Interspecific scaling patterns of talar articular surfaces within primates and their closest living relatives

PubMed Central

Yapuncich, Gabriel S; Boyer, Doug M

2014-01-01

The articular facets of interosseous joints must transmit forces while maintaining relatively low stresses. To prevent overloading, joints that transmit higher forces should therefore have larger facet areas. The relative contributions of body mass and muscle-induced forces to joint stress are unclear, but generate opposing hypotheses. If mass-induced forces dominate, facet area should scale with positive allometry to body mass. Alternatively, muscle-induced forces should cause facets to scale isometrically with body mass. Within primates, both scaling patterns have been reported for articular surfaces of the femoral and humeral heads, but more distal elements are less well studied. Additionally, examination of complex articular surfaces has largely been limited to linear measurements, so that ‘true area' remains poorly assessed. To re-assess these scaling relationships, we examine the relationship between body size and articular surface areas of the talus. Area measurements were taken from microCT scan-generated surfaces of all talar facets from a comprehensive sample of extant euarchontan taxa (primates, treeshrews, and colugos). Log-transformed data were regressed on literature-derived log-body mass using reduced major axis and phylogenetic least squares regressions. We examine the scaling patterns of muscle mass and physiological cross-sectional area (PCSA) to body mass, as these relationships may complicate each model. Finally, we examine the scaling pattern of hindlimb muscle PCSA to talar articular surface area, a direct test of the effect of mass-induced forces on joint surfaces. Among most groups, there is an overall trend toward positive allometry for articular surfaces. The ectal (= posterior calcaneal) facet scales with positive allometry among all groups except ‘sundatherians', strepsirrhines, galagids, and lorisids. The medial tibial facet scales isometrically among all groups except lemuroids. Scaling coefficients are not correlated with sample size, clade inclusivity or behavioral diversity of the sample. Muscle mass scales with slight positive allometry to body mass, and PCSA scales at isometry to body mass. PCSA generally scales with negative allometry to articular surface area, which indicates joint surfaces increase faster than muscles' ability to generate force. We suggest a synthetic model to explain the complex patterns observed for talar articular surface area scaling: whether ‘muscles or mass' drive articular facet scaling is probably dependent on the body size range of the sample and the biological role of the facet. The relationship between ‘muscle vs. mass' dominance is likely bone-and facet-specific, meaning that some facets should respond primarily to stresses induced by larger body mass, whereas others primarily reflect muscle forces. PMID:24219027

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

Miao, Yinbin; Mo, Kun; Yao, Tiankai

Here coordinated experimental efforts to quantitatively correlate crystallographic orientation and surface faceting features in UO2 are reported upon. A sintered polycrystalline UO2 sample was thermally etched to induce the formation of surface faceting features. Synchrotron Laue microdiffraction was used to obtain a precise crystallographic orientation map for the UO2 surface grains. Scanning electron microscopy (SEM) was utilized to collect the detailed information on the surface morphology of the sample. The surface faceting features were found to be highly dependent on the crystallographic orientation. In most cases, Triple-plane structures containing one {100} plane and two {111} planes were found to dominatemore » the surface of UO2. The orientation-faceting relationship established in this study revealed a practical and efficient method of determining crystallographic orientation based on the surface features captured by SEM images.« less

Controlling Surface Termination and Facet Orientation in Cu2O Nanoparticles for High Photocatalytic Activity: A Combined Experimental and Density Functional Theory Study.

PubMed

Su, Yang; Li, Hongfei; Ma, Hanbin; Robertson, John; Nathan, Arokia

2017-03-08

Cu 2 O nanoparticles with controllable facets are of great significance for photocatalysis. In this work, the surface termination and facet orientation of Cu 2 O nanoparticles are accurately tuned by adjusting the amount of hydroxylamine hydrochloride and surfactant. It is found that Cu 2 O nanoparticles with Cu-terminated (110) or (111) surfaces show high photocatalytic activity, while other exposed facets show poor reactivity. Density functional theory simulations confirm that sodium dodecyl sulfate surfactant can lower the surface free energy of Cu-terminated surfaces, increase the density of exposed Cu atoms at the surfaces and thus benefit the photocatalytic activity. It also shows that the poor reactivity of the Cu-terminated Cu 2 O (100) surface is due to the high energy barrier of holes at the surface region.

Domains and facets: hierarchical personality assessment using the revised NEO personality inventory.

PubMed

Costa, P T; McCrae, R R

1995-02-01

Personality traits are organized hierarchically, with narrow, specific traits combining to define broad, global factors. The Revised NEO Personality Inventory (NEO-PI-R; Costa & McCrae, 1992c) assesses personality at both levels, with six specific facet scales in each of five broad domains. This article describes conceptual issues in specifying facets of a domain and reports evidence on the validity of NEO-PI-R facet scales. Facet analysis-the interpretation of a scale in terms of the specific facets with which it correlates-is illustrated using alternative measures of the five-factor model and occupational scales. Finally, the hierarchical interpretation of personality profiles is discussed. Interpretation on the domain level yields a rapid understanding of the individual interpretation of specific facet scales gives a more detailed assessment.

Alkali-templated surface nanopatterning of chalcogenide thin films: a novel approach toward solar cells with enhanced efficiency.

PubMed

Reinhard, Patrick; Bissig, Benjamin; Pianezzi, Fabian; Hagendorfer, Harald; Sozzi, Giovanna; Menozzi, Roberto; Gretener, Christina; Nishiwaki, Shiro; Buecheler, Stephan; Tiwari, Ayodhya N

2015-05-13

Concepts of localized contacts and junctions through surface passivation layers are already advantageously applied in Si wafer-based photovoltaic technologies. For Cu(In,Ga)Se2 thin film solar cells, such concepts are generally not applied, especially at the heterojunction, because of the lack of a simple method yielding features with the required size and distribution. Here, we show a novel, innovative surface nanopatterning approach to form homogeneously distributed nanostructures (<30 nm) on the faceted, rough surface of polycrystalline chalcogenide thin films. The method, based on selective dissolution of self-assembled and well-defined alkali condensates in water, opens up new research opportunities toward development of thin film solar cells with enhanced efficiency.

A framework for modeling connections between hydraulics, water surface roughness, and surface reflectance in open channel flows

USGS Publications Warehouse

Legleiter, Carl; Mobley, Curtis D.; Overstreet, Brandon

2017-01-01

This paper introduces a framework for examining connections between the flow field, the texture of the air-water interface, and the reflectance of the water surface and thus evaluating the potential to infer hydraulic information from remotely sensed observations of surface reflectance. We used a spatial correlation model describing water surface topography to illustrate the application of our framework. Nondimensional relations between model parameters and flow intensity were established based on a prior flume study. Expressing the model in the spatial frequency domain allowed us to use an efficient Fourier transform-based algorithm for simulating water surfaces. Realizations for both flume and field settings had water surface slope distributions positively correlated with velocity and water surface roughness. However, most surface facets were gently sloped and thus unlikely to yield strong specular reflections; the model exaggerated the extent of water surface features, leading to underestimation of facet slopes. A ray tracing algorithm indicated that reflectance was greatest when solar and view zenith angles were equal and the sensor scanned toward the Sun to capture specular reflections of the solar beam. Reflected energy was concentrated in a small portion of the sky, but rougher water surfaces reflected rays into a broader range of directions. Our framework facilitates flight planning to avoid surface-reflected radiance while mapping other river attributes, or to maximize this component to exploit relationships between hydraulics and surface reflectance. This initial analysis also highlighted the need for improved models of water surface topography in natural rivers.

Theoretical and experimental studies of hydrogen adsorption and desorption on Ir surfaces

DOE PAGES

Kaghazchi, Payam; Jacob, Timo; Chen, Wenhua; ...

2013-06-03

Here, we report adsorption and desorption of hydrogen on planar Ir(210) and faceted Ir(210), consisting of nanoscale {311} and (110) facets, by means of temperature programmed desorption (TPD) and density functional theory (DFT) in combination with the ab initio atomistic thermodynamics approach. TPD spectra show that only one H 2 peak is seen from planar Ir(210) at all coverages whereas a single H 2 peak is observed at around 440 K (F1) at fractional monolayer (ML) coverage and an additional H 2 peak appears at around 360 K (F2) at 1 ML coverage on faceted Ir(210), implying structure sensitivity inmore » recombination and desorption of hydrogen on faceted Ir(210) versus planar Ir(210), but no evidence is found for size effects in recombination and desorption of hydrogen on faceted Ir(210) for average facet sizes of 5-14 nm. Calculations indicate that H prefers to bind at the two-fold short-bridge sites of the Ir surfaces. In addition, we studied the stability of the Ir surfaces in the presence of hydrogen at different H coverages through surface free energy plots as a function of the chemical potential, which is also converted to a temperature scale. Moreover, the calculations revealed the origin of the two TPD peaks of H 2 from faceted Ir(210): F1 from desorption of H 2 on {311} facets while F2 from desorption of H 2 on (110) facets.« less

Ceramic surfaces, interfaces and solid-state reactions

NASA Astrophysics Data System (ADS)

Heffelfinger, Jason Roy

Faceting, the decomposition of a surface into two or more surfaces of different orientation, is studied as a function of annealing time for ceramic surfaces. Single-crystals of Alsb2Osb3\\ (alpha-Alsb2Osb3 or corundum structure) are carefully prepared and characterized by atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The mechanisms by which the originally smooth vicinal surface transforms into either a hill-and-valley or a terrace-and-step structure have been characterized. The progression of faceting is found to have a series of stages: surface smoothing, nucleation and growth of individual facets, formation of facet domains, coalescence of individual and facet domains and facet coarsening. These stages provide a model for the mechanisms of how other ceramic surfaces may facet into hill-and-valley and terrace-and-step surface microstructures. The well characterized Alsb2Osb3 surfaces provide excellent substrates by which to study the effect of surface structure on thin-film growth. Pulsed-laser deposition was used to grow thin films of yttria stabilized zirconia (YSZ) and Ysb2Osb3 onto annealed Alsb2Osb3 substrates. The substrate surface structure, such as surface steps and terraces, was found to have several effects on thin-film growth. Thin-films grown onto single-crystal substrates serve as a model geometry for studying thin-film solid-state reactions. Here, the reaction sequence and orientation relationship between thin films of Ysb2Osb3 and an Alsb2Osb3 substrate were characterized for different reaction temperatures. In a system were multiple reaction phases can form, the yttria aluminum monoclinic phase (YAM) was found to form prior to formation of other phases in this system. In a second system, a titanium alloy was reacted with single crystal Alsb2Osb3 in order to study phase formation in an intermetallic system. Both Tisb3Al and TiAl were found to form as reaction products and their orientation relationships with the Alsb2Osb3 are discussed.

Photometric model of diffuse surfaces described as a distribution of interfaced Lambertian facets.

PubMed

Simonot, Lionel

2009-10-20

The Lambertian model for diffuse reflection is widely used for the sake of its simplicity. Nevertheless, this model is known to be inaccurate in describing a lot of real-world objects, including those that present a matte surface. To overcome this difficulty, we propose a photometric model where the surfaces are described as a distribution of facets where each facet consists of a flat interface on a Lambertian background. Compared to the Lambertian model, it includes two additional physical parameters: an interface roughness parameter and the ratio between the refractive indices of the background binder and of the upper medium. The Torrance-Sparrow model--distribution of strictly specular facets--and the Oren-Nayar model--distribution of strictly Lambertian facets--appear as special cases.

Machine-Learning Methods Enable Exhaustive Searches for Active Bimetallic Facets and Reveal Active Site Motifs for CO 2 Reduction

DOE PAGES

Ulissi, Zachary W.; Tang, Michael T.; Xiao, Jianping; ...

2017-07-27

Bimetallic catalysts are promising for the most difficult thermal and electrochemical reactions, but modeling the many diverse active sites on polycrystalline samples is an open challenge. Here, we present a general framework for addressing this complexity in a systematic and predictive fashion. Active sites for every stable low-index facet of a bimetallic crystal are enumerated and cataloged, yielding hundreds of possible active sites. The activity of these sites is explored in parallel using a neural-network-based surrogate model to share information between the many density functional theory (DFT) relaxations, resulting in activity estimates with an order of magnitude fewer explicit DFTmore » calculations. Sites with interesting activity were found and provide targets for follow-up calculations. This process was applied to the electrochemical reduction of CO 2 on nickel gallium bimetallics and indicated that most facets had similar activity to Ni surfaces, but a few exposed Ni sites with a very favorable on-top CO configuration. This motif emerged naturally from the predictive modeling and represents a class of intermetallic CO 2 reduction catalysts. These sites rationalize recent experimental reports of nickel gallium activity and why previous materials screens missed this exciting material. Most importantly these methods suggest that bimetallic catalysts will be discovered by studying facet reactivity and diversity of active sites more systematically.« less

Machine-Learning Methods Enable Exhaustive Searches for Active Bimetallic Facets and Reveal Active Site Motifs for CO 2 Reduction

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

Ulissi, Zachary W.; Tang, Michael T.; Xiao, Jianping

Bimetallic catalysts are promising for the most difficult thermal and electrochemical reactions, but modeling the many diverse active sites on polycrystalline samples is an open challenge. Here, we present a general framework for addressing this complexity in a systematic and predictive fashion. Active sites for every stable low-index facet of a bimetallic crystal are enumerated and cataloged, yielding hundreds of possible active sites. The activity of these sites is explored in parallel using a neural-network-based surrogate model to share information between the many density functional theory (DFT) relaxations, resulting in activity estimates with an order of magnitude fewer explicit DFTmore » calculations. Sites with interesting activity were found and provide targets for follow-up calculations. This process was applied to the electrochemical reduction of CO 2 on nickel gallium bimetallics and indicated that most facets had similar activity to Ni surfaces, but a few exposed Ni sites with a very favorable on-top CO configuration. This motif emerged naturally from the predictive modeling and represents a class of intermetallic CO 2 reduction catalysts. These sites rationalize recent experimental reports of nickel gallium activity and why previous materials screens missed this exciting material. Most importantly these methods suggest that bimetallic catalysts will be discovered by studying facet reactivity and diversity of active sites more systematically.« less

Nonlinear Wavelength Selection in Surface Faceting under Electromigration

NASA Astrophysics Data System (ADS)

Barakat, Fatima; Martens, Kirsten; Pierre-Louis, Olivier

2012-08-01

We report on the control of the faceting of crystal surfaces by means of surface electromigration. When electromigration reinforces the faceting instability, we find perpetual coarsening with a wavelength increasing as t1/2. For strongly stabilizing electromigration, the surface is stable. For weakly stabilizing electromigration, a cellular pattern is obtained, with a nonlinearly selected wavelength. The selection mechanism is not caused by an instability of steady states, as suggested by previous works in the literature. Instead, the dynamics is found to exhibit coarsening before reaching a continuous family of stable nonequilibrium steady states.

Surface Area of Patellar Facets: Inferential Statistics in the Iraqi Population

PubMed Central

Al-Zamili, Zaid; Omar, Rawan

2017-01-01

Background. The patella is the largest sesamoid bone in the body; its three-dimensional complexity necessitates biomechanical perfection. Numerous pathologies occur at the patellofemoral unit which may end in degenerative changes. This study aims to test the presence of statistical correlation between the surface areas of patellar facets and other patellar morphometric parameters. Materials and Methods. Forty dry human patellae were studied. The morphometry of each patella was measured using a digital Vernier Caliper, electronic balance, and image analyses software known as ImageJ. The patellar facetal surface area was correlated with patellar weight, height, width, and thickness. Results. Inferential statistics proved the existence of linear correlation of total facetal surface area and patellar weight, height, width, and thickness. The correlation was strongest for surface area versus patellar weight. The lateral facetal area was found persistently larger than the medial facetal area, the p value was found to be <0.001 (one-tailed t-test) for right patellae, and another significant p value of < 0.001 (one-tailed t-test) was found for left patellae. Conclusion. These data are vital for the restoration of the normal biomechanics of the patellofemoral unit; these are to be consulted during knee surgeries and implant designs and can be of an indispensable anthropometric, interethnic, and biometric value. PMID:28348891

Effects of Stress Ratio and Microstructure on Fatigue Failure Behavior of Polycrystalline Nickel Superalloy

NASA Astrophysics Data System (ADS)

Zhang, H.; Guan, Z. W.; Wang, Q. Y.; Liu, Y. J.; Li, J. K.

2018-05-01

The effects of microstructure and stress ratio on high cycle fatigue of nickel superalloy Nimonic 80A were investigated. The stress ratios of 0.1, 0.5 and 0.8 were chosen to perform fatigue tests in a frequency of 110 Hz. Cleavage failure was observed, and three competing failure crack initiation modes were discovered by a scanning electron microscope, which were classified as surface without facets, surface with facets and subsurface with facets. With increasing the stress ratio from 0.1 to 0.8, the occurrence probability of surface and subsurface with facets also increased and reached the maximum value at R = 0.5, meanwhile the probability of surface initiation without facets decreased. The effect of microstructure on the fatigue fracture behavior at different stress ratios was also observed and discussed. Based on the Goodman diagram, it was concluded that the fatigue strength of 50% probability of failure at R = 0.1, 0.5 and 0.8 is lower than the modified Goodman line.

Facet-controlled phase separation in supersaturated Au-Ni nanoparticles upon shape equilibration

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

Herz, A., E-mail: andreas.herz@tu-ilmenau.de, E-mail: dong.wang@tu-ilmenau.de; Rossberg, D.; Hentschel, M.

2015-08-17

Solid-state dewetting is used to fabricate supersaturated, submicron-sized Au-Ni solid solution particles out of thin Au/Ni bilayers by means of a rapid thermal annealing technique. Phase separation in such particles is studied with respect to their equilibrium crystal (or Wulff) shape by subsequent annealing at elevated temperature. It is found that (100) faceting planes of the equilibrated particles are enriched with Ni and (111) faces with Au. Both phases are considered by quantum-mechanical calculations in combination with an error-reduction scheme that was developed to compensate for a missing exchange-correlation potential that would reliably describe both Au and Ni. The observedmore » phase configuration is then related to the minimization of strongly anisotropic elastic energies of Au- and Ni-rich phases and results in a rather unique nanoparticle composite state that is characterized by nearly uniform value of elastic response to epitaxial strains all over the faceted surface. The same conclusion is yielded also by evaluating bi-axial elastic moduli when employing interpolated experimental elastic constants. This work demonstrates a useful route for studying features of physical metallurgy at the mesoscale.« less

The lumbar facet arthrosis syndrome. Clinical presentation and articular surface changes.

PubMed

Eisenstein, S M; Parry, C R

1987-01-01

We describe a lumbar facet syndrome in which disabling symptoms are associated with normal or near-normal plain radiographs. Local spinal fusion relieved symptoms in 12 patients; the excised facet joint surfaces showed some of the histological changes seen in chondromalacia patellae and in osteoarthritis of other large joints. The most frequent change was focal full-thickness cartilage necrosis or loss of cartilage with exposure of subchondral bone, but osteophyte formation was remarkably absent in all specimens. We suggest that there are both clinical and histological similarities between the facet arthrosis syndrome and chondromalacia patellae. Facet arthrosis may be a relatively important cause of intractable back pain in young and middle-aged adults.

Flux synthesis of regular Bi4TaO8Cl square nanoplates exhibiting dominant exposure surfaces of {001} crystal facets for photocatalytic reduction of CO2 to methane.

PubMed

Li, Liang; Han, Qiutong; Tang, Lanqin; Zhang, Yuan; Li, Ping; Zhou, Yong; Zou, Zhigang

2018-01-25

Herein, orthorhombic regular Bi 4 TaO 8 Cl square nanoplates with an edge length of about 500 nm and a thickness of about 100 nm were successfully synthesized using a facile molten salt route. The as-prepared square nanoplates have been proven to be of {001} crystal facets as two dominantly exposed surfaces. The density functional theory calculation and photo-deposition of noble metal experiment demonstrate the electron and hole separation on different crystal facets and reveal that {001} crystal facets are in favor of the reduction reaction. Since the square nanoplate structure exhibits dominant exposure surfaces of the {001} facets, the molten salt route-based samples basically possess an obviously higher photocatalytic activity than those prepared by the solid state reaction (SSR) method. This study may provide inspiration for fabricating efficient photocatalysts.

3D morphology of Au and Au@Ag nanobipyramids

NASA Astrophysics Data System (ADS)

Burgin, Julien; Florea, Ileana; Majimel, Jérôme; Dobri, Adam; Ersen, Ovidiu; Tréguer-Delapierre, Mona

2012-02-01

The morphologies of Au and Au@Ag nanobipyramids were investigated using electron tomography. The 3D reconstruction reveals that the Au bipyramids have an irregular six-fold twinning structure with highly stepped dominant {151} facets. These short steps/edges stabilized via surface adsorbed CTAB favor the growth of silver on the lateral facets leading to strong blue shifts in longitudinal plasmon surface resonance.The morphologies of Au and Au@Ag nanobipyramids were investigated using electron tomography. The 3D reconstruction reveals that the Au bipyramids have an irregular six-fold twinning structure with highly stepped dominant {151} facets. These short steps/edges stabilized via surface adsorbed CTAB favor the growth of silver on the lateral facets leading to strong blue shifts in longitudinal plasmon surface resonance. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr11454b

Restructuring of an Ir(210) electrode surface by potential cycling

PubMed Central

Soliman, Khaled A; Kolb, Dieter M; Jacob, Timo

2014-01-01

Summary This study addresses the electrochemical surface faceting and restructuring of Ir(210) single crystal electrodes. Cyclic voltammetry measurements and in situ scanning tunnelling microscopy are used to probe structural changes and variations in the electrochemical behaviour after potential cycling of Ir(210) in 0.1 M H2SO4. Faceted structures are obtained electrochemically as a function of time by cycling at a scanrate of 1 V·s−1 between −0.28 and 0.70 V vs SCE, i.e., between the onset of hydrogen evolution and the surface oxidation regime. The electrochemical behaviour in sulfuric acid solution is compared with that of thermally faceted Ir(210), which shows a sharp characteristic voltammetric peak for (311) facets. Structures similar to thermally-induced faceted Ir(210) are obtained electrochemically, which typically correspond to polyoriented facets at nano-pyramids. These structures grow anisotropically in a preferred direction and reach a height of about 5 nm after 4 h of cycling. The structural changes are reflected in variations of the electrocatalytic activity towards carbon monoxide adlayer oxidation. PMID:25247118

Restructuring of an Ir(210) electrode surface by potential cycling.

PubMed

Soliman, Khaled A; Kolb, Dieter M; Kibler, Ludwig A; Jacob, Timo

2014-01-01

This study addresses the electrochemical surface faceting and restructuring of Ir(210) single crystal electrodes. Cyclic voltammetry measurements and in situ scanning tunnelling microscopy are used to probe structural changes and variations in the electrochemical behaviour after potential cycling of Ir(210) in 0.1 M H2SO4. Faceted structures are obtained electrochemically as a function of time by cycling at a scanrate of 1 V·s(-1) between -0.28 and 0.70 V vs SCE, i.e., between the onset of hydrogen evolution and the surface oxidation regime. The electrochemical behaviour in sulfuric acid solution is compared with that of thermally faceted Ir(210), which shows a sharp characteristic voltammetric peak for (311) facets. Structures similar to thermally-induced faceted Ir(210) are obtained electrochemically, which typically correspond to polyoriented facets at nano-pyramids. These structures grow anisotropically in a preferred direction and reach a height of about 5 nm after 4 h of cycling. The structural changes are reflected in variations of the electrocatalytic activity towards carbon monoxide adlayer oxidation.

Insight of DFT and ab initio atomistic thermodynamics on the surface stability and morphology of In2O3

NASA Astrophysics Data System (ADS)

Zhang, Minhua; Wang, Wenyi; Chen, Yifei

2018-03-01

In2O3 catalysts show remarkable activity and selectivity in methanol synthesis from CO2 hydrogenation. In order to get insight into the surface stability of this catalyst, density functional theory and ab initio atomistic thermodynamics method were used to investigate the surface free energies of various facets as a function of oxygen chemical potential, as well as the influences of temperature, pressure and gas compositions. The results show that the (111) facet presents lowest surface free energy under oxygen-rich condition, while the indium-terminated (100) facet is the most stable one under oxygen-lean condition. Moreover, we applied Wulff construction to determine the equilibrium shape of In2O3 with different oxygen chemical potentials. The equilibrium shape under oxygen-lean condition is cubic, which only expose (100) facet, while, the equilibrium shape under oxygen-rich condition is octahedron, which only expose (111) facet. Meanwhile, the results agree well with what is observed experimentally. It is further predicted that Wulff shape of In2O3 exists in a truncated octahedron morphology in which the (100) surface becomes predominant plane under CO2 hydrogenation reaction conditions.

Facet-Dependent Cr(VI) Adsorption of Hematite Nanocrystals.

PubMed

Huang, Xiaopeng; Hou, Xiaojing; Song, Fahui; Zhao, Jincai; Zhang, Lizhi

2016-02-16

In this study, the adsorption process of Cr(VI) on the hematite facets was systematically investigated with synchrotron-based Cr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, density-functional theory calculation, and surface complexation models. Structural model fitting of EXAFS spectroscopy suggested that the interatomic distances of Cr-Fe were, respectively, 3.61 Å for the chromate coordinated hematite nanoplates with exposed {001} facets, 3.60 and 3.30 Å for the chromate coordinated hematite nanorods with exposed {001} and {110} facets, which were characteristic of inner-sphere complexation. In situ ATR-FTIR spectroscopy analysis confirmed the presence of two inner-sphere surface complexes with C3ν and C2ν symmetry, while the C3ν and C2ν species were assigned to monodentate and bidentate inner-sphere surface complexes with average Cr-Fe interatomic distances of 3.60 and 3.30 Å, respectively. On the basis of these experimental and theoretical results, we concluded that HCrO4(-) as dominated Cr(VI) species was adsorbed on {001} and {110} facets in inner-sphere monodentate mononuclear and bidentate binuclear configurations, respectively. Moreover, the Cr(VI) adsorption performance of hematite facets was strongly dependent on the chromate complexes formed on the hematite facets.

Extreme ultraviolet reflector

DOEpatents

Newnam, Brian E.

1990-01-01

A multi-faceted mirror forms a retroreflector for a resonator loop in a free electron laser (FEL) operating in the XUV (.lambda.=10-100 nm). The number of facets is determined by the angle-of-incidence needed to obtain total external reflectance (TER) from the facet surface and the angle through which the FEL beam is to be turned. Angles-of-incidence greater than the angle for TER may be used to increase the area of the beam incident on the surface and reduce energy absorption density. Suitable surface films having TER in the 10-100 nm range may be formed from a variety of materials, including Al, single-crystal Si, Ag, and Rh. One of the facets is formed as an off-axis conic section to collimate the output beam with minimum astigmatism.

Surface-structure sensitivity of CeO 2 nanocrystals in photocatalysis and enhancing the reactivity with nanogold

DOE PAGES

Lei, Wanying; Zhang, Tingting; Gu, Lin; ...

2015-06-19

Structure–function correlations are a central theme in heterogeneous (photo)catalysis. In this research, using aberration-corrected scanning transmission electron microscopy (STEM), the atomic surface structures of well-defined one-dimensional (1D) CeO 2 nanorods (NRs) and 3D nanocubes (NCs) are directly visualized at subangstrom resolution. CeO 2 NCs predominantly expose the {100} facet, with {110} and {111} as minor cutoff facets at the respective edges and corners. Notably, the outermost surface layer of the {100} facet is nearly O-terminated. Neither surface relaxations nor reconstructions on {100} are observed, indicating unusual polarity compensation, which is primarily mediated by near-surface oxygen vacancies. The surface of CeOmore » 2 NRs is highly stepped, with the enclosed {110} facet exposing Ce cations and O anions on terraces. On the basis of STEM profile-view imaging and electronic structure analysis, the photoreactivity of CeO2 nanocrystals toward aqueous methyl orange degradation under UV is revealed to be surface-structure-sensitive, following the order: {110} >> {100}. The underlying surface-structure sensitivity can be attributed to the variation in low-coordinate surface cerium cations between {110} and {100} facets. To further enhance light absorption, Au nanoparticles (NPs) are deposited on CeO 2 NRs to form Au/CeO 2 plasmonic nanocomposites, which dramatically promotes the photoreactivity that is Au particle size- and excitation light wavelength-dependent. The mechanisms responsible for the enhancement of photocatalytic activity are discussed, highlighting the crucial role of photoexcited charge carrier transfer.« less

Equilibrium shape of 4He crystal under zero gravity below 200 mK

PubMed Central

Takahashi, Takuya; Ohuchi, Haruka; Nomura, Ryuji; Okuda, Yuichi

2015-01-01

Equilibrium crystal shape is the lowest energy crystal shape that is hardly realized in ordinary crystals because of their slow relaxation. 4He quantum crystals in a superfluid have been expected as unique exceptions that grow extremely fast at very low temperatures. However, on the ground, gravity considerably deforms the crystals and conceals the equilibrium crystal shape, and thus, gravity-free environment is needed to observe the equilibrium shape of 4He. We report the relaxation processes of macroscopic 4He crystals in a superfluid below 200 mK under zero gravity using a parabolic flight of a jet plane. When gravity was removed from a gravity-flattened 4He crystal, the crystal rapidly transformed into a shape with flat surfaces. Although the relaxation processes were highly dependent on the initial condition, the crystals relaxed to a nearly homothetic shape in the end, indicating that they were truly in an equilibrium shape minimizing the interfacial free energy. Thanks to the equilibrium shape, we were able to determine the Wulff’s origin and the size of the c-facet together with the vicinal surface profile next to the c-facet. The c-facet size was extremely small in the quantum crystals, and the facet-like flat surfaces were found to be the vicinal surfaces. At the same time, the interfacial free energy of the a-facet and s-facet was also obtained. PMID:26601315

Equilibrium shape of (4)He crystal under zero gravity below 200 mK.

PubMed

Takahashi, Takuya; Ohuchi, Haruka; Nomura, Ryuji; Okuda, Yuichi

2015-10-01

Equilibrium crystal shape is the lowest energy crystal shape that is hardly realized in ordinary crystals because of their slow relaxation. (4)He quantum crystals in a superfluid have been expected as unique exceptions that grow extremely fast at very low temperatures. However, on the ground, gravity considerably deforms the crystals and conceals the equilibrium crystal shape, and thus, gravity-free environment is needed to observe the equilibrium shape of (4)He. We report the relaxation processes of macroscopic (4)He crystals in a superfluid below 200 mK under zero gravity using a parabolic flight of a jet plane. When gravity was removed from a gravity-flattened (4)He crystal, the crystal rapidly transformed into a shape with flat surfaces. Although the relaxation processes were highly dependent on the initial condition, the crystals relaxed to a nearly homothetic shape in the end, indicating that they were truly in an equilibrium shape minimizing the interfacial free energy. Thanks to the equilibrium shape, we were able to determine the Wulff's origin and the size of the c-facet together with the vicinal surface profile next to the c-facet. The c-facet size was extremely small in the quantum crystals, and the facet-like flat surfaces were found to be the vicinal surfaces. At the same time, the interfacial free energy of the a-facet and s-facet was also obtained.

Modeling the thermostability of surface functionalisation by oxygen, hydroxyl, and water on nanodiamonds.

PubMed

Lai, Lin; Barnard, Amanda S

2011-06-01

Understanding nanodiamond functionalisation is of great importance for biological and medical applications. Here we examine the stabilities of oxygen, hydroxyl, and water functionalisation of the nanodiamonds using the self-consistent charge density functional tight-binding simulations. We find that the oxygen and hydroxyl termination are thermodynamically favourable and form strong C–O covalent bonds on the nanodiamond surface in an O2 and H2 gas reservoir, which confirms previous experiments. Yet, the thermodynamic stabilities of oxygen and hydroxyl functionalisation decrease dramatically in a water vapour reservoir. In contrast, H2O molecules are found to be physically adsorbed on the nanodiamond surface, and forced chemical adsorption results in decomposition of H2O. Moreover, the functionalisation efficiency is found to be facet dependent. The oxygen functionalisation prefers the {100} facets as opposed to alternative facets in an O2 and H2 gas reservoir. The hydroxyl functionalisation favors the {111} surfaces in an O2 and H2 reservoir and the {100} facets in a water vapour reservoir, respectively. This facet selectivity is found to be largely dependent upon the environmental temperature, chemical reservoir, and morphology of the nanodiamonds.

Interface and facet control during Czochralski growth of (111) InSb crystals for cost reduction and yield improvement of IR focal plane array substrates

NASA Astrophysics Data System (ADS)

Gray, Nathan W.; Perez-Rubio, Victor; Bolke, Joseph G.; Alexander, W. B.

2014-10-01

Focal plane arrays (FPAs) made on InSb wafers are the key cost-driving component in IR imaging systems. The electronic and crystallographic properties of the wafer directly determine the imaging device performance. The "facet effect" describes the non-uniform electronic properties of crystals resulting from anisotropic dopant segregation during bulk growth. When the segregation coefficient of dopant impurities changes notably across the melt/solid interface of a growing crystal the result is non-uniform electronic properties across wafers made from these crystals. The effect is more pronounced in InSb crystals grown on the (111) axis compared with other orientations and crystal systems. FPA devices made on these wafers suffer costly yield hits due to inconsistent device response and performance. Historically, InSb crystal growers have grown approximately 9-19 degree off-axis from the (111) to avoid the facet effect and produced wafers with improved uniformity of electronic properties. It has been shown by researchers in the 1960s that control of the facet effect can produce uniform small diameter crystals. In this paper, we share results employing a process that controls the facet effect when growing large diameter crystals from which 4, 5, and 6" wafers can be manufactured. The process change resulted in an increase in wafers yielded per crystal by several times, all with high crystal quality and uniform electronic properties. Since the crystals are grown on the (111) axis, manufacturing (111) oriented wafers is straightforward with standard semiconductor equipment and processes common to the high-volume silicon wafer industry. These benefits result in significant manufacturing cost savings and increased value to our customers.

Monoclinic Tungsten Oxide with {100} Facet Orientation and Tuned Electronic Band Structure for Enhanced Photocatalytic Oxidations.

PubMed

Zhang, Ning; Chen, Chen; Mei, Zongwei; Liu, Xiaohe; Qu, Xiaolei; Li, Yunxiang; Li, Siqi; Qi, Weihong; Zhang, Yuanjian; Ye, Jinhua; Roy, Vellaisamy A L; Ma, Renzhi

2016-04-27

Exploring surface-exposed highly active crystal facets for photocatalytic oxidations is promising in utilizing monoclinic WO3 semiconductor. However, the previously reported highly active facets for monoclinic WO3 were mainly toward enhancing photocatalytic reductions. Here we report that the WO3 with {100} facet orientation and tuned surface electronic band structure can effectively enhance photocatalytic oxidation properties. The {100} faceted WO3 single crystals are synthesized via a facile hydrothermal method. The UV-visible diffuse reflectance, X-ray photoelectron spectroscopy valence band spectra, and photoelectrochemical measurements suggest that the {100} faceted WO3 has a much higher energy level of valence band maximum compared with the normal WO3 crystals without preferred orientation of the crystal face. The density functional theory calculations reveal that the shift of O 2p and W 5d states in {100} face induce a unique band structure. In comparison with the normal WO3, the {100} faceted WO3 exhibits an O2 evolution rate about 5.1 times in water splitting, and also shows an acetone evolution rate of 4.2 times as well as CO2 evolution rate of 3.8 times in gaseous degradation of 2-propanol. This study demonstrates an efficient crystal face engineering route to tune the surface electronic band structure for enhanced photocatalytic oxidations.

Confining the nucleation and overgrowth of Rh to the {111} facets of Pd nanocrystal seeds: the roles of capping agent and surface diffusion.

PubMed

Xie, Shuifen; Peng, Hsin-Chieh; Lu, Ning; Wang, Jinguo; Kim, Moon J; Xie, Zhaoxiong; Xia, Younan

2013-11-06

This article describes a systematic study of the spatially confined growth of Rh atoms on Pd nanocrystal seeds, with a focus on the blocking effect of a surface capping agent and the surface diffusion of adatoms. We initially used Pd cuboctahedrons as the seeds to illustrate the concept and to demonstrate the capabilities of our approach. Because the Pd{100} facets were selectively capped by a layer of chemisorbed Br(–) or I(–) ions, we were able to confine the nucleation and deposition of Rh atoms solely on the {111} facets of a Pd seed. When the synthesis was conducted at a relatively low temperature, the deposition of Rh atoms followed an island growth mode because of the high Rh–Rh interatomic binding energy. We also facilitated the surface diffusion of deposited Rh atoms by increasing the reaction temperature and decreasing the injection rate for the Rh precursor. Under these conditions, the deposition of Rh on the Pd{111} facets was switched to a layered growth mode. We further successfully extended this approach to a variety of other types of Pd polyhedral seeds that contained Pd{111} and Pd{100} facets in different proportions on the surface. As expected, a series of Pd–Rh bimetallic nanocrystals with distinctive elemental distributions were obtained. We could remove the Pd cores through selective chemical etching to generate Rh hollow nanoframes with different types and degrees of porosity. This study clearly demonstrates the importance of facet capping, surface diffusion, and reaction kinetics in controlling the morphologies of bimetallic nanocrystals during a seed-mediated process. It also provides a new direction for the rational design and synthesis of nanocrystals with spatially controlled distributions of elements for a variety of applications.

High symmetric 18-facet polyhedron nanocrystals of Cu7S4 with a hollow nanocage.

PubMed

Cao, Hongliang; Qian, Xuefeng; Wang, Cheng; Ma, Xiaodong; Yin, Jie; Zhu, Zikang

2005-11-23

On the basis of Kirkendall Effect, high symmetric 18-facet polyhedral nanocrystals of Cu7S4 with a hollow nanocage could be converted from cubic nanocrystals of Cu2O in an aqueous media. The presence of organic additives makes the surface energy of {110} smaller than those of {100} and {111}. The growth of nanocrystals along the normal direction of highest energy surface {100} leads to the formation of a 18-facet polyhedron.

Facet‐Engineered Surface and Interface Design of Photocatalytic Materials

PubMed Central

Wang, Lili; Li, Zhengquan

2016-01-01

The facet‐engineered surface and interface design for photocatalytic materials has been proven as a versatile approach to enhance their photocatalytic performance. This review article encompasses some recent advances in the facet engineering that has been performed to control the surface of mono‐component semiconductor systems and to design the surface and interface structures of multi‐component heterostructures toward photocatalytic applications. The review begins with some key points which should receive attention in the facet engineering on photocatalytic materials. We then discuss the synthetic approaches to achieve the facet control associated with the surface and interface design. In the following section, the facet‐engineered surface design on mono‐component photocatalytic materials is introduced, which forms a basis for the discussion on more complex systems. Subsequently, we elucidate the facet‐engineered surface and interface design of multi‐component photocatalytic materials. Finally, the existing challenges and future prospects are discussed. PMID:28105398

Physical-geometric optics method for large size faceted particles.

PubMed

Sun, Bingqiang; Yang, Ping; Kattawar, George W; Zhang, Xiaodong

2017-10-02

A new physical-geometric optics method is developed to compute the single-scattering properties of faceted particles. It incorporates a general absorption vector to accurately account for inhomogeneous wave effects, and subsequently yields the relevant analytical formulas effective and computationally efficient for absorptive scattering particles. A bundle of rays incident on a certain facet can be traced as a single beam. For a beam incident on multiple facets, a systematic beam-splitting technique based on computer graphics is used to split the original beam into several sub-beams so that each sub-beam is incident only on an individual facet. The new beam-splitting technique significantly reduces the computational burden. The present physical-geometric optics method can be generalized to arbitrary faceted particles with either convex or concave shapes and with a homogeneous or an inhomogeneous (e.g., a particle with a core) composition. The single-scattering properties of irregular convex homogeneous and inhomogeneous hexahedra are simulated and compared to their counterparts from two other methods including a numerically rigorous method.

“Soft that molds the hard:” Geometric morphometry of lateral atlantoaxial joints focusing on the role of cartilage in changing the contour of bony articular surfaces

PubMed Central

Prasad, Prashant Kumar; Salunke, Pravin; Sahni, Daisy; Kalra, Parveen

2017-01-01

Purpose: The existing literature on lateral atlantoaxial joints is predominantly on bony facets and is unable to explain various C1-2 motions observed. Geometric morphometry of facets would help us in understanding the role of cartilages in C1-2 biomechanics/kinematics. Objective: Anthropometric measurements (bone and cartilage) of the atlantoaxial joint and to assess the role of cartilages in joint biomechanics. Materials and Methods: The authors studied 10 cadaveric atlantoaxial lateral joints with the articular cartilage in situ and after removing it, using three-dimensional laser scanner. The data were compared using geometric morphometry with emphasis on surface contours of articulating surfaces. Results: The bony inferior articular facet of atlas is concave in both sagittal and coronal plane. The bony superior articular facet of axis is convex in sagittal plane and is concave (laterally) and convex medially in the coronal plane. The bony articulating surfaces were nonconcordant. The articular cartilages of both C1 and C2 are biconvex in both planes and are thicker than the concavities of bony articulating surfaces. Conclusion: The biconvex structure of cartilage converts the surface morphology of C1-C2 bony facets from concave on concavo-convex to convex on convex. This reduces the contact point making the six degrees of freedom of motion possible and also makes the joint gyroscopic. PMID:29403249

Learning-based 3D surface optimization from medical image reconstruction

NASA Astrophysics Data System (ADS)

Wei, Mingqiang; Wang, Jun; Guo, Xianglin; Wu, Huisi; Xie, Haoran; Wang, Fu Lee; Qin, Jing

2018-04-01

Mesh optimization has been studied from the graphical point of view: It often focuses on 3D surfaces obtained by optical and laser scanners. This is despite the fact that isosurfaced meshes of medical image reconstruction suffer from both staircases and noise: Isotropic filters lead to shape distortion, while anisotropic ones maintain pseudo-features. We present a data-driven method for automatically removing these medical artifacts while not introducing additional ones. We consider mesh optimization as a combination of vertex filtering and facet filtering in two stages: Offline training and runtime optimization. In specific, we first detect staircases based on the scanning direction of CT/MRI scanners, and design a staircase-sensitive Laplacian filter (vertex-based) to remove them; and then design a unilateral filtered facet normal descriptor (uFND) for measuring the geometry features around each facet of a given mesh, and learn the regression functions from a set of medical meshes and their high-resolution reference counterparts for mapping the uFNDs to the facet normals of the reference meshes (facet-based). At runtime, we first perform staircase-sensitive Laplacian filter on an input MC (Marching Cubes) mesh, and then filter the mesh facet normal field using the learned regression functions, and finally deform it to match the new normal field for obtaining a compact approximation of the high-resolution reference model. Tests show that our algorithm achieves higher quality results than previous approaches regarding surface smoothness and surface accuracy.

Photo-assisted Kelvin probe force microscopy investigation of three dimensional GaN structures with various crystal facets, doping types, and wavelengths of illumination

NASA Astrophysics Data System (ADS)

Ali Deeb, Manal; Ledig, Johannes; Wei, Jiandong; Wang, Xue; Wehmann, Hergo-Heinrich; Waag, Andreas

2017-08-01

Three dimensional GaN structures with different crystal facets and doping types have been investigated employing the surface photo-voltage (SPV) method to monitor illumination-induced surface charge behavior using Kelvin probe force microscopy. Various photon energies near and below the GaN bandgap were used to modify the generation of electron-hole pairs and their motion under the influence of the electric field near the GaN surface. Fast and slow processes for Ga-polar c-planes on both Si-doped n-type as well as Mg-doped p-type GaN truncated pyramid micro-structures were found and their origin is discussed. The immediate positive (for n-type) and negative (for p-type) SPV response dominates at band-to-band and near-bandgap excitation, while only the slow process is present at sub-bandgap excitation. The SPV behavior for the semi-polar facets of the p-type GaN truncated pyramids has a similar characteristic to that on its c-plane, which indicates that it has a comparable band bending and no strong influence of the polarity-induced charges is detectable. The SPV behavior of the non-polar m-facets of the Si-doped n-type part of a transferred GaN column is similar to that of a clean c-plane GaN surface during illumination. However, the SPV is smaller in magnitude, which is attributed to intrinsic surface states of m-plane surfaces and their influence on the band bending. The SPV behavior of the non-polar m-facet of the slightly Mg-doped part of this GaN column is found to behave differently. Compared to c- and r-facets of p-type surfaces of GaN-light-emitting diode micro-structures, the m-plane is more chemically stable.

Surface Proton Transfer Promotes Four-Electron Oxygen Reduction on Gold Nanocrystal Surfaces in Alkaline Solution

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

Lu, Fang; Zhang, Yu; Liu, Shizhong

Four-electron oxygen reduction reaction (4e-ORR), as a key pathway in energy conversion, is preferred over the two-electron reduction pathway that falls short in dissociating dioxygen molecules. Gold (Au) surfaces exhibit high sensitivity of the ORR pathway to its atomic structures. The long-standing puzzle remains unsolved why the Au surfaces with {100} sub-facets were exceptionally capable to catalyze the 4e-ORR in alkaline solution, though limited within a narrow potential window. Herein we report the discovery of a dominant 4e-ORR over the whole potential range on {310} surface of Au nanocrystal shaped as truncated ditetragonal prism (TDP). In contrast, ORR pathways onmore » single-crystalline facets of shaped nanoparticles, including {111} on nano-octahedra and {100} on nano-cubes, are similar to their single-crystal counterparts. Combining our experimental results with density functional theory calculations, we elucidate the key role of surface proton transfers from co-adsorbed H 2O molecules in activating the facet- and potential-dependent 4e ORR on Au in alkaline solutions. These results elucidate how surface atomic structures determine the reaction pathways via bond scission and formation among weakly adsorbed water and reaction intermediates. The new insight helps in developing facet-specific nanocatalysts for various reactions.« less

Surface Proton Transfer Promotes Four-Electron Oxygen Reduction on Gold Nanocrystal Surfaces in Alkaline Solution

DOE PAGES

Lu, Fang; Zhang, Yu; Liu, Shizhong; ...

2017-05-11

Four-electron oxygen reduction reaction (4e-ORR), as a key pathway in energy conversion, is preferred over the two-electron reduction pathway that falls short in dissociating dioxygen molecules. Gold (Au) surfaces exhibit high sensitivity of the ORR pathway to its atomic structures. The long-standing puzzle remains unsolved why the Au surfaces with {100} sub-facets were exceptionally capable to catalyze the 4e-ORR in alkaline solution, though limited within a narrow potential window. Herein we report the discovery of a dominant 4e-ORR over the whole potential range on {310} surface of Au nanocrystal shaped as truncated ditetragonal prism (TDP). In contrast, ORR pathways onmore » single-crystalline facets of shaped nanoparticles, including {111} on nano-octahedra and {100} on nano-cubes, are similar to their single-crystal counterparts. Combining our experimental results with density functional theory calculations, we elucidate the key role of surface proton transfers from co-adsorbed H 2O molecules in activating the facet- and potential-dependent 4e ORR on Au in alkaline solutions. These results elucidate how surface atomic structures determine the reaction pathways via bond scission and formation among weakly adsorbed water and reaction intermediates. The new insight helps in developing facet-specific nanocatalysts for various reactions.« less

Electron affinity and surface states of GaN m -plane facets: Implication for electronic self-passivation

NASA Astrophysics Data System (ADS)

Portz, V.; Schnedler, M.; Eisele, H.; Dunin-Borkowski, R. E.; Ebert, Ph.

2018-03-01

The electron affinity and surface states are of utmost importance for designing the potential landscape within (heterojunction) nanowires and hence for tuning conductivity and carrier lifetimes. Therefore, we determined for stoichiometric nonpolar GaN (10 1 ¯0 ) m -plane facets, i.e., the dominating sidewalls of GaN nanowires, the electron affinity to 4.06 ±0.07 eV and the energy of the empty Ga-derived surface state in the band gap to 0.99 ±0.08 eV below the conduction band minimum using scanning tunneling spectroscopy. These values imply that the potential landscape within GaN nanowires is defined by a surface state-induced Fermi-level pinning, creating an upward band bending at the sidewall facets, which provides an electronic passivation.

A model for the geomorphic development of normal-fault facets

NASA Astrophysics Data System (ADS)

Tucker, G. E.; Hobley, D. E. J.; McCoy, S. W.

2014-12-01

Triangular facets are among the most striking landforms associated with normal faulting. The genesis of facets is of great interest both for the information facets contain about tectonic motion, and because the progressive emergence of facets makes them potential recorders of both geomorphic and tectonic history. In this report, we present observations of triangular facets in the western United States and in the Italian Central Apennines. Facets in these regions typically form quasi-planar surfaces that are aligned in series along and above the trace of an active fault. Some facet surfaces consist mainly of exposed bedrock, with a thin and highly discontinuous cover of loose regolith. Other facets are mantled by a several-decimeter-thick regolith cover. Over the course of its morphologic development, a facet slope segment may evolve from a steep (~60 degree) bedrock fault scarp, well above the angle of repose for soil, to a gentler (~20-40 degree) slope that can potentially sustain a coherent regolith cover. This evolutionary trajectory across the angle of repose renders nonlinear diffusion theory inapplicable. To formulate an alternative process-based theory for facet evolution, we use a particle-based approach that acknowledges the possibility for both short- and long-range sediment-grain motions, depending on the topography. The processes of rock weathering, grain entrainment, and grain motion are represented as stochastic state-pair transitions with specified transition rates. The model predicts that facet behavior can range smoothly along the spectrum from a weathering-limited mode to a transport-limited mode, depending on the ratio of fault-slip rate to bare-bedrock regolith production rate. The model also implies that facets formed along a fault with pinned tips should show systematic variation in slope angle that correlates with along-fault position and slip rate. Preliminary observations from central Italy and the eastern Basin and Range are consistent with this prediction.

Facet-Dependent Deposition of Highly Strained Alloyed Shells on Intermetallic Nanoparticles for Enhanced Electrocatalysis

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

Wang, Chenyu; Sang, Xiahan; Gamler, Jocelyn T. L.

Compressive surface strains can enhance the performance of platinum-based core@shell electrocatalysts for the oxygen reduction reaction (ORR). Bimetallic core@shell nanoparticles (NPs) are widely studied nanocatalysts but often have limited lattice mismatch and surface compositions; investigations of core@shell NPs with greater compositional complexity and lattice misfit are in their infancy. Here, a new class of multimetallic NPs composed of intermetallic cores and random alloy shells is reported. Specifically, face-centered cubic (fcc) Pt- Cu random alloy shells were deposited non-epitaxially on PdCu B2 intermetallic seeds, giving rise to faceted core@shell NPs with highly strained surfaces. In fact, high resolution transmission electron microscopymore » (HRTEM) revealed orientation-dependent surface strains, where the compressive strains were minimal on Pt-Cu {111} facets but greater on {200} facets. These core@shell NPs provide higher specific and mass activities for the ORR when compared to conventional Pt-Cu NPs. Moreover, these intermetallic@random alloy NPs displayed high endurance, undergoing 10,000 cycles with only a slight decay in activity and no apparent structural changes.« less

Facet-Dependent Deposition of Highly Strained Alloyed Shells on Intermetallic Nanoparticles for Enhanced Electrocatalysis

DOE PAGES

Wang, Chenyu; Sang, Xiahan; Gamler, Jocelyn T. L.; ...

2017-08-25

Compressive surface strains can enhance the performance of platinum-based core@shell electrocatalysts for the oxygen reduction reaction (ORR). Bimetallic core@shell nanoparticles (NPs) are widely studied nanocatalysts but often have limited lattice mismatch and surface compositions; investigations of core@shell NPs with greater compositional complexity and lattice misfit are in their infancy. Here, a new class of multimetallic NPs composed of intermetallic cores and random alloy shells is reported. Specifically, face-centered cubic (fcc) Pt- Cu random alloy shells were deposited non-epitaxially on PdCu B2 intermetallic seeds, giving rise to faceted core@shell NPs with highly strained surfaces. In fact, high resolution transmission electron microscopymore » (HRTEM) revealed orientation-dependent surface strains, where the compressive strains were minimal on Pt-Cu {111} facets but greater on {200} facets. These core@shell NPs provide higher specific and mass activities for the ORR when compared to conventional Pt-Cu NPs. Moreover, these intermetallic@random alloy NPs displayed high endurance, undergoing 10,000 cycles with only a slight decay in activity and no apparent structural changes.« less

Low optical-loss facet preparation for silica-on-silicon photonics using the ductile dicing regime

NASA Astrophysics Data System (ADS)

Carpenter, Lewis G.; Rogers, Helen L.; Cooper, Peter A.; Holmes, Christopher; Gates, James C.; Smith, Peter G. R.

2013-11-01

The efficient production of high-quality facets for low-loss coupling is a significant production issue in integrated optics, usually requiring time consuming and manually intensive lapping and polishing steps, which add considerably to device fabrication costs. The development of precision dicing saws with diamond impregnated blades has allowed optical grade surfaces to be machined in crystalline materials such as lithium niobate and garnets. In this report we investigate the optimization of dicing machine parameters to obtain optical quality surfaces in a silica-on-silicon planar device demonstrating high optical quality in a commercially important glassy material. We achieve a surface roughness of 4.9 nm (Sa) using the optimized dicing conditions. By machining a groove across a waveguide, using the optimized dicing parameters, a grating based loss measurement technique is used to measure precisely the average free space interface loss per facet caused by scattering as a consequence of surface roughness. The average interface loss per facet was calculated to be: -0.63 dB and -0.76 dB for the TE and TM polarizations, respectively.

Edge facet dynamics during the growth of heavily doped n-type silicon by the Czochralski-method

NASA Astrophysics Data System (ADS)

Stockmeier, L.; Kranert, C.; Raming, G.; Miller, A.; Reimann, C.; Rudolph, P.; Friedrich, J.

2018-06-01

During the growth of [0 0 1]-oriented, heavily n-type doped silicon crystals by the Czochralski (CZ) method dislocation formation occurs frequently which leads to a reduction of the crystal yield. In this publication the evolution of the solid-liquid interface and the formation of the {1 1 1} edge facets are analyzed on a microscopic scale as possible reason for dislocation formation in heavily n-type doped [0 0 1]-oriented CZ crystals. A correlation between the length of the {1 1 1} edge facets and the curvature of the interface is found. They ultimately promote supercooled areas and interrupted growth kinetics, which increase the probability for dislocation formation at the boundary between the {1 1 1} edge facets and the atomically rough interface.

Preparation of atomically flat rutile TiO 2(001) surfaces for oxide film growth

DOE PAGES

Wang, Yang; Lee, Shinbuhm; Vilmercati, P.; ...

2016-01-01

The availability of low-index rutile TiO 2 single crystal substrates with atomically flat surfaces is essential for enabling epitaxialgrowth of rutile transition metal oxide films. The high surface energy of the rutile (001) surface often leads to surface faceting, which precludes the sputter and annealing treatment commonly used for the preparation of clean and atomically flat TiO 2(110) substrate surfaces. In this work, we reveal that stable and atomically flat rutile TiO 2(001) surfaces can be prepared with an atomically ordered reconstructedsurface already during a furnace annealing treatment in air. We tentatively ascribe this result to the decrease in surfacemore » energy associated with the surface reconstruction, which removes the driving force for faceting. Despite the narrow temperature window where this morphology can initially be formed, we demonstrate that it persists in homoepitaxialgrowth of TiO 2(001) thin films. The stabilization of surface reconstructions that prevent faceting of high-surface-energy crystal faces may offer a promising avenue towards the realization of a wider range of high quality epitaxial transition metal oxide heterostructures.« less

A microscale three-dimensional urban energy balance model for studying surface temperatures

NASA Astrophysics Data System (ADS)

Krayenhoff, E. Scott; Voogt, James A.

2007-06-01

A microscale three-dimensional (3-D) urban energy balance model, Temperatures of Urban Facets in 3-D (TUF-3D), is developed to predict urban surface temperatures for a variety of surface geometries and properties, weather conditions, and solar angles. The surface is composed of plane-parallel facets: roofs, walls, and streets, which are further sub-divided into identical square patches, resulting in a 3-D raster-type model geometry. The model code is structured into radiation, conduction and convection sub-models. The radiation sub-model uses the radiosity approach and accounts for multiple reflections and shading of direct solar radiation. Conduction is solved by finite differencing of the heat conduction equation, and convection is modelled by empirically relating patch heat transfer coefficients to the momentum forcing and the building morphology. The radiation and conduction sub-models are tested individually against measurements, and the complete model is tested against full-scale urban surface temperature and energy balance observations. Modelled surface temperatures perform well at both the facet-average and the sub-facet scales given the precision of the observations and the uncertainties in the model inputs. The model has several potential applications, such as the calculation of radiative loads, and the investigation of effective thermal anisotropy (when combined with a sensor-view model).

Thermally stable single-atom platinum-on-ceria catalysts via atom trapping

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

Jones, John; Xiong, Haifeng; DelaRiva, Andrew

2016-07-08

Catalysts based on single atoms of scarce precious metals can lead to more efficient use through enhanced reactivity and selectivity. However, single atoms on catalyst supports can be mobile and aggregate into nanoparticles when heated at elevated temperatures. High temperatures are detrimental to catalyst performance unless these mobile atoms can be trapped. We used ceria powders having similar surface areas but different exposed surface facets. When mixed with a platinum/ aluminum oxide catalyst and aged in air at 800°C, the platinum transferred to the ceria and was trapped. Polyhedral ceria and nanorods were more effective than ceria cubes at anchoringmore » the platinum. Performing synthesis at high temperatures ensures that only the most stable binding sites are occupied, yielding a sinter-resistant, atomically dispersed catalyst.« less

Fabrication of lithographically defined optical coupling facets for silicon-on-insulator waveguides by inductively coupled plasma etching

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

Yap, K.P.; Lamontagne, B.; Delage, A.

2006-05-15

We present a technique to lithographically define and fabricate all required optical facets on a silicon-on-insulator photonic integrated circuit by an inductively coupled plasma etch process. This technique offers 1 {mu}m positioning accuracy of the facets at any location within the chip and eliminates the need of polishing. Facet fabrication consists of two separate steps to ensure sidewall verticality and minimize attack on the end surfaces of the waveguides. Protection of the waveguides by a thermally evaporated aluminum layer before the 40-70 {mu}m deep optical facet etching has been proven essential in assuring the facet smoothness and integrity. Both scanningmore » electron microscopy analysis and optical measurement results show that the quality of the facets prepared by this technique is comparable to the conventional facets prepared by polishing.« less

Laser-induced asymmetric faceting and growth of a nano-protrusion on a tungsten tip

NASA Astrophysics Data System (ADS)

Yanagisawa, Hirofumi; Zadin, Vahur; Kunze, Karsten; Hafner, Christian; Aabloo, Alvo; Kim, Dong Eon; Kling, Matthias F.; Djurabekova, Flyura; Osterwalder, Jürg; Wuensch, Walter

2016-12-01

Irradiation of a sharp tungsten tip by a femtosecond laser and exposed to a strong DC electric field led to reproducible surface modifications. By a combination of field emission microscopy and scanning electron microscopy, we observed asymmetric surface faceting with sub-ten nanometer high steps. The presence of faceted features mainly on the laser-exposed side implies that the surface modification was driven by a laser-induced transient temperature rise on a scale of a couple of picoseconds in the tungsten tip apex. Moreover, we identified the formation of a nano-tip a few nanometers high located at one of the corners of a faceted plateau. The results of simulations emulating the experimental conditions are consistent with the experimental observations. The presented technique would be a new method to fabricate a nano-tip especially for generating coherent electron pulses. The features may also help to explain the origin of enhanced field emission, which leads to vacuum arcs, in high electric field devices such as radio-frequency particle accelerators.

Enhancing the photoresponse and photocatalytic properties of TiO 2 by controllably tuning defects across {101} facets

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

Wan, Piaopiao; Hood, Zachary D.; Oak Ridge National Lab.

Introducing defects into semiconductors with well-controlled exposed facets offers an effective route for the development of photocatalytic materials with greatly improved properties. Here, we report a facile ethylene glycol reduction procedure to make anatase titanium dioxide (TiO 2) with different concentrations of exposed {001} and {101} facets, leading to different surficial defects. TiO 2 with increased concentrations of {101} facets shows a 5-fold improvement in photocurrent generation as well as improved photocatalytic activity towards water splitting under visible light irradiation. Thus, the improved activity is ascribed to the oxygen vacancies as well as the variable surface chemical states, which collectivelymore » induce a slower recombination rate of photo-induced electron-hole pairs. This work also highlights a feasible strategy to obtain the defective TiO 2 and explore the synergistic effect of surface defects and different concentrations of exposed {001} and {101} facets for photocurrent and photocatalytic properties under visible light irradiation.« less

The Role of Surface Passivation in Controlling Ge Nanowire Faceting.

PubMed

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

2015-12-09

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

Isolation and Characterization of Human Mesenchymal Stem Cells From Facet Joints and Interspinous Ligaments.

PubMed

Kristjánsson, Baldur; Limthongkul, Worawat; Yingsakmongkol, Wicharn; Thantiworasit, Pattarawat; Jirathanathornnukul, Napaphat; Honsawek, Sittisak

2016-01-01

A descriptive in vitro study on isolation and differentiation of human mesenchymal stem cells (MSCs) derived from the facet joints and interspinous ligaments. To isolate cells from the facet joints and interspinous ligaments and investigate their surface marker profile and differentiation potentials. Lumbar spinal canal stenosis and ossification of the posterior longitudinal ligament are progressive conditions characterized by the hypertrophy and ossification of ligaments and joints within the spinal canal. MSCs are believed to play a role in the advancement of these diseases and the existence of MSCs has been demonstrated within the ligamentum flavum and posterior longitudinal ligament. The aim of this study was to investigate whether these cells could also be found within facet joints and interspinous ligaments. Samples were harvested from 10 patients undergoing spinal surgery. The MSCs from facet joints and interspinous ligaments were isolated using direct tissue explant technique. Cell surface antigen profilings were performed via flow cytometry. Their lineage differentiation potentials were analyzed. The facet joints and interspinous ligaments-derived MSCs have the tri-lineage potential to be differentiated into osteogenic, adipogenic, and chondrogenic cells under appropriate inductions. Flow cytometry analysis revealed both cell lines expressed MSCs markers. Both facet joints and interspinous ligaments-derived MSCs expressed marker genes for osteoblasts, adipocytes, and chondrocytes. The facet joints and interspinous ligaments may provide alternative sources of MSCs for tissue engineering applications. The facet joints and interspinous ligaments-derived MSCs are part of the microenvironment of the human ligaments of the spinal column and might play a crucial role in the development and progression of degenerative spine conditions.

Probing the Surface Charge on the Basal Planes of Kaolinite Particles with High-Resolution Atomic Force Microscopy

PubMed Central

2017-01-01

High-resolution atomic force microscopy is used to map the surface charge on the basal planes of kaolinite nanoparticles in an ambient solution of variable pH and NaCl or CaCl2 concentration. Using DLVO theory with charge regulation, we determine from the measured force–distance curves the surface charge distribution on both the silica-like and the gibbsite-like basal plane of the kaolinite particles. We observe that both basal planes do carry charge that varies with pH and salt concentration. The silica facet was found to be negatively charged at pH 4 and above, whereas the gibbsite facet is positively charged at pH below 7 and negatively charged at pH above 7. Investigations in CaCl2 at pH 6 show that the surface charge on the gibbsite facet increases for concentration up to 10 mM CaCl2 and starts to decrease upon further increasing the salt concentration to 50 mM. The increase of surface charge at low concentration is explained by Ca2+ ion adsorption, while Cl– adsorption at higher CaCl2 concentrations partially neutralizes the surface charge. Atomic resolution imaging and density functional theory calculations corroborate these observations. They show that hydrated Ca2+ ions can spontaneously adsorb on the gibbsite facet of the kaolinite particle and form ordered surface structures, while at higher concentrations Cl– ions will co-adsorb, thereby changing the observed ordered surface structure. PMID:29140711

Probing the Surface Charge on the Basal Planes of Kaolinite Particles with High-Resolution Atomic Force Microscopy.

PubMed

Kumar, N; Andersson, M P; van den Ende, D; Mugele, F; Siretanu, I

2017-12-19

High-resolution atomic force microscopy is used to map the surface charge on the basal planes of kaolinite nanoparticles in an ambient solution of variable pH and NaCl or CaCl 2 concentration. Using DLVO theory with charge regulation, we determine from the measured force-distance curves the surface charge distribution on both the silica-like and the gibbsite-like basal plane of the kaolinite particles. We observe that both basal planes do carry charge that varies with pH and salt concentration. The silica facet was found to be negatively charged at pH 4 and above, whereas the gibbsite facet is positively charged at pH below 7 and negatively charged at pH above 7. Investigations in CaCl 2 at pH 6 show that the surface charge on the gibbsite facet increases for concentration up to 10 mM CaCl 2 and starts to decrease upon further increasing the salt concentration to 50 mM. The increase of surface charge at low concentration is explained by Ca 2+ ion adsorption, while Cl - adsorption at higher CaCl 2 concentrations partially neutralizes the surface charge. Atomic resolution imaging and density functional theory calculations corroborate these observations. They show that hydrated Ca 2+ ions can spontaneously adsorb on the gibbsite facet of the kaolinite particle and form ordered surface structures, while at higher concentrations Cl - ions will co-adsorb, thereby changing the observed ordered surface structure.

On the composition dependence of faceting behaviour of primary phases during solidification

NASA Astrophysics Data System (ADS)

Saroch, Mamta; Dubey, K. S.; Ramachandrarao, P.

1993-02-01

The entropy of solution of the primary aluminium-rich phase in the aluminium-tin melts has been evaluated as a function of temperature using available thermodynamic and phase equilibria data with a view to understand the faceting behaviour of this phase. It was noticed that the range of compositions in which alloys of aluminium and tin yield a faceted primary phase is correlated with the domain of compositions over which the entropy of solution shows a strong temperature dependence. It is demonstrated that both a high value of the entropy of solution and a strong temperature dependence of it are essential for providing faceting. A strong temperature dependence of the entropy of solution is in turn a consequence of negligible liquidus slope and existence of retrograde solubility. The AgBi and AgPb systems have similar features.

Facet Dependent Disorder in the Pristine High Voltage Lithium-Manganese-Rich Cathode Material

DOE PAGES

Dixit, Hemant M.; Zhou, Wu; Idrobo Tapia, Juan Carlos; ...

2014-11-21

Defects and surface reconstructions are thought to be crucial for the long term stability of high-voltage lithium-manganese-rich cathodes. Unfortunately, many of these defects arise only after electrochemical cycling which occur under harsh conditions making it difficult to fully comprehend the role they play in degrading material performance. Recently, it has been observed that defects are present even in the pristine material. This study, therefore, focuses on examining the nature of the disorder observed in pristine Limore » $$_{1.2}$$Ni$$_{0.175}$$Mn$$_{0.525}$$Co$$_{0.1}$$O$$_2$$ (LNMCO) particles. Using atomic resolution Z-contrast imaging and electron energy-loss spectroscopy measurements we show that there are indeed a significant amount of anti-site defects present in this material; with transition metals substituting on Li metal sites. Furthermore, we find a strong tendency of segregation of these types of defects towards open facets (surfaces perpendicular to the layered arrangement of atoms), rather than closed facets (surfaces parallel to the layered arrangement of atoms). First principles calculations identify anti-site defect pairs of Ni swapping with Li ions as the predominant defect in the material. Furthermore, energetically favorable swapping of Ni on the Mn sites were observed to lead to Mn depletion at open facets. Relatively, low Ni migration barriers also support the notion that Ni are the predominant cause of disorder. These insights suggests that certain facets of the LNMCO particles may be more useful for inhibiting surface reconstruction and improving the stability of these materials through careful consideration of the exposed surface.« less

A study of fractography in the low-temperature brittle fracture of an 18Cr-18Mn-0.7N austenitic steel

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

Liu, S.C.; Hashida, T.; Takahashi, H.

1998-03-01

The fracture mode and crack propagation behavior of brittle fracture at 77 and 4 K in an 18Cr-18Mn-0.7N austenitic stainless were investigated using optical and scanning electron microscopy. The fracture path was examined by observing the side surface in a partially ruptured specimen. The relationship of the fracture facets to the microstructures were established by observing the fracture surface and the adjacent side surface simultaneously. Three kinds of fracture facets were identified at either temperature. The first is a smooth curved intergranular fracture facet with characteristic parallel lines on it. The second is a fairly planar facet formed by partingmore » along an annealing twin boundary, a real {l_brace}111{r_brace} plane. There are three sets of parallel lines on the facet and the lines in different sets intersect at 60 deg. The third is a lamellar transgranular fracture facet with sets of parallel steps on it. Fracture propagated by the formation of microcracks on a grain boundary, annealing twin boundary, and coalescence of these cracks. The observation suggests that the ease of crack initiation and propagation along the grain boundary and the annealing twin boundary may be the main reason for the low-temperature brittleness of this steel. A mechanism for grain boundary cracking, including annealing twin boundary parting, has been discussed based on the stress concentration induced by impinging planar deformation structures on the grain boundaries.« less

Offset truss hex solar concentrator

NASA Technical Reports Server (NTRS)

White, John E. (Inventor); Sturgis, James D. (Inventor); Erikson, Raymond J. (Inventor); Waligroski, Gregg A. (Inventor); Scott, Michael A. (Inventor)

1991-01-01

A solar energy concentrator system comprises an offset reflector structure made up of a plurality of solar energy reflector panel sections interconnected with one another to form a piecewise approximation of a portion of a (parabolic) surface of revolution rotated about a prescribed focal axis. Each panel section is comprised of a plurality of reflector facets whose reflective surfaces effectively focus reflected light to preselected surface portions of the interior sidewall of a cylindrically shaped solar energy receiver. The longitudinal axis of the receiver is tilted at an acute angle with respect to the optical axis such that the distribution of focussed solar energy over the interior surface of the solar engine is optimized for dynamic solar energy conversion. Each reflector panel section comprises a flat, hexagonally shaped truss support framework and a plurality of beam members interconnecting diametrically opposed corners of the hexagonal framework recessed within which a plurality of (spherically) contoured reflector facets is disposed. The depth of the framework and the beam members is greater than the thickness of a reflector facet such that a reflector facet may be tilted (for controlling the effective focus of its reflected light through the receiver aperture) without protruding from the panel section.

Hexahedron Prism-Anchored Octahedronal CeO2: Crystal Facet-Based Homojunction Promoting Efficient Solar Fuel Synthesis.

PubMed

Li, Ping; Zhou, Yong; Zhao, Zongyan; Xu, Qinfeng; Wang, Xiaoyong; Xiao, Min; Zou, Zhigang

2015-08-05

An unprecedented, crystal facet-based CeO2 homojunction consisting of hexahedron prism-anchored octahedron with exposed prism surface of {100} facets and octahedron surface of {111} facets was fabricated through solution-based crystallographic-oriented epitaxial growth. The photocatalysis experiment reveals that growth of the prism arm on octahedron allows to activate inert CeO2 octahedron for an increase in phototocatalytic reduction of CO2 into methane. The pronounced photocatalytic performance is attributed to a synergistic effect of the following three factors: (1) band alignment of the {100} and {111} drives electrons and holes to octahedron and prism surfaces, respectively, aiming to reach the most stable energy configuration and leading to a spatial charge separation for long duration; (2) crystallographic-oriented epitaxial growth of the CeO2 hexahedron prism arm on the octahedron verified by the interfacial lattice fringe provides convenient and fast channels for the photogenerated carrier transportation between two units of homojuntion; (3) different effective mass of electrons and holes on {100} and {111} faces leads to high charge carrier mobility, more facilitating the charge separation. The proposed facet-based homojunction in this work may provide a new concept for the efficient separation and fast transfer of photoinduced charge carriers and enhancement of the photocatalytic performance.

Thermodynamic stability and structure of cuprous chloride surfaces: a DFT investigation.

PubMed

Suleiman, Ibrahim A; Radny, Marian W; Gladys, Michael J; Smith, Phillip V; Mackie, John C; Kennedy, Eric M; Dlugogorski, Bogdan Z

2015-03-14

Density functional theory together with ab initio atomistic thermodynamics has been utilized to study the structures and stabilities of the low index CuCl surfaces. It is shown that the Cl-terminated structures are more stable than the Cu-terminated configurations, and that the defective CuCl(110)-Cu structure is more stable than the stoichiometric CuCl(110) surface. The equilibrium shape of a cuprous chloride nanostructure terminated by low-index CuCl surfaces has also been predicted using a Wulff construction. It was found that the (110) facets dominate at low chlorine concentration. As the chlorine concentration is increased, however, the contributions of the (100) and (111) facets to the Wulff construction also increase giving the crystal a semi-prism shape. At high chlorine concentration, and close to the rich limit, the (111) facets were found to be the only contributors to the Wulff construction, resulting in prismatic nanocrystals.

The role of surface passivation in controlling Ge nanowire faceting

DOE PAGES

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

2015-11-05

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

The surface structure of silver-coated gold nanocrystals and its influence on shape control

DOE PAGES

Padmos, J. Daniel; Personick, Michelle L.; Tang, Qing; ...

2015-07-08

Understanding the surface structure of metal nanocrystals with specific facet indices is important due to its impact on controlling nanocrystal shape and functionality. However, this is particularly challenging for halide-adsorbed nanocrystals due to the difficulty in analysing interactions between metals and light halides (for example, chloride). Here we uncover the surface structures of chloride-adsorbed, silver-coated gold nanocrystals with {111}, {110}, {310} and {720} indexed facets by X-ray absorption spectroscopy and density functional theory modelling. The silver–chloride, silver–silver and silver–gold bonding structures are markedly different between the nanocrystal surfaces, and are sensitive to their formation mechanism and facet type. A uniquemore » approach of combining the density functional theory and experimental/simulated X-ray spectroscopy further verifies the surface structure models and identifies the previously indistinguishable valence state of silver atoms on the nanocrystal surfaces. Overall, this work elucidates the thus-far unknown chloride–metal nanocrystal surface structures and sheds light onto the halide-induced growth mechanism of anisotropic nanocrystals.« less

Biomimetic synthesis of noble metal nanocrystals

NASA Astrophysics Data System (ADS)

Chiu, Chin-Yi

At the nanometer scale, the physical and chemical properties of materials heavily depend on their sizes and shapes. This fact has triggered considerable efforts in developing controllable nanomaterial synthesis. The controlled growth of colloidal nanocrystal is a kinetic process, in which high-energy facets grow faster and then vanish, leading to a nanocrystal enclosed by low-energy facets. Identifying a surfactant that can selectively bind to a particular crystal facet and thus lower its surface energy, is critical and challenging in shape controlled synthesis of nanocrystals. Biomolecules exhibiting exquisite molecular recognition properties can be exploited to precisely engineer nanostructured materials. In the first part of my thesis, we employed the phage display technique to select a specific multifunctional peptide sequence which can bind on Pd surface and mediate Pd crystal nucleation and growth, achieving size controlled synthesis of Pd nanocrystals in aqueous solution. We further demonstrated a rational biomimetic approach to the predictable synthesis of nanocrystals enclosed by a particular facet in the case of Pt. Specifically, Pt {100} and Pt {111} facet-specific peptides were identified and used to synthesize Pt nanocubes and Pt nano-tetrahedrons, respectively. The mechanistic studies of Pt {111} facet-specific peptide had led us to study the facet-selective adsorption of aromatic molecules on noble metal surfaces. The discoveries had achieved the development of design strategies to select facet-selective molecules which can synthesize nanocrystals with expected shapes in both Pt and Pd system. At last, we exploited Pt facet-specific peptides and controlled the molecular interaction to produce one- and three- dimensional nanostructures composed of anisotropic nanoparticles in synthetic conditions without supramolecular pre-organization, demonstrating the full potential of biomolecules in mediating material formation process. My research on biomimetic synthesis of nanocrystals with shape control and nanostructures with control over the anisotropy are unprecedented, representing a step forward in achieving the goal of producing complex nanostructures with required properties. The fundamental studies on the biomolecule-inorganic interfaces have contributed to advancing the synthesis tool of colloidal nanomaterials and enriching understating of organic-inorganic interface, impacting many applications.

Nature of peptide wrapping onto metal nanoparticle catalysts and driving forces for size control.

PubMed

Ramezani-Dakhel, Hadi; Bedford, Nicholas M; Woehl, Taylor J; Knecht, Marc R; Naik, Rajesh R; Heinz, Hendrik

2017-06-22

Colloidal metal nanocrystals find many applications in catalysis, energy conversion devices, and therapeutics. However, the nature of ligand interactions and implications on shape control have remained uncertain at the atomic scale. Large differences in peptide adsorption strength and facet specificity were found on flat palladium surfaces versus surfaces of nanoparticles of 2 to 3 nm size using accurate atomistic simulations with the Interface force field. Folding of longer peptides across many facets explains the formation of near-spherical particles with local surface disorder, in contrast to the possibility of nanostructures of higher symmetry with shorter ligands. The average particle size in TEM correlates inversely with the surface coverage with a given ligand and with the strength of ligand adsorption. The role of specific amino acids and sequence mutations on the nanoparticle size and facet composition is discussed, as well as the origin of local surface disorder that leads to large differences in catalytic reactivity.

Crack Front Segmentation and Facet Coarsening in Mixed-Mode Fracture

NASA Astrophysics Data System (ADS)

Chen, Chih-Hung; Cambonie, Tristan; Lazarus, Veronique; Nicoli, Matteo; Pons, Antonio J.; Karma, Alain

2015-12-01

A planar crack generically segments into an array of "daughter cracks" shaped as tilted facets when loaded with both a tensile stress normal to the crack plane (mode I) and a shear stress parallel to the crack front (mode III). We investigate facet propagation and coarsening using in situ microscopy observations of fracture surfaces at different stages of quasistatic mixed-mode crack propagation and phase-field simulations. The results demonstrate that the bifurcation from propagating a planar to segmented crack front is strongly subcritical, reconciling previous theoretical predictions of linear stability analysis with experimental observations. They further show that facet coarsening is a self-similar process driven by a spatial period-doubling instability of facet arrays.

