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Determination of neuronal morphology in spinal monolayer cultures

Description: The objective of the completed research was to characterize the morphology of individual neurons within monolayer networks of fetal mouse spinal tissue via intraperikaryal injections of horseradish peroxidase (HRP). Thirty labelled neurons were reconstructed via camera lucida drawings and morphometrically analyzed.
Date: May 1989
Creator: De La Garza, Richard
Partner: UNT Libraries

Projection Methods for Interdendritic Flows

Description: In spite of recent advances in the mathematical modeling of fluid dynamics for materials processing applications, no significant advances have been made in the numerical discretization of these equations. In this work, the application of two-step projection methods for the numerical simulation of interdendritic flows is, discussed. Unlike previous methods, the methods presented here are constructed for the exact equations which are characterized by variable density and volumetric fraction of the liquid. The drag terms, which describe the momentum loss due to the flow around and through the dendrite structures, are treated implicitly. Numerical examples for shrinkage-induced flow during solidification of an AI-4.5% Cu alloy bar is used to illustrate the effectiveness of the proposed algorithm.
Date: February 28, 1999
Creator: Han, Q.; Sabau, A.S. & Viswanathan, S.
Partner: UNT Libraries Government Documents Department

Self-Diffusion Along Step-Bottoms on Pt(111)

Description: First-principles total energies of periodic vicinals are used to estimate barriers for Pt-adatom diffusion along straight and kinked steps on Pt(111), and around a corner where straight steps intersect. In all cases studied, hopping diffusion has a lower barrier than concerted substitution. In conflict with simulations of dendritic Pt island formation on Pt(111), hopping from a corner site to a step whose riser is a (111)-micro facet is predicted to be more facile than to one whose riser is a (100).
Date: April 5, 1999
Creator: Feibelman, P.J.
Partner: UNT Libraries Government Documents Department

UPTAKE OF [3H]-COLCHICINE INTO BRAIN AND LIVER OF MOUSE, RAT, AND CHICK

Description: The uptake of [ring A-4-{sup 3}H] colchicine and [ring C-methoxy-{sup 3}H]colchicine has been compared in mice from 1 to 24 hr after administration. Less radioactivity was found in brain after administration of ring-labeled colchicine than after administration of the methoxy-labeled colchicine. Three hr after administration of ring-labeled colchicine, 5% of the label was in liver and about 0.01% of the label was present in brain. Forty percent of the brain radioactivity was bound to tubulin as determined by vinblastine precipitation. After 3 hr, an average of 8% of the radioactivity from methoxy-labeled colchicine was found in the liver and 0.16% in brain. However, less than 5% of the activity in brain was precipitated by vinblastine, and the colchicine equivalent was comparable to that found after administration of the ring-labeled colchicine. The amount of colchicine entering mouse brain after subcutaneous injection is comparable to the minimum behaviorally effective dose when administered to the caudate. The metabolism of [ring C-methoxy-{sup 3}H] and [ring A-{sup 3}H]colchicine was also studied in rats. the general pattern was similar to mice; less radioactivity was found in brain after administration of the ring-labeled alkoloid than after administration of methoxy-labeled colchicine. Again, 40-50% of ring-labeled colchicine was precipitated by vinblastine. A much smaller percentage of the methoxy-labeled drug was precipitated by vinblastine than of the ring A-labeled colchicine. These experiments, together with behavioral experiments [7], support the hypotheses that structural alteration in synapses by recently synthesized proteins which are transported down the axons and dendrites may be an essential process for long-term memory formation.
Date: July 1, 1980
Creator: Bennett, Edward L.; Alberti, Marie Hebert & Flood, James F.
Partner: UNT Libraries Government Documents Department

