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Sample records for surface role des

  1. Simulation de l'accretion de glace sur un obstacle bidimensionnel par la methode des bissectrices et par la modelisation des ruisselets et des gouttes de surface

    NASA Astrophysics Data System (ADS)

    Fortin, Guy

    Le LIMA (Laboratoire International des Materiaux Antigivre) en collaboration avec le CIRA (Italian Aerospace Research Centre) a developpe un logiciel simulant l'accretion de la glace en regimes sec et humide sur un objet bidimensionnel fixe. L'approche utilisee s'appuie sur les travaux de Lozowski pour les bilans energetiques, sur une etude du comportement du film d'eau, des ruisselets et des gouttes de surface pour le calcul des rugosites et des masses d'eau residuelle, ainsi que sur une methode de bissectrice pour l'evolution de la surface de glace. La contribution du CIRA a ete de fournir le logiciel pour le calcul des ecoulements et de la captation. Le bilan energetique base sur la conservation de l'energie est la sommation de la chaleur latente de fusion, d'evaporation et de sublimation, du rechauffement adiabatique et cinetique, et des pertes de chaleur par convection et conduction, ainsi que de l'evolution thermodynamique de l'eau de son etat initial a son etat final. La densite de la glace, qui a un impact important sur la simulation, est calculee a partir d'une correlation empirique developpee avec les cylindres tournants. En se basant sur les travaux de Al-Khalil et Hansman, le comportement des gouttes en regimes sec et humide a ete decrit analytiquement, ce qui a mene a determiner la hauteur maximale que peuvent atteindre les gouttes avant mouvement. Cette hauteur, appelee hauteur de mouvement, permet de determiner l'etat de l'eau sur la surface (film, ruisselets ou gouttes), ainsi que la hauteur des rugosites lorsque l'eau existe sous forme de gouttes ou de ruisselets. La hauteur de mouvement est determinee par l'equilibre entre les forces de cisaillement, induites par les effets aerodynamiques et gravitationnels evalues pour une goutte non deformee, et la force de cisaillement, induite par la tension de surface et la deformation de la goutte. Elle a ete validee en laboratoire et la precision obtenue pour la partie aerodynamique et gravitationnelle est

  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. Microscopie interférentielle X-UV : un outil pour l'étude des endommagements des surfaces optiques

    NASA Astrophysics Data System (ADS)

    Jamelot, G.; Ros, D.; Cassou, K.; Kazamias, S.; Klisnick, A.; Kozlová, M.; Mocek, T.; Homer, P.; Polan, J.; Stupka, M.

    2006-12-01

    Nous présentons des résultats récents concernant des premières investigations de microscopie interférentielle par laser X-UV d'endommagement optique. Le laser X-UV utilisé est un laser collisionnel en régime quasi-stationnaire émettant à 21.2 nm, développé au Prague Asterix Laser System (PALS, Prague, République Tchèque). Des échantillons de silice fondue de haute qualité, avec ou sans rayure, étaient irradiées en face avant par un laser bleu, correspondant au 3selectfontfontsize{7{9}{textrm{ème}}} harmonique du laser à iode du PALS (1.315 μ m), servant également à réaliser le laser X-UV à 21.2 nm. Celui-ci était utilisé, 5 ns après l'irradiation pour réaliser une imagerie microscopique et interférentielle de la face arrière de l'échantillon. Les résultats font apparaître des déformations locales transitoires. Des premières analyses mettent en évidence une probable variation de la rugosité de la surface. Cette démonstration expérimentale encourageante ouvre la voie à de futures investigations, notamment sur notre prochaine installation laser : LASERIX.

  4. Le role du phytoplancton de petite taille (<20 mum) dans les variations des proprietes optiques des eaux du Saint-Laurent

    NASA Astrophysics Data System (ADS)

    Mas, Sebastien

    Les mesures satellitaires de couleur des oceans sont largement determinees par les proprietes optiques inherentes (IOPs) des eaux de surface. D'autre part, le phytoplancton de petite taille (<20 mum) est le plus souvent dominant dans les oceans, et peut donc etre une source importante de variation des IOPs dans les oceans. Dans ce contexte, le but principal de ce doctorat etait de definir l'impact du phytoplancton (<20 mum) sur les variations des proprietes optiques de l'Estuaire et du Golfe du Saint-Laurent (Canada). Afin d'atteindre cet objectif, il etait necessaire de determiner en milieu controle les facteurs de variabilite des proprietes optiques cellulaires et des IOPs du phytoplancton (<20 mum) des eaux du Saint-Laurent, et d'evaluer la contribution du phytoplancton (<20 mum) aux proprietes optiques totales des eaux du Saint-Laurent. Des experiences en laboratoire ont montre que les variations des proprietes optiques des cellules phytoplanctoniques soumises a un cycle jour-nuit, ainsi qu'a des changements concomitants d'intensite lumineuse, peuvent contribuer significativement a la variabilite des proprietes optiques observee en milieu naturel. D'autres experiences ont, quant a elles, mis en evidence que les variations des proprietes optiques des cellules phytoplanctoniques dues aux phases de croissance peuvent alterer les IOPs des oceans, particulierement pendant les periodes de floraison. De plus, la presence de bacteries et de particules detritiques peut egalement affecter la variabilite des IOPs totales, notamment la diffusion. Au printemps, dans l'Estuaire et le Golfe du Saint-Laurent, la contribution du phytoplancton <20 mum aux IOPs presentait des differences regionales evidentes pour les proprietes d'absorption et de diffusion. En plus de la variabilite spatiale, les proprietes optiques cellulaires presentaient des variations journalieres, et ce particulierement pour le picophytoplancton. Enfin, la plupart des differences observees dans les

  5. Caracterisation des etats de surface par teledetection infrarouge thermique multispectrale: Contribution a l'etude des conditions de viabilite hivernale

    NASA Astrophysics Data System (ADS)

    Chagnon, Frederic

    La mesure de temperature d'une surface et de son emissivite thermique constitue encore de nos jours, un defi de taille. D'un point de vue microclimatique, la temperature significative d'une surface est celle qui reflete l'etat des echanges energetiques qui y ont lieu. La radiometrie infrarouge thermique permet de lire la temperature de l'interface air-sol pour une couche infiniment petite de la surface (de l'ordre de quelques microns). Dans le cadre d'un systeme d'aide aux decisions en viabilite hivernale, nous avons defini un prototype de station de mesures mobiles. Cette station permet de determiner, avec precision, la temperature radiative de la surface de la chaussee ainsi que de determiner, avec un taux de succes de plus de 65 %, l'etat de cette meme surface. Par la conception de ce prototype, nous avons aborde le principe physique de la mesure de temperature de surface par radiometrie multispectrale infrarouge thermique. Ce travail aura permis d'evaluer une approche standard de mesure a bande spectrale unique (de 8 a 14 mum). Dans la correction de la temperature radiative de surface, nous avons considere trois methodes distinctes. La premiere methode utilisee est celle de l'algorithme TES (Gillespie et al., 1998). Cet algorithme etablit le spectre d'emissivite, puis calcule une temperature de surface corrigee, en tenant compte de la reflexion du rayonnement thermique incident a la surface. La seconde methode consideree est l'indice TISI (Li et al., 1999) qui consiste en un indice d'emissivite relatif independant de la temperature de la surface et qui tient compte du rayonnement incident a la surface. La troisieme methode est un indice de temperature relative (ITR) qui correspond au contraste normalise des temperatures radiatives de surface. L'identification du type de surface a montre un taux de succes de 54,8 % pour les resultats de l'indice ITR, de 51,9 % pour les resultats de l'indice TISI et de 67,3 % pour les resultats de l'algorithme TES. Quant a la

  6. Étude par chromatographie gazeuse inverse, à concentration finie, des propriétés de surface d'échantillons obtenus par traitement thermique de la goethite : distribution des sites d'adsorption des alcanes

    NASA Astrophysics Data System (ADS)

    Brendlé, E.; Balard, H.; Papirer, E.

    1998-07-01

    Inverse Gas Chromatography (IGC), at finite concentration conditions, was applied for the evaluation of the surface properties of hematite samples obtained by heat treatment of goethite. From the alkane adsorption isotherms, the distribution of surface sites according to the adsorption energy is determined. It is shown that the surface of hematite undergoes significant changes when heated up to 500 circC. La chromatographie Gazeuse Inverse (CGI), à concentration finie, a été utilisée pour évaluer les propriétés de surface d'échantillons d'hématite obtenus par traitement thermique de la goethite. A partir des isothermes d'adsorption des alcanes, on détermine la courbe de distribution des sites de surface en fonction de l'énergie d'adsorption de molécules sondes. On montre que ces courbes évoluent en fonction du traitement thermique de la goethite et traduisent une importante modification de surface de l'hématite formée après un chauffage à 500 circC.

  7. Hydrogeology and ground-water/surface water interactions in the Des Moines River valley, southwestern Minnesota, 1997-2001

    USGS Publications Warehouse

    Cowdery, Timothy K.

    2005-01-01

    Long-term withdrawals of water for public supplies may cause a net decrease in ground-water discharge to surface water. Water that does not evaporate, or that is not exported, is discharged to the Des Moines River but with changed water quality. Because ground-water and surface-water qualities in the study area are similar, the ground-water discharge probably has little effect on river water quality.

  8. 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.

  9. Réponse diélectrique de surface des phonons optiques d'un film de cristal ionique

    NASA Astrophysics Data System (ADS)

    Lambin, Ph.; Senet, P.; Castiaux, A.; Philippe, L.

    1993-06-01

    The paper begins with a short review on the theory of the surface dielectric response function of optical phonons in thin films, which is an important quantity for the understanding of various surface phenomena. The dielectric response of surface phonons to infra-red excitations is analysed with some details for two test cases: a SiO2(0001) self-supported film and NaCl(001) slabs on a thick Ge substrate. The results obtained from lattice-dynamics calculations for short wave vectors are compared with the predictions of electrostatics. The latter is shown to provide a valuable description — at the level of the energy resolution achieved today in electron-energy-loss spectroscopy — of the surface dielectric response function, even for the thinnest films (11 Å) considered in this paper. L'article commence par une dérivation rapide de la fonction de réponse diélectrique de surface des phonons optiques d'un film. Cette fonction de réponse est une grandeur fondamentale des matériaux qui intervient dans l'étude de nombreux phénomènes de surface. La réponse diélectrique des phonons de surface est analysée avec détail pour deux systèmes modèles : (a) un film de SiO2(0001) auto-supporté et (b) des couches de NACl(001) sur un substrat massif de Ge. Les résultats que donne la dynamique cristalline pour ces deux systèmes sont comparés aux prédictions d'une approche basée sur l'électrostatique. On montre ainsi qu'à l'échelle des résolutions en fréquence couramment atteintes en spectroscopie de perte d'énergie d'électrons, l'électrostatique fournit une description valable de la réponse diélectrique de surface à grande longueur d'onde, même pour les films les plus minces examinés ici (11 Å).

  10. 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.

  11. Self-assembly of gold nanoparticles on deep eutectic solvent (DES) surfaces.

    PubMed

    Raghuwanshi, V S; Ochmann, M; Polzer, F; Hoell, A; Rademann, K

    2014-08-14

    Self-assembly of gold nanoparticles was obtained by sputter deposition on DES. SAXS and TEM investigations reveal the formation of spherical nanoparticles with a mean diameter of 5 ± 0.5 nm. For extended sputtering times, the number density of AuNPs increases linearly and a very pronounced 1st and 2nd shell ordering is observed.

  12. Progrès récents dans l'utilisation de la Chromatographie Gazeuse Inverse pour la détermination des propriétés acide-base des surfaces solides

    NASA Astrophysics Data System (ADS)

    Papirer, E.; Brendlé, E.

    1998-01-01

    Inverse Gas Chromatography (IGC) is a method well suited for the study of divided solids, but also of fibres. In this paper, the principles of IGC, its advantages such as ease and rapidity of measurement, but also limitations due essentially to the energetic heterogeneity of the solid surfaces are discussed. Finally, a new procedure allowing to estimate the acidity and basicity of the surface involving topology concepts of the molecules used to probe the surface is presented. Experimental results of the Laboratory, but also results extracted from the literature concerning silica, titanium dioxide, poly(methyl methacrylate) and poly(ethylene) fibers, are taken to verify the proposed method. La chromatographie Gazeuse Inverse (CGI) s'avère comme une méthode de choix pour l'étude des solides divisés, mais aussi de fibres. Après avoir rappelé quelques principes de base de la CGI, les avantages de la méthode comme la facilité de mise en oeuvre, sa rapidité..., nous soulignerons ses limites qui sont essentiellement à attribuer à l'hétérogénéité énergétique des surfaces solides. Finalement, nous décrirons une nouvelle approche de l'acidité et de la basicité de surface grâce à l'utilisation des concepts de topologie des molécules employées pour sonder la surface. Des résultats expérimentaux obtenus au Laboratoire, mais aussi tirés de la littérature et concernant la silice, l'oxyde de titane, la poly(méthacrylate de méthyle) et les fibres de poly(éthylène), permettent d'illustrer la pertinence de la méthode proposée.

  13. Surface Water Qualit: Revisiting Nitrate Concentrations in the Des Moines River: 1945 and 1976-2001

    USGS Publications Warehouse

    McIsaac, G.F.; Libra, R.D.

    2003-01-01

    Recent compilations of historical and contemporary riverine nitrate (NO3) concentrations indicate that concentrations in many rivers in the north-central USA increased during the second half of the 20th century. The Des Moines River near Des Moines, Iowa, however, was reported to have had similar NO3 concentrations in 1945 and the 1980s, in spite of substantially greater N input to the watershed during the latter period. The objective of this study was to reconsider the comparison of historical and contemporary NO3 concentrations in the Des Moines River near Des Moines in light of the following: (i) possible errors in the historical data used, (ii) variations in methods of sample collection, (iii) variations in location of sampling, and (iv) additional data collected since 1990. We discovered that an earlier study had compared the flow-weighted average concentration in 1945 to arithmetic annual average concentrations in the 1980s. The intertemporal comparison also appeared to be influenced by differences in sample collection methods and locations used at different times. Depending on the model used and the estimated effects of composite sample collection, the 1945 arithmetic average NO3 concentration was between 44 and 57% of the expected mean value at a similar water yield during 1976-2001. The flow-weighted average NO3 concentration for 1945 was between 54 and 73% of the expected mean value at a similar water yield during 1976-2001. The difference between NO3 concentrations in 1945 and the contemporary period are larger than previously reported for the Des Moines River.

  14. 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

  15. Role of surface properties in bacterial attachment

    NASA Astrophysics Data System (ADS)

    Conrad, Jacinta; Sharma, Sumedha

    2014-03-01

    Bacterial biofilms foul a wide range of engineered surfaces, from pipelines to membranes to biomedical implants, and lead to deleterious costs for industry and for human health. Designing strategies to reduce bacterial fouling requires fundamental understanding of mechanisms by which bacteria attach to surfaces. We investigate the attachment of Escherichia coli on silanized glass surfaces during flow through a linear channel at flow rates of 0.1-1 mL/min using confocal microscopy. We deposit self-assembled monolayers of organosilanes on glass and track the position and orientation of bacteria deposited on these surfaces during flow using high-throughput image processing algorithms. Here, we report differences in deposition rate and surface-tethered motion of cells as a function of surface charge and surface energy, suggesting that attachment of bacteria on these engineered surfaces is dominated by different physical mechanisms.

  16. 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.

  17. Diffusion des rayonnements X et visibles ; microscopie en champ proche : utilisation comparée pour la caractérisation des surfaces

    NASA Astrophysics Data System (ADS)

    Tollens, E.; Menecier, S.; Haidar, Y.; Zerrouki, C.; Chassevent, M.; de Fornel, F.; Bonnet, J. J.

    2004-11-01

    Trois méthodes ont été utilisées pour caractériser la rugosité de quelques échantillons. Deux de ces méthodes sont basées sur la mesure du rayonnement diffusé (visible et X). La troisième utilise la microscopie en champ proche (MCP). Dans un premier temps, une comparaison des deux premières techniques a été menée en utilisant une même théorie vectorielle de la diffusion. Bien adaptée au domaine du visible, cette théorie peut aussi être utilisée dans le cas du rayonnement X. Les densités spectrales de puissance (dsp) de la rugosité, déterminées expérimentalement pour deux échantillons d'Alacrite XSH (alliage quaternaire à base de cobalt utilisé en métrologie des masses), montrent des allures identiques dans le cas du visible et du rayonnement X à des incidences très rasantes. Dans un deuxième temps, la hauteur quadratique moyenne δ , caractéristique de la rugosité de ces deux échantillons, a été déterminée de façon "directe" par microscopie en champ proche, et à partir des dsp pour les deux autres techniques. La restriction à une bande commune des fréquences spatiales accessibles à ces techniques, conduit à des valeurs de δ comparables aux incertitudes près. Une validation des mesures X ainsi faite, un accent est mis sur leur apport complémentaire par rapport au visible.

  18. Role of surface roughness in superlubricity

    NASA Astrophysics Data System (ADS)

    Tartaglino, U.; Samoilov, V. N.; Persson, B. N. J.

    2006-05-01

    We study the sliding of elastic solids in adhesive contact with flat and rough interfaces. We consider the dependence of the sliding friction on the elastic modulus of the solids. For elastically hard solids with planar surfaces with incommensurate surface structures we observe extremely low friction (superlubricity), which very abruptly increases as the elastic modulus decreases. We show that even a relatively small surface roughness may completely kill the superlubricity state.

  19. Role of surface roughness in superlubricity.

    PubMed

    Tartaglino, U; Samoilov, V N; Persson, B N J

    2006-05-03

    We study the sliding of elastic solids in adhesive contact with flat and rough interfaces. We consider the dependence of the sliding friction on the elastic modulus of the solids. For elastically hard solids with planar surfaces with incommensurate surface structures we observe extremely low friction (superlubricity), which very abruptly increases as the elastic modulus decreases. We show that even a relatively small surface roughness may completely kill the superlubricity state.

  20. Dynamics of surface catalyzed reactions; the roles of surface defects, surface diffusion, and hot electrons.

    PubMed

    Somorjai, Gabor A; Bratlie, Kaitlin M; Montano, Max O; Park, Jeong Y

    2006-10-12

    The mechanism that controls bond breaking at transition metal surfaces has been studied with sum frequency generation (SFG), scanning tunneling microscopy (STM), and catalytic nanodiodes operating under the high-pressure conditions. The combination of these techniques permits us to understand the role of surface defects, surface diffusion, and hot electrons in dynamics of surface catalyzed reactions. Sum frequency generation vibrational spectroscopy and kinetic measurements were performed under 1.5 Torr of cyclohexene hydrogenation/dehydrogenation in the presence and absence of H(2) and over the temperature range 300-500 K on the Pt(100) and Pt(111) surfaces. The structure specificity of the Pt(100) and Pt(111) surfaces is exhibited by the surface species present during reaction. On Pt(100), pi-allyl c-C6H9, cyclohexyl (C6H11), and 1,4-cyclohexadiene are identified adsorbates, while on the Pt(111) surface, pi-allyl c-C6H9, 1,4-cyclohexadiene, and 1,3-cyclohexadiene are present. A scanning tunneling microscope that can be operated at high pressures and temperatures was used to study the Pt(111) surface during the catalytic hydrogenation/dehydrogenation of cyclohexene and its poisoning with CO. It was found that catalytically active surfaces were always disordered, while ordered surface were always catalytically deactivated. Only in the case of the CO poisoning at 350 K was a surface with a mobile adsorbed monolayer not catalytically active. From these results, a CO-dominated mobile overlayer that prevents reactant adsorption was proposed. By using the catalytic nanodiode, we detected the continuous flow of hot electron currents that is induced by the exothermic catalytic reaction. During the platinum-catalyzed oxidation of carbon monoxide, we monitored the flow of hot electrons over several hours using a metal-semiconductor Schottky diode composed of Pt and TiO2. The thickness of the Pt film used as the catalyst was 5 nm, less than the electron mean free path

  1. 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.

  2. Surface disturbances: Their role in accelerating desertification.

    PubMed

    Belnap, J

    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.

  3. Theory of adhesion: role of surface roughness.

    PubMed

    Persson, B N J; Scaraggi, M

    2014-09-28

    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.

  4. 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.

  5. Role of surface plasmons in the Casimir effect

    SciTech Connect

    Intravaia, F.; Henkel, C.; Lambrecht, A.

    2007-09-15

    In this paper we study the role of surface plasmon modes in the Casimir effect. The Casimir energy can be written as a sum over the modes of a real cavity and one may identify two sorts of modes, two evanescent surface plasmon modes and propagative modes. As one of the surface plasmon modes becomes propagative for some choice of parameters we adopt an adiabatic mode definition where we follow this mode into the propagative sector and count it together with the surface plasmon contribution, calling this contribution 'plasmonic'. We evaluate analytically the contribution of the plasmonic modes to the Casimir energy. Surprisingly we find that this becomes repulsive for intermediate and large mirror separations. The contribution of surface plasmons to the Casimir energy plays a fundamental role not only at short but also at large distances. This suggests possibilities to tailor the Casimir force via a manipulation of the surface plasmons properties.

  6. 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

  7. 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

  8. Mechanical durability of superhydrophobic surfaces: The role of surface modification technologies

    NASA Astrophysics Data System (ADS)

    Zhi, Jing-Hui; Zhang, Li-Zhi; Yan, Yuying; Zhu, Jie

    2017-01-01

    Various surface modification technologies have been used to develop superhydrophobic surface, however their durability has been recognized as the major obstacle for the real applications. Here a quantitative investigation was conducted to evaluate the effects of different surface modification methods on the surfaces' mechanical durability. The superhydrophobic surfaces were prepared by the combination of two surface roughing methods (etching and sandblasting) with chemical modifications with four low surface energy materials: silica sol (SS), octadecanoic acid (OA), heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane (HDFS) and hexadecyltriethoxysilane (HTS). XPS was used to analyze the elements composition and AFM was used to measure the roughness of the surfaces. The durability of these surfaces was tested by a sandpaper abrasion experiment. The collective results showed that the low surface energy materials had significant effects on the surface roughness, which would then play an important role in the durability of these rough surfaces. The SS modified rough surfaces possessed higher roughness and better durability than the surfaces modified by other three low surface energy materials. SS modified rough surfaces could bear 60 cycles of abrasion with 10 g weights on 1500 CW sandpaper.

  9. Role of surface heat fluxes underneath cold pools.

    PubMed

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

    2016-01-28

    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.

  10. 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

  11. Enterococcus in surface waters from the Des Moines River (Iowa) watershed: location, persistence and vancomycin resistance.

    PubMed

    Larsen, Bryan; Essmann, Michael K; Geletta, Simon; Duff, Barbara

    2012-01-01

    The object of this study was to quantify vancomycin-resistant enterococci in surface water from Central Iowa obtained from April 2007 to August 2007. Water from established sampling sites in four watersheds was plated on bile-esculin agar. Presumptively identified enterococci were categorized as "above the level of concern" if the sample contained ≥ 107 CFU per 100 ml. Confirmation of isolates as enterococci was based on growth at elevated temperature in high salt and on Enterococcus agar. Isolates that grew on 6 μg/ml vancomycin agar were deemed resistant. PCR analysis of resistant strains characterized vancomycin resistance genes. 77.2% of surface water samples from Central Iowa contained enterococci. Among enterococcal isolates, 10.4% grew on media containing 6 μg/ml vancomycin. PCR analysis of resistance genes showed a preponderance of VanC2/C3 in the area studied and VanB was not detected. Vancomycin-resistant Enterococcus is present in Central Iowa surface waters but resistance rarely involved VanA genotypes. Nevertheless, the potential for community-acquired infections remains a risk.

  12. Role of Surface Temperature Inversions in Arctic Amplification

    NASA Astrophysics Data System (ADS)

    Lesins, G. B.; Duck, T. J.; Drummond, J. R.

    2010-12-01

    Arctic surface temperatures are warming at a rate several times larger than the global average in a phenomenon called Arctic Amplification. Although a number of feedback mechanisms, including sea ice reduction, enhanced meridional heat transport and changing aerosol and cloud properties, have been proposed to explain the amplification, the role of low level atmospheric stability has not received as much attention. The Arctic atmospheric boundary layer typically possesses a surface-based temperature inversion that is particularly stable and deep during the winter half of the year. The presence of the inversion stratifies the boundary layer inhibiting the vertical transport of sensible and latent heats. Hence the surface temperature response to a perturbation in the downward radiative forcing is enhanced by the presence of a stable surface layer. By using the operational surface weather observations and tropospheric soundings it was found that the magnitude of the surface temperature warming from 1984 to 2007 at Eureka (80N, 86.2W), in the Canadian High Arctic, has a large seasonal dependence that is linked to the strength of the surface-based temperature inversion. The Arctic Amplification Factor at Eureka in this time period is ~5x. The enhanced warming in the presence of a stronger inversion is an important contributor to the Arctic amplification phenomenon. The inversion augments the amplification caused by forcing and feedback mechanisms associated with regional climate change. Partitioning the data set according to cloud cover and surface wind speeds helps to demonstrate more clearly the role of the inversion.

  13. La situation des traducteurs dans les pays arabes (The Role of Translators in the Arab Countries).

    ERIC Educational Resources Information Center

    Hanafi, Benaissa

    1980-01-01

    Reviews the services provided by translators under colonialism, as compared with their new role in independent Algeria. Stresses the socioeconomic and political importance of translation as a tool for the diffusion of technological and scientific information in Arabic. (MES)

  14. 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…

  15. 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.

  16. 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.

  17. 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.

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

    SciTech Connect

    Sailor, David Jean

    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°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. 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

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

    PubMed Central

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

    2002-01-01

    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

  1. 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

  2. The role of "inert" surface chemistry in marine biofouling prevention.

    PubMed

    Rosenhahn, Axel; Schilp, Sören; Kreuzer, Hans Jürgen; Grunze, Michael

    2010-05-07

    review is written to outline for non-experts the hierarchical structure in length- and timescale of marine biofouling and the role of surface chemistry in fouling prevention. Experts in the field are referred to more specialized recent reviews.

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

    DOE PAGES

    Gamalski, A. D.; Tersoff, J.; Kodambaka, S.; ...

    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

  4. 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.

  5. Role of surface in apparent viscosity of glasses

    NASA Astrophysics Data System (ADS)

    Avramov, I.

    2014-03-01

    Two problems have intrigued experts for a long time: The one is within the context of the legend of flowing cathedral glass windows and the second is the inaccuracy appearing in very old thermometers of famous scientists. We relate this with the role of the surface on the apparent viscosity of glasses. The apparent viscosity could deviate from the bulk viscosity if the fraction w of the surface molecules, of small samples, is sufficiently large. The effect is more prominent at low temperatures, correspondingly at high viscosities. The interpretation is within the Avramov and Milchev viscosity model, combined with the predictions of the change of heat capacity for extremely small samples. We find that the apparent glass transition temperature could depend on the sample size, in agreement with experimental observations existing in the literature. In addition to glasses, the present results could be of importance for thin films and foams.

  6. Role of surface in apparent viscosity of glasses.

    PubMed

    Avramov, I

    2014-03-01

    Two problems have intrigued experts for a long time: The one is within the context of the legend of flowing cathedral glass windows and the second is the inaccuracy appearing in very old thermometers of famous scientists. We relate this with the role of the surface on the apparent viscosity of glasses. The apparent viscosity could deviate from the bulk viscosity if the fraction w of the surface molecules, of small samples, is sufficiently large. The effect is more prominent at low temperatures, correspondingly at high viscosities. The interpretation is within the Avramov and Milchev viscosity model, combined with the predictions of the change of heat capacity for extremely small samples. We find that the apparent glass transition temperature could depend on the sample size, in agreement with experimental observations existing in the literature. In addition to glasses, the present results could be of importance for thin films and foams.

  7. 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.

  8. 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.

  9. Role of specific amine surface configurations for grafted surfaces: implications for nanostructured CO2 adsorbents.

    PubMed

    Shimizu, Steven; Song, Changsik; Strano, Michael

    2011-03-15

    Amine-grafted porous materials that capture CO2 from emission streams have been considered to be potential alternatives to the more energy-intensive liquid amine systems currently employed. An underappreciated fact in the uptake mechanism of these materials is that under dry, anhydrous conditions each CO2 molecule must react with two adjacent amine groups to adsorb onto the surface, which makes the configuration of amine groups on the surface critically important. Using this chemical mechanism, we developed a semiempirical adsorption isotherm equation that allows straightforward computation of the adsorption isotherm from an arbitrary surface configuration of grafted amines for honeycomb, square, and triangular lattices. The model makes use of the fact that the distribution of amines with respect to the number of nearest neighbors, referred to as the z-histogram, along with the amine loading and equilibrium constant, uniquely determine the adsorption characteristics to a very good approximation. This model was used to predict the range of uptakes possible just through surface configuration, and it was used to fit experimental data in the literature to give a meaningful equilibrium constant and show how efficiently amines were utilized. We also demonstrate how the model can be utilized to design more efficient nanostructured adsorbents and polymer-based adsorbents. Recommendations for exploiting the role of surface configuration include the use of linear instead of branched polyamines, higher amine grafting densities, the use of flexible, less bulky, long, and rotationally free amine groups, and increased silanol densities.

  10. The role of surface albedo in the parameterization of the relationship between system and surface absorbed solar radiation

    SciTech Connect

    Major, G.

    1994-12-31

    The radiation budget of the atmosphere, its layers and the surface is one of the basic forces in the climate and weather processes. A surface solar radiation budget database could be derived from satellite measurements using different parameterization between the top of atmosphere (TOA) and surface solar radiation budget values. The proposed parameterizations suggest that the role of surface albedo is not significant; therefore it should not be taken into account. In this paper an empirical validation is made of the proposed model-based parameterizations using Nimbus-7 and ERBE satellites and the corresponding surface data. It is shown that the role of surface albedo cannot be neglected.

  11. 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.

  12. Role of the endothelial surface layer in neutrophil recruitment.

    PubMed

    Marki, Alex; Esko, Jeffrey D; Pries, Axel R; Ley, Klaus

    2015-10-01

    Neutrophil recruitment in most tissues is limited to postcapillary venules, where E- and P-selectins are inducibly expressed by venular endothelial cells. These molecules support neutrophil rolling via binding of PSGL-1 and other ligands on neutrophils. Selectins extend ≤ 38 nm above the endothelial plasma membrane, and PSGL-1 extends to 50 nm above the neutrophil plasma membrane. However, endothelial cells are covered with an ESL composed of glycosaminoglycans that is ≥ 500 nm thick and has measurable resistance against compression. The neutrophil surface is also covered with a surface layer. These surface layers would be expected to completely shield adhesion molecules; thus, neutrophils should not be able to roll and adhere. However, in the cremaster muscle and in many other models investigated using intravital microscopy, neutrophils clearly roll, and their rolling is easily and quickly induced. This conundrum was thought to be resolved by the observation that the induction of selectins is accompanied by ESL shedding; however, ESL shedding only partially reduces the ESL thickness (to 200 nm) and thus is insufficient to expose adhesion molecules. In addition to its antiadhesive functions, the ESL also presents neutrophil arrest-inducing chemokines. ESL heparan sulfate can also bind L-selectin expressed by the neutrophils, which contributes to rolling and arrest. We conclude that ESL has both proadhesive and antiadhesive functions. However, most previous studies considered either only the proadhesive or only the antiadhesive effects of the ESL. An integrated model for the role of the ESL in neutrophil rolling, arrest, and transmigration is needed.

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

    PubMed

    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

    2013-06-07

    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 Fe(3+) 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 Ca(2+) 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

  14. Role of the surface chemistry of ceria surfaces on silicate adsorption.

    PubMed

    Seo, Jihoon; Lee, Jung Woo; Moon, Jinok; Sigmund, Wolfgang; Paik, Ungyu

    2014-05-28

    Ceria nanoparticles (NPs) have been widely explored as a promising material in various fields. As synthesized under various physicochemical conditions, it exhibits the different surface chemistry. Here, the role of hydroxyl and nitrate group on ceria surface, formed under various physicochemical conditions, for the silicate adsorption was experimentally and theoretically investigated based on the adsorption isotherms and theoretical analyses using density functional theory (DFT) calculation. Experimental results acquired from adsorption isotherms with Freundlich model indicated that the nitrate group shows a much higher affinity with silicate than the hydroxyl groups. These phenomena were demonstrated through the theoretical approaches that exhibit the binding energy of the NO3-ceria (-4.383 eV) on the SiO2 surface being much higher than that of the OH-ceria (-3.813 eV). In good agreement with the experimental and the theoretical results based on adsorption properties, the results of chemical mechanical planarization (CMP) also show that the nitrate groups significantly enhance the removal of SiO2 than the hydroxyl groups. The results investigated in this study will provide researchers, studying the ceria NPs, with guidelines on the importance of exploring the surface chemistry of ceria.

  15. A possible energetic role of mineral surfaces in chemical evolution

    NASA Astrophysics Data System (ADS)

    Coyne, Lelia M.

    1985-09-01

    The postulated roles of clays and other minerals in chemical evolution and the origin of life are reconsidered in terms of the interaction of these minerals with penetrating sources of energy such as ionizing radiation and mechanical stress. This interaction, including such facets as excitation, degradation, storage, and transfer, is considered here with regard to its profound potential for altering the capabilities of minerals to serve both as substrates for prebiological chemistry and as inorganic prototypic life forms. The interaction of minerals and energy in relationship to surface chemistry is discussed in terms of the spectroscopic properties of minerals, the interaction of energy with condensed phases, some commonly accepted concepts of heterogeneous catalysis in the absence of electronic energy inputs, and some commonly accepted and novel means by which surface activity might be enhanced in the presence of energy inputs. An estimation is made of the potential contribution of two poorly characterized prebiotic energy sources, natural radioactive decay and triboelectric energy. These estimates place a conservative lower limit on their prebiotic abundance. Also some special properties of these energy sources, relative to solar energy, are pointed out which might give them particular suitability for driving reactions occurring under geological conditions. Skeletal support for this broadly defined framework of demonstrated and potential relationships between minerals, electronic excitation, and surface reactivity, as applied to chemical evolution, is provided from the results of our studies on 1/1 clays. We have discovered and partially characterized a number of novel luminescent properties of these clays, that indicate energy storage and transfer processes in clays. These luminescent properties are interpreted in relationship to the electron spin resonance phenomena, to provide a basis for estimating the potential significance of energy storage and

  16. Modèle d'estimation de l'irradiation solaire globale d'une surface horizontale au sol à partir des images satellitaires

    NASA Astrophysics Data System (ADS)

    Mechaqrane, A.; Chaoui-Roquaï, M.; Buret-Bahraoui, J.

    1993-05-01

    A physical model based on the radiative transfer equation in the earth-atmosphere system was used to estimate hourly and daily global solar irradiance on a horizontal surface from measurements in the Meteosat-2 satellite visible band (0.4-1.1 μm). In this model we only account for the Rayleigh scattering, the ozone and water vapor absorptions. This model was used for two moroccan sites: Rabat and Marrakech. Ground trusts for the two sites indicate that satellite derived values agree respectively within 21 and 15 percent for hourly and daily values. Un modèle physique basé sur l'équation générale de transfert radiatif du rayonnement solaire dans le système sol-atmosphère a été utilisé pour l'estimation des irradiations globales horaires et joumalières d'une surface horizontale au sol à partir des mesures dans la bande 0,4-1,1 μm du satellite Météosat-2. Dans ce modèle on ne tient compte que de la diffusion Rayleigh et de l'absorption par l'ozone et par la vapeur d'eau. Ce modèle a été utilisé pour deux sites marocains Rabat et Marrakech, pour l'année 1985. Les résultats obtenus pour les deux sites montrent que l'on peut obtenir les irradiations globales horaires à 21% et les valeurs journalières à 15%.

  17. Identification of classical anaphylatoxin as the des-Arg form of the C5a molecule: Evidence of a modulator role for the oligosaccharide unit in human des-Arg74-C5a

    PubMed Central

    Gerard, Craig; Hugli, Tony E.

    1981-01-01

    A functionally active and potentially lethal fragment of the fifth component of complement (C5) is generated during complement activation in serum from animals of various species. This factor, termed the “classical” anaphylatoxin, was isolated from porcine serum and was identified chemically as the des-Arg derivative of the well-characterized C5a molecule. Unlike the C3a and C4a anaphylatoxins, porcine C5a does not require the COOH-terminal arginyl residue for spasmogenic activity. Further degradation of porcine des-Arg74-C5a by carboxypeptidase Y removed glycine-73 and leucine-72 and decreased the intrinsic spasmogenic activity by >90%. Hence, we conclude that, although the arginyl residue is not essential, the COOH-terminal sequence Leu-Gly-Arg contributes structural information that accounts for >90% of C5a activity. Human des-Arg74-C5a, like its porcine counterpart, has instrinsic anaphylatoxin activity; however, higher concentrations were needed to contract the guinea pig ileal tissue (i.e., 1 μM for human des-Arg74-C5a versus 1 nM for porcine des-Arg74-C5a). Furthermore, the des-Arg form of human C5a was only 0.1% as active as porcine des-Arg74-C5a for enhancing vascular permeability in guinea pig skin. In addition to these biological differences, numerous chemical differences exist between the human and porcine des-Arg74-C5a molecules, the most prominent feature being an oligosaccharide entity associated uniquely with the human C5a. When the oligosaccharide unit of human des-Arg74-C5a was removed by glycosidases, leaving a single glucosamine residue attached to the side chain of asparagine-64, activity was enhanced. The human des-Arg74-C5a molecule devoid of the complex oligosaccharide unit exhibited 10-fold stronger spasmogenic activity and 20- to 50-fold greater permeability-enhancing activity than did human des-Arg74-C5a containing the oligosaccharide. Consequently, the oligosaccharide associated with human C5a modulates or suppresses potentially

  18. 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.

  19. 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

  20. 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…

  1. Role of water in polymer surface modification using organosilanes

    NASA Astrophysics Data System (ADS)

    Thallapalle, Pradeep Kumar; Zhang Newby, Bi-Min

    2002-03-01

    In general, polymers exhibit excellent bulk properties but may not possess specific surface properties for successful applications in biomaterials and nanotechnology. Surface modification of polymers with the self-assembled monolayers (SAMs) of organosilanes - ‘Silanization’ - is an attractive approach to alter surface properties without altering the polymer’s desired bulk properties. However, a pretreatment such as exposure to UV/O or plasma is normally required to generate active surface groups prior to silanization. These pretreatments cause undesirable surface changes such as severe surface roughening and excessive surface damage. Recent studies in silanization suggest that the presence of water or OH groups on the surface is essential to form SAMs. In this study we investigated the importance of surface water layer and OH groups in the formation of SAMs for a variety of polymers. The pre and post-modified polymers were examined using fourier transform infrared spectrometry, scanning probe microscopy and contact angle measurements. The results show that organosilanes can be grafted to a polymer surface as long as a water layer can be physisorbed to the surface or the polymer itself contains OH groups. However the monolayers formed are less organized compared to those formed on silicon wafers due to the amorphous nature of the polymers.

  2. 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.

  3. 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.

  4. 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.

  5. The role of dynamic surface tension in cloud droplet activation

    NASA Astrophysics Data System (ADS)

    Petters, Markus D.; Suda, Sarah R.; Christensen, Sara I.

    2013-05-01

    We present new data on the cloud droplet forming abilities of two-component particles that contain the surfactant sodium dodecyl sulfate and sodium chloride or ammonium sulfate. The experiments were designed to test specific predictions made by Kohler theory that accounts for the reduction of surface tension and the partitioning of the surfactant between the interior and the surface of the droplet. We also introduced a pre-humidification step followed by a six minute time delay to test whether dynamic surface tension may lead to kinetic limitations on the partitioning process. Our results confirm previous studies that show that surfactants do not enhance cloud droplet activation relative to what would be predicted from water activity alone. The data obtained with and without time delay were indistinguishable within measurement uncertainty, suggesting that dynamic surface tension does not need to be considered in Kohler theory.