The lustering of TBC-2

NASA Astrophysics Data System (ADS)

Diver, Richard B.; Jones, Scott; Robb, Stacy; Mahoney, A. Rod

1995-05-01

Two test bed concentrators (TBC's) were designed to provide high-performance test beds for advanced solar receivers and converters. However, the second-surface silvered-glass mirror facets on the TBC's, which were originally manufactured by the Jet Propulsion Laboratory, have experienced severe silver corrosion. To restore reflectance, TBC-2 was refurbished with a lustering technique developed at Sandia National Laboratories. In the lustering technique, second-surface silvered thin-glass mirrors were applied over the corroded facets, thereby increasing the dish reflectivity and raising the available power of TBC-2 from approximately 70 to 78 kW(sub t). Degradation of the original optical accuracy of the TBC facets was determined to be minimal. Lustering was chosen over facet replacement because of the lower cost, the anticipated improvement in corrosion resistance, and the shorter project duration. This report includes background information, details of the lustering process, and test results from TBC-2 characterization, both before and after lustering.

CO-CO coupling on Cu facets: Coverage, strain and field effects

DOE PAGES

Sandberg, Robert B.; Montoya, Joseph H.; Chan, Karen; ...

2016-08-21

We present a DFT study on the effect of coverage, strain, and electric field on CO-CO coupling energetics on Cu (100), (111), and (211). Our calculations indicate that CO-CO coupling is facile on all three facets in the presence of a cation-induced electric field in the Helmholtz plane, with the lowest barrier on Cu(100). The CO dimerization pathway is therefore expected to play a role in C 2 formation at potentials negative of the Cu potential of zero charge, corresponding to CO 2/CO reduction conditions at high pH. Both increased *CO coverage and tensile strain further improve C-C coupling energeticsmore » on Cu (111) and (211). Since CO dimerization is facile on all 3 Cu facets, subsequent surface hydrogenation steps may also play an important role in determining the overall activity towards C 2 products. Adsorption of *CO, *H, and *OH on the 3 facets were investigated with a Pourbaix analysis. Here, the (211) facet has the largest propensity to co-adsorb *CO and *H, which would favor surface hydrogenation following CO dimerization.« less

On the Faceting and Linking of PROV for Earth Science Data Systems

NASA Astrophysics Data System (ADS)

Hua, H.; Manipon, G.; Wilson, B. D.; Tan, D.; Starch, M.

2015-12-01

Faceted search has yielded powerful capabilities for discovery of information by applying multiple filters to explore information. This is often more effective when the information is decomposed into faceted components that can be sliced and diced during faceted navigation. We apply this approach to the representation of PROV for Earth Science (PROV-ES) to facilitate more atomic units of provenance for discovery. Traditional bundles of PROV are then decomposed to enable finer-grain discovery of provenance. Linkages across provenance components can then be explored across seemingly disparate bundles. We will show how mappings into this provenance approach can be used to explore more data life-cycle relationships from observation to data to findings. We will also show examples of how this approach can be used to improve the discovery, access, and transparency of NASA datasets and the science data systems that were used to capture, manage, and produce the provenance information.

Parallel CARLOS-3D code development

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

Putnam, J.M.; Kotulski, J.D.

1996-02-01

CARLOS-3D is a three-dimensional scattering code which was developed under the sponsorship of the Electromagnetic Code Consortium, and is currently used by over 80 aerospace companies and government agencies. The code has been extensively validated and runs on both serial workstations and parallel super computers such as the Intel Paragon. CARLOS-3D is a three-dimensional surface integral equation scattering code based on a Galerkin method of moments formulation employing Rao- Wilton-Glisson roof-top basis for triangular faceted surfaces. Fully arbitrary 3D geometries composed of multiple conducting and homogeneous bulk dielectric materials can be modeled. This presentation describes some of the extensions tomore » the CARLOS-3D code, and how the operator structure of the code facilitated these improvements. Body of revolution (BOR) and two-dimensional geometries were incorporated by simply including new input routines, and the appropriate Galerkin matrix operator routines. Some additional modifications were required in the combined field integral equation matrix generation routine due to the symmetric nature of the BOR and 2D operators. Quadrilateral patched surfaces with linear roof-top basis functions were also implemented in the same manner. Quadrilateral facets and triangular facets can be used in combination to more efficiently model geometries with both large smooth surfaces and surfaces with fine detail such as gaps and cracks. Since the parallel implementation in CARLOS-3D is at high level, these changes were independent of the computer platform being used. This approach minimizes code maintenance, while providing capabilities with little additional effort. Results are presented showing the performance and accuracy of the code for some large scattering problems. Comparisons between triangular faceted and quadrilateral faceted geometry representations will be shown for some complex scatterers.« less

Patchy particles made by colloidal fusion

NASA Astrophysics Data System (ADS)

Gong, Zhe; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

2017-10-01

Patches on the surfaces of colloidal particles provide directional information that enables the self-assembly of the particles into higher-order structures. Although computational tools can make quantitative predictions and can generate design rules that link the patch motif of a particle to its internal microstructure and to the emergent properties of the self-assembled materials, the experimental realization of model systems of particles with surface patches (or `patchy' particles) remains a challenge. Synthetic patchy colloidal particles are often poor geometric approximations of the digital building blocks used in simulations and can only rarely be manufactured in sufficiently high yields to be routinely used as experimental model systems. Here we introduce a method, which we refer to as colloidal fusion, for fabricating functional patchy particles in a tunable and scalable manner. Using coordination dynamics and wetting forces, we engineer hybrid liquid-solid clusters that evolve into particles with a range of patchy surface morphologies on addition of a plasticizer. We are able to predict and control the evolutionary pathway by considering surface-energy minimization, leading to two main branches of product: first, spherical particles with liquid surface patches, capable of forming curable bonds with neighbouring particles to assemble robust supracolloidal structures; and second, particles with a faceted liquid compartment, which can be cured and purified to yield colloidal polyhedra. These findings outline a scalable strategy for the synthesis of patchy particles, first by designing their surface patterns by computer simulation, and then by recreating them in the laboratory with high fidelity.

A model for the microwave emissivity of the ocean's surface as a function of wind speed

NASA Technical Reports Server (NTRS)

Wilheit, T. T.

1979-01-01

A quanitative model is presented which describes the ocean surface as a ensemble of flat facets with a normal distribution of slopes. The variance of the slope distribution is linearly related to frequency up to 35 GHz and constant at higher frequencies. These facets are partially covered with an absorbing nonpolarized foam layer. Experimental evidence is presented for this model.

(100) facets of γ-Al2O3: the active surfaces for alcohol dehydration reactions

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

Kwak, Ja Hun; Mei, Donghai; Peden, Charles HF

2011-05-01

Temperature programmed desorption (TPD) of ethanol, and methanol dehydration reaction were studied on γ-Al2O3 in order to identify the catalytic active sites for alcohol dehydration reactions. Two high temperature (> 473 K) desorption features were observed following ethanol adsorption. Samples calcined at T≤473 K displayed a desorption feature in the 523-533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. The switch from the high to low temperature ethanol desorption correlated well with the dehydroxylation of the (100) facets of γ-Al2O3 that was predicted at 550 K DFT calculations. Theoreticalmore » DFT simulations of the mechanism of dehydration. on clean and hydroxylated γ-Al2O3(100) surfaces, find that a concerted elimination of ethylene from an ethanol molecule chemisorbed at an Al3+ pentacoordinated site is the rate limiting step for catalytic cycle on both surfaces. Furthermore, titration of the pentacoordinate Al3+ sites on the (100) facets of γ-Al2O3 by BaO completely turned off the methanol dehydration reaction activity. These results unambiguously demonstrate that only the (100) facets on γ-Al2O3 are the catalytic active surfaces for alcohol dehydration.« less

Engineering Controlled Spalling in (100)-Oriented GaAs for Wafer Reuse

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

Sweet, Cassi A.; McNeely, Joshua E.; Gorman, Brian

Controlled spalling offers a way to cleave thin, single-crystal films or devices from wafers, particularly if the fracture planes in the material are oriented parallel to the wafer surface. Unfortunately, misalignment between the favored fracture planes and the wafer surface preferred for photovoltaic growth in (100)-oriented GaAs produces a highly faceted surface when subject to controlled spalling. This highly faceted cleavage surface is problematic in several ways: (1) it can result in large variations of spall depth due to unstable crack propagation; (2) it may introduce defects into the device zone or underlying substrate; and (3) it consumes many micronsmore » of material outside of the device zone. We present the ways in which we have engineered controlled spalling for (100)-oriented GaAs to minimize these effects. We expand the operational window for controlled spalling to avoid spontaneous spalling, find no evidence of dislocation activity in the spalled film or the parent wafer, and reduce facet height and facet height irregularity. Resolving these issues provides a viable path forward for reducing III-V device cost through the controlled spalling of (100)-oriented GaAs devices and subsequent wafer reuse when these processes are combined with a high-throughput growth method such as Hydride Vapor Phase Epitaxy.« less

Shape-Selective Syntheses of Gold and Copper Nanostructures: Insights From Density-Functional Theory and Molecular Dynamics

NASA Astrophysics Data System (ADS)

Liu, Shih-Hsien

Density-functional theory (DFT) and molecular dynamics (MD) were used to resolve the origins of shape-selective syntheses of {111}-faceted Au nanostructures mediated by polyvinylpyrrolidone (PVP) as well as {100}-faceted Cu nanostructures mediated by hex- adecylamine(HDA) seen in experiment. For the work in PVP on Au surfaces, the hexagonal reconstruction of Au(100) was considered. DFT results indicate that the Au(111) surface covered by the PVP segment, 2-pyrrolidone (2P), has a lower surface energy than the 2P- covered (5 x 1) Au(100)-hex surface, and that PVP may exhibit a binding affinity for Au(111) comparable to or greater than (5 x 1) Au(100)-hex. With MD, it is shown that the PVP-covered Au(111) surface has a lower surface energy than the PVP-covered (5 x 1) Au(100)-hex surface, and that the atactic PVP isosamer chains have a binding affinity for Au(111) comparable to (5 x 1) Au(100)-hex. Also, the (5 x 1) Au(100)-hex surface may have a higher flux of Au atoms than the Au(111) surface. Therefore, the Au(111) surface would be thermodynamically and kinetically favored in PVP-mediated syntheses, leading to {111}-faceted Au nanostructures. For the work in HDA on Cu surfaces, DFT results show that the HDA-covered Cu(100) surface has a slightly higher surface energy than the HDA- covered Cu(111) surface. However, HDA has a significant binding preference on Cu(100) over Cu(111). Therefore, the Cu(100) surface would be kinetically favored in HDA-mediated syn- theses, leading to {100}-faceted Cu nanostructures. Further, a metal-organic many-body (MOMB) force field for HDA-Cu interactions was developed based on the DFT work, and the force field was used to resolve the HDA binding patterns on Cu(100) at molecular level. With MD, it is found that decylamine (DA) may be used as an effective capping agent in the synthesis of {100}-faceted Cu nanostructures since DA as well as HDA are organized on Cu surfaces and have the same binding preference on Cu(100) over Cu(111). It is also found that the HDA structures on Cu surfaces remain intact in aqueous solution due to hydrophobicity of alkyl tails and long alkyl chains in the HDA molecules, which could prevent Cu oxidation during the synthesis.

Tailoring molecular specificity toward a crystal facet: a lesson from biorecognition toward Pt{111}.

PubMed

Ruan, Lingyan; Ramezani-Dakhel, Hadi; Chiu, Chin-Yi; Zhu, Enbo; Li, Yujing; Heinz, Hendrik; Huang, Yu

2013-02-13

Surfactants with preferential adsorption to certain crystal facets have been widely employed to manipulate morphologies of colloidal nanocrystals, while mechanisms regarding the origin of facet selectivity remain an enigma. Similar questions exist in biomimetic syntheses concerning biomolecular recognition to materials and crystal surfaces. Here we present mechanistic studies on the molecular origin of the recognition toward platinum {111} facet. By manipulating the conformations and chemical compositions of a platinum {111} facet specific peptide, phenylalanine is identified as the dominant motif to differentiate {111} from other facets. The discovered recognition motif is extended to convert nonspecific peptides into {111} specific peptides. Further extension of this mechanism allows the rational design of small organic molecules that demonstrate preferential adsorption to the {111} facets of both platinum and rhodium nanocrystals. This work represents an advance in understanding the organic-inorganic interfacial interactions in colloidal systems and paves the way to rational and predictable nanostructure modulations for many applications.

A Meta-Analytic Test of Redundancy and Relative Importance of the Dark Triad and Five-Factor Model of Personality.

PubMed

O'Boyle, Ernest H; Forsyth, Donelson R; Banks, George C; Story, Paul A; White, Charles D

2015-12-01

We examined the relationships between Machiavellianism, narcissism, and psychopathy-the three traits of the Dark Triad (DT)-and the Five-Factor Model (FFM) of personality. The review identified 310 independent samples drawn from 215 sources and yielded information pertaining to global trait relationships and facet-level relationships. We used meta-analysis to examine (a) the bivariate relations between the DT and the five global traits and 30 facets of the FFM, (b) the relative importance of each of the FFM global traits in predicting DT, and (c) the relationship between the DT and FFM facets identified in translational models of narcissism and psychopathy. These analyses identified consistent and theoretically meaningful associations between the DT traits and the facets of the FFM. The five traits of the FFM, in a relative importance analysis, accounted for much of the variance in Machiavellianism, narcissism, and psychopathy, respectively, and facet-level analyses identified specific facets of each FFM trait that were consistently associated with narcissism (e.g., angry/hostility, modesty) and psychopathy (e.g., straightforwardness, deliberation). The FFM explained nearly all of the variance in psychopathy (R(2) c  = .88) and a substantial portion of the variance in narcissism (R(2) c  = .42). © 2014 Wiley Periodicals, Inc.

Quantitative three-dimensional ice roughness from scanning electron microscopy

NASA Astrophysics Data System (ADS)

Butterfield, Nicholas; Rowe, Penny M.; Stewart, Emily; Roesel, David; Neshyba, Steven

2017-03-01

We present a method for inferring surface morphology of ice from scanning electron microscope images. We first develop a novel functional form for the backscattered electron intensity as a function of ice facet orientation; this form is parameterized using smooth ice facets of known orientation. Three-dimensional representations of rough surfaces are retrieved at approximately micrometer resolution using Gauss-Newton inversion within a Bayesian framework. Statistical analysis of the resulting data sets permits characterization of ice surface roughness with a much higher statistical confidence than previously possible. A survey of results in the range -39°C to -29°C shows that characteristics of the roughness (e.g., Weibull parameters) are sensitive not only to the degree of roughening but also to the symmetry of the roughening. These results suggest that roughening characteristics obtained by remote sensing and in situ measurements of atmospheric ice clouds can potentially provide more facet-specific information than has previously been appreciated.

Sensing the facet orientation in silver nano-plates using scanning Kelvin probe microscopy in air

NASA Astrophysics Data System (ADS)

Abdellatif, M. H.; Salerno, M.; Polovitsyn, Anatolii; Marras, Sergio; De Angelis, Francesco

2017-05-01

The work function of nano-materials is important for a full characterization of their electronic properties. Because the band alignment, band bending and electronic noise are very sensitive to work function fluctuations, the dependence of the work function of nano-scale crystals on facet orientation can be a critical issue in optimizing optoelectronic devices based on these materials. We used scanning Kelvin probe microscopy to assess the local work function on samples of silver nano-plates at sub-micrometric spatial resolution. With the appropriate choice of the substrate and based on statistical analysis, it was possible to distinguish the surface potential of the different facets of silver nano-plates even if the measurements were done in ambient conditions without the use of vacuum. A phenomenological model was used to calculate the differences of facet work function of the silver nano-plates and the corresponding shift in Fermi level. This theoretical prediction and the experimentally observed difference in surface potential on the silver nano-plates were in good agreement. Our results show the possibility to sense the nano-crystal facets by appropriate choice of the substrate in ambient conditions.

FacetModeller: Software for manual creation, manipulation and analysis of 3D surface-based models

NASA Astrophysics Data System (ADS)

Lelièvre, Peter G.; Carter-McAuslan, Angela E.; Dunham, Michael W.; Jones, Drew J.; Nalepa, Mariella; Squires, Chelsea L.; Tycholiz, Cassandra J.; Vallée, Marc A.; Farquharson, Colin G.

2018-01-01

The creation of 3D models is commonplace in many disciplines. Models are often built from a collection of tessellated surfaces. To apply numerical methods to such models it is often necessary to generate a mesh of space-filling elements that conforms to the model surfaces. While there are meshing algorithms that can do so, they place restrictive requirements on the surface-based models that are rarely met by existing 3D model building software. Hence, we have developed a Java application named FacetModeller, designed for efficient manual creation, modification and analysis of 3D surface-based models destined for use in numerical modelling.

Facet personality and surface-level diversity as team mental model antecedents: implications for implicit coordination.

PubMed

Fisher, David M; Bell, Suzanne T; Dierdorff, Erich C; Belohlav, James A

2012-07-01

Team mental models (TMMs) have received much attention as important drivers of effective team processes and performance. Less is known about the factors that give rise to these shared cognitive structures. We examined potential antecedents of TMMs, with a specific focus on team composition variables, including various facets of personality and surface-level diversity. Further, we examined implicit coordination as an important outcome of TMMs. Results suggest that team composition in terms of the cooperation facet of agreeableness and racial diversity were significantly related to team-focused TMM similarity. TMM similarity was also positively predictive of implicit coordination, which mediated the relationship between TMM similarity and team performance. Post hoc analyses revealed a significant interaction between the trust facet of agreeableness and racial diversity in predicting TMM similarity. Results are discussed in terms of facilitating the emergence of TMMs and corresponding implications for team-related human resource practices. (PsycINFO Database Record (c) 2012 APA, all rights reserved).

Atomistics of vapour–liquid–solid nanowire growth

PubMed Central

Wang, Hailong; Zepeda-Ruiz, Luis A.; Gilmer, George H.; Upmanyu, Moneesh

2013-01-01

Vapour–liquid–solid route and its variants are routinely used for scalable synthesis of semiconducting nanowires, yet the fundamental growth processes remain unknown. Here we employ atomic-scale computations based on model potentials to study the stability and growth of gold-catalysed silicon nanowires. Equilibrium studies uncover segregation at the solid-like surface of the catalyst particle, a liquid AuSi droplet, and a silicon-rich droplet–nanowire interface enveloped by heterogeneous truncating facets. Supersaturation of the droplets leads to rapid one-dimensional growth on the truncating facets and much slower nucleation-controlled two-dimensional growth on the main facet. Surface diffusion is suppressed and the excess Si flux occurs through the droplet bulk which, together with the Si-rich interface and contact line, lowers the nucleation barrier on the main facet. The ensuing step flow is modified by Au diffusion away from the step edges. Our study highlights key interfacial characteristics for morphological and compositional control of semiconducting nanowire arrays. PMID:23752586

Direct water decomposition on transition metal surfaces: Structural dependence and catalytic screening

DOE PAGES

Tsai, Charlie; Lee, Kyoungjin; Yoo, Jong Suk; ...

2016-02-16

Density functional theory calculations are used to investigate thermal water decomposition over the close-packed (111), stepped (211), and open (100) facets of transition metal surfaces. A descriptor-based approach is used to determine that the (211) facet leads to the highest possible rates. As a result, a range of 96 binary alloys were screened for their potential activity and a rate control analysis was performed to assess how the overall rate could be improved.

A topological screening heuristic for low-energy, high-index surfaces

NASA Astrophysics Data System (ADS)

Sun, Wenhao; Ceder, Gerbrand

2018-03-01

Robust ab initio investigations of nanoparticle surface properties require a method to identify candidate low-energy surface facets a priori. By assuming that low-energy surfaces are planes with high atomic density, we devise an efficient algorithm to screen for low-energy surface orientations, even if they have high (hkl) miller indices. We successfully predict the observed low-energy, high-index { 10 12 bar } and { 10 1 bar 4 } surfaces of hematite α-Fe2O3, the {311} surfaces of cuprite Cu2O, and the {112} surfaces of anatase TiO2. We further tabulate candidate low-energy surface orientations for nine of the most common binary oxide structures. Screened surfaces are found to be generally applicable across isostructural compounds with varying chemistries, although relative surface energies between facets may vary based on the preferred coordination of the surface atoms.

Understanding the facet formation mechanisms of Si thin-film solidification through three-dimensional phase-field modeling

NASA Astrophysics Data System (ADS)

Chen, G. Y.; Lan, C. W.

2017-09-01

Adaptive phase field modeling is used in order to model the formation mechanism of a silicon faceted interface in three dimensions. We investigate the faceting condition for equilibrium shapes and dynamic situations. In this study, we propose a new anisotropic function of surface energy for the phase-field simulations in three-dimension, and negative stiffness is further considered. The morphological evolutions are presented and compare well with experimental findings. The growth mechanism is further discussed.

Facet-Controlled Synthetic Strategy of Cu2O-Based Crystals for Catalysis and Sensing.

PubMed

Shang, Yang; Guo, Lin

2015-10-01

Shape-dependent catalysis and sensing behaviours are primarily focused on nanocrystals enclosed by low-index facets, especially the three basic facets ({100}, {111}, and {110}). Several novel strategies have recently exploded by tailoring the original nanocrystals to greatly improve the catalysis and sensing performances. In this Review, we firstly introduce the synthesis of a variety of Cu 2 O nanocrystals, including the three basic Cu 2 O nanocrystals (cubes, octahedra and rhombic dodecahedra, enclosed by the {100}, {111}, and {110} facets, respectively), and Cu 2 O nanocrystals enclosed by high-index planes. We then discuss in detail the three main facet-controlled synthetic strategies (deposition, etching and templating) to fabricate Cu 2 O-based nanocrystals with heterogeneous, etched, or hollow structures, including a number of important concepts involved in those facet-controlled routes, such as the selective adsorption of capping agents for protecting special facets, and the impacts of surface energy and active sites on reaction activity trends. Finally, we highlight the facet-dependent properties of the Cu 2 O and Cu 2 O-based nanocrystals for applications in photocatalysis, gas catalysis, organocatalysis and sensing, as well as the relationship between their structures and properties. We also summarize and comment upon future facet-related directions.

A practical scale for Multi-Faceted Organizational Health Climate Assessment.

PubMed

Zweber, Zandra M; Henning, Robert A; Magley, Vicki J

2016-04-01

The current study sought to develop a practical scale to measure 3 facets of workplace health climate from the employee perspective as an important component of a healthy organization. The goal was to create a short, usable yet comprehensive scale that organizations and occupational health professionals could use to determine if workplace health interventions were needed. The proposed Multi-faceted Organizational Health Climate Assessment (MOHCA) scale assesses facets that correspond to 3 organizational levels: (a) workgroup, (b) supervisor, and (c) organization. Ten items were developed and tested on 2 distinct samples, 1 cross-organization and 1 within-organization. Exploratory and confirmatory factor analyses yielded a 9-item, hierarchical 3-factor structure. Tests confirmed MOHCA has convergent validity with related constructs, such as perceived organizational support and supervisor support, as well as discriminant validity with safety climate. Lastly, criterion-related validity was found between MOHCA and health-related outcomes. The multi-faceted nature of MOHCA provides a scale that has face validity and can be easily translated into practice, offering a means for diagnosing the shortcomings of an organization or workgroup's health climate to better plan health and well-being interventions. (c) 2016 APA, all rights reserved).

Radial wedge flange clamp

DOEpatents

Smith, Karl H.

2002-01-01

A radial wedge flange clamp comprising a pair of flanges each comprising a plurality of peripheral flat wedge facets having flat wedge surfaces and opposed and mating flat surfaces attached to or otherwise engaged with two elements to be joined and including a series of generally U-shaped wedge clamps each having flat wedge interior surfaces and engaging one pair of said peripheral flat wedge facets. Each of said generally U-shaped wedge clamps has in its opposing extremities apertures for the tangential insertion of bolts to apply uniform radial force to said wedge clamps when assembled about said wedge segments.

Effect of dipolar fields, surface termination, and surface orientation on photochemical reactions on transition metal oxides

NASA Astrophysics Data System (ADS)

Giocondi, Jennifer Lynn

Experiments have been conducted to determine the effects of dipolar fields, surface termination, and surface orientation on the photochemical reactivity of several transition metal oxides. These compounds include BaTiO3, SrTiO3, BaTi4O9, Sr2Nb2O 7, and Sr2Ta2O7 which were studied as polycrystalline ceramics, single crystals, micron-sized faceted particles, or some combination of these forms. The reduction of Ag+ from an aqueous AgNO3 solution (Ag0 product) and the oxidation of Pb2+ from an aqueous lead acetate solution (PbO 2 product) were selected as probe reactions because they leave insoluble products on the oxide surfaces. The reactivity of ferroelectric BaTiO3 was dominated by the effect of dipolar fields on the transport of photogenerated charge carriers. Silver was reduced on domains with a positive surface charge while lead was oxidized on domains with a negative surface charge. This reactivity implies that the dipolar field in individual domains drives photogenerated charge carriers to oppositely charged surfaces. This reaction mechanism results in a physical separation of the photogenerated charge carriers and the locations of the oxidation and reduction half reactions on the catalyst surface. Experiments performed on polycrystalline ceramics, single crystals, and micron-sized particles all showed this domain specific reactivity. SrTiO3 has the ideal cubic perovskite structure from which the tetragonally distorted ferroelectric BaTiO3 phase is derived. Polished and annealed surfaces of randomly oriented grain surfaces were bound by some combination of the following three planes: {110}, {111}, and a complex facet inclined approximately 24° from {100}. Surfaces with the complex {100} facet were found to be the most active for Ag reduction. Single crystal studies also showed that the nonpolar (100) surface is the most reactive and that the composition of the termination layer does not influence this reaction. However, the polar (111) and (110) surfaces had a non-uniform distribution of reaction products. For these orientations, the location of the reduction and oxidation reactions is determined by the chemical and charge terminations of the different terraces or facets. The reactivity for silver reduction on the faceted particles is ranked as (100) > (111) > (110) while the (100) surface was least reactive for lead oxidation. Overall, these results show that the photochemical reactivity of SrTiO3 is anisotropic and that on polar surfaces, dipolar fields arising from charged surface domains influence the transport of photogenerated charge carriers and promote spatially selective oxidation and reduction reactions. (Abstract shortened by UMI.)

Cervical facet force analysis after disc replacement versus fusion.

PubMed

Patel, Vikas V; Wuthrich, Zachary R; McGilvray, Kirk C; Lafleur, Matthew C; Lindley, Emily M; Sun, Derrick; Puttlitz, Christian M

2017-05-01

Cervical total disc replacement was developed to preserve motion and reduce adjacent-level degeneration relative to fusion, yet concerns remain that total disc replacement will lead to altered facet joint loading and long-term facet joint arthrosis. This study is intended to evaluate changes in facet contact force, pressure and surface area at the treated and superior adjacent levels before and after discectomy, disc replacement, and fusion. Ten fresh-frozen human cadaveric cervical spines were potted from C2 to C7 with pressure sensors placed into the facet joints of C3-C4 and C4-C5 via slits in the facet capsules. Moments were applied to the specimens to produce axial rotation, lateral bending and extension. Facet contact force and pressure were measured at both levels for intact, discectomy at C4-C5, disc replacement with ProDisc-C (Synthes Spine, West Chester, Pennsylvania, USA) at C4-C5, and anterior discectomy and fusion with Cervical Spine Locking Plate (Synthes Spine, West Chester, Pennsylvania, USA) at C4-C5. Facet contact area was calculated from the force and pressure measurements. An analysis of variance was used to determine significant differences with P-values <0.05 indicating significance. Facet contact force was elevated at the treated level under extension following both discectomy and disc replacement, while facet contact pressure and area were relatively unchanged. Facet contact force and area were decreased at the treated level following fusion for all three loading conditions. Total disc replacement preserved facet contact force for all scenarios except extension at the treated level, highlighting the importance of the anterior disco-ligamentous complex. This could promote treated-level facet joint disease. Copyright © 2017 Elsevier Ltd. All rights reserved.

Tin Oxide Crystals Exposed by Low-Energy {110} Facets for Enhanced Electrochemical Heavy Metal Ions Sensing: X-ray Absorption Fine Structure Experimental Combined with Density-Functional Theory Evidence.

PubMed

Jin, Zhen; Yang, Meng; Chen, Shao-Hua; Liu, Jin-Huai; Li, Qun-Xiang; Huang, Xing-Jiu

2017-02-21

Herein, we revealed that the electrochemical behaviors on the detection of heavy metal ions (HMIs) would largely rely on the exposed facets of SnO 2 nanoparticles. Compared to the high-energy {221} facet, the low-energy {110} facet of SnO 2 possessed better electrochemical performance. The adsorption/desorption tests, density-functional theory (DFT) calculations, and X-ray absorption fine structure (XAFS) studies showed that the lower barrier energy of surface diffusion on {110} facet was critical for the superior electrochemical property, which was favorable for the ions diffusion on the electrode, and further leading the enhanced electrochemical performance. Through the combination of experiments and theoretical calculations, a reliable interpretation of the mechanism for electroanalysis of HMIs with nanomaterials exposed by different crystal facets has been provided. Furthermore, it provides a deep insight into understanding the key factor to improve the electrochemical performance for HMIs detection, so as to design high-performance electrochemical sensors.

Understanding the true shape of Au-catalyzed GaAs nanowires.

PubMed

Jiang, Nian; Wong-Leung, Jennifer; Joyce, Hannah J; Gao, Qiang; Tan, Hark Hoe; Jagadish, Chennupati

2014-10-08

With increasing interest in nanowire-based devices, a thorough understanding of the nanowire shape is required to gain tight control of the quality of nanowire heterostructures and improve the performance of related devices. We present a systematic study of the sidewalls of Au-catalyzed GaAs nanowires by investigating the faceting process from the beginning with vapor-liquid-solid (VLS) nucleation, followed by the simultaneous radial growth on the sidewalls, and to the end with sidewall transformation during annealing. The VLS nucleation interface of our GaAs nanowires is revealed by examining cross sections of the nanowire, where the nanowire exhibits a Reuleaux triangular shape with three curved surfaces along {112}A. These curved surfaces are not thermodynamically stable and adopt {112}A facets during radial growth. We observe clear differences in radial growth rate between the ⟨112⟩A and ⟨112⟩B directions with {112}B facets forming due to the slower radial growth rate along ⟨112⟩B directions. These sidewalls transform to {110} facets after high temperature (>500 °C) annealing. A nucleation model is proposed to explain the origin of the Reuleaux triangular shape of the nanowires, and the sidewall evolution is explained by surface kinetic and thermodynamic limitations.

Site-dependent atomic and molecular affinities of hydrocarbons, amines and thiols on diamond nanoparticles

NASA Astrophysics Data System (ADS)

Lai, Lin; Barnard, Amanda S.

2016-04-01

Like many of the useful nanomaterials being produced on the industrial scale, the surface of diamond nanoparticles includes a complicated mixture of various atomic and molecular adsorbates, attaching to the facets following synthesis. Some of these adsorbates may be functional, and adsorption is encouraged to promote applications in biotechnology and nanomedicine, but others are purely adventurous and must be removed prior to use. In order to devise more effective treatments it is advantageous to know the relative strength of the interactions of the adsorbates with the surface, and ideally how abundant they are likely to be under different conditions. In this paper we use a series of explicit electronic structure simulations to map the distribution of small hydrocarbons, amines and thiols on a 2.9 nm diamond nanoparticle, with atomic level resolution, in 3-D. We find a clear relationship between surface reconstructions, facet orientation, and the distribution of the different adsorbates; with a greater concentration expected on the (100) and (110) facets, particularly when the supersaturation in the reservoir is high. Adsorption on the (111) facets is highly unlikely, suggesting that controlled graphitization may be a useful stage in the cleaning and treatment of nanodiamonds, prior to the deliberate coating with functional adsorbates needed for drug delivery applications.

Boundary Recovery For Delaunay Tetrahedral Meshes Using Local Topological Transformations

PubMed Central

Ghadyani, Hamid; Sullivan, John; Wu, Ziji

2009-01-01

Numerous high-quality, volume mesh-generation systems exist. However, no strategy can address all geometry situations without some element qualities being compromised. Many 3D mesh generation algorithms are based on Delaunay tetrahedralization which frequently fails to preserve the input boundary surface topology. For biomedical applications, this surface preservation can be critical as they usually contain multiple material regions of interest coherently connected. In this paper we present an algorithm as a post-processing method that optimizes local regions of compromised element quality and recovers the original boundary surface facets (triangles) regardless of the original mesh generation strategy. The algorithm carves out a small sub-volume in the vicinity of the missing boundary facet or compromised element, creating a cavity. If the task is to recover a surface boundary facet, a natural exit hole in the cavity will be present. This hole is patched with the missing boundary surface face first followed by other patches to seal the cavity. If the task was to improve a compromised region, then the cavity is already sealed. Every triangular facet of the cavity shell is classified as an active face and can be connected to another shell node creating a tetrahedron. In the process the base of the tetrahedron is removed from the active face list and potentially 3 new active faces are created. This methodology is the underpinnings of our last resort method. Each active face can be viewed as the trunk of a tree. An exhaustive breath and depth search will identify all possible tetrahedral combinations to uniquely fill the cavity. We have streamlined this recursive process reducing the time complexity by orders of magnitude. The original surfaces boundaries (internal and external) are fully restored and the quality of compromised regions improved. PMID:20305743

High-temperature morphological evolution of lithographically introduced cavities in silicon carbide

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

Narushima, Takayuki; Glaeser, Andreas M.

2000-12-01

Internal cavities of controlled geometry and crystallography were introduced in 6H silicon carbide single crystals by combining lithographic methods, ion beam etching, and solid-state diffusion bonding. The morphological evolution of these internal cavities (negative crystals) in response to anneals of up to 128 h duration at 1900 degrees C was examined using optical microscopy. Surface energy anisotropy and faceting have a strong influence on both the geometric and kinetic characteristics of evolution. Decomposition of 12{bar 1}0 cavity edges into 101{bar 0} facets was observed after 16 h anneals, indicating that 12{bar 1}0 faces are not components of the Wulff shape.more » The shape evolution kinetics of penny-shaped cavities were also investigated. Experimentally observed evolution rates decreased much more rapidly with those predicted by a model in which surface diffusion is assumed to be rate-limiting. This suggests that the development of facets, and the associated loss of ledges and terraces during the initial stages of evolution results in an evolution process limited by the nucleation rate of attachment/detachment sites (ledges) on the facets.« less

Microstructural Influences on Very High Cycle Fatigue Crack Initiation in Ti-6246 (PREPRINT)

DTIC Science & Technology

2008-04-01

surface (in degrees). Facet # 1 2 3 4 5a 5b 6 7 8 9 Angle 46 45 39 19 26 35 33 31 32 21 Table II. Orientation of facets (in degrees). Facet # 1* 2 3 4 ...TYPE 3. DATES COVERED (From - To) April 2008 Journal Article Preprint 4 . TITLE AND SUBTITLE MICROSTRUCTURAL INFLUENCES ON VERY HIGH CYCLE...FATIGUE CRACK INITIATION IN Ti-6246 (PREPRINT) 5a. CONTRACT NUMBER In-house 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 62102F 6 . AUTHOR(S

Improving the Photo-Oxidative Performance of Bi2MoO6 by Harnessing the Synergy between Spatial Charge Separation and Rational Co-Catalyst Deposition.

PubMed

Wu, Xuelian; Hart, Judy N; Wen, Xiaoming; Wang, Liang; Du, Yi; Dou, Shi Xue; Ng, Yun Hau; Amal, Rose; Scott, Jason

2018-03-21

It has been reported that photogenerated electrons and holes can be directed toward specific crystal facets of a semiconductor particle, which is believed to arise from the differences in their surface electronic structures, suggesting that different facets can act as either photoreduction or photo-oxidation sites. This study examines the propensity for this effect to occur in faceted, plate-like bismuth molybdate (Bi 2 MoO 6 ), which is a useful photocatalyst for water oxidation. Photoexcited electrons and holes are shown to be spatially separated toward the {100} and {001}/{010} facets of Bi 2 MoO 6 , respectively, by facet-dependent photodeposition of noble metals (Pt, Au, and Ag) and metal oxides (PbO 2 , MnO x , and CoO x ). Theoretical calculations revealed that differences in energy levels between the conduction bands and valence bands of the {100} and {001}/{010} facets can contribute to electrons and holes being drawn to different surfaces of the plate-like Bi 2 MoO 6 . Utilizing this knowledge, the photo-oxidative capability of Bi 2 MoO 6 was improved by adding an efficient water oxidation co-catalyst, CoO x , to the system, whereby the extent of enhancement was shown to be governed by the co-catalyst location. A greater oxygen evolution occurred when CoO x was selectively deposited on the hole-rich {001}/{010} facets of Bi 2 MoO 6 compared to when CoO x was randomly located across all of the facets. The elevated performance exhibited for the selectively loaded CoO x /Bi 2 MoO 6 was ascribed to the greater opportunity for hole trapping by the co-catalyst being accentuated over other potentially detrimental effects, such as the co-catalyst acting as a recombination medium and/or covering reactive sites. The results indicate that harnessing the synergy between the spatial charge separation and the co-catalyst location on the appropriate facets of plate-like Bi 2 MoO 6 can promote its photocatalytic activity.

Facet-Specific Adsorption of Tripeptides at Aqueous Au Interfaces: Open Questions in Reconciling Experiment and Simulation.

PubMed

Hughes, Zak E; Kochandra, Raji; Walsh, Tiffany R

2017-04-18

The adsorption of three homo-tripeptides, HHH, YYY, and SSS, at the aqueous Au interface is investigated, using molecular dynamics simulations. We find that consideration of surface facet effects, relevant to experimental conditions, opens up new questions regarding interpretations of current experimental findings. Our well-tempered metadynamics simulations predict the rank ordering of the tripeptide binding affinities at aqueous Au(111) to be YYY > HHH > SSS. This ranking differs with that obtained from existing experimental data which used surface-immobilized Au nanoparticles as the target substrate. The influence of Au facet on these experimental findings is then considered, via our binding strength predictions of the relevant amino acids at aqueous Au(111) and Au(100)(1 × 1). The Au(111) interface supports an amino acid ranking of Tyr > HisA ≃ HisH > Ser, matching that of the tripeptides on Au(111), while the ranking on Au(100) is HisA > Ser ≃ Tyr ≃ HisH, with only HisA showing non-negligible binding. The substantial reduction in Tyr amino acid affinity for Au(100) vs Au(111) offers one possible explanation for the experimentally observed weaker adsorption of YYY on the nanoparticle-immobilized substrate compared with HHH. In a separate set of simulations, we predict the structures of the adsorbed tripeptides at the two aqueous Au facets, revealing facet-dependent differences in the adsorbed conformations. Our findings suggest that Au facet effects, where relevant, may influence the adsorption structures and energetics of biomolecules, highlighting the possible influence of the structural model used to interpret experimental binding data.

A parallel efficient partitioning algorithm for the statistical model of dynamic sea clutter at low grazing angle

NASA Astrophysics Data System (ADS)

Wu, Tao; Wu, Zhensen; Linghu, Longxiang

2017-10-01

Study of characteristics of sea clutter is very important for signal processing of radar, detection of targets on sea surface and remote sensing. The sea state is complex at Low grazing angle (LGA), and it is difficult with its large irradiation area and a great deal simulation facets. A practical and efficient model to obtain radar clutter of dynamic sea in different sea condition is proposed, basing on the physical mechanism of interaction between electromagnetic wave and sea wave. The classical analysis method for sea clutter is basing on amplitude and spectrum distribution, taking the clutter as random processing model, which is equivocal in its physical mechanism. To achieve electromagnetic field from sea surface, a modified phase from facets is considered, and the backscattering coefficient is calculated by Wu's improved two-scale model, which can solve the statistical sea backscattering problem less than 5 degree, considering the effects of the surface slopes joint probability density, the shadowing function, the skewness of sea waves and the curvature of the surface on the backscattering from the ocean surface. We make the assumption that the scattering contribution of each facet is independent, the total field is the superposition of each facet in the receiving direction. Such data characters are very suitable to compute on GPU threads. So we can make the best of GPU resource. We have achieved a speedup of 155-fold for S band and 162-fold for Ku/Χ band on the Tesla K80 GPU as compared with Intel® Core™ CPU. In this paper, we mainly study the high resolution data, and the time resolution is millisecond, so we may have 10,00 time points, and we analyze amplitude probability density distribution of radar clutter.

Facet-Dependent Property of Sequentially Deposited Perovskite Thin Films: Chemical Origin and Self-Annihilation.

PubMed

Zhang, Tiankai; Long, Mingzhu; Yan, Keyou; Zeng, Xiaoliang; Zhou, Fengrui; Chen, Zefeng; Wan, Xi; Chen, Kun; Liu, Pengyi; Li, Faming; Yu, Tao; Xie, Weiguang; Xu, Jianbin

2016-11-30

Quantification of intergrain length scale properties of CH 3 NH 3 PbI 3 (MAPbI 3 ) can provide further understanding of material physics, leading to improved device performance. In this work, we noticed that two typical types of facets appear in sequential deposited perovskite (SDP) films: smooth and steplike morphologies. By mapping the surface potential as well as the photoluminescence (PL) peak position, we revealed the heterogeneity of SDP thin films that smooth facets are almost intrinsic with a PL peak at 775 nm, while the steplike facets are p-type-doped with 5-nm blue-shifted PL peak. Considering the reaction process, we propose that the smooth facets have well-defined crystal lattices that resulted from the interfacial reaction between MAI and PbI 2 domains containing low trap states density. The steplike facets are MAI-rich originated from the grain boundaries of PbI 2 film and own more trap states. Conversion of steplike facets to smooth facets can be controlled by increasing the reaction time through Ostwald ripening. The improved stability, photoresponsivity up to 0.3 A/W, on/off ratio up to 3900, and decreased photo response time to ∼160 μs show that the trap states can be annihilated effectively to improve the photoelectrical conversion with prolonged reaction time and elimination of steplike facets. Our findings demonstrate the relationship between the facet heterogeneity of SDP films and crystal growth process for the first time, and imply that the systematic control of crystal grain modification will enable amelioration of crystallinity for more-efficient perovskite photoelectrical applications.

Microstructure and Mechanical Properties of Fiber-Laser-Welded and Diode-Laser-Welded AZ31 Magnesium Alloy

NASA Astrophysics Data System (ADS)

Chowdhury, S. M.; Chen, D. L.; Bhole, S. D.; Powidajko, E.; Weckman, D. C.; Zhou, Y.

2011-07-01

The microstructures, tensile properties, strain hardening, and fatigue strength of fiber-laser-welded (FLW) and diode-laser-welded (DLW) AZ31B-H24 magnesium alloys were studied. Columnar dendrites near the fusion zone (FZ) boundary and equiaxed dendrites at the center of FZ, with divorced eutectic β-Mg17Al12 particles, were observed. The FLW joints had smaller dendrite cell sizes with a narrower FZ than the DLW joints. The heat-affected zone consisted of recrystallized grains. Although the DLW joints fractured at the center of FZ and exhibited lower yield strength (YS), ultimate tensile strength (UTS), and fatigue strength, the FLW joints failed at the fusion boundary and displayed only moderate reduction in the YS, UTS, and fatigue strength with a joint efficiency of ~91 pct. After welding, the strain rate sensitivity basically vanished, and the DLW joints exhibited higher strain-hardening capacity. Stage III hardening occurred after yielding in both base metal (BM) and welded samples. Dimple-like ductile fracture characteristics appeared in the BM, whereas some cleavage-like flat facets together with dimples and river marking were observed in the welded samples. Fatigue crack initiated from the specimen surface or near-surface defects, and crack propagation was characterized by the formation of fatigue striations along with secondary cracks.

Unidirectionally aligned line patterns driven by entropic effects on faceted surfaces

PubMed Central

Hong, Sung Woo; Huh, June; Gu, Xiaodan; Lee, Dong Hyun; Jo, Won Ho; Park, Soojin; Xu, Ting; Russell, Thomas P.

2012-01-01

A simple, versatile approach to the directed self-assembly of block copolymers into a macroscopic array of unidirectionally aligned cylindrical microdomains on reconstructed faceted single crystal surfaces or on flexible, inexpensive polymeric replicas was discovered. High fidelity transfer of the line pattern generated from the microdomains to a master mold is also shown. A single-grained line patterns over arbitrarily large surface areas without the use of top-down techniques is demonstrated, which has an order parameter typically in excess of 0.97 and a slope error of 1.1 deg. This degree of perfection, produced in a short time period, has yet to be achieved by any other methods. The exceptional alignment arises from entropic penalties of chain packing in the facets coupled with the bending modulus of the cylindrical microdomains. This is shown, theoretically, to be the lowest energy state. The atomic crystalline ordering of the substrate is transferred, over multiple length scales, to the block copolymer microdomains, opening avenues to large-scale roll-to-roll type and nanoimprint processing of perfectly patterned surfaces and as templates and scaffolds for magnetic storage media, polarizing devices, and nanowire arrays. PMID:22307591

The role of surface nonuniformity in controlling the initiation of a galvanic replacement reaction.

PubMed

Cobley, Claire M; Zhang, Qiang; Song, Wilbur; Xia, Younan

2011-06-06

The use of silver nanocrystals--asymmetrically truncated octahedrons and nanobars--characterized by a nonuniform surface as substrates for a galvanic replacement reaction was investigated. As the surfaces of these nanocrystals contain facets with a variety of different areas, shapes, and atomic arrangements, we were able to examine the roles of these parameters in different stages of the galvanic replacement reaction with HAuCl(4) (e.g., pitting, hollowing, pit closing, and pore formation), and thus obtain a deeper understanding of the reaction mechanism than is possible with silver nanocubes. We found that the most important of these parameters was the atomic arrangement, that is, whether the surface was capped by a {100} or {111} facet, and that the area and shape of the facet had essentially no effect on the initiation of the reaction. Interestingly, through the reaction with asymmetrically truncated octahedrons, we were also able to demonstrate that even when pitting occurred over a large area, this region would be sealed through a combination of atomic diffusion and deposition during the intermediate stages of the reaction. Consequently, even if pitting occurred across a large percentage of the nanocrystal surface, it was still possible to maintain the morphology of the template throughout the reaction. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stability, surface features, and atom leaching of palladium nanoparticles: toward prediction of catalytic functionality.

PubMed

Ramezani-Dakhel, Hadi; Mirau, Peter A; Naik, Rajesh R; Knecht, Marc R; Heinz, Hendrik

2013-04-21

Surfactant-stabilized metal nanoparticles have shown promise as catalysts although specific surface features and their influence on catalytic performance have not been well understood. We quantify the thermodynamic stability, the facet composition of the surface, and distinct atom types that affect rates of atom leaching for a series of twenty near-spherical Pd nanoparticles of 1.8 to 3.1 nm size using computational models. Cohesive energies indicate higher stability of certain particles that feature an approximate 60/20/20 ratio of {111}, {100}, and {110} facets while less stable particles exhibit widely variable facet composition. Unique patterns of atom types on the surface cause apparent differences in binding energies and changes in reactivity. Estimates of the relative rate of atom leaching as a function of particle size were obtained by the summation of Boltzmann-weighted binding energies over all surface atoms. Computed leaching rates are in good qualitative correlation with the measured catalytic activity of peptide-stabilized Pd nanoparticles of the same shape and size in Stille coupling reactions. The agreement supports rate-controlling contributions by atom leaching in the presence of reactive substrates. The computational approach provides a pathway to estimate the catalytic activity of metal nanostructures of engineered shape and size, and possible further refinements are described.

A Psychometric Evaluation of the Revised Temperament and Character Inventory (TCI-R) and the TCI-140

PubMed Central

Farmer, Richard F.; Goldberg, Lewis R.

2010-01-01

The psychometric properties of the newest version of the Temperament and Character Inventory, the TCI-R, were evaluated in a large (n = 727) community sample, as was the TCI-140, a short inventory derivative. Facets-to-scale confirmatory and exploratory factor analyses of the TCI-R did not support the organization of temperament and character facet scales within their superordinate domains. Five of the 29 facet scales also displayed relatively low internal consistency (α < .70). Factor analyses of the TCI-140 item set yielded only limited support for hypothesized item-to-scale memberships. Harm Avoidance, Novelty Seeking, and Self-directedness items, in particular, were not well differentiated. Although psychometrically comparable, the TCI-R and the TCI-140 demonstrate many of the limitations of earlier inventory versions. Implications associated with the use of the TCI-R and TCI-140 and Cloninger’s theory of personality are discussed. PMID:18778164

Spiritual quality of life and spiritual coping: evidence for a two-factor structure of the WHOQOL spirituality, religiousness, and personal beliefs module.

PubMed

Krägeloh, Christian U; Billington, D Rex; Henning, Marcus A; Chai, Penny Pei Minn

2015-02-25

The WHOQOL-SRPB has been a useful module to measure aspects of QOL related to spirituality, religiousness, and personal beliefs, but recent research has pointed to potential problems with its proposed factor structure. Three of the eight facets of the WHOQOL-SRPB have been identified as potentially different from the others, and to date only a limited number of factor analyses of the instrument have been published. Analyses were conducted using data from a sample of 679 university students who had completed the WHOQOL-BREF quality of life questionnaire, the WHOQOL-SRPB module, the Perceived Stress scale, and the Brief COPE coping strategies questionnaire. Informed by these analyses, confirmatory factor analyses suitable for ordinal-level data explored the potential for a two-factor solution as opposed to the originally proposed one-factor solution. The facets WHOQOL-SRPB facets connected, strength, and faith were highly correlated with each other as well as with the religious coping sub-scale of the Brief COPE. Combining these three facets to one factor in a two-factor solution for the WHOQOL-SRPB yielded superior goodness-of-fit indices compared to the original one-factor solution. A two-factor solution for the WHOQOL-SRPB is more tenable, in which three of the eight WHOQOL-SRPB facets group together as a spiritual coping factor and the remaining facets form a factor of spiritual quality of life. While discarding the facets connectedness, strength, and faith without additional research would be premature, users of the scale need to be aware of this alternative two-factor structure, and may wish to analyze scores using this structure.

Multi-facet concentrator of solar setup for irradiating the objects placed in a target plane with solar light

DOEpatents

Lewandowski, Allan A.; Yampolskiy, Vladislav; Alekseev, Valerie; Son, Valentin

2001-01-01

According to the proposed invention, this technical result is achieved so that many-facet concentrator of a solar setup for exposure of objects, placed in a target plane, to the action of solar radiation containing a supporting frame and facets differing by that the facets of the concentrator are chosen with spherical focusing reflective surfaces of equal focal lengths and with selective coatings reflecting a desired spectral fraction of solar radiation, and are arranged on the supporting frame symmetrically with respect to the common axis of the concentrator, their optical axes being directed to the single point on the optical axis of the concentrator located before the nominal focus point of the concentrator and determining the position of arranging the target plane.

Atomic scale study of surface orientations and energies of Ti 2 O 3 crystals

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

Gu, Meng; Wang, Zhiguo; Wang, Chongmin

2017-10-30

For nanostructured particles, the faceting planes and their terminating chemical species are two critical factors that govern the chemical behavior of the particle. The surface atomistic structure and termination of the Ti2O3 crystals were analyzed using atomic-scale aberration-corrected scanning transmission electron microscopy (STEM) combining with density functional theory (DFT) calculations. STEM imaging reveals that the Ti2O3 crystal are most often faceted along (001), (012), (-114) and (1-20) planes. DFT calculation indicates that the (012) surface with TiO-termination have the lowest cleavage energy and correspondingly the lowest surface energy, indicating that (012) will be the most stable and prevalent surfaces inmore » Ti2O3 nanocrystals. These observations provide insights for exploring the interfacial process involving Ti2O3 nanoparticles.« less

Small nanoparticles, surface geometry and contact forces.

PubMed

Takato, Yoichi; Benson, Michael E; Sen, Surajit

2018-03-01

In this molecular dynamics study, we examine the local surface geometric effects of the normal impact force between two approximately spherical nanoparticles that collide in a vacuum. Three types of surface geometries-(i) crystal facets, (ii) sharp edges, and (iii) amorphous surfaces of small nanoparticles with radii R <10 nm-are considered. The impact forces are compared with their macroscopic counterparts described by nonlinear contact forces based on Hertz contact mechanics. In our simulations, edge and amorphous surface contacts with weak surface energy reveal that the average impact forces are in excellent agreement with the Hertz contact force. On the other hand, facet collisions show a linearly increasing force with increasing compression. Our results suggest that the nearly spherical nanoparticles are likely to enable some nonlinear dynamic phenomena, such as breathers and solitary waves observed in granular materials, both originating from the nonlinear contact force.

Shape-dependence of the thermal and photochemical reactions of methanol on nanocrystalline anatase TiO2

NASA Astrophysics Data System (ADS)

Bennett, David A.; Cargnello, Matteo; Diroll, Benjamin T.; Murray, Christopher B.; Vohs, John M.

2016-12-01

Structure-activity relationships and the influence of particle size and shape on the partial- and photo-oxidation of methanol on nanocrystalline anatase TiO2 were investigated using temperature-programmed desorption. The study employed two distinct nanoparticle morphologies: truncated bipyramids exposing primarily {101} facets, and flatter platelets exposing primarily {001} surfaces, whose nominal sizes ranged from 10 to 25 nm. The platelets were found to be more active for thermally-driven reactions, such as coupling of methoxide groups to produce dimethyl ether, and deoxygenation to produce methane. A dependence of the reactivity of {001} facets for the coupling of methoxide groups to produce dimethyl ether on facet size was also observed. In contrast to the thermally-driven reactions, the bipyramidal nanoparticles were observed to be more active for a range of photochemical reactions, including oxidation and coupling to produce methyl formate, and photo-decomposition of surface methoxide species. This study also shows how well-defined nanocrystals can be used to help bridge the materials gap between studies of single crystal model catalysts and their high surface area industrial analogs.

Asymmetric shape transitions of epitaxial quantum dots

PubMed Central

2016-01-01

We construct a two-dimensional continuum model to describe the energetics of shape transitions in fully faceted epitaxial quantum dots (strained islands) via minimization of elastic energy and surface energy at fixed volume. The elastic energy of the island is based on a third-order approximation, enabling us to consider shape transitions between pyramids, domes, multifaceted domes and asymmetric intermediate states. The energetics of the shape transitions are determined by numerically calculating the facet lengths that minimize the energy of a given island type of prescribed island volume. By comparing the energy of different island types with the same volume and analysing the energy surface as a function of the island shape parameters, we determine the bifurcation diagram of equilibrium solutions and their stability, as well as the lowest barrier transition pathway for the island shape as a function of increasing volume. The main result is that the shape transition from pyramid to dome to multifaceted dome occurs through sequential nucleation of facets and involves asymmetric metastable transition shapes. We also explicitly determine the effect of corner energy (facet edge energy) on shape transitions and interpret the results in terms of the relative stability of asymmetric island shapes as observed in experiment. PMID:27436989

Electrons to Reactors Multiscale Modeling: Catalytic CO Oxidation over RuO 2

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

Sutton, Jonathan E.; Lorenzi, Juan M.; Krogel, Jaron T.

First-principles kinetic Monte Carlo (1p-kMC) simulations for CO oxidation on two RuO 2 facets, RuO 2(110) and RuO 2(111), were coupled to the computational fluid dynamics (CFD) simulations package MFIX, and reactor-scale simulations were then performed. 1p-kMC coupled with CFD has recently been shown as a feasible method for translating molecular scale mechanistic knowledge to the reactor scale, enabling comparisons to in situ and online experimental measurements. Only a few studies with such coupling have been published. This work incorporates multiple catalytic surface facets into the scale-coupled simulation, and three possibilities were investigated: the two possibilities of each facet individuallymore » being the dominant phase in the reactor, and also the possibility that both facets were present on the catalyst particles in the ratio predicted by an ab initio thermodynamics-based Wulff construction. When lateral interactions between adsorbates were included in the 1p-kMC simulations, the two surfaces, RuO 2(110) and RuO 2(111), were found to be of similar order-of-magnitude in activity for the pressure range of 1 × 10 –4 bar to 1 bar, with the RuO 2(110) surface-termination showing more simulated activity than the RuO 2(111) surface-termination. Coupling between the 1p-kMC and CFD was achieved with a lookup table generated by the error-based modified Shepard interpolation scheme. Isothermal reactor scale simulations were performed and compared to two separate experimental studies, conducted with reactant partial pressures of ≤0.1 bar. Simulations without an isothermality restriction were also conducted and showed that the simulated temperature gradient across the catalytic reactor bed is <0.5 K, which validated the use of the isothermality restriction for investigating the reactor-scale phenomenological temperature dependences. The approach with the Wulff construction based reactor simulations reproduced a trend similar to one experimental data set relatively well, with the (110) surface being more active at higher temperaures; in contrast, for the other experimental data set, our reactor simulations achieve surprisingly and perhaps fortuitously good agreement with the activity and phenomenological pressure dependence when it is assumed that the (111) facet is the only active facet present. Lastly, the active phase of catalytic CO oxidation over RuO 2 remains unsettled, but the present study presents proof of principle (and progress) toward more accurate multiscale modeling from electrons to reactors and new simulation results.« less

Electrons to Reactors Multiscale Modeling: Catalytic CO Oxidation over RuO 2

DOE PAGES

Sutton, Jonathan E.; Lorenzi, Juan M.; Krogel, Jaron T.; ...

2018-04-20

First-principles kinetic Monte Carlo (1p-kMC) simulations for CO oxidation on two RuO 2 facets, RuO 2(110) and RuO 2(111), were coupled to the computational fluid dynamics (CFD) simulations package MFIX, and reactor-scale simulations were then performed. 1p-kMC coupled with CFD has recently been shown as a feasible method for translating molecular scale mechanistic knowledge to the reactor scale, enabling comparisons to in situ and online experimental measurements. Only a few studies with such coupling have been published. This work incorporates multiple catalytic surface facets into the scale-coupled simulation, and three possibilities were investigated: the two possibilities of each facet individuallymore » being the dominant phase in the reactor, and also the possibility that both facets were present on the catalyst particles in the ratio predicted by an ab initio thermodynamics-based Wulff construction. When lateral interactions between adsorbates were included in the 1p-kMC simulations, the two surfaces, RuO 2(110) and RuO 2(111), were found to be of similar order-of-magnitude in activity for the pressure range of 1 × 10 –4 bar to 1 bar, with the RuO 2(110) surface-termination showing more simulated activity than the RuO 2(111) surface-termination. Coupling between the 1p-kMC and CFD was achieved with a lookup table generated by the error-based modified Shepard interpolation scheme. Isothermal reactor scale simulations were performed and compared to two separate experimental studies, conducted with reactant partial pressures of ≤0.1 bar. Simulations without an isothermality restriction were also conducted and showed that the simulated temperature gradient across the catalytic reactor bed is <0.5 K, which validated the use of the isothermality restriction for investigating the reactor-scale phenomenological temperature dependences. The approach with the Wulff construction based reactor simulations reproduced a trend similar to one experimental data set relatively well, with the (110) surface being more active at higher temperaures; in contrast, for the other experimental data set, our reactor simulations achieve surprisingly and perhaps fortuitously good agreement with the activity and phenomenological pressure dependence when it is assumed that the (111) facet is the only active facet present. Lastly, the active phase of catalytic CO oxidation over RuO 2 remains unsettled, but the present study presents proof of principle (and progress) toward more accurate multiscale modeling from electrons to reactors and new simulation results.« less

Facet joint disturbance induced by miniscrews in plated cervical laminoplasty

PubMed Central

Chen, Hua; Li, Huibo; Wang, Beiyu; Li, Tao; Gong, Quan; Song, Yueming; Liu, Hao

2016-01-01

Abstract A retrospective cohort study. Plated cervical laminoplasty is an increasingly common technique. A unique facet joint disturbance induced by lateral mass miniscrews penetrating articular surface was noticed. Facet joints are important to maintain cervical spine stability and kinetic balance. Whether this facet joint disturbance could affect clinical and radiologic results is still unknown. The objective of this study is to investigate the clinical and radiologic outcomes of patients with facet joints disturbance induced by miniscrews in plated cervical laminoplasty. A total of 105 patients who underwent cervical laminoplasty with miniplate fixation between May 2010 and February 2014 were comprised. Postoperative CT images were used to identify whether facet joints destroyed by miniscrews. According to facet joints destroyed number, all the patients were divided into: group A (none facet joint destroyed), group B (1–2 facet joints destroyed), and group C (≥3 facet joints destroyed). Clinical data (JOA, VAS, and NDI scores), radiologic data (anteroposterior diameter and Palov ratio), and complications (axial symptoms and C5 palsy) were evaluated and compared among the groups. There were 38, 40, and 27 patients in group A, B, and C, respectively. The overall facet joints destroyed rate was 30.7%. All groups gained significant JOA and NDI scores improvement postoperatively. The preoperative JOA, VAS, NDI scores, and postoperative JOA scores did not differ significantly among the groups. The group C recorded significant higher postoperative VAS scores than group A (P = 0.002) and B (P = 0.014) and had significant higher postoperative NDI scores than group A (P = 0.002). The pre- and postoperative radiologic data were not significant different among the groups. The group C had a significant higher axial symptoms incidence than group A (12/27 vs 8/38, P = 0.041). Facet joints disturbance caused by miniscrews in plated cervical laminoplasty may not influence neurological recovery and spinal canal expansion, but may negatively affect postoperative axial symptoms. PMID:27661016

Oxidation of CO by NO on planar and faceted Ir(210)

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

Chen, Wenhua; Bartynski, Robert A.; Kaghazchi, Payam

2012-06-11

Oxidation of CO by pre-adsorbed NO has been studied on planar Ir(210) and nanofaceted Ir(210) with average facet sizes of 5 nm and 14 nm by temperature programmed desorption (TPD). Both surfaces favor oxidation of CO to CO 2, which is accompanied by simultaneous reduction of NO with high selectivity to N 2. At low NO pre-coverage, the temperature (T i) for the onset of CO 2 desorption as well as CO 2 desorption peak temperature (T p) decreases with increasing CO exposure, and NO dissociation is affected by co-adsorbed CO. At high NO pre-coverage, T i and T pmore » are independent of CO exposure, and co-adsorbed CO has no influence on dissociation of NO. Moreover, at low NO pre-coverage, planar Ir(210) is more active than faceted Ir(210) for oxidation of CO to CO 2: T i and T p are much lower on planar Ir(210) than that on faceted Ir(210). In addition, faceted Ir(210) with an average facet size of 5 nm is more active for oxidation of CO to CO 2 than faceted Ir(210) with an average facet size of 14 nm, i.e., oxidation of CO by pre-adsorbed NO on faceted Ir(210) exhibits size effects on the nanometer scale. In comparison, at low O pre-coverage planar Ir(210) is more active than faceted Ir(210) for oxidation of CO to CO 2 but no evidence has been found for size effects in oxidation of CO by pre-adsorbed oxygen on faceted Ir(210) for average facet sizes of 5 nm and 14 nm. The TPD data indicate the same reaction pathway for CO 2 formation from CO + NO and CO + O reactions on planar Ir(210). Lastly, the adsorption sites of CO, NO, O, CO + O, and CO + NO on Ir are characterized by density functional theory.« less

Radiological analysis of minimal safe distance and optimal screw angle to avoid facet violation in open-door laminoplasty using precontoured plate.

PubMed

Min, Woo-Kie; Seo, Il; Na, Sang-Bong; Choi, Young-Seo; Choi, Ji-Yeon

2017-01-01

This study aimed to present radiologic analysis of minimal safe distance (MSD) and optimal screw angle (OSA) that enables to fix screws in a lateral mass safely without facet joint violation in open-door laminoplasty using a plate. A retrospective analysis was made of 22 patients (male: 17; female: 5), average age 62 years. Seventy-nine lateral mass screws were fixed among a total of 158 screws. MSD that doesn't allow 5-mm screws to violate a facet joint was measured for C3-C7 and a comparative analysis was performed. If the MSD is not secured, the OSA to be given to the cephalad direction is calculated to avoid violation of the facet joint. The screws violating inferior facet joints accounted for 34.1% of the screws fixed in inferior lateral mass. Joint surface to distal mini-screw distances were 3.18 ± 1.46 mm and 4.75 ± 1.71 mm in groups of facet joint violation and non-facet violation (FV), respectively ( p = 0.001). When 5-mm screws were inserted into a lateral mass, MSD was 4.39 ± 0.83 mm. The average MSD of C3, C4, and C5 was 4.05 ± 0.78 mm, 4.10 ± 0.70 mm, and 4.26 ± 0.74 mm, respectively. There was no significant differences among levels ( p > 0.05). The average MSD of C6 and C7 was 4.92 ± 0.81 mm and 4.80 ± 0.96 mm, respectively, showing significant differences from those of C3, C4, and C5 ( p < 0.05). If 6 mm of the MSD isn't secured, OSA showed in the cephalad direction of 11.5° for 5 mm and 22° for 4 mm approximately. We suggest that mini-screw on lateral mass can be fixed safely without FV, if they are fixed at MSD of 6 mm from a joint surface. Facet joint violation doesn't occur if an OSA is given in the cephalad direction in case of not enough MSD for mini-screws.

Optimal area of lateral mass mini-screws implanted in plated cervical laminoplasty: a radiography anatomy study.

PubMed

Chen, Hua; Li, Huibo; Deng, Yuxiao; Rong, Xin; Gong, Quan; Li, Tao; Song, Yueming; Liu, Hao

2017-04-01

Lateral mass mini-screws used in plated cervical laminoplasty might penetrate into facet joints. The objective is to observe this complication incidence and to identify the optimal areas for 5- and 7-mm-long mini-screws to implant on lateral mass. 47 patients who underwent plated cervical laminoplasty were included. The optimal area for mini-screws implanting was set according to pre-operative 3D CT reconstruction data. Then, each posterior-lateral mass surface was divided into three regions: 7-mm region, 5-mm region, and dangerous area. The mini-screw implanted region was recorded. Post-operative CT images were used to identify whether the mini-screws penetrated into facet joints. 235 mini-plates and 470 lateral mass mini-screws were used in the study. 117 (24.9%) mini-screws penetrated 88 (37.4%) facet joints. The 5-mm-long mini-screw optimal area occupied the upper 72, 65, 65, 64, and 65 % area of the posterior-lateral mass surface for C3-7, while the 7-mm-long mini-screw optimal area encompassed the upper 54, 39, 40, 33, and 32 %. Only 7-mm-long mini-screws were used to fix the plate to the lateral mass. 4 of 240 mini-screws in 7-mm region, 67 of the 179 mini-screws in 5-mm region, and 46 of the 51 mini-screws in dangerous region penetrated into the facet joint. The differences in the rate of facet joint penetration related to region were statistically significant (P < 0.001). The facet joint destruction by mini-screws was not a rare complication in plated cervical laminoplasty. The optimal areas we proposed may help guide the mini-screw implantation positions.

Method of forming oriented block copolymer line patterns, block copolymer line patterns formed thereby, and their use to form patterned articles

DOEpatents

Russell, Thomas P.; Hong, Sung Woo; Lee, Doug Hyun; Park, Soojin; Xu, Ting

2015-10-13

A block copolymer film having a line pattern with a high degree of long-range order is formed by a method that includes forming a block copolymer film on a substrate surface with parallel facets, and annealing the block copolymer film to form an annealed block copolymer film having linear microdomains parallel to the substrate surface and orthogonal to the parallel facets of the substrate. The line-patterned block copolymer films are useful for the fabrication of magnetic storage media, polarizing devices, and arrays of nanowires.

Method of forming oriented block copolymer line patterns, block copolymer line patterns formed thereby, and their use to form patterned articles

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

Russell, Thomas P.; Hong, Sung Woo; Lee, Dong Hyun

A block copolymer film having a line pattern with a high degree of long-range order is formed by a method that includes forming a block copolymer film on a substrate surface with parallel facets, and annealing the block copolymer film to form an annealed block copolymer film having linear microdomains parallel to the substrate surface and orthogonal to the parallel facets of the substrate. The line-patterned block copolymer films are useful for the fabrication of magnetic storage media, polarizing devices, and arrays of nanowires.

Surface roughness estimation by inversion of the Hapke photometric model on optical data simulated using a ray tracing code

NASA Astrophysics Data System (ADS)

Champion, J.; Ristorcelli, T.; Ferrari, C. C.; Briottet, X.; Jacquemoud, S.

2013-12-01

Surface roughness is a key physical parameter that governs various processes (incident radiation distribution, temperature, erosion,...) on Earth and other Solar System objects. Its impact on the scattering function of incident electromagnetic waves is difficult to model. In the 80's, Hapke provided an approximate analytic solution for the bidirectional reflectance distribution function (BRDF) of a particulate medium and, later on, included the effect of surface roughness as a correction factor for the BRDF of a smooth surface. This analytical radiative transfer model is widely used in solar system science whereas its ability to remotely determine surface roughness is still a question at issue. The validation of the Hapke model has been only occasionally undertaken due to the lack of radiometric data associated with field measurement of surface roughness. We propose to validate it on Earth, on several volcanic terrains for which very high resolution digital elevation models are available at small scale. We simulate the BRDF of these DEMs thanks to a ray-tracing code and fit them with the Hapke model to retrieve surface roughness. The mean slope angle of the facets, which quantifies surface roughness, can be fairly well retrieved when most conditions are met, i.e. a random-like surface and little multiple scattering between the facets. A directional sensitivity analysis of the Hapke model confirms that both surface intrinsic optical properties (facet's reflectance or single scattering albedo) and roughness are the most influential variables on ground BRDFs. Their interactions in some directions explain why their separation may be difficult, unless some constraints are introduced in the inversion process. Simulation of soil surface BRDF at different illumination and viewing angles

Reverse Non-Equilibrium Molecular Dynamics Demonstrate That Surface Passivation Controls Thermal Transport at Semiconductor-Solvent Interfaces.

PubMed

Hannah, Daniel C; Gezelter, J Daniel; Schaller, Richard D; Schatz, George C

2015-06-23

We examine the role played by surface structure and passivation in thermal transport at semiconductor/organic interfaces. Such interfaces dominate thermal transport in semiconductor nanomaterials owing to material dimensions much smaller than the bulk phonon mean free path. Utilizing reverse nonequilibrium molecular dynamics simulations, we calculate the interfacial thermal conductance (G) between a hexane solvent and chemically passivated wurtzite CdSe surfaces. In particular, we examine the dependence of G on the CdSe slab thickness, the particular exposed crystal facet, and the extent of surface passivation. Our results indicate a nonmonotonic dependence of G on ligand-grafting density, with interfaces generally exhibiting higher thermal conductance for increasing surface coverage up to ∼0.08 ligands/Å(2) (75-100% of a monolayer, depending on the particular exposed facet) and decreasing for still higher coverages. By analyzing orientational ordering and solvent penetration into the ligand layer, we show that a balance of competing effects is responsible for this nonmonotonic dependence. Although the various unpassivated CdSe surfaces exhibit similar G values, the crystal structure of an exposed facet nevertheless plays an important role in determining the interfacial thermal conductance of passivated surfaces, as the density of binding sites on a surface determines the ligand-grafting densities that may ultimately be achieved. We demonstrate that surface passivation can increase G relative to a bare surface by roughly 1 order of magnitude and that, for a given extent of passivation, thermal conductance can vary by up to a factor of ∼2 between different surfaces, suggesting that appropriately tailored nanostructures may direct heat flow in an anisotropic fashion for interface-limited thermal transport.

Optimization of spherical facets for parabolic solar concentrators

NASA Technical Reports Server (NTRS)

White, J. E.; Erikson, R. J.; Sturgis, J. D.; Elfe, T. B.

1986-01-01

Solar concentrator designs which employ deployable hexagonal panels are being developed for space power systems. An offset optical configuration has been developed which offers significant system level advantages over previously proposed collector designs for space applications. Optical analyses have been performed which show offset reflector intercept factors to be only slightly lower than those for symmetric reflectors with the same slope error. Fluxes on the receiver walls are asymmetric but manageable by varying the tilt angle of the receiver. Greater producibility is achieved by subdividing the hexagonal panels into triangular mirror facets of spherical contour. Optical analysis has been performed upon these to yield near-optimum sizes and radii.

Solvothermal synthesis of TiO2 nanocrystals with {001} facets using titanic acid nanobelts for superior photocatalytic activity

NASA Astrophysics Data System (ADS)

Cao, Yuhui; Zong, Lanlan; Li, Qiuye; Li, Chen; Li, Junli; Yang, Jianjun

2017-01-01

Anatase TiO2 nanocrystals exposed with {001} facets were fabricated by solvothermal strategy in HF-C4H9OH mixed solution, using titanic acid nanobelts (TAN) as a precursor. The shape of TAN is a long flat plane with a high aspect ratio, and F- is easily adsorbed on the surface of the nanobelts, inducing a higher exposure of {001} facet of TiO2 nanoparticles during the structure reorganization. The exposed percentage of {001} facets could vary from 40 to 77% by adjusting the amount of HF. The as-prepared samples were characterized by transmission electron microscopy, N2 adsorption-desorption isotherms, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscope. The photocatalytic measurement showed that TiO2 nanocrystals with 77% {001} facets exhibited much superior photocatalytic activity for photodegradation of methyl orange, methylene blue, and rhodamine B. And what's more, the mineralization rate of methyl orange was as high as 96% within 60 min. The photocatalytic enhancement is due to a large amount of the high energetic {001} facets exposing, the special truncated octahedral morphology and a stronger ability for dyes adsorption.

Atomic scale study of surface orientations and energies of Ti 2O 3 crystals

DOE PAGES

Gu, Meng; Wang, Zhiguo; Wang, Chongmin; ...

2017-11-01

For nanostructured particles, the faceting planes and their terminating chemical species are two critical factors that govern their chemical behavior. In this paper, the surface atomistic structure and termination of Ti 2O 3 crystals were analyzed using atomic-scale aberration-corrected scanning transmission electron microscopy (STEM) combined with density functional theory (DFT) calculations. STEM imaging reveals that the Ti 2O 3 crystals are most often faceted along (001), (012), (-114), and (1–20) planes. The DFT calculation indicates that the (012) surface with TiO-termination has the lowest cleavage energy and correspondingly the lowest surface energy, indicating that (012) will be the most stablemore » and prevalent surfaces in Ti 2O 3 nanocrystals. Finally, these observations provide insights for exploring the interfacial process involving Ti 2O 3 nanoparticles.« less

Development of image mappers for hyperspectral biomedical imaging applications

PubMed Central

Kester, Robert T.; Gao, Liang; Tkaczyk, Tomasz S.

2010-01-01

A new design and fabrication method is presented for creating large-format (>100 mirror facets) image mappers for a snapshot hyperspectral biomedical imaging system called an image mapping spectrometer (IMS). To verify this approach a 250 facet image mapper with 25 multiple-tilt angles is designed for a compact IMS that groups the 25 subpupils in a 5 × 5 matrix residing within a single collecting objective's pupil. The image mapper is fabricated by precision diamond raster fly cutting using surface-shaped tools. The individual mirror facets have minimal edge eating, tilt errors of <1 mrad, and an average roughness of 5.4 nm. PMID:20357875

Surface faceting and elemental diffusion behaviour at atomic scale for alloy nanoparticles during in situ annealing

PubMed Central

Chi, Miaofang; Wang, Chao; Lei, Yinkai; Wang, Guofeng; Li, Dongguo; More, Karren L.; Lupini, Andrew; Allard, Lawrence F.; Markovic, Nenad M.; Stamenkovic, Vojislav R.

2015-01-01

The catalytic performance of nanoparticles is primarily determined by the precise nature of the surface and near-surface atomic configurations, which can be tailored by post-synthesis annealing effectively and straightforwardly. Understanding the complete dynamic response of surface structure and chemistry to thermal treatments at the atomic scale is imperative for the rational design of catalyst nanoparticles. Here, by tracking the same individual Pt3Co nanoparticles during in situ annealing in a scanning transmission electron microscope, we directly discern five distinct stages of surface elemental rearrangements in Pt3Co nanoparticles at the atomic scale: initial random (alloy) elemental distribution; surface platinum-skin-layer formation; nucleation of structurally ordered domains; ordered framework development and, finally, initiation of amorphization. Furthermore, a comprehensive interplay among phase evolution, surface faceting and elemental inter-diffusion is revealed, and supported by atomistic simulations. This work may pave the way towards designing catalysts through post-synthesis annealing for optimized catalytic performance. PMID:26576477

Surface faceting and elemental diffusion behaviour at atomic scale for alloy nanoparticles during in situ annealing

DOE PAGES

Chi, Miaofang; Wang, Chao; Lei, Yinkai; ...

2015-11-18

The catalytic performance of nanoparticles is primarily determined by the precise nature of the surface and near-surface atomic configurations, which can be tailored by post-synthesis annealing effectively and straightforwardly. Understanding the complete dynamic response of surface structure and chemistry to thermal treatments at the atomic scale is imperative for the rational design of catalyst nanoparticles. Here, by tracking the same individual Pt 3Co nanoparticles during in situ annealing in a scanning transmission electron microscope, we directly discern five distinct stages of surface elemental rearrangements in Pt 3Co nanoparticles at the atomic scale: initial random (alloy) elemental distribution; surface platinum-skin-layer formation;more » nucleation of structurally ordered domains; ordered framework development and, finally, initiation of amorphization. Furthermore, a comprehensive interplay among phase evolution, surface faceting and elemental inter-diffusion is revealed, and supported by atomistic simulations. In conlcusion, this work may pave the way towards designing catalysts through post-synthesis annealing for optimized catalytic performance.« less

High-power single-stage thulium-doped superfluorescent fiber source

NASA Astrophysics Data System (ADS)

Hu, Z. Y.; Yan, P.; Liu, Q.; Ji, E. C.; Xiao, Q. R.; Gong, M. L.

2015-01-01

In this paper, we report a high-power thulium (Tm)-doped superfluorescent fiber source (SFS) in the 2-μm spectral region. The SFS is based on double angle-cleaved facet operation and uses a simple single-stage geometry. The copropagating amplified spontaneous emission (ASE) yields a maximum output of 20.7 W at a center wavelength of 1,960.7 nm, with a full width at half maximum (FWHM) of ~45 nm. The counterpropagating ASE yields a maximum output of 25.2 W at a center wavelength of 1,948.2 nm, with a FWHM of ~50 nm. The maximum combined output of the SFS is as much as 45.9 W, which corresponds to a slope efficiency of 38.9 %. In addition, a model of the ~2 μm SFS in Tm-doped silica fibers pumped at ~790 nm is developed, and the influence of fiber length and end-facet reflectivity on the ASE output performance and the parasitic lasing threshold are studied numerically.

