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1

Optical diagnostics of surface layers containing oriented particles  

NASA Astrophysics Data System (ADS)

Experimental results on energy and polarization characteristics of the radiation reflected by a layer containing oriented particles are presented. Two models of surface layer are considered: isotropically absorbing particles (model 1), and anisotropically absorbing particles (model 2). Model 1 refers to a layer containing (gamma) -Fe2O3 particles with different orientations. Estimates of the particle orientation degree were made from the photomicrographs taken at 1030x magnification. Model 2 refers to a polaroid film containing fully oriented (B equals 0.99) needle-like herapathite microcrystals.

Podkamen, L. I.; Arkhelyuk, A. D.

1992-04-01

2

The surface modified composite layer formation with boron carbide particles on magnesium alloy surfaces through pulse gas tungsten arc treatment  

Microsoft Academic Search

A novel fabrication process of surface modified composite layer by pulse current gas tungsten arc (GTA) surface modification process was used to deposit B4C particles on the surface of magnesium alloy AZ31. This method is an effective technique in producing a high performance surface modified composite layer. During the pulse current GTA surface modification process, considerable convection can exist in

W. B. Ding; H. Y. Jiang; X. Q. Zeng; D. H. Li; S. S. Yao

2007-01-01

3

Ti particle-reinforced surface layers in Al: Effect of particle size on microstructure, hardness and wear  

SciTech Connect

Two types of Ti particles are used in an ultrasonic impact peening (UIP) process to modify sub-surface layers of cp aluminium atomized, with an average size of approx. 20 {mu}m and milled (0.3-0.5 {mu}m). They are introduced into a zone of severe plastic deformation induced by UIP. The effect of Ti particles of different sizes on microstructure, phase composition, microhardness and wear resistance of sub-surface composite layers in aluminium is studied in this paper. The formed layers of a composite reinforced with smaller particles have a highly misoriented fine-grain microstructure of its matrix with a mean grain size of 200-400 nm, while reinforcement with larger particles results in relatively large Al grains (1-2 {mu}m). XRD, SEM, EDX and TEM studies confirm significantly higher particle/matrix bonding in the former case due to formation of a Ti{sub 3}Al interlayer around Ti particles with rough surface caused by milling. Different microstructures determine hardness and wear resistance of reinforced aluminium layers: while higher magnitudes of microhardness are observed for both composites (when compared with those of annealed and UIP-treated aluminium), the wear resistance is improved only in the case of reinforcement with small particles.

Mordyuk, B.N., E-mail: mordyuk@imp.kiev.ua [Kurdyumov Institute for Metal Physics, 36 Academician Vernadsky Boulevard, UA-03680, Kyiv (Ukraine); Silberschmidt, V.V. [Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, LE11 3TU (United Kingdom); Prokopenko, G.I. [Kurdyumov Institute for Metal Physics, 36 Academician Vernadsky Boulevard, UA-03680, Kyiv (Ukraine); Nesterenko, Yu.V. [National Technical University 'Kyiv Polytechnic Institute', 37 Peremohy Avenue, UA-03056, Kyiv (Ukraine); Iefimov, M.O. [Frantzevich Institute for Problems of Materials Science, 3 Krzhyzhanivsky Street, UA-03142, Kyiv (Ukraine)

2010-11-15

4

Effect of surface layering time of lactose carrier particles on dry powder inhalation properties of salbutamol sulfate.  

PubMed

The effect of the surface layering time of lactose carrier particles on the dry powder inhalation properties of salbutamol sulfate was investigated. Lactose carrier particles were layered with vegetable magnesium stearate by physical mixing. In the present study, drug/carrier powder mixtures were designed consisting of micronized salbutamol sulfate and lactose carriers with various particle surface conditions prepared by surface layering. These powder mixtures were aerosolized by a Jethaler, and the in vitro deposition properties of salbutamol sulfate were evaluated by a twin impinger. Compared with the powder mixed with unlayered lactose carrier, the in vitro inhalation properties of the powder mixture prepared using the surface layering lactose carrier were significantly different, showing that the in vitro inhalation properties of the drug/carrier powder mixtures were improved. In vitro deposition properties (RP) increased with surface layering time. Using this surface layering system would thus be valuable for increasing the inhalation properties of dry powder inhalation. PMID:14993760

Iida, Kotaro; Hayakawa, Youhei; Okamoto, Hirokazu; Danjo, Kazumi; Luenberger, Hans

2004-03-01

5

Controlling mixed-protein adsorption layers on colloidal alumina particles by tailoring carboxyl and hydroxyl surface group densities.  

PubMed

We show that different ratios of bovine serum albumin (BSA) and lysozyme (LSZ) can be achieved in a mixed protein adsorption layer by tailoring the amounts of carboxyl (-COOH) and aluminum hydroxyl (AlOH) groups on colloidal alumina particles (d50 ? 180 nm). The particles are surface-functionalized with -COOH groups, and the resultant surface chemistry, including the remaining AlOH groups, is characterized and quantified using elemental analysis, ? potential measurements, acid-base titration, IR spectroscopy, electron microscopy, nitrogen adsorption, and dynamic light scattering. BSA and LSZ are subsequently added to the particle suspensions, and protein adsorption is monitored by in situ ? potential measurements while being quantified by UV spectroscopy and gel electrophoresis. A comparison of single-component and sequential protein adsorption reveals that BSA and LSZ have specific adsorption sites: BSA adsorbs primarily via AlOH groups, whereas LSZ adsorbs only via -COOH groups (1-2 -COOH groups on the particle surface is enough to bind one LSZ molecule). Tailoring such groups on the particle surface allows control of the composition of a mixed BSA and LSZ adsorption layer. The results provide further insight into how particle surface chemistry affects the composition of protein adsorption layers on colloidal particles and is valuable for the design of such particles for biotechnological and biomedical applications. PMID:23875793

Meder, Fabian; Kaur, Supreet; Treccani, Laura; Rezwan, Kurosch

2013-07-31

6

Structure and function of airway surface layer of the human lungs & mobility of probe particles in complex fluids  

NASA Astrophysics Data System (ADS)

Numerous infectious particles such as bacteria and pathogens are deposited on the airway surface of the human lungs during our daily breathing. To avoid infection the lung has evolved to develop a smart and powerful defense system called mucociliary clearance. The airway surface layer is a critical component of this mucus clearance system, which consists of two parts: (1) a mucus layer, that traps inhaled particles and transports them out of the lung by cilia-generated flow; and (2) a periciliary layer, that provides a favorable environment for ciliary beating and cell surface lubrication. For 75 years, it has been dogma that a single gel-like mucus layer, which is composed of secreted mucin glycoproteins, is transported over a "watery" periciliary layer. This one-gel model, however, does not explain fundamental features of the normal system, e.g. formation of a distinct mucus layer, nor accurately predict how the mucus clearance system fails in disease. In the first part of this thesis we propose a novel "Gel-on-Brush" model with a mucus layer (the "gel") and a "brush-like" periciliary layer, composed of mucins tethered to the luminal of airway surface, and supporting data accurately describes both the biophysical and cell biological bases for normal mucus clearance and its failure in disease. Our "Gel-on-Brush" model describes for the first time how and why mucus is efficiently cleared in health and unifies the pathogenesis of major human diseases, including cystic fibrosis and chronic obstructive pulmonary disease. It is expected that this "Gel-on-Brush" model of airway surface layer opens new directions for treatments of airway diseases. A dilemma regarding the function of mucus is that, although mucus traps any inhaled harmful particulates, it also poses a long-time problem for drug delivery: mobility of cargos carrying pharmaceutical agents is slowed down in mucus. The second part of this thesis aims to answer the question: can we theoretically understand the relation between the motion of a probe particle and the local structure and dynamics of complex fluids such as mucus, or even one step back, simple polymer solutions and gels? It is well known that the thermal motion of a particle in simple solutions like water can be described by Stokes-Einstein relation, in which the mean-square displacement of the particle is (1) linearly proportional to time and (2) inversely proportional to the bulk viscosity of the solution. We found that these two statements become questionable if the particle size is relatively small and the solutions become complex fluids such as polymer solutions and gels. The motion of small particles with size smaller than the entanglement length (network mesh size) of a polymer solution (gel) is sub-diffusive with mean-square displacement proportional to the square root of time at relatively short time scales. Even at long time scales at which the mean-square displacement of the particles is diffusive, the mean-square displacement of the particles is not necessarily determined by the bulk viscosity, and is inversely proportional to an effective viscosity that is much smaller than the bulk value. An interesting question related to the particle motion in polymer gels is whether particles with size larger than the network mesh size can move through the gel? An intuitive answer would be that such large particles are trapped by the local network cages. We argue that the large particles can still diffuse via hopping mechanism, i.e., particles can wait for fluctuations of surrounding network cages that could be large enough to allow them to slip though. This hopping diffusion can be applied to understand the motion of large particles subjected to topological constraints such as permanent or reversible crosslinked networks as well as entanglements in high molecular weight polymer solutions, melts, and networks.

Cai, Liheng

7

Can Aerosol Particles Develop Organic Surface Layers Under UT/LS Conditions?  

NASA Astrophysics Data System (ADS)

Tropospheric aerosol particles contain oligomers and macromolecular humic-like substances that may be created by reactions in or on the surface of particles. Marine aerosols have been observed to possess surface films of fatty acids which can survive the evaporation of water from the interior of the particle. This phenomenon of surface films is of current interest with regard to their potential influence on the rate of water uptake by atmospheric particles, particularly in the tropical tropopause region. Understanding the composition, morphology, and behavior of mixed aqueous/organic particles is important for evaluating effects on cloud growth and the resulting climate implications. We have observed very reproducible formation of self-assembled films on the surface of acidic solutions containing aldehydes such as propanal. These resilient films were highly colored, and their formation has definite temperature and acidity dependences. Thus, formation of such a surface film may depend critically on the temperature history of UT aerosols, and aerosols exposed to different temperature and relative humidity conditions may demonstrate differing behavior. We will present an exploration of the conditions necessary for film formation from acidic aqueous solutions of oxygenated compounds and describe several film stability and identification studies.

Iraci, L. T.; Deng, P. H.

2007-05-01

8

Electrokinetics of Concentrated Suspensions of Spherical Colloidal Particles with Surface Conductance, Arbitrary Zeta Potential, and Double-Layer Thickness in Static Electric Fields  

Microsoft Academic Search

In this paper the electrophoretic mobility and the electrical conductivity of concentrated suspensions of spherical colloidal particles have been numerically studied under arbitrary conditions including zeta potential, particle volume fraction, double-layer thickness (overlapping of double layers is allowed), surface conductance by a dynamic Stern layer model (DSL), and ionic properties of the solution. We present an extensive set of numerical

F. Carrique; F. J. Arroyo; A. V. Delgado

2002-01-01

9

Characterisation by X-ray photoelectron spectroscopy of surface layers of poly(vinyl alcohol) on particles formed by dispersion polymerisation of divinylbenzene  

Microsoft Academic Search

Well-defined dispersions of polydivinylbenzene in methanol and a binary liquid mixture of methanol and water were stabilised by samples of partially hydrolysed poly(vinyl alcohol) (PVOH). Mean particle diameters in the range 0.3–1.0 ?m were produced in dispersion polymerisations. In order to assess surface coverage by PVOH, alcohol groups in the stabilising surface layer were derivatised with trifluoroacetic anhydride. Characterisation of trifluoroacetate

Luke Alger; Claire E. Madden; Ian Sutherland; John V. Dawkins

2005-01-01

10

Particle drag along the surface  

Microsoft Academic Search

I will discuss the drag of particles on granular surfaces by a fluid. I will present simulations using FLUENT of Aeolian saltation under Earth and Mars conditions obtaining among others the static and dynamic threshold shear and the height of the saltation layer as function of the wind strength. A universal quadratic increase of the saturated flux as function of

Hans J. Herrmann; MuriIo P. Almeidat; Eric J. R. Partelit; Jose S. Andrade Jr

11

Formation of multilayered structures in the layer by layer deposition of colloid particles  

Microsoft Academic Search

Theoretical calculations of particle film formation in the layer by layer (LbL) self-assembling processes have been performed according to the generalized random sequential adsorption (RSA) scheme. The first (precursor) layer was generated using the standard RSA scheme pertinent to homogeneous surface. Formation of the consecutive layers (up to twenty) was simulated for two kinds of particles of equal size. The

Zbigniew Adamczyk; Pawe? Wero?ski; Jakub Barbasz

2008-01-01

12

Formation of a wear-resistant nanocrystalline layer strengthened by TiO2 (Rutile) particles on the surface of titanium  

NASA Astrophysics Data System (ADS)

The effect of a thermomechanical treatment including severe plastic deformation under dry sliding friction conditions and subsequent heating in air to 350-650°C with further holding for 1 h on the structure and wear resistance of commercial titanium of grade VT1-0 has been studied. It has been shown that the deformation by friction leads to the formation of a nanocrystalline structure with ? crystals 20-100 nm in size in a surface layer of titanium of about 10 ?m thick. The heating of titanium deformed by friction at temperatures of 450-650°C for 1 h in air leads to the formation in the surface layer of this material ˜10 ?m thick of nanocrystalline particles of the titanium oxide TiO2 (rutile), the volume fraction of which reaches tens of percents, while the dimensions are ˜10 nm. The presence in the surface layer of titanium of a nanocrystalline two-phase (?-Ti + rutile) structure leads to a significant increase in the wear resistance of the VT1-0 titanium in pair with steel 40Kh13. This is explained by the enhanced strength of the arising nanocrystalline layer and its positive influence (as of a transition layer) on the reduction of the level of internal stresses that exist at the interface between the titanium oxide TiO2 and the host metal.

Korshunov, L. G.; Chernenko, N. L.

2013-09-01

13

Particle-laden boundary layers and singularities  

NASA Astrophysics Data System (ADS)

The dusty-gas model for flow in dilute particle suspensions generates a singularity in particle volume fraction in a variety of viscous boundary layer problems. Such a singularity, at say x=xs along the wall, makes it impossible to continue the solution to the equations. Previously, we have found that computation of the Blasius boundary layer, with a modified equation set that permits fluid volume fraction significantly different from 1, still leads to a velocity singularity at a slightly modified location.ootnotetextFoster, Duck & Hewitt, Bull. Amer. Phys. Soc., November, 2006 Contrary to some published work, the Saffman force has not been found to mitigate the singularity for the conventional equation set, and again here, though the Saffman force does become comparable to the Stokes drag near the singularity, it alters the structure only slightly, and does not remove it. If ?o is the particle volume fraction of the fluid in which the boundary layer is embedded, then in certain re-scaled coordinates, the singularity occurs in a region ?ox?o/|?o| about xs, where a reduced set of equations applies. Within this region, there is a downstream-running ray from the origin on which ??1. However, the vertical fluid and particle velocity components are unbounded on that line. On replacing the line with a solid surface of particle material, a narrow boundary layer may be inserted, in which velocity singularities are removed.

Foster, M. R.

2007-11-01

14

Surface analysis of particles  

Microsoft Academic Search

Summaries  Normally, commercial coatings are filled with small particles in the form of pigments or fillers. The general properties of\\u000a surface coating systems significantly depend on the stability of such systems, and on the interaction forces between polymer\\u000a matrix and particle. The knowledge about the mechanism of these interaction forces enables us to control the lacquer properties.\\u000a One of the well

C. Bellmann; N. Petong; A. Caspari; W. Jenschke; F. Simon; K. Grundke

2006-01-01

15

Influence of the surface viscosity on the drag and torque coefficients of a solid particle in a thin liquid layer  

Microsoft Academic Search

The present paper provides a short literature survey of the treatment of particle motion in fluids as a basis of the author's own work in this field. The work relates to the motion of a small solid particle inside a thin liquid film. The particle motion is treated numerically to provide information of interest to thin film liquid coating. The

R. Aust; F. Durst; U. Lange

1995-01-01

16

Boundary Layer Transport of Small Particles.  

National Technical Information Service (NTIS)

The transport of small particles across the aerodynamic boundary layer that developed over a smooth, flat, acrylic plate and their subsequent deposition was investigated. The velocity boundary layer over the flat plate was characterized for a wind tunnel ...

D. McCready

1984-01-01

17

The Lunar Surface Layer.  

National Technical Information Service (NTIS)

Direct and indirect evidence for the nature of lunar surface materials are examined and compared with theoretical predictions. Conclusions are then drawn concerning the most probable character of these materials. It is concluded that the lunar surface is ...

J. W. Salisbury V. G. Smalley

1964-01-01

18

Kinetic double-layer model of aerosol surface chemistry and gas-particle interactions (K2SURF): degradation of polycyclic aromatic hydrocarbons exposed to O3, NO2, H2O, OH and NO3  

Microsoft Academic Search

We present a kinetic double-layer surface model (K2-SURF) that describes the degradation of polycyclic aromatic hydrocarbons (PAHs) on aerosol particles exposed to ozone, nitrogen dioxide, water vapor, hydroxyl and nitrate radicals. The model is based on multiple experimental studies of PAH degradation and on the PRA framework (Pöschl et al., 2007) for aerosol and cloud surface chemistry and gas-particle interactions.

M. Shiraiwa; R. M. Garland; U. Pöschl

2009-01-01

19

Kinetic double-layer model of aerosol surface chemistry and gas-particle interactions (K2SURF): Degradation of polycyclic aromatic hydrocarbons exposed to O3, NO2, H2O, OH and NO3  

Microsoft Academic Search

We present a kinetic double-layer surface model (K2-SURF) that describes the degradation of polycyclic aromatic hydrocarbons (PAHs) on aerosol particles exposed to ozone, nitrogen dioxide, water vapor, hydroxyl and nitrate radicals [1]. The model is based on multiple experimental studies of PAH degradation and on the Pöschl-Rudich-Ammann (PRA) framework [2] for aerosol and cloud surface chemistry and gas-particle interactions. For

Manabu Shiraiwa; Rebecca M. Garland; Ulrich Pöschl

2010-01-01

20

Surface layers of bacteria.  

PubMed Central

Since bacteria are so small, microscopy has traditionally been used to study them as individual cells. To this end, electron microscopy has been a most powerful tool for studying bacterial surfaces; the viewing of macromolecular arrangements of some surfaces is now possible. This review compares older conventional electron-microscopic methods with new cryotechniques currently available and the results each has produced. Emphasis is not placed on the methodology but, rather, on the importance of the results in terms of our perception of the makeup and function of bacterial surfaces and their interaction with the surrounding environment. Images

Beveridge, T J; Graham, L L

1991-01-01

21

Dead Layers in Charged-Particle Detectors  

Microsoft Academic Search

This paper presents the results of dead-layer thickness measurements on silicon surface-barrier and ion-implanted detectors and a comparison of various methods for measuring dead-layer thicknesses. Our experimental arrangement and estimates of experimental error are discussed. Data on dead-layer thicknesses of n-type and p-type surface-barrier detectors and boron-implanted position-sensitive detectors are given. A linear relation was observed between the dead-layer thickness

E. Elad; C. N. Inskeep; R. A. Sareen; P. Nestor

1973-01-01

22

Near-Surface Deformed Layers on Rolled Aluminum Alloys  

NASA Astrophysics Data System (ADS)

Near-surface deformed layers, which are characterized by nano-sized fine grains, are generated in aluminum alloys by hot and cold rolling. During the rolling processes, the alloy surface and near-surface regions experience a high level of shear deformation that results in significant microstructure refinement, leading to formation of near-surface deformed layers with microstructures different from that of the underlying bulk alloy. Two types of near-surface deformed layers are observed. Type A is characterized by fine grains with grain boundaries decorated by oxide particles; type B is characterized also by fine grains but with the grain boundaries free of oxide particles. The high levels of shear deformation result in dynamic recrystallization. Together with mechanical alloying, this is responsible for the formation of the near-surface deformed layer. Furthermore, the structure in the near-surface deformed layer can survive the typical annealing process particularly if the grain boundaries are pinned by oxide particles.

Zhou, X.; Liu, Y.; Thompson, G. E.; Scamans, G. M.; Skeldon, P.; Hunter, J. A.

2011-05-01

23

Kinetic double-layer model of aerosol surface chemistry and gas-particle interactions (K2-SURF): Degradation of polycyclic aromatic hydrocarbons exposed to O3, NO2, H2O, OH and NO3  

NASA Astrophysics Data System (ADS)

We present a kinetic double-layer surface model (K2-SURF) that describes the degradation of polycyclic aromatic hydrocarbons (PAHs) on aerosol particles exposed to ozone, nitrogen dioxide, water vapor, hydroxyl and nitrate radicals. The model is based on multiple experimental studies of PAH degradation and on the PRA framework (Pöschl-Rudich-Ammann, 2007) for aerosol and cloud surface chemistry and gas-particle interactions. For a wide range of substrates, including solid and liquid organic and inorganic substances (soot, silica, sodium chloride, octanol/decanol, organic acids, etc.), the concentration- and time-dependence of the heterogeneous reaction between PAHs and O3 can be efficiently described with a Langmuir-Hinshelwood-type mechanism. Depending on the substrate material, the Langmuir adsorption constants for O3 vary over three orders of magnitude (Kads,O3 ? 10-15-10-13 cm3), and the second-order rate coefficients for the surface layer reaction of O3 with different PAH vary over two orders of magnitude (kSLR,PAH,O3 ? 10-18-10-17 cm2 s-1). The available data indicate that the Langmuir adsorption constants for NO2 are similar to those of O3, while those of H2O are several orders of magnitude smaller (Kads,H2O ? 10-18-10-17 cm3). The desorption lifetimes and adsorption enthalpies inferred from the Langmuir adsorption constants suggest chemisorption of NO2 and O3 and physisorption of H2O. Note, however, that the exact reaction mechanisms, rate limiting steps and possible intermediates still remain to be resolved (e.g., surface diffusion and formation of O atoms or O3- ions at the surface). The K2-SURF model enables the calculation of ozone uptake coefficients, ?O3, and of PAH concentrations in the quasi-static particle surface layer. Competitive adsorption and chemical transformation of the surface (aging) lead to a strong non-linear dependence of ?O3 on time and gas phase composition, with different characteristics under dilute atmospheric and concentrated laboratory conditions. Under typical ambient conditions, ?O3 of PAH-coated aerosol particles are expected to be in the range of 10-6-10-5. At ambient temperatures, NO2 alone does not efficiently degrade PAHs, but it was found to accelerate the degradation of PAHs exposed to O3. The accelerating effect can be attributed to highly reactive NO3 radicals formed in the gas phase or on the surface. Estimated second-order rate coefficients for O3-NO2 and PAH-NO3 surface layer reactions are in the range of 10-17-10-16 cm2 s-1 and 10-15-10-12 cm2 s-1, respectively. The chemical half-life of PAHs is expected to range from a few minutes on the surface of soot to multiple hours on organic and inorganic solid particles and days on liquid particles. On soot, the degradation of particle-bound PAHs in the atmosphere appears to be dominated by a surface layer reaction with adsorbed ozone. On other substrates, it is likely dominated by gas-surface reactions with OH or NO3 radicals (Eley-Rideal-type mechanism). To our knowledge, K2-SURF is the first atmospheric process model describing multiple types of parallel and sequential surface reactions between multiple gaseous and particle-bound chemical species. It illustrates how the general equations of the PRA framework can be simplified and adapted for specific reaction systems, and we suggest that it may serve as a basis for the development of a general master mechanism of aerosol and cloud surface chemistry.

Shiraiwa, M.; Garland, R. M.; Pöschl, U.

2009-12-01

24

Kinetic double-layer model of aerosol surface chemistry and gas-particle interactions (K2-SURF): Degradation of polycyclic aromatic hydrocarbons exposed to O3, NO2, H2O, OH and NO3  

NASA Astrophysics Data System (ADS)

We present a kinetic double-layer surface model (K2-SURF) that describes the degradation of polycyclic aromatic hydrocarbons (PAHs) on aerosol particles exposed to ozone, nitrogen dioxide, water vapor, hydroxyl and nitrate radicals [1]. The model is based on multiple experimental studies of PAH degradation and on the Pöschl-Rudich-Ammann (PRA) framework [2] for aerosol and cloud surface chemistry and gas-particle interactions. For a wide range of substrates, including solid and liquid organic and inorganic substances (soot, silica, sodium chloride, octanol/decanol, organic acids, etc.), the concentration- and time-dependence of the heterogeneous reaction between PAHs and O3 can be efficiently described with a Langmuir-Hinshelwood-type mechanism. Depending on the substrate material, the Langmuir adsorption constants for O3 vary over three orders of magnitude, and the second-order rate coefficients for the surface layer reaction of O3 with different PAH vary over two orders of magnitude. The available data indicate that the Langmuir adsorption constants for NO2 are similar to those of O3, while those of H2O are several orders of magnitude smaller. The desorption lifetimes and adsorption enthalpies suggest chemisorption of NO2 and O3 and physisorption of H2O. Note, however, that the exact reaction mechanisms, rate limiting steps and possible intermediates still remain to be resolved (e.g., surface diffusion and formation of O atoms or O3- ions at the surface). The K2-SURF model enables the calculation of ozone uptake coefficients, ?O3, and of PAH concentrations in the quasi-static particle surface layer. Competitive adsorption and chemical transformation of the surface (aging) lead to a strong non-linear dependence of ?O3 on time and gas phase composition, with different characteristics under dilute atmospheric and concentrated laboratory conditions. Under typical ambient conditions, ?O3 of PAH-coated aerosol particles are expected to be in the range of 10-6 - 10-5. At ambient temperatures, NO2 alone does not efficiently degrade PAHs, but it was found to accelerate the degradation of PAHs exposed to O3. The accelerating effect can be attributed to highly reactive NO3 radicals formed in the gas phase or on the surface. Estimated second-order rate coefficients for O3-NO2 and PAH-NO3 surface layer reactions are in the range of 10-17 - 10-16 cm2 s-1 and 10-15 - 10-12 cm2 s-1, respectively. The chemical half-life of PAHs is expected to range from a few minutes on the surface of soot to multiple hours on organic and inorganic solid particles and days on liquid particles. On soot, the degradation of particle-bound PAHs in the atmosphere appears to be dominated by a surface layer reaction with adsorbed ozone. On other substrates, it is likely dominated by gas-surface reactions with OH or NO3 radicals (Eley-Rideal-type mechanism). To our knowledge, K2-SURF is the first atmospheric process model describing multiple types of parallel and sequential surface reactions between multiple gaseous and particle-bound chemical species. It illustrates how the general equations of the PRA framework can be simplified and adapted for specific reaction systems. References: [1] Shiraiwa et al., Atmos. Chem. and Phys., 9, 9571-9586 (2009). [2] Pöschl et al., Atmos. Chem. and Phys., 7, 5989-6023 (2007).

Shiraiwa, Manabu; Garland, Rebecca M.; Pöschl, Ulrich

2010-05-01

25

Kinetic double-layer model of aerosol surface chemistry and gas-particle interactions (K2-SURF): degradation of polycyclic aromatic hydrocarbons exposed to O3, NO2, H2O, OH and NO3  

NASA Astrophysics Data System (ADS)

We present a kinetic double-layer surface model (K2-SURF) that describes the degradation of polycyclic aromatic hydrocarbons (PAHs) on aerosol particles exposed to ozone, nitrogen dioxide, water vapor, hydroxyl and nitrate radicals. The model is based on multiple experimental studies of PAH degradation and on the PRA framework (Pöschl et al., 2007) for aerosol and cloud surface chemistry and gas-particle interactions. For a wide range of substrates, including solid and liquid organic and inorganic substances (soot, silica, sodium chloride, octanol/decanol, organic acids, etc.), the concentration- and time-dependence of the heterogeneous reaction between PAHs and O3 can be efficiently described with a Langmuir-Hinshelwood-type mechanism. Depending on the substrate material, the Langmuir adsorption constants for O3 vary over three orders of magnitude (Kads,O3?10-15-10-13 cm3), and the second-order rate coefficients for the surface layer reaction of O3 with different PAH vary over two orders of magnitude (kSLR,PAH,O3?10-18-10-17 cm2 s-1). The available data indicate that the Langmuir adsorption constants for NO2 are similar to those of O3, while those of H2O are several orders of magnitude smaller (Kads,H2O?10-18-10-17 cm3). The desorption lifetimes and adsorption enthalpies inferred from the Langmuir adsorption constants suggest chemisorption of NO2 and O3 - possibly in the form of O atoms - and physisorption of H2O. The K2-SURF model enables the calculation of ozone uptake coefficients, ?O3, and of PAH concentrations in the quasi-static particle surface layer. Competitive adsorption and chemical transformation of the surface (aging) lead to a strong non-linear dependence of ?O3 on time and gas phase composition, with different characteristics under dilute atmospheric and concentrated laboratory conditions. Under typical ambient conditions, ?O3 of PAH-coated aerosol particles are expected to be in the range of 10-6-10-5. At ambient temperatures, NO2 alone does not efficiently degrade PAHs, but it was found to accelerate the degradation of PAHs exposed to O3. The accelerating effect can be attributed to highly reactive NO3 radicals formed in the gas phase or on the surface. Estimated second-order rate coefficients for O3-NO2 and PAH-NO3 surface layer reactions are in the range of 10-17-10-16 cm2 s-1 and 10-15-10-12 cm2 s-1, respectively. The chemical half-life of PAH is expected to range from a few minutes on the surface of soot to multiple hours on organic and inorganic solid particles and days on liquid particles. On soot, the degradation of particle-bound PAHs in the atmosphere appears to be dominated by a surface layer reaction with adsorbed ozone. On other substrates, it is likely dominated by gas-surface reactions with OH or NO3 radicals (Eley-Rideal-type mechanism). To our knowledge, K2-SURF is the first atmospheric process model describing multiple types of parallel and sequential surface reactions between multiple gaseous and particle-bound chemical species. It illustrates how the general equations of the PRA framework can be simplified and adapted for specific reaction systems, and we suggest that it may serve as a basis for the development of a general master mechanism of aerosol and cloud surface chemistry.

Shiraiwa, M.; Garland, R. M.; Pöschl, U.

2009-09-01

26

Layer-by-Layer Polymer Coating on Discrete Particles of Cubic Lyotropic Liquid Crystalline Dispersions (Cubosomes).  

PubMed

Cubic phase lyotropic liquid crystalline colloidal dispersions (cubosomes) were surface-modified with seven polyelectrolyte layers using a layer-by-layer (LbL) approach. The first layer consisted of a copolymer synthesized from methacrylic acid and oleoyl methacrylate for enhanced incorporation within the bilayer of the cubic nanostructure. Six additional layers of poly(l-lysine) and poly(methacrylic acid) were then sequentially added, followed by a washing procedure to remove polymer aggregates from the soft matter particles. Polymer buildup was monitored via microelectrophoresis, dynamic light scattering, and small-angle X-ray scattering. Polymer-coated cubosomes were observed with cryo-transmission electron microscopy. A potential application of the modified nanostructured particles presented in this study is to reduce the burst-release effect associated with drug-loaded cubosomes. The effectiveness of this approach was demonstrated through loading and release results from a model hydrophilic small molecule (fluorescein). PMID:24033086

Driever, Chantelle D; Mulet, Xavier; Waddington, Lynne J; Postma, Almar; Thissen, Helmut; Caruso, Frank; Drummond, Calum J

2013-10-08

27

Multicomponent double layers and selective acceleration of charged particles.  

National Technical Information Service (NTIS)

Multicomponent double layers, defined as layers composed of more than two kinds of charged particles, are supposed to constitute the predominant type of double layer in cosmic plasmas. A model of a steady and strong multicomponent double layer is studied ...

P. Carlqvist

1994-01-01

28

Polyelectrolyte adsorption layers studied by streaming potential and particle deposition.  

PubMed

Adsorption of a cationic polyelectrolyte, polyallylamine hydrochloride (PAH), having a molecular weight of 70,000 on mica was characterized by the streaming potential method and by deposition of negative polystyrene latex particles. Formation of PAH layers was followed by determining the apparent zeta potential of surface zeta as function of bulk PAH concentration. The zeta potential was calculated from the streaming potential measured in the parallel-plate channel formed by two mica plates precovered by the polyelectrolyte. The experimental data were expressed as the dependence of the reduced zeta potential zeta/zeta0 on the PAH coverage Theta(PAH), calculated using the convective diffusion theory. It was found that for the ionic strength of 10(-2) M, the dependence of zeta/zeta0 on Theta(PAH) can be reflected by the theoretical model formulated previously for surfaces covered by colloid particles. The electrokinetic measurements were complemented by particle deposition experiments on PAH-covered mica surfaces. A direct correlation between the polymer coverage and the initial deposition rate of particles, as well as the jamming coverage, was found. For ThetaPAH > 0.3 the initial deposition rate attained the value predicted from the convective diffusion theory for homogeneous surfaces. The initial deposition rates for surfaces modified by PAH were compared with previous experimental and theoretical results obtained for heterogeneous surfaces formed by preadsorption of colloid particles. It was revealed that negative latex deposition occurred at surfaces exhibiting negative apparent zeta potential, which explained the anomalous deposition of particles observed in previous works. It was suggested that the combined electrokinetic and particle deposition methods can be used for detecting adsorbed polyelectrolytes at surfaces for coverage range of a percent. This enables one to measure bulk polyelectrolyte concentrations at the level of 0.05 ppm. PMID:16949085

Adamczyk, Z; Zembala, M; Michna, A

2006-09-01

29

Layer-by-layer surface modification of lipid nanocapsules  

Microsoft Academic Search

Lipid nanocapsules (LNCs) were modified by adsorbing sequentially dextran sulfate (DS) and chitosan (CS) on their surface by the layer-by-layer (LBL) approach. Tangential flow filtration (TFF) was used in intermediate purifications of the LNC dispersion during the LBL process. The surface modification was based on electrostatic interactions between the coating polyelectrolytes (PEs) and the LNCs. Therefore, a cationic surfactant, lipochitosan

Samuli Hirsjärvi; Yan Qiao; Audrey Royere; Jérôme Bibette; Jean-Pierre Benoit

2010-01-01

30

Cloaking of 2D particle geometries in a surface medium  

NASA Astrophysics Data System (ADS)

We theoretically examine the cloaking condition for two-dimensional particles with varying geometry embedded inside a surface medium. General solutions are obtained for multi-layer particle configurations with either all positive or partially negative constitutive parameters respectively. Cloaking of particle geometries that are large relative to the incident wavelength is demonstrated. Theoretical predictions are compared to full-wave numerical simulations for arrays of particles consisting of different geometries.

Alexopoulos, A.; Yau, K. S. B.

2013-06-01

31

Distribution of elements in the surface layer of plasma-electrolytic coatings formed on titanium in electrolytes with MnO2 particles  

NASA Astrophysics Data System (ADS)

The influence of electrolytes (aqueous solutions of H2SO4, Na2SO3, and K2B4O7 (group I) and Na2SiO3 (group II)), as well as the effects of pores and ridges around them, on the element composition of oxide coatings was studied. The addition of MnO2 particles to electrolytes initiated the formation of large pores. The pores had increased titanium and decreased oxygen contents. Coatings I contained, on average, up to 1 at % Mn, and coatings II had up to 8 at % Mn; in the pores of II, the Mn concentration was increased to 18 at %. The coatings contained 7-28 at % carbon, which was concentrated in pores in I and on the surface of the oxide coating in II.

Rudnev, V. S.; Vasilyeva, M. S.; Nedozorov, P. M.; Korotenko, I. A.; Vaganov-Vil'Kins, A. A.

2011-10-01

32

Friction microprobe investigation of particle layer effects on sliding friction  

SciTech Connect

Interfacial particles (third-bodies), resulting from wear or external contamination, can alter and even dominate the frictional behavior of solid-solid sliding in the absence of effective particle removal processes (e.g., lubricant flow). A unique friction microprobe, developed at Oak Ridge National Laboratory, was used to conduct fine- scale friction studies using 1.0 mm diameter stainless steel spheres sliding on several sizes of loose layers of fine aluminum oxide powders on both aluminum and alumina surfaces. Conventional, pin-on-disk experiments were conducted to compare behavior with the friction microprobe results. The behavior of the relatively thick particle layers was found to be independent of the nature of underlying substrate, substantiating previous work by other investigators. The time-dependent behavior of friction, for a spherical macrocontact starting from rest, could generally be represented by a series of five rather distinct phases involving static compression, slider breakaway, transition to steady state, and dynamic layer instability. A friction model for the steady state condition, which incorporates lamellar powder layer behavior, is described.

Blau, P.J.

1993-01-01

33

Modification of surface layer of magnesium oxide via partial dissolution and re-growth of crystallites  

Microsoft Academic Search

A procedure to modify surface layer of metal oxide is presented. By way of partial dissolution and re-growth of crystallites, a new MgO surface layer on the “core” of the original MgO particles was formed. XRD analyses indicate that the new surface layer is different from the original MgO particles in crystallinity. Thus a higher reducibility of surface non-lattice oxygen

Zhiming Gao; Lingyan Wei; Tingting Yan; Ming Zhou

2011-01-01

34

Mercury: Remote Estimation of Surface Layer Structure  

NASA Astrophysics Data System (ADS)

Results of the optical observations of Mercury and the Moon confirm the close simi- larity of photometric properties of the bodies. Experience of lunar studies shows that space weathering processes on the Mercury (such as micrometeorite bombardment, solar wind ion bombardment etc.) can form properties of the upper layer of regolith. The amount of fused glassy particles and others agglutinates in the lunar upper layer is the direct index of the soil reworking caused be the micrometeorite bombardment. Besides, this micrometeorite bombardment is also responsible for the mechanical pro- cess through which the large particles are broken down into smaller ones. For lunar re- golith was showed that increasingly mature soils become progressively finer-grained, better-sorted, and composed of a greater proportion of agglutinates. The increasing rate of the fused glassy fragments, of agglutinates, and of fine size fraction in the regolith during its space weathering affects the polarization of the light reflected by an exposed lunar or Mercurian soil. Therefore, polarimetric properties of the regolith may be modified by the soil reworking process in the course of time. Comparison of the lunar and Mercurian optic observations confirms the remarkable similarity of the polarimetric properties of Mercury and the Moon. From of summary of polarization measurements of whole disk of Mercury it is possible to conclude that maturity of the soil on the Mercurian surface in scale of whole disk is similar to one in large old craters on the lunar highland. Comparison of the lunar and Mercurian disk-integrated photometric functions indicates the likeness of the surface layer structures of the bod- ies. Analysis of the phase curve inclination and magnitude of the opposition effect shows that Mercurian relief in scale of meter details is smoother than lunar one. It was measured brightness of number of small plots (10x10 cm) on the lunar surface (Luna-13 data). The range of phase angles was from 68 to 75 deg. These values close correlate with corresponding part of the Mercurian disk-integrated phase function. ItSs possible if Mercurian phase function received from Earth-based telescopes and lunar one received in cm-scale is coincided the structures of regolith may be similar in both cases. These conclusions may be used for planning BepiColombo mission. This work was supported by INTAS-ESA grant No. 99-00403.

Shevchenko, V. V.

35

New particle formation in the marine boundary layer  

SciTech Connect

Aerosol measurements were made in the marine boundary layer along the coast of Washington State during the Pacific Stratus Sulfur Investigation. On April 22 the particle concentration increased to levels much higher than usual for the clean marine boundary layer. The total particulate number concentration greater than 3 nm diameter increased rapidly from about 250 cm[sup [minus]3] to 3,200 cm[sup [minus]3], remained near that level for 7 hours, and then decreased over the next 2 hours to less than 400 cm[sup [minus]3]. The change could not be attributed to either local or distant contamination. Immediately before the increase particulate surface area concentration dropped from 25 [mu]m[sup 2] cm[sup [minus]3] to less than 5 [mu]m[sup 2] cm[sup [minus]3]. The SO[sub 2] concentration increased from about 20 pptv to 40-60 pptv just before the increase in particle concentration. While these measurements cannot distinguish between changes in number concentration caused by particle nucleation versus advection or vertical mixing, clearly there was recent or continuing particle production on a mesoscale in the air mass. Related aircraft measurements and model results support the hypothesis of new particle formation. These data provide evidence that at times high concentrations of new, ultrafine particles are formed at low SO[sub 2] concentrations under mareine conditions. This homogeneous nucleation, as opposed to heterogeneous condensation on existing particles, is strongly and inversely dependent on the concentration of existing particles. 19 refs., 4 figs.

Covert, D.S. (Univ. of Washington, Seattle (United States)); Kapustin, V.N. (Inst. of Atmospheric Physics, Moscow (Russian Federation)); Quinn, P.K.; Bates, T.S. (NOAA Pacific Marine Environmental Lab., Seattle, WA (United States))

1992-12-20

36

Effect of ice particles on the mesospheric potassium layer at Spitsbergen (78°N)  

Microsoft Academic Search

This paper quantitatively evaluates the influence of ice particles on the K layer by using radar and lidar measurements. The methodology involves determination of the volumetric surface area [Aice] of the ice particles in a noctilucent cloud by combining a microphysical ice particle model with a charging model to produce an empirical proxy for polar mesosphere summer echoes (PMSE) based

Shikha Raizada; Markus Rapp; F.-J. Lübken; J. Höffner; M. Zecha; J. M. C. Plane

2007-01-01

37

Layer-by-layer surface modification of lipid nanocapsules.  

PubMed

Lipid nanocapsules (LNCs) were modified by adsorbing sequentially dextran sulfate (DS) and chitosan (CS) on their surface by the layer-by-layer (LBL) approach. Tangential flow filtration (TFF) was used in intermediate purifications of the LNC dispersion during the LBL process. The surface modification was based on electrostatic interactions between the coating polyelectrolytes (PEs) and the LNCs. Therefore, a cationic surfactant, lipochitosan (LC), was synthesised by coupling stearic anhydride on chitosan, and the surface of LNCs was first modified by this LC by the post-insertion technique. The PEs could be successfully adsorbed on the LNC surface as verified by alternating zeta potential and increase in size. To present a therapeutic application, fondaparinux sodium (FP), a heparin-like synthetic pentasaccharide, was introduced on the LNC surface instead of DS. PMID:20656028

Hirsjärvi, Samuli; Qiao, Yan; Royere, Audrey; Bibette, Jérôme; Benoit, Jean-Pierre

2010-07-23

38

Correlation studies on surface particle detection methods  

NASA Astrophysics Data System (ADS)

The accurate determination of dust levels on optical surfaces is necessary to assess sensor system performance. A comparison study was made on several particle measurement methods including those based on direct imaging and light scattering. The effectiveness of removing the particles from the surface prior to determining partice size distributions was also assessed. These studies revealed that some methods, especially those requiring particle removal before analysis, are subject to large systematic errors affecting particle size distributions. Thus, an understanding of the particle measurement methods employed is necessary before any surface cleanliness or obstruction value assignments are accepted as a true representation of an optical surface contamination condition.

Peterson, Ronald V.; White, James C., II

1990-04-01

39

Calcium phosphate composite layers for surface-mediated gene transfer.  

PubMed

In this review, the surface-mediated gene transfer system using calcium phosphate composite layers is described. Calcium phosphate ceramics are osteoconductive bioceramics used typically in orthopedic and dental applications. Additionally, calcium phosphate particles precipitated by a liquid-phase process have long been used as a safe and biocompatible transfection reagent in molecular biology. Recently, calcium phosphate composite layers immobilizing DNA were fabricated on the surfaces of base materials through a biomimetic process using supersaturated solutions. These composite layers possess useful characteristics of both osteoconductive bioceramics and transfection reagents; they thus provide a biocompatible surface to support cell adhesion and growth, and can stimulate the cell effectively via surface-mediated gene transfer. By modifying the fabrication conditions, physicochemical and biological properties of the composite layers can be varied. With such an approach, these composite layers can be designed to have improved affinity for cells and to exhibit increased gene transfer efficiency over that of conventional lipid transfection reagents. The composite layers with the increased gene transfer efficiency induced specific cell differentiation and tissue regeneration in vivo. These composite layers, given their good biocompatibility and the potential to control cell behavior on their surfaces, have great potential in tissue engineering applications. PMID:22343517

Oyane, Ayako; Wang, Xiupeng; Sogo, Yu; Ito, Atsuo; Tsurushima, Hideo

2012-02-17

40

Turbulent boundary layer on a moving surface  

Microsoft Academic Search

An integral and a numerical method are proposed for calculating the turbulent boundary layer on a moving surface (flap) in the presence of a longitudinal pressure gradient under conditions of monotonic velocity profiles. The integral method is a modification of Fediaevskii's et al. (1973) integral method (for calculating turbulent boundary layers in an incompressible fluid) to include an airfoil moving

A. S. Ginevskii; G. N. Emalianova; A. V. Kolesnikov

1976-01-01

41

Concentration-elastic-stress instabilities in the distribution of ions and neutral particles in the insulator layer at the semiconductor surface  

SciTech Connect

Mobile impurities in the form of ions and neutral associations are present in the insulator films that isolate the semiconductor from the metal electrode. If temperatures and the polarizing electric field are sufficiently high, impurities concentrate at the insulator-semiconductor interface where they exchange electrons with the semiconductor. It is shown that the pairwise interaction of particles via the field of elastic stresses caused by the concentration-related expansion of the insulator can give rise to an instability in the impurity distribution that is uniform over the contact. The stationary small-scale ordering of the particles over the contact of the insulator with the semiconductor arises in the solution of point defects, which is accompanied by annular flows of the particles.

Gol'dman, E. I. [Russian Academy of Sciences, Institute of Radio Engineering and Electronics (Fryazino Branch) (Russian Federation)], E-mail: gvc@ms.ire.rssi.ru

2006-10-15

42

Modeling impact cratering in layered surfaces  

Microsoft Academic Search

Impact craters are potentially powerful tools for probing large-scale structure beneath planetary surfaces. However, the details of how target structure affects the impact cratering process and final crater forms remain poorly understood. Here, we present a study of cratering in layered surfaces using numerical simulations. We implement the rheologic model for geologic materials described by Collins et al. (2004) into

Laurel E. Senft; Sarah T. Stewart

2007-01-01

43

Surface layer characterization at Paranal Observatory  

NASA Astrophysics Data System (ADS)

In this paper the Paranal Surface Layer characterization is presented. Causes, physics and behavior of the SL above Paranal surface are discussed. The analysis is developed using data from different turbulence profilers operated during several campaigns between 2007 and 2009. Instruments used are SL-SLODAR, DIMM, Elevated DIMM, MASS, Lunar Scintillometer and Ultrasonic Anemometers with temperature sensors positioned at different strategic heights.

Lombardi, G.; Melnick, J.; Hinojosa Goñi, R. H.; Navarrete, J.; Sarazin, M.; Berdja, A.; Tokovinin, A.; Wilson, R.; Osborn, J.; Butterley, T.; Shepherd, H.

2010-07-01

44

Using particles to sample and control implicit surfaces  

Microsoft Academic Search

We present a new particle-based approach to sampling and controlling implicit surfaces. A simple constraint locks a set of particles onto a surface while the particles and the surface move. We use the constraint to make surfaces follow particles, and to make particles follow surfaces. We implement control points for direct manipulation by specifying particle motions, then solving for surface

Andrew P. Witkin; Paul S. Heckbert

2005-01-01

45

Using particles to sample and control implicit surfaces  

Microsoft Academic Search

We present a new particle-based approach to sampling and controlling implicit surfaces. A simple constraint locks a set of particles onto a surface while the particles and the surface move. We use the constraint to make surfaces follow particles, and to make particles follow surfaces. We implement control points for direct manipulation by specifying particle motions, then solving for surface

Andrew P. Witkin; Paul S. Heckbert

1994-01-01

46

Limiting diffusion current at rotating disk electrode with dense particle layer  

NASA Astrophysics Data System (ADS)

Exploiting the concept of diffusion permeability of multilayer gel membrane and porous multilayer we have derived a simple analytical equation for the limiting diffusion current at rotating disk electrode (RDE) covered by a thin layer with variable tortuosity and porosity, under the assumption of negligible convection in the porous film. The variation of limiting diffusion current with the porosity and tortuosity of the film can be described in terms of the equivalent thickness of stagnant solution layer, i.e., the average ratio of squared tortuosity to porosity. In case of monolayer of monodisperse spherical particles, the equivalent layer thickness is an algebraic function of the surface coverage. Thus, by means of cyclic voltammetry of RDE with a deposited particle monolayer we can determine the monolayer surface coverage. The effect of particle layer adsorbed on the surface of RDE increases non-linearly with surface coverage. We have tested our theoretical results experimentally by means of cyclic voltammetry measurements of limiting diffusion current at the glassy carbon RDE covered with a monolayer of 3 ?m silica particles. The theoretical and experimental results are in a good agreement at the surface coverage higher than 0.7. This result suggests that convection in a monolayer of 3 ?m monodisperse spherical particles is negligibly small, in the context of the coverage determination, in the range of very dense particle layers.

Wero?ski, P.; Nosek, M.; Batys, P.

2013-09-01

47

Paracrystalline surface layers of dairy propionibacteria.  

PubMed Central

We examined 70 dairy propionibacteria and detected a crystalline surface layer (S-layer) in only 2 organisms (Propionibacterium freudenreichii CNRZ 722 and Propionibacterium jensenii CNRZ 87) by freeze-etching and sodium dodecyl sulfate-polyacrylamide electrophoresis (SDS-PAGE). Both S-layers exhibited oblique (p2) symmetry (a = 9.9 nm; b = 5.4 nm; gamma = 80 degrees) and completely covered the cell surface. Treatment for 15 min at the ambient temperature with 5 M guanidine hydrochloride or acidic conditions (250 mM ammonium acetate, pH 2.7) efficiently extracted the S-layer protein from intact cells of strain CNRZ 722, whereas treatment with 5 M guanidine hydrochloride at 100 degrees C for 15 min was necessary to isolate the S-layer protein of strain CNRZ 87. The precipitates obtained after dialysis of the extracting agents produced no regular patterns. The molecular masses of the two S-layer proteins, as estimated by SDS-PAGE, were 58.5 kDa for the strain CNRZ 722 and 67.3 kDa for the strain CNRZ 87. Mass spectrometry of the isolated S-layer protein of strain CNRZ 722 gave a molecular mass value close to the expected value (56,533 Da). The N-terminal sequences of the two purified S-layer proteins differed, as did their amino acid compositions, except that the same high hydrophobic amino acid content (52%) was observed. Images

Lortal, S; Rouault, A; Cesselin, B; Sleytr, U B

1993-01-01

48

Faulted surface layers in dysprosium silicide nanowires  

NASA Astrophysics Data System (ADS)

The crystallography and microstructure of epitaxial dysprosium silicide nanowires on Si(001) have been studied using high-resolution transmission electron microscopy. Islands grown at 750°C have a compact three-dimensional shape and are identified as hexagonal DySi2 . Islands grown at 650°C have an elongated nanowire (NW) shape. They contain one or two layers of hexagonal silicide at the buried interface and two to three surface layers with faulted stacking similar to tetragonal DySi2 . The faulted layers are believed to provide stress relief during growth of the coherently strained NW islands.

