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1

Layer-by-layer assembly of polymersomes and polyelectrolytes on planar surfaces and microsized colloidal particles.  

PubMed

Hybrid polyelectrolyte multilayer systems were fabricated on top of planar surfaces and colloidal particles via layer by layer (LbL) assembly of polystyrene sulphonate (PSS) and polybenzyl methacrylate-block-poly(dimethylamino)ethyl methacrylate (PBzMA-b-PDMAEMA) polymersomes. Polymersomes were prepared by self assembly of PBzMA-b-PDMAEMA copolymer, synthesised by group transfer polymerisation. Polymersomes display a diameter of 270 nm and a shell thickness of 11nm. Assembly on planar surfaces was followed by means of the Quartz Crystal Microbalance with Dissipation (QCM-D) and Atomic Force Microscopy (AFM). Detailed information on the assembly mechanism and surface topology of the polymersome/polyelectrolyte films was thereby obtained. The assembly of polymersomes and PSS on top of silica particles of 500 nm in diameter was confirmed by ?-potential measurements. Confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that polymersome/PSS coated silica particles increase in total diameter up to 3-5?m. This hints toward the formation of densely packed polymersome layers. In addition, CLSM showed that polymersome/PSS films exhibit a high loading capacity that could potentially be used for encapsulation and delivery of diverse chemical species. These results provide an insight into the formation of multilayered films with compartmentalised hydrophilic/hydrophobic domains and may lead to the successful application of polymersomes in surface-engineered colloidal systems. PMID:24594041

Coustet, Marcos; Irigoyen, Joseba; Garcia, Teodoro Alonso; Murray, Richard A; Romero, Gabriela; Susana Cortizo, M; Knoll, Wolfgang; Azzaroni, Omar; Moya, Sergio E

2014-05-01

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

Layer by Layer, Nano-particle "Only" Surface Modification of Filtration Membranes  

NASA Astrophysics Data System (ADS)

Layer by Layer (LbL) deposition using primarily inorganic silica nanoparticles is employed for the modification of polymeric micro and ultrafiltration (MF/UF) membranes to produce thin film composites (TFC) with potential nanofiltration (NF) and reverse osmosis (RO) capabilities.. A variety of porous substrate membranes with different membrane surface characteristics are employed, but exhibiting in common that wicking of water does not readily occur into the pore structure, including polycarbonate track etched (PCTE), polyethersulfone (PES) and sulfonated PES (SPEES) MF/UF membranes. Both spherical (cationic/anionic) and eccentric elongated (anionic) silica nanoparticles are deposited using conditions similar to those reported by Lee et al. Appropriate selection of the pH's for anionic and cationic particle deposition enables the construction of nanoparticle only layers 100--1200 nm in thickness atop the original membrane substrates. The surface layer thickness varies monotonically with the number of bilayers (anionic/cationic deposition cycles) as expected. The deposition process is optimized to eliminate drying induced cracking and to improve mechanical durability via thickness control and post-deposition hydro-thermal treatment. The hydrodynamic permeability of these TFC membranes is measured to evaluate their performance under typical NF operating conditions using dead-end permeation experiments and their performance compared quantitatively with realistic hydrodynamic models, with favorable results. For track etched polycarbonate MF substrates, surface modification causes a permeability reduction of approximately two orders of magnitude with respect to the bare substrates, to values comparable to those for typical commercial NF membranes. Good quantitative agreement with hydrodynamic models with no adjustable parameters was also established for this case, providing indirect confirmation that the LbL deposited surface layers are largely defect (crack) free. Imaging of our TFC membranes after permeation tests confirmed that no significant mechanical damage resulted, indicating integrity and robustness of the LbL deposited surface layers in typical applications. The selectivity of these novel TFC membranes was also tested using standard "rejection" tests normally used to characterize NF and RO membranes for their capabilities in typical applications, such as water softening or desalination. We report the dextran standards molecular weight "cut-off" (MWCO) using mixed dextrans from 1.5 to 500 KDa in dead-end stir cells, and the percentage of rejection of standard bivalent and monovalent salt solutions using steady cross flow permeation experiments. The results confirm rejection of at least 60% of even the smallest dextrans, an estimated dextran MWCO of 20 KDa, and rejection of 10% and 20% for monovalent (NaCl) and bivalent (MgSO4) salts, respectively, for all the TFC membranes studied, while the unmodified membranes showed no rejection capability at all. The work supports that nanoparticle based LbL surface modification of MF/UF membranes can produce filtration quality media for important water purification applications, such as nanofiltration (NF) softening processes, natural organic matter (NOM) elimination and possibly reverse osmosis (RO) desalination.

Escobar-Ferrand, Luis

4

Nanocrystalline Surface Layer on AISI 52100 Steel Induced by Supersonic Fine Particles Bombarding  

NASA Astrophysics Data System (ADS)

Surface treatment of AISI 52100 steel by supersonic fine particles bombarding (SFPB) was studied in this article. The surface topography, morphology of the surface layer, and microhardness distribution of the surface layer have been investigated using a surface profiler system, a scanning electron microscopy (SEM), and a microvickers hardness tester. The microstructure, phase composition, and residual stress distribution of the surface layer in AISI 52100 steel after the SFBP treatment have been characterized by means of x-ray diffraction, SEM, and transmission electron microscopy. The results showed that a nanocrystalline surface (NS) layer was formed on the top surface of the SFBP-treated AISI 52100 steel samples. The NS layer is about 2 ?m in thickness with a surface roughness of R a = 1.2 ?m, R y = 6.7 ?m, R z = 6.0 ?m. Phase transitions occurred in the surface of the SFBP-treated samples. Residual compressive stress is obtained at the surface of the SFBP-treated samples. The maximum value of compressive stress appears at the outermost of the surface, and the affection region of the whole surface is about 60 ?m in thickness. A hardened surface layer has been fabricated in the AISI 52100 steel. The thickness of the hardened surface layer is about 70 ?m. The maximum value of hardness occurs at the depth of 20 ?m from the outermost surface.

Kong, Lingyan; Lao, Yuanxia; Xiong, Tianying; Li, Tiefan

2013-08-01

5

ISEE particle observations of surface waves at the magnetopause boundary layer  

Microsoft Academic Search

The dual-spacecraft ISEE mission provides a unique opportunity to study the motions of the magnetopause and adjacent boundary layer. By comparing high-time-resolution energetic particle data from ISEE 1 to those of ISEE 2, the velocity and orientation of the inner boundary of the boundary layer can be determined. Two cases are presented. In one, tailward propagating sinusoidally shaped surface waves

D. Couzens; G. K. Parks; K. A. Anderson; R. P. Lin; H. Reme

1985-01-01

6

Formation of the Spectrum of Sizes of Aerosol Particles in the Surface Layer of the Atmosphere.  

National Technical Information Service (NTIS)

A study of the spectrum of sizes of aerosol particles in the surface layer of the atmosphere which was carried out recently in the Soviet Union. It was found that in areas where the air is clear and there is high relative humidity, there is a multimodal d...

L. S. Ivlev

1974-01-01

7

Immunoevasive protein (IEP)-containing surface layer covering polydnavirus particles is essential for viral infection.  

PubMed

Polydnaviruses (PDVs) are unique symbiotic viruses associated with parasitoid wasps: PDV particles are injected into lepidopteran hosts along with the wasp eggs and express genes that interfere with aspects of host physiology such as immune defenses and development. Recent comparative genomic studies of PDVs have significantly improved our understanding of their origin as well as the genome organization. However, the structural features of functional PDV particles remain ambiguous. To clear up the structure of Cotesia kariyai PDV (CkPDV) particles, we focused on immunoevasive protein (IEP), which is a mediator of immunoevasion by the wasp from the encapsulation reaction of the host insect's hemocytes, because it has been demonstrated to be present on the surface of the virus particle. We discovered that IEP tends to polymerize and constitutes a previously unidentified thin surface layer covering CkPDV particles. This outermost surface layer looked fragile and was easily removed from CkPVD particles by mechanical stressors such as shaking, which prevented CkPDV from expressing the encoded genes in the host target tissues such as fat body or hemocytes. Furthermore, we detected IEP homologue gene expression in the wasp's venom reservoirs, implying IEP has another unknown biological function in the wasp or parasitized hosts. Taken together, the present results demonstrated that female C. kariyai wasps produce the fragile thin layer partly composed of IEP to cover the outer surfaces of CkPDV particles; otherwise, they cannot function as infectious agents in the wasp's host. The fact that IEP family proteins are expressed in both venom reservoirs and oviducts suggests an intimate relationship between both tissues in the development of the parasitism strategy of the wasp. PMID:24184953

Furihata, Shunsuke; Tanaka, Kohjiro; Ryuda, Masasuke; Ochiai, Masanori; Matsumoto, Hitoshi; Csikos, Gyorge; Hayakawa, Yoichi

2014-01-01

8

Effect of Plasma-Polymerized Layer Formed on a Surface of Titanium Dioxide Particle on Its Photocatalytic Activity  

Microsoft Academic Search

If TiO2 particles are used as components of paint without any surface modification, binding resin of the paint will be easily decomposed by the photocatalytic activity of the particles. In this work, plasma polymerization of octamethylcyclotetrasiloxane as a siloxane monomer is tried to form thin layer stable to the photocatalytic activity on the surface of TiO2 particles. The plasma-polymerized layer

Kenji Yamada; Naoko Iwasawa; Tatsuhiko Sonoda; Hirokazu Yamane; Shigenori Matsushima; Hiroyuki Nakamura

2008-01-01

9

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

Microsoft Academic Search

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

L. T. Iraci; P. H. Deng

2007-01-01

10

Compliant layer chucking surface  

DOEpatents

A method and apparatus are described wherein a thin layer of complaint material is deposited on the surface of a chuck to mitigate the deformation that an entrapped particle might cause in the part, such as a mask or a wafer, that is clamped to the chuck. The harder particle will embed into the softer layer as the clamping pressure is applied. The material composing the thin layer could be a metal or a polymer for vacuum or electrostatic chucks. It may be deposited in various patterns to affect an interrupted surface, such as that of a "pin" chuck, thereby reducing the probability of entrapping a particle.

Blaedel, Kenneth L. (Dublin, CA); Spence, Paul A. (Pleasanton, CA); Thompson, Samuel L. (Pleasanton, CA)

2004-12-28

11

Stereo digital particle image velocimetry investigation of a free surface mixing layer  

NASA Astrophysics Data System (ADS)

Shear flows in the vicinity of a free surface are a problem with numerous applications, perhaps the most obvious being the wakes of seagoing surface vessels. The flow behind a full-scale ship is extremely complex---so much so that it is frequently more instructive to consider simpler cases highlighting particular elements of the larger problem. To that end, an experimental investigation has been conducted to study the behavior of a turbulent plane mixing layer intersecting a free surface at low Froude number. The local Reynolds number, based on the velocity differential across the layer and the momentum thickness, was approximately 10,000. The technique of Stereoscopic Digital Particle Image Velocimetry (SDPIV) was implemented to obtain instantaneous three-component velocity measurements within planar slices of the steady-state, spatially developing mixing layer flow. Guided by previous studies of the same flow conditions, specific depths were chosen at a single downstream station for investigation---specifically those in and around counter-rotating streamwise vortices known to exist in the mean flow very near the free surface. 3,000 consecutive SDPIV image pairs were recorded at a rate of 15 per second at each location, giving ample data for Reynolds decomposition and spectral analysis of the velocity fields. The present study has found that the anisotropy known to exist in some other free surface flows, such as surface-parallel submerged jets, is also present in the case of the mixing layer. Power spectra of all three velocity components are shown to capture part of the inertial subrange; the isotropic energy cascade seen to be present away from the free surface is also seen to disappear near the surface, as surface-normal velocity fluctuations are severely attenuated. Additionally, a low-frequency spanwise oscillation is deduced from the velocity power spectra and cospectra in the immediate vicinity of the mean streamwise vortices. Not present at all at significant depth, the motions at this frequency are also observed to markedly decrease---in all components---at locations closer to the surface. These observations appear to have both parallels and key differences compared to previously observed meandering of model boat wakes, and the possibility that the oscillation stems from the vortex-pair instability is discussed.

Dooley, Bradley S.

12

Ultrathin films of functional polyelectrolytes on flat surfaces and colloidal particles using the layer-by-layer deposition technique  

Microsoft Academic Search

Layer-by-layer (LbL) self-assembly techniques have been used to prepare ultrathin polymer films with controlled thicknesses and compositions. The technique is based on the alternate adsorption of oppositely charged polyelectrolyte layers on substrates. This dissertation details the investigation of ultrathin films with functional polyelectrolytes coated on flat substrates and colloidal particles. Several systems were investigated including: liquid crystal (LC) photoalignment layers,

Mi-Kyoung Park

2003-01-01

13

Ultrathin films of functional polyelectrolytes on flat surfaces and colloidal particles using the layer-by-layer deposition technique  

NASA Astrophysics Data System (ADS)

Layer-by-layer (LbL) self-assembly techniques have been used to prepare ultrathin polymer films with controlled thicknesses and compositions. The technique is based on the alternate adsorption of oppositely charged polyelectrolyte layers on substrates. This dissertation details the investigation of ultrathin films with functional polyelectrolytes coated on flat substrates and colloidal particles. Several systems were investigated including: liquid crystal (LC) photoalignment layers, photo-crosslinkable permselective membranes, luminescent hollow-shell particles, and conducting polymer colloidal particles. The multilayer films of an azo-polymer and a polycation were utilized to control azimuthal alignment of liquid crystals. Irradiation of a hybrid LC cell with linearly polarized light resulted in in-plane homogeneous LC alignment, which is dependent on the thickness, and irradiation time. The director of the LC molecules was found to be perpendicular to the polarization plane and can be reoriented. The photocross-linkable multilayer membranes comprising poly(acrylic acid) and poly(allyamine hydrochloride) modified with benzophenone groups have been prepared. It was demonstrated that the permeability of the multilayer films can be controlled by the number of layers as well as the UV irradiation time. Furthermore, a "smart" pH-switchable membrane was produced by adjusting the pH of the dipping solution while maintaining stability throughout the cross-linked structure. The membrane showed pH-sensitive permselectivity, that is, the film was permeable to the cationic molecules, but impermeable to the anionic molecules at pH 10 and vise versa at pH 3. Luminescent core-shell particles and hollow capsules were prepared by the LbL deposition of polystyrenesulfonate (PSS) and a water-soluble ionene precursor polymer containing fluorene units (PI) onto spherical colloid particles. Subsequent cross-linking of the PI in the multilayer shell formed luminescent conjugated oligo-fluorenes. Conductive core-shell particles were prepared by the deposition of polyaniline (PANI) and PSS multilayers onto polystyrene (PS) colloidal particles. PSS was used as a polymeric counter-ion for multilayer formation as well as a stabilizer and codopant for PANI. It was found that the PSS/PANI-coated particle is oxidatively more stable due to stabilization of the partially oxidized emeraldine salt by PSS. This dissertation describes unique approaches towards the science of materials design, synthesis and fabrication strategies, ultrathin film and colloid characterization, and development of potential applications.

Park, Mi-Kyoung

14

EVALUATION OF CONDUCTIVE HEAT TRANSFER MECHANISMS BETWEEN AN IMMERSED SURFACE AND THE ADJACENT LAYER OF PARTICLES IN BUBBLING FLUIDIZED BEDS  

Microsoft Academic Search

The evaluation of the heat transfer coefficient hwp between a heat exchanging surface immersed in a gas fluidized bed and the adjacent layer of dense phase particles is analyzed in this contribution. Gas convective and radiant effects are not included in the present analysis.The inclusion of hwp, or an equivalent formation, in mechanistic models describing heat transfer has been necessary

G. D. MAZZA; N. J. MARIANI; G. F. BARRETO

1997-01-01

15

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

16

Aerosol Measurements in the Atmospheric Surface Layer at L'Aquila, Italy: Focus on Biogenic Primary Particles  

NASA Astrophysics Data System (ADS)

Two year measurements of aerosol concentration and size distribution (0.25 ?m < d < 30 ?m) in the atmospheric surface layer, collected in L'Aquila (Italy) with an optical particle counter, are reported and analysed for the different modes of the particle size distribution. A different seasonal behaviour is shown for fine mode aerosols (largely produced by anthropogenic combustion), coarse mode and large-sized aerosols, whose abundance is regulated not only by anthropogenic local production, but also by remote natural sources (via large scale atmospheric transport) and by local sources of primary biogenic aerosols. The observed total abundance of large particles with diameter larger than 10 ?m is compared with a statistical counting of primary biogenic particles, made with an independent technique. Results of these two observational approaches are analysed and compared to each other, with the help of a box model driven by observed meteorological parameters and validated with measurements of fine and coarse mode aerosols and of an atmospheric primary pollutant of anthropogenic origin (NOx). Except in winter months, primary biogenic particles in the L'Aquila measurement site are shown to dominate the atmospheric boundary layer population of large aerosol particles with diameter larger than 10 ?m (about 80 % of the total during summer months), with a pronounced seasonal cycle, contrary to fine mode aerosols of anthropogenic origin. In order to explain these findings, the main mechanisms controlling the abundance and variability of particulate matter tracers in the atmospheric surface layer are analysed with the numerical box-model.

Pitari, Giovanni; Coppari, Eleonora; De Luca, Natalia; Di Carlo, Piero; Pace, Loretta

2014-03-01

17

Application of thin layer activation technique for surface wear studies in Zr based materials using charged particle induced nuclear reactions  

NASA Astrophysics Data System (ADS)

Thin layer activation (TLA) technique has been developed in Zr based alloy materials, e.g., zircaloy II, using 40 MeV ?-particles from Variable Energy Cyclotron Centre at Calcutta. A brief description of the methodology of TLA technique is presented to determine the surface wear. The sensitivity of the measurement of surface wear in zircaloy material is found to be 0.22±0.05 ?m. The surface wear is determined by TLA technique in zircaloy material which is used in pressurised heavy water reactor and the values have been compared with that obtained by conventional technique for the analytical validation of the TLA technique.

Chowdhury, D. P.; Pal, Sujit; Parthasarathy, R.; Mathur, P. K.; Kohli, A. K.; Limaye, P. K.

1998-09-01

18

Molecularly imprinted polydopamine nano-layer on the pore surface of porous particles for protein capture in HPLC column.  

PubMed

Bio-inspired Human Serum Albumin (HSA) imprinted polydopamine nano-layer was produced through oxidative polymerization of dopamine on the pore surface of HSA modified porous silica particles. The coating thickness was controlled by the reaction time and thereby varied within 0-12 nm. The samples were characterized by elemental analysis, FT-IR, DSC, SEM, TEM, TGA, physisorption and thermoporometry. The characterization confirmed the success of evolution and deposition of polydopamine layer on the silica pore surface. Batch rebinding experiment showed that the molecularly imprinted polymer (MIP) with 8.7 nm coating thickness, in comparison with the thinner and thicker coatings, displays the highest uptake of the target protein. The chromatographic evaluation of the materials packed in HPLC columns showed that the HSA imprinted polydopamine offers good mechanical stability and retains practically all the target protein from an HSA solution or human plasma. Affinity of the imprinting column was examined by using Bovine Serum Albumin (BSA) and Immunoglobulin G (IgG) as competitive proteins. The results showed that the template, HSA, was the most adsorbed protein by the imprinted polydopamine layer. PMID:23692917

Nematollahzadeh, Ali; Shojaei, Akbar; Abdekhodaie, Mohammad J; Sellergren, Börje

2013-08-15

19

Removal of residual CuO particles on the post CMP wafer surface of multi-layered copper  

NASA Astrophysics Data System (ADS)

This article introduces the removal technology of CuO particles on the post CMP wafer surface of multi-layered copper. According to the Cu film corrosion curve with different concentrations of H2O2 and the effect curve of time on the growth rate of CuO film, CuO film with the thickness of 220 nm grown on Cu a surface was successfully prepared without the interference of CuCl2-2H2O. Using the static corrosion experiment the type of chelating agent (FA/O II type chelating agent) and the concentration range (10–100 ppm) for CuO removal was determined, and the Cu removal rate was close to zero. The effect of surfactant on the cleaning solution properties was studied, and results indicated that the surfactant has the effect of reducing the surface tension and viscosity of the cleaning solution, and making the cleaning agent more stable. The influence of different concentrations of FA/O I type surfactant and the mixing of FA/O II type chelating agent and FA/O I type surfactant on the CuO removal effect and the film surface state was analyzed. The experimental results indicated that when the concentration of FA/O I type surfactant was 50 ppm, CuO particles were quickly removed, and the surface state was obviously improved. The best removal effect of CuO on the copper wiring film surface was achieved with the cleaning agent ratio of FA/O II type chelating agent 75 ppm and FA/O I type surfactant 50 ppm. Finally, the organic residue on the copper pattern film after cleaning with that cleaning agent was detected, and the results showed that the cleaning used agent did not generate organic residues on the film surface, and effectively removes the organic residue on the wafer.

Yan, Li; Ming, Sun; Xinhuan, Niu; Yuling, Liu; Yangang, He; Hailong, Li; Aochen, Wang; Hongbo, Li

2014-04-01

20

Characterizing the lower log region of the atmospheric surface layer via large-scale particle tracking velocimetry  

NASA Astrophysics Data System (ADS)

As a first step toward characterizing coherent structures within the atmospheric surface layer (ASL), measurements obtained via a large-scale particle tracking velocimetry (LS-PTV) system were validated against wind-measurement station data as well as canonical turbulent boundary layer studies. The LS-PTV system resolves three-dimensional, Lagrangian tracks over a 16 m3 volume. Mean-velocity measurements, as well as vertical and shear Reynolds-stress measurements, generally agreed with wind-measurement station data and Reynolds-stress profiles referenced from literature. The probability distributions for streamwise, spanwise and vertical velocity-fluctuation components appear normally distributed about zero. Furthermore, the probability distributions for all three components of Lagrangian acceleration were exponential and followed the parametrization curve from LaPorta et al. (Lett Nat 409:1017-1019, 2001). Lastly, the vorticity probability distributions were exponential and symmetric about zero, which matches findings from Balint et al. (Fluid Mech 228:53-86, 1991). The vorticity intensity measured by the LS-PTV system was less than values from Priyadarshana et al. (Fluid Mech 570:307-346, 2007), which is attributed to the low spatial resolution. However, the average spacing of 0.5 m between tracer particles is deemed sufficient for the future characterization of vortical structures within the ASL.

Rosi, Giuseppe A.; Sherry, Michael; Kinzel, Matthias; Rival, David E.

2014-05-01

21

Stereo digital particle image velocimetry investigation of a free surface mixing layer  

Microsoft Academic Search

Shear flows in the vicinity of a free surface are a problem with numerous applications, perhaps the most obvious being the wakes of seagoing surface vessels. The flow behind a full-scale ship is extremely complex---so much so that it is frequently more instructive to consider simpler cases highlighting particular elements of the larger problem. To that end, an experimental investigation

Bradley S. Dooley

2005-01-01

22

Diffusion of gaseous products through a particle surface layer in a fluidized bed reactor  

Microsoft Academic Search

This paper examines a solid conversion process during hydrolysis and decomposition of cupric chloride in a thermochemical copper–chlorine (Cu–Cl) cycle of hydrogen production. Reaction rate constants and the time required for complete solid conversion are determined by a shrinking-core model. Diffusion of gaseous reactant occurs through a film surrounding the particle, after which the reactant penetrates and diffuses through a

V. N. Daggupati; G. F. Naterer; K. S. Gabriel

2010-01-01

23

A Method of Measuring Hydrogen Isotopes in Surface Layers of Planetary Soils by Spectroscopy of Recoil Protons in Alpha Particle Elastic Scattering  

Microsoft Academic Search

A theoretical and experimental feasibility study of possible determination of the hydrogen and deuterium concentrations in the surface layers of planetary bodies is presented. The method under study is the recoil proton and deuteron spectrometry of forward scattering in the course of elastic interaction of alpha particles with the nuclei of hydrogen isotopes. The spectra of recoil protons and deuterons

B. N. Korchuganov; G. G. Dol'nikov; M. V. Gerasimov; O. F. Prilutskii; R. Rider; G. Waenke; T. Economou

2004-01-01

24

Particle-particle interactions between layered double hydroxide nanoparticles.  

PubMed

Changes in chemical properties of nanoscale particles include quantum size effect, changes in the cell parameters and lattice symmetry, and surface and interface effects. In the case of layered double hydroxides (LDHs), surface and interface effects dominate for nanoparticles of MgAl LDHs. Using TEM micrographs of nanoparticle-sized LDHs, we have found that the increased number of surface atoms relative to the internal atoms increases the surface-to-surface interparticle attractions. As a result, nanosize LDH particles are able to form continuous oriented films that adhere well to a polar substrate. PMID:16802784

Gursky, Jennifer A; Blough, Sandra D; Luna, Cesar; Gomez, Clarissa; Luevano, Amber N; Gardner, Elizabeth A

2006-07-01

25

The endothelial surface layer  

Microsoft Academic Search

The endothelial lining of blood vessels presents a large surface area for exchange of materials between blood and tissues, and is critically involved in many other processes such as regulation of blood flow, inflammatory responses and blood coagulation. It has long been known that the luminal surface of the endothelium is lined with a glycocalyx, a layer of membrane-bound macromolecules

A. R. Pries; T. W. Secomb; P. Gaehtgens

2000-01-01

26

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

27

Protein Surface Layers of Bacteria.  

National Technical Information Service (NTIS)

On the outer surface, many genera of bacteria assemble layers composed of repetitive, regularly aligned, proteinaceous subunits. These layers, essentially two-dimensional paracrystalline arrays, are usually the outer molecular layer of the organism and so...

J. Smit

1986-01-01

28

The Martian surface layer  

NASA Technical Reports Server (NTRS)

The global characteristics of the Martian surface layer are discussed on the basis of thermal, albedo, color, and radar data for the region between approximately 60 deg S and 60 deg N. Thermal data reveal the presence of large low- and high-inertia regions of the northern hemisphere, with much of the south covered by material of moderate inertia. There is a strong anticorrelation between inertia and albedo, a correlation between inertia and rock abundance, and, over much of the planet, a correlation of radar-derived density with inertia. Viking Orbiter color data indicate the presence of three major surface materials: low-inertia, bright-red material that is presumably dust; high-inertia, dark-grey material interpreted to be lithic material mixed with palagonitelike dust; and moderate-inertia, dark-red material that is rough at subpixel scales and interpreted to be indurated. Observations from the Viking landing sites show rocks, fines of varying cohesion and crusts. These sites have indications of aeolian erosion and deposition in the recent past.

Christensen, Philip R.; Moore, Henry J.

1992-01-01

29

The neutral surface layer above rough surfaces  

NASA Astrophysics Data System (ADS)

It is generally accepted that turbulent fluxes (momentum and scalar fluxes) are approx. constant with height above horizontal surfaces with low roughness. But what will happen when the roughness sub-layer is large as found over cities, forests and rough seas? In a study of the kinematic structure of the near neutral atmospheric surface layer, Högström, Hunt and Smedman, 2002, it was demonstrated that a model with detached eddies from above the surface layer impinging on to the surface (Hunt and Morison, 2000) could explain some of the observed features in the neutral atmospheric boundary layer. Thus the detached eddy model proved successful in explaining the dynamic structure of the near neutral atmospheric surface layer, especially the shape of the spectra of the wind components and scalars and corresponding fluxes. Here we make the hypothesis that the detached-eddy model can also be used to explain the experimental results related to the 3-dimensional turbulence structure above rough surfaces. Measurements are taken both over land (grass and forest) and over sea (Baltic Sea and hurricane Fabian in the Atlantic) above the roughness sub-layer. Analysis of the turbulence structure shows a striking similarity between the different sites. Hunt, J.C.R and Morrison, J.F., 2000: Eddy structure in turbulent boundary layers, Euro. J. Mech. B-Fluids, 19, 673-694. Högström, U., Hunt, J.C.R., and Smedman, A., 2002: Theory and measurements for turbulence spectra and variances in the atmospheric neutral surface layer, Bound.-Layer Meteorol., 103,101-124.

Smedman, Ann-Sofi; Sahlee, Erik

2014-05-01

30

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

31

Boundary layers in dilute particle suspensions  

NASA Astrophysics Data System (ADS)

Boundary layers in dilute particle suspensions have been found to have a number of interesting features. The development of a singularity at the wall has recently been found to be common to many of these flows, ootnotetextSee Foster, Duck & Hewitt, J. Fluid Mech. 474 (2003) and Duck, Hewitt & Foster, J. Fluid Mech. 514, (2004) and we note here that Falkner-Skan-type boundary layers (layers with `edge' velocity proportional to x^m) and the boundary layer under a linearly decelerating flow ootnotetextHowarth (1934) also break down at the wall in the absence of gravity, but can be singularity-free for heavy particles. In addition, we find that matching of the Falkner-Skan profile to an outer flow is problematic for some values of m, though the case most studied heretofore---the Blasius case (for m=0)---does not feature this difficulty. Finally, a boundary layer that does not develop a singularity takes on a the typical Falkner-Skan self-similarity far downstream, in the absence of gravity. For heavy particles, however, gravity causes a constant drift of particles toward the wall, and a constant-thickness far-downstream layer. The far-downstream behavior in a light-particle suspension is different, with a particle-free zone between the wall and a particle `shock' that grows like x^(1-m).

Foster, M. R.; Duck, P. W.; Hewitt, R. E.

2005-11-01

32

Boundary layer effects on particle impaction and capture  

NASA Technical Reports Server (NTRS)

The inertial impaction and deposition of small particles on larger bodies with viscous boundary layers are considered theoretically, in a detailed comment on a paper by Menguturk et al. (1983). Topics addressed include cushion effects, the dimensionless groups corresponding to the diameter range (3-6 microns) examined by Menguturk et al. in a numerical example, analogous effects of particle-gas energy and mass exchange in boundary layers, and the combined effects of particle inertia and diffusion. It is argued that the inertial effects can be characterized in terms of a body, boundary-layer, or sublayer Stokes number. In a reply by Menguturk et al., the focus is on the application of the theoretical model to the erosion of blade surfaces in large gas turbines; the Stokes number is found to be of limited practical value in these cases, because the particle motion is not primarily normal to the blade surfaces.

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

1984-01-01

33

The Martian Surface Boundary Layer  

NASA Technical Reports Server (NTRS)

The acquisition of meteorological data from the surface of Mars by the two Viking Landers and Mars Pathfinder make it possible to estimate atmospheric boundary layer parameters and surface properties at three different locations on the planet. Because the Martian atmosphere is so thin the majority of the solar radiance is converted to heat at the surface. The difference between surface and atmospheric temperature can also constraint surface albedo, thermal inertia, and infrared emissivity. The Mars Pathfinder Atmospheric Structure Instrument/Meteorological package (ASI/MET) was the most capable weather monitoring system ever sent to the surface of another planet to date. One of the prime objectives of the ASI/MET package is to characterize the surface boundary layer parameters, particularly the heat and momentum fluxes, scaling temperature and friction velocity, and estimate surface roughness. Other important boundary layer parameters, such as Richardson Number, Monin-Obukhov length, analysis of turbulence characteristics of wind and temperature, and atmospheric stability class can also be determined from these measurements.

Wilson, G. R.; Joshi, M.

1999-01-01

34

Surface sulfur measurements on stratospheric particles  

NASA Technical Reports Server (NTRS)

The surface chemistries of three particulate samples collected from the lower stratosphere have been determined using a Scanning Auger Microprobe (SAM). These samples are typical of the most abundant natural and anthropogenic particles observed within the stratosphere in the greater-than-2-micron diameter size fraction. Succsessive sputtering and analysis below the first few adsorbed monolayers of all particles shows the presence of a thin (less than 150A) sulfur layer. These sulfur regions probably formed by surface reaction of sulfur-rich aerosols with each particle within the stratosphere. Settling rate calculations show that a typical sphere (10-micron diameter) may reside within the aerosol layer for 20 days and thus provide a qualitative guide to surface sulfur reaction rates.

Mackinnon, I. D. R.; Mogk, D. W.

1985-01-01

35

Particle motion in atmospheric boundary layers of Mars and Earth  

NASA Technical Reports Server (NTRS)

To study the eolian mechanics of saltating particles, both an experimental investigation of the flow field around a model crater in an atmospheric boundary layer wind tunnel and numerical solutions of the two- and three-dimensional equations of motion of a single particle under the influence of a turbulent boundary layer were conducted. Two-dimensional particle motion was calculated for flow near the surfaces of both Earth and Mars. For the case of Earth both a turbulent boundary layer with a viscous sublayer and one without were calculated. For the case of Mars it was only necessary to calculate turbulent boundary layer flow with a laminar sublayer because of the low values of friction Reynolds number; however, it was necessary to include the effects of slip flow on a particle caused by the rarefied Martian atmosphere. In the equations of motion the lift force functions were developed to act on a single particle only in the laminar sublayer or a corresponding small region of high shear near the surface for a fully turbulent boundary layer. The lift force functions were developed from the analytical work by Saffman concerning the lift force acting on a particle in simple shear flow.

White, B. R.; Iversen, J. D.; Greeley, R.; Pollack, J. B.

1975-01-01

36

Layer-by-Layer assembly and redox properties of undoped HPHT diamond particles  

Microsoft Academic Search

The surface properties of undoped diamond particles are investigated by a combination of zeta potential measurements in solution and electrochemical studies in thin layer assemblies. High-Pressure High-Temperature (HPHT) 500nm diamond particles exhibit positive and negative zeta potentials depending on pH. The estimated point of zero zeta potential (pzzp) was 6.6, while mobility measurements provided an average charge per particle of

Wiphada Hongthani; David J. Fermín

2010-01-01

37

Mars Surface Layers in Infrared  

NASA Technical Reports Server (NTRS)

(Released 29 May 2002) Infrared imaging from NASA's Mars Odyssey spacecraft shows signs of layering exposed at the surface in a region of Mars called Terra Meridiani. The brightness levels show daytime surface temperatures, which range from about minus 20 degrees to zero degrees Celsius (minus 4 degrees to 32 degrees Fahrenheit). Many of the temperature variations are due to slope effects, with sun-facing slopes warmer than shaded slopes. However, several rock layers can be seen to have distinctly different temperatures, indicating that physical properties vary from layer to layer. These differences suggest that the environment on this part of Mars varied through time as these layers were formed. The image is a mosaic combining four exposures taken by the thermal emission imaging system aboard Odyssey during the first two months of the Odyssey mapping mission, which began in February 2002. The area shown is about 120 kilometers (75 miles) across, at approximately 358 degrees east (2 degrees west) longitude and 3 degrees north latitude.

2002-01-01

38

Mars Surface Layers in Infrared  

NASA Technical Reports Server (NTRS)

Infrared imaging from NASA's Mars Odyssey spacecraft shows signs of layering exposed at the surface in a region of Mars called Terra Meridiani.

The brightness levels show daytime surface temperatures, which range from about minus 20 degrees to zero degrees Celsius (minus 4 degrees to 32 degrees Fahrenheit). Many of the temperature variations are due to slope effects, with sun-facing slopes warmer than shaded slopes. However, several rock layers can be seen to have distinctly different temperatures, indicating that physical properties vary from layer to layer. These differences suggest that the environment on this part of Mars varied through time as these layers were formed.

The image is a mosaic combining four exposures taken by the thermal emission imaging system aboard Odyssey during the first two months of the Odyssey mapping mission, which began in February 2002. The area shown is about 120 kilometers (75 miles) across, at approximately 358 degrees east (2 degrees west) longitude and 3 degrees north latitude.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The thermal emission imaging system was provided by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. Lockheed Martin Astronautics, Denver, is the prime contractor for the project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and JPL. JPL is a division of the California Institute of Technology in Pasadena.

2002-01-01

39

Particle detection on flat surfaces  

NASA Astrophysics Data System (ADS)

Since 2006 EUV Lithographic tools have been available for testing purposes giving a boost to the development of fab infrastructure for EUV masks. The absence of a pellicle makes the EUV reticles extremely vulnerable to particles. Therefore, the fab infrastructure for masks must meet very strict particle requirements. It is expected that all new equipment must be qualified on particles before it can be put into operation. This qualification requirement increases the need for a low cost method for particle detection on mask substrates. TNO developed its fourth generation particle scanner, the Rapid Nano. This scanner is capable of detecting nanometer sized particles on flat surfaces. The particle detection is based on dark field imaging techniques and fast image processing. The tool was designed for detection of a single added particle in a handling experiment over a reticle sized substrate. Therefore, the Rapid Nano is very suitable for the validation of particle cleanliness of equipment. During the measurement, the substrate is protected against particle contamination by placing it in a protective environment. This environment shields the substrate from all possible contamination source in the Nano Rapid (stages, elevator, cabling). The imaging takes place through a window in the protective cover. The geometry of the protective environment enables large flexibility in substrate shape and size. Particles can be detected on substrates varying from 152 x 152 mm mask substrates to wafers up to 200 mm. PSL particles of 50 nm were detected with signal noise ratio of 26. Larger particles had higher signal noise ratios. By individually linking particles in two measurements the addition of particles can be detected. These results show that the Rapid Nano is capable of detecting particles of 50 nm and larger of a full reticle substrate.

van der Donck, Jacques; Snel, Rob; Stortelder, Jetske; Abutan, Alfred; Oostrom, Sjoerd; van Reek, Sander; van der Zwan, Bert; van der Walle, Peter

2011-03-01

40

Production Rates of Noble Gases in the Near-Surface Layers of Europa by Energetic Charged Particles and the Potential for Determining Exposure Ages  

NASA Technical Reports Server (NTRS)

The surface of Europa is expected to be extremely active, undergoing tectonic and/or tidal geological activity and sputtering/ deposition, as well as impact cratering. Determination of the actual age of the surface at one or more places would greatly simplify trying to sort out what processes are occurring, and at what rate. If there is K present, as the spectral and compositional modeling discussed predict, it should be possible, in principle, to determine K-Ar crystallization ages. Whether or not there is K present, a consideration of the environment suggests we can determine an energetic particle exposure age if we can make in situ measurements of the abundances of major elements and of noble gas isotopes. This requires instrumentation that is within reach of current technology. In this paper, we calculate production rates for noble-gas isotopes in a simplified Europan surface, to quantify the amount of light noble gases produced by exposure to energetic particles.

