorites.

PubMed

Smith, Joseph P; Smith, Frank C; Booksh, Karl S

2018-03-01

Lunar meteorites provide a more random sampling of the surface of the Moon than do the returned lunar samples, and they provide valuable information to help estimate the chemical composition of the lunar crust, the lunar mantle, and the bulk Moon. As of July 2014, ∼96 lunar meteorites had been documented and ten of these are unbrecciated mare basalts. Using Raman imaging with multivariate curve resolution-alternating least squares (MCR-ALS), we investigated portions of polished thin sections of paired, unbrecciated, mare-basalt lunar meteorites that had been collected from the LaPaz Icefield (LAP) of Antarctica-LAP 02205 and LAP 04841. Polarized light microscopy displays that both meteorites are heterogeneous and consist of polydispersed sized and shaped particles of varying chemical composition. For two distinct probed areas within each meteorite, the individual chemical species and associated chemical maps were elucidated using MCR-ALS applied to Raman hyperspectral images. For LAP 02205, spatially and spectrally resolved clinopyroxene, ilmenite, substrate-adhesive epoxy, and diamond polish were observed within the probed areas. Similarly, for LAP 04841, spatially resolved chemical images with corresponding resolved Raman spectra of clinopyroxene, troilite, a high-temperature polymorph of anorthite, substrate-adhesive epoxy, and diamond polish were generated. In both LAP 02205 and LAP 04841, substrate-adhesive epoxy and diamond polish were more readily observed within fractures/veinlet features. Spectrally diverse clinopyroxenes were resolved in LAP 04841. Factors that allow these resolved clinopyroxenes to be differentiated include crystal orientation, spatially distinct chemical zoning of pyroxene crystals, and/or chemical and molecular composition. The minerals identified using this analytical methodology-clinopyroxene, anorthite, ilmenite, and troilite-are consistent with the results of previous studies of the two meteorites using electron microprobe analysis. To our knowledge, this is the first report of MCR-ALS with Raman imaging used for the investigation of both lunar and other types of meteorites. We have demonstrated the use of multivariate analysis methods, namely MCR-ALS, with Raman imaging to investigate heterogeneous lunar meteorites. Our analytical methodology can be used to elucidate the chemical, molecular, and structural characteristics of phases in a host of complex, heterogeneous geological, geochemical, and extraterrestrial materials.

How Do Particle Shape and Internal Composition Affect Optical Properties of Atmospheric Dust: Studies of Individual Particles Based on Focused Ion-Beam Tomography

NASA Astrophysics Data System (ADS)

Conny, J. M.; Ortiz-Montalvo, D. L.

2017-12-01

In the remote sensing of atmospheric aerosols, coarse-mode dust particles are often modeled optically as a collection of spheroids. However, atmospheric particles rarely resemble simplified shapes such as spheroids. Moreover, individual particles often have a heterogenous composition and may not be sufficiently modeled as a single material. In this work, we determine the optical properties of dust particles based on 3-dimensional models of individual particles from focused ion-beam (FIB) tomography. We compare the optical properties of the actual particles with the particles as simplified shapes including one or more spheres, an ellipsoid, cube, rectangular prism, or tetrahedron. FIB tomography is performed with a scanning electron microscope equipped with an ion-beam column. The ion beam slices through the particle incrementally as the electron beam images each slice. Element maps of the particle may be acquired with energy-dispersive x-ray spectroscopy. The images and maps are used to create the 3-D spatial model, from which the discrete dipole approximation method is used to calculate extinction, single scattering albedo, asymmetry parameter, and the phase function. Models of urban dust show that shape is generally more important than accounting for composition heterogeneity. However, if a particle has material phases with widely-varying refractive indexes, a geometric model may be insufficient if it does not incorporate heterogeneity. Models of Asian dust show that geometric models generally exhibit lower extinction efficiencies than the actual particles suggesting that simplified models do not adequately account for particle surface roughness. Nevertheless, in most cases the extinction from the tetrahedron model comes closest to that of the actual particles suggesting that accounting for particle angularity is important. The phase function from the tetrahedron model is comparable to the ellipsoid model and generally close to the actual particle, particularly in the backscatter direction (90° to 180°). Current work focuses on optical models of particles with a strongly-absorbing soot phase attached to a scattering mineral phase.

Effects of geometric modulation and surface potential heterogeneity on electrokinetic flow and solute transport in a microchannel

NASA Astrophysics Data System (ADS)

Bera, Subrata; Bhattacharyya, S.

2017-12-01

A numerical investigation is performed on the electroosmotic flow (EOF) in a surface-modulated microchannel to induce enhanced solute mixing. The channel wall is modulated by placing surface-mounted obstacles of trigonometric shape along which the surface potential is considered to be different from the surface potential of the homogeneous part of the wall. The characteristics of the electrokinetic flow are governed by the Laplace equation for the distribution of external electric potential; the Poisson equation for the distribution of induced electric potential; the Nernst-Planck equations for the distribution of ions; and the Navier-Stokes equations for fluid flow simultaneously. These nonlinear coupled set of governing equations are solved numerically by a control volume method over the staggered system. The influence of the geometric modulation of the surface, surface potential heterogeneity and the bulk ionic concentration on the EOF is analyzed. Vortical flow develops near a surface modulation, and it becomes stronger when the surface potential of the modulated region is in opposite sign to the surface potential of the homogeneous part of the channel walls. Vortical flow also depends on the Debye length when the Debye length is in the order of the channel height. Pressure drop along the channel length is higher for a ribbed wall channel compared to the grooved wall case. The pressure drop decreases with the increase in the amplitude for a grooved channel, but increases for a ribbed channel. The mixing index is quantified through the standard deviation of the solute distribution. Our results show that mixing index is higher for the ribbed channel compared to the grooved channel with heterogeneous surface potential. The increase in potential heterogeneity in the modulated region also increases the mixing index in both grooved and ribbed channels. However, the mixing performance, which is the ratio of the mixing index to pressure drop, reduces with the rise in the surface potential heterogeneity.

Effects of geometric modulation and surface potential heterogeneity on electrokinetic flow and solute transport in a microchannel

NASA Astrophysics Data System (ADS)

Bera, Subrata; Bhattacharyya, S.

2018-04-01

A numerical investigation is performed on the electroosmotic flow (EOF) in a surface-modulated microchannel to induce enhanced solute mixing. The channel wall is modulated by placing surface-mounted obstacles of trigonometric shape along which the surface potential is considered to be different from the surface potential of the homogeneous part of the wall. The characteristics of the electrokinetic flow are governed by the Laplace equation for the distribution of external electric potential; the Poisson equation for the distribution of induced electric potential; the Nernst-Planck equations for the distribution of ions; and the Navier-Stokes equations for fluid flow simultaneously. These nonlinear coupled set of governing equations are solved numerically by a control volume method over the staggered system. The influence of the geometric modulation of the surface, surface potential heterogeneity and the bulk ionic concentration on the EOF is analyzed. Vortical flow develops near a surface modulation, and it becomes stronger when the surface potential of the modulated region is in opposite sign to the surface potential of the homogeneous part of the channel walls. Vortical flow also depends on the Debye length when the Debye length is in the order of the channel height. Pressure drop along the channel length is higher for a ribbed wall channel compared to the grooved wall case. The pressure drop decreases with the increase in the amplitude for a grooved channel, but increases for a ribbed channel. The mixing index is quantified through the standard deviation of the solute distribution. Our results show that mixing index is higher for the ribbed channel compared to the grooved channel with heterogeneous surface potential. The increase in potential heterogeneity in the modulated region also increases the mixing index in both grooved and ribbed channels. However, the mixing performance, which is the ratio of the mixing index to pressure drop, reduces with the rise in the surface potential heterogeneity.

Mapping microbubble viscosity using fluorescence lifetime imaging of molecular rotors

PubMed Central

Hosny, Neveen A.; Mohamedi, Graciela; Rademeyer, Paul; Owen, Joshua; Wu, Yilei; Tang, Meng-Xing; Eckersley, Robert J.; Stride, Eleanor; Kuimova, Marina K.

2013-01-01

Encapsulated microbubbles are well established as highly effective contrast agents for ultrasound imaging. There remain, however, some significant challenges to fully realize the potential of microbubbles in advanced applications such as perfusion mapping, targeted drug delivery, and gene therapy. A key requirement is accurate characterization of the viscoelastic surface properties of the microbubbles, but methods for independent, nondestructive quantification and mapping of these properties are currently lacking. We present here a strategy for performing these measurements that uses a small fluorophore termed a “molecular rotor” embedded in the microbubble surface, whose fluorescence lifetime is directly related to the viscosity of its surroundings. We apply fluorescence lifetime imaging to show that shell viscosities vary widely across the population of the microbubbles and are influenced by the shell composition and the manufacturing process. We also demonstrate that heterogeneous viscosity distributions exist within individual microbubble shells even with a single surfactant component. PMID:23690599

Engineering Metallic Nanoparticles for Enhancing and Probing Catalytic Reactions.

PubMed

Collins, Gillian; Holmes, Justin D

2016-07-01

Recent developments in tailoring the structural and chemical properties of colloidal metal nanoparticles (NPs) have led to significant enhancements in catalyst performance. Controllable colloidal synthesis has also allowed tailor-made NPs to serve as mechanistic probes for catalytic processes. The innovative use of colloidal NPs to gain fundamental insights into catalytic function will be highlighted across a variety of catalytic and electrocatalytic applications. The engineering of future heterogenous catalysts is also moving beyond size, shape and composition considerations. Advancements in understanding structure-property relationships have enabled incorporation of complex features such as tuning surface strain to influence the behavior of catalytic NPs. Exploiting plasmonic properties and altering colloidal surface chemistry through functionalization are also emerging as important areas for rational design of catalytic NPs. This news article will highlight the key developments and challenges to the future design of catalytic NPs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Microprobe studies of microtomed particles of white druse salts in shergottite EETA 79001

NASA Technical Reports Server (NTRS)

Lindstrom, D. J.

1991-01-01

The white druse material in Antarctic shergottite EETA 79001 has attracted much attention as a possible sample fo Martian aqueous deposits. Instrumental Neutron Activation Analysis (INAA) was used to determine trace element analyses of small particles of this material obtained by handpicking of likely grains from broken surfaces of the meteorite. Electron microprobe work was attempted on grain areas as large as 150x120 microns. Backscattered electron images show considerable variations in brightness, and botryoidal structures were observed. Microprobe analyses showed considerable variability both within single particles and between different particles. Microtomed surfaces of small selected particles were shown to be very useful in obtaining information on the texture and composition of rare lithologies like the white druse of EETA 79001. This material is clearly heterogeneous on all distance scales, so a large number of further analyses will be required to characterize it.

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

Ye, Rong; Hurlburt, Tyler J.; Sabyrov, Kairat

Colloidal chemistry is used to control the size, shape, morphology, and composition of metal nanoparticles. Model catalysts as such are applied to catalytic transformations in the three types of catalysts: heterogeneous, homogeneous, and enzymatic. Real-time dynamics of oxidation state, coordination, and bonding of nanoparticle catalysts are put under the microscope using surface techniques such as sumfrequency generation vibrational spectroscopy and ambient pressure X-ray photoelectron spectroscopy under catalytically relevant conditions. It was demonstrated that catalytic behavior and trends are strongly tied to oxidation state, the coordination number and crystallographic orientation of metal sites, and bonding and orientation of surface adsorbates. Itmore » was also found that catalytic performance can be tuned by carefully designing and fabricating catalysts from the bottom up. Homogeneous and h eterogeneous catalysts, and likely enzymes, behave similarly at the molecular level. Finally, unifying the fields of catalysis is the key to achieving the goal of 100% selectivity in catalysis.« less

Direct monolithic integration of vertical single crystalline octahedral molecular sieve nanowires on silicon

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

Carretero-Genevrier, Adrian; Oro-Sole, Judith; Gazquez, Jaume

2013-12-13

We developed an original strategy to produce vertical epitaxial single crystalline manganese oxide octahedral molecular sieve (OMS) nanowires with tunable pore sizes and compositions on silicon substrates by using a chemical solution deposition approach. The nanowire growth mechanism involves the use of track-etched nanoporous polymer templates combined with the controlled growth of quartz thin films at the silicon surface, which allowed OMS nanowires to stabilize and crystallize. α-quartz thin films were obtained after thermal activated crystallization of the native amorphous silica surface layer assisted by Sr 2+- or Ba 2+-mediated heterogeneous catalysis in the air at 800 °C. These α-quartzmore » thin films work as a selective template for the epitaxial growth of randomly oriented vertical OMS nanowires. Furthermore, the combination of soft chemistry and epitaxial growth opens new opportunities for the effective integration of novel technological functional tunneled complex oxides nanomaterials on Si substrates.« less

Diffusion and Surface Reaction in Heterogeneous Catalysis

ERIC Educational Resources Information Center

Baiker, A.; Richarz, W.

1978-01-01

Ethylene hydrogenation on a platinum catalyst, electrolytically applied to a tube wall, is a good system for the study of the interactions between diffusion and surface reaction in heterogeneous catalysis. Theoretical background, apparatus, procedure, and student performance of this experiment are discussed. (BB)

Commensurability and transformations of adsorbed phases on a heterogeneous solid with periodic distribution of surface energy

NASA Astrophysics Data System (ADS)

Cortés, Joaquin; Valencia, Eliana

1997-07-01

Monte Carlo experiments are used to investigate the adsorption of argon on a heterogeneous solid with a periodic distribution of surface energy. A study is made of the relation between the adsorbate molecule's diameter and the distance between the sites of maximum surface energy on the critical temperature, the observed phase changes, and the commensurability of the surface phase structure determined in the simulation.

Surface wettability of an atomically heterogeneous system and the resulting intermolecular forces

NASA Astrophysics Data System (ADS)

Chatterjee, Sanghamitro; Bhattacharjee, Sudeep; Maurya, Sanjeev K.; Srinivasan, Vyas; Khare, Krishnacharya; Khandekar, Sameer

2017-06-01

We present the effect of 0.5 keV Ar+ beam irradiation on the wetting properties of metallic thin films. Observations reveal a transition from hydrophilic to hydrophobic nature at higher beam fluences which can be attributed to a reduction in net surface free energy. In this low-energy regime, ion beams do not induce significant surface roughness and chemical heterogeneity. However, they cause implantation of atomic impurities in the near surface region of the target and thus form a heterogeneous system at atomic length scales. Interestingly, the presence of implanted Ar atoms in the near surface region modifies the dispersive intermolecular interaction near the surface but induces no chemical modification due to their inert nature. On this basis, we have developed a theoretical model consistent with the experimental observations that reproduces the effective Hamaker constant with a reasonable accuracy.

Modification of heterogeneous chemistry by complex substrate morphology

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

Henson, B.F.; Buelow, S.J.; Robinson, J.M.

1998-12-31

This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). Chemistry in many environmental systems is determined at some stage by heterogeneous reaction with a surface. Typically the surface exists as a dispersion or matrix of particulate matter or pores, and a determination of the heterogeneous chemistry of the system must address the extent to which the complexity of the environmental surface affects the reaction rates. Reactions that are of current interest are the series of chlorine nitrate reactions important in polar ozone depletion. The authors have applied surfacemore » spectroscopic techniques developed at LANL to address the chemistry of chlorine nitrate reactions on porous nitric and sulfuric acid ice surfaces as a model study of the measurement of complex, heterogeneous reaction rates. The result of the study is an experimental determination of the surface coverage of one adsorbed reagent and a mechanism of reactivity based on the dependence of this coverage on temperature and vapor pressure. The resulting mechanism allows the first comprehensive modeling of chlorine nitrate reaction probability data from several laboratories.« less

Hydrocarbon ices in extra-red TNOs and Centaurs

NASA Astrophysics Data System (ADS)

Dalle Ore, C. M.; Barucci, M.; Emery, J. P.; Cruikshank, D. P.; Merlin, F.; Perna, D.

2012-12-01

We present an analysis of the reddest trans-neptunian objects (TNOs) and Centaurs - those belonging to the RR taxon. The RR class contains more than ¼ of the population of TNOs for which photometric colors are available, including a variety of dynamically different objects. The available data cover the spectral range from 0.3 to 2.2 μm. Previous work investigated possible relations between spectral characteristics and other physical and dynamical parameters. The distribution of ices on TNOs has been analyzed as a function of the object absolute magnitude, taxonomy and dynamical class. In a sample of 76 objects for which visible and near-IR spectroscopic measurements are available, CH3OH ice was detected only on three objects belonging to the RR taxonomic class (5145 Pholus, 55638 2002 VE95 and 90377 Sedna). These three objects are among the reddest, they belong to different dynamical classes, and they have different dimensions. However, all three have similar compositions with Sedna showing a more significant heterogeneity in the kind of hydrocarbon ices found on its surface than the others. To further investigate the presence of hydrocarbon ices, and in particular CH3OH, as part of the composition of the RR taxon we used Spitzer IRAC data available for a subgroup of nine objects. Both methanol and methane have a strong absorption at 3.6 μm, the first of the Spitzer IRAC channels, and a much higher albedo at the following channel at 4.5 μm. This albedo pattern is characteristic of some hydrocarbon ices and is very different from H2O ice that shows instead very low albedos at both channels. Our technique makes use of a large database of models including H2O, CH3OH, CH4, and N 2 ices combined with tholins, amorphous carbon, hydrogenated amorphous carbon, serpentine and olivine in different combinations of relative abundances and grain sizes. We automatically extract the models that match the observations at all color wavelengths therefore obtaining for each object a set of compositions that are consistent with its colors. We detect hydrocarbon ices on most objects in our sample. The presence of methanol, or more generally hydrocarbons, on these extra red objects could imply that they exhibit an almost primordial surface. In fact, laboratory experiments of irradiation of compounds rich in methanol show strong reddening. The reddening effect on a Centaur or TNO depends on the composition of the object and on the irradiation history while the thickness of the organic crust depends on the irradiation dose. These objects, following the hypothesis of Brown et al (2011) that objects that formed farther away might be able to retain their methanol ice, have the surface composition and colors set by formation-location-dependent volatile loss in the early solar system. The results of the current work also support the hypothesis that a substantial mixing has occurred after the TNOs formation but cannot exclude the hypothesis of initial heterogeneity.

Predator-guided sampling reveals biotic structure in the bathypelagic.

PubMed

Benoit-Bird, Kelly J; Southall, Brandon L; Moline, Mark A

2016-02-24

We targeted a habitat used differentially by deep-diving, air-breathing predators to empirically sample their prey's distributions off southern California. Fine-scale measurements of the spatial variability of potential prey animals from the surface to 1,200 m were obtained using conventional fisheries echosounders aboard a surface ship and uniquely integrated into a deep-diving autonomous vehicle. Significant spatial variability in the size, composition, total biomass, and spatial organization of biota was evident over all spatial scales examined and was consistent with the general distribution patterns of foraging Cuvier's beaked whales (Ziphius cavirostris) observed in separate studies. Striking differences found in prey characteristics between regions at depth, however, did not reflect differences observed in surface layers. These differences in deep pelagic structure horizontally and relative to surface structure, absent clear physical differences, change our long-held views of this habitat as uniform. The revelation that animals deep in the water column are so spatially heterogeneous at scales from 10 m to 50 km critically affects our understanding of the processes driving predator-prey interactions, energy transfer, biogeochemical cycling, and other ecological processes in the deep sea, and the connections between the productive surface mixed layer and the deep-water column. © 2016 The Author(s).

Modeling the effects of structure on seismic anisotropy in the Chester gneiss dome, southeast Vermont

NASA Astrophysics Data System (ADS)

Saif, S.; Brownlee, S. J.

2017-12-01

Compositional and structural heterogeneity in the continental crust are factors that contribute to the complex expression of crustal seismic anisotropy. Understanding deformation and flow in the crust using seismic anisotropy has thus proven difficult. Seismic anisotropy is affected by rock microstructure and mineralogy, and a number of studies have begun to characterize the full elastic tensors of crustal rocks in an attempt to increase our understanding of these intrinsic factors. However, there is still a large gap in length-scale between laboratory characterization on the scale of centimeters and seismic wavelengths on the order of kilometers. To address this length-scale gap we are developing a 3D crustal model that will help us determine the effects of rotating laboratory-scale elastic tensors into field-scale structures. The Chester gneiss dome in southeast Vermont is our primary focus. The model combines over 2000 structural data points from field measurements and published USGS structural data with elastic tensors of Chester dome rocks derived from electron backscatter diffraction data. We created a uniformly spaced grid by averaging structural measurements together in equally spaced grid boxes. The surface measurements are then projected into the third dimension using existing subsurface interpretations. A measured elastic tensor for the specific rock type is rotated according to its unique structural input at each point in the model. The goal is to use this model to generate artificial seismograms using existing numerical wave propagation codes. Once completed, the model input can be varied to examine the effects of different subsurface structure interpretations, as well as heterogeneity in rock composition and elastic tensors. Our goal is to be able to make predictions for how specific structures will appear in seismic data, and how that appearance changes with variations in rock composition.

ToF-SIMS analysis of poly(L-lysine)-graft-poly(2-methyl-2-oxazoline) ultrathin adlayers.

PubMed

Pidhatika, Bidhari; Chen, Yin; Coullerez, Geraldine; Al-Bataineh, Sameer; Textor, Marcus

2014-02-01

Understanding of the interfacial chemistry of ultrathin polymeric adlayers is fundamentally important in the context of establishing quantitative design rules for the fabrication of nonfouling surfaces in various applications such as biomaterials and medical devices. In this study, seven poly(L-lysine)-graft-poly(2-methyl-2-oxazoline) (PLL-PMOXA) copolymers with grafting density (number of PMOXA chains per lysine residue) 0.09, 0.14, 0.19, 0.33, 0.43, 0.56, and 0.77, respectively, were synthesized and characterized by means of nuclear magnetic resonance spectroscopy (NMR). The copolymers were then adsorbed on Nb2O5 surfaces. Optical waveguide lightmode spectroscopy method was used to monitor the surface adsorption in situ of these copolymers and provide information on adlayer masses that were then converted into PLL and PMOXA surface densities. To investigate the relationship between copolymer bulk architecture (as shown by NMR data) and surface coverage as well as surface architecture, time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis was performed. Furthermore, ToF-SIMS method combined with principal component analysis (PCA) was used to verify the protein resistant properties of PLL-PMOXA adlayers, by thorough characterization before and after adlayer exposure to human serum. ToF-SIMS analysis revealed that the chemical composition as well as the architecture of the different PLL-PMOXA adlayers indeed reflects the copolymer bulk composition. ToF-SIMS results also indicated a heterogeneous surface coverage of PLL-PMOXA adlayers with high grafting densities higher than 0.33. In the case of protein resistant surface, PCA results showed clear differences between protein resistant and nonprotein-resistant surfaces. Therefore, ToF-SIMS results combined with PCA confirmed that the PLL-PMOXA adlayer with brush architecture resists protein adsorption. However, low increases of some amino acid signals in ToF-SIMS spectra were detected after the adlayer has been exposed to human serum.

