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The complete mitochondrial sequence of the"living fossil" Tricholepidion gertschi: structure, phylogenetic implications, and the description of a novel A/T asymmetrical bias

Description: Traditionally, the 'Apterygota' has been thought to consist of five orders of wingless hexapods (Protura, Collembola, Diplura, Microcoryphia and Zygentoma) believed to be collectively basal to insects (i.e., the Pterygota). However, some studies have questioned this affinity with insects (Dallai, Abele, Spears, Nardi). Further, within these groups are hotly debated issues, including the monophyly of Entognata (Koch, 1997; Kukalova Peck, 1987), the monophyly of Diplura (Bilinski, 1993; Stys and Bilinski, 1990), the affinity between Collembola and Protura (Dallai, 1994; Kristensen, 1981) and the position of Lepidotrichidae (below). In fact, these relationships constitute one of the most debated issues in hexapod phylogeny. The family Lepidotrichidae was first described by (Silvestri, 1912) (1912: 'Lepidothricinae') from a Baltic Amber fossil (Lepidothrix pilifera Menge). The only living representative of this family is Tricholepidion gertschi Wygodzinski. Since this species was first described (Wygodzinsky, 1961) its phylogenetic position has been difficult to establish, due to an 'array of unique characters' that are difficult to interpret in a phylogenetic framework. Tricholepidion (and therefore the whole family Lepidotrichidae) has been considered either as belonging to the order Zygentoma (Kristensen, 1997; Wygodzinsky, 1961), or basal to the rest of the Zygentoma plus the Pterygota (Beutel, 2001; Bitsch and Bitsch, 2000; Staniczek, 2000), although the significance of some of the morphological characters on which these analyses are based have been questioned (Dallai et al., 2001; Kristensen, 1997). If the latter hypothesis proved to be true, the family Lepidotrichidae, would better deserve the ordinal rank. Since studies based on morphological characters have failed to give a satisfactory answer, a broad scale molecular study is under way ((Nardi et al., 2001), Frati et al, submitted, il Gomphiocephalus) in order to use mitochondrial genome sequences to study the evolution and differentiation of the most basal hexapod groups, including Tricholepidion. Mitochondrial genomics, that is ...
Date: June 23, 2002
Creator: Nardi, F.; Frati, F.; Carapelli, A.; Dallai, R. & Boore, J.
Partner: UNT Libraries Government Documents Department

Affinity functions for modeling glass dissolution rates

Description: Glass dissolution rates decrease dramatically as glasses approach "saturation" with respect to the leachate solution. This effect may lower the dissolution rate to 1/100 to 1/1000 of the unsaturated rate. Although rate controls on glass dissolution are best understood for conditions far from saturation, most repository sites are chosen where water fluxes are minimal, and therefore the waste glass is most likely to dissolve under conditions close to saturation. Our understanding of controls on dissolution rates close to saturation, versus far from saturation, are therefore of greater significance for assessing release rates of radionuclides from repositories. The key term in the rate expression used to predict glass dissolution rates close to saturation is the affinity term, which accounts for saturation effects on dissolution rates. The form of the affinity term and parameters used to model glass dissolution are clearly critical for accurate estimates of glass performance in a repository. The concept of saturation with respect to glass dissolution is problematic because of the thermodynamically unstable nature of glass. Saturation implies similar rates of forward (dissolution) and back (precipitation) reactions, but glasses cannot precipitate from aqueous solutions; there can be no back reaction to form glass. However experiments have shown that glasses do exhibit saturation effects when dissolving, analogous to saturation effects observed for thermodynamically stable materials. Attempts to model the glass dissolution process have therefore employed theories and rate equations more commonly used to model dissolution of crystalline solids, as described below
Date: July 8, 1998
Creator: Bourcier, W L
Partner: UNT Libraries Government Documents Department

The Influence of the Linker Geometry in Bis(3-hydroxy-N-methyl-pyridin-2-one) Ligands on Solution-Phase Uranyl Affinity