Self-Healing Thermal Annealing: Surface Morphological Restructuring Control of GaN Nanorods

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

Conroy, Michele; Li, Haoning; Zubialevich, Vitaly Z.

With advances in nanolithography and dry etching, top-down methods of nanostructuring have become a widely used tool for improving the efficiency of optoelectronics. These nano dimensions can offer various benefits to the device performance in terms of light extraction and efficiency, but often at the expense of emission color quality. Broadening of the target emission peak and unwanted yellow luminescence are characteristic defect-related effects due to the ion beam etching damage, particularly for III–N based materials. In this article we focus on GaN based nanorods, showing that through thermal annealing the surface roughness and deformities of the crystal structure canmore » be “self-healed”. Correlative electron microscopy and atomic force microscopy show the change from spherical nanorods to faceted hexagonal structures, revealing the temperature-dependent surface morphology faceting evolution. The faceted nanorods were shown to be strain- and defect-free by cathodoluminescence hyperspectral imaging, micro-Raman, and transmission electron microscopy (TEM). In-situ TEM thermal annealing experiments allowed for real time observation of dislocation movements and surface restructuring observed in ex-situ annealing TEM sampling. This thermal annealing investigation gives new insight into the redistribution path of GaN material and dislocation movement post growth, allowing for improved understanding and in turn advances in optoelectronic device processing of compound semiconductors.« less

In vivo facet joint loading of the canine lumbar spine.

PubMed

Buttermann, G R; Schendel, M J; Kahmann, R D; Lewis, J L; Bradford, D S

1992-01-01

This study describes a technique to measure in vivo loads and the resultant load-contact locations in the facet joint of the canine lumbar spine. The technique is a modification of a previously described in vitro method that used calibrated surface strains of the lateral aspect of the right L3 cranial articular process. In the present study, strains were measured during various in vivo static and dynamic activities 3 days after strain gage implantation. The in vivo recording technique and its errors, which depend on the location of the applied facet loads, is described. The results of applying the technique to five dogs gave the following results. Relative resultant contact load locations on the facet tended to be in the central and caudal portion of the facet in extension activities, central and cranial in standing, and cranial and ventral in flexion or right-turning activities. Right-turning contact locations were ventral and cranial to left-turning locations. Resultant load locations at peak loading during walking were in the central region of the facet, whereas resultant load locations at minimum loading during walking were relatively craniad. This resultant load-contact location during a walk gait cycle typically migrated in an arc with a displacement of 4 mm from minimum to maximum loading. Static tests resulted in a range of facet loads of 0 N in flexion and lying to 185 N for two-legged standing erect, and stand resulted in facet loads of 26 +/- 15 N (mean +/- standard deviation [SD]). Dynamic tests resulted in peak facet loads ranging from 55 N while walking erect to 170 N for climbing up stairs. Maximum walk facet loads were 107 +/- 27 N. The technique is applicable to in vivo studies of a canine facet joint osteoarthritis model and may be useful for establishing an understanding of the biomechanics of low-back pain.

Evolution of triangular topographic facets along active normal faults

NASA Astrophysics Data System (ADS)

Balogun, A.; Dawers, N. H.; Gasparini, N. M.; Giachetta, E.

2011-12-01

Triangular shaped facets, which are generally formed by the erosion of fault - bounded mountain ranges, are arguably one of the most prominent geomorphic features on active normal fault scarps. Some previous studies of triangular facet development have suggested that facet size and slope exhibit a strong linear dependency on fault slip rate, thus linking their growth directly to the kinematics of fault initiation and linkage. Other studies, however, generally conclude that there is no variation in triangular facet geometry (height and slope) with fault slip rate. The landscape of the northeastern Basin and Range Province of the western United States provides an opportunity for addressing this problem. This is due to the presence of well developed triangular facets along active normal faults, as well as spatial variations in fault scale and slip rate. In addition, the Holocene climatic record for this region suggests a dominant tectonic regime, as the faulted landscape shows little evidence of precipitation gradients associated with tectonic uplift. Using GIS-based analyses of USGS 30 m digital elevation data (DEMs) for east - central Idaho and southwestern Montana, we analyze triangular facet geometries along fault systems of varying number of constituent segments. This approach allows us to link these geometries with established patterns of along - strike slip rate variation. For this study, we consider major watersheds to include only catchments with upstream and downstream boundaries extending from the drainage divide to the mapped fault trace, respectively. In order to maintain consistency in the selection criteria for the analyzed triangular facets, only facets bounded on opposite sides by major watersheds were considered. Our preliminary observations reflect a general along - strike increase in the surface area, average slope, and relief of triangular facets from the tips of the fault towards the center. We attribute anomalies in the along - strike geometric measurements of the triangular facets to represent possible locations of fault segment linkage associated with normal fault evolution.

Effect of nickel monolayer deposition on the structural and electronic properties of the low miller indices of (bcc) iron: A DFT study

NASA Astrophysics Data System (ADS)

Kwawu, Caroline R.; Tia, Richard; Adei, Evans; Dzade, Nelson Y.; Catlow, C. Richard A.; de Leeuw, Nora H.

2017-04-01

Metal clusters of both iron (Fe) and nickel (Ni) have been found in nature as active electro-catalytic sites, for example in the enzyme carbon mono-oxide dehydrogenase found in autotrophic organisms. Thus, surface modification of iron with nickel could improve the surface work function to enhance catalytic applications. The effects of surface modifications of iron by nickel on the structural and electronic properties have been studied using spin-polarised density functional theory calculations within the generalised gradient approximation. The thermodynamically preferred sites for Ni adsorption on the Fe (100), (110) and (111) surfaces have been studied at varying monolayer coverages (including 0.25 ML and 1 ML). The work function of the bare Fe surfaces is found to be of the order (100) ∼ (111) < (110) i.e. 3.80 eV ∼ 3.84 eV < 4.76 eV, which is consistent with earlier studies. The adsorption energies show that monolayer Ni deposition is thermodynamically favoured on the (100) and (111) surfaces, but not on the (110) surface. Expansion of the first interlayer spacing (d12) of all three Fe surfaces is observed upon Ni deposition with the extent of expansion decreasing in the order (111) > (110) > (100), i.e. 6.78% > 5.76% > 1.99%. The extent of relaxation is magnified on the stepped (111) surface (by 1.09% to 30.88%), where the Ni coordination number is highest at 7 compared to 5 on the (100) facet and 4 on the (110) facet. The Ni deposition changes the work functions of the various surfaces due to charge reordering illustrated by charge density plots, where the work function is reduced only on the (110) surface by 0.04 eV, 0.16 eV and 0.17 eV at 1 ML, 0.5 ML and 0.25 ML respectively, with a concomitant increase in the surface dipole (polarity). This result implies enhanced electron activity and electrochemical reactivity on the most stable and therefore frequently occurring Ni-doped (110) facet compared to the clean (110) facet, which has implications for the development of improved Fe electro-catalysts (for example for CO2 activation and reduction). These findings improve our understanding of the role of surface topology and stability on the extent of Ni interactions with Fe surfaces and the extent to which the Fe surface structures and properties are altered by the Ni deposition.

Location Of Hole And Electron Traps On Nanocrystalline Anatase TiO2

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

Mercado, Candy C.; Knorr, Fritz J.; McHale, Jeanne L.

2012-05-17

The defect photoluminescence from TiO2 nanoparticles in the anatase phase is reported for nanosheets which expose predominantly (001) surfaces, and compared to that from conventional anatase nanoparticles which expose mostly (101) surfaces. Also reported is the weak defect photoluminescence of TiO2 nanotubes, which we find using electron back-scattered diffraction to consist of walls which expose (110) and (100) facets. The nanotubes exhibit photoluminescence that is blue-shifted and much weaker than that from conventional TiO2 nanoparticles. Despite the preponderance of (001) surfaces in the nanosheet samples, they exhibit photoluminescence similar to that of conventional nanoparticles. We assign the broad visible photoluminescencemore » of anatase nanoparticles to two overlapping distributions: hole trap emission associated with oxygen vacancies on (101) exposed surfaces, which peaks in the green, and a broader emission extending into the red which results from electron traps on under-coordinated titanium atoms, which are prevalent on (001) facets. The results of this study suggest how morphology of TiO2 nanoparticles could be optimized to control the distribution and activity of surface traps. Our results also shed light on the mechanism by which the TiCl4 surface treatment heals traps on anatase and mixed-phase TiO2 films, and reveals distinct differences in the trap-state distributions of TiO2 nanoparticles and nanotubes. The molecular basis for electron and hole traps and their spatial separation on different facets is discussed.« less

Surface morphological evolution of epitaxial CrN(001) layers

NASA Astrophysics Data System (ADS)

Frederick, J. R.; Gall, D.

2005-09-01

CrN layers, 57 and 230 nm thick, were grown on MgO(001) at Ts=600-800 °C by ultrahigh-vacuum magnetron sputter deposition in pure N2 discharges from an oblique deposition angle α=80°. Layers grown at 600 °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 °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 °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 Ts is raised from 600 to 700 to 800 °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 °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 β>0.5. In contrast, kinetic roughening controls the surface morphology for Ts=800 °C, as well as the epitaxial fraction of the layers grown at 600 and 700 °C, yielding relatively smooth surfaces and β<=0.27.

X-ray Fluorescence Observations of the Moon by SMART-1/D-CIXS

NASA Astrophysics Data System (ADS)

Grande, Manuel; Swinyard, B.; Joy, K. H.; Kellett, Barry J.; Crawford, Ian A.; Howe, Chris J.

2008-09-01

Introduction The SMART-1 mission to the Moon included in its payload D-CIXS, a compact X-ray spectrometer [1], [2] SMART-1 was a technology evaluation mission, and D-CIXS was the first of a new generation of planetary X-ray spectrometers. Novel technologies enabled new capabilities for measuring the fluorescent yield of a planetary surface or atmosphere which is illuminated by solar X-rays. During the extended SMART-1 cruise phase, observations of the Earth showed strong argon emission, providing a good source for calibration and demonstrating the potential of the technique. At the Moon, observations showed a first unambiguous remote sensing of calcium in the lunar regolith (Grande et al 2007) (Fig 1). Data obtained were broadly consistent with current understanding of mare and highland composition. Ground truth was provided by the returned Apollo and Luna sample sets. We have extended our observations to comparisons of Lunar near and farside, and by careful analysis enabled new elemental lines to be observed. Observations: In March, 2005, the SMART-1 spacecraft reached its nominal lunar orbit, and we began full commissioning for lunar operations. During the pre-commissioning period in mid-January, 2005, observations of the lunar surface were made which coincided with the occurrence of several major M and X class flares. This opportunity provided an excellent chance to observe spatially localized fluorescence from the lunar surface. X-ray fluorescent elemental lines from the lunar surface are detected by all three facets of D-CIXS while the XSM instrument observes the input solar spectrum. At the end of this interval, a long duration M-class solar flare began at 06:00 UTC on the 15th of January, 2005. The flare lasted for more than 1 hour but only ~30 minutes corresponded to D-CIXS observations. At this time SMART-1 was orbiting over the Moon's near-side eastern limb from about the equator, traveling northwards. As SMART-1 flew north, its altitude was also increasing from around 2100 km at 06:00 to ~3100 km at 06:35. Due to the nature of SMART-1's orbit and thermal dynamics, the spacecraft was performing a mid-orbit slew (rotation), and so D-CIXS's three facets had different surface ground tracks during the observation of interest. However, this variability in footprints was very fortuitous as the instrument FOVs included areas of both mare basalt and highland lithologies, which have different and recognizable elemental signatures. Facet 1 (thin Al-filter, 12º FOV) was oriented throughout the observation toward highland areas to the northeast of Mare Crisium. Facet 3 (Mg-filter, 12º FOV) had a ground track that crossed Mare Crisium. Due to the 12º FOV and the 2100 km altitude, the facet 3 footprint always contains a mixture of mare and highland regions. The footprint of facet 2 (thin Alfilter, 8º FOV) encompassed the regions between the two facets shown and covered a mixture of mare and highland regions but with a smaller signal due to its narrower FOV. Fig. 1 shows the particle background corrected spectra from summed data of the 3 D-CIXS facets for the interval 06:00 UTC to 06:35 UTC. Separate facet spectra have been derived by co-adding data from detectors. Essentially, elemental lines seen in the three different facet spectra represent an averaged geochemical signature from the areas covered by the D-CIXS ground tracks. The spectra shown in figure 5 indicate that lowenergy lines (Mg: 1.25 keV, Al; 1.49 keV and Si: 1.74 keV) are observed in detectors from Facet 1 and 2 (Alfilter). Detectors in Facet 3 are covered by a Magnesium filter which was designed to attenuate the signal from Al and Si X-rays, and so in the Facet 3 spectrum Mg is the only significant low-energy peak detected. Data taken from the Facet 3 spectrum also show a clear Fe peak at around 6.4 keV which is interpreted to be related to fluorescence from Mare Crisium (see below). All three facets clearly show the detection of a Ca emission peak at ~3.69 keV. Although inferences about the distribution of Ca in the lunar crust have been made indirectly from neutron and gamma ray measurements [3], this observation represents the first ever unambiguous remote sensing of Ca on the Moon. Discussion: The areas of the lunar surface observed during the flare of January 15 include Mare Crisium, and highlands to the north and east. The basaltic lavas of Mare Crisium, which appear dark in, are iron-rich owing to high modal abundances of mafic minerals (principally pyroxene). In contrast, the adjacent highlands are expected to be anorthositic (i.e., composed largely of the mineral plagioclase), and thus iron poor but relatively enriched in calcium and aluminium. Some `ground truth' is provided by samples collected at the Luna 20 and 24 landing sites, both of which were located within the footprint of facet 3 during these observations . Remote sensing by Clementine [4] and Lunar Prospector [5] suggests that the Soviet Luna 24 and Luna 20 iron abundances are reasonably representative of the Mare Crisium basalts, and the adjacent highlands, respectively. These remote sensing data also suggest that the highlands north and east of Crisium, are more anorthositic (i.e. poorer in Fe and richer in Ca) than those immediately adjacent to the Crisium basin and which were sampled by Luna 20. These expectations are confirmed by the D-CIXS data shown in Figure 1, when facet 3 was over the centre of Crisium and facet 1 was observing the highlands approximately 900 km to the north (material apparently similar to that of the highlands of the Luna 20 landing site). As expected, the Fe flux is strongly enhanced over Crisium, while Ca is somewhat enhanced over the highlands. Moreover, although there is strictly no ground truth available for the facet 1 footprint, the greater variability of Fe relative to Ca between mare and highland regions apparent in Fig. 6 is explicable in terms of the Luna 20 and 24 results presented in Table 2: while Fe is almost three times as abundant in the Crisium basalts than in the adjacent highlands, the Ca abundance is only some 20% less. Essentially the same trend is obtained by comparing the Fe and Ca Lunar Prospector data [3], which imply a factor of 2 difference in Fe, but less than a 10% difference in Ca, between these two footprints. Figure 2 shows a comparison of a spectrum obtained close to the Apollo 12 site, with a modelled spectrum, derived from averaged Apollo 12 soil compositions [6]. The match between data (black line) and model (grey) is reasonable, with the exception of the low energy continuum, where the model clearly needs refinement. We have extended our observations to comparison of Lunar near and farside, and by careful analysis enabled new elemental lines to be observed (Swinyard et al 2008)[8]. Conclusions: The instrument demonstrates the capability of this method to perform X-ray fluorescence measurements of the Moon. A number of rock forming elements have been successfully detected from the Moon during solar flare events, and we have made the first unambiguous remote detection of Calcium from the lunar surface. For more detail see Grande et al 2007 [7].All of this has been achieved during solar minimum and proves that the technique will be highly suitable for the upcoming Chandrayaan- 1 mission [9]), when the mission will take place during the rising phase of the solar cycle, and for which it forms part of the core payload. Acknowledgements We acknowledge the contributions of the entire DCIXS team (M. Grande, J. Huovelin, B. Kellett, R Browning, C. Howe, B. Swinyard, C. H. Perry, S. Dunkin, N. Waltham, B. Kent, D. Parker, I. Crawford, K. Joy, J. Guest, S. Russell, M. Grady, A. Christou, H. Alleyne, D. Hughes, C. D. Murray, S. Maurice C. L. Duston , O. Gasnaut, N. Bhandari, R. Lundin, S. Barabash, D Lawrence, V. Fernandes, I. Casanova, M. Kato, T. Okada, P. Clark, B. Foing, D. Heather, M. Wieczorek). We acknowledge the SMART-1 teams from ESA/ESTEC project, industrial teams, STOC Science and Technology Operations Centre and ESOC spacecraft operations, SMART-1 Science and Technology Working Team. The D-CIXS instrument development was supported with SMART-1 funding from ESA Science and Technology Research Programmes, and funding sources (BNSC, RAL, PPARC/STFC). Additional hardware was provided by CESR, Toulouse, University of Helsinki observatory and IRF Kiruna, Sweden. References [1] Grande, (2001) Earth Moon And Planets, Vol 85-6, pp 143-152). [2] Grande et al., (2003), Planet. & Sp. Sci., 51 (6), 427. [3] Prettyman et al, 33rd LPS XXXIII #2012. [4] Bussey & Spudis (2000), JGR- Planets, 105, 4235- 4243. [5] Lawrence et al (2002) JGRPlanets, 107, (#E12), 5130, 10.1029/2001JE001530, 2002. [6] Haskin and Warren. 1991. The Lunar Sourcebook. Eds. Heiken [7] Grande et al (2007), in press Planet. & Sp. Sci 2006 [8] Swinyard et al 2008 submitted Science [9] Grande et al., (2008), Submitted Planet. & Sp. Sci.,

OFFSET - RAY TRACING OPTICAL ANALYSIS OF OFFSET SOLAR COLLECTOR FOR SPACE STATION SOLAR DYNAMIC POWER SYSTEM

NASA Technical Reports Server (NTRS)

Jefferies, K.

1994-01-01

OFFSET is a ray tracing computer code for optical analysis of a solar collector. The code models the flux distributions within the receiver cavity produced by reflections from the solar collector. It was developed to model the offset solar collector of the solar dynamic electric power system being developed for Space Station Freedom. OFFSET has been used to improve the understanding of the collector-receiver interface and to guide the efforts of NASA contractors also researching the optical components of the power system. The collector for Space Station Freedom consists of 19 hexagonal panels each containing 24 triangular, reflective facets. Current research is geared toward optimizing flux distribution inside the receiver via changes in collector design and receiver orientation. OFFSET offers many options for experimenting with the design of the system. The offset parabolic collector model configuration is determined by an input file of facet corner coordinates. The user may choose other configurations by changing this file, but to simulate collectors that have other than 19 groups of 24 triangular facets would require modification of the FORTRAN code. Each of the roughly 500 facets in the assembled collector may be independently aimed to smooth out, or tailor, the flux distribution on the receiver's wall. OFFSET simulates the effects of design changes such as in receiver aperture location, tilt angle, and collector facet contour. Unique features of OFFSET include: 1) equations developed to pseudo-randomly select ray originating sources on the Sun which appear evenly distributed and include solar limb darkening; 2) Cone-optics technique used to add surface specular error to the ray originating sources to determine the apparent ray sources of the reflected sun; 3) choice of facet reflective surface contour -- spherical, ideal parabolic, or toroidal; 4) Gaussian distributions of radial and tangential components of surface slope error added to the surface normals at the ten nodal points on each facet; and 5) color contour plots of receiver incident flux distribution generated by PATRAN processing of FORTRAN computer code output. OFFSET output includes a file of input data for confirmation, a PATRAN results file containing the values necessary to plot the flux distribution at the receiver surface, a PATRAN results file containing the intensity distribution on a 40 x 40 cm area of the receiver aperture plane, a data file containing calculated information on the system configuration, a file including the X-Y coordinates of the target points of each collector facet on the aperture opening, and twelve P/PLOT input data files to allow X-Y plotting of various results data. OFFSET is written in FORTRAN (70%) for the IBM VM operating system. The code contains PATRAN statements (12%) and P/PLOT statements (18%) for generating plots. Once the program has been run on VM (or an equivalent system), the PATRAN and P/PLOT files may be transferred to a DEC VAX (or equivalent system) with access to PATRAN for PATRAN post processing. OFFSET was written in 1988 and last updated in 1989. PATRAN is a registered trademark of PDA Engineering. IBM is a registered trademark of International Business Machines Corporation. DEC VAX is a registered trademark of Digital Equipment Corporation.

Facet-dependent photocatalytic properties of TiO(2) -based composites for energy conversion and environmental remediation.

PubMed

Ong, Wee-Jun; Tan, Lling-Lling; Chai, Siang-Piao; Yong, Siek-Ting; Mohamed, Abdul Rahman

2014-03-01

Titanium dioxide (TiO2 ) is one of the most widely investigated metal oxides because of its extraordinary surface, electronic, and photocatalytic properties. However, the large band gap of TiO2 and the considerable recombination of photogenerated electron-hole pairs limit its photocatalytic efficiency. Therefore, research attention is being increasingly directed towards engineering the surface structure of TiO2 on the atomic level (namely morphological control of {001} facets on the micro- and nanoscale) to fine-tune its physicochemical properties; this could ultimately lead to the optimization of selectivity and reactivity. This Review encompasses the fundamental principles to enhance the photocatalytic activity by using highly reactive {001}-faceted TiO2 -based composites. The current progress of such composites, with particular emphasis on the photodegradation of pollutants and photocatalytic water splitting for hydrogen generation, is also discussed. The progresses made are thoroughly examined for achieving remarkable photocatalytic performances, with additional insights with regard to charge transfer. Finally, a summary and some perspectives on the challenges and new research directions for future exploitation in this emerging frontier are provided, which hopefully would allow for harnessing the outstanding structural and electronic properties of {001} facets for various energy- and environmental-related applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modeling the Adsorbate Coverage Distribution Over a Multi-Faceted Catalytic Grain in the Presence of an Electric Field: O/Fe from First Principles

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

Bray, Jacob; Hensley, Alyssa J. R.; Collinge, Greg

The impact of an external electric field on the concerted behavior of oxygen over a multi-faceted catalytic Fe grain is determined via the interpolation of ab initio models of oxygen adsorption on Fe(100), Fe(110), and Fe(111) in the presence of an external electric field. The application of both negative and positive electric fields weaken the adsorption strength for oxygen on all three surface facets, with Fe(110) experiencing the greatest effect. Kinetic models of a multi-faceted catalytic Fe grain show that the average oxygen coverage over the grain surface is reduced under the influence of both a negative and positive electricmore » field, which are consistent with phase diagram results at comparable pressures. Furthermore, we show that there is a weak synergistic effect between a Pd promoter and a positive electric field on the oxygen adsorption energy, i.e. the Pd promoter and electric field combination weaken the oxygen adsorption energy to a greater degree than the simple addition of both components separately. In conclusion, the work shows that the application of an applied external electric field may be a useful tool in fine-tuning chemical properties of Fe-based catalysts in hydrodeoxygenation applications.« less

Study of TiO2 anatase nano and microstructures with dominant {001} facets for NO oxidation.

PubMed

Sofianou, Maria-Veronica; Trapalis, Christos; Psycharis, Vassils; Boukos, Nikos; Vaimakis, Tiverios; Yu, Jiaguo; Wang, Wenguang

2012-11-01

TiO(2) anatase nanoplates and hollow microspheres were fabricated by a solvothermal-hydrothermal method using titanium isopropoxide as a titanium precursor and hydrofluoric acid as a capping agent in order to enhance the formation of the {001} crystal facets of the anatase nanocrystals. These different morphological structures of TiO(2) anatase can be achieved by only changing the solvent, keeping the amount of the precursor and of the capping agent identical during the solvothermal-hydrothermal process. After calcination of the samples, the adsorbed fluoride atoms on the {001} crystal facets of the TiO(2) anatase nanocrystals were completely removed from their surface according to XPS analysis. The calcined TiO(2) anatase structures were higher crystallized and the specific surface area of the catalysts increased, enhancing their photocatalytic activity in comparison to the non-calcined TiO(2) anatase structures. All TiO(2) anatase samples with adsorbed as well as non-adsorbed fluoride atoms on their {001} crystal facets, exhibited a higher photonic efficiency than Degussa P25, which was used as a reference. The fluoride free TiO(2) anatase nanoplates exhibited the best photocatalytic activity in oxidizing the NO gas to NO(2) and NO(3) (-).

Combined application of electron backscatter diffraction and stereo-photogrammetry in fractography studies.

PubMed

Davies, P A; Randle, V

2001-10-01

The main aim of this paper is to report on recent experimental developments that have succeeded in combining electron back-scatter diffraction (EBSD) with stereo-photogrammetry, compared with two other methods for study of fracture surfaces, namely visual fractography analysis in the scanning electron microscope (SEM) and EBSD directly from facets. These approaches will be illustrated with data relating to the cleavage plane orientation analysis in a ferritic and C-Mn steel. It is demonstrated that the combined use of EBSD and stereo-photogrammetry represents a significant advance in the methodology for facet crystallography analysis. The results of point counting from fractograph characterization determined that the proportions of intergranular fracture in C-Mn and ferritic steels were 10.4% and 9.4%, respectively. The crystallographic orientation was determined directly from the fracture surface of a ferritic steel sample and produced an orientation distribution with a clear trend towards the [001] plane. A stereo-photogrammetry technique was validated using the known geometry of a Vickers hardness indent. The technique was then successfully employed to measure the macroscopic orientation of individual cleavage facets in the same reference frame as the EBSD measurements. Correlating the results of these measurements indicated that the actual crystallographic orientation of every cleavage facet identified in the steel specimens is [001].

Modeling the Adsorbate Coverage Distribution Over a Multi-Faceted Catalytic Grain in the Presence of an Electric Field: O/Fe from First Principles

DOE PAGES

Bray, Jacob; Hensley, Alyssa J. R.; Collinge, Greg; ...

2018-04-15

The impact of an external electric field on the concerted behavior of oxygen over a multi-faceted catalytic Fe grain is determined via the interpolation of ab initio models of oxygen adsorption on Fe(100), Fe(110), and Fe(111) in the presence of an external electric field. The application of both negative and positive electric fields weaken the adsorption strength for oxygen on all three surface facets, with Fe(110) experiencing the greatest effect. Kinetic models of a multi-faceted catalytic Fe grain show that the average oxygen coverage over the grain surface is reduced under the influence of both a negative and positive electricmore » field, which are consistent with phase diagram results at comparable pressures. Furthermore, we show that there is a weak synergistic effect between a Pd promoter and a positive electric field on the oxygen adsorption energy, i.e. the Pd promoter and electric field combination weaken the oxygen adsorption energy to a greater degree than the simple addition of both components separately. In conclusion, the work shows that the application of an applied external electric field may be a useful tool in fine-tuning chemical properties of Fe-based catalysts in hydrodeoxygenation applications.« less

Uniform Si nano-dot fabrication using reconstructed structure of Si(110)

NASA Astrophysics Data System (ADS)

Yano, Masahiro; Uozumi, Yuki; Yasuda, Satoshi; Asaoka, Hidehito

2018-06-01

Si nano-dot (ND) formation on Si(110) is observed by means of a scanning tunneling microscope (STM). The initial Si-NDs are Si crystals that are continuous from the substrate and grow during the oxide layer desorption. The NDs fabricated on the flat surface of Si(110)-1 × 1 are surrounded by four types of facets with almost identical appearance probabilities. An increase in the size of the NDs increases the variety of its morphology. In contrast, most Si-NDs fabricated on straight-stepped surface of Si(110)-16 × 2 reconstructed structure are surrounded by only a single type of facet, namely the \\text{Si}(17,15,1)-2 × 1 plane. An appearance probability of the facet in which the base line is along the step of Si(110)-16 × 2 exceeds 75%. This finding provides a fabrication technique of uniformed structural Si-NDs by using the reconstructed structure of Si(110).

Growth and characterization of epitaxially stabilized ceria(001) nanostructures on Ru(0001)

DOE PAGES

Flege, Jan Ingo; Hocker, Jan; Kaemena, Bjorn; ...

2016-05-03

We have studied (001) surface terminated cerium oxide nanoparticles grown on a ruthenium substrate using physical vapor deposition. Their morphology, shape, crystal structure, and chemical state are determined by low-energy electron microscopy and micro-diffraction, scanning probe microscopy, and synchrotron-based X-ray absorption spectroscopy. Square islands are identified as CeO 2 nanocrystals exhibiting a (001) oriented top facet of varying size; they have a height of about 7 to 10 nm and a side length between about 50 and 500 nm, and are terminated with a p(2 × 2) surface reconstruction. Micro-illumination electron diffraction reveals the existence of a coincidence lattice atmore » the interface to the ruthenium substrate. The orientation of the side facets of the rod-like particles is identified as (111); the square particles are most likely of cuboidal shape, exhibiting (100) oriented side facets. Lastly, the square and needle-like islands are predominantly found at step bunches and may be grown exclusively at temperatures exceeding 1000 °C.« less

Space configuration as an explanation for lithology-related cross-polarized radar image anomalies

NASA Technical Reports Server (NTRS)

Mccauley, J. R.

1972-01-01

Three rock types are described that produce dark cross-polarized images on Ka-band imagery: lava flows dating from Pleistocene and Holocene, some Tertiary volcanics, and certain massive sandstones. Their planar surfaces are large with respect to the wavelength of the Ka-band system, yet are small in comparison to the resolution. It is found that only outcrops with proper faceted surface orientations produce significant radar returns showing the dominance of specular reflectors. The omnidirectional attitude of the facets and their wide distribution on the outcrops explains the independence of look-direction that the flat-lying anomalous outcrops exhibit in production of darker cross-polarized images.

Photocatalytic mechanism of high-activity anatase TiO2 with exposed (001) facets from molecular-atomic scale: HRTEM and Raman studies

NASA Astrophysics Data System (ADS)

Wu, Jun; Shi, Chentian; Zhang, Yupeng; Fu, Qiang; Pan, Chunxu

2017-12-01

Anatase TiO2 with a variant percentage of exposed (001) facets was prepared under hydrothermal processes by adjusting the volume of HF, and the photocatalytic mechanism was studied from atomic-molecular scale by HRTEM and Raman spectroscopy. It was revealed that: 1) From HRTEM observations, the surface of original TiO2 with exposed (001) facets was clean without impurity, and the crystal lattice was clear and completed; however, when mixed with methylene blue (MB) solution, there were many 1 nm molecular absorbed at the surface of TiO2; after the photocatalytic experiment, MB molecules disappeared and the TiO2 lattice image became fuzzy. 2) The broken path of the MB chemical bond was obtained by Raman spectroscopy, i.e., after the irradiation of the light, the vibrational mode of C-N-C disappeared due to the chemical bond breakage, and the groups containing C-N bond and carbon rings were gradually decomposed. Accordingly, we propose that the driving force for breaking the chemical bond and the disappearance of groups is from the surface lattice distortion of TiO2 during photocatalyzation.

Second-order distributed-feedback surface plasmon resonator for single-mode fiber end-facet biosensing

NASA Astrophysics Data System (ADS)

Lei, Zeyu; Zhou, Xin; Yang, Jie; He, Xiaolong; Wang, Yalin; Yang, Tian

2017-04-01

Integrating surface plasmon resonance (SPR) devices upon single-mode fiber (SMF) end facets renders label-free biosensing systems that have a dip-and-read configuration, high compatibility with fiber-optic techniques, and in vivo monitoring capability, which however meets the challenge to match the performance of free-space counterparts. We report a second-order distributed feedback (DFB) SPR cavity on an SMF end facet and its application in protein interaction analysis. In our device, a periodic array of nanoslits in a gold film is used to couple fiber guided lightwaves to surface plasmon polaritons (SPPs) with its first order spatial Fourier component, while the second order spatial Fourier component provides DFB to SPP propagation and produces an SPP bandgap. A phase shift section in the DFB structure introduces an SPR defect state within the SPP bandgap, whose mode profile is optimized to match that of the SMF to achieve a reasonable coupling efficiency. We report an experimental refractive index sensitivity of 628 nm RIU-1, a figure-of-merit of 80 RIU-1, and a limit of detection of 7 × 10-6 RIU. The measurement of the real-time interaction between human immunoglobulin G molecules and their antibodies is demonstrated.

Real time analysis of self-assembled InAs/GaAs quantum dot growth by probing reflection high-energy electron diffraction chevron image

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

Kudo, Takuya; Inoue, Tomoya; Kita, Takashi

2008-10-01

Self-assembling process of InAs/GaAs quantum dots has been investigated by analyzing reflection high-energy electron diffraction chevron images reflecting the crystal facet structure surrounding the island. The chevron image shows dramatic changes during the island formation. From the temporal evolution of the chevron tail structure, the self-assembling process has been found to consist of four steps. The initial islands do not show distinct facet structures. Then, the island surface is covered by high-index facets, and this is followed by the formation of stable low-index facets. Finally, the flow of In atoms from the islands occurs, which contributes to flatten the wettingmore » layer. Furthermore, we have investigated the island shape evolution during the GaAs capping layer growth by using the same real-time analysis technique.« less

CW Performance of an InGaAs-GaAs-AlGaAs Laterally-Coupled Distributed Feedback (LC-DFB) Ridge Laser Diode

NASA Technical Reports Server (NTRS)

Martin, R. D.; Forouhar, S.; Keo, S.; Lang, R. J.; Hunsperger, R. G.; Tiberio, R. C.; Chapman, P. F.

1995-01-01

Single-mode distributed feedback (DFB) laser diodes typically require a two-step epitaxial growth or use of a corrugated substrate. We demonstrate InGaAs-GaAs-AlGaAs DFB lasers fabricated from a single epitaxial growth using lateral evanescent coupling of the optical field to a surface grating etehed along the sides of the ridge. A CW threshold current of 25 mA and external quantum efficiency of 0.48 mW/mA per facet were measured for a 1 mm cavity length device with anti-reflection coated facets. Single-mode output powers as high as 11 mW per facet at 935 nm wavelength were attained. A coupling coefficient of at least 5.8/cm was calculated from the subthreshold spectrum taking into account the 2% residual facet reflectivity.

Enhanced visible-light-driven photocatalytic H2-production activity of CdS-loaded TiO2 microspheres with exposed (001) facets

NASA Astrophysics Data System (ADS)

Gao, Bifen; Yuan, Xia; Lu, Penghui; Lin, Bizhou; Chen, Yilin

2015-12-01

CdS-loaded TiO2 microspheres with highly exposed (001) facets were prepared by hydrothermal treatment of a TiF4-HCl-H2O mixed solution followed by a chemical bath deposition of CdS onto TiO2 microspheres. The crystal structure, surficial micro-structure and photo-absorption property of the samples were characterized by XRD, FE-SEM, TEM and UV-vis diffuse reflectance spectroscopy, etc. The as-prepared samples exhibited superior visible-light-driven photocatalytic H2-production activity from lactic acid aqueous solution in comparison with CdS-sensitized TiO2 nanoparticles, whose surface was dominated by (101) facets. Photoelectrochemical measurement confirmed that (001) facet is beneficial for the transfer of photo-generated electron from CdS to TiO2 microsphere, which led to the unexpected high photocatalytic activity of CdS-loaded TiO2 microspheres.

Controlled synthesis and facets-dependent photocatalysis of TiO2 nanocrystals

NASA Astrophysics Data System (ADS)

Roy, Nitish; Park, Yohan; Sohn, Youngku; Pradhan, Debabrata

2015-04-01

Titanium dioxide (TiO2) is a wide band gap semiconductor that has been extensively used in several environmental applications including degradation of organic hazardous chemicals, water splitting to generate hydrogen, dye sensitized solar cells, self cleaning agents, and pigments. Herein we demonstrate the synthesis of TiO2 nanocrystals (NCs) with the shapes of ellipsoids, rods, cuboids, and sheets with different exposed facets using a noncorrosive and nontoxic chemical (i.e. diethanolamine) as the shape controlling agent, unlike hydrofluoric acid commonly used. The TiO2 NCs of diverse shapes with different exposed facets were tested for photocatalytic hydroxyl radical (OH•) formation, which determines their photocatalytic behavior and the results were compared with the standard P-25 Degussa. The formation rate of OH• per specific surface area was found to be >6 fold higher for rod-shaped TiO2 NCs than that of commercial Degussa P25 catalyst. The highest photocatalytic activity of rod-shaped TiO2 NCs is ascribed to the unique chemical environment of {010} exposed facets which facilitates the electron/hole separation in presence of {101} facets.

The Active Sites of a Rod-Shaped Hollandite DeNOx Catalyst.

PubMed

Hu, Pingping; Schuster, Manfred Erwin; Huang, Zhiwei; Xu, Fei; Jin, Shifeng; Chen, Yaxin; Hua, Weiming; Su, Dang Sheng; Tang, Xingfu

2015-06-26

The identification of catalytically active sites (CASs) in heterogeneous catalysis is of vital importance to design and develop improved catalysts, but remains a great challenge. The CASs have been identified in the low-temperature selective catalytic reduction of nitrogen oxides by ammonia (SCR) over a hollandite manganese oxide (HMO) catalyst with a rod-shaped morphology and one-dimensional tunnels. Electron microscopy and synchrotron X-ray diffraction determine the surface and crystal structures of the one-dimensional HMO rods closed by {100} side facets and {001} top facets. A combination of X-ray absorption spectra, molecular probes with potassium and nitric oxide, and catalytic tests reveals that the CASs are located on the {100} side facets of the HMO rods rather than on the top facets or in the tunnels, and hence semi-tunnel structural motifs on the {100} facets are evidenced to be the CASs of the SCR reaction. This work paves the way to further investigate the intrinsic mechanisms of SCR reactions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Systematic study on the influence of the morphology of α-MoO{sub 3} in the selective oxidation of propylene

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

Schuh, Kirsten; Kleist, Wolfgang; Høj, Martin

2015-08-15

A variety of morphologically different α-MoO{sub 3} samples were prepared by hydrothermal synthesis and applied in the selective oxidation of propylene. Their catalytic performance was compared to α-MoO{sub 3} prepared by flame spray pyrolysis (FSP) and a classical synthesis route. Hydrothermal synthesis from ammonium heptamolybdate (AHM) and nitric acid at pH 1–2 led to ammonium containing molybdenum oxide phases that were completely transformed into α-MoO{sub 3} after calcination at 550 °C. A one-step synthesis of α-MoO{sub 3} rods was possible starting from MoO{sub 3}·2H{sub 2}O with acetic acid or nitric acid and from AHM with nitric acid at 180 °C.more » Particularly, if nitric acid was used during synthesis, the rod-like morphology of the samples could be stabilized during calcination at 550 °C and the following catalytic activity tests, which was beneficial for the catalytic performance in propylene oxidation. Characterization studies using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy showed that those samples, which retained their rod-like morphology during the activity tests, yielded the highest propylene conversion. - Graphical abstract: Hydrothermal synthesis from MoO{sub 3}·2H{sub 2}O in the presence of HNO{sub 3} led to rod-shaped particles which mainly expose (1 0 0) facets which are the most active surfaces. - Highlights: • Hydrothermal synthesis of MoO3 resulted in either rod or slab shaped particles depending on pH. • At pH<0 rods stable towards calcination and catalytic activity testing were formed. • Rod shaped particles had significantly higher activity than slab shaped ones. • The rod shaped particles mainly expose the (1 0 0) facets which are the most active surfaces. • Total surface area is not main determining factor for catalytic activity.« less

Preparation and characterization of ultraflat Pt facets by atom-height-resolved differential optical microscopy

NASA Astrophysics Data System (ADS)

Azhagurajan, M.; Wen, R.; Kim, Y. G.; Itoh, T.; Sashikata, K.; Itaya, K.

2015-01-01

We recently demonstrated that improvements to our technique, laser confocal microscopy with differential interference microscopy (LCM-DIM), has rendered it fully capable of resolving monatomic steps with heights of ca. 0.25 nm on Au(111) and Pd(111) surfaces, even as low as 0.14 nm on Si(100), in aqueous solution. In this paper, we describe in detail a method to prepare and characterize, via atomic-layer-resolved LCM-DIM, ultraflat Pt(111) and Pt(100) facets over a wide surface area. The preparation of ultraflat surfaces is important in the characterization at the atomic scale of electrochemical processes under reaction conditions. To showcase the elegance of LCM-DIM, the anodic dissolution of Pt in aqueous HCl is briefly recounted.

A Comprehensive Study of Formic Acid Oxidation on Palladium Nanocrystals with Different Types of Facets and Twin Defects

DOE PAGES

Choi, Sang-Il; Herron, Jeffrey A.; Scaranto, Jessica; ...

2015-04-13

Palladium has been recognized as the best anodic, monometallic electrocatalyst for the formic acid oxidation (FAO) reaction in a direct formic acid fuel cell. Here we report a systematic study of FAO on a variety of Pd nanocrystals, including cubes, right bipyramids, octahedra, tetrahedra, decahedra, and icosahedra. These nanocrystals were synthesized with approximately the same size, but different types of facets and twin defects on their surfaces. Our measurements indicate that the Pd nanocrystals enclosed by {100} facets have higher specific activities than those enclosed by {111} facets, in agreement with prior observations for Pd single-crystal substrates. If comparing nanocrystalsmore » predominantly enclosed by a specific type of facet, {100} or {111}, those with twin defects displayed greatly enhanced FAO activities compared to their single-crystal counterparts. To rationalize these experimental results, we performed periodic, self-consistent DFT calculations on model single-crystal substrates of Pd, representing the active sites present in the nanocrystals used in the experiments. The calculation results suggest that the enhancement of FAO activity on defect regions, represented by Pd(211) sites, compared to the activity of both Pd(100) and Pd(111) surfaces, could be attributed to an increased flux through the HCOO-mediated pathway rather than the COOH-mediated pathway on Pd(211). Since COOH has been identified as a precursor to CO, a site-poisoning species, a lower coverage of CO at the defect regions will lead to a higher activity for the corresponding nanocrystal catalysts, containing those defect regions.« less

Nanocrystalline Anatase Titania Supported Vanadia Catalysts: Facet-dependent Structure of Vanadia

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

Li, Wei-Zhen; Gao, Feng; Li, Yan

2015-07-09

Titania supported vanadia, a classic heterogeneous catalyst for redox reactions, typically has nonhomogeneous vanadia species on various titania facets, making it challenging not only to determine and quantify each species but also to decouple their catalytic contributions. We prepared truncated tetragonal bipyramidal (TiO2-TTB) and rod-like (TiO2-Rod) anatase titania with only {101} and {001} facets at ratios of about 80:20 and 93:7, respectively, and used them as supports of sub-monolayer vanadia. The structure and redox properties of supported vanadia were determined by XRD, TEM, XPS, EPR, Raman, FTIR and TPR, etc. It was found that vanadia preferentially occupy TiO2 {001} facetsmore » and form isolated O=V4+(O-Ti)2 species, and with further increase in vanadia surface coverage, isolated O=V5+(O-Ti)3 and oligomerized O=V5+(O-M)3 (M = Ti or V) species form on TiO2 {101} facets. The discovery on support facet-dependent structure of vanadia on anatase titania is expected to enable the elucidation of structure-function correlations on high surface area TiO2 supported vanadia catalysts. This work was supported by U. S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences and Geosciences. The research was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE Office of Biological and Environmental Research, and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for DOE by Battelle.« less

The Influence of Artificial Cervical Disc Prosthesis Height on the Cervical Biomechanics: A Finite Element Study.

PubMed

Yuan, Wei; Zhang, Haiping; Zhou, Xiaoshu; Wu, Weidong; Zhu, Yue

2018-05-01

Artificial cervical disc replacement is expected to maintain normal cervical biomechanics. At present, the effect of the Prestige LP prosthesis height on cervical biomechanics has not been thoroughly studied. This finite element study of the cervical biomechanics aims to predict how the parameters, like range of motion (ROM), adjacent intradiscal pressure, facet joint force, and bone-implant interface stress, are affected by different heights of Prestige LP prostheses. The finite element model of intact cervical spine (C3-C7) was obtained from our previous study, and the model was altered to implant Prestige LP prostheses at the C5-C6 level. The effects of the height of 5, 6, and 7 mm prosthesis replacement on ROM, adjacent intradiscal pressure, facet joint force, as well as the distribution of bone-implant interface stress were examined. ROM, adjacent intradiscal pressure, and facet joint force increased with the prosthesis height, whereas ROM and facet joint force decreased at C5-C6. The maximal stress on the inferior surface of the prostheses was greater than that on the superior surface, and the stresses increased with the prosthesis height. The biomechanical changes were slightly affected by the height of 5 and 6 mm prostheses, but were strongly affected by the 7-mm prosthesis. An appropriate height of the Prestige LP prosthesis can preserve normal ROM, adjacent intradiscal pressure, and facet joint force. Prostheses with a height of ≥2 mm than normal can lead to marked changes in the cervical biomechanics and bone-implant interface stress. Copyright © 2018 Elsevier Inc. All rights reserved.

Corner wetting during the vapor-liquid-solid growth of faceted nanowires

NASA Astrophysics Data System (ADS)

Spencer, Brian; Davis, Stephen

2016-11-01

We consider the corner wetting of liquid drops in the context of vapor-liquid-solid growth of nanowires. Specifically, we construct numerical solutions for the equilibrium shape of a liquid drop on top of a faceted nanowire by solving the Laplace-Young equation with a free boundary determined by mixed boundary conditions. A key result for nanowire growth is that for a range of contact angles there is no equilibrium drop shape that completely wets the corner of the faceted nanowire. Based on our numerical solutions we determine the scaling behavior for the singular surface behavior near corners of the nanowire in terms of the Young contact angle and drop volume.

The digital step edge

NASA Technical Reports Server (NTRS)

Haralick, R. M.

1982-01-01

The facet model was used to accomplish step edge detection. The essence of the facet model is that any analysis made on the basis of the pixel values in some neighborhood has its final authoritative interpretation relative to the underlying grey tone intensity surface of which the neighborhood pixel values are observed noisy samples. Pixels which are part of regions have simple grey tone intensity surfaces over their areas. Pixels which have an edge in them have complex grey tone intensity surfaces over their areas. Specially, an edge moves through a pixel only if there is some point in the pixel's area having a zero crossing of the second directional derivative taken in the direction of a non-zero gradient at the pixel's center. To determine whether or not a pixel should be marked as a step edge pixel, its underlying grey tone intensity surface was estimated on the basis of the pixels in its neighborhood.

Formation of neutral and charged gold carbonyls on highly facetted gold nanostructures

NASA Astrophysics Data System (ADS)

Chau, Thoi-Dai; Visart de Bocarmé, Thierry; Kruse, Norbert; Wang, Richard L. C.; Kreuzer, Hans Jürgen

2003-12-01

We show that gold mono- and di-carbonyls are formed on gold field emitter tips during interaction with carbon monoxide gas at room temperature and in the presence of high electrostatic fields. The experiments are done in a time-of-flight atom probe to obtain mass spectra. The yield of monocarbonyl cations is about twice that of di-carbonyl ions. Density functional theory calculations are reported that explain the field stabilization of adsorbed carbonyls and the desorption yield of their cations.

Effect of crystal habits on the surface energy and cohesion of crystalline powders.

PubMed

Shah, Umang V; Olusanmi, Dolapo; Narang, Ajit S; Hussain, Munir A; Gamble, John F; Tobyn, Michael J; Heng, Jerry Y Y

2014-09-10

The role of surface properties, influenced by particle processing, in particle-particle interactions (powder cohesion) is investigated in this study. Wetting behaviour of mefenamic acid was found to be anisotropic by sessile drop contact angle measurements on macroscopic (>1cm) single crystals, with variations in contact angle of water from 56.3° to 92.0°. This is attributed to variations in surface chemical functionality at specific facets, and confirmed using X-ray photoelectron spectroscopy (XPS). Using a finite dilution inverse gas chromatography (FD-IGC) approach, the surface energy heterogeneity of powders was determined. The surface energy profile of different mefenamic acid crystal habits was directly related to the relative exposure of different crystal facets. Cohesion, determined by a uniaxial compression test, was also found to relate to surface energy of the powders. By employing a surface modification (silanisation) approach, the contribution from crystal shape from surface area and surface energy was decoupled. By "normalising" contribution from surface energy and surface area, needle shaped crystals were found to be ∼2.5× more cohesive compared to elongated plates or hexagonal cuboid shapes crystals. Copyright © 2014. Published by Elsevier B.V.

Step free energies at faceted solid surfaces: Theory and atomistic calculations for steps on the Cu(111) surface

NASA Astrophysics Data System (ADS)

Freitas, Rodrigo; Frolov, Timofey; Asta, Mark

2017-04-01

A theory for the thermodynamic properties of steps on faceted crystalline surfaces is presented. The formalism leads to the definition of step excess quantities, including an excess step stress that is the step analogy of surface stress. The approach is used to develop a relationship between the temperature dependence of the step free energy (γst) and step excess quantities for energy and stress that can be readily calculated by atomistic simulations. We demonstrate the application of this formalism in thermodynamic-integration (TI) calculations of the step free energy, based on molecular-dynamics simulations, considering <110 > steps on the {111 } surface of a classical potential model for elemental Cu. In this application we employ the Frenkel-Ladd approach to compute the reference value of γst for the TI calculations. Calculated results for excess energy and stress show relatively weak temperature dependencies up to a homologous temperature of approximately 0.6, above which these quantities increase strongly and the step stress becomes more isotropic. From the calculated excess quantities we compute γst over the temperature range from zero up to the melting point (Tm). We find that γst remains finite up to Tm, indicating the absence of a roughening temperature for this {111 } surface facet, but decreases by roughly fifty percent from the zero-temperature value. The strongest temperature dependence occurs above homologous temperatures of approximately 0.6, where the step becomes configurationally disordered due to the formation of point defects and appreciable capillary fluctuations.

Faceting of {sigma}3 and {sigma}9 grain boundaries in Cu-Bi alloys

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

Straumal, B.B.; Polyakov, S.A.; Max-Planck-Institut fuer Metallforschung and Institut fuer Metallkunde, Heisenbergstr. 3, 70569 Stuttgart

2005-01-10

The faceting of {sigma}3 and {sigma}9 tilt grain boundaries (GBs) has been studied in bicrystals of pure Cu and Cu-Bi alloys containing 2.5 x 10{sup -3}, 10 x 10{sup -3} and 16 x 10{sup -3} at.% Bi. The {sigma}3(1 0 0), {sigma}9(1 0 0), {sigma}9(-1 1 0), and {sigma}9(-1 2 0) facets and non-CSL {sigma}3 82 deg 9R facet were observed, where {sigma} is the inverse density of coincidence sites. The ratio between GB energy, {sigma}{sub GB}, and surface energy, {sigma}{sub sur}, was measured by atomic force microscopy using the GB thermal-groove method. The GB energy and thermal-groove deepening ratemore » increased slightly between 0 and 10 x 10{sup -3} at.% Bi for all facets studied. However, between 10 x 10{sup -3} and 16 x 10{sup -3} at.% Bi the GB energy increased dramatically [from a factor 2 for the {sigma}9(1 1 0) facet to 15 times larger for the {sigma}3(1 0 0) facet]. The thermal-groove deepening rate also increased by a factor of 10 in this concentration range. This change corresponds well with the GB solidus line (i.e., the formation of a stable layer of a liquid-like GB phase called GB prewetting) observed previously. Wulff diagrams were constructed using measured {sigma}{sub GB}/{sigma}{sub sur} values.« less

Relating Sexual Sadism and Psychopathy to One Another, Non-Sexual Violence, and Sexual Crime Behaviors

PubMed Central

Robertson, Carrie A.; Knight, Raymond A.

2014-01-01

Sexual sadism and psychopathy have been theoretically, clinically, and empirically linked to violence. Although both constructs are linked to predatory violence, few studies have sought to explore the covariation of the two constructs, and even fewer have sought to conceptualize the similarities of violence prediction in each. The current study considered all four Psychopathy Checklist-Revised (PCL-R) facets and employed well-defined, validated measures of sadism to elucidate the relation between sadism and psychopathy, as well as to determine the role of each in the prediction of non-sexual violence and sexual crime behaviors. Study 1 assessed 314 adult, male sex offenders using archival ratings, as well as the self-report Multidimensional Inventory of Development, Sex, and Aggression (the MIDSA). Study 2 used archival ratings to assess 599 adult, male sex offenders. Exploratory and confirmatory factor analyses of crime scene descriptions yielded four sexual crime behavior factors: Violence, Physical Control, Sexual Behavior, and Paraphilic. Sadism and psychopathy covaried, but were not coextensive; sadism correlated with Total PCL-R, Facet 1, and Facet 4 scores. The constructs predicted all non-sexual violence measures, but predicted different sexual crime behavior factors. The PCL-R facets collectively predicted the Violence and Paraphilic factors, whereas sadism only predicted the Violence factor. PMID:24019144

Relating sexual sadism and psychopathy to one another, non-sexual violence, and sexual crime behaviors.

PubMed

Robertson, Carrie A; Knight, Raymond A

2014-01-01

Sexual sadism and psychopathy have been theoretically, clinically, and empirically linked to violence. Although both constructs are linked to predatory violence, few studies have sought to explore the covariation of the two constructs, and even fewer have sought to conceptualize the similarities of violence prediction in each. The current study considered all four Psychopathy Checklist-Revised (PCL-R) facets and employed well-defined, validated measures of sadism to elucidate the relation between sadism and psychopathy, as well as to determine the role of each in the prediction of non-sexual violence and sexual crime behaviors. Study 1 assessed 314 adult, male sex offenders using archival ratings, as well as the self-report Multidimensional Inventory of Development, Sex, and Aggression (the MIDSA). Study 2 used archival ratings to assess 599 adult, male sex offenders. Exploratory and confirmatory factor analyses of crime scene descriptions yielded four sexual crime behavior factors: Violence, Physical Control, Sexual Behavior, and Paraphilic. Sadism and psychopathy covaried, but were not coextensive; sadism correlated with Total PCL-R, Facet 1, and Facet 4 scores. The constructs predicted all non-sexual violence measures, but predicted different sexual crime behavior factors. The PCL-R facets collectively predicted the Violence and Paraphilic factors, whereas sadism only predicted the Violence factor. © 2013 Wiley Periodicals, Inc.

Simple, Green, and High-Yield Production of Boron-Based Nanostructures with Diverse Morphologies by Dissolution and Recrystallization of Layered Magnesium Diboride Crystals in Water.

PubMed

Gunda, Harini; Das, Saroj Kumar; Jasuja, Kabeer

2018-04-05

Layered metal diborides that contain metal atoms sandwiched between boron honeycomb planes offer a rich opportunity to access graphenic forms of boron. We recently demonstrated that magnesium diboride (MgB 2 ) could be exfoliated by ultrasonication in water to yield boron-based nanosheets. However, knowledge of the fate of metal boride crystals in aqueous phases is still in its incipient stages. This work presents our preliminary findings on the discovery that MgB 2 crystals can undergo dissolution in water under ambient conditions to result in precursors (prenucleation clusters) that, upon aging, undergo nonclassical crystallization preferentially growing in lateral directions by two-dimensional (2D) oriented attachment. We show that this recrystallization can be utilized as an avenue to obtain a high yield (≈92 %) of boron-based nanostructures, including nanodots, nanograins, nanoflakes, and nanosheets. These nanostructures comprise boron honeycomb planes chemically modified with hydride and oxy functional groups, which results in an overall negative charge on their surfaces. This ability of MgB 2 crystals to yield prenucleation clusters that can self-seed to form nanostructures comprising chemically modified boron honeycomb planes presents a new facet to the physicochemical interaction of MgB 2 with water. These findings also open newer avenues to obtain boron-based nanostructures with tunable morphologies by varying the chemical milieu during recrystallization. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atomic force microscopy of atomic-scale ledges and etch pits formed during dissolution of quartz

NASA Technical Reports Server (NTRS)

Gratz, A. J.; Manne, S.; Hansma, P. K.

1991-01-01

The processes involved in the dissolution and growth of crystals are closely related. Atomic force microscopy (AFM) of faceted pits (called negative crystals) formed during quartz dissolution reveals subtle details of these underlying physical mechanisms for silicates. In imaging these surfaces, the AFM detected ledges less than 1 nm high that were spaced 10 to 90 nm apart. A dislocation pit, invisible to optical and scanning electron microscopy measurements and serving as a ledge source, was also imaged. These observations confirm the applicability of ledge-motion models to dissolution and growth of silicates; coupled with measurements of dissolution rate on facets, these methods provide a powerful tool for probing mineral surface kinetics.

Mechanisms of the Wurtzite to Rocksalt Transformation in CdSe Nanocrystals

NASA Astrophysics Data System (ADS)

Grünwald, Michael; Rabani, Eran; Dellago, Christoph

2006-06-01

We study the pressure-driven phase transition from the four-coordinate wurtzite to the six-coordinate rocksalt structure in CdSe nanocrystals with molecular dynamics computer simulations. With an ideal gas as the pressure medium, we apply hydrostatic pressure to spherical and faceted nanocrystals ranging in diameter from 25 to 62 Å. In spherical crystals, the main mechanism of the transformation involves the sliding of (100) planes, but depending on the specific surface structure we also observe a second mechanism proceeding through the flattening of (100) planes. In faceted crystals, the transition proceeds via a five-coordinated hexagonal structure, which is stabilized at intermediate pressures due to dominant surface energetics.

A Mass Diffusion Model for Dry Snow Utilizing a Fabric Tensor to Characterize Anisotropy

NASA Astrophysics Data System (ADS)

Shertzer, Richard H.; Adams, Edward E.

2018-03-01

A homogenization algorithm for randomly distributed microstructures is applied to develop a mass diffusion model for dry snow. Homogenization is a multiscale approach linking constituent behavior at the microscopic level—among ice and air—to the macroscopic material—snow. Principles of continuum mechanics at the microscopic scale describe water vapor diffusion across an ice grain's surface to the air-filled pore space. Volume averaging and a localization assumption scale up and down, respectively, between microscopic and macroscopic scales. The model yields a mass diffusivity expression at the macroscopic scale that is, in general, a second-order tensor parameterized by both bulk and microstructural variables. The model predicts a mass diffusivity of water vapor through snow that is less than that through air. Mass diffusivity is expected to decrease linearly with ice volume fraction. Potential anisotropy in snow's mass diffusivity is captured due to the tensor representation. The tensor is built from directional data assigned to specific, idealized microstructural features. Such anisotropy has been observed in the field and laboratories in snow morphologies of interest such as weak layers of depth hoar and near-surface facets.

Anatase TiO2 single crystals with dominant {0 0 1} facets: Synthesis, shape-control mechanism and photocatalytic activity

NASA Astrophysics Data System (ADS)

Tong, Huifen; Zhou, Yingying; Chang, Gang; Li, Pai; Zhu, Ruizhi; He, Yunbin

2018-06-01

Anatase TiO2 micro-crystals with 51% surface exposing highly active {0 0 1} facets are prepared by hydrothermal synthesis using TiF4 as Ti resource and HF as morphology control agent. In addition, anatase TiO2 single crystals exposing large {0 0 1} crystal facets are facilely synthesized with "green" NaF plus HCl replacing HF for the morphology control. A series of comparative experiments are carried out for separately studying the effects of F- and H+ concentrations on the growth of TiO2 crystals, which have not been understood very much in depth so far. The results indicate that both F- and H+ synergistically affect the synthesis of truncated anatase octahedrons, where F- is preferentially adsorbed on the {0 0 1} facets resulting in lateral growth of these facets and H+ adjusts the growth rate of anatase TiO2 along different orientations by tuning the hydrolysis rate. Based on this information, anatase TiO2 single crystals with small size (1.3 μm) and large exposure of {0 0 1} facets (45%) are successfully prepared under optimal conditions ([H+]/[F-] = 20:1). Photocatalytic activities of the as-prepared products toward methylene blue photo-degradation are further tested. It is revealed that both crystal size and percentage of {0 0 1} facets are decisive for the photocatalytic performance, and the crystals with a small size (1.3 μm) and large exposure of {0 0 1} facets (45%) are catalytically most active. This work has clarified the main factors that control the growth process and morphology of anatase TiO2 single crystals for achieving superior photocatalytic properties.

Optical Antenna Arrays on a Fiber Facet for In Situ Surface Enhanced Raman Scattering Detection

PubMed Central

Smythe, Elizabeth J.; Dickey, Michael D.; Bao, Jiming; Whitesides, George M.

2009-01-01

This paper reports a bidirectional fiber optic probe for the detection of surface enhanced Raman scattering (SERS). One facet of the probe features an array of gold optical antennas designed to enhance Raman signal, while the other facet of the fiber is used for the input and collection of light. Simultaneous detection of benzenethiol and 2-[(E)-2-pyridin-4-ylethenyl]pyridine is demonstrated through a 35 cm long fiber. The array of nanoscale optical antennas was first defined by electron-beam lithography on a silicon wafer. The array was subsequently stripped from the wafer and then transferred to the facet of a fiber. Lithographic definition of the antennas provides a method for producing two-dimensional arrays with well-defined geometry, which allows (i) the optical response of the probe to be tuned and (ii) the density of ‘hot spots’ generating the enhanced Raman signal to be controlled. It is difficult to determine the Raman signal enhancement factor (EF) of most fiber optic Raman sensors featuring ‘hot spots’ because the geometry of the Raman enhancing nanostructures is poorly defined. The ability to control the size and spacing of the antennas enables the EF of the transferred array to be estimated. EF values estimated after focusing a laser directly onto the transferred array ranged from 2.6 × 105 to 5.1 × 105. PMID:19236032

Why are Buckyonions Round?

NASA Technical Reports Server (NTRS)

Bates, Kevin R.; Scuseria, Gustavo E.

1998-01-01

Multi-layered round carbon particles (onions) containing tens to hundreds of thousands of atoms form during electron irradiation of graphite. However. theoretical models or large icosahedral fullerenes predict highly faceted shapes for molecules with more than a few hundred atoms. This discrepancy in shape may be explained by the presence of defects during the formation of carbon onions. Here, we use the semi-empirical tight-binding method for carbon to simulate the incorporation of pentagon-heptagon defects on to the surface of large icosahedral fullerenes. We show a simple mechanism that results in energetically competitive derivative structures and a global change in molecular shape from faceted to round. Our results provide a plausible explanation of the apparent discrepancy between experimental observations or round buckyonions and theoretical predictions of faceted icosahedral fullerenes.

What Difference Does It Make? Implicit, Explicit and Complex Social Cognition in Autism Spectrum Disorders

ERIC Educational Resources Information Center

Schaller, Ulrich M.; Rauh, Reinhold

2017-01-01

We tested social cognition abilities of adolescents with autism spectrum disorders (ASD) and neurotypically developed peers (NTD). A multi-faceted test-battery including facial emotion categorization (FEC), classical false belief tasks (FBT), and complex social cognition (SC), yielded significantly lower accuracy rates for FEC and complex SC tasks…

Long-term impact of a precision agriculture system on grain crop production

USDA-ARS?s Scientific Manuscript database

Research is lacking on the long-term impacts of field-scale precision agriculture practices on grain production. Following more than a decade (1993-2003) of yield and soil mapping and water quality assessment, a multi-faceted, ‘precision agriculture system’ (PAS) was implemented from 2004 to 2014 on...

Latent Class Analysis of Peer Conformity: Who Is Yielding to Pressure and Why?

ERIC Educational Resources Information Center

Kosten, Paul A.; Scheier, Lawrence M.; Grenard, Jerry L.

2013-01-01

This study used latent class analysis to examine typologies of peer conformity in a community sample of middle school students. Students responded to 31 items assessing diverse facets of conformity dispositions. The most parsimonious model produced three qualitatively distinct classes that differed on the basis of conformity to recreational…

Thermophysical modelling for high-resolution digital terrain models

NASA Astrophysics Data System (ADS)

Pelivan, I.

2018-07-01

A method is presented for efficiently calculating surface temperatures for highly resolved celestial body shapes. A thorough investigation of the necessary conditions leading to reach model convergence shows that the speed of surface temperature convergence depends on factors such as the quality of initial boundary conditions, thermal inertia, illumination conditions, and resolution of the numerical depth grid. The optimization process to shorten the simulation time while increasing or maintaining the accuracy of model results includes the introduction of facet-specific boundary conditions such as pre-computed temperature estimates and pre-evaluated simulation times. The individual facet treatment also allows for assigning other facet-specific properties such as local thermal inertia. The approach outlined in this paper is particularly useful for very detailed digital terrain models in combination with unfavourable illumination conditions such as little-to-no sunlight at all for a period of time as experienced locally on comet 67P/Churyumov-Gerasimenko. Possible science applications include thermal analysis of highly resolved local (landing) sites experiencing seasonal, environment, and lander shadowing. In combination with an appropriate roughness model, the method is very suitable for application to disc-integrated and disc-resolved data. Further applications are seen where the complexity of the task has led to severe shape or thermophysical model simplifications such as in studying surface activity or thermal cracking.

Free energy of steps using atomistic simulations

NASA Astrophysics Data System (ADS)

Freitas, Rodrigo; Frolov, Timofey; Asta, Mark

The properties of solid-liquid interfaces are known to play critical roles in solidification processes. Particularly special importance is given to thermodynamic quantities that describe the equilibrium state of these surfaces. For example, on the solid-liquid-vapor heteroepitaxial growth of semiconductor nanowires the crystal nucleation process on the faceted solid-liquid interface is influenced by the solid-liquid and vapor-solid interfacial free energies, and also by the free energies of associated steps at these faceted interfaces. Crystal-growth theories and mesoscale simulation methods depend on quantitative information about these properties, which are often poorly characterized from experimental measurements. In this work we propose an extension of the capillary fluctuation method for calculation of the free energy of steps on faceted crystal surfaces. From equilibrium atomistic simulations of steps on (111) surfaces of Copper we computed accurately the step free energy for different step orientations. We show that the step free energy remains finite at all temperature up to the melting point and that the results obtained agree with the more well established method of thermodynamic integration if finite size effects are taken into account. The research of RF and MA at UC Berkeley were supported by the US National Science Foundation (Grant No. DMR-1105409). TF acknowledges support through a postdoctoral fellowship from the Miller Institute for Basic Research in Science.

Associative desorption of hydrogen isotopologues from copper surfaces: Characterization of two reaction mechanisms

NASA Astrophysics Data System (ADS)

Kaufmann, Sven; Shuai, Quan; Auerbach, Daniel J.; Schwarzer, Dirk; Wodtke, Alec M.

2018-05-01

We report quantum-state resolved measurements of angular and velocity distributions of the associative desorption of H2, HD, and D2 from Cu(111) and Cu(211) surfaces. The desorbing molecules have bimodal velocity distributions comprising a "fast" channel and a "slow" channel on both facets. The "fast channel" is promoted by both hydrogen incidence translational and vibrational energy, while the "slow channel" is promoted by vibrational energy but inhibited by translational energy. Using detailed balance, we determine state-specific reaction probabilities for dissociative adsorption and compare these to theoretical calculations. The results for the activation barrier for the "fast channel" on Cu(111) are in agreement with theory within "chemical accuracy" (1 kcal/mole). Results on the Cu(211) facet provide direct information on the effect of increasing step density, which is commonly believed to increase reactivity. Differences in reactivity on the (111) and (211) facets are subtle - quantum state specific reactivity on the (211) surface is characterized by a broader distribution of barrier heights whose average values are higher than for reaction on (111). We fully characterize the "slow channel," which has not been found in theoretical calculations although it makes up a large fraction of the reactivity in these experiments.

Thermophysical modeling for high-resolution digital terrain models

NASA Astrophysics Data System (ADS)

Pelivan, I.

2018-04-01

A method is presented for efficiently calculating surface temperatures for highly resolved celestial body shapes. A thorough investigation of the necessary conditions leading to reach model convergence shows that the speed of surface temperature convergence depends on factors such as the quality of initial boundary conditions, thermal inertia, illumination conditions, and resolution of the numerical depth grid. The optimization process to shorten the simulation time while increasing or maintaining the accuracy of model results includes the introduction of facet-specific boundary conditions such as pre-computed temperature estimates and pre-evaluated simulation times. The individual facet treatment also allows for assigning other facet-specific properties such as local thermal inertia. The approach outlined in this paper is particularly useful for very detailed digital terrain models in combination with unfavorable illumination conditions such as little to no sunlight at all for a period of time as experienced locally on comet 67P/Churyumov-Gerasimenko. Possible science applications include thermal analysis of highly resolved local (landing) sites experiencing seasonal, environment and lander shadowing. In combination with an appropriate roughness model, the method is very suitable for application to disk-integrated and disk-resolved data. Further applications are seen where the complexity of the task has led to severe shape or thermophysical model simplifications such as in studying surface activity or thermal cracking.

Controllable synthesis of palladium nanocubes/reduced graphene oxide composites and their enhanced electrocatalytic performance

NASA Astrophysics Data System (ADS)

Zhang, Yuting; Huang, Qiwei; Chang, Gang; Zhang, Zaoli; Xia, Tiantian; Shu, Honghui; He, Yunbin

2015-04-01

Homogeneous distribution of cube-shaped Pd nanocrystals on the surface of reduced graphene oxide is obtained via a facile one-step method by employing AA and KBr as the reductant and capping agent, respectively. The experimental factors affecting the morphology and structure of Pd nanoparticles have been systematically investigated to explore the formation mechanism of Pd nanocubes (PdNCs). It is revealed that PdNCs enclosed by active {100} facets with an average side length of 15 nm were successfully synthesized on the surface of reduced graphene oxide. KBr plays the role for facet selection by surface passivation and AA controls the reduction speed of Pd precursors, both of which govern the morphology changes of palladium nanoparticles. In the further electrochemical evaluations, the Pd nanocubes/reduced graphene oxide composites show better electrocatalytic activity and stability towards the electro-oxidation of ethanol than both reduced graphene oxide supported Pd nanoparticles and free-standing PdNCs. It could be attributed to the high electrocatalytic activity of the dominated active {100} crystal facets of Pd nanocubes and the enhanced electron transfer of graphene. The developed approach provide a versatile way for shape-controlled preparation of noble metal nanoparticles, which can work as novel electrocatalysts in the application of direct alcohols fuel cells.

Impact of P/In flux ratio and epilayer thickness on faceting for nanoscale selective area growth of InP by molecular beam epitaxy.

PubMed

Fahed, M; Desplanque, L; Coinon, C; Troadec, D; Wallart, X

2015-07-24

The impact of the P/In flux ratio and the deposited thickness on the faceting of InP nanostructures selectively grown by molecular beam epitaxy (MBE) is reported. Homoepitaxial growth of InP is performed inside 200 nm wide stripe openings oriented either along a [110] or [1-10] azimuth in a 10 nm thick SiO2 film deposited on an InP(001) substrate. When varying the P/In flux ratio, no major shape differences are observed for [1-10]-oriented apertures. On the other hand, the InP nanostructure cross sections strongly evolve for [110]-oriented apertures for which (111)B facets are more prominent and (001) ones shrink for large P/In flux ratio values. These results show that the growth conditions allow tailoring the nanocrystal shape. They are discussed in the framework of the equilibrium crystal shape model using existing theoretical calculations of the surface energies of different low-index InP surfaces as a function of the phosphorus chemical potential, directly related to the P/In ratio. Experimental observations strongly suggest that the relative (111)A surface energy is probably smaller than the calculated value. We also discuss the evolution of the nanostructure shape with the InP-deposited thickness.

A Comprehensive Study of Formic Acid Oxidation on Palladium Nanocrystals with Different Types of Facets and Twin Defects

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

Choi, Sang; Herron, Jeffrey A.; Scaranto, Jessica

2015-07-13

Palladium has been recognized as the best anodic, monometallic electrocatalyst for the formic acid oxidation (FAO) reaction in a direct formic acid fuel cell. Here we report a systematic study of FAO on a variety of Pd nanocrystals, including cubes, right bipyramids, octahedra, tetrahedra, decahedra, and icosahedra. These nanocrystals were synthesized with approximately the same size, but different types of facets and twin defects on their surfaces. Our measurements indicate that the Pd nanocrystals enclosed by {1 0 0} facets have higher specific activities than those enclosed by {1 1 1} facets, in agreement with prior observations for Pd single-crystalmore » substrates. If comparing nanocrystals predominantly enclosed by a specific type of facet, {1 0 0} or {1 1 1}, those with twin defects displayed greatly enhanced FAO activities compared to their single-crystal counterparts. To rationalize these experimental results, we performed periodic, self-consistent DFT calculations on model single-crystal substrates of Pd, representing the active sites present in the nanocrystals used in the experiments. The calculation results suggest that the enhancement of FAO activity on defect regions, represented by Pd(2 1 1) sites, compared to the activity of both Pd(1 0 0) and Pd(1 1 1) surfaces, could be attributed to an increased flux through the HCOO-mediated pathway rather than the COOH-mediated pathway on Pd(2 1 1). Since COOH has been identified as a precursor to CO, a site-poisoning species, a lower coverage of CO at the defect regions will lead to a higher activity for the corresponding nanocrystal catalysts, containing those defect regions.« less

Friction at ice-Ih / water interfaces

NASA Astrophysics Data System (ADS)

Louden, Patrick B.; Gezelter, J. Daniel

We present evidence that the prismatic and secondary prism facets of ice-Ih crystals possess structural features that alter the effective hydrophilicity of the ice / water interface. This is shown through molecular dynamics simulations of solid-liquid friction, where the prismatic { 10 1 0 } , secondary prism { 11 2 0 } , basal { 0001 } , and pyramidal { 20 2 1 } facets are drawn through liquid water. We find that the two prismatic facets exhibit differential solid-liquid friction coefficients when compared with the basal and pyramidal facets. These results are complemented by a model solid/liquid interface with tunable hydrophilicity. These simulations provide evidence that the two prismatic faces have a significantly smaller effective surface area in contact with the liquid water. The ice / water interfacial widths for all four crystal facets are similar (using both structural and dynamic measures), and were found to be independent of the shear rate. Additionally, decomposition of orientational time correlation functions show position-dependence for the short- and longer-time decay components close to the interface. Support for this project was provided by the National Science Foundation under Grant CHE-1362211. Computational time was provided by the Center for Research Computing (CRC) at the University of Notre Dame.

Acoustic scattering from phononic crystals with complex geometry.

PubMed

Kulpe, Jason A; Sabra, Karim G; Leamy, Michael J

2016-05-01

This work introduces a formalism for computing external acoustic scattering from phononic crystals (PCs) with arbitrary exterior shape using a Bloch wave expansion technique coupled with the Helmholtz-Kirchhoff integral (HKI). Similar to a Kirchhoff approximation, a geometrically complex PC's surface is broken into a set of facets in which the scattering from each facet is calculated as if it was a semi-infinite plane interface in the short wavelength limit. When excited by incident radiation, these facets introduce wave modes into the interior of the PC. Incorporation of these modes in the HKI, summed over all facets, then determines the externally scattered acoustic field. In particular, for frequencies in a complete bandgap (the usual operating frequency regime of many PC-based devices and the requisite operating regime of the presented theory), no need exists to solve for internal reflections from oppositely facing edges and, thus, the total scattered field can be computed without the need to consider internal multiple scattering. Several numerical examples are provided to verify the presented approach. Both harmonic and transient results are considered for spherical and bean-shaped PCs, each containing over 100 000 inclusions. This facet formalism is validated by comparison to an existing self-consistent scattering technique.

Numerical reproduction and explanation of road surface mirages under grazing-angle scattering.

PubMed

Lu, Jia; Zhou, Huaichun

2017-07-01

The mirror-like reflection image of the road surface under grazing-angle scattering can be easily observed in daily life. It was suggested that road surface mirages may occur due to a light-enhancing effect of the rough surface under grazing-angle scattering. The main purpose of this work is to explain the light-enhancing mechanism of rough surfaces under grazing-angle scattering. The off-specular reflection from a random rough magnesium oxide ceramic surface is analyzed by using the geometric optics approximation method. Then, the geometric optics approximation method is employed to develop a theoretical model to predict the observation effect of the grazing-angle scattering phenomenon of the road surface. The rough surface is assumed to consist of small-scale rough surface facets. The road surface mirage is reproduced from a large number of small-scale rough surface facets within the eye's resolution limit at grazing scattering angles, as the average bidirectional reflectance distribution function value at the bright location is about twice that of the surface in front of the mirage. It is suggested that the light-enhancing effect of the rough surface under grazing-angle scattering is not proper to be termed as "off-specular reflection," since it has nothing to do with the "specular" direction with respect to the incident direction.

Simulation and optimization of faceted structure for illumination

NASA Astrophysics Data System (ADS)

Liu, Lihong; Engel, Thierry; Flury, Manuel

2016-04-01

The re-direction of incoherent light using a surface containing only facets with specific angular values is proposed. A new photometric approach is adopted since the size of each facet is large in comparison with the wavelength. A reflective configuration is employed to avoid the dispersion problems of materials. The irradiance distribution of the reflected beam is determined by the angular position of each facet. In order to obtain the specific irradiance distribution, the angular position of each facet is optimized using Zemax OpticStudio 15 software. A detector is placed in the direction which is perpendicular to the reflected beam. According to the incoherent irradiance distribution on the detector, a merit function needs to be defined to pilot the optimization process. The two dimensional angular position of each facet is defined as a variable which is optimized within a specified varying range. Because the merit function needs to be updated, a macro program is carried out to update this function within Zemax. In order to reduce the complexity of the manual operation, an automatic optimization approach is established. Zemax is in charge of performing the optimization task and sending back the irradiance data to Matlab for further analysis. Several simulation results are given for the verification of the optimization method. The simulation results are compared to those obtained with the LightTools software in order to verify our optimization method.

Selectivity of Glycine for Facets on Gold Nanoparticles.