A geochemical approach to constraining the formation of glassy fallout debris from nuclear tests

DOE PAGES

Bonamici, Chloë E.; Kinman, William S.; Fournelle, John H.; ...

2016-12-15

Reprocessed earth material is a glassy nuclear fallout debris from near-surface nuclear tests. A geochemical approach to analysis of glassy fallout is uniquely suited to determine the means of reprocessing and shed light on the mechanisms of fallout formation. An improved understanding of fallout formation is of interest both for its potential to guide post-detonation nuclear forensic investigations and in the context of possible affinities between glassy debris and other glasses generated by high-energy natural events, such as meteorite impacts and lightning strikes. Our study presents a large major-element compositional dataset for glasses within aerodynamic fallout from the Trinity nuclearmore » test (“trinitite”) and a geochemically based analysis of the glass compositional trends. Silica-rich and alkali-rich trinitite glasses show compositions and textures consistent with formation through melting of individual mineral grains—quartz and alkali feldspar, respectively—from the test-site sediment. Furthermore, the volumetrically dominant glass phase—called the CaMgFe glass—shows extreme major-element compositional variability. Compositional trends in the CaMgFe glass are most consistent with formation through volatility-controlled condensation from compositionally heterogeneous plasma. Radioactivity occurs only in CaMgFe glass, indicating that co-condensation of evaporated bulk ground material and trace device material was the main mechanism of radioisotope incorporation into trinitite. CaMgFe trinitite glasses overlap compositionally with basalts, rhyolites, fulgurites, tektites, and microtektites but display greater compositional diversity than all of these naturally formed glasses. Indeed, the most refractory CaMgFe glasses compositionally resemble early solar system condensates—specifically, CAIs.« less

A geochemical approach to constraining the formation of glassy fallout debris from nuclear tests

NASA Astrophysics Data System (ADS)

Bonamici, Chloë E.; Kinman, William S.; Fournelle, John H.; Zimmer, Mindy M.; Pollington, Anthony D.; Rector, Kirk D.

2017-01-01

Glassy nuclear fallout debris from near-surface nuclear tests is fundamentally reprocessed earth material. A geochemical approach to analysis of glassy fallout is uniquely suited to determine the means of reprocessing and shed light on the mechanisms of fallout formation. An improved understanding of fallout formation is of interest both for its potential to guide post-detonation nuclear forensic investigations and in the context of possible affinities between glassy debris and other glasses generated by high-energy natural events, such as meteorite impacts and lightning strikes. This study presents a large major-element compositional dataset for glasses within aerodynamic fallout from the Trinity nuclear test ("trinitite") and a geochemically based analysis of the glass compositional trends. Silica-rich and alkali-rich trinitite glasses show compositions and textures consistent with formation through melting of individual mineral grains—quartz and alkali feldspar, respectively—from the test-site sediment. The volumetrically dominant glass phase—called the CaMgFe glass—shows extreme major-element compositional variability. Compositional trends in the CaMgFe glass are most consistent with formation through volatility-controlled condensation from compositionally heterogeneous plasma. Radioactivity occurs only in CaMgFe glass, indicating that co-condensation of evaporated bulk ground material and trace device material was the main mechanism of radioisotope incorporation into trinitite. CaMgFe trinitite glasses overlap compositionally with basalts, rhyolites, fulgurites, tektites, and microtektites but display greater compositional diversity than all of these naturally formed glasses. Indeed, the most refractory CaMgFe glasses compositionally resemble early solar system condensates—specifically, CAIs.

The influence of idealized surface heterogeneity on virtual turbulent flux measurements

NASA Astrophysics Data System (ADS)

De Roo, Frederik; Mauder, Matthias

2018-04-01

The imbalance of the surface energy budget in eddy-covariance measurements is still an unsolved problem. A possible cause is the presence of land surface heterogeneity, which affects the boundary-layer turbulence. To investigate the impact of surface variables on the partitioning of the energy budget of flux measurements in the surface layer under convective conditions, we set up a systematic parameter study by means of large-eddy simulation. For the study we use a virtual control volume approach, which allows the determination of advection by the mean flow, flux-divergence and storage terms of the energy budget at the virtual measurement site, in addition to the standard turbulent flux. We focus on the heterogeneity of the surface fluxes and keep the topography flat. The surface fluxes vary locally in intensity and these patches have different length scales. Intensity and length scales can vary for the two horizontal dimensions but follow an idealized chessboard pattern. Our main focus lies on surface heterogeneity of the kilometer scale, and one order of magnitude smaller. For these two length scales, we investigate the average response of the fluxes at a number of virtual towers, when varying the heterogeneity length within the length scale and when varying the contrast between the different patches. For each simulation, virtual measurement towers were positioned at functionally different positions (e.g., downdraft region, updraft region, at border between domains, etc.). As the storage term is always small, the non-closure is given by the sum of the advection by the mean flow and the flux-divergence. Remarkably, the missing flux can be described by either the advection by the mean flow or the flux-divergence separately, because the latter two have a high correlation with each other. For kilometer scale heterogeneity, we notice a clear dependence of the updrafts and downdrafts on the surface heterogeneity and likewise we also see a dependence of the energy partitioning on the tower location. For the hectometer scale, we do not notice such a clear dependence. Finally, we seek correlators for the energy balance ratio in the simulations. The correlation with the friction velocity is less pronounced than previously found, but this is likely due to our concentration on effectively strongly to freely convective conditions.

Methods for chromosome-specific staining

DOEpatents

Gray, Joe W.; Pinkel, Daniel

1995-01-01

Methods and compositions for chromosome-specific staining are provided. Compositions comprise heterogenous mixtures of labeled nucleic acid fragments having substantially complementary base sequences to unique sequence regions of the chromosomal DNA for which their associated staining reagent is specific. Methods include methods for making the chromosome-specific staining compositions of the invention, and methods for applying the staining compositions to chromosomes.

Heterogeneous Oxidation of Laboratory-generated Mixed Composition and Biomass Burning Particles

NASA Astrophysics Data System (ADS)

Lim, C. Y.; Sugrue, R. A.; Hagan, D. H.; Cappa, C. D.; Kroll, J. H.; Browne, E. C.

2016-12-01

Heterogeneous oxidation of organic aerosol (OA) can significantly transform the chemical and physical properties of particulate matter in the atmosphere, leading to changes to the chemical composition of OA and potential volatilization of organic compounds. It has become increasingly apparent that the heterogeneous oxidation kinetics of OA depend on the phase and morphology of the particles. However, most laboratory experiments to date have been performed on single-component, purely organic precursors, which may exhibit fundamentally different behavior than more complex particles in the atmosphere. Here we present laboratory studies of the heterogeneous oxidation of two more complex chemical systems: thin, organic coatings on inorganic seed particles and biomass burning OA. In the first system, squalane (C30H62), a model compound for reduced OA, is coated onto dry ammonium sulfate particles at various thicknesses (10-20 nm) and exposed to hydroxyl radical (OH) in a flow tube reactor. In the second, we use a semi-batch reactor to study the heterogeneous OH-initiated oxidation of biomass burning particles as a part of the 2016 FIREX campaign in Missoula, MT. The resulting changes in chemical composition are monitored with an Aerodyne High Resolution Time-of-flight Aerosol Mass Spectrometer (AMS) and a soot-particle AMS for the non-refractory and refractory systems, respectively. We show that the heterogeneous oxidation kinetics of these multicomponent particles are substantially different than that of the single-component particles. The oxidation of organic coatings is rapid, undergoing dramatic changes to carbon oxidation state and losing a significant amount of organic mass after relatively low OH exposures (equivalent to several days of atmospheric processing). In the case of biomass burning particles, the kinetics are complex, with different components (inferred by aerosol mass spectrometry) undergoing oxidation at different rates.

Numerical simulation of two-dimensional flow over a heated carbon surface with coupled heterogeneous and homogeneous reactions

NASA Astrophysics Data System (ADS)

Johnson, Ryan Federick; Chelliah, Harsha Kumar

2017-01-01

For a range of flow and chemical timescales, numerical simulations of two-dimensional laminar flow over a reacting carbon surface were performed to understand further the complex coupling between heterogeneous and homogeneous reactions. An open-source computational package (OpenFOAM®) was used with previously developed lumped heterogeneous reaction models for carbon surfaces and a detailed homogeneous reaction model for CO oxidation. The influence of finite-rate chemical kinetics was explored by varying the surface temperatures from 1800 to 2600 K, while flow residence time effects were explored by varying the free-stream velocity up to 50 m/s. The reacting boundary layer structure dependence on the residence time was analysed by extracting the ratio of chemical source and species diffusion terms. The important contributions of radical species reactions on overall carbon removal rate, which is often neglected in multi-dimensional simulations, are highlighted. The results provide a framework for future development and validation of lumped heterogeneous reaction models based on multi-dimensional reacting flow configurations.

A kinetic model for heterogeneous condensation of vapor on an insoluble spherical particle.

PubMed

Luo, Xisheng; Fan, Yu; Qin, Fenghua; Gui, Huaqiao; Liu, Jianguo

2014-01-14

A kinetic model is developed to describe the heterogeneous condensation of vapor on an insoluble spherical particle. This new model considers two mechanisms of cluster growth: direct addition of water molecules from the vapor and surface diffusion of adsorbed water molecules on the particle. The effect of line tension is also included in the model. For the first time, the exact expression of evaporation coefficient is derived for heterogeneous condensation of vapor on an insoluble spherical particle by using the detailed balance. The obtained expression of evaporation coefficient is proved to be also correct in the homogeneous condensation and the heterogeneous condensation on a planar solid surface. The contributions of the two mechanisms to heterogeneous condensation including the effect of line tension are evaluated and analysed. It is found that the cluster growth via surface diffusion of adsorbed water molecules on the particle is more important than the direct addition from the vapor. As an example of our model applications, the growth rate of the cap shaped droplet on the insoluble spherical particle is derived. Our evaluation shows that the growth rate of droplet in heterogeneous condensation is larger than that in homogeneous condensation. These results indicate that an explicit kinetic model is benefit to the study of heterogeneous condensation on an insoluble spherical particle.

[Spatial and temporal dynamics of the weed community in the Zoysia matrella lawn].

PubMed

Liu, Jia-Qi; Li, You-Han; Zeng, Ying; Xie, Xin-Ming

2014-02-01

The heterogeneity of species composition is one of the main attributes in weed community dynamics. Based on species frequency and power law, this paper studied the variations of weed community species composition and spatial heterogeneity in a Zoysia matrella lawn in Guangzhou at different time. The results showed that there were 43 weed species belonging to 19 families in the Z. matrella lawn from 2007 to 2009, in which Gramineae, Compositae, Cyperaceae and Rubiaceae had a comparative advantage. Perennial weeds accounted for the largest proportion of weeds and increased gradually in the three years. Weed communities distributed in higher heterogeneity than in a random model. Dominant weeds varied with season and displayed regularity in the order of 'dicotyledon-monocotyledon-dicotyledon weeds' and 'perennial-annual-perennial weeds'. The spatial heterogeneity of weed community in Z. matrella lawn was higher in summer than in winter. The diversity and evenness of weed community were higher in summer and autumn than in winter and spring. The number of weed species with high heterogeneity in summer was higher than in the other seasons. The spatial heterogeneity and diversity of weed community had no significant change in the three years, while the evenness of weed community had the tendency to decline gradually.

Influence of surface flattening on biodiversity of terrestrial arthropods during early stages of brown coal spoil heap restoration.

PubMed

Moradi, Jabbar; Potocký, Pavel; Kočárek, Petr; Bartuška, Martin; Tajovský, Karel; Tichánek, Filip; Frouz, Jan; Tropek, Robert

2018-08-15

Heterogeneity of environmental conditions is the crucial factor supporting biodiversity in various habitats, including post-mining sites. The effects of micro-topographic heterogeneity on biodiversity and conservation potential of arthropod communities in post-industrial habitats had not been studied before now. At one of the largest European brown coal spoil heaps, we sampled eight groups of terrestrial arthropods with different life strategies (moths, spiders, ground beetles, ants, orthopteroids, centipedes, millipedes, and woodlice), in successionally young plots (5-18 y), with a heterogeneous wavy surface after heaping, and compared the communities with plots flattened by dozing. A combination of the standardized quantitative sampling, using two different methods, and a paired design of the plot selection enabled a robust analysis. Altogether, we recorded 380 species of the focal arthropods, 15 of them nationally threatened. We revealed the importance of the micro-topographic heterogeneity for the formation of the biodiversity of arthropods in their secondary refuges. The communities with higher biodiversity and conservation value were detected in the plots with heterogeneous surfaces; exceptions were ground beetles and millipedes. The surface flattening, often the first step of technical reclamation projects, thus suppress biodiversity of most terrestrial arthropods during the restoration of post-mining sites. Since the communities of both surface types differed, the proportional presence on both surfaces could be more efficient in supporting the local biodiversity. We suggest reducing the surface dozing for the cases with other concerns only, to achieve a proportional representation of both surface types. Such a combination of different restoration approaches would, thus, efficiently support high biodiversity of groups with various needs. Copyright © 2018 Elsevier Ltd. All rights reserved.

Sea spray aerosol chemical composition: elemental and molecular mimics for laboratory studies of heterogeneous and multiphase reactions.

PubMed

Bertram, Timothy H; Cochran, Richard E; Grassian, Vicki H; Stone, Elizabeth A

2018-04-03

Sea spray aerosol particles (SSA), formed through wave breaking at the ocean surface, contribute to natural aerosol particle concentrations in remote regions of Earth's atmosphere, and alter the direct and indirect effects of aerosol particles on Earth's radiation budget. In addition, sea spray aerosol serves as suspended surface area that can catalyze trace gas reactions. It has been shown repeatedly that sea spray aerosol is heavily enriched in organic material compared to the surface ocean. The selective enrichment of organic material complicates the selection of representative molecular mimics of SSA for laboratory or computational studies. In this review, we first provide a short introduction to SSA formation processes and discuss chemical transformations of SSA that occur in polluted coastal regions and remote pristine air. We then focus on existing literature of the chemical composition of nascent SSA generated in controlled laboratory experiments and field investigations. We combine the evidence on the chemical properties of nascent SSA with literature measurements of SSA water uptake to assess SSA molecular composition and liquid water content. Efforts to speciate SSA organic material into molecular classes and specific molecules have led to the identification of saccharides, alkanes, free fatty acids, anionic surfactants, dicarboxylic acids, amino acids, proteinaceous matter, and other large macromolecules. However to date, less than 25% of the organic mass of nascent SSA has been quantified at a molecular level. As discussed here, quantitative measurements of size resolved elemental ratios, combined with determinations of water uptake properties, provides unique insight on the concentration of ions within SSA as a function of particle size, pointing to a controlling role for relative humidity and the hygroscopicity of SSA organic material at small particle diameters.

Igneous lithologies on asteroid (4) Vesta mapped using gamma-ray and neutron data

NASA Astrophysics Data System (ADS)

Beck, Andrew W.; Lawrence, David J.; Peplowski, Patrick N.; Viviano-Beck, Christina E.; Prettyman, Thomas H.; McCoy, Timothy J.; McSween, Harry Y.; Yamashita, Naoyuki

2017-04-01

We use data collected by the Dawn Gamma-Ray and Neutron Detector (GRaND) at Vesta to map compositions corresponding to nearly pure igneous lithologies in the howardite, eucrite, diogenite (HED) meteorite clan (samples likely from Vesta). At the ∼300-km spatial scale of GRaND measurements, basaltic eucrite occurs on only 3% of the surface, whereas cumulate eucrite and orthopyroxenitic diogenite are not detected. The basaltic eucrite region is generally coincident with an area of the surface with thick regolith, elevated H, and moderate crater density, and may represent the best compositional sample of primordial vestan crust. We observe an absence of pure orthopyroxenitic diogenite terrains in the Rheasilvia basin and its ejecta, an observation corroborated by VIR (0.1%), which suggests the south-polar crust was a polymict mixture of igneous lithologies (howardite) at the time of the Rheasilvia impact, or was a thick basaltic eucrite crust with heterogeneously distributed orthopyroxenitic diogenite plutons. The most dominant igneous composition detected (11% of the surface) corresponds to one of the least-abundant igneous lithologies in the HED meteorite collection, the Yamato Type B diogenites (plagioclase-bearing pyroxenites). The distribution of Type B diogenite is spatially correlated with post-Rheasilvia craters in the north-polar region that are in close proximity to the Rheasilvia basin antipode. This suggests that north-polar Type B plutonism may have been associated with the Rheasilvia impact event. We propose that this was either through 1) uplift of pre-existing plutons at the antipode through focusing of Rheasilvia impact stress, or 2) Rheasilvia impact antipodal crustal melting, creating magmas that underwent fractionation to produce Type B plutons.

Heterogeneous porous structures for the fastest liquid absorption

NASA Astrophysics Data System (ADS)

Shou, Dahua; Ye, Lin; Fan, Jintu

2013-08-01

Engineered porous materials, which have fast absorption of liquids under global constraints (e.g. volume, surface area, or cost of the materials), are useful in many applications including moisture management fabrics, medical wound dressings, paper-based analytical devices, liquid molding composites, etc.. The absorption in capillary tubes and porous media is driven by the surface tension of liquid, which is inversely proportional to the pore size. On the contrary, the ability of conduction (or permeability) of liquid in porous materials is linear with the square of pore size. Both mechanisms superimpose with each other leading to a possibility of the fastest absorption for a porous structure. In this work, we explore the flow behaviors for the fastest absorption using heterogeneous porous architectures, from two-portion tubes to two-layer porous media. The absorption time for filling up the voids in these porous materials is expressed in terms of pore size, height and porosity. It is shown that under the given height and void volume, these two-component porous structures with a negative gradient of pore size/porosity against the imbibition direction, have a faster absorption rate than controlled samples with uniform pore size/porosity. Particularly, optimal structural parameters including pore size, height and porosity are found for the minimum absorption time. The obtained results will be used as a priori for the design of porous structures with excellent water absorption and moisture management property in various fields.

Computing Global Mosaics of Titan With the VIMS Imaging Spectrometer

NASA Astrophysics Data System (ADS)

Le Mouelic, S.; Cornet, T.; Rodriguez, S.; Sotin, C.; Barnes, J. W.; Brown, R. H.; Baines, K. H.; Buratti, B. J.; Clark, R. N.; Nicholson, P. D.

2015-12-01

The Visual and Infrared Mapping Spectrometer (VIMS) onboard Cassini observes the surface of Titan in seven narrow atmospheric windows in the infrared at 0.93, 1.08, 1.27, 1.59, 2.01, 2.68-2.78, and 4.9-5.1 microns. We have produced a global hyperspectral mosaic of the complete VIMS data set of Titan between T0 (July 2004) and T112 flyby (July 2015), by merging all the data cubes sorted by increasing spatial resolution, with the high resolution images on top of the mosaic and the low resolution images used as background. We filtered out the observing geometry in order to remove the pixels acquired in too extreme illuminating and viewing conditions, which systematically produce atmospheric artifacts. We used thresholds of 80° both on the incidence and emission angles, 100° on the phase angle, and 7 on the airmass. These thresholds corresponds to a trade-off between surface coverage and data quality. The viewing geometry is normalized at first order using a surface photometric function derived from the observation at 5 μm, where the atmospheric scattering is almost negligible. We also use the wings of the atmospheric windows as a proxy to correct for the amount of additive scattering present in the center of these windows, where the surface is seen by VIMS. Various color composites can then be produced using combinations of different wavelengths to emphasize surface heterogeneities. Among these, a RGB composite with red controlled by the 5 μm image, the green by the 2 μm image and the blue by the 1.27 μm, reveals the extent of equatorial dune fields appearing in brownish tones. Bluish areas corresponds to regions possibly enriched in water ice or other organic compounds. Composite of band ratios such as 1.59/1.27 μm, 2.03/1.27 μm and 1.27/1.08 also prove to be more useful to better emphasize surface variations, even if they are also more sensitive to residual artefacts due to atmospheric and geometric effects or calibration residuals.

Phase behavior and reactive transport of partial melt in heterogeneous mantle model

NASA Astrophysics Data System (ADS)

Jordan, J.; Hesse, M. A.

2013-12-01

The reactive transport of partial melt is the key process that leads to the chemical and physical differentiation of terrestrial planets and smaller celestial bodies. The essential role of the lithological heterogeneities during partial melting of the mantle is increasingly recognized. How far can enriched melts propagate while interacting with the ambient mantle? Can the melt flow emanating from a fertile heterogeneity be localized through a reactive infiltration feedback in a model without exogenous factors or contrived initial conditions? A full understanding of the role of heterogeneities requires reactive melt transport models that account for the phase behavior of major elements. Previous work on reactive transport in the mantle focuses on trace element partitioning; we present the first nonlinear chromatographic analysis of reactive melt transport in systems with binary solid solution. Our analysis shows that reactive melt transport in systems with binary solid solution leads to the formation of two separate reaction fronts: a slow melting/freezing front along which enthalpy change is dominant and a fast dissolution/precipitation front along which compositional changes are dominated by an ion-exchange process over enthalpy change. An intermediate state forms between these two fronts with a bulk-rock composition and enthalpy that are not necessarily bounded by the bulk-rock composition and enthalpy of either the enriched heterogeneity or the depleted ambient mantle. The formation of this intermediate state makes it difficult to anticipate the porosity changes and hence the stability of reaction fronts. Therefore, we develop a graphical representation for the solution that allows identification of the intermediate state by inspection, for all possible bulk-rock compositions and enthalpies of the heterogeneity and the ambient mantle. We apply the analysis to the partial melting of an enriched heterogeneity. This leads to the formation of moving precipitation front that followes a stationary melting front which creates low porosity intermediate states. Therefore, localization of the melt flow is not observed because the precipitation front is stable and the melting front is always stationary under these conditions. This analysis illustrates the counterintuitive behavior that can arise when the phase behavior is taken into account and is a first step to understanding reactive melt transport and the reactive constraints on channelization in partial melts. ¬¬

Enhancing Europa surface characterization with ice penetrating radar: A Comparative study in Antarctica

NASA Astrophysics Data System (ADS)

Curra, C.; Arnold, E.; Karwoski, B.; Grima, C.; Schroeder, D. M.; Young, D. A.; Blankenship, D. D.

