bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative Structure-Activity Relationships for New Aerospace Fuels
Authors: Trohalaki Steven , Pachter Ruth 
Published: June 2019

AbstractThe design of new materials can be made more efficient if toxicity screening is performed in early rather than in late stages of development, especially for volatile materials such as lubricants, fire retardants, fuels, and fuel additives. In our continuing efforts to develop methods for the prediction of the toxicological response to materials of interest to the U.S. Air Force, we have constructed Quantitative Structure-Activity Relationships (QSARs) for thirteen newly proposed propellant compounds. We employed two previously published in vitro toxicity endpoints in primary cultures of isolated rat hepatocytes, which measured decrease in mitochondrial function and glutathione depletion [1]. Molecular descriptors were obtained using ab initio molecular orbital theory. QSAR models were then derived for each endpoint. Correlation coefficients for 2- and 3-parameter QSARs exceed 0.9, possibly enabling toxicity predictions for similar compounds. Insight into the biophysical mechanism of toxic response can be gained from interpretation of the descriptors comprising the QSARs.
Porous Silicon Electrical Biosensors
Authors: Archer Marie , Christophersen Marc , Fauchet Philippe M. 
Published: June 2019

ABSTRACTThe highly sensitive surface of porous silicon (PSi) and the possibility to measure changes in its electrical properties can be used for electrical biosensor applications. The sensing scenario can be extended from the well-characterized organic solvents and pH sensors to detection of biological processes involving the presence of charged molecules. We have investigated the change in electrical properties (capacitance and conductance) of macroporous silicon layers upon exposure to organic solvents and water. Evaluation of our sensor to detect a biological event was done by addressing DNA hybridization. As opposed to the previous work published in this field, in our devices the electrical contact is made on the crystalline silicon (c-Si) substrate. This allows a complete exposure of the surface to the sensing species and reduces the generation of ionic currents through the porous silicon matrix. We will report results of a complete characterization of our device including response speed, selectivity and sensitivity.
Laser Direct-Metallization of Silicon Carbide without Metal Deposition
Authors: Salama I.A. , Kar A. , Quick N.R. 
Published: June 2019

AbstractLaser direct-write (LDW) is used forin-situmetallization in single crystal 4H- and 6H-SiC wafers without metal deposition. Nanosecond-pulsed Nd:YAG (λ= 1064 and 532 nm) and excimer (λ = 193, 248 and 351 nm) lasers are utilized to create metal-like conductive phases in both n-type and p-type SiC wafers. Frequency-doubled Nd:YAG irradiation(Ephoton< Eg) induces a carbon rich conductive phase due to thermal decomposition of SiC. However, pulsed excimer laser irradiation (Ephoton> Eg) produces a Si- rich conductive phases due to carbon photo ablation. The Schottky barrier heights (SBH) between the laser-metallized layer and the original n-type SiC (ND= 1018cm-3) is determined to be 0.8 eV and 1.0 eV by the current-voltage and capacitance-voltage measurements at room temperature, respectively. Linear transmission line method pattern is directly fabricated in n-type doped (ND=1018cm-3) SiC substrate by pulsed laser irradiation allowing to extract the specific contact resistance (rc)of the laser fabricated metal-like tracks (rc= 0.04-0.12 Ωcm2).The specific contact resistance is unchanged after annealing up to 3 hrs at 950°C.
High Reflectivity AlGaN/GaN Bragg Mirrors Grown by MOCVD for Microcavities Applications.
Authors: Moret M. , Ruffenach S. , Briot O. , Gil B. , Aulombard R.L. 
Published: June 2019

AbstractBragg mirrors are highly interesting structures for a large set of applications including vertical cavity lasers and the upcoming range of devices based on microcavities. Although the nitride semiconductors are performing fairly well in optoelectronic applications, it is not straightforward to realize Bragg mirrors based on this material system, due to the low optical index differences between GaN and AlN. Moreover, the lattice parameter difference between these materials will generate crystal defects, which prevent the stacking of a large number of periods, adding to the difficulty. In this work, we have grown high reflectivity Bragg mirrors, with a band centered in the visible blue range. The structures were first modelled, then grown by low pressure MOCVD, and were optimised using an in-situ reflectivity system.This in-situ reflectivity measurement was compared to a calculated profile, to enable real-time control of the structures. The samples were characterized by transmission electron microscopy and reflectivity. It was possible to realize samples with 90% reflectivity near 400 nm.
Optical and Electrical Characterization of Annealed Silicon-implanted GaN
Authors: Wang H. T. , Tan L.S. , Chor E. F. 
Published: June 2019

