797 research outputs found
Massive Upper Gastrointestinal Bleeding Secondary to Duodenal Metastasis of Transitional Cell Carcinoma of the Urinary Bladder
Acute upper gastrointestinal (UGI) bleeding is a common problem in our clinical practice and is often due to peptic ulcer diseases. Occasionally, malignancy may be implicated in these situations. Here we report a rare case of UGI bleeding secondary to metastatic transitional cell carcinoma (TCC) of the urinary bladder. A 62-year-old man with a history of stage IIIb TCC of the urinary bladder presented with hematemesis. Endoscopy showed a large tumor in the second stage of the duodenum that occupied 40% of the duodenal circumference, over 7 cm in length. Biopsies revealed a poorly differentiated malignant neoplasm consistent with metastasis from urothelial carcinoma that was identical to the previous surgical specimen of the urinary bladder. He was treated with supportive therapy and intravenous proton pump inhibitor and was discharged home 2 weeks later. Two weeks after discharge, the patient returned to the hospital with a painful swelling of the floor of his mouth. Biopsy again showed the same cancer type. He had unremitting bleeding from his mouth requiring multiple transfusions and a course of palliative radiation therapy. He progressively deteriorated in his cardiopulmonary and neurological functions and expired with cardiopulmonary arrest one month later
Bloch oscillations, Zener tunneling and Wannier-Stark ladders in the time-domain
We present a time-domain analysis of carrier dynamics in a semiconductor
superlattice with two minibands. Integration of the density-matrix equations of
motion reveals a number of new features: (i) for certain values of the applied
static electric field strong interband transitions occur; (ii) in static fields
the complex time-dependence of the density-matrix displays a sequence of stable
plateaus in the low field regime, and (iii) for applied fields with a periodic
time-dependence the dynamic response can be understood in terms of the
quasienergy spectra.Comment: 4 pages, 6 PostScript figures available from [email protected], REVTEX
3.
Current oscillations in a metallic ring threaded by a time-dependent magnetic flux
We study a mesoscopic metallic ring threaded by a magnetic flux which varies
linearly in time PhiM(t)=Phi t with a formalism based in Baym-Kadanoff-Keldysh
non-equilibrium Green functions. We propose a method to calculate the Green
functions in real space and we consider an experimental setup to investigate
the dynamics of the ring by recourse to a transport experiment. This consists
in a single lead connecting the ring to a particle reservoir. We show that
different dynamical regimes are attained depending on the ratio hbar Phi/Phi0
W, being Phi0=h c/e and W, the bandwidth of the ring. For moderate lengths of
the ring, a stationary regime is achieved for hbar Phi/Phi0 >W. In the opposite
case with hbar Phi/Phi0 < W, the effect of Bloch oscillations driven by the
induced electric field manifests itself in the transport properties of the
system. In particular, we show that in this time-dependent regime a tunneling
current oscillating in time with a period tau=2piPhi0/Phi can be measured in
the lead. We also analyze the resistive effect introduced by inelastic
scattering due to the coupling to the external reservoir.Comment: 17 pages, 13 figure
Superfluid Dynamics of a Bose-Einstein Condensate in a Periodic Potential
We investigate the superfluid properties of a Bose-Einstein condensate (BEC)
trapped in a one dimensional periodic potential. We study, both analytically
(in the tight binding limit) and numerically, the Bloch chemical potential, the
Bloch energy and the Bogoliubov dispersion relation, and we introduce {\it two}
different, density dependent, effective masses and group velocities. The
Bogoliubov spectrum predicts the existence of sound waves, and the arising of
energetic and dynamical instabilities at critical values of the BEC
quasi-momentum which dramatically affect its coherence properties. We
investigate the dependence of the dipole and Bloch oscillation frequencies in
terms of an effective mass averaged over the density of the condensate. We
illustrate our results with several animations obtained solving numerically the
time-dependent Gross-Pitaevskii equation.Comment: 13 pages, 7 figures, movies and published paper available at
http://www.iop.org/EJ/abstract/1367-2630/5/1/11
Effects of impurity scattering on electron-phonon resonances in semiconductor superlattice high-field transport
A non-equilibrium Green's function method is applied to model high-field
quantum transport and electron-phonon resonances in semiconductor
superlattices. The field-dependent density of states for elastic (impurity)
scattering is found non-perturbatively in an approach which can be applied to
both high and low electric fields. I-V curves, and specifically electron-phonon
resonances, are calculated by treating the inelastic (LO phonon) scattering
perturbatively. Calculations show how strong impurity scattering suppresses the
electron-phonon resonance peaks in I-V curves, and their detailed sensitivity
to the size, strength and concentration of impurities.Comment: 7 figures, 1 tabl
Zener transitions between dissipative Bloch bands. II: Current Response at Finite Temperature
We extend, to include the effects of finite temperature, our earlier study of
the interband dynamics of electrons with Markoffian dephasing under the
influence of uniform static electric fields. We use a simple two-band
tight-binding model and study the electric current response as a function of
field strength and the model parameters. In addition to the Esaki-Tsu peak,
near where the Bloch frequency equals the damping rate, we find current peaks
near the Zener resonances, at equally spaced values of the inverse electric
field. These become more prominenent and numerous with increasing bandwidth (in
units of the temperature, with other parameters fixed). As expected, they
broaden with increasing damping (dephasing).Comment: 5 pages, LateX, plus 5 postscript figure
Theory of Coherent Time-dependent Transport in One-dimensional Multiband Semiconductor Superlattices
We present an analytical study of one-dimensional semiconductor superlattices
in external electric fields, which may be time-dependent. A number of general
results for the (quasi)energies and eigenstates are derived. An equation of
motion for the density matrix is obtained for a two-band model, and the
properties of the solutions are analyzed. An expression for the current is
obtained. Finally, Zener-tunneling in a two-band tight-binding model is
considered. The present work gives the background and an extension of the
theoretical framework underlying our recent Letter [J. Rotvig {\it et al.},
Phys. Rev. Lett. {\bf 74}, 1831 (1995)], where a set of numerical simulations
were presented.Comment: 15 pages, Revtex 3.0, uses epsf, 2 ps figures attache
Schrodinger cat states prepared by Bloch oscillation in a spin-dependent optical lattice
We propose to use Bloch oscillation of ultra-cold atoms in a spin-dependent
optical lattice to prepare schrodinger cat states. Depending on its internal
state, an atom feels different periodic potentials and thus has different
energy band structures for its center-of-mass motion. Consequently, under the
same gravity force, the wave packets associated with different internal states
perform Bloch oscillation of different amplitudes in space and in particular
they can be macroscopically displaced with respect to each other. In this way,
a cat state can be prepared.Comment: 4 pages, 3 figures; slightly modifie
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