190 research outputs found
Impurity and soliton dynamics in a Fermi gas with nearest-neighbor interactions
We study spinless fermions with repulsive nearest-neighbor interactions
perturbed by an impurity particle or a local potential quench. Using the
numerical time-evolving block decimation method and a simplified analytic
model, we show that the pertubations create a soliton-antisoliton pair. If
solitons are already present in the bath, the two excitations have a
drastically different dynamics: The antisoliton does not annihilate with the
solitons and is therefore confined close to its origin while the soliton
excitation propagates. We discuss the consequences for experiments with
ultracold gases.Comment: 12 pages, 16 figure
Sine-Gordon dynamics in spin transport
We study spin transport in a one-dimensional finite-length wire connected to
fermionic leads. The interacting wire is described by the sine-Gordon model
while the leads are either noninteracting or interacting Luttinger liquids. We
calculate the spin current driven by a spin bias by solving numerically the
classical equation of motion, and find that the cosine term in the sine-Gordon
model gives rise to an oscillating spin current when the spin bias exceeds its
critical value. We discuss the results in connection with transport experiments
with ultracold atoms.Comment: 13 pages, 7 figure
Nonlinear transport in the presence of a local dissipation
We characterize the particle transport, particle loss, and nonequilibrium
steady states in a dissipative one-dimensional lattice connected to reservoirs
at both ends. The free-fermion reservoirs are fixed at different chemical
potentials, giving rise to particle transport. The dissipation is due to a
local particle loss acting on the center site. We compute the conserved current
and loss current as functions of voltage in the nonlinear regime using a
Keldysh description. The currents show step-like features which are affected
differently by the local loss: The steps are either smoothened, nearly
unaffected, or even enhanced, depending on the spatial symmetry of the
single-particle eigenstate giving rise to the step. Additionally, we compute
the particle density and momentum distributions in the chain. At a finite
voltage, two Fermi momenta can occur, connected to different wavelengths of
Friedel oscillations on either side of the lossy site. We find that the
wavelengths are determined by the chemical potentials in the reservoirs rather
than the average density in the lattice.Comment: 19 pages, 19 figure
Spin transport in a one-dimensional quantum wire
We analyze the spin transport through a finite-size one-dimensional
interacting wire connected to noninteracting leads. By combining
renormalization-group arguments with other analytic considerations such as the
memory function technique and instanton tunneling, we find the temperature
dependence of the spin conductance in different parameter regimes in terms of
interactions and the wire length. The temperature dependence is found to be
nonmonotonic. In particular, the system approaches perfect spin conductance at
zero temperature for both attractive and repulsive interactions, in contrast
with the static spin conductivity. We discuss the connection of our results to
recent experiments with ultracold atoms and compare the theoretical prediction
to experimental data in the parameter regime where temperature is the largest
energy scale.Comment: 16 pages, 10 figure
Combined Surgical Treatment for Chronic Upper Extremity Lymphedema Patients Simultaneous Lymph Node Transfer and Liposuction
Background Upper limb lymphedema is a common problem after axillary lymph node dissection. Lymphatic drainage can be improved by microvascular lymph node transfer, whereas liposuction can be used to reduce arm volume and excess of adipose tissue. We present the results of chronic lymphedema patients who have undergone lymph node transfer and liposuction simultaneously in 1 operation and compare the results with patients who have undergone lymph node transfer without liposuction. Methods During May 2007 to February 2015, 20 postmastectomy patients and 1 Hodgkin's lymphoma patient presenting with chronic nonpitting lymphedema (age between 37 and 74 years, average 56.7 years) were operated using the combined technique and 27 postmastectomy patients presenting with early-stage lymphedema (age between 31 and 68 years, average age 50.2 years) were operated using only the lymph node transfer. Compression therapy was started immediately after the operation and the patients used compression 24 h/d at least 6 months postoperatively. Changes in clinical parameters (number of erysipelas infections, pain), arm volume, transport indexes calculated form lymphoscintigraphy images, and daily usage of compression garments were compared preoperatively and postoperatively and between groups (combined technique vs lymph node transfer). The study was a retrospective observational study. Results In the combined technique group, the average arm volume excess decreased postoperatively 87.7%, and in 7 of 10 patients, the edema volume did not increase even without compression. Seventeen of 21 patients were able to reduce the use of compression garment. Lymphoscintigraphy results were improved in 12 of 15 patients and the improvement was significantly greater in the combined technique group than in the lymph node transfer group (P = 0.01). The number of erysipelas infections was decreased in 7 of 10 patients and the decrease was significantly greater in the combined technique group than in the lymph node transfer group (P = 0.02). In the lymph node transfer group, the average excess volume decreased postoperatively 27.5%. Fourteen of 27 patients were able to reduce the use of compression garments. Lymphoscintigraphy results were improved in 8 of 19 patients, and the number of erysipelas infections was decreased in 1 of 3 patients. Conclusions Liposuction can safely be performed with lymph node transfer in 1 operation to achieve optimal results in patients with chronic lymphedema. The combined technique provides immediate volume reduction and further regenerative effects on the lymphatic circulation. The significantly greater reduction in lymphoscintigraphy values and erysipelas infections suggests that the combined technique might be better for late-stage lymphedema patients than lymph node transfer alone
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Simulations of laser-initiated stress waves
We present a study of the short-time scale (< 250 ns) fluid dynamic response of water to a fiber-delivered laser pulse of variable energy and spatial profile. The laser pulse was deposited on a stress confinement time scale. The spatial profile was determined by the fiber core radius r (110 and 500 microns) and the water absorption coefficient {mu}{sub 2} (200 and 50 l/cm). Considering 2D cylindrical symmetry, the combination of fiber radius and absorption coefficient parameters can be characterized as near planar (1{mu}{sub 2} greater than r), symmetric (1/{mu}{sub 2}=r), and side-directed (1/{mu}{sub 2} less than r). The spatial profile study shows how the stress wave various as a function of geometry. For example, relatively small absorption coefficients can result in side-propagating shear and tensile fields
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