Swindle, T. D.; Reedy, R. C.; Masarik, J.

2003-01-01

41

Particle simulation of auroral double layers  

NASA Technical Reports Server (NTRS)

Work on the simulation of auroral double layers (DLs) with realistic particle-in-cell models is presented. An early model simulated weak DLs formed in a self-consistent circuit but under conditions subject to the ion-acoustic instability. Recent work has focused on strong DLs formed when currentless jets are injected into a dipole magnetic field.

Smith, Bruce L.; Okuda, Hideo

1987-01-01

42

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

43

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

44

Formation of the Surface Space Charge Layer in Fair Weather  

NASA Astrophysics Data System (ADS)

It is widely known that the positive space charge, caused by electrode effect action, is obtained near surface in fair weather. Space charge density depends on the different local features: meteorological conditions, aerosol particles concentration, convective transfer of the surface layer. Namely space charge determines the local variations of electric field. Space charge could be negative in condition of strong ionization rate in thin air layer near surface. The electrodynamic model, consisting of transfer equations of light ions and nucleuses, generated by interactions between lights ions and aerosol particles, and Poisson equation. The turbulent transfer members, electric field near the surface, the mobility of positive and negative ions, recombination coefficient, ionization rate, the number of elementary charges on the nuclei were took into account in the model equations. The time-space variations of positive and negative small and heavy ions, electric field, electrical conductivity, current density and space charge, depending on aerosol particles concentrations, turbulence and convective transfer ionization rate, aerosol particles size and number of charged on the particles are calculated. The mechanisms of turbulent and convection-turbulent surface layer electrodynamic structure forming in dependence of single and multi-charged aerosol particles for different physical and meteorological conditions are investigated. Increasing of turbulent mixing intensity leads to increasing of character electrode layer thickness, decreasing of space charge density value, decreasing of electric current conductivity value. The electrode effect of the whole layer remains constant. Increasing of aerosol particles concentration leads to decreasing of electrode effect within the whole electrode layer and increasing of electric field values, decreasing of space charge density values and current conductivity density. It was received that increasing of the aerosol particles concentration under weak turbulent mixing leads to increasing of the negative space charge density and its displacement to the surface level. Under severe contamination condition the electrodynamic structure of surface layer is primarily determined by negative space charge, generated by nucleuses. It was received that in case of small aerosol particles the surface layer electrodynamic structure is basically established by single- and double-charged particles. Single-charged and double-charged as triply-charged, fourfold-charged and fivefold-charged aerosol particles primarily affect on electrodynamic structure of the surface layer in case of increasing of aerosol particles size. The local variations of the electric field in different conditions were studied. Theoretical results are in a good agreement with experimental facts.

Redin, Alexander; Kupovykh, Gennady; Boldyreff, Anton

2014-05-01

45

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

46

Air layer on superhydrophobic surface underwater  

Microsoft Academic Search

Sustaining an air layer on superhydrophobic surface is known necessary for the applications of the “air layer effect” underwater on basis of previous literatures. However, the air layer becomes unstable when put underwater and even disappears when the hydraulic pressure increases. Thus much attention has been focused on the sustainability of an air layer on a superhydrophobic surface. This article

Xianliang Sheng; Jihua Zhang

2011-01-01

47

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

48

Optical sensing quantum dot-labeled polyacrolein particles prepared by layer-by-layer deposition technique.  

PubMed

Optical sensing polymer particles with tailored semiconductor nanocrystal (QD) loading are prepared by layer-by-layer deposition technique (LbL). Polyacrolein particles of 1.2 ?m diameter are used as solid support for deposition of hydrophilic CdSe/ZnS nanocrystal/polyelectrolyte multilayers formed by electrostatic interactions. The pH-dependent fluorescence of QDs and pH-dependent conformations of polyelectrolytes, which likely passivate the surface state of nanocrystals, allow a creation of both mono- and multiplex coded polymer particles with pH-dependent fluorescence intensity. Bovine serum albumin (BSA) as outermost layer makes it possible to design the optical sensing polymer particles with reversibly responded fluorescence at pH variations. The fluorescence of such polymer particles with BSA outer layer is sensitive to copper(II) ion while the fluorescence of these particles is practically insensitive to the other divalent cations (Zn(2+), Ca(2+), Ba(2+), Co(2+), Mg(2+)). The detection limit of Cu(2+) is about 15 nM. Adaptation of LbL method to prepare QD-labeled polymer particles with enhanced complexity (e.g. several types of QDs, multiple biofunctionality) is expected to open new opportunities in biotechnological applications. PMID:21377163

Generalova, Alla N; Oleinikov, Vladimir A; Zarifullina, Margarita M; Lankina, Ekaterina V; Sizova, Svetlana V; Artemyev, Michail V; Zubov, Vitali P

2011-05-15

49

Blobtacular: Surfacing particle systems in \\  

Microsoft Academic Search

Figure 1: Left: Blobtacular was used to animate water dripping off a pirate ship in POTC3. Right: A teapot is sprayed with micro-teapots. We have developed a tool for efficient and flexible surfacing of par- ticle systems using various optimized level set techniques and data structures. Smoothed Particle Hydrodynamics (SPH) is a popular technique in production environments since it allows

Ken Museth; Michael Clive; Nafees Bin Zafar

50

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

2006-11-15

51

Effect of cysteamine layer formed on gold surfaces interacting with TiO 2 surfaces  

Microsoft Academic Search

It is investigated that the formation of cysteamine layer on gold surfaces may make an effect on the distribution of either gold particle adsorbed to the TiO2 surface or vice versa with the adjustment of the electrostatic interactions. The atomic force microscope (AFM) was used to measure the surface forces between the surfaces as a function of the salt concentration

Jin-Won Park

2011-01-01

52

Respirable Particle Transport from Surfaces by Shock Waves  

NASA Astrophysics Data System (ADS)

Resuspension of particles from planar surfaces was studied in a shock tube. Respirable particles (aerodyn. diam.<= 5 ?m) and slightly larger non-respirable particles were tested on smooth and rough surfaces at Mach 1.2 to 2.0. Particles of specified size were deposited on substrates of prescribed roughness. Surface roughness and particle-surface adhesion forces were quantified by atomic force microscopy. Alkylthiol self assembled monolayers (SAMs) were applied to precisely control surface roughness and surface chemistry. The advection of particles initially at rest on the surface by the rapidly accelerated flow were measured by Mie scattering. An ultra-high-speed digital camera with pulsed laser sheet illumination enables time-resolved particle transport diagnostics. Although particles are initially swept off a smooth surface with greater ease, cloud propagation speed is higher for a rough surface. At late times the cloud height is greater for a rough surface so that particles end up in a faster region of the boundary layer. Because our respirable and non-respirable particle size distributions overlap, further study is required. Shear-driven Kelvin-Helmholtz vortices clearly visible in some images likely play a prominent role in particle transport.

Truman, C. R.; Vorobieff, P.; Conroy, J.; Wayne, P.; White, R.; Anderson, M.; Kumar, S.

2011-11-01

53

Surface Chemistry in Electrochemical Atomic Layer Processing.  

National Technical Information Service (NTIS)

Atomic layer processing involves the formation and/or etching of materials an atomic layer at a time. Atomic layer epitaxy is the most obvious example, where a thin film of a material is formed an atomic layer at a time. That is, surface limited reactions...

J. L. Stickney

1997-01-01

54

Surface rheology of saponin adsorption layers.  

PubMed

Extracts of the Quillaja saponaria tree contain natural surfactant molecules called saponins that very efficiently stabilize foams and emulsions. Therefore, such extracts are widely used in several technologies. In addition, saponins have demonstrated nontrivial bioactivity and are currently used as essential ingredients in vaccines, food supplements, and other health products. Previous preliminary studies showed that saponins have some peculiar surface properties, such as a very high surface modulus, that may have an important impact on the mechanisms of foam and emulsion stabilization. Here we present a detailed characterization of the main surface properties of highly purified aqueous extracts of Quillaja saponins. Surface tension isotherms showed that the purified Quillaja saponins behave as nonionic surfactants with a relatively high cmc (0.025 wt %). The saponin adsorption isotherm is described well by the Volmer equation, with an area per molecule of close to 1 nm(2). By comparing this area to the molecular dimensions, we deduce that the hydrophobic triterpenoid rings of the saponin molecules lie parallel to the air-water interface, with the hydrophilic glucoside tails protruding into the aqueous phase. Upon small deformation, the saponin adsorption layers exhibit a very high surface dilatational elasticity (280 ± 30 mN/m), a much lower shear elasticity (26 ± 15 mN/m), and a negligible true dilatational surface viscosity. The measured dilatational elasticity is in very good agreement with the theoretical predictions of the Volmer adsorption model (260 mN/m). The measured characteristic adsorption time of the saponin molecules is 4 to 5 orders of magnitude longer than that predicted theoretically for diffusion-controlled adsorption, which means that the saponin adsorption is barrier-controlled around and above the cmc. The perturbed saponin layers relax toward equilibrium in a complex manner, with several relaxation times, the longest of them being around 3 min. Molecular interpretations of the observed trends are proposed when possible. Surprisingly, in the course of our study we found experimentally that the drop shape analysis method (DSA method) shows a systematically lower surface elasticity, in comparison with the other two methods used: Langmuir trough and capillary pressure tensiometry with spherical drops. The possible reasons for the observed discrepancy are discussed, and the final conclusion is that the DSA method has specific problems and may give incorrect results when applied to study the dynamic properties of systems with high surface elasticity, such as adsorption layers of saponins, lipids, fatty acids, solid particles, and some proteins. The last conclusion is particularly important because the DSA method recently became the preferred method for the characterization of fluid interfaces because of its convenience. PMID:21894983

Stanimirova, R; Marinova, K; Tcholakova, S; Denkov, N D; Stoyanov, S; Pelan, E

2011-10-18

55

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

56

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.

57

Deposition of hard surfacing layer by friction surfacing  

Microsoft Academic Search

Although several surfacing processes have been proposed and applied, none has been able to apply a 1 mm thick hard layer. This paper describes fundamental research to establish friction surfacing as a technique for applying a 1 mm thick hard layer.Experiments were run to clarify the effects of operating parameters on surface quality using a conventional friction welder fitted with

T. Shinoda; S. Okamoto; S. Takemoto; Y. Kato; T. Shimizu

1996-01-01

58

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

59

Particle-Surface Interaction Model and Method of Determining Particle-Surface Interactions  

NASA Technical Reports Server (NTRS)

A method and model of predicting particle-surface interactions with a surface, such as the surface of a spacecraft. The method includes the steps of: determining a trajectory path of a plurality of moving particles; predicting whether any of the moving particles will intersect a surface; predicting whether any of the particles will be captured by the surface and/or; predicting a reflected trajectory and velocity of particles reflected from the surface.

Hughes, David W. (Inventor)

2012-01-01

60

Laser treatment of alumina surface with chemically distinct carbide particles  

NASA Astrophysics Data System (ADS)

Laser treatment of pre-prepared alumina tile surface with a carbon film containing a mixture of 3 wt% TiC and 3 wt% B4C hard particles was conducted. Morphological and metallurgical changes at the laser treated surface were examined using optical and electron scanning microscopes, energy dispersive spectroscopy, and X-ray diffraction. Microhardness and fracture toughness of the treated surface were measured together with indentation tests. Residual stress generated at the surface region was determined from the X-ray diffraction data. It was found that TiC and B4C hard particles cause micro-crack formation in the vicinity of hard particles on the surface. This behavior is attributed to the differences between the thermal expansion coefficients of these particles. The laser treated surface is composed of a dense layer with fine sized grains and columnar structures formed below the dense layer. The presence of hard particles enhances the microhardness and lowers the fracture toughness of the surface. The formation of nitride compounds (AlN and AlON) contributes to volume shrinkage in the dense layer. Residual stress formed in the surface region is compressive.

Yilbas, Bekir S.; Ali, Haider

2014-12-01

61

Porous Layers at Glass Surfaces  

Microsoft Academic Search

PREVIOUS investigations have shown that porous modifications of the surfaces of glasses may be formed by the action of liquid water1 and water vapour2. I have now studied the formation of porosity in the surface of grains of soda-lime-silica glass in various conditions.

P. A. Sewell

1968-01-01

62

Volumetric Layer Segmentation Using Coupled Surfaces Propagation  

Microsoft Academic Search

The problem of segmenting a volumetric layer of fl- nite thickness is encountered in several important ar- eas within medical image analysis. Key examples in- clude the extraction of the cortical gray matter of the brain and the left ventricle myocardium of the heart. The coupling between the two bounding surfaces of such a layer provides important information that helps

Xiaolan Zeng; Lawrence H. Staib; Robert T. Schultz; James S. Duncan

63

Effect of induced surface charge of metal particles on particle sizing by resistive pulse sensing technique.  

PubMed

Effect of induced surface charge of metal particles on particle sizing by Resistive Pulse Sensing (RPS) technique is reported in this paper. The relationship between the magnitude of the RPS signal and the applied voltage was experimentally studied with 5?m polystyrene particles and 5?m magnetic particles in a microfluidic chip. It is shown that the magnitude of RPS signal of the magnetic particles is larger than that of the polystyrene particle under the same measuring voltage. This may be understood by the induced thicker electrical double layer (EDL) around the magnetic particles. This effect is important and should be considered when sizing metal particles and other highly-polarizable particles by using the RPS technique. PMID:24703663

Song, Yongxin; Wang, Chengfa; Sun, Runzhe; Pan, Xinxiang; Li, Dongqing

2014-06-01

64

The elasticity of structured surface liquid layers  

Microsoft Academic Search

The notion of “elasticity of structured surface liquid layers” has been introduced and considered in detail for the first\\u000a time. It is shown to be reasonably connected with the thermodynamics of condensed matter, allowing the logical derivation\\u000a of the general equations for the surface tension of liquids and solids which had been impossible before.

V. A. Marichev

2011-01-01

65

Turbulent Boundary Layer Flow over Superhydrophobic Surfaces.  

National Technical Information Service (NTIS)

The objective of this project was to determine whether drag caused by turbulence in boundary layer flow can be reduced through the use of modified surfaces. This study encompassed the testing of four different surfaces: 1) Teflon SLIP, 2) Aluminum SLIP, 3...

A. J. Rydalch

2013-01-01

66

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

67

Electrohydrodynamic removal of particles from drop surfaces  

Microsoft Academic Search

A uniform electric field is used for cleaning drops of the particles they often carry on their surface. In a first step, particles migrate to either the drop's poles or equator. This is due to the presence of an electrostatic force for which an analytical expression is derived. In a second step, particles concentrated near the poles are released into

S. Nudurupati; M. Janjua; P. Singh; N. Aubry

2009-01-01

68

Bottom Boundary Layer Wave Measurements for Particle Studies  

Microsoft Academic Search

Suspended particles, which attenuate light and restrict visibility in moderate depths of the ocean, are commonly resuspended from the bottom by waves. This turbid layer initially consists of fine particles with settling rates of 0.01 mm\\/s that require weeks to settle out. However, the relaxation of the turbid conditions is often only a day or less implying particle settling rates

A. J. Williams

2006-01-01

69

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

70

Limiting diffusion current at rotating disk electrode with dense particle layer.  

PubMed

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. PMID:24089793

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

2013-09-28

71

Generation of alginate gel particles with AuNPs layers by polydimethylsiloxan template  

Microsoft Academic Search

The authors report a feasible and simple microfluidic approach for synthesizing anisotropic gel particles based on template method. By filling arrays of microwells with alginate hydrogel and synthesizing gold nanoparticles (AuNPs) on the gel surface, anisotropic alginate gel particles with single side gold nanoparticles layers were produced in microwells on the polydimethylsiloxan template. AuNPs and the anisotropic feature were characterized

Zhi-Xiao Guo; Meng Zhang; Li-Bo Zhao; Shi-Shang Guo; Xing-Zhong Zhao

2011-01-01

72

Algorithm for Computing Particle/Surface Interactions  

NASA Technical Reports Server (NTRS)

An algorithm has been devised for predicting the behaviors of sparsely spatially distributed particles impinging on a solid surface in a rarefied atmosphere. Under the stated conditions, prior particle-transport models in which (1) dense distributions of particles are treated as continuum fluids; or (2) sparse distributions of particles are considered to be suspended in and to diffuse through fluid streams are not valid.

Hughes, David W.

2009-01-01

73

Interaction forces between particles containing grafted or adsorbed polymer layers.  

PubMed

The interaction forces between particles containing grafted or adsorbed polymer layers have been investigated using rheological and surface force measurements. Polystyrene latex dispersions with grafted poly(ethylene oxide) (PEO) chains (M=2000) were used for the rheological measurements. Results were also obtained for latex dispersions stabilised with adsorbed graft copolymers of poly(methyl methacrylate-methacrylic acid) with methoxy capped PEO chains (M=750). The relative viscosity eta(r)-volume fraction phi curves for the latex dispersions with grafted PEO chains were established for three particle radii of 77.5, 306 and 502 nm. For comparison the eta(r)-phi curve was calculated using the Dougherty-Krieger equation. This allows one to obtain the adsorbed layer thickness delta as a function of phi. The results showed a decrease of delta with increase of phi, which was attributed to the interpenetration and/or compression of the PEO chains on increasing phi. Viscoelastic measurements as a function of phi showed a change from predominantly viscous to predominantly elastic response at a critical volume fraction, which indicated the onset of the strong steric repulsion when the polymer layers begin to overlap. A similar trend was obtained with the latex particles containing adsorbed graft copolymer layers. A scaling law was used to fit the elastic part of the logG'-log phi curve (where G' is the elastic modulus). This fit could be used to estimate the compressibility of the PEO chains. The correlation of the rheology of concentrated sterically stabilised dispersions with interparticle interactions was investigated by measuring the energy-distance curves for the graft copolymer that was adsorbed on smooth mica sheets. Using de Gennes scaling theory, it was possible to calculate the energy of interaction between the polymer layers. The high frequency modulus of the latex dispersions was obtained as a function of the volume fraction and the results were compared with those calculated from the potential of the mean force. The trends in the variation of the modulus with volume fraction were similar for the experimental rheological results and those calculated using the directly measured interaction forces. The above results demonstrated the powerful use of rheological measurements for studying the interaction between sterically stabilised dispersions in concentrated systems. PMID:12818496

Tadros, Tharwat

2003-07-01

74

The structure and magnetic properties of ultrafine iron particles with oxide layer  

SciTech Connect

Ultrafine iron particles (UFIPs) are promising as materials for high-density magnetic recording and ferrofluids because the superparamagnetic state in these particles develops at smaller particle sizes than in conventional magnetic materials. The basic obstacle to producing UFIPs is their high reactivity, which leads to strong oxidation of these particles. Given this, effort is being devoted to extending chemical stabilization to iron particles of the smallest size possible. One possible approach involves the formation of a thin passivating oxide layer on iron particles [1-3], for example, by atmospheric-air oxidation or by oxidation in a special atmosphere. This results in the formation of an interesting structure - an ultrafine particle whose magnetic properties exhibit a marked variation from its center to the surface. The UFIP oxidized at room temperature was shown to consist of an unoxidized {alpha}-Fe core with an average diameter of 110 {Angstrom} and a 45-{Angstrom}-thick oxide layer with a spinel-type structure. The hyperfine magnetic field at the particle core coincides with the field in an infinite sample, whereas in the oxide layer, the average magnetic field was lower. Magnetic interaction between the central region of the UFIP and the oxide layer was found to suppress superparamagnetism and to result in development of a hyperfine structure in the Moessbauer subspectrum of the oxide layer. The observed shape of the Moessbauer spectrum is related to the surface state of the oxide phase and, to some extent, to the presence of defects.

Gavrilyuk, A.G.; Sadykov, R.A. [Vereshchagin Institute of High-Pressure Physics, Moscow (Russian Federation)

1994-12-01

75

Nanomaterial sensing layer based surface acoustic wave hydrogen sensors  

Microsoft Academic Search

Pd-cluster coated, engineered tobacco mosaic virus (TMV) and similarly coated single-walled carbon nanotube (SWNT) particles have been studied for hydrogen detection with the help of surface acoustic wave (SAW) resonators. SAW resonators were coated with these two different nano-structured sensing layers (Pd-TMV and Pd-SWNT) which produced differently useful hydrogen sensor responses. The Pd-TMV coated resonator responded to hydrogen with nearly

krishnan Srinivasan; Stefan Cular; V. R. Bhethanabotla; Sang Yup Lee; Michael T. Harris

2005-01-01

76

Surface shear rheology of saponin adsorption layers.  

PubMed

Saponins are a wide class of natural surfactants, with molecules containing a rigid hydrophobic group (triterpenoid or steroid), connected via glycoside bonds to hydrophilic oligosaccharide chains. These surfactants are very good foam stabiliziers and emulsifiers, and show a range of nontrivial biological activities. The molecular mechanisms behind these unusual properties are unknown, and, therefore, the saponins have attracted significant research interest in recent years. In our previous study (Stanimirova et al. Langmuir 2011, 27, 12486-12498), we showed that the triterpenoid saponins extracted from Quillaja saponaria plant (Quillaja saponins) formed adsorption layers with unusually high surface dilatational elasticity, 280 ± 30 mN/m. In this Article, we study the shear rheological properties of the adsorption layers of Quillaja saponins. In addition, we study the surface shear rheological properties of Yucca saponins, which are of steroid type. The experimental results show that the adsorption layers of Yucca saponins exhibit purely viscous rheological response, even at the lowest shear stress applied, whereas the adsorption layers of Quillaja saponins behave like a viscoelastic two-dimensional body. For Quillaja saponins, a single master curve describes the data for the viscoelastic creep compliance versus deformation time, up to a certain critical value of the applied shear stress. Above this value, the layer compliance increases, and the adsorption layers eventually transform into viscous ones. The experimental creep-recovery curves for the viscoelastic layers are fitted very well by compound Voigt rheological model. The obtained results are discussed from the viewpoint of the layer structure and the possible molecular mechanisms, governing the rheological response of the saponin adsorption layers. PMID:22830458

Golemanov, Konstantin; Tcholakova, Slavka; Denkov, Nikolai; Pelan, Edward; Stoyanov, Simeon D

2012-08-21

77

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 ...

78

Characterization of the Martian Surface Layer  

Microsoft Academic Search

The authors have estimated the diurnal evolution of Monin-Obukhov length, friction velocity, tempera- ture scale, surface heat flux, eddy-transfer coefficients for momentum and heat, and turbulent viscous dissipation rate on the Martian surface layer for a complete sol belonging to the Pathfinder mission. All these magnitudes have been derived from in situ wind and temperature measurements at around 1.3-m height

F RANCISCOVALERO GERMÁNMARTÍNEZ

79

Inclined lidar observations of boundary layer aerosol particles above the Kongsfjord, Svalbard  

NASA Astrophysics Data System (ADS)

An inclined lidar with vertical resolution of 0.4 m was used for detailed boundary layer studies and to link observations at Zeppelin Mountain (474 m) and Ny-Ålesund, Svalbard. We report on the observation of aerosol layers directly above the Kongsfjord. On 29 April 2007, a layer of enhanced backscatter was observed in the lowest 25 m above the open water surface. The low depolarization ratio indicated spherical particles. In the afternoon, this layer disappeared. The ultrafine particle concentration at Zeppelin and Corbel station (close to the Kongsfjord) was low. On 1 May 2007, a drying process in the boundary layer was observed. In the morning, the atmosphere up to Zeppelin Mountain showed enhanced values of the backscatter coefficient. Around noon, the top of the highly reflecting boundary layer decreased from 350 to 250 m. The top of the boundary layer observed by lidar was confirmed by radiosonde data.

Lampert, Astrid; Ström, Johan; Ritter, Christoph; Neuber, Roland; Yoon, Young Jun; Chae, Nam Yi; Shiobara, Masataka

2012-10-01

80

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

81

Particle transfer mechanisms and segregation in turbulent boundary layer  

NASA Astrophysics Data System (ADS)

Particle transfer in the wall region of turbulent boundary layers is dominated by the Coherent Structures (CS) which control the turbulence regeneration cycle and favour particle segregation in the viscous region. We performed pseudo-spectral DNS of vertical channel flow at Re_?=150 and Lagrangian particle tracking to examine turbulent transfer of heavy particles in connection with the CS of the boundary layer. We found that sweeps transfer particles toward the wall and ejections transfer particles away from the wall. However, transfer mechanisms are conditioned by the presence of particles, which, in the case of ejections, are more rarely available since, when in the viscous wall layer, they preferentially accumulate under the low-speed streaks for long times. Following the regeneration cycle for near-wall quasi-streamwise vortices (Brooke and Hanratty, 1993), we found that the coupling of mature vortices with associated newly-born vortices enhances particle trapping in a sediment layer below the low-speed streak and may explain the existence of net wall-directed particle fluxes (turbophoretic drift).

Soldati, Alfredo; Marchioli, Cristian

2001-11-01

82

Nonlinear dynamics of incommensurate surface layers.  

PubMed

We describe analytically the nonlinear dynamics of the incommensurate surface layer ("self-modulated" system) with a spatially periodical structure. In the framework of the Frenkel-Kontorova model the nonlinear excitations of the periodic soliton lattice, such as moving additional kinks and gap solitons, are investigated. PMID:15245083

Kovalev, Alexander S; Gerasimchuk, Igor V; Maugin, Gerard A

2004-06-18

83

Surface state and normal layer effects  

SciTech Connect

In addition to the conducting CuO{sub 2} (S) layers, most high-T{sub c} superconductors also contain other conducting (N) layers, which are only superconducting due to the proximity effect. The combination of S and N layers can give rise to complicated electronic densities of states, leading to quasilinear penetration depth and NMR relaxation rate behavior at low temperatures. Surface states can also complicate the analysis of tunneling and, photoemission measurements. Moreover, geometrical considerations and in homogeneously trapped flux axe possible explanations of the paramagnetic Meissner effect and of corner and ring SQUID experiments. Hence, all of the above experiments could be consistent with isotropic s-wave superconductivity within the S layers.

Klemm, R.A.; Ledvij, M. [Argonne National Lab., IL (United States); Liu, S.H. [Univ. of California, San Diego, CA (United States). Dept. of Physics

1995-08-01

84

Separation of rotavirus double-layered particles and triple-layered particles by capillary zone electrophoresis.  

PubMed

Cell culture derived rotavirus preparations contain a mixture of double-layered particles (DLPs) and triple-layered particles (TLPs). Characterization of rotavirus vaccine products is important to demonstrate a consistent manufacturing process. A capillary zone electrophoresis (CZE) method was developed to separate and quantitate rotavirus DLPs and TLPs in cell lysate samples and CsCl-purified vaccine preparations of each of the five reassortant rotavirus vaccine strains (G1, G2, G3, G4 and P1) contained in the pentavalent rotavirus vaccine, RotaTeq. The CZE electropherograms showed that migration of DLPs and TLPs from both CsCl-purified and cell lysates resulted in a separation distance of approximately 3 min between the two rotavirus particle types. The identification of the peak(s) containing TLPs was confirmed for both CsCl-purified and cell lysate samples by treatment of the samples with 50mM EDTA, which converted TLPs to DLPs. The migration pattern of the DLPs was consistent (23-24 min) among all reassortant strains tested, whether the DLPs were CsCl-purified or from cell lysates. However, the migration pattern of the TLP electropherograms of the reassortant rotavirus strains in cell lysates differed from those of the CsCl-purified reassortant rotavirus strains. In the cell lysate samples, the TLPs of the G1 and G2 reassortant rotavirus strains migrated slower that the corresponding TLPs from the CsCl-purified samples, while the migration time of the TLPs of the G3, G4 and P1 reassortants strains from the cell lysate and CsCl-purified samples appeared similar. Also, the TLPs from the CsCl-purified samples appeared as a defined single peak, while most of the TLPs from the cell lysate samples appeared as a broad peak or as multiple peaks. All the migration patterns were reproducible and consistent. Taking into account reproducibility, objective quantitation, and minimal sample manipulation as well as volume, CZE allowed consistent and quantitative characterization of rotavirus vaccine preparations, which is required for evaluation of vaccine products, including process validation. PMID:20599561

Mathis, Pamela K; Ciarlet, Max; Campbell, Kathryn M; Wang, Shiyi; Owen, Katey Einterz; Ranheim, Todd S

2010-10-01

85

The refraction in the atmospheric surface layer  

NASA Astrophysics Data System (ADS)

An analytical theory of refraction for the atmospheric layer is developed in which the vertical profiles of the refraction are calculated based on the theory of Monin and Obukhov (1954). A similarity parameter is found for the refraction in such conditions. These results are used to clarify the idea of Moroz (1976) that the nearness of the horizon as recorded by the automatic stations on the surface of Venus can be explained by the decrease in the temperature at the very surface of the planet. In addition, several other optical phenomena which occur near the surface of the earth are examined.

Golitsyn, G. S.

1982-12-01

86

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

87

Silicon Surface-Barrier Nuclear Particle Spectrometer  

Microsoft Academic Search

Gold silicon surface-barrier counters which give good resolution at room temperature have been made. Counters from 150 ohm-cm material have given 15-kev (~1\\/4 per cent) resolution for Cm244 (5.801 mev) and Am241 (5.477 mev) alpha particles. A large-area 1-cm2 counter has given 0.7 per cent resolution for Po210 (5.30 mev) alpha particles. The detector has resolved alpha particle groups which

J. L. BLANKENSHIPt; C. J. Borkowski

1960-01-01

88

Characteristics of the Martian atmosphere surface layer  

NASA Technical Reports Server (NTRS)

Elements of various terrestrial boundary layer models are extended to Mars in order to estimate sensible heat, latent heat, and momentum fluxes within the Martian atmospheric surface ('constant flux') layer. The atmospheric surface layer consists of an interfacial sublayer immediately adjacent to the ground and an overlying fully turbulent surface sublayer where wind-shear production of turbulence dominates buoyancy production. Within the interfacial sublayer, sensible and latent heat are transported by non-steady molecular diffusion into small-scale eddies which intermittently burst through this zone. Both the thickness of the interfacial sublayer and the characteristics of the turbulent eddies penetrating through it depend on whether airflow is aerodynamically smooth or aerodynamically rough, as determined by the Roughness Reynold's number. Within the overlying surface sublayer, similarity theory can be used to express the mean vertical windspeed, temperature, and water vapor profiles in terms of a single parameter, the Monin-Obukhov stability parameter. To estimate the molecular viscosity and thermal conductivity of a CO2-H2O gas mixture under Martian conditions, parameterizations were developed using data from the TPRC Data Series and the first-order Chapman-Cowling expressions; the required collision integrals were approximated using the Lenard-Jones potential. Parameterizations for specific heat and binary diffusivity were also determined. The Brutsart model for sensible and latent heat transport within the interfacial sublayer for both aerodynamically smooth and rough airflow was experimentally tested under similar conditions, validating its application to Martian conditions. For the surface sublayer, the definition of the Monin-Obukhov length was modified to properly account for the buoyancy forces arising from water vapor gradients in the Martian atmospheric boundary layer. It was found that under most Martian conditions, the interfacial and surface sublayers offer roughly comparable resistance to sensible heat and water vapor transport and are thus both important in determining the associated fluxes.

Clow, G. D.; Haberle, R. M.

1990-01-01

89

Beta particle monitor for surfaces  

DOEpatents

A beta radiation detector which is capable of reliably detecting beta radiation emitted from a surface. An electrically conductive signal collector is adjustably mounted inside an electrically conductive enclosure which may define a single large opening for placing against a surface. The adjustable mounting of the electrically conductive signal collector can be based on the distance from the surface or on the expected beta energy range. A voltage source is connected to the signal collector through an electrometer or other display means for creating an electric field between the signal collector and the enclosure. Air ions created by the beta radiation are collected and the current produced is indicated on the electrometer or other display means. 2 figs.

MacArthur, D.W.

1997-10-21

90

Lunar particle shadows and boundary layer experiment: Plasma and energetic particles on the Apollo 15 and 16 subsatellites  

NASA Technical Reports Server (NTRS)

The lunar particle shadows and boundary layer experiments aboard the Apollo 15 and 16 subsatellites and scientific reduction and analysis of the data to date are discussed with emphasis on four major topics: solar particles; interplanetry particle phenomena; lunar interactions; and topology and dynamics of the magnetosphere at lunar orbit. The studies of solar and interplanetary particles concentrated on the low energy region which was essentially unexplored, and the studies of lunar interaction pointed up the transition from single particle to plasma characteristics. The analysis concentrated on the electron angular distributions as highly sensitive indicators of localized magnetization of the lunar surface. Magnetosphere experiments provided the first electric field measurements in the distant magnetotail, as well as comprehensive low energy particle measurements at lunar distance.

Anderson, K. A.; Chase, L. M.; Lin, R. P.; Mccoy, J. E.; Mcguire, R. E.

1974-01-01

91

Effect of the Double Layer on the Dielectrophoretic Motion of Particles  

NASA Astrophysics Data System (ADS)

Most suspensions involve the formation of ionic double layers next to the surface of particles. The double layer formed due to the induced-charge on the particle affects its motion even under sinusoidal electric fields through a phenomenon termed as induced-charge electro-osmosis. A method to numerically evaluate the effect of the double layer on the dielectrophoretic motion of particles has been developed. The technique, developed herein, involves a matched asymptotic expansion of the electric field near the particle surface, where the double layer is formed, and is written as a jump-boundary-condition for the electric potential when the thickness of the double layer is small compared to the size of the particle. The developed jump-boundary-condition is amenable to numerical evaluation and has been implemented in an Arbitrary Lagrangian Eulerian based finite element scheme using a discontinuous Galerkin method which naturally permits for such discontinuous boundary conditions in its formulation. The effect of the induced-charge electro-osmosis on the dielectrophoretic motion of particles has been observed using this technique.

Swaminathan, T. N.

2005-11-01

92

Solid-Particle Erosion Behaviour of WC/Ni Composite Clad layers with Different Contents of WC Particles  

NASA Astrophysics Data System (ADS)

We investigated the solid particle erosion behaviour of WC-reinforced Ni-matrix based laser clad layers to improve the performance of engineering components for potential power plant applications. WC-reinforced Ni-matrix based laser clad layers having various compositions of WC (5, 10 and 15wt%) were deposited on austenitic stainless steel substrates. The laser clad layers were characterised using optical and scanning electron microscopy, microhardness testing and air-jet erosion testing. In solid particle erosion studies using the air-jet erosion tester, the set of testing parameters, including air-erodent compositions, erodent particle velocities and impact angles, was selected by using the Taguchi technique. The morphologies of the worn surfaces were used to predict the wear mechanisms. The results of a microstructural examination of the cross-sections of laser clad revealed a good metallurgical bond between the WC-reinforced Ni matrix and the austenitic stainless steel substrate. Dissociation/partial melting/full melting of WC particles was not observed in the laser clad layers. The microhardness value in the laser cladding zone was between 900–2400 VHN, while it was 230–270 VHN on the substrate. The results of erosion wear studies of the WC-Ni laser clad surface revealed that the erosion behaviour of the WC-Ni laser clad is primarily governed by erodent jet velocity followed by impact angle. The erosion does not much depend on the Ni-concentration in the MMC or the erodent feed rate. The wear signature at the erosion wear surface indicated that the erosion was primarily governed by a ductile erosion mechanism followed by the removal of WC particles from the matrix. The erosion resistance of the Ni-clad layer with WC was found to be at least four times higher than that without WC particles. The quantified contribution of various erosion parameters is useful for function-based design of components with extended service life.

Paul, C. P.; Mishra, S. K.; Tiwari, P.; Kukreja, L. M.

2013-09-01

93

Dynamic air layer on textured superhydrophobic surfaces.  

