853 research outputs found
Perturbation of Tunneling Processes by Mechanical Degrees of Freedom in Mesoscopic Junctions
We investigate the perturbation in the tunneling current caused by
non-adiabatic mechanical motion in a mesoscopic tunnel junction. A theory
introduced by Caroli et al. \cite{bi1,bi2,bi3} is used to evaluate second order
self-energy corrections for this non-equilibrium situation lacking
translational invariance. Inelastic signatures of the mechanical degrees of
freedom are found in the current-voltage characteristics. These give
rise to sharp features in the derivative spectrum, .Comment: 22 pages LaTeX + 3 uuencoded PS picture
Measurement induced quantum-classical transition
A model of an electrical point contact coupled to a mechanical system
(oscillator) is studied to simulate the dephasing effect of measurement on a
quantum system. The problem is solved at zero temperature under conditions of
strong non-equilibrium in the measurement apparatus. For linear coupling
between the oscillator and tunneling electrons, it is found that the oscillator
dynamics becomes damped, with the effective temperature determined by the
voltage drop across the junction. It is demonstrated that both the quantum
heating and the quantum damping of the oscillator manifest themselves in the
current-voltage characteristic of the point contact.Comment: in RevTex, 1 figure, corrected notatio
Capture of particles of dust by convective flow
Interaction of particles of dust with vortex convective flows is under
theoretical consideration. It is assumed that the volume fraction of solid
phase is small, variations of density due to nonuniform distribution of
particles and those caused by temperature nonisothermality of medium are
comparable. Equations for the description of thermal buoyancy convection of a
dusty medium are developed in the framework of the generalized Boussinesq
approximation taking into account finite velocity of particle sedimentation.
The capture of a cloud of dust particles by a vortex convective flow is
considered, general criterion for the formation of such a cloud is obtained.
The peculiarities of a steady state in the form of a dust cloud and backward
influence of the solid phase on the carrier flow are studied in detail for a
vertical layer heated from the sidewalls. It is shown that in the case, when
this backward influence is essential, a hysteresis behavior is possible. The
stability analysis of the steady state is performed. It turns out that there is
a narrow range of governing parameters, in which such a steady state is stable.Comment: 14 pages, 10 figures, published in Physics of Fluid
Fluid-solid phase transitions in 3D complex plasmas under microgravity conditions
Phase behavior of large three-dimensional complex plasma systems under
microgravity conditions onboard the International Space Station is
investigated. The neutral gas pressure is used as a control parameter to
trigger phase changes. Detailed analysis of structural properties and
evaluation of three different melting/freezing indicators reveal that complex
plasmas can exhibit melting by increasing the gas pressure. Theoretical
estimates of complex plasma parameters allow us to identify main factors
responsible for the observed behavior. The location of phase states of the
investigated systems on a relevant equilibrium phase diagram is estimated.
Important differences between the melting process of 3D complex plasmas under
microgravity conditions and that of flat 2D complex plasma crystals in ground
based experiments are discussed.Comment: 13 pages, 10 figures; submitted to Phys. Rev.
Quantum theory of electromechanical noise and momentum transfer statistics
A quantum mechanical theory is developed for the statistics of momentum
transferred to the lattice by conduction electrons. Results for the
electromechanical noise power in the semiclassical diffusive transport regime
agree with a recent theory based on the Boltzmann-Langevin equation. All
moments of the transferred momentum are calculated for a single-channel
conductor with a localized scatterer, and compared with the known statistics of
transmitted charge.Comment: 10 pages, 2 figure
Approximation of excitonic absorption in disordered systems using a compositional component weighted CPA
Employing a recently developed technique of component weighted two particle
Green's functions in the CPA of a binary substitutional alloy we
extend the existing theory of excitons in such media using a contact potential
model for the interaction between electrons and holes to an approximation which
interpolates correctly between the limits of weak and strong disorder. With our
approach we are also able to treat the case where the contact interaction
between carriers varies between sites of different types, thus introducing
further disorder into the system. Based on this approach we study numerically
how the formation of exciton bound states changes as the strengths of the
contact potentials associated with either of the two site types are varied
through a large range of parameter values.Comment: 27 pages RevTeX (preprint format), 13 Postscript figure file
The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction across a tunneling junction out of equilibrium
The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic
- spin impurities across a tunneling junction is studied when the system
is driven out of equilibrium through biasing the junction. The nonequilibrium
situation is handled with the Keldysh time-loop perturbation formalism in
conjunction with appropriate coupling methods for tunneling systems due to
Caroli and Feuchtwang. We find that the presence of a nonequilibrium bias
across the junction leads to an interference of several fundamental
oscillations, such that in this tunneling geometry, it is possible to tune the
interaction between ferromagnetic and antiferromagnetic coupling at a fixed
impurity configuration, simply by changing the bias across the junction.
