3,853 research outputs found
Kinetics of non-equilibrium quasiparticle tunneling in superconducting charge qubits
We directly observe low-temperature non-equilibrium quasiparticle tunneling
in a pair of charge qubits based on the single Cooper-pair box. We measure
even- and odd-state dwell time distributions as a function of temperature, and
interpret these results using a kinetic theory. While the even-state lifetime
is exponentially distributed, the odd-state distribution is more heavily
weighted to short times, implying that odd-to-even tunnel events are not
described by a homogenous Poisson process. The mean odd-state dwell time
increases sharply at low temperature, which is consistent with quasiparticles
tunneling out of the island before reaching thermal equilibrium.Comment: Replaced Figure 1 with color version, corrected more typos. Version
submitted to PR
Properties of the energy landscape of network models for covalent glasses
We investigate the energy landscape of two dimensional network models for
covalent glasses by means of the lid algorithm. For three different particle
densities and for a range of network sizes, we exhaustively analyse many
configuration space regions enclosing deep-lying energy minima. We extract the
local densities of states and of minima, and the number of states and minima
accessible below a certain energy barrier, the 'lid'. These quantities show on
average a close to exponential growth as a function of their respective
arguments. We calculate the configurational entropy for these pockets of states
and find that the excess specific heat exhibits a peak at a critical
temperature associated with the exponential growth in the local density of
states, a feature of the specific heat also observed in real glasses at the
glass transition.Comment: RevTeX, 19 pages, 7 figure
Electrochemical processes and systems: application for tutors
The features of redox reactions and the principles of their balancing according to the medium composition are considered. The basic representations about electrochemical processes and systems are outlined. The reactions and principles of chemical sources of electric energy and electrolysis systems functioning are analyzed. A general idea is given about the chemical properties of metals, corrosion resistance in environments of various aggressiveness, and the protection principles are given. Multivariate tasks and exercises for students, and PhD student’s classroom and independent work are offered. For teachers, PhD students and students of universities of specialties "Chemical technologies and engineering", "Biotechnologies and bioengineering", "Oil and gas engineering and technologies".Розглянуто особливості окисно-відновних реакцій і принципи їх балансування залежно від складу середовища. Викладено фундаментальні уявлення про електрохімічні процеси і системи. Проаналізовано перебіг реакцій і принципи функціонування хімічних джерел електричної енергії та систем електролізу. Узагальнено уявлення щодо хімічних властивостей металів, корозійної стійкості у
середовищах різної агресивності та наведено принципи організації захисту від руйнування. Запропоновано багатоваріантні завдання та вправи для аудиторної та самостійної роботи студентів і аспірантів. Розраховано на викладачів, аспірантів і студентів вищих навчальних закладів спеціальностей "Хімічні технології та інженерія”, "Біотехнології та біоінженерія", "Нафтогазова інженерія та
технології"
Enhancing Tc in field-doped Fullerenes by applying uniaxial stress
Capitalizing on the two-dimensional nature of superconductivity in
field-effect doped C60, we show that it should be possible to increase the
transition temperature Tc by applying uniaxial stress perpendicular to the gate
electrode. This method not only holds the promise of substantially enhancing Tc
(by about 30 K per GPa), but also provides a sensitive check of the current
understanding of superconductivity in the doped Fullerenes.Comment: 3 pages RevTe
Shape computations without compositions
Parametric CAD supports design explorations through generative methods which compose and transform geometric elements. This paper argues that elementary shape computations do not always correspond to valid compositional shape structures. In many design cases generative rules correspond to compositional structures, but for relatively simple shapes and rules it is not always possible to assign a corresponding compositional structure of parts which account for all operations of the computation. This problem is brought into strong relief when design processes generate multiple compositions according to purpose, such as product structure, assembly, manufacture, etc. Is it possible to specify shape computations which generate just these compositions of parts or are there additional emergent shapes and features? In parallel, combining two compositions would require the associated combined computations to yield a valid composition. Simple examples are presented which throw light on the issues in integrating different product descriptions (i.e. compositions) within parametric CAD
