bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Thermal Gravitational Convection on Solidi Fication Processes
Authors: Tensi Hans M. , Schmidt Joachim J. 
Published: March 2011

AbstractThe aim of these experiments in the Gradient Furnace with Quenching device (GFQ) during the German D-1 Mission was to study the influence of thermal convection on– the diffusion in the melt ahead of the solidification front in an AlCu-alloy– the stability of a smooth solidification front in an Al-Cualloy and– the morphology of the solidification front in an AlSi-alloyduring the directional solidification of the binary alloys AlCu with 0.3 wght.-% Cu and AlSi with 7.0 wght.-% Si. Altogether five samples had been successfully processed during the D1-Mission. After getting the complete values from the process data (above all the velocity of the solidification front and the temperature gradient) reference experiments were made in the same GFQ under lg-conditions.Additional experiments under lg with a transparent fluid were done to obtain information about the thermal convection in a cylindrical cell while measuring temperature distribution at the same time.A first result having the same crystallization condition is the more than twice thicker diffusion boundary layer in AlCu 0,3-specimen than in the lg-reference specimen. The diffusion coefficient and the dendritic morphology are to be determined. The evaluation of all specimens (flight- and lg-samples) is not finished in the moment.
Synthesis and Characterization of TiO2-Nb2O5Borosilicate Glasses for Nonlinear Optical Waveguides
Authors: Vogel E. M. , Fribérg S. R. , Jackel L. , Smith P. W. 
Published: March 2011

ABSTRACTNonlinear optical glasses with fast responding nonlinearities and very low absorption are promising materials for use in ultra-fast (picosecond) all-optical switches. We have synthesized a TiO2Nb2O5. B2O3Na2O SiO2glass with the intention of optimizing both the third order optical nonlinearity and suitability for fabrication of optical waveguides. The nonlinear index coefficient n2for this glass composition was found to be 4X 10-19m2/W, a factor of two greater than the largest value previously reported for commercially available TiO2-silicate glasses. Optical waveguides with a maximum index change of Δn = 0.12 were made using silver-sodium ion exchange. These waveguides may become building blocks for future all-optical logic elements and circuits.
Synthesis, Ultrapurification and Analysis of LaF3 for Fluoride Optical Fibers
Authors: Gabbe D. R. , Folweiler R. C. , Pink F. X. 
Published: March 2011

ABSTRACTLanthanum chloride was synthesized by reacting La2O3 with CCl4. Purification carried out by zone refining resulted in reduction of Nd and Eu concentrations by at least a factor of 103. Impurity segregation coefficients were calculated from the concentration profiles in the charge measured by neutron activation analysis. Values of 0.85, 0.5, and 0.15 were found for Ce, Nd and Eu while a value of 0.65 was obtained for Pr from a plot of measured distribution coefficient versus ionic radius. These results show the feasibility of removing rare earth impurities to the ppb level from LaCl3. After purification, LaC13 is converted to LaF3
Optical Fiber Coating Evaluations for Composite Embedment Applications
Authors: Martin David A. 
Published: March 2011

ABSTRACTAn emerging growth market for integrated optic devices and data transmission is in non-metallic composite aircraft structures. There is a regional need to identify optical fiber coatings which are suitable for embedment in composite structures. This paper assesses fibers with various coatings for the following: 1) critical structural test performance, 2) reproducibility, and 3) low attenuation when subjected to representative manufacturing and service conditions. A brief discussion of follow-on system verification tests, and an overview of desirable fiber and coating developments to meet future application requirements are also included.
Control of Radiation Induced Defects of Pure Silica Fiber Prepared by VAD Process
Authors: Muta K. , Kashiwazaki A. , Kohketsu M. , Kawazoe H. 
Published: March 2011

ABSTRACTThe γ-induced centers in SiO2 glass such as the Si-E' center and OHC were found to be effected by the atmosphere present during melting. In the case of the VAD process, a porous preform rod is sintered to fabricate a transparent preform rod. The generation of defect species could be easily controlled by controlling the atmosphere of the sintering process. Only small amounts of OHC are generated in fibers sintered in Cl2 or H2 atmospheres, and most of the OHC is recovered at room temperature. This indicates the possibility of making fibers which are highly resistant to irradiation. The correlation between the γ-induced loss increase and the formation of these defects was examined.
The Use of an Organosilsesquioxane for the Coating/Cladding of Silica Fibers
Authors: Bagley B. G. , Kurkjian C. R. , Quinn W. E. 
Published: March 2011