He, Zhian; Smith, David J.; Bennett, P. A.

2004-12-01

49

Introduction of Coating Technology of Superfine Particle Surface  

NASA Astrophysics Data System (ADS)

With the fast development of new materials investigation, attention is paid to. The performance of superfine powders, which must be modified on the surface to acquire some points. Coating technology of particles is one especial method of surface modification. In this paper, coating methods of particles are classified into solid state, liquid state, and gaseous state, main methods and mechanisms during current time are reviewed, respectively, and some research examples are listed. The choice of diversified coating technologies is decided synthetically based on powder materials, performance of the modified substance, and application of coated powders. In the future, the researches of the core-shell modification mechanism, coated particles with an ordered arrangement coating layer, a new surface active agent, the facilities of suiting surface modification, and the evaluation methodology of the surface coating effect are very exigent and necessary for the preparation and application of superfine powders.

Song, Jieguang; Zhang, Lianmeng; Li, Junguo; Song, Jianrong

50

Extending the Diffuse Layer Model of Surface Acidity Constant Behavior: IV. Diffuse Layer Charge/Potential Relationships  

EPA Science Inventory

Most current electrostatic surface complexation models describing ionic binding at the particle/water interface rely on the use of Poisson - Boltzmann (PB) theory for relating diffuse layer charge densities to diffuse layer electrostatic potentials. PB theory is known to contain ...

51

Surface Temperature and Surface-Layer Turbulence in a Convective Boundary Layer  

NASA Astrophysics Data System (ADS)

Previous laboratory and atmospheric experiments have shown that turbulence influences the surface temperature in a convective boundary layer. The main objective of this study is to examine land-atmosphere coupled heat transport mechanism for different stability conditions. High frequency infrared imagery and sonic anemometer measurements were obtained during the boundary layer late afternoon and sunset turbulence (BLLAST) experimental campaign. Temporal turbulence data in the surface-layer are then analyzed jointly with spatial surface-temperature imagery. The surface-temperature structures (identified using surface-temperature fluctuations) are strongly linked to atmospheric turbulence as manifested in several findings. The surface-temperature coherent structures move at an advection speed similar to the upper surface-layer or mixed-layer wind speed, with a decreasing trend with increase in stability. Also, with increasing instability the streamwise surface-temperature structure size decreases and the structures become more circular. The sequencing of surface- and air-temperature patterns is further examined through conditional averaging. Surface heating causes the initiation of warm ejection events followed by cold sweep events that result in surface cooling. The ejection events occur about 25 % of the time, but account for 60-70 % of the total sensible heat flux and cause fluctuations of up to 30 % in the ground heat flux. Cross-correlation analysis between air and surface temperature confirms the validity of a scalar footprint model.

Garai, Anirban; Pardyjak, Eric; Steeneveld, Gert-Jan; Kleissl, Jan

2013-03-01

52

Saltating Particles in a Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

Experiments on aeolian sand transport were carried out in a wind tunnel at the University of Aarhus in Denmark for a wide range of wind speeds. The saltating particles were analyzed using imaging techniques (PIV and PTV). Vertical profiles of particle concentration and velocity were extracted. The particle concentration was found to decrease exponentially with the height above the bed and the characteristic decay height was independent of the wind speed [1]. In contrast with the logarithmic profile of the wind speed, the particle velocity was found to vary linearly with the height. In addition, the particle slip velocity is finite and invariant with the wind speed. These results are shown to be closely related to the features of the splash function that characterizes the impact of the saltating particles onto a sand bed. A numerical simulation was developed that explicitly incorporates low velocity moments of the splash function in a calculation of the boundary conditions that apply at the bed [1]. The overall features of the experimental measurements are well reproduced by the simulation.

Valance, A.; El Moctar, A. Ould; Dupont, P.; Cantat, I.; Jenkins, J. T.

2010-05-01

53

Diffusion in the Diabatic Surface Layer  

Microsoft Academic Search

Diffusion from point and line sources in an adiabatic surface layer were briefly discussed using a similarity method by Ellison, following a suggestion made at the 1058 Ox- ford Symposium by Batchclot. The chief result is that the ground concentration at a down- wind distance x, from a point source at ground level, is found to be proportional to x'%

F. A. Gifford

1962-01-01

54

Charged particles constrained to a curved surface  

NASA Astrophysics Data System (ADS)

We study the motion of charged particles constrained to arbitrary two-dimensional curved surfaces but interacting in three-dimensional space via the Coulomb potential. To speed up the interaction calculations, we use the parallel compute capability of the Compute Unified Device Architecture of today's graphics boards. The particles and the curved surfaces are shown using the Open Graphics Library. This paper is intended to give graduate students, who have basic experiences with electrostatics and the Lagrangian formalism, a deeper understanding of charged particle interactions and a short introduction of how to handle a many particle system using parallel computing on a single home computer.

Müller, Thomas; Frauendiener, Jörg

2013-01-01

55

Polymer surface treatment with particle beams  

DOEpatents

A polymer surface and near surface treatment process produced by irradiation with high energy particle beams is disclosed. The process is preferably implemented with pulsed ion beams. The process alters the chemical and mechanical properties of the polymer surface in a manner useful for a wide range of commercial applications. 16 figs.

Stinnett, R.W.; VanDevender, J.P.

1999-05-04

56

Transition induced by fixed and freely convecting spherical particles in laminar boundary layers  

NASA Astrophysics Data System (ADS)

An experimental and analytical study of aspects of transition induced by disturbances from spherical particles in laminar boundary layers is discussed. The generation of turbulent wedges by fixed spherical particles in a laminar boundary layer on or near the surface of a flat plate is considered experimentally using flow visualization with fluorescent dye and laser Doppler velocimetry. Turbulent spots generated by freely convecting spherical particles that are released in the freestream to fall into a flat plate laminar boundary layer and impact the plate are also discussed. A combination of dye flow visualization and a video based particle tracking technique was used to study the convecting particle problem. Although the Reynolds number at the critical condition for turbulent wedge generation by fixed particles and turbulent spot generation by convecting particles are similar, transition in these two situations appears to be fundamentally different. The development of a turbulent wedge near the critical condition is a relatively gradual process. In contrast, turbulent spots form relatively quickly after the convecting particles enter the boundary layer and impact the plate. Turbulent wedge formation downstream of a fixed particle results from the destabilization of the near wall flow by the vortical structures shed into particle wake. This shedding process is dominated by periodically shed loop shaped hairpin vortices. Observation of subharmonic oscillations at 1/2 and 1/4 of this shedding frequency suggest that a chaotic route to turbulence by a series of period doubling bifurcations is possible.

Petrie, H. L.; Morris, P. J.; Bajwa, A. R.; Vincent, D. C.

1993-08-01

57

Hygroscopic behavior and liquid-layer composition of aerosol particles generated from natural and artificial seawater  

NASA Astrophysics Data System (ADS)

Sea-salt aerosol (SSA) particles affect the Earth's radiative balance and moderate heterogeneous chemistry in the marine boundary layer. Using conventional and environmental transmission electron microscopes (ETEM), we investigated the hygroscopic growth and liquid-layer compositions of particles generated from three types of aqueous salt solutions: sodium chloride, laboratory-synthesized seawater (S-SSA particles), and natural seawater (N-SSA particles). Three levels of morphological change were observed with the ETEM as the laboratory-generated particles were exposed to increasing relative humidity (RH). The first level, onset of observable morphological changes, occurred on average at 70, 48, and 35% RH for the NaCl, S-SSA, and N-SSA particles, respectively. The second level, rounding, occurred at 74, 66, and 57% RH for NaCl, S-SSA, and N-SSA particles, respectively. The third level, complete deliquescence, occurred at 75% RH for all particles. Collected ambient SSA particles were also examined. With the exception of deliquescence, they did not exhibit the same hygroscopic characteristics as the NaCl particles. The ambient particles, however, behaved most similarly to the synthesized and natural SSA particles, although the onset of morphological change was slightly higher for the S-SSA particles. We used energy-dispersive X-ray spectrometry to study the composition of the liquid layer formed on the S-SSA and N-SSA particles. The layer was enriched in Mg, S, and O relative to the solid particle core. An important implication of these results is that MgSO4-enriched solutions on the surface of SSA particles may be the solvents of many heterogeneous reactions.

Wise, Matthew E.; Freney, Evelyn J.; Tyree, Corey A.; Allen, Jonathan O.; Martin, Scot T.; Russell, Lynn M.; Buseck, Peter R.

2009-02-01

58

Particle deposition and layer formation at the crossflow microfiltration  

Microsoft Academic Search

A microscopic model of the layer formation and the cake growth at the crossflow microfiltration will be introduced. The model considers the hydrodynamic, adhesive and friction forces acting on a single particle during the filtration process. It can be shown that mainly the balance between the lift force and the drag force of the filtrate flow determines the layer formation

Justus Altmann; Siegfried Ripperger

1997-01-01

59

Spontaneous dispersion of particles on liquid surfaces  

PubMed Central

When small particles (e.g., flour, pollen, etc.) come in contact with a liquid surface, they immediately disperse. The dispersion can occur so quickly that it appears explosive, especially for small particles on the surface of mobile liquids like water. This explosive dispersion is the consequence of capillary force pulling particles into the interface causing them to accelerate to a relatively large velocity. The maximum velocity increases with decreasing particle size; for nanometer-sized particles (e.g., viruses and proteins), the velocity on an air-water interface can be as large as ?47 m/s. We also show that particles oscillate at a relatively high frequency about their floating equilibrium before coming to stop under viscous drag. The observed dispersion is a result of strong repulsive hydrodynamic forces that arise because of these oscillations.

Singh, Pushpendra; Joseph, Daniel D.; Gurupatham, Sathish K.; Dalal, Bhavin; Nudurupati, Sai

2009-01-01

60

Electronic structure of bacterial surface protein layers  

NASA Astrophysics Data System (ADS)

We report an approach for the calculation of the electronic density of states of the dried two-dimensional crystalline surface protein layer ( S layer) of the bacterium Bacillus sphaericus NCTC 9602. The proposed model is based on the consideration of individual amino acids in the corresponding conformation of the peptide chain which additively contribute to the electronic structure of the entire protein complex. The derived results agree well with the experimental data obtained by means of photoemission (PE), resonant PE, and near-edge x-ray absorption spectroscopy.

Maslyuk, Volodymyr V.; Mertig, Ingrid; Bredow, Thomas; Mertig, Michael; Vyalikh, Denis V.; Molodtsov, Serguei L.

2008-01-01

61

Electronic structure of bacterial surface protein layers  

SciTech Connect

We report an approach for the calculation of the electronic density of states of the dried two-dimensional crystalline surface protein layer (S layer) of the bacterium Bacillus sphaericus NCTC 9602. The proposed model is based on the consideration of individual amino acids in the corresponding conformation of the peptide chain which additively contribute to the electronic structure of the entire protein complex. The derived results agree well with the experimental data obtained by means of photoemission (PE), resonant PE, and near-edge x-ray absorption spectroscopy.

Maslyuk, Volodymyr V.; Mertig, Ingrid; Bredow, Thomas; Mertig, Michael; Vyalikh, Denis V.; Molodtsov, Serguei L. [Martin-Luther-Universitaet Halle-Wittenberg, Fachbereich Physik, D-06099 Halle (Germany); Institut fuer Physikalische und Theoretische Chemie, Universitaet Bonn, D-53115 Bonn (Germany); Max-Bergmann-Zentrum fuer Biomaterialien, Technische Universitaet Dresden, D-01062 Dresden (Germany); Institut fuer Festkoerperphysik, Technische Universitaet Dresden, D-01062 Dresden (Germany)

2008-01-15

62

Chalk-Ex—Fate of CaCO3 particles in the mixed layer: Evolution of patch optical properties  

Microsoft Academic Search

The fate of particles in the mixed layer is of great relevance to the global carbon cycle as well as to the propagation of light in the sea. We conducted four manipulative field experiments called “Chalk-Ex” in which known quantities of uniform, calcium carbonate particles were injected into the surface mixed layer. Since the production term for these patches was

W. M. Balch; A. J. Plueddeman; B. C. Bowler; D. T. Drapeau

2009-01-01

63

Resuspension onset and crater erosion by a vortex ring interacting with a particle layer  

NASA Astrophysics Data System (ADS)

This paper presents results from an experimental investigation of the interaction of a vortex ring with a particle layer. The flow dynamics during the onset of particle resuspension are analysed using particle image velocimetry, while a light attenuation method provides accurate measurements of the final eroded crater shape. This work is a continuation of the research described in R. J. Munro, N. Bethke, and S. B. Dalziel, ``Sediment resuspension and erosion by vortex rings,'' Phys. Fluids 21, 046601 (2009), which focussed on the general resuspension onset dynamics and initial crater formation. Here, we analyse the velocity induced by the vortex ring on the particle layer surface during the resuspension of particles for different particle sizes, and the shape and size of the final craters that are formed by the impact of the vortex ring. We find that the boundary condition is characterised by a quasi-slip velocity at the particle layer surface, independent of the particle size. The particle diameter, and thus bed permeability, is found to have a significant effect on the final crater characteristics.

Bethke, N.; Dalziel, S. B.

2012-06-01

64

Numerical Modelling of Saltation in the Atmospheric Surface Layer  

NASA Astrophysics Data System (ADS)

A numerical model is developed to study the hopping motion of sand grains (saltation) in neutral atmospheric surface layers. Saltation is considered as a self-limiting process governed by the interaction of four components: aerodynamic entrainment, particle motion, splash entrainment and wind modification. The model comprises a large eddy simulation model for atmospheric surface-layer flows, a Lagrangian model for particle trajectories and a statistical description for aerodynamic entrainment and splash entrainment. The numerical simulation is focused on the aspects of saltation that are not well understood from experimental studies, including the role of splash, the evolution of wind and momentum flux profiles, and the effective roughness length, z 0s . It is shown that for splash to be effective, the surface friction velocity must exceed a critical value for a given particle size. The numerically estimated z 0s is compared with the analytical model of Raupach and the experimental data of Gillette et al. The model is also used to calculate the streamwise sand drift and the numerical results found to be in agreement with the existing wind-tunnel measurements.

Shao, Yaping; Li, An

65

Frictional forces between hydrophilic and hydrophobic particle coated nanostructured surfaces.  

PubMed

Friction forces have long been associated with the famous Amontons' rule that states that the friction force is linearly dependent on the applied normal load, with the proportionality constant being known as the friction coefficient. Amontons' rule is however purely phenomenological and does not in itself provide any information on why the friction coefficient is different for different material combinations. In this study, friction forces between a colloidal probe and nanostructured particle coated surfaces in an aqueous environment exhibiting different roughness length scales were measured by utilizing the atomic force microscope (AFM). The chemistry of the surfaces and the probe was varied between hydrophilic silica and hydrophobized silica. For hydrophilic silica surfaces, the friction coefficient was significantly higher for the particle coated surfaces than on the flat reference surface. All the particle coated surfaces exhibited similar friction coefficients, from which it may be concluded that the surface geometry, and not the roughness amplitude per se, influenced the measured friction. During measurements with hydrophobic surfaces, strong adhesive forces related to the formation of a bridging air cavity were evident from both normal force and friction force measurements. In contrast to the frictional forces between the hydrophilic surfaces, the friction coefficient for hydrophobic surfaces was found to depend on the surface structure and we believe that this dependence is related to the restricted movement of the three-phase line of the bridging air cavity. For measurements using a hydrophobic surface and a hydrophilic probe, the friction coefficient was significantly smaller compared to the two homogeneous systems. A layer of air or air bubbles on the hydrophobic surface working as a lubricating layer is a possible mechanism behind this observation. PMID:24056733

Hansson, Petra M; Claesson, Per M; Swerin, Agne; Briscoe, Wuge H; Schoelkopf, Joachim; Gane, Patrick A C; Thormann, Esben

2013-10-01

66

Microthermal Instrument for Measuring Surface Layer Seeing  

NASA Astrophysics Data System (ADS)

Microthermal fluctuations are introduced by atmospheric turbulence very near the ground. In order to detect microthermal fluctuations at Fuxian Solar Observatory (FSO), a microthermal instrument has been developed. The microthermal instrument consists of a microthermal sensor, which is based on a Wheatstone bridge circuit and uses fine tungsten filaments as resistance temperature detectors, an associated signal processing unit, and a data collection, & communication subsystem. In this paper, after a brief introduction to surface layer seeing, we discuss the instrumentation behind the microthermal detector we have developed and then present the results obtained. The results of the evaluation indicate that the effect of the turbulent surface boundary layer to astronomical seeing would become sufficiently small when installing a telescope at a height of 16m or higher from the ground at FSO.

Li, Xue-Bao; Zheng, Yan-Fang; Deng, Lin Hua; Xu, Guang

2012-02-01

67

Turbulent Boundary Layers on Rough Surfaces  

Microsoft Academic Search

The incompressible zero-pressure-gradient turbulent boundary layers on rough surface are investigated in light of the effects of the Reynolds number and roughness. The experimental data from various researchers were collected and analyzed. The true asymptotic profile (self-preserving solution) for the outer flow is found when the profiles are normalized by the Zagarola\\/Smits (1998) scaling, U_? delta\\/delta. This scaling successfully remove

Junghwa Seo; Luciano Castillo

2003-01-01

68

Electrorotation of colloidal particles and cells depends on surface charge.  

PubMed Central

The importance of surface conductivity to the frequency-dependent polarizability and the rotation of particles in circular electric fields (electrorotation) is emphasized by various theoretical and experimental investigations. Although surface conductivity seems to be naturally related to the ionic double layer, there is rare experimental evidence of a direct relationship. To highlight the role of surface charges in electrorotation, an apparatus was developed with a symmetrical three-electrode arrangement for field frequencies between 25 Hz and 80 MHz. The three-dimensional electrostatic field distribution between the electrodes was evaluated numerically. With this device, rotating, gradient, and homogeneous electric fields of defined precision and homogeneity could be applied to slightly conducting suspensions. Surface properties of monodisperse latex particles (O 9.67 microm), carrying weak acid groups, were characterized by suspension conductometric titration. This procedure determined the amount of carboxyl groups and showed that strong acid groups were missing on the surface of these particles. To obtain the electrophoretic mobility, the spheres were separated by free-flow electrophoresis, and the zeta-potential was calculated from these data. Single-particle rotation experiments on fractions of specified electrophoretic mobility were carried out at frequencies between 25 Hz and 20 MHz. By analyzing the pH dependence of the rotation velocity, it could be shown that the rotation rate is determined by surface charges, both at the peak in rotation rate near the Maxwell-Wagner frequency (MWF) and at low frequencies. The inversion of the rotation direction at the MWF peak for vanishing surface charges was demonstrated. An analytical model for the double layer and dissociation on a charged surface was developed that is valid for low and high zeta-potentials. This model could provide convincing evidence of the linear dependence of the MWF rotation velocity on surface charge. Images FIGURE 1

Maier, H

1997-01-01

69

Charged grafted polymer layers: Interactions, particle adsorption, and phase behavior  

Microsoft Academic Search

Three different model systems involving grafted charged polymer layers have been studied. In the first chapter, the interactions between charged surfaces and surfaces with grafted polymers with a functional charged group have been studied using a molecular theory. We have studied the ability to control the range and strength of the interactions by changing the polymer chain length, surface coverage,

Peng Gong

2006-01-01

70

How to affect number, size, and location of metal particles deposited in conducting polymer layers  

Microsoft Academic Search

This paper presents a review on a series of recent investigations focused on the understanding of the role of various factors\\u000a for the number, size, and location of the metal particles electrodeposited in conducting polymer (CP) layers. It is demonstrated\\u000a that the initial oxidation state of the CP layer and its surface and bulk structure play an important role for

V. Tsakova

2008-01-01

71

Direct observation of particle deposition on the membrane surface during crossflow microfiltration  

Microsoft Academic Search

In the crossflow microfiltration of particles, a deposit cake layer tends to form on the membrane and this usually controls the performance of the filtration process. This paper presents observations of particle deposition on membrane surfaces using a non-invasive, in situ, continuous direct observation through the membrane (DOTM) technique. The particles used in the experiments were typical of microfiltration processes,

H. Li; A. G. Fane; H. G. L. Coster; S. Vigneswaran

1998-01-01

72

Rebound characteristics for ash particles impacting a planar surface  

NASA Astrophysics Data System (ADS)

The formation of ash deposition on the heat transfer tubes in a boiler reduces the heat transfer coefficient by about 25%. Because of these fouling layers, the efficiency with which energy can be absorbed from flue gases is reduced. The growth of ash deposition is strongly dependent on the interaction of the incident particle with the surface of heat transfer tubes. In this study the interaction is modeled as the outcome of collision between an incident fly ash particle and planar surface that represents a heat transfer surface. The present paper focuses on the applicability of the experimental results to indicate the rebound characteristics of fly ash particles impacting a planar surface. This is studied by impaction experiments of fly ash particles from the power plant dust, under various particle diameters and with different velocities (ranging from 0.1 to 20 m/s). The experiments are carried out in an atmospheric column, and using a digital camera system, individual impacts are recorded. Furthermore, the measured coefficient of restitution values can be predicted by a dynamic simulation model.

Dong, Ming; Li, Sufen; Han, Jian; Xie, Jun

2013-06-01

73

Surface electron accumulation layers in oxide semiconductors  

NASA Astrophysics Data System (ADS)

In contrast to the electron depletion at the surface of almost all n-type semiconductors, electron accumulation has long been known to be observable at ZnO surfaces. It has recently been found to be a characteric of several other oxide semiconductors, including CdO [1,2], In2O3 [3] and SnO2. They all have a significant size and electronegativity mismatch between their cation and anion. As a result, they have a particularly low ?-point conduction band minimum which is ultimately responsible for the propensity for electron accumulation. In addition to the mere existence of an electron-rich surface layer, it has been found, using angle-resolved photoemission spectroscopy (ARPES), to be quantized into two dimensional subbands [1]. Moreover, the conventional one-electron picture of surface space-charge in semiconductors is shown to be inconsistent with the electronic structure that we observe directly from ARPES, indicating that many-body interactions play a large role in the surface electronic properties of these semiconductors. Such interactions lead to a depth-dependent shrinkage of the semiconductor band gap, resulting in a surface band gap which differs from the bulk value [1]. The most recent studies have focussed on the influence of depositing alkali metals onto the surface of these semiconductors. Many collaborators are acknowledged for samples and ARPES expertise.[4pt] [1] P. D. C. King, T. D. Veal et al., Phys. Rev. Lett. 104, 256803 (2010)[0pt] [2] P. D. C. King, T. D. Veal et al., Phys. Rev. B 79, 035203 (2009)[0pt] [3] P. D. C. King, T. D. Veal et al., Phys. Rev. Lett. 101, 116808 (2008)

Veal, Tim

2013-03-01

74

Layered surface fluid simulation for surgical training.  

PubMed

We present a novel approach to fluid simulation over complex dynamic geometry designed for the specific context of virtual surgery simulation. The method combines a surface-based fluid simulation model with a multi-layer depth peeling representation to allow realistic yet efficient simulation of bleeding on complex surfaces undergoing geometry and topology modifications. Our implementation allows for fast fluid propagation and accumulation over the entire scene, and runs on the GPU at a constant low cost that is independent of the amount of blood in the scene. The proposed bleeding simulation is integrated in a complete simulator for brain tumor resection, where trainees have to manage blood aspiration and tissue/vessel cauterization while they perform virtual surgery tasks. PMID:22003633

Borgeat, Louis; Massicotte, Philippe; Poirier, Guillaume; Godin, Guy

2011-01-01

75

Correlative surface analysis studies of environmental particles  

SciTech Connect

Various surface analysis techniques (scanning electron microscopy/energy dispersive X-ray microanalysis (SEM/EDX), electron spectroscopy for chemical analysis (ESCA), and secondary ion mass spectrometry (SIMS)) were evaluated in a correlative regimen for the chemical characterization of particulate pollutants. Analytical capabilities were demonstrated by using particles derived from steel blast furnaces. The ESCA studies of ''bottom ashes'' suggest highly water-soluble species enriched in sulfates on particles consisting primarily of iron oxides. Comparisons of SEM/EDX and SIMS data for selected metals (e.g., Cr, Cu, Fe, Mn, Mo, Pb, and Zn) in unleached and water-leached particles were used to estimate the extent of enrichment and aqueous solubility of surface species. Accessibility to the environment (via washout, rainout, groundwater leaching, lung fluids, etc.) is governed by both metal surface accessibility (extent of surface enrichment) and metal surface solubility (surface speciation). The unique combination of direct surface analysis and time-resolved solvent leaching experiments enables the relative importance of the two factors to be estimated for individual elements of environmental interest. 26 references.

Farmer, M.E.; Linton, R.W.

1984-05-01

76

The contribution of boundary layer nucleation events to total particle concentrations on regional and global scales  

NASA Astrophysics Data System (ADS)

The contribution of boundary layer (BL) nucleation events to total particle concentrations on the global scale has been studied by including a new particle formation mechanism in a global aerosol microphysics model. The mechanism is based on an analysis of extensive observations of particle formation in the BL at a continental surface site. It assumes that molecular clusters form at a rate proportional to the gaseous sulfuric acid concentration to the power of 1. The formation rate of 3 nm diameter observable particles is controlled by the cluster formation rate and the existing particle surface area, which acts to scavenge condensable gases and clusters during growth. Modelled sulfuric acid vapour concentrations, particle formation rates, growth rates, coagulation loss rates, peak particle concentrations, and the daily timing of events in the global model agree well with observations made during a 22-day period of March 2003 at the SMEAR II station in Hyytiälä, Finland. The nucleation bursts produce total particle concentrations (>3 nm diameter) often exceeding 104 cm-3, which are sustained for a period of several hours around local midday. The predicted global distribution of particle formation events broadly agrees with what is expected from available observations. Over relatively clean remote continental locations formation events can sustain mean total particle concentrations up to a factor of 8 greater than those resulting from anthropogenic sources of primary organic and black carbon particles. However, in polluted continental regions anthropogenic primary particles dominate particle number and formation events lead to smaller enhancements of up to a factor of 2. Our results therefore suggest that particle concentrations in remote continental regions are dominated by nucleated particles while concentrations in polluted continental regions are dominated by primary particles. The effect of BL particle formation over tropical regions and the Amazon is negligible. These first global particle formation simulations reveal some interesting sensitivities. We show, for example, that significant reductions in primary particle emissions may lead to an increase in total particle concentration because of the coupling between particle surface area and the rate of new particle formation. This result suggests that changes in emissions may have a complicated effect on global and regional aerosol properties. Overall, our results show that new particle formation is a significant component of the aerosol particle number budget.

Spracklen, D. V.; Carslaw, K. S.; Kulmala, M.; Kerminen, V.-M.; Mann, G. W.; Sihto, S.-L.

2006-12-01

77

Regular arrangement of nanoparticles from the gas phase on bacterial surface-protein layers  

NASA Astrophysics Data System (ADS)

FePt nanoparticles from the gas phase are deposited onto the two-dimensional crystalline surface layer protein from the bacterium Bacillus sphaericus NCTC 9602. The potential of this protein layer to facilitate the ordered spatial arrangement of the otherwise statistically distributed nanoparticles on the substrate is studied. Transmission electron microscopy reveals the particles positions to be directed by the regular protein template.

Queitsch, Ute; Mohn, Elias; Schäffel, Franziska; Schultz, Ludwig; Rellinghaus, Bernd; Blüher, Anja; Mertig, Michael

2007-03-01

78

Modeled heating and surface erosion comparing motile (gas borne) and stationary (surface coating) inert particle additives  

SciTech Connect

The unsteady, non-similar, chemically reactive, turbulent boundary layer equations are modified for gas plus dispersed solid particle mixtures, for gas phase turbulent combustion reactions and for heterogeneous gas-solid surface erosive reactions. The exterior (ballistic core) edge boundary conditions for the solutions are modified to include dispersed particle influences on core propellant combustion-generated turbulence levels, combustion reactants and products, and reaction-induced, non-isentropic mixture states. The wall surface (in this study it is always steel) is considered either bare or coated with a fixed particle coating which is conceptually non-reactive, insulative, and non-ablative. Two families of solutions are compared. These correspond to: (1) consideration of gas-borne, free-slip, almost spontaneously mobile (motile) solid particle additives which influence the turbulent heat transfer at the uncoated steel surface and, in contrast, (2) consideration of particle-free, gas phase turbulent heat transfer to the insulated surface coated by stationary particles. Significant differences in erosive heat transfer are found in comparing the two families of solutions over a substantial range of interior ballistic flow conditions. The most effective influences on reducing erosive heat transfer appear to favor mobile, gas-borne particle additives.

Buckingham, A.C.; Siekhaus, W.J.

1982-09-27

79

Superhydrophobic surfaces fabricated by surface modification of alumina particles  

NASA Astrophysics Data System (ADS)

The fabrication of superhydrophobic surfaces has attracted intense interest because of their widespread potential applications in various industrial fields. Recently, some attempts have been carried out to prepare superhydrophobic surfaces using metal oxide nanoparticles. In the present work, superhydrophobic surfaces were fabricated with low surface energy material on alumina particles with different sizes. It was found that particle size of alumina is an important factor in achieving stable superhydrophobic surface. It was possible to obtain alumina surface with water contact angle (WCA) of 156° and a sliding angle of <2°. Superhydrophobicity of the modified alumina is attributed to the combined effect of the micro-nanostructure and low surface energy of fatty acid on the surface. The surface morphology of the alumina powder and coatings was determined by FESEM. The stability of the coatings was assessed by conducting water immersion test. Effect of heat treatment on WCA of the coating was also studied. The transition of alumina from hydrophilic to superhydrophobic state was explained using Wenzel and Cassie models. The method is shown to have potential application for creating superhydrophobic surface on cotton fabrics.

Richard, Edna; Aruna, S. T.; Basu, Bharathibai J.

2012-10-01

80

Turbulent boundary layers developing over compliant surfaces  

NASA Astrophysics Data System (ADS)

The problem of reducing drag due to skin friction remains of interest. This is the case because of the significant benefits that would result from an application of a drag reducing scheme on airplanes, ships or underwater vehicles. One of the techniques that have been proposed for such a scheme is wall compliance. Wall compliance could, in principle, work in two ways: either it could delay transition, or it could modify the inner part of a turbulent boundary layer so that reduced skin friction would result. The objective of this research program was to develop prediction techniques for high Reynolds number turbulent flows over compliant surfaces. This objective was pursued by evaluating the wall induced Reynolds stresses using solutions of the liner momentum equations.

Lekoudis, S. G.; Sengupta, T.

1983-05-01

81

Reducing the adhesion between surfaces using surface structuring with PS latex particle.  

PubMed

The adhesion between a micro-object and a microgripper end-effector is an important problem in micromanipulation. Canceling or reducing this force is a great challenge. This force is directly linked to the surface chemical structure of the object and the gripper. We propose to reduce the adhesion force by using a self-assembled monolayer structuring on one surface. The surface was structured by polystyrene latex particles (PS particles) with radii from 100 to 1500 nm. The adhesion force measurements obtained by AFM were compared to a multisphere van der Waals force model. The model suggests the existence of an optimal value of the sphere radius which minimizes the adhesion. In that case, the pull-off force is reduced to 20 nN by the PS particles layer with a radius of 45 nm. A wide range of applications in the field of telecommunications, bioengineering, and more generally speaking, MEMS can be envisaged for these substrates. PMID:20518550

Dejeu, Jérôme; Bechelany, Mikhael; Philippe, Laetitia; Rougeot, Patrick; Michler, Johann; Gauthier, Michaël

2010-06-01

82

Small particle transport across turbulent nonisothermal boundary layers  

NASA Astrophysics Data System (ADS)

The interaction between turbulent diffusion, Brownian diffusion, and particle thermophoresis in the limit of vanishing particle inertial effects is quantitatively modeled for applications in gas turbines. The model is initiated with consideration of the particle phase mass conservation equation for a two-dimensional boundary layer, including the thermophoretic flux term directed toward the cold wall. A formalism of a turbulent flow near a flat plate in a heat transfer problem is adopted, and variable property effects are neglected. Attention is given to the limit of very large Schmidt numbers and the particle concentration depletion outside of the Brownian sublayer. It is concluded that, in the parameter range of interest, thermophoresis augments the high Schmidt number mass-transfer coefficient by a factor equal to the product of the outer sink and the thermophoretic suction.

Rosner, D. E.; Fernandez de La Mora, J.

1982-10-01

83

Lunar Surface Outgassing and Alpha Particle Measurements  

Microsoft Academic Search

The Lunar Prospector Alpha Particle Spectrometer (LP APS) searched for lunar surface gas release events and mapped their distribution by detecting alpha particles produced by the decay of gaseous radon-222 (5.5 MeV, 3.8 day half-life), solid polonium-218 (6.0 MeV, 3 minute half-life), and solid polonium-210 (5.3 MeV, 138 day half-life, but held up in production by the 21 year half-life

S. L. Lawson; W. C. Feldman; David J. Lawrence; K. R. Moore; R. C. Elphic; S. Maurice; Richard D. Belian; Alan B. Binder

2002-01-01

84

Lunar surface outgassing and alpha particle measurements  

SciTech Connect

The Lunar Prospector Alpha Particle Spectrometer (LP APS) searched for lunar surface gas release events and mapped their distribution by detecting alpha particle?; produced by the decay of gaseous radon-222 (5.5 MeV, 3.8 day half-life), solid polonium-2 18 (6.0 MeV, 3 minute half-life), and solid polonium-210 (5.3 MeV, 138 day half-life, but held up in production by the 21 year half-life of lead-210). These three nuclides are radioactive daughters from the decay of uranium-238.

Lawson, S. L. (Stefanie L.); Feldman, W. C. (William C.); Lawrence, David J. (David Jeffery),; Moore, K. R. (Kurt R.); Elphic, R. C. (Richard C.); Maurice, S. (Sylvestre); Belian, Richard D.; Binder, Alan B.

2002-01-01

85

Lunar Surface Outgassing and Alpha Particle Measurements  

NASA Astrophysics Data System (ADS)

The Lunar Prospector Alpha Particle Spectrometer (LP APS) searched for lunar surface gas release events and mapped their distribution by detecting alpha particles produced by the decay of gaseous radon-222 (5.5 MeV, 3.8 day half-life), solid polonium-218 (6.0 MeV, 3 minute half-life), and solid polonium-210 (5.3 MeV, 138 day half-life, but held up in production by the 21 year half-life of lead-210). These three nuclides are radioactive daughters from the decay of uranium-238. Radon reaches the lunar surface either at areas of high soil porosity or where fissures release the trapped gases in which radon is entrained. Once released, the radon spreads out by "bouncing" across the surface on ballistic trajectories in a randomwalk process. The half-life of radon-222 allows the gas to spread out by several 100 km before it decays (depositing approximately half of the polonium-218 recoil nuclides on the lunar surface) and allows the APS to detect gas release events up to several days after they occur. The long residence time of the lead-210 precursor to polonium-210 allows the mapping of gas vents which have been active over the last approximately 60 years. Because radon and polonium are daughter products of the decay of uranium, the background level of alpha particle activity is a function of the lunar crustal uranium distribution.

Lawson, S. L.; Feldman, W. C.; Lawrence, D. J.; Moore, K. R.; Elphic, R. C.; Maurice, S.; Belian, R. D.; Binder, A. B.

2002-01-01

86

Strength improvement via coating of a cylindrical hole by layer-by-layer assembled polymer particles.  

PubMed

Negatively charged colloidal poly(methyl methacrylate-co-butyl acrylate) (P(MMA-BA)) particles and positively charged dissolved poly(ethyleneimine) (PEI) were adsorbed onto a cement block using a layer-by-layer (LBL) assembly technique. The block was fashioned so as to have a cylindrical hole running from one face to another along the long axis of the rectangular block, and a fluid containing either of the two charged materials was pumped through the block. The result was a film tens of micrometers thick, and the pressure required to crack the cement block was measured after one end of the hole was sealed. Latex particles with a T(g) near the use temperature showed the maximum improvement in the cracking stress of the blocks. In a multilayer coating with identically sized particles, the cracking stress of the blocks increased to an improvement of 25% and then dropped off with increasing number of layers, even though the relationship between film thickness and the number of layers was linear. An improvement of about 30% in the cracking stress of the coated blocks was obtained when using multiple layers with different particle sizes. The effects of the number of layers and particle size on the cracking stress suggest that both the morphology and the thickness of the film play a role in performance. Tests done under confinement, e.g., with an external stress applied to the outside of the blocks, suggest that not only does a film-forming mechanism contribute to performance but that filling of microcracks in the rock may also play a role. PMID:20423142

Wu, Shuqing; Garfield, Lucas B; Rupert, Nicholas E; Grady, Brian P; Funkhouser, Gary P

2010-04-01

87

Surface engineering of nanoparticles in suspension for particle based bio-sensing  

PubMed Central

Surface activation of nanoparticles in suspension using amino organosilane has been carried out via strict control of a particle surface ad-layer of water using a simple but efficient protocol ‘Tri-phasic Reverse Emulsion’ (TPRE). This approach produced thin and ordered layers of particle surface functional groups which allowed the efficient conjugation of biomolecules. When used in bio-sensing applications, the resultant conjugates were highly efficient in the hybrid capture of complementary oligonucleotides and the detection of food borne microorganism. TPRE overcomes a number of fundamental problems associated with the surface modification of particles in aqueous suspension viz. particle aggregation, density and organization of resultant surface functional groups by controlling surface condensation of the aminosilane. The approach has potential for application in areas as diverse as nanomedicine, to food technology and industrial catalysis.

Sen, Tapas; Bruce, Ian J.

2012-01-01

88

A new weir surface repair layer with shock absorbing cushion design  

NASA Astrophysics Data System (ADS)

A shock absorbing cushion has never been introduced into any traditional weir surface repair layer design. However, shocks induced by high discharge with heavy sediment can easily produce brittle fracture and peeling over a weir surface repair layer as it is impacted by floods accompanied by particles of different sizes. In this study, transcending traditional designs, the authors developed a composite unit designed with a shock absorbing cushion that has performed well during field tests, proving that the weir body can be effectively protected even if the composite units are directly laid on a severely uneven weir surface repair layer.

Hsu, Tse-Shan; Hsieh, Yi-Lang

2013-09-01

89

Charged particle detectors with active detector surface for partial energy deposition of the charged particles and related methods  

DOEpatents

A radiation detector is disclosed. The radiation detector comprises an active detector surface configured to generate charge carriers in response to charged particles associated with incident radiation. The active detector surface is further configured with a sufficient thickness for a partial energy deposition of the charged particles to occur and permit the charged particles to pass through the active detector surface. The radiation detector further comprises a plurality of voltage leads coupled to the active detector surface. The plurality of voltage leads is configured to couple to a voltage source to generate a voltage drop across the active detector surface and to separate the charge carriers into a plurality of electrons and holes for detection. The active detector surface may comprise one or more graphene layers. Timing data between active detector surfaces may be used to determine energy of the incident radiation. Other apparatuses and methods are disclosed herein.

Gerts, David W; Bean, Robert S; Metcalf, Richard R

2013-02-19

90

Correlative surface analysis studies of environmental particles  

Microsoft Academic Search

Various surface analysis techniques (scanning electron microscopy\\/energy dispersive X-ray microanalysis (SEM\\/EDX), electron spectroscopy for chemical analysis (ESCA), and secondary ion mass spectrometry (SIMS)) were evaluated in a correlative regimen for the chemical characterization of particulate pollutants. Analytical capabilities were demonstrated by using particles derived from steel blast furnaces. The ESCA studies of ''bottom ashes'' suggest highly water-soluble species enriched in

Martha E. Farmer; Richard W. Linton

1984-01-01

91

Layer-by-layer epitaxy in limited mobility nonequilibrium models of surface growth  

NASA Astrophysics Data System (ADS)

We study, using noise-reduction techniques, layer-by-layer epitaxial growth in limited mobility solid-on-solid nonequilibrium surface growth models, which have been introduced in the context of kinetic surface roughening in ideal molecular beam epitaxy. Multiple hit noise reduction and long surface diffusion length lead to qualitatively similar layer-by-layer epitaxy in (1+1)- and (2+1)-dimensional limited mobility growth simulations. We discuss the dynamic scaling characteristics connecting the transient layer-by-layer growth regime with the asymptotic kinetically rough growth regime.

Chatraphorn, P. Punyindu; Das Sarma, S.

2002-10-01

92

Turbulent transport process in atmospheric surface layer  

NASA Astrophysics Data System (ADS)

The organized motion or the coherent motion can be detected in wind tunnel and water channel experiments and those motions play an important role for the production of turbulent energy and transport of turbulent fluxes. Similar phenomena can be found in the atmospheric surface layer (Gao et al., 1989). The purpose of this study is to clarify the transport structure and process of turbulent fluxes, especially heat, water vapor and carbon dioxide. The organized motions are detected by using the wavelet transform analysis as well as the conventional statistical method such as Fourier spectral analysis. We consider the dependency of transport process by the organized motion to the atmospheric stability in the surface layer. The observation was carried out at the test field of Shionomisaki Wind Effect Laboratory, where two sets of the combination of sonic anemometer thermometer and open path H2O/CO2 analyzer were mounted at 2m and 20m height. The evident ramp and inverse ramp structures can be found in the time series of temperature, water vapor and CO2 in the unstable stability, using the Mexican hut wavelet transform analysis. The co-spectral density in wavelet analysis is considered as the flux at each time scale. The large amount of fluxes is transported at the sudden decrease in scalar ramp structure and the sudden increase in inverse ramp structure in several tens of seconds. The scalar and vertical wind velocity are completely either in phase or out of phase, which means that the turbulent transport by the organized motion occurs at time scales of several tens of seconds. The quadrant analysis of turbulent flux shows that the rate of the transport amount of scalar by ejection and sweep to the total transport flux increases according to the increase of the atmospheric stability. At 2m height, the transport by ejection is dominant in unstable condition, and that by sweep is larger in the stable condition. At 20m height, transport by ejection is larger than that by sweep in all stability condition. The flux transport by the organized motions is evaluated quantitatively by using the several conditional analysis methods.

Hayashi, T.; Awasaki, T.

2012-04-01

93

Propagation of surface waves in deformed, anisotropic thin layered solids  

Microsoft Academic Search

This paper provides a method to determine the velocities of surface waves propagating in finitely predeformed, anisotropic thin layered solids based on acoustoelasticity of surface waves. First, the constitutive equations and the equations of motion required for examining the propagation of surface waves in deformed layered solids are derived, by reexamining the theory of small (infinitesimal) wave motions superimposed on

Zuliang Yu; Siegfried Boseck

2002-01-01

94

Microencapsulation of ultramarine particles in water oil emulsion and surface fractal dimensionality of the particles  

Microsoft Academic Search

An approach to the microencapsulation of ultramarine particles in water-in-oil (WO) emulsion was investigated. The surface shape of the particles was quantitatively characterized via the study of the surface fractal dimensionality. The results showed that there were ultramarine particles in the aqueous beads of WO emulsion, and that microcapsulizing reactions took place on the surface of the particles, forming a

Yang Guiqin; Li Xiaozeng; Yan Lemei; Cui Jianzhong; Guo Congrong

1997-01-01

95

In situ observation of surface oxide layers on medical grade Ni-Ti alloy during straining.  

PubMed

Medical grade Ni-Ti alloys with shape memory or pseudo-elastic behavior exhibit good biocompatibility because of an electrochemically passive oxide layer on the surface. In this work, the mechanical stability of surface oxide layers is investigated during reversible pseudo-elastic deformation of commonly applied medical grade Ni-Ti wires. Surface oxide layers with varying thickness were generated by varying annealing times under air atmosphere. The thicknesses of the surface oxide layers were determined by means of Rutherford backscattering spectrometry. In situ scanning electron microscopy investigations reveal a damage mechanism, which is assumed to have a significant influence on the biocompatibility of the material. The conditions that lead to the appearance of cracks in the surface oxide layer or to the flaking of surface oxide layer particles are identified. The influence of the thickness of the surface oxide layer on the damage mode is characterized. The possible impact of the damaged surface oxide layer on the material's biocompatibility and the potentials to reduce or avoid the damage are discussed. PMID:18384174

Undisz, A; Schrempel, F; Wesch, W; Rettenmayr, M

2009-03-15

96

Energetic Particle Synthesis of Metastable Layers for Superior Mechanical Properties  

SciTech Connect

Energetic particle methods have been used to synthesize two metastable layers with superior mechanical properties: amorphous Ni implanted with overlapping Ti and C, and amorphous diamond-like carbon (DLC) formed by vacuum-arc deposition or pulsed laser deposition. Elastic modulus, yield stress and hardness were reliably determined for both materials by fitting finite-element simulations to the observed layer/substrate responses during nanoindentation. Both materials show exceptional properties, i.e., the yield stress of amorphous Ni(Ti,C) exceeds that of hardened steels and other metallic glasses, and the hardness of DLC (up to 88 GPa) approaches that of crystalline diamond (approx. 100 GPa). Tribological performance of the layers during unlubricated sliding contact appears favorable for treating Ni-based micro-electromechanical systems: stick-slip adhesion to Ni is eliminated, giving a low coefficient of friction (approx. 0.3-0.2) and greatly reduced wear. We discuss how energetic particle synthesis is critical to forming these phases and manipulating their properties for optimum performance.

Follstaedt, D.M.; Knapp, J.A.; Myers, S.M.; Dugger, M.T.; Friedmann, T.A.; Sullivan, J.P. [Sandia National Labs., Albuquerque, NM (United States); Monteiro, O.R.; Ager, J.W. III; Brown, I.G.; Christenson, T. [Lawrence Berkeley National Lab., CA (United States)

1998-01-01

97

Dry deposition of large, airborne particles onto a surrogate surface  

NASA Astrophysics Data System (ADS)

Simultaneous measurements of particle dry deposition flux and airborne number concentration in the open atmosphere were made using three different types of artificially generated particles in the size range 10-100 ?m - perlite, diatomaceous earth and glass beads. A combination of gravimetric analysis, automated microscopy and sonic anemometry provided size-resolved estimates of both the inertial and gravitational components of the quasi-laminar layer particle deposition velocity, ( Vd) b, as a function of size. Eddy inertial deposition efficiency ( ?dI) was determined as a function of dimensionless eddy Stokes number (Stk e). In the range 3particles and gases to environmental surfaces. DOE Report PNL-SA-6721, Pacific Northwest Laboratories, Richland, WA), used in several regulatory models, significantly under-predicted (up to seven times) ( Vd) b for large particles ( da>10 ?m).

Kim, Eugene; Kalman, David; Larson, Timothy

98

Instrinsic Insulators at the Surfaces of Layered Ferromagnetic Manganites  

Microsoft Academic Search

To explore loss of ferromagnetic order at the surfaces of manganites, we brought together a powerful combination of two surface probes, tunneling and polarized x-ray interactions, to study the intrinsic electronic and magnetic surface states of a layered manganite, La2-2xSr1+2xMn2O7, that is ferromagnetic and conducting in the bulk. These probes present clear evidence for an intrinsic insulating nonferromagnetic surface layer

J. W. Freeland; K. E. Gray; J. J. Kavich

2005-01-01

99

Surface heating due to turbulent boundary-layer flows  

SciTech Connect

Numerical analysis is made of surface-heating history when a surface is exposed to transient thermal fluxes from a turbulent compressible boundary layer. The conservation equations are solved by means of a factored ADI method. Results display high heat fluxes at the surface, causing sufficient rise in surface temperatures to quickly reach melting in some substances. The melting liquid-layer case is also briefly discussed.

Kang, S.W.; Levatin, J.L.

1981-01-20

100

Remote estimation of the Mercury surface layer structure  

NASA Astrophysics Data System (ADS)

Results of the optical observations of Mercury and the Moon confirm the close similarity of photometric properties of the bodies. Experience of lunar studies shows that space weathering processes on the Mercury (such as micrometeorite bombardment, solar wind ion bombardment etc.) can form properties of the upper layer of regolith. The amount of fused glassy particles and others agglutinates in the lunar upper layer is the direct index of the soil reworking caused be the micrometeorite bombardment. Besides, this micrometeorite bombardment is also responsible for the mechanical process through which the large particles are broken down into smaller ones. For lunar regolith was showed that increasingly mature soils become progressively finer-grained, better-sorted, and composed of a greater proportion of agglutinates. The increasing rate of the fused glassy fragments, of agglutinates, and of fine size fraction in the regolith during its space weathering affects the polarization of the light reflected by an exposed lunar or Mercurian soil. Therefore, polarimetric properties of the regolith may be modified by the soil reworking process in the course of time. Comparison of the lunar and Mercurian optic observations confirms the remarkable similarity of the polarimetric properties of Mercury and the Moon. From of summary of polarization measurements of whole disk of Mercury it is possible to conclude that maturity of the soil on the Mercurian surface in scale of whole disk is similar to one in large old craters on the lunar highland. Comparison of the lunar and Mercurian disk-integrated photometric functions indicates the likeness of the surface layer structures of the bodies. Analysis of the phase curve inclination and magnitude of the opposition effect shows that Mercurian relief in scale of meter details is smoother than lunar one. It was measured brightness of number of small plots (10x10 cm) on the lunar surface (Luna-13 data). The range of phase angles was from 68 to 75 deg. These values close correlate with corresponding part of the Mercurian disk-integrated phase function. ItSs possible if Mercurian phase function received from Earth-based telescopes and lunar one received in cm-scale is coincided the structures of regolith may be similar in both cases. These conclusions may be used for planning BepiColombo mission. This work was supported by INTAS-ESA grant No. 99-00403.

Shevchenko, V.