2013-12-01

The shape and composition of the surface of Europa result from multiple processes, most of them involving direct and indirect interactions between the liquid and solid phases of its outer water layer. The surface ice composition is likely to reflect the material exchanged with the sub-glacial ocean and potentially holds signatures of organic compounds that could demonstrate the ability of the icy moon to sustain life. Therefore, the most likely targets for in-situ landing missions are primarily located in complex terrains disrupted by exchange mechanisms with the ocean/lenses of sub-glacial liquid water. Any landing site selection process to ensure a safe delivery of a future lander, will then have to confidently characterize its surface roughness. We evaluate the capability of an ice-penetrating radar to characterize the roughness using a statistical method applied to the surface echoes. Our approach is to compare radar-derived data with nadir-imagery and laser altimetry simultaneously acquired on an airborne platform over Marie Byrd Land, West Antarctica, during the 2012-13 GIMBLE survey. The radar is the High-Capability Radar Sounder 2 (HiCARS 2, 60 MHz) system operated by the University of Texas Institute for Geophysics (UTIG), with specifications similar to the Ice Penetrating Radar (IPR) of the Europa Clipper project. Surface textures as seen by simultaneously collected nadir imagery are manually classified, allowing individual contrast stretching for better identification. We identified crevasse fields, blue ice patches, and families of wind-blown patterns. Homogeneity/heterogeneity of the textures has also been an important classification criterion. The various textures are geolocated and compared to the evolution and amplitude of laser-derived and radar-derived roughness. Similarities and discrepancies between these three datasets are illustrated and analyzed to qualitatively constrain radar sensitivity to the surface textures. The result allows for a first insight and discussion into how to interpret statistically-inverted radar data from an icy planetary surface.

Methods for chromosome-specific staining

DOEpatents

Gray, J.W.; Pinkel, D.

1995-09-05

Methods and compositions for chromosome-specific staining are provided. Compositions comprise heterogeneous mixtures of labeled nucleic acid fragments having substantially complementary base sequences to unique sequence regions of the chromosomal DNA for which their associated staining reagent is specific. Methods include ways for making the chromosome-specific staining compositions of the invention, and methods for applying the staining compositions to chromosomes. 3 figs.

Immobilization of myoglobin on Au nanoparticle-decorated carbon nanotube/polytyramine composite as a mediator-free H2O2 and nitrite biosensor

PubMed Central

Vilian, A. T. Ezhil; Veeramani, Vediyappan; Chen, Shen-Ming; Madhu, Rajesh; Kwak, Cheol Hwan; Huh, Yun Suk; Han, Young-Kyu

2015-01-01

A novel composite film was designed for use as a highly selective mediator-free amperometric biosensor, and a method was created for accomplishing direct electrochemistry of myoglobin on a multi-walled carbon nanotube and tyramine-modified composite decorated with Au nanoparticles on a glassy carbon electrode. The ultraviolet-visible and electrochemical impedance spectroscopy results showed that myoglobin retained its native conformation in the interaction with Au-PTy-f-MWCNT. The surface coverage of Mb-heme-Fe(II)/(III) immobilized on Au-PTy-f-MWCNT and the heterogeneous electron-transfer rate constant were 2.12 × 10−9 mol cm−2 and 4.86 s−1, respectively, indicating a higher loading capacity of the nanocomposite for direct electron transfer of Mb onto the electrode surface. The proposed Mb/Au-PTy-f-MWCNT biofilm exhibited excellent electrocatalytic behavior toward the reduction of H2O2 and the oxidation of nitrite with linear ranges of 2 to 5000 μM and 1 to 8000 μM and lower detection limits of 0.01 μM and 0.002 μM, respectively. An apparent Michaelis-Menten constant of 0.12 mM indicated that the Mb immobilized on the Au-PTy-f-MWCNT film retained its native activity. This biosensor can be successfully applied to detect H2O2 and nitrite in disinfectant cream, eye drops, pickle juice, and milk samples. PMID:26672985

New nano-sized Al2O3-BN coating 3Y-TZP ceramic composites for CAD/CAM-produced all-ceramic dental restorations. Part I. Fabrication of powders.

PubMed

Yang, Se Fei; Yang, Li Qiang; Jin, Zhi Hao; Guo, Tian Wen; Wang, Lei; Liu, Hong Chen

2009-06-01

Partially sintered 3 mol % yttria-stabilized tetragonal zirconium dioxide (ZrO(2), zirconia) polycrystal (3Y-TZP) ceramics are used in dental posterior restorations with computer-aided design-computer-aided manufacturing (CAD/CAM) techniques. High strength is acquired after sintering, but shape distortion of preshaped compacts during their sintering is inevitable. The aim of this study is to fabricate new machinable ceramic composites with strong mechanical properties that are fit for all-ceramic dental restorations. Aluminum oxide (Al(2)O(3))-coated 3Y-TZP powders were first prepared by the heterogeneous precipitation method starting with 3Y-TZP, Al(NO(3))(3) . 9H(2)O, and ammonia, then amorphous boron nitride (BN) was produced and the as-received composite powders were coated via in situ reaction with boric acid and urea. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to analyze the status of Al(2)O(3)-BN on the surface of the 3Y-TZP particles. TEM micrographs show an abundance of Al(2)O(3) particles and amorphous BN appearing uniformly on the surface of the 3Y-TZP particles after the coating process. The size of the Al(2)O(3) particles is about 20 nm. The XRD pattern shows clearly the peak of amorphous BN among the peaks of ZrO(2).

Induced spatial heterogeneity in forest canopies: responses of small mammals.

Treesearch

A.B. Carey

2001-01-01

We hypothesized that creating a mosaic of interspersed patches of different densities of canopy trees in a second-growth Douglas-fir (Pseudotsuga menziesiz) forest would accelerate development of biocomplexity (diversity in ecosystem structure, composition, and processes) by promoting spatial heterogeneity in understory, midstory, and canopy,...

Imaging density and seismic velocities in the Eastern Mediterranean

NASA Astrophysics Data System (ADS)

Fichtner, A.; Blom, N.; Gokhberg, A.

2017-12-01

The Mediterranean domain is a geologically complicated region, a result of its complex tectonic and geodynamic evolution. Our understanding of it draws from surface geology, modeling and imaging of the subsurface. Here, we present a seismic waveform tomography of the Eastern Mediterranean. While computationally more expensive than ray-based imaging methods, the advantage of waveform methods lies in their ability to incorporate in a consistent manner all the information in seismograms - not just the arrivals of certain, specified phases. As a result, body and multimode surface waves, source effects, frequency-dependence, wavefront healing, anisotropy and attenuation are naturally and coherently incorporated. This not only allows us to image P- and S-wave velocity jointly for the crust and mantle, but also makes it possible to put constraints on density that ray tomography cannot provide. This is of special interest because heterogeneities in density drive geodynamics, and the combined knowledge of all parameters can help to distinguish between thermal and compositional effect.Our tomography makes use of a multi-scale approach, initially using only the very lowest frequency signals with periods of 100-150 s. The low-frequency data is not only important in order to avoid local minima in the optimisation, also the recovery of density relies crucially on it. As the model is updated and more of the data is explained by it, higher-frequency data is added and more parts of the seismogram are included. Only those parts are used in which data and synthetics are similar enough to allow for meaningful comparison. Our aim is to go down to periods of 10 s, which corresponds to structures of 15 km size in the crust to 25 km in the mantle. Resolution of the final model is assessed using a resolution analysis strategy developed by Fichtner & van Leeuwen (JGR, 2015). This helps us to evaluate the effects of smearing and heterogeneous ray coverage in a quantitative manner and gives an indication of trade-offs between parameters. Our work aims to provide a coherent model for the crust and upper mantle in the Eastern Mediterranean that includes seismic velocities, anisotropy and density. Taken together, these parameters may help shed light on the nature of anomalies as slabs, thermal provinces or compositional heterogeneity.

Effect of Stratification on Surface Properties of Corneal Epithelial Cells

PubMed Central

Yáñez-Soto, Bernardo; Leonard, Brian C.; Raghunathan, Vijay Krishna; Abbott, Nicholas L.; Murphy, Christopher J.

2015-01-01

Purpose The purpose of this study was to determine the influence of mucin expression in an immortalized human corneal epithelial cell line (hTCEpi) on the surface properties of cells, such as wettability, contact angle, and surface heterogeneity. Methods hTCEpi cells were cultured to confluence in serum-free medium. The medium was then replaced by stratification medium to induce mucin biosynthesis. The mucin expression profile was analyzed using quantitative PCR and Western blotting. Contact angles were measured using a two-immiscible liquid method, and contact angle hysteresis was evaluated by tilting the apparatus and recording advancing and receding contact angles. The spatial distribution of mucins was evaluated with fluorescently labeled lectin. Results hTCEpi cells expressed the three main ocular mucins (MUC1, MUC4, and MUC16) with a maximum between days 1 and 3 of the stratification process. Upon stratification, cells caused a very significant increase in contact angle hysteresis, suggesting the development of spatially discrete and heterogeneously distributed surface features, defined by topography and/or chemical functionality. Although atomic force microscopy measurements showed no formation of appreciable topographic features on the surface of the cells, we observed a significant increase in surface chemical heterogeneity. Conclusions The surface chemical heterogeneity of the corneal epithelium may influence the dynamic behavior of tear film by “pinning” the contact line between the cellular surface and aqueous tear film. Engineering the surface properties of corneal epithelium could potentially lead to novel treatments in dry eye disease. PMID:26747762

Understanding how the shape and spatial distribution of ULVZs provides insight into their cause and to the nature of global-scale mantle convection

NASA Astrophysics Data System (ADS)

McNamara, Allen; Li, Mingming; Garnero, Ed; Marin, Nicole

2017-04-01

Seismic observations of the lower mantle infer multiple scales of compositional heterogeneity. The largest-scale heterogeneity, observed in seismic tomography models, is in the form of large, nearly antipodal regions referred to as the Large Low Shear Velocity Provinces (LLSVPs). In contrast, diffracted wave and core-reflection precursor seismic studies reveal small-scale Ultra Low Velocity Zones (ULVZs) at the base of the mantle that are almost two orders of magnitude smaller than the LLSVPs. We hypothesize that ULVZs provide insight into the nature of LLSVPs, and the LLSVPs, in turn, provide clues to the nature of global-scale mantle convection and compositional state. However, both LLSVPs and ULVZs are observations, and it remains unclear what is causing them. Here, we examine several related questions to aid in understanding their cause and the dynamical processes associated with them. Can we use seismic observations of ULVZ locations to differentiate whether they are caused by compositional heterogeneity or simply partial melting in otherwise normal mantle? Can we use the map-view shape of ULVZs to tell us about lowermost mantle flow directions and the temporal stability of these flow directions? Can the cross-sectional morphology of ULVZs tell us something about the viscosity difference between LLSVPs and background mantle? We performed geodynamical experiments to help answer these questions. We find that ULVZs caused by compositional heterogeneity preferentially form patch-like shapes along the margins of LLSVPs. Rounded patches indicate regions with long-lived stable mantle flow patterns, and linear patches indicate changing mantle flow patterns. Typically, these ULVZ patches have an asymmetrical cross-sectional shape; however, if LLSVPs have a larger grain-size than background mantle, their increased diffusion creep viscosity will act to make them more symmetrical. Alternatively, ULVZs caused simply by partial melting of normal mantle are preferentially located significantly inboard of LLSVP margins and have relatively symmetrical cross-sectional shapes. These results can prompt new seismic studies to better constrain the cause and dynamic significance of multi-scale compositional heterogeneity in the Earth's mantle.

Cell-Surface Expression of Neuron-Glial Antigen 2 (NG2) and Melanoma Cell Adhesion Molecule (CD146) in Heterogeneous Cultures of Marrow-Derived Mesenchymal Stem Cells

PubMed Central

Russell, Katie C.; Tucker, H. Alan; Bunnell, Bruce A.; Andreeff, Michael; Schober, Wendy; Gaynor, Andrew S.; Strickler, Karen L.; Lin, Shuwen; Lacey, Michelle R.

2013-01-01

Cellular heterogeneity of mesenchymal stem cells (MSCs) impedes their use in regenerative medicine. The objective of this research is to identify potential biomarkers for the enrichment of progenitors from heterogeneous MSC cultures. To this end, the present study examines variation in expression of neuron-glial antigen 2 (NG2) and melanoma cell adhesion molecule (CD146) on the surface of MSCs derived from human bone marrow in response to culture conditions and among cell populations. Multipotent cells isolated from heterogeneous MSC cultures exhibit a greater than three-fold increase in surface expression for NG2 and greater than two-fold increase for CD146 as compared with parental and lineage-committed MSCs. For both antigens, surface expression is downregulated by greater than or equal to six-fold when MSCs become confluent. During serial passage, maximum surface expression of NG2 and CD146 is associated with minimum doubling time. Upregulation of NG2 and CD146 during loss of adipogenic potential at early passage suggests some limits to their utility as potency markers. A potential relationship between proliferation and antigen expression was explored by sorting heterogeneous MSCs into rapidly and slowly dividing groups. Fluorescence-activated cell sorting revealed that rapidly dividing MSCs display lower scatter and 50% higher NG2 surface expression than slowly dividing cells, but CD146 expression is comparable in both groups. Heterogeneous MSCs were sorted based on scatter properties and surface expression of NG2 and CD146 into high (HI) and low (LO) groups. ScLONG2HI and ScLONG2HICD146HI MSCs have the highest proliferative potential of the sorted groups, with colony-forming efficiencies that are 1.5–2.2 times the value for the parental controls. The ScLO gate enriches for rapidly dividing cells. Addition of the NG2HI gate increases cell survival to 1.5 times the parental control. Further addition of the CD146HI gate does not significantly improve cell division or survival. The combination of low scatter and high NG2 surface expression is a promising selection criterion to enrich a proliferative phenotype from heterogeneous MSCs during ex vivo expansion, with potentially numerous applications. PMID:23611563

Generating Facial Expressions Using an Anatomically Accurate Biomechanical Model.

PubMed

Wu, Tim; Hung, Alice; Mithraratne, Kumar

2014-11-01

This paper presents a computational framework for modelling the biomechanics of human facial expressions. A detailed high-order (Cubic-Hermite) finite element model of the human head was constructed using anatomical data segmented from magnetic resonance images. The model includes a superficial soft-tissue continuum consisting of skin, the subcutaneous layer and the superficial Musculo-Aponeurotic system. Embedded within this continuum mesh, are 20 pairs of facial muscles which drive facial expressions. These muscles were treated as transversely-isotropic and their anatomical geometries and fibre orientations were accurately depicted. In order to capture the relative composition of muscles and fat, material heterogeneity was also introduced into the model. Complex contact interactions between the lips, eyelids, and between superficial soft tissue continuum and deep rigid skeletal bones were also computed. In addition, this paper investigates the impact of incorporating material heterogeneity and contact interactions, which are often neglected in similar studies. Four facial expressions were simulated using the developed model and the results were compared with surface data obtained from a 3D structured-light scanner. Predicted expressions showed good agreement with the experimental data.

Storage and interaction of compositionally heterogeneous magmas from the 1986 eruption of Augustine Volcano, Alaska

USGS Publications Warehouse

Roman, Diana C.; Cashman, Katharine V.; Gardner, Cynthia A.; Wallace, Paul J.; Donovan, John J.

2006-01-01

Compositional heterogeneity (56–64 wt% SiO2 whole-rock) in samples of tephra and lava from the 1986 eruption of Augustine Volcano, Alaska, raises questions about the physical nature of magma storage and interaction beneath this young and frequently active volcano. To determine conditions of magma storage and evolutionary histories of compositionally distinct magmas, we investigate physical and chemical characteristics of andesitic and dacitic magmas feeding the 1986 eruption. We calculate equilibrium temperatures and oxygen fugacities from Fe-Ti oxide compositions and find a continuous range in temperature from 877 to 947°C and high oxygen fugacities (ΔNNO=1–2) for all magmas. Melt inclusions in pyroxene phenocrysts analyzed by Fourier-transform infrared spectroscopy and electron probe microanalysis are dacitic to rhyolitic and have water contents ranging from <1 to ∼7 wt%. Matrix glass compositions are rhyolitic and remarkably similar (∼75.9–76.6 wt% SiO2) in all samples. All samples have ∼25% phenocrysts, but lower-silica samples have much higher microlite contents than higher-silica samples. Continuous ranges in temperature and whole-rock composition, as well as linear trends in Harker diagrams and disequilibrium mineral textures, indicate that the 1986 magmas are the product of mixing between dacitic magma and a hotter, more mafic magma. The dacitic endmember is probably residual magma from the previous (1976) eruption of Augustine, and we interpret the mafic endmember to have been intruded from depth. Mixing appears to have continued as magmas ascended towards the vent. We suggest that the physical structure of the magma storage system beneath Augustine contributed to the sustained compositional heterogeneity of this eruption, which is best explained by magma storage and interaction in a vertically extensive system of interconnected dikes rather than a single coherent magma chamber and/or conduit. The typically short repose period (∼10 years) between Augustine's recent eruptive pulses may also inhibit homogenization, as short repose periods and chemically heterogeneous magmas are observed at several volcanoes in the Cook Inlet region of Alaska.

Effects of a natural dam-break flood on geomorphology and vegetation on the Elwha River, Washington, U.S.A.

USGS Publications Warehouse

Acker, S.A.; Beechie, T.J.; Shafroth, P.B.

2008-01-01

Ephemeral dams caused by landslides have been observed around the world, yet little is known about the effects of their failure on landforms and vegetation. In 1967, a landslide-dam-break flood in a pristine reach of the Elwha River valley filled the former channel and diverted the river. The reach is a reference site for restoration following the planned removal of dams on the river. We identified five surfaces on the 25 ha debris fan deposited by the flood. Based on tree ages and historic air photos, three of the surfaces formed in 1967, while two formed later. The surfaces varied in substrate (silt and sand, to boulders), and height above the river channel. Tree mortality resulted from tree removal and burial by sediment, the latter leaving snags and some surviving trees. Tree species composition was generally consistent within each surface. Dominant species included red alder (Alnus rubra) and Sitka willow (Salix sitchensis), alone or in combination, a combination of Douglas-fir (Pseudotsuga menziesii) and black cottonwood (Populus balsamifera ssp. trichocarpa), or a combination of alder and Cottonwood. There were significant differences between surfaces in stem density, basal area, and rate of basal area growth. The large degree of heterogeneity in forest structure, composition, and productivity within a relatively small floodplain feature is in part due to spatial variability in the intensity of a single disturbance event, and in part due to the occurrence of subsequent, smaller events. To recreate natural diversity of riparian forests may require mimicking the variety of physical and biotic habitats that a single, complex disturbance event may create.

Equilibrium Isotherm, Kinetic Modeling, Optimization, and Characterization Studies of Cadmium Adsorption by Surface-Engineered Escherichia coli

PubMed Central

Tafakori, Vida; Zadmard, Reza; Tabandeh, Fatemeh; Amoozegar, Mohammad Ali; Ahmadian, Gholamreza

2017-01-01

Background: Amongst the methods that remove heavy metals from environment, biosorption approaches have received increased attention because of their environmentally friendly and cost-effective feature, as well as their superior performances. Methods: In the present study, we investigated the ability of a surface-engineered Escherichia coli, carrying the cyanobacterial metallothionein on the cell surface, in the removal of Ca (II) from solution under different experimental conditions. The biosorption process was optimized using central composite design. In parallel, the kinetics of metal biosorption was studied, and the rate constants of different kinetic models were calculated. Results: Cadmium biosorption is followed by the second-order kinetics. Freundlich and Langmuir equations were used to analyze sorption data; characteristic parameters were determined for each adsorption isotherm. The biosorption process was optimized using the central composite design. The optimal cadmium sorption capacity (284.69 nmol/mg biomass) was obtained at 40°C (pH 8) and a biomass dosage of 10 mg. The influence of two elutants, EDTA and CaCl2, was also assessed on metal recovery. Approximately, 68.58% and 56.54% of the adsorbed cadmium were removed by EDTA and CaCl2 during desorption, respectively. The Fourier transform infrared spectrophotometer (FTIR) analysis indicated that carboxyl, amino, phosphoryl, thiol, and hydroxyl are the main chemical groups involved in the cadmium bioadsorption process. Conclusion: Results from this study implied that chemical adsorption on the heterogeneous surface of E. coli E and optimization of adsorption parameters provides a highly efficient bioadsorbent. PMID:28555492

[Spatial pattern of land surface dead combustible fuel load in Huzhong forest area in Great Xing'an Mountains].

PubMed

Liu, Zhi-Hua; Chang, Yu; Chen, Hong-Wei; Zhou, Rui; Jing, Guo-Zhi; Zhang, Hong-Xin; Zhang, Chang-Meng

2008-03-01

By using geo-statistics and based on time-lag classification standard, a comparative study was made on the land surface dead combustible fuels in Huzhong forest area in Great Xing'an Mountains. The results indicated that the first level land surface dead combustible fuel, i. e., 1 h time-lag dead fuel, presented stronger spatial auto-correlation, with an average of 762.35 g x m(-2) and contributing to 55.54% of the total load. Its determining factors were species composition and stand age. The second and third levels land surface dead combustible fuel, i. e., 10 h and 100 h time-lag dead fuels, had a sum of 610.26 g x m(-2), and presented weaker spatial auto-correlation than 1 h time-lag dead fuel. Their determining factor was the disturbance history of forest stand. The complexity and heterogeneity of the factors determining the quality and quantity of forest land surface dead combustible fuels were the main reasons for the relatively inaccurate interpolation. However, the utilization of field survey data coupled with geo-statistics could easily and accurately interpolate the spatial pattern of forest land surface dead combustible fuel loads, and indirectly provide a practical basis for forest management.

Testing for qualitative heterogeneity: An application to composite endpoints in survival analysis.