  6. The role of dimensionality in the decay of surface effects

    NASA Astrophysics Data System (ADS)

    Reuter, Matthew G.; Boffi, Nicholas M.; Ratner, Mark A.; Seideman, Tamar

    2013-02-01

    We computationally investigate the decay of surface effects in one-, two-, and three-dimensional materials using two-band tight-binding models. These general models facilitate a direct comparison between materials of differing dimensionality, which reveals that material dimensionality (not material-specific chemistry/physics) is the primary factor controlling the decay of surface effects. Our results corroborate more sophisticated, material-specific studies, finding that surface effects decay after ˜10, ˜25, and ≳ 100 layers in three-dimensional, two-dimensional, and one-dimensional materials, respectively. Physically, higher-dimensional materials screen surface effects more efficiently, as theoretically described by integration over each layer's Brillouin zone. Finally, we discuss several implications of these results.

  7. Role of Steel Object Surface Condition on Behavior During Deformation

    NASA Astrophysics Data System (ADS)

    D'yachenko, S. S.; Ponomarenko, I. V.; Dub, S. N.

    2015-09-01

    Comparative analysis is provided for specimen mechanical properties of steels 18KhGT and 20Kh with tensile testing in relation to surface treatment: grinding, polishing, nitriding, carburizing, and ion-plasma treatment. It is shown that surface condition has a considerable effect on specimen behavior during deformation. It is established that the most favorable effect applies to ion bombardment with low-energy ions recommended as an effective method for improving component structural strength.

  8. 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

    2013-06-05

    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.

  9. 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.

  10. 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

  11. 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

  12. Modélisation De La Température De Surface Des Bacs Évaporométriques

    NASA Astrophysics Data System (ADS)

    Dehon, P.

    1981-02-01

    A simple method is presented to estimate the surface temperature of evaporatIOn pans. The model requires the measurement of the following climatological variables: the shortwave radiation of the sun, the air temperature, the actual vapour pressure, the relative sunshine and the wind speed. The method is valid for shallow and deep pans (depth between 0.20 m and 2.0 m). The model describes also the daily development of the terms of the energy balance.

  13. 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.

  14. 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.

  15. ROLE OF NUCLEONIC FERMI SURFACE DEPLETION IN NEUTRON STAR COOLING

    SciTech Connect

    Dong, J. M.; Zuo, W.; Lombardo, U.; Zhang, H. F.

    2016-01-20

    The Fermi surface depletion of beta-stable nuclear matter is calculated to study its effects on several physical properties that determine the neutron star (NS) thermal evolution. The neutron and proton Z factors measuring the corresponding Fermi surface depletions are calculated within the Brueckner–Hartree–Fock approach, employing the AV18 two-body force supplemented by a microscopic three-body force. Neutrino emissivity, heat capacity, and in particular neutron {sup 3}PF{sub 2} superfluidity, turn out to be reduced, especially at high baryonic density, to such an extent that the cooling rates of young NSs are significantly slowed.

  16. 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.

  17. Roles for E-cadherin cell surface regulation in cancer

    PubMed Central

    Petrova, Yuliya I.; Schecterson, Leslayann; Gumbiner, Barry M.

    2016-01-01

    The loss of E-cadherin expression in association with the epithelial–mesenchymal transition (EMT) occurs frequently during tumor metastasis. However, metastases often retain E-cadherin expression, an EMT is not required for metastasis, and metastases can arise from clusters of tumor cells. We demonstrate that the regulation of the adhesive activity of E-cadherin present at the cell surface by an inside-out signaling mechanism is important in cancer. First, we find that the metastasis of an E-cadherin–expressing mammary cell line from the mammary gland to the lung depends on reduced E-cadherin adhesive function. An activating monoclonal antibody to E-cadherin that induces a high adhesive state significantly reduced the number of cells metastasized to the lung without affecting the growth in size of the primary tumor in the mammary gland. Second, we find that many cancer-associated germline missense mutations in the E-cadherin gene in patients with hereditary diffuse gastric cancer selectively affect the mechanism of inside-out cell surface regulation without inhibiting basic E-cadherin adhesion function. This suggests that genetic deficits in E-cadherin cell surface regulation contribute to cancer progression. Analysis of these mutations also provides insights into the molecular mechanisms underlying cadherin regulation at the cell surface. PMID:27582386

  18. PHOTOREACTIONS IN SURFACE WATERS AND THEIR ROLE IN BIOGEOCHEMICAL CYCLES

    EPA Science Inventory

    During the past decade significant interest has developed in the influence of photochemical reactions on biogeochemical cycles in surface waters of lakes and the sea. A major portion of recent research on these photoreactions has focused on the colored component of dissolved org...

  19. Self-cleaning of Surfaces: the Role of Surface Wettability and Dust Types

    PubMed Central

    Quan, Yun-Yun; Zhang, Li-Zhi; Qi, Rong-Hui; Cai, Rong-Rong

    2016-01-01

    The self-cleaning property is usually connected to superhydrophobic surfaces (SHSs) where the dust particles can be easily removed by the rolling motion of droplets. It seems that superhydrophobicity (its durability is questionable nowadays) is a necessity. However here, it is disclosed that self-cleaning can also be realized on an ordinary surface by droplet impinging. The effects of surface wettability and the types of dust particles are considered. The self-cleaning is realized by two steps: (1) the pickup of particles by the water-air interface of an impinging droplet, (2) the release of the impinging droplets from the surface. It can be observed that only the trailing edges of the droplets can pick up particles when the droplets recoil from the inclined surfaces. The hydrophilic surface can also achieve self-cleaning under some conditions. This interesting finding may be helpful for the successful implementation of self-cleaning with common surfaces. PMID:27917900

  20. Self-cleaning of Surfaces: the Role of Surface Wettability and Dust Types

    NASA Astrophysics Data System (ADS)

    Quan, Yun-Yun; Zhang, Li-Zhi; Qi, Rong-Hui; Cai, Rong-Rong

    2016-12-01

    The self-cleaning property is usually connected to superhydrophobic surfaces (SHSs) where the dust particles can be easily removed by the rolling motion of droplets. It seems that superhydrophobicity (its durability is questionable nowadays) is a necessity. However here, it is disclosed that self-cleaning can also be realized on an ordinary surface by droplet impinging. The effects of surface wettability and the types of dust particles are considered. The self-cleaning is realized by two steps: (1) the pickup of particles by the water-air interface of an impinging droplet, (2) the release of the impinging droplets from the surface. It can be observed that only the trailing edges of the droplets can pick up particles when the droplets recoil from the inclined surfaces. The hydrophilic surface can also achieve self-cleaning under some conditions. This interesting finding may be helpful for the successful implementation of self-cleaning with common surfaces.

  1. Role of the international organisation for animal health (Office International des Epizooties: OIE) in the control of foot and mouth disease.

    PubMed

    Vallat, B

    2002-10-01

    The author describes activities conducted by the International Organisation for Animal Health (OIE: Office International des Epizooties) to control foot and mouth disease (FMD) world-wide. These activities fall within the framework of the principal missions of the OIE. The first of these missions is the collection and dissemination of epidemiological information and of scientific knowledge on animal diseases, the socio-economic or disease implications of which can be particularly serious. The implementation of the measures required to control the disease and to protect countries threatened by FMD depends on the quality and rapidity of the transmission of this information. The co-ordination of studies, research and control programmes against FMD is equally important for the OIE. This work is based, in particular, on work conducted by the OlE foot and mouth disease and other epizootics Commission. OIE Member Countries not only have access to the most recent data on the diagnosis, surveillance and control of FMD but also have recourse to the official recognition procedure for disease-free status provided by this Commission. Finally, through the standardisation of health recommendations, diagnostic tests, manufacture protocols and the control of biological products, made available by the OIE International Animal Health Code Commission in regard to the former and by the OIE Standards Commission in regard to the latter, the OIE provides the reference for international trade in animals and animal products, and is recognised in this role by the World Trade Organization.

  2. 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.

  3. 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

  4. Theory of Brillouin scattering on a surface grating: Role of surface polaritons

    NASA Astrophysics Data System (ADS)

    Marvin, A. M.; Nizzoli, F.

    1992-05-01

    In a recent paper [W. M. Robertson et al., Phys. Rev. B 41, 4986 (1990)] an empirical and unexplained selection rule governing light scattering by surface acoustic waves on corrugated metal surfaces has been found experimentally, whenever a surface polariton acts as an intermediate state giving rise to a Rayleigh wave replica in the spectra. The replica occurs only when the scattered light is s polarized, independently of the incident polarization. In this paper the Brillouin cross section for a corrugated surface is evaluated theoretically within the extinction-theorem formalism and the above-mentioned selection rule is shown to be valid in the limit of large dielectric constant.

  5. Cubic versus spherical magnetic nanoparticles: the role of surface anisotropy.

    PubMed

    Salazar-Alvarez, G; Qin, J; Sepelák, V; Bergmann, I; Vasilakaki, M; Trohidou, K N; Ardisson, J D; Macedo, W A A; Mikhaylova, M; Muhammed, M; Baró, M D; Nogués, J

    2008-10-08

    The magnetic properties of maghemite (gamma-Fe2O3) cubic and spherical nanoparticles of similar sizes have been experimentally and theoretically studied. The blocking temperature, T(B), of the nanoparticles depends on their shape, with the spherical ones exhibiting larger T(B). Other low temperature properties such as saturation magnetization, coercivity, loop shift or spin canting are rather similar. The experimental effective anisotropy and the Monte Carlo simulations indicate that the different random surface anisotropy of the two morphologies combined with the low magnetocrystalline anisotropy of gamma-Fe2O3 is the origin of these effects.

  6. Towards proteomics-on-chip: the role of the surface.

    PubMed

    Salim, Malinda; McArthur, Sally L; Vaidyanathan, S; Wright, Phillip C

    2011-01-01

    Miniaturisation is revolutionary to high-throughput proteomics. These technologies have gained much interest in the past decade, as they allow for sensitive parallel analysis of small amounts of biological materials. This review describes the state of the art of proteomics-on-chip, with a particular focus on the fundamental proteomics-on-chip challenges. The important role of bio-interfacial interactions and strategies to control them are presented. Various coating methodologies for on-chip protein/peptide separation are reviewed to provide an overview of the principles of protein-resistant and protein immobilisation coatings, and their effectiveness.

  7. 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.

  8. 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.

  9. (Roles of additives and surface control in slurry atomization)

    SciTech Connect

    Not Available

    1992-01-01

    Our experimental results clearly demonstrate that the shape of particles with aspect ratio close to unity dictates the relative suspension viscosity. Suspensions of irregularly shaped particles have higher relative viscosities than suspensions of spherical particles at same volume fractions, in agreement with the reported results at high shear conditions. The relative viscosity of a Newtonian suspension is in excellent agreement with that predicted by the Krieger/Dougherty rigid sphere model using the maximum packing fraction determined from sedimentation as the sole parameter. The relative viscosity of a pseudoplastic suspension is independent of the particle density. It correlates well with the particle Peclet number. The extent of particle diffusion at high shear rates decreases considerably as the particle size increases, and less energy is dissipated as a result. The interparticle electrostatic repulsion plays no significant role in the rheology of pseudoplastic nonaqueous and aqueous glycerol suspensions of noncolloidal particles.

  10. Surface microtopography regulates osteointegration: the role of implant surface microtopography in osteointegration.

    PubMed

    Schwartz, Zvi; Nasazky, Erez; Boyan, Barbara D

    2005-07-01

    Increased surface roughness of dental implants enhances the process of osseointegration. It increases bone conduction and increases BIC in all types of bone, resulting in elevated removal torque values. Surface roughness elevated the CSR of implants implanted in adverse conditions as augmented ridges and sinuses and areas of poor bone, such as the posterior maxilla, and in some cases abolished the deleterious effect of smoking. A growing number of clinical studies suggest that early and immediate loading of rough-surfaced implants may lead to predictable osseointegration. However, it is important to note that these studies provide short-term results based on radiographic observation and clinical mobility only. Before we adopt new surgical and prosthetic guidelines, longer and broader studies are needed. Most recent research has examined the effect of surface roughness on bone healing around implants in vivo and the influence of surface roughness on osteoblasts in vitro. In a study just published, it was found that changing the surface chemistry by submerging an implant in an isotonic sodium chloride solution following acid etching to avoid contamination with molecules from the atmosphere significantly increased osteoblast differentiation in vitro and BIC in vivo. This finding may lead us to a new era in dental implants.

  11. 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.

  12. 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.

  13. Marathon Race Affects Neutrophil Surface Molecules: Role of Inflammatory Mediators.

    PubMed

    Santos, Vinicius Coneglian; Sierra, Ana Paula Renno; Oliveira, Rodrigo; Caçula, Kim Guimarães; Momesso, César Miguel; Sato, Fabio Takeo; Silva, Maysa Braga Barros; Oliveira, Heloisa Helena; Passos, Maria Elizabeth Pereira; de Souza, Diego Ribeiro; Gondim, Olivia Santos; Benetti, Marino; Levada-Pires, Adriana Cristina; Ghorayeb, Nabil; Kiss, Maria Augusta Peduti Dal Molin; Gorjão, Renata; Pithon-Curi, Tânia Cristina; Cury-Boaventura, Maria Fernanda

    2016-01-01

    The fatigue induced by marathon races was observed in terms of inflammatory and immunological outcomes. Neutrophil survival and activation are essential for inflammation resolution and contributes directly to the pathogenesis of many infectious and inflammatory conditions. The aim of this study was to investigate the effect of marathon races on surface molecules related to neutrophil adhesion and extrinsic apoptosis pathway and its association with inflammatory markers. We evaluated 23 trained male runners at the São Paulo International Marathon 2013. The following components were measured: hematological and inflammatory mediators, muscle damage markers, and neutrophil function. The marathon race induced an increased leukocyte and neutrophil counts; creatine kinase (CK), lactate dehydrogenase (LDH), CK-MB, interleukin (IL)-6, IL-10, and IL-8 levels. C-reactive protein (CRP), IL-12, and tumor necrosis factor (TNF)-α plasma concentrations were significantly higher 24 h and 72 h after the marathon race. Hemoglobin and hematocrit levels decreased 72 h after the marathon race. We also observed an increased intercellular adhesion molecule-1 (ICAM-1) expression and decreasedTNF receptor-1 (TNFR1) expression immediately after and 24 h after the marathon race. We observed an increased DNA fragmentation and L-selectin and Fas receptor expressions in the recovery period, indicating a possible slow rolling phase and delayed neutrophil activation and apoptosis. Marathon racing affects neutrophils adhesion and survival in the course of inflammation, supporting the "open-window" post-exercise hypothesis.

  14. Marathon Race Affects Neutrophil Surface Molecules: Role of Inflammatory Mediators

    PubMed Central

    2016-01-01

    The fatigue induced by marathon races was observed in terms of inflammatory and immunological outcomes. Neutrophil survival and activation are essential for inflammation resolution and contributes directly to the pathogenesis of many infectious and inflammatory conditions. The aim of this study was to investigate the effect of marathon races on surface molecules related to neutrophil adhesion and extrinsic apoptosis pathway and its association with inflammatory markers. We evaluated 23 trained male runners at the São Paulo International Marathon 2013. The following components were measured: hematological and inflammatory mediators, muscle damage markers, and neutrophil function. The marathon race induced an increased leukocyte and neutrophil counts; creatine kinase (CK), lactate dehydrogenase (LDH), CK-MB, interleukin (IL)-6, IL-10, and IL-8 levels. C-reactive protein (CRP), IL-12, and tumor necrosis factor (TNF)-α plasma concentrations were significantly higher 24 h and 72 h after the marathon race. Hemoglobin and hematocrit levels decreased 72 h after the marathon race. We also observed an increased intercellular adhesion molecule-1 (ICAM-1) expression and decreasedTNF receptor-1 (TNFR1) expression immediately after and 24 h after the marathon race. We observed an increased DNA fragmentation and L-selectin and Fas receptor expressions in the recovery period, indicating a possible slow rolling phase and delayed neutrophil activation and apoptosis. Marathon racing affects neutrophils adhesion and survival in the course of inflammation, supporting the “open-window” post-exercise hypothesis. PMID:27911915

  15. Surface affinity role in graphoepitaxy of lamellar block copolymers

    NASA Astrophysics Data System (ADS)

    Claveau, Guillaume; Quemere, Patrick; Argoud, Maxime; Hazart, Jerome; Barros, Patricia Pimenta; Sarrazin, Aurelien; Posseme, Nicolas; Tiron, Raluca; Chevalier, Xavier; Nicolet, Celia; Navarro, Christophe

    2016-07-01

    Overcoming the optical limitations of 193-nm 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 300-mm pilot line available in LETI and Arkema's advanced materials, we investigate process optimization of DSA line/space patterning of a 38-nm period lamellar PS-b-PMMA BCP (L38). Our integration scheme 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 function of either commensurability, morphology, or roughness. This work is meant as a guideline for the graphoepitaxy optimization of materials and process parameters on a 300-mm platform.

  16. Impact de la preparation des anodes crues et des conditions de cuisson sur la fissuration dans des anodes denses

    NASA Astrophysics Data System (ADS)

    Amrani, Salah

    La fabrication de l'aluminium est realisee dans une cellule d'electrolyse, et cette operation utilise des anodes en carbone. L'evaluation de la qualite de ces anodes reste indispensable avant leur utilisation. La presence des fissures dans les anodes provoque une perturbation du procede l'electrolyse et une diminution de sa performance. Ce projet a ete entrepris pour determiner l'impact des differents parametres de procedes de fabrication des anodes sur la fissuration des anodes denses. Ces parametres incluent ceux de la fabrication des anodes crues, des proprietes des matieres premieres et de la cuisson. Une recherche bibliographique a ete effectuee sur tous les aspects de la fissuration des anodes en carbone pour compiler les travaux anterieurs. Une methodologie detaillee a ete mise au point pour faciliter le deroulement des travaux et atteindre les objectifs vises. La majorite de ce document est reservee pour la discussion des resultats obtenus au laboratoire de l'UQAC et au niveau industriel. Concernant les etudes realisees a l'UQAC, une partie des travaux experimentaux est reservee a la recherche des differents mecanismes de fissuration dans les anodes denses utilisees dans l'industrie d'aluminium. L'approche etait d'abord basee sur la caracterisation qualitative du mecanisme de la fissuration en surface et en profondeur. Puis, une caracterisation quantitative a ete realisee pour la determination de la distribution de la largeur de la fissure sur toute sa longueur, ainsi que le pourcentage de sa surface par rapport a la surface totale de l'echantillon. Cette etude a ete realisee par le biais de la technique d'analyse d'image utilisee pour caracteriser la fissuration d'un echantillon d'anode cuite. L'analyse surfacique et en profondeur de cet echantillon a permis de voir clairement la formation des fissures sur une grande partie de la surface analysee. L'autre partie des travaux est basee sur la caracterisation des defauts dans des echantillons d'anodes crues

  17. Global Climatology of Surface Precipitation: Role of TRMM and GPM

    NASA Astrophysics Data System (ADS)

    Adler, R. F.; Wang, J.; Gu, G.

    2011-12-01

    An accurate estimate of global and regional precipitation in terms of climatology, inter-annual variations and trends is critical to understand our planet's state in terms of water availability and the impact of climate change phenomena such as global warming. The Global Precipitation Climatology Project (GPCP) data set has been a highly used satellite and gauge merged product for studies in these areas. Data from the Tropical Rainfall Measuring Mission (TRMM), now spanning almost 14 years in length, is considered to be the most accurate satellite estimation of tropical precipitation, due to its passive microwave, radar and combined estimates of surface precipitation. The Global Precipitation Measurement (GPM) mission will follow in TRMM's footsteps, improving the quality of the precipitation estimations even more with improved instrumentation and expanding the latitude range to middle and high latitudes. The development of accurate climatologies and even monthly estimates from these missions will be valuable in themselves, but also presents an opportunity to incorporate their advanced information into merged, long-term observational data sets such as the GPCP analysis. An example of the use of TRMM (and eventually GPM) data in developing a new tropical climatology will be described as the TRMM Composite Climatology (TCC), based on a combination of thirteen years (1998-2010) of various precipitation products (Version 6) from TRMM. The TCC consists of a merger of three selected TRMM rainfall products over both land and ocean to give a "TRMM-best" climatological estimate. Inputs to the composite were selected based on knowledge of the performance of the retrievals, limitations of the algorithms, and the presence of artifacts. In addition to the mean precipitation estimates, the TCC includes the variation among the three estimates at each point to give an estimate of the error in the estimated mean value. Comparison of the TCC with validation data and with the GPCP

  18. Traitement des conditions aux limites intérieures et extérieures pour la simulation numérique unidimensionnelle de l'écoulement de l'eau dans les canaux à surface libre

    NASA Astrophysics Data System (ADS)

    Abdallah, M.; Vazquez, J.; Mose, R.; Zoaeter, M.

    2005-05-01

    Dans ce papier, on décrit le traitement des conditions aux limites intérieures et extérieures couplé avec la méthode explicite aux différences finies de Roe pour le développement d'une modélisation unidimensionnelle qui sert à résoudre les équations de Saint-Venant décrivant l'écoulement de l'eau à surface libre. Les deux méthodes les plus utilisées pour trouver la solution aux nœuds intérieurs et extérieurs définissant les conditions aux limites intérieures et extérieures d'un schéma numérique sont décrites et comparées dans deux exemples: Le premier traite le problème du ressaut hydraulique et le second décrit l'écoulement de l'eau au dessus des seuils. Deux types de discrétisation du terme source, pointwise et upwind, sont considérés et comparés aussi. Les résultats obtenus et comparés avec la solution analytique dans le cas du ressaut, et avec les résultats numériques déjà publiés dans le cas des seuils, montrent l'avantage de la méthode des caractéristiques sur la méthode de l'extrapolation pour les conditions aux limites, et la discrétisation upwind du terme source sur la discrétisation pointwise.

  19. Adhesion of Cryptosporidium parvum and Giardia lamblia to solid surfaces: the role of surface charge and hydrophobicity.

    PubMed

    Dai, X; Boll, J; Hayes, M E; Aston, D E

    2004-04-15

    Adhesion of Cryptosporidium parvum and Giardia lamblia to four materials of different surface charge and hydrophobicity was investigated. Glass beads were used with and without three polymer coatings: aminosilines (A0750), fluorosilines (T2494), an amino cationic polymer. Surface charge density and hydrophobicity of the beads were characterized by measuring the zeta potential (ZP) and the contact angle, respectively. Adhesion was derived from batch experiments where negatively charged (oo)cysts were mixed with the beads and recovery was determined by counting (oo)cysts remaining in suspension using a flow cytometer. Experimental results clearly show that adhesion to solid surfaces of C. parvum is different from G. lamblia. Adhesion of C. parvum to positively charged, hydrophilic beads (82% recovery relative to control) indicated that surface charge was the more important factor for C. parvum, dominating any hydrophobic effects. Adhesion of G. lamblia cysts to negatively charged, hydrophobic beads (0% recovery relative to control) indicated that although hydrophobicity and surface charge both played a role in the adhesion of G. lamblia to solid surfaces, hydrophobicity was more important than surface charge.

  20. Etude de la migration des interstitiels dans des austenites Fe, Cr (18), Ni (14) pures et industrielles par irradiation dans un microscope a tres haute tension: Role du carbone et du titane

    NASA Astrophysics Data System (ADS)

    Housseau, N.; Pelissier, J.

    1983-12-01

    Nous avons étudié le rôle des impurtés (C ou Ti) dans la condensation et la migration des défauts interstitiels. Les échantillons étudiés sont des aciers austénitiques: (a) acier de synthèse de haute pureté (Cr 18, Ni 14, Fe) avec ou sans carbone; (b) acier industriel avec C (800 ppm) ou Ti (0,45%). Les échantillons ont été irradiés dans un microscope à très haute tension aux doses allant de 10 -4 jusqu'à 10 -1 dpa aux températures de 300°C à 400°C. Dans de telles conditions les défauts observés sont des boucles interstitielles. L'étude de la variation de l'épaisseur de la zone dénudée près du bord de la lame mince en fonction de la température nous a permis d'évaluer l'énergie de migration effective de l'interstitiel dans ces alliages. Dans l'austénite de synthèse carburée ou non sa valeur est de 0.8 eV. Dans l'acier industriel au titane carburé ou non on obtient 2.0 eV. Nous n'avons pas observé d'effet lié au carbone. L'examen de la densité de boucles à saturation dans les divers aciers suggère une forte énergie de liaison interstitiel-titane. Cette énergie de liaison, si l'ont admet que le titane est la seule impureté agissante du système, peut être estimée à 1.2 eV.

  1. 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

  2. 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.

  3. 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

    2014-10-17

    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.

  4. 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

  5. Larval settlement: the role of surface topography for sessile coral reef invertebrates.

    PubMed

    Whalan, Steve; Wahab, Muhammad A Abdul; 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.

  6. Biosorption of thorium on the external shell surface of bivalve mollusks: the role of shell surface microtopography.

    PubMed

    Zuykov, Michael; Pelletier, Emilien; Saint-Louis, Richard; Checa, Antonio; Demers, Serge

    2012-02-01

    External shell surface (ESS) of bivalve mollusks is known to adsorb various metals dissolved in ambient water in high concentration. It is hypothesized here that the surface microtopography of the thin organic coating layer, periostracum, or calcareous shell (if periostracum was destroyed) plays a major role in the adsorption of actinides on ESS. Thorium (natural alpha-emitter) was used in short-term biosorption experiment with shell fragments of five bivalve mollusks. After a 72 h exposure to Th (~6 kBq L(-1)), thorium concentration was measured on ESS using laser ablation inductively coupled plasma mass spectrometry; the distribution and density of alpha tracks were subsequently visualized by α-track autoradiography. A trend in reduced Th concentrations on the ESS was observed depending upon the species tested: (group 1 ~4000 μg g(-1)) Chlamys islandica (M.), Mercenaria mercenaria (L.), Dreissena polymorpha (P.)>(group 2 ~1200 μg g(-1)) Crassostrea virginica (G.)≫(group 3 ~150 μg g(-1)) Mytilus edulis L. The microtopography of ESS was characterized by scanning electron microscopy revealing the high porosity of the calcareous surface of C. islandica and M. mercenaria, lamellate surface of periostracum in D. polymorpha, uneven but a weakly porous surface of periostracum of C. virginica, and a nearly smooth surface of the periostracum of M. edulis. This work has demonstrated, for the first time, the presence of a strong correlation between concentration of adsorbed Th and ESS microtopography, and the role of the periostracum in this process is discussed.

  7. The role of amine surface density in carbon dioxide adsorption on functionalized mixed oxide surfaces.

    PubMed

    Young, Pria D; Notestein, Justin M

    2011-11-18

    Supported amines are considered as adsorbents to replace aqueous amines for carbon capture and for CO(2) capture/conversion into chemicals. Here, amines are grafted to SiO(2) or Ti-SiO(2) by using aminopropyl triethoxysilane (APTES) or (3-triethoxysilylpropyl)-tert-butylcarbamate (TESPtBC) and then removing the carbamate group introduced by the latter by mild heating to 'deprotect' the amine. Structures are verified by using (13) C cross polarization magic angle spinning (CP/MAS) NMR spectroscopy, acid titration, thermogravimetric analysis, and elemental analysis. Diffuse reflectance UV/Visible spectroscopy shows that amines from APTES coordinate directly to Ti cations, whereas Ti cations remain coordinatively unsaturated after grafting of TESPtBC and deprotection. CO(2) chemisorption is studied as a function of amine precursor, average surface density, and the presence of Ti. CO(2) uptake increases from <0.02 CO(2) per amine for as-synthesized TESPtBC materials to only approximately 0.05 CO(2) per amine for the isolated amines present after deprotection. In contrast, clustered amines from APTES chemisorb up to approximately 0.35 CO(2) per amine. Cooperative ammonium carbamates form preferentially above an apparent local density of 0.6 amines per nm(2) from APTES, but do not form even up to 0.9 amines per nm(2) for TESPtBC-derived materials. This suggests that the true local surface density form APTES is underestimated by as much as 150 %. CO(2) uptake falls to <0.01 CO(2) per amine for ATPES on TiSiO(2), but uptake is less affected for the 'protected' TESPtBC precursor. These results show that TESPtBC may be a viable precursor for applications in acid-base cooperative CO(2) conversion catalysts, and that variation in the local amine surface density and the chemistry of the underlying support may account for some of the large variability in reported CO(2) capacities of supported amine materials in literature.

  8. Independent and collective roles of surface structures at different length scales on pool boiling heat transfer

    PubMed Central

    Li, Calvin H.; Rioux, Russell P.

    2016-01-01

    Spherical Cu nanocavity surfaces are synthesized to examine the individual role of contact angles in connecting lateral Rayleigh-Taylor wavelength to vertical Kevin-Helmholtz wavelength on hydrodynamic instability for the onset of pool boiling Critical Heat Flux (CHF). Solid and porous Cu pillar surfaces are sintered to investigate the individual role of pillar structure pitch at millimeter scale, named as module wavelength, on hydrodynamic instability at CHF. Last, spherical Cu nanocavities are coated on the porous Cu pillars to create a multiscale Cu structure, which is studied to examine the collective role and relative significance of contact angles and module wavelength on hydrodynamic instability at CHF, and the results indicate that module wavelength plays the dominant role on hydrodynamic instability at CHF when the height of surface structures is equal or above ¼ Kelvin-Helmholtz wavelength. Pool boiling Heat Transfer Coefficient (HTC) enhancements on spherical Cu nanocavity surfaces, solid and porous Cu pillar surfaces, and the integrated multiscale structure have been investigated, too. The experimental results reveal that the nanostructures and porous pillar structures can be combined together to achieve even higher enhancement of HTC than that of individual structures. PMID:27841322

  9. Independent and collective roles of surface structures at different length scales on pool boiling heat transfer.

    PubMed

    Li, Calvin H; Rioux, Russell P

    2016-11-14

    Spherical Cu nanocavity surfaces are synthesized to examine the individual role of contact angles in connecting lateral Rayleigh-Taylor wavelength to vertical Kevin-Helmholtz wavelength on hydrodynamic instability for the onset of pool boiling Critical Heat Flux (CHF). Solid and porous Cu pillar surfaces are sintered to investigate the individual role of pillar structure pitch at millimeter scale, named as module wavelength, on hydrodynamic instability at CHF. Last, spherical Cu nanocavities are coated on the porous Cu pillars to create a multiscale Cu structure, which is studied to examine the collective role and relative significance of contact angles and module wavelength on hydrodynamic instability at CHF, and the results indicate that module wavelength plays the dominant role on hydrodynamic instability at CHF when the height of surface structures is equal or above ¼ Kelvin-Helmholtz wavelength. Pool boiling Heat Transfer Coefficient (HTC) enhancements on spherical Cu nanocavity surfaces, solid and porous Cu pillar surfaces, and the integrated multiscale structure have been investigated, too. The experimental results reveal that the nanostructures and porous pillar structures can be combined together to achieve even higher enhancement of HTC than that of individual structures.

  10. Independent and collective roles of surface structures at different length scales on pool boiling heat transfer

    NASA Astrophysics Data System (ADS)

    Li, Calvin H.; Rioux, Russell P.

    2016-11-01

    Spherical Cu nanocavity surfaces are synthesized to examine the individual role of contact angles in connecting lateral Rayleigh-Taylor wavelength to vertical Kevin-Helmholtz wavelength on hydrodynamic instability for the onset of pool boiling Critical Heat Flux (CHF). Solid and porous Cu pillar surfaces are sintered to investigate the individual role of pillar structure pitch at millimeter scale, named as module wavelength, on hydrodynamic instability at CHF. Last, spherical Cu nanocavities are coated on the porous Cu pillars to create a multiscale Cu structure, which is studied to examine the collective role and relative significance of contact angles and module wavelength on hydrodynamic instability at CHF, and the results indicate that module wavelength plays the dominant role on hydrodynamic instability at CHF when the height of surface structures is equal or above ¼ Kelvin-Helmholtz wavelength. Pool boiling Heat Transfer Coefficient (HTC) enhancements on spherical Cu nanocavity surfaces, solid and porous Cu pillar surfaces, and the integrated multiscale structure have been investigated, too. The experimental results reveal that the nanostructures and porous pillar structures can be combined together to achieve even higher enhancement of HTC than that of individual structures.

  11. The role of strain in the surface structures of III-V alloyed semiconductor films

    NASA Astrophysics Data System (ADS)

    Bickel, Jessica E.

    As length scales continue to decrease, it is vital to understand the fundamental physical parameters governing surfaces and surface interactions. In semiconductors particularly, surface reconstructions are known to impact film growth, bulk atomic ordering and the development of interfacial structure, all of which can drastically impact device growth. While the parameters that determine surface reconstructions in homoepitaxially grown films are well known and understood, those that impact alloy film growth are less studied. This work examines the impact of strain on alloy surface reconstructions, using the III-V semiconductors as a model system for any covalently bonded crystal structure. The presence of surface reconstruction coexistence in both mixed cation and mixed anion systems suggests that localized strain fields on alloy surfaces stabilize elastic relaxation at boundaries, resulting in more complex surface structures than those seen on binary, unstrained films. Atomic size mismatch strain is shown to induce an ordering in alloyed surface reconstructions that is not seen in the non-alloyed constituent surfaces. Lattice mismatch strain is shown to both stabilize new reconstructions not common to the homoepitaxial system and to induce surface reconstruction coexistence on alloy surfaces. The supplied flux of material is shown to affect the kinetics of transformation between the two coexisting surface reconstructions and an incorporation model for material on the alloy surface is developed. The effects of strained surface reconstructions on subsequent film growth is explored and it is shown that identical films grown on two different surfaces have very different strain relaxation profiles, surface topographies and defect structures. The strain fields of surface reconstructions and defects are also shown to interact which may have an impact on the insertion of dislocations in these films. Combined together, this deep understanding of the role that alloy induced

  12. The role of motility and chemotaxis in the bacterial colonization of protected surfaces

    PubMed Central

    Tamar, Einat; Koler, Moriah; Vaknin, Ady

    2016-01-01

    Internal epithelial surfaces in humans are both oxygenated and physically protected by a few hundred microns thick hydrogel mucosal layer, conditions that might support bacterial aerotaxis. However, the potential role of aerotaxis in crossing such a thin hydrogel layer is not clear. Here, we used a new setup to study the potential role of motility and chemotaxis in the bacterial colonization of surfaces covered by a thin hydrogel layer and subjected to a vertical oxygen gradient. Using the bacterium Escherichia coli, we show that both non-motile and motile-but-non-chemotactic bacteria could barely reach the surface. However, an acquired mutation in the non-chemotactic bacteria that altered their inherent swimming behavior led to a critical enhancement of surface colonization. Most chemotactic strains accumulated within the bulk of the hydrogel layer, except for the MG1655 strain, which showed a unique tendency to accumulate directly at the oxygenated surface and thus exhibited distinctly enhanced colonization. Even after a long period of bacterial growth, non-motile bacteria could not colonize the hydrogel. Thus, switching motility, which can be spontaneously acquired or altered in vivo, is critical for the colonization of such protected surfaces, whereas aerotaxis capacity clearly expedites surface colonization, and can lead to diverse colonization patterns. PMID:26792493

  13. Role of Flagella in Adhesion of Escherichia coli to Abiotic Surfaces.

    PubMed

    Friedlander, Ronn S; Vogel, Nicolas; Aizenberg, Joanna

    2015-06-09

    Understanding the interfacial activity of bacteria is of critical importance due to the huge economic and public health implications associated with surface fouling and biofilm formation. The complexity of the process and difficulties of predicting microbial adhesion to novel materials demand study of the properties of specific bacterial surface features and their potential contribution to surface attachment. Here, we examine flagella, cell appendages primarily studied for their cell motility function, to elucidate their potential role in the surface adhesion of Escherichia coli-a model organism and potential pathogen. We use self-assembled monolayers (SAMs) of thiol-bearing molecules on gold films to generate surfaces of varying hydrophobicity, and measure adhesion of purified flagella using quartz crystal microbalance. We show that flagella adhere more extensively and bind more tightly to hydrophobic SAMs than to hydrophilic ones, and we propose a two-step vs a single-step adhesion mechanism that accounts for the observed dissipation and frequency changes for the two types of surfaces, respectively. Subsequently, study of the adhesion of wild-type and flagella knockout cells confirms that flagella improve adhesion to hydrophobic substrates, whereas cells lacking flagella do not show preferred affinity to hydrophobic substrates. Together, these properties bring about an interesting ability of cells with flagella to stabilize emulsions of aqueous culture and dodecane, not observed for cells lacking flagella. This work contributes to our overall understanding of nonspecific bacterial adhesion and confirms that flagella, beyond motility, may play an important role in surface adhesion.

  14. Role of biomechanical cues on neuronal growth on asymmetric textured surfaces

    NASA Astrophysics Data System (ADS)

    Staii, Cristian; Spedden, Elise; Atherton, Timothy; Sekeroglu, Koray; Demirel, Melik

    2013-03-01

    Axonal growth and the formation of synaptic connections are key steps in the development of the nervous system. Here we present experimental and theoretical results on axonal growth on unidirectional nanotextured surface, and demonstrate that these surface can bias axonal growth. We also perform a systematic investigation of neuronal processes on these surfaces and quantify the role that biomechanical surface cues play in neuronal growth. We show that these surfaces provide a model growth substrates, which allow us to perform systematic studies of the interplay between mechanical, biochemical and topographical cues that contribute to neuronal growth. The authors gratefully acknowledge financial support from the National Institutes of Health (1R21HL112114-01), National Science Foundation (NSF-CBET 1067093), Tufts University and The Pennsylvania State University

  15. Insight in the role of bovine serum albumin for promoting the in situ surface growth of polyhydroxybutyrate (PHB) on patterned surfaces via enzymatic surface-initiated polymerization.

    PubMed

    Niamsiri, Nuttawee; Bergkvist, Magnus; Delamarre, Soazig C; Cady, Nathan C; Coates, Geoffrey W; Ober, Christopher K; Batt, Carl A

    2007-10-15

    Polyhydroxyalkanoates (PHAs) are a family of aliphatic polyesters produced by a variety of microorganisms as a reserve of carbon and energy. Enzymes involved in the synthesis of PHAs can be utilized to produce polymers in vitro, both in bulk and on solid surfaces. Here, site-specific attachment of the key catalytic enzyme, PHA synthase, on lithographically patterned surfaces and subsequent addition of (R)-3-hydroxybutyryl-CoA substrate allowed us to fabricate spatially ordered polyhydroxybutyrate (PHB) polymeric structures via an in situ enzymatic surface-initiated polymerization (ESIP). By varying the reaction conditions, we enhanced the growth of PHB on solid surfaces and analyzed the resulting structures by fluorescence microscopy, atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and gel permeation chromatography (GPC). We found that stabilization of smaller PHB granule structures by an addition of bovine serum albumin (BSA) was the most important factor for a successful synthesis of a PHB layer up to 1mum in thickness, consisting mainly of larger cluster assemblies of PHB granules that cover the entire patterned area. Immunofluorescence detection and surface contact angle analysis revealed that BSA was physically bound to the PHB polymer all through the cluster, and reduced the overall hydrophobicity of the polymer surface. Based on information obtained from AFM, kinetic measurements and various polymer characterization methods, a plausible model for roles of BSA in the enhancement of PHB formation on surfaces is discussed. Furthermore, by using biotinylated BSA conjugates, we were able to incorporate biotin groups into the PHB polymer matrix, thus generating a bioactive surface that can be used for displaying other functional biomolecules through streptavidin-biotin interaction on the PHB structures. Because of its versatility, our fabrication strategy is expected to be a useful surface

  16. Role of surface defects and microstructure in infrared optical properties of thermochromic VO2 materials

    NASA Astrophysics Data System (ADS)

    Guinneton, Frédéric; Sauques, Laurent; Valmalette, Jean-Christophe; Cros, Frédéric; Gavarri, Jean-Raymond

    2005-01-01

    Thermochromic vanadium dioxide VO2 exhibits a semi-conducting to metallic phase transition at Tc=68 °C, involving strong variations in optical transmittance, reflectance and emissivity. However, the optical contrasts observed in thin films or nanostructured compacted samples seem to depend on both surface microstructure and surface crystal texture. In the case of opaque materials, surface defects might play a drastic role in optical reflectivity. As the high temperature metallic phase of VO2 is opaque for infrared radiations, we used aluminum samples as standards allowing us to correlate reflectivity responses with porosity and surface defects. Then, various polycrystalline and nanostructured VO2 samples compacted at various pressures and presenting variable surface roughness were prepared. Thin films were deposited by radio frequency sputtering process. The samples were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Optical properties (reflectance and emissivity) were analyzed above and below the transition temperature, making use of specific FTIR equipments. In thin films, the deposited VO2 phase was systematically oriented and surface porosity was very weak. In polycrystalline samples, as the compaction pressure increased, surface porosity decreased, and infrared optical contrast increased. In such samples, preferred orientations were favored for low applied pressures. These features clearly show that the main parameters conditioning the optical contrast should be the surface defects and porosity, not the preferred crystal orientations. As an additional interesting result, the surfaces formed from compacted nanocrystalline VO2 powders present improved optical contrast for reflectance and emissivity properties.