AbstractIn this paper, we investigate the effect of post-implant annealing on the optical and electrical properties of Si-implanted GaN films. Results from several measurement techniques including room temperature photoluminescence (PL), micro-Raman scattering, high resolution X-ray diffraction (HRXRD) and Hall measurement are correlated to study the behavior of damage removal, dopant activation, crystalline quality and residual stress, etc. The Hall measurement demonstrates that reasonable activation percentage is achieved though there is only partial recovery of the PL intensity. Raman scattering shows the decrease of stress within the implanted films after thermal annealing. The carrier concentration increases monotonically with increasing annealing temperature up to 1100°C, which is in agreement with linewidth broadening of near band edge in PL spectrum. Moreover, systematic measurements implies that the implantation induced defects, especially point defects, which could play significant role in either the optical or electrical properties of films, cannot be completely annealed out at 1100°C.
Low-Temperature Operation of Green, Blue and UV InGaN/GaN Multiple-Quantum-Well Light-Emitting Diodes
Authors: Cao X. A. , LeBoeuf S. F. , Garrett J. L. , Ebong A. , Rowland L. B. , Arthur S. D. 
Published: June 2019

Absract:Temperature-dependent electroluminescence (EL) of InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with peak emission energies ranging from 2.3 eV (green) to 3.3 eV (UV) has been studied over a wide temperature range (5-300 K). As the temperature is decreased from 300 K to 150 K, the EL intensity increases in all devices due to reduced nonradiative recombination and improved carrier confinement. However, LED operation at lower temperatures (150-5 K) is a strong function of In ratio in the active layer. For the green LEDs, emission intensity increases monotonically in the whole temperature range, while for the blue and UV LEDs, a remarkable decrease of the light output was observed, accompanied by a large redshift of the peak energy. The discrepancy can be attributed to various amounts of localization states caused by In composition fluctuation in the QW active regions. Based on a rate equation analysis, we find that the densities of the localized states in the green LEDs are more than two orders of magnitude higher than that in the UV LED. The large number of localized states in the green LEDs are crucial to maintain high-efficiency carrier capture at low temperatures.
Stimulated Emission at 258 nm in AlN/AlGaN Quantum Wells Grown on Bulk AlN Substrates
Authors: Gaska R. , Fareed Q. , Tamulaitis G. , Yilmaz I. , Shur M.S. , Chen C. , Yang J. , Kuokstis E. , Khan A. , Rojo J.C. , Schowalter L. J. 
Published: June 2019

AbstractWe report on observation of stimulated emission at 258 nm in AlN/AlGaN multiple quantum wells. The structures were grown over Al-face single crystal bulk AlN substrates. AlN/AlGaN structures with 50% of Al in the well material were grown using low-pressure metalorganic chemical vapour deposition. Characterization by using X-ray, AFM, SEM, and photoluminescence techniques indicated high structural quality of the structures. The stimulated emission was measured using the variable stripe length method under excitation by 4-ns-long pulses of the fifth harmonic of Nd:YAG laser radiation at 213 nm (5.82 eV). The stimulated emission exhibited a characteristic superlinear dependence of emission intensity on the pump intensity as well as an exponential increase of the sample-edge emission intensity with increasing stripe length up to ∼430 μm and the intensity saturation beyond this range. The observation of stimulated emission at 258 nm is very promising for the future development of III-nitride-based deep-UV laser diodes on bulk AlN substrates.
Investigation of Epitaxial GaN Films by Conductive Atomic Force Microscopy
Authors: Dogan S. , Spradlin J. , Xie J. , Pomarico A. A. , Cingolani R. , Huang D. , Dickinson J. , Baski A. A. , Morkoç H. , Molnar R. 
Published: June 2019