101

Silicon dioxide sacrificial layer etching in surface micromachining  

Microsoft Academic Search

Silicon dioxide sacrificial layer etching has become a major surface micromachining method to fabricate microsensors and microactuators often made of polycrystalline silicon. An overview of the materials available in integrated circuit manufacturing is given, and the etch mechanism and sacrificial layer etch kinetics are reviewed. Selectivity issues important for the proper choice of layers and etchants are addressed discussing the

J Bühler; F-P Steiner; H Baltes

1997-01-01

102

Carbon Surface Layers on a High-Rate LiFePO4  

SciTech Connect

Transmission electron microscopy (TEM) was used to image particles of a high-rate LiFePO4 sample containing a small amount of in situ carbon. The particle morphology is highly irregular, with a wide size distribution. Nevertheless, coatings, varying from about 5-10 nm in thickness, could readily be detected on surfaces of particles as well as on edges of agglomerates. Elemental mapping using Energy Filtered TEM (EFTEM) indicates that these very thin surface layers are composed of carbon. These observations have important implications for the design of high-rate LiFePO4 materials in which, ideally, a minimal amount of carbon coating is used.

Gabrisch, Heike; Wilcox, James D.; Doeff, Marca M.

2005-09-06

103

Dielectric properties of ferroelectric thin films with surface transition layers  

PubMed Central

By taking into account surface transition layers (STL), the dielectric properties of ferroelectric thin films described by the transverse Ising model are discussed in the framework of the mean field approximation. Functions of the intra-layer and inter-layer couplings are introduced to characterize STL, which makes the model more realistic compared to previous treatment of surface layers using uniform surface exchange interactions and a transverse field. The effects of physical parameters on the dielectric properties are quantified. The results obtained indicate that STL has very strong influence on the dielectric properties of ferroelectric thin films. Some of our theoretical results are in accord with the available experimental data.

Chen, Hui; Lu, Tianquan; Cui, Lian; Cao, Wenwu

2009-01-01

104

Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer.  

National Technical Information Service (NTIS)

An experimental investigation of the response of a hypersonic turbulent boundary layer to a step change in surface roughness has been performed. The boundary layer on a flat nozzle wall of a Mach 6 wind tunnel was subjected to abrupt changes in surface ro...

T. Kubota D. E. Berg

1977-01-01

105

Surface plasma source with anode layer plasma accelerator  

SciTech Connect

Proposed plasma generation system can be used for high current negative ion beam production and for directed deposition by flux of sputtered neutrals and negative ions. The main mechanism of negative ion formation in surface plasma sources is the secondary emission from low work function surface bombarded by a flux of positive ion or neutrals. The emission of negative ions is enhanced significantly by introducing a small amount of cesium or other substance with low ionization potential. In the proposed source are used positive ions generated by Hall drift plasma accelerator (anode layer plasma accelerator or plasma accelerator with insulated channel, with cylindrical or race track configuration of emission slit). The target-emitter is bombarded by the ion beam accelerated in crossed ExB fields. Negative ions are extracted from the target surface with geometrical focusing and are accelerated by negative voltage applied between emitter and plasma, contacting with the plasma accelerator. Hall drift ion source has a special design with a space for passing of the emitted negative ions and sputtered particles through the positive ion source.

Dudnikov, Vadim [Muons, Inc., Batavia, Illinois 60510 (United States)

2012-02-15

106

Synthesis and characterization of macromolecular layers grafted to polymer surfaces  

Microsoft Academic Search

The composition and behavior of surfaces and interfaces play a pivotal role in dictating the overall efficiency of the majority of polymeric materials and devices. Surface properties of the materials can be altered using surface modification techniques. It is necessary to highlight that successful methods of surface modification should affect only the upper layer of the polymer material without changing

Oleksandr Burtovyy

2008-01-01

107

The dominant role of adsorbed fluid layers on the polar surfaces of ZnO in ambient atmospheric conditions  

Microsoft Academic Search

Polar ZnO surfaces with O- and Zn-termination were studied with atomic and lateral force microscopy and force curves. Adsorbed fluid layers on both surfaces are found to dominate their adhesion properties in air. The hydrophilic O-surface has a substantially thicker adsorbed layer and larger residual particle densities. Our data suggest that different preparation is required for the two surfaces before

James Fryar; Enda McGlynn; Martin O. Henry; A. Anthony Cafolla; Claire J. Hanson

2004-01-01

108

Surface Chemical Analysis and Electrokinetic Properties of Spherical Hematite Particles Coated with Yttrium Compounds  

Microsoft Academic Search

We describe in this work the chemical and electrokinetic surface characterization of core–shell particles consisting of a practically spherical hematite nucleus coated by a layer of yttrium basic carbonate or yttrium oxide (obtained after calcination of the carbonate-coated particles, following the method of E. Matijevi? and B. Aiken (J. Colloid Interface Sci.126,645 (1988))). The morphological and surface characteristics of the

R. C. Plaza; J. D. G. Durán; A. Quirantes; M. J. Ariza; A. V. Delgado

1997-01-01

109

Numerical Investigation of Spalled Particle Behavior Ejected from an Ablator Surface  

NASA Astrophysics Data System (ADS)

During ablation experiments in an arc-heated facility, the presence of spalled particles has been observed upstream of a detached shock wave or a stagnation-point boundary layer. In the past experiments using spectroscopic measurement for nitrogen arc-jet, the CN violet band spectra owing to the spallation particles ejected from the ablator were observed upstream of the shock layer. Based on this fact, in this study, the flight path of a single spallation particle ejected into a nonequilibrium flow field is numerically analyzed and the particle properties are obtained. The simulation is carried out about a solid particle ejected vertically from the front surface of an ablator, including various initial speeds, sizes, and positions. Moreover, by classifying the obtained results, the particle behavior is carefully investigated and the possibility of a particle being observed upstream of a shock wave is discussed.

Nozawa, Sohey; Kihara, Hisashi; Abe, Ken-Ichi

110

Influence of surface-adhered nanoparticles and nanoporous structure on particle–particle interaction of silica  

Microsoft Academic Search

In cosmetic powders, there are several kinds of powder materials widely used such as mica and silica on which nanoparticles are adhered on surface of the particle. However, it is not widely known that nanoparticles are adhered on the surface of these particles. In order to analyze the effect of these nanoparticles and silica particle nanopores on silica–mica surface interaction,

Toshiyuki Kani; Maki Tamonoki; Takahiro Suzuki; Mayumi Tsukada; Hidehiro Kamiya

2007-01-01

111

Generation and characterization of surface layers on acoustically levitated drops  

Microsoft Academic Search

Surface layers of natural and technical amphiphiles, e.g., octadecanol, stearic acid and related compounds as well as perfluorinated fatty alcohols (PFA), have been investigated on the surface of acoustically levitated drops. In contrast to Langmuir troughs, traditionally used in the research of surface layers at the air–water interface, acoustic levitation offers the advantages of a minimized and contact-less technique. Although

Rudolf Tuckermann; Sigurd Bauerecker; Heiko K. Cammenga

2007-01-01

112

Monte Carlo simulation of light reflection from cosmetic powder particles near the human skin surface  

NASA Astrophysics Data System (ADS)

The reflection and scattering properties of light incident on human skin covered with powder particles have been investigated. A three-layer skin structure with a pigmented area is modeled, and the propagation of light in the skin's layers and in a layer of particles near the skin's surface is simulated using the Monte Carlo method. Assuming that only single scattering of light occurs in the powder layer, the simulation results show that the reflection spectra of light from the skin change with the size of powder particles. The color difference between normal and discolored skin is found to decrease considerably when powder particles with a diameter of approximately 0.25 ?m are present near the skin's surface. The effects of the medium surrounding the particles, and the influence of the distribution of particle size (polydispersity), are also examined. It is shown that a surrounding medium with a refractive index close to that of the skin substantially suppresses the extreme spectral changes caused by the powder particles covering the skin surface.

Okamoto, Takashi; Kumagawa, Tatsuya; Motoda, Masafumi; Igarashi, Takanori; Nakao, Keisuke

2013-06-01

113

The rebound of small particles impacting a free surface  

NASA Astrophysics Data System (ADS)

The impact of small particles on a free surface is a problem of fundamental interest with various applications including biolocomotion, pollination and contaminant transport. We present the results of a combined theoretical and experimental investigation of the normal impact of spherical particles on an air-water surface, and give particular focus to deducing criteria for particle rebound. Computing particle trajectories requires consideration of the particle's inertia and weight, in addition to the forces resisting its motion, specifically, buoyancy, hydrodynamic drag forces and contact or curvature forces associated with the surface tension. Simplified models for these forces yield criteria for particle rebound that are tested against experimental observations.

Hancock, Matthew; Aristoff, Jeffrey; Bush, John

2007-11-01

114

Interactions of hyaluronan layers with similarly charged surfaces: the effect of divalent cations.  

PubMed

We used colloidal probe atomic force microscopy to measure the normal forces between the surface of a silica colloidal particle and a sparse layer of hyaluronan (hyaluronic acid, HA, MW ? 10(6) Da) covalently attached to a planar silica surface, both across pure water and following the addition of 1 mM MgCl2. It was found that in the absence of salt the HA layer repelled the colloidal silica surface during both approach and retraction. The addition of the MgCl2, however, changes the net force between the negatively charged HA layer and the opposing negatively charged silica surface from repulsion to adhesion. This interaction reversal is attributed to the bridging effect of the added Mg(2+) ions. Our results provide first direct force data to support earlier simulation and predictions that such divalent cations could bridge between negative charges on opposing surfaces, leading to an overall reversal of force from repulsion to attraction. PMID:24011082

Jiang, Lei; Titmuss, Simon; Klein, Jacob

2013-09-19

115

A surface layer model for thin film lubrication  

SciTech Connect

A rheological model has been developed which can be applied to thin film lubrication. It is known that great differences are seen between behavior in thin (molecular scale) films and in bulk (macroscopic) rheological measurements. There appear to be layers near the surface in which viscosity is increased by many orders of magnitude. The model contains three material property parameters, i.e., the conventional viscosity, the thickness of the surface layer, and a surface layer viscosity. A modified Reynolds` equation is developed. Behavior of correction factors to Reynolds` equation and to the shear stress are shown. Results are computed for a one-dimensional converging wedge contact. The effect of increasing the layer thickness parameter is to increase the load and reduce the friction coeffcient. Increasing the surface layer vicosity also tends to increase the load and reduce the friction coefficient.

Tichy, J.A. [Rensselaer Polytechnic Institute, Troy, NY (United States)

1995-07-01

116

Nonlinear optical probe of molecular structure on colloidal particle surfaces  

Microsoft Academic Search

The structure of molecules adsorbed at the colloidal particle surface has great influence on how the colloidal particles interact among themselves and with the environment. In this presentation we show that Second Harmonic Generation from molecules adsorbed at the particle surface can be used for determining the orientation of the molecules at this buried interface. The determination is facilitated by

Shih-Hui Jen

2005-01-01

117

Cake Filtration With Particle Penetration at the Cake Surface  

Microsoft Academic Search

Particles in drilling muds build a filter cake on borehole walls and can migrate into the adjacent porous formation and cause formation damage. This study analyzes cake formation, including particle penetration at the cake surface. Mass-balance equations for captured and suspended particles and the fluid phase are averaged along the cake thickness, taking into account conditions of the surface and

M. Y. Corapcioglu; Nelly Abboud

1990-01-01

118

Lipid chemistry of eastern Mediterranean surface layers  

Microsoft Academic Search

IT has been well established that organic surface films exist in most of the world's major oceans1-9. They consist mainly of natural lipid material, with generally much smaller, though variable, amounts of petroleum hydrocarbons. Because the Mediterranean Sea is a restricted area the input of petroleum hydrocarbon is more noticeable than in most oceanic areas, and the level of surface

R. J. Morris; F. Culkin

1974-01-01

119

The surface potential of perforated dielectric layers  

Microsoft Academic Search

The maximum value of the surface potential or of the related equivalent voltage of perforated dielectric sheets may be of special interest in application of materials such as electrostatic-polymeric electret filters, fabrics, non-wovens and others. Experimental investigations carried out on polymeric fabrics with application of the corona triode have shown that the surface potential is limited mainly by the back

Ryszard Kacprzyk; W. Mista

2006-01-01

120

Generation and characterization of surface layers on acoustically levitated drops.  

PubMed

Surface layers of natural and technical amphiphiles, e.g., octadecanol, stearic acid and related compounds as well as perfluorinated fatty alcohols (PFA), have been investigated on the surface of acoustically levitated drops. In contrast to Langmuir troughs, traditionally used in the research of surface layers at the air-water interface, acoustic levitation offers the advantages of a minimized and contact-less technique. Although the film pressure cannot be directly adjusted on acoustically levitated drops, it runs through a wide pressure range due to the shrinking surface of an evaporating drop. During this process, different states of the generated surface layer have been identified, in particular the phase transition from the gaseous or liquid-expanded to the liquid-condensed state of surface layers of octadecanol and other related amphiphiles. Characteristic parameters, such as the relative permeation resistance and the area per molecule in a condensed surface layer, have been quantified and were found comparable to results obtained from surface layers generated on Langmuir troughs. PMID:17376468

Tuckermann, Rudolf; Bauerecker, Sigurd; Cammenga, Heiko K

2007-02-16

121

Temperature Dependence of Surface Layering in a Dielectric Liquid  

SciTech Connect

The temperature dependence of the density oscillations (layers) at the free surface of tetrakis(2-ethylhexoxy)silane, a nonmetallic molecular liquid, was investigated using x-ray reflectivity. Below {approx}215K , the layer parameters weakly vary with temperature, if at all. Above this temperature, the layer spacings and intrinsic layer widths increase continuously, until there is no identifiable layering above 230K . This transition occurs at T/{Tc}{approx}0.23 , a temperature region that is usually accessible in metallic liquids but is preempted by freezing in many dielectric liquids.

Mo,H.; Kewalramani, S.; Evmenenko, G.; Kim, K.; Ehrlich, S.; Dutta, P.

2007-01-01

122

Observation of Surface Layering in a Nonmetallic Liquid  

SciTech Connect

Oscillatory density profiles (layers) have previously been observed at the free surfaces of liquid metals but not in other isotropic liquids. We have used x-ray reflectivity to study a molecular liquid, tetrakis(2-ethylhexoxy)silane. When cooled to T/T{sub c}{approx}0.25 (well above the freezing point for this liquid), density oscillations appear at the surface. Lateral order within the layers is liquidlike. Our results confirm theoretical predictions that a surface-layered state will appear even in dielectric liquids at sufficiently low temperatures, if not preempted by freezing.

Mo,H.; Evmenenko, G.; Kewalramani, S.; Kim, K.; Ehrlich, S.; Dutta, P.

2006-01-01

123

Very strong accumulation layers on ZnO surfaces  

Microsoft Academic Search

Extremely strong accumulation layers with surface electron densities DeltaN approaching 1014 cm-2 have been achieved on ZnO surfaces in contact with an electrolyte. Experimental results of DeltaN versus surface barrier height VS are compared with self-consistent calculations.

D. Eger; A. Many; Y. Goldstein

1975-01-01

124

Reflection from layered surfaces due to subsurface scattering  

Microsoft Academic Search

The reflection of light from most materials consists of two ma- jor terms: the specular and the diffuse. Specular reflection may be modeled from first principles by considering a rough surface consisting of perfect reflectors, or micro-facets. Diffuse reflection is generally considered to result from multiple scattering either from a rough surface or from within a layer near the surface.

Pat Hanrahan; Wolfgang Krueger

1993-01-01

125

Laser removal of oxides and particles from copper surfaces for microelectronic fabrication.  

PubMed

Laser removal of surface oxides and small particles from copper surfaces was carried out using a Q-switched Nd:YAG laser. Oxide layers and small particles on copper surfaces should be removed for the improvement of solder quality on printed circuit boards (PCBs) and for the prevention of circuit failure or loss of production yield during the fabrication of microelectronic devices. A selective removal of surface oxides from a copper surface was achieved by the laser treatment, which was confirmed by on-line acoustic monitoring of the process. An angular laser cleaning technique in which the laser irradiates the surface at a glancing angle was used for effective removal of the particles from the surface. The unique characteristics of this technique and the cleaning mechanism are discussed. PMID:19404371

Lee, J M; Watkins, K

2000-07-17

126

Electrostatic double layer force between a sphere and a planar substrate in the presence of previously deposited spherical particles.  

PubMed

A finite element model of the electrostatic double layer interaction between an approaching colloidal particle and a small region of a charged planar surface containing four previously deposited particles is presented. The electrostatic interaction force experienced by the approaching particle is obtained by solving the Poisson-Boltzmann equation with appropriate boundary conditions representing this complex geometry. The interaction forces obtained from the detailed three-dimensional finite element simulations suggest that for the many-body scenario addressed here, the electrostatic double layer repulsion experienced by the approaching particle is less than the corresponding sphere-plate interaction due to the presence of the previously deposited particles. The reduction in force is quite significant when the screening length of the electric double layer becomes comparable to the particle radius (kappaa approximately 1). The results also suggest that the commonly used technique of pairwise addition of binary interactions can grossly overestimate the net electrostatic double layer interaction forces in such situations. The simulation methodology presented here can form a basis for investigating the influence of several previously deposited particles on the electrostatic repulsion experienced by a particle during deposition onto a substrate. PMID:16032900

Das, Prodip K; Bhattacharjee, Subir

2005-05-10

127

Dusty plasma system in the surface layer of the illuminated part of the moon  

NASA Astrophysics Data System (ADS)

The dusty plasma system in the surface layer of the illuminated part of the Moon has been considered. The maximum height of the dust rise has been determined. It has been shown that a dead zone, where dust particles cannot rise over the surface of the Moon, is absent near a lunar latitude of 80°. The size and height distributions of dust have been determined.

Golub', A. P.; Dol'nikov, G. G.; Zakharov, A. V.; Zelenyi, L. M.; Izvekova, Yu. N.; Kopnin, S. I.; Popel, S. I.

2012-04-01

128

Influences of Surface Iron Oxide Layer on Magnetic Properties of Iron Pigment  

Microsoft Academic Search

Mössbauer spectroscopy and other methods were used to study the oxide layer on the surface of fine Fe particles. On the basis of X-ray and electron diffraction, the surface oxide phase was characterized as consisting of extremely fine spinel crystals of Fe3O4 and ¿-Fe2O3, and mixtures of these. Comparisons of the Mössbauer spectra under strong magnetic fields (25 and 50

K. Haneda; K. Goto

1985-01-01

129

Surface layer dynamics in the pyrolysis of ammonium perchlorate-hydrocarbon binder propellants  

Microsoft Academic Search

Mixtures of ammonium perchlorate particles and polybutadiene binder appear to exhibit preferential accumulation of one or\\u000a the other component on the pyrolyzing surface over a range of rocket-operating pressures. At low pressures, the surface layer\\u000a is enriched with the oxidizer, and at high pressures, it is enriched with the binder. The degree of accumulation of the oxidizer\\u000a is found to

S. R. Chakravarthy

2000-01-01

130

Characteristics of surface layer structure formation during laser boriding  

NASA Astrophysics Data System (ADS)

The surface layers of a mild steel and steels 40 and U8 were studied metallographically following a laser boriding treatment. In particular, the structure and properties of the borided layer were investigated as a function of the irradiation rate and the thickness of the coating compound. It is shown that laser boriding produces a sharp increase in the hardness of the steels and leads to the formation of hardened layers that are as thick as those produced by diffusion boriding treatments.

Tananko, I. A.; Levchenko, A. A.; Guiva, R. T.; Guiva, V. A.; Sittsevaia, E. Iu.

1989-08-01

131

Ordered equilibrium structures of soft particles in thin layers  

NASA Astrophysics Data System (ADS)

Considering a system of Gaussian particles confined between two hard, parallel plates, we investigate at T = 0, ordered equilibrium configurations that the system forms as the distance D between the plates gradually increases. Using a very sensitive and reliable optimization technique that is based on ideas of genetic algorithms, we are able to identify the emerging sequences of the energetically most favorable structures. Although the resulting phase diagram is rather complex, its essential features can be reduced to the discussion of two archetypes of structural transitions: (i) a continuous transformation at a fixed number of layers, leading from a square to a centered rectangular and then to a hexagonal lattice; (ii) a discontinuous transition, transforming a hexagonal to a square lattice via complex intermediate structures, i.e., the so-called buckling transition, which is encountered as the system forms a new layer. Detailed Monte Carlo simulations are able to confirm the theoretical predictions on a semiquantitative level but are not able to grasp the tiny energetic differences between competing structures.

Kahn, Mario; Weis, Jean-Jacques; Kahl, Gerhard

2010-12-01

132

Fabrication of Nano-Composite Surface Layers on Aluminium Employing Friction Stir Processing Technique  

SciTech Connect

Al/Al{sub 2}O{sub 3} nano-composite surface layer was fabricated via friction stir processing technique. Commercial AA6082 aluminium alloy extruded bar and nanometric Al{sub 2}O{sub 3} powder were subjected to friction stir processing at a substrate travel speed of 80 mm/min and a tool rotation speed of 1000 rpm using a hardened H-13 tool steel. The grain structure and reinforcement particles were investigated by using optical and scanning electron microscopy. Results show that Al{sub 2}O{sub 3} particles can be more uniformly dispread in aluminium substrate by increasing the number of processing passes. Also, hardness enhancement of the nano-composite surface layer was found. This is attributed to uniform dispersion of Al{sub 2}O{sub 3} particles.

Bozorg, S. F. K.; Zarghani, A. S.; Zarei-Hanzaki, A. [School of Metallurgy and Materials Engineering, Faculty of Engineering, University of Tehran, Tehran, P.O. Box: 14395-553 (Iran, Islamic Republic of)

2010-03-11

133

Structure Inclination Angles in the Convective Atmospheric Surface Layer  

NASA Astrophysics Data System (ADS)

Two-point correlations of the fluctuating streamwise velocity are examined in the atmospheric surface layer over the salt flats of Utah's western desert, and corresponding structure inclination angles are obtained for neutral, stable and unstable conditions. The neutral surface-layer results supplement evidence for the invariance of the inclination angle given in Marusic and Heuer (Phys Rev Lett 99:114504, 2007). In an extension of those results it is found that the inclination angle changes drastically under different stability conditions in the surface layer, varying systematically with the Monin-Obukhov stability parameter in the unstable regime. The variation is parametrized and subsequently can be used to improve existing near-wall models in the large-eddy simulation of the atmospheric surface layer.

Chauhan, Kapil; Hutchins, Nicholas; Monty, Jason; Marusic, Ivan

2013-04-01

134

Structure Inclination Angles in the Convective Atmospheric Surface Layer  

NASA Astrophysics Data System (ADS)

Two-point correlations of the fluctuating streamwise velocity are examined in the atmospheric surface layer over the salt flats of Utah's western desert, and corresponding structure inclination angles are obtained for neutral, stable and unstable conditions. The neutral surface-layer results supplement evidence for the invariance of the inclination angle given in Marusic and Heuer (Phys Rev Lett 99:114504, 2007). In an extension of those results it is found that the inclination angle changes drastically under different stability conditions in the surface layer, varying systematically with the Monin-Obukhov stability parameter in the unstable regime. The variation is parametrized and subsequently can be used to improve existing near-wall models in the large-eddy simulation of the atmospheric surface layer.

Chauhan, Kapil; Hutchins, Nicholas; Monty, Jason; Marusic, Ivan

2012-11-01

135

Triterpenes from the surface layer of Poria cocos  

Microsoft Academic Search

The surface layer of Poria cocos has yielded five new triterpenes; two of the lanostane type and three of the 3,4-secolanostane type. The structures of these compounds were elucidated mainly by two-dimensional NMR techniques.

Takaaki Tai; Tetsuro Shingu; Tohru Kikuchi; Yasuhiro Tezuka; Akira Akahori

1995-01-01

136

The Bacterial Surface Layer Provides Protection against Antimicrobial Peptides  

PubMed Central

This report describes a previously unrecognized role for bacterial surface layers as barriers that confer protection against antimicrobial peptides. As antimicrobial peptides exist in natural environments, S-layers may provide a bacterial survival mechanism that has been selected for through evolution.

de la Fuente-Nunez, Cesar; Mertens, Jan; Smit, John

2012-01-01

137

Effect of silicon particles on the rapidly resolidified layer of Al-Si alloys in the electro discharge machining process  

Microsoft Academic Search

The rapidly resolidified layer is formed by the re-solidification of residual molten materials on the machined surface during\\u000a the electric discharge machining (EDM) process. This study adopts a range of 4–29 wt% to change the silicon content in Al-Si\\u000a alloy specimens to clarify the effect of silicon particles including the content, area fraction and intercept length of primary\\u000a silicon particles on

Ko-Ta Chiang; De-Chang Tsai

2008-01-01

138

Measurements of Kinetic Energy Loss for Particles Impacting Surfaces  

Microsoft Academic Search

Incoming and rebounding particle velocities were measured to within several particle diameters of the impaction surface using laser Doppler velocimetry. Impacts occurred normal to the surface and ranged from 1 m\\/s, near the threshold for particle bounce, to 100 m\\/s, well into the plastic damage regime. Monodisperse ammonium fluorescein spheres, 2.6–6.9 ?m in diameter, impacted target surfaces including polished molybdenum

Stephen Wall; Walter John; Hwa-Chi Wang; Simon L. Goren

1990-01-01

139

Measurement of surface heat transfer due to particle impact  

Microsoft Academic Search

Heat transfer coefficients for a surface continuously impacted by a stream of falling particles in air and in helium were measured as functions of particle flux and particle velocity. The purpose was to provide well-controlled data to clarify the mechanisms of heat transfer in particle suspension flows. The particles were spherical glass beads with mean diameters of 0.5, 1.13, and

J. G. Sun; M. M. Chen

1995-01-01

140

Polymer hollow particles with controllable holes in their surfaces  

NASA Astrophysics Data System (ADS)

Colloidal particles with hollow interiors play important roles in microencapsulation-a process that has found widespread use in applications such as controlled release of drugs, cosmetics, inks, pigments or chemical reagents; protection of biologically active species; and removal of pollutants. The hollow particles are most commonly prepared by coating the surfaces of colloidal templates with thin layers of the desired material (or its precursor), followed by selective removal of the templates by means of calcination or chemical etching. This simple and straightforward approach works for a variety of materials that include polymers, ceramics, composites and metals. For polymers, methods such as emulsion polymerization, phase separation, crosslinking of micelles and self-assembly have also been demonstrated for generating hollow structures. However, diffusion through these closed shells with pores <10 nm is often a slow process. To solve this problem, macroporous capsules have been fabricated by organizing colloids around liquid droplets to form colloidosomes or by controlling the mixing of liquid droplets. Here we report the preparation of another class of macroporous capsules-polymer shells with controllable holes in their surfaces. After loading of functional materials, the holes can be closed by means of thermal annealing or solvent treatment.

Hyuk Im, Sang; Jeong, Unyong; Xia, Younan

2005-09-01

141

Improvement of luminescence degradation in pure water of nanocrystalline silicon particles covered by a hydrogenated amorphous carbon layer  

NASA Astrophysics Data System (ADS)

The stability of luminescence in pure water of surface-modified nanocrystalline silicon (nc-Si) particles has been studied. The surfaces of nc-Si particles were modified with more stable silicon-oxygen (Si-O) and silicon-carbon (Si-C) bonds by the formation of a thin native oxide layer and a hydrogenated amorphous carbon (a-C:H) layer consisting of both disordered regions and graphite bands. The peak position of luminescence in pure water of the sample with the a-C:H layer was similar to that in the sample without the a-C:H layer. Moreover, the degradation rate of the luminescence intensity of the sample with the a-C:H layer was less than that of the sample without the a-C:H layer, for immersion in pure water above 100 h. The luminescence in pure water of the a-C:H coated sample could be seen with the naked eye even after aging for 200 h. The degradation of the luminescence in pure water can be improved remarkably by the formation of Si-O and Si-C bonds with strong bond strengths on the surfaces of the nc-Si particles.

Sato, Keisuke; Kishimoto, Naoki; Oku, Takahiro; Hirakuri, Kenji

2007-07-01

142

Observations of turbulence-induced new particle formation in the residual layer  

NASA Astrophysics Data System (ADS)

Aerosol particle measurements in the atmospheric boundary layer performed by a helicopter-borne measurement payload and by a lidar system from a case study during the IMPACT field campaign in Cabauw (NL) are presented. Layers of increased number concentrations of ultrafine particles were observed in the residual layer, indicating relatively recent new-particle formation. These layers were characterized by a sub-critical Richardson number and concomitant increased turbulence. Turbulent mixing is likely to lead to local supersaturation of possible precursor gases which are essential for new particle formation. Observed peaks in the number concentrations of ultrafine particles at ground level are connected to the new particle formation in the residual layer by boundary layer development and vertical mixing.

Wehner, B.; Siebert, H.; Ansmann, A.; Ditas, F.; Seifert, P.; Stratmann, F.; Wiedensohler, A.; Apituley, A.; Shaw, R. A.; Manninen, H. E.; Kulmala, M.

2010-01-01

143

Observations of turbulence-induced new particle formation in the residual layer  

NASA Astrophysics Data System (ADS)

Aerosol particle measurements in the atmospheric boundary layer performed by a helicopter-borne measurement payload and by a lidar system from a case study during the IMPACT field campaign in Cabauw (NL) are presented. Layers of increased number concentrations of ultrafine particles were observed in the residual layer, indicating relatively recent new-particle formation. These layers were characterized by a sub-critical Richardson number and concomitant increased turbulence. Turbulent mixing is likely to lead to local supersaturation of possible precursor gases which are essential for new particle formation. Observed peaks in the number concentrations of ultrafine particles at ground level are connected to the new particle formation in the residual layer by boundary layer development and vertical mixing.

Wehner, B.; Siebert, H.; Ansmann, A.; Ditas, F.; Seifert, P.; Stratmann, F.; Wiedensohler, A.; Apituley, A.; Shaw, R. A.; Manninen, H. E.; Kulmala, M.

2010-05-01

144

Compact Layer of Alkali Ions at the Surface of Colloidal Silica  

SciTech Connect

The forces of electrical imaging strongly polarize the surface of colloidal silica. I used X-ray scattering to study the adsorbed 2-nm-thick compact layer of alkali ions at the surface of concentrated solutions of 5-nm, 7-nm, and 22-nm particles, stabilized by either NaOH or a mixture of NaOH and CsOH, with the total bulk concentration of alkali ions ranging from 0.1 to 0.7 mol/L. The observed structure of the compact layer is almost independent of the size of the particles and the concentration of alkali base in the sol; it can be described by a two-layer model, that is, a {approx}6--8-{angstrom}-thick layer of directly adsorbed hydrated alkali ions with a surface concentration of {approx}3 x 10{sup 18} m{sup -2}, and a {approx}13-{angstrom}-thick layer with a surface concentration of sodium ions of {approx}8 x 10{sup 18} m{sup -2}. In cesium-enriched sols, Cs{sup +} ions preferentially adsorb in the first layer replacing Na{sup +}; their density in the second layer does not depend on the presence of cesium in the sol. The difference in the adsorption of Cs{sup +} and Na{sup +} ions can be explained by the ion-size-dependent term in the electrostatic Gibbs energy equation derived earlier by others. I also discuss the surface charge density and the value of surface tension at both the air/sol and the hexane/sol interfaces.

Tikhonov,A.

2007-01-01

145

Surface-Layer Lattices as Patterning Element for Multimeric Extremozymes.  

PubMed

A promising new approach for the production of biocatalysts comprises the use of surface-layer (S-layer) lattices that present functional multimeric enzymes on their surface, thereby guaranteeing most accurate spatial distribution and orientation, as well as maximal effectiveness and stability of these enzymes. For proof of concept, a tetrameric and a trimeric extremozyme are chosen for the construction of S-layer/extremozyme fusion proteins. By using a flexible peptide linker, either one monomer of the tetrameric xylose isomerase XylA from the thermophilic Thermoanaerobacterium strain JW/SL-YS 489 or, in another approach, one monomer of the trimeric carbonic anhydrase from the methanogenic archaeon Methanosarcina thermophila are genetically linked to one monomer of the S-layer protein SbpA of Lysinibacillus sphaericus CCM 2177. After isolation and purification, the self-assembly properties of both S-layer fusion proteins as well as the specific activity of the fused enzymes are confirmed, thus indicating that the S-layer protein moiety does not influence the nature of the multimeric enzymes and vice versa. By recrystallization of the S-layer/extremozyme fusion proteins on solid supports, the active enzyme multimers are exposed on the surface of the square S-layer lattice with 13.1 nm spacing. PMID:23757161

Ferner-Ortner-Bleckmann, Judith; Gelbmann, Nicola; Tesarz, Manfred; Egelseer, Eva M; Sleytr, Uwe B

2013-06-12

146

Dusty boundary layer in a surface-burst explosion  

SciTech Connect

Dusty boundary layers are an inherent feature of explosions over ground surfaces. Detailed knowledge of dusty boundary layer characteristics is needed in explosion safety analysis (e.g., to calculate the drag loads on structures). Also, to predicct the amount of dust in the rising fireball of an explsion, one must know the dusty boundary layer swept up during the positive and negative phases of the blast wave and how much of this boundary layer dust is entrained into the stem of the dust cloud. This paper describes the results of numerical simulations of the dusty boundary layer created by a surface burst explosion. The evolution of the flow was calculated by a high-order Godunov code that solves the nonsteady conservation laws.

Kuhl, A.L. [Lawrence Livermore National Lab., El Segundo, CA (United States); Ferguson, R.E.; Chien, K.Y.; Collins, J.P. [Naval Surface Warfare Center, Silver Spring, MD (United States)

1993-08-01

147

Mechanisms for particle transfer and segregation in a turbulent boundary layer  

Microsoft Academic Search

Particle transfer in the wall region of turbulent boundary layers is dominated by the coherent structures which control the turbulence regeneration cycle. Coherent structures bring particles toward and away from the wall and favour particle segre- gation in the viscous region, giving rise to non-uniform particle distribution proles which peak close to the wall. The object of this work is

ALFREDO S OLDATI

2002-01-01

148

Mechanisms for particle transfer and segregation in a turbulent boundary layer  

Microsoft Academic Search

Particle transfer in the wall region of turbulent boundary layers is dominated by the coherent structures which control the turbulence regeneration cycle. Coherent structures bring particles toward and away from the wall and favour particle segregation in the viscous region, giving rise to non-uniform particle distribution profiles which peak close to the wall. The object of this work is to

Cristian Marchioli; Alfredo Soldati

2002-01-01

149

Metal-induced nanostructures on surfaces of layered chalcogenides  

NASA Astrophysics Data System (ADS)

The development of layered dichalcogenide crystal surfaces during early stages of metal deposition has been investigated, using ultra-high vacuum electron beam evaporation of copper at ambient temperature onto (0 0 0 1) VSe2 crystal surfaces as model case. Analytical transmission electron microscopy techniques, scanning electron microscopy, and atomic force microscopy have been combined to characterize the microscopic nature of the surface structures and the self-assembled formation of surface nanostructures that form as large nanostructures (lateral dimensions > 100 nm) and as networks of smaller nanostructures (lateral dimensions ˜ several 10 nm). Nearly contiguous ultrathin layers of a copper-rich crystalline surface phase are observed for deposition stages at a nominal Cu coverage of 1 nm and above. The observations indicate that compressive in-plane strains are induced in the VSe2 surface layers by the formation of a copper-rich crystalline phase by intercalation, with possible contributions of an electronic charge transfer from copper atoms to the substrate during the earliest deposition stages. Above a critical value the surface layer strains are relaxed by formation of surface folds, nanostructure networks and interface dislocations.

Hollensteiner, S.; Spiecker, E.; Jäger, W.

2005-02-01

150

Shock Wave / Boundary Layer Interaction Experiment on Control Surface.  

National Technical Information Service (NTIS)

The shock wave / boundary layer interaction (SWBLI) experiment is part of the EXPERT mission. SWBLI is studied on two identical fixed compression ramps made of C/SiC, which are models for control surfaces. The flow separates on the flat surfaces upstream ...

L. Prochazka S. Schlamp T. Rosgen

2007-01-01

151

The effects of cylindrical surface modifications on turbulent boundary layers  

Microsoft Academic Search

A study employing a combination of hydrogen bubble-wire flow visualization and hot-film anemometry measurements has been conducted to determine the effects sublayer scale streamwise surface modifications on the structure and flow characteristics of turbulent boundary layers. The surface modifications were created using very fine monofilament fishing line of an approximate non-dimensional height of h + = 4. Spanwise line spacings

J. B. Johansen; C. R. Smith

1983-01-01

152

Role of surface active layers on localized breakdown of aluminum alloy 7075  

NASA Astrophysics Data System (ADS)

Potentiodynamic polarization curves for AA7075-T6 in NaCl solution exhibit two breakdowns. The current increases at the first breakdown, reaches a peak and then decreases. At the second, higher breakdown potential, the current increases again. The second breakdown is dominated by sustained localized corrosion and the first one is believed to be associated with transient dissolution that precedes the onset of stable localized corrosion. This study is aimed at understanding the details of the transient dissolution phenomenon. The first breakdown mechanism of AA7xxx was studied by an in-situ observation system in which a combination of a magnified image of the surface with the instantaneous polarization curve allowed determination of the corrosion process as a function of potential. As-polished (to 1 mum) AA7075-T6 clearly exhibited dissolution of a thin surface layer corresponding to a sharp increase of current just above the first breakdown. No surface layer dissolution was observed for samples that were either ion milled or chemically etched to remove the effects of polishing. This susceptible surface layer was apparently the result of the mechanical polishing process. The surface microstructure of an as-polished sample was analyzed by TEM and several distinct features were found: (1) a unique thin layer with thickness of 100 nm on average; (2) many fewer fine hardening particles in the thin layer compared to bulk matrix, which means that the fine particles were destroyed and eliminated by polishing; (3) high aspect ratio nano-grains elongate along the final polishing direction; EDS analysis in STEM mode revealed a higher concentration of Zn at the nano-grain boundaries. The attack of the surface layer might initiate at the active nanograin boundary followed by nano-grain dissolution. Samples in other tempers were also examined. No surface layer dissolution and no first breakdown peak were observed for the solutionized + quenched alloy because no comparable Zn enriched bands were present and the composition of the surface layer was not substantially different than the bulk matrix. The solutionized samples did not contain hardening particles so there was no effect of the shearing on the surface composition. The overaged samples also exhibited no layer attack and only one breakdown potential. The particles in the overaged samples were larger and farther apart so that the shear associated with polishing was unable to destroy them fully. Zn-rich bands were observed at the nano-brain boundaries for the overaged temper, but the localized attack propagated into the bulk matrix rather than laterally as layer attack. Underaged samples showed thin layer dissolution and current peaks associated with a first breakdown phenomenon. However, the magnitude of the current peaks changed with the extent of aging as a result of differences in the hardness, and thus layer thickness and dissolution rate of the thin layer. A study of filiform corrosion (FFC) was performed on T6 and T7 temper samples either as-polished or chemically etched. FFC kinetics were higher on as-polished samples than on chemically etched samples, which confirmed higher activity of the altered surface layer induced by polishing. FFC on T6 sample of all the conditions was worse than T7 tempered samples.

Zhao, Zhijun

153

Hygroscopic behavior and liquid-layer composition of aerosol particles generated from natural and artificial seawater  

Microsoft Academic Search

Sea-salt aerosol (SSA) particles affect the Earth's radiative balance and moderate heterogeneous chemistry in the marine boundary layer. Using conventional and environmental transmission electron microscopes (ETEM), we investigated the hygroscopic growth and liquid-layer compositions of particles generated from three types of aqueous salt solutions: sodium chloride, laboratory-synthesized seawater (S-SSA particles), and natural seawater (N-SSA particles). Three levels of morphological change

Matthew E. Wise; Evelyn J. Freney; Corey A. Tyree; Jonathan O. Allen; Scot T. Martin; Lynn M. Russell; Peter R. Buseck

2009-01-01

154

Sh-matrices method as applied to scattering by particles with layered structure  

Microsoft Academic Search

We develop a modification of the T-matrix method that allows for fast calculations of light-scattering properties of non-spherical particles with layered structure. This modification uses the Sh-matrices that depend on the shape of particles only and do not depend on the particle size or optical constants. The matrices are obtained for any number of discrete layers of a particle with

D. Petrov; Yu. Shkuratov; E. Zubko; G. Videen

2007-01-01

155

Enhanced magnetoresistance and surface state of CrO 2 particles improved by chemical process  

Microsoft Academic Search

The paper presents an approach to enhance a magnetoresistance (MR) effect in CrO2 powder compact by an oxidization reaction process. An aqueous potassium permanganate (KMnO4) was used to react with the CrO2 particles coated naturally with Cr2O3 layer. The experiment indicates that the strong oxidant can effectively adjust thickness of the natural Cr2O3 layer, and thereby change the surface state

Xiaoyu Zhang; Yajie Chen; Zhenya Li

2006-01-01

156

Dual-layered-coated mechanically-durable superomniphobic surfaces with anti-smudge properties.  

PubMed

Bio-inspired surfaces that exhibit high contact angle and low contact angle hysteresis for various liquids and demonstrate mechanical durability and anti-smudge properties are of interest for various applications. The fabrication of such surfaces has often involved complex or expensive processes, required techniques that may not be suitable for various substrates and particles, may require surface post-treatment, or may lack durability. Dual layered coatings of roughness-induced superomniphobic surfaces that demonstrate good mechanical durability were fabricated on glass substrates using hydrophobic SiO2 nanoparticles and low surface energy fluorobinders using dip coating and spray coating techniques. The particle-to-binder ratio was optimized for contact angles of interest. The mechanical durability of these coatings was examined under mechanical rubbing action. The anti-smudge properties were examined by wiping an artificially contaminated coating using oil-impregnated microfiber cloth. PMID:23993782

Muthiah, Palanikkumaran; Bhushan, Bharat; Yun, Kyungsung; Kondo, Hirofumi

2013-07-30

157

Energetic charged-particle interactions with atmospheres and surfaces  

Microsoft Academic Search

The surfaces of interstellar and interplanetary grains, planetary satellites, ring particles, asteroids, Mercury and the Moon, etc. are all directly exposed to radiation bombardment, as are the upper atmospheres of the planets and large satellites. The sources of this radiation include the solar wind, magnetospheric plasmas, cosmic rays, solar energetic particles and U.V. photons. The interaction of these particles with

R. E. Johnson

1990-01-01

158

Surface charge and wetting characteristics of layered silicate minerals.  

PubMed

The surface characteristics, including surface charge and wettability, of layered silicates are reviewed based on experimental results and molecular dynamics simulation (MDS) results. The surface charge features of important layered silicates including mica, talc, and kaolinite are described from atomic force microscopy (AFM) measurements, electrophoresis measurements, and/or results from potentiometric titration. In addition, the wetting characteristics of the silica tetrahedral surface which is common to all layered silicates are examined with different experimental techniques and results are discussed. The wettability of trilayer silicates and bilayer silicates is discussed, particularly the wettability of the silica tetrahedral face and alumina octahedral face of kaolinite based on MDS results as well as recent AFM results. PMID:22809732

Yin, Xihui; Gupta, Vishal; Du, Hao; Wang, Xuming; Miller, Jan D

2012-06-30

159

A particle-in-cell method for the solution of two-layer shallow-water equations  

Microsoft Academic Search

A particle-in-cell (PIC) numerical method developed for the study of shallow-water dynamics, when the moving fluid layer is laterally confined by the intersection of its top and bottom surfaces, is described. The effect of ambient rotation is included for application to geophysical fluids, particularly open-ocean buoyant vortices in which the underlying density interface outcrops to the surface around the rim

Benoit Cushman-Roisin; Oleg E. Esenkov; Benedict J. Mathias

2000-01-01

160

Medical applications of diamond particles and surfaces.  

SciTech Connect

Diamond has been considered for use in several medical applications due to its unique mechanical, chemical, optical, and biological properties. In this paper, methods for preparing synthetic diamond surfaces and particles are described. In addition, recent developments involving the use of diamond in prostheses, sensing, imaging, and drug delivery applications are reviewed. These developments suggest that diamond-containing structures will provide significant improvements in the diagnosis and treatment of medical conditions over the coming years. Diamond is an allotrope of carbon that is being considered for use in several medical applications. Ramachandran determined that the crystal structure of diamond consists of two close packed interpenetrating face centered cubic lattices; one lattice is shifted with respect to the other along the elemental cube space diagonal by one-quarter of its length. If one approximates carbon atoms as equal diameter rigid spheres, the filling of this construction is 34%. Due to the carbon-carbon distance (1.54 {angstrom}), diamond crystal exhibits the highest atomic density (1.76 x 10{sup 23} cm{sup -3}) of any solid. The very high bond energy between two carbon atoms (83 kcal/mol) and the directionality of tetrahedral bonds are the main reasons for the high strength of diamond. Diamond demonstrates the highest Vickers hardness value of any material (10,000 kg/mm{sup 2}). The tribological properties of diamond are also impressive; the coefficient of friction of polished diamond is 0.07 in argon and 0.05 in humid air. Diamond is resistant to corrosion except in an oxygen atmosphere at temperatures over 800 C. In addition, type IIa diamond exhibits the highest thermal conductivity of all materials (20 W cm{sup -1} K{sup -1} at room temperature).

Narayan, R. J.; Boehm, R. D.; Sumant, A. V. (Center for Nanoscale Materials); (Univ. of California)

2011-04-01

161

Energetic Charged-Particle Interactions with Atmospheres and Surfaces  

Microsoft Academic Search

The surfaces of interstellar and interplanetary grains, planetary satellites, ring particles, asteroids, Mercury and the Moon, etc. are all directly exposed to radiations. Solar wind, magnetospheric plasmas, cosmic rays, solar energetic particles, and U.V. photons can all produce chemical and physical alterations. These alterations affect the surface reflection properties and can eject species into the gas phase affecting the ambient

Robert E. Johnson

1990-01-01

162

Keeping in Touch: Microbial Life on Soil Particle Surfaces  

Microsoft Academic Search

Microorganisms in unsaturated soil live in a world dominated by the presence of extensive surfaces, both solid and gas–liquid interfacial surfaces. Particle attachment in soils is similar to particle attachment in aquatic systems, which, because of the high abundance of suspended populations has been widely studied. Although there seems to be a general advantage to the microbes living at the

Aaron L Mills

2003-01-01

163

Surface layer formation on Sn anode: ATR FTIR spectroscopic characterization  

Microsoft Academic Search

Surface layer formed on Sn thin film electrode in 1M LiPF6\\/EC:DMC electrolyte was characterized using ex situ FTIR spectroscopy with the attenuated total reflection technique. IR spectral analyses showed that the immersion of Sn film in the electrolyte resulted in a chemical interfacial reaction leading to the passivation of Sn surface with primarily PF-containing inorganic surface species and small amount

Seung-Wan Song; Seung-Won Baek

2009-01-01

164

Surface Area and Particle Size of Evaporated Lead Sulfide Films  

Microsoft Academic Search

Physical adsorption isotherms of lead sulfide films evaporated in vacuum and through oxygen were measured in order to determine their surface area and particle size. The surface areas of fresh and of annealed vacuum evaporated films were found to increase linearly with film thickness. Annealing the films in vacuum decreased the surface area considerably. The average specific surfaces of the

Roy H. Harada

1956-01-01

165

Method for producing functionally graded nanocrystalline layer on metal surface  

DOEpatents

An improved process for the creation or formation of nanocrystalline layers on substrates' surfaces is provided. The process involves "prescuffing" the surface of a substrate such as a metal by allowing friction to occur on the surface by a load-bearing entity making rubbing contact and moving along and on the substrate's surface. The "prescuffing" action is terminated when the coefficient of friction between the surface and the noise is rising significantly. Often, the significant rise in the coefficient of friction is signaled by a change in pitch of the scuffing action sound emanating from the buffeted surface. The "prescuffing" gives rise to a harder and smoother surface which withstands better any inadequate lubrication that may take place when the "prescuffed" surface is contacted by other surfaces.

Ajayi, Oyelayo O. (Oswego, IL); Hershberger, Jeffrey G. (Berwyn, IL)

2010-03-23

166

Method for producing functionally graded nanocrystalline layer on metal surface  

SciTech Connect

An improved process for the creation or formation of nanocrystalline layers on substrates' surfaces is provided. The process involves "prescuffing" the surface of a substrate such as a metal by allowing friction to occur on the surface by a load-bearing entity making rubbing contact and moving along and on the substrate's surface. The "prescuffing" action is terminated when the coefficient of friction between the surface and the noise is rising significantly. Often, the significant rise in the coefficient of friction is signaled by a change in pitch of the scuffing action sound emanating from the buffeted surface. The "prescuffing" gives rise to a harder and smoother surface which withstands better any inadequate lubrication that may take place when the "prescuffed" surface is contacted by other surfaces.

Ajayi, Oyelayo O. (Oswego, IL); Hershberger, Jeffrey G. (Berwyn, IL)

2010-03-23

167

Lactobacillus surface layer proteins: structure, function and applications.  

PubMed

Bacterial surface (S) layers are the outermost proteinaceous cell envelope structures found on members of nearly all taxonomic groups of bacteria and Archaea. They are composed of numerous identical subunits forming a symmetric, porous, lattice-like layer that completely covers the cell surface. The subunits are held together and attached to cell wall carbohydrates by non-covalent interactions, and they spontaneously reassemble in vitro by an entropy-driven process. Due to the low amino acid sequence similarity among S-layer proteins in general, verification of the presence of an S-layer on the bacterial cell surface usually requires electron microscopy. In lactobacilli, S-layer proteins have been detected on many but not all species. Lactobacillus S-layer proteins differ from those of other bacteria in their smaller size and high predicted pI. The positive charge in Lactobacillus S-layer proteins is concentrated in the more conserved cell wall binding domain, which can be either N- or C-terminal depending on the species. The more variable domain is responsible for the self-assembly of the monomers to a periodic structure. The biological functions of Lactobacillus S-layer proteins are poorly understood, but in some species S-layer proteins mediate bacterial adherence to host cells or extracellular matrix proteins or have protective or enzymatic functions. Lactobacillus S-layer proteins show potential for use as antigen carriers in live oral vaccine design because of their adhesive and immunomodulatory properties and the general non-pathogenicity of the species. PMID:23677442

Hynönen, Ulla; Palva, Airi

2013-05-16

168

Formation and manipulation of regular metallic nanoparticle arrays on bacterial surface layers: an advanced TEM study  

NASA Astrophysics Data System (ADS)

The template-directed formation of regular nanoparticle arrays on two-dimensional crystalline protein layers after their treatment with metal salt complexes was studied by transmission electron microscopy. For these investigations, bacterial surface layers (S layers), recrystallized in vitro into sheets and tube-shaped protein crystals with typical dimensions in the micrometer range, were used as the template. As identified by electron holography and scanning force microscopy, the S-layer tubes form alternating double layers when deposited onto a solid substrate surface. Two distinct pathways for the metal particle formation at the templates have been found: the site-specific growth of metal clusters by chemical reduction of the metal salt complexes, and the electron-beam induced growth of nanoparticles in the transmission electron microscope. Both mechanisms lead to regular arrays with particle densities > 6×1011cm-2. Nanoparticle formation by electron exposure takes exclusively place in the flat-lying double-layered protein tubes, where a sufficient amount of metal complexes can be accumulated during sample preparation.

