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Sample records for surface role des

  1. Le rôle des plantes dans le transfert du silicium à la surface des continentsThe role of plants in the transfer of silicon at the surface of the continents

    NASA Astrophysics Data System (ADS)

    Meunier, Jean-Dominique

    2003-12-01

    Silicon is the most abundant element after oxygen in the lithosphere (27 wt%). Plants and soil microorganisms are important contributors to the weathering of silicates. Plants are able to accumulate several percent of Si in the biomass. The importance of plants in the rates of Si output to surface waters is discussed in this paper. To cite this article: J.-D. Meunier, C. R. Geoscience 335 (2003).

  2. Caracterisation du coefficient de retrodiffusion radar des surfaces d'hydrocarbure: Modelisation et interpretation

    NASA Astrophysics Data System (ADS)

    Charbonneau, Francois

    La surveillance maritime est un domaine d'applications ou l'interet politique et scientifique croit constamment au Canada. Un des outils privilegies pour la surveillance maritime est l'acquisition de donnees radars, par des systemes aeroportes ou spatio-portes (ERS-2, RADARSAT et Envisat). Par leur grande couverture spatiale, ainsi que leur sensibilite a la geometrie de surface, les donnees radars permettent, en autres, la detection de cibles ponctuelles (bateaux), estimation des vents, detection des glaces de mer, ainsi que la detection de deversement d'hydrocarbure. Les limites et les avantages de la detection d'hydrocarbure par acquisitions de donnees radars sont bien connus, mais il reste encore des lacunes au niveau de l'extraction des parametres physiques d'une surface d'hydrocarbure. Ce projet a pour objectif de caracteriser le coefficient de retrodiffusion radar associe a une surface d'hydrocarbure en milieu oceanique, par l'introduction d'un modele thermodynamique d'attenuation de la surface, au modele theorique radar IEM. Le modele global permet de simuler le comportement de sigma° en fonction des proprietes visco-elastiques, ainsi que de l'epaisseur de la couche d'hydrocarbure et en fonction des parametres d'acquisition radar. Le modele developpe fut valide a partir des donnees SIR-C acquises lors d'experimentations controlees. A partir des informations environnementales et du type d'hydrocarbure, notre modele a permis d'estime le contraste d'intensite avec une precision de 1 a 1,5 dB, a la bande C. Alors qu'a la bande L, l'erreur sur le contraste est d'environ 1,5 a 2 dB sur l'ensemble des mesures. Ce qui est excellant considerant l'heterogeneite des surfaces analysees. Egalement, nous effectuons des analyses multi-polarisees et polarimetriques avec les donnees SIR-C acquises au-dessus de sites experimentaux. II en ressort que le ratio de polarisation VV/HH, ainsi que le facteur d'anisotropie sont des pistes de recherche prometteuses qu'il faudra

  3. Modelisations des effets de surface sur les jets horizontaux subsoniques d'hydrogene et de methane

    NASA Astrophysics Data System (ADS)

    Gomez, Luis Fernando

    Le developpement des codes et de normes bases sur une methodologie scientifique requiert la capacite de predire l'etendue inflammable de deversements gazeux d'hydrogene sous differentes conditions. Des etudes anterieures ont deja etabli des modeles bases sur les lois de conservation de la mecanique des fluides basees sur des correlations experimentales qui permettent de predire la decroissance de la concentration et de la vitesse d'un gaz le long de l'axe d'un jet libre vertical. Cette etude s'interesse aux effets de proximite a une surface horizontale parallele sur un jet turbulent. Nous nous interessons a son impact sur l'etendue du champ de la concentration et sur l'enveloppe inflammable en particulier. Cette etude est comparative : l'hydrogene est compare au methane. Ceci permet de degager l'influence des effets de difference de la densite sur le comportement du jet, et de comparer le comportement de l'hydrogene aux correlations experimentales, qui ont ete essentiellement etablies pour le methane. Un modele decrivant l'evolution spatio-temporelle du champ de concentration du gaz dilue est propose, base sur la mecanique des fluides computationnelle. Cette approche permet de varier systematiquement les conditions aux frontieres (proximite du jet a la surface, par exemple) et de connaitre en detail les proprietes de l'ecoulement. Le modele est implemente dans le code de simulations par volumes finis de FLUENT. Les resultats des simulations sont compares avec les lois de similitudes decoulant de la theorie des jets d'ecoulements turbulents libres ainsi qu'avec les resultats experimentaux disponibles. L'effet de la difference des masses molaires des constituantes du jet et des constituantes du milieu de dispersion est egalement etudie dans le contexte du comportement d'echelle de la region developpee du jet.

  4. Role of wild small ruminants in the epidemiology of peste des petits ruminants.

    PubMed

    Munir, M

    2014-10-01

    Peste des petits ruminants virus (PPRV) causes one of the most contagious and highly infectious respiratory diseases in sheep and goats known as peste des petits ruminants (PPR). Reports of outbreaks of PPR in captive and wild small ruminants have extended the known spectrum of susceptible species to include antelopes. Phylogenetic analysis of nucleoprotein and fusion genes indicates that all PPRVs isolated from wild ungulate outbreaks belong to lineage IV. While it is clear that a number of wildlife species are susceptible to infection, the role of wildlife in the epidemiology of PPR remains uncertain. The available information about the occurrence of disease in free-ranging wildlife is mainly derived from surveys based on serological evidence. Data on the genetic nature of circulating PPRV strains are scarce. Given the scope of PPR in wild ungulates that are widespread in many countries, current disease surveillance efforts are inadequate and warrant additional investment. This is crucial because domestic and wild ruminants mingle together at several points, allowing inter-species transmission of PPRV. There is no reason to believe that PPRV circulates in wild animals and acts as a potential source of virus for domestic species. Irrespective of the possibility of wild small ruminants as the reservoir of PPRV, concerns about the role of susceptible species of antelopes need to be addressed, due to the fact that the disease can pose a serious threat to the survival of endangered species of wild ruminants on the one hand and could act as a constraint to the global eradication of PPR on the other hand. In this review, knowledge gained through research or surveillance on the sustainability of PPRV in wild ruminants is discussed. PMID:23305511

  5. Role of surface temperature in fluorocarbon plasma-surface interactions

    SciTech Connect

    Nelson, Caleb T.; Overzet, Lawrence J.; Goeckner, Matthew J.

    2012-07-15

    This article examines plasma-surface reaction channels and the effect of surface temperature on the magnitude of those channels. Neutral species CF{sub 4}, C{sub 2}F{sub 6}, and C{sub 3}F{sub 8} are produced on surfaces. The magnitude of the production channel increases with surface temperature for all species, but favors higher mass species as the temperature is elevated. Additionally, the production rate of CF{sub 2} increases by a factor of 5 as the surface temperature is raised from 25 Degree-Sign C to 200 Degree-Sign C. Fluorine density, on the other hand, does not change as a function of either surface temperature or position outside of the plasma glow. This indicates that fluorine addition in the gas-phase is not a dominant reaction. Heating reactors can result in higher densities of depositing radical species, resulting in increased deposition rates on cooled substrates. Finally, the sticking probability of the depositing free radical species does not change as a function of surface temperature. Instead, the surface temperature acts together with an etchant species (possibly fluorine) to elevate desorption rates on that surface at temperatures lower than those required for unassisted thermal desorption.

  6. Water-surface profiles of Raccoon River at Des Moines, Iowa

    USGS Publications Warehouse

    Carpenter, Philip J.; Appel, David H.

    1966-01-01

    The Raccoon River., having a drainage area of 3,630 square miles, borders the south edge of the Des Moines downtown business district before flowing into the Des Moines River at mile 201.6. A large residential area and the city airport are separated from downtown Des Moines by the Raccoon River (fig. 1). Five highway bridges and one railroad bridge span the river between the mouth and mile 205.75, the limits of this report (fig. 1). The river is confined to a narrow channel from the mouth to the Chicago, Burlington, and Quincy Railroad bridge (mile 202.6); upstream of this bridge the river is not confined and during high water spreads over a wide flood plain. Fleur Drive, a principal traffic artery to the downtown area, is the only roadway of the five that crosses this wide flood plain. It has been flooded 15 times during the period 1903, 1918-1965.

  7. Chemical analyses of surface water in Illinois, 1975-77; Volume 1, Des Plaines River basin and Lake Michigan

    USGS Publications Warehouse

    Grason, David; Healy, R.W.

    1979-01-01

    Samples of surface water were collected and analyzed by the Illinois Environmental Protection Agency. The results from water years 1975 to 1977 are presented in three volumes. The history of sampling and analytical methods used during that period are summarized. Stream discharge data from records of the U.S. Geological Survey are included for all sites where samples were collected at gaging stations or near enough that reliable discharge estimates could be made. Volume I includes the Des Plaines River basin and Lake Michigan. (Woodard-USGS)

  8. Surface disturbances: their role in accelerating desertification

    USGS Publications Warehouse

    Belnap, Jayne

    1995-01-01

    Maintaining soil stability and normal water and nutrient cycles in desert systems is critical to avoiding desertification. These particular ecosystem processes are threatened by trampling of livestock and people, and by off-road vehicle use. Soil compaction and disruption of cryptobiotic soil surfaces (composed of cyanobacteria, lichens, and mosses) can result in decreased water availability to vascular plants through decreased water infiltration and increased albedo with possible decreased precipitation. Surface disturbance may also cause accelerated soil loss through wind and water erosion and decreased diversity and abundance of soil biota. In addition, nutrient cycles can be altered through lowered nitrogen and carbon inputs and slowed decomposition of soil organic matter, resulting in lower nutrient levels in associated vascular plants. Some cold desert systems may be especially susceptible to these disruptions due to the paucity of surface-rooting vascular plants for soil stabilization, fewer nitrogen-fixing higher plants, and lower soil temperatures, which slow nutrient cycles. Desert soils may recover slowly from surface disturbances, resulting in increased vulnerability to desertification. Recovery from compaction and decreased soil stability is estimated to take several hundred years. Re-establishment rates for soil bacterial and fungal populations are not known. The nitrogen fixation capability of soil requires at least 50 years to recover. Recovery of crusts can be hampered by large amounts of moving sediment, and re-establishment can be extremely difficult in some areas. Given the sensitivity of these resources and slow recovery times, desertification threatens million of hectares of semiarid lands in the United States.

  9. Theory of adhesion: Role of surface roughness

    NASA Astrophysics Data System (ADS)

    Persson, B. N. J.; Scaraggi, M.

    2014-09-01

    We discuss how surface roughness influences the adhesion between elastic solids. We introduce a Tabor number which depends on the length scale or magnification, and which gives information about the nature of the adhesion at different length scales. We consider two limiting cases relevant for (a) elastically hard solids with weak (or long ranged) adhesive interaction (DMT-limit) and (b) elastically soft solids with strong (or short ranged) adhesive interaction (JKR-limit). For the former cases we study the nature of the adhesion using different adhesive force laws (F ˜ u-n, n = 1.5-4, where u is the wall-wall separation). In general, adhesion may switch from DMT-like at short length scales to JKR-like at large (macroscopic) length scale. We compare the theory predictions to results of exact numerical simulations and find good agreement between theory and simulation results.

  10. Effets des electrons secondaires sur l'ADN

    NASA Astrophysics Data System (ADS)

    Boudaiffa, Badia

    Les interactions des electrons de basse energie (EBE) representent un element important en sciences des radiations, particulierement, les sequences se produisant immediatement apres l'interaction de la radiation ionisante avec le milieu biologique. Il est bien connu que lorsque ces radiations deposent leur energie dans la cellule, elles produisent un grand nombre d'electrons secondaires (4 x 104/MeV), qui sont crees le long de la trace avec des energies cinetiques initiales bien inferieures a 20 eV. Cependant, il n'y a jamais eu de mesures directes demontrant l'interaction de ces electrons de tres basse energie avec l'ADN, du principalement aux difficultes experimentales imposees par la complexite du milieu biologique. Dans notre laboratoire, les dernieres annees ont ete consacrees a l'etude des phenomenes fondamentaux induits par impact des EBE sur differentes molecules simples (e.g., N2, CO, O2, H2O, NO, C2H 4, C6H6, C2H12) et quelques molecules complexes dans leur phase solide. D'autres travaux effectues recemment sur des bases de l'ADN et des oligonucleotides ont montre que les EBE produisent des bris moleculaires sur les biomolecules. Ces travaux nous ont permis d'elaborer des techniques pour mettre en evidence et comprendre les interactions fondamentales des EBE avec des molecules d'interet biologique, afin d'atteindre notre objectif majeur d'etudier l'effet direct de ces particules sur la molecule d'ADN. Les techniques de sciences des surfaces developpees et utilisees dans les etudes precitees peuvent etre etendues et combinees avec des methodes classiques de biologie pour etudier les dommages de l'ADN induits par l'impact des EBE. Nos experiences ont montre l'efficacite des electrons de 3--20 eV a induire des coupures simple et double brins dans l'ADN. Pour des energies inferieures a 15 eV, ces coupures sont induites par la localisation temporaire d'un electron sur une unite moleculaire de l'ADN, ce qui engendre la formation d'un ion negatif transitoire

  11. The role of surface rheology in liquid film formation

    NASA Astrophysics Data System (ADS)

    Scheid, B.; Delacotte, J.; Dollet, B.; Rio, E.; Restagno, F.; van Nierop, E. A.; Cantat, I.; Langevin, D.; Stone, H. A.

    2010-04-01

    The role of surface rheology in fundamental fluid dynamical systems, such as liquid coating flows and soap film formation, is poorly understood. We investigate the role of surface viscosity in the classical film-coating problem. We propose a theoretical model that predicts film thickening based on a purely surface-viscous theory. The theory is supported by a set of new experimental data that demonstrates slight thickening even at very high surfactant concentrations for which Marangoni effects are irrelevant. The model and experiments represent a new regime that has not been identified before.

  12. Calreticulin: Roles in Cell-Surface Protein Expression

    PubMed Central

    Jiang, Yue; Dey, Sandeepa; Matsunami, Hiroaki

    2014-01-01

    In order to perform their designated functions, proteins require precise subcellular localizations. For cell-surface proteins, such as receptors and channels, they are able to transduce signals only when properly targeted to the cell membrane. Calreticulin is a multi-functional chaperone protein involved in protein folding, maturation, and trafficking. However, evidence has been accumulating that calreticulin can also negatively regulate the surface expression of certain receptors and channels. In these instances, depletion of calreticulin enhances cell-surface expression and function. In this review, we discuss the role of calreticulin with a focus on its negative effects on the expression of cell-surface proteins. PMID:25230046

  13. Chemical analyses of surface water in Illinois, 1958-74; Volume I, Des Plaines River basin and Lake Michigan

    USGS Publications Warehouse

    Healy, R.W.; Toler, L.G.

    1978-01-01

    Samples of surface water were collected and analyzed by the Illinois Environmental Protection Agency and its predecessor, the Stream Pollution Control Bureau of the Illinois Department of Public Health. The results for the period 1958 to 1974 are presented in tabular form and the history of sampling and analytical methods are summarized. Stream discharge data from records of the U.S. Geological Survey are included for all sites where samples were collected at gaging stations or near enough that reliable discharge estimates could be made. The report is contained in three volumes. This volume (Volume I) includes Des Plaines River basin and Lake Michigan. (See also W78-10035 and W78-10036) (Woodard-USGS)

  14. Role of surface heat fluxes underneath cold pools

    NASA Astrophysics Data System (ADS)

    Gentine, Pierre; Garelli, Alix; Park, Seung-Bu; Nie, Ji; Torri, Giuseppe; Kuang, Zhiming

    2016-01-01

    The role of surface heat fluxes underneath cold pools is investigated using cloud-resolving simulations with either interactive or horizontally homogenous surface heat fluxes over an ocean and a simplified land surface. Over the ocean, there are limited changes in the distribution of the cold pool temperature, humidity, and gust front velocity, yet interactive heat fluxes induce more cold pools, which are smaller, and convection is then less organized. Correspondingly, the updraft mass flux and lateral entrainment are modified. Over the land surface, the heat fluxes underneath cold pools drastically impact the cold pool characteristics with more numerous and smaller pools, which are warmer and more humid and accompanied by smaller gust front velocities. The interactive fluxes also modify the updraft mass flux and reduce convective organization. These results emphasize the importance of interactive surface fluxes instead of prescribed flux boundary conditions, as well as the formulation of surface heat fluxes, when studying convection.

  15. Role of surface heat fluxes underneath cold pools

    PubMed Central

    Garelli, Alix; Park, Seung‐Bu; Nie, Ji; Torri, Giuseppe; Kuang, Zhiming

    2016-01-01

    Abstract The role of surface heat fluxes underneath cold pools is investigated using cloud‐resolving simulations with either interactive or horizontally homogenous surface heat fluxes over an ocean and a simplified land surface. Over the ocean, there are limited changes in the distribution of the cold pool temperature, humidity, and gust front velocity, yet interactive heat fluxes induce more cold pools, which are smaller, and convection is then less organized. Correspondingly, the updraft mass flux and lateral entrainment are modified. Over the land surface, the heat fluxes underneath cold pools drastically impact the cold pool characteristics with more numerous and smaller pools, which are warmer and more humid and accompanied by smaller gust front velocities. The interactive fluxes also modify the updraft mass flux and reduce convective organization. These results emphasize the importance of interactive surface fluxes instead of prescribed flux boundary conditions, as well as the formulation of surface heat fluxes, when studying convection. PMID:27134320

  16. Role of the Office International des Epizooties in protecting the health of free-ranging mammals.

    PubMed

    Blancou, J

    1992-12-01

    The various activities undertaken by the Office International des Epizooties (OIE) since 1924 to protect the helth of free-ranging mammals are outlined and discussed. Two types of activity have been conducted over the years: --The first type promotes measures to protect the health of free-ranging mammals in order to safeguard the health of domestic animals and human beings. These measures have prevented the propagation of the highly contagious diseases of animals and the more serious zoonoses. --The second type aims at protecting the health of free-ranging mammals in order to maintain the fauna and the natural equilibrium. Ecological and epidemiological studies are promoted with a view to effective management of wildlife populations and overcoming the associated health risks. By virtue of its close contacts with officials in charge of animal health in 126 Member Countries, the OIE has made a noteworthy contribution to the protection of populations of free-ranging mammals. PMID:1305849

  17. Role(s) of adsorbed water in the surface chemistry of environmental interfaces.

    PubMed

    Rubasinghege, Gayan; Grassian, Vicki H

    2013-04-18

    The chemistry of environmental interfaces such as oxide and carbonate surfaces under ambient conditions of temperature and relative humidity is of great interest from many perspectives including heterogeneous atmospheric chemistry, heterogeneous catalysis, photocatalysis, sensor technology, corrosion science, and cultural heritage science. As discussed here, adsorbed water plays important roles in the reaction chemistry of oxide and carbonate surfaces with indoor and outdoor pollutant molecules including nitrogen oxides, sulfur dioxide, carbon dioxide, ozone and organic acids. Mechanisms of these reactions are just beginning to be unraveled and found to depend on the details of the reaction mechanism as well as the coverage of water on the surface. As discussed here, adsorbed water can: (i) alter reaction pathways and surface speciation relative to the dry surface; (ii) hydrolyze reactants, intermediates and products; (iii) enhance surface reactivity by providing a medium for ionic dissociation; (iv) inhibit surface reactivity by blocking sites; (v) solvate ions; (vi) enhance ion mobility on surfaces and (vii) alter the stability of surface adsorbed species. In this feature article, drawing on research that has been going on for over a decade on the reaction chemistry of oxide and carbonate surfaces under ambient conditions of temperature and relative humidity, a number of specific examples showing the multi-faceted roles of adsorbed water are presented. PMID:23417201

  18. Role of Surface Characteristics in Urban Meteorology and Air Quality

    NASA Astrophysics Data System (ADS)

    Sailor, David Jean

    Urbanization results in a landscape with significantly modified surface characteristics. The lower values of reflectivity to solar radiation, surface moisture availability, and vegetative cover, along with the higher values of anthropogenic heat release and surface roughness combine to result in higher air temperatures in urban areas relative to their rural counterparts. Through their role in the surface energy balance and surface exchange processes, these surface characteristics are capable of modifying the local meteorology. The impacts on wind speeds, air temperatures, and mixing heights are of particular importance, as they have significant implications in terms of urban energy use and air quality. This research presents several major improvements to the meteorological modeling methodology for highly heterogeneous terrain. A land-use data base is implemented to provide accurate specification of surface characteristic variability in simulations of the Los Angeles Basin. Several vegetation parameterizations are developed and implemented, and a method for including anthropogenic heat release into the model physics is presented. These modeling advancements are then used in a series of three-dimensional simulations which were developed to investigate the potential meteorological impact of several mitigation strategies. Results indicate that application of moderate tree-planting and urban-lightening programs in Los Angeles may produce summertime air temperature reductions on the order of 4^circ C with a concomitant reduction in air pollution. The analysis also reveals several mechanisms whereby the application of these mitigation strategies may potentially increase pollutant concentrations. The pollution and energy use consequences are discussed in detail.

  19. Role of surface characteristics in urban meteorology and air quality

    SciTech Connect

    Sailor, D.J.

    1993-08-01

    Urbanization results in a landscape with significantly modified surface characteristics. The lower values of reflectivity to solar radiation, surface moisture availability, and vegetative cover, along with the higher values of anthropogenic heat release and surface roughness combine to result higher air temperatures in urban areas relative to their rural counterparts. Through their role in the surface energy balance and surface exchange processes, these surface characteristics are capable of modifying the local meteorology. The impacts on wind speeds, air temperatures, and mixing heights are of particular importance, as they have significant implications in terms of urban energy use and air quality. This research presents several major improvements to the meteorological modeling methodology for highly heterogeneous terrain. A land-use data-base is implemented to provide accurate specification of surface characteristic variability in simulations of the Los Angeles Basin. Several vegetation parameterizations are developed and implemented, and a method for including anthropogenic heat release into the model physics is presented. These modeling advancements are then used in a series of three-dimensional simulations which were developed to investigate the potential meteorological impact of several mitigation strategies. Results indicate that application of moderate tree-planting and urban-lightening programs in Los Angeles may produce summertime air temperature reductions on the order of 4{degree}C with a concomitant reduction in air pollution. The analysis also reveals several mechanisms whereby the application of these mitigation strategies may potentially increase pollutant concentrations. The pollution and energy use consequences are discussed in detail.

  20. Role of surface chemistry in the ignition of pyrotechnic materials

    SciTech Connect

    Moddeman, W.E.; Collins, L.W.; Wang, P.S.; Wittberg, T.N.

    1980-01-01

    The surface chemistry of fuels has been shown to play a key role in the ignition of pyrotechnic materials. Since these fuels are usually easily oxidized, the surface must provide protection from undesirable oxidation processes such as pyrophoricity while permitting the desirable pyrotechnic reactions. For both titanium and aluminum, these criteria are met by metal oxide coatings which control the accessibility of the fuel to the oxidizer. However, we have shown that the mechanisms through which this control is exerted are substantially different. The ignition of titanium based pyrotechnics seems to be kinetically controlled by the dissolution of the titanium oxide coating to generate a reactive surface for the pyrotechnic reaction. Reactions of aluminum seem to depend on diffusion of aluminum (or oxygen at higher temperatures) through its oxide coating. It was also shown that the accessibility of aluminum can be improved by alloying.

  1. Caractérisation de l'état de surface et des contraintes résiduelles engendrées par meulage

    NASA Astrophysics Data System (ADS)

    Gognau, D.; Blehaut, H.; Dürr, J.; Hariri, S.; Khouchaf, L.; Flahaut, P.

    2002-07-01

    grinding operations are generally used to prepare surfaces or improve surface state before or after welding. These operations, when carried out manually with portable machines, induce superficial work hardening, modification of the structure of material and residual stresses. An experimental study about the influence of grinding has been carried out on two metallic materials, a low carbon steel (A42-CP) and an austenitic stainless steel (316L), in order to characterise the grinding effects. Manual grinding being difficult to control (no repeatable effects), a test rig using a portable machine has been made. This test rig enables to control the grinding parameters in order to obtain repeatable grinding operations. Characterisation of the ground surfaces was made by 2D profilometry and measurements of residual stresses have been carried out with a Set-X Elphyse apparatus. The profiles of residual stresses obtained show, on the one hand, that on each material, identical grindings generate identical states of stresses and on the other hand, that materials have not the same behaviour, From a metallurgical point of view, we also observe that the grinding effects are different for both materials. The grinding of the A42 steel highlights a crushing of the grain near the surface while the 316L stainless steel grinding reveals sliding bands. Des opérations de meulage sont régulièrement effectuées sur des matériaux métalliques pour préparer les surfaces ou pour améliorer l'état de ces surfaces après soudage. Ces opérations réalisées manuellement engendrent un écrouissage superficiel, une modification de la structure du matériau et par conséquent des contraintes résiduelles. Une étude expérimentale a été menée sur un acier à bas carbone (A42-CP) et un acier inoxydable austénitique (316L) afin de caractériser les effets du meulage. Le meulage manuel étant difficile à maîtriser (effets non reproductibles), un banc d'essai utilisant une machine

  2. The role of surface disinfection in infection prevention

    PubMed Central

    Gebel, Jürgen; Exner, Martin; French, Gary; Chartier, Yves; Christiansen, Bärbel; Gemein, Stefanie; Goroncy-Bermes, Peter; Hartemann, Philippe; Heudorf, Ursel; Kramer, Axel; Maillard, Jean-Yves; Oltmanns, Peter; Rotter, Manfred; Sonntag, Hans-Günther

    2013-01-01

    Background: The Rudolf Schuelke Foundation addresses topics related to hygiene, infection prevention and public health. In this context a panel of scientists from various European countries discussed “The Role of Surface Disinfection in Infection Prevention”. The most important findings and conclusions of this meeting are summarised in the present consensus paper. Aim: Although the relevance of surface disinfection is increasingly being accepted, there are still a number of issues which remain controversial. In particular, the following topics were addressed: Transferral of microbes from surface to patients as a cause of infection, requirements for surface disinfectants, biocidal resistance and toxicity, future challenges. Methods and findings: After discussion and review of current scientific literature the authors agreed that contaminated surfaces contribute to the transmission of pathogens and may thus pose an infection hazard. Targeted surface disinfection based on a risk profile is seen as an indispensable constituent in a multibarrier approach of universal infection control precautions. Resistance and cross-resistance depend on the disinfectant agent as well as on the microbial species. Prudent implementation of surface disinfection regimens tested to be effective can prevent or minimize adverse effects. Conclusions: Disinfection must be viewed as a holistic process. There is a need for defining standard principles for cleaning and disinfection, for ensuring compliance with these principles by measures such as written standard operating procedures, adequate training and suitable audit systems. Also, test procedures must be set up in order to demonstrate the efficacy of disinfectants including new application methods such as pre-soaked wipes for surface disinfection. PMID:23967396

  3. Mutations des roles techniques et formation. Etude documentaire (Changes in the Roles and Education of Technicians. Documentary Study).

    ERIC Educational Resources Information Center

    Pinard, Helene

    Drawing from research conducted in 1990-91, this report examines trends affecting the future work of technicians in Quebec, their pre-employment education, and the link between college and work. Part 1 focuses on aspects of the economic, technological, and social environment that will influence the future role of technicians. Economic concerns…

  4. The role of nitric oxide in ocular surface cells.

    PubMed

    Kim, Jae Chan; Park, Gun Sic; Kim, Jin Kook; Kim, Young Myeong

    2002-06-01

    The role of nitric oxide (NO) in the ocular surface remains unknown. We investigated the conditions leading to an increase of NO generation in tear and the main sources of NO in ocular surface tissue. We evaluated the dual action (cell survival or cell death) of NO depending on its amount. We measured the concentration of nitrite plus nitrate in the tears of ocular surface diseases and examined the main source of nitric oxide synthase (NOS). When cultured human corneal fibroblast were treated with NO producing donor with or without serum, the viabilities of cells was studied. We found that the main sources of NO in ocular surface tissue were corneal epithelium, fibroblast, endothelium, and inflammatory cells. Three forms of NOS (eNOS, bNOS, and iNOS) were expressed in experimentally induced inflammation. In the fibroblast culture system, the NO donor (SNAP, S-nitroso-N-acetyl-D, L-penicillamine) prevented the death of corneal fibroblast cells caused by serum deprivation in a dose dependent manner up to 500 micrometer SNAP, but a higher dose decreased cell viability. This study suggested that NO might act as a double-edged sword in ocular surface diseases depending on the degree of inflammation related with NO concentration. PMID:12068145

  5. Mixed role of surface on intrinsic losses in silicon nanostructures

    NASA Astrophysics Data System (ADS)

    De, Subhadeep; Kunal, K.; Aluru, N. R.

    2016-03-01

    We utilize molecular dynamics simulations and show opposing roles of surface on dissipation in nanostructures. While the surface defects always aid in the entropy generation process, the scattering of phonons from rough surfaces can suppress Akhiezer damping. For the case of a silicon (2 × 1) reconstructed surface, the former dominates and Q-1 (Q is the quality factor) is found to increase with the decrease in size. However, different scaling trends are observed in the case of a hydrogen (H) terminated silicon surface with no defects and dimers. Particularly, in the case of a H-terminated silicon, if the resonator is operated with a frequency Ω such that Ωτph<1 , where τph is the phonon relaxation time and Q-1 is found to decrease with the decrease in size. The opposite scaling is observed for Ωτph>1 . A simplified model, based on two phonon groups (with positive and negative Grüneisen parameters), is considered to explain the observed trend. We show that the equilibration time between the two mode groups decreases with the decrease in size for the H-terminated structure. We also study the scaling of Q-1 factor with frequency for these cases.

  6. Etude des phenomenes de penetration des especes chimiques dans les revetements cathodiques des cuves d'electrolyse de l'aluminium

    NASA Astrophysics Data System (ADS)

    Brisson, Pierre-Yves

    Cette these decrit l'etude effectuee sur les phenomenes d'insertion du sodium et de penetration du bain electrolytique dans les revetements cathodiques des cuves d'electrolyse de l'aluminium. L'etude fut effectuee a l'aide d'un montage permettant d'effectuer l'electrolyse en laboratoire. Trois types de revetement cathodiques furent etudies : des blocs semi-graphitique, des blocs graphitiques et des blocs graphitises. L'insertion du sodium dans les trois differents types de blocs fut etudiee a l'aide de la spectrometrie des photoelectrons X (XPS). L'analyse a permis de mettre en evidence deux formes de sodium dans l'anthracite et la phase liante des materiaux semi-graphitiques et graphitiques, indiquant qu'une fraction du sodium se retrouve sous forme adsorbee dans les micropores des materiaux alors que l'autre fraction est inseree dans la structure cristalline du carbone. Dans les phases graphitiques (materiaux graphitises et graphitiques), seuls les micropores sont occupes par le sodium Ce resultat explique la tendance observee selon laquelle l'ajout de graphite dans les blocs permet d'abaisser le gonflement sodique. Les mecanismes de penetration du bain dans le reseau poreux des materiaux furent etudies en microscopie electronique et en diffraction des rayons X sur des echantillons apres differents temps d'electrolyses et en variant l'atmosphere (soit sous argon ou sous azote). Ces analyses ont permis d'identifier le mecanisme conduisant a la mouillabilite du bain sur le carbone en fonction de l'atmosphere entourant l'electrolyse. Ainsi, sous azote, la formation de NaCN dans les pores des materiaux par reactions entre le sodium et l'azote permet une mouillabilite accrue du bain alors qu'en absence d'azote (sous argon), le carbure d'aluminium, formes a la surface des pores, joue un role similaire. Dans ce dernier cas, la penetration du bain est moins rapide etant donnee la necessite de toujours amener des especes contenant de l'aluminium en tete du front de

  7. The role of surface passivation in controlling Ge nanowire faceting

    DOE PAGESBeta

    Gamalski, A. D.; Tersoff, J.; Kodambaka, S.; Zakharov, D. N.; Ross, F. M.; Stach, E. A.

    2015-11-05

    In situ transmission electron microscopy observations of nanowire morphologies indicate that during Au-catalyzed Ge nanowire growth, Ge facets can rapidly form along the nanowire sidewalls when the source gas (here, digermane) flux is decreased or the temperature is increased. This sidewall faceting is accompanied by continuous catalyst loss as Au diffuses from the droplet to the wire surface. We suggest that high digermane flux and low temperatures promote effective surface passivation of Ge nanowires with H or other digermane fragments inhibiting diffusion and attachment of Au and Ge on the sidewalls. Furthermore, these results illustrate the essential roles of themore » precursor gas and substrate temperature in maintaining nanowire sidewall passivation, necessary to ensure the growth of straight, untapered, <111>-oriented nanowires.« less

  8. The role of surface generated radicals in catalytic combustion

    NASA Technical Reports Server (NTRS)

    Santavicca, D. A.; Stein, Y.; Royce, B. S. H.

    1985-01-01

    Experiments were conducted to better understand the role of catalytic surface reactions in determining the ignition characteristics of practical catalytic combustors. Hydrocarbon concentrations, carbon monoxide and carbon dioxide concentrations, hydroxyl radical concentrations, and gas temperature were measured at the exit of a platinum coated, stacked plate, catalytic combustor during the ignition of lean propane-air mixtures. The substrate temperature profile was also measured during the ignition transient. Ignition was initiated by suddenly turning on the fuel and the time to reach steady state was of the order of 10 minutes. The gas phase reaction, showed no pronounced effect due to the catalytic surface reactions, except the absence of a hydroxyl radical overshoot. It is found that the transient ignition measurements are valuable in understanding the steady state performance characteristics.

  9. The role of surface passivation in controlling Ge nanowire faceting

    SciTech Connect

    Gamalski, A. D.; Tersoff, J.; Kodambaka, S.; Zakharov, D. N.; Ross, F. M.; Stach, E. A.

    2015-11-05

    In situ transmission electron microscopy observations of nanowire morphologies indicate that during Au-catalyzed Ge nanowire growth, Ge facets can rapidly form along the nanowire sidewalls when the source gas (here, digermane) flux is decreased or the temperature is increased. This sidewall faceting is accompanied by continuous catalyst loss as Au diffuses from the droplet to the wire surface. We suggest that high digermane flux and low temperatures promote effective surface passivation of Ge nanowires with H or other digermane fragments inhibiting diffusion and attachment of Au and Ge on the sidewalls. Furthermore, these results illustrate the essential roles of the precursor gas and substrate temperature in maintaining nanowire sidewall passivation, necessary to ensure the growth of straight, untapered, <111>-oriented nanowires.

  10. The role of probe oxide in local surface conductivity measurements

    SciTech Connect

    Barnett, C. J.; Kryvchenkova, O.; Wilson, L. S. J.; Maffeis, T. G. G.; Cobley, R. J.; Kalna, K.

    2015-05-07

    Local probe methods can be used to measure nanoscale surface conductivity, but some techniques including nanoscale four point probe rely on at least two of the probes forming the same low resistivity non-rectifying contact to the sample. Here, the role of probe shank oxide has been examined by carrying out contact and non-contact I V measurements on GaAs when the probe oxide has been controllably reduced, both experimentally and in simulation. In contact, the barrier height is pinned but the barrier shape changes with probe shank oxide dimensions. In non-contact measurements, the oxide modifies the electrostatic interaction inducing a quantum dot that alters the tunneling behavior. For both, the contact resistance change is dependent on polarity, which violates the assumption required for four point probe to remove probe contact resistance from the measured conductivity. This has implications for all nanoscale surface probe measurements and macroscopic four point probe, both in air and vacuum, where the role of probe oxide contamination is not well understood.

  11. Imagerie Resolue dans le Temps des Photons et Neutres Metastables Emis D'une Surface Par Stimulation Electronique

    NASA Astrophysics Data System (ADS)

    Leclerc, Gregoire

    L'appareil que nous presentons ici a ete mis au point pour permettre d'accumuler des images numeriques, resolues dans le temps, de la desorption par stimulation electronique (DSE) d'ions positifs et negatifs, de photons et de neutres metastables, tout en conservant des capacites de base de diffraction d'electrons lents (DEL) et de transmission d'electrons lents (TEL). Le spectrometre comporte un monochromateur d'electrons a secteur cylindrique de 127^ circ dont l'optique de sortie permet la focalisation du faisceau d'electrons sur une large gamme d'energies. Le detecteur consiste en un empilement de galettes de microcanaux et d'une anode resistive a encodage de division de charges. La reponse spatiale du detecteur a ete calibree et plusieurs causes de non-linearite ont ete localisees et corrigees. Des methodes de correction materielle et logicielle des distorsions spatiales sont presentees. La resolution temporelle des evenements est obtenue en pulsant le faisceau d'electrons, et de facon synchrone la detection, laquelle est couplee a un micro-ordinateur. La premiere partie de ce travail est consacree a la caracterisation du spectrometre et la presentation de nombreux parametres operationnels, obtenus soit au moment de la conception, soit experimentalement. Suit la presentation de donnees de DEL et de DSE pour le systeme Ar/Pt(111) en films minces a 15K. Les sequences temporelles d'images de metastables d'Ar desorbes ont revele la presence de plusieurs populations distinctes, ayant des distributions angulaires et distributions d'energie cinetique que nous avons pu separer. Les fonctions d'excitation de l'emission de photons et de la desorption de differentes composantes de metastables, ainsi que la dependance de ces signaux sur l'epaisseur des films d'Ar, sont aussi presentees et analysees. Les techniques que nous avons developpees ont permis de cerner les mecanismes en jeu pour la desorption et la luminescence.

  12. Role of surface states in Auger neutralization of He{sup +} ions on Ag surfaces

    SciTech Connect

    Sarasola, A.; Silkin, V. M.; Arnau, A.

    2007-01-15

    Recent measurements of He{sup +} ion fractions that survive to a whole scatterig event when they impinge on Ag surfaces have shown two different and interesting effects: (1) a notable difference of surviving ion fraction depending on which crystallographic face of the target surface is studied [Yu. Bandurin et al., Phys. Rev. Lett. 92, 017601 (2004)], and (2) an uncommonly high ion fraction in the very-low-energy range (tens of eV) [S. Wethekam et al., Phys. Rev. Lett. 90, 037602 (2003)]. Apart from the geometry, one of the differences between the surfaces of a crystal can be seen in the electronic structure: while the (111) surface has an occupied surface state near the Fermi level at the {gamma} point the (110) and (100) faces have not. Motivated by these facts, in this work we study the role that the occupied surface state plays on the Auger neutralization rate and we present an estimation of the ion fractions that survive for the different Ag faces.

  13. Photo-induced surface functionalization of carbon surfaces: The role of photoelectron ejection

    SciTech Connect

    Colavita, Paula E.; Sun Bin; Tse, K.-Y.; Hamers, Robert J.

    2008-07-15

    Carbon-based materials are attractive for a wide range of applications, from biomaterials to fuel cells; however, their effective use often requires controlling the surface chemistry to incorporate recognition moieties or reactive centers. The high stability of carbon also makes it a challenging material to functionalize; recently, the use of ultraviolet light (254 nm) to initiate functionalization of carbon surfaces has emerged as a way to obtain carbon/organic interfaces with tailored properties. The authors have investigated the mechanism of covalent grafting of amorphous carbon surfaces with functional organic molecules using the photochemical reaction of terminal alkenes. Measurements comparing the reactivity of different n-alkenes bearing different terminal groups at the terminus opposite the olefin showed pronounced differences in reactivity. They characterized the rate and final coverage of the resulting organic layers using x-ray photoelectron spectroscopy and infrared reflection-absorption spectroscopy. Ultraviolet photoelectron spectroscopy and photocurrent measurements suggested that the reaction involves photoelectron emission from the carbon surface into the liquid phase. Density functional calculations show a strong correlation between the electron affinity of the alkenes and the observed reactivity. The specific terminal group opposite to the olefin was found to play an important role in the stabilization of excess negative charges on the molecule, thus explaining the strong dependence of reactivity on the particular terminal group. These findings suggest that the reaction involves injection of photoelectrons into the alkene acceptor levels, leading to the formation of radical anions in the liquid phase. Finally, the authors demonstrate that the grafting of marginally reactive alkenes can be enhanced by seeding the surface with a small amount of good electron accepting groups. These results provide fundamental new insights into the role of

  14. Roles of additives and surface control in slurry atomization

    SciTech Connect

    Tsai, S.C.

    1992-01-01

    This project studies the rheology and airblast atomization of micronized coal slurries. Its major objectives are (1) to promote further understanding of the mechanisms and the roles of additives in airblast atomization of coal water slurry (CWS), and (2) to investigate the impacts of coal particle surface properties and interparticle forces on CWS rheology. We have found that the flow behavior index (n) of a suspension (or slurry) is determined by the relative importance of the interparticle van der Waals attraction and the interparticle electrostatic repulsion. The interparticle attraction, measured by the Hamaker constant scaled to the thermal energy at 25[degrees]C (A/kT), causes particle aggregation, which breaks down at high shear rates, and thus leads to slurry pseudoplastic behavior (n< 1). At a constant particle volume fraction and surface charge density (qualitatively measured by the zeta potential in deionized water), n decreases linearly as A/kT increases. The relative viscosity of the pseudoplastic suspension with respect to that of the suspending liquid is found to be independent of particle density and correlate well with the particle Peclet number which equals the particle diffusional relaxation time multiplied by shear rate. Specifically, the relative viscosities of the pseudoplastic glycerol/water coal slurry and the ethylene glycol/glycerol sand slurry, at same volume fractions as well as similar particle size distributions and liquid viscosities, as functions of the particle Peclet number fall along the same line.

  15. Modification et caractérisation de la surface de fibres de verre pour son insertion postérieure dans des matériaux cimentaires

    NASA Astrophysics Data System (ADS)

    Bismarck, A.; Ajuriagojeaskoa, E. E.; Springer, J.; Habel, W. R.

    1999-07-01

    Optical fibres are widely used as physical and mechanical sensors in various matrices. Those commercial available fibres are mostly coated with different polymers (e.g. polyimide). The problem of using such coatings is the undefined adhesion and the stress transmission from the matrix material into the fibre as well as the alkaline attack from the cementitious environments onto the glass surface. Therefore the known silanisation process with alkylsilanes for surface modification was studied. To achieve a silane film onto the fibre surface as close as possible a fibre pre-treatment in oxygen plasma was applied. The wetting behaviour of the oxygen plasma treated fibres as well as the silanized fibres were studied using the Wilhelmy-method. The influence of the silane concentration and the time of the pre-treatment on the wetting properties was investigated. By scanning electron microscopy, changes of the surface morphology were detected. Additionally, the mechanical properties of the oxygen plasma treated fibres, and silanized fibres exposed to a highly alkaline pore solution were measured. For selected fibre samples (decoated and untreated as well as silanized fibres) the adhesion to a concrete matrix was studied using the indention test. Les fibres optiques sont de plus en plus utilisées comme capteurs des propriétés physiques et mécaniques de nombreuses matrices. Ces fibres commerciales sont généralement enrobées avec différents polymères (par exemple polyimide). Les problèmes dus à l'enrobage des fibres optiques sont une adhésion et une transmission de charge de la matrice du béton à la fibre non définies. Un autre problème majeur est l'alcalinité du béton et son influence sur la surface de la fibre. Nous avons utilisé le procédé de silanisation. Pour obtenir un film de silane le plus homogène possible sur la surface, les fibres sont pré-traitées par le plasma d?oxygène. Le mouillage de fibres traitées par le plasma d?oxygène, ainsi que

  16. Role of cutaneous surface fluid in frog osmoregulation.

    PubMed

    Larsen, Erik Hviid; Ramløv, Hans

    2013-07-01

    The study investigated whether evaporative water loss (EWL) in frogs stems from water diffusing through the skin or fluid secreted by mucous glands. Osmolality of cutaneous surface fluid (CSF) of Rana esculenta (Pelophylax kl. esculentus) subjected to isoproterenol or 30°C-34°C was 191±9.3 and 181±7.5 mosm/kg, respectively, as compared to lymph osmolality of, 249±10 mosm/kg. Cation concentrations of CSF were likewise independent of pre-treatment with averages of, [Na(+)]=65.5±5.1 and [K(+)]=14.9±1.6 mmol/L, and lymph concentrations of 116 mmol Na(+)/L and 5.1 mmol K(+)/L. The relatively high [K(+)] confirms that CSF is produced by submucosal glands. Since the chemical energy of water of CSF was always higher than that of body fluids, diffusion of water would be from CSF to the interstitial fluid and not in the opposite direction. It is concluded that volume and composition of CSF are regulated by subepidermal exocrine gland secretion balanced by EWL into the atmosphere and ion reuptake by the epidermal epithelium. Previously discovered regulatory mechanisms of epithelial ion absorption, hitherto not ascribed a body function, fit well with a role in regulating turnover of CSF. As a regulated external physiological compartment, CSF would be of importance for the immune defenses that amphibians employ in protecting their skin. PMID:23587876

  17. Symmetry of surface nanopatterns induced by ion-beam sputtering: Role of anisotropic surface diffusion

    NASA Astrophysics Data System (ADS)

    Renedo, Javier; Cuerno, Rodolfo; Castro, Mario; Muñoz-García, Javier

    2016-04-01

    Ion-beam sputtering (IBS) is a cost-effective technique able to produce ordered nanopatterns on the surfaces of different materials. To date, most theoretical studies of this process have focused on systems which become amorphous under irradiation, e.g., semiconductors at room temperature. Thus, in spite of the large amount of experimental work on metals, or more recently on semiconductors at high temperatures, such experimental contexts have received relatively little theoretical attention. These systems are characterized by transport mechanisms, e.g., surface diffusion, which are anisotropic as a reflection of the crystalline structure not being overruled by the irradiation. Here, we generalize a previous continuum theory of IBS at normal incidence, in order to account for anisotropic surface diffusion. We explore systematically our generalized model in order to understand the role of anisotropy in the space-ordering properties of the resulting patterns. In particular, we derive a height equation which predicts morphological transitions among hexagonal and rectangular patterns as a function of system parameters and employ an angular correlation function to assess these pattern symmetries. By suitably choosing experimental conditions, it is found that one might be able to experimentally control the type of order displayed by the patterns produced.

  18. Cytotoxicity of surface-functionalized silicon and germanium nanoparticles: the dominant role of surface charges

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, Sourav; Rietjens, Ivonne M. C. M.; Singh, Mani P.; Atkins, Tonya M.; Purkait, Tapas K.; Xu, Zejing; Regli, Sarah; Shukaliak, Amber; Clark, Rhett J.; Mitchell, Brian S.; Alink, Gerrit M.; Marcelis, Antonius T. M.; Fink, Mark J.; Veinot, Jonathan G. C.; Kauzlarich, Susan M.; Zuilhof, Han

    2013-05-01

    Although it is frequently hypothesized that surface (like surface charge) and physical characteristics (like particle size) play important roles in cellular interactions of nanoparticles (NPs), a systematic study probing this issue is missing. Hence, a comparative cytotoxicity study, quantifying nine different cellular endpoints, was performed with a broad series of monodisperse, well characterized silicon (Si) and germanium (Ge) NPs with various surface functionalizations. Human colonic adenocarcinoma Caco-2 and rat alveolar macrophage NR8383 cells were used to clarify the toxicity of this series of NPs. The surface coatings on the NPs appeared to dominate the cytotoxicity: the cationic NPs exhibited cytotoxicity, whereas the carboxylic acid-terminated and hydrophilic PEG- or dextran-terminated NPs did not. Within the cationic Si NPs, smaller Si NPs were more toxic than bigger ones. Manganese-doped (1% Mn) Si NPs did not show any added toxicity, which favors their further development for bioimaging. Iron-doped (1% Fe) Si NPs showed some added toxicity, which may be due to the leaching of Fe3+ ions from the core. A silica coating seemed to impart toxicity, in line with the reported toxicity of silica. Intracellular mitochondria seem to be the target for the toxic NPs since a dose-, surface charge- and size-dependent imbalance of the mitochondrial membrane potential was observed. Such an imbalance led to a series of other cellular events for cationic NPs, like decreased mitochondrial membrane potential (ΔΨm) and ATP production, induction of ROS generation, increased cytoplasmic Ca2+ content, production of TNF-α and enhanced caspase-3 activity. Taken together, the results explain the toxicity of Si NPs/Ge NPs largely by their surface characteristics, provide insight into the mode of action underlying the observed cytotoxicity, and give directions on synthesizing biocompatible Si and Ge NPs, as this is crucial for bioimaging and other applications in for example

  19. Surface activity of Corophium volutator: A role for parasites?

    NASA Astrophysics Data System (ADS)

    Damsgaard, Jacob Tørring; Mouritsen, Kim N.; Jensen, K. Thomas

    2005-08-01

    In soft-bottom intertidal habitats, the normally infaunal amphipod Corophium volutator is often found active on the sediment surface during low tide, exposed to desiccation and shorebird predation. Here we examine whether such risky behaviour is related to parasite infections. Surface-active and buried C. volutator were collected during a low tide period in the Danish Wadden Sea, and the infection patterns of the two groups were described in relation to sex and size. Surface-active males and females were more heavily infested by microphallid trematodes (four species) than buried specimens of the same sex and size class. Although the density of surfaced amphipods decreased as a function of exposure time, the mean parasite load of those that remained on the surface increased. A narrow size-specific parasite intensity threshold above which the amphipods were always surface active did not exist: heavily infected individuals were also found buried in the substrate. Although likely to be beneficial to the parasites, this suggests that the behavioural alteration is a side-effect of the infections rather than a consequence of direct parasitic manipulation. Besides the presumed mortality associated with the parasite-related surface activity in a range of size-classes, the intensity-size frequency distribution indicated that larger and hence heavily infected hosts are removed from the population. Together it demonstrates that microphallid trematodes impact the population dynamics of C. volutator.

  20. The role of nanopore shape in surface-induced crystallization

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

    Crystallization of a molecular liquid from solution often initiates at solid-liquid interfaces, and nucleation rates are generally believed to be enhanced by surface roughness. Here we show that, on a rough surface, the shape of surface nanopores can also alter nucleation kinetics. Using lithographic methods, we patterned polymer films with nanopores of various shapes and found that spherical nanopores 15-120 nm in diameter hindered nucleation of aspirin crystals, whereas angular nanopores of the same size promoted it. We also show that favourable surface-solute interactions are required for angular nanopores to promote nucleation, and propose that pore shape affects nucleation kinetics through the alteration of the orientational order of the crystallizing molecule near the angles of the pores. Our findings have clear technological implications, for instance in the control of pharmaceutical polymorphism and in the design of ‘seed’ particles for the regulation of crystallization of fine chemicals.

  1. Adhesion: role of bulk viscoelasticity and surface roughness.

    PubMed

    Lorenz, B; Krick, B A; Mulakaluri, N; Smolyakova, M; Dieluweit, S; Sawyer, W G; Persson, B N J

    2013-06-01

    We study the adhesion between smooth polydimethylsiloxane (PDMS) rubber balls and smooth and rough poly(methyl methacrylate) (PMMA) surfaces, and between smooth silicon nitride balls and smooth PDMS surfaces. From the measured viscoelastic modulus of the PDMS rubber we calculate the viscoelastic contribution to the crack-opening propagation energy γeff(v,T) for a wide range of crack tip velocities v and for several temperatures T. The Johnson-Kendall-Roberts (JKR) contact mechanics theory is used to analyze the ball pull-off force data, and γeff(v,T) is obtained for smooth and rough surfaces. We conclude that γeff(v,T) has contributions of similar magnitude from both the bulk viscoelastic energy dissipation close to the crack tip, and from the bond-breaking process at the crack tip. The pull-off force on the rough surfaces is strongly reduced compared to that of the flat surface, which we attribute mainly to the decrease in the area of contact on the rough surfaces. PMID:23649298

  2. Adhesion: role of bulk viscoelasticity and surface roughness

    NASA Astrophysics Data System (ADS)

    Lorenz, B.; Krick, B. A.; Mulakaluri, N.; Smolyakova, M.; Dieluweit, S.; Sawyer, W. G.; Persson, B. N. J.

    2013-06-01

    We study the adhesion between smooth polydimethylsiloxane (PDMS) rubber balls and smooth and rough poly(methyl methacrylate) (PMMA) surfaces, and between smooth silicon nitride balls and smooth PDMS surfaces. From the measured viscoelastic modulus of the PDMS rubber we calculate the viscoelastic contribution to the crack-opening propagation energy γeff(v,T) for a wide range of crack tip velocities v and for several temperatures T. The Johnson-Kendall-Roberts (JKR) contact mechanics theory is used to analyze the ball pull-off force data, and γeff(v,T) is obtained for smooth and rough surfaces. We conclude that γeff(v,T) has contributions of similar magnitude from both the bulk viscoelastic energy dissipation close to the crack tip, and from the bond-breaking process at the crack tip. The pull-off force on the rough surfaces is strongly reduced compared to that of the flat surface, which we attribute mainly to the decrease in the area of contact on the rough surfaces.

  3. The role of surface elasticity in liquid film formation

    NASA Astrophysics Data System (ADS)

    Champougny, Lorene; Scheid, Benoit; Restagno, Frederic; Rio, Emmanuelle; Laboratoire de Physique des Solides Team; TIPS-Fluid Physics Unit Team

    2014-11-01

    The formation of thin liquid films, either free standing (soap films) or deposited on a solid substrate (coated films), is of utmost importance for many applications, ranging from the control of foam stability to surface functionalization. In this work, the behavior of thin liquid films during their generation from a surfactant solution is investigated through comparison between a hydrodynamic model including surface elasticity and experiments. ``Twin'' models are proposed to describe the coating of films onto a solid plate (Landau-Levich-Derjaguin configuration) as well as soap film pulling (Frankel configuration) in a single framework. Experimental data are successfully fitted using the models, surface elasticity being the only adjustable parameter. For a given surfactant solution, the analyses of soap and coated films both yield the same value for the effective surface elasticity, showing that it is an intrinsic parameter of a surfactant solution. Conversely, we demonstrate that Frankel- or Landau-Levich-like experiments can be used in practice as surface rheometers to determine the numerical value of the (effective) surface elasticity of a solution, especially for values lower than those measurable by classical devices. L.C. was supported by ANR F2F. B.S. thanks the F.R.S.-FNRS for funding as well as the IAP-MicroMAST project.

  4. Surface wettability plays a significant role in gecko adhesion underwater.

    PubMed

    Stark, Alyssa Y; Badge, Ila; Wucinich, Nicholas A; Sullivan, Timothy W; Niewiarowski, Peter H; Dhinojwala, Ali

    2013-04-16

    Although we now have thousands of studies focused on the nano-, micro-, and whole-animal mechanics of gecko adhesion on clean, dry substrates, we know relatively little about the effects of water on gecko adhesion. For many gecko species, however, rainfall frequently wets the natural surfaces they navigate. In an effort to begin closing this gap, we tested the adhesion of geckos on submerged substrates that vary in their wettability. When tested on a wet hydrophilic surface, geckos produced a significantly lower shear adhesive force (5.4 ± 1.33 N) compared with a dry hydrophilic surface (17.1 ± 3.93 N). In tests on an intermediate wetting surface and a hydrophobic surface, we found no difference in shear adhesion between dry and wet contact. Finally, in tests on polytetrafluoroethylene (PTFE), we found that geckos clung significantly better to wet PTFE (8.0 ± 1.09 N) than dry PTFE (1.6 ± 0.66 N). To help explain our results, we developed models based on thermodynamic theory of adhesion for contacting surfaces in different media and found that we can predict the ratio of shear adhesion in water to that in air. Our findings provide insight into how geckos may function in wet environments and also have significant implications for the development of a synthetic gecko mimic that retains adhesion in water. PMID:23576727

  5. Surface wettability plays a significant role in gecko adhesion underwater

    PubMed Central

    Stark, Alyssa Y.; Badge, Ila; Wucinich, Nicholas A.; Sullivan, Timothy W.; Niewiarowski, Peter H.; Dhinojwala, Ali

    2013-01-01

    Although we now have thousands of studies focused on the nano-, micro-, and whole-animal mechanics of gecko adhesion on clean, dry substrates, we know relatively little about the effects of water on gecko adhesion. For many gecko species, however, rainfall frequently wets the natural surfaces they navigate. In an effort to begin closing this gap, we tested the adhesion of geckos on submerged substrates that vary in their wettability. When tested on a wet hydrophilic surface, geckos produced a significantly lower shear adhesive force (5.4 ± 1.33 N) compared with a dry hydrophilic surface (17.1 ± 3.93 N). In tests on an intermediate wetting surface and a hydrophobic surface, we found no difference in shear adhesion between dry and wet contact. Finally, in tests on polytetrafluoroethylene (PTFE), we found that geckos clung significantly better to wet PTFE (8.0 ± 1.09 N) than dry PTFE (1.6 ± 0.66 N). To help explain our results, we developed models based on thermodynamic theory of adhesion for contacting surfaces in different media and found that we can predict the ratio of shear adhesion in water to that in air. Our findings provide insight into how geckos may function in wet environments and also have significant implications for the development of a synthetic gecko mimic that retains adhesion in water. PMID:23576727

  6. The role of surface microstructure in the sputtering of graphite

    SciTech Connect

    Youchison, D.L.; Nahemow, M.D. ); McGrath, R.T. ); Baratta, A.J. )

    1991-05-01

    Extensive exposure to tokamak plasmas may result in significant alterations to the surface microstructure of graphite plasma-facing components. A change in microstructure from a commercial isotropic graphite to an amorphous carbon film may produce a significant change in the total sputtering yield and the level of plasma contamination. To investigate this sensitivity to surface microstructure, sputtering experiments on a variety of graphites with various surface structures were performed using the ion--surface interaction system (ISIS).{sup 1} ISIS is a computerized ion beam sputtering system equipped with twin quartz crystal microbalances capable of simultaneously monitoring both sputtering and redeposition of the beam target material. ISIS was used to obtain sputtering data on two orientations of pyrolytic graphite at seven energies between 100 eV and 10 keV. Helium bombardment perpendicular to the prism plane produced yields 2 to 7 times higher than on the basal plane. Proton bombardment perpendicular to the prism plane produced yields 45% higher than those on the basal plane. Amorphous graphite films produced from Poco AXF-5Q and Union Carbide ATJ graphites using an argon radio-frequency (rf) plasma discharge were also irradiated. Sputtering yields on the amorphous films were as much as 50% to an order of magnitude higher than those measured on commercial bulk samples. Pre and post-irradiation scanning electron microscopy of selected targets was performed to monitor surface microstructure. A structural mechanism responsible for the magnitude of physical sputtering is suggested, and an effective surface binding energy is introduced to quantify this structural dependence.

  7. The Role of Surface Layer Processes in Solid Propellant Combustion.

    NASA Astrophysics Data System (ADS)

    Chakravarthy, Satyanarayanan R.

    The qualitative multidimensional theory of composite solid propellant combustion based on the sandwich burning methodology was applied to certain specific problems: (a) burning rate enhancement by ferric oxide, (b) plateau burning behavior caused by binder melt flow effects, and (c) characterization of the combustion of new energetic oxidizers--ADN and HNIW. Exothermic reactions at the interfacial contact lines between AP particles and the binder in the surface layer of the burning propellant assume significance in the presence of ferric oxide, and control the burning rate. Binder melt flow covers adjacent AP particle surfaces increasingly at higher pressures, and disperses the O/F leading edge flames attached to coarse particles. It also causes fine AP/binder matrix areas on the surface not to support a steady premixed flame at intermediate pressures, resulting in an overall decrease in the burning rate with increasing pressure, which implies plateau or mesa effects. ADN self -deflagration rate is significantly higher than that of AP, and controls the sandwich burning rate to a great extent. The O/F flame of ADN and binder still behaves as rate limiting, although strongly supported by ADN self-deflagration. ADN melts and vaporizes substantially before the binder, allowing for the possibility of complex physical processes in the surface layer. The strong exothermic decomposition of HNIW at moderate temperatures causes the oxidizer particles in the surface layer to be the sites of burning rate control. The problems addressed in this study combinedly point to the significance of crucial surface layer processes under the situations of interest, and signal a need to characterize such processes directly and in greater detail.

  8. The Role of Surface Chemistry in Filter Feeding by Zooplankton

    NASA Astrophysics Data System (ADS)

    Gerritsen, Jeroen; Porter, Karen G.

    1982-06-01

    Surface chemistry of both particles and animals is important in filter feeding at low Reynolds number. Daphnia magna, fed mixtures of three sizes of polystyrene particles, retained particles that were smaller than the mesh size of the animals (1.0 micrometer) at greater efficiencies than predicted by a sieving model. Retention efficiency of the smallest particles (0.5 micrometer) was increased when negative surface charge on the particles was neutralized, and retention was decreased when a nonionic surfactant was added to reduce wettability.

  9. Role of Surface Chemistry in Nanoscale Electrokinetic Transport

    NASA Astrophysics Data System (ADS)

    Atalay, Selcuk

    This dissertation work presents the efforts to study the electrofluidics phenomena, with a focus on surface charge properties in nanoscale systems with the potential applications in imaging, energy conversion, ultrafiltration, DNA analysis/sequencing, DNA and protein transport, drug delivery, biological/chemical agent detection and micro/nano chip sensors. Since the ion or molecular or particle transport and also liquid confinement in nano-structures are strongly dominated by the surface charge properties, in regards of the fundamental understanding of electrofluidics at nanoscale, we have used surface charge chemistry properties based on 2-pK charging mechanism. Using this mechanism, we theoretically and analytically showed the surface charge properties of silica nanoparticles as a function of their size, pH level and salt ionic strength of aqueous solution. For a fixed particle size, the magnitude of the surface charge typically increases with an increase in pH or background salt concentration. Furthermore, we investigated the surface charge properties of a charged dielectric nanoparticle and flat wall in electrostatic interactions. According to the theoretical results strong interactions cause a non-uniform surface charge density on the nanoparticle and the plate as a result of the enhancement of proton concentration in the gap between the particle and the plate. This effect increases with decreased separation distance (Kh). We moreover investigated the ion confinement inside the nanospaces and using a continuum model, we showed the proton enhancement in extended nanochannels. The proton enrichment at the center of the nanochannel is significant when the bulk pH is medium high and the salt concentration is relatively low. The results gathered are informative for the development of biomimetic nanofluidic apparatuses and the interpretation of relevant experimental data. Later, we have developed an analytical model for electroosmotic ion transport inside p

  10. TiN surface dynamics: role of surface and bulk mass transport processes

    SciTech Connect

    Bareno, J.; Swiech, W.; Petrova, V.; Petrov, I.; Greene, J. E.; Kodambaka, S.; Khare, S. V.

    2007-02-09

    Transition-metal nitrides, such as TiN, have a wide variety of applications as hard, wear-resistant coatings, as diffusion barriers, and as scratch-resistant and anti-reflective coatings in optics. Understanding the surface morphological and microstructural evolution of these materials is crucial for improving the performance of devices. Studies of surface step dynamics enable determination of the rate-limiting mechanisms, corresponding surface mass transport parameters, and step energies. However, most models describing these phenomena are limited in application to simple elemental metal and semiconductor surfaces. Here, we summarize recent progress toward elucidating the interplay of surface and bulk diffusion processes on morphological evolution of compound surfaces. Specifically, we analyze the coarsening/decay kinetics of two- and three-dimensional TiN(111) islands and the effect of surface-terminated dislocations on TiN(111) steps.

  11. Role of surface electromagnetic waves in metamaterial absorbers.

    PubMed

    Chen, Wen-Chen; Cardin, Andrew; Koirala, Machhindra; Liu, Xianliang; Tyler, Talmage; West, Kevin G; Bingham, Christopher M; Starr, Tatiana; Starr, Anthony F; Jokerst, Nan M; Padilla, Willie J

    2016-03-21

    Metamaterial absorbers have been demonstrated across much of the electromagnetic spectrum and exhibit both broad and narrow-band absorption for normally incident radiation. Absorption diminishes for increasing angles of incidence and transverse electric polarization falls off much more rapidly than transverse magnetic. We unambiguously demonstrate that broad-angle TM behavior cannot be associated with periodicity, but rather is due to coupling with a surface electromagnetic mode that is both supported by, and well described via the effective optical constants of the metamaterial where we achieve a resonant wavelength that is 19.1 times larger than the unit cell. Experimental results are supported by simulations and we highlight the potential to modify the angular response of absorbers by tailoring the surface wave. PMID:27136864

  12. The Role of Glottal Surface Adhesion on Vocal Folds Biomechanics

    PubMed Central

    Bhattacharya, Pinaki; Siegmund, Thomas

    2014-01-01

    The airway surface liquid (ASL) is a very thin mucus layer and covers the vocal fold (VF) surface. Adhesion mediated by the ASL occurs during phonation as the VFs separate after collision. Such adhesion is hypothesized to determine voice quality and health. However, biomechanical insights into the adhesive processes during VF oscillation are lacking. Here, a computational study is reported on self-sustained VF vibration involving contact and adhesion. The VF structural model and the glottal airflow are considered fully three-dimensional. The mechanical behavior of the ASL is described through a constitutive traction–separation law where mucosal cohesive strength, cohesive energy and rupture length enter. Cohesive energy values considered are bound below by the cohesive energy of water at standard temperature and pressure. Cohesive strength values considered are bound above by prior reported data on the adhesive strength of mucosal surface of rat small intestine. This model introduces a mechanical length scale into the analysis. The sensitivity of various aspects of VF dynamics such as flow-declination rate, VF separation under adhesive condition and formation of multiple local fluid bridges is determined in relation to specific ASL adhesive properties. It is found that for the ASL considered here, the characteristics of the VF separation process are of debond type. Instabilities lead to the breakup of the bond area into several smaller bond patches. Such finding is consistent with in-vivo observations. PMID:25034504

  13. Role of radiogenic heat generation in surface heat flow formation

    NASA Astrophysics Data System (ADS)

    Khutorskoi, M. D.; Polyak, B. G.

    2016-03-01

    Heat generation due to decay of long-lived radioactive isotopes is considered in the Earth's crust of the Archean-Proterozoic and Paleozoic provinces of Eurasia and North America. The heat flow that forms in the mantle is calculated as the difference between the heat flow observed at the boundary of the solid Earth and radiogenic heat flow produced in the crust. The heat regime in regions with anomalously high radiogenic heat generation is discussed. The relationship between various heat flow components in the Precambrian and Phanerozoic provinces has been comparatively analyzed, and the role of erosion of the surfaceheat- generating layer has been estimated.

  14. Roles of Surface and Interface Spins in Exchange Coupled Nanostructures

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong

    Exchange bias (EB) in magnetic nanostructures has remained a topic of global interest because of its potential use in spin valves, MRAM circuits, magnetic tunnel junctions, and spintronic devices. The exploration of EB on the nanoscale provides a novel approach to overcoming the superparamagnetic limit and increasing the thermoremanence of magnetic nanoparticles, a critical bottleneck for magnetic data storage applications. Recent advances in chemical synthesis have given us a unique opportunity to explore the EB in a variety of nanoparticle systems ranging from core/shell nanoparticles of Fe/γFe2O3, Co/CoO,and FeO/Fe3O4 to hollow nanoparticles of γFe2O3 and hybrid composite nanoparticles of Au/Fe3O4. Our studies have addressed the following fundamental and important questions: (i) Can one decouple collective contributions of the interface and surface spins to the EB in a core/shell nanoparticle system? (ii) Can the dynamic and static response of the core and shell be identified separately? (iii) Can one tune ``minor loop'' to ``exchange bias'' effects in magnetic hollow nanoparticles by varying the number of surface spins? (iv) Can one decouple collective contributions of the inner and outer surface spins to the EB in a hollow nanoparticle system? (v) Can EB be induced in a magnetic nanoparticle by forming its interface with a non-magnetic metal? Such knowledge is essential to tailor EB in magnetic nanostructures for spintronics applications. In this talk, we will discuss the aforementioned findings in terms of our experimental and atomistic Monte Carlo studies. The work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No. DE-FG02-07ER46438.

  15. Scaling Forces to the Asteroid Surface: The Role of Cohesion

    NASA Astrophysics Data System (ADS)

    Scheeres, Daniel J.; Hartzell, C. M.; Sanchez, P.; Swift, M.

    2010-10-01

    The surfaces and interiors of asteroids are characterized by their low ambient gravitational accelerations which range from milli-Gs on the surface of Eros to much less than micro-Gs at the equator of rapidly spinning bodies such as 1999 KW4 Alpha. We report research on performing a full accounting for all relevant physical forces, in addition to a particle's weight, in such regimes and find that cohesive van der Waals forces become significant for macroscopic grains (Scheeres et al., Icarus in press). For example, theory predicts that on the surface of Itokawa the cohesive attraction between two centimeter-sized grains in contact should exceed their weight, implying that a collection of such gravels should behave more like a cohesive powder (such as bread flour) than as a terrestrial gravel pile. Extending the theory to the self-gravitation of two boulders in contact, such as in a rubble pile, predicts that mutual cohesive forces dominate mutual gravitation for component sizes less than a few meters. One implication of this is that higher rotation rates are necessary to cause smaller grains to fission from an asteroid, while larger aggregates should be less affected and fission at lower rotation rates, introducing a size-scale into an otherwise scale-invariant physical process. A simple model for this cohesive effect is presented and its implications for asteroid science are discussed. This research was supported in part by NASA's DDAP and PGG Programs via Grants NNG06GG22G and NNX08AL51G.

  16. Surface Physicochemistry and Ionic Strength Affects eDNA’s Role in Bacterial Adhesion to Abiotic Surfaces

    PubMed Central

    Regina, Viduthalai R.; Lokanathan, Arcot R.; Modrzyński, Jakub J.; Sutherland, Duncan S.; Meyer, Rikke L.

    2014-01-01

    Extracellular DNA (eDNA) is an important structural component of biofilms formed by many bacteria, but few reports have focused on its role in initial cell adhesion. The aim of this study was to investigate the role of eDNA in bacterial adhesion to abiotic surfaces, and determine to which extent eDNA-mediated adhesion depends on the physicochemical properties of the surface and surrounding liquid. We investigated eDNA alteration of cell surface hydrophobicity and zeta potential, and subsequently quantified the effect of eDNA on the adhesion of Staphylococcus xylosus to glass surfaces functionalised with different chemistries resulting in variable hydrophobicity and charge. Cell adhesion experiments were carried out at three different ionic strengths. Removal of eDNA from S. xylosus cells by DNase treatment did not alter the zeta potential, but rendered the cells more hydrophilic. DNase treatment impaired adhesion of cells to glass surfaces, but the adhesive properties of S. xylosus were regained within 30 minutes if DNase was not continuously present, implying a continuous release of eDNA in the culture. Removal of eDNA lowered the adhesion of S. xylosus to all surfaces chemistries tested, but not at all ionic strengths. No effect was seen on glass surfaces and carboxyl-functionalised surfaces at high ionic strength, and a reverse effect occurred on amine-functionalised surfaces at low ionic strength. However, eDNA promoted adhesion of cells to hydrophobic surfaces irrespective of the ionic strength. The adhesive properties of eDNA in mediating initial adhesion of S. xylosus is thus highly versatile, but also dependent on the physicochemical properties of the surface and ionic strength of the surrounding medium. PMID:25122477

  17. The Role of Cooling in Pahohoe Emplacement on Planetary Surfaces.

    NASA Technical Reports Server (NTRS)

    Glaze, L. S.; Baloga, S. M.

    2015-01-01

    Abundant evidence is emerging that many lavas on Mars were emplaced as slow-moving pahoehoe flows. Models for such scenarios contrast sharply with those for steep-sloped applications where gravity is the dominant force. The mode of flow emplacement on low slopes is characterized by toe formation and inflation. In the latter phase of pahoehoe flow emplacement, stagnation, inflation, and toe formation are most closely tied to the final topography, dimensions, and morphologic features. This mode of emplacement is particularly relevant to the low slopes of planetary surfaces such as the plains of Mars, Io and the Moon.

  18. Bioavailability enhancement of zaleplon via proliposomes: Role of surface charge.

    PubMed

    Janga, Karthik Y; Jukanti, Raju; Velpula, Ashok; Sunkavalli, Sharath; Bandari, Suresh; Kandadi, Prabhakar; Veerareddy, Prabhakar Reddy

    2012-02-01

    The present systematic study focused to investigate the combined advantage of proliposomes and surface charge for improved oral delivery of zaleplon. The zaleplon loaded proliposomes were prepared using hydrogenated soyphosphatidylcholine (HSPC) and cholesterol (CHOL) in varying ratios, and the optimized formulation was tailored with dicetyl phosphate and stearylamine to obtain negative and positive charged vesicles, respectively. The formulations were characterized for micromeritics, size, zeta potential, and entrapment efficiency. Further, in vitro release and dissolution study carried out provide an insight on the stability and enhanced dissolution of zaleplon from proliposome formulations. The solid state characterization (SEM, DSC, and PXRD) studies unravel the transformation of zaleplon to amorphous or molecular state from the native crystalline form. To depict the conclusions, in situ single-pass perfusion and bioavailability studies were carried out in rats. The significant increase in effective permeability coefficient (Peff) and rate and extent of absorption from cationic vesicles indicate the importance of surface charge for effective uptake across the gastrointestinal tract. Overall a two- to fivefold enhancement in bioavailability in comparison with control confers the potential of proliposomes as suitable carriers for improved oral delivery of zaleplon. PMID:22041602

  19. Roles of additives and surface control in slurry atomization

    SciTech Connect

    Tsai, S.C.

    1990-01-01

    This report focuses on the effects of interparticle forces on the rheology and airblast atomization of micronized coal water slurry (CWS). We found that the CWS flow behavior index is determined by the relative importance of the interparticle van der Waals attraction and the interparticle electrostatic repulsion. The former intensifies as the Hamaker constant increases and the interparticle distance reduces while the latter increases as the particle surface charge density increases. The interparticle attraction causes particle aggregation, which breaks down at high shear rates, and thus leads to slurry pseudoplastic behavior. In contrast, the interparticle repulsion prevents particle aggregation and thus leads to Newtonian behavior. Both atomized at low atomizing air pressures (less than 270 kPa) using twin-fluid jet atomizers of various distributor designs. We found that the atomized drop sizes of micronized coal water slurries substantially decrease as the atomizing air pressure exceeds a threshold value. The effects of coal volume fraction, coal particle surface charge, liquid composition and liquid viscosity on slurry atomization can be accounted for by their effects on slurry rheology. 26 refs.

  20. Glass breaking strength: The role of surface flaws and treatments

    NASA Technical Reports Server (NTRS)

    Moore, D.

    1985-01-01

    Although the intrinsic strength of silicon dioxide glass is of the order of 10 to the 6th power lb/sq in, the practical strength is roughly two orders of magnitude below this theoretical limit, and depends almost entirely on the surface condition of the glass, that is, the number and size of flaws and the residual surface compression (temper) in the glass. Glass parts always fail in tension when these flaws grow under sustained loading to some critical size. Research associated with glass encapsulated crystalline-Si photovoltaic (PV) modules has greatly expanded our knowledge of glass breaking strength and developed sizeable data base for commercially available glass types. A detailed design algorithm is developed for thickness sizing of rectangular glass plates subject to pressure loads. Additional studies examine the strength of glass under impact loading conditions such as that caused by hail. Although the fundamentals of glass breakage are directly applicable to thin film modules, the fracture strength of typical numerical glass must be replaced with data that reflect the high temperature tin oxide processing, laser scribing, and edge processing peculiar to thin film modules. The fundamentals of glass breakage applicable to thin film modules and preliminary fracture strength data for a variety of 1 ft square glass specimens representing preprocessed and post processed sheets from current amorphous-Si module manufacturers are presented.

  1. [Roles of additives and surface control in slurry atomization

    SciTech Connect

    Tsai, S.C.

    1992-06-01

    As reported in the quarterly report of March of 1992, the relative viscosity of a Newtonian Coal Water Slurry (CWS) in the presence of an anionic polymeric dispersant is an order of magnitude higher than the prediction of the well established Krieger-Dougherty Equation which describes the relative viscosity of a non-aggregated Newtonian suspension as a function of particle volume fraction. Note that the anionic dispersant is used in such a quantity that the resulting interparticle electrostatic repulsion counter-balances the interparticle van der Waals attraction. Investigation continues to determine the mechanisms of such excess energy dissipation under shear. New experimental results are presented in this report to verify the role of the anionic polymeric dispersant in such excess energy dissipation of CWS.

  2. The role of exogenic factors in the formation of the lunar surface

    NASA Technical Reports Server (NTRS)

    Florenskiy, K. P.; Bazilevskiy, A. T.; Ivanov, A. V.

    1977-01-01

    The formation of the surface of planetary bodies is determined by the interaction of endogenic and exogenic forces. Clarification of the mutual role of these forces is one of the most important trends in the geological sciences.

  3. Molecular simulation of mineral surfaces and the role of impurities on surface stability

    SciTech Connect

    Parker, Stephen C.; Allen, Jeremy P.; Arrouvel, Corrine; Spagnoli, Dino; Kerisit, Sebastien N.; Dean, Sayle C.

    2008-08-08

    Molecular simulation techniques represent a powerful complement to experiment for studying the surfaces and interfaces of minerals, not least because we can easily visualize the surface processes. The aim of this presentation is to describe recent work using molecular simulation methods to model the structure, stability and reactivity of mineral surfaces and how the simulation of these properties can be used to predict morphologies. Initially, we will describe how molecular simulation techniques can be used to give a reliable description of the surfaces. One of the significant contributions that atom-based simulation methods can make is in the investigation of competitive adsorption of impurities at surfaces and several examples are shown. Finally, two approaches for increasing the scope and reliability of the simulations are discussed, namely, electronic structure calculations, which enable us to explore the mineral surface stoichiometry and potential-based molecular dynamics simulations, which introduce dynamical contribution to the surface processes and hence allows for detailed characterization of the mineral-water interface.

