The Structure and Freezing of fluids interacting via the Gay-Berne (n-6) potentials

We have calculated the pair correlation functions of a fluid interacting via the Gay-Berne(n-6) pair potentials using the \PY integral equation theory and have shown how these correlations depend on the value of n which measures the sharpness of the repulsive core of the pair potential. These results have been used in the density-functional theory to locate the freezing transitions of these fluids. We have used two different versions of the theory known as the second-order and the modified weighted density-functional theory and examined the freezing of these fluids for $8 \leq n \leq 30$ and in the reduced temperature range lying between 0.65 and 1.25 into the nematic and the smectic A phases. For none of these cases smectic A phase was found to be stabilized though in some range of temperature for a given $n$ it appeared as a metastable state. We have examined the variation of freezing parameters for the isotropic-nematic transition with temperature and $n$. We have also compared our results with simulation results wherever they are available. While we find that the density-functional theory is good to study the freezing transitions in such fluids the structural parameters found from the \PY theory need to be improved particularly at high temperatures and lower values of $n$.Comment: 21 Pages (in RevTex4), 6 GIF and 4 Postscript format Fig

X-ray emission from O-type stars : DH Cep and HD 97434

We present X-ray emission characteristics of the massive O-type stars DH Cep and HD 97434 using archival XMM-Newton observations. There is no convincing evidence for short term variability in the X-ray intensity during the observations. However, the analysis of their spectra reveals X-ray structure being consistent with two-temperature plasma model. The hydrogen column densities derived from X-ray spectra of DH Cep and HD 97434 are in agreement with the reddening measurements for their corresponding host clusters NGC 7380 and Trumpler 18, indicating that the absorption by stellar wind is negligible. The X-ray emission from these hot stars is interpreted in terms of the standard instability-driven wind shock model.Comment: 13 pages ; 2 figures; 2 tables (Accepted for publication in New Astronomy

Pair Correlation Functions and a Free-Energy Functional for the Nematic Phase

In this paper we have presented the calculation of pair correlation functions in a nematic phase for a model of spherical particles with the long-range anisotropic interaction from the mean spherical approximation(MSA) and the Percus-Yevick (PY) integral equation theories. The results found from the MSA theory have been compared with those found analytically by Holovko and Sokolovska (J. Mol. Liq. $\bf 82$, 161(1999)). A free energy functional which involves both the symmetry conserving and symmetry broken parts of the direct pair correlation function has been used to study the properties of the nematic phase. We have also examined the possibility of constructing a free energy functional with the direct pair correlation function which includes only the principal order parameter of the ordered phase and found that the resulting functional gives results that are in good agreement with the original functional. The isotropic-nematic transition has been located using the grand thermodynamic potential. The PY theory has been found to give nematic phase with pair correlation function harmonic coefficients having all the desired features. In a nematic phase the harmonic coefficient of the total pair correlation function $h({\bf x_1},{\bf x_2})$ connected with the correlations of the director transverse fluctuations should develop a long-range tail. This feature has been found in both the MSA and PY theories.Comment: 27 pages, 11 figures, Accepted in J. Chem. Phy

Nonparametric Estimation of the Survival Function Based on Censored Data with Additional Observations from the Residual Distribution

We derive the nonparametric maximum likelihood estimator (NPMLE) of the distribution of the test items using a random, right-censored sample combined with an additional right-censored, residual-lifetime sample in which only lifetimes past a known, fixed time are collected. This framework is suited for samples for which individual test data are combined with left-truncated and randomly censored data from an operating environment. The NPMLE of the survival function using the combined sample is identical to the Kaplan-Meier product-limit estimator only up to the time at which the test items corresponding to the residual sample were known to survive. The limiting distribution for the NPMLE, discussed in detail, leads to confidence bounds for the survival function. For the uncensored case, we study the relative efficiency for the estimator based on the combined sample with respect to the analogous estimator based only on the simple random sample

A comparative genetic diversity analysis in mungbean (Vigna radiata L.) using inter-simple sequence repeat (ISSR) and amplified fragment length polymorphism (AFLP)

Amplified fragment length polymorphism (AFLP) and inter-simple sequence repeat (ISSR) markers were used to study the DNA polymorphism in elite mungbean genotypes. A total of nine AFLP primer combination and 22 ISSR primers were used. Amplification of genomic DNA of the 30 genotypes, using AFLP analysis, yielded 300 fragments that could be scored, of which 192 were polymorphic, with an average of 21.3 polymorphic fragments per primer. Number of amplified fragments with AFLP primers ranged from 29 (E-AAC: M-CAG) to 10 (E-ACG: M-CAT). Percentage polymorphism ranged from 46.3% (E-AAC: M-CCA) to a maximum of 100% (E-AAC: M-CAC), with an average of 64%. The 22 ISSR primers used in the study produced 108 bands across 30 genotypes, of which 68 were polymorphic. The number of amplified bands varied from two UBC820) to ten URP 6F). The average numbers of bands per primer and polymorphic bands per primer were 4.9 and 3.1, respectively. Percentage polymorphism ranged from 25% (UBC844) to 85% (UBC846, UBC864, UBC895), with an average percentage polymorphism of 58.3% across all the genotypes. AFLP markers were more efficient than the ISSR assay, as they detected 64% polymorphic DNA markers in Vigna radiata as compared to 58.3% for ISSR markers. The Mantel test between the two Jaccard's similarity matrices gave r = 0.19, showing low correlation between AFLP- and ISSR-based similarities. Clustering of genotypes within groups was not similar when AFLP and ISSR derived dendrograms were compared.Key words: AFLP, ISSR, Vigna radiata (mung bean), marker index, unweighted pair-group method with arithmetic averages (UPGMA)

Role of Ionic & Non-ionic Surfactants in the Suppression of Polarographic Maxima of Ni(II)

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DEVELOPMENT OF UV SPECTROPHOTOMETRIC METHOD FOR THE DETERMINATION OF BENIDIPINE HYDROCHLORIDE BY USING QUALITY BY DESIGN (QbD) APPROACH

Objective: To develop a simple, rapid, accurate, robust and inexpensive spectrophotometric method for the estimation of benidipine hydrochloride by using quality by design (QbD)†approach.Methods: A UV spectrophotometric method was developed on Shimadzu UV-1800 double beam spectrophotometer using methanol as solvent and wavelength of 236 nm was selected as absorbance maxima (ðœ†max). Effect of input variables on spectrum characteristics were studied for the selection of critical parameters and proposed method was validated for various parameters like system suitability, linearity, precision, accuracy, detection limits and quantification limits as per the International Conference on Harmonization guidelines ICH Q2(R1).Results: Linearity of the method was found to be excellent over the concentration range 3 to 18 µg/ml with high correlation coefficient value of 0.9999. Limits of detection and quantification were found to be 0.20 µg/ml and 0.60 µg/ml respectively. The mean recovery was found to be 100.35 % with low percentage relative standard deviation (% RSD) value. The precision study also has shown low % RSD value (<1). No interfering peaks were observed during specificity studies.Conclusion: Obtained result indicated that the developed spectrophotometric method is robust and efficient for the determination of benidipine hydrochloride