2,478 research outputs found
Perturbations in higher derivative gravity beyond maximally symmetric spacetimes
We study (covariant) scalar-vector-tensor (SVT) perturbations of infinite
derivative gravity (IDG), at the quadratic level of the action, around
conformally-flat, covariantly constant curvature backgrounds which are not
maximally symmetric spacetimes (MSS). This extends a previous analysis of
perturbations done around MSS, which were shown to be ghost-free. We motivate
our choice of backgrounds which arise as solutions of IDG in the UV, avoiding
big bang and black hole singularities. Contrary to MSS, in this paper we show
that, generically, all SVT modes are coupled to each other at the quadratic
level of the action. We consider simple examples of the full IDG action, and
illustrate this mixing and also a case where the action can be diagonalized and
ghost-free solutions constructed. Our study is widely applicable for both
non-singular cosmology and black hole physics where backgrounds depart from
MSS. In appendices, we provide SVT perturbations around conformally-flat and
arbitrary backgrounds which can serve as a compendium of useful results when
studying SVT perturbations of various higher derivative gravity models.Comment: 36 pages, 1 figur
SOLID AS SOLVENTâ€- NOVEL SPECTROPHOTOMETRIC ANALYSIS OF NORFLOXACIN TABLETS USING PHENOL AS SOLVENT
Commonly used organic solvents for spectrophotometric analysis of water insoluble drugs include methanol, ethanol, chloroform, benzene, dichloromethane, dimethyl formamide, acetonitrile, ethyl acetate, toluene, carbon tetrachloride, acetone, hexane etc. The main drawbacks of organic solvents include high cost, toxicity and pollution. Organic solvents have innumerous adverse effects caused by single exposure like dermatitis, headache, drowsiness, nausea, eye irritation and long term exposure causes serious effects such as neurological disorders, chronic renal failure, liver damage, necrosis, mutagenesis disorder. They should be replaced by other eco-friendly alternative sources. The present investigation is an attempt to show that solids can also be wisely used to act as solvent precluding the use of organic solvents. In a separate study, author has attempted soxhelation using phenol as solvent. The vapours of boiling phenol got condensed in extraction chamber to effect the extraction of active constituents from powder of crude drugs. The main objective of the present study is to demonstrate the solvent action of solids. Solid excipients can nicely be employed as solubilizers in the development of pharmaceutical dosage forms in solution form of poorly soluble drugs (mixed solvency concept). Present study describes the application of solvent character of melted phenol (at 50-60°C) for spectroscopic estimation of norfloxacin tablets. Solubility of norfloxacin in distilled water is 0.88 mg/ml. More than 100 mg of nofloxacin dissolves in one gram of melted phenol (at 50-60°C). In the present investigation, melted phenol (at 50-60°C) was utilized to extract out (dissolve) the drug from powder of norfloxacin tablets. Distilled water was used for dilution purpose. Absorbances of standard solutions containing 5, 10, 15, 20, and 25 µg/ml were noted at 324 nm against reagent blanks to obtain calibration curve. Proposed method is novel, economic, eco-friendly, rapid, free from toxicity of organic solvent, accurate and reproducible. Recovery studies and statistical data proved the accuracy, reproducibility and precision of the proposed method. The presence of tablet excipients and phenol did not interfere in the spectrophotometric estimation at 324 nm
REITs and Idiosyncratic Risk
This study examines various determinants of idiosyncratic risk from the perspective of un-diversified REIT investors, managers holding options, other option holders, and arbitrageurs. Since real estate investment trusts (REITs) enjoy a unique organizational structure and tax status, the relevant determinants derived from the two-stage regression model are different from other industrial firms. Results suggest that efficiency, liquidity and earnings variability are the important determinants of idiosyncratic risk, whereas size and capital do not
Flux free growth of large FeSe1/2Te1/2 superconducting single crystals by an easy high temperature melt and slow cooling method
We report successful growth of flux free large single crystals of
superconducting FeSe1/2Te1/2 with typical dimensions of up to few cm. The AC
and DC magnetic measurements revealed the superconducting transition
temperature (Tc) value of around 11.5K and the iso-thermal MH showed typical
type-II superconducting behavior. The lower critical field being estimated by
measuring the low field iso-thermal magnetization in superconducting regime is
found to be above 200 Oe at 0K.Comment: 15 pages text + Figs. Novel large cm size FeSe1/2Te1/2
superconducting crystal
High Field (up to 140kOe) Angle Dependent Magneto Transport of Bi2Te3 Single Crystals
We report the angle dependent high field (up to 140kOe) magneto transport of
Bi2Te3 single crystals, a well-known topological insulator. The crystals were
grown from melt of constituent elements via solid state reaction route by
self-flux method. Details of crystal growth along with their brief
characterization up to 5 Tesla applied field was reported by some of us
recently [J. Magn. Mag. Mater. 428, 213 (2017)]. The angle dependence of the
magneto-resistance (MR) of Bi2Te3 follows the cos Theta function i.e., MR is
responsive, when the applied field is perpendicular (tilt angle Theta = o
and/or 180) to the transport current. The low field (10 kOe) MR showed the
signatures of weak anti localization (WAL) character with typical cusp near
origin at 5 K. Further, the MR is linear right up to highest applied field of
140 kOe. The large positive MR are observed up to high temperatures and are
above 250 and 150 percent at 140 kOe in perpendicular fields at 50 K and 100 K
respectively. Heat capacity CP(T) measurements revealed the value of Debye
temperature to be 135 K. ARPES (angle resolved photoemission spectroscopy) data
clearly showed that the bulk Bi2Te3 single crystal consists of a single Dirac
cone.Comment: 13 Pages text + Figs... Letter - Mat. Res. Ex
Use of microconidia for testing the genetic purity of Neurospora stocks
Uninucleate microconidia have been used to check the purity of laboratory stocks of Neurospora. Stock cultures of N. crassa and N. intermedia become heterokaryotic due to spontaneous mutation
Performance analysis of microcellization for supporting two mobility classes in cellular wireless networks
We study the call blocking performance obtained by microcellizing a macrocell network. Each macrocell is partitioned into microcells, and some of the channels originally allocated to the macrocell are assigned to the microlayer cells according to a reuse pattern. The arriving calls are classified as fast or slow; fast calls are always assigned only to macrocell channels, whereas for slow calls a microcell channel is first sought. Slow calls may be allowed to overflow to the macrolayer, but may be repacked to vacated microcell channels. Calls can change their mobility class during a conversation. We develop an approximate analysis for computing the slow and fast call blocking probabilities in such a system. We adopt the technique of analyzing an isolated macrocell with the Poisson arrival assumption and then iterating on the stationary analysis of the isolated macrocell to obtain stationary results for the multicell system. Simple, but accurate approximations are developed for analyzing the isolated macrocell and its associated microcells. The analyses based on the approximate isolated cell model are validated against simulations of a multicell model
- …