1,283 research outputs found
Rashba-coupling modelling for two-dimensional and high-order Rashba Hamiltonian for one-dimensional confined heavy holes
Based on standard k.p (8 x 8) multiband Hamiltonian, we have deduced an
explicit analytical expression for the Rashba-coupling parameter which
clarifies its anomalous behavior for heavy holes (hh), gated in
quasi-two-dimensional (Q2D) systems, by letting grow the density. Our modelling
remarkable better agrees with experimental results in comparison with earlier
theoretical models, while recovers the expected cubic dependence on the
quasi-momentum. For quasi-one-dimensional (Q1D) hh systems, we have formally
derived an effective Rashba Hamiltonian with two competitive terms on the
quasi-momentum, a linear term and a cubic one as predicted from suitable
approximations to the Q2D scope. The Rashba-coupling parameters also behave
anomalously and qualitatively support recent experiments in core/shell
nanowires. Furthermore, they exhibit an essential asymptotic discontinuity in
the low density regime as a function of the lateral confinement length. For hh,
we present closed schemes to accurately quote the Rashba-coupling parameters
both for the Q2D and Q1D systems, which become unprecedented for holes.Comment: 6 pages, 4 figure
The Stationary Phase Method for a Wave Packet in a Semiconductor Layered System. The applicability of the method
Using the formal analysis made by Bohm in his book, {\em "Quantum theory"},
Dover Publications Inc. New York (1979), to calculate approximately the phase
time for a transmitted and the reflected wave packets through a potential
barrier, we calculate the phase time for a semiconductor system formed by
different mesoscopic layers. The transmitted and the reflected wave packets are
analyzed and the applicability of this procedure, based on the stationary phase
of a wave packet, is considered in different conditions. For the applicability
of the stationary phase method an expression is obtained in the case of the
transmitted wave depending only on the derivatives of the phase, up to third
order. This condition indicates whether the parameters of the system allow to
define the wave packet by its leading term. The case of a multiple barrier
systems is shown as an illustration of the results. This formalism includes the
use of the Transfer Matrix to describe the central stratum, whether it is
formed by one layer (the single barrier case), or two barriers and an inner
well (the DBRT system), but one can assume that this stratum can be comprise of
any number or any kind of semiconductor layers.Comment: 15 pages, 4 figures although figure 4 has 5 graph
Dynamic Obstacle Avoidance
Report on the methodology and results of experimental software development in order to produce an efficient and effective mechanism whereby entities controlled by computer generated forces systems can avoid collisions with other moving entities within a distributed interactive simulation environment
A prospective randomized trial comparing sequential ganciclovir-high dose acyclovir to high dose acyclovir for prevention of cytomegalovirus disease in adult liver transplant recipients
Cytomegalovirus disease is an important cause of morbidity following liver transplantation. To date there has not been an effective prophylaxis for CMV disease after liver transplantation. One hundred forty-three patients were randomized to receive either high dose oral acyclovir (800 mg 4 times a day) alone for 3 months after transplantation (acyclovir group) or intravenous ganciclovir (5 mg/kg twice a day) for 14 days followed by high dose oral acyclovir to complete a 3-month regimen (ganciclovir group). Of 139 patients available for evaluation, 43 of 71 (61%) patients from the acyclovir group developed CMV infection compared with 16 of 68 (24%) from the ganciclovir group (relative risk, 3.69; 95% confidence interval, 2.07-6.56; PcO.OOOOl). Of those randomized, CMV disease was seen in 20 (28%) of the acyclovir group compared with 6 (9%) of the ganciclovir group (relative risk, 5.11; 95% confidence interval, 2.05-12.75; P=0.0001). The median time to onset of CMV infection was 45 days in the acyclovir group compared with 78 days in the ganciclovir group (P=0.004). The median time to onset of CMV disease was 40 days in the acyclovir group compared with 78 days in the ganciclovir patients (P=0.02). With respect to primary CMV infection, there was no difference in the rates in the 2 groups, but tissue invasive disease and recurrent CMV disease were less frequent in the ganciclovir group. It is concluded that a course of 2 weeks of ganciclovir immediately after transplantation followed by high dose oral acyclovir for 10 weeks is superior to a 12-week course of high dose oral acyclovir alone for prevention of both CMV infection and CMV disease after liver transplantation. However, the lack of significant effect in seronegative recipients who received grafts from seropositive donors suggests that other strategies are needed to prevent CMV infection in this high risk population. © 1994 by Williams & Wilkins
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