PubMed

Shao, Qing; Hall, Carol K

2018-04-05

The performance of nanoparticles in medical applications depends on their interactions with various molecules. Despite extensive research on this subject, it remains unclear where on an inhomogeneous nanoparticle molecules prefer to adsorb. Here we investigate the selectivity of glycine molecules for facets on five bare gold nanoparticles with diameters from 1.0 to 5.0 nm. Well-tempered metadynamics simulations are conducted to calculate the adsorption free-energy landscapes of a glycine molecule on various locations for the five gold nanoparticles in explicit water. We also calculate the glycine molecule's adsorption free energies on the five gold nanoparticles in vacuum and on three flat gold surfaces as a reference. The simulation results show that glycine molecules prefer to adsorb on the (110) facet for the 1.0 and 2.0 nm nanoparticles, the edges for the 3.0 nm nanoparticle, and the (111) facet for the 4.0 and 5.0 nm nanoparticles in water. The effect of water solvent on the selectivity is investigated through comparing the adsorption free-energy landscapes for glycine molecules on the nanoparticles in water and in vacuum. The area of the facet plays a key role in determining the selectivity of glycine molecules for the different facets, especially the shift of the selectivity as the nanoparticle diameter changes. Our simulations suggest that nanoparticle size and shape can be engineered to control the preferred adsorption location of molecules.

Can extra-articular strains be used to measure facet contact forces in the lumbar spine? An in-vitro biomechanical study.

PubMed

Zhu, Q A; Park, Y B; Sjovold, S G; Niosi, C A; Wilson, D C; Cripton, P A; Oxland, T R

2008-02-01

Experimental measurement of the load-bearing patterns of the facet joints in the lumbar spine remains a challenge, thereby limiting the assessment of facet joint function under various surgical conditions and the validation of computational models. The extra-articular strain (EAS) technique, a non-invasive measurement of the contact load, has been used for unilateral facet joints but does not incorporate strain coupling, i.e. ipsilateral EASs due to forces on the contralateral facet joint. The objectives of the present study were to establish a bilateral model for facet contact force measurement using the EAS technique and to determine its effectiveness in measuring these facet joint contact forces during three-dimensional flexibility tests in the lumbar spine. Specific goals were to assess the accuracy and repeatability of the technique and to assess the effect of soft-tissue artefacts. In the accuracy and repeatability tests, ten uniaxial strain gauges were bonded to the external surface of the inferior facets of L3 of ten fresh lumbar spine specimens. Two pressure-sensitive sensors (Tekscan) were inserted into the joints after the capsules were cut. Facet contact forces were measured with the EAS and Tekscan techniques for each specimen in flexion, extension, axial rotation, and lateral bending under a +/- 7.5 N m pure moment. Four of the ten specimens were tested five times in axial rotation and extension for repeatability. These same specimens were disarticulated and known forces were applied across the facet joint using a manual probe (direct accuracy) and a materials-testing system (disarticulated accuracy). In soft-tissue artefact tests, a separate set of six lumbar spine specimens was used to document the virtual facet joint contact forces during a flexibility test following removal of the superior facet processes. Linear strain coupling was observed in all specimens. The average peak facet joint contact forces during flexibility testing was greatest in axial rotation (71 +/- 25 N), followed by extension (27 +/- 35 N) and lateral bending (25 +/- 28 N), and they were most repeatable in axial rotation (coefficient of variation, 5 per cent). The EAS accuracy was about 20 per cent in the direct accuracy assessment and about 30 per cent in the disarticulated accuracy test. The latter was very similar to the Tekscan accuracy in the same test. Virtual facet loads (r.m.s.) were small in axial rotation (12 N) and lateral bending (20 N), but relatively large in flexion (34 N) and extension (35 N). The results suggested that the bilateral EAS model could be used to determine the facet joint contact forces in axial rotation but may result in considerable error in flexion, extension, and lateral bending.

X-ray diffraction gratings: Precise control of ultra-low blaze angle via anisotropic wet etching

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

Voronov, Dmitriy L.; Naulleau, Patrick; Gullikson, Eric M.

2016-07-25

Diffraction gratings are used from micron to nanometer wavelengths as dispersing elements in optical instruments. At shorter wavelengths, crystals can be used as diffracting elements, but due to the 3D nature of the interaction with light are wavelength selective rather than wavelength dispersing. There is an urgent need to extend grating technology into the x-ray domain of wavelengths from 1 to 0.1 nm, but this requires the use of gratings that have a faceted surface in which the facet angles are very small, typically less than 1°. Small facet angles are also required in the extreme ultra-violet and soft x-ray energymore » ranges in free electron laser applications, in order to reduce power density below a critical damage threshold. In this work, we demonstrate a technique based on anisotropic etching of silicon designed to produce very small angle facets with a high degree of perfection.« less

Facile synthesis of bird's nest-like TiO2 microstructure with exposed (001) facets for photocatalytic degradation of methylene blue

NASA Astrophysics Data System (ADS)

Zhang, Guozhong; Zhang, Shuqu; Wang, Longlu; Liu, Ran; Zeng, Yunxiong; Xia, Xinnian; Liu, Yutang; Luo, Shenglian

2017-01-01

The scrupulous design of hierarchical structure and highly active crystal facets exposure is essential for the creation of photocatalytic system. However, it is still a big challenge for scrupulous design of TiO2 architectures. In this paper, bird's nest-like anatase TiO2 microstructure with exposed highly active (001) surface has been successfully synthesized by a facile one-step solvothermal method. Methylene blue (MB) is chosen as a model pollutant to evaluate photocatalytic activity of as-obtained TiO2 samples. The results show that the photocatalytic activity of the bird's nest-like sample is more excellent than P25 in the degradation of MB due to high specific surface area and highly active (001) crystal facets exposure when tested under simulated solar light. Besides, it can be readily separated from the photocatalytic system by sedimentation after photocatalytic reaction, which is a significant advantage against conventional powder photocatalyst. The bird's nest-like microspheres with novel structure may have potential application in photocatalysis and other fields.

Correlating Scatter in Fatigue Life with Fracture Mechanisms in Forged Ti-6242Si Alloy

NASA Astrophysics Data System (ADS)

Sinha, V.; Pilchak, A. L.; Jha, S. K.; Porter, W. J.; John, R.; Larsen, J. M.

2018-04-01

Unlike the quasi-static mechanical properties, such as strength and ductility, fatigue life can vary significantly (by an order of magnitude or more) for nominally identical material and test conditions in many materials, including Ti-alloys. This makes life prediction and management more challenging for components that are subjected to cyclic loading in service. The differences in fracture mechanisms can cause the scatter in fatigue life. In this study, the fatigue fracture mechanisms were investigated in a forged near- α titanium alloy, Ti-6Al-2Sn-4Zr-2Mo-0.1Si, which had been tested under a condition that resulted in life variations by more than an order of magnitude. The crack-initiation and small crack growth processes, including their contributions to fatigue life variability, were elucidated via quantitative characterization of fatigue fracture surfaces. Combining the results from quantitative tilt fractography and electron backscatter diffraction, crystallography of crack-initiating and neighboring facets on the fracture surface was determined. Cracks initiated on the surface for both the shortest and the longest life specimens. The facet plane in the crack-initiating grain was aligned with the basal plane of a primary α grain for both the specimens. The facet planes in grains neighboring the crack-initiating grain were also closely aligned with the basal plane for the shortest life specimen, whereas the facet planes in the neighboring grains were significantly misoriented from the basal plane for the longest life specimen. The difference in the extent of cracking along the basal plane can explain the difference in fatigue life of specimens at the opposite ends of scatter band.

Wind Tunnel Application of a Pressure-Sensitive Paint Technique to a Faceted Missile Model at Subsonic and Transonic Speeds

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

2004-01-01

A pressure-sensitive paint (PSP) technique was applied in a wind tunnel experiment in the NASA Langley Research Center 8-Foot Transonic Pressure Tunnel to quantify the vortex-induced surface static pressures on a slender, faceted missile model at subsonic and transonic speeds. Global PSP calibrations were obtained using an in-situ method featuring the simultaneous electronically-scanned pressures (ESP) measurements. Both techniques revealed the significant influence leading-edge vortices on the surface pressure distributions. The mean error in the PSP measurements relative to the ESP data was approximately 0.6 percent at M(sub infinity)=0.70 and 2.6 percent at M(sub infinity)=0.90 and 1.20. The vortex surface pressure signatures obtained from the PSP and ESP techniques were correlated with the off-surface vortex cross-flow structures obtained using a laser vapor screen (LVS) flow visualization technique. The on-surface and off-surface techniques were complementary, since each provided details of the vortex-dominated flow that were not clear or apparent in the other.

Evaluation of an urban land surface scheme over a tropical suburban neighborhood

NASA Astrophysics Data System (ADS)

Harshan, Suraj; Roth, Matthias; Velasco, Erik; Demuzere, Matthias

2017-07-01

The present study evaluates the performance of the SURFEX (TEB/ISBA) urban land surface parametrization scheme in offline mode over a suburban area of Singapore. Model performance (diurnal and seasonal characteristics) is investigated using measurements of energy balance fluxes, surface temperatures of individual urban facets, and canyon air temperature collected during an 11-month period. Model performance is best for predicting net radiation and sensible heat fluxes (both are slightly overpredicted during daytime), but weaker for latent heat (underpredicted during daytime) and storage heat fluxes (significantly underpredicted daytime peaks and nighttime storage). Daytime surface temperatures are generally overpredicted, particularly those containing horizontal surfaces such as roofs and roads. This result, together with those for the storage heat flux, point to the need for a better characterization of the thermal and radiative characteristics of individual urban surface facets in the model. Significant variation exists in model behavior between dry and wet seasons, the latter generally being better predicted. The simple vegetation parametrization used is inadequate to represent seasonal moisture dynamics, sometimes producing unrealistically dry conditions.

More vertical etch profile using a Faraday cage in plasma etching

NASA Astrophysics Data System (ADS)

Cho, Byeong-Ok; Hwang, Sung-Wook; Ryu, Jung-Hyun; Moon, Sang Heup

1999-05-01

Scanning electron microscope images of sidewalls obtained by plasma etching of an SiO2 film with and without a Faraday cage have been compared. When the substrate film is etched in the Faraday cage, faceting is effectively suppressed and the etch profile becomes more vertical regardless of the process conditions. This is because the electric potential in the cage is nearly uniform and therefore distortion of the electric field at the convex corner of a microfeature is prevented. The most vertical etch profile is obtained when the cage is used in fluorocarbon plasmas, where faceting is further suppressed due to the decrease in the chemical sputtering yield and the increase in the radical/ion flux on the substrate.

Extraversion and psychopathology: A facet-level analysis.

PubMed

Watson, David; Stasik, Sara M; Ellickson-Larew, Stephanie; Stanton, Kasey

2015-05-01

The goal of this study was to explicate how the lower order facets of extraversion are related to psychopathology. We used a "bottom-up" approach in which specific extraversion scales from 3 comprehensive personality inventories were used to model these facets as latent factors. We collected both self-report and interview measures of a broad range of psychopathology from a large community sample. Replicating previous findings using a similar approach (Naragon-Gainey & Watson, 2014; Naragon-Gainey, Watson, & Markon, 2009), structural analyses yielded four factors: Positive Emotionality, Sociability, Assertiveness, and Experience Seeking. Scores on these latent dimensions were related to psychopathology in correlational analyses and in two sets of regressions (the first series used the four facets as predictors; the second included composite scores on the other Big Five domains as additional predictors). These results revealed a striking level of specificity. As predicted, Positive Emotionality displayed especially strong negative links to depressive symptoms and diagnoses. Sociability also was negatively related to psychopathology, showing particularly strong associations with indicators of social dysfunction and the negative symptoms of schizotypy (i.e., social anxiety, social aloofness, and restricted affectivity). Assertiveness generally had weak associations at the bivariate level but was negatively related to social anxiety and was positively correlated with some forms of externalizing. Finally, Experience Seeking had substantial positive associations with a broad range of indicators related to externalizing and bipolar disorder; it also displayed negative links to agoraphobia. These differential correlates demonstrate the importance of examining personality-psychopathology relations at the specific facet level. (c) 2015 APA, all rights reserved).

Morphology evolution of single-crystalline hematite nanocrystals: magnetically recoverable nanocatalysts for enhanced facet-driven photoredox activity

NASA Astrophysics Data System (ADS)

Patra, Astam K.; Kundu, Sudipta K.; Bhaumik, Asim; Kim, Dukjoon

2015-12-01

We have developed a new green chemical approach for the shape-controlled synthesis of single-crystalline hematite nanocrystals in aqueous medium. FESEM, HRTEM and SAED techniques were used to determine the morphology and crystallographic orientations of each nanocrystal and its exposed facets. PXRD and HRTEM techniques revealed that the nanocrystals are single crystalline in nature; twins and stacking faults were not detected in these nanocrystals. The structural, vibrational, and electronic spectra of these nanocrystals were highly dependent on their shape. Different shaped hematite nanocrystals with distinct crystallographic planes have been synthesized under similar reaction conditions, which can be desired as a model for the purpose of properties comparison with the nanocrystals prepared under different reaction conditions. Here we investigated the photocatalytic performance of these different shaped-nanocrystals for methyl orange degradation in the presence of white light (λ > 420 nm). In this study, we found that the density of surface Fe3+ ions in particular facets was the key factor for the photocatalytic activity and was higher on the bitruncated-dodecahedron shape nanocrystals by coexposed {104}, {100} and {001} facets, attributing to higher catalytic activity. The catalytic activity of different exposed facet nanocrystals were as follows: {104} + {100} + {001} (bitruncated-dodecahedron) > {101} + {001} (bitruncated-octahedron) > {001} + {110} (nanorods) > {012} (nanocuboid) which provided the direct evidence of exposed facet-driven photocatalytic activity. The nanocrystals were easily recoverable using an external magnet and reused at least six times without significant loss of its catalytic activity.We have developed a new green chemical approach for the shape-controlled synthesis of single-crystalline hematite nanocrystals in aqueous medium. FESEM, HRTEM and SAED techniques were used to determine the morphology and crystallographic orientations of each nanocrystal and its exposed facets. PXRD and HRTEM techniques revealed that the nanocrystals are single crystalline in nature; twins and stacking faults were not detected in these nanocrystals. The structural, vibrational, and electronic spectra of these nanocrystals were highly dependent on their shape. Different shaped hematite nanocrystals with distinct crystallographic planes have been synthesized under similar reaction conditions, which can be desired as a model for the purpose of properties comparison with the nanocrystals prepared under different reaction conditions. Here we investigated the photocatalytic performance of these different shaped-nanocrystals for methyl orange degradation in the presence of white light (λ > 420 nm). In this study, we found that the density of surface Fe3+ ions in particular facets was the key factor for the photocatalytic activity and was higher on the bitruncated-dodecahedron shape nanocrystals by coexposed {104}, {100} and {001} facets, attributing to higher catalytic activity. The catalytic activity of different exposed facet nanocrystals were as follows: {104} + {100} + {001} (bitruncated-dodecahedron) > {101} + {001} (bitruncated-octahedron) > {001} + {110} (nanorods) > {012} (nanocuboid) which provided the direct evidence of exposed facet-driven photocatalytic activity. The nanocrystals were easily recoverable using an external magnet and reused at least six times without significant loss of its catalytic activity. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06509g

Enhanced Visible-Light Photocatalytic H2 Evolution in Cu2O/Cu2Se Multilayer Heterostructure Nanowires Having {111} Facets and Physical Mechanism.

PubMed

Liu, Bin; Ning, Lichao; Zhang, Congjie; Zheng, Hairong; Liu, Shengzhong Frank; Yang, Heqing

2018-06-21

It is rather challenging to develop photocatalysts based on narrow-band-gap semiconductors for water splitting under solar irradiation. Herein, we synthesized the Cu 2 O/Cu 2 Se multilayer heterostructure nanowires exposing {111} crystal facets by a hydrothermal reaction of Se with Cu and KBH 4 in ethanol amine aqueous solution and subsequent annealing in air. The photocatalytic H 2 production activity of Cu 2 O/Cu 2 Se multilayer heterostructure nanowires is dramatically improved, with an increase on the texture coefficient of Cu 2 O(111) and Cu 2 Se(111) planes, and thus the exposed {111} facets may be the active surfaces for photocatalytic H 2 production. On the basis of the polar structure of Cu 2 O {111} and Cu 2 Se {111} surfaces, we presented a model of charge separation between the Cu-Cu 2 Se(111) and O-Cu 2 O(1̅ 1̅ 1̅) polar surfaces. An internal electric field is created between Cu-Cu 2 Se(111) and O-Cu 2 O(1̅ 1̅ 1̅) polar surfaces, because of spontaneous polarization. As a result, this internal electric field drives the photocreated charge separation. The oxidation and reduction reactions selectively occur at the negative O-Cu 2 O(1̅ 1̅ 1̅) and the positive Cu-Cu 2 Se(111) surfaces. The polar surface-engineering may be a general strategy for enhancing the photocatalytic H 2 -production activity of semiconductor photocatalysts. The charge separation mechanism not only can deepen the understanding of photocatalytic H 2 production mechanism but also provides a novel insight into the design of advanced photocatalysts, other photoelectric devices, and solar cells.

(113) Facets of Si-Ge/Si Islands; Atomic Scale Simulation

NASA Astrophysics Data System (ADS)

Kassem, Hassan

We have studied, by computer simulation, some static and vibrationnal proprieties of SiGe/Si islands. We have used a Valence Force Field combined to Monte Carlo technique to study the growth of Ge and SiGe on (001)Si substrates. We have focalised on the case of large pyramidal islands presenting (113) facets on the free (001)Si surface with various non uniform composition inside the islands. The deformation inside the islands and Raman spectroscopy are discussed.

Inverse gravity modeling for depth varying density structures through genetic algorithm, triangulated facet representation, and switching routines

NASA Astrophysics Data System (ADS)

King, Thomas Steven

A hybrid gravity modeling method is developed to investigate the structure of sedimentary mass bodies. The method incorporates as constraints surficial basement/sediment contacts and topography of a mass target with a quadratically varying density distribution. The inverse modeling utilizes a genetic algorithm (GA) to scan a wide range of the solution space to determine initial models and the Marquardt-Levenberg (ML) nonlinear inversion to determine final models that meet pre-assigned misfit criteria, thus providing an estimate of model variability and uncertainty. The surface modeling technique modifies Delaunay triangulation by allowing individual facets to be manually constructed and non-convex boundaries to be incorporated into the triangulation scheme. The sedimentary body is represented by a set of uneven prisms and edge elements, comprised of tetrahedrons, capped by polyhedrons. Each underlying prism and edge element's top surface is located by determining its point of tangency with the overlying terrain. The remaining overlying mass is gravitationally evaluated and subtracted from the observation points. Inversion then proceeds in the usual sense, but on an irregular tiered surface with each element's density defined relative to their top surface. Efficiency is particularly important due to the large number of facets evaluated for surface representations and the many repeated element evaluations of the stochastic GA. The gravitation of prisms, triangular faceted polygons, and tetrahedrons can be formulated in different ways, either mathematically or by physical approximations, each having distinct characteristics, such as evaluation time, accuracy over various spatial ranges, and computational singularities. A decision tree or switching routine is constructed for each element by combining these characteristics into a single cohesive package that optimizes the computation for accuracy and speed while avoiding singularities. The GA incorporates a subspace technique and parameter dependency to maintain model smoothness during development, thus minimizing creating nonphysical models. The stochastic GA explores the solution space, producing a broad range of unbiased initial models, while the ML inversion is deterministic and thus quickly converges to the final model. The combination allows many solution models to be determined from the same observed data.

High-Energy Faceted SnO₂-Coated TiO₂ Nanobelt Heterostructure for Near-Ambient Temperature-Responsive Ethanol Sensor.

PubMed

Chen, Guohui; Ji, Shaozheng; Li, Haidong; Kang, Xueliang; Chang, Sujie; Wang, Yana; Yu, Guangwei; Lu, Jianren; Claverie, Jerome; Sang, Yuanhua; Liu, Hong

2015-11-11

A SnO2 gas sensor was prepared by a two-step oxidation process whereby a Sn(II) precursor was partially oxidized by a hydrothermal process and the resulting Sn3O4 nanoplates were thermally oxidized to yield SnO2 nanoplates. The SnO2 sensor was selective and responsive toward ethanol at a temperature as low as 43 °C. This low sensing temperature stems from the rapid charge transport within SnO2 and from the presence of high-energy (001) facets available for oxygen chemisorption. SnO2/TiO2 nanobelt heterostructures were fabricated by a similar two-step process in which TiO2 nanobelts acted as support for the epitaxial growth of intermediate Sn3O4. At temperatures ranging from 43 to 276 °C, the response of these branched nanobelts is more than double the response of SnO2 for ethanol detection. Our observations demonstrate the potential of low-cost SnO2-based sensors with controlled morphology and reactive facets for detecting gases around room temperature.

High-index faceted Ni3S2 nanosheet arrays as highly active and ultrastable electrocatalysts for water splitting.

PubMed

Feng, Liang-Liang; Yu, Guangtao; Wu, Yuanyuan; Li, Guo-Dong; Li, Hui; Sun, Yuanhui; Asefa, Tewodros; Chen, Wei; Zou, Xiaoxin

2015-11-11

Elaborate design of highly active and stable catalysts from Earth-abundant elements has great potential to produce materials that can replace the noble-metal-based catalysts commonly used in a range of useful (electro)chemical processes. Here we report, for the first time, a synthetic method that leads to in situ growth of {2̅10} high-index faceted Ni3S2 nanosheet arrays on nickel foam (NF). We show that the resulting material, denoted Ni3S2/NF, can serve as a highly active, binder-free, bifunctional electrocatalyst for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Ni3S2/NF is found to give ∼100% Faradaic yield toward both HER and OER and to show remarkable catalytic stability (for >200 h). Experimental results and theoretical calculations indicate that Ni3S2/NF's excellent catalytic activity is mainly due to the synergistic catalytic effects produced in it by its nanosheet arrays and exposed {2̅10} high-index facets.

Thermal inertia and surface heterogeneity on Mars

NASA Astrophysics Data System (ADS)

Putzig, Nathaniel E.

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

The IRGen infrared data base modeler

NASA Technical Reports Server (NTRS)

Bernstein, Uri

1993-01-01

IRGen is a modeling system which creates three-dimensional IR data bases for real-time simulation of thermal IR sensors. Starting from a visual data base, IRGen computes the temperature and radiance of every data base surface with a user-specified thermal environment. The predicted gray shade of each surface is then computed from the user specified sensor characteristics. IRGen is based on first-principles models of heat transport and heat flux sources, and it accurately simulates the variations of IR imagery with time of day and with changing environmental conditions. The starting point for creating an IRGen data base is a visual faceted data base, in which every facet has been labeled with a material code. This code is an index into a material data base which contains surface and bulk thermal properties for the material. IRGen uses the material properties to compute the surface temperature at the specified time of day. IRGen also supports image generator features such as texturing and smooth shading, which greatly enhance image realism.

Tuning selectivity in catalysis by controlling particle shape

NASA Astrophysics Data System (ADS)

Lee, Ilkeun; Delbecq, Françoise; Morales, Ricardo; Albiter, Manuel A.; Zaera, Francisco

2009-02-01

A catalytic process for the selective formation of cis olefins would help minimize the production of unhealthy trans fats during the partial hydrogenation of edible oils. Here we report on the design of such a process on the basis of studies with model systems. Temperature programmed desorption data on single crystals showed that the isomerization of trans olefins to their cis counterparts is promoted by (111) facets of platinum, and that such selectivity is reversed on more open surfaces. Quantum mechanics calculations suggested that the extra stability of cis olefins seen on hydrogen-saturated Pt(111) surfaces may be due to a lesser degree of surface reconstruction, a factor found to be significant in the adsorption on close-packed platinum surfaces. Kinetic data using catalysts made out of dispersed tetrahedral Pt nanoparticles corroborated the selective promotion of the trans-to-cis isomerization on the (111) facets of the metal. Our work provides an example for how catalytic selectivity may be controlled by controlling the shape of the catalytic particles.

Kinetically controlled fabrication of single-crystalline TiO 2 nanobrush architectures with high energy {001} facets

DOE PAGES

Fan, Lisha; Gao, Xiang; Lee, Dongkyu; ...

2017-03-01

Here, this study demonstrates that precise control of nonequilibrium growth conditions during pulsed laser deposition (PLD) can be exploited to produce single-crystalline anatase TiO 2 nanobrush architectures with large surface areas terminated with high energy {001} facets. The data indicate that the key to nanobrush formation is controlling the atomic surface transport processes to balance defect aggregation and surface-smoothing processes. High-resolution scanning transmission electron microscopy data reveal that defect-mediated aggregation is the key to TiO 2 nanobrush formation. The large concentration of defects present at the intersection of domain boundaries promotes aggregation of PLD growth species, resulting in the growthmore » of the single-crystalline nanobrush architecture. This study proposes a model for the relationship between defect creation and growth mode in nonequilibrium environments, which enables application of this growth method to novel nanostructure design in a broad range of materials.« less

Study of gain-coupled distributed feedback laser based on high order surface gain-coupled gratings

NASA Astrophysics Data System (ADS)

Gao, Feng; Qin, Li; Chen, Yongyi; Jia, Peng; Chen, Chao; Cheng, LiWen; Chen, Hong; Liang, Lei; Zeng, Yugang; Zhang, Xing; Wu, Hao; Ning, Yongqiang; Wang, Lijun

2018-03-01

Single-longitudinal-mode, gain-coupled distributed feedback (DFB) lasers based on high order surface gain-coupled gratings are achieved. Periodic surface metal p-contacts with insulated grooves realize gain-coupled mechanism. To enhance gain contrast in the quantum wells without the introduction of effective index-coupled effect, groove length and depth were well designed. Our devices provided a single longitudinal mode with the maximum CW output power up to 48.8 mW/facet at 971.31 nm at 250 mA without facet coating, 3dB linewidth (<3.2 pm) and SMSR (>39 dB). Optical bistable characteristic was observed with a threshold current difference. Experimentally, devices with different cavity lengths were contrasted on power-current and spectrum characteristics. Due to easy fabrication technique and stable performance, it provides a method of fabricating practical gain-coupled distributed feedback lasers for commercial applications.

Nucleation and Early Stages of Layer-by-Layer Growth of Metal Organic Frameworks on Surfaces

PubMed Central

2015-01-01

High resolution atomic force microscopy (AFM) is used to resolve the evolution of crystallites of a metal organic framework (HKUST-1) grown on Au(111) using a liquid-phase layer-by-layer methodology. The nucleation and faceting of individual crystallites is followed by repeatedly imaging the same submicron region after each cycle of growth and we find that the growing surface is terminated by {111} facets leading to the formation of pyramidal nanostructures for [100] oriented crystallites, and triangular [111] islands with typical lateral dimensions of tens of nanometres. AFM images reveal that crystallites can grow by 5–10 layers in each cycle. The growth rate depends on crystallographic orientation and the morphology of the gold substrate, and we demonstrate that under these conditions the growth is nanocrystalline with a morphology determined by the minimum energy surface. PMID:26709359

Growth and modelling of spherical crystalline morphologies of molecular materials

NASA Astrophysics Data System (ADS)

Shalev, O.; Biswas, S.; Yang, Y.; Eddir, T.; Lu, W.; Clarke, R.; Shtein, M.

2014-10-01

Crystalline, yet smooth, sphere-like morphologies of small molecular compounds are desirable in a wide range of applications but are very challenging to obtain using common growth techniques, where either amorphous films or faceted crystallites are the norm. Here we show solvent-free, guard flow-assisted organic vapour jet printing of non-faceted, crystalline microspheroids of archetypal small molecular materials used in organic electronic applications. We demonstrate how process parameters control the size distribution of the spheroids and propose an analytical model and a phase diagram predicting the surface morphology evolution of different molecules based on processing conditions, coupled with the thermophysical and mechanical properties of the molecules. This experimental approach opens a path for exciting applications of small molecular organic compounds in optical coatings, textured surfaces with controlled wettability, pharmaceutical and food substance printing and others, where thick organic films and particles with high surface area are needed.

First principles studies on anatase surfaces

NASA Astrophysics Data System (ADS)

Selcuk, Sencer

TiO2 is one of the most widely studied metal oxides from both the fundamental and the technological points of view. A variety of applications have already been developed in the fields of energy production, environmental remediation, and electronics. Still, it is considered to have a high potential for further improvement and continues to be of great interest. This thesis describes our theoretical studies on the structural and electronic properties of anatase surfaces, and their (photo)chemical behavior. Recently much attention has been focused on anatase crystals synthesized by hydrofluoric acid assisted methods. These crystals exhibit a high percentage of {001} facets, generally considered to be highly reactive. We used first principles methods to investigate the structure of these facets, which is not yet well understood. Our results suggest that (001) surfaces exhibit the bulk-terminated structure when in contact with concentrated HF solutions. However, 1x4-reconstructed surfaces, as observed in UHV, become always more stable at the typical temperatures used to clean the as-prepared crystals in experiments. Since the reconstructed surfaces are only weakly reactive, we predict that synthetic anatase crystals with dominant {001} facets should not exhibit enhanced photocatalytic activity. Understanding how defects in solids interact with external electric fields is important for technological applications such as memristor devices. We studied the influence of an external electric field on the formation energies and diffusion barriers of the surface and the subsurface oxygen vacancies at the anatase (101) surface from first principles. Our results show that the applied field can have a significant influence on the relative stabilities of these defects, whereas the effect on the subsurface-to-surface defect migration is found to be relatively minor. Charge carriers play a key role in the transport properties and the surface chemistry of TiO2. Understanding their behavior is essential for further improving the technologically relevant features of this material. We used first principles simulations to study the dynamical behavior of excess electrons near the anatase (101) and (001) surfaces, and their interfaces with water. Excess electrons prefer localizing on the (101) surface, also triggering water dissociation on this surface, while they strongly avoid the (001) surface.

Highly reactive {001} facets of TiO2-based composites: synthesis, formation mechanism and characterization

NASA Astrophysics Data System (ADS)

Ong, Wee-Jun; Tan, Lling-Lling; Chai, Siang-Piao; Yong, Siek-Ting; Mohamed, Abdul Rahman

2014-01-01

Titanium dioxide (TiO2) is one of the most widely investigated metal oxides due to its extraordinary surface, electronic and catalytic properties. However, the large band gap of TiO2 and massive recombination of photogenerated electron-hole pairs limit its photocatalytic and photovoltaic efficiency. Therefore, increasing research attention is now being directed towards engineering the surface structure of TiO2 at the most fundamental and atomic level namely morphological control of {001} facets in the range of microscale and nanoscale to fine-tune its physicochemical properties, which could ultimately lead to the optimization of its selectivity and reactivity. The synthesis of {001}-faceted TiO2 is currently one of the most active interdisciplinary research areas and demonstrations of catalytic enhancement are abundant. Modifications such as metal and non-metal doping have also been extensively studied to extend its band gap to the visible light region. This steady progress has demonstrated that TiO2-based composites with {001} facets are playing and will continue to play an indispensable role in the environmental remediation and in the search for clean and renewable energy technologies. This review encompasses the state-of-the-art research activities and latest advancements in the design of highly reactive {001} facet-dominated TiO2via various strategies, including hydrothermal/solvothermal, high temperature gas phase reactions and non-hydrolytic alcoholysis methods. The stabilization of {001} facets using fluorine-containing species and fluorine-free capping agents is also critically discussed in this review. To overcome the large band gap of TiO2 and rapid recombination of photogenerated charge carriers, modifications are carried out to manipulate its electronic band structure, including transition metal doping, noble metal doping, non-metal doping and incorporating graphene as a two-dimensional (2D) catalyst support. The advancements made in these aspects are thoroughly examined, with additional insights related to the charge transfer events for each strategy of the modified-TiO2 composites. Finally, we offer a summary and some invigorating perspectives on the major challenges and new research directions for future exploitation in this emerging frontier, which we hope will advance us to rationally harness the outstanding structural and electronic properties of {001} facets for various environmental and energy-related applications.

Highly reactive {001} facets of TiO2-based composites: synthesis, formation mechanism and characterization.

PubMed

Ong, Wee-Jun; Tan, Lling-Lling; Chai, Siang-Piao; Yong, Siek-Ting; Mohamed, Abdul Rahman

2014-02-21

Titanium dioxide (TiO2) is one of the most widely investigated metal oxides due to its extraordinary surface, electronic and catalytic properties. However, the large band gap of TiO2 and massive recombination of photogenerated electron-hole pairs limit its photocatalytic and photovoltaic efficiency. Therefore, increasing research attention is now being directed towards engineering the surface structure of TiO2 at the most fundamental and atomic level namely morphological control of {001} facets in the range of microscale and nanoscale to fine-tune its physicochemical properties, which could ultimately lead to the optimization of its selectivity and reactivity. The synthesis of {001}-faceted TiO2 is currently one of the most active interdisciplinary research areas and demonstrations of catalytic enhancement are abundant. Modifications such as metal and non-metal doping have also been extensively studied to extend its band gap to the visible light region. This steady progress has demonstrated that TiO2-based composites with {001} facets are playing and will continue to play an indispensable role in the environmental remediation and in the search for clean and renewable energy technologies. This review encompasses the state-of-the-art research activities and latest advancements in the design of highly reactive {001} facet-dominated TiO2via various strategies, including hydrothermal/solvothermal, high temperature gas phase reactions and non-hydrolytic alcoholysis methods. The stabilization of {001} facets using fluorine-containing species and fluorine-free capping agents is also critically discussed in this review. To overcome the large band gap of TiO2 and rapid recombination of photogenerated charge carriers, modifications are carried out to manipulate its electronic band structure, including transition metal doping, noble metal doping, non-metal doping and incorporating graphene as a two-dimensional (2D) catalyst support. The advancements made in these aspects are thoroughly examined, with additional insights related to the charge transfer events for each strategy of the modified-TiO2 composites. Finally, we offer a summary and some invigorating perspectives on the major challenges and new research directions for future exploitation in this emerging frontier, which we hope will advance us to rationally harness the outstanding structural and electronic properties of {001} facets for various environmental and energy-related applications.

Rough surface scattering based on facet model

NASA Technical Reports Server (NTRS)

Khamsi, H. R.; Fung, A. K.; Ulaby, F. T.

1974-01-01

A model for the radar return from bare ground was developed to calculate the radar cross section of bare ground and the effect of the frequency averaging on the reduction of the variance of the return. It is shown that, by assuming that the distribution of the slope to be Gaussian and that the distribution of the length of the facet to be in the form of the positive side of a Gaussian distribution, the results are in good agreement with experimental data collected by an 8- to 18-GHz radar spectrometer system. It is also shown that information on the exact correlation length of the small structure on the ground is not necessary; an effective correlation length may be calculated based on the facet model and the wavelength of the incident wave.

Why Are Buckyonions Round?

NASA Technical Reports Server (NTRS)

Bates, Kevin R.; Scuseria, Gustavo E.

1997-01-01

Multi-layered round carbon particles (onions) containing tens to hundreds of thousands of atoms form during electron irradiation of graphite carbon. However, theoretical models of large icosahedral fullerenes predict highly faceted shapes for molecules with more than a few hundred atoms. This discrepancy in shape may be explained by the presence of defects during the formation of carbon onions. Here, we use the semi-empirical tight-binding method for carbon to simulate the incorporation of pentagon-heptagon defects on to the surface of large icosahedral fullerenes. We show a simple mechanism that results in energetically competitive derivative structures and a global change in molecular shape from faceted to round. Our results provide a plausible explanation of the apparent discrepancy between experimental observations of round buckyonions and theoretical predictions of faceted icosahedral fullerenes.

Platinum-Based Nanocages with Subnanometer-Thick Walls and Well-Defined Facets

DOE PAGES

Zhang, Lei; Wang, Xue; Chi, Miaofang; ...

2015-07-24

A cost-effective catalyst should have a high dispersion of the active atoms, together with a controllable surface structure for the optimization of activity, selectivity, or both. We fabricated nanocages by depositing a few atomic layers of platinum (Pt) as conformal shells on palladium (Pd) nanocrystals with well-defined facets and then etching away the Pd templates. Density functional theory calculations suggest that the etching is initiated via a mechanism that involves the formation of vacancies through the removal of Pd atoms incorporated into the outermost layer during the deposition of Pt. With the use of Pd nanoscale cubes and octahedra asmore » templates, we obtained Pt cubic and octahedral nanocages enclosed by {100} and {111} facets, respectively, which exhibited distinctive catalytic activities toward oxygen reduction.« less

Shape Effect Undermined by Surface Reconstruction: Ethanol Dehydrogenation over Shape-Controlled SrTiO 3 Nanocrystals

DOE PAGES

Foo, Guo Shiou; Hood, Zachary D.; Wu, Zili

2017-12-05

For this research, to gain an in-depth understanding of the surface properties relevant for catalysis using ternary oxides, we report the acid–base pair reactivity of shape-controlled SrTiO 3 (STO) nanocrystals for the dehydrogenation of ethanol. Cubes, truncated cubes, dodecahedra, and etched cubes of STO with varying ratios of (001) and (110) crystal facets were synthesized using a hydrothermal method. Low-energy ion scattering (LEIS) analysis revealed that the (001) surface on cubes of STO is enriched with SrO due to surface reconstruction, resulting in a high ratio of strong base sites. Chemical treatment with dilute nitric acid to form etched cubesmore » of STO resulted in a surface enriched with Ti cations and strong acidity. Furthermore, the strength and distribution of surface acidic sites increase with the ratio of (110) facet from cubes to truncated cubes to dodecahedra for STO. Kinetic, isotopic, and spectroscopy methods show that the dehydrogenation of ethanol proceeds through the facile dissociation of the alcohol group, followed by the cleavage of the C α–H bond, which is the rate-determining step. Co-feeding of various probe molecules during catalysis, such as NH 3, 2,6-di-tert-butylpyridine, CO 2, and SO 2, reveals that a pair of Lewis acid site and basic surface oxygen atom is involved in the dehydrogenation reaction. The surface density of acid–base site pairs was measured using acetic acid as a probe molecule, allowing initial acetaldehyde formation turnover rates to be obtained. Comparison among various catalysts reveals no simple correlation between ethanol turnover rate and the percentage of either surface facet ((001) or (110)) of the STO nanocrystals. Instead, the reaction rate is found to increase with the strength of acid sites but reversely with the strength of base sites. The acid–base property is directly related to the surface composition as a result from different surface reconstruction behaviors of the shaped STO nanocrystals. Lastly, the finding in this work underscores the importance of characterizing the top surface compositions and sites properties when assessing the catalytic performance of shape-controlled complex oxides such as perovskites.« less

Surface Structure Dependence of SO 2 Interaction with Ceria Nanocrystals with Well-defined Surface Facets

DOE PAGES

Tumuluri, Uma; Li, Meijun; Cook, Brandon G.; ...

2015-12-02

The effects of the surface structure of ceria (CeO 2) on the nature, strength, and amount of species resulting from SO 2 adsorption were studied using in situ IR and Raman spectroscopies coupled with mass spectrometry, along with first-principles calculations based on density functional theory (DFT). CeO 2 nanocrystals with different morphologies, namely, rods (representing a defective structure), cubes (100 facet), and octahedra (111 facet), were used to represent different CeO 2 surface structures. IR and Raman spectroscopic studies showed that the structure and binding strength of adsorbed species from SO 2 depend on the shape of the CeO 2more » nanocrystals. SO 2 adsorbs mainly as surface sulfites and sulfates at room temperature on CeO 2 rods, cubes, and octahedra that were either oxidatively or reductively pretreated. The formation of sulfites is more evident on CeO 2 octahedra, whereas surface sulfates are more prominent on CeO 2 rods and cubes. This is explained by the increasing reducibility of the surface oxygen in the order octahedra < cubes < rods. Bulk sulfites are also formed during SO 2 adsorption on reduced CeO 2 rods. The formation of surface sulfites and sulfates on CeO 2 cubes is in good agreement with our DFT results of SO 2 interactions with the CeO 2(100) surface. CeO 2 rods desorb SO2 at higher temperatures than cubes and octahedra nanocrystals, but bulk sulfates are formed on CeO 2 rods and cubes after high-temperature desorption whereas only some surface sulfates/sulfites are left on octahedra. This difference is rationalized by the fact that CeO 2 rods have the highest surface basicity and largest amount of defects among the three nanocrystals, so they bind and react with SO 2 strongly and are the most degraded after SO 2 adsorption cycles. The fundamental understanding obtained in this work on the effects of the surface structure and defects on the interaction of SO 2 with CeO 2 provides insights for the design of more sulfur-resistant CeO 2-based catalysts.« less

Shape Effect Undermined by Surface Reconstruction: Ethanol Dehydrogenation over Shape-Controlled SrTiO 3 Nanocrystals

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

Foo, Guo Shiou; Hood, Zachary D.; Wu, Zili

For this research, to gain an in-depth understanding of the surface properties relevant for catalysis using ternary oxides, we report the acid–base pair reactivity of shape-controlled SrTiO 3 (STO) nanocrystals for the dehydrogenation of ethanol. Cubes, truncated cubes, dodecahedra, and etched cubes of STO with varying ratios of (001) and (110) crystal facets were synthesized using a hydrothermal method. Low-energy ion scattering (LEIS) analysis revealed that the (001) surface on cubes of STO is enriched with SrO due to surface reconstruction, resulting in a high ratio of strong base sites. Chemical treatment with dilute nitric acid to form etched cubesmore » of STO resulted in a surface enriched with Ti cations and strong acidity. Furthermore, the strength and distribution of surface acidic sites increase with the ratio of (110) facet from cubes to truncated cubes to dodecahedra for STO. Kinetic, isotopic, and spectroscopy methods show that the dehydrogenation of ethanol proceeds through the facile dissociation of the alcohol group, followed by the cleavage of the C α–H bond, which is the rate-determining step. Co-feeding of various probe molecules during catalysis, such as NH 3, 2,6-di-tert-butylpyridine, CO 2, and SO 2, reveals that a pair of Lewis acid site and basic surface oxygen atom is involved in the dehydrogenation reaction. The surface density of acid–base site pairs was measured using acetic acid as a probe molecule, allowing initial acetaldehyde formation turnover rates to be obtained. Comparison among various catalysts reveals no simple correlation between ethanol turnover rate and the percentage of either surface facet ((001) or (110)) of the STO nanocrystals. Instead, the reaction rate is found to increase with the strength of acid sites but reversely with the strength of base sites. The acid–base property is directly related to the surface composition as a result from different surface reconstruction behaviors of the shaped STO nanocrystals. Lastly, the finding in this work underscores the importance of characterizing the top surface compositions and sites properties when assessing the catalytic performance of shape-controlled complex oxides such as perovskites.« less

Machinability of drilling T700/LT-03A carbon fiber reinforced plastic (CFRP) composite laminates using candle stick drill and multi-facet drill

NASA Astrophysics Data System (ADS)

Wang, Cheng-Dong; Qiu, Kun-Xian; Chen, Ming; Cai, Xiao-Jiang

2015-03-01

Carbon Fiber Reinforced Plastic (CFRP) composite laminates are widely used in aerospace and aircraft structural components due to their superior properties. However, they are regarded as difficult-to-cut materials because of bad surface quality and low productivity. Drilling is the most common hole making process for CFRP composite laminates and drilling induced delamination damage usually occurs severely at the exit side of drilling holes, which strongly deteriorate holes quality. In this work, the candle stick drill and multi-facet drill are employed to evaluate the machinability of drilling T700/LT-03A CFRP composite laminates in terms of thrust force, delamination, holes diameter and holes surface roughness. S/N ratio is used to characterize the thrust force while an ellipse-shaped delamination model is established to quantitatively analyze the delamination. The best combination of drilling parameters are determined by full consideration of S/N ratios of thrust force and the delamination. The results indicate that candle stick drill will induce the unexpected ellipse-shaped delamination even at its best drilling parameters of spindle speed of 10,000 rpm and feed rate of 0.004 mm/tooth. However, the multi-facet drill cutting at the relative lower feed rate of 0.004 mm/tooth and lower spindle speed of 6000 rpm can effectively prevent the delamination. Comprehensively, holes quality obtained by multi-facet drill is much more superior to those obtained by candle stick drill.

Observations of Screw Dislocation Driven Growth and Faceting During CVD Homoepitaxy on 4H-SiC On-Axis Mesa Arrays

NASA Technical Reports Server (NTRS)

Neudeck, Philip G.; Trunek, Andrew J.; Powell, J. Anthony; Picard, Yoosuf N.; Twigg, Mark E.

2009-01-01

Previous studies of (0001) homoepitaxial growth carried out on arrays of small-area mesas etched into on-axis silicon-face 4H-SiC wafers have demonstrated that spiral growth emanating from at least one screw dislocation threading the mesa is necessary in order for a mesa to grow taller in the <0001> (c-axis vertical) direction while maintaining 4H stacking sequence [1]. However, even amongst mesas containing the screw dislocation step source necessary for vertical c-axis growth, we have observed striking differences in the height and faceting that evolve during prolonged homoepitaxial growths. This paper summarizes Atomic Force Microscopy (AFM), Electron Channeling Contrast Imaging (ECCI), Scanning Electron Microscopy (SEM), and optical microscopy observations of this phenomenon. These observations support our initially proposed model [2] that the observed large variation (for mesas where 3C-SiC nucleation has not occurred) is related to the lateral positioning of a screw dislocation step source within each etched mesa. When the screw dislocation step source is located close enough to the developing edge/sidewall facet of a mesa, the c-axis growth rate and facet angle are affected by the resulting interaction. In particular, the intersection (or near intersection) of the inward-sloping mesa sidewall facet with the screw dislocation appears to impede the rate at which the spiral provides new steps required for c-axis growth. Also, the inward slope of the sidewall facet during growth (relative to other sidewalls of the same mesa not near the screw dislocation) seems to be impeded by the screw dislocation. In contrast, mesas whose screw dislocations are centrally located grow vertically, but inward sloping sidewall facets shrink the area of the top (0001) growth surface almost to the point of vanishing.

On the Structure Sensitivity of Dimethyl Ether Electro-oxidation on Eight FCC Metals: A First-Principles Study

DOE PAGES

Herron, Jeffrey A.; Ferrin, Peter; Mavrikakis, Manos

2015-09-24

The electro-oxidation of dimethyl ether (DME) was investigated using periodic, self-consistent density functional theory (DFT) calculations on the (111) and (100) facets of eight fcc metals: Au, Ag, Cu, Pt, Pd, Ni, Ir, and Rh. The goal of this study is to understand the experimentally observed structure sensitivity of this reaction on Pt, and to predict trends in structure sensitivity of this reaction across the other seven metals studied. The main conclusion is that the enhanced activity of Pt(100) originates from more facile C–O bond breaking and removal of surface poisoning species, including CO and CH. When comparing C–O bondmore » breaking energetics, we do not find a universal trend where these elementary steps are always more exergonic on the (100) facet. However, we find that, at a given potential, DME can be dehydrogenated (prior to breaking the C–O bond) to a greater extent on the (100) facet. Additionally, we find that the reaction energy for C–O bond breaking in CHxOCHy-type species becomes increasingly exergonic as the species becomes increasingly dehydrogenated. Together, the more facile dehydrogenation on the (100) facets provides more favorable routes to C–O bond activation. Though we calculate a lower onset potential on Au(100), Ag(100), Cu(100), Pt(100), and Pd(100) than their respective (111) facets, the calculated onset potential for Ni(100), Ir(100), and Rh(100) are actually higher than for their respective (111) facets. Lastly, by constructing theoretical volcano plots, we conclude that Au(100), Ag(100), Cu(100), Pt(100), and Pd(100) should be more active than their respective (111) facets, while Ni(100), Rh(100), and Ir(100) will show the opposite trend.« less

Light-induced charge separation across bio-inorganic interface.

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

Dimitrijevic, N. M.; Rajh, T.; De La Garza, L.

Rational design of hybrid biomolecule - nanoparticulate semiconductor conjugates enables coupling of functionality of biomolecules with the capability of semiconductors for solar energy capture, that can have potential application in energy conversion, sensing and catalysis. The particular challenge is to obtain efficient charge separation analogous to the natural photosynthesis process. The synthesis of axially anisotropic TiO{sub 2} nano-objects such as tubes, rods and bricks, as well as spherical and faceted nanoparticles has been developed in our laboratory. Depending on their size and shape, these nanostructures exhibit different domains of crystallinity, surface areas and aspect ratios. Moreover, in order to accommodatemore » for high curvature in nanoscale regime, the surfaces of TiO{sub 2} nano-objects reconstructs resulting in changes in the coordination of surface Ti atoms from octahedral (D{sub 2d}) to square pyramidal structures (C{sub 4v}). The formation of these coordinatively unsaturated Ti atoms, thus depends strongly on the size and shape of nanocrystallites and affects trapping and reactivity of photogenerated charges. We have exploited these coordinatively unsaturated Ti atoms to coupe electron-donating (such as dopamine) and electron-accepting (pyrroloquinoline quinone) conductive linkers that allow wiring of biomolecules and proteins resulting in enhanced charge separation which increases the yield of ensuing chemical transformations.« less

Comparison of PARASOL Observations with Polarized Reflectances Simulated Using Different Ice Habit Mixtures

NASA Technical Reports Server (NTRS)

Cole, Benjamin H.; Yang, Ping; Baum, Bryan A.; Riedi, Jerome; Labonnote, Laurent C.; Thieuleux, Francois; Platnick, Steven

2012-01-01

Insufficient knowledge of the habit distribution and the degree of surface roughness of ice crystals within ice clouds is a source of uncertainty in the forward light scattering and radiative transfer simulations required in downstream applications involving these clouds. The widely used MODerate Resolution Imaging Spectroradiometer (MODIS) Collection 5 ice microphysical model assumes a mixture of various ice crystal shapes with smooth-facets except aggregates of columns for which a moderately rough condition is assumed. When compared with PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) polarized reflection data, simulations of polarized reflectance using smooth particles show a poor fit to the measurements, whereas very rough-faceted particles provide an improved fit to the polarized reflectance. In this study a new microphysical model based on a mixture of 9 different ice crystal habits with severely roughened facets is developed. Simulated polarized reflectance using the new ice habit distribution is calculated using a vector adding-doubling radiative transfer model, and the simulations closely agree with the polarized reflectance observed by PARASOL. The new general habit mixture is also tested using a spherical albedo differences analysis, and surface roughening is found to improve the consistency of multi-angular observations. It is suggested that an ice model incorporating an ensemble of different habits with severely roughened surfaces would potentially be an adequate choice for global ice cloud retrievals.

Surface Structure Dependence of SO 2 Interaction with Ceria Nanocrystals with Well-Defined Surface Facets

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

Tumuluri, Uma; Li, Meijun; Cook, Brandon G.

2015-12-31

The effects of the surface structure of ceria (CeO2) on the nature, strength, and amount of species resulting from SO2 adsorption were studied using in situ IR and Raman spectroscopies coupled with mass spectrometry, along with first-principles calculations based on density functional theory (DFT). CeO2 nanocrystals with different morphologies, namely, rods (representing a defective structure), cubes (100 facet), and octahedra (111 facet), were used to represent different CeO2 surface structures. IR and Raman spectroscopic studies showed that the structure and binding strength of adsorbed species from SO2 depend on the shape of the CeO2 nanocrystals. SO2 adsorbs mainly as surfacemore » sulfites and sulfates at room temperature on CeO2 rods, cubes, and octahedra that were either oxidatively or reductively pretreated. The formation of sulfites is more evident on CeO2 octahedra, whereas surface sulfates are more prominent on CeO2 rods and cubes. This is explained by the increasing reducibility of the surface oxygen in the order octahedra < cubes < rods. Bulk sulfites are also formed during SO2 adsorption on reduced CeO2 rods. The formation of surface sulfites and sulfates on CeO2 cubes is in good agreement with our DFT results of SO2 interactions with the CeO2(100) surface. CeO2 rods desorb SO2 at higher temperatures than cubes and octahedra nanocrystals, but bulk sulfates are formed on CeO2 rods and cubes after high-temperature desorption whereas only some surface sulfates/sulfites are left on octahedra. This difference is rationalized by the fact that CeO2 rods have the highest surface basicity and largest amount of defects among the three nanocrystals, so they bind and react with SO2 strongly and are the most degraded after SO2 adsorption cycles. The fundamental understanding obtained in this work on the effects of the surface structure and defects on the interaction of SO2 with CeO2 provides insights for the design of more sulfur-resistant CeO2-based catalysts.« less

A job-satisfaction measure for internal medicine residency program directors.

PubMed

Beasley, B W; Kern, D E; Howard, D M; Kolodner, K

1999-03-01

To develop a job-satisfaction measure that encompasses the multifaceted job of internal medicine residency program directors. Questions were devised to measure program directors satisfaction with various facets of their jobs. In 1996, the authors surveyed all non-military internal medicine program directors in the United States. Of the program directors surveyed, 301 (78%) responded. More respondents than non-respondents held the title of department chairperson in addition to the title of program director (22% vs 7%). Factor analysis and correlation analysis yielded a multifaceted measure (termed PD-Sat) composed of 20 questions and six facets (work with residents, colleague relationships, resources, patient care, pay, and promotion) that made sense based on literature review and discussions with program directors (face validity). The PD-Sat had good internal reliability (Cronbach's alpha = .88), as had each of its six facets (Cronbach's alphas = .60-.90). The six facets correlated modestly with one another (Pearson's r2 = .12-.67), suggesting they were measuring different aspects of a common concept. The PD-Sat correlated significantly with an established four-question global job-satisfaction scale used in previous studies (Pearson's r2 = .33) demonstrating concurrent validity. Scores on the PD-Sat predicted whether program directors were considering, seeking, or making a job change (predictive validity). The PD-Sat performed comparably well in subsets of program directors who were and were not department chairs, suggesting that it might be applicable to different populations of program directors. The authors have developed a new facet-specific job-satisfaction measure that is reliable and valid for assessing the job satisfaction of internal medicine program directors. Because job descriptions for program directors in other specialties are similar, it may also be useful in these populations.

Edge enhanced growth induced shape transition in the formation of GaN nanowall network

NASA Astrophysics Data System (ADS)

Nayak, Sanjay; Kumar, Rajendra; Shivaprasad, S. M.

2018-01-01

We address the mechanism of early stages of growth and shape transition of the unique nanowall network (NwN) of GaN by experimentally monitoring its morphological evolution and complementing it by first-principles calculations. Using atomic force and scanning electron microscopy, we observe the formation of oval shaped islands at very early stages of the growth which later transformed into tetrahedron shaped (3 faced pyramid) islands. These tetrahedron shaped islands further grow anisotropically along their edges of the (20 2 ¯ 1) facets to form the wall-like structure as the growth proceeds. The mechanism of this crystal growth is discussed in light of surface free energies of the different surfaces, adsorption energy, and diffusion barrier of Ga ad-atoms on the (20 2 ¯ 1) facets. By first-principles calculations, we find that the diffusion barrier of ad-atoms reduces with decreasing width of facets and is responsible for the anisotropic growth leading to the formation of NwN. This study suggests that formation of NwN is an archetype example of structure dependent attachment kinetic instability induced shape transition in thin film growth.

Pathways toward unidirectional alignment in block copolymer thin films on faceted surfaces

NASA Astrophysics Data System (ADS)

Gunkel, Ilja; Gu, Xiaodan; Sarje, Abhinav; Hexemer, Alexander; Russell, Thomas

2015-03-01

Solvent vapor annealing (SVA) has been shown recently to be an effective means to produce long-range lateral order in block copolymer (BCP) thin films in relatively short times. Furthermore, using substrates with faceted surfaces allows for generating unidirectionally aligned BCP microdomains on the size scale of an entire wafer. While in recent years SVA has been largely demystified, the detailed pathways toward obtaining unidirectional alignment still remain unclear. Grazing-incidence X-ray scattering (GISAXS) is a very powerful tool for characterizing the structure and morphology of BCPs in thin films, and is particularly useful for studying structural changes in BCP thin films during SVA. We here present in situ GISAXS experiments on cylinder-forming PS-b-P2VP BCP thin films on faceted Sapphire substrates during annealing in THF. We show that the degree of alignment of cylindrical microdomains is greatly enhanced at solvent concentrations close to the order-disorder transition of the copolymer. Furthermore, we observed that inducing disorder by further increasing the solvent concentration and subsequent quenching to the ordered (not yet glassy) state induced the highest degree of alignment with nearly unidirectional alignment of the microdomains in less than 30 min.

White light emission of monolithic InGaN/GaN grown on morphology-controlled, nanostructured GaN templates.

PubMed

Song, Keun Man; Kim, Do-Hyun; Kim, Jong-Min; Cho, Chu-Young; Choi, Jehyuk; Kim, Kahee; Park, Jinsup; Kim, Hogyoug

2017-06-02

We demonstrated an InGaN/GaN-based, monolithic, white light-emitting diode (LED) without phosphors by using morphology-controlled active layers formed on multi-facet GaN templates containing polar and semipolar surfaces. The nanostructured surface morphology was controlled by changing the growth time, and distinct multiple photoluminescence peaks were observed at 360, 460, and 560 nm; these features were caused by InGaN/GaN-based multiple quantum wells (MQWs) on the nanostructured facets. The origin of each multi-peak was related to the different indium (In) compositions in the different planes of the quantum wells grown on the nanostructured GaN. The emitting units of MQWs in the LED structures were continuously connected, which is different from other GaN-based nanorod or nanowire LEDs. Therefore, the suggested structure had a larger active area. From the electroluminescence spectrum of the fabricated LED, monolithic white light emission with CIE color coordinates of x = 0.306 and y = 0.333 was achieved via multi-facet control combined with morphology control of the metal organic chemical vapor deposition-selective area growth of InGaN/GaN MQWs.

Realistic Analytical Polyhedral MRI Phantoms

PubMed Central

Ngo, Tri M.; Fung, George S. K.; Han, Shuo; Chen, Min; Prince, Jerry L.; Tsui, Benjamin M. W.; McVeigh, Elliot R.; Herzka, Daniel A.

2015-01-01

Purpose Analytical phantoms have closed form Fourier transform expressions and are used to simulate MRI acquisitions. Existing 3D analytical phantoms are unable to accurately model shapes of biomedical interest. It is demonstrated that polyhedral analytical phantoms have closed form Fourier transform expressions and can accurately represent 3D biomedical shapes. Theory The derivations of the Fourier transform of a polygon and polyhedron are presented. Methods The Fourier transform of a polyhedron was implemented and its accuracy in representing faceted and smooth surfaces was characterized. Realistic anthropomorphic polyhedral brain and torso phantoms were constructed and their use in simulated 3D/2D MRI acquisitions was described. Results Using polyhedra, the Fourier transform of faceted shapes can be computed to within machine precision. Smooth surfaces can be approximated with increasing accuracy by increasing the number of facets in the polyhedron; the additional accumulated numerical imprecision of the Fourier transform of polyhedra with many faces remained small. Simulations of 3D/2D brain and 2D torso cine acquisitions produced realistic reconstructions free of high frequency edge aliasing as compared to equivalent voxelized/rasterized phantoms. Conclusion Analytical polyhedral phantoms are easy to construct and can accurately simulate shapes of biomedical interest. PMID:26479724

White light emission of monolithic InGaN/GaN grown on morphology-controlled, nanostructured GaN templates

NASA Astrophysics Data System (ADS)

Song, Keun Man; Kim, Do-Hyun; Kim, Jong-Min; Cho, Chu-Young; Choi, Jehyuk; Kim, Kahee; Park, Jinsup; Kim, Hogyoug

2017-06-01

We demonstrated an InGaN/GaN-based, monolithic, white light-emitting diode (LED) without phosphors by using morphology-controlled active layers formed on multi-facet GaN templates containing polar and semipolar surfaces. The nanostructured surface morphology was controlled by changing the growth time, and distinct multiple photoluminescence peaks were observed at 360, 460, and 560 nm; these features were caused by InGaN/GaN-based multiple quantum wells (MQWs) on the nanostructured facets. The origin of each multi-peak was related to the different indium (In) compositions in the different planes of the quantum wells grown on the nanostructured GaN. The emitting units of MQWs in the LED structures were continuously connected, which is different from other GaN-based nanorod or nanowire LEDs. Therefore, the suggested structure had a larger active area. From the electroluminescence spectrum of the fabricated LED, monolithic white light emission with CIE color coordinates of x = 0.306 and y = 0.333 was achieved via multi-facet control combined with morphology control of the metal organic chemical vapor deposition-selective area growth of InGaN/GaN MQWs.

A first principles study of commonly observed planar defects in Ti/TiB system

DOE PAGES

Nandwana, Peeyush; Gupta, Niraj; Srinivasan, Srivilliputhur G.; ...

2018-04-20

Here, TiB exhibits a hexagonal cross-section with growth faults on (1 0 0) planes and contains B27-B f bicrystals. The hexagonal cross-section is presently explained by surface free energy minimization principle. We show that interfacial energy calculations explain the longer (1 0 0) facet compared to (1 0 1) type facets whereas free surface energy arguments do not provide the true picture. No quantitative explanation of stacking faults and B27-B f interfaces in TiB exists. We show that the low formation energy of stacking faults and B27-B f interfaces explain their abundance. The low energy barrier for B f formationmore » is shown to be responsible for their presence in TiB.« less

A first principles study of commonly observed planar defects in Ti/TiB system

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

Nandwana, Peeyush; Gupta, Niraj; Srinivasan, Srivilliputhur G.

Here, TiB exhibits a hexagonal cross-section with growth faults on (1 0 0) planes and contains B27-B f bicrystals. The hexagonal cross-section is presently explained by surface free energy minimization principle. We show that interfacial energy calculations explain the longer (1 0 0) facet compared to (1 0 1) type facets whereas free surface energy arguments do not provide the true picture. No quantitative explanation of stacking faults and B27-B f interfaces in TiB exists. We show that the low formation energy of stacking faults and B27-B f interfaces explain their abundance. The low energy barrier for B f formationmore » is shown to be responsible for their presence in TiB.« less

Dispersion-compensated fresnel lens

DOEpatents

Johnson, Kenneth C.

1992-01-01

A transmission grating is used to reduce chromatic aberration in a Fresnel lens, wherein the lens chromatic dispersion is offset and substantially canceled by the grating's diffraction-induced dispersion. The grating comprises a Fresnel-type pattern of microscopic facets molded directly into the lens surface. The facets would typically have a profile height of around 4.multidot.10.sup.-5 inch and a profile width of at least 10.sup.-3 inch. In its primary intended application, the invention would function to improve the optical performance of a Fresnel lens used to concentrate direct sunlight.

Dynamical Scaling Implications of Ferrari, Prähofer, and Spohn's Remarkable Spatial Scaling Results for Facet-Edge Fluctuations

NASA Astrophysics Data System (ADS)

Einstein, T. L.; Pimpinelli, Alberto

2014-06-01

Spurred by theoretical predictions from Ferrari et al. (Phys Rev E 69:035102(R), 2004), we rederived and extended their result heuristically. With experimental colleagues we used STM line scans to corroborate their prediction that the fluctuations of the step bounding a facet exhibit scaling properties distinct from those of isolated steps or steps on vicinal surfaces. The correlation functions was shown to go as , decidedly different from the behavior for fluctuations of isolated steps.

Directed self-assembly of Ge nanostructures on very high index, highly anisotropic Si(hkl) surfaces.

PubMed

Ohmori, Kenji; Foo, Y L; Hong, Sukwon; Wen, J G; Greene, J E; Petrov, I

2005-02-01

Families of very high-index planes, such as those which bifurcate spontaneously to form a hill-and-valley structure composed of opposing facets, provide natural templates for the directed growth of position-controlled self-organized nanostructures with shapes determined by the facet width ratio R. For example, deposition of a few ML of Ge on Si(173 100 373), corresponding to R(113/517) = 1.7, results in a field of 40-nm-wide Ge nanowires along [72 187] with a uniform period of 60 nm.

Dispersion-compensated Fresnel lens

DOEpatents

Johnson, K.C.

1992-11-03

A transmission grating is used to reduce chromatic aberration in a Fresnel lens, wherein the lens chromatic dispersion is offset and substantially canceled by the grating's diffraction-induced dispersion. The grating comprises a Fresnel-type pattern of microscopic facets molded directly into the lens surface. The facets would typically have a profile height of around 4[times]10[sup [minus]5] inch and a profile width of at least 10[sup [minus]3] inch. In its primary intended application, the invention would function to improve the optical performance of a Fresnel lens used to concentrate direct sunlight. 10 figs.

From Cylindrical to Stretching Ridges and Wrinkles in Twisted Ribbons

NASA Astrophysics Data System (ADS)

Pham Dinh, Huy; Démery, Vincent; Davidovitch, Benny; Brau, Fabian; Damman, Pascal

2016-09-01

Twisted ribbons under tension exhibit a remarkably rich morphology, from smooth and wrinkled helicoids, to cylindrical or faceted patterns. This complexity emanates from the instability of the natural, helicoidal symmetry of the system, which generates both longitudinal and transverse stresses, thereby leading to buckling of the ribbon. Here, we focus on the tessellation patterns made of triangular facets. Our experimental observations are described within an "asymptotic isometry" approach that brings together geometry and elasticity. The geometry consists of parametrized families of surfaces, isometric to the undeformed ribbon in the singular limit of vanishing thickness and tensile load. The energy, whose minimization selects the favored structure among those families, is governed by the tensile work and bending cost of the pattern. This framework describes the coexistence lines in a morphological phase diagram, and determines the domain of existence of faceted structures.

Achieving High Current Density of Perovskite Solar Cells by Modulating the Dominated Facets of Room-Temperature DC Magnetron Sputtered TiO2 Electron Extraction Layer.

PubMed

Huang, Aibin; Lei, Lei; Zhu, Jingting; Yu, Yu; Liu, Yan; Yang, Songwang; Bao, Shanhu; Cao, Xun; Jin, Ping

2017-01-25

The short circuit current density of perovskite solar cell (PSC) was boosted by modulating the dominated plane facets of TiO 2 electron transport layer (ETL). Under optimized condition, TiO 2 with dominant {001} facets showed (i) low incident light loss, (ii) highly smooth surface and excellent wettability for precursor solution, (iii) efficient electron extraction, and (iv) high conductivity in perovskite photovoltaic application. A current density of 24.19 mA cm -2 was achieved as a value near the maximum limit. The power conversion efficiency was improved to 17.25%, which was the record value of PSCs with DC magnetron sputtered carrier transport layer. What is more, the room-temperature process had a great significance for the cost reduction and flexible application of PSCs.

Fabrication of precision high quality facets on molecular beam epitaxy material

DOEpatents

Petersen, Holly E.; Goward, William D.; Dijaili, Sol P.

2001-01-01

Fabricating mirrored vertical surfaces on semiconductor layered material grown by molecular beam epitaxy (MBE). Low energy chemically assisted ion beam etching (CAIBE) is employed to prepare mirrored vertical surfaces on MBE-grown III-V materials under unusually low concentrations of oxygen in evacuated etching atmospheres of chlorine and xenon ion beams. UV-stabilized smooth-surfaced photoresist materials contribute to highly vertical, high quality mirrored surfaces during the etching.

Adsorption of benzene on low index surfaces of platinum in the presence of van der Waals interactions

NASA Astrophysics Data System (ADS)

K, Ayishabi P.; Chatanathodi, Raghu

2017-10-01

We have studied the adsorption of benzene on three low index surfaces of platinum using plane-wave Density Functional Theory (DFT) calculations, taking into consideration van der Waals (vdW) interaction. Experimentally, it is known that benzene adsorbs at the bridge site on the (111) surface, but in case of (110) and (100), this is not known yet. Our calculations show that benzene preferably adsorbs on bridge position on Pt(111) surface, whereas on Pt(110) and Pt(100) surfaces, the hollow position is energetically more favoured. The structural and electronic modifications of molecule and the surfaces are also examined. In all cases, adsorption-induced distortions of adsorbate-substrate complex are found to be modest in character, but relatively maximum in case of the (110) facet. The molecule is bound most strongly to the (110) surface. Importantly, we find that adsorption at bridge and atop positions are energetically feasible on the (110) surface, with the canting of benzene ring at a small angle from the metal plane. We study changes in electronic structure and the net charge transfer upon adsorption of benzene on all three low index planes. Inclusion of vdW interactions is important for obtaining realistic adsorption strengths for benzene on various Pt facets.

Thermal behavior of horizontally mixed surfaces on Mars

NASA Astrophysics Data System (ADS)

Putzig, Nathaniel E.; Mellon, Michael T.

2007-11-01

Current methods for deriving thermal inertia from spacecraft observations of planetary brightness temperature generally assume that surface properties are uniform for any given observation or co-located set of observations. As a result of this assumption and the nonlinear relationship between temperature and thermal inertia, sub-pixel horizontal heterogeneity may yield different apparent thermal inertia at different times of day or seasons. We examine the effects of horizontal heterogeneity on Mars by modeling the thermal behavior of various idealized mixed surfaces containing differing proportions of either dust, sand, duricrust, and rock or slope facets at different angles and azimuths. Latitudinal effects on mixed-surface thermal behavior are also investigated. We find large (several 100 J m -2 K -1 s -1/2) diurnal and seasonal variations in apparent thermal inertia even for small (˜10%) admixtures of materials with moderately contrasting thermal properties or slope angles. Together with similar results for layered surfaces [Mellon, M.T., Putzig, N.E., 2007. Lunar Planet. Sci. XXXVIII. Abstract 2184], this work shows that the effects of heterogeneity on the thermal behavior of the martian surface are substantial and may be expected to result in large variations in apparent thermal inertia as derived from spacecraft instruments. While our results caution against the over-interpretation of thermal inertia taken from median or average maps or derived from single temperature measurements, they also suggest the possibility of using a suite of apparent thermal inertia values derived from single observations over a range of times of day and seasons to constrain the heterogeneity of the martian surface.

Direct visualization of quasi-ordered oxygen chain structures on Au(110)-(1 × 2)

NASA Astrophysics Data System (ADS)

Hiebel, F.; Montemore, M. M.; Kaxiras, E.; Friend, C. M.

2016-08-01

The Au(110) surface offers unique advantages for atomically-resolved model studies of catalytic oxidation processes on gold. We investigate the adsorption of oxygen on Au(110) using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) methods. We identify the typical (empty-states) STM contrast resulting from adsorbed oxygen as atomic-sized dark features of electronic origin. DFT-based image simulations confirm that chemisorbed oxygen is generally detected indirectly, from the binding-induced electronic structure modification of gold. STM images show that adsorption occurs without affecting the general structure of the pristine Au(110) missing-row reconstruction. The tendency to form one-dimensional structures is observed already at low coverage (< 0.05 ML), with oxygen adsorbing on alternate sides of the reconstruction ridges. Consistently, calculations yield preferred adsorption on the (111) facets of the reconstruction, on a 3-fold coordination site, with increased stability when adsorbed in chains. Gold atoms with two oxygen neighbors exhibit enhanced electronic hybridization with the O states. Finally, the species observed are reactive to CO oxidation at 200 K and desorption of CO2 leaves a clean and ordered gold surface.

Ab initio simulation of structure and surface energy of low-index surfaces of stoichiometric α-Fe2O3

NASA Astrophysics Data System (ADS)

Stirner, Thomas; Scholz, David; Sun, Jizhong

2018-05-01

The structure and surface energy of a series of low-index surfaces of stoichiometric α-Fe2O3 (hematite) are investigated using the periodic Hartree-Fock approach with an a posteriori correction of the correlation energy. The simulations show that, amongst the modeled facets, (01 1 bar2) and (0001) are the most stable surfaces of hematite, which is consistent with the fact that the latter are the dominant growth faces exposed on natural α-Fe2O3. The Fe-terminated (0001) surface is shown to exhibit a large relaxation of the surface atoms. It is argued that this arises mainly due to the fact that the surface cations are located opposite empty cation sites in the filled-filled-unfilled cation sequence along the c-axis. In contrast, the (01 1 bar2) plane cuts the crystal through a plane of empty cation sites, thus giving rise to relatively small relaxations and surface energies. The small relaxations and concomitant exposure of five-coordinate cation sites may be important for the catalytic activity of hematite. The simulations also show that the relative stability of the investigated surfaces changes after a full lattice relaxation with the (0001) and (11 2 bar6) facets relaxing disproportionately large. Wherever possible, the simulations are compared with previous simulation data and experimental results. A Wulff-Gibbs construction is also presented.

Occlusal wear and occlusal condition in a convenience sample of young adults.

PubMed

Van't Spijker, A; Kreulen, C M; Bronkhorst, E M; Creugers, N H J

2015-01-01

To study progression of tooth wear quantitatively in a convenient sample of young adults and to assess possible correlations with occlusal conditions. Twenty-eight dental students participated in a three-year follow up study on tooth wear. Visible wear facets on full arch gypsum casts were assessed using a flatbed scanner and measuring software. Regression analyses were used to assess possible associations between the registered occlusal conditions 'occlusal guidance scheme', 'vertical overbite', 'horizontal overbite', 'depth of sagittal curve', 'canine Angle class relation', 'history of orthodontic treatment', and 'self-reported grinding/clenching' (independent variables) and increase of wear facets (dependent variable). Mean increase in facet surface areas ranged from 1.2 mm2 (premolars, incisors) to 3.4 mm2 (molars); the relative increase ranged from 15% to 23%. Backward regression analysis showed no significant relation for 'group function', 'vertical overbite', 'depth of sagittal curve', 'history of orthodontic treatment' nor 'self-reported clenching. The final multiple linear regression model showed significant associations amongst 'anterior protected articulation' and 'horizontal overbite' and increase of facet surface areas. For all teeth combined, only 'anterior protected articulation' had a significant effect. 'Self reported grinding' did not have a significant effect (p>0.07). In this study 'anterior protected articulation' and 'horizontal overbite', were significantly associated with the progression of tooth wear. Self reported grinding was not significantly associated with progression of tooth wear. Occlusal conditions such as anterior protected articulation and horizontal overbite seem to have an effect on the progression of occlusal tooth wear in this convenient sample of young adults. Copyright © 2014 Elsevier Ltd. All rights reserved.

DOE Award No. FG02-93ER14331 Final Technical Report

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

Bartynski, Robert

We have studyed new aspects of the relationships between nanoscale surface features and heterogeneous catalysis or electrocatalysis. We concentrate on atomically rough and morphologically unstable surfaces of catalytic metal single crystals (Re, Ru, Ir) that undergo nanoscale faceting when interacting with strongly adsorbed species (e.g. O, N, C) at elevated temperatures.

Surface enrichment of Pt in stable Pt-Ir nano-alloy particles on MgAl 2O 4 spinel in oxidizing atmosphere

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

Li, Wei -Zhen; Nie, Lei; Cheng, Yingwen

With the capability of MgAl 2O 4 spinel {111} nano-facets in stabilizing small Rh, Ir and Pt particles, bimetallic Ir-Pt catalysts on the same support were investigated in this paper, aiming at further lowering the catalyst cost by substituting expensive Pt with cheaper Ir in the bulk. Small Pt-Ir nano-alloy particles (< 2 nm) were successfully stabilized on the spinel {111} nano-facets as expected. Interestingly, methanol oxidative dehydrogenation (ODH) rate on the surface Pt atoms increases with oxidizing aging but decreases upon reducing treatment, where Ir is almost inactive under the same reaction conditions. Up to three times enhancement inmore » Pt exposure was achieved when the sample was oxidized at 800 °C in air for 1 week and subsequently reduced by H 2 for 2 h, demonstrating successful surface enrichment of Pt on Pt-Ir nano-alloy particles. Finally, a dynamic stabilization mechanism involving wetting/nucleation seems to be responsible for the evolution of surface compositions upon cyclic oxidizing and reducing thermal treatments.« less

An Automated Method for Landmark Identification and Finite-Element Modeling of the Lumbar Spine.

PubMed

Campbell, Julius Quinn; Petrella, Anthony J

2015-11-01

The purpose of this study was to develop a method for the automated creation of finite-element models of the lumbar spine. Custom scripts were written to extract bone landmarks of lumbar vertebrae and assemble L1-L5 finite-element models. End-plate borders, ligament attachment points, and facet surfaces were identified. Landmarks were identified to maintain mesh correspondence between meshes for later use in statistical shape modeling. 90 lumbar vertebrae were processed creating 18 subject-specific finite-element models. Finite-element model surfaces and ligament attachment points were reproduced within 1e-5 mm of the bone surface, including the critical contact surfaces of the facets. Element quality exceeded specifications in 97% of elements for the 18 models created. The current method is capable of producing subject-specific finite-element models of the lumbar spine with good accuracy, quality, and robustness. The automated methods developed represent advancement in the state of the art of subject-specific lumbar spine modeling to a scale not possible with prior manual and semiautomated methods.

Adsorption and Reaction of Acetaldehyde on Shape-Controlled CeO2 Nanocrystals: Elucidation of Structure-function Relationships

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

Mann, Amanda K; Wu, Zili; Calaza, Florencia

2014-01-01

CeO2 cubes with {100} facets, octahedra with {111} facets, and wires with highly defective structures were utilized to probe the structure-dependent reactivity of acetaldehyde. Using temperature-programmed desorption (TPD), temperature-programmed surface reactions (TPSR), and in situ infrared spectroscopy it was found that acetaldehyde desorbs unreacted or undergoes reduction, coupling, or C-C bond scission reactions depending on the surface structure of CeO2. Room temperature FTIR indicates that acetaldehyde binds primarily as 1-acetaldehyde on the octahedra, in a variety of conformations on the cubes, including coupling products and acetate and enolate species, and primarily as coupling products on the wires. The percent consumptionmore » of acetaldehyde follows the order of wires > cubes > octahedra. All the nanoshapes produce the coupling product crotonaldehyde; however, the selectivity to produce ethanol follows the order wires cubes >> octahedra. The selectivity and other differences can be attributed to the variation in the basicity of the surfaces, defects densities, coordination numbers of surface atoms, and the reducibility of the nanoshapes.« less

Theoretical Investigations of Transition Metal Surface Energies under Lattice Strain and CO Environment

DOE PAGES

Tang, Michael T.; Ulissi, Zachary W.; Chan, Karen

2018-05-30

Here, an understanding of the relative stability of surface facets is crucial to develop predictive models of catalyst activity and to fabricate catalysts with a controlled morphology. In this work, we present a systematic density functional theory study of the effect of lattice strain and CO environment on the surface formation energies of Cu, Pt, and Ni. First, we show that both compressive and tensile lattice strains favor the formation of stepped versus low-index terraces such as (111) and (100). Then, we investigate the effect of the CO environment using configurations of CO at various coverages, determined using a greedy,more » systematic approach, inspired by forward stepwise feature selection. We find that the CO environment favors stepped facets on Ni, Cu, and Pt. These trends are illustrated with the corresponding equilibrium Wulff shapes at various strains and CO pressures. In general, the surface energies of the studied transition metals are highly sensitive to strain and CO coverage, which should be considered when rationalizing trends in the catalytic activity.« less

Surface enrichment of Pt in stable Pt-Ir nano-alloy particles on MgAl 2O 4 spinel in oxidizing atmosphere

DOE PAGES

Li, Wei -Zhen; Nie, Lei; Cheng, Yingwen; ...