On a solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses

Description: The recent development of metallic glass-matrix composites represents a particular milestone in engineering materials for structural applications owing to their remarkable combinations of strength and toughness. However, metallic glasses are highly susceptible to cyclic fatigue damage and previous attempts to solve this problem have been largely disappointing. Here we propose and demonstrate a microstructural design strategy to overcome this limitation by matching the microstructural length scales (of the second phase) to mechanical crack-length scales. Specifically, semi-solid processing is used to optimize the volume fraction, morphology, and size of second phase dendrites to confine any initial deformation (shear banding) to the glassy regions separating dendrite arms having length scales of {approx} 2 {micro}m, i.e., to less than the critical crack size for failure. Confinement of the damage to such interdendritic regions results in enhancement of fatigue lifetimes and increases the fatigue limit by an order of magnitude making these 'designed' composites as resistant to fatigue damage as high-strength steels and aluminum alloys. These design strategies can be universally applied to any other metallic glass systems.
Date: January 9, 2009
Creator: Launey, Maximilien E.; Hofmann, Douglas C.; Johnson, William L. & Ritchie, Robert O.
Partner: UNT Libraries Government Documents Department

DOE STI Product/Final Report Number 3 Electrochemical Investigation of Novel Electrolytes for Ambient Temperature Sodium Batteries

Description: The need for low-cost, high-energy density, durable, secondary batteries continues to rise with the demands of the electronics and automobile industries. A room-temperature version of the (high-temperature) ''Zebra Cell'' may provide an interesting technology for portable electronics and transportation. Sodium-based batteries have received attention as an alternative to the lithium-based batteries due to several factors including the absence of dendrite formation during sodium deposition and the abundance of sodium. This work focused on (1) the development of room-temperature ionic liquids (IL) for use in electrochemical devices, including batteries, (2) development and evaluation of secondary sodium batteries using room-temperature ILs, and (3) advancing the fundamental understanding of the electrochemical processes involving ILs and battery technology. Several objectives were accomplished during this program.
Date: December 1, 2005
Creator: Kim, Ketack; Lang, Christopher M.; Doyle, Kevin & Kohl, Paul A.
Partner: UNT Libraries Government Documents Department

Summary of research output from DOE grant DE-FG02-92ER45471 during the period 1992-2006: publications, invited talks, conference organization, and PhD students graduated.

Description: In this report I summarize some of the main results obtained during the present grant period. They are: (1) Orientation selection in dendritic evolution; (2) Globubar-dendritic transition; and (3) Physics and prediction of grain boundary mobility.
Date: August 1, 2006
Creator: Karma, Alain, PhD.
Partner: UNT Libraries Government Documents Department

Fracture toughness and crack-resistance curve behavior in metallic glass-matrix composites

Description: Nonlinear-elastic fracture mechanics methods are used to assess the fracture toughness of bulk metallic glass (BMG) composites; results are compared with similar measurements for other monolithic and composite BMG alloys. Mechanistically, plastic shielding gives rise to characteristic resistance?curve behavior where the fracture resistance increases with crack extension. Specifically, confinement of damage by second?phase dendrites is shown to result in enhancement of the toughness by nearly an order of magnitude relative to unreinforced glass.
Date: May 26, 2009
Creator: Launey, Maximilien E.; Hofmann, Douglas C.; Suh, Jin-Yo; Kozachkov, Henry; Johnson, William L. & Ritchie, Robert O.
Partner: UNT Libraries Government Documents Department

Mechanistic Selection and Growth of Twinned Bicrystalline Primary Si in Near Eutectic Al-Si Alloys