  4. Surface enhanced Raman scattering in electrochemical systems: The complex roles of surface roughness

    NASA Astrophysics Data System (ADS)

    Pemberton, Jeanne E.; Guy, Anita L.; Sobocinski, Raymond L.; Tuschel, David D.; Cross, Nathan A.

    1988-06-01

    A series of experiments designed to elucidate the presence and properties of large-scale and atomic-scale roughness produced on Ag electrodes with electrochemical oxidation-reduction cycle (ORC) pretreatments are presented. This report reviews surface enhanced Raman scattering (SERS) and scanning electron microscopic (SEM) characterization of Ag electrodes roughened with controlled-rate ORCs, and presents new results for the laser-induced thermal decay of SERS as a probe of Ag surface active sites and differential reflectance spectroscopy of electrochemically roughened Ag electrodes. These results are interpreted in terms of the presence and properties of both large-scale and atomic-scale roughness on these surfaces.

  5. Structural and dynamical properties of water on chemically modified surfaces: The role of the instantaneous surface

    NASA Astrophysics Data System (ADS)

    Bekele, Selemon; Tsige, Mesfin

    Surfaces of polymers such as atactic polystyrene (aPS) represent very good model systems for amorphous material surfaces. Such polymer surfaces are usually modified either chemically or physically for a wide range of applications that include friction, lubrication and adhesion. It is thus quite important to understand the structural and dynamical properties of liquids that come in contact with them to achieve the desired functional properties. Using molecular dynamics (MD) simulations, we investigate the structural and dynamical properties of water molecules in a slab of water in contact with atactic polystyrene surfaces of varying polarity. We find that the density of water molecules and the number distribution of hydrogen bonds as a function of distance relative to an instantaneous surface exhibit a structure indicative of a layering of water molecules near the water/PS interface. For the dynamics, we use time correlation functions of hydrogen bonds and the incoherent structure function for the water molecules. Our results indicate that the polarity of the surface dramatically affects the dynamics of the interfacial water molecules with the dynamics slowing down with increasing polarity. This work was supported by NSF Grant DMR1410290.

  6. Role of surface crossings in the photochemistry of nitromethane

    SciTech Connect

    Arenas, Juan F.; Otero, Juan C.; Pelaez, Daniel; Soto, Juan

    2005-02-22

    The photodissociation dynamics of nitromethane (CH{sub 3}NO{sub 2}) starting at the S{sub 3} excited state has been studied at the complete active space self-consistent field level of theory in conjunction with atomic natural orbital type basis sets. In addition, the energies of all the critical points and the energy profiles connecting them have been recomputed with the multiconfigurational second-order perturbation method. It is found that the key step in the reaction mechanism is a radiationless decay through an S{sub 3}/S{sub 2} conical intersection. The branching space spanned by the gradient difference and nonadiabatic coupling vectors of this crossing point comprises dissociation into excited nitromethane plus singlet atomic oxygen [CH{sub 3}NO(1A{sup ''})+O({sup 1}D)] and S{sub 3}{yields}S{sub 2} deactivation, respectively. Furthermore, deactivated nitromethane S{sub n(nlt3)} can decompose in subsequent steps into CH{sub 3}+NO{sub 2}, where NO{sub 2} is generated at least in two different electronic states (1 {sup 2}B{sub 2} and 1 {sup 2}A{sub 1}). It is shown that formation of excited nitric oxide NO(A {sup 2}{sigma}) arises from CH{sub 3}NO(1A{sup ''}) generated in the previous step. In addition, four crossings between singlet and triplet states are localized; however, no evidence is found for a relevant role of such crossings in the photochemistry of CH{sub 3}NO{sub 2} initiated at S{sub 3} state in the gas phase.

  7. Surface affinity role in graphoepitaxy of lamellar block copolymers

    NASA Astrophysics Data System (ADS)

    Claveau, G.; Quemere, P.; Argoud, M.; Hazart, J.; Pimenta Barros, P.; Sarrazin, A.; Posseme, N.; Tiron, R.; Chevalier, X.; Nicolet, C.; Navarro, C.

    2016-03-01

    Overcoming the optical limitations of 193nm immersion lithography can be achieved using Directed Self Assembly (DSA) of block-copolymers (BCPs) as a low-cost and versatile complementary technique. The goal of this paper is to investigate the potential of DSA to address line and space (L/S) high resolution patterning by performing the density multiplication of lines with the graphoepitaxy approach. As surface affinity is a key parameter in self-assembly, three variations, or "flavors", of DSA template affinity are investigated regarding several success criteria such as morphology control or defectivity. More precisely, both the methodology to register DSA defects and the impact of process parameters on defectivity are detailed. Using the 300mm pilot line available in LETI and Arkema's advanced materials, we investigate process optimization of DSA line/space patterning of a 38nm period lamellar PS-b-PMMA BCP (L38). For this study, our integration scheme, depicted in figure 2-1, is based on BCP self-assembly inside organic hard mask guiding patterns obtained using 193i nm lithography. Defect analysis coupled with the fine tuning of process parameters (annealing, brush material) provided the optimum conditions for the L38 self-assembly. Using such conditions, DSA using the three affinity flavors is investigated by means of SEM top-view and cross-section review. Lithographic performances of one selected flavor are then evaluated with the comparison of Process Windows (PWs) function of either commensurability, morphology or LWR. This work is a first step in finding the best process for an industrial graphoepitaxy approach.

  8. Thin film lubrication of hexadecane confined by iron and iron oxide surfaces: A crucial role of surface structure.

    PubMed

    Ta, D T; Tieu, A K; Zhu, H T; Kosasih, B

    2015-10-28

    A comparative analysis of thin film lubrication of hexadecane between different iron and its oxide surfaces has been carried out using classical molecular dynamic simulation. An ab initio force-field, COMPASS, was applied for n-hexadecane using explicit atom model. An effective potential derived from density functional theory calculation was utilized for the interfacial interaction between hexadecane and the tribo-surfaces. A quantitative surface parameterization was introduced to investigate the influence of surface properties on the structure, rheological properties, and tribological performance of the lubricant. The results show that although the wall-fluid attraction of hexadecane on pure iron surfaces is significantly stronger than its oxides, there is a considerable reduction of shear stress of confined n-hexadecane film between Fe(100) and Fe(110) surfaces compared with FeO(110), FeO(111), Fe2O3(001), and Fe2O3(012). It was found that, in thin film lubrication of hexadecane between smooth iron and iron oxide surfaces, the surface corrugation plays a role more important than the wall-fluid adhesion strength. PMID:26520538

  9. Thin film lubrication of hexadecane confined by iron and iron oxide surfaces: A crucial role of surface structure

    NASA Astrophysics Data System (ADS)

    Ta, D. T.; Tieu, A. K.; Zhu, H. T.; Kosasih, B.

    2015-10-01

    A comparative analysis of thin film lubrication of hexadecane between different iron and its oxide surfaces has been carried out using classical molecular dynamic simulation. An ab initio force-field, COMPASS, was applied for n-hexadecane using explicit atom model. An effective potential derived from density functional theory calculation was utilized for the interfacial interaction between hexadecane and the tribo-surfaces. A quantitative surface parameterization was introduced to investigate the influence of surface properties on the structure, rheological properties, and tribological performance of the lubricant. The results show that although the wall-fluid attraction of hexadecane on pure iron surfaces is significantly stronger than its oxides, there is a considerable reduction of shear stress of confined n-hexadecane film between Fe(100) and Fe(110) surfaces compared with FeO(110), FeO(111), Fe2O3(001), and Fe2O3(012). It was found that, in thin film lubrication of hexadecane between smooth iron and iron oxide surfaces, the surface corrugation plays a role more important than the wall-fluid adhesion strength.

  10. Thin film lubrication of hexadecane confined by iron and iron oxide surfaces: A crucial role of surface structure

    SciTech Connect

    Ta, D. T.; Tieu, A. K.; Zhu, H. T. Kosasih, B.

    2015-10-28

    A comparative analysis of thin film lubrication of hexadecane between different iron and its oxide surfaces has been carried out using classical molecular dynamic simulation. An ab initio force-field, COMPASS, was applied for n-hexadecane using explicit atom model. An effective potential derived from density functional theory calculation was utilized for the interfacial interaction between hexadecane and the tribo-surfaces. A quantitative surface parameterization was introduced to investigate the influence of surface properties on the structure, rheological properties, and tribological performance of the lubricant. The results show that although the wall-fluid attraction of hexadecane on pure iron surfaces is significantly stronger than its oxides, there is a considerable reduction of shear stress of confined n-hexadecane film between Fe(100) and Fe(110) surfaces compared with FeO(110), FeO(111), Fe{sub 2}O{sub 3}(001), and Fe{sub 2}O{sub 3}(012). It was found that, in thin film lubrication of hexadecane between smooth iron and iron oxide surfaces, the surface corrugation plays a role more important than the wall-fluid adhesion strength.

  11. Towards a Dynamic DES model

    NASA Astrophysics Data System (ADS)

    Subbareddy, Pramod; Candler, Graham

    2009-11-01

    Hybrid RANS/LES methods are being increasingly used for turbulent flow simulations in complex geometries. Spalart's detached eddy simulation (DES) model is one of the more popular ones. We are interested in examining the behavior of the Spalart-Allmaras (S-A) Detached Eddy Simulation (DES) model in its ``LES mode.'' The role of the near-wall functions present in the equations is analyzed and an explicit analogy between the S-A and a one-equation LES model based on the sub-grid kinetic energy is presented. A dynamic version of the S-A DES model is proposed based on this connection. Validation studies and results from DES and LES applications will be presented and the effect of the proposed modification will be discussed.

  12. A critical study of the role of the surface oxide layer in titanium bonding

    NASA Technical Reports Server (NTRS)

    Dias, S.; Wightman, J. P.

    1982-01-01

    The molecular understanding of the role which the surface oxide layer of the adherend plays in titanium bonding is studied. The effects of Ti6-4 adherends pretreatment, bonding conditions, and thermal aging of the lap shear specimens were studied. The use of the SEM/EDAX and ESCA techniques to study surface morphology and surface composition was emphasized. In addition, contact angles and both infrared and visible reflection spectroscopy were used in ancillary studies.

  13. Roles in Modulation of Molecular Structures on Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Gao, H.-J.

    2007-03-01

    We studied the adsorption of organic molecules, their growth behavior, and their physical properties on silver and gold surfaces at the single molecule or sub-molecular scale by using low-temperature scanning tunneling microscopes. Combined with low energy electron diffraction and first-principles density functional theory calculations, the key parameters in modulating molecular structures on metals are analyzed. It is found that the alkyl chains of quinacridone derivatives (QA) determine the orientation of molecular overlayers on an Ag(110) substrate. The interaction of QA and the Ag substrate is primarily due to chemical bonding of oxygen to specific positions at the silver substrate, determining the molecular orientation and preferred adsorption site. However, the intermolecular arrangement can be adjusted via the length of attached alkyl chains. We are thus able to fabricate uniform QA films with very well controlled physical properties. Furthermore, by thermal and chemical control, we are able to self-assemble three dimensional molecular nanostructures, e.g. ordered PTCDA structures exclusively on flat Ag(111) facets, or DMe-DCNQI structures exclusively on stepped Ag(221) facets. It is demonstrated that bonding, the key factor for selectivity, occurs via the end-atoms, while the molecule's mid-region arches away from the substrate. Theoretical results, obtained by high-level theory, are consistent with the experimental observations, which have previously been interpreted in terms of bonding through the mid-region. In collaboration with D.X. Shi, S.X. Du, W. Ji, Z.T. Deng, L. Gao, Institute of Physics, and X. Lin, Chinese Academy of Sciences, China; C. Seidel and H. Fuchs, Universit"at M"unster, Germany; W.A. Hofer, The University of Liverpool, Britain; and S. T. Pantelides, Vanderbilt University, USA. [1] D.X. Shi et al., Phys. Rev. Lett. 96, 226101(2006). [2] S.X. Du et al., Phys. Rev. Lett. 96, 226101(2006). [3] L. Gao et al., Phys. Rev. B 73, 075424(2006).

  14. Des Moines.

    ERIC Educational Resources Information Center

    Gore, Deborah, Ed.

    1988-01-01

    This document, intended for elementary students, contains articles and activities designed to acquaint young people with the history of Des Moines, Iowa. The articles are short, and new or difficult words are highlighted and defined for young readers. "The Raccoon River Indian Agency" discusses the archeological exploration of the indian…

  15. Effect of impurities in the description of surface nanobubbles: Role of nonidealities in the surface layer

    NASA Astrophysics Data System (ADS)

    Das, Siddhartha

    2011-06-01

    In a recent study [S. Das, J. H. Snoeijer, and D. Lohse, Phys. Rev. E1539-375510.1103/PhysRevE.82.056310 82, 056310 (2010)], we provided quantitative demonstration of the conjecture [W. A. Ducker, LangmuirLANGD50743-746310.1021/la902011v 25, 8907 (2009)] that the presence of impurities at the surface layer (or the air-water interface) of surface nanobubbles can substantially lower the gas-side contact angle and the Laplace pressure of the nanobubbles. Through an analytical model for any general air-water interface without nonideality effects, we showed that a large concentration of soluble impurities at the air-water interface of the nanobubbles ensures significantly small contact angles (matching well with the experimental results) and Laplace pressure (though large enough to forbid stability). In this paper this general model is extended to incorporate the effect of nonidealities at the air-water interface in impurity-induced alteration of surface nanobubble properties. Such nonideality effects arise from finite enthalpy or entropy of mixing or finite ionic interactions of the impurity molecules at the nanobubble air-water interface and ensure significant lowering of the nanobubble contact angle and Laplace pressure even at relatively small impurity coverage. In fact for impurity molecules that show enhanced tendency to get adsorbed at the nanobubble air-water interface from the bulk phase, impurity-induced lowering of the nanobubble contact angle is witnessed for extremely small bulk concentration. Surface nanobubble experiments being typically performed in an ultraclean environment, the bulk concentration of impurities is inevitably very small, and in this light the present calculations can be viewed as a satisfactory explanation of the conjecture that impurities, even in trace concentration, have significant impact on surface nanobubbles.

  16. The Role of Surface Chemistry in Adhesion and Wetting of Gecko Toe Pads

    NASA Astrophysics Data System (ADS)

    Badge, Ila; Stark, Alyssa Y.; Paoloni, Eva L.; Niewiarowski, Peter H.; Dhinojwala, Ali

    2014-10-01

    An array of micron-sized setal hairs offers geckos a unique ability to walk on vertical surfaces using van der Waals interactions. Although many studies have focused on the role of surface morphology of the hairs, very little is known about the role of surface chemistry on wetting and adhesion. We expect that both surface chemistry and morphology are important, not only to achieve optimum dry adhesion but also for increased efficiency in self-cleaning of water and adhesion under wet conditions. Here, we used a plasma-based vapor deposition process to coat the hairy patterns on gecko toe pad sheds with polar and non-polar coatings without significantly perturbing the setal morphology. By a comparison of wetting across treatments, we show that the intrinsic surface of gecko setae has a water contact angle between 70-90°. As expected, under wet conditions, adhesion on a hydrophilic surface (glass) was lower than that on a hydrophobic surface (alkyl-silane monolayer on glass). Surprisingly under wet and dry conditions the adhesion was comparable on the hydrophobic surface, independent of the surface chemistry of the setal hairs. This work highlights the need to utilize morphology and surface chemistry in developing successful synthetic adhesives with desirable adhesion and self-cleaning properties.

  17. The Role of Surface Chemistry in Adhesion and Wetting of Gecko Toe Pads

    PubMed Central

    Badge, Ila; Stark, Alyssa Y.; Paoloni, Eva L.; Niewiarowski, Peter H.; Dhinojwala, Ali

    2014-01-01

    An array of micron-sized setal hairs offers geckos a unique ability to walk on vertical surfaces using van der Waals interactions. Although many studies have focused on the role of surface morphology of the hairs, very little is known about the role of surface chemistry on wetting and adhesion. We expect that both surface chemistry and morphology are important, not only to achieve optimum dry adhesion but also for increased efficiency in self-cleaning of water and adhesion under wet conditions. Here, we used a plasma-based vapor deposition process to coat the hairy patterns on gecko toe pad sheds with polar and non-polar coatings without significantly perturbing the setal morphology. By a comparison of wetting across treatments, we show that the intrinsic surface of gecko setae has a water contact angle between 70–90°. As expected, under wet conditions, adhesion on a hydrophilic surface (glass) was lower than that on a hydrophobic surface (alkyl-silane monolayer on glass). Surprisingly under wet and dry conditions the adhesion was comparable on the hydrophobic surface, independent of the surface chemistry of the setal hairs. This work highlights the need to utilize morphology and surface chemistry in developing successful synthetic adhesives with desirable adhesion and self-cleaning properties. PMID:25323067

  18. The role of surface chemistry in adhesion and wetting of gecko toe pads.

    PubMed

    Badge, Ila; Stark, Alyssa Y; Paoloni, Eva L; Niewiarowski, Peter H; Dhinojwala, Ali

    2014-01-01

    An array of micron-sized setal hairs offers geckos a unique ability to walk on vertical surfaces using van der Waals interactions. Although many studies have focused on the role of surface morphology of the hairs, very little is known about the role of surface chemistry on wetting and adhesion. We expect that both surface chemistry and morphology are important, not only to achieve optimum dry adhesion but also for increased efficiency in self-cleaning of water and adhesion under wet conditions. Here, we used a plasma-based vapor deposition process to coat the hairy patterns on gecko toe pad sheds with polar and non-polar coatings without significantly perturbing the setal morphology. By a comparison of wetting across treatments, we show that the intrinsic surface of gecko setae has a water contact angle between 70-90°. As expected, under wet conditions, adhesion on a hydrophilic surface (glass) was lower than that on a hydrophobic surface (alkyl-silane monolayer on glass). Surprisingly under wet and dry conditions the adhesion was comparable on the hydrophobic surface, independent of the surface chemistry of the setal hairs. This work highlights the need to utilize morphology and surface chemistry in developing successful synthetic adhesives with desirable adhesion and self-cleaning properties. PMID:25323067

  19. On the Role of Fe2O3 Surface States for Water Splitting

    NASA Astrophysics Data System (ADS)

    Caspary Toroker, Maytal

    Understanding the chemical nature and role of electrode surface states is crucial for improved electrochemical cell operation. For iron (III) oxide (α-Fe2O3) , which is one of the most widely studied anode electrodes used for water splitting, surface states were related to the appearance of a dominant absorption peak during water splitting. The chemical origin of this signature is still unclear and this open question has provoked tremendous debate. In order to pin down the origin and role of surface states, we perform first principle calculations with density functional theory +U on several possible adsorbates at the α-Fe2O3(0001) surface. We show that the origin of the surface absorption peak could be a Fe-Otype bond that functions as an essential intermediate of water oxidation

  20. Larval Settlement: The Role of Surface Topography for Sessile Coral Reef Invertebrates

    PubMed Central

    Whalan, Steve; Abdul Wahab, Muhammad A.; Sprungala, Susanne; Poole, Andrew J.; de Nys, Rocky

    2015-01-01

    For sessile marine invertebrates with complex life cycles, habitat choice is directed by the larval phase. Defining which habitat-linked cues are implicated in sessile invertebrate larval settlement has largely concentrated on chemical cues which are thought to signal optimal habitat. There has been less effort establishing physical settlement cues, including the role of surface microtopography. This laboratory based study tested whether surface microtopography alone (without chemical cues) plays an important contributing role in the settlement of larvae of coral reef sessile invertebrates. We measured settlement to tiles, engineered with surface microtopography (holes) that closely matched the sizes (width) of larvae of a range of corals and sponges, in addition to surfaces with holes that were markedly larger than larvae. Larvae from two species of scleractinian corals (Acropora millepora and Ctenactis crassa) and three species of coral reef sponges (Luffariella variabilis, Carteriospongia foliascens and Ircinia sp.,) were used in experiments. L. variabilis, A. millepora and C. crassa showed markedly higher settlement to surface microtopography that closely matched their larval width. C. foliascens and Ircinia sp., showed no specificity to surface microtopography, settling just as often to microtopography as to flat surfaces. The findings of this study question the sole reliance on chemical based larval settlement cues, previously established for some coral and sponge species, and demonstrate that specific physical cues (surface complexity) can also play an important role in larval settlement of coral reef sessile invertebrates. PMID:25671562

  1. Roles of Oxygen and Water Vapor in the Oxidation of Halogen Terminated Ge(111) Surfaces

    SciTech Connect

    Sun, Shiyu; Sun, Yun; Liu, Zhi; Lee, Dong-Ick; Pianette, Piero; /SLAC, SSRL

    2006-12-18

    The initial stage of the oxidation of Cl and Br terminated Ge(111) surfaces is studied using photoelectron spectroscopy. The authors perform controlled experiments to differentiate the effects of different factors in oxidation, and find that water vapor and oxygen play different roles. Water vapor effectively replaces the halogen termination layers with the hydroxyl group, but does not oxidize the surfaces further. In contrast, little oxidation is observed for Cl and Br terminated surfaces with dry oxygen alone. However, with the help of water vapor, oxygen oxidizes the surface by breaking the Ge-Ge back bonds instead of changing the termination layer.

  2. The Role of Surface Receptor Density in Surface-Initiated Polymerizations for Cancer Cell Isolation.

    PubMed

    Lilly, Jacob L; Berron, Brad J

    2016-06-01

    Fluid biopsies potentially offer a minimally invasive alternative to traditional tissue biopsies for the continual monitoring of metastatic cancer. Current established technologies for isolating circulating tumor cells (CTCs) suffer from poor purity and yield and require fixatives that preclude the collection of viable cells for longitudinal analyses of biological function. Antigen specific lysis (ASL) is a rapid, high-purity method of cell isolation based on targeted protective coatings on antigen-presenting cells and lysis depletion of unprotected antigen-negative cells. In ASL, photoinitiators are specifically labeled on cell surfaces that enable subsequent surface-initiated polymerization. Critically, the significant determinants of process yield have yet to be investigated for this emerging technology. In this work, we show that the labeling density of photoinitiators is strongly correlated with the yield of intact cells during ASL by flow cytometry analysis. Results suggest ASL is capable of delivering ∼25% of targeted cells after isolation using traditional antibody labeling approaches. Monomer formulations of two molecular weights of PEG-diacrylate (Mn ∼ 575 and 3500) are examined. The gelation response during ASL polymerization is also investigated via protein microarray analogues on planar glass. Finally, a density threshold of photoinitiator labeling required for protection during lysis is determined for both monomer formulations. These results indicate ASL is a promising technology for high yield CTC isolation for rare-cell function assays and fluid biopsies. PMID:27206735

  3. Role of multiple shots of femtosecond laser pulses in periodic surface nanoablation

    SciTech Connect

    Miyaji, Godai; Miyazaki, Kenzo

    2013-08-12

    Using a pump and probe technique, we observed time-dependent change in reflectivity of crystalline silicon surface to study the dynamic process of periodic surface nanostructure formation in femtosecond (fs) laser ablation. The results have shown that multiple shots of low-fluence fs laser pulses play the crucial role in the non-thermal process for nanostructuring through the increasing bonding structure change to amorphous silicon and resulting decrease in the ablation threshold.

  4. Annuaire du Bureau des longitudes - 2006

    NASA Astrophysics Data System (ADS)

    Imcce; Bureau Des Longitudes

    2005-07-01

    This annual publication provides ephemerides and data to the use of professionnal and amateur astronomers. Divided in 11 chapters it covers concordance of various calendars, explanation of fondamental astronomy and various time scales, explanation for the use of ephemerides; tables provide ephemerides (positions, rise/set/passage) of the Sun and the Moon, planets, planetary satellites, asteroids, comets, bright stars; data and explanation for the physical observation of the surface of the Sun, the Moon, and planets; chart of the sky and a list of constellations and galaxies; prediction and ephemerides for astronomical phenomenon: occultation by the moon, stellar occultations by asteroids and appulses, solar eclipses and lunar eclipses; and an additional review about a hot scientific topic, this year: "Legendre et le méridien terrestre, 200 ans après". Cette publication annuelle fournit des éphémérides et des données à l'usage des astronomes professionnels et des astronomes amateurs. Composée de 11 chapitres elle comprend les rubriques sur les différents calendriers et leurs concordance, les fêtes légales en France, les dates et décrets sur les heures légales en France métropolitaine ; une introduction à l'astronomie fondamentale et aux différentes échelles de temps, des explications sur l'utilisation des éphémérides ; des tables fournissent les éphémérides (positions, heures de lever/coucher/passage) du Soleil et de la Lune, de planètes, de satellites naturels, d'astéroïdes, de comètes, d'étoiles brillantes ; des données pour l'observation de la surface du Soleil, de la Lune, et des planètes ; des cartes du ciel ainsi qu'une liste de constellations et de galaxies ; des prédictions des phénomènes astronomiques : occultation par la Lune, occultation stellaires par des astéroïdes et appulses, éclipses de Soleil et de la Lune; la liste et les coordonnées des observatoires astronomiques les plus connus ; et enfin un cahier th

  5. Condensation on superhydrophobic surfaces: the role of local energy barriers and structure length scale.

    PubMed

    Enright, Ryan; Miljkovic, Nenad; Al-Obeidi, Ahmed; Thompson, Carl V; Wang, Evelyn N

    2012-10-01

    Water condensation on surfaces is a ubiquitous phase-change process that plays a crucial role in nature and across a range of industrial applications, including energy production, desalination, and environmental control. Nanotechnology has created opportunities to manipulate this process through the precise control of surface structure and chemistry, thus enabling the biomimicry of natural surfaces, such as the leaves of certain plant species, to realize superhydrophobic condensation. However, this "bottom-up" wetting process is inadequately described using typical global thermodynamic analyses and remains poorly understood. In this work, we elucidate, through imaging experiments on surfaces with structure length scales ranging from 100 nm to 10 μm and wetting physics, how local energy barriers are essential to understand non-equilibrium condensed droplet morphologies and demonstrate that overcoming these barriers via nucleation-mediated droplet-droplet interactions leads to the emergence of wetting states not predicted by scale-invariant global thermodynamic analysis. This mechanistic understanding offers insight into the role of surface-structure length scale, provides a quantitative basis for designing surfaces optimized for condensation in engineered systems, and promises insight into ice formation on surfaces that initiates with the condensation of subcooled water. PMID:22931378

  6. The role of moisture on controlling dust emissions from crusted supply-limited surfaces

    NASA Astrophysics Data System (ADS)

    King, James; Wiggs, Giles F. S.; Thomas, David S. G.; Washington, Richard

    2013-04-01

    emissions and wind erosion threshold although much variation remains unexplained. As pan surfaces can exhibit a range of aerodynamic roughness lengths over three orders of magnitude the small-scale partition of wind stress could be considered. Surface soil moisture also had a very large range and due to the fine texture of salt pans produced a crucial threshold for potential emissions equal to or even greater in importance than surface crusting. Although the role of surface moisture in dust emissions is understood it remains a very difficult (yet critical) parameter to measure and a call for more precise estimations of this metric is highly encouraged.

  7. The role of vegetation change on surface energy partitioning: insights from a global flux monitoring network

    NASA Astrophysics Data System (ADS)

    Stoy, Paul; Juang, Jehn-Yih; Siqueira, Mario; Novick, Kim; Katul, Gabriel

    2010-05-01

    Vegetation contributes to the absorption and partitioning of energy at the Earth's surface and the surface-atmosphere flux of important greenhouse gases. Changes to vegetation alter the surface energy balance and biogeochemical fluxes. Recent publications have stressed the need to quantify both biogeochemical and biogeophysical effects of land cover change on regional and global climate using a combination of observations and models. This presentation focuses on the observational record by synthesizing surface-atmosphere radiation balance characteristics - including surface albedo and the fluxes of latent and sensible heat - across global ecosystems in the FLUXNET database. We present characteristic seasonal courses of energy balance components across globally distributed ecosystems and demonstrate the impacts of vegetation change on the surface energy balance. We then perform a perturbation analysis on the energy balance equation to quantify the effects of land cover change on surface radiometric and aerodynamic temperatures in paired eddy covariance towers across the globe. Results emphasize the importance of evapotranspiritive cooling in addition to alterations in albedo on surface temperature change. For example, in the Duke Forest experiment, increases in albedo during a shift from abandoned field to pine or hardwood forest warmed the surface by ca. 1° C on an annual basis, but enhanced evapotranspiration cooled the surface by ca. 2 to 3° C such that reforestation induced a net surface cooling. Results using a general methodology agreed with previous results (Juang et al., 2007, Geophysical Research Letters, L21408). Global modeling exercises may underemphasize the role of evaporative cooling versus that of albedo in surface energy balance studies.

  8. The role of subsurface soil temperature feedbacks in summer surface air temperature variability over East Asia

    NASA Astrophysics Data System (ADS)

    Zhang, J.

    2012-12-01

    Soil temperature, an important component of land surface, can influence the climate through its effects on surface energy and water budgets and resulted changes in regional atmospheric circulation. However, the effects of soil temperature on climate variations have been less discussed. This study investigates the role of subsurface soil temperature feedbacks in influencing summer surface air temperature variability over East Asia by means of regional climate model (RCM) simulations. For this aim, two long-term simulations with and without subsurface soil temperature feedbacks are performed with the Weather Research and Forecasting (WRF) model. From our investigation, it is evident that subsurface soil temperature feedbacks make a dominant contribution to amplifying summer surface air temperature variability over the arid/semi-arid regions. Further analysis reveals that subsurface soil temperature exhibits an asymmetric effect on summer daytime and nighttime surface air temperature variability, with a stronger effect on daily minimum temperature variability than that of daily maximum temperature variability. This study provides the first RCM-based demonstration that subsurface soil temperature feedbacks play an important role in influencing climate variability over East Asia, such as summer surface air temperature. In the meanwhile, the model bias should be recognized. The results achieved by this study thus need to be further confirmed in a multi-model framework to eliminate the model dependence.

  9. Vecteurs Singuliers des Theories des Champs Conformes Minimales

    NASA Astrophysics Data System (ADS)

    Benoit, Louis

    sont elements de la serie h_{p,q}= [ (p(m+2)-qm)^2-4] /(8m(m+2)) ou p,q et m sont des entiers positifs, p et q etant de meme parite, et p+q<= m+2. La charge centrale est donnee par c(m)={3over 2}-{12over m(m+2)} avec m >= 2. Les vecteurs singuliers | Psi_{p,q}> et |Psi_{m-p,m+2-q} > sont respectivement de poids h _{p,q}+pq/2 et h_ {p,q}+(m-p)(m+2-q)/2.. Les vecteurs singuliers ont une norme nulle et on doit les eliminer des representations pour que celles -ci soient unitaires. Cette elimination engendrent des equations (super-)differentielles qui dependent directement de la forme explicite des vecteurs singuliers et auxquelles doivent obeir les fonctions de correlations de la theorie. Ainsi la connaissance de ces vecteurs singuliers est intimement reliee au calcul des fonctions de correlation. Les equations definissant les vecteurs singuliers forment un systeme lineaire surdetermine dont le nombre d'equations est de l'ordre de N(pq), le nombre de partitions de l'entier pq. Puisque les vecteurs singuliers jouent un role capital en theorie conforme, il est naturel de chercher des formes explicites pour les vecteurs (ou pour des familles infinies de ceux -ci). Nous donnons ici la forme explicite pour la famille infinie de vecteurs singuliers ayant un de ses indices egal a 1, pour les algebres de Virasoro et de Neveu-Schwarz. Depuis ces decouvertes, d'autres techniques de construction des vecteurs singuliers ont ete developpees, dont celle de Bauer, Di Francesco, Itzykson et Zuber pour l'algebre de Virasoro qui reproduit directement l'expression explicite des vecteurs singuliers |Psi _{1,q}> et |Psi_{p,1}>. Ils ont utilise l'algebre des produits d'operateurs et la fusion entre representations irreductibles pour engendrer des relations de recurence produisant les vecteurs singuliers. Dans le dernier chapitre de cette these nous adaptons cet algorithme a la construction des vecteurs singuliers de l'algebre de Neveu-Schwarz.

  10. Role of Surface Termination in Atomic Layer Deposition of Silicon Nitride.

    PubMed

    Ande, Chaitanya Krishna; Knoops, Harm C M; de Peuter, Koen; van Drunen, Maarten; Elliott, Simon D; Kessels, Wilhelmus M M

    2015-09-17

    There is an urgent need to deposit uniform, high-quality, conformal SiN(x) thin films at a low-temperature. Conforming to these constraints, we recently developed a plasma enhanced atomic layer deposition (ALD) process with bis(tertiary-butyl-amino)silane (BTBAS) as the silicon precursor. However, deposition of high quality SiNx thin films at reasonable growth rates occurs only when N2 plasma is used as the coreactant; strongly reduced growth rates are observed when other coreactants like NH3 plasma, or N2-H2 plasma are used. Experiments reported in this Letter reveal that NH(x)- or H- containing plasmas suppress film deposition by terminating reactive surface sites with H and NH(x) groups and inhibiting precursor adsorption. To understand the role of these surface groups on precursor adsorption, we carried out first-principles calculations of precursor adsorption on the β-Si3N4(0001) surface with different surface terminations. They show that adsorption of the precursor is strong on surfaces with undercoordinated surface sites. In contrast, on surfaces with H, NH2 groups, or both, steric hindrance leads to weak precursor adsorption. Experimental and first-principles results together show that using an N2 plasma to generate reactive undercoordinated surface sites allows strong adsorption of the silicon precursor and, hence, is key to successful deposition of silicon nitride by ALD. PMID:26722730

  11. Force of adhesion on supersolvophobic surfaces: The role of capillary necks

    NASA Astrophysics Data System (ADS)

    Escobar, Juan V.; Castillo, Rolando

    2016-02-01

    We study theoretically the force of adhesion of pinned liquid drops in contact with supersolvophobic surfaces. We develop a method to calculate the contact and excess surface areas vs compression of the drops against surfaces characterized by an effective interfacial energy in the Cassie-Baxter wetting regime. We find that a 9° difference in contact angle can increase the force of adhesion by almost three orders of magnitude. We investigate the role that the inevitable formation of capillary necks has on this force, which has the same functional form of Derjaguin's result for elastic solids. Our results suggest that measuring the force of adhesion directly on nearly perfectly solvophobic surfaces may be a more precise technique to quantify the effective interfacial energy than traditional contact angle measurements on macroscopic drops.

  12. Aquarius surface salinity and the Madden-Julian Oscillation: The role of salinity in surface layer density and potential energy

    NASA Astrophysics Data System (ADS)

    Guan, Bin; Lee, Tong; Halkides, Daria J.; Waliser, Duane E.

    2014-04-01

    Sea surface salinity (SSS) data from the Aquarius satellite are analyzed along with auxiliary data to investigate the SSS signature of the Madden-Julian Oscillation (MJO) in the equatorial Indian and Pacific Oceans, the effect of evaporation-minus-precipitation (E-P), the implication for the role of ocean dynamics, and the SSS influence on surface density and potential energy. MJO-related SSS changes are consistent with E-P forcing in the western Indian Ocean throughout the MJO cycle and in the central Indian Ocean during the wet phase of the MJO cycle. However, SSS changes cannot be explained by E-P in the central Indian Ocean during the dry phase and in the eastern Indian and western Pacific Oceans throughout the MJO cycle, implying the importance of ocean dynamics. SSS has an overall larger contribution to MJO-related surface density and potential energy anomalies than SST. It partially offsets the SST effect in the western-to-central Indian Ocean and reinforces the SST effect in the eastern Indian and western Pacific Oceans. Ocean modeling and assimilation need to properly account for salinity effects in order to correctly represent mixed layer variability associated with the MJO. Our results also clarify some discrepancy in previous studies about the E-P effect on MJO-related SSS variations.

  13. Cd adsorption properties of components in different freshwater surface coatings: the important role of ferromanganese oxides.

    PubMed

    Dong, Deming; Hua, Xiuyi; Li, Yu; Zhang, Jingjing; Yan, Dongxu

    2003-09-15

    Surface coatings developed in different natural waters were used to study the role of the composition of surface coatings in controlling Cd adsorption in aquatic environments. To investigate the adsorption property of each component, the method of extraction techniques followed by Cd adsorption and statistical analysis were employed. Hydroxylamine hydrochloride was used to remove Mn oxides selectively, sodium dithionite was used to remove Mn and Fe oxides, and oxalic acid was used to remove most metal oxides and part of the organic material. Adsorption of Cd to surface coatings was measured before and after extraction under controlled laboratory conditions. The observed Cd adsorptions to unextracted and extracted surface coatings were analyzed using nonlinear least-squares fitting to estimate the adsorption property of each surface coating constituent. In different waters, the relative contribution to Cd adsorption of each component was different, but in all the waters studied, ferromanganese oxides contributed most with lesser roles indicated for organic phase and Al oxides. The Cd adsorption ability of manganese oxides was significantly higher than that of the other components. PMID:14524442

  14. The role of surface passivation for efficient and photostable PbS quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Cao, Yiming; Stavrinadis, Alexandros; Lasanta, Tania; So, David; Konstantatos, Gerasimos

    2016-04-01

    For any emerging photovoltaic technology to become commercially relevant, both its power conversion efficiency and photostability are key parameters to be fulfilled. Colloidal quantum dot solar cells are a solution-processed, low-cost technology that has reached an efficiency of about 9% by judiciously controlling the surface of the quantum dots to enable surface passivation and tune energy levels. However, the role of the quantum dot surface on the stability of these solar cells has remained elusive. Here we report on highly efficient and photostable quantum dot solar cells with efficiencies of 9.6% (and independently certificated values of 8.7%). As a result of optimized surface passivation and the suppression of hydroxyl ligands—which are found to be detrimental for both efficiency and photostability—the efficiency remains within 80% of its initial value after 1,000 h of continuous illumination at AM1.5G. Our findings provide insights into the role of the quantum dot surface in both the stability and efficiency of quantum dot solar cells.

  15. Role of silicon surface in the removal of point defects in ultra-shallow junctions

    SciTech Connect

    Sultan, A.; Banerjee, S.; List, S.; Rodder, M.

    1996-12-31

    The role of the Si surface in the annihilation of point defects has been studied for ultra-shallow p{sup +}/n junctions. The dopant and defect distributions for low energy implants lie within a few hundred Angstroms of the surface. The proximity of the Si surface has been shown to help in the efficient removal of point defects for the shallower junctions. A 5 keV, 1{times}10{sup 15} cm{sup -2} BF{sub 2} implant and a 30 keV, 3.3{times}10{sup 14} cm{sup -2} BF{sub 2} implant were estimated to create comparable damage at different depths. After identical anneals, the higher energy implant sample showed end-of-range dislocation loops in cross-sectional transmission electron microscopy analysis, while the low energy sample, for which the point defect distribution was closer to the surface, was defect-free. This is attributed to the role of the Si surface as an efficient sink for the removal of point defects.

  16. Understanding the Role of Wind in Reducing the Surface Mass Balance Estimates over East Antarctica

    NASA Astrophysics Data System (ADS)

    Das, I.; Scambos, T. A.; Koenig, L.; Creyts, T. T.; Bell, R. E.; van den Broeke, M. R.; Lenaerts, J.; Paden, J. D.

    2014-12-01

    Accurate quantification of surface snow-accumulation over Antarctica is important for mass balance estimates and climate studies based on ice core records. An improved estimate of surface mass balance must include the significant role near-surface wind plays in the sublimation and redistribution of snow across Antarctica. We have developed an empirical model based on airborne radar and lidar observations, and modeled surface mass balance and wind fields to produce a continent-wide prediction of wind-scour zones over Antarctica. These zones have zero to negative surface mass balance, are located over locally steep ice sheet areas (>0.002) and controlled by bedrock topography. The near-surface winds accelerate over these zones, eroding and sublimating the surface snow. This scouring results in numerous localized regions (≤ 200 km2) with reduced surface accumulation. Each year, tens of gigatons of snow on the Antarctic ice sheet are ablated by persistent near-surface katabatic winds over these wind-scour zones. Large uncertainties remain in the surface mass balance estimates over East Antarctica as climate models do not adequately represent the small-scale physical processes that lead to mass loss through sublimation or redistribution over the wind-scour zones. In this study, we integrate Operation IceBridge's snow radar over the Recovery Ice Stream with a series of ice core dielectric and depth-density profiles for improved surface mass balance estimates that reflect the mass loss over the wind-scour zones. Accurate surface mass balance estimates from snow radars require spatially variable depth-density profiles. Using an ensemble of firn cores, MODIS-derived surface snow grain size, modeled accumulation rates and surface temperatures from RACMO2, we assemble spatially variable depth-density profiles and use our mapping of snow density variations to estimate layer mass and net accumulation rates from snow radar layer data. Our study improves the quantification of

  17. Geometrical evolution of interlocked rough slip surfaces: The role of normal stress

    NASA Astrophysics Data System (ADS)

    Badt, Nir; Hatzor, Yossef H.; Toussaint, Renaud; Sagy, Amir

    2016-06-01

    distribution clearly increase with increasing normal stress. Wear loss is measured by subtracting the post-shear surface from the pre-shear surface matrices using known reference points. Our measurements indicate that wear loss and roughness evolution are both positively correlated with the mechanical shear work applied during the experiments. We argue, therefore, that normal stress plays a significant role in the evolution of interlocked surfaces, such as geological faults, and strongly affects the energy partitioning during slip.

  18. Tuning cell adhesion on polymeric and nanocomposite surfaces: Role of topography versus superhydrophobicity.

    PubMed

    Zangi, Sepideh; Hejazi, Iman; Seyfi, Javad; Hejazi, Ehsan; Khonakdar, Hossein Ali; Davachi, Seyed Mohammad

    2016-06-01

    Development of surface modification procedures which allow tuning the cell adhesion on the surface of biomaterials and devices is of great importance. In this study, the effects of different topographies and wettabilities on cell adhesion behavior of polymeric surfaces are investigated. To this end, an improved phase separation method was proposed to impart various wettabilities (hydrophobic and superhydrophobic) on polypropylene surfaces. Surface morphologies and compositions were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Cell culture was conducted to evaluate the adhesion of 4T1 mouse mammary tumor cells. It was found that processing conditions such as drying temperature is highly influential in cell adhesion behavior due to the formation of an utterly different surface topography. It was concluded that surface topography plays a more significant role in cell adhesion behavior rather than superhydrophobicity since the nano-scale topography highly inhibited the cell adhesion as compared to the micro-scale topography. Such cell repellent behavior could be very useful in many biomedical devices such as those in drug delivery and blood contacting applications as well as biosensors. PMID:27040256

  19. Magnetotransport in Weyl semimetals in the quantum limit: Role of topological surface states

    NASA Astrophysics Data System (ADS)

    Ominato, Yuya; Koshino, Mikito

    2016-06-01

    We theoretically study the magnetoconductivity of Weyl semimetals with a surface boundary under E ||B geometry and demonstrate that the topological surface state plays an essential role in the magnetotransport. In the long-range-disorder limit where the scattering between the two Weyl nodes vanishes, the conductivity diverges in the bulk model (i.e., periodic boundary condition) as usually expected since the direct internode relaxation is absent. In the presence of the surface, however, the internode relaxation always takes place through the mediation by the surface states, and that prevents the conductivity divergence. The magnetic-field dependence becomes also quite different between the two cases, where the conductivity linearly increases in B in the surface boundary case, in contrast to B -independent behavior in the bulk periodic case. This is an interesting example in which the same system exhibits completely different properties in the surface boundary condition and the periodic boundary condition even in the macroscopic size limit. In the short-range regime where the direct intervalley scattering is dominant, the surface states are irrelevant, and the conductivity approaches that of the bulk periodic model.

  20. Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides

    SciTech Connect

    Khan, Sami; Varanasi, Kripa K.; Azimi, Gisele; Yildiz, Bilge

    2015-02-09

    Hydrophobic surfaces that are robust can have widespread applications in drop-wise condensation, anti-corrosion, and anti-icing. Recently, it was shown that the class of ceramics comprising the lanthanide series rare-earth oxides (REOs) is intrinsically hydrophobic. The unique electronic structure of the rare-earth metal atom inhibits hydrogen bonding with interfacial water molecules resulting in a hydrophobic hydration structure where the surface oxygen atoms are the only hydrogen bonding sites. Hence, the presence of excess surface oxygen can lead to increased hydrogen bonding and thereby reduce hydrophobicity of REOs. Herein, we demonstrate how surface stoichiometry and surface relaxations can impact wetting properties of REOs. Using X-ray Photoelectron Spectroscopy and wetting measurements, we show that freshly sputtered ceria is hydrophilic due to excess surface oxygen (shown to have an O/Ce ratio of ∼3 and a water contact angle of ∼15°), which when relaxed in a clean, ultra-high vacuum environment isolated from airborne contaminants reaches close to stoichiometric O/Ce ratio (∼2.2) and becomes hydrophobic (contact angle of ∼104°). Further, we show that airborne hydrocarbon contaminants do not exclusively impact the wetting properties of REOs, and that relaxed REOs are intrinsically hydrophobic. This study provides insight into the role of surface relaxation on the wettability of REOs.

  1. Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides

    NASA Astrophysics Data System (ADS)

    Khan, Sami; Azimi, Gisele; Yildiz, Bilge; Varanasi, Kripa K.

    2015-02-01

    Hydrophobic surfaces that are robust can have widespread applications in drop-wise condensation, anti-corrosion, and anti-icing. Recently, it was shown that the class of ceramics comprising the lanthanide series rare-earth oxides (REOs) is intrinsically hydrophobic. The unique electronic structure of the rare-earth metal atom inhibits hydrogen bonding with interfacial water molecules resulting in a hydrophobic hydration structure where the surface oxygen atoms are the only hydrogen bonding sites. Hence, the presence of excess surface oxygen can lead to increased hydrogen bonding and thereby reduce hydrophobicity of REOs. Herein, we demonstrate how surface stoichiometry and surface relaxations can impact wetting properties of REOs. Using X-ray Photoelectron Spectroscopy and wetting measurements, we show that freshly sputtered ceria is hydrophilic due to excess surface oxygen (shown to have an O/Ce ratio of ˜3 and a water contact angle of ˜15°), which when relaxed in a clean, ultra-high vacuum environment isolated from airborne contaminants reaches close to stoichiometric O/Ce ratio (˜2.2) and becomes hydrophobic (contact angle of ˜104°). Further, we show that airborne hydrocarbon contaminants do not exclusively impact the wetting properties of REOs, and that relaxed REOs are intrinsically hydrophobic. This study provides insight into the role of surface relaxation on the wettability of REOs.

  2. Role of molecular properties of ulvans on their ability to elaborate antiadhesive surfaces.

    PubMed

    Gadenne, Virginie; Lebrun, Laurent; Jouenne, Thierry; Thebault, Pascal

    2015-03-01

    Antiadhesive properties of polysaccharides (such ulvans) once immobilized on a surface are described in the literature but the parameters governing their antifouling properties are not yet well identified. In the present study, the relationship between molecular parameters of ulvans and the inhibition of bacterial adhesion was investigated. To this aim, various ulvans were grafted on silicon wafers under two different experimental immobilization conditions. Results showed that the experimental immobilization conditions and the polysaccharides molecular weight led to specific layer conformations which exhibited a key role in the surface antiadhesive properties. PMID:24890284

  3. Role of surface plasmon in second harmonic generation from gold nanorods

    SciTech Connect

    Hubert, C.; Billot, L.; Adam, P.-M.; Bachelot, R.; Royer, P.; Grand, J.; Gindre, D.; Dorkenoo, K. D.; Fort, A.

    2007-04-30

    The role of surface plasmon in second harmonic generation from arrays of gold nanorod particles excited by femtosecond laser pulses is investigated as a function of incident light polarization and irradiation wavelength. In addition to photoluminescence, a peak of second harmonic is observed and is found to depend on the polarization and wavelength of the fundamental frequency laser beam. In particular, the authors found similarities between extinction spectra of the nanoparticles and spectra of emmitted second harmonic. This behavior can be explained by resonant excitation of localized surface plasmon resonances.

  4. Des Vents et des Jets Astrophysiques

    NASA Astrophysics Data System (ADS)

    Sauty, C.

    Plasma outflows from a central gravitating object are a widespread phenomenon in astrophysics. They include the solar and stellar winds, jets from Young Stellar Objects, jets from compact stellar objects and extra-galactic jets associated with Active Galactic Nuclei and quasars. Beyond this huge zoology, a common theoretical ground exists. The aim of this review is to present qualitatively the various theories of winds (Part 1) and how different astrophysical domains interplay. A more or less complete catalog of the ideas proposed for explaining the acceleration and the morphologies of winds and jets is intended. All this part avoids getting into any mathematical formalism. Some macroscopic properties of such outflows may be described by solving the time-independent and axisymmetric magnetohydrodynamic equations. This formalism, underlying most of the theories, is presented in Part 2. It helps to introduce quantitatively the free integrals that such systems possess. Those integrals play an important role in the basic physics of acceleration and collimation, in particular the mass loss rate, the angular momentum loss rate and the energy of the magnetic rotator. Most of the difficulty in modelling flows lies in the necessity to cross critical points, characteristic of non linear equations. The physical nature and the location of such critical points is debated because they are the clue towards the resolution. We thus introduce the notions of topology and critical points (Parts 3 and 4) from the simplest hydrodynamic and spherically symmetric case to the most sophisticated, MHD and axisymmetric cases. Particular attention is given to self-similar models which allows to give some general and simple ideas on the problem due to their semi-analytical treatment. With the use of these notions, a more quantitative comparison of the various models is given (Parts 3 and 4), especially on the shape of the flows. It is thus shown that magnetic collimation of winds into jets is a

  5. Roles of regulated internalization in the polarization of cell surface receptors

    PubMed Central

    Tian, Wei; Cao, Youfang; Ismael, Amber; Stone, David

    2016-01-01

    Cell polarization, the generation of cellular asymmetries, is a fundamental biological process. Polarity of different molecules can arise through several mechanisms. Among these, internalization has been shown to play an important role in the polarization of cell surface receptors. The internalization of cell surface receptors can be upregulated upon ligand binding. Additional regulatory mechanism can downregulate the internalization process. Here we describe a general model, which incorporates these two opposing processes, to study the role of internalization in the establishment of cell polarity. We find that the competition between these two processes is sufficient to induce receptor polarization. Our results show that regulated internalization provides additional regulation on polarization as well. In addition, we discuss applications of our model to the yeast system, which shows the capability and potential of the model. PMID:25570171

  6. The role of near-surface plastic deformation in the wear of lamellar solids

    NASA Technical Reports Server (NTRS)

    Kennedy, F. E.; Hartman, L. A.; Hauck, K. E.; Surprenant, V. A.

    1985-01-01

    It is shown in this paper that the role of surface and near-surface plastic deformation is especially significant in both sliding and abrasive wear of lamellar composites. Lamellar structures were produced artificially from alternate layers of pure copper and pure tin or lead foils. The resulting composites were tested in three different wear tests: single-pass abrasion by a sharp, hard abrader; multiple-pass rubbing by a hard, rounded abrader; and pin-on-disk sliding. In each case the counterface was a hard alloy steel. Tests were run with the composite lamellae in two orientations: perpendicular and parallel to the sliding direction. It was found that the composites had much less wear resistance and greater abradability when oriented perpendicular to the rub direction. The mechanisms for wear particle removal and the role of plastic deformation in the process were studied by plasticity analysis and by microscopic (SEM and optical) observation.

  7. The Role of Interfacial Molecular Structure and Hydrogen-Bonding in Gas-Surface Energy Exchange

    NASA Astrophysics Data System (ADS)

    Day, Scott; Fergusion, Melinda; Morris, John

    2004-03-01

    Atomic-beam scattering experiments using n-alkanethiol and w-functionalized alkanethiol self-assembled monolayers (SAMs) on gold are employed to explore the dynamics of gas-surface energy exchange in collisions with model organic surfaces. The studies are performed by directing a nearly monoenergetic beam of 80 kJ/mol Ar atoms onto a particular SAM at an incident angle of 30° with respect to the surface normal and recording the time-of-flight distributions for the atoms as they scatter from the surface at a final angle of 30°. Among the monolayers studied, long-chain methyl-terminated SAMs are found to be the most effective at dissipating the translational energy of impinging atoms. For alkanethiols with greater than seven total carbon atoms, we find that, for specular scattering conditions, over 80the incident energy is transferred to the surface and that over 60with the surface before scattering back into the gas phase. In contrast to methyl-terminated monolayers, SAMs constructed from hydrogen-bonding alkanethiols exhibit characteristics of more rigid collision partners. The Ar atoms transfer about 77with only 43equilibrium before recoiling. Further comparisons of mixed hydroxyl- and methyl-terminated SAMs and alkene-terminated SAMs suggest that intramonolayer hydrogen bonding of terminal functional groups may play an important role in determining the extent of energy transfer and thermalization.

  8. Role of Viscous Dissipative Processes on the Wetting of Textured Surfaces

    PubMed Central

    Grewal, H. S.; Nam Kim, Hong; Cho, Il-Joo; Yoon, Eui-Sung

    2015-01-01

    We investigate the role of viscous forces on the wetting of hydrophobic, semi-hydrophobic, and hydrophilic textured surfaces as second-order effects. We show that during the initial contact, the transition from inertia- to viscous-dominant regime occurs regardless of their surface topography and chemistry. Furthermore, we demonstrate the effect of viscosity on the apparent contact angle under quasi-static conditions by modulating the ratio of a water/glycerol mixture and show the effect of viscosity, especially on the semi-hydrophobic and hydrophobic textured substrates. The reason why the viscous force does not affect the apparent contact angle of the hydrophilic surface is explained based on the relationship between the disjoining pressure and surface chemistry. We further propose a wetting model that can predict the apparent contact angle of a liquid drop on a textured substrate by incorporating a viscous force component in the force balance equation. This model can predict apparent contact angles on semi-hydrophobic and hydrophobic textured surfaces exhibiting Wenzel state more accurately than the Wenzel model, indicating the importance of viscous forces in determining the apparent contact angle. The modified model can be applied for estimating the wetting properties of arbitrary engineered surfaces. PMID:26390958

  9. Role of uppermost superficial surface layer of articular cartilage in the lubrication mechanism of joints

    PubMed Central

    KUMAR, P.; OKA, M.; TOGUCHIDA, J.; KOBAYASHI, M.; UCHIDA, E.; NAKAMURA, T.; TANAKA, K.

    2001-01-01

    The uppermost superficial surface layer of articular cartilage, the ‘lamina splendens’ which provides a very low friction lubrication surface in articular joints, was investigated using atomic force microscopy (AFM). Complementary specimens were also observed under SEM at −10 °C without dehydration or sputter ion coating. Fresh adult pig osteochondral specimens were prepared from the patellas of pig knee joints and digested with the enzymes, hyaluronidase, chondroitinase ABC and alkaline protease. Friction coefficients between a pyrex glass plate and the osteochondral specimens digested by enzymes as well as natural (undigested) specimens were measured, using a thrust collar apparatus. Normal saline, hyaluronic acid (HA) and a mixture of albumin, globulin, HA (AGH) were used as lubrication media. The surface irregularities usually observed in SEM studies were not apparent under AFM. The articular cartilage surface was resistant to hyaluronidase and also to chondroitinase ABC, but a fibrous structure was exhibited in alkaline protease enzymes-digested specimens. AFM analysis revealed that the thickness of the uppermost superficial surface layer of articular cartilage was between 800 nm and 2 μm in adult pig articular cartilage. The coefficient of friction (c.f.) was significantly higher in chondroitinase ABC and alkaline protease enzymes digested specimens. Generally, in normal saline lubrication medium, c.f. was higher in comparison to HA and AGH lubrication media. The role of the uppermost, superficial surface layer of articular cartilage in the lubrication mechanism of joints is discussed. PMID:11554503

  10. Role of uppermost superficial surface layer of articular cartilage in the lubrication mechanism of joints.

    PubMed

    Kumar, P; Oka, M; Toguchida, J; Kobayashi, M; Uchida, E; Nakamura, T; Tanaka, K

    2001-09-01

    The uppermost superficial surface layer of articular cartilage, the 'lamina splendens' which provides a very low friction lubrication surface in articular joints, was investigated using atomic force microscopy (AFM). Complementary specimens were also observed under SEM at -10 degrees C without dehydration or sputter ion coating. Fresh adult pig osteochondral specimens were prepared from the patellas of pig knee joints and digested with the enzymes, hyaluronidase, chondroitinase ABC and alkaline protease. Friction coefficients between a pyrex glass plate and the osteochondral specimens digested by enzymes as well as natural (undigested) specimens were measured, using a thrust collar apparatus. Normal saline, hyaluronic acid (HA) and a mixture of albumin, globulin, HA (AGH) were used as lubrication media. The surface irregularities usually observed in SEM studies were not apparent under AFM. The articular cartilage surface was resistant to hyaluronidase and also to chondroitinase ABC, but a fibrous structure was exhibited in alkaline protease enzymes-digested specimens. AFM analysis revealed that the thickness of the uppermost superficial surface layer of articular cartilage was between 800 nm and 2 microm in adult pig articular cartilage. The coefficient of friction (c.f.) was significantly higher in chondroitinase ABC and alkaline protease enzymes digested specimens. Generally, in normal saline lubrication medium, c.f. was higher in comparison to HA and AGH lubrication media. The role of the uppermost, superficial surface layer of articular cartilage in the lubrication mechanism of joints is discussed. PMID:11554503

  11. Copper plasmonics and catalysis: role of electron-phonon interactions in dephasing localized surface plasmons

    NASA Astrophysics Data System (ADS)

    Sun, Qi-C.; Ding, Yuchen; Goodman, Samuel M.; H. Funke, Hans; Nagpal, Prashant

    2014-10-01

    Copper metal can provide an important alternative for the development of efficient, low-cost and low-loss plasmonic nanoparticles, and selective nanocatalysts. However, poor chemical stability and lack of insight into photophysics and plasmon decay mechanisms has impeded study. Here, we use smooth conformal ALD coating on copper nanoparticles to prevent surface oxidation, and study dephasing time for localized surface plasmons on different sized copper nanoparticles. Using dephasing time as a figure of merit, we elucidate the role of electron-electron, electron-phonon, impurity, surface and grain boundary scattering on the decay of localized surface plasmon waves. Using our quantitative analysis and different temperature dependent measurements, we show that electron-phonon interactions dominate over other scattering mechanisms in dephasing plasmon waves. While interband transitions in copper metal contributes substantially to plasmon losses, tuning surface plasmon modes to infrared frequencies leads to a five-fold enhancement in the quality factor. These findings demonstrate that conformal ALD coatings can improve the chemical stability for copper nanoparticles, even at high temperatures (>300 °C) in ambient atmosphere, and nanoscaled copper is a good alternative material for many potential applications in nanophotonics, plasmonics, catalysis and nanoscale electronics.Copper metal can provide an important alternative for the development of efficient, low-cost and low-loss plasmonic nanoparticles, and selective nanocatalysts. However, poor chemical stability and lack of insight into photophysics and plasmon decay mechanisms has impeded study. Here, we use smooth conformal ALD coating on copper nanoparticles to prevent surface oxidation, and study dephasing time for localized surface plasmons on different sized copper nanoparticles. Using dephasing time as a figure of merit, we elucidate the role of electron-electron, electron-phonon, impurity, surface and grain

  12. The role of substrate surface alteration in the fabrication of vertically aligned CdTe nanowires.

    PubMed

    Neretina, S; Hughes, R A; Devenyi, G A; Sochinskii, N V; Preston, J S; Mascher, P

    2008-05-01

    Previously we have described the deposition of vertically aligned wurtzite CdTe nanowires derived from an unusual catalytically driven growth mode. This growth mode could only proceed when the surface of the substrate was corrupted with an alcohol layer, although the role of the corruption was not fully understood. Here, we present a study detailing the remarkable role that this substrate surface alteration plays in the development of CdTe nanowires; it dramatically improves the size uniformity and largely eliminates lateral growth. These effects are demonstrated to arise from the altered surface's ability to limit Ostwald ripening of the catalytic seed material and by providing a surface unable to promote the epitaxial relationship needed to sustain a lateral growth mode. The axial growth of the CdTe nanowires is found to be exclusively driven through the direct impingement of adatoms onto the catalytic seeds leading to a self-limiting wire height associated with the sublimation of material from the sidewall facets. The work presented furthers the development of the mechanisms needed to promote high quality substrate-based vertically aligned CdTe nanowires. With our present understanding of the growth mechanism being a combination of selective area epitaxy and a catalytically driven vapour-liquid-solid growth mode, these results also raise the intriguing possibility of employing this growth mode in other material systems in an effort to produce superior nanowires. PMID:21825689

  13. Role of van der Waals forces in the diffraction of noble gases from metal surfaces

    NASA Astrophysics Data System (ADS)

    del Cueto, M.; Muzas, A. S.; Füchsel, G.; Gatti, F.; Martín, F.; Díaz, C.

    2016-02-01

    The role of van der Waals (vdW) forces in the description of scattering processes of noble gases from metal surfaces is currently under debate. Although features of the potential energy surface such as anticorrugation or adsorption energies are sometimes found to be well described by standard density functional theory (DFT), the performance of DFT to describe diffraction spectra may rely on the accuracy of the vdW functionals used. To analyze the precise role of these vdW forces in noble gas diffraction by metal surfaces, we have thoroughly studied the case of Ne/Ru(0001), for which accurate experimental results are available. We have carried out classical and quantum dynamics calculations by using DFT-based potentials that account for the effect of vdW interactions at different levels of accuracy. From the comparison of our results with experimental data, we conclude that the inclusion of vdW effects is crucial to properly describe diffraction of noble gases from metal surfaces. We show that among the vdW-DFT functionals available in the literature, not all of them can be used to accurately describe this process.

  14. Structure of GaAs(001) surfaces: The role of electrostatic interactions

    SciTech Connect

    Northrup, J.E. ); Froyen, S. )

    1994-07-15

    We report first-principles total-energy calculations for the GaAs(001) surface. Our results indicate that the 2[times]4 reconstruction corresponds to the [beta]2(2[times]4) structure, which exhibits two As dimers in the top layer and a third As dimer in the third layer. This structure has a lower surface energy than the [beta](2[times]4) model, which has three As dimers in the top layer. We also find that a model recently proposed by Skala [ital et] [ital al]. [Phys. Rev. B [bold 48], 9138 (1993)] for the structure of the Ga-rich 4[times]2 phase is energetically unfavorable. From our results we conclude that electrostatic interactions between the charged building blocks of polar semiconductor surfaces play an important role in determining the equilibrium structure. We introduce a simple model for estimating these interactions.

  15. Role of LiCoO2 Surface Terminations in Oxygen Reduction and Evolution Kinetics.

    PubMed

    Han, Binghong; Qian, Danna; Risch, Marcel; Chen, Hailong; Chi, Miaofang; Meng, Ying Shirley; Shao-Horn, Yang

    2015-04-16

    Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities of LiCoO2 nanorods with sizes in the range from 9 to 40 nm were studied in alkaline solution. The sides of these nanorods were terminated with low-index surfaces such as (003), while the tips were terminated largely with high-index surfaces such as (104), as revealed by high-resolution transmission electron microscopy. Electron energy loss spectroscopy demonstrated that low-spin Co(3+) prevailed on the sides, while the tips exhibited predominantly high- or intermediate-spin Co(3+). We correlated the electronic and atomic structure to higher specific ORR and OER activities at the tips as compared to the sides, which was accompanied by more facile redox of Co(2+/3+) and higher charge transferred per unit area. These findings highlight the critical role of surface terminations and electronic structures of transition-metal oxides on the ORR and OER activity. PMID:26263135

  16. The Role of Body Surface Area in Quantity Discrimination in Angelfish (Pterophyllum scalare)

    PubMed Central

    Gómez-Laplaza, Luis M.; Gerlai, Robert

    2013-01-01

    Although some fish species have been shown to be able to discriminate between two groups (shoals) of conspecifics differing in the number of members, most studies have not controlled for continuous variables that covary with number. Previously, using angelfish (Pterophyllum scalare) we started the systematic analysis of the potential influence of such continuous variables, and found that they play different roles in shoal discrimination depending on whether large (≥4 fish) or small (<4 fish) shoals were contrasted. Here, we examine the potential role of the overall body surface area of stimulus fish in shoal preference, a prominent variable not yet examined in angelfish. We report that both when numerically large (5 versus 10 fish) and when small (2 versus 3 fish) shoals were contrasted, angelfish were unable to discriminate the numerically different shoals as long as the surface area of the contrasted shoals was equated. Thus, we conclude that body surface may be an important continuous variable in shoal discrimination. This conclusion was further supported by the analysis of preference when shoals of the same numerical size but different body surface area were contrasted. We found subjects to spend significantly more time close to the shoals with the greater overall surface area. Last, we conducted an experiment in which we simultaneously controlled a set of continuous variables, including overall surface area, and found angelfish to use the number of shoal members as a cue only in large shoal contrasts but not in small shoal contrasts. This result suggests the potential existence of different processing systems for large and small numbers in fish. PMID:24386299

  17. The role of body surface area in quantity discrimination in angelfish (Pterophyllum scalare).

    PubMed

    Gómez-Laplaza, Luis M; Gerlai, Robert

    2013-01-01

    Although some fish species have been shown to be able to discriminate between two groups (shoals) of conspecifics differing in the number of members, most studies have not controlled for continuous variables that covary with number. Previously, using angelfish (Pterophyllum scalare) we started the systematic analysis of the potential influence of such continuous variables, and found that they play different roles in shoal discrimination depending on whether large (≥ 4 fish) or small (<4 fish) shoals were contrasted. Here, we examine the potential role of the overall body surface area of stimulus fish in shoal preference, a prominent variable not yet examined in angelfish. We report that both when numerically large (5 versus 10 fish) and when small (2 versus 3 fish) shoals were contrasted, angelfish were unable to discriminate the numerically different shoals as long as the surface area of the contrasted shoals was equated. Thus, we conclude that body surface may be an important continuous variable in shoal discrimination. This conclusion was further supported by the analysis of preference when shoals of the same numerical size but different body surface area were contrasted. We found subjects to spend significantly more time close to the shoals with the greater overall surface area. Last, we conducted an experiment in which we simultaneously controlled a set of continuous variables, including overall surface area, and found angelfish to use the number of shoal members as a cue only in large shoal contrasts but not in small shoal contrasts. This result suggests the potential existence of different processing systems for large and small numbers in fish. PMID:24386299

  18. The role of lattice parameter in water adsorption and wetting of a solid surface.

    PubMed

    Massey, A; McBride, F; Darling, G R; Nakamura, M; Hodgson, A

    2014-11-21

    Ice formation is a complex cooperative process that is almost invariably catalysed by the presence of an interface on which ice crystals nucleate. As yet there is no clear picture of what factors make a surface particularly good at nucleating ice, but the importance of having a template with a suitable lattice parameter has often been proposed. Here we report the contrasting wetting behaviour of a series of pseudomorphic surfaces, designed to form an ordered template that matches the arrangement of water in a bulk ice Ih(0001) bilayer. The close-packed M(111) surfaces (M = Pt, Pd, Rh, Cu and Ni) form a (√3 × √3) R30° Sn substitutional alloy surface, with Sn atoms occupying sites that match the symmetry of an ice bilayer. The lattice constant of the alloy changes from 4% smaller to 7% greater than the lateral spacing of ice across the series. We show that only the PtSn surface, with a lattice parameter some 7% greater than that of a bulk ice layer, forms a stable water layer, all the other surfaces being non-wetting and instead forming multilayer ice clusters. This observation is consistent with the idea that the repeat spacing of the surface should ideally match the O-O spacing in ice, rather than the bulk ice lattice parameter, in order to form a continuous commensurate water monolayer. We discuss the role of the lattice parameter in stabilising the first layer of water and the factors that lead to formation of a simple commensurate structure rather than an incommensurate or large unit cell water network. We argue that lattice match is not a good criteria for a material to give low energy nucleation sites for bulk ice, and that considerations such as binding energy and mobility of the surface layer are more relevant. PMID:25286238

  19. Role of cell surface oligosaccharides of mouse mammary tumor cell lines in cancer metastasis.

    PubMed

    Zhao, Yunxue; Li, Jing; Wang, Jingjian; Xing, Yanli; Geng, Meiyu

    2007-06-01

    Malignant transformation is associated with changes in the glycosylation of cell surface proteins and lipids. In tumor cells, alterations in cellular glycosylation may play a key role in their metastatic behaviour. In the present study, we have assessed the relationship between cell surface oligosaccharides and the metastasis ability of mouse mammary tumor cell lines 67NR and 4TO7. The cell surface oligosaccharides have been analyzed using specific binding assays with some plant lectins and the metastasis ability has been studied using transwell migration and invasion assays. In addition, we investigated the role of terminal sialic acids in the metastatic potential (cell adhesion on fibronectin, cell migration and invasion) in the 4TO7 cells on treatment with neuraminidase. The cell lines used in study have different metastasis abilities in vivo - the 67NR form primary tumors, but no tumor cells are detectable in any distant tissues, while cells of the 4TO7 line are able to spread to lung. In vitro metastasis experiments have revealed higher ability of adhesion, cell migration and invasion in the 4TO7 cells than the 67NR cells. Specific lectins binding assays show that the 4TO7 cells expressed more high-mannose type, multi-antennary complex-type N-glycans, beta-1,6-GlcNAc-branching, alpha-2,6-linked sialic acids, N-acetylgalactosamine and galactosyl(beta-1,3)-N-acetylgalactosamine. Removal of sialic acids on treatment with neuraminidase decreases adhesion, but increases the migration and has shown no significant change in the invasion ability of the 4TO7 cells. The study suggests that the sialic acids are not crucial for the cell migration and invasion in the 4TO7 cells. The findings provide the new insights in understanding the role of cell surface oligosaccharides in cancer metastasis. PMID:17650582

  20. Role of hydrogen plasma pretreatment in improving passivation of the silicon surface for solar cells applications.

    PubMed

    Wang, Fengyou; Zhang, Xiaodan; Wang, Liguo; Jiang, Yanjian; Wei, Changchun; Sun, Jian; Zhao, Ying

    2014-09-10

    We have investigated the role of hydrogen plasma pretreatment in promoting silicon surface passivation, in particular examining its effects on modifying the microstructure of the subsequently deposited thin hydrogenated amorphous silicon (a-Si:H) passivation film. We demonstrate that pretreating the silicon surface with hydrogen plasma for 40 s improves the homogeneity and compactness of the a-Si:H film by enhancing precursor diffusion and thus increasing the minority carrier lifetime (τ(eff)). However, excessive pretreatment also increases the density of dangling bond defects on the surface due to etching effects of the hydrogen plasma. By varying the duration of hydrogen plasma pretreatment in fabricating silicon heterojunction solar cells based on textured substrates, we also demonstrate that, although the performance of the solar cells shows a similar tendency to that of the τ(eff) on polished wafers, the optimal duration is prolonged owing to the differences in the surface morphology of the substrates. These results suggest that the hydrogen plasma condition must be carefully regulated to achieve the optimal level of surface atomic hydrogen coverage and avoid the generation of defects on the silicon wafer. PMID:25141300

  1. Wetting Properties of Chemically Modified Surfaces: The role of hydrogen bonding

    NASA Astrophysics Data System (ADS)

    Bekele, Selemon; Tsige, Mesfin

    2015-03-01

    Many industrial processing operations involve the spreading of a liquid on a solid material. Controlling the wetting of one material by another is of crucial importance in such applications as adhesion, coating and oil recovery. A strategy often employed to control the wettability of solid surfaces is a combination of surface patterning and chemical surface modification. In order to understand the effect of surface chemistry on the wetting process, we have carried out all-atom molecular dynamics (MD) simulations of a water droplet spreading on pure and oxidized polystyrene surfaces. Our previous results show that the contact angle generally decreases with increasing oxygen concentration and there is a correlation between the spreading and hydrogen bonding. In this talk, we will present results on the structure and dynamics of the hydrogen bonds in the interfacial region between water and the polystyrene substrate. We will discuss our findings on hydrogen bond lifetimes, time correlations functions and number of hydrogen bonds per water molecule for the hydrogen bonds around the water/polystyrene interface which are found to play a role in the spreading process. This work was supported by NSF Grant DMR0847580.

  2. Magnetism of Zn-doped SnO{sub 2}: Role of surfaces

    SciTech Connect

    Pushpa, Raghani Ramanujam, Balaji

    2014-05-07

    Surface effects on the magnetization of Zn-doped SnO{sub 2} are investigated using first principles method. Magnetic behavior of Zn-doped bulk and highest and lowest energy surfaces—(001) and (110), respectively, are investigated in presence and absence of other intrinsic defects. The Zn-doped (110) and (001) surfaces of SnO{sub 2} show appreciable increase in the magnetic moment (MM) compared to Zn-doped bulk SnO{sub 2}. Formation energies of Zn defects on both the surfaces are found to be lower than those in bulk SnO{sub 2}. Zn doping favors the formation of oxygen vacancies. The density of states analysis on the Zn-doped (110) surface reveals that the spin polarization of the host band occurs primarily from p-orbitals of bridging oxygen atoms and the Zn atom itself contributes minimally. The present work provides a key understanding on the role played by the surfaces in inducing the magnetism of doped nanoparticles and thin films.

  3. Bacterial cell surface properties: role of loosely bound extracellular polymeric substances (LB-EPS).

    PubMed

    Zhao, Wenqiang; Yang, Shanshan; Huang, Qiaoyun; Cai, Peng

    2015-04-01

    This study investigated the effect of loosely bound extracellular polymeric substances (LB-EPS) on the comprehensive surface properties of four bacteria (Bacillus subtilis, Streptococcus suis, Escherichia coli and Pseudomonas putida). The removal of LB-EPS from bacterial surfaces by high-speed centrifugation (12,000×g) was confirmed by SEM images. Viability tests showed that the percentages of viable cells ranged from 95.9% to 98.0%, and no significant difference was found after treatment (P>0.05). FTIR spectra revealed the presence of phosphodiester, carboxylic, phosphate, and amino functional groups on bacteria surfaces, and the removal of LB-EPS did not alter the types of cell surface functional groups. Potentiometric titration results suggested the total site concentrations on the intact bacteria were higher than those on LB-EPS free bacteria. Most of the acidity constants (pKa) were almost identical, except the increased pKa values of phosphodiester groups on LB-EPS free S. suis and E. coli surfaces. The electrophoretic mobilities and hydrodynamic diameters of the intact and LB-EPS free bacteria were statistically unchanged (P>0.05), indicating LB-EPS had no influence on the net surface charges and size distribution of bacteria. However, LB-ESP could enhance cell aggregation processes. The four LB-EPS free bacteria all exhibited fewer hydrophobicity values (26.1-65.0%) as compared to the intact cells (47.4-69.3%), suggesting the removal of uncharged nonpolar compounds (e.g., carbohydrates) in LB-EPS. These findings improve our understanding of the changes in cell surface characterizations induced by LB-EPS, and have important implications for assessing the role of LB-EPS in bacterial adhesion and transport behaviors. PMID:25805151

  4. Bridging Adhesion of Mussel-Inspired Peptides: Role of Charge, Chain Length, and Surface Type

    PubMed Central

    2015-01-01

    The 3,4-dihydroxyphenylalanine (Dopa)-containing proteins of marine mussels provide attractive design paradigms for engineering synthetic polymers that can serve as high performance wet adhesives and coatings. Although the role of Dopa in promoting adhesion between mussels and various substrates has been carefully studied, the context by which Dopa mediates a bridging or nonbridging macromolecular adhesion to surfaces is not understood. The distinction is an important one both for a mechanistic appreciation of bioadhesion and for an intelligent translation of bioadhesive concepts to engineered systems. On the basis of mussel foot protein-5 (Mfp-5; length 75 res), we designed three short, simplified peptides (15–17 res) and one relatively long peptide (30 res) into which Dopa was enzymatically incorporated. Peptide adhesion was tested using a surface forces apparatus. Our results show that the short peptides are capable of weak bridging adhesion between two mica surfaces, but this adhesion contrasts with that of full length Mfp-5, in that (1) while still dependent on Dopa, electrostatic contributions are much more prominent, and (2) whereas Dopa surface density remains similar in both, peptide adhesion is an order of magnitude weaker (adhesion energy Ead ∼ −0.5 mJ/m2) than full length Mfp-5 adhesion. Between two mica surfaces, the magnitude of bridging adhesion was approximately doubled (Ead ∼ −1 mJ/m2) upon doubling the peptide length. Notably, the short peptides mediate much stronger adhesion (Ead ∼ −3.0 mJ/m2) between mica and gold surfaces, indicating that a long chain length is less important when different interactions are involved on each of the two surfaces. PMID:25540823

  5. Key Role of Teichoic Acid Net Charge in Staphylococcus aureus Colonization of Artificial Surfaces

    PubMed Central

    Gross, Matthias; Cramton, Sarah E.; Götz, Friedrich; Peschel, Andreas

    2001-01-01

    Staphylococcus aureus is responsible for a large percentage of infections associated with implanted biomedical devices. The molecular basis of primary adhesion to artificial surfaces is not yet understood. Here, we demonstrate that teichoic acids, highly charged cell wall polymers, play a key role in the first step of biofilm formation. An S. aureus mutant bearing a stronger negative surface charge due to the lack of d-alanine esters in its teichoic acids can no longer colonize polystyrene or glass. The mutation abrogates primary adhesion to plastic while production of the glucosamine-based polymer involved in later steps of biofilm formation is not affected. Our data suggest that repulsive electrostatic forces can lead to reduced staphylococcal biofilm formation, which could have considerable impact on the design of novel implanted materials. PMID:11292767

  6. Role of needle surface waxes in dynamic exchange of mono- and sesquiterpenes

    NASA Astrophysics Data System (ADS)

    Joensuu, Johanna; Altimir, Nuria; Hakola, Hannele; Rostás, Michael; Raivonen, Maarit; Vestenius, Mika; Aaltonen, Hermanni; Riederer, Markus; Bäck, Jaana

    2016-06-01

    Biogenic volatile organic compounds (BVOCs) produced by plants have a major role in atmospheric chemistry. The different physicochemical properties of BVOCs affect their transport within and out of the plant as well as their reactions along the way. Some of these compounds may accumulate in or on the waxy surface layer of conifer needles and participate in chemical reactions on or near the foliage surface. The aim of this work was to determine whether terpenes, a key category of BVOCs produced by trees, can be found on the epicuticles of Scots pine (Pinus sylvestris L.) and, if so, how they compare with the terpenes found in shoot emissions of the same tree. We measured shoot-level emissions of pine seedlings at a remote outdoor location in central Finland and subsequently analysed the needle surface waxes for the same compounds. Both emissions and wax extracts were clearly dominated by monoterpenes, but the proportion of sesquiterpenes was higher in the wax extracts. There were also differences in the terpene spectra of the emissions and the wax extracts. The results, therefore, support the existence of BVOC associated to the epicuticular waxes. We briefly discuss the different pathways for terpenes to reach the needle surfaces and the implications for air chemistry.