Mertig, M.; Wahl, R.; Lehmann, M.; Simon, P.; Pompe, W.

169

Immobilization of the Aminopeptidase from Aeromonas Proteolytica on Mg2+/Al3+ Layered Double Hydroxide Particles  

PubMed Central

A novel biomaterial formed by the immobilization of the Aminopeptidase from Aeromonas Proteolytica (AAP) on synthetic Mg2+ and Al3+ ion-containing layered double hydroxide (LDH) particles was prepared. Immobilization of AAP on the LDH particles in a buffered, aqueous mixture is rapid such that the maximum loading capacity, 1 × 10-9 moles of AAP/mg LDH, is achieved in a few minutes. X-ray powder diffraction of LDH samples before and after treatment with AAP indicates that the enzyme does not intercalate between the layers of LDH, but instead binds to the surface. Treatment of AAP/LDH with various amounts of salt in a buffered mixture demonstrates that between 15 and 20% of AAP can be removed from the LDH by washing the composite material in 0.2 M NaCl. However, the residual AAP remains bound to the LDH even at 1 M salt concentrations. A suspension of the AAP/LDH biomaterial in 10 mM Tricine buffered, aqueous solution (pH 8.0 and 25 ° C) catalyzes the hydrolysis of l-leucine-p-nitroanilide demonstrating that immobilized AAP remains available to substrate and retains its catalytic activity. Recycling experiments reveal that the AAP/LDH particles can be recovered and reused multiple times without appreciable loss of activity. This work provides the foundation for the development of materials that will function in the degradation or detection of peptide hormones or neurotoxins.

Frey, Steven T.; Guilmet, Stephanie L.; Egan, Richard G.; Bennett, Alyssa; Soltau, Sarah R.; Holz, Richard C.

2010-01-01

170

Synthesis and characterization of macromolecular layers grafted to polymer surfaces  

NASA Astrophysics Data System (ADS)

The composition and behavior of surfaces and interfaces play a pivotal role in dictating the overall efficiency of the majority of polymeric materials and devices. Surface properties of the materials can be altered using surface modification techniques. It is necessary to highlight that successful methods of surface modification should affect only the upper layer of the polymer material without changing bulk properties. The processes must introduce new functionalities to the surface, optimize surface roughness, lubrication, hydrophobicity, hydrophilicity, adhesion, conductivity, and/or biocompatibility. Research presented in this dissertation is dedicated to the synthesis, characterization, and application of thin macromolecular layers anchored to polymer substrates. Specifically, attachment of functional polymers via a "grafting to" approach has been extensively studied using PET and nylon model substrates. First, poly(glycidyl methacrylate) was used to introduce permanent functionalities to the model substrates by anchoring it to model films. Then, three different functional polymers were grafted on top of the previous layer. As one part of this study, the temperature and time dependence of grafting functional layers were studied. The surface coverage by hydrophobic polymer was determined from experimental data and predicted by a model. In general, the model has a high degree of predictive capability. Next, surface modification of polymeric fibers and membranes is presented as an important application of the polymer thin layers targeted in the study. Specifically, the procedures developed for surface modification of model substrates was employed for modification of PET, nylon, and cotton fabrics as well as PET track-etched membranes. Since epoxy groups are highly reactive in various chemical reactions, the approach becomes virtually universal, allowing both various surfaces and end-functionalized macromolecules to be used in the grafted layer synthesis. PET membranes modified with a reactive anchoring layer can be successfully used to build membrane assemblies by incorporating silica, aluminum, or titanium oxide microparticles as spacers. It is expected that the proposed approaches for the surface modification of the membranes and for the generation of multilayered membrane assemblies can be employed straightforwardly to provide an efficient platform for fabrication of breathable protective materials. Characterization of modified membranes with a cantilever-based method, which can be used for prediction of properties and behavior of thin grafted films, is reported. This technique can be used as a method for fast screening of modified membranes. The method is very robust and capable of detecting very small quantities of substance adsorbed; kinetics of the process can be tracked, as well. This approach can be further developed as a handheld sensor for early warning of the presence of chemical vapors and nerve agents.

Burtovyy, Oleksandr

171

Alternative barrier layers for surface covers in dry climates  

SciTech Connect

Surface covers are one of the most widespread remediation and waste management options in all climates. Barrier layers to limit percolation through cover systems are principal features of engineered, multi-component cover designs. Conventional barrier layer components developed for humid climates have limitations in dry climates. One alternative barrier layer is a capillary barrier, which consists of a fine-over-coarse soil arrangement. The capacity of capillary barrier to laterally divert downward moving water is the key to their success. Another alternative is a dry barrier, in which atmospheric air is circulated through a coarse layer within the cover to remove water vapor. Incorporating a coarse layer which stores water for subsequent removal by air flow reduces the requirements for the air flow velocity and increases the applicability of the dry barrier.

Stormont, J.C.

1994-09-01

172

Cake filtration with particle penetration at the cake surface  

SciTech Connect

Particles in drilling muds build a filter cake on borehole walls and can migrate into the adjacent porous formation and cause formation damage. This study analyzes cake formation, including particle penetration at the cake surface. Mass-balance equations for captured and suspended particles and the fluid phase are averaged along the cake thickness, taking into account conditions of the surface and the septum. Capture mechanisms, such as surface straining, and internal cake erosion and particle capture are included in the analysis. The results are ordinary differential equations in terms of thickness, average particle concentration, average porosity, and such operational parameters as slurry concentration, injection rate, and volumetric solid fraction. Results show that during early stages of cake formation, penetrated-particle concentration peaks and then declines rapidly shortly thereafter.

Corapcioglu, M.Y. (Washington State Univ., Olympia, WA (USA)); Abboud, N.M. (Univ. of Connecticut, CT (US))

1990-08-01

173

Time-resolved surface infrared spectroscopy during atomic layer deposition.  

PubMed

This work presents a novel method for obtaining surface infrared spectra with sub-second time resolution during atomic layer deposition (ALD). Using a rapid-scan Fourier transform infrared (FT-IR) spectrometer, we obtain a series of synchronized interferograms (120 ms) during multiple ALD cycles to observe the dynamics of an average ALD cycle. We use a buried metal layer (BML) substrate to enhance absorption by the surface species. The surface selection rules of the BML allow us to determine the contribution from the substrate surface as opposed to that from gas-phase molecules and species adsorbed at the windows. In addition, we use simulation to examine the origins of increased reflectivity associated with phonon absorption by the oxide layers. The simulations are also used to determine the decay in enhancement by the buried metal layer substrate as the oxide layer grows during the experiment. These calculations are used to estimate the optimal number of ALD cycles for our experimental method. PMID:24067630

Sperling, Brent A; Hoang, John; Kimes, William A; Maslar, James E

2013-09-01

174

Using ?-PIV to Interrogate the Endothelial Surface Layer in Arterioles in vivo  

Microsoft Academic Search

The existence of a hydrodynamically relevant endothelial surface layer (ESL) is well established in capillaries and venules. Since the ESL on vascular endothelial cells likely has broad implications for endothelial-cell function, it is necessary to determine the extent of its presence in arterioles. We applied microviscometric analysis to data obtained using micro-particle image velocimetry (?-PIV) in arterioles of wild-type mice.

Michele D. Savery; E. R. Damiano

2007-01-01

175

Effect of nanoconfinement on polymer dynamics: surface layers and interphases.  

PubMed

We present neutron spin echo experiments that address the much debated topic of dynamic phenomena in polymer melts that are induced by interacting with a confining surface. We find an anchored surface layer that internally is highly mobile and not glassy as heavily promoted in the literature. The polymer dynamics in confinement is, rather, determined by two phases, one fully equal to the bulk polymer and another that is partly anchored at the surface. By strong topological interaction, this phase confines further chains with no direct contact to the surface. These form the often invoked interphase, where the full chain relaxation is impeded through the interaction with the anchored chains. PMID:23521308

Krutyeva, M; Wischnewski, A; Monkenbusch, M; Willner, L; Maiz, J; Mijangos, C; Arbe, A; Colmenero, J; Radulescu, A; Holderer, O; Ohl, M; Richter, D

2013-03-05

176

Application of atomic force microscopy to microbial surfaces: from reconstituted cell surface layers to living cells.  

PubMed

The application of atomic force microscopy (AFM) to probe the ultrastructure and physical properties of microbial cell surfaces is reviewed. The unique capabilities of AFM can be summarized as follows: imaging surface topography with (sub)nanometer lateral resolution; examining biological specimens under physiological conditions; measuring local properties and interaction forces. AFM is being used increasingly for: (i) visualizing the surface ultrastructure of microbial cell surface layers, including bacterial S-layers, purple membranes, porin OmpF crystals and fungal rodlet layers; (ii) monitoring conformational changes of individual membrane proteins; (iii) examining the morphology of bacterial biofilms, (iv) revealing the nanoscale structure of living microbial cells, including fungi, yeasts and bacteria, (v) mapping interaction forces at microbial surfaces, such as van der Waals and electrostatic forces, solvation forces, and steric/bridging forces; and (vi) probing the local mechanical properties of cell surface layers and of single cells. PMID:10936459

Dufrêne, Y F

2001-02-01

177

On the mechanism of particle deposition through boundary layers in heat exchange systems  

NASA Astrophysics Data System (ADS)

A theory is developed that will enable the prediction of particle deposition through laminar and turbulent boundary layers under the influence of thermal and concentration gradients. Various mechanisms are described, and the simultaneous occurrence of different mechanisms is examined. The effect of changing heat flux to the deposition surface is investigated, and a pseudovelocity term is developed which serves to increase or decrease the heat flux to the wall depending on the species present. Special emphasis is placed on the fouling and deposition associated with exchange systems exposed to high, moderate, and low temperatures. The various mechanisms associated with fouling and deposition are discussed, and areas for future research are identified. A suggestion is made for examining the deposition of particulates on transfer surfaces with regard to their diffusion rates at low temperatures and high concentration gradients in order to provide better predictive capability.

Gupta, A. K.; Jackson, T. W.

1986-01-01

178

Effects of WC particle size on the wear resistance of laser surface alloyed medium carbon steel  

NASA Astrophysics Data System (ADS)

The CO 2 laser surface alloying technique was used to form wear resistance layers on medium carbon steel with a kind of spherical WC powder. The effects of WC particle size on the abrasive wear resistance were thoroughly investigated. The results indicate that the laser alloyed layer is characterized by dendritic primary phase and ledeburite microstructure, consisting of austenite, martensite and carbides of Fe 3W 3C, W 2C and WC. The laser surface alloying with WC powder could improve the abrasive wear resistance of the medium carbon steel by over 63%. The factors such as the hardness, the amount and the distribution of WC particle determined the laser alloyed samples' wear resistance, and the laser alloyed sample with WC powder of 88-100 ?m diameter presented the best wear resistance in this study. Furthermore, the wear resistance mechanisms of the laser alloyed layers were also explored.

Tong, Xin; Li, Fu-hai; Kuang, Min; Ma, Wen-you; Chen, Xing-chi; Liu, Min

2012-01-01

179

Production of micron-sized polystyrene particles containing PEG near the particles surface  

Microsoft Academic Search

Polystyrene (PS) particles in the size range of 1-7 µm, containing poly(ethylene glycol) or PEG on the particles surface, were prepared by multi-step seeded polymerizations. Micron-sized PS particles were first prepared by dispersion polymerization using 2,2'-azobisisobutyronitrile as initiator and polyvinyl pyrrolidone as stabilizer. Conventional swelling method was then used to increase the size of the PS particles with a large

H. Ahmad; K. Tauer

2003-01-01

180

Deterioration of ZrC-coated fuel particle caused by failure of pyrolytic carbon layer  

Microsoft Academic Search

The ZrC coating layer is a candidate to replace the SiC coating layer of the Triso-coated fuel particles for high-temperature gas-cooled reactors. To understand the behavior of the ZrC-Triso-coated fuel particles at 1800 to 2000°C, a ceramographic examination and an electron probe microanalysis were performed on the ZrC-Triso-coated fuel particles after the post-irradiation heating tests and a thermodynamic analysis of

Kazuo Minato; Kousaku Fukuda; Hajime Sekino; Akiyoshi Ishikawa; Etsuro Oeda

1998-01-01

181

Electromagnetic fluctuation forces on a particle moving near a surface  

Microsoft Academic Search

Using the Lifshitz electromagnetic theory, general (nonrelativistic) expressions are derived of normal\\/lateral forces on a single spherical atom, a dipolar molecule and a charged particle moving near a surface. The dependences of the forces involved on the velocity, temperature, distance to the surface and dielectric properties are considered. The resonant effect of dynamical interaction between an atom and the surface

A. A. Kyasov; G. V. Dedkov

2000-01-01

182

Nonlinear optical probe of molecular structure on colloidal particle surfaces  

NASA Astrophysics Data System (ADS)

The structure of molecules adsorbed at the colloidal particle surface has great influence on how the colloidal particles interact among themselves and with the environment. In this presentation we show that Second Harmonic Generation from molecules adsorbed at the particle surface can be used for determining the orientation of the molecules at this buried interface. The determination is facilitated by nonlinear Rayleigh-Gans-Debye analysis of polarization and scattering angle dependent SHG. The first demonstration is performed on the cationic Malachite Green (MG) molecule adsorbed on three types of polystyrene microspheres with different surface composition and charges.

Jen, Shih-Hui

2005-03-01

183

Fluid-dynamics of the nuclear surface Fermi-layer  

Microsoft Academic Search

In the framework of the long-mean-free-path approach the fluid-dynamical model of the nuclear surface as a spherical Fermi-layer is formulated. It is shown that the model reproduces known results of Fermi-drop dynamics and permits the description of more low energy collective states in spherical nuclei. The quantum-capillary branch of low-lying surface excitations is predicted. The model gives an adequate description

S. I. Bastrukov; J. A. Maruhn

1990-01-01

184

The effects of cylindrical surface modifications on turbulent boundary layers  

Microsoft Academic Search

A study employing hydrogen bubble-wire flow visualization and hot-film anemometry measurements has been conducted to determine the effects of sublayer-scale streamwise surface modifications of approximate nondimensional height of h(+) = 4 on the structure and flow characteristics of turbulent boundary layers. The visualization results indicate that the surface modifications did affect the streak spacing characteristics, with the greatest effect occurring

J. B. Johansen; C. R. Smith

1985-01-01

185

Surface-tension-driven liquid layer flows in aerospace applications  

SciTech Connect

Surface-tension-driven liquid layer flows are reviewed and the basis for a complete model of such flows is presented. Particular emphasis is placed upon the modeling of cellular flows involving mass transfer. An Oseen-approximation in concert with an approximate evaporation law is used to develop analytical expressions for the coupled flow and concentration field. Specific applications involving laser surface processing are described. 17 references.

Legner, H.H.

1986-01-01

186

Super-hydrophobic surfaces of layer-by-layer structured film-coated electrospun nanofibrous membranes  

NASA Astrophysics Data System (ADS)

We have recently fabricated super-hydrophobic membrane surfaces based on the inspiration of self-cleaning silver ragwort leaves. This biomimetic super-hydrophobic surface was composed of fluoroalkylsilane (FAS)-modified layer-by-layer (LBL) structured film-coated electrospun nanofibrous membranes. The rough fibre surface caused by the electrostatic LBL coating of TiO2 nanoparticles and poly(acrylic acid) (PAA) was used to imitate the rough surface of nanosized grooves along the silver ragwort leaf fibre axis. The results showed that the FAS modification was the key process for increasing the surface hydrophobicity of the fibrous membranes. Additionally, the dependence of the hydrophobicity of the membrane surfaces upon the number of LBL coating bilayers was affected by the membrane surface roughness. Moreover, x-ray photoelectron spectroscopy (XPS) results further indicated that the surface of LBL film-coated fibres absorbed more fluoro groups than the fibre surface without the LBL coating. A (TiO2/PAA)10 film-coated cellulose acetate nanofibrous membrane with FAS surface modification showed the highest water contact angle of 162° and lowest water-roll angle of 2°.

Ogawa, Tasuku; Ding, Bin; Sone, Yuji; Shiratori, Seimei

2007-04-01

187

Particle size distributions of the cloud layer of the Venus atmosphere (The VEGA experiment)  

Microsoft Academic Search

Vega-probe measurements of particle size distributions in the Venus cloud layer indicate that only the accumulation mode operates on the nocturnal side of the planet; this mode is characteristic for aerosols formed through the transformation of gaseous components of the atmosphere into particles. This mode corresponds to the first mode in the Pioneer-Venus distributions; however, larger particles of the second

Iu. V. Zhulanov; L. M. Mukhin; D. F. Nenarokov; A. A. Lushnikov; I. V. Petrianov-Sokolov

1987-01-01

188

Modification of a commercial condensation particle counter for boundary layer balloon-borne aerosol studies  

Microsoft Academic Search

It was shown that the newly designed balloon-borne CPC is able to measure vertical profiles of meteorological parameters simultaneously with the particle number concentration >12 nm.In order to investigate further new particle production in the upper part of the boundary layer a second counting channel was added to the balloon payload allowing concurrent measurement of particle concentrations >5 nm and

J. Heintzenberg; A. Wiedensohler; T. Conrath; S. Kütz; R. Dubois

1998-01-01

189

Assembled monolayers of hydrophilic particles on water surfaces.  

PubMed

A facile and quick approach to prepare self-assembled monolayers of water-dispersible particles on the water surface is presented. Particle suspensions in alcohols were dropped on a water reservoir to form long-range ordered monolayers of various particles, including spherical solid particles, soft hydrogel particles, metal nanoparticles, quantum dots, nanowires, single-wall carbon nanotubes (SWCNTs), nanoplates, and nanosheets. A systematic study was conducted on the variables affecting the monolayer assembly: the solubility parameter of spreading solvents, particle concentration, zeta potential of the particles in the suspension, surface tension of the water phase, hardness of the particles, and addition of a salt in the suspension. This method requires no hydrophobic surface treatment of the particles, which is useful to exploit these monolayer films without changing the native properties of the particles. The study highlights a quick 2D colloidal assembly without cracks in the wafer scale as well as transparent conductive thin films made of SWCNTs and graphenes. PMID:21962177

Moon, Geon Dae; Lee, Tae Il; Kim, Bongsoo; Chae, GeeSung; Kim, Jinook; Kim, SungHee; Myoung, Jae-Min; Jeong, Unyong

2011-10-06

190

Tape method of forming a thin layer of doped lanthanum chromite particles and of bonding such on an electrode  

DOEpatents

A combustible polymer film, useful for application of an interconnection on an electrode is made by: (1) providing doped LaCro.sub.3 particles; (2) dispersing doped LaCrO.sub.3 particles in a solvent, to provide a dispersion; (3) screening the dispersion to provide particles in the range of from 30 micrometers to 80 micrometers; (4) admixing a fugitive polymer with the particles; (5) casting the dispersion to provide a film; (6) drying the film; and (7) stripping the film. The film can then be applied to a porous, preheated electrode top surface, and then electrochemical vapor depositing a dense skeletal LaCrO.sub.3 structure, between and around the doped LaCrO.sub.3 particles. Additional solid oxide electrolyte and fuel electrode layers can then be added to provide a fuel cell.

Richards, Von L. (Murrysville, PA); Singhal, Subhash C. (Murrysville, PA); Pal, Uday B. (Cambridge, MA)

1992-01-01

191

Tape method of forming a thin layer of doped lanthanum chromite particles and of bonding such on an electrode  

DOEpatents

A combustible polymer film, useful for application of an interconnection on an electrode is made by: (1) providing doped LaCro[sub 3] particles; (2) dispersing doped LaCrO[sub 3] particles in a solvent, to provide a dispersion; (3) screening the dispersion to provide particles in the range of from 30 micrometers to 80 micrometers; (4) admixing a fugitive polymer with the particles; (5) casting the dispersion to provide a film; (6) drying the film; and (7) stripping the film. The film can then be applied to a porous, preheated electrode top surface, and then a dense skeletal LaCrO[sub 3] structure is electrochemically vapor deposited between and around the doped LaCrO[sub 3] particles. Additional solid oxide electrolyte and fuel electrode layers can then be added to provide a fuel cell. 4 figs.

Richards, V.L.; Singhal, S.C.; Pal, U.B.

1992-07-21

192

Water-Based Layer-by-Layer Surface Chemical Modification of Biomimetic Materials: Oil Repellency.  

PubMed

Biomimetic materials possessing hierarchical surface roughness thrive when complementary terminal chemical functionality is introduced. However, incorporating terminal functionality on the biomimetic material is the challenge, especially, when its roughness needs to be preserved. Hence, we report surface chemical modification of biomimetic materials through water-based layer-by-layer deposition. The amine terminated biomimetic replica PDMS-replica(Silica/NH2) was prepared by treating silica-modified replica (i.e., PDMS-replica(Silica)) with the aqueous solution of branched ethoxylated polyethylenimine (EPEI). Next, -CF3 terminal PDMS-replica(Silica/NH2/CF3) was obtained by treating PDMS-replica(Silica/NH2) with the aqueous solution of phosphate ester fluorosurfactant. PDMS-replica(Silica/NH2/CF3) showed superhydrophobicity (advancing ?water ? 140°) and high oil repellency (advancing ?oil ? 110°). X-ray photoelectron spectroscopy (XPS) revealed well-organized terminal -CF3 groups present on the PDMS-replica(Silica/NH2/CF3) surface. During the process of layer-by-layer deposition, the surface topography was monitored using scanning electron microscopy (SEM). This method could be extended to get desired terminal chemical functionality on the biomimetic materials which would furnish interesting surface properties in air or under water. PMID:23942547

Ghosh, Nilmoni; Singh, Amit Vikram; Vaidya, Ashish Anant

2013-09-09

193

Fluid-dynamics of the nuclear surface Fermi-layer.  

National Technical Information Service (NTIS)

In the framework of the long-mean-free-path approach the fluid-dynamical model of the nuclear surface as a spherical Fermi-layer is formulated. It is shown that the model reproduces known results of Fermi-drop dynamics and permits the description of more ...

S. I. Bastrukov J. A. Maruhn

1989-01-01

194

Terahertz surface plasmon propagation in nanoporous silicon layers  

Microsoft Academic Search

We describe the fabrication and measurement of a terahertz surface plasmon waveguide in which the optical mode is localized within a nanoporous silicon slab. We compare the propagation characteristics among waveguides with different porous layer thickness, and present an analytical model that accurately describes the dispersion and loss in the waveguides.

Shu-Zee A. Lo; Thomas E. Murphy

2010-01-01

195

Surface-layer formation on a nuclear-waste glass  

SciTech Connect

Surface layers are a common feature of leached surfaces of borosilicate waste glasses. The question of whether these layers can protect the glass against further attack by decreasing the leach rate is still a subject of controversy. The present study investigates the effects of layer formation on leaching kinetics of a borosilicate waste glass containing 20 wt % LWR-type simulated waste oxides: (1) surface layer formation on the borosilicate waste glass in a closed system can be divided in a sequence of overlapping processes. The formation of amorphous phases on the glass surface is observed first, followed by crystalline phase formation, with new phases still appearing after one year in NaCl solution; (2) the complexity of the kinetics is reflected in the variation of concentration of different elements in solution; (3) the overall leaching process varies as a function of time with t/sup n/ and n < 0.3. This reflects that the process cannot be described in terms of either diffusion (n = 0.5) or linear dissolution (n = 1), or a combination of both; and (4) though the details of the process are not yet understood, it is possible to extract a parameter, n, to describe the total mass release from the glass in the longer term in NaCl solution if leaching data are measured for at least one year.

Lutze, W.; Malow, G.; Rabe, H.; Headley, T.J.

1982-01-01

196

Effects of Surface Layer on Plastic Deformation and Crack Propagation.  

National Technical Information Service (NTIS)

The crack propagation of 2014-T6 aluminum, titanium (6Al-4V), and 4130 steel (YS = 180,000 psi) was measured under plane stress and plane strain, and a comparison was made to determine the effect of eliminating or decreasing the surface layer on the crack...

I. R. Kramer

1973-01-01

197

Theoretical investigation of turbulent boundary layer over a wavy surface  

Microsoft Academic Search

The important features of the two-dimensional incompressible turbulent flow over a wavy surface of wavelength comparable with the boundary layer thickness are analyzed. A turbulent field method using a model equation for turbulent shear stress was employed with suitable modification to cover the viscous sublayer. The governing differential equations are linearized based on the small but finite amplitude to wavelength

L. C. Chang

1975-01-01

198

Surface layer turbulence processes in low wind speeds over land  

Microsoft Academic Search

The atmospheric diffusion in the tropics is generally associated with low wind speeds, typically of magnitudes less than 3 ms?1. Low wind speeds would cause significant free convection in the daytime and strong stable conditions in the nighttime. Hence, the atmospheric surface layer turbulence associated with low wind speeds could be different from that of moderate to high wind speeds.

P. Agarwal; Anil Kumar Yadav; Amita Gulati; Sethu Raman; Suman Rao; M. P. Singh; S. Nigam; Neeraja Reddy

1995-01-01

199

Effect of polyethylene oxide on the viscosity of dispersions of charged silica particles: interplay between rheology, adsorption, and surface charge  

Microsoft Academic Search

In this study a systematic investigation on the adsorption of polyethylene oxide (PEO) onto the surface of silica particles\\u000a and the viscosity behavior of concentrated dispersions of silica particles with adsorbed PEO has been performed. The variation\\u000a of shear viscosity with the adsorbed layer density, concentration of free polymer in the solution (depletion forces), polymer\\u000a molecular weight, and adsorbed layer

A. A. Zaman

2000-01-01

200

Properties of titanium biomaterial fabricated by sinter-bonding of titanium\\/hydroxyapatite composite surface-coated layer to pure bulk titanium  

Microsoft Academic Search

A new titanium biomaterial was fabricated by hot press sinter-bonding of titanium\\/hydroxyapatite composite surface-coated layer to pure bulk titanium. The distribution of the hydroxyapatite particles in the composite surface-coated layer was mainly influenced by the hydroxyapatite volume fraction (Vha) of the composite surface-coated layer. When the Vha was less than 15%, it was uniform. At the temperature of 1023 K,

Wen Shi; Akira Kamiya; Jun Zhu; Akira Watazu

2002-01-01

201

Influence of liquid layers on energy absorption during particle impact  

Microsoft Academic Search

The influence of the thickness of a covering liquid layer and its viscosity as well as the impact velocity on energy loss during the normal impact on a flat steel wall of spherical granules with a liquid layer was studied. Free-fall experiments were performed to obtain the restitution coefficient of elastic–plastic ?-Al2O3 granules by impact on the liquid layer, using

Sergiy Antonyuk; Stefan Heinrich; Niels Deen; Hans Kuipers

2009-01-01

202

NMR of thin layers using a meanderline surface coil  

DOEpatents

A miniature meanderline sensor coil which extends the capabilities of nuclear magnetic resonance (NMR) to provide analysis of thin planar samples and surface layer geometries. The sensor coil allows standard NMR techniques to be used to examine thin planar (or curved) layers, extending NMRs utility to many problems of modern interest. This technique can be used to examine contact layers, non-destructively depth profile into films, or image multiple layers in a 3-dimensional sense. It lends itself to high resolution NMR techniques of magic angle spinning and thus can be used to examine the bonding and electronic structure in layered materials or to observe the chemistry associated with aging coatings. Coupling this sensor coil technology with an arrangement of small magnets will produce a penetrator probe for remote in-situ chemical analysis of groundwater or contaminant sediments. Alternatively, the sensor coil can be further miniaturized to provide sub-micron depth resolution within thin films or to orthoscopically examine living tissue. This thin-layer NMR technique using a stationary meanderline coil in a series-resonant circuit has been demonstrated and it has been determined that the flat meanderline geometry has about he same detection sensitivity as a solenoidal coil, but is specifically tailored to examine planar material layers, while avoiding signals from the bulk.

Cowgill, Donald F. (San Ramon, CA)

2001-01-01

203

Microstructural Characterization of CdTe Surface Passivation Layers  

NASA Astrophysics Data System (ADS)

The microstructure of CdTe (CT) surface passivation layers deposited on HgCdTe (MCT) heterostructures has been evaluated using transmission electron microscopy (TEM). The MCT heterostructures were grown by liquid-phase epitaxy and consisted of thick (approximately 10 ?m to 20 ?m) n-type MCT layers and thin (approximately 1 ?m to 3 ?m) p-type MCT layers. The final CT (approximately 0.3 ?m to 0.6 ?m) capping layers were grown either by hot-wall epitaxy (HWE) or molecular-beam epitaxy (MBE). One of the wafers with the CT layer grown by MBE was also annealed in Hg atmosphere at 250°C for 96 h. The as-deposited CT passivation layers were polycrystalline and columnar. The CT grains were larger and more irregular when deposited by HWE, whereas those deposited by MBE were generally well textured with mostly vertical grain boundaries. Observations and measurements with several TEM abrupt structurally after annealing techniques showed that the CT/MCT interface became considerably more abrupt structurally after annealing, and the crystallinity of the CT layer was also improved.

Zhao, W. F.; Cook, J.; Parodos, T.; Tobin, S.; Smith, David J.

2010-07-01

204

Tailoring surface properties of paper using nanosized precipitated calcium carbonate particles.  

PubMed

Pigment particles used in paper coatings are typically of micrometer size and consequently the thickness of the coatings is, even at its lowest, in micrometer scale. Progress in nanotechnology has given way to the development of nanosized materials to be used in coatings, yet their exploitation has not been studied to a great extent. This study examines utilization of nanosized precipitated calcium carbonate (nanoPCC) particles in nanoscale thin coating layers. In contrast to commonly used coatings, a thin nanoparticle-based coating was targeted to change the substrate surface characteristics via controlled surface structure rather than via high coat weight. A novel approach for stabilizing and modifying the nanoPCC particles with pectin and alkenyl succinic anhydride (ASA) was utilized and a nanoparticle coating with uniform particle distribution was created. The coating applied on paper substrate was hydrophobic, having a water contact angle of 125°. Particle surface modification provided dispersion stability, enabling control of the coating layer structure. The introduced concept provides a new approach to paper coatings utilizing controlled deposition of nanoparticles with extremely low coat weight, yet having high impact on substrate surface properties. Additionally, as paper is an environmentally sound product, the approach to form a controllable nanostructure on a green substrate has potential in applications outside the traditional paper products. PMID:21888413

Nypelö, Tiina; Österberg, Monika; Laine, Janne

2011-09-02

205

Synthesis and surface chemistry of nano silver particles  

Microsoft Academic Search

In this report, we present a simple wet chemical route to synthesize nano-sized silver particles, and their surface properties are discussed in detail. Silver nano particles of the size 40–80nm are formed in the process of oxidation of glucose to gluconic acid by amine in the presence of silver nitrate, and the gluconic acid caps the nano silver particle. The

Revathi Janardhanan; Murugan Karuppaiah; Neha Hebalkar; Tata Narsinga Rao

2009-01-01

206

Surface layer mixing during the SAGE ocean fertilization experiment  

NASA Astrophysics Data System (ADS)

Vessel-based observations of the oceanic surface layer during the 14-day 2004 SAGE ocean fertilization experiment were conducted using ADCP, CTD and temperature microstructure in a frame of reference moving with a patch of injected SF 6 tracer. During the experiment the mixed layer depth z mld ranged between 50 and 80 m, with several re-stratifying events that brought z mld up to less than 40 m. These re-stratifying events were not directly attributable to local surface-down development of stratification and were more likely associated with horizontal variation in density structure. Comparison between the CTD and a one-dimensional model confirmed that the SAGE experiment was governed by 3-d processes. A new method for estimating z mld was developed that incorporates a component that is proportional to density gradient. This highlighted the need for well-conditioned near-surface data which are not always available from vessel-based survey CTD profiles. A centred-displacement scale, Lc, equivalent to the Thorpe lengthscale, reached a maximum of 20 m, with the eddy-centroid located at around 40 m depth. Temperature gradient microstructure-derived estimates of the vertical turbulent eddy diffusivity of scalar (temperature) material yielded bin-averaged values around 10 -3 m 2 s -1 in the pycnocline rising to over 10 -2 m 2 s -1 higher in the surface layer. This suggests transport rates of nitrate and silicate at the base of the surface layer generate mixed layer increases of the order of 38 and 13 mmol/m 2/day, respectively, during SAGE. However, the variability in measured vertical transport processes highlights the importance of transient events like wind mixing and horizontal intrusions.

Stevens, Craig; Ward, Brian; Law, Cliff; Walkington, Matt

2011-03-01

207

Surface modification of silicon nitride nanofibers with titanium nitride particles  

Microsoft Academic Search

Silicon nitride nanofibers coated with titanium nitride particles are formed by deposition of TiO(OH)2 and Ti(O)2(OH)2 using controlled hydrolysis of TiCl4 followed by nitriding in an NH3 flow. The nitriding at 700–900°C permits the formation of 5 to 15 nm titanium nitride particles. The amorphous layer on Si3N4 fibers limits the nucleation of titanium nitride and thus the formation of

N. I. Tishchenko; V. G. Kolesnichenko; N. V. Dubovitskaya; P. M. Silenko; N. I. Danilenko; O. B. Zgalat-Lozinskii; V. N. Bulanov; A. V. Ragulya

2009-01-01

208

Metallurgical Analysis of Wear Particles and Wearing Surfaces.  

National Technical Information Service (NTIS)

The initial approach has been concerned primarily with the examination of particles recovered by the ferrographic technique from samples of lubricating oils taken periodically during tests and service of bearings, gears, sliding surfaces, etc., in which s...

A. W. Ruff

1974-01-01

209

A particle tracking scheme for coupled surface and subsurface flows  

NASA Astrophysics Data System (ADS)

A Lagrangian, particle tracking scheme has been extended to simulate transport through coupled surface and subsurface flows in watersheds. This technique assumes a two-dimensional flow field for the overland domain and a three-dimensional flow field for the subsurface domain. Transport in both the subsurface and the overland domain is based on classical particle tracking methods. However, while a particle is being tracked, the exchange of particles between the two domains is calculated by specific algorithms developed though this work. In the subsurface domain knowledge about a particle's trajectory is enough to detect a jump to the overland domain. If this trajectory crosses the land surface, and if this land surface is not dry, a particle then becomes a member of the overland flow domain. In the two-dimensional overland domain trajectories are parallel to the land surface. As such the velocity field in the overland domain alone is not enough to detect a jump. We propose a relatively simple algorithm to calculate the probability of a jump to the subsurface domain. This algorithm is based on the mass balance of water in the vicinity of the land surface. Analytical solutions for transit times are used to verify this particle tracking approach. Cases demonstrating that our scheme is a valuable tool for diagnosing transit times in watersheds are presented.

Graham, W. D.; De Rooij, R.; Maxwell, R. M.

2011-12-01

210

Quantum size effects in ?-plutonium (020) surface layers  

NASA Astrophysics Data System (ADS)

We present a systematic first principles density functional theory (DFT) based study of the (020) surface of ?-plutonium using the projector-augmented-wave formalism as implemented in the Vienna Ab Initio Simulation Package (VASP). The surface was modeled by a periodic slab geometry comprised of anti-ferromagnetic atomic layers, with a thickness of up to ten atomic layers. The total and cohesive energies indicate a monotonically decreasing and increasing slope to the bulk values, respectively. The surface energies, in contrast to the work functions, exhibit a significant oscillatory pattern indicating persistent quantum size effects and possible magnetic frustration as well as other effects. The 5f electron density of states indicates progressive delocalization with increasing slab thickness.

Hernandez, S. C.; Ray, A. K.; Taylor, C. D.

2013-10-01

211

Optimizing particle collection for enhanced surface-based biosensors  

Microsoft Academic Search

In this article, electrode structures that combine dielectrophoretic effects with electrohydrodynamic fluid flow to concentrate particles on active sensor surfaces were presented. To optimize the collection effect on a surface, a novel electrode configuration called zipper electrodes has been developed. The local enrichment effect of these electrodes is such that particles at local concentration of 5×103 spores\\/mL can be collected

KAI F. HOETTGES; MICHAEL P. HUGHES; ANDREW COTTON; N. A. E. Hopkins; M. B. McDonnell

2003-01-01

212

Rapid Particle Size Measurement Using 3D Surface Imaging  

Microsoft Academic Search

The present study introduces a new three-dimensional (3D) surface image analysis technique in which white light illumination\\u000a from different incident angles is used to create 3D surfaces with a photometric approach. The three-dimensional features of\\u000a the surface images created are then used in the characterization of particle size distributions of granules. This surface\\u000a image analysis method is compared to sieve

Ira Soppela; Sari Airaksinen; Juha Hatara; Heikki Räikkönen; Osmo Antikainen; Jouko Yliruusi; Niklas Sandler

2011-01-01

213

Surface layer similarity in the nocturnal boundary layer: the application of Hilbert-Huang transform  

NASA Astrophysics Data System (ADS)

Turbulence statistics such as flux-variance relationship are critical information in measuring and modeling ecosystem exchanges of carbon, water, energy, and momentum at the biosphere-atmosphere interface. Using a recently proposed mathematical technique, the Hilbert-Huang transform (HHT), this study highlights its possibility to quantify impacts of non-turbulent flows on turbulence statistics in the stable surface layer. The HHT is suitable for the analysis of non-stationary and intermittent data and thus very useful for better understanding the interplay of the surface layer similarity with complex nocturnal environment. Our analysis showed that the HHT can successfully sift non-turbulent components and be used as a tool to estimate the relationships between turbulence statistics and atmospheric stability in complex environments such as nocturnal stable boundary layer.

Hong, J.; Kim, J.; Ishikawa, H.; Ma, Y.

2010-04-01

214

Surface layer similarity in the nocturnal boundary layer: the application of Hilbert-Huang transform  

NASA Astrophysics Data System (ADS)

Turbulence statistics such as flux-variance relationship is critical information in measuring and modeling carbon, water, energy, and momentum exchanges at the biosphere-atmosphere interface. Using a recently proposed mathematical technique, the Hilbert-Huang transform (HHT), this study highlights its possibility to quantify impacts of non-turbulent flows on turbulence statistics in the stable surface layer. The HHT is suitable for the analysis of non-stationary and intermittent data and thus very useful for better understanding of the interplay of the surface layer similarity with complex nocturnal environment. Our analysis showed that the HHT can successfully sift non-turbulent components and be used as a tool to estimate the relationships between turbulence statistics and atmospheric stability in complex environment such as nocturnal stable boundary layer.

Hong, J.; Kim, J.; Ishikawa, H.; Ma, Y.

2009-10-01

215

MICROANALYSIS OF INDIVIDUAL LAYERED PARTICLES BY SECONDARY ION MASS SPECTROMETRY  

EPA Science Inventory

Secondary ion mass spectrometry is evaluated for application to the determination of the composition and structure of individual particles. Analyses of many elemental constituents at the ppm level can be obtained in individual particles as small as micrometers in diameter. Molecu...

216

Microhydrodynamics of flotation processes in the sea surface layer  

NASA Astrophysics Data System (ADS)

The uppermost surface of the ocean forms a peculiarly important ecosystem, the sea surface microlayer (SML). Comprising the top 1-1000 ?m of the ocean surface, the SML concentrates many chemical substances, particularly those that are surface active. Important economically as a nursery for fish eggs and larvae, the SML unfortunately is also especially vulnerable to pollution. Contaminants that settle out from the air, have low solubility, or attach to floatable matter tend to accumulate in the SML. Bubbles contribute prominently to the dynamics of air-sea exchanges, playing an important role in geochemical cycling of material in the upper ocean and SML. In addition to the movement of bubbles, the development of a bubble cloud interrelates with the single particle dynamics of all other bubbles and particles. In the early sixties, several in situ oceanographic techniques revealed an "unbelievably immense" number of coastal bubbles of radius 15-300 ?m. The spatial and temporal variation of bubble numbers were studied; acoustical oceanographers now use bubbles as tracers to determine ocean processes near the ocean surface. Sea state and rain noises have both been definitively ascribed to the radiation from huge numbers of infant micro bubbles [The Acoustic Bubble. Academic Press, San Diego]. Our research programme aims at constructing a hydrodynamic model for particle transport processes occurring at the microscale, in multi-phase flotation suspensions. Current research addresses bubble and floc microhydrodynamics as building blocks for a microscale transport model. This paper reviews sea surface transport processes in the microlayer and the lower atmosphere, and identifies those amenable to microhydrodynamic modelling and simulation. It presents preliminary simulation results including the multi-body hydrodynamic mobility functions for the modelling of "dynamic bubble filters" and floc suspensions. Hydrodynamic interactions versus spatial anisotropy and size of particle clouds are investigated.

Grammatika, Marianne; Zimmerman, William B.

2001-10-01

217

Interactions between protein coated particles and polymer surfaces studied with the rotating particles probe.  

PubMed

Nonspecific interactions between proteins and polymer surfaces have to be minimized in order to control the performance of biosensors based on immunoassays with particle labels. In this paper we investigate these nonspecific interactions by analyzing the response of protein coated magnetic particles to a rotating magnetic field while the particles are in nanometer vicinity to a polymer surface. We use the fraction of nonrotating (bound) particles as a probe for the interaction between the particles and the surface. As a model system, we study the interaction of myoglobin coated particles with oxidized polystyrene surfaces. We measure the interaction as a function of the ionic strength of the solution, varying the oxidation time of the polystyrene and the pH of the solution. To describe the data we propose a model in which particles bind to the polymer by crossing an energy barrier. The height of this barrier depends on the ionic strength of the solution and two interaction parameters. The fraction of nonrotating particles as a function of ionic strength shows a characteristic shape that can be explained with a normal distribution of energy barrier heights. This method to determine interaction parameters paves the way for further studies to quantify the roles of protein coated particles and polymers in their mutual nonspecific interactions in different matrixes. PMID:22571333

Kemper, M; Spridon, D; van IJzendoorn, L J; Prins, M W J

2012-05-16

218

Charge fluctuations for particles on a surface exposed to plasma  

SciTech Connect

We develop a stochastic model for the charge fluctuations on a microscopic dust particle resting on a surface exposed to plasma. We find in steady state that the fluctuations are normally distributed with a standard deviation that is proportional to (CT{sub e}){sup 1/2}, where C is the particle-surface capacitance and T{sub e} is the plasma electron temperature. The time for an initially uncharged ensemble of particles to reach the steady state distribution is directly proportional to CT{sub e}.

Sheridan, T. E. [Department of Physics and Astronomy, Ohio Northern University, Ada, Ohio 45810 (United States); Hayes, A. [Veeco Process Equipment, Terminal Dr., Plainview, New York 11803 (United States)

2011-02-28

219

Nonvolatile Particle Transport from Etched Surface in 2-D CCP Modeling  

NASA Astrophysics Data System (ADS)

Byproducts in etching processes are strongly linked to the incident ion flux on a wafer. We first discuss the radial uniformity of the ion flux incident on a substrate of the powered electrode as a function of reactor geometry. Nonvolatile particles ejected by etching( physical sputtering ) from the substrate will be the origin of an absorbed layer on the etched surface as well as the particle growth in the plasma. We investigate the nonvolatile particle transport in a 2-D capacitively coupled plasma( CCP ) under gas flow by using the relaxation continuum ( RCT ) model. We use a difussion equation to analize the nonvolatile particle transport with the gas flow. CCP is mainly maintained at 13.56 MHz with amplitude of 300 V at 100 mTorr in Ar. We also show a series of 2-D space distributions of CCP in various reactor geometry and the nonvolatile particle transport.

Hasebe, M.; Nakano, N.; Makabe, T.

1997-10-01

220

Precipitation and Corrosion Behaviour of Nano-Structured Near-Surface Layers on an AA6111 Aluminium Alloy  

NASA Astrophysics Data System (ADS)

A nano-structured, near-surface layer has been generated by mechanically grinding an AA6111 alloy. After heat treatment at 180°C for 30 minutes, Q phase particles, ~20 nm diameter, were precipitated preferentially at grain boundaries within the nano-structured nearsurface layer. No such precipitates were observed in the bulk alloy after this heat treatment. This preferential precipitation results in the near-surface layers having increased corrosion susceptibility than the bulk microstructure, due to the micro-galvanic coupling between the precipitates at grain boundary and the grain matrix. The localized attack is predominately intergranular.

Liu, Y.; Zhou, X.; Thompson, G. E.; Hashimoto, T.; Scamans, G. M.; Afseth, A.

2006-02-01

221

Numerical simulation of saltating particles in atmospheric boundary layer over flat bed and sand ripples  

NASA Astrophysics Data System (ADS)

In this work, we numerically simulated the saltating particles in a turbulent boundary layer over flat bed and sand ripples. By using natural sand grains in a wind tunnel, we obtained the initial conditions for the simulation and also verified the correctness of the numerical model. We carefully analyzed the numerically simulated saltating particle movement over the two sand beds, and we found the following. (1) The aeolian sand transport is a dynamic equilibrium process on both sand beds, and it took longer to reach equilibration on the sand ripples than on the flat bed. (2) According to the mass flux profile at the trough of the sand ripples, there is a maximum mass flux at about 4 cm height in the leeward section. The mass flux increases with height below 4 cm and decreases with height above 4 cm. (3) The wind profile near the surface is modified by saltating particles on the two different sand beds, and the flow field characteristics of the sand ripples are more complex than that of the flat bed.

Tong, Ding; Huang, Ning

2012-08-01

222

Particle and photon interactions with surfaces  

Microsoft Academic Search

This book contains papers from the Sixth International Workshop on Inelastic Ion Surfrace Collisions. There are eight sections in this book covering the following topics: theory of sputtering and molecular scattering, ion scattering and secondary ion emission, photon interactions with sputtered atoms and molecules, photon- and electron-induced desorption, energy flows in atom and molecule surface interactions, sputtering of clusters and

D. M. Gruen; A. R. Krauss; M. J. Pellin; C. E. Young

1987-01-01

223

Consideration of the Effect on Fuel Particle Behavior from Shrinkage Cracks in the Inner Pyrocarbon Layer  

SciTech Connect

The fundamental design for a gas-cooled pebble bed reactor relies on an understanding of the behavior of coated particle fuel. The coating layers surrounding the fuel kernels in these spherical particles consist of pyrolytic carbon layers and a silicon carbide (SiC) layer. These coating layers act as a pressure vessel that retains fission product gases. A small percentage of fuel particles may fail during irradiation in the mode of a traditional pressure vessel failure. Fuel performance models used to predict particle behavior have traditionally been one-dimensional models that focus on this failure mechanism. Results of irradiation experiments, however, show that many more fuel particles fail than would be predicted by this mechanism alone. Post-irradiation examinations indicate that multi-dimensional effects, such as the presence of shrinkage cracks in the inner pyrolytic carbon layer (IPyC), contribute to these unexplained failures. Results of a study performed to evaluate the significance of cracking in the IPyC layer on behavior of a fuel particle are presented herein, which indicate that shrinkage cracks could contribute significantly to fuel particle failures.

Miller, Gregory Kent; Petti, David Andrew; Varacalle, Dominic Joseph; Maki, John Thomas

2001-06-01

224

Characterizing the Effect of Surface Hydrophobicity on the Depletion Layer  

NASA Astrophysics Data System (ADS)

When water is forced into contact with an extended hydrophobic surface, a uniform region of reduced density forms along the interface. We seek to identify both a qualitative and a quantitative relationship between the hydrophobicity of a surface and the characteristics of the corresponding depletion layer, specifically its thickness and density. We determine these qualities using surface plasmon resonance spectroscopy (SPR). We produce surfaces of different hydrophobicities through the formation of self-assembled monolayers of organothiols on gold-plated slides. Self-assembled monolayers (SAMs) of 1-octadecanethiol are used to produce surfaces with high hydrophobicity, as the terminal methyl group is highly nonpolar, while 11-mercapto-1-undecanol is used to produce surfaces with minimal hydrophobicity, as the terminal hydroxyl group is hydrophilic. Surfaces of intermediate hydrophobicity are fabricated using mixed SAMs of 1-octadecanethiol and 11-mercapto-1-undecanol. We measure surface hydrophobicity for the resulting SAM-coated slides by their contact angle with water droplets. In order to ensure an unchanging hydrophobicity throughout SPR trials, we analyze the stability of the surfaces to through repeated testing of contact angle variability over time and after extended submersion both in water and in ethanol.

Brown, Erin; Petersen, Shannon; Jeroski, Jessica; Statman, Ariel; Poynor, Adele

2013-03-01

225

Activity of Components in Surface Layer of Chloride-Fluoride Mutual Melts  

Microsoft Academic Search

The activities of components in the bulk, surface layer of melts of chloride-fluoride ternarymutual systems were calculated in the framework of the regular solution model using surface tension valuesand considering the surface layer is a separate phase.

B. V. Patrov

2003-01-01

226

Surface Collisions Involving Particles and Moisture (SCIP'M).  

National Technical Information Service (NTIS)

Experiments were performed on the collision of a solid sphere with a nearly horizontal flat surface covered with a thin layer of viscous liquid. High-speed collisions were obtained by dropping the ball onto the surface from various heights, using gravitat...

R. H. Davis

2005-01-01

227

Outgassing of icy bodies in the Solar System - The influence of surface dust layers on the sublimation of H2O ice  

NASA Astrophysics Data System (ADS)

The absorption of solar radiation by surface layers of icy bodies in the Solar System (such as icy satellites, Mars and comets) leads to a sublimation of the icy constituents and alters the surface properties. While the energy absorption and its distribution inside the surface layers are not fully understood in detail, there is observational evidence of the formation of nonvolatile surface dust layers and sublimation beneath the residuals of the surface layers (Prialnik and Bar- Nun, 1988; Kömle, 1992; Sunshine et al., 2007). The formation of a non-volatile surface dust layer further decreases the sublimation rate of the icy constituents. Gas molecules escaping through the residuals are scattered by the dust particles, which can lead to a collimation of the gas flux. As a consequence, loose dust particles can be ejected by the gas drag of the outflowing gas.