PubMed

Oulhaj, Abderrahim; El Ghouch, Anouar; Holman, Rury R

2017-01-01

Composite endpoints are frequently used in clinical outcome trials to provide more endpoints, thereby increasing statistical power. A key requirement for a composite endpoint to be meaningful is the absence of the so-called qualitative heterogeneity to ensure a valid overall interpretation of any treatment effect identified. Qualitative heterogeneity occurs when individual components of a composite endpoint exhibit differences in the direction of a treatment effect. In this paper, we develop a general statistical method to test for qualitative heterogeneity, that is to test whether a given set of parameters share the same sign. This method is based on the intersection-union principle and, provided that the sample size is large, is valid whatever the model used for parameters estimation. We propose two versions of our testing procedure, one based on a random sampling from a Gaussian distribution and another version based on bootstrapping. Our work covers both the case of completely observed data and the case where some observations are censored which is an important issue in many clinical trials. We evaluated the size and power of our proposed tests by carrying out some extensive Monte Carlo simulations in the case of multivariate time to event data. The simulations were designed under a variety of conditions on dimensionality, censoring rate, sample size and correlation structure. Our testing procedure showed very good performances in terms of statistical power and type I error. The proposed test was applied to a data set from a single-center, randomized, double-blind controlled trial in the area of Alzheimer's disease.

Magnetic cobalt ferrite composite as an efficient catalyst for photocatalytic oxidation of carbamazepine.

PubMed

He, Yongzhen; Dai, Chaomeng; Zhou, Xuefei

2017-01-01

A magnetic spinel cobalt ferrite nanoparticle composite (CFO) was prepared via an ultrasonication-assisted co-precipitation method. The morphological structure and surface composition of CFO before and after reaction were investigated by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray, and Fourier transform infrared spectroscopy, indicating the consumption of iron oxide during photodegradation. X-ray photoelectron spectroscopy and vibrating sample magnetometry confirm the preparation of the ferrite nanoparticle composite and its magnetic properties. The prepared CFO was then used for the photocatalytic degradation of carbamazepine (CBZ) as an example of pharmaceuticals and personal care products (PPCPs) from aqueous solution. The effects of the nanocomposite dosage, contact time, and solution pH on the photodegradation process were investigated. More than 96% of the CBZ was degraded within 100 min at 0.2 g·L -1 CFO in the presence of UV light. The reactive species for CBZ degradation in the CFO/UV system was identified as hydroxyl radicals by the methanol scavenging method. Combined with the detection of leached iron ions during the process, the CBZ degradation mechanism can be presumed to be heterogeneous and homogeneous photocatalytic degradation in the CFO/UV system. Furthermore, iminostilbene and acridine were detected as intermediate products by GC-MS.

Anodization Mechanism on SiC Nanoparticle Reinforced Al Matrix Composites Produced by Power Metallurgy.

PubMed

Ferreira, Sonia C; Conde, Ana; Arenas, María A; Rocha, Luis A; Velhinho, Alexandre

2014-12-19

Specimens of aluminum-based composites reinforced by silicon carbide nanoparticles (Al/SiC np ) produced by powder metallurgy (PM) were anodized under voltage control in tartaric-sulfuric acid (TSA). In this work, the influence of the amount of SiC np on the film growth during anodizing was investigated. The current density versus time response and the morphology of the porous alumina film formed at the composite surface are compared to those concerning a commercial aluminum alloy (AA1050) anodized under the same conditions. The processing method of the aluminum alloys influences the efficiency of the anodizing process, leading to a lower thicknesses for the unreinforced Al-PM alloy regarding the AA1050. The current density versus time response is strongly dependent on the amount of SiC np . The current peaks and the steady-state current density recorded at each voltage step increases with the SiC np volume fraction due to the oxidation of the SiC np . The formation mechanism of the anodic film on Al/SiC np composites is different from that occurring in AA1050, partly due the heterogeneous distribution of the reinforcement particles in the metallic matrix, but also to the entrapment of SiC np in the anodic film.

Anodization Mechanism on SiC Nanoparticle Reinforced Al Matrix Composites Produced by Power Metallurgy

PubMed Central

Ferreira, Sonia C.; Conde, Ana; Arenas, María A.; Rocha, Luis A.; Velhinho, Alexandre

2014-01-01

Specimens of aluminum-based composites reinforced by silicon carbide nanoparticles (Al/SiCnp) produced by powder metallurgy (PM) were anodized under voltage control in tartaric-sulfuric acid (TSA). In this work, the influence of the amount of SiCnp on the film growth during anodizing was investigated. The current density versus time response and the morphology of the porous alumina film formed at the composite surface are compared to those concerning a commercial aluminum alloy (AA1050) anodized under the same conditions. The processing method of the aluminum alloys influences the efficiency of the anodizing process, leading to a lower thicknesses for the unreinforced Al-PM alloy regarding the AA1050. The current density versus time response is strongly dependent on the amount of SiCnp. The current peaks and the steady-state current density recorded at each voltage step increases with the SiCnp volume fraction due to the oxidation of the SiCnp. The formation mechanism of the anodic film on Al/SiCnp composites is different from that occurring in AA1050, partly due the heterogeneous distribution of the reinforcement particles in the metallic matrix, but also to the entrapment of SiCnp in the anodic film. PMID:28788295

Hybrid ray-FDTD model for the simulation of the ultrasonic inspection of CFRP parts

NASA Astrophysics Data System (ADS)

Jezzine, Karim; Ségur, Damien; Ecault, Romain; Dominguez, Nicolas; Calmon, Pierre

2017-02-01

Carbon Fiber Reinforced Polymers (CFRP) are commonly used in structural parts in the aeronautic industry, to reduce the weight of aircraft while maintaining high mechanical performances. Simulation of the ultrasonic inspections of these parts has to face the highly heterogeneous and anisotropic characteristics of these materials. To model the propagation of ultrasound in these composite structures, we propose two complementary approaches. The first one is based on a ray model predicting the propagation of the ultrasound in an anisotropic effective medium obtained from a homogenization of the material. The ray model is designed to deal with possibly curved parts and subsequent continuously varying anisotropic orientations. The second approach is based on the coupling of the ray model, and a finite difference scheme in time domain (FDTD). The ray model handles the ultrasonic propagation between the transducer and the FDTD computation zone that surrounds the composite part. In this way, the computational efficiency is preserved and the ultrasound scattering by the composite structure can be predicted. Inspections of flat or curved composite panels, as well as stiffeners can be performed. The models have been implemented in the CIVA software platform and compared to experiments. We also present an application of the simulation to the performance demonstration of the adaptive inspection technique SAUL (Surface Adaptive Ultrasound).

Antifouling composites with self-adaptive controlled release based on an active compound intercalated into layered double hydroxides

NASA Astrophysics Data System (ADS)

Yang, Miaosen; Gu, Lianghua; Yang, Bin; Wang, Li; Sun, Zhiyong; Zheng, Jiyong; Zhang, Jinwei; Hou, Jian; Lin, Cunguo

2017-12-01

This paper reports a novel method to prepare the antifouling composites with properties of self-adaptive controlled release (defined as control the release rate autonomously and adaptively according to the change of environmental conditions) by intercalation of sodium paeonolsilate (PAS) into MgAl and ZnAl layered double hydroxide (LDH) with the molar ratio (M2+/M3+) of 2:1 and 3:1, respectively. The powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) confirm the intercalation of PAS into the galleries of LDH. The controlled release behavior triggered by temperature for the PAS-LDH composites has been investigated, and the results show that the release rate of all PAS-LDH composites increases as the increase of temperature. However, the MgAl-PAS-LDH composites (Mg2Al-PAS-LDH and Mg3Al-PAS-LDH) exhibit the increased release rate of 0.21 ppm/°C from 15 to 30 °C in 3.5% NaCl solution, more than three times of the ZnAl-PAS-LDH composites (0.06 ppm/°C), owing to the confined microenvironment influenced by metal types in LDH layers. In addition, a possible diffusion-controlled process with surface diffusion, bulk diffusion and heterogeneous flat surface diffusion has been revealed via fitting four kinetic equations. Moreover, to verify the practical application of the PAS-LDH composites, a model coating denoted as Mg2Al-PAS-LDH coating was fabricated. The release result displays that the release rate increases or decreases as temperature altered at 15 and 25 °C alternately, indicating its self-adaptive controlled release behavior with temperature. Moreover, the superior resistance to the settlement of Ulva spores at 15 and 25 °C was observed for the Mg2Al-PAS-LDH coating, as a result of the controllable release of antifoulant. Therefore, this work provides a facile and effective method for the fabrication of antifouling composites with self-adaptive controlled release behavior in response to temperature, which can be used to prolong the lifetime of antifouling coatings.

Heterogeneous interactions of chlorine nitrate, hydrogen chloride, and nitric acid with sulfuric acid surfaces at stratospheric temperatures

NASA Technical Reports Server (NTRS)

Tolbert, Margaret A.; Rossi, Michel J.; Golden, David M.

1988-01-01

The heterogeneous interactions of ClONO2, HCl, and HNO3 with sulfuric acid surfaces were studied using a Knudsen cell flow reactor. The surfaces studied, chosen to simulate global stratospheric particulate, were composed of 65-75 percent H2SO4 solutions at temperatures in the range -63 to -43 C. Heterogeneous loss, but not reaction, of HNO3 and HCl occurred on these surfaces; the measured sticking coefficients are reported. Chlorine nitrate reacted on the cold sulfuric acid surfaces, producing gas-phase HOCl and condensed HNO3. CLONO2 also reacted with HCl dissolved in the 65-percent H2SO4 solution at -63 C, forming gaseous Cl2. In all cases studied, the sticking and/or reaction coefficients were much larger for the 65-percent H2SO4 solution at -63 C than for the 75-percent solution at -43 C.

Zinc-oxide-silica-silver nanocomposite: Unique one-pot synthesis and enhanced catalytic and anti-bacterial performance.

PubMed

Kokate, Mangesh; Garadkar, Kalyanrao; Gole, Anand

2016-12-01

We describe herein a unique approach to synthesize zinc oxide-silica-silver (ZnO-SiO2-Ag) nanocomposite, in a simple, one-pot process. The typical process for ZnO synthesis by alkaline precipitation of zinc salts has been tweaked to replace alkali by alkaline sodium silicate. The free acid from zinc salts helps in the synthesis of silica nanoparticles, whereas the alkalinity of sodium silicate precipitates the zinc salts. Addition of silver ions into the reaction pot prior to addition of sodium silicate, and subsequent reduction by borohydride, gives additional functionality of metallic centres for catalytic applications. The synthesis strategy is based on our recent work typically involving acid-base type of cross-reactions and demonstrates a novel strategy to synthesize nanocomposites in a one-pot approach. Each component in the composite offers a unique feature. ZnO besides displaying mild catalytic and anti-bacterial behaviour is an excellent and a cheap 3-D support for heterogeneous catalysis. Silver nanoparticles enhance the catalytic & anti-bacterial properties of ZnO. Silica is an important part of the composite; which not only "glues" the two nanoparticles thereby stabilizing the nanocomposite, but also significantly enhances the surface area of the composite; which is an attractive feature of any catalyst composite. The nanocomposite is found to show excellent catalytic performance with very high turnover frequencies (TOFs) when studied for catalytic reduction of Rhodamine B (RhB) and 4-Nitrophenol (4-NP). Additionally, the composite has been tested for its anti-bacterial properties on three different bacterial strains i.e. E. coli, B. Cereus and Bacillus firmus. The mechanism for enhancement of catalytic performance has been probed by understanding the role of silica in offering accessibility to the catalyst via its porous high surface area network. The nanocomposite has been characterized by a host of different analytical techniques. The uniqueness of our product and process stems from the novel synthesis strategy, the choice and combination of the three moieties, increased surface area offered by silica, and cost effectiveness, thereby making our product and process commercially viable and sustainable for industrial applications. Copyright © 2016 Elsevier Inc. All rights reserved.

The scale of landscape fragmentation affects herbivore response to vegetation heterogeneity.

PubMed

Banks, John E

1998-11-01

Using alternating bands of weeds and broccoli I experimentally manipulated vegetation composition and the spatial scale at which the landscape was fragmented in a factorial design. This experimental approach allowed me to distinguish the effect of spatial scale from that of simple crop heterogeneity on crop herbivores. The importance of scale depended on which insect species were examined. Cabbage aphids (Brevicoryne brassicae) were influenced by vegetation composition at all tested scales of fragmentation; cabbage butterflies (Pieris rapae) were not affected by scale or by composition and flea beetles (Phyllotreta cruciferae) revealed a striking dependence on scale of fragmentation as well as an interaction between scale and composition. This approach shows the importance of dissecting out the effects of scale from other aspects of landscape manipulation, and emphasizes the challenge of developing a theory that will enable prediction of species-specific responses to scale.

Beyond Cassie equation: Local structure of heterogeneous surfaces determines the contact angles of microdroplets

PubMed Central

Zhang, Bo; Wang, Jianjun; Liu, Zhiping; Zhang, Xianren

2014-01-01

The application of Cassie equation to microscopic droplets is recently under intense debate because the microdroplet dimension is often of the same order of magnitude as the characteristic size of substrate heterogeneities, and the mechanism to describe the contact angle of microdroplets is not clear. By representing real surfaces statistically as an ensemble of patterned surfaces with randomly or regularly distributed heterogeneities (patches), lattice Boltzmann simulations here show that the contact angle of microdroplets has a wide distribution, either continuous or discrete, depending on the patch size. The origin of multiple contact angles observed is ascribed to the contact line pinning effect induced by substrate heterogeneities. We demonstrate that the local feature of substrate structure near the contact line determines the range of contact angles that can be stabilized, while the certain contact angle observed is closely related to the contact line width. PMID:25059292

Land quality, sustainable development and environmental degradation in agricultural districts: A computational approach based on entropy indexes

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

Zambon, Ilaria, E-mail: ilaria.zambon@unitus.it; Colantoni, Andrea; Carlucci, Margherita

Land Degradation (LD) in socio-environmental systems negatively impacts sustainable development paths. This study proposes a framework to LD evaluation based on indicators of diversification in the spatial distribution of sensitive land. We hypothesize that conditions for spatial heterogeneity in a composite index of land sensitivity are more frequently associated to areas prone to LD than spatial homogeneity. Spatial heterogeneity is supposed to be associated with degraded areas that act as hotspots for future degradation processes. A diachronic analysis (1960–2010) was performed at the Italian agricultural district scale to identify environmental factors associated with spatial heterogeneity in the degree of landmore » sensitivity to degradation based on the Environmentally Sensitive Area Index (ESAI). In 1960, diversification in the level of land sensitivity measured using two common indexes of entropy (Shannon's diversity and Pielou's evenness) increased significantly with the ESAI, indicating a high level of land sensitivity to degradation. In 2010, surface area classified as “critical” to LD was the highest in districts with diversification in the spatial distribution of ESAI values, confirming the hypothesis formulated above. Entropy indexes, based on observed alignment with the concept of LD, constitute a valuable base to inform mitigation strategies against desertification. - Highlights: • Spatial heterogeneity is supposed to be associated with degraded areas. • Entropy indexes can inform mitigation strategies against desertification. • Assessing spatial diversification in the degree of land sensitivity to degradation. • Mediterranean rural areas have an evident diversity in agricultural systems. • A diachronic analysis carried out at the Italian agricultural district scale.« less

A Universal Isotherm Model to Capture Adsorption Uptake and Energy Distribution of Porous Heterogeneous Surface.

PubMed

Ng, Kim Choon; Burhan, Muhammad; Shahzad, Muhammad Wakil; Ismail, Azahar Bin

2017-09-06

The adsorbate-adsorbent thermodynamics are complex as it is influenced by the pore size distributions, surface heterogeneity and site energy distribution, as well as the adsorbate properties. Together, these parameters defined the adsorbate uptake forming the state diagrams, known as the adsorption isotherms, when the sorption site energy on the pore surfaces are favorable. The available adsorption models for describing the vapor uptake or isotherms, hitherto, are individually defined to correlate to a certain type of isotherm patterns. There is yet a universal approach in developing these isotherm models. In this paper, we demonstrate that the characteristics of all sorption isotherm types can be succinctly unified by a revised Langmuir model when merged with the concepts of Homotattic Patch Approximation (HPA) and the availability of multiple sets of site energy accompanied by their respective fractional probability factors. The total uptake (q/q*) at assorted pressure ratios (P/P s ) are inextricably traced to the manner the site energies are spread, either naturally or engineered by scientists, over and across the heterogeneous surfaces. An insight to the porous heterogeneous surface characteristics, in terms of adsorption site availability has been presented, describing the unique behavior of each isotherm type.

Influence of the three-dimensional heterogeneous roughness on electrokinetic transport in microchannels.

PubMed

Hu, Yandong; Werner, Carsten; Li, Dongqing

2004-12-15

Surface roughness has been considered as a passive means of enhancing species mixing in electroosmotic flow through microfluidic systems. It is highly desirable to understand the synergetic effect of three-dimensional (3D) roughness and surface heterogeneity on the electrokinetic flow through microchannels. In this study, we developed a three-dimensional finite-volume-based numerical model to simulate electroosmotic transport in a slit microchannel (formed between two parallel plates) with numerous heterogeneous prismatic roughness elements arranged symmetrically and asymmetrically on the microchannel walls. We consider that all 3D prismatic rough elements have the same surface charge or zeta potential, the substrate (the microchannel wall) surface has a different zeta potential. The results showed that the rough channel's geometry and the electroosmotic mobility ratio of the roughness elements' surface to that of the substrate, epsilon(mu), have a dramatic influence on the induced-pressure field, the electroosmotic flow patterns, and the electroosmotic flow rate in the heterogeneous rough microchannels. The associated sample-species transport presents a tidal-wave-like concentration field at the intersection between four neighboring rough elements under low epsilon(mu) values and has a concentration field similar to that of the smooth channels under high epsilon(mu) values.

Debye potentials for heterogeneous media

NASA Astrophysics Data System (ADS)

Panamarev, N. S.; Donchenko, V. A.; Zemlyanov, Al. A.; Samokhvalov, I. V.; Apeksimov, D. V.; Panamaryova, A. N.; Trifonova, A. V.

2017-11-01

The paper presents the results of the Helmholtz equation solution by the method of perturbation theory in the spherical coordinate system for the Debye potentials for weakly heterogeneous media based on metal nanoparticles and the dielectric matrix. In that case, the dielectric function of a composite changes in space in the radial direction.

Initial assessment of a model relating intratumoral genetic heterogeneity to radiological morphology

PubMed Central

Noterdaeme, O; Kelly, M; Friend, P; Soonowalla, Z; Steers, G; Brady, M

2010-01-01

Tumour heterogeneity has major implications for tumour development and response to therapy. Tumour heterogeneity results from mutations in the genes responsible for mismatch repair or maintenance of chromosomal stability. Cells with different genetic properties may grow at different rates and exhibit different resistance to therapeutic interventions. To date, there exists no approach to non-invasively assess tumour heterogeneity. Here we present a biologically inspired model of tumour growth, which relates intratumoral genetic heterogeneity to gross morphology visible on radiological images. The model represents the development of a tumour as a set of expanding spheres, each sphere representing a distinct clonal centre, with the sprouting of new spheres corresponding to new clonal centres. Each clonal centre may possess different characteristics relating to genetic composition, growth rate and response to treatment. We present a clinical example for which the model accurately tracks tumour growth and shows the correspondence to genetic variation (as determined by array comparative genomic hybridisation). One clinical implication of our work is that the assessment of heterogeneous tumours using Response Evaluation Criteria In Solid Tumours (RECIST) or volume measurements may not accurately reflect tumour growth, stability or the response to treatment. We believe that this is the first model linking the macro-scale appearance of tumours to their genetic composition. We anticipate that our model will provide a more informative way to assess the response of heterogeneous tumours to treatment, which is of increasing importance with the development of novel targeted anti-cancer treatments. PMID:19690073

Influence of Specimen Preparation and Specimen Size on Composite Transverse Tensile Strength and Scatter

NASA Technical Reports Server (NTRS)

OBrien, T. Kevin; Chawan, Arun D.; DeMarco, Kevin; Paris, Isabelle

2001-01-01

The influence of specimen polishing, configuration, and size on the transverse tension strength of two glass-epoxy materials, and one carbon-epoxy material, loaded in three and four point bending was evaluated. Polishing machined edges, arid/or tension side failure surfaces, was detrimental to specimen strength characterization instead of yielding a higher, more accurate, strength as a result of removing inherent manufacture and handling flaws. Transverse tension strength was typically lower for longer span lengths due to the classical weakest link effect. However, strength was less sensitive to volume changes achieved by increasing specimen width. The Weibull scaling law typically over-predicted changes in transverse tension strengths in three point bend tests and under-predicted changes in transverse tension strengths in four point bend tests. Furthermore, the Weibull slope varied with specimen configuration, volume, and sample size. Hence, this scaling law was not adequate for predicting transverse tension strength of heterogeneous, fiber-reinforced, polymer matrix composites.

Impacts on the Hubble Space Telescope Wide Field and Planetary Camera 2: Microanalysis and Recognition of Micrometeoroid Compositions

NASA Technical Reports Server (NTRS)

Kearsley, A. T.; Ross, D. K.; Anz-Meador, P.; Liou, J. C.; Opiela, J.; Grime, G. W.; Webb, R. P.; Jeynes, C.; Palitsin, V. V.; Colaux, J. L.;

Ca2+-induced phase separation in black lipid membranes and its effect on the transport of a hydrophobic ion.

PubMed

Miller, A; Schmidt, G; Eibl, H; Knoll, W

1985-03-14

Voltage jump-current relaxation studies have been performed with dipicrylamine-doped black membranes of binary lipid mixtures. As in the case of the carrier-mediated ion transport (Schmidt, G., Eibl, H. and Knoll, W. (1982) J. Membrane Biol. 70, 147-155) no evidence was found that the neutral lipid phosphatidylcholine (DPMPC) and the charged phosphatidic acid (DPMPA) are heterogeneously distributed in the membrane over the whole range of composition. However, besides a continuous dilution of the surface charges of DPMPA by the addition of DPMPC molecules, different structural properties of mixed membranes influence the kinetics of the dipicrylamine transport. The addition of Ca2+ to the electrolyte induces a lipid phase separation within the membrane into two fluid phases of distinctly different characteristics of the translocation of hydrophobic ions. Thus, it is possible to determine a preliminary composition phase diagram for the DPMPA/DPMPC mixtures as a function of the Ca2+ concentration.