PubMed

We provide an experimental demonstration that a novel macroscopic, dynamic continuous air layer or plastron can be sustained indefinitely on textured superhydrophobic surfaces in air-supersaturated water by a natural gas influx mechanism. This type of plastron is an intermediate state between Leidenfrost vapor layers on superheated surfaces and the equilibrium Cassie-Baxter wetting state on textured superhydrophobic surfaces. We show that such a plastron can be sustained on the surface of a centimeter-sized superhydrophobic sphere immersed in heated water and variations of its dynamic behavior with air saturation of the water can be regulated by rapid changes of the water temperature. The simple experimental setup allows for quantification of the air flux into the plastron and identification of the air transport model of the plastron growth. Both the observed growth dynamics of such plastrons and millimeter-sized air bubbles seeded on the hydrophilic surface under identical air-supersaturated solution conditions are consistent with the predictions of a well-mixed gas transport model. PMID:23919719

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

2013-09-01

94

Particle desorption mass spectrometric surface characterization  

SciTech Connect

The feasibility of utilizing /sup 252/Cf-Particle Desorption Mass Spectrometry (PDMS) to characterize the surface region of solid samples has been evaluated. The PDMS experiment was adapted to an ultrahigh vacuum (UHV) environment and was configured so as to allow the analysis of thick as well as thin samples. This apparatus included an in situ sputter cleaning/depth profiling facility. The mass resolution was variable from 300 to 200 at 133 daltons by changing the drift length from 27 cm to 20 cm. Desorbed ions were focused by using either a dual grid assembly or an einzel lens. The overall instrumental transmission efficiency with the einzel lens operative was approximately 50%. The applicability of /sup 252/Cf-PDMS to samples that were thick and insulating was demonstrated in the analysis of geological specimens. Pollucite, Microcline, Amblygonite, and Lepidolite were analyzed without complications associated with sample thickness or charge accumulation. Substitution occurring between the alkali metals in the environment was observed by PDMS and was corroborated by SIMS, XPS, and EMP analyses. The analysis of NBM SRM glasses addressed the suitability of combining the PDMS technique was sputter etching. This application demonstrated the ability of this technique to sense changes in the chemical environment brought about by sputter cleaning. The analysis of these samples also allowed the estimation of detection limits for lithium, rubidium, and cesium in a glass matrix as 300 ppm, 400 ppm, and 400 ppm, respectively. Sputter depth profiling combined with /sup 252/Cf-PDMS analysis of an aluminum layer on a silicon substrate established the utility of the PDMS technique in surface characterization.

Summers, W.R.

1986-01-01

95

Characteristics of the Martian atmosphere surface layer  

NASA Technical Reports Server (NTRS)

Researchers extend elements of various terrestrial boundary layer models to Mars in order to estimate sensible heat, latent heat, and momentum fluxes within the Martian atmospheric surface layer. To estimate the molecular viscosity and thermal conductivity of a CO2-H2O gas mixture under Martian conditions, parameterizations were developed. Parameterizations for specific heat and and binary diffusivity were also determined. The Prandtl and Schmidt numbers derived from these thermophysical properties were found to range from 0.78 - 1.0 and 0.47 - 0.70, respectively, for Mars. Brutsaert's model for sensible and latent heat transport within the interfacial sublayer for both aerodynamically smooth and rough airflow was experimentally tested under similar conditions, validating its application to Martian conditions. For the surface sublayer, the researchers modified the definition of the Monin-Obukhov length to properly account for the buoyancy forces arising from water vapor gradients in the Martian atmospheric boundary layer. This length scale was then utilized with similarity theory turbulent flux profiles with the same form as those used by Businger et al. and others. It was found that under most Martian conditions, the interfacial and surface sublayers offer roughly comparable resistance to sensible heat and water vapor transport and are thus both important in determining the associated fluxes.

Clow, G. D.; Haberle, R. M.

1991-01-01

96

All-Nanoparticle Layer-by-Layer Surface Modification of Micro- and Ultrafiltration Membranes.  

PubMed

Layer-by-layer (LbL) deposition using primarily inorganic silica nanoparticles is employed for surface modification of polymeric micro- and ultrafiltration (MF/UF) membranes to produce novel thin film composite (TFC) membranes intended for nanofiltration (NF) and reverse osmosis (RO) applications. A wide variety of porous substrate membranes with different surface characteristics are successfully employed. This report gives detailed results for polycarbonate track etched (PCTE), polyethersulfone (PES), and sulfonated PES (SPEES) MF/UF substrates. Both spherical (cationic/anionic) and eccentric elongated (anionic) silica nanoparticles are deposited using conditions similar to those in prior works for solid substrates (e.g., Lee et al.1). Appropriate selection of the pH for anionic and cationic particle deposition enables construction of nanoparticle-only layers 100-1200 nm in thickness atop the original porous membrane substrates. The surface layer thickness appears to vary linearly with the number of bilayers deposited, i.e., with the number of anionic/cationic deposition cycles. The deposition process is optimized to eliminate drying-induced cracking and improve mechanical durability via thickness control and postdeposition hydrothermal treatment. "Dead-end" permeation tests using dextran standards reveal the hydraulic characteristics and separations capability for the PCTE-based TFC membranes. The results show that nanoparticle-based LbL surface modification of MF and UF rated media can produce TFC membranes with NF capabilities. PMID:24568094

Escobar-Ferrand, Luis; Li, Diya; Lee, Daeyeon; Durning, Christopher J

2014-05-20

97

VERTICAL PROFILES OF MASS FLUX FOR DIFFERENT PARTICLE DIAMETERS IN DRIFTING SNOW OVER HARD SNOW SURFACES  

Microsoft Academic Search

The vertical profile of horizontal snow mass flux is a fundamental structure of drifting snow. It is widely recognized that most of drifting snow particles are transported within the saltation layer near the snow surface. However, little is clarified about the dependencies of the vertical mass flux profile in the saltation layer on conditions such as snow particle diameter, snow

Kenji Kosugi; Takeshi Sato; Masaki Nemoto; Shigeto Mochizuki; Atsushi Sato

98

Colloidal dynamics near a particle-covered surface.  

PubMed

How the diffusive dynamics of colloidal spheres changes in the vicinity of a particle-coated surface is of importance for industrial challenges such as fouling and sedimentation as well as for fundamental studies into confinement effects. We addressed this question by studying colloidal dynamics in a partially coated surface layer, using video microscopy. Particle mean squared displacement (MSD) functions were measured as a function of a (local) effective volume fraction (EVF), which was varied by making use of gravity settling. Comparison of MSDs at the bare and coated surfaces for EVF of 0.2-0.4 revealed that at the latter surface the motion amplitudes are strongly reduced, accompanied by a sharp transition from diffusive to nearly caged motion. This clearly indicates that the surface-attached particles cannot be taken into account via volume fraction and that their immobility has a distinct effect. For EVF > 0.45, the caging becomes dominated by the suspended particles, making the dynamics at the bare and coated surfaces similar. PMID:21827156

Eral, H B; Mugele, F; Duits, M H G

2011-10-18

99

Particle aggregation with simultaneous surface growth  

NASA Astrophysics Data System (ADS)

Particle aggregation with simultaneous surface growth was modeled using a dynamic Monte Carlo method. The Monte Carlo algorithm begins in the particle inception zone and constructs aggregates via ensemble-averaged collisions between spheres and deposition of gaseous species on the sphere surfaces. Simulations were conducted using four scenarios. The first, referred to as scenario 0, is used as a benchmark and simulates aggregation in the absence of surface growth. Scenario 1 forces all balls to grow at a uniform rate while scenario 2 only permits them to grow once they have collided and stuck to each other. The last one is a test scenario constructed to confirm conclusions drawn from scenarios 0 2. The transition between the coalescent and the fully developed fractal aggregation regimes is investigated using shape descriptors to quantify particle geometry. They are used to define the transition between the coalescent and fractal growth regimes. The simulations demonstrate that the morphology of aggregating particles is intimately related to both the surface deposition and particle nucleation rates.

Mitchell, Pablo; Frenklach, Michael

2003-06-01

100

Numerical simulation of particle transport in planar shear layers  

Microsoft Academic Search

Numerical simulations of particle dispersion in a planar shear dominated by large scale vortical structures are reported. The shear layer is formed by two co-flowing streams past a splitter plate. The emphasis of this work is on examining how the particle dynamics are affected by the large-scale coherent structures in the initial development of the instabilities in a spatially-developing mixing

S. K. Aggarwal; J. B. Yapo; F. F. Grinstein; K. Kailasanath

1996-01-01

101

NUMERICAL SIMULATION OF PARTICLE TRANSPORT IN PLANAR SHEAR LAYERS  

Microsoft Academic Search

Numerical simulations of particle dispersion in a planar shear dominated by large scale vertical structures alre reported. The shear layer is formed by two co-flowing streams past a splitter plate. The emphasis of this work is on examining how the particle dynamics are affected by the large-scale coherent structures in the initial development of the instabilities in a spatially-developing mixing

S. K. AG' GARWAL; J. B. YAPO; F. F. GRINSTEIN

1996-01-01

102

Diurnal ocean surface layer model validation  

NASA Technical Reports Server (NTRS)

The diurnal ocean surface layer (DOSL) model at the Fleet Numerical Oceanography Center forecasts the 24-hour change in a global sea surface temperatures (SST). Validating the DOSL model is a difficult task due to the huge areas involved and the lack of in situ measurements. Therefore, this report details the use of satellite infrared multichannel SST imagery to provide day and night SSTs that can be directly compared to DOSL products. This water-vapor-corrected imagery has the advantages of high thermal sensitivity (0.12 C), large synoptic coverage (nearly 3000 km across), and high spatial resolution that enables diurnal heating events to be readily located and mapped. Several case studies in the subtropical North Atlantic readily show that DOSL results during extreme heating periods agree very well with satellite-imagery-derived values in terms of the pattern of diurnal warming. The low wind and cloud-free conditions necessary for these events to occur lend themselves well to observation via infrared imagery. Thus, the normally cloud-limited aspects of satellite imagery do not come into play for these particular environmental conditions. The fact that the DOSL model does well in extreme events is beneficial from the standpoint that these cases can be associated with the destruction of the surface acoustic duct. This so-called afternoon effect happens as the afternoon warming of the mixed layer disrupts the sound channel and the propagation of acoustic energy.

Hawkins, Jeffrey D.; May, Douglas A.; Abell, Fred, Jr.

1990-01-01

103

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

104

The singularity in particle-laden boundary layers  

NASA Astrophysics Data System (ADS)

The classical ``dusty gas'' equations have been used recently in a number of investigations by the authors to model boundary-layer flows of dilute suspensions of heavy particles. Though none of the difficulties of well-posedness that so often occur in more complicated particle-laden flow models seems to arise for this equation set, what does nearly always appear, and is now well documented in a variety of boundary layers, is a wall singularity that occurs at a finite distance from the leading edge, where the volume fraction is unbounded. The dusty-gas approximation replaces the quantity ``1-?'' everywhere in the particle-laden equations by ``1''. One is forced to seek a more complicated model in order to remove the unphysical singularity, and there are plenty of candidates--including particle pressure, added mass, particle-particle interactions. From the point of view of modifying the theory in the simplest possible way, we restore ``1-?'' where it had been replaced by ``1,'' and do nothing more. Such a procedure removes the singularity in boundary-layer flows, and we present computational and analytical results under such a change See, most recently, Foster, Duck & Hewitt (2006) Proc. Roy. Soc A 462, 1145

Foster, M. R.; Duck, P. W.; Hewitt, R. E.

2006-11-01

105

Inertial particle entrainment in a shearless mixing layer  

Microsoft Academic Search

This article accompanies the submission of a fluid dynamics video (entry V032) of inertial particle entrainment in a shearless mixing layer for the Gallery of Fluid Motion of the 64th Annual Meeting of the American Physical Society, Division of Fluid Dynamics.

Peter J. Ireland; Martin S. Henke; Lance R. Collins

2011-01-01

106

Two-Dimensional Particle Simulation of the Magnetopause Current Layer.  

National Technical Information Service (NTIS)

We have developed a 2/1/2/-D (x, y, v/sub x/, v/sub y/, v/sub z/) electromagnetic code to study the formation and the stability of the magnetopause current layer. This code computes the trajectories of ion and electron particles in their self-consistently...

J. Berchem H. Okuda

1988-01-01

107

Thermal characteristics of the lunar surface layer.  

NASA Technical Reports Server (NTRS)

The thermophysical properties of the fines from the Apollo 12 landing site have been determined as a function of their relevant parameters. These properties include the thermal conductivity, thermal diffusivity, directional reflectance and emittance. The density used was the same as that observed from the returned core-tube samples and so should be close to the true density of the surface layer at the Apollo 12 site. The measured properties are used to calculate the diurnal temperature variation of the moon's surface as well as for several depths below the surface. The maximum surface of 389 K is obtained at lunar noon while the minimum temperature of 86.1 K is obtained at sunrise. It is shown that the most significant effects on temperature, as compared with previous calculations, are caused by using the directional reflectance which controls the amount of solar energy absorption during the day in place of a constant hemispherical reflectance. The results are compared with previous analyses and remote measurements.

Cremers, C. J.; Birkebak, R. C.; White, J. E.

1972-01-01

108

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

109

Surface preparation of substances for continuous convective assembly of fine particles  

DOEpatents

A method for producing periodic nanometer-scale arrays of metal or semiconductor junctions on a clean semiconductor substrate surface is provided comprising the steps of: etching the substrate surface to make it hydrophilic, forming, under an inert atmosphere, a crystalline colloid layer on the substrate surface, depositing a metal or semiconductor material through the colloid layer onto the surface of the substrate, and removing the colloid from the substrate surface. The colloid layer is grown on the clean semiconductor surface by withdrawing the semiconductor substrate from a sol of colloid particles.

Rossi, Robert (Rochester, MN)

2003-01-01

110

Convective Surface Layers: Influence of the Boundary Layer Depth  

NASA Astrophysics Data System (ADS)

Two methods, one semi-empirical and the other theoretical, are employed to develop a new theory for predicting the behavior of turbulence characteristics in convective surface layers. This theory is based on three length scales; the height above the ground, the Monin-Obukhov length, and the boundary layer depth (h). The chief advantages are its relative simplicity, its ability to predict the height dependence of the mean gradients and second moments in a manner consistent with their observed behavior in the atmosphere and in large-eddy simulations, and it is consistent with the theoretical requirements of free convection similarity. The semi-empirical method is based on nonlinear least squares fits to a generalized Businger-Dyer formulation with up to four unknown parameters. Using data obtained primarily from the Kansas and Minnesota field experiments, this method is applied to the universal functions for the wind and temperature gradients, the standard deviation of the horizontal wind velocity (v(,*)), the variances of vertical velocity and temperature, the streamwise heat flux, and the turbulence dissipation. Analyses of the Kansas data are performed using both drag-plate and eddy -correlation measurements of u(,*). To indirectly include the influence of h and also obtain the best statisti- cal results, the dimensionless shear, (xi) and Ri are modified by the ratio (kappa)v(,*)/u(,*). Unfortunately, this procedure often results in solutions which do not satisfy the requirements of free convection theory. An apparent reason for this is found when the differences between the drag-plate and eddy-correlation values of n(,*) are analyzed. Using the flow distortion equations developed by Wyngaard (1982), results in close agreement with Wieringa (1980) are obtained. Despite this, it is found that the ratio (kappa)v(,*)/u(,*) is apparently equal to unity in neutral conditions and that the height dependence of some quantities may not be the same as is currently accepted. A theoretical approach which imposes free convection require- ments is developed. Vector-like quantities are found to be propor- tional to the shear stress and all quantities are found to depend on both w(,*) and w(theta)(' )in an identical manner. New flux-gradient relationships are proposed.

Loveland, Kurt Tyler

111

Small particle transport across turbulent nonisothermal boundary layers  

NASA Technical Reports Server (NTRS)

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.

1982-01-01

112

Surface modification of layered zirconium phosphates: a novel pathway to multifunctional materials.  

PubMed

The intercalation of inorganic layered materials has resulted in a wide range of applicability. In such cases the applicability of the material is largely dependent upon the species intercalated within the layer, and the layered material acts largely as a host. Recently, the surface modification of inorganic layered materials has been investigated and it has been shown that the exterior layers can be exclusively functionalized. The advent of surface chemistry allows for the synthesis of particles with both a controlled interlayer and surface. This approach can be used to tailor nanoparticles for specific applications. Herein we review the surface chemistry of ?-zirconium bis(monohydrogen orthophosphate) monohydrate (Zr(HPO4)2·H2O, ?-ZrP) along with some applications of recent interest. Not only can these reactions be applied to ?-ZrP, but similar chemistry can also be expanded to other layered materials and systems. PMID:24737164

Mosby, Brian M; Díaz, Agustín; Clearfield, Abraham

2014-07-21

113

Acoustic tomography in the atmospheric surface layer  

NASA Astrophysics Data System (ADS)

Acoustic tomography is presented as a technique for remote monitoring of meteorological quantities. This method and a special algorithm of analysis can directly produce area-averaged values of meteorological parameters. As a result consistent data will be obtained for validation of numerical atmospheric micro-scale models. Such a measuring system can complement conventional point measurements over different surfaces. The procedure of acoustic tomography uses the horizontal propagation of sound waves in the atmospheric surface layer. Therefore, to provide a general overview of sound propagation under various atmospheric conditions a two-dimensional ray-tracing model according to a modified version of Snell's law is used. The state of the crossed atmosphere can be estimated from measurements of acoustic travel time between sources and receivers at different points. Derivation of area-averaged values of the sound speed and furthermore of air temperature results from the inversion of travel time values for all acoustic paths. Thereby, the applied straight ray two-dimensional tomographic model using SIRT (simultaneous iterative reconstruction technique) is characterised as a method with small computational requirements, satisfactory convergence and stability properties as well as simple handling, especially, during online evaluation.

Ziemann, A.; Arnold, K.; Raabe, A.

1999-01-01

114

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

115

Diffusive behavior of a thin particle layer in fluid by hydrodynamic interaction  

NASA Astrophysics Data System (ADS)

The hydrodynamic effect on a thin particle layer, which moves relative to fluid by an external force, is investigated theoretically and numerically. Because of the presence of layer ends, the arrangement of particles in the layer is anisotropic and the drag force acting on them varies according to the position. The resulting relative motion of particles brings about the spreading of the layer. We have studied such a diffusive behavior of particle layers, which have various internal arrangements. We have assumed a non-Brownian system in which the particles move relatively owing to only the variance of hydrodynamic force. The hydrodynamic force on each particle was calculated by Stokesian dynamics approach. The results show that the relative motion of particles is greatly influenced by the internal arrangement of the particle layer. In consequence, the overall diffusive motion of particle layer varies with the arrangement even if the particle concentration is similar. It is in contrast to the gradient diffusion of Brownian particles.

Harada, Shusaku; Otomo, Ryoko

2009-12-01

116

Fluorescent particle tracers for surface hydrology  

NASA Astrophysics Data System (ADS)

Accurate estimates of flow velocity in natural environments are essential for the understanding of runoff and overland flow formation, rill development, erosion, and infiltration and evaporation mechanisms. Tracing technologies are generally considered valuable tools to estimate flow velocity in small watershed streams and shallow water flows. In this framework, a novel tracing methodology based on the deployment and observation of enhanced fluorescence particles for surface flow measurements is proposed. This approach aims at mitigating practical limitations of traditional techniques for monitoring stream and overland flows. Specifically, the insolubility of the particles minimizes tracer adhesion to natural substrates and, therefore, is expected to reduce the requisite quantity of tracing material as compared to liquid dyes. Further, the enhanced visibility of the fluorescent particles allows for non-intrusively detecting the tracer through imaging techniques without deploying bulky probes and samplers in the water. These features along with the use of basic and resilient equipment provide grounding for applying the proposed methodology in ephemeral micro-channels, high-sediment load flows, and heavy floods. The feasibility of the methodology is studied by conducting characterization analysis in laboratory settings and proof-of-concept experiments in natural environments. In addition, image analysis techniques are developed to automatically and noninvasively detect and trace the trajectory of the particles on surface flows. Experiments are performed in a natural mountainous river to assess the performance of the particles in stream flow settings, where high velocity regimes, presence of foam, and light reflections pose serious challenges to bead detection. Particles are used to conduct flow measurements at a stream cross-section and travel time experiments in stream reaches of up to 30 m. Bead diameters of a few millimeters are selected to compensate for high flow rates. Experimental results demonstrate that the fluorescent particles can be used to reliably trace high velocity streams in adverse illumination conditions and in the presence of foam and reflections on the water surface. Furthermore, flow velocities and travel times calculated through an array of commonly used tracers are consistent with results obtained through the proposed methodology and demonstrate a higher reliability of the fluorescent particles versus traditional tracers that are affected by dispersions and turbulence. Additional proof-of-concept experiments are conducted on a semi-natural hillslope plot under high turbidity loads and soil and rain drops interaction. Ad-hoc experiments with particles of varying diameters ranging from 75 to 1180 ?m are performed to assess the visibility and detectability of the particle tracers in these severe environmental conditions and their feasibility in estimating overland flow velocities. Videos of beads' transit are processed through both supervised and unsupervised techniques to obtain average surface velocities of water flowing on the hill. Experimental results have demonstrated the feasibility of using the particles for environmental applications and have led to the identification of optimal diameters, namely, 1000-1180 ?m, for flow measurements in the described hillslope plot.

Tauro, F.; Grimaldi, S.; Rapiti, E.; Porfiri, M.

2012-12-01

117

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

PubMed

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. PMID:22872809

Sen, Tapas; Bruce, Ian J

2012-01-01

118

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

NASA Astrophysics Data System (ADS)

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.

2012-08-01

119

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

120

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

121

Methotrexate intercalated layered double hydroxides with different particle sizes: structural study and controlled release properties.  

PubMed

To study the influence of particle size on release properties, drug efficacy and other properties, a series of methotrexate intercalated layered double hydroxides (MTX/LDHs) nanohybrids with different particle sizes were synthesized through traditional coprecipitation method, by using the mixture of water and polyethylene glycol (volume ratio is 3:1) as solvent. The relationship between particle size and hydrothermal treatment conditions (i.e., time and temperature) had been systematically investigated, and the results indicate that the particle size can be precisely controlled between 70 and 300 nm. Elemental C/H/N and inductive coupled plasma (ICP) analysis indicated that different hydrothermal treatment almost has no effect on compositions of the nanohybrids. X-ray diffraction (XRD) patterns and fourier transform infrared spectroscopy (FTIR) investigations manifested the successful intercalation of MTX anions. MTX/LDHs particles exhibited hexagonal platelet morphology with round corner, due to the adsorption of MTX anions on positively charged LDHs surface. In addition, the crystallinity of MTX/LDHs increased with the particle diameters and the thermal stability of MTX anions was enhanced by holding together with LDHs layers. The in vitro release showed that bigger particles have much longer release duration, and the bioassay tests indicated that bigger particles are more efficient in the suppression of the tumor cells. PMID:24632036

Zhang, Xiao-Qing; Zeng, Mei-Gui; Li, Shu-Ping; Li, Xiao-Dong

2014-05-01

122

Radiative transfer theory for active remote sensing of a layer of nonspherical particles  

NASA Technical Reports Server (NTRS)

The radiative transfer theory is applied to calculate the scattering by a layer of randomly positioned and oriented nonspherical particles. The scattering amplitude functions of each individual particle are calculated with Waterman's T matrix method, which utilizes vector spherical wave functions for expansion of incident, scattered, and surface fields. The orientation of the particles is described by a probability density function of the Eulerian angles of rotation. A rotation matrix is used to relate the T matrix of the principal frame to that of the natural frame of the particle. The extinction matrix and phase matrix of the radiative transfer equations are expressed in terms of the T matrix elements. The extinction matrix for nonspherical particles is generally nondiagonal. There are only two attenuation rates in a specified direction of propagation. The radiative transfer equations are solved by an iterative method to first order in albedo. Numerical results are illustrated as functions of incidence angle and frequency with applications to active remote sensing.

Tsang, L.; Kong, J. A.; Shin, R. T.

1984-01-01

123

Fluid-driven motion of passive cilia enables the layer to expel sticky particles.  

PubMed

Inspired by marine organisms that utilize active cilia to prevent the biofouling of their surfaces, we use computational and theoretical modeling to determine if passive cilia, which are driven to undulate by an oscillatory shear flow, can be harnessed for antifouling applications. By modeling the oscillating shear flow near a ciliated wall within a channel, we show that the fluid-driven motion of cilia enables the layer to repel adhesive particles away from the surface. Compared to the behavior of the system in a non-oscillating shear, the oscillations also help transport the particles more rapidly along the flow direction. Moreover, the oscillations allow "stickier" particles to be conveyed by the flow relative to the case involving non-oscillatory flow. A simple theoretical model that considers the motion of an adhesive particle interacting with an oscillating, elastic layer captures the behavior observed in the simulations and indicates that the adhesive particle can be repelled away for a wide range of oscillation frequencies. The findings suggest that passive cilia can be used to create self-cleaning surfaces, utilizing oscillations in the flow to prevent the attachment of microparticles and biological cells. PMID:24652071

Tripathi, Anurag; Shum, Henry; Balazs, Anna C

2014-03-01

124

Thermally-responsive surfaces comprising grafted poly(N-isopropylacrylamide) chains: Surface characterisation and reversible capture of dispersed polymer particles  

Microsoft Academic Search

In this study we investigate thermally-responsive surfaces prepared by grafting PNIPAm from a cationic macroinitiator (MI) that was adsorbed onto a range of anionic substrates. The substrates used were mica, glass, quartz and high surface area carbon foam. The carbon foam was rendered thermally responsive by first coating it with a layer of calcined laponite particles. PNIPAm brushes were grown

R. Liu; P. De Leonardis; N. Tirelli; B. R. Saunders

2009-01-01

125

Euler-Lagrange Modeling of Vortex Interaction with a Particle-Laden Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

Rotorcraft operation in austere environments can result in difficult operating conditions, particularly in the vicinity of sandy areas. The uplift of sediment by rotorcraft downwash, a phenomenon known as brownout, hinders pilot visual cues and may result in a potentially dangerous situation. Brownout is a complex multiphase flow problem that is not unique and depends on both the characteristics of the rotorcraft and the sediment. The lack of fundamental understanding constrains models and limits development of technologies that could mitigate the adverse effects of brownout. This provides the over-arching motivation of the current work focusing on models of particle-laden sediment beds. The particular focus of the current investigations is numerical modeling of near-surface fluid-particle interactions in turbulent boundary layers with and without coherent vortices superimposed on the background flow, that model rotorcraft downwash. The simulations are performed with two groups of particles having different densities both of which display strong vortex-particle interaction close to the source location. The simulations include cases with inter-particle collisions and gravitational settling. Particle effects on the fluid are ignored. The numerical simulations are performed using an Euler- Lagrange method in which a fractional-step approach is used for the fluid and with the particulate phase advanced using Discrete Particle Simulation. The objectives are to gain insight into the fluid-particle dynamics that influence transport near the bed by analyzing the competing effects of the vortices, inter-particle collisions, and gravity. Following the introduction of coherent vortices into the domain, the structures convect downstream, dissipate, and then recover to an equilibrium state with the boundary layer. The particle phase displays an analogous return to an equilibrium state as the vortices dissipate and the boundary layer recovers, though this recovery is slower than for the fluid and is sensitive to the particle response time. The effects of inter-particle collisions are relatively strong and apparent throughout the flow, being most effective in the boundary layer. Gravitational settling increases the particle concentration near the wall and consequently increase inter-particle collisions.

Morales, Fernando

126

Neutral surface layer turbulence over complex terrain  

SciTech Connect

Accurate turbulence estimates are important input to atmospheric dispersion models since they characterize downwind dispersion and hence, potential pollutant concentrations. When only basic wind information is available, an atmospheric modeler must first estimate roughness length (z{sub 0},) at the location of interest, ({mu}*) from similarity theory using average wind speed ({mu}) and z{sub 0}, and finally apply experimentally derived relationships to determine the turbulence intensities. Even when turbulence coefficients are measured, the turbulence profile must be estimated in the surface layer, using, for example, the power law recommended in a US Environmental Protection Agency guidance document. In this study, turbulent intensities and wind profiles are analyzed in eight direction sectors during near neutral stability. ``Local`` and ``regional`` roughness lengths are calculated from wind speed profiles and from longitudinal turbulence intensities ({sigma}{sub {mu}}) at both sites. With ``regional`` roughness length, complex terrain features are in effect the roughness elements. Profiles of median, 15-minute averaged turbulence intensities {sigma}{sub {mu}}, {sigma}{sub {nu}} and {sigma}{sub w} are calculated at both sites. Profiles of median {sigma}{sub {theta}} and {sigma}{sub {phi}} are also calculated using four mean values of regional z{sub 0} at both sites. Finally, differences between widely-used turbulence relationships and the relationships determined in this study, and their possible effect on model results, are discussed.

Bowen, B.M.

1995-09-01

127

Correlation and prediction of thermophoretic and inertial effects on particle deposition from non-isothermal turbulent boundary layers  

NASA Technical Reports Server (NTRS)

The problem of small particle deposition which can cause hot stage corrosion and/or fouling in combustion turbines operating on fuels containing ash or inorganic salts is investigated. Two boundary layer transport phenomena are shown to assume importance in these cases: particle thermophoresis (migration down a temperature gradient) and particle inertia. Thermophoretic and eddy transport across turbulent boundary layers without and with particle inertia effects are quantitatively analyzed. The effects of streamwise blade curvature on particle transport across turbulent boundary layers are determined. It is shown that these phenomena destroy the analogy between mass and heat transfer or mass and momentum transfer. Also studied are the effects on particle deposition of distributed or localized wall blowing, surface roughness, and mainstream turbulence.

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

1982-01-01

128

Measuring the surface conductance of kaolinite particles  

SciTech Connect

In this paper the authors use a procedure devised by Dukhin and Shilov to derive a formula for the electric dipole strength of a disc-shaped particle with surface conductance K[sup s]. The theory is then compared with experimental results obtained from complex conductivity measurements on a Na-kaolinite sol in the megahertz range. K[sup s] is determined by fitting the experimental and theoretical curves of dipole strength as a function of frequency, assuming a particle aspect ratio of 0.1. The value of K[sup s] obtained in this way is much greater than would be expected from the electrophoretic [zeta] potential, indicating that a substantial fraction of the conductance comes from the ions below the shear plane in the kaolinite. Such anomalous conductance will have a profound effect on all electrokinetic properties of kaolinite.

O'Brien, R.W.; Rowlands, W.N. (Univ. of Sydney, New South Wales (Australia). School of Chemistry)

1993-09-01

129

Layer silicates in a chondritic porous interplanetary dust particle  

NASA Technical Reports Server (NTRS)

Analytical electron microscopy on individual grains from a portion of a chondritic porous interplanetary dust particle (aggregate W7029C1 from the NASA Johnson Space Center Cosmic Dust Collection) shows that layer silicates compose 50 percent of the silicate fraction examined. These layer silicates can be classified into two distinct crystallochemical groups: (1) fine-grained, polycrystalline smectite minerals; and (2) well-ordered, single crystals of kaolinite and Mg-poor talc. The layer silicates in this portion of sample W7029(asterisk)A are dissimilar to those described in other chondritic porous aggregates. The predominant layer silicate assemblage in W7029(asterisk)A indicates that heating of the aggregate during atmospheric entry was brief and probably to a temperature less than 300 C. Comparison with terrestrial phyllosilicate occurrences suggests that some layer silicates in aggregate W7029(asterisk)A may have been formed by alteratiton from preexisting silicate minerals at low temperatures (less than 25 C) after aggregate formation.

Rietmeijer, F. J. M.; Mackinnon, I. D. R.

1985-01-01

130

Layer silicates in a chondritic porous interplanetary dust particle  

NASA Astrophysics Data System (ADS)

Analytical electron microscopy on individual grains from a portion of a chondritic porous interplanetary dust particle (aggregate W7029C1 from the NASA Johnson Space Center Cosmic Dust Collection) shows that layer silicates compose 50 percent of the silicate fraction examined. These layer silicates can be classified into two distinct crystallochemical groups: (1) fine-grained, polycrystalline smectite minerals; and (2) well-ordered, single crystals of kaolinite and Mg-poor talc. The layer silicates in this portion of sample W7029(asterisk)A are dissimilar to those described in other chondritic porous aggregates. The predominant layer silicate assemblage in W7029(asterisk)A indicates that heating of the aggregate during atmospheric entry was brief and probably to a temperature less than 300 C. Comparison with terrestrial phyllosilicate occurrences suggests that some layer silicates in aggregate W7029(asterisk)A may have been formed by alteratiton from preexisting silicate minerals at low temperatures (less than 25 C) after aggregate formation.

Rietmeijer, F. J. M.; MacKinnon, I. D. R.

1985-11-01

131

Purification and Characterization ofCampylobacter rectus Surface Layer Proteins  

Microsoft Academic Search

Campylobacter rectus is a putative periodontopathogen which expresses a proteinaceous surface layer (S- layer) external to the outer membrane. S-layers are considered to play a protective role for the microorganism in hostile environments. The S-layer proteins from six different C. rectus strains (five human isolates and a nonhuman primate (NHP) isolate) were isolated, purified, and characterized. The S-layer proteins of

Hiroshi Nitta; Stanley C. Holt; Andjeffrey L. Ebersole

132

Surface Characterization of an Organized Titanium Dioxide Layer  

NASA Astrophysics Data System (ADS)

Soft lithographic printing techniques can be used to control the surface morphology of titanium dioxide layers on length scales of several hundred nanometers. Controlling surface morphology and volumetric organization of titanium dioxide electrodes can potentially be used in dye-sensitized solar cell devices. This thesis explores how layer-by-layer replication can lead to well defined, dimensionally controlled volumes and details how these control mechanisms influence surface characteristics of the semiconducting oxide.

Curtis, Travis

133

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

134

Wind Tunnel Experiments and Modelling of Particle-Laden Boundary Layer Flows  

NASA Astrophysics Data System (ADS)

Particle-laden boundary flows occur in many geophysical and industrial environments yet are difficult to understand and quantitatively describe because the interactions of an often turbulent boundary layer flow with surface and particle dynamics are complex. The SLF wind tunnel allows the investigation of snow and sand particle laden boundary layer flows over their natural surfaces with and without the presence of a grass canopy.The experimental results are used to investigate the two possible approaches in describing the surface dynamics: (i) Models of particle transport, which assume a stationary flow situation and predict a mass flux for an hypothetical equilibrium; (ii) Models that take the temporal variability of the mass flux explicitly into account such as Lagrangian Stochastic particle tracking Models (LSM) on the basis of large eddy simulation (LES) or direct numerical simulation (DNS) of flow and turbulence. This presentation shows that wind tunnel data support the form of semi-empirical equilibrium models, which predict mass flux, q, as a function of the mean wind speed or the friction velocity, u, and a threshold velocity, uth: q=a(u-uth)x. For the exponent "x", a value of approximately 3, as based on theoretical considerations, is consistent with the data. This simple form of equilibrium models as well as more complicated equilibrium models are all based on the hypothesis that the surface shear stress induced by a fluid on the ground during sediment saltation is constant, i.e. independent of the magnitude of the particle mass flux (Owen's second hypothesis). Our surface shear stress measurements in a drifting-sand wind tunnel show a constant value of the fluid shear stress for saltation layers of various mass-flux magnitudes, directly validating Owen's second hypothesis for the first time. The equilibrium models, however, only insufficiently describe the full dynamics of particle-laden flows. The second part of the presentation therefore discusses non-equilibrium features such as a high variability of the particle mass flux caused by flow turbulence and surface heterogeneity. Mass flux intermittency is primarily observed around the threshold value uth. Using a combination of LES and LSM models, we show how the simulation of individual feed-back processes leads to a more complete understanding of the mechanisms behind the flux variability.

Lehning, M.; Walter, B.; Horender, S.; Groot Zwaaftink, C.

2013-12-01

135

Thermally-responsive surfaces comprising grafted poly(N-isopropylacrylamide) chains: Surface characterisation and reversible capture of dispersed polymer particles.  

PubMed

In this study we investigate thermally-responsive surfaces prepared by grafting PNIPAm from a cationic macroinitiator (MI) that was adsorbed onto a range of anionic substrates. The substrates used were mica, glass, quartz and high surface area carbon foam. The carbon foam was rendered thermally responsive by first coating it with a layer of calcined laponite particles. PNIPAm brushes were grown from the substrates using surface-initiated atom transfer radical polymerisation. The thermally-responsive PNIPAm layers were characterised in detail at room temperature and 50 degrees C using atomic force microscopy (AFM) and contact angle measurements. The surfaces changed from being non-adhesive to adhesive when the temperature was increased to 50 degrees C. Young's modulus values and adhesive force values are reported. Particle capture experiments involving dispersed polystyrene or poly(BD/MAA) (butadiene and methacrylic acid) particles were conducted. High extents of particle capture were observed. It was shown that the highest extents of thermally-triggered particle capture at 50 degrees C occurred for surfaces that exhibited the largest increases in contact angle upon increasing the temperature. Importantly, thermally-triggered capture for both anionic polystyrene and poly(BD/MAA) particles was shown to be partially reversible with up to 30% of the captured particles released during cooling. This is the first time that significant reversibility of thermally-triggered capture of polymer particles has been reported. PMID:19781710

Liu, R; De Leonardis, P; Tirelli, N; Saunders, B R

2009-12-15

136

On the effect of induced electro-osmosis on a cylindrical particle next to a surface.  

PubMed

The effect of induced electro-osmosis on a cylindrical particle positioned next to a planar surface (wall) is studied theoretically both under the thin double layer approximation utilizing the Smoluchowski slip velocity approximation and under thick electric double layer conditions by solving the Poisson-Nernst-Planck (PNP) equations. The imposed, undisturbed electric field is parallel to the planar surface. The induced hydrodynamic and electrostatic forces are calculated as functions of the particle's and the medium's dielectric constants and the distance between the particle and the surface. The resultant force acting on the particle is directed normal to and away from the wall. The presence of such a repulsive force may adversely affect the interactions between macromolecules suspended in solution and wall-immobilized molecules and may be significant to near-wall particle imaging velocimetry (PIV) in electrokinetic flows. PMID:17311434

Zhao, Hui; Bau, Haim H

2007-03-27

137

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.

138

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

139

Surface plasma source with anode layer plasma accelerator  

NASA Astrophysics Data System (ADS)

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

2012-02-01

140

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

141

Formation of Surface Layers of Icosahedral Al(Mn).  

