bluuebunny/crossref_metadata_2025_split huggingface dataset:
Increased Osteoblast and Decreased Smooth Muscle Cell Adhesion on Biologically-inspired Carbon Nanofibers
Authors: Price Rachel L. , Haberstroh Karen M. , Webster Thomas J. 
Published: April 2011

ABSTRACTOsteoblast (the bone-forming cells) and smooth muscle cell adhesion was investigated on carbon nanofiber formulations of various diameters (specifically, from 60 to 200 nm) and surface energies (from 25 to 140 mJ/m2) in the present in vitro study. Results provided the first evidence that osteoblast adhesion increased with decreased carbon nanofiber diameter after 1 hour. In contrast, smooth muscle cell adhesion was not dependent on carbon nanofiber diameter. Moreover, the present study demonstrated that smooth muscle cell adhesion decreased with increased carbon nanofiber surface energy after 1 hour. Alternatively, osteoblast adhesion was not affected by carbon nanofiber surface energy. Since adhesion is a crucial prerequisite for subsequent functions of cells (such as the deposition of bone by osteoblasts), the present results of controlled adhesion of both osteoblasts and a competitive cell line (i.e., smooth muscle cells) demonstrate that carbon nanofibers with small diameters and high surface energies may become the next-generation of orthopedic implant materials to enhance new bone synthesis. These criteria may prove critical in the clinical success of bone prostheses.
Computational model for multiscale simulation of laser ablation
Authors: Zhigilei Leonid V. 
Published: April 2011

ABSTRACTMultiscale computational approach that combines different methods to study laser ablation phenomenon is presented. The methods include the molecular dynamics (MD) breathing sphere model for simulation of the initial stage of laser ablation, a combined MD - finite element method (FEM) approach for simulation of propagation of the laser-induced pressure waves out from the MD computational cell, and the direct simulation Monte Carlo (DSMC) method for simulation of the ablation plume expansion. The multiscale approach addresses different processes involved in laser ablation with appropriate resolutions and, at the same time, accounts for the interrelations between the processes. A description of the ablation plume appropriate for making a connection between the MD simulation of laser ablation and the DSMC simulation of the ablation plume expansion is discussed.
Electronic Excitations in Initiation of Chemistry in Molecular Solids
Authors: Kuklja Maija M. 
Published: April 2011

ABSTRACTAn ab initio study is performed for the initiation of chemistry in high explosive crystals from a solid-state physics viewpoint. Specifically, we are looking for the relationship between the defect-induced deformation of the electronic structure of solids, electronic excitations, and chemical reactions under shock conditions. Band structure calculations by means of the Hartree- Fock method with correlation corrections were done to model an effect of a strong compression induced by a shock/impact wave on the crystals with and without edge dislocations. Based on the results obtained, an excitonic mechanism of the earliest stages for initiation of high explosive solids is discussed with application to cyclotrimethylene trinitramine (also known as RDX) crystal. Experimental verification of the validity of the proposed model is reported for RDX and heavy metal azides. Thus, the key role of electronic excitations facilitated by edge dislocations in explosive solids is established and analyzed. Practical applications of the suggested mechanisms are discussed.
First Principles Simulations of Phase Stability in Stoichiometric and Doped LiMnO2
Authors: Landa Alexander I. , Chang Chun-Chieh , Kumta Prashant N. , Magyari-Köpe Blanka , Vitos Levente , Ahuja Rajeev , Abrikosov Igor A. 
Published: April 2011

ABSTRACTThe full charge density exact muffin-tin orbitals method has been used to study the stability of lithium-manganese oxides exhibiting different crystallographic allotropes. Calculations have been performed for ferromagnetic and antiferromagnetic phases of LiMnO2 as well as for the phase with local moment disorder. For the ordered LiMnO2 compound we reproduced the correct ground state, the antiferromagnetic orthorhombic structure. The effect of doping LiMnO2 by Co was considered with the aim to predict the stabilization of the layered structure.
Disorder Defects Modelling for Some Ternary Crystals
Authors: Voevodin Valeriy G. , Voevodina Olga.V. 
Published: April 2011