  17. Role of vimA in cell surface biogenesis in Porphyromonas gingivalis

    PubMed Central

    Osbourne, Devon O.; Aruni, Wilson; Roy, Francis; Perry, Christopher; Sandberg, Lawrence; Muthiah, Arun; Fletcher, Hansel M.

    2010-01-01

    The Porphyromonas gingivalis vimA gene has been previously shown to play a significant role in the biogenesis of gingipains. Further, in P. gingivalis FLL92, a vimA-defective mutant, there was increased auto-aggregation, suggesting alteration in membrane surface proteins. In order to determine the role of the VimA protein in cell surface biogenesis, the surface morphology of P. gingivalis FLL92 was further characterized. Transmission electron microscopy demonstrated abundant fimbrial appendages and a less well defined and irregular capsule in FLL92 compared with the wild-type. In addition, atomic force microscopy showed that the wild-type had a smoother surface compared with FLL92. Western blot analysis using anti-FimA antibodies showed a 41 kDa immunoreactive protein band in P. gingivalis FLL92 which was missing in the wild-type P. gingivalis W83 strain. There was increased sensitivity to globomycin and vancomycin in FLL92 compared with the wild-type. Outer membrane fractions from FLL92 had a modified lectin-binding profile. Furthermore, in contrast with the wild-type strain, nine proteins were missing from the outer membrane fraction of FLL92, while 20 proteins present in that fraction from FLL92 were missing in the wild-type strain. Taken together, these results suggest that the VimA protein affects capsular synthesis and fimbrial phenotypic expression, and plays a role in the glycosylation and anchorage of several surface proteins. PMID:20378652

  18. The role of surface heterogeneity and lateral interactions in the adsorption of volatile organic compounds on rutile surface

    NASA Astrophysics Data System (ADS)

    Metaxa, E.; Kolliopoulos, A.; Agelakopoulou, T.; Roubani-Kalantzopoulou, F.

    2009-04-01

    Volatile organic compounds (VOCs) are pollutants of great interest because they are very harmful for both human health and the environment, even at very low concentrations. In this work we present and discuss the results of the experimental chromatographic study of the role of surface heterogeneity and lateral interactions in the adsorption of volatile organic compounds - ethanol, acetaldehyde and acetone - on the surface of rutile (TiO 2), a typical oxide widely used as a white pigment and a photocatalyst, as well. The ethanol, acetaldehyde and acetone were chosen because they contain the same heteroatom (O) and they have small carbon-chains. The novel method of Reversed Flow-Inverse Gas Chromatography is used, which has a powerful mathematical background and comprises a simple experimental arrangement for the determination of energetic physicochemical quantities directly from the experimental data, by means of a time-resolved analysis. In particular, several important physicochemical quantities are determined, as local adsorption energy, local adsorption isotherm, local monolayer capacity, non-adsorbed gaseous concentration of adsorbate, density probability function for the adsorption energy values, as well as the differential energy of adsorption due to lateral interactions among molecules adsorbed on the heterogeneous solid surface of TiO 2. By means of these quantities, appropriate answers are achieved to critical questions of: (a) What is the type of the adsorption isotherm of a system? (b) Where are the adsorbed molecules located on the heterogeneous surface? (c) What is the nature of the surface bonds? (d) What is the type of non-ideality of the system and (e) How does the adsorbate affect the adsorbent properties?

  19. 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.

  20. 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.

  1. Surface proteins of Staphylococcus aureus play an important role in experimental skin infection.

    PubMed

    Kwiecinski, Jakub; Jin, Tao; Josefsson, Elisabet

    2014-12-01

    Staphylococcus aureus is the most common cause of skin infections that range from mild diseases up to life-threatening conditions. Mechanisms of S. aureus virulence in those infections remain poorly studied. To investigate the impact of S. aureus surface proteins on skin infection, we used mouse models of skin abscess formation and skin necrosis, induced by a subcutaneous injection of bacteria. In the skin abscess model, a sortase-deficient S. aureus strain lacking all of its cell-wall anchored proteins was less virulent than its wild-type strain. Also, strains specifically lacking protein A, fibronecting binding proteins, clumping factor A or surface protein SasF were impaired in their virulence. When a model of dermonecrosis was studied, the S. aureus surface proteins could not be shown to be involved. In summary, surface proteins play an important role in virulence of S. aureus skin abscess infections, but not in formation of skin necrosis.

  2. Defining the Role of Excess Electrons in the Surface Chemistry of TiO2

    SciTech Connect

    Deskins, N. Aaron; Rousseau, Roger J.; Dupuis, Michel

    2010-04-08

    We have performed a systematic study of the role of excess electrons resulting from points defects such as oxygen vacancies, bridging row hydroxyls, and interstitial Ti species in TiO2 on adsorbed surface species using density functional theory. Strong charge transfer to adsorbates affects significantly their binding and reactivity. Specifically we examined the adsorption and reactivity of O2 in detail. We also present a generalization of these findings for a variety of species by characterizing the Lewis acid/base properties of the surface/adsorbate complex: when the electronegativity of the adsorbate is greater than the surface electronegativity (or work function) charge transfer from the reduced surface to the absorbate occurs. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Role of nanostructured gold surfaces on monocyte activation and Staphylococcus epidermidis biofilm formation

    PubMed Central

    Svensson, Sara; Forsberg, Magnus; Hulander, Mats; Vazirisani, Forugh; Palmquist, Anders; Lausmaa, Jukka; Thomsen, Peter; Trobos, Margarita

    2014-01-01

    The role of material surface properties in the direct interaction with bacteria and the indirect route via host defense cells is not fully understood. Recently, it was suggested that nanostructured implant surfaces possess antimicrobial properties. In the current study, the adhesion and biofilm formation of Staphylococcus epidermidis and human monocyte adhesion and activation were studied separately and in coculture in different in vitro models using smooth gold and well-defined nanostructured gold surfaces. Two polystyrene surfaces were used as controls in the monocyte experiments. Fluorescent viability staining demonstrated a reduction in the viability of S. epidermidis close to the nanostructured gold surface, whereas the smooth gold correlated with more live biofilm. The results were supported by scanning electron microscopy observations, showing higher biofilm tower formations and more mature biofilms on smooth gold compared with nanostructured gold. Unstimulated monocytes on the different substrates demonstrated low activation, reduced gene expression of pro- and anti-inflammatory cytokines, and low cytokine secretion. In contrast, stimulation with opsonized zymosan or opsonized live S. epidermidis for 1 hour significantly increased the production of reactive oxygen species, the gene expression of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and IL-10, as well as the secretion of TNF-α, demonstrating the ability of the cells to elicit a response and actively phagocytose prey. In addition, cells cultured on the smooth gold and the nanostructured gold displayed a different adhesion pattern and a more rapid oxidative burst than those cultured on polystyrene upon stimulation. We conclude that S. epidermidis decreased its viability initially when adhering to nanostructured surfaces compared with smooth gold surfaces, especially in the bacterial cell layers closest to the surface. In contrast, material surface properties neither strongly

  10. Fluctuations Magnetiques des Gaz D'electrons Bidimensionnels: Application AU Compose Supraconducteur LANTHANE(2-X) Strontium(x) Cuivre OXYGENE(4)

    NASA Astrophysics Data System (ADS)

    Benard, Pierre

    Nous presentons une etude des fluctuations magnetiques de la phase normale de l'oxyde de cuivre supraconducteur La_{2-x}Sr _{x}CuO_4 . Le compose est modelise par le Hamiltonien de Hubbard bidimensionnel avec un terme de saut vers les deuxiemes voisins (modele tt'U). Le modele est etudie en utilisant l'approximation de la GRPA (Generalized Random Phase Approximation) et en incluant les effets de la renormalisation de l'interaction de Hubbard par les diagrammes de Brueckner-Kanamori. Dans l'approche presentee dans ce travail, les maximums du facteur de structure magnetique observes par les experiences de diffusion de neutrons sont associes aux anomalies 2k _{F} de reseau du facteur de structure des gaz d'electrons bidimensionnels sans interaction. Ces anomalies proviennent de la diffusion entre particules situees a des points de la surface de Fermi ou les vitesses de Fermi sont tangentes, et conduisent a des divergences dont la nature depend de la geometrie de la surface de Fermi au voisinage de ces points. Ces resultats sont ensuite appliques au modele tt'U, dont le modele de Hubbard usuel tU est un cas particulier. Dans la majorite des cas, les interactions ne determinent pas la position des maximums du facteur de structure. Le role de l'interaction est d'augmenter l'intensite des structures du facteur de structure magnetique associees a l'instabilite magnetique du systeme. Ces structures sont souvent deja presentes dans la partie imaginaire de la susceptibilite sans interaction. Le rapport d'intensite entre les maximums absolus et les autres structures du facteur de structure magnetique permet de determiner le rapport U_ {rn}/U_{c} qui mesure la proximite d'une instabilite magnetique. Le diagramme de phase est ensuite etudie afin de delimiter la plage de validite de l'approximation. Apres avoir discute des modes collectifs et de l'effet d'une partie imaginaire non-nulle de la self-energie, l'origine de l'echelle d'energie des fluctuations magnetiques est examinee

  11. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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.

  13. [Adhesion of corynebacterium diphtheriae: the role of surface structures and formation mechanism].

    PubMed

    Kharseeva, G G; Alieva, A A

    2014-01-01

    The paper is devoted to the study of surface structures including pili (fimbriae) 67-72p surface protein, DIP 1281 surface protein, lipoarabinomannan CdiLAM and their role in the adhesion and colonization of the mucous membrane of the throat by Corynebacterium diphtheriae. A description is offered for the main stages in the adhesion process of diphtheria causative agent and the ability of its adhesins to stimulate the effect of innate and acquired immunity factors. The paper stresses prospectiveness of the development of vaccines forming immunoprotection of the organism against adhesive activity of C. diphtheriae and also preventing their colonization and reproduction. That would facilitate a solution for the problem of diphtheria carrier state, which cannot be solved using the existing means of preventive vaccination.

  14. The role of surface chemistry in the cytotoxicity profile of graphene.

    PubMed

    Majeed, Waqar; Bourdo, Shawn; Petibone, Dayton M; Saini, Viney; Vang, Kieng Bao; Nima, Zeid A; Alghazali, Karrer M; Darrigues, Emilie; Ghosh, Anindya; Watanabe, Fumiya; Casciano, Daniel; Ali, Syed F; Biris, Alexandru S

    2017-04-01

    Graphene and its derivative, because of their unique physical, electrical and chemical properties, are an important class of nanomaterials being proposed as foundational materials in nanomedicine as well as for a variety of industrial applications. A major limitation for graphene, when used in biomedical applications, is its poor solubility due to its rather hydrophobic nature. Therefore, chemical functionalities are commonly introduced to alter both its surface chemistry and biochemical activity. Here, we show that surface chemistry plays a major role in the toxicological profile of the graphene structures. To demonstrate this, we chemically increased the oxidation level of the pristine graphene and compared the corresponding toxicological effects along with those for the graphene oxide. X-ray photoelectron spectroscopy revealed that pristine graphene had the lowest amount of surface oxygen, while graphene oxide had the highest at 2.5% and 31%, respectively. Low and high oxygen functionalized graphene samples were found to have 6.6% and 24% surface oxygen, respectively. Our results showed a dose-dependent trend in the cytotoxicity profile, where pristine graphene was the most cytotoxic, with decreasing toxicity observed with increasing oxygen content. Increased surface oxygen also played a role in nanomaterial dispersion in water or cell culture medium over longer periods. It is likely that higher dispersity might result in graphene entering into cells as individual flakes ~1 nm thick rather than as more cytotoxic aggregates. In conclusion, changes in graphene's surface chemistry resulted in altered solubility and toxicity, suggesting that a generalized toxicity profile would be rather misleading. Copyright © 2016 John Wiley & Sons, Ltd.

  15. 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

  16. Exploring the Role of Adsorption and Surface State on the Hydrophobicity of Rare Earth Oxides.

    PubMed

    Lundy, Ross; Byrne, Conor; Bogan, Justin; Nolan, Kevin; Collins, Maurice N; Dalton, Eric; Enright, Ryan

    2017-04-06

    Rare earth oxides (REOs) are attracting attention for use as cost-effective, high-performance dropwise condensers because of their favorable thermal properties and robust nature. However, to engineer a suitable surface for industrial applications, the mechanism governing wetting must be first fully elucidated. Recent studies exploring the water-wetting state of REOs have suggested that these oxides are intrinsically hydrophobic owing to the unique electronic structure of the lanthanide series. These claims have been countered with evidence that they are inherently hydrophilic and that adsorption of contaminants from the environment is responsible for the apparent hydrophobic nature of these surfaces. Here, using X-ray photoelectron spectroscopy and dynamic water contact angle measurements, we provide further evidence to show that REOs are intrinsically hydrophilic, with ceria demonstrating advancing water contact angles of ≈6° in a clean surface state and similar surface energies to two transition metal oxides (≳72 mJ/m(2)). Using two model volatile species, it is shown that an adsorption mechanism is responsible for the apparent hydrophobic property observed in REOs as well as in transition metal oxides and silica. This is correlated with the screening of the polar surface energy contribution of the underlying oxide with apparent surface energies reduced to <40 mJ/m(2) for the case of nonane adsorption. Moreover, we show that the degree of surface hydroxylation plays an important role in the observed contact angle hysteresis with the receding contact angle of ceria increasing from ∼10° to 45° following thermal annealing in an inert atmosphere. Our findings suggest that high atomic number metal oxides capable of strongly adsorbing volatile species may represent a viable paradigm toward realizing robust surface coating for industrial condensers if certain challenges can be overcome.

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

    PubMed

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

    2014-11-07

    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.

  18. 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.

  19. The role of surface kinetics on composition and quality of AlGaN

    NASA Astrophysics Data System (ADS)

    Bryan, Isaac; Bryan, Zachary; Mita, Seiji; Rice, Anthony; Hussey, Lindsay; Shelton, Christopher; Tweedie, James; Maria, Jon-Paul; Collazo, Ramón; Sitar, Zlatko

    2016-10-01

    Metal-polar, Al-rich AlGaN films were grown on both single crystalline AlN and sapphire substrates. The role of surface morphology and surface kinetics on AlGaN composition is presented. With the reduced dislocation density of the films grown on AlN substrates, atomically smooth bilayer stepped surfaces are achieved with RMS roughness of less than 50 pm for a 5×5 μm2 AFM scan area. By controlling the surface supersaturation through adjusting the growth rate, a transition from 2D nucleation to step flow was observed. The critical misorientation angle for step-bunching in nominal Al0.70Ga0.30N grown with a growth rate of 600 nm/h on AlN substrates was found to be 0.4°. The composition of bilayer stepped AlGaN was strongly dependent on substrate misorientation angle, where a compositional variation by a factor of two for a change in misorientation angle from 0.05 to 0.40° was observed; this is explained by the different surface diffusion lengths of Ga and Al. Step-bunching resulted in strong compositional inhomogeneity as observed by photoluminescence and scanning transmission electron microscopy studies.

  20. Role of the oxidation state of cerium on the ceria surfaces for silicate adsorption

    NASA Astrophysics Data System (ADS)

    Seo, Jihoon; Moon, Jinok; Kim, Joo Hyun; Lee, Kangchun; Hwang, Junha; Yoon, Heesung; Yi, Dong Kee; Paik, Ungyu

    2016-12-01

    In this study, we have investigated the role of the Ce oxidation state (Ce3+/Ce4+) on the CeO2 surfaces for silicate adsorption. In aqueous medium, the Ce3+ sites lead to the formation of -OH groups at the CeO2 surface through H2O dissociation. Silicate ions can adsorb onto the CeO2 surface through interaction with the -OH groups (-Ce-OH- + -Si-O- ↔ -Ce-O-Si- + OH-). As the Ce3+ concentration increased from 19.3 to 27.6%, the surface density of -OH group increased from 0.34 to 0.72 OH/nm2. To evaluate the adsorption behaviors of silicate ions onto CeO2 NPs, we carried out an adsorption isothermal analysis, and the adsorption isotherm data followed the Freundlich model. The Freundlich constant for the relative adsorption capacity (KF) and adsorption intensity (1/n) indicated that CeO2 NPs with high Ce3+ concentration show higher adsorption affinity with silicate ions. As a result, we have demonstrated that the Ce oxidation state (Ce3+/Ce4+) on the CeO2 surface can have a significant influence on the silicate adsorption.

  1. The Role of Spatially-variable Surface Dust in GCM Simulations of the Martian Dust Cycle

    NASA Astrophysics Data System (ADS)

    Wilson, R. John

    An outstanding problem for simulating the present Mars climate is representing the spatial and temporal variability of aerosols and the feedbacks that connect dust raising and transport with the evolving atmospheric circulation. A particular challenge has been the inability of Mars global circulation models (MGCMs) to realistically simulate interannual variability, most notably in the occurrence of major dust storms. The threshold for dust lifting by resolved surface stresses plays a central role in the current parameterizations of dust lifting used in these simulations. In the results to be presented, the GFDL MGCM is run with fairly typical representations of convective ("dust devils") and wind stress lifting. A new type of negative feedback has been introduced to the model climate system by providing a finite surface dust reservoir and allowing the stress threshold for dust lifting is vary as a function of the surface dust depth. The simulated surface dust typically evolves toward a relatively statistically-stable distribution that reflects the seasonally-integrated effects of stress dust lifting. Dust is preferentially depleted in regions with unusually high stress but surfaces are never stripped clean. Thus the stress lifting scheme continues to allow dust to be raised in these regions, but on a more episodic basis that is dependent on the replenishment by local and remote dust lifting activity. This work provides support for the concept, first proposed in a pair of papers by A. Pankine and A. Ingersoll, that surface/atmosphere dust interactions are able to organize to yield aperiodic global dust storm activity. The influence of an equilibrated finite dust reservoir with a spatially variable surface stress lifting threshold will additionally be illustrated in simulations of the 2001 planet-encircling dust storm.

  2. 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

  3. Bridging adhesion of mussel-inspired peptides: role of charge, chain length, and surface type.

    PubMed

    Wei, Wei; Yu, Jing; Gebbie, Matthew A; Tan, Yerpeng; Martinez Rodriguez, Nadine R; Israelachvili, Jacob N; Waite, J Herbert

    2015-01-27

    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 E(ad) ∼ -0.5 mJ/m(2)) than full length Mfp-5 adhesion. Between two mica surfaces, the magnitude of bridging adhesion was approximately doubled (E(ad) ∼ -1 mJ/m(2)) upon doubling the peptide length. Notably, the short peptides mediate much stronger adhesion (E(ad) ∼ -3.0 mJ/m(2)) 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.

  4. Mécanismes des failles des séismes des 17 et 21 juin 2000 dans la Zone sismique sud-islandaise, d'après les traces de surface des failles d'Árnes et de l'HestfjallMechanisms of the faults of 17 and 21 June 2000 earthquakes in the South Iceland Seismic Zone from the surface traces of the Árnes and Hestfjall faults

    NASA Astrophysics Data System (ADS)

    Bergerat, Françoise; Angelier, Jacques

    2001-07-01

    Two major earthquakes ( Ms=6.6) occurred on 17 and 21 June 2000 in the South Iceland Seismic Zone. This paper presents characteristic examples of surface traces of these seismic faults, called the Árnes and Hestfjall faults. The surface trace of the Árnes fault at Mykjunes shows a conjugate strike-slip pattern with a N30°E trending right-lateral fault and a N60°E trending left-lateral fault. Each of these faults is formed by 'en-échelon' arrays of fractures and push-ups. The surface trace of the Hestfjall fault near Bitra reveals a N50°-60°E trending left-lateral strike-slip fault including large open fractures, 'en-échelon' fractures and some push-ups. These observations show that the actual earthquake-related fault pattern is not restricted to the north-south-trending dextral strike-slip revealed by focal mechanisms and north-south alignment of aftershocks, but includes conjugate systems consistent with the structural pattern of the SISZ.

  5. Gold nanoparticles: role of size and surface chemistry on blood protein adsorption

    NASA Astrophysics Data System (ADS)

    Benetti, F.; Fedel, M.; Minati, L.; Speranza, G.; Migliaresi, C.

    2013-06-01

    Material interaction with blood proteins is a critical issue, since it could influence the biological processes taking place in the body following implantation/injection. This is particularly important in the case of nanoparticles, where innovative properties, such as size and high surface to volume ratio can lead to a behavioral change with respect to bulk macroscopic materials and could be responsible for a potential risk for human health. The aim of this work was to compare gold nanoparticles (AuNP) and planar surfaces to study the role of surface curvature moving from the macro- to the nano-size in the process of blood protein adsorption. In the course of the study, different protocols were tested to optimize the analysis of protein adsorption on gold nanoparticles. AuNP with different size (10, 60 and 200 nm diameter) and surface coatings (citrate and polyethylene glycol) were carefully characterized. The stabilizing action of blood proteins adsorbed on AuNP was studied measuring the variation of size and solubility of the nanoparticles following incubation with single protein solutions (human serum albumin and fibrinogen) and whole blood plasma. In addition, we developed a method to elute proteins from AuNP to study the propensity of gold materials to adsorb plasma proteins in function of dimensional characteristics and surface chemistry. We showed a different efficacy of the various eluting media tested, proving that even the most aggressive agent cannot provide a complete detachment of the protein corona. Enhanced protein adsorption was evidenced on AuNP if compared to gold laminae (bare and PEGylated) used as macroscopic control, probably due to the superior AuNP surface reactivity.

  6. The role of flexibility and molecular shape in the crystallization of proteins by surface mutagenesis

    PubMed Central

    Devedjiev, Yancho D.

    2015-01-01

    Proteins are dynamic systems and interact with their environment. The analysis of crystal contacts in the most accurately determined protein structures (d < 1.5 Å) reveals that in contrast to current views, static disorder and high side-chain entropy are common in the crystal contact area. These observations challenge the validity of the theory that presumes that the occurrence of well ordered patches of side chains at the surface is an essential prerequisite for a successful crystallization event. The present paper provides evidence in support of the approach for understanding protein crystallization as a process dependent on multiple factors, each with its relative contribution, rather than a phenomenon driven by a few dominant physicochemical characteristics. The role of the molecular shape as a factor in the crystallization of proteins by surface mutagenesis is discussed. PMID:25664789

  7. 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.

  8. 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

  9. 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.

  10. Alternative mechanism for coffee-ring deposition based on active role of free surface

    NASA Astrophysics Data System (ADS)

    Jafari Kang, Saeed; Vandadi, Vahid; Felske, James D.; Masoud, Hassan

    2016-12-01

    When a colloidal sessile droplet dries on a substrate, the particles suspended in it usually deposit in a ringlike pattern. This phenomenon is commonly referred to as the "coffee-ring" effect. One paradigm for why this occurs is as a consequence of the solutes being transported towards the pinned contact line by the flow inside the drop, which is induced by surface evaporation. From this perspective, the role of the liquid-gas interface in shaping the deposition pattern is somewhat minimized. Here, we propose an alternative mechanism for the coffee-ring deposition. It is based on the bulk flow within the drop transporting particles to the interface where they are captured by the receding free surface and subsequently transported along the interface until they are deposited near the contact line. That the interface captures the solutes as the evaporation proceeds is supported by a Lagrangian tracing of particles advected by the flow field within the droplet. We model the interfacial adsorption and transport of particles as a one-dimensional advection-generation process in toroidal coordinates and show that the theory reproduces ring-shaped depositions. Using this model, deposition patterns on both hydrophilic and hydrophobic surfaces are examined in which the evaporation is modeled as being either diffusive or uniform over the surface.

  11. 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.

  12. Role of nanoparticle size, shape and surface chemistry in oral drug delivery.

    PubMed

    Banerjee, Amrita; Qi, Jianping; Gogoi, Rohan; Wong, Jessica; Mitragotri, Samir

    2016-09-28

    Nanoparticles find intriguing applications in oral drug delivery since they present a large surface area for interactions with the gastrointestinal tract and can be modified in various ways to address the barriers associated with oral delivery. The size, shape and surface chemistry of nanoparticles can greatly impact cellular uptake and efficacy of the treatment. However, the interplay between particle size, shape and surface chemistry has not been well investigated especially for oral drug delivery. To this end, we prepared sphere-, rod- and disc-shaped nanoparticles and conjugated them with targeting ligands to study the influence of size, shape and surface chemistry on their uptake and transport across intestinal cells. A triple co-culture model of intestinal cells was utilized to more closely mimic the intestinal epithelium. Results demonstrated higher cellular uptake of rod-shaped nanoparticles in the co-culture compared to spheres regardless of the presence of active targeting moieties. Transport of nanorods across the intestinal co-culture was also significantly higher than spheres. The findings indicate that nanoparticle-mediated oral drug delivery can be potentially improved with departure from spherical shape which has been traditionally utilized for the design of nanoparticles. We believe that understanding the role of nanoparticle geometry in intestinal uptake and transport will bring forth a paradigm shift in nanoparticle engineering for oral delivery and non-spherical nanoparticles should be further investigated and considered for oral delivery of therapeutic drugs and diagnostic materials.

  13. 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.

  14. Role of surface recombination in affecting the efficiency of nanostructured thin-film solar cells.

    PubMed

    Da, Yun; Xuan, Yimin

    2013-11-04

    Nanostructured light trapping is a promising way to improve the efficiency in thin-film solar cells recently. In this work, both the optical and electrical properties of thin-film solar cells with 1D periodic grating structure are investigated by using photoelectric coupling model. It is found that surface recombination plays a key role in determining the performance of nanostructured thin-film solar cells. Once the recombination effect is considered, the higher optical absorption does not mean the higher conversion efficiency as most existing publications claimed. Both the surface recombination velocity and geometric parameters of structure have great impact on the efficiency of thin-film solar cells. Our simulation results indicate that nanostructured light trapping will not only improve optical absorption but also boost the surface recombination simultaneously. Therefore, we must get the tradeoffs between optical absorption and surface recombination to obtain the maximum conversion efficiency. Our work makes it clear that both the optical absorption and electrical recombination response should be taken into account simultaneously in designing the nanostructured thin-film solar cells.

  15. Roles of trichomes with silica particles on the surface of leaves in Aphananthe aspera

    NASA Astrophysics Data System (ADS)

    Takeda, Hiroyuki; Ito, Fuyu; Yamanaka, Shigeru; Takiyama, Naoyuki; Yoshino, Katsumi

    2013-03-01

    There exist many trichomes with silica particles on the surface of leaves in Aphananthe aspera (Muku tree). The size of the trichomes is on the order of some tens to hundreds of micrometers. Investigating the electric-field local densities of the states and distributions of electromagnetic wave propagation, we theoretically revealed that while trichomes play a role as waveguides for the far-infrared, silica particles help incident far-infrared light efficiently propagate inside the trichomes and leaves. These properties would be useful for efficiently warming plants, since absorbed far-infrared light is converted to heat.

  16. 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

  17. 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.

  18. Interfacial biocatalysis on charged and immobilized substrates: the roles of enzyme and substrate surface charge.

    PubMed

    Feller, Bob E; Kellis, James T; Cascão-Pereira, Luis G; Robertson, Channing R; Frank, Curtis W

    2011-01-04

    An enzyme charge ladder was used to examine the role of electrostatic interactions involved in biocatalysis at the solid-liquid interface. The reactive substrate consisted of an immobilized bovine serum albumin (BSA) multilayer prepared using a layer-by-layer technique. The zeta potential of the BSA substrate and each enzyme variant was measured to determine the absolute charge in solution. Enzyme adsorption and the rate of substrate surface hydrolysis were monitored for the enzyme charge ladder series to provide information regarding the strength of the enzyme-substrate interaction and the rate of interfacial biocatalysis. First, each variant of the charge ladder was examined at pH 8 for various solution ionic strengths. We found that for positively charged variants the adsorption increased with the magnitude of the charge until the surface became saturated. For higher ionic strength solutions, a greater positive enzyme charge was required to induce adsorption. Interestingly, the maximum catalytic rate was not achieved at enzyme saturation but at an invariable intermediate level of adsorption for each ionic strength value. Furthermore, the maximum achievable reaction rate for the charge ladder was larger for higher ionic strength values. We propose that diffusion plays an important role in interfacial biocatalysis, and for strong enzyme-substrate interaction, the rate of diffusion is reduced, leading to a decrease in the overall reaction rate. We investigated the effect of substrate charge by varying the solution pH from 6.1 to 8.7 and by examining multiple ionic strength values for each pH. The same intermediate level of adsorption was found to maximize the overall reaction rate. However, the ionic strength response of the maximum achievable rate was clearly dependent on the pH of the experiment. We propose that this observation is not a direct effect of pH but is caused by the change in substrate surface charge induced by changing the pH. To prove this

  19. Inhomogeneites dans le Vent des Etoiles Wolf-Rayet

    NASA Astrophysics Data System (ADS)

    Robert, Carmelle

    1992-01-01

    autres, une correlation entre le nombre d'inhomogeneites detectees et la vitesse terminale. Cette relation explique bien l'anti-correlation observee entre le niveau de variabilite spectroscopique, photometrique ou polarimetrique et la vitesse terminale. On estime pour toutes les etoiles une masse moyenne des inhomogeneites de 7 times 10^{ -10} Modot et un taux de perte de masse sous la forme d'inhomogeneites detectables qui correspond a 10% de la perte de masse du vent total. L'histogramme du nombre d'inhomogeneites en fonction du leur flux pourrait cependant predire l'existence d'un grand nombre de petites structures non-detectees ici a cause du rapport signal sur bruit relativement trop faible. Ce resultat interessant, qui demande cependant a etre verifie, suggere que le vent pourrait etre forme d'un ensemble quasi infini d'inhomogeneites. En ajustant une loi de puissance dans l'histogramme du flux de chaque etoile, on calcule, pour les plus grosses structures, un exposant = -2.4 +/- 0.2. On constate alors que cette valeur est compatible avec celle que predit la turbulence supersonique. Les structures observees dans les spectres des etoiles WR ont des caracteristiques tres semblables a celles des etoiles O. On propose alors que les perturbations observees chez ces 2 types d'etoiles ont une meme origine. Parmi les mecanismes deja proposes dans le passe pour expliquer les variations des etoiles O et WR (instabilites radiatives, pulsations et champ magnetique) on ne saurait encore dire <=uel, ou lesquels, correspondent le mieux aux observations. Dans les projets futurs, on propose de considerer aussi le role que pourrait avoir la turbulence pour expliquer les perturbations du vent stellaire.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Does seed size and surface anatomy play role in combating phytotoxicity of nanoparticles?

    PubMed

    Jain, Navin; Bhargava, Arpit; Pareek, Vikram; Sayeed Akhtar, Mohd; Panwar, Jitendra

    2017-03-01

    Rapid utilization of nano-based products will inevitably release nanoparticles into the environment with unidentified consequences. Plants, being an integral part of ecosystem play a vital role in the incorporation of nanoparticles in food chain and thus, need to be critically assessed. The present study assesses the comparative phytotoxicity of nanoparticle, bulk and ionic forms of zinc at different concentrations on selected plant species with varying seed size and surface anatomy. ZnO nanoparticles were chosen in view of their wide spread use in cosmetics and health care products, which allow their direct release in the environment. The impact on germination rate, shoot & root length and vigour index were evaluated. A concentration dependent inhibition of seed germination as well as seedling length was observed in all the tested plants. Due to the presence of thick cuticle on testa and root, pearl millet (xerophytic plant) was found to be relatively less sensitive to ZnO nanoparticles as compared to wheat and tomato (mesophytic plants) with normal cuticle layer. No correlation was observed between nanoparticles toxicity and seed size. The results indicated that variations in surface anatomy of seeds play a crucial role in determining the phytotoxicity of nanoparticles. The present findings significantly contribute to assess potential consequences of nanoparticle release in environment particularly with major emphasis on plant systems. It is the first report which suggests that variations observed in phytotoxicity of nanoparticles is mainly due to the predominant differences in size and surface anatomy of tested plant seeds and root architecture. Effect of various concentrations of nano ZnO, bulk ZnO and zinc sulphate on the growth of pearl millet (A), tomato (B) and wheat (C) seedlings.

  7. 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

  8. 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.

  9. Distinct roles of phenol-soluble modulins in spreading of Staphylococcus aureus on wet surfaces.

    PubMed

    Tsompanidou, Eleni; Denham, Emma L; Becher, Dörte; de Jong, Anne; Buist, Girbe; van Oosten, Marleen; Manson, Willem L; Back, Jaap Willem; van Dijl, Jan Maarten; Dreisbach, Annette

    2013-02-01

    The human pathogen Staphylococcus aureus is renowned for the rapid colonization of contaminated wounds, medical implants, and food products. Nevertheless, little is known about the mechanisms that allow S. aureus to colonize the respective wet surfaces. The present studies were therefore aimed at identifying factors used by S. aureus cells to spread over wet surfaces, starting either from planktonic or biofilm-associated states. Through proteomics analyses we pinpoint phenol-soluble modulins (PSMs) as prime facilitators of the spreading process. To dissect the roles of the eight PSMs produced by S. aureus, these peptides were chemically synthesized and tested in spreading assays with different psm mutant strains. The results show that PSMα3 and PSMγ are the strongest facilitators of spreading both for planktonic cells and cells in catheter-associated biofilms. Compared to the six other PSMs of S. aureus, PSMα3 and PSMγ combine strong surfactant activities with a relatively low overall hydropathicity. Importantly, we show that PSM-mediated motility of S. aureus facilitates the rapid colonization of wet surfaces next to catheters and the colonization of fresh meat.

  10. 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.

  11. Role of attachment to surfaces on the prevalence and survival of Campylobacter through food systems.

    PubMed

    Nguyen, Vu Tuan; Fegan, Narelle; Turner, Mark S; Dykes, Gary A

    2012-01-01

    Campylobacter continues to be one of the bacterial pathogens most frequently associated with human gastrointestinal illness worldwide. Because Campylobacter primarily colonizes the intestines of animals used for food production, food products of animal origin can become contaminated with this pathogen and thus represent a significant risk factor. Despite application of numerous physical and chemical interventions to control Campylobacter during food processing, the high isolation rate of this pathogen from some retail meat products indicates that Campylobacter is able to persist from animal slaughterhouses through food systems. Given the fastidious growth requirements and high susceptibility of this pathogen to environmental conditions, the ability of Campylobacter to attach to food and food-related surfaces is likely to play an important role in food contamination and movement through food systems. This review was compiled to (i) describe how the attachment of Campylobacter to surfaces influences the prevalence and survival of the organism through food systems, (ii) examine the potential factors affecting the ability of Campylobacter to attach to surfaces, and (iii) suggest strategies for controlling this attachment process.

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

    DOE PAGES

    Han, Binghong; Qian, Danna; Risch, Marcel; ...

    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

  13. Role of Staphylococcus aureus surface adhesins in orthopaedic device infections: are results model-dependent?

    PubMed

    Darouiche, R O; Landon, G C; Patti, J M; Nguyen, L L; Fernau, R C; McDevitt, D; Greene, C; Foster, T; Klima, M

    1997-01-01

    Bacterial colonisation of prosthetic material can lead to clinical infection or implant failure, or both, often requiring removal of the device. Adherence of Staphylococcus aureus to bioprosthetic materials is mediated by adhesins belonging to the MSCRAMM (microbial surface components recognising adhesive matrix molecules) family of microbial cell surface proteins. The objective of this study was to compare the virulence of a mutant strain of S. aureus Newman that possesses all three fibrinogen-, fibronectin- and collagen-binding MSCRAMMs (MSCRAMM-positive strain) with that of a mutant strain that lacks all three types of MSCRAMMs (MSCRAMM-negative strain) in a rabbit model of orthopaedic device-related infection. After a hole was drilled into the knee joint of each animal, a group of 10 rabbits was inoculated with the MSCRAMM-positive strain and another group of 10 rabbits received the MSCRAMM-negative strain. A stainless steel screw was then placed into the drilled hole. Two weeks later, the rabbits were killed and serum samples, bone tissue and implants were harvested for bacteriological and histopathological evaluation. No significant difference in infection rates was demonstrated between the two groups. The ability to delineate the role of S. aureus surface adhesins in causing orthopaedic device-related infection could be model-dependent.

  14. Surface binding sites in amylase have distinct roles in recognition of starch structure motifs and degradation.

    PubMed

    Cockburn, Darrell; Nielsen, Morten M; Christiansen, Camilla; Andersen, Joakim M; Rannes, Julie B; Blennow, Andreas; Svensson, Birte

    2015-04-01

    Carbohydrate converting enzymes often possess extra substrate binding regions that enhance their activity. These can be found either on separate domains termed carbohydrate binding modules or as so-called surface binding sites (SBSs) situated on the catalytic domain. SBSs are common in starch degrading enzymes and critically important for their function. The affinity towards a variety of starch granules as well as soluble poly- and oligosaccharides of barley α-amylase 1 (AMY1) wild-type and mutants of two SBSs (SBS1 and SBS2) was investigated using Langmuir binding analysis, confocal laser scanning microscopy, affinity gel electrophoresis and surface plasmon resonance to unravel functional roles of the SBSs. SBS1 was critical for binding to different starch types as Kd increased by 7-62-fold or was not measurable upon mutation. By contrast SBS2 was particularly important for binding to soluble polysaccharides and oligosaccharides with α-1,6 linkages, suggesting that branch points are key structural elements in recognition by SBS2. Mutation at both SBS1 and SBS2 eliminated binding to all starch granule types tested. Taken together, the findings indicate that the two SBSs act in concert to localize AMY1 to the starch granule surface and that SBS2 works synergistically with the active site in the degradation of amylopectin.

  15. 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.

  16. 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

    2010-11-02

    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.