ABSTRACTThe properties necessary for a material to be useful as a fiber cladding (appropriate Δn) and/or coating (provide mechanical protection) were evaluated for an organosilsesquioxane (Owens-Illinois Resin GR 650). The samples were 120 μm silica fibers coated with 12 μm of the cured organosilicon polymer. We observe, from an index profile of the clad fiber, that Δn = 0.04. The tensile strength measured in air (65% RH, 25 °C) was 765 ksi and the dynamic fatigue constant determined under the same ambient conditions was 29, both of which are typical of a mechanically protected fiber. From aging experiments in 90 °C distilled water we observe that the onset for a marked loss of strength with time is ∼1 day for an epoxy-acrylate coated fiber and slightly more than a week for the organosilicon polymer coated fiber, a notable improvement.
Influence of Formation Parameters on the Mechanical Properties of Wet Gels
Authors: Pardenek S. A. , Fleming J. W. , Klein L. C. 
Published: March 2011

ABSTRACTThe mechanical behavior of wet silica gels formed by various sol-gel processes has been studied. Samples were analyzed with a beam-bending apparatus specifically designed for accurate measurements of very low strength solids. Breaking strength, viscosity and relaxation measurements were made on gelled bodies. Specimens were studied in an undried gel state, molded in shapes suitable for the particular experiments. Tests were made in several ambient conditions including immersion in a liquid bath. The mechanical properties of gels are dependent upon the gel composition, gel age and other formation parameters such as pH, temperature and pressure. An understanding of these properties is particularly important in determining the nature of subsequent processing steps. Models for the structures of the various gels are proposed which explain variation in mechanical behavior.
Advanced Ti-Implanted Optical Waveguides in LiNbO3
Authors: Buchal Ch. , Ashley P. R. , Thomas D. K. , Appleton B. R. 
Published: March 2011

ABSTRACTLiNbO3 is the best substrate for modulators and switches for integrated optics. Efficient low loss waveguides for light in LiNbO3 are formed by introducing Ti-ions into its lattice, thus increasing locally the ordinary and the extraordinary indices of refraction. We are the first to use the very versatile technique of ion-implantation to administer Ti into LiNbO3. This implantation process offers the possibility to introduce significantly more Ti into a well-defined volume than conventional diffusion techniques. During this process first an amorphous non-equilibrium phase is generated, which has to be kept at low temperatures in order to prevent segregation. Subsequent thermal treatment leads to solid phase epitaxy and restores the desired stable crystalline state. We have used this technique to fabricate excellent planar waveguides, channel waveguides and Mach-Zehnder modulators.
Semimagnetic Lead Salt Alloys
Authors: Bauer Günther 
Published: March 2011

AbstractThe magnetic and electronic properties of pseudobinary alloys of the lead compounds (PbTe,PbSe)with Manganese, Europium and Gadolinium are reviewed. These materials have a direct minimum gap at the L-point of the Brillouin zone. The addition of Mn, Eu, or Gd to the diamagnetic hosts causes a rather weak antiferromagnetic exchange interaction. For sufficiently high carrier concentrations (10 2 0 -102 1 cm−3) a ferromagnetic interaction occurs due to RKKY interaction. The spin-spin exchange interaction between the Bloch states and the localized 3d or 4f states is characterized by rather small exchange integrals and the limited applicability of the mean field approximation for the description of energy band parameters like g-factors. Interband transitions in PbMnTe and PbMnS lend support to a zeromagnetic field splitting (“spin-splitting”)of band states which increases linearly with Mn-content up to several meV at temperatures below 4K.
Electronic Theory of Mn - Alloyed Diluted Magnetic Semiconductors
Authors: Ehrenreich H. , Hass K. C. , Larson B. E. , Johnson N. F. 
Published: March 2011