Description: Seven water-soluble, tetradentate bis(3-hydroxy-N-methyl-pyridin-2-one) (bis-Me-3,2-HOPO) ligands were synthesized that vary only in linker geometry and rigidity. Solution phase thermodynamic measurements were conducted between pH 1.6 and pH 9.0 to determine the effects of these variations on proton and uranyl cation affinity. Proton affinity decreases by introduction of the solubilizing triethylene glycol group as compared to un-substituted reference ligands. Uranyl affinity was found to follow no discernable trends with incremental geometric modification. The butyl-linked 4Li-Me-3,2-HOPO ligand exhibited the highest uranyl affinity, consistent with prior in vivo decorporation results. Of the rigidly-linked ligands, the o-phenylene linker imparted the best uranyl affinity to the bis-Me-3,2-HOPO ligand platform.
Date: August 12, 2010
Creator: Szigethy, Geza & Raymond, Kenneth
Partner: UNT Libraries Government Documents Department

AGONIST-INDUCED AFFINITY ALTERATIONS OF A CENTRAL NERVOUS SYSTEM NICOTINIC ACETYLCHOLINE RECEPTOR

Description: Pretreatment of {alpha}-bungarotoxin ({alpha}-Bgt) binding sites from rat brain with cholinergic agonists causes transformation of sites to a high-affinity form toward agonist over a time course of minutes, consistent with identity of those sites as central nicotinic acetylcholine receptors (nAChR). This agonist-induced alteration in receptor state may be correlated with physiological densensitization. Agonist inhibition of toxin binding to the high-affinity state is non-competitive, suggesting the existence of discrete toxin-binding and agonist-binding sites on the central nAChR. These results thus offer a possible explanation of observed impotency of {alpha}-Bgt toward blocking in vivo cholinergic responses in the central nervous system.
Date: May 1, 1978
Creator: Lukasiewicz, Ronald J. & Bennett, Edward L.
Partner: UNT Libraries Government Documents Department

Synthesis, structure, and reactivity of high oxidation state silver fluorides and related compounds

Description: This thesis has been largely concerned with defining the oxidizing power of Ag(III) and Ag(II) in anhydrous hydrogen fluoride (aHF) solution. Emphasis was on cationic species, since in a cation the electronegativity of a given oxidation state is greatest. Cationic Ag(III) solv has a short half life at ordinary temperatures, oxidizing the solvent to elemental fluorine with formation of Ag(II). Salts of such a cation have not yet been preparable, but solutions which must contain such a species have proved to be effective and powerful oxidizers. In presence of PtF{sub 6}{sup {minus}}, RuF{sub 6}{sup {minus}}, or RhF{sub 6}{sup {minus}}, Ag(III) solv effectively oxidizes the anions to release the neutral hexafluorides. Such reactivity ranks cationic Ag(III) as the most powerfully oxidizing chemical agent known as far. Unlike its trivalent relative Ag (II) solv is thermodynamically stable in acid aHF. Nevertheless, it oxidizes IrF{sub 6}{sup {minus}} to IrF{sub 6} at room temperature, placing its oxidizing potential not more than 2 eV below that of cationic Ag(III). Range of Ag{sup 2+} (MF{sub 6}{sup {minus}}){sub 2} salts attainable in aHF has been explored. An anion must be stable with respect to electron loss to Ag{sup 2+}. The anion must also be a poor F{sup {minus}} donor; otherwise, either AgF{sup +} salts or AgF{sub 2} are generated.
Date: May 1, 1995
Creator: Lucier, G.M.
Partner: UNT Libraries Government Documents Department

Receptor-targeted metalloradiopharmaceuticals. Final technical report

Description: Copper (II) and platinum (II) coordination complexes were prepared and characterized. These complexes were designed to afford structural homology with steroidal and non-steroidal estrogens for possible use as receptor-targeted radiopharmaceuticals. While weak affinity for the estrogen receptor was detectable, none would appear to have sufficient receptor-affinity for estrogen-receptor-targeted imaging or therapy.
Date: March 22, 2000
Creator: Green, Mark A.
Partner: UNT Libraries Government Documents Department