AbstractThe current conduction in GaN is very topical and is the topic of a vast amount of research. By simultaneously mapping the topography and the current distribution, conductive atomic force microscopy (C-AFM) has the potential to establish a correlation between topological features and localized current paths. In this study, this technique was applied to image the conduction properties of as-grown and post-growth chemically etched samples GaN epitaxial layers on a microscopic scale. Our results show that prismatic planes have a significantly higher conductivity than the surrounding areas of the sample surface. A large and stable local current was mainly observed from the walls of the etched pits, under forward and reverse bias of the metallized AFM tip/semiconductor junction.
High Remanent Polarization in Laser Ablated SrBi2Nb2O9Thin Films
Authors: Das Rasmi R. , Bhattacharya P. , Pérez W. , Katiyarxya Ram S. 
Published: June 2019

AbstractPulsed-laser-deposition technique was used to grow SrBi2Nb2O9(SBN) thin films on platinized silicon substrates. The effect of annealing temperature and film thicknesses on the structural and electrical properties has been studied. The average grain size and rms surface roughness was found to increase with increasing annealing temperature. The degree of orientation along the (200) direction was increased with the film thicknesses. The remanent polarization was found to be increased with the film thicknesses and was attributed to the selftexturing characteristics of SBN films. Thin films with higher thickness (∼570 nm) exhibited high value of remanent polarization (∼38 ν/cm2) with coercive field of 185 kV/cm. There was a reduction of coercive field with the film thickness. The dielectric constant was observed to be independent of the film thickness. The increase in loss tangent with increasing film thicknesses was attributed to the reduction of dielectric breakdown strength of the films. The SBN thin films showed minimal fatigue characteristics and suitable material for memory devices.
Generation and Formation of Gold Nanoparticles with Spatial Control by Two-Photon Femtosecond Laser Interference
Authors: Duan Xuan-Ming , Sun Hong-Bo , Kaneko Koshiro , Kawata Satoshi 
Published: June 2019

AbstractA simple strategy for generating and distributing metallic nanoparticles in polymer matrix with a spatial control in micrometer/nanometer scale has been proposed and successfully demonstrated by combination of two-photon photoreduction and femtosecond laser interference technique. The simultaneous spatially controlling generation and organization of metallic nanopartciles were controllable by designing interference patterns and varying laser intensity and exposure time. This strategy provides a simple and rapid approach for creating templates with designed spatial distribution of the nanoparticles, which is favorable for current microelectronics technology. This method also can be utilized in developing mass production processes for future nanodevices.
ZrC Thin Films Grown by Pulsed Laser Deposition
Authors: Craciun V. , Craciun D. , Howard J. M. , Singh R. K. 
Published: June 2019

AbstractZrC thin films were grown on Si substrates by the pulsed laser deposition (PLD) technique. X- ray photoelectron spectroscopy, x-ray diffraction and reflectivity, variable angle spectroscopic ellipsometry, and four point probe measurements were used to investigate the composition, density, thickness, surface morphology, optical and electrical properties of the grown structures. It has been found that crystalline films could be grown only by using fluences above 6 J/cm2 and substrate temperatures in excess of 500 °C. For a fluence of 10 J/cm2 and a substrate temperature of 700 °C, highly (100)-textured ZrC films exhibiting a cubic structure (a=0.469 nm) and a density of 6.7 g/cm3 were deposited. The use of a low-pressure atmosphere of C2H2 had a beneficial effect on crystallinity and stoichiometry of the films. All films contained high levels of oxygen contamination, especially in the surface region, because of the rather reactive nature of Zr atoms.
Effect of Oxygen Pressure During Zno:Al Coating of Zns:Ag Phosphor on Cathodoluminescent Degradation Lifetime
Authors: Ollinger M. , Craciun V. , Nagore S. , Singh R.K. 
Published: June 2019

AbstractThe reduction in cathodoluminescent (CL) degradation of ZnS:Ag phosphor particles coated with aluminum doped zinc oxide (ZAO) films has been investigated. The films were deposited under various oxygen pressures using the atomic flux coating process. The characteristics of the coated phosphor particles with respect to as-received ones were investigated by x-ray photoelectron spectroscopy, CL degradation and scanning electron microscopy. All coated phosphor particles exhibited less CL degradation than the uncoated particles. The coatings deposited under 1.6×10-4 Torr of oxygen, a pressure much lower than the optimum one required to obtain highly transparent and conductive ZnO:Al films, provided the longest brightness lifetime. This increased phosphors lifetime was attributed to the high reactivity of the oxygen deficient ZAO coatings which acted as a sacrificial layer and trapped reactive species before they can reach the phosphor particles and alter their chemical composition.
Comparison of Uranium Release from Spent Fuel and Unirradiated U02in Salt Brine
Authors: Gray W. J. 
Published: June 2019

