521 research outputs found

    Josephson Coupling through a Quantum Dot

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    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

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    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

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

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    Travelling waves in a drifting flux lattice

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    Starting from the time-dependent Ginzburg-Landau (TDGL) equations for a type II superconductor, we derive the equations of motion for the displacement field of a moving vortex lattice without inertia or pinning. We show that it is linearly stable and, surprisingly, that it supports wavelike long-wavelength excitations arising not from inertia or elasticity but from the strain-dependent mobility of the moving lattice. It should be possible to image these waves, whose speeds are a few \mu m/s, using fast scanning tunnelling microscopy.Comment: 4 pages, revtex, 2 .eps figures imbedded in paper, title shortened, minor textual change

    Subcutaneous Plasmacytoma Metastasis Precipitated by Tunneled Central Venous Catheter Insertion

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    Extramedullary plasmacytomas are tumors of monoclonal plasma cells arising within soft tissue that uncommonly occur in multiple myeloma patients. While sporadic development of these tumors at cutaneous trauma sites, including venous catheter access sites, has been reported, interventional radiologists seldom encounter this disease. Herein, we describe a case of metastatic subcutaneous plasmacytoma precipitated by tunneled central venous catheter insertion in a male patient undergoing stem cell therapy for treatment of multiple myeloma. In addition, we review the identification, diagnostic pitfalls, pathogenesis, and treatment of this rare entity

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

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    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

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

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    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 dx2−y2d_{x^2-y^2} symmetry in the charge and spin channels respectively. For t′=0t' = 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
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