  17. Distinct Roles of Phenol-Soluble Modulins in Spreading of Staphylococcus aureus on Wet Surfaces

    PubMed Central

    Tsompanidou, Eleni; Denham, Emma L.; Becher, Dörte; de Jong, Anne; Buist, Girbe; van Oosten, Marleen; Manson, Willem L.; Back, Jaap Willem; Dreisbach, Annette

    2013-01-01

    The human pathogen Staphylococcus aureus is renowned for the rapid colonization of contaminated wounds, medical implants, and food products. Nevertheless, little is known about the mechanisms that allow S. aureus to colonize the respective wet surfaces. The present studies were therefore aimed at identifying factors used by S. aureus cells to spread over wet surfaces, starting either from planktonic or biofilm-associated states. Through proteomics analyses we pinpoint phenol-soluble modulins (PSMs) as prime facilitators of the spreading process. To dissect the roles of the eight PSMs produced by S. aureus, these peptides were chemically synthesized and tested in spreading assays with different psm mutant strains. The results show that PSMα3 and PSMγ are the strongest facilitators of spreading both for planktonic cells and cells in catheter-associated biofilms. Compared to the six other PSMs of S. aureus, PSMα3 and PSMγ combine strong surfactant activities with a relatively low overall hydropathicity. Importantly, we show that PSM-mediated motility of S. aureus facilitates the rapid colonization of wet surfaces next to catheters and the colonization of fresh meat. PMID:23183971

  18. Adherence of platelets to in situ albumin-binding surfaces under flow conditions: role of surface-adsorbed albumin.

    PubMed

    Guha Thakurta, Sanjukta; Miller, Robert; Subramanian, Anuradha

    2012-08-01

    Surfaces that preferentially bind human serum albumin (HSA) were generated by grafting albumin-binding linear peptide (LP1) onto silicon surfaces. The research aim was to evaluate the adsorption pattern of proteins and the adhesion of platelets from platelet-poor plasma and platelet-rich plasma, respectively, by albumin-binding surfaces under physiological shear rate (96 and 319 s(-1)) conditions. Bound proteins were quantified using enzyme-linked immunosorbent assays (ELISAs) and two-dimensional gel electrophoresis. A ratio of ∼1000:100:1 of adsorbed HSA, human immunoglobulin (HIgG) and human fibrinogen (HFib) was noted, respectively, on LP1-functionalized surfaces, and a ratio of ∼5:2:1 of the same was noted on control surfaces, as confirmed by ELISAs. The surface-adsorbed von Willebrand factor was undetectable by sensitive ELISAs. The amount of adhered platelets correlated with the ratio of adsorbed HSA/HFib. Platelet morphology was more rounded on LP1-functionalized surfaces when compared to control surfaces. The platelet adhesion response on albumin-binding surfaces can be explained by the reduction in the co-adsorption of other plasma proteins in a surface environment where there is an excess of albumin molecules, coupled with restrictions in the conformational transitions of other surface-adsorbed proteins into hemostatically active forms.

  19. 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.

  20. Role of Black Carbon and Absorbing Organic Carbon Aerosols in Surface Dimming Trends

    NASA Astrophysics Data System (ADS)

    Feng, Y.; Ramanathan, V.; Kotamarthi, V. R.

    2010-12-01

    Solar radiation reaching at the Earth’s surface plays an essential role in driving both atmosphere hydrological and land/ocean biogeochemical processes. Measurements have shown significant decreases in surface solar radiation (dimming) in many regions since 1960s. At least half of the observed dimming could be linked to the direct radiative effect of anthropogenic aerosols, especially absorbing aerosols like black carbon (BC) due to their strong atmospheric absorption. However, previous model-data comparisons indicate that absorption by aerosols is commonly and significantly underestimated in current GCM simulations by several factors over regions. Using a global chemical transport model coupled with a radiative transfer model, we include a treatment for absorbing organic carbons (OC) from bio-fuel and open biomass burnings in optical calculations and estimate aerosol radiative forcings for two anthropogenic aerosol emission scenarios representative of 1975 and 2000. Assumptions about aerosol mixing and the OC absorption spectrum are examined by comparing simulated atmospheric heating against aircraft optical and radiation measurements. The calculated aerosol single scattering albedo distribution (0.93+/-0.044) is generally comparable to the AERONET data (0.93+/-0.030) for year 2001, with best agreements in Europe and N. America, while overestimated in E. Asia and underestimated in the S. American biomass burning areas. On a global scale, inclusion of absorbing OC enhances the absorption in the atmosphere by 11% for July. The estimated aerosol direct radiative forcing at TOA (-0.24 W/m2) is similar to the average value of the AeroCom models based on the same 2000 emissions, but significantly enhanced negatively at surface by about 53% (-1.56 W/m2) and the atmosphere absorption is increased by +61% (+1.32 W/m2). About 87% of the estimated atmosphere absorption and 42% of the surface dimming is contributed by BC. Between 1975 and 2000, the calculated all-sky flux

  1. Role of extracellular polymeric substances in the surface chemical reactivity of Hymenobacter aerophilus, a psychrotolerant bacterium.

    PubMed

    Baker, M G; Lalonde, S V; Konhauser, K O; Foght, J M

    2010-01-01

    Bacterial surface layers, such as extracellular polymeric substances (EPS), are known to play an important role in metal sorption and biomineralization; however, there have been very few studies investigating how environmentally induced changes in EPS production affect the cell's surface chemistry and reactivity. Acid-base titrations, cadmium adsorption assays, and Fourier transform infrared spectroscopy (FT-IR) were used to characterize the surface reactivities of Hymenobacter aerophilus cells with intact EPS (WC) or stripped of EPS (SC) and purified EPS alone. Linear programming modeling of titration data showed SC to possess functional groups corresponding to phosphoryl (pKa approximately 6.5), phosphoryl/amine (pKa approximately 7.9), and amine/hydroxyl (pKa approximately 9.9). EPS and WC both possess carboxyl groups (pKa approximately 5.1 to 5.8) in addition to phosphoryl and amine groups. FT-IR confirmed the presence of polysaccharides and protein in purified EPS that can account for the additional carboxyl groups. An increased ligand density was observed for WC relative to that for SC, leading to an increase in the amount of Cd adsorbed (0.53 to 1.73 mmol/liter per g [dry weight] and 0.53 to 0.59 mmol/liter per g [dry weight], respectively). Overall, the presence of EPS corresponds to an increase in the number and type of functional groups on the surface of H. aerophilus that is reflected by increased metal adsorption relative to that for EPS-free cells.

  2. 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

  3. 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

    2013-06-04

    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.

  4. Maladie des vibrations

    PubMed Central

    Shen, Shixin (Cindy); House, Ronald A.

    2017-01-01

    Résumé Objectif Permettre aux médecins de famille de comprendre l’épidémiologie, la pathogenèse, les symptômes, le diagnostic et la prise en charge de la maladie des vibrations, une maladie professionnelle importante et courante au Canada. Sources d’information Une recherche a été effectuée sur MEDLINE afin de relever les recherches et comptes rendus portant sur la maladie des vibrations. Une recherche a été effectuée sur Google dans le but d’obtenir la littérature grise qui convient au contexte canadien. D’autres références ont été tirées des articles relevés. Message principal La maladie des vibrations est une maladie professionnelle répandue touchant les travailleurs de diverses industries qui utilisent des outils vibrants. La maladie est cependant sous-diagnostiquée au Canada. Elle compte 3 éléments : vasculaire, sous la forme d’un phénomène de Raynaud secondaire; neurosensoriel; et musculosquelettique. Aux stades les plus avancés, la maladie des vibrations entraîne une invalidité importante et une piètre qualité de vie. Son diagnostic exige une anamnèse minutieuse, en particulier des antécédents professionnels, un examen physique, des analyses de laboratoire afin d’éliminer les autres diagnostics, et la recommandation en médecine du travail aux fins d’investigations plus poussées. La prise en charge consiste à réduire l’exposition aux vibrations, éviter les températures froides, abandonner le tabac et administrer des médicaments. Conclusion Pour assurer un diagnostic rapide de la maladie des vibrations et améliorer le pronostic et la qualité de vie, les médecins de famille devraient connaître cette maladie professionnelle courante, et pouvoir obtenir les détails pertinents durant l’anamnèse, recommander les patients aux cliniques de médecine du travail et débuter les demandes d’indemnisation de manière appropriée. PMID:28292812

  5. Determination des Parametres Atmospheriques des Etoiles Naines Blanches de Type DB

    NASA Astrophysics Data System (ADS)

    Beauchamp, Alain

    1995-01-01

    Les etoiles naines blanches dont les spectres visibles sont domines par des raies fortes d'helium neutre sont subdivisees en trois classes, DB (raies d'helium neutre seulement), DBA (raies d'helium neutre et d'hydrogene) et DBZ (raies d'helium neutre et d'elements lourds). Nous analysons trois echantillons de spectres observes de ces types de naines blanches. Les echantillons consistent, respectivement, de 48 spectres dans le domaine du visible (3700-5100 A). 24 dans l'ultraviolet (1200-3100 A) et quatre dans la partie rouge du visible (5100-6900) A). Parmi les objets de l'echantillon visible, nous identifions quatre nouvelles DBA, ainsi que deux nouvelles DBZ, auparavant classees DB. L'analyse nous permet de determiner spectroscopiquement les parametres atmospheriques, soit la temperature effective, la gravite de surface, ainsi que l'abondance relative de l'hydrogene, N(H)/N(He), dans le cas des DBA. Pour les objets plus chauds que ~15,000 K, la gravite de surface determinee est fiable, et nous obtenons les masses stellaires avec une relation masse -rayon theorique. Les exigences propres a l'analyse de ces objets ont requis d'importantes ameliorations dans la modelisation de leurs atmospheres et distributions de flux de radiation emis par ces derniers. Nous avons inclus dans les modeles d'atmospheres, pour la premiere fois a notre connaissance, les effets dus a la molecule He_sp{2 }{+}, ainsi que l'equation d'etat de Hummer et Mihalas (1988), qui tient compte des perturbations entre particules dans le calcul des populations des differents niveaux atomiques. Nous traitons la convection dans le cadre de la theorie de la longueur de melange. Trois grilles de modeles d'atmospheres a l'ETL (equilibre thermodynamique local) ont ete produites, pour un ensemble de temperatures effectives, gravites de surface et abondances d'hydrogene couvrant les proprietes des etoiles de nos echantillons; elles sont caracterisees par differentes parametrisations appelees, respectivement

  6. The Reduction of Aqueous Metal Species on the Surfaces of Fe(II)-Containing Oxides: The Role of Surface Passivation

    USGS Publications Warehouse

    White, A.F.; Peterson, M.L.

    1998-01-01

    The reduction of aqueous transition metal species at the surfaces of Fe(II)- containing oxides has important ramifications in predicting the transport behavior in ground water aquifers. Experimental studies using mineral suspensions and electrodes demonstrate that structural Fe(II) heterogeneously reduces aqueous ferric, cupric, vanadate and chromate ions on magnetite and ilmenite surfaces. The rates of metal reduction on natural oxides is strongly dependent on the extent of surface passivation and redox conditions in the weathering environment. Synchrotron studies show that surface oxidation of Fe(II)-containing oxide minerals decreases their capacity for Cr(VI) reduction at hazardous waste disposal sites.

  7. Phagosome-lysosome fusions in macrophages infected by Mycobacterium avium: role of mycosides-C and other cells surface components.

    PubMed

    Fréhel, C; Rastogi, N

    1989-01-01

    The phagosome-lysosome fusions (PLE) were assessed in case of bone-marrow macrophages infected by the opportunistic species Mycobacterium avium, employing the acid-phosphatase (AcPase) electron-cytochemistry. The role of surface components was evaluated by coating the bacteria prior to phagocytosis by specific M. avium antiserum or the anti-mycosides-C serum raised in rabbit. PLF was evaluated under the electron microscope during (2, 4 hours), or after (24 hours) phagocytosis. The preliminary results suggest that although M. avium surface components intervene in PLF inhibition, the role of mycosides-C among these surface components (effectively intervening in PLF inhibition) is questionable.

  8. Synthese et utilisation de fibres cellulosiques phosphatees pour la valorisation de la fibre vegetale dans l'amelioration des proprietes de surface du papier et la fabrication de materiaux ignifuges

    NASA Astrophysics Data System (ADS)

    Lentsolo Yalli, Gym Clerc

    Dans cette etude, nous souhaitions principalement greffer des groupements phosphates directement sur la cellulose comme materiau modele, et par la suite transposer les conditions optimales du design concu pour la cellulose, determine par modelisation a l'aide de l'outil JMP, sur la pate kraft. Ensuite, evaluer les proprietes physico-chimiques, optiques, d'hydrophilie, thermiques et d'inflammabilite des materiaux fabriques (feuilles ou pastilles fabriquees) a partir des fibres phosphorylees. Pour ce faire, nous avons pretraite la cellulose et la pate kraft dans une solution aqueuse de 10 a 15 % de LiCl a 70°C pendant 7 heures. Par la suite, nous avons procede a la reaction de phosphorylation in situ avec l'acide phosphorique et l'uree, dans des conditions de temperatures et de reactifs decrites par un design experimental, pendant 3 heures. La reaction de phosphorylation s'est realisee avec succes pour l'ensemble des resultats sur la cellulose, avec des taux de greffage variables selon les conditions operatoires. Les degres de substitutions (DSP), determines par ICP-OES, et les degres de polymerisation (DP), determines par viscosimetrie, etaient aussi variables, selon les conditions. L'etude des parametres experimentaux a permis de determiner les conditions optimales transposables sur la pate kraft (DSP = 1,47 et DP = 142,42 pour la cellulose, qui represente un taux de coupure de 38% de la fibre) et les facteurs critiques de la reaction. Les resultats de la reaction sur la fibre ont permis, non seulement de constater que les conditions utilisees pour la cellulose n'etaient directement transposables a la fibre, mais permettaient quand d'obtenir un DSP interessant ≥ a 1 avec un taux de coupure de 50 a 60 %. La structure du produit principal de la reaction (le sel de calcium du pyrophosphate d'ester de cellulose ou de pate kraft) a ete determinee par les analyses FTIR, XPS, RMN-13C et RMN-31P. L'etude de l'effet de la reaction de phosphorylation sur les proprietes

  9. Apatite deposition on titanium surfaces--the role of albumin adsorption.

    PubMed

    Serro, A P; Fernandes, A C; Saramago, B; Lima, J; Barbosa, M A

    1997-07-01

    Titanium implant surfaces are known to spontaneously nucleate apatite layers when in contact with simulated body fluids. However, adsorption of proteins may influence the process of apatite layer formation. In this study the role of bovine serum albumin (BSA) adsorption in the process of apatite deposition on titanium substrates is investigated. Deposition of calcium phosphate was induced by immersing titanium substrates in a Hank's balanced salt solution (HBSS) for times ranging from 1 to 23 days. The resulting substrates were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), wettability measurements and electrochemical impedance determinations. All these methods indicate the presence of a calcium phosphate layer. The same procedure was repeated substituting HBSS with a solution of BSA in HBSS. Although SEM, EDS and electrochemical impedance spectra do not reveal the presence of an apatite layer, XPS analysis strongly indicates that the inhibition of apatite formation by BSA is only partial. The competition between BSA adsorption and apatite deposition seems to lead to a mixed film where the protein co-exists with calcium phosphate. Wettability studies suggest that this surface film is heterogeneous and porous, similar to the thicker films formed in albumin-free HBSS.

  10. Role of the Bp35 cell surface polypeptide in human B-cell activation.

    PubMed Central

    Clark, E A; Shu, G; Ledbetter, J A

    1985-01-01

    A 35-kDa polypeptide, Bp35, expressed on the surface of all B cells, plays a role in B-cell activation. Monoclonal antibodies to Bp35 stimulate human tonsillar B cells to proliferate. The activation induced by anti-Bp35 is similar to anti-Ig-mediated in several ways: the activation does not require T cells but is augmented by T-cell-derived allogeneic factors; monovalent Fab fragments to Bp35 do not trigger proliferation but instead block activation by whole antibody, indicating that cross-linking is required; and induction by anti-Bp35, like the induction by anti-Ig, is inhibited by monoclonal anti-IgM via an Fc domain-dependent mechanism. However, several features of anti-Bp35-mediated proliferation are clearly different from activation by anti-Ig: anti-Bp35 monoclonal antibodies do not require attachment to beads to function, the proliferation induced by anti-Bp35 and anti-Ig is additive, and Fab fragments of anti-Bp35 augment proliferation induced by anti-Ig. Models for the possible function of the Bp35 polypeptide as either a "bridge" or a "second signal" with surface Ig in B-cell activation are discussed. PMID:3872456

  11. 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

  12. Interpretation of friction and wear in DLC film: role of surface chemistry and test environment

    NASA Astrophysics Data System (ADS)

    Polaki, S. R.; Kumar, N.; Madapu, K.; Ganesan, K.; Krishna, N. G.; Srivastava, S. K.; Abhaya, S.; Kamruddin, M.; Dash, S.; Tyagi, A. K.

    2016-11-01

    In spite of the large amount of tribological work carried out to explain the friction and wear mechanism in diamond-like carbon (DLC) films, some of the core issues relating to the evolution of reactive species across sliding interfaces and their role on the friction and wear mechanism remain unclear. The phase composition, film density and hydrogen content present in a DLC film can be tailored by substrate biasing during film deposition to achieve a nearly vanishing friction coefficient. Furthermore, nitrogen doping in DLC films significantly improves wear resistance, and sliding occurs in a nearly wearless regime. Undoped and nitrogen-doped DLC films exhibit a nearly frictionless value with ultra-low wear behavior when tests are performed in argon, nitrogen and methane atmospheres. The antifriction and antiwear properties of the DLC films were improved with the reduction of adsorbed oxygen impurities on the film surface. This behavior was understood by correlating the oxygen impurities present at the surface/subsurface region of the DLC film while using x-ray photoelectron spectroscopy and depth-resolved Auger electron spectroscopy.

  13. Catalytic conversion of aliphatic alcohols on carbon nanomaterials: The roles of structure and surface functional groups

    NASA Astrophysics Data System (ADS)

    Tveritinova, E. A.; Zhitnev, Yu. N.; Chernyak, S. A.; Arkhipova, E. A.; Savilov, S. V.; Lunin, V. V.

    2017-03-01

    Carbon nanomaterials with the structure of graphene and different compositions of the surface groups are used as catalysts for the conversion of C2-C4 aliphatic alcohols. The conversions of ethanol, propanol- 1, propanol-2, butanol-1, butanol-2, and tert-butanol on carbon nanotubes, nanoflakes, and nanoflakes doped with nitrogen are investigated. Oxidized and nonoxidized multiwalled carbon nanotubes, nanoflakes, and nanoflakes doped with nitrogen are synthesized. X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning and transmission electronic microscopies, Brunauer-Emmett-Teller method, derivatographic analyses, and the pulsed microcatalytic method are used to characterize comprehensively the prepared catalysts. It was established that all of the investigated carbon nanomaterials (with the exception of nondoped carbon nanoflakes) are bifunctional catalysts for the conversion of aliphatic alcohols, and promote dehydration reactions with the formation of olefins and dehydrogenation reactions with the formation of aldehydes or ketones. Nanoflakes doped with nitrogen are inert with respect to secondary alcohols and tert-butanol. The role of oxygen-containing and nitrogen-containing surface groups, and of the geometrical structure of the carbon matrix of graphene nanocarbon materials in the catalytic conversion of aliphatic alcohols, is revealed. Characteristics of the conversion of aliphatic alcohols that are associated with their structure are identified.

  14. 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.

  15. 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.

  16. Roles of spatially varying vegetation on surface fluxes within a small mountainous catchment

    NASA Astrophysics Data System (ADS)

    Flerchinger, G. N.; Marks, D.; Reba, M. L.; Yu, Q.; Seyfried, M. S.

    2010-01-01

    Understanding the role of ecosystems in modulating energy, water and carbon fluxes is critical to quantifying the variability in energy, carbon, and water balances across landscapes. This study compares and contrasts the seasonal surface fluxes of sensible heat, latent heat and carbon fluxes measured over different vegetation in a rangeland mountainous environment within the Reynolds Creek Experimental Watershed. Eddy covariance systems were used to measure surface fluxes over low sagebrush (Artemesia arbuscula), aspen (Populus tremuloides) and the understory of grasses and forbs beneath the aspen canopy. Peak leaf area index of the sagebrush, aspen, and aspen understory was 0.77, 1.35, and 1.20, respectively. The sagebrush and aspen canopies were subject to similar meteorological forces, while the understory of the aspen was sheltered from the wind. Estimated cumulative evapotranspiratation from the sagebrush, aspen understory, and aspen trees were 399 mm, 205 mm and 318 mm. A simple water balance of the catchment indicated that of the 700 mm of areal average precipitation, 442 mm was lost to evapotranspiration, and 254 mm of streamflow was measured from the catchment; water balance closure for the catchment was within 7 mm. Fluxes of latent heat and carbon for all sites were minimal through the winter. Growing season fluxes of latent heat and carbon were consistently higher above the aspen canopy than from the other sites. While growing season carbon fluxes were very similar for the sagebrush and aspen understory, latent heat fluxes for the sagebrush were consistently higher. Higher evapotranspiration from the sagebrush was likely because it is more exposed to the wind. Sensible heat flux from the aspen tended to be slightly less than the sagebrush site during the growing season when the leaves were actively transpiring, but exceeded that from the sagebrush in May, September and October when the net radiation was offset by evaporative cooling. Results from this

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

    DOE PAGES

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

    2016-07-27

    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 Pu3+ and Pu4+ 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/pyrochloremore » bicrystals A2B2O7/A2'B2'O7 can be used to immobilize Pu3+ and Pu4+ either in the same or separate phases of the compound, depending on the chemistry of the material. Finally, we find that Pu4+ segregates to the disordered phase of an order/disorder bicrystal, driven by the occurrence of local oxygen-rich environments. However, Pu3+ 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. Particularly, the phase structure of a multi-phase pyrochlore composite can be used to independently getter decay products based on their valence and size.« less

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

    SciTech Connect

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

    2016-07-27

    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 Pu3+ and Pu4+ 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 Pu3+ and Pu4+ either in the same or separate phases of the compound, depending on the chemistry of the material. Finally, we find that Pu4+ segregates to the disordered phase of an order/disorder bicrystal, driven by the occurrence of local oxygen-rich environments. However, Pu3+ 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. Particularly, the phase structure of a multi-phase pyrochlore composite can be used to independently getter decay products based on their valence and size.

  19. The role of localized cell surface-associated glycoproteins during fertilization in the hydrozoan Aequorea.

    PubMed

    Freeman, G

    1996-10-10

    Hydrozoan eggs can be fertilized only at the site of polar body formation and first acquire this ability during second polar body formation. The eggs of Aequorea victoria form a discrete Triticum lectin binding moiety in the jelly coat near the first polar body as it is being given off and also a discrete concanavalin A binding moiety associated with the egg surface where the second polar body forms, which disappears immediately after fertilization. The germinal vesicle has an eccentric position in full grown Aequorea oocytes. The region of oocyte surface closest to the germinal vesicle is the site where the polar bodies normally form. When oocytes are centrifuged during oocyte maturation, the meiotic apparatus sometimes shifts to a different position with reference to the egg surface and polar bodies are given off at this new site. There is a corresponding shift in the position of the Triticum and concanavalin A lectin binding moieties, indicating that their formation is associated with local events occurring at the site of polar body formation. Treatment of Aequorea eggs with Triticum or concanavalin A causes a marked reduction in the ability of these eggs to be fertilized, suggesting that sugar-containing moieties, to which the lectins bind, play a role in fertilization. Removal of sugars on these moieties with mannosidase or N-acetylglucosaminidase, or the cleavage of the protein the sugars are attached to with trypsin, results in eggs that do not bind Triticum or concanavalin A and also show a marked reduction in the ability to be fertilized. These experiments suggest that the lectin binding moieties are glycoproteins.

  20. 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

  1. 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.

  2. 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

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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…

  8. Pathogenesis of Campylobacter fetus infections. Role of surface array proteins in virulence in a mouse model.

    PubMed Central

    Pei, Z; Blaser, M J

    1990-01-01

    We developed a mouse model to compare the virulence of Campylobacter fetus strains with (S-plus) and without (S-minus) surface array protein (S-protein) capsules. In adult HA/ICR mice pretreated with ferric chloride, the LD50 for S-plus strain 84-32 was 43.3 times lower than its spontaneous S-minus mutant 84-54. Seven strains of inbred mice were no more susceptible than the outbred strain. In contrast to the findings with Salmonella typhimurium by others, 3 X 10(7) CFU of strain 84-32 caused 90% mortality in C3H/HeN (LPSn) mice and 40% mortality in C3H/HeJ (LPSd) mice. High-grade bacteremia in HA/ICR mice occurred after oral challenge with S-plus C. fetus strains and continued for at least 2 d, but was not present in any mice challenged with S-minus strains. Bacteremia at 30 min after challenge was 51.6-fold lower in mice pretreated with 10 microliters of rabbit antiserum to purified S-protein than after pretreatment with normal rabbit serum. Challenge of mice with a mixture of S-minus strain 84-54 and free S-proteins at a concentration 31.1-fold higher than found in wild-type strain 84-32 caused 30% mortality, compared with 0% with strain 84-54 or S-protein alone. These findings in a mouse model point toward the central role of the S-protein in the pathogenesis of C. fetus infection. The S-protein is not toxic per se, but enhances virulence when present on the bacterial cell surface as a capsule. Images PMID:2318963

  9. Factors Promoting a Cool Cambrian Climate: Role of Land Surface Conditions and Atmospheric Greenhouse Gases

    NASA Astrophysics Data System (ADS)

    Shellito, L. J.

    2011-12-01

    In light of recent work suggesting episodic cooling during the Late Cambrian (~500 Ma), an Earth System Model of Intermediate Complexity is utilized to evaluate the roles of Late Cambrian continental configuration, mountain height, and atmospheric CO2 concentration on Earth's climate. The Planetary Simulator (PLASIM), developed at the Meteorological Institute of the University of Hamburg, is utilized at T21 spectral resolution (5.6° latitude x 5.6° longitude) with a 50 m deep slab ocean in four experiments. The first three experiments are run with a Late Cambrian continental configuration. Two experiments are run with an atmospheric CO2 concentration of 10 x pre-industrial (2800 ppm). This is in the range estimated for the Late Cambrian by carbon cycle modeling studies. One of these experiments utilizes a flat topography (CAMB_FLAT), and the other, includes mountains (CAMB_MTN). A third experiment is identical to CAMB_MTN, but CO2 is set to 280 ppm (CAMB_COLD). All Cambrian experiments are integrated without any vegetation, and with solar luminosity reduced by 6%. The Cambrian experiments also utilize a uniform land surface boundary condition consisting of sand with an albedo of 0.37. A fourth scenario was run with pre-industrial boundary conditions (modern geography and vegetation and 280 ppm CO2) as a control experiment (CONTROL). Despite the high level of CO2, global average temperatures in CAMB_FLAT and CAMB_MTN are cooler than that of CONTROL. In CAMB_COLD, the oceans freeze over completely and 'snowball Earth' conditions are present. These results highlight the importance of vegetation, land surface albedo, and continental position in maintaining an equable climate in modern times. They also suggest that a drop in greenhouse gases during the Cambrian, whether due to reduced natural emissions from biologic or volcanic sources, or an increase in biologic activity in the oceans, could have been responsible for the initiation of cooler climatic conditions.

  10. 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.

  11. Role of surface protective antigen A in the pathogenesis of Erysipelothrix rhusiopathiae strain C43065.

    PubMed

    Borrathybay, Entomack; Gong, Feng-Juan; Zhang, Lei; Nazierbieke, Wulumuhan

    2015-02-01

    To clarify the role of surface protective antigen A (SpaA) in the pathogenesis of Erysipelothrix rhusiopathiae C43065 (serotype 2), the spaA deletion mutant of E. rhusiopathiae ΔspaA was constructed by homologous recombination. The virulence of the ΔspaA mutant decreased more than 76-fold compared with that of the wild-type strain C43065 in mice. The mutant strain was sensitive to the bactericidal action of swine serum, whereas the wild-type strain was resistant. The adhesion of wild-type strain to MEF cells was inhibited significantly by treatment with rabbit antiserum against recombinant SpaA (rSpaA) as compared with the treatment with normal rabbit serum, but the mutant strain was not affected. The mutant strain was readily taken up by mouse peritoneal macrophages in the normal rabbit serum, whereas the wild-type strain was resistant. Whereas the rabbit antiserum against rSpaA promoted the phagocytosis of wild-type strain by macrophages, the mutant strain was not affected. In addition, mice vaccinated with the formalin-killed mutant strain were provided 40% protection against challenge by the homologous virulent strain as compared with those with wild-type strain, NaOH-extracted antigen, or rSpaA, which provided more than 80% protection against the same infection. These suggested that SpaA has an important role in the pathogenesis of E. rhusiopathiae infection and could be a target for vaccination against swine erysipelas.

  12. 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

  13. Investigating the role of surface micro/nano structure in cell adhesion behavior of superhydrophobic polypropylene/nanosilica surfaces.

    PubMed

    Hejazi, Iman; Seyfi, Javad; Hejazi, Ehsan; Sadeghi, Gity Mir Mohamad; Jafari, Seyed Hassan; Khonakdar, Hossein Ali

    2015-03-01

    The main aim of the current study was to investigate the effects of different topographical features on the biological performance of polypropylene (PP)/silica coatings. To this end, a novel method including combined use of nanoparticles and non-solvent was used for preparation of superhydrophobic PP coatings. The proposed method led to a much more homogeneous appearance with a better adhesion to the glass substrate. Moreover, a notable reduction was observed in the required contents of nanoparticles (100-20 wt% with respect to the polymer) and non-solvent (35.5-9 vol%) for achieving superhydrophobicity. Surface composition and morphology of the coatings were also investigated via X-ray photoelectron spectroscopy and scanning electron microscopy. Based on both qualitative and quantitative evaluations, it was found that the superhydrophobic coatings with only nano-scale roughness strongly prevented adhesion and proliferation of 4T1 mouse mammary tumor cells as compared to the superhydrophobic surfaces with micro-scale structure. Such results demonstrate that the cell behavior could be controlled onto the polymer and nanocomposite-based surfaces via tuning the surface micro/nano structure.

  14. Interaction energy evaluation of soluble microbial products (SMP) on different membrane surfaces: role of the reconstructed membrane topology.

    PubMed

    Chen, Lin; Tian, Yu; Cao, Chu-qing; Zhang, Jun; Li, Zhi-neng

    2012-05-15

    Soluble microbial products (SMP), a majority of organic matter in effluents, play a key role in membrane fouling. A series of filtration experiments were conducted, and demonstrated that the flux decrement rate was in order of cellulose acetate membrane (CA, 65.4%), polyvinylidene fluoride (PVDF, 47.9%) and polyether sulfones (PES, 29.2%). Results showed that the fouling behavior of membrane should be predicted from the combined knowledge of solution chemistry, surface chemical properties and surface morphology. To better understand the interactions between the SMP and different membranes, a technique for reconstructing the membrane surface topology was developed on the basis of statistical parameters obtained from atomic force microscopy. The interaction energy, represented by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) potential, was calculated by surface element integration, allowing exploring the interaction energy profiles for different surfaces and providing considerable insights into the role of such interactions on the macroscopic fouling behavior. The resulting interaction energy differed considerably from the corresponding interaction between perfectly smooth surfaces. The great influence of protrusion on the membrane surface was to reduce the primary energy barrier height, thus rendering rough surface more favorable for deposition. An attractive energy region was immediately surrounded by each positive asperity as demonstrated in the roughness-engendered interaction energy maps. As the SMP approached closer to the membrane, they had a high probability of getting trapped in the attractive energy region, leading to a more rapid loss of flux than smooth membrane.

  15. Peste des petits ruminants in Arabian wildlife.

    PubMed

    Kinne, J; Kreutzer, R; Kreutzer, M; Wernery, U; Wohlsein, P

    2010-08-01

    Recurrence of peste des petits ruminants (PPR) was diagnosed in the United Arabian Emirates in several wild ruminants confirmed by morphological, immunohistochemical, serological and molecular findings. Phylogenetic analysis revealed that the virus strain belongs to lineage IV, which is different to some previously isolated PPR strains from the Arabian Peninsula. This study shows that wild ruminants may play an important epidemiological role as virus source for domestic small ruminants.

  16. 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

  17. Role of volcanic and anthropogenic aerosols in the recent global surface warming slowdown

    NASA Astrophysics Data System (ADS)

    Smith, Doug M.; Booth, Ben B. B.; Dunstone, Nick J.; Eade, Rosie; Hermanson, Leon; Jones, Gareth S.; Scaife, Adam A.; Sheen, Katy L.; Thompson, Vikki

    2016-10-01

    The rate of global mean surface temperature (GMST) warming has slowed this century despite the increasing concentrations of greenhouse gases. Climate model experiments show that this slowdown was largely driven by a negative phase of the Pacific Decadal Oscillation (PDO), with a smaller external contribution from solar variability, and volcanic and anthropogenic aerosols. The prevailing view is that this negative PDO occurred through internal variability. However, here we show that coupled models from the Fifth Coupled Model Intercomparison Project robustly simulate a negative PDO in response to anthropogenic aerosols implying a potentially important role for external human influences. The recovery from the eruption of Mount Pinatubo in 1991 also contributed to the slowdown in GMST trends. Our results suggest that a slowdown in GMST trends could have been predicted in advance, and that future reduction of anthropogenic aerosol emissions, particularly from China, would promote a positive PDO and increased GMST trends over the coming years. Furthermore, the overestimation of the magnitude of recent warming by models is substantially reduced by using detection and attribution analysis to rescale their response to external factors, especially cooling following volcanic eruptions. Improved understanding of external influences on climate is therefore crucial to constrain near-term climate predictions.

  18. The role of surface reactions on the active and selective catalyst design for bioethanol steam reforming

    NASA Astrophysics Data System (ADS)

    Benito, M.; Padilla, R.; Serrano-Lotina, A.; Rodríguez, L.; Brey, J. J.; Daza, L.

    In order to study the role of surface reactions involved in bioethanol steam reforming mechanism, a very active and selective catalyst for hydrogen production was analysed. The highest activity was obtained at 700 °C, temperature at which the catalyst achieved an ethanol conversion of 100% and a selectivity to hydrogen close to 70%. It also exhibited a very high hydrogen production efficiency, higher than 4.5 mol H 2 per mol of EtOH fed. The catalyst was operated at a steam to carbon ratio (S/C) of 4.8, at 700 °C and atmospheric pressure. No by-products, such as ethylene or acetaldehyde were observed. In order to consider a further application in an ethanol processor, a long-term stability test was performed under the conditions previously reported. After 750 h, the catalyst still exhibited a high stability and selectivity to hydrogen production. Based on the intermediate products detected by temperature programmed desorption and reaction (TPD and TPR) experiments, a reaction pathway was proposed. Firstly, the adsorbed ethanol is dehydrogenated to acetaldehyde producing hydrogen. Secondly, the adsorbed acetaldehyde is transformed into acetone via acetic acid formation. Finally, acetone is reformed to produce hydrogen and carbon dioxide, which were the final reaction products. The promotion of such reaction sequence is the key to develop an active, selective and stable catalyst, which is the technical barrier for hydrogen production by ethanol reforming.

  19. 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

  20. Role of surface and subsurface processes in scaling N2O emissions along riverine networks.

    PubMed

    Marzadri, Alessandra; Dee, Martha M; Tonina, Daniele; Bellin, Alberto; Tank, Jennifer L

    2017-04-11

    Riverine environments, such as streams and rivers, have been reported as sources of the potent greenhouse gas nitrous oxide ([Formula: see text]) to the atmosphere mainly via microbially mediated denitrification. Our limited understanding of the relative roles of the near-surface streambed sediment (hyporheic zone), benthic, and water column zones in controlling [Formula: see text] production precludes predictions of [Formula: see text] emissions along riverine networks. Here, we analyze [Formula: see text] emissions from streams and rivers worldwide of different sizes, morphology, land cover, biomes, and climatic conditions. We show that the primary source of [Formula: see text] emissions varies with stream and river size and shifts from the hyporheic-benthic zone in headwater streams to the benthic-water column zone in rivers. This analysis reveals that [Formula: see text] production is bounded between two [Formula: see text] emission potentials: the upper [Formula: see text] emission potential results from production within the benthic-hyporheic zone, and the lower [Formula: see text] emission potential reflects the production within the benthic-water column zone. By understanding the scaling nature of [Formula: see text] production along riverine networks, our framework facilitates predictions of riverine [Formula: see text] emissions globally using widely accessible chemical and hydromorphological datasets and thus, quantifies the effect of human activity and natural processes on [Formula: see text] production.

  1. Stability issues in Pd-based catalysts: the role of surface Pt in improving the stability and oxygen reduction reaction (ORR) activity.

    PubMed

    Singh, R K; Rahul, R; Neergat, M

    2013-08-21

    Carbon-supported Pd and Pd3Co catalysts have been electrochemically characterized in 0.1 M HClO4 solution and we found that both catalysts were unstable. On repeated potential cycling, the electrochemical surface area of the catalysts decreases and the oxygen reduction reaction (ORR) activity suffers. To stabilize surface Pd atoms of both Pd and Pd3Co catalysts, we deposited Pt using adsorbed hydrogen on the catalytically active Pd sites. The Pt : Pd ratio of Pt-coated Pd and Pt-coated Pd3Co catalysts suggests half-a-monolayer coverage of Pt (two hydrogen atoms required for reducing a Pt(2+) ion). The Pt : Pd ratio of Pt-coated Pd3Co catalyst obtained from the simple geometrical hard sphere model, energy-dispersive X-ray spectroscopy (EDS) line scan and bulk EDS agrees very well with that calculated from the hydrogen desorption (H(des)) charge of Pd3Co. At the same time, the Pt : Pd ratio of Pt-coated Pd calculated from the H(des) charge of Pd catalyst is significantly lower than the ratio obtained from the other methods. Thus, the Pt : Pd ratio of the Pt-coated Pd catalyst estimated from the H(des) region of Pd is an underestimation of the composition. This suggests that Pd forms an electrochemically inactive species from the H(upd) region itself and Co in Pd3Co seems to stabilize Pd against oxidation by delaying the formation of electrochemically inactive species to higher potentials above the H(upd) region. The voltammograms along with the peroxide formation characteristics of the catalysts support the above observations. The deposited Pt on the surface of the Pd and Pd3Co catalysts masks active Pd sites from the electrochemical environment and even partial coverage with Pt improves the stability and ORR activity of the catalysts when compared to that of the respective Pt-free counterparts.

  2. 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.

  3. 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

  4. The roles of titanium surface micro/nanotopography and wettability on the differential response of human osteoblast lineage cells.

    PubMed

    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

    2013-04-01

    Surface micro- and nanostructural modifications of dental and orthopedic 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, remain unclear. In the current study, surface wettability analyses (optical sessile drop analysis, environmental scanning electron microscopic 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 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.

  5. Injectabilite des coulis de ciment dans des milieux fissures

    NASA Astrophysics Data System (ADS)

    Mnif, Thameur

    Le travail presente ici est un bilan du travaux de recherche effectues sur l'injectabilite des coulis de ciment dans lu milieux fissures. Un certain nombre de coulis a base de ciment Portland et microfin ont ete selectionnes afin de caracteriser leur capacite a penetrer des milieux fissures. Une partie des essais a ete menee en laboratoire. L'etude rheologique des differents melanges a permis de tester l'influence de l'ajout de superplastifiant et/ou de fumee de silice sur la distribution granulometrique des coulis et par consequent sur leur capacite a injecter des colonnes de sable simulant un milieu fissure donne. La classe granulometrique d'un coulis, sa stabilite et sa fluidite sont apparus comme les trois facteurs principaux pour la reussite d'une injection. Un facteur de finesse a ete defini au cours de cette etude: base sur la classe granulometrique du ciment et sa stabilite, il peut entrer dans la formulation theorique du debit d'injection avant application sur chantier. La deuxieme et derniere partie de l'etude presente les resultats de deux projets de recherche sur l'injection realises sur chantier. L'injection de dalles de beton fissurees a permis le suivi de l'evolution des pressions avec la distance au point d'injection. L'injection de murs de maconnerie a caractere historique a montre l'importance de la definition de criteres de performance des coulis a utiliser pour traiter un milieu donne et pour un objectif donne. Plusieurs melanges peuvent ainsi etre predefinis et mis a disposition sur le chantier. La complementarite des ciments traditionnels et des ciments microfins devient alors un atout important. Le choix d'utilisation de ces melanges est fonction du terrain rencontre. En conclusion, cette recherche etablit une methodologie pour la selection des coulis a base de ciment et des pressions d'injection en fonction de l'ouverture des fissures ou joints de construction.

  6. 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.

  7. Electrical Resistivity of Crystalline Rocks: Role of Carbon Films on Fracture Surfaces

    NASA Astrophysics Data System (ADS)

    Duba, A.; Kronenberg, A.; Karner, S.; Mathez, E.; Roberts, J.