AbstractSpent fuel and unirradiated U02were previously reported [1] to have exhibited a 100-fold difference in the total amount of uranium released during static leach tests in salt brine. Two additional studies designed to investigate that difference have now been completed. The first study involved leach tests with U02pellets that had been doped with plutonium to simulate the alpha activity in spent fuel. The second study consisted of leach tests on spent fuel specimens that originated in the same reactor assembly as those used in previous tests but handled differently following discharge from the reactor. Results from the recently completed tests show that at least 90% of the reported difference between the dissolution behavior of spent fuel and U02can be attributed to an apparent surface oxidation of the spent fuel specimens after their discharge from the reactor. The effect of alpha radiolysis on the leaching of spent fuel and U02in salt brine in the presence of an air atmosphere was found to be relatively small in these tests.
High-Level Waste Package Licensing Considerations for Extrapolating test Data
Authors: Johnson T.C. , Chang K.C. , Jungling T.L. , Person L.S. , Peterson C.H. , Voglewede J.C. , Wick E.A. 
Published: June 2019

AbstractPrograms intended to provide supporting information for the high-level radioactive waste (HLW) repository program must consider the licensing requirements and the technical issues involved with extrapolation of short-term test data to periods of up to 10,000 years. The licensing requirements of the Nuclear Regulatory Commission (NRC), and the issues the NRC staff considers important for the development of predictive methods, are described. Because performance predictions of the geologic repository and particular components of the waste package must largely be based upon inference, a reasonable assurance, on the basis of the record before the Commission, is the general standard that will be required.
Effect of Pore Solution Composition on Cesium Leachability of Cement-Based Waste Forms
Authors: Hoyle Susan Q. , Grutzeck Michael W. 
Published: June 2019

AbstractThe relationship of pore solution composition to observed leach behavior for cesium-doped, cement-based waste form has been demonstrated.A leaching model is proposed, based on early diffusion and homogenization of the pore solution and leachant followed by re-equilibration of the waste form with the greater pore solution (pore solution plus leachant) over the long term.
Calculation of Near-Field Radioactivity Release Rates from Neutron-Activated Reactor Parts in a Shallow-Land Burial site at Oak Ridge National Laboratory
Authors: Hightower J. R. , Kelmers A. D. 
Published: June 2019

AbstractThe purpose of this work was to estimate the near-field radioactivity release rates associated with the high-activity, low-level radioactive wastes currently emplaced in Solid Waste Storage Area 6 (SWSA-6) at Oak Ridge National Laboratory (ORNL). Examination of the existing records [1] showed that about 84% of the radioactivity emplaced in SWSA-6 could apparently be accounted for by neutron-activated metal parts discharged from the High Flux Isotope Reactor (HFIR); therefore, this analysis was limited to consideration of those HFIR wastes. The radio- nuclide inventory contained in the HFIR wastes was first calculated, and then realistic or conservative assumptions as well as existing data were employed to calculate near-field radionuclide release rates. The dominant uncertainties in the calculations were summarized, and the research which would be needed to reduce these uncertainties was described. A more complete description of this work can be found in reference [2].
Multicomponent Systems Tests on Used Fuel and Fuel Recycle Waste Glass at 200 °C
Authors: Heimann Robert B. 
Published: June 2019

AbstractExperiments were performed at 200 °C and 8.5 MPa on used fuel and a borosilicate waste glass in contact with clay, container metals, groundwater and granite selected as reference materials in the Canadian Nuclear Fuel Waste Management Program. The experimental design considered five parameters that determine a fractional factorial design 25-1. The parameters varied were: waste form (used fuel or Moly 99“W” glass), cation exchange capacity of the clay (calcium bentonite, 1360 meq/kg or illite, 160 meq/kg), ionic strength of the groundwater (Standard Canadian Shield Saline Solution, SCSSS, 1.4 mol/L or granitic groundwater GGW, 1 × 10−3 mol/L), surface area to volume ratio (SA/V) (120 or 12 m−1), and container material 3Inconel 625 or Ticode 12). The results show that (i) maximum release of 137Cs from used fuel and waste glass occurs in the presence of illite and GGW, (ii) maximum releases of 90Sr and the actinides from used fuel occur in the presence of bentonite and SCSSS, and (iii) maximum release of 90Sr from the waste glass occurs in the presence of illite and GGW.
Development and Evaluation of a Tracer-Injection Hydrothermal Technique for Studies of Waste Package Interactions
Authors: Jones Thomas E. , Coles D.G. , Britton R.C. , Burnell J.R. 
Published: June 2019

