2,235 research outputs found
Spin current and electrical polarization in GaN double-barrier structures
Tunnel spin polarization in a piezoelectric AlGaN/GaN double barrier
structure is calculated. It is shown that the piezoelectric field and the
spontaneous electrical polarization increase an efficiency of the tunnel spin
injection. The relation between the electrical polarization and the spin
orientation allows engineering a zero magnetic field spin injection
manipulating the lattice-mismatch strain with an Al-content in the barriers.Comment: 13 pages, 6 figure
Weak antilocalization and zero-field electron spin splitting in AlGaN/AlN/GaN heterostructures with a polarization induced two-dimensional electron gas
Spin-orbit coupling is studied using the quantum interference corrections to
conductance in AlGaN/AlN/GaN two-dimensional electron systems where the carrier
density is controlled by the persistent photoconductivity effect. All the
samples studied exhibit a weak antilocalization feature with a spin-orbit field
of around 1.8 mT. The zero-field electron spin splitting energies extracted
from the weak antilocalization measurements are found to scale linearly with
the Fermi wavevector with an effective linear spin-orbit coupling parameter
5.5x10^{-13} eV m. The spin-orbit times extracted from our measurements varied
from 0.74 to 8.24 ps within the carrier density range of this experiment.Comment: 16 pages, 4 figure
Dynamics of perpendicular recording heads
3D modeling and inductance measurements were used to design an ultra-high frequency perpendicular system. Kerr microscopy and spin-stand experiments with focused ion beam (FI-B) trimmed perpendicular heads and perpendicular media directly verified the high frequency concepts
Obesity Induces Hypothalamic Endoplasmic Reticulum Stress and Impairs Proopiomelanocortin (POMC) Post-translational Processing
It was shown previously that abnormal prohormone processing or inactive proconverting enzymes that are responsible for this processing cause profound obesity. Our laboratory demonstrated earlier that in the diet-induced obesity (DIO) state, the appetite-suppressing neuropeptide -melanocyte-stimulating hormone ( -MSH) is reduced, yet the mRNA of its precursor protein proopiomelanocortin (POMC) remained unaltered. It was also shown that the DIO condition promotes the development of endoplasmic reticulum (ER) stress and leptin resistance. In the current study, using an in vivo model combined with in vitro experiments, we demonstrate that obesity-induced ER stress obstructs the post-translational processing of POMC by decreasing proconverting enzyme 2, which catalyzes the conversion of adrenocorticotropin to -MSH, thereby decreasing -MSH peptide production. This novel mechanism of ER stress affecting POMC processing in DIO highlights the importance of ER stress in regulating central energy balance in obesity.Fil: Cakir, Isin. Brown University; Estados UnidosFil: Cyr, Nicole E.. Brown University; Estados UnidosFil: Perello, Mario. Brown University; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Litvinov, Bogdan Patedakis. Brown University; Estados UnidosFil: Romero, Amparo. Brown University; Estados UnidosFil: Stuart, Ronald C.. Brown University; Estados UnidosFil: Nillni, Eduardo A.. Brown University; Estados Unido
The choice of the reliability model of technical systems in the Mathcad package based on operational data
The subject of the research includes selection procedures, which allows determining the most adequate reliability model. Various goodness-of-fit tests and information criteria are objects of the research. Work objective is to select from predefined set the reliability model which represents given failure data sample best, by application of various statistical and information criteria
q-Legendre Transformation: Partition Functions and Quantization of the Boltzmann Constant
In this paper we construct a q-analogue of the Legendre transformation, where
q is a matrix of formal variables defining the phase space braidings between
the coordinates and momenta (the extensive and intensive thermodynamic
observables). Our approach is based on an analogy between the semiclassical
wave functions in quantum mechanics and the quasithermodynamic partition
functions in statistical physics. The basic idea is to go from the
q-Hamilton-Jacobi equation in mechanics to the q-Legendre transformation in
thermodynamics. It is shown, that this requires a non-commutative analogue of
the Planck-Boltzmann constants (hbar and k_B) to be introduced back into the
classical formulae. Being applied to statistical physics, this naturally leads
to an idea to go further and to replace the Boltzmann constant with an infinite
collection of generators of the so-called epoch\'e (bracketing) algebra. The
latter is an infinite dimensional noncommutative algebra recently introduced in
our previous work, which can be perceived as an infinite sequence of
"deformations of deformations" of the Weyl algebra. The generators mentioned
are naturally indexed by planar binary leaf-labelled trees in such a way, that
the trees with a single leaf correspond to the observables of the limiting
thermodynamic system
Oil-free control systems of steam turbines
В статье рассмотрены перспективные системы автоматического регулирования паровых турбин на базе электромеханических приводов. Описано применение клапана с электромеханическим приводом в качестве регулирующего органа на лини дополнительного отбора пара из турбины. Рассмотрена возможность применения электромеханических приводов в качестве привода стопорного и регулирующих клапанов высокого давления.In article perspective control systems of steam turbines on the basis of electromechanical drives are considered. Use of the valve with the electromechanical drive as regulator on additional steam extraction from the turbine is described. The possibility of use of electromechanical drives as drive for high pressure stop and control valves is considered
Application of the RMF mass model to the r-process and the influence of mass uncertainties
A new mass table calculated by the relativistic mean field approach with the
state-dependent BCS method for the pairing correlation is applied for the first
time to study r-process nucleosynthesis. The solar r-process abundance is well
reproduced within a waiting-point approximation approach. Using an exponential
fitting procedure to find the required astrophysical conditions, the influence
of mass uncertainty is investigated. R-process calculations using the FRDM,
ETFSI-Q and HFB-13 mass tables have been used for that purpose. It is found
that the nuclear physical uncertainty can significantly influence the deduced
astrophysical conditions for the r-process site. In addition, the influence of
the shell closure and shape transition have been examined in detail in the
r-process simulations.Comment: to be published in Phys. Rev. C, 22 pages, 9 figure
Correlation functions in conformal Toda field theory I
Two-dimensional sl(n) quantum Toda field theory on a sphere is considered.
This theory provides an important example of conformal field theory with higher
spin symmetry. We derive the three-point correlation functions of the
exponential fields if one of the three fields has a special form. In this case
it is possible to write down and solve explicitly the differential equation for
the four-point correlation function if the fourth field is completely
degenerate. We give also expressions for the three-point correlation functions
in the cases, when they can be expressed in terms of known functions. The
semiclassical and minisuperspace approaches in the conformal Toda field theory
are studied and the results coming from these approaches are compared with the
proposed analytical expression for the three-point correlation function. We
show, that in the framework of semiclassical and minisuperspace approaches
general three-point correlation function can be reduced to the
finite-dimensional integral.Comment: 54 pages, JHEP styl
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