Absrtact:The attempt to obtain the data on thermodynamic parameters and equilibrium concentra- tions of disorder defects was made. Quasi-chemical model of the defects formation with allow- ance for Schottky and Frenkel defects was used. Thermodynamic parameters were calculated based on Weiser's technique. Six types of the disorder defects in II-IV-V2 and I-III-VI2 were considered. Used models, approaches and initial parameters give that the greatest concentration (∼ 1019 cm−3) and accordingly the greatest influence on properties of the crystals have defects AB or BA.
Stoichiometry and Adhesion of Al/WC
Authors: Siegel Donald J. , Hector Louis G. , Adams James B. 
Published: April 2011

ABSTRACTWe examine the relative stability and adhesion of nonstoichiometric (polar) Al/WC interfaces and WC(0001) surfaces using Density Functional Theory as implemented in a planewave, pseudopo- tential formalism. Relaxed atomic geometries and the ideal work of adhesion were calculated for six different interfacial structures, taking into account both W- and C-terminations of the carbide. Based on the surface and interfacial free energies, we find that both the clean surface and the optimal interface geometry are W-terminated. However, the largest adhesion energies are obtained with the C-termination, consistent with an argument based on surface reactivity.
Transmittance Quantities Probability Distributions of Waves through Disordered Systems
Authors: Cwilich Gabriel , Zypman Fredy R 
Published: April 2011

ABSTRACTWaves propagate through disordered systems in a variety of regimes. There is a threshold of disorder beyond which waves become localized and transport becomes restricted. The intensity I of the wave transmitted through a system has a dependence on the length L of the sample that is characteristic of the regime. For example, I decays as L−1 in the diffusive regime. It is of current interest to characterize the transport regime of a wave, from statistical studies of the transmittance quantities through it. Studies suggest that the probability distribution of the intensity could be used to characterize the localized regime. There is an ongoing debate on what deviations from the classical Rayleigh distribution are to be expected. In this numerical work, we use scalar waves to obtain the intensity, transmission, and conductance of waves through a disordered system. We calculate the intensity, by setting an incoming plane wave towards the sample from a fixed direction. The outgoing intensity is then calculated at one point in space. This process is repeated for a collection of samples belonging to the same ensemble that characterizes the disorder, and we construct the probability distribution of the intensity. In the case of transmission, we evaluate the field arriving to a series of points distributed in the far field, and repeat the same statistical analysis. For the conductance, we calculate the field at the same series of points for incoming waves in different directions. We analyze the distribution of the transmittance quantities and their change with the degree of disorder.
A Molecular Orbital Study on the Optical Properties of Fluorescent Dyes
Authors: Park Su-Jin , Shin Dae-Yup , Choi Seung-Hoon , Lee Han-Yong , Chung Ho-Kyoon , Kim Jung-Sik , Lee Jin-Kyu 
Published: April 2011

ABSTRACTFluorescent dyes including Nile Red (NR), fluorescein, rhodamine and 4- (dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) derivatives were investigated to find an application for the organic light emitting device (OLED). Relationship between the molecular structure and optical property was calculated by ab initio (HF and DFT/6-31G*) and semiempirical (AM1/PM3 and INDO/S) calculation methods for the geometry optimization and for the information of electronic transition, respectively. The absorption maximum and the oscillator strength of molecules strongly depended on the molecular dipole moment, especially for the molecules having both strong electron donor and acceptor group. Since the calculated results were comparable with several experimental results, these semiempirical molecular orbital calculation methods could be used as a powerful prediction tool for optical properties of the luminescent molecules.
Linear Scaling DFT Calculations with Numerical Atomic Orbitals
Authors: Ordejón P. , Artacho E. , Cachau R. , Gale J. , García A. , Junquera J. , Kohanoff J. , Machado M. , Sanchez-Portal D. , Soler J. M. , Weht R. 
Published: April 2011

ABSTRACTWe have recently developed a method to perform Density Functional Theory calculations in systems with a very large number of atoms, which is based on the use of numerical atomic orbitals as basis sets. The method incorporates Order-N techniques both in the calculation of the Kohn-Sham hamiltonian matrix elements and in the solution of the wave functions, which make the CPU time and memory to scale linearly with the number of atoms, allowing calculations in very large system. In this work, we present results on several test systems to show that the approach and the basis sets used with our method are able to provide an accuracy similar to that of other standard DFT techniques.
Synchrotron X-Ray Study of Texture in Cold-Worked Shape-Memory NiTi-Wires
Authors: Schuster Andreas , Voggenreiter Heinz , Balch Dorian K. , Dunand David C. 
Published: April 2011