  7. Revealing the role of catechol moieties in the interactions between peptides and inorganic surfaces.

    PubMed

    Das, Priyadip; Reches, Meital

    2016-08-18

    Catechol (1,2-dihydroxy benzene) moieties are being widely used today in new adhesive technologies. Understanding their mechanism of action is therefore of high importance for developing their applications in materials science. This paper describes a single-molecule study of the interactions between catechol-related amino acid residues and a well-defined titanium dioxide (TiO2) surface. It is the first quantified measurement of the adhesion of these residues with a well-defined TiO2 surface. Single-molecule force spectroscopy measurements with AFM determined the role of different substitutions of the catechol moiety on the aromatic ring in the adhesion to the surface. These results shed light on the nature of interactions between these residues and inorganic metal oxide surfaces. This information is important for the design and fabrication of catechol-based materials such as hydrogels, coatings, and composites. Specifically, the interaction with TiO2 is important for the development of solar cells. PMID:27503417

  8. Role of the advanced IR sounder in land surface remote sensing

    NASA Astrophysics Data System (ADS)

    Knuteson, Robert O.

    2005-09-01

    A new era of Earth remote sensing began with the launch of the NASA EOS Aqua platform with the Atmospheric InfraRed Sounder (AIRS) in May 2002. The EOS AIRS instrument is the first in a series of high spectral resolution infrared spectrometers that will allow improved characterization of the global atmospheric temperature and water vapor structure. Follow-on operational sensors with similar sounding capability include the Cross-track InfraRed Sounder (CrIS) on the NPP/NPOESS satellites and the Infrared Advanced Sounding Interferometer (IASI) on the European METOP series. These so-called advanced infrared sounders will have a vital role to play in the remote sensing of land ecosystems. This paper describes how the use of Advanced IR Sounder data can be used to improve the accuracy of atmospheric corrections in the thermal IR and provide detailed information on the spectral dependence of the infrared land surface emissivity. Radiance observations from AIRS have been obtained over a large, uniform sandy desert region in the Libyan Desert suitable for evaluation of the 15-km footprints of the NASA AIRS advanced sounder. Analysis of this data indicates a spectral contrast of more than 30% between 12 mm and 9 mm in the surface infrared emissivity due to the presence of the mineral quartz with somewhat smaller contrast at 4 mm. Results of a method for separation of infrared surface emissivity and effective surface skin temperature are presented also.

  9. Role of the surface chemistry of activated carbons in dye removal from aqueous solution

    NASA Astrophysics Data System (ADS)

    Zhou, Hua-lei; Zhen, Wen-juan; Zhu, Qian; Wu, Xiao-bin; Chang, Zhi-dong; Li, Wen-jun

    2015-07-01

    Commercial activated carbons were modified by a series of chemical or physical treatments using H2O2, NH3, and heating under N2 flow without notably changing their pore structures. The resultant carbons were characterized by N2 adsorption and Bohem titration and then used to remove Ponceau 4R, methyl orange and brilliant blue from aqueous solutions. Surface chemistry was found to play a significantly different role in removing these three compounds. The removal of anionic Ponceau 4R increases with increasing carbon surface basicity due to the predominant dispersive interaction mechanism. In contrast, surface chemistry has little effect on the removal of anionic methyl orange, which can be explained by two parallel mechanisms involving electrostatic and dispersive interactions due to the basic amine group in a dye molecule. The influence of surface chemistry on the removal of amphoteric brilliant blue dye can also be ignored due to a weak interaction between the carbons and dye molecules, which is resulted from strong cohesive energy from electrostatic forces inside amphoteric dye molecules.

  10. Roles of surface chemistry on safety and electrochemistry in lithium ion batteries.

    PubMed

    Lee, Kyu Tae; Jeong, Sookyung; Cho, Jaephil

    2013-05-21

    Motivated by new applications including electric vehicles and the smart grid, interest in advanced lithium ion batteries has increased significantly over the past decade. Therefore, research in this field has intensified to produce safer devices with better electrochemical performance. Most research has focused on the development of new electrode materials through the optimization of bulk properties such as crystal structure, ionic diffusivity, and electric conductivity. More recently, researchers have also considered the surface properties of electrodes as critical factors for optimizing performance. In particular, the electrolyte decomposition at the electrode surface relates to both a lithium ion battery's electrochemical performance and safety. In this Account, we give an overview of the major developments in the area of surface chemistry for lithium ion batteries. These ideas will provide the basis for the design of advanced electrode materials. Initially, we present a brief background to lithium ion batteries such as major chemical components and reactions that occur in lithium ion batteries. Then, we highlight the role of surface chemistry in the safety of lithium ion batteries. We examine the thermal stability of cathode materials: For example, we discuss the oxygen generation from cathode materials and describe how cells can swell and heat up in response to specific conditions. We also demonstrate how coating the surfaces of electrodes can improve safety. The surface chemistry can also affect the electrochemistry of lithium ion batteries. The surface coating strategy improved the energy density and cycle performance for layered LiCoO2, xLi2MnO3·(1 - x)LiMO2 (M = Mn, Ni, Co, and their combinations), and LiMn2O4 spinel materials, and we describe a working mechanism for these enhancements. Although coating the surfaces of cathodes with inorganic materials such as metal oxides and phosphates improves the electrochemical performance and safety properties of

  11. The role of antecedent land surface conditions in North American Monsoon warm season precipitation

    NASA Astrophysics Data System (ADS)

    Zhu, C.; Lettenmaier, D. P.; Cavazos, T.

    2005-12-01

    Mexico, the previous winter and spring's precipitation influences spring soil moisture enough to explain a negative relationship with pre-monsoon early summer surface air temperature, and hence the strength of the NAM precipitation. However, these relationships are not strong enough to provide a reliable predictor of NAMS precipitation at seasonal lead times. Also, compared to land surface conditions, atmospheric circulation conditions seem to play a more important role in NAM precipitation anomalies.

  12. Roles for glycosylation of cell surface receptors involved in cellular immune recognition.

    PubMed

    Rudd, P M; Wormald, M R; Stanfield, R L; Huang, M; Mattsson, N; Speir, J A; DiGennaro, J A; Fetrow, J S; Dwek, R A; Wilson, I A

    1999-10-22

    The majority of cell surface receptors involved in antigen recognition by T cells and in the orchestration of the subsequent cell signalling events are glycoproteins. The length of a typical N-linked sugar is comparable with that of an immunoglobulin domain (30 A). Thus, by virtue of their size alone, oligosaccharides may be expected to play a significant role in the functions and properties of the cell surface proteins to which they are attached. A databank of oligosaccharide structures has been constructed from NMR and crystallographic data to aid in the interpretation of crystal structures of glycoproteins. As unambiguous electron density can usually only be assigned to the glycan cores, the remainder of the sugar is then modelled into the crystal lattice by superimposing the appropriate oligosaccharide from the database. This approach provides insights into the roles that glycosylation might play in cell surface receptors, by providing models that delineate potential close packing interactions on the cell surface. It has been proposed that the specific recognition of antigen by T cells results in the formation of an immunological synapse between the T cell and the antigen-presenting cell. The cell adhesion glycoproteins, such as CD2 and CD48, help to form a cell junction, providing a molecular spacer between opposing cells. The oligosaccharides located on the membrane proximal domains of CD2 and CD48 provide a scaffold to orient the binding faces, which leads to increased affinity. In the next step, recruitment of the peptide major histocompatibility complex (pMHC) by the T-cell receptors (TCRs) requires mobility on the membrane surface. The TCR sugars are located such that they could prevent non-specific aggregation. Importantly, the sugars limit the possible geometry and spacing of TCR/MHC clusters which precede cell signalling. We postulate that, in the final stage, the sugars could play a general role in controlling the assembly and stabilisation of the

  13. Roles of surface water areas for water and solute cycle in Hanoi city, Viet Nam

    NASA Astrophysics Data System (ADS)

    Hayashi, Takeshi; Kuroda, Keisuke; Do Thuan, An; Tran Thi Viet, Nga; Takizawa, Satoshi

    2013-04-01

    Hanoi city, the capital of Viet Nam, has developed beside the Red river. Recent rapid urbanization of this city has reduced a large number of natural water areas such as lakes, ponds and canals not only in the central area but the suburban area. Contrary, the urbanization has increased artificial water areas such as pond for fish cultivation and landscaping. On the other hand, the urbanization has induced the inflow of waste water from households and various kinds of factories to these water areas because of delay of sewerage system development. Inflow of the waste water has induced eutrophication and pollution of these water areas. Also, there is a possibility of groundwater pollution by infiltration of polluted surface water. However, the role of these water areas for water cycle and solute transport is not clarified. Therefore, this study focuses on the interaction between surface water areas and groundwater in Hanoi city to evaluate appropriate land development and groundwater resource management. We are carrying out three approaches: a) understanding of geochemical characteristics of surface water and groundwater, b) monitoring of water levels of pond and groundwater, c) sampling of soil and pond sediment. Correlation between d18O and dD of precipitation (after GNIP), the Red River (after GNIR) and the water samples of this study showed that the groundwater is composed of precipitation, the Red River and surface water that has evaporation process. Contribution of the surface water with evaporation process was widely found in the study area. As for groundwater monitoring, the Holocene aquifers at two sites were in unconfined condition in dry season and the groundwater levels in the aquifer continued to increase through rainy season. The results of isotopic analysis and groundwater level monitoring showed that the surface water areas are one of the major groundwater sources. On the other hand, concentrations of dissolved Arsenic (filtered by 0.45um) in the pore

  14. Micellisation et activité de surface des bromures de n-alkyltriméthylammonium en milieu eau-acide orthophosphorique

    NASA Astrophysics Data System (ADS)

    Ouni, S.; Hafiane, A.; Dhahbi, M.

    1998-05-01

    Measurements of superficial tension of n-alkyltrimethylammonium bromides in air/water-orthophosphoric acid interface have been made by “stripping method". Data were evaluated by approximation to the Von Szyszkowski equation. Thermodynamic parameters as (Γmax, F, A, B, Δ G^circ_A, Δ GM and CMC) at different concentrations of orhophosphoric acid (0 at 3 M) are calculted. The CMC values of the homologous series in relation to the chain length were determined. They showed a good correlation with the Klevens equation. A minimum of CMC and (-ΔGM) was observed for the n-octadecyltrimethylammonium bromide, which has been attributed to the cosolvant effect and the change of medium properties. L'adsorption, de bromure de n-alkyltriméthylammonium à l'interface air/eau-acide orthophosphorique, a été étudiée par la mesure de tension superficielle en fonction du nombre d'atomes de carbone du groupement alkyle et de la concentration en acide orthophosphorique (0 à 3 M). L'analyse des résultats a été effectuée à l'aide de l'équation de Von Szyszkowski. Les grandeurs et paramètres thermodynamiques (Γmax, F, A, B, Δ G^circ_A, Δ GM and CMC) ont été déterminés et discutés selon l'équilibre de forces de répulsion électrostatique entre les têtes polaires et d'attraction hydrophobe des chaînes aliphatiques. Les valeurs des CMC obéissent à l'équation de Klevens. Dans le cas du bromure de n-octadécyltriméthylammonium les valeurs de la CMC et de (-ΔGM) présentent un minimum, attribué au changement des propriétés du binaire eau-acide orthophosphorique.

  15. Assessing the role of Pseudomonas aeruginosa surface-active gene expression in hexadecane biodegradation in sand.

    PubMed

    Holden, P A; LaMontagne, M G; Bruce, A K; Miller, W G; Lindow, S E

    2002-05-01

    Low pollutant substrate bioavailability limits hydrocarbon biodegradation in soils. Bacterially produced surface-active compounds, such as rhamnolipid biosurfactant and the PA bioemulsifying protein produced by Pseudomonas aeruginosa, can improve bioavailability and biodegradation in liquid culture, but their production and roles in soils are unknown. In this study, we asked if the genes for surface-active compounds are expressed in unsaturated porous media contaminated with hexadecane. Furthermore, if expression does occur, is biodegradation enhanced? To detect expression of genes for surface-active compounds, we fused the gfp reporter gene either to the promoter region of pra, which encodes for the emulsifying PA protein, or to the promoter of the transcriptional activator rhlR. We assessed green fluorescent protein (GFP) production conferred by these gene fusions in P. aeruginosa PG201. GFP was produced in sand culture, indicating that the rhlR and pra genes are both transcribed in unsaturated porous media. Confocal laser scanning microscopy of liquid drops revealed that gfp expression was localized at the hexadecane-water interface. Wild-type PG201 and its mutants that are deficient in either PA protein, rhamnolipid synthesis, or both were studied to determine if the genetic potential to make surface-active compounds confers an advantage to P. aeruginosa biodegrading hexadecane in sand. Hexadecane depletion rates and carbon utilization efficiency in sand culture were the same for wild-type and mutant strains, i.e., whether PG201 was proficient or deficient in surfactant or emulsifier production. Environmental scanning electron microscopy revealed that colonization of sand grains was sparse, with cells in small monolayer clusters instead of multilayered biofilms. Our findings suggest that P. aeruginosa likely produces surface-active compounds in sand culture. However, the ability to produce surface-active compounds did not enhance biodegradation in sand culture

  16. Bicomponent lignocellulose thin films to study the role of surface lignin in cellulolytic reactions.

    PubMed

    Hoeger, Ingrid C; Filpponen, Ilari; Martin-Sampedro, Raquel; Johansson, Leena-Sisko; Osterberg, Monika; Laine, Janne; Kelley, Stephen; Rojas, Orlando J

    2012-10-01

    Ultrathin bicomponent films of cellulose and lignin derivatives were deposited on silica supports by spin coating, and after conversion into the respective polymer precursor, they were used as a model system to investigate interfacial phenomena relevant to lignocellulose biocatalysis. Film morphology, surface chemical composition, and wettability were determined by atomic force microscopy, X-ray photoelectron spectroscopy, and water contact angle, respectively. Phase separation of cellulose and lignin produced structures that resembled the cell wall of fibers and were used to monitor enzyme binding and cellulolytic reactions via quartz crystal microgravimetry. The rate and extent of hydrolysis was quantified by using kinetic models that indicated the role of the surface lignin domains in enzyme inhibition. Hydrophobic interactions between cellulases and the substrates and their critical role on irreversible adsorption were elucidated by using acetylated lignin films with different degrees of substitution. Overall, it is concluded that sensors based on the proposed ultrathin films of lignocellulose can facilitate a better understanding of the complex events that occur during bioconversion of cellulosic biomass. PMID:22954385

  17. Role of surface defects on the formation of the 2-dimensional electron gas at polar interfaces

    NASA Astrophysics Data System (ADS)

    Artacho, Emilio; Aguado-Puente, Pablo

    2014-03-01

    The discovery of a 2-dimensional electron gas (2DEG) at the interface between two insulators, LaAlO3 and SrTiO3, has fuelled a great research activity on this and similar systems in the last years. The electronic reconstruction model, typically invoked to explain the formation of the 2DEG, while being intuitive and successful on predicting fundamental aspects of this phenomenon like the critical thickness of LaAlO3, fails to explain many other experimental observations. Oxygen vacancies, on the other hand, are known to dramatically affect the physical behaviour of this system, but their role at the atomic level is far from well understood. Here we perform ab initio simulations in order to assess whether the formation of oxygen vacancies at the surface of the polar material can account for various recent experimental results that defy the current theoretical understanding of these interfaces. We simulate SrTiO3/LaAlO3 slabs with various concentrations of surface oxygen vacancies and analyze the role of the defects on the formation of the metallic interface, their electrostatic coupling with the 2DEG and the interplay with the different instabilities of the materials involved. Financial support from Spanish MINECO under grant FIS2012-37549-C05-01. Computational resources provided by the Red Espñola de Supercomputación and DIPC.

  18. The role of basic residues in the adsorption of blood proteins onto the graphene surface

    NASA Astrophysics Data System (ADS)

    Gu, Zonglin; Yang, Zaixing; Wang, Lingle; Zhou, Hong; Jimenez-Cruz, Camilo A.; Zhou, Ruhong

    2015-06-01

    With its many unique properties, graphene has shown great potential in various biomedical applications, while its biocompatibility has also attracted growing concerns. Previous studies have shown that the formation of protein-graphene corona could effectively reduce its cytotoxicity; however, the underlying molecular mechanism remains not well-understood. Herein, we use extensive molecular dynamics simulations to demonstrate that blood proteins such as bovine fibrinogen (BFG) can absorb onto the graphene surface quickly and tightly to form a corona complex. Aromatic residues contributed significantly during this adsorption process due to the strong π-π stacking interactions between their aromatic rings and the graphene sp2-carbons. Somewhat surprisingly, basic residues like arginine, also played an equally or even stronger role during this process. The strong dispersion interactions between the sidechains of these solvent-exposed basic residues and the graphene surface provide the driving force for a tight binding of these basic residues. To the best of our knowledge, this is the first study with blood proteins to show that, in addition to the aromatic residues, the basic residues also play an important role in the formation of protein-graphene corona complexes.

  19. The role of basic residues in the adsorption of blood proteins onto the graphene surface

    PubMed Central

    Gu, Zonglin; Yang, Zaixing; Wang, Lingle; Zhou, Hong; Jimenez-Cruz, Camilo A.; Zhou, Ruhong

    2015-01-01

    With its many unique properties, graphene has shown great potential in various biomedical applications, while its biocompatibility has also attracted growing concerns. Previous studies have shown that the formation of protein-graphene corona could effectively reduce its cytotoxicity; however, the underlying molecular mechanism remains not well-understood. Herein, we use extensive molecular dynamics simulations to demonstrate that blood proteins such as bovine fibrinogen (BFG) can absorb onto the graphene surface quickly and tightly to form a corona complex. Aromatic residues contributed significantly during this adsorption process due to the strong π−π stacking interactions between their aromatic rings and the graphene sp2-carbons. Somewhat surprisingly, basic residues like arginine, also played an equally or even stronger role during this process. The strong dispersion interactions between the sidechains of these solvent-exposed basic residues and the graphene surface provide the driving force for a tight binding of these basic residues. To the best of our knowledge, this is the first study with blood proteins to show that, in addition to the aromatic residues, the basic residues also play an important role in the formation of protein-graphene corona complexes. PMID:26034971

  20. The Role of the Persian Gulf in Shaping Southwest Asian Surface Climate

    NASA Astrophysics Data System (ADS)

    Pal, J. S.; Eltahir, E. A. B.

    2015-12-01

    Summer surface climate of the Persian Gulf region is characterized by hot and humid conditions. Despite such conditions - which in other regions tends to trigger moist convection - typically this region experiences clear sky conditions and very little rainfall in the summer. In this study, we customize the MIT Regional Climate Model specifically for the Southwest Asia region and apply it at a 25-km grid spacing using reanalysis boundary conditions for present-day climate (1975-2005). Specific customizations include accurate representations of surface albedo and emissivity as well as mineral dust processes, all of which improve model bias. To assess the role of the Persian Gulf in shaping the region's climate, a 30-year experiment is performed without the Persian Gulf characterized. Results suggest that observed conditions over the Persian Gulf are due to a combination of physical processes involving adiabatic and diabatic descent. First, virtually clear sky conditions, due to subsidence during summer associated with the rising air motion over the monsoon region to the east, suppress upward motion and deep convection and increase incoming solar radiation. Second, the low surface albedo of the Persian Gulf results in enhanced absorption of solar radiation and total heat flux. Third, high evaporation rates increase water vapor, and therefore trap heat at the surface via the greenhouse effect for water vapor. Fourth, the relatively shallow boundary layer over the Persian Gulf concentrates water vapor and heat close to the surface. These combined factors maximize the total flux of heat in the boundary layer and hence moist static energy over the Persian Gulf.

  1. Groundwater-surface water interaction and its role on TCE groundwater plume attenuation.

    PubMed

    Chapman, Steven W; Parker, Beth L; Cherry, John A; Aravena, Ramon; Hunkeler, Daniel

    2007-05-14

    A field investigation of a TCE plume in a surficial sand aquifer shows that groundwater-surface water interactions strongly influence apparent plume attenuation. At the site, a former industrial facility in Connecticut, depth-discrete monitoring along three cross-sections (transects) perpendicular to groundwater flow shows a persistent VOC plume extending 700 m from the DNAPL source zone to a mid-size river. Maximum TCE concentrations along a transect 280 m from the source were in the 1000s of microg/L with minimal degradation products. Beyond this, the land surface drops abruptly to a lower terrace where a shallow pond and small streams occur. Two transects along the lower terrace, one midway between the facility and river just downgradient of the pond and one along the edge of the river, give the appearance that the plume has strongly attenuated. At the river, maximum TCE concentrations in the 10s of microg/L and similar levels of its degradation product cis-DCE show direct plume discharge from groundwater to the river is negligible. Although degradation plays a role in the strong plume attenuation, the major attenuation factor is partial groundwater plume discharge to surface water (i.e. the pond and small streams), where some mass loss occurs via water-air exchange. Groundwater and stream mass discharge estimates show that more than half of the plume mass discharge crossing the first transect, before surface water interactions occur, reaches the river directly via streamflow, although river concentrations were below detection due to dilution. This study shows that groundwater and surface water concentration measurements together provide greater confidence in identifying and quantifying natural attenuation processes at this site, rather than groundwater measurements alone. PMID:17182152

  2. Critical role of surface roughness on colloid retention and release in porous media.

    PubMed

    Torkzaban, Saeed; Bradford, Scott A

    2016-01-01

    This paper examines the critical role of surface roughness (both nano- and micro-scale) on the processes of colloid retention and release in porous media under steady-state and transient chemical conditions. Nanoscale surface roughness (NSR) in the order of a few nanometers, which is common on natural solid surfaces, was incorporated into extended-DLVO calculations to quantify the magnitudes of interaction energy parameters (e.g. the energy barrier to attachment, ΔΦa , and detachment, ΔΦd , from a primary minimum). This information was subsequently used to explain the behavior of colloid retention and release in column and batch experiments under different ionic strength (IS) and pH conditions. Results demonstrated that the density and height of NSR significantly influenced the interaction energy parameters and consequently the extent and kinetics of colloid retention and release. In particular, values of ΔΦa and ΔΦd significantly decreased in the presence of NSR. Therefore, consistent with findings of column experiments, colloid retention in the primary minimum was predicted to occur at some specific locations on the sand surface, even at low IS conditions. However, NSR yielded a much weaker primary minimum interaction compared with that of smooth surfaces. Colloid release from primary minima upon decreasing IS and increasing pH was attributed to the impact of NSR on the values of ΔΦd . Pronounced differences in the amount of colloid retention in batch and column experiments indicated that primary minimum interactions were weak even at high IS conditions. Negligible colloid retention in batch experiments was attributed to hydrodynamic torques overcoming adhesive torques, whereas significant colloid retention in column experiments was attributed to nano- and micro-scale roughness which would dramatically alter the lever arms associated with hydrodynamic and adhesive torques. PMID:26512805

  3. Understanding the role of London dispersion forces in molecular surface processes

    NASA Astrophysics Data System (ADS)

    Cooper, Valentino R.

    2012-02-01

    The interactions and dynamics of molecules at surfaces and within pores are essential to many chemical processes, ranging from molecular storage to catalysis and self-assembly. A molecular level understanding of molecule-surface interactions is crucial for tuning surface/pore selectivity and reactivity. While it is clear that strong chemisorption bonds facilitate these interactions, the role of weaker van der Waals (vdW) forces, which include London dispersion and π-π stacking interactions, are often unknown or overlooked. Recent advances in density functional theory (DFT) have now made it possible to reliably account for London dispersion interactions. In this paper, I will discuss the use of one such technique, the Rutgers-Chalmers vdW non-local correlation functional,ootnotetextM. Dion, H. Rydberg, E. Schr"oder, B. I. Lundqvist and D. C. Langreth, Phys. Rev. Lett., 92, 246401 (2004)^,ootnotetextT. Thonhauser, V. R. Cooper, S. Li, A. Puzder, P. Hyldgaard, and David C. Langreth, Phys. Rev. B, 76, 125112 (2007) to demonstrate how the inclusion of London dispersion forces is critical for a truly first principles understanding of processes sensitive to molecule-surface interactions, such as the loading of H2 within porous materials and the chemisorption of organic molecules at surfaces. These works highlight the fundamental importance of London dispersion interactions in the broader context of chemical physics. This work was supported by the Department of Energy, BES, Materials Sciences and Engineering Division.ootnotetextCollaborators: Guo Li, Isaac Tamblyn, Yungok Ihm, Jun-Hyung Cho, Shixuan Du, Jeffrey B. Neaton, Hong-Jun Gao, Zhenyu Zhang, James R. Morris

  4. The role of serum proteins in Staphylococcus aureus adhesion to ethylene glycol coated surfaces.

    PubMed

    Schuster, Swen; Yu, Wenqi; Nega, Mulugeta; Chu, Ya-Yun; Zorn, Stefan; Zhang, Fajun; Götz, Friedrich; Schreiber, Frank

    2014-11-01

    Bacterial adhesion on implants is a first step in the development of chronic foreign body associated infections. Finding strategies to minimize bacterial adhesion may contribute to minimize such infections. It is known that surfaces with oligo-ethylene-glycol (EG3OMe) or poly-ethylene-glycol (PEG2k) terminations decrease unspecific protein adsorption and bacterial adhesion. However, little is known about the influence of serum and its components on bacterial adhesion. We therefore prepared two coatings on gold surface with HS-(CH2)11EG3OMe (EG3OMe) and PEG2k-thiol and studied the role of bovine serum albumin (BSA), γ-globulins, and serum on Staphylococcus aureus adhesion. While BSA and lysozyme showed no adherence even when applied at very high concentrations (100 mg/ml), γ-globulins adsorbed already from 10 mg/ml on. The adsorption of γ-globulins was, however, significantly decreased when it was mixed with BSA in a ratio of 3:1, as it is in the serum. Pretreatment of EG3OMe and PEG2k coatings with γ-globulins or serum strongly promoted adherence of S. aureus when resuspended in buffer, suggesting that γ-globulins play a pivotal role in promoting S. aureus adhesion by its IgG binding proteins; the finding that a spa-deletion mutant, lacking the IgG binding protein A, showed decreased adherence corroborated this. Similarly, when S. aureus was pretreated with serum or γ-globulins its adherence was also significantly decreased. Our findings show that particularly γ-globulins bind to the coated surfaces thus mediating adherence of S. aureus via its protein A. As pretreatment of S. aureus with serum or γ-globulins significantly decreased adherence, treatment of patients with γ-globulins before implant surgery might lower the risk of implant-associated infections. PMID:24980510

  5. Drought and Heat Waves: The Role of SST and Land Surface Feedbacks

    NASA Technical Reports Server (NTRS)

    Schubert, Siegfried

    2011-01-01

    Drought occurs on a wide range of time scales, and within a variety of different types of regional climates. At the shortest time scales it is often associated with heat waves that last only several weeks to a few months but nevertheless can have profound detrimental impacts on society (e.g., heat-related impacts on human health, desiccation of croplands, increased fire hazard), while at the longest time scales it can extend over decades and can lead to long term structural changes in many aspects of society (e.g., agriculture, water resources, wetlands, tourism, population shifts). There is now considerable evidence that sea surface temperatures (SSTs) play a leading role in the development of drought world-wide, especially at seasonal and longer time scales, though land-atmosphere feedbacks can also play an important role. At shorter (subseasonal) time scales, SSTs are less important, but land feedbacks can play a critical role in maintaining and amplifying the atmospheric conditions associated with heat waves and short-term droughts. This talk reviews our current understanding of the physical mechanisms that drive precipitation and temperature variations on subseasonal to centennial time scales. This includes an assessment of predictability, prediction skill, and user needs at all time scales.

  6. The role of airborne volcanic ash for the surface ocean biogeochemical iron-cycle: a review

    NASA Astrophysics Data System (ADS)

    Duggen, S.; Olgun, N.; Croot, P.; Hoffmann, L.; Dietze, H.; Teschner, C.

    2009-07-01

    Iron is a key micronutrient for phytoplankton growth in the surface ocean. Yet the significance of volcanism for the marine biogeochemical iron-cycle is poorly constrained. Recent studies, however, suggest that offshore deposition of airborne ash from volcanic eruptions is a way to inject significant amounts of bio-available iron into the surface ocean. Volcanic ash may be transported up to several tens of kilometres high into the atmosphere during large-scale eruptions and fine ash may encircle the globe for years, thereby reaching even the remotest and most iron-starved oceanic areas. Scientific ocean drilling demonstrates that volcanic ash layers and dispersed ash particles are frequently found in marine sediments and that therefore volcanic ash deposition and iron-injection into the oceans took place throughout much of the Earth's history. The data from geochemical and biological experiments, natural evidence and satellite techniques now available suggest that volcanic ash is a so far underestimated source for iron in the surface ocean, possibly of similar importance as aeolian dust. Here we summarise the development of and the knowledge in this fairly young research field. The paper covers a wide range of chemical and biological issues and we make recommendations for future directions in these areas. The review paper may thus be helpful to improve our understanding of the role of volcanic ash for the marine biogeochemical iron-cycle, marine primary productivity and the ocean-atmosphere exchange of CO2 and other gases relevant for climate throughout the Earth's history.

  7. Role of surfaces and interfaces in controlling the mechanical properties of metallic alloys.

    PubMed

    Lee, Won-Jong; Chia, Wen-Jui; Wang, Jinliu; Chen, Yanfeng; Vaynman, Semyon; Fine, Morris E; Chung, Yip-Wah

    2010-11-01

    This article explores the subtle effects of surfaces and interfaces on the mechanical properties of bulk metallic alloys using three examples: environmental effects on fatigue life, hydrogen embrittlement effects on the ductility of intermetallics, and the role of coherent precipitates in the toughness of steels. It is demonstrated that the marked degradation of the fatigue life of metals is due to the strong chemisorption of adsorbates on exposed slip steps that are formed during fatigue deformation. These adsorbates reduce the reversibility of slip, thus accelerating fatigue damage in a chemically active gas environment. For certain intermetallic alloys such as Ni(3)Al and Ni(3)Fe, the ductility depends on the ambient gas composition and the atomic ordering in these alloys, both of which govern the complex surface chemical reactions taking place in the vicinity of crack tips. Finally, it is shown that local stresses at a coherent precipitate-matrix interface can activate dislocation motion at low temperatures, thus improving the fracture toughness of bulk alloys such as steels at cryogenic temperatures. These examples illustrate the complex interplay between surface chemistry and mechanics, often yielding unexpected results. PMID:20527827

  8. Fluoride adsorption onto amorphous aluminum hydroxide: Roles of the surface acetate anions.

    PubMed

    Zhang, Yong-Xing; Jia, Yong

    2016-12-01

    Amorphous aluminum hydroxide with hydroxyl groups, acetate anions and chlorine anions enriched surface was synthesized, and was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption isotherms. Batch experiments were performed to study the influence of various experimental parameters such as contact time, initial fluoride concentration, temperature, pH value and the presence of competing anions on the adsorption of fluoride on amorphous aluminum hydroxide. The kinetic data was well fitted to pseudo-second-order model. The fluoride adsorption on the amorphous aluminum hydroxide can be well described by the Langmuir model, and the maximum adsorption capacity was 63.94mgg(-1) at pH 7.0. Thermodynamic parameters including the Gibbs free energy, standard enthalpy and standard entropy were calculated, and the results suggested that the adsorption of fluoride on the amorphous aluminum hydroxide was a feasible, spontaneous and exothermic process. The adsorption mechanism was revealed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis. The results suggested that the surface acetate anions and surface chlorine anions played important roles in the fluoride removal process. PMID:27565961

  9. Root surface acid phosphatases and their role in phosphorus assimilation by Eriophorum vaginatum

    SciTech Connect

    Kroehler, C.J.; Linkins, A.E.

    1988-01-01

    Eriophorum vaginatum is a dominant plant in much of the arctic tundra ecosystem where phosphorus is frequently a limiting nutrient. The mineralization of this organic phosphorus was thought to be principally controlled by microbial respiration, however, more recent work shows that extracellular soil phosphatases are the principal regulators. The existence of plant root and mycorrhizal surface phosphatases which are capable of hydrolyzing organic phosphorus compounds, suggests that soil organic phosphorus may be directly utilized by plants. Since E. vaginatum is a tussock forming sedge with a very dense annually produced rooting system which can exploit most of the tussock soil volume, its surface phosphatases may play a dominant role in organic phosphorus hydrolysis into inorganic phosphorus. Of equal significance would be the potential for this activity to contribute to the phosphorus nutrition through the coupling of phosphorus hydrolysis on the root and root uptake of the resultant inorganic phosphorus. Phosphatase activity was investigated and found to be uniformly distributed along the surface of the root. Kinetic analysis of the enzyme gave estimates of 9.23 mM for the apparent Km and 1.61 * 10/sup -3/ ..mu..moles mm-2 hr/sup -1/ for the apparent Vmax. Saturation values for E. vaginatum phosphatases are about 3 times higher than average soil solution organic phosphorus concentrations. 12 refs., 4 figs.

  10. Role of hydroxyl groups on the stability and catalytic activity of Au clusters on rutile surface

    SciTech Connect

    Kent, Paul R

    2011-01-01

    Hydroxyls are present as surface terminations of transition metal oxides under ambient conditions and may modify the properties of supported catalysts. We perform first-principles density functional theory calculations to investigate the role of hydroxyls on the catalytic activity of supported gold clusters on TiO{sub 2} (rutile). We find that they have a long-range effect increasing the adhesion of gold clusters on rutile. While hydroxyls make one gold atom more electronegative, a more complex charge-transfer scenario is observed on larger clusters which are important for catalytic applications. This enhances the molecular adsorption and coadsorption energies of CO and O{sub 2}, thereby increasing the catalytic activity of gold clusters for CO oxidation, consistent with reported experiments. Hydroxyls at the interface between gold and rutile surface are most important to this process, even when not directly bound to gold. As such, accurate models of catalytic processes on gold and other catalysts should include the effect of surface hydroxyls.

  11. Role of LiCoO2 Surface Terminations in Oxygen Reduction and Evolution Kinetics

    DOE PAGESBeta

    Han, Binghong; Qian, Danna; Risch, Marcel; Chi, Miaofang; Meng, Ying Shirley; Yang, Shao-horn

    2015-03-22

    Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities of LiCoO2 nanorods with sizes in the range from 9 to 40 nm were studied in alkaline solution. The sides of these nanorods were terminated with low-index surfaces such as (003) while the tips were terminated largely with high-index surfaces such as (104) as revealed by high-resolution transmission electron microscopy. Electron energy loss spectroscopy demonstrated that low-spin Co3+ prevailed on the sides, while the tips exhibited predominantly high- or intermediate-spin Co3+. We correlated the electronic and atomic structure to higher specific ORR and OER activities at the tips as comparedmore » to the sides, which was accompanied by more facile redox of Co2+/3+ and higher charge transferred per unit area. These findings highlight the critical role of surface terminations and electronic structures of transition metal oxides on the ORR and OER activity.« less

  12. Solar Wind Sputtering of Lunar Surface Materials: Role and Some Possible Implications of Potential Sputtering

    NASA Technical Reports Server (NTRS)

    Barghouty, A. F.; Adams, J. H., Jr.; Meyer, F.; Reinhold, c.

    2010-01-01

    Solar-wind induced sputtering of the lunar surface includes, in principle, both kinetic and potential sputtering. The role of the latter mechanism, however, in many focused studies has not been properly ascertained due partly to lack of data but can also be attributed to the assertion that the contribution of solar-wind heavy ions to the total sputtering is quite low due to their low number density compared to solar-wind protons. Limited laboratory measurements show marked enhancements in the sputter yields of slow-moving, highly-charged ions impacting oxides. Lunar surface sputtering yields are important as they affect, e.g., estimates of the compositional changes in the lunar surface, its erosion rate, as well as its contribution to the exosphere as well as estimates of hydrogen and water contents. Since the typical range of solar-wind ions at 1 keV/amu is comparable to the thickness of the amorphous rim found on lunar soil grains, i.e. few 10s nm, lunar simulant samples JSC-1A AGGL are specifically enhanced to have such rims in addition to the other known characteristics of the actual lunar soil particles. However, most, if not all laboratory studies of potential sputtering were carried out in single crystal targets, quite different from the rim s amorphous structure. The effect of this structural difference on the extent of potential sputtering has not, to our knowledge, been investigated to date.

  13. Role of Surface Area, Primary Particle Size, and Crystal Phase on Titanium Dioxide Nanoparticle Dispersion Properties

    PubMed Central

    2011-01-01

    Characterizing nanoparticle dispersions and understanding the effect of parameters that alter dispersion properties are important for both environmental applications and toxicity investigations. The role of particle surface area, primary particle size, and crystal phase on TiO2 nanoparticle dispersion properties is reported. Hydrodynamic size, zeta potential, and isoelectric point (IEP) of ten laboratory synthesized TiO2 samples, and one commercial Degussa TiO2 sample (P25) dispersed in different solutions were characterized. Solution ionic strength and pH affect titania dispersion properties. The effect of monovalent (NaCl) and divalent (MgCl2) inert electrolytes on dispersion properties was quantified through their contribution to ionic strength. Increasing titania particle surface area resulted in a decrease in solution pH. At fixed pH, increasing the particle surface area enhanced the collision frequency between particles and led to a higher degree of agglomeration. In addition to the synthesis method, TiO2 isoelectric point was found to be dependent on particle size. As anatase TiO2 primary particle size increased from 6 nm to 104 nm, its IEP decreased from 6.0 to 3.8 that also results in changes in dispersion zeta potential and hydrodynamic size. In contrast to particle size, TiO2 nanoparticle IEP was found to be insensitive to particle crystal structure. PMID:27502650

  14. Role of surface-active elements during keyhole-mode laser welding

    NASA Astrophysics Data System (ADS)

    Ribic, B.; Tsukamoto, S.; Rai, R.; DebRoy, T.

    2011-12-01

    During high power density laser welding of mild steel, the keyhole depth, liquid metal flow, weld geometry and weld integrity are affected by base-metal sulfur content and oxygen (O2) present in the atmosphere or shielding gas. The role of these surface-active elements during keyhole-mode laser welding of steels is not well understood. In order to better understand their effects, welding of mild steel specimens containing various concentrations of oxygen and sulfur are examined. In addition, a numerical model is used to evaluate the influence of the surface-active elements on heat transfer and fluid flow in keyhole-mode laser welding. Increase in base-metal sulfur concentration or O2 content of shielding gas results in decreased weld widths. Sulfur results in a negligible increase in penetration depth whereas the presence of O2 in shielding gas significantly affects the weld penetration. It has earlier been proposed that oxygen, if present in the shielding gas, can get introduced into the weld pool resulting in formation of carbon monoxide (CO) at the keyhole surface and additional pressure from CO can result in increased penetration. Numerical modelling has been used in this work to understand the effects of formation of CO on the keyhole and weld geometries.

  15. The Role of Grain Surface Reactions in the Chemistry of Star Forming Regions

    NASA Technical Reports Server (NTRS)

    Kress, M. E.; Tielens, A. G. G. M.; Roberge, W. G.

    1998-01-01

    The importance of reactions at the surfaces of dust grains has long been recognized to be one of the two main chemical processes that form molecules in cold, dark interstellar clouds where simple, saturated (fully-hydrogenated) molecules such as H2 water, methanol, H2CO, H2S, ammonia and CH4 are present in quantities far too high to be consistent with their extremely low gas phase formation rates. In cold dark regions of interstellar space, dust grains provide a substrate onto which gas-phase species can accrete and react. Grains provide a "third body" or a sink for the energy released in the exothermic reactions that form chemical bonds. In essence, the surfaces of dust grains open up alternative reaction pathways to form observed molecules whose abundances cannot be explained with gas-phase chemistry alone. This concept is taken one step further in this work: instead of merely acting as a substrate onto which radicals and molecules may physically adsorb, some grains may actively participate in the reaction itself, forming chemical bonds with the accreting species. Until recently, surface chemical reactions had not been thought to be important in warm circumstellar media because adspecies rapidly desorb from grains at very low temperatures; thus, the residence times of molecules and radicals on the surface of grains at all but the lowest temperatures are far too short to allow these reactions to occur. However, if the adspecies could adsorb more strongly, via a true chemical bond with surfaces of some dust grains, then grain surface reactions will play an important role in warm circumstellar regions as well. In this work, the surface-catalyzed reaction CO + 3 H2 yields CH4 + H2O is studied in the context that it may be very effective at converting the inorganic molecule CO into the simplest organic compound, methane. H2 and CO are the most abundant molecules in space, and the reaction converting them to methane, while kinetically inhibited in the gas phase under

  16. Numerical study on the deposition rate of hematite particle on polypropylene walls: role of surface roughness.

    PubMed

    Henry, Christophe; Minier, Jean-Pierre; Lefèvre, Grégory; Hurisse, Olivier

    2011-04-19

    In this paper, we investigate the deposition of nanosized and microsized particles on rough surfaces under electrostatic repulsive conditions in an aqueous suspension. This issue arises in the general context of modeling particle deposition which, in the present work, is addressed as a two-step process: first particles are transported by the motions of the flow toward surfaces and, second, in the immediate vicinity of the walls, the forces between the incoming particles and the walls are determined using the classical DLVO theory. The interest of this approach is to take into account both hydrodynamical and physicochemical effects within a single model. Satisfactory results have been obtained in attractive conditions but some discrepancies have been revealed in the case of repulsive conditions, in line with other studies which have noted differences between predictions based on the DLVO theory and experimental measurements for similar repulsive conditions. Consequently, the aim of the present work is to focus on this particular range and, more specifically, to assess the influence of surface roughness on the DLVO potential energy. For this purpose, we introduce a new simplified model of surface roughness where spherical protruding asperities are placed randomly on a smooth plate. On the basis of this geometrical description, approximate DLVO expressions are used and numerical calculations are performed. We first highlight the existence of a critical asperity size which brings about the highest reduction of the DLVO interaction energy. Then, the influence of the surface covered by the asperities is investigated as well as retardation effects which can play a role in the reduction of the interaction energy. Finally, by considering the random distribution of the energy barrier of the DLVO potential due to the random geometrical configurations, the overall effect of surface roughness is demonstrated with one application of the complete deposition model in an industrial

  17. Short-term inactivation rates of selected Gram-positive and Gram-negative bacteria attached to metal oxide mineral surfaces: role of solution and surface chemistry.

    PubMed

    Asadishad, Bahareh; Ghoshal, Subhasis; Tufenkji, Nathalie

    2013-06-01

    Metal oxides such as ferric or aluminum oxides can play an important role in the retention of bacteria in granular aquatic environments; however, their role in bacterial inactivation is not well understood. Herein, we examined the role of water chemistry and surface chemistry on the short-term inactivation rates of three bacteria when adhered to surfaces. To evaluate the role of water chemistry on the inactivation of attached bacteria, the loss in membrane integrity of bacteria attached to an iron oxide (Fe2O3) surface was measured over a range of water ionic strengths of either monovalent or divalent salts in the absence of a growth substrate. The influence of surface chemistry on the inactivation of attached bacteria was examined by measuring the loss in membrane integrity of cells attached to three surfaces (SiO2, Fe2O3, and Al2O3) at a specific water chemistry (10 mM KCl). Bacteria were allowed to attach onto the SiO2 or metal oxide coated slides mounted in a parallel-plate flow cell, and their inactivation rate (loss in membrane integrity) was measured directly without removing the cells from the surface and without disturbing the system. X-ray photoelectron spectroscopy analysis revealed a high correlation between the amounts of C-metal or O-metal bonds and the corresponding bacterial inactivation rates for each surface. Finally, for all three surfaces, a consistent increase in inactivation rate was observed with the type of bacterium in the order: Enterococcus faecalis, Escherichia coli O157:H7, and Escherichia coli D21f2. PMID:23679056

  18. The role of land-surface processes in modulating the Indian monsoon annual cycle

    NASA Astrophysics Data System (ADS)

    Bollasina, Massimo A.; Ming, Yi

    2013-11-01

    The annual cycle of solar radiation, together with the resulting land-ocean differential heating, is traditionally considered the dominant forcing controlling the northward progression of the Indian monsoon. This study makes use of a state-of-the-art atmospheric general circulation model in a realistic configuration to conduct “perpetual” experiments aimed at providing new insights into the role of land-atmosphere processes in modulating the annual cycle of precipitation over India. The simulations are carried out at three important stages of the monsoon cycle: March, May, and July. Insolation and SSTs are held fixed at their respective monthly mean values, thus eliminating any external seasonal forcing. In the perpetual May experiment both precipitation and circulation are able to considerably evolve only by regional internal land-atmosphere processes and the mediation of soil hydrology. A large-scale equilibrium state is reached after approximately 270 days, closely resembling mid-summer climatological conditions. As a result, despite the absence of external forcing, intense and widespread rains over India are able to develop in the May-like state. The interaction between soil moisture and circulation, modulated by surface heating over the northwestern semi-arid areas, determines a slow northwestward migration of the monsoon, a crucial feature for the existence of desert regions to the west. This also implies that the land-atmosphere system in May is far from being in equilibrium with the external forcing. The inland migration of the precipitation front comprises a succession of large-scale 35-50 day coupled oscillations between soil moisture, precipitation, and circulation. The oscillatory regime is self-sustained and entirely due to the internal dynamics of the system. In contrast to the May case, minor changes in the land-atmosphere system are found when the model is initialized in March and, more surprisingly, in July, the latter case further emphasizing

  19. Role of Vibrio cholerae O139 surface polysaccharides in intestinal colonization.

    PubMed

    Nesper, Jutta; Schild, Stefan; Lauriano, Crystal M; Kraiss, Anita; Klose, Karl E; Reidl, Joachim

    2002-11-01

    Since the first occurrence of O139 Vibrio cholerae as a cause of cholera epidemics, this serogroup has been investigated intensively, and it has been found that its pathogenicity is comparable to that of O1 El Tor strains. O139 isolates express a thin capsule, composed of a polymer of repeating units structurally identical to the lipopolysaccharide (LPS) O side chain. In this study, we investigated the role of LPS O side chain and capsular polysaccharide (CPS) in intestinal colonization by with genetically engineered mutants. We constructed CPS-negative, CPS/LPS O side chain-negative, and CPS-positive/LPS O side chain-negative mutants. Furthermore, we constructed two mutants with defects in LPS core oligosaccharide (OS) assembly. Loss of LPS O side chain or CPS resulted in a approximately 30-fold reduction in colonization of the infant mouse small intestine, indicating that the presence of both LPS O side chain and CPS is important during the colonization process. The strain lacking both CPS and LPS O side chain and a CPS-positive, LPS O side chain-negative core OS mutant were both essentially unable to colonize. To characterize the role of surface polysaccharides in survival in the host intestine, resistance to several antimicrobial substances was investigated in vitro. These investigations revealed that the presence of CPS protects the cell against attack of the complement system and that an intact core OS is necessary for survival in the presence of bile. PMID:12379674

  20. Unsaturated phosphatidylcholines lining on the surface of cartilage and its possible physiological roles

    PubMed Central

    Chen, Yi; Crawford, Ross W; Oloyede, Adekunle

    2007-01-01

    Background Evidence has strongly indicated that surface-active phospholipid (SAPL), or surfactant, lines the surface of cartilage and serves as a lubricating agent. Previous clinical study showed that a saturated phosphatidylcholine (SPC), dipalmitoyl-phosphatidylcholine (DPPC), was effective in the treatment of osteoarthritis, however recent studies suggested that the dominant SAPL species at some sites outside the lung are not SPC, rather, are unsaturated phosphatidylcholine (USPC). Some of these USPC have been proven to be good boundary lubricants by our previous study, implicating their possible important physiological roles in joint if their existence can be confirmed. So far, no study has been conducted to identify the whole molecule species of different phosphatidylcholine (PC) classes on the surface of cartilage. In this study we identified the dominant PC molecule species on the surface of cartilage. We also confirmed that some of these PC species possess a property of semipermeability. Methods HPLC was used to analyse the PC profile of bovine cartilage samples and comparisons of DPPC and USPC were carried out through semipermeability tests. Results It was confirmed that USPC are the dominant SAPL species on the surface of cartilage. In particular, they are Dilinoleoyl-phosphatidylcholine (DLPC), Palmitoyl-linoleoyl-phosphatidylcholine, (PLPC), Palmitoyl-oleoyl-phosphatidylcholine (POPC) and Stearoyl-linoleoyl-phosphatidylcholine (SLPC). The relative content of DPPC (a SPC) was only 8%. Two USPC, PLPC and POPC, were capable of generating osmotic pressure that is equivalent to that by DPPC. Conclusion The results from the current study confirm vigorously that USPC is the endogenous species inside the joint as against DPPC thereby confirming once again that USPC, and not SPC, characterizes the PC species distribution at non-lung sites of the body. USPC not only has better anti-friction and lubrication properties than DPPC, they also possess a level of

  1. On the role of nighttime meteorology in modeling dispersion of near surface emissions in urban areas

    NASA Astrophysics Data System (ADS)

    Venkatram, Akula; Cimorelli, Alan J.

    This paper examines the role of meteorology in linking near surface emissions of particulate matter and associated ambient concentrations in urban areas. The examination is conducted with two models: a steady state model based on urban dispersion models developed earlier, and an unsteady state model that accounts for time varying meteorological and emission inputs. After conducting sensitivity studies with the models, they are applied in Pune, India to (a) check consistency between estimates of surface emissions of particulate matter (with aerodynamic diameters of less than 10μm, referred to as PM 10) and observed ambient concentrations and (b) identify the variables that govern air quality. Results from the modeling exercise indicate that (1) nighttime meteorology governs both hourly as well as 24 h averaged concentrations and (2) because the wind speeds in urban areas are typically low, concentration estimates from the steady state model differ substantially from those of the unsteady state model during the nighttime hours both in magnitude and in timing of the peaks; however, the difference between the 24 h averaged concentrations from the two models is less than 5% for the cases considered here. Because our understanding of nighttime meteorology in urban areas is limited, there is a need for experimental programs to relate the diurnal variation of concentrations with associated meteorology, especially during the night.

  2. Role of Surface Precipitation in Copper Sorption by the Hydrous Oxides of Iron and Aluminum.

    PubMed

    Karthikeyan; Elliott; Chorover

    1999-01-01

    Isotherms were developed at pH 6.9 for adsorption (ADS) and coprecipitation (CPT) of Cu by hydrous oxides of Fe (HFO) and Al (HAO) to study the role of sorbate/sorbent ratio in metal cation removal. For low sorbate/sorbent conditions, HFO had a higher Cu retention capacity than HAO regardless of contact methodology. For either oxide, CPT was consistently more effective than ADS in removing Cu from solution. At high sorbate/sorbent ratios, surface precipitation dominates and the oxide's net cation retention capacity depends on the nature and solubility of the precipitate formed at the oxide-water interface. X-ray diffraction patterns and isotherms of HAO for both ADS and CPT suggest formation of a solid solution [e.g., CuAl2O4(s)] with dramatically lower solubility than Cu(OH)2(s) precipitated in bulk solution. In contrast, Cu precipitated on the HFO surface exhibited a solubility comparable to the bulk precipitated Cu(OH)2(s). Therefore, at high sorbate/sorbent ratios, HAO has a higher Cu "apparent" sorption capacity than HFO. The relative utility of these oxides as metal scavengers thus depends markedly on sorbate/sorbent conditions. Copyright 1999 Academic Press. PMID:9878138

  3. Biofilm Formation by Psychrobacter arcticus and the Role of a Large Adhesin in Attachment to Surfaces

    PubMed Central

    Koid, Cassandra; Tiedje, James M.; Schultzhaus, Janna N.

    2013-01-01

    Psychrobacter arcticus strain 273-4, an isolate from a Siberian permafrost core, is capable of forming biofilms when grown in minimal medium under laboratory conditions. Biofilms form at 4 to 22°C when acetate is supplied as the lone carbon source and with 1 to 7% sea salt. P. arcticus is also capable of colonizing quartz sand. Transposon mutagenesis identified a gene important for biofilm formation by P. arcticus. Four transposon mutants were mapped to a 20.1-kbp gene, which is predicted to encode a protein of 6,715 amino acids (Psyc_1601). We refer to this open reading frame as cat1, for cold attachment gene 1. The cat1 mutants are unable to form biofilms at levels equivalent to that of the wild type, and there is no impact on the planktonic growth characteristics of the strains, indicating a specific role in biofilm formation. Through time course studies of the static microtiter plate assay, we determined that cat1 mutants are unable to form biofilms equivalent to that of the wild type under all conditions tested. In flow cell experiments, cat1 mutants initially are unable to attach to the surface. Over time, however, they form microcolonies, an architecture very different from that produced by wild-type biofilms. Our results demonstrate that Cat1 is involved in the initial stages of bacterial attachment to surfaces. PMID:23603675

  4. In-cell thermodynamics and a new role for protein surfaces.

    PubMed

    Smith, Austin E; Zhou, Larry Z; Gorensek, Annelise H; Senske, Michael; Pielak, Gary J

    2016-02-16

    There is abundant, physiologically relevant knowledge about protein cores; they are hydrophobic, exquisitely well packed, and nearly all hydrogen bonds are satisfied. An equivalent understanding of protein surfaces has remained elusive because proteins are almost exclusively studied in vitro in simple aqueous solutions. Here, we establish the essential physiological roles played by protein surfaces by measuring the equilibrium thermodynamics and kinetics of protein folding in the complex environment of living Escherichia coli cells, and under physiologically relevant in vitro conditions. Fluorine NMR data on the 7-kDa globular N-terminal SH3 domain of Drosophila signal transduction protein drk (SH3) show that charge-charge interactions are fundamental to protein stability and folding kinetics in cells. Our results contradict predictions from accepted theories of macromolecular crowding and show that cosolutes commonly used to mimic the cellular interior do not yield physiologically relevant information. As such, we provide the foundation for a complete picture of protein chemistry in cells. PMID:26755596

  5. The role of surface charge in cellular uptake and cytotoxicity of medical nanoparticles

    PubMed Central

    Fröhlich, Eleonore

    2012-01-01

    Many types of nanoparticles (NPs) are tested for use in medical products, particularly in imaging and gene and drug delivery. For these applications, cellular uptake is usually a prerequisite and is governed in addition to size by surface characteristics such as hydrophobicity and charge. Although positive charge appears to improve the efficacy of imaging, gene transfer, and drug delivery, a higher cytotoxicity of such constructs has been reported. This review summarizes findings on the role of surface charge on cytotoxicity in general, action on specific cellular targets, modes of toxic action, cellular uptake, and intracellular localization of NPs. Effects of serum and intercell type differences are addressed. Cationic NPs cause more pronounced disruption of plasma-membrane integrity, stronger mitochondrial and lysosomal damage, and a higher number of autophagosomes than anionic NPs. In general, nonphagocytic cells ingest cationic NPs to a higher extent, but charge density and hydrophobicity are equally important; phagocytic cells preferentially take up anionic NPs. Cells do not use different uptake routes for cationic and anionic NPs, but high uptake rates are usually linked to greater biological effects. The different uptake preferences of phagocytic and nonphagocytic cells for cationic and anionic NPs may influence the efficacy and selectivity of NPs for drug delivery and imaging. PMID:23144561

  6. Roles of additives and surface control in slurry atomization. Final project report

    SciTech Connect

    Tsai, S.C.

    1992-12-31

    This project studies the rheology and airblast atomization of micronized coal slurries. Its major objectives are (1) to promote further understanding of the mechanisms and the roles of additives in airblast atomization of coal water slurry (CWS), and (2) to investigate the impacts of coal particle surface properties and interparticle forces on CWS rheology. We have found that the flow behavior index (n) of a suspension (or slurry) is determined by the relative importance of the interparticle van der Waals attraction and the interparticle electrostatic repulsion. The interparticle attraction, measured by the Hamaker constant scaled to the thermal energy at 25{degrees}C (A/kT), causes particle aggregation, which breaks down at high shear rates, and thus leads to slurry pseudoplastic behavior (n< 1). At a constant particle volume fraction and surface charge density (qualitatively measured by the zeta potential in deionized water), n decreases linearly as A/kT increases. The relative viscosity of the pseudoplastic suspension with respect to that of the suspending liquid is found to be independent of particle density and correlate well with the particle Peclet number which equals the particle diffusional relaxation time multiplied by shear rate. Specifically, the relative viscosities of the pseudoplastic glycerol/water coal slurry and the ethylene glycol/glycerol sand slurry, at same volume fractions as well as similar particle size distributions and liquid viscosities, as functions of the particle Peclet number fall along the same line.

  7. In-cell thermodynamics and a new role for protein surfaces

    PubMed Central

    Smith, Austin E.; Zhou, Larry Z.; Gorensek, Annelise H.; Senske, Michael; Pielak, Gary J.

    2016-01-01

    There is abundant, physiologically relevant knowledge about protein cores; they are hydrophobic, exquisitely well packed, and nearly all hydrogen bonds are satisfied. An equivalent understanding of protein surfaces has remained elusive because proteins are almost exclusively studied in vitro in simple aqueous solutions. Here, we establish the essential physiological roles played by protein surfaces by measuring the equilibrium thermodynamics and kinetics of protein folding in the complex environment of living Escherichia coli cells, and under physiologically relevant in vitro conditions. Fluorine NMR data on the 7-kDa globular N-terminal SH3 domain of Drosophila signal transduction protein drk (SH3) show that charge–charge interactions are fundamental to protein stability and folding kinetics in cells. Our results contradict predictions from accepted theories of macromolecular crowding and show that cosolutes commonly used to mimic the cellular interior do not yield physiologically relevant information. As such, we provide the foundation for a complete picture of protein chemistry in cells. PMID:26755596

  8. Les effets des interfaces sur les proprietes magnetiques et de transport des multicouches nickel/iron et cobalt/silver

    NASA Astrophysics Data System (ADS)

    Veres, Teodor

    Cette these est consacree a l'etude de l'evolution structurale des proprietes magnetiques et de transport des multicouches Ni/Fe et nanostructures a base de Co et de l'Ag. Dans une premiere partie, essentiellement bibliographique, nous introduisons quelques concepts de base relies aux proprietes magnetiques et de transport des multicouches metalliques. Ensuite, nous presentons une breve description des methodes d'analyse des resultats. La deuxieme partie est consacree a l'etude des proprietes magnetiques et de transport des multicouches ferromagnetiques/ferromagnetiques Ni/Fe. Nous montrerons qu'une interpretation coherente de ces proprietes necessite la prise en consideration des effets des interfaces. Nous nous attacherons a mettre en evidence, a evaluer et a etudier les effets de ces interfaces ainsi que leur evolution, et ce, suite a des traitements thermiques tel que le depot a temperature elevee et l'irradiation ionique. Les analyses correlees de la structure et de la magnetoresistance nous permettront d'emettre des conclusions sur l'influence des couches tampons entre l'interface et le substrat ainsi qu'entre les couches elles-memes sur le comportement magnetique des couches F/F. La troisieme partie est consacree aux systemes a Magneto-Resistance Geante (MRG) a base de Co et Ag. Nous allons etudier l'evolution de la microstructure suite a l'irradiation avec des ions Si+ ayant une energie de 1 MeV, ainsi que les effets de ces changements sur le comportement magnetique. Cette partie debutera par l'analyse des proprietes d'une multicouche hybride, intermediaire entre les multicouches et les materiaux granulaires. Nous analyserons a l'aide des mesures de diffraction, de relaxation superparamagnetique et de magnetoresistance, les evolutions structurales produites par l'irradiation ionique. Nous etablirons des modeles qui nous aideront a interpreter les resultats pour une serie des multicouches qui couvrent un large eventail de differents comportements magnetiques

  9. The role of airborne volcanic ash for the surface ocean biogeochemical iron-cycle: a review

    NASA Astrophysics Data System (ADS)

    Duggen, S.; Olgun, N.; Croot, P.; Hoffmann, L.; Dietze, H.; Delmelle, P.; Teschner, C.

    2010-03-01

    Iron is a key micronutrient for phytoplankton growth in the surface ocean. Yet the significance of volcanism for the marine biogeochemical iron-cycle is poorly constrained. Recent studies, however, suggest that offshore deposition of airborne ash from volcanic eruptions is a way to inject significant amounts of bio-available iron into the surface ocean. Volcanic ash may be transported up to several tens of kilometers high into the atmosphere during large-scale eruptions and fine ash may stay aloft for days to weeks, thereby reaching even the remotest and most iron-starved oceanic regions. Scientific ocean drilling demonstrates that volcanic ash layers and dispersed ash particles are frequently found in marine sediments and that therefore volcanic ash deposition and iron-injection into the oceans took place throughout much of the Earth's history. Natural evidence and the data now available from geochemical and biological experiments and satellite techniques suggest that volcanic ash is a so far underestimated source for iron in the surface ocean, possibly of similar importance as aeolian dust. Here we summarise the development of and the knowledge in this fairly young research field. The paper covers a wide range of chemical and biological issues and we make recommendations for future directions in these areas. The review paper may thus be helpful to improve our understanding of the role of volcanic ash for the marine biogeochemical iron-cycle, marine primary productivity and the ocean-atmosphere exchange of CO2 and other gases relevant for climate in the Earth's history.

  10. The role of surfaces, chemical interfaces, and disorder on plutonium incorporation in pyrochlores.

    PubMed

    Perriot, Romain; Dholabhai, Pratik P; Uberuaga, Blas P

    2016-08-17

    Pyrochlores, a class of complex oxides with formula A2B2O7, are one of the candidates for nuclear waste encapsulation, due to the natural occurrence of actinide-bearing pyrochlore minerals and laboratory observations of high radiation tolerance. In this work, we use atomistic simulations to determine the role of surfaces, chemical interfaces, and cation disorder on the plutonium immobilization properties of pyrochlores as a function of pyrochlore chemistry. We find that both Pu(3+) and Pu(4+) segregate to the surface for the four low-index pyrochlore surfaces considered, and that the segregation energy varies with the chemistry of the compound. We also find that pyrochlore/pyrochlore bicrystals A2B2O7/A2'B2'O7 can be used to immobilize Pu(3+) and Pu(4+) either in the same or separate phases of the compound, depending on the chemistry of the material. Finally, we find that Pu(4+) segregates to the disordered phase of an order/disorder bicrystal, driven by the occurrence of local oxygen-rich environments. However, Pu(3+) is weakly sensitive to the oxygen environment, and therefore only slightly favors the disordered phase. This behavior suggests that, at some concentration, Pu incorporation can destabilize the pyrochlore structure. Together, these results provide new insight into the ability of pyrochlore compounds to encapsulate Pu and suggest new considerations in the development of waste forms based on pyrochlores. In particular, the phase structure of a multi-phase pyrochlore composite can be used to independently getter decay products based on their valence and size. PMID:27480791

  11. Role of integrin subunits in mesenchymal stem cell differentiation and osteoblast maturation on graphitic carbon-coated microstructured surfaces.

    PubMed

    Olivares-Navarrete, Rene; Rodil, Sandra E; Hyzy, Sharon L; Dunn, Ginger R; Almaguer-Flores, Argelia; Schwartz, Zvi; Boyan, Barbara D

    2015-05-01

    Surface roughness, topography, chemistry, and energy promote osteoblast differentiation and increase osteogenic local factor production in vitro and bone-to-implant contact in vivo, but the mechanisms involved are not well understood. Knockdown of integrin heterodimer alpha2beta1 (α2β1) blocks the osteogenic effects of the surface, suggesting signaling by this integrin homodimer is required. The purpose of the present study was to separate effects of surface chemistry and surface structure on integrin expression by coating smooth or rough titanium (Ti) substrates with graphitic carbon, retaining surface morphology but altering surface chemistry. Ti surfaces (smooth [Ra < 0.4 μm], rough [Ra ≥ 3.4 μm]) were sputter-coated using a magnetron sputtering system with an ultrapure graphite target, producing a graphitic carbon thin film. Human mesenchymal stem cells and MG63 osteoblast-like cells had higher mRNA for integrin subunits α1, α2, αv, and β1 on rough surfaces in comparison to smooth, and integrin αv on graphitic-carbon-coated rough surfaces in comparison to Ti. Osteogenic differentiation was greater on rough surfaces in comparison to smooth, regardless of chemistry. Silencing integrins β1, α1, or α2 decreased osteoblast maturation on rough surfaces independent of surface chemistry. Silencing integrin αv decreased maturation only on graphitic carbon-coated surfaces, not on Ti. These results suggest a major role of the integrin β1 subunit in roughness recognition, and that integrin alpha subunits play a major role in surface chemistry recognition. PMID:25770999

  12. Role of Integrin Subunits in Mesenchymal Stem Cell Differentiation and Osteoblast Maturation on Graphitic Carbon-coated Microstructured Surfaces

    PubMed Central

    Olivares-Navarrete, Rene; Rodil, Sandra E.; Hyzy, Sharon L.; Dunn, Ginger R.; Almaguer-Flores, Argelia; Schwartz, Zvi; Boyan, Barbara D.

    2015-01-01

    Surface roughness, topography, chemistry, and energy promote osteoblast differentiation and increase osteogenic local factor production in vitro and bone-to-implant contact in vivo, but the mechanisms involved are not well understood. Knockdown of integrin heterodimer alpha2beta1 (α2β1) blocks the osteogenic effects of the surface, suggesting signaling by this integrin homodimer is required. The purpose of the present study was to separate effects of surface chemistry and surface structure on integrin expression by coating smooth or rough titanium (Ti) substrates with graphitic carbon, retaining surface morphology but altering surface chemistry. Ti surfaces (smooth [Ra<0.4μm], rough [Ra≥3.4μm]) were sputter-coated using a magnetron sputtering system with an ultrapure graphite target, producing a graphitic carbon thin film. Human mesenchymal stem cells and MG63 osteoblast-like cells had higher mRNA for integrin subunits α1, α2, αv, and β1 on rough surfaces in comparison to smooth, and integrin αv on graphitic-carbon-coated rough surfaces in comparison to Ti. Osteogenic differentiation was greater on rough surfaces in comparison to smooth, regardless of chemistry. Silencing integrins β1, α1, or α2 decreased osteoblast maturation on rough surfaces independent of surface chemistry. Silencing integrin αv decreased maturation only on graphitic carbon-coated surfaces, not on Ti. These results suggest a major role of the integrin β1 subunit in roughness recognition, and that integrin alpha subunits play a major role in surface chemistry recognition. PMID:25770999

  13. Catalytic Activity and Stability of Oxides: The Role of Near-Surface Atomic Structures and Compositions.

    PubMed

    Feng, Zhenxing; Hong, Wesley T; Fong, Dillon D; Lee, Yueh-Lin; Yacoby, Yizhak; Morgan, Dane; Shao-Horn, Yang

    2016-05-17

    Electrocatalysts play an important role in catalyzing the kinetics for oxygen reduction and oxygen evolution reactions for many air-based energy storage and conversion devices, such as metal-air batteries and fuel cells. Although noble metals have been extensively used as electrocatalysts, their limited natural abundance and high costs have motivated the search for more cost-effective catalysts. Oxides are suitable candidates since they are relatively inexpensive and have shown reasonably high activity for various electrochemical reactions. However, a lack of fundamental understanding of the reaction mechanisms has been a major hurdle toward improving electrocatalytic activity. Detailed studies of the oxide surface atomic structure and chemistry (e.g., cation migration) can provide much needed insights for the design of highly efficient and stable oxide electrocatalysts. In this Account, we focus on recent advances in characterizing strontium (Sr) cation segregation and enrichment near the surface of Sr-substituted perovskite oxides under different operating conditions (e.g., high temperature, applied potential), as well as their influence on the surface oxygen exchange kinetics at elevated temperatures. We contrast Sr segregation, which is associated with Sr redistribution in the crystal lattice near the surface, with Sr enrichment, which involves Sr redistribution via the formation of secondary phases. The newly developed coherent Bragg rod analysis (COBRA) and energy-modulated differential COBRA are uniquely powerful ways of providing information about surface and interfacial cation segregation at the atomic scale for these thin film electrocatalysts. In situ ambient pressure X-ray photoelectron spectroscopy (APXPS) studies under electrochemical operating conditions give additional insights into cation migration. Direct COBRA and APXPS evidence for surface Sr segregation was found for La1-xSrxCoO3-δ and (La1-ySry)2CoO4±δ/La1-xSrxCoO3-δ oxide thin films, and

  14. Adsorption of pentacene on (100) vicinal surfaces: role of coordination, surface chemistry and vdWs effects

    NASA Astrophysics Data System (ADS)

    Matos, Jeronimo; Kara, Abdelkader

    2015-03-01

    In contrast to low miller index surfaces, vicinal surfaces are characterized by steps and step edges that not only present an interesting atomic landscape for the adsorption organic molecules, but also a unique electronic structure resulting in part from the low coordinated atoms at the step edges. The adsorption of pentacene on the stepped (511), (711), (911) surfaces (respectively 3, 4 and 5-atom wide terraces) of Cu and Ag (coinage transition metals); Pt (reactive transition metal); and Ni (reactive, magnetic transition metal) are studied using density functional theory, in order to investigate the support effects arising from differing surface chemistry. We compare the adsorption energy, adsorption geometry and electronic structure predicted by the PBE functional with those obtained from one of the optimized vdW-DF methods: optB88-vdW. Work supported by the U.S. Department of Energy Basic Energy Science under Contract No. DE-FG02-11ER16243.

  15. Kinetics and roles of solution and surface species of chalcopyrite dissolution at 650 mV

    NASA Astrophysics Data System (ADS)

    Li, Yubiao; Qian, Gujie; Li, Jun; Gerson, Andrea R.

    2015-07-01

    To better understand chalcopyrite dissolution in hydrogeochemical processes and the related environmental issue of acid and metalliferous drainage (AMD), the kinetics as well as the influence of solution composition and the nature of surface species formed during chalcopyrite dissolution have been examined under the controlled conditions of Eh 650 mV (SHE), pH 1.0-2.0 and 75 °C, with/without 4 mM Fe2+ addition. SEM and XPS analyses indicate that the surface products, both at micro- and nano-scales, did not passivate dissolution under the conditions examined. Extensive S0 was formed mostly as discrete particles rather than coatings on the chalcopyrite surface. Jarosite was only observed for dissolution at pH 2.0 with 4 mM added Fe2+. Without Fe2+ addition, the initial dissolution rate was observed to be only correlated to H+ activity as aH+0.12(±0.01), indicating chalcopyrite dissolution was controlled via chemical oxidation of chalcopyrite by H+/O2. When reaction between chalcopyrite and Fe3+ predominated chalcopyrite dissolution (i.e. later stage of dissolution without Fe2+ addition), the dissolution rate was found to be positively correlated to the activities of Fe3+, as aFe3+1.54(±0.07), and H+, as aH+0.13(±0.05). When 4 mM Fe2+ was added, no clear correlation was observed between the dissolution rate and the activities of either Fe3+or H+. It is proposed that the relative reactive surface area may not be proportional to that predicted by a shrinking sphere model as was assumed for derivation of the rate laws for the systems without added Fe2+, with the predicted rate being greater than the measured rate. Irrespective, it is clear that the addition of a relatively low Fe2+ concentration plays an important role in accelerating the copper dissolution rate at this Eh.

  16. The role of nest surface temperatures and the brain in influencing ant metabolic rates.

    PubMed

    Andrew, Nigel R; Ghaedi, Behnaz; Groenewald, Berlizé

    2016-08-01

    Thermal limits of insects can be influenced by recent thermal history: here we used thermolimit respirometry to determine metabolic rate responses and thermal limits of the dominant meat ant, Iridomyrmex purpureus. Firstly, we tested the hypothesis that nest surface temperatures have a pervasive influence on thermal limits. Metabolic rates and activity of freshly field collected individuals were measured continuously while ramping temperatures from 44°C to 62°C at 0.25°C/minute. At all the stages of thermolimit respirometry, metabolic rates were independent of nest surface temperatures, and CTmax did not differ between ants collected from nest with different surface temperatures. Secondly, we tested the effect of brain control on upper thermal limits of meat ants via ant decapitation experiments ('headedness'). Decapitated ants exhibited similar upper critical temperature (CTmax) results to living ants (Decapitated 50.3±1.2°C: Living 50.1±1.8°C). Throughout the temperature ramping process, 'headedness' had a significant effect on metabolic rate in total (Decapitated V̇CO2 140±30µlCO2mg(-1)min(-1): Living V̇CO2 250±50 CO2mg(-1)min(-1)), as well as at temperatures below and above CTmax. At high temperatures (>44°C) pre- CTmax the relationships between I. purpureus CTmax values and mass specific metabolic rates for living ants exhibited a negative slope whilst decapitated ants exhibited a positive slope. The decapitated ants also had a significantly higher Q10:25-35°C when compared to living ants (1.91±0.43 vs. 1.29±0.35). Our findings suggest that physiological responses of ants may be able to cope with increasing surface temperatures, as shown by metabolic rates across the thermolimit continuum, making them physiologically resilient to a rapidly changing climate. We also demonstrate that the brain plays a role in respiration, but critical thermal limits are independent of respiration levels. PMID:27503725

  17. The role of extensional inheritance and surface processes on mountain belt evolution

    NASA Astrophysics Data System (ADS)

    Erdos, Zoltan; Huismans, Ritske S.; van der Beek, Peter

    2015-04-01

    The crustal structure of collisional orogens around the world shows a wide range of deformation styles from narrow, asymmetric doubly vergent wedges like the Pyrenees to wide, plateau-like orogens such as the Zagros mountain belt in Iran. Inherited structures and surface processes are widely regarded as factors playing significant role in the evolution of such mountain belts. These parameters have been studied extensively throughout the last decades, yet questions still remain about their exact effects on the style of orogenic development. We use lithospheric scale plane-strain thermo-mechanical model experiments to study the effects of extensional inheritance and surface processes on the internal structure of contractional orogens and their foreland basins. Extensional inheritance is modeled explicitly by forward modeling the formation of a rift basin before reversing the velocity boundary conditions to model its inversion. Surface processes are modeled through the combination of a simple sedimentation algorithm, where all negative topography is filled up to a prescribed reference level, and an elevation-dependent erosion model. We test the sensitivity of our models to the amount of crustal extension, and to the length of post-rift thermal relaxation. Moreover, the interaction of thin-skinned and thick-skinned tectonics is explored with the use of a shallow frictionally weak detachment at the base of a pre-deformation sedimentary layer. Our results show that extensional inheritance facilitates the propagation of basement deformation in the retro-wedge and increases the width of the orogen. Additionally, sedimentation increases the length-scale of both thin-skinned and thick-skinned thrust sheets and results in a wider orogen while erosion helps to localize deformation resulting in a narrower orogen. However, the length of post-rift thermal relaxation seems to have very little effect on the following mountain building. A comparison of the modeled behaviors to the

  18. Numerical study on the adhesion and reentrainment of nondeformable particles on surfaces: the role of surface roughness and electrostatic forces.

    PubMed

    Henry, Christophe; Minier, Jean-Pierre; Lefèvre, Grégory

    2012-01-10

    In this paper, the reentrainment of nanosized and microsized particles from rough walls under various electrostatic conditions and various hydrodynamic conditions (either in air or aqueous media) is numerically investigated. This issue arises in the general context of particulate fouling in industrial applications, which involves (among other phenomena) particle deposition and particle reentrainment. The deposition phenomenon has been studied previously and, in the present work, we focus our attention on resuspension. Once particles are deposited on a surface, the balance between hydrodynamic forces (which tend to move particles away from the surface) and adhesion forces (which maintain particles on the surface) can lead to particle removal. Adhesion forces are generally described using van der Waals attractive forces, but the limit of these models is that any dependence of adhesion forces on electrostatic forces (due to variations in pH or ionic strength) cannot be reproduced numerically. For this purpose, we develop a model of adhesion forces that is based on the DLVO (Derjaguin and Landau, Verwey and Overbeek) theory and which includes also the effect of surface roughness through the use of hemispherical asperities on the surface. We first highlight the effect of the curvature radius on adhesion forces. Then some numerical predictions of adhesion forces or adhesion energies are compared to experimental data. Finally, the overall effects of surface roughness and electrostatic forces are demonstrated with some applications of the complete reentrainment model in some simple test cases. PMID:22107171

  19. On the role of defects and surface chemistry for surface-assisted laser desorption ionization from silicon

    NASA Astrophysics Data System (ADS)

    Alimpiev, S.; Grechnikov, A.; Sunner, J.; Karavanskii, V.; Simanovsky, Ya.; Zhabin, S.; Nikiforov, S.

