Dissipative Phase Fluctuations In A Superconductor In Proximity To An Electron Gas

We study a two-dimensional superconductor in close proximity to a two-dimensional metallic sheet. The electrons in the superconducting sheet are coupled to those in the metallic sheet by the Coulomb interaction only. We obtain an effective phase-only action for the superconductor by integrating out all the electronic degrees of freedom in the problem. The Coulomb drag of the normal electrons in the metallic sheet is found to make the spectrum of phase-fluctuations in the superconductor, dissipative at long wavelengths. The dissipative co-efficient $\eta$ is shown to be simply related to the normal state conductivities of the superconducting layer ($\sigma_S$)and the metallic sheet ($\sigma_E$) by the relation $\eta \propto {\sigma_S\sigma_E\over \sigma_S+\sigma_E}$.Comment: 11 pages; To appear in Int. Jour. of Mod. Phys.

Fluctuation Effects And Order Parameter Symmetry In The Cuprate Superconductors

Effect of phase fluctuations on superconducting states with anisotropic order parameters is studied in a BCS like lattice model of cuprate superconductors. The degradation of the mean field transition temperature due to phase fluctuations is estimated within a Kosterlitz-Thouless scenario. Values of the interaction parameters for optimal doping, corresponding to a stable superconducting state of $S_{xy}$ symmetry, which fit the nodal structure of the superconducting order parameter in the Bi2212 compound, are obtained. The angular position of the node is found to be insensitive to the dopant concentration.Comment: Latex file, 8 output pages, 5 figures (available from Authors on request), to appear in Europhysics Letter

Josephson Coupling through a Quantum Dot

We derive, via fourth order perturbation theory, an expression for the Josephson current through a gated interacting quantum dot. We analyze our expression for two different models of the superconductor-dot-superconductor (SDS) system. When the matrix elements connecting dot and leads are featureless constants, we compute the Josephson coupling J_c as a function of the gate voltage and Coulomb interaction. In the diffusive dot limit, we compute the probability distribution P(J_c) of Josephson couplings. In both cases, pi junction behavior (J_c < 0) is possible, and is not simply dependent on the parity of the dot occupancy.Comment: 9 pages; 3 encapsulated PostScript figure

Determination of absorption of vitamin B<SUB>12</SUB> by a double isotope tracer technique

A new simple method for the study of vitamin B12 absorption involving the use of two tracers is described. Along with 58Co labeled vitamin B12 an unabsorbable marker in the form of 51Cr labeled chromic oxide is administered to the patients. The ratio of the activities of the two isotopes in the standard is compared with the ratio of the activies of these isotopes in an aliquot of a stool sample collected after 24 or 48 hours. The absorption of labeled vitamin B12 is estimated from the alteration in the ratio of absorbable and unabsorbable isotopes in the stool sample. The method compares well with other methods of estimating vitamin B12 absorption such as Schilling's test, total faecal collection and whole body counting

A pulse size estimation method for reduced-order models

Model-Order Reduction (MOR) is an important technique that allows Reduced-Order Models (ROMs) of physical systems to be generated that can capture the dominant dynamics, but at lower cost than the full order system. One approach to MOR that has been successfully implemented in fluid dynamics is the Eigensystem Realization Algorithm (ERA). This method requires only minimal changes to the inputs and outputs of a CFD code so that the linear responses of the system to unit impulses on each input channel can be extracted. One of the challenges with the method is to specify the size of the input pulse. An inappropriate size may cause a failure of the code to converge due to non-physical behaviour arising during the solution process. This paper addresses this issue by using piston theory to estimate the appropriate input pulse size

Effective Vortex Mass from Microscopic Theory

We calculate the effective mass of a single quantized vortex in the BCS superconductor at finite temperature. Based on effective action approach, we arrive at the effective mass of a vortex as integral of the spectral function $J(\omega)$ divided by $\omega^3$ over frequency. The spectral function is given in terms of the quantum-mechanical transition elements of the gradient of the Hamiltonian between two Bogoliubov-deGennes (BdG) eigenstates. Based on self-consistent numerical diagonalization of the BdG equation we find that the effective mass per unit length of vortex at zero temperature is of order $m (k_f \xi_0)^2$ ($k_f$=Fermi momentum, $\xi_0$=coherence length), essentially equaling the electron mass displaced within the coherence length from the vortex core. Transitions between the core states are responsible for most of the mass. The mass reaches a maximum value at $T\approx 0.5 T_c$ and decreases continuously to zero at $T_c$.Comment: Supercedes prior version, cond-mat/990312

Friedel-crafts reaction. Part IX. The action of propionic and butyric anhydrides on orcinol and further evidence of λ-substitution in resorcinol derivatives

This article does not have an abstract

Phase Diagram of the Half-Filled Extended Hubbard Model in Two Dimensions

We consider an extended Hubbard model of interacting fermions on a lattice. The fermion kinetic energy corresponds to a tight binding Hamiltonian with nearest neighbour (-t) and next nearest neighbour (t') hopping matrix elements. In addition to the onsite Hubbard interaction (U) we also consider a nearest neighbour repulsion (V). We obtain the zero temperature phase diagram of our model within the Hartree-Fock approximation. We consider ground states having charge and spin density wave ordering as well as states with orbital antiferromagnetism or spin nematic order. The latter two states correspond to particle-hole binding with $d_{x^2-y^2}$ symmetry in the charge and spin channels respectively. For $t' = 0$, only the charge density wave and spin density wave states are energetically stable. For non-zero t', we find that orbital antiferromagnetism (or spin nematic) order is stable over a finite portion of the phase diagram at weak coupling. This region of stability is seen to grow with increasing values of t'.Comment: Latex file, 10 output pages, 3 Figures (available on request to [email protected]), to appear in Phys. Rev. B (BR

Thyroid hormones And [<SUP>14</SUP>C] glucose metabolism in bacteria

The effects of triiodothyronine and thyroxine on metabolism and growth of bacteria were studied. It was observed that over a certain range of concentration thyroxine and triiodothyronine produced increase in 14CO2 release from [14C]-labeled glucose and also stimulated bacteria growth