bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamics and Kinetics in Model Light Harvesting Dendrimers
Authors: Bar-Haim Arie , Klafter Joseph 
Published: April 2011

AbstractThermodynamic and kinetic properties of model dendrimers are investigated. We show that for ideal dendrimers, with a superimposed energy funnel descending from the periphery to the center, one should be able to control the preferred location of the excitation by monitoring the temperature relative to the energy funnel. This opens the possibility for a controlled drive of photochemical processes in these supermolecules. The mean first passage time (MFPT) of excitations to reach the center of a dendrimer is calculated. A minimum in the MFPT as a function of temperature is predicted.
About Computations of Hele-Shaw Flow of Non-Newtonian Fluids
Authors: Kondic L. , Fast P. , Shelley M. J. 
Published: April 2011

AbstractThe flow of a fluid confined between two solid plates (Hele-Shaw cell) is of considerable interest in a variety of applications. Further interest in two phase flow in this geometry stems from the close analogy between the dynamics of fluid-fluid interface and the propagation of the solidification front. While the flow of Newtonian fluids is rather well understood, it is much more complicated to compute flows of non-Newtonian fluids. We find that the dense-branching morphology of Newtonian liquids may be replaced by dendritic fingers with stable tips and sidebranches, and discuss resulting length scales.
Large Area Deposition of Cadmium Sulfide by Chemical Bath Deposition for Photovoltaic Applications
Authors: Boyle David S. , O'brien Paul 
Published: April 2011

AbstractThere is considerable interest in the deposition of compound semiconductors by methods which involve relatively low capital expense and are technically undemanding on the experimentalist. One process to meet these criteria is Chemical Bath Deposition (CBD). Such processing methods are particularly appropriate for the production of devices for which large areas and low cost are essential, such as the BP Solar Ltd “Apollo” cells based on CdS:CdTe heterojunctions.The electrical and optical properties of these devices have been investigated with respect to impurity profiles of 16-O, 34-S, 35-Cl and 12-C in the CdTe and CdS:CdTe interface. Device characteristics (e.g. Voc and Rs) have been correlated with SIMS data. The distribution of the carbon contaminant appears to influence the chloride-promoted recrystallisation of CdTe. XPS analysis of CdS layers appears to indicate that the annealing process induces the formation of a chloride-rich surface layer, which may promote the n- to p- type thermal conversion of CdTe.
Carbonization and/or Nitridation of Titanium and Zirconium for Increasing Melting Temperature
Authors: Nunogaki M. , Susuki Y. , Kitahama K. , Nakata Y , Hori F , Oshima R. , Emura S. 
Published: April 2011

AbstractSamples of Ti and Zr metals have been carbonized or nitrided at high temperature by means of reactive plasma processing. Thickness and hardness of modified layers increased with the processing temperature and time in an experimental range below 1500°C for less 5h. The maximum hardness of TiC-layer modified at 1300°C for 3h was about 5000Hv(kg/mm2) and the maximum thickness of ZrC-layer formed at 1400°C for 5h reached about 100μm. A TiC-layer was analyzed with EPMA, XRD, EXAFS and PAS(Positron Annihilation Spectroscopy). It was confirmed that the sub-surface layer of Ti metal was the mixture of TiC ceramics and Ti metal, and that the thickness of TiC with NaCI type structure was very large.
Metal Alloy Propellants Produced from Lunar Resources
Authors: Hepp Aloysius F. , Linne Diane L. , Landis Geoffrey A. 
Published: April 2011

AbstractThe ultimate success of a permanent lunar base will depend upon the use of available resources. Two important resources available on the moon are oxygen and metals. We examine issues, including lunar resources, processing, power, and engine performance, surrounding the use of lunar resources for metal/oxygen engines, including the performance of metal alloys as rocket fuels. Results of this analysis have uncovered several promising candidates including alloys of Al-Ca, Al-Mg, Al-Si, Ca-Mg, and Ca-Si.
High Efficiency Monolithic Multi-Junction Solar Cells Using Lattice-Mismatched Growth
Authors: Hoffman R.W. , Fatemi N.S. , Stan M.A. , Jenkins P. , Weizer V.G. , Scheiman D.A. , Brinker D.J. 
Published: April 2011