AbstractRecent calculations of the electronic structure and magnetic interactions in Mn - alloyed II-VI diluted magnetic semiconductors (DMS) are summarized. Detailed band structure results are obtained using an empirical tight-binding, coherent potential approximation approach with input from experiment and local spin density band calculations. The dominant magnetic interactions in these systems result from hybridization between spin-split Mn d states and sp valence bands. Superexchange between Mn moments is well described by a simple three-level model which yields accurate Mn - Mn exchange constants for a variety of II-VI DMS as well as the rocksalt insulators MnO and α-MnS.
Magnetization of Random and Nonrandom (Cd,Mn)Te Alloys
Authors: Heiman D. , Isaacs E. D. , Becla P. , Foner S. 
Published: March 2011

AbstractPulsed-field magnetization measurements up to 40 T by Faraday rotation were made for random alloy Cd1−xMnx Te with 0.1 < x < 0.5. At liquid helium temperature the magnetization can be separated into the sum of two components: a paramagnetic Brillouin-like part that saturates by B=15 T, and a part linear in B. For large x, the linear part dominates and becomes independent of x. Mean-field calculations suggest that an enhanced magnetization can be obtained with new ordered-alloy crystal structures which have reduced antiferromagnetic cancellations.
Surface and Bulk Photoconductivity of Cd1−xMnxTe
Authors: Neff H. , Lay K. Y. , Park K. , Bachmann K. J. 
Published: March 2011

AbstractDouble beam photoconductivity experiments are reported for the system Cd1−xMnxTe. The technique allows a separation of surface and bulk contributions, respectively. Bulk effects dominate for manganese rich material and reveal a sharp peak at the band gap energy while surface conductivity reveals a step function type spectral behavior. The growth of a native oxide on the surface causes an increase in the surface recombination velocity and a change from surface to bulk conduction. An oxide related trap state was discovered that is located at approximately 400 meV above the valence band edge.
Influence of Electric Fields on Exciton Luminescence in ZnSe/(Zn,Mn)Se Superlattices
Authors: Fu Qiang , Nurmikko A. V. , Kolodziejski L. A. , Gunshor R. L. 
Published: March 2011

AbstractApplication of moderate external electric fields to ZnSe/(Zn,Mn)Se superlattices is shown to yield readily measurable spectral shifts of the exciton ground state resonance in the quantum well limit. This shows that confinement effects increase the classical field ionization threshold. At high applied fields and low temperatures, externally injected hot electron excited luminescence from internal excitations of the Mn-ion is observed.
Optical Properties of (Pb,Eu)Te Thin Films and Superlattices
Authors: Goltsos W. C. , Nurmikko A. V. , Partin D. L. 
Published: March 2011

AbstractPhotoluminescence, transmission, and reflectance measurements have yielded information about the states defining an optical gap in thin films and superlattices based on the (Pb,Eu)Te system, including the limit of high Eu concentration. Magneto-optical measurements show the presence of finite spin exchange processes at low Eu-concentrations.
Atomic Layer Epitaxy of Diluted Magnetic Semiconductors
Authors: Pessa M. , Lilja J. , Jylhä O. , Ishiko M. , Asonen H. 
Published: March 2011

AbstractAt the time being, there is evidently a sharp increase of interest in growth of low-dimensional thin-film structures of semiconducting compounds by the Atomic Layer Epitaxy (ALE) method. Many of the wide-gap II-VI compounds can be grown from elemental source materials by an ALE mode related to Molecular Beam Epitaxy (MBE). This paper concentrates on recent ALE work involving ZnSe- and CdTe- derived diluted magnetic semiconductors (DMS) where a fraction of Zn or Cd is substituted by Mn atoms. It shows that Zn1-xMnxSe/ZnSe and Cd1-xMnxTe/CdTe DMS structures with abrupt interfaces and high structural perfection can be produced at low growth temperatures by the ALE method.
Low-Temperature Magnetic Spectroscopy of Dilute Magnetic Systems
Authors: Awschalom D. D. , Warnock J. 
Published: March 2011

AbstractOptically induced magnetization has been observed in a 10 micron diameter sample of Cd.8Mn.2Te. A newly developed integrated SQUID magnetic spectrometer was used to study both the magnitude and the picosecond dynamics of the magnetic response as function of the energy and polarization of the optical excitation. The dramatic energy dependence of the response provides an understanding of the way in which the overall sample magnetization changes upon illumination, and the subsequent relaxation through the spin lattice interaction.
Spin-Texture in Acceptor-Bound Magnetic Polarons
Authors: Isaacs Eric D. , Wolff Peter A. 
Published: March 2011

