Distinguishing black holes from naked singularities through their accretion disk properties

We show that, in principle, a slowly evolving gravitationally collapsing perfect fluid cloud can asymptotically settle to a static spherically symmetric equilibrium configuration with a naked singularity at the center. We consider one such asymptotic final configuration with a finite outer radius, and construct a toy model in which it is matched to a Schwarzschild exterior geometry. We examine the properties of circular orbits in this model. We then investigate observational signatures of a thermal accretion disk in this spacetime, comparing them with the signatures expected for a disk around a black hole of the same mass. Several notable differences emerge. A disk around the naked singularity is much more luminous than one around an equivalent black hole. Also, the disk around the naked singularity has a spectrum with a high frequency power law segment that carries a major fraction of the total luminosity. Thus, at least some naked singularities can, in principle, be distinguished observationally from black holes of the same mass. We discuss possible implications of these results.Comment: 18 pages, 5 figures, replaced with published versio

Structure-Function Studies Of The Serotonin Type -3 Receptor Ligand -Binding Domain

Thesis (Ph.D.) University of Alaska Fairbanks, 2005The serotonin type-3 receptor (5-HT3R) is widely distributed in peripheral and central nervous systems. This pentameric protein is a member of the Cys-loop superfamily of ligand gated ion channels and plays a role in mediating physiological processes in nervous, cardiovascular, and digestive systems. The ligand-binding domain of this receptor is extracellularly located and is composed of multiple putative loop structures. Based on structural and sequence homology with other members of the superfamily, it has been proposed that at least six such loops (loops A to F) contribute to the ligand-binding domain. Binding of agonist initiates a conformational change which is transduced to the channel, leading to channel opening (gating). The aim of this study was to elucidate the contribution of residues in loops B and E to the mechanism of channel gating in the 5-HT3R. To this end, the three critical tyrosine residues in the loop E region were characterized employing site-directed mutagenesis, electrophysiological studies as well as radio-ligand binding assays involving two structural classes of 5-HT3R agonists. In addition, structure/function analysis of the loop B region was carried out alanine-scanning mutagenesis. Experimental data were correlated with molecular modeling studies. These studies show that the hydroxytryptamine and phenylbiguanide class of compounds utilize different mechanisms of ligand binding and gating in the 5-HT3R. Studies involving the loop B reveal that this region plays a critical role in ligand binding and channel gating. Data obtained from comparison of ground state and agonist-bound models of the 5-HT 3R was correlated with biochemical data. Taken together, these data suggest that agonist interaction with loop B region probably initiates a conformational wave that results in intra- and inter- subunit hydrogen bonding interactions. Our data suggest that these interactions play a critical role in agonist-induced channel opening

Applications of halloysite nanocontainers for functional protective coating

In this study we have explored the applications of halloysite clay nanotubes as a nanocontainer. Halloysite nanotubes are used as a storage unit for anticorrosion agents, flame retardants, and a dopant to extend the curing time for geopolymer composites. Halloysite is a naturally occurring clay mineral with a chemical formula of Al2Si2O 5(OH)4 · 2 H2O and is identical to kaolinite with the exception that it holds an additional water monolayer in its interlayered spaces. Upon heating at higher temperatures, halloysite loses the additional water monolayer, and this variant known colloquially as meta-halloysite has a chemical formula of Al2Si2O5(OH) 4 [1][3]. This study has been divided into five sections. The first section explores the implementation of acid etching for interlayered alumina to increase the loading efficiency of the halloysite. Halloysite is mixed with the sulfuric acid at 0.5 M, I M and 2 M concentrations at varying temperature. It is observed that the alumina that composes the halloysite is degraded faster at temperatures above room temperature and at higher concentrations of sulfuric acid. The second section addresses the application of halloysite as a nanocontainer for the anticorrosion agents for the protection of ASTM A366 steel plates. Halloysite nanotubes are loaded with different types of anticorrosion agents, and are then admixed with an acrylic paint. Samples are exposed to a saline environment for one month. Compared to the controlled samples, halloysite loaded with corrosion inhibitors are found to enhance self-healing. This makes halloysite nanotubes a strong candidate for self-healing composites. In the third section, controlled release of dodecylamine from halloysite nanotubes is used in the implementation of metal-organic and polymeric stoppers. Different types of metal stoppers and polymeric stoppers are analyzed and release studies for dodecylamine are performed in water and paint thinner. In the fourth section, halloysite is explored as a flame retardant. Halloysite nanotubes are mixed with latex paint in concentrations of 5 wt% and 7 wt%, and the samples are tested for flame retardancy by exposing them to a flame torch following the ASTM E84 standard. Simultaneously, paint is mixed with a commercial flame retardant additive and the results are compared pre and post-flame exposure for both samples, with and without halloysite mixed paint. In the final section, halloysite nanotubes used to extend the curing time of geopolymer samples can be achieved for the fly ash samples with a higher calcium content. High calcium content fly ash samples set faster than normal fly ashes. Halloysite coating increases the curing time, therefore giving ample time for the cement sample to flow and set in any desired shape. Utilizing the Layer-by-Layer (LbL) technique, fly ash particles are coated with halloysite, and the curing time is analyzed using Theological testing at room temperature and at 100° C. The coating of halloysite on the fly ash particles is characterized with SEM and Zeta-potential resulting in an optimized shell coating on the fly ash. An extension of curing time from 2 to 8 hrs is reached which is patented (pending) as an important technological development in this new constructional material

Assessment of genetic fidelity in microclones of curry leaf plants [Murrayakoenigii (L.) Spreng.]using ISSR markers

286-291Murrayakoenigii (L.) Spreng., commonly called Indian curry leaf, is an aromatic shrub highly valued for its medicinal potentialviz. anticonvulsant, antitumor, anti-inflammatory, antidiabetic, antiviral and diuretic.Its leaves, locally known as curry patta, are used widely for culinary purpose, particularly in India. However, M. koenigii,due to poor rate of fruit set and seeds with short viability period and poor rate of germination, are sparsely distributedin wild, and has attractedresearchers for propagation through biotechnological approaches. In this context, maintaining genetic fidelity is a vital for assessing genetic uniformity in micropropagated plantlets as variations within the progeny can result in serious losses to the end users.Therefore, it is necessary to screen them for their genetic makeup whether they are true-to-type or not. Molecular techniques like Inter Simple Sequence Repeat (ISSR) that are not influenced by environmental factors are appropriate tools to analyse genetic fidelity of in vitro propagated plantsas, and generate reliable and reproducible results. In this study, we tried to evaluate genetic fidelity of micro-clones of tissue culture raised M. koenigii using ISSR technique. Twenty five ISSR primers were used to amplify genomic DNA from in vitro raised field grown plants and mother plant. Out of 25 primers screened, a total 465 amplified products were obtained from 10 ISSR primers. Out of which, 55 were monomorphic across the mother plant and its micropropagated progenies of 10 ISSR primers 05 showed profiles identical to mother plant. Similarity matrix based on Jaccard’s coefficient and pair-wise values between mother plant and tissue cultured plant ranged from 0.91 to 1.00, indicating a high degree of genetic fidelity