AbstractThe demand for spacecraft power has dramatically increased recently. Higher efficiency, multi-junction devices are being developed to satisfy the demand. The multi-junction cells presently being developed and flown do not employ optimized bandgap combinations for ultimate efficiency due to the traditional constraint of maintaining lattice match to available substrates. We are developing a new approach to optimize the bandgap combination and improve the device performance that is based on relaxing the condition of maintaining lattice match to the substrate. We have designed cells based on this approach, fabricated single junction components cells and tested their performance. We will report on our progress toward achieving beginning-of-life AMO multi-junction device conversion efficiencies above 30%.
Creep Mechanisms of Fully-Lamellar TiAl Based Upon Interface Sliding
Authors: Hsiung L. M. , Nieh T. G. 
Published: April 2011

ABSTRACTDeformation mechanisms of fully lamellar TiAl with a refined microstructure (γ lamellae: 100 ∼ 300 nm thick, α2 lamellae: 10 ∼50 nm thick) crept at 760°C have been investigated. As a result of a fine structure, the motion and multiplication of lattice dislocations within both γ and α2 lamellae are limited at low creep stresses (< 400 MPa). Therefore, the glide and climb of lattice dislocations are insignificant to creep deformation. The cooperative motion of interfacial dislocations on γ/α2 and -γ/γ interfaces (i.e. interface sliding) is proposed to be the dominant deformation mechanism at low stresses. Lattice dislocations impinged on lamellar interfaces are found to be the major obstacles impeding the motion of interfacial dislocations. The number of impinged lattice dislocations increases as the applied stress increases and, subsequently, causes the pileup of interfacial dislocations along the interfaces. Accordingly, deformation twinning activated by the pileup of interfacial dislocations is proposed to be the dominant deformation mechanism at high stresses (> 400 MPa).
Plastic Deformation of Ni3Nb Single Crystals
Authors: Hagihara Kouji , Nakano Takayoshi , Umakoshi Yukichi 
Published: April 2011

ABSTRACTTemperature dependence of yield stress and operative slip system in Ni3Nb single crystals with the DOastructure was investigated in comparison with that in an analogous L12structure. Compression tests were performed at temperatures between 20 °C and 1200 °C for specimens with loading axes perpendicular to (110), (331) and (270).(010)[100] slip was operative for three orientations, while (010)[001] slip for (331) and {211} <107 13> twin for (270) orientations were observed, depending on deformation temperature. The critical resolved shear stress (CRSS) for the (010)[100] slip anomaly increased with increasing temperature showing a maximum peak between 400 °C and 800 °C depending on crystal orientation. The CRSS showed orientation dependence and no significant strain rate dependence in the temperature range for anomalous strengthening. The [100] dislocations with a screw character were aligned on the straight when the anomalous strengthening occurred. The anomalous strengthening mechanism for (010)[100] slip in Ni3Nb single crystals is discussed on the basis of a cross slip model which has been widely accepted for some L12-type compounds.
Microstructural Development of Mo(ss) + T2 Two-Phase Alloys
Authors: Sakidja R. , Wilde G. , Sieber H. , Perepezko J. H. 
Published: April 2011

ABSTRACTThe microstructure evolution involving Mo-B-Si as-solidified alloys with compositions in the Mo solid-solution(ss) + T2 two-phase field has been examined following arc-melting and rapid solidification processing (RSP). Several solidification pathways in the arc-melted alloys have been identified. Compositional segregation during conventional solidification results in the formation of additional phases such as borides in the arc-melted alloys which require a prolonged solid-state annealing to obtain equilibrated two-phase microstructures. The RSP methods employed, splat-quenching (SQ) and powder drop tube processing (DTP), allow for significant microstructural modifications that facilitate the attainment of uniform dispersions of Mo(ss) phase in a T2 phase matrix.
Low Temperature Deformation Kinetics of Ruthenium Aluminide Alloys
Authors: Lu D. C. , Pollock T. M. 
Published: April 2011

ABSTRACTThe kinetics of low temperature deformation were investigated in several different polycrystalline RuAl alloys with the use of strain rate change experiments at 77 K and 298 K. Compositions investigated include RuAl, RuAl+0.5%B, Ru51.5 A48.5, Ru52 Al48, RU53 A147+0.5%B, Ru54.5 Al45.5, and Ru52 Al43 Sc5. Flow stresses did not vary substantially with temperature between 77 K and 298 K. Rate sensitivities were low compared to other B2 compounds and similar in all compositions investigated. Analyses of dislocation substructures after low strain deformation were conducted. The deformation kinetics and substructural observations suggest a higher intrinsic deformability for RuAI alloys with respect to the other high temperature B2 aluminides.
Microstructure, Creep and Fracture Toughness of Directionally Solidified NiAl/(Cr,Mo) Alloys Modified with Hf, Si, Ta, Ti Additions
Authors: Locci I. E. , Raj S. V. , Whittenberger J. D. , Salem J. A. , Keller D. J. 
Published: April 2011