Fox-2 Splicing Factor Binds to a Conserved Intron Motif to PromoteInclusion of Protein 4.1R Alternative Exon 16

Description: Activation of protein 4.1R exon 16 (E16) inclusion during erythropoiesis represents a physiologically important splicing switch that increases 4.1R affinity for spectrin and actin. Previous studies showed that negative regulation of E16 splicing is mediated by the binding of hnRNP A/B proteins to silencer elements in the exon and that downregulation of hnRNP A/B proteins in erythroblasts leads to activation of E16 inclusion. This paper demonstrates that positive regulation of E16 splicing can be mediated by Fox-2 or Fox-1, two closely related splicing factors that possess identical RNA recognition motifs. SELEX experiments with human Fox-1 revealed highly selective binding to the hexamer UGCAUG. Both Fox-1 and Fox-2 were able to bind the conserved UGCAUG elements in the proximal intron downstream of E16, and both could activate E16 splicing in HeLa cell co-transfection assays in a UGCAUG-dependent manner. Conversely, knockdown of Fox-2 expression, achieved with two different siRNA sequences resulted in decreased E16 splicing. Moreover, immunoblot experiments demonstrate mouse erythroblasts express Fox-2, but not Fox-1. These findings suggest that Fox-2 is a physiological activator of E16 splicing in differentiating erythroid cells in vivo. Recent experiments show that UGCAUG is present in the proximal intron sequence of many tissue-specific alternative exons, and we propose that the Fox family of splicing enhancers plays an important role in alternative splicing switches during differentiation in metazoan organisms.
Date: March 1, 2006
Creator: Ponthier, Julie L.; Schluepen, Christina; Chen, Weiguo; Lersch,Robert A.; Gee, Sherry L.; Hou, Victor C. et al.
Partner: UNT Libraries Government Documents Department

Exceptional Electron Transport Properties of In-rich InGaN

Description: Recent years have seen an explosion of interest in the narrow band gap end of the InGaN alloy system, particularly in InN. The existence of surface electron accumulation and a tendency for n-type conductivity have been well-established and are explained by an extremely large electron affinity and the location of the Fermi level stabilization energy (E{sub FS}) high in the conduction band [1]. These characteristics pose significant challenges to the integration of In-rich InGaN into devices and demonstrate the need for a better understanding of the relationship between native defects and electronic transport in the alloy system. It has been previously shown that high-energy particle irradiation can predictably control the electronic properties of In-rich InGaN [1]. With increasing irradiation dose, the electron concentration (n) increases and the electron mobility ({mu}) decreases until the Fermi level reaches E{sub FS}, which is the saturation point. The value of n at saturation decreases with decreasing In fraction, due to the raising of the conduction band edge with respect to E{sub FS}.
Date: October 22, 2006
Creator: Jones, R.E.; van Genuchten, H.C.M.; Yu, K.M.; Walukiewicz, W.; Li, S.X.; Liliental-Weber, Z. et al.
Partner: UNT Libraries Government Documents Department

New Tools for the site-specific attachment of proteins to surface

Description: Protein microarrays in which proteins are immobilized to a solid surface are ideal reagents for high-throughput experiments that require very small amounts of analyte. Such protein microarrays ('protein chips') can be used very efficiently to analyze all kind of protein interactions en masse. Although a variety of methods are available for attaching proteins on solid surfaces. Most of them rely on non-specific adsorption methods or on the reaction of chemical groups within proteins (mainly, amino and carboxylic acid groups) with complementary reactive groups. In both cases the protein is attached to the surface in random orientations. The use of recombinant affinity tags addresses the orientation issue, however in most of the cases the interaction of the tags are reversible (e.g., glutathione S-transferase, maltose binding protein and poly-His) and, hence, are not stable over the course of subsequent assays or require large mediator proteins (e.g., biotin-avidin and antigen antibody). The key for the covalent attachment of a protein to a solid support with a total control over the orientation is to introduce two unique and mutually reactive groups on both the protein and the surface. The reaction between these two groups should be highly selective thus behaving like a molecular 'Velcro'.
Date: June 17, 2005
Creator: Camarero, J A; Kwon, Y & Coleman, M A
Partner: UNT Libraries Government Documents Department