National Technical Information Service (NTIS)

Surfaces layers of the icosahedral phase of Al(Mn) have been formed from thin, alternating Al/Mn layers deposited on Al or Fe surfaces by rapid electron-beam or laser melting, by ion beam mixing, and by solid-state diffusion. The electron beam and laser t...

J. A. Knapp D. M. Follstaedt

1985-01-01

142

ILLIAC 4 and lifting surface theory with boundary layer  

NASA Technical Reports Server (NTRS)

Aerodynamic flutter and a re-written computer program for its study are discussed. Data cover: (1) lifting surface theory with boundary layer, (2) incompressible, two dimensional, unsteady flow with control surfaces, (3) improved unsteady theory, (4) combined transonic airfoil thickness and shear layer thickness effects, and (5) bending-torsion flutter calculations.

Dowell, E. H.

1976-01-01

143

Phase diagrams of ferroelectric thin film with two surface layers  

Microsoft Academic Search

Phase diagram of a ferroelectric thin film with two surface layers is studied in frame of the effective field theory (EFT) of transverse Ising model (TIM). The surface of the system is formed from two layers characterized by the exchange interaction anisotropy Rs =frac{Js }{J} and the transverse field Omega s. The crossover from the ferroelectric phase (FP) to the

H. Arhchoui; Y. El Amraoui; D. Mezzane; I. Luk'yanchuk

2009-01-01

144

Aspects Of The Atmospheric Surface Layers On Mars And Earth  

Microsoft Academic Search

The structures of mean flow and turbulence in the atmospheric surface boundary layer have been extensively studied on Earth, and to a far less extent on Mars, where only the Viking missions and the Pathfinder mission have delivered in-situ data. Largely the behaviour of surface-layer turbulence and mean flow on Mars is found to obey the same scaling laws as

S. E. Larsen; H. E. Jørgensen; L. Landberg; J. E. Tillman

2002-01-01

145

Effects of solar particle events on the hydroxyl airglow layer  

NASA Astrophysics Data System (ADS)

The so-called Meinel emissions of vibrationally-rotationally excited hydroxyl molecules OH* near the mesopause are useful indicators for dynamical and chemical processes in this region. It is well established that the main source of OH* in the Earth's mesosphere is the reaction H + O3 ? OH* + O2. During solar particle events (SPEs) energetic protons and electrons enter the polar atmosphere. The precipitating particles give rise to chemical perturbations. Of particular interest for the OH chemistry is the ion-chemical conversion of water molecules into H + OH. Additionally, there is SPE induced ozone loss. As the formation of OH* is dependent on O3 and H, large SPEs are expected to affect the hydroxyl airglow layer. Additionally, the changed abundance of atomic oxygen will impact the quenching of OH*. In addition to the direct initial chemical composition changes, SPEs are known to affect temperatures, and in turn reaction rates coefficients. We present satellite (SABER) observations of OH* emissions during the large SPE in October/November 2003. Preliminary results indicate significant disturbances of the OH* airglow layer, and a decrease in the OH* emission altitude. The measurement data are compared to results of model simulations. SPE effects on OH* are modelled by means of the UBIC (University of Bremen Ion Chemistry) model using SPE ionisation rates from AIMOS (Atmospheric Ionization Module Osnabrück). Temperature effects are accounted for by synthetic temperature disturbances as well as Aura-MLS measurements.

Winkler, Holger; von Savigny, Christian; Maik Wissing, Jan

2014-05-01

146

Deposition of colloid particles on protein layers: fibrinogen on mica.  

PubMed

Colloid particle deposition was applied to characterize fibrinogen (Fb) monolayers on mica, which were produced by controlled adsorption under diffusion transport. By adjusting the time of adsorption and the bulk Fb concentration, monolayers of desired surface concentration were obtained. The surface concentration of Fb was determined directly by AFM enumeration of single molecules adsorbed over the substrate surface. It was proven that Fb adsorbed irreversibly on mica both at pH 3.5 and at pH 7.4 with the rate governed by bulk transport. The electrokinetic properties of Fb monolayers produced in this way were studied using the streaming potential method. The dependence of the apparent zeta potential of Fb monolayers was determined as a function of the coverage. It was shown that for pH 3.5 the initial negative zeta potential of the mica substrate was converted to positive for Fb coverage exceeding 0.16. On the other hand, for pH 7.4, the zeta potential of a Fb-covered mica remained negative for the entire coverage range. The charge distribution in Fb monolayers was additionally studied using the colloid deposition method, in which negatively and positively charged polystyrene latex particles (ca. 800 nm in diameter) were used. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential was observed. Results of these experiments were quantitatively interpreted in terms of the fluctuation theory assuming that adsorption sites consisted of two and three Fb molecules, for pH 3.5 and 7.4, respectively. These results suggested that for pH 7.4, the distribution of charge on Fb molecules was heterogeneous, characterized by the presence of positive patches, whereas the average zeta potential was negative, equal to -19 mV. The utility of the colloid deposition method for studying Fb monolayers was further demonstrated in deposition experiments involving positive latex particles. It was shown that for a rather broad range of fibrinogen coverage, both the positive and the negative latex particles can adsorb on surfaces covered by Fb, which behaved, therefore, as superadsorbing surfaces. It was also concluded that the colloid deposition method can be used to determine the Fb bulk concentration for the range inaccessible for other methods. PMID:21316698

Adamczyk, Z; Nattich, M; Wasilewska, M; Sadowska, M

2011-04-15

147

Use of the photoacoustic spectroscopy for surface characterization of nanometer-sized cobalt-ferrite particles  

Microsoft Academic Search

Photoacoustic spectroscopy was used in the investigation of cobalt ferrite nanosized particles (about 5 nm in diameter) surface-uncoated or surface-coated with different species. The surface-coated nanoparticles display well defined photoacoustic features in the wavelength region typical of d-d transitions of the transition element ions. Removal of the surface-coating layer by thermal treatment strongly quenches the photoacoustic feature, probably due to

P. C. Morais; L. B. Silveira; J. G. Santos; A. C. Oliveira; A. L. Tronconi; R. L. Santos; E. C. D. Lima; J. M. Marchetti; A. C. Tedesco

2005-01-01

148

Modeling of turbulent transport in the surface layer  

NASA Technical Reports Server (NTRS)

The turbulence equations as written by Donaldson using the method of invariant modeling have been applied to the following limiting cases of the surface or constant flux layer of the planetary boundary layer: (1) Neutrally stable; (2) stable (above influence of surface roughness); (3) nearly neutrally stable; and (4) very unstable (free convection). For the neutrally stable case, the equations are shown to admit as a solution the familiar logarithmic profile. By use of this result, boundary conditions suitable for the surface layer are defined and are simple to apply to rough surfaces.

Smith, G. L.

1973-01-01

149

Characterization of interfacial morphology in polymer electrolyte fuel cells: Microporous layer and catalyst layer surfaces  

Microsoft Academic Search

The interface between the micro-porous layer (MPL) and the catalyst layer (CL) can have an impact on thermal, electrical and two-phase mass transport in a polymer electrolyte fuel cell (PEFC). However, there is scant information available regarding the true morphology of the MPL and CL surfaces. In this work, optical profilometry is used to characterize the MPL and CL surfaces

F. E. Hizir; S. O. Ural; E. C. Kumbur; M. M. Mench

2010-01-01

150

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

151

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

152

Ferromagnetism on surface of YBa2Cu3O7 particle  

NASA Astrophysics Data System (ADS)

In recent experiments, a special ferromagnetism of YBa2Cu3O7 (YBCO) particles has been found at room-temperature. In this paper we mimic a YBCO particle using a small YBCO cluster and different YBCO surfaces. The magnetic properties of the small cluster and surfaces are calculated using ab initio density functional theory (DFT). According to our calculations, we infer that the ferromagnetism of the YBCO particle comes from the surfaces of the YBCO particle, which is contributed by both p electrons of oxygen atoms and d electrons of Cu atoms, and extends to several atomic layers beneath surface. The surface magnetism is similar to the itinerant magnetism and closely relative to low coordination number, spatial-inversion symmetry breaking and electric neutral condition. Our results indicate that the enhanced magneto-electric coupling induced by broken spatial inversion symmetry near surface layer plays an important role on the surface ferromagnetism of YBCO particle. The ferromagnetism on surface of YBCO particle can be significantly depressed in highly c-axis unique oriented films because the proportions of weak-links are small due to the reductions of pores, voids and micro-cracks.

Fan, Wei; Zou, Liang-Jian; Zeng, Zhi

2013-09-01

153

Effect of the solar wind on the formation of a photoinduced dusty plasma layer near the surface of the Moon  

NASA Astrophysics Data System (ADS)

A dusty plasma layer formed near the illuminated part of the surface of the Moon under the action of ultraviolet radiation, as well as fast and slow solar wind, has been numerically simulated. The numerical calculations including the photoemission properties of lunar regolith samples delivered to the Earth have been compared to estimates within known theoretical models. It has been shown that the flux of solar wind particles plays an important role in the formation of the surface photoelectron layer. The conditions of the charging and stable levitation of dust particles in the surface plasma layer of the Moon have been analyzed.

Lisin, E. A.; Tarakanov, V. P.; Petrov, O. F.; Popel', S. I.; Dol'nikov, G. G.; Zakharov, A. V.; Zelenyi, L. M.; Fortov, V. E.

2014-02-01

154

Surface cracking in layers under biaxial, residual compressive stress  

Microsoft Academic Search

Thin two-phase, AlâOâ\\/t-Zr(3Y)Oâ layers bounded by much thicker Zr(3Y)Oâ layers were fabricated by co-sintering powders. After cooling, cracks were observed along the center of the two-phase, AlâOâ\\/t-Zr(3Y)Oâ layers. Although the AlâOâ\\/t-Zr(3Y)Oâ layers are under residual, biaxial compression far from the surface, tensile stresses, normal to the center line, exist at and near the surface. These highly localized tensile stresses can

S. Ho; C. Hillman; F. F. Lange; Z. Suo

1995-01-01

155

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

156

Microstructure of Fe-B-Si Alloy Surface Layers Produced by Laser-Quenching  

NASA Astrophysics Data System (ADS)

Laser-quenching was performed to produce an amorphous alloy layer on metal blocks. Fe78B13Si9 alloy film brazed onto the surface of a stainless steel plate was melt-quenched by pulsed YAG or cw CO2 laser irradiation. Transmission electron microscope and high-resolution electron microscope observations were carried out to study the microstructure of the laser-quenched layers. In both cases, at the region very close to the free surface in the laser-quenched layer, amorphous and crystalline phases were observed. The internal area of the pulsed YAG laser-quenched layer consisted of an amorphous phase including a small amount of nanometer-size crystalline particles, while that of the cw CO2 laser-quenched layer consisted of mainly an amorphous single phase, partially including heat-affected zones in the neighborhood of the overlapped area of laser irradiation.

Hirose, Fusao; Takagi, Makoto; Mori, Hideshi; Kitoh, Yasuo; Imura, Toru

1992-12-01

157

Manganese–nitrogen–sulphur surface layers produced on aluminium alloys  

Microsoft Academic Search

The main reason of the surface modification of the components such as pistons and cylinder blocks made of cast aluminium alloys is to obtain high hardness, wear and corrosion resistance of the working surface for larger lifetime of the motor-car and aircraft engines. In that aspect, the new conception of creating — by hybrid method — surface layers containing manganese,

W. Serbi?ski

2005-01-01

158

LETTER TO THE EDITOR: Surface-sensitive particle selection by driving particles in a nematic solvent  

Microsoft Academic Search

Electrophoresis and sedimentation (or ultracentrifugation) are powerful means for separating particles, proteins, and DNA, exploiting the difference in particle charge, mass, and size. Surface properties of colloids and proteins are closely related to their physical, chemical, and biological functions. Thus, the selection of particles in terms of their surface properties is highly desirable. The possibility of replacing a simple liquid

Takeaki Araki; Hajime Tanaka

2006-01-01

159

Kinetics of dust particles around the scrape off layer in fusion devices  

NASA Astrophysics Data System (ADS)

A kinetic model based on the balance of charge and energy over the dust particle surface around the scrape off layer (SOL) region in fusion devices has been developed; for describing the dust mass diminution, its temperature evolution and phase change process have been taken into account. The formulation has been utilized to determine the lifetime of cylindrical and spherical dust particles. A realistic situation in fusion devices, when the plasma exhibits meso-thermal flow, has been taken into account; for this purpose a rigorous approach, pioneered by Mott-Smith and Langmuir (1926 Phys. Rev. 28 727), has been adopted to derive the general expressions for the electron (ion) current on cylindrical dust surfaces and the corresponding mean energy of accreting electrons/ions in a flowing plasma. On the basis of analytical modelling the numerical results for the dust electric potential energy and the lifetime of the dust particles corresponding to a typical plasma environment near the SOL region of Mega Ampere Spherical tokamak (MAST)/Joint European Torus (JET) fusion devices have been evaluated for graphite and tungsten dust particles. The results are graphically illustrated as functions of particle size, electron/ion temperature and plasma ionization. It is seen that a large dust particle immersed in low temperature plasma can survive for long time; as an important outcome it is also noticed that the cylindrical particles of tungsten last longer than spherical particles. The findings are of relevance in characterizing and simulating the effects of a variety of dusts for experimental campaigns in large scale (ITER/Demo-like) fusion devices.

Mishra, S. K.; Misra, Shikha; Sodha, M. S.

2014-05-01

160

Effect of precursor-layer surface charge on the layer-by-layer assembly of polyelectrolyte/nanoparticle multilayers.  

PubMed

In this Article, we investigate the effect of a precursor layer, which is composed of four bilayers of polyethyleneimine (PEI) and poly(sodium styrene sulfonate) (PSS), on the subsequent LBL assembly of hybrid films composed of indium tin oxide (ITO) nanoparticles and PSS. A precursor polyelectrolyte layer is usually deposited to minimize interference by the substrate. It is shown here that the "effective" surface charge of the precursor layer can significantly affect the subsequent assembly behavior of [ITO/PSS](9.5) hybrid thin films. Depending on the surface charge of the precursor layer, the subsequent LbL assembly of [ITO/PSS](9.5) hybrid films can exhibit either one or two regimes. When two growth regimes are present, the first one consists of a "recovery regime", and the second is the expected "linear growth regime." The length of the "recovery regime" is dependent on how much positive charge the precursor layer possesses and how fast this surface charge can be compensated. This work reveals for the first time that changes in the surface charge of the precursor layer can have a significant effect on the subsequent LBL assembly process. The surface charge of the precursor layer was investigated using ?-potential measurements on model silica microspheres. These experiments showed that the surface charge of the precursor layer, [PEI/PSS](4), is dependent on the pH of the solution in which it is immersed, and that it can reverse from a negatively charged surface to a positively charged one, at sufficiently low pH due to the protonation of PEI, despite having the negatively charged PSS layer as the outermost layer. PMID:22087546

Peng, Chunqing; Thio, Yonathan S; Gerhardt, Rosario A

2012-01-10

161

Modulating Particle Adhesion with Micro-patterned Surfaces.  

PubMed

We report the first experimental study on the modulation of adhesion force distribution by surface micro-patterns and its impact on particle attachment. The effect of substratum topography on particle adhesion was evaluated using well-defined microscopic surface patterns consisting of orthogonal arrays of cuboid pillars or pits with different sizes and spacing fabricated by the conventional photolithography and reactive ion etching (RIE). Adhesion of carboxyl modified poly(styrene-co-acrylic-acid) particles of 6 ?m in diameter under favorable deposition conditions was found to be markedly lower on all the micro-patterned surfaces compared with that on the smooth control surface, and particle adhesion depended on the characteristic dimensions of the surface micro-structures relative to the particle size. Particle adhesion was minimal when the pillar cross-sectional dimension was below a critical value close to the diameter of the particle while the spacing between pillars was less important. Meanwhile, particles adhered displayed unique distribution on the micro-patterned surfaces. The majority of particles preferentially adhered on or close to the edge of the pillars (in the valley). Atomic force microscopy measurements using a colloidal probe revealed that the surface features strongly modulated the spatial and probability distribution of adhesion forces on the micro-patterned surfaces. Micro-sized pillars changed the adhesion force probability distribution from monomodal to bimodal, with significantly reduced maximum adhesion force. This was hypothesized to be responsible for the reduced total particle adhesion. PMID:24773375

Yu, Cong; Ma, Jianwei; Zhang, Jiangnan; Lou, Jun; Wen, Donghui; Li, Qilin

2014-06-11

162

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

163

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

164

FEM modelling of surface acoustic wave in diamond layered structure  

Microsoft Academic Search

This paper describes a general finite element method (FEM) for the AC steady state analysis of two-dimensional piezoelectric devices. The method is applied to a diamond based surface acoustic wave (SAW) layered structure. We determined the penetration depth of the elastic waves corresponding to ZnO layer of 1 mum thick and spatial periodicity of 4 mum. The structure admittance response

L. Le Brizoual; F. Sarry; F. Moreira; O. Elmazria

2006-01-01

165

Thin gold layer in Ni electroforming process: optical surface characterization  

NASA Astrophysics Data System (ADS)

Mandrel replication by Nickel electroforming is a well-suited process to manufacture X-ray mirrors, making use of Gold layer playing the twofold role of release agent and reflective coating. To increase the optical performances of mirrors it is crucial to minimize the impact of X-ray scattering effects related to surface microroughness, especially when the mirror is intended to operate in hard X-rays. In this case, the Gold layer simply acts as release agent because the reflection is demanded to interferential over-coatings. Even though the replicated optical surface is usually believed to reproduce the smooth topography of the master, a surface degradation is commonly observed. Such a worsening can also suffer from a contribution from the spontaneous roughness growth of the Gold layer itself: if this is the case, the mirror's optical quality could potentially benefit from the utilization of a thin Gold layer (< 100 nm) instead of the traditional thick gold layer (> 100 nm). To prove the effectiveness of the Gold thickness reduction, a microroughness characterization of replicated thin gold layers has been achieved. We report here a preliminary roughness study of 3 electroformed Ni samples replicated from a super-polished Zerodur flat master with various Gold layer thicknesses, in the spectral range 0.02-1000 ?m. The study is organized as follows: (a) characterization of the 3 replicated samples; (b) comparison of the Gold roughness for thin vs. thick layers; (c) comparison of the two sides of Gold layers.

Sironi, G.; Spiga, D.; Pareschi, G.; Missaglia, N.; Paganini, L.

2009-08-01

166

Tribological properties of adsorbed water layer on silicon surfaces  

Microsoft Academic Search

Tribological properties of adsorbed water layer on solid surface in sliding contact have not yet been fully understood. In\\u000a this regard, it is important to better understand how surface hydrophilicity and humidity influence the tribological behavior\\u000a of adsorbed water-mediated microcontact. In this study, we investigated the influence of adsorbed water layer and capillary\\u000a force on friction as a function of

Doo-In Kim; Kwang-Ho Kim; Hyo-Sok Ahn

2010-01-01

167

Surface characterisation of cerium layers on galvanised steel  

Microsoft Academic Search

The present paper investigates the inhibition mechanisms of CeCl3·7H2O in a range of concentrations, 100–1000 ppm, on hot dip galvanised steel in 3.5 wt.% NaCl solution. Following 4 h immersion in the studied solution, galvanised steel develops a yellow layer on the surface. X-ray photoelectron spectroscopy (XPS) revealed that the layer is composed of two regions: a surface region, which

M. A. Arenas; J. J. de Damborenea

2004-01-01

168

Markov chain simulations of vertical dispersion in the neutral surface layer for surface and elevated releases  

Microsoft Academic Search

Vertical dispersion in the neutral surface layer is investigated using a Markov Chain simulation procedure. The conceptual basis of the procedure is discussed and computation procedures outlined. Wind and turbulence parameterizations appropriate to the neutral surface layer are considered with emphasis on the Lagrangian time scale. Computations for a surface release are compared with field data. Good agreement is found

John D. Reid

1979-01-01

169

Surface acoustic wave-induced precise particle manipulation in a trapezoidal glass microfluidic channel  

NASA Astrophysics Data System (ADS)

Surface acoustic wave (SAW) excitation of an acoustic field in a trapezoidal glass microfluidic channel for particle manipulation in continuous flow has been demonstrated. A unidirectional interdigital transducer (IDT) on a Y-cut Z-propagation lithium niobate (LiNbO3) substrate was used to excite a surface acoustic wave at approximately 35 MHz. An SU8 layer was used for adhesive bonding of the superstrate glass layer and the substrate piezoelectric layer. This work extends the use of SAWs for acoustic manipulation to also include glass channels in addition to prior work with mainly poly-di-methyl-siloxane channels. Efficient alignment of 1.9 µm polystyrene particles to narrow nodal regions was successfully demonstrated. In addition, particle alignment with only one IDT active was realized. A finite element method simulation was used to visualize the acoustic field generated in the channel and the possibility of 2D alignment into small nodal regions was demonstrated.

Johansson, L.; Enlund, J.; Johansson, S.; Katardjiev, I.; Wiklund, M.; Yantchev, V.

2012-02-01

170

[Linear clusters of gold nanoparticles in quasinematic layers of DNA liquid-crystalline dispersion particles].  

PubMed

The effects of small size (approximately 2 nm) gold nanoparticles on the properties of particles of cholesteric liquid-crystalline dispersions formed by double-stranded DNA molecules were analyzed. It has been shown that gold nanoparticles induce two different processes. First, they facilitate reorganization of the spatial cholesteric structure of dispersion particles to nematic one. This process is accompanied by the fast decrease in the amplitude of abnormal band in the CD spectrum. Second, they can form ensembles consisting of gold nanoparticles. This process is accompanied by the development and displacement of surface plasmon resonance band in the visible region of the absorption spectrum. The appearance of this band is analyzed by considering two different models of the formation of ensembles consisting of gold nanoparticles. By small-angle X-ray scattering we performed structural analysis of phases formed by DNA cholesteric liquid-crystalline dispersion particles treated with gold nanoparticles. As a result of this study it was possible to prove the formation of linear clusters of gold nanoparticles in the "free space" between the adjacent DNA molecules fixed in the quasinematic layers of liquid-crystalline particles. It has been hypothesized that the formation of linear clusters of gold nanoparticles is most likely related to DNA molecules, ordered in the spatial structure of quasinematic layers, and the toxicity of these nanoparticles in biological systems hypothesized. PMID:23755545

Evdokimov, Iu M; Shtykova, E V; Salianov, V I; Skuridin, S G

2013-01-01

171

Tribological Properties of Surface Layer with Boron in Friction Pairs  

NASA Astrophysics Data System (ADS)

The aim of the present work is to determine the influence of technologically produced boron surface layers on the friction parameters in the sliding pairs under the conditions of mixed friction. The tribological evaluation included ion nitrided, pack borided, laser borided, quenched and tempered surface layers and TiB2 coating deposited on 38CrAlMo5-10, 46Cr2 and 30MnB4 steels. Modified surface layers of annular samples were matched under test conditions with counter-sample made from AlSn20 bearing alloy. Tested sliding pairs were lubricated with 15 W/40 Lotos mineral engine oil. The tribological tests were conducted on a T-05 block on ring tester. The applied steel surface layer modification with boron allows surface layers to be created with pre-determined tribological characteristics required for the elements of kinematic pairs operating in the conditions of sliding friction. Pack boronizing reduces the friction coefficient during the start-up of the frictional pair and the maximum start-up resistance level is similar to the levels of pairs with nitrided surface layers.

Lubas, Janusz

172

Turbulent boundary layer on a convex, curved surface  

NASA Technical Reports Server (NTRS)

The effects of strong convex curvature on boundary layer turbulence were investigated. The data gathered on the behavior of Reynolds stress suggested the formulation of a simple turbulence model. Three sets of data were taken on two separate facilities. Both rigs had flow from a flat surface, over a convex surface with 90 deg of turning, and then onto a flat recovery surface. The geometry was adjusted so that, for both rigs, the pressure gradient along the test surface was zero - thus avoiding any effects of streamwise acceleration on the wall layers. Results show that after a sudden introduction of curvature, the shear stress in the outer part of the boundary layer is sharply diminished and is even slightly negative near the edge. The wall shear also drops off quickly downstream. In contrast, when the surface suddenly becomes flat again, the wall shear and shear stress profiles recover very slowly towards flat wall conditions.

Gillis, J. C.; Johnston, J. P.; Kays, W. M.; Moffat, R. J.

1980-01-01

173

Layer-by-layer deposition of praseodymium oxide on tin-doped indium oxide (ITO) surface  

Microsoft Academic Search

Praseodymium oxide as a thin film of controllable layer is known to display many unique physiochemical properties, which can be useful to ceramic, semiconductive and sensor industries. Here in this short paper, we describe a new chemical method of depositing praseodymium oxide on tin-doped indium oxide (ITO) surface using a layer-by-layer approach. The process is carried out by dipping the

S. Shrestha; C. M. Y. Yeung; F. Marken; C. E. Mills; S. C. Tsang

2007-01-01

174

Laser remelting of thermal-sprayed surface layers  

NASA Astrophysics Data System (ADS)

This paper deals with creation of the surface layer by means of the laser remelting of thermal sprayed coating. Thermal spraying of Ni, Cr, B and S created the primary coats onto the surface of specimens which base was made of the ordinary carbon steel 45-grade. The coated specimens were remelted with the beam CO2 1750W Wagner Basel layer. The hardiness of the remelted layers have highly increased when one compare with it the basic material and, almost twice if one compare it with the hardness of nickel, chromium, boron and silicon.

Bien, Anna

2000-11-01

175

Measurements near Bluff Bodies in Turbulent Boundary Layers Intended to Simulate Atmospheric Surface Layers.  

National Technical Information Service (NTIS)

A relatively new counter-jet technique is shown to be suitable for producing thick turbulent boundary layers which may be used to simulate neutral atmospheric surface layers in wind tunnels of moderate length. The increased thickness is achieved by provid...

J. Tan-Atichat H. M. Nagib

1974-01-01

176

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

177

Roughness Characterization of and Turbulent Boundary Layer Flow over flat Snow Surfaces  

NASA Astrophysics Data System (ADS)

The surface roughness is essential for all turbulent exchange processes within the lower part of the atmospheric boundary layer. Consequently, a proper representation of the surfaces roughness is needed in every mathematical description of near surface mass-, energy- and momentum exchange processes. Considering the vertical mean velocity profile of turbulent boundary layer flow, this is done by assigning an aerodynamic roughness length z0 to the surface. We followed two procedures to describe the roughness of freshly fallen snow surfaces. First, photographs of snow surfaces have been taken and evaluated using digital image analysis giving snow surface contour line coordinates. Applying structure functions to the snow surface coordinates and statistical fitting procedures, resulted in classes of surface characteristic length scales and scaling exponents. These results allow to identify the deposition process of snow fall as scaling exponents corresponded to that of Ballistic Deposition. Moreover, the resulting characteristic length scales can be assigned to typical particle size and aggregation size length scales consistent with results found by Lowe et al. (2007) and Manes et al. (2008). Second, aerodynamic roughness lengths z0 have been estimated from log-law fitting of velocity profiles over the snow surfaces measured in the SLF cold atmospheric boundary layer wind tunnel. The aerodynamic roughness lengths found are in general agreement with available literature data and suggest the presence of aerodynamically rough regimes with flow independent z0. In the synthesis of both approaches, we found evidence for a linear relationship between one class of surface characteristic length scales, which is associated with typical snow particle sizes, and aerodynamic roughness lengths z0. The correlation with the aggregation length scale is weaker for the few (4) samples analyzed thus far. The relatively weak pronounced scale separation between particle and aggregation size scales as found from the random field approach analysis can serve as a possible explanation.

Gromke, C.; Guala, M.; Manes, C.; Walter, B.; Lehning, M.

2009-12-01

178

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

2013-11-25

179

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

180

Thermocapillary convection in two immiscible liquid layers with free surface  

NASA Technical Reports Server (NTRS)

Thermocapillary convection is studied in two immiscible liquid layers with one free surface, one liquid/liquid interface, and differential heating applied parallel to the interfaces. An analytical solution is introduced for infinite horizontal layers. The defining parameter for the flow pattern is lambda, the ratio of the temperature coefficient of the interfacial tension to that of the surface tension. Four different flow patterns exist under zero gravity conditions. 'Halt' conditions which halt the fluid motion in the lower encapsulated liquid layer have been found. A numerical experiment is carried out to study effects of vertical end walls on the double layer convection in a 2D cavity. The halt condition obtained from the analytical study is found to be valid in the limit of small Reynolds numbers. The flow in the encapsulated liquid layer can be suppressed substantially.

Doi, Takao; Koster, Jean N.

1993-01-01

181

Thermocapillary convection in two immiscible liquid layers with free surface  

NASA Astrophysics Data System (ADS)

Thermocapillary convection is studied in two immiscible liquid layers with one free surface, one liquid/liquid interface, and differential heating applied parallel to the interfaces. An analytical solution is introduced for infinite horizontal layers. The defining parameter for the flow pattern is lambda, the ratio of the temperature coefficient of the interfacial tension to that of the surface tension. Four different flow patterns exist under zero gravity conditions. 'Halt' conditions which halt the fluid motion in the lower encapsulated liquid layer have been found. A numerical experiment is carried out to study effects of vertical end walls on the double layer convection in a 2D cavity. The halt condition obtained from the analytical study is found to be valid in the limit of small Reynolds numbers. The flow in the encapsulated liquid layer can be suppressed substantially.

Doi, Takao; Koster, Jean N.

1993-08-01

182

Surface density of states of layered f-electron materials  

NASA Astrophysics Data System (ADS)

We theoretically analyze the surface density of states of heavy fermion materials such as CeCoIn5. Recent experimental progress has made it possible to locally probe the formation of heavy quasiparticles in these systems via scanning tunneling microscopy, in which strongly temperature-dependent resonances at the Fermi energy have been observed. The shape of these resonances varies depending on the surface layer, i.e., if cerium or cobalt terminates the sample. We clarify the microscopic origin of this difference by taking into account the layered structure of the material. Our simple model explains all the characteristic properties observed experimentally, such as a layer-dependent shape of the resonance at the Fermi energy, displaying a hybridization gap for the cerium layer and a peak or dip structure for the other layers. Our proposal resolves the seemingly unphysical assumptions in the preceding analysis based on the two-channel cotunneling model.

Peters, Robert; Kawakami, Norio

2014-01-01

183

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

184

Characterization of triboelectrically charged particles deposited on dielectric surfaces  

NASA Astrophysics Data System (ADS)

A device for the measurement of q/m-values and charge degradation of triboelectrically charged particles deposited on a surface was developed. The setup is based on the integration of currents, which are induced in a Faraday cage by insertion of a solid support covered with charged particles. The conductivity of different particle supports was taken into account. The 'blow-off' method, in which the particles are first deposited, and then blown off using an air stream, can be used for characterization of triboelectric properties of particles relative to different surfaces.

Nesterov, A.; Löffler, F.; Cheng, Yun-Chien; Torralba, G.; König, K.; Hausmann, M.; Lindenstruth, V.; Stadler, V.; Bischoff, F. R.; Breitling, F.

2010-04-01

185

Imaging of sub-surface nano particles by tapping-mode atomic force microscopy  

Microsoft Academic Search

Time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and tapping mode atomic force microscopy (TM-AFM) were used to study the surface of a poly(N-vinyl-2-pyrrolidone) thin film containing nano silica particles. ToF-SIMS results illustrate that the topmost layer of the thin film consists of PVP and a small amount of poly(dimethyl siloxane) (PDMS). Nano silica particles are localized underneath

Jiyun Feng; Lu-Tao Weng; Chi-Ming Chan; Jie Xhie; Lin Li

2001-01-01

186

Particle-surface interactions in chemical mechanical polishing  

SciTech Connect

Material removal in chemical mechanical polishing (CMP) occurs by a pressure accentuated chemical attack of the surface. The polishing slurry typically consists of abrasive particles and reactive chemicals that may or may not include an oxidant. Post-CMP cleaning processes must remove both the ionic contaminants and any remaining polishing slurry particles. Central to the effectiveness of a clean is the use of conditions that will minimize the binding force between the residual particles and the wafer surface. The morphology and composition of the particle, the surface from which it must be removed, and the environment surrounding the wafer will determine the magnitude of forces that hold a particle to the wafer surface. At the Sandia/SEMATECH Center for Contamination Free Manufacturing, two techniques--atomic force microscopy (AFM) and electrokinetic deposition--are being used to explore these interactions for CMP of both oxide and tungsten surfaces. A basic understanding of particle-surface interaction forces and how they are affected by the chemical/physical environment of the particle and surface is the objective of this task. Modification of the binding forces between particles and wafer surfaces may be used to maximize post-CMP cleaning effectiveness.

Dugger, M.T.; Adkins, C.L.J.; Resnick, P.J. [Sandia National Labs., Albuquerque, NM (United States); Jeon, J.S.; Raghavan, S. [Univ. of Arizona, Tucson, AZ (United States). Dept. of Materials Science and Engineering

1996-10-01

187

Response of the Tropical Boundary Layer to Weak Surface Forcing  

NASA Technical Reports Server (NTRS)

During the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE), a series of airborne thermal infrared observations and in situ atmospheric measurements were made near the sea surface through heights exceeding 4 km. Air movements associated with the sea surface temperature and the marine atmospheric boundary layer were studied.

Hagan, D.; Rogers, D.

1995-01-01

188

Spray in the Atmospheric Surface Layer: Laboratory Study  

Microsoft Academic Search

The air-sea interface is disrupted at high wind velocities, when water droplets are found in the atmospheric surface layer. Kraus [1967] has suggested that an appreciable momentum transfer from air to water may take place as the droplets accelerated by rapidly moving air fall back into slowly moving water. An increase of gross evaporation from the sea surface is expected

Jin Wu

1973-01-01

189

Aerosol influences on marine atmospheric surface layer optics  

Microsoft Academic Search

Shipboard optical system are used as passive sensors for threat detection. When a threat is at low altitude part of the optical path from it may lie in the marine surface layer where it is distorted by refractivity gradients caused by large vertical changes in temperature and humidity in the first several meters above the sear surface. In addition, the

Philip L. Walker

1998-01-01

190

Nano-porous layer on steel surface as lubricant carrier.  

PubMed

In cold forging of steels, metal soap on zinc-phosphate coating is excellent lubrication system. However, the system is not only less productive, but produces hazardous wastes. In this study, an alternative lubrication system using surface porous layer is proposed. Surface oxide on low carbon steel turns into porous layer by chemical reduction using hydrogen. It is found that liquid lubricant decreases the friction coefficient in compression greatly. The porous surface enhances the decrease, especially in the cases of heavy deformation. PMID:21456283

Utsunomiya, Hiroshi; Kawajiri, Shogo; Takahira, Nobuyuki; Sakai, Tetsuo; Tanaka, Toshihiro

2011-02-01

191

Designing structured surfaces that repel fluid-borne particles  

NASA Astrophysics Data System (ADS)

Using computational modeling, we examine particle-laden flows along surfaces decorated with periodic arrays of tilted posts. We show that when high-aspect-ratio posts are tilted against the flow direction, cross-stream circulatory secondary flows emerge. These circulatory flows enhance the net lift force acting on finite-sized particles transported by fluid, thereby repelling the particles from the wall and preventing their deposition. This hydrodynamic effect can potentially be used for designing antifouling and self-cleaning surfaces.

Semmler, Carina; Alexeev, Alexander

2011-12-01

192

Surface morphology and phase transitions in mixed NaCl/MgSO4 aerosol particles.  

PubMed

Probe molecule spectroscopy characterizes the surface environment of mixed NaCl/MgSO(4) (0.01-50 wt % MgSO(4)) aerosol particles as a model for marine aerosol. Two complementary measurements, the probe's excited state spectroscopy and photoionization efficiency, measure the electronic properties of the particle surface and monitor phase changes that are driven by changes in relative humidity (RH). The results illustrate that over a wide range of composition, these particles have a layered structure with NaCl in the core and primarily hydrated MgSO(4) at the surface. Modeling the spectroscopic data reveals that the surface layer is not a uniform shell and that the coumarin 314 probe molecules partition selectively to the MgSO(4) domains. The surface layer has a pi* value of 1.7, indicative of a very high interfacial polarity. In cases where MgSO(4) is a minor component (< or = 10 wt %), the NaCl component crystallizes at 44% RH, consistent with the single salt NaCl result. Deliquescence-mode experiments with these particles show that the MgSO(4) component forms a solution at 42% RH, prior to the full deliquescence of the particle. For mixed particles with 50 wt % MgSO(4), the crystallization of NaCl occurs at 35% RH, and the predeliquescence of MgSO(4) occurs at 38% RH owing to the contribution of MgCl(2) in the surface layer. A model surfactant, SDS, slightly lowers the RH of the NaCl formation to approximately 42% and leads to the formation of a thin soap film that persists to low values of RH. PMID:20131889

Woods, Ephraim; Chung, Daniel; Lanney, Howard M; Ashwell, Benjamin A

2010-03-01

193

Forming Nanocrystalline Surface Layers in Copper Using Friction Stir Processing  

Microsoft Academic Search

In the present work, a nanostructured layer was formed on the surface of pure copper via friction stir processing (FSP). The surface nanostructuring can be of significant importance in terms of surface-dependent properties such as fatigue, wear, coating, and even corrosion. During FSP, the applied rotating and traverse speeds were 1600 rpm and 50 mm\\/min, respectively. The results show that a nanograin

K. Dehghani; M. Mazinani

2011-01-01

194

Generalized optical theorem for surface waves and layered media  

SciTech Connect

We present a generalized optical theorem for surface waves. The theorem also applies to body waves since under many circumstances body waves can be written in terms of surface-wave modal summations. This theorem therefore extends the domain of applicability of the optical theorem from homogeneous background media to a general class of body and surface-wave propagation regimes within layered elastic media.