Covariant boost and structure functions of baryons in Gross-Neveu models
Baryons in the large N limit of two-dimensional Gross-Neveu models are
reconsidered. The time-dependent Dirac-Hartree-Fock approach is used to boost a
baryon to any inertial frame and shown to yield the covariant energy-momentum
relation. Momentum distributions are computed exactly in arbitrary frames and
used to interpolate between the rest frame and the infinite momentum frame,
where they are related to structure functions. Effects from the Dirac sea
depend sensitively on the occupation fraction of the valence level and the bare
fermion mass and do not vanish at infinite momentum. In the case of the kink
baryon, they even lead to divergent quark and antiquark structure functions at
x=0.Comment: 13 pages, 12 figures; v2: minor correction
Xenogeneic, extracorporeal liver perfusion in primates improves the ratio of branched-chain amino acids to aromatic amino acids (Fischer's ratio)
In fulminant hepatic failure (FHF), the development of hepatic encephalopathy is associated with grossly abnormal concentrations of plasma amino acids (PAA). Normalization of the ratio of branched-chain amino acids to aromatic amino acids (Fischer's ratio) correlates with clinical improvement. This study evaluated changes in PAA metabolism during 4 h of isolated, normothermic extracorporeal liver perfusion using a newly designed system containing human blood and a rhesus monkey liver. Bile and urea production were within the physiological range. Release of the transaminases AST, ALT and LDH were minimal. The ratio of branched (valine, leucine, isoleucine) to aromatic (tyrosine, phenylalanine) amino acids increased significantly. These results indicate that a xenogeneic extracorporeal liver perfusion system is capable of significantly increasing Fischer's ratio and may play a role in treating and bridging patients in FHF in the future
Geometrical spin dephasing in quantum dots
We study spin-orbit mediated relaxation and dephasing of electron spins in
quantum dots. We show that higher order contributions provide a relaxation
mechanism that dominates for low magnetic fields and is of geometrical origin.
In the low-field limit relaxation is dominated by coupling to electron-hole
excitations and possibly noise rather than phonons.Comment: Replaced with final published versio
The possible explanation of electric-field-doped C60 phenomenology in the framework of Eliashberg theory
In a recent paper (J.H. Schon, Ch. Kloc, R.C. Haddon and B. Batlogg, Nature
408 (2000) 549) a large increase in the superconducting critical temperature
was observed in C60 doped with holes by application of a high electric field.
We demonstrate that the measured Tc versus doping curves can be explained by
solving the (four) s-wave Eliashberg equations in the case of a finite,
non-half-filled energy band. In order to reproduce the experimental data, we
assume a Coulomb pseudopotential depending on the filling in a very simple and
plausible way. Reasonable values of the physical parameters involved are
obtained. The application of the same approach to new experimental data (J.H.
Schon, Ch. Kloc and B. Batlogg, Science 293 (2001) 2432) on electric
field-doped, lattice-expanded C60 single crystals (Tc=117 K in the hole-doped
case) gives equally good results and sets a theoretical limit to the linear
increase of Tc at the increase of the lattice spacing.Comment: latex2e, 6 pages, 7 figures, 1 table, revised versio
How to get from imaginary to real chemical potential
Using the exactly solvable Gross-Neveu model as theoretical laboratory, we
analyse in detail the relationship between a relativistic quantum field theory
at real and imaginary chemical potential. We find that one can retrieve the
full information about the phase diagram of the theory from an imaginary
chemical potential calculation. The prerequisite is to evaluate and
analytically continue the effective potential for the chiral order parameter,
rather than thermodynamic observables or phase boundaries. In the case of an
inhomogeneous phase, one needs to compute the full effective action, a
functional of the space-dependent order parameter, at imaginary chemical
potential.Comment: revtex, 9 pages, 10 figures; v2: add more references, modify
concluding sectio
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