Joining of Beryllium

Description: A handbook dealing with the many aspects of beryllium that would be important for the users of this metal is currently being prepared. With an introduction on the applications, advantages and limitations in the use of this metal the following topics will be discussed in this handbook: physical, thermal, and nuclear properties; extraction from the ores; purification and casting of ingots; production and types of beryllium powders; consolidation methods, grades, and properties; mechanical properties with emphasis on the various factors affecting these properties; forming and mechanical working; welding, brazing, bonding, and fastening; machining; powder deposition; corrosion; health aspects; and examples of production of components. This report consists of ''Section X--Joining'' from the handbook. The prefix X is maintained here for the figures, tables and references. In this section the different methods used for joining beryllium and the advantages, disadvantages and limitations of each are presented. The methods discussed are fusion welding, brazing, solid state bonding (diffusion bonding and deformation bonding), soldering, and mechanical fastening. Since beryllium has a high affinity for oxygen and nitrogen with the formation of oxides and nitrides, considerable care must be taken on heating the metal, to protect it from the ambient atmosphere. In addition, mating surfaces must be cleaned and joints must be designed to minimize residual stresses as well as locations for stress concentration (notch effects). In joining any two metals the danger exists of having galvanic corrosion if the part is subjected to moisture or to any type of corroding environment. This becomes a problem if the less noble (anodic) metal has a significantly smaller area than the more noble (cathodic) metal since the ions (positive charges) from the anodic (corroding) metal must correspond to the number of electrons (negative charges) involved at the cathode. Beryllium is anodic to almost all metals; thus, ...
Date: February 1, 2006
Creator: Goldberg, A
Partner: UNT Libraries Government Documents Department

REVIEW OF ACTINIDE AND STRONTIUM LOADING DATA FOR MST AND MMST

Description: SRNL reviewed the relevant data from MST and mMST fissile loading studies to determine if further studies were required. With respect to MST, SRNL found that the published results adequately bound the expected conditions that Small Column Ion Exchange (SCIX) process will operate under. The lack of strontium data does not represent an issue as strontium is not relevant to criticality. There is no threat to criticality safety from the lack of strontium loading data. However, SRNL proposes a single test with MST to ensure that future SCIX operations are conservatively bounded and strontium maximum loading is understood. With respect to attempts to maximally load mMST, SRNL's knowledge on actinide and strontium loading is limited to uranium behavior. mMST has a very weak affinity for uranium, and even extended contact time at high uranium concentration shows minimal loading onto mMST. This leaves questions about the ability to load plutonium, neptunium and strontium. SRNL proposes to perform two tests with mMST to ensure that questions on plutonium, neptunium, and strontium sorption are answered, as well as ensuring that future mMST operations are conservatively bounded.
Date: October 20, 2010
Creator: Peters, T.; Hobbs, D. & Fink, S.
Partner: UNT Libraries Government Documents Department

A role for cell adhesion in beryllium-mediated lung disease

Description: Chronic beryllium disease (CBD) is a debilitating lung disorder in which exposure to the lightweight metal beryllium (Be) causes the accumulation of beryllium-specific CD4+ T cells in the lung and formation of noncaseating pulmonary granulomas. Treatment for CBD patients who exhibit progressive pulmonary decline is limited to systemic corticosteroids, which suppress the severe host inflammatory response. Studies in the past several years have begun to highlight cell-cell adhesion interactions in the development of Be hypersensitivity and CBD. In particular, the high binding affinity between intercellular adhesion molecule 1 (I-CAM1) on lung epithelial cells and the {beta}{sub 2} integrin LFA-1 on migrating lymphocytes and macrophages regulates the concerted rolling of immune cells to sites of inflammation in the lung. In this review, we discuss the evidence that implicates cell adhesion processes in onset of Be disease and the potential of cell adhesion as an intervention point for development of novel therapies.
Date: January 1, 2008
Creator: Hong-geller, Elizabeth
Partner: UNT Libraries Government Documents Department