ABSTRACTA statistical design of experiments (DOE) strategy was implemented to optimize alloys based on the Ni-33AI-31Cr-3Mo eutectic system using small amounts of potential strengthening elements (Hf, Si, Ta, Ti). Following the analysis of the DOE results, several alloys were selected for directionally solidification (DS) utilizing a modified Bridgeman technique. The as-grown alloys were microstructurally examined by optical and scanning electron microscopy. They were also evaluated for fracture toughness at room temperature and compressive properties at 1300K. The microstructures and mechanical properties of these DS DOE alloys are discussed and compared to the directionally solidified Ni–33Al–3lCr–3Mo base composition.
Microstructural Evaluation During Mechanical Milling and Consolidation of ODS LI2-(AI,Cr)3Ti
Authors: Saage H. , Heilmaier M. , Eckert J. , Schultz L. 
Published: April 2011

ABSTRACTThe effect of different oxide particles on the microstructure and the high temperature creep behavior of ODS ternary L12-(Al,Cr)3Ti intermetallic compounds, which were prepared by high energy ball milling, was analyzed. Particular attention was paid to the development of the dispersoid size and distribution after the milling process, the consolidation and the heat treatment.X-ray diffraction (XRD) and transmission electron microscopy (TEM) of the as-milled powders indicate that the ordered matrix can nearly be amorphizied during milling. Moreover, independent of the type of oxide the dispersoids with a mean diameter ≤ 20 nm are homogeneously distributed in the metallic matrix. Using hot pressing under protective atmosphere the powders were compacted to nearly full density, followed by heat treatment. This results in grain sizes varying between 200 nanometers and several micrometers. However, due to the nature of the dispersoids used different particle diameters were found after consolidation and annealing. Although known to be the thermodynamically most stable oxide the initial Y2O3powder has formed a mixed yttrium-aluminum oxide during manufacturing and, hence, significant particle growth has been observed. While CeO2shows a similar behavior, the line compound A12O3remains stable, but the average particle size of this oxide also increases during the heat treatment. First preliminary mechanical tests supported by TEM observations show the significant influence of the grain size on the creep resistance at high temperatures.
An Explanation for the Environmental Sensitivity of Ni3Al
Authors: Lillig D. B. , Legzdina D. , Robertson I. M. , Birnbaum H. K. 
Published: April 2011

ABSTRACTSecondary Ion Mass Spectrometry has been used to study the distribution of elements in and near grain boundaries in boron-free and boron-doped Ni76Al24 alloys with and without ∼220 wt. ppm of deuterium. In boron-free alloys, sulfur was distributed about the grain boundaries in both deuterium- free and deuterium-charged samples. The distribution of deuterium followed that of sulfur and was segregated to grain boundaries. In the boron-doped material, sulfur was not found at most grain boundaries in the uncharged material, but was in the charged material. No deuterium was found at the grain boundaries in the boron-doped material. It is proposed that in the boron-free material it is the synergistic effect of sulfur and hydrogen that is responsible for the environmental sensitivity of this alloy. In boron-doped material, boron segregation to the grain boundary prevents sulfur, and to some extent hydrogen, segregating to the grain boundary.
Effect of Nb Content and Temperature on the TiN Formation During the Oxidation of Ti3Al
Authors: Zhang Lanting , Wu Jiansheng , Jiang Kai , Wang Fei 
Published: April 2011

ABSTRACTNb addition to Ti3Al has been found to be effective to improve its oxidation resistance. Recently, the beneficial effect of nitrogen in the oxidation behaviour of Nb contained T3AI-based alloys has been noticed. In this paper, the oxidation behaviour of five alloys with different Nb content from 0 to 20 at. % exposed in room air at different temperatures (from 600 to 950,C) has been examined with the focus on the TiN formation in the oxide scale. No TiN is detected in the scales of binary Ti3Al under all temperatures tested. On the contrary, in alloys containing Nb, TiN is identified in the scales irrespective of the oxidation temperature. The amount of TiN formation differs with differentNb content. EPMA analysis of the cross section of the scales is performed and discussion is made accordingly.
Creep of Mechanically-Alloyed NiAl Containing 13 Vol % Mo or Mo2C Dispersoids
Authors: Lakki A. , Dunand D. C. 
Published: April 2011