AbstractWe outline a theory of the acceptor-bound magnetic polaron in cubic diluted magnetic semiconductors that exhibits a nonuniform magnetization. Calculations show that the manganese spins have an overall z-alignment, but are canted in an azimuthally symmetric way from that direction. This is new phenomenon we call BMP spin-texture. Spin-texture results from valence band degeneracy, and the important spin-orbit effects associated with it. The possibility of studying BMP spin-texture via neutron scattering is discussed.
Investigation of Metallic and Metallic Glass Hollow Spheres for Fusion Target Application
Authors: Lee Mark C. , Kendall James M. , Wang Taylor G. , Johnson William L. , Keck W. M. 
Published: March 2011

ABSTRACTHigh quality metallic and metallic-glass microballoons (MMB and MGMB) are of considerable interest for fusion target applications on account of the intrinsic properties of these materials such as high density, high strength and high atomic number. We report the first successfully formed submillimeter and millimeter spherical shells of tin and of a gold-lead-antimony alloy by means of the hollow-jet instability technique developed by one of us (JMK). Examination of tin specimens by means of SEM has revealed that surface quality varied from poor to excellent. Whereas this metal has been employed only as a convenient and inexpensive material, the gold alloy is important because it is hard, has high atomic number, and may be solidified into the amorphous state through the provision of a modest cooling rate. We have produced AuPbSb spherules up to 1.5 mm in diameter using LN2 or chilled methanol as a coolant, and have found that these amorphous samples possess a superb surface smoothness compatible with fusion target requirements. Hollow spheres currently made of this alloy have an average O.D. of 2000 μm.
The Calculation of Transport Phenomena in Electromagnetically Levitated Metal Droplets
Authors: El-Kaddah N. , Szekely J. 
Published: March 2011

ABSTRACTA mathematical representation has been developed for the electromagnetic force field, the fluid flow field, the temperature field (and for transport controlled kinetics) in a levitation melted metal droplet. The technique of mutual inductances was employed for the calculation of the electromagnetic force field, while the turbulent Navier-Stokes equations and the turbulent convective transport equations were used to represent the fluid flow field, the temperature field and the concentration field. The governing differential equations, written in spherical coordinates, were solved numerically.The computed results were found to be in good agreement with measurements reported in the literature, regarding the lifting force and the average temperature of the specimen.
Effect of Rayleigh Accelerations Applied to an Initially Moving Fluid
Authors: Dressler Robert F. , Robertson S. J. , Spradley L. W. 
Published: March 2011

ABSTRACTAlthough the instability of an initially motionless fluid subjected to a Rayleigh-type acceleration is well known, this type of excitation applied to an initially moving fluid has not been studied previously. We have therefore performed numerical analyses for two-dimensional unsteady thermal convection in circular cylinders under variable low-g conditions associated with space flight. When an acceleration vector is applied parallel to the thermal gradient for a fluid at rest, no convection results for the stable direction, and an instability leads to Rayleigh convection for the opposite direction. However, when the acceleration has a component which is orthogonal to the gradient, convection always results at any Rayleigh number; this is the usual situation during space flight. We therefore study the resultant effect on convection when both types of acceleration are applied, concurrently or sequentially, and when the resultant vector varies in direction with time. Our results indicate that for space flight conditions, the Rayleigh accelerations impose significant, but not dominating, alterations in the established convection even when the Rayleigh number is less than critical.
Theoretical Studies in Isoelectric Focusing
Authors: Mosher R. A. , Palusinski O. A. , Bier M. 
Published: March 2011

ABSTRACTOur overall objective is the development of a process for large scale purification of biologicals by isoelectric focusing (IEF). Thus, it was important to gain a better understanding of the underlying physical phenomena through mathematical modeling and computer simulation of the process. A mathematical model of the steady state in IEF was developed for an L-component system of ampholytes or monovalent buffers. It is based on the fundamental equations describing the components' dissociation equilibria, mass transport due to diffusion and electromigration, electroneutrality, and the conservation of charge. The model consists of ordinary differential equations coupled to a system of algebraic equations. The validity and usefulness of these simulationshas been confirmed in the formulation of actual buffer mixtures for experimental IEF. This model was recently extended to include the transient evolution to a steady state. Furthermore the new formulation applies to other electrophoretic processes, notably isotachophoresis and zone electrophoresis. As a result, we now have the first general model which predicts the behavior of a given chemical system in a variety of electrophoretic processes.
Atomic Fluorescence Study of High Temperature Aerodynamic Levitation
Authors: Nordine Paul C. , Schiffman Robert A. , Sethi D. S. 
Published: March 2011