Peroxotitanates for Biodelivery of Metals

Description: Metal-based drugs are largely undeveloped in pharmacology. One limiting factor is the systemic toxicity of metal-based compounds. A solid-phase, sequestratable delivery agent for local delivery of metals could reduce systemic toxicity, facilitating new drug development in this nascent area. Amorphous peroxotitanates (APT) are ion exchange materials with high affinity for several heavy metal ions, and have been proposed to deliver or sequester metal ions in biological contexts. In the current study, we tested a hypothesis that APT are able to deliver metals or metal compounds to cells. We exposed fibroblasts (L929) or monocytes (THP1) to metal-APT materials for 72 h in vitro, then measured cellular mitochondrial activity (SDH-MTT method) to assess the biological impact of the metal-APT materials vs. metals or APT alone. APT alone did not significantly affect cellular mitochondrial activity, but all metal-APT materials suppressed the mitochondrial activity of fibroblasts (by 30-65% of controls). The concentration of metal-APT materials required to suppress cellular mitochondrial activity was below that required for metals alone, suggesting that simple extracellular release of the metals from the metal-APT materials was not the primary mechanism of mitochondrial suppression. In contrast to fibroblasts, no metal-APT material had a measurable effect on THP1 monocyte mitochondrial activity, despite potent suppression by metals alone. This latter result suggested that 'biodelivery' by metal-APT materials may be cell type-specific. Therefore, it appears that APT are plausible solid phase delivery agents of metals or metal compounds to some types of cells for potential therapeutic effect.
Date: February 11, 2009
Creator: Hobbs, David & Elvington, M.
Partner: UNT Libraries Government Documents Department

ELECTRON AMPLIFICATION IN DIAMOND.

Description: We report on recent progress toward development of secondary emission ''amplifiers'' for photocathodes. Secondary emission gain of over 300 has been achieved in transmission mode and emission mode for a variety of diamond samples. Techniques of sample preparation, including hydrogenation to achieve negative electron affinity (NEA), have been adapted to this application.
Date: July 10, 2006
Creator: SMEDLEY, J.; BEN-ZVI, I.; BURRILL, A.; CHANG, X.; GRIMES, J.; RAO, T. et al.
Partner: UNT Libraries Government Documents Department

Development of Superior Sorbents for Separation of CO2 from Flue Gas at a Wide Temperature range during Coal Combustion

Description: A number basic sorbents based on CaO were synthesized, characterized with novel techniques and tested for sorption of CO{sub 2} and selected gas mixtures simulating flue gas from coal fired boilers. Our studies resulted in highly promising sorbents which demonstrated zero affinity for N{sub 2}, O{sub 2}, SO{sub 2}, and NO very low affinity for water, ultrahigh CO{sub 2} sorption capacities, and rapid sorption characteristics, CO{sub 2} sorption at a very wide temperature range, durability, and low synthesis cost. One of the 'key' characteristics of the proposed materials is the fact that we can control very accurately their basicity (optimum number of basic sites of the appropriate strength) which allows for the selective chemisorption of CO{sub 2} at a wide range of temperatures. These unique characteristics of this family of sorbents offer high promise for development of advanced industrial sorbents for the effective CO{sub 2} removal.
Date: September 17, 2002
Creator: Smirniotis, Panagiotis
Partner: UNT Libraries Government Documents Department

Structural dynamics and ssDNA binding activity of the three N-terminal domains of the large subunit of Replication Protein A from small angle X-ray scattering