ABSTRACTDispersion-strengthened nickel aluminide NiAl was synthesized by reactive mechanical alloying from elemental powders. The microstructure and creep properties of these materials was compared for two cases: (i) NiAl-Mo, where dispersoids are in the form of a ductile, metallic phase and (ii) NiAl- Mo2C, where the dispersoids are a brittle, ceramic phase. Also, the effect of annealing treatments which coarsened both matrix grains and dispersoids was investigated. Inhibited diffusional creep is identified as the rate-controlling creep mechanism.
Glide Mechanisms of <001> Dislocations in NiAl
Authors: Caillard D. 
Published: April 2011

ABSTRACTThe glide properties of <001> dislocations have been studied by in situ straining experiments at and below room temperature, with the aim of studying slip, cross-slip, Peierls friction forces, and pinning at small obstacles. Most results are in a good agreement with atomistic calculations. It is concluded that unpinning from small extrinsic obstacles is probably the rate controlling mechanism in this temperature range and in the soft orientation.
Deformation Behavior And Internal Stress Of Icosahedral Al-Pd-Mn With Decagonal Phase Lamellae At Elevated Temperatures
Authors: Hirai H. , Tomita T. , Yoshida F. , Nakashima H. 
Published: April 2011

AbstractFine decagonal phase lamellae-bearing icosahedral Al-Pd-Mn quasicrystals were tested compressionally at temperatures of 997 to 1073 K and initial strain rate of 3 × 10−5. to I × 10−4 S−1, and stress relaxation tests were performed at various stages of deformation. The results confirmed the thermally activated nature of deformation, and the stress exponent of strain rate was around 4. Internal stress for deformation estimated by Kikuchi's method reached 50 to 90 % of applied stress. The effective stress exponent of strain rate was revealed to be about 1.3. At least a part of high internal stress was attributable to complicated dislocation microstructure.
Thermal And Electronic Properties Of An AICoFeCr Approximant Of The Decagonal Phase
Authors: Archambault P. , Plaindoux P. , Belin-Ferre E , Dubois J. M. 
Published: April 2011

AbstractWe have studied the dependence versus nominal composition and temperature of the thermal conductivity in the AlCoFeCr system close to the region where an approximant of the decagonal phase forms. This compound of the Al5Co2type shows a melting temperature above 1100°C and is of interest because it dispays low thermal conductivity whereas its expansion coefficient is comparable to those of metallic substrates. Used as a coating, it is of potential value for the sake of producing thermal barriers. From a study of the occupied band by X-ray emission spectroscopy, we show that its poor thermal conductivity above room temperature fits with the recurrent localization scheme of electronic states.
Measurements Of The Hydrogen Absorption Pressurecomposition Isotherms IN Ti/Zr-Based Quasicrystals
Authors: Kim J. Y. , Majzoub E. H. , Gibbons P. C. , Kelton K. F. 
Published: April 2011

AbstractThe first hydrogen absorption pressure-composition isotherms (p-c-T) were measured in quasicrystalline Ti45Zr38Ni17. No evidence for a pressure plateau was found, indicating a distribution of energies for the hydrogen in interstitial sites. Fits to the p-c-T data confirmed this, giving energy peaks at -0.19 eV with a full width at half maximum (half-width) of 0.06 eV, and at -0.09 eV with a half-width of 0.08 eV. This is in contrast with the broad site energy distribution that is characteristic of a metallic glass. In agreement, fits to data taken from amorphous Ti45Zr27Ni20Si8 gave a single broad energy distribution at -0.10 eV with a half-width of 0.35 eV. Based on the weighted averages of the site energies for the pure components, the energies assigned to the tetrahedral sites in the Ti44Zr40Ni16 1/1 approximant phase are in qualitative agreement with the measured data for the quasicrystal, supporting a local structural similarity between these two phases. Almost all of the absorbed hydrogen can be desorbed at 650°C in one hour by pumping, without transforming the quasicrystal phase and without powdering the rapidly-quenched samples.
Holographic Grating Formed by Photochemical Phase Transition of Polymer Azobenzene Liquid Crystal
Authors: Yamamoto T. , Yoneyama S. , Hasegawa M. , Kanazawa A. , Shiono T. , Ikeda T. 
Published: April 2011