Halliday, David; Curtis, Andrew [School of GeoSciences, Grant Institute, University of Edinburgh, Kings Buildings, West Mains Road, Edinburgh EH93JW (United Kingdom)

2009-05-15

195

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

196

Entrainment of fine particles from surfaces by impinging shock waves  

NASA Astrophysics Data System (ADS)

When a shock wave impinges on a surface, it reflects and propagates across the surface at supersonic velocity. The gas is impulsively accelerated by the passing shock wave. The resulting high-speed flow imparts sufficiently strong forces to particles on the surface to overcome strong adhesive forces and entrain the surface-bound particles into the gas. This paper describes an experimental study of the removal of fine particles from a surface by impinging shock waves. The surfaces examined in this study were glass slides on which uniformly sized (8.3 ?m diameter), spherical polystyrene particles had been deposited. Shock waves were generated in a small, open-ended shock tube at various heights above and impingement angles to the surface. Particle detachment from the carefully prepared substrates was determined from images of the surfaces recorded before and after shock impingement. A single shock wave effectively cleaned a large surface area. The centerline length of the cleared region was used to characterize the efficacy of shock cleaning. A model based upon the far field solution for a point source surface shock provides a good fit to the clearance length data and yields an estimate to the threshold shock strength for particle removal.

Smedley, G. T.; Phares, D. J.; Flagan, R. C.

197

Assembly of erodible, DNA-containing thin films on the surfaces of polymer microparticles: Toward a layer-by-layer approach to the delivery of DNA to antigen-presenting cells  

Microsoft Academic Search

We report a layer-by-layer approach to the assembly of ultrathin and erodible DNA-containing films on the surfaces of polymer microparticles. DNA-containing multilayered films were fabricated layer-by-layer on the surfaces of polystyrene microspheres (?6?m) by iterative and alternating cycles of particle suspension, centrifugation and resuspension in solutions of plasmid DNA and a hydrolytically degradable polyamine. Film growth occurred in a stepwise

Eric M. Saurer; Christopher M. Jewell; Jon M. Kuchenreuther; David M. Lynn

2009-01-01

198

Effect of sequential layer-by-layer surface modifications on the surface energy of plasma-modified poly(dimethylsiloxane).  

PubMed

Surface-initiated grafting of N,N-dimethylacrylamide, styrenesulfonate (SS), and (ar-vinylbenzyl)trimethylammonium chloride (VBTAC) from microwave plasma carboxylated, initiator-functionalized poly(dimethylsiloxane) (PDMS) surfaces was accomplished utilizing reversible addition-fragmentation chain transfer (RAFT) polymerization. Surface spectroscopic attenuated total reflectance (ATR) FT-IR analysis and atomic force microscopy (AFM) measurements were utilized to determine surface grafting and morphological surface features. The VBTAC-grafted PDMS provided a smooth, hydrophilic cationic surface for creating layer-by-layer (LBL) surfaces via alternating deposition of well-defined poly(SS) and poly(VBTAC), also prepared via aqueous RAFT. Comparisons of the ATR FT-IR spectra of the LBL assemblies and those of respective anionic poly(SS) and cationic poly(VBTAC) components confirmed strong electrostatic complexation of a fraction of the sulfonate and quarternary ammonium species in the layers as well as the existence of noncomplexed species. AFM images of surface topology indicated the presence of domains, likely phase-separated segments of the respective homopolymers, as well as interlayer mixing. The employed LBL methodology results in formation of stable, highly hydrophilic surfaces on a PDMS substrate. To our knowledge, this is the first study that illustrates surface functionalization of PDMS using microwave plasma and RAFT polymerization, followed by LBL deposition of polyelectrolytes. PMID:17209618

Bae, Woo-Sung; Convertine, Anthony J; McCormick, Charles L; Urban, Marek W

2007-01-16

199

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

200

Particle current on flexible surfaces excited by harmonic waves  

NASA Astrophysics Data System (ADS)

In this paper, a study on the directed particle current on flexible surfaces excited by a harmonic wave is reported. The proposed theory considers three different models for the kinematics of the surface, namely the Euler-Bernoulli, Timoshenko, and Rayleigh surface wave models. The particle-surface interaction terms in the theory incorporate Coulomb friction and inelastic collision between the particle and the surface. Three possible phases of motion, namely sticking, sliding, and jumping, are considered, and the phase transition boundaries are estimated analytically for a general surface model. The effect of various parameters on the particle current and certain statistical features of the particle motion are then studied numerically. Remarkably, the particle current spectra exhibit, in addition to resonance modes, antiresonance and secondary resonance modes and transversal zero crossings. These features have interesting implications for the particle dynamics in terms of dynamic jamming states and particle eddies, which are pointed out. Under certain restricted conditions, averaging calculations are also performed and compared with the corresponding numerical simulations.

Verma, Neeta; DasGupta, Anirvan

2013-11-01

201

Surface modes in sheared boundary layers over impedance linings  

NASA Astrophysics Data System (ADS)

Surface modes, being duct modes localized close to the duct wall, are analysed within a lined cylindrical duct with uniform flow apart from a thin boundary layer. As well as full numerical solutions of the Pridmore-Brown equation, simplified mathematical models are given where the duct lining and boundary layer are lumped together and modelled using a single boundary condition (a modification of the Myers boundary condition previously proposed by the author), from which a surface mode dispersion relation is derived. For a given frequency, up to six surface modes are shown to exist, rather than the maximum of four for uniform slipping flow. Not only is the different number and behaviour of surface modes important for frequency-domain mode-matching techniques, which depend on having found all relevant modes during matching, but the thin boundary layer is also shown to lead to different convective and absolute stability than for uniform slipping flow. Numerical examples are given comparing the predictions of the surface mode dispersion relation to full solutions of the Pridmore-Brown equation, and the accuracy with which surface modes are predicted is shown to be significantly increased compared with the uniform slipping flow assumption. The importance of not only the boundary layer thickness but also its profile (tanh or linear) is demonstrated. A Briggs–Bers stability analysis is also performed under the assumption of a mass–spring–damper or Helmholtz resonator impedance model.

Brambley, E. J.

2013-08-01

202

Evaluating Langmuir turbulence parameterizations in the ocean surface boundary layer  

NASA Astrophysics Data System (ADS)

is expected that surface gravity waves play an important role in the dynamics of the ocean surface boundary layer (OSBL), quantified with the turbulent Langmuir number (La=?{u&/us0}, where u* and us0 are the friction velocity and surface Stokes drift, respectively). However, simultaneous measurements of the OSBL dynamics along with accurate measurements of the wave and atmospheric forcing are lacking. Measurements of the turbulent dissipation rate ? were collected using the Air-Sea Interaction Profiler (ASIP), a freely rising microstructure profiler. Two definitions for the OSBL depth are used: the mixed layer derived from measurements of density >(h?>), and the mixing layer >(h?>) determined from direct measurements of ?. When surface buoyancy forces are relatively small, ??La-2 only near the surface with no dependency on La at mid-depths of the OSBL when using h? as the turbulent length scale. However, if h? is used then the dependence of ? with La-2 is more uniform throughout the OSBL. For relatively high destabilizing surface buoyancy forces, ? is proportional to the ratio of the OSBL depth against the Langmuir stability length LL. During destabilizing conditions, the mixed and mixing layer depths are nearly identical, but we have relatively few measurements under these conditions, rather than any physical implications. Observations of epsilon are compared with the OSBL regime diagram of Belcher et al. (2012) and are generally within an order of magnitude, but there is an improved agreement if h? is used as the turbulent length scale rather than h?.

Sutherland, G.; Christensen, K. H.; Ward, B.

2014-03-01

203

Surface layer mixing during the SAGE ocean fertilization experiment  

Microsoft Academic Search

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 SF6 tracer. During the experiment the mixed layer depth zmld ranged between 50 and 80m, with several re-stratifying events that brought zmld up to less than

Craig Stevens; Brian Ward; Cliff Law; Matt Walkington

2011-01-01

204

Single-layer graphene oxide films on a silicon surface  

NASA Astrophysics Data System (ADS)

A method is proposed to produce large-area single-layer graphene oxide films on the surface of semiconductor silicon wafers by precipitation from aqueous suspensions. Graphene oxide is synthesized from natural crystalline graphite during chemical oxidation and represents a wide-gap insulator. Single-layer graphene with a homogeneous-fragment size up to 50 ?m can be formed by the reduction of graphene oxide films, and this size is significantly larger than those achieved to date.

Aleksenskii, A. E.; Brunkov, P. N.; Dideikin, A. T.; Kirilenko, D. A.; Kudashova, Yu. V.; Sakseev, D. A.; Sevryuk, V. A.; Shestakov, M. S.

2013-11-01

205

Light scattering by surface waves on a vertical layer of liquid toluene.  

PubMed

It is demonstrated that light scattering from surface waves on a vertical liquid layer can be used for the determination of surface tension and kinematic viscosity of the liquid under investigation. In contrast to usual approaches of surface light scattering, a setup is described that enables measurements with the same setup as that with experiments for the determination of other thermophysical properties by light scattering from bulk fluids and without an imposed grating or seed particles. The experiments rely on a heterodyne detection scheme and a signal analysis by photon correlation spectroscopy. First results are presented for toluene over a temperature range from 323 to 483 K at saturation conditions. PMID:18264276

Fröoba, A P; Will, S; Leipertz, A

1997-10-20

206

New particle formation in the continental boundary layer: Meteorological and gas phase parameter influence  

Microsoft Academic Search

New particle formation in the polluted continental boundary layer was studied, based on 1.5-year observations of the particle size distribution, meteorological and gas phase parameters. Events of new particle formation involving significant ultrafine particle number concentrations (>104cm-3 in the size range 3-11 nm) were observed on 20% of all days, pointing out that a frequent particle production from gaseous precursors

Wolfram Birmili; Alfred Wiedensohler

2000-01-01

207

Superhydrophobic surfaces formed using layer-by-layer self-assembly with aminated multiwall carbon nanotubes.  

PubMed

A convenient and simple route to functionalized multiwall carbon nanotubes (MWNTs) using the reaction of the amine (NH) groups of polyethyleneimine (PEI) with MWNTs in N,N-dimethylformamide (DMF) at 50 degrees C is described. The product functionalized MWNTs (MWNT-NH-PEI) contain 6-8% by weight PEI based on elemental analysis, thermal gravimetric analysis, and titration. The products form stable emulsions in water below pH 9 and can be derivatized to form alkylated MWNTs that are dispersible in organic media. Such MWNT-NH-PEI nanoparticles can also be used in covalent or ionic layer-by-layer assembly to form nanocomposite thin films on functionalized polyethylene (PE) films and powders. Such nanocomposite films were analyzed by contact angle analysis, atomic force microscopy (AFM), and confocal Raman microscopy. These analyses show that these superhydrophilic surfaces have micro/nanoroughness with a roughly uniform distribution of MWNT nanoparticles. Superhydrophobic PE films can be formed either from ionic layer-by-layer self-assembly of MWNT-NH-PEIs and poly(acrylic acid) or from covalent layer-by-layer self-assembly of MWNT-NH-PEIs and Gantrez if the final graft is acrylated with a mixed anhydride prepared from ethyl chloroformate and octadecanoic acid. The resulting octadecylated surface produced by five covalent layer-by-layer deposition steps has a water contact angle of 165 degrees and a sliding angle of less than 5 degrees. The corresponding surface produced by five ionic layer-by-layer deposition steps has a water contact angle of 155 degrees but exhibits water pinning. The ionically assembled nanocomposite graft is labile under acidic conditions. The covalently assembled graft is more chemically robust. PMID:18324860

Liao, Kang-Shyang; Wan, Albert; Batteas, James D; Bergbreiter, David E

2008-04-15

208

The Turbulent Boundary Layer on a Rough Curvilinear Surface  

NASA Technical Reports Server (NTRS)

A number of semiempirical approximate methods exist for determining the characteristics of the turbulent boundary layer on a curvilinear surface. At present, among these methods, the one proposed by L. G. Loitsianskii is given frequent practical application. This method is sufficiently effective and permits, in the case of wing profiles with technically smooth surfaces, calculating the basic characteristics of the boundary layer and the values of the overall drag with an accuracy which suffices for practical purposes. The idea of making use of the basic integral momentum equation ((d delta(sup xx))/dx) + ((V' delta(sup xx))/V) (2 + H) = (tau(sub 0))/(rho V(exp 2)) proves to be fruitful also for the solution of the problems in the determination of the characteristics of the turbulent boundary layer on a rough surface.

Droblenkov, V. F.

1958-01-01

209

Long-time self-diffusion of charged spherical colloidal particles in parallel planar layers.  

PubMed

The long-time self-diffusion coefficient, D(L), of charged spherical colloidal particles in parallel planar layers is studied by means of Brownian dynamics computer simulations and mode-coupling theory. All particles (regardless which layer they are located on) interact with each other via the screened Coulomb potential and there is no particle transfer between layers. As a result of the geometrical constraint on particle positions, the simulation results show that D(L) is strongly controlled by the separation between layers. On the basis of the so-called contraction of the description formalism [C. Contreras-Aburto, J. M. Méndez-Alcaraz, and R. Castañeda-Priego, J. Chem. Phys. 132, 174111 (2010)], the effective potential between particles in a layer (the so-called observed layer) is obtained from integrating out the degrees of freedom of particles in the remaining layers. We have shown in a previous work that the effective potential performs well in describing the static structure of the observed layer (loc. cit.). In this work, we find that the D(L) values determined from the simulations of the observed layer, where the particles interact via the effective potential, do not agree with the exact values of D(L). Our findings confirm that even when an effective potential can perform well in describing the static properties, there is no guarantee that it will correctly describe the dynamic properties of colloidal systems. PMID:24985627

Contreras-Aburto, Claudio; Báez, César A; Méndez-Alcaraz, José M; Castañeda-Priego, Ramón

2014-06-28

210

An experimental investigation of turbulent boundary layers along curved surfaces  

NASA Technical Reports Server (NTRS)

A curved wall tunnel was designed, and an equilibrium turbulent boundary layer was set up on the straight section preceding the curved test section. Turbulent boundary layer flows with uniform and adverse pressure distributions along convex and concave walls were investigated. Hot-wire measurements along the convex surface indicated that turbulent mixing between fluid layers was very much reduced. However, the law of the wall held and the skin friction, thus determined, correlated well with other measurements. Hot-wire measurements along the concave test wall revealed a system of longitudinal vortices inside the boundary layer and confirmed that concave curvature enhances mixing. A self-consistent set of turbulent boundary layer equations for flows along curved surfaces was derived together with a modified eddy viscosity. Solution of these equations together with the modified eddy viscosity gave results that correlated well with the present data on flows along the convex surface with arbitrary pressure distribution. However, it could only be used to predict the mean characteristics of the flow along concave walls because of the existence of the system of longitudinal vortices inside the boundary layer.

So, R. M. C.; Mellor, G. L.

1972-01-01

211

Deposition Behavior of Copper Fine Particles onto Flat Substrate Surface in Cold Spraying  

NASA Astrophysics Data System (ADS)

Cold spray is a promising process to fabricate high-quality metallic coatings. However, it is necessary to improve some properties, especially the adhesive strength of the coating to the substrate to clarify deposition mechanism of the solid particles onto substrate surface. In this study, deposition behavior of the cold sprayed copper fine particles was observed precisely and the adhesive strength of the coating was evaluated. The deposition behavior of the sprayed individual copper particles on mirror polished stainless steel substrate was fundamentally investigated. The interface microstructure between sprayed particle and substrate revealed that an amorphous-like band region was recognized at interface during coating fabrication at high power conditions. For the deposition mechanism of the cold sprayed particles onto substrate surface, it was indicated that the deformation of the particles initially induce the destruction of its surface oxide and an appearance of the active fresh surface of the material may enhance the bonding between particles and substrate. On the other hand, in coating fabrication at high power condition, bonding between particle and substrate may be possibly formed via oxygen-rich amorphous-like layer at interface.

Fukumoto, M.; Mashiko, M.; Yamada, M.; Yamaguchi, E.

2010-01-01

212

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

213

Particle adhesion to surfaces under vacuum  

NASA Technical Reports Server (NTRS)

The release of glass beads and standard dust from aluminum and glass substrates under centrifugation (simulating atmospheric pressure, low vacuum, and high vacuum conditions) was measured, with application to the estimation of contaminant particle release during spacecraft launch. For particles in the 10-100 micron range, dust was found to adhere more strongly than glass beads in all the cases considered. For most of the cases, dust and glass beads adhered more strongly to glass than to aluminum at all pressures. The adhesion force for dust on glass at 10 torr was shown to be as small as the value for dust on aluminum.

Barengoltz, Jack B.

1988-01-01

214

Surface Dead Layer for Quasiparticles Near a Mott Transition  

NASA Astrophysics Data System (ADS)

Electron quasiparticles are progressively weakened by correlations upon approaching a continuos Mott metal-insulator transition in a bulk solid. We show that corresponding to the bulk weakening, a dead layer forms below the surface of the solid, where quasiparticles are exponentially suppressed. The surface dead layer depth is a bulk property and diverges when the Mott transition is approached. We describe this phenomenon in a Hubbard model within a self-consistent Gutzwiller approximation. The photoemission data of Rodolakis et al. [Phys. Rev. Lett. 102, 066805 (2009)] in V2O3 appear to be in accord with this physical picture.

Borghi, Giovanni; Fabrizio, Michele; Tosatti, Erio

2009-02-01

215

Surface dead layer for quasiparticles near a mott transition.  

PubMed

Electron quasiparticles are progressively weakened by correlations upon approaching a continuos Mott metal-insulator transition in a bulk solid. We show that corresponding to the bulk weakening, a dead layer forms below the surface of the solid, where quasiparticles are exponentially suppressed. The surface dead layer depth is a bulk property and diverges when the Mott transition is approached. We describe this phenomenon in a Hubbard model within a self-consistent Gutzwiller approximation. The photoemission data of Rodolakis et al. [Phys. Rev. Lett. 102, 066805 (2009)] in V2O3 appear to be in accord with this physical picture. PMID:19257622

Borghi, Giovanni; Fabrizio, Michele; Tosatti, Erio

2009-02-13

216

Effect of Nanoconfinement on Polymer Dynamics: Surface Layers and Interphases  

NASA Astrophysics Data System (ADS)

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.

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

2013-03-01

217

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

2013-03-01

218

The particle track record of the lunar surface.  

NASA Technical Reports Server (NTRS)

Information about lunar surface history revealed by fossil particle tracks is summarized. Such tracks are the result of damage left in dielectric materials by highly ionizing charged particles including heavy solar and galactic cosmic ray nuclei, heavy nuclei recoiling from cosmic ray induced spallation reactions, and induced- and spontaneous-fission fragments. From the distribution of cosmic ray and spallation tracks in the lunar rock, surface residence times of 1 to 30 million years and rock erosion rates of 1 to 10 A/yr have been determined. Particle tracks also record surface orientation and depth history of the rocks and contain information about ancient solar activity.

Comstock, G. M.

1972-01-01

219

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

220

Dead layer on silicon p–i–n diode charged-particle detectors  

NASA Astrophysics Data System (ADS)

Semiconductor detectors in general have a dead layer at their surfaces that is either a result of natural or induced passivation, or is formed during the process of making a contact. Charged particles passing through this region produce ionization that is incompletely collected and recorded, which leads to departures from the ideal in both energy deposition and resolution. The silicon p-i-n diode used in the KATRIN neutrino-mass experiment has such a dead layer. We have constructed a detailed Monte Carlo model for the passage of electrons from vacuum into a silicon detector, and compared the measured energy spectra to the predicted ones for a range of energies from 12 to 20 keV. The comparison provides experimental evidence that a substantial fraction of the ionization produced in the “dead” layer evidently escapes by diffusion, with 46% being collected in the depletion zone and the balance being neutralized at the contact or by bulk recombination. The most elementary model of a thinner dead layer from which no charge is collected is strongly disfavored.

Wall, B. L.; Amsbaugh, J. F.; Beglarian, A.; Bergmann, T.; Bichsel, H. C.; Bodine, L. I.; Boyd, N. M.; Burritt, T. H.; Chaoui, Z.; Corona, T. J.; Doe, P. J.; Enomoto, S.; Harms, F.; Harper, G. C.; Howe, M. A.; Martin, E. L.; Parno, D. S.; Peterson, D. A.; Petzold, L.; Renschler, P.; Robertson, R. G. H.; Schwarz, J.; Steidl, M.; Van Wechel, T. D.; VanDevender, B. A.; Wüstling, S.; Wierman, K. J.; Wilkerson, J. F.

2014-04-01

221

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

2011-11-22

222

Strength of silicon carbide layers of fuel particles for high-temperature gas-cooled reactors  

Microsoft Academic Search

A fuel design being developed for the high-temperature gas-cooled reactor consists of microspheres (particles) of a very small kernel of dense, sintered, enriched [sup 235]UCO encapsulated by several layers of pyrolytic carbon and a layer of silicon carbide (SiC). The coated fuel particles are often called TRISO[reg sign] particles. The SiC is derived via thermal decomposition of methyltrichlorosilane. This strong,

P. A. Lessing; R. J. Heaps

1994-01-01

223

Analytical models for describing cation adsorption\\/desorption kinetics as considering the electrostatic field from surface charges of particles  

Microsoft Academic Search

Surface charges of particles together with the adsorbed counter ions in diffuse layer can set up a strong electrostatic field around the particles in aqueous solution. The existent kinetic models for describing cation exchange on solid\\/liquid interface were either empirical or semi-empirical, and in which the electrostatic field is not considered. In this paper, as considering the important effect of

Rui Li; Hang Li; Chenyang Xu; Xinmin Liu; Rui Tian; Hualing Zhu; Laosheng Wu

224

The suppression of tin whisker growth by the coating of tin oxide nano particles and surface treatment  

Microsoft Academic Search

Tin oxide nano particles dispersed in water solution were sprayed on the tin-plated copper surface and served as coating layer in order to study its effect on the prevention of tin whisker formation. The results indicated that tin oxide nano particles could inhibit the growth of tin whiskers to certain extent. Many hillocks instead of long whiskers grew on the

Albert T. Wu; Y. C. Ding

2009-01-01

225

Motion and ablation of meteor particles in the upper layers of the atmosphere  

Microsoft Academic Search

A theoretical study of the motion of a meteor particle of arbitrary shape in the rarefied layers of the earth's atmosphere is presented. The mechanism of particle heating due to interaction with the outer gas flow is examined, with allowance for internal thermal conductivity; and changes of particle shape along its trajectory due to ablation are considered. Numerical calculations are

E. Z. Apshtein; N. N. Piliugin

1980-01-01

226

Evolving surface cusps during strained-layer epitaxy  

SciTech Connect

We have combined Z-contrast imaging and Ge marker layer experiments to study the evolving surface morphology of Si{sub x}Ge{sub 1-x} alloys grown by molecular beam epitaxy (MBE). Surface cusps are seen to arise as the intersection lines between coherent islands. The potential implications of stress concentrations associated with cusps are considered with a view to strain relaxation in the film via dislocation nucleation.

Jesson, D.E.; Pennycook, S.J. [Oak Ridge National Lab., TN (United States); Baribeau, J.M.; Houghton, D.C. [National Research Council of Canada, Ottawa, ON (Canada). Inst. for Microstructural Sciences

1993-04-01

227

Similarity forms for ground-source surface-layer diffusion  

Microsoft Academic Search

Past work on analyzing ground-source diffusion data in terms of surface-layer similarity theory is reviewed; these analyses assume that Sz\\/L orh\\/L is a function of u*x\\/uL (where h = Q\\/u ? ? dy). It is argued that an alternative scaling, h*\\/L versus x\\/L, is nearly as universal in that it is very weakly influenced by surface roughness, except for a

Gary A. Briggs

1982-01-01

228

Surface modification of polypropylene based particle foams  

NASA Astrophysics Data System (ADS)

This paper deals with the modification of the surface properties of expanded polypropylene (EPP). EPP is a semi-hard to soft elastic thermoplastic foam. The characteristic surface of EPP shows process-related steam nozzle imprints and gussets. Therefore EPP does not satisfy the quality requirements for visible automotive applications. In order to meet these demands, plastic surfaces are usually enhanced with functional or decorative coatings, e.g. textiles, plastic films or paint. The coating of plastics with low surface energies such as PP often leads to adhesion problems by reason of the missing polar and functional groups. This paper gives an evaluation of activation and pre-treatment methods of EPP, with the aim to identify the most suitable pre-treatment method. For this purpose five typical surface treatment methods - flame treatment, corona, fluorination, atmospheric and low-pressure plasma - were performed on EPP samples. As a comparison criterion the maximum increase in the adhesion force between a polyurethane-based coating and the modified EPP substrate was selected. Moreover the influence of the selected pre-treatment method on the increase in the total surface energy and its polar component was investigated by the drop shape analysis method. The results showed that the contact angle measurement is a suitable method to determine the polar and disperse fractions of the surface tension of EPP. Furthermore, all performed methods increased the adhesion of EPP.

Schreier, P.; Trassl, C.; Altstädt, V.

2014-05-01

229

A scheme for computing surface layer turbulent fluxes from mean flow surface observations  

NASA Technical Reports Server (NTRS)

A physical model and computational scheme are developed for generating turbulent surface stress, sensible heat flux and humidity flux from mean velocity, temperature and humidity at some fixed height in the atmospheric surface layer, where conditions at this reference level are presumed known from observations or the evolving state of a numerical atmospheric circulation model. The method is based on coupling the Monin-Obukov surface layer similarity profiles which include buoyant stability effects on mean velocity, temperature and humidity to a force-restore formulation for the evolution of surface soil temperature to yield the local values of shear stress, heat flux and surface temperature. A self-contained formulation is presented including parameterizations for solar and infrared radiant fluxes at the surface. Additional parameters needed to implement the scheme are the thermal heat capacity of the soil per unit surface area, surface aerodynamic roughness, latitude, solar declination, surface albedo, surface emissivity and atmospheric transmissivity to solar radiation.

Hoffert, M. I.; Storch, J.

1978-01-01

230

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

231

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

232

Characterization of triboelectrically charged particles deposited on dielectric surfaces  

Microsoft Academic Search

A device for the measurement of q\\/m-values and charge degradation of triboelectrically charged particles deposited on a surface was developed. The setup is based on the integration of currents, which are induced in a Faraday cage by insertion of a solid support covered with charged particles. The conductivity of different particle supports was taken into account. The 'blow-off' method, in

A. Nesterov; F. Löffler; Yun-Chien Cheng; G. Torralba; K. König; M. Hausmann; V. Lindenstruth; V. Stadler; F. R. Bischoff; F. Breitling

2010-01-01

233

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

234

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

235

Particle-surface interactions in chemical mechanical polishing.  

National Technical Information Service (NTIS)

Material removal in chemical mechanical polishing (CMP) occurs by a pressure accentuated chemical attack of the surface. The polishing slurry typically consists of abrasive particles and reactive chemicals that may or may not include an oxidant. Post-CMP ...

M. T. Dugger C. L. J. Adkins P. J. Resnick J. S. Jeon S. Raghavan

1996-01-01

236

Architecting boron nanostructure on the diamond particle surface  

NASA Astrophysics Data System (ADS)

The present study provides an efficient approach for nano-functionalization of diamond powders. Boron nanostructure can be grown on diamond particle entire surface by a simple heat-treatment process. After treatment, various boron nanoforms were grown on the diamond particle surface at different processing temperature. High-density boron nanowires (BNWs) grow on the diamond particle entire surface at 1333 K, while nanopillars cover diamond powders when the heat treatment process is performed at 1393 K. The influence of the pretreatment temperature on the microstructure and thermal conductivity of Cu/diamond composites were investigated. Cu/diamond composites with high thermal conductivity of 670 W (m K)-1 was obtained, which was achieved by the formation of large number of nanowires and nanopillars on the diamond particle surface.

Bai, H.; Dai, D.; Yu, J. H.; Nishimura, K.; Sasaoka, S.; Jiang, N.

2014-02-01

237

Saturn's rings - Particle size distributions for thin layer model  

NASA Technical Reports Server (NTRS)

A model incorporating limited interaction between the incident energy and particles in the ring is considered which appears to be consistent with the multiple scattering process in Saturn's rings. The model allows for the small physical thickness of the rings and can be used to relate Voyager 1 observations of 3.6- and 13-cm wavelength microwave scatter from the rings to the ring particle size distribution function for particles with radii ranging from 0.001 to 20 m. This limited-scatter model yields solutions for particle size distribution functions for eight regions in the rings, which exhibit approximately inverse-cubic power-law behavior.

Zebker, H. A.; Marouf, E. A.; Tyler, G. L.

1985-01-01

238

Particle\\/applicator interactions in household surface cleaning  

Microsoft Academic Search

Despite the wide use of household cleaning fluids, fundamental understanding of their performance is not extensive. Aside from the chemical compounds, abrasive particles are often integrated in cleaning fluids to increase their capacity to remove soil from surfaces.The mechanical actions of the particles (which operate in conjunction with a suitable applicator under a certain load) typically result in two wear

A. Zorcolo; R. Lewis; R. S. Dwyer-Joyce

2011-01-01

239

Surface energy balance and boundary layer development during snowmelt  

NASA Astrophysics Data System (ADS)

Improved prediction of snowmelt requires comprehensive data collection, including surface, subsurface, and atmospheric processes, during the snowmelt period. We report results of field research in which all components of the surface energy balance were measured during two different snowmelt periods, along with boundary layer soundings. The two periods were quite different, the first being overcast and the second occurring under clear skies. However, snowmelt was estimated relatively well from the cumulative residual of the energy balance in both cases. Downward infrared radiation and sensible heat flux were important contributors to the melt during overcast conditions, with net radiation providing about two thirds of the energy for melt and sensible heat providing the remainder. The sunny melt was dominated by direct solar heating of the surface. In both cases, estimation of melt as a residual of the energy balance agreed well with visual and gravimetric observations. The boundary layer soundings revealed the importance of advection, which was generally consistent with synoptic patterns during the period of the study. The data also showed a transition from advection-dominated to turbulence-dominated boundary layer budgets as the snowpack disappeared. The potential for convective cloud formation was also examined. Surface heating and entrainment outweighed adiabatic cooling and evaporation, resulting in the boundary layer top relative humidity decreasing as the snow melted and turbulent mixing increased.

Baker, J. M.; Davis, K. J.; Liknes, G. C.

1999-08-01

240

Surface Energy Balance and The Mixed Layer at Lake Tanganyika  

NASA Astrophysics Data System (ADS)

Lake Tanganyika is a very large (670 by 50 km) and deep rift lake (max depth 1.5 km) in East Africa between 3.5 and 9 degree south of the equator. Mixing of the upper layers in this meromictic lake is most intense in the trade wind season (May - September). Apart from increased wind speeds, lower air temperatures and evaporative cooling of the surface layer combine to enhance mixing. Previous work indicated that correlation of evaporation and heat loss from the lake leaves room for a significant portion in the variability of heat content to be explained by other factors. The components of the energy balance which contribute to mixing were compared among seasons and between the north and south ends of the lake, over diel and annual cycles. Sensible heat and latent heat fluxes were estimated with bulk aerodynamic formulas and the heat storage change in the surface water layer was determined. Solar radiation was measured and longwave and all-wave net radiation calculated. Evaporation provided a major contribution to mixing but varied per site and over seasons. Mixing intensity was related to oxygen and nutrient cycles. Apart from evaporative cooling, sensible heat transfer and the emission of long wave radiation were important mechanisms in cooling the surface layer at night. Sensible heat transfer and outgoing longwave radiation were relatively more important at the north end of the lake, compared with the south end, in explaining nocturnal heat loss from the surface.

Verburg, P.; Hecky, R.

2002-12-01

241

Luna 9 photographs: Evidence for a fragmental surface layer  

USGS Publications Warehouse

The morphological features of the lunar surface photographed by Luna 9 indicate a surficial layer of weakly cohesive to noncohesive fragmental material. Most of this material is finer than a centimeter and probably finer than a few millimeters, although objects of centimeter size and larger are plentiful.

Gault, D. E.; Quaide, W. L.; Oberbeck, V. R.; Moore, H. J.

1966-01-01

242

Corrosion of Aluminum IC Metaillization with Defective Surface Passivation Layer  

Microsoft Academic Search

Corrosion rates and corrosion current of aluminum line patterns passivated with PSG and silicon nitride were measured. Relationships between corrosion and various parameters including temperature, relative humidity, aluminum deposition method, alloying treatment, passivation layer type and defect density and contaminants are reported. A surface treatment which lowers corrosion currents is also discussed.

R. B. Comizzoli; L. K. White; W. Kern; G. L. Schnable; D. A. Peters; C. E. Tracy; R. D. Vibronek

1980-01-01

243

Laminarization of Turbulent Boundary Layer on Flexible and Rigid Surfaces  

NASA Technical Reports Server (NTRS)

An investigation of the control of turbulent boundary layer flow over flexible and rigid surfaces downstream of a concave-convex geometry has been made. The concave-convex curvature induces centrifugal forces and a pressure gradient on the growth of the turbulent boundary layer. The favorable gradient is not sufficient to overcome the unfavorable; thus, the net effect is a destabilizing, of the flow into Gortler instabilities. This study shows that control of the turbulent boundary layer and structural loading can be successfully achieved by using localized surface heating because the subsequent cooling and geometrical shaping downstream over a favorable pressure gradient is effective in laminarization of the turbulence. Wires embedded in a thermally insulated substrate provide surface heating. The laminarized velocity profile adjusts to a lower Reynolds number, and the structure responds to a lower loading. In the laminarization, the turbulent energy is dissipated by molecular transport by both viscous and conductivity mechanisms. Laminarization reduces spanwise vorticity because of the longitudinal cooling gradient of the sublayer profile. The results demonstrate that the curvature-induced mean pressure gradient enhances the receptivity of the flow to localized surface heating, a potentially viable mechanism to laminarize turbulent boundary layer flow; thus, the flow reduces the response of the flexible structure and the resultant sound radiation.

Maestrello, Lucio

2001-01-01

244

Laboratory simulation for microclimate environment of atmospheric surface layer  

Microsoft Academic Search

To simulate the microclimate environment of atmospheric surface layer (ASL), an environment simulation laboratory was constructed. The layout, functions and performance of the lab are discussed in detail, and the equipment and instruments of the lab are introduced. The key techniques of ASL environmental test are analyzed. This paper presents some results of environmental simulation for some climate parameters, such

Qinglong Meng; Yanling Guan; Yaxiu Gu; Yuan Wang

2011-01-01

245

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

246

Surface plasmon induced enhancement with magneto-optical layer  

NASA Astrophysics Data System (ADS)

In this study, we examined surface plasmon resonance (SPR) induced magneto-optical (MO) Kerr signals, and obtained a complete SPR curve in multilayered metallic structures comprising 6-nm-thick Au, t-nm-thick Permalloy (Py), and 26-nm-thick Au layers (with various thicknesses of Py). As the thickness of the Py layer increased, the SPR weakened. The MO signals were exhibited to various magnitudes of amplification while measuring the hysteresis loop at different segments of the SPR curve, which were the product of the MO Kerr effect. The MO signals between the reflectance maximum and reflectance minimum of the SPR were enhanced significantly in the samples with a 2 to 20-nm-thick Py layer. After measuring and analyzing the MO signals from multiple specimens with various thicknesses of Py, the optimal thickness of the Py layer was 10 nm, at which the strongest signal amplification was obtained.

Huang, Hao-Ting; Ger, Tzong-Rong; Xu, You-Ren; Huang, Chen-Yu; Liao, Kuei-Tien; Lai, Jun-Yang; Chen, Jiann-Yeu; Chen, Cheng-Huan; Wei, Zung-Hang

2014-05-01

247

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

248

Stabilization of Leidenfrost vapour layer by textured superhydrophobic surfaces.  

PubMed

In 1756, Leidenfrost observed that water drops skittered on a sufficiently hot skillet, owing to levitation by an evaporative vapour film. Such films are stable only when the hot surface is above a critical temperature, and are a central phenomenon in boiling. In this so-called Leidenfrost regime, the low thermal conductivity of the vapour layer inhibits heat transfer between the hot surface and the liquid. When the temperature of the cooling surface drops below the critical temperature, the vapour film collapses and the system enters a nucleate-boiling regime, which can result in vapour explosions that are particularly detrimental in certain contexts, such as in nuclear power plants. The presence of these vapour films can also reduce liquid-solid drag. Here we show how vapour film collapse can be completely suppressed at textured superhydrophobic surfaces. At a smooth hydrophobic surface, the vapour film still collapses on cooling, albeit at a reduced critical temperature, and the system switches explosively to nucleate boiling. In contrast, at textured, superhydrophobic surfaces, the vapour layer gradually relaxes until the surface is completely cooled, without exhibiting a nucleate-boiling phase. This result demonstrates that topological texture on superhydrophobic materials is critical in stabilizing the vapour layer and thus in controlling--by heat transfer--the liquid-gas phase transition at hot surfaces. This concept can potentially be applied to control other phase transitions, such as ice or frost formation, and to the design of low-drag surfaces at which the vapour phase is stabilized in the grooves of textures without heating. PMID:22972299

Vakarelski, Ivan U; Patankar, Neelesh A; Marston, Jeremy O; Chan, Derek Y C; Thoroddsen, Sigurdur T

2012-09-13

249

Financial Brownian particle in the layered order-book fluid and fluctuation-dissipation relations.  