    2006-12-01

    Electrical resistivity of dense crystalline quartzite is reduced by carbon films deposited on fractures during failure experiments performed at T=400°C in the presence of carbon- bearing fluids. Hollow cylinders of Sioux quartzite, jacketed by silver, were hydrostatically loaded to failure by applying pressurized argon gas at the outer diameter (reaching ~290 MPa at a rate of 0.1 MPa/s) while maintaining a constant pore pressure at the inner diameter. Pore fluids consisted of CO, CO2, CH4, a 1:1 mixture of CO2 and CH4 (each with pore pressures of 2.0 to 4.1 MPa) and air (at atmospheric pressure). Biaxial-stress states are calculated using elastic-stress solutions that account for the applied pressures and hollow-cylinder dimensions. For the inner wall of the cylinders, effective radial stress (σr) is zero and calculated effective differential stresses (σq- σr) reach 1225 MPa. Failure of hollow Sioux quartzite cylinders occurred by the formation of mode II shear fractures that transect the cylinder wall. The distribution of carbon in the run products was mapped by electron probe. Samples deformed in CO2 and air contained little or no carbon above the small amount that exists in the undeformed rock. Samples deformed in CO contain ubiquitous carbon films on the fracture surfaces that formed during deformation. Because carbon is absent on other free quartz surfaces that existed during the experiments, we conclude that the carbon films formed preferentially on the fractures as they formed. The radial resistivity of dry, undeformed Sioux quartzite cylinders is extremely large in the ambient laboratory atmosphere (>23 MØmega-m). The radial resistivity of Sioux quartzite cylinders that failed in pore fluids that promote carbon deposition are lower (2.8 to 4.6 MØmega-m for CO tests; 15.2 to 18.4 MØmega-m for CO2:CH4 tests). The results of this study help to isolate the role of carbon deposition on fresh fracture surfaces in altering the electrical properties of rocks

  8. Role of surface tension and roughness on the wettability of Er:YAG laser irradiated dentin: In vitro study

    PubMed Central

    Brulat, Nathalie; Rocca, Jean-Paul; Darque-Ceretti, Evelyne

    2013-01-01

    Introduction: The aim of this “in vitro” study was to evaluate the role of surface tension and surface roughness in the wettability, considered essential for a good adhesion, comparing Er:YAG laser - to bur-prepared dentin. Materials and Methods: Dentin surfaces of third human molars were Er:YAG laser- and bur-prepared to evaluate the effects of surface tension and roughness on wettability and interferometric analysis was used to compare the roughness of the two groups surfaces, after gold-coating them. Results: In bur-prepared samples the time taken for the water drop to spread out was approximately the same with or without metallization while, in the Er:YAG laser-prepared surfaces the spreading-out time was less than 10 seconds but longer after metallization i.e. nearly two minutes. Large differences in wettability measurements were observed because the water drop was almost immediately absorbed on the Er:YAG laser-prepared surface. The wettability test demonstrated that the porous and hydrophilic properties of Er:YAG laser-prepared surfaces are higher than bur-prepared surfaces. Conclusion: Surface tension, surface morphology and porosity had different effects on the spreading time of a water drop on both Er:YAG laser- and bur-prepared surfaces. And, while surface tension does not seem to influence the results, roughness appears to be the main parameter involved in water drop spreading, this being an indication, by the clinical point of view, to the choice of Er:YAG laser parameters in conservative dentistry. PMID:24204092

  9. 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

  10. Note des Éditeurs scientifiques

    NASA Astrophysics Data System (ADS)

    Averbuch, P.

    'équilibre, une séparation de l'énergie libre en énergie libre de volume et en énergie libre de surface devrait donner les mêmes résultats ; par contre les choses deviennent troublantes dès que l'on passe aux coefficients de transport, c'est-à-dire à l'aspect macroscopique de la dynamique moléculaire. Il y a là un écart notable avec les conceptions courantes, ce qui rend très surprenante la lecture de ces articles. On peut mentionner la liste des problèmes théoriques posés par la description phénoménologique qui est celle de cette série d'articles : la généralisation de lois d'échelle en dehors de zones critiques n'est pas absolument nouvelle, par contre la simplicité des lois reliant l'exposant v à la température pose problème ; le sens des temps de relaxation utilisés est sans doute également à préciser. Enfin les modes considérés semblent n'intervenir dans les propriétés thermodynamiques que par un facteur par mode, comme si seulement l'énergie potentielle devait intervenir, les termes cinétiques ne participant pas vraiment aux transitions de phase. Tout cela pose donc problème, et l'on peut se demander si un pareil modèle peut être compatible avec tout ce qui est connu par ailleurs en physique statistique. Mais s'il rend bien compte de beaucoup de résultats expérimentaux, ce sont ces derniers qui seraient en difficulté avec la mécanique statistique. Il a donc semblé préférable de publier le modèle, sa justification expérimentale et de poser quelques problèmes, tant aux théoriciens, qui pourraient expliquer pourquoi un tel modèle rend compte de résultats observés, qu'aux expérimentateurs, qui pourraient reprendre certaines mesures, et délimiter le caractère plus ou moins général du modèle.

  11. 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...

  12. 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…

  13. 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...

  14. 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

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

    SciTech Connect

    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 salinity 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.

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

    DOE PAGES

    Lago, Veronique; Wijffels, Susan E.; Durack, Paul 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

  17. 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.

  18. 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.

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

    PubMed

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

    2015-07-16

    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 the dentin matrix on the wettability and the long-term reduced modulus of elasticity (Er) of 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 assessed 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. Er of the adhesive, hybrid layer and underlying dentin was evaluated after 24h and 30 months in artificial saliva. The dentin hydrophilicity significantly decreased after application of the priming solutions. Aging significantly decreased Er in the hybrid layer and underlying dentin of control groups. 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 24h. 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.

  20. Developpement d'une methode calorimetrique de mesure des pertes ac pour des rubans supraconducteurs a haute temperature critique

    NASA Astrophysics Data System (ADS)

    Dolez, Patricia

    Le travail de recherche effectue dans le cadre de ce projet de doctorat a permis la mise au point d'une methode de mesure des pertes ac destinee a l'etude des supraconducteurs a haute temperature critique. Pour le choix des principes de cette methode, nous nous sommes inspires de travaux anterieurs realises sur les supraconducteurs conventionnels, afin de proposer une alternative a la technique electrique, presentant lors du debut de cette these des problemes lies a la variation du resultat des mesures selon la position des contacts de tension sur la surface de l'echantillon, et de pouvoir mesurer les pertes ac dans des conditions simulant la realite des futures applications industrielles des rubans supraconducteurs: en particulier, cette methode utilise la technique calorimetrique, associee a une calibration simultanee et in situ. La validite de la methode a ete verifiee de maniere theorique et experimentale: d'une part, des mesures ont ete realisees sur des echantillons de Bi-2223 recouverts d'argent ou d'alliage d'argent-or et comparees avec les predictions theoriques donnees par Norris, nous indiquant la nature majoritairement hysteretique des pertes ac dans nos echantillons; d'autre part, une mesure electrique a ete realisee in situ dont les resultats correspondent parfaitement a ceux donnes par notre methode calorimetrique. Par ailleurs, nous avons compare la dependance en courant et en frequence des pertes ac d'un echantillon avant et apres qu'il ait ete endommage. Ces mesures semblent indiquer une relation entre la valeur du coefficient de la loi de puissance modelisant la dependance des pertes avec le courant, et les inhomogeneites longitudinales du courant critique induites par l'endommagement. De plus, la variation en frequence montre qu'au niveau des grosses fractures transverses creees par l'endommagement dans le coeur supraconducteur, le courant se partage localement de maniere a peu pres equivalente entre les quelques grains de matiere

  1. Studies on the function of cell surface glycoproteins. II. Possible role of surface glycoproteins in the control of cytoskeletal organization and surface morphology

    PubMed Central

    1979-01-01

    Immunoglobulin from goat antiserum directed against purified surface membranes from transformed BHK21/C13 cells (anti-M) has been shown to cause both control and transformed hamster cells to round and detach from the substrate (see accompanying paper). This paper documents the effects of the antiserum on the cytoskeletal organization and cell surface morphology of control BHK21/C13 cells examined by scanning and transmission electron microscopy. As a result of antiserum-induced rounding, the normally smooth cell surface becomes covered with filopodia and blebs, and the organization of all three components of the filamentous cytoskeleton is altered. In terms of cell surface morphology and cytoskeletal organization, the cells resemble rounded, postmitotic or trypsinized BHK cells rather than cells treated with either anticytoskeletal drugs or lectins. Immunocytochemical and radioimmune assay experiments support the suggestion that the rounding reaction induced by anti-M serum results from the specific interaction of antibodies with molecules on the cell surface. It is suggested that anti-M serum induces alterations in cytoskeletal organization via a transmembrane signal and that cytoskeletal reorganization is a fundamental part of the rounding and detachment process. PMID:457749

  2. Grundlagen des Tissue Engineering

    NASA Astrophysics Data System (ADS)

    Mayer, Jörg; Blum, Janaki; Wintermantel, Erich

    Die Organtransplantation stellt eine verbreitete Therapie dar, um bei krankheitsoder unfallbedingter Schädigung eines Organs die Gesamtheit seiner Funktionen wieder herzustellen, indem es durch ein Spenderorgan ersetzt wird. Organtransplantationen werden für die Leber, die Niere, die Lunge, das Herz oder bei schweren grossflächigen Verbrennungen der Haut vorgenommen. Der grosse apparative, personelle und logistische Aufwand und die Risiken der Transplantationschirurgie (Abstossungsreaktionen) sowie die mangelnde Verfügbarkeit von immunologisch kompatiblen Spenderorganen führen jedoch dazu, dass der Bedarf an Organtransplantaten nur zu einem sehr geringen Teil gedeckt werden kann. Sind Spenderorgane nicht verfügbar, können in einzelnen Fällen lebenswichtige Teilfunktionen, wie beispielsweise die Filtrationsfunktion der Niere durch die Blutreinigung mittels Dialyse ersetzt oder, bei mangelnder Funktion der Bauchspeicheldrüse (Diabetes), durch die Verabreichung von Insulin ein normaler Zustand des Gesamtorganismus auch über Jahre hinweg erhalten werden. Bei der notwendigen lebenslangen Anwendung apparativer oder medikamentöser Therapie können für den Patienten jedoch häufig schwerwiegende, möglicherweise lebensverkürzende Nebenwirkungen entstehen. Daher werden in der Forschung Alternativen gesucht, um die Funktionen des ausgefallenen Organs durch die Implantation von Zellen oder in vitro gezüchteten Geweben möglichst umfassend wieder herzustellen. Dies erfordert biologisch aktive Implantate, welche die für den Stoffwechsel des Organs wichtigen Zellen enthalten und einen organtypischen Stoffwechsel entfalten.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    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.

  4. 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

  5. Wettability and surface forces measured by atomic force microscopy: the role of roughness

    NASA Astrophysics Data System (ADS)

    Gavoille, J.; Takadoum, J.; Martin, N.; Durand, D.

    2009-10-01

    Thin films of titanium, copper and silver with various roughnesses were prepared by physical vapour deposition technique: dc magnetron sputtering. By varying the deposition time from few minutes to one hour it was possible to obtain metallic films with surface roughness average ranging from 1 to 20 nm. The wettability of these films was studied by measuring the contact angle using the sessile drop method and surface forces were investigated using the atomic force microscopy (AFM) by measuring the pull-off force between the AFM tip and the surfaces. Experimental results have been mainly discussed in terms of metal surface reactivity, Young modulus of the materials and real surface of contact between the AFM tip and the film surfaces.

  6. The role of specular reflectance in surface anisotropy. [in remote sensing

    NASA Technical Reports Server (NTRS)

    Ahmad, Suraiya P.; Deering, Donald W.

    1992-01-01

    For smooth surfaces, specular reflection constitutes a major source of anisotropy in the surface bidirectional reflectance and introduces a strong illumination angle dependence in diurnal albedo. A prior formulation has been employed by the authors to account for the surface anisotropy of other natural surfaces. It is shown that this formulation is appropriate to successfully explain the specular characteristics of other rough surfaces as well as that of the ocean. The angular dependence of the diffuse component of the reflected radiance is explained using the Ahmad-Deering formulation, which is based on Chandrasekhar's radiative transfer solution. Results for a smooth silt-playa lake bed in a volcanic region of Nevada are presented. It is shown that this formulation is capable of explaining the specular features measured in the field and can be effectively used in any surface bidirectional reflectance model.

  7. 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

  8. 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.

  9. The role of electrostatic interactions in protease surface diffusion and the consequence for interfacial biocatalysis.

    PubMed

    Feller, Bob E; Kellis, James T; Cascão-Pereira, Luis G; Robertson, Channing R; Frank, Curtis W

    2010-12-21

    This study examines the influence of electrostatic interactions on enzyme surface diffusion and the contribution of diffusion to interfacial biocatalysis. Surface diffusion, adsorption, and reaction were investigated on an immobilized bovine serum albumin (BSA) multilayer substrate over a range of solution ionic strength values. Interfacial charge of the enzyme and substrate surface was maintained by performing the measurements at a fixed pH; therefore, electrostatic interactions were manipulated by changing the ionic strength. The interfacial processes were investigated using a combination of techniques: fluorescence recovery after photobleaching, surface plasmon resonance, and surface plasmon fluorescence spectroscopy. We used an enzyme charge ladder with a net charge ranging from -2 to +4 with respect to the parent to systematically probe the contribution of electrostatics in interfacial enzyme biocatalysis on a charged substrate. The correlation between reaction rate and adsorption was determined for each charge variant within the ladder, each of which displayed a maximum rate at an intermediate surface concentration. Both the maximum reaction rate and adsorption value at which this maximum rate occurs increased in magnitude for the more positive variants. In addition, the specific enzyme activity increased as the level of adsorption decreased, and for the lowest adsorption values, the specific enzyme activity was enhanced compared to the trend at higher surface concentrations. At a fixed level of adsorption, the specific enzyme activity increased with positive enzyme charge; however, this effect offers diminishing returns as the enzyme becomes more highly charged. We examined the effect of electrostatic interactions on surface diffusion. As the binding affinity was reduced by increasing the solution ionic strength, thus weakening electrostatic interaction, the rate of surface diffusion increased considerably. The enhancement in specific activity achieved at

  10. 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

  11. Predicting the infrared transition intensities in the Ar-HF complex: the key role of the dipole moment surface accuracy.

    PubMed

    Jankowski, Piotr; Ziółkowski, Marcin

    2008-01-21

    The method proposed earlier for the generation of the full-dimensional energy surface for van der Waals complexes [P. Jankowski, J. Chem. Phys. 121, 1655 (2004)] is used to obtain a fulldimensional dipole moment surface for the atom-diatom complex in calculations based on the coupled-cluster with single, double, and noniterative triple excitation approach and the aug-cc-pVQZ basis sets. This surface has been employed to calculate transition intensities of the infrared spectra of Ar-HF. Special attention has been paid to study the problem of relative intensities of the different bands which have not been properly predicted within the long-range models of the dipole moment [A. E. Thornley and J. M. Hutson, J. Chem. Phys. 101, 5578 (1994)]. The intensities calculated with the present dipole moment surface agree very well with the experimental data, which indicate that the short-range interactions significantly affect the dipole moment surface and the calculated intensities. To investigate the role of the accuracy of the dipole moment surface on infrared transition intensities in atom-diatom complexes, four models of increasing complexity are studied. Their performance is shown to strongly depend on the region of the interaction energy surface probed by the initial and final states of the individual transitions.

  12. Role of hospital surfaces in the transmission of emerging health care-associated pathogens: norovirus, Clostridium difficile, and Acinetobacter species.

    PubMed

    Weber, David J; Rutala, William A; Miller, Melissa B; Huslage, Kirk; Sickbert-Bennett, Emily

    2010-06-01

    Health care-associated infections (HAI) remain a major cause of patient morbidity and mortality. Although the main source of nosocomial pathogens is likely the patient's endogenous flora, an estimated 20% to 40% of HAI have been attributed to cross infection via the hands of health care personnel, who have become contaminated from direct contact with the patient or indirectly by touching contaminated environmental surfaces. Multiple studies strongly suggest that environmental contamination plays an important role in the transmission of methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus spp. More recently, evidence suggests that environmental contamination also plays a role in the nosocomial transmission of norovirus, Clostridium difficile, and Acinetobacter spp. All 3 pathogens survive for prolonged periods of time in the environment, and infections have been associated with frequent surface contamination in hospital rooms and health care worker hands. In some cases, the extent of patient-to-patient transmission has been found to be directly proportional to the level of environmental contamination. Improved cleaning/disinfection of environmental surfaces and hand hygiene have been shown to reduce the spread of all of these pathogens. Importantly, norovirus and C difficile are relatively resistant to the most common surface disinfectants and waterless alcohol-based antiseptics. Current hand hygiene guidelines and recommendations for surface cleaning/disinfection should be followed in managing outbreaks because of these emerging pathogens.

  13. 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.

  14. Role of Subsurface Physics in the Assimilation of Surface Soil Moisture Observations

    NASA Technical Reports Server (NTRS)

    Reichle, R. H.

    2010-01-01

    Root zone soil moisture controls the land-atmosphere exchange of water and energy and exhibits memory that may be useful for climate prediction at monthly scales. Assimilation of satellite-based surface soil moisture observations into a land surface model is an effective way to estimate large-scale root zone soil moisture. The propagation of surface information into deeper soil layers depends on the model-specific representation of subsurface physics that is used in the assimilation system. In a suite of experiments we assimilate synthetic surface soil moisture observations into four different models (Catchment, Mosaic, Noah and CLM) using the Ensemble Kalman Filter. We demonstrate that identical twin experiments significantly overestimate the information that can be obtained from the assimilation of surface soil moisture observations. The second key result indicates that the potential of surface soil moisture assimilation to improve root zone information is higher when the surface to root zone coupling is stronger. Our experiments also suggest that (faced with unknown true subsurface physics) overestimating surface to root zone coupling in the assimilation system provides more robust skill improvements in the root zone compared with underestimating the coupling. When CLM is excluded from the analysis, the skill improvements from using models with different vertical coupling strengths are comparable for different subsurface truths. Finally, the skill improvements through assimilation were found to be sensitive to the regional climate and soil types.

  15. Inhibition and enhancement of microbial surface colonization: the role of silicate composition

    USGS Publications Warehouse

    Roberts, Jennifer A.

    2004-01-01

    Classical treatment of cell attachment by models of filtration or coulombic attraction assumes that attachment of cells to mineral surfaces would be controlled by factors such as response to predation, collision efficiency, or coulombic attraction between the charged groups at the mineral and cell surfaces. In the study reported here, the passive model of attachment was investigated using a native microbial consortium and a variety of Al- and Fe-bearing silicates and oxides to determine if other controls, such as mineral composition, also influence the interaction between cells and surfaces. Results from in situ colonization studies in an anaerobic groundwater at pH 6.8 combined with most probable number analyses (MPN) of surface-adherent cells demonstrate that electrostatic effects dominate microbial colonization on positively charged oxide surfaces regardless of mineral composition. In contrast, on negatively charged silicate minerals and glasses, the solid phase composition is a factor in determining the extent of microbial colonization, as well as the diversity of the attached community. In particular, silicates containing more than 1.2% Al exhibit less biomass than Al-poor silicates and MPN suggests a shift in community diversity, possibly indicating Al toxicity on these surfaces. When Fe is present in the silicate, however, this trend is reversed and abundant colonization of the surface is observed. Here, microorganisms preferentially colonize those silicate surfaces that offer beneficial nutrients and avoid those that contain potentially toxic elements.

  16. 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.

  17. 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.

  18. Role of oxygen in wetting of copper nanoparticles on silicon surfaces at elevated temperature

    PubMed Central

    Ghosh, Tapas

    2017-01-01

    Copper nanoparticles have been deposited on silicon surfaces by a simple galvanic displacement reaction, and rapid thermal annealing has been performed under various atmospheric conditions. In spite of the general tendency of the agglomeration of nanoparticles to lower the surface energy at elevated temperatures, our plan-view and cross-sectional transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis shows that the thermal oxidation of the copper nanoparticles and formation of cupric oxide (CuO) on silicon surfaces leads to wetting rather than agglomeration. In contrast, agglomeration has been observed when copper nanoparticles were annealed in a nitrogen environment. The lattice transformation from cubic Cu to monoclinic CuO, and hence the change in surface energy of the particles, assists the wetting process. The occurrence of wetting during the oxidation step implies a strong interaction between the oxidized film and the silicon surface. PMID:28326232

  19. La diffraction des neutrons et des rayons X pour l'étude structurale des liquides et des verres

    NASA Astrophysics Data System (ADS)

    Fischer, H. E.; Salmon, P. S.; Barnes, A. C.

    2003-02-01

    La compréhension de mainte propriété physique d'un verre ou d'un liquide nécessite la connaissance des facteurs de structure partiels (PSFs) qui décrivent chacun la distribution d'une espèce atomique autour d'une autre. La technique de diffraction des neutrons avec substitution isotopique (NDIS) [1,2,3], ayant bien réussi a déterminer les PSFs de certains composés [4,5], est pourtant restreinte aux isotopes présentant un contraste suffisant en longueur de diffusion. D'un autre cote, la technique de diffusion anomale des rayons X (AXS ou AXD) [6] permet de faire varier la longueur de diffusion d'une espèce atomique pourvu que son énergie d'absorption soit à la fois accessible et suffisamment élevée pour donner un assez grand transfert du moment. La combinaison des techniques de diffraction des neutrons (avec ou sans substitution isotopique) et de diffraction des rayons X (avec ou sans diffusion anomale) peut donc permettre d'obtenir un meilleur contraste en longueurs de diffusion pour un système donné, mais exige une analyse de données plus soignée pour pouvoir bien tenir compte des erreurs systématiques qui sont différentes pour les 2 techniques [7]. Pour les atomes ayant des distributions électroniques quasi-sphériques, e.g. dans le cas d'un alliage liquide, la combinaison des techniques de NDIS et de diffraction des rayons X s'est déjà montrée très avantageuse pour la détermination des PSFs [8,9]. Dans le cas des verres ayant d'importantes liaisons covalentes, l'effective combinaison des 2 techniques peut être moins directe mais facilitée lorsqu'il s'agit des atomes de grand Z [10,11]. Nous présentons ici un sommaire du méthode et quelques exemples des résultats.

  20. Role of roughness parameters on the tribology of randomly nano-textured silicon surface.

    PubMed

    Gualtieri, E; Pugno, N; Rota, A; Spagni, A; Lepore, E; Valeri, S

    2011-10-01

    This experimental work is oriented to give a contribution to the knowledge of the relationship among surface roughness parameters and tribological properties of lubricated surfaces; it is well known that these surface properties are strictly related, but a complete comprehension of such correlations is still far to be reached. For this purpose, a mechanical polishing procedure was optimized in order to induce different, but well controlled, morphologies on Si(100) surfaces. The use of different abrasive papers and slurries enabled the formation of a wide spectrum of topographical irregularities (from the submicro- to the nano-scale) and a broad range of surface profiles. An AFM-based morphological and topographical campaign was carried out to characterize each silicon rough surface through a set of parameters. Samples were subsequently water lubricated and tribologically characterized through ball-on-disk tribometer measurements. Indeed, the wettability of each surface was investigated by measuring the water droplet contact angle, that revealed a hydrophilic character for all the surfaces, even if no clear correlation with roughness emerged. Nevertheless, this observation brings input to the purpose, as it allows to exclude that the differences in surface profile affect lubrication. So it is possible to link the dynamic friction coefficient of rough Si samples exclusively to the opportune set of surface roughness parameters that can exhaustively describe both height amplitude variations (Ra, Rdq) and profile periodicity (Rsk, Rku, Ic) that influence asperity-asperity interactions and hydrodynamic lift in different ways. For this main reason they cannot be treated separately, but with dependent approach through which it was possible to explain even counter intuitive results: the unexpected decreasing of friction coefficient with increasing Ra is justifiable by a more consistent increasing of kurtosis Rku.

  1. 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

  2. Adsorption of water on NaCl (100) surfaces: Role of atomic steps

    SciTech Connect

    Dai, Q.; Hu, J.; Salmeron, M. |

    1997-03-13

    Using an atomic force microscope operated in contact and noncontact mode, we have studied the structures formed on the (100) cleavage surface of NaCl when exposed to water vapor. Above approximately 35% relative humidity (RH), a uniform layer of water is formed and the surface steps are observed to evolve slowly. At approximately 73% RH, the step structure becomes unstable and disappears abruptly because of dissolution (deliquescence) of the salt surface. Reversing the process by drying leads to the reappearance of new, more uniform monatomic steps. At humidity levels less than 30%, water adsorbs primarily at the step edges. 17 refs., 4 figs.

  3. Missile Aerodynamics (Aerodynamique des Missiles)

    DTIC Science & Technology

    1998-11-01

    guerre froide la production des missiles a baisse’, avec pour consequence une diminution des budgets de d6veloppement. Les nouveaux types de conflits ...Roma) Directeur - Gestion de l’information LUXEMBOURG (Recherche et developpement) - DRDGI 3 Voir Belgique Ministbre de la Difense nationale NORVEGE

  4. Multifunctional and Redundant Roles of Borrelia burgdorferi Outer Surface Proteins in Tissue Adhesion, Colonization, and Complement Evasion

    PubMed Central

    Caine, Jennifer A.; Coburn, Jenifer

    2016-01-01

    Borrelia burgdorferi is the causative agent of Lyme disease in the U.S., with at least 25,000 cases reported to the CDC each year. B. burgdorferi is thought to enter and exit the bloodstream to achieve rapid dissemination to distal tissue sites during infection. Travel through the bloodstream requires evasion of immune surveillance and pathogen clearance in the host, a process at which B. burgdorferi is adept. B. burgdorferi encodes greater than 19 adhesive outer surface proteins many of which have been found to bind to host cells or components of the extracellular matrix. Several others bind to host complement regulatory factors, in vitro. Production of many of these adhesive proteins is tightly regulated by environmental cues, and some have been shown to aid in vascular interactions and tissue colonization, as well as survival in the blood, in vivo. Recent work has described multifaceted and redundant roles of B. burgdorferi outer surface proteins in complement component interactions and tissue targeted adhesion and colonization, distinct from their previously identified in vitro binding capabilities. Recent insights into the multifunctional roles of previously well-characterized outer surface proteins such as BBK32, DbpA, CspA, and OspC have changed the way we think about the surface proteome of these organisms during the tick–mammal life cycle. With the combination of new and old in vivo models and in vitro techniques, the field has identified distinct ligand binding domains on BBK32 and DbpA that afford tissue colonization or blood survival to B. burgdorferi. In this review, we describe the multifunctional and redundant roles of many adhesive outer surface proteins of B. burgdorferi in tissue adhesion, colonization, and bloodstream survival that, together, promote the survival of Borrelia spp. throughout maintenance in their multi-host lifestyle. PMID:27818662

  5. Assessing the sensitivity of precipitation to surface heat fluxes : the role of the land and the atmosphere

    NASA Astrophysics Data System (ADS)

    Berg, A. M.; Findell, K. L.; Lintner, B. R.; Gentine, P.

    2012-12-01

    One of the key issues associated with land/atmosphere interactions is the feedback between surface turbulent energy fluxes and precipitation. Observational constraints on this feedback have so far been hard to obtain. Using the NARR reanalysis data, Findell et al. (2011) recently provided an assessment of the impacts of morning surface latent and sensible heat fluxes on the frequency and intensity of afternoon convective rainfall over North America: convective rainfall probability increases with higher evaporative fraction over the Eastern US and in Mexico, albeit with very little effect on rainfall amounts. Here, we apply the same metrics to simulations from GFDL's atmospheric models AM2.1 and AM3 - which, in particular, include different convective schemes. Using AMIP-like experiments, we show that AM2.1 reproduces more realistically the spatial and seasonal patterns of the sensitivity of convective rainfall to surface fluxes over North America. Beyond model mean biases, the ability of both models to represent the physical relationship between surface fluxes, boundary layer processes and precipitation is investigated. We then compare the two models on the global scale, showing that they display different spatio-temporal patterns of sensitivity. The sources of these differences, and in particular the respective role of the land surface and the atmosphere, are investigated using an intermediate model version that couples AM2.1's atmospheric component with AM3's land surface component.

  6. Deformation of graphene on an oxidizing nickel surface: the role of graphene layer number

    NASA Astrophysics Data System (ADS)

    George, Lijin; Shaina, P. R.; Gupta, Aparna; Das Gupta, Nandita; Jaiswal, Manu

    2016-11-01

    Few-layer graphene grown on nickel substrates by chemical vapour deposition is typically characterised by thickness inhomogeneity. In this work, we investigate the thickness-dependent changes induced in graphene during the surface oxidation of the underlying metal. Temperature-dependent Raman spectroscopy and scanning electron microscopy are used to monitor the lattice strain and defect formation induced in graphene, as well as the oxidation of Ni surface. Significant lattice strain is induced in thin layers of graphene (1-2 layers) during the oxidation process, for T > 400 °C. This is followed by the formation of boundary-type defects, and graphene loses structural integrity. In contrast, lattice strain induced in thicker graphene (up to 7 layers) during the metal surface oxidation is quite subdued. These thicker layers de-pin and remain structurally intact even after the underneath metal surface has oxidized.

  7. 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.

  8. The Role of Surface Tension in Colloid Retention and Remobilization during Two-phase Flow

    NASA Astrophysics Data System (ADS)

    Zhang, Q.

    2015-12-01

    During unsaturated flow, the accumulation of colloids at fluid-fluid interfaces (AWIs) and fluid-fluid-solid contact lines (AWSs) depend on those areas and surface tension. The area and capillary forces exerting on colloids can be different by adjusting the liquid-liquid surface tension. In the present work, we adjust only surface tension to change the configuration of AWI and AWSs. Experiments were performed in a Polydimethylsiloxane (PDMS) micro-model. Fluorescent carboxylate-modified polystyrene microspheres, with diameter of 300nm were used as model colloids. Water and fluorinert-FC43 were used as the two immiscible liquids. Given the fact that PDMS is a hydrophobic material, fluorinert was the wetting phase and water was the non-wetting phase in this micro-model. Surface tension was changed by adding fluorinert soluble surfactant into fluorinert-FC43. We visualized colloids interacting with the moving fluid-fluid interfaces by confocal microscopy. We also obtained colloid concentration breakthrough curves by measuring the fluorescent intensities in the outlet of the micro-model. The breakthrough curves showed that under steady-state unsaturated flow, less colloid were retained in the system under low surface tension. The visualization results showed that, under low surface tension, the fluid-fluid interfaces are almost flat, thus less area and short contact line available for colloids to attach to. During transient flow, more colloids were remobilized by the moving fluorinert-water interfaces (FWIs) and fluorinert-water-solid contact lines (FWSCs) under high surface tension. Confocal results and measured breakthrough curves confirmed that lowing surface tension decreased capillary force and liquid-liquid area, resulting less retention and remobilization of colloids.

  9. Utilisation des micro-ordinateurs en ecriture aux cycles primaire et moyen: methodes, roles, attitudes et produits. L'education et la technologie (Writing with Microcomputers in the Elementary Grades: Process, Roles, Attitudes, and Products. Education and Technology Series).

    ERIC Educational Resources Information Center

    Larter, Sylvia; And Others

    A study examined and compared writing with and without microcomputers in elementary schools. Specifically, the study examined (1) how the products of writing instruction with a computer differ from the products of traditionally taught writing, (2) the process of teaching writing, (3) teacher-pupil roles when pupils are writing, (4) teacher…

  10. 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.

  11. The possible role of solid surface area in condensation reactions during chemical evolution: reevaluation.

    PubMed

    Lahav, N; Chang, S

    1976-12-30

    Published data on adsorption and condensation of amino acids, purine and pyrimidine bases, sugars, nucleosides, and nucleotides are analyzed in connection with Bernal's hypothesis that clays and other minerals may have provided the most likely surface for adsorption and condensation of these molecules in prebiotic times. 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 dehysration (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.

  12. The role of surface microtopography in the modulation of osteoblast differentiation.

    PubMed

    Hayes, J S; Khan, I M; Archer, C W; Richards, R G

    2010-07-21

    The osteoinductive and conductive capabilities of commercially pure titanium and its alloys is well documented, as is their ability to provide long-term stability for permanent implantable devices. Fracture fixation in paediatric and trauma patients generally requires transient fixation after which the implant becomes redundant and requires removal. Removal can be complicated due to excessive bony over-growth which is encouraged by the standard micro-rough implant surface. We have shown in vivo that removal related morbidity can be significantly reduced with surface polishing, a technique which reduces the micro-roughness of clinically available materials. However, tissue integration at the bone-implant interface requires activation of key regulatory pathways which influences osteoblastic differentiation and maturation therefore we do not believe this effect to be purely mechanical. To elucidate potential mechanisms by which surface polishing exerts its effect on bone regeneration this study assessed in vitro the effect of surface polishing commercially pure titanium on cell growth, morphology and on the regulation of core binding factor 1, osterix, collagen I, alkaline phosphatase, bone sialoprotein and osteocalcin for primary rat calvarial osteoblasts. Results indicate that polishing differentially influences osteoblast differentiation in a surface dependent manner and that these changes are potentially linked to surface dependent morphology, but not to differences in cell proliferation.

  13. 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.

  14. Role of deep level trapping on surface photovoltage of semi-insulating GaAs

    SciTech Connect

    Liu, Q.; Ruda, H.E.; Koutzarov, I.P.; Jedral, L.; Chen, G.; Prasad, M.

    1996-12-31

    Dual beam (bias and probe) transient Surface Photovoltage (SPV) measurements were made on undoped Semi-Insulating (SI) GaAs over an extended temperature range. Above 270 K, SPV recovery transients following a bias pulse were shown to reflect near surface conductivity changes; these are in turn controlled by surface/interface state thermal emission. Owing to the absence of a strong surface electric field in this material, the emitted carriers are not immediately removed from the near surface region. The recapturing of the emitted carriers is shown to be responsible for non-exponential conductivity and reciprocal-SPV transients. This behavior is considered to be characteristic of relaxation-type semiconductors with near-surface ungated structures. Below 150 K, the photoinduced transition of EL2 from its ground to metastable state El2* was shown to change the effective electron and hole mobilities and augment the SPV signals immediately following the bias pulse. Thermally induced EL2* recovery above 120 K decreases the SPV signal from its maximum. This decay transient was analyzed and the decay rate fitted to a single exponential. An activation energy of 0.32 eV and a pre-exponential constant of 1.9 {times} 10{sup 12} s{sup {minus}1} were obtained, and attributed to the thermal recovery rate for EL2*.

  15. 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.

  16. (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.

  17. The relative roles of passive surface forces and active ion transport in the modulation of airway surface liquid volume and composition.

    PubMed

    Tarran, R; Grubb, B R; Gatzy, J T; Davis, C W; Boucher, R C

    2001-08-01

    Two hypotheses have been proposed recently that offer different views on the role of airway surface liquid (ASL) in lung defense. The "compositional" hypothesis predicts that ASL [NaCl] is kept low (<50 mM) by passive forces to permit antimicrobial factors to act as a chemical defense. The "volume" hypothesis predicts that ASL volume (height) is regulated isotonically by active ion transport to maintain efficient mechanical mucus clearance as the primary form of lung defense. To compare these hypotheses, we searched for roles for: (1) passive forces (surface tension, ciliary tip capillarity, Donnan, and nonionic osmolytes) in the regulation of ASL composition; and (2) active ion transport in ASL volume regulation. In primary human tracheobronchial cultures, we found no evidence that a low [NaCl] ASL could be produced by passive forces, or that nonionic osmolytes contributed substantially to ASL osmolality. Instead, we found that active ion transport regulated ASL volume (height), and that feedback existed between the ASL and airway epithelia to govern the rate of ion transport and volume absorption. The mucus layer acted as a "reservoir" to buffer periciliary liquid layer height (7 microm) at a level optimal for mucus transport by donating or accepting liquid to or from the periciliary liquid layer, respectively. These data favor the active ion transport/volume model hypothesis to describe ASL physiology.

  18. 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

  19. 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.

  20. 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

  1. 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.

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

    SciTech Connect

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

    2014-12-14

    Atomic- or nanometer-scale surface roughening has been investigated during Si etching in inductively coupled Cl{sub 2} plasmas, as a function of rf bias power or ion incident energy E{sub i}, by varying feed gas flow rate, wafer stage temperature, and etching time. The experiments revealed two modes of surface roughening which occur depending on E{sub i}: one is the roughening mode at low E{sub i} < 200–300 eV, where the root-mean-square (rms) roughness of etched surfaces increases with increasing E{sub i}, exhibiting an almost linear increase with time during etching (t < 20 min). The other is the smoothing mode at higher E{sub i}, where the rms surface roughness decreases substantially with E{sub i} 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 E{sub i} were also observed in the etch rate versus √(E{sub i}) curve, and in the evolution of the power spectral density distribution of surfaces. Such changes from the roughening to smoothing modes with increasing E{sub i} were found to correspond to changes in the predominant ion flux from feed gas ions Cl{sub x}{sup +} to ionized etch products SiCl{sub x}{sup +} caused by the increased etch rates at increased E{sub i}, 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.

  3. Fluid Dynamics Problems of Vehicles Operating Near or in the Air-Sea Interface (Problemes de Dynamique des Fluides des Vehicules Evoluant dans ou pres de L’interface Air-Mer).

    DTIC Science & Technology

    1999-02-01

    ecoulement ä surface libre, instationnaire, couple avec des effets thermodynamiques lies aux gaz de chasse chauds et condensables. Dans une premiere...fermeture de la bulle. Dans une seconde partie une decomposition des phenomenes thermodynamiques basee sur une modelisation et des calculs numeriques [4... thermodynamiques interviennent si les gaz de chasse sont condensables. C’est ce qui arrive lorsque ces gaz resultent d’une combustion et qu’ils sont

  4. Role of the Deposition Precursor Molecules in Defining Oxidation State of Deposited Copper in Surface Reduction Reactions on H-Terminated Si(111) Surface

    PubMed Central

    Duan, Yichen; Gao, Fei; Teplyakov, Andrew V.

    2016-01-01

    Surface-limited deposition reactions leading to the formation of copper nanoparticles on H-terminated Si(111) surface can serve as a model for understanding the role of structure of the deposition precursor molecules in determining the oxidation state of the metal deposited. This study compares three different precursor molecules: Cu(acac)2 (Cu(II) acetylacetonate), Cu(hfac)2, and Cu(hfac)VTMS (Cu(I)-(hexafluoroacetylacetonato)-vinyltrimethylsilane) as copper deposition sources in a process with a controlled oxidation state of copper. X-ray photoelectron spectroscopy suggests that single-electron reduction governs the deposition of Cu(I) from the first two precursor molecules and that the last of the precursors studied yields predominantly metallic copper. Time-of-fight secondary ion mass spectrometry (ToF-SIMS) and infrared spectroscopy are utilized to interrogate surface species produced. Atomic force microscopy is used to quantify the deposition process and to follow the size distribution of the deposited copper containing nanoparticles. A plausible explanation supported by density functional theory calculations is offered on the basis of the difference in the reaction pathways for Cu(I) and Cu(II) precursors. PMID:27482303

  5. 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.

  6. The key role of the surface membrane in why gastropod nacre grows in towers

    PubMed Central

    Checa, Antonio G.; Cartwright, Julyan H. E.; Willinger, Marc-Georg

    2009-01-01

    The nacre of gastropod molluscs is intriguingly stacked in towers. It is covered by a surface membrane, which protects the growing nacre surface from damage when the animal withdraws into its shell. The surface membrane is supplied by vesicles that adhere to it on its mantle side and secretes interlamellar membranes from the nacre side. Nacre tablets rapidly grow in height and later expand sideways; the part of the tablet formed during this initial growth phase is here called the core. During initial growth, the tips of the cores remain permanently submerged within the surface membrane. The interlamellar membranes, which otherwise separate the nacre tablet lamellae, do not extend across cores, which are aligned in stacked tablets forming the tower axis, and thus towers of nacre tablets are continuous along the central axis. We hypothesize that in gastropod nacre growth core formation precedes that of the interlamellar membrane. Once the core is complete, a new interlamellar membrane, which covers the area of the tablet outside the core, detaches from the surface membrane. In this way, the tower-like growth of gastropod nacre becomes comprehensible. PMID:19116274

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Motion of liquid drops on surfaces induced by asymmetric vibration: role of contact angle hysteresis.

