Phase separation of binary condensates in harmonic and lattice potentials

We propose a modified Gaussian ansatz to study binary condensates, trapped in harmonic and optical lattice potentials, both in miscible and immiscible domains. The ansatz is an apt one as it leads to the smooth transition from miscible to immiscible domains without any {\em a priori} assumptions. In optical lattice potentials, we analyze the squeezing of the density profiles due to the increase in the depth of the optical lattice potential. For this we develop a model with three potential wells, and define the relationship between the lattice depth and profile of the condensate.Comment: 13 pages, 11 figures, additional references adde

Neutrinos from Stellar Collapse: Comparison of signatures in water and heavy water detectors

Signatures of neutrino and antineutrino signals from stellar collapse in heavy water detectors are contrasted with those in water detectors. The effects of mixing, especially due to the highly dense matter in the supernova core, are studied. The mixing parameters used are those sets allowed by current understanding of available neutrino data: from solar, atmospheric and laboratory neutrino experiments. Signals at a heavy water detector, especially the dominant charged current reactions on deuteron, are very sensitive to some of these sets of allowed mixing parameters. Theoretical uncertainties on supernova neutrino spectra notwithstanding, a combination of supernova measurements with water and heavy water detectors may be able to distinguish many of these mixing possibilities and thus help in ruling out many of them.Comment: 36 pages Latex file, with 13 postscript figures; important improvements in the analysis and more detailed presentation of results. To appear in Phys. Rev.

Annihilation of vortex dipoles in an Oblate Bose-Einstein Condensate

We theoretically explore the annihilation of vortex dipoles, generated when an obstacle moves through an oblate Bose-Einstein condensate, and examine the energetics of the annihilation event. We show that the gray soliton, which results from the vortex dipole annihilation, is lower in energy than the vortex dipole. We also investigate the annihilation events numerically and observe that the annihilation occurs only when the vortex dipole overtakes the obstacle and comes closer than the coherence length. Furthermore, we find that the noise reduces the probability of annihilation events. This may explain the lack of annihilation events in experimental realizations.Comment: 8 pages and 9 figure

A Representation of Symmetry Generators for the Type IIB Superstring on a Plane Wave in the U(4) Formalism

We calculate the symmetry currents for the type IIB superstring on a maximally supersymmetric plane wave background using the N=(2,2) superconformally covariant U(4) formulation developed by Berkovits, Maldacena and Maoz. An explicit realization of the U(4) generators together with 16 fermionic generators is obtained in terms of the N=(2,2) worldsheet fields. Because the action is no longer quadratic, we use a light-cone version to display the currents in terms of the covariant worldsheet variables.Comment: 9 pages, harvmac, Corrected some typographical errors, Added reference

Shear viscosity of a superfluid Fermi gas in the unitarity limit

We compute the shear viscosity of a superfluid atomic Fermi gas in the unitarity limit. The unitarity limit is characterized by a divergent scattering length between the atoms, and it has been argued that this will result in a very small viscosity. We show that in the low temperature T limit the shear viscosity scales as xi^5/T^5, where the universal parameter 'xi' relates the chemical potential and the Fermi energy, mu=xi E_F. Combined with the high temperature expansions of the viscosity our results suggest that the viscosity has a minimum near the critical temperature T_c. A naive extrapolation indicates that the minimum value of the ratio of viscosity over entropy density is within a factor of ~ 5 of the proposed lower bound hbar/(4\pi k_B).Comment: 9 pages, 7 figures, LaTeX2

Magnetic and humidity sensing properties of nanostructured Cu[x]Co[1-x]Fe2O4 synthesized by auto combustion technique

Magnetic nanomaterials (23-43 nm) of Cu$_x$Co$_{1-x}$Fe$_2$O$_4$\ (x = 0.0, 0.5 and 1.0) were synthesized by auto combustion method. The crystallite sizes of these materials were calculated from X-ray diffraction peaks. The band observed in Fourier transform infrared spectrum near 575 cm$^{-1}$ in these samples confirm the presence of ferrite phase. Conductivity measurement shows the thermal hysteresis and demonstrates the knee points at 475$^o$C, 525$^o$C and 500$^o$C for copper ferrite, cobalt ferrite and copper-cobalt mixed ferrite respectively. The hystersis M-H loops for these materials were traced using the Vibrating Sample Magnetometer (VSM) and indicate a significant increase in the saturation magnetization (M$_s$) and remanence (M$_r$) due to the substitution of Cu$^{2+}$ ions in cobalt ferrite, while the intrinsic coercivity (H$_c$) was decreasing. Among these ferrites, copper ferrite exhibits highest sensitivity for humidity.Comment: 12 pages, 7 figure

Molecular Structure of Polystyrene at Air/Polymer and Solid/Polymer Interfaces

IR-visible sum-frequency generation(SFG) spectroscopy has been used in a total internal reflection geometry to study the molecular structure of polystyrene (PS) at PS/sapphire and PS/air interfaces, simultaneously. The symmetric vibrational modes of the phenyl rings dominate the SFG spectra at the PS/air interface as compared to the antisymmetric vibrational modes at the PS/sapphire interface. This indicates approximately parallel orientation of the phenyl rings at the PS/air interface while nearly perpendicular orientation at the PS/sapphire interface, with respect to the surface normal

Developing procedures for assessment of ecological status of Indian River basins in the context of environmental water requirements

River basins / Ecology / Indicators / Environmental flows / Environmental management / Habitats / Biota / Fish / Ecosystems / India / Krishna River Basin / Chauvery River Basin / Narmada River Basin / Periyar River Basin / Ganga River Basin