2017-01-13

With the capability of MgAl 2O 4 spinel {111} nano-facets in stabilizing small Rh, Ir and Pt particles, bimetallic Ir-Pt catalysts on the same support were investigated in this paper, aiming at further lowering the catalyst cost by substituting expensive Pt with cheaper Ir in the bulk. Small Pt-Ir nano-alloy particles (< 2 nm) were successfully stabilized on the spinel {111} nano-facets as expected. Interestingly, methanol oxidative dehydrogenation (ODH) rate on the surface Pt atoms increases with oxidizing aging but decreases upon reducing treatment, where Ir is almost inactive under the same reaction conditions. Up to three times enhancement inmore » Pt exposure was achieved when the sample was oxidized at 800 °C in air for 1 week and subsequently reduced by H 2 for 2 h, demonstrating successful surface enrichment of Pt on Pt-Ir nano-alloy particles. Finally, a dynamic stabilization mechanism involving wetting/nucleation seems to be responsible for the evolution of surface compositions upon cyclic oxidizing and reducing thermal treatments.« less

Theoretical Investigations of Transition Metal Surface Energies under Lattice Strain and CO Environment

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

Tang, Michael T.; Ulissi, Zachary W.; Chan, Karen

Here, an understanding of the relative stability of surface facets is crucial to develop predictive models of catalyst activity and to fabricate catalysts with a controlled morphology. In this work, we present a systematic density functional theory study of the effect of lattice strain and CO environment on the surface formation energies of Cu, Pt, and Ni. First, we show that both compressive and tensile lattice strains favor the formation of stepped versus low-index terraces such as (111) and (100). Then, we investigate the effect of the CO environment using configurations of CO at various coverages, determined using a greedy,more » systematic approach, inspired by forward stepwise feature selection. We find that the CO environment favors stepped facets on Ni, Cu, and Pt. These trends are illustrated with the corresponding equilibrium Wulff shapes at various strains and CO pressures. In general, the surface energies of the studied transition metals are highly sensitive to strain and CO coverage, which should be considered when rationalizing trends in the catalytic activity.« less

Surface enrichment of Pt in stable Pt-Ir nano-alloy particles on MgAl 2 O 4 spinel in oxidizing atmosphere

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

Li, Wei-Zhen; Nie, Lei; Cheng, Yingwen

With the capability of MgAl2O4 spinel {111} nano-facets in stabilizing small Rh, Ir and Pt particles, bimetallic Ir-Pt catalysts on the same support were investigated, aiming at further lowering the catalyst cost by substituting expensive Pt with cheaper Ir in the bulk. Small Pt-Ir nano-alloy particles (< 2nm) were successfully stabilized on the spinel {111} nano-facets as expected. Interestingly, methanol oxidative dehydrogenation (ODH) rate on the surface Pt atoms increases with oxidizing aging but decreases upon reducing treatment, where Ir is almost inactive under the same reaction conditions. Up to three times enhancement in Pt exposure was achieved when themore » sample was oxidized at 800 °C in air for 1 week and subsequently reduced by H2 for 2 h, demonstrating successful surface enrichment of Pt on Pt-Ir nano-alloy particles. A dynamic stabilization mechanism involving wetting\

On the limited recognition of inorganic surfaces by short peptides compared with antibodies.

PubMed

Artzy-Schnirman, Arbel; Abu-Shah, Enas; Dishon, Matan; Soifer, Hadas; Sivan, Yotam; Reiter, Yoram; Benhar, Itai; Sivan, Uri

2014-06-01

The vast potential applications of biomolecules that bind inorganic surfaces led mostly to the isolation of short peptides that target selectively specific materials. The demonstrated differential affinity toward certain surfaces created the impression that the recognition capacity of short peptides may match that of rigid biomolecules. In the following, we challenge this view by comparing the capacity of antibody molecules to discriminate between the (100) and (111A) facets of a gallium arsenide semiconductor crystal with the capacity of short peptides to do the same. Applying selection from several peptide and single chain phage display libraries, we find a number of antibody molecules that bind preferentially a given crystal facet but fail to isolate, in dozens of attempts, a single peptide capable of such recognition. The experiments underscore the importance of rigidity to the recognition of inorganic flat targets and therefore set limitations on potential applications of short peptides in biomimetics. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.

Revealing Anisotropic Spinel Formation on Pristine Li- and Mn-Rich Layered Oxide Surface and Its Impact on Cathode Performance

DOE PAGES

Kuppan, Saravanan; Shukla, Alpesh Khushalchand; Membreno, Daniel; ...

2017-01-06

Surface properties of cathode particles play important roles in the transport of ions and electrons and they may ultimately dominate cathode's performance and stability in lithium-ion batteries. Through the use of carefully prepared Li 1.2Ni 0.13Mn 0.54Co 0.13O 2 crystal samples with six distinct morphologies, surface transition-metal redox activities and crystal structural transformation are investigated as a function of surface area and surface crystalline orientation. Complementary depth-profiled core-level spectroscopy, namely, X-ray absorption spectroscopy, electron energy loss spectroscopy, and atomic-resolution scanning transmission electron microscopy, are applied in the study, presenting a fine example of combining advanced diagnostic techniques with a well-definedmore » model system of battery materials. Here, we report the following findings: (1) a thin layer of defective spinel with reduced transition metals, similar to what is reported on cycled conventional secondary particles in the literature, is found on pristine oxide surface even before cycling, and (2) surface crystal structure and chemical composition of both pristine and cycled particles are facet dependent. Oxide structural and cycling stabilities improve with maximum expression of surface facets stable against transition-metal reduction. Finally, the intricate relationships among morphology, surface reactivity and structural transformation, electrochemical performance, and stability of the cathode materials are revealed.« less

Effects of surface stability on the morphological transformation of metals and metal oxides as investigated by first-principles calculations.

PubMed

Andrés, Juan; Gracia, Lourdes; Gouveia, Amanda Fernandes; Ferrer, Mateus Meneghetti; Longo, Elson

2015-10-09

Morphology is a key property of materials. Owing to their precise structure and morphology, crystals and nanocrystals provide excellent model systems for joint experimental and theoretical investigations into surface-related properties. Faceted polyhedral crystals and nanocrystals expose well-defined crystallographic planes depending on the synthesis method, which allow for thoughtful investigations into structure-reactivity relationships under practical conditions. This feature article introduces recent work, based on the combined use of experimental findings and first-principles calculations, to provide deeper knowledge of the electronic, structural, and energetic properties controlling the morphology and the transformation mechanisms of different metals and metal oxides: Ag, anatase TiO2, BaZrO3, and α-Ag2WO4. According to the Wulff theorem, the equilibrium shapes of these systems are obtained from the values of their respective surface energies. These investigations are useful to gain further understanding of how to achieve morphological control of complex three-dimensional crystals by tuning the ratio of the surface energy values of the different facets. This strategy allows the prediction of possible morphologies for a crystal and/or nanocrystal by controlling the relative values of surface energies.

Interlocked by nanoscale sculpturing: pure aluminum copper contacts (Conference Presentation)

NASA Astrophysics Data System (ADS)

Gerngross-Baytekin, Melike; Gerngross, Mark Daniel; Carstensen, Jürgen; Adelung, Rainer

2017-06-01

Connecting metals reliable with different corrosion potential is a well-known challenge. An extreme example are copper aluminum contacts. Galvanic corrosion occurs if the two different metals are in contact with each other and an electrolyte, the aluminum becomes susceptible to corrosion under current flow. Usually, antioxidant pastes containing metals are employed but create difficulties e.g. for fatigue resistant power electronic connections. The recently described process of nanoscale sculpturing [1] offers an alternative. Usually, if the surface of metals like aluminium are prepared they are just arbitrary cuts through the bulk. There is no optimization of the surface grain structure towards stability at all. Neither the crystalline facets in the grains are in their most stable orientation nor is the protective oxide shell the most stable one. The nanoscale sculpturing approach is carving out the most stable grains and planes by chemical or electrochemical treatment. The decisive trick is that the chemistry is targeting towards the instable oxide and not the metal. Aluminium sample surfaces including alloys like AA575 exhibit afterwards single crystalline surface facets covered with nanoscale stable oxide films. Galvanically deposited copper forms extremely reliable interlocked connections on top, even allowing for soldering on top of their surface.

Atomic Scale Analysis of the Enhanced Electro- and Photo-Catalytic Activity in High-Index Faceted Porous NiO Nanowires

NASA Astrophysics Data System (ADS)

Shen, Meng; Han, Ali; Wang, Xijun; Ro, Yun Goo; Kargar, Alireza; Lin, Yue; Guo, Hua; Du, Pingwu; Jiang, Jun; Zhang, Jingyu; Dayeh, Shadi A.; Xiang, Bin

2015-02-01

Catalysts play a significant role in clean renewable hydrogen fuel generation through water splitting reaction as the surface of most semiconductors proper for water splitting has poor performance for hydrogen gas evolution. The catalytic performance strongly depends on the atomic arrangement at the surface, which necessitates the correlation of the surface structure to the catalytic activity in well-controlled catalyst surfaces. Herein, we report a novel catalytic performance of simple-synthesized porous NiO nanowires (NWs) as catalyst/co-catalyst for the hydrogen evolution reaction (HER). The correlation of catalytic activity and atomic/surface structure is investigated by detailed high resolution transmission electron microscopy (HRTEM) exhibiting a strong dependence of NiO NW photo- and electrocatalytic HER performance on the density of exposed high-index-facet (HIF) atoms, which corroborates with theoretical calculations. Significantly, the optimized porous NiO NWs offer long-term electrocatalytic stability of over one day and 45 times higher photocatalytic hydrogen production compared to commercial NiO nanoparticles. Our results open new perspectives in the search for the development of structurally stable and chemically active semiconductor-based catalysts for cost-effective and efficient hydrogen fuel production at large scale.

Carbonate-mediated Mars-van Krevelen mechanism for CO oxidation on cobalt-doped ceria catalysts: facet-dependence and coordination-dependence.

PubMed

Liu, Bing; Li, Wenping; Song, Weiyu; Liu, Jian

2018-06-13

Carbonate intermediates have been reported to play an active role in CO oxidation over ceria-based catalysts in recent experimental studies. However, the detailed CO oxidation mechanism involving carbonate intermediates over ceria-based catalysts remains obscure. In this work, we carried out systematic density functional theory calculations corrected by on-site Coulomb interactions (DFT+U) to investigate the complete CO oxidation mechanism involving carbonate intermediates over cobalt-doped CeO2 catalysts, aiming to unravel how the carbonate participates in CO oxidation and shed light on the underlying factors that control the carbonate-mediated reaction mechanism. A novel carbonate-mediated Mars-van Krevelen (M-vK) mechanism was proposed, in which the carbonate acts as an active intermediate rather than a spectator and can react with CO to form CO2. This carbonate-mediated M-vK mechanism is facet-dependent because it is predominant on the (110) surface whereas the conventional M-vK mechanism is more favorable on (111) and (100) surfaces. The origin of facet-dependence was discussed by analyzing the geometric and electronic structures. It is found that the negatively charged bent CO2- intermediate formed on the (110) surface plays a critical role in the carbonate-mediated M-vK mechanism, whereas the formation of a neutral linear CO2 intermediate on (111) and (100) surfaces hinders the carbonate-mediated M-vK mechanism. The surface oxygen vacancy hinders the formation of carbonate intermediates, indicating that the carbonate-mediated M-vK mechanism is also vacancy-dependent. The formation of carbonate intermediates on different metal (Ti, V, W, Mo and Re) doped CeO2(110) surfaces was studied and the results indicate that the coordination environment of the dopant species is a key factor that determines the carbonate-mediated M-vK mechanism. This study provides atomic-scale insights into the reaction mechanism involving carbonate intermediates and the structure-mechanism relationship for CO oxidation over cobalt-ceria catalysts.

Structure sensitivity in oxide catalysis: First-principles kinetic Monte Carlo simulations for CO oxidation at RuO 2(111)

DOE PAGES

Wang, Tongyu; Reuter, Karsten

2015-11-24

We present a density-functional theory based kinetic Monte Carlo study of CO oxidation at the (111) facet of RuO 2. We compare the detailed insight into elementary processes, steady-state surface coverages, and catalytic activity to equivalent published simulation data for the frequently studied RuO 2(110) facet. Qualitative differences are identified in virtually every aspect ranging from binding energetics over lateral interactions to the interplay of elementary processes at the different active sites. Nevertheless, particularly at technologically relevant elevated temperatures, near-ambient pressures and near-stoichiometric feeds both facets exhibit almost identical catalytic activity. As a result, these findings challenge the traditional definitionmore » of structure sensitivity based on macroscopically observable turnover frequencies and prompt scrutiny of the applicability of structure sensitivity classifications developed for metals to oxide catalysis.« less

Fabrication of a novel quartz micromachined gyroscope

NASA Astrophysics Data System (ADS)

Xie, Liqiang; Xing, Jianchun; Wang, Haoxu; Wu, Xuezhong

2015-04-01

A novel quartz micromachined gyroscope is proposed in this paper. The novel gyroscope is realized by quartz anisotropic wet etching and 3-dimensional electrodes deposition. In the quartz wet etching process, the quality of Cr/Au mask films affecting the process are studied by experiment. An excellent mask film with 100 Å Cr and 2000 Å Au is achieved by optimization of experimental parameters. Crystal facets after etching seriously affect the following sidewall electrodes deposition process and the structure's mechanical behaviours. Removal of crystal facets is successfully implemented by increasing etching time based on etching rate ratios between facets and crystal planes. In the electrodes deposition process, an aperture mask evaporation method is employed to prepare electrodes on 3-dimensional surfaces of the gyroscope structure. The alignments among the aperture masks are realized by the ABM™ Mask Aligner System. Based on the processes described above, a z-axis quartz gyroscope is fabricated successfully.

Structure sensitivity in oxide catalysis: First-principles kinetic Monte Carlo simulations for CO oxidation at RuO{sub 2}(111)

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

Wang, Tongyu; Reuter, Karsten, E-mail: karsten.reuter@ch.tum.de; SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory and Stanford University, 443 Via Ortega, Stanford, California 94035-4300

2015-11-28

We present a density-functional theory based kinetic Monte Carlo study of CO oxidation at the (111) facet of RuO{sub 2}. We compare the detailed insight into elementary processes, steady-state surface coverages, and catalytic activity to equivalent published simulation data for the frequently studied RuO{sub 2}(110) facet. Qualitative differences are identified in virtually every aspect ranging from binding energetics over lateral interactions to the interplay of elementary processes at the different active sites. Nevertheless, particularly at technologically relevant elevated temperatures, near-ambient pressures and near-stoichiometric feeds both facets exhibit almost identical catalytic activity. These findings challenge the traditional definition of structure sensitivitymore » based on macroscopically observable turnover frequencies and prompt scrutiny of the applicability of structure sensitivity classifications developed for metals to oxide catalysis.« less

Optical characterization of synthetic faceted gem materials grown from hydrothermal solutions

NASA Astrophysics Data System (ADS)

Lu, Taijin; Shigley, James E.

1998-10-01

Various non-destructive optical characterization techniques have been used to characterize and identify synthetic gem materials grown from hydrothermal solutions, to include ruby, sapphire, emerald, amethyst and ametrine (amethyst-citrine), from their natural counterparts. The ability to observe internal features, such as inclusions, dislocations, twins, color bands, and growth zoning in gem materials is strongly dependent on the observation techniques and conditions, since faceted gemstones have many polished surfaces which can reflect and scatter light in various directions which can make observation difficult. However, diagnostic gemological properties of these faceted synthetic gem materials can be obtained by choosing effective optical characterization methods, and by modifying optical instruments. Examples of some of the distinctive features of synthetic amethyst, ametrine, pink quartz, ruby and emerald are presented to illustrate means of optical characterization of gemstones. The ability to observe defects by light scattering techniques is discussed.

Ab initio calculation of transport properties between PbSe quantum dots facets with iodide ligands

NASA Astrophysics Data System (ADS)

Wang, B.; Patterson, R.; Chen, W.; Zhang, Z.; Yang, J.; Huang, S.; Shrestha, S.; Conibeer, G.

2018-01-01

The transport properties between Lead Selenide (PbSe) quantum dots decorated with iodide ligands has been studied using density functional theory (DFT). Quantum conductance at each selected energy levels has been calculated along with total density of states and projected density of states. The DFT calculation is carried on using a grid-based planar augmented wave (GPAW) code incorporated with the linear combination of atomic orbital (LCAO) mode and Perdew Burke Ernzerhof (PBE) exchange-correlation functional. Three iodide ligand attached low index facets including (001), (011), (111) are investigated in this work. P-orbital of iodide ligand majorly contributes to density of state (DOS) at near top valence band resulting a significant quantum conductance, whereas DOS of Pb p-orbital shows minor influence. Various values of quantum conductance observed along different planes are possibly reasoned from a combined effect electrical field over topmost surface and total distance between adjacent facets. Ligands attached to (001) and (011) planes possess similar bond length whereas it is significantly shortened in (111) plane, whereas transport between (011) has an overall low value due to newly formed electric field. On the other hand, (111) plane with a net surface dipole perpendicular to surface layers leading to stronger electron coupling suggests an apparent increase of transport probability. Apart from previously mentioned, the maximum transport energy levels located several eVs (1 2 eVs) from the edge of valence band top.

Plane stress problems using hysteretic rigid body spring network models

NASA Astrophysics Data System (ADS)

Christos, Sofianos D.; Vlasis, Koumousis K.

2017-10-01

In this work, a discrete numerical scheme is presented capable of modeling the hysteretic behavior of 2D structures. Rigid Body Spring Network (RBSN) models that were first proposed by Kawai (Nucl Eng Des 48(1):29-207, 1978) are extended to account for hysteretic elastoplastic behavior. Discretization is based on Voronoi tessellation, as proposed specifically for RBSN models to ensure uniformity. As a result, the structure is discretized into convex polygons that form the discrete rigid bodies of the model. These are connected with three zero length, i.e., single-node springs in the middle of their common facets. The springs follow the smooth hysteretic Bouc-Wen model which efficiently incorporates classical plasticity with no direct reference to a yield surface. Numerical results for both static and dynamic loadings are presented, which validate the proposed simplified spring-mass formulation. In addition, they verify the model's applicability on determining primarily the displacement field and plastic zones compared to the standard elastoplastic finite element method.

Characterisation of 3D-GaN/InGaN nanostructured Light Emitting Diodes by Transmission Electron Microscopy

NASA Astrophysics Data System (ADS)

Griffiths, I. J.; Cherns, D.; Wang, X.; Waag, A.; Wehmann, H.-H.

2013-11-01

Transmission and scanning electron microscopy have been used to characterise GaN/InGaN 3D nanostructures grown on patterned GaN/sapphire substrates by MOVPE. It has been found that the growth of well ordered arrays of such nanostructures, containing multiple quantum wells on non-polar side-facets, can be achieved with a low density of defects. Growth changes and surface morphology play a major role in the nucleation of any defects present. The nanostructure morphology has been investigated and non-uniform growth on adjacent facets studied.

The effect of radiometer placement and view on inferred directional and hemispheric radiometric temperatures of an urban canopy

NASA Astrophysics Data System (ADS)

Adderley, C.; Christen, A.; Voogt, J. A.

2015-07-01

Any radiometer at a fixed location has a biased view when observing a convoluted, three-dimensional surface such as an urban canopy. The goal of this contribution is to determine the bias of various sensors views observing a simple urban residential neighbourhood (nadir, oblique, hemispherical) over a 24 hour cycle under clear weather conditions. The error in measuring a longwave radiation flux density (L) and/or inferring surface temperatures (T0) is quantified for different times over a diurnal cycle. Panoramic time-sequential thermography (PTST) data were recorded by a thermal camera on a hydraulic mast above a residential canyon in Vancouver, BC. The data set resolved sub-facet temperature variability of all representative urban facets in a 360° swath repetitively over a 24-hour cycle. This data set is used along with computer graphics and vision techniques to project measured fields of L for a given time and pixel onto texture sheets of a three-dimensional urban surface model at a resolution of centimetres. The resulting data set attributes L of each pixel on the texture sheets to different urban facets and associates facet location, azimuth, slope, material, and sky view factor. The texture sheets of L are used to calculate the complete surface temperature (T0,C) and to simulate the radiation in the field of view (FOV) of narrow and hemispheric radiometers observing the same urban surface (in absence of emissivity and atmospheric effects). The simulated directional (T0,d) and hemispheric (T0,h) radiometric temperatures inferred from various biased views are compared to T0,C. For a range of simulated off-nadir (φ) and azimuth (Ω) angles, T0,d(φ,Ω) and T0,C differ between -2.6 and +2.9 K over the course of the day. The effects of effective anisotropy are highest in the daytime, particularly around sunrise and sunset when different views can lead to differences in T0,d(φ,Ω) that are as high as 3.5 K. For a sensor with a narrow FOV in the nadir of the urban surface, T0,d(φ=0) differs from T0,C by +1.9 K (day) and by -1.6 K (night). Simulations of the FOV of hemispherical, downward-facing pyrgeometers at 270 positions show considerable variations in the measured L and inferred hemispherical radiometeric temperature T0,h as a function of both horizontal placement and height. The root mean squared error (RMSE) between different horizontal positions in retrieving outgoing longwave emittance L↑ decreased exponentially with height, and was 11.2, 6.3 and 2.0 W m-2 at 2, 3, and 5 times the mean building height zb. Generally, above 3.5zb the horizontal positional error is less than the typical accuracy of common pyrgeometers. The average T0,h over 24 h determined from the hemispherical radiometer sufficiently above an urban surface is in close agreement with the average T0,C. However, over the course of the day, the difference between T0,h and T0,C shows an RMSE of 1.7 K (9.4 W m-2) because the relative contributions of facets within the projected FOV of a pyrgeometer do not correspond to their fractions of the complete urban surface.

The effect of radiometer placement and view on inferred directional and hemispheric radiometric temperatures of a urban canopy

NASA Astrophysics Data System (ADS)

Adderley, C.; Christen, A.; Voogt, J. A.

2015-02-01

Any radiometer at a fixed location has a biased view when observing a convoluted, three dimensional surface such as an urban canopy. The goal of this contribution is to determine the bias of various sensors views observing a simple urban residential neighbourhood (nadir, oblique, hemispherical) over a 24 h cycle under clear weather conditions. The error in measuring longwave radiance (L) and/or inferring surface temperatures (T0) is quantified for different times over a diurnal cycle. Panoramic time-sequential thermography (PTST) data was recorded by a thermal camera on a hydraulic mast above a residential canyon in Vancouver, BC. The dataset resolved sub-facet temperature variability of all representative urban facets in a 360° swath repetitively over a 24 h cycle. This dataset is used along with computer graphics and vision techniques to project measured fields of L for a given time and pixel onto texture sheets of a three-dimensional urban surface model at a resolution of centimetres. The resulting dataset attributes L of each pixel on the texture sheets to different urban facets and associates facet location, azimuth, slope, material, and sky view factor. The texture sheets of L are used to calculate the complete surface temperature (T0,C) and to simulate the instantaneous field of view (IFOV) of narrow and hemispheric radiometers observing the same urban surface (in absence of emissivity and atmospheric effects). The simulated directional (T0,d) and hemispheric (T0,h) radiometric temperatures inferred from various biased views are compared to T0,C. For a range of simulated off-nadir (ϕ) and azimuth (Ω) angles, T0,d (ϕ, Ω) and T0,C differ between -2.7 and +2.9 K over the course of the day. The effects of effective anisotropy are highest in the daytime, particularly around sunrise and sunset when different views can lead to differences in T0,d (ϕ, Ω) that are as high as 3.5 K. For a sensor with a narrow IFOV in the nadir of the urban surface, T0,d (ϕ = 0°) differs from T0,C by -2.2 K (day) and by +1.6 K (night). Simulations of the IFOV of hemispherical, downward-facing pyrgeometers at 270 positions show considerable variations in the measured L and inferred hemispherical radiometeric temperature T0,h as a function of both horizontal placement and height. The root mean squared error (RMSE) between different horizontal positions in retrieving outgoing longwave emittance L↑ decreased exponentially with height, and was 11.2, 6.3 and 2.0 W m-2 at 2, 3, and 5 times the mean building height zb. Generally, above 3.5 zb the horizontal positional error is less than the typical accuracy of common pyrgeometers. The average T0,h over 24 h determined from the hemispherical radiometer sufficiently above an urban surface is in close agreement with the average T0,C. However, over the course of the day, the difference between T0,h and T0,C shows an RMSE of 1.8 K (9.9 W m-2) because the relative contributions of facets within the projected IFOV of a pyrgeometer do not correspond to their fractions of the complete urban surface.

Enhanced and Facet-specific Electrocatalytic Properties of Ag/Bi2Fe4O9 Composite Nanoparticles.

PubMed

Wang, Kai; Xu, Xiaoguang; Lu, Liying; Wang, Haicheng; Li, Yan; Wu, Yong; Miao, Jun; Zhang, Jin Zhong; Jiang, Yong

2018-04-18

Ag/Bi 2 Fe 4 O 9 nanoparticles (BFO NPs) have been synthesized using a two-step approach involving glycine combustion and visible light irradiation. Their structures were characterized in detail using X-ray diffraction, transmission electron microscope, scanning electron microscopy, and scanning transmission electron microscopy techniques. Their electrocatalytic properties were studied through enzymatic glucose detection with an amperometric biosensor. The Ag deposited on selective crystal facets of BFO NPs significantly enhanced their electrocatalytic activity. To gain insights into the origin of the enhanced electrocatalytic activities, we have carried out studies of Ag + reduction and Mn 2+ oxidation reaction at the {200} and {001} facets, respectively. The results suggest effective charge separation on the BFO NP surfaces, which is likely responsible for the enhanced electrocatalytic properties. Furthermore, enhanced ferromagnetism was observed after the Ag deposition on BFO NPs, which may be related to the improved electrocatalytic properties through spin-dependent charge transport. The facet-specific electrocatalytic properties are highly interesting and desired for chemical reactions. This study demonstrates that Ag/BFO NPs are potentially useful for electrocatalytic applications including biosensing and chemical synthesis with high product selectivity.

Thermal etching of silver: Influence of rolling defects

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

Ollivier, M., E-mail: o.maelig@imperial.ac.uk

2016-08-15

Silver is well known to be thermally etched in an oxygen-rich atmosphere and has been extensively studied in the laboratory to understand thermal etching and to limit its effect when this material is used as a catalyst. Yet, in many industrial applications the surface of rolled silver sheets is used without particular surface preparation. Here, it is shown by combining FIB-tomography, FIB-SIMS and analytical SEM that the kinetics of thermal etch pitting are significantly faster on rolled Ag surfaces than on polished surfaces. This occurs due to range of interacting phenomena including (i) the reaction of subsurface carbon-contamination with dissolvedmore » oxygen to form pores that grow to intersect the surface, (ii) surface reconstruction around corrosion pits and surface scratches, and (iii) sublimation at low pressure and high temperature. A method to identify subsurface pores is developed to show that the pores have (111) and (100) internal facets and may be filled with a gas coming from the chemical reaction of oxygen and carbon contamination. - Highlights: Thermal etching of industrial silver sheets vs. polished silver sheets Effect of annealing atmosphere on the thermal etching of silver: surface and subsurface characterization Link between etch pitting and defects induced by rolling. FIB-tomography coupled with EBSD for determining crystal planes of the facets of subsurface pores. FIB-SIMS characterization to probe the gas confined inside subsurface pores.« less

Transverse Mode Dynamics and Ultrafast Modulation of Vertical-Cavity Surface-Emitting Lasers

NASA Technical Reports Server (NTRS)

Ning, Cun-Zheng; Biegel, Bryan A. (Technical Monitor)

2002-01-01

We show that multiple transverse mode dynamics of VCSELs (Vertical-Cavity Surface-Emitting Lasers) can be utilized to generate ultrafast intensity modulation at a frequency over 100 GHz, much higher than the relaxation oscillation frequency. Such multimode beating can be greatly enhanced by taking laser output from part of the output facet.

Comparison of S-adsorption on (111) and (100) facets of Cu nanoclusters

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

Boschen, Jeffery S.; Lee, Jiyoung; Windus, Theresa L.

2016-10-31

In order to gain insight into the nature of chemical bonding of sulfur atoms on coinage metal surfaces, we compare the adsorption energy and structural parameters for sulfur at four-fold hollow (4fh) sites on (100) facets and at three-fold hollow (3fh) sites on (111) facets of Cu nanoclusters. Consistent results are obtained from localized atomic orbital and plane-wave based density functional theory using the same functionals. PBE and its hybrid counterpart (PBE0 or HSE06) also give similar results. 4fh sites are preferred over 3fh sites with stronger bonding by ~0.6 eV for nanocluster sizes above ~280 atoms. However, for smallermore » sizes there are strong variations in the binding strength and the extent of the binding site preference. In addition, we show that suitable averaging over clusters of different sizes, or smearing the occupancy of orbitals, provide useful strategies to aid assessment of the behavior in extended surface systems. From site-projected density of states analysis using the smearing technique, we show that S adsorbed on a 4fh site has similar bonding interactions with the substrate as that on a 3fh site, but with much weaker antibonding interactions.« less

Density Functional Theory Calculations Revealing Metal-like Band Structures for Ultrathin Ge {111} and {211} Surface Layers.

PubMed

Tan, Chih-Shan; Huang, Michael Hsuan-Yi

2018-05-21

To find out if germanium should also possess facet-dependent electrical conductivity properties, surface state density functional theory (DFT) calculations were performed on 1-6 layers of Ge (100), (110), (111), and (211) planes. Tunable Ge (100) and (110) planes always present the same semiconducting band structure with a band gap of 0.67 eV expected of bulk germanium. In contrast, 1, 2, 4, and 5 layers of Ge (111) and (211) plane models show metal-like band structures with continuous density of states (DOS) throughout the entire band. For 3 and 6 layers of Ge (111) and (211) plane models, the normal semiconducting band structure was obtained. The plane layers with metal-like band structures also show Ge-Ge bond length deviations and bond distortions, as well as significantly different 4s and 4p frontier orbital electron count and their relative percentages integrated over the valence and conduction bands from those of the semiconducting state. These differences should contribute to strikingly dissimilar band structures. The calculation results suggest observation of facet-dependent electrical conductivity properties of germanium materials, and transistors made of germanium may also need to consider the facet effects with shrinking dimensions approaching 3 nm. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Design of a novel dual Z-scheme photocatalytic system composited of Ag{sub 2}O modified Ti{sup 3+} self doped TiO{sub 2} nanocrystals with individual exposed (001) and (101) facets

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

Li, Mengyan; Liu, Hui, E-mail: liuhui@sust.edu.cn

A novel dual Z-scheme photocatalytic system composited of Ag{sub 2}O nanocrystals modified Ti{sup 3+} self doped TiO{sub 2} nanocrystals with individual exposed (001) and (101) facets were successfully fabricated. In which, the Ti{sup 3+} self doped TiO{sub 2} nanocrystals with individual exposed (001) and (101) facets have been firstly prepared by a simple hydrothermal method, subsequently the as-prepared products were modified with Ag{sub 2}O nanocrystals through a sonochemical depositing process in order to build a novel dual Z-scheme photocatalytic system. The samples were carefully characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–visible diffuse reflectancemore » spectra (UV–vis DRS), and Brunauer-Emmett-Teller (BET). The photocatalytic activity toward degradation of Rhodamine B (Rh B) aqueous solution under stimulated solar light was investigated. The experimental results showed this new dual Z-scheme photocatalytic system possess an enhanced photocatalytic degradation activity compared to that similar surface heterojunction photocatalysts composed of Ti{sup 3+} self doped TiO{sub 2} nanocrystals with individual exposed (001) and (101) facets. This novel photocatalytic system presents a high charge-separation efficiency and strong redox ability. This study will help us to better understand the photocatalytic mechanism of semiconductor photocatalysts with exposed different facets, and provide a new insight into the design and fabrication of advanced photocatalytic materials. - Highlights: •A novel dual Z-scheme system was built by Ag{sub 2}O and facet exposed TiO{sub 2} nanocrystals. •The individual TiO{sub 2} nanocrystals exposed (001) and (101) facets respectively. •Ag{sub 2}O coupled with Ti{sup 3+} self doped TiO{sub 2} nanocrystals through a sonochemical process. •The as-prepared sample possesses a super photocatalytic activity.« less

Contact pressure in the facet joint during sagittal bending of the cadaveric cervical spine.

PubMed

Jaumard, Nicolas V; Bauman, Joel A; Weisshaar, Christine L; Guarino, Benjamin B; Welch, William C; Winkelstein, Beth A

2011-07-01

The facet joint contributes to the normal biomechanical function of the spine by transmitting loads and limiting motions via articular contact. However, little is known about the contact pressure response for this joint. Such information can provide a quantitative measure of the facet joint's local environment. The objective of this study was to measure facet pressure during physiologic bending in the cervical spine, using a joint capsule-sparing technique. Flexion and extension bending moments were applied to six human cadaveric cervical spines. Global motions (C2-T1) were defined using infra-red cameras to track markers on each vertebra. Contact pressure in the C5-C6 facet was also measured using a tip-mounted pressure transducer inserted into the joint space through a hole in the postero-inferior region of the C5 lateral mass. Facet contact pressure increased by 67.6 ± 26.9 kPa under a 2.4 Nm extension moment and decreased by 10.3 ± 9.7 kPa under a 2.7 Nm flexion moment. The mean rotation of the overall cervical specimen motion segments was 9.6 ± 0.8° and was 1.6 ± 0.7° for the C5-C6 joint, respectively, for extension. The change in pressure during extension was linearly related to both the change in moment (51.4 ± 42.6 kPa/Nm) and the change in C5-C6 angle (18.0 ± 108.9 kPa/deg). Contact pressure in the inferior region of the cervical facet joint increases during extension as the articular surfaces come in contact, and decreases in flexion as the joint opens, similar to reports in the lumbar spine despite the difference in facet orientation in those spinal regions. Joint contact pressure is linearly related to both sagittal moment and spinal rotation. Cartilage degeneration and the presence of meniscoids may account for the variation in the pressure profiles measured during physiologic sagittal bending. This study shows that cervical facet contact pressure can be directly measured with minimal disruption to the joint and is the first to provide local pressure values for the cervical joint in a cadaveric model.

The osteopontin-controlled switching of calcium oxalate monohydrate morphologies in artificial urine provides insights into the formation of papillary kidney stones.

PubMed

Langdon, Aaron; Grohe, Bernd

2016-10-01

The protein osteopontin (OPN) plays an important role in preventing the formation of calcium oxalate monohydrate (COM) kidney stones. To gain insight into these mechanisms, crystallization was induced by addition of human kidney OPN to artificial urine (ionic strength comparable to urine; without citrate), and the OPN-COM interaction studied using a combination of scanning electron (SEM) and confocal microscopy. By SEM, we found that increasing OPN concentrations formed large monoclinic penetration twins (no protein added) and, at higher concentrations (1-, 2μg/ml OPN), super and hyper twins with crystal habits not found in previous studies. For instance, the hyper twins indicate well-facetted gearwheel-like habits with "teeth" developed in all crystallographic directions. At OPN concentrations ≥2μg/ml, a switching to small dumbbell-shaped COM habits with fine-textured surfaces occurred. Confocal microscopy of these dumbbells indicates protein incorporation in almost the entire crystal structure (in contrast to facetted COM), proposing a threshold concentration of ∼2μg/ml OPN for the facetted to the non-facetted habit transformation. Both the gearwheel-like and the dumbbell-shaped habit are again found side-by-side (presumably triggered by OPN concentration gradients within the sample) in in-vitro formed conglomerates, which resemble cross-sections of papillary kidney stones. The abrupt transformation from facetted to non-facetted habits and the unique compliance of the two in-vitro formed habits with the two main morphologies found in papillary kidney stones propose that OPN is a main effector in direct stone-forming processes. Moreover, stone structures which exhibit these two morphologies side-by-side might serve as a novel indicator for OPN concentrations surrounding those structures. Copyright © 2016 Elsevier B.V. All rights reserved.

Enhancing the Ion Transport in LiMn1.5Ni0.5O4 by Altering the Particle Wulff Shape via Anisotropic Surface Segregation.

PubMed

Huang, Jiajia; Liu, Haodong; Zhou, Naixie; An, Ke; Meng, Ying Shirley; Luo, Jian

2017-10-25

Spontaneous and anisotropic surface segregation of W cations in LiMn 1.5 Ni 0.5 O 4 particles can alter the Wulff shape and improve surface stability, thereby significantly improving the electrochemical performance. An Auger electron nanoprobe was employed to identify the anisotropic surface segregation, whereby W cations prefer to segregate to {110} surface facets to decrease its relative surface energy according to Gibbs adsorption theory and subsequently increase its surface area according to Wulff theory. Consequently, the rate performance is improved (e.g., by ∼5-fold at a high rate of 25C) because the {110} facets have more open channels for fast lithium ion diffusion. Furthermore, X-ray photoelectron spectroscopy (XPS) depth profiling suggested that the surface segregation and partial reduction of W cation inhibit the formation of Mn 3+ on surfaces to improve cycling stability via enhancing the cathode electrolyte interphase (CEI) stability at high charging voltages. This is the first report of using anisotropic surface segregation to thermodynamically control the particle morphology as well as enhancing CEI stability as a facile, and potentially general, method to significantly improve the electrochemical performance of battery electrodes. Combining neutron diffraction, an Auger electron nanoprobe, XPS, and other characterizations, we depict the underlying mechanisms of improved ionic transport and CEI stability in high-voltage LiMn 1.5 Ni 0.5 O 4 spinel materials.

In situ nanoscale observations of gypsum dissolution by digital holographic microscopy.

PubMed

Feng, Pan; Brand, Alexander S; Chen, Lei; Bullard, Jeffrey W

2017-06-01

Recent topography measurements of gypsum dissolution have not reported the absolute dissolution rates, but instead focus on the rates of formation and growth of etch pits. In this study, the in situ absolute retreat rates of gypsum (010) cleavage surfaces at etch pits, at cleavage steps, and at apparently defect-free portions of the surface are measured in flowing water by reflection digital holographic microscopy. Observations made on randomly sampled fields of view on seven different cleavage surfaces reveal a range of local dissolution rates, the local rate being determined by the topographical features at which material is removed. Four characteristic types of topographical activity are observed: 1) smooth regions, free of etch pits or other noticeable defects, where dissolution rates are relatively low; 2) shallow, wide etch pits bounded by faceted walls which grow gradually at rates somewhat greater than in smooth regions; 3) narrow, deep etch pits which form and grow throughout the observation period at rates that exceed those at the shallow etch pits; and 4) relatively few, submicrometer cleavage steps which move in a wave-like manner and yield local dissolution fluxes that are about five times greater than at etch pits. Molar dissolution rates at all topographical features except submicrometer steps can be aggregated into a continuous, mildly bimodal distribution with a mean of 3.0 µmolm -2 s -1 and a standard deviation of 0.7 µmolm -2 s -1 .

Examining the Psychometric Properties of the Family Accommodation Scale-Parent-Report (FAS-PR)

PubMed Central

Sapyta, Jeffrey; Garcia, Abbe; Freeman, Jennifer B.; Franklin, Martin E.; Foa, Edna; March, John

2011-01-01

Growing research has examined parental accommodation among the families of children with obsessive-compulsive disorder (OCD). However, these studies have utilized a parent-report (PR) version of a measure, the Family Accommodation Scale (FAS) that has never received proper psychometric validation. In turn, previously derived subscales have been developed via clinical rather than empirical evidence. This study aims to conduct a comprehensive psychometric analysis of the FAS-PR utilizing data collected from 96 youths with OCD. Exploratory factors analysis was conducted and revealed a 12-item scale yielding two separate, yet related subscales, Avoidance of Triggers (AT) and Involvement in Compulsions (IC). Subsequent analyses revealed good internal consistency and convergent and discriminant validity. These findings suggest that future research should seek to examine factors that may impact various facets to accommodation as well as the role these facets plays in predicting treatment outcome. Limitations are discussed. PMID:21743772

Shaped Ceria Nanocrystals Catalyze Efficient and Selective Para-Hydrogen-Enhanced Polarization.

PubMed

Zhao, Evan W; Zheng, Haibin; Zhou, Ronghui; Hagelin-Weaver, Helena E; Bowers, Clifford R

2015-11-23

Intense para-hydrogen-enhanced NMR signals are observed in the hydrogenation of propene and propyne over ceria nanocubes, nano-octahedra, and nanorods. The well-defined ceria shapes, synthesized by a hydrothermal method, expose different crystalline facets with various oxygen vacancy densities, which are known to play a role in hydrogenation and oxidation catalysis. While the catalytic activity of the hydrogenation of propene over ceria is strongly facet-dependent, the pairwise selectivity is low (2.4% at 375 °C), which is consistent with stepwise H atom transfer, and it is the same for all three nanocrystal shapes. Selective semi-hydrogenation of propyne over ceria nanocubes yields hyperpolarized propene with a similar pairwise selectivity of (2.7% at 300 °C), indicating product formation predominantly by a non-pairwise addition. Ceria is also shown to be an efficient pairwise replacement catalyst for propene. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Real-time ultrasound image classification for spine anesthesia using local directional Hadamard features.

PubMed

Pesteie, Mehran; Abolmaesumi, Purang; Ashab, Hussam Al-Deen; Lessoway, Victoria A; Massey, Simon; Gunka, Vit; Rohling, Robert N

2015-06-01

Injection therapy is a commonly used solution for back pain management. This procedure typically involves percutaneous insertion of a needle between or around the vertebrae, to deliver anesthetics near nerve bundles. Most frequently, spinal injections are performed either blindly using palpation or under the guidance of fluoroscopy or computed tomography. Recently, due to the drawbacks of the ionizing radiation of such imaging modalities, there has been a growing interest in using ultrasound imaging as an alternative. However, the complex spinal anatomy with different wave-like structures, affected by speckle noise, makes the accurate identification of the appropriate injection plane difficult. The aim of this study was to propose an automated system that can identify the optimal plane for epidural steroid injections and facet joint injections. A multi-scale and multi-directional feature extraction system to provide automated identification of the appropriate plane is proposed. Local Hadamard coefficients are obtained using the sequency-ordered Hadamard transform at multiple scales. Directional features are extracted from local coefficients which correspond to different regions in the ultrasound images. An artificial neural network is trained based on the local directional Hadamard features for classification. The proposed method yields distinctive features for classification which successfully classified 1032 images out of 1090 for epidural steroid injection and 990 images out of 1052 for facet joint injection. In order to validate the proposed method, a leave-one-out cross-validation was performed. The average classification accuracy for leave-one-out validation was 94 % for epidural and 90 % for facet joint targets. Also, the feature extraction time for the proposed method was 20 ms for a native 2D ultrasound image. A real-time machine learning system based on the local directional Hadamard features extracted by the sequency-ordered Hadamard transform for detecting the laminae and facet joints in ultrasound images has been proposed. The system has the potential to assist the anesthesiologists in quickly finding the target plane for epidural steroid injections and facet joint injections.

Noble metal free photocatalytic H 2 generation on black TiO 2: On the influence of crystal facets vs. crystal damage

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

Liu, Ning; Steinrück, Hans-Georg; Osvet, Andres

In this study, we investigate noble metal free photocatalytic water splitting on natural anatase single crystal facets and on wafer slices of the [001] plane before and after these surfaces have been modified by high pressure hydrogenation and hydrogen ion-implantation. Here, we find that on the natural, intact low index planes, photocatalytic H 2 evolution (in the absence of a noble metal co-catalyst) can only be achieved when the hydrogenation treatment is accompanied by the introduction of crystal damage, such as simple scratching and miscut in the crystal, or by implantation damage. X-ray reflectivity, Raman, and optical reflection measurements showmore » that plain hydrogenation leads to a ≈ 1 nm thick black titania surface layer without activity, while a colorless, density modified, and ≈7 nm thick layer with broken crystal symmetry is present on the ion implanted surface. These results demonstrate that (i) the H-treatment of an intact anatase surface needs to be combined with defect formation for catalytic activation and (ii) activation does not necessarily coincide with the presence of black color.« less

Noble metal free photocatalytic H 2 generation on black TiO 2: On the influence of crystal facets vs. crystal damage

DOE PAGES

Liu, Ning; Steinrück, Hans-Georg; Osvet, Andres; ...

2017-02-13

In this study, we investigate noble metal free photocatalytic water splitting on natural anatase single crystal facets and on wafer slices of the [001] plane before and after these surfaces have been modified by high pressure hydrogenation and hydrogen ion-implantation. Here, we find that on the natural, intact low index planes, photocatalytic H 2 evolution (in the absence of a noble metal co-catalyst) can only be achieved when the hydrogenation treatment is accompanied by the introduction of crystal damage, such as simple scratching and miscut in the crystal, or by implantation damage. X-ray reflectivity, Raman, and optical reflection measurements showmore » that plain hydrogenation leads to a ≈ 1 nm thick black titania surface layer without activity, while a colorless, density modified, and ≈7 nm thick layer with broken crystal symmetry is present on the ion implanted surface. These results demonstrate that (i) the H-treatment of an intact anatase surface needs to be combined with defect formation for catalytic activation and (ii) activation does not necessarily coincide with the presence of black color.« less

How faceted liquid droplets grow tails: from surface topology to active motion

NASA Astrophysics Data System (ADS)

Sloutskin, Eli

Among all possible shapes of a volume V, a sphere has the smallest surface area A. Therefore, liquid droplets are spherical, minimizing their interfacial energy γA for a given interfacial tension γ > 0 . This talk will demonstrate that liquid oil (alkane) droplets in water, stabilized by a common surfactant can be temperature-tuned to adopt icosahedral and other faceted shapes, above the bulk melting temperature of the oil. Although emulsions have been studied for centuries no faceted liquid droplets have ever been reported. The formation of an icosahedral shape is attributed to the interplay between γ and the elastic properties of the interfacial monomolecular layer, which crystallizes here 10-15K above bulk melting, leaving the droplet's bulk liquid. The icosahedral symmetry is dictated by twelve five-fold topological defects, forming within the hexagonally-packed interfacial crystalline monolayer. Moreover, we demonstrate that upon further cooling this `interfacial freezing' effect makes γ transiently switch its sign, leading to a spontaneous splitting of droplets and an active growth of their surface area, reminiscent of the classical spontaneous emulsification, yet driven by completely different physics. The observed phenomena allow deeper insights to be gained into the fundamentals of molecular elasticity and open new vitas for a wide range of novel nanotechnological applications, from self-assembly of complex shapes to new delivery strategies in bio-medicine. Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for support of this research and to the Kahn Foundation for the purchase of equipment.

Dynamics and Removal Pathway of Edge Dislocations in Imperfectly Attached PbTe Nanocrystal Pairs: Toward Design Rules for Oriented Attachment.

PubMed

Ondry, Justin C; Hauwiller, Matthew R; Alivisatos, A Paul

2018-04-24

Using in situ high-resolution TEM, we study the structure and dynamics of well-defined edge dislocations in imperfectly attached PbTe nanocrystals. We identify that attachment of PbTe nanocrystals on both {100} and {110} facets gives rise to b = a/2⟨110⟩ edge dislocations. Based on the Burgers vector of individual dislocations, we can identify the glide plane of the dislocations. We observe that defects in particles attached on {100} facets have glide planes that quickly intersect the surface, and HRTEM movies show that the defects follow the glide plane to the surface. For {110} attached particles, the glide plane is collinear with the attachment direction, which does not provide an easy path for the dislocation to reach the surface. Indeed, HRTEM movies of dislocations for {110} attached particles show that defect removal is much slower. Further, we observe conversion from pure edge dislocations in imperfectly attached particles to dislocations with mixed edge and screw character, which has important implications for crystal growth. Finally, we observe that dislocations initially closer to the surface have a higher speed of removal, consistent with the strong dislocation free surface attractive force. Our results provide important design rules for defect-free attachment of preformed nanocrystals into epitaxial assemblies.

Influence of nanoscale faceting on the tunneling properties of near broken gap InAs/AlGaSb heterojunctions grown by selective area epitaxy.

PubMed

Desplanque, L; Fahed, M; Han, X; Chinni, V K; Troadec, D; Chauvat, M-P; Ruterana, P; Wallart, X

2014-11-21

We report on the selective area molecular beam epitaxy of InAs/AlGaSb heterostructures on a GaSb (001) substrate. This method is used to realize Esaki tunnel diodes with a tunneling area down to 50 nm × 50 nm. The impact of the size reduction on the peak current density of the diode is investigated, and we show how the formation of the InAs facets can deeply affect the band-to-band tunneling properties of the heterostructure. This phenomenon is explained by the surface-dependent incorporation of Si dopant during growth.

Spectral Mapping at Asteroid 101955 Bennu

NASA Astrophysics Data System (ADS)

Clark, Beth Ellen; Hamilton, Victoria E.; Emery, Joshua P.; Hawley, C. Luke; Howell, Ellen S.; Lauretta, Dante; Simon, Amy A.; Christensen, Philip R.; Reuter, Dennis

2017-10-01

The OSIRIS-REx Asteroid Sample Return mission was launched in September 2016. The main science surveys of asteroid 101955 Bennu start in March 2019. Science instruments include a Visible-InfraRed Spectrometer (OVIRS) and a Thermal Emission Spectrometer (OTES) that will produce observations that will be co-registered to the tessellated shape model of Bennu (the fundamental unit of which is a triangular facet). One task of the science team is to synthesize the results in real time during proximity operations to contribute to selection of the sampling site. Hence, we will be focused on quickly producing spectral maps for: (1) mineral abundances; (2) band strengths of minerals and chemicals (including a search for the subtle ~5% absorption feature produced by organics in meteorites); and (3) temperature and thermal inertia values. In sum, we will be producing on the order of ~60 spectral maps of Bennu’s surface composition and thermophysical properties. Due to overlapping surface spots, simulations of our spectral maps show there may be an opportunity to perform spectral super-resolution. We have a large parameter space of choices available in creating spectral maps of Bennu, including: (a) mean facet size (shape model resolution), (b) percentage of overlap between subsequent spot measurements, (c) the number of spectral spots measured per facet, and (d) the mathematical algorithm used to combine the overlapping spots (or bin them on a per-facet basis). Projection effects -- caused by irregular sampling of an irregularly shaped object with circular spectrometer fields-of-view and then mapping these circles onto triangular facets -- can be intense. To prepare for prox ops, we are simulating multiple mineralogical “truth worlds” of Bennu to study the projection effects that result from our planned methods of spectral mapping. This presentation addresses: Can we combine the three planned global surveys of the asteroid (to be obtained at different phase angles) to create a spectral map with higher spatial resolution than the native spectrometer field-of-view in order to increase our confidence in detection of a spatially small occurrence of organics on Bennu?

Topographic expression of active faults in the foothills of the Northern Apennines

NASA Astrophysics Data System (ADS)

Picotti, Vincenzo; Ponza, Alessio; Pazzaglia, Frank J.

2009-09-01

Active faults that rupture the earth's surface leave an imprint on the topography that is recognized using a combination of geomorphic and geologic metrics including triangular facets, the shape of mountain fronts, the drainage network, and incised river valleys with inset terraces. We document the presence of a network of active, high-angle extensional faults, collectively embedded in the actively shortening mountain front of the Northern Apennines, that possess unique geomorphic expressions. We measure the strain rate for these structures and find that they have a constant throw-to-length ratio. We demonstrate the necessary and sufficient conditions for triangular facet development in the footwalls of these faults and argue that rock-type exerts the strongest control. The slip rates of these faults range from 0.1 to 0.3 mm/yr, which is similar to the average rate of river incision and mountain front unroofing determined by corollary studies. The faults are a near-surface manifestation of deeper crustal processes that are actively uplifting rocks and growing topography at a rate commensurate with surface processes that are eroding the mountain front to base level.

Direct Synthesis of Anatase Films with ~100% (001) Facets and [001] Preferred Orientation.

PubMed

Ichimura, Andrew S; Mack, Brianne; Usmani, Shirin M; Mars, Diana

2012-06-26

Anatase films exhibiting ~100% (001) reactive facets at the surface were grown hydrothermally on gold substrate from a homogeneous solution of TiF(4) and NaF. In addition to NaF, it was found that TiO(2) films with very similar properties could be prepared with the fluoride salts LiF, CsF, HF, NH(4)F, and N(CH(2)CH(3))(4)F. The polycrystalline anatase films are continuous, approximately 1 μm thick, and evenly coat the substrate. The surface grain size is ~400 nm. Grazing angle XRD measurements show that the films exhibit a high degree of preferred orientation with the c-axis normal to the substrate surface. SEM images reveal that the grains span the thickness of the films. Annealing the films at 500 °C removes fluorine and causes crystallites within the grains to restructure as shown by SEM, XRD, and Raman spectroscopy. Supported anatase films grown from this one-pot method may serve as oxidative photocatalysts and electrodes for photoelectrochemical applications such as solar cells and hydrogen evolution.

Step-by-step growth of epitaxially aligned polythiophene by surface-confined reaction

PubMed Central

Lipton-Duffin, J. A.; Miwa, J. A.; Kondratenko, M.; Cicoira, F.; Sumpter, B. G.; Meunier, V.; Perepichka, D. F.; Rosei, F.

2010-01-01

One of the great challenges in surface chemistry is to assemble aromatic building blocks into ordered structures that are mechanically robust and electronically interlinked—i.e., are held together by covalent bonds. We demonstrate the surface-confined growth of ordered arrays of poly(3,4-ethylenedioxythiophene) (PEDOT) chains, by using the substrate (the 110 facet of copper) simultaneously as template and catalyst for polymerization. Copper acts as promoter for the Ullmann coupling reaction, whereas the inherent anisotropy of the fcc 110 facet confines growth to a single dimension. High resolution scanning tunneling microscopy performed under ultrahigh vacuum conditions allows us to simultaneously image PEDOT oligomers and the copper lattice with atomic resolution. Density functional theory calculations confirm an unexpected adsorption geometry of the PEDOT oligomers, which stand on the sulfur atom of the thiophene ring rather than lying flat. This polymerization approach can be extended to many other halogen-terminated molecules to produce epitaxially aligned conjugated polymers. Such systems might be of central importance to develop future electronic and optoelectronic devices with high quality active materials, besides representing model systems for basic science investigations. PMID:20534511

Argentinean outdoor test facility for mirrors

NASA Astrophysics Data System (ADS)

Medina, M. C.; Dipold, J.; García, B.; Mansilla, A.; Maya, J.; Rasztocky, E.; de Souza, V.; Larrarte, J. J.; Benitez, M.

2015-08-01

The Cherenkov Telescope Array (CTA) is planned to be an Observatory for very high energy -ray astronomy and will consist of several tens of telescopes which account for a reflective surface of more than 10000 m. These mirrors will be formed by a set of reflective facets. Different technological solutions, for a fast and cost efficient production of light-weight mirror facets are under test inside the CTA Consortium. Most of them involve composite structures whose behavior under real observing conditions is not yet fully tested. An outdoor test facility has been built in one of the former candidate sites for CTA, in Argentina (San Antonio de los Cobres [SAC], 3600 m a.s.l) in order to monitor the optical and mechanical properties of these facets exposed to the local atmospheric conditions for a given period of time. Four prototype mirrors built with different technologies have been installed and have been monitored for 6 months. In this work we present the preliminary results of this characterization.

Interface shape and crystallinity in LEC GaAs

NASA Astrophysics Data System (ADS)

Tower, J. P.; Tobin, R.; Pearah, P. J.; Ware, R. M.

1991-12-01

Growth striation mapping was used to relate the growth interface shape to crystallinity failure modes in LEC growth of undoped <100> GaAs. The onset of twinning and polycrystallinity were both found to depend on the interface shape near the crystal periphery. The origins of polycrystalline growth were investigated in 8 kg, 3-inch and 4-inch diameter crystals. Interface maps of these crystals show that polycrystalline growth begins when the growth interface periphery turns down, independent of the shape of the central portions. The cause of initial grain boundary formation was found to be included gallium droplets which originate on the surface and migrate through the crystal toward the growth interface. Twinning occurs on {111} facets, usually during shoulder growth. Growth striations show that the sequence of events leading to twin formation consists of deep facet growth, followed by meltback and rapid regrowth. We found it possible to avoid twinning by reducing melt instabilities or by reducing the extent of facet growth.

Orientation-Dependent Oxygen Evolution on RuO 2 without Lattice Exchange

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

Stoerzinger, Kelsey A.; Diaz-Morales, Oscar; Kolb, Manuel

RuO2 catalysts exhibit record activities towards the oxygen evolution reaction (OER), which is crucial to enable efficient and sustainable energy storage. Here we examine the RuO2 OER kinetics on rutile (110), (100), (101), and (111) orientations, finding (100) the most active. We assess the potential involvement of lattice oxygen in the OER mechanism with online 3 electrochemical mass spectrometry, which showed no evidence of oxygen exchange on these oriented facets in acidic or basic electrolytes. Similar results were obtained for polyoriented RuO2 films and particles, in contrast to previous work, suggesting lattice oxygen is not exchanged in catalyzing OER onmore » crystalline RuO2 surfaces. This hypothesis is supported by the correlation of activity with the number of active Ru-sites calculated by DFT, where more active facets bind oxygen more weakly. This new understanding of the active sites provides a design strategy to enhance the OER activity of RuO2 nanoparticles by facet engineering.« less

CNTs threaded (001) exposed TiO2 with high activity in photocatalytic NO oxidation.

PubMed

Xiao, Shuning; Zhu, Wei; Liu, Peijue; Liu, Fanfan; Dai, Wenrui; Zhang, Dieqing; Chen, Wei; Li, Hexing

2016-02-07

A microwave-ionothermal strategy was developed for in situ synthesis of CNTs threaded TiO2 single crystal with a tunable percentage of surface exposed (001) active facets. The CNTs were used as microwave antennas to create local "super hot" dots to induce Ti(3+) adsorption and hydrolysis, thereby leading to a good assembly of (001) facets exposed single crystalline TiO2 threaded by the CNTs in the presence of Hmim[BF4] ionic liquid. Due to the high percentage of the active (001) facets of single crystal TiO2 and the direct electron transfer property of the CNTs, the as-prepared CNTs-TiO2 composite showed a photocatalytic NO removal ratio of up to 76.8% under UV irradiation. In addition, with self-doped Ti(3+), the CNTs-TiO2 composite also exhibited an enhanced activity under irradiation with either solar lights or visible lights, showing good potential in practical applications for environmental remediation.

Abrasive wear of resin composites as related to finishing and polishing procedures.

PubMed

Turssi, Cecilia P; Ferracane, Jack L; Serra, Mônica C

2005-07-01

Finishing and polishing procedures may cause topographical changes and introduce subsurface microcracks in dental composite restoratives. Since both of these effects may contribute toward the kinetics of wear, the purpose of this study was to assess and correlate the wear and surface roughness of minifilled and nanofilled composites finished and polished by different methods. Specimens (n=10) made of a minifilled and a nanofilled composite were finished and polished with one of the four sequences: (1) tungsten carbide burs plus Al(2)O(3)-impregnated brush (CbBr) or (2) tungsten carbide burs plus diamond-impregnated cup (CbCp), (3) diamond burs plus brush (DmBr) or (4) diamond burs plus cup (DmCp). As a control, abrasive papers were used. After surface roughness had been quantified, three-body abrasion was simulated using the OHSU wear machine. The wear facets were then scanned to measure wear depth and post-testing roughness. All sets of data were subjected to ANOVA and Tukey's tests (alpha=0.05). Pearson's correlation test was applied to check for the existence of a relationship between pre-testing roughness and wear. Significantly smoother surfaces were attained with the sequences CbBr and CbCp, whereas DmCp yielded the roughest surface. Regardless of the finishing/polishing technique, the nanofilled composite exhibited the lowest pre-testing roughness and wear. There was no correlation between the surface roughness achieved after finishing/polishing procedures and wear (p=0.3899). Nano-sized materials may have improved abrasive wear resistance over minifilled composites. The absence of correlation between wear and surface roughness produced by different finishing/polishing methods suggests that the latter negligibly influences material loss due to three-body abrasion.

Proceedings of the DICE THROW Symposium 21-23 June 1977. Volume 1

DTIC Science & Technology

1977-07-01

different scaled ANFO events to insure yield scalability. Phase 1 of the program consisted of a series of one-pound events to examine cratering and...characterization of a 500-ton-equivalent event. A large number of agencies were involved in different facets of the development program. Probably most...charge geometry observed in the 1000-pound series, supported the observations from the Phase 1 program. Differences were observed in the fireball

Theoretical and Numerical Modeling of faceted Ionic crystalline vesicles

NASA Astrophysics Data System (ADS)

Olvera de La Cruz, Monica

2007-03-01

Icosahedral shape is found in several natural structures including large viruses, large fullerenes and cationic-anionic vesicles. Faceting into icosahedral shape can occur in large crystalline membranes via elasticity theory. Icosahedral symmetry is found in small systems of particles with short-range interactions on a sphere. Dr G. Vernizzi and I show a novel electrostatic-driven mechanism of ionic crystalline shells faceting into icosahedral shapes even for systems with a small number of particles. Icosahedral shape is possible in cationic and anionic molecules adsorbed onto spherical interfaces, such as emulsions or other immiscible liquid droplets because the large concentration of charges at the interface can lead to ionic crystals on the curved interface. Such self-organized ionic structures favors the formation of flat surfaces. We find that these ionic crystalline shells can have lower energy when faceted into icosahedra along particular directions. Indeed, the ``ionic'' buckling is driven by preferred bending directions of the planar ionic structure, along which is more likely for the icosahedral shape to develop an edge. Since only certain orientations are allowed, rotational symmetry is broken. One can hope to exploit this mechanism to generate functional materials where, for instance, proteins with specific charge groups can orient at specific directions along an icosahedral cationic-anionic vesicle.

Facet‐Controlled Synthetic Strategy of Cu2O‐Based Crystals for Catalysis and Sensing

PubMed Central

Shang, Yang

2015-01-01

Shape‐dependent catalysis and sensing behaviours are primarily focused on nanocrystals enclosed by low‐index facets, especially the three basic facets ({100}, {111}, and {110}). Several novel strategies have recently exploded by tailoring the original nanocrystals to greatly improve the catalysis and sensing performances. In this Review, we firstly introduce the synthesis of a variety of Cu2O nanocrystals, including the three basic Cu2O nanocrystals (cubes, octahedra and rhombic dodecahedra, enclosed by the {100}, {111}, and {110} facets, respectively), and Cu2O nanocrystals enclosed by high‐index planes. We then discuss in detail the three main facet‐controlled synthetic strategies (deposition, etching and templating) to fabricate Cu2O‐based nanocrystals with heterogeneous, etched, or hollow structures, including a number of important concepts involved in those facet‐controlled routes, such as the selective adsorption of capping agents for protecting special facets, and the impacts of surface energy and active sites on reaction activity trends. Finally, we highlight the facet‐dependent properties of the Cu2O and Cu2O‐based nanocrystals for applications in photocatalysis, gas catalysis, organocatalysis and sensing, as well as the relationship between their structures and properties. We also summarize and comment upon future facet‐related directions. PMID:27980909

Synthesis of Wurtzite Cu2ZnSnS4 Nanosheets with Exposed High-Energy (002) Facets for Fabrication of Efficient Pt-Free Solar Cell Counter Electrodes.

PubMed

Zhang, Xiaoyan; Xu, You; Zhang, Junjie; Dong, Shuai; Shen, Liming; Gupta, Arunava; Bao, Ningzhong

2018-01-10

Two-dimensional (2D) semiconducting nanomaterials have generated much interest both because of fundamental scientific interest and technological applications arising from the unique properties in two dimensions. However, the colloidal synthesis of 2D quaternary chalcogenide nanomaterials remains a great challenge owing to the lack of intrinsic driving force for its anisotropic growth. 2D wurtzite Cu 2 ZnSnS 4 nanosheets (CZTS-NS) with high-energy (002) facets have been obtained for the first time via a simple one-pot thermal decomposition method. The CZTS-NS exhibits superior photoelectrochemical activity as compared to zero-dimensional CZTS nanospheres and comparable performance to Pt counter electrode for dye sensitized solar cells. The improved catalytic activity can be attributed to additional reactive catalytic sites and higher catalytic reactivity in high-energy (002) facets of 2D CZTS-NS. This is in accordance with the density functional theory (DFT) calculations, which indicates that the (002) facets of wurtzite CZTS-NS possess higher surface energy and exhibits remarkable reducibility for I 3 - ions. The developed synthetic method and findings will be helpful for the design and synthesis of 2D semiconducting nanomaterials, especially eco-friendly copper chalcogenide nanocrystals for energy harvesting and photoelectric applications.

Wind Tunnel Application of a Pressure-Sensitive Paint Technique to a Faceted Missile Model at Subsonic and Transonic Speeds

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

2004-01-01

A pressure-sensitive paint (PSP) technique was applied in a wind tunnel experiment in the NASA Langley Research Center 8-Foot Transonic Pressure Tunnel to quantify the vortex-induced surface static pressures on a slender, faceted missile model at subsonic and transonic speeds. Satisfactory global calibrations of the PSP were obtained at =0.70, 0.90, and 1.20, angles of attack from 10 degrees to 20 degrees, and angles of sideslip of 0 and 2.5 degrees using an in-situ method featuring the simultaneous acquisition of electronically-scanned pressures (ESP) at 57 discrete locations on the model. Both techniques clearly revealed the significant influence on the surface pressure distributions of the vortices shed from the sharp, chine-like leading edges. The mean error in the PSP measurements relative to the ESP data was approximately 0.6 percent at M infinity =0.70 and 2.6 percent at M infinity =0.90 and 1.20. The vortex surface pressure signatures obtained from the PSP and ESP techniques were correlated with the off-surface vortex cross-flow structures obtained using a laser vapor screen (LVS) flow visualization technique. The on-surface and off-surface techniques were complementary, since each provided details of the vortex-dominated flow that were not clear or apparent in the other.

Seedless synthesis of gold nanorods using resveratrol as a reductant

NASA Astrophysics Data System (ADS)

Wang, Wenjing; Li, Jing; Lan, Shijie; Rong, Li; Liu, Yi; Sheng, Yu; Zhang, Hao; Yang, Bai

2016-04-01

Gold nanorods (GNRs) attract extensive attention in current diagnostic and therapeutic applications which require the synthesis of GNRs with high yields, adjustable aspect ratio, size monodispersity, and easy surface decoration. In the seed-mediated synthesis of GNRs using cetyl trimethyl ammonium bromide (CTAB) micelles as templates, the additives of aromatic compounds have been found to be important for improving the size monodispersity of the as-synthesized GNRs; this is hopeful in terms of the further optimization of the synthetic methodology of GNRs. In this work, resveratrol, a natural polyphenol in grapes with an anti-oxidization behavior, is employed as the reductant for the seedless synthesis of GNRs with a good size monodispersity and a tunable aspect ratio. Accordingly, the longitudinal localized surface plasmon resonance (LSPR) peak is tunable from 570 to 950 nm. The success of our approach is attributed to the aromatic structure and mild reducibility of resveratrol. The embedment of resveratrol into CTAB micelles strengthens the facet-selective adsorption of CTAB, and therewith facilitates the anisotropic growth of GNRs. In addition, the mild reducibility of resveratrol is capable of supporting GNR growth by avoiding secondary nucleation, thus allowing the seedless synthesis of GNRs with a good size monodispersity. As a chemopreventive agent, the combination of resveratrol in GNR synthesis will consolidate the theranostic applications of GNRs.

A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS.

PubMed

Suturin, S M; Fedorov, V V; Korovin, A M; Valkovskiy, G A; Konnikov, S G; Tabuchi, M; Sokolov, N S

2013-08-01

In this work epitaxial growth of cobalt on CaF 2 (111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF 2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright 〈111〉 streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles.

A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS

PubMed Central

Suturin, S. M.; Fedorov, V. V.; Korovin, A. M.; Valkovskiy, G. A.; Konnikov, S. G.; Tabuchi, M.; Sokolov, N. S.

2013-01-01

In this work epitaxial growth of cobalt on CaF2(111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright 〈111〉 streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles. PMID:24046491

Three-dimensional kinetic Monte Carlo simulations of cubic transition metal nitride thin film growth

NASA Astrophysics Data System (ADS)

Nita, F.; Mastail, C.; Abadias, G.

2016-02-01

A three-dimensional kinetic Monte Carlo (KMC) model has been developed and used to simulate the microstructure and growth morphology of cubic transition metal nitride (TMN) thin films deposited by reactive magnetron sputtering. Results are presented for the case of stoichiometric TiN, chosen as a representative TMN prototype. The model is based on a NaCl-type rigid lattice and includes deposition and diffusion events for both N and Ti species. It is capable of reproducing voids and overhangs, as well as surface faceting. Simulations were carried out assuming a uniform flux of incoming particles approaching the surface at normal incidence. The ballistic deposition model is parametrized with an interaction parameter r0 that mimics the capture distance at which incoming particles may stick on the surface, equivalently to a surface trapping mechanism. Two diffusion models are implemented, based on the different ways to compute the site-dependent activation energy for hopping atoms. The influence of temperature (300-500 K), deposition flux (0.1-100 monolayers/s), and interaction parameter r0 (1.5-6.0 Å) on the obtained growth morphology are presented. Microstructures ranging from highly porous, [001]-oriented straight columns with smooth top surface to rough columns emerging with different crystallographic facets are reproduced, depending on kinetic restrictions, deposited energy (seemingly captured by r0), and shadowing effect. The development of facets is a direct consequence of the diffusion model which includes an intrinsic (minimum energy-based) diffusion anisotropy, although no crystallographic diffusion anisotropy was explicitly taken into account at this stage. The time-dependent morphological evolution is analyzed quantitatively to extract the growth exponent β and roughness exponent α , as indicators of kinetic roughening behavior. For dense TiN films, values of α ≈0.7 and β =0.24 are obtained in good agreement with existing experimental data. At this stage a single lattice is considered but the KMC model will be extended further to address more complex mechanisms, such as anisotropic surface diffusion and grain boundary migration at the origin of the competitive columnar growth observed in polycrystalline TiN-based films.

Solvothermal fabrication of TiO2/sepiolite composite gel with exposed {0 0 1} and {1 0 1} facets and its enhanced photocatalytic activity

NASA Astrophysics Data System (ADS)

Liu, Ruirui; Ji, Zhijiang; Wang, Jing; Zhang, Jinjun

2018-05-01

A novel TiO2/sepiolite composite gel (TiSG) was fabricated in the presence of cetyltrimethylammonium bromide (CTAB) through a simple solvothermal reaction in an acetic acid-water solvent. A homogeneous anchoring of TiO2 nanoparticles with exposed {0 0 1} and {1 0 1} facets on sepiolite nanofibers was achieved. CTAB content, solvothermal temperature/time, and HAc content play crucial roles in the morphological and facet formation of TiSG. A possible mechanism for the formation of TiSG was further proposed. CTAB as capping/shape-controlling agent can strongly bind to the more reactive (0 0 1) facet of TiO2 and then mitigate the thermodynamically favored (0 0 1) plane growth. Eventually, the truncated octahedral TiO2 was obtained by controlling the growth rates in 〈0 0 1〉 and 〈1 0 1〉 directions. Sepiolite as a cross-linking agent provides sufficient crosslinking sites for TiO2 to induce three-dimensional (3D) network formation, thereby generating the composite gel. The synthesized TiSG samples were then used as photocatalysts, which exhibited increased methyl orange removal under UV-vis light (350-780 nm) by the synergistic effect of adsorption and in-situ photocatalytic degradation as compared to P25 and bare TiO2. The excellent photocatalytic performance of TiSG was mainly ascribed to the formations of 3D gel structure and surface heterojunctions between (0 0 1) and (1 0 1) facets.

AlxGa1-xAs Single-Quantum-Well Surface-Emitting Lasers

NASA Technical Reports Server (NTRS)

Kim, Jae H.

1992-01-01

Surface-emitting solid-state laser contains edge-emitting Al0.08Ga0.92As single-quantum-well (SQW) active layer sandwiched between graded-index-of-refraction separate-confinement-heterostructure (GRINSCH) layers of AlxGa1-xAs, includes etched 90 degree mirrors and 45 degree facets to direct edge-emitted beam perpendicular to top surface. Laser resembles those described in "Pseudomorphic-InxGa1-xAs Surface-Emitting Lasers" (NPO-18243). Suitable for incorporation into optoelectronic integrated circuits for photonic computing; e.g., optoelectronic neural networks.

Far-infrared BRDFs and reflectance spectra of candidate SOFIA telescope, cavity, and focal-plane instrument surfaces

NASA Astrophysics Data System (ADS)

Meyer, Allan W.; Smith, Sheldon M.; Koerber, Christopher T.

2000-06-01

The far-infrared reflectance and scattering properties of telescope surfaces, surrounding cavity walls, and surfaces within focal-plane instruments can be significant contributors to background noise. Radiation from sources well off-axis, such as the earth, moon or aircraft engines may be multiply scattered by the cavity walls and/or surface facets of a complex telescope structure. The Non-Specular Reflectometer at NASA Ames Research Center was reactivated and upgraded, and used to measure reflectance and Bi- directional Reflectance Distribution Functions for samples of planned telescope system structural materials and associated surface treatments.

Self-organization in complex oxide thin films: from 2D to 0D nanostructures of SrRuO3 and CoCr2O4

NASA Astrophysics Data System (ADS)

Sánchez, F.; Lüders, U.; Herranz, G.; Infante, I. C.; Fontcuberta, J.; García-Cuenca, M. V.; Ferrater, C.; Varela, M.

2005-05-01

We report here on the controlled fabrication of nanostructures of varied dimensionality by self-organization processes in the heteroepitaxial growth of SrRuO3 (SRO) and CoCr2O4 (CCO) films. The surface of SRO films on SrTiO3(001) substrates can show extremely smooth terraces (2D objects) separated by atomic steps, a structure of faceted islands (0D objects), a cross-hatch morphology (1D objects), an array of finger-like units (1D objects), or an array of giant bunched steps (1D objects). The surface can be tailored to a particular structure by controlling the vicinality of the substrate and the growth rate and nominal thickness of the film. In the case of CCO films, grown on (001)-oriented MgAl2O4 or MgO substrates, high aspect ratio {111}-faceted pyramids and hut clusters (0D objects), highly oriented and having a similar size, appear above a critical thickness. The size and spatial density can be tuned by varying deposition temperature, nominal thickness, and substrate. This dependence allows the fabrication of surfaces being fully faceted (2D objects), or having arrays of dislocated pyramids of up to micrometric size, or small coherently lattice strained pyramids having a nanometric size. We discuss the driving forces that originate the peculiar SRO and CCO nanostructures. The findings illustrate that the growth of complex oxides can promote a variety of novel self-organized morphologies, and suggest original strategies to fabricate templates or hybrid structures of oxides combining varied functionalities.

Photocatalytic Oxidation of Acetone Over High Thermally Stable TiO2 Nanosheets With Exposed (001) Facets.

PubMed

Shi, Ting; Duan, Youyu; Lv, Kangle; Hu, Zhao; Li, Qin; Li, Mei; Li, Xiaofang

2018-01-01

Anatase TiO 2 (A-TiO 2 ) usually exhibits superior photocatalytic activity than rutile TiO 2 (R-TiO 2 ). However, the phase transformation from A-TiO 2 to R-TiO 2 will inevitably happens when the calcination temperature is up to 600°C, which hampers the practical applications of TiO 2 photocatalysis in hyperthermal situations. In this paper, high energy faceted TiO 2 nanosheets (TiO 2 -NSs) with super thermal stability was prepared by calcination of TiOF 2 cubes. With increase in the calcination temperature from 300 to 600°C, TiOF 2 transforms into TiO 2 hollow nanoboxes (TiO 2 -HNBs) assembly from TiO 2 -NSs via Ostwald Rippening process. Almost all of the TiO 2 -HNBs are disassembled into discrete TiO 2 -NSs when calcination temperature is higher than 700°C. Phase transformation from A-TiO 2 to R-TiO 2 begins at 1000°C. Only when the calcination temperature is higher than 1200°C can all the TiO 2 -NSs transforms into R-TiO 2 . The 500°C-calcined sample (T500) exhibits the highest photoreactivity toward acetone oxidation possibly because of the production of high energy TiO 2 -NSs with exposed high energy (001) facets and the surface adsorbed fluorine. Surface oxygen vacancy, due to the heat-induced removal of surface adsorbed fluoride ions, is responsible for the high thermal stability of TiO 2 -NSs which are prepared by calcination of TiOF 2 cubes.

Simulation of Mirror Electron Microscopy Caustic Images in Three-Dimensions

NASA Astrophysics Data System (ADS)

Kennedy, S. M.; Zheng, C. X.; Jesson, D. E.

A full, three-dimensional (3D) ray tracing approach is developed to simulate the caustics visible in mirror electron microscopy (MEM). The method reproduces MEM image contrast resulting from 3D surface relief. To illustrate the potential of the simulation methods, we study the evolution of crater contrast associated with a movie of GaAs structures generated by the droplet epitaxy technique. Specifically, we simulate the image contrast resulting from both a precursor stage and the final crater morphology which is consistent with an inverted pyramid consisting of (111) facet walls. The method therefore facilities the study of how self-assembled quantum structures evolve with time and, in particular, the development of anisotropic features including faceting.