Description: Replication Protein A (RPA) is the primary eukaryotic ssDNA binding protein utilized in diverse DNA transactions in the cell. RPA is a heterotrimeric protein with seven globular domains connected by flexible linkers, which enable substantial inter-domain motion that is essential to its function. Small angle X-ray scattering (SAXS) experiments on two multi-domain constructs from the N-terminus of the large subunit (RPA70) were used to examine the structural dynamics of these domains and their response to the binding of ssDNA. The SAXS data combined with molecular dynamics simulations reveal substantial interdomain flexibility for both RPA70AB (the tandem high affinity ssDNA binding domains A and B connected by a 10-residue linker) and RPA70NAB (RPA70AB extended by a 70-residue linker to the RPA70N protein interaction domain). Binding of ssDNA to RPA70NAB reduces the interdomain flexibility between the A and B domains, but has no effect on RPA70N. These studies provide the first direct measurements of changes in orientation of these three RPA domains upon binding ssDNA. The results support a model in which RPA70N remains structurally independent of RPA70AB in the DNA bound state and therefore freely available to serve as a protein recruitment module.
Date: March 11, 2010
Creator: Pretto, Dalyir I.; Tsutakawa, Susan; Brosey, Chris A.; Castillo, Amalchi; Chagot, Marie-Eve; Smith, Jarrod A. et al.
Partner: UNT Libraries Government Documents Department

Molecular analysis of phosphate limitation in Geobacteraceae during the bioremediation of a uranium-contaminated aquifer

Description: Nutrient limitation is an environmental stress that may reduce the effectiveness of bioremediation strategies, especially when the contaminants are organic compounds or when organic compounds are added to promote microbial activities such as metal reduction. Genes indicative of phosphate-limitation were identified via microarray analysis of chemostat cultures of Geobacter sulfureducens. This analysis revealed that genes in the pst-pho operon, which is associated with a high affinity phosphate uptake system in other microorganisms, had significantly higher transcript abundance under phosphate-limiting conditions, with the genes pstB and phoU the most up-regulated. Quantitative PCR analysis of pstB and phoU transcript levels in G. sulfurreducens grown in chemostats demonstrated that the expression of these genes increased when phosphate was removed from the culture medium. Transcripts of pstB and phoU within the subsurface Geobacter species predominating during an in situ uranium bioremediation field experiment were more abundant than in chemostat cultures of G. sulfurreducens that were not limited for phosphate. Addition of phosphate to incubations of subsurface sediments did not stimulate dissimilatory metal reduction. The added phosphate was rapidly adsorbed onto the sediments. The results demonstrate that Geobacter species can effectively reduce U(VI) even when experiencing suboptimal phosphate concentrations and that increasing phosphate availability with phosphate additions is difficult to achieve due to the high reactivity of this compound. This transcript-based approach developed for diagnosing phosphate limitation should be applicable to assessing the potential need for additional phosphate in other bioremediation processes.
Date: September 1, 2009
Creator: N'Guessan, L.A.; Elifantz, H.; Nevin, K.P.; Mouser, P.J.; Methe, B.; Woodard, T. L. et al.
Partner: UNT Libraries Government Documents Department