Description: Morphological evolution and selection of angular primary silicon is investigated in near-eutectic Al-Si alloys. Angular silicon arrays are grown directionally in a Bridgman furnace at velocities in the regime of 10{sup -3} m/sec and with a temperature gradient of 7.5 x 10{sup 3} K/m. Under these conditions, the primary Si phase grows as an array of twinned bicrystalline dendrites, where the twinning gives rise to a characteristic 8-pointed star-shaped primary morphology. While this primary Si remains largely faceted at the growth front, a complex structure of coherent symmetric twin boundaries enables various adjustment mechanisms which operate to optimize the characteristic spacings within the primary array. In the work presented here, this primary silicon growth morphology is examined in detail. In particular, this thesis describes the investigation of: (1) morphological selection of the twinned bicrystalline primary starshape morphology; (2) primary array behavior, including the lateral propagation of the starshape grains and the associated evolution of a strong <100> texture; (3) the detailed structure of the 8-pointed star-shaped primary morphology, including the twin boundary configuration within the central core; (4) the mechanisms of lateral propagation and spacing adjustment during array evolution; and (5) the thermosolutal conditions (i.e. operating state) at the primary growth front, including composition and phase fraction in the vicinity of the primary tip.
Date: December 12, 2006
Creator: Jung, Choonho
Partner: UNT Libraries Government Documents Department

Effect of Colchicine on Neuronal Excitabilty

Description: The abundance of microtubules in receptive dendrites suggests they may function in sensory transduction. Responses of frog muscle spindle receptors and joint receptors is inhibited within 25 minutes by 50 mM colchicine, a microtubuledisrupting agent. The inhibition is reversible upon removal of colchicine, and the time course of recovery is comparable to that of inhibition. Frog olfactory responses are briefly inhibited by washing the olfactory mucosa with perfusion fluid. Colchicine accentuates the inhibition and substantially retards the rate of recovery in a dose-dependent fashion. Colchicine does not affect axonal conduction, nor the oxygen uptake of isolated crab or frog leg nerves. The inhibitory action of colchicine is therefore an effect on the electrical excitability of the receptive dendrites or soma, and not an effect on axonal conduction.
Date: August 1978
Creator: Okafo, Ngozi
Partner: UNT Libraries

Magnetic resonance imaging of polymer electrolytes and insertion electrodes.

Description: This program seeks to better define electrode-electrolyte interfaces and solid-state ion transport mechanisms that are a central feature of fuel cells and advanced electrochemical systems. The goal is to develop a new generation of materials with enhanced energy efficiency and reduced tendency toward dendrite or passive film formation at the electrode-electrolyte interface.
Date: May 19, 1999
Creator: Gerald, R. E., II; Klingler, R. J. & Rathke, J. W.
Partner: UNT Libraries Government Documents Department

Origin of Compact Triangular Islands in Metal-on-Metal Growth

Description: The microscopic origin of compact triangular islands on close-packed surfaces is identified using kinetic Monte Carlo simulations with energy barriers obtained from density-functional calculations. In contrast to earlier accounts, corner diffusion anisotropy is found to control the shape of compact islands at intermediate temperatures. We rationalize the correlation between the orientation of dendrites grown at low temperatures and triangular islands grown at higher temperatures, and explain why in some systems dendrites grow fat before turning compact.
Date: July 12, 1999
Creator: Bogicevic, Alexander; Lundqvist, Bengt I. & Ovesson, Staffan
Partner: UNT Libraries Government Documents Department

Length Scale Correlations of Cellular Microstructures in Directionally Solidified Binary System

Description: In a cellular array, a range of primary spacing is found to be stable under given growth conditions. Since a strong coupling of solute field exists between the neighboring cells, primary spacing variation should also influence other microstructure features such as cell shape and cell length. The existence of multiple solutions is examined in this study both theoretically as well as experimentally. A theoretical model is developed that identifies and relates four important microstructural lengths, which are found to be primary spacing, tip radius, cell width and cell length. This general microstructural relationship is shown to be valid for different cells in an array as well as for other cellular patterns obtained under different growth conditions. The unique feature of the model is that the microstructure correlation does not depend on composition or growth conditions since these variables scale microstructural lengths to satisfy the relationship obtained in this study. Detailed directional solidification experimental studies have been carried out in the succinonitrile-salol system to characterize and measure these four length scales. Besides the validation of the model, experimental results showed additional scaling laws to be present. In the regime where only a cellular structure is formed, the shape of the cell, the cell tip radius and the length of the cell are all found to scale individually with the local primary spacing. The presence of multiple solutions of primary spacing is also shown to influence the cell-dendrite transition that is controlled not only by the processing variables (growth velocity, thermal gradient and composition) but also by the local cell spacing. The cell-dendrite transition was found not to be sharp, but occurred over a range of processing conditions. Two critical conditions have been identified such that only cells are present below lower critics condition, and only dendrites are formed above the upper ...
Date: August 1, 2002
Creator: Shen, Yunxue
Partner: UNT Libraries Government Documents Department