Aluminum silicide microparticles transformed from aluminum thin films by hypoeutectic interdiffusion

PubMed Central

2014-01-01

Aluminum silicide microparticles with oxidized rough surfaces were formed on Si substrates through a spontaneous granulation process of Al films. This microparticle formation was caused by interdiffusion of Al and Si atoms at hypoeutectic temperatures of Al-Si systems, which was driven by compressive stress stored in Al films. The size, density, and the composition of the microparticles could be controlled by adjusting the annealing temperature, time, and the film thickness. High-density microparticles of a size around 10 μm and with an atomic ratio of Si/Al of approximately 0.8 were obtained when a 90-nm-thick Al film on Si substrate was annealed for 9 h at 550°C. The microparticle formation resulted in a rapid increase of the sheet resistance, which is a consequence of substantial consumption of Al film. This simple route to size- and composition-controllable microparticle formation may lay a foundation stone for the thermoelectric study on Al-Si alloy-based heterogeneous systems. PMID:24994964

Aluminum silicide microparticles transformed from aluminum thin films by hypoeutectic interdiffusion.

PubMed

Noh, Jin-Seo

2014-01-01

Aluminum silicide microparticles with oxidized rough surfaces were formed on Si substrates through a spontaneous granulation process of Al films. This microparticle formation was caused by interdiffusion of Al and Si atoms at hypoeutectic temperatures of Al-Si systems, which was driven by compressive stress stored in Al films. The size, density, and the composition of the microparticles could be controlled by adjusting the annealing temperature, time, and the film thickness. High-density microparticles of a size around 10 μm and with an atomic ratio of Si/Al of approximately 0.8 were obtained when a 90-nm-thick Al film on Si substrate was annealed for 9 h at 550°C. The microparticle formation resulted in a rapid increase of the sheet resistance, which is a consequence of substantial consumption of Al film. This simple route to size- and composition-controllable microparticle formation may lay a foundation stone for the thermoelectric study on Al-Si alloy-based heterogeneous systems.

Physiographic position, disturbance and species composition in North Carolina coastal plain forests

Treesearch

James G. Wyant; Ralph J. Alig; William A. Bechtold

1991-01-01

Relations among physiographic heterogeneity, disturbance and temporal change in forest composition were analyzed on 765 forest stands in the southern coastal plain of North Carolina. Physiographic position strongly restricted the species composition of forest stands, though broad overlap of some physiographic classes was noted. Forest stands in different physiographic...

Flexible and Hierarchical Metal-Organic Framework Composites for High-Performance Catalysis.

PubMed

Huang, Ning; Drake, Hannah; Li, Jialuo; Pang, Jiangdong; Wang, Ying; Yuan, Shuai; Wang, Qi; Cai, Peiyu; Qin, Junsheng; Zhou, Hong-Cai

2018-05-18

The development of new types of porous composite materials is of great significance owing to their potentially improved performance over those of individual components and extensive applications in separation, energy storage, and heterogeneous catalysis. In this work, we integrated mesoporous metal-organic frameworks (MOFs) with macroporous melamine foam (MF) using a one-pot process, generating a series of MOF/MF composite materials with preserved crystallinity, hierarchical porosity, and increased stability over that of melamine foam. The MOF nanocrystals were threaded by the melamine foam networks, resembling a ball-and-stick model overall. As a proof-of-concept study, the resulting MOF/MF composite materials were employed as an effective heterogeneous catalyst for the epoxidation of cholesteryl esters. Combining the advantages of interpenetrative mesoporous and macroporous structures, the MOF/melamine foam composite provided higher dispersibility and more accessibility of catalytic sites, exhibiting excellent catalytic performance. This strategy constitutes an important step forward the development of other MOF composites and exploration of their high-performance catalysis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Large-Eddy Atmosphere-Land-Surface Modelling over Heterogeneous Surfaces: Model Development and Comparison with Measurements

NASA Astrophysics Data System (ADS)

Shao, Yaping; Liu, Shaofeng; Schween, Jan H.; Crewell, Susanne

2013-08-01

A model is developed for the large-eddy simulation (LES) of heterogeneous atmosphere and land-surface processes. This couples a LES model with a land-surface scheme. New developments are made to the land-surface scheme to ensure the adequate representation of atmosphere-land-surface transfers on the large-eddy scale. These include, (1) a multi-layer canopy scheme; (2) a method for flux estimates consistent with the large-eddy subgrid closure; and (3) an appropriate soil-layer configuration. The model is then applied to a heterogeneous region with 60-m horizontal resolution and the results are compared with ground-based and airborne measurements. The simulated sensible and latent heat fluxes are found to agree well with the eddy-correlation measurements. Good agreement is also found in the modelled and observed net radiation, ground heat flux, soil temperature and moisture. Based on the model results, we study the patterns of the sensible and latent heat fluxes, how such patterns come into existence, and how large eddies propagate and destroy land-surface signals in the atmosphere. Near the surface, the flux and land-use patterns are found to be closely correlated. In the lower boundary layer, small eddies bearing land-surface signals organize and develop into larger eddies, which carry the signals to considerably higher levels. As a result, the instantaneous flux patterns appear to be unrelated to the land-use patterns, but on average, the correlation between them is significant and persistent up to about 650 m. For a given land-surface type, the scatter of the fluxes amounts to several hundred W { m }^{-2}, due to (1) large-eddy randomness; (2) rapid large-eddy and surface feedback; and (3) local advection related to surface heterogeneity.

Climate Implications of the Heterogeneity of Anthropogenic Aerosol Forcing

NASA Astrophysics Data System (ADS)

Persad, Geeta Gayatri

Short-lived anthropogenic aerosols are concentrated in regions of high human activity, where they interact with radiation and clouds, causing horizontally heterogeneous radiative forcing between polluted and unpolluted regions. Aerosols can absorb shortwave energy in the atmosphere, but deplete it at the surface, producing opposite radiative perturbations between the surface and atmosphere. This thesis investigates climate and policy implications of this horizontal and vertical heterogeneity of anthropogenic aerosol forcing, employing the Geophysical Fluid Dynamics Laboratory's AM2.1 and AM3 models, both at a global scale and using East Asia as a regional case study. The degree of difference between spatial patterns of climate change due to heterogeneous aerosol forcing versus homogeneous greenhouse gas forcing deeply impacts the detection, attribution, and prediction of regional climate change. This dissertation addresses a gap in current understanding of these two forcings' response pattern development, using AM2.1 historical forcing simulations. The results indicate that fast atmospheric and land-surface processes alone substantially homogenize the global pattern of surface energy flux response to heterogeneous aerosol forcing. Aerosols' vertical redistribution of energy significantly impacts regional climate, but is incompletely understood. It is newly identified here, via observations and historical and idealized forcing simulations, that increased aerosol-driven atmospheric absorption may explain half of East Asia's recent surface insolation decline. Further, aerosols' surface and atmospheric effects counteract each other regionally---atmospheric heating enhances summer monsoon circulation, while surface dimming suppresses it---but absorbing aerosols' combined effects reduce summer monsoon rainfall. This thesis constitutes the first vertical decomposition of aerosols' impacts in this high-emissions region and elucidates the monsoonal response to aerosols' surface versus atmospheric forcing. Future aerosol emissions patterns will affect the distribution of regional climate impacts. This dissertation interrogates how international trade affects existing assumptions about East Asia's future black carbon aerosol emissions, using integrated assessment modeling, emissions and economic data, and AM3 simulations. Exports emerge as a uniquely large and potentially growing source of Chinese black carbon emissions that could impede projected regional emissions reductions, with substantial climate and health consequences. The findings encourage greater emissions projection sophistication and illustrate how societal decisions may influence future aerosol forcing heterogeneity.

Accounting for Heterogeneous-Phase Chemistry in Air Quality Models - Research Needs and Applications

EPA Science Inventory

Understanding the extent to which heterogeneous chemical reactions affect the burden and distribution of atmospheric pollutants is important because heterogeneous surfaces are ubiquitous throughout our environment. They include materials such as aerosol particles, clouds and fog,...

Modeling the expected performance of the REgolith X-ray Imaging Spectrometer (REXIS)

NASA Astrophysics Data System (ADS)

Inamdar, Niraj K.; Binzel, Richard P.; Hong, Jae Sub; Allen, Branden; Grindlay, Jonathan; Masterson, Rebecca A.

2014-09-01

OSIRIS-REx is the third spacecraft in the NASA New Frontiers Program and is planned for launch in 2016. OSIRIS-REx will orbit the near-Earth asteroid (101955) Bennu, characterize it, and return a sample of the asteroid's regolith back to Earth. The Regolith X-ray Imaging Spectrometer (REXIS) is an instrument on OSIRIS-REx designed and built by students at MIT and Harvard. The purpose of REXIS is to collect and image sun-induced fluorescent X-rays emitted by Bennu, thereby providing spectroscopic information related to the elemental makeup of the asteroid regolith and the distribution of features over its surface. Telescopic reflectance spectra suggest a CI or CM chondrite analog meteorite class for Bennu, where this primitive nature strongly motivates its study. A number of factors, however, will influence the generation, measurement, and interpretation of the X-ray spectra measured by REXIS. These include: the compositional nature and heterogeneity of Bennu, the time-variable solar state, X-ray detector characteristics, and geometric parameters for the observations. In this paper, we will explore how these variables influence the precision to which REXIS can measure Bennu's surface composition. By modeling the aforementioned factors, we place bounds on the expected performance of REXIS and its ability to ultimately place Bennu in an analog meteorite class.

Single-cell adhesion probed in-situ using optical tweezers: A case study with Saccharomyces cerevisiae

NASA Astrophysics Data System (ADS)

Castelain, Mickaël; Rouxhet, Paul G.; Pignon, Frédéric; Magnin, Albert; Piau, Jean-Michel

2012-06-01

A facile method of using optical trapping to measure cell adhesion forces is presented and applied to the adhesion of Saccharomyces cerevisiae on glass, in contact with solutions of different compositions. Trapping yeast cells with optical tweezers (OT) is not perturbed by cell wall deformation or cell deviation from a spherical shape. The trapping force calibration requires correction not only for the hydrodynamic effect of the neighboring wall but also for spherical aberrations affecting the focal volume and the trap stiffness. Yeast cells trapped for up to 5 h were still able to undergo budding but showed an increase of doubling time. The proportion of adhering cells showed the expected variation according to the solution composition. The detachment force varied in the same way. This observation and the fact that the detachment stress was exerted parallel to the substrate surface point to the role of interactions involving solvated macromolecules. Both the proportion of adhering cells and the removal force showed a distribution which, in our experimental conditions, must be attributed to a heterogeneity of surface properties at the cell level or at the subcellular scale. As compared with magnetic tweezers, atomic force microscopy, and more conventional ways of studying cell adhesion (shear-flow cells), OT present several advantages that are emphasized in this paper.

Collagenous microstructure of the glenoid labrum and biceps anchor

PubMed Central

Hill, A M; Hoerning, E J; Brook, K; Smith, C D; Moss, J; Ryder, T; Wallace, A L; Bull, A M J

2008-01-01

The glenoid labrum is a significant passive stabilizer of the shoulder joint. However, its microstructural form remains largely unappreciated, particularly in the context of its variety of functions. The focus of labral microscopy has often been histology and, as such, there is very little appreciation of collagen composition and arrangement of the labrum, and hence the micromechanics of the structure. On transmission electron microscopy, significant differences in diameter, area and perimeter were noted in the two gross histological groups of collagen fibril visualized; this suggests a heterogeneous collagenous composition with potentially distinct mechanical function. Scanning electron microscopy demonstrated three distinct zones of interest: a superficial mesh, a dense circumferential braided core potentially able to accommodate hoop stresses, and a loosely packed peri-core zone. Confocal microscopy revealed an articular surface fine fibrillar mesh potentially able to reduce surface friction, bundles of circumferential encapsulated fibres in the bulk of the tissue, and bone anchoring fibres at the osseous interface. Varying microstructure throughout the depth of the labrum suggests a role in accommodating different types of loading. An understanding of the labral microstructure can lead to development of hypotheses based upon an appreciation of this component of material property. This may aid an educated approach to surgical timing and repair. PMID:18429974

Polyhedral 3D structure of human plasma very low density lipoproteins by individual particle cryo-electron tomography

DOE PAGES

Yu, Yadong; Kuang, Yu-Lin; Lei, Dongsheng; ...

2016-08-18

Human VLDLs assembled in the liver and secreted into the circulation supply energy to peripheral tissues. VLDL lipolysis yields atherogenic LDLs and VLDL remnants that strongly correlate with CVD. Although the composition of VLDL particles has been well-characterized, their 3D structure is elusive because of their variations in size, heterogeneity in composition, structural flexibility, and mobility in solution. Here, we employed cryo-electron microscopy and individual-particle electron tomography to study the 3D structure of individual VLDL particles (without averaging) at both below and above their lipid phase transition temperatures. The 3D reconstructions of VLDL and VLDL bound to antibodies revealed anmore » unexpected polyhedral shape, in contrast to the generally accepted model of a spherical emulsion-like particle. The smaller curvature of surface lipids compared with HDL may also reduce surface hydrophobicity, resulting in lower binding affinity to the hydrophobic distal end of the N-terminal β-barrel domain of cholesteryl ester transfer protein (CETP) compared with HDL. The directional binding of CETP to HDL and VLDL may explain the function of CETP in transferring TGs and cholesteryl esters between these particles. This first visualization of the 3D structure of VLDL could improve our understanding of the role of VLDL in atherogenesis.« less

Chemistry of Urban Grime: Inorganic Ion Composition of Grime vs Particles in Leipzig, Germany.

PubMed

Baergen, Alyson M; Styler, Sarah A; van Pinxteren, Dominik; Müller, Konrad; Herrmann, Hartmut; Donaldson, D James

2015-11-03

Deposition of atmospheric constituents--either gas phase or particulate--onto urban impervious surfaces gives rise to a thin "urban grime" film. The area exposed by these impervious surfaces in a typical urban environment is comparable to, or greater than, that of particles present in the urban boundary layer; however, it is largely overlooked as a site for heterogeneous reactions. Here we present the results of a field campaign to determine and compare the chemical composition of urban grime and of particles collected simultaneously during the autumn of 2014 at an urban site in central Leipzig, Germany. We see dramatically reduced ammonium and nitrate levels in the film as compared to particles, suggesting a significant loss of ammonium nitrate, thus enhancing the mobility of these species in the environment. Nitrate levels are 10% lower for films exposed to sunlight compared to those that were shielded from direct sun, indicating a possible mechanism for recycling nitrate anion to reactive nitrogen species. Finally, chloride levels in the film suggest that urban grime could represent an unrecognized source of continental chloride available for ClNO2 production even in times of low particulate chloride. Such source and recycling processes could prove to be important to local and regional air quality.

Flexibility Matters: Cooperative Active Sites in Covalent Organic Framework and Threaded Ionic Polymer.

PubMed

Sun, Qi; Aguila, Briana; Perman, Jason; Nguyen, Nicholas; Ma, Shengqian

2016-12-07

The combination of two or more reactive centers working in concert on a substrate to facilitate the reaction is now considered state of the art in catalysis, yet there still remains a tremendous challenge. Few heterogeneous systems of this sort have been exploited, as the active sites spatially separated within the rigid framework are usually difficult to cooperate. It is now shown that this roadblock can be surpassed. The underlying principle of the strategy presented here is the integration of catalytic components with excellent flexibility and porous heterogeneous catalysts, as demonstrated by the placement of linear ionic polymers in close proximity to surface Lewis acid active sites anchored on the walls of a covalent organic framework (COF). Using the cycloaddition of the epoxides and CO 2 as a model reaction, dramatic activity improvements have been achieved for the composite catalysts in relation to the individual catalytic component. Furthermore, they also clearly outperform the benchmark catalytic systems formed by the combination of the molecular organocatalysts and heterogeneous Lewis acid catalysts, while affording additional recyclability. The extraordinary flexibility and enriched concentration of the catalytically active moieties on linear polymers facilitate the concerted catalysis, thus leading to superior catalytic performance. This work therefore uncovers an entirely new strategy for designing bifunctional catalysts with double-activation behavior and opens a new avenue in the design of multicapable systems that mimic biocatalysis.

Diversity Revisited, or Composition's Alien History.

ERIC Educational Resources Information Center

Bender, Daniel

1993-01-01

Argues that certain "ancient" writing practices can help attain the objective of making writing instruction truly democratic. Outlines key features in the discredited "old history" of composition to adduce ways of helping students think, feel, and write in heterogeneous ways. (HB)

Solar-Powered Plasmon-Enhanced Heterogeneous Catalysis

NASA Astrophysics Data System (ADS)

Naldoni, Alberto; Riboni, Francesca; Guler, Urcan; Boltasseva, Alexandra; Shalaev, Vladimir M.; Kildishev, Alexander V.

2016-06-01

Photocatalysis uses semiconductors to convert sunlight into chemical energy. Recent reports have shown that plasmonic nanostructures can be used to extend semiconductor light absorption or to drive direct photocatalysis with visible light at their surface. In this review, we discuss the fundamental decay pathway of localized surface plasmons in the context of driving solar-powered chemical reactions. We also review different nanophotonic approaches demonstrated for increasing solar-to-hydrogen conversion in photoelectrochemical water splitting, including experimental observations of enhanced reaction selectivity for reactions occurring at the metalsemiconductor interface. The enhanced reaction selectivity is highly dependent on the morphology, electronic properties, and spatial arrangement of composite nanostructures and their elements. In addition, we report on the particular features of photocatalytic reactions evolving at plasmonic metal surfaces and discuss the possibility of manipulating the reaction selectivity through the activation of targeted molecular bonds. Finally, using solar-to-hydrogen conversion techniques as an example, we quantify the efficacy metrics achievable in plasmon-driven photoelectrochemical systems and highlight some of the new directions that could lead to the practical implementation of solar-powered plasmon-based catalytic devices.

Preparation of nanobiochar as magnetic solid acid catalyst by pyrolysis-carbonization from oil palm empty fruit bunches

NASA Astrophysics Data System (ADS)

Jenie, S. N. Aisyiyah; Kristiani, Anis; Kustomo, Simanungkalit, Sabar; Mansur, Dieni

2017-11-01

Nanomaterials based on carbon exhibits unique properties, both physical and chemical, that can be utilized in various application, including catalyst. These nanomaterials were prepared through pyrolysis-carbonization process of biomass, oil palm empty fruit bunches. The effect of carbonization temperature in range of 500°C-600°C were also studied. The magnetic nanobiochar samples, MBC, were sulfonated by using sulfuric acid to increase their properties as solid acid catalyst. Their chemical and physical properties were characterized by Surface Area Analyzer and Porositymeter, X-Ray Diffraction, Scanning Electron Microscopy, Fourier Transform Infra-Red. The magnetic biochar samples obtained from carbonization at 873 K, MBC02-SO3H, was proven to have higher surface area, crystallinity properties and surface chemical composition after sulfonation process, which were confirmed by the BET, XRD and FT-IR analysis. Moreover, sample MBC02-SO3H exhibit promising catalytic acitivity in a catalysed esterification reaction, producing an ester yield of 64%. The result from this work opens new opportunities for the development of magnetic heterogenous acid catalyst from biomass waste.

One-pot hydrothermal synthesis of zeolite/sodium tantalate composite and its photodegradation of methyl orange

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

Gu, Xiaoli; Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing 210096; Lu, Haiqiang

2015-08-15

Highlights: • Sodalite/NaTaO{sub 3} composite is prepared by a one-pot hydrothermal synthesis. • Enhanced photodegradation is achieved due to the heterogeneous doping effect. • Structure distortion is found for NaTaO{sub 3} after removing sodalite by acid washing. - Abstract: Sodalite/NaTaO{sub 3} composite was prepared by a one-pot hydrothermal synthesis method. Sodalite and NaTaO{sub 3} grow interpenetrated, and the resulting composites have similar morphology as the pure sodalite. The sodalite/NaTaO{sub 3} composite has a lower band gap of 3.35 eV due to the heterogeneous doping effect, and exhibits an enhanced photodegradation of methyl orange under UV irradiation as compared to themore » pure NaTaO{sub 3}. A slight structure distortion is found for NaTaO{sub 3} after removing sodalite by acid washing the sodalite/NaTaO{sub 3} composite, and such result further confirms the co-growth of the two crystals. This one-pot hydrothermal method opens up new avenues for the preparation of photocatalytic composites.« less

Diversity and Activity of Diazotrophs in Great Barrier Reef Surface Waters.

PubMed

Messer, Lauren F; Brown, Mark V; Furnas, Miles J; Carney, Richard L; McKinnon, A D; Seymour, Justin R

2017-01-01

Discrepancies between bioavailable nitrogen (N) concentrations and phytoplankton growth rates in the oligotrophic waters of the Great Barrier Reef (GBR) suggest that undetermined N sources must play a significant role in supporting primary productivity. One such source could be biological dinitrogen (N 2 ) fixation through the activity of "diazotrophic" bacterioplankton. Here, we investigated N 2 fixation and diazotroph community composition over 10° S of latitude within GBR surface waters. Qualitative N 2 fixation rates were found to be variable across the GBR but were relatively high in coastal, inner and outer GBR waters, reaching 68 nmol L -1 d -1 . Diazotroph assemblages, identified by amplicon sequencing of the nifH gene, were dominated by the cyanobacterium Trichodesmium erythraeum , γ-proteobacteria from the Gamma A clade, and δ-proteobacterial phylotypes related to sulfate-reducing genera. However, diazotroph communities exhibited significant spatial heterogeneity, correlated with shifts in dissolved inorganic nutrient concentrations. Specifically, heterotrophic diazotrophs generally increased in relative abundance with increasing concentrations of phosphate and N, while Trichodesmium was proportionally more abundant when concentrations of these nutrients were low. This study provides the first in-depth characterization of diazotroph community composition and N 2 fixation dynamics within the oligotrophic, N-limited surface waters of the GBR. Our observations highlight the need to re-evaluate N cycling dynamics within oligotrophic coral reef systems, to include diverse N 2 fixing assemblages as a potentially significant source of dissolved N within the water column.

Anatomy of triply-periodic network assemblies: characterizing skeletal and inter-domain surface geometry of block copolymer gyroids.