AbstractA series of martensitic, near-equiatomic NiTi shape-memory alloy wires was deformed to strains ranging from 1 to 40% up to stresses of 920 MPa. After deformation, the wires were exposed to a monochromatic, parallel beam of high energy x-rays oriented perpendicular to the wire axis. The transmitted low index diffraction rings show that martensitic texture is increasing with prestrain up to ε=15% after twinning is complete. Further prestraining in the plastic range lowers the texture again indicating that twinning- and plasticity-textures cancel partially each other. Also, deformed NiTi-wires were heated and cooled from 20°C to 200°C under a small constant stress of 6 MPa. The strain change due to the Two-Way Shape-Memory Effect was measured and correlated to the diffraction results.
X-ray Scattering Measurements of the Ag(111) Surface Thermal Expansion
Authors: Botez Cristian E. , Elliott William C. , Miceli Paul F. , Stephens Peter W. 
Published: April 2011

AbstractWe have used synchrotron X-ray diffraction to study the thermal expansion of the Ag(111) surface. Throughout the temperature interval between 300 and 1100K, we observed that the separation between the first and the second atomic layers at the surface, 12 d, differs from its bulk counterpart, d, by less than 1%, indicating that the thermal expansion at the surface is similar to the one in the bulk. This result represents the first experimental confirmation of the predictions from molecular dynamics simulations, which indicate a small enhancement of the anharmonic effects at this surface.
Electronic Properties of Bismuth Nanowires
Authors: Cronin Stephen B. , Lin Yu-Ming , Rabin Oded , Black Marcie R. , Dresselhaus Gene , Dresselhaus Mildred S. 
Published: April 2011

ABSTRACTThe pressure filling of anodic alumina templates with molten bismuth has been used to synthesize single crystalline bismuth nanowires with diameters ranging from 7 to 200nm and lengths of 50μm. The nanowires are separated by dissolving the template, and electrodes are affixed to single Bi nanowires on Si substrates. A focused ion beam (FIB) technique is used first to sputter off the oxide from the nanowires with a Ga ion beam and then to deposit Pt without breaking vacuum. The resistivity of a 200nm diameter Bi nanowire is found to be only slightly greater than the bulk value, while preliminary measurements indicate that the resistivity of a 100nm diameter nanowire is significantly larger than bulk. The temperature dependence of the resistivity of a 100nm nanowire is modeled by considering the temperature dependent band parameters and the quantized band structure of the nanowires. This theoretical model is consistent with the experimental results.
A Microfabricated Device for the Characterization of Biological Entities
Authors: Chang H. , Ikram A. , Young M. , Kosari F. , Vasmatzis G. , Bhunia A. , Bashir R. 
Published: April 2011

ABSTRACTA micro-fabricated pore is constructed and tested so that it can be used to characterize biological entities. The pore is prepared by bulk micro-machining of a silicon wafer. An oxide coated silicon diaphragm with the pore is placed between two chambers containing ionic buffer solutions to mimic a bilayer system. If a voltage is applied across the pore, electrophoretic passage of charged entities can be electrically detected through changes in the ionic current flow. When the entities traverse the pore, the ionic current is blocked and a decrease in the current can be observed. As an initial test case, negatively charged polystyrene beads which were 2.38μm in diameter, were electrophoretically driven across the pore. Then the bacteriumListeria innocua, suspended in Tris-glycine buffer, was also electrophoretically driven through the pore and its effective mobility was extracted. The device can also be used to study the interactions between organisms and the micro-fabricated surfaces. Work is continuing to scale the pore to the sub-100A range to be used for characterization and possible sequencing of single molecules such as DNA.
Relation Between Microstructures and Constitutive Behavior of Advanced Tempered Martensitic Steels
Authors: Spätig Philippe , Schäublin Robin , Victoria Max 
Published: April 2011

ABSTRACTIn an effort to better understand the plasticity of the tempered martensitic steels, the strain-hardening of two 7-9Cr steels is examined in terms of dislocation mechanics. It is shown that, over the temperature range investigated (173K-523K), the strain-hardening as a function of stress can be described by an equation taking account the dislocation storage and annihilation. The model of strain-hardening used in this study is based on the original Kocks description of the dislocation density evolution with plastic strain but the heterogeneous distribution of dislocations resulting from the lath boundaries and prior austenite grain boundaries is taking into account. The effect of stress and temperature on the storage and annihilation is discussed. The relation between the determined mean dislocation path associated to the heterogeneous lath dislocation structure and the transmission electron microscope observations performed on the two different steels is outlined.
Characterization of very low defect-density free-standing GaN Substrate Grown by Hydride-Vapor-Phase-Epitaxy.
Authors: Visconti P. , Reshchikov M. A. , Jones K. M. , Yun F. , Cingolani R. , Morkoç H. , Jasinski J. , Swider W. , Liliental-Weber Z. , Park S. S. , Lee K. Y. 
Published: April 2011