Length Scale Correlations of Cellular Microstructures in Directionally Solidified Binary System

Description: In a cellular array, a range of primary spacing is found to be stable under given growth conditions. Since a strong coupling of solute field exists between the neighboring cells, primary spacing variation should also influence other microstructure features such as cell shape and cell length. The existence of multiple solutions is examined in this study both theoretically as well as experimentally. A theoretical model is developed that identifies and relates four important microstructural lengths, which are found to be primary spacing, tip radius, cell width and cell length. This general microstructural relationship is shown to be valid for different cells in an array as well as for other cellular patterns obtained under different growth conditions. The unique feature of the model is that the microstructure correlation does not depend on composition or growth conditions since these variables scale microstructural lengths to satisfy the relationship obtained in this study. Detailed directional solidification experimental studies have been carried out in the succinonitrile-salol system to characterize and measure these four length scales. Besides the validation of the model, experimental results showed additional scaling laws to be present. In the regime where only a cellular structure is formed, the shape of the cell, the cell tip radius and the length of the cell are all found to scale individually with the local primary spacing. The presence of multiple solutions of primary spacing is also shown to influence the cell-dendrite transition that is controlled not only by the processing variables (growth velocity, thermal gradient and composition) but also by the local cell spacing. The cell-dendrite transition was found not to be sharp, but occurred over a range of processing conditions. Two critical conditions have been identified such that only cells are present below lower critics condition, and only dendrites are formed above the upper ...
Date: June 27, 2002
Creator: Shen, Yunxue
Partner: UNT Libraries Government Documents Department

Neuronal Survival After Dendrite Amputation: Investigation of Injury Current Blockage

Description: After dendrite transection, two primary injury current pathways may acount for cell death: (1) the lesion current at the site of injury and (2) the voltage sensitive calcium channels along the dendrite. Lesions were made with a laser microbeam in mouse spinal monolayer cell cultures. Polylysine was tried as a positively charged "molecular bandage" to block the lesion current. The calcium channel blockers, verapamil and nifedipine, were used to reduce the calcium channel current. Control toxicity curves were obtained for all three compounds. The results show that neither verapamil, nifedipine, nor polylysine (MW: 3,300) protect nerve cells after dendrite amputation 100 ptm from the soma. The data also indicate that these compounds do not slow the process of cell death after such physical trauma.
Date: December 1988
Creator: Shi, Ri Yi
Partner: UNT Libraries

The influence of VAR processes and parameters on white spot formation in Alloy 718

Description: Significant progress has occurred lately regarding the classification, characterization, and formation of white spots during vacuum arc remelting (VAR). White spots have been generally split into three categories: discrete white spots, which are believed to be associated with undissolved material which has fallen in from the shelf, crown, or torus regions; dendritic white spots, usually associated with dendrite clusters having fallen from the electrode; and solidification white spots, believed to be caused by local perturbations in the solidifications conditions. Characteristics and proposed formation mechanisms of white spots are reviewed and discussed in context of physical processes occurring during VAR, such as fluid flow and arc behavior. Where possible, their formation mechanisms will be considered with respect to specific operating parameters. In order to more fully understand the formation of solidification white spots, an experimental program has been begun to characterize the solidification stability of Alloy 718 and variants with respect to changes in growth rate and thermal environment. A description of the experimental program and preliminary results are included.
Date: May 1, 1994
Creator: Damkroger, B. K.; Kelley, J. B.; Schlienger, M. E.; Van Den Avyle, J. A.; Williamson, R. L. & Zanner, F. J.
Partner: UNT Libraries Government Documents Department