    2008-01-01

    The generation of ions from silicon substrates in surface-assisted laser desorption ionization (SALDI) has been studied using silicon substrates prepared and etched by a variety of different methods. The different substrates were compared with respect to their ability to generate peptide mass spectra using standard liquid sample deposition. The desorption/ionization processes were studied using gas-phase analyte deposition. Mass spectra were obtained from compounds with gas-phase basicities above 850kJ/mol and with molecular weights up to 370Da. UV, VIS, and IR lasers were used for desorption. Ionization efficiencies were measured as a function of laser fluence and accumulated laser irradiance dose. Solvent vapors were added to the ion source and shown to result in fundamental laser-induced chemical and physical changes to the substrate surfaces. It is demonstrated that both the chemical properties of the substrate surface and the presence of a highly disordered structure with a high concentration of "dangling bonds" or deep gap states are required for efficient ion generation. In particular, amorphous silicon is shown to be an excellent SALDI substrate with ionization efficiencies as high as 1%, while hydrogen-passivated amorphous silicon is SALDI inactive. Based on the results, a novel model for SALDI ion generation is proposed with the following reaction steps: (1) the adsorption of neutral analyte molecules on the SALDI surface with formation of a hydrogen bond to surface Si-OH groups, (2) the electronic excitation of the substrate to form free electron/hole pairs (their relaxation results in trapped positive charges in near-surface deep gap states, causing an increase in the acidity of the Si-OH groups and proton transfer to the analyte molecules), and (3) the thermally activated dissociation of the analyte ions from the surface via a "loose" transition state.

  20. Pneumococcal Surface Protein A Plays a Major Role in Streptococcus pneumoniae-Induced Immunosuppression.

    PubMed

    Saumyaa; Pujanauski, Lindsey; Colino, Jesus; Flora, Michael; Torres, Raul M; Tuomanen, Elaine; Snapper, Clifford M

    2016-05-01

    Intact, inactivated Streptococcus pneumoniae [including the unencapsulated S. pneumoniae, serotype 2 strain (R36A)] markedly inhibits the humoral immune response to coimmunized heterologous proteins, a property not observed with several other intact Gram-positive or Gram-negative bacteria. In this study, we determined the nature of this immunosuppressive property. Because phosphorylcholine (PC), a major haptenic component of teichoic acid in the S. pneumoniae cell wall, and lipoteichoic acid in the S. pneumoniae membrane were previously reported to be immunosuppressive when derived from filarial parasites, we determined whether R36A lacking PC (R36A(pc-)) was inhibitory. Indeed, although R36A(pc-) exhibited a markedly reduced level of inhibition of the IgG response to coimmunized chicken OVA (cOVA), no inhibition was observed when using several other distinct PC-expressing bacteria or a soluble, protein-PC conjugate. Further, treatment of R36A with periodate, which selectively destroys PC residues, had no effect on R36A-mediated inhibition. Because R36A(pc-) also lacks choline-binding proteins (CBPs) that require PC for cell wall attachment, and because treatment of R36A with trypsin eliminated its inhibitory activity, we incubated R36A in choline chloride, which selectively strips CBPs from its surface. R36A lacking CBPs lost most of its inhibitory property, whereas the supernatant of choline chloride-treated R36A, containing CBPs, was markedly inhibitory. Coimmunization studies using cOVA and various S. pneumoniae mutants, each genetically deficient in one of the CBPs, demonstrated that only S. pneumoniae lacking the CBP pneumococcal surface protein A lost its ability to inhibit the IgG anti-cOVA response. These results strongly suggest that PspA plays a major role in mediating the immunosuppressive property of S. pneumoniae. PMID:27029587

  1. Role of Surface Termination on Hot Electron Relaxation in Silicon Quantum Dots: A First-Principles Dynamics Simulation Study.

    PubMed

    Reeves, Kyle G; Schleife, André; Correa, Alfredo A; Kanai, Yosuke

    2015-10-14

    The role of surface termination on phonon-mediated relaxation of an excited electron in quantum dots was investigated using first-principles simulations. The surface terminations of a silicon quantum dot with hydrogen and fluorine atoms lead to distinctively different relaxation behaviors, and the fluorine termination shows a nontrivial relaxation process. The quantum confined electronic states are significantly affected by the surface of the quantum dot, and we find that a particular electronic state dictates the relaxation behavior through its infrequent coupling to neighboring electronic states. Dynamical fluctuation of this electronic state results in a slow shuttling behavior within the manifold of unoccupied electronic states, controlling the overall dynamics of the excited electron with its characteristic frequency of this shuttling behavior. The present work revealed a unique role of surface termination, dictating the hot electron relaxation process in quantum-confined systems in the way that has not been considered previously. PMID:26331672

  2. The role of angiogenesis in implant dentistry part I: Review of titanium alloys, surface characteristics and treatments

    PubMed Central

    Asatourian, Armen; Garcia-Godoy, Franklin; Sheibani, Nader

    2016-01-01

    Background Angiogenesis plays an important role in osseointegration process by contributing to inflammatory and regenerative phases of surrounding alveolar bone. The present review evaluated the effect of titanium alloys and their surface characteristics including: surface topography (macro, micro, and nano), surface wettability/energy, surface hydrophilicity or hydrophobicity, surface charge, and surface treatments of dental implants on angiogenesis events, which occur during osseointegration period. Material and Methods An electronic search was performed in PubMed, MEDLINE, and EMBASE databases via OVID using the keywords mentioned in the PubMed and MeSH headings regarding the role of angiogenesis in implant dentistry from January 2000-April 2014. Results Of the 2,691 articles identified in our initial search results, only 30 met the inclusion criteria set for this review. The hydrophilicity and topography of dental implants are the most important and effective surface characteristics in angiogenesis and osteogenesis processes. The surface treatments or modifications of dental implants are mainly directed through the enhancement of biological activity and functionalization in order to promote osteogenesis and angiogenesis, and accelerate the osseointegration procedure. Conclusions Angiogenesis is of great importance in implant dentistry in a manner that most of the surface characteristics and treatments of dental implants are directed toward creating a more pro-angiogenic surface on dental implants. A number of studies discussed the effect of titanium alloys, dental implant surface characteristic and treatments on agiogenesis process. However, clinical trials and in-vivo studies delineating the mechanisms of dental implants, and their surface characteristics or treatments, action in angiogenesis processes are lagging. Key words:Angiogenesis, dental implant, osseointergration. PMID:27031073

  3. Essential Role of Surface-Bound Complement Factor H in Controlling Immune Complex–Induced Arthritis

    PubMed Central

    Mehta, Gaurav; Ferreira, Viviana P.; Cortes, Claudio; Pickering, Matthew C.; Pangburn, Michael K.; Arend, William P.

    2013-01-01

    Factor H (fH) is an endogenous negative regulator of the alternative pathway (AP) that binds polyanions as well as complement activation fragments C3b and C3d. The AP is both necessary and sufficient to develop collagen Ab–induced arthritis (CAIA) in mice; the mechanisms whereby normal control of the AP is overcome and injury develops are unknown. Although primarily a soluble circulating protein, fH can also bind to tissues in a manner dependent on the carboxyl-terminal domain containing short consensus repeats 19 and 20. We examined the role of fH in CAIA by blocking its binding to tissues through administration of a recombinant negative inhibitor containing short consensus repeats 19 and 20 (rfH19-20), which impairs fH function and amplifies surface AP activation in vitro. Administration of rfH19-20, but not control rfH3-5, significantly worsened clinical disease activity, histopathologic injury, and C3 deposition in the synovium and cartilage in wild-type and fH+/− mice. In vitro studies demonstrated that rfH19-20 increased complement activation on cartilage extracts and injured fibroblast-like synoviocytes, two major targets of complement deposition in the joint. We conclude that endogenous fH makes a significant contribution to inhibition of the AP in CAIA through binding to sites of immune complex formation and complement activation. PMID:23436934

  4. The Role of Snow Cover on Surface Trace Gas Exchanges at Toolik Lake, AK

    NASA Astrophysics Data System (ADS)

    Helmig, D.; Obrist, D.; Moore, C.; Van Dam, B.; Jacques, H.; Molnar, T.; Williams, M. W.; Kramer, L. J.; Doskey, P. V.; Fain, X.

    2014-12-01

    Snow has a profound influence on the emission and deposition of atmospheric trace gases in the arctic environment. Processes that play a role in modulating gas exchanges include biological, soil biogeochemical, snow chemical, and snow physical processes. Environmental conditions underneath the snow are relatively stable throughout the winter period. Above the snow surface, variations in temperature, radiation, and wind exert a wide range of influences on snowpack gas chemistry, gas exchanges at the snow-air interface, and chemical interactions between the interstitial snowpack air and vegetation and soil below the snowpack. This presentation will present an overview of experimental approaches for continuous, all winter-long experiments conducted at a permafrost site at the Long-Term Ecological Research (LTER) station at Toolik Lake on the north slope of the Brooks Range, Alaska. These studies include observations of carbon dioxide and the reactive gases ozone, nitrogen oxides, and gaseous elemental mercury. Parameterizations developed from these measurements are used for improving descriptions of trace gas budgets and their feedbacks on climate and associated snow cover changes in the Arctic and seasonally snow-covered midlatitude environments.

  5. Role of the North Pacific sea surface temperature in the East Asian winter monsoon decadal variability

    NASA Astrophysics Data System (ADS)

    Sun, Jianqi; Wu, Sha; Ao, Juan

    2016-06-01

    In this study, a possible mechanism for the decadal variability in the East Asian winter monsoon (EAWM) is proposed. Specifically, the North Pacific sea surface temperature (SST) may play an important role. An analysis of the observations shows that the North Pacific SST has a remarkable decadal pattern whose phase shifted around the mid-1980s. This North Pacific SST decadal pattern can weaken the East Asian trough and enhance the North Pacific Oscillation through changing air-sea interactions over the North Pacific. The weak East Asian trough enhances the zonal circulation and weakens the meridional circulation over East Asia, consequently leading to a weaker southward cold surge and East Asia warming around the mid-1980s. The numerical experiment further confirms the pronounced physical processes. In addition, over the longer period of 1871-2012, the indices of the EAWM and North Pacific SST decadal pattern are also highly consistent on the decadal timescale, which further confirms the impact of the North Pacific SST decadal pattern on the EAWM decadal variability.

  6. Role of soluble and cell surface molecules in the pathogenesis of autoimmune skin diseases.

    PubMed

    Drosera, M; Facchetti, F; Landolfo, S; Mondini, M; Nyberg, F; Parodi, A; Santoro, A; Zampieri, S; Doria, A

    2006-01-01

    The skin is one of the most commonly involved tissue in rheumatic autoimmune diseases. Different mechanisms are thought to be implicated in the pathogenesis of skin lesions. In genetically predisposed individuals, ultraviolet (UV) light can contribute to the induction of skin lesions via an inflammatory process. UV light promotes the release of cytokines by keratinocytes and the induction of adhesion molecules on the surface of epidermal cells initiating a cascade of inflammatory events and recruiting immunoinflammatory cells into the skin. In this review data regarding the expression of TNF-alpha in lesional skin tissue from subacute cutaneous lupus erythematosus patients and the role of interferons in the pathogenesis of skin manifestations of rheumatic autoimmune diseases are reported. In addition, an overview on the expression of cellular adhesion molecules in these diseases is provided.UV light can also induce apoptosis in keratinocytes. During this cell death several enzymes became activated. Among them, desoxyribonuclease (DNase) is an enzyme involved in degrading DNA during apoptosis. Data regarding the activity of DNAse in patients with cutaneous lupus erythematosus as a possible risk factor for the development of systemic disease are here reported. PMID:16466628

  7. The role of prenucleation clusters in surface-induced calcium phosphate crystallization

    NASA Astrophysics Data System (ADS)

    Dey, Archan; Bomans, Paul H. H.; Müller, Frank A.; Will, Julia; Frederik, Peter M.; de With, Gijsbertus; Sommerdijk, Nico A. J. M.

    2010-12-01

    Unravelling the processes of calcium phosphate formation is important in our understanding of both bone and tooth formation, and also of pathological mineralization, for example in cardiovascular disease. Serum is a metastable solution from which calcium phosphate precipitates in the presence of calcifiable templates such as collagen, elastin and cell debris. A pathological deficiency of inhibitors leads to the uncontrolled deposition of calcium phosphate. In bone and teeth the formation of apatite crystals is preceded by an amorphous calcium phosphate (ACP) precursor phase. ACP formation is thought to proceed through prenucleation clusters-stable clusters that are present in solution already before nucleation-as was recently demonstrated for CaCO3 (refs 15,16). However, the role of such nanometre-sized clusters as building blocks for ACP has been debated for many years. Here we demonstrate that the surface-induced formation of apatite from simulated body fluid starts with the aggregation of prenucleation clusters leading to the nucleation of ACP before the development of oriented apatite crystals.

  8. The Role of Anthropogenic-Induced Surface Temperature Change on Regional Enhanced Warming over East Asia

    NASA Astrophysics Data System (ADS)

    Guan, X.; Huang, J.; Guo, R.

    2014-12-01

    In this study, the long-term trend and decadal variability of surface air temperature (SAT) are studied by using observation data from 1901-2009. We found that the warming trends of the semi-arid regions are higher than other lands, which have increased 2.42°C as compared to the global annual mean temperature increase of 1.13°C over land. To investigate the causes of Enhanced Semi-Arid Warming (ESAW), we used an advanced dynamic-adjusted method proposed by Wallace et al. (2012) to analyse the contribution of dynamically-induced and anthropogenic-induced SAT changes to ESAW. In the process of dynamic adjustment, the temperature has been divided into two parts, one for the dynamic forcing induced temperature, and the other for the temperature associated with the build-up of greenhouse gases and the other various radiative forcing. The results show that the anthropogenic-warming peak over semi-arid region plays the main role in the ESAW. Such anthropogenic warming peak may be related to reduction of snow cover due to black carbon (BC) emission by fuels for winter residential heating. Besides the impact of BC in snow, the agricultural mulch creation, wind farms and other types of human activities may also make attribution to local SAT changes that need to be further studied.

  9. The Influence of Gender, Age, Matriline and Hierarchical Rank on Individual Social Position, Role and Interactional Patterns in Macaca sylvanus at ‘La Forêt des Singes’: A Multilevel Social Network Approach

    PubMed Central

    Sosa, Sebastian

    2016-01-01

    A society is a complex system composed of individuals that can be characterized by their own attributes that influence their behaviors. In this study, a specific analytical protocol based on social network analysis was adopted to investigate the influence of four attributes (gender, age, matriline, and hierarchical rank) on affiliative (allogrooming) and agonistic networks in a non-human primate species, Macaca sylvanus, at the park La Forêt des Singes in France. The results show significant differences with respect to the position (i.e., centric, peripheral) and role (i.e., implication in the network cohesiveness) of an individual within a social network and hence interactional patterns. Females are more central, more active, and have a denser ego network in the affiliative social network tan males; thus, they contribute in a greater way to the cohesive structure of the network. High-ranking individuals are likely to receive fewer agonistic behaviors than low-ranking individuals, and high-ranking females receive more allogrooming. I also observe homophily for affiliative interactions regarding all attributes and homophily for agonistic interactions regarding gender and age. Revealing the positions, the roles, and the interactional behavioral patterns of individuals can help understand the mechanisms that shape the overall structure of a social network. PMID:27148137

  10. Diffusion des Metaux et Evolution Stellaire

    NASA Astrophysics Data System (ADS)

    Turcotte, Sylvain

    Nous presentons dans cette these des modeles d'evolution stellaire incorporant la diffusion microscopique de maniere consistante. Pour la premiere fois, on a calcule l'evolution d'etoiles en tenant compte en detail de l'impact des variations d'abondances sur leur structure. Nous utilisons des spectres monochromatiques pour chacun des elements les plus abondants dans un melange solaire pour recalculer l'opacite pour les abondances et les conditions locales dans l'interieur d'une etoile au cours de son evolution. Nos modeles montrent que la diffusion atomique des metaux a un effet important sur les opacites dan les etoiles de plus de 1.3Msolar ou l'abondance du fer et des autres elements du pic du fer varient substantiellement. Ces etoiles, sans rotation ou champ magnetique, sont proches des etoiles de type Fm-Am dans lesquelles on observe une legere surabondance d'elements du pic du fer en plus d'une sous-abondance de calcium, sous-abondance que l'on obtient egalement. Nous obtenons cependant des surabondances depassant un facteur 10 pour les etoiles de plus de 1.4Msolar ce qui suggere qu'il existe un ou plusieurs mecanismes limitant la diffusion microscopique. La surabondance du fer en surface cause une augmentation, qui peut atteindre un facteur sept, de l'opacite a la limite de la zone convective. Ceci cause un accroissement de la temperature effective et de la masse de la zone convective comparativement aux modeles n'incluant que la diffusion de l'helium. Il s'agit la du principal effet de la diffusion sur la structure interne de ces etoiles. La diffusions n'a pas d'influence sur l'evolution de coeur stellaire dans les etoiles significativement plus massives quie le Soleil. Nous avons verife que l'utilisation de modeles consistants avec diffusion n'apporte pas d'amelioration sensible aux modeles solaires. Les forces radiatives calculees a partir des spectres d'OPAL pour les elements du pic du fer representent une fraction importante de la gravite. On obtient des

  11. The Roles of Titanium Surface Micro/Nanotopography and Wettability on the Differential Response of Human Osteoblast Lineage Cells

    PubMed Central

    Gittens, Rolando A.; Olivares-Navarrete, Rene; Cheng, Alice; Anderson, David M.; McLachlan, Taylor; Stephan, Ingrid; Geis-Gerstorfer, Jürgen; Sandhage, Kenneth H.; Fedorov, Andrei G.; Rupp, Frank; Boyan, Barbara D.; Tannenbaum, Rina; Schwartz, Zvi

    2013-01-01

    Surface micro and nanostructural modifications of dental and orthopaedic implants have shown promising in vitro, in vivo, and clinical results. Surface wettability has also been suggested to play an important role in osteoblast differentiation and osseointegration. However, the available techniques to measure surface wettability are not reliable on clinically-relevant, rough surfaces. Furthermore, how the differentiation state of osteoblast lineage cells impacts their response to micro/nanostructured surfaces, and the role of wettability on this response, remains unclear. In the current study, surface wettability analyses (optical sessile drop analysis, ESEM analysis, and the Wilhelmy technique) indicated hydrophobic static responses for deposited water droplets on microrough and micro/nanostructured specimens, while hydrophilic responses were observed with dynamic analyses of micro/nanostructured specimens. The maturation and local factor production of human immature osteoblast-like MG63 cells was synergistically influenced by nanostructures superimposed onto microrough titanium (Ti) surfaces. In contrast, human mesenchymal stem cells (MSCs) cultured on micro/nanostructured surfaces in the absence of exogenous soluble factors, exhibited less robust osteoblastic differentiation and local factor production compared to cultures on unmodified microroughened Ti. Our results support previous observations using Ti6Al4V surfaces showing that recognition of surface nanostructures and subsequent cell response is dependent on the differentiation state of osteoblast lineage cells. The results also indicate that this effect may be partly modulated by surface wettability. These findings support the conclusion that the successful osseointegration of an implant depends on contributions from osteoblast lineage cells at different stages of osteoblast commitment. PMID:23232211

  12. Possible role of pre-monsoon sea surface warming in driving the summer monsoon onset over the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Li, Kuiping; Liu, Yanliang; Yang, Yang; Li, Zhi; Liu, Baochao; Xue, Liang; Yu, Weidong

    2015-10-01

    Sea surface temperature (SST) reaches its annual maximum just before the summer monsoon onset and collapses soon after in the central areas of the Bay of Bengal (BoB). Here, the impact of the peak in the pre-monsoon SST on triggering the earliest monsoon onset in the BoB is investigated, with a focus on the role they play in driving the first-branch northward-propagating intra-seasonal oscillations (FNISOs) over the equatorial Eastern Indian Ocean (EIO). During the calm pre-monsoon period, sea surface warming in the BoB could increase the surface equivalent potential temperature (θe) in several ways. Firstly, warming of the sea surface heats the surface air through sensible heating, which forces the air temperature to follow the SST. The elevated air surface temperature accounts for 30 % of the surface θe growth. Furthermore, the elevated air temperature raises the water vapor capacity of the surface air to accommodate more water vapor. Constrained by the observation that the surface relative humidity is maintained nearly constant during the monsoon transition period, the surface specific humidity exhibits a significant increase, according to the Clausius-Clapeyron relationship. Budget analysis indicates that the additional moisture is primarily obtained from sea surface evaporation, which also exhibits a weak increasing trend due to the sea surface warming. In this way, it contributes about 70 % to the surface θe growth. The rapid SST increase during the pre-monsoon period preconditions the summer monsoon onset over the BoB through its contributions to significantly increase the surface θe, which eventually establishes the meridional asymmetry of the atmospheric convective instability in the EIO. The pre-established greater convective instability leads to the FNISO convections, and the summer monsoon is triggered in the BoB region.

  13. Possible role of pre-monsoon sea surface warming in driving the summer monsoon onset over the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Li, Kuiping; Liu, Yanliang; Yang, Yang; Li, Zhi; Liu, Baochao; Xue, Liang; Yu, Weidong

    2016-08-01

    Sea surface temperature (SST) reaches its annual maximum just before the summer monsoon onset and collapses soon after in the central areas of the Bay of Bengal (BoB). Here, the impact of the peak in the pre-monsoon SST on triggering the earliest monsoon onset in the BoB is investigated, with a focus on the role they play in driving the first-branch northward-propagating intra-seasonal oscillations (FNISOs) over the equatorial Eastern Indian Ocean (EIO). During the calm pre-monsoon period, sea surface warming in the BoB could increase the surface equivalent potential temperature (θe) in several ways. Firstly, warming of the sea surface heats the surface air through sensible heating, which forces the air temperature to follow the SST. The elevated air surface temperature accounts for 30 % of the surface θe growth. Furthermore, the elevated air temperature raises the water vapor capacity of the surface air to accommodate more water vapor. Constrained by the observation that the surface relative humidity is maintained nearly constant during the monsoon transition period, the surface specific humidity exhibits a significant increase, according to the Clausius-Clapeyron relationship. Budget analysis indicates that the additional moisture is primarily obtained from sea surface evaporation, which also exhibits a weak increasing trend due to the sea surface warming. In this way, it contributes about 70 % to the surface θe growth. The rapid SST increase during the pre-monsoon period preconditions the summer monsoon onset over the BoB through its contributions to significantly increase the surface θe, which eventually establishes the meridional asymmetry of the atmospheric convective instability in the EIO. The pre-established greater convective instability leads to the FNISO convections, and the summer monsoon is triggered in the BoB region.

  14. Roles of low-level thermodynamics on surface-convection interactions over West-Africa

    NASA Astrophysics Data System (ADS)

    Guichard, F.; Couvreux, F.; Gounou, A.; Nuret, M.

    2009-09-01

    This study aims to characterize the thermodynamics of the atmospheric low levels across West Africa (WA), on the basis of observations provided by the AMMA project. A dataset made of several thousands of high-resolution soundings is used for this purpose. Moist-convection related indexes, boundary layer (BL) parameters, and a combination of two indexes proposed by Findell and Eltahir (2003) (FE03) are compted for each sounding. These latter indexes are well suited for distinguishing between aspects of surface-atmosphere interactions involving atmospheric vertical structures. The variability of the low levels is found to be stronger in the Sahelian zone than in the Soudanian zone, from daily scale up to the monsoon season (JJAS). FE03 indexes suggest that surface-atmosphere feedbacks are actually significantly operating over West-Africa, but that the feedback loops change sign with latitude and season. Thus, thermodynamic environment at low level is broadly consistent with the idea of daytime convection being either suppressed or favoured over wet surface versus dry ones, depending on latitude and seasonal variations. This finding is consistent with observations that daytime convection is not always favoured over wet land surfaces. It remains to assess the scale down to which the local thermodynamic environment is actually playing a role, and how it combines with other factors, such as turbulence, clouds and mesoscale circulations, to explain observations. Variations of the lifting condensation level (LCL) and level of free convection (LFC) are further consistent with the previous analysis. For instance, in Niamey (Sahelian), a strong diurnal cycle of LCL is found, especially early in the season, while the LFC does not fluctuates much with the hour in the day, but shifts downwards from June to August. The LCL is however not such a good indicator of BL height when the low levels are the driest. This is particularly true in June in the Sahel, on days when none of the

  15. Role of cationic size in the optical properties of the LiCl crystal surface: theoretical study.

    PubMed

    Abdel Halim, Wael Salah; Abdullah, Noha; Abdel-Aal, Safaa; Shalabi, A S

    2012-06-01

    The size of the cations (either Ca(2+), Sr(2+), Ga(+), or Au(+)) at the F(A1)-type color centers on the (100) surface of LiCl crystal plays an important role in the optical properties of this surface. In this work, double-well potentials at this surface were investigated using ab initio quantum mechanical methods. Quantum clusters were embedded in simulated Coulomb fields that closely approximate the Madelung fields of the host surface, and the ions that were the nearest neighbors to the F(A1) site were allowed to relax to equilibrium. The calculated Stokes-shifted optical transition bands, optical-optical conversion efficiency, and relaxed excited states of the defect-containing surface, as well as the orientational destruction of the color centers, recording sensitivity, exciton (energy) transfer, and the Glasner-Tompkins empirical relation were all found to be sensitive to the size of the dopant cation. PMID:22033757

  16. ROLE OF SURFACE FUNCTIONAL GROUPS IN THE CAPTURE OF ELEMENTAL MERCURY AND MERCURIC CHLORIDE BY ACTIVATED CARBONS

    EPA Science Inventory

    The paper discusses using a laboratory-scale, fixed bed apparatus to study the role of surface functional groups (SFGs) in the capture of mercuric chloride (HgC12) and elemental mercury (Hgo) in nitrogen (N2) prior to flue gas atmosphere studies. The study focused on two activat...

  17. On the Role of Discipline-Related Self-Concept in Deep and Surface Approaches to Learning among University Students

    ERIC Educational Resources Information Center

    Platow, Michael J.; Mavor, Kenneth I.; Grace, Diana M.

    2013-01-01

    The current research examined the role that students' discipline-related self-concepts may play in their deep and surface approaches to learning, their overall learning outcomes, and continued engagement in the discipline itself. Using a cross-lagged panel design of first-year university psychology students, a causal path was observed in which…

  18. A review of our understanding of the role played in the climate system by land surface processes (Invited)

    NASA Astrophysics Data System (ADS)

    Nicholson, S. E.

    2013-12-01

    The paper provides an historical review of research on the impact of the land surface on climate. It commences will the seminal work of Jule Charney on albedo as a potential cause of drought and follows the trail of follow-up studies on the question of desertification and its role in climate. With the exception of a very early paper by Namias, early work was limited mainly to modeling efforts. At the same time, several observational studies provided evidence that land surface feedbacks could enhance and prolong drought, especially in the African Sahel. Later work emphasized the role of soil moisture rather than albedo. Several important field studies also examined the role of the land surface. Examples include FIFE, HAPEX-Sahel and BOREAS. In recent years some major changes in the concept have occurred. There is now substantial observational evidence of an impact at the mesoscale. The role of land surface feedback on climate has become mainstream. Finally, a new subdiscipline has emerged that emphasizes feedbacks between the water cycle, vegetation and climate, namely ecohydrology.

  19. Des ballons pour demain

    NASA Astrophysics Data System (ADS)

    Régipa, R.

    A partir d'une théorie sur la détermination des formes et des contraintes globales d'un ballon de révolution, ou s'en rapprochant, une nouvelle famille de ballons a été définie. Les ballons actuels, dits de ``forme naturelle'', sont calculés en général pour une tension circonférencielle nulle. Ainsi, pour une mission donnée, la tension longitudinale et la forme de l'enveloppe sont strictement imposées. Les ballons de la nouvelle génération sont globalement cylindriques et leurs pôles sont réunis par un câble axial, chargé de transmettre une partie des efforts depuis le crochet (pôle inférieur), directement au pôle supérieur. De plus, la zone latérale cylindrique est soumise à un faible champ de tensions circonférencielles. Ainsi, deux paramètres permettent de faire évoluer la distribution des tensions et la forme de l'enveloppe: - la tension du câble de liaison entre pôles (ou la longueur de ce câble) - la tension circonférencielle moyenne désirée (ou le rayon du ballon). On peut donc calculer et réaliser: - soit des ballons de forme adaptée, comme les ballons à fond plat pour le bon fonctionnement des montgolfières infrarouge (projet MIR); - soit des ballons optimisés pour une bonne répartition des contraintes et une meilleure utilisation des matériaux d'enveloppe, pour l'ensemble des programmes stratosphériques. Il s'ensuit une économie sensible des coûts de fabrication, une fiabilité accrue du fonctionnement de ces ballons et une rendement opérationnel bien supérieur, permettant entre autres, d'envisager des vols à très haute altitude en matériaux très légers.

  20. Assessing the role of cell-surface molecules in central synaptogenesis in the Drosophila visual system.

    PubMed

    Berger-Müller, Sandra; Sugie, Atsushi; Takahashi, Fumio; Tavosanis, Gaia; Hakeda-Suzuki, Satoko; Suzuki, Takashi

    2013-01-01

    A hallmark of the central nervous system is its spatial and functional organization in synaptic layers. During neuronal development, axons form transient contacts with potential post-synaptic elements and establish synapses with appropriate partners at specific layers. These processes are regulated by synaptic cell-adhesion molecules. In the Drosophila visual system, R7 and R8 photoreceptor subtypes target distinct layers and form en passant pre-synaptic terminals at stereotypic loci of the axonal shaft. A leucine-rich repeat transmembrane protein, Capricious (Caps), is known to be selectively expressed in R8 axons and their recipient layer, which led to the attractive hypothesis that Caps mediates R8 synaptic specificity by homophilic adhesion. Contradicting this assumption, our results indicate that Caps does not have a prominent role in synaptic-layer targeting and synapse formation in Drosophila photoreceptors, and that the specific recognition of the R8 target layer does not involve Caps homophilic axon-target interactions. We generated flies that express a tagged synaptic marker to evaluate the presence and localization of synapses in R7 and R8 photoreceptors. These genetic tools were used to assess how the synaptic profile is affected when axons are forced to target abnormal layers by expressing axon guidance molecules. When R7 axons were mistargeted to the R8-recipient layer, R7s either maintained an R7-like synaptic profile or acquired a similar profile to r8s depending on the overexpressed protein. When R7 axons were redirected to a more superficial medulla layer, the number of presynaptic terminals was reduced. These results indicate that cell-surface molecules are able to dictate synapse loci by changing the axon terminal identity in a partially cell-autonomous manner, but that presynapse formation at specific sites also requires complex interactions between pre- and post-synaptic elements. PMID:24386266

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

    PubMed

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

    2008-05-27

    The Hadley Centre coupled climate-carbon cycle model (HadCM3LC) predicts loss of the Amazon rainforest in response to future anthropogenic greenhouse gas emissions. In this study, the atmospheric component of HadCM3LC is used to assess the role of simulated changes in mid-twenty-first century sea surface temperature (SST) in Amazon Basin climate change. When the full HadCM3LC SST anomalies (SSTAs) are used, the atmosphere model reproduces the Amazon Basin climate change exhibited by HadCM3LC, including much of the reduction in Amazon Basin rainfall. This rainfall change is shown to be the combined effect of SSTAs in both the tropical Atlantic and the Pacific, with roughly equal contributions from each basin. The greatest rainfall reduction occurs from May to October, outside of the mature South American monsoon (SAM) season. This dry season response is the combined effect of a more rapid warming of the tropical North Atlantic relative to the south, and warm SSTAs in the tropical east Pacific. Conversely, a weak enhancement of mature SAM season rainfall in response to Atlantic SST change is suppressed by the atmospheric response to Pacific SST. This net wet season response is sufficient to prevent dry season soil moisture deficits from being recharged through the SAM season, leading to a perennial soil moisture reduction and an associated 30% reduction in annual Amazon Basin net primary productivity (NPP). A further 23% NPP reduction occurs in response to a 3.5 degrees C warmer air temperature associated with a global mean SST warming. PMID:18267896

  2. Surface Characteristics and Adhesion Behavior of Escherichia coli O157:H7: Role of Extracellular Macromolecules

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Surface macromolecule cleavage experiments were conducted on enterohaemorrhagic Escherichia coli O157:H7 cells to investigate the influence of these macromolecules on cell surface properties. Electrophoretic mobility, hydrophobicity, and titration experiments were carried out on proteinase K treate...

  3. Role of surface coating on cathode materials for lithium-ion batteries.

    SciTech Connect

    Chen, Z.; Qin, Y.; Amine, K.; Sun, Y.-K.

    2010-01-01

    Surface coating of cathode materials has been widely investigated to enhance the life and rate capability of lithium-ion batteries. The surface coating discussed here was divided into three different configurations which are rough coating, core shell structure coating and ultra thin film coating. The mechanism of surface coating in achieving improved cathode performance and strategies to carry out this surface modification is discussed. An outlook on atomic layer deposition for lithium ion battery is also presented.

  4. Primary role of electron work function for evaluation of nanostructured titania implant surface against bacterial infection.

    PubMed

    Golda-Cepa, M; Syrek, K; Brzychczy-Wloch, M; Sulka, G D; Kotarba, A

    2016-09-01

    The electron work function as an essential descriptor for the evaluation of metal implant surfaces against bacterial infection is identified for the first time. Its validity is demonstrated on Staphylococcus aureus adhesion to nanostructured titania surfaces. The established correlation: work function-bacteria adhesion is of general importance since it can be used for direct evaluation of any electrically conductive implant surfaces. PMID:27207043

  5. Simulating the role of surface forcing on observed multidecadal upper-ocean salinity changes

    DOE PAGESBeta

    Lago, Veronique; Wijffels, Susan E.; Durack, Paul J.; Church, John A.; Bindoff, Nathaniel L.; Marsland, Simon J.

    2016-07-18

    The ocean’s surface salinity field has changed over the observed record, driven by an intensification of the water cycle in response to global warming. However, the origin and causes of the coincident subsurface salinity changes are not fully understood. The relationship between imposed surface salinity and temperature changes and their corresponding subsurface changes is investigated using idealized ocean model experiments. The ocean’s surface has warmed by about 0.5°C (50 yr)–1 while the surface salinity pattern has amplified by about 8% per 50 years. The idealized experiments are constructed for a 50-yr period, allowing a qualitative comparison to the observed salinitymore » and temperature changes previously reported. The comparison suggests that changes in both modeled surface salinity and temperature are required to replicate the three-dimensional pattern of observed salinity change. The results also show that the effects of surface changes in temperature and salinity act linearly on the changes in subsurface salinity. In addition, surface salinity pattern amplification appears to be the leading driver of subsurface salinity change on depth surfaces; however, surface warming is also required to replicate the observed patterns of change on density surfaces. This is the result of isopycnal migration modified by the ocean surface warming, which produces significant salinity changes on density surfaces.« less

  6. How Escherichia coli lands and forms cell clusters on a surface: a new role of surface topography

    PubMed Central

    Gu, Huan; Chen, Aaron; Song, Xinran; Brasch, Megan E.; Henderson, James H.; Ren, Dacheng

    2016-01-01

    Bacterial response to surface topography during biofilm formation was studied using 5 μm tall line patterns of poly (dimethylsiloxane) (PDMS). Escherichia coli cells attached on top of protruding line patterns were found to align more perpendicularly to the orientation of line patterns when the pattern narrowed. Consistently, cell cluster formation per unit area on 5 μm wide line patterns was reduced by 14-fold compared to flat PDMS. Contrasting the reduced colony formation, cells attached on narrow patterns were longer and had higher transcriptional activities, suggesting that such unfavorable topography may present a stress to attached cells. Results of mutant studies indicate that flagellar motility is involved in the observed preference in cell orientation on narrow patterns, which was corroborated by the changes in cell rotation pattern before settling on different surface topographies. These findings led to a set of new design principles for creating antifouling topographies, which was validated using 10 μm tall hexagonal patterns. PMID:27412365

  7. Using extremely halophilic bacteria to understand the role of surface charge and surface hydration in protein evolution, folding, and function

    NASA Astrophysics Data System (ADS)

    Hoff, Wouter; Deole, Ratnakar; Osu Collaboration

    2013-03-01

    Halophilic Archaea accumulate molar concentrations of KCl in their cytoplasm as an osmoprotectant, and have evolved highly acidic proteomes that only function at high salinity. We examine osmoprotection in the photosynthetic Proteobacteria Halorhodospira halophila. We find that H. halophila has an acidic proteome and accumulates molar concentrations of KCl when grown in high salt media. Upon growth of H. halophila in low salt media, its cytoplasmic K + content matches that of Escherichia coli, revealing an acidic proteome that can function in the absence of high cytoplasmic salt concentrations. These findings necessitate a reassessment of two central aspects of theories for understanding extreme halophiles. We conclude that proteome acidity is not driven by stabilizing interactions between K + ions and acidic side chains, but by the need for maintaining sufficient solvation and hydration of the protein surface at high salinity through strongly hydrated carboxylates. We propose that obligate protein halophilicity is a non-adaptive property resulting from genetic drift in which constructive neutral evolution progressively incorporates weakly stabilizing K + binding sites on an increasingly acidic protein surface.

  8. How Escherichia coli lands and forms cell clusters on a surface: a new role of surface topography.

    PubMed

    Gu, Huan; Chen, Aaron; Song, Xinran; Brasch, Megan E; Henderson, James H; Ren, Dacheng

    2016-01-01

    Bacterial response to surface topography during biofilm formation was studied using 5 μm tall line patterns of poly (dimethylsiloxane) (PDMS). Escherichia coli cells attached on top of protruding line patterns were found to align more perpendicularly to the orientation of line patterns when the pattern narrowed. Consistently, cell cluster formation per unit area on 5 μm wide line patterns was reduced by 14-fold compared to flat PDMS. Contrasting the reduced colony formation, cells attached on narrow patterns were longer and had higher transcriptional activities, suggesting that such unfavorable topography may present a stress to attached cells. Results of mutant studies indicate that flagellar motility is involved in the observed preference in cell orientation on narrow patterns, which was corroborated by the changes in cell rotation pattern before settling on different surface topographies. These findings led to a set of new design principles for creating antifouling topographies, which was validated using 10 μm tall hexagonal patterns. PMID:27412365

  9. Amputation des quatre membres

    PubMed Central

    Feruzi, Maruis Kitembo; Milindi, Cédrick Sangwa; Zabibu, Mireille Kakinga; Mulefu, Jules Panda; Katombe, Francois Tshilombo

    2014-01-01

    Les auteurs présentent les cas d'amputation des quatre membres réalisée chez trois patients différents. Ce sont des amputations réalisées pour chaque patient au cours d'une seule hospitalisation et en un seul temps opératoire. Deux patients pour gangrène sèche infectée et un pour amputation traumatique des quatre membres. L'amputation d'urgence a été pratiquée en premier temps suivie de remodelage des moignons d'amputation en second temps. L’évolution de tous les patients a été bonne. PMID:25469177

  10. Mesenchymal Stem/Stromal Cells Protect the Ocular Surface by Suppressing Inflammation in an Experimental Dry Eye

    PubMed Central

    Lee, Min Joung; Ko, Ah Young; Ko, Jung Hwa; Lee, Hyun Ju; Kim, Mee Kum; Wee, Won Ryang; Khwarg, Sang In; Oh, Joo Youn

    2015-01-01

    Dry eye syndrome (DES) is one of the most common ocular diseases affecting nearly 10% of the US population. Most of the currently available treatments are palliative, and few therapeutic agents target biological pathway of DES. Although DES is a multifactorial disease, it is well-known that inflammation in the ocular surface plays an important role in the pathogenesis of DES. Mesenchymal stem/stromal cells (MSCs) have been shown to repair tissues by modulating excessive immune responses in various diseases. Therefore, we here investigated the therapeutic potential of MSCs in a murine model of an inflammation-mediated dry eye that was induced by an intraorbital injection of concanavalin A. We found that a periorbital administration of MSCs reduced the infiltration of CD4+ T cells and the levels of inflammatory cytokines in the intraorbital gland and ocular surface. Also, MSCs significantly increased aqueous tear production and the number of conjunctival goblet cells. Subsequently, corneal epithelial integrity was well-preserved by MSCs. Together, the results demonstrate that MSCs protect the ocular surface by suppressing inflammation in DES, and suggest that MSCs may offer a therapy for a number of ocular surface diseases where inflammation plays a key role. PMID:25152016

  11. Potential role of surface wettability on the long-term stability of dentin bonds after surface biomodification

    PubMed Central

    Leme, Ariene A.; Vidal, Cristina M. P.; Hassan, Lina Saleh; Bedran-Russo, Ana K.

    2015-01-01

    Degradation of the adhesive interface contributes to the failure of resin composite restorations. The hydrophilicity of the dentin matrix during and after bonding procedures may result in an adhesive interface that is more prone to degradation over time. This study assessed the effect of chemical modification of dentin matrix on the wettability and the long-term reduced modulus of elasticity (Er) of the adhesive interfaces. Human molars were divided into groups according to the priming solutions: distilled water (control), 6.5% Proanthocyanidin-rich grape seed extract (PACs), 5.75% 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride/1.4% n-hydroxysuccinimide (EDC/NHS) and 5% Glutaraldehyde (GA). The water-surface contact angle was verified before and after chemical modification of the dentin matrix. The demineralized dentin surface was treated with the priming solutions and restored with One Step Plus (OS) and Single Bond Plus (SB) and resin composite. The Er of the adhesive, hybrid layer and underlying dentin was evaluated after 24 h and 30 months in artificial saliva. The dentin hydrophilicity significantly decreased after application of the priming solutions. Aging significantly decreased the Er in the hybrid layer and underlying dentin of control groups. The Er of GA groups remained stable over time at the hybrid layer and underlying dentin. Significant higher Er was observed for PACs and EDC/NHS groups at the hybrid layer after 24 h. The decreased hydrophilicity of the modified dentin matrix likely influence the immediate mechanical properties of the hybrid layer. Dentin biomodification prevented substantial aging at the hybrid layer and underlying dentin after 30 months storage. PMID:25869721

  12. In situ investigation of titanium nitride surface dynamics: The role of surface and bulk mass transport processes

    NASA Astrophysics Data System (ADS)

    Bareno, Javier

    NaCl-structure TiN and related transition-metal (TM) nitrides are widely used as hard wear-resistant coatings on cutting tools, diffusion-barriers in microelectronic devices, corrosion-resistant layers on mechanical components, and abrasion-resistant thin films on optics and architectural glass. Since the elastic and physical properties of TiN are highly anisotropic, controlling the microstructural and surface morphological evolution of polycrystalline TM nitride films is important for all of the above applications. In this thesis, I used in-situ high-temperature low-energy electron microscopy (LEEM) to gain insight into film growth and microstructure development dynamics by studying mass-transport processes occurring during annealing of three dimensional (3D) structures on TiN surfaces. Additionally, in order to extend the current understanding of nanostructure development in binary nitride films to more complex ternary TM-nitride-based nanocomposites, I employed in-situ scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED), as well as ab-initio modeling, to investigate the atomic structure of the SiNx/TiN heterointerfaces which control the properties of SiNx-TiN nanocomposites. The LEEM studies of mass transport on TiN(111) focus on two specific surface morphologies which are observed to be present during growth of TiN single-crystals. (1) I investigated the temperature-dependent coarsening/decay kinetics of three-dimensional TiN island mounds on large (>1000 A) atomically-flat terraces; showing that TiN(111) steps are highly permeable and exhibit strong repulsive temperature-dependent step-step interactions that vary from 0.03 eV-A at 1559 K to 0.76 eV-A at 1651 K. (2) I studied the nucleation and growth of spiral steps originating at surface-terminated screw dislocations; I developed a model of spiral growth relating the emission rate of point defects from the bulk to the temperature-dependent spiral rotation frequency o(T); and I

  13. Facilitated biological reduction of nitroaromatic compounds by reduced graphene oxide and the role of its surface characteristics

    PubMed Central

    Li, Lei; Liu, Qi; Wang, Yi-Xuan; Zhao, Han-Qing; He, Chuan-Shu; Yang, Hou-Yun; Gong, Li; Mu, Yang; Yu, Han-Qing

    2016-01-01

    How reduced graphene oxide (RGO) mediates the reductive transformation of nitroaromatic pollutants by mixed cultures and the role of its surface characteristics were evaluated in this study. Different electron donors were applied to investigate the interaction between RGO and anaerobic microbes. Moreover, the influence of the surface properties of RGO on biological nitroaromatic removal was further elucidated. The results show that RGO could achieve an approximate one-fold rate increase of nitrobenzene reduction by mixed culture with glucose as an electron donor. Selective elimination of oxygen moieties on the RGO surface, such as quinone groups, decreased the nitrobenzene transformation rate, whereas doping nitrogen into the RGO framework exhibited a positive effect. The study indicates that graphene-based carbon nanomaterials have the potential to accelerate the biological transformation of nitroaromatic compounds and that the functionalization of these carbon nanomaterials, especially through surface modification, would further enhance the conversion efficiency of contaminants. PMID:27439321

  14. Facilitated biological reduction of nitroaromatic compounds by reduced graphene oxide and the role of its surface characteristics.

    PubMed

    Li, Lei; Liu, Qi; Wang, Yi-Xuan; Zhao, Han-Qing; He, Chuan-Shu; Yang, Hou-Yun; Gong, Li; Mu, Yang; Yu, Han-Qing

    2016-01-01

    How reduced graphene oxide (RGO) mediates the reductive transformation of nitroaromatic pollutants by mixed cultures and the role of its surface characteristics were evaluated in this study. Different electron donors were applied to investigate the interaction between RGO and anaerobic microbes. Moreover, the influence of the surface properties of RGO on biological nitroaromatic removal was further elucidated. The results show that RGO could achieve an approximate one-fold rate increase of nitrobenzene reduction by mixed culture with glucose as an electron donor. Selective elimination of oxygen moieties on the RGO surface, such as quinone groups, decreased the nitrobenzene transformation rate, whereas doping nitrogen into the RGO framework exhibited a positive effect. The study indicates that graphene-based carbon nanomaterials have the potential to accelerate the biological transformation of nitroaromatic compounds and that the functionalization of these carbon nanomaterials, especially through surface modification, would further enhance the conversion efficiency of contaminants. PMID:27439321

  15. Perfecting and Understanding Roles in Education. Proceedings of the Annual National Conference of People United for Rural Education (6th, Des Moines, Iowa, February 3-4, 1983).

    ERIC Educational Resources Information Center

    People United for Rural Education, Alden, IA.

    Proceedings of the 1983 People United for Rural Education conference are developed around the theme of "Perfecting and Understanding Roles in Education." Following the introductory materials are 12 papers which were presented at the meeting. Major addresses and authors include: "A Federal Perspective for Excellence in Rural Education," Lawrence…

  16. Deuteration and evolution in the massive star formation process. The role of surface chemistry

    NASA Astrophysics Data System (ADS)

    Fontani, F.; Busquet, G.; Palau, Aina; Caselli, P.; Sánchez-Monge, Á.; Tan, J. C.; Audard, M.

    2015-03-01

    Context. An ever growing number of observational and theoretical evidence suggests that the deuterated fraction (column density ratio between a species containing D and its hydrogenated counterpart, Dfrac) is an evolutionary indicator both in the low- and the high-mass star formation process. However, the role of surface chemistry in these studies has not been quantified from an observational point of view. Aims: Because many abundant species, such as NH3, H2CO, and CH3OH, are actively produced on ice mantles of dust grains during the early cold phases, their Dfrac is expected to evolve differently from species formed only (or predominantly) in the gas, such as N2H+, HNC, HCN, and their deuterated isotopologues. The differences are expected to be relevant especially after the protostellar birth, in which the temperature rises, causing the evaporation of ice mantles. Methods: To compare how the deuterated fractions of species formed only in the gas and partially or uniquely on grain surfaces evolve with time, we observed rotational transitions of CH3OH, 13CH3OH, CH2DOH, and CH3OD at 3 mm and 1.3 mm, of NH2D at 3 mm with the IRAM-30 m telescope, and the inversion transitions (1, 1) and (2, 2) of NH3 with the GBT, towards most of the cores already observed in N2H+, N2D+, HNC, and DNC. Results: NH2D is detected in all but two cores, regardless of the evolutionary stage. Dfrac(NH3) is on average above 0.1 and does not change significantly from the earliest to the most evolved phases, although the highest average value is found in the protostellar phase (~0.3). Few lines of CH2DOH and CH3OD are clearly detected, and then only towards protostellar cores or externally heated starless cores. In quiescent starless cores, we have only one doubtful detection of CH2DOH. Conclusions: This work clearly confirms an expected different evolutionary trend of the species formed exclusively in the gas (N2D+ and N2H+) and those formed partially (NH2D and NH3) or totally (CH2DOH and CH3

  17. Photoluminescence properties of AgInS2-ZnS nanocrystals: the critical role of the surface

    NASA Astrophysics Data System (ADS)

    Chevallier, Théo; Le Blevennec, Gilles; Chandezon, Frédéric

    2016-03-01

    AgInS2-ZnS (ZAIS) nanocrystals are very good candidates for easily synthesized, highly efficient cadmium-free nano-phosphors. They can be employed for the development of next generation white-LED technologies, taking advantage of their nanometric size. This paper describes the combined use of time-resolved emission spectroscopy and photoluminescence quantum yield measurements to quantitatively compare the efficiency of each recombination pathway involved in the photoluminescence of ZAIS nanocrystals. This approach, applied to nanocrystals of different sizes, compositions and surface chemistry revealed the critical role of surface effects. Moreover, we developed a new type of surface passivation that increases the photoluminescence quantum yield of all nanocrystal compositions by 15 to 20%. This molecular surface passivation can be applied as a replacement or in addition to the already established ZnS shell passivation method.AgInS2-ZnS (ZAIS) nanocrystals are very good candidates for easily synthesized, highly efficient cadmium-free nano-phosphors. They can be employed for the development of next generation white-LED technologies, taking advantage of their nanometric size. This paper describes the combined use of time-resolved emission spectroscopy and photoluminescence quantum yield measurements to quantitatively compare the efficiency of each recombination pathway involved in the photoluminescence of ZAIS nanocrystals. This approach, applied to nanocrystals of different sizes, compositions and surface chemistry revealed the critical role of surface effects. Moreover, we developed a new type of surface passivation that increases the photoluminescence quantum yield of all nanocrystal compositions by 15 to 20%. This molecular surface passivation can be applied as a replacement or in addition to the already established ZnS shell passivation method. Electronic supplementary information (ESI) available. See DOI: 10.1039/C5NR07082A

  18. Entropic depletion in colloidal suspensions and polymer liquids: role of nanoparticle surface topography.

    PubMed

    Banerjee, Debapriya; Yang, Jian; Schweizer, Kenneth S

    2015-12-21

    We employ a hybrid Monte Carlo plus integral equation theory approach to study how dense fluids of small nanoparticles or polymer chains mediate entropic depletion interactions between topographically rough particles where all interaction potentials are hard core repulsion. The corrugated particle surfaces are composed of densely packed beads which present variable degrees of controlled topographic roughness and free volume associated with their geometric crevices. This pure entropy problem is characterized by competing ideal translational and (favorable and unfavorable) excess entropic contributions. Surface roughness generically reduces particle depletion aggregation relative to the smooth hard sphere case. However, the competition between ideal and excess packing entropy effects in the bulk, near the particle surface and in the crevices, results in a non-monotonic variation of the particle-monomer packing correlation function as a function of the two dimensionless length scale ratios that quantify the effective surface roughness. As a result, the inter-particle potential of mean force (PMF), second virial coefficient, and spinodal miscibility volume fraction vary non-monotonically with the surface bead to monomer diameter and particle core to surface bead diameter ratios. A miscibility window is predicted corresponding to an optimum degree of surface roughness that completely destroys depletion attraction resulting in a repulsive PMF. Variation of the (dense) matrix packing fraction can enhance or suppress particle miscibility depending upon the amount of surface roughness. Connecting the monomers into polymer chains destabilizes the system via enhanced contact depletion attraction, but the non-monotonic variations with surface roughness metrics persist. PMID:26411493

  19. Surface modification influencing adsorption of red wine constituents: The role of functional groups

    NASA Astrophysics Data System (ADS)

    Mierczynska-Vasilev, Agnieszka; Smith, Paul A.

    2016-11-01

    The adsorption of wine constituents at solid surfaces is important in applications such as filtration and membrane fouling, binding to tanks and fittings and interactions with processing aids such as bentonite. The interaction of wine constituents with surfaces is mediated through adsorbed wine components, where the type of constituents, amount, orientation, and conformation are of consequence for the surface response. This study examines the effect of surface chemical functionalities on the adsorption of red wine constituents. Plasma-polymerized films rich in amine, carboxyl, hydroxyl, formyl and methyl functional groups were generated on solid substrates whereas, glycidyltrimethylammonium chloride was covalently attached to allylamine plasma-polymer modified surface and poly(sodium styrenesulfonate) was electrostatically adsorbed to an amine plasma-polymerized surface. The surface chemical functionalities were characterized by X-ray photoelectron spectroscopy. The ability of different substrates to adsorb red wine constituents was evaluated by quartz crystal microbalance and atomic force microscopy. The results showed that substrates modified with -SO3H and -COOH groups can adsorb more of the wine nitrogen-containing compounds whereas -NH2 and -NR3 groups encourage carbon-containing compounds adsorption. Red wine constituents after filtration were adsorbed in higher extend on -NR3 and -CHO surfaces. The -OH modified surfaces had the lowest ability to absorb wine components.

  20. Survival following a vertical free fall from 300 feet: the crucial role of body position to impact surface.

    PubMed

    Weckbach, Sebastian; Flierl, Michael A; Blei, Michael; Burlew, Clay Cothren; Moore, Ernest E; Stahel, Philip F

    2011-01-01

    We report the case of a 28-year old rock climber who survived an "unsurvivable" injury consisting of a vertical free fall from 300 feet onto a solid rock surface. The trauma mechanism and injury kinetics are analyzed, with a particular focus on the relevance of body positioning to ground surface at the time of impact. The role of early patient transfer to a level 1 trauma center, and "damage control" management protocols for avoiding delayed morbidity and mortality in this critically injured patient are discussed. PMID:22027092

  1. Role of Nanostructure Coating Quality in Delay of Surface Flooding during Jumping Droplet Condensation

    NASA Astrophysics Data System (ADS)

    Preston, Daniel J.; Antao, Dion; Miljkovic, Nenad; Barabadi, Banafsheh; Queeney, John; Wang, Evelyn

    Vapor condensation is commonly observed in everyday life and routinely used in industry as an effective means of transferring heat. In industrial systems, condensed vapor typically forms a thin liquid film which is not desired due to the large thermal resistance to heat transfer; however, if the condensing surface is functionalized with a hydrophobic coating, the condensate forms discrete liquid droplets which shed at sizes approaching the capillary length and refresh the surface for re-nucleation, resulting in a 5-7x heat transfer improvement. Furthermore, when a micro- or nanostructured surface is functionalized, a superhydrophobic surface can be created on which small (~10-100 µm) droplets coalesce and can spontaneously jump away from the surface due to release of excess surface energy; this jumping droplet mode of condensation has been shown to increase heat transfer by an additional 30 - 40%. However, at elevated supersaturations, nanostructured superhydrophobic surfaces can become flooded with condensate and form pinned droplets which cannot jump, thereby eliminating the desired heat transfer improvement. In this work, we experimentally demonstrated a delay in the supersaturation at which surface flooding occurs by reducing the hydrophobic coating defect density. This resulted in a lower proportion of structure unit cells occupied by condensate, which allowed higher droplet mobility and jumping at elevated supersaturation.

  2. The Role of Surface Viscosity in the Escape Mechanism of the Stenus Beetle.

    PubMed

    Dietz, Alexander A; Hofmann, Matthias J; Motschmann, Hubert

    2016-07-28

    Beetles of the species Stenus comma live and hunt close to ponds and rivers, where they occasionally fall on the water surface. To escape this jeopardized state, the beetle developed a strategy relying on the excretion of a secretion containing the substances stenusine and norstenusine. They reduce surface tension and propel the bug to the saving river bank. These substances were synthesized and analyzed with respect to their equilibrium and dynamic adsorption properties at the air-water interface (pH 7, 23 ± 1 °C). The surface dilatational rheological characteristics in a frequency range from 2 to 500 Hz at molar bulk concentrations of 20.6 mmol L(-1) were studied using the oscillating bubble technique. Both alkaloids formed surface viscoelastic adsorption layers. The frequency dependence of the surface dilatational modulus E could successfully be described by the extended Lucassen-van den Tempel model accounting for a nonzero intrinsic surface viscosity κ. The findings confirmed a dual purpose of the spreading alkaloids in the escape mechanism of the Stenus beetle. Next to generating a surface pressure, a transition to surface viscoelastic behavior of the adsorbed layers was observed. PMID:27367059

  3. A Spectral Analysis of the Surface Temperature Field During Evaporative Convection: The Role of Surfactant Monolayers

    NASA Astrophysics Data System (ADS)

    Saylor, J. R.; Smith, G. B.; Flack, K. A.

    1999-11-01

    The presence of a surfactant monolayer changes the hydrodynamic boundary condition of a free surface from one which is shear-free to one which supports shear. This change in boundary condition alters the temperature field observed at the free surface. In this work the surface temperature field of a body of water undergoing evaporation was measured using infrared imaging techniques. These temperature fields were acquired rapidly in time, revealing both the spatial characteristics and the temporal evolution of the surface temperature field during evaporative convection. The temporal and spatial spectra of the surface temperature field are presented for the case of a clean water surface and of a water surface coated with a monolayer of oleyl alcohol. Both experimental cases were conducted at the same heat flux. The spectra reveal significant differences between the clean and surfactant cases. Images of the surface temperature fields for the two cases will be presented along with the spectra. The effect of heat flux on the spectra will also be discussed.

  4. Role of Point Defects on the Reactivity of Reconstructed Anatase Titanium Dioxide (001) Surface

    SciTech Connect

    Wang, Yang; Sun, Huijuan; Tan, Shijing; Feng, Hao; Cheng, Zhengwang; Zhao, Jin; Zhao, Aidi; Wang, Bing; Luo, Yi; Yang, Jinlong; Hou, J. G.

    2013-07-30

    The chemical reactivity of different surfaces of titanium dioxide (TiO2) has been the subject of extensive studies in recent decades. The anatase TiO2(001) and its (1x4) reconstructed surfaces were theoretically considered to be the most reactive and have been heavily pursued by synthetic chemists. However, the lack of direct experimental verification or determination of the active sites on these surfaces has caused controversy and debate. Here we report a systematic study on an anatase TiO2(001)-(1x4) surface by means of microscopic and spectroscopic techniques in combination with first-principles calculations. Two types of intrinsic point defects are identified, among which only the Ti3+ defect site on the reduced surface demonstrates considerable chemical activity. The perfect surface itself can be fully oxidized, but shows no obvious activity. Our findings suggest that the reactivity of the anatase TiO2(001) surface should depend on its reduction status, similar to that of rutile TiO2 surfaces.

  5. Role of surface finishing on pitting corrosion of a duplex stainless steel in seawater

    NASA Astrophysics Data System (ADS)

    Salah-Rousset, N. Ben; Chaouachi, M. A.; Chellouf, A.

    1996-04-01

    Localized corrosion of duplex UNS S32550 stainless steel in seawater was investigated in the laboratory and in field trials for several surface finish conditions: polished, ground, and sandblasted. Electrochemical data obtained by polarization curves showed that the smoother, polished surface had better characteristics (higher pitting and protection potentials) than the ground or sandblasted surfaces. However, despite its high degree of roughness, the sandblasted surface was the most resistant in field conditions, exhibiting the lowest number of sites attacked. Internal compressive stresses created by sandblasting seem also to have an “unsensitizing” effect on sensitized zones that exist in cast steel (due to repairs of mold defects), reducing its susceptibility to microbiologically influenced corrosion (MIC). Such stresses are not generated in polished or ground surfaces, and localized MIC attack can occur.

  6. The possible role of solid surface area in condensation reactions during chemical evolution - Reevaluation

    NASA Technical Reports Server (NTRS)

    Lahav, N.; Chang, S.

    1976-01-01

    Using surface concentration and reaction rate as the main criteria for the feasibility of condensation reactions, four types of prebiotic environments were analyzed: (1) an ocean-sediment system, (2) a dehydrated lagoon bed produced by evaporation, (3) the surface of a frozen sediment, and (4) a fluctuating system where hydration (rainstorms, tidal variations, flooding) and dehydration (evaporation) take place in a cyclic manner. With the possible exception of nucleotides, low adsorption of organomonomers on sediment surfaces of a prebiotic ocean (pH 8) is expected, and significant condensation is considered unlikely. In dehydrated and frozen systems, high surface concentrations are probable and condensation is more likely. In fluctuating environments, condensation rates will be enhanced and the size distribution of the oligomers formed during dehydration may be influenced by a 'redistribution mechanism' in which adsorbed oligomers and monomers are desorbed and redistributed on the solid surface during the next hydration-dehydration cycle.

  7. A Numerical Experiment on the Role of Surface Shear Stress in the Generation of Sound

    NASA Technical Reports Server (NTRS)

    Shariff, Karim; Wang, Meng; Merriam, Marshal (Technical Monitor)

    1996-01-01

    The sound generated due to a localized flow over an infinite flat surface is considered. It is known that the unsteady surface pressure, while appearing in a formal solution to the Lighthill equation, does not constitute a source of sound but rather represents the effect of image quadrupoles. The question of whether a similar surface shear stress term constitutes a true source of dipole sound is less settled. Some have boldly assumed it is a true source while others have argued that, like the surface pressure, it depends on the sound field (via an acoustic boundary layer) and is therefore not a true source. A numerical experiment based on the viscous, compressible Navier-Stokes equations was undertaken to investigate the issue. A small region of a wall was oscillated tangentially. The directly computed sound field was found to to agree with an acoustic analogy based calculation which regards the surface shear as an acoustically compact dipole source of sound.

  8. Role of functional groups in surface bonding of planar π-conjugated molecules

    NASA Astrophysics Data System (ADS)

    Bauer, Oliver; Mercurio, Giuseppe; Willenbockel, Martin; Reckien, Werner; Heinrich Schmitz, Christoph; Fiedler, Benjamin; Soubatch, Serguei; Bredow, Thomas; Tautz, Frank Stefan; Sokolowski, Moritz

    2012-12-01

    The trends in the bonding mechanism of 3,4,9,10-perylenetetracarboxylic acid dianhydride (PTCDA) to the Ag(111), Ag(100), and Ag(110) surfaces were analyzed on the basis of data obtained from x-ray standing waves and dispersion-corrected density functional theory. Of importance are the attractive local O-Ag bonds on the anhydride groups. They are the shorter, the more open the surface is, and lead even to partly repulsive interactions between the perylene core and the surface. In parallel, there is an increasing charge donation from the Ag surface into the π system of the PTCDA. This synergism explains the out-of-plane distortion of the adsorbed PTCDA and the surface buckling.

  9. Ferrocene-1,1'-dithiol as molecular wire between Ag electrodes: The role of surface defects

    NASA Astrophysics Data System (ADS)

    Bredow, T.; Tegenkamp, C.; Pfnür, H.; Meyer, J.; Maslyuk, V. V.; Mertig, I.

    2008-02-01

    The interaction of ferrocene-1,1'-dithiol (FDT) with two parallel Ag(111) surfaces has been theoretically studied at density-functional level. The effect of surface defects on the energetic and electronic structure was investigated. The electronic transport properties are studied with the nonequilibrium Green's function approach. The adsorption geometry has a strong effect on the electronic levels and conductivity. The presence of point defects strongly enhances the molecule-surface interaction but has a surprisingly small effect on the density of states near the Fermi energy. The FDT-surface bond is particularly strong near terraces or steps and leads to significant shifts of the molecular orbitals relative to the gas phase. For all considered defect types except the single adatom the electronic conductivity through the FDT molecule is decreased compared to adsorption on perfect surfaces.

  10. The role of phosphorylation in dentin phosphoprotein peptide absorption to hydroxyapatite surfaces: a molecular dynamics study

    PubMed Central

    Villarreal-Ramirez, Eduardo; Garduño-Juarez, Ramon; Gericke, Arne; Boskey, Adele

    2015-01-01

    Dentin phosphoprotein (DPP) is a protein expressed mainly in dentin and to a lesser extent in bone. DPP has a disordered structure, rich in glutamic acid, aspartic acid and phosphorylated serine/threonine residues. It has a high capacity for binding to calcium ions and to hydroxyapatite (HA) crystal surfaces. We used molecular dynamics (MD) simulations as a method for virtually screening interactions between DPP motifs and HA. The goal was to determine which motifs are absorbed to HA surfaces. For these simulations, we considered five peptides from the human DPP sequence. All-atom MD simulations were performed using GROMACS, the peptides were oriented parallel to the {100} HA crystal surface, the distance between the HA and the peptide was 3 nm. The system was simulated for 20 ns. Preliminary results show that for the unphosphorylated peptides, the acidic amino acids present an electrostatic attraction where their side chains are oriented towards HA. This attraction, however, is slow to facilitate bulk transport to the crystal surface. On the other hand, the phosphorylated (PP) peptides are rapidly absorbed on the surface of the HA with their centers of mass closer to the HA surface. More importantly, the root mean square fluctuation (RMSF) indicates that the average structures of the phosphorylated peptides are very inflexible and elongate, while that of the unphosphorylated peptides are flexible. Radius of gyration (Rg) analysis showed the compactness of un-phosphorylated peptides is lower than phosphorylated peptides. Phosphorylation of the DPP peptides is necessary for binding to HA surfaces. PMID:25158198

  11. The role of land cover in high latitude land surface temperature heterogeneity

    NASA Astrophysics Data System (ADS)

    Wang, D.; Nagol, J. R.; Morton, D. C.; Masek, J. G.

    2011-12-01

    Near-surface air temperature governs a range of land surface processes, such as photosynthesis, respiration, and evapotranspiration. However, the spatiotemporal patterns of near-surface air temperature are complex. Meteorological stations provide a detailed account of temporal variations in air temperature, but fail to capture spatial heterogeneity in surface temperature, especially over remote regions with sparse station networks. Gridded climate datasets (0.5° - 2.0° spatial resolution) produced from the meteorological station observations therefore inherit these same shortcomings, since current algorithms use only latitude, longitude, and elevation to interpolate between station locations. Here, we explored the use of MODIS-based estimates of land surface temperature (LST) and land cover to estimate fine-scale heterogeneity in land surface temperature during summer months over boreal North America. We combined nighttime MODIS LST with meteorological station and gridded climate data records. Our analysis quantified the contribution from station distance (latitude and longitude) and land cover type for differences between MODIS and station-based estimates of nighttime temperatures. Finally, we estimated the impact of sub-grid cell heterogeneity in LST for ecosystem processes by comparing seasonal respiration fluxes from an ecosystem model driven by gridded climate data and MODIS LST. Our study suggests that downscaling coarse resolution temperature data using MODIS LST and land cover information can improve estimates of spatial variability in surface temperature data and related ecosystem processes.

  12. Developpement des betons semi autoplacants a rheologie adaptee pour des infrastructures

    NASA Astrophysics Data System (ADS)

    Sotomayor Cruz, Cristian Daniel

    BSAP-I optimisés à travers une caractérisation complète des propriétés mécaniques et de la durabilité a été réalisée. A la suite de cette étude, les résultats obtenus nous permettent de conclure que : (1) L'utilisation d'un BSAP-I avec un gros granulat de 5 - 14 mm, des rapports E/L = 0,37 et S/G = 0,52 et une teneur en air de 6 à 9% a été possible en conférant un équilibre optimal fluidité / stabilité à l'état frais, ainsi qu'un niveau de thixotropie adéquate au chantier permettant d'optimiser la conception du coffrage des piliers de pont et de conférer des qualités de surfaces très acceptables de ces infrastructures. (2) La méthode adaptée pour l'essai L-Box contenant 2 barres et une vibration de 5 secondes a permis de bien caractériser la capacité de remplissage d'un BSAP-I. (3) L'utilisation d'un plan factoriel 23 a permis d'obtenir des modèles statistiques fiables, capables de prédire les propriétés rhéologiques à l'état frais et les résistances en compression des BSAP-I avec des dosages en liant entre 370 et 420 kg/m3, des rapports E/L entre 0,34 et 0,40 et S/G entre 0,47 et 0,53. (4) Des mesures de vitesse d'écoulement T40 d'un BSAP-I sont très semblables à celles d'un BAP. En plus, des valeurs T40 montrent une bonne corrélation linéaire avec celles de T400 mesurés dans la boîte L-Box. (5) À la frontière du BAP et du BCV, une bande rhéologique possédant un τ0 entre 30 et 320 Pa et un η entre 10 et 140 Pa.s a été trouvée pour la conception optimale des BSAP-I. (6) Les BSAP-I optimisés ont également conféré une très bonne performance à l'état frais, en permettant maintenir un bon équilibre entre la rhéologie et la stabilité dans le temps, lorsqu'on utilise une énergie de vibration minimale pour amorcer son écoulement. (7) À l'état durci Les BSAP-I ont conféré une bonne performance présentant des résistances mécaniques élevées et des niveaux négligeables de pénétration aux ions chlores

  13. The role of surface electronic structure in thin film molecular ordering.

    SciTech Connect

    Sakurai, T.; Tromp, R. M.; Meyer zu Heringdorf, F.; Sadowski, J.; Thayer, Gayle Echo

    2005-05-01

    We show that the orientation of pentacene molecules is controlled by the electronic structure of the surface on which they are deposited. We suggest that the near-Fermi level density of states above the surface controls the interaction of the substrate with the pentacene {pi} orbitals. A reduction of this density as compared to noble metals, realized in semimetallic Bi(001) and Si(111)(5 x 2)Au surfaces, results in pentacene standing up. Interestingly, pentacene grown on Bi(001) is highly ordered, yielding the first vertically oriented epitaxial pentacene thin films observed to date.

  14. Etude theorique et experimentale des evaporateurs de dioxyde de carbone operant dans des conditions de givrage

    NASA Astrophysics Data System (ADS)

    Bendaoud, Adlane Larbi

    . Dans la partie theorique, un modele traitant les aspects thermique, hydrodynamique et massique a ete elabore. Sur la base de ce modele a ete ecrit un programme informatique en langage FORTRAN 6.6. Il est base sur la discretisation du serpentin en volumes de controle, est entierement automatise et peut traiter des echangeurs de chaleur avec des circuits de refrigerant complexes pouvant avoir des entrees et sorties multiples ainsi que des bifurcations. La presence simultanee des trois phases thermodynamiques du refrigerant (liquide sous refroidi, fluide sature, vapeur surchauffee) dans le serpentin est aussi prise en charge. Le modele a ete valide pour un fonctionnement avec et sans formation de givre en utilisant des donnees experimentales disponibles dans la litterature et celles obtenues sur le banc d'essai de CanmetENERGIE. Celui-ci a ete mis a jour pour les besoins de la presente recherche et pour cela, un systeme de surchauffe et d'injection de la vapeur d'eau dans une enceinte a tres basse temperature a ete dimensionne, fabrique et installe. Un dispositif de visualisation de la formation de givre, ainsi qu'un equipement de mesure de la temperature, de la pression et de l'humidite relative de l'air ont aussi ete ajoutes. Une fois le modele valide, des simulations numeriques sur le serpentin avec et sans formation de givre ont ete effectuees. Un premier cas de base a servi comme reference pour d'autres cas pour lesquels une etude parametrique sur la geometrie et le fonctionnement a ete menee. Il a ete montre par rapport au cas de base que : 1. la diminution de la densite des ailettes sur des rangees specifiques du serpentin donne une surface minimale (Amin) plus grande, retardant ainsi l'obstruction totale du serpentin par le givre et permet donc un temps de fonctionnement plus grand et une frequence de degivrage plus faible. 2. une bonne configuration de circuit de refrigerant augmente le temps de fonctionnement du serpentin de 200 % et delivre une puissance

  15. Profil epidemiologique des brulures d'enfants admis au Centre National des Brules, Maroc

    PubMed Central

    Zahid, A.; Atannaz, J.; Alaoui, M.; Rafik, A.; Ezzoubi, M.; Diouri, M.; Chlihi, A.; Bahechar, N.; Boukind, E.H.

    2011-01-01

    Summary Ce travail rétrospectif analyse les particularités épidémiologiques de 543 cas de brûlures d'enfants, représentant 45,7% des admissions de notre centre, en vue de déterminer les éléments pouvant contribuer à renforcer la prévention, qui reste le traitement de choix de cette pathologie. La moyenne d'âge est de 4,25 ans avec une prédilection pour la tranche d'âge d'un à cinq ans, avec 42,5% des cas. Une atteinte masculine est retrouvée dans 63,5% des cas. La brûlure survient à domicile dans 85,1% et accidentellement dans 95% des cas. Les brûlures thermiques représentent 96,5% des causes dominées par les liquides dans 69,3% des cas. La surface cutanée brûlée est ≥ 20% dans 52,3%. La brûlure intéresse essentiellement les membres supérieurs (79,1%). 56,8% des enfants sont transférés par d'autres hôpitaux et le délai de prise en charge hospitalière est supérieur à 6 heures dans 65,5%. Le taux de mortalité a été de 13,2%. PMID:22639559

  16. Biophysical bases of human plasma lipoprotein polydispersity: role of surface modification

    SciTech Connect

    Shahrokh, Z.

    1984-11-01

    Metabolic depletion of the core of the triglyceride-rich lipoproteins via lipolysis results in the production of polydisperse species of particles within the density range of low density lipoproteins (LDL). Modifications of surface properties of plasma LDL may further contribute to LDL polydispersity. In this dissertation, we study the interactions with LDL of models of lipolysis-related surface products (i.e., phosphatidylcholine vesicles (PCV) and discoidal complexes (DC) of apoprotein AI and phosphatidylcholine) and examine the influence on such interactions of high density lipoproteins (HDL) and other relevant plasma components (lecithin:cholesterol acyltransferase (LCAT), lipid transfer proteins (LTPs), albumin, lysolecithin (LPC)). Based on the studies obtained in this dissertation LDL surface modification may contribute to LDL polydispersity. Since HDL is a major acceptor of PL, formation of surface-modified LDL (e.g., PL-enriched, larged LDL) in vivo would depend on LDL/HDL weight ratio in plasma. 140 references, 50 figures, 15 tables.

  17. How light gets through periodically nanostructured metal films: a role of surface polaritonic crystals.

    PubMed

    Zayats, A V; Salomon, L; De Fornel, F

    2003-06-01

    The physical origin of the enhanced optical transmission of periodically structured films related to surface plasmon polaritons is discussed from first principles. The enhancement of transmission through smooth, randomly rough and periodically nanostructured films is considered. Analysis shows that any metal (or dielectric) nanostructured film can exhibit enhanced transmission in certain spectral ranges corresponding to surface plasmon (or phonon) polariton Bloch mode states on a periodic structure. Resonant tunnelling via these states is responsible for the transmission enhancement. The properties of surface polaritonic crystals are analogous to those of photonic crystals and can find numerous applications for scaling down optical devices to nanometric dimensions as well as for designing novel nanostructured materials whose optical properties are determined by surface polariton interaction in a periodic structure. PMID:12787112

  18. Role of surface vibrational properties on cooperative phenomena in spin-crossover nanomaterials

    NASA Astrophysics Data System (ADS)

    Mikolasek, Mirko; Félix, Gautier; Molnár, Gábor; Terki, Férial; Nicolazzi, William; Bousseksou, Azzedine

    2014-08-01

    The influence of surface/interface on the lattice dynamics of spin crossover nanoparticles has been investigated by a spring-ball model solved by Monte Carlo methods. The bond cohesion energy of the model has been extracted from Mössbauer spectroscopy measurements performed on the model compound Ni3[Fe(CN)6]. We show that the coupling between bulk and surface vibrational properties, which drastically affects the mechanical properties of the whole particle below a characteristic size, has a major impact on the phase stability of the particles. In the case of free surfaces, the Debye temperature decreases with the size and the first-order nature of the spin transition disappears. On the other hand, a hardening of the surface bonds leads to increasing particle stiffness with the size reduction. In this case, a persistence of the hysteretic behavior in the spin transition curve is also predicted in good agreement with previous theoretical and experimental results.

  19. Condensed-Phase Photochemical Processes in Titan's Aerosols and Surface: The Role of Longer Wavelength Photochemistry

    NASA Technical Reports Server (NTRS)

    Gudipati, Murthy S.; Jacovi, Ronen; Lignell, Antti; Couturier, Isabelle

    2011-01-01

    We will discuss photochemical properties of Titan's organic molecules in the condensed phase as solid aerosols or surface material, from small linear polyyenes (polyacetylenes and polycyanoacetylenes) such as C2H2, C4N2, HC5N, etc. In particular we will focus on photochemistry caused by longer wavelength UV-VIS photons (greater than 250 nm) photons that make it through Titan's atmosphere to the haze region (approximately 100 km) and on to the surface of Titan.