Furthermore, it is shown that the range of the RKKY interaction is altered out
of equilibrium, such that in particular the interaction energy between two
slabs of spins scales extensively with the thickness of the slabs in the
presence of an applied bias.Comment: 38 pages revtex preprint; 5 postscript figures; submitted to Phys.
Rev.
Tunneling through a multigrain system: deducing the sample topology from the nonlinear conductance
We study a current transport through a system of a few grains connected with
tunneling links. The exact solution is given for an arbitrarily connected
double-grain system with a shared gate in the framework of the orthodox model.
The obtained result is generalized for multigrain systems with strongly
different tunneling resistances. We analyse the large-scale nonlinear
conductance and demonstrate how the sample topology can be unambiguously
deduced from the spectroscopy pattern (differential conductance versus
gate-bias plot). We present experimental data for a multigrain sample and
reconstruct the sample topology. A simple selection rule is formulated to
distinguish samples with spectral patterns free from spurious disturbance
caused by recharging of some grains nearby. As an example, we demonstrate
experimental data with additional peaks in the spectroscopy pattern, which can
not be attributed to coupling to additional grains. The described approach can
be used to judge the sample topology when it is not guaranteed by fabrication
and direct imaging is not possible.Comment: 13 pages (including 8 figures
New Antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in Antarctica
Gravity surveying is challenging in Antarctica because of its hostile environment and
inaccessibility. Nevertheless, many ground-based, airborne, and shipborne gravity campaigns have been
completed by the geophysical and geodetic communities since the 1980s. We present the first modern
Antarctic-wide gravity data compilation derived from 13 million data points covering an area of 10 million
km2, which corresponds to 73% coverage of the continent. The remove-compute-restore technique was
applied for gridding, which facilitated leveling of the different gravity data sets with respect to an Earth
gravity model derived from satellite data alone. The resulting free-air and Bouguer gravity anomaly grids of
10 km resolution are publicly available. These grids will enable new high-resolution combined Earth gravity
models to be derived and represent a major step forward toward solving the geodetic polar data gap
problem. They provide a new tool to investigate continental-scale lithospheric structure and geological
evolution of Antarctica
A novel albumin gene mutation (R222I) in familial dysalbuminemic hyperthyroxinemia
Context: Familial dysalbuminemic hyperthyroxinemia, characterized by abnormal circulating albuminwith increased T4 affinity, causes artefactual elevation of free T4 concentrations in euthyroid individuals. Objective: Four unrelated index cases with discordant thyroid function tests in different assay platforms were investigated. Design and Results: Laboratory biochemical assessment, radiolabeled T4 binding studies, and ALB sequencing were undertaken. 125I-T4 binding to both serum and albumin in affected individuals was markedly increased, comparable with known familial dysalbuminemic hyperthyroxinemia cases. Sequencing showed heterozygosity for a novel ALB mutation (arginine to isoleucine at codon 222, R222I) in all four cases and segregation of the genetic defect with abnormal biochemical phenotype in one family. Molecular modeling indicates that arginine 222 is located within a high-affinity T4 binding site in albumin, with substitution by isoleucine, which has a smaller side chain predicted to reduce steric hindrance, thereby facilitating T 4 and rT3 binding. When tested in current immunoassays, serum free T4 values from R222I heterozygotes were more measurably abnormal in one-step vs two-step assay architectures. Total rT3 measurements were also abnormally elevated. Conclusions: A novel mutation (R222I) in the ALB gene mediates dominantly inherited dysalbuminemic hyperthyroxinemia. Susceptibility of current free T4 immunoassays to interference by this mutant albumin suggests likely future identification of individuals with this variant binding protein
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