Controllable synthesis of Bi2MoO6 nanosheets and their facet-dependent visible-light-driven photocatalytic activity

NASA Astrophysics Data System (ADS)

Yang, Zixin; Shen, Min; Dai, Ke; Zhang, Xuehao; Chen, Hao

2018-02-01

Bi2MoO6 nanosheets with exposed {010} facets were selectively synthesized through hydrothermal method by adjusting the pH value in the presence of cetyltrimethyl ammonium bromide (CTAB) as the templates. The effects of CTAB content and hydrothermal conditions on the morphologies and crystal phases of the products were determined by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy (FTIR), Raman spectrometry, and Brunauer-Emmett-Teller surface area analyses. It is found that Bi2MoO6 nanosheets with relatively large particle sizes (plate length 0.5-3 μm) and special anisotropic growth along the {010} plane can be obtained from an alkaline hydrothermal environment. The band gap of Bi2MoO6 can be fine-tuned from 2.30 to 2.57 eV by adjusting the pH value of hydrothermal solution. The pH value has a significant effect on the composition of hydrothermal precursors, which results in Bi2MoO6 nanosheets with different ratio of {010} faces, especially the formation of Bi2O3 in the primary stage of the hydrothermal treatment is a key factor for the exposure of {010} facets. The visible-light-driven photocatalytic activities of the Bi2MoO6 products with different ratio of {010} facets exposed are investigated through the degradation of Rhodamine B, oxytetracycline, and tetracycline. Bi2MoO6 nanosheets synthesized at pH 10.0 with highest {010} facet exposed ratio exhibited highly efficient visible light photocatalytic activity for pollutant decomposition, which can be mainly attributed to the flake structures, the crystallinity and most importantly, the exposed {010} facet which generate high concentration of rad O2-.

Surface structure-dependent pyrite oxidation in relatively dry and moist air: Implications for the reaction mechanism and sulfur evolution

NASA Astrophysics Data System (ADS)

Zhu, Jianxi; Xian, Haiyang; Lin, Xiaoju; Tang, Hongmei; Du, Runxiang; Yang, Yiping; Zhu, Runliang; Liang, Xiaoliang; Wei, Jingming; Teng, H. Henry; He, Hongping

2018-05-01

Pyrite oxidation not only is environmentally significant in the formation of acid mine (or acid rock) drainage and oxidative acidification of lacustrine sediment but also is a critical stage in geochemical sulfur evolution. The oxidation process is always controlled by the reactivity of pyrite, which in turn is controlled by its surface structure. In this study, the oxidation behavior of naturally existing {1 0 0}, {1 1 1}, and {2 1 0} facets of pyrite was investigated using a comprehensive approach combining X-ray photoelectron spectroscopy, diffuse reflectance Fourier transform infrared spectroscopy, and time-of-flight secondary-ion mass spectrometry with periodic density functional theoretical (DFT) calculations. The experimental results show that (i) the initial oxidation rates of both pyrite {1 1 1} and {2 1 0} are much greater than that of pyrite {1 0 0}; (ii) the initial oxidation rate of pyrite {2 1 0} is greater than that of pyrite {1 1 1} in low relative humidity, which is reversed in high relative humidity; and (iii) inner sphere oxygen-bearing sulfur species are originally generated from surface reactions and then converted to outer sphere species. The facet dependent rate law can be expressed as: r{hkl} =k{hkl}haP0.5(t + 1) - 0.5 , where r{hkl} is the orientation dependent reaction rate, k{hkl} is the orientation dependent rate constant, h is the relative humidity, P is the oxygen partial pressure, and t is the oxidation time in seconds. {1 1 1} is the most sensitive facet for pyrite oxidation. Combined with DFT theoretical investigations, water catalyzed electron transfer is speculated as the rate-limiting step. These findings disclose the structure-reactivity dependence of pyrite, which not only presents new insight into the mechanism of pyrite oxidation but also provides fundamental data to evaluate sulfur speciation evolution, suggesting that the surface structure sensitivity should be considered to estimate the reactivity at the mineral-water interface.

Localized Surface Plasmon Resonance (LSPR)-Coupled Fiber-Optic Nanoprobe for the Detection of Protein Biomarkers.

PubMed

Wei, Jianjun; Zeng, Zheng; Lin, Yongbin

2017-01-01

Here is presented a miniaturized, fiber-optic (FO) nanoprobe biosensor based on the localized surface plasmon resonance (LSPR) at the reusable dielectric-metallic hybrid interface with a robust, gold nano-disk array at the fiber end facet. The nanodisk array is directly fabricated using electron beam lithography (EBL) and metal lift-off process. The free prostate-specific antigen (f-PSA) has been detected with a mouse anti-human prostate-specific antigen (PSA) monoclonal antibody (mAb) as a specific receptor linked with a self-assembled monolayer (SAM) at the LSPR-FO facet surfaces. Experimental investigation and data analysis found near field refractive index (RI) sensitivity at ~226 nm/RIU with the LSPR-FO nanoprobe, and demonstrated the lowest limit of detection (LOD) at 100 fg/mL (~3 fM) of f-PSA in PBS solutions. The SAM shows insignificant nonspecific binding to the target biomarkers in the solution. The control experimentation using 5 mg/mL bovine serum albumin in PBS and nonspecific surface test shows the excellent specificity and selectivity in the detection of f-PSA in PBS. These results indicate important progress toward a miniaturized, multifunctional fiber-optic technology that integrates informational communication and sensing function for developing a high-performance, label-free, point-of-care (POC) device.

Localized and generalized simulated wear of resin composites.

PubMed

Barkmeier, W W; Takamizawa, T; Erickson, R L; Tsujimoto, A; Latta, M; Miyazaki, M

2015-01-01

A laboratory study was conducted to examine the wear of resin composite materials using both a localized and generalized wear simulation model. Twenty specimens each of seven resin composites (Esthet•X HD [HD], Filtek Supreme Ultra [SU], Herculite Ultra [HU], SonicFill [SF], Tetric EvoCeram Bulk Fill [TB], Venus Diamond [VD], and Z100 Restorative [Z]) were subjected to a wear challenge of 400,000 cycles for both localized and generalized wear in a Leinfelder-Suzuki wear simulator (Alabama machine). The materials were placed in custom cylinder-shaped stainless steel fixtures. A stainless steel ball bearing (r=2.387 mm) was used as the antagonist for localized wear, and a stainless steel, cylindrical antagonist with a flat tip was used for generalized wear. A water slurry of polymethylmethacrylate (PMMA) beads was used as the abrasive media. A noncontact profilometer (Proscan 2100) with Proscan software was used to digitize the surface contours of the pretest and posttest specimens. AnSur 3D software was used for wear assessment. For localized testing, maximum facet depth (μm) and volume loss (mm(3)) were used to compare the materials. The mean depth of the facet surface (μm) and volume loss (mm(3)) were used for comparison of the generalized wear specimens. A one-way analysis of variance (ANOVA) and Tukey post hoc test were used for data analysis of volume loss for both localized and generalized wear, maximum facet depth for localized wear, and mean depth of the facet for generalized wear. The results for localized wear simulation were as follows [mean (standard deviation)]: maximum facet depth (μm)--Z, 59.5 (14.7); HU, 99.3 (16.3); SU, 102.8 (13.8); HD, 110.2 (13.3); VD, 114.0 (10.3); TB, 125.5 (12.1); SF, 195.9 (16.9); volume loss (mm(3))--Z, 0.013 (0.002); SU, 0.026 (0.006); HU, 0.043 (0.008); VD, 0.057 (0.009); HD, 0.058 (0.014); TB, 0.061 (0.010); SF, 0.135 (0.024). Generalized wear simulation results were as follows: mean depth of facet (μm)--Z, 9.3 (3.4); SU, 12.8 (3.1); HU, 15.6 (3.2); TB, 19.2 (4.8); HD, 26.8 (6.5); VD, 29.1 (5.5); SF, 35.6 (8.4); volume loss (mm(3))--Z, 0.132 (0.049); SU, 0.0179 (0.042); HU, 0.224 (0.044); TB, 0.274 (0.065); HD, 0.386 (0.101); VD, 0.417 (0.076); SF, 0.505 (0.105). The ANOVA showed a significant difference among materials (p<0.001) for facet depth and volume loss for both localized and generalized wear. The post hoc test revealed differences (p<0.05) in localized and generalized wear values among the seven resin composites examined in this study. The findings provide valuable information regarding the relative wear characteristics of the materials in this study.

Development of high-performance supercapacitor electrode derived from sugar industry spent wash waste.

PubMed

Mahto, Ashesh; Gupta, Rajeev; Ghara, Krishna Kanta; Srivastava, Divesh N; Maiti, Pratyush; D, Kalpana; Rivera, Paul-Zavala; Meena, R; Nataraj, S K

2017-10-15

This study aims at developing supercapacitor materials from sugar and distillery industry wastes, thereby mediating waste disposal problem through reuse. In a two-step process, biomethanated spent wash (BMSW) was acid treated to produce solid waste sludge and waste water with significantly reduced total organic carbon (TOC) and biological oxygen demand (BOD) content. Further, waste sludge was directly calcined in presence of activating agent ZnCl 2 in inert atmosphere resulting in high surface area (730-900m 2 g -1 ) carbon of unique hexagonal morphology. Present technique resulted in achieving two-faceted target of liquid-solid waste remediation and production of high-performance carbon material. The resulted high surface area carbon was tested in both three and two electrode systems. Electrochemical tests viz. cyclic voltammetry, galvanostatic charge-discharge and impedance measurement were carried out in aqueous KOH electrolyte yielding specific capacitance as high as 120Fg -1 , whereas all solid supercapacitor devised using PVA/H 3 PO 4 polyelectrolyte showed stable capacitance of 105Fg -1 at 0.2Ag -1 . The presence of transition metal particles and hetero-atoms on carbon surface were confirmed by XPS, EDX and TEM analysis which enhanced the conductivity and imparted pseudocapacitance to some extent into the working electrode. The present study successfully demonstrated production of high-performance electrode material from dirtiest wastewater making process green, sustainable and economically viable. Copyright © 2017. Published by Elsevier B.V.

Preparation of atomically flat TiO2(001) surfaces

NASA Astrophysics Data System (ADS)

Wang, Yang; Weitering, Hanno H.; Snijders, Paul C.

2015-03-01

Transition metal oxides with the rutile structure (MO2, M = e.g. Ti, V, or Nb) have highly directional partially occupied t2g orbitals. Some of these orbitals form quasi-1D electronic bands along the rutile c-axis, and Peierls-like ordering phenomena have been observed in VO2 and NbO2. Tailoring the electronic properties of these materials via quantum confinement requires epitaxial growth on suitable substrates such as low index TiO2 surfaces. Because of the high surface energy of rutile TiO2(001), the standard approach of sputtering and annealing usually introduces faceting. Here we demonstrate a facile method to create atomically flat, non-faceted TiO2(001) surfaces. Using scanning tunneling microscopy we observe terraces with a width of approximately 150 nm. Step heights of approximately 0.3 nm are observed, consistent with the c lattice parameter of rutile TiO2. Low energy electron diffraction patterns reveal sharp diffraction spots with an in-plane lattice constant of 0.358 nm which is consistent with a (1x1) ordering of the (001) plane. These TiO2(001) single crystal surfaces can serve as an ideal substrate for further growth of rutile heterostructures. Research sponsored by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

Optimal Magnetorheological Fluid for Finishing of Chemical-Vapor-Deposited Zinc Sulfide

NASA Astrophysics Data System (ADS)

Salzman, Sivan

Magnetorheological finishing (MRF) of polycrystalline, chemical-vapor- deposited zinc sulfide (ZnS) optics leaves visible surface artifacts known as "pebbles". These artifacts are a direct result of the material's inner structure that consists of cone-like features that grow larger (up to a few millimeters in size) as deposition takes place, and manifest on the top deposited surface as "pebbles". Polishing the pebble features from a CVD ZnS substrate to a flat, smooth surface to below 10 nm root-mean-square is challenging, especially for a non-destructive polishing process such as MRF. This work explores ways to improve the surface finish of CVD ZnS processed with MRF through modification of the magnetorheological (MR) fluid's properties. A materials science approach is presented to define the anisotropy of CVD ZnS through a combination of chemical and mechanical experiments and theoretical predictions. Magnetorheological finishing experiments with single crystal samples of ZnS, whose cuts and orientations represent most of the facets known to occur in the polycrystalline CVD ZnS, were performed to explore the influence of material anisotropy on the material removal rate during MRF. By adjusting the fluid's viscosity, abrasive type concentration, and pH to find the chemo-mechanical conditions that equalize removal rates among all single crystal facets during MRF, we established an optimized, novel MR formulation to polish CVD ZnS without degrading the surface finish of the optic.

The surface chemistry of nanocrystalline MgO catalysts for FAME production: An in situ XPS study of H2O, CH3OH and CH3OAc adsorption

NASA Astrophysics Data System (ADS)

Montero, J. M.; Isaacs, M. A.; Lee, A. F.; Lynam, J. M.; Wilson, K.

2016-04-01

An in situ XPS study of water, methanol and methyl acetate adsorption over as-synthesised and calcined MgO nanocatalysts is reported with a view to gaining insight into the surface adsorption of key components relevant to fatty acid methyl esters (biodiesel) production during the transesterification of triglycerides with methanol. High temperature calcined NanoMgO-700 adsorbed all three species more readily than the parent material due to the higher density of electron-rich (111) and (110) facets exposed over the larger crystallites. Water and methanol chemisorb over the NanoMgO-700 through the conversion of surface O2 - sites to OH- and coincident creation of Mg-OH or Mg-OCH3 moieties respectively. A model is proposed in which the dissociative chemisorption of methanol occurs preferentially over defect and edge sites of NanoMgO-700, with higher methanol coverages resulting in physisorption over weakly basic (100) facets. Methyl acetate undergoes more complex surface chemistry over NanoMgO-700, with C-H dissociation and ester cleavage forming surface hydroxyl and acetate species even at extremely low coverages, indicative of preferential adsorption at defects. Comparison of C 1s spectra with spent catalysts from tributyrin transesterification suggest that ester hydrolysis plays a key factor in the deactivation of MgO catalysts for biodiesel production.

Synthesis of belt-like BiOBr hierarchical nanostructure with high photocatalytic performance

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

Li, Haiping; Liu, Jingyi; Hu, Tingxia

2016-05-15

Highlights: • BiOBr hierarchical nanobelts (NBs) were solvothermally prepared. • NBs show higher specific surface area and photoabsorption than BiOBr nanosheets. • NBs exhibit higher photoactivity than the nanosheets. - Abstract: One-dimensional (1D) bismuth oxyhalide (BiOX) hierarchical nanostructures are always difficult to prepare. Herein, we report, for the first time, a simple synthesis of BiOBr nanobelts (NBs) via a facile solvothermal route, using bismuth subsalicylate as the template and bismuth source. The BiOBr nanobelts are composed of irregular single crystal nanoparticles with highly exposed (0 1 0) facets. Compared with the BiOBr nanosheets (NSs) with dominant exposed (0 0 1)more » facets, they exhibit higher photocatalytic activity toward degradation of Rhodamine B and Methylene Blue under visible light irradiation. The higher photocatalytic performance of BiOBr NBs arises from their larger specific surface area and higher photoabsorption capability. This study provides a simple route for synthesis of belt-like Bi-based hierarchical nanostructures.« less

An optical biosensor using MEMS-based V-grooves

NASA Astrophysics Data System (ADS)

Tian, Ye; Ma, Xiaodong; Zou, Xiaotian; Wu, Nan; Wang, Xingwei

2011-05-01

An optical fiber biosensor featuring miniaturization, electromagnetic interference (EMI)-immunity, and flexibility is presented. The sensor was fabricated by aligning two gold-deposited optical single-mode fiber facets inside V-grooves on a silicon chip to form a Fabry-Perot (FP) cavity. The mirrors on the fiber facets were made of deposited gold (Au) films, which provided a high finesse to produce a highly sensitivity. Microelectromechanical systems (MEMS) fabrication techniques were used to precisely control the profile and angle of the V-grooves on the silicon. The biotin-terminated thiol molecule was firstly immobilized on the gold surface. Subsequently, the molecules of Neutravidin were specifically bound to the biotin-terminated self-assembled monolayers (SAMs). The induced changes of cavity length and refractive index (RI) upon the gold surface lead to an optical path difference (OPD) of the FP cavity, which was detected by demodulating the transmission spectrum phase shift. By taking advantage of MEMS techniques, multiple biosensors can be integrated into one small silicon chip for detecting various biomolecule targets simultaneously.

Holocene surface-rupturing earthquakes along the Yadong Cross Structure (Himalaya)

NASA Astrophysics Data System (ADS)

Ferry, M. A.; Roth, T.; Jean-Francois, R.; Cattin, R.

2017-12-01

The Himalayan Arc accommodates 2 cm/yr of shortening from the India-Eurasia collision, mostly along the Main Himalayan Thust. Perpendicularly to the main structures, regional cross structures formed by en échelon grabens and half-grabens mark Quaternary extension from central Tibet to the Himalayas. The Yadong-Gulu Rift system is the most striking one with a total length of 500 km. Its southernmost segment -the 100-km-long Yadong half-graben- entrenches through the Himalayas and forms a 500-to-1500-m-deep asymmetric basin. The average basin surface elevation of 4500 m contrasts with high reliefs of the Jomolhari range that reach 7326 m. They are separated by the N15 Yadong normal fault (also called Jomolhari Fault System, JFS) that forms spectacular triangular facets and affects glacial landforms. Though observed as early as the 1980s, offset moraines were never studied in detail in terms of measured displacement or age determination. Recent efforts from paleoclimate studies yielded a high-resolution framework to identify the various stages of Holocene glacial advances and associated moraine formation. These landforms display specific geomorphometric features recognized regionally (ELA, rugosity, crest freshness) that allow correlating across the various glacial valleys within the Yadong Rift and across similar settings in western Bhutan and eastern Nepal. This serves as a robust basis to place our moraine sequence within the Holocene paleoclimatic record and propose formation ages. By combining satellite images from Sentinel-2 (10 m, visible and NIR), Pléiades (0.5 m, visible) and a Pléiades-derived tri-stereo photogrammetric DEM (1 m), we map the fault trace and affected landforms in details and extract topographic profiles to measure vertical offsets. Paleoclimatic age constraints yield age-vs-displacement measurements along the whole 100-km-long JFS and define a chronology of Holocene deformation events. Within the limits of our observations, we conclude that the last surface-rupturing earthquake likely occurred between 3 and 8 ka BP and produced an average surface displacement of 2 m. According to scaling relationships, the associated earthquake would have reached Mw 7.2. In addition, cumulative deformation suggests an average vertical slip rate of 1 mm/yr for the Holocene.

Skeletal development of hallucal tarsometatarsal joint curvature and angulation in extant apes and modern humans.

PubMed

Gill, Corey M; Bredella, Miriam A; DeSilva, Jeremy M

2015-11-01

The medial cuneiform, namely the curvature and angulation of its distal facet with metatarsal 1, is crucial as a stabilizer in bipedal locomotion and an axis upon which the great toe medially deviates during arboreal locomotion in extant apes. Previous work has shown that facet curvature and angulation in adult dry-bone specimens can distinguish African apes from Homo, and can even distinguish among species of Gorilla. This study provides the first ontogenetic assessment of medial cuneiform curvature and angulation in juvenile (n = 68) and adult specimens (n = 102) using computed tomography in humans and extant ape specimens, including Pongo. Our data find that modern human juveniles initially have a convex and slightly medially oriented osseous surface of the developing medial cuneiform distal facet that flattens and becomes more distally oriented with age. The same pattern (though of a different magnitude) occurs developmentally in the chimpanzee medial cuneiform, but not in Gorilla or Pongo, whose medial cuneiform facet angulation remains unchanged ontogenetically. These data suggest that the medial cuneiform ossifies in a distinguishable pattern between Pongo, Gorilla, Pan, and Homo, which may in part be due to subtle differences in the loading environment at the hallucal tarsometatarsal joint-a finding that has important implications for interpreting fossil medial cuneiforms. Copyright © 2015 Elsevier Ltd. All rights reserved.

Effects of the interaction between TiO2 with different percentages of exposed {001} facets and Cu2+ on biotoxicity in Daphnia magna

PubMed Central

Liu, Lingling; Fan, Wenhong; Lu, Huiting; Xiao, Wei

2015-01-01

Anatase TiO2 nanosheets (NSs) with exposed {001} facets have been widely used because of their high activity and particular surface atomic configuration. However, investigations on their biotoxicity are rare. In this study, bioaccumulation of five different TiO2 (with 10%, 61%, 71%, 74% and 78% exposed {001} facets), as well as copper and enzyme activities in Daphnia magna, are systematically investigated and rationalized. The results indicated that the addition of Cu2+ enhanced agglomeration–sedimentation of TiO2, resulting in the reduction of TiO2 bioaccumulation by 10% to 26%. TiO2 nanoparticles (NPs) increased copper bioaccumulation by 9.8%, whereas the other four TiO2 nanosheets (NSs) decreased it by 43% to 53%, which depended on TiO2 variant adsorption and free Cu2+ concentrations in the supernatant. The levels of superoxide dismutase (SOD) enzyme and Na+/K+-ATPase activities suggested that oxidative stress, instead of membrane damage, was the main toxicity in D. magna. Meanwhile, the SOD enzyme activities increased with decreasing Cu accumulation and increasing Ti accumulation because of the different functions of Cu and Ti in organisms. This research highlighted the important role of the percentage of exposed {001} facets in nanostructured TiO2 on bioaccumulation and biotoxicity of TiO2 and Cu2+ in Daphnia magna. PMID:26242603

Properties of GaN grown on sapphire substrates

NASA Technical Reports Server (NTRS)

Crouch, R. K.; Debnam, W. J.; Fripp, A. L.

1978-01-01

Epitaxial growth of GaN on sapphire substrates using an open-tube growth furnace has been carried out to study the effects of substrate orientation and transfer gas upon the properties of the layers. It has been found that for the (0001) substrates, surface appearance was virtually independent of carrier gas and of doping levels. For the (1(-1)02) substrates surface faceting was greatly reduced when He was used as a transfer gas as opposed to H2. Faceting was also reduced when the GaN was doped with Zn, and the best surfaces for the (1(-1)02) substrates were obtained in a Zn-doped run using He as the transfer gas. The best sample in terms of electrical properties for the (1(-1)02) substrate had a mobility greater than 400 sq cm/V per sec and a carrier concentration of about 10 to the 17th per cu cm. This sample was undoped and used He as the transfer gas. The best (0001) sample was also grown undoped with He as the transfer gas and had a mobility of 300 sq cm/V per sec and a carrier concentration of 1 x 10 to the 18th per cu cm.

Effect of Facet Displacement on Radiation Field and Its Application for Panel Adjustment of Large Reflector Antenna

NASA Astrophysics Data System (ADS)

Wang, Wei; Lian, Peiyuan; Zhang, Shuxin; Xiang, Binbin; Xu, Qian

2017-05-01

Large reflector antennas are widely used in radars, satellite communication, radio astronomy, and so on. The rapid developments in these fields have created demands for development of better performance and higher surface accuracy. However, low accuracy and low efficiency are the common disadvantages for traditional panel alignment and adjustment. In order to improve the surface accuracy of large reflector antenna, a new method is presented to determinate panel adjustment values from far field pattern. Based on the method of Physical Optics (PO), the effect of panel facet displacement on radiation field value is derived. Then the linear system is constructed between panel adjustment vector and far field pattern. Using the method of Singular Value Decomposition (SVD), the adjustment value for all panel adjustors are obtained by solving the linear equations. An experiment is conducted on a 3.7 m reflector antenna with 12 segmented panels. The results of simulation and test are similar, which shows that the presented method is feasible. Moreover, the discussion about validation shows that the method can be used for many cases of reflector shape. The proposed research provides the instruction to adjust surface panels efficiently and accurately.

Constraining the fault slip rate using morphology of normal fault footwalls: insights from analog and numerical models (Invited)

NASA Astrophysics Data System (ADS)

Strak, V.; Dominguez, S.; Petit, C.; Meyer, B.; Loget, N.

2013-12-01

Relief evolution in active tectonic areas is controlled by the interactions between tectonics and surface processes (erosion, transport and sedimentation). These interactions lead to the formation of geomorphologic markers that remain stable during the equilibrium reached in the long-term between tectonics and erosion. In regions experiencing active extension, drainage basins and faceted spurs (triangular facets) are such long-lived morphologic markers and they can help in quantifying the competing effects between tectonics, erosion and sedimentation. We performed analog and numerical models simulating the morphologic evolution of a mountain range bounded by a normal fault. In each approach we imposed identical initial conditions. We carried out several models by varying the fault slip rate (V) and keeping a constant rainfall rate allowing us to study the effect of V on morphology. Both approaches highlight the main control of V on the topographic evolution of the footwall. The experimental approach shows that V controls erosion rates (incision rate, erosion rate of slopes and regressive erosion rate) and possibly the height of triangular facets. This approach indicates likewise that the parameter K of the stream power law depends on V even for non-equilibrium topography. The numerical approach corroborates the control of V on erosion rates and facet height. It also shows a correlation between the shape of drainage basins and V (slope-area relationship) and it suggests the same for the parameters of the stream power law. Therefore both approaches suggest the possibility of using the height of triangular facets and the slope-area relationship to infer the fault slip rate of normal faults situated in a given climatic context.

Delaminated graphene at silicon carbide facets: atomic scale imaging and spectroscopy.

PubMed

Nicotra, Giuseppe; Ramasse, Quentin M; Deretzis, Ioannis; La Magna, Antonino; Spinella, Corrado; Giannazzo, Filippo

2013-04-23

Atomic-resolution structural and spectroscopic characterization techniques (scanning transmission electron microscopy and electron energy loss spectroscopy) are combined with nanoscale electrical measurements (conductive atomic force microscopy) to study at the atomic scale the properties of graphene grown epitaxially through the controlled graphitization of a hexagonal SiC(0001) substrate by high temperature annealing. This growth technique is known to result in a pronounced electron-doping (∼10(13) cm(-2)) of graphene, which is thought to originate from an interface carbon buffer layer strongly bound to the substrate. The scanning transmission electron microscopy analysis, carried out at an energy below the knock-on threshold for carbon to ensure no damage is imparted to the film by the electron beam, demonstrates that the buffer layer present on the planar SiC(0001) face delaminates from it on the (112n) facets of SiC surface steps. In addition, electron energy loss spectroscopy reveals that the delaminated layer has a similar electronic configuration to purely sp2-hybridized graphene. These observations are used to explain the local increase of the graphene sheet resistance measured around the surface steps by conductive atomic force microscopy, which we suggest is due to significantly lower substrate-induced doping and a resonant scattering mechanism at the step regions. A first-principles-calibrated theoretical model is proposed to explain the structural instability of the buffer layer on the SiC facets and the resulting delamination.

The design of the layout of faceted multi-channel electro-optical spatial coordinates measuring instrument for point-like bright objects

NASA Astrophysics Data System (ADS)

Repin, Vladislav A.; Gorbunova, Elena V.; Chertov, Aleksandr N.; Korotaev, Valery V.

2017-06-01

For many applied problems it is necessary to obtain information about the situation in a wide angular field in order to measure various parameters of objects: their spatial coordinates, instantaneous velocities, and so on. In this case, one interesting bionic approach can be used - a mosaic (or discrete, otherwise, facet) angular field. Such electro-optical system constructively imitates the visual apparatus of insects: many photodetectors like ommatidia (elements of the facet eye structure) are located on a non-planar surface. Such devices can be used in photogrammetry and aerial photography systems (if the space is sufficient), in the transport sector as vehicle orientation organs, as systems for monitoring in unmanned aerial vehicles, in endoscopy for obtaining comprehensive information on the state of various cavities, in intelligent robotic systems. In this manuscript discusses the advantages and disadvantages of multi-channeled optoelectronic systems with a mosaic angular field, presents possible options for their use, and discusses some of the design procedures performed when developing a layout of a coordinate measuring device.

Highly exposed {001} facets of titanium dioxide modified with reduced graphene oxide for dopamine sensing.

PubMed

How, Gregory Thien Soon; Pandikumar, Alagarsamy; Ming, Huang Nay; Ngee, Lim Hong

2014-05-23

Titanium dioxide (TiO2) with highly exposed {001} facets was synthesized through a facile solvo-thermal method and its surface was decorated by using reduced graphene oxide (rGO) sheets. The morphology and chemical composition of the prepared rGO/TiO2 {001} nanocomposite were examined by using suitable characterization techniques. The rGO/TiO2 {001} nanocomposite was used to modify glassy carbon electrode (GCE), which showed higher electrocatalytic activity towards the oxidation of dopamine (DA) and ascorbic acid (AA), when compared to unmodified GCE. The differential pulse voltammetric studies revealed good sensitivity and selectivity nature of the rGO/TiO2 {001} nanocomposite modified GCE for the detection of DA in the presence of AA. The modified GCE exhibited a low electrochemical detection limit of 6 μM over the linear range of 2-60 μM. Overall, this work provides a simple platform for the development of GCE modified with rGO/TiO2 {001} nanocomposite with highly exposed {001} facets for potential electrochemical sensing applications.

Highly exposed {001} facets of titanium dioxide modified with reduced graphene oxide for dopamine sensing

NASA Astrophysics Data System (ADS)

How, Gregory Thien Soon; Pandikumar, Alagarsamy; Ming, Huang Nay; Ngee, Lim Hong

2014-05-01

Titanium dioxide (TiO2) with highly exposed {001} facets was synthesized through a facile solvo-thermal method and its surface was decorated by using reduced graphene oxide (rGO) sheets. The morphology and chemical composition of the prepared rGO/TiO2 {001} nanocomposite were examined by using suitable characterization techniques. The rGO/TiO2 {001} nanocomposite was used to modify glassy carbon electrode (GCE), which showed higher electrocatalytic activity towards the oxidation of dopamine (DA) and ascorbic acid (AA), when compared to unmodified GCE. The differential pulse voltammetric studies revealed good sensitivity and selectivity nature of the rGO/TiO2 {001} nanocomposite modified GCE for the detection of DA in the presence of AA. The modified GCE exhibited a low electrochemical detection limit of 6 μM over the linear range of 2-60 μM. Overall, this work provides a simple platform for the development of GCE modified with rGO/TiO2 {001} nanocomposite with highly exposed {001} facets for potential electrochemical sensing applications.

Highly exposed {001} facets of titanium dioxide modified with reduced graphene oxide for dopamine sensing

PubMed Central

How, Gregory Thien Soon; Pandikumar, Alagarsamy; Ming, Huang Nay; Ngee, Lim Hong

2014-01-01

Titanium dioxide (TiO2) with highly exposed {001} facets was synthesized through a facile solvo-thermal method and its surface was decorated by using reduced graphene oxide (rGO) sheets. The morphology and chemical composition of the prepared rGO/TiO2 {001} nanocomposite were examined by using suitable characterization techniques. The rGO/TiO2 {001} nanocomposite was used to modify glassy carbon electrode (GCE), which showed higher electrocatalytic activity towards the oxidation of dopamine (DA) and ascorbic acid (AA), when compared to unmodified GCE. The differential pulse voltammetric studies revealed good sensitivity and selectivity nature of the rGO/TiO2 {001} nanocomposite modified GCE for the detection of DA in the presence of AA. The modified GCE exhibited a low electrochemical detection limit of 6 μM over the linear range of 2–60 μM. Overall, this work provides a simple platform for the development of GCE modified with rGO/TiO2 {001} nanocomposite with highly exposed {001} facets for potential electrochemical sensing applications. PMID:24853929

Facet-controlled synthesis of polyhedral hematite/carbon composites with enhanced photoactivity

NASA Astrophysics Data System (ADS)

Hu, Xiaoyi; Han, Sancan; Zhu, Yufang

2018-06-01

Much effort has been made to develop the semiconductor photocatalysis, but it is still challenging to fabricate low-cost and high-activity photocatalysts. In this study, Hematite (α-Fe2O3) with three kinds of morphologies including dodecahedron, tetrakaidecahedron and hexagonal nanoplates have been synthesized without any organic reagents. The photocatalytic performance reveals that the dodecahedron with exposed {1 0 1} facets is superior to the hexagonal nanoplates with predominant exposure of {0 0 1} facets in the case of similar BET surface area. For further enhancement of photocatalytic activity, carbon layer was coated on dodecahedral α-Fe2O3 through the self-polymerization of dopamine and following pyrolysis at 400 °C under Ar flow. Compared with the pristine dodecahedral α-Fe2O3, the α-Fe2O3/C composites exhibit stronger visible absorption, lower photoexcited electron-hole pairs recombination rate and better photodegradation activity. The photocatalytic performance showed the degradation rate of α-Fe2O3-D/4.5C is nearly 6 times higher than pristine α-Fe2O3, which have great potential for photocatalysis applications.

VISdish: A new tool for canting and shape-measuring solar-dish facets.

PubMed

Montecchi, Marco; Cara, Giuseppe; Benedetti, Arcangelo

2017-06-01

Solar dishes allow us to obtain highly concentrated solar fluxes used to produce electricity or feed thermal processes/storage. For practical reasons, the reflecting surface is composed by a number of facets. After the dish assembly, facet-canting is an important task for improving the concentration of solar radiation around the focus-point, as well as the capture ratio at the receiver placed there. Finally, flux profile should be measured or evaluated to verify the concentration quality. All these tasks can be achieved by the new tool we developed at ENEA, named VISdish. The instrument is based on the visual inspection system (VIS) approach and can work in two functionalities: canting and shape-measurement. The shape data are entered in a simulation software for evaluating the flux profile and concentration quality. With respect to prior methods, VISdish offers several advantages: (i) simpler data processing, because light point-source and its reflections are univocally related, (ii) higher accuracy. The instrument functionality is illustrated through the preliminary experimental results obtained on the dish recently installed in ENEA-Casaccia in the framework of the E.U. project OMSoP.

Geometric Processing and Its Relational Graphics

DTIC Science & Technology

1976-10-01

20, If different from Report) f3. SUPPLEMENTARY NOTES 9. KEY WORDS (Cbnttnue on reverse aide if neceaaary .mdldentlfy by bfock number) Graphics GIFT ...are typified by defining an object as a series of adjacent triangular or rectangular patches or surfaces (ruled surfaces may also be used). The GIFT ...code embodies the Patch code concept in one of its solids, the ARS; however, processing of a many-faceted GIFT solid takes longer to process than its

Qualitative and quantitative assessment of degeneration of cervical intervertebral discs and facet joints.

PubMed

Walraevens, Joris; Liu, Baoge; Meersschaert, Joke; Demaerel, Philippe; Delye, Hans; Depreitere, Bart; Vander Sloten, Jos; Goffin, Jan

2009-03-01

Degeneration of intervertebral discs and facet joints is one of the most frequently encountered spinal disorders. In order to describe and quantify degeneration and evaluate a possible relationship between degeneration and biomechanical parameters, e.g., the intervertebral range of motion and intradiscal pressure, a scoring system for degeneration is mandatory. However, few scoring systems for the assessment of degeneration of the cervical spine exist. Therefore, two separate objective scoring systems to qualitatively and quantitatively assess the degree of cervical intervertebral disc and facet joint degeneration were developed and validated. The scoring system for cervical disc degeneration consists of three variables which are individually scored on neutral lateral radiographs: "height loss" (0-4 points), "anterior osteophytes" (0-3 points) and "endplate sclerosis" (0-2 points). The scoring system for facet joint degeneration consists of four variables which are individually scored on neutral computed tomography scans: "hypertrophy" (0-2 points), "osteophytes" (0-1 point), "irregularity" on the articular surface (0-1 point) and "joint space narrowing" (0-1 point). Each variable contributes with varying importance to the overall degeneration score (max 9 points for the scoring system of cervical disc degeneration and max 5 points for facet joint degeneration). Degeneration of 20 discs and facet joints of 20 patients was blindly assessed by four raters: two neurosurgeons (one senior and one junior) and two radiologists (one senior and one junior), firstly based on first subjective impression and secondly using the scoring systems. Measurement errors and inter- and intra-rater agreement were determined. The measurement error of the scoring system for cervical disc degeneration was 11.1 versus 17.9% of the subjective impression results. This scoring system showed excellent intra-rater agreement (ICC = 0.86, 0.75-0.93) and excellent inter-rater agreement (ICC = 0.78, 0.64-0.88). Surgeons as well as radiologists and seniors as well as juniors obtained excellent inter- and intra-rater agreement. The measurement error of the scoring system for cervical facet joint degeneration was 20.1 versus 24.2% of the subjective impression results. This scoring system showed good intra-rater agreement (ICC = 0.71, 0.42-0.89) and fair inter-rater agreement (ICC = 0.49, 0.26-0.74). Both scoring systems fulfilled the criteria for recommendation proposed by Kettler and Wilke. Our scoring systems can be reliable and objective tools for assessing cervical disc and facet joint degeneration. Moreover, the scoring system of cervical disc degeneration was shown to be experience- and discipline-independent.

Oxidative dehydrogenation of isobutane over vanadia catalysts supported by titania nanoshapes

DOE PAGES

Kraemer, Shannon K.; Rondinone, Adam Justin; Tsai, Yu-Tung; ...

2015-11-02

Support plays a complex role in catalysis by supported metal oxides and the exact support effect still remains elusive. One of the approaches to gain fundamental insights into the support effect is to utilize model support systems. In this study, we employed for the first time titania nanoshapes as the model supports and investigated how the variation of surface structure of the support (titania, TiO 2) impacts the catalysis of supported oxide (vanadia, VO x). TiO 2 truncated rhombi, spheres and rods were synthesized via hydrothermal method and characterized with XRD and TEM. These TiO 2 nanoshapes represent different mixturesmore » of surface facets including [1 0 1], [0 1 0] and [0 0 1] and were used to support vanadia. The structure of supported VO x species was characterized in detail with in situ Raman spectroscopy as a function of loading on the three TiO 2 nanoshapes. Oxidative dehydrogenation (ODH) of isobutane to isobutene was used as a model reaction to test how the support shape influences the activity, selectivity and activation energy of the surface VO x species. It was shown that the shape of TiO 2 support does not pose evident effect on either the structure of surface VO x species or the catalytic performance of surface VO x species in isobutane ODH reaction. Finally, this insignificant support shape effect was ascribed to the small difference in the surface oxygen vacancy formation energy among the different TiO 2 surfaces and the multi-faceting nature of the TiO 2 nanoshapes.« less

Oxidative dehydrogenation of isobutane over vanadia catalysts supported by titania nanoshapes

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

Kraemer, Shannon; Rondinone, Adam J.; Tsai, Yu-Tong

2016-04-01

Support plays a complex role in catalysis by supported metal oxides and the exact support effect still remains elusive. One of the approaches to gain fundamental insights into the support effect is to utilize model support systems. In this paper, we employed for the first time titania nanoshapes as the model supports and investigated how the variation of surface structure of the support (titania, TiO2) impacts the catalysis of supported oxide (vanadia, VOx). TiO2 truncated rhombi, spheres and rods were synthesized via hydrothermal method and characterized with XRD and TEM. These TiO2 nanoshapes represent different mixtures of surface facets includingmore » [1 0 1], [0 1 0] and [0 0 1] and were used to support vanadia. The structure of supported VOx species was characterized in detail with in situ Raman spectroscopy as a function of loading on the three TiO2 nanoshapes. Oxidative dehydrogenation (ODH) of isobutane to isobutene was used as a model reaction to test how the support shape influences the activity, selectivity and activation energy of the surface VOx species. It was shown that the shape of TiO2 support does not pose evident effect on either the structure of surface VOx species or the catalytic performance of surface VOx species in isobutane ODH reaction. This insignificant support shape effect was ascribed to the small difference in the surface oxygen vacancy formation energy among the different TiO2 surfaces and the multi-faceting nature of the TiO2 nanoshapes.« less

FacetGist: Collective Extraction of Document Facets in Large Technical Corpora.

PubMed

Siddiqui, Tarique; Ren, Xiang; Parameswaran, Aditya; Han, Jiawei

2016-10-01

Given the large volume of technical documents available, it is crucial to automatically organize and categorize these documents to be able to understand and extract value from them. Towards this end, we introduce a new research problem called Facet Extraction. Given a collection of technical documents, the goal of Facet Extraction is to automatically label each document with a set of concepts for the key facets ( e.g. , application, technique, evaluation metrics, and dataset) that people may be interested in. Facet Extraction has numerous applications, including document summarization, literature search, patent search and business intelligence. The major challenge in performing Facet Extraction arises from multiple sources: concept extraction, concept to facet matching, and facet disambiguation. To tackle these challenges, we develop FacetGist, a framework for facet extraction. Facet Extraction involves constructing a graph-based heterogeneous network to capture information available across multiple local sentence-level features, as well as global context features. We then formulate a joint optimization problem, and propose an efficient algorithm for graph-based label propagation to estimate the facet of each concept mention. Experimental results on technical corpora from two domains demonstrate that Facet Extraction can lead to an improvement of over 25% in both precision and recall over competing schemes.

FacetGist: Collective Extraction of Document Facets in Large Technical Corpora

PubMed Central

Siddiqui, Tarique; Ren, Xiang; Parameswaran, Aditya; Han, Jiawei

2017-01-01

Given the large volume of technical documents available, it is crucial to automatically organize and categorize these documents to be able to understand and extract value from them. Towards this end, we introduce a new research problem called Facet Extraction. Given a collection of technical documents, the goal of Facet Extraction is to automatically label each document with a set of concepts for the key facets (e.g., application, technique, evaluation metrics, and dataset) that people may be interested in. Facet Extraction has numerous applications, including document summarization, literature search, patent search and business intelligence. The major challenge in performing Facet Extraction arises from multiple sources: concept extraction, concept to facet matching, and facet disambiguation. To tackle these challenges, we develop FacetGist, a framework for facet extraction. Facet Extraction involves constructing a graph-based heterogeneous network to capture information available across multiple local sentence-level features, as well as global context features. We then formulate a joint optimization problem, and propose an efficient algorithm for graph-based label propagation to estimate the facet of each concept mention. Experimental results on technical corpora from two domains demonstrate that Facet Extraction can lead to an improvement of over 25% in both precision and recall over competing schemes. PMID:28210517

Recent progress on the development of anisotropic gold nanoparticles: Design strategies and growth mechanism.

PubMed

Jones, Stacy; Pramanik, Avijit; Sweet, Carrie; Keyes, Anthony; Begum, Salma; Vangra, Aruna; Yu, Hongtal; Fu, Peter P; Ray, Paresh Chandra

2017-01-02

This review summarizes recent advances on design strategies for shape-controlled anisotropic gold nanoparticles. Detailed chemical mechanism has been discussed to understand the anisotropic growth. The effect of various chemical parameters and surface facets for the formation of different shaped anisotropic nanoparticles have been addressed.

Development of composite facets for the surface of a space-based solar dynamic concentrator

NASA Technical Reports Server (NTRS)

Ayers, Schuyler R.; Morel, Donald E.; Sanborn, James A.

1986-01-01

An account is given of the composite fabrication techniques envisioned for the production of mirror-quality substrates furnishing the specular reflectance required for the NASA Space Station's solar dynamic concentrator energy system. The candidate materials were graphite fiber-reinforced glass, aluminum, and polymer matrices whose surfaces would be coated with thin metal layers and with atomic oxygen degradation-inhibiting protective coatings to obtain the desired mirror surface. Graphite-epoxy mirror substrate samples have been found to perform satisfactorily for the required concentrator lifetime.

Surface topography and ordering-variant segregation in GaInP[sub 2

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

Friedman, D.J.; Zhu, J.G.; Kibbler, A.E.

1993-09-27

Using transmission electron diffraction dark-field imaging, atomic force microscopy (AFM), and Nomarski microscopy, we demonstrate a direct connection between surface topography and cation site ordering in GaInP[sub 2]. We study epilayers grown by organometallic vapor-phase epitaxy on GaAs substrates oriented 2[degree] off (100) towards (110). Nomarski microscopy shows that, as growth proceeds, the surface of ordered material forms faceted structures aligned roughly along [011]. A comparison with the dark-field demonstrates that the [1[bar 1]1] and [11[bar 1

Arthropod eyes: The early Cambrian fossil record and divergent evolution of visual systems.

PubMed

Strausfeld, Nicholas J; Ma, Xiaoya; Edgecombe, Gregory D; Fortey, Richard A; Land, Michael F; Liu, Yu; Cong, Peiyun; Hou, Xianguang

2016-03-01

Four types of eyes serve the visual neuropils of extant arthropods: compound retinas composed of adjacent facets; a visual surface populated by spaced eyelets; a smooth transparent cuticle providing inwardly directed lens cylinders; and single-lens eyes. The first type is a characteristic of pancrustaceans, the eyes of which comprise lenses arranged as hexagonal or rectilinear arrays, each lens crowning 8-9 photoreceptor neurons. Except for Scutigeromorpha, the second type typifies Myriapoda whose relatively large eyelets surmount numerous photoreceptive rhabdoms stacked together as tiers. Scutigeromorph eyes are facetted, each lens crowning some dozen photoreceptor neurons of a modified apposition-type eye. Extant chelicerate eyes are single-lensed except in xiphosurans, whose lateral eyes comprise a cuticle with a smooth outer surface and an inner one providing regular arrays of lens cylinders. This account discusses whether these disparate eye types speak for or against divergence from one ancestral eye type. Previous considerations of eye evolution, focusing on the eyes of trilobites and on facet proliferation in xiphosurans and myriapods, have proposed that the mode of development of eyes in those taxa is distinct from that of pancrustaceans and is the plesiomorphic condition from which facetted eyes have evolved. But the recent discovery of enormous regularly facetted compound eyes belonging to early Cambrian radiodontans suggests that high-resolution facetted eyes with superior optics may be the ground pattern organization for arthropods, predating the evolution of arthrodization and jointed post-protocerebral appendages. Here we provide evidence that compound eye organization in stem-group euarthropods of the Cambrian can be understood in terms of eye morphologies diverging from this ancestral radiodontan-type ground pattern. We show that in certain Cambrian groups apposition eyes relate to fixed or mobile eyestalks, whereas other groups reveal concomitant evolution of sessile eyes equipped with optics typical of extant xiphosurans. Observations of fossil material, including that of trilobites and eurypterids, support the proposition that the ancestral compound eye was the apposition type. Cambrian arthropods include possible precursors of mandibulate eyes. The latter are the modified compound eyes, now sessile, and their underlying optic lobes exemplified by scutigeromorph chilopods, and the mobile stalked compound eyes and more elaborate optic lobes typifying Pancrustacea. Radical divergence from an ancestral apposition type is demonstrated by the evolution of chelicerate eyes, from doublet sessile-eyed stem-group taxa to special apposition eyes of xiphosurans, the compound eyes of eurypterids, and single-lens eyes of arachnids. Different eye types are discussed with respect to possible modes of life of the extinct species that possessed them, comparing these to extant counterparts and the types of visual centers the eyes might have served. Copyright © 2015 Elsevier Ltd. All rights reserved.

Design of a lattice-based faceted classification system

NASA Technical Reports Server (NTRS)

Eichmann, David A.; Atkins, John

1992-01-01

We describe a software reuse architecture supporting component retrieval by facet classes. The facets are organized into a lattice of facet sets and facet n-tuples. The query mechanism supports precise retrieval and flexible browsing.

Multi-Faceted Geophysical Analysis of a Mountain Watershed in the Snowy Range, WY: from Airborne Electromagnetics to NMR

NASA Astrophysics Data System (ADS)

Armstrong, R. S.; Holbrook, W. S.; Flinchum, B. A.; Provart, M.; Carr, B. J.; Auken, E.; Pedersen, J. B.

2014-12-01

Surface/groundwater interactions are an important, but poorly understood, facet of mountain hydrology. We utilize ground electrical resistivity data as a key tool for mapping groundwater pathways and aquifers. However, surface resistivity profiling is limited in both spatial extent and depth, especially in mountainous headwater environments because of inaccessibility and terrain. Because this important groundwater recharge environment is poorly understood, WyCEHG has focused efforts to increase knowledge about the dynamics and location of groundwater recharge. Currently, traditional hydrologic measurements estimate that only 10% of annual snowmelt enters the groundwater system while the rest is immediately available to surface flow. The Wyoming Center for Environmental Hydrology and Geophysics (WyCEHG) collected a 40 sq. km survey of helicopter transient electromagnetic (HTEM) and aeromagnetic data during the fall of 2013 as the first step in a "top down" geophysical characterization of a mountainous headwater catchment in the Snowy Range, Wyoming. Furthermore, mountain springs in the Snowy Range suggests that the "groundwatershed" acts as both a sink and source to surface watersheds. HTEM data show horizontal electrical conductors at depth, which are currently interpreted as fluid-filled subsurface fractures. Because these fractures eventually connect to the surface, they could be geophysical evidence of connectivity between the watershed and "groundwatershed." However, current HTEM inversion techniques assume a layered homogenous subsurface model, which directly contradicts two characteristics of the Snowy Range: the subvertical bedding of the Cheyenne Belt and heterogeneous distribution of surface water. Ground electrical resistivity surveys and surface nuclear magnetic resonance (NMR) measurements collected during the summer of 2014 target these anomalies to determine their validity and further understand the complicated dynamic of surface and groundwater flow.

Surface-Mediated Solvent Decomposition in Li–Air Batteries: Impact of Peroxide and Superoxide Surface Terminations

DOE PAGES

Kumar, Nitin; Radin, Maxwell D.; Wood, Brandon C.; ...

2015-04-13

A viable Li/O 2 battery will require the development of stable electrolytes that do not continuously decompose during cell operation. In some recent experiments it is suggested that reactions occurring at the interface between the liquid electrolyte and the solid lithium peroxide (Li 2O 2) discharge phase are a major contributor to these instabilities. To clarify the mechanisms associated with these reactions, a variety of atomistic simulation techniques, classical Monte Carlo, van der Waals-augmented density functional theory, ab initio molecular dynamics, and various solvation models, are used to study the initial decomposition of the common electrolyte solvent, dimethoxyethane (DME), onmore » surfaces of Li 2O 2. Comparisons are made between the two predominant Li 2O 2 surface charge states by calculating decomposition pathways on peroxide-terminated (O 2 2–) and superoxide-terminated (O 2 1–) facets. For both terminations, DME decomposition proceeds exothermically via a two-step process comprised of hydrogen abstraction (H-abstraction) followed by nucleophilic attack. In the first step, abstracted H dissociates a surface O 2 dimer, and combines with a dissociated oxygen to form a hydroxide ion (OH –). In the remaining surface oxygen then attacks the DME, resulting in a DME fragment that is strongly bound to the Li 2O 2 surface. DME decomposition is predicted to be more exothermic on the peroxide facet; nevertheless, the rate of DME decomposition is faster on the superoxide termination. The impact of solvation (explicit vs implicit) and an applied electric field on the reaction energetics are investigated. Finally, our calculations suggest that surface-mediated electrolyte decomposition should out-pace liquid-phase processes such as solvent auto-oxidation by dissolved O 2.« less

Self-assembled monolayer structures of hexadecylamine on Cu surfaces: density-functional theory.

PubMed

Liu, Shih-Hsien; Balankura, Tonnam; Fichthorn, Kristen A

2016-12-07

We used dispersion-corrected density-functional theory to probe possible structures for adsorbed layers of hexadecylamine (HDA) on Cu(100) and Cu(111). HDA forms self-assembled layers on these surfaces, analogous to alkanethiols on various metal surfaces, and it binds by donating electrons in the amine group to the Cu surface atoms, consistent with experiment. van der Waals interactions between the alkyl tails of HDA molecules are stronger than the interaction between the amine group and the Cu surfaces. Strong HDA-tail interactions lead to coverage-dependent tilting of the HDA layers, such that the tilt angle is larger for lower coverages. At full monolayer coverage, the energetically preferred binding configuration for HDA on Cu(100) is a (5 × 3) pattern - although we cannot rule out incommensurate structures - while the pattern is preferred on Cu(111). A major motivation for this study is to understand the experimentally observed capability of HDA as a capping agent for producing {100}-faceted Cu nanocrystals. Consistent with experiment, we find that HDA binds more strongly to Cu(100) than to Cu(111). This strong binding stems from the capability of HDA to form more densely packed layers on Cu(100), which leads to stronger HDA-tail interactions, as well as the stronger binding of the amine group to Cu(100). We estimate the surface energies of HDA-covered Cu(100) and Cu(111) surfaces and find that these surfaces are nearly isoenergetic. By drawing analogies to previous theoretical work, it seems likely that HDA-covered Cu nanocrystals could have kinetic shapes that primarily express {100} facets, as is seen experimentally.

Modeling elastic anisotropy in strained heteroepitaxy

NASA Astrophysics Data System (ADS)

Krishna Dixit, Gopal; Ranganathan, Madhav

2017-09-01

Using a continuum evolution equation, we model the growth and evolution of quantum dots in the heteroepitaxial Ge on Si(0 0 1) system in a molecular beam epitaxy unit. We formulate our model in terms of evolution due to deposition, and due to surface diffusion which is governed by a free energy. This free energy has contributions from surface energy, curvature, wetting effects and elastic energy due to lattice mismatch between the film and the substrate. In addition to anisotropy due to surface energy which favors facet formation, we also incorporate elastic anisotropy due to an underlying crystal lattice. The complicated elastic problem of the film-substrate system subjected to boundary conditions at the free surface, interface and the bulk substrate is solved by perturbation analysis using a small slope approximation. This permits an analysis of effects at different orders in the slope and sheds new light on the observed behavior. Linear stability analysis shows the early evolution of the instability towards dot formation. The elastic anisotropy causes a change in the alignment of dots in the linear regime, whereas the surface energy anisotropy changes the dot shapes at the nonlinear regime. Numerical simulation of the full nonlinear equations shows the evolution of the surface morphology. In particular, we show, for parameters of the Ge0.25 Si0.75 on Si(0 0 1), the surface energy anisotropy dominates the shapes of the quantum dots, whereas their alignment is influenced by the elastic energy anisotropy. The anisotropy in elasticity causes a further elongation of the islands whose coarsening is interrupted due to < 1 0 5 > facets on the surface.

Modeling elastic anisotropy in strained heteroepitaxy.

PubMed

Dixit, Gopal Krishna; Ranganathan, Madhav

2017-09-20

Using a continuum evolution equation, we model the growth and evolution of quantum dots in the heteroepitaxial Ge on Si(0 0 1) system in a molecular beam epitaxy unit. We formulate our model in terms of evolution due to deposition, and due to surface diffusion which is governed by a free energy. This free energy has contributions from surface energy, curvature, wetting effects and elastic energy due to lattice mismatch between the film and the substrate. In addition to anisotropy due to surface energy which favors facet formation, we also incorporate elastic anisotropy due to an underlying crystal lattice. The complicated elastic problem of the film-substrate system subjected to boundary conditions at the free surface, interface and the bulk substrate is solved by perturbation analysis using a small slope approximation. This permits an analysis of effects at different orders in the slope and sheds new light on the observed behavior. Linear stability analysis shows the early evolution of the instability towards dot formation. The elastic anisotropy causes a change in the alignment of dots in the linear regime, whereas the surface energy anisotropy changes the dot shapes at the nonlinear regime. Numerical simulation of the full nonlinear equations shows the evolution of the surface morphology. In particular, we show, for parameters of the [Formula: see text] [Formula: see text] on Si(0 0 1), the surface energy anisotropy dominates the shapes of the quantum dots, whereas their alignment is influenced by the elastic energy anisotropy. The anisotropy in elasticity causes a further elongation of the islands whose coarsening is interrupted due to [Formula: see text] facets on the surface.

Roughness transitions of diamond(100) induced by hydrogen-plasma treatment

NASA Astrophysics Data System (ADS)

Koslowski, B.; Strobel, S.; Wenig, M. J.; Ziemann, P.

To investigate the influence of hydrogen-plasma treatment on diamond(100) surfaces, heavily boron (B)-doped HPHT diamond crystals were mechanically and chemo-mechanically polished, and exposed to a microwave-assisted hydrogen plasma on a time scale of several minutes. The resulting surface morphology was analyzed on macroscopic scales by stylus profilometry (PFM) and on microscopic scales by STM and AFM. The polished samples have a roughness of typically 100 pmrms (PFM), with no obvious anisotropic structures at the surface. After exposure of the B-doped diamond(100) to the H-plasma, the roughness increases dramatically, and pronounced anisotropic structures appear, these being closely aligned with the crystallographic axis' and planes. An exposure for 3 minutes to the plasma leads to an increase of the roughness to 2-4 nmrms (STM), and a `brick-wall' pattern appears, formed by weak cusps running along <110>. Very frequently, the cusps are replaced by `negative' pyramids that are bordered by {11X} facets. After an exposure of an additional 5 minutes, the surface roughness of the B-doped samples increases further to 20-40 nmrms (STM), and frequently exhibits a regular pattern with structures at a characteristic length scale of about 100 nm. Those structures are aligned approximately with <110> and they are faceted with faces of approximately {XX1}. These results will be discussed in terms of strain relaxation, similar to the surface roughening observed on SiGe/Si and anisotropic etching.

JOCG Aircraft/Stores Compatibility Symposium Proceedings (8th) Held in Fort Walton Beach, Florida on 23-25 October 1990

DTIC Science & Technology

1990-10-25

Compatibility Sub- Group Steering Committee Sub- Group Chairman Wiley I. Robinson Air Force Systems Command Study Group Chairmen Electrical Interface Joe...on the surface of the body organized into groups defining the corners of a series of four -sided surface panel elements which represent a faceted...Structures Technology. In the Aeroanalysis Group , Dr. Cunningham has conducted many studies leading to devel- opments in the area of analytically

Water adsorbate phases on ZnO and impact of vapor pressure on the equilibrium shape of nanoparticles

NASA Astrophysics Data System (ADS)

Kenmoe, Stephane; Biedermann, P. Ulrich

2018-02-01

ZnO nanoparticles are used as catalysts and have potential applications in gas-sensing and solar energy conversion. A fundamental understanding of the exposed crystal facets, their surface chemistry, and stability as a function of environmental conditions is essential for rational design and improvement of synthesis and properties. We study the stability of water adsorbate phases on the non-polar low-index (10 1 ¯ 0 ) and (11 2 ¯ 0 ) surfaces from low coverage to multilayers using ab initio thermodynamics. We show that phonon contributions and the entropies due to a 2D lattice gas at low coverage and multiple adsorbate configurations at higher coverage have an important impact on the stability range of water adsorbate phases in the (T,p) phase diagram. Based on this insight, we compute and analyze the possible growth mode of water films for pressures ranging from UHV via ambient conditions to high pressures and the impact of water adsorption on the equilibrium shape of nanoparticles in a humid environment. A 2D variant of the Wulff construction shows that the (10 1 ¯ 0 ) and (11 2 ¯ 0 ) surfaces coexist on 12-faceted prismatic ZnO nanoparticles in dry conditions, while in humid environment, the (10 1 ¯ 0 ) surface is selectively stabilized by water adsorption resulting in hexagonal prisms.

An improved methodology for heliostat testing and evaluation at the Plataforma Solar de Almería

NASA Astrophysics Data System (ADS)

Monterreal, Rafael; Enrique, Raúl; Fernández-Reche, Jesús

2017-06-01

The optical quality of a heliostat basically quantifies the difference between the scattering effects of the actual solar radiation reflected on its optical surface, compared to the so called canonical dispersion, that is, the one reflected on an optical surface free of constructional errors (paradigm). However, apart from the uncertainties of the measuring process itself, the value of the optical quality must be independent of the measuring instrument; so, any new measuring techniques that provide additional information about the error sources on the heliostat reflecting surface would be welcome. That error sources are responsible for the final optical quality value, with different degrees of influence. For the constructor of heliostats it will be extremely useful to know the value of the classical sources of error and their weight on the overall optical quality of a heliostat, such as facets geometry or focal length, as well as the characteristics of the heliostat as a whole, i.e., its geometry, focal length, facets misalignment and also the possible dependence of these effects with mechanical and/or meteorological factors. It is the goal of the present paper to unfold these optical quality error sources by exploring directly the reflecting surface of the heliostat with the help of a laser-scanner device and link the result with the traditional methods of heliostat evaluation at the Plataforma Solar de Almería.

An End of Service Life Assessment of PMMA Lenses from Veteran Concentrator Photovoltaic Systems

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

Miller, David C.; Khonkar, Hussameldin I.; Herrero, Rebecca

The optical performance of poly(methyl methacrylate) lenses from veteran concentrator photovoltaic modules was examined after the end of their service life. Lenses from the Martin-Marietta and Intersol module designs were examined from the 'Solar Village' site near Riyadh, Saudi Arabia, as well as the Phoenix Sky Harbor airport, followed by the Arizona Public Service Solar Test and Research (APS-STaR) center in Tempe, Arizona. The various lens specimens were deployed for 20, 27, and 22 years, respectively. Optical characterizations included lens efficiency (Solar Simulator instrument), material transmittance and haze (of coupons cut from veteran lenses, then measured again after their facetedmore » back surface was polished, and then measured again after the incident front surface was polished), and direct transmittance (as a function of detector's acceptance angle, using the Very Low Angular Beam Spread ('VLABS') instrument). Lens efficiency measurements compared the central region to the entire lens, also using hot and cold mirror measurements to diagnose differences in performance. A series of subsequent characterizations was performed because a decrease in performance of greater than 10% was observed for some of the veteran lenses. Surface roughness was examined using atomic force microscopy and scanning electron microscopy. Facet geometry (tip and valley radius) was quantified on cross-sectioned specimens. Molecular weight was compared between the incident and faceted surfaces of the lenses.« less

Quantitative morphometric analysis of the lumbar vertebral facets and evaluation of feasibility of lumbar spinal nerve root and spinal canal decompression using the Goel intraarticular facetal spacer distraction technique: A lumbar/cervical facet comparison

PubMed Central

Satoskar, Savni R.; Goel, Aimee A.; Mehta, Pooja H.; Goel, Atul

2014-01-01

Objective: The authors evaluate the anatomic subtleties of lumbar facets and assess the feasibility and effectiveness of use of ‘Goel facet spacer’ in the treatment of degenerative spinal canal stenosis. Materials and Methods: Twenty-five lumbar vertebral cadaveric dried bones were used for the purpose. A number of morphometric parameters were evaluated both before and after the introduction of Goel facet spacers within the confines of the facet joint. Results: The spacers achieved distraction of facets that was more pronounced in the vertical perspective. Introduction of spacers on both sides resulted in an increase in the intervertebral foraminal height and a circumferential increase in the spinal canal dimensions. Additionally, there was an increase in the disc space or intervertebral body height. The lumbar facets are more vertically and anteroposteriorly oriented when compared to cervical facets that are obliquely and transversely oriented. Conclusions: Understanding the anatomical peculiarities of the lumbar and cervical facets can lead to an optimum utilization of the potential of Goel facet distraction arthrodesis technique in the treatment of spinal degenerative canal stenosis. PMID:25558146

Enhanced simultaneous PEC eradication of bacteria and antibiotics by facilely fabricated high-activity {001} facets TiO2 mounted onto TiO2 nanotubular photoanode.

PubMed

Li, Guiying; Nie, Xin; Chen, Jiangyao; Wong, Po Keung; An, Taicheng; Yamashita, Hiromi; Zhao, Huijun

2016-09-15

Biohazards and coexisted antibiotics are two groups of emerging contaminants presented in various aquatic environments. They can pose serious threat to the ecosystem and human health. As a result, inactivation of biohazards, degradation of antibiotics, and simultaneous removal of them are highly desired. In this work, a novel photoanode with a hierarchical structured {001} facets exposed nano-size single crystals (NSC) TiO2 top layer and a perpendicularly aligned TiO2 nanotube array (NTA) bottom layer (NSC/NTA) was successfully fabricated. The morphology and facets of anatase TiO2 nanoparticles covered on the top of NTA layer could be controlled by adjusting precalcination temperature and heating rate as the pure NTA was clamped with glasses. Appropriate recalcination can timely remove surface F from {001} facets, and the photocatalytic activity of the resultant photoanode was subsequently activated. NSC/NTA photoanode fabricated under 500 °C precalcination with 20 °C min(-1) followed by 550 °C recalcination possessed highest photoelectrocatalytic efficiency to simultaneously remove bacteria and antibiotics. Results suggest that two-step calcination is necessary for fabrication of high photocatalytic activity NSC/NTA photoanode. The capability of simultaneous eradication of bacteria and antibiotics shows great potential for development of a versatile approach to effectively purify various wastewaters contaminated with complex pollutants. Copyright © 2016 Elsevier Ltd. All rights reserved.

Shape effect on the antibacterial activity of silver nanoparticles synthesized via a microwave-assisted method.

PubMed

Hong, Xuesen; Wen, Junjie; Xiong, Xuhua; Hu, Yongyou

2016-03-01

Silver nanoparticles (AgNPs) are used as sustained-release bactericidal agents for water treatment. Among the physicochemical characteristics of AgNPs, shape is an important parameter relevant to the antibacterial activity. Three typically shaped AgNPs, nanocubes, nanospheres, and nanowires, were prepared via a microwave-assisted method and characterized by TEM, UV-vis, and XRD. The antibacterial activity of AgNPs was determined by OD growth curves tests, MIC tests, and cell viability assay against Escherichia coli. The interaction between AgNPs and bacterial cells was observed by TEM. The results showed that the three differently shaped AgNPs were nanoscale, 55 ± 10 nm in edge length for nanocubes, 60 ± 15 nm in diameter for nanospheres, 60 ± 10 nm in diameter and 2-4 μm in length for nanowires. At the bacterial concentration of 10(4) CFU/mL, the MIC of nanocubes, nanospheres, and nanowires were 37.5, 75, and 100 μg/mL, respectively. Due to the worst contact with bacteria, silver nanowires exhibited the weakest antibacterial activity compared with silver nanocubes and silver nanospheres. Besides, silver nanocubes mainly covered by {100} facets showed stronger antibacterial activity than silver nanospheres covered by {111} facets. It suggests that the shape effect on the antibacterial activity of AgNPs is attributed to the specific surface areas and facets reactivity; AgNPs with larger effective contact areas and higher reactive facets exhibit stronger antibacterial activity.

Localized wear of compomer restorative materials.

PubMed

Latta, M A; Barkmeier, W W; Wilwerding, T M; Blake, S M

2001-08-01

To determine and compare the localized wear of six compomer restorative materials. Ten specimens of Dyract, Dyract AP, F2000, Compoglass F, Elan and Hytac were prepared in a custom fixture and polished. A pretest surface profile was generated using an MTS 3-D surface profilometer and the specimens were subjected to 400,000 cycles in a Leinfelder wear machine equipped with a conical stylus tip to simulate localized wear. A post-test profile was generated and the before and after profiles were fitted and analyzed using AnSur 3-D software. The total volume loss and depth of the wear facet on each specimen was calculated and statistical analysis was accomplished (ANOVA and Tukey's test). Volume loss (mm3) was as follows: F2000, 0.027 +/- 0.002; Hytac, 0.007 +/- 0.023; Elan, 0.054 +/- 0.013; Compoglass F, 0.135 +/- 0.006; Dyract AP, 0.135 +/- 0.023; Dyract, 0.185 +/- 0.032. Maximum depth of the wear facets (microm) was as follows: F2000, 112.2 +/- 10.2; Hytac, 132.8 +/- 9.3; Elan, 144.3 +/- 23. 1; Compoglass F, 168.3 +/- 13.0; Dyract AP, 194.0 +/- 19.7; Dyract, 220.6 +/- 15.8. There was not a difference (P > 0.05) in volumetric loss between F2000 and Hytac or between Hytac and Elan. The volume loss and maximum depth of the wear facets of F2000, Hytac and Elan was significantly less (P< 0.05) than Compoglass F, Dyract AP and Dyract The results of this study indicate that there are significant differences in the in vitro wear rates of compomer materials.

Synthesis of {111} Facet-Exposed MgO with Surface Oxygen Vacancies for Reactive Oxygen Species Generation in the Dark.

PubMed

Hao, Ying-Juan; Liu, Bing; Tian, Li-Gang; Li, Fa-Tang; Ren, Jie; Liu, Shao-Jia; Liu, Ying; Zhao, Jun; Wang, Xiao-Jing

2017-04-12

Seeking a simple and moderate route to generate reactive oxygen species (ROS) for antibiosis is of great interest and challenge. This work demonstrates that molecule transition and electron rearrangement processes can directly occur only through chemisorption interaction between the adsorbed O 2 and high-energy {111} facet-exposed MgO with abundant surface oxygen vacancies (SOVs), hence producing singlet oxygen and superoxide anion radicals without light irradiation. These ROS were confirmed by electron paramagnetic resonance, in situ Raman, and scavenger experiments. Furthermore, heat plays a crucial role for the electron transfer process to accelerate the formation of ·O 2 - , which is verified by temperature kinetic experiments of nitro blue tetrazolium reduction in the dark. Therefore, the presence of oxygen vacancy can be considered as an intensification of the activation process. The designed MgO is acquired in one step via constructing a reduction atmosphere during the combustion reaction process, which has an ability similar to that of noble metal Pd to activate molecular oxygen and can be used as an effective bacteriocide in the dark.

Solar module having reflector between cells

DOEpatents

Kardauskas, Michael J.

1999-01-01

A photovoltaic module comprising an array of electrically interconnected photovoltaic cells disposed in a planar and mutually spaced relationship between a light-transparent front cover member in sheet form and a back sheet structure is provided with a novel light-reflecting means disposed between adjacent cells for reflecting light falling in the areas between cells back toward said transparent cover member for further internal reflection onto the solar cells. The light-reflecting comprises a flexible plastic film that has been embossed so as to have a plurality of small V-shaped grooves in its front surface, and a thin light-reflecting coating on said front surface, the portions of said coating along the sides of said grooves forming light-reflecting facets, said grooves being formed so that said facets will reflect light impinging thereon back into said transparent cover sheet with an angle of incidence greater than the critical angle, whereby substantially all of the reflected light will be internally reflected from said cover sheet back to said solar modules, thereby increasing the current output of the module.

Mechanics of couple-stress fluid coatings

NASA Technical Reports Server (NTRS)

Waxman, A. M.

1982-01-01

The formal development of a theory of viscoelastic surface fluids with bending resistance - their kinematics, dynamics, and rheology are discussed. It is relevant to the mechanics of fluid drops and jets coated by a thin layer of immiscible fluid with rather general rheology. This approach unifies the hydrodynamics of two-dimensional fluids with the mechanics of an elastic shell in the spirit of a Cosserat continuum. There are three distinct facets to the formulation of surface continuum mechanics. Outlined are the important ideas and results associated with each: the kinematics of evolving surface geometries, the conservation laws governing the mechanics of surface continua, and the rheological equations of state governing the surface stress and moment tensors.

Vapor-phase hydrothermal transformation of HTiOF3 intermediates into {001} faceted anatase single-crystalline nanosheets.

PubMed

Liu, Porun; Wang, Yun; Zhang, Haimin; An, Taicheng; Yang, Huagui; Tang, Zhiyong; Cai, Weiping; Zhao, Huijun

2012-12-07

For the first time, a facile, one-pot hydrofluoric acid vapor-phase hydrothermal (HF-VPH) method is demonstrated to directly grow single-crystalline anatase TiO(2) nanosheets with 98.2% of exposed {001} faceted surfaces on the Ti substrate via a distinctive two-stage formation mechanism. The first stage produces a new intermediate crystal (orthorhombic HTiOF(3) ) that is transformed into anatase TiO(2) nanosheets during the second stage. The findings reveal that the HF-VPH reaction environment is unique and differs remarkably from that of liquid-phase hydrothermal processes. The uniqueness of the HF-VPH conditions can be readily used to effectively control the nanostructure growth. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Vibrations of single-crystal gold nanorods and nanowires

NASA Astrophysics Data System (ADS)

Saviot, L.

2018-04-01

The vibrations of gold nanowires and nanorods are investigated numerically in the framework of continuum elasticity using the Rayleigh-Ritz variational method. Special attention is paid to identify the vibrations relevant in Raman scattering experiments. A comprehensive description of the vibrations of nanorods is proposed by determining their symmetry, comparing with standing waves in the corresponding nanowires, and estimating their Raman intensity. The role of experimentally relevant parameters such as the anisotropic cubic lattice structure, the presence of faceted lateral surfaces, and the shape of the ends of the nanorods is evaluated. Elastic anisotropy is shown to play a significant role contrarily to the presence of facets. Localized vibrations are found for nanorods with flat ends. Their evolution as the shape of the ends is changed to half-spheres is discussed.

Design of a Shape Memory Alloy deployment hinge for reflector facets

NASA Technical Reports Server (NTRS)

Anders, W. S.; Rogers, C. A.

1991-01-01

A design concept for a Shape Memory Alloy (SMA) actuated hinge mechanism for deploying segmented facet-type reflector surfaces on antenna truss structures is presented. The mechanism uses nitinol, a nickel-titanium shape memory alloy, as a displacement-force micro-actuator. An electrical current is used to resistively heat a 'plastically' elongated SMA actuator wire, causing it to contract in response to a thermally-induced phase transformation. The resulting tension creates a moment, imparting rotary motion between two adjacent panels. Mechanical stops are designed into the device to limit its range of motion and to establish positioning accuracy at the termination of deployment. The concept and its operation are discussed in detail, and an analytical dynamic simulation model is presented. The model has been used to perform nondimensionalized parametric design studies.

Facet orientation in the thoracolumbar spine: three-dimensional anatomic and biomechanical analysis.

PubMed

Masharawi, Youssef; Rothschild, Bruce; Dar, Gali; Peleg, Smadar; Robinson, Dror; Been, Ella; Hershkovitz, Israel

2004-08-15

Thoracolumbar facet orientations were measured and analyzed. To establish a comprehensive database for facet orientation in the thoracolumbar vertebrae and to determine the normal human condition. Most studies on facet orientation have based their conclusions on two-dimensional measurements, in small samples or isolated vertebrae. The amount of normal asymmetry in facet orientation is poorly addressed. Transverse and longitudinal facet angles were measured directly from 240 human vertebral columns (males/females, blacks/whites). The specimens' osteologic material is part of the Hamann-Todd Osteological Collection housed at the Cleveland Museum of Natural History (Cleveland, OH). A total of 4,080 vertebrae (T1-L5) from the vertebral columns of individuals 20 to 80 years of age were measured, using a Microscribe three-dimensional apparatus (Immersion Co., San Jose, CA). Data were recorded directly on computer software. Statistical analysis included paired t tests and analysis of variance. RESULTS.: Facet orientation is independent of gender, age, and ethnic group. Asymmetry in facet orientation is found in the thorax. All thoracolumbar facets are positioned in an oblique plane. In the transverse plane, all facets from T1 to T11 are positioned with an anterior inclination of approximately 25 degrees to 30 degrees from the frontal plane. The facets of T12-L2 are oriented closer to the midsagittal plane of the vertebral body (mean range, 25.89 degrees-33.87 degrees), while the facets of L3-L5 are oriented away from that plane (mean range, 40.40 degrees-56.30 degrees). Facet transverse orientation at the thoracolumbar junction is highly variable (approximately 80% with approximately 101 degrees and approximately 20% with 35 degrees). All facets are oriented more vertically from T1 (approximately 150 degrees) to L5 (approximately 170 degrees). The facet sagittal orientations of the lumbar zygoapophyseal joints are not equivalent. CONCLUSIONS.: Asymmetry in facet orientation is a normal characteristic in the thorax.

The high surface energy of NiO {110} facets incorporated into TiO2 hollow microspheres by etching Ti plate for enhanced photocatalytic and photoelectrochemical activity

NASA Astrophysics Data System (ADS)

Li, Jian; Cui, Hongzhi; Song, Xiaojie; Wei, Na; Tian, Jian

2017-02-01

We present a rational design for the controllable synthesis of NiO/TiO2 hollow microspheres (NTHMs) with Ti plate via a one-pot template-free synthesis strategy. Specifically, to enhance the formation of hollow microspheres, part of the titanium source is provided by the Ti plate. The hollow spherical NiO/TiO2 particles possess unique microstructural characteristics, namely, a higher specific surface area (∼65.82 m2 g-1), a larger mesoporous structure (∼7.79 nm), and hierarchical nanoarchitectures connected with mesopores within the shell (monodispersed size of ∼1 μm and shell thickness of ∼80 nm). In addition, as a cocatalyst for improved catalytic activity, the incorporated NiO nanoparticles with exposed high surface energy {110} facets displayed an outstanding performance. It has been proven that this facile nanostructure possesses remarkably high photoelectrochemical and photocatalytic activities. The main mechanism for enhancement of photocatalytic activity is attributed to the construction of p-n junctions with an inner electric field between TiO2 and NiO, which can dramatically enhance the separation efficiency of the photogenerated electron-hole pairs. This strategy could be applied to fabricate mixed metal oxide hollow microspheres toward the photoelectrochemical catalysis.

Surface modification of mixed-phase hydrogenated TiO2 and corresponding photocatalytic response

NASA Astrophysics Data System (ADS)

Samsudin, Emy Marlina; Hamid, Sharifah Bee Abd; Juan, Joon Ching; Basirun, Wan Jefrey; Kandjani, Ahmad Esmaielzadeh

2015-12-01

Preparation of highly photo-activated TiO2 is achievable by hydrogenation at constant temperature and pressure, with controlled hydrogenation duration. The formation of surface disorders and Ti3+ is responsible for the color change from white unhydrogenated TiO2 to bluish-gray hydrogenated TiO2. This color change, together with increased oxygen vacancies and Ti3+ enhanced the solar light absorption from UV to infra-red region. Interestingly, no band gap narrowing is observed. The photocatalytic activity in the UV and visible region is controlled by Ti3+ and oxygen vacancies respectively. Both Ti3+ and oxygen vacancies increases the electron density on the catalyst surface thus facilitates rad OH radicals formation. The lifespan of surface photo-excited electrons and holes are also sustained thus prevents charge carrier recombination. However, excessive amount of oxygen vacancies deteriorates the photocatalytic activity as it serves as charge traps. Hydrogenation of TiO2 also promotes the growth of active {0 0 1} facets and facilitates the photocatalytic activity by higher concentration of surface OH radicals. However, the growth of {0 0 1} facets is small and insignificant toward the overall photo-kinetics. This work also shows that larger role is played by Ti3+ and oxygen vacancies rather than the surface disorders created during the hydrogenation process. It also demonstrates the ability of hydrogenated TiO2 to absorb wider range of photons even though at a similar band gap as unhydrogenated TiO2. In addition, the photocatalytic activity is shown to be decreased for extended hydrogenation duration due to excessive catalyst growth and loss in the total surface area. Thus, a balance in the physico-chemical properties of hydrogenated TiO2 is crucial to enhance the photocatalytic activity by simply controlling the hydrogenation duration.