Interfacial behavior of polymer electrolytes

Description: Evidence is presented concerning the effect of surfaces on the segmental motion of PEO-based polymer electrolytes in lithium batteries. For dry systems with no moisture the effect of surfaces of nano-particle fillers is to inhibit the segmental motion and to reduce the lithium ion transport. These effects also occur at the surfaces in composite electrodes that contain considerable quantities of carbon black nano-particles for electronic connection. The problem of reduced polymer mobility is compounded by the generation of salt concentration gradients within the composite electrode. Highly concentrated polymer electrolytes have reduced transport properties due to the increased ionic cross-linking. Combined with the interfacial interactions this leads to the generation of low mobility electrolyte layers within the electrode and to loss of capacity and power capability. It is shown that even with planar lithium metal electrodes the concentration gradients can significantly impact the interfacial impedance. The interfacial impedance of lithium/PEO-LiTFSI cells varies depending upon the time elapsed since current was turned off after polarization. The behavior is consistent with relaxation of the salt concentration gradients and indicates that a portion of the interfacial impedance usually attributed to the SEI layer is due to concentrated salt solutions next to the electrode surfaces that are very resistive. These resistive layers may undergo actual phase changes in a non-uniform manner and the possible role of the reduced mobility polymer layers in dendrite initiation and growth is also explored. It is concluded that PEO and ethylene oxide-based polymers are less than ideal with respect to this interfacial behavior.
Date: June 3, 2003
Creator: Kerr, John; Kerr, John B.; Han, Yong Bong; Liu, Gao; Reeder, Craig; Xie, Jiangbing et al.
Partner: UNT Libraries Government Documents Department

Characterization of uranium and uranium-zirconium deposits produced in electrorefining of spent nuclear fuel

Description: This paper describes the metallurgical characterization of deposits produced in molten salt electrorefining of uranium and uranium - 10.% zirconium alloy. The techniques of characterization are described with emphasis on considerations given to the radioactive and pyrophoric nature of the samples. The morphologies observed and their implications for deposit performance are also presented - samples from pure uranium deposits were comprised of chains of uranium crystals with a characteristic rhomboidal shape, while morphologies of samples from deposits containing zirconium showed more polycrystalline features. Zirconium was found to be present as a second, zirconium metal phase at or very near the uranium-zirconium dendrite surfaces. Higher collection efficiencies and total deposit weights were observed for the uranium-zirconium deposits; this performance increase is likely a result of better mechanical properties exhibited by the uranium-zirconium dendrite morphology. 18 refs., 10 figs., 1 tab.
Date: September 1, 1997
Creator: Totemeier, T.C.
Partner: UNT Libraries Government Documents Department

Direct numerical simulation of solidification microstructures affected by fluid flow

Description: The effects of fluid flow on the solidification morphology of pure materials and solute microsegregation patterns of binary alloys are studied using a computational methodology based on a front tracking/finite difference method. A general single field formulation is presented for the full coupling of phase change, fluid flow, heat and solute transport. This formulation accounts for interfacial rejection/absorption of latent heat and solute, interfacial anisotropies, discontinuities in material properties between the liquid and solid phases, shrinkage/expansion upon solidification and motion and deformation of the solid. Numerical results are presented for the two dimensional dendritic solidification of pure succinonitrile and the solidification of globulitic grains of a plutonium-gallium alloy. For both problems, comparisons are made between solidification without fluid flow and solidification within a shear flow.
Date: December 1, 1997
Creator: Juric, D.
Partner: UNT Libraries Government Documents Department