Gundlach, B.; Skorv, Y. V.; Blum, J.

2011-10-01

228

Surface morphological evolution of epitaxial CrN(001) layers  

SciTech Connect

CrN layers, 57 and 230 nm thick, were grown on MgO(001) at T{sub s}=600-800 deg. C by ultrahigh-vacuum magnetron sputter deposition in pure N{sub 2} discharges from an oblique deposition angle {alpha}=80 deg. . Layers grown at 600 deg. C nucleate as single crystals with a cube-on-cube epitaxial relationship with the substrate. However, rough surfaces with cauliflower-type morphologies cause the nucleation of misoriented CrN grains that develop into cone-shaped grains that protrude out of the epitaxial matrix to form triangular faceted surface mounds. The surface morphology of epitaxial CrN(001) grown at 700 deg. C is characterized by dendritic ridge patterns extending along the orthogonal <110> directions superposed by square-shaped super mounds with <100> edges. The ridge patterns are attributed to a Bales-Zangwill instability while the supermounds form due to atomic shadowing which leads to the formation of epitaxial inverted pyramids that are separated from the surrounding layer by tilted nanovoids. Growth at 800 deg. C yields complete single crystals with smooth surfaces. The root-mean-square surface roughness for 230-nm-thick layers decreases from 18.8 to 9.3 to 1.1 nm as T{sub s} is raised from 600 to 700 to 800 deg. C. This steep decrease is due to a transition in the roughening mechanism from atomic shadowing to kinetic roughening. Atomic shadowing is dominant at 600 and 700 deg. C, where misoriented grains and supermounds, respectively, capture a larger fraction of the oblique deposition flux in comparison to the surrounding epitaxial matrix, resulting in a high roughening rate that is described by a power law with an exponent {beta}>0.5. In contrast, kinetic roughening controls the surface morphology for T{sub s}=800 deg. C, as well as the epitaxial fraction of the layers grown at 600 and 700 deg. C, yielding relatively smooth surfaces and {beta}{<=}0.27.

Frederick, J.R.; Gall, D. [Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

2005-09-01

229

THEORETICAL MODEL OF SOILING OF SURFACES BY AIRBORNE PARTICLES  

EPA Science Inventory

A model is developed which can be used to predict the change in reflectance from a surface as a function of time. Reflectance change is a measure of soiling caused by the deposition of particles on a surface. The major inputs to the model are the parameters to a bimodal distribut...

230

Retargeting gene delivery using surface-engineered retroviral vector particles  

Microsoft Academic Search

Retroviral vectors with the capacity to deliver transgenes to specific tissues are expected to be of great value for various gene transfer applications in vivo. Initial attempts to modify vector host-range by the insertion of ligands on their surface glycoproteins have frequently failed, essentially owing to the impairment of the fusogenicity of the vector particles bound to the targeted cell-surface

Dimitri Lavillette; Stephen J Russell

2001-01-01

231

Using Particles to Sample and Control More Complex Implicit Surfaces  

Microsoft Academic Search

In 1994, Witkin and Heckbert developed a method for interactively modeling implicit surfaces by simultaneously constaining a particle system to lie on an implicit surface and vice-versa. This interface was demonstrated to be ef- fective and easy to use on example models containing a few blobby spheres and cylinders. This system becomes much more difficult to implement and operate on

John C. Hart; Ed Bachta; Wojciech Jarosz; Terry Fleury

2002-01-01

232

Lag model for turbulent boundary layers over rough bleed surfaces  

NASA Astrophysics Data System (ADS)

Boundary-layer mass removal (bleed) through spanwise bands of holes on a surface is used to prevent or control separation and to stabilize the normal shock in supersonic inlets. The addition of a transport equation lag relationship for eddy viscosity to the rough wall algebraic turbulence model of Cebeci and Chang was found to improve agreement between predicted and measured mean velocity distributions downstream of a bleed band. The model was demonstrated for a range of bleed configurations, bleed rates, and local freestream Mach numbers. In addition, the model was applied to the boundary-layer development over acoustic lining materials for the inlets and nozzles of commercial aircraft. The model was found to yield accurate results for integral boundary-layer properties unless there was a strong adverse pressure gradient.

Lee, J.; Sloan, M. L.; Paynter, G. C.

1994-07-01

233

Measurement of boundary-layer receptivity at suction surfaces  

NASA Astrophysics Data System (ADS)

The receptivity of a boundary layer to external acoustic disturbances in the vicinity of a narrow suction slot is experimentally investigated. The relative importance of the leading-edge and suction-slot receptivity mechanisms is explored. A flat-plate, zero-pressure-gradient boundary layer with and without passive suction surfaces is irradiated by acoustic plane waves, and the coupling between the incident sound field and Tollmien-Schlichting waves is characterized. Suction slot locations and forcing frequencies are chosen so that the slot is positioned near the streamwise location corresponding to the lower branch of the neutral stability curve. Both amplified and damped modes are considered. The slot receptivity mechanism is validated and shown to produce a boundary-layer response at the slot of the same order as waves convected from the leading edge.

Wlezien, R. W.

1989-03-01

234

The Role of Adsorbed Water on the Friction of a Layer of Submicron Particles  

NASA Astrophysics Data System (ADS)

Anomalously low values of friction observed in layers of submicron particles deformed in simple shear at high slip velocities are explained as the consequence of a one nanometer thick layer of water adsorbed on the particles. The observed transition from normal friction with an apparent coefficient near ?=0.6 at low slip speeds to a coefficient near ?=0.3 at higher slip speeds is attributed to a competition between the time required to extrude the water layer from between neighboring particles in a force chain and the average lifetime of the chain. At low slip speeds the time required for extrusion is less than the average lifetime of a chain so the particles make contact and lock. As slip speed increases, the average lifetime of a chain decreases until it is less than the extrusion time and the particles in a force chain never come into direct contact. If the adsorbed water layer allows the otherwise rough particles to rotate, then the coefficient of friction will drop to ?=0.3 appropriate for rotating spheres. At the highest slip speeds particle temperatures rise above 100 C, the water layer vaporizes, the particles contact and lock, and the coefficient of friction rises to ?=0.6. The observed onset of weakening at slip speeds near 0.001 m/s is consistent with the measured viscosity of a 1nm thick layer of adsorbed water, with a minimum particle radius of about 20 nm, and with reasonable assumptions about the distribution of force chains guided by experimental observation. The reduction of friction and range of velocities over which it occurs decreases with increasing normal stress as predicted by the model. Moreover, the analysis predicts that this high speed weakening mechanism should operate only for particles with radii smaller than about 1 ?m. For larger particles the slip speed required for weakening is so large that frictional heating will evaporate the adsorbed water and weakening will not occur.

Sammis, C. G.; Lockner, D. A.; Reches, Z.

2011-12-01

235

The role of adsorbed water on the friction of a layer of submicron particles  

USGS Publications Warehouse

Anomalously low values of friction observed in layers of submicron particles deformed in simple shear at high slip velocities are explained as the consequence of a one nanometer thick layer of water adsorbed on the particles. The observed transition from normal friction with an apparent coefficient near ? = 0.6 at low slip speeds to a coefficient near ? = 0.3 at higher slip speeds is attributed to competition between the time required to extrude the water layer from between neighboring particles in a force chain and the average lifetime of the chain. At low slip speeds the time required for extrusion is less than the average lifetime of a chain so the particles make contact and lock. As slip speed increases, the average lifetime of a chain decreases until it is less than the extrusion time and the particles in a force chain never come into direct contact. If the adsorbed water layer enables the otherwise rough particles to rotate, the coefficient of friction will drop to ? = 0.3, appropriate for rotating spheres. At the highest slip speeds particle temperatures rise above 100°C, the water layer vaporizes, the particles contact and lock, and the coefficient of friction rises to ? = 0.6. The observed onset of weakening at slip speeds near 0.001 m/s is consistent with the measured viscosity of a 1 nm thick layer of adsorbed water, with a minimum particle radius of approximately 20 nm, and with reasonable assumptions about the distribution of force chains guided by experimental observation. The reduction of friction and the range of velocities over which it occurs decrease with increasing normal stress, as predicted by the model. Moreover, the analysis predicts that this high-speed weakening mechanism should operate only for particles with radii smaller than approximately 1 ?m. For larger particles the slip speed required for weakening is so large that frictional heating will evaporate the adsorbed water and weakening will not occur.

Sammis, Charles G.; Lockner, David A.; Reches, Ze’ev

2011-01-01

236

Programming nanostructured soft biological surfaces by atomic layer deposition.  

PubMed

Here, we present the first successful attempt to programme the surface properties of nanostructured soft biological tissues by atomic layer deposition (ALD). The nanopatterned surface of lotus leaf was tuned by 3-125 nm TiO2 thin films. The lotus/TiO2 composites were studied by SEM-EDX, XPS, Raman, TG-DTA, XRR, water contact angle and photocatalysis measurements. While we could preserve the superhydrophobic feature of lotus, we managed to add a new property, i.e. photocatalytic activity. We also explored how surface passivation treatments and various ALD precursors affect the stability of the sensitive soft biological tissues. As we were able to gradually change the number of nanopatterns of lotus, we gained new insight into how the hollow organic nanotubes on the surface of lotus influence its superhydrophobic feature. PMID:23680967

Szilágyi, Imre Miklós; Teucher, Georg; Härkönen, Emma; Färm, Elina; Hatanpää, Timo; Nikitin, Timur; Khriachtchev, Leonid; Räsänen, Markku; Ritala, Mikko; Leskelä, Markku

2013-05-16

237

Programming nanostructured soft biological surfaces by atomic layer deposition  

NASA Astrophysics Data System (ADS)

Here, we present the first successful attempt to programme the surface properties of nanostructured soft biological tissues by atomic layer deposition (ALD). The nanopatterned surface of lotus leaf was tuned by 3-125 nm TiO2 thin films. The lotus/TiO2 composites were studied by SEM-EDX, XPS, Raman, TG-DTA, XRR, water contact angle and photocatalysis measurements. While we could preserve the superhydrophobic feature of lotus, we managed to add a new property, i.e. photocatalytic activity. We also explored how surface passivation treatments and various ALD precursors affect the stability of the sensitive soft biological tissues. As we were able to gradually change the number of nanopatterns of lotus, we gained new insight into how the hollow organic nanotubes on the surface of lotus influence its superhydrophobic feature.

Miklós Szilágyi, Imre; Teucher, Georg; Härkönen, Emma; Färm, Elina; Hatanpää, Timo; Nikitin, Timur; Khriachtchev, Leonid; Räsänen, Markku; Ritala, Mikko; Leskelä, Markku

2013-06-01

238

Study of oblique particle-wall collisions in the presence of a thin viscous oil layer  

NASA Astrophysics Data System (ADS)

Collisions between wetted particles and between particles and the walls of containers occur in industrial processes such as filtration, coagulation, fluidization, sedimentation and slurry transport. To understand and model these collisions, the physical interactions occurring during contact should be known. In this work, we present the experimental results of oblique particle-wall collisions along with a brief model used to explain the observed results. Collisions of spheres with a quartz target covered with a thin oil layer at different angles of impact were observed to determine the coefficient of restitution (ratio of the rebound velocity to the approach velocity) for both normal and tangential components of motion. High-velocity impacts were performed by dropping spheres from various heights onto an oil-laden target. Low-velocity impacts were performed by suspending spheres with a light and long string to form a simple pendulum. The swinging sphere was impacted with a wet target at different angles. Low-velocity collisions were also performed in the low-gravity environment afforded in KC-135 parabolic flights of NASA. The results show that, for smooth spheres (e.g., steel), the normal coefficient of restitution of the spheres is unaffected by the tangential velocity or the angle of impact. However, for plastic spheres (e.g., teflon, nylon) that have significant surface roughness, it is seen that the normal restitution observed is slightly higher for oblique collisions than it is for head-on collisions. The normal restitution coefficient is adequately described by the theory for head-on collisions [Davis et. al. (2002) J. Fluid Mech. 468, 107-119] extended to oblique collisions. In particular, the spheres stick at low impact velocities due to lubrication forces and viscous dissipation in the thin oil layer. Above a critical impact velocity, however, a sufficient fraction of the initial kinetic energy becomes stored in elastic deformation, and rebound is observed. The tangential velocity of the spheres does not change significantly during wet or dry collisions except at very small impact velocities. As a first approximation, the normal and tangential components of motion of the sphere are considered decoupled and a scaling approximation for the tangential viscous force exerted by the fluid layer is developed. Scaling estimates show that the change in tangential velocity is small, as is seen in the experimental results. A rotational velocity is imparted to the sphere by the tangential viscous force exerted by the oil layer and/or solid-solid contact.

Kantak, Advait; Davis, Robert

2003-11-01

239

EFFECTS OF PARTICLES THICKNESS AND VENEER REIFORCED LAYER IN THE PROPERTIES OF ORIENTED STRAND BOARDS OSB  

Microsoft Academic Search

This work evaluated the effects of particle thickness and veneer reinforced layer on the physical and mechanical properties of OSB made of Pinus taeda L. The boards were manufactured with particle thickness of 0.4, 0.7 and 1.0 mm and phenol- formaldehyde resin in the proportion of 6% of solid content. To the veneer reinforced layer was used veneer from Pinus

Setsuo Iwakiri; Leopoldo Karman; Carlos Eduardo; Camargo de Albuquerque; Lourival Marin Mendes

240

Microstructure and wear properties of the electroslag remelting layer reinforced by TiC particles  

Microsoft Academic Search

The electroslag remelting (ESR) layer reinforced by TiC particles was obtained by electroslag remelting. The microstructure and wear properties of the ESR layer were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and wear test. The results indicate that TiC particles are synthesized by self-propagating high-temperature synthesis (SHS) reaction during the electroslag remelting process. The size of

Qianlin Wu; Yangshan Sun; Guoqing Li

2008-01-01

241

Metal biosorption by surface-layer proteins from Bacillus species.  

PubMed

Bacillus species have been involved in metal association as biosorbents, but there is not a clear understanding of this chelating property. In order to evaluate this metal chelating capacity, cultures and spores from Grampositive bacteria of species either able or unable to produce surface layer proteins (S-layers) were analyzed for their capacity of copper biosorption. Only those endowed of S-layers, like Bacillus sphaericus and B. thuringiensis, showed a significant biosorption capacity. This capacity (nearly 50%) was retained after heating of cultures, thus supporting that structural elements of the envelopes are responsible for such activity. Purified Slayers from two Bacillus sphaericus strains had the ability to biosorb copper. Copper biosorption parameters were determined for strain B. sphaericus 2362, and after analyses by means of the Langmuir model, the affinity and capacity were shown to be comparable to other bacterial biosorbents. A competitive effect of Ca2+ and Zn2+, but not of Cd2+, was also observed, thus indicating that other cations may be biosorbed by this protein. Spores that have been shown to be proficient for copper biosorption were further analyzed for the presence of Slayer content. The retention of S-layers by these spores was clearly observed, and after extensive treatment to eliminate the S-layers, the biosorption capacity of these spores was significantly reduced. For the first time, a direct correlation between S-layer protein content and metal biosorption capacity is shown. This capacity is linked to the retention of S-layer proteins attached to Bacillus spores and cells. PMID:21364296

Allievi, Mariana Claudia; Sabbione, Florencia; Prado-Acosta, Mariano; Palomino, María Mercedes; Ruzal, Sandra M; Sanchez-Rivas, Carmen

2011-02-01

242

Formation of Cold-Sprayed Ceramic Titanium Dioxide Layers on Metal Surfaces  

NASA Astrophysics Data System (ADS)

Titanium dioxide (TiO2) coatings have potential applications in biomedical implants or as photo-catalytic functional systems. Cold spraying is a well-established method for metal on metal coatings. In cold spraying, the required heat for bonding is provided by plastic deformation of the impacting ductile particles. In contrast, few authors have investigated the impact phenomena and layer formation process for spraying brittle ceramic materials on ductile metal surfaces. In this study, the formation of TiO2 coatings on aluminum, copper, titanium, and steel substrates was investigated by SEM, TEM, XRD, and Raman spectroscopy. The results show that the deposition efficiency depends on spray temperature, powder properties, and in particular on substrate ductility, even for impact of ceramic particles during a second pass over already coated areas. Ceramic particles bond to metallic substrates showing evidence of shear instabilities. High-resolution TEM images revealed no crystal growth or phase transitions at the ceramic/metal interfaces.

Kliemann, J.-O.; Gutzmann, H.; Gärtner, F.; Hübner, H.; Borchers, C.; Klassen, T.

2011-01-01

243

Detection of charged particles in thick hydrogenated amorphous silicon layers  

SciTech Connect

We show our results in detecting particles of various linear energy transfer, including minimum ionizing electrons from a Sr-90 source with 5 to 12 micron thick n-i-p and p-i-n diodes. We measured W ( average energy to produce one electron-hole pair) using 17keV filtered xray pulses with a result W = 6.0 /+-/ 0.2eV. This is consistent with the expected value for a semiconductor with band gap of 1.7 to 1.9eV. With heavily ionizing particles such as 6 MeV alphas and 1 to 2 MeV protons, there was some loss of signal due to recombination in the particle track. The minimum ionizing electrons showed no sign of recombination. Applications to pixel and strip detectors for physics experiments and medical imaging will be discussed. 7 refs., 8 figs.

Fujieda, I.; Cho, G.; Kaplan, S.N.; Perez-Mendez, V.; Qureshi, S.; Ward, W.; Street, R.A.

1988-03-01

244

Particle transport and reattachment on a mask surface  

NASA Astrophysics Data System (ADS)

The cleaning processes used today for photomasks were developed over decades and optimized to fulfill customer specifications. Some mask procedures were adapted from wafer cleaning technology. A principal technique, megasonic (MS) cleaning, yields high particle removal efficiencies (PRE). However, MS can frequently cause feature damage, and so damage becomes the principle limitation to MS power levels applied to small feature sizes. The use of lower MS power levels can benefit from a better understanding of removal mechanisms. In several publications the effects influencing the mechanisms of particle cleaning were discussed [1]. Particle transfer was investigated experimentally on wafer surfaces using bath tools and was tracked using fluorescent optical microscopy [2]. The goal of our investigation is to test the validity of the aforementioned models for mask cleaning using a spinning mask and a megasonic head mounted on a arm swinging over the mask surface, which is the most common hardware setup used for mask cleaning tools. While this equipment setup provides a useful variability, it also introduces disadvantages e.g. non-equal distribution of the megasonic power across the cleaned surface as will be shown. We will focus on some of the main parameters e.g. chuck speed, arm swing speed and media flow, which are strongly coupled by the fluid dynamics and cannot be treated separately. All three parameters influence particle-mask decoupling and reattachment during particle transport by the media stream across the mask surface. The approach to estimate the particle removal and reattachment rate is illustrated. The experiments performed allow the conclusion that the reattachment rate on a flat spinning mask surface is lower than previously assumed and the most critical part of the cleaning process is the detachment of the particle from the surface.

Nesladek, Pavel; Osborne, Steve; Kohl, Christian

2009-01-01

245

Gas-particle interactions above a Dutch heathland: II. Concentrations and surface exchange fluxes of atmospheric particles  

NASA Astrophysics Data System (ADS)

Size-dependent particle number fluxes measured by eddy-covariance (EC) and continuous fluxes of ammonium (NH4+) measured with the aerodynamic gradient method (AGM) are reported for a Dutch heathland. Daytime deposition velocities (Vd) by EC with peak values of 5 to 10 mm s-1 increased with particle diameter (dp) over the range 0.1-0.5 ?m, and are faster than predicted by current models. With a mean Vd of 2.0 mm s-1 (daytime: 2.7; night-time 0.8 mm s-1) NH4+ fluxes by AGM are overall in agreement with former measurements and NH4+-N dry deposition amounts to 20% of the dry input of NH3-N over the measurement period. These surface exchange fluxes are analyzed together with simultaneous gas-phase flux measurements for indications of gas-particle interactions. On warm afternoons the apparent fluxes of acids and aerosol above the heathland showed several coinciding anomalies, all of which are consistent with NH4+ evaporation during deposition: (i) canopy resistances for HNO3 and HCl of up to 100 s m-1, (ii) simultaneous particle emission of small particles (Dp<0.18 ?m) and deposition of larger particles (Dp>0.18 ?m), (iii) NH4+ deposition faster than derived from size-distributions and size-segregated EC particle fluxes. These observations coincide with the observations of (i) surface concentration products of NH3 and HNO3 well below the thermodynamic equilibrium value and (ii) Damköhler numbers that indicate chemical conversion to be sufficiently fast to modify exchange fluxes. The measurements imply a removal rate of volatile NH4+ of 3-30×10-6s-1 averaged over the 1 km boundary-layer, while NH3 deposition is underestimated by typically 20 ng m-2 s-1 (28%) and flux reversal may occur.

Nemitz, E.; Sutton, M. A.; Wyers, G. P.; Otjes, R. P.; Mennen, M. G.; van Putten, E. M.; Gallagher, M. W.

2004-03-01

246

Gas-particle interactions above a Dutch heathland: II. Concentrations and surface exchange fluxes of atmospheric particles  

NASA Astrophysics Data System (ADS)

Size-dependent particle number fluxes measured by eddy-covariance (EC) and continuous fluxes of ammonium (NH4+) measured with the aerodynamic gradient method (AGM) are reported for a Dutch heathland. Daytime deposition velocities (Vd) by EC with peak values of 5 to 10 mm s-1 increased with particle diameter (dp) over the range 0.1-0.5 µm, and are faster than predicted by current models. With a mean Vd of 2.0 mm s-1 (daytime: 2.7; night-time 0.8 mm s-1) NH4+ fluxes by AGM are overall in agreement with former measurements and NH4+-N dry deposition amounts to 20% of the dry input of NH3-N over the measurement period. These surface exchange fluxes are analyzed together with simultaneous gas-phase flux measurements for indications of gas-particle interactions. On warm afternoons the apparent fluxes of acids and aerosol above the heathland showed several coinciding anomalies, all of which are consistent with NH4+ evaporation during deposition: (i) canopy resistances for HNO3 and HCl of up to 100 s m-1, (ii) simultaneous particle emission of small particles (Dp<0.18 µm) and deposition of larger particles (Dp>0.18 µm), (iii) NH4+ deposition faster than derived from size-distributions and size-segregated EC particle fluxes. These observations coincide with the observations of (i) surface concentration products of NH3 and HNO3 well below the thermodynamic equilibrium value and (ii) Damköhler numbers that indicate chemical conversion to be sufficiently fast to modify exchange fluxes. The measurements imply a removal rate of volatile NH4+ of 3-30×10-6 s-1 averaged over the 1 km boundary-layer, while NH3 deposition is underestimated by typically 20 ng m-2 s-1 (28%) and flux reversal may occur.

Nemitz, E.; Sutton, M. A.; Wyers, G. P.; Otjes, R. P.; Mennen, M. G.; van Putten, E. M.; Gallagher, M. W.

2004-07-01

247

"Sticky Business": the Influence of Surface Biofilm on Particle Deposition and Infiltration in Streams  

NASA Astrophysics Data System (ADS)

Fine particulate matter is an important component of many streambed processes. For example, the deposition and infiltration of fine inorganic sediment has been repeatedly shown to degrade benthic habitat for fish and other organisms (Hynes, 1970). In contrast, fine organic particles are a significant source of carbon to benthic organisms (Webster et al., 1987). The mechanisms and rates of particle entrainment and deposition are highly complex and ill-predicted by simple physical relations. For example, a number of field studies have shown that measured rates of particle deposition often differ from still-water particle settling velocities calculated from particle size and density (e.g. Cushing et al., 1993). Several studies have proposed that adhesion of particles to surface biofilm may explain why deposition rates are faster than predicted, but few have investigated this phenomenon (Battin et al., 2003). In addition, although biofilms have been shown to significantly alter near-bed and interstitial flow velocities (Dodds and Biggs, 2002), the effect of these changes on particle depositionhas not been explored. Biofilm is pervasive in rivers and streams throughout the world, thus it may play an important, and heretofore underestimated, role in the deposition of fine particles to the streambed. This study tests the hypothesis that biofilm amount and structure may alter fine particle deposition, entrainment, and infiltration by either direct adhesion or by changes to near-bed hydraulics. A series of experiments are being conducted in a small recirculating flume to test how the amount and structure of surface biofilm influences the water column distribution, surface deposition, and infiltration of fine particles under two different flow levels ('high' and 'low'). Two types of surface biofilm are being tested: open-weave, filamentous assemblages and low-profile, mucilaginous forms; both are compared to a reference substrate without biofilm. Natural rocks hosting filamentous assemblages are collected from nearby channels and used to replace the surface layer of flume substrate. Low-profile forms are cultivated on a cobble-gravel substrate in an artificial stream system and tested at each of three growth stages. Immediately following a dose of fine particles (< 125 µm ground silica), short-term rates of particle deposition are determined by continuous measurements of near-bed particle concentrations. Hourly vertical concentration, grain size profiles, and 3-D velocity profiles are measured for the duration of the experiment (8h). Infiltration rate is determined from bed samplers sealed from the flow at 1, 2, 4, and 8 hours. At the end of each experiment, three surface samples are collected and analyzed for ash-weight, ash-free dry weight, and chlorophyll a. Four stratified bed samples and samplers are removed, dried, sieved and weighed to determine the amount and depth of fine particle infiltration into the bed with time and surface condition. Preliminary results indicate that particle deposition is significantly enhanced by biofilm presence relative to surfaces without biofilm; this effect is greater for mucilaginous forms. However, near-bed shear stresses and velocity profiles are not significantly altered by either mucilaginous or filamentous forms; bed topography has a dominant effect. Results also indicate that particle deposition is more strongly influenced by surface condition (e.g. particle size, biofilm presence) than by flow level or duration. Particle infiltration below the surface, however, is more a function of pore space and flow level than biofilm coverage on the streambed surface.

Salant, N. L.; Hassan, M. A.

2007-12-01

248

Coating mechanism of nano-TiO2 films on the surface of ultra-fine calcined coal kaolin particles  

NASA Astrophysics Data System (ADS)

A new type of mineral composite was made by calcined coal kaolin. The interaction mechanism of an inorganic modification reagent TiOSO4 with the surface of ultra-fine calcined coal kaolin particles (substrate) was studied by X-ray photoelectron spectroscopy. The results show that chemisorption exists in the phase boundary between the modification agent and the substrate surface, while physical adsorption occurs on the modification layers of hydrate titanium dioxide. The interaction force was calculated and analyzed according to DLVO theory between ultra-fine calcined coal kaolin particles and hydrate titanium dioxide nano-particles in the modification system. It is shown that the both electrostatic force and van der Waals force are attractive, and the coacervation between ultra-fine calcined coal kaolin particles and hydrate titanium dioxide nano-particles leads to the coating of hydrate titanium dioxide on the surface of ultra-fine calcined coal kaolin particles.

Lin, Hai; Dong, Ying-Bo

2011-08-01

249

In situ ceramic layer growth on coated fuel particles dispersed in a zirconium metal matrix  

SciTech Connect

The extent and nature of the chemical interaction between the outermost coating layer of coated fuel particles embedded in zirconium metal during fabrication of metal matrix microencapsulated fuels was examined. Various particles with outermost coating layers of pyrocarbon, SiC, and ZrC have been investigated in this study. ZrC-Zr interaction was least substantial while PyC-Zr reaction can be exploited to produce a ZrC layer at the interface in an in situ manner. The thickness of the ZrC layer in the latter case can be controlled by adjusting the time and temperature during processing. The kinetics of ZrC layer growth is significantly faster from what is predicted using literature carbon diffusivity data in ZrC. SiC-Zr interaction is more complex and results in formation of various chemical phases in a layered aggregate morphology at the interface.

Terrani, Kurt A [ORNL; Silva, G W Chinthaka M [ORNL; Kiggans, Jim [ORNL; Cai, Zhonghou [Argonne National Laboratory (ANL); Shin, Dongwon [ORNL; Snead, Lance Lewis [ORNL

2013-01-01

250

Elemental analyses of hypervelocity micro-particle impact sites on interplanetary dust experiment sensor surfaces  

NASA Astrophysics Data System (ADS)

The Interplanetary Dust Experiment (IDE) had over 450 electrically active ultra-high purity metal-oxide-silicon impact detectors located on the six primary sides of the Long Duration Exposure Facility (LDEF). Hypervelocity micro-particles that struck the active sensors with enough energy to breakdown the 0.4 to 1.0 micron thick SiO2 insulator layer separating the silicon base (the negative electrode), and the 1000 A thick surface layer of aluminum (the positive electrode) caused electrical discharges that were recorded for the first year of orbit. These discharge features, which include 50 micron diameter areas where the aluminum top layer has been vaporized, facilitate the location of the impacts. The high purity Al-SiO2-Si substrates allow detection of trace (ppm) amounts of hypervelocity impactor residues. After sputtering through a layer of surface contamination, secondary ion mass spectrometry (SIMS) is used to create two-dimensional elemental ion intensity maps of micro-particle impact sites on the IDE sensors. The element intensities in the central craters of the impacts are corrected for relative ion yields and instrumental conditions and then normalized to silicon. The results are used to classify the particles' origins as 'manmade', 'natural' or 'indeterminate'. The last classification results from the presence of too little impactor residue (a frequent occurrence on leading edge impacts), analytical interference from high background contamination, the lack of information on silicon residue, the limited usefulness of data on aluminum in the central craters, or a combination of these circumstances. Several analytical 'blank' discharges were induced on flight sensors by pressing down on the sensor surface with a pure silicon shard. Analyses of these blank discharges showed that the discharge energy blasts away the layer of surface contamination. Only Si and Al were detected inside the discharge zones, including the central craters, of these features. A total of 35 impacts on leading edge sensors and 22 impacts on trailing edge sensors were analyzed.

Simon, Charles G.; Hunter, J. L.; Griffis, D. P.; Misra, V.; Ricks, D. R.; Wortman, Jim J.

1992-06-01

251

Controlling protein-particle adsorption by surface tailoring colloidal alumina particles with sulfonate groups.  

PubMed

In this study, we demonstrate the control of protein adsorption by tailoring the sulfonate group density on the surface of colloidal alumina particles. The colloidal alumina (d(50)=179±8nm) is first accurately functionalized with sulfonate groups (SO(3)H) in densities ranging from 0 to 4.7SO(3)H nm(-2). The zeta potential, hydrophilic/hydrophobic properties, particle size, morphology, surface area and elemental composition of the functionalized particles are assessed. The adsorption of three model proteins, bovine serum albumin (BSA), lysozyme (LSZ) and trypsin (TRY), is then investigated at pH 6.9±0.3 and an ionic strength of 3mM. Solution depletion and zeta potential experiments show that BSA, LSZ and TRY adsorption is strongly affected by the SO(3)H surface density rather than by the net zeta potential of the particles. A direct correlation between the SO(3)H surface density, the intrinsic protein amino acid composition and protein adsorption is observed. Thus a continuous adjustment of the protein adsorption amount can be achieved between almost no coverage and a theoretical monolayer by varying the density of SO(3)H groups on the particle surface. These findings enable a deeper understanding of protein-particle interactions and, moreover, support the design and engineering of materials for specific biotechnology, environmental technology or nanomedicine applications. PMID:23164944

Meder, Fabian; Brandes, Christoph; Treccani, Laura; Rezwan, Kurosch

2012-11-17

252

Experimental determination of the concentration Probability Density Function for a saltating particle layer  

Microsoft Academic Search

A horizontal saltation layer of glass particles in air was investigated experimentally in a wind tunnel. Particle concentrations are measured by light scattering diffusion and image processing and all the statistical characteristics were evaluated and thus the probability density function. Our experimental results confirm that the mean concentration decreases exponentially with height, the mean Eulerian dispersion height H being a

XiaoHang Zhang; HongTao Wang; ZhiBao Dong; Michel Ayrault

2006-01-01

253

Transient Particle Deposition in a Boundary Layer of Impulsive Flow Over a Flat Plate.  

National Technical Information Service (NTIS)

The transport and deposition of fine particles in a boundary layer of impulsive flow over a flat plate have been examined by numerical methods. The transient impulsive flow over a flat plate is solved by a vortex sheet method and the particle transport eq...

J. N. Chung

1987-01-01

254

Local properties of the surface layer(s) of BiFeO3 single crystals  

NASA Astrophysics Data System (ADS)

The surface of BiFeO3 single crystals has been characterized at the local level using several AFM-based techniques. We have observed the presence of two different epilayers showing electrical and mechanical properties different from those of the bulk: a ferroelectrically ``dead'' outer skin of 5 nm sitting upon a subsurface layer that displays an extremely fine pattern of hierarchical self-ordered nanodomains. Based on the size of the nanodomains and applying a Kittel-like analysis, we argue that the nanotwinned region should be confined in a layer less than a micron deep. The superficial phase transition at T* = 275 °C is restricted to the outer skin layer (the ``dead'' layer), while the nanotwinned layer is insensitive to this transition. In view of the photovoltaic properties and spin-dependent transport of domain walls in BiFeO3, the existence of nanodomains (and thus a high density of domain walls) in bulk single crystals is likely to be relevant for understanding their functional properties.

Domingo, Neus; Narvaez, Jackeline; Alexe, Marin; Catalan, Gustau

2013-05-01

255

Surface charge features of kaolinite particles and their interactions  

NASA Astrophysics Data System (ADS)

Kaolinite is both a blessing and a curse. As an important industrial mineral commodity, kaolinite clays are extensively used in the paper, ceramic, paint, plastic and rubber industries. In all these applications the wettability, aggregation, dispersion, flotation and thickening of kaolinite particles are affected by its crystal structure and surface properties. It is therefore the objective of this research to investigate selected physical and surface chemical properties of kaolinite, specifically the surface charge of kaolinite particles. A pool of advanced analytical techniques such as XRD, XRF, SEM, AFM, FTIR and ISS were utilized to investigate the morphological and surface chemistry features of kaolinite. Surface force measurements revealed that the silica tetrahedral face of kaolinite is negatively charged at pH>4, whereas the alumina octahedral face of kaolinite is positively charged at pH<6, and negatively charged at pH>8. Based on electrophoresis measurements, the apparent iso-electric point for kaolinite particles was determined to be less than pH 3. In contrast, the point of zero charge was determined to be pH 4.5 by titration techniques, which corresponds to the iso-electric point of between pH 4 and 5 as determined by surface force measurements. Results from kaolinite particle interactions indicate that the silica face--alumina face interaction is dominant for kaolinite particle aggregation at low and intermediate pH values, which explains the maximum shear yield stress at pH 5-5.5. Lattice resolution images reveal the hexagonal lattice structure of these two face surfaces of kaolinite. Analysis of the silica face of kaolinite showed that the center of the hexagonal ring of oxygen atoms is vacant, whereas the alumina face showed that the hexagonal surface lattice ring of hydroxyls surround another hydroxyl in the center of the ring. High resolution transmission electron microscopy investigation of kaolinite has indicated that kaolinite is indeed composed of silica/alumina bilayers with a c-spacing of 7.2 A. The surface charge densities of the silica face, the alumina face and the edge surface of kaolinite all influence particle interactions, and thereby affect the mechanical properties of kaolinite suspensions. The improved knowledge of kaolinite surface chemistry from this dissertation research provides a foundation for the development of improved process strategies for both the use and disposal of clay particles such as kaolinite.

Gupta, Vishal

256

Surface-sensitive macrobolometers for the identification of external charged particles  

SciTech Connect

We report the performance of two prototype TeO{sub 2} macrobolometers, operated at {approx}25 mK, able to identify events due to energy deposited at the detector surface. This capability is obtained by thermally coupling thin Ge active layers to the main energy absorber of the bolometer, and is demonstrated by irradiating the detectors with {alpha} particles. The temperature variations of the main absorber and of the active layer are measured independently with doped Ge thermistors. These results show clearly that an intrinsic limitation of monolithic low temperature calorimeters, e.g., the impossibility to give information about event position, can be efficiently overcome using composite structures.

Foggetta, Luca; Giuliani, Andrea; Nones, Claudia; Pedretti, Marisa; Sangiorgio, Samuele [Department of Physics and Mathematics, University of Insubria, and INFN-Milano, Via Valleggio 11, 22100 Como (Italy)

2005-03-28

257

Surface plasmon dynamics of a metallic nano-particle  

Microsoft Academic Search

The paper presents a theoretical framework to explain the surface plasmon dynamics in a single metallic nano-particle (MNP). The plasmon physical mechanisms, i.e, internal oscillation energy, electromagnetic near-field energy and power-flow are analyzed here in terms of electric dipole moment of a single metallic nano-particle. The resonant mode shift and hybridization of a metallic nano-shell with annular metallic region are

Kyungjun Song; Piniki Mazumder

2007-01-01

258

Effective Modification of Particle Surface Properties Using Ultrasonic Water Mist  

Microsoft Academic Search

The goal of the present study was to design a new technique to modify particle surface properties and, through that, to improve\\u000a flowability of poorly flowing drug thiamine hydrochloride and pharmaceutical sugar lactose monohydrate of two different grades.\\u000a The powdered particles were supplied by a vibratory feeder and exposed to an instantaneous effect of water mist generated\\u000a from an ultrasound

Natalja Genina; Heikki Räikkönen; Jyrki Heinämäki; Osmo Antikainen; Simo Siiriä; Peep Veski; Jouko Yliruusi

2009-01-01

259

Characterization of particle size evolution of the deposited layer during electrostatic powder coating processes  

Microsoft Academic Search

This experimental study investigated particle size evolution in deposited layers during typical electrostatic powder coating processes, using two powder (coarse and ultrafine) systems. Results disclosed that powder coating is a size-selective process in which the motions of in-flight particles are size-dependent. As a result, particles deposited on different regions of the substrate present some size discrepancy which accounts for a

Xiangbo Meng; Hui Zhang

2009-01-01

260

The Zeta Potential of Surface-Functionalized Metallic Nanorod Particles in Aqueous Solution  

SciTech Connect

Metallic nanoparticles suspended in aqueous solutions, and functionalized with chemical and biological surface coatings, are important elements in basic and applied nanoscience research. Many applications require an understanding of the electrokinetic or colloidal properties of such particles. In this paper we describe the results of experiments to measure the zeta potential of metallic nanorod particles in aqueous saline solutions, including the effects of pH, ionic strength, metallic composition, and surface functionalization state. Particle substrates tested include gold, silver, and palladium monometallic particles as well as gold/silver bimetallic particles. Surface functionalization conditions included 11-mercaptoundecanoic acid (MUA), mercaptoethanol (ME), and mercaptoethanesulfonic acid (MESA) self-assembled monolayers (SAMs), as well as MUA layers subsequently derivatized with proteins. Zeta potential data for typical charge-stabilized polystyrene particles are also presented for comparison. Experimental data are compared with theory. The results of these studies are useful in predicting and controlling the aggregation, adhesion, and transport of functionalized metallic nanoparticles within microfluidic devices and other systems.

Dougherty, G M; Rose, K A; Tok, J B; Pannu, S S; Chuang, F S; Sha, M Y; Chakarova, G; Penn, S G

2007-05-07

261

Enhanced magnetoresistance and surface state of CrO2 particles improved by chemical process  

NASA Astrophysics Data System (ADS)

The paper presents an approach to enhance a magnetoresistance (MR) effect in CrO2 powder compact by an oxidization reaction process. An aqueous potassium permanganate (KMnO4) was used to react with the CrO2 particles coated naturally with Cr2O3 layer. The experiment indicates that the strong oxidant can effectively adjust thickness of the natural Cr2O3 layer, and thereby change the surface state of the CrO2 particles. Structural and magnetic properties for the improved CrO2 particles have been characterized by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and SQUID magnetometer. The results exhibit that the magnetotransport behavior of CrO2 particles depends sensitively on the chemical reaction time. An optimal reaction process yields an obvious increase up to -33% in magnetoresistance at a temperature of 5 K for the chemical treated CrO2 powder, compared to MR=-27% for the original CrO2 powder. The mechanism of magnetotransport is assumed to originate from the spin-dependent tunneling in the granular system, which is consistent with our experimental results. The simple chemical approach has a potential to achieve an enhanced magnetoresistance in a metallic particle system by adjusting the surface state of the magnetic nanoparticle.

Zhang, Xiaoyu; Chen, Yajie; Li, Zhenya

2006-12-01

262

Tunable surface free energies of functionalized molecular layers on Si surfaces for microfluidic immunosensor applications  

NASA Astrophysics Data System (ADS)

Enhanced antigen-antibody interactions in microfluidic immunosensors can be effected by tailoring the surface free energies of the antibody immobilized surfaces to obtain the appropriate fluid-wall interactions. We report a systematic study to evaluate the surface free energies from contact angle measurements, using the LWAB method, of different antibody (anti-BSA, anti-PSA, and anti-CRP) surfaces, each immobilized separately on to non- and nanotextured Si surfaces via a stack of functionalized layers including aminosilanes of which three different types were used. The apolar surface free energy components were independent of the physical modification in the non-functionalized and the intermediate hydrolyzed surfaces where as they depended on the nature of the surface and the chemical modifications in the subsequent functionalized stages. Surface free energies of the different antibodies immobilized with the shorter chain length aminosilane (APTES) on non- and nanotextured surfaces were in the order of anti-BSA < anti-PSA < anti-CRP. A tunability of the surface free energy up to 9.6 mJ/m2 was achieved which is reasonably significant when compared to the surface free energy window (??s = 40 mJ/m2) of biofunctionalized surfaces. This fundamental understanding of the surface energetics of the biofunctionalized surfaces can be utilized in modulating the surface properties to design efficient immunosensors.

Chepyala, Ramchander; Panda, Siddhartha

2013-04-01

263

Charged particle detectors made from thin layers of amorphous silicon  

SciTech Connect

A series of experiments was conducted to determine the feasibility of using hydrogenated amorphous silicon (..cap alpha..-Si:H) as solid state thin film charged particle detectors. /sup 241/Am alphas were successfully detected with ..cap alpha..-Si:H devices. The measurements and results of these experiments are presented. The problems encountered and changes in the fabrication of the detectors that may improve the performance are discussed.

Morel, J.R.

1986-05-01

264

Particle simulation of auroral double layers. Doctoral thesis  

SciTech Connect

Externally driven magnetic reconnection has been proposed as a possible mechanism for production of auroral electrons during magnetic substorms. Fluid simulations of magnetic reconnection lead to strong plasma flows towards the increasing magnetic field of the earth. These plasma flows must generate large scale potential drops to preserve global charge neutrality. We have examined currentless injection of plasma along a dipole magnetic field into a bounded region using both analytic techniques and particle simulation.

Smith, B.L.

1992-06-01

265

Detection of charged particles in amorphous silicon layers  

SciTech Connect

The successful development of radiation detectors made from amorphous silicon could offer the possibility for relatively easy construction of large area position-sensitive detectors. We have conducted a series of measurements with prototype detectors, on signals derived from alpha particles. The measurement results are compared with simple model calculations, and projections are made of potential applications in high-energy and nuclear physics. 4 refs., 7 figs.

Kaplan, S.N.; Morel, J.R.; Mulera, T.A.; Perez-Mendez, V.; Schnurmacher, G.; Street, R.A.

1985-10-01

266

Cellular interactions of surface modified nanoporous silicon particles  

NASA Astrophysics Data System (ADS)

In this study, the self-assembly of hydrophobin class II (HFBII) on the surface of thermally hydrocarbonized porous silicon (THCPSi) nanoparticles was investigated. The HFBII-coating converted the hydrophobic particles into more hydrophilic ones, improved the particles' cell viability in both HT-29 and Caco-2 cell lines compared to uncoated particles, and enhanced the particles' cellular association. The amount of HFBII adsorbed onto the particles was also successfully quantified by both the BCA assay and a HPLC method. Importantly, the permeation of a poorly water-soluble drug, indomethacin, loaded into THCPSi particles across Caco-2 monolayers was not affected by the protein coating. In addition, 125I-radiolabelled HFBII did not extensively permeate the Caco-2 monolayer and was found to be stably adsorbed onto the THCPSi nanoparticles incubated in pH 7.4, which renders the particles the possibility for further track-imaging applications. The results highlight the potential of HFBII coating for improving wettability, increasing biocompatibility and possible intestinal association of PSi nanoparticulates for drug delivery applications.In this study, the self-assembly of hydrophobin class II (HFBII) on the surface of thermally hydrocarbonized porous silicon (THCPSi) nanoparticles was investigated. The HFBII-coating converted the hydrophobic particles into more hydrophilic ones, improved the particles' cell viability in both HT-29 and Caco-2 cell lines compared to uncoated particles, and enhanced the particles' cellular association. The amount of HFBII adsorbed onto the particles was also successfully quantified by both the BCA assay and a HPLC method. Importantly, the permeation of a poorly water-soluble drug, indomethacin, loaded into THCPSi particles across Caco-2 monolayers was not affected by the protein coating. In addition, 125I-radiolabelled HFBII did not extensively permeate the Caco-2 monolayer and was found to be stably adsorbed onto the THCPSi nanoparticles incubated in pH 7.4, which renders the particles the possibility for further track-imaging applications. The results highlight the potential of HFBII coating for improving wettability, increasing biocompatibility and possible intestinal association of PSi nanoparticulates for drug delivery applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr30397c

Bimbo, Luis M.; Sarparanta, Mirkka; Mäkilä, Ermei; Laaksonen, Timo; Laaksonen, Päivi; Salonen, Jarno; Linder, Markus B.; Hirvonen, Jouni; Airaksinen, Anu J.; Santos, Hélder A.

2012-05-01

267

Seaglider observations of surface mixed layer physics and biogeochemistry  

NASA Astrophysics Data System (ADS)

The Ocean Surface Mixing, Ocean Sub-mesoscale Interaction Study (OSMOSIS) aims to develop new, physically-based parameterisations of processes that deepen and shoal the ocean surface boundary layer. As part of this project, 2 Seagliders were deployed in September 2012 at the Porcupine Abyssal Plain (PAP) site in the North Atlantic, to measure the structure and evolution of the ocean surface boundary layer over the seasonal cycle. The gliders measured temperature, salinity, dissolved oxygen, dive-averaged currents, chlorophyll fluorescence, CDOM fluorescence and PAR. We present results from the first 6 months of the Seaglider deployments, examining particular case studies of deepening/shoaling events and their impact on the biogeochemistry. Shoaling events appear to be more abrupt than deepening events. We also discuss the water masses found in the area, in particular, the occurrences of Mediterranean Water observed at a depth of approximately 800 m. As a contribution to the GROOM project, we assess the advantages and challenges of maintaining a continuous glider-based multidisciplinary observing system at the PAP site, with 2 gliders being turned around approximately every 4 months.

Damerell, Gillian; Heywood, Karen; Thompson, Andrew; Henson, Stephanie; Rumyantseva, Anya

2013-04-01

268

Capillary Interception of Floating Particles by Surface-Piercing Vegetation  

NASA Astrophysics Data System (ADS)

Surface-piercing vegetation often captures particles that flow on the water surface, where surface tension forces contribute to capture. Yet the physics of capillary capture in flow has not been addressed. Here we model the capture of floating particles by surface-piercing collectors at moderately low Reynolds numbers (Re<10). We find a trade-off between the capillary force, which increases with the collector diameter, and the relative size of the meniscus, which decreases with the collector diameter, resulting in an optimal collector diameter of ˜1-10mm that corresponds to the regime in which many aquatic plant species operate. For this diameter range the angular distribution of capture events is nearly uniform and capture can be orders of magnitude more efficient than direct interception, showing that capillary forces can be major contributors to the capture of seeds and particulate matter by organisms.

Peruzzo, Paolo; Defina, Andrea; Nepf, Heidi M.; Stocker, Roman

2013-10-01

269

[Particle dispersion by ordered motion in mixing layers]. [Annual report  

SciTech Connect

Multiphase mixing in turbulent flows is a key element in many practical energy conversion, chemical mixing and pollutant dispersal problems. Numerous important technological and environmental processes could be better addressed with improvements in understanding in this area. Progress in developing understanding of this field, however, has traditionally been difficult because of the complexities involved with the turbulent flows employed to provide the mixing mechanisms. To address this problem from a new perspective several years ago this research group initiated an ongoing investigation concerning the potential connections between organized turbulent vortex structures and the particle dispersion process. This report details activities during this reporting period.

Troutt, T.R.

1989-12-31

270

Influence of surface charge distributions and particle size distributions on particle attachment in granular media filtration.  

PubMed

Filtration experiments were performed with a laboratory-scale filter using spherical glass beads with 0.55 mm diameter as collectors. Suspensions were made with Min-U-Sil 5 particles, and two different methods (pH control and polymer dosing) were used for destabilization. In the pH control experiments, all particles had negative surface charge, and those with lower (absolute value) charge were selectively attached to the collectors, especially during the early stage of filtration. This selective attachment of the lower charged particles caused the zeta potential distribution (ZPD) of the effluent to move to a more negative range. However, the ZPD of the effluent did not continue moving to more negative values during the later stages of filtration, and this result was attributed to two reasons: ripening effects and detachment of flocs. In the polymer experiments, substantial differences were found between experiments performed with negatively charged particles (underdosing) and those with positively charged particles (overdosing). With under-dosing, the results were similar to the pH control experiments (which also had negatively charged particles), but with overdosing, the effluent's ZPDs in the early stages did not overlap with those of the influent and more highly charged particles were removed more efficiently than lesser-charged particles. It is hypothesized that, despite a substantial period of pre-equilibration of media and coagulant, this equilibrium shifted when particles were also added. It was assumed that coagulant molecules previously adsorbed to the particles desorbed and subsequently attached to the filter media because of surface area differences in the particle and filter media. PMID:18504996

Kim, Jinkeun; Nason, Jeffrey A; Lawler, Desmond F

2008-04-01

271

Surface structure of nascent particles of ultrahigh molecular weight poly(ethylene) reactor powders  

NASA Astrophysics Data System (ADS)

A comparative investigation of the surface structure of three ultrahigh molecular weight poly(eth-ylene) (UHMWPE) reactor powders that differ by their ability to be processed to high-performance fibers is carried out with a JEOL 6300 scanning electron microscope and a nanoluminograph, which makes it possible to study thermoluminescence of ultrathin near-surface layers of solids. The activation energies of relaxation processes in near-surface layers of nascent particles and the sizes of kinetic units of motion, for which the mobility is defrozen in the temperature range of the corresponding transitions, are calculated from the glow curves. The possible location of kinetic units in supermolecular formations resolved in micrographs and their influence on the dissolution of the reactor powder are discussed.