ABSTRACTUltraviolet laser induced atomic fluorescence has been used to characterize supersonic jet aerodynamic levitation experiments. The levitated specimen was a 0.4 cm sapphire sphere that was separately heated at temperatures up to 2327K by an infrared laser. The supersonic jet expansion and thermal gradients in the specimen wake were studied by measuring spatial variations in the concentration of atomic Hg added to the levitating argon gas stream. Further applications of atomic fluorescence in containerless experiments, such as ideal gas fluorescence thermometry and containerless process control are discussed.
A Study of the Coalescence Process Inside the Miscibility Gap in Zn-Bi Alloys
Authors: Bergman Å. , Fredriksson H. 
Published: March 2011

ABSTRACTThe coalescence process has been studied in four different hyper-monotectic Zn-Bi alloys with 4–10wt % Bi . The alloys have been studied by isothermal treatments at a temperature just above the monotectic temperature and at different holding times. The alloys have been studied both at microgravity and at normal gravity. The change of the particle distribution as a function of composition and holding time has been investigated. The changing of the particle distribution has been compared with the theory of particle collision. The validity of the collision theory is investigated with respect to the theory of liquid phase sintering.
Levitation, Coating and Transport of Particulate Materials
Authors: Hendricks Charles D. 
Published: March 2011

ABSTRACTSeveral processes in various fields require uniformly thick coatings and layers on small particles. The particles may be used as carriers of catalytic materials (platinum or other coatings), as laser fusion targets (various polymer or metallic coatings), or for biological or other tracer or interactive processes. We have devisea both molecular beam and electro-dynamic techniques for levitation of the particles during coating and electrodynamic methods of controlling and transporting the particles between coating steps and to final use locations. Both molecular beam and electrodynamic techniques are describea and several advantages and limitations of each will be discussed. A short movie of an operating electrodynamic levitation and transport apparatus will be shown.
The Effect of Solute on the homogeneous Crystal Nucleation Frequency in Metallic Melts
Authors: Thompson C.V. , Spaepen F. 
Published: March 2011

ABSTRACTWe have made a complete calculation that extends the classical theory for crystal nucleation in pure melts to binary alloys. Using a regular solution model, we have developed approximate expressions for the free energy change upon crystallization as a function of solute concentration. They are used, together with model-based estimates of the interfacial tension, to calculate the nucleation frequency. The predictions of the theory for the maximum attainable undercooling are compared with existing experimental results for non-glass forming alloys. The theory is also applied to several easy glass-forming alloys (Pd-Si, Au-Si, Fe-B) for qualitative comparison with the present experimental experience on the ease of glass formation, and for assessment of the potential for formation of the glass in bulk.
Finite Elenent Analysis of The Effect of a Non-Planar Solid-Liquid Interface on The Lateral Solute Segregation During Unidirectional Solidification.
Authors: Carlson F. M. , Chin L-Y , Fripp A. L. , Crouch R. K. 
Published: March 2011

ABSTRACTThe effect of solid-liquid interface shape on lateral solute segregation during steady-state unidirectional solidification of a binary mixture is calculated under the assumption of no convection in the liquid. A finite element technique is employed to compute the concentration field in the liquid and the lateral segregation in the solid with a curved boundary between the liquid and solid phases. The computational model is constructed assuming knowledge of the solid-liquid interface shape; no attempt is made to relate this shape to the thermal field. The influence of interface curvature on the lateral compositional variation is investigated over a range of system parameters including diffusivity, growth speed, distribution coefficient, and geometric factors of the system. In the limiting case of a slightly non-planar interface, numerical results from the finite element technique are in good agreement with the analytical solutions of Coriell and Sekerka obtained by using linear theory. For the general case of highly non-planar interface shapes, the linear theory fails and the concentration field in the liquid as well as the lateral solute segregation in the solid can be calculated by using the finite element method.