Microstructural development of rapid solidification in Al-Si powder

Description: The microstructure and the gradient of microstructure that forms in rapidly solidificated powder were investigated for different sized particles. High pressure gas atomization solidification process has been used to produce a series of Al-Si alloys powders between 0.2 {mu}m to 150 {mu}m diameter at the eutectic composition (12.6 wt pct Si). This processing technique provides powders of different sizes which solidify under different conditions (i.e. interface velocity and interface undercooling), and thus give different microstructures inside the powders. The large size powder shows dendritic and eutectic microstructures. As the powder size becomes smaller, the predominant morphology changes from eutectic to dendritic to cellular. Microstructures were quantitatively characterized by using optical microscope and SEM techniques. The variation in eutectic spacing within the powders were measured and compared with the theoretical model to obtain interface undercooling, and growth rate during the solidification of a given droplet. Also, nucleation temperature, which controls microstructures in rapidly solidified fine powders, was estimated. A microstructural map which correlates the microstructure with particle size and processing parameters is developed.
Date: November 1, 1995
Creator: Jin, F.
Partner: UNT Libraries Government Documents Department

Hierarchical electrode architectures for electrical energy storage & conversion.

Description: The integration and stability of electrocatalytic nanostructures, which represent one level of porosity in a hierarchical structural scheme when combined with a three-dimensional support scaffold, has been studied using a combination of synthetic processes, characterization techniques, and computational methods. Dendritic platinum nanostructures have been covalently linked to common electrode surfaces using a newly developed chemical route; a chemical route equally applicable to a range of metals, oxides, and semiconductive materials. Characterization of the resulting bound nanostructure system confirms successful binding, while electrochemistry and microscopy demonstrate the viability of these electroactive particles. Scanning tunneling microscopy has been used to image and validate the short-term stability of several electrode-bound platinum dendritic sheet structures toward Oswald ripening. Kinetic Monte Carlo methods have been applied to develop an understanding of the stability of the basic nano-scale porous platinum sheets as they transform from an initial dendrite to hole containing sheets. Alternate synthetic strategies were pursued to grow dendritic platinum structures directly onto subunits (graphitic particles) of the electrode scaffold. A two-step photocatalytic seeding process proved successful at generating desirable nano-scale porous structures. Growth in-place is an alternate strategy to the covalent linking of the electrocatalytic nanostructures.
Date: January 1, 2012
Creator: Zavadil, Kevin Robert; Missert, Nancy A.; Shelnutt, John Allen & van Swol, Frank B.
Partner: UNT Libraries Government Documents Department

Versatile materials for use as chemically sensitive interfaces in SAW-based sensor arrays

Description: The primary research objective of the work described here is to design, synthesize, and characterize new materials for use as chemical sensor interfaces, integrate these materials, using appropriate transducers, into sensor arrays, and then develop appropriate mathematical algorithms for interpreting the array response. In this paper, we will discuss two new types of materials we have developed that are ideally suited for use as chemically sensitive interfaces for array-based chemical sensing applications, since they: (1) provide general specificity towards classes of functional groups rather than individual compounds; (2) are intermediate in structure between monolayers and polymers; (3) exhibit both endo- and exo-recognition. The first class of materials is surface-confined dendrimers and the second is hyperbranched polymers.
Date: July 1, 1996
Creator: Crooks, R.M.; Bergbrieter, D.E.; Bruening, M.L.; Wells, M.; Zhou, Yuefen; Ricco, A.J. et al.
Partner: UNT Libraries Government Documents Department

Synthesis of organosilicon compounds

Description: Silicon-containing polymers have been a focus of synthesis and study in Dr. Barton`s group because of their chemistry and properties which are not offered by other systems or materials. For example, the polymer -[-SiMe{sub 2}C{triple_bond}C-]{sub n}-can be easily processed to films or fibers from melt or solution, and thermally converted to a SiC-containing ceramic in high yield at high temperature. In recent years, carbosilane dendritic polymers have been of great interests in many research groups. However, no synthesis of carbosilane dendrimers with functionalties both inside and outside the dendrimer has been reported. Functionality is very important in the synthesis of preceramic polymers. This thesis will be devoted to exploring several new organosilicon polymer systems.
Date: December 31, 1996
Creator: Zhao, G.
Partner: UNT Libraries Government Documents Department