Lebedev, D. V.; Ivan'kova, E. M.; Marikhin, V. A.; Myasnikova, L. P.; Seydewitz, V.

2009-08-01

272

Incipient space weathering observed on the surface of Itokawa dust particles.  

PubMed

The reflectance spectra of the most abundant meteorites, ordinary chondrites, are different from those of the abundant S-type (mnemonic for siliceous) asteroids. This discrepancy has been thought to be due to space weathering, which is an alteration of the surfaces of airless bodies exposed to the space environment. Here we report evidence of space weathering on particles returned from the S-type asteroid 25143 Itokawa by the Hayabusa spacecraft. Surface modification was found in 5 out of 10 particles, which varies depending on mineral species. Sulfur-bearing Fe-rich nanoparticles exist in a thin (5 to 15 nanometers) surface layer on olivine, low-Ca pyroxene, and plagioclase, which is suggestive of vapor deposition. Sulfur-free Fe-rich nanoparticles exist deeper inside (<60 nanometers) ferromagnesian silicates. Their texture suggests formation by metamictization and in situ reduction of Fe(2+). PMID:21868670

Noguchi, T; Nakamura, T; Kimura, M; Zolensky, M E; Tanaka, M; Hashimoto, T; Konno, M; Nakato, A; Ogami, T; Fujimura, A; Abe, M; Yada, T; Mukai, T; Ueno, M; Okada, T; Shirai, K; Ishibashi, Y; Okazaki, R

2011-08-26

273

Molecular orientation of rhodamine dyes on surfaces of layered silicates.  

PubMed

Films of the layered silicates fluorohectorite (FH) and saponite (Sap) with various rhodamine dyes were prepared. The dyes with acidic as well as large hydrophobic groups in their molecule were not adsorbed on the surface of FH, which was interpreted in terms of high charge density on the surface of this silicate. All adsorbed dyes formed similar forms, such as isolated cations and H-type molecular aggregates, which were characterized by different spectral properties. Polarized ultraviolet-visible (UV-vis) spectroscopy was used for the characterization of the molecular orientation of dye chromophores on the silicate surface. The isolated dye cations and species, which absorbed light at the low energy part of the spectra, were only slightly tilted with respect to the plane of the silicate surface. The cations forming H-aggregates and absorbing light at low wavelengths were oriented in a nearly perpendicular fashion. The nearly perpendicular orientation was observed as a strong increase of dichroic ratio with film tilting. The orientation of the cations in H-aggregates depends partially on the structure of the dye molecule, namely, on the type of amino group (primary, secondary, or tertiary) in the dye molecule. The type of amino groups probably plays a role in the suitable orientation of dye cations for effective electrostatic interaction between the cations and the negatively charged siloxane surface. X-ray powder diffraction could not distinguish dye phases of dye monomers and molecular aggregates. PMID:16851539

Bujdák, Juraj; Iyi, Nobuo

2005-03-17

274

Tuning the surface plasmon resonance of core-shell particles  

NASA Astrophysics Data System (ADS)

Gold coated silica core-shell microspheres were synthesized using chemical reduction growth method. Coreshell microspheres were characterized using Scanning electron microscopy (SEM) and Ultraviolet-Visible (UV-Visible) spectroscopy. SEM images show that the surface of microspheres becomes rough which reflects the presence of gold nanoparticles (AuNPs) after coating. UV-Visible spectroscopy shows that the surface plasmon resonance peak undergoes red shift with the shell growth. Core-shell particles were also investigated for different gold concentrations.

Sharma, Ankita; Singh, Bhanu P.; Gathania, Arvind K.

2013-06-01

275

Nanographene layers and particles and lubricants incorporating the same  

US Patent & Trademark Office Database

A method of making at least one nanographene layer is disclosed herein. The method includes selecting X hydrocarbon precursor and Y hydrogen gas (H.sub.2) such that a ratio of X/Y ranges from 0.5 to 1, the hydrocarbon precursor including at least one of CH.sub.4, C.sub.2H.sub.2 or C.sub.3H.sub.8. The method further includes submitting the hydrocarbon precursor to chemical vapor deposition using the hydrogen gas and argon gas (Ar). As a result, i) the hydrocarbon precursor reacts with the hydrogen gas and argon gas (Ar) according to the following reaction: X hydrocarbon precursor+YH.sub.2+ZAr.fwdarw.2X graphene+(Y+2X)H.sub.2+ZAr, where Z ranges from 5*(X+Y) to 10*(X+Y), and ii) the hydrocarbon precursor decomposes and self-assembles to form the at least one nanographene layer.

2012-07-24

276

Surface Chemical Analysis and Electrokinetic Properties of Spherical Hematite Particles Coated with Yttrium Compounds  

PubMed

We describe in this work the chemical and electrokinetic surface characterization of core-shell particles consisting of a practically spherical hematite nucleus coated by a layer of yttrium basic carbonate or yttrium oxide (obtained after calcination of the carbonate-coated particles, following the method of E. Matijevic and B. Aiken (J. Colloid Interface Sci. 126, 645 (1988))). The morphological and surface characteristics of the particles were controlled by modifying the initial yttrium nitrate concentration and the growing time. A total of 14 samples of hematite-yttrium basic carbonate composites were obtained, and three of them (obtained by keeping at 90degreesC solutions containing 6.5 x 10(-4) M alpha-Fe2O3, 1.8 M urea, and 1.1, 3, and 4.9 mM Y(NO3)3, respectively) were then converted into hematite-Y2O3 particles. Transmission electron microscopy was used to ascertain the shape and size of the particles. The spherical geometry of the core hematite is found, as a rule, on the core-shell particles; in general, carbonate samples obtained with intermediate initial concentration of Y(NO3)3 have the maximum coating thickness, whereas increasing that concentration does not lead to thicker coatings. Hence, formation of individual yttrium basic carbonate, together with coated hematite, cannot be completely ruled out under such conditions. Two techniques were employed for the elucidation of the surface composition of the particles, namely EDX and XPS (or ESCA). In particular, XPS data show that the coating of hematite by yttrium carbonate is almost complete in the case of particles obtained with 3 mM Y(NO3)3 concentration and 9-h heating time. The oxide samples obtained after calcination show high contents of yttrium and low iron surface concentration for initial [Y(NO3)3] = 1.1 mM (sample OB9) and 3 mM. According to XPS analysis, both types of particles have a quite similar surface composition and structure. For all types of particles but the carbonate-coated ones obtained at the shortest reaction times, the pHiep was found to be above that of pure hematite, approaching that of yttrium basic carbonate or oxide. In particular, among the oxide-coated particles, it is sample OB9 the one that most closely approaches its pHiep to that of Y2O3, in good agreement with the surface chemical analysis performed with XPS. Copyright 1997 Academic Press. Copyright 1997Academic Press PMID:9398422

Plaza; Duran; Quirantes; Ariza; Delgado

1997-10-15

277

Boundary layer flow of nanofluid over an exponentially stretching surface  

PubMed Central

The steady boundary layer flow of nanofluid over an exponential stretching surface is investigated analytically. The transport equations include the effects of Brownian motion parameter and thermophoresis parameter. The highly nonlinear coupled partial differential equations are simplified with the help of suitable similarity transformations. The reduced equations are then solved analytically with the help of homotopy analysis method (HAM). The convergence of HAM solutions are obtained by plotting h-curve. The expressions for velocity, temperature and nanoparticle volume fraction are computed for some values of the parameters namely, suction injection parameter ?, Lewis number Le, the Brownian motion parameter Nb and thermophoresis parameter Nt.

2012-01-01

278

Dynamic Cell Surface Hydrophobicity of Lactobacillus Strains with and without Surface Layer Proteins  

PubMed Central

Variations in surface hydrophobicity of six Lactobacillus strains with and without an S-layer upon changes in ionic strength are derived from contact angle measurements with low- and high-ionic-strength aqueous solutions. Cell surface hydrophobicity changed in response to changes in ionic strength in three out of the six strains, offering these strains a versatile mechanism to adhere to different surfaces. The dynamic behavior of the cell surface hydrophobicity could be confirmed for two selected strains by measuring the interaction force between hydrophobic and hydrophilic tips with use of atomic force microscopy.

Vadillo-Rodriguez, Virginia; Busscher, Henk J.; Norde, Willem; de Vries, Joop; van der Mei, Henny C.

2004-01-01

279

Plasma-enhanced deposition of antifouling layers on silicone rubber surfaces  

NASA Astrophysics Data System (ADS)

In food processing and medical environments, biofilms serve as potential sources of contamination, and lead to food spoilage, transmission of diseases or infections. Because of its ubiquitous and recalcitrant nature, Listeria monocytogenes biofilm is especially hard to control. Generating antimicrobial surfaces provide a method to control the bacterial attachment. The difficulty of silver deposition on polymeric surfaces has been overcome by using a unique two-step plasma-mediated method. First silicone rubber surfaces were plasma-functionalized to generate aldehyde groups. Then thin silver layers were deposited onto the functionalized surfaces according to Tollen's reaction. X-ray photoelectron spectroscopy (XPS), atomic force spectroscopy (AFM) and scanning electron microscopy (SEM) showed that silver particles were deposited. By exposing the silver coated surfaces to L. monocytogenes, it was demonstrated that they were bactericidal to L. monocytogenes. No viable bacteria were detected after 12 to 18 h on silver-coated silicone rubber surfaces. Another antifouling approach is to generate polyethylene glycol (PEG) thin layer instead of silver on polymer surfaces. Covalent bond of PEG structures of various molecular weights to cold-plasma-functionalized polymer surfaces, such as silicone rubber, opens up a novel way for the generation of PEG brush-like or PEG branch-like anti-fouling layers. In this study, plasma-generated surface free radicals can react efficiently with dichlorosilane right after plasma treatment. With the generation of halo-silane groups, this enables PEG molecules to be grafted onto the modified surfaces. XPS data clearly demonstrated the presence of PEG molecules on plasma-functionalized silicone rubber surfaces. AFM images showed the changed surface morphologies as a result of covalent attachment to the surface of PEG molecules. Biofilm experiment results suggest that the PEG brush-like films have the potential ability to be the next generation antifouling deposition. However, the coverage on FSR needs to be improved. Different PEG structures (brush, branched, oxirane-group terminated and PEG terminated structures) were developed in this study to understand the bacterial attachment behavior and the antifouling mechanism of PEG-like structures. Results from biofilm experiments demonstrated the absence of antifouling behavior. The presence of PEG structure on substrate surfaces cannot guarantee antifouling ability.

Jiang, Hongquan

280

Diffusioosmosis and electroosmosis in a capillary slit with surface charge layers  

Microsoft Academic Search

This study analytically examines the steady diffusioosmotic and electroosmotic flows of an electrolyte solution in a fine capillary slit with each of its inside walls covered by a layer of adsorbed polyelectrolytes. In this solvent-permeable and ion-penetrable surface charge layer, idealized polyelectrolyte segments are assumed to distribute at a uniform density. The electric double layer and the surface charge layer

Jan H. Wu; Huan J. Keh

2003-01-01

281

Layer-like Structure of Radio-Frequency Discharge with Dust Particles  

SciTech Connect

In this paper we are carried out the computer simulation of the dust particles dynamics in the radio frequency discharges at the microgravity conditions using PIC/MCC method for electrons and ions and hydrodynamics model for dust particles. The moving of dust particles is governed by the electrostatic force, ion and neutral drag forces, which are averaged over period of RF discharge. The obtained results show that dust particles form layers with sharp boundaries in the discharge chamber that is response on the instability of the radio-frequency discharge.

Kravchenko, O. Y.; Vakulenko, A. V.; Lisitchenko, T. Y.; Levada, G. I. [National Taras Shevchenko University of Kyiv, Volodymirs'ka str. 64, 01033 Kyiv (Ukraine)

2008-09-07

282

Control of test particle transport in a turbulent electrostatic model of the Scrape-Off-Layer  

NASA Astrophysics Data System (ADS)

The E × B drift motion of charged test particle dynamics in the Scrape-Off-Layer (SOL) is analyzed to investigate a transport control strategy based on Hamiltonian dynamics. We model SOL turbulence using a 2D non-linear fluid code based on interchange instability which was found to exhibit intermittent dynamics of the particle flux. The effect of a small and appropriate modification of the turbulent electric potential is studied with respect to the chaotic diffusion of test particle dynamics. Over a significant range in the magnitude of the turbulent electrostatic field, a three-fold reduction of the test particle diffusion coefficient is achieved.

Ciraolo, G.; Ghendrih, Ph.; Sarazin, Y.; Chandre, C.; Lima, R.; Vittot, M.; Pettini, M.

2007-06-01

283

ELECTROSTATIC SURFACE STRUCTURES OF COAL AND MINERAL PARTICLES  

SciTech Connect

This is the third semi-annual, technical progress report for this project. The following items are covered in the report: (1) Progress on the development of an instrument to perform ultraviolet photoelectron spectroscopy, UPS, on surfaces in air. (2) Further development plans for the video particle image analyzer. (3) Calculations on the effect of space charge on the electric field inside a separator. (4) Outreach education involving two Arkansas high school students in the project. (5) Additional data on the effects of processing atmosphere on beneficiation. Included in the last section is a description of planned experiments using charged, fluorescent, polystyrene micro-particles to map the charge distribution on the larger coal particles and on polished coal surfaces.

NONE

1998-04-01

284

Development of surfaces repelling negatively buoyant solid particles  

NASA Astrophysics Data System (ADS)

Using a hybrid computational method that integrates the lattice Boltzmann model for fluid dynamics and the lattice spring model for solids, we examine the motion of negatively buoyant solid microparticles in shear flow near a solid wall decorated with regularly distributed rigid posts. The posts are arranged in a square pattern and tilted relative to the flow direction. We show that when rigid posts are tilted against flow, secondary flows emerge that prevent the deposition of suspended particles on the solid surface. We probe the effect of post geometry on the development of secondary flows and identify the optimal post architecture in terms of the mass of levitated solid particles. Our results are useful for designing anti-fouling surfaces that repel colloidal particles carried by fluid.

Semmler, Carina; Alexeev, Alexander

2011-03-01

285

Physico-chemical characterisation of surface modified particles for inhalation.  

PubMed

Surface modification of drugs for inhalation is a possibility to influence interparticulate forces. This can be necessary to achieve a sufficient aerosolisation during powder inhalation as the cohesiveness of the micronised drug can be reduced. In addition, the interaction with propellants in pressurised metered dose inhaler can be changed. This can be used to improve the physical stability of the suspension based formulations. A dry particle coating process was used for the alteration of particle surfaces. The blending of micronised salbutamol sulphate (SBS) with different concentrations of magnesium stearate (Mgst) or glycerol monostearate (GMS) was followed by co-milling with an air jet mill. The powder properties were characterised by SEM, EDX, laser diffraction, BET and inverse gas chromatography. Physical mixtures generated by Turbula blending were compared to co-milled samples. A slight particle size reduction was determined. The Mgst deposition on SBS particles was detected by EDX measurements. The dispersive surface energy of SBS is lowered and the energy distribution is more homogenous for the co-milled samples. This study proves the application of co-milling for surface modification in the inhalation area. PMID:23518364

Stank, Katharina; Steckel, Hartwig

2013-03-18

286

Interactions of Particle Dry Deposition with Solid Surfaces  

Microsoft Academic Search

The processes of particle deposition, bounceoff, and resuspension have been studied in wind tunnel experiments and in the ambient atmosphere. A variety of man-made materials as well as natural leaves have been used as depositing surfaces in both environments. The man-made materials used include greased and ungreased Teflon, greased and ungreased mylar, nylon filter paper, and Whatman cellulose filter paper.

Yee-Lin Wu

1992-01-01

287

On the determination of vertical profiles of temperature, charge concentration, and potential in the surface layer of an aircraft  

NASA Astrophysics Data System (ADS)

A “3/2 law” law has been established for the vertical charge concentration profile (i.e., the particle concentration is proportional to temperature to a power of 3/2). The expression is derived for the electric field potential produced by charged particles at the upper boundary of the viscous sublayer, as well as for the density current produced by charged particles moving in the air flow streamlining an aircraft. It is shown that all these parameters increase with altitude and assume maximum values at the turbulent layer surface.

Zakinyan, R. G.

2006-11-01

288

Theory and particle simulation of nonlinear double layers in a magnetized plasma  

SciTech Connect

Theoretical investigation and particle simulation of obliquely propagating nonlinear double layers (NDLs) of nonmonotonic type are performed in a magnetized plasma, which consists of a positively charged ion fluid and trapped, as well as free electrons. The modified Zakharov-Kuznetsov equation is derived by the usual reductive perturbation technique in a three-dimensional system. A nonlinear double layer solution is presented. Furthermore using Sagdeev's pseudopotential technique, nonlinear double layer solution, which is associated with a set of nonlinear eigenvalue conditions, is also presented. These solutions are the analytic extensions of the monotonic double layers and solitary holes. The effects of physical parameters of nonlinear double layers are discussed. In particle simulations of a current driven system, physical relations among the obliqueness, the propagating velocity, the inverse scale length, and the maximum potential are investigated. The maximum potential and the width of the NDL decreases as the degree of the angle increases. In a chosen field, a decrease of potential width (or maximum potential) is clearly shown in the case of less than 10 deg. Variation of propagating velocity is clearly shown in the range of 10 deg. -16 deg. Particle simulations are performed with an axially bounded electrostatic particle-in-cell code XPDP1, which is a workstation version of a one-dimensional bounded plasma code PDW1 [J. Comput. Phys. 80, 253 (1989)]. These particle simulation results are in good agreement with the qualitative theoretical results.

Kim, Seung-Shik; Kim, Tae-Han; Kim, Ho-Yeun [Manmin Research Center, 851, Guro-dong, Guro-gu, Seoul 152-879, South Korea and Institute of Basic Sciences, Hankuk University of Foreign Studies, 270, Imun-dong, Dongdaemun-gu, Seoul 130-791 (Korea, Republic of); Manmin Research Center, 851, Guro-dong, Guro-gu, Seoul 152-879 (Korea, Republic of); School of Materials Science and Engineering, Seoul National University, San 56-1, Sillim-dong, Gwanak-gu, Seoul 151-742 (Korea, Republic of)

2007-05-15

289

The optical properties of nanoscale coatings on particles fabricated by atomic layer deposition  

NASA Astrophysics Data System (ADS)

The optical properties of nanoscale thin films can be vastly different from those of the bulk material. This dissertation studies the optical properties of films deposited using atomic layer deposition (ALD), which is a highly-conformal precision growth technique with sub-nanometer thickness control. The quantifiable optical properties of interest are scattering and absorption (or extinction), which are fully described by the indices of refraction (n) and extinction (k). The pieces of equipment that are readily available to measure these optical properties operate throughout the UV, visible and IR wavelength range (lambda = 250 ˜ 1600 nm). Semiconducting materials possess a bandgap, or energy barrier required to allow electrons to be elevated from the valence band to the conduction band, that typically falls within this wavelength range. Zinc oxide (ZnO) and titanium dioxide (TiO2 or titania) are wide-bandgap semiconductor materials that have been deposited using the ALD technique, but no research had been performed to study the nanoscale thin-film optical properties of these materials. Moreover, the ALD technique seemingly had never been studied as a pathway to create films that exhibit quantum confinement, which manifests itself as an increase in bandgap as a function of film thickness at the nanoscale. In order for novel breakthroughs in the field of nanotechnology to become commercial products, processes must be developed that leverage the economics of scale. Particle ALD in continuous-flow reactors provides a scale-up pathway from classical ALD processes that coat low surface area substrates. Mass spectrometry is used to monitor precursor utilization during this gas-phase deposition technique, and is viable at any scale. TiO2 and ZnO ALD processes are studied here on bulk quantities of particle substrates using a fluidized bed reactor. Low-temperature particle ALD processes are developed to mitigate issues that arise when coating batch surface areas that are four or five orders of magnitude larger than well-studied ALD processes on flats. TiO2 and ZnO ALD films exhibit quantum confinement and can be modeled using the effective mass approximation. Quantum confined nanocomposite particles can be economically-fabricated using ALD in scalable reactors, thereby allowing their incorporation in mainstream commercial products.

King, David Michael

290

Influence of microshot peening on surface layer characteristics of structural steel  

Microsoft Academic Search

The influence of microshot peening on the surface layer characteristics of the structural steel was investigated. Shot peening is one of the surface treatments and it is a mechanical surface treatment widely used in automotive industry to enhance fatigue life and surface layer characteristics of mechanical parts. In this process, the surface is collided repeatedly with small spherical media called

Y. Harada; K. Fukaura; S. Haga

2007-01-01

291

Photometric imaging in particle size measurement and surface visualization.  

PubMed

The aim of this paper is to give an insight into photometric particle sizing approaches, which differ from the typical particle size measurement of dispersed particles. These approaches can often be advantageous especially for samples that are moist or cohesive, when dispersion of particles is difficult or sometimes impossible. The main focus of this paper is in the use of photometric stereo imaging. The technique allows the reconstruction of three-dimensional images of objects using multiple light sources in illumination. The use of photometric techniques is demonstrated in at-line measurement of granules and on-line measurement during granulation and dry milling. Also, surface visualization and roughness measurements are briefly discussed. PMID:21075186

Sandler, Niklas

2010-11-12

292

ELECTROSTATIC SURFACE STRUCTURES OF COAL AND MINERAL PARTICLES  

SciTech Connect

We have developed a video image analyzer for measuring the size and charge of airborne particles. Particles are illuminated by laser light and subjected to a sinusoidal electric field while images of the trajectories of the particles are captured using a video camera and a frame grabber. Analysis of the particle tracks allows the size and charge of the particles to be determined. The instrument can be used to measure size and charge spectra of charged coal and mineral particles in real time. Appendix I shows size and charge distributions of coal and flyash particles measured with the image analyzer. A second instrument, an Ultraviolet Photoelectron Spectrometer (UPS) for measuring effective work functions of insulator and semiconductor surfaces in air is under development. Work function data for individual macerals and minerals in a coal matrix will be related to triboelectric charging properties. In this instrumental method, originally developed by Kirhata, the surface of a test sample is bombarded by monochromatic ultraviolet light of known wavelength. At atmospheric pressure, the photo-ejected electrons attach to air molecules forming negative ions. The ions are attracted by an applied electric field into a detector where they are accelerated to sufficient energy that they cause momentary dielectric breakdown or discharge in the air inside the detector. The rate at which these discharges occur is proportional to the rate at which photoelectrons are generated at the sample surface. From a plot of the discharge rate as a function of photon energy the minimum energy needed to remove an electron can be determined. The mechanical components of our instrument have been completed. A number of electronic circuit difficulties remain to be solved. The counting circuits are able to produce a count rate proportional to the ion concentration generated using a corona gun. However, when the high voltage accelerating potential is applied the circuit oscillates preventing proper operation. Our current focus on this instrument is to attain stability of operation.

M.K. Mazumder; D.A. Lindquist; K.B. Tennal

1999-04-01

293

Cellular interactions of surface modified nanoporous silicon particles.  

PubMed

In this study, the self-assembly of hydrophobin class II (HFBII) on the surface of thermally hydrocarbonized porous silicon (THCPSi) nanoparticles was investigated. The HFBII-coating converted the hydrophobic particles into more hydrophilic ones, improved the particles' cell viability in both HT-29 and Caco-2 cell lines compared to uncoated particles, and enhanced the particles' cellular association. The amount of HFBII adsorbed onto the particles was also successfully quantified by both the BCA assay and a HPLC method. Importantly, the permeation of a poorly water-soluble drug, indomethacin, loaded into THCPSi particles across Caco-2 monolayers was not affected by the protein coating. In addition, (125)I-radiolabelled HFBII did not extensively permeate the Caco-2 monolayer and was found to be stably adsorbed onto the THCPSi nanoparticles incubated in pH 7.4, which renders the particles the possibility for further track-imaging applications. The results highlight the potential of HFBII coating for improving wettability, increasing biocompatibility and possible intestinal association of PSi nanoparticulates for drug delivery applications. PMID:22508528

Bimbo, Luis M; Sarparanta, Mirkka; Mäkilä, Ermei; Laaksonen, Timo; Laaksonen, Päivi; Salonen, Jarno; Linder, Markus B; Hirvonen, Jouni; Airaksinen, Anu J; Santos, Hélder A

2012-04-16

294

Characterization of poly(ethylene imine) layers on mica by the streaming potential and particle deposition methods.  

PubMed

Deposition kinetics of polystyrene latex (averaged particle size of 0.66 microm) on mica covered by poly(ethylene imine) (PEI), a cationic polyelectrolyte having an average molecular mass of 75,000 g mol(-1), was studied using the impinging-jet method. The hydrodynamic radius of PEI, determined by PCS measurements, was 5.3 nm. The electrophoretic mobility of PEI was measured as a function of pH for ionic strengths of 10(-3) and 10 (-2) M, which made it possible one to determine the amount of electrokinetic charge of the molecule and its zeta potential. Formation of the polyelectrolyte layer on mica was followed by measuring the streaming potential in the parallel-plate channel. From these measurements, the dependence of the apparent zeta potential of mica on the surface coverage of PEI was determined. The amount of adsorbed PEI on mica was calculated from the convective diffusion theory. These results were quantitatively interpreted in terms of the theoretical model postulating a particle-like adsorption mechanism for PEI with not too significant shape deformation upon adsorption. On the other hand, the Gouy-Chapman model postulating the adsorption in the form of flat disks was proved inappropriate. After the surface was fully characterized, particle deposition experiments were carried out with the aim of finding the correlation between the polymer coverage and the initial rate of latex particle deposition. In the range of small polyelectrolyte coverage, a monotonic relation between the polymer coverage and the initial deposition rate of particles, as well as the jamming coverage, was found. For Theta(PEI)>0.25, the initial particle deposition rate attained the value predicted from the convective diffusion theory for homogeneous surfaces. These results were interpreted theoretically by postulating that an effective immobilization of colloid particles occurred on local polyelectrolyte assemblages containing between two and three PEI molecules. PMID:17521663

Adamczyk, Zbigniew; Michna, Aneta; Szaraniec, Magdalena; Bratek, Anna; Barbasz, Jakub

2007-05-22

295

Thermal stability of nanocrystalline layers fabricated by surface nanocrystallization  

NASA Astrophysics Data System (ADS)

A nanocrystalline layer with ultrafine grains (about 30-40 nm) on the surface of 7050 aluminum alloy was fabricated by a new technique called High Pressure Shot Peening (HPSP) which is the combination of common Shot Peening equipment with a pressurizing vessel. Relationship between hot flow and temperature was observed by Differential Scanning Calorimetry (DSC) and the activation energy, calculated by Kisssinger equation, of the as-treated sample increased 26.6 kJ/mol when it is compared with the as-reserved sample. The Bragg peaks of the as-prepared samples, respectively treated with various annealing treatments were characterized by XRD and the microhardness distribution along the depth from the treated surface were measured at the same time, which indicated that the broadening of Bragg peaks decreased with the increasing of anneal temperature; the grain size, calculated by Scherrer-Wilson equation, increased obviously during 180-220 °C, accordingly, the microhardness obviously decreased. According to the results of DSC, XRD and microhardness, it is reasonable to deduce that the temperature range of thermal stability for aluminum alloy nanocrystalline layer is lower than 200 °C.

Mai, Yong-jin; Jie, Xiao-hua; Liu, Li-li; Yu, Neng; Zheng, Xiang-xin

2010-01-01

296

Water-soluble sacrificial layers for surface micromachining.  

PubMed

This manuscript describes the use of water-soluble polymers for use as sacrificial layers in surface micromachining. Water-soluble polymers have two attractive characteristics for this application: 1) They can be deposited conveniently by spin-coating, and the solvent removed at a low temperature (95-150 degrees C), and 2) the resulting layer can be dissolved in water; no corrosive reagents or organic solvents are required. This technique is therefore compatible with a number of fragile materials, such as organic polymers, metal oxides and metals-materials that might be damaged during typical surface micromachining processes. The carboxylic acid groups of one polymer-poly(acrylic acid) (PAA)-can be transformed by reversible ion-exchange from water-soluble (Na+ counterion) to water-insoluble (Ca2+ counterion) forms. The use of PAA and dextran polymers as sacrificial materials is a useful technique for the fabrication of microstructures: Examples include metallic structures formed by the electrodeposition of nickel, and freestanding, polymeric structures formed by photolithography. PMID:17193516

Linder, Vincent; Gates, Byron D; Ryan, Declan; Parviz, Babak A; Whitesides, George M

2005-07-01

297

Parameterization of turbulence characteristics of Atmospheric surface layer in Qatar  

NASA Astrophysics Data System (ADS)

Turbulent characteristics of atmospheric boundary layer are of utmost importance in modeling the large-scale meteorological processes, diffusion of atmospheric contaminants, heat transfer and evaporation from the earth surface. Available data are for some areas on the globe and are really sparse in tropical regions, except a few recent studies in Asia. There had been some recent studies in tropical weather in southwestern Asia but no study is carried out in Persian Gulf region. An atmospheric measurement station has been designed and installed in a site in the coastal region of Doha, Qatar, to characterize the nature of atmosphere surface layer (ASL) and ocean wave characteristics in this field. The aim of the present study is to report the micrometeorological data collected from this site. The normalized variation of the turbulent velocity components and temperature were studied using Monin-Obukhov similarity theory (MOST). This study also attempts to verify the validity of MOST in the context of the data collected for a marine ASL in Qatar, and compares the modeling parameters with other investigations around the world. This is the first ever study of ASL in this area, and is expected to be a foundation of further atmospheric research endeavors in Qatar.

Singha, Arindam; Sadr, Reza

2011-11-01

298

In vivo measurement of the mouse pulmonary endothelial surface layer.  

PubMed

The endothelial glycocalyx is a layer of proteoglycans and associated glycosaminoglycans lining the vascular lumen. In vivo, the glycocalyx is highly hydrated, forming a substantial endothelial surface layer (ESL) that contributes to the maintenance of endothelial function. As the endothelial glycocalyx is often aberrant in vitro and is lost during standard tissue fixation techniques, study of the ESL requires use of intravital microscopy. To best approximate the complex physiology of the alveolar microvasculature, pulmonary intravital imaging is ideally performed on a freely-moving lung. These preparations, however, typically suffer from extensive motion artifact. We demonstrate how closed-chest intravital microscopy of a freely-moving mouse lung can be used to measure glycocalyx integrity via ESL exclusion of fluorescently-labeled high molecular weight dextrans from the endothelial surface. This non-recovery surgical technique, which requires simultaneous brightfield and fluorescent imaging of the mouse lung, allows for longitudinal observation of the subpleural microvasculature without evidence of inducing confounding lung injury. PMID:23462690

Yang, Yimu; Yang, Gaoqing; Schmidt, Eric P

2013-02-22

299

a Study on Particle Dispersion in Two-Dimensional Mixing Layer Flows  

NASA Astrophysics Data System (ADS)

The study of solid particle dispersion in mixing layer flows is undertaken to improve the understanding of technological processes and natural phenomena. Mixing layer flows are characterized by large scale vortical structures which grow and interact in time. The particle dispersion model proposed by Crowe, Gore and Troutt (1985), which is based on the ratio of the particle aerodynamic response time to the large scale structure time scale, is investigated experimentally and numerically. Laser Doppler Anemometry (LDA) measurements of particle velocity and number density show that when the particle aerodynamic response time is close to the flow time scale, particles tend to move away from the vortex central cores and yield dispersion rates that are greater than that of fluid particles. Complementary numerical simulations of particle dispersion have been developed using a trajectory method in concert with the discrete vortex approach for the gas phase. The studies show the centrifuging effect of the rotating flow structures on the particle dispersion. The degree of dispersion depends on the time scale ratio and is maximized when the ratio is of the order of unity. The concentration distributions from the numerical simulations are in agreement with those by the LDA measurements. The study of instantaneous particle dispersion patterns reveals the dynamics of the dispersion process. The stretching and folding operations associated with the vortex rotation and pairing interaction are suggested as possible mechanisms for the particle dispersion in mixing layers. The kinematic description of the dispersion patterns using the correlation dimension appears to be a useful approach for quantifying the relative organization and the degree of mixing.

Wen, Feng

1990-01-01

300

Silicon surface modification with a mixed silanes layer to immobilize proteins for biosensor with imaging ellipsometry  

Microsoft Academic Search

One kind of surface modification method on silicon wafer was presented in this paper. A mixed silanes layer was used to modify silicon surface and rendered the surface medium hydrophobic. The mixed silanes layer contained two kinds of compounds, aminopropyltriethoxysilane (APTES) and methyltriethoxysilane (MTES). A few of APTES molecules in the layer was used to immobilize covalently human immunoglobulin G

Zhan-Hui Wang; Gang Jin

2004-01-01

301

Quality of the surface layer and operating properties of aircraft engine components  

Microsoft Academic Search

The papers presented in this volume are concerned with analytical determination of the distribution of surface layer parameters in aircraft engine parts during machining, effect of surface layer parameters on the service-related characteristics of gas turbine engines, and automation of the design of technological processes which would ensure the required properties of the surface layer. Specific topics discussed include determination

V. F. Bez'iazychnyi

1990-01-01

302

Large-eddy simulation of particle-laden atmospheric boundary layer  

NASA Astrophysics Data System (ADS)

Pollen dispersion in the atmospheric boundary layer (ABL) is numerically investigated using a hybrid large-eddy simulation (LES) Lagrangian approach. Interest in prediction of pollen dispersion stems from two reasons, the allergens in the pollen grains and increasing genetic manipulation of plants leading to the problem of cross pollination. An efficient Eulerian-Lagrangian particle dispersion algorithm for the prediction of pollen dispersion in the atmospheric boundary layer is outlined. The volume fraction of the dispersed phase is assumed to be small enough such that particle-particle collisions are negligible and properties of the carrier flow are not modified. Only the effect of turbulence on particle motion has to be taken into account (one-way coupling). Hence the continuous phase can be treated separate from the particulate phase. The continuous phase is determined by LES in the Eulerian frame of reference whereas the dispersed phase is simulated in a Lagrangian frame of reference. Numerical investigations are conducted for the convective, neutral and stable boundary layer as well different topographies. The results of the present study indicate that particles with small diameter size follow the flow streamlines, behaving as tracers, while particles with large diameter size tend to follow trajectories which are independent of the flow streamlines. Particles of ellipsoidal shape travel faster than the ones of spherical shape.

Ilie, Marcel; Smith, Stefan Llewellyn

2008-11-01

303

Optical glass surfaces polishing by cerium oxide particles  

NASA Astrophysics Data System (ADS)

The use of powders in metallic oxides as means of grinding and polishing of the optical glass components have seen recently a large application in optical industry. In fact, cerium oxide abrasive is more used in the optical glass polishing. It is used as grains abrasive in suspension or fixed abrasive (pellets); these pellets are manufactured from a mixture made of cerium oxide abrasive and a organic binder. The cerium oxide used in the experiments is made by (Logitech USA) of 99 % purity, the average grain size of the particle is 300 nm, the density being 6,74 g /cm3 and the specific surface is 3,3042 m2/g. In this study, we are interested in the surfaces quality of the optical glass borosilicate crown (BK7) polished by particles in cerium oxide bounded by epoxy. The surfaces of the optical glass treated are characterized by the roughness, the flatness by using the microscope Zygo and the SEM.

Bouzid, D.; Belkhie, N.; Aliouane, T.

2012-02-01

304

Enhancing surface plasmon polariton propagation by two-layer dielectric-loaded waveguides on silver surface  

NASA Astrophysics Data System (ADS)

We report a study of a two-layer dielectric-loaded surface plasmon polariton waveguide (TDLSPPW) which consisted of two dielectric layers (high-index/low-index) on a silver film. The discontinuity of the electric field at the interfaces resulted in a concentrated field in the low-index region. It efficiently reduced the propagation loss of the surface plasmon polariton mode. The mode fields and corresponding complex propagation constants were calculated by a vector finite-difference method. The propagation properties were measured by a modified near-field optical microscope. It is confirmed that the propagation length of the proposed TDLSPPW was about 1.6 times longer than conventional single-layer SPP waveguides. In addition, a 90? waveguide turn with 3 ?m radius showed that the bending loss was smaller than 2 dB.

Pan, Ming-Yang; Lin, En-Hong; Wang, Likarn; Wei, Pei-Kuen

2013-10-01

305

Particle Interactions in Mixed Solvents and Rough Surfaces Formed by Sedimenting Particles  

NASA Astrophysics Data System (ADS)

The quasi-two-dimensional sedimentation of silica particles in a viscous fluid results in quasi-one-dimensional rough surfaces. These surfaces are rough on all length -scales between the particle size and the cell size, but different roughness exponents are observed in two well defined length-scale regimes. The range of hydrodynamic forces should play an important role in determining which, if either, length-scale regime shows universal properties. The strong similarity between the height-height correlations of the surface and the density-density correlations inside the flow at longer lengthscales suggests that the roughness at longer lengthscales is very closely tied to the hydrodynamic interactions in the fluid. Measurements have been performed at three different cell-aspect-ratios and at three different fluid viscosities and in no case is there an observable change in the cross-over length-scales of the system. In another work we have measured the interactions of charged colloidal particles in near critical mixtures of 2.6 lutidine and water (LW). An earlier survey has found a temperature dependent flocculation of particles in the one phase region of the liquid mixture. We have now measured static light scattering as a function of number density of colloidal particles and system temperature at two solvent-mixture compositions on the aggregation side of the coexistence curve of one choice of particles. Using a Zimm analysis in the non-aggregating region where the structure factor does not change rapidly with scattering angle, we have extracted values of the 2nd viral coefficient of the colloidal particles. It is possible to extend this measurement to temperatures close enough to the aggregation temperature to establish the temperature at which the virial coefficient falls through zero as the net particle interaction becomes attractive.

Kurnaz, Mehmet Levent

306

Real-time assessment of surface interactions with titanium passivation layer by surface plasmon resonance  

PubMed Central

The high corrosion resistance and strength-to-density ratio makes titanium widely used in major industry, but also in a gamut of medical applications. Here we report for the first time on our development of a titanium passivation layer sensor that makes use of surface plasmon resonance (SPR). The deposited titanium metal layer on the sensor was passivated in air, like titanium medical devices. Our ‘Ti-SPR sensor’ enables analysis of biomolecules interactions with the passivated surface of titanium in real time. As a proof of concept, corrosion of titanium passivation layer exposed to acid was monitored in real time. Also, the Ti-SPR sensor can accurately measure the time-dependence of protein adsorption onto titanium passivation layer with a sub-nanogram per square millimeter accuracy. Besides such SPR analyses, an SPR-imaging (SPRI) enables real-time assessment of chemical surface processes that occur simultaneously at ‘multiple independent spots’ on the Ti-SPR sensor, such as acid-corrosion or adhesion of cells. Our Ti-SPR sensor will therefore be very useful to study titanium-corrosion phenomena and biomolecular titanium-surface interactions with application in a broad range of industrial and biomedical fields.

Hirata, Isao; Yoshida, Yasuhiro; Nagaoka, Noriyuki; Hiasa, Kyou; Abe, Yasuhiko; Maekawa, Kenji; Kuboki, Takuo; Akagawa, Yasumasa; Suzuki, Kazuomi; Van Meerbeek, Bart; Messersmith, Phillip B.; Okazaki, Masayuki

2011-01-01

307

Turbulent Boundary Layer in the Presence of Chemical Reactions on the Surface (Applied to Carbon Surfaces).  

National Technical Information Service (NTIS)

Formulas are obtained for the limiting heat exchange law when chemical reactions occur on an entrainable surface, as well as within the boundary layer. Formulas are constructed to determine the heat content of walls for the complex heat exchange case taki...

E. G. Zaulichnyi S. S. Kutateladze A. N. Leontev

1967-01-01

308

Low energy charged particles interacting with amorphous solid water layers.  

PubMed

The interaction of charged particles with condensed water films has been studied extensively in recent years due to its importance in biological systems, ecology as well as interstellar processes. We have studied low energy electrons (3-25 eV) and positive argon ions (55 eV) charging effects on amorphous solid water (ASW) and ice films, 120-1080 ML thick, deposited on ruthenium single crystal under ultrahigh vacuum conditions. Charging the ASW films by both electrons and positive argon ions has been measured using a Kelvin probe for contact potential difference (CPD) detection and found to obey plate capacitor physics. The incoming electrons kinetic energy has defined the maximum measurable CPD values by retarding further impinging electrons. L-defects (shallow traps) are suggested to be populated by the penetrating electrons and stabilize them. Low energy electron transmission measurements (currents of 0.4-1.5 ?A) have shown that the maximal and stable CPD values were obtained only after a relatively slow change has been completed within the ASW structure. Once the film has been stabilized, the spontaneous discharge was measured over a period of several hours at 103 ± 2 K. Finally, UV laser photo-emission study of the charged films has suggested that the negative charges tend to reside primarily at the ASW-vacuum interface, in good agreement with the known behavior of charged water clusters. PMID:22482574

Horowitz, Yonatan; Asscher, Micha

2012-04-01

309

ELECTRONIC SURFACE STRUCTURES OF COAL AND MINERAL PARTICLES  

SciTech Connect

Surface science studies related to tribocharging and charge separation studies were performed on electrostatic beneficiation of coal. In contrast to other cleaning methods, electrostatic beneficiation is a dry cleaning process requiring no water or subsequent drying. Despite these advantages, there is still uncertainty in implementing large-scale commercial electrostatic beneficiation of coal. The electronic surface states of coal macerals and minerals are difficult to describe due to their chemical complexity and variability. The efficiency in separation of mineral particles from organic macerals depends upon these surface states. Therefore, to further understand and determine a reason for the bipolar charging observed in coal separation, surface analysis studies using Ultra-violet Photoelectron Spectroscopy (UPS) and X-ray Photoelectron Spectroscopy (XPS) were performed on coal samples and several materials that are used or considered for use in tribocharging. Electrostatic charging is a surface phenomenon, so the electronic surface states of the particles, which are influenced by the environmental conditions, determine both polarity and magnitude of tribocharging. UPS was used to measure the work function of the materials as typically used in ambient air. XPS was used to determine the surface chemistry in the form of contamination and degree of oxidation under the same environmental conditions.

M.K.Mazumder; D.A. Linduist; K.B. Tennal

2001-04-01

310

Magnetic-field generation and particle acceleration in relativistic shear layers  

NASA Astrophysics Data System (ADS)

Both observational evidence and theoretical considerations suggest that the relativistic jets of AGN and GRBs are likely to be cylindrically stratified with a fast, inner spine and a slower, outer sheath. The resulting relativistic shear layer is expected to be a site of self-generation of magnetic fields due to the Weibel instability, and of relativistic particle acceleration. We here present first results of particle-in-cell (PIC) simulations of relativistic shear layers in both electron-proton and electron-positron jets. We demonstrate that magnetic fields close to equipartition can be self-generated in initially unmagnetized flows, and strong electric fields and MHD turbulence in the shear layer lead to the acceleration of highly anisotropic particle distributions. The resulting highly beamed synchrotron and Compton emission, in addition to beaming due to the bulk motion of the plasma, may offer a solution to the Lorentz factor crisis for AGN jets.

Böttcher, Markus; Liang, Edison P.; Smith, Ian A.; Roustazadeh, Parisa

2012-12-01

311

Crystalline particle packings on constant mean curvature (Delaunay) surfaces.  

PubMed

We investigate the structure of crystalline particle arrays on constant mean curvature (CMC) surfaces of revolution. Such curved crystals have been realized physically by creating charge-stabilized colloidal arrays on liquid capillary bridges. CMC surfaces of revolution, classified by Delaunay in 1841, include the 2-sphere, the cylinder, the vanishing mean curvature catenoid (a minimal surface), and the richer and less investigated unduloid and nodoid. We determine numerically candidate ground-state configurations for 1000 pointlike particles interacting with a pairwise-repulsive 1/r^{3} potential, with distance r measured in three-dimensional Euclidean space R^{3}. We mimic stretching of capillary bridges by determining the equilibrium configurations of particles arrayed on a sequence of Delaunay surfaces obtained by increasing or decreasing the height at constant volume starting from a given initial surface, either a fat cylinder or a square cylinder. In this case, the stretching process takes one through a complicated sequence of Delaunay surfaces, each with different geometrical parameters, including the aspect ratio, mean curvature, and maximal Gaussian curvature. Unduloids, catenoids, and nodoids all appear in this process. Defect motifs in the ground state evolve from dislocations at the boundary to dislocations in the interior to pleats and scars in the interior and then isolated sevenfold disclinations in the interior as the capillary bridge narrows at the waist (equator) and the maximal (negative) Gaussian curvature grows. We also check theoretical predictions that the isolated disclinations are present in the ground state when the surface contains a geodesic disk with integrated Gaussian curvature exceeding -?/3. Finally, we explore minimal energy configurations on sets of slices of a given Delaunay surface, and we obtain configurations and defect motifs consistent with those seen in stretching. PMID:23944467

Bendito, Enrique; Bowick, Mark J; Medina, Agustin; Yao, Zhenwei

2013-07-29

312

Crystalline particle packings on constant mean curvature (Delaunay) surfaces  

NASA Astrophysics Data System (ADS)

We investigate the structure of crystalline particle arrays on constant mean curvature (CMC) surfaces of revolution. Such curved crystals have been realized physically by creating charge-stabilized colloidal arrays on liquid capillary bridges. CMC surfaces of revolution, classified by Delaunay in 1841, include the 2-sphere, the cylinder, the vanishing mean curvature catenoid (a minimal surface), and the richer and less investigated unduloid and nodoid. We determine numerically candidate ground-state configurations for 1000 pointlike particles interacting with a pairwise-repulsive 1/r3 potential, with distance r measured in three-dimensional Euclidean space R3. We mimic stretching of capillary bridges by determining the equilibrium configurations of particles arrayed on a sequence of Delaunay surfaces obtained by increasing or decreasing the height at constant volume starting from a given initial surface, either a fat cylinder or a square cylinder. In this case, the stretching process takes one through a complicated sequence of Delaunay surfaces, each with different geometrical parameters, including the aspect ratio, mean curvature, and maximal Gaussian curvature. Unduloids, catenoids, and nodoids all appear in this process. Defect motifs in the ground state evolve from dislocations at the boundary to dislocations in the interior to pleats and scars in the interior and then isolated sevenfold disclinations in the interior as the capillary bridge narrows at the waist (equator) and the maximal (negative) Gaussian curvature grows. We also check theoretical predictions that the isolated disclinations are present in the ground state when the surface contains a geodesic disk with integrated Gaussian curvature exceeding ??/3. Finally, we explore minimal energy configurations on sets of slices of a given Delaunay surface, and we obtain configurations and defect motifs consistent with those seen in stretching.

Bendito, Enrique; Bowick, Mark J.; Medina, Agustin; Yao, Zhenwei

2013-07-01

313

Particle-surface interactions in heat exchanger fouling  

SciTech Connect

The problem of fouling is of vital importance to heat exchanger efficiency and should be considered during the design phase of the heat exchanger. The purpose of the present paper is to introduce a novel method to aid in the evaluation of the various parameters that affect the fouling phenomenon. The method considers the particle-surface interaction from the energy balance at the point of impaction and takes into consideration the material properties of the particle and surface as well as the effect of the surrounding flow field on the particle movement and impaction. The calculated deposition flux is used to form the deposit evolution in time considering the removal mechanisms resulting from fluid shear stress and the eroding impacts of the particles. The model is validated against experimental measurements of particle deposition from a two phase flow of hot gases around a circular cylinder. The experimentally measured flow field around a staggered tube bundle is also predicted and a fouling analysis is performed regarding the validity of fouling studies in scaled down model configurations. It is concluded that the actual dimensions of the heat exchanger configuration are of vital importance to its fouling behavior and scaling laws are difficult to apply.

Bouris, D.; Bergeles, G. [National Technical Univ. of Athens (Greece)

1996-09-01

314

Transport of dust particles from the Bodélé region to the monsoon layer - AMMA case study of the 9-14 June 2006 period  

NASA Astrophysics Data System (ADS)

Aerosol properties were measured during an airborne campaign experiment that took place in June 2006 in West Africa within the framework of the African Monsoon Multidisciplinary Analyses (AMMA). The goal of the present study was to investigate a dynamical mechanism able to facilitate the sedimentation of dust particles from the Saharan Air Layer (SAL) into the boundary layer. A significant change in the dust particle concentration measured along the meridian between Niamey (Niger) and Cotonou (Benin) was found in the boundary layer (~700 m), where the dust particle concentration increased in a zone where local emission is not possible. Moreover, the boundary layer top observed with the dropsondes launched with the F-F20 shows a strong relationship with the surface cover anomalies, with higher Boundary Layer (BL) tops over the warmer surfaces, such as croplands, as opposed to adjacent forest. A mesoscale atmospheric model with a new on-line dust parameterization, resulting from the Alfaro and Gomes (2001) parametrisation and AMMA observations, was used to interpret the impact of vegetation anomalies on dust particle sedimentation. The results of the simulation are consistent with the observations, with higher dust concentration over the warm surface cover anomalies.

Crumeyrolle, S.; Tulet, P.; Gomes, L.; Garcia-Carreras, L.; Flamant, C.; Parker, D. J.; Matsuki, A.; Formenti, P.; Schwarzenboeck, A.

2011-01-01

315

Transport of dust particles from the Bodélé region to the monsoon layer: AMMA case study of the 9-14 June 2006 period  

NASA Astrophysics Data System (ADS)

Aerosol properties were measured during an airborne campaign experiment that took place in June 2006 in West Africa within the framework of the African Monsoon Multidisciplinary Analyses (AMMA). The goal of the present study was to determine the process that facilitates the sedimentation of dust particles from the Saharan Air Layer (SAL) to the boundary layer. A significant change in the dust particle concentration measured along the meridian between Niamey (Niger) and Cotonou (Benin) was found in the boundary layer (~700 m), where the dust particle concentration increased in a zone where local emission is not possible. Moreover, the boundary layer top observed with the dropsondes launched with the F-F20 shows a strong relationship with the surface cover anomalies, with higher Boundary Layer (BL) tops over the warmer surfaces, such as croplands, as opposed to adjacent forest. A mesoscale atmospheric model with a new on-line dust parameterization, resulting from the Alfaro and Gomes (2001) parametrisation and AMMA observations, was used to interpret the impact of vegetation anomalies on dust particle sedimentation. The results of the simulation are consistent with the observations, with higher dust over the warm surface cover anomalies.