PubMed

We introduce a novel description of the dynamics of the order book of financial markets as that of an effective colloidal Brownian particle embedded in fluid particles. The analysis of comprehensive market data enables us to identify all motions of the fluid particles. Correlations between the motions of the Brownian particle and its surrounding fluid particles reflect specific layering interactions; in the inner layer the correlation is strong and with short memory, while in the outer layer it is weaker and with long memory. By interpreting and estimating the contribution from the outer layer as a drag resistance, we demonstrate the validity of the fluctuation-dissipation relation in this nonmaterial Brownian motion process. PMID:24655287

Yura, Yoshihiro; Takayasu, Hideki; Sornette, Didier; Takayasu, Misako

2014-03-01

250

Homogenous Surface Nucleation of Solid Polar Stratospheric Cloud Particles  

NASA Technical Reports Server (NTRS)

A general surface nucleation rate theory is presented for the homogeneous freezing of crystalline germs on the surfaces of aqueous particles. While nucleation rates in a standard classical homogeneous freezing rate theory scale with volume, the rates in a surface-based theory scale with surface area. The theory is used to convert volume-based information on laboratory freezing rates (in units of cu cm, seconds) of nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) aerosols into surface-based values (in units of sq cm, seconds). We show that a surface-based model is capable of reproducing measured nucleation rates of NAT and NAD aerosols from concentrated aqueous HNO3 solutions in the temperature range of 165 to 205 K. Laboratory measured nucleation rates are used to derive free energies for NAT and NAD germ formation in the stratosphere. NAD germ free energies range from about 23 to 26 kcal mole, allowing for fast and efficient homogeneous NAD particle production in the stratosphere. However, NAT germ formation energies are large (greater than 26 kcal mole) enough to prevent efficient NAT particle production in the stratosphere. We show that the atmospheric NAD particle production rates based on the surface rate theory are roughly 2 orders of magnitude larger than those obtained from a standard volume-based rate theory. Atmospheric volume and surface production of NAD particles will nearly cease in the stratosphere when denitrification in the air exceeds 40 and 78%, respectively. We show that a surface-based (volume-based) homogeneous freezing rate theory gives particle production rates, which are (not) consistent with both laboratory and atmospheric data on the nucleation of solid polar stratospheric cloud particles.

Tabazadeh, A.; Hamill, P.; Salcedo, D.; Gore, Warren J. (Technical Monitor)

2002-01-01

251

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

252

Gold Nanoparticle Clusters in Quasinematic Layers of Liquid-Crystalline Dispersion Particles of Double-Stranded Nucleic Acids  

PubMed Central

The interaction between gold nanoparticles and particles of cholesteric liquid-crystalline dispersions formed by double-stranded DNA and poly(I)×poly(C) molecules is considered. It is shown that small-sized (~ 2 nm) gold nanoparticles induce two different structural processes. First, they facilitate the reorganization of the spatial cholesteric structure of the particles into a nematic one. This process is accompanied by a fast decrease in the amplitude of an abnormal band in the CD spectrum. Second, they induce cluster formation in a “free space” between neighboring nucleic acid molecules fixed in the structure of the quasinematic layers of liquid-crystalline particles. This process is accompanied by slow development of the surface plasmon resonance band in the visible region of the absorption spectrum. Various factors influencing these processes are outlined. Some assumptions concerning the possible mechanism(s) of fixation of gold nanoparticles between the neighboring double-stranded nucleic acid molecules in quasinematic layers are formulated.

Yevdokimov, Yu.M.; Salyanov, V.I.; Katz, E.I.; Skuridin, S.G.

2012-01-01

253

Surface-induced superparamagnetic relaxation in nanoscale ferrihydrite particles  

SciTech Connect

The effect of surface on superparamagnetic relaxation for nanoscale ferrihydrite particles ({ital d}{approximately}5 nm) has been investigated using M{umlt o}ssbauer spectroscopy. With increasing surface chemisorption of SiO{sub 4}{sup 4{minus}}, the superparamagnetic transition temperature ({ital T}{sub {ital B}}) falls from 100 to 40 K and the transition sharpens. This indicates that the SiO{sub 4}{sup 4{minus}} species eliminate the surface unpaired spins and create a nonmagnetic medium, thereby significantly reducing the magnetic coupling between the particles. For ferrihydrite particles impregnated on a silica support, the particle interaction becomes negligible and the superparamagnetic transition occurs at a still lower temperature of {approximately}12 K; the spectra exhibit characteristic size-dependent features. {copyright} {ital 1996 The American Physical Society.}

Zhao, J.; Huggins, F.E.; Feng, Z.; Huffman, G.P. [The Consortium for Fossil Fuel Liquefaction Science, 341 Bowman Hall, University of Kentucky, Lexington, Kentucky 40506 (United States)] [The Consortium for Fossil Fuel Liquefaction Science, 341 Bowman Hall, University of Kentucky, Lexington, Kentucky 40506 (United States)

1996-08-01

254

Surface enrichment of aluminosilicate minerals and coal combustion ash particles  

NASA Astrophysics Data System (ADS)

Auger electron spectroscopy has been used to provide evidence of surface segregation in illite, an aluminosilicate mineral representative of those which produce coal combustion ash particles. For the temperature range of 150-1100°C., the segregation of Fe, K, Ca and S has been observed, and the temperature dependence of the segregation levels of these elements has been determined. A comparison of these results with the reported data for surface enrichment of coal combustion ash particles indicates that the segregation levels of Fe, K, Ca and S in heated illite are comparable to the levels observed for the ash particles. Order-of-magnitude calculations indicate that appreciable segregation may occur on a time scale compatible with the residence time of ash particles in the combustor. These results are particularly significant because the surface enrichment of coal combustion ash has been generally attributed solely to adsorption/condensation processes.

Stinespring, C. D.; Stewart, G. W.

255

Surface properties of solids and surface acoustic waves: Application to chemical sensors and layer characterization  

NASA Astrophysics Data System (ADS)

A general phenomenological approach is given for the description of mechanical surface properties of solids and their influence on surface acoustic wave propogation. Surface properties under consideration may be changes of the stress distribution in subsurface atomic layers, the presence of adsorbed gas molecules, surface degradation as a result of impacts from an aggressive environment, damage due to mechanical manufacturing or polishing, deposition of thin films or liquid layers, surface corrugations, etc. If the characteristic thickness of the affected layers is much less than the wavelengths of the propagating surface waves, then the effects of all these irregularities can be described by means of non-classical boundary conditions incorporating the integral surface parameters such as surface tension, surface moduli of elasticity and surface mass density. The effect of surface properties on the propagation of Rayleigh surface waves is analysed in comparison with the results of traditional approaches, in particular with Auld's energy perturbation method. One of the important implications of the above-mentioned boudnary conditions is that they are adequate for the description of the effect of rarely distributed adsorbed atoms or molecules. This allows, in particular, to obtain a rigorous theoretical description of chemical sensors using surface acoustic waves and to derive analytical expressions for their sensitivity.

Krylov, V. V.

1995-09-01

256

The impact of surface properties on particle-interface interactions  

NASA Astrophysics Data System (ADS)

The propensity for particles to bind to oil-water interfaces was first noted by Ramsden and Pickering over a century ago, and has been attributed to the huge reduction in surface energy when a particle breaches an oil-water interface and straddles it at its equilibrium height. Since then materials on a variety of length scales have been fabricated using particles at interfaces, from Pickering emulsions to Janus particles. In these applications, it is simply assumed that the particle sits at its hugely energetically favourable equilibrium position. However, it was recently shown that the relaxation of particles towards their equilibrium position is logarithmic in time and could take months, much longer than typical experiments. Here we investigate how surface charge and particle 'hairiness' impact the interaction between micron-sized particles and oil-water interfaces, and explore a molecular kinetic theory model to help understand these results. We use digital holographic microscopy to track micron-sized particles as they approach an oil-water interface with a resolution of 2 nm in all three dimensions at up to thousands of frames per second.

Wang, Anna; Kaz, David; McGorty, Ryan; Manoharan, Vinothan N.

2013-03-01

257

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...

258

Quasi particles and fermi surfaces of heavy fermion systems  

Microsoft Academic Search

It is shown that reliable calculations of quasi particle dispersion and Fermi surfaces of real heavy fermion materials are possible. The existence of several Fermi surface constituents is presupposed. Most experiments in heavy fermion systems are interpreted, using relations which are valid for the translation invariant Fermi fluidity, e.g., the case of a single Fermi sphere. A simple multiparticle model

Erich Karl Rainer Runge

1990-01-01

259

MODELING PARTICLE DEPOSITION ON COMPRESSOR AND TURBINE BLADE SURFACES  

Microsoft Academic Search

1. ABSTRACT Particle deposition on turbine blade surfaces is studied in this work. The turbine blade geometry is chosen from experimental results. The grid has been generated and adopted using software preBFC. The flow field is solved in FLUENT using k- ? Model. The velocity distribution deduced from the static pressure distribution on blade surface has been compared with that

Hesham El-Batsh

260

Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries  

NASA Astrophysics Data System (ADS)

The present study sheds light on the long-standing challenges associated with high-voltage operation of LiNixMnxCo1?2xO2 cathode materials for lithium-ion batteries. Using correlated ensemble-averaged high-throughput X-ray absorption spectroscopy and spatially resolved electron microscopy and spectroscopy, here we report structural reconstruction (formation of a surface reduced layer, to transition) and chemical evolution (formation of a surface reaction layer) at the surface of LiNixMnxCo1?2xO2 particles. These are primarily responsible for the prevailing capacity fading and impedance buildup under high-voltage cycling conditions, as well as the first-cycle coulombic inefficiency. It was found that the surface reconstruction exhibits a strong anisotropic characteristic, which predominantly occurs along lithium diffusion channels. Furthermore, the surface reaction layer is composed of lithium fluoride embedded in a complex organic matrix. This work sets a refined example for the study of surface reconstruction and chemical evolution in battery materials using combined diagnostic tools at complementary length scales.

Lin, Feng; Markus, Isaac M.; Nordlund, Dennis; Weng, Tsu-Chien; Asta, Mark D.; Xin, Huolin L.; Doeff, Marca M.

2014-03-01

261

Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries.  

PubMed

The present study sheds light on the long-standing challenges associated with high-voltage operation of LiNi(x)Mn(x)Co(1-2x)O2 cathode materials for lithium-ion batteries. Using correlated ensemble-averaged high-throughput X-ray absorption spectroscopy and spatially resolved electron microscopy and spectroscopy, here we report structural reconstruction (formation of a surface reduced layer, to transition) and chemical evolution (formation of a surface reaction layer) at the surface of LiNi(x)Mn(x)Co(1-2x)O2 particles. These are primarily responsible for the prevailing capacity fading and impedance buildup under high-voltage cycling conditions, as well as the first-cycle coulombic inefficiency. It was found that the surface reconstruction exhibits a strong anisotropic characteristic, which predominantly occurs along lithium diffusion channels. Furthermore, the surface reaction layer is composed of lithium fluoride embedded in a complex organic matrix. This work sets a refined example for the study of surface reconstruction and chemical evolution in battery materials using combined diagnostic tools at complementary length scales. PMID:24670975

Lin, Feng; Markus, Isaac M; Nordlund, Dennis; Weng, Tsu-Chien; Asta, Mark D; Xin, Huolin L; Doeff, Marca M

2014-01-01

262

A scanning fluid dynamic gauging technique for probing surface layers  

NASA Astrophysics Data System (ADS)

Fluid dynamic gauging (FDG) is a technique for measuring the thickness of soft solid deposit layers immersed in a liquid environment, in situ and in real time. This paper details the performance of a novel automated, scanning FDG probe (sFDG) which allows the thickness of a sample layer to be monitored at several points during an experiment, with a resolution of ±5 µm. Its application is demonstrated using layers of gelatine, polyvinyl alcohol (PVA) and baked tomato purée deposits. Swelling kinetics, as well as deformation behaviour—based on knowledge of the stresses imposed on the surface by the gauging flow—can be determined at several points, affording improved experimental data. The use of FDG as a surface scanning technique, operating as a fluid mechanical analogue of atomic force microscopy on a millimetre length scale, is also demonstrated. The measurement relies only on the flow behaviour, and is thus suitable for use in opaque fluids, does not contact the surface itself and does not rely on any specific physical properties of the surface, provided it is locally stiff.

Gordon, Patrick W.; Brooker, Anju D. M.; Chew, Y. M. John; Wilson, D. Ian; York, David W.

2010-08-01

263

Particle concentrations and number size distributions in the planetary boundary layer derived from airship based measurements  

NASA Astrophysics Data System (ADS)

Atmospheric particles play a key role for regional and global climate due to their direct and indirect radiative forcing effects. The concentration and size of the particles are important variables to these effects. Within the continental planetary boundary layer (PBL) the particle number size distribution is influenced by meteorological parameters, local sinks and sources resulting in variable spatial distributions. However, measurements of particle number size distributions over a broad vertical range of the PBL are rare. The airship ZEPPELIN NT is an ideal platform to measure atmospheric aerosols on a regional scale within an altitude range up to 1000 m. For campaigns in the Netherlands, Northern Italy and South Finland in 2012 and 2013 the airship was deployed with a wide range of instruments, including measurements of different trace gases, short lived radicals, solar radiation, aerosols and meteorological parameters. Flights were carried out at different times of the day to investigate the influence of the diurnal evolution of the PBL on atmospheric trace gases and aerosols. During night and early morning hours the concentration and size distribution of atmospheric particles were found to be strongly influenced by the layered structure of the PBL, i.e. the nocturnal boundary layer and the residual layer. Within the residual layer particle concentrations stay relatively constant as this layer is decoupled from ground sources. The particles persist in the accumulation mode as expected for an aged aerosol. In the nocturnal boundary layer particle concentrations and size are more dynamic with higher concentrations than in the residual layer. A few hours after sunrise, the layered structure of the PBL intermixes. During daytime the PBL is well mixed and a negative concentration gradient with increasing height is observed. Several height profiles at different times of the day and at different locations in Europe were measured. The aerosol measurements will be discussed together with meteorological parameters and trace gas measurements. Acknowledgement: PEGASOS project funded by the European Commission and the Framework Program 7 (FP7-ENV-2010-265148).

Tillmann, Ralf; Zhao, Defeng; Ehn, Mikael; Hofzumahaus, Andreas; Holland, Frank; Rohrer, Franz; Kiendler-Scharr, Astrid; Wahner, Andreas

2014-05-01

264

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

265

Lateral optical force on chiral particles near a surface  

NASA Astrophysics Data System (ADS)

Light can exert radiation pressure on any object it encounters and that resulting optical force can be used to manipulate particles. It is commonly assumed that light should move a particle forward and indeed an incident plane wave with a photon momentum ?k can only push any particle, independent of its properties, in the direction of k. Here we demonstrate, using full-wave simulations, that an anomalous lateral force can be induced in a direction perpendicular to that of the incident photon momentum if a chiral particle is placed above a substrate that does not break any left–right symmetry. Analytical theory shows that the lateral force emerges from the coupling between structural chirality (the handedness of the chiral particle) and the light reflected from the substrate surface. Such coupling induces a sideway force that pushes chiral particles with opposite handedness in opposite directions.

Wang, S. B.; Chan, C. T.

2014-03-01

266

Lateral optical force on chiral particles near a surface.  

PubMed

Light can exert radiation pressure on any object it encounters and that resulting optical force can be used to manipulate particles. It is commonly assumed that light should move a particle forward and indeed an incident plane wave with a photon momentum ?k can only push any particle, independent of its properties, in the direction of k. Here we demonstrate, using full-wave simulations, that an anomalous lateral force can be induced in a direction perpendicular to that of the incident photon momentum if a chiral particle is placed above a substrate that does not break any left-right symmetry. Analytical theory shows that the lateral force emerges from the coupling between structural chirality (the handedness of the chiral particle) and the light reflected from the substrate surface. Such coupling induces a sideway force that pushes chiral particles with opposite handedness in opposite directions. PMID:24598792

Wang, S B; Chan, C T

2014-01-01

267

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

268

Electron Scattering at Surfaces of Epitaxial Metal Layers  

NASA Astrophysics Data System (ADS)

In the field of electron transport in metal films and wires, the 'size effect' refers to the increase in the resistivity of the films and wires as their critical dimensions (thickness of film, width and height of wires) approach or become less than the electron mean free path lambda, which is, for example, 39 nm for bulk copper at room temperature. This size-effect is currently of great concern to the semiconductor industry because the continued downscaling of feature sizes has already lead to Cu interconnect wires in this size effect regime, with a reported 2.5 times higher resistivity for 40 nm wide Cu wires than for bulk Cu. Silver is a possible alternate material for interconnect wires and titanium nitride is proposed as a gate metal in novel field-effect-transistors. Therefore, it is important to develop an understanding of how the growth, the surface morphology, and the microstructure of ultrathin (few nanometers) Cu, Ag and TiN layers affect their electrical properties. This dissertation aims to advance the scientific knowledge of electron scattering at surfaces (external surfaces and grain boundaries), that are, the primary reasons for the size-effect in metal conductors. The effect of surface and grain boundary scattering on the resistivity of Cu thin films and nanowires is separately quantified using (i) in situ transport measurements on single-crystal, atomically smooth Cu(001) layers, (ii) textured polycrystalline Cu(111) layers and patterned wires with independently varying grain size, thickness and line width, and (iii) in situ grown interfaces including Cu-Ta, Cu-MgO, Cu-vacuum and Cu-oxygen. In addition, the electron surface scattering is also measured in situ for single-crystal Ag(001), (111) twinned epitaxial Ag(001), and single-crystal TiN(001) layers. Cu(001), Ag(001), and TiN(001) layers with a minimum continuous thickness of 4, 3.5 and 1.8 nm, respectively, are grown by ultra-high vacuum magnetron sputter deposition on MgO(001) substrates with and without thin epitaxial TiN(001) wetting layers and are studied for structure, crystalline quality, surface morphology, density and composition by a combination of x-ray diffraction theta-2theta scans, o-rocking curves, pole figures, reciprocal space mapping, Rutherford backscattering, x-ray reflectometry and transmission electron microscopy. The TiN(001) surface suppresses Cu and Ag dewetting, yielding lower defect density, no twinning, and smaller surface roughness than if grown on MgO(001). Textured polycrystalline Cu(111) layers 25-50-nm-thick are deposited on a stack of 7.5-nm-Ta on SiO2/Si(001), and subsequent in situ annealing at 350°C followed by sputter etching in Ar plasma yields Cu layers with independently variable thickness and grain size. Cu nanowires, 75 to 350 nm wide, are fabricated from Cu layers with different average grain size using a subtractive patterning process. In situ electron transport measurements at room temperature in vacuum and at 77 K in liquid nitrogen for single-crystal Cu and Ag layers is consistent with the Fuchs-Sondheimer (FS) model and indicates specular scattering at the metal-vacuum boundary with an average specularity parameter p = 0.8 and 0.6, respectively. In contrast, layers measured ex situ show diffuse surface scattering due to sub-monolayer oxidation. Also, addition of Ta atoms on Cu(001) surface perturbs the smooth interface potential and results in completely diffuse scattering at the Cu-Ta interface, and in turn, a higher resistivity of single-crystal Cu layers. In situ exposure of Cu(001) layers to O2 between 10 -3 and 105 Pa-s results in a sequential increase, decrease and increase of the electrical resistance which is attributed to specular surface scattering for clean Cu(001) and for surfaces with a complete adsorbed monolayer, but diffuse scattering at partial coverage and after chemical oxidation. Electron transport measurements for polycrystalline Cu layers and wires show a 10-15% and 7-9% decrease in resistivity, respectively, when increasing the average lateral grain size by a factor of 1.8. The

Chawla, Jasmeet Singh

269

Barrier coated drug layered particles for enhanced performance of amorphous solid dispersion dosage form.  

PubMed

Amorphous solid dispersions (ASDs) may entail tailor-made dosage form design to exploit their solubility advantage. Surface phenomena dominated the performance of amorphous celecoxib solid dispersion (ACSD) comprising of amorphous celecoxib (A-CLB), polyvinylpyrrolidone, and meglumine (7:2:1, w/w). ACSD cohesive interfacial interactions hindered its capsule dosage form dissolution (Puri V, Dhantuluri AK, Bansal AK 2011. J Pharm Sci 100:2460-2468). Furthermore, ACSD underwent significant devitrification under environmental stress. In the present study, enthalpy relaxation studies revealed its free surface to contribute to molecular mobility. Based on all these observations, barrier coated amorphous CLB solid dispersion layered particles (ADLP) were developed by Wurster process, using microcrystalline cellulose as substrate and polyvinyl alcohol (PVA), inulin, and polyvinyl acetate phthalate (PVAP) as coating excipients. Capsule formulations of barrier coated-ADLP could achieve rapid dispersibility and high drug release. Evaluation under varying temperature and RH conditions suggested the crystallization inhibitory efficiency in order of inulin < PVA ? PVAP; however, under only temperature treatment, crystallization inhibition increased with increase in T(g) of the coating material. Simulated studies using DSC evidenced drug-polymer mixing at the interface as a potential mechanism for surface stabilization. In conclusion, surface modification yielded a fast dispersing robust high drug load ASD based dosage form. PMID:21935949

Puri, Vibha; Dantuluri, Ajay K; Bansal, Arvind K

2012-01-01

270

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

271

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

272

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

NASA Technical Reports Server (NTRS)

The observed effects of sharp changes in sea surface temperature (SST) on the air-sea fluxes, surface roughness, and the turbulence structure in the surface layer and the marine atmospheric boundary layer are discussed. In situ flux and turbulence observations were carried out from three aircraft and two ships within the FASINEX framework. Three other aircraft used remote sensors to measure waves, microwave backscatter, and lidar signatures of cloud tops. Descriptions of the techniques, intercomparison of aircraft and ship flux data, and use of different methods for analyzing the fluxes from the aircraft data are described. Changing synoptic weather on three successive days yielded cases of wind direction both approximately parallel and perpendicular to a surface temperature front. For the wind perpendicular to the front, wind over both cold-to-warm and warm-to-cold surface temperatures occurred. Model results consistent with the observations suggest that an internal boundary layer forms at the SST.

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

1991-01-01

273

Properties of white birch ( Betula papyrifera ) outer bark particleboards with reinforcement of coarse wood particles in the core layer  

Microsoft Academic Search

– \\u000a \\u000a • This study proposes substituting traditional raw materials in the surface layers of wood particle-boards with the water\\u000a resistant white birch (Betula papyrifera) outer bark particles, which can help improve the dimensional stability of manufactured mixed particleboards, thereby alleviating\\u000a shortages of raw material in a cost-efficient manner.\\u000a \\u000a \\u000a \\u000a \\u000a – \\u000a \\u000a • Mixed particleboards were fabricated in the laboratory using untreated or

Roger Pedieu; Bernard Riedl; André Pichette

2008-01-01

274

Interaction between surface and atmosphere in a convective boundary layer  

NASA Astrophysics Data System (ADS)

Solar heating of the surface causes the near surface air to warm up and with sufficient buoyancy it ascends through the atmosphere as surface-layer plumes and thermals. The cold fluid from the upper part of the boundary layer descends as downdrafts. The downdrafts and thermals form streamwise roll vortices. All these turbulent coherent structures are important because they contribute most of the momentum and heat transport. While these structures have been studied in depth, their imprint on the surface through energy budget in a convective atmospheric boundary layer has received little attention. The main objective of the present study is to examine the turbulence-induced surface temperature fluctuations for different surface properties and stratification. Experiments were performed to measure atmospheric turbulence using sonic anemometers, fine wire thermocouples and LIDAR; and surface temperature using an infra-red camera over grass and artificial turf fields. The surface temperature fluctuations were found to be highly correlated to the turbulent coherent structures and follow the processes postulated in the surface renewal theory. The spatio-temporal scales and advection speed of the surface temperature fluctuation were found to match with those of turbulent coherent structures. A parametric direct numerical simulation (DNS) study was then performed by solving the solid-fluid heat transport mechanism numerically for varying solid thermal properties, solid thickness and strength of stratification. Even though there were large differences in the friction Reynolds and Richardson numbers between the experiments and numerical simulations, similar turbulent characteristics were observed. The ejection (sweep) events tend to be aligned with the streamwise direction to form roll vortices with unstable stratification. The solid-fluid interfacial temperature fluctuations increase with the decreases in solid thermal inertia; and with the increase in solid thickness to attain a constant value for a sufficiently thick solid. The temperature fluctuation changes from a Gaussian distribution near the wall to a positively skewed distribution away from the wall. The turbulent temperature fluctuations influence the solid interfacial temperature by thermal conduction only. These studies provided unique insights into the solid-fluid coupled heat transport in low and high Reynolds number flows. This turbulence induced surface temperature fluctuation can influence the performances of several satellite remote sensing models.

Garai, Anirban

275

Effect of coating temperature on properties of the SiC layer in TRISO-coated particles  

NASA Astrophysics Data System (ADS)

The effect of coating temperature on properties of the SiC layer in TRISO-coated particles was investigated. An increase in coating temperature resulted in a significant coarsening of surface microstructures and an increase of the pore size and porosity of SiC layers. The SiC layers formed at 1400-1550 °C had nearly stoichiometric compositions whereas the SiC layer formed at 1600 °C contained a small amount of free carbon. The degradation of hardness and elastic modulus of the SiC layers coated at 1550 and 1600 °C was attributed to the increased porosity of the specimens and partly to the existence of free carbon. The fracture stress of the SiC layer measured by the crush test of hemispherical shell specimen did not correlate with the hardness and elastic modulus, and there was no clear dependence of the fracture stress on the coating temperature; this lack of correlation can be explained by the large roughness of the inner surface of the SiC layer.

Kim, Weon-Ju; Park, Jeong Nam; Cho, Moon Sung; Park, Ji Yeon

2009-07-01

276

Effects of surface wave breaking on the oceanic boundary layer  

NASA Astrophysics Data System (ADS)

Existing laboratory studies suggest that surface wave breaking may exert a significant impact on the formation and evolution of oceanic surface boundary layer, which plays an important role in the ocean-atmosphere coupled system. However, present climate models either neglect the effects of wave breaking or treat them implicitly through some crude parameterization. Here we use a one-dimensional ocean model (General Ocean Turbulence Model, GOTM) to investigate the effects of wave breaking on the oceanic boundary layer on diurnal to seasonal time scales. First a set of idealized experiments are carried out to demonstrate the basic physics and the necessity to include wave breaking. Then the model is applied to simulating observations at the northern North Sea and the Ocean Weather Station Papa, which shows that properly accounting for wave breaking effects can improve model performance and help it to successfully capture the observed upper ocean variability.

He, Hailun; Chen, Dake

2011-04-01

277

On the Effects of Surface Roughness on Boundary Layer Transition  

NASA Technical Reports Server (NTRS)

Surface roughness can influence laminar-turbulent transition in many different ways. This paper outlines selected analyses performed at the NASA Langley Research Center, ranging in speed from subsonic to hypersonic Mach numbers and highlighting the beneficial as well as adverse roles of the surface roughness in technological applications. The first theme pertains to boundary-layer tripping on the forebody of a hypersonic airbreathing configuration via a spanwise periodic array of trip elements, with the goal of understanding the physical mechanisms underlying roughness-induced transition in a high-speed boundary layer. The effect of an isolated, finite amplitude roughness element on a supersonic boundary layer is considered next. The other set of flow configurations examined herein corresponds to roughness based laminar flow control in subsonic and supersonic swept wing boundary layers. A common theme to all of the above configurations is the need to apply higher fidelity, physics based techniques to develop reliable predictions of roughness effects on laminar-turbulent transition.

Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan; Edwards, Jack

2009-01-01

278

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

2013-06-21

279

Structure analysis of surface layer on passivated magnesium powders  

Microsoft Academic Search

The combustion-time of the passivated magnesium powders as desulfurizer was determined to be about 15.7 s, much higher than that of non-passivated magnesium powders. The surface layer of the passivated magnesium powders was studied by using SEM, XRD and AES. It is uniform and compact and no obvious holes or cracks have been found from the SEM micrographs. The result of

Junlin Huang; Jianfeng F. Wan; Chaoying Xie; Jinsong Chen; Chuanjiang Long

2007-01-01

280

Surface plasmons reveal spin crossover in nanometric layers.  

PubMed

Nano-objects and thin films displaying molecular spin-crossover phenomena have recently attracted much attention. However, the investigation of spin crossover at reduced sizes is still a big challenge. Here we demonstrate that surface plasmon polariton waves propagating along the interface between a metal and a dielectric layer can be used to detect the spin-state changes in the latter with high sensitivity, even at the nanometer scale. PMID:21902237

Félix, Gautier; Abdul-Kader, Khaldoun; Mahfoud, Tarik; Gural'skiy, Il'ya A; Nicolazzi, William; Salmon, Lionel; Molnár, Gábor; Bousseksou, Azzedine

2011-10-01

281

Heat budget of the surface mixed layer south of Africa  

Microsoft Academic Search

ARGO hydrographic profiles, two hydrographic transects and satellite measurements of air–sea exchange parameters were used\\u000a to characterize the properties and seasonal heat budget variations of the Surface Mixed Layer (SML) south of Africa. The analysis\\u000a distinguishes the Subtropical domain (STZ) and the Subantarctic Zone (SAZ), Polar Frontal Zone (PFZ) and Antarctic Zone (AZ)\\u000a of the Antarctic Circumpolar Current. While no

Vincent Faure; Michel Arhan; Sabrina Speich; Sergey Gladyshev

2011-01-01

282

Control of Boundary-Layer Separation for Lifting Surfaces  

Microsoft Academic Search

The lack of understanding of most of the relevant physical mechanisms when applying flow control limits the prospects of successfully transitioning flow-control technologies into real flight vehicles. Successful control of boundary-layer separation for lifting surfaces promises major performance gains especially when large laminar runs are desired in order to minimize the skin-friction drag. We systematically explore the fundamental mechanisms of

W. Balzer; A. Gross; H. F. Fasel

2009-01-01

283

Convective Planetary Boundary Layer Evolution and Land Surface Energy Balance  

NASA Astrophysics Data System (ADS)

The relationships among convective planetary boundary layer (PBL) properties and land surface energy balance on diurnal and regional scales are explored using 132 days worth of data from ARM-SGP. Previous attempts to infer land-surface properties from observations of the PBL have been constrained by difficulties in accurately parameterizing the conservation equation, and have been limited to multi-day averages or small samples of daily case studies. A empirical investigation of relationships among PBL and land surface properties indicates that atmospheric stability in the layer of PBL growth is the most influential variable controlling PBL development, followed by soil moisture, 2m-potential temperature, and 2m-specific humidity. These relationships are exploited using a statistical technique to predict and explain PBL growth from observations of stability and soil water content. Using this approach, it is possible to use limited observations of the PBL to estimate soil moisture, and by extension, land surface energy balance on daily timescales without the need for detailed land surface parameterizations.

Sun, D.; Pinker, R. T.; Santanello, J. A.; Friedl, M. A.

2004-05-01

284

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

2013-03-01

285

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

286

Cationic amino-containing N -isopropyl- acrylamide-styrene copolymer particles: 2-surface and colloidal characteristics  

Microsoft Academic Search

In a previous paper [1], the synthesis of various polystyrene– poly[NIPAM] core–shell latexes bearing cationic amidino and\\/or\\u000a amino charges has been described. Several colloidal properties of these cationic latexes have been charac-terized such as:\\u000a particle size, surface charge density, electrophoretic mobility and finally colloidal stability. Due to the poly[NIPAM]-rich\\u000a layer in the shell, it was found that temperature played a

D. Duracher; F. Sauzedde; A. Elaïssari; C. Pichot; L. Nabzar

1998-01-01

287

Dust Devils on Mars: Effects of Surface Roughness on Particle Threshold  

NASA Technical Reports Server (NTRS)

Dust devils have been proposed as effective mechanisms for lofting large quantities of dust into the martian atmosphere. Previous work showed that vortices lift dust more easily than simple boundary layer winds. The aim of this study is to determine experimentally the effects of non-erodable roughness elements on vortex particle threshold through laboratory simulations of natural surfaces. Additional information is included in the original extended abstract.

Neakrase, Lynn D.; Greeley, Ronald; Iversen, James D.; Balme, Matthew L.; Foley, Daniel J.; Eddlemon, Eric E.

2005-01-01

288

Influence of Particle Characteristics and Surface Roughness on Friction in Granular Fault Gouge  

Microsoft Academic Search

Particle characteristics (shape, size, and roughness) and surface roughness affect friction and the amount of shear localization that occurs within granular shear zones. In order to improve our understanding of grain-scale deformation mechanisms within fault gouge, we performed laboratory experiments using a double-direct-shear testing apparatus. This assembly includes three rigid forcing blocks with two gouge layers sandwiched between rough or

J. L. Anthony; C. Marone

2004-01-01

289

Exoelectronic emission of particles of lunar surface material  

NASA Technical Reports Server (NTRS)

A secondary electron multiplier was used to study the thermostimulated exoelectronic emission of particles of lunar surface material returned by the Soviet Luna 16 automatic station. The natural exoemission from fragments of slag, glass, anorthosite, and a metallic particle was recorded in the isochronic and isothermal thermostimulation regimes. The temperature of emission onset depended on the type of regolith fragment. For the first three particles the isothermal drop in emission is described by first-order kinetic equations. For the anorthosite fragment, exoemission at constant temperature is characterized by a symmetric curve with a maximum. These data indicate the presence of active surface defects, whose nature can be due to the prehistory of the particles.

Mints, R. I.; Alimov, V. I.; Melekhin, V. P.; Milman, I. I.; Kryuk, V. I.; Kunin, L. L.; Tarasov, L. S.

1974-01-01

290

[Particle dispersion by order motion in mixing layers  

SciTech Connect

Multiphase mixing in turbulent flows is a key element in many energy conversion and chemical processes. There is considerable need for improving the design and control of these processes. Free turbulent shear flows are the primary agents for particle mixing in these systems. Previous studies by this research group have shown that, if particle coupling effects are neglected, the organized vortex structures generated by these shear flows control the character of the particle mixing process. A coordinated experimental and numerical study is proposed to investigate the coupled effects of droplet mass and energy transfer on the turbulent multiphase mixing process in free shear flows. This study has important implications concerning the design of reacting flow systems. Experimental visualizations of the multiphase flow will be carried out using laser-sheet lighting and high speed photography. Local measurements of droplet size, velocity and concentration diagnostics, will be made with laser anemometry and phase Doppler diagnostics. Complementary analytical and numerical analyses will be carried out to assess the effect of coupling on vortex structure, stability and growth. The results of the proposed research will provide basic understanding concerning the coupled effects of particle concentration on the rate of multiphase mixing in turbulent flows. Information of this nature is essential to the improved designs of engineering systems with particulate or droplet flows.

Troutt, T.R.

1993-09-01

291

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.

Perez-Mendez, V.; Morel, J.; Kaplan, S.N.; Street, R.A.

1986-02-01

292

Tribology and Superhydrophobicity of Laser-Controlled-Melted Alumina Surfaces with Hard Particles  

NASA Astrophysics Data System (ADS)

Laser-controlled melting of alumina surface with a carbon film of about 40- ?m thickness formed prior to the laser treatment process is carried out to improve its hardness, durability, and superhydrophocity. The carbon film consisted of a uniformly distributed mixture of hard particles of WC, SiC, and B4C. The presence of carbon film improves the absorption of the laser beam during the treatment process. The morphology and hydrophobicity of the laser-treated surface were evaluated using optical microscopy, atomic force microscopy, and the contact angle measurement, respectively. The chemical changes of the treated layer were examined using scanning electron microscopy and energy-dispersive spectroscopy. The structure of the nitride compound formed at the surface was characterized using x-ray diffraction, which was also used to determine the residual stress at the surface. Both microhardness and fracture toughness of the laser-treated surface were determined using indentation tests. Scratch tests were conducted to measure the friction coefficient and scratch resistance of the laser-treated surface. Laser treatment produces micropoles, nanopoles, and small size cavities at the surface, which enhance hydrophobicity of the surface. The microhardness of the laser-treated surface increases almost 50% because of the dense layer formed at the surface and the residual stress is in the order of -2 GPa, which is compressive. The scratch resistance and friction coefficient of the laser-treated surface is superior.

Yilbas, Bekir Sami; Bhushan, Bharat; Abdul Aleem, B. J.; Gaseem, Zuhair

2014-06-01

293

Tribology and Superhydrophobicity of Laser-Controlled-Melted Alumina Surfaces with Hard Particles  

NASA Astrophysics Data System (ADS)

Laser-controlled melting of alumina surface with a carbon film of about 40-?m thickness formed prior to the laser treatment process is carried out to improve its hardness, durability, and superhydrophocity. The carbon film consisted of a uniformly distributed mixture of hard particles of WC, SiC, and B4C. The presence of carbon film improves the absorption of the laser beam during the treatment process. The morphology and hydrophobicity of the laser-treated surface were evaluated using optical microscopy, atomic force microscopy, and the contact angle measurement, respectively. The chemical changes of the treated layer were examined using scanning electron microscopy and energy-dispersive spectroscopy. The structure of the nitride compound formed at the surface was characterized using x-ray diffraction, which was also used to determine the residual stress at the surface. Both microhardness and fracture toughness of the laser-treated surface were determined using indentation tests. Scratch tests were conducted to measure the friction coefficient and scratch resistance of the laser-treated surface. Laser treatment produces micropoles, nanopoles, and small size cavities at the surface, which enhance hydrophobicity of the surface. The microhardness of the laser-treated surface increases almost 50% because of the dense layer formed at the surface and the residual stress is in the order of -2 GPa, which is compressive. The scratch resistance and friction coefficient of the laser-treated surface is superior.