Surface complexation of Pb(II) by hexagonal birnessite nanoparticles

Description: Natural hexagonal birnessite is a poorly-crystalline layer type Mn(IV) oxide precipitated by bacteria and fungi which has a particularly high adsorption affinity for Pb(II). X-ray spectroscopic studies have shown that Pb(II) forms strong inner-sphere surface complexes mainly at two sites on hexagonal birnessite nanoparticles: triple corner-sharing (TCS) complexes on Mn(IV) vacancies in the interlayers and double edge-sharing (DES) complexes on lateral edge surfaces. Although the TCS surface complex has been well characterized by spectroscopy, some important questions remain about the structure and stability of the complexes occurring on the edge surfaces. First-principles simulation techniques such as density functional theory (DFT) offer a useful way to address these questions by providing complementary information that is difficult to obtain by spectroscopy. Following this computational approach, we used spin-polarized DFT to perform total-energy-minimization geometry optimizations of several possible Pb(II) surface complexes on model birnessite nanoparticles similar to those that have been studied experimentally. We first validated our DFT calculations by geometry optimizations of (1) the Pb-Mn oxyhydroxide mineral, quenselite (PbMnO{sub 2}OH), and (2) the TCS surface complex, finding good agreement with experimental structural data while uncovering new information about bonding and stability. Our geometry optimizations of several protonated variants of the DES surface complex led us to conclude that the observed edge-surface species is very likely to be this complex if the singly-coordinated terminal O that binds to Pb(II) is protonated. Our geometry optimizations also revealed that an unhydrated double corner-sharing (DCS) species that has been proposed as an alternative to the DES complex is intrinsically unstable on nanoparticle edge surfaces, but could become stabilized if the local coordination environment is well-hydrated. A significant similarity exists in the structural parameters for the TCS complex and those for a DCS edge-surface complex that is protonated in the same manner as the optimal DES complex, ...
Date: October 15, 2010
Creator: Kwon, K.; Refson, K. & Sposito, G.
Partner: UNT Libraries Government Documents Department

Determination of Dissociation Constants for GABAA Receptor Antagonists using Spontaneously Active Neuronal Networks in vitro

Description: Changes in spontaneous spike activities recorded from murine frontal cortex networks grown on substrate-integrated microelectrodes were used to determine the dissociation constant (KB) of three GABAA antagonists. Neuronal networks were treated with fixed concentrations of GABAA antagonists and titrated with muscimol, a GABAA receptor agonist. Muscimol decreased spike activity in a concentration dependent manner with full efficacy (100% spike inhibition) and a 50% inhibitory concentration (IC50) of 0.14 ± 0.05 µM (mean ± SD, n=6). At 10, 20, 40 and 80 µM bicuculline, the muscimol IC50 values were shifted to 4.3 ± 1.8 µM (n=6), 6.8 ± 1.7 µM (n=6), 19.3 ± 3.54 µM (n=10) and 43.5 µM (n=2), respectively (mean ± SD). Muscimol titration in the presence of 10, 20, 40 µM of gabazine resulted in IC50s values of 20.1 (n=2), 37.17 (n=4), and 120.45 (n=2), respectively. In the presence of 20, 80, and 160 µM of TMPP (trimethylolpropane phosphate) the IC50s were 0.86 (n=2), 3.07 (n=3), 6.67 (n=2) µM, respectively. Increasing concentrations of GABAA antagonists shifted agonist log concentration-response curves to the right with identical efficacies, indicating direct competition for the GABAA receptor. A Schild plot analysis with linear regression resulted in slopes of 1.18 ± 0.18, 1.29 ± 0.23 and 1.05 ± 0.03 for bicuculline, gabazine and TMPP, respectively. The potency of antagonists was determined in terms of pA2 values. The pA2 values were 6.63 (gabazine), 6.21 (bicuculline), and 5.4 (TMPP). This suggests that gabazine has a higher binding affinity to the GABAA receptor than bicuculline and TMPP. Hence, using spike rate data obtained from population responses of spontaneously active neuronal networks, it is possible to determine key pharmacological properties of drug-receptor interactions.
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Date: December 2005
Creator: Oli-Rijal, Sabnam
Partner: UNT Libraries

Crystalline silicotitanate gate review analysis

Description: Crystalline silicotitanate (CST) is an ion-exchange method for removing radioactive cesium from tank waste to allow the separation of the waste into high- and low-level fractions. The CST, originally developed Sandia National Laboratories personnel in association with Union Oil Products Corporation, has both a high affinity and selectivity for sorbing cesium-137 from highly alkaline or acidic solutions. For several years now, the U.S. Department of Energy has funded work to investigate applying CST to large-scale removal of cesium-137 from radioactive tank wastes. In January 1997, an expert panel sponsored by the Tanks Focus Area met to review the current state of the technology and to determine whether it was ready for routine use. The review also sought to identify any technical issues that must be resolved or additional CST development that must occur before full implementation by end-users. The CST Gate Review Group concluded that sufficient work has been done to close developmental work on CST and turn the remaining site-specific tasks over to the users. This report documents the review group`s findings, issues, concerns, and recommendations as well as responses from the Tanks Focus Area expert staff to specific pretreatment and immobilization issues.
Date: November 1, 1997
Creator: Schlahta, S.N.; Carreon, R. & Gentilucci, J.A.
Partner: UNT Libraries Government Documents Department