  20. (A structural assessment of the role of the cell surface carbohydrates of Rhizobium in the Rhizobium/legume symbiosis)

    SciTech Connect

    Hollingsworth, R.I.

    1991-01-01

    Research continued on the study of cell surface carbohydrates of Rhizobium. Objectives include: To characterize, at a structural level, the differences between the lipopolysaccharides of a representative number of strains from different Rhizobium species to determine which features of LPS structure are species-specific and might, therefore, be determinants of host specificity. Determine the effect(s) of nod gene induction on the structure of Rhizobium lipopolysaccharides and determine whether synthesis of a modified LPS molecule or a new surface glycoconjugate is initiated by nod gene induction. Develop a non-chemical means for rapidly screening large numbers of bacterial strains in order to determine which glycoconjugate structural features are conserved between strains of the same species. Provide the necessary structural information which, when coupled with developments in the rapidly expanding field of Rhizobium genetics, should lead to a clear understanding of the role of Rhizobium surface glycoconjugates in host/symbiont interactions. Progress is discussed.

  1. Magnetic frustration, short-range correlations and the role of the paramagnetic Fermi surface of PdCrO2

    PubMed Central

    Billington, David; Ernsting, David; Millichamp, Thomas E.; Lester, Christopher; Dugdale, Stephen B.; Kersh, David; Duffy, Jonathan A.; Giblin, Sean R.; Taylor, Jonathan W.; Manuel, Pascal; Khalyavin, Dmitry D.; Takatsu, Hiroshi

    2015-01-01

    Frustrated interactions exist throughout nature, with examples ranging from protein folding through to frustrated magnetic interactions. Whilst magnetic frustration is observed in numerous electrically insulating systems, in metals it is a rare phenomenon. The interplay of itinerant conduction electrons mediating interactions between localised magnetic moments with strong spin-orbit coupling is likely fundamental to these systems. Therefore, knowledge of the precise shape and topology of the Fermi surface is important in any explanation of the magnetic behaviour. PdCrO2, a frustrated metallic magnet, offers the opportunity to examine the relationship between magnetic frustration, short-range magnetic order and Fermi surface topology. By mapping the short-range order in reciprocal space and experimentally determining the electronic structure, we have identified the dual role played by the Cr electrons in which the itinerant ones on the nested paramagnetic Fermi surface mediate the frustrated magnetic interactions between local moments. PMID:26206589

  2. Normal and shear forces between charged solid surfaces immersed in cationic surfactant solution: the role of the alkyl chain length.

    PubMed

    Silbert, Gilad; Kampf, Nir; Klein, Jacob

    2014-05-13

    Using a surface force balance (SFB), we measured the boundary friction and the normal forces between mica surfaces immersed in a series of alkyltrimethylammonium chloride (TAC) surfactant solutions well above the critical micelle concentration (CMC). The surfactants that were used--C14TAC, C16TAC, and C18TAC--varied by the length of the alkyl chain. The structures of the adsorbed layers on the mica were obtained using AFM imaging and ranged from flat bilayers to rodlike micelles. Despite the difference in alkyl chain, all the surfactant solutions reduce the friction between the two mica surfaces enormously relative to immersion in water, and have similar friction coefficients (μ ≈ 0.001). The pressure at which such lubrication breaks down is higher for the surfactants with longer chain lengths and indicates that an important role of the chain length is to provide a more robust structure of the adsorbed layers which maintains its integrity to higher pressures. PMID:24720712

  3. Magnetic frustration, short-range correlations and the role of the paramagnetic Fermi surface of PdCrO2.

    PubMed

    Billington, David; Ernsting, David; Millichamp, Thomas E; Lester, Christopher; Dugdale, Stephen B; Kersh, David; Duffy, Jonathan A; Giblin, Sean R; Taylor, Jonathan W; Manuel, Pascal; Khalyavin, Dmitry D; Takatsu, Hiroshi

    2015-01-01

    Frustrated interactions exist throughout nature, with examples ranging from protein folding through to frustrated magnetic interactions. Whilst magnetic frustration is observed in numerous electrically insulating systems, in metals it is a rare phenomenon. The interplay of itinerant conduction electrons mediating interactions between localised magnetic moments with strong spin-orbit coupling is likely fundamental to these systems. Therefore, knowledge of the precise shape and topology of the Fermi surface is important in any explanation of the magnetic behaviour. PdCrO2, a frustrated metallic magnet, offers the opportunity to examine the relationship between magnetic frustration, short-range magnetic order and Fermi surface topology. By mapping the short-range order in reciprocal space and experimentally determining the electronic structure, we have identified the dual role played by the Cr electrons in which the itinerant ones on the nested paramagnetic Fermi surface mediate the frustrated magnetic interactions between local moments. PMID:26206589

  4. Role of rough surface topography on gas slip flow in microchannels.

    PubMed

    Zhang, Chengbin; Chen, Yongping; Deng, Zilong; Shi, Mingheng

    2012-07-01

    We conduct a lattice Boltzmann simulation of gas slip flow in microchannels incorporating rough surface effects as characterized by fractal geometry with a focus on gas-solid interaction. The gas slip flow in rough microchannels, which is characterized by Poiseuille number and mass flow rate, is evaluated and compared with smooth microchannels. The effects of roughness height, surface fractal dimension, and Knudsen number on slip behavior of gas flow in microchannels are all investigated and discussed. The results indicate that the presence of surface roughness reduces boundary slip for gas flow in microchannels with respect to a smooth surface. The gas flows at the valleys of rough walls are no-slip while velocity slips are observed over the top of rough walls. We find that the gas flow behavior in rough microchannels is insensitive to the surface topography irregularity (unlike the liquid flow in rough microchannels) but is influenced by the statistical height of rough surface and rarefaction effects. In particular, decrease in roughness height or increase in Knudsen number can lead to large wall slip for gas flow in microchannels. PMID:23005537

  5. Role of Oxygen as Surface-Active Element in Linear GTA Welding Process

    NASA Astrophysics Data System (ADS)

    Yadaiah, Nirsanametla; Bag, Swarup

    2013-11-01

    Although the surface-active elements such as oxygen and sulfur have an adverse effect on momentum transport in liquid metals during fusion welding, such elements can be used beneficially up to a certain limit to increase the weld penetration in the gas tungsten arc (GTA) welding process. The fluid flow pattern and consequently the weld penetration and width change due to a change in coefficient of surface tension from a negative value to a positive value. The present work is focused on the analysis of possible effects of surface-active elements to change the weld pool dimensions in linear GTA welding. A 3D finite element-based heat transfer and fluid flow model is developed to study the effect of surface-active elements on stainless steel plates. A velocity in the order of 180 mm/s due to surface tension force is estimated at an optimum concentration of surface-active elements. Further, the differential evolution-based global optimization algorithm is integrated with the numerical model to estimate uncertain model parameters such as arc efficiency, effective arc radius, and effective values of material properties at high temperatures. The effective values of thermal conductivity and viscosity are estimated to be enhanced nine and seven times, respectively, over corresponding room temperature values. An error analysis is also performed to find out the overall reliability of the computed results, and a maximum reliability of 0.94 is achieved.

  6. Role of gravity in the formation of bacterial colonies with a hydrophobic surface layer

    NASA Astrophysics Data System (ADS)

    Puzyr, A. P.; Tirranen, L. K.; Krylova, T. Y.; Borodina, E. V.

    A simple technique for determining hydrophobic-hydrophilic properties of bacterial colonies surface, which involves putting a drop of liquid with known properties (e.g. water, oil) on their surface, has been described. This technique allows quick estimate of wettability of bacterial colony surface, i.e. its hydrophobic-hydrophilic properties. The behaviour of water drops on colonies of bacteria Bacillus five strains (of different types) has been studied. It was revealed that 1) orientation in the Earth gravity field during bacterial growth can define the form of colonies with hydrophobic surface; 2) the form and size of the colony are dependent on the extention ability, most probably, of the hydrophobic layer; 3) the Earth gravity field (gravity) serves as a 'pump' providing and keeping water within the colony. We suppose that at growing colonies on agar media the inflow of water-soluble nutrient materials takes place both due to diffusion processes and directed water current produced by the gravity. The revealed effect probably should be taken into consideration while constructing the models of colonies growing on dense nutrient media. The easily determined hydrophobic properties of colonies surface can become a systematic feature after collecting more extensive data on the surface hydrophobic-hydrophilic properties of microorganism colonies of other types and species.

  7. Role of Exposed Surfaces on Zinc Oxide Nanostructures in the Catalytic Ethanol Transformation.

    PubMed

    Morales, María V; Asedegbega-Nieto, Esther; Iglesias-Juez, Ana; Rodríguez-Ramos, Inmaculada; Guerrero-Ruiz, Antonio

    2015-07-01

    For a series of nanometric ZnO materials, the relationship between their morphological and surface functionalities and their catalytic properties in the selective decomposition of ethanol to yield acetaldehyde was explored. Six ZnO solids were prepared by a microemulsion-precipitation method and the thermal decomposition of different precursors and compared with a commercial sample. All these materials were characterized intensively by XRD and SEM to obtain their morphological specificities. Additionally, surface area determinations and IR spectroscopy were used to detect differences in the surface properties. The density of acid surface sites was determined quantitatively using an isopropanol dehydration test. Based on these characterization studies and on the results of the catalytic tests, it has been established that ZnO basal surfaces seem to be responsible for the production of ethylene as a minor product as well as for secondary reactions that yield acetyl acetate. Furthermore, one specific type of exposed hydroxyl groups appears to govern the surface catalytic properties. PMID:26087720

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

    PubMed

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

    2016-08-16

    Nitrous acid (HONO) accumulates in the nocturnal boundary layer where it is an important source of daytime hydroxyl radicals. Although there is clear evidence for the involvement of heterogeneous reactions of NO2 on surfaces as a source of HONO, mechanisms remain poorly understood. We used coated-wall flow tube measurements of NO2 reactivity on environmentally relevant surfaces (Fe (hydr)oxides, clay minerals, and soil from Arizona and the Saharan Desert) and detailed mineralogical characterization of substrates to show that reduction of NO2 by Fe-bearing minerals in soil can be a more important source of HONO than the putative NO2 hydrolysis mechanism. The magnitude of NO2-to-HONO conversion depends on the amount of Fe(2+) present in substrates and soil surface acidity. Studies examining the dependence of HONO flux on substrate pH revealed that HONO is formed at soil pH < 5 from the reaction between NO2 and Fe(2+)(aq) present in thin films of water coating the surface, whereas in the range of pH 5-8 HONO stems from reaction of NO2 with structural iron or surface complexed Fe(2+) followed by protonation of nitrite via surface Fe-OH2(+) groups. Reduction of NO2 on ubiquitous Fe-bearing minerals in soil may explain HONO accumulation in the nocturnal boundary layer and the enhanced [HONO]/[NO2] ratios observed during dust storms in urban areas. PMID:27409359

  9. Role of Extracellular Structures of Escherichia coli O157:H7 in Initial Attachment to Biotic and Abiotic Surfaces

    PubMed Central

    Nagy, Attila; Mowery, Joseph; Bauchan, Gary R.; Wang, Lili; Nichols-Russell, Lydia

    2015-01-01

    Infection by human pathogens through the consumption of fresh, minimally processed produce and solid plant-derived foods is a major concern of the U.S. and global food industries and of public health services. Enterohemorrhagic Escherichia coli O157:H7 is a frequent and potent foodborne pathogen that causes severe disease in humans. Biofilms formed by E. coli O157:H7 facilitate cross-contamination by sheltering pathogens and protecting them from cleaning and sanitation operations. The objective of this research was to determine the role that several surface structures of E. coli O157:H7 play in adherence to biotic and abiotic surfaces. A set of isogenic deletion mutants lacking major surface structures was generated. The mutant strains were inoculated onto fresh spinach and glass surfaces, and their capability to adhere was assessed by adherence assays and fluorescence microscopy methods. Our results showed that filament-deficient mutants bound to the spinach leaves and glass surfaces less strongly than the wild-type strain did. We mimicked the switch to the external environment—during which bacteria leave the host organism and adapt to lower ambient temperatures of cultivation or food processing—by decreasing the temperature from 37°C to 25°C and 4°C. We concluded that flagella and some other cell surface proteins are important factors in the process of initial attachment and in the establishment of biofilms. A better understanding of the specific roles of these structures in early stages of biofilm formation can help to prevent cross-contaminations and foodborne disease outbreaks. PMID:25956766

  10. The role of advanced reactive surface area characterization in improving predictions of mineral reaction rates

    NASA Astrophysics Data System (ADS)

    Beckingham, L. E.; Zhang, S.; Mitnick, E.; Cole, D. R.; Yang, L.; Anovitz, L. M.; Sheets, J.; Swift, A.; Kneafsey, T. J.; Landrot, G.; Mito, S.; Xue, Z.; Steefel, C. I.; DePaolo, D. J.; Ajo Franklin, J. B.

    2014-12-01

    Geologic sequestration of CO2 in deep sedimentary formations is a promising means of mitigating carbon emissions from coal-fired power plants but the long-term fate of injected CO2 is challenging to predict. Reactive transport models are used to gain insight over long times but rely on laboratory determined mineral reaction rates that have been difficult to extrapolate to field systems. This, in part, is due to a lack of understanding of mineral reactive surface area. Many models use an arbitrary approximation of reactive surface area, applying orders of magnitude scaling factors to measured BET or geometric surface areas. Recently, a few more sophisticated approaches have used 2D and 3D image analyses to determine mineral-specific reactive surface areas that account for the accessibility of minerals. However, the ability of these advanced surface area estimates to improve predictions of mineral reaction rates has yet to be determined. In this study, we fuse X-ray microCT, SEM QEMSCAN, XRD, SANS, and SEM-FIB analysis to determine mineral-specific accessible reactive surface areas for a core sample from the Nagaoka pilot CO2 injection site (Japan). This sample is primarily quartz, plagioclase, smectite, K-feldspar, and pyroxene. SEM imaging shows abundant smectite cement and grain coatings that decrease the fluid accessibility of other minerals. However, analysis of FIB-SEM images reveals that smectite nano-pores are well connected such that access to underlying minerals is not occluded by smectite coatings. Mineral-specific accessible surfaces are determined, accounting for the connectivity of the pore space with and without connected smectite nano-pores. The large-scale impact of variations in accessibility and dissolution rates are then determined through continuum scale modeling using grid-cell specific information on accessible surface areas. This approach will be compared with a traditional continuum scale model using mineral abundances and common surface area

  11. The role of surface charge on the uptake and biocompatibility of hydroxyapatite nanoparticles with osteoblast cells

    PubMed Central

    Chen, Liang; Mccrate, Joseph M.; Lee, James C-M.; Li, Hao

    2011-01-01

    The objective of this study is to evaluate the effect of hydroxyapatite (HAP) nanoparticles with different surface charges on the cellular uptake behavior and in vitro cell viability and proliferation of MC3T3-E1 cell lines (osteoblast). The nanoparticles surface charge was varied by the surface modification with two carboxylic acids: 12-aminododecanoic acid (positive) and dodecanedioic acid (negative). The untreated HAP nanoparticles and dodecanoic acid modified HAP nanoparticles (neutral) were used as the control. X-ray diffraction (XRD) revealed that surface modifications by the three carboxylic acids did not change the crystal structure of HAP nanoparticles; Fourier transform infrared spectroscopy (FTIR) confirmed the adsorption and binding of the carboxylic acids on HAP nanoparticle surface; and zeta potential measurement confirmed that the chemicals successfully modified the surface charge of HAP nanoparticles in water based solution. Transmission electron microscopy (TEM) images showed that positively charged, negatively charged and untreated HAP nanoparticles, with similar size and shape, all penetrated into the cells and cells had more uptake of HAP nanoparticles with positive charge compared to those with negative charge, which might be attributed to the attractive or repulsive interaction between the negatively charged cell membrane and positively/negatively charged HAP nanoparticles. The neutral HAP nanoparticles could not penetrate cell membrane due to the larger size. MTT assay and LDH assay results indicated that as compared with the polystyrene control, greater cell viability and cell proliferation were measured on MC3T3-E1 cells treated with the three kinds of the HAP nanoparticles (neutral, positive, and untreated), among which positively charged HAP nanoparticles shows strongest improvement for cell viability and cell proliferation. In summary, the surface charge of HAP nanoparticles can be modified to influence the cellular uptake of HAP

  12. Two modes of surface roughening during plasma etching of silicon: Role of ionized etch products

    NASA Astrophysics Data System (ADS)

    Nakazaki, Nobuya; Tsuda, Hirotaka; Takao, Yoshinori; Eriguchi, Koji; Ono, Kouichi

    2014-12-01

    Atomic- or nanometer-scale surface roughening has been investigated during Si etching in inductively coupled Cl2 plasmas, as a function of rf bias power or ion incident energy Ei, by varying feed gas flow rate, wafer stage temperature, and etching time. The experiments revealed two modes of surface roughening which occur depending on Ei: one is the roughening mode at low Ei < 200-300 eV, where the root-mean-square (rms) roughness of etched surfaces increases with increasing Ei, exhibiting an almost linear increase with time during etching (t < 20 min). The other is the smoothing mode at higher Ei, where the rms surface roughness decreases substantially with Ei down to a low level < 0.4 nm, exhibiting a quasi-steady state after some increase at the initial stage (t < 1 min). Correspondingly, two different behaviors depending on Ei were also observed in the etch rate versus √{Ei } curve, and in the evolution of the power spectral density distribution of surfaces. Such changes from the roughening to smoothing modes with increasing Ei were found to correspond to changes in the predominant ion flux from feed gas ions Clx+ to ionized etch products SiClx+ caused by the increased etch rates at increased Ei, in view of the results of several plasma diagnostics. Possible mechanisms for the formation and evolution of surface roughness during plasma etching are discussed with the help of Monte Carlo simulations of the surface feature evolution and classical molecular dynamics simulations of etch fundamentals, including stochastic roughening and effects of ion reflection and etch inhibitors.

  13. Annuaire du bureau des Longitudes : guide de données astronomiques 2011 pour l'observation du ciel

    NASA Astrophysics Data System (ADS)

    Institut de Mécanique Céleste Et de Calcul Des Ephémérides (Imcce); Bureau Des Longitudes (Bdl)

    2010-07-01

    Destiné aux astronomes, professionnels ou amateurs, cet ouvrage se décompose de la façon suivante : Les trois premiers chapitres de cet ouvrage contiennent : les données sur les différents calendriers et leur concordance, les fêtes légales en France, les différentes échelles de temps, les dates de décrets sur les heures légales en France métropolitaine parues au Journal Officiel depuis 1916 ; des notions nécessaires à la compréhension et à l'emploi des éphémérides contenues dans l'ouvrage. Les chapitres suivant fournissent des éphémérides astronomiques : les positions du Soleil et de la Lune ; les positions des planètes et de leurs satellites ; les positions des astéroïdes et des comètes ; les explications et des données pour l'observation de la surface du Soleil, de la Lune et des planètes ; des cartes du ciel, une liste de constellations et les positions et occultations des étoiles ; des données sur les éclipses de Soleil et de Lune et sur les phénomènes astronomiques ; la liste des observatoires astronomiques les plus connus.

  14. Annuaire du bureau des Longitudes : guide de données astronomiques 2012 pour l'observation du ciel

    NASA Astrophysics Data System (ADS)

    Institut de Mécanique Céleste Et de Calcul Des Ephémérides (Imcce); Bureau Des Longitudes (Bdl)

    2011-07-01

    Destiné aux astronomes, professionnels ou amateurs, cet ouvrage se décompose de la façon suivante : Les trois premiers chapitres de cet ouvrage contiennent : les données sur les différents calendriers et leur concordance, les fêtes légales en France, les différentes échelles de temps, les dates de décrets sur les heures légales en France métropolitaine parues au Journal Officiel depuis 1916 ; des notions nécessaires à la compréhension et à l'emploi des éphémérides contenues dans l'ouvrage. Les chapitres suivant fournissent des éphémérides astronomiques : les positions du Soleil et de la Lune ; les positions des planètes et de leurs satellites ; les positions des astéroïdes et des comètes ; les explications et des données pour l'observation de la surface du Soleil, de la Lune et des planètes ; des cartes du ciel, une liste de constellations et les positions et occultations des étoiles ; des données sur les éclipses de Soleil et de Lune et sur les phénomènes astronomiques ; la liste des observatoires astronomiques les plus connus.

  15. An assessment of recharge estimates from stream and well data and from a coupled surface-water/groundwater model for the des Anglais catchment, Quebec (Canada)

    NASA Astrophysics Data System (ADS)

    Chemingui, Asma; Sulis, Mauro; Paniconi, Claudio

    2015-12-01

    Estimation of groundwater recharge is of critical importance for effective management of freshwater resources. Three common and distinct approaches for calculating recharge rely on techniques of baseflow separation, well hydrograph analysis, and numerical modeling. In this study, these three methods are assessed for a watershed in southwestern Quebec, Canada. A physically based surface-subsurface model provides estimates of spatially distributed recharge; two baseflow separation filters estimate recharge from measured streamflow; and a well hydrograph master recession curve technique calculates recharge from water-table elevation records. The recharge results obtained are in good agreement over the entire catchment, producing an annual aquifer recharge of 10-30 % of rainfall. The annual average estimated across all methods is 200 mm/year. High variability is obtained for the monthly and seasonal recharge patterns (e.g. respectively, 0-30 mm for September and 0-95 mm for the summer), in particular between the baseflow filters and the well hydrograph technique and between the hydrograph technique and the simulated estimates at the observation wells. Recharge occurs predominantly in the spring months for the different approaches, except for the master recession curve method for which the highest recharge estimates are obtained during the summer. The recharge distribution obtained with the model shows that the main recharge area of the aquifer is the Covey Hill region. The use of a fully integrated physically based model enables the construction of an arbitrary number of well hydrographs to enhance the representativity of the master recession curve technique.

  16. Role of moist processes in the trajectories of mid-latitude surface cyclones within idealized simulations.

    NASA Astrophysics Data System (ADS)

    Coronel, Benoit; Ricard, Didier; Rivière, Gwendal; Arbogast, Philippe

    2014-05-01

    Recent studies suggest that it is the misrepresentation of moist processes within extratropical cyclones that is responsible for many forecast failures. The effect of the latent heat release intensifying perturbations has been demonstrated in numerous studies but its effect on the trajectory has been less extensively studied. Our objective is to systematically study the influence of wet processes on the trajectories of surface cyclones using idealized simulations of the MESO-NH non-hydrostatic mesoscale model. The initial state of the simulations is defined as the sum of a zonal baroclinic jet and finite-amplitude synoptic-scale anomalies located to the south of the jet. Special attention is paid to identifying the dynamical processes acting on the motion of the surface cyclone along and across the jet. Two sets of initial conditions are introduced, one with a unique cyclonic anomaly near the surface, and another one with two cyclonic anomalies near the surface and tropopause in such a way that they interact baroclinically with each other. A first comparison is made between dry simulations having these two different initial conditions to see the impact of the upper-level anomaly in the motion of the surface cyclone. The second comparison is made between wet and dry simulations to study the influence of moist processes. The difference between the different simulations is interpreted in terms of potential vorticity (PV). In all simulations, a dipolar PV anomaly which is composed of an upstream cyclone and a downstream anticyclone is formed near the tropopause and above the surface depression. Using a PV inversion algorithm, we show that the trajectories of the surface cyclone in the various experiments mainly depend on the intensity and orientation of the upper-level dipolar PV anomaly. The upper-level anticyclonic PV being more intense in the moist run than in the dry run, it more rapidly advects the surface cyclone poleward. The consequence is that the surface

  17. The role of van der Waals interactions in the adsorption of noble gases on metal surfaces

    SciTech Connect

    Chen, De-Li; Al-Saidi, W A; Johnson, J Karl

    2012-10-03

    Adsorption of noble gases on metal surfaces is determined by weak interactions. We applied two versions of the nonlocal van der Waals density functional (vdW-DF) to compute adsorption energies of Ar, Kr, and Xe on Pt(111), Pd(111), Cu(111), and Cu(110) metal surfaces. We have compared our results with data obtained using other density functional approaches, including the semiempirical vdW corrected DFT-D2. The vdW-DF results show considerable improvements in the description of adsorption energies and equilibrium distances over other DFTbased methods, giving good agreement with experiments. We have also calculated perpendicular vibrational energies for noble gases on the metal surfaces using vdWDF data and found excellent agreement with available experimental results. Our vdW-DF calculations show that adsorption of noble gases on low-coordination sites is energetically favored over high-coordination sites, but only by a few meV. Analysis of the 2-dimensional potential energy surface shows that the high-coordination sites are local maxima on the 2-dimensional potential energy surface and therefore unlikely to be observed in experiments, which provides an explanation of the experimental observations. The DFT-D2 approach with the standard parameterization was found to overestimate the dispersion interactions, and to give the wrong adsorption site preference for four of the nine systems we studied.

  18. Subtropical surface layer salinity budget and the role of mesoscale turbulence

    NASA Astrophysics Data System (ADS)

    Busecke, Julius; Gordon, Arnold L.; Li, Zhijin; Bingham, Frederick M.; Font, Jordi

    2014-07-01

    The subtropical North Atlantic exhibits the saltiest surface waters of the open ocean. Eventually that water subducted from the surface and exported toward the Equator, as a subsurface salinity maximum (S-max) forming the lower limb of the subtropical cell. Climatologically, the winter subtropical surface water, coinciding with the deepest mixed layer of ˜100 m, is saltier and colder than the S-max. Towed CTD measurements in March/April 2013 (a component of the field program SPURS) within the North Atlantic subtropical surface salinity maximum reveal several relatively fresh, warm anomalies, which deviate strongly from climatological conditions. These features introduce a large amount of freshwater into the subtropical region, exceeding the amount introduced by local rain events. Observed scales and evolution of the features strongly suggest a connection to mesoscale dynamics. This is supported by high-resolution regional model output, which produces an abundance of features that are similar in scale and structure to those observed. It is hypothesized that turbulent transport in the surface ocean is a crucial process for setting mixed layer characteristics, which spread into S-max stratum. High variability in the EKE implies a high potential for interannual variability in the resulting S-max water properties by ocean dynamics in addition to the variability caused by air sea fluxes. This has likely consequences to the meridional transport of heat and freshwater of the subtropical cell in the North Atlantic and to the larger-scale ocean and climate system.

  19. Laboratory investigations of the role of the grain surface in astrochemical models.

    PubMed

    Brown, Wendy A; Viti, Serena; Wolff, Angela J; Bolina, Amandeep S

    2006-01-01

    The rich chemistry often detected in star forming regions is now recognized to be a consequence of solid-state astrochemistry and the thermal desorption of its products. In recent experimental studies, desorption of a range of ices from a gold surface was investigated using temperature programmed desorption (TPD). These data were then used in astrochemical models. In this paper we investigate the sensitivity of these models to the inclusion of TPD data obtained from different surfaces (simulating different dust grains) and different thicknesses of the icy mantles. Detailed laboratory TPD studies of the desorption of ices from a highly oriented pyrolytic graphite (HOPG) surface have been performed. Desorption temperatures and kinetic parameters have been determined directly from the TPD data and have been used to determine the expected desorption temperature for the ices from grain surfaces. The results of these experiments have been incorporated into astrochemical models of high mass star forming regions and have then been compared with the results of previous experiments. From this comparison, we are able to determine whether the nature and composition of the grain surface is important in dictating the chemistry that occurs in star forming regions. PMID:17191445

  20. The role of interfacial chemistry in surface nucleation and growth of calcium oxalate

    SciTech Connect

    Song, L.; Campbell, A.A.; Bunker, B.C.

    1993-06-01

    The surface adsorption of Ca{sup 2+} and oxalate anions (Ox{sup 2{minus}}) on SiO{sub 2}, TiO{sub 2} and Al{sub 2}O{sub 3} oxide colloids were by electrosonic amplitude measurements. Kinetics studies of CaO{sub x} formation on the model oxide surfaces were carried out using constant composition method. Results suggested Ca{sup 2+} and Ox{sup 2{minus}} adsorptiopn was promoted on the oxide surfaces with opposite charges, and the specific adsorption of the divalent ions also resulted in surface charge reversal. For heterogeous nucleation of CaO{sub x} on the three model oxide surfaces, induction times ranged from 270 to 360 minutes compared with 1200 minutes estimated for homogeneous nucleation and 700 minutes for spontaneous or nucleation at pH 6.5 and S = 3.3. Lower nucleation barriers, 27 mJ/m{sup 2} for SiO{sub 2}, 26 mJ/m{sup 2} for TiO{sub 2}, were observed by studying the dependence of nucleation induction times as the function of solution supersaturation.

  1. The role of fire on soil mounds and surface roughness in the Mojave Desert

    USGS Publications Warehouse

    Soulard, Christopher E.; Esque, Todd C.; Bedford, David R.; Bond, Sandra

    2013-01-01

    A fundamental question in arid land management centers on understanding the long-term effects of fire on desert ecosystems. To assess the effects of fire on surface topography, soil roughness, and vegetation, we used terrestrial (ground-based) LiDAR to quantify the differences between burned and unburned surfaces by creating a series of high-resolution vegetation structure and bare-earth surface models for six sample plots in the Grand Canyon-Parashant National Monument, Arizona. We find that 11 years following prescribed burns, mound volumes, plant heights, and soil-surface roughness were significantly lower on burned relative to unburned plots. Results also suggest a linkage between vegetation and soil mounds, either through accretion or erosion mechanisms such as wind and/or water erosion. The biogeomorphic implications of fire-induced changes are significant. Reduced plant cover and altered soil surfaces from fire likely influence seed residence times, inhibit seed germination and plant establishment, and affect other ecohydrological processes.

  2. Fast Crystal Growth in o-Terphenyl Glasses: A Possible Role for Fracture and Surface Mobility.

    PubMed

    Powell, C Travis; Xi, Hanmi; Sun, Ye; Gunn, Erica; Chen, Yinshan; Ediger, M D; Yu, Lian

    2015-08-01

    Molecular liquids can develop a fast mode of crystal growth ("GC growth") near the glass transition temperature. This phenomenon remains imperfectly understood with several explanations proposed. We report that GC growth in o-terphenyl conserves the overall volume, despite a 5% higher density of the crystal, and produces fine crystal grains with the same unit cell as normally grown crystals. These results indicate that GC growth continuously creates voids and free surfaces, possibly by fracture. This aspect of the phenomenon has not been considered by previous treatments and is a difficulty for those models that hypothesize a 5% strain without voids. Given the existence of even faster crystal growth on the free surface of molecular glasses, we consider the possibility that GC growth is facilitated by fracture and surface mobility. This notion has support from the fact that GC growth and surface growth are both highly correlated with surface diffusivity and with fast crystal growth along preformed cracks in the glass. PMID:26161577

  3. The role of haptic cues from rough and slippery surfaces in human postural control

    NASA Technical Reports Server (NTRS)

    Jeka, J. J.; Lackner, J. R.

    1995-01-01

    Haptic information is critically important in complex sensory-motor tasks such as manipulating objects. Its comparable importance in spatial orientation is only beginning to be recognized. We have shown that postural sway in humans is significantly reduced by lightly touching a stable surface with a fingertip at contact force levels far below those physically necessary to stabilize the body. To investigate further the functional relationship between contact forces at the hand and postural equilibrium, we had subjects stand in the tandem Romberg stance while being allowed physically supportive (force contact) and non-physically supportive (touch contact) amounts of index fingertip force on surfaces with different frictional characteristics. Mean sway amplitude (MSA) was reduced by over 50% with both touch and force contact of the fingertip, compared to standing without fingertip contact. No differences in MSA were observed when touching rough or slippery surfaces. The amplitude of EMG activity in the peroneal muscles and the timing relationships between fingertip forces, body sway and EMG activity suggested that with touch contact of the finger or with force contact on a slippery surface long-loop "reflexes" involving postural muscles were stabilizing sway. With force contact of the fingertip on a rough surface, MSA reduction was achieved primarily through physical support of the body. This pattern of results indicates that light touch contact cues from the fingertip in conjunction with proprioceptive signals about arm configuration are providing information about body sway that can be used to reduce MSA through postural muscle activation.

  4. The role of electronic mechanisms in surface erosion and glow phenomena

    NASA Technical Reports Server (NTRS)

    Haglund, Richard F., Jr.

    1987-01-01

    Experimental studies of desorption induced by electronic transitions (DIET) are described. Such studies are producing an increasingly complete picture of the dynamical pathways through which incident electronic energy is absorbed and rechanneled to produce macroscopic erosion and glow. These mechanistic studies can determine rate constants for erosion and glow processes in model materials and provide valuable guidance in materials selection and development. Extensive experiments with electron, photon, and heavy particle irradiation of alkali halides and other simple model materials have produced evidence showing that: (1) surface erosion, consisting primarily in the ejection or desorption of ground-state neutral atoms, occurs with large efficiencies for all irradiated species; (2) surface glow, resulting from the radiative decay of desorbed atoms, likewise occurs for all irradiating species; (3) the typical mechanism for ground-state neutral desorption is exciton formation, followed by relaxation to a permanent, mobile electronic defect which is the precursor to bond-breaking in the surface or near-surface bulk of the material; and (4) the mechanisms for excited atom formation may include curve crossing in atomic collisions, interactions with surface defect or impurity states, or defect diffusion.

  5. On the role of electronic friction for dissociative adsorption and scattering of hydrogen molecules at a Ru(0001) surface.

    PubMed

    Füchsel, Gernot; Schimka, Selina; Saalfrank, Peter

    2013-09-12

    The role of electronic friction and, more generally, of nonadiabatic effects during dynamical processes at the gas/metal surface interface is still a matter of discussion. In particular, it is not clear if electronic nonadiabaticity has an effect under "mild" conditions, when molecules in low rovibrational states interact with a metal surface. In this paper, we investigate the role of electronic friction on the dissociative sticking and (inelastic) scattering of vibrationally and rotationally cold H2 molecules at a Ru(0001) surface theoretically. For this purpose, classical molecular dynamics with electronic friction (MDEF) calculations are performed and compared to MD simulations without friction. The two H atoms move on a six-dimensional potential energy surface generated from gradient-corrected density functional theory (DFT), that is, all molecular degrees of freedom are accounted for. Electronic friction is included via atomic friction coefficients obtained from an embedded atom, free electron gas (FEG) model, with embedding densities taken from gradient-corrected DFT. We find that within this model, dissociative sticking probabilities as a function of impact kinetic energies and impact angles are hardly affected by nonadiabatic effects. If one accounts for a possibly enhanced electronic friction near the dissociation barrier, on the other hand, reduced sticking probabilities are observed, in particular, at high impact energies. Further, there is always an influence on inelastic scattering, in particular, as far as the translational and internal energy distribution of the reflected molecules is concerned. Additionally, our results shed light on the role played by the velocity distribution of the incident molecular beam for adsorption probabilities, where, in particular, at higher impact energies, large effects are found. PMID:23750588

  6. Graphene nucleation on transition metal surface: structure transformation and role of the metal step edge.

    PubMed

    Gao, Junfeng; Yip, Joanne; Zhao, Jijun; Yakobson, Boris I; Ding, Feng

    2011-04-01

    The nucleation of graphene on a transition metal surface, either on a terrace or near a step edge, is systematically explored using density functional theory calculations and applying the two-dimensional (2D) crystal nucleation theory. Careful optimization of the supported carbon clusters, C(N) (with size N ranging from 1 to 24), on the Ni(111) surface indicates a ground state structure transformation from a one-dimensional C chain to a 2D sp(2) C network at N ≈ 10-12. Furthermore, the crucial parameters controlling graphene growth on the metal surface, nucleation barrier, nucleus size, and nucleation rate on a terrace or near a step edge are calculated. In agreement with numerous experimental observations, our analysis shows that graphene nucleation near a metal step edge is superior to that on a terrace. On the basis of our analysis, we propose the use of graphene seeds to synthesize high-quality graphene in large area. PMID:21384854

  7. The role of surface energy in guanosine nucleotide alignment: an intriguing scenario.

    PubMed

    Tone, Caterina M; De Santo, Maria P; Ciuchi, Federica

    2014-07-01

    In this paper we report how the confining surfaces and the ionic effects of different concentration of guanosine solution can be used to vary the alignment of liquid crystal phases of guanosine nucleotides. Liquid crystal phases of guanosine 5'-monophosphate ammonium salt and guanosine 5'-monophosphate free acid in pure water, with and without silver sulphate, were studied by polarized optical microscope. A periodic modulation of the texture was observed. This modulation depends on both on the concentration and on the presence of silver ions in the liquid crystal phase. We demonstrate that, according to the surface energy of the alignment layers, it is possible to homeotropically align the guanosine chromonic phase without applying any external magnetic field. Finally, we report the formation of spherical, vesicle-like guanosine 5'-monophosphate aggregates, when the solution was confined between two hydrophobic surfaces containing exposed Si groups. PMID:24832053

  8. The dominant role of surface conduction in electro-osmotic flows through periodically varying narrow channels

    NASA Astrophysics Data System (ADS)

    Ludar, Lotan; Yariv, Ehud

    2015-11-01

    As surface conduction has no effect on electro-osmosis in uniform channel flows, where the tangential Debye-layer currents are longitudinally uniform, it may appear as it would only result in a small modifying correction in lubrication analyses of slowly varying channels. This misconception is refuted here by analyzing flows through periodic channels of slowly varying but otherwise arbitrary geometry. Assuming that the channel width is still large compared with the Debye thickness we employ the simplest thin-double-layer model which incorporates surface conduction. We find that surface conduction affects the leading-order flow and the consequent net volumetric flux, introducing a nonlinear dependence upon the zeta potential. Remarkably, as the channel becomes more and more narrow, the scaled flux approaches a limit which is independent of the Dukhin number yet different from that calculated for zero Dukhin number.

  9. Role of Tensorial Electronic Friction in Energy Transfer at Metal Surfaces.

    PubMed

    Askerka, Mikhail; Maurer, Reinhard J; Batista, Victor S; Tully, John C

    2016-05-27

    An accurate description of nonadiabatic energy relaxation is crucial for modeling atomistic dynamics at metal surfaces. Interfacial energy transfer due to electron-hole pair excitations coupled to motion of molecular adsorbates is often simulated by Langevin molecular dynamics with electronic friction. Here, we present calculations of the full electronic friction tensor by using first order time-dependent perturbation theory at the density functional theory level. We show that the friction tensor is generally anisotropic and nondiagonal, as found for hydrogen atom on Pd(100) and CO on Cu(100) surfaces. This implies that electron-hole pair induced nonadiabatic coupling at metal surfaces leads to friction-induced mode coupling, therefore, opening an additional channel for energy redistribution. We demonstrate the robustness and accuracy of our results by direct comparison to established methods and experimental data. PMID:27284673

  10. Role of Tensorial Electronic Friction in Energy Transfer at Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Askerka, Mikhail; Maurer, Reinhard J.; Batista, Victor S.; Tully, John C.

    2016-05-01

    An accurate description of nonadiabatic energy relaxation is crucial for modeling atomistic dynamics at metal surfaces. Interfacial energy transfer due to electron-hole pair excitations coupled to motion of molecular adsorbates is often simulated by Langevin molecular dynamics with electronic friction. Here, we present calculations of the full electronic friction tensor by using first order time-dependent perturbation theory at the density functional theory level. We show that the friction tensor is generally anisotropic and nondiagonal, as found for hydrogen atom on Pd(100) and CO on Cu(100) surfaces. This implies that electron-hole pair induced nonadiabatic coupling at metal surfaces leads to friction-induced mode coupling, therefore, opening an additional channel for energy redistribution. We demonstrate the robustness and accuracy of our results by direct comparison to established methods and experimental data.

  11. Role of the surface properties of dispersed carbon in its inflammation

    SciTech Connect

    Kuryatnikov, V.V.

    1984-03-01

    The authors examine the internal diffusion problem for burning up of a porous carbon particle with an exponential distribution of internal sources. The problem is solved analagous to the well-known solution obtained by Khitrin with a difference in the parameter 2, which in the present case includes the coefficients a/sub 0/ and b/sub 0/, characterizing the chemical activity and roughness of the particle surface. It is concluded that the increase in the reaction rate in the course of the inflammation and combustion of carbon particles is related to the increase in the concentration of active centers, forming at locations of the surface defects as a result of dispersion with a large destructive impact. The surface of particles in stream dispersion has a high concentration of atoms, localized on defects, with broken bonds, which enter into the reaction with a minimum value of the activation energy and which are active centers in the oxidation reaction.

  12. The role of the tropical super greenhouse effect in heating the ocean surface.

    PubMed

    Lubin, D

    1994-07-01

    Measurements made by a Fourier transform infrared (FTIR) spectroradiometer operating in the middle infrared (5 to 20 micrometers, with a spectral resolution of one inverse centimeter) imply that there is an anomalously large greenhouse effect over equatorial oceans that is caused by water vapor. As sea-surface temperature increased from 297 to 303 degrees kelvin, the net infrared cooling at the surface decreased by 30 to 50 watts per square meter. Thus, according to the FTIR data, the super greenhouse effect that had been inferred from satellite measurements contributes directly to radiative heating of the sea surface. The data demonstrate that most of this heating occurs in the middle infrared by means of the continuum emission window of water vapor and that tropical deep convection contributes substantially to this super greenhouse effect. PMID:17750664

  13. Role of particle size and composition in metal adsorption by solids deposited on urban road surfaces.

    PubMed

    Gunawardana, Chandima; Egodawatta, Prasanna; Goonetilleke, Ashantha

    2014-01-01

    Despite common knowledge that the metal content adsorbed by fine particles is relatively higher compared to coarser particles, the reasons for this phenomenon have gained little research attention. The research study discussed in the paper investigated the variations in metal content for different particle sizes of solids associated with pollutant build-up on urban road surfaces. Data analysis confirmed that parameters favourable for metal adsorption to solids such as specific surface area, organic carbon content, effective cation exchange capacity and clay forming minerals content decrease with the increase in particle size. Furthermore, the mineralogical composition of solids was found to be the governing factor influencing the specific surface area and effective cation exchange capacity. There is high quartz content in particles >150 μm compared to particles <150 μm. As particle size reduces below 150 μm, the clay forming minerals content increases, providing favourable physical and chemical properties that influence adsorption. PMID:24021928

  14. Role of the non-opioid dynorphin peptide des-Tyr-dynorphin (DYN-A(2-17)) in food intake and physical activity, and its interaction with orexin-A.

    PubMed

    Gac, L; Butterick, T A; Duffy, C M; Teske, J A; Perez-Leighton, C E

    2016-02-01

    Food intake and physical activity are regulated by multiple neuropeptides, including orexin and dynorphin (DYN). Orexin-A (OXA) is one of two orexin peptides with robust roles in regulation of food intake and spontaneous physical activity (SPA). DYN collectively refers to several peptides, some of which act through opioid receptors (opioid DYN) and some whose biological effects are not mediated by opioid receptors (non-opioid DYN). While opioid DYN is known to increase food intake, the effects of non-opioid DYN peptides on food intake and SPA are unknown. Neurons that co-express and release OXA and DYN are located within the lateral hypothalamus. Limited evidence suggests that OXA and opioid DYN peptides can interact to modulate some aspects of behaviors classically related to orexin peptide function. The paraventricular hypothalamic nucleus (PVN) is a brain area where OXA and DYN peptides might interact to modulate food intake and SPA. We demonstrate that injection of des-Tyr-dynorphin (DYN-A(2-17), a non opioid DYN peptide) into the PVN increases food intake and SPA in adult mice. Co-injection of DYN-A(2-17) and OXA in the PVN further increases food intake compared to DYN-A(2-17) or OXA alone. This is the first report describing the effects of non-opioid DYN-A(2-17) on food intake and SPA, and suggests that DYN-A(2-17) interacts with OXA in the PVN to modulate food intake. Our data suggest a novel function for non-opioid DYN-A(2-17) on food intake, supporting the concept that some behavioral effects of the orexin neurons result from combined actions of the orexin and DYN peptides. PMID:26654796

  15. Accuracy of surface tension measurement from drop shapes: the role of image analysis.

    PubMed

    Kalantarian, Ali; Saad, Sameh M I; Neumann, A Wilhelm

    2013-11-01

    Axisymmetric Drop Shape Analysis (ADSA) has been extensively used for surface tension measurement. In essence, ADSA works by matching a theoretical profile of the drop to the extracted experimental profile, taking surface tension as an adjustable parameter. Of the three main building blocks of ADSA, i.e. edge detection, the numerical integration of the Laplace equation for generating theoretical curves and the optimization procedure, only edge detection (that extracts the drop profile line from the drop image) needs extensive study. For the purpose of this article, the numerical integration of the Laplace equation for generating theoretical curves and the optimization procedure will only require a minor effort. It is the aim of this paper to investigate how far the surface tension accuracy of drop shape techniques can be pushed by fine tuning and optimizing edge detection strategies for a given drop image. Two different aspects of edge detection are pursued here: sub-pixel resolution and pixel resolution. The effect of two sub-pixel resolution strategies, i.e. spline and sigmoid, on the accuracy of surface tension measurement is investigated. It is found that the number of pixel points in the fitting procedure of the sub-pixel resolution techniques is crucial, and its value should be determined based on the contrast of the image, i.e. the gray level difference between the drop and the background. On the pixel resolution side, two suitable and reliable edge detectors, i.e. Canny and SUSAN, are explored, and the effect of user-specified parameters of the edge detector on the accuracy of surface tension measurement is scrutinized. Based on the contrast of the image, an optimum value of the user-specified parameter of the edge detector, SUSAN, is suggested. Overall, an accuracy of 0.01mJ/m(2) is achievable for the surface tension determination by careful fine tuning of edge detection algorithms. PMID:24018120

  16. Surface states in a 3D topological insulator: The role of hexagonal warping and curvature

    SciTech Connect

    Repin, E. V.; Burmistrov, I. S.

    2015-09-15

    We explore a combined effect of hexagonal warping and a finite effective mass on both the tunneling density of electronic surface states and the structure of Landau levels of 3D topological insulators. We find the increasing warping to transform the square-root van Hove singularity into a logarithmic one. For moderate warping, an additional logarithmic singularity and a jump in the tunneling density of surface states appear. By combining the perturbation theory and the WKB approximation, we calculate the Landau levels in the presence of hexagonal warping. We predict that due to the degeneracy removal, the evolution of Landau levels in the magnetic field is drastically modified.

  17. Symmetry plays a key role in the erasing of patterned surface features

    SciTech Connect

    Benzaquen, Michael; Salez, Thomas; Raphaël, Elie; Ilton, Mark; Massa, Michael V.; Fowler, Paul; Dalnoki-Veress, Kari

    2015-08-03

    We report on how the relaxation of patterns prepared on a thin film can be controlled by manipulating the symmetry of the initial shape. The validity of a lubrication theory for the capillary-driven relaxation of surface profiles is verified by atomic force microscopy measurements, performed on films that were patterned using focused laser spike annealing. In particular, we observe that the shape of the surface profile at late times is entirely determined by the initial symmetry of the perturbation, in agreement with the theory. The results have relevance in the dynamical control of topographic perturbations for nanolithography and high density memory storage.

  18. Positive role of surface defects on carbon nanotube cathodes in overpotential and capacity retention of rechargeable lithium-oxygen batteries.

    PubMed

    Huang, Shiting; Fan, Wugang; Guo, Xiangxin; Meng, Fanhao; Liu, Xuanyong

    2014-12-10

    Surface defects on carbon nanotube cathodes have been artificially introduced by bombardment with argon plasma. Their roles in the electrochemical performance of rechargeable Li-O2 batteries have been investigated. In batteries with tetraethylene glycol dimethyl ether (TEGDME)- and N-methyl-N-propylpiperidinium bis(trifluoromethansulfonyl)imide (PP13TFSI)-based electrolytes, the defects increase the number of nucleation sites for the growth of Li2O2 particles and reduce the size of the formed particles. This leads to increased discharge capacity and reduced cycle overpotential. However, in the former batteries, the hydrophilic surfaces induced by the defects promote carbonate formation, which imposes a deteriorating effect on the cycle performance of the Li-O2 batteries. In contrast, in the latter case, the defective cathodes promote Li2O2 formation without enhancing formation of carbonates on the cathode surfaces, resulting in extended cycle life. This is most probably attributable to the passivation effect on the functional groups of the cathode surfaces imposed by the ionic liquid. These results indicate that defects on carbon surfaces may have a positive effect on the cycle performance of Li-O2 batteries if they are combined with a helpful electrolyte solvent such as PP13TFSI. PMID:25397991

  19. The role of surface charge density in cationic liposome-promoted dendritic cell maturation and vaccine-induced immune responses

    NASA Astrophysics Data System (ADS)

    Ma, Yifan; Zhuang, Yan; Xie, Xiaofang; Wang, Ce; Wang, Fei; Zhou, Dongmei; Zeng, Jianqiang; Cai, Lintao

    2011-05-01

    Cationic liposomes have emerged as a novel adjuvant and antigen delivery system to enhance vaccine efficacy. However, the role of surface charge density in cationic liposome-regulated immune responses has not yet been elucidated. In the present study, we prepared a series of DOTAP/DOPC cationic liposomes with different surface densities by incorporating varying amounts of DOPC (a neutral lipid) into DOTAP (a cationic lipid). The results showed that DOTAP/DOPC cationic liposome-regulated immune responses relied on the surface charge density, and might occur through ROS signaling. The liposomes with a relatively high charge density, such as DOTAP/DOPC 5 : 0 and 4 : 1 liposomes, potently enhanced dendritic cell maturation, ROS generaion, antigen uptake, as well as the production of OVA-specific IgG2a and IFN-γ. In contrast, low-charge liposomes, such as DOTAP/DOPC 1 : 4 liposome, failed to promote immune responses even at high concentrations, confirming that the immunoregulatory effect of cationic liposomes is mostly attributable to their surface charge density. Moreover, the DOTAP/DOPC 1 : 4 liposome suppressed anti-OVA antibody responses in vivo. Overall, maintaining an appropriate surface charge is crucial for optimizing the adjuvant effect of cationic liposomes and enhancing the efficacy of liposome-based vaccines.

  20. Role of surface charge in determining the biological effects of CdSe/ZnS quantum dots

    PubMed Central

    Liu, Qiangqiang; Li, Hongxia; Xia, Qiyue; Liu, Ying; Xiao, Kai

    2015-01-01

    The growing potential of quantum dots (QDs) in biomedical applications has provoked the urgent need to thoroughly address their interaction with biological systems. However, only limited studies have been performed to explore the effects of surface charge on the biological behaviors of QDs. In the present study, three commercially available QDs with different surface coatings were used to systematically evaluate the effects of surface charge on the cellular uptake, cytotoxicity, and in vivo biodistribution of QDs. Our results demonstrated that charged QDs entered both cancer cells and macrophages more efficiently than neutral ones, while negative QDs internalized mostly. Upon entry into cells, QDs were localized in different subcellular compartments (eg, cytoplasm and lysosomes) depending on the surface charge. Interestingly, inconsistent with the result of internalization, positive QDs but not negative QDs exhibited severe cytotoxicity, which was likely due to their disruption of cell membrane integrity, and production of reactive oxygen species. Biodistribution studies demonstrated that negative and neutral QDs preferentially distributed in the liver and the spleen, whereas positive QDs mainly deposited in the kidney with obvious uptake in the brain. In general, surface charge plays crucial roles in determining the biological interactions of QDs. PMID:26604757

  1. Identification des facteurs environnementaux responsables de la presence de Campylobacter Jejuni dans les eaux de surface de l'Estrie (Quebec)

    NASA Astrophysics Data System (ADS)

    Bonfils, Djoan

    Background: The sources and the epidemiology of Campylobacter jejuni (CJ) in environmental water are not well understood. We developed a spatial analysis methodology able to identify the main environmental factors predicting the presence and quantity of Campylobacter in river water. Methods: For two years, water samples were collected weekly and scanned for CJ and fecal coliforms at 32 sampling sites of Estrie hydrographic network, Québec. The quantity of CJ in water was estimated using the Most Probable Number method (MPN). The 32 sampling sites were linked to their catchment area; 10 of them were excluded from the analysis, because their hydrographic basin was not independent from the other sites. For each site, the following environmental variables were included: Water flow, slope, land-cover, land-use including type of farming, animal density, total precipitation in the 3 days prior to water sampling. A stepwise multivariate regression was realized across the different analysis windows to define the size of the area upstream from the sampling sites (from 1.5 to 24 km) which was the most closely associated with the mean quantity of CJ, and which environmental factors were associated with a higher mean quantity of CJ in water. Results: Preliminary results show that an area defined by a radius of 14 km upstream of the sample site was the most contributing zone for the bacteria (r2=0.38, p=0.002). Within this 14 km area, the only significant variable associated with a higher mean quantity of CJ was bovine density (p=0.002). When analyzing the data within a 120 m buffer zone across 14 km upstream of the sampling sites (r2=0.40, p=0.001), the only significant variable associated with a higher mean quantity of CJ was the percentage of agricultural surface (p=0.001). Conclusions: These results suggest a strong implication of bovine density in conjunction with

  2. The role of the surface on microglia function: implications for central nervous system tissue engineering

    PubMed Central

    Pires, Liliana R.; Rocha, Daniela N.; Ambrosio, Luigi; Pêgo, Ana Paula

    2015-01-01

    In tissue engineering, it is well accepted that a scaffold surface has a decisive impact on cell behaviour. Here we focused on microglia—the resident immune cells of the central nervous system (CNS)—and on their response to poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-CL)) fibrous and flat surfaces obtained by electrospinning and solvent cast, respectively. This study aims to provide cues for the design of instructive surfaces that can contribute to the challenging process of CNS regeneration. Cell morphology was evidently affected by the substrate, mirroring the surface main features. Cells cultured on flat substrates presented a round shape, while cells with elongated processes were observed on the electrospun fibres. A higher concentration of the pro-inflammatory cytokine tumour necrosis factor-α was detected in culture media from microglia on fibres. Still, astrogliosis is not exacerbated when astrocytes are cultured in the presence of microglia-conditioned media obtained from cultures in contact with either substrate. Furthermore, a significant percentage of microglia was found to participate in the process of myelin phagocytosis, with the formation of multinucleated giant cells being observed only on films. Altogether, the results presented suggest that microglia in contact with the tested substrates may contribute to the regeneration process, putting forward P(TMC-CL) substrates as supporting matrices for nerve regeneration. PMID:25540243

  3. The role of the surface on microglia function: implications for central nervous system tissue engineering.

    PubMed

    Pires, Liliana R; Rocha, Daniela N; Ambrosio, Luigi; Pêgo, Ana Paula

    2015-02-01

    In tissue engineering, it is well accepted that a scaffold surface has a decisive impact on cell behaviour. Here we focused on microglia-the resident immune cells of the central nervous system (CNS)-and on their response to poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-CL)) fibrous and flat surfaces obtained by electrospinning and solvent cast, respectively. This study aims to provide cues for the design of instructive surfaces that can contribute to the challenging process of CNS regeneration. Cell morphology was evidently affected by the substrate, mirroring the surface main features. Cells cultured on flat substrates presented a round shape, while cells with elongated processes were observed on the electrospun fibres. A higher concentration of the pro-inflammatory cytokine tumour necrosis factor-α was detected in culture media from microglia on fibres. Still, astrogliosis is not exacerbated when astrocytes are cultured in the presence of microglia-conditioned media obtained from cultures in contact with either substrate. Furthermore, a significant percentage of microglia was found to participate in the process of myelin phagocytosis, with the formation of multinucleated giant cells being observed only on films. Altogether, the results presented suggest that microglia in contact with the tested substrates may contribute to the regeneration process, putting forward P(TMC-CL) substrates as supporting matrices for nerve regeneration. PMID:25540243

  4. Groundwater surface water interactions and the role of phreatophytes in identifying recharge zones

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Groundwater and surface water interactions within riparian corridors impact the distribution of phreatophytes that tap into groundwater stores. The changes in canopy area of phreatophytes over time is related to changes in depth to groundwater, distance from a stream or river, and hydrologic soil gr...

  5. Role of Environmental Conditions on the Interaction of L-Arginine with Oxide Mineral Surfaces

    NASA Astrophysics Data System (ADS)

    Klochko, K.; Jonsson, C. M.; Jonsson, C. L.; Lee, N.; Cleaves, H. J., II; Sverjensky, D. A.; Hazen, R. M.

    2010-04-01

    The current study is focused on surface interactions between L-arginine, the most basic protein amino acid, and rutile in NaCl media over a wide range of solution pH conditions, amino acid concentrations, and solution ionic strengths.

  6. Role of subsurface physics in the assimilation of surface soil moisture observations

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil moisture controls the exchange of water and energy between the land surface and the atmosphere and exhibits memory that may be useful for climate prediction at monthly time scales. Though spatially distributed observations of soil moisture are increasingly becoming available from remotely sense...

  7. Spontaneous deposition of polylysine on surfaces: role of the secondary structure to optimize noncovalent coating strategies.

    PubMed

    Di Mauro, Alessandro; Mirabella, Francesca; D'Urso, Alessandro; Randazzo, Rosalba; Purrello, Roberto; Fragalà, Maria Elena

    2015-01-01

    Understanding the factors that governs spontaneous molecular transfer from solution to solid surface is fundamental to control noncovalent surface functionalization strategies, both in term of robustness and reproducibility. The comprehension of the nature of interaction involved in the mechanism of spontaneous adsorption will allow for a fine modulation of the deposition process. Herein, we provide experimental evidences to demonstrate that poly-lysine secondary structure represents a crucial factor profoundly influencing the outcome of its spontaneous deposition on quartz surfaces. In particular, random coil to α-helix transition is required to drive an effective transfer of the poly-l-lysine at the liquid-solid interface. β-sheet deposition requires longer times to be accomplished, while random-coil deposition is highly unfavored. Accordingly, polylysine deposition on quartz and silicon is effective when α-helix is formed in solution (pH>10). This surface noncovalent functionalization represents a simple strategy to fabricate hybrid organic-inorganic or biocompatible materials. In fact, the proposed methodology is proven robust and repeatable and compatible for combination with solution or vapor phases (i.e. MOCVD) nanomaterial deposition approaches. PMID:25441360

  8. The sorption of humic acids to mineral surfaces and their roles in contaminant binding

    SciTech Connect

    Murphy, E.M.; Zachara, J.M.; Smith, S.C.; Phillips, J.L.

    1990-11-01

    Humic substances dissolved in groundwater may adsorb to certain mineral surfaces, rendering hydrophilic surfaces hydrophobic and making them sorbents for hydrophobic organic compounds (HOC). The sorption of humic and fulvic acids (International Humic Substance Society, IHSS, reference samples) on hematite and kaolinite was investigated to determine how natural organic coatings influence HOC sorption. The sorption behavior of the humic substances was consistent with a ligand-exchange mechanism, and the amount of sorption depended on the concentration of hydroxylated surface sites on the mineral and the properties of the humic substance. The sorption of the humic substances to two solids was proportional to their aromatic carbon content and inversely proportional to the O/C ratio. Increasing quantities of sorbed humic substances (f{sub oc}0.01 to 0. 5%) increased the sorption of carbazole, dibenzothiophene, and anthracene. Peat humic acid, the most aromatic coating, showed the greatest sorption enhancement of HOC when sorbed to hematite. In addition, HOC sorption was greater on organic coating formed at low ionic strength (I = 0.005) as compared to higher ionic strength (I = 0.1). We suggest that both the mineral surface and the ionic strength of the electrolyte affect the interfacial configuration of the sorbed humic substance, altering the size or accessibly of hydrophobic domains on the humic molecule to HOC. 30 refs., 5 figs.

  9. Essential protective role attributed to the surface lipoproteins of Borrelia burgdorferi against innate defenses

    PubMed Central

    Xu, Qilong; McShan, Kristy; Liang, Fang Ting

    2008-01-01

    Summary To initiate infection, a microbial pathogen must be able to evade innate immunity. Here we show that the Lyme disease spirochete Borrelia burgdorferi depends on its surface lipoproteins for protection against innate defenses. The deficiency for OspC, an abundantly expressed surface lipoprotein during early infection, led to quick clearance of B. burgdorferi after inoculation into the skin of SCID mice. Increasing expression of any of the four randomly chosen surface lipoproteins, OspA, OspE, VlsE or DbpA, fully protected the ospC mutant from elimination from the skin tissue of SCID mice; moreover, increased OspA, OspE, or VlsE expression allowed the mutant to cause disseminated infection and restored the ability to effectively colonize both joint and skin tissues, albeit the dissemination process was much slower than that of the mutant restored with OspC expression. When the ospC mutant was modified to express OspA under control of the ospC regulatory elements, it registered only a slight increase in the 50% infectious dose than the control in SCID mice but a dramatic increase in immunocompetent mice. Taken together, the study demonstrated that the surface lipoproteins provide B. burgdorferi with an essential protective function against host innate elimination. PMID:18452586

  10. 'MYCOPLASMA PNEUMONIAE' INFECTION: ROLE OF A SURFACE PROTEIN IN THE ATTACHMENT ORGANELLE

    EPA Science Inventory

    Attachment of Mycoplasma pneumoniae to host cells by means of a specialized terminus initiates infection. Monoclonal antibodies to a surface protein (Pl) inhibit this process, and react with a region of the tip covered with peplomer-like particles. Since antibodies against the Pl...

  11. Critical role of surface roughness on colloid retention and release in porous media

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A thorough understanding of colloid transport in porous media is of great importance in many environmental and industrial applications. Extended-DLVO theory was employed to investigate the influence of nanoscale surface roughness (NSR) on the magnitudes of the secondary (F2min) and primary energy (F...

  12. A Preliminary Examination of Science Backroom Roles and Activities for Robotic Lunar Surface Science

    NASA Astrophysics Data System (ADS)

    Fong, T.; Deans, M.; Smith, T.; Lee, P.; Heldmann, J.; Pacis, E.; Schreckenghost, D.; Landis, R.; Osborn, J.; Kring, D.; Heggy, E.; Mishkin, A.; Snook, K.; Stoker, C.

    2008-07-01

    To understand the utility of a science backroom for the current lunar architecture, we are developing a new ground control structure for human and robot surface activity. In June 2008, we began examining this structure through a series of analog field tests.

  13. Role of surface plasmon polaritons and other waves in the radiation of resonant optical dipole antennas

    PubMed Central

    Jia, Hongwei; Liu, Haitao; Zhong, Ying

    2015-01-01

    The radiation of an electric dipole emitter can be drastically enhanced if the emitter is placed in the nano-gap of a metallic dipole antenna. By assuming that only surface plasmon polaritons (SPPs) are excited on the antenna, we build up an intuitive pure-SPP model that is able to comprehensively predict the electromagnetic features of the antenna radiation, such as the total or radiative emission rate and the far-field radiation pattern. With the model we can distinguish the respective contributions from SPPs and from other surface waves to the antenna radiation. It is found that for antennas with long arms that support higher-order resonances, SPPs provide a dominant contribution to the antenna radiation, while for other cases, the contribution of surface waves other than SPPs should be considered. The model reveals an intuitive picture that the enhancement of the antenna radiation is due to surface waves that are resonantly excited on the two antenna arms and that are further coupled into the nano-gap or scattered into free space. From the model we can derive a phase-matching condition that predicts the antenna resonance and the resultant enhanced radiation. The model is helpful for a physical understanding and intuitive design of antenna devices. PMID:25678191

  14. Investigation of the Role of Surface Oxides in Catalysis by Gold Nanoparticles

    NASA Astrophysics Data System (ADS)

    Shi, Hongqing; Stampfl, Catherine

    2007-03-01

    In contrast to the long held view that gold is catalytically inert, it is now well known that supported gold nanoparticles are notably more active than other transition metals for low temperature catalytic oxidation of CO, as well as promoting several other catalytic reactions [1]. This has stimulated huge efforts in an attempt to understand the mechanisms responsible for the high activity, including investigations into the nature of oxygen on gold surfaces [2]. Through density-functional theory and the approach of ab initio thermodynamics [3] we have found that on the gold (111) surface, thin oxide-like structures are significantly more stable for the pressure and temperature conditions of CO oxidation. The energetic preference for such partially oxidized gold, is in accord with very recent experimental results [4]. For the identified lowest energy surface oxide-like structure, we investigate the adsorption of CO on the surface and determine the reaction pathways for CO oxidation. [1] Haruta, Catal. J. New. Mater. Electro. Sys. 7, 163 (2004). [2] R. Meyer et al., Gold Bull. 37, 72 (2004), and references therein. [3] K. Reuter, C. Stampfl and M. Scheffler, in Handbook of Materials Modeling, Volume 1, Fundamental Models and Methods, Sidney Yip (Ed) 2005, 149-194. [4] L. Fu et al. J. Phys. Chem. B 109, 3704 (2005).

  15. The Role of Nanoparticle Surface Functionality in the Disruption of Model Cell Membranes

    PubMed Central

    Moghadam, Babak Y.; Hou, Wen-Che; Corredor, Charlie; Westerhoff, Paul; Posner, Jonathan D.

    2012-01-01

    Lipid bilayers are biomembranes common to cellular life and constitute a continuous barrier between cells and their environment. Understanding the interaction of engineered nanomaterials (ENMs) with lipid bilayers is an important step toward predicting subsequent biological effects. In this study, we assess the effect of varying the surface functionality and concentration of 10 nm-diameter gold (Au) and titanium dioxide (TiO2) ENMs on the disruption of negatively charged lipid bilayer vesicles (liposomes) using a dye leakage assay. Our findings show that Au ENMs having both positive and negative surface charge induce leakage that reaches a steady state after several hours. Positively charged particles with identical surface functionality and different core composition show similar leakage effects and result in faster and greater leakage than negatively charged particles, which suggests that surface functionality, not particle core composition, is a critical factor in determining the interaction between ENMs and lipid bilayers. The results suggest that particles permanently adsorb to bilayers and that only one positively charged particle is required to disrupt a liposome and trigger leakage of its entire contents in contrast to mellitin molecules, the most widely studied membrane lytic peptide, which requires hundred of molecules to generate leakage. PMID:22921268

  16. Sea surface temperature and torrential rains in the Valencia region: modelling the role of recharge areas

    NASA Astrophysics Data System (ADS)

    Pastor, Francisco J.

    2016-04-01

    Heavy rain events are frequently recorded in the Western Mediterranean causing economic and human losses. A main factor in the development of torrential rains is ocean-atmosphere exchange of heat and moisture that can destabilize air masses travelling over the sea. The study of air mass trajectories previous to the rain event permits the identification of sea areas that could probably contribute to the development or intensification of rainfall. From a Mediterranean sea surface temperature climatology, its spatio-temporal distribution patterns have been studied showing two main distribution modes in winter and summer and transitional regimes in spring and autumn. Hence, three heavy precipitation events, for such winter and summer sea temperature regimes and for fall transition, affecting the Valencia region have been selected to study the effect of sea surface temperature in torrential rains. Simulations with perturbed sea surface temperature in different areas along the air mass path were run to compare results with unperturbed simulation. The variation of sea surface temperature in certain areas caused significant changes in model accumulated values and its spatial distribution. Therefore, the existence of areas that at a greater extent favour air-sea interaction leading to the development of torrential rainfall in the Valencia region is shown. This methodology could be extended to other Mediterranean regions to look for such potential recharge areas. The identification of sea areas that contribute to the development or intensification of heavy rain events in the Mediterranean countries could be a useful prognosis and/or monitoring tool.

  17. The role of deformable structured surfaces on viscous forces during peeling

    NASA Astrophysics Data System (ADS)

    Dhong, Charles; Frechette, Joelle

    It is known that tree frogs are able to adhere well in flooded environments, presumably due to their interconnected network of drainage channels formed by hexagonal epithelial cells in their toe pads. To investigate this effect, a patterned surface of hexagonally arranged cylindrical posts was brought close to a stationary substrate in a submerged, viscous fluid via a normal load, and then peeled off to measure a retraction force. Because these structured surfaces were made from PDMS, they are able to deform throughout the process. We find that these deformable surfaces further reduce the work required to peel apart the two surfaces, even when compared to previous studies in the same system with rigid structures, and we isolated these contributions independent of conservative forces. We then conducted experiments to compare the effect of deformation on the viscous forces and conservative forces. We find that there are several regimes where deformation either increases or decreases the retraction force since we have found that elasticity decreases retraction forces when considering viscous contributions but is also known to increase adhesion in the context of conservative forces. Office of Naval Research, National Science Foundation, Hopkins Extreme Materials Institute.

  18. Roles for Cell Wall Glycopeptidolipid in Surface Adherence and Planktonic Dispersal of Mycobacterium avium

    EPA Science Inventory

    The opportunistic pathogen Mycobacterium avium is a significant inhabitant of biofilms in drinking water distribution systems. M. avium expresses on its cell surface serovar-specific glycopeptidolipids (ssGPLs). Studies have implicated the core GPL in biofilm formation by M. aviu...

  19. Surface active properties of polyoxyethylene macromonomers and their role in radical polymerization in disperse systems.

    PubMed

    Capek, I

    2000-12-26

    Conventional dispersion polymerization and copolymerization of low-molecular weight (conventional) unsaturated monomers allows preparation of monodisperse and micronsize polymer particles. A similar behavior can be found in the surfactant-free dispersion polymerization of non-traditional vinyl monomers, unsaturated macromonomers. The latter systems allow preparation of random, comb-like, star-like and graft copolymers as well. An interesting alternative arises with the use of amphiphilic reactive macromonomers that contain a polymerizable group and aggregate into an organized structure -- a micelle. Under such conditions the high rate of polymerization and ultrafine (microparticles) polymer dispersions are generated. Thus, the surface-active macromonomers promote the formation of micelles and polymer growth within the main reaction loci -- polymer particles. Furthermore, the surface-active compounds can be formed during the copolymerization of hydrophilic macromonomer and hydrophobic low-molecular weight comonomer. The reactive surface-active oligomeric radicals are incorporated into the polymer matrix or the particle surface layer, which prevents them from subsequent migration. Besides, the covalently bound surface-active groups at the particle surface strongly increase the colloidal stability of final polymer dispersion. This article presents a review of the current literature in the field of the surfactant-free dispersion polymerization of the polyoxyethylene unsaturated macromonomers. Besides a short introduction into some kinetic aspects of radical polymerization of traditional monomers in homogeneous and disperse systems, we mainly focus on the organized aggregation of amphiphilic polyoxyethylene macromonomers, the characterization of amphiphilic graft copolymers and their aggregation properties, and radical copolymerization of polyoxyethylene macromonomers. We discuss the birth and growth of chains, the transfer of reaction loci from the continuous phase to

  20. Role of Cl - ions in photooxidation of propylene on TiO 2 surface

    NASA Astrophysics Data System (ADS)

    Guo, Jianhui; Mao, Liqun; Zhang, Jiwei; Feng, Caixia

    2010-01-01

    The effect of Cl - ions on photooxidation of propylene on TiO 2 semiconductor was investigated. Cl -/TiO 2 catalysts were prepared by annealing Degussa P25 TiO 2 in the gas flow of N 2 and Cl 2 under 100-400 °C. The photocatalytic oxidation of propylene was carried out in a continuous flow system, with the chromatograph to analyze the products on line. The experimental results showed that the activity of Cl -/TiO 2 catalysts increased as heat-treated temperature decreased. The activity of the sample heat-treated at 100 °C was about two times higher than that of pure TiO 2. Moreover, as to TiO 2, the main product of the propylene photocatalytic oxidation was CO 2, but with Cl -/TiO 2 catalysts, not only CO 2 but also trace CO was determined. The adsorbed species on TiO 2 surface before and after reaction were analyzed by X-ray photoelectron spectroscopy (XPS) and thermogravimetric/differential thermal analyses (TG-DTA) coupled to a mass spectrometer (MS). XPS analysis showed that there was Cl - absorbed on the Cl -/TiO 2 surface, and the absorption amount of Cl - decreased after the photooxidation reaction of propylene. TG-DTA-MS analysis confirmed chlorine absorbed on the surface of TiO 2 in the form of Cl - ion. These results illuminated that absorbed Cl - on the surface of TiO 2 formed a weak physical absorption on TiO 2 at low temperature, and subsequently participated in the photooxidation of propylene, finally removed from TiO 2 surface.

  1. Quantifying the role of forest soil and bedrock in the acid neutralization of surface water in steep hillslopes.

    PubMed

    Asano, Yuko; Uchida, Taro

    2005-02-01

    The role of soil and bedrock in acid neutralizing processes has been difficult to quantify because of hydrological and biogeochemical uncertainties. To quantify those roles, hydrochemical observations were conducted at two hydrologically well-defined, steep granitic hillslopes in the Tanakami Mountains of Japan. These paired hillslopes are similar except for their soils; Fudoji is leached of base cations (base saturation <6%), while Rachidani is covered with fresh soil (base saturation >30%), because the erosion rate is 100-1000 times greater. The results showed that (1) soil solution pH at the soil-bedrock interface at Fudoji (4.3) was significantly lower than that of Rachidani (5.5), (2) the hillslope discharge pH in both hillslopes was similar (6.7-6.8), and (3) at Fudoji, 60% of the base cations leaching from the hillslope were derived from bedrock, whereas only 20% were derived from bedrock in Rachidani. Further, previously published results showed that the stream pH could not be predicted from the acid deposition rate and soil base saturation status. These results demonstrate that bedrock plays an especially important role when the overlying soil has been leached of base cations. These results indicate that while the status of soil acidification is a first-order control on vulnerability to surface water acidification, in some cases such as at Fudoji, subsurface interaction with the bedrock determines the sensitivity of surface water to acidic deposition. PMID:15519722

  2. Springtime high surface ozone events over the western United States: Quantifying the role of stratospheric intrusions

    NASA Astrophysics Data System (ADS)

    Fiore, A. M.; Lin, M.; Cooper, O. R.; Horowitz, L. W.; Naik, V.; Levy, H.; Langford, A. O.; Johnson, B. J.; Oltmans, S. J.; Senff, C. J.

    2011-12-01

    As the National Ambient Air Quality (NAAQS) standard for ozone (O_{3}) is lowered, it pushes closer to policy-relevant background levels (O_{3} concentrations that would exist in the absence of North American anthropogenic emissions), making attainment more difficult with local controls. We quantify the Asian and stratospheric components of this North American background, with a primary focus on the western United States. Prior work has identified this region as a hotspot for deep stratospheric intrusions in spring. We conduct global simulations at 200 km and 50 km horizontal resolution with the GFDL AM3 model, including a stratospheric O_{3} tracer and two sensitivity simulations with anthropogenic emissions from Asia and North America turned off. The model is evaluated with a suite of in situ and satellite measurements during the NOAA CalNex campaign (May-June 2010). The model reproduces the principle features in the observed surface to near tropopause distribution of O_{3} along the California coast, including its latitudinal variation and the development of regional high-O_{3} episodes. Four deep tropopause folds are diagnosed and we find that the remnants of these stratospheric intrusions are transported to the surface of Southern California and Western U.S. Rocky Mountains, contributing 10-30 ppbv positive anomalies relative to the simulated campaign mean stratospheric component in the model surface layer. We further examine the contribution of North American background, including its stratospheric and Asian components, to the entire distribution of observed MDA8 O_{3} at 12 high-elevation CASTNet sites in the Mountain West. We find that the stratospheric O_{3} tracer constitutes 50% of the North American background, and can enhance surface maximum daily 8-hour average (MDA8) O_{3} by 20 ppb when observed surface O_{3} is in the range of 60-80 ppbv. Our analysis highlights the potential for natural sources such as deep stratospheric intrusions to contribute

  3. The role of emotion in patient safety: Are we brave enough to scratch beneath the surface?

    PubMed

    Heyhoe, Jane; Birks, Yvonne; Harrison, Reema; O'Hara, Jane K; Cracknell, Alison; Lawton, Rebecca

    2016-02-01

    Healthcare professionals work in emotionally charged settings; yet, little is known about the role of emotion in ensuring safe patient care. This article presents current knowledge in this field, drawing upon psychological approaches and evidence from clinical settings. We explore the emotions that health professionals experience in relation to making a medical error and describe the impact on healthcare professionals and on their professional and patient relationships. We also explore how positive and negative emotions can contribute to clinical decision making and affect responses to clinical situations. Evidence to date suggests that emotion plays an integral role in patient safety. Implications for training, practice and research are discussed in addition to strategies to facilitate health services to understand and respond to the influence of emotion in clinical practice. PMID:26682568

  4. Reduction of Water/Oil Interfacial Tension by Model Asphaltenes: The Governing Role of Surface Concentration.

    PubMed

    Jian, Cuiying; Poopari, Mohammad Reza; Liu, Qingxia; Zerpa, Nestor; Zeng, Hongbo; Tang, Tian

    2016-06-30

    In this work, pendant drop techniques and molecular dynamics (MD) simulations were employed to investigate the effect of asphaltene concentrations on the interfacial tension (IFT) of the oil/water interface. Here, oil and asphaltene were represented by, respectively, common organic solvents and Violanthrone-79, and two types of concentration, i.e., bulk concentration and surface concentration, were examined. Correlations between the IFTs from experiments and MD simulations revealed that surface concentration, rather than the commonly used bulk concentration, determines the reduction of oil/water IFTs. Through analyzing the hydrogen bonding, the underlying mechanism for the IFT reduction was proposed. Our discussions here not only enable the direct comparison between experiments and MD simulations on the IFTs but also help with future interfacial studies using combined experimental and simulation approaches. The methodologies used in this work can be extended to many other oil/water interfaces in the presence of interfacially active compounds. PMID:27268710

  5. On the role of terahertz field acceleration and beaming of surface plasmon generated ultrashort electron pulses

    SciTech Connect

    Greig, S. R. Elezzabi, A. Y.

