1,307 research outputs found
Exciton Beats in GaAs Quantum Wells: Bosonic Representation and Collective Effects
We discuss light-heavy hole beats observed in transient optical experiments
in GaAs quantum wells in terms of a free-boson coherent state model. This
approach is compared with descriptions based on few-level representations.
Results lead to an interpretation of the beats as due to classical
electromagnetic interference. The boson picture correctly describes photon
excitation of extended states and accounts for experiments involving coherent
control of the exciton density and Rayleigh scattering beating.Comment: 4 pages, no figures. Accepted for publication in Solid State
Communication
Detailed dynamics of discrete Gaussian semiflexible chains with arbitrary stiffness along the contour
We revisit a model of semiflexible Gaussian chains proposed by Winkler
\textit{et al}, solve the dynamics of the discrete description of the model and
derive exact algebraic expressions for some of the most relevant dynamical
observables, such as the mean-square displacement of individual monomers, the
dynamic structure factor, the end-to-end vector relaxation and the shear stress
relaxation modulus. The mathematical expressions are verified by comparing them
with results from Brownian dynamics simulations, reporting an excellent
agreement. Then, we generalize the model to linear polymer chains with
arbitrary stiffness. In particular, we focus on the case of a linear polymer
with stiffness that changes linearly from one end of the chain to the other,
and study the same dynamical functions previously presented. We discuss
different approaches to check whether a polymer has constant or heterogeneous
stiffness along its contour. Overall, this work presents a new insight for a
well known model for semiflexible chains and provides tools that can be
exploited to compare the predictions of the model with simulations of coarse
grained semiflexible polymers
Silicon purification using a Cu-Si alloy source
Production of 99.9999% pure silicon from 98% pure metallurgical grade (MG) silicon by a vapor transport filtration process (VTP) is described. The VTF process is a cold wall version of an HCl chemical vapor transport technique using a Si:Cu3Si alloy as the silicon source. The concentration, origin, and behavior of the various impurities involved in the process were determined by chemically analyzing alloys of different purity, the slag formed during the alloying process, and the purified silicon. Atomic absorption, emission spectrometry, inductively coupled plasma, spark source mass spectrometry, and secondary ion mass spectroscopy were used for these analyses. The influence of the Cl/H ratio and the deposition temperature on the transport rate was also investigated
Electroproduction of the d* dibaryon
The unpolarized cross section for the electroproduction of the isoscalar
di-delta dibaryon is calculated for deuteron target using a
simple picture of elastic electron-baryon scattering from the and the components of the deuteron. The calculated
differential cross section at the electron lab energy of 1 GeV has the value of
about 0.24 (0.05) nb/sr at the lab angle of 10 (30) for the
Bonn B potential when the dibaryon mass is taken to be 2.1 GeV. The cross
section decreases rapidly with increasing dibaryon mass. A large calculated
width of 40 MeV for combined with a small
experimental upper bound of 0.08 MeV for the decay width appears to have
excluded any low-mass model containing a significant admixture of the
configuration.Comment: 11 journal-style pages, 8 figure
Anomalous diffusion in correlated continuous time random walks
We demonstrate that continuous time random walks in which successive waiting
times are correlated by Gaussian statistics lead to anomalous diffusion with
mean squared displacement ~t^{2/3}. Long-ranged correlations of the
waiting times with power-law exponent alpha (0<alpha<=2) give rise to
subdiffusion of the form ~t^{alpha/(1+alpha)}. In contrast correlations
in the jump lengths are shown to produce superdiffusion. We show that in both
cases weak ergodicity breaking occurs. Our results are in excellent agreement
with simulations.Comment: 6 pages, 6 figures. Slightly revised version, accepted to J Phys A as
a Fast Track Communicatio
Spin depolarization in the transport of holes across GaMnAs/GaAlAs/p-GaAs
We study the spin polarization of tunneling holes injected from ferromagnetic
GaMnAs into a p-doped semiconductor through a tunneling barrier. We obtain an
upper limit to the spin injection rate. We find that spin-orbit interaction
interaction in the barrier and in the drain limits severely spin injection.
Spin depolarization is stronger when the magnetization is parallel to the
current than when is perpendicular to it.Comment: Accepted in Phys. Rev. B. 4 pages, 4 figure
Scaling of the conductance in gold nanotubes
A new form of gold nanobridges has been recently observed in ultrahigh-vacuum
experiments, where the gold atoms rearrange to build helical nanotubes, akin in
some respects to carbon nanotubes. The good reproducibility of these wires and
their unexpected stability will allow for conductance measurements and make
them promising candidates for future applications . We present here a study of
the transport properties of these nanotubes in order to understand the role of
chirality and of the different orbitals in quantum transport observables. The
conductance per atomic row shows a light decreasing trend as the diameter
grows, which is also shown through an analytical formula based on a one-orbital
model.Comment: 5 pages, 6 figure
Dynamics of formation and decay of coherence in a polariton condensate
We study the dynamics of formation and decay of a condensate of microcavity
polaritons. We investigate the relationship between the number of particles,
the emission's linewidth and its degree of linear polarization which serves as
the order parameter. Tracking the condensate's formation, we show that, even
when interactions are negligible, coherence is not determined only by
occupation of the ground state. As a result of the competition between the
coherent and thermal fractions of the condensate, the highest coherence is
obtained some time after the particle number has reached its maximum
Polarization entanglement visibility of photon pairs emitted by a quantum dot embedded in a microcavity
We study the photon emission from a quantum dot embedded in a microcavity.
Incoherent pumping of its excitons and biexciton provokes the emission of leaky
and cavity modes. By solving a master equation we obtain the correlation
functions required to compute the spectrum and the relative efficiency among
the emission of pairs and single photons. A quantum regime appears for low
pumping and large rate of emission. By means of a post-selection process, a two
beams experiment with different linear polarizations could be performed
producing a large polarization entanglement visibility precisely in the quantum
regime.Comment: 13 pages and 6 figure
Vascular resection in perihilar cholangiocarcinoma
Among the cholangiocarcinomas, the most common type is perihilar (phCC), accounting for approximately 60% of cases, after which are the distal and then intrahepatic forms. There is no staging system that allows for a comparison of all series and extraction of conclusions that increase the long-term survival rate of this dismal disease. The extension of the resection, which theoretically depends on the type of phCC, is not a closed subject. As surgery is the only known way to achieve a cure, many aggressive approaches have been adopted. Despite extended liver resections and even vascular resections, margins are positive in around one third of patients. In the past two decades, with advances in diagnostic and surgical techniques, surgical outcomes and survival rates have gradually improved, although variability is the rule, with morbidity and mortality rates ranging from 14% to 76% and from 0% to 19%, respectively. Extended hepatectomies and portal vein resection, or even right hepatic artery reconstruction for the left side tumors are frequently needed. Salvage procedures when arterial reconstruction is not feasible, as well as hepatopancreatoduodenectomy, are still under evaluation too. In this article, we discuss the aggressive surgical approach to phCC focused on vascular resection. Disparate results on the surgical treatment of phCC made it impossible to reach clear-cut conclusions. © 2021 by the authors. Licensee MDPI, Basel, Switzerland
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