Atomic hydrogen cleaning of semiconductor photocathodes

Description: Negative Electron Affinity (NEA) semiconductor photocathodes are widely used for the production of polarized electron beams, and are also useful for the production of high brightness electron beams which can be modulated at very high frequencies. Preparation of an atomically clean semiconductor surface is an essential step in the fabrication of a NEA photocathode. This cleaning step is difficult for certain semiconductors, such as the very thin materials which produce the highest beam polarization, and those which have tightly bound oxides and carbides. Using a small RF dissociation atomic hydrogen source, the authors have reproducibly cleaned GaAs wafers which have been only degreased prior to installation in vacuum. They have consistently prepared very high quantum efficiency photocathodes following atomic hydrogen cleaning. Details of their apparatus and most recent results are presented.
Date: June 1, 1997
Creator: Sinclair, C. K.; Poelker, B. M. & Price, J. S.
Partner: UNT Libraries Government Documents Department

Aggregation of dialkyl-substituted diphosphonic acids and its effect on metal ion extraction.

Description: Solvent extraction reagents containing the diphosphonic acid group exhibit an extraordinary affinity for tri-, tetra- and hexavalent actinides. Their use has been considered for actinide separation and pre-concentration procedures. Solvent extraction data obtained with P,P{prime}-di(2-ethylhexyl) methane-, ethane- and butanediphosphonic acids exhibit features that are difficult to explain without Knowledge of the aggregation state of the extractants. Information about the aggregation of the dialkyl-substituted diphosphonic acids in aromatic diluents has been obtained using the complementary techniques of vapor pressure osmometry (VPO), small angle neutron scattering (SANS), infrared spectroscopy and molecular mechanics. The results from these techniques provide an understanding of the aggregation behavior of these extractants that is fully compatible with the solvent extraction data. The most important results and their relevance to solvent extraction are reviewed in this paper.
Date: October 22, 1999
Creator: Chiarizia, R.; Barrans, R. E., Jr.; Ferraro, J. R. Herlinger, A. W. & McAlister, D. R.
Partner: UNT Libraries Government Documents Department

STRATEGIES FOR QUANTIFYING PET IMAGING DATA FROM TRACER STUDIES OF BRAIN RECEPTORS AND ENZYMES.

Description: A description of some of the methods used in neuroreceptor imaging to distinguish changes in receptor availability has been presented in this chapter. It is necessary to look beyond regional uptake of the tracer since uptake generally is affected by factors other than the number of receptors for which the tracer has affinity. An exception is the infusion method producing an equilibrium state. The techniques vary in complexity some requiring arterial blood measurements of unmetabolized tracer and multiple time uptake data. Others require only a few plasma and uptake measurements and those based on a reference region require no plasma measurements. We have outlined some of the limitations of the different methods. Laruelle (1999) has pointed out that test/retest studies to which various methods can be applied are crucial in determining the optimal method for a particular study. The choice of method will also depend upon the application. In a clinical setting, methods not involving arterial blood sampling are generally preferred. In the future techniques for externally measuring arterial plasma radioactivity with only a few blood samples for metabolite correction will extend the modeling options of clinical PET. Also since parametric images can provide information beyond that of ROI analysis, improved techniques for generating such images will be important, particularly for ligands requiring more than a one-compartment model. Techniques such as the wavelet transform proposed by Turkheimer et al. (2000) may prove to be important in reducing noise and improving quantitation.
Date: April 2, 2001
Creator: Logan, J.
Partner: UNT Libraries Government Documents Department