Yilbas, Bekir Sami; Bhushan, Bharat; Abdul Aleem, B. J.; Gaseem, Zuhair

2014-04-01

294

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

295

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

296

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

NASA Technical Reports Server (NTRS)

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.

1992-01-01

297

Spatially selective surface platforms for binding fibrinogen prepared by particle lithography with organosilanes  

PubMed Central

We introduce an approach based on particle lithography to prepare spatially selective surface platforms of organosilanes that are suitable for nanoscale studies of protein binding. Particle lithography was applied for patterning fibrinogen, a plasma protein that has a major role in the clotting cascade for blood coagulation and wound healing. Surface nanopatterns of mercaptosilanes were designed as sites for the attachment of fibrinogen within a protein-resistant matrix of 2-[methoxy(polyethyleneoxy)propyl] trichlorosilane (PEG-silane). Preparing site-selective surfaces was problematic in our studies, because of the self-reactive properties of PEG-organosilanes. Certain organosilanes presenting hydroxyl head groups will cross react to form mixed surface multi-layers. We developed a clever strategy with particle lithography using masks of silica mesospheres to protect small, discrete regions of the surface from cross reactions. Images acquired with atomic force microscopy (AFM) disclose that fibrinogen attached primarily to the surface areas presenting thiol head groups, which were surrounded by PEG-silane. The activity for binding anti-fibrinogen was further evaluated using ex situ AFM studies, confirming that after immobilization the fibrinogen nanopatterns retained capacity for binding immunoglobulin G. Studies with AFM provide advantages of achieving nanoscale resolution for detecting surface changes during steps of biochemical surface reactions, without requiring chemical modification of proteins or fluorescent labels.

Englade-Franklin, Lauren E.; Saner, ChaMarra K.; Garno, Jayne C.

2013-01-01

298

Effects of particle size on flame spread over magnesium powder layer  

Microsoft Academic Search

The spreading of a flame over a layer of magnesium powder has been examined to clarify the mechanisms of flame spread over metal powder layers and to establish effective ways to extinguish metal fires. Four grades of magnesium powder were used, with average grain diameters of 60, 170, 360 and 500?m. The flame spread rate for larger particle sizes (D>170?m)

Yuji Kudo; Yudai Kudo; Hiroyuki Torikai; Akihiko Ito

2010-01-01

299

Studies of dust acoustic double layers in the presence of trapped particles  

NASA Astrophysics Data System (ADS)

An analytical solution for time stationary weak double layers in an unmagnetized dusty plasma by using Sagdeev's pseudopotential method is studied considering dusts with constant charge and mass. Here, the plasma consists of electrons, ions and negatively-charged micron-sized dust particles. From the study, expressions for the potential and the dust acoustic velocity of the double layer is determined.

Mahanta, M. K.; Moulick, R.; Goswami, K. S.

2014-01-01

300

Engineering of an MBR supernatant fouling layer by fine particles addition: a possible way to control cake compressibility.  

PubMed

For membrane bioreactors (MBR) applied to wastewater treatment membrane fouling is still the prevalent issue. The main limiting phenomena related to fouling is a sudden jump of the transmembrane pressure (TMP) often attributed to the collapse of the fouling layer. Among existing techniques to avoid or to delay this collapse, the addition of active particles membrane fouling reducers (polymer, resins, powdered activated carbon (PAC), zeolithe...) showed promising results. Thus the main objective of this work is to determine if fouling can be reduced by inclusion of inert particles (500 nm and inert compared to other fouling reducers) and which is the impact on filtration performances of the structuring of the fouling. Those particles were chosen for their different surface properties and their capability to form well structured layer. Results, obtained at constant pressure in dead end mode, show that the presence of particles changes foulant deposition and induces non-compressible fouling (in the range of 0.5-1 bar) and higher rejection values compared to filtration done on supernatant alone. Indeed dead end filtration tests show that whatever interactions between biofluid and particles, the addition of particles leads to better filtration performances (in terms of rejection, and fouling layer compressibility). Moreover results confirm the important role played by macromolecular compounds, during supernatant filtration, creating highly compressible and reversible fouling. In conclusion, this study done at lab-scale suggests the potential benefit to engineer fouling structure to control or to delay the collapse of the fouling layer. Finally this study offers the opportunities to enlarge the choice of membrane fouling reducers by taking into consideration their ability to form more consistent fouling (i.e. rigid, structured fouling). PMID:21232780

Teychene, Benoît; Guigui, Christelle; Cabassud, Corinne

2011-02-01

301

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

302

Stereo particle image velocimetry of nonequilibrium turbulence relaxation in a supersonic boundary layer  

Microsoft Academic Search

Measurements using stereo particle image velocimetry are presented for a developing turbulent boundary layer in a wind tunnel\\u000a with a Mach 2.75 free stream. As the boundary layer exits from the tunnel nozzle and moves through the wave-free test section,\\u000a small initial departures from equilibrium turbulence relax, and the boundary layer develops toward the equilibrium zero-pressure-gradient\\u000a form. This relaxation process

Andrew P. LapsaWerner; Werner J. A. Dahm

2011-01-01

303

Dynamic cell surface hydrophobicity of Lactobacillus strains with and without surface layer proteins  

Microsoft Academic Search

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

V. Vadillo-Rodriguez; Henk J. Busscher; Willem Norde; Joop de Vries; Mei van der H. C

2004-01-01

304

Particle detectors based on semiconducting InP epitaxial layers  

Microsoft Academic Search

A study of electrical properties and detection performance of two types of Indium Phosphide detector structures was performed: (i) with p-n-junction and (ii) with Schottky contact prepared on high purity p-type InP. The p-n junction detectors were based on a high purity InP:Pr layers of both n- and p- type conductivity with carrier concentration on the order of 1014 cm-3

R. Yatskiv; J. Grym; K. Zdansky

2011-01-01

305

Surface fluxes and vertical profiles in the radix layer  

NASA Astrophysics Data System (ADS)

The bottom two kilometers of the earth's atmosphere, called the atmospheric boundary layer (ABL), can be vigorously mixed by convective circulations when the underlying surface is warmer than the air. Mixing can be so complete that the mean wind speed, MUL , and potential temperature, MUL , in the interior of the ABL are uniform with height. Between this uniform layer (UL) and the surface is a region of order 100 m thick called the radix layer (RxL), named because it contains the roots of convective thermals. These thermals not only cause vertical heat and momentum fluxes near the surface, but they control the shape of wind and temperature profiles in the RxL and UL. A new field campaign called Boundary-Layer Experiment 1996 (BLX96) was conducted using an instrumented aircraft to study these convective processes. The BLX96 flight pattern was designed by first test ``flying'' a virtual aircraft through a synthetic ABL. Results from BLX96 suggest that convective transport theory should be modified to give the surface kinematic heat flux as w'q' s=CH*?w* ?Dq+w'q'o, where CH*, is an empirical coefficient, w* is the Deardorff velocity, Dq is the potential temperature difference between the UL and the surface skin, and w'q' o is a radiative or non-stationary flux contribution. A similar formula is found for friction velocity u* as a measure of momentum flux: u2 *=CD*?w* ?MUL , where CD* is shown to depend on surface aerodynamic roughness. These relationships are validated against published data from seven other field programs. In the RxL, the vertical profiles of wind and potential temperature are found to obey new similarity equations: M(z)/MUL=F(z*) , and [q(z)-qUL]/( qskin- qUL)=1- F(z* ) , where F(z*)=( zD*)A ?[A?(1-z D*)] in the RxL, and F = 1 in the UL. The dimensionless height is found to be z*?(1/C) ?(z/zi)?( w*/u*)B , where physical height z must be measured above the canopy displacement distance, and zi, is ABL depth. RxL parameters A, B and C are found to be universal when validated against published data from two other field programs. Shape parameter D for wind profile is found to depend on the standard deviation of terrain elevation.

Santoso, Edi

306

Backscatter effects of surfaces composed of dry biological particles  

NASA Astrophysics Data System (ADS)

We present the backscattering of particulate surfaces consisting of dry biological particles using two laboratory photopolarimeters that measure intensity and degree of linear polarization in a phase-angle range 0.2 60°. We measure scattering properties from three samples composed of dry biological particles, Bacillus subtilis var. niger (BG) spores and samples of fungi Aspergillus terreus and Sporisorium cruentum spores. We find that the surfaces display a prominent brightness opposition effect and significant negative polarization near backscattering angles. The brightness and polarimetric phase curves are different for B. subtilis and the fungi.

Ovcharenko, Andrey; Bondarenko, Sergey; Shkuratov, Yuriy; Scotto, Cathy; Merritt, Charles; Hart, Matthew; Eversole, Jay; Videen, Gorden

2006-10-01

307

Dense medium radiative transfer theory for two scattering layers with a Rayleigh distribution of particle sizes  

SciTech Connect

Dense medium radiative transfer theory is applied to a three-layer model consisting of two scattering layers overlying a homogeneous half space with a size distribution of particles in each layer. A model with a distribution of sizes gives quite different results than those obtained from a model with a single size. The size distribution is especially important in the low frequency limit when scattering is strongly dependent on particle size. The size distribution and absorption characteristics also affect the extinction behavior as a function of fractional volume. Theoretical results are also compared with experimental data. The sizes, permittivities, and densities used in the numerical illustrations are typical values for snow.

West, R.; Tsang, Leung; Winebrenner, D.P. (Univ. of Washington, Seattle (United States))

1993-03-01

308

Metal-like conductivity exhibited by triboelectrically deposited polyaniline (emeraldine base) particles on microtextured SiC surfaces  

NASA Astrophysics Data System (ADS)

We demonstrate a simple and rapid way to deposit layers of polyaniline (emeraldine base) particles on flexible microtextured silicon carbide surfaces by contact charging them using a smooth dielectric rubber. Wetting of the layers by trifluoroacetic acid creates conductive, continuous polymeric films after drying. Pre-functionalization of the textured surfaces with anionic surfactants prevents particle coagulation during contact charging and decreases sheet resistance to metal-like levels (~60 ?/\\squarelg). Conductivity of the films can be tuned by controlling the rate of acid evaporation. Conductive films are highly stable under ambient conditions and show no hysteresis when biased with zero delay-time.

Bayer, I. S.; Caramia, V.; Biswas, A.; Cingolani, R.; Athanassiou, A.

2012-05-01

309

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

310

Linear stability of a layered fluid with mobile surface plates  

NASA Technical Reports Server (NTRS)

We develop a general method of calculating the linear stability of a fluid with homogeneous layers that is heated from below. The method employs a propagator technique to obtain expressions for the fluid velocity, stress, and temperature. The principal advantage of the method is the ease with which solutions are adapted to a wide variety of boundary conditions and fluid properties. We demonstrate the utility of the method using three examples which quantify the effects of (1) rheological layering, (2) mobile plates at the surface, and (3) multiple phase transitions. Each example is presented in the context of Earth's mantle. In the first example, we predict that convection becomes confined to the upper mantle once the viscosity increase between the upper and lower mantle exceeds a factor of 2000, consistent with the nonlinear calculations of Davies (1977). In the second example we find that the heat flux variations in a convecting fluid with variably sized, surface plates can be attributed, in part, to changes in the critical Rayleigh number. The linear stability of a fluid with multiple phase transitions is significantly affects by the locations of the transitions. We find that phase transitions have their largest effect when they are located at the center of the fluid layer and become much less important when they are located near the exterior boundaries.

Buffett, B. A.; Gable, C. W.; O'Connell, R. J.

1994-01-01

311

Copolyimide Surface Modifying Agents for Particle Adhesion Mitigation  

NASA Technical Reports Server (NTRS)

Marine biofouling, insect adhesion on aircraft surfaces, microbial contamination of sterile environments, and particle contamination all present unique challenges for which researchers have adopted an array of mitigation strategies. Particulate contamination is of interest to NASA regarding exploration of the Moon, Mars, asteroids, etc.1 Lunar dust compromised seals, clogged filters, abraded visors and space suit surfaces, and was a significant health concern during the Apollo missions.2 Consequently, NASA has instituted a multi-faceted approach to address dust including use of sacrificial surfaces, active mitigation requiring the use of an external energy source, and passive mitigation utilizing materials with an intrinsic resistance to surface contamination. One passive mitigation strategy is modification of a material s surface energy either chemically or topographically. The focus of this paper is the synthesis and evaluation of novel copolyimide materials with surface modifying agents (SMA, oxetanes) enabling controlled variation of surface chemical composition.

Wohl, Christopher J.; Connell, John W.

2011-01-01

312

Analysis of surface composition and internal structure of fly ash particles using an ion and electron multibeam microanalyzer  

NASA Astrophysics Data System (ADS)

An ion and electron multibeam microanalyzer was developed and applied to analysis of coal fly ash particles. Employing ordinary TOF-SIMS function, it was found that the surface of the fly ash particles mainly consisted of Ca, C, Si, and Na. A special analysis technique with a combination of "shave-off" cross-sectioning and TOF-SIMS mapping of the cross section was adopted to a single fly ash particle in order to reveal the internal structure. It was found that the particle had a cenosphere structure. TOF-SIMS mapping of the cross-sectioned particle clarified that the particle had the following layers, outermost layer (Na, Si, Ca-rich), shell (Na-rich), inner shell (Na, Si, Al-rich).

Sakamoto, T.; Shibata, K.; Takanashi, K.; Owari, M.; Nihei, Y.

2003-01-01

313

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

314

Synthesis and surface properties of submicron barium sulfate particles  

NASA Astrophysics Data System (ADS)

Barium sulfate particles were synthesized in the presence of EDTA at room temperature. X-ray diffractometry (XRD), Fourier transform infrared resonance (FTIR) and scanning electron microscopy (SEM) were used to characterize the structure and morphology of BaSO 4 particles. The effect of the preparation parameters on the particle size distribution and morphology was investigated. The conditional formation constants of Ba-EDTA at different pH values were calculated. The results show that the size and morphology of BaSO 4 particles can be effectively controlled by adding EDTA in the precipitation process. Among all the operation conditions, the pH value has significant effect on the particle size. The obtained barium sulfate particles are spherical and well dispersed at pH = 9-10. Zeta potentials of BaSO 4 were measured at different pH. The isoelectric point (IEP) of barium sulfate colloid appears at pH 6.92. The model of the solid-solution interface at a particle of BaSO 4 was presented. The FTIR result indicates that the surface of the prepared BaSO 4 absorbs the functional groups of EDTA, which lower the IEP of the barium sulfate particles.

Zhang, Ming; Zhang, Bao; Li, Xinhai; Yin, Zhoulan; Guo, Xueyi

2011-10-01

315

Electric Double Layer Structures near Rough Surfaces: Molecular Dynamics Simulation  

NASA Astrophysics Data System (ADS)

S. S. Dukhin in Surface and Colloid Science (1974) mentioned both the possibility of increase in zeta potential due to surface roughness and the possibility of decrease, depending on Debye length relative to surface roughness. In this work we report our results of molecular dynamic (MD) simulations on electric double layer structures near solid surfaces having roughness with the order of magnitude of Debye length. For computational simplicity only counter-ions are present. We computed static and dynamics properties including density profiles of water and ions, electrostatic potential distributions due to ions, polarization density profiles and self-diffusivities of water and ions. We also performed nonequilibrium MD to simulate electroosmotic flows. From electrostatic potential distributions and slip plane locations, we computed zeta potential and found that it decreases with surface roughness. It also showed a dependency on the spatial frequency of surface roughness. For comparison we used the Helmholtz-Smoluchowski relation and found the same trend. Currently we are studying pressure-driven flows, a computational counterpart to streaming current experiments. One of the purposes is to find more exact locations of slip planes by fitting to Poiseuille flow solutions. We are also simulating model systems with co-ions to investigate the possibility of charge inversion and other effects.

Kim, Daejoong; Darve, Eric

2006-03-01

316

A blank slate? Layer-by-layer deposition of hyaluronic acid and chitosan onto various surfaces.  

PubMed

Although poly(alpha-hydroxy esters), especially the PLGA family of lactic acid/glycolic acid copolymers, have many properties which make them promising materials for tissue engineering, the inherent chemistry of surfaces made from these particular polymers is problematic. In vivo, they promote a strong foreign-body response as a result of nonspecific adsorption and denaturation of serum proteins, which generally results in the formation of a nonfunctional fibrous capsule. Surface modification post-production of the scaffolds is an often-utilized approach to solving this problem, conceptually allowing the formation of a scaffold with mechanical properties defined by the bulk material and molecular-level interactions defined by the modified surface properties. A promising concept is the so-called "blank slate": essentially a surface that is rendered resistant to nonspecific protein adsorption but can be readily activated to covalently bind bio-functional molecules such as extracellular matrix proteins, growth factors or polysaccharides. This study focuses on the use of the quartz crystal microbalance (QCM) to follow the layer-by-layer (LbL) electrostatic deposition of high molecular weight hyaluronic acid and chitosan onto PLGA surfaces rendered positively charged by aminolysis, to form a robust, protein-resistant coating. We further show that this surface may be further functionalized via the covalent attachment of collagen IV, which may then be used as a template for the self-assembly of basement membrane components from dilute Matrigel. The response of NIH-3T3 fibroblasts to these surfaces was also followed and shown to closely parallel the results observed in the QCM. PMID:16677046

Croll, Tristan I; O'Connor, Andrea J; Stevens, Geoffrey W; Cooper-White, Justin J

2006-05-01

317

Nature of the Martian surface as inferred from the particle-size distribution of lunar-surface material.  

NASA Technical Reports Server (NTRS)

Analysis of lunar particle size distribution data indicates that the surface material is composed of two populations. One population is caused by comminution from the impact of the larger-sized meteorites, while the other population is caused by the melting of fine material by the impact of smaller-sized meteorites. The results are referred to Mars, and it is shown that the Martian atmosphere would vaporize the smaller incoming meteorites and retard the incoming meteorites of intermediate and large size, causing comminution and stirring of the particulate layer. The combination of comminution and stirring would result in fine material being sorted out by the prevailing circulation of the Martian atmosphere and the material being transported to regions where it could be deposited. As a result, the Martian surface in regions of prevailing upward circulation is probably covered by either a rubble layer or by desert pavement; regions of prevailing downward circulation are probably covered by sand dunes.

Mason, C. C.

1971-01-01

318

Capillary interception of floating particles by surface-piercing vegetation.  

PubMed

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 ~1-10 mm 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. PMID:24182270

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

2013-10-18

319

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

320

Controlling rejections of spoof surface plasmon polaritons using metamaterial particles.  

PubMed

Based on the dispersion relation, surface plasmon polaritons (SPPs) or spoof SPPs are always propagating surface waves when the operating frequency is below the asymptotic limit - the surface plasma frequency. Here we propose a method to control the rejections of spoof SPPs using metamaterial particles. By introducing electrically resonant metamaterials near an ultrathin corrugated metallic strip - the spoof SPP waveguide - to produce tight coupling and mismatch of surface impedance, we show that the SPP modes are rejected near the resonant frequencies within the propagating band. Through the modulation of scaling factor of metamaterial particles, we can manipulate the rejections of SPP modes from narrowband to broadband. Both simulation and experiment results verify the tunability of SPP rejections, which have important applications in filtering SPP waves in plasmonic circuits and systems. PMID:24921585

Pan, Bai Cao; Liao, Zhen; Zhao, Jie; Cui, Tie Jun

2014-06-01

321

Surface layer in composites containing 4- n-octyl-4'-cyanobiphenyl. FTIR spectroscopic characterization  

NASA Astrophysics Data System (ADS)

Composites containing 4- n-octyl-4'-cyanobiphenyl (8CB) either confined to nanopores of molecular sieves with very large pores or coating silica nanoparticles of aerosil type at high silica-to-8CB ratios are investigated by IR spectroscopy. Band shape analysis was performed in wavenumber regions in which the peaks due to CN stretching, CH stretching and CH out-of-plane vibrations appear. Some of molecules confined to molecular sieves show spectroscopic features characteristic to a bulk-like 8CB matter located in the centre of the pores or in the inter-grain space. Other features of the IR spectra are due to 8CB molecules located in the surface layer, mostly forming hydrogen bonds between their CN groups and surface OH groups. Another part of the 8CB molecules in the surface layer may also interact by ? electrons of the aromatic rings. Hydrogen bonding is less hindered for the molecules of the surface layers onto aerosil particles than inside pores of the molecular sieves. Comparison is also made with the case of composites based on molecular sieves with small pores.

Frunza, L.; Kosslick, H.; Bentrup, U.; Pitsch, I.; Fricke, R.; Frunza, S.; Schönhals, A.

2003-06-01

322

Atomic-layer electroless deposition: a scalable approach to surface-modified metal powders.  

PubMed

Palladium has a number of important applications in energy and catalysis in which there is evidence that surface modification leads to enhanced properties. A strategy for preparing such materials is needed that combines the properties of (i) scalability (especially on high-surface-area substrates, e.g. powders); (ii) uniform deposition, even on substrates with complex, three-dimensional features; and (iii) low-temperature processing conditions that preserve nanopores and other nanostructures. Presented herein is a method that exhibits these properties and makes use of benign reagents without the use of specialized equipment. By exposing Pd powder to dilute hydrogen in nitrogen gas, sacrificial surface PdH is formed along with a controlled amount of dilute interstitial hydride. The lattice expansion that occurs in Pd under higher H2 partial pressures is avoided. Once the flow of reagent gas is terminated, addition of metal salts facilitates controlled, electroless deposition of an overlayer of subnanometer thickness. This process can be cycled to create thicker layers. The approach is carried out under ambient processing conditions, which is an advantage over some forms of atomic layer deposition. The hydride-mediated reaction is electroless in that it has no need for connection to an external source of electrical current and is thus amenable to deposition on high-surface-area substrates having rich, nanoscale topography as well as on insulator-supported catalyst particles. STEM-EDS measurements show that conformal Rh and Pt surface layers can be formed on Pd powder with this method. A growth model based on energy-resolved XPS depth profiling of Rh-modified Pd powder is in general agreement. After two cycles, deposits are consistent with 70-80% coverage and a surface layer with a thickness from 4 to 8 Å. PMID:24738575

Cappillino, Patrick J; Sugar, Joshua D; El Gabaly, Farid; Cai, Trevor Y; Liu, Zhi; Stickney, John L; Robinson, David B

2014-04-29

323

Layer-by-layer PMIRRAS characterization of DMPC bilayers deposited on a Au111 electrode surface.  

PubMed

A combination of Langmuir-Blodgett and Langmuir-Schaefer techniques was employed to deposit 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers at a gold electrode surface. One leaflet consisted of hydrogen-substituted acyl chains, and the second leaflet was composed of molecules with deuterium-substituted acyl chains. This architecture allowed for layer-by-layer analysis of the structure of the bilayer. Photon polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was used to determine the conformation and orientation of the acyl chains of DMPC molecules in the individual leaflets as a function of the potential applied to the gold electrode. The bilayer is adsorbed onto the metal surface when the field applied to the membrane does not exceed approximately 108 V/m. When adsorbed, the bottom leaflet is in contact with a hydrophobic metal surface, and the top leaflet is interacting with the aqueous solution. The asymmetry of the environment has an effect on the orientation of the DMPC molecules in each leaflet. The tilt angle of the acyl chains of the DMPC molecules in the bottom leaflet that is in contact with the gold is approximately 10 degrees smaller than that observed for the top leaflet that is exposed to the solution. These studies provide direct evidence that the structure of a phospholipid bilayer deposited at an electrode surface is affected by interaction with the metal. PMID:17129004

Garcia-Araez, Nuria; Brosseau, Christa L; Rodriguez, Paramaconi; Lipkowski, Jacek

2006-12-01

324

Effect of surface particle interactions during pool boiling of nanofluids  

Microsoft Academic Search

The pool boiling characteristics of nanofluids is affected by the relative magnitudes of the average surface roughness and the average particle diameter. In the present work, an attempt has been made to study the interactions between the nanoparticles and the heater surface. The experimental methodology accounts for the transient nature of the boiling phenomena. The boiling curves of electro-stabilized Al2O3

G. Harish; V. Emlin; V. Sajith

2011-01-01

325

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

326

Simultaneous detection of separation and transition in surface shear layers  

NASA Technical Reports Server (NTRS)

Flush-mounted hot-film gages have proved effective in detecting boundary-layer transition and in measuring skin friction but with limited success in detecting laminar separation and reattachment. The development of multielement micro hot-film sensors, and the recent discovery of the phase reversal phenomena associated with low-frequency dynamic shear stress signals across regions of laminar separation and turbulent reattachment, have made it possible to simultaneously and unambiguously detect these surface shear layer characteristics. Experiments were conducted on different airfoils at speeds ranging from low subsonic to transonic speeds to establish the technique for incompressible and compressible flow applications. The multielement dynamic shear stress sensor technique was successfully used to detect laminar separation, turbulent reattachment, as well as, shock induced laminar and turbulent separation.

Mangalam, Siva M.; Stack, J. P.; Sewall, W. G.

1989-01-01

327

Atmospheric surface and boundary layers of the Amazon Basin  

NASA Technical Reports Server (NTRS)

Three phases of work were performed: design of and preparation for the Amazon Boundary Layer Experiment (ABLE 2-A); execution of the ABLE 2-A field program; and analysis of the ABLE 2-A data. Three areas of experiment design were dealt with: surface based meteorological measurements; aircraft missions; and project meteorological support. The primary goal was to obtain a good description of the structure of the atmosphere immediately above the rain forest canopy (top of canopy to a few thousand meters), to describe this region during the growing daytime phase of the boundary layer; and to examine the nighttime stratified state. A secondary objective was to examine the role that deep convective storms play in the vertical transport of heat, water vapor, and other trace gases. While significant progress was made, much of the analysis remains to be done.

Garstang, Michael

1987-01-01

328

A scheme for computing surface fluxes from mean flow observations. [of atmospheric surface layer  

NASA Technical Reports Server (NTRS)

A computational method for estimating turbulent surface stress, sensible heat flux, and humidity flux from mean velocity, temperature, and humidity at a single height in the atmospheric surface layer is presented. The method is based on coupling a Monin-Obukhov similarity profile to a 'force-restore' formulation for the evolution of surface soil temperature to yield the local values of shear stress, heat flux, and surface temperature. In addition to reference-level mean flow properties, the parameters required to implement this method are the thermal heat capacity of the soil, the surface aerodynamic roughness, latitude, solar declination, surface albedo, surface emissivity, and atmospheric transmissivity. Sample calculations are presented for (1) constant atmospheric forcing at the reference level, and (2) variable atmospheric forcing corresponding to Kahle's (1977) measurements of windspeed, air temperature, and radiometer soil surface temperature under dry vegetatively sparse conditions in the Mohave Desert, Calif.

Hoffert, M. I.; Storch, J.

1979-01-01

329

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

330

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

331

Oil emulsification using surface-tunable carbon black particles.  

PubMed

Emulsification of oil from a subsurface spill and keeping it stable in the water is an important component of the natural remediation process. Motivated by the need to find alternate dispersants for emulsifying oil following a spill, we examine particle-stabilized oil-in-water emulsions. Emulsions that remain stable for months are prepared either by adding acid or salt to carboxyl-terminated carbon black (CB) suspension in water to make the particles partially hydrophobic, adding the oil to this suspension and mixing. When naphthalene, a model potentially toxic polycyclic aromatic hydrocarbon, is added to octane and an emulsion formed, it gets adsorbed significantly by the CB particles, and its transport into the continuous water is markedly reduced. In contrast to an undesirable seawater-in-crude oil emulsion produced using a commercially used dispersant, Corexit 9500A, we demonstrate the formation of a stable crude oil-in-seawater emulsion using the CB particles (with no added acid or salt), important for natural degradation. The large specific surface area of these surface functionalized CB particles, their adsorption capability and their ability to form stable emulsions are an important combination of attributes that potentially make these particles a viable alternative or supplement to conventional dispersants for emulsifying crude oil following a spill. PMID:23527962

Saha, Amitesh; Nikova, Ani; Venkataraman, Pradeep; John, Vijay T; Bose, Arijit

2013-04-24

332

Incipient Space Weathering Observed on the Surface of Itokawa Dust Particles  

NASA Astrophysics Data System (ADS)

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 Fe2+.

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.

2011-08-01

333

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

334

Prediction of transport behaviors of particulate composites considering microstructures of soft interfacial layers around ellipsoidal aggregate particles.  

PubMed

The effect of microstructures of interfacial layers on transport behaviors of particulate composites has been found to be significant, thus microstructural characteristics of interfacial layers should be considered in the analysis for better prediction of transport properties of particulate composites. However, it is very difficult to determine the volume fraction of soft interfacial layers around polydisperse three-dimensional (3D) ellipsoidal aggregate particles and to practically estimate the influence of such a microstructural characteristic on transport properties of particulate composites by traditional experimental methods and simple models proposed so far. In this article, an approximate analytical model for the volume fraction of soft interfacial layers is proposed on the basis of a theory of the nearest-surface distribution functions and geometric characteristics of polydisperse ellipsoidal particle systems. A theoretical model that adopts a three-phase composite ellipsoid structure by a generalized self-consistent scheme is further presented to predict the effective transport properties of particulate composites containing such soft interfacial layers. To test the developed models, numerical results of the soft interfacial volume fraction from the previous work, experimental data in the literature, the Hashin-Shtrikman bounds model and the Maxwell-Garnett model for the effective electrical conductivity are compared respectively. Finally, by virtue of the present models, the effects of key factors on the effective electrical conductivity of particulate composites are investigated in a quantitative manner. PMID:24651952

Xu, Wenxiang; Chen, Huisu; Chen, Wen; Jiang, Linhua

2014-01-28

335

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

2013-05-01

336

Laser modification of ceramic surfaces with micro- and nano- particles  

Microsoft Academic Search

Laser supported processes can be used to modify the electrical and thermal properties of ceramic substrates locally. These processes are characterised by a strong thermal interaction between the laser beam and the ceramic surface which leads to localised melting. During the dynamic melting process metal particles are introduced into the melt pool in order to modify the physical properties. Different

Magnus Rohde

2007-01-01

337

Surface scattering of core-shell particles with anisotropic shell.  

PubMed

The Bobbert-Vlieger solution to light scattering of a spherical particle suspended above a surface is extended to model the scattering of core-shell structures with anisotropic shell. Numerical modeling demonstrates that ellipsometry has potential to resolve particle shell anisotropy down to 1.8×10(-4) for SiO(2)@Au core-shell particles in air with 50 nm core diameter and 10 nm shell thickness deposited on a silicon Si [100] substrate with a density of 1???m(-2). Application of the Ibrahim and Bashara criterion for ellipsometer parameter cross correlation identifies variable-angle ellipsometry as a viable experimental approach to separate particle core radius and shell thickness from the shell anisotropy. Ellipsometry is also identified as an alternative technique for determination of liposome anisotropy and for the study of liposome fusion with a substrate in the formation process of supported lipid bilayers. PMID:24561952

De Beule, Pieter A A

2014-01-01

338

New states of surface waves in a linear layered structure  

NASA Astrophysics Data System (ADS)

The existence of hyperbolic surface waves in a linear carrier layer, which are associated with the presence of a superlattice and have an N-shaped spectrum, is demonstrated. It is further shown that, for each fixed frequency, there exist three independent modes with different propagation constants. The descending branches of this spectrum are characterized by a negative group velocity and are similar to the decay parts of the spectrum. Experimentally, a breakdown of the waveguide propagation mode should be expected in this frequency and wave vector range.

Bolshinskii, L. G.; Lomtev, A. I.

1987-01-01

339

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

340

Boundary layer flow of nanofluid over an exponentially stretching surface.  

PubMed

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. PMID:22289390

Nadeem, Sohail; Lee, Changhoon

2012-01-01

341

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

2012-05-21

342

Surface potentials and layer charge distributions in few-layer graphene films.  

PubMed

Graphene-derived nanomaterials are emerging as ideal candidates for postsilicon electronics. Elucidating the electronic interaction between an insulating substrate and few-layer graphene (FLG) films is crucial for device applications. Here, we report electrostatic force microscopy (EFM) measurements revealing that the FLG surface potential increases with film thickness, approaching a "bulk" value for samples with five or more graphene layers. This behavior is in sharp contrast with that expected for conventional conducting or semiconducting films, and derives from unique aspects of charge screening by graphene's relativistic low energy carriers. EFM measurements resolve previously unseen electronic perturbations extended along crystallographic directions of structurally disordered FLGs, likely resulting from long-range atomic defects. These results have important implications for graphene nanoelectronics and provide a powerful framework by which key properties can be further investigated. PMID:18613730

Datta, Sujit S; Strachan, Douglas R; Mele, E J; Johnson, A T Charlie

2009-01-01

343

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

344

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

345

Distributions of Surface-Layer Buoyancy Versus Lifting Condensation Level over a Heterogeneous Land Surface  

Microsoft Academic Search

Onset and coverage of small cumulus clouds depend on the relative abundance of surface-layer air parcels possessing favourable buoyancy and moisture-two variables that are coupled through the surface energy budget. This abundance is described using a joint frequency distribution (JFD) as a function of virtual potential temperature v. and height of lifting condensation level zLCL. It is shown analytically that

Kelly Schrieber; Roland Stull; Qing Zhang

1996-01-01

346

Distributions of surface-layer buoyance versus lifting condensation level over a heterogeneous land surface  

Microsoft Academic Search

Onset and coverage of small cumulus clouds depend on the relative abundance of surface-layer air parcels possessing favorable buoyancy and moisture - two variables that are coupled through the surface energy budget. This abundance is described using a joint frequency distribution (JFD) as a function of virtual potential temperature θ{sub v} and height of the lifting condensation level z{sub LCL}.

K. Schrieber; Qing Zhang; R. Stull

1996-01-01

347

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

348

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

349

Observation of surface-induced layering in bicontinuous microemulsions  

NASA Astrophysics Data System (ADS)

Neutron-specular-reflectivity measurements were made on liquid surfaces of disordered one-phase microemulsions consisting of mixtures of nonionic surfactant C10E4, D2O, and octane, with equal volume fractions of water and oil, in the region of the phase diagram where the bulk microemulsion structure was known to be bicontinuous. From these measured reflectivity data, the one-dimensional scattering-length-density profiles in the vertical direction of the air-microemulsion interfaces were reconstructed directly by using a model-independent inversion scheme developed recently by one of us. From the reconstructed scattering-length-density profiles, we constructed the one-dimensional Debye correlation functions. From these correlation functions, we deduced the surface-induced layering with periods that correlate well with the bulk water-water domain average repeat distance known from a previous small-angle neutron-scattering study. We discuss in particular the effect of a finite-Q range of data on the height of the first D2O layer.

Zhou, Xiao-Lin; Lee, Lay-Theng; Chen, Sow-Hsin; Strey, R.

1992-11-01

350

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

351

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

352

NMR Spectroscopy of the Hydrated Layer of Composite Particles Based on Nanosized Al2O3 and Vitreous Humor  

NASA Astrophysics Data System (ADS)

The hydrated layer of composite particles prepared using Al2O3 and cattle vitreous humor was investigated using NMR spectroscopy. It was found that water bound to Al2O3 nanoparticles was present in the form of clusters with different degrees of association and energies of interaction with the surface. Water bound to the surface of the Al2O3/vitreous humor composite became more uniform upon immobilization of vitreous humor components on the surface of the Al2O3. With this, the clusters of adsorbed water had characteristics that were close to those found in air and weakly polar CHCl3 media. Addition of polar CH3CN led to the formation of very small water clusters. PMR spectra of the surface of the Al2O3/vitreous humor composite in the presence of trifluoroacetic acid differentiated four types of hydrated structures that differed in the degree of water association.

Turov, V. V.; Gerashchenko, I. I.; Markina, A. I.

2013-11-01

353

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

354

Characteristics of structure formation in the surface layers of metal during vacuum carburizing  

Microsoft Academic Search

At longer saturation times the carbon concentration in microvolumes of the surface layer exceeds the solubility of carbon in 7 iron. From the results of a layer-by-layer chemical analysis (with removal of layers 25 ~m thick) we plotted concentration curves of the carbon distribution through the thickness of the carburized layer. These curves differ from the standard curves by the

S. N. Tsepov; M. A. Krishtal

1983-01-01

355

Surface tension and wetting effects with smoothed particle hydrodynamics  

NASA Astrophysics Data System (ADS)

For flows at the micro and nano scales the surface to volume fraction is increased and therefore the behavior of fluids in contact with solid structures is primarily dominated by surface tension effects. Modeling of surface tension effects at nano and micro scales using smoothed particle hydrodynamics requires an efficient description not only of the interface between liquid and gas, but also of the triple line defined by the three phase contact between the solid, liquid and gas. In this study, we propose an efficient and reliable implementation, which takes the liquid-gas surface tension and the equilibrium contact angle as input parameters and prescribes the normal direction of the liquid-gas interface at the triple line based on the desired equilibrium contact angle. This results in a robust algorithm capable of capturing the physics of equilibrium wetting and treating a large variety of cases including different wetting angles, pinning effects and wetting of structured surfaces.