ABSTRACTStructural, electrical and optical properties of free-standing 200-μm thick GaN films grown by hydride vapor phase epitaxy (HVPE) have been investigated. After laser lift-off, the GaN substrates were mechanically polished on both Ga and N-sides and dry etched only on the Ga- side to obtain a smooth epi-ready surface. Hot H3PO4 chemical etching on both surfaces was used to reveal the defect sites, which appeared as hexagonal pits. The etched surfaces were then examined by atomic force microscopy. A few seconds of etching was sufficient to smooth the N- face surface and produce etch pits with a density of ≈ 1×107 cm−2. In contrast, a 50 minute etching was needed to delineate the defect sites on the Ga-face which led to a density as low as 5×105 cm−2. From plan-view and cross-sectional transmission electron microscopy (TEM) analysis, we have estimated that the dislocation density is less than about 5×106 cm−2 and ≈ 3×107 cm−2 for the Ga and N-faces respectively. The full-width at half-maximum (FWHM) of the symmetric (0002) X-ray diffraction rocking curve was 69 and 160 arcsec for the Ga and N-faces, respectively. That for the asymmetric (10 4) peak was 103 and 140 arcsec for Ga and N-faces, respectively. Hall measurements demonstrated very high mobility (1100 and 6800 cm2/V.s at 295 and 50 K, respectively) and very low concentration of donors (2.1×1016 cm−3) and acceptors (4.9×1015 cm−3). In the photoluminescence (PL) spectrum taken at 10 K, a rich excitonic structure has been observed with the highest peak attributed to the exciton bound to neutral shallow donor (BDE). The FWHM of the BDE peak was about 1.0 meV on the Ga face before and after hot chemical etching, whereas that on the N-face decreased from about 20 to 1.0 meV after chemical etching owing to the removal of the surface damage originated from the mechanical polishing.
Reduction of incorporation of B, Al, Ti and N in 4H-SiC epitaxial-layer grown by chemical vapor deposition at higher growth temperature
Authors: Kushibe Mitsuhiro , Masahara Koh , Kojima Kzutoshi , Ohno Tshiyuki , Ishida Yuki , Takahashi Tetsuo , Nishio Johji , Suzuki Takaya , Tanaka Tomoyuki , Yoshida Sadahumi , Arai Kazuo 
Published: April 2011

ABSTRACTThe influence of growth conditions and susceptor purity on the residual contamination in undoped 4H-SiC epitaxial layer grown at higher temperature such as 1600 °C is investigated. Residual N concentration is found to increase with growth temperature. Growth temperature dependence of residual N concentration is stronger than that of Al or B. The effect of degradation of SiC coating layer on the purity of the epitaxial layer is studied. SiC coating layer is degraded after very few repetition of growth-run. SIMS measurement reveals that the concentration of N, Al, B, Ti and V in epitaxial layer increases with the deterioration of SiC coating layer. Therefore, serious consideration on the effect of contamination from the susceptor graphite is required. By using various grades of graphite as susceptor, the dependence of the purity of epitaxial layer on the susceptor purity is studied. High concentration (1017 to 1018 cm−3) of N is found in graphite. Contamination of all types of impurities such as p-type impurities, transition metal impurities and N in graphite is found to affect the purity of epitaxial layers.
Surface Photovoltage Spectroscopy of InGaN/GaN/AlGaN Multiple Quantum Well Light Emitting Diodes
Authors: Mishori B. , Muñoz Martin , Mourokh L. , Pollak Fred H. , DeBray J.P. , Ting S. , Ferguson I. 
Published: April 2011

ABSTRACTInGaN/GaN/AlGaN multiple quantum well light emitting diodes (MWQ LED's) with different levels of p-doping in the contact layer have been characterized using surface photovoltage spectroscopy (SPS). Due to the high sensitivity of the SPS technique to the electric field, there is a strong correlation between the p-doping level in the contact layer and the magnitude of the SPS signal originating from the MQW region. The experimental results are confirmed by a numerical simulation.
Photoluminescence and Excitation Spectra of Deep Defects in GaN
Authors: Reshchikov Michael A. , Molnar Richard J. , Morkoç Hadis 
Published: April 2011