    2014-07-28

    A mechanism for control of the energy and pitch angle of surface plasmon accelerated electron pulses is proposed. Electrons generated via multi-photon absorption in a silver film on a glass prism are ponderomotively accelerated in the surface plasmon field excited by a 30 fs, 800 nm optical pulse. Through introduction of a single-cycle terahertz (THz) pulse, the energy spectrum and trajectory of the generated electron pulse can be controlled via the THz field strength. Generated electron pulses achieve peak kinetic energies up to 1.56 keV, while utilizing an incident optical field strength five times less than comparable plasmon accelerated electron pulses. These results demonstrate that THz pulses can be utilized to achieve tunable, high energy, trajectory controlled electron pulses necessary for various applications that require ultrafast electron pulse manipulation.

  6. The role of hydrogen in room-temperature ferromagnetism at graphite surfaces

    SciTech Connect

    Ohldag, H.; Esquinazi, P.; Arenholz, E.; Spemann, D.; Rothermel, M.; Setzer, A.; Butz, T.

    2010-05-01

    We present a x-ray dichroism study of graphite surfaces that addresses the origin and magnitude of ferromagnetism in metal-free carbon. We find that, in addition to carbon {pi} states, also hydrogen-mediated electronic states exhibit a net spin polarization with significant magnetic remanence at room temperature. The observed magnetism is restricted to the top {approx}10 nm of the irradiated sample where the average magnetization reaches {approx_equal} 15 emu/g at room temperature. We prove that the ferromagnetism found in metal-free untreated graphite is intrinsic and has a similar origin as the one found in proton bombarded graphite. Also, our findings show that the magnetic properties of graphite surfaces, thin films or two dimensional graphene samples can be reliably studied using soft x-ray dichroism. Fundamental new insight into the magnetic properties of carbon based systems can thus be obtained.

  7. Role of surface gauging in extended particle interactions: The case for spin

    NASA Astrophysics Data System (ADS)

    Mazilu, Nicolae; Ghizdovat, Vlad; Agop, Maricel

    2016-05-01

    The matter, being extended in space, should be first characterized by a surface of separation from the empty space. This surface cannot be neatly, i.e. purely geometrically, defined. When it comes to extended particles, which thereby are to be considered the fundamental structural units of the matter, the physical evidence points out that they are not even stable: they are in a continuous transformation; and so is their limit of separation from space. The present work describes a concept of extended particle with special emphasis on this limit of separation. It turns out that the properties of inertia, as classically understood, are intrinsically related to the spin properties of quantum origin. Thus, an extended particle model cannot be but "holographic" when it comes to imbedding it in a physical structure. The spin properties turn out to be essential, inasmuch as they decide the forces of interaction issuing from particles.

  8. The role of surface modification for TiO2 nanoparticles in cancer cells.

    PubMed

    Xie, Jin; Pan, Xiaobo; Wang, Mengyan; Ma, Jiong; Fei, Yiyan; Wang, Pei-Nan; Mi, Lan

    2016-07-01

    Titanium dioxide nanoparticles (TiO2 NPs) have a potential in the field of biological application. However, its poor dispersibility in water hampered its applications. In this study, 3-phosphonopropionic acid and 3-aminopropyl-triethoxysilane were respectively used for surface modification on TiO2 NPs with negative and positive surface charges (denoted as TiO2-COOH and TiO2-NH2). Zeta potentials of the prepared samples with high absolute value demonstrate the great improvement in their dispersibility. In terms of viability experiment, both TiO2-COOH and TiO2-NH2 showed low cytotoxicity. The cellular uptake efficiency and the uptake pathways of TiO2-COOH and TiO2-NH2 for cancer cells were studied. The exocytosis of TiO2-NH2 was also observed in the experiment. PMID:27003465

  9. Cell-surface nucleolin is sequestered into EPEC microcolonies and may play a role during infection.

    PubMed

    Dean, Paul; Kenny, Brendan

    2011-06-01

    Nucleolin is a prominent nucleolar protein that is mobilized into the cytoplasm during infection by enteropathogenic Escherichia coli (EPEC). Nucleolin also exists at low levels at the cell surface of eukaryotic cells and here we show that upon infection of an intestinal cell model, EPEC recruits and subsequently sequesters cell-surface EGFP-nucleolin into extracellularly located bacterial microcolonies. The recruitment of nucleolin was evident around bacteria within the centre of the microcolonies that were not directly associated with actin-based pedestals. Incubation of host intestinal cells with different ligands that specifically bind nucleolin impaired the ability of EPEC to disrupt epithelial barrier function but did not inhibit bacterial attachment or other effector-driven processes such as pedestal formation or microvilli effacement. Taken together, this work suggests that EPEC exploits two spatially distinct pools of nucleolin during the infection process. PMID:21436219

  10. The role of geological surfaces in determining visible-near infra red spectral signatures

    NASA Technical Reports Server (NTRS)

    Sommer, S. E.; Buckingham, W. F.

    1981-01-01

    The goal of the study described here is to determine new criteria for improved target discrimination in areas of hydrothermal mineralization. It is noted that the portion of materials, that is, geological surfaces detected by sensing devices, must be accurately determined before elemental and mineralogical characterization. The depth from which visible-near infrared radiation is reflected from target surfaces depends on composition and fabric. Reflectance spectra are obtained from binary mixtures of hematite, goethite, kaolinite and montmorillonite with a reflecting sphere spectrometer over a wavelength range of 400-2500 nm. The reflection (or absorption) intensity is plotted vs. the sample thickness (determined by scanning electron microscopy) to determine the sample thickness at which absorption saturates. The optical depth is seen to vary as a function of mineralogy and wavelength. In general, the maximum depth from which reflection features are discerned is from 12 to 47 microns measured in the visible-near infrared spectral region.

  11. Mn segregation in Ge/Mn5Ge3 heterostructures: The role of surface carbon adsorption

    NASA Astrophysics Data System (ADS)

    Dau, Minh-Tuan; Thanh, Vinh Le; Le, Thi-Giang; Spiesser, Aurélie; Petit, Mathieu; Michez, Lisa A.; Daineche, Rachid

    2011-10-01

    Mn5Ge3 compound, with its room-temperature ferromagnetism and possibility to epitaxially grow on Ge, acts as a potential spin injector into group-IV semiconductors. However, the realization of Ge/Mn5Ge3 multilayers is highly hampered by Mn segregation toward the Ge growing surface. Here, we show that adsorption of some monolayers of carbon on top of the Mn5Ge3 surface prior to Ge deposition allows to greatly reduce Mn segregation. In addition, a fraction of deposited carbon can diffuse down to the underneath Mn5Ge3 layers, resulting in an enhancement of the Curie temperature up to ˜360 K. The obtained results will be discussed in terms of the formation of a diffusion barrier by filling interstitial sites of Mn5Ge3 by carbon.

  12. The role of van der Waals interactions in surface-supported supramolecular networks.

    PubMed

    Nguyen, Manh-Thuong; Pignedoli, Carlo A; Treier, Matthias; Fasel, Roman; Passerone, Daniele

    2010-01-28

    The development of a detailed theoretical understanding of surface-supported supramolecular networks is important for designing novel organic nanodevices. By comparing with STM experiments, we show that van der Waals corrections to density functional theory (DFT) in the generalized gradient approximation (GGA) are mandatory to correctly reproduce the electronic and geometric structure of a prototypical system of this kind, the self-assembled hydrogen bonded network formed by 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and 4,4''-diamino-p-terphenyl (DATP) deposited on Au(111). Our results reproduce both the network structure and its higher stability with respect to homomolecular networks. By successful comparison with the experiments, we demonstrate that dispersive interactions must be taken into account when rationally designing organic semiconductor nanostructures on a metallic substrate. DFT-GGA alone would fail in predicting geometric and electronic properties for weakly bounded large organic adsorbates on coinage metal surfaces. PMID:20066384

  13. The Role of Hierarchy in Response Surface Modeling of Wind Tunnel Data

    NASA Technical Reports Server (NTRS)

    DeLoach, Richard

    2010-01-01

    This paper is intended as a tutorial introduction to certain aspects of response surface modeling, for the experimentalist who has started to explore these methods as a means of improving productivity and quality in wind tunnel testing and other aerospace applications. A brief review of the productivity advantages of response surface modeling in aerospace research is followed by a description of the advantages of a common coding scheme that scales and centers independent variables. The benefits of model term reduction are reviewed. A constraint on model term reduction with coded factors is described in some detail, which requires such models to be well-formulated, or hierarchical. Examples illustrate the consequences of ignoring this constraint. The implication for automated regression model reduction procedures is discussed, and some opinions formed from the author s experience are offered on coding, model reduction, and hierarchy.

  14. Biomaterial design for specific cellular interactions: Role of surface functionalization and geometric features

    NASA Astrophysics Data System (ADS)

    Kolhar, Poornima

    The areas of drug delivery and tissue engineering have experienced extraordinary growth in recent years with the application of engineering principles and their potential to support and improve the field of medicine. The tremendous progress in nanotechnology and biotechnology has lead to this explosion of research and development in biomedical applications. Biomaterials can now be engineered at a nanoscale and their specific interactions with the biological tissues can be modulated. Various design parameters are being established and researched for design of drug-delivery carriers and scaffolds to be implanted into humans. Nanoparticles made from versatile biomaterial can deliver both small-molecule drugs and various classes of bio-macromolecules, such as proteins and oligonucleotides. Similarly in the field of tissue engineering, current approaches emphasize nanoscale control of cell behavior by mimicking the natural extracellular matrix (ECM) unlike, traditional scaffolds. Drug delivery and tissue engineering are closely connected fields and both of these applications require materials with exceptional physical, chemical, biological, and biomechanical properties to provide superior therapy. In the current study the surface functionalization and the geometric features of the biomaterials has been explored. In particular, a synthetic surface for culture of human embryonic stem cells has been developed, demonstrating the importance of surface functionalization in maintaining the pluripotency of hESCs. In the second study, the geometric features of the drug delivery carriers are investigated and the polymeric nanoneedles mediated cellular permeabilization and direct cytoplasmic delivery is reported. In the third study, the combined effect of surface functionalization and geometric modification of carriers for vascular targeting is enunciated. These studies illustrate how the biomaterials can be designed to achieve various cellular behaviors and control the

  15. Mycoplasma pneumoniae Infection: Role of a Surface Protein in the Attachment Organelle

    NASA Astrophysics Data System (ADS)

    Hu, P. C.; Cole, R. M.; Huang, Y. S.; Graham, J. A.; Gardner, D. E.; Collier, A. M.; Clyde, W. A.

    1982-04-01

    Attachment of Mycoplasma pneumoniae to host cells by means of a specialized terminus initiates infection. Monoclonal antibodies to a surface protein (P1) inhibit this process, and react with a region of the tip covered with peplomer-like particles. Since antibodies against the P1 protein are generated by natural and experimental infection and by immunization, the substance may be an important determinant of protective immunity.

  16. The Eco-Hydrological Role of Physical Surface Sealing in Dry Environments

    NASA Astrophysics Data System (ADS)

    Sela, Shai; Svoray, Tal; Assouline, Shmuel

    2016-04-01

    Soil surface sealing is a widespread natural process in dry environments occurring frequently in bare soil areas between vegetation patches. The low hydraulic conductivity that characterizes the seal layer reduces both infiltration and evaporation fluxes from the soil, and thus has the potential to affect local vegetation water availability and consequently transpiration rates. This effect is investigated here using two separate physically based models - a runoff model, and a root water uptake model. High resolution rainfall data is used to demonstrate the seal layer effect on runoff generation and vegetation water availability, while the seal layer effect on vegetation water uptake is studied using a long-term climatic dataset (44 years) from three dry sites presenting a climatic gradient in the Negev Desert, Israel. The Feddes water uptake parameters for the dominant shrub at the study site (Sarcopoterium spinosum) were acquired using an inverse calibration procedure using data from a lysimeter experiment. The results indicate that the presence of surface sealing increases significantly vegetation water availability through runoff generation. Following water infiltration, the shrub transpiration generally increases if the shrub is surrounded by a seal layer, but this effect can switch from positive to negative depending on initial soil water content, rainfall intensity, and the duration of the subsequent drying intervals. These factors have a marked effect on inter-annual variability of the seal layer effect on the shrub transpiration, which on average was found to be 26% higher under sealed conditions than in the case of unsealed soil surfaces. These results shed light on the importance of surface sealing on the eco-hydrology of dry environments and its contribution to the resilience of woody vegetation.

  17. Sea surface temperature and torrential rains in the Valencia region: modelling the role of recharge areas

    NASA Astrophysics Data System (ADS)

    Pastor, F.; Valiente, J. A.; Estrela, M. J.

    2015-02-01

    Heavy rain events are frequently recorded in the Western Mediterranean causing economic losses and even human casualties. The Western Mediterranean is a deep and almost closed sea surrounded by high mountain ranges and with little exchange of water with the Atlantic ocean. A main factor in the development of torrential rains are ocean-atmosphere exchanges of heat and moisture that can potentially destabilize air masses travelling over the sea. The study of air mass trajectories previous to the rain event permits the identification of sea areas that could probably contribute to the development or intensification of rainfall. From a previous Mediterranean sea surface temperature climatology, its spatio-temporal distribution patterns have been studied showing two main distribution modes in winter and summer and transitional regimes in spring and autumn. Hence, three heavy precipitation events, for such winter and summer sea temperature regimes and for fall transition, affecting the Valencia region have been selected to study the effect of sea surface temperature in torrential rains. Simulations with perturbed sea surface temperature in different areas along the air mass path were run to compare results with unperturbed simulation. The variation of sea surface temperature in certain areas caused significant changes in model accumulated values and its spatial distribution. Therefore, the existence of recharge areas where air-sea interaction favors the development of torrential rainfall in Valencia region has been shown. This methodology could be extended to the whole Mediterranean basin to look for such potential recharge areas. The identification of sea areas that contribute to the development or intensification of heavy rain events in the Mediterranean countries could be a useful prognosis and/or monitoring tool.

  18. Sea surface temperature and torrential rains in the Valencia region: modelling the role of recharge areas

    NASA Astrophysics Data System (ADS)

    Pastor, F.; Valiente, J. A.; Estrela, M. J.

    2015-07-01

    Heavy rain events are frequently recorded in the Western Mediterranean causing economic losses and even human casualties. The Western Mediterranean is a deep and almost closed sea surrounded by high mountain ranges and with little exchange of water with the Atlantic ocean. A main factor in the development of torrential rains is ocean-atmosphere exchanges of heat and moisture that can potentially destabilize air masses travelling over the sea. The study of air mass trajectories previous to the rain event permits the identification of sea areas that could probably contribute to the development or intensification of rainfall. From a previous Mediterranean sea surface temperature climatology, its spatio-temporal distribution patterns have been studied showing two main distribution modes in winter and summer and transitional regimes in spring and autumn. Hence, three heavy precipitation events, for such winter and summer sea temperature regimes and for fall transition, affecting the Valencia region have been selected to study the effect of sea surface temperature in torrential rains. Simulations with perturbed sea surface temperature in different areas along the air mass path were run to compare results with unperturbed simulation. The variation of sea surface temperature in certain areas caused significant changes in model accumulated values and its spatial distribution. Therefore, the existence of areas that at a greater extent favour air-sea interaction leading to the development of torrential rainfall in the Valencia region has been shown. This methodology could be extended to the whole Mediterranean basin to look for such potential recharge areas. The identification of sea areas that contribute to the development or intensification of heavy rain events in the Mediterranean countries could be a useful prognosis and/or monitoring tool.

  19. Roles of the reproductive tract in modifications of the sperm membrane surface

    PubMed Central

    KUO, Yu-Wen; LI, Sheng-Hsiang; MAEDA, Kei-Ichiro; GADELLA, Bart M.; TSAI, Pei Shiue J.

    2016-01-01

    Successful fertilization requires viable and functional spermatozoa to recognize and fuse with the oocyte. In most mammalian species, mature spermatozoa are not capable of fertilizing the oocytes immediately after ejaculation. However, unlike somatic cells, spermatozoa, after leaving the testis, are transcriptionally and translationally silent; therefore, upon completion of spermiogenesis, spermatozoa carry only a minimal amount of essential proteins on their membranes as well as within their restricted volume of cytoplasm. To develop into a fully functional and competent sperm that is capable of successful fertilization, modifications of the sperm membrane surface during its transit in the reproductive tracts is critical. These post-spermatogenesis modifications advance the maturation of epididymal spermatozoa. In addition, components secreted into the lumen of the reproductive tracts that are later added onto the sperm membrane surface also regulate (inhibit or activate) the functions of the spermatozoa. This acquisition of additional proteins from the reproductive tracts may compensate for the inactivity of morphologically mature spermatozoa. In this review, we discuss the contributions of the male and female genital tracts to modifications of the sperm membrane surface at different stages of fertilization. PMID:27009019

  20. Untangling the biological effects of cerium oxide nanoparticles: the role of surface valence states

    NASA Astrophysics Data System (ADS)

    Pulido-Reyes, Gerardo; Rodea-Palomares, Ismael; Das, Soumen; Sakthivel, Tamil Selvan; Leganes, Francisco; Rosal, Roberto; Seal, Sudipta; Fernández-Piñas, Francisca

    2015-10-01

    Cerium oxide nanoparticles (nanoceria; CNPs) have been found to have both pro-oxidant and anti-oxidant effects on different cell systems or organisms. In order to untangle the mechanisms which underlie the biological activity of nanoceria, we have studied the effect of five different CNPs on a model relevant aquatic microorganism. Neither shape, concentration, synthesis method, surface charge (ζ-potential), nor nominal size had any influence in the observed biological activity. The main driver of toxicity was found to be the percentage of surface content of Ce3+ sites: CNP1 (58%) and CNP5 (40%) were found to be toxic whereas CNP2 (28%), CNP3 (36%) and CNP4 (26%) were found to be non-toxic. The colloidal stability and redox chemistry of the most and least toxic CNPs, CNP1 and CNP2, respectively, were modified by incubation with iron and phosphate buffers. Blocking surface Ce3+ sites of the most toxic CNP, CNP1, with phosphate treatment reverted toxicity and stimulated growth. Colloidal destabilization with Fe treatment only increased toxicity of CNP1. The results of this study are relevant in the understanding of the main drivers of biological activity of nanoceria and to define global descriptors of engineered nanoparticles (ENPs) bioactivity which may be useful in safer-by-design strategies of nanomaterials.

  1. Untangling the biological effects of cerium oxide nanoparticles: the role of surface valence states.

    PubMed

    Pulido-Reyes, Gerardo; Rodea-Palomares, Ismael; Das, Soumen; Sakthivel, Tamil Selvan; Leganes, Francisco; Rosal, Roberto; Seal, Sudipta; Fernández-Piñas, Francisca

    2015-01-01

    Cerium oxide nanoparticles (nanoceria; CNPs) have been found to have both pro-oxidant and anti-oxidant effects on different cell systems or organisms. In order to untangle the mechanisms which underlie the biological activity of nanoceria, we have studied the effect of five different CNPs on a model relevant aquatic microorganism. Neither shape, concentration, synthesis method, surface charge (ζ-potential), nor nominal size had any influence in the observed biological activity. The main driver of toxicity was found to be the percentage of surface content of Ce(3+) sites: CNP1 (58%) and CNP5 (40%) were found to be toxic whereas CNP2 (28%), CNP3 (36%) and CNP4 (26%) were found to be non-toxic. The colloidal stability and redox chemistry of the most and least toxic CNPs, CNP1 and CNP2, respectively, were modified by incubation with iron and phosphate buffers. Blocking surface Ce(3+) sites of the most toxic CNP, CNP1, with phosphate treatment reverted toxicity and stimulated growth. Colloidal destabilization with Fe treatment only increased toxicity of CNP1. The results of this study are relevant in the understanding of the main drivers of biological activity of nanoceria and to define global descriptors of engineered nanoparticles (ENPs) bioactivity which may be useful in safer-by-design strategies of nanomaterials. PMID:26489858

  2. Groundwater surface water interactions and the role of phreatophytes in identifying recharge zones

    NASA Astrophysics Data System (ADS)

    Ahring, T. S.; Steward, D. R.

    2012-11-01

    Groundwater and surface water interactions within riparian corridors impact the distribution of phreatophytes that tap into groundwater stores. The changes in canopy area of phreatophytes over time is related to changes in depth to groundwater, distance from a stream or river, and hydrologic soil group. Remote sensing was used to determine the location of trees with pre-development and post-development aerial photography over the Ogallala Aquifer in the central plains of the United States. It was found that once the depth to groundwater becomes greater than about 3 m, tree populations decrease as depth to water increases. This subsequently limited the extent of phreatophytes to within 700 m of the river. It was also found that phreatophytes have a higher likelihood of growing on hydrologic soil groups with higher saturated hydraulic conductivity. Phreatophytes exist along portions of the Arkansas River corridor where significant decreases in groundwater occurred as long as alluvium exists to create perched conditions where trees survive dry periods. Significant decreases (more that 50%) in canopy cover exists along river segments where groundwater declined by more than 10 m, indicating areas with good hydraulic connectivity between surface water and groundwater. Thus, interpretation of changes in phreatophyte distribution using historical and recent aerial photography is important in delineating zones of enhanced recharge where aquifers might be effectively recharged through diversion of surface water runoff.

  3. Groundwater surface water interactions through streambeds and the role of phreatophytes in identifying important recharge zones

    NASA Astrophysics Data System (ADS)

    Ahring, T. S.; Steward, D. R.

    2012-06-01

    Groundwater and surface water interactions within riparian corridors impact the distribution of phreatophytes that tap into groundwater stores. The changes in canopy area of phreatophytes over time is related to changes in depth to groundwater, distance from a stream or river, and hydrologic soil group. Remote sensing was used to determine the location of trees with predevelopment and post-development aerial photography over the Ogallala Aquifer in the central plains of the United States. It was found that once the depth to groundwater becomes greater than about 3 m, tree populations decrease as depth to water increases. This subsequently limited the extent of phreatophytes to within 700 m of the river. It was also found that phreatophytes have a higher likelihood of growing on hydrologic soil groups with higher saturated hydraulic conductivity. Phreatophytes exist along portions of the Arkansas River corridor where significant decreases in groundwater occurred as long as alluvium exists to create perched conditions where trees survive dry periods. Significant decreases (more that 50%) in canopy cover exists along river segments where groundwater declined by more than 10 m, indicating areas with good hydraulic connectivity between surface water and groundwater. Thus, interpretation of changes in phreatophyte distribution using historical and recent aerial photophaphy is important in delineating zones of enhanced recharge where aquifers might be effectively recharged through diversion of surface water runoff.

  4. The role of willow-birch forest in the surface energy balance at arctic treeline

    SciTech Connect

    Blanken, P.D. ); Rouse, W.R. )

    1994-11-01

    Continuous measurements of the energy balance components were made during the 1991 growing season over a willow-birch forest located near Churchill, Manitoba, Canada. On the basis of measurements of leaf area index, the growing season was divided into three distinct periods: growth, mature, and senescence. Changes in surface albedo were strongly correlated with changing leaf area index during the growth period with albedo increasing as leaf area increased. The latent heat flux density, Q[sub E], represented 74% of net radiation during the mature period compared to 55 and 54% during the growth and senescence periods, respectively. The greater Q[sub E] at plant maturity is due primarily to canopy transpiration. The sensitivity of Q[sub E] to net radiation was largest during the growth period. In contrast, the sensitivity of Q[sub E] to the surface resistance and aerodynamic resistance was the largest during the mature period. The implications of climate variability on the timing of leaf development and the surface energy and water balance are discussed. 28 refs., 8 figs., 1 tab.

  5. Developmental prosopagnosia and super-recognition: no special role for surface reflectance processing

    PubMed Central

    Russell, Richard; Chatterjee, Garga; Nakayama, Ken

    2011-01-01

    Face recognition by normal subjects depends in roughly equal proportions on shape and surface reflectance cues, while object recognition depends predominantly on shape cues. It is possible that developmental prosopagnosics are deficient not in their ability to recognize faces per se, but rather in their ability to use reflectance cues. Similarly, super-recognizers’ exceptional ability with face recognition may be a result of superior surface reflectance perception and memory. We tested this possibility by administering tests of face perception and face recognition in which only shape or reflectance cues are available to developmental prosopagnosics, super-recognizers, and control subjects. Face recognition ability and the relative use of shape and pigmentation were unrelated in all the tests. Subjects who were better at using shape or reflectance cues were also better at using the other type of cue. These results do not support the proposal that variation in surface reflectance perception ability is the underlying cause of variation in face recognition ability. Instead, these findings support the idea that face recognition ability is related to neural circuits using representations that integrate shape and pigmentation information. PMID:22192636

  6. Tuning surface reactivity by finite size effects: role of orbital symmetry in the d - band model

    NASA Astrophysics Data System (ADS)

    Snijders, Paul; Yin, Xiangshi; Cooper, Valentino; Weitering, Hanno

    Catalytic activity depends sensitively on the strength of the interactions between reactant molecules and catalyst surface: too weak and the catalyst cannot capture enough molecules to react; too strong and the reaction products do not desorb, blocking further reactions. The ability to control the binding strength of molecules to metal surfaces is thus fundamental to the design of efficient and selective catalysts. Catalyst design often relies on increasing the interaction strength on relatively non-reactive materials by introducing active sites. Here, we present a complementary approach: we exploit finite size effects in the electronic structure of ultrathin Pd(111) films grown on Ru(0001) to tune their reactivity by changing the film thickness one atom layer at a time. While bulk Pd(111) is reactive toward oxygen, we find that Pd films thinner than 6 atom layers are surprisingly inert to oxidation. This observation can be explained with the d-band model only when it is applied to the orbitals directly involved in the bonding. The insight into orbital specific contributions to surface reactivity could be useful in the design of catalysts. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

  7. The role of beaded activated carbon's surface oxygen groups on irreversible adsorption of organic vapors.

    PubMed

    Jahandar Lashaki, Masoud; Atkinson, John D; Hashisho, Zaher; Phillips, John H; Anderson, James E; Nichols, Mark

    2016-11-01

    The objective of this study is to determine the contribution of surface oxygen groups to irreversible adsorption (aka heel formation) during cyclic adsorption/regeneration of organic vapors commonly found in industrial systems, including vehicle-painting operations. For this purpose, three chemically modified activated carbon samples, including two oxygen-deficient (hydrogen-treated and heat-treated) and one oxygen-rich sample (nitric acid-treated) were prepared. The samples were tested for 5 adsorption/regeneration cycles using a mixture of nine organic compounds. For the different samples, mass balance cumulative heel was 14 and 20% higher for oxygen functionalized and hydrogen-treated samples, respectively, relative to heat-treated sample. Thermal analysis results showed heel formation due to physisorption for the oxygen-deficient samples, and weakened physisorption combined with chemisorption for the oxygen-rich sample. Chemisorption was attributed to consumption of surface oxygen groups by adsorbed species, resulting in formation of high boiling point oxidation byproducts or bonding between the adsorbates and the surface groups. Pore size distributions indicated that different pore sizes contributed to heel formation - narrow micropores (<7Å) in the oxygen-deficient samples and midsize micropores (7-12Å) in the oxygen-rich sample. The results from this study help explain the heel formation mechanism and how it relates to chemically tailored adsorbent materials. PMID:27295065

  8. Role of Resonances in the Transmission of Surface Plasmon Polaritons between Nanostructures.

    PubMed

    Johns, Paul; Yu, Kuai; Devadas, Mary Sajini; Hartland, Gregory V

    2016-03-22

    Understanding how surface plasmon polaritons (SPPs) propagate in metal nanostructures is important for the development of plasmonic devices. In this paper, we study the transmission of SPPs between single-crystal gold nanobars on a glass substrate using transient absorption microscopy. The coupled structures were produced by creating gaps in single nanobars by focused ion beam milling. SPPs were launched by focusing the pump laser at the end of the nanobar, and the transmission across the gaps was imaged by scanning the probe laser over the nanostructure. The results show larger losses at small gap sizes. Finite element method calculations were used to investigate this effect. The calculations show two main modes for nanobars on a glass surface: a leaky mode localized at the air-gold interface, and a bound mode localized at the glass-gold interface. At specific gap sizes (approximately 50 nm for our system), these SPP modes can excite localized surface plasmon modes associated with the gap, which dissipate energy. This increases the energy losses at small gap sizes. Experiments and simulations were also performed for the nanobars in microscope immersion oil, which creates a more homogeneous optical environment, and consistent results were observed. PMID:26866536

  9. Computational analysis of microbubble flows in bifurcating airways: role of gravity, inertia, and surface tension.

    PubMed

    Chen, Xiaodong; Zielinski, Rachel; Ghadiali, Samir N

    2014-10-01

    Although mechanical ventilation is a life-saving therapy for patients with severe lung disorders, the microbubble flows generated during ventilation generate hydrodynamic stresses, including pressure and shear stress gradients, which damage the pulmonary epithelium. In this study, we used computational fluid dynamics to investigate how gravity, inertia, and surface tension influence both microbubble flow patterns in bifurcating airways and the magnitude/distribution of hydrodynamic stresses on the airway wall. Direct interface tracking and finite element techniques were used to simulate bubble propagation in a two-dimensional (2D) liquid-filled bifurcating airway. Computational solutions of the full incompressible Navier-Stokes equation were used to investigate how inertia, gravity, and surface tension forces as characterized by the Reynolds (Re), Bond (Bo), and Capillary (Ca) numbers influence pressure and shear stress gradients at the airway wall. Gravity had a significant impact on flow patterns and hydrodynamic stress magnitudes where Bo > 1 led to dramatic changes in bubble shape and increased pressure and shear stress gradients in the upper daughter airway. Interestingly, increased pressure gradients near the bifurcation point (i.e., carina) were only elevated during asymmetric bubble splitting. Although changes in pressure gradient magnitudes were generally more sensitive to Ca, under large Re conditions, both Re and Ca significantly altered the pressure gradient magnitude. We conclude that inertia, gravity, and surface tension can all have a significant impact on microbubble flow patterns and hydrodynamic stresses in bifurcating airways. PMID:25068642

  10. Soil surface acidity plays a determining role in the atmospheric-terrestrial exchange of nitrous acid

    PubMed Central

    Donaldson, Melissa A.; Bish, David L.; Raff, Jonathan D.

    2014-01-01

    Nitrous acid (HONO) is an important hydroxyl (OH) radical source that is formed on both ground and aerosol surfaces in the well-mixed boundary layer. Recent studies report the release of HONO from nonacidic soils, although it is unclear how soil that is more basic than the pKa of HONO (∼3) is capable of protonating soil nitrite to serve as an atmospheric HONO source. Here, we used a coated-wall flow tube and chemical ionization mass spectrometry (CIMS) to study the pH dependence of HONO uptake onto agricultural soil and model substrates under atmospherically relevant conditions (1 atm and 30% relative humidity). Experiments measuring the evolution of HONO from pH-adjusted surfaces treated with nitrite and potentiometric titrations of the substrates show, to our knowledge for the first time, that surface acidity rather than bulk aqueous pH determines HONO uptake and desorption efficiency on soil, in a process controlled by amphoteric aluminum and iron (hydr)oxides present. The results have important implications for predicting when soil nitrite, whether microbially derived or atmospherically deposited, will act as a net source or sink of atmospheric HONO. This process represents an unrecognized mechanism of HONO release from soil that will contribute to HONO emissions throughout the day. PMID:25512517

  11. Untangling the biological effects of cerium oxide nanoparticles: the role of surface valence states

    PubMed Central

    Pulido-Reyes, Gerardo; Rodea-Palomares, Ismael; Das, Soumen; Sakthivel, Tamil Selvan; Leganes, Francisco; Rosal, Roberto; Seal, Sudipta; Fernández-Piñas, Francisca

    2015-01-01

    Cerium oxide nanoparticles (nanoceria; CNPs) have been found to have both pro-oxidant and anti-oxidant effects on different cell systems or organisms. In order to untangle the mechanisms which underlie the biological activity of nanoceria, we have studied the effect of five different CNPs on a model relevant aquatic microorganism. Neither shape, concentration, synthesis method, surface charge (ζ-potential), nor nominal size had any influence in the observed biological activity. The main driver of toxicity was found to be the percentage of surface content of Ce3+ sites: CNP1 (58%) and CNP5 (40%) were found to be toxic whereas CNP2 (28%), CNP3 (36%) and CNP4 (26%) were found to be non-toxic. The colloidal stability and redox chemistry of the most and least toxic CNPs, CNP1 and CNP2, respectively, were modified by incubation with iron and phosphate buffers. Blocking surface Ce3+ sites of the most toxic CNP, CNP1, with phosphate treatment reverted toxicity and stimulated growth. Colloidal destabilization with Fe treatment only increased toxicity of CNP1. The results of this study are relevant in the understanding of the main drivers of biological activity of nanoceria and to define global descriptors of engineered nanoparticles (ENPs) bioactivity which may be useful in safer-by-design strategies of nanomaterials. PMID:26489858

  12. Soil surface acidity plays a determining role in the atmospheric-terrestrial exchange of nitrous acid.

    PubMed

    Donaldson, Melissa A; Bish, David L; Raff, Jonathan D

    2014-12-30

    Nitrous acid (HONO) is an important hydroxyl (OH) radical source that is formed on both ground and aerosol surfaces in the well-mixed boundary layer. Recent studies report the release of HONO from nonacidic soils, although it is unclear how soil that is more basic than the pKa of HONO (∼ 3) is capable of protonating soil nitrite to serve as an atmospheric HONO source. Here, we used a coated-wall flow tube and chemical ionization mass spectrometry (CIMS) to study the pH dependence of HONO uptake onto agricultural soil and model substrates under atmospherically relevant conditions (1 atm and 30% relative humidity). Experiments measuring the evolution of HONO from pH-adjusted surfaces treated with nitrite and potentiometric titrations of the substrates show, to our knowledge for the first time, that surface acidity rather than bulk aqueous pH determines HONO uptake and desorption efficiency on soil, in a process controlled by amphoteric aluminum and iron (hydr)oxides present. The results have important implications for predicting when soil nitrite, whether microbially derived or atmospherically deposited, will act as a net source or sink of atmospheric HONO. This process represents an unrecognized mechanism of HONO release from soil that will contribute to HONO emissions throughout the day. PMID:25512517

  13. On the critical role of Rayleigh scattering in single-molecule surface-enhanced Raman scattering via a plasmonic nanogap.

    PubMed

    Chen, Bao-Qin; Zhang, Chao; Li, Jiafang; Li, Zhi-Yuan; Xia, Younan

    2016-08-25

    Electromagnetic and chemical enhancement mechanisms are commonly used to account for single-molecule surface-enhanced Raman scattering (SM-SERS). Due to many practical limitations, however, the overall enhancement factor summed up from these two mechanisms is typically 5-6 orders of magnitude below the level of 10(14)-10(15) required for SM-SERS. Here, we demonstrate that the multiple elastic Rayleigh scattering of a molecule could play a critical role in further enhancing the Raman signal, when the molecule is trapped in a 2 nm gap between two Ag nanoparticles, pushing the overall enhancement factor close to the level needed for SM-SERS. As a universal physical process for all molecules interacting with light, we believe that Rayleigh scattering plays a pivotal and as yet unrecognized role in SERS, in particular, for enabling single-molecule sensitivity. PMID:27526632

  14. The role of loamy sediment ( terra rossa) in the context of steady state karst surface lowering

    NASA Astrophysics Data System (ADS)

    Šušteršič, France; Rejšek, Klement; Mišič, Miha; Eichler, František

    2009-05-01

    Reddish, loamy material ( terra rossa), found on many karstified surfaces, has long been accepted as a characteristic karst feature. Two basic views of terra rossa formation were distinguished, related to either a residual or a detrital origin. More recently it has been suggested that it could derive from isovolumetric reactions between the parent carbonate rock and airborne material. This paper reviews possible sources of terra rossa, explores its behaviour on the karst surface from the karst geomorphology viewpoint, and considers whether its existence is better explained in terms of a closed or open karst geomorphic system. Two approximately west-east traverses were laid out across Slovenia and the Czech Republic, comprising nine sample locations in each country previously known to be characterized by terra rossa. General geomorphic/speleomorphic conditions were estimated, and loamy material and parent rock samples were collected. Insoluble residues extracted from the rock were processed in the same ways as the loamy material. Basic geochemical and mineralogical investigations were run. The data obtained were processed statistically. Results show that statistical relationships between the adjacent rock insoluble residues and adjacent terra rossa bodies exist only at sampling sites recognised as "vertical". Most such sites are cutters, which are "karren-like grooves formed beneath the soil, more commonly referred to as subsoil karren" (US Environmental Protection Agency, 2002. A Lexicon of Cave and Karst Terminology. Field, M.S. (Ed.). , p.53). Possible sources of terra rossa material as well as the possibilities of material accumulating on the karst surface are discussed in detail, with special emphasis upon cutters. Theoretical considerations indicate that cutters are the only features that can collect sufficient insoluble residue to be detectable after a period of evolution within a surface that is lowering under

  15. The role of roughness in predicting transport thresholds on desert surfaces: temporal and spatial variability

    NASA Astrophysics Data System (ADS)

    King, James; Haustein, Karsten; Wiggs, Giles F. S.; Eckardt, Frank; Thomas, David S. G.; Washington, Richard

    2013-04-01

    Dust emission schemes in climate models are relatively simple and tuned to represent observed background aerosol concentrations. A key component of the dust emission scheme is the sediment transport threshold, which is a function of soil size distribution, soil moisture, air and soil particle density, and surface roughness. For a particular region or landform that is not vegetated the variable that controls the transport threshold is soil moisture. This is because it is assumed that the other components vary little (air and soil particle densities) or are kept constant (soil size distribution and surface roughness). This in turn puts the emphasis very heavily on soil moisture and wind stress as the key drivers of dust emission for specific landforms and dust emission schemes. This highlights the necessity for current models to tune their model parameters to observations. Observations of dust emission were undertaken in 2011 and 2012 on Sua Pan in Botswana, a large, flat, unvegetated salt pan, as part of the Dust Observation for Models (DO4 Models) campaign. The observations consisted of eleven meteorological stations placed within a 144 km2 region recording wind velocity, soil moisture, soil and air temperature, horizontal transport, vertical transport, and radiative properties. Out of the measured and calculated erodibility parameters responsible for predicting transport threshold within current schemes, surface soil moisture and aerodynamic roughness length varied the most over the duration of the project and spatially across the pan. In some cases, the aerodynamic roughness length of the bare soil increased by three orders of magnitude within a three month period. This increase in roughness would almost double the modelled threshold shear velocity required for this surface to be emissive. The temporal and spatial variability of the calculated transport threshold is explored with observed data and compared with the modelled transport threshold for this region for

  16. On the role of anomalous ocean surface temperatures for promoting the record Madden-Julian Oscillation in March 2015

    NASA Astrophysics Data System (ADS)

    Marshall, Andrew G.; Hendon, Harry H.; Wang, Guomin

    2016-01-01

    A Madden-Julian Oscillation (MJO) event dramatically amplified at the beginning of March 2015 as the convective phase traversed an unusually warm central Pacific Ocean. This record amplification also resulted in record amplitude of the MJO based on index measurements since 1974. We explore the possible role of the anomalously high ocean surface temperatures in the equatorial central Pacific for promoting the extraordinary amplification of this MJO event. Forecast sensitivity experiments with the Predictive Ocean Atmosphere Model for Australia show that the enhanced growth of the MJO resulted from amplification of the convective anomaly as it encountered the unusually warm central Pacific. Our results indicate that anomalous sea surface temperature (SST) at the onset of El Niño 2015 promoted the intensification of the MJO. We suggest a two-way interaction whereby initial SST anomalies promoted enhanced MJO activity which then possibly led to enhanced El Niño development.

  17. Mesdc2 plays a key role in cell-surface expression of Lrp4 and postsynaptic specialization in myotubes.

    PubMed

    Hoshi, Taisuke; Tezuka, Tohru; Yokoyama, Kazumasa; Iemura, Shun-ichiro; Natsume, Tohru; Yamanashi, Yuji

    2013-11-29

    Low-density lipoprotein receptor-related protein 4 (Lrp4) is essential for pre- and post-synaptic specialization at the neuromuscular junction (NMJ), an indispensable synapse between a motor nerve and skeletal muscle. Muscle-specific receptor tyrosine kinase MuSK must form a complex with Lrp4 to organize postsynaptic specialization at NMJs. Here, we show that the chaperon Mesdc2 binds to the intracellular form of Lrp4 and promotes its glycosylation and cell-surface expression. Furthermore, knockdown of Mesdc2 suppresses cell-surface expression of Lrp4, activation of MuSK, and postsynaptic specialization in muscle cells. These results suggest that Mesdc2 plays an essential role in NMJ formation by promoting Lrp4 maturation. PMID:24140340

  18. Role of atmospheric corrosion of aluminum alloys in viability of intrinsic-surface methods for tagging military hardware

    SciTech Connect

    Maiya, P.S.; Kassner, T.F.

    1991-11-01

    A primary requirement for authentication of tags for military equipment desigated as treaty-limited items (TLIs) is that the surface topograhy of the tag area be maintained after exposure to a variety of atmospheric conditions over many years. This report summarizes the chemical and physical properties of atmospheric as they relate to localized corrosion of aluminum and aluminum alloys. The role of impurity species that exacerbate corrison, and that hence may interfere with tag verification, is discussed. Because exposure times for the tag materials are much longer than those practical in laboratory experiments, it is important to understand the kinetics of processes occurring in these alloys and the viability of various protection schemes. General principles and limitations of testing in natural atmospheres and in the laboratory are discussed. Corrosion results indicate that the tag surface must be protected, and a tag protection scheme is proposed.

  19. Journey to the cell surface--the central role of the trans-Golgi network in plants.

    PubMed

    Gendre, Delphine; Jonsson, Kristoffer; Boutté, Yohann; Bhalerao, Rishikesh P

    2015-03-01

    The secretion of proteins, lipids, and carbohydrates to the cell surface is essential for plant development and adaptation. Secreted substances synthesized at the endoplasmic reticulum pass through the Golgi apparatus and trans-Golgi network (TGN) en route to the plasma membrane via the conventional secretion pathway. The TGN is morphologically and functionally distinct from the Golgi apparatus. The TGN is located at the crossroads of many trafficking pathways and regulates a range of crucial processes including secretion to the cell surface, transport to the vacuole, and the reception of endocytic cargo. This review outlines the TGN's central role in cargo secretion, showing that its behavior is more complex and controlled than the bulk-flow hypothesis suggests. Its formation, structure, and maintenance are discussed along with the formation and release of secretory vesicles. PMID:25187082

  20. Using AFM to probe the complexation of DNA with anionic lipids mediated by Ca(2+): the role of surface pressure.

    PubMed

    Luque-Caballero, Germán; Martín-Molina, Alberto; Sánchez-Treviño, Alda Yadira; Rodríguez-Valverde, Miguel A; Cabrerizo-Vílchez, Miguel A; Maldonado-Valderrama, Julia

    2014-04-28

    Complexation of DNA with lipids is currently being developed as an alternative to classical vectors based on viruses. Most of the research to date focuses on cationic lipids owing to their spontaneous complexation with DNA. Nonetheless, recent investigations have revealed that cationic lipids induce a large number of adverse effects on DNA delivery. Precisely, the lower cytotoxicity of anionic lipids accounts for their use as a promising alternative. However, the complexation of DNA with anionic lipids (mediated by cations) is still in early stages and is not yet well understood. In order to explore the molecular mechanisms underlying the complexation of anionic lipids and DNA we proposed a combined methodology based on the surface pressure-area isotherms, Gibbs elasticity and Atomic Force Microscopy (AFM). These techniques allow elucidation of the role of the surface pressure in the complexation and visualization of the interfacial aggregates for the first time. We demonstrate that the DNA complexes with negatively charged model monolayers (DPPC/DPPS 4 : 1) only in the presence of Ca(2+), but is expelled at very high surface pressures. Also, according to the Gibbs elasticity plot, the complexation of lipids and DNA implies a whole fluidisation of the monolayer and a completely different phase transition map in the presence of DNA and Ca(2+). AFM imaging allows identification for the first time of specific morphologies associated with different packing densities. At low surface coverage, a branched net like structure is observed whereas at high surface pressure fibers formed of interfacial aggregates appear. In summary, Ca(2+) mediates the interaction between DNA and negatively charged lipids and also the conformation of the ternary system depends on the surface pressure. Such observations are important new generic features of the interaction between DNA and anionic lipids. PMID:24668321

  1. The surface coat of plant-parasitic nematodes: chemical composition, origin, and biological role-a review.

    PubMed

    Spiegel, Y; McClure, M A

    1995-06-01

    Chemical composition, origin, and biological role of the surface coat (SC) of plant-parasitic nematodes are described and compared with those of animal-parasitic and free-living nematodes. The SC of the plant-parasitic nematodes is 5-30 nm thick and is characterized by a net negative charge. It consists, at least in part, of glycoproteins and proteins with various molecular weights, depending upon the nematode species. The lability of its components and the binding of human red blood cells to the surface of many tylenchid plant-parasitic nematodes, as well as the binding of several neoglycoproteins to the root-knot nematode Meloidogyne, suggest the presence of carbohydrate-recognition-domains for host plants and parasitic or predatory soil microorganisms (Pasteuria penetrans and Dactylaria spp., for example). These features may also assist in nematode adaptations to soil environments and to plant hosts with defense mechanisms that depend on reactions to nematode surfaces. Surface coat proteins can be species and race specific, a characteristic with promising diagnostic potential. PMID:19277272

  2. The role of surface chemical analysis in a study to select replacement processes for TCA vapor degreasing

    NASA Technical Reports Server (NTRS)

    Lesley, Michael W.; Davis, Lawrence E.; Moulder, John F.; Carlson, Brad A.

    1995-01-01

    The role of surface-sensitive chemical analysis (ESCA, AES, and SIMS) in a study to select a process to replace 1, 1, 1-trichloroethane (TCA) vapor degreasing as a steel and aluminum bonding surface preparation method is described. The effort was primarily concerned with spray-in-air cleaning processes involving aqueous alkaline and semi-aqueous cleaners and a contamination sensitive epoxy-to-metal bondline. While all five cleaners tested produced bonding strength results equal to or better than those produced by vapor degreasing, the aqueous alkaline cleaners yielded results which were superior to those produced by the semi-aqueous cleaners. The main reason for the enhanced performance appears to be a silicate layer left behind by the aqueous alkaline cleaners. The silicate layer increases the polarity of the surface and enhances epoxy-to-metal bonding. On the other hand, one of the semi-aqueous cleaners left a nonpolar carbonaceous residue which appeared to have a negative effect on epoxy-to-metal bonding. Differences in cleaning efficiency between cleaners/processes were also identified. These differences in surface chemistry, which were sufficient to affect bonding, were not detected by conventional chemical analysis techniques.

  3. cGMP decreases surface NKCC2 levels in the thick ascending limb: role of phosphodiesterase 2 (PDE2)

    PubMed Central

    Ares, Gustavo R.; Caceres, Paulo; Alvarez-Leefmans, Francisco J.; Ortiz, Pablo A.

    2008-01-01

    NaCl absorption in the medullary thick ascending limb of the loop of Henle (THAL) is mediated by the apical Na/K/2Cl cotransporter (NKCC2). Hormones that increase cGMP, such as nitric oxide (NO) and natriuretic peptides, decrease NaCl absorption by the THAL. However, the mechanism by which cGMP decreases NaCl absorption in THALs is not known. We hypothesized that cGMP decreases surface NKCC2 levels in the THAL. We used surface biotinylation to measure surface NKCC2 levels in rat THAL suspensions. We tested the effect of the membrane-permeant cGMP analog dibutyryl-cGMP (db-cGMP) on surface NKCC2 levels. Incubating THALs with db-cGMP for 20 min decreased surface NKCC2 levels in a concentration-dependent manner (basal = 100%; db-cGMP 100 μM = 77 ± 7%; 500 μM = 54 ± 10% and 1,000 μM = 61 ± 8%). A different cGMP analog 8-bromo-cGMP (8-Br-cGMP) also decreased surface NKCC2 levels by 25%, (basal = 100%; 8-Br-cGMP = 75 ± 5%). Incubation of isolated, perfused THALs with db-cGMP decreased apical surface NKCC2 labeling levels as measured by immunofluorescence and confocal microscopy. cGMP-stimulated phosphodiesterase 2 (PDE2) mediates the inhibitory effect of NO on NaCl absorption by THALs. Thus we examined the role of PDE2 and found that PDE2 inhibitors blocked the effect of db-cGMP on surface NKCC2. Also, a nonstimulatory concentration of db-cAMP blocked the cGMP-induced decrease in surface NKCC2. Finally, db-cGMP inhibited THAL net Cl absorption by 48 ± 4%, and this effect was completely blocked by PDE2 inhibition. We conclude that cGMP decreases NKCC2 levels in the apical membrane of THALs and that this effect is mediated by PDE2. This is an important mechanism by which cGMP inhibits NaCl absorption by the THAL. PMID:18684888

  4. Illuminating CO2 reduction on frustrated Lewis pair surfaces: investigating the role of surface hydroxides and oxygen vacancies on nanocrystalline In2O(3-x)(OH)y.

    PubMed

    Ghuman, Kulbir Kaur; Wood, Thomas E; Hoch, Laura B; Mims, Charles A; Ozin, Geoffrey A; Singh, Chandra Veer

    2015-06-14

    Designing catalytic nanostructures that can thermochemically or photochemically convert gaseous carbon dioxide into carbon based fuels is a significant challenge which requires a keen understanding of the chemistry of reactants, intermediates and products on surfaces. In this context, it has recently been reported that the reverse water gas shift reaction (RWGS), whereby carbon dioxide is reduced to carbon monoxide and water, CO2 + H2 → CO + H2O, can be catalysed by hydroxylated indium oxide nanocrystals, denoted In2O(3-x)(OH)y, more readily in the light than in the dark. The surface hydroxide groups and oxygen vacancies on In2O(3-x)(OH)y were both shown to assist this reaction. While this advance provides a first step toward the rational design and optimization of a single-component gas-phase CO2 reduction catalyst for solar fuels generation, the precise role of the hydroxide groups and oxygen vacancies in facilitating the reaction on In2O(3-x)(OH)y nanocrystals has not been resolved. In the work reported herein, for the first time we present in situ spectroscopic and kinetic observations, complemented by density functional theory analysis, that together provide mechanistic information into the surface reaction chemistry responsible for the thermochemical and photochemical RWGS reaction. Specifically, we demonstrate photochemical CO2 reduction at a rate of 150 μmol gcat(-1) hour(-1), which is four times better than the reduction rate in the dark, and propose a reaction mechanism whereby a surface active site of In2O(3-x)(OH)y, composed of a Lewis base hydroxide adjacent to a Lewis acid indium, together with an oxygen vacancy, assists the adsorption and heterolytic dissociation of H2 that enables the adsorption and reaction of CO2 to form CO and H2O as products. This mechanism, which has its analogue in molecular frustrated Lewis pair (FLP) chemistry and catalysis of CO2 and H2, is supported by preliminary kinetic investigations. The results of this study

  5. Modeling atmospheric longwave radiation at the surface during overcast skies: The role of cloud base height

    NASA Astrophysics Data System (ADS)

    Viúdez-Mora, A.; Costa-Surós, M.; Calbó, J.; González, J. A.

    2015-01-01

    behavior of the atmospheric downward longwave radiation at the surface under overcast conditions is studied. For optically thick clouds, longwave radiation depends greatly on the cloud base height (CBH), besides temperature and water vapor profiles. The CBH determines the cloud emission temperature and the air layers contributing to the longwave radiation that reaches the surface. Overcast situations observed at Girona (NE Iberian Peninsula) were studied by using a radiative transfer model. The data set includes different seasons, and a large range of CBH (0-5000 m). The atmosphere profiles were taken from the European Center for Medium-Range Weather Forecast analysis. The CBH was determined from ceilometer measurements and also estimated by using a suitable method applied to the vertical profile of relative humidity. The agreement between calculations and pyrgeometer measurements is remarkably good (1.6 ± 6.2 W m-2) if the observed CBH is used; poorer results are obtained with the estimated CBH (4.3 ± 7.0 W m-2). These results are better than those obtained from a simple parameterization based upon ground-level data (1.1 ± 11.6 W m-2), which can be corrected by adding a term that takes into account the CBH (-0.1 ± 7.3 W m-2). At this site, the cloud radiative effect (CRE) at the surface lies in the range 50-80 W m-2, has a clear seasonal behavior (higher CRE in winter), and depends upon the CBH. For the cold and the warm seasons, CRE decreases with CBH at a rate of -5 and -4 W m-2/km, respectively. Results obtained for other climates (subarctic and tropical) are also presented.

  6. The role of hydrogen in room-temperature ferromagnetism at graphite surfaces

    SciTech Connect

    Ohldag, Hendrik

    2011-08-12

    We present a x-ray dichroism study of graphite surfaces that addresses the origin and magnitude of ferromagnetism in metal-free carbon. We find that, in addition to carbon {pi} states, also hydrogen-mediated electronic states exhibit a net spin polarization with significant magnetic remanence at room temperature. The observed magnetism is restricted to the top {approx}10 nm of the irradiated sample where the actual magnetization reaches {approx_equal} 15 emu/g at room temperature. We prove that the ferromagnetism found in metal-free untreated graphite is intrinsic and has a similar origin as the one found in proton bombarded graphite.

  7. Further insights into the role of carbon surface functionalities in the mechanism of phenol adsorption.

    PubMed

    Terzyk, Artur P

    2003-12-15

    The presented study describes the temperature as well as pH dependence of phenol adsorption (and adsorption kinetics) on four carbons with different chemical compositions of the surface layer but almost identical porosity. In the first part, it is shown, applying the most sophisticated method of carbon porosity characterization (i.e., the method of Do and co-workers-ND method), that the porosity does not change much after the chemical modification of carbons. Then it is shown that the ND method leads to the same results as the DFT (density functional theory) does. Next, the TPD results for D43/1 carbons (initial, modified with HNO(3), fuming H(2)SO(4), and with NH(3)) are described. The TPD results for carbon modified with fuming sulphuric acid has not been reported yet by others. The deconvolution of peaks is performed. The obtained results, together with those already published, lead to the chemical structures of surface functionalities for all studied carbons. The thermogravimetric analysis of phenol adsorption shows that the amount of chemically bonded molecules is small. Then it is shown that the adsorption at the acidic pH (1.5) level is lower for all studied carbons than that at the neutral one. The description of the isotherms applying adsorbability, quasi-Freundlich and DA models, together with enthalpy measurements, lead to the mechanism of phenol adsorption at both pH values. The mechanism is, furthermore, confirmed by some empirical correlations. The analysis of the average hysteresis on adsorption-desorption isotherms as well as the comparison of phenol adsorption in oxic and anoxic conditions leads to the mechanism of irreversible phenol adsorption. It is suggested that the irreversibility is caused by two effects: the creation of strong complexes between phenol and surface carbonyl and lactones as well as by the polymerization. The last effect is due to the ability of carbon to adsorb the oxygen from solution and form superoxo ions. Finally, the

  8. Surface voltage gradient role in high voltage solar array-plasma interaction: Center Director's discretionary fund

    NASA Technical Reports Server (NTRS)

    Carruth, M. R., Jr.

    1985-01-01

    A large amount of experimental and analytical effort has been directed toward understanding the plasma sheath growth and discharge phenomena which lead to high voltage solar array-space plasma interactions. An important question which has not been addressed is how the surface voltage gradient on such an array may affect these interactions. The results of this study indicate that under certain conditions, the voltage gradient should be taken into account when evaluating the effect on a solar array operating in a plasma environment.

  9. A critical study of the role of the surface oxide layer in titanium bonding

    NASA Technical Reports Server (NTRS)

    Dias, S.; Wightman, J. P.

    1983-01-01

    Scanning electron microscope/X-ray photoelectron spectroscopy (SEM/XPS) analysis of fractured adhesively bonded Ti 6-4 samples is discussed. The text adhesives incuded NR 056X polyimide, polypheylquinoxaline (PPQ), and LARC-13 polyimide. Differentiation between cohesive and interfacial failure was based on the absence of presence of a Ti 2p XPS photopeak. In addition, the surface oxide layer on Ti-(6A1-4V) adherends is characterized and bond strength and durability are addressed. Bond durability in various environmental conditions is discussed.

  10. Diffusion around a cardiac calcium channel and the role of surface bound calcium.

    PubMed Central

    Bers, D M; Peskoff, A

    1991-01-01

    The diffusion of Ca as it converges to the external mouth of a Ca channel is examined. Diffusional limitation on Ca ions entering Ca channels during current flow, cause local extracellular Ca depletions. Such extracellular Ca depletions have been reported in cardiac muscle. The cardiac sarcolemma has a large number of low-affinity Ca binding sites that can buffer these local Ca depletions. For a hemisphere of extracellular space (of radius less than 0.33 microns) centered on the external mouth of a Ca channel the amount of Ca bound at the membrane surface exceeds that which is free within the associated hemisphere. The ratio of bound Ca/free Ca increases as r decreases, such that the [Ca] nearest the Ca channel is the most strongly buffered by sarcolemmal bound Ca. It is demonstrated that Ca ions coming from these sarcolemmal Ca binding sites contribute quantitatively to the integrated Ca current. The electric field generated by the local depletion of Ca near the channel mouth has little impact on the extent of Ca depletion, but if an additional electric field exists at the mouth of the channel, Ca depletion can be significantly altered. Other low-affinity Ca binding sites in the interstitium may also contribute to the buffering of extracellular Ca. The complex geometry of the extracellular space in cardiac muscle (e.g., transverse tubules and restrictions of extracellular space between cells) increases both the predicted Ca depletions (in the absence of binding) and the bound/free ratio. Thus, the impact of this surface Ca binding is greatly increased. By considering arrays of Ca channels in transverse tubules or in parallel planes (e.g., membranes of neighboring cells), extracellular Ca depletions are predicted which agree with those measured experimentally. Membrane Ca binding may also be expected to buffer increases in [Ca] around the inner mouth of Ca channels. It is demonstrated that in the absence of other intracellular systems most of the Ca entering the

  11. Role of Mechanical Stress in Regulating Airway Surface Hydration and Mucus Clearance Rates

    PubMed Central

    Button, Brian; Boucher, Richard C.

    2008-01-01

    Effective clearance of mucus is a critical innate airway defense mechanism, and under appropriate conditions, can be stimulated to enhance clearance of inhaled pathogens. It has become increasingly clear that extracellular nucleotides (ATP and UTP) and nucleosides (adenosine) are important regulators of mucus clearance in the airways as a result of their ability to stimulate fluid secretion, mucus hydration, and cilia beat frequency (CBF). One ubiquitous mechanism to stimulate ATP release is through external mechanical stress. This article addresses the role of physiologically-relevant mechanical forces in the lung and their effects on regulating mucociliary clearance (MCC). The effects of mechanical forces on the stimulating ATP release, fluid secretion, CBF, and MCC are discussed. Also discussed is evidence suggesting that airway hydration and stimulation of MCC by stress-mediated ATP release may play a role in several therapeutic strategies directed at improving mucus clearance in patients with obstructive lung diseases, including cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). PMID:18585484

  12. Strain Partitioning During Continental Extension: Role of Frictional Weakening and Surface Processes

    NASA Astrophysics Data System (ADS)

    Buiter, Susanne J. H.; Huismans, Ritske S.; Beaumont, Christopher

    Extension of continental lithosphere is accommodated in the crust by normal faults leading to the development of symmetric or asymmetric sedimentary basins. In previ- ous work (Huismans and Beaumont, Geology) we have focussed on the role of strain softening in generating asymmetric extensional structures on a lithospheric scale. Here we test whether strain softening in crustal scale models may also control the develop- ment of asymmetric half-grabens versus symmetric graben systems. Our second aim is to investigate the feedback between basin geometry, and sedimentary and erosional processes. To examine the evolution of extensional sedimentary basins we perform viscoplastic thermo-mechanical numerical experiments. We achieve a high resolution by limiting ourselves to the crustal domain and choose our model set-up to agree with findings of large scale model studies. Normal faults bounding the extensional basins are not incorporated a priori, but form as shear zones in response to the dynamic evo- lution of the model. Our results illustrate the important role of both strain softening and sedimentation in localising deformation during crustal extension and promoting the development of asymmetric basins.

  13. The complementary role of SMOS sea surface salinity observations for estimating global ocean salinity state

    NASA Astrophysics Data System (ADS)

    Lu, Zeting; Cheng, Lijing; Zhu, Jiang; Lin, Renping

    2016-06-01

    Salinity is a key ocean state property, changes in which reveal the variation of the water cycle and the ocean thermohaline circulation. However, prior to this century, in situ salinity observations were extremely sparse, which decreased the reliability of simulations of ocean general circulation by ocean and climate models. In 2009, sea surface salinity (SSS) observations covered the global ocean via the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission, and several versions of global SSS products were subsequently released. How can these data benefit model performance? Previous studies found contradictory results. In this work, we assimilated SMOS-SSS data into the LASG/IAP Climate system Ocean Model (LICOM) using the Ensemble Optimum Interpolation (EnOI) assimilation scheme. To assess and quantify the contribution of SMOS-SSS data to model performance, several tests were conducted. The results indicate that the CECOS/CATDS 2010.V02 SMOS-SSS product can significantly improve model simulations of sea surface/subsurface salinity fields. This study provides the basis for the future assimilation of SMOS-SSS data for short-range climate forecasting.

  14. Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry

    NASA Astrophysics Data System (ADS)

    Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; Del Río, J. Antonio; Tagüeña-Martínez, Julia

    2016-04-01

    Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications.

  15. Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry

    PubMed Central

    Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; del Río, J. Antonio; Tagüeña-Martínez, Julia

    2016-01-01

    Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications. PMID:27097767

  16. Space Weathering Effects in Lunar Soils: The Roles of Surface Exposure Time and Bulk Chemical Composition

    NASA Technical Reports Server (NTRS)

    Zhang, Shouliang; Keller, Lindsay P.

    2011-01-01

    Space weathering effects on lunar soil grains result from both radiation-damaged and deposited layers on grain surfaces. Typically, solar wind irradiation forms an amorphous layer on regolith silicate grains, and induces the formation of surficial metallic Fe in Fe-bearing minerals [1,2]. Impacts into the lunar regolith generate high temperature melts and vapor. The vapor component is largely deposited on the surfaces of lunar soil grains [3] as is a fraction of the melt [4, this work]. Both the vapor-deposits and the deposited melt typically contain nanophase Fe metal particles (npFe0) as abundant inclusions. The development of these rims and the abundance of the npFe0 in lunar regolith, and thus the optical properties, vary with the soil mineralogy and the length of time the soil grains have been exposed to space weathering effects [5]. In this study, we used the density of solar flare particle tracks in soil grains to estimate exposure times for individual grains and then perform nanometer-scale characterization of the rims using transmission electron microscopy (TEM). The work involved study of lunar soil samples with different mineralogy (mare vs. highland) and different exposure times (mature vs. immature).

  17. The role of SO42- surface distribution in arsenic removal by iron oxy-hydroxides

    NASA Astrophysics Data System (ADS)

    Tresintsi, S.; Simeonidis, K.; Pliatsikas, N.; Vourlias, G.; Patsalas, P.; Mitrakas, M.

    2014-05-01

    This study investigates the contribution of chemisorbed SO42- in improving arsenic removal properties of iron oxy-hydroxides through an ion-exchange mechanism. An analytical methodology was developed for the accurate quantification of sulfate ion (SO42-) distribution onto the surface and structural compartments of iron oxy-hydroxides synthesized by FeSO4 precipitation. The procedure is based on the sequential determination of SO42- presence in the diffuse and Stern layers, and the structure of these materials as defined by the sulfate-rich environments during the reaction and the variation in acidity (pH 3-12). Physically sorbed SO42-, extracted in distilled water, and physically/chemically adsorbed ions on the oxy-hydroxide's surface leached by a 5 mM NaOH solution, were determined using ion chromatography. Total sulfate content was gravimetrically measured by precipitation as BaSO4. To validate the suggested method, results were verified by X-ray photoelectron and Fourier-transformed infrared spectroscopy. Results showed that low precipitation pH-values favor the incorporation of sulfate ions into the structure and the inner double layer, while under alkaline conditions ions shift to the diffuse layer.

  18. Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry.

    PubMed

    Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; Del Río, J Antonio; Tagüeña-Martínez, Julia

    2016-01-01

    Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications. PMID:27097767

  19. Role of surface charge in cytotoxicity of charged manganese ferrite nanoparticles towards macrophages

    NASA Astrophysics Data System (ADS)

    Yang, Seung-Hyun; Heo, Dan; Park, Jinsung; Na, Sungsoo; Suh, Jin-Suck; Haam, Seungjoo; Park, Sahng Wook; Huh, Yong-Min; Yang, Jaemoon

    2012-12-01

    Amphiphilic surfactants have been used to disperse magnetic nanoparticles in biological media, because they exhibit a dual hydrophobic/hydrophilic affinity that facilitates the formation of a nanoemulsion, within which nanoparticle surfaces can be modified to achieve different physicochemical properties. For the investigation of the interactions of cells with charged magnetic nanoparticles in a biological medium, we selected the nanoemulsion method to prepare water-soluble magnetic nanoparticles using amphiphilic surfactant (polysorbate 80). The hydroxyl groups of polysorbate 80 were modified to carboxyl or amine groups. The chemical structures of carboxylated and aminated polysorbate 80 were confirmed, and water-soluble manganese ferrite nanoparticles (MFNPs) were synthesized with three types of polysorbate 80. Colloidal size, morphology, monodispersity, solubility and T2 relaxivity were found to be similar between the three types of MFNP. However, cationic MFNPs exhibited greater cytotoxicity in macrophages (RAW264.7 cells) and lower cellular membrane effective stiffness than anionic and non-ionic MFNPs. Moreover, cationic MFNPs exhibited large uptake efficiency for RAW264.7 cells compared with anionic or non-ionic MFNPs under the same conditions. Therefore, we propose that surface charge should be a key consideration factor in the design of magnetic nanoparticles for theragnostic applications.

  20. Role of the surface effect on the structural, electronic and mechanical properties of the carbide MXenes

    NASA Astrophysics Data System (ADS)

    Zha, Xian-Hu; Luo, Kan; Li, Qiuwu; Huang, Qing; He, Jian; Wen, Xiaodong; Du, Shiyu

    2015-07-01

    The two-dimensional material MXene has recently attracted interest for its excellent performance in diverse perspectives. Etched from the parental MAX phase with hydrofluoric acid, the synthesized MXene surface is normally functionalized by oxygen (-O), fluorine (-F) or hydroxyl (-OH) groups. Herein, using first-principles density functional calculations, we investigate the structural, mechanical and electronic properties of the carbide MXene M2CT2 (M=Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W; T=-O, -F, -OH). Both the M atom and the surface group T have a significant effect on the MXenes properties. Generally, oxygen functionalized MXenes present smaller lattice parameters and stronger mechanical strength compared to those functionalized by fluorine and hydroxyl groups. \\text{Sc}2\\text{CO}2 exhibits the smallest interlayer thickness and \\text{W}2\\text{CO}2 shows the strongest mechanical strength. In regard to electronic properties, five oxygen functionalized members M2CO2 (M=Sc, Ti, Zr, Hf, W), two fluorine functionalized members M2CF2 (M=Sc, Mo), and hydroxyl functionalized Sc2C(OH)2 present semiconducting characteristics, but only Sc2C(OH)2 exhibits a direct band gap.

  1. Factors Affecting P Loads to Surface Waters: Comparing the Roles of Precipitation and Land Management Practices

    NASA Astrophysics Data System (ADS)

    Motew, M.; Booth, E.; Carpenter, S. R.; Kucharik, C. J.

    2014-12-01

    Surface water quality is a major concern in the Yahara watershed (YW) of southern Wisconsin, home to a thriving dairy industry, the city of Madison, and five highly valued lakes that are eutrophic. Despite management interventions to mitigate runoff, there has been no significant trend in P loading to the lakes since 1975. Increases in manure production and heavy rainfall events over this time period may have offset any effects of management. We developed a comprehensive, integrated modeling framework that can simulate the effects of multiple drivers on ecosystem services, including surface water quality. The framework includes process-based representation of terrestrial ecosystems (Agro-IBIS) and groundwater flow (MODFLOW), hydrologic routing of water and nutrients across the landscape (THMB), and assessment of lake water quality (YWQM). Biogeochemical cycling and hydrologic transport of P have been added to the framework to enable detailed simulation of P dynamics within the watershed, including interactions with climate and management. The P module features in-soil cycling of organic, inorganic, and labile forms of P; manure application, decomposition, and subsequent loss of dissolved P in runoff; loss of particulate-bound P with erosion; and transport of dissolved and particulate P within waterways. Model results will compare the effects of increased heavy rainfall events, increased manure production, and implementation of best management practices on P loads to the Yahara lakes.

  2. The Role of Gas-Silicate Chemisorption Reactions in Modifying Planetary Crusts and Surfaces

    NASA Astrophysics Data System (ADS)

    King, P. L.; Henley, R. W.; Wykes, J. L.; Renggli, C.; Troitzsch, U.; Clark, D.; O'Neill, H. S.

    2014-12-01

    Evidence for gas-solid reactions is found throughout the solar system: for example, sulfidation reactions in some meteorites and secondary phases coating lunar pyroclastic glasses. On Earth, the products of gas-solid reactions are documented in volcanic systems, metalliferous mineral deposits, impact craters, and on dust or meteorites after passage through the atmosphere - such reactions are also likely on the surfaces of Mars and Venus. To understand the chemical dynamics of such gas-solid reactions, we are undertaking systematic experiments and thermochemical modelling. Experiments were conducted in a vertical gas-mixing furnace at 600 - 800 °C and 1 bar, using SO2and a range of Ca-bearing materials: labradorite, feldspar glass and anorthosite (rock). In each case, anhydrite formed rapidly. In shorter experiments with labradorite, isolated anhydrite is observed surrounded by 'moats' of Ca-depleted silicate. In longer experiments, anhydrite is found as clusters of crystals that, in some cases, extend from the substrate forming precarious 'towers' (Figure). Anhydrite fills cracks in porous samples. We propose that the nucleation and rapid growth of anhydrite on the surface of these Ca-rich phases occurs by chemisorption of SO2(g) molecules with slightly negatively charged oxygen onto available near-surface calcium with slight positive charge. Anhydrite growth is sustained by SO2(g) chemisorption and Ca migration through the reacting silicate lattice, accelerated by increased bond lengths at high temperature. Significantly, the chemisorption reaction indicates that SO2 disproportionates to form both oxidized sulfur (as anhydrite) and a reduced sulfur species (e.g., an S* radical ion). On Earth, in the presence of H2O, the predominant reduced sulfur species is H2S, through an overall reaction: 3CaAl2Si2O8 + 4 SO2(g)+ H2O(g) → 3CaSO4 + 3Al2SiO5 + 3SiO2 + H2S(g)The reduced sulfur may react with gas phase Fe, Ni, Zn and Cu cluster compounds to form metal sulfides

  3. Role of satellite-derived surface soil moisture retrievals for determining eco-hydrological feedback (Invited)

    NASA Astrophysics Data System (ADS)

    Crow, W. T.; Qiu, J.; Bolten, J. D.

    2013-12-01

    Satellite-derived surface soil moisture products are entering a new era in terms of their availability, time/space coverage and retrieval accuracy. However, the value of these products for diagnosing (and/or quantifying) land-atmosphere-vegetation feedbacks involving soil moisture is still largely undermined. Arguably the most direct of these feedbacks in the coupling between vegetation health/biomass and soil moisture availability within water-limited ecosystems. In data poor areas of the world, remotely-sensed surface soil moisture retrievals can potentially contribute to the study of soil moisture vegetation feedback by filtering errors in model-based predictions of root-zone derived from forcing a soil water balance with uncertain precipitation forcing. In this presentation, we will evaluate this potential by examining the cross-correlation between remotely-sensed vegetation index anomalies and root-zone soil moisture anomalies derived from a global soil water balance model both before and after the assimilation of a satellite-based surface soil moisture retrieval product. An increase in soil moisture/vegetation anomaly cross-correlation can be interpreted as evidence that the assimilation step is enhancing our ability to characterize root-zone soil moisture and the subsequent feedback of root-zone soil moisture anomalies of vegetation health and productivity. Using a retrospective soil moisture product derived from the Advanced Microwave Scanning Radiometer-EOS sensor between July 2002 and October 2011, results clearly demonstrate the value satellite-derived soil moisture for characterizing the coupling between (current) soil moisture and (near-future) vegetation anomalies. A key aspect of this result is overcoming the difference between the vertical support of satellite-derived soil moisture retrievals (typically assumed to be on the order of 1-5 cm) and the vertical root-zone depth of vegetation (typically assumed to be at least 40 cm). Specific strategies

  4. [Roles of additives and surface control in slurry atomization]. Quarterly report

    SciTech Connect

    Tsai, S.C.

    1992-06-01

    As reported in the quarterly report of March of 1992, the relative viscosity of a Newtonian Coal Water Slurry (CWS) in the presence of an anionic polymeric dispersant is an order of magnitude higher than the prediction of the well established Krieger-Dougherty Equation which describes the relative viscosity of a non-aggregated Newtonian suspension as a function of particle volume fraction. Note that the anionic dispersant is used in such a quantity that the resulting interparticle electrostatic repulsion counter-balances the interparticle van der Waals attraction. Investigation continues to determine the mechanisms of such excess energy dissipation under shear. New experimental results are presented in this report to verify the role of the anionic polymeric dispersant in such excess energy dissipation of CWS.

  5. Integrin subunit beta3 plays a crucial role in the movement of osteoclasts from the periosteum to the bone surface.

    PubMed

    Holt, I; Marshall, M J

    1998-04-01

    We have shown that, when mouse parietal bones were incubated in culture medium containing indomethacin, the number of tartrate-resistant acid phosphatase-positive osteoclasts (TRAP + OCs) on the bone surface was drastically reduced (down-regulation), and the number on the periosteal membrane adjacent to the resorbing surface was increased. Subsequent incubation of bones with prostaglandin E2 (PGE2) rapidly reversed these changes (up-regulation). In the work reported here, the osteoclast-associated integrin subunit beta3 was stained by immunohistochemistry. The beta3-positive osteoclast (beta3 + OC) population on freshly isolated bone was comprised of about 67% TRAP + OCs and 33% TRAP OCs. Like TRAP + OCs, beta3 + OCs were reduced in number on the surface of bones incubated with indomethacin, but, in contrast to the TRAP + OCs, beta3 + OCs were not seen on the periosteal membrane. Following up-regulation of TRAP + OCs with PGE2, large numbers of beta3 + OCs appeared on the bone surface and, again, were not seen on the periosteal membrane. Echistatin, a peptide that binds to the alphavbeta3 integrin on osteoclasts, was found to inhibit the up-regulation of TRAP + OCs in a dose-dependent manner but had no effect on the down-regulation of TRAP + OCs. Similarly, echistatin inhibited the upregulation of beta3 + OCs on the bone surface, and, under these conditions, beta3 + OCs were observed on the periosteal membrane. The addition of anti-beta3 antibody also inhibited the up-regulation of TRAP + OCs in response to PGE2. The association of beta3 protein expression with the up-regulated osteoclast and the inhibition of up-regulation by echistatin and by anti-beta3 antibody provide strong evidence that beta3 plays an essential role in the movement of osteoclasts from the membrane to the bone. PMID:9491775

  6. High second-order nonlinear response of platinum nanoflowers: the role of surface corrugation.

    PubMed

    Ngo, Hoang Minh; Lai, Ngoc Diep; Ledoux-Rak, Isabelle

    2016-02-14

    Platinum nanoflowers (PtNFs) were elaborated using the seed-mediated growth technique applied to monodisperse platinum nanoparticles (∼3.0 nm) synthesized by the chemical reduction method. The X-ray diffraction pattern confirmed the formation of face-centered-cubic platinum nanocrystals. We report the Harmonic Light Scattering (HLS) properties of PtNFs for six different diameters (∼7.0; 8.0; 10.0; 14.0; 20.0 and 31.0 nm). From these HLS data we infer, for the first time, large hyperpolarizability β values of PtNFs. These very high β values of PtNFs are assigned mainly to highly corrugated surfaces for nanoparticles with irregular shapes. PMID:26795722

  7. Effect of surface roughness on runoff and erosion in a mediterranean ecosystem: the role of fire

    NASA Astrophysics Data System (ADS)

    Lavee, H.; Kutiel, P.; Segev, M.; Benyamini, Y.

    1995-02-01

    Mechanisms at the micro (patch) scale influencing runoff and erosion processes following a forest fire were investigated. The study was conducted in a Mediterranean mountainous region with a mean annual rainfall of 690 mm, Terra Rossa soil, and vegetation composed of a dense shrubland of Pinus halepensis and Quercus calliprinos. Simulated rainfall experiments were carried out on plots representing different intervals of time elapsed since a fire; i.e., immediately after fire, two weeks after fire, one year after fire. Unburned plots were also used for comparison. At a local scale, great variability was found whereby some patches produced high runoff and sediment yields following fire, while others did not. The conclusion is that the main effect of fires of low to moderate intensity is to produce a mosaic-like surface containing both rough patches in which there is almost no chance for runoff generation, and relatively smooth patches in which fire can subsequently lead to higher runoff and erosion rates.

