231 research outputs found
Very General Holographic Superconductors and Entanglement Thermodynamics
We construct and analyze holographic superconductors with generalized higher
derivative couplings, in single R-charged black hole backgrounds in four and
five dimensions. These systems, which we call very general holographic
superconductors, have multiple tuning parameters and are shown to exhibit a
rich phase structure. We establish the phase diagram numerically as well as by
computing the free energy, and then validated the results by calculating the
entanglement entropy for these systems. The entanglement entropy is shown to be
a perfect indicator of the phase diagram. The differences in the nature of the
entanglement entropy in R-charged backgrounds compared to the AdS-Schwarzschild
cases are pointed out. We also compute the analogue of the entangling
temperature for a subclass of these systems and compare the results with
non-hairy backgrounds.Comment: 1 + 32 pages, LaTeX, 27 .eps figure
Generalized Holographic Superconductors with Higher Derivative Couplings
We introduce and study generalized holographic superconductors with higher
derivative couplings between the field strength tensor and a complex scalar
field, in four dimensional AdS black hole backgrounds. We study this theory in
the probe limit, as well as with backreaction. There are multiple tuning
parameters in the theory, and with two non-zero parameters, we show that the
theory has a rich phase structure, and in particular, the transition from the
normal to the superconducting phase can be tuned to be of first order or of
second order within a window of one of these. This is established numerically
as well as by computing the free energy of the boundary theory. We further
present analytical results for the critical temperature of the model, and
compare these with numerical analysis. Optical properties of this system are
also studied numerically in the probe limit, and our results show evidence for
negative refraction at low frequencies.Comment: 1 + 27 pages, LaTeX, 24 .eps figures. References added, typos fixed,
discussion on optical properties expanded. Version accepted in JHE
Generalized Superconductors and Holographic Optics
We study generalized holographic s-wave superconductors in four dimensional
R-charged black hole and Lifshitz black hole backgrounds, in the probe limit.
We first establish the superconducting nature of the boundary theories, and
then study their optical properties. Numerical analysis indicates that a
negative Depine-Lakhtakia index may appear at low frequencies in the theory
dual to the R-charged black hole, for certain temperature ranges, for specific
values of the charge parameter. The corresponding cut-off values for these are
numerically established in several cases. Such effects are seen to be absent in
the Lifshitz background where this index is always positive.Comment: 1 + 22 Pages, LaTeX, 18 .eps figures. Discussions expanded and
results on Lifshitz backgrounds added. Published versio
The Hsp60C gene in the 25F cytogenetic region in Drosophila melanogaster is essential for tracheal development and fertility
Earlier studies have shown that of the four genes (Hsp60A, Hsp60B, Hsp60C, Hsp60D genes) predicted to encode the conserved Hsp60 family chaperones in Drosophila melanogaster, the Hsp60A gene (at the 10A polytene region) is expressed in all cell types of the organism and is essential from early embryonic stages, while the Hsp60B gene (at 21D region) is expressed only in testis, being essential for sperm individualization. In the present study, we characterized the Hsp60C gene (at 25F region), which shows high sequence homology with the other three Hsp60 genes of D. melanogaster. In situ hybridization of Hsp60C-specific riboprobe shows that expression of this gene begins in late embryonic stages (stage 14 onwards), particularly in the developing tracheal system and salivary glands; during larval and adult stages, it is widely expressed in many cell types but much more strongly in tracheae and in developing and differentiating germ cells. A P-insertion mutant (Hsp60C1 ) allele with the P transposon inserted at -251 position of the Hsp60C gene promoter was generated. This early larval recessive lethal mutation significantly reduces levels of Hsp60C transcripts in developing tracheae and this is associated with a variety of defects in the tracheal system, including lack of liquid clearance. About 10% of the homozygotes survive as weak, shortlived and completely sterile adults. Testes of the surviving mutant males are significantly smaller, with fewer spermatocytes, most of which do not develop beyond the round spermatid stage. In situ and Northern hybridizations show significantly reduced levels of the Hsp60C transcripts in Hsp60C1 homozygous adult males. The absence of early meiotic stages in the Hsp60C1 homozygous testes contrasts with the effect of testis-specific Hsp60B (21D) gene, whose mutation affects individualization of sperm bundles later in spermiogenesis. In view of the specific effects in tracheal development and in early stages of spermatogenesis, it is likely that, besides its functions as a chaperone, Hsp60C may have signalling functions and may also be involved in cation transport across the developing tracheal epithelial cells
Emerging role of Garcinol, the antioxidant chalcone from Garcinia indica Choisy and its synthetic analogs
Garcinol, harvested from Garcinia indica, has traditionally been used in tropical regions and appreciated for centuries; however its biological properties are only beginning to be elucidated. There is ample data to suggest potent antioxidant properties of this compound which have been used to explain most of its observed biological activities. However, emerging evidence suggests that garcinol could be useful as an anti-cancer agent, and it is increasingly being realized that garcinol is a pleiotropic agent capable of modulating key regulatory cell signaling pathways. Here we have summarized the progress of our current research knowledge on garcinol and its observed biological activities. We have also provided an explanation of observed properties based on its chemical structure and provided an insight into the structure and properties of chalcones, the precursors of garcinol. The available data is promising but more detailed investigations into the various properties of this compound, particularly its anti-cancer activity are urgently needed, and it is our hope that this review will stimulate further research for elucidating and appreciating the value of this nature's wonder agent
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