Crumeyrolle, S.; Tulet, P.; Garcia-Carreras, L.; Flamant, C.; Parker, D. J.; Matsuki, A.; Schwarzenboeck, A.; Formenti, P.; Gomes, L.

2010-02-01

316

On the interaction between marine boundary layer cellular cloudiness and surface heat fluxes  

NASA Astrophysics Data System (ADS)

The interaction between marine boundary layer cellular cloudiness and surface fluxes of sensible and latent heat is investigated. The investigation focuses on the non-precipitating closed-cell state and the precipitating open-cell state at low geostrophic wind speed. The Advanced Research WRF model is used to conduct cloud-system-resolving simulations with interactive surface fluxes of sensible heat, latent heat, and of sea salt aerosol, and with a detailed representation of the interaction between aerosol particles and clouds. The mechanisms responsible for the temporal evolution and spatial distribution of the surface heat fluxes in the closed- and open-cell state are investigated and explained. It is found that the closed-cell state imposes its horizontal spatial structure on surface air temperature and water vapor, and, to a lesser degree, on the surface sensible and latent heat flux. The responsible mechanism is the entrainment of dry free tropospheric air into the boundary layer. The open-cell state drives oscillations in surface air temperature, water vapor, and in the surface fluxes of sensible heat, latent heat, and of sea salt aerosol. Here, the responsible mechanism is the periodic formation of clouds, rain, and of cold and moist pools with elevated wind speed. Open-cell cloud formation, cloud optical depth and liquid water path, and cloud and rain water path are identified as good predictors of the spatial structure of surface air temperature and sensible heat flux, but not of surface water vapor and latent heat flux. It is shown that the open-cell state creates conditions conducive to its maintenance by enhancing the surface sensible heat flux. The open-cell state also enhances the sea-salt flux relative to the closed-cell state. While the open-cell state under consideration is not depleted in aerosol and is insensitive to variations in sea-salt fluxes, in aerosol-depleted conditions, the enhancement of the sea-salt flux may replenish the aerosol needed for cloud formation and hence contribute to the maintenance of the open-cell state. Spatial homogenization of the surface fluxes is found to have only a small effect on cloud properties in the investigated cases. This indicates that sub-grid scale spatial variability in the surface flux of sensible and latent heat and of sea salt aerosol may not be required in large scale and global models to describe marine boundary layer cellular cloudiness.

Kazil, J.; Feingold, G.; Wang, H.; Yamaguchi, T.

2013-07-01

317

Preparation of organic\\/inorganic composites by deposition of silica onto shell layers of polystyrene (core)\\/poly[2-( N, N-dimethylamino)ethyl methacrylate] (shell) particles  

Microsoft Academic Search

Organic\\/inorganic composites were prepared by catalytic hydrolysis and subsequent condensation of tetraethoxysilane (TEOS) in a shell layer of core–shell polymer particles. First, core–shell particles were prepared by emulsifier-free emulsion polymerization of styrene (St) with 2-chloropropionyloxyethyl methacrylate (CPEM) using potassium persulfate as an initiator, followed by surface-initiated activator generated electron transfer–atom transfer radical polymerization (AGET–ATRP) of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA). Dynamic light

Tatsuo Taniguchi; Takuya Kashiwakura; Takumi Inada; Yusuke Kunisada; Masakatsu Kasuya; Michinari Kohri; Takayuki Nakahira

2010-01-01

318

Paint removal and surface cleaning using ice particles  

NASA Astrophysics Data System (ADS)

Research into the possibility of using ice particles as a blast medium was first initiated at Defence Research Establishment Pacific (DREP) in an effort to develop a more environmentally acceptable paint removal method. A paint removal process was also required that could be used in areas where normal grit blasting could not be used due to the possibility of the residual blasting grit contaminating machinery and other equipment. As a result of this research a commercial ice blasting system was developed by RETECH. This system is now being used to remove paint from substrates that cannot be easily blasted by conventional techniques and also to clean soiled or contaminated surfaces. The problems involved in the development of an ice blast system and its components and their functions are described. Due to the complexity of paint removal using ice blasting, parameters such as air pressure, ice particle size and ice particle flow rate were studied and adjusted to suit the nature of the particular coating and substrate of interest. The mechanism of paint removal by ice particles has also been investigated. A theoretical model has been developed to explain the different paint removal mechanisms such as erosion by abrasion and erosion by fracture as they relate to ice blasting. Finally, the use of ice blasting to removal paint from a variety of substrates is presented as well as examples of surface cleaning and surface decontamination.

Foster, Terry; Visaisouk, S.

1995-04-01

319

Paint removal and surface cleaning using ice particles  

NASA Astrophysics Data System (ADS)

Research into the possibility of using ice particles as a blast medium was first initiated at Defence Research Establishment Pacific (DREP) in an effort to develop a more environmentally acceptable paint removal method. A paint removal process was also required that could be used in areas where normal grit blasting could not be used due to the possibility of the residual blasting grit contaminating machinery and other equipment. As a result of this research a commercial ice blasting system was developed by RETECH. This system is now being used to remove paint from substrates that cannot be easily blasted by conventional techniques and also to clean soiled or contaminated surfaces. The problems involved in the development of an ice blast system, and its components and their functions are described. Due to the complexity of paint removal using ice blasting, parameters such as air pressure, ice particle size and ice particle flow rate were studied and adjusted to suit the nature of the particular coating and substrate of interest. The mechanism of paint removal by ice particles has also been investigated. A theoretical model has been developed to explain the different paint removal mechanisms such as erosion by abrasion and erosion by fracture as they relate to ice blasting. Finally, the use of ice blasting to removal paint from a variety of substrates is presented as well as examples of surface cleaning and surface decontamination.

Foster, Terry; Visaisouk, S.

1993-03-01

320

A new type of protective surface layer for high-capacity Ni-based cathode materials: nanoscaled surface pillaring layer.  

PubMed

A solid solution series of lithium nickel metal oxides, Li[Ni(1-x)M(x)]O2 (with M = Co, Mn, and Al) have been investigated intensively to enhance the inherent structural instability of LiNiO2. However, when a voltage range of Ni-based cathode materials was increased up to >4.5 V, phase transitions occurring above 4.3 V resulted in accelerated formation of the trigonal phase (P3m1) and NiO phases, leading to and pulverization of the cathode during cycling at 60 °C. In an attempt to overcome these problems, LiNi0.62Co0.14Mn0.24O2 cathode material with pillar layers in which Ni(2+) ions were resided in Li slabs near the surface having a thickness of ?10 nm was prepared using a polyvinylpyrrolidone (PVP) functionalized Mn precursor coating on Ni0.7Co0.15Mn0.15(OH)2. We confirmed the formation of a pillar layer via various analysis methods (XPS, HRTEM, and STEM). This material showed excellent structural stability due to a pillar layer, corresponding to 85% capacity retention between 3.0 and 4.5 V at 60 °C after 100 cycles. In addition, the amount of heat generation was decreased by 40%, compared to LiNi0.70Co0.15Mn0.15O2. PMID:23421879

Cho, Yonghyun; Oh, Pilgun; Cho, Jaephil

2013-03-01

321

Generic Nitric Oxide (NO) Generating Surface by Immobilizing Organoselenium Species via Layer-by-Layer Assembly  

PubMed Central

A universal nitric oxide (NO) generating surface is assembled via Layer-by-Layer (LbL) deposition of sodium alginate (Alg) and organoselenium modified polyethyleneimine (SePEI) on quartz and polymeric substrates. The immobilized SePEI species is capable of catalytically decomposing S-nitrosothiol species (RSNO) to NO in the presence of thiol reducing agents (e.g., glutathione, cysteine, etc.). The stepwise buildup of the multilayer films is monitored by UV-Vis spectroscopy, SEM and surface contact angle measurements. X-ray photoelectron spectroscopy is used to study the stoichiometry between the polyanion and polycation, and also the presence of Se in the catalytic LbL film. A reductive annealing process is necessary to improve the stability of freshly coated multilayer films via chain rearrangement. Chemiluminescence measurements illustrate the ability of the LbL films to generate NO from S-nitrosoglutathione (GSNO) in the presence of S-glutathione (GSH). Enhanced NO fluxes can be achieved by increasing the number of catalytic (SePEI/Alg) bilayers coated on the substrates. Nitric oxide generation is observed even after prolonged contact with sheep whole blood. Preliminary applications of this LbL on silicone rubber tubings and polyurethane catheters reveal similar NO generation behavior from these biomedical grade polymeric substrates.

Yang, Jun; Welby, Jenna L.; Meyerhoff, Mark E.

2010-01-01

322

Land-Surface Heterogeneity Effects in the Planetary Boundary Layer  

NASA Astrophysics Data System (ADS)

We investigate the cumulative added value of assimilating temperature, moisture, and wind observations in the three-dimensional non-hydrostatic Fifth-Generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model MM5 and use these forecasts to analyze the relationship between surface forcing and planetary boundary-layer (PBL) depth. A data assimilation methodology focused on the surface and the PBL, previously tested in a one-dimensional version of MM5, is applied to 29 May, 6 June, and 7 June 2002 during the International {H}2{O} Project over the Southern Great Plains. Model-predicted PBL depth is evaluated against PBL depth diagnosed from data across 4,800 km of airborne lidar data (flight tracks 100-300 km long). The forecast with data assimilation verifies better against observations and is thus used to investigate the environmental conditions that govern PBL depth. The spatial structure in PBL depth is found to be most affected by spatial variations in surface buoyancy flux and capping inversion strength. The spatial scales of surface flux forcing reflected in the PBL depth are found through Fourier analysis and multiresolution decomposition. Correlations are {<}0.50 at scales of 64 km or less and increase at larger scales for 29 May and 6 June, but on 7 June low correlations are found at all scales, possibly due to greater within-PBL wind speeds, a stronger capping inversion on this day, and clouds. The results suggest a minimum scale, a function of wind speed, below which heterogeneity in surface buoyancy fluxes is not reflected directly in PBL depth.

Reen, Brian P.; Stauffer, David R.; Davis, Kenneth J.

2013-10-01

323

Layered reactive particles with controlled geometries, energies, and reactivities, and methods for making the same  

DOEpatents

An energetic composite having a plurality of reactive particles each having a reactive multilayer construction formed by successively depositing reactive layers on a rod-shaped substrate having a longitudinal axis, dividing the reactive-layer-deposited rod-shaped substrate into a plurality of substantially uniform longitudinal segments, and removing the rod-shaped substrate from the longitudinal segments, so that the reactive particles have a controlled, substantially uniform, cylindrically curved or otherwise rod-contoured geometry which facilitates handling and improves its packing fraction, while the reactant multilayer construction controls the stability, reactivity and energy density of the energetic composite.

Fritz, Gregory M; Knepper, Robert Allen; Weihs, Timothy P; Gash, Alexander E; Sze, John S

2013-04-30

324

An oriented particle level set method based on surface coordinates  

NASA Astrophysics Data System (ADS)

In this work we present a new method for tracking evolving interfaces. Like the Adaptive Oriented Particle Level Set method (AOPLS, Ianniello and Mascio, 2010), it uses a combination of unconnected particles containing geometric information and a level set function to track the interface. In the present method, the geometric information, solved for in each particle, is a set of tangent vectors and the corresponding curvature tensor of the interface. Compared to the AOPLS method, the amount of geometric data stored in each particle is roughly halved, while still retaining a description of the interface that includes both orientation and curvature. A mechanism for ensuring a sufficiently dense distribution of particles on the interface is also included. From the information stored in each particle, a "continuous" representation of the interface is obtained by transferring the information to a level set function stored on an Eulerian grid. Unlike the AOPLS method, the present method takes the curvature into account when the zero level set is constructed. This results in significant improvements in regions of high curvature. Two different formulations of the new method have been explored. In the first, the tangent vectors deform purely according to the velocity field. In the second, the tangent vectors are forced to coincide with the principal directions of the surface. Both formulations are shown to be applicable.

Vartdal, Magnus; Bøckmann, Arne

2013-10-01

325

Magnetic behavior of layered films of submicronic Fe3O4 particles  

Microsoft Academic Search

A special aggregate of six glass slides, glued together, has been prepared. Each side of each slide contained a thin layer (?0.2 ?m) of dispersed Fe3O4 particles of mean diameter ?0.17 ?m prepared by reduction of ?-Fe2O3 particles. Magnetization measurements on the above aggregate have been carried out at 300 K as a function of the angle between the direction

Sigurds Arajs; Nurul Amin; Elmer E. Anderson

1990-01-01

326

Light backscatter by surfaces composed of small spherical particles.  

PubMed

We present measurements of phase angle curves of intensity and degree of linear polarization of powdery surfaces at two spectral bands centered near 0.44 and 0.63 microm. Three powder samples consisting of nonabsorbing spherical particles of sizes comparable with the wavelengths 0.5, 1.0, and 1.5 microm were examined. The particulate surfaces were measured in the phase angle range of 0.2 degrees-50 degrees by two different photometers and/or polarimeters. At small phase angles, powdery samples consisting of spherical particles (having very high albedo that resulted in significant multiple scattering) showed prominent features that corresponded to single-particle scattering. These features became more prominent after compressing the surfaces when we changed the packing density of the powders from 0.29 to 0.48. Noticeable differences were observed between polarimetric curves corresponding to different wavelengths. All the samples demonstrated prominent opposition intensity spikes at phase angles <2 degrees likely caused by the coherent backscatter enhancement due to multiple scattering within the particulate surface. The intensity phase curves at these two wavelengths were similar. The photopolarimetric measurements may have broad applications to the interpretation of photometry, spectroscopy, and polarimetry of the ice regoliths of high albedo satellites. PMID:16724152

Bondarenko, Sergey; Ovcharenko, Andrey; Shkuratov, Yuriy; Videen, Gorden; Eversole, Jay; Hart, Matthew

2006-06-01

327

Microtribology of alumina particles on metal-coated surfaces  

NASA Astrophysics Data System (ADS)

The friction of alumina micro-size particles with radii between 0.5 and 30 µm on Co, Cr and Au — coated Si(100) surfaces is presented and analyzed in terms of classical mechanical and unconventional components relevant to these scales. Friction parameters related to the rolling and the sliding friction ( K 1 and y 0), the van der Walls forces ( K 2) and the depth of electromagnetic penetration (t) are estimated from the experimental results. The development of the friction parameters when the surfaces are coated is described and discussed. The measurements are based on optical observation of the motion of a single micro-particle on a surface under ambient conditions. The motion is initiated by using a mechanical vibration with a micrometer amplitude at frequencies in the acoustic range. The long-range van der Waals forces and the short-range adhesive forces are found to become dominant with contributions of up to 80% for particle sizes below 7 µm and 9 µm for the coated and the bare surfaces, respectively.

Paul, K. B.

2013-07-01

328

Defect Ordering on the Surface of Layered Strontium Ruthenates  

NASA Astrophysics Data System (ADS)

Surfaces of layered strontium ruthenates, Sr_2RuO4 and Sr_3Ru_2O_7, exhibit an array of defects after cleaving in vacuum which have been observed using atomic resolution scanning tunneling microscopy (STM). ^1 At room temperature, surface defects are randomly distributed, but are surprisingly ordered at below 200 K and form extended lines, which on Sr_3Ru_2O7 produce a new super-lattice structure with a periodicity of 1.3 nm. We identify these defects for the first time as a pair of missing atoms: SrO. This idea is supported by the observation of SrO desorption from SrRuO3 during heating. First principles calculations compare removal of this neutral pair to removal of a single atom and simulate the observed STM images. The missing SrO pair leaves a surface defect with an effective dipole moment which provides the interaction producing alignment at low temperatures. ^1 E. W. Plummer, Ismail. R. Matzdorf, A. V. Melechko. and Jiandi Zhang, Prog. Surf. Sci., 67, 17 (2001)

Kalinin, S. V.; Meunier, V.; Plummer, E. W.; Guo, J.; Moore, Rob G.; Baddorf, A. P.

2004-03-01

329

Air-sea fluxes and surface layer turbulence around a sea surface temperature front  

NASA Astrophysics Data System (ADS)

The response of the lower marine atmospheric boundary layer to sharp changes in sea surface temperature was studied in the Frontal Air-Sea Interaction Experiment (FASINEX) with aircraft and ships measuring mean and turbulence quantities, sea surface temperature, and wave state. Changing synoptic weather on 3 successive days provided cases of wind direction both approximately parallel and perpendicular to a surface temperature front. For the wind perpendicular to the front, both wind over cold-to-warm and warm-to-cold surface temperatures occurred. For the cold-to-warm case, the unstable boundary layer was observed to thicken, with increased convective activity on the warm side. For the warm-to-cold case, the surface layer buoyant stability changed from unstable to neutral or slightly stable, and the sea state and turbulence structure in the lower 100 m were immediately altered, with a large decrease in stress and slowing of the wind. Measurements for this case with two aircraft in formation at 30 and 100 m show a slightly increased stress divergence on the cold side. The turbulent velocity variances changed anisotropically across the front: the streamwise variance was practically unchanged, whereas the vertical and cross-stream variances decreased. Model results, consistent with the observations, suggest that an internal boundary layer forms at the sea surface temperature front. The ocean wave, swell, and microwave radar backscatter fields were measured from several aircraft which flew simultaneously with the low-level turbulence aircraft. Significant reductions in backscatter and wave height were observed on the cold side of the front.

Friehe, C. A.; Shaw, W. J.; Rogers, D. P.; Davidson, K. L.; Large, W. G.; Stage, S. A.; Crescenti, G. H.; Khalsa, S. J. S.; Greenhut, G. K.; Li, F.

1991-05-01

330

Influence of surface chemistry on particle-particle aggregation as measured by a Coulter Counter in the low concentration regime  

Microsoft Academic Search

The link between particle concentration, surface properties, and particle aggregation has been investigated for polystyrene latex in the low particle concentration regime, volume fractions less than 1 × 10. The particles used in this model study were 9.14-?m diameter polystyrene beads, approximately the same size as red blood cells, using a Coulter Counter with a 100-?m aperture as a gauge

Scott Trenor; Kelly Renshaw; Monica Marek; Kimberlye. Forsten; Brian Love

2001-01-01

331

Diffusion layers produced on carbon steel surface by means of vacuum chromizing process  

NASA Astrophysics Data System (ADS)

This work investigated diffusion layers produced on carbon (C) steel surfaces in the vacuum chromizing process. Studies of layer, thickness, morphology, and chromium (Cr), C, and iron (Fe) concentration depth profiles in the diffusion zone of chromized layers were carried out. The effect of process parameters such as time and temperature on the kinetics of layer growth on steel surface was investigated. The tribocorrosion resistance of chromized layers was determined.

Kasprzycka, Ewa; Senatorski, Jan; Nakonieczny, Aleksander; Babul, Tomasz

2003-12-01

332

Structure of Surface Layer Homology (SLH) Domains from Bacillus anthracis Surface Array Protein*  

PubMed Central

Surface (S)-layers, para-crystalline arrays of protein, are deposited in the envelope of most bacterial species. These surface organelles are retained in the bacterial envelope through the non-covalent association of proteins with cell wall carbohydrates. Bacillus anthracis, a Gram-positive pathogen, produces S-layers of the protein Sap, which uses three consecutive repeats of the surface-layer homology (SLH) domain to engage secondary cell wall polysaccharides (SCWP). Using x-ray crystallography, we reveal here the structure of these SLH domains, which assume the shape of a three-prong spindle. Each SLH domain contributes to a three-helical bundle at the spindle base, whereas another ?-helix and its connecting loops generate the three prongs. The inter-prong grooves contain conserved cationic and anionic residues, which are necessary for SLH domains to bind the B. anthracis SCWP. Modeling experiments suggest that the SLH domains of other S-layer proteins also fold into three-prong spindles and capture bacterial envelope carbohydrates by a similar mechanism.

Kern, Justin; Wilton, Rosemarie; Zhang, Rongguang; Binkowski, T. Andrew; Joachimiak, Andrzej; Schneewind, Olaf

2011-01-01

333

Turbulent Mixing in the Surface Layers of Accreting Neutron Stars  

NASA Astrophysics Data System (ADS)

During accretion, a neutron star (NS) is spun up as angular momentum is transported through its surface layers. We study the resulting differentially rotating profile, focusing on the impact this has for type I X-ray bursts. The predominant viscosity is likely provided by the Tayler-Spruit dynamo, where toroidal magnetic field growth and Tayler instabilities balance to support a steady state magnetic field. The radial and azimuthal components have strengths of ~105 and ~1010 G, respectively. This leads to nearly uniform rotation at the depths of X-ray bursts. A remaining small shear transmits the accreted angular momentum inward to the NS interior. Although this shear gives little viscous heating, it can trigger turbulent mixing. Detailed simulations will be required to fully understand the consequences of mixing, but our models illustrate some general features. Mixing has the greatest impact when the buoyancy at the compositional discontinuity between accreted matter and ashes is overcome. This occurs preferentially at high accretion rates or low spin frequencies and may depend on the ash composition from the previous burst. We then find two new regimes of burning. The first is ignition in a layer containing a mixture of heavier elements from the ashes. If ignition occurs at the base of the mixed layer, recurrence times as short as ~5-30 minutes are possible. This may explain the short recurrence time of some bursts, but incomplete burning is still needed to explain these bursts' energetics. When mixing is sufficiently strong, a second regime is found where accreted helium mixes deep enough to burn stably, quenching X-ray bursts. The carbon-rich material produced by stable helium burning would be important for triggering and fueling superbursts.

Piro, Anthony L.; Bildsten, Lars

2007-07-01

334

Thermodynamic model of hydrogen-induced silicon surface layer cleavage  

SciTech Connect

A thermodynamic model of hydrogen-induced silicon surface layer splitting with the help of a bonded silicon wafer is proposed in this article. Wafer splitting is the result of lateral growth of hydrogen blisters in the entire hydrogen-implanted region during annealing. The blister growth rate depends on the effective activation energies of both hydrogen complex dissociation and hydrogen diffusion. The hydrogen blister radius was studied as a function of annealing time, annealing temperature, and implantation dose. The critical radius was obtained according to the Griffith energy condition. The time required for wafer splitting at the cut temperature was calculated in accordance with the growth of hydrogen blisters. {copyright} 2001 American Institute of Physics.

Han, Weihua; Yu, Jinzhong

2001-06-01

335

A macromolecular model for the endothelial surface layer  

NASA Astrophysics Data System (ADS)

The endothelial surface layer (ESL) is a micron-scale macromolecular lining of the luminal side of blood vessels composed of proteoglycans, glycoproteins, polysaccharides and associated plasma proteins all in dynamic equilibrium. It has numerous physiological roles including the regulation of blood flow and microvascular permeability, and active participation in mechanotransduction and stress regulation, coagulation, cell adhesion, and inflammatory response. The dynamic structure and the mechanical properties of the ESL are crucial for many of its physiological properties. We present a topological model for the ESL composed of three basic macromolecular elements: branched proteoglycans, linear polysaccharide chains, and small plasma proteins. The model was studied using non-equilibrium molecular dynamics simulations and compared with scaling theories for associating tethered polymers. We discuss the observed dynamical and mechanical properties of the ESL captured by this model, and the possible physical insight it provides into the physiological behavior of the ESL.

Harden, James; Danova-Okpetu, Darina; Grest, Gary

2006-03-01

336

Erosion processes due to energetic particle-surface interaction  

NASA Astrophysics Data System (ADS)

The interaction of the fast particles from the hot plasma of a magnetic confinement fusion experiment with the first wall is one of the most challenging problems toward the realization of a fusion power plant. The erosion of the first wall by the fast particles leads to life time limitations and the radiative cooling of the plasma by the eroded impurity species lowers the energy confinement. Apart from these obvious consequences also the trapping of large quantities of the fuelling species (deuterium and tritium) in re-deposited layers of the eroded species poses a problem due to accumulation of large radiative inventories and plasma fuelling inefficiency. The source of all these challenges is the erosion of first wall components due to physical sputtering, chemical erosion and radiation enhanced sublimation. This paper will give an overview about the physical principles behind these erosion channels.

Schmid, K.; Roth, J.

2010-05-01

337

DNS of high speed boundary layers over ablating surfaces  

NASA Astrophysics Data System (ADS)

Ablation of thermal protection shields is an important design problem in developing reentry vehicles. Development of predictive computational models for this problem will enable optimization of the size and hence weight of the protective layer. In this work, direct numerical simulation (DNS) of a compressible ablating boundary layer is used to understand the modeling issues in the context of Reynolds-averaged Navier Stokes (RANS) equations. The DNS is performed at conditions obtained from a detailed RANS study of a reentry vehicle. The free stream conditions of the two simulations are Mach 0.6, temperature 5940 K, and Re? 1000; and Mach 1.2, temperature 5580 K, and Re? 2000. The surface ablation of a graphite ablator is modeled using a locally 1-D, quasi-steady state formulation with control volume mass and energy balances over the interior of the ablator. A 10-species gas phase chemistry mechanism is used. A priori studies are used to evaluate scalar flux models and the reaction source term closure in RANS.

Braman, Kalen; Raman, Venkat; Upadhyay, Rochan; Ezekoye, Ofodike

2010-11-01

338

Particle-layering effect in wall-bounded dissipative particle dynamics  

NASA Astrophysics Data System (ADS)

Dissipative particle dynamics (DPD) is a mesoscopic simulation method that describes “clusters” of molecules as a single numerical particle. DPD is a very effective method but it introduces numerical artifacts through the coarse-graining procedure, such as particle ordering in the near-wall region. These artifacts can result in nonphysical phenomena during a simulation of a polymer tethered to the wall undergoing shear flow: polymer sticking and overextension for higher shear rates. In this paper we report that a version of DPD with a so-called solidification boundary formulation and conservative-force interactions based on the equation of state allows to reduce number density fluctuations in near-wall region significantly.

Litvinov, Sergey; Ellero, Marco; Hu, Xiangyu; Adams, Nikolaus A.

2010-12-01

339

GYROSCOPIC PUMPING IN THE SOLAR NEAR-SURFACE SHEAR LAYER  

SciTech Connect

We use global and local helioseismic inversions to explore the prevailing dynamical balances in the solar near-surface shear layer (NSSL). The differential rotation and meridional circulation are intimately linked, with a common origin in the turbulent stresses of the upper solar convection zone. The existence and structure of the NSSL cannot be attributed solely to the conservation of angular momentum by solar surface convection, as is often supposed. Rather, the turbulent angular momentum transport accounts for the poleward meridional flow while the often overlooked meridional force balance is required to maintain the mid-latitude rotational shear. We suggest that the base of the NSSL is marked by a transition from baroclinic to turbulent stresses in the meridional plane which suppress Coriolis-induced circulations that would otherwise establish a cylindrical rotation profile. The turbulent angular momentum transport must be nondiffusive and directed radially inward. Inferred mean flows are consistent with the idea that turbulent convection tends to mix angular momentum but only if the mixing efficiency is inhomogeneous and/or anisotropic. The latitudinal and longitudinal components of the estimated turbulent transport are comparable in amplitude and about an order of magnitude larger than the vertical component. We estimate that it requires 2%-4% of the solar luminosity to maintain the solar NSSL against the inertia of the mean flow. Most of this energy is associated with the turbulent transport of angular momentum out of the layer, with a spin-down timescale of {approx}600 days. We also address implications of these results for numerical modeling of the NSSL.

Miesch, Mark S. [High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307-3000 (United States); Hindman, Bradley W., E-mail: miesch@ucar.edu [JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309-0440 (United States)

2011-12-10

340

ELECTROSTATIC SURFACE STRUCTURES OF COAL AND MINERAL PARTICLES  

SciTech Connect

It is the purpose of this research to study electrostatic charging mechanisms related to electrostatic beneficiation of coal with the goal of improving models of separation and the design of electrostatic separators. Areas addressed in this technical progress report are (a) electrostatic beneficiation of Pittsburgh #8 coal powders as a function of grind size and processing atmosphere; (b) the use of fluorescent micro-spheres to probe the charge distribution on the surfaces of coal particles; (c) the use of electrostatic beneficiation to recover unburned carbon from flyash; (d) the development of research instruments for investigation of charging properties of coal. Pittsburgh #8 powders were beneficiated as a function of grind size and under three atmosphere conditions: fresh ground in air , after 24 hours of air exposure, or under N2 atmosphere. The feed and processed powders were analyzed by a variety of methods including moisture, ash, total sulfur, and pyritic sulfur content. Mass distribution and cumulative charge of the processed powders were also measured. Fresh ground coal performed the best in electrostatic beneficiation. Results are compared with those of similar studies conducted on Pittsburgh #8 powders last year (April 1, 1997 to September 30, 1997). Polystyrene latex spheres were charged and deposited onto coal particles that had been passed through the electrostatic separator and collected onto insulating filters. The observations suggest bipolar charging of individual particles and patches of charge on the particles which may be associated with particular maceral types or with mineral inclusions. A preliminary investigation was performed on eletrostatic separation of unburned carbon particles from flyash. Approximately 25% of the flyash acquired positive charge in the copper tribocharger. This compares with 75% of fresh ground coal. The negatively charged material had a slightly reduced ash content suggesting some enrichment of carbonaceous material. There was also evidence that the carbon is present at a higher ratio in larger particles than in small particles. An ultraviolet photoelectron counter for use in ambient atmosphere is nearing completion. The counter will be used to measure work functions of different maceral and mineral types in the coal matrix. A Particle Image Analyzer for measuring size and charge of airborne particles is also under contruction and its current status is presented. A charged, monodisperse, droplet generator is also being constructed for calibration of the Particle Image Analyzer and other airborne particle analyzers in our labs.

NONE

1998-12-01

341

Tokamak dust particle size and surface area measurement  

SciTech Connect

The INEEL has analyzed a variety of dust samples from experimental tokamaks: General Atomics` DII-D, Massachusetts Institute of Technology`s Alcator CMOD, and Princeton`s TFTR. These dust samples were collected and analyzed because of the importance of dust to safety. The dust may contain tritium, be activated, be chemically toxic, and chemically reactive. The INEEL has carried out numerous characterization procedures on the samples yielding information useful both to tokamak designers and to safety researchers. Two different methods were used for particle characterization: optical microscopy (count based) and laser based volumetric diffraction (mass based). Surface area of the dust samples was measured using Brunauer, Emmett, and Teller, BET, a gas adsorption technique. The purpose of this paper is to present the correlation between the particle size measurements and the surface area measurements for tokamak dust.

Carmack, W.J.; Smolik, G.R.; Anderl, R.A.; Pawelko, R.J.; Hembree, P.B.

1998-07-01

342

Charged particle sputtering of ice surfaces in Saturn's magnetosphere  

NASA Astrophysics Data System (ADS)

Following recent investigations of the Saturn system in situ by Pioneer 11 and Voyager 1 and 2 and remotely by the International Ultraviolet Explorer, the sputtering of water ice surfaces by magnetospheric ions has been reconsidered as a possible source of hydrogen atoms and heavy ions. Results from laboratory measurements of water ice sputtering and dissociation rates as a function of ice temperature are used, as well as Voyager charged particle data from the low energy charged particle experiment to obtain more accurate assessments of energetic ion fluxes and loss rates. Ion phase space densities show that, if charged particle sputtering is an important physical process, it will occur predominantly in the vicinity of Saturn's E ring and the moons Dione and Tethys, not at the outer edge of the A ring as previously suggested prior to the availability of in situ data. Charged particle sputtering of ice surfaces between 4.5 and 8 Saturnian radii followed by the ionization of H2O and dissociation fragments, may be an important local source of the heavy ion plasma reported in the magnetosphere by Pioneer 11. Several existing theories for the ring atmosphere are reviewed and it is concluded that difficulties remain with all of them.

Cheng, A. F.; Lanzerotti, L. J.; Pirronello, V.

1982-06-01

343

Particle diffusional layer thickness in a USP dissolution apparatus II: a combined function of particle size and paddle speed.  

PubMed

This work was to investigate the effects of particle size and paddle speed on the particle diffusional layer thickness h(app) in a USP dissolution apparatus II. After the determination of the powder dissolution rates of five size fractions of fenofibrate, including <20, 20-32, 32-45, 63-75, and 90-106 microm, the present work shows that the dependence of h(app) on particle size follows different functions in accordance with the paddle speed. At 50 rpm, the function of h(app) is best described by a linear plot of h{app} = 9.91sqrt d-23.31 (R(2) = 0.98) throughout the particle diameter, d, from 6.8 to 106 microm. In contrast, at 100 rpm a transitional particle radius, r, of 23.7 microm exists, under which linear relationship h(app) = 1.59r (R(2) = 0.98) occurs, but above which h(app) becomes a constant of 43.5 microm. Thus, h(app) changes not only with particle size, but also with the hydrodynamics under standard USP configurations, which has been overlooked in the past. Further, the effects of particle size and paddle speed on h(app) were combined using dimensionless analysis. Within certain fluid velocity/particle regime, linear correlation of h(app)/d with the square-root of Reynolds number (d\\varpi/upsilon){1/2}, that is, h{app}/d = 1.5207 - 9.25 x 10{- 4} (d\\varpi/n){1/2} (R(2) = 0.9875), was observed. PMID:18314890

Sheng, Jennifer J; Sirois, Paul J; Dressman, Jennifer B; Amidon, Gordon L

2008-11-01

344

High Energy Particle Collisions Near the Bifurcation Surface  

NASA Astrophysics Data System (ADS)

We consider generic nonextremal stationary dirty black holes. It is shown that in the vicinity of any bifurcation surface the energy of collision of two particles in the center of mass frame can grow unbound. This is a generic property that, in particular, includes collisions near the inner black hole horizon analyzed earlier by different methods. The similar results are also valid for cosmological horizons. The case of the de Sitter metric is discussed.

Zaslavskii, Oleg B.

2013-07-01

345

Ads Manifolds With Particles and Earthquakes on Singular Surfaces  

Microsoft Academic Search

.  We prove two related results. The first is an “earthquake theorem” for closed hyperbolic surfaces with cone singularities\\u000a where the total angle is less than ?: any two such metrics in are connected by a unique left earthquake. The second result\\u000a is that the space of “globally hyperbolic” AdS manifolds with “particles” – cone singularities (of given angle) along time-like

Francesco Bonsante; Jean-Marc Schlenker

2009-01-01

346

Calcination kinetics and surface area of dispersed limestone particles  

Microsoft Academic Search

The paper gives results of measurements of the rates of calcination of two types of limestones, ranging in particle size from 1 to 90 micrometers, and over the temperature range of 516 to 1000 C. A kinetic model, based on the B.E.T. (Brunauer-Emmett-Teller) surface area of the CaCOâ, correlates the results over five orders of magnitude in reaction rate. The

R. H. Borgwardt

1985-01-01

347

Method of evaluating the integrity of the outer carbon layer of triso-coated reactor fuel particles  

DOEpatents

This invention relates to a method for determining defective final layers of carbon on triso-coated fuel particles and the like. Samples of the particles are subjected to a high temperature treatment with gaseous chlorine and thereafter radiographed. The chlorine penetrates through any defective carbon layer and reacts with the underlying silicon carbide resulting in the volatilization of the silicon as SiCl.sub.4 leaving carbon as a porous layer. This porous carbon layer is easily detected by the radiography.

Caputo, Anthony J. (Knoxville, TN); Costanzo, Dante A. (Oak Ridge, TN); Lackey, Jr., Walter J. (Oak Ridge, TN); Layton, Frank L. (Clinton, TN); Stinton, David P. (Knoxville, TN)

1980-01-01

348

Novel routes for direct preparation of surface-modifying polyelectrolyte layers and patterned polymer surfaces  

NASA Astrophysics Data System (ADS)

The focus of this research was on the use of surface-confined atom transfer radical polymerization (SC-ATRP) for growing surface-tethered brushes of electrolytic or charged monomers on solid substrates. The use of SC-ATRP to produce well-defined polymer brushes from monomers with non-ionic functionalities in aprotic solvents has been well documented. Although it is possible to produce PE brushes by postpolymerization chemical conversion of some neutral brushes, this approach limits the types of PE brushes that can be produced and uses organic solvents. Thus, to more widely open the design envelope in terms of types of PE brushes that can be made and to reduce the use of organic solvents, it would be beneficial to directly synthesize PE brushes using more environmentally friendly, "green" solvents, such as water, for the reaction media. But the direct ATRP of hydrophilic monomers with ionic groups presents new challenges due to the complex interactions of the charged monomers and water with the ATRP catalyst. In this dissertation, I report findings on SC-ATRP of charged monomers such as itaconic acid (IA), methacrylic acid (MAA) and sodium 4-styrenesulfonate (SS) in aqueous solutions. Surface-tethered polyelectrolyte brushes comprised of poly(itaconic acid) (PIA), poly(methacrylic acid) (PMAA) and poly(4-styrenesulfonate) (PSS) were grown using surface-confined atom transfer radical polymerization (ATRP). The surface-tethered initiator monolayer was formed by self-assembling 2-bromoisobutyryl bromide terminated thiol molecules on gold coated silicon substrates. This polymerization initiator molecule and a copper-based organometallic catalyst allowed tethered polyelectrolyte chains to be grown via radical polymerization at room temperature in aqueous solutions. To suppress consumption of the ATRP deactivator, a halide salt was added to the reaction mixture, which enabled controlled growth of the polyelectrolyte layers. Phase-modulated ellipsometry was used to follow the kinetics of layer growth and also to study the stretching and swelling behavior of the polyelectrolyte layers as a function of pH. It was found that the change in layer thickness of the diacid PIA brush was greater than that of the monoacid PMAA brush. Combining inkjet printing and atom-transfer radical polymerization (ATRP) provides a facile and versatile method for producing patterned surfaces that may serve as platforms for a variety of applications. Through this dissertation, I also report the use of drop-on-demand technology to print chemically-graded interfacial layers or simple patterns that allow surface wetting characteristics to be tailored. (Abstract shortened by UMI.)

Sankhe, Amit Y.

349

X ray and charged particle detection with CsI(Tl) layer coupled to a-Si:H photodiode layers  

NASA Astrophysics Data System (ADS)

A compact real-time X ray and charged particle imager with digitized position output can built either by coupling a fast scintillator to a photodiode array or by forming one on a photodiode array directly. CsI(Tl) layers 100 to 1000 microns thick were evaporated on glass substrates from a crystal CsI(Tl). When coupled to a crystalline Si or amorphous silicon (a-Si:H) photodiode and exposed to calibrated X ray pulses, their light yields and speed were found to be comparable to those of a crystal CsI(Tl). Single beta particle detection was demonstrated with this combination. The light spread inside evaporated CsI(Tl) was suppressed by its columnar structure. Scintillation detection gives much larger signals than direct X ray detection due to the increased energy deposition in the detector material. Fabrication of monolithic type X-ray sensors consisting of CsI + a-Si:H photodiodes is discussed.

Fujieda, I.; Cho, G.; Drewery, J.; Gee, T.; Jing, T.; Kaplan, S. N.; Perez-Mendez, V.; Wildermuth, D.; Street, R. A.

1990-10-01

350

In situ synthesis of nanocrystalline intermetallic layer during surface plastic deformation of zirconium  

Microsoft Academic Search

By means of a surface plastic deformation method a nanocrystalline (NC) intermetallic compound was in situ synthesized on the surface layer of bulk zirconium (Zr). Hardened steel shots (composition: 1.0C, 1.5Cr, base Fe in wt.%) were used to conduct repetitive and multidirectional peening on the surface layer of Zr. The microstructure evolution of the surface layer was investigated by X-ray

P. Jiang; Q. Wei; Y. S. Hong; J. Lu; X. L. Wu

2007-01-01

351

Atomic layer deposition of high-? dielectrics on nitrided silicon surfaces  

NASA Astrophysics Data System (ADS)

An atomistic mechanism for the initiation of atomic layer deposition (ALD) of hafnium oxide (HfO2) on nitrided silicon surfaces was investigated using density functional theory. Reactions involving two different metal precursors are studied. Hf[N(CH3)2]4 does not form an adsorbed molecular complex, while HfCl4 has an adsorption energy of 0.30 eV. The ALD ligand exchange reaction is direct and 0.19 eV exothermic for Hf[N(CH3)2]4 with a barrier of 0.63 eV, while it is mediated by a complex intermediate and 0.40 eV endothermic for HfCl4 with a barrier of 0.97 eV. These results indicate that Hf[N(CH3)2]4 is both thermodynamically and kinetically superior to HfCl4 for the initial ALD of HfO2 on nitrided silicon surfaces.

Xu, Ye; Musgrave, Charles B.

2005-05-01

352

Global ocean wind power sensitivity to surface layer stability  

NASA Astrophysics Data System (ADS)

Global ocean wind power has recently been assessed (W. T. Liu et al., 2008) using scatterometry-based 10 m winds. We characterize, for the first time, wind power at 80 m (typical wind turbine hub height) above the global ocean surface, and account for the effects of surface layer stability. Accounting for realistic turbine height and atmospheric stability increases mean global ocean wind power by +58% and -4%, respectively. Our best estimate of mean global ocean wind power is 731 W m-2, about 50% greater than the 487 W m-2 based on previous methods. 80 m wind power is 1.2-1.5 times 10 m power equatorward of 30° latitude, between 1.4 and 1.7 times 10 m power in wintertime storm track regions and >6 times 10 m power in stable regimes east of continents. These results are relatively insensitive to methodology as wind power calculated using a fitted Weibull probability density function is within 10% of power calculated from discrete wind speed measurements over most of the global oceans.

Capps, Scott B.; Zender, Charles S.

2009-05-01

353

Large-Eddy Simulations of the Convective Atmospheric Boundary Layer over Heterogeneous Land Surfaces  

Microsoft Academic Search

The parameterization of the atmospheric boundary layer is essential for accurate numerical weather predictions. The near-surface values of air temperature or wind speed for instance are highly dependent on the complex land - atmosphere interactions over heterogeneous terrain. Over such surfaces, several open challenges remain regarding the growth of internal boundary layers, the determination of mixing layer heights and the

D. Nadeau; V. Kumar; C. W. Higgins; M. B. Parlange

2009-01-01

354

A Study of the Surface Photovoltage of ZnO-Resin Layers.  

PubMed

The surface photovoltage of ZnO resin layer has been used as the basis for an imaging process generally known as chargeless electrophotography. This paper explores effects of the ambient air pressure and the layer temperature on the surface photovoltage of ZnO resin layers. Experiments were made by using ZnO-silicone resin layer, ZnO-alkyd resin layer, and ZnO-acryl resin layer. The surface potential of the dark adapted layers were measured while the ambient air pressure decreased, and the surface photovoltage and its decay curve were measured under various ambient air pressures. ZnO-silicone resin layer showed a remarkably high sensitivity in terms of surface photovoltage to the ambient air pressure changes. Marked variations were observed in the surface potential of the dark adapted layers both in air and in a vacuum of 5 x 10(-5) Torr when the layer temperature had been slowly raised. The surface potential exhibited a maximum peak when silicone resin was used as a binder and a minimum peak when alkyd resin or acryl resin was used, both peaks being registered at a temperature slightly higher than room temperature in air. After the layers had been annealed for a few hours at a high temperature, relationships between the surface photovoltage and the layer temperature were measured while the layer temperature decreased. The surface photovoltage and its decay of the ZnO-silicone resin layer revealed higher sensitivity to the changes of ambient air pressure and layer temperature than to those of other ZnO-resin layers. This difference is accounted for by a specific property of the silicone resin that enforces adsorption of the water molecule onto the surface of ZnO. Some applications of the above experiments are also discussed. PMID:20076122

Tashiro, I; Kimura, T; Endo, K

1969-01-01

355

Modelling Analysis of Influence of Substrate Surface Defect on Optical Characteristics of Single-Layer Coating  

Microsoft Academic Search

A simple and practical model is used to analyse the influence of substrate surface defect on the optical characteristics of a single-layer coating. A single-layer coating is prepared and its optical properties are fitted. Some explanations for the origin of the transition layer are presented. It is concluded that there is a transition layer forming between the substrate and coating,

Zi-Cai Shen; Wei-Jin Kong; Jian-Da Shao; Zheng-Xiu Fan

2005-01-01

356

Hierarchically structured superhydrophobic coatings fabricated by successive Langmuir Blodgett deposition of micro-/nano-sized particles and surface silanization  

NASA Astrophysics Data System (ADS)

The present study demonstrates the creation of a stable, superhydrophobic surface by coupling of successive Langmuir-Blodgett (LB) depositions of micro- and nano-sized (1.5 µm/50 nm, 1.0 µm/50 nm, and 0.5 µm/50 nm) silica particles on a glass substrate with the formation of a self-assembled monolayer of dodecyltrichlorosilane on the surface of the particulate film. Particulate films, in which one layer of 50 nm particles was deposited over one to five sublayers of larger micro-sized particles, with hierarchical surface roughness and superhydrophobicity, were successfully fabricated. Furthermore, the present 'two-scale' (micro- and nano-sized particles) approach is superior to the previous 'one-scale' (micro-sized particles) approach in that both higher advancing contact angle and lower contact angle hysteresis can be realized. Experimental results revealed that the superhydrophobicity exhibited by as-fabricated particulate films with different sublayer particle diameters increases in the order of 0.5 µm>1.0 µm>1.5 µm. However, no clear trend between sublayer number and surface superhydrophobicity could be discerned. An explanation of superhydrophobicity based on the surface roughness introduced by two-scale particles is also proposed.

Tsai, Ping-Szu; Yang, Yu-Min; Lee, Yuh-Lang

2007-11-01

357

Fabrication of bifunctional core-shell Fe3O4 particles coated with ultrathin phosphor layer  

NASA Astrophysics Data System (ADS)

Bifunctional monodispersed Fe3O4 particles coated with an ultrathin Y2O3:Tb3+ shell layer were fabricated using a facile urea-based homogeneous precipitation method. The obtained composite particles were characterized by powder X-ray diffraction, transmission electron microscopy (TEM), quantum design vibrating sample magnetometry, and photoluminescence (PL) spectroscopy. TEM revealed uniform spherical core-shell-structured composites ranging in size from 306 to 330 nm with a shell thickness of approximately 25 nm. PL spectroscopy confirmed that the synthesized composites displayed a strong eye-visible green light emission. Magnetic measurements indicated that the composite particles obtained also exhibited strong superparamagnetic behavior at room temperature. Therefore, the inner Fe3O4 core and outer Y2O3:Tb3+ shell layer endow the composites with both robust magnetic properties and strong eye-visible luminescent properties. These composite materials have potential use in magnetic targeting and bioseparation, simultaneously coupled with luminescent imaging.

Atabaev, Timur Sh; Kim, Hyung-Kook; Hwang, Yoon-Hwae

2013-08-01

358

Surface Softening in Polymers and Their Nanocomposites Determined by Surface Mechanical Properties through Spontaneous Particle Embedment  

NASA Astrophysics Data System (ADS)

In the present work, we have used the particle embedment technique with sub-micron particles to estimate the surface modulus of epoxy/POSS composites at a temperature far below the glass transition temperature. The embedment of the particle is determined from atomic force microscope measurements and the modulus was determined using the elastic analysis of Johnson, Kendall and Roberts (JKR) with surface energy estimates of the work of adhesion as the driving force for embedment. The surface modulus values were found much smaller than the macroscopic modulus values. The maximum embedment depth obtained for all surfaces was low enough so that it did not cause plastic deformation on the surface. The maximum stress values on all surfaces induced by the particle embedment were estimated to verify the expected response in close to the linear regime. [4pt] [1] K. L. Johnson, K. Kendall and A. D. Roberts, P. Royal Society of Lonodon A, 324, 301-313 (1971). [0pt] [2] J. H. Teichroeb and J. A. Forrest, Physical Review Letter, 91, 016104 (2003).

Karim, Taskin; McKenna, Gregory

2011-03-01

359

Inhalation of poorly soluble particles. II. Influence Of particle surface area on inflammation and clearance.  

PubMed

In this article the volumetric overload hypothesis, which predicts the impairment of clearance of particles deposited in the lung in terms of particle volume, is reevaluated. The degree to which simple expressions of retained lung burden explain pulmonary responses to overload was investigated using data from a series of chronic inhalation experiments on rats with two poorly soluble dusts, titanium dioxide and barium sulfate. The results indicated that the difference between the dusts in the level of inflammation and translocation to the lymph nodes could be explained most simply when the lung burden was expressed as total particle surface area. The shape of the statistical relationship for both lung responses indicated the presence of a threshold at approximately 200-300 cm(2) of lung burden. On the basis of this and other similar results, a hypothesis regarding a generic mechanism for the impairment of clearance and associated lung responses is proposed for such "low-toxicity" dusts. PMID:11114784

Tran, C L; Buchanan, D; Cullen, R T; Searl, A; Jones, A D; Donaldson, K

2000-12-01

360

Detailed heterogeneous oxidation of soot surfaces in a particle-resolved aerosol model  

NASA Astrophysics Data System (ADS)

Using the particle-resolved aerosol model PartMC-MOSAIC, we simulate the heterogeneous oxidation of a monolayer of polycyclic aromatic hydrocarbons (PAHs) on soot particles in an urban atmosphere. We focus on the interaction of the major atmospheric oxidants (O3, NO2, OH, and NO3) with PAHs and include competitive co-adsorption of water vapour for a range of atmospheric conditions. For the first time detailed heterogeneous chemistry based on the Pöschl-Rudich-Ammann (PRA) framework is modelled on soot particles with a realistic size distribution and a continuous range of chemical ages. We find PAHs half-lives, ?1/2, on the order of seconds during the night, when the PAHs are rapidly oxidised by the gas-surface reaction with NO3. During the day, ?1/2 is on the order of minutes and determined mostly by the surface layer reaction of PAHs with adsorbed O3. Such short half-lives of surface-bound PAHs may lead to efficient conversion of hydrophobic soot into more hygroscopic particles, thus increasing the particles' aerosol-cloud interaction potential. Despite its high reactivity OH appears to have a negligible effect on PAH degradation which can be explained by its very low concentration in the atmosphere. An increase of relative humidity (RH) from 30 % to 80 % increases PAH half-lives by up to 50 % for daytime degradation and by up to 100 % or more for nighttime degradation. Uptake coefficients, averaged over the particle population, are found to be relatively constant over time for O3 (∼2 × 10-7 to ∼2 × 10-6) and NO2 (∼5 × 10-6 to ∼10-5) at the different levels of NOx emissions and RH considered in this study. In contrast, those for OH and NO3 depend strongly on the surface concentration of PAHs. We do not find a significant influence of heterogeneous reactions on soot particles on the gas phase composition. The derived half-lives of surface-bound PAHs and the time and particle population averaged uptake coefficients for O3 and NO2 presented in this paper can be used as parameterisations for the treatment of heterogeneous chemistry in large-scale atmospheric chemistry models.