  8. The Role of the Exploration Science Officer in Lunar Surface Operations

    NASA Technical Reports Server (NTRS)

    Osborn, John H.

    2009-01-01

    A review has been performed of exploration science and payload operations during the Apollo and Space Shuttle programs to extract information of potential usefulness to the Constellation program. That work has resulted in creation of the concept for a unique type of flight controller: the exploration science officer. The controller s primary responsibility is to integrate the tasks and goals of the spacecraft flight control team and the science team in order to maximize science return while maximizing crew safety. Far from being just a mouthpiece for either team, this individual must be fluent in the knowledge and language of two communities: spacecraft operations and planetary science. Responsibilities begin during the requirements phase of vehicle and lunar surface systems development and continue through development, training, planning, mission execution, and post-flight mission phases.

  9. The role of GMES / Sentinels in Land-Surface Earth System Science

    NASA Astrophysics Data System (ADS)

    Moreno, J.

    2009-04-01

    A general trend in the current status of representation of Land Surface schemes into Earth System models is driven by the parameterisation of "cycles" instead of individual processes. Particular emphasis is made to account for couplings among the individual cycles, as between the carbon and water cycles. Moreover, the current tendency is to use the measured data -time series in most cases- together with models, in a data assimilation scenario where inputs from multiple sources are integrated. Such approach is more and more necessary as land models tend to be more complex, and particularly due to the fact that land surface variability is not just driven by physical and chemical processes, but intricate biological processes also altered by anthropogenic influences. Human influences in the land system (land use changes, urban development, etc.) and the impacts of natural disasters are becoming also part of land models, but critical data in high spatial and temporal resolutions are needed to properly model such processes. Until now, problems with data availability, data inconsistency and lack of adequate temporal sampling have limited the potential usefulness of such observations in modelling land surface processes. The availability of the GMES / Sentinel series of satellites represents a quite unique opportunity for consolidation of current tendencies and development of new science based on the new type of data that soon will become available. The usefulness of the different Sentinel missions for Land science has been recognised. Although the Sentinel satellite series were primarily designed to provide observations for operational services and routine applications, there is a growing interest in the scientific community towards the usage of Sentinel data for more advanced and innovative science. Moreover, the availability of consistent time series covering a period of over 20 years opens possibilities never explored before, such as systematic data assimilation

  10. Role of Polymer Segment-Particle Surface Interactions in Controlling Nanoparticle Dispersions in Concentrated Polymer Solutions

    SciTech Connect

    Kim, So Youn; Zukoski, Charles F.

    2014-09-24

    The microstructure of particles suspended in concentrated polymer solutions is examined with small-angle X-ray scattering and small-angle neutron scattering. Of interest are changes to long wavelength particle density fluctuations in ternary mixtures of silica nanoparticles suspended in concentrated solutions of poly(ethylene glycol). The results are understood in terms of application of the pseudo-two-component polymer reference interaction site model (PRISM) theory modified to account for solvent addition via effective contact strength of interfacial attraction, εpc, in an implicit manner. The combined experimental-theoretical study emphasizes the complex interactions between solvent, polymer, and particle surface that control particle miscibility but also demonstrate that these factors can all be understood in terms of variations of εpc.

  11. Polar sediment accumulation: Role of surface winds at the two poles

    NASA Technical Reports Server (NTRS)

    Thomas, P. C.; Gierasch, P. J.

    1993-01-01

    The accumulation of the large deposits of volatile and nonvolatile sediments at both Martian poles has occurred through periods of likely climate change. Most data on wind directions near the Martian poles and seasonal activity relate to a very short period of time, at one point in climate cycles. It is still uncertain what the net budgets to the poles are and how this budget (if known) would fit into longer climate/sediment cycles. Pending further data we examined the full suite of Viking high-resolution, high-latitude images for wind markers of all sizes and types. These probably represent timescales of formation from days to several tens of thousands of years. The goal is to estimate the effectiveness, and possible drivers, of wind systems that bring materials near the surface to the regions of polar sediments and that also remove materials from the polar areas.

  12. Nanoparticle technology for treatment of Parkinson's disease: the role of surface phenomena in reaching the brain.

    PubMed

    Leyva-Gómez, Gerardo; Cortés, Hernán; Magaña, Jonathan J; Leyva-García, Norberto; Quintanar-Guerrero, David; Florán, Benjamín

    2015-07-01

    The absence of a definitive treatment for Parkinson's disease has driven the emerging investigation in the search for novel therapeutic alternatives. At present, the formulation of different drugs on nanoparticles has represented several advantages over conventional treatments. This type of multifunctional carrier, owing to its size and composition, has different interactions in biological systems that can lead to a decrease in ability to cross the blood-brain barrier. Therefore, this review focuses on the latest advances in obtaining nanoparticles for Parkinson's disease and provides an overview of technical aspects in the design of brain drug delivery of nanoparticles and an analysis of surface phenomena, a key aspect in the development of functional nanoparticles for Parkinson's disease. PMID:25701281

  13. Flavonoid-membrane Interactions: A Protective Role of Flavonoids at the Membrane Surface?

    PubMed Central

    Oteiza, Patricia I.; Erlejman, Alejandra G.; Verstraeten, Sandra V.; Keen, Carl L.; Fraga, César G.

    2005-01-01

    Flavonoids can exert beneficial health effects through multiple mechanisms. In this paper, we address the important, although not fully understood, capacity of flavonoids to interact with cell membranes. The interactions of polyphenols with bilayers include: (a) the partition of the more non-polar compounds in the hydrophobic interior of the membrane, and (b) the formation of hydrogen bonds between the polar head groups of lipids and the more hydrophilic flavonoids at the membrane interface. The consequences of these interactions are discussed. The induction of changes in membrane physical properties can affect the rates of membrane lipid and protein oxidation. The partition of certain flavonoids in the hydrophobic core can result in a chain breaking antioxidant activity. We suggest that interactions of polyphenols at the surface of bilayers through hydrogen bonding, can act to reduce the access of deleterious molecules (i.e. oxidants), thus protecting the structure and function of membranes. PMID:15712595

  14. Role of Surface Water-Groundwater Interaction in Regulating Stream Water Chemistry in Urban Streams

    NASA Astrophysics Data System (ADS)

    Ledford, S. H.; Lautz, L. K.; Holdsworth, M.

    2012-12-01

    Urbanization is a major cause of stream degradation in the United States. Surface water -groundwater interaction may naturally mitigate impaired water quality associated with urbanization. Meadowbrook Creek, in Syracuse, New York, flows along a declining urbanization gradient, from headwaters that are highly channelized with armored banks to an outlet that is unconstrained and meanders through a broad, riparian floodplain. Biweekly, longitudinal stream samples were collected every 100 - 600 m in the summer and every 500 - 1000 m in the winter and analyzed for conductivity and major ions. A five well transect in the downstream floodplain was also sampled. A constant rate tracer test was used to quantify groundwater inflow longitudinally during summer baseflow. Specific conductivity decreased along the urban, channelized reach and then increased along the meandering, unconstrained section during the summer, while the opposite occurred during the winter. Nitrate concentrations along the channelized reach were low to below detection (<0.09 - 1.48 mg/L NO3-) in summer; however, nitrate concentrations were consistently higher along the unconstrained reach, ranging from 2.96 - 4.03 mg/L NO3-. The entire stream length had uniformly low nitrate concentrations during winter (0.12-0.57 mg/L NO3-). Sodium and chloride concentrations varied greatly between seasons, with stream concentrations similar to groundwater in the summer (93.28 - 176.45 mg/L Na+ in surface water, 94.81 - 227.05 mg/L Na+ in groundwater; 181.97 - 304.71 mg/L Cl- in surface water, 150.72 - 330.60 mg/L Cl- in groundwater) and an order of magnitude higher in winter, during snowmelt events (450 - 1956 mg/L Na+ and 805.12 - 4517.88 mg/L Cl- in stream water). In winter, sodium and chloride concentrations declined by a maximum of 1189 and 3176.21 mg/L respectively with distance in the unconstrained reach, whereas in summer they increased by 10.01 and 16.12 mg/L respectively with distance. The unconstrained

  15. The role of nanotechnology in control of human diseases: perspectives in ocular surface diseases.

    PubMed

    Rai, Mahendra; Ingle, Avinash P; Gaikwad, Swapnil; Padovani, Felipe Hering; Alves, Monica

    2016-10-01

    Nanotechnology is the creation and use of materials and devices on the same scale as molecules and intracellular structures, typically less than 100 nm in size. It is an emerging science and has made its way into pharmaceuticals to significantly improve the delivery and efficacy of drugs in a number of therapeutic areas, due to development of various nanoparticle-based products. In recent years, there has been increasing evidence that nanotechnology can help to overcome many of the ocular diseases and hence researchers are keenly interested in this science. Nanomedicines offer promise as viable alternatives to conventional drops, gels or ointments to improve drug delivery to the eye. Because of their small size, they are well tolerated, thus preventing washout, increase bioavailability and also help in specific drug delivery. This review describes the application of nanotechnology in the control of human diseases with special emphasis on various eye and ocular surfaces diseases. PMID:26189355

  16. The role of diffusive architectural surfaces on auditory spatial discrimination in performance venues.

    PubMed

    Robinson, Philip W; Pätynen, Jukka; Lokki, Tapio; Jang, Hyung Suk; Jeon, Jin Yong; Xiang, Ning

    2013-06-01

    In musical or theatrical performance, some venues allow listeners to individually localize and segregate individual performers, while others produce a well blended ensemble sound. The room acoustic conditions that make this possible, and the psycho-acoustic effects at work are not fully understood. This research utilizes auralizations from measured and simulated performance venues to investigate spatial discrimination of multiple acoustic sources in rooms. Signals were generated from measurements taken in a small theater, and listeners in the audience area were asked to distinguish pairs of speech sources on stage with various spatial separations. This experiment was repeated with the proscenium splay walls treated to be flat, diffusive, or absorptive. Similar experiments were conducted in a simulated hall, utilizing 11 early reflections with various characteristics, and measured late reverberation. The experiments reveal that discriminating the lateral arrangement of two sources is possible at narrower separation angles when reflections come from flat or absorptive rather than diffusive surfaces. PMID:23742348

  17. Role of calcium in growth inhibition induced by a novel cell surface sialoglycopeptide

    NASA Technical Reports Server (NTRS)

    Betz, N. A.; Westhoff, B. A.; Johnson, T. C.; Spooner, B. S. (Principal Investigator)

    1995-01-01

    Our laboratory has purified an 18 kDa cell surface sialoglycopeptide growth inhibitor (CeReS-18) from intact bovine cerebral cortex cells. Evidence presented here demonstrates that sensitivity to CeReS-18-induced growth inhibition in BALB-c 3T3 cells is influenced by calcium, such that a decrease in the calcium concentration in the growth medium results in an increase in sensitivity to CeReS-18. Calcium did not alter CeReS-18 binding to its cell surface receptor and CeReS-18 does not bind calcium directly. Addition of calcium, but not magnesium, to CeReS-18-inhibited 3T3 cells results in reentry into the cell cycle. A greater than 3-hour exposure to increased calcium is required for escape from CeReS-18-induced growth inhibition. The calcium ionophore ionomycin could partially mimic the effect of increasing extracellular calcium, but thapsigargin was ineffective in inducing escape from growth inhibition. Increasing extracellular calcium 10-fold resulted in an approximately 7-fold increase in total cell-associated 45Ca+2, while free intracellular calcium only increased approximately 30%. However, addition of CeReS-18 did not affect total cell-associated calcium or the increase in total cell-associated calcium observed with an increase in extracellular calcium. Serum addition induced mobilization of intracellular calcium and influx across the plasma membrane in 3T3 cells, and pretreatment of 3T3 cells with CeReS-18 appeared to inhibit these calcium mobilization events. These results suggest that a calcium-sensitive step exists in the recovery from CeReS-18-induced growth inhibition. CeReS-18 may inhibit cell proliferation through a novel mechanism involving altering the intracellular calcium mobilization/regulation necessary for cell cycle progression.

  18. The Role of Mass Transfer between Martian satellites on Surface Geology

    NASA Astrophysics Data System (ADS)

    Nayak, M.; Nimmo, F.; Udrea, B.

    2015-12-01

    It has recently been recognized that impact ejecta can lead not only to prompt secondary craters, but projectiles that reimpact the target body or nearby companions after an extended period, producing so-called sesquinary craters [1]. Here we examine sesquinary cratering on the moons of Mars (cf. [2] for Phobos). We model the impact that formed Voltaire, the largest crater on Deimos, and explore the orbital evolution of resulting ejecta across 500 years using four-body physics and particle following. The bulk of mass transfer to Phobos occurs in the first 100 years after impact, while reaccretions of ejecta to Deimos continue out to the 104 year timescale as predicted by [3]. In the velocity range capable of reaching Phobos, 25-42% of ejecta mass reaccretes to Deimos and 12-21% impacts Phobos. Mass flux to Mars is <10%. The time-averaged flux of Deimos material to Phobos can be as high as 11% of the background direct-to-Phobos impactor flux, a relatively minor contribution. However the ejecta mass reaccreted to Deimos from a Voltaire-sized impact is comparable to the expected direct-to-Deimos mass accumulated between Voltaire-size events. We find that the characteristic impact velocity of sesquinaries is an order of magnitude smaller than those of background (heliocentric) hypervelocity impactors and will likely result in different crater morphologies. A Voltaire-sized impact could feasibly resurface large parts of the moon, erasing the previous geological record. Dating the surface of Deimos may be more challenging than previously suspected. Deimos craters have been characterized as containing large amounts of fill due to sediment deposition [4]; our results suggest this fill to be sesquinary, as opposed to suborbital, in nature, which may also have implications for the smoothness of the Deimos surface. [1] Zahnle et al., 2008, Icarus. [2] Chappaz et al., 2011, AAS. [3] Soter, 1971, Cornell. [4] Thomas and Veverka, 1980, Icarus.

  19. Role of water vapor desublimation in the adhesion of an iced droplet to a superhydrophobic surface.

    PubMed

    Boinovich, Ludmila; Emelyanenko, Alexandre M

    2014-10-28

    The study of the adhesion of solid and liquid aqueous phases to superhydrophobic surfaces has become an attractive topic for researchers in various fields as a vital step in the design of icephobic coatings. The analysis of the available results shows that the experimentally measured values of adhesion strength for superhydrophobic substrates, which in some cases are quite small, are still essentially higher than might be expected from the portion of the actual wetted area. In this study we have considered the peculiarities of the three-phase contact zone between sessile supercooled water or ice droplets and a superhydrophobic coating at negative temperatures (below 0 °C) and during the water-ice phase transition. Two types of superhydrophobic coatings with very different textures were used to analyze the evolution of shape parameters of a sessile water droplet during droplet cooling and freezing. It was shown that the evolution of the contact angle and droplet contact diameter of a water droplet deposited on a superhydrophobic surface does not undergo essential changes when the droplet is cooled simultaneously with the substrate and the surrounding environment, and the humidity is maintained close to 100% during the cooling process. However, the phase transition from supercooled water to ice droplets leads to the growth of a metastable iced meniscus and a frost halo in the vicinity of the three-phase contact zone. The meniscus effectively increases the area of adhesive contact between the droplet and the substrate. This phenomenon is intrinsically related to the release of the heat of crystallization and is responsible for the enhancement of adhesion to a superhydrophobic substrate upon droplet transition from supercooled water to ice. At the same time, it was shown that the metastable state of the above meniscus leads to its spontaneous sublimation during exposure at negative temperatures. PMID:25286023

  20. On the role of long range interactions for the adsorption of sexithiophene on Ag(110) surface

    SciTech Connect

    Matos, Jeronimo; Rojas, Tomas; Yildirim, Handan E-mail: Abdelkader.Kara@ucf.edu; Kara, Abdelkader E-mail: Abdelkader.Kara@ucf.edu

    2014-04-14

    The adsorption characteristics of the sexithiophene (6T) molecule on Ag(110) are studied using density functional theory with the inclusion of van der Waals (vdW) interactions. The stable adsorption configurations on 6T on Ag(110) as well as the nature of bonding the Ag substrate are evaluated. We also assess the performance of the vdW-DF method in describing the adsorption, energetics, heights, as well as the interface characteristics with the Ag(110) surface. We find two lowest adsorption energy configurations, at which the 6T molecule aligns with its molecular long axis parallel and perpendicular to the [001] direction, to be energetically close to each other, suggesting that they may coexist. Our findings indicate a significant increase in the 6T adsorption energies upon the inclusion of vdW interactions with the highest increase obtained using the opt-type functionals, in particular with the optB86b-vdW functional. The revPBE-vdW and rPW86-vdW2 functionals lead to less enhancement in adsorption energies that is attributed to the strong repulsive nature of these functionals, in agreement with earlier predictions. Upon adsorption of the 6T molecule, the changes in the atomic and electronic structures of the 6T molecule and Ag surface are found to be negligible; there is no charge transfer, and no interface state is observed. The work function is reduced upon adsorption with the largest change is ∼0.6 eV obtained using the optB88-vdW functional. The results are in good agreement with the available experimental observations of the adsorption configurations and the work function changes. Based on our results, we conclude that the nature of bonding for 6T on Ag(110) can be classified as strong physisorption.

  1. Role of Surface Interactions in the Synergizing Polymer/Clay Flame Retardant Properties

    SciTech Connect

    Pack, S.; Kashiwagi, T; Cao, C; Korach, C; Lewin, M; Rafailovich, M

    2010-01-01

    The absorption of resorcinol di(phenyl phosphate) (RDP) oligomers on clay surfaces has been studied in detail and is being proposed as an alternative method for producing functionalized clays for nanocomposite polymers. The ability of these clays to be exfoliated or intercalated in different homopolymers was investigated using both transmission electron microscopy and small-angle X-ray scattering results, compared with contact angle measurements on Langmuir-Blodgett clay monolayers, where the interfacial energies were used as predictors of the polymer/clay interactions. We found that the contact angle between PS/RDP clay monolayer substrates was {approx}2.5{sup o}, whereas the angle for polystyrene (PS)/Cloisite 20A clays substrates was {approx}32{sup o}, consistent with the large degree of exfoliation observed in PS for the RDP-coated clays. The interfacial activity of these clays was also measured, and we found that the RDP-coated clays segregated to the interfaces of PC/poly(styrene-co-acrylonitrile) blends, while they segregated into the poly(methyl methacrylate) (PMMA) domain of PS/PMMA blends. This morphology was explained in terms of the relative energy advantage in placing the RDP versus the Cloisite clays at the interfaces. Finally, we demonstrated the effects of the relative surface energies of the clays in segregating to the blend air interface when heated to high temperatures. The segregation was shown to affect the composition and mechanical properties of the resulting chars, which in turn could determine their flame retardant response.

  2. CHEMICAL MODELING OF INFRARED DARK CLOUDS: THE ROLE OF SURFACE CHEMISTRY

    SciTech Connect

    Vasyunina, T.; Vasyunin, A. I.; Herbst, Eric; Linz, H.

    2012-06-01

    We simulate the chemistry of infrared dark clouds (IRDCs) with a model in which the physical conditions are homogeneous and time independent. The chemistry is solved as a function of time with three networks: one purely gas phase, one that includes accretion and desorption, and one, the complete gas-grain network, that includes surface chemistry in addition. We compare our results with observed molecular abundances for two representative IRDCs-IRDC013.90-1 and IRDC321.73-1-using the molecular species N{sub 2}H{sup +}, HC{sub 3}N, HNC, HCO{sup +}, HCN, C{sub 2}H, NH{sub 3}, and CS. IRDC013.90-1 is a cold IRDC, with a temperature below 20 K, while IRDC321.73-1 is somewhat warmer, in the range 20-30 K. We find that the complete gas-grain model fits the data very well, but that the goodness of fit is not sharply peaked at a particular temperature. Surface processes are important for the explanation of the high gas-phase abundance of N{sub 2}H{sup +} in IRDC321.73-1. The general success of the zero-dimensional model in reproducing single-dish observations of our limited sample of eight species shows that it is probably sufficient for an explanation of this type of data. To build and justify more complicated models, including spatial temperature and density structure, contraction, and heating, we require high-resolution interferometric data.

  3. The role of direct photolysis and indirect photochemistry in the environmental fate of ethylhexyl methoxy cinnamate (EHMC) in surface waters.

    PubMed

    Vione, D; Calza, P; Galli, F; Fabbri, D; Santoro, V; Medana, C

    2015-12-15

    The aquatic environmental fate of ethylhexyl methoxy cinnamate (EHMC), one of the most used UVB filters worldwide, was studied by assessing its environmental persistence and photoinduced transformations. The role of direct and indirect photolysis was evaluated. Direct photolysis was shown to play a key role, and this process is expected to be the main attenuation route of EHMC in sunlit surface waters. In contrast, the reaction with OH radicals would be negligible and that with (3)CDOM* would at most be a secondary process. The measurement of the quantum yield of direct photolysis and of the rate constants of reaction with photogenerated transient species (or, sometimes, the use of reasonable values for the latter) allowed the prediction of the EHMC half-life time in surface waters, by means of a validated photochemical model. The predicted EHMC lifetime is of the order of hours to a few days in fair-weather summertime, and the main factors controlling the EHMC phototransformation in sunlit surface waters would be the water depth and the dissolved organic carbon (DOC) content. The formation of transformation products (TPs) was followed as well via HPLC/HRMS. Three TPs were detected in the samples exposed to UVA radiation, while one additional TP was detected in the samples exposed to UVB radiation. The detected TPs comprised 4-methoxybenzaldehyde, a hydroxylated derivative and dimeric species. Through the use of heterogeneous photocatalysis with TiO2, seven additional TPs were identified, most of them resulting from the further degradation of primary TPs formed through direct photolysis and that might be detected in aquatic systems as well. The photodegradation of EHMC in the presence of TiO2 yielded more toxic TPs than the parent compound (as determined with the Vibrio fischeri Microtox assay). The increased toxicity is partially accounted for by the formation of 4-methoxybenzaldehyde. PMID:26282740

  4. Activation of cord T lymphocytes. IV. Analysis of surface expression and functional role of 1F7 (CD26) molecule.

    PubMed

    Gerli, R; Agea, E; Muscat, C; Ercolani, R; Bistoni, O; Tognellini, R; Mariggió, M A; Spinozzi, F; Bertotto, A

    1994-04-15

    A role for CD26 surface antigen (Ag) in both CD3- and CD2-mediated T cell activation has been previously demonstrated. To analyze the functional role of CD26 in the CD3- and CD2-induced activation pathways of cord T cells, which represent the most reliable source of Ag-unprimed T cells, we employed a newly developed anti-CD26 monoclonal antibody, termed anti-1F7, anti-CD3 and anti-CD2 in activating T lymphocytes. The results showed that CD26 Ag is expressed on the surface of almost all resting cord T cells and that its fluorescence intensity is enhanced by activation. The binding of anti-1F7 induced a decrease in CD26 membrane expression, with no detectable effect on the surface expression of other cord T cell-related molecules. Moreover, the modulation of CD26 resulted in an increase in anti-CD3-mediated cord T cell activation through an enhancement in intracellular calcium levels, IL-2 receptor expression, and IL-2 synthesis, whereas it had no effect on cord T cell activation induced by anti-CD2 or anti-CD2 plus exogenous IL-2. The fact that the selective involvement of CD26 in the activation pathway triggered by anti-CD3, but not anti-CD2, could be reversed by prior stimulation of cord T cells with anti-CD3 suggests that this functional feature, which resembles that of mature thymocytes, may be linked to the Ag-unprimed cell phenotype of cord T lymphocytes. PMID:7909498

  5. The role of GMES / Sentinels in Land-Surface Earth System Science

    NASA Astrophysics Data System (ADS)

    Moreno, J.

    2009-04-01

    A general trend in the current status of representation of Land Surface schemes into Earth System models is driven by the parameterisation of "cycles" instead of individual processes. Particular emphasis is made to account for couplings among the individual cycles, as between the carbon and water cycles. Moreover, the current tendency is to use the measured data -time series in most cases- together with models, in a data assimilation scenario where inputs from multiple sources are integrated. Such approach is more and more necessary as land models tend to be more complex, and particularly due to the fact that land surface variability is not just driven by physical and chemical processes, but intricate biological processes also altered by anthropogenic influences. Human influences in the land system (land use changes, urban development, etc.) and the impacts of natural disasters are becoming also part of land models, but critical data in high spatial and temporal resolutions are needed to properly model such processes. Until now, problems with data availability, data inconsistency and lack of adequate temporal sampling have limited the potential usefulness of such observations in modelling land surface processes. The availability of the GMES / Sentinel series of satellites represents a quite unique opportunity for consolidation of current tendencies and development of new science based on the new type of data that soon will become available. The usefulness of the different Sentinel missions for Land science has been recognised. Although the Sentinel satellite series were primarily designed to provide observations for operational services and routine applications, there is a growing interest in the scientific community towards the usage of Sentinel data for more advanced and innovative science. Moreover, the availability of consistent time series covering a period of over 20 years opens possibilities never explored before, such as systematic data assimilation

  6. Role of LiCoO2 Surface Terminations in Oxygen Reduction and Evolution Kinetics

    SciTech Connect

    Han, Binghong; Qian, Danna; Risch, Marcel; Chi, Miaofang; Meng, Ying Shirley; Yang, Shao-horn

    2015-03-22

    Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities of LiCoO2 nanorods with sizes in the range from 9 to 40 nm were studied in alkaline solution. The sides of these nanorods were terminated with low-index surfaces such as (003) while the tips were terminated largely with high-index surfaces such as (104) as revealed by high-resolution transmission electron microscopy. Electron energy loss spectroscopy demonstrated that low-spin Co3+ prevailed on the sides, while the tips exhibited predominantly high- or intermediate-spin Co3+. We correlated the electronic and atomic structure to higher specific ORR and OER activities at the tips as compared to the sides, which was accompanied by more facile redox of Co2+/3+ and higher charge transferred per unit area. These findings highlight the critical role of surface terminations and electronic structures of transition metal oxides on the ORR and OER activity.

  7. The Role of Large-Coherent-Eddy Transport in the Atmospheric Surface Layer Based on CASES-99 Observations

    NASA Astrophysics Data System (ADS)

    Sun, Jielun; Lenschow, Donald H.; LeMone, Margaret A.; Mahrt, Larry

    2016-07-01

    The analysis of momentum and heat fluxes from the Cooperative Atmosphere-Surface Exchange Study 1999 (CASES-99) field experiment is extended throughout the diurnal cycle following the investigation of nighttime turbulence by Sun et al. (J Atmos Sci 69:338-351, 2012). Based on the observations, limitations of Monin-Obukhov similarity theory (MOST) are examined in detail. The analysis suggests that strong turbulent mixing is dominated by relatively large coherent eddies that are not related to local vertical gradients as assumed in MOST. The HOckey-Stick Transition (HOST) hypothesis is developed to explain the generation of observed large coherent eddies over a finite depth and the contribution of these eddies to vertical variations of turbulence intensity and atmospheric stratification throughout the diurnal cycle. The HOST hypothesis emphasizes the connection between dominant turbulent eddies and turbulence generation scales, and the coupling between the turbulence kinetic energy and the turbulence potential energy within the turbulence generation layer in determining turbulence intensity. For turbulence generation directly influenced by the surface, the HOST hypothesis recognizes the role of the surface both in the vertical variation of momentum and heat fluxes and its boundary effect on the size of the dominant turbulence eddies.

  8. Institutional outbreaks of rotavirus diarrhoea: potential role of fomites and environmental surfaces as vehicles for virus transmission.

    PubMed Central

    Sattar, S. A.; Lloyd-Evans, N.; Springthorpe, V. S.; Nair, R. C.

    1986-01-01

    To assess the potential of fomites and environmental surfaces as vehicles in the transmission of rotaviral diarrhoea, disks (1 cm diameter) of various porous and non-porous materials were contaminated with about 10(5) plaque-forming units of the Wa strain of human rotavirus (HRV) suspended in faecal matter. The contaminated disks were then held for 10 days at either room temperature (22 +/- 2 degrees C) or 4 degrees C with the relative humidity (RH) at the high (85 +/- 5%), medium (50 +/- 5%) or low (25 +/- 5%) level. Survival was longer on non-porous surfaces at the lower temperature and at lower humidity. In contrast, survival on porous surfaces was very variable; better on cotton-polyester than on poster card or paper currency on which HRV survived very poorly. These results suggest that under the right environmental conditions, HRV-contaminated objects could play a role in the transmission of rotavirus infections in hospitals, nursing homes and day-care centres. PMID:3701042

  9. Hemagglutinin of influenza A virus binds specifically to cell surface nucleolin and plays a role in virus internalization.

    PubMed

    Chan, Che-Man; Chu, Hin; Zhang, Anna Jinxia; Leung, Lai-Han; Sze, Kong-Hung; Kao, Richard Yi-Tsun; Chik, Kenn Ka-Heng; To, Kelvin Kai-Wang; Chan, Jasper Fuk-Woo; Chen, Honglin; Jin, Dong-Yan; Liu, Liang; Yuen, Kwok-Yung

    2016-07-01

    The hemagglutinin (HA) protein of influenza A virus initiates cell entry by binding to sialic acids on target cells. In the current study, we demonstrated that in addition to sialic acids, influenza A/Puerto Rico/8/34 H1N1 (PR8) virus HA specifically binds to cell surface nucleolin (NCL). The interaction between HA and NCL was initially revealed with virus overlay protein binding assay (VOPBA) and subsequently verified with co-immunoprecipitation. Importantly, inhibiting cell surface NCL with NCL antibody, blocking PR8 viruses with purified NCL protein, or depleting endogenous NCL with siRNA all substantially reduced influenza virus internalization. We further demonstrated that NCL was a conserved cellular factor required for the entry of multiple influenza A viruses, including H1N1, H3N2, H5N1, and H7N9. Overall, our findings identified a novel role of NCL in influenza virus life cycle and established NCL as one of the host cell surface proteins for the entry of influenza A virus. PMID:27085069

  10. Role of surface-electrical properties on the cell-viability of carbon thin films grown in nanodomain morphology

    NASA Astrophysics Data System (ADS)

    Javid, Amjed; Kumar, Manish; Yoon, Seokyoung; Lee, Jung Heon; Tajima, Satomi; Hori, Masaru; Geon Han, Jeon

    2016-07-01

    Carbon thin films, having a combination of unique physical and chemical properties, exhibit an interesting biocompatibility and biological response to living entities. Here, the carbon films are developed in the morphology form of nano-domains with nanoscale inter-domain separations, tuned by plasma conditions in the facing target magnetron sputtering process. The wettability and surface energy are found to have a close relation to the inter-domain separations. The chemical structure of carbon films exhibited the relative enhancement of sp3 in comparison to sp2 with the increase of domain separations. The cell-viability of these films shows promising results for L929 mouse fibroblast and Saos-2 bone cells, when inter-domain separation is increased. Electrical conductivity and surface energy are identified to play the key role in different time-scales during the cell-proliferation process. The contribution from electrical conductivity is dominant in the beginning of the cultivation, whereas with the passage of time (~3–5 d) the surface energy takes control over conductivity to enhance the cell proliferation.

  11. Understanding the wetting properties of nanostructured selenium coatings: the role of nanostructured surface roughness and air-pocket formation

    PubMed Central

    Tran, Phong A; Webster, Thomas J

    2013-01-01

    Wetting properties of biomaterials, in particular nanomaterials, play an important role, as these influence interactions with biological elements, such as proteins, bacteria, and cells. In this study, the wetting phenomenon of titanium substrates coated with selenium nanoparticles was studied using experimental and mathematical modeling tools. Importantly, these selenium-coated titanium substrates were previously reported to increase select protein adsorption (such as vitronectin and fibronectin), to decrease bacteria growth, and increase bone cell growth. Increased selenium nanoparticle coating density resulted in higher contact angles but remained within the hydrophilic regime. This trend was found in disagreement with the Wenzel model, which is widely used to understand the wetting properties of rough surfaces. The trend also did not fit well with the Cassie–Baxter model, which was developed to understand the wetting properties of composite surfaces. A modified wetting model was thus proposed in this study, to understand the contributing factors of material properties to the hydrophilicity/hydrophobicity of these nanostructured selenium-coated surfaces. The analysis and model created in this study can be useful in designing and/or understanding the wetting behavior of numerous biomedical materials and in turn, biological events (such as protein adsorption as well as bacteria and mammalian cell functions). PMID:23737667

  12. Unforeseen distance-dependent SERS spectroelectrochemistry from surface-tethered Nile Blue: the role of molecular orientation.

    PubMed

    Wilson, Andrew J; Willets, Katherine A

    2016-08-15

    Covalent immobilization of redox-active dyes is an important strategy to evaluate structure-activity relationships in nanoscale electrochemistry by using optical readouts such as surface-enhanced Raman scattering (SERS). Here we investigate the role of the tether length in the SERS spectroelectrochemistry of surface-attached Nile Blue. Differential pulse voltammetry and a potential-dependent SERS derivative analysis reveal that the Nile Blue molecules adopt a different orientation with respect to the electrode surface as the number of carbons in a carboxylic acid-terminated alkanethiol monolayer is varied, which leads to unique SERS spectroelectrochemical behaviors. We use the relative molecular orientations and spectral characteristics to propose a model in which tethers shorter than the length of the molecule limit molecular motion under electrochemical perturbation, but tethers longer than the length of the molecule allow dye intercalation into the hydrophobic self-assembled monolayer, producing an unexpected decrease in the SERS intensity when the molecule is in the oxidized form. PMID:27337143

  13. Roles of ionic strength and biofilm roughness on adhesion kinetics of Escherichia coli onto groundwater biofilm grown on PVC surfaces

    PubMed Central

    Janjaroen, Dao; Ling, Fangqiong; Monroy, Guillermo; Derlon, Nicolas; Mogenroth, Eberhard; Boppart, Stephen A.; Liu, Wen-Tso; Nguyen, Thanh H.

    2013-01-01

    Mechanisms of Escherichia coli attachment on biofilms grown on PVC coupons were investigated. Biofilms were grown in CDC reactors using groundwater as feed solution over a period up to 27 weeks. Biofilm physical structure was characterized at the micro- and meso-scales using Scanning Electron Microscopy (SEM) and Optical Coherence Tomography (OCT), respectively. Microbial community diversity was analyzed with Terminal Restricted Fragment Length Polymorphism (T-RFLP). Both physical structure and microbial community diversity of the biofilms were shown to be changing from 2 weeks to 14 weeks, and became relatively stable after 16 weeks. A parallel plate flow chamber coupled with an inverted fluorescent microscope was also used to monitor the attachment of fluorescent microspheres and E. coli on clean PVC surfaces and biofilms grown on PVC surfaces for different ages. Two mechanisms of E. coli attachment were identified. The adhesion rate coefficients (kd) of E. coli on nascent PVC surfaces and 2-week biofilms increased with ionic strength. However, after biofilms grew for 8 weeks, the adhesion was found to be independent of solution chemistry. Instead, a positive correlation between kd and biofilm roughness as determined by OCT was obtained, indicating that the physical structure of biofilms could play an important role in facilitating the adhesion of E. coli cells. PMID:23497979

  14. Erosion processes in molassic cliffs: the role of the rock surface temperature and atmospheric conditions

    NASA Astrophysics Data System (ADS)

    Carrea, Dario; Abellán, Antonio; Guerin, Antoine; Jaboyedoff, Michel; Voumard, Jérémie

    2014-05-01

    The morphology of the Swiss Plateau is modeled by numerous steep cliffs of Molasse. These cliffs are mainly composed of sub-horizontal alternated layers of sandstone, shale and conglomerates deposed in the Alps foreland basin during the Tertiary period. These Molasse cliffs are affected by erosion processes inducing numerous rockfall events. Thus, it is relevant to understand how different external factors influence Molasse erosion rates. In this study, we focus on analyzing temperature variation during a winter season. As pilot study area we selected a cliff which is formed by a sub-horizontal alternation of outcropping sandstone and shale. The westward facing test site (La Cornalle, Vaud, Switzerland), which is a lateral scarp of a slow moving landslide area, is currently affected by intense erosion. Regarding data acquisition, we monitored both in-situ rock and air temperatures at 15 minutes time-step since October 2013: (1) on the one hand we measured Ground Surface Temperature (GST) at near-surface (0.1 meter depth) using a GST mini-datalogger M-Log5W-Rock model; (2) On the other hand we monitored atmospheric conditions using a weather station (Davis Vantage pro2 plus) collecting numerous parameters (i.e. temperature, irradiation, rain, wind speed, etc.). Furthermore, the area was also seasonally monitored by Ground-Based (GB) LiDAR since 2010 and monthly monitored since September 2013. In order to understand how atmospheric conditions (such as freeze and thaw effect) influence the erosion of the cliff, we modeled the temperature diffusion through the rock mass. To this end, we applied heat diffusion and radiation equation using a 1D temperature profile, obtaining as a result both temperature variations at different depths together with the location of the 0°C isotherm. Our model was calibrated during a given training set using both in-situ rock temperatures and atmospheric conditions. We then carried out a comparison with the rockfall events derived from the

  15. A role for surface lymphotoxin in experimental autoimmune encephalomyelitis independent of LIGHT

    PubMed Central

    Gommerman, Jennifer L.; Giza, Keith; Perper, Stuart; Sizing, Irene; Ngam-ek, Apinya; Nickerson-Nutter, Cheryl; Browning, Jeffrey L.

    2003-01-01

    In studies using genetically deficient mice, a role for the lymphotoxin (LT) system in the pathogenesis of experimental autoimmune encephalomyelitis (EAE) has remained controversial. Here, we have reassessed this conclusion by using a fusion protein decoy that blocks the LT pathway in vivo without evoking the developmental defects inherent in LT-deficient mice. We have found that inhibition of the LT pathway prevented disease in two models of EAE that do not rely on the administration of pertussis toxin. Surprisingly, disease attenuation was due to specific blockade of LTαβ binding rather than the binding of LIGHT to its receptors. In a third system that requires pertussis toxin, LT inhibition did not affect disease, as was observed when the same model was used with LT-deficient mice. Disease prevention in pertussis toxin–free models was associated with defects in T cell responses and migration. When the DO11.10 T cell transgenic system was used, inhibition of the LT pathway was shown to uncouple T cell priming from T cell recall responses. Therefore, it is hypothesized that the LT pathway and its ability to maintain lymphoid microenvironments is critical for sustaining late-phase T cell responses in multiple sclerosis. PMID:12952924

  16. Role of Raman spectroscopy and surface enhanced Raman spectroscopy in colorectal cancer

    PubMed Central

    Jenkins, Cerys A; Lewis, Paul D; Dunstan, Peter R; Harris, Dean A

    2016-01-01

    Colorectal cancer (CRC) is the fourth most common cancer in the United Kingdom and is the second largest cause of cancer related death in the United Kingdom after lung cancer. Currently in the United Kingdom there is not a diagnostic test that has sufficient differentiation between patients with cancer and those without cancer so the current referral system relies on symptomatic presentation in a primary care setting. Raman spectroscopy and surface enhanced Raman spectroscopy (SERS) are forms of vibrational spectroscopy that offer a non-destructive method to gain molecular information about biological samples. The techniques offer a wide range of applications from in vivo or in vitro diagnostics using endoscopic probes, to the use of micro-spectrometers for analysis of biofluids. The techniques have the potential to detect molecular changes prior to any morphological changes occurring in the tissue and therefore could offer many possibilities to aid the detection of CRC. The purpose of this review is to look at the current state of diagnostic technology in the United Kingdom. The development of Raman spectroscopy and SERS in clinical applications relation for CRC will then be discussed. Finally, future areas of research of Raman/SERS as a clinical tool for the diagnosis of CRC are also discussed. PMID:27190582

  17. The role of Ag nanoparticles in inverted polymer solar cells: Surface plasmon resonance and backscattering centers

    NASA Astrophysics Data System (ADS)

    Xu, Peng; Shen, Liang; Meng, Fanxu; Zhang, Jiaqi; Xie, Wenfa; Yu, Wenjuan; Guo, Wenbin; Jia, Xu; Ruan, Shengping

    2013-03-01

    Here, we demonstrate silver (Ag) nanoparticles (NPs) existing in molybdenum trioxide (MoO3) buffer layers can improve the photocurrent by surface plasmon resonance (SPR) and backscattering enhancement. The device structure is glass/indium tin oxides/titanium dioxide (TiO2)/regioregular poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester/MoO3/Ag NPs/MoO3/Ag. Compared to the device without Ag NPs, the short current density (Jsc) is improved from 7.76 ± 0.14 mA/cm2 to 8.89 ± 0.12 mA/cm2, and the power conversion efficiency is also enhanced from 2.70% ± 0.11% to 3.35% ± 0.08%. The transmittance spectra show that the device with Ag NPs has weaker transmittance than the device without, which could be attributed to the photons absorption of Ag NPs and light scattering by Ag NPs. The absorption profile of the devices with or without Ag NPs is simulated using finite-difference time-domain methods. It is approved that the Ag NPs result in the absorption improvement by SPR and backscattering enhancement.

  18. Dominant Role of Molybdenum in the Electrochemical Deposition of Biological Macromolecules on Metallic Surfaces

    PubMed Central

    2014-01-01

    The corrosion of CoCrMo, an alloy frequently used in orthopedic implants, was studied with an electrochemical quartz crystal microbalance (QCM) in three physiologically relevant solutions. Mass changes were measured during potentiodynamic tests, showing material deposition in protein solutions at potential levels that caused mass loss when the proteins were not present. X-ray photoelectron spectroscopy (XPS) data indicated that the deposited material was primarily organic and therefore was most likely derived from proteins in the electrolyte. Material deposition consistently occurred at a critical potential and was not dependent on the current density or total charge released into solution. Corrosion studies on pure Co, Cr, and Mo in protein solutions found material deposition only on Mo. We hypothesize that organic deposition results from the interaction of Mo(VI) with proteins in the surrounding solution. The organic layer is reminiscent of tribochemical reaction layers that form on the surface of CoCrMo hip bearings, suggesting that these types of layers can be formed by purely electrochemical means. PMID:23550942

  19. The role of wastewater treatment in reducing pollution of surface waters with zearalenone.

    PubMed

    Gromadzka, Karolina; Waśkiewicz, Agnieszka; Świetlik, Joanna; Bocianowski, Jan; Goliński, Piotr

    2015-06-01

    Zearalenone (ZEA) is a mycotoxin produced by some Fusarium species in food and feed. The toxicity of ZEA and its metabolites is related to the chemical structure of the mycotoxin, which is similar to naturally occurring oestrogens. Currently, there is increasing awareness of the presence of fungi and their toxic metabolites in the aquatic environment. One of the sources of these compounds are the effluents from wastewater treatment plants. The average annual efficiency of zearalenone reduction in the Łęczyca plant in our three-year study was in the range from 51.35 to 69.70 %. The threeway analysis of variance (year, month, and kind of wastewater) shows that the main effects of all factors and all interactions between them were significant for zearalenone and dissolved organic carbon content. Our findings suggest that wastewater is not the main source of surface water pollution with zearalenone. Future research should investigate the means to reduce ZEA and its migration from the fields through prevention strategies such as breeding for crops, plant debris management (crop rotation, tillage), and/or chemical and biological control. PMID:26110478

  20. Surface plasmon polaritons in a semi-bounded degenerate plasma: Role of spatial dispersion and collisions

    SciTech Connect

    Tyshetskiy, Yu.; Kompaneets, R.; Vladimirov, S. V.

    2012-11-15

    Surface plasmon polaritons (SPPs) in a semi-bounded degenerate plasma (e.g., a metal) are studied using the quasiclassical mean-field kinetic model, taking into account the spatial dispersion of the plasma (due to quantum degeneracy of electrons) and electron-ion (electron-lattice, for metals) collisions. SPP dispersion and damping are obtained in both retarded ({omega}/k{sub z}{approx}c) and non-retarded ({omega}/k{sub z} Much-Less-Than c) regions, as well as in between. It is shown that the plasma spatial dispersion significantly affects the properties of SPPs, especially at short wavelengths (less than the collisionless skin depth, {lambda} Less-Than-Or-Equivalent-To c/{omega}{sub pe}). Namely, the collisionless (Landau) damping of SPPs (due to spatial dispersion) is comparable to the purely collisional (Ohmic) damping (due to electron-lattice collisions) in a wide range of SPP wavelengths, e.g., from {lambda}{approx}20 nm to {lambda}{approx}0.8 nm for SPP in gold at T = 293 K and from {lambda}{approx}400 nm to {lambda}{approx}0.7 nm for SPPs in gold at T = 100 K. The spatial dispersion is also shown to affect, in a qualitative way, the dispersion of SPPs at short wavelengths {lambda} Less-Than-Or-Equivalent-To c/{omega}{sub pe}.

  1. The role of Ag buffer layer in Fe islands growth on Ge (111) surfaces

    SciTech Connect

    Fu, Tsu-Yi Wu, Jia-Yuan; Jhou, Ming-Kuan; Hsu, Hung-Chan

    2015-05-07

    Sub-monolayer iron atoms were deposited at room temperature on Ge (111)-c(2 × 8) substrates with and without Ag buffer layers. The behavior of Fe islands growth was investigated by using scanning tunneling microscope (STM) after different annealing temperatures. STM images show that iron atoms will cause defects and holes on substrates at room temperature. As the annealing temperature rises, iron atoms pull out germanium to form various kinds of alloyed islands. However, the silver layer can protect the Ag/Ge(111)-(√3×√3) reconstruction from forming defects. The phase diagram shows that ring, dot, and triangular defects were only found on Ge (111)-c(2 × 8) substrates. The kinds of islands found in Fe/Ge system are similar to Fe/Ag/Ge system. It indicates that Ge atoms were pulled out to form islands at high annealing temperatures whether there was a Ag layer or not. But a few differences in big pyramidal or strip islands show that the silver layer affects the development of islands by changing the surface symmetry and diffusion coefficient. The structure characters of various islands are also discussed.

  2. Osteogenic lineage restriction by osteoprogenitors cultured on nanometric grooved surfaces: the role of focal adhesion maturation.

    PubMed

    Cassidy, John W; Roberts, Jemma N; Smith, Carol-Anne; Robertson, Mary; White, Kate; Biggs, Manus J; Oreffo, Richard O C; Dalby, Matthew J

    2014-02-01

    The differentiation of progenitor cells is dependent on more than biochemical signalling. Topographical cues in natural bone extracellular matrix guide cellular differentiation through the formation of focal adhesions, contact guidance, cytoskeletal rearrangement and ultimately gene expression. Osteoarthritis and a number of bone disorders present as growing challenges for our society. Hence, there is a need for next generation implantable devices to substitute for, or guide, bone repair in vivo. Cellular responses to nanometric topographical cues need to be better understood in vitro in order to ensure the effective and efficient integration and performance of these orthopedic devices. In this study, the FDA-approved plastic polycaprolactone was embossed with nanometric grooves and the response of primary and immortalized osteoprogenitor cells observed. Nanometric groove dimensions were 240 nm or 540 nm deep and 12.5 μm wide. Cells cultured on test surfaces followed contact guidance along the length of groove edges, elongated along their major axis and showed nuclear distortion; they formed more focal complexes and lower proportions of mature adhesions relative to planar controls. Down-regulation of the osteoblast marker genes RUNX2 and BMPR2 in primary and immortalized cells was observed on grooved substrates. Down-regulation appeared to directly correlate with focal adhesion maturation, indicating the involvement of ERK 1/2 negative feedback pathways following integrin-mediated FAK activation. PMID:24252447

  3. Role of Carbon-Addition and Hydrogen-Migration Reactions in Soot Surface Growth.

    PubMed

    Zhang, Hong-Bo; Hou, Dingyu; Law, Chung K; You, Xiaoqing

    2016-02-11

    Using density functional theory and master equation modeling, we have studied the kinetics of small unsaturated aliphatic molecules reacting with polycyclic aromatic hydrocarbon (PAH) molecules having a diradical character. We have found that these reactions follow the mechanism of carbon addition and hydrogen migration (CAHM) on both spin-triplet and open-shell singlet potential energy surfaces at a rate that is about ten times those of the hydrogen-abstraction-carbon-addition (HACA) reactions at 1500 K in the fuel-rich postflame region. The results also show that the most active reaction sites are in the center of the zigzag edges of the PAHs. Furthermore, the reaction products are more likely to form straight rather than branched aliphatic side chains in the case of reacting with diacetylene. The computed rate constants are also found to be independent of pressure at conditions of interest in soot formation, and the activation barriers of the CAHM reactions are linearly correlated with the diradical characters. PMID:26799641

  4. The Role of OOH Binding Site and Pt Surface Structure on ORR Activities

    PubMed Central

    Jia, Qingying; Caldwell, Keegan; Ziegelbauer, Joseph M.; Kongkanand, Anusorn; Wagner, Frederick T.; Mukerjee, Sanjeev; Ramaker, David E.

    2015-01-01

    We present experimentally observed molecular adsorbate coverages (e.g., O(H), OOH and HOOH) on real operating dealloyed bimetallic PtMx (M = Ni or Co) catalysts under oxygen reduction reaction (ORR) conditions obtained using X-ray absorption near edge spectroscopy (XANES). The results reveal a complex Sabatier catalysis behavior and indicate the active ORR mechanism changes with Pt–O bond weakening from the O2 dissociative mechanism, to the peroxyl mechanism, and finally to the hydrogen peroxide mechanism. An important rearrangement of the OOH binding site, an intermediate in the ORR, enables facile H addition to OOH and faster O–O bond breaking on 111 faces at optimal Pt–O bonding strength, such as that occurring in dealloyed PtM core-shell nanoparticles. This rearrangement is identified by previous DFT calculations and confirmed from in situ measured OOH adsorption coverages during the ORR. The importance of surface structural effects and 111 ordered faces is confirmed by the higher specific ORR rates on solid core vs porous multi-core nanoparticles. PMID:26190857

  5. La physique des bulles de champagne Une première approche des processus physico-chimiques liés à l'effervescence des vins de Champagne

    NASA Astrophysics Data System (ADS)

    Liger-Belair, G.

    2002-07-01

    bubble interface continuously increases and therefore continuously offers newly created surface to the adsorbed surface-active materials (around 5 mg/l, mostly composed of proteins and glycoproteins). Champagne bubbles experience an interesting competition between two opposing effects. Our results suggest that the bubble growth during ascent approximately balance the adsorption rate of surface-active compounds on the rising bubble. We also compared the behaviour of champagne bubbles with that of beer bubbles. It was found that beer bubbles showed a behaviour, very close to that of rigid spheres. This is not a surprising result, since beer contains much higher amounts of surface-active molecules (of order of several hundreds mg/l) likely to be adsorbed at a bubble interface. Furthermore, since the gas content is lower in beer, growth rates of beer bubbles are lower than those of champagne. As a result, the dilution effect due to the rate of dilatation of the bubble area may be too weak to avoid the rigidification of the beer bubble interface. In a third set of experiments, we used instantaneous high-speed photography techniques to freeze the dynamics of bubbles collapsing at the free surface of a glass poured with champagne. The process following bubble collapse and leading to the projection of a high-speed liquid jet above the free surface was captured. A structural analogy between the liquid jet following a bubble collapse and the liquid jet following a drop impact was presented. By drawing a parallel between the fizz in champagne wines and the “fizz of the ocean", we also suggested that droplets issued from champagne bursting bubbles contain much higher amounts of surface-active and potentially aromatic materials than the liquid bulk. The bursting of champagne bubbles is thus expected to play a major role in flavour release. Otherwise, since the first photographic investigation were published about fifty years ago, numerous experiments have been conducted with single

  6. The role of basic amino acid surface clusters on the collagenase activity of cathepsin K

    PubMed Central

    Nallaseth, Ferez S.; Lecaille, Fabien; Li, Zhenqiang; Brömme, Dieter

    2013-01-01

    Cathepsin K is a highly potent collagenase in osteoclasts and responsible for bone degradation. We have previously demonstrated that its unique collagenolytic activity is modulated by glycosaminoglycans that form high molecular complexes with the protease. However, mutational analysis of a specific glycosaminoglycan-cathepsin K binding site only led to a 60% reduction of the collagenolytic activity suggesting additional glycosaminoglycan binding sites or other determinants controlling this activity. We identified 8 cathepsin K specific arginine/lysine residues that form three positively charged clusters at the bottom part of the protease opposing the active site. These residues are highly conserved among mammalian, avian, and reptilian cathepsin K orthologues and to a lesser degree in amphibian and fish specimens. Mutational analysis of these residues revealed an approximately 50% reduction of the collagenolytic activity when the basic amino acids in cluster 2 (K106, K108, R108, R111) were mutated into alanine residues and resulted in a 100% loss of this activity when the mutations were expanded into cluster 3 (K122, R127). Cluster 1 mutations (K77, R79) had no effect. A partial rescue effect was observed when the hexa-mutant variant was combined with three mutations in the previously identified glycosaminoglycan binding site (N190, K101, L195K) indicating the relevance of at least two independent interaction sites. Amino acid substitutions in all sites had no effect on the catalytic efficacy of the protease variants as reflected in their unaltered peptidolytic and gelatinolytic activities and their overall protein stabilities. This study suggests that the basic amino acid clusters in cathepsin K are either involved in alternative glycoasaminoglycan binding sites, play other roles in the formation of collagenolytically active protease complexes or contribute in a yet unknown manner to the specific binding to collagen. PMID:24088021

  7. Role of Climate Variability in Modulating Surface Water and Groundwater Interaction over the Southeast United States

    NASA Astrophysics Data System (ADS)

    Almanaseer, N.; Arumugam, S.; Bales, J. D.

    2010-12-01

    We investigate the role of climatic variability on interannual groundwater variability in the Southeast U.S. For this purpose, streamflow and associated groundwater levels are analyzed for 20 basins that are minimally affected by reservoirs and groundwater pumping. Using the spatially-averaged monthly precipitation time series obtained from the Precipitation Regressions on Independent Slope Model (PRISM), we identify the recharge and discharge periods that influence the groundwater levels during the winter (January-February-March, JFM) and summer (July-August-September, JAS) seasons. Recharge-discharge dependency analyses indicate that precipitation during the previous three months influence the groundwater level in a given month. Streamflow in any given month depends on the groundwater level during the previous three months. Singular spectrum analysis (SSA) on the precipitation, temperature, streamflow and groundwater data indicate that groundwater levels and streamflow are the two dominant variables influencing the basin hydroclimatology. Further, relating the percentage variance explained from the SSA to baseflow index (BFI) clearly show that basins with high BFI have higher eigenvalues indicating groundwater being a spatial integrator of hydroclimatic processes. Relating the groundwater levels with El Nino Southern Oscillation (ENSO) index, Nino3.4, show that interannual variability in JFM groundwater levels could be partially explained by the ENSO conditions, but the relationship between JAS groundwater levels and JAS Nino3.4 is statistically not significant. Investigating the ability of precipitation forecasts from ECHAM4.5 General Circulation Model shows that there is potential to quantify groundwater availability during the winter season based on the forecasted precipitation and ENSO conditions.

  8. Investigating the role of the land surface in explaining the interannual variation of the net radiation balance over the Northwest Sahara and sub-Sahara

    NASA Technical Reports Server (NTRS)

    Smith, Eric A.; Nicholson, Sharon E.

    1987-01-01

    How much of the interannual variation in the satellite derived radiation balance can be purely attributed to changes taking place at the land surface, was examined. The role of surface latent heating was examined in relation to its control of the precipitation pattern from one year to the next.

  9. Fish population losses from Adirondack lakes: The role of surface water acidity and acidification

    SciTech Connect

    Baker, J.P. ); Warren-Hicks, W.J. ); Gallagher, J. ); Christensen, S.W. )

    1993-04-01

    Within the United States, the Adirondack region of New York State has the largest percentage of waters that are acidic and classified as deposition dominated. Thus, the Adirondacks have been the focus of much of the debate regarding the extent and magnitude of effects to date from acidic deposition. Completion of the Adirondack Lakes Survey in 1987, a survey of 1,469 lakes, in combination with the relatively extensive historical record on fish communities in the region, provided the opportunity for a thorough evaluation of changes in Adirondack fish communities over the last 50-60 years, and the degree to which these changes may have resulted from changes in surface water acid-base chemistry. Results indicate that 16-19% of the lakes with adequate historical data appeared to have lost one or more fish populations as a result of acidification. Brook trout and acid-sensitive minnows had experienced the most widespread effects, with losses in 11-19% of the lakes. Fish species occurring in lower elevation and larger lakes such as bass and brown trout, experienced little or no effects. Lakes judged to have lost fish populations to acidification had significantly lower pH and higher concentrations of inorganic aluminum and occurred at higher elevations than other lakes. No other lake characteristics showed consistent associations with fish population losses. Acidification is not the only factor, nor even the dominant factor affecting Adirondack fish communities, however. Other causes of fish loses include lake reclamation, changes in stocking policy, and the introduction (or invasion) of competitors or predators.

  10. Ultrasound-induced lung hemorrhage: Role of acoustic boundary conditions at the pleural surface

    NASA Astrophysics Data System (ADS)

    O'Brien, William D.; Kramer, Jeffrey M.; Waldrop, Tony G.; Frizzell, Leon A.; Miller, Rita J.; Blue, James P.; Zachary, James F.

    2002-02-01

    In a previous study [J. Acoust. Soc. Am. 108, 1290 (2000)] the acoustic impedance difference between intercostal tissue and lung was evaluated as a possible explanation for the enhanced lung damage with increased hydrostatic pressure, but the hydrostatic-pressure-dependent impedance difference alone could not explain the enhanced occurrence of hemorrhage. In that study, it was hypothesized that the animal's breathing pattern might be altered as a function of hydrostatic pressure, which in turn might affect the volume of air inspired and expired. The acoustic impedance difference between intercostal tissue and lung would be affected with altered lung inflation, thus altering the acoustic boundary conditions. In this study, 12 rats were exposed to 3 volumes of lung inflation (inflated: approximately tidal volume; half-deflated: half-tidal volume; deflated: lung volume at functional residual capacity), 6 rats at 8.6-MPa in situ peak rarefactional pressure (MI of 3.1) and 6 rats at 16-MPa in situ peak rarefactional pressure (MI of 5.8). Respiration was chemically inhibited and a ventilator was used to control lung volume and respiratory frequency. Superthreshold ultrasound exposures of the lungs were used (3.1-MHz, 1000-Hz PRF, 1.3-μs pulse duration, 10-s exposure duration) to produce lesions. Deflated lungs were more easily damaged than half-deflated lungs, and half-deflated lungs were more easily damaged than inflated lungs. In fact, there were no lesions observed in inflated lungs in any of the rats. The acoustic impedance difference between intercostal tissue and lung is much less for the deflated lung condition, suggesting that the extent of lung damage is related to the amount of acoustic energy that is propagated across the pleural surface boundary.

  11. Les neuropeptides gastro-intestinaux cibles des effets des rayonnements ionisants : altérations fonctionnelles

    NASA Astrophysics Data System (ADS)

    Linard, C.; Esposito, V.; Wysocki, J.; Griffiths, N. M.

    1998-04-01

    The symptoms associated with exposure to ionizing radiation are nausea, vomiting, diarrhoea. The response of the gut is complex involving modifications of motility and fluid and electrolyte transport. Gastrointestinal regulatory peptides have an important role in these functions. This study showed that radiation-induced tissue variations of neuropeptides have some repercussions on intestinal biological activity of these peptides soon after irradiation. In addition such modifications are also seen a few years after irradiation. Les symptômes associés à l'exposition aux rayonnements ionisants sont des nausées, vomissements et diarrhées. La réponse du système digestif est complexe, impliquant des modifications de la motilité et du transport d'eau et d'électrolytes. les neuropeptides gastro-intestinaux ont un rôle important dans ces fonctions. Cette étude montre que les variations tissulaires de ces neuropeptides induites par l'irradiation ont des répercussions sur l'activité biologique intestinale pour des temps précoces mais que ces perturbations sont encore visibles quelques années après l'irradiation.

  12. Bacteria transport and deposition under unsaturated conditions: the role of the matrix grain size and the bacteria surface protein.

    PubMed

    Gargiulo, G; Bradford, S; Simůnek, J; Ustohal, P; Vereecken, H; Klumpp, E

    2007-07-17

    Unsaturated (80% water saturated) packed column experiments were conducted to investigate the influence of grain size distribution and bacteria surface macromolecules on bacteria (Rhodococcus rhodochrous) transport and deposition mechanisms. Three sizes of silica sands were used in these transport experiments, and their median grain sizes were 607, 567, and 330 microm. The amount of retained bacteria increased with decreasing sand size, and most of the deposited bacteria were found adjacent to the column inlet. The deposition profiles were not consistent with predictions based on classical filtration theory. The experimental data could be accurately characterized using a mathematical model that accounted for first-order attachment, detachment, and time and depth-dependent straining processes. Visual observations of the bacteria deposition as well as mathematical modelling indicated that straining was the dominant mechanism of deposition in these sands (78-99.6% of the deposited bacteria), which may have been enhanced due to the tendency of this bacterium to form aggregates. An additional unsaturated experiment was conducted to better deduce the role of bacteria surface macromolecules on attachment and straining processes. In this case, the bacteria surface was treated using a proteolitic enzyme. This technique was assessed by examining the Fourier-transform infrared spectrum and hydrophobicity of untreated and enzyme treated cells. Both of these analytical procedures demonstrated that this enzymatic treatment removed the surface proteins and/or associated macromolecules. Transport and modelling studies conducted with the enzyme treated bacteria, revealed a decrease in attachment, but that straining was not significantly affected by this treatment. PMID:17337313

  13. Role of Rective Mineral Surface Area on the CO2 Mineralisation of CO2 Under Natural Conditions

    NASA Astrophysics Data System (ADS)

    Zuddas, P.; Rillard, J.

    2011-12-01

    The understanding of complex reactions between CO2 rich fluids and rock is fundamental to secured, long-term CO2 storage in geological reservoirs. A natural hydrothermal field is considered to be a useful analogue of carbon dioxide mineralization because it integrates the long-term interaction signal. The hydrothermal field of Galicia (Spain) is characterized by co-genetic fluids resulting from a mostly homogeneous granite reservoir with pCO2 partial pressure ranging from 104 to105 Pa and pH from 10 to 6. Fluids are characterized by an increase of major elements (Ca, Mg, K and Na) and alkalinity, both correlated to pCO2. We evaluated the effects of deep CO2 perturbation on the fluid-rock interaction system. Mineral reactivity which produces changes in the fluid mineral composition is mainly dependent on the 'real' reactive surface area. The mineral surface area participating in reactions resulting from this pCO2 gradient was estimated by an inverse model approach. Input data was based on the chemical composition of the fluids we sampled. The rate of mineral dissolution was estimated by the observed pH and equilibrium conditions. Moreover, the major elemental concentrations allowed us to quantify the variation of the reactive surface area of minerals involved with the overall water-rock interaction. The irreversible mass transfer process, ruled by the continuum equilibrium condition, was defined by the overall degree of reaction advancement, using a set of polynomial equations solved independently of time scale. We found that reactive surface area of calcite, albite and K-feldspar increases by 2 orders of magnitude over the entire CO2 fluid-rock interaction process, while the reactive surface area of biotite increases by 4 orders of magnitude. This shows that fluid neutralisation and consequent CO2 mineralization under the form of carbonate species is greatly dependent on the behaviour of the reactive surface area of the mineral association in this geological

  14. Fish population losses from Adirondack Lakes: The role of surface water acidity and acidification

    NASA Astrophysics Data System (ADS)

    Baker, Joan P.; Warren-Hicks, William J.; Gallagher, James; Christensen, Sigurd W.

    1993-04-01

    Changes over time in the species composition of fish communities in Adirondack lakes were assessed to determine (1) the approximate numbers offish populations that have been lost and (2) the degree to which fish population losses may have resulted from surface water acidification and acidic deposition. Information on the present-day status offish communities was obtained by the Adirondack Lakes Survey Corporation, which surveyed 1469 Adirondack lakes in 1984-1987 (53% of the total ponded waters in the Adirondack ecological zone). Two hundred and ninety-five of these lakes had been surveyed in 1929-1934 during the first statewide biological survey; 720 had been surveyed in one or more years prior to 1970. Sixteen to 19% of the lakes with adequate historical data appeared to have lost one or more fish populations as a result of acidification. Brook trout and acid-sensitive minnow species had experienced the most widespread effects. Populations of brook trout and acid-sensitive minnows had been lost apparently as a result of acidification from 11% and 19%, respectively, of the lakes with confirmed historical occurrence of these taxa. By contrast, fish species that tend to occur primarily in lower elevation and larger lakes, such as largemouth and smallmouth bass and brown trout, have experienced little to no documented adverse effects. Lakes that were judged to have lost fish populations as a result of acidification had significantly lower; pH and, in most cases, also had higher estimated concentrations of inorganic aluminum and occurred at higher elevations than did lakes with the fish species still present. No other lake characteristics were consistently associated with fish population losses attributed to acidification. The exact numbers and proportions of fish populations affected could not be determined because of limitations on the quantity and quality of historical data. Lakes for which we had adequate historical data to assess long-term trends in fish

  15. Reticulation des fibres lignocellulosiques

    NASA Astrophysics Data System (ADS)

    Landrevy, Christel

    Pour faire face à la crise économique la conception de papier à valeur ajoutée est développée par les industries papetières. Le but de se projet est l'amélioration des techniques actuelles de réticulation des fibres lignocellulosiques de la pâte à papier visant à produire un papier plus résistant. En effet, lors des réactions de réticulation traditionnelles, de nombreuses liaisons intra-fibres se forment ce qui affecte négativement l'amélioration anticipée des propriétés physiques du papier ou du matériau produit. Pour éviter la formation de ces liaisons intra-fibres, un greffage sur les fibres de groupements ne pouvant pas réagir entre eux est nécessaire. La réticulation des fibres par une réaction de « click chemistry » appelée cycloaddition de Huisgen entre un azide et un alcyne vrai, catalysée par du cuivre (CuAAC) a été l'une des solutions trouvée pour remédier à ce problème. De plus, une adaptation de cette réaction en milieux aqueux pourrait favoriser son utilisation en milieu industriel. L'étude que nous désirons entreprendre lors de ce projet vise à optimiser la réaction de CuAAC et les réactions intermédiaires (propargylation, tosylation et azidation) sur la pâte kraft, en milieu aqueux. Pour cela, les réactions ont été adaptées en milieu aqueux sur la cellulose microcristalline afin de vérifier sa faisabilité, puis transférée à la pâte kraft et l'influence de différents paramètres comme le temps de réaction ou la quantité de réactifs utilisée a été étudiée. Dans un second temps, une étude des différentes propriétés conférées au papier par les réactions a été réalisée à partir d'une série de tests papetiers optiques et physiques. Mots Clés Click chemistry, Huisgen, CuAAC, propargylation, tosylation, azidation, cellulose, pâte kraft, milieu aqueux, papier.

  16. The Role of Defects in the Local Reaction Kinetics of CO Oxidation on Low-Index Pd Surfaces

    PubMed Central

    2013-01-01

    The role of artificially created defects and steps in the local reaction kinetics of CO oxidation on the individual domains of a polycrystalline Pd foil was studied by photoemission electron microscopy (PEEM), mass spectroscopy (MS), and scanning tunneling microscopy (STM). The defects and steps were created by STM-controlled Ar+ sputtering and the novel PEEM-based approach allowed the simultaneous determination of local kinetic phase transitions on differently oriented μm-sized grains of a polycrystalline sample. The independent (single-crystal-like) reaction behavior of the individual Pd(hkl) domains in the 10–5 mbar pressure range changes upon Ar+ sputtering to a correlated reaction behavior, and the reaction fronts propagate unhindered across the grain boundaries. The defect-rich surface shows also a significantly higher CO tolerance as reflected by the shift of both the global (MS-measured) and the local (PEEM-measured) kinetic diagrams toward higher CO pressure. PMID:23785524

  17. Dual role of CO in the stability of subnano Pt clusters at the Fe3O4(001) surface

    PubMed Central

    Bliem, Roland; van der Hoeven, Jessi E. S.; Hulva, Jan; Pavelec, Jiri; Gamba, Oscar; de Jongh, Petra E.; Schmid, Michael; Blaha, Peter; Diebold, Ulrike; Parkinson, Gareth S.

    2016-01-01

    Interactions between catalytically active metal particles and reactant gases depend strongly on the particle size, particularly in the subnanometer regime where the addition of just one atom can induce substantial changes in stability, morphology, and reactivity. Here, time-lapse scanning tunneling microscopy (STM) and density functional theory (DFT)-based calculations are used to study how CO exposure affects the stability of Pt adatoms and subnano clusters at the Fe3O4(001) surface, a model CO oxidation catalyst. The results reveal that CO plays a dual role: first, it induces mobility among otherwise stable Pt adatoms through the formation of Pt carbonyls (Pt1–CO), leading to agglomeration into subnano clusters. Second, the presence of the CO stabilizes the smallest clusters against decay at room temperature, significantly modifying the growth kinetics. At elevated temperatures, CO desorption results in a partial redispersion and recovery of the Pt adatom phase. PMID:27457953

  18. Dual role of CO in the stability of subnano Pt clusters at the Fe3O4(001) surface.

    PubMed

    Bliem, Roland; van der Hoeven, Jessi E S; Hulva, Jan; Pavelec, Jiri; Gamba, Oscar; de Jongh, Petra E; Schmid, Michael; Blaha, Peter; Diebold, Ulrike; Parkinson, Gareth S

    2016-08-01

    Interactions between catalytically active metal particles and reactant gases depend strongly on the particle size, particularly in the subnanometer regime where the addition of just one atom can induce substantial changes in stability, morphology, and reactivity. Here, time-lapse scanning tunneling microscopy (STM) and density functional theory (DFT)-based calculations are used to study how CO exposure affects the stability of Pt adatoms and subnano clusters at the Fe3O4(001) surface, a model CO oxidation catalyst. The results reveal that CO plays a dual role: first, it induces mobility among otherwise stable Pt adatoms through the formation of Pt carbonyls (Pt1-CO), leading to agglomeration into subnano clusters. Second, the presence of the CO stabilizes the smallest clusters against decay at room temperature, significantly modifying the growth kinetics. At elevated temperatures, CO desorption results in a partial redispersion and recovery of the Pt adatom phase. PMID:27457953

  19. Variability and Predictability of West African Droughts. A review in the role of Sea Surface Temperature Anomalies

    NASA Astrophysics Data System (ADS)

    Rodríguez de Fonseca, Belen; Mohino, Elsa; Mechoso, Carlos R.

    2015-04-01

    The Sahel experienced a severe drought during the 1970's and 1980's after wet periods in the 1950's and 1960's. Although rainfall partially recovered since the 1990's, the drought had devastating impacts on societies. Most studies agree that this dry period resulted primarily from remote effects of sea surface temperature (SST) anomalies amplified by local land surface/atmospheric interactions. This paper reviews advances made during the last decade to better understand the impact of global SST variability on West African rainfall at interanual to decadal time scales. At interanual time scales, a warming of the equatorial Atlantic and Pacific/Indian oceans results in rainfall reduction over the Sahel and positive SST anomalies over the Mediterranean sea tend to be associated with increased rainfall. At decadal time scales, a warming over the Tropics leads to drought over the Sahel, while the warming over the North Atlantic promotes increased rainfall. The skill of numerical forecasts has improved during the last decades, due to better dynamical vegetation schemes. Prediction systems have evolved from seasonal to decadal forecasting.The agreement among future projections has improved from CMIP3 to CMIP5, with a general tendency for slightly wetter conditions over central part, drier conditions over the western part and a delay in the monsoon onset. The role of the Indian ocean, the stationarity of teleconnections, the determination of the leader ocean basin in driving decadal variability, the antropogenic role, the reduction of the model rainfall spread and the improvement of some model components are among the most important remaining questions that will be the focus of current international projects.

  20. Variability and Predictability of West African Droughts. A Review in the Role of Sea Surface Temperature Anomalies

    NASA Technical Reports Server (NTRS)

    Rodriguez-Fonseca, Belen; Mohino, Elsa; Mechoso, Carlos R.; Caminade, Cyril; Biasutti, Michela; Gaetani, Marco; Garcia-Serrano, J.; Vizy, Edward K.; Cook, Kerry; Xue, Yongkang; Polo, Irene; Losada, Teresa; Druyan, Leonard M.; Fontaine, Bernard; Bader, Juergen; Doblas-Reyes, Francisco J.; Goddard, Lisa; Janicot, Serge; Arribas, Alberto; Lau, William; Colman, Andrew; Vellinga, M.; Rowell, David P.; Kucharski, Fred; Voldoire, Aurore

    2015-01-01

    The Sahel experienced a severe drought during the 1970s and 1980s after wet periods in the 1950s and 1960s. Although rainfall partially recovered since the 1990s, the drought had devastating impacts on society. Most studies agree that this dry period resulted primarily from remote effects of sea surface temperature (SST) anomalies amplified by local land surface-atmosphere interactions. This paper reviews advances made during the last decade to better understand the impact of global SST variability on West African rainfall at interannual to decadal time scales. At interannual time scales, a warming of the equatorial Atlantic and Pacific/Indian Oceans results in rainfall reduction over the Sahel, and positive SST anomalies over the Mediterranean Sea tend to be associated with increased rainfall. At decadal time scales, warming over the tropics leads to drought over the Sahel, whereas warming over the North Atlantic promotes increased rainfall. Prediction systems have evolved from seasonal to decadal forecasting. The agreement among future projections has improved from CMIP3 to CMIP5, with a general tendency for slightly wetter conditions over the central part of the Sahel, drier conditions over the western part, and a delay in the monsoon onset. The role of the Indian Ocean, the stationarity of teleconnections, the determination of the leader ocean basin in driving decadal variability, the anthropogenic role, the reduction of the model rainfall spread, and the improvement of some model components are among the most important remaining questions that continue to be the focus of current international projects.

  1. The Role of Putative Phosphatidylserine-Interactive Residues of Tissue Factor on Its Coagulant Activity at the Cell Surface

    PubMed Central

    Ansari, Shabbir A.; Pendurthi, Usha R.; Sen, Prosenjit; Rao, L. Vijaya Mohan

    2016-01-01

    Exposure of phosphatidylserine (PS) on the outer leaflet of the cell membrane is thought to play a critical role in tissue factor (TF) decryption. Recent molecular dynamics simulation studies suggested that the TF ectodomain may directly interact with PS. To investigate the potential role of TF direct interaction with the cell surface phospholipids on basal TF activity and the enhanced TF activity following the decryption, one or all of the putative PS-interactive residues in the TF ectodomain were mutated and tested for their coagulant activity in cell systems. Out of the 9 selected TF mutants, five of them -TFS160A, TFS161A, TFS162A, TFK165A, and TFD180A- exhibited a similar TF coagulant activity to that of the wild-type TF. The specific activity of three mutants, TFK159A, TFS163A, and TFK166A, was reduced substantially. Mutation of the glycine residue at the position 164 markedly abrogated the TF coagulant activity, resulting in ~90% inhibition. Mutation of all nine lipid binding residues together did not further decrease the activity of TF compared to TFG164A. A similar fold increase in TF activity was observed in wild-type TF and all TF mutants following the treatment of THP-1 cells with either calcium ionomycin or HgCl2, two agents that are commonly used to decrypt TF. Overall, our data show that a few select TF residues that are implicated in interacting with PS contribute to the TF coagulant activity at the cell surface. However, our data also indicate that TF regions outside of the putative lipid binding region may also contribute to PS-dependent decryption of TF. PMID:27348126

  2. The Role of Putative Phosphatidylserine-Interactive Residues of Tissue Factor on Its Coagulant Activity at the Cell Surface.

    PubMed

    Ansari, Shabbir A; Pendurthi, Usha R; Sen, Prosenjit; Rao, L Vijaya Mohan

    2016-01-01

    Exposure of phosphatidylserine (PS) on the outer leaflet of the cell membrane is thought to play a critical role in tissue factor (TF) decryption. Recent molecular dynamics simulation studies suggested that the TF ectodomain may directly interact with PS. To investigate the potential role of TF direct interaction with the cell surface phospholipids on basal TF activity and the enhanced TF activity following the decryption, one or all of the putative PS-interactive residues in the TF ectodomain were mutated and tested for their coagulant activity in cell systems. Out of the 9 selected TF mutants, five of them -TFS160A, TFS161A, TFS162A, TFK165A, and TFD180A- exhibited a similar TF coagulant activity to that of the wild-type TF. The specific activity of three mutants, TFK159A, TFS163A, and TFK166A, was reduced substantially. Mutation of the glycine residue at the position 164 markedly abrogated the TF coagulant activity, resulting in ~90% inhibition. Mutation of all nine lipid binding residues together did not further decrease the activity of TF compared to TFG164A. A similar fold increase in TF activity was observed in wild-type TF and all TF mutants following the treatment of THP-1 cells with either calcium ionomycin or HgCl2, two agents that are commonly used to decrypt TF. Overall, our data show that a few select TF residues that are implicated in interacting with PS contribute to the TF coagulant activity at the cell surface. However, our data also indicate that TF regions outside of the putative lipid binding region may also contribute to PS-dependent decryption of TF. PMID:27348126

  3. Role of surface oxides in the formation of solid-electrolyte interphases at silicon electrodes for lithium-ion batteries.