PubMed

Prasad, Ishan; Jinnai, Hiroshi; Ho, Rong-Ming; Thomas, Edwin L; Grason, Gregory M

2018-05-09

Triply-periodic networks (TPNs), like the well-known gyroid and diamond network phases, abound in soft matter assemblies, from block copolymers (BCPs), lyotropic liquid crystals and surfactants to functional architectures in biology. While TPNs are, in reality, volume-filling patterns of spatially-varying molecular composition, physical and structural models most often reduce their structure to lower-dimensional geometric objects: the 2D interfaces between chemical domains; and the 1D skeletons that thread through inter-connected, tubular domains. These lower-dimensional structures provide a useful basis of comparison to idealized geometries based on triply-periodic minimal, or constant-mean curvature surfaces, and shed important light on the spatially heterogeneous packing of molecular constituents that form the networks. Here, we propose a simple, efficient and flexible method to extract a 1D skeleton from 3D volume composition data of self-assembled networks. We apply this method to both self-consistent field theory predictions as well as experimental electron microtomography reconstructions of the double-gyroid phase of an ABA triblock copolymer. We further demonstrate how the analysis of 1D skeleton, 2D inter-domain surfaces, and combinations therefore, provide physical and structural insight into TPNs, across multiple length scales. Specifically, we propose and compare simple measures of network chirality as well as domain thickness, and analyze their spatial and statistical distributions in both ideal (theoretical) and non-ideal (experimental) double gyroid assemblies.

Characterization of the silver coins of the Hoard of Beçin by X-ray based methods

NASA Astrophysics Data System (ADS)

Rodrigues, M.; Schreiner, M.; Melcher, M.; Guerra, M.; Salomon, J.; Radtke, M.; Alram, M.; Schindel, N.

2011-12-01

Four hundred sixteen silver coins stemming from the Ottoman Empire (16th and 17th centuries) were analyzed in order to confirm the fineness of the coinage as well as to study the provenance of the alloy used for the coins. As most of the coins showed the typical green patina on their surfaces due to corrosion processes which have led to the depletion of copper in the near-surface domains of the silver coins in comparison to their core composition, small samples by cutting splinters from the coins had to be taken, embedded in synthetic resin and cross-sectioned in order to investigate the true-heart metal composition. The type of the alloy was investigated as well as if coins minted in different locations demonstrated homogeneous traits concerning the predominant impurities which could suggest a common ore. Several X-ray based techniques (μ-XRF, μ-SRXRF and μ-PIXE) could be applied in order to determine the silver contents as well as the minor and trace elements. Finally, SEM/EDX was applied in order to study the homogeneity/heterogeneity of the coins and the presence of surface enrichments. In general, the silver content of the analyzed specimen varies between 90% and 95%. These outcomes have not supported the historical interpretations, which predict that during the period studied a debasement of approximately 44% of the silver content of the coins should have occurred.

Effects of specialized drill bits on hole defects of CFRP laminates

NASA Astrophysics Data System (ADS)

Li, Chao; Xu, Jinyang; Chen, Ming

2018-05-01

Drilling is a conventional machining process widely applied to carbon fiber reinforced plastics (CFRP) for the riveting and fastening purposes in the aerospace and automotive industries. However, the machining mechanism of CFRP composites differ significantly from that of homogeneous metal alloys owing to their prominent anisotropy and heterogeneity. Serious hole defects such as fiber pullout, matrix debonding and delamination are generally produced during the hole-making process, resulting in the poor machined surface quality, low fatigue durability or even the part rejections. In order to minimize the defects especially the delamination damage in composites drilling, specialized drill bits are often a primary choice being widely adopted in a real production. This paper aims to study the effects of two drills differing in geometrical characteristics during the drilling of CFRP laminates. A number of drilling experiments were carried out with the aim to evaluate the drilling performance of different drill bits. A scanning electron microscope (SEM) was used to observe the drilled surfaces to study the surface roughness. A high frequency scanning acoustic microscope (SAM) was applied to characterize the drilled hole morphologies with a particular focus on the delamination damage occurring in the CFRP laminates. The obtained results indicate that the fiber orientation relative to the cutting direction is a key factor affecting hole morphology and hole wall defects can be reduced by utilizing specialized drill geometries. Moreover, the dagger drill was confirmed outperforming the brad spur drill from the aspect of reducing drilling-induced delamination.

Collagen density gradient on three-dimensional printed poly(ε-caprolactone) scaffolds for interface tissue engineering.

PubMed

D'Amora, Ugo; D'Este, Matteo; Eglin, David; Safari, Fatemeh; Sprecher, Christoph M; Gloria, Antonio; De Santis, Roberto; Alini, Mauro; Ambrosio, Luigi

2018-02-01

The ability to engineer scaffolds that resemble the transition between tissues would be beneficial to improve repair of complex organs, but has yet to be achieved. In order to mimic tissue organization, such constructs should present continuous gradients of geometry, stiffness and biochemical composition. Although the introduction of rapid prototyping or additive manufacturing techniques allows deposition of heterogeneous layers and shape control, the creation of surface chemical gradients has not been explored on three-dimensional (3D) scaffolds obtained through fused deposition modelling technique. Thus, the goal of this study was to introduce a gradient functionalization method in which a poly(ε-caprolactone) surface was first aminolysed and subsequently covered with collagen via carbodiimide reaction. The 2D constructs were characterized for their amine and collagen contents, wettability, surface topography and biofunctionality. Finally, chemical gradients were created in 3D printed scaffolds with controlled geometry and porosity. The combination of additive manufacturing and surface modification is a viable tool for the fabrication of 3D constructs with controlled structural and chemical gradients. These constructs can be employed for mimicking continuous tissue gradients for interface tissue engineering. Copyright © 2017 John Wiley & Sons, Ltd.

Contact angle and local wetting at contact line.

PubMed

Li, Ri; Shan, Yanguang

2012-11-06

This theoretical study was motivated by recent experiments and theoretical work that had suggested the dependence of the static contact angle on the local wetting at the triple-phase contact line. We revisit this topic because the static contact angle as a local wetting parameter is still not widely understood and clearly known. To further clarify the relationship of the static contact angle with wetting, two approaches are applied to derive a general equation for the static contact angle of a droplet on a composite surface composed of heterogeneous components. A global approach based on the free surface energy of a thermodynamic system containing the droplet and solid surface shows the static contact angle as a function of local surface chemistry and local wetting state at the contact line. A local approach, in which only local forces acting on the contact line are considered, results in the same equation. The fact that the local approach agrees with the global approach further demonstrates the static contact angle as a local wetting parameter. Additionally, the study also suggests that the wetting described by the Wenzel and Cassie equations is also the local wetting of the contact line rather than the global wetting of the droplet.

Molecular mobility in the monolayers of foam films stabilized by porcine lung surfactant.

PubMed Central

Lalchev, Z I; Todorov, R K; Christova, Y T; Wilde, P J; Mackie, A R; Clark, D C

1996-01-01

Certain physical properties of a range of foam film types that are believed to exist in vivo in the lung have been investigated. The contribution of different lung surfactant components found in porcine lung surfactant to molecular surface diffusion in the plane of foam films has been investigated for the first time. The influence of the type and thickness of black foam films, temperature, electrolyte concentration, and extract composition on surface diffusion has been studied using the fluorescence recovery after photobleaching technique. Fluorescent phospholipid probe molecules in foam films stabilized by porcine lung surfactant samples or their hydrophobic extracts consisting of surfactant lipids and hydrophobic lung surfactant proteins, SP-B and SP-C, exhibited more rapid diffusion than observed in films of its principal lipid component alone, L-alpha-phosphatidylcholine dipalmitoyl. This effect appears to be due to contributions from minor lipid components present in the total surfactant lipid extracts. The minor lipid components influence the surface diffusion in foam films both by their negative charge and by lowering the phase transition temperature of lung surfactant samples. In contrast, the presence of high concentrations of the hydrophillic surfactant protein A (SP-A) and non-lung-surfactant proteins in the sample reduced the diffusion coefficient (D) of the lipid analog in the adsorbed layer of the films. Hysteresis behavior of D was observed during temperature cycling, with the cooling curve lying above the heating curve. However, in cases where some surface molecular aggregation and surface heterogeneity were observed during cooling, the films became more rigid and molecules at the interfaces became immobilized. The thickness, size, capillary pressure, configuration, and composition of foam films of lung surfactant prepared in vitro support their investigation as realistic structural analogs of the surface films that exist in vivo in the lung. Compared to other models currently in use, foam films provide new opportunities for studying the properties and function of physiologically important alveolar surface films. Images FIGURE 1 FIGURE 2 PMID:8913597

Composition of the Cayley Formation at Apollo 16 as inferred from impact melt splashes

NASA Technical Reports Server (NTRS)

Morris, Richard V.; Horz, Friedrich; See, Thomas H.

1986-01-01

Abundances of major and trace elements and magnetic properties of 50 impact melt splashes (IMSs) from the Apollo 16 landing site are analzyed to determine the composition of their meteoritic component. MgO-Sc and Ca-Sc variation diagrams and least-squares mixing models are utilized to analyze the IMS, soil, and rock data. Consideration is given to progenitor lithologies of the IMS, the number of impact events represented by the IMS, and the heterogeneity of impact melts from single events. It is observed that the IMSs are composed of either a mixture of anorthosite and low-Sc impact melt rocks or anorthositic norite. It is determined that the surface Cayley layer is composed of TiO2, MgO, Sc, and La concentrations of 0.69, and 7.1 wt pct and 10.5 and 21.2 microg/g, respectively and 0.38 and 5.9 wt pct and 6.1 and 11.8 microg/g, respectively, for the subsurface Cayley layer. The Descartes Formation composition is estimated as TiO2, MgO, Sc, and La concentrations of 0.25, and 3.5 wt pct and 7.7 and 2.2 microg/g, respectively.

TEMPO functionalized C60 fullerene deposited on gold surface for catalytic oxidation of selected alcohols

NASA Astrophysics Data System (ADS)

Piotrowski, Piotr; Pawłowska, Joanna; Sadło, Jarosław Grzegorz; Bilewicz, Renata; Kaim, Andrzej

2017-05-01

C60TEMPO10 catalytic system linked to a microspherical gold support through a covalent S-Au bond was developed. The C60TEMPO10@Au composite catalyst had a particle size of 0.5-0.8 μm and was covered with the fullerenes derivative of 2.3 nm diameter bearing ten nitroxyl groups; the organic film showed up to 50 nm thickness. The catalytic composite allowed for the oxidation under mild conditions of various primary and secondary alcohols to the corresponding aldehyde and ketone analogues with efficiencies as high as 79-98%, thus giving values typical for homogeneous catalysis, while retaining at the same time all the advantages of heterogeneous catalysis, e.g., easy separation by filtration from the reaction mixture. The catalytic activity of the resulting system was studied by means of high pressure liquid chromatography. A redox mechanism was proposed for the process. In the catalytic cycle of the oxidation process, the TEMPO moiety was continuously regenerated in situ with an applied primary oxidant, for example, O2/Fe3+ system. The new intermediate composite components and the final catalyst were characterized by various spectroscopic methods and thermogravimetry.

Off-Axis Seamount Lavas at 8°20' N Span the Entire Range of East Pacific Rise MORB Compositions

NASA Astrophysics Data System (ADS)

Anderson, M.; Wanless, V. D.; Perfit, M. R.; Gregg, P. M.; Fornari, D. J.; McCully, E.; Ridley, W. I.

2017-12-01

Lavas erupted at off-axis seamounts can provide a window into mantle heterogeneity and melting systematics that are not easily observed on-axis at fast-spreading mid-ocean ridges (MORs), where melts are efficiently mixed and homogenized within shallow axial magma chambers. To investigate off-axis magmatism, we systematically mapped the 8°20' N seamount chain in November of 2016 on R/V Atlantis using shipboard EM122 multibeam system and AUV Sentry. This 160-km long chain of off-axis seamounts and ridges is located perpendicular to the ridge axis, west of the East Pacific Rise (EPR) and north of the Siqueiros Fracture Zone. The high-resolution surface and AUV-based multibeam and AUV sidescan maps are combined with geochemical analyses of 300 basalt samples, collected using HOV Alvin and dredging, to evaluate magmatic plumbing and sources off-axis. Preliminary major and trace element concentrations reveal remarkable geochemical heterogeneity (including both normal and enriched basalt compositions) across the entire seamount chain and within individual seamounts. For example, (La/Sm)N contents span the entire range of known values for basalts from northern Pacific MORs and seamounts (0.45—2.76). MgO contents vary from 10.25 to 4.56 wt. % across the seamount chain and by as much as 3.61 wt. % from volcanic features sampled at an individual seamount (Beryl). Additionally, K2O/TiO2 ratios range from 4.9 to 61.3 across the seamount chain, and by as much as 54.4 at a single seamount (Beryl), indicating heterogeneous mantle sources or variable extents of melting occur at both regional and local scales. We combine the geochemical results and bathymetric maps with petrologic models to evaluate extents and depths of fractional crystallization and mantle melting in the off-axis environment.

Compositional changes in the UCC through time revealed by tungsten isotopes

NASA Astrophysics Data System (ADS)

Mundl, A.; Walker, R. J.; Reimink, J. R.; Rudnick, R. L.; Gaschnig, R. M.

2017-12-01

During periods of glaciation, ice scrapes off large areas of Earth's surface. The resulting sediments, termed glacial diamictites, are typically little affected by chemical alteration during their accumulation and lithification. The fine-grained matrix of a diamictite can therefore provide important information about the average composition of a portion of the upper continental crust (UCC) preceding the time of its deposition. Major and trace element studies of diamictites have reported compositional changes in the UCC through Earth's history, documenting changes in its average lithology. Short-lived radiogenic isotope systems are useful tools to further study crustal evolution via diamictites, as small-scale 182W (182Hf → 182W, t½ = 8.9 Ma) and 142Nd (146Nd → 142Nd, t½= 103 Ma) anomalies may reflect mantle or crustal processes that occurred very early in Earth history. We have investigated 182W/184W ratios in thirteen glacial diamictite composites from four different continents. These rocks were deposited during the Archean (3.0 Ga), Proterozoic (2.4, 2.3, 2.2, 0.6 Ga) and Paleozoic (0.3 Ga) in South Africa, as well as during the Proterozoic (2.4, 0.7, 0.6 Ga) in North America, and the Paleozoic (0.3 Ga) in South America. Individual glacial diamictites sample multiple crustal sources, so the isotopic compositions of the diamictites are more representative of the UCC at the time of deposition, than the komatiites and early Archean supracrustal rocks, which have been the focus of most prior studies. Tungsten isotope compositions reveal well-resolved deficits in 182W/184W of as much as 14 ppm in three of the four Archean samples from South Africa. By contrast, there are no clearly resolved deficits in Paleoproterozoic diamictites from the same area, although results for multiple analyses of the same samples suggest that a small deficit of 6 ppm may be present. No anomalies are present in younger diamictites. The Archean diamictites provide additional evidence for considerable heterogeneity in 182W in Archean crustal rocks, consistent with prior studies of individual rock units. The lack of anomalies in younger diamictites suggests that the isotopically heterogeneous nature of 182W in the Archean crust had disappeared by the beginning of the Proterozoic, as with 142Nd. Reasons for the transition remain unclear.

Satellite-based remote sensing of running water habitats at large riverscape scales: Tools to analyze habitat heterogeneity for river ecosystem management

NASA Astrophysics Data System (ADS)

Hugue, F.; Lapointe, M.; Eaton, B. C.; Lepoutre, A.

2016-01-01

We illustrate an approach to quantify patterns in hydraulic habitat composition and local heterogeneity applicable at low cost over very large river extents, with selectable reach window scales. Ongoing developments in remote sensing and geographical information science massively improve efficiencies in analyzing earth surface features. With the development of new satellite sensors and drone platforms and with the lowered cost of high resolution multispectral imagery, fluvial geomorphology is experiencing a revolution in mapping streams at high resolution. Exploiting the power of aerial or satellite imagery is particularly useful in a riverscape research framework (Fausch et al., 2002), where high resolution sampling of fluvial features and very large coverage extents are needed. This study presents a satellite remote sensing method that requires very limited field calibration data to estimate over various scales ranging from 1 m to many tens or river kilometers (i) spatial composition metrics for key hydraulic mesohabitat types and (ii) reach-scale wetted habitat heterogeneity indices such as the hydromorphological index of diversity (HMID). When the purpose is hydraulic habitat characterization applied over long river networks, the proposed method (although less accurate) is much less computationally expensive and less data demanding than two dimensional computational fluid dynamics (CFD). Here, we illustrate the tools based on a Worldview 2 satellite image of the Kiamika River, near Mont Laurier, Quebec, Canada, specifically over a 17-km river reach below the Kiamika dam. In the first step, a high resolution water depth (D) map is produced from a spectral band ratio (calculated from the multispectral image), calibrated with limited field measurements. Next, based only on known river discharge and estimated cross section depths at time of image capture, empirical-based pseudo-2D hydraulic rules are used to rapidly generate a two-dimensional map of flow velocity (V) over the 17-km Kiamika reach. The joint distribution of D and V variables over wetted zones then is used to reveal structural patterns in hydraulic habitat availability at patch, reach, and segment scales. Here we analyze 156 bivariate (D, V) density function plots estimated over moving reach windows along the satellite scene extent to extract 14 physical habitat metrics (such as river width, mean and modal depths and velocity, variances and covariance in D and V over 1-m pixels, HMID, entropy). A principal component analysis on the set of metrics is then used to cluster river reaches in regard to similarity in their hydraulic habitat composition and heterogeneity. Applications of this approach can include (i) specific fish habitat detection at riverscape scales (e.g., large areas of riffle spawning beds, deeper pools) for regional management, (ii) studying how river habitat heterogeneity is correlated to fish distribution and (iii) guidance for site location for restoration of key habitats or for post regulation monitoring of representative reaches of various types.

Group Composition of Cooperative Learning: Does Heterogeneous Grouping Work in Asian Classrooms?

ERIC Educational Resources Information Center

Thanh, Pham Thi Hong; Gillies, Robyn

2010-01-01

Constructing an appropriate group is important to teamwork success. Although, heterogeneous grouping is widely recommended in Western countries, this method of grouping is questioned in Asian classrooms because Asian and Western students have different cultures of learning. Unfortunately, this issue has not been addressed in any research to date.…

Transition-metal-free catalysts for the sustainable epoxidation of alkenes: from discovery to optimisation by means of high throughput experimentation.

PubMed

Lueangchaichaweng, Warunee; Geukens, Inge; Peeters, Annelies; Jarry, Benjamin; Launay, Franck; Bonardet, Jean-Luc; Jacobs, Pierre A; Pescarmona, Paolo P

2012-02-01

Transition-metal-free oxides were studied as heterogeneous catalysts for the sustainable epoxidation of alkenes with aqueous H₂O₂ by means of high throughput experimentation (HTE) techniques. A full-factorial HTE approach was applied in the various stages of the development of the catalysts: the synthesis of the materials, their screening as heterogeneous catalysts in liquid-phase epoxidation and the optimisation of the reaction conditions. Initially, the chemical composition of transition-metal-free oxides was screened, leading to the discovery of gallium oxide as a novel, active and selective epoxidation catalyst. On the basis of these results, the research line was continued with the study of structured porous aluminosilicates, gallosilicates and silica-gallia composites. In general, the gallium-based materials showed the best catalytic performances. This family of materials represents a promising class of heterogeneous catalysts for the sustainable epoxidation of alkenes and offers a valid alternative to the transition-metal heterogeneous catalysts commonly used in epoxidation. High throughput experimentation played an important role in promoting the development of these catalytic systems.

Aquifer modification: an approach to improve the mobility of nanoscale zero-valent iron particles used for in situ groundwater remediation

NASA Astrophysics Data System (ADS)

MicicBatka, Vesna; Schmid, Doris; Marko, Florian; Velimirovic, Milica; Wagner, Stephan; von der Kammer, Frank; Hofmann, Thilo

2015-04-01

Successful emplacement of nanoscale zero-valent iron (nZVI) within the contaminated source zone is a prerequisite for the use of nZVI technology in groundwater remediation. Emplacement of nZVI is influenced i.e., by the injection technique and the injection velocity applied, as well as by the mobility of nZVI in the subsurface. Whereas processes linked to the injection can be controlled by the remediation practitioners, the mobility of nZVI in the subsurface remains limited. Even though mobility of nZVI is somewhat improved by surface coating with polyelectrolytes, it is still greatly affected by the groundwater composition and physical and chemical heterogeneities of aquifer grains. In order to promote mobility of nZVI it is needed to alter the surface charge heterogeneities of aquifer grains. Modifying the aquifer grain's surfaces by means of polyelectrolyte coating is an approach proposed to increase the overall negative surface charge of the aquifer grain surfaces, hinder deposition of nZVI onto aquifer grains, and finally promote nZVI mobility. In this study the effect of different polyelectrolytes on the nZVI mobility is tested in natural sands deriving from real brownfield sites that are proposed to be remediated using the nZVI technology. Sands collected from brownfield sites were characterized in terms of grain size distribution, mineralogical and chemical composition, and organic carbon content. Furthermore, surface charge of these sands was determined in both, low- and high ionic strength background solutions. Finally, changes of the sand's surface charges were examined after addition of the proposed aquifer modifiers, lignin sulfonate and humic acid. Surface charge of brownfield sands in low ionic strength background solution is more negative compared to that in high ionic strength background solution. An increase in negative surface potential of brownfield sand was recorded when aquifer modifiers were applied in a background solution with low ionic strength, indicating their potential to improve nZVI mobility under comparable environmental conditions. In contrast, no significant change of the surface potential of brownfield sand was observed when aquifer modifiers were applied in a background solution with high ionic strength. The potential of the aquifer modifiers to promote the mobility of nZVI was furthermore tested in flow-through columns, starting with the one filled with natural quartz sand with rough surface, low ionic strength background solutions and pre-injecting lignin sulfonate in concentration of 50 mg/L. The preliminary results showed that the pre-injection of lignin sulfonate does increase mobility of nZVI under this experimental condition. Further mobility tests will be carried out in order to elucidate the potential of the aquifer modifiers to promote the mobility of nZVI in sands with a complex mineralogy and in the background solutions with varying ionic strength, in order to account for the condition that resemble those at polluted sites. This research receives funding from the European Union's Seventh Framework Programme FP7/2007-2013 under grant agreement n°309517.

