3,822 research outputs found
Weyl type theorems for restrictions of bounded linear operators
In this paper we give sufficient conditions for which Weylâs theorems for a bounded linear operator T, acting on a Banach space X, can be reduced to the study of Weylâs theorems for some restriction of T.peerReviewe
Weyl type theorems for restrictions of bounded linear operators
In this paper we give sufficient conditions for which Weylâs theorems for a bounded linear operator T, acting on a Banach space X, can be reduced to the study of Weylâs theorems for some restriction of T.peerReviewe
Exact Solution of the Munoz-Eaton Model for Protein Folding
A transfer-matrix formalism is introduced to evaluate exactly the partition
function of the Munoz-Eaton model, relating the folding kinetics of proteins of
known structure to their thermodynamics and topology. This technique can be
used for a generic protein, for any choice of the energy and entropy
parameters, and in principle allows the model to be used as a first tool to
characterize the dynamics of a protein of known native state and equilibrium
population. Applications to a -hairpin and to protein CI-2, with
comparisons to previous results, are also shown.Comment: 4 pages, 5 figures, RevTeX 4. To be published in Phys. Rev. Let
Hall-effect and resistivity measurements in CdTe and ZnTe at high pressure: Electronic structure of impurities in the zincblende phase and the semi-metallic or metallic character of the high-pressure phases
We carried out high-pressure resistivity and Hall-effect measurements in
single crystals of CdTe and ZnTe up to 12 GPa. Slight changes of transport
parameters in the zincblende phase of CdTe are consitent with the shallow
character of donor impurities. Drastic changes in all the transport parameters
of CdTe were found around 4 GPa, i.e. close to the onset of the cinnabar to
rock-salt transition. In particular, the carrier concentration increases by
more than five orders of magnitude. Additionally, an abrupt decrease of the
resistivity was detected around 10 GPa. These results are discussed in
comparison with optical, thermoelectric, and x-ray diffraction experiments. The
metallic character of the Cmcm phase of CdTe is confirmed and a semi-metallic
character is determined for the rock-salt phase. In zincblende ZnTe, the
increase of the hole concentration by more than two orders of magnitude is
proposed to be due to a deep-to-shallow transformation of the acceptor levels.
Between 9 and 11 GPa, transport parameters are consistent with the
semiconducting character of cinnabar ZnTe. A two orders of magnitude decrease
of the resistivity and a carrier-type inversion occurs at 11 GPa, in agreement
with the onset of the transition to the Cmcm phase of ZnTe. A metallic
character for this phase is deduced.Comment: 20 pages, 4 figure
Critical wetting of a class of nonequilibrium interfaces: A mean-field picture
A self-consistent mean-field method is used to study critical wetting
transitions under nonequilibrium conditions by analyzing Kardar-Parisi-Zhang
(KPZ) interfaces in the presence of a bounding substrate. In the case of
positive KPZ nonlinearity a single (Gaussian) regime is found. On the contrary,
interfaces corresponding to negative nonlinearities lead to three different
regimes of critical behavior for the surface order-parameter: (i) a trivial
Gaussian regime, (ii) a weak-fluctuation regime with a trivially located
critical point and nontrivial exponents, and (iii) a highly non-trivial
strong-fluctuation regime, for which we provide a full solution by finding the
zeros of parabolic-cylinder functions. These analytical results are also
verified by solving numerically the self-consistent equation in each case.
Analogies with and differences from equilibrium critical wetting as well as
nonequilibrium complete wetting are also discussed.Comment: 11 pages, 2 figure
Absence of long-range chemical ordering in equimolar FeCoCrNi
Equimolar FeCoCrNi alloys have been the topic of recent research as "high-entropy alloys," where the name is derived from the high configurational entropy of mixing for a random solid solution. Despite their name, no systematic study of ordering in this alloy system has been performed to
date. Here, we present results from anomalous x-ray scattering and neutron scattering on quenched and annealed samples. An alloy of FeNi_3 was prepared in the same manner to act as a control. Evidence of long-range chemical ordering is clearly observed in the annealed FeNi_3 sample from both experimental techniques. The FeCoCrNi sample given the same heat treatment lacks long-range chemical order
Anisotropic model of kinetic roughening:he strong-coupling regime
We study the strong coupling (SC) limit of the anisotropic Kardar-Parisi-Zhang (KPZ) model. A systematic mapping of the continuum model to its lattice equivalent shows that in the SC limit, anisotropic perturbations destroy all spatial correlations but retain a temporal scaling which shows a remarkable crossover along one of the two spatial directions, the choice of direction depending on the relative strength of anisotropicity. The results agree with exact numerics and are expected to settle the long-standing SC problem of a KPZ model in the infinite range limit. © 2007 The American Physical Society
Electroreflectance spectroscopy in self-assembled quantum dots: lens symmetry
Modulated electroreflectance spectroscopy of semiconductor
self-assembled quantum dots is investigated. The structure is modeled as dots
with lens shape geometry and circular cross section. A microscopic description
of the electroreflectance spectrum and optical response in terms of an external
electric field () and lens geometry have been considered. The field
and lens symmetry dependence of all experimental parameters involved in the
spectrum have been considered. Using the effective mass formalism
the energies and the electronic states as a function of and dot
parameters are calculated. Also, in the framework of the strongly confined
regime general expressions for the excitonic binding energies are reported.
Optical selection rules are derived in the cases of the light wave vector
perpendicular and parallel to . Detailed calculation of the Seraphin
coefficients and electroreflectance spectrum are performed for the InAs and
CdSe nanostructures. Calculations show good agreement with measurements
recently performed on CdSe/ZnSe when statistical distribution on size is
considered, explaining the main observed characteristic in the
electroreflectance spectra
Temperature and pressure dependence of the Fe-specific phonon density of states in Ba(Fe_(1âx)Co_x)_2As_2
The ^(57)Fe-specific phonon density of states (DOS) of Ba(Fe_(1âx)Co_x)_2As_2 single crystals (x=0.0,0.08) was measured at cryogenic temperatures and at high pressures with nuclear-resonant inelastic x-ray scattering. Measurements were conducted for two different orientations of the single crystals, yielding the orientation-projected ^(57)Fe-phonon density of states for phonon polarizations in-plane and out-of-plane with respect to the basal plane of the crystal structure. In the tetragonal phase at 300 K, a clear stiffening was observed upon doping with Co. Increasing pressure to 4 GPa caused a marked increase of phonon frequencies, with the doped material still stiffer than the parent compound. Upon cooling, both the doped and undoped samples showed a stiffening and the parent compound exhibited a discontinuity across the magnetic and structural phase transitions. These findings are generally compatible with the changes in volume of the system upon doping, increasing pressure, or increasing temperature, but an extra softening of high-energy modes occurs with increasing temperature. First-principles computations of the phonon DOS were performed and showed an overall agreement with the experimental results, but underestimate the GrĂŒneisen parameter. This discrepancy is explained in terms of a magnetic GrĂŒneisen parameter, causing an extra phonon stiffening as magnetism is suppressed under pressure
- âŠ