The multi-faceted assessment of independence in patients with rheumatoid arthritis: preliminary validation from the ATTAIN study.

PubMed

Hassett, Afton L; Li, Tracy; Buyske, Steven; Savage, Shantal V; Gignac, Monique A M

2008-05-01

To consider the feasibility of assessing multiple facets of independence in rheumatoid arthritis (RA) using a measure developed from existing items and examining its face validity, construct validity and responsiveness to change. The ATTAIN (Abatacept Trial in Treatment of Anti-tumor necrosis factor [TNF] Inadequate responders) database was used. Patients with RA were randomized 2:1, abatacept (n = 258) and placebo (n = 133). A multi-faceted scale to measure physical and psychosocial independence was constructed using items from the Health Assessment Questionnaire (HAQ) and Short Form 36 Health Survey (SF-36). Questions assessing activity limitations and need for outside caregiver help were also examined. Interviews with 20 RA patients assessed face validity. Item Response Theory analysis yielded two traits - 'Psychosocial Independence', derived from the number of days with activity limitations plus the Role Emotional, Social Functioning and Role Physical subscale items from the SF-36; and 'Physical Independence', derived from 15 HAQ items assessing need for help from another. The two traits showed no significant differential item functioning for age or gender and demonstrated good face validity. Changes over 169 days on Psychosocial Independence were greater (mean 0.46 units, 95% confidence interval [CI]: 0.17-0.75) for the abatacept group than for placebo (p = 0.002). Changes in Physical Independence were greater (mean 0.59 units, 95% CI: 0.35-0.82) for the abatacept group than for placebo (p < 0.001). The multi-faceted assessment of independence in RA based on items from commonly used instruments is feasible suggesting promise for evaluating independence in future clinical trials. This approach demonstrated good face and construct validity and responsiveness in RA patients who had previously failed anti-TNF therapy. However, we caution against an interpretation that these data suggest that abatacept improves independence because the component parts of this assessment came from instruments used in the ATTAIN trial where data had been previously analyzed.

Behavior of Three Metallic Alloys Under Combined Axial-Shear Stress at 650 C

NASA Technical Reports Server (NTRS)

Colaiuta, Jason F.; Lerch, Bradley (Technical Monitor)

2001-01-01

Three materials, Inconel 718, Haynes 188, and 316 stainless steel, were tested under an axial-torsional stress state at 650 C. The objective of this study was to quantify the evolution of the material while in the viscoplastic domain. Initial and subsequent yield surfaces were experimentally determined to quantify hardening. Subsequent yield surfaces (yield surfaces taken after a preload) had a well-defined front side, in the prestrain direction, but a poorly defined back side, opposite the prestrain direction. Subsequent yield surfaces exhibited isotropic hardening by expansion of the yield surface, kinematic hardening by translation of the yield surface, and distortional hardening by flattening of the yield surface in the direction opposite to the last prestrain. An existing yield function capable of representing isotropic, kinematic, and distortional hardening was used to fit each yield surface. Four variables are used to describe each surface. These variables evolve as the material state changes and have been regressed to the yield surface data.

Study of Chemistry and Structure-Property Relationship on Tunable Plasmonic Nanostructures

NASA Astrophysics Data System (ADS)

Jing, Hao

In this dissertation, the rational design and controllable fabrication of an array of novel plasmonic nanostructures with geometrically tunable optical properties are demonstrated, including metal-semiconductor hybrid hetero-nanoparticles, bimetallic noble metal nanoparticles and hollow nanostructures (nanobox and nanocage). Firstly, I have developed a robust wet chemistry approach to the geometry control of Ag-Cu2O core-shell nanoparticles through epitaxial growth of Cu2O nanoshells on the surfaces of various Ag nanostructures, such as quasi-spherical nanoparticles, nanocubes, and nanocuboids. Precise control over the core and the shell geometries enables me to develop detailed, quantitative understanding of how the Cu2O nanoshells introduce interesting modifications to the resonance frequencies and the extinction spectral line shapes of multiple plasmon modes of the Ag cores. Secondly, I present a detailed and systematic study of the controlled overgrowth of Pd on Au nanorods. The overgrowth of Pd nanoshells with fine-controlled dimensions and architectures on single-crystalline Au nanorods through seed-mediated growth protocol in the presence of various surfactants is investigated. Thirdly, I have demonstrated that creation of high-index facets on subwavelength metallic nanoparticles provides a unique approach to the integration of desired plasmonic and catalytic properties on the same nanoparticle. Through site-selective surface etching of metallic nanocuboids whose surfaces are dominated by low-index facets, I have controllably fabricated nanorice and nanodumbbell particles, which exhibit drastically enhanced catalytic activities arising from the catalytically active high index facets abundant on the particle surfaces. And the nanorice and nanodumbbell particles also possess appealing tunable plasmonic properties that allow us to gain quantitative insights into nanoparticle-catalyzed reactions with unprecedented sensitivity and detail through time-resolved plasmon-enhanced spectroscopic measurements, such as surface-enhanced Raman scattering (SERS). Last but not least, I have demonstrated that the capability of geometry control over Ag-Pd bimetallic hollow nanostructures through nanoscale galvanic replacement can be greatly enhanced by the use of appropriate mild reducing agents, such as ascorbic acid and formaldehyde. With the aid of mild reducing agents, we have been able to fine-tailor the compositions, interior architectures, and surface morphologies of Ag-Pd bimetallic hollow nanoparticles with increased structural complexity through surface ligand-free galvanic replacement processes at room temperature. This reducing agent-mediated galvanic replacement provides a unique way of achieving both enhanced optical tunability and optimized catalytic activities through deliberate control over the geometries of complex Ag-Pd bimetallic nanoparticles.

MultiFacet: A Faceted Interface for Browsing Large Multimedia Collections

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

Henry, Michael J.; Hampton, Shawn D.; Endert, Alexander

2013-10-31

Faceted browsing is a common technique for exploring collections where the data can be grouped into a number of pre-defined categories, most often generated from textual metadata. Historically, faceted browsing has been applied to a single data type such as text or image data. However, typical collections contain multiple data types, such as information from web pages that contain text, images, and video. Additionally, when browsing a collection of images and video, facets are often created based on the metadata which may be incomplete, inaccurate, or missing altogether instead of the actual visual content contained within those images and video.more » In this work we address these limitations by presenting MultiFacet, a faceted browsing interface that supports multiple data types. MultiFacet constructs facets for images and video in a collection from the visual content using computer vision techniques. These visual facets can then be browsed in conjunction with text facets within a single interface to reveal relationships and phenomena within multimedia collections. Additionally, we present a use case based on real-world data, demonstrating the utility of this approach towards browsing a large multimedia data collection.« less

Means for phase locking the outputs of a surface emitting laser diode array

NASA Technical Reports Server (NTRS)

Lesh, James R. (Inventor)

1987-01-01

An array of diode lasers, either a two-dimensional array of surface emitting lasers, or a linear array of stripe lasers, is phase locked by a diode laser through a hologram which focuses the output of the diode laser into a set of distinct, spatially separated beams, each one focused onto the back facet of a separate diode laser of the array. The outputs of the diode lasers thus form an emitted coherent beam out of the front of the array.

Tuning TiO2 nanoparticle morphology in graphene-TiO2 hybrids by graphene surface modification

NASA Astrophysics Data System (ADS)

Sordello, Fabrizio; Zeb, Gul; Hu, Kaiwen; Calza, Paola; Minero, Claudio; Szkopek, Thomas; Cerruti, Marta

2014-05-01

We report the hydrothermal synthesis of graphene (GNP)-TiO2 nanoparticle (NP) hybrids using COOH and NH2 functionalized GNP as a shape controller. Anatase was the only TiO2 crystalline phase nucleated on the functionalized GNP, whereas traces of rutile were detected on unfunctionalized GNP. X-Ray Photoelectron spectroscopy (XPS) showed C-Ti bonds on all hybrids, thus confirming heterogeneous nucleation. GNP functionalization induced the nucleation of TiO2 NPs with specific shapes and crystalline facets exposed. COOH functionalization directed the synthesis of anatase truncated bipyramids, bonded to graphene sheets via the {101} facets, while NH2 functionalization induced the formation of belted truncated bipyramids, bonded to graphene via the {100} facets. Belted truncated bipyramids formed on unfunctionalized GNP too, however the NPs were more irregular and rounded. These effects were ascribed to pH variations in the proximity of the functionalized GNP sheets, due to the high density of COOH or NH2 groups. Because of the different reactivity of anatase {100} and {101} crystalline facets, we hypothesize that the hybrid materials will behave differently as photocatalysts, and that the COOH-GNP-TiO2 hybrids will be better photocatalysts for water splitting and H2 production.We report the hydrothermal synthesis of graphene (GNP)-TiO2 nanoparticle (NP) hybrids using COOH and NH2 functionalized GNP as a shape controller. Anatase was the only TiO2 crystalline phase nucleated on the functionalized GNP, whereas traces of rutile were detected on unfunctionalized GNP. X-Ray Photoelectron spectroscopy (XPS) showed C-Ti bonds on all hybrids, thus confirming heterogeneous nucleation. GNP functionalization induced the nucleation of TiO2 NPs with specific shapes and crystalline facets exposed. COOH functionalization directed the synthesis of anatase truncated bipyramids, bonded to graphene sheets via the {101} facets, while NH2 functionalization induced the formation of belted truncated bipyramids, bonded to graphene via the {100} facets. Belted truncated bipyramids formed on unfunctionalized GNP too, however the NPs were more irregular and rounded. These effects were ascribed to pH variations in the proximity of the functionalized GNP sheets, due to the high density of COOH or NH2 groups. Because of the different reactivity of anatase {100} and {101} crystalline facets, we hypothesize that the hybrid materials will behave differently as photocatalysts, and that the COOH-GNP-TiO2 hybrids will be better photocatalysts for water splitting and H2 production. Electronic supplementary information (ESI) available: Statistical analysis of the D : G intensity ratio, additional XPS analysis and TEM micrographs. See DOI: 10.1039/c4nr01322k

Examining the prevalence and characteristics of abfractionlike cervical lesions in a population of U.S. veterans.

PubMed

Piotrowski, B T; Gillette, W B; Hancock, E B

2001-12-01

Abfraction is believed to be caused by biomechanical loading forces. It may be due to flexure and ultimate fatigue of tooth tissues that occur away from the point of occlusal loading. Other possible causes of cervical lesions include toothbrush abrasion and erosion. The purpose of this study was to investigate the characteristics and prevalence of abfraction-like lesions in a population of U.S. veterans. The authors evaluated 103 teeth with noncarious cervical lesions in 32 subjects and characterized them based on the surface on which the lesion was located, history of toothbrush abrasion, size of the lesion, presence of plaque, surface texture, and presence and size of occlusal wear facets. Clinical examination revealed that adjacent control teeth had a significantly lower percentage of surfaces with plaque than did teeth with cervical lesions. Control teeth also had significantly less gingival recession than did affected teeth. Seventy-five percent of subjects reported a history of using a firm toothbrush, and 78.1 percent reported using a brushing technique that is known to cause toothbrush abrasion in the affected area. Affected teeth had neither significantly different occlusal wear facets nor occlusal contacts than control teeth. No significant correlations were found between cervical lesion dimensions and facet area. Toothbrush abrasion is strongly suspected as contributing to the formation of the majority of wedge-shaped lesions in this group of subjects. A small subset of lesions is thought to have resulted from some other phenomenon. Although the presence or contribution of occlusal stresses in the direct formation of these lesions could not be measured directly, the possibility of abfraction could not be eliminated. Because the existence of abfraction could not be ruled out in about 15 percent of the cases, teeth with noncarious, wedge-shaped lesions warrant careful occlusal evaluation, with the possible need for occlusal adjustment or bitesplint therapy to treat bruxism.

The morphogenic features of otoconia during larval development of Cynops pyrrhogaster, the Japanese red-bellied newt

NASA Technical Reports Server (NTRS)

Steyger, P. S.; Wiederhold, M. L.; Batten, J.

1995-01-01

Otoconia are calcified protein matrices within the gravity-sensing organs of the vertebrate vestibular system. Mammalian otoconia are barrel-shaped with triplanar facets at each end. Reptilian otoconia are commonly prismatic or fusiform in shape. Amphibians have all three otoconial morphologies, barrel-shaped otoconia within the utricle, with prismatic and fusiform otoconia in the saccule. Scanning electron microscopy revealed a sequential appearance of all three otoconial morphologies during larval development of the newt, Cynops pyrrhogaster. The first otoconia appear within a single, developing otolith, and some resemble adult barrel-shaped otoconia. As the larvae hatch, around stages 39-42, the single otolith divides into two anatomically separate regions, the utricle and saccule, and both contain otoconia similar to those seen in the single otolith. Throughout development, these otoconia may have variable morphologies, with serrated surfaces, or circumferential striations with either separated facets or adjacent facets in the triplanar end-regions. Small fusiform otoconia occur later, at stage 51, and only in the saccule. Prismatic otoconia appear later still, at stage 55, and again only in the saccule. Thus, although prismatic otoconia are the most numerous in adult newts, it is the last vestibular otoconial morphology to be expressed.

Self-organised synthesis of Rh nanostructures with tunable chemical reactivity

PubMed Central

2007-01-01

Nonequilibrium periodic nanostructures such as nanoscale ripples, mounds and rhomboidal pyramids formed on Rh(110) are particularly interesting as candidate model systems with enhanced catalytic reactivity, since they are endowed with steep facets running along nonequilibrium low-symmetry directions, exposing a high density of undercoordinated atoms. In this review we report on the formation of these novel nanostructured surfaces, a kinetic process which can be controlled by changing parameters such as temperature, sputtering ion flux and energy. The role of surface morphology with respect to chemical reactivity is investigated by analysing the carbon monoxide dissociation probability on the different nanostructured surfaces.

Unpolarized emissivity with shadow and multiple reflections from random rough surfaces with the geometric optics approximation: application to Gaussian sea surfaces in the infrared band.

PubMed

Bourlier, Christophe

2006-08-20

The emissivity from a stationary random rough surface is derived by taking into account the multiple reflections and the shadowing effect. The model is applied to the ocean surface. The geometric optics approximation is assumed to be valid, which means that the rough surface is modeled as a collection of facets reflecting locally the light in the specular direction. In particular, the emissivity with zero, single, and double reflections are analytically calculated, and each contribution is studied numerically by considering a 1D sea surface observed in the near infrared band. The model is also compared with results computed from a Monte Carlo ray-tracing method.

Milestone Completion Report WBS 1.3.5.05 ECP/VTK-m FY17Q3 [MS-17/02] Faceted Surface Normals STDA05-3.

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

Moreland, Kenneth D.

2017-07-01

The FY17Q3 milestone of the ECP/VTK-m project includes the completion of a VTK-m filter that computes normal vectors for surfaces. Normal vectors are those that point perpendicular to the surface and are an important direction when rendering the surface. The implementation includes the parallel algorithm itself, a filter module to simplify integrating it into other software, and documentation in the VTK-m Users’ Guide. With the completion of this milestone, we are able to necessary information to rendering systems to provide appropriate shading of surfaces. This milestone also feeds into subsequent milestones that progressively improve the approximation of surface direction.

Reflectance of a vegetation canopy using the Adding method

NASA Technical Reports Server (NTRS)

Cooper, K.; Smith, J. A.; Pitts, D.

1982-01-01

A modified vegetation reflectance model based on the Adding method is presented as a means to measure the interaction of shortwave radiation within a vegetation canopy. The canopy is conceptualized with reflecting and transmitting leaf facets, with the leaf orientations described by a leaf slope distribution, thereby yielding scattering matrices for canopy layers. The model predictions, when compared with ground-truth measurements, show good agreement except at visible wavelengths, where overestimations are observed. Conditions under which the model satisfies the reciprocity theorem are defined. Extension of the model by including azimuth is indicated.

High performance, low dissipation quantum cascade lasers across the mid-IR range.

PubMed

Bismuto, Alfredo; Blaser, Stéphane; Terazzi, Romain; Gresch, Tobias; Muller, Antoine

2015-03-09

In this work, we present the development of low consumption quantum cascade lasers across the mid-IR range. In particular, short cavity single-mode lasers with optimised facet reflectivities have been fabricated from 4.5 to 9.2 μm. Threshold dissipated powers as low as 0.5 W were obtained in continuous wave operation at room temperature. In addition, the beneficial impact of reducing chip length on laser mounting yield is discussed. High power single-mode lasers from the same processed wafers are also presented.

Correlation of the Features of the Lumbar Multifidus Muscle With Facet Joint Osteoarthritis.

PubMed

Yu, Bo; Jiang, Kaibiao; Li, Xinfeng; Zhang, Jidong; Liu, Zude

2017-09-01

Facet joint osteoarthritis is considered a consequence of the aging process; however, there is evidence that it may be associated with degenerative changes of other structures. The goal of this study was to investigate the correlation between lumbar multifidus muscle features and facet joint osteoarthritis. This retrospective study included 160 patients who had acute or chronic low back pain and were diagnosed with facet joint osteoarthritis on computed tomography scan. Morphometric parameters, including cross-sectional area, muscle-fat index, and percentage of bilateral multifidus asymmetry at L3-L4, L4-L5, and L5-S1, were evaluated with T2-weighted magnetic resonance imaging. Patients with facet joint osteoarthritis had a smaller cross-sectional area and a higher muscle-fat index than those without facet joint osteoarthritis (P<.001). In multivariate regression analysis, older age and higher muscle-fat index were independently associated with facet joint osteoarthritis at all 3 spinal levels (P<.001). Smaller cross-sectional area was independently associated with facet joint osteoarthritis only at L4-L5 (P=.005). Asymmetry of the bilateral multifidus cross-sectional area was independently associated with facet joint osteoarthritis at L5-S1 (P=.009), but did not seem to be responsible for asymmetric degeneration of the bilateral facet joints. A higher multifidus muscle-fat index was independently associated with facet joint osteoarthritis, and bilateral multifidus size asymmetry was associated with the development of facet joint osteoarthritis at L5-S1. It seems more accurate to consider facet joint osteoarthritis a failure of the whole joint structure, including the paraspinal musculature, rather than simply a failure of the facet joint cartilage. [Orthopedics. 2017; 40(5):e793-e800.]. Copyright 2017, SLACK Incorporated.

Fabrication of Polyhedral Particles from Spherical Colloids and Their Self-Assembly into Rotator Phases**

PubMed Central

Vutukuri, Hanumantha Rao; Imhof, Arnout; van Blaaderen, Alfons

2014-01-01

Particle shape is a critical parameter that plays an important role in self-assembly, for example, in designing targeted complex structures with desired properties. Over the last decades, an unprecedented range of monodisperse nanoparticle systems with control over the shape of the particles have become available. In contrast, the choice of micrometer-sized colloidal building blocks of particles with flat facets, that is, particles with polygonal shapes, is significantly more limited. This can be attributed to the fact that in contrast to nanoparticles, the larger colloids are significantly harder to synthesize as single crystals. It is now shown that a very simple building block, such as a micrometer-sized polymeric spherical colloidal particle, is already enough to fabricate particles with regularly placed flat facets, including completely polygonal shapes with sharp edges. As an illustration that the yields are high enough for further self-assembly studies, the formation of three-dimensional rotator phases of fluorescently labelled, micrometer-sized, and charged rhombic dodecahedron particles was demonstrated. This method for fabricating polyhedral particles opens a new avenue for designing new materials. PMID:25366869

Emission and Propagation Properties of Midinfrared Quantum Cascade Lasers

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

Krishnaswami, Kannan; Bernacki, Bruce E.; Cannon, Bret D.

2008-02-15

We report divergence, astigmatism and M 2 measurements of quantum cascade lasers (QCL) with an emission wavelength of 8.77 mum. Emission profiles from the QCL facet showed divergence angles of 62° and 32° FWHM ± 2° for the fast and slow axes, respectively. The observation of far field structure superimposed on the fast axes profiles was attributed to the position of the QCL die with respect to the edge of the laser submount, emphasizing the need for careful placement. Two diffraction-limited Germanium aspheric microlenses were designed and fabricated to efficiently collect, collimate, and focus QCL emission. A confocal system comprisedmore » of these lenses was used to measure the beam propagation figure of merit (M2) yielding 1.8 and 1.2 for the fast and slow axes, respectively. Astigmatism at the exit facet was calculated to be about 3.4 mum, or less than half a wave. To the best of our knowledge, this is the first experimental measurement of astigmatism and M 2 reported for mid-IR QCLs.« less

Utilization of Facet Joint and Sacroiliac Joint Interventions in Medicare Population from 2000 to 2014: Explosive Growth Continues!

PubMed

Manchikanti, Laxmaiah; Hirsch, Joshua A; Pampati, Vidyasagar; Boswell, Mark V

2016-10-01

Increasing utilization of interventional techniques in managing chronic spinal pain, specifically facet joint interventions and sacroiliac joint injections, is a major concern of healthcare policy makers. We analyzed the patterns of utilization of facet and sacroiliac joint interventions in managing chronic spinal pain. The results showed significant increase of facet joint interventions and sacroiliac joint injections from 2000 to 2014 in Medicare FFS service beneficiaries. Overall, the Medicare population increased 35 %, whereas facet joint and sacroiliac joint interventions increased 313.3 % per 100,000 Medicare population with an annual increase of 10.7 %. While the increases were uniform from 2000 to 2014, there were some decreases noted for facet joint interventions in 2007, 2010, and 2013, whereas for sacroiliac joint injections, the decreases were noted in 2007 and 2013. The increases were for cervical and thoracic facet neurolysis at 911.5 % compared to lumbosacral facet neurolysis of 567.8 %, 362.9 % of cervical and thoracic facet joint blocks, 316.9 % of sacroiliac joints injections, and finally 227.3 % of lumbosacral facet joint blocks.

Bipolar Radiofrequency Facet Ablation of the Lumbar Facet Capsule: An Adjunct to Conventional Radiofrequency Ablation for Pain Management

PubMed Central

Palea, Ovidiu; Granville, Michelle

2017-01-01

Radiofrequency facet ablation (RFA) has been performed using the same technique for over 50 years. Except for variations in electrode size, tip shape, and change in radiofrequency (RF) stimulation parameters, using standard, pulsed, and cooled RF wavelengths, the target points have remained absolutely unchanged from the original work describing RFA for lumbar pain control. Degenerative changes in the facet joint and capsule are the primary location for the majority of lumbar segmental pathology and pain. Multiple studies show that the degenerated facet joint is richly innervated as a result of the inflammatory overgrowth of the synovium. The primary provocative clinical test to justify an RFA is to perform an injection with local anesthetic into the facet joint and the posterior capsule and confirm pain relief. However, after a positive response, the radiofrequency lesion is made not to the facet joint but to the more proximal fine nerve branches that innervate the joint. The accepted target points for the recurrent sensory branch ignore the characteristic rich innervation of the pathologic lumbar facet capsule and assume that lesioning of these recurrent branches is sufficient to denervate the painful pathologic facet joint. This report describes the additional targets and technical steps for further coagulation points along the posterior capsule of the lumbar facet joint and the physiologic studies of the advantage of the bipolar radiofrequency current in this location. Bipolar RF to the facet capsule is a simple, extra step that easily creates a large thermo-coagulated lesion in this capsule region of the pathologic facet joint. Early studies demonstrate bipolar RF to the facet capsule can provide long-term pain relief when used alone for specific localized facet joint pain, to coagulate lumbar facet cysts to prevent recurrence, and to get more extensive pain control by combining it with traditional lumbar RFA, especially when RFA is repeated. PMID:29119066

Bipolar Radiofrequency Facet Ablation of the Lumbar Facet Capsule: An Adjunct to Conventional Radiofrequency Ablation for Pain Management.

PubMed

Jacobson, Robert E; Palea, Ovidiu; Granville, Michelle

2017-09-01

Radiofrequency facet ablation (RFA) has been performed using the same technique for over 50 years. Except for variations in electrode size, tip shape, and change in radiofrequency (RF) stimulation parameters, using standard, pulsed, and cooled RF wavelengths, the target points have remained absolutely unchanged from the original work describing RFA for lumbar pain control. Degenerative changes in the facet joint and capsule are the primary location for the majority of lumbar segmental pathology and pain. Multiple studies show that the degenerated facet joint is richly innervated as a result of the inflammatory overgrowth of the synovium. The primary provocative clinical test to justify an RFA is to perform an injection with local anesthetic into the facet joint and the posterior capsule and confirm pain relief. However, after a positive response, the radiofrequency lesion is made not to the facet joint but to the more proximal fine nerve branches that innervate the joint. The accepted target points for the recurrent sensory branch ignore the characteristic rich innervation of the pathologic lumbar facet capsule and assume that lesioning of these recurrent branches is sufficient to denervate the painful pathologic facet joint. This report describes the additional targets and technical steps for further coagulation points along the posterior capsule of the lumbar facet joint and the physiologic studies of the advantage of the bipolar radiofrequency current in this location. Bipolar RF to the facet capsule is a simple, extra step that easily creates a large thermo-coagulated lesion in this capsule region of the pathologic facet joint. Early studies demonstrate bipolar RF to the facet capsule can provide long-term pain relief when used alone for specific localized facet joint pain, to coagulate lumbar facet cysts to prevent recurrence, and to get more extensive pain control by combining it with traditional lumbar RFA, especially when RFA is repeated.

Alignment and focus of mirrored facets of a heliosat

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

Yellowhair, Julius E; Ho, Clifford Kuofei; Diver, Richard B

2013-11-12

Various technologies pertaining to aligning and focusing mirrored facets of a heliostat are described herein. Updating alignment and/or focus of mirrored facets is undertaken through generation of a theoretical image, wherein the theoretical image is indicative of a reflection of the target via the mirrored facets when the mirrored facets are properly aligned. This theoretical image includes reference points that are overlaid on an image of the target as reflected by the mirrored facets of the heliostat. A technician adjusts alignment/focus of a mirrored facet by causing reflected reference markings to become aligned with the reference points in the theoreticalmore » image.« less

Interpreting Circularly Polarized 75-cm Oblique-Incidence Martian Surface Echoes Received by Mars Odyssey

NASA Astrophysics Data System (ADS)

Gunnarsdottir, Hrefna M.; Linscott, I. R.; Callas, J. L.; Tyler, G. L.; Cousins, M. D.

2006-09-01

Between August and December 2005, we conducted 76 oblique-incidence scattering experiments using the SRI 46-m antenna in the Stanford foothills to illuminate Mars for 20 min. periods with an unmodulated 75 cm-λ, circularly polarized wave. The direct signal and a Martian surface echo, which are separated by Doppler frequency, were received simultaneously by the one-bit receiver on board the Mars Odyssey spacecraft. Out of 45 experiments with high signal-to-noise ratios, 27 were in the northern hemisphere, while 18 were in the southern hemisphere, where preliminary data analysis is available. The surface echoes are characterized by both fluctuating amplitude and varying spectral width, which correspond roughly to the surface reflectivity and roughness, respectively. Analysis of the data is based on quasi-specular scattering theory, but interpretation of the echoes is complicated by Odyssey's reception of only the right-circular polarized (RCP) wave component, and by the high incidence angles involved (f > 60 deg.), for which the scattering theory is not well developed. Our analysis of the echoes makes use of MOLA topographic maps at a resolution of 128 points per deg. of longitude and latitude, to model the scattering surface in three dimensions along the specular track. We can account for most of the echo amplitude fluctuations by the variation in number of surface-model facets tilted to produce a specular reflection towards Odyssey, indicating that MOLA scale topography is sufficient to capture an important scattering mechanism at this wavelength. With this we have accomplished a first step in differentiating between changes in echo signal strength due to surface reflectivity and surface shape. At the same time, we obtain a measure of the small scale surface roughness by finding the maximum tilt angle away from a perfectly mirroring surface facet which contributes significantly to the echo at each time step.

Photothermal effects from Au-Cu2O core-shell nanocubes, octahedra, and nanobars with broad near-infrared absorption tunability

NASA Astrophysics Data System (ADS)

Wang, Hsiang-Ju; Yang, Kung-Hsun; Hsu, Shih-Chen; Huang, Michael H.

2015-12-01

Other than the display of purely optical phenomenon, the recently-discovered facet-dependent optical properties of metal-Cu2O nanocrystals have become useful by illuminating Au-Cu2O nanocubes and octahedra having a surface plasmon resonance (SPR) absorption band in the near-infrared (NIR) region from octahedral Au cores with 808 nm light for heat generation. After 5 min of light irradiation, a solution of Au-Cu2O nanocubes can reach 65 °C with their Au SPR band matching the illuminating light wavelength. Photothermal efficiency has been found to be facet-dependent. In addition, short gold nanorods were employed to synthesize {100}-bound rectangular Au-Cu2O nanobars with a tunable longitudinal Au SPR absorption band covering a broad NIR range from ~1050 to 1400 nm. Because the Au SPR bands can become fixed with relatively thin Cu2O shells of less than 15 nm, ultrasmall nanobars having a size of 61 nm directly red-shift the Au SPR band to 1047 nm. And 73 nm nanobars can give a Au SPR band at 1390 nm. Truncated nanobars exposing {100}, {110}, and {111} facets give a very blue-shifted Au SPR band. The nanobars also exhibit photothermal activity when illuminated by 1064 nm light. These small Au-Cu2O nanocrystals represent the simplest nanostructure design to absorb light covering the entire NIR wavelengths.Other than the display of purely optical phenomenon, the recently-discovered facet-dependent optical properties of metal-Cu2O nanocrystals have become useful by illuminating Au-Cu2O nanocubes and octahedra having a surface plasmon resonance (SPR) absorption band in the near-infrared (NIR) region from octahedral Au cores with 808 nm light for heat generation. After 5 min of light irradiation, a solution of Au-Cu2O nanocubes can reach 65 °C with their Au SPR band matching the illuminating light wavelength. Photothermal efficiency has been found to be facet-dependent. In addition, short gold nanorods were employed to synthesize {100}-bound rectangular Au-Cu2O nanobars with a tunable longitudinal Au SPR absorption band covering a broad NIR range from ~1050 to 1400 nm. Because the Au SPR bands can become fixed with relatively thin Cu2O shells of less than 15 nm, ultrasmall nanobars having a size of 61 nm directly red-shift the Au SPR band to 1047 nm. And 73 nm nanobars can give a Au SPR band at 1390 nm. Truncated nanobars exposing {100}, {110}, and {111} facets give a very blue-shifted Au SPR band. The nanobars also exhibit photothermal activity when illuminated by 1064 nm light. These small Au-Cu2O nanocrystals represent the simplest nanostructure design to absorb light covering the entire NIR wavelengths. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06847a

Enhanced dye-sensitized solar cells performance using anatase TiO2 mesocrystals with the Wulff construction of nearly 100% exposed {101} facets as effective light scattering layer.

PubMed

Zhou, Yu; Wang, Xinyu; Wang, Hai; Song, Yeping; Fang, Liang; Ye, Naiqing; Wang, Linjiang

2014-03-28

Anatase TiO2 mesocrystals with a Wulff construction of nearly 100% exposed {101} facets were successfully synthesized by a facile, green solvothermal method. Their morphology, and crystal structure are characterized by powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Accordingly, a possible growth mechanism of anatase TiO2 mesocrystals is elucidated in this work. The as-prepared single anatase TiO2 mesocrystal's mean center diameter is about 500 nm, and the length is about 1 μm. They exhibit high light adsorbance, high reflectance and low transmittance in the visible region due to the unique nearly 100% exposed {101} facets. When utilized as the scattering layer in dye-sensitized solar cells (DSSCs), such mesocrystals effectively enhanced light harvesting and led to an increase of the photocurrent of the DSSCs. As a result, by using an anatase TiO2 mesocrystal film as a scattering overlayer of a compact commercial P25 TiO2 nanoparticle film, the double layered DSSCs show a power conversion efficiency of 7.23%, indicating a great improvement compared to the DSSCs based on a P25 film (5.39%) and anatase TiO2 mesocrystal films, respectively. The synergetic effect of P25 and the mesocrystals as well as the latters unique feature of a Wulff construction of nearly 100% exposed (101) facets are probably responsible for the enhanced photoelectrical performance. In particular, we explore the possibility of the low surface area and exposed {101} facets as an efficient light scattering layer of DSSCs. Our work suggests that anatase TiO2 mesocrystals with the Wulff construction is a promising candidate as a superior scattering material for high-performance DSSCs.

Reduction of radiation dose during facet joint injection using the new image guidance system SabreSource™: a prospective study in 60 patients

PubMed Central

Proschek, Dirk; Kafchitsas, K.; Rauschmann, M. A.; Kurth, A. A.; Vogl, T. J.

2008-01-01

Interventional procedures are associated with high radiation doses for both patients and surgeons. To reduce the risk from ionizing radiation, it is essential to minimize radiation dose. This prospective study was performed to evaluate the effectiveness in reducing radiation dose during facet joint injection in the lumbar spine and to evaluate the feasibility and possibilities of the new real time image guidance system SabreSource™. A total of 60 patients, treated with a standardized injection therapy of the facet joints L4–L5 or L5–S1, were included in this study. A total of 30 patients were treated by fluoroscopy guidance alone, the following 30 patients were treated using the new SabreSource™ system. Thus a total of 120 injections to the facet joints were performed. Pain, according to the visual analogue scale (VAS), was documented before and 6 h after the intervention. Radiation dose, time of radiation and the number of exposures needed to place the needle were recorded. No significant differences concerning age (mean age 60.5 years, range 51–69), body mass index (mean BMI 26.2, range 22.2–29.9) and preoperative pain (VAS 7.9, range 6–10) were found between the two groups. There was no difference in pain reduction between the two groups (60 vs. 61.5%; P = 0.001) but the radiation dose was significantly smaller with the new SabreSource™ system (reduction of radiation dose 32.7%, P = 0.01; reduction of mean entrance surface dose 32.3%, P = 0.01). The SabreSource™ System significantly reduced the radiation dose received during the injection therapy of the lumbar facet joints. With minimal effort for the setup at the beginning of a session, the system is easy to handle and can be helpful for other injection therapies (e.g. nerve root block therapies). PMID:19082641

Rotational injury of cervical facets: CT analysis of fracture patterns with implications for management and neurologic outcome.

PubMed

Shanmuganathan, K; Mirvis, S E; Levine, A M

1994-11-01

Imaging studies of patients with rotational facet injuries of the cervical spine were retrospectively reviewed to determine the prevalence and pattern of associated fractures, to correlate injury pattern with recommended surgical stabilization, and to assess neurologic outcome. Radiographs and CT scans obtained for 40 consecutive patients with rotational facet injuries of the cervical spine during a 70-month period were retrospectively reviewed to determine injury level, presence, and orientation of facet fractures, and concurrent nonfacet injuries. Imaging findings were reviewed to assess the likelihood of instability and to determine the most appropriate stabilization requirement. Medical records were reviewed to ascertain mechanism of injury, initial neurologic deficit, and surgical findings. Among the 40 patients with cervical rotational facet injuries, 11 (27%) had pure unilateral facet dislocation or subluxation without associated fractures, and 29 (73%) had concurrent facet fractures involving the inferior facet of the rotated vertebra (n = 13), the superior facet of the subjacent vertebra (n = 9), or both (n = 7). Injury of the rotated vertebra was unilateral in 22 patients but bilateral in 18 patients. Facet fractures frequently extended into the ipsilateral lamina or articular pillar or both. An avulsion fracture from the posteroinferior aspect of the rotated vertebral body, indicating disk disruption, occurred in 10 patients (25%), and seven patients (17%) had complete isolation of an articular pillar. Facet fractures were confirmed for 27 patients who underwent surgical stabilization. Neurologic deficits developed in 29 (73%) of the 40 patients and included radiculopathy in 11 patients and cord syndromes in 18 patients. Pure dislocation without a facet fracture was more likely to lead to a cord syndrome (p = .006). Cervical rotational facet injuries are often accompanied by facet fractures and bilateral damage of the rotated vertebra. These injuries contribute to rotational instability and require specific internal fixation based on a precise delineation of all injuries. Facet dislocations without fractures have a significantly higher association with cord syndromes than do rotational facet injuries with fractures. CT, particularly with parasagittal reformations, is valuable in identifying all injuries of the rotated and subjacent vertebrae.

Surface effects on mean inner potentials studied using density functional theory.

PubMed

Pennington, Robert S; Boothroyd, Chris B; Dunin-Borkowski, Rafal E

2015-12-01

Quantitative materials characterization using electron holography frequently requires knowledge of the mean inner potential, but reported experimental mean inner potential measurements can vary widely. Using density functional theory, we have simulated the mean inner potential for materials with a range of different surface conditions and geometries. We use both "thin-film" and "nanowire" specimen geometries. We consider clean bulk-terminated surfaces with different facets and surface reconstructions using atom positions from both structural optimization and experimental data and we also consider surfaces both with and without adsorbates. We find that the mean inner potential is surface-dependent, with the strongest dependency on surface adsorbates. We discuss the outlook and perspective for future mean inner potential measurements. Copyright © 2015 Elsevier B.V. All rights reserved.

Heliostat with Stowing and Wind Survival Capabilities

NASA Technical Reports Server (NTRS)

Nesmith, Bill J. (Inventor)

2018-01-01

A low cost thin-film based heliostat with advanced stowing and wind survival capabilities. The heliostat may include a plurality of reflective surfaces held together via a plurality of double acting magnetic hinges. The heliostat may also include a drive mechanism attached to a post, and configured to stow the plurality of facets in any desired position.

Atomic-Scale Design of Iron Fischer-Tropsch Catalysts; A Combined Computational Chemistry, Experimental, and Microkinetic Modeling Approach

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

Manos Mavrikakis; James Dumesic; Rahul Nabar

2008-09-29

This work focuses on (1) searching/summarizing published Fischer-Tropsch synthesis (FTS) mechanistic and kinetic studies of FTS reactions on iron catalysts; (2) preparation and characterization of unsupported iron catalysts with/without potassium/platinum promoters; (3) measurement of H{sub 2} and CO adsorption/dissociation kinetics on iron catalysts using transient methods; (3) analysis of the transient rate data to calculate kinetic parameters of early elementary steps in FTS; (4) construction of a microkinetic model of FTS on iron, and (5) validation of the model from collection of steady-state rate data for FTS on iron catalysts. Three unsupported iron catalysts and three alumina-supported iron catalysts weremore » prepared by non-aqueous-evaporative deposition (NED) or aqueous impregnation (AI) and characterized by chemisorption, BET, temperature-programmed reduction (TPR), extent-of-reduction, XRD, and TEM methods. These catalysts, covering a wide range of dispersions and metal loadings, are well-reduced and relatively thermally stable up to 500-600 C in H{sub 2} and thus ideal for kinetic and mechanistic studies. Kinetic parameters for CO adsorption, CO dissociation, and surface carbon hydrogenation on these catalysts were determined from temperature-programmed desorption (TPD) of CO and temperature programmed surface hydrogenation (TPSR), temperature-programmed hydrogenation (TPH), and isothermal, transient hydrogenation (ITH). A microkinetic model was constructed for the early steps in FTS on polycrystalline iron from the kinetic parameters of elementary steps determined experimentally in this work and from literature values. Steady-state rate data were collected in a Berty reactor and used for validation of the microkinetic model. These rate data were fitted to 'smart' Langmuir-Hinshelwood rate expressions derived from a sequence of elementary steps and using a combination of fitted steady-state parameters and parameters specified from the transient measurements. The results provide a platform for further development of microkinetic models of FTS on Fe and a basis for more precise modeling of FTS activity of Fe catalysts. Calculations using periodic, self-consistent Density Functional Theory (DFT) methods were performed on various realistic models of industrial, Fe-based FTS catalysts. Close-packed, most stable Fe(110) facet was analyzed and subsequently carbide formation was found to be facile leading to the choice of the FeC(110) model representing a Fe facet with a sub-surface C atom. The Pt adatom (Fe{sup Pt}(110)) was found to be the most stable model for our studies into Pt promotion and finally the role of steps was elucidated by recourse to the defected Fe(211) facet. Binding Energies(BEs), preferred adsorption sites and geometries for all FTS relevant stable species and intermediates were evaluated on each model catalyst facet. A mechanistic model (comprising of 32 elementary steps involving 19 species) was constructed and each elementary step therein was fully characterized with respect to its thermochemistry and kinetics. Kinetic calculations involved evaluation of the Minimum Energy Pathways (MEPs) and activation energies (barriers) for each step. Vibrational frequencies were evaluated for the preferred adsorption configuration of each species with the aim of evaluating entropy-changes, pre exponential factors and serving as a useful connection with experimental surface science techniques. Comparative analysis among these four facets revealed important trends in their relative behavior and roles in FTS catalysis. Overall the First Principles Calculations afforded us a new insight into FTS catalysis on Fe and modified-Fe catalysts.« less

Canopy BRF simulation of forest with different crown shape and height in larger scale based on Radiosity method

NASA Astrophysics Data System (ADS)

Song, Jinling; Qu, Yonghua; Wang, Jindi; Wan, Huawei; Liu, Xiaoqing

2007-06-01

Radiosity method is based on the computer simulation of 3D real structures of vegetations, such as leaves, branches and stems, which are composed by many facets. Using this method we can simulate the canopy reflectance and its bidirectional distribution of the vegetation canopy in visible and NIR regions. But with vegetations are more complex, more facets to compose them, so large memory and lots of time to calculate view factors are required, which are the choke points of using Radiosity method to calculate canopy BRF of lager scale vegetation scenes. We derived a new method to solve the problem, and the main idea is to abstract vegetation crown shapes and to simplify their structures, which can lessen the number of facets. The facets are given optical properties according to the reflectance, transmission and absorption of the real structure canopy. Based on the above work, we can simulate the canopy BRF of the mix scenes with different species vegetation in the large scale. In this study, taking broadleaf trees as an example, based on their structure characteristics, we abstracted their crowns as ellipsoid shells, and simulated the canopy BRF in visible and NIR regions of the large scale scene with different crown shape and different height ellipsoids. Form this study, we can conclude: LAI, LAD the probability gap, the sunlit and shaded surfaces are more important parameter to simulate the simplified vegetation canopy BRF. And the Radiosity method can apply us canopy BRF data in any conditions for our research.

Thermodynamics of Alkanethiol Self-Assembled Monolayer Assembly on Pd Surfaces.

PubMed

Kumar, Gaurav; Van Cleve, Timothy; Park, Jiyun; van Duin, Adri; Medlin, J Will; Janik, Michael J

2018-06-05

We investigate the structure and binding energy of alkanethiolate self-assembled monolayers (SAMs) on Pd (111), Pd (100), and Pd (110) facets at different coverages. Dispersion-corrected density functional theory calculations are used to correlate the binding energy of alkanethiolates with alkyl chain length and coverage. The equilibrium coverage of thiolate layers strongly prefers 1/3 monolayer (ML) on the Pd (111) surface. The coverage of thiolates varies with chemical potential on Pd (100) and Pd (110), increasing from 1/3 to 1/2 ML on (100) and from 1/4 to 1/2 ML on (110) as the thiol chemical potential is increased. Higher coverages are driven by attractive dispersion interactions between the extended alkyl chains, such that transitions to higher coverages occur at lower thiol chemical potentials for longer chain thiolates. Stronger adsorption to the Pd (100) surface causes the equilibrium Wulff construction of Pd particles to take on a cubic shape upon saturation with thiols. The binding of H, O, and CO adsorbates is weakened as the thiolate coverage is increased, with saturation coverages causing unfavorable binding of O and CO on Pd (100) and weakened binding on other facets. Temperature-dependent CO diffuse reflectance infrared Fourier transform spectroscopy experiments are used to corroborate the weakened binding of CO in the presence of thiolate SAMs of varying surface density. Preliminary results of multiscale modeling efforts on the Pd-thiol system using a reactive force field, ReaxFF, are also discussed.

Applying tribology to teeth of hoofed mammals.

PubMed

Schulz, Ellen; Calandra, Ivan; Kaiser, Thomas M

2010-01-01

Mammals inhabit all types of environments and have evolved chewing systems capable of processing a huge variety of structurally diverse food components. Surface textures of cheek teeth should thus reflect the mechanisms of wear as well as the functional traits involved. We employed surface textures parameters from ISO/DIS 25178 and scale-sensitive fractal analysis (SSFA) to quantify dental wear in herbivorous mammals at the level of an individual wear enamel facet. We evaluated cheek dentitions of two grazing ungulates: the Blue Wildebeest (Connochaetes taurinus) and the Grevy's Zebra (Equus grevyi). Both inhabit the east African grassland savanna habitat, but they belong to fundamentally different taxonomic units. We tested the hypothesis that the foregut fermenting wildebeest and the hindgut fermenting zebra show functional traits in their dentitions that relate to their specific mode of food-composition processing and digestion. In general, surface texture parameters from SSFA as well as ISO/DIS 25178 indicated that individual enamel ridges acting as crushing blades and individual wear facets of upper cheek teeth are significantly different in surface textures in the zebra when compared with the wildebeest. We interpreted the complexity and anisotropy signals to be clearly related to the brittle, dry grass component in the diet of the zebra, unlike the wildebeest, which ingests a more heterogeneous diet including fresh grass and herbs. Thus, SSFA and ISO parameters allow distinctions within the subtle dietary strategies that evolved in herbivorous ungulates with fundamentally different systematic affinities but which exploit a similar dietary niche. © 2010 Wiley Periodicals, Inc.

Linking interfacial chemistry of CO2 to surface structures of hydrated metal oxide nanoparticles: hematite.

PubMed

Chernyshova, Irina V; Ponnurangam, Sathish; Somasundaran, Ponisseril

2013-05-14

A better understanding of interaction with dissolved CO2 is required to rationally design and model the (photo)catalytic and sorption processes on metal (hydr)oxide nanoparticles (NPs) in aqueous media. Using in situ FTIR spectroscopy, we address this problem for rhombohedral 38 nm hematite (α-Fe2O3) nanoparticles as a model. We not only resolve the structures of the adsorbed carbonate species, but also specify their adsorption sites and their location on the nanoparticle surface. The spectral relationships obtained present a basis for a new method of characterizing the microscopic structural and acid-base properties (related to individual adsorption sites) of hydrated metal (hydr)oxide NPs using atmospherically derived CO2 as a probe. Specifically, we distinguish two carbonate species suggesting two principally different adsorption mechanisms. One species, which is more weakly adsorbed, has an inner-sphere mononuclear monodentate structure which is formed by a conventional ligand-exchange mechanism. At natural levels of dissolved carbonate and pH from 3 to 11, this species is attached to the most acidic/reactive surface cations (surface states) associated with ferrihydrite-like surface defects. The second species, which is more strongly adsorbed, presents a mixed C and O coordination of bent CO2. This species uniquely recognizes the stoichiometric rhombohedral {104} facets in the NP texture. Like in gas phase, it is formed through the surface coordination of molecular CO2. We address how the adsorption sites hosting these two carbonate species are affected by the annealing and acid etching of the NPs. These results support the nanosize-induced phase transformation of hematite towards ferrihydrite under hydrous conditions, and additionally show that the process starts from the roughened areas of the facet intersections.

Virtual ellipsometry on layered micro-facet surfaces.

PubMed

Wang, Chi; Wilkie, Alexander; Harcuba, Petr; Novosad, Lukas

2017-09-18

Microfacet-based BRDF models are a common tool to describe light scattering from glossy surfaces. Apart from their wide-ranging applications in optics, such models also play a significant role in computer graphics for photorealistic rendering purposes. In this paper, we mainly investigate the computer graphics aspect of this technology, and present a polarisation-aware brute force simulation of light interaction with both single and multiple layered micro-facet surfaces. Such surface models are commonly used in computer graphics, but the resulting BRDF is ultimately often only approximated. Recently, there has been work to try to make these approximations more accurate, and to better understand the behaviour of existing analytical models. However, these brute force verification attempts still emitted the polarisation state of light and, as we found out, this renders them prone to mis-estimating the shape of the resulting BRDF lobe for some particular material types, such as smooth layered dielectric surfaces. For these materials, non-polarising computations can mis-estimate some areas of the resulting BRDF shape by up to 23%. But we also identified some other material types, such as dielectric layers over rough conductors, for which the difference turned out to be almost negligible. The main contribution of our work is to clearly demonstrate that the effect of polarisation is important for accurate simulation of certain material types, and that there are also other common materials for which it can apparently be ignored. As this required a BRDF simulator that we could rely on, a secondary contribution is that we went to considerable lengths to validate our software. We compare it against a state-of-art model from graphics, a library from optics, and also against ellipsometric measurements of real surface samples.

Structural Equation Modelling of Multiple Facet Data: Extending Models for Multitrait-Multimethod Data

ERIC Educational Resources Information Center

Bechger, Timo M.; Maris, Gunter

2004-01-01

This paper is about the structural equation modelling of quantitative measures that are obtained from a multiple facet design. A facet is simply a set consisting of a finite number of elements. It is assumed that measures are obtained by combining each element of each facet. Methods and traits are two such facets, and a multitrait-multimethod…

Airborne sand and dust soiling of solar collecting mirrors

NASA Astrophysics Data System (ADS)

Sansom, Christopher; Almond, Heather; King, Peter; Endaya, Essam; Bouaichaoui, Sofiane

2017-06-01

The reflectance of solar collecting mirrors can be significantly reduced by sand and dust soiling, particularly in arid environments. Larger airborne sand and dust particles can also cause damage by erosion, again reducing reflectance. This work describes investigations of the airborne particle size, shape, and composition in three arid locations that are considered suitable for CSP plants, namely in Iran, Libya, and Algeria. Sand and dust has been collected at heights between 0.5 to 2.0m by a variety of techniques, but are shown not to be representative of the particle size found either in ground dust and sand, or on the solar collecting mirror facets themselves. The possible reasons for this are proposed, most notably that larger particles may rebound from the mirror surface. The implications for mirror cleaning and collector facet erosion are discussed.

Reactor for nano-focused x-ray diffraction and imaging under catalytic in situ conditions

NASA Astrophysics Data System (ADS)

Richard, M.-I.; Fernández, S.; Hofmann, J. P.; Gao, L.; Chahine, G. A.; Leake, S. J.; Djazouli, H.; De Bortoli, Y.; Petit, L.; Boesecke, P.; Labat, S.; Hensen, E. J. M.; Thomas, O.; Schülli, T.

2017-09-01

A reactor cell for in situ studies of individual catalyst nanoparticles or surfaces by nano-focused (coherent) x-ray diffraction has been developed. Catalytic reactions can be studied in flow mode in a pressure range of 10-2-103 mbar and temperatures up to 900 °C. This instrument bridges the pressure and materials gap at the same time within one experimental setup. It allows us to probe in situ the structure (e.g., shape, size, strain, faceting, composition, and defects) of individual nanoparticles using a nano-focused x-ray beam. Here, the setup was used to observe strain and facet evolution of individual model Pt catalysts during in situ experiments. It can be used for heating other (non-catalytically active) nanoparticles (e.g., nanowires) in inert or reactive gas atmospheres or vacuum as well.

Reactor for nano-focused x-ray diffraction and imaging under catalytic in situ conditions.

PubMed

Richard, M-I; Fernández, S; Hofmann, J P; Gao, L; Chahine, G A; Leake, S J; Djazouli, H; De Bortoli, Y; Petit, L; Boesecke, P; Labat, S; Hensen, E J M; Thomas, O; Schülli, T

2017-09-01

A reactor cell for in situ studies of individual catalyst nanoparticles or surfaces by nano-focused (coherent) x-ray diffraction has been developed. Catalytic reactions can be studied in flow mode in a pressure range of 10 -2 -10 3 mbar and temperatures up to 900 °C. This instrument bridges the pressure and materials gap at the same time within one experimental setup. It allows us to probe in situ the structure (e.g., shape, size, strain, faceting, composition, and defects) of individual nanoparticles using a nano-focused x-ray beam. Here, the setup was used to observe strain and facet evolution of individual model Pt catalysts during in situ experiments. It can be used for heating other (non-catalytically active) nanoparticles (e.g., nanowires) in inert or reactive gas atmospheres or vacuum as well.

Morphological, compositional, and geometrical transients of V-groove quantum wires formed during metalorganic vapor-phase epitaxy

NASA Astrophysics Data System (ADS)

Dimastrodonato, Valeria; Pelucchi, Emanuele; Zestanakis, Panagiotis A.; Vvedensky, Dimitri D.

2013-07-01

We present a theoretical model of the formation of self-limited (Al)GaAs quantum wires within V-grooves on GaAs(001) substrates during metalorganic vapor-phase epitaxy. We identify the facet-dependent rates of the kinetic processes responsible for the formation of the self-limiting profile, which is accompanied by Ga segregation along the axis perpendicular to the bottom of the original template, and analyze their interplay with the facet geometry in the transient regime. A reduced model is adopted for the evolution of the patterned profile, as determined by the angle between the different crystallographic planes as a function of the growth conditions. Our results provide a comprehensive phenomenological understanding of the self-ordering mechanism on patterned surfaces which can be harnessed for designing the quantum optical properties of low-dimensional systems.

Migrating lumbar facet joint cysts.

PubMed

Palmieri, Francesco; Cassar-Pullicino, Victor N; Lalam, Radhesh K; Tins, Bernhard J; Tyrrell, Prudencia N M; McCall, Iain W

2006-04-01

The majority of lumbar facet joint cysts (LFJCs) are located in the spinal canal, on the medial aspect of the facet joint with characteristic diagnostic features. When they migrate away from the joint of origin, they cause diagnostic problems. In a 7-year period we examined by computed tomography (CT) and magnetic resonance (MR) imaging five unusual cases of facet joint cysts which migrated from the facet joint of origin. Three LFJCs were identified in the right S1 foramen, one in the right L5-S1 neural foramen and one in the left erector spinae and multifidus muscles between the levels of L2-L4 spinous process. Awareness that spinal lesions identified at MRI and CT could be due to migrating facet joint cyst requires a high level of suspicion. The identification of the appositional contact of the cyst and the facet joint needs to be actively sought in the presence of degenerative facet joints.

[Feasibility and accuracy of ultrasound-guided methodology in the examination of lumbar spine facet joints].

PubMed

Wen, Chuan-Bing; Li, Yong-Zhong; Tang, Qin-Qin; Sun, Lin; Xiao, Hong; Yang, Bang-Xiang; Song, Li; Liu, Hui

2013-03-01

To investigate the feasibility, accuracy of B ultrasound in the examination of joint space of lumbar spine facet joints compared with CT scan. Ten healthy adult volunteers were enrolled. The joint space of lumbar facet joints was measured by ultrasound. To identify the spinal levels, the posterior parasagittal sonograms were obtained at levels L1 to S1. The lumbar facet joints were delineated with the help of transverse sonograms at each level. Meanwhile, the lumbar facet joints were evaluated by spiral CT on the same plane, reformatted to 1-mm axial slices. A total of 88 lumbar facet joints from L1 to S1 were clearly visualized in the 10 volunteers. Both ultrasound and CT measurements showed the same average depth and lateral distance of lumbar facet joint space (P > 0.05). The lumbar facet joint space can be accurately demonstrated by ultrasound.

A Meta-Analysis of the Relationship between Trait Mindfulness and Substance Use Behaviors

PubMed Central

Karyadi, Kenny A.; VanderVeen, J. Davis; Cyders, Melissa A.

2014-01-01

Background The relationship between trait mindfulness and substance use behaviors has been inconsistent across studies. The current study is a meta-analysis aimed at quantifying the magnitude of this relationship, and at determining how this relationship varies in context of (1) mindfulness facets, (2) substance type, (3) sample characteristics, and (4) substance use severity. Methods A literature search was conducted using electronic databases. The literature search yielded 303 articles, but only 39 articles met inclusion criteria to be included in this meta-analysis. The relationship was quantified as a Pearson's r correlation coefficient for all studies. Results Findings indicated a small, negative, and significant relationship between trait mindfulness and substance use behaviors (r = -0.13). This relationship varied across substance type, clinical status of the sample, and substance use severity. Although not significant, relationship sizes showed different patterns across mindfulness facets. Conclusions This meta-analysis quantified the relationship between trait mindfulness and substance use behaviors, which can be used as future effect size estimates. Findings also clarify inconsistency in previous work by indicating that the trait mindfulness-substance use behaviors relationship was more robust: (1) for alcohol use and tobacco use behaviors; (2) for problematic substance use behaviors; and (3) with inpatient clinical samples. Further work should continue to examine if acting with awareness, non-judgment, and non-reactivity mindfulness facets are more robustly associated with substance use behaviors. Failure to consider these factors, or collapsing across these factors, could explain the smaller or inconsistently reported associations across previous studies. PMID:25113434

Hierarchical representations of the five-factor model of personality in predicting job performance: integrating three organizing frameworks with two theoretical perspectives.

PubMed

Judge, Timothy A; Rodell, Jessica B; Klinger, Ryan L; Simon, Lauren S; Crawford, Eean R

2013-11-01

Integrating 2 theoretical perspectives on predictor-criterion relationships, the present study developed and tested a hierarchical framework in which each five-factor model (FFM) personality trait comprises 2 DeYoung, Quilty, and Peterson (2007) facets, which in turn comprise 6 Costa and McCrae (1992) NEO facets. Both theoretical perspectives-the bandwidth-fidelity dilemma and construct correspondence-suggest that lower order traits would better predict facets of job performance (task performance and contextual performance). They differ, however, as to the relative merits of broad and narrow traits in predicting a broad criterion (overall job performance). We first meta-analyzed the relationship of the 30 NEO facets to overall job performance and its facets. Overall, 1,176 correlations from 410 independent samples (combined N = 406,029) were coded and meta-analyzed. We then formed the 10 DeYoung et al. facets from the NEO facets, and 5 broad traits from those facets. Overall, results provided support for the 6-2-1 framework in general and the importance of the NEO facets in particular. (c) 2013 APA, all rights reserved.

FACETS: multi-faceted functional decomposition of protein interaction networks.

PubMed

Seah, Boon-Siew; Bhowmick, Sourav S; Dewey, C Forbes

2012-10-15

The availability of large-scale curated protein interaction datasets has given rise to the opportunity to investigate higher level organization and modularity within the protein-protein interaction (PPI) network using graph theoretic analysis. Despite the recent progress, systems level analysis of high-throughput PPIs remains a daunting task because of the amount of data they present. In this article, we propose a novel PPI network decomposition algorithm called FACETS in order to make sense of the deluge of interaction data using Gene Ontology (GO) annotations. FACETS finds not just a single functional decomposition of the PPI network, but a multi-faceted atlas of functional decompositions that portray alternative perspectives of the functional landscape of the underlying PPI network. Each facet in the atlas represents a distinct interpretation of how the network can be functionally decomposed and organized. Our algorithm maximizes interpretative value of the atlas by optimizing inter-facet orthogonality and intra-facet cluster modularity. We tested our algorithm on the global networks from IntAct, and compared it with gold standard datasets from MIPS and KEGG. We demonstrated the performance of FACETS. We also performed a case study that illustrates the utility of our approach. Supplementary data are available at the Bioinformatics online. Our software is available freely for non-commercial purposes from: http://www.cais.ntu.edu.sg/~assourav/Facets/

Fabrication and metrology of km-scale radii on surfaces of master tooling

NASA Astrophysics Data System (ADS)

Leistner, Achim J.; Oreb, Bozenko F.; Seckold, Jeffrey A.; Walsh, Christopher J.

1999-08-01

The Laser Interferometer Gravitational-wave Observatory (LIGO) core optical components have been manufactured by CSIRO. These optical substrates are optically polished on a lap surface that is made of Teflon coated onto a thick rigid faceted Zerodur base. To produce the km-scale radii (> 10 km) on these substrates the lap surface is shaped by abrading it with a fine ground silica plate whose radius of curvature corresponds to the one specified for the LIGO component. The plates are measured by a commercial phase stepping interferometer which is used in a grazing incidence arrangement. We describe the process of shaping and measuring the conditioning plates and laps.

Surface Aesthetics and Analysis.

PubMed

Çakır, Barış; Öreroğlu, Ali Rıza; Daniel, Rollin K

2016-01-01

Surface aesthetics of an attractive nose result from certain lines, shadows, and highlights with specific proportions and breakpoints. Analysis emphasizes geometric polygons as aesthetic subunits. Evaluation of the complete nasal surface aesthetics is achieved using geometric polygons to define the existing deformity and aesthetic goals. The relationship between the dome triangles, interdomal triangle, facet polygons, and infralobular polygon are integrated to form the "diamond shape" light reflection on the nasal tip. The principles of geometric polygons allow the surgeon to analyze the deformities of the nose, define an operative plan to achieve specific goals, and select the appropriate operative technique. Copyright © 2016 Elsevier Inc. All rights reserved.

Tuning bacterial hydrodynamics with magnetic fields

NASA Astrophysics Data System (ADS)

Pierce, C. J.; Mumper, E.; Brown, E. E.; Brangham, J. T.; Lower, B. H.; Lower, S. K.; Yang, F. Y.; Sooryakumar, R.

2017-06-01

Magnetotactic bacteria are a group of motile prokaryotes that synthesize chains of lipid-bound, magnetic nanoparticles called magnetosomes. This study exploits their innate magnetism to investigate previously unexplored facets of bacterial hydrodynamics at surfaces. Through use of weak, uniform, external magnetic fields and local, micromagnetic surface patterns, the relative strength of hydrodynamic, magnetic, and flagellar force components is tuned through magnetic control of the bacteria's orientation. The resulting swimming behaviors provide a means to experimentally determine hydrodynamic parameters and offer a high degree of control over large numbers of living microscopic entities. The implications of this controlled motion for studies of bacterial motility near surfaces and for micro- and nanotechnology are discussed.

Facet joint laser radiation: tissue effects of a new clinical laser application

NASA Astrophysics Data System (ADS)

Werkmann, Klaus; Thal, Dietmar R.

1996-01-01

Chronic unilateral and bilateral back pain with pseudoradicular symptoms, is a common clinical syndrome, which in many cases can be related to the facet joint syndrome. The pain is caused by mechanical affection of synovial and capsular nerve terminals. Therefore, current therapeutical attempts including physical therapy, intra-articular injection of local anesthetics and steroids and thermocoagulation of the facet joint with a thermocoagulator, are performed. We confirmed laser coagulation of the facet joint. Porcine cadaveric spines were treated immediately after death by intra-articular facet joint laser radiation. With the pulsed Nd:YAG laser (1064 nm) altogether 600 J were applied in three different places 4 mm apart at the top of the facet joint. The results showed that facet joint laser radiation leads to a small (about 1 - 2 mm diameter) lesion restricted to the facet joint cavity and its synovia. Histologically, we found a central carbonization zone and necrosis, including almost the whole cartilage and approximately 0.2 mm of the adjacent bone. These changes are similar to Nd:Yag-laser applications in other skeletal regions. It is suggested that these changes may lead to facet joint denervation by coagulation of the synovial nerve terminals. Cicatration of the laser lesion might cause ankylosis of this joint. In sum, facet joint laser radiation could be an alternative therapeutical tool for lower back pain of the facet joint syndrome type. Therefore, future clinical application of this technique seems to be very promising.

Backward-gazing method for heliostats shape errors measurement and calibration

NASA Astrophysics Data System (ADS)

Coquand, Mathieu; Caliot, Cyril; Hénault, François

2017-06-01

The pointing and canting accuracies and the surface shape of the heliostats have a great influence on the solar tower power plant efficiency. At the industrial scale, one of the issues to solve is the time and the efforts devoted to adjust the different mirrors of the faceted heliostats, which could take several months if the current methods were used. Accurate control of heliostat tracking requires complicated and onerous devices. Thus, methods used to adjust quickly the whole field of a plant are essential for the rise of solar tower technology with a huge number of heliostats. Wavefront detection is widely use in adaptive optics and shape error reconstruction. Such systems can be sources of inspiration for the measurement of solar facets misalignment and tracking errors. We propose a new method of heliostat characterization inspired by adaptive optics devices. This method aims at observing the brightness distributions on heliostat's surface, from different points of view close to the receiver of the power plant, in order to calculate the wavefront of the reflection of the sun on the concentrated surface to determine its errors. The originality of this new method is to use the profile of the sun to determine the defects of the mirrors. In addition, this method would be easy to set-up and could be implemented without sophisticated apparatus: only four cameras would be used to perform the acquisitions.

Surface passivation and self-regulated shell growth in selective area-grown GaN-(Al,Ga)N core-shell nanowires.

PubMed

Hetzl, Martin; Winnerl, Julia; Francaviglia, Luca; Kraut, Max; Döblinger, Markus; Matich, Sonja; Fontcuberta I Morral, Anna; Stutzmann, Martin

2017-06-01

The large surface-to-volume ratio of GaN nanowires implicates sensitivity of the optical and electrical properties of the nanowires to their surroundings. The implementation of an (Al,Ga)N shell with a larger band gap around the GaN nanowire core is a promising geometry to seal the GaN surface. We investigate the luminescence and structural properties of selective area-grown GaN-(Al,Ga)N core-shell nanowires grown on Si and diamond substrates. While the (Al,Ga)N shell allows a suppression of yellow defect luminescence from the GaN core, an overall intensity loss due to Si-related defects at the GaN/(Al,Ga)N interface has been observed in the case of Si substrates. Scanning transmission electron microscopy measurements indicate a superior crystal quality of the (Al,Ga)N shell along the nanowire side facets compared to the (Al,Ga)N cap at the top facet. A nucleation study of the (Al,Ga)N shell reveals a pronounced bowing of the nanowires along the c-direction after a short deposition time which disappears for longer growth times. This is assigned to an initially inhomogeneous shell nucleation. A detailed study of the proceeding shell growth allows the formulation of a strain-driven self-regulating (Al,Ga)N shell nucleation model.

Solar concentrator advanced development project

NASA Technical Reports Server (NTRS)

Corrigan, Robert D.; Ehresman, Derik T.

1987-01-01

A solar dynamic concentrator design developed for use with a solar-thermodynamic power generation module intended for the Space Station is considered. The truss hexagonal panel reflector uses a modular design approach and is flexible in attainable flux profiles and assembly techniques. Preliminary structural, thermal, and optical analysis results are discussed. Accuracy of the surface reflectors should be within 5 mrad rms slope error, resulting in the need for close fabrication tolerances. Significant fabrication issues to be addressed include the facet reflective and protective coating processes and the surface specularity requirements.

Computational Study of the Adsorption of Dimethyl Methylphosphonate (DMMP) on the (010) Surface of Anatase TiO2 With and Without Faceting

DTIC Science & Technology

2009-12-05

surface area of anatase nanocrystals [6] and to be es- pecially active in photocatalysis [7]. Recent work by Dzwigaj et al. [8] has clearly shown that the...two-fold-coordinated (O2c) sites can also be involved in hydrogen bond (H-bond) formation. The effects, on the structure of the (100) and other...To reduce the computational cost , geometry optimization was done at the restricted Hartree Fock (RHF) level. This has previously been shown [36,37

Topological defects and shapes of triatic liquid crystal vesicles

NASA Astrophysics Data System (ADS)

Serafin, Francesco; Manyuhina, Oksana; Bowick, Mark

Is shape the manifestation of function, or does shape determine function? Since the time of Aristotle, the study of shape has proven to be a fruitful way to understand the behavior of physical systems, from atomic to biological systems scales. Two dimensional soft membranes are a perfect setting to understand the emergence of shape. An interesting possibility is to control and design new self-assemblable supramolecular shapes by coating the surface of soft closed vesicles with liquid crystals (LC) of various symmetries. The microscopic geometry of the liquid crystal molecules, in particular the structure of topological defects, when combined with the topology of the vesicle's surface, ultimately determines the vesicle's shape. Recent work has shown that the minimal energy shapes of smectic and nematic vesicles are faceted polyhedra. A very soft smectic vesicle develops sharp creases and forms a faceted tetrahedron. When the coating LC has the symmetries of the square, the vesicle forms a cube. In this work we extend these results to a 3-fold symmetric LC, proving that the vesicle's ground state is an octahedron. This gives a systematic way of predicting vesicle's shapes as we change the liquid crystal's symmetry. Soft Matter Program of Syracuse University.

Tracking and shape errors measurement of concentrating heliostats

NASA Astrophysics Data System (ADS)

Coquand, Mathieu; Caliot, Cyril; Hénault, François

2017-09-01

In solar tower power plants, factors such as tracking accuracy, facets misalignment and surface shape errors of concentrating heliostats are of prime importance on the efficiency of the system. At industrial scale, one critical issue is the time and effort required to adjust the different mirrors of the faceted heliostats, which could take several months using current techniques. Thus, methods enabling quick adjustment of a field with a huge number of heliostats are essential for the rise of solar tower technology. In this communication is described a new method for heliostat characterization that makes use of four cameras located near the solar receiver and simultaneously recording images of the sun reflected by the optical surfaces. From knowledge of a measured sun profile, data processing of the acquired images allows reconstructing the slope and shape errors of the heliostats, including tracking and canting errors. The mathematical basis of this shape reconstruction process is explained comprehensively. Numerical simulations demonstrate that the measurement accuracy of this "backward-gazing method" is compliant with the requirements of solar concentrating optics. Finally, we present our first experimental results obtained at the THEMIS experimental solar tower plant in Targasonne, France.

Evaluation of Giga-cycle Fatigue Properties of Austenitic Stainless Steels Using Ultrasonic Fatigue Test

NASA Astrophysics Data System (ADS)

Takahashi, Kyouhei; Ogawa, Takeshi

Ultrasonic fatigue tests have been performed in austenitic stainless steel, SUS316NG, in order to investigate giga-cycle fatigue strength of pre-strained materials, i.e. 5, 10 and 20% tensile pre-strains and -20% compressive pre-strain. The pre-strains were applied before specimen machining. The austenitic stainless steels are known to exhibit remarkable self-heating during the fatigue experiment. Therefore, heat radiation method was established by setting fatigue specimens in a low temperature chamber at about -100°C. The self-heating was controlled by intermittent loading condition, which enabled us to maintain the test section of the specimens at about room temperature. The results revealed that the fatigue strength increased with increasing pre-strain levels. Fish-eye fracture was observed for -20% pre-strained specimen fractured at 4.11×107 cycles, while the other specimens exhibited ordinary fatigue fracture surface originated from stage I facet on the specimen surface. The increase in fatigue limit was predicted by Vickers hardness, HV, which depended on the size of indented region. The prediction was successful using HV values obtained by the size of the indented region similar to those of the stage I facets.

Arecibo and Goldstone radar images of near-Earth Asteroid (469896) 2005 WC1

NASA Astrophysics Data System (ADS)

Lawrence, Kenneth J.; Benner, Lance A. M.; Brozovic, Marina; Ostro, Steven J.; Jao, Joseph S.; Giorgini, Jon D.; Slade, Martin A.; Jurgens, Raymond F.; Nolan, Michael C.; Howell, Ellen S.; Taylor, Patrick A.

2018-01-01

We report radar observations of near-Earth asteroid (469896) 2005 WC1 that were obtained at Arecibo (2380 MHz, 13 cm) and Goldstone (8560 MHz, 3.5 cm) on 2005 December 14-15 during the asteroid's approach within 0.020 au The asteroid was a strong radar target. Delay-Doppler images with resolutions as fine as 15 m/pixel were obtained with 2 samples per baud giving a correlated pixel resolution of 7.5 m. The radar images reveal an angular object with 100 m-scale surface facets, radar-dark regions, and an estimated diameter of 400 ± 50 m. The rotation of the facets in the images gives a rotation period of ∼2.6 h that is consistent with the estimated period of 2.582 h ± 0.002 h from optical lightcurves reported by Miles (private communication). 2005 WC1 has a circular polarization ratio of 1.12 ± 0.05 that is one of the highest values known, suggesting a structurally-complex near-surface at centimeter to decimeter spatial scales. It is the first asteroid known with an extremely high circular polarization ratio, relatively low optical albedo, and high radar albedo.

In Situ Graphene Growth Dynamics on Polycrystalline Catalyst Foils

PubMed Central

2016-01-01

The dynamics of graphene growth on polycrystalline Pt foils during chemical vapor deposition (CVD) are investigated using in situ scanning electron microscopy and complementary structural characterization of the catalyst with electron backscatter diffraction. A general growth model is outlined that considers precursor dissociation, mass transport, and attachment to the edge of a growing domain. We thereby analyze graphene growth dynamics at different length scales and reveal that the rate-limiting step varies throughout the process and across different regions of the catalyst surface, including different facets of an individual graphene domain. The facets that define the domain shapes lie normal to slow growth directions, which are determined by the interfacial mobility when attachment to domain edges is rate-limiting, as well as anisotropy in surface diffusion as diffusion becomes rate-limiting. Our observations and analysis thus reveal that the structure of CVD graphene films is intimately linked to that of the underlying polycrystalline catalyst, with both interfacial mobility and diffusional anisotropy depending on the presence of step edges and grain boundaries. The growth model developed serves as a general framework for understanding and optimizing the growth of 2D materials on polycrystalline catalysts. PMID:27576749

T2 mapping in patellar chondromalacia.

PubMed

Ruiz Santiago, Fernando; Pozuelo Calvo, Rocío; Almansa López, Julio; Guzmán Álvarez, Luis; Castellano García, María Del Mar

2014-06-01

To study the correlation between the T2 relaxation times of the patellar cartilage and morphological MRI findings of chondromalacia. This prospective study comprises 50 patients, 27 men and 23 women suffering of anterior knee pain (mean age: 29.7, SD 8.3 years; range: 16-45 years). MRI of 97 knees were performed in these patients at 1.5T magnet including sagittal T1, coronal intermediate, axial intermediate fat sat and T2 mapping. Chondromalacia was assessed using a modified version of Noyes classification. The relaxation time, T2, was studied segmenting the full thickness of the patellar cartilage in 12 areas: 4 proximal (external facet-proximal-lateral (EPL), external facet-proximal-central (EPC), internal facet-proximal-central (IPC), internal facet-proximal-medial (IPM), 4 in the middle section (external facet-middle-lateral (EML), external facet-middle-central (EMC), internal facet-middle-central (IMC), internal facet-middle-medial (IMM) and 4 distal (external facet-distal-lateral (EDL), external facet-distal-central (EDC), internal facet-distal-central (IDC), internal facet-distal-medial (IDM). T2 values showed a significant increase in mild chondromalacia regarding normal cartilage in most of the cartilage areas (p<0.05), except in the internal distal facet (IDC and IDM), EPC, EDL, and IMM. Severe chondromalacia was characterized by a fall of T2 relaxation times with loss of statistical significant differences in comparison with normal cartilage, except in EMC and IMC, where similar values as mild chondromalacia were maintained (p<0.05). Steepest increase in T2 values of patellar cartilage occurs in early stages of patellar cartilage degeneration. Progression of morphologic changes of chondromalacia to more severe degrees is associated to a new drop of T2 relaxation times approaching basal values in most of the areas of the patellar cartilage, except in the central area of the middle section, where T2 values remain increased. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Facet tropism and interfacet shape in the thoracolumbar vertebrae: characterization and biomechanical interpretation.

PubMed

Masharawi, Youssef; Rothschild, Bruce; Salame, Khalil; Dar, Gali; Peleg, Smadar; Hershkovitz, Israel

2005-06-01

Thoracolumbar facet and interfacet linear dimensions were measured and analyzed. To characterize and analyze the thoracolumbar facet and interfacet size and shape in relation to gender, ethnic group, and age and to detect the extent of normal facet tropism along the thoracolumbar spine. Knowledge on facet tropism and interfacet shape is limited in the literature as most data are based on 2-dimensional measurements, small samples, or isolated vertebrae. Facet shape as represented by width, length, width/length ratio and interfacet distances was obtained directly from dry vertebrae of 240 adult human spines. The specimen's osteologic material is part of the Hamann-Todd Osteological Collection housed at the Cleveland Museum of Natural History, Cleveland, OH. A total of 4080 vertebrae (T1-L5) from the vertebral columns of individuals 20 to 80 years of age were measured, using a Microscribe 3-dimensional apparatus (Immersion Co., San Jose, CA). Data were recorded directly on computer software. Statistical analysis included paired t tests and ANOVA. A significant correlation was found between all thoracolumbar facet dimensions and an individual's height and weight. Facet tropism is a major characteristic of the thoracolumbar spine, the left being longer in the thorax while the right is longer in the lumbar. In general, facet size is age-independent and greater in males compared with females with a significant ethnic component. Facet length is similar for all thoracic vertebrae, whereas it sharply and continuously increases in the lumbar vertebrae. Facet dimension manifests a bipolar distribution along the thoracolumbar vertebrae. Width/length ratio indicates that facets are longer than wider for most verte-brae. The interarticular area manifests a marked inverted trapezoidal shape at T1-T2, a rectangular shape at T3-L3, and an ordinary trapezoidal shape at L4-L5. Facet tropism is a normal characteristic in humans, yet it varies along the thoracolumbar spine.

Direct transfer of metallic photonic structures onto end facets of optical fibers

NASA Astrophysics Data System (ADS)

Zhang, Xinping; Liu, Feifei; Lin, Yuanhai

2016-07-01

We present a flexible approach to transfer metallic photonic crystals (MPCs) onto end facets of optical fibers. The MPCs were initially fabricated on a glass substrate with a spacer layer of indium tin oxide (ITO), which was used as a buffer layer in the transferring process. The fiber ends were firstly welded on the top surface of the MPCs by a drop of polymer solution after the solvent evaporated. The ITO layer was then etched by hydrochloric acid (HCl), so that the MPCs got off the substrate and were transferred to the fiber ends. Alternatively, the MPCs may be also etched off the substrate first by immersing the sample in HCl. The ultra-thin MPC sheet consisting of gold nanolines interlaced with photoresist gratings was then transferred to cap the fiber ends. In the later approach, we can choose which side of the MPCs to be used as the contact with the fiber facet. Such methods enabled convenient nanostructuring on optical fiber tips and achieving miniaturized MPC devices with compact integration, extending significantly applications of MPCs. In particular, the fabrications presented in this manuscript enrich the lab-on-fiber engineering techniques and the resultant devices have potential applications in remote sensing and detection systems.

rf breakdown tests of mm-wave metallic accelerating structures

DOE PAGES

Dal Forno, Massimo; Dolgashev, Valery; Bowden, Gordon; ...