Breinlinger, Thomas; Polfer, Pit; Hashibon, Adham; Kraft, Torsten

2013-06-01

356

Characterization of the Greenland Ice Sheet Basal and Surface Layer Microwave Angular Scattering Characteristics  

Microsoft Academic Search

The use of microwave backscatter signatures to characterize the physical attributes of surfaces and layers, such as roughness and dielectric constant, has been used for many geophysical applications. For ice sheet studies, the characterization of these parameters for the basal and surface layers could aid in the identification of the presence of liquid water, bed roughness, and surface snow layer

E. Rodriguez; A. Bertran; C. Veeramachaneni; K. Jezek; P. Gogineni; X. Wu; J. E. Belz

2008-01-01

357

Thermal characterization of high temperature reactor particle layers by photothermal microscopy  

NASA Astrophysics Data System (ADS)

Thermal diffusivity of particle pyrolytic carbon layers deposited on 500 ?m diameter spherical particle before irradiation has been measured using photoreflectance microscopy (PM). This technique is used to characterize of such small constituents at a microscopic scale and temperature controlled up to 1000 °C. Nevertheless, one of the layers - buffer layer - needs a particular analysis due to its porous structure. Indeed, measurements by PM on this material only permit to obtain the thermal diffusivity of the solid skeleton. These require the use of a numerical homogenization technique to estimate an effective thermal conductivity. The effect of temperature is discussed. Mapping of the thermal diffusivity of coated fuel particles provides useful data for modelling fuel performance during the nuclear reactors operation.

Marchand, D.; Rochais, D.

2010-03-01

358

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

2014-04-01

359

Surface modification of poly(ethylene terephthalate) via hydrolysis and layer-by-layer assembly of chitosan and chondroitin sulfate to construct cytocompatible layer for human endothelial cells  

Microsoft Academic Search

Surface modification of poly(ethylene terephthalate) (PET) film was performed by surface hydrolysis and layer-by-layer (LBL) assembly followed a mechanism of electrostatic adsorption of oppositely charged polymers, exemplified with chitosan and chondroitin sulfate (CS). Hydrolysis of PET in concentrated alkaline solution produced a carboxyl-enriched surface. The changes of weight loss and surface chemistry, morphology and wettability were monitored and verified by

Yunxiao Liu; Tao He; Changyou Gao

2005-01-01

360

Numerical Computations of Hypersonic Boundary-Layer over Surface Irregularities  

NASA Technical Reports Server (NTRS)

Surface irregularities such as protuberances inside a hypersonic boundary layer may lead to premature transition on the vehicle surface. Early transition in turn causes large localized surface heating that could damage the thermal protection system. Experimental measurements as well as numerical computations aimed at building a knowledge base for transition Reynolds numbers with respect to different protuberance sizes and locations have been actively pursued in recent years. This paper computationally investigates the unsteady wake development behind large isolated cylindrical roughness elements and the scaled wind-tunnel model of the trip used in a recent flight measurement during the reentry of space shuttle Discovery. An unstructured mesh, compressible flow solver based on the space-time conservation element, solution element (CESE) method is used to perform time-accurate Navier-Stokes calculations for the flow past a roughness element under several wind-tunnel conditions. For a cylindrical roughness element with a height to the boundary-layer thickness ratio from 0.8 to 2.5, the wake flow is characterized by a mushroom-shaped centerline streak and horse-shoe vortices. While time-accurate solutions converged to a steady-state for a ratio of 0.8, strong flow unsteadiness is present for a ratio of 1.3 and 2.5. Instability waves marked by distinct disturbance frequencies were found in the latter two cases. Both the centerline streak and the horse-shoe vortices become unstable downstream. The oscillatory vortices eventually reach an early breakdown stage for the largest roughness element. Spectral analyses in conjunction with the computed root mean square variations suggest that the source of the unsteadiness and instability waves in the wake region may be traced back to possible absolute instability in the front-side separation region.

Chang, Chau-Lyan; Choudhari, Meelan M.; Li, Fei

2010-01-01

361

Physiochemical Properties of Sodium Chloride Particles on Laboratory Ice Surfaces  

NASA Astrophysics Data System (ADS)

Aqueous halides (e.g. Cl- and Br-) on environmental ice surfaces are converted to reactive gases through heterogeneous chemistry that has broad consequences for springtime Arctic tropospheric oxidation chemistry. Recent studies indicate that atmospherically contaminated snow (e.g. more acidic snow) is more effective at activating halogens than frozen seawater. This study investigates the microstructure created by the addition of salts onto ice surfaces as a function of temperature. Microscopic sodium chloride salt crystals were labeled with a fluorescent dye (fluorescein) and placed onto laboratory ice surface below the hydrohalite (NaCl 2H2O)-water eutectic temperature. As temperature was increased above the eutectic, a discrete brine area formed around the crystal. Size and morphology of the brine area was determined using an Axioscope II epifluorescence microscope. Initially, the salt crystal did not entirely dissolve and three distinct phases (solid salt, brine, ice) were present for some time. Timescales for crystal dissolving, brine formation, and wetting across the ice surfaces where thus constrained. Similar experiments using a fluorescently labeled, laboratory-generated sea salt aerosol particles were also carried out and compared to the larger microscopic sodium chloride crystals. This work gives insight into how atmospheric particles deliver contaminants to ice surfaces, how those contaminants interact with ice surfaces and thus how they may impact halogen activation.

Gleason, E. P.; Simpson, W. R.

2013-12-01

362

Erosive particle kinematics in the turbulent combustion boundary layer contacting a solid wall  

SciTech Connect

Measurements and numerical modeling are applied to observe and predict the interactive influence of sub-micron gas borne particles in an erosive turbulent combustion wall boundary layer. Some of the experiments and computations discussed are directed to study of turbulent free shear layers. Others ephasize wall boundary layers. The common purpose of all of these studies is to generate information on the particle interaction mechanisms active in alteration and reduction of the turbulent transport and the consequent reduction of the erosive heat and mass transfer. Primary emphasis here is given to analysis of erosive two phase wall boundary layers encountered in solid propellant combustion situations. Examples are gun barrel, rocket nozzle, and coal-fired gas turbine combustion flow fields.

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

1983-04-15

363

Surface-imprinted nanostructured layer-by-layer film for molecular recognition of theophylline derivatives.  

PubMed

In this article we report the introduction of the cooperativity of various specific interactions combined with photo-cross-linking of the interlayers to yield binding sites that can realize better selectivity and imprinting efficiency of a surface molecularly imprinted LbL film (SMILbL), thus providing a new approach toward fabrication of nanostructured molecularly imprinted thin films. It involves preassembly of poly(acrylic acid) (PAA) conjugated of the theophylline residue template via a disulfide bridge, denoted as PAAtheo 15, in solution, and layer-by-layer (LbL) assembly of PAAtheo 15 and a positively charged photoreactive diazo resin (DAR) to form multilayer thin film with designed architecture. After photo-cross-linking of the film and template removal, binding sites specific to 7-(beta-hydroxyethyl)theophylline (Theo-ol) molecules are introduced within the film. Binding assay demonstrates that the SMILbL has a high selectivity of SMILbL to Theo-ol over caffeine. A control experiment demonstrates that the selectivity of SMILbL derives from nanostructured recognition sites among the layers. The imprinting amount per unit mass of the film can be 1 order of magnitude larger than that of the conventional bulk molecular imprinting systems. As this concept of construction SMILbL can be easily extended to the other molecules by the following similar protocol: its applications in building many other different molecular recognition systems are greatly anticipated. PMID:18788771

Niu, Jia; Liu, Zhihua; Fu, Long; Shi, Feng; Ma, Hongwei; Ozaki, Yukihiro; Zhang, Xi

2008-10-21

364

Thermoresponsive surfaces prepared using adsorption of a cationic graft copolymer: a versatile method for triggered particle capture.  

PubMed

In this study we investigate triggered particle capture at substrates containing adsorbed thermally responsive graft copolymers. The copolymers used were PDMA(x)(+)-g-(PNIPAm(n))(y), where DMA(+) is quaternized N,N-dimethylaminoethyl methacrylate and NIPAm is N-isopropylacrylamide. The x and y values originate from the macroinitiator used for copolymer preparation. In this study the copolymers are adsorbed onto two different substrates: quartz microscope slides and microporous, high surface area carbon foam. The substrates were coated with a layer of calcined laponite. The laponite acted as a conditioning layer and promoted strong adsorption of the copolymer. The hydrophobicity of the thermoresponsive surfaces was probed using variable-temperature contact angle measurements. The contact angles generally increased considerably upon increasing the temperature to above the lower critical solution temperature (LCST) of the copolymers. The ability of the thermoresponsive surfaces to capture dispersed particles was investigated using anionic and cationic polystyrene (PS) particles. PDMA(30)(+)-g-(PNIPAm(210))(14) was the most effective copolymer in terms of providing high capture efficiencies of anionic PS particles using temperature as the trigger. The thermoresponsive surfaces strongly held the anionic PS particles even when cooled to below the LCST. The relationships between copolymer structure and particle capture efficiency are discussed. The new approach used here for preparation thermoresponsive surfaces is potentially scalable to high volume applications. PMID:19545877

Liu, R; Saunders, B R

2009-10-01

365

Mechanisms for particle transfer and segregation in a turbulent boundary layer  

NASA Astrophysics Data System (ADS)

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 understand the reasons for higher particle concentration in the wall region by examining turbulent transfer of heavy particles to and away from the wall in connection with the coherent structures of the boundary layer. We will examine the behaviour of a dilute dispersion of heavy particles flyashes in air in a vertical channel flow, using pseudo-spectral direct numerical simulation to calculate the turbulent flow field at a shear Reynolds number Re[tau] = 150, and Lagrangian tracking to describe the dynamics of particles. Drag force, gravity and Saffman lift are used in the equation of motion for the particles, which are assumed to have no influence on the flow field. Particle interaction with the wall is fully elastic. As reported in several previous investigations, we found that particles are transferred by sweeps Q2 type events in the wall region, where they preferentially accumulate in the low-speed streak environments, whereas ejections Q4 type events transfer particles from the wall region to the outer flow. We quantify the efficiency of the instantaneous realizations of the Reynolds stresses events in transferring different size particles to the wall and away from the wall, respectively. Our findings confirm that sweeps and ejections are efficient transfer mechanisms for particles. In particular, we find that only those sweep and ejection events with substantial spatial coherence are effective in transferring particles. However, the efficiency of the transfer mechanisms is conditioned by the presence of particles to be transferred. In the case of ejections, particles are more rarely available since, when in the viscous wall layer, they are concentrated under the low-speed streaks. Even though the low-speed streaks are ejection-like environments, particles remain trapped for a long time. This phenomenon, which causes accumulation of particles in the near-wall region, can be interpreted in terms of overall fluxes toward and away from the wall by the theory of turbophoresis. This theory, proposed initially by Caporaloni et al. (1975) and re-examined later by Reeks (1983), can help to explain the existence of net particle fluxes toward the wall as a manifestation of the skewness in the velocity distribution of the particles (Reeks 1983). To understand the local and instantaneous mechanisms which give rise to the phenomenon of turbophoresis, we focus on the near-wall region of the turbulent boundary layer. We examine the role of the rear-end of a quasistreamwise vortex very near to the wall in preventing particles in the proximity of the wall from being re-entrained by the pumping action of the large, farther from the wall, forward-end of a following quasi-streamwise vortex. We examine several mechanisms for turbulence structures near the wall and we find that the mechanism based on the archetypal quasi-streamwise structures identified by Schoppa & Hussain (1997), the parent offspring regeneration cycle for near-wall quasi-streamwise vortices discussed by Brooke & Hanratty (1993), and the mechanism based on coherent packets of hairpin vortices, the fundamental super-structure characterized by Adrian, Meinhart & Tomkins (2000), all depict the same characteristic pattern which is responsible for particle trapping very near to the wall.

Marchioli, Cristian; Soldati, Alfredo

2002-10-01

366

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

2013-03-13

367

Modeling Fragmentation of the Self-Gravitating Molecular Layer by Smoothed Particle Hydrodynamics  

NASA Astrophysics Data System (ADS)

We revisit the modeling of ion-neutral (or ambipolar) diffusion with two fluid smoothed particle hydrodynamics, as discussed by Hosking & Whitworth (2004). Some parts of the technique are optimized to satisfy the pioneer works on behavior of the ambipolar diffusion in isothermal self-gravitating layers. The frictional heating by ambipolar diffusion is examined, and its effect on fragmentation of the layer is studied. The results are compared to the thermal phases of instability as obtained by Nejad-Asghar (2007, submitted).

Nejad-Asghar, Mohsen; Molteni, Diego

2007-08-01

368

Can new particle formation occur in the clean marine boundary layer?  

Microsoft Academic Search

An analysis of new particle formation probability in the marine boundary layer (MBL) is conducted using a detailed aerosol dynamics and gas-phase chemistry model, thermodynamically correct classical binary (H2O-H2SO4) nucleation theory, and recently developed ternary (H2O-H2SO4-NH3) nucleation theory. Additionally, the effect of boundary-layer meteorology (i.e., adiabatic cooling, small scale fluctuations, and entrainment) in enhancing nucleation is also examined. The results

Liisa Pirjola; Colin D. O'Dowd; Ian M. Brooks; Markku Kulmala

2000-01-01

369

Numerical simulation of a shock wave propagation in the solid particle layer  

Microsoft Academic Search

A numerical simulation of the dust entrainment and dispersion from the dust layer behind a shock wave is performed using a two-dimensional gas-solid two-phase Euler equation to understand their mechanisms. The volume fraction of solid particles is included in the equation to consider the strong solid-phase effect. The numerical result shows that the normal shock wave above the dust layer

Manabu Hishida; Koichi Hayashi

1989-01-01

370

Flotation in inorganic electrolytes; the relationship between recover of hydrophobic particles, surface tension, bubble coalescence and gas solubility  

Microsoft Academic Search

The influence of a series of aqueous solutions of inorganic electrolytes on the flotation performance of graphite particles was determined. The results were related to the electrostatic interaction (as expressed in terms of the thickness of the electrostatic double layer) the surface tension and the solubility of gases in the electrolyte solutions. Overall, high flotation recoveries were attributed to an

R. J. Pugh; P. Weissenborn; O. Paulson

1997-01-01

371

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

372

Erosion processes due to energetic particle-surface interaction  

SciTech Connect

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. [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Boltzmannstrasse 2, 85748 Garching (Germany)

2010-05-20

373

Characterization of cathode keeper wear by surface layer activation  

NASA Technical Reports Server (NTRS)

In this study, the erosion rates of the discharge cathode keeper in a 30 cm NSTAR configuration ion thruster were measured using a technique known as Surface Layer Activation (SLA). This diagnostic technique involves producing a radioactive tracer in a given surface by bombardment with high energy ions. The decrease in activity of the tracer material may be monitored as the surface is subjected to wear processes and correlated to a depth calibration curve, yielding the eroded depth. Analysis of the activities was achieved through a gamma spectroscopy system. The primary objectives of this investigation were to reproduce erosion data observed in previous wear studies in order to validate the technique, and to determine the effect of different engine operating parameters on erosion rate. The erosion profile at the TH 15 (23 kw) setting observed during the 8200 hour Life Demonstration Test (LDT) was reproduced. The maximum keeper erosion rate at this setting was determined to be 0.085 pm/hr. Testing at the TH 8 (1.4 kw) setting demonstrated lower erosion rates than TH 15, along with a different wear profile. Varying the keeper voltage was shown to have a significant effect on the erosion, with a positive bias with respect to cathode potential decreasing the erosion rate significantly. Accurate measurements were achieved after operating times of only 40 to 70 hours, a significant improvement over other erosion diagnostic methods.

Polk, James E.

2003-01-01

374

Particle image velocimetry measurements of a shock wave/turbulent boundary layer interaction  

NASA Astrophysics Data System (ADS)

Particle image velocimetry is used to investigate the interaction between an incident shock wave and a turbulent boundary layer at Mach 2.1. A particle response assessment establishes the fidelity of the tracer particles. The undisturbed boundary layer is characterized in detail. The mean velocity field of the interaction shows the incident and reflected shock wave pattern, as well as the boundary layer distortion. Significant reversed flow is measured instantaneously, although, on average no reversed flow is observed. The interaction instantaneously exhibits a multi-layered structure, namely, a high-velocity outer region and a low-velocity inner region. Flow turbulence shows the highest intensity in the region beneath the impingement of the incident shock wave. The turbulent fluctuations are found to be highly anisotropic, with the streamwise component dominating. A distinct streamwise-oriented region of relatively large kinematic Reynolds shear stress magnitude appears within the lower half of the redeveloping boundary layer. Boundary layer recovery towards initial equilibrium conditions appears to be a gradual process.

Kolling, S.; Bois, P. A. Du; Benson, D. J.; Feng, W. W.

2007-08-01

375

Surface composition of atmospheric aerosol: individual particle characterization by TOF-SIMS  

NASA Astrophysics Data System (ADS)

Size segregated atmospheric aerosol samples collected from the summer 2000 Montana forest fires, from Hawaiian sea salt, and from an Asian Dust event reaching Salt Lake City, Utah, in April 2001 have been studied. Multivariate statistical analysis has been used to extract information from the SIMS images. Images of the particles have been separated from the image background, which significantly improved our ability to acquire the composition of individual aerosol particles. Montana forest fire aerosol was predominantly submicrometer, well within the respirable range (PM2.5), and had a characteristic surface composition identified as the amides of stearic acid and palmitic acid. Sea salt showed a layered structure of organic compounds on the surface of aqueous NaCl. The Asian Dust event could be clearly distinguished from normal Salt Lake City particulate pollution.

Peterson, R. E.; Tyler, B. J.

2003-01-01

376

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

377

Surface-charging behavior of Zn-Cr layered double hydroxide.  

PubMed

A Zn-Cr layered double hydroxide (LDH) having the formula Zn(2)Cr(OH)(6)Cl(0.7)(CO(3))(0.15)2.1H(2)O was synthesized and characterized by powder X-ray diffraction, infrared spectroscopy, acid-base potentiometric titration, mass titration, electrophoretic mobility, and modeling of the electrical double layer. Adsorption of alizarin was also performed in order to show some particular features of the HDL. Net hydroxyl adsorption, which increases with increasing pH and decreasing supporting electrolyte concentration, takes place above pH 5. The electrophoretic mobility of the particles was always positive and it decreased when the pH was higher than 9. An isoelectric point of 12 could be estimated by extrapolating the data. The modified MUSIC model was used to estimate deprotonation constants of surface groups and different adsorption models were compared. Good fit of hydroxyl adsorption and electrophoresis could be achieved by considering both OH(-)/Cl(-) exchange at structural sites and proton desorption from surface hydroxyl groups. The modeling, in agreement with alizarin adsorption, indicates that most of the structural positive charge of the LDH is screened at the surface by exchanged anions and negatively charged surface groups. It also suggests that only structural charge sites initially neutralized by chloride ions are active for anion exchange. The remaining sites are blocked by carbonate and do not participate in the exchange. PMID:15533416

Rojas Delgado, R; Arandigoyen Vidaurre, M; De Pauli, C P; Ulibarri, M A; Avena, M J

2004-12-15

378

Method and apparatus for measuring surface density of explosive and inert dust in stratified layers  

DOEpatents

A method for determining the surface density of coal dust on top of rock dust or rock dust on top of coal dust is disclosed which comprises directing a light source at either a coal or rock dust layer overlaying a substratum of the other, detecting the amount of light reflected from the deposit, generating a signal from the reflected light which is converted into a normalized output (V), and calculating the surface density from the normalized output. The surface density S.sub.c of coal dust on top of rock dust is calculated according to the equation: S.sub.c =1/-a.sub.c ln(V) wherein a.sub.c is a constant for the coal dust particles, and the surface density S.sub.r of rock dust on top of coal dust is determined by the equation: ##EQU1## wherein a.sub.r is a constant based on the properties of the rock dust particles. An apparatus is also disclosed for carrying out the method of the present invention.

Sapko, Michael J. (Finleyville, PA); Perlee, Henry E. (Bethel Park, PA)

1988-01-01

379

Entropic Control of Particle Motion Using Surface Microstructures  

NASA Astrophysics Data System (ADS)

We show how passive structures etched into the walls of a sample container may be used to create localized and directional entropic force fields that can trap, repel, or induce the drift of large particles in colloidal mixtures of spheres of two different sizes. The experiments illustrate how entropy and surface texture lead to novel colloidal assembly and control. Measurements employing laser tweezers and video microscopy reveal the size of these forces (A.D. Dinsmore, A.G. Yodh and D.J. Pine, Nature 383, 239-242 (1996).) along stepped and curved surfaces. Further implications of these ideas in connection with soft membranes, and for particle arrays will be discussed. THIS SECTION IS FOR APS USE ONLY

Yodh, Arjun G.

1997-03-01

380

Liquid drops and surface tension with smoothed particle applied mechanics  

PubMed

Smoothed particle applied mechanics (SPAM), also referred to as smoothed particle hydrodynamics, is a Lagrangian particle method for the simulation of continuous flows. Here we apply it to the formation of a liquid drop, surrounded by its vapor, for a van der Waals (vdW) fluid in two dimensions. The cohesive pressure of the vdW equation of state gives rise to an attractive, central force between the particles with an interaction range which is assumed to exceed the interaction range of all the other smoothed forces in the SPAM equations of motion. With this assumption, stable drops are formed, and the vdW phase diagram is well reproduced by the simulations. Below the critical temperature, the surface tension for equilibrated drops may be computed from the pressure excess in their centers. It agrees very well with the surface tension independently determined from the vibrational frequency of weakly excited drops. We also study strongly deformed drops performing large-amplitude oscillations, which are reminiscent of the oscillations of a large ball of water under microgravity conditions. In an appendix we comment on the limitations of SPAM by studying the violation of angular momentum conservation, which is a consequence of noncentral forces contributed by the full Newtonian viscous stress tensor. PMID:11089045

Nugent; Posch

2000-10-01

381

Effective surface viscosities of a particle-laden fluid interface  

Microsoft Academic Search

The Einstein formula for the effective shear viscosity of low Reynolds number suspension flows is generalized to the case of flat, low-concentration, particle-laden interfaces separating two immiscible fluids. The effective surface shear and dilational viscosities of this system is found to be etas=(5)\\/(3)(eta1+eta2)Rvarphi and zetas=5(eta1+eta2)Rvarphi , correspondingly, where eta1 and eta2 are the shear viscosities of two bulk fluids and

S. V. Lishchuk; I. Halliday

2009-01-01

382

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

383

Surface-modified hemispherical polystyrene\\/polybutyl methacrylate composite particles  

Microsoft Academic Search

Micrometer-sized polystyrene\\/poly(n-butyl methacrylate) composite particles of hemisphere morphology and narrow size distribution were prepared by a process of single-step swelling of uniform polystyrene template microspheres with emulsion droplets of the monomer n-butyl methacrylate containing the initiator benzoyl peroxide in the presence, or absence, of the co-swelling agent toluene. Butyl methacrylate was then polymerized at 73?°C within the template microspheres. Surface

Udi Akiva; Shlomo Margel

2005-01-01

384

Phase transitions and surface morphology of surfactant-coated aerosol particles.  

PubMed

Probe molecule spectroscopy and hygroscopic growth curves characterize the morphology of surfactant-coated aerosol particles as a function of relative humidity (RH). This study focuses on particles composed of either potassium iodide or sodium chloride and sodium dodecyl sulfate (SDS). At high RH, these mixed particles assume a reverse micelle type structure, and at low RH, they comprise a solid core of either KI or NaCl coated with SDS and water. The deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH) of the inorganic fraction of the mixed particles are very similar to those of the pure salts. The surface polarity and morphology sampled by the coumarin 314 probe molecule ranges from that of a water-organic interface to that of an ionic surface and depends strongly on the RH and the amount of SDS. When the SDS coverage of the droplet just prior to efflorescence reaches approximately one monolayer, a thin soap film persists on the surface to values of RH much lower than the ERH. Both the electronic spectroscopy and photoelectric charging efficiency show a separate efflorescence for this layer at RH < 5%. The spectroscopy further reveals that there is a hysteresis associated with this low RH phase transition for both KI and NaCl cores. PMID:17929784

Woods, Ephraim; Kim, Hannah S; Wivagg, Carl N; Dotson, Sarah J; Broekhuizen, Keith E; Frohardt, Erin F

2007-11-01

385

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

386

Laser modification of ceramic surfaces with micro- and nano- particles  

NASA Astrophysics Data System (ADS)

Laser supported processes can be used to modify the electrical and thermal properties of ceramic substrates locally. These processes are characterised by a strong thermal interaction between the laser beam and the ceramic surface which leads to localised melting. During the dynamic melting process metal particles are introduced into the melt pool in order to modify the physical properties. Different alumina samples were treated with metal powders of tungsten, copper, and oxides of these metals. The interface between the metal and the ceramic can be designed by using selected combinations of metal- and metal-oxide-powders and also by a thermal post-processing. The application of nano-particles during the laser-dispersing process resulted in completely different characteristics of the micro-structure and the electrical properties compared to the conventional metal powders with an average grain size of 5 - 15 microns. The micron sized metal particles are embedded within the ceramic matrix as particle agglomerates or as distinct metal phase the nano-particle phase covers the grain boundaries of the ceramics leading to network of nano-scaled electrically conducting "wires". The resulting resistance of the laser tracks can be adjusted from semi-conducting to metallic behavior with a resistivity down to 2x10 -6W/m. The modified ceramic can be used for heating elements working at operation temperatures of up to 1000 °C, high current resistances which can be loaded with currents of up to 100 A.

Rohde, Magnus

2007-03-01

387

Estimates of surface heat flux from sodar and laser scintillation measurements in the unstable boundary layer  

Microsoft Academic Search

Measurements of acoustic backscatter in the lower planetary boundary layer and optical line-of-sight scintillation in the surface layer are each used to compute sensible heat fluxes in the unstable surface layer. Comparisons with simultaneous low-level point measurements by eddy correlation show good agreement, indicating that remote-sensing methods can be successful over less homogeneous terrain where conventional surface layer measurement techniques

R. L. Coulter; M. L. Wesely

1980-01-01

388

Estimates of Surface Heat Flux from Sodar and Laser Scintillation Measurements in the Unstable Boundary Layer  

Microsoft Academic Search

Measurements of acoustic backscatter in the lower planetary boundary layer and optical line-of-sight scintillation in the surface layer are each used to compute sensible heat fluxes in the unstable surface layer. Comparisons with simultaneous low-level point measurements by eddy correlation show good agreement, indicating that remote-sensing methods can be successful over less homogeneous terrain where conventional surface layer measurement techniques

R. L. Coulter; M. L. Wesely

1980-01-01

389

Microstructures and properties of ceramic particle-reinforced metal matrix composite layers produced by laser cladding  

NASA Astrophysics Data System (ADS)

Different weight ratio of titanium, zirconium, WC and Fe-based alloy powders were mixed, and cladded onto a medium carbon steel substrate using a 3kW continuous wave CO2 laser, aiming at producing Ceramic particles- reinforced metal matrix composites (MMCs) layers. The microstructures of the layers are typical hypoeutectic, and the major phases are Ni3Si2, TiSi2, Fe3C, FeNi, MC, Fe7Mo3, Fe3B, ?(residual austenite) and M(martensite). The microstructure morphologies of MMCs layers are dendrites/cells. The MC-type reinforcements are in situ synthesis Carbides which main compositions consist of transition elements Zr, Ti, W. The MC-type particles distributed within dendrite and interdendritic regions with different volume fractions for single and overlapping clad layers. The MMCs layers are dense and free of cracks with a good metallurgical bonding between the layer and substrate. The addition ratio of WC in the mixtures has the remarkable effect on the microhardness of clad layers.

Zhang, Qingmao; He, Jingjiang; Liu, Wenjin; Zhong, Minlin

2005-01-01

390

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

SciTech Connect

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 sicl4 leaving carbon as a porous layer. This porous carbon layer is easily detected by the radiography.

Caputo, A.J.; Costanzo, D.A.; Lackey, W.J.; Layton, F.L.; Stinton, D.P.

1980-10-07

391

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

392

The Point of Departure of a Particle Sliding on a Curved Surface  

ERIC Educational Resources Information Center

A particle is thrown tangentially on a surface. It is shown that for some surfaces and for special initial velocities the thrown particle immediately leaves the surface, and for special conditions it never leaves the surface. The conditions for leaving the surface are investigated. The problem is studied for a surface with the cross-section y =…

Aghamohammadi, Amir

2012-01-01

393

Compressible dusty-gas boundary-layer flow over a flat surface  

SciTech Connect

Equations governing compressible boundary-layer laminar flow of a two-phase particulate suspension are developed based on a continuum representation of both phases. These equations include such effects as particle-phase viscous stresses, variable position-dependent particle slip coefficient, and general power-law viscosity-temperature and thermal conductivity-temperature relations. The dimensionless form of the equations are applied to the problem of flow over a semi-infinite flat surface. An appropriate transformation is employed to allow proper comparison with previously published results for special cases of this problem. The full coupled system of equations is solved numerically via an implicit finite-difference method. Graphical results for the density, and temperature profiles as well as the displacement thicknesses, skin-friction coefficients, and the wall heat transfer coefficient for both the fluid and particle phases are presented and discussed in detail. In addition, a parametric study is performed to illustrate the influence of the particle to fluid viscosity ratio and the viscosity-temperature power exponent on the flow properties.

Chamkha, A.J. [Kuwait Univ., Safat (Kuwait). Dept. of Mechanical and Industrial Engineering

1996-03-01

394

The North Atlantic surface layer and the shallow overturning circulation  

NASA Astrophysics Data System (ADS)

The sea surface salinity maximum (SSS-max) is an integral part of the shallow overturning (SOC) circulation in the North Atlantic. The temperature and salinity of the SSS-max set the density of the subducted water thus are important for the transport properties of the SOC, which has been shown to be important for the large-scale climate. The region requires a net influx of freshwater at near surface level to balance net evaporation. The processes that achieve this task likely influence the variability of SSS-max properties on various time scales in addition to the surface forcing. We are testing the hypothesis that changes in the large-scale wind field in the North Atlantic drive variability of freshwater import by ocean processes into the SSS-max, resulting in seasonal and interannual variability as previously documented. To evaluate the role of said processes for the variability of the upper limb of the SOC, AQUARIUS sea surface salinity (SSS), eddy kinetic energy (EKE) derived from altimetry data (AVISO), sea surface temperature (SST, NOAA OI SST V2) and wind fields (NCEP reanalysis) are used. Previous studies point out the importance of mesoscale dynamics for the freshwater flux into the region which seems to be enhanced by an increased density gradient at the southern edge of the SSS-max as seen from 2012 to 2013. The interannual comparison of meridional density gradient and EKE underline the importance of baroclinic instability for the formation of mesoscale turbulence in the SSS-max in accordance with previous studies. Further analysis, using the SST gradient (extending further back in time than the SSS satellite record) reveals significant seasonal cycles of zonal wind, SST gradient and EKE within the SSS-max region. Spatial correlations between aforementioned variables within the SSS-max region are found, with the EKE peaking about 2-4 months after the large-scale temperature gradient and the zonal wind. Ekman induced set up of the meridional density gradient might be a mechanism for seasonally enhanced mesoscale turbulence, which could be important for the seasonal mixed layer budget as well as interannual variability in surface properties within the SSS-max.

Busecke, Julius; Gordon, Arnold L.

2014-05-01

395

Boundary-layer charged-particle density profiles in an atmospheric pressure plasma flow  

Microsoft Academic Search

The charged-particle density profiles inside the boundary layer formed on a flat plate or a circular cylinder located in an atmospheric-pressure plasma flow were measured with electrostatic probes. Theoretical profiles were obtained through numerical solution of momentum, species, and energy conservation equations taking account of variable transport properties. Comparison of these results leads to the following conclusions: For the flat

M. Suzuki; A. Kanzawa

1979-01-01

396

Limited Particle Scavenging in Biomass Burning Layers Transported to the Alaskan Arctic During ARCPAC  

Microsoft Academic Search

Layers of dense smoke from wildfires in Russia were frequently encountered at altitudes from 0.1-7 km in the Alaskan Arctic in early spring 2008 during the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) project. The ratios of particle mass to carbon monoxide in these biomass burning (BB) plumes, which had been transported over distances >5000 km, were comparable

C. A. Brock; J. Cozic; R. Bahreini; J. Brioude; O. R. Cooper; J. Degouw; K. D. Froyd; J. Holloway; G. Hubler; D. A. Lack; A. M. Middlebrook; J. W. Peischl; T. B. Ryerson; J. P. Schwarz; J. R. Spackman; T. D. Thornberry; P. R. Veres; C. Warneke; A. G. Wollny

2009-01-01

397

Light transport through disordered layers of dense gallium arsenide submicron particles  

Microsoft Academic Search

We present a study of optical transport properties of powder layers with submicrometer, strongly scattering gallium arsenide (GaAs) particles. Uniform, thin samples with well controlled thicknesses were created through the use of varying grinding times, sedimentation fractionation, annealing, and a new sedimentation technique. These fabrication parameters were optimized to produce maximum scattering and minimum absorption. The physical properties were characterized

T. Van der Beek; P. J. C. Barthelemy; P. M. Johnson; D. S. Wiersma; A. Lagendijk

2012-01-01

398

Modulation on coherent vortex structures by dispersed solid particles in a three-dimensional mixing layer.  

PubMed

Large-scale vortex structures and their effects on the dispersion of particles in turbulent free shear flows are very important in many industrial applications, such as combustion, pollution control, and materials processing. In order to understand large-scale vortex structures and particle dispersion in depth, as well as their interaction effects, a two-way-coupled three-dimensional mixing layer laden with particles at a Stokes number of 5 initially located in the upper half region is studied numerically. A pseudospectral method was used to directly simulate the flow fluid, and the Lagrangian approach was used to trace particles. The concept of computational particles is introduced to vary the mass loading of particles. The momentum coupling effect introduced by a particle approximates to a point force. The simulation results show that coherent structures are still dominant in the mixing layer, but the flow dynamics and particle dispersion are modulated. The length of large-scale vortex structures is shortened and the pairing is delayed. Higher mass loading results in lower energy of the fluid in the phase of Kelvin-Helmholtz rolling up, while in the pairing process of large-scale vortex structures, the energy of the fluid increases as the mass loading increases. Higher mass loading also leads to larger mixed fluid thickness and Reynolds stresses of the flow. In addition, the particle dispersion along the transverse direction differs from that along the spanwise direction, which indicates that the effects of the addition of a particle on the spanwise large-scale vortex structures are different from those on the streamwise large-scale vortex structures. PMID:14524892

Fan, Jianren; Luo, Kun; Zheng, Youqu; Jin, Hanhui; Cen, Kefa

2003-09-01

399

Airborne observations of new particle formation events in the boundary layer using a Zeppelin  

NASA Astrophysics Data System (ADS)

Atmospheric new particle formation (NPF) is a frequent and ubiquitous process in the atmosphere and a major source of newly formed aerosol particles [1]. However, it is still unclear how the aerosol particle distribution evolves in space and time during an NPF. We investigated where in the planetary boundary layer does NPF begin and how does the aerosol number size distribution develop in space and time during it. We measured in Hyytiälä, southern Finland using ground based and airborne measurements. The measurements were part of the PEGASOS project. NPF was studied on six scientific flights during spring 2013 using a Zeppelin NT class airship. Ground based measurements were simultaneously conducted at SMEAR II station located in Hyytiälä. The flight profiles over Hyytiälä were flown between sunrise and noon during the growth of the boundary layer. The profiles over Hyytiälä covered vertically a distance of 100-1000 meters reaching the mixed layer, stable (nocturnal) boundary layer and the residual layer. Horizontally the profiles covered approximately a circular area of four kilometers in diameter. The measurements include particle number size distribution by Neutral cluster and Air Ion Spectrometer (NAIS), Differential Mobility Particle Sizer (DMPS) and Particle Size Magnifier (PSM) [2], meteorological parameters and position (latitude, longitude and altitude) of the Zeppelin. Beginning of NPF was determined from an increase in 1.7-3 nm ion concentration. Height of the mixed layer was estimated from relative humidity measured on-board the Zeppelin. Particle growth rate during NPF was calculated. Spatial inhomogeneities in particle number size distribution during NPF were located and the birthplace of the particles was estimated using the growth rate and trajectories. We observed a regional NPF event that began simultaneously and evolved uniformly inside the mixed layer. In the horizontal direction we observed a long and narrow high concentration plume of growing particles that moved over the measurement site. The particles of the regional event as well as the particles of the plume were uniformly distributed in the vertical direction and showed a similar growth rate of approximately 2 nm/h. The plume caused sharp discontinuities in the number size distribution of the growing particle mode. These kinds of discontinuities are seen quite often on SMEAR II data during NPF events and it is likely that they are caused by inhomogeneous NPF in the horizontal direction (possibly narrow long plumes). This work is supported by European Commission under the Framework Programme 7 (FP7-ENV-2010-265148) and by the Academy of Finland Centre of Excellence program (project no. 1118615). The Zeppelin is accompanied by an international team of scientists and technicians. They are all warmly acknowledged. References [1] Kulmala, M., et al., (2013), Direct Observations of Atmospheric Aerosol Nucleation, Science, 339, 943-946 [2] Kulmala, M., et al., (2012), Measurement of the nucleation of atmospheric aerosol particles, Nature Protocols, 7, 1651-1667

Lampilahti, Janne; Manninen, Hanna E.; Nieminen, Tuomo; Mirme, Sander; Pullinen, Iida; Yli-Juuti, Taina; Schobesberger, Siegfried; Kangasluoma, Juha; Kontkanen, Jenni; Lehtipalo, Katrianne; Ehn, Mikael; Mentel, Thomas F.; Petäjä, Tuukka; Kulmala, Markku

2014-05-01

400

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 a