    PubMed

    Mettu, Srinivas; Chaudhury, Manoj K

    2011-08-16

    Hysteresis of wetting, like the Coulombic friction at solid/solid interface, impedes the motion of a liquid drop on a surface when subjected to an external field. Here, we present a counterintuitive example, where some amount of hysteresis enables a drop to move on a surface when it is subjected to a periodic but asymmetric vibration. Experiments show that a surface either with a negligible or high hysteresis is not conducive to any drop motion. Some finite hysteresis of contact angle is needed to break the periodic symmetry of the forcing function for the drift to occur. These experimental results are consistent with simulations, in which a drop is approximated as a linear harmonic oscillator. The experiment also sheds light on the effect of the drop size on flow reversal, where drops of different sizes move in opposite directions due to the difference in the phase of the oscillation of their center of mass.

  12. Macrophage-mediated tumor cytotoxicity: role of macrophage surface sialic acid.

    PubMed

    Cameron, D J

    1983-02-01

    Cell surface sialic acid levels were compared for monocytes and macrophages obtained from normal volunteers and breast cancer patients. Equal quantities of sialic acid were found on the monocytes obtained from normal volunteers and breast cancer patients. Approximately 60% more cell surface sialic acid was found on the macrophages from breast cancer patients than was found on the macrophages from normal volunteers. In order to determine whether cell surface sialic acid had any effect on macrophage-mediated cytotoxicity, macrophages were pretreated with neuraminidase (NANAse) prior to co-cultivation with tumor cells. The normal macrophages, after neuraminidase treatment, no longer retained their ability to kill tumor cells. However, when macrophages from breast cancer patients were treated with NANAse, no difference was observed in the ability of untreated and NANAse treated macrophages to kill tumor cells.

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

    SciTech Connect

    Lubin, D. )

    1994-07-08

    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 has 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.

  14. 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.

  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.

  16. Electrocardiographic markers of ischemia during mental stress testing in postinfarction patients. Role of body surface mapping

    SciTech Connect

    Bosimini, E.; Galli, M.; Guagliumi, G.; Giubbini, R.; Tavazzi, L. )

    1991-04-01

    In patients with coronary artery disease, radionuclide investigations have documented a high incidence of mental stress-induced myocardial ischemia in the absence of significant electrocardiographic changes and/or angina. To investigate the causes of the low electrocardiographic sensitivity, we recorded body surface maps during mental arithmetic in 22 normal volunteers and 37 postinfarction patients with residual exercise ischemia. Myocardial perfusion was studied with thallium-201 or technetium-99 (SESTAMIBI) planar scans. In 14 patients, body surface maps were also recorded during atrial pacing at the heart rate values achieved during mental stress. While taking the body surface maps, the area from J point to 80 msec after this point (ST-80) was analyzed by integral maps, difference maps, and departure maps. The body surface mapping criteria for ischemia were a new negative area on the integral maps, a negative potential of more than 2 SD from mean normal values on the difference maps, and a negative departure index of more than 2. Scintigraphy showed asymptomatic myocardial hypoperfusion in 33 patients. Eight patients had significant ST segment depression. The ST-80 integral and difference maps identified 17 ischemic patients. Twenty-four patients presented abnormal departure maps. One patient presented ST depression and abnormal body surface maps without reversible tracer defect. In 14 of 14 patients, atrial pacing did not reproduce the body surface map abnormalities. The analyses of the other electrocardiographic variables showed that in patients with mental stress-induced perfusion defects, only changes of T apex-T offset (aT-eT) interval in Frank leads and changes of maximum negative potential value of aT-eT integral maps significantly differed from those of normal subjects.

  17. Role of leaf surface sugars in colonization of plants by bacterial epiphytes.

    PubMed

    Mercier, J; Lindow, S E

    2000-01-01

    The relationship between nutrients leached onto the leaf surface and the colonization of plants by bacteria was studied by measuring both the abundance of simple sugars and the growth of Pseudomonas fluorescens on individual bean leaves. Data obtained in this study indicate that the population size of epiphytic bacteria on plants under environmentally favorable conditions is limited by the abundance of carbon sources on the leaf surface. Sugars were depleted during the course of bacterial colonization of the leaf surface. However, about 20% of readily utilizable sugar, such as glucose, present initially remained on fully colonized leaves. The amounts of sugars on a population of apparently identical individual bean leaves before and after microbial colonization exhibited a similar right-hand-skewed distribution and varied by about 25-fold from leaf to leaf. Total bacterial population sizes on inoculated leaves under conditions favorable for bacterial growth also varied by about 29-fold and exhibited a right-hand-skewed distribution. The amounts of sugars on leaves of different plant species were directly correlated with the maximum bacterial population sizes that could be attained on those species. The capacity of bacteria to deplete leaf surface sugars varied greatly among plant species. Plants capable of supporting high bacterial population sizes were proportionally more depleted of leaf surface nutrients than plants with low epiphytic populations. Even in species with a high epiphytic bacterial population, a substantial amount of sugar remained after bacterial colonization. It is hypothesized that residual sugars on colonized leaves may not be physically accessible to the bacteria due to limitations in wettability and/or diffusion of nutrients across the leaf surface.

  18. 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.

  19. 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.

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

    PubMed

    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.

  1. 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.

  2. A calving law for ice sheet models; Investigating the role of surface melt on dynamics of Greenland outlet glaciers

    NASA Astrophysics Data System (ADS)

    Nick, F. M.; van der Veen, C. J.; Vieli, A.

    2008-12-01

    alving of icebergs accounts for perhaps as much as half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. We have formulated a calving model that can be readily incorporated into time-evolving numerical ice-flow models. Our model is based on downward penetration of water-filled surface crevasses and upward propagation of basal crevasses. A calving event occurs when the depth of the surface crevasse (which increases as melting progresses through the summer) reaches the height of the basal crevasse. Our numerical ice sheet model is able to reproduce observed seasonal changes of Greenland outlet glaciers, such as fluctuations in flow speed and terminus positions. We have applied the model to Helheim Glacier on the east coast, and Petermann Glacier in the northwest. Our model suggests that rapid retreat of the claving front is highly affected by the amplified calving rate due to increasing water level in surface crevasses during warmer summers. Our results show little response to seasonally enhanced basal lubrication from surface melt. This modeling study provides insights into the role of surface and basal hydrology to ice sheet dynamics and on how to incorporate calving in ice sheet models and therefore advances our ability to predict future ice sheet change.

  3. Bidirectional diffusion of ammonium and sodium cations in forward osmosis: role of membrane active layer surface chemistry and charge.

    PubMed

    Lu, Xinglin; Boo, Chanhee; Ma, Jun; Elimelech, Menachem

    2014-12-16

    Systematic fundamental understanding of mass transport in osmosis-driven membrane processes is important for further development of this emerging technology. In this work, we investigate the role of membrane surface chemistry and charge on bidirectional solute diffusion in forward osmosis (FO). In particular, bidirectional diffusion of ammonium (NH4(+)) and sodium (Na(+)) is examined using FO membranes with different materials and surface charge characteristics. Using an ammonium bicarbonate (NH4HCO3) draw solution, we observe dramatically enhanced cation fluxes with sodium chloride feed solution compared to that with deionized water feed solution for thin-film composite (TFC) FO membrane. However, the bidirectional diffusion of cations does not change, regardless of the type of feed solution, for cellulose triacetate (CTA) FO membrane. We relate this phenomenon to the membrane fixed surface charge by employing different feed solution pH to foster different protonation conditions for the carboxyl groups on the TFC membrane surface. Membrane surface modification is also carried out with the TFC membrane using ethylenediamine to alter carboxyl groups into amine groups. The modified TFC membrane, with less negatively charged groups, exhibits a significant decrease in the bidirectional diffusion of cations under the same conditions employed with the pristine TFC membrane. Based on our experimental observations, we propose Donnan dialysis as a mechanism responsible for enhanced bidirectional diffusion of cations in TFC membranes.

  4. 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

  5. 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.

  6. Heterogeneous reaction of SO2 with soot: The roles of relative humidity and surface composition of soot in surface sulfate formation

    NASA Astrophysics Data System (ADS)

    Zhao, Yan; Liu, Yongchun; Ma, Jinzhu; Ma, Qingxin; He, Hong

    2017-03-01

    The conversion of SO2 to sulfates on the surface of soot is still poorly understood. Soot samples with different fractions of unsaturated hydrocarbons and oxygen-containing groups were prepared by combusting n-hexane under well-controlled conditions. The heterogeneous reaction of SO2 with soot was investigated using in situ attenuated total internal reflection infrared (ATR-IR) spectroscopy, ion chromatography (IC) and a flow tube reactor at the ambient pressure and relative humidity (RH). Water promoted SO2 adsorption and sulfate formation at the RH range from 6% to 70%, while exceeded water condensed on soot was unfavorable for sulfate formation due to inhibition of SO2 adsorption when RH was higher than 80%. The surface composition of soot, which was governed by combustion conditions, also played an important role in the heterogeneous reaction of SO2 with soot. This effect was found to greatly depend on RH. At low RH of 6%, soot with the highest fuel/oxygen ratio of 0.162 exhibited a maximum uptake capacity for SO2 because it contained a large amount of aromatic Csbnd H groups, which acted as active sites for SO2 adsorption. At RH of 54%, soot produced with a fuel/oxygen ratio of 0.134 showed the highest reactivity toward SO2 because it contained appropriate amounts of aromatic Csbnd H groups and oxygen-containing groups, subsequently leading to the optimal surface concentrations of both SO2 and water. These results suggest that variation in the surface composition of soot from different sources and/or resulting from chemical aging in the atmosphere likely affects the conversion of SO2 to sulfates.

  7. Surface-active compounds and their role in the access to hydrocarbons in Gordonia strains.

    PubMed

    Franzetti, Andrea; Bestetti, Giuseppina; Caredda, Paolo; La Colla, Paolo; Tamburini, Elena

    2008-02-01

    Three new bacterial strains (M22, BS25 and BS29) belonging to the Gordonia genus were isolated from a site chronically contaminated by diesel. Those Gordonia strains were able to grow using a wide range of straight and branched aliphatic hydrocarbons as carbon and energy sources and to produce at least two classes of surface-active compounds. Emulsifying agents were released in the culture medium when bacteria grew both on hydrocarbons and water-soluble substrates. Cell-bound biosurfactants, which reduce the surface tension, were produced on hydrocarbons; however, their production was significantly lower on water soluble substrates. The relationship of growth phase, surface-active compound production and cell-surface properties was analyzed in kinetic experiments on hydrocarbons. Gordonia sp. BS29 synthesized, and released extracellularly, bioemulsans during the exponential phase with n-hexadecane as carbon and energy source. The production of biosurfactants started in the exponential phase and their concentration increased during the following linear growth. Furthermore, the adhesion of bacterial cells to hydrocarbons decreased during growth. Our results led us to hypothesize a change in the mode by which Gordonia cells access the substrate during growth on hydrocarbons.

  8. The role of hydrology in connecting agricultural phosphorus sources to surface water

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Minimizing the risk of phosphorus (P) loss from land to water represents one of the most important priorities of nutrient management in the Chesapeake Bay watershed. Simply put, for P to pose a water quality problem, there must be a source of P that can readily be connected to surface water by hydro...

  9. 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

  10. Kinetics of Membrane Flux Decline: The Role of Natural Colloids and Mitigation via Membrane Surface Modification

    NASA Astrophysics Data System (ADS)

    Kilduff, James E.; Mattaraj, Supatpong; Zhou, Mingyan; Belfort, Georges

    2005-10-01

    Applications of membrane technologies for potable water production have been expanding significantly, leading to increased efforts to control membrane fouling, which can significantly reduce membrane performance, increase operating costs, and shorten membrane life. Natural organic matter is ubiquitous in all water supplies and has been implicated as a major contributor to fouling during filtration of natural water. In this review, we discuss factors that influence NOM fouling, including hydrodynamics; properties of the feed constituents such as size, hydrophobicity, charge density and isoelectric point; properties of the membrane including hydrophobicity, charge density, surface roughness, and porosity; and properties of the solution phase such as pH, ionic strength and concentration of metals. We review approaches to identify and mathematically describe fouling kinetics, including effects of pore blockage, cake formation, and osmotic pressure. Finally, we discuss strategies to mitigate fouling, with a focus on strategies that involve a modification of the nanostructure of membrane surfaces, via UV-assisted graft polymerization of hydrophilic monomers to increase surface wettability and reduce interactions between NOM and the membrane surface.

  11. [Role of the gravity vector in blood cell interaction with solid surface].

    PubMed

    Tiurin-Kuz'min, A Iu

    2007-01-01

    The gravity vector was shown to bear importance to the blood cell interaction with a foreign macroscopic solid surface. Contacting of human whole blood with the underside but not top side of a solid plate out of foreign material amplifies many times generation of active forms of oxygen. This observation may be testimony to gravitational polarization of intracell processes.

  12. 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...

  13. Multi-decadal trends of solar radiation reaching the surface: What is the role of aerosols?

    NASA Astrophysics Data System (ADS)

    Chin, M.; Diehl, T. L.; Bian, H.; Yu, H.; Qian, Y.; Wild, M.; Streets, D. G.; Stackhouse, P. W.

    2014-12-01

    We present an investigation on multi-decadal changes of atmospheric aerosols and their effects on surface radiation using a global chemistry transport model along with the near-term to long-term data records. We present the aerosol trends in the past 3 decades (1980-2009) in different regions and assess their effects on the multi-decadal change of solar radiation reaching the surface (known as "dimming" or "brightening"). The regions include the major anthropogenic source regions (North America, Europe, Asia) that have been experiencing considerable changes of pollution emissions, dust and biomass burning influenced regions that have large interannual variabilities, and relatively remote regions that maybe considered as "background". We will compare the GOCART model simulated surface radiation trends with data from the Global Energy Balance Archive (GEBA), the Baseline Solar Radiation Network (BSRN), and the China Meteorological Administration (CMA), as well as the satellite derived products. We will use the model to attribute the surface radiation changes to aerosol amount and type under all sky and clear sky conditions and link the changes to the emission trends in major source regions.

  14. 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

  15. 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

  16. 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

    2015-02-06

    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.

  17. 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...

  18. Role of surface chemistry in modified ACF (activated carbon fiber)-catalyzed peroxymonosulfate oxidation

    NASA Astrophysics Data System (ADS)

    Yang, Shiying; Li, Lei; Xiao, Tuo; Zheng, Di; Zhang, Yitao

    2016-10-01

    A commercial activated carbon fiber (ACF-0) was modified by three different methods: nitration treatment (ACF-N), heat treatment (ACF-H) and heat treatment after nitration (ACF-NH), and the effects of textural and chemical properties on the ability of the metal-free ACF-catalyzed peroxymonosulfate (PMS) oxidation of Reactive Black 5 (RB5), an azo dye being difficultly adsorbed onto ACF, in aqueous solution were investigated in this work. Surface density of functional groups, surface area changes, surface morphology and the chemical state inside ACF samples were characterized by Boehm titration, N2 adsorption, scanning electron microscopy in couple with energy dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS), respectively. XPS spectra deconvolution was applied to figure out the importance of surface nitrogen-containing function groups. We found that π-π, pyridine and amine have promoting effect on the catalytic oxidation while the -NO2 has inhibitory effect on the ACF/PMS systems for RB5 destroy. Sustainability and renewability of the typical ACF-NH for catalytic oxidation of RB5 were also discussed in detail. Information about our conclusions are useful to control and improve the performance of ACF-catalyzed PMS oxidation for organic pollutants in wastewater treatment.

  19. 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...

  20. 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.

  1. Liquid transfer mechanism between two surfaces and the role of contact angles.

    PubMed

    Chen, H; Tang, T; Amirfazli, A

    2014-04-21

    The transfer ratio of quasi-static liquid transfer was found to strongly depend on the difference between the receding contact angles of the two surfaces. In contrast to traditional thinking, the transfer ratio was quite insensitive to the adhesion force between the solid and the liquid when the liquid bridge broke.

  2. 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.

  3. 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...

  4. Adhesion of phospholipid vesicles to Chinese hamster fibroblasts: Role of cell surface proteins

    PubMed Central

    Pagano, RE; Takeichi, M

    1977-01-01

    The adhesion of artificially generated lipid membrane vesicles to Chinese hamster V79 fibroblasts in suspension was used as a model system for studying membrane interactions. Below their gel-liquid crystalline phase transition temperature, vesicles comprised of dipalmitoyl lecithin (DPL) or dimyristoyl lecithin (DML) absorbed to the surfaces of EDTA- dissociated cells. These adherent vesicles could not be removed by repeated washings of the treated cells but could be released into the medium by treatment with trypsin. EM autoradiographic studies of cells treated with[(3)H]DML or [(3)H]DPL vesicles showed that most of the radioactive lipids were confined to the cell periphery. Scanning electron microscopy and fluorescence microscopy further confirmed the presence of adherent vesicles at the cell surface. Adhesion of DML or DPL vesicles to EDTA-dissociated cells modified the lactoperoxidase-catalyzed iodination pattern of the cell surface proteins; the inhibition of labeling of two proteins with an approximately 60,000- dalton mol wt was particularly evident. Incubation of cells wit h (3)H-lipid vesicles followed by sodium dodecyl sulfate (SDS)- polyacrylamide gel electrophoresis showed that some of the (3)H-lipid migrated preferentially with these approximately 60,000-mol wt proteins. Studies of the temperature dependence of vesicle uptake and subsequent release by trypsin showed that DML or DPL vesicle adhesion to EDTA- dissociated cells increased with decreasing temperatures. In contrast, cells trypsinized before incubation with vesicles showed practically no temperature dependence of vesicle uptake. These results suggest two pathways for adhesion of lipid vesicles to the cell surface-a temperature-sensitive one involving cell surface proteins, and a temperature-independent one. These findings are discussed in terms of current models for cell-cell interactions. PMID:407233

  5. The Role of Steps and Defects in Electron Stimulated Desorption: Oxygen on Stepped W (110) Surfaces.

    DTIC Science & Technology

    1980-01-20

    RECIPIENT’S CATALOG NUMBER Technical Report Nio . 10/ 4TI TLE (end Subtitle) .TPE OF REPORT & PERIOD COVERED The Role of Steps and Defects in Electron...and defects on electron stimulated desorption (ESO) phenomenia, we have studied the adsorption of oxygen on a polyhedral tungste crystal containing a

  6. Glycoprotein C of equine herpesvirus 4 plays a role in viral binding to cell surface heparan sulfate.

    PubMed

    Azab, Walid; Tsujimura, Koji; Maeda, Ken; Kobayashi, Kyousuke; Mohamed, Yassir Mahgoub; Kato, Kentaro; Matsumura, Tomio; Akashi, Hiroomi

    2010-07-01

    Heparan sulfate moieties of cell surface proteoglycans serve as receptors for several herpesviruses. For herpes simplex virus 1, pseudorabies virus and equine herpesvirus 1, glycoprotein C (gC) homologues have been shown to mediate the binding to cell surface heparan sulfate. However, the role of gC in equine herpesvirus 4 (EHV-4) infection has not yet been analyzed. Using pull-down assay, we first determined that EHV-4 gC as well as gB are heparin-binding glycoproteins. To study the role of gC in EHV-4 infection, we constructed a gC-deletion mutant, WA79DeltagC, where the kanamycin resistant gene was inserted instead of the open reading frame encoding gC. We found that soluble heparin was capable of blocking both wild-type EHV-4 and WA79DeltagC infection of fetal horse kidney. Furthermore, pretreatment of cells with heparinase reduces considerably the ability of both viruses to adsorb to these cells and to form plaques. Similar results were obtained when cellular glycosaminoglycan synthesis was inhibited by chlorate treatment. In addition, we did find that gC protects EHV-4 from complement-mediated neutralization. These results suggest that, like other herpesviruses, EHV-4 gC plays a role in the interaction of the virus with cellular heparan sulfate. Moreover, gC can protect the virus from complement-mediated neutralization.

  7. 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.

  8. 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.

  9. Adsorption of hydrogen on Pt(111) and Pt(100) surfaces and its role in the HOR.

    SciTech Connect

    Strmcnik, D.; Tripkovic, D.; van der Vliet, D.; Stamenkovic, V.; Markovic, N. M.; Materials Science Division

    2008-10-01

    Hydrogen adsorption isotherms, evaluated by combination of cyclic voltammetry and chronoamperometry, are reported on Pt(1 1 1) and Pt(1 0 0) surfaces in 0.1 M HClO{sub 4}. We found that at E > 0.05 V Pt(1 1 1) and Pt(1 0 0) are only partially covered by the adsorbed hydrogen (H{sub ad}). On both surfaces, a full monolayer of the adsorbed hydrogen is completed at -0.1 V, i.e. the adsorption of atomic hydrogen is observed in the hydrogen evolution potential region. We also found, that the activity of the hydrogen oxidation reaction is mirrored by the shape of the hydrogen adsorption isotherms, implying that H{sub ad} is in fact a spectator in the HOR.

  10. Role of the kinematics of probing electrons in electron energy-loss spectroscopy of solid surfaces

    NASA Astrophysics Data System (ADS)

    Nazarov, V. U.; Silkin, V. M.; Krasovskii, E. E.

    2016-01-01

    Inelastic scattering of electrons incident on a solid surface is determined by two properties: (i) electronic response of the target system and (ii) the detailed quantum-mechanical motion of the projectile electron inside and in the vicinity of the target. We emphasize the equal importance of the second ingredient, pointing out the fundamental limitations of the conventionally used theoretical description of the electron energy-loss spectroscopy (EELS) in terms of the "energy-loss functions." Our approach encompasses the dipole and impact scattering as specific cases, with the emphasis on the quantum-mechanical treatment of the probe electron. Applied to the high-resolution EELS of Ag surface, our theory largely agrees with recent experiments, while some instructive exceptions are rationalized.

  11. Sensitivity of Southern Ocean overturning to wind stress changes: Role of surface restoring time scales

    NASA Astrophysics Data System (ADS)

    Zhai, Xiaoming; Munday, David R.

    2014-12-01

    The influence of different surface restoring time scales on the response of the Southern Ocean overturning circulation to wind stress changes is investigated using an idealised channel model. Regardless of the restoring time scales chosen, the eddy-induced meridional overturning circulation (MOC) is found to compensate for changes of the direct wind-driven Eulerian-mean MOC, rendering the residual MOC less sensitive to wind stress changes. However, the extent of this compensation depends strongly on the restoring time scale: residual MOC sensitivity increases with decreasing restoring time scale. Strong surface restoring is shown to limit the ability of the eddy-induced MOC to change in response to wind stress changes and as such suppresses the eddy compensation effect. These model results are consistent with qualitative arguments derived from residual-mean theory and may have important implications for interpreting past and future observations.

  12. 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.

  13. Role of Surface Termination on the Growth of Graphene on Cu

    NASA Astrophysics Data System (ADS)

    Mowll, Tyler R.; Ong, Eng Wen; Tyagi, Parul; Robinson, Zachary R.; Ventrice, Carl A., Jr.

    2015-03-01

    Graphene growth on on-axis Cu(100) and Cu(111) substrates and a Cu(111) substrate intentionally miscut by 5° was performed to determine the effect that the substrate termination has on both the rate of carbon deposition and the crystal quality of the graphene. A CVD process using C2H4 was used to grow the graphene. All experiments were performed in a UHV chamber, and the surfaces were cleaned using multiple Ar sputtering and annealing cycles until the LEED demonstrated a clean surface. By heating the substrates to 900 °C in UHV and then backfilling with 5 mTorr of C2H4, graphene could only be grown on the off-axis Cu(111) surface. This is attributed to the high vapor pressure of Cu and the low reactivity of the on-axis surfaces. By first backfilling with 5 mTorr of C2H4 and heating the substrate to 900 °C, graphene could be grown on both the on-axis Cu(100) and off-axis Cu(111) substrates. To achieve growth on the on-axis Cu(111) substrate, an argon overpressure was used to suppress Cu sublimation. Growth of graphene at 900 °C using a mixture of 5 mTorr C2H4 and 45 mTorr of argon produced single domain epitaxial films on the Cu(111) substrates and two domain epitaxial films on the Cu(100) substrate. This research was supported by the NSF (DMR-1006411).

  14. Organic Nitrogen Utilization by Phytoplankton: The Role of Cell-Surface Deaminases

    DTIC Science & Technology

    1989-06-01

    inhibited by cell-impermeable protein Marler 1966: Zika 1984). This highly re- modification reagents. A cell-surface redox en- active species may have a...from wet and dry deposition ( Zika sured in cultures of I. carterae could be et al. 1982; Thompson and Zafiriou 1983), generalized, marine phytoplankton...would be an is generated in photochemical reactions important sourceofthe hydrogen peroxide found (Cooper and Zika 1983), and can also be in the manne

  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. Unravelling the surface chemistry of metal oxide nanocrystals, the role of acids and bases.

    PubMed

    De Roo, Jonathan; Van den Broeck, Freya; De Keukeleere, Katrien; Martins, José C; Van Driessche, Isabel; Hens, Zeger

    2014-07-09

    We synthesized HfO2 nanocrystals from HfCl4 using a surfactant-free solvothermal process in benzyl alcohol and found that the resulting nanocrystals could be transferred to nonpolar media using a mixture of carboxylic acids and amines. Using solution (1)H NMR, FTIR, and elemental analysis, we studied the details of the transfer reaction and the surface chemistry of the resulting sterically stabilized nanocrystals. As-synthesized nanocrystals are charge-stabilized by protons, with chloride acting as the counterion. Treatment with only carboxylic acids does not lead to any binding of ligands to the HfO2 surface. On the other hand, we find that the addition of amines provides the basic environment in which carboxylic acids can dissociate and replace chloride. This results in stable, aggregate-free dispersions of HfO2 nanocrystals, sterically stabilized by carboxylate ligands. Moreover, titrations with deuterated carboxylic acid show that the charge on the carboxylate ligands is balanced by coadsorbed protons. Hence, opposite from the X-type/nonstoichiometric nanocrystals picture prevailing in literature, one should look at HfO2/carboxylate nanocrystals as systems where carboxylic acids are dissociatively adsorbed to bind to the nanocrystals. Similar results were obtained with ZrO2 NCs. Since proton accommodation on the surface is most likely due to the high Brønsted basicity of oxygen, our model could be a more general picture for the surface chemistry of metal oxide nanocrystals with important consequences on the chemistry of ligand exchange reactions.

  17. Role of Ferric Oxide Surface Area in Propellant Burn Rate Enhancement (First Step Toward Modeling)

    DTIC Science & Technology

    1975-06-30

    specific surface and catalytic effectiveness indicates that one of the kinetic models used to describe heterogeneous catalysis of chemical reactions may...be described in this manner, equations like No. 2 above are preferred when heterogeneous catalysis is involved. In either case, the constants in these... heterogeneous catalysis . 42/ R-4889 Rocketiyne DM~ion 01% Rockwell International REFERENCES 1. Beckstead, M. W.; I. L. Derr; and C. F. Price: "A Model of

  18. 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

  19. 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.

  20. 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

  1. 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

  2. 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

  3. 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.

  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. 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.

  6. The role of aragonite matrix surface chemistry on the chondrogenic differentiation of mesenchymal stem cells.

    PubMed

    Gross-Aviv, Talia; Vago, Razi

    2009-02-01

    In the present research we study the effects of surface chemistry of an aragonite crystalline biomatrix on the chondrogenesis of mesenchymal stem cells (MSCs). An aragonite matrix obtained from the coral Porites lutea and a gold-coated P. lutea matrix were seeded with MSCs, with and without the addition of growth factors (GFs). Scanning electron microscopy, histochemical staining, immunofluorescence, biochemical analyses and quantitative polymerase chain reaction showed that the chemistry of the matrix influenced the differentiation process of the MSCs. The calcium carbonate composition of the coral promoted osteogenesis, while impeding cell-material contact (by gold coating) altered the differentiation lineage of MSCs towards chondrogenic fate. Supplementation of the culture medium with GFs intensified the influence of the surface composition on the differentiation of MSCs, and the synergistic effect of the biomatrix surface composition and the GFs induced chondrogenesis and facilitated maintenance of the chondrocyte phenotype. Therefore, we suggest that scaffolding material candidates for tissue engineering should be examined for their effects on the MSCs differentiation process and their effect on signal transduction events in the cells.

  7. 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.

  8. Mecanique et mecanisme de la dechirure des materiaux textiles

    NASA Astrophysics Data System (ADS)

    Triki, Ennouri

    Cette thèse vise à apporter une contribution à l’étude et à la modélisation de la déchirure des textiles et des textiles enduits. Notons que la résistance à la déchirure est l’une des caractéristiques mesurées pour les équipements de protection contre les agresseurs mécaniques en milieu de travail. Jusqu'à présent, ce comportement en déchirure a été étudié en mesurant la force de déchirure et le travail de déchirure. De fait, aucun critère de rupture en déchirure n’existe actuellement. Par conséquent, en s’inspirant de la théorie du Griffith et de la mécanique de la rupture, une formulation d’un nouveau critère de rupture des structures textiles a été proposée. Cette approche offre la possibilité de déterminer d’une manière plus précise l’énergie nécessaire pour la création d’une nouvelle surface de rupture. Ce critère nous permet d’analyser l’effet des caractéristiques des tissus sur la variation de l’énergie de rupture. Cette étude montre que la résistance au glissement des fils dans la structure est le principal facteur qui contrôle la propagation de la fissure. En se basant sur la théorie de la mécanique de la rupture, un modèle de calcul de l’énergie de rupture par déchirure a été aussi élaboré. Ce modèle de déchirure relie l’énergie aux paramètres caractérisant les phénomènes affectant la déchirure des tissus, notamment la force de glissement et la force à la rupture des fils. Cette modélisation a tenu compte de certaines caractéristiques des tissus tels que l’épaisseur du matériau, la densité des fils, etc. Par l’étude de la variation de l’énergie de rupture par déchirure en fonction du rapport établi entre la force à la rupture et la force de glissement d’un fil ( FYB/FS), l’effet des mécanismes de la propagation de la fissure dans les tissus sur leur comportement en déchirure a été aussi observé. Les résultats obtenus

  9. Role of different classes of mammalian cell surface molecules in adherence of coagulase positive and coagulase negative staphylococci.

    PubMed

    Hafez, Mohamed M; Aboulwafa, Mohammad M; Yassien, Mahmoud A; Hassouna, Nadia A

    2008-10-01

    In the present study the role of different mammalian cell receptors in adherence of the coagulase positive pathogen, Staphylococcus aureus and some coagulase negative staphylococci, namely Staphylococcus epidermidis and Staphylococcus saprophyticus was investigated. Upon testing the adherence to Vero and Hep-2 cells, S. aureus isolates showed an adherence to both cell lines while S. epidermidis and S. saprophyticus isolates adhered to Vero cells only. According to the obtained results, both O-linked and N-linked mammalian cell surface glycoproteins are involved in the adherence of S. aureus isolates to Vero and Hep-2 cells, whereas only the O-linked ones serve as receptors for adherence of S. epidermidis and S. saprophyticus isolates to Vero cells. Of the O-linked glycoproteins, GAG-like receptors are involved in adherence of all tested isolates to Vero cells. The coagulase positive staphylococci preferred to adhere to the highly sulphated GAGs (Heparin and chondroitin sulphate B) while the coagulase negative isolates showed higher affinity to the less sulphated ones (Chondroitin sulphate A and C). Mucin like receptors appeared to be important for the adherence of all tested staphylococci. The role exhibited by fibronectin- and fibrinogen-like receptors was detected with S. aureus and S. epidermidis but not with S. saprophyticus isolates. While, collagen and gelatin were found to contribute to the adherence of S. aureus isolates only. Neither carbohydrate moieties of the glycoconjugates nor lipid molecules on the mammalian cell surface played a role in the adherence of the tested staphylococcal isolates. Taken together, the results revealed that both coagulase negative and coagulase positive staphylococcal tested isolates adhere to the same classes of mammalian cell surface receptors such as mucin-like, fibrinogen-like, fibronectin-like and GAG-like receptors. However, the tested isolates exhibited different degrees of affinities to such receptors.

  10. 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.

  11. NATO Independent Cost Estimating and the Role of Life Cycle Cost Analysis in Managing the Defence Enterprise (Estimation independante des couts de l’OTAN et role de l’analyse des couts globaux de possesssion au sen de l’OTAN)

    DTIC Science & Technology

    2012-08-01

    Acknowledgements xviii SAS-076 Membership List xix Executive Summary and Synthèse ES-1 1.0 Introduction 2 1.1 Background 2 1.2 Provenance and...Methodology C-10 4.3.1 Assessing Capability – System Architecture C-10 4.3.2 Assessing Capability – Execution Details C-11 4.3.3 Estimating...NATO Independent Cost Estimating and the Role of Life Cycle Cost Analysis in Managing the Defence Enterprise (RTO-TR-SAS-076) Executive Summary At

  12. 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.

  13. Role of GaAs surface clearing in plasma deposition of silicon nitride films for encapsulated annealing

    NASA Technical Reports Server (NTRS)

    Valco, G. J.; Kapoor, V. J.

    1985-01-01

    The role of GaAs surface cleaning and plasma reactor cleaning prior to deposition of silicon nitride films for encapsulated annealing has been investigated. X-ray photoelectron spectroscopy was employed to determine the surface characteristics of GaAs treated with HCl, HF, and NH4OH solutions preceded by a degreasing procedure. The HCl clean left the least amount of oxygen on the surface. Fluorine contamination resulting from the CF4 plasma used to clean the reactor was found to be located at the film-substrate interface by Auger electron spectroscopy with argon-ion sputtering. A modified deposition procedure was developed to eliminate the fluorine contamination. Plasma deposition of silicon nitride encapsulating films was found to modify the I-V characteristics of Schottky diodes subsequently formed on GaAs surface. The reverse current of the diodes was slightly reduced. Substrates implanted with Si at 100 keV and a dose of 5 x 10 to the 12th/sq cm showed a peak electron concentration of 1.7 x 10 to the 17th/cu cm at a depth of 0.1-micron with 60 percent activation after encapsulation and annealing at 800 C for 7 min.

  14. Motif selection in a model of evolving replicators: The role of surfaces and limited transport in network topology

    NASA Astrophysics Data System (ADS)

    Manrubia, S. C.; Poyatos, J. F.

    2003-11-01

    A system of replicators evolving on a surface is analysed. Population dynamics together with environmental constraints determine the network of interactions among species. We show that the mobility of individual elements, implemented as different values of the diffusion coefficient, plays a major role in shaping the topology of the emerging network by selecting simple network motifs during its evolution. This effect is fully quantified through the relative abundance of 3-node motifs and the clustering coefficient distribution. For large enough diffusion the behaviour crosses over to that of a well-stirred reactor, and parasites are able to disrupt the otherwise dynamically stable coexistence of species.

  15. 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.

  16. Peptide synthesis in aqueous environments: the role of extreme conditions and pyrite mineral surfaces on formation and hydrolysis of peptides.

    PubMed

    Schreiner, Eduard; Nair, Nisanth N; Wittekindt, Carsten; Marx, Dominik

    2011-06-01

    A comprehensive study of free energy landscapes and mechanisms of COS-mediated polymerization of glycine via N-carboxy anhydrides (NCAs, "Leuchs anhydrides") and peptide hydrolysis at the water-pyrite interface at extreme thermodynamic conditions is presented. Particular emphasis is set on the catalytic effects of the mineral surface including the putative role of the ubiquitous sulfur vacancy defects. It is found that the mere presence of a surface is able to change the free energetics of the elementary reaction steps. This effect can be understood in terms of a reduction of entropic contributions to the reactant state by immobilizing the reactants and/or screening them from bulk water in a purely geometric ("steric") sense. Additionally, the pyrite directly participates chemically in some of the reaction steps, thus changing the reaction mechanism qualitatively compared to the situation in bulk water. First, the adsorption of reactants on the surface can preform a product-like structure due to immobilizing and scaffolding them appropriately. Second, pyrite can act as a proton acceptor, thus replacing water in this role. Third, sulfur vacancies are found to increase the reactivity of the surface. The finding that the presence of pyrite speeds up the rate-determining step in the formation of peptides with respect to the situation in bulk solvent while stabilizing the produced peptide against hydrolysis is of particular interest to the hypothesis of prebiotic peptide formation at hydrothermal aqueous conditions. Apart from these implications, the generality of the studied organic reactions are of immediate relevance to many fields such as (bio)geochemistry, biomineralization, and environmental chemistry.

  17. The roles of surface heat flux and ocean heat transport convergence in determining Atlantic Ocean temperature variability

    NASA Astrophysics Data System (ADS)

    Grist, Jeremy P.; Josey, Simon A.; Marsh, Robert; Good, Simon A.; Coward, Andrew. C.; de Cuevas, Beverly A.; Alderson, Steven G.; New, Adrian L.; Madec, Gurvan

    2010-08-01

    The temperature variability of the Atlantic Ocean is investigated using an eddy-permitting (1/4°) global ocean model (ORCA-025) forced with historical surface meteorological fields from 1958 to 2001. The simulation of volume-averaged temperature and the vertical structure of the zonally averaged temperature trends are compared with those from observations. In regions with a high number of observations, in particular above a depth of 500 m and between 22° N and 65° N, the model simulation and the dataset are in good agreement. The relative contribution of variability in ocean heat transport (OHT) convergence and net surface heat flux to changes in ocean heat content is investigated with a focus on three regions: the subpolar and subtropical gyres and the tropics. The surface heat flux plays a relatively minor role in year-to-year changes in the subpolar and subtropical regions, but in the tropical North Atlantic, its role is of similar significance to the ocean heat transport convergence. The strongest signal during the study period is a cooling of the subpolar gyre between 1970 and 1990, which subsequently reversed as the mid-latitude OHT convergence transitioned from an anomalously weak to an anomalously strong state. We also explore whether model OHT anomalies can be linked to surface flux anomalies through a Hovmöller analysis of the Atlantic sector. At low latitudes, increased ocean heat gain coincides with anomalously strong northward transport, whereas at mid-high latitudes, reduced ocean heat loss is associated with anomalously weak heat transport.