ABSTRACTWe explored the formation of holographic gratings by means of a polymer azobenzene liquid crystal (PALC). When two writing beams (argon-ion laser, 488 nm, unpolarized) were interfered on the surface of the PALC film (thickness, 500 ∼ 600 nm), multiple diffraction beams were observed immediately, resulting from grating formation. Such generation of the diffraction beams was assumed to be due to a periodic induction of photochemical phase transition in the bright fringes of the interference pattern. The grating is namely made up of a periodic arrangement of nematic (N, dark fringes) and isotropic (I, bright fringes) phases. Observation of recorded interference patterns under a cross-polarized optical microscope supported our speculation for the structure of the grating. On the basis of these results, we succeeded in recording an image hologram of a photomask as an object.
Two-Dimensional Superlattice Self-Formed by Novel Ionic Liquid Crystals and Its Photofunctional Property
Authors: Kanazawa A. , Ikeda T. 
Published: April 2011

ABSTRACTThermotropic liquid-crystalline behavior of various complex salts, which are structurally simple amphiphiles without rigid cores, was evaluated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry. The phosphonium salts, consisting of positive phosphorus and negative chloride ions, were found to show a smectic A phase in which a homeotropic structure was formed spontaneously. It is significant that the phosphonium salts possess an advantageous feature as thermotropic liquid crystals and show a stable liquid-crystalline phase and a simple phase transition behavior in comparison with commonly available ammonium analogs. Furthermore, the introduction of divalent metal ions into the amphiphiles was revealed to result in enhancement of the thermal properties. Although the ammonium chlorides as parent compounds showed no liquid-crystalline phase (or indistinct transition behavior), the ammonium complexes possessing tetrachlorometalate ions exhibited clearly the smectic A phase in the expanded temperature range. Additionally, through the evaluation of dipolar alignment in the solid-state phosphonium assembly by second harmonic generation, it was assumed that the self-assembly can be regarded as layered polar thin films produced by two-dimensional ionic layers with an overall permanent electric polarization.
Electrooptic Characteristics of Polymer Stabilized Flcd: Application to field Sequential Fullcolor Display
Authors: Takahashi T. , Furue H. , Miyama T. , Shikaday M. , Kurihara R. , Kobayashi S. 
Published: April 2011

ABSTRACTLiquid crystal displays (LCDs) will be classified into miniature display, reflective type, projection type, direct view type, and holography type. All of these LCDs will be widely utilized in the coming multimedia network era. Along with this trends, in the first part of this paper we will discuss the social background of this research. In this paper we will place an emphasis on a polymer stabilized (PS) FLCD that is featured by fast response speed (40 µsec), high contrast (230:1) with grayscale, wide viewing angle, and high resolution (4001p/mmn). The PS-FLCD, which is referred to as Liquid Crystal Optical Diode owing to its strong asymmetric electrooptical characteristics, will be a promising technology for displaying a moving video image, and optical computing.
Microstructure and Surface Structure Evolution in AlCu Polycrystalline Thin Films
Authors: Lita Adriana E. , Sanchez John E. 
Published: April 2011

ABSTRACTThe evolution of crystallographic texture, grain size and surface morphology in magnetron sputter deposited Al-0.5wt.% Cu polycrystalline thin films is reported as a function of film thickness for SiO2 and SiO2/Ti underlayers for several deposition rates. Regardless of the underlayer type, the initial ≈ 10 nm of the Al-Cu films is nearly randomly oriented, with the films developing a (111) out-of-plane texture which increases in strength with thickness during deposition. The AlCu films on sputtered Ti underlayers developed an exact (111) fiber orientation while Al-Cu films on oxide substrates were offset ≈ 5° from exact fiber orientation. Higher deposition rates were found to result in slightly better (111) textured 20 nm AlCu films. The surface morphology of films, determined by Atomic Force Microscopy (AFM), revealed two regimes of average roughness (Rrms) evolution during deposition. Rrms decreased early in the deposition process, followed by a roughening regime where Rrms increased with thickness. These results are discussed in terms of mechanisms such as grain growth, which help to determine microstructure development during film formation from the vapor.