Kaiser, J. C.; Riemer, N.; Knopf, D. A.

2011-05-01

361

Auroral particle acceleration by strong double layers: The upward current region  

NASA Astrophysics Data System (ADS)

Satellite observations have established that parallel electric fields of both upward and downward current regions of the aurora are supported, at least in part, by strong double layers. The purpose of this article is to examine the role of double layers in auroral electron acceleration using direct measurements of parallel electric fields and the accompanying particle distributions, electrostatic waves, and nonlinear structures; the concentration is on the upward current region. Direct observations of the ionospheric boundary of the auroral cavity suggest that a stationary, oblique double layer carries a substantial, albeit a minority fraction (˜10% to ˜50%) of the auroral potential. An order of magnitude density gradient results in an asymmetric electric field signature. Oblique double layers with amplitudes greater than 100 mV/m have been verified in ˜3% and may occur in up to 11% of auroral cavity crossings, so it is feasible that strong double layers are a principal acceleration mechanism. In this article we also present a second type of double layer that has a symmetric electric field signature and is seen inside of the auroral cavity. These structures are a possible signature of a midcavity or high-altitude acceleration mechanism. Numerical solutions of the Vlasov-Poisson equations support the possibility of midcavity double layers and indicate that trapped electrons can play an important role in the double-layer structure.

Ergun, R. E.; Andersson, L.; Main, D.; Su, Y.-J.; Newman, D. L.; Goldman, M. V.; Carlson, C. W.; Hull, A. J.; McFadden, J. P.; Mozer, F. S.

2004-12-01

362

Downward propagating internal waves generated at the base of the surface layer of a stratified fluid  

Microsoft Academic Search

Downward propagating internal waves are observed in laboratory experiments. They appear to be generated by the 'obstacle effect' beneath a turbulent surface layer in a surface stress driven stratified flow experiment in a rectangular cavity. The obstacles are the perturbations at the base of the surface layer and the shear is created by a combination of an internal seiche and

Craig Stevens; Jorg Imberger

1994-01-01

363

Investigation of morphology and fractal behaviour on compound semiconductor surface after electrochemical layer removal  

Microsoft Academic Search

The electrochemical method is a very versatile tool for characterization and processing of compound semiconductors. In this paper we investigate the surface morphology and pattern formation of GaAs and InP surfaces after electrochemical layer removal. Different aqueous HCl based electrolites were used for the layer removal. The investigation of the surface pattern formation was carried out using the box counting

Ákos Nemcsics; Imre Mojzes; László Dobos

1999-01-01

364

Particle-in-cell simulations of a current-free double layer  

SciTech Connect

Current-free double layers of the type reported in plasmas in the presence of an expanding magnetic field [C. Charles and R. W. Boswell, Appl. Phys. Lett. 82, 1356 (2003)] are modeled theoretically and with particle-in-cell/Monte Carlo simulations. Emphasis is placed on determining what mechanisms affect the electron velocity distribution function (EVDF) and how the EVDF influences the double layer. A theoretical model is developed based on depletion of electrons in certain velocity intervals due to wall losses and repletion of these intervals due to ionization and elastic electron scattering. This model is used to predict the range of neutral pressures over which a double layer can form and the electrostatic potential drop of the double layer. These predictions are shown to compare well with simulation results.

Baalrud, S. D.; Lafleur, T.; Boswell, R. W.; Charles, C. [Space Plasma, Power and Propulsion Group, Research School of Physics and Engineering, Australian National University, Canberra ACT 0200 (Australia)

2011-06-15

365

Deposition of Colloidal Particles on Homogeneous Surfaces: Integral-Equation Theory and Monte Carlo Simulation  

Microsoft Academic Search

Deposition of large particles such as colloidal or bio-particles on a solid surface is usually modeled by the random sequential adsorption (RSA). The model was previously described by the integral-equation theory whose validity was proved by Monte Carlo simulation. This work generalized the model to include the concentration effect of added particles on the surface. The fraction of particles inserted

Panu Danwanichakul

2009-01-01

366

Statistics of particle concentration in free-surface turbulence  

SciTech Connect

Particles on the surface of an incompressible fluid maintained in a turbulent steady-state cluster into spatio-temporally complex flow structures. We experimentally study the statistics of particle concentration n(r, t) over various coarse-grained scales r' in the inertial range. Another control parameter is the Taylor Microscale Reynolds number Re{sub {lambda}}. The focus is on the steady state probability density function {Pi}(n{sub r}). Attention is also given to the variance {sigma}{sup 2}(r, t) of this PDF, since it yields information about the topology of the coagulated structures. Where possible, the results are compared and contrasted with those obtained in a recent analytical and numerical study of two-dimensional synthetic turbulence by Ducasse and Pumir. There, but not here, the dimensionless compressibility C is an important control parameter.

Bandi, Mahesh M [Los Alamos National Laboratory; Larkin, J [UNIV. OF PITTSBURGH; Goldburg, W [UNIV. OF PITTSBURGH

2009-01-01

367

Determination of particle dry deposition velocities to a surrogate surface  

SciTech Connect

Dry deposition of atmospheric aerosol particles is thought to be an important pathway for the introduction of toxic trace elements and heavy metals into Lake Michigan, which lies in close proximity to the large urban and heavily industrialized Chicago, Illinois/Gary, Indiana area. However, dry deposition fluxes are difficult to measure and, instead, are often estimated as the product of the dry deposition velocity (V{sub d}) and the corresponding ambient pollutant concentration. Herein, we apply a new chemical mass balance deposition (CMBD) model to derive size-dependent deposition velocities for atmospheric particles to a surrogate surface. The CMBD model results are compared with those calculated with the Williams model under the prevailing meteorological conditions.

Caffrey, P.F.; Ondov, J.M. [Univ. of Maryland, College Park, MD (United States); Zufall, M.J.; Davidson, C.I. [Carnegie-Mellon Univ., Pittsburgh, PA (United States)

1997-12-01

368

In situ laser surface coating of TiC metal-matrix composite layer  

Microsoft Academic Search

Surface alloys are of great interest for improving the mechanical and\\/or chemical properties of the near-surface region on metallic materials. A new method, in situ laser surface coating of metal-matrix composite, is described, by which to produce a surface composite layer. Using this process, ?-Ni-TiCx composite surface layers were achieved on mild steel; they exhibited increased hardness, and in situ

Meng Yan; Hu Hanqi

1996-01-01

369

Characterizing atmospheric surface layer turbulence using chaotic return map analysis  

NASA Astrophysics Data System (ADS)

Nonlinear time series analysis methods are used to investigate the dynamics of mechanical and convective turbulences in the atmospheric surface layer flow. Using dynamical invariant analysis (e.g. correlation dimension, Lyapunov exponent and mutual information) along with recurrence quantification analysis (e.g. recurrent rate, determinism, average diagonal length of recurrence plot, etc.) of the vertical wind component data, it is confirmed that a convective turbulence is a lower order manifold in its phase space exhibiting higher degree of organization than a mechanical turbulence. Applying a quasi-one-dimensional chaotic return map technique, the topological differences between the mechanical and convective turbulences are explored. These quasi-one-dimensional return maps are produced using the local maxima of the first principal component of the reconstructed turbulence data. A comparison of the probability distribution of the local maxima of a forced Lorenz model with the turbulence data indicates the possible existence of a stable fixed point for both type of turbulences. Furthermore, dynamically the mechanical turbulence is found to resemble an unforced Lorenz model whereas the convective turbulence resembles a forced Lorenz model.

Mukherjee, Sandipan; Zawar-Reza, Peyman; Sturman, Andrew; Mittal, Ashok Kumar

2013-10-01

370

Characterization of the magnesium diffused lithium mobate surface layer by gixrd  

Microsoft Academic Search

Characteristics of MgO-rich layer in the magnesium diffused lithium niobate single crystal surface layer are investigated with the conventional X-ray diffraction and glancing-incidence X-ray diffraction. It is found that the MgO-rich layer is composed of an unknown compound and MgNb2O6. The MgNb2O6 is in the surface layer of MgO-rich layer, the unknown compound is in the subsurface layer beneath the

Wenxiu Que; Xi Yao; Liangying Zhang

1997-01-01

371

Electronic Surface Structures of Coal and Mineral Particles  

SciTech Connect

Surface science studies related to tribocharging and charge separation studies were performed on electrostatic beneficiation of coal. In contrast to other cleaning methods, electrostatic beneficiation is a dry cleaning process requiring no water or subsequent drying. Despite these advantages, there is still uncertainty in implementing large scale commercial electrostatic beneficiation of coal. The electronic surface states of coal macerals and minerals are difficult to describe due to their chemical complexity and variability [1]. The efficiency in separation of mineral particles from organic macerals depends upon these surface states. Therefore, to further understand and determine a reason for the bipolar charging observed in coal separation, surface analysis studies using Ultra-violet Photoelectron Spectroscopy (UPS) and X-ray Photoelectron Spectroscopy (XPS) were performed on coal samples and several materials that are used or considered for use in tribocharging. Electrostatic charging is a surface phenomenon, so the electronic surface states of the particles, which are influenced by the environmental conditions, determine both polarity and magnitude of tribocharging. UPS was used to measure the work function of the materials as typically used in ambient air. XPS was used to determine the surface chemistry in the form of contamination and degree of oxidation under the same environmental conditions. Mineral bearing coals are those amenable to electrostatic beneficiation. Three types of coal, Illinois No. 6, Pittsburgh No. 8, and Kentucky No. 9 were investigated in this study. Pulverized coal powder was tribocharged against copper. Pyritic and other ashes forming minerals in coal powders should charge with a negative polarity from triboelectrification, and organic macerals should acquire positive charge, according to the relative differences in the surface work functions between the material being charged and the charging medium. Different types of minerals exhibit different magnitudes of negative charge and some may also charge positively against copper [2]. Only the mineral sulfur fraction of the total sulfur content is accessible by the electrostatic method since organic sulfur is covalently bound with carbon in macerals. The sizes of mineral constituents in coal range from about 0.1 to 100 {micro}m, but pyrites in many coals are on the lower end of this scale necessitating fine grinding for their liberation and separation. A ready explanation for coal powder macerals to charge positively by triboelectrification is found in the large numbers of surface carbon free radicals available to release electrons to form aromatic carbocations. There is evidence that these cationic charges are delocalized over several atoms [3]. Only perhaps one in one hundred thousand of the surface atoms is charged during triboelectrification [4], making it difficult to predict charging levels since the data depends upon the surface chemical species involved in charging. Based on the high electron affinity of oxygen atoms, oxidation is expected to decrease the extent of a coal particle to charge positively. Also, ion transfer may contribute to the increasingly negative charging character of oxidized coal carbons. A variety of oxidized surface functional groups may influence charge properties. For example, carboxylic acid functions can lose protons to form carboxylate anions. The samples of coal investigated in this study showed differing degrees of beneficiation, consistent with a more extensively oxidized Illinois No. 6 coal sample relative to that of Pittsburgh No. 8. Even though oxygen in air is deleterious to coal stored prior to beneficiation, other gases might favorably influence charge properties. To this end, coal exposed to vapors of acetone, ammonia, and sulfur dioxide also were beneficiated and analyzed in this study.

M.K. Mazumder; D.A. Lindquist; K.B. Tennal; Steve Trigwell; Steve Farmer; Albert Nutsukpul; Alex Biris

2001-04-01

372

Rate of evolution of the specific surface area of surface snow layers.  

PubMed

The snowpack can impact atmospheric chemistry by exchanging adsorbed or dissolved gases with the atmosphere. Modeling this impact requires the knowledge of the specific surface area (SSA) of snow and its variations with time. We have therefore measured the evolution of the SSA of eight recent surface snow layers in the Arctic and the French Alps, using CH4 adsorption at liquid nitrogen temperature (77 K). The SSA of fresh snow layers was found to decrease with time, from initial values in the range 613-1540 cm2/g to values as low as 257 cm2/g after 6 days. This is explained by snow metamorphism, which causes modifications in crystal shapes, here essentially crystal rounding and the disappearance of microstructures. A parametrization of the rate of SSA decrease is proposed. We fit the SSA decrease to an exponential law and find that the time constant alpha(exp) (day(-1)) depends on temperature according to alpha(exp) = 76.6 exp (-1708/7), with Tin kelvin. Our parametrization predicts that the SSA of a snow layer evolving at -40 degrees C will decrease by a factor of 2 after 14 days, while a similar decrease at -1 degrees C will only require 5 days. Wind was found to increase the rate of SSA decrease, but insufficient data did not allow a parametrization of this effect. PMID:12636262

Cabanes, Axel; Legagneux, Loïc; Dominé, Florent

2003-02-15

373

Hydrate layers on ice particles and superheated ice: a {sup 1}H NMR microimaging study  

SciTech Connect

Recent observations on the interaction of methane gas with ice surfaces have led to the suggestion that the resulting hydrate layer prevents the encapsulated ice from melting at its usual temperature. This would require ice to exist in a superheated state. The authors have examined the product of the gas-solid reaction with {sup 1}H NMR imaging. The imaging experiments show that the hydrate-encapsulated ice is able to melt at its usual melting point. As a possible alternative model, the authors suggest that a considerable amount of ice inside the hydrate layer can be converted to hydrate and liquid water under isothermal and constant volume conditions, the hydrate layer acting as an insulating, semipermeable layer that insulates processes inside the hydrate layer from external bulk temperature and pressure measurements.

Moudrakovski, I.L.; Ratcliffe, C.I.; McLaurin, G.E.; Simard, B.; Ripmeester, J.A. [National Research Council of Canada, Ottawa, Ontario (Canada). Steacie Inst. for Molecular Sciences

1999-07-01

374

Primary versus secondary contributions to particle number concentrations in the European boundary layer  

NASA Astrophysics Data System (ADS)

It is important to understand the relative contribution of primary and secondary particles to regional and global aerosol so that models can attribute aerosol radiative forcing to different sources. In large-scale models, there is considerable uncertainty associated with treatments of particle formation (nucleation) in the boundary layer (BL) and in the size distribution of emitted primary particles, leading to uncertainties in predicted cloud condensation nuclei (CCN) concentrations. Here we quantify how primary particle emissions and secondary particle formation influence size-resolved particle number concentrations in the BL using a global aerosol microphysics model and aircraft and ground site observations made during the May 2008 campaign of the European Integrated Project on Aerosol Cloud Climate Air Quality Interactions (EUCAARI). We tested four different parameterisations for BL nucleation and two assumptions for the emission size distribution of anthropogenic and wildfire carbonaceous particles. When we emit carbonaceous particles at small sizes (as recommended by the Aerosol Intercomparison project, AEROCOM), the spatial distributions of campaign-mean number concentrations of particles with diameter >50 nm (N50) and >100 nm (N100) were well captured by the model (R2?0.8) and the normalised mean bias (NMB) was also small (-18% for N50 and -1% for N100). Emission of carbonaceous particles at larger sizes, which we consider to be more realistic for low spatial resolution global models, results in equally good correlation but larger bias (R2?0.8, NMB = -52% and -29%), which could be partly but not entirely compensated by BL nucleation. Within the uncertainty of the observations and accounting for the uncertainty in the size of emitted primary particles, BL nucleation makes a statistically significant contribution to CCN-sized particles at less than a quarter of the ground sites. Our results show that a major source of uncertainty in CCN-sized particles in polluted European air is the emitted size of primary carbonaceous particles. New information is required not just from direct observations, but also to determine the "effective emission size" and composition of primary particles appropriate for different resolution models.

Reddington, C. L.; Carslaw, K. S.; Spracklen, D. V.; Frontoso, M. G.; Collins, L.; Merikanto, J.; Minikin, A.; Hamburger, T.; Coe, H.; Kulmala, M.; Aalto, P.; Flentje, H.; Plass-Dülmer, C.; Birmili, W.; Wiedensohler, A.; Wehner, B.; Tuch, T.; Sonntag, A.; O'Dowd, C. D.; Jennings, S. G.; Dupuy, R.; Baltensperger, U.; Weingartner, E.; Hansson, H.-C.; Tunved, P.; Laj, P.; Sellegri, K.; Boulon, J.; Putaud, J.-P.; Gruening, C.; Swietlicki, E.; Roldin, P.; Henzing, J. S.; Moerman, M.; Mihalopoulos, N.; Kouvarakis, G.; Ždímal, V.; Zíková, N.; Marinoni, A.; Bonasoni, P.; Duchi, R.

2011-12-01

375

Phosphate recovery from wastewater using engineered superparamagnetic particles modified with layered double hydroxide ion exchangers.  

PubMed

An innovative nanocomposite material is proposed for phosphate recovery from wastewater using magnetic assistance. Superparamagnetic microparticles modified with layered double hydroxide (LDH) ion exchangers of various compositions act as phosphate adsorbers. Magnetic separation and chemical regeneration of the particles allows their reuse, leading to the successful recovery of phosphate. Based upon the preliminary screening of different LDH ion exchanger modifications for phosphate selectivity and uptake capacity, MgFe-Zr LDH coated magnetic particles were chosen for further characterization and application. The adsorption kinetics of phosphate from municipal wastewater was studied in dependence with particle concentration, contact time and pH. Adsorption isotherms were then determined for the selected particle system. Recovery of phosphate and regeneration of the particles was examined via testing a variety of desorption solutions. Reusability of the particles was demonstrated for 15 adsorption/desorption cycles. Adsorption in the range of 75-97% was achieved in each cycle after 1 h contact time. Phosphate recovery and enrichment was possible through repetitive application of the desorption solution. Finally, a pilot scale experiment was carried out by treating 125 L of wastewater with the particles in five subsequent 25 L batches. Solid-liquid separation on this scale was carried out with a high-gradient magnetic filter (HGMF). PMID:23863389

Drenkova-Tuhtan, Asya; Mandel, Karl; Paulus, Anja; Meyer, Carsten; Hutter, Frank; Gellermann, Carsten; Sextl, Gerhard; Franzreb, Matthias; Steinmetz, Heidrun

2013-07-01

376

Resonant absorption and scattering suppression of localized surface plasmons in Ag particles on green LED.  

PubMed

The metallic-structure dependent localized surface plasmons (LSPs) coupling behaviors with InGaN QWs in a green LED epitaxial wafer are investigated by optical transmission, scanning electron microscopy (SEM) and photoluminescence (PL) measurements. Ag nanoparticles (NPs) are formed by thermal annealing Ag layer on the green LED wafer. SEM images show that for higher annealing temperature and/or thicker deposited Ag layer, larger Ag NPs can be produced, leading to the redshift of absorption peaks in the transmission spectra. Time resolved PL (TRPL) measurements indicate when LSP-MQW coupling occurs, PL decay rate is greatly enhanced especially at the resonant wavelength 560 nm. However, the PL intensity is suppressed by 3.5 folds compared to the bare LED. The resonant absorption and PL suppression are simulated by three dimension finite-difference-time-domain (FDTD), which suggests that Ag particle with smaller size and lower height lead to the larger dissipation of LSP. PMID:23736430

Jiang, Shuang; Hu, Zhe; Chen, Zhizhong; Fu, Xingxing; Jiang, Xianzhe; Jiao, Qianqian; Yu, Tongjun; Zhang, Guoyi

2013-05-20

377

Alpha-particle dosimetry for the basal layer of the skin and the radon progeny 218-Po and 214-Po  

NASA Astrophysics Data System (ADS)

The population average dose to the basal layer of the skin is evaluated, in terms of dose per alpha-particle decay per unit area, for radon progeny 218-Po and 214-Po attached to the skin surface. Account is taken of the variation in basal layer depth between different individuals, and results are presented for several anatomical regions. On the face, for example, the population average dose to the basal layer from 218-Po is of the order of while that from 214-Po is of the order of . Radiation induced stochastic effects in the skin are generally assumed to originate from target cells located in the basal layer. Provided this assumption is correct, these results suggest that both 218-Po and 214-Po could be regarded as potential carcinogenic agents for the induction of skin cancer.

Eatough, J. P.

1997-10-01

378

Thermomechanical behavior of nano aluminum particles with oxide layers during melting  

Microsoft Academic Search

Molecular dynamics simulations were performed to study the thermo-mechanical behavior of nano aluminum particles coated with\\u000a crystalline and amorphous oxide layers during melting. The analysis employs the Streitz–Mintmire potential, along with micro-canonical\\u000a (NVE) and isobaric–isoenthalpic (NPH) ensembles. The effect of particle size in the range of 5–10 nm with oxide thickness\\u000a in the range of 1–2.5 nm was investigated. The melting phenomenon

Puneesh Puri; Vigor Yang

2010-01-01

379

Mass transport of deposited particles by surface-to-surface contact.  

PubMed

The spread of particle-borne contamination by surface-to-surface contact and its implications for exposures within the indoor environment have been observed - largely qualitatively. The present study was conducted with the aim of quantifying the mass transfer efficiency (TE) of deposited aerosol particles when selected soft and hard surfaces come in contact. The surfaces used were 100% cotton, synthetic fleece, plastic laminate and brass. Contact transfer efficiencies ranging from 2 to 45% were observed; these are very significant numbers in terms of hazardous aerosol transport in the environment. Other observations include an increase in the mass transferred with increased surface roughness. An increase in the applied pressure between the two surfaces in contact leads to a step change in transfer efficiency, so that two pressure regimes can be identified, with a transition pressure between them that depends on surface type. Time of contact appears to have little to no effect on the mass transfer efficiency for the surfaces studied, while contaminant loading has some effect that is not systematic. PMID:22683108

McDonagh, A; Sextro, R G; Byrne, M A

2012-05-27

380

Particle transport in a turbulent boundary layer: Non-local closures for particle dispersion tensors accounting for particle-wall interactions  

NASA Astrophysics Data System (ADS)

Continuum equations derived from a probability density function kinetic equation contain dispersion tensors that describe the interaction between inertial particles and the underlying turbulent flow in which they are transported. These tensors require closure treatment and recent work has shown that traditional closure approximations perform poorly when applied to the case of particle dispersion in turbulent boundary layers. The dispersion tensors are intrinsically non-local, being sensitive to both the strong inhomogeneity of wall-bounded turbulence and the influence of particle-wall collisions. A new strategy for constructing non-local closure models is presented to account for such influences. An important feature of the approach is that it utilizes exactly the same input parameters required for the traditional closures. Differences between the two approaches are therefore a reflection of the improved closure strategy, rather than a consequence of improved or additional input data. Predictions from both new and standard models are compared with benchmark statistics obtained from the simulation of particle trajectories in a synthetic boundary layer flow, generated via an inhomogeneous kinematic simulation technique. The results demonstrate the significant advance offered by the new approach.

Bragg, A.; Swailes, D. C.; Skartlien, R.

2012-10-01

381

Direct electron transfer and electrocatalysis of hemoglobin in layer-by-layer films assembled with Al-MSU-S particles.  

PubMed

In this paper, layer-by-layer (LBL) {MSU/Hb}(n)/PDDA films assembled by alternate adsorption of positively charged hemoglobin (Hb) and negatively charged mesoporous molecular sieves of Al-MSU-S onto a glassy carbon electrode (GCE) were reported. Al-MSU-S was synthesized by the precursor of zeolite Y and ionic liquids 1-hexadecane-3-methylimidazolium bromide (CMIMB) as a template in basic medium. It exhibited larger pore diameter, pore volume and surface area. Direct electrochemical and electrocatalytic properties of Hb in these layer-by-layer films were investigated. A pair of well-defined nearly reversible cyclic voltammetric peaks was observed and the formal potential of the heme Fe(III)/Fe(II) redox couple was found to be -0.295V (vs. SCE). The influences of layer's number and the pH of the external solution to the electron transfer behavior of Hb in {MSU/Hb}(n)/PDDA films were also estimated by cyclic voltammetry and a set of optimized conditions for film fabrication was inferred. The hemoglobin in{MSU/Hb}(n)/PDDA films displayed a good electrocatalytic activity to the reduction of hydrogen peroxide, which had linear current responses from 1.0 x 10(-6) to 1.86 x 10(-4)mol/L with the detection limit of 5.0 x 10(-7)mol/L (S/N=3). The apparent Michaeli-Menten constant (K(m)(app)) was 0.368 mmol/L. Thus, this methodology shows potential application of the preparation of third-generation biosensors. PMID:18371838

Sun, Zhiyu; Li, Youqin; Zhou, Tianshu; Liu, Ye; Shi, Guoyue; Jin, Litong

2007-10-13

382

Primary versus secondary contributions to particle number concentrations in the European boundary layer  

NASA Astrophysics Data System (ADS)

It is important to understand the relative contribution of primary and secondary particles to regional and global aerosol so that models can attribute aerosol radiative forcing to different sources. In large-scale models, there is considerable uncertainty associated with treatments of particle formation (nucleation) in the boundary layer (BL) and in the size distribution of emitted primary particles, leading to uncertainties in predicted cloud condensation nuclei (CCN) concentrations. Here we quantify how primary particle emissions and secondary particle formation influence size-resolved particle number concentrations in the BL using a global aerosol microphysics model and observations made during the May 2008 campaign of the European Integrated Project on Aerosol Cloud Climate Air Quality Interactions (EUCAARI). Observations are available from the DLR Falcon 20 aircraft and from 15 ground sites of the European Supersites for Atmospheric Aerosol Research (EUSAAR) and the German Ultrafine Aerosol Network (GUAN). Measurements include total and non-volatile particle number concentrations and the particle size distribution between ~3 nm and ~1 ?m. We tested four different parameterisations for BL nucleation and two assumptions for the emission size distribution of anthropogenic and wildfire carbonaceous particles. When we emit small carbonaceous particles (recommended by the Aerosol Intercomparison project, AEROCOM), the spatial distributions of campaign-mean number concentrations >50 nm (N50) and >100 nm (N100) dry diameter were well captured by the model (R2~0.9) and the normalised mean bias (NMB) was also small (-5 % for N50 and 12 % for N100). Emission of larger particles, which we consider to be more realistic for global models, results in equally good correlation but larger bias (R2~0.8, NMB = -51 % and -21 %), which could be partly but not entirely compensated by BL nucleation. The model also predicts the particle concentration frequency distribution fairly well, with an overlap of modelled and observed N50 hourly histograms of ~60 % across all sites. However, the model-observation temporal correlation on an hourly time scale is poor (R2?0.1) for this period. These comparisons show that caution is required when drawing conclusions about model realism from time or site-averaged data or frequency histograms when deterministic behaviour is not captured at individual sites. From this 1-month intensive European dataset it is not possible to determine a reliable estimate of the fraction of CCN-sized particles from primary and secondary sources, although the size of primary emitted particles is shown to be a major source of uncertainty.

Reddington, C. L.; Carslaw, K. S.; Spracklen, D. V.; Frontoso, M. G.; Collins, L.; Merikanto, J.; Minikin, A.; Hamburger, T.; Coe, H.; Kulmala, M.; Aalto, P.; Flentje, H.; Plass-Dülmer, C.; Birmili, W.; Wiedensohler, A.; Wehner, B.; Tuch, T.; Sonntag, A.; O'Dowd, C. D.; Jennings, S. G.; Dupuy, R.; Baltensperger, U.; Weingartner, E.; Hansson, H.-C.; Tunved, P.; Laj, P.; Sellegri, K.; Boulon, J.; Putaud, J.-P.; Gruening, C.; Swietlicki, E.; Roldin, P.; Henzing, J. S.; Moerman, M.; Mihalopoulos, N.; Kouvarakis, G.; Ždímal, V.; Zíková, N.; Marinoni, A.; Bonasoni, P.; Duchi, R.

2011-06-01

383

Effect of Powder Particle Sizes on the Development of Ultra Hard Surface Through Superplastic Boronizing of Duplex Stainless Steel  

NASA Astrophysics Data System (ADS)

In this work, a further study on boronizing using compression method called superplastic boronizing (SPB) was conducted. This process was conducted on duplex stainless steel (DSS) which has been thermo-mechanically treated to obtain fine grain microstructure and exhibit superplasticity. Effort was being put in obtaining ultra hard surface through SPB by focusing on the boron powder particle size. The microstructure, hardness, and layer thickness of the boronized materials were investigated. The formation of hard boride layers were confirmed by XRD analysis. Metallographic studies and scanning electron microscope (SEM) revealed a uniform, dense and smooth morphology of boride layer produced on all the boronized specimens. Comparison using as-received DSS with coarse microstructure also was performed. The overall results from the study showed that the SPB process can produce a very hard surface and significantly improve the surface properties of DSS.

Jauhari, Iswadi; Yusof, Hanis Ayuni Mohd; Rozali, Shaifulazuar; Ogiyama, Hiroyuki

384

Skin temperature perturbations induced by surface layer turbulence above a grass surface  

NASA Astrophysics Data System (ADS)

High-frequency (5 Hz) atmospheric surface layer (ASL) turbulent velocity (u') and infrared skin temperature perturbations (T's) were measured above a grass-covered forest clearing and analyzed for cloud free conditions. These measurements were used to investigate mechanisms responsible for the production of large short-lived T's perturbations caused by rapid excursions in u'. To quantify the effects of u' on rapid surface cooling, wavelet spectra of u' and T's and cospectra of u'T's were computed. The u' wavelet power spectra were then analyzed using Townsend's [1961, 1976] hypothesis. Townsend's hypothesis states that ASL eddy motion can be decomposed into an active component, which is a function of the ground shear stress (u*) and height (z) above the zero plane displacement, and an inactive component, which is produced in the atmospheric boundary layer (ABL) outer region. A -1 power law in the u' power spectrum was used as a signature for inactive eddy motion. Therefore the -1 power law was used to identify wavenumber ranges (about 1.5 decades) associated with inactive eddy motion. The measured T's wavelet spectra and u'T's cospectra identified with this wavenumber range demonstrate that much of the T's energy and are due to inactive eddy motion, where the angle brackets indicate time averaging. Hence, in contrast to the laboratory experiments of Owen and Thomson [1963], it is argued that skin temperature perturbations at the canopy-atmosphere interface of a grass-covered surface (small thermal inertia) are strongly dependent on the inactive eddy motion produced in the outer layer of the ABL.

Katul, Gabriel G.; Schieldge, John; Hsieh, Cheng-I.; Vidakovic, Brani

1998-05-01

385

Characterization of silane layers on modified stainless steel surfaces and related stainless steel-plastic hybrids  

NASA Astrophysics Data System (ADS)

The aim of this work was to characterize silane layers on the modified stainless steel surfaces and relate it to the adhesion in the injection-molded thermoplastic urethane-stainless steel hybrids. The silane layers were characterized with scanning electron microscope and transmission electron microscope, allowing the direct quantization of silane layer thickness and its variation. The surface topographies were characterized with atomic force microscope and chemical analyses were performed with X-ray photoelectron spectroscopy. The mechanical strength of the respective stainless steel-thermoplastic urethane hybrids was determined by peel test. Polishing and oxidation treatment of the steel surface improved the silane layer uniformity compared to the industrially pickled surface and increased the adhesion strength of the hybrids, resulting mainly cohesive failure in TPU. XPS analysis indicated that the improved silane bonding to the modified steel surface was due to clean Fe 2O 3-type surface oxide and stronger interaction with TPU was due to more amino species on the silane layer surface compared to the cleaned, industrially pickled surface. Silane layer thickness affected failure type of the hybrids, with a thick silane layer the hybrids failed mainly in the silane layer and with a thinner layer cohesively in plastic.

Honkanen, Mari; Hoikkanen, Maija; Vippola, Minnamari; Vuorinen, Jyrki; Lepistö, Toivo; Jussila, Petri; Ali-Löytty, Harri; Lampimäki, Markus; Valden, Mika

2011-09-01

386

Viscous dissipation effects on thermophoretically augmented aerosol particle transport across laminar boundary layers  

NASA Astrophysics Data System (ADS)

The effect of viscous dissipation on mass transport across nonisothermal low-mass-loading laminar boundary layers of dusty gas is investigated theoretically by means of numerical simulations. The derivation of the model is outlined, and numerical results are presented in extensive graphs and characterized in detail. The dissipation effects are found to be significant, increasing total particle-deposition rates; the intensity of the effects depends on the ratio of wall temperature to mainstream static temperature.

Gokoglu, S. A.; Rosner, D. E.

1985-12-01

387

Observations of the sensitivity of beam attenuation to particle size in a coastal bottom boundary layer  

NASA Astrophysics Data System (ADS)

The goal of this study was to test the hypothesis that the aggregated state of natural marine particles constrains the sensitivity of optical beam attenuation to particle size. An instrumented bottom tripod was deployed at the 12-m node of the Martha's Vineyard Coastal Observatory to monitor particle size distributions, particle size-versus-settling-velocity relationships, and the beam attenuation coefficient (cp) in the bottom boundary layer in September 2007. An automated in situ filtration system on the tripod collected 24 direct estimates of suspended particulate mass (SPM) during each of five deployments. On a sampling interval of 5 min, data from a Sequoia Scientific LISST 100x Type B were merged with data from a digital floc camera to generate suspended particle volume size distributions spanning diameters from approximately 2 ?m to 4 cm. Diameter-dependent densities were calculated from size-versus-settling-velocity data, allowing conversion of the volume size distributions to mass distributions, which were used to estimate SPM every 5 min. Estimated SPM and measured cp from the LISST 100x were linearly correlated throughout the experiment, despite wide variations in particle size. The slope of the line, which is the ratio of cp to SPM, was 0.22 g m-2. Individual estimates of cp:SPM were between 0.2 and 0.4 g m-2 for volumetric median particle diameters ranging from 10 to 150 ?m. The wide range of values in cp:SPM in the literature likely results from three factors capable of producing factor-of-two variability in the ratio: particle size, particle composition, and the finite acceptance angle of commercial beam-transmissometers.

Hill, P. S.; Boss, E.; Newgard, J. P.; Law, B. A.; Milligan, T. G.

2011-02-01

388

Modelling of the solar wind interaction with the Moon: Magnetic anomaly region and Debye sheath layer near the surface  

NASA Astrophysics Data System (ADS)

The recent lunar missions have shown that the solar wind interaction with the Moon is more complex than anticipated before and scientifically highly interesting, as shown by new in situ plasma, neutral atom and magnetic field observations. Especially, an unexpectedly high fraction of the incident solar wind protons is reflected from the surface, and even larger fraction at the location of lunar magnetic anomalies. This effect has been observed both by measuring deviated solar wind flow near the magnetic anomalies and by observing decreased flux of energetic neutral hydrogen atoms, H-ENAs, from the surface region of strong magnetic anomalies [1, 2, 3]. These global scale processes affect the properties of plasma near the lunar surface. Consequently, also physical processes at much smaller spatial scale, within the Debye sheath layer, where the electric potential of the surface and near surface region are controlled by photoelectrons and solar wind particles, are affected. In this work we use two numerical kinetic simulation models developed to study the solar wind interaction with the Moon: (1) a local 3-D hybrid model (HYBMoon) to study a plasma region near lunar magnetic anomaly and (2) a full kinetic 1-D electrostatic Particle-In-Cell PIC model (HYB-es) to study the Debye layer a few meters above the surface. Both models are part of the HYB planetary plasma modelling platform developed at the Finnish Meteorological Institute. In the hybrid model ions are modelled as particles while electrons form a charge neutralizing massless fluid. In the PIC simulation both ions and electrons are modelled as particles. In the presentation we will show results based on these models.

Kallio, E.; Jarvinen, R.; Dyadechkin, S.; Wurz, P.; Barabash, S.; Rantala, A.; Alho, M.

2012-09-01

389

Sensitivity Tests of a Surface-Layer Windflow Model to Effects of Stability and Vegetation.  

National Technical Information Service (NTIS)

This study examines the sensitivity of surface-layer windflow over gently rolling terrain to different stability conditions, both with and without the effects of vegetation used to modify terrain heights and determine surface roughness. The numerical mode...

J. M. Lanicci

1985-01-01

390

Effect of Mass Transport Boundary Layers on the Ellipsometry of Surfaces.  

National Technical Information Service (NTIS)

The effect of mass-transport boundary layers, that are often associated with surface reactions proceeding at high rates, on ellipsometer measurements of the underlying surface were investigated for typical transport conditions in liquids. The effect can b...

C. G. Smith

1975-01-01

391

Superconductivity of the surface layers of the doped PbTe:Eu crystals  

NASA Astrophysics Data System (ADS)

We present evidence of superconductivity of the surface layers of PbTe crystals grown from melt and doped with Eu during growth. We have studied two different type of the powder samples made out of the surface layer and from bulk of the PbTe:Eu ingots. The magnetization in the range of magnetic field 0-5 T and the magnetic susceptibility (MS) in the temperature range 1.7-400 K were investigated. At low temperatures, a strong diamagnetism of the surface layers of the PbTe:Eu ingot is observed whereas at high temperatures a transition to strong paramagnetism takes place. This effect is attributed to the transition of the PbTe:Eu surface layers to state of superconductivity at low temperature. The superconductivity of the doped surface layers is explained by formation of the Pb-based inclusions within the ingot surface.

Zayachuk, D. M.; Mikityuk, V. I.; Shlemkevych, V. V.; Kaczorowski, D.; Ilyina, O. S.

2012-12-01

392

Layer-by-layer coating of bacteria with noble metal nanoparticles for surface-enhanced Raman scattering  

Microsoft Academic Search

A simple layer-by-layer method to coat the bacterial cells with gold and silver nanoparticles (AuNPs and AgNPs) for the acquisition\\u000a of surface-enhanced Raman scattering (SERS) spectra is reported. First, the bacteria cell wall is coated with poly (allylamine\\u000a hydrochloride) (PAH), a positively charged polymer, and then with citrate reduced Au or AgNPs. In order to increase the stability\\u000a of the

Mehmet Kahraman; Alsu I. Zamaleeva; Rawil F. Fakhrullin; Mustafa Culha

2009-01-01

393

Nano-tube-like surface structure in graphite particles and its formation mechanism: A role in anodes of lithium-ion secondary batteries  

Microsoft Academic Search

Nano-structures on the surface of graphite based carbon particles have been investigated by means of high resolution transmission electron microscopy. The surfaces consist of ``closed-edge'' structures in a similar manner as carbon nano-tube. That is, they are composed of coaxial carbon tubes consisting of adequate coupling of graphite layer edges. These graphite particles are chemically stable and, therefore, applicable for

K. Moriguchi; S. Munetoh; M. Abe; M. Yonemura; K. Kamei; A. Shintani; Y. Maehara; A. Omaru; M. Nagamine

2000-01-01

394

A simple model of the atmospheric boundary layer; sensitivity to surface evaporation  

Microsoft Academic Search

A simple formulation of the boundary layer is developed for use in large-scale models and other situations where simplicity is required. The formulation is suited for use in models where some resolution is possible within the boundary layer, but where the resolution is insufficient for resolving the detailed boundary-layer structure and overlying capping inversion. Surface fluxes are represented in terms

I B Troen; L. Mahrt

1986-01-01

395

The Adaptation of the Atmospheric Boundary Layer to a Change in Surface Roughness  

Microsoft Academic Search

The adaptation of the atmospheric boundary layer to a change in the underlying surface roughness is an interesting problem and hence much research, theoretical, experimental, and numerical, has been undertaken. Within the atmospheric boundary layer an accurate numerical model for the turbulent properties of the atmospheric boundary layer needs to be implemented if physically realistic results are to be obtained.

S. D. Wright; L. ELLIOTT; D. B. INGHAM; M. J. C. HEWSON

1998-01-01

396

Chlorophyll Content Observations of the Near-Surface Scattering Layers in the Mediterranean Sea  

Microsoft Academic Search

In several areas of the Mediterranean Sea near-surface sound-reflecting layers have been studied. The amount of total pigment occurring in these layers has been determined. Since these layers occur near the basis of the euphotic zone, the degree of degradation of the pigments has been determined by a fluorimetric method. An increase in total pigment has been noticed in the

Duilio Lausi

1968-01-01

397

Turbulent Boundary Layers Over Rigid and Moving Wavy Surfaces  

Microsoft Academic Search

A numerical solution is obtained for fully developed turbulent flow over small amplitude sinusoidal wavy surfaces. The cases considered are for both rigid and flexible surfaces. For the rigid surface case, the numerical solution indicated no drag reduction. On the contrary, the total drag of such a surface is more than the drag of an equivalent flat plate. The predictions

Tapan Kumar Sengupta

1984-01-01

398

Modeling aerosol surface chemistry and gas-particle interaction kinetics with K2-SURF: PAH oxidation  

NASA Astrophysics Data System (ADS)

Atmospheric aerosols are ubiquitous in the atmosphere. They have the ability to impact cloud properties, radiative balance and provide surfaces for heterogeneous reactions. The uptake of gaseous species on aerosol surfaces impacts both the aerosol particles and the atmospheric budget of trace gases. These subsequent changes to the aerosol can in turn impact the aerosol chemical and physical properties. However, this uptake, as well as the impact on the aerosol, is not fully understood. This uncertainty is due not only to limited measurement data, but also a dearth of comprehensive and applicable modeling formalizations used for the analysis, interpretation and description of these heterogeneous processes. Without a common model framework, comparing and extrapolating experimental data is difficult. In this study, a novel kinetic surface model (K2-SURF) [Ammann & Pöschl, 2007; Pöschl et al., 2007] was used to describe the oxidation of a variety of polycyclic aromatic hydrocarbons (PAHs). Integrated into this consistent and universally applicable kinetic and thermodynamic process model are the concepts, terminologies and mathematical formalizations essential to the description of atmospherically relevant physicochemical processes involving organic and mixed organic-inorganic aerosols. Within this process model framework, a detailed master mechanism, simplified mechanism and parameterizations of atmospheric aerosol chemistry are being developed and integrated in analogy to existing mechanisms and parameterizations of atmospheric gas-phase chemistry. One of the key aspects to this model is the defining of a clear distinction between various layers of the particle and surrounding gas phase. The processes occurring at each layer can be fully described using known fluxes and kinetic parameters. Using this system there is a clear separation of gas phase, gas-surface and surface bulk transport and reactions. The partitioning of compounds can be calculated using the flux values between the layers. By describing these layers unambiguously, the interactions of all species in the system can be appropriately modeled. In describing the oxidation of PAHs, the focus was on the interactions between the sorption layer and quasi-static surface layer. The results from a variety of published experimental studies [Pöschl et al., 2001; Kahan et al., 2006; Kwamena et al., 2004, 2006, 2007; Mmereki and Donaldson, 2003; Mmereki et al., 2004; Dubowski et al., 2004; Donaldson et al., 2005; Segal-Rosenheimer and Dubowski, 2007] were analyzed and compared utilizing K2-SURF. The heterogeneous reaction of PAH and O3 are found to follow a Langmuir-Hinshelwood mechanism, in which ozone first absorbs to the surface and then reacts with PAH. The Langmuir equilibrium constants and second-order-rate coefficients of surface reaction were estimated. In PAH/O3/solid substrate system, they showed similar reaction rate (×10), but large difference (×1000) in adsorption. The mean residence time and adsorption enthalpy were estimated for O3 at the surface of substrates, suggesting the chemisorption of O3 molecules or O atoms, respectively. Initial uptake coefficients of O3 under different conditions were also investigated. The observed dependence on gas-phase O3 concentration was well explained with K2-SURF model in five-order range. In addition, competitive adsorption of other gas phase species (NO2, H2O) was well described by the model. Possible mechanism of PAH degradation system and atmospheric implications are discussed.

Shiraiwa, M.; Garland, R.; Pöschl, U.

2009-04-01

399

A general analytical equation for phase diagrams of an N-layer ferroelectric thin film with two surface layers  

NASA Astrophysics Data System (ADS)

Within the framework of effective-field theory with correlations, the phase diagrams of an N-layer ferroelectric thin film with two surface layers are studied by the differential operator technique based on the spin-1/2 transverse Ising model. A general analytical equation for the phase diagram of a ferroelectric thin film with arbitrary layer number as well as exchange interactions and transverse fields is derived, and then the effects of exchange interactions and transverse fields on phase diagrams are discussed for an arbitrary layer number N. Meanwhile, the crossover features, from the ferroelectric-dominant phase diagram (FPD) to the paraelectric-dominant phase diagram (PPD), for various parameters of an N-layer ferroelectric thin film with two surface layers are investigated. As a result, an N-independent common intersection point equation is obtained, and the three-dimensional curved surfaces for the crossover values are constructed. In comparison with the usual mean-field approximation, the differential operator technique with correlations reduces to some extent the ferroelectric features of a ferroelectric thin film.

Lu, Z. X.; Teng, B. H.; Rong, Y. H.; Lu, X. H.; Yang, X.

2010-03-01

400

TASTRAK spectroscopy of polonium-210 alpha-particle activity at bone surfaces: Evidence for a concentrated surface deposit less than 3 {mu}m deep  

SciTech Connect

The technique of {alpha}-particle spectroscopy by CR-39 type TASTRAK plastic has been used to study the depth distribution of natural {alpha}-particle emitters at the surface of human bone. The predominant component of this {alpha}-particle activity was {sup 210}Po supported by {sup 210}Pb, although a smaller activity of {sup 226}Ra was also detected. Autopsy samples of human femur and cranium were obtained from subjects age 63 to 86. Both cortical and trabecular surfaces were analyzed. The results indicate that {sup 210}Pb-supported {sup 210}Po is concentrated at the surfaces of human bone from elderly subjects, in a narrow band 3 {mu}m deep or less, by a factor of about four. As a result, the {alpha}-particle dose to the nuclei of cells lining bone surfaces is around 1.8 times greater than that calculated for a uniform volume distribution. Polonium-210 activity indicates the distribution of {sup 210}Pb, and of stable lead, received by continuous intake throughout life at a very low level. A persistent bone surface concentration of lead and other osteotropic metals may be associated with the hypermineralized layer about 1 {mu}m thick which occurs at the surface of resting bone mineral. 31 refs., 9 figs., 3 tabs.

Salmon, P.L.; Henshaw, D.L.; Keitch, P.A.; Allen, J.E.; Fews, A.P. [Bristol Univ. (United Kingdom)

1994-10-01

401

Electromotive force measurements in the combustion wave front during layer-by-layer surface laser sintering of exothermic powder compositions.  

PubMed

Electric potentials arise between the combustion wave front and final products during layer-by-layer surface laser sintering of exothermic powder compositions (Ni-Ti, Ni-Al, Ti-Al). By using an analog-digital-analog converter to control the laser movement and hence the exothermic reaction itself, we show that near optimal conditions can be obtained for the formation of layered 3D articles. Comparative results of the structural-phase transformations that occur during laser-controlled SHS in related reaction-capable compositions are also presented. PMID:19421554

Shishkovskiy, Igor V; Morozov, Yury G; Kuznetsov, Maxim V; Parkin, Ivan P

2009-03-06

402

Exploratory investigation of the effect of porous surfaces on hypersonic turbulent boundary layers  

Microsoft Academic Search

Four different test surfaces were studied to determine the effect of porous walls on the characteristics of a hypersonic turbulent flat-plate boundary layer. The investigation was an attempt to decrease the surface shear of the boundary layer by transmitting fluctuating pressure energy through the wall and absorbing it in a cavity beneath the wall. Pitot surveys were made at two

R. D. Watson

1979-01-01

403

A multi-layer finite element model of the surface EMG signal  

Microsoft Academic Search

The influence of skin, adipose tissue and bone on the rate of decay of the surface EMG signal around the limb was explored using a new finite element model. Replacing the outer layer of a homogeneous muscle model with a layer of highly resistive tissue, such as skin or fat, results in an increase In the surface potential. This also

M. Lowery; N. Stoykov; A. Taflove; T. Kuiken

2001-01-01

404

Method and Apparatus for Removing the Surface Layer from a Concrete Object.  

National Technical Information Service (NTIS)

A method and an apparatus are disclosed for removing the surface layer from a concrete object. The method consists of providing a hole having a circular wall in the surface layer of the object, the hole being at least as deep as the thickness of the surfa...

C. H. Allen

1978-01-01

405

Experimental study on the turbulent boundary layer flow over riblets surface  

Microsoft Academic Search

The laser Doppler velocimeter (LDV) and hydrogen bubble flow visualization techniques have been used to measure the characteristics of turbulent boundary layer flow over riblets surface and to observe its coherent structure in the near wall region. The experimental results indicate that, in comparison with the turbulent boundary layer flow over a smooth surface, greater values are obtained for the

Jin-jun Wang; Shi-long Lan; Guang Chen

2000-01-01

406

Charge effects on the hindered transport of macromolecules across the endothelial surface glycocalyx layer.  

PubMed

A fluid mechanical and electrostatic model for the transport of solute molecules across the vascular endothelial surface glycocalyx layer (EGL) was developed to study the charge effect on the diffusive and convective transport of the solutes. The solute was assumed to be a spherical particle with a constant surface charge density, and the EGL was represented as an array of periodically arranged circular cylinders of like charge, with a constant surface charge density. By combining the fluid mechanical analyses for the flow around a solute suspended in an electrolyte solution and the electrostatic analyses for the free energy of the interaction between the solute and cylinders based on a mean field theory, we estimated the transport coefficients of the solute across the EGL. Both of diffusive and convective transports are reduced compared to those for an uncharged system, due to the stronger exclusion of the solute that results from the repulsive electrostatic interaction. The model prediction for the reflection coefficient for serum albumin agreed well with experimental observations if the charge density in the EGL is ranged from approximately -10 to -30 mEq/l. PMID:23380897

Sugihara-Seki, Masako; Akinaga, Takeshi; O-Tani, Hideyuki

2012-01-01

407

Wave energy in surface layers for energy-based damage evaluation  

Microsoft Academic Search

Seismic wave energy in surface layers is calculated based on vertical array records at four sites during the 1995 Hyogo-ken Nambu earthquake by assuming vertical propagation of SH waves. The upward energy generally tends to decrease as it goes up from the base layer to the ground surface particularly in soft soil sites. Theoretical study on 1D multi-layers model to

Takaji Kokusho; Ryuichi Motoyama; Hiroshi Motoyama

2007-01-01

408

Surface Layer Investigation of a Shot-Peened Duplex Stainless Steel Utilizing X-ray Diffraction  

NASA Astrophysics Data System (ADS)

Distributions of residual stresses and microstructure in the surface layers of shot-peened duplex stainless steel (DSS) S32205 were investigated. The results reveal that both compressive residual st