ABSTRACTDeep defects responsible for broad bands in the red-to-green range of the photoluminescence (PL) spectrum of undoped and Si-doped GaN grown by molecular beam epitaxy (MBE) and hydride vapor phase epitaxy (HVPE) were studied by employing PL and PL excitation (PLE) methods. In HVPE grown samples, a red luminescence (RL) and a green luminescence (GL) bands were observed, respectively, at about 1.9 and 2.4 eV. Similar in positions but different in properties red and green bands (RL2 and GL2, respectively) dominated in the samples grown in Ga-rich conditions by MBE with radio frequency plasma as a nitrogen source (RF-MBE). A yellow luminescence (YL) with a maximum at about 2.2 eV dominated in the samples with ammonia used as a nitrogen source (NH3-MBE). It has been established from the variation of temperature, excitation intensity and excitation wavelength that the abovementioned five bands are related to different deep-level defects.
Defect investigation of GaN thin films etched by photo-electrochemical and hot wet etching by atomic force and transmission electron microscopy
Authors: Visconti P. , Jones K. M. , Reshchikov M. A. , Cingolani R. , Morkoç H. , Molnar R. J. , Smith D. J. 
Published: April 2011

ABSTRACTThe availability of reliable and quick methods to investigate defects in GaN films is of great interest. Photo-electrochemical (PEC), and hot wet etching using both H3PO4 acid and molten KOH have been used to study structural defects in GaN layers grown by hydride vapor phase epitaxy and molecular beam epitaxy. The purpose of this work is to determine whether, and under what conditions, these different methods of investigation are consistent and to get to a more accurate estimation of the defect density. As-grown and etched surfaces were investigated by atomic force microscopy (AFM), and plan-view and cross-sectional transmission electron microscopy (TEM). Free-standing whisker-like features and hexagonal etch pits were formed on the etched sample surfaces by PEC and wet etching, respectively. Using plan-view AFM, we found the density of whiskers (8x108-1×109 cm−2) to be similar to the etch pit densities when etched in both H3PO4 and molten KOH under precise etching conditions. During the wet etching process, a careful balance must be struck to ensure that every defect is delineated, but not overetched to cause merging which would lead to an underestimation of the defect density. Additionally, TEM observations confirmed the dislocation densities obtained by etching, which increased our confidence in the consistency of the methods used.
Effects of Plasma Surface treatment on Ohmic Contact to n-GaN
Authors: Chor E.F. , Kang X. J. 
Published: April 2011

ABSTRACTWe have investigated the effects of plasma surface treatment on ohmic contacts to n-type GaN. Prior to metal evaporation, n-GaN surface was etched either chemically using aqua-regia (control sample) or by means of inductively coupled Cl2/BCl3, N2 or Ar plasmas. The metal system adopted in our investigation was Ti/Al/Pd/Au. The as-deposited Ti/Al/Pd/Au contact on aqua-regia treated n-GaN exhibits an ohmic behavior with a specific contact resistance (ρc) of 2×10−4ωcm2. After annealing at 500°C for 5min, ρc is reduced by approximately 2 orders of magnitude to 5×10−6ωcm2. For Cl2/BCl3 and N2 plasma treated n-GaN surface, the as-deposited Ti/Al/Pd/Au contacts also yield ohmic behavior and ρc's are about 2×10−4 and 5×10−4 ωcm2 respectively. After annealing at 500°C for 5min, ρc's are reduced by about 3 orders of magnitude to around 5×10−7 and 8×10−7 ωcm2 respectively. On the other hand, the as-deposited Ti/Al/Pd/Au contact on Ar plasma treated n-GaN exhibits a non-ohmic behavior. After annealing at 500°C for 5min, ρc is about 5×10−7 ωcm2 and the lowest ρc of 7×10−8 ωcm2 is obtained after annealing at 700°C for 5min. The contacts on other surface treated n-GaN are found to degrade at 700°C annealing. By comparing the values of ρc for various surface treatments, particularly those after annealing, it is observed that plasma etching can be used beneficially in the formation of ohmic contacts – plasma surface treatment using Cl2/BCl3, N2 or Ar has resulted in an order of magnitude reduction in ρc compared to chemical surface treatment by aqua-regia.