The Small Bodies Thermal Mapper: An Instrument for Future Missions to Study the Compositional and Thermal Properties of Phobos

NASA Astrophysics Data System (ADS)

Donaldson Hanna, Kerri; Bowles, Neil; Calcutt, Simon; Greenhagen, Benjamin; Glotch, Timothy; Edwards, Christopher

2015-04-01

The surface of Phobos holds many keys for understanding its formation and evolution as well as the history and dynamics of the Mars-Phobos system. Phobos has been the target for numerous flyby and sample return missions in the past (e.g. Rosetta [Pajola et al., 2012] and Phobos Grunt [Kuzmin et al., 2003]). Previous telescopic and spacecraft observations have revealed a surface that is compositionally heterogeneous [e.g. Pang et al., 1978; Pollack et al., 1978, Lunine et al., 1982; Murchie and Erard, 1996; Roush and Hogan, 2001; Rivkin et al., 2002; Giuranna et al., 2011; Fraeman et al., 2014] and with large variations in surface topography [e.g. Shi et al., 2011; 2012; Willner et al., 2014]. For any future sample return mission, remote sensing observations, in particular thermal infrared observations, will be key in characterising possible landing/sampling sites and placing returned samples into their geological context. The European Space Agency has identified Phootprint, a European sample return mission to Phobos, as a candidate mission of the Mars Robotic Exploration Preparation Programme 2 (MREP-2). Using this mission concept as a baseline, we have studied the options for a simple multichannel radiometer to provide thermal mapping and compositional remote sensing data. By mapping Phobos' diurnal thermal response, a thermal imaging instrument will provide key information on the nature of the surface and near sub-surface (the thermal inertia) and composition. These measurements will support visible imaging observations to determine landing sites that are compatible with the spacecraft's sampling mechanisms. Remotely sensed thermal maps of the surface will also prevent otherwise unpredictable thermal loads on the spacecraft due to variations in local topography and albedo. The instrument design resulting from this study, the Small Bodies Thermal Mapper (SBTM), is a compact multichannel radiometer and thermal imager. The SBTM is based on the Compact Modular Sounder (CMS) instrument currently flying on the UK's TechDemoSat-1 spacecraft in low Earth orbit. This gives a significant level of flight heritage with optimisations for the expected Phobos environment. The SBTM instrument uses a two-dimensional uncooled thermal detector array to provide imaging of Phobos. In addition, ten narrow-band infrared filters located around diagnostic mineral spectral features provide additional compositional discrimination. For the SBTM, the optimisations studied include options for the detector and filters required to cover the wide range of diurnal temperatures expected at Phobos (e.g. 130 to > 300 K) [e.g. Kuzmin et al., 2003]. Options studied include the use of a broadband micro bolometer array (e.g. http://www.ulis-ir.com/uploads/Products/PICO640E-041-BroadBand.pdf) or a thermopile detector [Foote et al., 1998] array. Optimisation of filter band passes for remote measurement of composition is also considered, based on mineral spectra measured under simulated Phobos environment [e.g. Glotch et al., 2014].

Trace Elements in Basalts From the Siqueiros Fracture Zone: Implications for Melt Migration Models

NASA Astrophysics Data System (ADS)

Pickle, R. C.; Forsyth, D. W.; Saal, A. E.; Nagle, A. N.; Perfit, M. R.

2008-12-01

Incompatible trace element (ITE) ratios in MORB from a variety of locations may provide insights into the melt migration process by constraining aggregated melt compositions predicted by mantle melting and flow models. By using actual plate geometries to create a 3-D thermodynamic mantle model, melt volumes and compositions at all depths and locations may be calculated and binned into cubes using the pHMELTS algorithm [Asimow et al., 2004]. These melts can be traced from each cube to the surface assuming several migration models, including a simplified pressure gradient model and one in which melt is guided upwards by a low permeability compacted layer. The ITE ratios of all melts arriving at the surface are summed, averaged, and compared to those of the actual sample compositions from the various MOR locales. The Siqueiros fracture zone at 8° 20' N on the East Pacific Rise (EPR) comprises 4 intra-transform spreading centers (ITSCs) across 140 km of offset between two longer spreading ridges, and is an excellent study region for several reasons. First, an abundance of MORB data is readily available, and the samples retrieved from ITSCs are unlikely to be aggregated in a long-lived magma chamber or affected by along-axis transport, so they represent melts extracted locally from the mantle. Additionally, samples at Siqueiros span a compositional range from depleted to normal MORB within the fracture zone yet have similar isotopic compositions to samples collected from the 9-10° EPR. This minimizes the effect of assuming a uniform source composition in our melting model despite a heterogeneous mantle, allowing us to consistently compare the actual lava composition with that predicted by our model. Finally, it has been demonstrated with preliminary migration models that incipient melts generated directly below an ITSC may not necessarily erupt at that ITSC but migrate laterally towards a nearby ridge due to enhanced pressure gradients. The close proximity of the ITSCs at Siqueiros to the large ridges bounding the fracture zone provide a good opportunity to model this phenomenon and may help explain the variable ITE ratios found between samples collected within the transform and those near the ridges.

The Landsat Phenology Study (LaPS): Preliminary CONUS Results for 2008

NASA Astrophysics Data System (ADS)

Henebry, Geoffrey M.; Roy, David P.; Ju, Junchang; Kovalskyy, Valeriy

2010-05-01

Most studies of land surface phenology (LSP) have used time series derived from moderate spatial resolution satellite sensor data (e.g., AVHRR, MODIS, VEGETATION) because these data are freely available and because they provide an acceptable trade-off between higher, near daily, temporal frequency of observation needed to reduce cloud contamination against lower (500m-5km) spatial resolution. The recent opening of the USGS Landsat archive to web-enabled access presents the opportunity to explore how well Landsat time series can portray LSPs at high spatial resolution. The NASA Web-enabled Landsat data (WELD) project (http://landsat.usgs.gov/WELD.php) has produced 30m composited mosaics for all the conterminous US (CONUS) from Landsat 7 ETM+ data. The composited mosaics are generated on monthly, seasonal, and annual basis and include spectral reflectance, normalized difference vegetation index (NDVI), and the acquisition date of each composited pixel. The WELD compositing approach is designed to select valid land surface observations with minimal cloud, snow, and atmospheric contamination. We extracted 30m pixel time series from the twelve monthly WELD composited mosaics for 2008 at 320 locations across the CONUS where we have ground phenological observations that are heterogeneous with respect to the types of plants observed, the phenophases recorded (predominantly spring green-up) and the ground sampling protocols used. The ground data came from several sources, including the cloned lilac/honeysuckle network, the Phenocam network, five LTER sites (H.J. Andrews, Harvard Forest, Jornada, Konza Prairie, and Sevilleta), and a private woodlot in Maine. Temporal profiles of the 30m WELD Landsat NDVI, the green NDVI (GNDVI), the normalized difference infrared index (NDII) derived from the composited reflectances, are compared to the ground observations. Results show that (i) inclusion of the Landsat acquisition date for each pixel improves the characterization of the LSP, (ii) the use of the NDII and GNDVI in conjunction with the NDVI improves identification of the onset both of canopy development and senescence, and (iii) the WELD compositing approach and the resulting mosaics provide a rich new data source for phenological investigations.

The Landsat Phenology Study (LaPS): Preliminary CONUS Results for 2008

NASA Astrophysics Data System (ADS)

Henebry, G. M.; Roy, D.; Ju, J.; Kovalskyy, V.

2009-12-01

Most studies of land surface phenology (LSP) have used time series derived from moderate spatial resolution satellite sensor data (e.g., AVHRR, MODIS, VEGETATION) because these data are freely available and because they provide an acceptable trade-off between higher, near daily, temporal frequency of observation needed to reduce cloud contamination against lower (500m-5km) spatial resolution. The recent opening of the USGS Landsat archive to web-enabled access presents the opportunity to explore how well Landsat time series can portray LSPs at high spatial resolution. The NASA Web-enabled Landsat data (WELD) project has produced 30m composited mosaics for all the conterminous US (CONUS) from Landsat 7 ETM+ data. The composited mosaics are generated on monthly, seasonal, and annual basis and include spectral reflectance, normalized difference vegetation index (NDVI), and the acquisition date of each composited pixel. The WELD compositing approach is designed to select valid land surface observations with minimal cloud, snow, and atmospheric contamination. We extracted 30m pixel time series from the twelve monthly WELD composited mosaics for 2008 at 320 locations across the CONUS where we have ground phenological observations that are heterogeneous with respect to the types of plants observed, the phenophases recorded (predominantly spring green-up) and the ground sampling protocols used. The ground data came from several sources, including the cloned lilac/honeysuckle network, the Phenocam network, five LTER sites (H.J. Andrews, Harvard Forest, Jornada, Konza Prairie, and Sevilleta), and a private woodlot in New Hampshire. Temporal profiles of the 30m WELD Landsat NDVI and the normalized difference infrared index (NDII) derived from the composited reflectances, are compared to the ground observations. Results show that (i) inclusion of the Landsat acquisition date for each pixel improves the characterization of the LSP, (ii) the use of the NDII in conjunction with the NDVI improves identification of the onset both of canopy development and senescence, and (iii) the WELD compositing approach and the resulting mosaics provide a rich new data source for phenological investigations.

Species effects on ecosystem processes are modified by faunal responses to habitat composition.

PubMed

Bulling, Mark T; Solan, Martin; Dyson, Kirstie E; Hernandez-Milian, Gema; Luque, Patricia; Pierce, Graham J; Raffaelli, Dave; Paterson, David M; White, Piran C L

2008-12-01

Heterogeneity is a well-recognized feature of natural environments, and the spatial distribution and movement of individual species is primarily driven by resource requirements. In laboratory experiments designed to explore how different species drive ecosystem processes, such as nutrient release, habitat heterogeneity is often seen as something which must be rigorously controlled for. Most small experimental systems are therefore spatially homogeneous, and the link between environmental heterogeneity and its effects on the redistribution of individuals and species, and on ecosystem processes, has not been fully explored. In this paper, we used a mesocosm system to investigate the relationship between habitat composition, species movement and sediment nutrient release for each of four functionally contrasting species of marine benthic invertebrate macrofauna. For each species, various habitat configurations were generated by selectively enriching patches of sediment with macroalgae, a natural source of spatial variability in intertidal mudflats. We found that the direction and extent of faunal movement between patches differs with species identity, density and habitat composition. Combinations of these factors lead to concomitant changes in nutrient release, such that habitat composition effects are modified by species identity (in the case of NH4-N) and by species density (in the case of PO4-P). It is clear that failure to accommodate natural patterns of spatial heterogeneity in such studies may result in an incomplete understanding of system behaviour. This will be particularly important for future experiments designed to explore the effects of species richness on ecosystem processes, where the complex interactions reported here for single species may be compounded when species are brought together in multi-species combinations.

Algebraic dynamic multilevel method for compositional flow in heterogeneous porous media

NASA Astrophysics Data System (ADS)

Cusini, Matteo; Fryer, Barnaby; van Kruijsdijk, Cor; Hajibeygi, Hadi

2018-02-01

This paper presents the algebraic dynamic multilevel method (ADM) for compositional flow in three dimensional heterogeneous porous media in presence of capillary and gravitational effects. As a significant advancement compared to the ADM for immiscible flows (Cusini et al., 2016) [33], here, mass conservation equations are solved along with k-value based thermodynamic equilibrium equations using a fully-implicit (FIM) coupling strategy. Two different fine-scale compositional formulations are considered: (1) the natural variables and (2) the overall-compositions formulation. At each Newton's iteration the fine-scale FIM Jacobian system is mapped to a dynamically defined (in space and time) multilevel nested grid. The appropriate grid resolution is chosen based on the contrast of user-defined fluid properties and on the presence of specific features (e.g., well source terms). Consistent mapping between different resolutions is performed by the means of sequences of restriction and prolongation operators. While finite-volume restriction operators are employed to ensure mass conservation at all resolutions, various prolongation operators are considered. In particular, different interpolation strategies can be used for the different primary variables, and multiscale basis functions are chosen as pressure interpolators so that fine scale heterogeneities are accurately accounted for across different resolutions. Several numerical experiments are conducted to analyse the accuracy, efficiency and robustness of the method for both 2D and 3D domains. Results show that ADM provides accurate solutions by employing only a fraction of the number of grid-cells employed in fine-scale simulations. As such, it presents a promising approach for large-scale simulations of multiphase flow in heterogeneous reservoirs with complex non-linear fluid physics.

High-resolution observations of combustion in heterogeneous surface fuels

Treesearch

E. Louise Loudermilk; Gary L. Achtemeier; Joseph J. O' Brien; J. Kevin Hiers; Benjamin S. Hornsby

2014-01-01

In ecosystems with frequent surface fires, fire and fuel heterogeneity at relevant scales have been largely ignored. This could be because complete burns give an impression of homogeneity, or due to the difficulty in capturing fine-scale variation in fuel characteristics and fire behaviour. Fire movement between patches of fuel can have implications for modelling fire...

Heterogeneous Nucleation Induced by Capillary Wave During Acoustic Levitation

NASA Astrophysics Data System (ADS)

Lü, Yong-Jun; Xie, Wen-Jun; Wei, Bing-Bo

2003-08-01

The rapid solidification of acoustically levitated drops of Pb-61.9 wt.%Sn eutectic alloy is accomplished. A surface morphology of spreading ripples is observed on a sample undercooled by 15 K. The ripples originate from the centre of sample surface, which is also the heterogeneous nucleation site for eutectic growth. The Faraday instability excited by forced surface vibration has brought about these ripples. They are retained in the solidified sample if the sound pressure level exceeds the threshold pressure required for the appearance of capillary waves. Theoretical calculations indicate that both the pressure and displacement maxima exist in the central part of a levitated drop. The pressure near the sample centre can promote heterogeneous nucleation, which is in agreement qualitatively with the experimental results.

Surface sodium lignosulphonate-immobilized sawdust particle as an efficient adsorbent for capturing Hg2+ from aqueous solution.

PubMed

Gao, Shan; Luo, Tiantian; Zhou, Qi; Luo, Wenjun; Li, Haifeng; Jing, Luru

2018-05-01

In this work, the soluble sodium lignosulphonate (LS Na ) molecules were successfully grafted onto the surface of pine sawdust (PSD) particles to obtain an efficient adsorbent (PSD-LS) for removing Hg 2+ from wastewater. In advance, the surface of sawdust particles were carboxymethylated by chloroacetic acid, the LS Na would be anchored on the surface by a heterogeneous esterification reaction occurred between the hydroxyl of LS Na and carboxyl on PSD surface. The resultant product (PSD-LS) exhibited a good adsorption performance for Hg 2+ with adsorption capacity up to 164.77 mg/g and it was characterized by scanning electron microscope (SEM), energy dispersive X-ray diffraction (EDX), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The effects of pH, contact time, adsorption temperature and initial concentration on the adsorption of Hg 2+ were investigated. Results showed that the pseudo-second-order kinetics and Langmuir isotherm model could describe the adsorption process better. In addition, the composite adsorbent has outstanding reusability with high and stable desorption rates under several continuous cycle. These findings suggested that PSD-LS was a potential adsorbent to remove hazardous metal ions from wastewater. Copyright © 2018 Elsevier Inc. All rights reserved.

Photochemical preparation of sub-wavelength heterogeneous laser-induced periodic surface structures.

PubMed

Kim, Hee-Cheol; Reinhardt, Hendrik; Hillebrecht, Pierre; Hampp, Norbert A

2012-04-17

Laser-induced periodic surface structures (LIPSS) are a phenomenon caused by interaction of light with solid surfaces. We present a photochemical concept which uses LIPSS-related light intensity patterns for the generation of heterogeneous nanostructures. The process facilitates arbitrary combinations of substrate and LIPSS-pattern materials. An efficient method for the generation of organometallic hybrid-nanowire arrays on porous anodic aluminum oxide is demonstrated. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Normal-mode and free-Air gravity constraints on lateral variations in velocity and density of Earth's mantle

PubMed

Ishii; Tromp

1999-08-20

With the use of a large collection of free-oscillation data and additional constraints imposed by the free-air gravity anomaly, lateral variations in shear velocity, compressional velocity, and density within the mantle; dynamic topography on the free surface; and topography on the 660-km discontinuity and the core-mantle boundary were determined. The velocity models are consistent with existing models based on travel-time and waveform inversions. In the lowermost mantle, near the core-mantle boundary, denser than average material is found beneath regions of upwellings centered on the Pacific Ocean and Africa that are characterized by slow shear velocities. These anomalies suggest the existence of compositional heterogeneity near the core-mantle boundary.

Frictional heterogeneities on carbonate-bearing normal faults: Insights from the Monte Maggio Fault, Italy

NASA Astrophysics Data System (ADS)

Carpenter, B. M.; Scuderi, M. M.; Collettini, C.; Marone, C.

2014-12-01

Observations of heterogeneous and complex fault slip are often attributed to the complexity of fault structure and/or spatial heterogeneity of fault frictional behavior. Such complex slip patterns have been observed for earthquakes on normal faults throughout central Italy, where many of the Mw 6 to 7 earthquakes in the Apennines nucleate at depths where the lithology is dominated by carbonate rocks. To explore the relationship between fault structure and heterogeneous frictional properties, we studied the exhumed Monte Maggio Fault, located in the northern Apennines. We collected intact specimens of the fault zone, including the principal slip surface and hanging wall cataclasite, and performed experiments at a normal stress of 10 MPa under saturated conditions. Experiments designed to reactivate slip between the cemented principal slip surface and cataclasite show a 3 MPa stress drop as the fault surface fails, then velocity-neutral frictional behavior and significant frictional healing. Overall, our results suggest that (1) earthquakes may readily nucleate in areas of the fault where the slip surface separates massive limestone and are likely to propagate in areas where fault gouge is in contact with the slip surface; (2) postseismic slip is more likely to occur in areas of the fault where gouge is present; and (3) high rates of frictional healing and low creep relaxation observed between solid fault surfaces could lead to significant aftershocks in areas of low stress drop.

SU-E-T-481: Dosimetric Effects of Tissue Heterogeneity in Proton Therapy: Monte Carlo Simulation and Experimental Study Using Animal Tissue Phantoms.

PubMed

Liu, Y; Zheng, Y

2012-06-01

Accurate determination of proton dosimetric effect for tissue heterogeneity is critical in proton therapy. Proton beams have finite range and consequently tissue heterogeneity plays a more critical role in proton therapy. The purpose of this study is to investigate the tissue heterogeneity effect in proton dosimetry based on anatomical-based Monte Carlo simulation using animal tissues. Animal tissues including a pig head and beef bulk were used in this study. Both pig head and beef were scanned using a GE CT scanner with 1.25 mm slice thickness. A treatment plan was created, using the CMS XiO treatment planning system (TPS) with a single proton spread-out-Bragg-peak beam (SOBP). Radiochromic films were placed at the distal falloff region. Image guidance was used to align the phantom before proton beams were delivered according to the treatment plan. The same two CT sets were converted to Monte Carlo simulation model. The Monte Carlo simulated dose calculations with/without tissue omposition were compared to TPS calculations and measurements. Based on the preliminary comparison, at the center of SOBP plane, the Monte Carlo simulation dose without tissue composition agreed generally well with TPS calculation. In the distal falloff region, the dose difference was large, and about 2 mm isodose line shift was observed with the consideration of tissue composition. The detailed comparison of dose distributions between Monte Carlo simulation, TPS calculations and measurements is underway. Accurate proton dose calculations are challenging in proton treatment planning for heterogeneous tissues. Tissue heterogeneity and tissue composition may lead to isodose line shifts up to a few millimeters in the distal falloff region. By simulating detailed particle transport and energy deposition, Monte Carlo simulations provide a verification method in proton dose calculation where inhomogeneous tissues are present. © 2012 American Association of Physicists in Medicine.

Architecture and reservoir quality of low-permeable Eocene lacustrine turbidite sandstone from the Dongying Depression, East China

NASA Astrophysics Data System (ADS)

Munawar, Muhammad Jawad; Lin, Chengyan; Chunmei, Dong; Zhang, Xianguo; Zhao, Haiyan; Xiao, Shuming; Azeem, Tahir; Zahid, Muhammad Aleem; Ma, Cunfei

2018-05-01

The architecture and quality of lacustrine turbidites that act as petroleum reservoirs are less well documented. Reservoir architecture and multiscale heterogeneity in turbidites represent serious challenges to production performance. Additionally, establishing a hierarchy profile to delineate heterogeneity is a challenging task in lacustrine turbidite deposits. Here, we report on the turbidites in the middle third member of the Eocene Shahejie Formation (Es3), which was deposited during extensive Middle to Late Eocene rifting in the Dongying Depression. Seismic records, wireline log responses, and core observations were integrated to describe the reservoir heterogeneity by delineating the architectural elements, sequence stratigraphic framework and lithofacies assemblage. A petrographic approach was adopted to constrain microscopic heterogeneity using an optical microscope, routine core analyses and X-ray diffraction (XRD) analyses. The Es3m member is interpreted as a sequence set composed of four composite sequences: CS1, CS2, CS3 and CS4. A total of forty-five sequences were identified within these four composite sequences. Sand bodies were mainly deposited as channels, levees, overbank splays, lobes and lobe fringes. The combination of fining-upward and coarsening-upward lithofacies patterns in the architectural elements produces highly complex composite flow units. Microscopic heterogeneity is produced by diagenetic alteration processes (i.e., feldspar dissolution, authigenic clay formation and quartz cementation). The widespread kaolinization of feldspar and mobilization of materials enhanced the quality of the reservoir by producing secondary enlarged pores. In contrast, the formation of pore-filling authigenic illite and illite/smectite clays reduced its permeability. Recovery rates are higher in the axial areas and smaller in the marginal areas of architectural elements. This study represents a significant insight into the reservoir architecture and heterogeneity of lacustrine turbidites, and the understanding of compartmentalization and distribution of high-quality sand reservoirs can be applied to improve primary and secondary production in these fields.