    PubMed

    Schroder, Kjell W; Dylla, Anthony G; Harris, Stephen J; Webb, Lauren J; Stevenson, Keith J

    2014-12-10

    Nonaqueous solvents in modern battery technologies undergo electroreduction at negative electrodes, leading to the formation of a solid-electrolyte interphase (SEI). The mechanisms and reactions leading to a stable SEI on silicon electrodes in lithium-ion batteries are still poorly understood. This lack of understanding inhibits the rational design of electrolyte additives, active material coatings, and the prediction of Li-ion battery life in general. We prepared SEI with a common nonaqueous solvent (LiPF6 in PC and in EC/DEC 1:1 by wt %) on silicon oxide and etched silicon (001) surfaces in various states of lithiation to understand the role of surface chemistry on the SEI formation mechanism and SEI structure. Anhydrous and anoxic techniques were used to prevent air and moisture contamination of prepared SEI films, allowing for more accurate characterization of SEI chemical stratification and composition by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth profiling. Additionally, multivariate statistical methods were used to better understand TOF-SIMS depth profiling studies. We conclude that the absence of native-oxide layer on silicon has a significant impact on the formation, composition, structure, and thickness of the SEI. PMID:25402271

  4. Critical hydraulic gradient for nonlinear flow through rock fracture networks: The roles of aperture, surface roughness, and number of intersections

    NASA Astrophysics Data System (ADS)

    Liu, Richeng; Li, Bo; Jiang, Yujing

    2016-02-01

    Transition of fluid flow from the linear to the nonlinear regime has been confirmed in single rock fractures when the Reynolds number (Re) exceeds some critical values, yet the criterion for such a transition in discrete fracture networks (DFNs) has received little attention. This study conducted flow tests on crossed fracture models with a single intersection and performed numerical simulations on fluid flow through DFNs of various geometric characteristics. The roles of aperture, surface roughness, and number of intersections of fractures on the variation of the critical hydraulic gradient (Jc) for the onset of nonlinear flow through DFNs were systematically investigated. The results showed that the relationship between hydraulic gradient (J) and flow rate can be well quantified by Forchheimer's law; when J drops below Jc, it reduces to the widely used cubic law, by diminishing the nonlinear term. Larger apertures, rougher fracture surfaces, and a greater number of intersections in a DFN would result in the onset of nonlinear flow at a lower Jc. Mathematical expressions of Jc and the coefficients involved in Forchheimer's law were developed based on multi-variable regressions of simulation results, which can help to choose proper governing equations when solving problems associated with fluid flow in fracture networks.

  5. Buffering the negative effects of employee surface acting: the moderating role of employee-customer relationship strength and personalized services.

    PubMed

    Wang, Karyn L; Groth, Markus

    2014-03-01

    The impact of emotional labor on customer outcomes is gaining considerable attention in the literature, with research suggesting that the authenticity of emotional displays may positively impact customer outcomes. However, research investigating the impact of more inauthentic emotions on service delivery outcomes is mixed (see Chi, Grandey, Diamond, & Krimmel, 2011). This study explores 2 potential reasons for why the service outcomes of inauthentic emotions are largely inconsistent: the impact of distinct surface acting strategies and the role of service delivery context. Drawing on social-functional theories of emotions, we surveyed 243 dyads of employees and customers from a wide variety of services to examine the links between employee surface acting and customer service satisfaction, and whether this relationship is moderated by relationship strength and service personalization. Our findings suggest that faking positive emotions has no bearing on service satisfaction, but suppressing negative emotions interacts with contextual factors to predict customers' service satisfaction, in line with social-functional theories of emotions. Specifically, customers who know the employee well are less sensitive to the negative effects of suppressed negative emotions, and customers in highly personalized service encounters are more sensitive to the negative effects of suppressed negative emotions. We conclude with a discussion of theoretical and practical implications. PMID:24079672

  6. A Magellanic origin of the DES dwarfs

    NASA Astrophysics Data System (ADS)

    Jethwa, P.; Erkal, D.; Belokurov, V.

    2016-09-01

    We establish the connection between the Magellanic Clouds (MCs) and the dwarf galaxy candidates discovered in the Dark Energy Survey (DES) by building a dynamical model of the MC satellite populations, based on an extensive suite of tailor-made numerical simulations. Our model takes into account the response of the Galaxy to the MCs infall, the dynamical friction experienced by the MCs and the disruption of the MC satellites by their hosts. The simulation suite samples over the uncertainties in the MC's proper motions, the masses of the MW and the Clouds themselves, and allows for flexibility in the intrinsic volume density distribution of the MC satellites. As a result, we can accurately reproduce the DES satellites' observed positions and kinematics. Assuming that Milky Way (MW) dwarfs follow the distribution of sub-haloes in Λ cold dark matter, we further demonstrate that, of 14 observed satellites, the MW halo contributes fewer than 4(8) of these with 68(95) per cent confidence and that 7(12) DES dwarfs have probabilities greater than 0.7(0.5) of belonging to the Large Magellanic Cloud (LMC). Marginalizing over the entire suite, we constrain the number of Magellanic satellites in the range -7 < MV < -1 which exceed the DES surface brightness threshold at ˜70, and the mass of the LMC around 1011 M⊙. The data also strongly support a first-infall scenario for the LMC. Finally, we give predictions for the line-of-sight velocities and the proper motions of the satellites discovered in the vicinity of the LMC.

  7. A Magellanic Origin of the DES Dwarfs

    NASA Astrophysics Data System (ADS)

    Jethwa, P.; Erkal, D.; Belokurov, V.

    2016-06-01

    We establish the connection between the Magellanic Clouds (MCs) and the dwarf galaxy candidates discovered in the Dark Energy Survey (DES) by building a dynamical model of the MC satellite populations, based on an extensive suite of tailor-made numerical simulations. Our model takes into account the response of the Galaxy to the MCs infall, the dynamical friction experienced by the MCs and the disruption of the MC satellites by their hosts. The simulation suite samples over the uncertainties in the MC's proper motions, the masses of the MW and the Clouds themselves and allows for flexibility in the intrinsic volume density distribution of the MC satellites. As a result, we can accurately reproduce the DES satellites' observed positions and kinematics. Assuming that Milky Way (MW) dwarfs follow the distribution of subhaloes in ΛCDM, we further demonstrate that, of 14 observed satellites, the MW halo contributes fewer than 4(8) of these with 68(95)% confidence and that 7(12) DES dwarfs have probabilities greater than 0.7(0.5) of belonging to the LMC. Marginalising over the entire suite, we constrain the number of Magellanic satellites in the range -7 < MV < -1 which exceed the DES surface brightness threshold at ˜70, and the mass of the LMC around 1011M⊙. The data also strongly support a first-infall scenario for the LMC. Finally, we give predictions for the line-of-sight velocities and the proper motions of the satellites discovered in the vicinity of the LMC.

  8. Role of Wind and Sea Surface Temperature Over Moisture Source Region in Determining the Stable Isotopic Ratios in Rainwater

    NASA Astrophysics Data System (ADS)

    Rahul, P.; Ghosh, P.

    2012-12-01

    Rainwater stable isotope ratio is controlled by several factors such as distance from the coast, latitudinal location, altitudes, temperature and amount of rainfall (Dansgard 1964;Rozanski 1993). Amount of rainfall plays a significant role in controlling the distribution of stable isotopes especially in the tropics experiencing seasonal precipitation from monsoonal wind circulation. In recent years with more observations on rainfall stable isotopes being documented from tropical regions, the effect of parameters like wind, sea surface temperature, drop size distribution on stable isotopic composition of rainwater are better understood (Wright et al 2001;Vochon et al 2009; Rao et al 2006; Srivastava et al 2012). The isotopic compositions of 2010 ISMR (Indian Summer Monsoon Rainfall) from Bangalore, India along with a few other observations of similar kind retrieved from the literatures are studied for amount effect relationship. Bangalore region provide nice opportunity to understand the different monsoonal influence due to its location ( ~300 km ) from coastal boundaries in east and west. The air parcel back trajectories obtained from NOAA HYSPLIT shows Arabian Sea region as the prominent source of moisture for the rainfall occurring during Southwest Monsoon (SWM). In this study we investigated the role of Sea Surface temperature (SST) and wind conditions over the moisture source and its effect on the intra seasonal variability of rainfall isotopic composition recorded at Bangalore region. The isotope analysis of δ18O in rainwater during the Indian summer monsoon rainfall shows a range of values from 2.77‰ to -9.07‰ over a period covering June to September. The observations fail to establish any relationship between stable isotope ratio and rainfall amount. We observed that the temporal variability of SST and wind over Arabian Sea region having strong role in driving the isotopic composition of rainwater. The relationship between SST and isotope ratio is found

  9. A three-dimensional WRF-based precipitation equation and its application in the analysis of roles of surface evaporation in a torrential rainfall event

    NASA Astrophysics Data System (ADS)

    Huang, Yongjie; Cui, Xiaopeng; Li, Xiaofan

    2016-03-01

    Based on the governing equations for water species in the Weather Research and Forecasting (WRF) model, a three-dimensional WRF-based surface precipitation equation was obtained and applied to investigate the surface rainfall processes of a torrential rain event. Sensitivity experiments were performed to further explore roles of surface evaporation in the heavy rainfall event. The results show that the contributions of moisture-related processes to precipitation (QWV, including water vapor local change (QWVL), surface evaporation (QWVE), moisture advection (QWVA), and so on) dominate the torrential rain event, while the contributions of cloud-related processes (QCM) also play indispensable roles whose maximum net contributions could exceed 20%. QWVA dominates the budget of water vapor, while QWVL and QWVE play smaller but by no means negligible roles in the event. Sensitivity experiments show that the changes of surface evaporation affect both moisture-related processes and cloud-related processes, and then influence the intensity and regional redistribution of precipitation. Surface evaporation favors the accumulation of convective available potential energy and enhances the instability of atmosphere, being prone to the development of convective systems. Meanwhile, it also affects the development of vertical motions and cloud systems. Thus accurate estimation of surface evaporation is necessary for accurate simulation and forecast of surface precipitation.

  10. Delineation of flooding within the upper Mississippi River Basin-flood of June 18 through August 4, 1993, in Des Moines and vicinity, Iowa

    USGS Publications Warehouse

    Schaap, Bryan D.

    1996-01-01

    This hydrologic investigations atlas shows the areas in and near Des Moines, Iowa, that were flooded by the Des Moines and the Raccoon Rivers and Walnut, Fourmile, and Beaver Creeks from June 18 through August 4, 1993. This map also depicts the Federal Emergency Management Agency 100-year flood boundaries. The area drained by the Des Moines River upstream from Des Moines received more than 100 percent of normal rainfall in May, June, and July, 1993. At Boone, which is located about 35 miles north-northeast of Des Moines, July rainfall was 424 percent of normal. The discharges at streamflow- gaging stations on the Des Moines River near Stratford, downstream from Saylorville Lake, and at Des Moines are shown. The cumulative discharge for inflow-gaging stations in the Des Moines area and discharge for the Des Moines River below the Raccoon River at Des Moines from July 8 through 21, 1993, are shown. The water-surface elevations of Saylorville Lake from June 18 through August 4, 1993, are shown. Profiles of the maximum water- surface elevations of the Des Moines and Raccoon Rivers during the 1993 flood in Des Moines and vicinity are higher than the respective Federal Emergency Management Agency 100- and 500-year flood profiles.

  11. Polydopamine-based surface modification of mesoporous silica nanoparticles as pH-sensitive drug delivery vehicles for cancer therapy.

    PubMed

    Chang, Danfeng; Gao, Yongfeng; Wang, Lijun; Liu, Gan; Chen, Yuhan; Wang, Teng; Tao, Wei; Mei, Lin; Huang, Laiqiang; Zeng, Xiaowei

    2016-02-01

    A novel pH-sensitive drug delivery system of mesoporous silica nanoparticles (MSNs) which were modified by polydopamine (PDA) for controlled release of cationic amphiphilic drug desipramine (DES) was prepared. MSNs-DES-PDA were characterized in terms of size, size distribution, surface morphology, BET surface area, mesoporous size and pore volume, drug loading content and in vitro drug release profile. MSNs-DES-PDA had high drug loading content and pH sensitivity. The DES release profiles of MSNs-DES and MSNs-DES-PDA were totally different, and the drug release of MSNs-DES-PDA accelerated with increasing acidity. MSNs-DES-PDA can be internalized into cells. In vitro experiments demonstrated that MSNs-DES-PDA had higher cytotoxicity and inhibitory effects on acid sphingomyelinase than those of free DES. This drug delivery system was beneficial for controlled release and cancer therapy. PMID:26550786

  12. A study into the role of surface capping on energy transfer in metal cluster-semiconductor nanocomposites

    NASA Astrophysics Data System (ADS)

    Bain, Dipankar; Paramanik, Bipattaran; Sadhu, Suparna; Patra, Amitava

    2015-12-01

    Metal cluster-semiconductor nanocomposite materials remain a frontier area of research for the development of optoelectronic, photovoltaic and light harvesting devices because metal nanoclusters and semiconductor QDs are promising candidates for photon harvesting. Here, we have designed well defined metal cluster-semiconductor nanostructures using different surface capped negatively charged Au25 nanoclusters (Au NCs) and positively charged cysteamine capped CdTe quantum dots using electrostatic interactions. The main focus of this article is to address the impact of surface capping agents on the photophysical properties of Au cluster-CdTe QD hybrid nanocomposites. Steady state and time resolved spectroscopic studies reveal that photoluminescence quenching, radiative and nonradiative rate, and energy transfer between Au nanoclusters and CdTe QDs have been influenced by the nature of the capping agent. We have calculated the energy transfer related parameters such as the overlap integral, distance between donor and acceptor, Förster distance, efficiency of energy transfer and rate of energy transfer from CdTe QDs to three different Au NCs. Photoluminescence quenching varies from 73% to 43% when changing the capping agents from bovine serum albumin (BSA) to glutathione (GSH). The efficiency of the energy transfer from CdTe QDs to BSA-capped Au NCs is found to be 83%, for Cys-capped Au NCs it was 46% and for GSH-capped Au NCs it was 35%. The efficiency depends on the number of Au clusters attached per QD. This reveals that the nature of capping ligands plays a crucial role in the energy transfer phenomena from CdTe QDs to Au NCs. Interesting findings reveal that the efficient energy transfer in metal cluster-semiconductor nanocomposites may open up new possibilities in designing artificial light harvesting systems for future applications.Metal cluster-semiconductor nanocomposite materials remain a frontier area of research for the development of optoelectronic

  13. Sorption behavior and modeling of endocrine-disrupting chemicals on natural sediments: role of biofilm covered on surface.

    PubMed

    Ding, Haixia; Li, Yi; Hou, Jun; Wang, Qing; Wu, Yue

    2015-01-01

    The surfaces of natural sediments are ubiquitously coated by biofilms that increase the content of organic matter in sediments. However, it is less understood whether the biofilms act as a sorbent or a barrier of mass transfer from water column to sediment phase. This study focused on the role of biofilms coverage on sediments in the sorption of bisphenol A (BPA), 17α-ethinyl estradiol (EE2), and 4-nonylphenols (4-NP) as model compounds for endocrine-disrupting chemicals (EDCs). The OC-normalized distribution coefficients (k OC) for BPA, EE2 and 4-NP ranged from 10(1.87) to 10(3.09) l/kg, the k OC of EE2 was slightly higher (10(2.23) l/kg) for sediment after H2O2 oxidation than before (10(1.93) l/kg). A two-stage model with a fast section and slow section was employed to describe the sorption process (r (2) > 0.95). The model results showed that the fast sorption section played a main role in the sorption process, while the slow section determined the extent of the reaction (the second-phase partition coefficient (k p2) ranged from 11.7 to 118.9 l/kg). The ratios of the mass transfer rate constant of the two stages for the natural sediment ranged from 6.0 to 7.2, which were somewhat lower than those for soil samples. These results indicated that the biofilm coverage on sediment may act as a barrier in mass transfer from water to sediment and scarcely increased the sorption capacity of sediments. PMID:25146118

  14. Critical role of surface chemical modifications induced by length shortening on multi-walled carbon nanotubes-induced toxicity

    PubMed Central

    2012-01-01

    Given the increasing use of carbon nanotubes (CNT) in composite materials and their possible expansion to new areas such as nanomedicine which will both lead to higher human exposure, a better understanding of their potential to cause adverse effects on human health is needed. Like other nanomaterials, the biological reactivity and toxicity of CNT were shown to depend on various physicochemical characteristics, and length has been suggested to play a critical role. We therefore designed a comprehensive study that aimed at comparing the effects on murine macrophages of two samples of multi-walled CNT (MWCNT) specifically synthesized following a similar production process (aerosol-assisted CVD), and used a soft ultrasonic treatment in water to modify the length of one of them. We showed that modification of the length of MWCNT leads, unavoidably, to accompanying structural (i.e. defects) and chemical (i.e. oxidation) modifications that affect both surface and residual catalyst iron nanoparticle content of CNT. The biological response of murine macrophages to the two different MWCNT samples was evaluated in terms of cell viability, pro-inflammatory cytokines secretion and oxidative stress. We showed that structural defects and oxidation both induced by the length reduction process are at least as responsible as the length reduction itself for the enhanced pro-inflammatory and pro-oxidative response observed with short (oxidized) compared to long (pristine) MWCNT. In conclusion, our results stress that surface properties should be considered, alongside the length, as essential parameters in CNT-induced inflammation, especially when dealing with a safe design of CNT, for application in nanomedicine for example. PMID:23181604

  15. A study into the role of surface capping on energy transfer in metal cluster-semiconductor nanocomposites.

    PubMed

    Bain, Dipankar; Paramanik, Bipattaran; Sadhu, Suparna; Patra, Amitava

    2015-12-28

    Metal cluster-semiconductor nanocomposite materials remain a frontier area of research for the development of optoelectronic, photovoltaic and light harvesting devices because metal nanoclusters and semiconductor QDs are promising candidates for photon harvesting. Here, we have designed well defined metal cluster-semiconductor nanostructures using different surface capped negatively charged Au25 nanoclusters (Au NCs) and positively charged cysteamine capped CdTe quantum dots using electrostatic interactions. The main focus of this article is to address the impact of surface capping agents on the photophysical properties of Au cluster-CdTe QD hybrid nanocomposites. Steady state and time resolved spectroscopic studies reveal that photoluminescence quenching, radiative and nonradiative rate, and energy transfer between Au nanoclusters and CdTe QDs have been influenced by the nature of the capping agent. We have calculated the energy transfer related parameters such as the overlap integral, distance between donor and acceptor, Förster distance, efficiency of energy transfer and rate of energy transfer from CdTe QDs to three different Au NCs. Photoluminescence quenching varies from 73% to 43% when changing the capping agents from bovine serum albumin (BSA) to glutathione (GSH). The efficiency of the energy transfer from CdTe QDs to BSA-capped Au NCs is found to be 83%, for Cys-capped Au NCs it was 46% and for GSH-capped Au NCs it was 35%. The efficiency depends on the number of Au clusters attached per QD. This reveals that the nature of capping ligands plays a crucial role in the energy transfer phenomena from CdTe QDs to Au NCs. Interesting findings reveal that the efficient energy transfer in metal cluster-semiconductor nanocomposites may open up new possibilities in designing artificial light harvesting systems for future applications. PMID:26603192

  16. Role of the Surface in Solid-Solid Phase Transitions: Molecular Dynamics Study of the α-γ Transition in Fe

    NASA Astrophysics Data System (ADS)

    Wang, Binjun; Urbassek, Herbert M.

    2016-05-01

    Using classical molecular dynamics simulation, we study the role of surfaces on solid-solid phase transformations. We contrast the transformation behavior of a thin film (two free surfaces) with a bulk system and with a system containing only one free surface. We focus on bcc Fe and induce the transformation from the bcc to the fcc phase by applying biaxial strain. We find that the critical strain at which the material transforms is independent of whether the system has a free surface or not. However, the nucleation mechanism of the new phase and also the transformation speed are strongly influenced by the existence of surfaces. While bulk systems fail early (after phase transformation to a polycrystal) under the applied load, systems with a free surface show a considerably higher ductility.

  17. Médecine des voyages

    PubMed Central

    Aw, Brian; Boraston, Suni; Botten, David; Cherniwchan, Darin; Fazal, Hyder; Kelton, Timothy; Libman, Michael; Saldanha, Colin; Scappatura, Philip; Stowe, Brian

    2014-01-01

    Résumé Objectif Définir la pratique de la médecine des voyages, présenter les éléments fondamentaux d’une consultation complète préalable aux voyages à des voyageurs internationaux et aider à identifier les patients qu’il vaudrait mieux envoyer en consultation auprès de professionnels de la médecine des voyages. Sources des données Les lignes directrices et les recommandations sur la médecine des voyages et les maladies liées aux voyages publiées par les autorités sanitaires nationales et internationales ont fait l’objet d’un examen. Une recension des ouvrages connexes dans MEDLINE et EMBASE a aussi été effectuée. Message principal La médecine des voyages est une spécialité très dynamique qui se concentre sur les soins préventifs avant un voyage. Une évaluation exhaustive du risque pour chaque voyageur est essentielle pour mesurer avec exactitude les risques particuliers au voyageur, à son itinéraire et à sa destination et pour offrir des conseils sur les interventions les plus appropriées en gestion du risque afin de promouvoir la santé et prévenir les problèmes médicaux indésirables durant le voyage. Des vaccins peuvent aussi être nécessaires et doivent être personnalisés en fonction des antécédents d’immunisation du voyageur, de son itinéraire et du temps qu’il reste avant son départ. Conclusion La santé et la sécurité d’un voyageur dépendent du degré d’expertise du médecin qui offre le counseling préalable à son voyage et les vaccins, au besoin. On recommande à ceux qui donnent des conseils aux voyageurs d’être conscients de l’ampleur de cette responsabilité et de demander si possible une consultation auprès de professionnels de la médecine des voyages pour tous les voyageurs à risque élevé.

  18. La prévention des blessures dans les terrains de jeux

    PubMed Central

    Fuselli, Pamela; Yanchar, Natalie L

    2012-01-01

    RÉSUMÉ Dans un climat d’inquiétude croissante à l’égard de l’obésité juvénile et de l’inactivité, les terrains de jeux permettent aux enfants d’être actifs. Ils comportent toutefois aussi des risques, les blessures causées par des chutes étant de loin les plus courants. Les recherches démontrent la possibilité de réduire les blessures dans les terrains de jeux si on abaisse la hauteur des structures de jeu et si on utilise des surfaces molles et profondes pour amortir les chutes. L’Association canadienne de normalisation a publié des normes volontaires qu’elle a mises à jour plusieurs fois pour tenir compte de ces risques. Afin de contribuer à les réduire, les parents peuvent respecter des stratégies simples. Le présent document de principes souligne le fardeau des blessures subies dans les terrains de jeux. Il procure également aux parents et aux dispensateurs de soins des occasions de réduire l’incidence et la gravité des blessures grâce à l’éducation et à la défense d’intérêts, ainsi que de mettre en œuvre des normes de sécurité probantes et des stratégies plus sécuritaires dans les terrains de jeux locaux. Enfin, il remplace le document de principes de la Société canadienne de pédiatrie publié en 2002 sur le sujet.

  19. Extrapolating surface structures to depth in transpressional systems: the role of rheology and convergence angle deduced from analogue experiments

    NASA Astrophysics Data System (ADS)

    Hsieh, Shang Yu; Neubauer, Franz; Cloetingh, Sierd; Willingshofer, Ernst; Sokoutis, Dimitrios

    2014-05-01

    thin and rheologically weaker layer in the middle of the brittle layer, deformation is distributed over more faults and the geometry of the fault zone below and above the weak zone shows significant differences, suggesting that the correlation of structures across a weak layer has to be supported by geophysical data, which help constraining the geometry of the deep part. This latter experiment has significantly similar phenomena in reality, such as few pressure ridges along Altyn fault. The experimental results underline the need to understand the role of the convergence angle and the influence of rheology on fault evolution, in order to connect between surface deformation and subsurface geometry. References Leever, K. A., Gabrielsen, R. H., Sokoutis, D., Willingshofer, E., 2011. The effect of convergence angle on the kinematic evolution of strain partitioning in transpressional brittle wedges: Insight from analog modeling and high-resolution digital image analysis. Tectonics, 30(2), TC2013. Molnar, P., Dayem, K.E., 2010. Major intracontinental strike-slip faults and contrasts in lithospheric strength. Geosphere, 6, 444-467.

  20. Evidence for the significant role of sea surface temperature distributions over remote tropical oceans in tropical cyclone intensity

    NASA Astrophysics Data System (ADS)

    Hegde, Anitha Kumari; Kawamura, Ryuichi; Kawano, Tetsuya

    2015-10-01

    The role of remote ocean sea surface temperature (SST) in regulating tropical cyclone (TC) characteristics has been examined by performing numerical experiments with a regional scale model. Model simulations have been carried out to simulate typhoon Man-yi (July 2007), in our case study, under a range of SST conditions over the Indian Ocean and the South China Sea. The intensity and track of the cyclone have been systematically changed in sensitivity simulations of cool and warm SSTs over that region, following its peak phase. Warm oceans can substantially reduce the intensification of western North Pacific cyclones, whereas cool oceans can enhance their strength. This is intimately associated with the enhancement/weakening of the moisture supply through the moisture conveyor belt (MCB) in the lower troposphere, from the Indian Ocean and South China Sea into the vicinity of the cyclone center. When the MCB is interrupted over the South China Sea in warm SST occurrences, the large-scale transport of moisture into the cyclone system is significantly reduced, leading to the weakening of the cyclone intensity and to the eastward shift of its track. This study shows that changes in remote tropical ocean SST can also modulate TCs and thus can help in improving the forecasting of TC intensities and tracks.

  1. The microbiome of coral surface mucus has a key role in mediating holobiont health and survival upon disturbance

    PubMed Central

    Glasl, Bettina; Herndl, Gerhard J; Frade, Pedro R

    2016-01-01

    Microbes are well-recognized members of the coral holobiont. However, little is known about the short-term dynamics of mucus-associated microbial communities under natural conditions and after disturbances, and how these dynamics relate to the host's health. Here we examined the natural variability of prokaryotic communities (based on 16S ribosomal RNA gene amplicon sequencing) associating with the surface mucus layer (SML) of Porites astreoides, a species exhibiting cyclical mucus aging and shedding. Shifts in the prokaryotic community composition during mucus aging led to the prevalence of opportunistic and potentially pathogenic bacteria (Verrucomicrobiaceae and Vibrionaceae) in aged mucus and to a twofold increase in prokaryotic abundance. After the release of aged mucus sheets, the community reverted to its original state, dominated by Endozoicimonaceae and Oxalobacteraceae. Furthermore, we followed the fate of the coral holobiont upon depletion of its natural mucus microbiome through antibiotics treatment. After re-introduction to the reef, healthy-looking microbe-depleted corals started exhibiting clear signs of bleaching and necrosis. Recovery versus mortality of the P. astreoides holobiont was related to the degree of change in abundance distribution of the mucus microbiome. We conclude that the natural prokaryotic community inhabiting the coral SML contributes to coral health and that cyclical mucus shedding has a key role in coral microbiome dynamics. PMID:26953605

  2. The microbiome of coral surface mucus has a key role in mediating holobiont health and survival upon disturbance.

    PubMed

    Glasl, Bettina; Herndl, Gerhard J; Frade, Pedro R

    2016-09-01

    Microbes are well-recognized members of the coral holobiont. However, little is known about the short-term dynamics of mucus-associated microbial communities under natural conditions and after disturbances, and how these dynamics relate to the host's health. Here we examined the natural variability of prokaryotic communities (based on 16S ribosomal RNA gene amplicon sequencing) associating with the surface mucus layer (SML) of Porites astreoides, a species exhibiting cyclical mucus aging and shedding. Shifts in the prokaryotic community composition during mucus aging led to the prevalence of opportunistic and potentially pathogenic bacteria (Verrucomicrobiaceae and Vibrionaceae) in aged mucus and to a twofold increase in prokaryotic abundance. After the release of aged mucus sheets, the community reverted to its original state, dominated by Endozoicimonaceae and Oxalobacteraceae. Furthermore, we followed the fate of the coral holobiont upon depletion of its natural mucus microbiome through antibiotics treatment. After re-introduction to the reef, healthy-looking microbe-depleted corals started exhibiting clear signs of bleaching and necrosis. Recovery versus mortality of the P. astreoides holobiont was related to the degree of change in abundance distribution of the mucus microbiome. We conclude that the natural prokaryotic community inhabiting the coral SML contributes to coral health and that cyclical mucus shedding has a key role in coral microbiome dynamics. PMID:26953605

  3. Role of polyphosphate kinase gene (ppk) for survival of Vibrio cholerae O1 in surface water of Bangladesh.

    PubMed

    Jahid, Iqbal Kabir; Hasan, Md Mahmud; Abdul Matin, Mohammad; Mahmud, Zahid Hayat; Neogi, Sucharit Basu; Uddin, Md Hafiz; Islam, Md Sirajul

    2013-11-15

    Polyphosphate provides a substitute for ATP and energy source when phosphorus is a limiting resource in nature. The present study focuses on the role ofpolyphosphate for the survival of Vibrio cholerae in the aquatic habitats as an autochthonous bacterium. The survival advantages of polyphosphate of V. cholerae O1 having (wild type) and lacking (mutant) polyphosphate kinase (ppk) gene in surface water and with Anabaena variabilis were compared by cultural, Direct Fluorescent Antibody (DFA) and polymerase chain reaction methods in natural water microcosms. The microcosm's water was prepared by filtering and physicochemical parameters were also investigated by standard methods. The results revealed that both fresh and saline water, the wild type strain enhanced survival in cultural conditioned than ppk mutant strain. However, Fluorescent Antibody Direct Viable Counts (FADVC) and Polymerase Chain Reaction (PCR) results noted both strains have the equal survival strategy in viable but nonculturable state (VNC). In conclusion, it could be hypothesized that the polyphosphate inclusion body might keep cultivable and survivable at low phosphate natural environment of the aquatic bacterium. PMID:24511696

  4. Role of surface charge and oxidative stress in cytotoxicity and genotoxicity of graphene oxide towards human lung fibroblast cells.

    PubMed

    Wang, Anxin; Pu, Kefeng; Dong, Bing; Liu, Yang; Zhang, Liming; Zhang, Zhijun; Duan, Wei; Zhu, Yimin

    2013-10-01

    Recently, attempts have been made to apply graphene oxide (GO) in the field of biology and medicine, such as DNA sensing and drug delivery with some necessary modifications. Therefore, the toxicity of GO must be evaluated before it is applied further in biomedicine. In this paper, the cytotoxicity and genotoxicity of GO to human lung fibroblast (HLF) cells have been assessed with methyl thiazolyl tetrazolium (MTT), sub-G1 measurement and comet assays, and the mechanism of its toxicity has been explored. Various modifications of GO have been made to help us determine the factors which could affect the toxicity of GO. The results indicated that cytotoxicity and genotoxicity of GO to HLF cells were concentration dependent, and the genotoxicity induced by GO was more severe than the cytotoxicity to HLF cells. Oxidative stress mediated by GO might explain the reason of its toxic effect. Furthermore, the electronic charge on the surface of GO would play a very important role in the toxicity of GO to HLF cells. PMID:23775274

  5. Evidence for the significant role of sea surface temperature distributions over remote tropical oceans in tropical cyclone intensity

    NASA Astrophysics Data System (ADS)

    Hegde, Anitha Kumari; Kawamura, Ryuichi; Kawano, Tetsuya

    2016-07-01

    The role of remote ocean sea surface temperature (SST) in regulating tropical cyclone (TC) characteristics has been examined by performing numerical experiments with a regional scale model. Model simulations have been carried out to simulate typhoon Man-yi (July 2007), in our case study, under a range of SST conditions over the Indian Ocean and the South China Sea. The intensity and track of the cyclone have been systematically changed in sensitivity simulations of cool and warm SSTs over that region, following its peak phase. Warm oceans can substantially reduce the intensification of western North Pacific cyclones, whereas cool oceans can enhance their strength. This is intimately associated with the enhancement/weakening of the moisture supply through the moisture conveyor belt (MCB) in the lower troposphere, from the Indian Ocean and South China Sea into the vicinity of the cyclone center. When the MCB is interrupted over the South China Sea in warm SST occurrences, the large-scale transport of moisture into the cyclone system is significantly reduced, leading to the weakening of the cyclone intensity and to the eastward shift of its track. This study shows that changes in remote tropical ocean SST can also modulate TCs and thus can help in improving the forecasting of TC intensities and tracks.

  6. Le contrôle des infections au cabinet du pédiatre

    PubMed Central

    2008-01-01

    RÉSUMÉ La transmission des infections au cabinet du pédiatre est de plus en plus préoccupante. Le présent document expose les voies de transmission des infections et les principes sous-jacents aux mesures actuelles pour contrôler les infections. Pour prévenir les infections, il faut bien concevoir le cabinet et adopter des politiques administratives et de triage convenables, de même que des pratiques de base pour les soins de tous les patients (p. ex., hygiène des mains, port de gants, de masques, de lunettes de protection et d’une blouse d’hôpital pour des interventions précises; nettoyage, désinfection et stérilisation convenables des surfaces et du matériel, y compris les jouets, et techniques d’asepsie en cas d’interventions effractives) et des précautions additionnelles en cas d’infections précises. Le personnel doit avoir reçu les vaccins pertinents, et les personnes infectées doivent respecter les politiques de restriction au travail.

  7. The role of free stream turbulence and blade surface conditions on the aerodynamic performance of wind turbine blades

    NASA Astrophysics Data System (ADS)

    Maldonado, Victor Hugo

    with a 24-grit abrasive sheet. The role of turbulence and surface roughness on the aerodynamic performance of the wind turbine blade was investigated utilizing the following experimental techniques: (i) static pressure measurements around the blade, (ii) constant temperature anemometry (CTA) hot-wire and pitottube measurements of the velocity deficit at the wake, and (iii) two-dimensional particle image velocimetry (2-D PIV) measurements of the mean global flow. Results indicate that turbulence significantly increases the blade's lift coefficient for moderate to post-stall angles of attack (where the range tested was from zero to 18 degrees). This was accompanied without an increase in the drag coefficient for angles of attack below 14 degrees (prior to stall) and a significant reduction in drag for post-stall angles of attack at 16 and 18 degrees. This resulted in considerable increases to the aerodynamic efficiency of the blade, as quantified by the lift to drag ratio, L/D for all angles of attack except zero degrees. Conversely, surface roughness had a detrimental effect on the aerodynamic performance, as verified by 2-D PIV measurements of the mean flow which indicates that surface roughness promotes flow separation. Vortex generators (which are a form of passive flow control and sometimes utilized in wind turbine blades to mitigate the adverse effects of surface roughness) were demonstrated to be very effective in restoring aerodynamic performance. There was a significant increase in the lift coefficient of the blade (while marginally reducing the drag coefficient) thereby increasing the L/D ratio drastically from 1.076 to 2.791 at 18 degrees angle of attack. Finally, earlier work focused on the feasibility of synthetic jets (active flow control) to improve the aerodynamic and aeroelastic performance of wind turbine blades without free stream turbulence or surface roughness. Wind turbine models (including S809 airfoil-based) demonstrated a re-attachment of the

  8. Role of crystallographic anisotropy in the formation of surface layers of single NiTi crystals after ion-plasma alloying

    SciTech Connect

    Poletika, T. M. Girsova, S. L.; Meisner, L. L. Meisner, S. N.; Shulepov, I. A.

    2015-10-27

    The structure of the surface and near-surface layers of single crystals of NiTi, differently oriented relative to the direction of ion beam treatment was investigated. The role of the crystallographic orientation in formation of structure of surface layers after ion-plasma alloying was revealed. It was found that the orientation effects of selective sputtering and channeling determine the thickness of the oxide and amorphous layers, the depth of penetration of ions and impurities, the distribution of Ni with depth.

  9. The role of aluminum surface alloying in improving the corrosion resistance of silicon nitride under the influence of sodium vapor

    NASA Astrophysics Data System (ADS)

    Cheong, Yong Suk

    Corrosion of silicon nitride (Sisb3Nsb4) and associated degradation processes can severely limit the performance and reliability of advanced engine and structural systems employing it as a key component. The corrosion resistance of Sisb3Nsb4 is adversely affected by sodium, a reactive species commonly present in many service environments. Despite a number of studies on the sodium-accelerated corrosion, few attempts have been made to reduce the adverse effects of sodium on the corrosion resistance of Sisb3Nsb4. This work aimed to investigate the detailed role of aluminum surface alloying in minimizing the detrimental effect of sodium on the corrosion behavior of Sisb3Nsb4. Ion implantation was used as an alloying tool and pure hot-isostatically-pressed Sisb3Nsb4 as a base material. Surface regions (˜200nm) of highly polished Sisb3Nsb4 platelets were implanted with aluminum at multi-energies and multi-doses to achieve a uniform concentration distribution of 1, 5, and 10 at.%. Unimplanted and implanted Sisb3Nsb4 samples were exposed in atmospheric pressure oxygen enriched with 100 and 220 ppm sodium nitrate vapor at 900sp°-1100sp°C for 0.5 to 8 hours. Kinetics of corrosion were evaluated using profilometry in conjunction with etch patterning. The morphological, structural, and chemical characteristics of the corrosion layers were studied using various analytical techniques which include x-ray diffraction, secondary electron microscopy, atomic absorption analysis, Raman spectroscopy, and secondary ion mass spectroscopy. This investigation has shown that, under the influence of sodium, corrosion of unimplanted Sisb3Nsb4 follows a rapid and linear kinetic law. The corrosion layers are non-protective and rough. They also exhibit a high degree of morphological and phase instability, which can be attributed to increased thermodynamic and kinetic tendency towards the formation of low eutectic products, phase separation, and devitrification in the corrosion layer. Aluminum

  10. Effects of the surface mobility on the oxidation of adsorbed CO on platinum electrodes in alkaline media. The role of the adlayer and surface defects.

    PubMed

    Herrero, Enrique; Chen, Qing-Song; Hernández, Javier; Sun, Shi-Gang; Feliu, Juan M

    2011-10-01

    The oxidation of adsorbed CO on Pt single crystal electrodes has been studied in alkaline media. The surfaces used in this study were the Pt(111) electrode and vicinal stepped and kinked surfaces with (111) terraces. The kinked surfaces have either (110) steps broken by (100) kinks or (100) steps broken by (110) kinks and different kink densities. The voltammetric profiles for the CO stripping on those electrodes show peaks corresponding to the oxidation of CO on the (111) terraces, on the (100) steps/kinks and on the (110) steps/kinks at very distinctive potentials. Additionally, the stripping voltammograms always present a prewave. The analysis of the results with the different stepped and kinked surfaces indicates that the presence of the prewave is not associated with defects or kinks in the electrode surface. Also, the clear separation of the CO stripping process in different peak contributions indicates that the mobility of CO on the surface is very low. Using partial CO stripping experiments and studies at different pH, it has been proposed that the low mobility is a consequence of the negative absolute potential at which the adlayers are formed in alkaline media. Also, the surface diffusion coefficient for CO in these media has been estimated from the dependence of the stripping charge of the peaks with the scan rate of the voltammetry. PMID:21863178

  11. The role of large-scale atmospheric circulation in the formation of temperature anomalies in surface waters as illustrated by the northern part of the Pacific Ocean

    NASA Technical Reports Server (NTRS)

    Sorkina, A. I.

    1975-01-01

    One important reason for thermal anomalies in the ocean is the dynamic action of anomalous wind systems that set masses of surface water in motion; predominant longitudinal transport of water and air leads to a significant redistribution of cold and warm waters. Heat exchange between the ocean and atmosphere plays an additional role in the formation of water temperature anomalies.

  12. Role of silicon hydride bonding environment in alpha-silicon:hydrogen films for c-silicon surface passivation

    NASA Astrophysics Data System (ADS)

    Burrows, Michael Z.

    High efficiency silicon solar cells achieve greater than 700 mV open circuit voltage through excellent surface passivation of the monocyrstalline absorber. This work studies the bifacial plasma enhanced chemical vapor deposited (PECVD) intrinsic amorphous silicon ((i) alpha-Si:H) passivation structure. To enable the correct interpretation of FTIR detected vibrational modes a model of the layered substructure of ultra-thin (i) alpha-Si:H is constructed. A high fraction of di-hydride bonding is associated with defective, low density amorphous film, and control of this parameter is established by varying hydrogen dilution ratio. The hypothesis that a high fraction of di-hydride bonding over mono-hydride within the film would lead to a poor passivation layer is tested and shown to be false. This is due to the bulk layer within the model defining the di-hydride fraction and indicates that the interface layer plays the more dominant role. A comparison between rf plasma PECVD deposited films and dc plasma shows that upon 30 min, 285°C annealing, large improvements in passivation occur when dc plasma was used with gains in minority carrier effective lifetimes over 1 msec possible. The passivation quality of rf generated films is less effected by annealing. rf plasma films show detectable mono-, di-, and tri-hydride high-potential modes in the as-deposited condition that are removed upon annealing. The finite loss of bulk mono-hydride and these interfacial hydrides do not have a strong impact on film passivation quality. It is concluded that the film has reached an equilibrium level of interfacial defect density which is unaffected by the limited loss of hydride bonding observed. dc plasma films undergo large improvements in passivation quality upon annealing. An increase in mono-hydride bonding at the internal surfaces of nanometer sized voids is detected. It is proposed that this mono-hydride bonding is reducing the density of unsaturated bonds, lowering the interfacial

  13. Prise en compte des ``courants de London'' dans la modélisation des supraconducteurs

    NASA Astrophysics Data System (ADS)

    Bossavit, Alain

    1997-10-01

    A model is given, in variational form, in which volumic “Bean currents”, ruled by Bean's law, and surface “London currents” coexist. This macroscopic model generalizes Bean's one, by appending to the critical density j_c a second parameter, with the dimension of a length, similar to London's depth λ. The one-dimensional version of the model is investigated, in order to link this parameter with the standard observable H-M characteristics On propose un modèle, sous forme variationnelle, associant des “courants de Bean” volumiques, décrits par la loi de Bean, et des “courants de London”, surfaciques. Ce modèle macroscopique généralise celui de Bean, caractérisé par le courant critique j_c, et fait intervenir un second paramètre, homogène à une longueur, analogue au λ de London. La version unidimensionnelle du modèle est étudiée en détail de manière à relier ce paramètre à l'observation des caractéristiques H-M usuelles.

  14. Possible Role of a Cell Surface Carbohydrate in Evolution of Resistance to Viral Infections in Old World Primates

    PubMed Central

    Rodriguez, Idalia A.

    2013-01-01

    Due to inactivation of the α1,3-galactosyltransferase gene (GGTA1, or the α1,3GT gene) approximately 28 million years ago, the carbohydrate αGal (Galα1,3Galβ1,4GlcNAc) is not expressed on the cells of Old World monkeys and apes (including humans) but is expressed in all other mammals. The proposed selective advantage of this mutation for these primates is the ability to produce anti-Gal antibodies, which may be an effective immune component in neutralizing αGal-expressing pathogens. However, loss of α1,3GT expression may have been advantageous by providing natural resistance against viral pathogens that exploited the α1,3GT pathway or cell surface αGal for infection. Infections of paired cell lines with differential expression of α1,3GT showed that Sindbis viruses (SINV) preferentially replicate in α1,3GT-positive cells, whereas herpes simplex viruses type 1 and type 2 (HSV-1 and HSV-2) preferentially grow in cells lacking α1,3GT. Viral growth and spread correlated with the ability of the different viruses to successfully initiate infection in the presence or absence of α1,3GT expression. GT knockout (KO) suckling mice infected with SINV strains (AR339 and S.A.AR86) experienced significant delay in onset of disease symptoms and mortality compared to wild-type (WT) B6 suckling mice. In contrast, HSV-2-infected GT KO mice had higher viral titers in spleen and liver and exhibited significantly more focal hepatic necrosis than WT B6 mice. This study demonstrates that α1,3GT activity plays a role in the course of infections for certain viruses. Furthermore, this study has implications for the evolution of resistance to viral infections in primates. PMID:23740988

  15. Lessons learnt from the Indian Ocean Tsunami 2004: the role of surface and subsurface topography in deep water tsunami propagation

    NASA Astrophysics Data System (ADS)

    Pattiaratchi, C. B.

    2014-12-01

    The Indian Ocean experienced its most devastating natural disaster through the action of a Tsunami, resulting from of an earthquake off the coast of Sumatra on 26th of December 2004. This resulted in widespread damage both to property and human lives with over 250,000 deaths in the region and many millions homeless. Our understanding of tsunami generation and propagation has increased significantly over the past decade. In this presentation, results obtained from detailed analysis of sea level data from Western Australia and Sri Lanka together with numerical modelling are presented to highlight the effects of topography both at the surface and subsurface. The major effects are due to wave reflection and refraction. Examples of wave reflection include: impacts on Malaysia/Thailand, Sri Lanka and Western Australia due to wave reflection from Sri Lanka, Maldives and Mascarene Ridge, respectively. In the case of Sri Lanka, the maximum wave height recorded along the west coast during the 2004 tsunami was due to the reflected wave from Maldives impacting 3 hours after the arrival of the initial waves. Similarly, along the West coast of Australia highest waves occurred 15 hours after the arrival of the first wave. Here, based on travel times, we postulate that the waves were reflected from the Mascarene Ridge and/or the island of Madagascar (Figure 1b). The conclusions based on observations were verified using numerical model simulations using the MOST and ComMIT models. Numerical modelling using the MOST model indicated the role of offshore susurface topography on tsunami propagation through wave wave refraction. Examples of wave refraction included the effects of deep water seamounts (Venin Meinesz) and plateaus (Wallaby, Cuvier and Exmouth) on tsunami propagation along the West Australian coast. The tsunami waves are first scattered by the Venin Meinesz seamounts and were then refracted by the Wallaby and Cuvier plateaus resulting in waves being deflected onto the

  16. Dual oncogenic and tumor suppressor roles of the promyelocytic leukemia gene in hepatocarcinogenesis associated with hepatitis B virus surface antigen.

    PubMed

    Chung, Yih-Lin; Wu, Mei-Ling

    2016-05-10

    Proteasome-mediated degradation of promyelocytic leukemia tumor suppressor (PML) is upregulated in many viral infections and cancers. We previously showed that PML knockdown promotes early-onset hepatocellular carcinoma (HCC) in hepatitis B virus surface antigen (HBsAg)-transgenic mice. Here we report the effects of PML restoration on late-onset HBsAg-induced HCC. We compared protein expression patterns, genetic mutations and the effects of pharmacologically targeting PML in wild-type, PML-/-, PML+/+HBsAgtg/o and PML-/-HBsAgtg/o mice. PML-/- mice exhibited somatic mutations in DNA repair genes and developed severe steatosis and proliferative disorders, but not HCC. PML-/-HBsAgtg/o mice exhibited early mutations in cancer driver genes and developed hyperplasia, fatty livers and indolent adipose-like HCC. In PML+/+HBsAg-transgenic mice, HBsAg expression declined over time, and HBsAg-associated PML suppression was concomitantly relieved. Nevertheless, these mice accumulated mutations in genes contributing to oxidative stress pathways and developed aggressive late-onset angiogenic trabecular HCC. PML inhibition using non-toxic doses of arsenic trioxide selectively killed long-term HBsAg-affected liver cells in PML+/+HBsAgtg/o mice with falling HBsAg and rising PML levels, but not normal liver cells or early-onset HCC cells in PML-/-HBsAgtg/0 mice. These findings suggest dual roles for PML as a tumor-suppressor lost in early-onset HBsAg-induced hepatocarcinogenesis and as an oncogenic promoter in late-onset HBsAg-related HCC progression. PMID:27058621

  17. Surface plasmon-polariton propagation in piecewise linear chains of composite nanospheres: the role of optical gain and chain layout.

    PubMed

    Udagedara, Indika B; Rukhlenko, Ivan D; Premaratne, Malin

    2011-10-10

    The energy transport properties of plasmonic waveguides can be analyzed by solving the dispersion relation for surface plasmon-polaritons (SPPs). We use this approach to derive an approximate analytical expression for SPP propagation length when the waveguide is composed of linearly arranged metallic nanoparticles, while assuming that metal losses are small or partially compensated by gain. Applied to metal-dielectric (composite) nanospheres, the obtained expression allows us to optimize the performance of the waveguide and arrive at a number of practical design rules. Specifically, we show that SPP attenuation can be minimized at a certain interparticle distance for transverse modes, but gradually grows for both longitudinal and transverse modes with the increase of particle separation. We also show that the two basic methods of supplying gain to the system, i.e., embedding the particles into a gain medium or having a metal-gain composition for the particles, do not perform equally well and the former method is more efficient, but the way the two methods affect depends on the polarization of SPPs. To investigate the role of the nanoparticles' arrangement in determining SPP characteristics, we follow a purely numerical approach and consider a two-segment bent waveguide as an example. Analyzing the waveguide's transmission shows that it behaves in an oscillatory manner with respect to the angle between the two segments and is therefore higher for certain angles than for the others. This suggests that, in the design of waveguides with bends, careful attention needs to be paid in order to avoid bend angles that yield low transmission and to choose angles that give maximum transmission. PMID:21997007

  18. Role of surface lysine residues of adipocyte fatty acid-binding protein in fatty acid transfer to phospholipid vesicles.

    PubMed

    Liou, H L; Storch, J

    2001-05-29

    The tertiary structure of murine adipocyte fatty acid-binding protein (AFABP) is a flattened 10-stranded beta-barrel capped by a helix-turn-helix segment. This helical domain is hypothesized to behave as a "lid" or portal for ligand entry into and exit from the binding cavity. Previously, we demonstrated that anthroyloxy-labeled fatty acid (AOFA) transfer from AFABP to phospholipid membranes occurs by a collisional process, in which ionic interactions between positively charged lysine residues on the protein surface and negatively charged phospholipid headgroups are involved. In the present study, the role of specific lysine residues located in the portal and other regions of AFABP was directly examined using site-directed mutagenesis. The results showed that isoleucine replacement for lysine in the portal region, including the alphaI- and alphaII-helices and the beta C-D turn, resulted in much slower 2-(9-anthroyloxy)palmitate (2AP) transfer rates to acidic membranes than those of native AFABP. An additive effect was found for mutant K22,59I, displaying the slowest rates of FA transfer. Rates of 2AP transfer from "nonportal" mutants on the beta-G and I strands were affected only moderately; however, a lysine --> isoleucine mutation in the nonportal beta-A strand decreased the 2AP transfer rate. These studies suggest that lysines in the helical cap domain are important for governing ionic interactions between AFABP and membranes. Furthermore, it appears that more than one distinct region, including the alphaI-helix, alphaII-helix, beta C-D turn, and the beta-A strand, is involved in these charge-charge interactions. PMID:11371211

  19. An extensive computational study of the adsorption of thiophene on transition metal surfaces: role of van der Waals

    NASA Astrophysics Data System (ADS)

    Rojas, Tomas; Kara, Abdelkader

    2014-03-01

    Van der Waals (vdWs) interactions play a significant role in the determination of the adsorption characteristics at the interface between a molecule and a substrate. In this study, self-consistent inclusion of vdW interactions in density functional theory provides a good perspective to understand the interaction between organic adsorbates and inorganic interfaces. We present the results of adsorption of thiophene (C4H4S) on various transition metal surfaces with the goal of comparing the performance of five different vdW functionals (optB86, optB88, optPBE, revPBE, rPW86). Seven metallic substrates (100) are used for our study; three coinage metals (Au, Ag, Cu) and four reactive metals (Pt, Pd, Rh, Ni). The results show that vdWs inclusion enhances the interaction for Ag (0.08 to 0.73 eV), Au (0.14 to 0.86 eV), Cu (0.12 eV to 0.77 eV), Ni(1.56 to 2.34 eV), Pt (1.6 to 2.51 eV), Pd (1.67 to 2.54), Rh (1.74 to 2.96 eV). In addition, we performed calculations for adsorption heights along with analysis of the electronic changes (charge transfer, changes in the d-band of the substrate, and change in the work function) to complement our understanding of these systems. This work is funded by the U.S. Department of Energy Basic Energy Science under Contract No DE-FG02-11ER16243.

  20. Composition of the Surface Proteome of Anaplasma marginale and Its Role in Protective Immunity Induced by Outer Membrane Immunization

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Surface proteins of tick-borne, intracellular bacterial pathogens mediate functions essential for invasion and colonization. Consequently, the surface proteome of these organisms is specifically relevant from two biological perspectives, induction of protective immunity in the mammalian host and un...

  1. Surface photochemistry of adsorbed nitrate: the role of adsorbed water in the formation of reduced nitrogen species on α-Fe2O3 particle surfaces.

    PubMed

    Nanayakkara, Charith E; Jayaweera, Pradeep M; Rubasinghege, Gayan; Baltrusaitis, Jonas; Grassian, Vicki H

    2014-01-01

    The surface photochemistry of nitrate, formed from nitric acid adsorption, on hematite (α-Fe2O3) particle surfaces under different environmental conditions is investigated using X-ray photoelectron spectroscopy (XPS). Following exposure of α-Fe2O3 particle surfaces to gas-phase nitric acid, a peak in the N1s region is seen at 407.4 eV; this binding energy is indicative of adsorbed nitrate. Upon broadband irradiation with light (λ > 300 nm), the nitrate peak decreases in intensity as a result of a decrease in adsorbed nitrate on the surface. Concomitant with this decrease in the nitrate coverage, there is the appearance of two lower binding energy peaks in the N1s region at 401.7 and 400.3 eV, due to reduced nitrogen species. The formation as well as the stability of these reduced nitrogen species, identified as NO(-) and N(-), are further investigated as a function of water vapor pressure. Additionally, irradiation of adsorbed nitrate on α-Fe2O3 generates three nitrogen gas-phase products including NO2, NO, and N2O. As shown here, different environmental conditions of water vapor pressure and the presence of molecular oxygen greatly influence the relative photoproduct distribution from nitrate surface photochemistry. The atmospheric implications of these results are discussed. PMID:24299394

  2. Roles of oxygen for methanol adsorption on polycrystalline copper surface revealed by sum frequency generation imaging microscopy

    NASA Astrophysics Data System (ADS)

    Fang, Ming; Santos, Greggy; Chen, Xiaole; Baldelli, Steven

    2016-06-01

    The adsorption of atmospheric pressure methanol on the polycrystalline copper surface has been studied by a combination of sum frequency generation imaging microscopy (SFGIM) and temperature programmed desorption (TPD). Methoxy species can be generated by exposing the polycrystalline copper surface to methanol vapor at room temperature. SFGIM results demonstrate that oxygen promotes the surface adsorption of methanol and the increase in the amount of methoxy produced on copper surface. SFGIM orientation analysis suggests the methoxy monolayer is oriented closer to the surface normal with introduction of oxygen. Employing the image statistical analysis approach, the heterogeneities and conformation distribution of methoxy monolayers on copper surface with and without oxygen adsorption are compared. These results illustrate SFGIM indeed could provide more insight for understanding the heterogeneous metal/metal oxide surface in the molecular level.

  3. Role of prostate apoptosis response 4 in translocation of GRP78 from the endoplasmic reticulum to the cell surface of trophoblastic cells.

    PubMed

    Cohen, Marie; Ribaux, Pascale; Epiney, Manuella; Irion, Olivier

    2013-01-01

    Glucose-regulated protein 78 (GRP78) is an endoplasmic reticulum (ER) molecular chaperone that belongs to the heat shock protein 70 family. GRP78 is also present on the cell surface membrane of trophoblastic cells, where it is associated with invasive or fusion properties of these cells. Impaired mechanism of GRP78 relocation from ER to the cell surface was observed in preeclamptic cytotrophoblastic cells (CTB) and could take part in the pathogenesis of preeclampsia. In this study, we have investigated whether prostate apoptosis response 4 (Par-4), a protein identified as a partner of GRP78 relocation to the cell surface in prostate cancer cells, is present in trophoblastic cells and is involved in the translocation of GRP78 to the cell surface of CTB. Par-4 is indeed present in trophoblastic cells and its expression correlates with expression of membrane GRP78. Moreover, overexpression of Par-4 led to an increase of cell surface expression of GRP78 and decreased Par-4 gene expression reduced cell surface localization of GRP78 confirming a role of Par-4 in relocation of GRP78 from ER to the cell surface. Accordingly, invasive property was modified in these cells. In conclusion, we show that Par-4 is expressed in trophoblastic cells and is involved in transport of GRP78 to the cell surface and thus regulates invasive property of extravillous CTB. PMID:24282526

  4. NMR solution structure of the glucagon antagonist [desHis1, desPhe6, Glu9]glucagon amide in the presence of perdeuterated dodecylphosphocholine micelles.

    PubMed

    Ying, Jinfa; Ahn, Jung-Mo; Jacobsen, Neil E; Brown, Michael F; Hruby, Victor J

    2003-03-18

    Glucagon, a 29-residue peptide hormone, plays an important role in glucose homeostasis and in diabetes mellitus. Several glucagon antagonists and agonists have been developed, but limited structural information is available to clarify the basis of their biological activity. The solution structure of the potent glucagon antagonist, [desHis1, desPhe6, Glu9]glucagon amide, was determined by homonuclear 2D NMR spectroscopy at pH 6.0 and 37 degrees C in perdeuterated dodecylphosphocholine micelles. The overall backbone root-mean-square deviation (rmsd) for the structured portion (residues 7-29, glucagon numbering) of the micelle-bound 27-residue peptide is 1.36 A for the 15 lowest-energy structures, after restrained molecular dynamics simulation. The structure consists of four regions (segment backbone rmsd in A): an unstructured N-terminal segment between residues 2 and 5 (1.68), an irregular helix between residues 7 and 14 (0.79), a hinge region between residues 15 and 18 (0.54), and a well-defined alpha-helix between residues 19 and 29 (0.33). The two helices form an L-shaped structure with an angle of about 90 degrees between the helix axes. There is an extended hydrophobic cluster, which runs along the inner surface of the L-structure and incorporates the side chains of the hydrophobic residues of each of the amphipathic helices. The outer surface contains the hydrophilic side chains, with two salt bridges (D15-R18 and R17-D21) implied from close approach of the charged groups. This result is the first clear indication of an overall tertiary fold for a glucagon analogue in the micelle-bound state. The relationship of the two helical structural elements may have important implications for the biological activity of the glucagon antagonist. PMID:12627948

  5. Role of Glucosyltransferase B in Interactions of Candida albicans with Streptococcus mutans and with an Experimental Pellicle on Hydroxyapatite Surfaces ▿ †

    PubMed Central

    Gregoire, S.; Xiao, J.; Silva, B. B.; Gonzalez, I.; Agidi, P. S.; Klein, M. I.; Ambatipudi, K. S.; Rosalen, P. L.; Bauserman, R.; Waugh, R. E.; Koo, H.

    2011-01-01

    Candida albicans and mutans streptococci are frequently detected in dental plaque biofilms from toddlers afflicted with early childhood caries. Glucosyltransferases (Gtfs) secreted by Streptococcus mutans bind to saliva-coated apatite (sHA) and to bacterial surfaces, synthesizing exopolymers in situ, which promote cell clustering and adherence to tooth enamel. We investigated the potential role Gtfs may play in mediating the interactions between C. albicans SC5314 and S. mutans UA159, both with each other and with the sHA surface. GtfB adhered effectively to the C. albicans yeast cell surface in an enzymatically active form, as determined by scintillation spectroscopy and fluorescence imaging. The glucans formed on the yeast cell surface were more susceptible to dextranase than those synthesized in solution or on sHA and bacterial cell surfaces (P < 0.05), indicating an elevated α-1,6-linked glucose content. Fluorescence imaging revealed that larger numbers of S. mutans cells bound to C. albicans cells with glucans present on their surface than to yeast cells without surface glucans (uncoated). The glucans formed in situ also enhanced C. albicans interactions with sHA, as determined by a novel single-cell micromechanical method. Furthermore, the presence of glucan-coated yeast cells significantly increased the accumulation of S. mutans on the sHA surface (versus S. mutans incubated alone or mixed with uncoated C. albicans; P < 0.05). These data reveal a novel cross-kingdom interaction that is mediated by bacterial GtfB, which readily attaches to the yeast cell surface. Surface-bound GtfB promotes the formation of a glucan-rich matrix in situ and may enhance the accumulation of S. mutans on the tooth enamel surface, thereby modulating the development of virulent biofilms. PMID:21803906

  6. Peste des petits ruminants

    PubMed Central

    Parida, S.; Muniraju, M.; Mahapatra, M.; Muthuchelvan, D.; Buczkowski, H.; Banyard, A.C.

    2015-01-01

    Peste des petits ruminants virus causes a highly infectious disease of small ruminants that is endemic across Africa, the Middle East and large regions of Asia. The virus is considered to be a major obstacle to the development of sustainable agriculture across the developing world and has recently been targeted by the World Organisation for Animal Health (OIE) and the Food and Agriculture Organisation (FAO) for eradication with the aim of global elimination of the disease by 2030. Fundamentally, the vaccines required to successfully achieve this goal are currently available, but the availability of novel vaccine preparations to also fulfill the requisite for differentiation between infected and vaccinated animals (DIVA) may reduce the time taken and the financial costs of serological surveillance in the later stages of any eradication campaign. Here, we overview what is currently known about the virus, with reference to its origin, updated global circulation, molecular evolution, diagnostic tools and vaccines currently available to combat the disease. Further, we comment on recent developments in our knowledge of various recombinant vaccines and on the potential for the development of novel multivalent vaccines for small ruminants. PMID:26443889

  7. Competition between Displacement and Dissociation of a Strong Acid Compared to a Weak Acid Adsorbed on Silica Particle Surfaces: The Role of Adsorbed Water.

    PubMed

    Fang, Yuan; Tang, Mingjin; Grassian, Vicki H

    2016-06-16

    The adsorption of nitric (HNO3) and formic (HCOOH) acids on silica particle surfaces and the effect of adsorbed water have been investigated at 296 K using transmission FTIR spectroscopy. Under dry conditions, both nitric and formic acids adsorb reversibly on silica. Additionally, the FTIR spectra show that both of these molecules remain in the protonated form. At elevated relative humidities (RH), adsorbed water competes both for surface adsorption sites with these acids as well as promotes their dissociation to hydronium ions and the corresponding anions. Compared to HNO3, the extent of dissociation is much smaller for HCOOH, very likely because it is a weaker acid. This study provides valuable insights into the interaction of HNO3 and HCOOH with silica surface on the molecular level and further reveals the complex roles of surface-adsorbed water in atmospheric heterogeneous chemistry of mineral dust particles-many of these containing silica. PMID:27220375

  8. Formation versus Hydrolysis of the Peptide Bond from a Quantum-mechanical Viewpoint: The Role of Mineral Surfaces and Implications for the Origin of Life

    PubMed Central

    Rimola, Albert; Ugliengo, Piero; Sodupe, Mariona

    2009-01-01

    The condensation (polymerization by water elimination) of molecular building blocks to yield the first active biopolymers (e.g. of amino acids to form peptides) during primitive Earth is an intriguing question that nowadays still remains open since these processes are thermodynamically disfavoured in highly dilute water solutions. In the present contribution, formation and hydrolysis of glycine oligopeptides occurring on a cluster model of sanidine feldspar (001) surface have been simulated by quantum mechanical methods. Results indicate that the catalytic interplay between Lewis and Brønsted sites both present at the sanidine surface, in cooperation with the London forces acting between the biomolecules and the inorganic surface, plays a crucial role to: i) favour the condensation of glycine to yield oligopeptides as reaction products; ii) inhibit the hydrolysis of the newly formed oligopeptides. Both facts suggest that mineral surfaces may have helped in catalyzing, stabilizing and protecting from hydration the oligopeptides formed in the prebiotic era. PMID:19399219

  9. The role of surface charge and hydrophobicity in the attachment of Anoxybacillus flavithermus isolated from milk powder.

    PubMed

    Palmer, J S; Flint, S H; Schmid, J; Brooks, J D

    2010-11-01

    The aim of the present study was to investigate the attachment mechanisms that enable the thermophile Anoxybacillus flavithermus (B12) to attach to stainless-steel surfaces. Passing a B12 culture through a column of stainless-steel chips, collecting the first cells to pass through, re-culturing, and repeating the process six times, resulted in the isolation of a mutant, labeled X7, with tenfold reduced ability to attach to stainless steel as well as a reduced ability to attach to plastic. A comparison of bacterial cell-surface properties indicated that X7 was less hydrophobic than its parental strain B12. Cell-surface charge measurements also suggest that X7 had a lower net-negative surface charge. Disruption of extracellular polysaccharides and DNA appeared to have no effect on the attachment process. Removal of surface proteins caused a reduction in attachment of both B12 and X7, suggesting surface protein involvement in attachment. PMID:20574738

  10. The role of hydrologic variability in the delivery of dissolved organic carbon and nitrogen to surface water

    NASA Astrophysics Data System (ADS)

    Martin, R. A.; Harrison, J.

    2011-12-01

    Hydrologic connectivity expands and contracts within watersheds as moisture conditions change, with implications for in-stream water quality. Dissolved organic carbon (DOC) concentration has been shown to increase in streams during high flow events, presumably as sources of DOC in side-channels, riparian soils, and/or uplands are mobilized and transported to surface water. Dissolved organic nitrogen (DON) has been less well studied, but behavior of DON is often assumed to mirror that of DOC. However, because DOC- and DON-rich pools of organic matter may be mobilized at different times, and because DOC and DON may undergo unbalanced abiotic and biotic processing along flowpaths, there is reason to suspect that DOC and DON respond divergently to high flow events. We use a meta-analysis to address the following questions: 1) To what extent do high flow events affect in-stream DON concentration? And 2) To what extent are DOC and DON concentrations decoupled during these events? Across 47 systems that included 78 high flow events, flow-weighted mean DON concentration increased, on average, 1.58-fold from baseflow to high flow, with a maximum increase of 9.5-fold. DOC and DON exhibited a complex relationship, with DOC and DON concentrations peaking at different times in over half of the events, and molar DOC:DON ratios varying, on average, 4-fold during high flow. An intensive field investigation of a tile-drained agricultural system in eastern Washington indicates that DOC and DON concentrations increase in tile drain discharge during winter runoff relative to baseflow, consistent with the mobilization of novel sources of DOM. However, DOM characteristics, including DOC and DON concentrations, DOC:DON, and fluorescence indices, of tile drain discharge can vary widely from potential sources identified in the watershed (ground water, soil water). For example, during a base flow period, DOC:DON was 41 in ground water, 24 in water-extractable soil organic matter, but only 1

  11. THY-1 Cell Surface Antigen (CD90) Has an Important Role in the Initial Stage of Human Cytomegalovirus Infection.

    PubMed

    Li, Qingxue; Wilkie, Adrian R; Weller, Melodie; Liu, Xueqiao; Cohen, Jeffrey I

    2015-07-01

    Human cytomegalovirus (HCMV) infects about 50% of the US population, is the leading infectious cause of birth defects, and is considered the most important infectious agent in transplant recipients. The virus infects many cell types in vivo and in vitro. While previous studies have identified several cellular proteins that may function at early steps of infection in a cell type dependent manner, the mechanism of virus entry is still poorly understood. Using a computational biology approach, correlating gene expression with virus infectivity in 54 cell lines, we identified THY-1 as a putative host determinant for HCMV infection in these cells. With a series of loss-of-function, gain-of-function and protein-protein interaction analyses, we found that THY-1 mediates HCMV infection at the entry step and is important for infection that occurs at a low m.o.i. THY-1 antibody that bound to the cell surface blocked HCMV during the initial 60 minutes of infection in a dose-dependent manner. Down-regulation of THY-1 with siRNA impaired infectivity occurred during the initial 60 minutes of inoculation. Both THY-1 antibody and siRNA inhibited HCMV-induced activation of the PI3-K/Akt pathway required for entry. Soluble THY-1 protein blocked HCMV infection during, but not after, virus internalization. Expression of exogenous THY-1 enhanced entry in cells expressing low levels of the protein. THY-1 interacted with HCMV gB and gH and may form a complex important for entry. However, since gB and gH have previously been shown to interact, it is uncertain if THY-1 directly binds to both of these proteins. Prior observations that THY-1 (a) interacts with αVβ3 integrin and recruits paxillin (implicated in HCMV entry), (b) regulates leukocyte extravasation (critical for HCMV viremia), and (c) is expressed on many cells targeted for HCMV infection including epithelial and endothelial cells, fibroblast, and CD34+/CD38- stem cells, all support a role for THY-1 as an HCMV entry mediator in

  12. THY-1 Cell Surface Antigen (CD90) Has an Important Role in the Initial Stage of Human Cytomegalovirus Infection

    PubMed Central

    Li, Qingxue; Wilkie, Adrian R.; Weller, Melodie; Liu, Xueqiao; Cohen, Jeffrey I.

    2015-01-01

    Human cytomegalovirus (HCMV) infects about 50% of the US population, is the leading infectious cause of birth defects, and is considered the most important infectious agent in transplant recipients. The virus infects many cell types in vivo and in vitro. While previous studies have identified several cellular proteins that may function at early steps of infection in a cell type dependent manner, the mechanism of virus entry is still poorly understood. Using a computational biology approach, correlating gene expression with virus infectivity in 54 cell lines, we identified THY-1 as a putative host determinant for HCMV infection in these cells. With a series of loss-of-function, gain-of-function and protein-protein interaction analyses, we found that THY-1 mediates HCMV infection at the entry step and is important for infection that occurs at a low m.o.i. THY-1 antibody that bound to the cell surface blocked HCMV during the initial 60 minutes of infection in a dose-dependent manner. Down-regulation of THY-1 with siRNA impaired infectivity occurred during the initial 60 minutes of inoculation. Both THY-1 antibody and siRNA inhibited HCMV-induced activation of the PI3-K/Akt pathway required for entry. Soluble THY-1 protein blocked HCMV infection during, but not after, virus internalization. Expression of exogenous THY-1 enhanced entry in cells expressing low levels of the protein. THY-1 interacted with HCMV gB and gH and may form a complex important for entry. However, since gB and gH have previously been shown to interact, it is uncertain if THY-1 directly binds to both of these proteins. Prior observations that THY-1 (a) interacts with αVβ3 integrin and recruits paxillin (implicated in HCMV entry), (b) regulates leukocyte extravasation (critical for HCMV viremia), and (c) is expressed on many cells targeted for HCMV infection including epithelial and endothelial cells, fibroblast, and CD34+/CD38- stem cells, all support a role for THY-1 as an HCMV entry mediator in

  13. Role of carbon impurities on the surface morphology evolution of tungsten under high dose helium ion irradiation

    NASA Astrophysics Data System (ADS)

    Al-Ajlony, A.; Tripathi, J. K.; Hassanein, A.

    2015-11-01

    The effect of carbon impurities on the surface evolution (e.g., fuzz formation) of tungsten (W) surface during 300 eV He ions irradiation was studied. Several tungsten samples were irradiated by He ion beam with a various carbon ions percentage. The presence of minute carbon contamination within the He ion beam was found to be effective in preventing the fuzz formation. At higher carbon concentration, the W surface was found to be fully covered with a thick graphitic layer on the top of tungsten carbide (WC) layer that cover the sample surface. Lowering the ion beam carbon percentage was effective in a significant reduction in the thickness of the surface graphite layer. Under these conditions the W surface was also found to be immune for the fuzz formation. The effect of W fuzz prevention by the WC formation on the sample surface was more noticeable when the He ion beam had much lower carbon (C) ions content (0.01% C). In this case, the fuzz formation was prevented on the vast majority of the W sample surface, while W fuzz was found in limited and isolated areas. The W surface also shows good resistance to morphology evolution when bombarded by high flux of pure H ions at 900 °C.

  14. The role of electrostatic charge in the adhesion of spherical particles onto planar surfaces in atmospheric systems

    SciTech Connect

    Kweon, Hyojin; Yiacoumi, Sotira Z.; Tsouris, Costas

    2015-06-19

    In this study, the influence of electrostatic charge on the adhesive force between spherical particles and planar surfaces in atmospheric systems was studied using atomic force microscopy. Electrical bias was applied to modify the surface charge, and it was found that application of a stronger positive bias to a particle induces a stronger total adhesive force. The sensitivity of the system to changes in the bias depended on the surface charge density. For larger-size particles, the contribution of the electrostatic force decreased, and the capillary force became the major contributor to the total adhesive force. The influence of water adsorption on the total adhesive force and, specifically, on the contribution of the electrostatic force depended on the hydrophobicity of interacting surfaces. For a hydrophilic surface, water adsorption either attenuated the surface charge or screened the effect of surface potential. An excessive amount of adsorbed water provided a path to surface charge leakage, which might cancel out the electrostatic force, leading to a reduction in the adhesive force. Theoretically calculated forces were comparable with measured adhesive forces except for mica which has a highly localized surface potential. The results of this study provide information on the behavior of charged colloidal particles in atmospheric systems.

  15. The role of electrostatic charge in the adhesion of spherical particles onto planar surfaces in atmospheric systems

    DOE PAGESBeta

    Kweon, Hyojin; Yiacoumi, Sotira Z.; Tsouris, Costas

    2015-06-19

    In this study, the influence of electrostatic charge on the adhesive force between spherical particles and planar surfaces in atmospheric systems was studied using atomic force microscopy. Electrical bias was applied to modify the surface charge, and it was found that application of a stronger positive bias to a particle induces a stronger total adhesive force. The sensitivity of the system to changes in the bias depended on the surface charge density. For larger-size particles, the contribution of the electrostatic force decreased, and the capillary force became the major contributor to the total adhesive force. The influence of water adsorptionmore » on the total adhesive force and, specifically, on the contribution of the electrostatic force depended on the hydrophobicity of interacting surfaces. For a hydrophilic surface, water adsorption either attenuated the surface charge or screened the effect of surface potential. An excessive amount of adsorbed water provided a path to surface charge leakage, which might cancel out the electrostatic force, leading to a reduction in the adhesive force. Theoretically calculated forces were comparable with measured adhesive forces except for mica which has a highly localized surface potential. The results of this study provide information on the behavior of charged colloidal particles in atmospheric systems.« less

  16. Modelisation de la diffusion sur les surfaces metalliques: De l'adatome aux processus de croissance

    NASA Astrophysics Data System (ADS)

    Boisvert, Ghyslain

    Cette these est consacree a l'etude des processus de diffusion en surface dans le but ultime de comprendre, et de modeliser, la croissance d'une couche mince. L'importance de bien mai triser la croissance est primordiale compte tenu de son role dans la miniaturisation des circuits electroniques. Nous etudions ici les surface des metaux nobles et de ceux de la fin de la serie de transition. Dans un premier temps, nous nous interessons a la diffusion d'un simple adatome sur une surface metallique. Nous avons, entre autres, mis en evidence l'apparition d'une correlation entre evenements successifs lorsque la temperature est comparable a la barriere de diffusion, i.e., la diffusion ne peut pas etre associee a une marche aleatoire. Nous proposons un modele phenomenologique simple qui reproduit bien les resultats des simulations. Ces calculs nous ont aussi permis de montrer que la diffusion obeit a la loi de Meyer-Neldel. Cette loi stipule que, pour un processus active, le prefacteur augmente exponentiellement avec la barriere. En plus, ce travail permet de clarifier l'origine physique de cette loi. En comparant les resultats dynamiques aux resultats statiques, on se rend compte que la barriere extraite des calculs dynamiques est essentiellement la meme que celle obtenue par une approche statique, beaucoup plus simple. On peut donc obtenir cette barriere a l'aide de methodes plus precises, i.e., ab initio, comme la theorie de la fonctionnelle de la densite, qui sont aussi malheureusement beaucoup plus lourdes. C'est ce que nous avons fait pour plusieurs systemes metalliques. Nos resultats avec cette derniere approche se comparent tres bien aux resultats experimentaux. Nous nous sommes attardes plus longuement a la surface (111) du platine. Cette surface regorge de particularites interessantes, comme la forme d'equilibre non-hexagonale des i lots et deux sites d'adsorption differents pour l'adatome. De plus, des calculs ab initio precedents n'ont pas reussi a confirmer la

  17. Approche à l’égard des nouveaux anticoagulants oraux en pratique familiale

    PubMed Central

    Douketis, James; Bell, Alan David; Eikelboom, John; Liew, Aaron

    2014-01-01

    Résumé Objectif Comparer les caractéristiques principales des nouveaux anticoagulants oraux (NACO), soit le dabigatran, le rivaroxaban et l’apixaban, et répondre aux questions qui font surface lors de la comparaison de ces agents. Qualité des données Une recherche dans PubMed a été effectuée afin de relever les études cliniques récentes (de janvier 2008 à la semaine 32 de 2013) portant sur l’emploi des NACO pour la prévention des AVC dans les cas de fibrillation auriculaire (FA) et pour le traitement de la thromboembolie veineuse aiguë. Message principal Selon 3 essais d’envergure, tous les NACO sont au moins aussi efficaces que la warfarine dans la prévention des AVC chez les patients atteints d’une FA non valvulaire, et au moins aussi sûrs pour ce qui est du risque de saignement. Des méta-analyses de ces essais ont montré que, comparativement au traitement par la warfarine, les NACO avaient réduit la mortalité totale, la mortalité d’origine cardiovasculaire et les saignements intracrâniens, et était aussi ressortie une tendance vers la réduction