  18. Unraveling the Role of Surface Mucus-Binding Protein and Pili in Muco-Adhesion of Lactococcus lactis

    PubMed Central

    Duviau, Marie-Pierre; Meyrand, Mickael; Guérardel, Yann; Castelain, Mickaël; Loubière, Pascal; Chapot-Chartier, Marie-Pierre; Dague, Etienne; Mercier-Bonin, Muriel

    2013-01-01

    Adhesion of bacteria to mucus may favor their persistence within the gut and their beneficial effects to the host. Interactions between pig gastric mucin (PGM) and a natural isolate of Lactococcus lactis (TIL448) were measured at the single-cell scale and under static conditions, using atomic force microscopy (AFM). In parallel, these interactions were monitored at the bacterial population level and under shear flow. AFM experiments with a L. lactis cell-probe and a PGM-coated surface revealed a high proportion of specific adhesive events (60%) and a low level of non-adhesive ones (2%). The strain muco-adhesive properties were confirmed by the weak detachment of bacteria from the PGM-coated surface under shear flow. In AFM, rupture events were detected at short (100−200 nm) and long distances (up to 600−800 nm). AFM measurements on pili and mucus-binding protein defective mutants demonstrated the comparable role played by these two surface proteinaceous components in adhesion to PGM under static conditions. Under shear flow, a more important contribution of the mucus-binding protein than the pili one was observed. Both methods differ by the way of probing the adhesion force, i.e. negative force contact vs. sedimentation and normal-to-substratum retraction vs. tangential detachment conditions, using AFM and flow chamber, respectively. AFM blocking assays with free PGM or O-glycan fractions purified from PGM demonstrated that neutral oligosaccharides played a major role in adhesion of L. lactis TIL448 to PGM. This study dissects L. lactis muco-adhesive phenotype, in relation with the nature of the bacterial surface determinants. PMID:24260308

  19. Role of Streptococcus gordonii Surface Proteins SspA/SspB and Hsa in Platelet Function▿

    PubMed Central

    Kerrigan, Steven W.; Jakubovics, Nicholas S.; Keane, Ciara; Maguire, Patricia; Wynne, Kieran; Jenkinson, Howard F.; Cox, Dermot

    2007-01-01

    Streptococcus gordonii colonization of damaged heart surfaces in infective endocarditis is dependent upon the recognition of host receptors by specific bacterial surface proteins. However, despite several attempts to identify the mechanisms involved in this interaction, the nature of the bacterial proteins required remains poorly understood. This study provides clear evidence that several S. gordonii surface proteins participate in the interaction with platelets to support platelet adhesion and induce platelet aggregation. S. gordonii strains were found to support strong (DL1-Challis, SK12, SK184, and Blackburn) or moderate (UB1545 Δhsa and CH1-Challis) adhesion or failed to support platelet adhesion (M5, M99, and Channon). In addition, under flow conditions, platelets rolled and subsequently adhered to immobilized S. gordonii at low shear (50 s−1) in an Hsa-dependent manner but did not interact with S. gordonii DL1 at any shear rate of >50 s−1. S. gordonii strains either induced (DL1-Challis, SK12, SK184, UB1545 Δhsa, and M99) or failed to induce (M5, CH1-Challis, Channon, and Blackburn) platelet aggregation. Using a proteomic approach to identify differential cell wall protein expression between aggregating (DL1) and nonaggregating (Blackburn) strains, we identified antigen I/antigen II family proteins SspA and SspB. The overexpression of SspA or SspB in platelet-nonreactive Lactococcus lactis induced GPIIb/GPIIIa-dependent platelet aggregation similar to that seen with S. gordonii DL1. However, they failed to support platelet adhesion. Thus, S. gordonii has distinct mechanisms for supporting platelet adhesion and inducing platelet aggregation. Differential protein expression between strains may be important for the pathogenesis of invasive diseases such as infective endocarditis. PMID:17893126

  20. The role of the interplanetary shock surface fluctuations in shaping energetic storm particle events

    NASA Astrophysics Data System (ADS)

    Lario, D.; Decker, R. B.

    2006-12-01

    Solar cycle 23 has provided us with a large variety of shocks and associated energetic particle storm (ESP) events. Statistical analysis of shocks and ESP events detected by ACE has shown a tendency for observing more quasi-perpendicular shocks; whereas the most common types of event are those that do not display any >47 keV ion intensity increase [Lario et al., 2005a; Proc. SW11, ESA SP-592, pp. 81-86]. Faster and stronger shocks have greater effects on the particle intensities at their passage by 1 AU, but the shock parameters do not determine unequivocally the characteristics of the ESP events. A few of these events show characteristics similar to those predicted by the theory of diffusive shock acceleration, although detailed analysis reveals significant inconsistencies between observations and theory [Lario et al., 2005b; Proc. 4th IGPP Conf., AIP-781, pp. 180-184]. A common type of event has irregular structure, showing multiple intensity bursts before and/or after the shock passage. We present both the observations of one of these events and the results of a test-particle, full-orbit-integration simulation of ion shock-acceleration in a corrugated shock surface [Decker, 1990; JGR 95, pp. 11993-12003]. Although meso-scale fluctuations of the shock surface or in magnetic field direction, or both, can produce similar features in shock-accelerated particle distributions, we invoke the rippled shock model in this case because the measured pre-shock field is relatively steady. These simulations allow us to reproduce not only the evolution of the ion intensities but also the observed ion anisotropies and energy spectra. Fluctuations of both the solar wind plasma where the shock travels and of the shock surface may determine the main features of those ESP events with irregular variations of intensities and angular distributions. This presentation constitutes a progress report on NASA LWS TR{&}T grant NAG5-13487.

  1. 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.

  2. The role of bandgap energy excess in surface emission of terahertz radiation from semiconductors

    NASA Astrophysics Data System (ADS)

    Alfaro-Gomez, M.; Castro-Camus, E.

    2017-01-01

    We use a Monte-Carlo model to simulate semi-classical photo-carrier dynamics of InAs, InGaAs, and GaAs that leads to terahertz emission. We compare the emission power of all three semiconductors as a function of excitation photon energy finding that the carrier excess excitation energy is more relevant to explain their performance difference than their mobilities. We conclude that ballistic transport after photoexcitation is the dominant mechanism for terahertz emission instead of diffusion driven or surface field driven charge separation, which were traditionally considered the most relevant mechanisms.

  3. Second-Harmonic Generation in Metallic Nanoparticles: Clarification of the Role of the Surface

    DTIC Science & Technology

    2012-09-27

    REVIEW B 86, 115451 (2012) Coulomb term (referred to as quadrupole-like term by virtue of its form), proportional to E (∇ · P), the magnetic Lorentz...proportional to ∇ · P1, a term that is nonzero only near the surface. That is, the Coulomb (quadrupole-like) and pressure terms, and the first of the...2005). 85M. W. Klein, M. Wegener, N. Feth, and S. Linden, Opt. Express 16, 8055 (2008). 86A. Aubry, D. Y. Lei , A. I. Fernández-Domı́nguez, Y

  4. The Role of Channel Bar Influences on Groundwater / Surface Water Interactions

    NASA Astrophysics Data System (ADS)

    Shope, C. L.; Constantz, J. E.; Cooper, C. A.; McKay, W. A.

    2010-12-01

    Channel bars are dominant in-stream geomorphic island features present in a large range of river classes throughout the world, particularly in the arid western United States. A quantitative understanding of groundwater and surface water exchange through channel bar features is necessary to understand near-stream hyporheic flow patterns. The Truckee River in northwestern Nevada was used as a research site to quantitatively examine the influence of channel bars on near-stream water fluxes using heat as a tracer. This study provided the near-stream hydraulic physical framework for current and future research on nutrient cycling and biogeochemical impacts of near-stream exchange and can be used for assessing critical water quality impacts. Field activities included the installation and development of monitoring wells and piezometers, instrumentation of the piezometers with pressure transducers and temperature thermistors, and slug tests to estimate hydraulic conductivity. The potentiometric surface throughout the study site was monitored over time and the temperature thermistors were used to estimate transport using heat as a tracer. Horizontal and vertical Darcian water fluxes were estimated from field observations. To increase confidence in the hydraulic conductivity values for water flux estimates, heat-based numerical simulations were completed. Three-dimensional models of the channel bar study area were constructed and hydraulic conductivity was inversely estimated by minimizing the difference between observed and simulated head and temperature measurements. Numerical simulations indicated that lateral water fluxes between the channel bar and the stream were an order of magnitude greater than between the adjacent streambank and the stream. The fluxes at the downstream end of the channel bar were an order of magnitude greater than upstream fluxes. Net groundwater and surface water fluxes at the channel bar and stream interface were at least 2 times greater than

  5. 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.

  6. Role of wrinkles in the corrosion of graphene domain-coated Cu surfaces

    NASA Astrophysics Data System (ADS)

    Zhang, Y. H.; Zhang, H. R.; Wang, B.; Chen, Z. Y.; Zhang, Y. Q.; Wang, B.; Sui, Y. P.; Zhu, B.; Tang, C. M.; li, X. L.; Xie, X. M.; Yu, G. H.; Jin, Z.; Liu, X. Y.

    2014-04-01

    We analyzed the protective ability of chemical vapor deposition (CVD) graphene domains against corrosion of Cu surfaces. Fresh graphene domains of various shapes were ideal corrosion-inhibiting layers. However, obvious corrosion was found within graphene domains exposed to the air for over a week. Our work demonstrates that the opportunities for corrosion of CVD graphene were provided by wrinkles but not others, such as Cu grain boundaries and graphene domain boundaries, which are always believed the primary factor for inferior quality of the CVD graphene at present.

  7. 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).

  8. 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.

  9. 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

  10. 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

    2016-04-21

    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.

  11. The role of peat double porosity on groundwater-surface water interaction in a drained fen

    NASA Astrophysics Data System (ADS)

    Rossi, P. M.; Ala-aho, P.; Ronkanen, A.-K.

    2012-04-01

    Groundwater discharge from an esker aquifer to a fen was studied to understand relevant hydrological processes for surface-groundwater interaction in an esker-peatland hillslope. Piezometric levels of the peat layer and esker sand layer were continuously monitored and compared to climate data. Groundwater exfiltration points were spatially mapped and related to peat depth. The study showed a clear interaction between fen surface water and sand esker groundwater although the hydraulic conductivity of peat was low and the peat depth thick. In the artesian aquifer beneath the fen, the piezometric head showed a clear response to precipitation and evapotranspiration. Wetting of the peat is rapidly seen as pressure increase in the confined aquifer. This provides new information on hydraulics of wetlands found in aquifer discharge areas. Groundwater exfiltrated through thick peat layers in vertical preferential point discharges demonstrating how double porosity provides flow through the peat layer with low hydraulic conductivity in the peat matrix. The "pipe flow" channels were found in the deep peat area in the transition zones from deep peat to shallow peat. Diffuse seepage through the ditch bottom was found where ditches cut into the sand layer. Increased discharge through the ditch bed reduced the flow resistance at the aquifer boundary which can lower the groundwater level in the esker. The results show new processes in the groundwater discharge zone that are useful for groundwater modeling and policy development for future groundwater protection.

  12. Review of the role of dielectric anisotropy in Dyakonov surface-wave propagation

    NASA Astrophysics Data System (ADS)

    Nelatury, Sudarshan R., II; Polo, John A., Jr.; Lakhtakia, Akhlesh

    2008-08-01

    Surface waves (SWs) are localized waves that travel along the planar interface between two different mediums when certain dispersion relations are satisfied. If both mediums have purely dielectric constitutive properties, the characteristics of SW propagation are determined by the anisotropy of both mediums. Surface waves are then called Dyakonov SWs (DSWs), after Dyakonov who theoretically established the possibility of SW propagation at the planar interface of an isotropic dielectric and a positive uniaxial dielectric. Since then, DSW propagation guided by interfaces between a variety of dielectrics has been studied. With an isotropic dielectric on one side, the dielectric on the other side of the interface can be not only positive uniaxial but also biaxial. DSW propagation can also occur along an interface between two uniaxial or biaxial dielectrics that are twisted about a common axis with respect to each other but are otherwise identical. Recently, DSW propagation has been studied taking (i) uniaxial dielectrics such as calomel and dioptase crystals; (ii) biaxial dielectrics such as hemimorphite, crocoite, tellurite, witherite, and cerussite; and (iii) electro-optic materials such as potassium niobate. With materials that are significantly anisotropic, the angular regime of directions for DSW propagation turns out to be narrow. In the case of naturally occurring crystals, one has to accept the narrow angular existence domain (AED). However, exploiting the Pockels effect not only facilitates dynamic electrical control of DSW propagation, but also widens the AED for DSW propagation.

  13. Second-harmonic generation in metallic nanoparticles: Clarification of the role of the surface

    NASA Astrophysics Data System (ADS)

    Ciracì, Cristian; Poutrina, Ekaterina; Scalora, Michael; Smith, David R.

    2012-09-01

    We present a numerical investigation of the second-order nonlinear optical properties of metal-based metamaterial nanoresonators. The nonlinear optical response of the metal is described by a hydrodynamic model, with the effects of electron pressure in the electron gas also taken into account. We show that as the pressure term tends to zero the amount of converted second-harmonic field tends to an asymptotic value. In this limit it becomes possible to rewrite the nonlinear surface contributions as functions of the value of the polarization vector inside the bulk region. Nonlocality thus can be incorporated into numerical simulations without actually utilizing the nonlocal equation of motion or solving for the rapidly varying fields that occur near the metal surface. We use our model to investigate the second-harmonic generation process with three-dimensional gold nanoparticle arrays and show that nanocrescents can easily attain conversion efficiencies of ˜6.0×10-8 for pumping peak intensities of a few tens of MW/cm2.

  14. 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.

  15. 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.

  16. 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.

  17. The role of a coarse surface layer in impeding evaporation from gravel bars

    NASA Astrophysics Data System (ADS)

    Edmaier, Katharina; Peter, Molnar; Clémentine, Cyprien; Paolo, Burlando

    2010-05-01

    The presence of a coarse surface layer (CSL) on bars in gravel bed rivers is expected to have an influence on evaporation rates from these surfaces and thereby on the water content in the underlying gravel-sand matrix. A statistically significant increase in soil water content in the presence of a CSL has recently been demonstrated in outdoor experiments by Meier and Hauer (2010). The authors argued that the CSL leads to a reduction in available energy for evaporation, decreases the advection of water vapour from the evaporating surface and reduces the supply of water from the underlying matrix to the evaporating surface. These findings are important because the germination of seeds and vegetative reproduction of riparian species on gravel bars are presumed to be driven by local soil moisture availability. Therefore local conditions of erosion-deposition which lead to the presence or absence of a CSL could be a crucial parameter for successful vegetation establishment on gravel bars. We conducted a simple laboratory experiment to verify the findings of Meier and Hauer (2010) under more controlled conditions. In the experiment 6 cylindrical buckets with a surface area of 720 cm2 and total volume of 19500 cm3 were filled with a sand-gravel mixture to replicate the sediment composition in the Thur River, Switzerland (d50 = 8 mm). This site is part of the research project RECORD (www.record.ethz.ch), which focuses on river restoration issues. Three treatments were investigated, each with a CSL of different thickness (H = 0, 40 and 80 mm) with one replicate each, roughly corresponding to 2 and 4 layers of typical CSL gravel diameters in the Thur River. We also measured the temperature in the sediment matrix underneath the CSL. The samples were saturated over several days and subsequently gravitationally drained in order to retain water held only by capillary forces as the initial condition. The samples were then weighed daily for 47 days and the evaporation rates and

  18. 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

  19. On the opposing roles of air temperature and wind speed variability in flux estimation from remotely sensed land surface states

    NASA Astrophysics Data System (ADS)

    Bertoldi, G.; Albertson, J. D.; Kustas, W. P.; Li, F.; Anderson, M. C.

    2007-10-01

    In semi-arid regions the evapotranspiration rates depend on both the spatial distribution of the vegetation and the soil moisture, for a given radiation regime. Remote sensing can provide high resolution spatially distributed estimation (o ˜ 10-100 m) of land surface states. However, data on the near surface air properties are not readily available at the same resolution and are often taken as spatially uniform over a greater region. Concern for how this scale mismatch might lead to erroneous flux estimations motivates this effort. This paper examines the relative roles of variability in the two dominant atmospheric states, wind speed and air temperature, on the variability of the surface fluxes. The study is conducted with a Large Eddy Simulation (LES) model of the Atmospheric Boundary Layer (ABL), where the boundary conditions are given by a surface energy balance model based on remotely sensed land surface data. Simulations have been performed for the late morning hours of two clear-sky summer days during the SGP97 experiment with different wetness conditions over an area characterized by a high contrast in surface temperature, canopy cover, and roughness between vegetated and dry bare soil areas. Spatial variability in canopy density effects both the air temperature Ta, through the energy partitioning, and the wind speed U, via the roughness, leading to local variations at 5 m above the ground of the order of 1 K and 1 m/s, respectively. Simulations show that the Ta variability tends to decrease the sensible heat flux H (- 30 W/m2) over bare soil areas and to increase it (+30 W/m2) over dense vegetation, thus reducing the total variability of the surface fluxes relative to those that would be estimated for spatially constant Ta, as observed in previous studies. The variability in U tends to increase H over bare soil (+50 W/m2), while having negligible effects over the vegetation, thus increasing the spatial variance of surface fluxes. However, when considered

  20. 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.

  1. 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

  2. High aspect ratio materials: role of surface chemistry vs. length in the historical "long and short amosite asbestos fibers".

    PubMed

    Tomatis, Maura; Turci, Francesco; Ceschino, Raffaella; Riganti, Chiara; Gazzano, Elena; Martra, Gianmario; Ghigo, Dario; Fubini, Bice

    2010-10-01

    In nanotoxicology the question arises whether high aspect ratio materials should be regarded as potentially pathogenic like asbestos, merely on the base of their biopersistence and length to diameter ratio. A higher pathogenicity of long asbestos fibers is associated to their slower clearance and frustrated phagocytosis. In the past decades, two amosite fibers were prepared and studied to confirm the role of fiber length in asbestos toxicity. Long fiber amosite (LFA) and short fiber amosite (SFA) have here been revisited, to check differences in their surface properties, known to modulate the biological responses elicited. We report: (i) micromorphology (abundance of exposed cylindrical vs. truncated surfaces; (ii) surface reactivity (oxidation and coordination state of surface iron, free radical generation and oxidizing potential); (iii) activation of nitric oxide (NO) synthase in lung epithelial cells, as representative of an inflammatory cell response. LFA shows a higher free radical yield, stimulates, more than SFA, NO production by cells and reacts with ascorbic acid, thus depriving the lung lining layer of its antioxidant defenses. The higher activity of LFA than SFA is ascribed to the presence of Fe2+ ions poorly coordinated to the surface. SFA shows only a large number of loosely bound Fe3+ ions, pristine Fe2+ ions having been oxidized during the grinding process converting LFA into SFA. Several factors determine a higher toxicity of LFA than SFA, beside length. The lesson from asbestos indicates that other features besides aspect ratio contribute to the pathogenic potential of a fiber type. All these aspects should be considered when predicting the possible hazard associated to any new fibrous material proposed to the market, let alone nanofibers.

  3. The role of surface roughness and slide-roll ratio on the decomposition of MoDTC in tribological contacts

    NASA Astrophysics Data System (ADS)

    Khaemba, Doris N.; Jarnias, Frederic; Thiebaut, Benoit; Neville, Anne; Morina, Ardian

    2017-03-01

    In this study, the role of surface roughness and slide-roll ratio in the decomposition and friction performance of molybdenum dialkyldithiocarbamate (MoDTC) has been investigated. Tribotests were carried out in a minitraction machine (MTM) using steel discs of varying roughness rubbing against smooth steel balls in a sliding/rolling contact. Tests were conducted at slide-roll ratio (SRR) values of SRR  =  100% and 200%. Raman spectroscopy was used to perform chemical characterisation on the resulting wear scars. The friction performance of rough discs was not affected by the SRR. On the other hand, increasing the SRR from 100% to 200% in tests with smooth discs resulted in higher friction with large instabilities. Raman analysis showed significant differences in chemical composition of the wear scars generated after tests with smooth and rough discs. Wear scars generated using rough discs were mainly composed of MoS2 indicating complete MoDTC decomposition while those generated using smooth discs were composed of a mixture of MoS2, MoS x (x  >  2) and FeMoO4 indicating partial MoDTC decomposition. Numerical simulation of the contact revealed that under similar loading conditions rough surfaces have higher local pressures than smoother surfaces. It is proposed that higher local pressures in rough surfaces promoted complete MoDTC decomposition. The novel finding from results presented in this study is that at similar temperature and MoDTC concentration, the degradation of MoDTC within tribocontacts is highly dependent on the roughness of the tribopair. This is because surface roughness determines the local pressure at the asperity–asperity contact.

  4. The role of defective silica surfaces in exogenous delivery of prebiotic compounds: clues from first principles calculations.

    PubMed

    Rimola, Albert; Ugliengo, Piero

    2009-04-14

    The reaction of glycine (Gly) with a strained (SiO)(2) four-membered ring defect (D2) at the surface of an interstellar silica grain dust has been studied at ONIOM2[B3LYP/6-31+G(d,p):MNDO] level within a cluster approach in the context of hypothetical reactions occurring in the interstellar medium. The D2 opens up exothermically for reaction with Gly (Delta(r)U(0)=-26.3 kcal mol(-1)) to give a surface mixed anhydride S(surf)-O-C([double bond, length as m-dash]O)-CH(2)NH(2) as a product. The reaction barriers, DeltaU( not equal)(0), are 0.1 and 10.4 kcal mol(-1) for reactive channels involving COOH and NH(2) as attacking groups, respectively. Calculations show the surface mixed anhydride to be rather stable under the action of interstellar processes, such as reactions with isolated H(2)O and NH(3) molecules or the exposure to cosmic rays and UV radiation. The hydrolysis of the surface mixed anhydride to release again Gly was modelled by microsolvation (from 1 to 4 H(2)O molecules) mimicking what could have happened to the interstellar dust after seeding the primordial ocean in the early Earth. Results for these calculations show that the reaction is exergonic and activated, the Delta(r)G(298) becoming more negative and the DeltaG( not equal)(298) being dramatically reduced as a function of increasing number of H(2)O molecules. The present results are relevant because they show that defects present at interstellar dust surfaces could have played a significant role in capturing, protecting and delivering essential prebiotic compounds on the early Earth.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. High second-order nonlinear response of platinum nanoflowers: the role of surface corrugation

    NASA Astrophysics Data System (ADS)

    Ngo, Hoang Minh; Lai, Ngoc Diep; Ledoux-Rak, Isabelle

    2016-02-01

    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.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. Electronic supplementary information (ESI) available: The recalculated β and β' values inferred from data by Galletto et al.15 in AuNSs using their reported β values per nanoparticle corrected. See DOI: 10.1039/c5nr07571h

  13. Ligand effects on nitrate reduction by zero-valent iron: Role of surface complexation.

    PubMed

    Song, Xiaojie; Chen, Zhihao; Wang, Xiaomeng; Zhang, Shujuan

    2017-05-01

    Surface passivation is a key limiting factor in the application of zero-valent iron (ZVI) for water remediation. Addition of ligands is a useful approach to overcome this issue. In this work, a small amount of acetylacetone (AA) (0.5 mM) was found highly efficient to enhance the reduction of nitrate by ZVI at near neutral conditions (pH 6.0) with the formation of considerable black coating on ZVI. At an initial nitrate concentration of 20 mg N/L, the pseudo first-order reduction rate constant of nitrate in the ZVI-AA-NO3(-) system was 0.0991 h(-1), which was 52 times higher than that in the ZVI-NO3(-) system. Under otherwise identical conditions, the other five ligands, including EDTA, formate, acetate, oxalate, and phosphate, had negligible effects. Based on the pKa values of these ligands and the final species of iron, the ligand effects on nitrate reduction by ZVI were summarized from three aspects: (1) the ability to offer potentially dissociable protons from the ligands; (2) the complexation ability to eliminate iron (hydr)oxide precipitates from the surface of ZVI; and (3) the ability to lower down the redox potentials of iron species. The good performance of AA in these three aspects makes it advantage over the other ligands. A cycle test up to six runs demonstrates that AA could continuously take effect in the ZVI system. The results here point out the potential of AA as an effective ligand in ZVI system for enhanced contaminant transformation.

  14. 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.

  15. [Roles of additives and surface control in slurry atomization]. Quarterly report, March 1992

    SciTech Connect

    Not Available

    1992-08-01

    Our experimental results clearly demonstrate that the shape of particles with aspect ratio close to unity dictates the relative suspension viscosity. Suspensions of irregularly shaped particles have higher relative viscosities than suspensions of spherical particles at same volume fractions, in agreement with the reported results at high shear conditions. The relative viscosity of a Newtonian suspension is in excellent agreement with that predicted by the Krieger/Dougherty rigid sphere model using the maximum packing fraction determined from sedimentation as the sole parameter. The relative viscosity of a pseudoplastic suspension is independent of the particle density. It correlates well with the particle Peclet number. The extent of particle diffusion at high shear rates decreases considerably as the particle size increases, and less energy is dissipated as a result. The interparticle electrostatic repulsion plays no significant role in the rheology of pseudoplastic nonaqueous and aqueous glycerol suspensions of noncolloidal particles.

  16. Impact of Materials Defects on Engine Structures Integrity (L’Impact des Defauts des Materiaux sur l’Integrite des Structures des Moteurs)

    DTIC Science & Technology

    1993-04-01

    participants ont fait le point des aspects traitement et contr6le des mat~riaux. en mettant I’accent sur les materiaux constitutifs des disques moteur en...adapte. Pour le physicien. un -d~faur’" peut tres bien se resumer A une imperfection de Ia structure rericulaire d’un materiau. En science des materiaux ... materiaux sur l~integrite des structures des moteurs Defence Research Ag~ency Matenials & Structures Department Farnborough. Hants GUt 14 fITD Rovaume-Uni

  17. The role of soil moisture in land surface-atmosphere coupling: climate model sensitivity experiments over India

    NASA Astrophysics Data System (ADS)

    Williams, Charles; Turner, Andrew

    2015-04-01

    It is generally acknowledged that anthropogenic land use changes, such as a shift from forested land into irrigated agriculture, may have an impact on regional climate and, in particular, rainfall patterns in both time and space. India provides an excellent example of a country in which widespread land use change has occurred during the last century, as the country tries to meet its growing demand for food. Of primary concern for agriculture is the Indian summer monsoon (ISM), which displays considerable seasonal and subseasonal variability. Although it is evident that changing rainfall variability will have a direct impact on land surface processes (such as soil moisture variability), the reverse impact is less well understood. However, the role of soil moisture in the coupling between the land surface and atmosphere needs to be properly explored before any potential impact of changing soil moisture variability on ISM rainfall can be understood. This paper attempts to address this issue, by conducting a number of sensitivity experiments using a state-of-the-art climate model from the UK Meteorological Office Hadley Centre: HadGEM2. Several experiments are undertaken, with the only difference between them being the extent to which soil moisture is coupled to the atmosphere. Firstly, the land surface is fully coupled to the atmosphere, globally (as in standard model configurations); secondly, the land surface is entirely uncoupled from the atmosphere, again globally, with soil moisture values being prescribed on a daily basis; thirdly, the land surface is uncoupled from the atmosphere over India but fully coupled elsewhere; and lastly, vice versa (i.e. the land surface is coupled to the atmosphere over India but uncoupled elsewhere). Early results from this study suggest certain 'hotspot' regions where the impact of soil moisture coupling/uncoupling may be important, and many of these regions coincide with previous studies. Focusing on the third experiment, i

  18. Early cystic fibrosis lung disease: Role of airway surface dehydration and lessons from preventive rehydration therapies in mice.

    PubMed

    Mall, Marcus A; Graeber, Simon Y; Stahl, Mirjam; Zhou-Suckow, Zhe

    2014-07-01

    Cystic fibrosis (CF) lung disease starts in the first months of life and remains one of the most common fatal hereditary diseases. Early therapeutic interventions may provide an opportunity to prevent irreversible lung damage and improve outcome. Airway surface dehydration is a key disease mechanism in CF, however, its role in the in vivo pathogenesis and as therapeutic target in early lung disease remains poorly understood. Mice with airway-specific overexpression of the epithelial Na(+) channel (βENaC-Tg) recapitulate airway surface dehydration and phenocopy CF lung disease. Recent studies in neonatal βENaC-Tg mice demonstrated that airway surface dehydration produces early mucus plugging in the absence of mucus hypersecretion, which triggers airway inflammation, promotes bacterial infection and causes early mortality. Preventive rehydration therapy with hypertonic saline or amiloride effectively reduced mucus plugging and mortality in neonatal βENaC-Tg mice. These results support clinical testing of preventive/early rehydration strategies in infants and young children with CF.

  19. Model polymer etching and surface modification by a time modulated RF plasma jet: role of atomic oxygen and water vapor

    NASA Astrophysics Data System (ADS)

    Luan, P.; Knoll, A. J.; Wang, H.; Kondeti, V. S. S. K.; Bruggeman, P. J.; Oehrlein, G. S.

    2017-01-01

    The surface interaction of a well-characterized time modulated radio frequency (RF) plasma jet with polystyrene, poly(methyl methacrylate) and poly(vinyl alcohol) as model polymers is investigated. The RF plasma jet shows fast polymer etching but mild chemical modification with a characteristic carbonate ester and NO formation on the etched surface. By varying the plasma treatment conditions including feed gas composition, environment gaseous composition, and treatment distance, we find that short lived species, especially atomic O for Ar/1% O2 and 1% air plasma and OH for Ar/1% H2O plasma, play an essential role for polymer etching. For O2 containing plasma, we find that atomic O initiates polymer etching and the etching depth mirrors the measured decay of O atoms in the gas phase as the nozzle-surface distance increases. The etching reaction probability of an O atom ranging from 10-4 to 10-3 is consistent with low pressure plasma research. We also find that adding O2 and H2O simultaneously into Ar feed gas quenches polymer etching compared to adding them separately which suggests the reduction of O and OH density in Ar/O2/H2O plasma.

  20. Roles of ionic strength and biofilm roughness on adhesion kinetics of Escherichia coli onto groundwater biofilm grown on PVC surfaces.

    PubMed

    Janjaroen, Dao; Ling, Fangqiong Q; Ling, Fangqiong; Monroy, Guillermo; Derlon, Nicolas; Morgenroth, Eberhard; Mogenroth, Eberhard; Boppart, Stephen A; Liu, Wen-Tso; Nguyen, Thanh H

    2013-05-01

    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.

  1. 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

  2. Limiting role of the mass transfer of gases in laser thermochemical reactions on the surface of solids

    NASA Astrophysics Data System (ADS)

    Sobol, Emil N.

    1990-10-01

    Growth kinetics of porous layers produced by gas-transfer controlled thermochemical reactions is described. The analysis of heat and mass-transfer problem allows to find the optimal regimes of laser treatment of solids. 1. GROWTH KINETICS OF SURFACE LAYERS The limiting role of gas transfer is characteristic of various processes in volved in the growth of solid layers of a new phase on the exposed surface'' in the course of laser oxidation and reduction of metals and laser synthesis and decomposition of nitrides and other compounds high-temperature superconductors included. When analyzing laser thermochemical reactions taking place in solids and involving the uptake or release of gases the absorbed energy flux q will be considered constant the thermooptical effects2 being disregarded. Let laser radiation incident on the surface of the original substance A give rise to a layer of a new phase B with a thickness of s through which a gas C migrates. We write the pertinent chemical decomposition and synthesis reactions in the form A 4 B + C and A + C ) B respectively. The direction of the reaction is determined by the sign of the Gibbs thermodynamic potential tG /H + TM where tH and tS are the changes of the enthalpy and entropy of the system respectively. According to the chemical equilibrium theory the pressure at the chemical reaction front is related to temperature by the Arrenius law:

  3. 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.

  4. [Reducing centers on the surface of Escherichia coli bacteria and their role in copper-induced plasma membrane permeability].

    PubMed

    Lebedev, V S; Veselovskiĭ, A V; Deĭnega, E Iu; Fedorov, Iu I

    2000-01-01

    The reducing properties of Escherichia coli and their role in the induction of nonselective cationic permeability of plasma membrane by the action of Cu2+ ions were studied. The ability of cells to reduce exogenous dithiopyridine was shown to be maximal in freshly collected culture and to decrease upon starvation or exhaustion of bacteria by dinitrophenol, in the presence of other oxidants of cell thiols in the medium, and after the disturbance of the barrier properties of membrane by tetrachloracetic acid or butanol. The alkylation of cell thiols accessible for N-ethyl maleimide completely disrupted the reducing activity of bacteria. These data are consistent with the conception that the reduction of dithiopyridine and Cu2+ ions by bacteria occurs on the thiol-containing centers of the cell surface, which are continuously reduced by the transfer of cell reducing equivalents from the inner to the outer surface of plasma membrane. The analysis of data on the effect of external oxidizing and reducing agents on the copper-induced plasmolysis of bacteria showed that the induction of membrane permeability by the action of copper can occur upon interaction with critical targets on the surface of Cu+ ions formed in the periplasmic space in the reaction of Cu2+ ions with reducing centers.

  5. 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.

  6. Simulation of extreme rainfall event of November 2009 over Jeddah, Saudi Arabia: the explicit role of topography and surface heating

    NASA Astrophysics Data System (ADS)

    Almazroui, Mansour; Raju, P. V. S.; Yusef, A.; Hussein, M. A. A.; Omar, M.

    2017-02-01

    In this paper, a nonhydrostatic Weather Research and Forecasting (WRF) model has been used to simulate the extreme precipitation event of 25 November 2009, over Jeddah, Saudi Arabia. The model is integrated in three nested (27, 9, and 3 km) domains with the initial and boundary forcing derived from the NCEP reanalysis datasets. As a control experiment, the model integrated for 48 h initiated at 0000 UTC on 24 November 2009. The simulated rainfall in the control experiment depicts in well agreement with Tropical Rainfall Measurement Mission rainfall estimates in terms of intensity as well as spatio-temporal distribution. Results indicate that a strong low-level (850 hPa) wind over Jeddah and surrounding regions enhanced the moisture and temperature gradient and created a conditionally unstable atmosphere that favored the development of the mesoscale system. The influences of topography and heat exchange process in the atmosphere were investigated on the development of extreme precipitation event; two sensitivity experiments are carried out: one without topography and another without exchange of surface heating to the atmosphere. The results depict that both surface heating and topography played crucial role in determining the spatial distribution and intensity of the extreme rainfall over Jeddah. The topography favored enhanced uplift motion that further strengthened the low-level jet and hence the rainfall over Jeddah and adjacent areas. On the other hand, the absence of surface heating considerably reduced the simulated rainfall by 30% as compared to the observations.

  7. 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.

  8. 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

  9. Role of Sea Surface Warming in Triggering Amplification of Coastal Rainfall Extremes

    NASA Astrophysics Data System (ADS)

    Meredith, Edmund; Semenov, Vladimir; Maraun, Douglas; Park, Wonsun; Chernokulsky, Alexander

    2015-04-01

    Whether recent changes in the occurrence of meteorological extremes are attributable to a warmer climate remains a challenging question. One area where the potential for extreme summertime convective precipitation has grown recently, along with substantial sea surface temperature (SST) increase, is the Black Sea and Mediterranean (BSM) region. To study mechanisms through which SST increase may impact BSM convective extremes, we take the July 2012 precipitation extreme near the Black Sea town of Krymsk as a recent showcase example. The event was related to a slow moving low pressure system crossing the eastern Black Sea, advecting warm and moist air towards the coast. Two waves of convection resulted in precipitation totals that dwarfed all previous events in the instrumental record, dating back to the 1930s, and over 170 deaths. The synoptic environment which led to this event is typical of that found with intense summertime precipitation in the BSM region. We carry out ensemble sensitivity experiments over an eastern Black Sea domain with the WRF regional model, using multiply nested sub-domains, increasing to 600 m convection resolving resolution. The model's ability to reproduce the event with observed SST forcing is first verified, before a series of additional ensembles with altered SST is created. These ensembles consist of subtracting (adding) the 1982 - 2012 trend in Black Sea SST from (to) the observed 2012 SST field in 20% increments, giving a total of 11 ensembles whose SST differ from the observed field by between -100% and +100% of the warming trend. We demonstrate that such an intense precipitation event would not have been possible without the recent Black Sea warming. The increased SST enhances low-level instability, allowing deep convection to be triggered and causing a more than 300% increase in precipitation. Additionally, a highly nonlinear precipitation response to incrementally increasing SST suggests that Black Sea SSTs have exceeded a

  10. Designing Morphology in Epitaxial Silicon Nanowires: The Role of Gold, Surface Chemistry, and Phosphorus Doping.

    PubMed

    Kim, Seokhyoung; Hill, David J; Pinion, Christopher W; Christesen, Joseph D; McBride, James R; Cahoon, James F

    2017-03-28

    Vertically aligned semiconductor nanowires (NWs) have many potential applications for NW-based technologies, ranging from solar cells to intracellular sensors. Aligned NWs can be fabricated by top-down etching of planar wafers or synthesized from the bottom up using the vapor-liquid-solid (VLS) mechanism to induce epitaxial growth on lattice-matched substrates. The VLS process permits the modulation of dopants along the NW growth axis, which if combined with dopant-dependent wet-chemical etching, can be used to encode precise morphology. However, the synthesis of vertical and linear NWs with complex morphology is nontrivial, requiring control over multiple interdependent aspects of the VLS process. Here, we demonstrate sub-10 nm morphology in ⟨111⟩ epitaxial silicon (Si) NWs grown by the VLS mechanism on (111) Si substrates with gold (Au) catalysts. Using silane (SiH4), phosphine (PH3), and hydrochloric acid (HCl) precursor gases at 480 °C, precise morphology is encoded through abrupt phosphorus (P) dopant transitions, which are found to be less than 5 nm in width. The results highlight three mechanistic attributes of the process. First, NW growth in the ⟨111⟩ direction is found to be unstable at high SiH4 partial pressures and growth rates unless using HCl, which stabilizes NW growth through chlorination of the NW sidewall. Second, aggregated Au deposited on the NW surface by the VLS catalyst is found to be immobile on the chlorinated surface and to impede selective wet-chemical etching by potassium hydroxide (KOH) solution, preventing the design of precise morphology. Third, the aggregation of Au is found to be strongly dependent on the SiH4 partial pressure and NW growth rate, and values exceeding ∼100 mTorr and ∼150 nm/min, respectively, are required to minimize Au and thereby enable selective wet-chemical etching. Under optimized growth conditions, we find that abrupt, complex, and arbitrary dopant profiles and morphologies can be encoded in

  11. The role of the surfaces in the photon absorption in Ge nanoclusters embedded in silica

    NASA Astrophysics Data System (ADS)

    Cosentino, Salvatore; Mirabella, Salvatore; Miritello, Maria; Nicotra, Giuseppe; Lo Savio, Roberto; Simone, Francesca; Spinella, Corrado; Terrasi, Antonio

    2011-12-01

    The usage of semiconductor nanostructures is highly promising for boosting the energy conversion efficiency in photovoltaics technology, but still some of the underlying mechanisms are not well understood at the nanoscale length. Ge quantum dots (QDs) should have a larger absorption and a more efficient quantum confinement effect than Si ones, thus they are good candidate for third-generation solar cells. In this work, Ge QDs embedded in silica matrix have been synthesized through magnetron sputtering deposition and annealing up to 800°C. The thermal evolution of the QD size (2 to 10 nm) has been followed by transmission electron microscopy and X-ray diffraction techniques, evidencing an Ostwald ripening mechanism with a concomitant amorphous-crystalline transition. The optical absorption of Ge nanoclusters has been measured by spectrophotometry analyses, evidencing an optical bandgap of 1.6 eV, unexpectedly independent of the QDs size or of the solid phase (amorphous or crystalline). A simple modeling, based on the Tauc law, shows that the photon absorption has a much larger extent in smaller Ge QDs, being related to the surface extent rather than to the volume. These data are presented and discussed also considering the outcomes for application of Ge nanostructures in photovoltaics. PACS: 81.07.Ta; 78.67.Hc; 68.65.-k

  12. 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

  13. 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.

  14. 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.

  15. 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}.

  16. Surface Glycans of Candida albicans and Other Pathogenic Fungi: Physiological Roles, Clinical Uses, and Experimental Challenges

    PubMed Central

    Masuoka, James

    2004-01-01

    Although fungi have always been with us as commensals and pathogens, fungal infections have been increasing in frequency over the past few decades. There is a growing body of literature describing the involvement of carbohydrate groups in various aspects of fungal disease. Carbohydrates comprising the cell wall or capsule, or as a component of glycoproteins, are the fungal cell surface entities most likely to be exposed to the surrounding environment. Thus, the fungus-host interaction is likely to involve carbohydrates before DNA, RNA, or even protein. The interaction between fungal and host cells is also complex, and early studies using whole cells or crude cell fractions often produced seemingly conflicting results. What was needed, and what has been developing, is the ability to identify specific glycan structures and determine how they interact with immune system components. Carbohydrate analysis is complicated by the complexity of glycan structures and by the challenges of separating and detecting carbohydrates experimentally. Advances in carbohydrate chemistry have enabled us to move from the foundation of composition analysis to more rapid characterization of specific structures. This, in turn, will lead to a greater understanding of how fungi coexist with their hosts as commensals or exist in conflict as pathogens. PMID:15084502

  17. The role of the sea-surface temperature distribution on numerically simulated cyclogenesis during ERICA

    NASA Technical Reports Server (NTRS)

    Lapenta, William M.; Perkey, Donald J.; Kreitzberg, Carl W.; Robertson, Franklin R.