AbstractA tracer-injection system has been developed for use in characterizing reactions of waste package materials under hydrothermal conditions. High-pressure liquid chromatographic instrumentation has been coupled with Dickson-type rocking autoclaves to allow injection of selected components into the hydrothermal fluid while maintaining run temperature and pressure. Hydrothermal experiments conducted using this system included the interactions of depleted uranium oxide and Zircaloy-4 metal alloy discs with trace levels of 99Tc and non-radioactive Cs and I in a simulated groundwater matrix. After waste-package components and simulated waste forms were pre-conditioned in the autoclave systems (usually 4 to 6 weeks), known quantities of tracer-doped fluids were injected into the autoclaves' gold reaction bag at run conditions. Time-sequenced sampling of the hydrothermal fluid provided kinetic data on the reactions of tracers with waste package materials. The injection system facilitates the design of experiments that will better define “steady-state” fluid compositions in hydrothermal reactions. The injection system will also allow for the formation of tracer-bearing solid phases in detectable quantities.
Effects of Aoueous Phase Composition on the Leach Behavior of Nuclear Waste Glasses
Authors: Feng Xiangdong , Barkatt Aaron 
Published: June 2019

AbstractA systematic matrix of leach tests on a Rest Valley waste glass composition is described. These tests are intended to provide quantitative systematic information on leachant composition effects. and accordingly elucidate the controlling orocesses in hiuh-solute media. e.g. silicate ground water. brine. etc. In order to separate the effects of the nature and concentration of solutes from pH effects. leach tests were first carried out on the glass in de-ionized water under highly interactive conditions (high surface to volume ratio) in a configuration which pre- vented lowering the pH due to the intrusion of CO:. After determination of the resulting pH. the leach behavior of the glass was characterized in a series of high-dilution tests in various leachants buffered at this pH value in order to quantify the effects of leachant composition and concen- trations on the leaching orocess. The high-dilution conditions were used at this stage to ensure that the leachant composition mould not be signifi- cantly affected by accumulation of leached glass components. It was concluded that increased ionic strength appears to depress the leach rates in near-neutral media but enhances the leach rates under moderately basic conditions.
Padiolytically Induced Oxidation Reactions of Actinide Ions in Concentrated Salt Solutions
Authors: Kim J.I. , Lierse Ch. , Büppelmann K. , Magirius S. 
Published: June 2019

AbstractThe autoradiolytic oxidation of Pu(IV) and Am(III) has been investigated in saline solution of different NaCl concentrations, pH and specific α-activities. The high linear energy transfer (LET) property of α-radiation in solution enhances the oxidation of the Cl ion and thus increases the redox potential (Eh) of the NaCI solution system to a value of more than +1000 mV vs. NHE. Radiolytic reaction products are found as being comparable with those from the Cl2 saturated NaCl solution 'and create a metastable system consisting of C12/HCl0/Cl0−/Cl−. The oxidation of Pu(IV) and Am(III) in such solutions is dependent on the NaCl concentration, pH and specific a-activity involved. The quantitative oxidation to Pu(VI) and Am(V) is ob- served in the concentrated NaCl solution at pH > 7 with a moderately high specific activity (> 1 Ci/L).
The Effects Of Gamma Radiation on Groundwater Chemistry and Glass Reaction In a Saturated Tuff Environment
Authors: Ebert William L. , Bates John K. , Gerding Thomas J. , Konynenburg Richard A. Van 
Published: June 2019

AbstractThe Nevada Nuclear Waste Storage Investigations project has completed a series of experiments that provide insight into groundwater chemistry and glass waste form performance in the presence of a gamma radiation field at 90°C. Results from experiments done at 1 × 103 and 0 R/hr are presented and compared to similar experiments done at 2 × 105 and 1 × 104R/hr. The major effect of radiation is to lower the groundwater pH to a value near 6.4. The addition of glass to the system results in slightly more basic final pH, both in the presence and absence of radiation. However, there is essentially no difference in the extent of glass reaction, as measured by elemental release, as a function of dose rate or total dose, for reaction periods up to 278 days.