Solar Wind sputtering from the surface of Comet Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Wurz, Peter; Rubin, Martin; Altwegg, Kathrin; Balsiger, Hans; Gasc, Sébastien; Galli, André; Jäckel, Annette; Le Roy, Lena; Calmonte, Ursina; Tzou, Chia-Yu; Mall, Urs; Korth, Axel; Fiethe, Björn; De Keyser, Johan; Berthelier, Jean-Jacques; Rème, Henri; Gombosi, Tamas; Fuselier, Steven

2015-04-01

While the European Space Agency's Rosetta spacecraft is orbiting close to the comet 67P/Churyumov-Gerasimenko (67P/C-G) we performed continuous measurements of the chemical inventory of its coma with the the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument suite. ROSINA consists of two mass spectrometers, the Double Focusing Mass Spectrometer (DFMS) and the Reflectron-type Time-Of-Flight (RTOF), as well as the COmet Pressure Sensor (COPS). Most of the observed species in the coma are volatile material that are released from the comet's surface by sublimation, for example H2O, CO, CO2 and many others. The number densities in the coma of these species show temporary variation compatible with the solar illumination (diurnal cycle), with seasonal variation (summer and winter hemispheres), and with compositional heterogeneity of the surface. We can trace back the measurements of the observed species to the cometary surface to create maps of their probable origin on the surface. In addition to the volatile material we detected atoms of Na, K, Si, S, and some more, which cannot or only partially be set free via sublimation. Again, we project these measurements down onto the surface of the comet. These maps for the sputtered atoms differ significantly from the maps for volatile species, like the water map, in some cases they are almost the opposite. Our present understanding is that these atoms are the result of solar wind sputtering of refractory material, i.e., of dust located on the cometary surface. Since the release of material from the surface by sputtering is almost stoichiometric we can infer the chemical composition of major elements for the areas affected by sputtering and the average mineralogy of these locations can be derived. The sputter signal will disappear with the comet getting closer to the Sun and becomes more active. Once the coma is dense enough, the solar wind will be absorbed by the gas layer above the surface and will not propagate to the surface anymore.

Heterogeneity of the Caribbean plateau mantle source: Sr, O and He isotopic compositions of olivine and clinopyroxene from Gorgona Island

NASA Astrophysics Data System (ADS)

Révillon, S.; Chauvel, C.; Arndt, N. T.; Pik, R.; Martineau, F.; Fourcade, S.; Marty, B.

2002-12-01

The composition of the mantle plumes that created large oceanic plateaus such as Ontong Java or the Caribbean is still poorly known. Geochemical and isotopic studies on accreted portions of the Caribbean plateau have shown that the plume source was heterogeneous and contained isotopically depleted and relatively enriched portions. A distinctive feature of samples from the Caribbean plateau is their unusual Sr isotopic compositions, which, at a given Nd isotopic ratio, are far higher than in samples from other oceanic plateaus. Sr, O and He isotopic compositions of whole rocks and magmatic minerals (clinopyroxene or olivine) separated from komatiites, gabbros and peridotites from Gorgona Island in Colombia were determined to investigate the origin of these anomalously radiogenic compositions. Sequentially leached clinopyroxenes have Sr isotopic compositions in the range 87Sr/ 86Sr=0.70271-0.70352, systematically lower than those of leached and unleached whole rocks. Oxygen isotopic ratios of clinopyroxene vary within the range δ 18O=5.18-5.35‰, similar to that recorded in oceanic island basalts. He isotopic ratios are high ( R/ Ra=8-19). The lower 87Sr/ 86Sr ratios of most of the clinopyroxenes shift the field of the Caribbean plateau in Nd-Sr isotope diagrams toward more 'normal' values, i.e. a position closer to the field defined by mid-ocean ridge basalts and oceanic-island basalts. Three clinopyroxenes have slightly higher 87Sr/ 86Sr ratios that cannot be explained by an assimilation model. The high 87Sr/ 86Sr and variations of 143Nd/ 144Nd are interpreted as a source characteristic. Trace-element ratios, however, are controlled mainly by fractionation during partial melting. We combine these isotopic data in a heterogeneous plume source model that accounts for the diversity of isotopic signatures recorded on Gorgona Island and throughout the Caribbean plateau. The heterogeneities are related to old recycled oceanic lithosphere in the plume source; the high 3He/ 4He ratios may indicate that the source material once resided in the lower mantle.

[Quantitative characterization of nuclear polymorphism of the epithelial cells in fibroadenomatosis and cancer of the breast].

PubMed

Ganina, K P; Petunin, Iu I; Timoshenko, Ia G

1989-01-01

A method for quantitative analysis of epithelial cell nuclear polymorphism was suggested, viz. identification of general statistical population using Petunin's criterion. This criterion was employed to assess heterogeneity of visible surface of interphase epithelial cell nuclei and to assay nuclear DNA level in fibroadenomatous hyperplasia and cancer of the breast. Heterogeneity index (h), alongside with other parameters, appeared useful for quantitative assessment of the disease: heterogeneity index values ranging 0.1-0.4 point to pronounced heterogeneity of epithelial cell nucleus surface and DNA level, and are suggestive of malignant transformation of tissue, whereas benign proliferation of the epithelium is usually characterized by 0.4 less than h less than or equal to 0.9.

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.

Adhesion mapping of chemically modified and poly(ethylene oxide)-grafted glass surfaces.

PubMed

Jogikalmath, G; Stuart, J K; Pungor, A; Hlady, V

1999-08-01

Two-dimensional mapping of the adhesion pull-off forces was used to study the origin of surface heterogeneity in the grafted poly(ethylene oxide) (PEO) layer. The variance of the pull-off forces measured over the μm-sized regions after each chemical step of modifying glass surfaces was taken to be a measure of the surface chemical heterogeneity. The attachment of γ-glycidoxypropyltrimethoxy silane (GPS) to glass decreased the pull-off forces relative to the clean glass and made the surface more uniform. The subsequent hydrolysis of the terminal epoxide groups resulted in a larger surface heterogeneity which was modeled by two populations of the terminal hydroxyl groups, each with its own distribution of adhesion forces and force variance. The activation of the hydroxyls with carbonyldiimmidazole (CDI) healed the surface and lowered its adhesion, however, the force variance remained rather large. Finally, the grafting of the α,ω-diamino poly(ethyleneoxide) chains to the CDI-activated glass largely eliminated adhesion except at a few discrete regions. The adhesion on the PEO grafted layer followed the Poisson distribution of the pull-off forces. With the exception of the glass surface, a correlation between the water contact angles and the mean pull-off forces measured with the Si(3)N(4) tip surfaces was found for all modified glass surfaces.

An Exploration of the Importance of Flood Heterogeneity for Regionalization in Arizona using the Expected Moments Algorithm

NASA Astrophysics Data System (ADS)

Zamora-Reyes, D.; Hirschboeck, K. K.; Paretti, N. V.

2012-12-01

Bulletin 17B (B17B) has prevailed for 30 years as the standard manual for determining flood frequency in the United States. Recently proposed updates to B17B include revising the issue of flood heterogeneity, and improving flood estimates by using the Expected Moments Algorithm (EMA) which can better address low outliers and accommodate information on historical peaks. Incorporating information on mixed populations, such as flood-causing mechanisms, into flood estimates for regions that have noticeable flood heterogeneity can be statistically challenging when systematic flood records are short. The problem magnifies when the population sample size is reduced by decomposing the record, especially if multiple flood mechanisms are involved. In B17B, the guidelines for dealing with mixed populations focus primarily on how to rule out any need to perform a mixed-population analysis. However, in some regions mixed flood populations are critically important determinants of regional flood frequency variations and should be explored from this perspective. Arizona is an area with a heterogeneous mixture of flood processes due to: warm season convective thunderstorms, cool season synoptic-scale storms, and tropical cyclone-enhanced convective activity occurring in the late summer or early fall. USGS station data throughout Arizona was compiled into a database and each flood peak (annual and partial duration series) was classified according to its meteorological cause. Using these data, we have explored the role of flood heterogeneity in Arizona flood estimates through composite flood frequency analysis based on mixed flood populations using EMA. First, for selected stations, the three flood-causing populations were separated out from the systematic annual flood series record and analyzed individually. Second, to create composite probability curves, the individual curves for each of the three populations were generated and combined using Crippen's (1978) composite probability equations for sites that have two or more independent flood populations. Finally, the individual probability curves generated for each of the three flood-causing populations were compared with both the site's composite probability curve and the standard B17B curve to explore the influence of heterogeneity using the 100-year and 200-year flood estimates as a basis of comparison. Results showed that sites located in southern Arizona and along the abrupt elevation transition zone of the Mogollon Rim exhibit a better fit to the systematic data using their composite probability curves than the curves derived from standard B17B analysis. Synoptic storm floods and tropical cyclone-enhanced floods had the greatest influence on 100-year and 200-year flood estimates. This was especially true in southern Arizona, even though summer convective floods are much more frequent and therefore dominate the composite curve. Using the EMA approach also influenced our results because all possible low outliers were censored by the built-in Multiple Grubbs-Beck Test, providing a better fit to the systematic data in the upper probabilities. In conclusion, flood heterogeneity can play an important role in regional flood frequency variations in Arizona and that understanding its influence is important when making projections about future flood variations.

Multidimensional Modeling of Atmospheric Effects and Surface Heterogeneities on Remote Sensing

NASA Technical Reports Server (NTRS)

Gerstl, S. A. W.; Simmer, C.; Zardecki, A. (Principal Investigator)

1985-01-01

The overall goal of this project is to establish a modeling capability that allows a quantitative determination of atmospheric effects on remote sensing including the effects of surface heterogeneities. This includes an improved understanding of aerosol and haze effects in connection with structural, angular, and spatial surface heterogeneities. One important objective of the research is the possible identification of intrinsic surface or canopy characteristics that might be invariant to atmospheric perturbations so that they could be used for scene identification. Conversely, an equally important objective is to find a correction algorithm for atmospheric effects in satellite-sensed surface reflectances. The technical approach is centered around a systematic model and code development effort based on existing, highly advanced computer codes that were originally developed for nuclear radiation shielding applications. Computational techniques for the numerical solution of the radiative transfer equation are adapted on the basis of the discrete-ordinates finite-element method which proved highly successful for one and two-dimensional radiative transfer problems with fully resolved angular representation of the radiation field.

Edge Effects Are Important in Supporting Beetle Biodiversity in a Gravel-Bed River Floodplain

PubMed Central

Langhans, Simone D.; Tockner, Klement

2014-01-01

Understanding complex, dynamic, and diverse ecosystems is essential for developing sound management and conservation strategies. Gravel-bed river floodplains are composed of an interlinked mosaic of aquatic and terrestrial habitats hosting a diverse, specialized, and endangered fauna. Therefore, they serve as excellent models to investigate the biodiversity of multiple ecotones and related edge effects. In this study, we investigated the abundance, composition, richness, and conservation status of beetle assemblages at varying sediment depth (0, 0.1, 0.6 and 1.1 m), distance from the channel (1, 5, 20, and 60–100 m, and 5 m within the riparian forest), and time of the year (February–November) across a 200 m-wide gravel bar at the near-natural Tagliamento River (Italy), to detect edge effects in four floodplain ecotones: aquatic-terrestrial, forest-active floodplain, sediment-air, and sediment-groundwater. We used conventional pitfall traps and novel tube traps to sample beetles comparably on the sediment surface and within the unsaturated sediments. We found a total of 308 beetle species (including 87 of conservation concern) that showed multiple, significant positive edge effects across the floodplain ecotones, mainly driven by spatial heterogeneity: Total and red list beetle abundance and richness peaked on the sediment surface, at channel margins, and at the edge of the riparian forest. All ecotones possessed edge/habitat specialists. Most red list species occurred on the sediment surface, including five species previously considered extinct – yet two of these species occurred in higher densities in the unsaturated sediments. Conservation and management efforts along gravel-bed rivers must therefore promote a dynamic flow and sediment regime to create and maintain habitat heterogeneity and ecotone diversity, which support a unique and high biodiversity. PMID:25545280

Egg shell waste as heterogeneous nanocatalyst for biodiesel production: Optimized by response surface methodology.

PubMed

Pandit, Priti R; Fulekar, M H

2017-08-01

Worldwide consumption of hen eggs results in availability of large amount of discarded egg waste particularly egg shells. In the present study, the waste shells were utilized for the synthesis of highly active heterogeneous calcium oxide (CaO) nanocatalyst to transesterify dry biomass into methyl esters (biodiesel). The CaO nanocatalyst was synthesied by calcination-hydration-dehydration technique and fully characterized by infrared spectroscopy, X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), brunauer-emmett-teller (BET) elemental and thermogravimetric analysis. TEM image showed that the nano catalyst had spherical shape with average particle size of 75 nm. BET analysis indicated that the catalyst specific surface area was 16.4 m 2  g -1 with average pore diameter of 5.07 nm. The effect of nano CaO catalyst was investigated by direct transesterification of dry biomass into biodiesel along with other reaction parameters such as catalyst ratio, reaction time and stirring rate. The impact of the transesterification reaction parameters and microalgal biodiesel yield were analyzed by response surface methodology based on a full factorial, central composite design. The significance of the predicted mode was verified and 86.41% microalgal biodiesel yield was reported at optimal parameter conditions 1.7% (w/w), catalyst ratio, 3.6 h reaction time and stirring rate of 140.6 rpm. The biodiesel conversion was determined by 1 H nuclear magnetic resonance spectroscopy (NMR). The fuel properties of prepared biodiesel were found to be highly comply with the biodiesel standard ASTMD6751 and EN14214. Copyright © 2017 Elsevier Ltd. All rights reserved.

Edge effects are important in supporting beetle biodiversity in a gravel-bed river floodplain.

PubMed

Langhans, Simone D; Tockner, Klement

2014-01-01

Understanding complex, dynamic, and diverse ecosystems is essential for developing sound management and conservation strategies. Gravel-bed river floodplains are composed of an interlinked mosaic of aquatic and terrestrial habitats hosting a diverse, specialized, and endangered fauna. Therefore, they serve as excellent models to investigate the biodiversity of multiple ecotones and related edge effects. In this study, we investigated the abundance, composition, richness, and conservation status of beetle assemblages at varying sediment depth (0, 0.1, 0.6 and 1.1 m), distance from the channel (1, 5, 20, and 60-100 m, and 5 m within the riparian forest), and time of the year (February-November) across a 200 m-wide gravel bar at the near-natural Tagliamento River (Italy), to detect edge effects in four floodplain ecotones: aquatic-terrestrial, forest-active floodplain, sediment-air, and sediment-groundwater. We used conventional pitfall traps and novel tube traps to sample beetles comparably on the sediment surface and within the unsaturated sediments. We found a total of 308 beetle species (including 87 of conservation concern) that showed multiple, significant positive edge effects across the floodplain ecotones, mainly driven by spatial heterogeneity: Total and red list beetle abundance and richness peaked on the sediment surface, at channel margins, and at the edge of the riparian forest. All ecotones possessed edge/habitat specialists. Most red list species occurred on the sediment surface, including five species previously considered extinct--yet two of these species occurred in higher densities in the unsaturated sediments. Conservation and management efforts along gravel-bed rivers must therefore promote a dynamic flow and sediment regime to create and maintain habitat heterogeneity and ecotone diversity, which support a unique and high biodiversity.

A Hybrid Density Functional Theory/Molecular Mechanics Approach for Linear Response Properties in Heterogeneous Environments.

PubMed

Rinkevicius, Zilvinas; Li, Xin; Sandberg, Jaime A R; Mikkelsen, Kurt V; Ågren, Hans

2014-03-11

We introduce a density functional theory/molecular mechanical approach for computation of linear response properties of molecules in heterogeneous environments, such as metal surfaces or nanoparticles embedded in solvents. The heterogeneous embedding environment, consisting from metallic and nonmetallic parts, is described by combined force fields, where conventional force fields are used for the nonmetallic part and capacitance-polarization-based force fields are used for the metallic part. The presented approach enables studies of properties and spectra of systems embedded in or placed at arbitrary shaped metallic surfaces, clusters, or nanoparticles. The capability and performance of the proposed approach is illustrated by sample calculations of optical absorption spectra of thymidine absorbed on gold surfaces in an aqueous environment, where we study how different organizations of the gold surface and how the combined, nonadditive effect of the two environments is reflected in the optical absorption spectrum.

A Holistic Landscape Description Reveals That Landscape Configuration Changes More over Time than Composition: Implications for Landscape Ecology Studies.

PubMed

Mimet, Anne; Pellissier, Vincent; Houet, Thomas; Julliard, Romain; Simon, Laurent

2016-01-01

Space-for-time substitution-that is, the assumption that spatial variations of a system can explain and predict the effect of temporal variations-is widely used in ecology. However, it is questionable whether it can validly be used to explain changes in biodiversity over time in response to land-cover changes. Here, we hypothesize that different temporal vs spatial trajectories of landscape composition and configuration may limit space-for-time substitution in landscape ecology. Land-cover conversion changes not just the surface areas given over to particular types of land cover, but also affects isolation, patch size and heterogeneity. This means that a small change in land cover over time may have only minor repercussions on landscape composition but potentially major consequences for landscape configuration. Using land-cover maps of the Paris region for 1982 and 2003, we made a holistic description of the landscape disentangling landscape composition from configuration. After controlling for spatial variations, we analyzed and compared the amplitudes of changes in landscape composition and configuration over time. For comparable spatial variations, landscape configuration varied more than twice as much as composition over time. Temporal changes in composition and configuration were not always spatially matched. The fact that landscape composition and configuration do not vary equally in space and time calls into question the use of space-for-time substitution in landscape ecology studies. The instability of landscapes over time appears to be attributable to configurational changes in the main. This may go some way to explaining why the landscape variables that account for changes over time in biodiversity are not the same ones that account for the spatial distribution of biodiversity.

A Holistic Landscape Description Reveals That Landscape Configuration Changes More over Time than Composition: Implications for Landscape Ecology Studies

PubMed Central

Mimet, Anne; Pellissier, Vincent; Houet, Thomas; Julliard, Romain; Simon, Laurent

2016-01-01

Background Space-for-time substitution—that is, the assumption that spatial variations of a system can explain and predict the effect of temporal variations—is widely used in ecology. However, it is questionable whether it can validly be used to explain changes in biodiversity over time in response to land-cover changes. Hypothesis Here, we hypothesize that different temporal vs spatial trajectories of landscape composition and configuration may limit space-for-time substitution in landscape ecology. Land-cover conversion changes not just the surface areas given over to particular types of land cover, but also affects isolation, patch size and heterogeneity. This means that a small change in land cover over time may have only minor repercussions on landscape composition but potentially major consequences for landscape configuration. Methods Using land-cover maps of the Paris region for 1982 and 2003, we made a holistic description of the landscape disentangling landscape composition from configuration. After controlling for spatial variations, we analyzed and compared the amplitudes of changes in landscape composition and configuration over time. Results For comparable spatial variations, landscape configuration varied more than twice as much as composition over time. Temporal changes in composition and configuration were not always spatially matched. Significance The fact that landscape composition and configuration do not vary equally in space and time calls into question the use of space-for-time substitution in landscape ecology studies. The instability of landscapes over time appears to be attributable to configurational changes in the main. This may go some way to explaining why the landscape variables that account for changes over time in biodiversity are not the same ones that account for the spatial distribution of biodiversity. PMID:26959363

Diurnal Variations of the Flux Imbalance Over Homogeneous and Heterogeneous Landscapes

NASA Astrophysics Data System (ADS)

Zhou, Yanzhao; Li, Dan; Liu, Heping; Li, Xin

2018-05-01

It is well known that the sum of the turbulent sensible and latent heat fluxes as measured by the eddy-covariance method is systematically lower than the available energy (i.e., the net radiation minus the ground heat flux). We examine the separate and joint effects of diurnal and spatial variations of surface temperature on this flux imbalance in a dry convective boundary layer using the Weather Research and Forecasting model. Results show that, over homogeneous surfaces, the flux due to turbulent-organized structures is responsible for the imbalance, whereas over heterogeneous surfaces, the flux due to mesoscale or secondary circulations is the main contributor to the imbalance. Over homogeneous surfaces, the flux imbalance in free convective conditions exhibits a clear diurnal cycle, showing that the flux-imbalance magnitude slowly decreases during the morning period and rapidly increases during the afternoon period. However, in shear convective conditions, the flux-imbalance magnitude is much smaller, but slightly increases with time. The flux imbalance over heterogeneous surfaces exhibits a diurnal cycle under both free and shear convective conditions, which is similar to that over homogeneous surfaces in free convective conditions, and is also consistent with the general trend in the global observations. The rapid increase in the flux-imbalance magnitude during the afternoon period is mainly caused by the afternoon decay of the turbulent kinetic energy (TKE). Interestingly, over heterogeneous surfaces, the flux imbalance is linearly related to the TKE and the difference between the potential temperature and surface temperature, ΔT; the larger the TKE and ΔT values, the smaller the flux-imbalance magnitude.

Identifying Mechanisms of Interfacial Dynamics Using Single-Molecule Tracking

PubMed Central

Kastantin, Mark; Walder, Robert; Schwartz, Daniel K.

2012-01-01

The “soft” (i.e. non-covalent) interactions between molecules and surfaces are complex and highly-varied (e.g. hydrophobic, hydrogen bonding, ionic) often leading to heterogeneous interfacial behavior. Heterogeneity can arise either from spatial variation of the surface/interface itself or from molecular configurations (i.e. conformation, orientation, aggregation state, etc.). By observing adsorption, diffusion, and desorption of individual fluorescent molecules, single-molecule tracking can characterize these types of heterogeneous interfacial behavior in ways that are inaccessible to traditional ensemble-averaged methods. Moreover, the fluorescence intensity or emission wavelength (in resonance energy transfer experiments) can be used to simultaneously track molecular configuration and directly relate this to the resulting interfacial mobility or affinity. In this feature article, we review recent advances involving the use of single-molecule tracking to characterize heterogeneous molecule-surface interactions including: multiple modes of diffusion and desorption associated with both internal and external molecular configuration, Arrhenius activated interfacial transport, spatially dependent interactions, and many more. PMID:22716995

Ozone destruction through heterogeneous chemistry following the eruption of El Chichon

NASA Technical Reports Server (NTRS)

Hofmann, David J.; Solomon, Susan

1989-01-01

The results of ozone observations at northern midlatitudes in late 1982 through 1983, following the eruption of El Chichon are discussed, together with the observations of other trace gases which may be linked to possible variations in ozone chemistry. These results are related to the in situ aerosol observations following the El Chicon eruption, with particular attention given to data relevant to heterogeneous reactions, such as the aerosol surface area and weight percent H2SO4. It is shown that, at midlatitudes, the observed volcanic-particle surface area reached a maximum of about 50 sq microns/cu m (above a typical background value of about 0.75) at an altitude of 18-20 km in early 1983; this enhancement of surface area is about the same as that encountered in stratospheric clouds in the Antarctic, suggesting a possible basis for ozone depletion through heterogeneous chemistry. The fraction of ozone reduction that may have occurred as a result of heterogeneous chemicl effects is estimated.