2016-01-06

In this study, we explore the physics and frequency-scaling of vacuum rf breakdowns at sub-THz frequencies. We present the experimental results of rf tests performed in metallic mm-wave accelerating structures. These experiments were carried out at the facility for advanced accelerator experimental tests (FACET) at the SLAC National Accelerator Laboratory. The rf fields were excited by the FACET ultrarelativistic electron beam. We compared the performances of metal structures made with copper and stainless steel. The rf frequency of the fundamental accelerating mode, propagating in the structures at the speed of light, varies from 115 to 140 GHz. The traveling wavemore » structures are 0.1 m long and composed of 125 coupled cavities each. We determined the peak electric field and pulse length where the structures were not damaged by rf breakdowns. We calculated the electric and magnetic field correlated with the rf breakdowns using the FACET bunch parameters. The wakefields were calculated by a frequency domain method using periodic eigensolutions. Such a method takes into account wall losses and is applicable to a large variety of geometries. The maximum achieved accelerating gradient is 0.3 GV/m with a peak surface electric field of 1.5 GV/m and a pulse length of about 2.4 ns.« less

Faceting, composition and crystal phase evolution in III-V antimonide nanowire heterostructures revealed by combining microscopy techniques.

PubMed

Xu, Tao; Dick, Kimberly A; Plissard, Sébastien; Nguyen, Thanh Hai; Makoudi, Younes; Berthe, Maxime; Nys, Jean-Philippe; Wallart, Xavier; Grandidier, Bruno; Caroff, Philippe

2012-03-09

III-V antimonide nanowires are among the most interesting semiconductors for transport physics, nanoelectronics and long-wavelength optoelectronic devices due to their optimal material properties. In order to investigate their complex crystal structure evolution, faceting and composition, we report a combined scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning tunneling microscopy (STM) study of gold-nucleated ternary InAs/InAs(1-x)Sb(x) nanowire heterostructures grown by molecular beam epitaxy. SEM showed the general morphology and faceting, TEM revealed the internal crystal structure and ternary compositions, while STM was successfully applied to characterize the oxide-free nanowire sidewalls, in terms of nanofaceting morphology, atomic structure and surface composition. The complementary use of these techniques allows for correlation of the morphological and structural properties of the nanowires with the amount of Sb incorporated during growth. The addition of even a minute amount of Sb to InAs changes the crystal structure from perfect wurtzite to perfect zinc blende, via intermediate stacking fault and pseudo-periodic twinning regimes. Moreover, the addition of Sb during the axial growth of InAs/InAs(1-x)Sb(x) heterostructure nanowires causes a significant conformal lateral overgrowth on both segments, leading to the spontaneous formation of a core-shell structure, with an Sb-rich shell.

The comparison of measurement between ultrasound and computed tomography for abnormal degenerative facet joints: A STROBE-compliant article.

PubMed

Shi, Wen; Tian, Dan; Liu, Da; Yin, Jing; Huang, Ying

2017-08-01

Besides the study on examining facet joints of lumbar spine by ultrasound in normal population, there has not been any related report about examining normal facet joints of lumbar spine by ultrasound so far. This study was aimed to explore the feasibility of ultrasound assessment of lumber spine facet joints by comparing ultrasound measure values of normal and degenerative lumber spine facet joints, and by comparing measure values of ultrasound and computed tomography (CT) of degenerative lumber spine facet joints.This study included 15 patients who had chronic low back pain because of degenerative change in lumbar vertebrae, and 19 volunteers who did not have low back pain or pain in the lower limb. The ultrasound measure values (height [H] and width [W]) of normal and degenerative lumber spine facet joints were compared. And the differentiation between measure values (H and W) of ultrasound and CT of degenerative lumber spine facet joints was also analyzed.The ultrasound clearly showed abnormal facet joints lesion, which was characterized by hyperostosis on the edge of joints, bone destruction under joints, and thinner or thicker articular cartilage. There were significant differences between the ultrasound measure values of the normal (H: 1.26 ± 0.03 cm, W: 0.18 ± 0.01 cm) and abnormal facet joints (H: 1.43 ± 0.05 cm, W: 0.15 ± 0.02 cm) (all P < .05). However, there were no significant differences between the measure values of the ultrasound (H: 1.43 ± 0.17 cm, W: 0.15 ± 0.03 cm) and CT (H: 1.42 ± 0.16, W: 0.14 ± 0.03) of the degenerative lumber spine facet joints (all P > .05).Ultrasound can clearly show the structure of facet joints of lumbar spine. It is precise and feasible to assess facet joints of lumbar spine by ultrasound. This study has important significance for the diagnosis of lumbar facet joint degeneration.

On the influence of ocean waves on simulated GNSS-R delay-doppler maps

NASA Astrophysics Data System (ADS)

Clarizia, M. P.; di Bisceglie, M.; Galdi, C.; Gommenginger, C.; Srokosz, M.

2012-04-01

Global Navigation Satellite System-Reflectometry (GNSS-R), is an established technique that exploits GNSS signals of opportunity reflected from the surface of the ocean, to look primarily at the ocean surface roughness. The strength of this technique, and the primary motivation to carry it forward, is in the fact that GNSS signals are available globally, all the time and over the long term, and could help dramatically improve the monitoring of ocean wind and waves. GNSS-R offers the prospect of high density global measurements of directional sea surface roughness, which are essential for scientific purposes (i.e. quantifying the air-sea exchanges of gases), operational weather and ocean forecasting (i.e. prediction of high winds, dangerous sea states, risk of flooding and storm surges) and to support important climate-relevant Earth Observation techniques (IR SST, or surface salinity retrieval). The retrieval of ocean roughness from GNSS-R data has now been demonstrated with a reasonable level of accuracy from both airborne [1] and spaceborne [2] platforms. In both cases, Directional Mean Square Slopes (DMSS) of the ocean surface have been retrieved from GNSS-R data, in the form of Delay-Doppler Maps (DDMs), using an established theoretical scattering model by Zavorotny and Voronovich (Z-V) [3]. The need for a better assessment of the way the ocean waves influence the scattering of GPS signals has recently led to a different approach, consisting of simulating the scattering of such signals, using a more sophisticated large-scale scattering model than Z-V, and explicit simulations of realistic seas. Initial results produced from these simulations have been recently published in [4], where the emphasis has been put on the effects of different sea states on Radar Cross Section (RCS) and Polarization Ratio (PR) in space domain. Linear wind wave surfaces have been simulated using the Elfouhaily wind wave spectrum [5], for different wind speeds and directions, and with or without a superimposed swell. Then, the scattering from such surfaces has been computed using the innovative Facet Approach (FA), which approximates the surface through a number of rectangular facets, differently oriented, and calculates the surface scattering as the ensemble of the signals scattered from all the facets. Here we proceed with the next step of the GPS-Reflectometry simulator, through investigation of the results in Delay- Doppler (DD) domain. Changes and variations of the DDMs, computed using the FA scattering model, are investigated for a variety of wind and wave conditions of the underlying sea surfaces simulated. Results are analysed for changing wind speed and direction of the waves, presence of a swell component superimposed on wind waves, and changing parameters (wavelength, amplitude, direction) of the swell, revealing some degree of sensitivity of these maps to different sea states. The effect of polarization is also taken into account, through an analysis of PR in DD domain. Finally, an initial investigation into the effect of nonlinearities on the sea surface in DD domain is carried out, by looking at DDMs of the signal scattered from non linear non gaussian sea surfaces explicitly simulated.

Facet joint geometry and intervertebral disk degeneration in the L5-S1 region of the vertebral column in German Shepherd dogs.

PubMed

Seiler, Gabriela S; Häni, Hansjürg; Busato, André R; Lang, Johann

2002-01-01

To evaluate the possible association between facet joint geometry and intervertebral disk degeneration in German Shepherd Dogs. 25 German Shepherd Dogs and 11 control dogs of similar body weight and condition. Facet joint angles in the caudal portion of the lumbar region of the vertebral column (L5-S1) were measured by use of computed tomography, and the intervertebral discs were evaluated microscopically. The relationship between facet joint geometry and disk degeneration was evaluated by use of statistical methods. German Shepherd Dogs had significantly more facet joint tropism than control dogs, but an association with disk degeneration was not found. However, German Shepherd Dogs had a different facet joint conformation, with more sagittally oriented facet joints at L5-L6 and L6-L7 and a larger angle difference between the lumbar and lumbosacral facet joints, compared with control dogs. A large difference between facet joint angles at L6-L7 and L7-S1 in German Shepherd Dogs may be associated with the frequent occurrence of lumbosacral disk degeneration in this breed.

[Does the French Big Five Inventory evaluate facets other than the Big Five factors?

PubMed

Courtois, R; Petot, J-M; Lignier, B; Lecocq, G; Plaisant, O

2017-03-29

The Big Five Inventory (BFI) developed by John et al. (1991) is one of the most widely accepted tools for assessing dimensions of personality. It comprises 44 items that assess five broad dimensions of personality (the Big Five Factors): Extraversion, Agreeableness, Conscientiousness, Neuroticism and Openness to experience. Based on correlations with the facets described in the NEO Personality Inventory Revised (NEO PI-R), another Big Five assessment tool with 240 items and 6 facets per dimension, Soto and John (2009) showed that the dimensions in the BFI could be divided into two facets each (ten facets altogether). These results are in line with those of DeYoung et al. (2007), who ran factorial analyses with all the NEO PI-R facets and the International Personality Item Pool (IPIP) and identified ten intermediate factors (between facets and dimensions) which they called "aspects" (two per dimension). The goal of the present study is to investigate the ten facets described by Soto and John in a French sample, using the French version of the BFI (BFI-Fr), which has good psychometric properties, and to check whether the pattern of correlations of these facets with the NEO PI-R match those of the American version. We created three groups. The first comprised 360 students from the Institut libre d'éducation physique supérieure (ILEPS) and Tours University (psychology undergraduates). Participants (mean age 21.1 years±2.30; 58% women) completed the BFI-Fr and the NEO PI-R. The second comprised 142 psychology students from Tours University (mean age 20.6 years±1.78; 81% women); they completed the BFI-Fr twice, two weeks apart (test and retest). The third comprised 252 psychology students from Paris-Nanterre University (mean age 23 years±4.2; 89% women) who described a total of 405 people they knew well (mean age 35.2±10.8; 49% women) using the peer-report format of the BFI-Fr. In the self-report format, eight of Soto and John's ten aspects had acceptable internal consistency (based on Guildford's (1954) internal consistency criteria, due to the small number of items), with Cronbach's α between 0.60 and 0.86 and test-retest correlations between 0.71 and 0.89, showing satisfactory temporal stability. We found a single facet for Extraversion (Assertiveness), two for Agreeableness (Altruism and Compliance), two for Conscientiousness (Self-Discipline and Order), one for Neuroticism (Anxiety), and two for Openness to Experience (Openness to aesthetics and Openness to ideas). Based on their convergence with the corresponding facets in the NEO PI-R, these eight facets showed satisfactory external validity. With regard to the peer-report format, the Activity facet of Extraversion, which did not have sufficient internal consistency in the self-report format, had acceptable properties (i.e. 9 out of 10 facets). Only the Depression facet of Neuroticism still had insufficient internal consistency. In this study, we proposed an improvement of two facets (Activity and Compliance) and added one facet specific to the French version (Emotional Instability) in place of the Depression facet. We showed that the BFI-Fr can be used to assess nine of the ten facets described by Soto and John. We also identified an Emotional Instability facet, replacing the Depression facet of Neuroticism. DeYoung et al. (2007) considered that anxiety and depression are indissociable and can be represented by a Neuroticism aspect they labeled Withdrawal. They suggested a second aspect of this dimension they called Volatility (with the N2 Angry Hostility facet of the NEO PI-R as main marker and the N5 Impulsiveness and N3 Depression as secondary markers). The Emotional Instability facet we found corresponds closely to the N2 Angry Hostility facet of the NEO PI-R and appears to be a satisfactory marker of DeYoung et al.'s (2007) Volatility aspect. Although this study has limitations, particularly related to the samples (students), the BFI-Fr facets (derived from those defined by Soto and John in the BFI or proposed as improvements on the original facets) match the corresponding NEO PI-R facets and can also be seen as main markers of the aspects defined by DeYoung et al. Copyright © 2017 L'Encéphale, Paris. Published by Elsevier Masson SAS. All rights reserved.

Toxic shock syndrome.

PubMed Central

Todd, J K

1988-01-01

In the past 10 years, we have learned much about TSS and S. aureus and its toxins. A number of important biologic principles have been reemphasized in this first decade of TSS research: S. aureus is a very complex organism, one not likely to yield quick answers; in vitro observations must always be confirmed in the patient; animal models may not always be reliable replicates of human disease; and epidemiologic associations cannot be equated with causation. Toxic shock is an intricate phenomenon with many interesting scientific facets. Unraveling its mysteries will undoubtedly teach us more about the complex interaction of patients and microorganisms. PMID:3069202

Facet orientation and tropism: Associations with asymmetric lumbar paraspinal and psoas muscle parameters in patients with chronic low back pain.

PubMed

Xu, W B; Chen, S; Fan, S W; Zhao, F D; Yu, X J; Hu, Z J

2016-08-10

Many studies have explored the relationship between facet tropism and facet joint osteoarthritis, disc degeneration and degenerative spondylolisthesis. However, the associations between facet orientation and tropism, and paraspinal muscles have not been studied. To analyze the associations between facet orientation and tropism, and parameters of paraspinal muscles in patients with chronic low back pain. Ninety-five patients with chronic low back pain were consecutively enrolled. Their facet joint angles were measured on computed tomography (CT) while gross cross-sectional area (GCSA), functional cross-sectional area (FCSA) and T2 signal intensity of lumbar paraspinal and psoas muscle were evaluated on magnetic resonance imaging (MRI). The GCSA and FCSA were significantly smaller for multifidus muscle (P< 0.001), but significantly larger for erector spinae and psoas muscles (P< 0.001), in coronally-orientated group than those in sagittally-orientated group. The differences of bilateral GCSA and FCSA of multifidus muscle were significantly larger in facet tropism group than those in no facet tropism group (P= 0.009 and P= 0.019). Muscular asymmetries may develop in the lumbar region of the spine, which are associated with facet asymmetry in patients with chronic low back pain. Longitudinal studies are needed to understand the causal relationship between facet orientation and tropism and muscular asymmetry in future.

Microwave remote sensing of Saharan ergs and Amazon vegetation

NASA Astrophysics Data System (ADS)

Stephen, Haroon

This dissertation focuses on relating spaceborne microwave data to the geophysical characteristics of the Sahara desert and the Amazon vegetation. Radar and radiometric responses of the Saharan ergs are related to geophysical properties of sand formations and near surface winds. The spatial and temporal variability of the Amazon vegetation is studied using multi-frequency and multi-polarization data. The Sahara desert includes large expanses of sand dunes called ergs that are constantly reshaped by prevailing winds. Radar backscatter (sigma°) measurements observed at various incidence (theta) and azimuth (φ) angles from the NASA Scatterometer (NSCAT), the ERS scatterometer (ESCAT), the SeaWinds scatterometer aboard QuikScat (QSCAT), and the Precipitation Radar (TRMM-PR) aboard the Tropical Rain Monitoring Mission (TRMM) are used to model the sigma° response from sand dunes. Backscatter theta and φ variation depends upon the slopes and orientations of the dune slopes. Sand dunes are modeled as a composite of tilted rough facets, which are characterized by a probability distribution of tilt. The small ripples are modeled as cosinusoidal surface waves that contribute to the return signal at Bragg angles. The sigma° response is high at look angles equal to the mean tilts of the rough facets and is lower elsewhere. The modeled sigma° response is similar to NSCAT and ESCAT observations. sigma° also varies spatially and reflects the spatial inhomogeneity of the sand surface. A model incorporating the sigma° φ-modulation and spatial inhomogeneity is proposed. The maxima of the φ-modulation at theta = 33° reflect the orientation of the slip-sides on the sand surface. These slip-side orientations are consistent with the European Centre for Medium-Range Weather Forecasts wind directions spatially and temporally. Radiometric emissions from the ergs have strong dependence on the surface geometry. The radiometric temperature (Tb) of ergs is modeled as the weighted sum of the Tb from all the composite tilted rough facets. The dual polarization Tb measurements at 19 GHz and 37 GHz from the Special Sensor Microwave Imager (SSM/I) aboard the Defense Meteorological Satellite Program and the Tropical Rainfall Measuring Mission Microwave Imager are used to analyze the radiometric response of erg surfaces and compared to the model results. It is found that longitudinal and transverse dune fields are differentiable based on their polarization difference (DeltaTb) φ-modulation, which reflects type and orientation of dune facets. DeltaT b measurements at 19 GHz and 37 GHz provide consistent results. In the Amazon, sigma° measurements from Seasat A scatterometer (SASS), ESCAT, NSCAT, QSCAT and TRMM-PR; and Tb measurements from SSM/I are used to study the multi-spectral microwave response of vegetation. sigma° versus theta signatures of data combined from scatterometers and the precipitation radar depend upon vegetation density. The multi-frequency signatures of sigma° and Tb provide unique responses for different vegetation densities. sigma° and Tb spatial inhomogeneity is related to spatial geophysical characteristics. Temporal variability of the Amazon basin is studied using C-band ERS data and a Ku-band time series formed by SASS, NSCAT and QSCAT data. Although the central Amazon forest represents an area of very stable radar backscatter measurements, portions of the southern region exhibit backscatter changes over the past two decades.

Within-trait heterogeneity in age group differences in personality domains and facets: implications for the development and coherence of personality traits.

PubMed

Mõttus, René; Realo, Anu; Allik, Jüri; Esko, Tõnu; Metspalu, Andres; Johnson, Wendy

2015-01-01

The study investigated differences in the Five-Factor Model (FFM) domains and facets across adulthood. The main questions were whether personality scales reflected coherent units of trait development and thereby coherent personality traits more generally. These questions were addressed by testing if the components of the trait scales (items for facet scales and facets for domain scales) showed consistent age group differences. For this, measurement invariance (MI) framework was used. In a sample of 2,711 Estonians who had completed the NEO Personality Inventory 3 (NEO PI-3), more than half of the facet scales and one domain scale did not meet the criterion for weak MI (factor loading equality) across 12 age groups spanning ages from 18 to 91 years. Furthermore, none of the facet and domain scales met the criterion for strong MI (intercept equality), suggesting that items of the same facets and facets of the same domains varied in age group differences. When items were residualized for their respective facets, 46% of them had significant (p < 0.0002) residual age-correlations. When facets were residualized for their domain scores, a majority had significant (p < 0.002) residual age-correlations. For each domain, a series of latent factors were specified using random quarters of their items: scores of such latent factors varied notably (within domains) in correlations with age. We argue that manifestations of aetiologically coherent traits should show similar age group differences. Given this, the FFM domains and facets as embodied in the NEO PI-3 do not reflect aetiologically coherent traits.

Within-Trait Heterogeneity in Age Group Differences in Personality Domains and Facets: Implications for the Development and Coherence of Personality Traits

PubMed Central

Mõttus, René; Realo, Anu; Allik, Jüri; Esko, Tõnu; Metspalu, Andres; Johnson, Wendy

2015-01-01

The study investigated differences in the Five-Factor Model (FFM) domains and facets across adulthood. The main questions were whether personality scales reflected coherent units of trait development and thereby coherent personality traits more generally. These questions were addressed by testing if the components of the trait scales (items for facet scales and facets for domain scales) showed consistent age group differences. For this, measurement invariance (MI) framework was used. In a sample of 2,711 Estonians who had completed the NEO Personality Inventory 3 (NEO PI-3), more than half of the facet scales and one domain scale did not meet the criterion for weak MI (factor loading equality) across 12 age groups spanning ages from 18 to 91 years. Furthermore, none of the facet and domain scales met the criterion for strong MI (intercept equality), suggesting that items of the same facets and facets of the same domains varied in age group differences. When items were residualized for their respective facets, 46% of them had significant (p < 0.0002) residual age-correlations. When facets were residualized for their domain scores, a majority had significant (p < 0.002) residual age-correlations. For each domain, a series of latent factors were specified using random quarters of their items: scores of such latent factors varied notably (within domains) in correlations with age. We argue that manifestations of aetiologically coherent traits should show similar age group differences. Given this, the FFM domains and facets as embodied in the NEO PI-3 do not reflect aetiologically coherent traits. PMID:25751273

Lumbar facet anatomy changes in spondylolysis: a comparative skeletal study.

PubMed

Masharawi, Youssef; Dar, Gali; Peleg, Smadar; Steinberg, Nili; Alperovitch-Najenson, Dvora; Salame, Khalil; Hershkovitz, Israel

2007-07-01

Opinions differ as to the exact mechanism responsible for spondylolysis (SP) and whether individuals with specific morphological characteristics of the lumbar vertebral neural arch are predisposed to SP. The aim of our study was to reveal the association between SP and the architecture of lumbar articular facets and the inter-facet region. Using a Microscribe three-dimensional apparatus (Immersion Co., San Jose, CA, USA), length, width and depth of all articular facets and all inter-facet distances in the lumbar spine (L1-L5) were measured. From the Hamann-Todd Human Osteological Collection (Cleveland Museum of Natural History, OH, USA) 120 normal male skeletons with lumbar spines in the control group and 115 with bilateral SP at L5 were selected. Analysis of variance was employed to examine the differences between spondylolytic and normal spines. Three profound differences between SP and the norm appeared: (1) in individuals with SP, the size and shape of L4's neural arch had significantly greater inter-facet widths, significantly shorter inter-facet heights and significantly shorter and narrower articular facets; (2) only in the L4 vertebra in individuals with SP was the inferior inter-facet width greater in size than the superior inter-facet width of the vertebra below (L5) (38.7 mm versus 40 mm); (3) in all lumbar vertebrae, the right inferior articular facets in individuals with SP were flatter compared to the control group. Individuals with L4 "SP" characteristics are at a greater risk of developing fatigue fractures in the form of spondylolysis at L5.

Copolyimide Surface Modifying Agents for Particle Adhesion Mitigation

NASA Technical Reports Server (NTRS)

Wohl, Christopher J.; Connell, John W.

2011-01-01

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.

Removal of nitric oxide by the highly reactive anatase TiO2 (001) surface: a density functional theory study.

PubMed

Zhao, Wenwen; Tian, Feng Hui; Wang, Xiaobin; Zhao, Linghuan; Wang, Yun; Fu, Aiping; Yuan, Shuping; Chu, Tianshu; Xia, Linhua; Yu, Jimmy C; Duan, Yunbo

2014-09-15

In this paper, density functional theory (DFT) calculation was employed to study the adsorption of nitric oxide (NO) on the highly reactive anatase TiO2 (001) surface. For comparison, the adsorption of NO on the (101) surface was also considered. Different from the physical adsorption on the (101) surface, NO molecules are found to chemisorb on the TiO2 (001) surface. The twofold coordinate oxygen atoms (O2c) on the anatase (001) surface are the active sites. Where NO is oxidized into a nitrite species (NO2(-)) trapping efficiently on the surface, with one of the surface Ti5c-O2c bonds adjacent to the adsorption site broken. Our results, therefore, supply a theoretical guidance to remove NO pollutants using highly reactive anatase TiO2 (001) facets. Copyright © 2014 Elsevier Inc. All rights reserved.

First principles determination of dislocation properties.

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

Hamilton, John C.

2003-12-01

This report details the work accomplished on first principles determination of dislocation properties. It contains an introduction and three chapters detailing three major accomplishments. First, we have used first principle calculations to determine the shear strength of an aluminum twin boundary. We find it to be remarkably small ({approx}17 mJ/m{sup 2}). This unexpected result is explained and will likely pertain for many other grain boundaries. Second, we have proven that the conventional explanation for finite grain boundary facets is wrong for a particular aluminum grain boundary. Instead of finite facets being stabilized by grain boundary stress, we find them tomore » originate from kinetic effects. Finally we report on a new application of the Frenkel-Kontorova model to understand reconstructions of (100) type surfaces. In addition to the commonly accepted formation of rectangular dislocation arrays, we find numerous other possible solutions to the model including hexagonal reconstructions and a clock-rotated structure.« less

Antenna coupled photonic wire lasers

DOE PAGES

Kao, Tsung-Kao; Cai, Xiaowei; Lee, Alan W. M.; ...

2015-06-22

Slope efficiency (SE) is an important performance metric for lasers. In conventional semiconductor lasers, SE can be optimized by careful designs of the facet (or the modulation for DFB lasers) dimension and surface. However, photonic wire lasers intrinsically suffer low SE due to their deep sub-wavelength emitting facets. Inspired by microwave engineering techniques, we show a novel method to extract power from wire lasers using monolithically integrated antennas. These integrated antennas significantly increase the effective radiation area, and consequently enhance the power extraction efficiency. When applied to wire lasers at THz frequency, we achieved the highest single-side slope efficiency (~450more » mW/A) in pulsed mode for DFB lasers at 4 THz and a ~4x increase in output power at 3 THz compared with a similar structure without antennas. This work demonstrates the versatility of incorporating microwave engineering techniques into laser designs, enabling significant performance enhancements.« less

Thermoreflectance spectroscopy—Analysis of thermal processes in semiconductor lasers

NASA Astrophysics Data System (ADS)

Pierścińska, D.

2018-01-01

This review focuses on theoretical foundations, experimental implementation and an overview of experimental results of the thermoreflectance spectroscopy as a powerful technique for temperature monitoring and analysis of thermal processes in semiconductor lasers. This is an optical, non-contact, high spatial resolution technique providing high temperature resolution and mapping capabilities. Thermoreflectance is a thermometric technique based on measuring of relative change of reflectivity of the surface of laser facet, which provides thermal images useful in hot spot detection and reliability studies. In this paper, principles and experimental implementation of the technique as a thermography tool is discussed. Some exemplary applications of TR to various types of lasers are presented, proving that thermoreflectance technique provides new insight into heat management problems in semiconductor lasers and in particular, that it allows studying thermal degradation processes occurring at laser facets. Additionally, thermal processes and basic mechanisms of degradation of the semiconductor laser are discussed.

Mechanism of interactions between CMC binder and Si single crystal facets.

PubMed

Vogl, U S; Das, P K; Weber, A Z; Winter, M; Kostecki, R; Lux, S F

2014-09-02

Interactions of the active material particles with the binder are crucial in tailoring the properties of composite electrodes used in lithium-ion batteries. The dependency of the protonation degree of the carboxyl group in the carboxymethyl cellulose (CMC) structure on the pH value of the preparation solution was investigated by Fourier transform infrared spectroscopy (FTIR). Three different distinctive chemical states of CMC binder were chosen (protonated, deprotonated, and half-half), and their interactions with different silicon single crystal facets were investigated. The different Si surface orientations display distinct differences of strength of interactions with the CMC binder. The CMC/Si adhesion forces in solution and Si wettability of the silicon are also strongly dependent on the protonation degree of the CMC. This work provides an insight into the nature of these interactions, which determine the electrochemical performance of silicon composite electrodes.

Optical design of a high radiative flux solar furnace for Mexico

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

Riveros-Rosas, D.; Perez-Rabago, C.A.; Arancibia-Bulnes, C.A.

2010-05-15

In the present work, the optical design of a new high radiative flux solar furnace is described. Several optical configurations for the concentrator of the system have been considered. Ray tracing simulations were carried out in order to determine the concentrated radiative flux distributions in the focal zone of the system, for comparing the different proposals. The best configuration was chosen in terms of maximum peak concentration, but also in terms of economical and other practical considerations. It consists of an arrangement of 409 first surface spherical facets with hexagonal shape, mounted on a spherical frame. The individual orientation ofmore » the facets is corrected in order to compensate for aberrations. The design considers an intercepted power of 30 kW and a target peak concentration above 10,000 suns. The effect of optical errors was also considered in the simulations. (author)« less

Arrangement for multiplexing and intensity splitting light beams for interface into fiber optic cables

DOEpatents

Johnson, Steve A.

1990-01-01

An arrangement especially suitable for use in a laser apparatus for converting a plurality of different input light beams, for example copper vapor laser beams, into a plurality of substantially identical light beams is disclosed herein. This arrangement utilizes an optical mixing bar which is preferably integrally formed as a single unit and which includes a main body for mixing light therein, a flat input surface on one end of the main body, and a multi-faceted output face on the opposite end of the main body. This arrangement also includes means for directing the plurality of different input light beams onto the input face of the mixing base, whereby to cause the different beams to mix within the main body of the mixing bar and exit the latter from its multi-faceted output face as the desired plurality of substantially identical output beams.

Application of photogrammetry for analysis of occlusal contacts.

PubMed

Shigeta, Yuko; Hirabayashi, Rio; Ikawa, Tomoko; Kihara, Takuya; Ando, Eriko; Hirai, Shinya; Fukushima, Shunji; Ogawa, Takumi

2013-04-01

The conventional 2D-analysis methods for occlusal contacts provided limited information on tooth morphology. This present study aims to detect 3D positional information of occlusal contacts from 2D-photos via photogrammetry. We propose an image processing solution for analysis of occlusal contacts and facets via the black silicone method and a photogrammetric technique. The occlusal facets were reconstructed from a 2D-photograph data-set of inter-occlusal records into a 3D image via photogrammetry. The configuration of the occlusal surface was reproduced with polygons. In addition, the textures of the occlusal contacts were mapped to each polygon. DIFFERENCE FROM CONVENTIONAL METHODS: Constructing occlusal facets with 3D polygons from 2D-photos with photogrammetry was a defining characteristic of this image processing technique. It allowed us to better observe findings of the black silicone method. Compared with conventional 3D analysis using a 3D scanner, our 3D models did not reproduce the detail of the anatomical configuration. However, by merging the findings of the inter-occlusal record, the deformation of mandible and the displacement of periodontal ligaments under occlusal force were reflected in our model. EFFECT OR PERFORMANCE: Through the use of polygons in the conversion of 2D images to 3D images, we were able to define the relation between the location and direction of the occlusal contacts and facets, which was difficult to detect via conventional methods. Through our method of making a 3D polygon model, the findings of inter-occlusal records which reflected the jaw/teeth behavior under occlusal force could be observed 3-dimensionally. Copyright © 2012 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.

Incidence of the coracoclavicular joint in South African populations.

PubMed Central

Nalla, S; Asvat, R

1995-01-01

The presence of a diarthrotic coracoclavicular joint, as represented by an articular facet on the conoid tubercle of the clavicle and the superior surface of the coracoid process of the scapula, was investigated. The sample consisted of 60 white and 180 black South African (60 Sotho, 60 Xhosa and 60 Zulu) skeletons. Each group consisted of 30 male and 30 female skeletons. The presence of the articular facet was recorded as either bilateral, unilateral left or unilateral right. The effect of clavicular length, scapular size and first rib angle on the presence of the coracoclavicular joint was also investigated. The presence of the articular facet was noted in 23 (9.6%) of the 240 individuals studied. Of these 23 individuals, 6 (26.1%) were white and 17 (73.9%) were black. Males (56.5%) presented a higher incidence of this anomaly than females (43.5%). The articular facet occurred bilaterally in 47.9% (11/23), unilaterally on the left in 30.4% (7/23) and unilaterally on the right in 21.7% (5/23). Sexual, racial and tribal differences were not statistically significant. Individuals possessing the joint showed statistically significantly (P < 0.01) larger scapulae (increased border lengths and superior angles), longer clavicles and longer first ribs. No statistically significant differences in the first rib angles were observed between individuals who possessed the joint and those who did not, thus implying similar thoracic inlet size. It is proposed that the aforementioned morphometry of the scapulae, clavicles and first ribs may restrict associated movements of the scapulae, resulting in the development of the coracoclavicular joint. Images Fig. 4 Fig. 5 PMID:7559137

Nano-Crystalline Diamond Films with Pineapple-Like Morphology Grown by the DC Arcjet vapor Deposition Method

NASA Astrophysics Data System (ADS)

Li, Bin; Zhang, Qin-Jian; Shi, Yan-Chao; Li, Jia-Jun; Li, Hong; Lu, Fan-Xiu; Chen, Guang-Chao

2014-08-01

A nano-crystlline diamond film is grown by the dc arcjet chemical vapor deposition method. The film is characterized by scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD) and Raman spectra, respectively. The nanocrystalline grains are averagely with 80 nm in the size measured by XRD, and further proven by Raman and HRTEM. The observed novel morphology of the growth surface, pineapple-like morphology, is constructed by cubo-octahedral growth zones with a smooth faceted top surface and coarse side surfaces. The as-grown film possesses (100) dominant surface containing a little amorphous sp2 component, which is far different from the nano-crystalline film with the usual cauliflower-like morphology.

Lumbar Facet Tropism: A Comprehensive Review.

PubMed

Alonso, Fernando; Kirkpatrick, Christina M; Jeong, William; Fisahn, Christian; Usman, Sameera; Rustagi, Tarush; Loukas, Marios; Chapman, Jens R; Oskouian, Rod J; Tubbs, R Shane

2017-06-01

Scattered reports exist in the medical literature regarding facet tropism. However, this finding has had mixed conclusions regarding its origin and impact on the normal spine. We performed a literature review of the anatomy, embryology, biomechanics, and pathology related to lumbar facet tropism. Facet tropism is most commonly found at L4-L5 vertebral segments and there is some evidence that this condition may lead to facet degenerative spondylolisthesis, intervertebral disc disease, and other degenerative conditions. Long-term analyses of patients are necessary to elucidate relationships between associated findings and facet tropism. In addition, a universally agreed definition that is more precise should be developed for future investigative studies. Copyright © 2017 Elsevier Inc. All rights reserved.

Effect of ZnO facet on ethanol steam reforming over Co/ZnO

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

Yu, Ning; Zhang, He; Davidson, Stephen D.

2016-01-01

The effects of ZnO facets on ethanol steam reforming (ESR) were investigated over Co/ZnO catalysts synthesized using ZnO with different fractions of (10-10) non-polar facet. Co supported on ZnO with a higher fraction of (10-10) non-polar facet shows higher C-C cleavage activity and higher selectivity to CO2 (lower selectivity to CO) compared with Co supported on ZnO with less (10-10) non-polar facet exposed. The improved ethanol steam reforming performances are attributed to the high fraction of metallic Co stabilized by the ZnO (10-10) non-polar facet, which enhanced C-C cleavage and water-gas-shift (WGS) activities.

A new technique to transfer metallic nanoscale patterns to small and non-planar surfaces: Application to a fiber optic device for surface enhanced Raman scattering detection

NASA Astrophysics Data System (ADS)

Smythe, Elizabeth Jennings

This thesis focuses on the development of a bidirectional fiber optic probe for the detection of surface enhanced Raman scattering (SERS). One facet of this fiber-based probe featured an array of coupled optical antennas, which we designed to enhance the Raman signal of nearby analytes. When this array interacted with an analyte, it generated SERS signals specific to the chemical composition of the sample; some of these SERS signals coupled back into the fiber. We used the other facet of the probe to input light into the fiber and collect the SERS signals that coupled into the probe. In this dissertation, the development of the probe is broken into three sections: (i) characterization of antenna arrays, (ii) fabrication of the probe, and (iii) device measurements. In the first section we present a comprehensive study of metallic antenna arrays. We carried out this study to determine the effects of antenna geometry, spacing, and composition on the surface plasmon resonance (SPR) of a coupled antenna array; the wavelength range and strength of the SPR are functions of the shape and interactions of the antennas. The SPR of the array ultimately amplified the Raman signal of analytes and produced a measurable SERS signal, thus determination of the optimal array geometries for SERS generation was an important first step in the development of the SERS fiber probe. We then introduce a new technique developed to fabricate the SERS fiber probes. This technique involves transferring antenna arrays (created by standard lithographic methods) from a large silicon substrate to a fiber facet. We developed this fabrication technique to bypass many of the limitations presented by previously developed methods for patterning unconventional substrates (i.e. small and/or non-planar substrates), such as focused ion-beam milling and soft lithography. In the third section of this thesis, we present SERS measurements taken with the fiber probe. We constructed a measurement system to couple light into the probe and filter out background noise; this allowed simultaneous detection of multiple chemicals. Antenna array enhancement factor (EF) calculations are shown; these allowed us to determine that the probe efficiently collected SERS signals.

Morphology effect on photocatalytic activity in Bi3Fe0.5Nb1.5O9.

PubMed

Yin, Xiaofeng; Li, Xiaoning; Gu, Wen; Zou, Wei; Liu, Huan; Zhu, Liuyang; Fu, Zhengping; Lu, Yalin

2018-06-29

In this work, the Aurivillius-phase ferroelectric Bi 3 Fe 0.5 Nb 1.5 O 9 were synthesized by hydrothermal (BFNO-H) and solid state methods (BFNO-S), respectively. The BFNO-H shows a hierarchical morphology, which is stacked by intersecting single-crystal nanosheets with {001} and {110} exposed facets, while the BFNO-S shows disorganized micron-scale morphology. BFNO-H shows a much stronger photodegradation activity (10.4 times and 9.8 times) than BFNO-S in the visible-light photodegradation of rhodamine B (RhB) and salicylic acid. The higher photodegradation activity of BFNO-H was firstly ascribed to the hierarchical structure and the larger specific surface area (16.586 m 2 g -1 ) because a large specific surface area can increase reactive sites and shorten photogenerated carrier migration distance. However, after being normalized by the specific surface area, BFNO-H still performs better than BFNO-S, implying that the specific surface area is not the only factor that determines the photocatalytic activity. Considering that the built-in electric field originating from spontaneous polarization in Bi 3 Fe 0.5 Nb 1.5 O 9 has existed in both ab plane and c direction, it matches well with the {001} and {110} exposed facets of BFNO-H nanosheets. This appropriate matching in BFNO-H nanosheets may improve the separation and transmission of photogenerated electron-hole pairs and further enhance its photocatalytic activity. Moreover, the trapping experiments reveals that holes (h + ) are the main active species and hole-derived oxidation is the main redox reaction during photodegradation of organic pollutions.

An end of service life assessment of PMMA lenses from veteran concentrator photovoltaic systems

DOE PAGES

Miller, David C.; Khonkar, Hussameldin I.; Herrero, Rebeca; ...

2017-04-04

The optical performance of poly(methyl methacrylate) lenses from veteran concentrator photovoltaic modules was examined after the end of their service life. Lenses from the Martin-Marietta and Intersol module designs were examined from the 'Solar Village' site near Riyadh, Saudi Arabia, as well as the Phoenix Sky Harbor airport, followed by the Arizona Public Service Solar Test and Research (APS-STaR) center in Tempe, Arizona. The various lens specimens were deployed for 20, 27, and 22 years, respectively. Optical characterizations included lens efficiency (Solar Simulator instrument), material transmittance and haze (of coupons cut from veteran lenses, then measured again after their facetedmore » back surface was polished, and then measured again after the incident front surface was polished), and direct transmittance (as a function of detector's acceptance angle, using the Very Low Angular Beam Spread ('VLABS') instrument). Lens efficiency measurements compared the central region to the entire lens, also using hot and cold mirror measurements to diagnose differences in performance. A series of subsequent characterizations was performed because a decrease in performance of greater than 10% was observed for some of the veteran lenses. The optimal focal distance of the lenses was quantified using the Solar Simulator, and then correlated to lens curvature using a recently developed measurement technique. Surface roughness was examined using atomic force microscopy and scanning electron microscopy. Facet geometry (tip and valley radius) was quantified on cross-sectioned specimens. As a result, molecular weight was compared between the incident and faceted surfaces of the lenses.« less

Reflectance, illumination, and appearance in color constancy

PubMed Central

McCann, John J.; Parraman, Carinna; Rizzi, Alessandro

2013-01-01

We studied color constancy using a pair of identical 3-D Color Mondrian displays. We viewed one 3-D Mondrian in nearly uniform illumination, and the other in directional, nonuniform illumination. We used the three dimensional structures to modulate the light falling on the painted surfaces. The 3-D structures in the displays were a matching set of wooden blocks. Across Mondrian displays, each corresponding facet had the same paint on its surface. We used only 6 chromatic, and 5 achromatic paints applied to 104 block facets. The 3-D blocks add shadows and multiple reflections not found in flat Mondrians. Both 3-D Mondrians were viewed simultaneously, side-by-side. We used two techniques to measure correlation of appearance with surface reflectance. First, observers made magnitude estimates of changes in the appearances of identical reflectances. Second, an author painted a watercolor of the 3-D Mondrians. The watercolor's reflectances quantified the changes in appearances. While constancy generalizations about illumination and reflectance hold for flat Mondrians, they do not for 3-D Mondrians. A constant paint does not exhibit perfect color constancy, but rather shows significant shifts in lightness, hue and chroma in response to the structure in the nonuniform illumination. Color appearance depends on the spatial information in both the illumination and the reflectances of objects. The spatial information of the quanta catch from the array of retinal receptors generates sensations that have variable correlation with surface reflectance. Models of appearance in humans need to calculate the departures from perfect constancy measured here. This article provides a dataset of measurements of color appearances for computational models of sensation. PMID:24478738

Surface properties and surficial deposits on Venus: New results from Magellan radar altimeter data analysis

NASA Astrophysics Data System (ADS)

Bondarenko, Nataliya V.; Kreslavsky, Mikhail A.

2018-07-01

Microwave remote sensing data acquired with Magellan Venus orbiter are the main source of information about the surface of the planet. We analyze variability of the backscattering function (dependence of radar cross-section on incidence angle) for steep incidence angles 0.25°-4.75° in the 75°N-55°S latitude zone with data from the Magellan radar altimeter at 12.6 cm wavelength. We show that all variability of the backscattering function can be described by three parameters, describing (1) surface reflectivity, (2) relative proportion of horizontal facets, and (3) general roughness. Analysis of maps of these parameters revealed that surficial deposits, for example, microdune fields, are abundant on Venus even in places, where they are not readily seen in the synthetic aperture radar images. Properties of surficial deposits rather than original volcanic flow roughness define the shape of the backscattering function on the majority of regional plains. A large radar-dark flow in Bereghinia Planitia has anomalously high proportion of horizontal facets, which is consistent with it being formed by a relatively recent plain-forming volcanic episode. Some crater-associated radar-dark diffuse features and splotches are also characterized by increased proportion of horizontal faces, which indicate the presence of mantles deposited from fluidized granular material. The backscattering functions of the anomalous radar-bright material of mountaintops are more consistent with the strong internal scattering hypothesis rather than the exotic surficial material hypothesis. Obtained maps can be useful for planning future lander missions to sites with access to surface material with known provenance.

Morphology effect on photocatalytic activity in Bi3Fe0.5Nb1.5O9

NASA Astrophysics Data System (ADS)

Yin, Xiaofeng; Li, Xiaoning; Gu, Wen; Zou, Wei; Liu, Huan; Zhu, Liuyang; Fu, Zhengping; Lu, Yalin

2018-06-01

In this work, the Aurivillius-phase ferroelectric Bi3Fe0.5Nb1.5O9 were synthesized by hydrothermal (BFNO-H) and solid state methods (BFNO-S), respectively. The BFNO-H shows a hierarchical morphology, which is stacked by intersecting single-crystal nanosheets with {001} and {110} exposed facets, while the BFNO-S shows disorganized micron-scale morphology. BFNO-H shows a much stronger photodegradation activity (10.4 times and 9.8 times) than BFNO-S in the visible-light photodegradation of rhodamine B (RhB) and salicylic acid. The higher photodegradation activity of BFNO-H was firstly ascribed to the hierarchical structure and the larger specific surface area (16.586 m2 g‑1) because a large specific surface area can increase reactive sites and shorten photogenerated carrier migration distance. However, after being normalized by the specific surface area, BFNO-H still performs better than BFNO-S, implying that the specific surface area is not the only factor that determines the photocatalytic activity. Considering that the built-in electric field originating from spontaneous polarization in Bi3Fe0.5Nb1.5O9 has existed in both ab plane and c direction, it matches well with the {001} and {110} exposed facets of BFNO-H nanosheets. This appropriate matching in BFNO-H nanosheets may improve the separation and transmission of photogenerated electron–hole pairs and further enhance its photocatalytic activity. Moreover, the trapping experiments reveals that holes (h +) are the main active species and hole-derived oxidation is the main redox reaction during photodegradation of organic pollutions.

An end of service life assessment of PMMA lenses from veteran concentrator photovoltaic systems

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

Miller, David C.; Khonkar, Hussameldin I.; Herrero, Rebeca

The optical performance of poly(methyl methacrylate) lenses from veteran concentrator photovoltaic modules was examined after the end of their service life. Lenses from the Martin-Marietta and Intersol module designs were examined from the 'Solar Village' site near Riyadh, Saudi Arabia, as well as the Phoenix Sky Harbor airport, followed by the Arizona Public Service Solar Test and Research (APS-STaR) center in Tempe, Arizona. The various lens specimens were deployed for 20, 27, and 22 years, respectively. Optical characterizations included lens efficiency (Solar Simulator instrument), material transmittance and haze (of coupons cut from veteran lenses, then measured again after their facetedmore » back surface was polished, and then measured again after the incident front surface was polished), and direct transmittance (as a function of detector's acceptance angle, using the Very Low Angular Beam Spread ('VLABS') instrument). Lens efficiency measurements compared the central region to the entire lens, also using hot and cold mirror measurements to diagnose differences in performance. A series of subsequent characterizations was performed because a decrease in performance of greater than 10% was observed for some of the veteran lenses. The optimal focal distance of the lenses was quantified using the Solar Simulator, and then correlated to lens curvature using a recently developed measurement technique. Surface roughness was examined using atomic force microscopy and scanning electron microscopy. Facet geometry (tip and valley radius) was quantified on cross-sectioned specimens. As a result, molecular weight was compared between the incident and faceted surfaces of the lenses.« less

Foundations of reusable and interoperable facet models using category theory

PubMed Central

2016-01-01

Faceted browsing has become ubiquitous with modern digital libraries and online search engines, yet the process is still difficult to abstractly model in a manner that supports the development of interoperable and reusable interfaces. We propose category theory as a theoretical foundation for faceted browsing and demonstrate how the interactive process can be mathematically abstracted. Existing efforts in facet modeling are based upon set theory, formal concept analysis, and light-weight ontologies, but in many regards, they are implementations of faceted browsing rather than a specification of the basic, underlying structures and interactions. We will demonstrate that category theory allows us to specify faceted objects and study the relationships and interactions within a faceted browsing system. Resulting implementations can then be constructed through a category-theoretic lens using these models, allowing abstract comparison and communication that naturally support interoperability and reuse. PMID:27942248

Formulation and Application of the Generalized Multilevel Facets Model

ERIC Educational Resources Information Center

Wang, Wen-Chung; Liu, Chih-Yu

2007-01-01

In this study, the authors develop a generalized multilevel facets model, which is not only a multilevel and two-parameter generalization of the facets model, but also a multilevel and facet generalization of the generalized partial credit model. Because the new model is formulated within a framework of nonlinear mixed models, no efforts are…

Job Stress, Employee Health, and Organizational Effectiveness: A Facet Analysis, Model, and Literature Review.

ERIC Educational Resources Information Center

Beehr, Terry A.; Newman, John E.

1978-01-01

The empirical research on job stress and employee health is reviewed within the context of six facets (environmental, personal, process, human consequences, organizational consequences, and time) of a seven facet conceptualization of the job stress-employee health research domain. Models are proposed for tying the facets together. (Author/SJL)

Impact of Growth in the Universe of Subjects on Classification.

ERIC Educational Resources Information Center

Ranganathan, Shiyali Ramamritam

The development of the removal of rigidity in library classification is traced from the Enumerative Classification of DC (1876) through the Nearly-Faceted Classification of UDC (1896), the rigidly, though fully faceted version of CC (1933), the generalized faceted structure of version 2 of CC (1949), down to the Freely Faceted Classification of…

Quantitative in vivo MRI evaluation of lumbar facet joints and intervertebral discs using axial T2 mapping.

PubMed

Stelzeneder, David; Messner, Alina; Vlychou, Marianna; Welsch, Goetz H; Scheurecker, Georg; Goed, Sabine; Pieber, Karin; Pflueger, Verena; Friedrich, Klaus M; Trattnig, Siegfried

2011-11-01

To assess the feasibility of T2 mapping of lumbar facet joints and intervertebral discs in a single imaging slab and to compare the findings with morphological grading. Sixty lumbar spine segments from 10 low back pain patients and 5 healthy volunteers were examined by axial T2 mapping and morphological MRI at 3.0 Tesla. Regions of interest were drawn on a single slice for the facet joints and the intervertebral discs (nucleus pulposus, anterior and posterior annulus fibrosus). The Weishaupt grading was used for facet joints and the Pfirrmann score was used for morphological disc grading ("normal" vs. "abnormal" discs). The inter-rater agreement was excellent for the facet joint T2 evaluation (r = 0.85), but poor for the morphological Weishaupt grading (kappa = 0.15). The preliminary results show similar facet joint T2 values in segments with normal and abnormal Pfirrmann scores. There was no difference in mean T2 values between facet joints in different Weishaupt grading groups. Facet joint T2 values showed a weak correlation with T2 values of the posterior annulus (r = 0.32) This study demonstrates the feasibility of a combined T2 mapping approach for the facet joints and intervertebral discs using a single axial slab.

Proximal attrition facets: morphometric, demographic, and aging characteristics.

PubMed

Sarig, Rachel; Hershkovitz, Israel; Shvalb, Nir; Sella-Tunis, Tatiana; May, Hila; Vardimon, Alexander D

2014-08-01

Although interproximal attrition is considered to be limited in modern populations, it has important clinical implications. However, in contrast to occlusal attrition, proximal attrition receives limited scientific attention. The main purpose of the current study was to fill this void. Seven-hundred and sixty-five teeth were collected from 255 skulls of subjects 18-75 yr of age. For each individual, three mandibular teeth (the first and second premolars and the first molar) were examined for proximal attrition facets (PAFs). The results provide detailed information on the size, shape, and location of the facets according to age cohort, gender, and ethnicity. The validity of the method used to measure the facets was also examined. The major findings were as follows: PAFs are usually located on the upper half of the crown proximal aspect; in each tooth, the mesial facet is more lingually positioned and the distal facet is more buccally positioned; the majority of the facets are subrectangular in shape; the size of the facets tends to increase in an anteroposterior direction (from premolars to molars); and facet size and location are age- and sex-dependent and ethnicity-independent. It is our recommendation that dentists bear in mind that interproximal attrition is a dynamic, long-term process and needs to be considered in many clinical scenarios. © 2014 Eur J Oral Sci.

FACETS: multi-faceted functional decomposition of protein interaction networks

PubMed Central

Seah, Boon-Siew; Bhowmick, Sourav S.; Forbes Dewey, C.

2012-01-01

Motivation: The availability of large-scale curated protein interaction datasets has given rise to the opportunity to investigate higher level organization and modularity within the protein–protein interaction (PPI) network using graph theoretic analysis. Despite the recent progress, systems level analysis of high-throughput PPIs remains a daunting task because of the amount of data they present. In this article, we propose a novel PPI network decomposition algorithm called FACETS in order to make sense of the deluge of interaction data using Gene Ontology (GO) annotations. FACETS finds not just a single functional decomposition of the PPI network, but a multi-faceted atlas of functional decompositions that portray alternative perspectives of the functional landscape of the underlying PPI network. Each facet in the atlas represents a distinct interpretation of how the network can be functionally decomposed and organized. Our algorithm maximizes interpretative value of the atlas by optimizing inter-facet orthogonality and intra-facet cluster modularity. Results: We tested our algorithm on the global networks from IntAct, and compared it with gold standard datasets from MIPS and KEGG. We demonstrated the performance of FACETS. We also performed a case study that illustrates the utility of our approach. Contact: seah0097@ntu.edu.sg or assourav@ntu.edu.sg Supplementary information: Supplementary data are available at the Bioinformatics online. Availability: Our software is available freely for non-commercial purposes from: http://www.cais.ntu.edu.sg/∼assourav/Facets/ PMID:22908217

Broad Bandwidth or High Fidelity? Evidence from the Structure of Genetic and Environmental Effects on the Facets of the Five Factor Model

PubMed Central

Briley, Daniel A.; Tucker-Drob, Elliot M.

2017-01-01

The Five Factor Model (FFM) of personality is well-established at the phenotypic level, but much less is known about the coherence of the genetic and environmental influences within each personality domain. Univariate behavioral genetic analyses have consistently found the influence of additive genes and nonshared environment on multiple personality facets, but the extent to which genetic and environmental influences on specific facets reflect more general influences on higher order factors is less clear. We applied a multivariate quantitative-genetic approach to scores on the CPI-Big Five facets for 490 monozygotic and 317 dizygotic twins who took part in the National Merit Twin Study. Our results revealed a complex genetic structure for facets composing all five factors, with both domain-general and facet-specific genetic and environmental influences. Models that required common genetic and environmental influences on each facet to occur by way of effects on a higher order trait did not fit as well as models allowing for common genetic and environmental effects to act directly on the facets for three of the Big Five domains. These results add to the growing body of literature indicating that important variation in personality occurs at the facet level which may be overshadowed by aggregating to the trait level. Research at the facet level, rather than the factor level, is likely to have pragmatic advantages in future research on the genetics of personality. PMID:22695681

Factors affecting results of fluoroscopy-guided facet joint injection: Probable differences in the outcome of treatment between pure facet joint hypertrophy and concomitant diseases.

PubMed

Albayrak, Akif; Ozkul, Baris; Balioglu, Mehmet Bulent; Atici, Yunus; Gultekin, Muhammet Zeki; Albayrak, Merih Dilan

2016-01-01

Retrospective cohort study. Facet joints are considered a common source of chronic low-back pain. To determine whether pathogens related to the facet joint arthritis have any effect on treatment failure. Facet joint injection was applied to 94 patients treated at our hospital between 2011 and 2012 (mean age 59.5 years; 80 women and 14 men). For the purpose of analysis, the patients were divided into two groups. Patients who only had facet hypertrophy were placed in group A (47 patients, 41 women and 6 men, mean age 55.3 years) and patients who had any additional major pathology to facet hypertrophy were placed in group B (47 patients, 39 women and 8 men, mean age 58.9 years). Injections were applied around the facet joint under surgical conditions utilizing fluoroscopy device guidance. A mixture of methylprednisolone and lidocaine was used as the injection ingredient. In terms of Oswestry Disability Index (ODI) and visual analog scale (VAS) scores, no significant difference was found between preinjection and immediate postinjection values in both groups, and the scores of group A patients were significantly lower (P < 0.005) compared with that of group B patients at the end of the third, sixth, and twelfth month. For low-back pain caused by facet hypertrophy, steroid injection around the facet joint is an effective treatment, but if there is an existing major pathology, it is not as effective.

Cervical facet oedema: prevalence, correlation to symptoms, and follow-up imaging.

PubMed

Nevalainen, M T; Foran, P J; Roedl, J B; Zoga, A C; Morrison, W B

2016-06-01

To evaluate the prevalence of cervical facet oedema in patients referred for magnetic resonance imaging (MRI) to investigate neck pain and/or radiculopathy, and to investigate whether there is a correlation between the presence of oedema and patients' symptoms. A retrospective report review of 1885 patients undergoing cervical spine MRI between July 2008 and June 2015 was performed. Exclusion criteria included acute trauma, surgery, neoplastic disease, or infection in the cervical spine. One hundred and seventy-three MRI studies with cervical facet oedema were evaluated by each of the two radiologists. In these patients, the grade of bone marrow oedema (BMO) and corresponding neuroforaminal narrowing at the cervical facets was assessed. Correlation with symptoms was performed based on pre-MRI questionnaire. The prevalence of cervical facet oedema was 9%; the most commonly affected levels were C3-4, C4-5, and C2-3. A total of 202 cervical facets were evaluated: mild BMO was seen in 35%, moderate in 41%, and severe in 24% of cases. Surrounding soft-tissue oedema was observed in 36%, 69%, and 92% of the BMO grades, respectively. The correlations between unilateral radiculopathy and ipsilateral facet BMO grades were 79%, 83%, and 73% (chi-square, p<0.001), respectively. Furthermore, neuroforaminal narrowing on the corresponding level was found in 35%, 38%, and 11% of cases, respectively. At follow-up imaging, facet oedema was most likely to remain unchanged or to decrease. The prevalence of cervical facet oedema is 9%. Cervical facet oedema is associated with ipsilateral radiculopathy. Neuroforaminal narrowing, however, is not associated with facet oedema. Copyright © 2016 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Lumbar facet anatomy changes in spondylolysis: a comparative skeletal study

PubMed Central

Dar, Gali; Peleg, Smadar; Steinberg, Nili; Alperovitch-Najenson, Dvora; Salame, Khalil; Hershkovitz, Israel

2007-01-01

Opinions differ as to the exact mechanism responsible for spondylolysis (SP) and whether individuals with specific morphological characteristics of the lumbar vertebral neural arch are predisposed to SP. The aim of our study was to reveal the association between SP and the architecture of lumbar articular facets and the inter-facet region. Methods: Using a Microscribe three-dimensional apparatus (Immersion Co., San Jose, CA, USA), length, width and depth of all articular facets and all inter-facet distances in the lumbar spine (L1–L5) were measured. From the Hamann-Todd Human Osteological Collection (Cleveland Museum of Natural History, OH, USA) 120 normal male skeletons with lumbar spines in the control group and 115 with bilateral SP at L5 were selected. Analysis of variance was employed to examine the differences between spondylolytic and normal spines. Results: Three profound differences between SP and the norm appeared: (1) in individuals with SP, the size and shape of L4’s neural arch had significantly greater inter-facet widths, significantly shorter inter-facet heights and significantly shorter and narrower articular facets; (2) only in the L4 vertebra in individuals with SP was the inferior inter-facet width greater in size than the superior inter-facet width of the vertebra below (L5) (38.7 mm versus 40 mm); (3) in all lumbar vertebrae, the right inferior articular facets in individuals with SP were flatter compared to the control group. Conclusions: Individuals with L4 “SP” characteristics are at a greater risk of developing fatigue fractures in the form of spondylolysis at L5. PMID:17440753

Biomechanical evaluation of the impact of various facet joint lesions on the primary stability of anterior plate fixation in cervical dislocation injuries: a cadaver study: Laboratory investigation.

PubMed

Oberkircher, Ludwig; Born, Sebastian; Struewer, Johannes; Bliemel, Christopher; Buecking, Benjamin; Wack, Christina; Bergmann, Martin; Ruchholtz, Steffen; Krüger, Antonio

2014-10-01

Injuries of the subaxial cervical spine including facet joints and posterior ligaments are common. Potential surgical treatments consist of anterior, posterior, or anterior-posterior fixation. Because each approach has its advantages and disadvantages, the best treatment is debated. This biomechanical cadaver study compared the effect of different facet joint injuries on primary stability following anterior plate fixation. Fractures and plate fixation were performed on 15 fresh-frozen intact cervical spines (C3-T1). To simulate a translation-rotation injury in all groups, complete ligament rupture and facet dislocation were simulated by dissecting the entire posterior and anterior ligament complex between C-4 and C-5. In the first group, the facet joints were left intact. In the second group, one facet joint between C-4 and C-5 was removed and the other side was left intact. In the third group, both facet joints between C-4 and C-5 were removed. The authors next performed single-level anterior discectomy and interbody grafting using bone material from the respective thoracic vertebral bodies. An anterior cervical locking plate was used for fixation. Continuous loading was performed using a servohydraulic test bench at 2 N/sec. The mean load failure was measured when the implant failed. In the group in which both facet joints were intact, the mean load failure was 174.6 ± 46.93 N. The mean load failure in the second group where only one facet joint was removed was 127.8 ± 22.83 N. In the group in which both facet joints were removed, the mean load failure was 73.42 ± 32.51 N. There was a significant difference between the first group (both facet joints intact) and the third group (both facet joints removed) (p < 0.05, Kruskal-Wallis test). In this cadaver study, primary stability of anterior plate fixation for dislocation injuries of the subaxial cervical spine was dependent on the presence of the facet joints. If the bone in one or both facet joints is damaged in the clinical setting, anterior plate fixation in combination with bone grafting might not provide sufficient stabilization; additional posterior stabilization may be needed.

American Jurassic symmetrodonts and Rhaetic "pantotheres".

PubMed

Crompton, A W; Jenkins, F A

1967-02-24

The molar morphology of the symmetrodonts Tinodon and Eurylambda from the late Jurassic of North America is virtually identical to that of so-called "pantotheres" from the Rhaetic of Wales. Therefore a primitive symmetrodont molar pattern was probably present in the phylogeny of pantotherian and tribosphenic molars. Occlusion of Tinodon and Eurylambda produced complex wear facets unlike the simple trigon-trigonid shear surfaces of Spalacotherium and Peralestes.

On the dissolution properties of GaAs in Ga

NASA Technical Reports Server (NTRS)

Davidson, M. C.; Moynahan, A. H.

1977-01-01

The dissolution of GaAs in Ga was studied to determine the nature and cause of faceting effects. Ga was allowed to dissolve single crystalline faces under isothermal conditions. Of the crystalline planes with low number indices, only the (100) surface showed a direct correlation of dissolution sites to dislocations. The type of dissolution experienced depended on temperature, and there were three distinct types of behavior.

A new and efficient theoretical model to analyze chirped grating distributed feedback lasers

NASA Astrophysics Data System (ADS)

Arif, Muhammad

Threshold conditions of a distributed feedback (DFB) laser with a linearly chirped grating are investigated using a new and efficient method. DFB laser with chirped grating is found to have significant effects on the lasing characteristics. The coupled wave equations for these lasers are derived and solved using a power series method to obtain the threshold condition. A Newton- Raphson routine is used to solve the threshold conditions numerically to obtain threshold gain and lasing wavelengths. To prove the validity of this model, it is applied to both conventional index-coupled and complex- coupled DFB lasers. The threshold gain margins are calculated as functions of the ratio of the gain coupling to index coupling (|κg|/|κ n|), and the phase difference between the index and gain gratings. It was found that for coupling coefficient |κ|l < 0.9, the laser shows a mode degeneracy at particular values of the ratio |κ g|/|κn|, for cleaved facets. We found that at phase differences π/2 and 3π/2, between the gain and index grating, for an AR-coated complex-coupled laser, the laser becomes multimode and a different mode starts to lase. We also studied the effect of the facet reflectivity (both magnitude and phase) on the gain margin of a complex- coupled DFB laser. Although, the gain margin varies slowly with the magnitude of the facet reflectivity, it shows large variations as a function of the phase. Spatial hole burning was found to be minimum at phase difference nπ, n = 0, 1, ... and maximum at phase differences π/2 and 3π/2. The single mode gain margin of an index-coupled linearly chirped CG-DFB is calculated for different chirping factors and coupling constants. We found that there is clearly an optimum chirping for which the single mode gain margin is maximum. The gain margins were calculated also for different positions of the cavity center. The effect of the facet reflectivities and their phases on the gain margin was investigated. We found the gain margin is maximum and the Spatial Hole Burning (SHB) is minimum for the cavity center at the middle of the laser cavity. Effect of chirping on the threshold gain, gain margin and spatial hole burning (SHB) for different parameters, such as the coupling coefficients, facet reflectivities, etc., of these lasers are studied. Single mode yield of these lasers are calculated and compared with that of a uniform grating DFB laser.

Engineering the internal surfaces of three-dimensional nanoporous catalysts by surfactant-modified dealloying.

PubMed

Wang, Zhili; Liu, Pan; Han, Jiuhui; Cheng, Chun; Ning, Shoucong; Hirata, Akihiko; Fujita, Takeshi; Chen, Mingwei

2017-10-20

Tuning surface structures by bottom-up synthesis has been demonstrated as an effective strategy to improve the catalytic performances of nanoparticle catalysts. Nevertheless, the surface modification of three-dimensional nanoporous metals, fabricated by a top-down dealloying approach, has not been achieved despite great efforts devoted to improving the catalytic performance of three-dimensional nanoporous catalysts. Here we report a surfactant-modified dealloying method to tailor the surface structure of nanoporous gold for amplified electrocatalysis toward methanol oxidation and oxygen reduction reactions. With the assistance of surfactants, {111} or {100} faceted internal surfaces of nanoporous gold can be realized in a controllable manner by optimizing dealloying conditions. The surface modified nanoporous gold exhibits significantly enhanced electrocatalytic activities in comparison with conventional nanoporous gold. This study paves the way to develop high-performance three-dimensional nanoporous catalysts with a tunable surface structure by top-down dealloying for efficient chemical and electrochemical reactions.

Phase-field model of vapor-liquid-solid nanowire growth

NASA Astrophysics Data System (ADS)

Wang, Nan; Upmanyu, Moneesh; Karma, Alain

2018-03-01

We present a multiphase-field model to describe quantitatively nanowire growth by the vapor-liquid-solid (VLS) process. The free-energy functional of this model depends on three nonconserved order parameters that distinguish the vapor, liquid, and solid phases and describe the energetic properties of various interfaces, including arbitrary forms of anisotropic γ plots for the solid-vapor and solid-liquid interfaces. The evolution equations for those order parameters describe basic kinetic processes including the rapid (quasi-instantaneous) equilibration of the liquid catalyst to a droplet shape with constant mean curvature, the slow incorporation of growth atoms at the droplet surface, and crystallization within the droplet. The standard constraint that the sum of the phase fields equals unity and the conservation of the number of catalyst atoms, which relates the catalyst volume to the concentration of growth atoms inside the droplet, are handled via separate Lagrange multipliers. An analysis of the model is presented that rigorously maps the phase-field equations to a desired set of sharp-interface equations for the evolution of the phase boundaries under the constraint of force balance at three-phase junctions (triple points) given by the Young-Herring relation that includes torque term related to the anisotropy of the solid-liquid and solid-vapor interface excess free energies. Numerical examples of growth in two dimensions are presented for the simplest case of vanishing crystalline anisotropy and the more realistic case of a solid-liquid γ plot with cusped minima corresponding to two sets of (10 ) and (11 ) facets. The simulations reproduce many of the salient features of nanowire growth observed experimentally, including growth normal to the substrate with tapering of the side walls, transitions between different growth orientations, and crawling growth along the substrate. They also reproduce different observed relationships between the nanowire growth velocity and radius depending on the growth condition. For the basic normal growth mode, the steady-state solid-liquid interface tip shape consists of a main facet intersected by two truncated side facets ending at triple points. The ratio of truncated and main facet lengths are in quantitative agreement with the prediction of sharp-interface theory that is developed here for faceted nanowire growth in two dimensions.

Crystal Structures, Surface Stability, and Water Adsorption Energies of La-Bastnäsite via Density Functional Theory and Experimental Studies

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

Srinivasan, Sriram Goverapet; Shivaramaiah, Radha; Kent, Paul R. C.

2016-07-11

Bastnasite is a fluoro-carbonate mineral that is the largest source of rare earth elements such as Y, La and Ce. With increasing demand for REE in many emerging technologies, there is an urgent need for improving the efficiency of ore beneficiation by froth flotation. In order to design improved flotation agents that can selectively bind to the mineral surface, a fundamental understanding of the bulk and surface properties of bastnasite is essential. Density functional theory calculations using the PBEsol exchange correlation functional and the DFT-D3 dispersion correction reveal that the most stable form of La bastnsite is isomorphic to themore » structure of Ce bastnasite belonging to the P2c space group, while the Inorganic Crystal Structure Database structure in the P2m space group is ca. 11.3 kJ/mol higher in energy per LaFCO 3 formula unit. We report powder X-ray diffraction measurements on synthetic of La bastnasite to support these theoretical findings. Six different surfaces are studied by DFT, namely [100], [0001], [101], [102], [104] and [112]. Among these, the [100] surface is the most stable with a surface energy of 0.73 J/m 2 in vacuum and 0.45 J/m 2 in aqueous solution. We predicted the shape of a La bastnasite nanoparticle via thermodynamic Wulff construction to be a hexagonal prism with [100] and [0001] facets, chiseled at its ends by the [101] and [102] facets. The average surface energy of the nanoparticle in the gas phase is estimated to be 0.86 J/m 2, in good agreement with a value of 1.11 J/m 2 measured by calorimetry. The calculated adsorption energy of a water molecule varies widely with the surface plane and specific adsorption sites on a given surface. Moreover, the first layer of water molecules is predicted to adsorb strongly on the La-bastnasite surface, in agreement with water adsorption calorimetry experiments. Our work provides an important step towards a detailed atomistic understanding of the bastnasite water interface and designing collector molecules that can bind specifically to bastnasite.« less

Improving Personality Facet Scores with Multidimensional Computer Adaptive Testing: An Illustration with the Neo Pi-R

ERIC Educational Resources Information Center

Makransky, Guido; Mortensen, Erik Lykke; Glas, Cees A. W.

2013-01-01

Narrowly defined personality facet scores are commonly reported and used for making decisions in clinical and organizational settings. Although these facets are typically related, scoring is usually carried out for a single facet at a time. This method can be ineffective and time consuming when personality tests contain many highly correlated…

Surgical Tips to Preserve the Facet Joint during Microdiscectomy

PubMed Central

Park, Man-Kyu; Cho, Dae-Chul; Sung, Joo-Kyung

2013-01-01

Lumbar microdiscectomy (MD) is the gold standard for treatment of lumbar disc herniation. Generally, the surgeon attempts to protect the facet joint in hopes of avoiding postoperative pain/instability and secondary degenerative arthropathy. We believe that preserving the facet joint is especially important in young patients, owing to their life expectancy and activity. However, preserving the facet joint is not easy during lumbar MD. We propose several technical tips (superolateral extension of conventional laminotomy, oblique drilling for laminotomy, and additional foraminotomy) for facet joint preservation during lumbar MD. PMID:24294466

Near-Infrared-Emitting CuInS2/ZnS Dot-in-Rod Colloidal Heteronanorods by Seeded Growth

PubMed Central

2018-01-01

Synthesis protocols for anisotropic CuInX2 (X = S, Se, Te)-based heteronanocrystals (HNCs) are scarce due to the difficulty in balancing the reactivities of multiple precursors and the high solid-state diffusion rates of the cations involved in the CuInX2 lattice. In this work, we report a multistep seeded growth synthesis protocol that yields colloidal wurtzite CuInS2/ZnS dot core/rod shell HNCs with photoluminescence in the NIR (∼800 nm). The wurtzite CuInS2 NCs used as seeds are obtained by topotactic partial Cu+ for In3+ cation exchange in template Cu2–xS NCs. The seed NCs are injected in a hot solution of zinc oleate and hexadecylamine in octadecene, 20 s after the injection of sulfur in octadecene. This results in heteroepitaxial growth of wurtzite ZnS primarily on the Sulfur-terminated polar facet of the CuInS2 seed NCs, the other facets being overcoated only by a thin (∼1 monolayer) shell. The fast (∼21 nm/min) asymmetric axial growth of the nanorod proceeds by addition of [ZnS] monomer units, so that the polarity of the terminal (002) facet is preserved throughout the growth. The delayed injection of the CuInS2 seed NCs is crucial to allow the concentration of [ZnS] monomers to build up, thereby maximizing the anisotropic heteroepitaxial growth rates while minimizing the rates of competing processes (etching, cation exchange, alloying). Nevertheless, a mild etching still occurred, likely prior to the onset of heteroepitaxial overgrowth, shrinking the core size from 5.5 to ∼4 nm. The insights provided by this work open up new possibilities in designing multifunctional Cu-chalcogenide based colloidal heteronanocrystals. PMID:29569443

Patterns of astragalar fibular facet orientation in extant and fossil primates and their evolutionary implications.

PubMed

Boyer, Doug M; Seiffert, Erik R

2013-07-01

A laterally sloping fibular facet of the astragalus (=talus) has been proposed as one of few osteological synapomorphies of strepsirrhine primates, but the feature has never been comprehensively quantified. We describe a method for calculating fibular facet orientation on digital models of astragali as the angle between the planes of the fibular facet and the lateral tibial facet. We calculated this value in a sample that includes all major extant primate clades, a diversity of Paleogene primates, and nonprimate euarchontans (n = 304). Results show that previous characterization of a divide between extant haplorhines and strepsirrhines is accurate, with little overlap even when individual data points are considered. Fibular facet orientation is conserved in extant strepsirrhines despite major differences in locomotion and body size, while extant anthropoids are more variable (e.g., low values for catarrhines relative to non-callitrichine platyrrhines). Euprimate outgroups exhibit a mosaic of character states with Cynocephalus having a more obtuse strepsirrhine-like facet and sampled treeshrews and plesiadapiforms having more acute haplorhine-like facets. Surprisingly, the earliest species of the adapiform Cantius have steep haplorhine-like facets as well. We used a Bayesian approach to reconstruct the evolution of fibular facet orientation as a continuous character across a supertree of living and extinct primates. Mean estimates for crown Primatomorpha (97.9°), Primates (99.5°), Haplorhini (98.7°), and Strepsirrhini (108.2°) support the hypothesis that the strepsirrhine condition is derived, while lower values for crown Anthropoidea (92.8°) and Catarrhini (88.9°) are derived in the opposite direction. Copyright © 2013 Wiley Periodicals, Inc.

Facet joint hypertrophy is a misnomer: A retrospective study.

PubMed

An, Sang Joon; Seo, Mi Sook; Choi, Soo Il; Lim, Tae-Ha; Shin, So Jin; Kang, Keum Nae; Kim, Young Uk

2018-06-01

One of the major causes of lumbar spinal canal stenosis (LSCS) has been considered facet joint hypertrophy (FJH). However, a previous study asserted that "FJH" is a misnomer because common facet joints are no smaller than degenerative facet joints; however, this hypothesis has not been effectively demonstrated. Therefore, in order to verify that FJH is a misnomer in patients with LSCS, we devised new morphological parameters that we called facet joint thickness (FJT) and facet joint cross-sectional area (FJA).We collected FJT and FJA data from 114 patients with LSCS. A total of 86 control subjects underwent lumbar magnetic resonance imaging (MRI) as part of routine medical examinations, and axial T2-weighted MRI images were obtained from all participants. We measured FJT by drawing a line along the facet area and then measuring the narrowest point at L4-L5. We measured FJA as the whole cross-sectional area of the facet joint at the stenotic L4-L5 level.The average FJT was 1.60 ± 0.36 mm in the control group and 1.11 ± 0.32 mm in the LSCS group. The average FJA was 14.46 ± 5.17 mm in the control group and 9.31 ± 3.47 mm in the LSCS group. Patients with LSCS had significantly lower FJTs (P < .001) and FJAs (P < .001).FJH, a misnomer, should be renamed facet joint area narrowing. Using this terminology would eliminate confusion in descriptions of the facet joint.

Technical Design Report for the FACET-II Project at SLAC National Accelerator Laboratory

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

None, None

Electrons can “surf” on waves of plasma – a hot gas of charged particles – gaining very high energies in very short distances. This approach, called plasma wakefield acceleration, has the potential to dramatically shrink the size and cost of particle accelerators. Research at the SLAC National Accelerator Laboratory has demonstrated that plasmas can provide 1,000 times the acceleration in a given distance compared with current technologies. Developing revolutionary and more efficient acceleration techniques that allow for an affordable high-energy collider has been the focus of FACET, a National User Facility at SLAC. FACET used part of SLAC’s two-mile-long linearmore » accelerator to generate high-density beams of electrons and their antimatter counterparts, positrons. Research into plasma wakefield acceleration was the primary motivation for constructing FACET. In April 2016, FACET operations came to an end to make way for the second phase of SLAC’s x-ray laser, the LCLS-II, which will use part of the tunnel occupied by FACET. FACET-II is a new test facility to provide the unique capability to develop advanced acceleration and coherent radiation techniques with high-energy electron and positron beams. FACET-II represents a major upgrade over current FACET capabilities and the breadth of the potential research program makes it truly unique.« less

Optimization and Control of Burning Plasmas Through High Performance Computing

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

Pankin, Alexei

This project has revived the FACETS code, that has been developed under SciDAC fund- ing in 2008-2012. The code has been dormant for a number of years after the SciDAC funding stopped. FACETS depends on external packages. The external packages and libraries such as PETSc, FFTW, HDF5 and NETCDF that are included in FACETS have evolved during these years. Some packages in FACETS are also parts of other codes such as PlasmaState, NUBEAM, GACODES, and UEDGE. These packages have been also evolved together with their host codes which include TRANSP, TGYRO and XPTOR. Finally, there is also a set ofmore » packages in FACETS that are being developed and maintained by Tech-X. These packages include BILDER, SciMake, and FcioWrappers. Many of these packages evolved significantly during the last several years and FACETS had to be updated to synchronize with the re- cent progress in the external packages. The PI has introduced new changes to the BILDER package to support the updated interfaces to the external modules. During the last year of the project, the FACETS version of the UEDGE code has been extracted from FACETS as a standalone package. The PI collaborates with the scientists from LLNL on the updated UEDGE model in FACETS. Drs. T. Rognlien, M. Umansky and A. Dimits from LLNL are contributing to this task.« less

Long-Term Developmental Changes in Children's Lower-Order Big Five Personality Facets.

PubMed

de Haan, Amaranta; De Pauw, Sarah; van den Akker, Alithe; Deković, Maja; Prinzie, Peter

2017-10-01

This study examined long-term developmental changes in mother-rated lower-order facets of children's Big Five dimensions. Two independent community samples covering early childhood (2-4.5 years; N = 365, 39% girls) and middle childhood to the end of middle adolescence (6-17 years; N = 579, 50% girls) were used. All children had the Belgian nationality. Developmental changes were examined using cohort-sequential latent growth modeling on the 18 facets of the Hierarchical Personality Inventory for Children. In early childhood, changes were mostly similar across child gender. Between 2 and 4.5 years, several facets showed mean-level stability; others changed in the direction of less Extraversion and Emotional Stability, and more Benevolence and Imagination. The lower-order facets of Conscientiousness showed opposite changes. Gender differences became more apparent from middle childhood onward for facets of all dimensions except Imagination, for which no gender differences were found. Between 6 and 17 years, same-dimension facets showed different shapes of growth. Facets that changed linearly changed mostly in the direction of less Extraversion, Benevolence, Conscientiousness, Emotional Stability, and Imagination. Changes in facets for which nonlinear growth was found generally moved in direction or magnitude during developmental transitions. This study provides comprehensive, fine-grained knowledge about personality development during the first two decades of life. © 2016 Wiley Periodicals, Inc.