    1991-01-01

    The goal was to quantify the extent to which a sea surface temperature (SST) front can influence cyclogenesis. The approach was to use the Drexel Limited-Area Mesoscale Prediction System (LAMPS) dynamical model to simulate cyclogenesis over various SST fields. Research during the past year focused on the development and testing of a four dimensional data assimilation (FDDA) technique within LAMPS. The technique is a continuous dynamical assimilation where forcing terms are added to the governing model equations to gradually nudge the model solution toward a gridded analysis. Here, the nudging is used as a dynamic initialization tool during a 12 hour preforecast to generate model balanced initial conditions for a subsequent 24 hour numerical prediction. Tests were performed to determine which variables to nudge and how to specify the four dimensional weighting function used to scale the nudging terms. To date, optimal results were obtained by nudging the u and v components of the wind along with the potential temperature. The weighting function ranged from 0 to 1 and varies in time as a quadratic polynomial. It was initialized at 0, reached its maximum at 9 hours into the preforecast, and fell back at 0 to 12 hours. The nudging terms are included in the model equations for all grid points except those within the model predicted oceanic boundary layer. This design attempts to confine changes imposed by the specified SST field to the oceanic boundary layer during the preforecast period.

  18. 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.

  19. Role of soil health in maintaining environmental sustainability of surface coal mining.

    PubMed

    Acton, Peter M; Fox, James F; Campbell, J Elliott; Jones, Alice L; Rowe, Harold; Martin, Darren; Bryson, Sebastian

    2011-12-01

    Mountaintop coal mining (MCM) in the Southern Appalachian forest region greatly impacts both soil and aquatic ecosystems. Policy and practice currently in place emphasize water quality and soil stability but do not consider upland soil health. Here we report soil organic carbon (SOC) measurements and other soil quality indicators for reclaimed soils in the Southern Appalachian forest region to quantify the health of the soil ecosystem. The SOC sequestration rate of the MCM soils was 1.3 MgC ha(-1) yr(-1) and stocks ranged from 1.3 ± 0.9 to 20.9 ± 5.9 Mg ha(-1) and contained only 11% of the SOC of surrounding forest soils. Comparable reclaimed mining soils reported in the literature that are supportive of soil ecosystem health had SOC stocks 2.5-5 times greater than the MCM soils and sequestration rates were also 1.6-3 times greater. The high compaction associated with reclamation in this region greatly reduces both the vegetative rooting depth and infiltration of the soil and increases surface runoff, thus bypassing the ability of soil to naturally filter groundwater. In the context of environmental sustainability of MCM, it is proposed that the entire watershed ecosystem be assessed and that a revision of current policy be conducted to reflect the health of both water and soil.

  20. Bacterial activation of human natural killer cells: role of cell surface lipopolysaccharide.

    PubMed Central

    Lindemann, R A

    1988-01-01

    Culture of human peripheral blood lymphocytes with gram-negative bacteria associated with periodontal disease caused a rapid increase in the cytotoxic potential of natural killer (NK) cells. The NK cells were activated to kill NK-resistant targets, the peak cytotoxicity occurring on day 1 of culture. The addition of anti-Tac, anti-CD3, or anti-OKT-11 antibodies to block activation via the interleukin-2 (IL-2), T-cell, or E rosette receptors had a minimal effect on this inductive process. Anti-IL-2 antiserum was effective in blocking a significant amount, but not all, of the cytotoxicity in bacterium-activated cultures. Modest IL-2 production (5 to 6 National Institutes of Health units) was measured in lymphocyte cultures activated by bacteria, but proliferation was not induced during a 1-week period. When polymixin B sulfate was added to bind and block lipopolysaccharides, bacterium-induced cytotoxicity was completely abrogated for all activating bacteria. In addition, when culture supernatants from Actinobacillus actinomycetemcomitans were tested, activation still occurred. However, again, this activation was totally inhibited by polymixin B sulfate. Monocytes were also activated by bacteria to produce tumor necrosis factor (TNF). To exclude the possibility that TNF was responsible for cytotoxicity, an antiserum to TNF was added to cocultures of bacteria and lymphocytes with adherent cells removed. The antiserum had no effect on the inductive process. In addition, exogenous TNF did not kill M14 targets. These results suggest that bacterial cell surface lipopolysaccharides provide a major activation signal for NK cells to enhance cytotoxicity. PMID:2895743

  1. Role of surface vegetation in 210Pb-dating of peat cores.

    PubMed

    Olid, Carolina; Garcia-Orellana, Jordi; Martínez-Cortizas, Antonio; Masqué, Pere; Peiteado, Eva; Sanchez-Cabeza, Joan-Albert

    2008-12-01

    210Pb-dated ombrotrophic peat cores have been widely used to reconstructthe atmospheric fluxes of heavy metals forthe past century. Many of these studies rarely include the overlying vegetation compartment (i.e., the aerial part of vegetation and decayed plant remains) in the analysis although it represents the first layer capturing atmospheric deposition. The aim of this study was to evaluate the radionuclide and Pb content of this biologically active layer in bogs and to assess its implications on the total inventories and the 210Pb-derived chronology. We analyzed two short ombrotrophic peat cores from the same bog (Chao de Lamoso, Galicia, Spain) for 210Pb, artificial radionuclides (137Cs and 241Am), and Pb. The total Pb inventory was underestimated by about 12% when the plant material was not included in the record. The atmospheric origin of 210Pb and the uptake of 137Cs by roots led to significant activities of these radionuclides in the upper layers. Therefore, removing them from the peat record would imply even larger underestimations of the total inventories, ranging from 25% to 36% for 137Cs and from 39% to 49% for 210Pb. In contrast to the chronologies inferred from the constant rate of supply (CRS) model when only peat layers are considered, the 210Pb chronology agreed well with artificial radionuclide dating when surface vegetation was included. These results suggest that an accurate peat chronology requires an initial evaluation of the relevance of plant inventories and emphasizes the need of considering the biologically active layer when atmospheric fluxes of heavy metals and other pollutants are reconstructed.

  2. 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.

  3. 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.

  4. Flocculation in ale brewing strains of Saccharomyces cerevisiae: re-evaluation of the role of cell surface charge and hydrophobicity.

    PubMed

    Holle, Ann Van; Machado, Manuela D; Soares, Eduardo V

    2012-02-01

    Flocculation is an eco-friendly process of cell separation, which has been traditionally exploited by the brewing industry. Cell surface charge (CSC), cell surface hydrophobicity (CSH) and the presence of active flocculins, during the growth of two (NCYC 1195 and NCYC 1214) ale brewing flocculent strains, belonging to the NewFlo phenotype, were examined. Ale strains, in exponential phase of growth, were not flocculent and did not present active flocculent lectins on the cell surface; in contrast, the same strains, in stationary phase of growth, were highly flocculent (>98%) and presented a hydrophobicity of approximately three to seven times higher than in exponential phase. No relationship between growth phase, flocculation and CSC was observed. For comparative purposes, a constitutively flocculent strain (S646-1B) and its isogenic non-flocculent strain (S646-8D) were also used. The treatment of ale brewing and S646-1B strains with pronase E originated a loss of flocculation and a strong reduction of CSH; S646-1B pronase E-treated cells displayed a similar CSH as the non-treated S646-8D cells. The treatment of the S646-8D strain with protease did not reduce CSH. In conclusion, the increase of CSH observed at the onset of flocculation of ale strains is a consequence of the presence of flocculins on the yeast cell surface and not the cause of yeast flocculation. CSH and CSC play a minor role in the auto-aggregation of the ale strains since the degree of flocculation is defined, primarily, by the presence of active flocculins on the yeast cell wall.

  5. Role of the Indian Ocean sea surface temperature in shaping the natural variability in the flow of Nile River

    NASA Astrophysics Data System (ADS)

    Siam, Mohamed S.; Wang, Guiling; Demory, Marie-Estelle; Eltahir, Elfatih A. B.

    2014-08-01

    A significant fraction of the inter-annual variability in the Nile River flow is shaped by El Niño Southern Oscillation (ENSO). Here, we investigate a similar role for the Indian Ocean (IO) sea surface temperature (SST) in shaping the inter-annual variability of the Nile River flow. Using observations of global SST distribution and river flow in addition to atmospheric general circulation model sensitivity experiments, we show that North and Middle IO SSTs play a significant intermediate role in the teleconnection between ENSO and the Nile flow. Applying partial coherency analyses, we demonstrate that the connection between North and Middle IO SSTs and Nile flow is strongly coupled to ENSO. During El Niño events, SST in the North and Middle IO increases in response to the warming in the Tropical Eastern Pacific Ocean and forces a Gill-type circulation with enhanced westerly low-level flow over East Africa and the Western IO. This anomalous low-level flow enhances the low-level flux of air and moisture away from the Upper Blue Nile (UBN) basin resulting in reduction of rainfall and river flow. SSTs in the South IO also play a significant role in shaping the variability of the Nile flow that is independent from ENSO. A warming over the South IO, generates a cyclonic flow in the boundary layer, which reduces the cross-equatorial meridional transport of air and moisture towards the UBN basin, favoring a reduction in rainfall and river flow. This independence between the roles of ENSO and South IO SSTs allows for development of new combined indices of SSTs to explain the inter-annual variability of the Nile flow. The proposed teleconnections have important implications regarding mechanisms that shape the regional impacts of climate change over the Nile basin.

  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. Peste des petits ruminants.

    PubMed

    Parida, S; Muniraju, M; Mahapatra, M; Muthuchelvan, D; Buczkowski, H; Banyard, A C

    2015-12-14

    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.

  8. LeČOns Sur Les Ondes De Gravité Des Fluides Incompressibles

    NASA Astrophysics Data System (ADS)

    van den Dungen, F. H.

    Le 3 Janvier 1814 au moment où les Alliés franchissant le Rhin allaient entamer la campagne de France, la classe des Sciences de l'Institut de France proposait comme sujet du grand prix de mathématique à décerner en Janvier 1816 la question suivante: "La théorie de la propagation des ondes à la surface d'un fluide pesant d'une profondeur infinie".

  9. Studying the role of protein dynamics in an SN2 enzyme reaction using free-energy surfaces and solvent coordinates.

    PubMed

    García-Meseguer, Rafael; Martí, Sergio; Ruiz-Pernía, J Javier; Moliner, Vicent; Tuñón, Iñaki

    2013-07-01

    Conformational changes are known to be able to drive an enzyme through its catalytic cycle, allowing, for example, substrate binding or product release. However, the influence of protein motions on the chemical step is a controversial issue. One proposal is that the simple equilibrium fluctuations incorporated into transition-state theory are insufficient to account for the catalytic effect of enzymes and that protein motions should be treated dynamically. Here, we propose the use of free-energy surfaces, obtained as a function of both a chemical coordinate and an environmental coordinate, as an efficient way to elucidate the role of protein structure and motions during the reaction. We show that the structure of the protein provides an adequate environment for the progress of the reaction, although a certain degree of flexibility is needed to attain the full catalytic effect. However, these motions do not introduce significant dynamical corrections to the rate constant and can be described as equilibrium fluctuations.

  10. Studying the role of protein dynamics in an SN2 enzyme reaction using free-energy surfaces and solvent coordinates

    NASA Astrophysics Data System (ADS)

    García-Meseguer, Rafael; Martí, Sergio; Ruiz-Pernía, J. Javier; Moliner, Vicent; Tuñón, Iñaki

    2013-07-01

    Conformational changes are known to be able to drive an enzyme through its catalytic cycle, allowing, for example, substrate binding or product release. However, the influence of protein motions on the chemical step is a controversial issue. One proposal is that the simple equilibrium fluctuations incorporated into transition-state theory are insufficient to account for the catalytic effect of enzymes and that protein motions should be treated dynamically. Here, we propose the use of free-energy surfaces, obtained as a function of both a chemical coordinate and an environmental coordinate, as an efficient way to elucidate the role of protein structure and motions during the reaction. We show that the structure of the protein provides an adequate environment for the progress of the reaction, although a certain degree of flexibility is needed to attain the full catalytic effect. However, these motions do not introduce significant dynamical corrections to the rate constant and can be described as equilibrium fluctuations.

  11. Selectivity tailoring of Pd/CNTs in phenol hydrogenation by surface modification: Role of Csbnd O oxygen species

    NASA Astrophysics Data System (ADS)

    Xu, Tieyong; Zhang, Qunfeng; Cen, Jie; Xiang, Yizhi; Li, Xiaonian

    2015-01-01

    The effect of different types of oxygen containing groups (OCGs) on the catalytic performance was investigated in this paper by performing the selective hydrogenation of phenol in aqueous phase over the carbon supported Pd catalysts. The type of OCGs on carbon nanotubes (CNTs) was regulated by pretreating it with HNO3, or HNO3 followed by hydrothermal or thermal oxidation treatment. A distinct difference in the amount of phenolic/ether groups (Csbnd O) was observed for CNTs treated by different methods, while the difference in the amount of carbonyl groups (Cdbnd O) and carboxylic groups was much smaller. The results showed that the selectivity to cyclohexanone decreased with the increase of Csbnd O amount on carbon surface. Csbnd O groups played an important role in adsorption/desorption behavior of phenol/cyclohexanone and was considered to be responsible for the dramatic selectivity difference.

  12. Role of electronic, geometric, and surface properties on the mechanism of the electrochemical hydriding/dehydriding reactions

    SciTech Connect

    Srinivasan, S.; Zhang, W.; Kumar, M.P.S.

    1996-03-01

    Since 1990 there has been an ongoing collaboration among the authors to investigate the role of individual elements on the thermodynamics and kinetics of hydriding/dehydriding reactions. This review article presents the electrochemical and physicochemical characteristics of hydriding/dehydriding reactions from the point of view of their dependence on electronic, geometric and surface properties of the hydride materials. X-ray absorption spectroscopy (XAS), x-ray diffraction spectroscopy (XRD) and scanning vibrating electrode technique (SVET) studies were based on AB{sub 5} type alloys, partially substituted by other elements. Expansion of the unit cell volume and a larger Ni d band vacancy are beneficial for increasing the amount of the hydrogen storage. XAS and SVET showed that the Ce substitution for La in an AB{sub 5} alloy enhances the lifetime of hydride electrode.

  13. 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

  14. The geological history of deep-sea colonization by echinoids: roles of surface productivity and deep-water ventilation

    PubMed Central

    Smith, Andrew B; Stockley, Bruce

    2005-01-01

    The origins and geological history of the modern fauna of deep-sea echinoids is explored using a combination of palaeontological and molecular data. We demonstrate that, whereas generalist omnivores have migrated into the deep sea in low numbers over the past 200 Myr, there was a short time-interval between approximately 75 and 55 Myr when the majority of specialist detritivore clades independently migrated off-shelf. This coincides with a marked increase in seasonality, continental run-off and surface water productivity, and suggests that increasing organic carbon delivery into ocean basins was an important controlling factor. Oceanic anoxic events, by contrast, appear to have played a subsidiary role in controlling deep-sea diversity. PMID:15888420

  15. The Role of Citric Acid in Perfecting Platinum Monolayer on Palladium Nanoparticles during the Surface Limited Redox Replacement Reaction

    SciTech Connect

    Zhu, Shangqian; Yue, Jeffrey; Qin, Xueping; Wei, Zidong; Liang, Zhixiu; Adzic, Radoslav R.; Brankovic, Stanko R.; Du, Zheng; Shao, Minhua

    2016-07-28

    Cu-mediated-Pt-displacement method that involves the displacement of an underpotentially deposited (UPD) Cu monolayer by Pt has been extensively studied to prepare core-shell catalysts. It has been found that Pt clusters instead of a uniform Pt monolayer were formed in the gram batch synthesis. With a suitable surfactant, such as citric acid, the Pt shell could be much more uniform. In this study, the role of citric acid in controlling the Cu-Pt displacement reaction kinetics was studied by electrochemical techniques and theoretical approaches. It was found that citric acid strongly adsorbed on Pd, Pt, Cu/Pd, and Pt/Pd surfaces, especially in the double layer region in acid solutions. The strong adsorption of citric acid slowed down the Cu-Pt displacement reaction. The main characteristics of such strong interaction most likely arises from the OH groups in the citric acid molecule according to the molecular dynamics simulation results.

  16. The Role of Defects in the Local Reaction Kinetics of CO Oxidation on Low-Index Pd Surfaces.

    PubMed

    Vogel, D; Spiel, C; Schmid, M; Stöger-Pollach, M; Schlögl, R; Suchorski, Y; Rupprechter, G

    2013-06-13

    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.

  17. 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.

  18. 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

  19. 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.

  20. Using time-dependent experiments and simulations to establish the role of surfactant in increasing drag over superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Luzzatto-Fegiz, Paolo; Peaudecerf, Francois; Landel, Julien R.; Goldstein, Raymond E.

    2016-11-01

    Superhydrophobic surfaces (SHS) can potentially achieve drag reduction for both internal and external flow applications. However, experiments have provided inconsistent results, with many studies reporting significantly decreased performance. While a complete explanation is yet to be found, it has been proposed that surfactants, ubiquitous in flow applications, could be responsible, as Marangoni stresses could develop when the edges of the SHS are not aligned with the flow. However, testing this hypothesis has been challenging. Even careful experiments with purified water have shown large interfacial stresses; adding surfactant yields only small drag increases, potentially revealing a pre-existing contamination of the interface. Other common physical processes, such as thermal Marangoni stresses and interface deflection, could also explain the lower performance. We address this question with numerical simulations, including surfactant kinetics, and SHS experiments in a micro-channel, where we control temperature gradients and interface deflections. By imposing a time-dependent pressure gradient, we are able to drive complex interface dynamics that can only be explained by surfactant gradients. Our results demonstrate the role of surfactants in increasing drag over superhydrophobic surfaces.

  1. The role of structure and surface chemistry of carbon nanomaterials in catalytic conversion of 1,2-dichloroethane

    NASA Astrophysics Data System (ADS)

    Tveritinova, Evgenya A.; Zhitnev, Yury N.; Kulakova, Inna I.; Cherkasov, Nikolay; Maslakov, Konstantin I.; Nesterova, Ekaterina A.; Ivanov, Anton S.; Savilov, Serguei V.; Lunin, Valery V.

    2015-11-01

    Catalytic activity of several graphene- and diamond-based carbon nanomaterials was compared in the reaction of the 1,2-dichloroethane (DCE) conversion using the impulse microcatalytic method. Only nanodiamonds and Ni-doped nanodiamonds were active in the reaction. A comparison of XRD, XPS, DRIFTS, and BET studies suggested that nitrogen or oxygen-containing groups could be responsible for the catalytic activity in the DCE reaction. However, nitrogen-doped carbon nanoflakes, which contain much more nitrogen-containing groups, showed no activity in the DCE conversion; hence, it is unlikely that nitrogen-containing groups of nanodiamond surface are active centers in DCE conversion. The role of oxygen-containing groups was studied in a test reaction of 2-propanol dehydrogenation/dehydration - both nanotubes and nanodiamonds were active in the reaction; however, no activity of carbon nanotubes in the DCE conversion suggests that oxygen-containing groups are not active in the DCE conversion. As a result, we suggest that the carbon surface of nanodiamonds might be catalytically active in the DCE reaction.

  2. Protective Mechanism of Articular Cartilage to Severe Loading: Roles of Lubricants, Cartilage Surface Layer, Extracellular Matrix and Chondrocyte

    NASA Astrophysics Data System (ADS)

    Murakami, Teruo; Sawae, Yoshinori; Ihara, Maki

    The natural synovial joints have excellent tribological performance known as very low friction and very low wear for various daily activities in human life. These functions are likely to be supported by the adaptive multimode lubrication mechanism, in which the various lubrication modes such as elastohydrodynamic lubrication, weeping, boundary and gel film lubrication appear to operate to protect articular cartilage, depending on the severity of the rubbing conditions. In this paper, various protective roles of synovial fluid, cartilage surface layer, extracellular matrix and chondrocyte to severe loading are described. In the first part, the protective mechanism by adsorbed films and underlying gel films was described on the basis of the frictional behaviors of articular cartilage against articular cartilage or glass. It was discussed that the replenishment of gel film removed during severe rubbing is likely to be controlled by supply of proteoglycan from the extracellular matrix, where the chondrocyte plays the main role in the metabolism. In the second part, the time-dependent local deformation of biphasic articular cartilage under constant total compressive strain condition was evaluated in the finite element analyses. The importance of clarification of actual stress-strain in chondrocyte was indicated in relation to the tribological property of articular cartilage.

  3. Characterization of surface antigen protein 1 (SurA1) from Acinetobacter baumannii and its role in virulence and fitness.

    PubMed

    Liu, Dong; Liu, Zeng-Shan; Hu, Pan; Cai, Ling; Fu, Bao-Quan; Li, Yan-Song; Lu, Shi-Ying; Liu, Nan-Nan; Ma, Xiao-Long; Chi, Dan; Chang, Jiang; Shui, Yi-Ming; Li, Zhao-Hui; Ahmad, Waqas; Zhou, Yu; Ren, Hong-Lin

    2016-04-15

    Acinetobacter baumannii is a Gram-negative bacillus that causes nosocomial infections, such as bacteremia, pneumonia, and meningitis and urinary tract and wound infections. In the present study, the surface antigen protein 1 (SurA1) gene of A. baumannii strain CCGGD201101 was identified, cloned and expressed, and then its roles in fitness and virulence were investigated. Virulence was observed in the human lung cancer cell lines A549 and HEp-2 at one week after treatment with recombinant SurA1. One isogenic SurA1 knock-out strain, GR0015, which was derived from the A. baumannii strain CCGGD201101 isolated from diseased chicks in a previous study, highlighted the effect of SurA1 on fitness and growth. Its growth rate in LB broth and killing activity in human sera were significantly decreased compared with strain CCGGD201101. In the Galleria mellonella insect model, the isogenic SurA1 knock-out strain exhibited a lower survival rate and decreased dissemination. These results suggest that SurA1 plays an important role in the fitness and virulence of A. baumannii.

  4. 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 des saignements généraux. Du côté pratique, les avantages des NACO par rapport à la warfarine sont : posologie orale fixe uniquotidienne ou biquotidienne sans devoir surveiller la coagulation et peu d’interactions connues ou définies avec d’autres médicaments ou des aliments. Les désavantages potentiels des NACO sont notamment un risque de saignement qui serait accru chez les patients de plus de 75 ans, une hausse des saignements gastro-intestinaux majeurs avec des doses élevées de dabigatran, une hausse des cas de dyspepsie avec le dabigatran, l’absence d’un test de laboratoire de routine visant à mesurer de façon fiable l’effet anticoagulant et l’absence d’antidote pour renverser l’effet anticoagulant. Aucun essai randomisé contrôlé n’a effectué de comparaison directe des NACO, et le choix d’un NACO est influencé par les caract

  5. Profil épidemio-clinique et radiologique des atteintes ostéo-articulaires des hémophiles à Madagascar

    PubMed Central

    Narindra, Lova Hasina Rajaonarison Ny Ony; Rabemanorintsoa, Feno Hasina; Randrianantenaina, Faralahy Ravelonarivo; Rakoto, Olivat Alson Aimée; Ahmad, Ahmad

    2014-01-01

    Introduction Déterminer le profil épidémio-clinique et radiologique des atteintes ostéo-articulaires des hémophiles malagasy. Méthodes Une étude prospective, descriptive portant sur 25 patients hémophiles venant de tout Madagascar a été réalisée. Des radiographies numérisées des genoux, des chevilles et des coudes en incidence de face et de profil ainsi qu'une échographie des hanches, des genoux, des chevilles et des coudes ont été réalisées chez ces patients. Le type et la sévérité de la maladie ainsi que l'aspect de la cavité articulaire, la synoviale, les noyaux épiphysaires et les surfaces articulaires ont été analysés. Résultats Soixante-huit pourcent des patients étaient hémophiles de type A et 32 % de type B. Quarante pourcent étaient classés sévères, 28 % modérés et 32 % mineurs. Les atteintes ostéo-articulaires ont été retrouvées chez 56 % des patients. Il n'existait pas de prédominance d'atteinte selon le type ni la sévérité de la maladie. Les plus jeunes étaient les plus atteints et l'articulation du genou et de la cheville étaient les plus touchées. Conclusion Les complications ostéo-articulaire de l'hémophilie sont graves et ne dépendent pas du type ni de la sévérité de l'affection. Elles touchent surtout les enfants d'âge scolaire. Le couple radiographie-échographie permet de diagnostiquer et de surveiller ces lésions. PMID:25870742

  6. Land surface controls on afternoon precipitation diagnosed from observational data: Uncertainties, confounding factors and the possible role of interception storage

    NASA Astrophysics Data System (ADS)

    Guillod, B. P.; Orlowsky, B.; Seneviratne, S. I.

    2013-12-01

    The feedback between soil moisture and precipitation has long been a topic of interest due to its potential for improving seasonal forecasts. The generally proposed feedbacks assume a control of soil moisture on the flux partitioning (i.e. the Evaporative Fraction, EF) at the land surface, which then influences precipitation. Our study (Guillod et al., in prep) addresses the poorly understood link between EF and precipitation by investigating the impact of before-noon EF on the frequency of afternoon precipitation over the contiguous US. We analyze remote sensing data products (EF from GLEAM, Miralles et al. 2011; radar precipitation from NEXRAD), FLUXNET station data, and the North American Regional Reanalysis (NARR). While most datasets agree on the existence of a region of positive relationship between between EF and precipitation in the Eastern US (e.g. Findell et al. 2011), observation-based estimates indicate a stronger relationship in the Western US, which is not found in NARR. Investigating these differences, we find that much of these relationships can be explained by precipitation persistence alone, with ambiguous results on the additional role of EF. Regional analyses reveal contrasting mechanisms over different regions which fit well with the known distribution of vegetation cover and soil moisture-climate regimes. Over the Eastern US, our analyses suggest that the EF-precipitation feedback, if present, takes place on a short day-to-day time scale, where interception evaporation drives the relationship rather than soil moisture, due to the high forest cover and the wet regime. Over the Western US, the impact of EF on convection triggering is additionally linked to soil moisture variations, owing to the soil moisture-limited climate regime. References: Findell, K. L., et al., 2011: Probability of afternoon precipitation in eastern United States and Mexico enhanced by high evaporation. Nature Geosci., 4 (7), 434-439, doi:10.1038/ngeo1174, URL http

  7. 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

  8. Étude par diffraction des rayons X des vernis rouges des sigillées du sud de la Gaule. Les ateliers de la Graufesenque

    NASA Astrophysics Data System (ADS)

    Vendier, L.; Sciau, Ph.; Dooryhee, E.

    2002-07-01

    La Graufesenque (Millau, Aveyron) 1^rst and 2^nd, centuries AC Sigillata red slips have been studied by x-ray diffraction at ESRF and on a conventional diffractometer. Although x-ray diffraction is a non-destructive characterisation technique adapted to surface study, it has not been used so mutch for Sigillata slip characterisation. The poor quality of the slip surface can be an explanation. In this work we demonstrate that it is possible to get good quality diffraction diagrams on 20-120 AC Sigillata slips. The results confirm the productions homogeneity and the hypothesis about a non-local clay used for the slips. On a counterpart, the late (second half of 2^nd century AC) Sigillata study needs because of their crackled surface a high quality beam, which can only be accessible on a synchrotron installation. These productions seems to be more heterogeneous: some Sigillata present similar diffraction diagrams for the slip and ceramic body (same clay?), some others present results similar to the precedent production period ones. Les vernis rouges de poteries sigillées (I^er et II^e siècles) de la Graufesenque (Millau, Aveyron) ont été étudiés par diffraction des rayons X à la fois à l'ESRF et sur une installation classique de laboratoire. Bien que la diffraction des rayons X soit une technique adaptée à l'étude des surfaces, cette technique a jusqu'à présent assez peu servi dans l'examen de ces objets. Ceci peut en partie s'expliquer par le mauvais état de surface de certains vernis. Dans ce travail, nous montrons que moyennant quelques précautions, il est possible d'obtenir sur une installation classique de bons diffractogranunes des vernis des sigillées datés entre 20 et 120 ap. J.C. Les résultats confirment l'homogénéité de ces productions et l'hypothèse selon laquelle ces vernis n'ont pas été fabriqués à partir des argiles locales du jurassique environnant le site. Par contre, l'étude des sigillées tardives de la deuxième moitié du

  9. Etude des Abondances de MG et de fe dans la Composante Stellaire des Disques des Galaxies Spirales

    NASA Astrophysics Data System (ADS)

    Beauchamp, Dominique

    Je presente ici une technique d'observation par imagerie des disques stellaires des galaxies spirales. Je tente, a l'aide d'un modele evolutif multiphase, de determiner les abondances de fer et de magnesium dans les disques. Dans ce but, je mesure les indices Mg2 et Fe5270 du systeme de Lick. Ces elements representent un choix judicieux d'indicateurs car ils sont formes par des supernovae de deux types differents ayant des durees de vie differentes. Le rapport d'abondances de ces deux elements est un indicateur du taux de formation des populations stellaires. Je decris, en premier lieu, les observations, la technique de mesure, ainsi que son application. J'analyse ensuite les indices mesures. A partir du modele multiphase, j'explore differents parametres physiques des spirales comme le taux de formation stellaire, l'evolution des abondances, les effets possibles de la presence de la barre, etc.

  10. Classification of 8 DES Supernova with OzDES

    NASA Astrophysics Data System (ADS)

    King, A.; Moller, A.; Sommer, N. E.; Tucker, B. E.; Childress, M. J.; Lewis, G. F.; Lidman, C.; OâNeill, C.; Casas, R.; Castander, F. J.; Desai, S.; Paech, K.; Smith, R. C.; Schubnell, M.; Kessler, R.; Lasker, J.; Scolnic, D.; Brout, D. J.; Gladney, L.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.; Nichol, R.; Papadopoulos, A.; D'Andrea, C.; Prajs, S.; Smith, M.; Sullivan, M.; Maartens, R.; Gupta, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.; Foley, R. J.; Pan, Y.-C.

    2016-09-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey (ATEL #4668). The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  11. Classification of 17 DES Supernova with OzDES

    NASA Astrophysics Data System (ADS)

    Hoormann, J. K.; Asorey, J.; Carollo, D.; Moller, A.; Sharp, R.; Sommer, N. E.; Tucker, B. E.; Zhang, B.; Lidman, C.; Brout, D. J.; D'Andrea, C.; Gladney, L.; March, M.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.; Macaulay, E.; Nichol, R.; Childress, M.; Prajs, S.; Smith, M.; Sullivan, M.; Maartens, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Gupta, R.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.; Foley, R. J.; Pan, Y.-C.; Casas, R.; Castander, F. J.; Papadopoulos, A.; Morganson, E.; Desai, S.; Paech, K.; Smith, R. C.; Schubnell, M.; Yuan, F.; Davis, T. M.; Hinton, S.; Muthukrishna, D.; Parkinson, D.; Lewis, G. F.; Uddin, S.; Kessler, R.; Lasker, J.; Scolnic, D.

    2016-12-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey (ATEL #4668). The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  12. Classification of 13 DES supernova with OzDES

    NASA Astrophysics Data System (ADS)

    Sommer, N.; Tucker, B. E.; Moller, A.; Zhang, B.; Macualay, E.; Lidman, C.; Gshwend, J.; Martini, P.; Foley, R. J.; Pan, Y.-C.; Casas, R.; Castander, F. J.; Desai, S.; Paech, K.; Smith, R. C.; Schubnell, M.; Kessler, R.; Lasker, J.; Scolnic, D.; Brout, D. J.; Gladney, L.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.; Nichol, R.; Papadopoulos, A.; Childress, M.; D'Andrea, C.; Prajs, S.; Smith, M.; Sullivan, M.; Maartens, R.; Gupta, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.

    2016-09-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey (ATEL #4668). The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  13. Classification of 11 DES supernova with OzDES

    NASA Astrophysics Data System (ADS)

    Sharp, R.; Zhang, B.; Sommer, N. E.; Tucker, B. E.; Lidman, C.; Davis, T. M.; Asorey, J.; Mould, J.; Smith, M.; Macaulay, E.; Nichol, R.; Childress, M.; Prajs, S.; Sullivan, M.; Maartens, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Gupta, R.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.; Foley, R. J.; Pan, Y.-C.; Casas, R.; Castander, F. J.; Papadopoulos, A.; Morganson, E.; Desai, S.; Paech, K.; Smith, R. C.; Schubnell, M.; Carollo, D.; Moller, A.; Yuan, F.; Hinton, S.; Muthukrishna, D.; Parkinson, D.; Lewis, G. F.; Uddin, S.; Kessler, R.; Lasker, J.; Scolnic, D.; Brout, D. J.; D'Andrea, C.; Gladney, L.; March, M.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.

    2017-01-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey (ATEL #4668). The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  14. Classification of 2 DES supernova with OzDES

    NASA Astrophysics Data System (ADS)

    O'Neill, C. R.; Moller, A.; Sommer, N. E.; Tucker, B. E.; Childress, M. J.; Lewis, G. F.; Lidman, C.; Desai, S.; Paech, K.; Smith, R. C.; Schubnell, M.; Kessler, R.; Lasker, J.; Scolnic, D.; Brout, D. J.; D'Andrea, C.; Gladney, L.; March, M.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.; Macaulay, E.; Nichol, R.; Prajs, S.; Smith, M.; Sullivan, M.; Maartens, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Gupta, R.; Nugent, P.; Perlmutter, S.; Foley, R. J.; Pan, Y.-C.; Casas, R.; Castander, F. J.; Papadopoulos, A.; Morganson, E.

    2016-10-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey (ATEL #4668). The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  15. Classification of 3 DES Supernovae with OzDES

    NASA Astrophysics Data System (ADS)

    Moller, A.; Tucker, B. E.; Yuan, F.; Lewis, G.; Lidman, C.; Macaulay, E.; Nichol, R.; Papadopoulos, A.; Childress, M.; D'Andrea, C.; Smith, M.; Sullivan, M.; Maartens, R.; Gupta, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.; Foley, R. J.; Pan, Y.-C.; Casas, R.; Castander, F. J.; Desai, S.; Paech, K.; Smith, R. C.; Schubnell, M.; Kessler, R.; Lasker, J.; Scolnic, D.; Brout, D. J.; Gladney, L.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.

    2016-02-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey (ATEL #4668). The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  16. Classification of 20 DES Supernova with OzDES

    NASA Astrophysics Data System (ADS)

    Davis, T. M.; Kim, A. G.; Macualay, E.; Lidman, C.; Sharp, R.; Tucker, B. E.; Yuan, F.; Zhang, B.; Lewis, G. F.; Sommer, N. E.; Martini, P.; Mould, J.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.; Foley, R. J.; Pan, Y.-C.; Casas, R.; Castander, F. J.; Desai, S.; Paech, K.; Smith, R. C.; Schubnell, M.; Kessler, R.; Lasker, J.; Scolnic, D.; Brout, D. J.; Gladney, L.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.; Nichol, R.; Papadopoulos, A.; Childress, M.; D'Andrea, C.; Smith, M.; Sullivan, M.; Maartens, R.; Gupta, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.

    2015-12-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey (ATEL #4668). The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  17. Classification of 14 DES Supernova with OzDES

    NASA Astrophysics Data System (ADS)

    Tucker, B. E.; Sharp, R.; Yuan, F.; Zhang, B.; Lidman, C.; Davis, T. M.; Hinton, S.; Mould, J.; Smith, R. C.; Schubnell, M.; Kessler, R.; Scolnic, D.; Covarrubias, R. A.; Brout, D. J.; Fischer, J. A.; Gladney, L.; March, M.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.; Nichol, R.; Papadopoulos, A.; D'Andrea, C.; Smith, M.; Sullivan, M.; Childress, M.; Maartens, R.; Gupta, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.; Foley, R. J.; Castander, F. J.; Desai, S.; Paech, K.

    2015-10-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey. The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  18. Classification of 4 DES supernovae by OzDES

    NASA Astrophysics Data System (ADS)

    Glazebrook, K.; Amon, A.; Lidman, C.; Martini, P.; Tucker, B. E.; Yuan, F.; Aldering, G.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.; Foley, R. J.; Pan, Y.-C.; Casas, R.; Castander, F. J.; Desai, S.; Paech, K.; Smith, R. C.; Schubnell, M.; Kessler, R.; Lasker, J.; Scolnic, D.; Brout, D. J.; Gladney, L.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.; Nichol, R.; Papadopoulos, A.; Childress, M.; D'Andrea, C.; Smith, M.; Sullivan, M.; Maartens, R.; Gupta, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.

    2015-12-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey (ATEL #4668). The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  19. Classification of 6 DES Supernova with OzDES

    NASA Astrophysics Data System (ADS)

    Lewis, G. F.; Mould, J.; Lidman, C.; Tucker, B. E.; Sharp, R.; Yuan, F.; Martini, P.; Kessler, R.; Scolnic, D.; Covarrubias, R. A.; Brout, D. J.; Fischer, J. A.; Gladney, L.; March, M.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.; Nichol, R.; Papadopoulos, A.; D'Andrea, C.; Smith, M.; Sullivan, M.; Childress, M.; Maartens, R.; Gupta, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.; Foley, R. J.; Casas, R.; Castander, F. J.; Desai, S.; Paech, K.; Smith, R. C.; Schubnell, M.

    2015-10-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey (ATEL #4668). The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  20. Classification of 15 DES supernovae by OzDES

    NASA Astrophysics Data System (ADS)

    Yuan, F.; Tucker, B. E.; Lidman, C.; Martini, P.; Gshwend, Julia; Moller, A.; Zhang, B.; Smith, R. C.; Schubnell, M.; Kessler, R.; Lasker, J.; Scolnic, D.; Brout, D. J.; Gladney, L.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.; Nichol, R.; Papadopoulos, A.; Childress, M.; D'Andrea, C.; Smith, M.; Sullivan, M.; Maartens, R.; Gupta, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.; Foley, R. J.; Pan, Y.-C.; Casas, R.; Castander, F. J.; Desai, S.; Paech, K.

    2015-12-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey (ATEL #4668). The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  1. Classification of 17 DES supernova with OzDES

    NASA Astrophysics Data System (ADS)

    Mudd, D.; Martini, P.; Lewis, G. F.; Moller, A.; Sharp, R. G.; Sommer, N. E.; Tucker, B. E.; Yuan, F.; Zhang, B.; Asorey, J.; Davis, T. M.; Hinton, S.; Muthukrishna, D.; Parkinson, D.; Carnero, A.; King, A.; Lidman, C.; Webb, S.; Uddin, S.; Kessler, R.; Lasker, J.; Scolnic, D.; Brout, D. J.; D'Andrea, C.; Gladney, L.; March, M.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.; Macaulay, E.; Nichol, R.; Childress, M.; Prajs, S.; Smith, M.; Sullivan, M.; Maartens, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Gupta, R.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.; Foley, R. J.; Pan, Y.-C.; Casas, R.; Castander, F. J.; Papadopoulos, A.; Morganson, E.; Desai, S.; Paech, K.; Smith, R. C.; Schubnell, M.

    2016-11-01

    We report new spectroscopic classifications by OzDES of supernovae discovered by the Dark Energy Survey (ATEL #4668). The spectra (370-885nm) were obtained with the AAOmega Spectrograph (Saunders et al. 2004, SPIE, 5492, 389) and the 2dF fibre positioner at the Anglo-Australian Telescope (AAT).

  2. Deposition of copper from Cu(i) and Cu(ii) precursors onto HOPG surface: Role of surface defects and choice of a precursor

    NASA Astrophysics Data System (ADS)

    Duan, Yichen; Teplyakov, Andrew V.

    2017-02-01

    The surface reactivity of two copper-containing precursors, (Cu(hfac)2 and Cu(hfac)VTMS, where hfac is hexafluoroacetyloacetonate and VTMS is vinyltrimethylsilane), was investigated by dosing the precursors onto a surface of highly ordered pyrolytic graphite (HOPG) at room temperature. The behavior of these precursors on a pristine HO