1,000 research outputs found
Hawking radiation of scalar particles from accelerating and rotating black holes
Hawking radiation of uncharged and charged scalars from accelerating and
rotating black holes is studied. We calculate the tunneling probabilities of
these particles from the rotation and acceleration horizons of these black
holes. Using the tunneling method we recover the correct Hawking temperature as
well
Stabilizing chaotic vortex trajectories: an example of high-dimensional control
A chaos control algorithm is developed to actively stabilize unstable
periodic orbits of higher-dimensional systems. The method assumes knowledge of
the model equations and a small number of experimentally accessible parameters.
General conditions for controllability are discussed. The algorithm is applied
to the Hamiltonian problem of point vortices inside a circular cylinder with
applications to an experimental plasma system.Comment: 15 LaTex pages, 4 Postscript figures adde
Valence band photoemission from the GaN(0001) surface
A detailed investigation by one-step photoemission calculations of the
GaN(0001)-(1x1) surface in comparison with recent experiments is presented in
order to clarify its structural properties and electronic structure. The
discussion of normal and off-normal spectra reveals through the identified
surface states clear fingerprints for the applicability of a surface model
proposed by Smith et al. Especially the predicted metallic bonds are confirmed.
In the context of direct transitions the calculated spectra allow to determine
the valence band width and to argue in favor of one of two theoretical bulk
band structures. Furthermore a commonly used experimental method to fix the
valence band maximum is critically tested.Comment: 8 pages, 11 eps files, submitted to PR
Recommended from our members
Typographic design of outdoor signage, restaurant authenticity, and consumersâ willingness to dine: extending semiotic theory
YesPurpose: Restaurantsâ outdoor signage plays an irreplaceable role in attracting potential diners, as it conveys important functional and symbolic meanings of the businesses. The purpose of this study is to investigate the effect of typographic design elements of outdoor signage on consumersâ perceptions of authenticity. This study also tests the linkage between authenticity and willingness to dine, as well as the moderating effect of frequency of dining in ethnic restaurants on the relationship.
Design/methodology/approach: Using a 2 (simplified vs traditional Chinese characters) Ă 2 (calligraphy vs computer font) Ă 2 (vertical vs horizontal text flow) between-subject design, the authors did two experiments with 786 Chinese diners. Restaurant authenticity and willingness to dine are dependent variables, and openness to ethnic cuisine is the control variable.
Findings: Display characters and text flow significantly affect restaurant authenticity. Furthermore, the results of this study demonstrate that display characters interact with typeface to influence restaurant authenticity. Consumersâ perceived authenticity significantly increases their willingness to dine. The frequency of dining in ethnic restaurants moderates the relationship between restaurant authenticity and willingness to dine.
Practical implications: Ethnic restaurateurs should pay attention to the outdoor signage design, as it affects potential consumersâ authenticity perceptions. Specifically, in Mainland China, traditional Chinese characters and vertical text direction increase potential consumersâ authenticity perceptions.
Originality/value: This study extends the semiotic theory and applies the cueâjudgmentâbehavior model in the hospitality literature. This study also provides new understanding of authenticity by identifying the influence of typographic design on authenticity, which confirms the semiotic theory that certain semiotic cues affect consumersâ judgments
Theory of Kondo lattices and its application to high-temperature superconductivity and pseudo-gaps in cuprate oxides
A theory of Kondo lattices is developed for the t-J model on a square
lattice. The spin susceptibility is described in a form consistent with a
physical picture of Kondo lattices: Local spin fluctuations at different sites
interact with each other by a bare intersite exchange interaction, which is
mainly composed of two terms such as the superexchange interaction, which
arises from the virtual exchange of spin-channel pair excitations of electrons
across the Mott-Hubbard gap, and an exchange interaction arising from that of
Gutzwiller's quasi-particles. The bare exchange interaction is enhanced by
intersite spin fluctuations developed because of itself. The enhanced exchange
interaction is responsible for the development of superconducting fluctuations
as well as the Cooper pairing between Gutzwiller's quasi-particles. On the
basis of the microscopic theory, we develop a phenomenological theory of
low-temperature superconductivity and pseudo-gaps in the under-doped region as
well as high-temperature superconductivity in the optimal-doped region.
Anisotropic pseudo-gaps open mainly because of d\gamma-wave superconducting
low-energy fluctuations: Quasi-particle spectra around (\pm\pi/a,0) and
(0,\pm\pi/a), with a the lattice constant, or X points at the chemical
potential are swept away by strong inelastic scatterings, and quasi-particles
are well defined only around (\pm\pi/2a,\pm\pi/2a) on the Fermi surface or
line. As temperatures decrease in the vicinity of superconducting critical
temperatures, pseudo-gaps become smaller and the well-defined region is
extending toward X points. The condensation of d\gamma-wave Cooper pairs
eventually occurs at low enough temperatures when the pair breaking by
inelastic scatterings becomes small enough.Comment: 15 pages, 14 figure
Slot Coating Minimum Film Thickness in Air and in Rarefied Helium
YesThis study assesses experimentally the role of gas viscosity in controlling the minimum film thickness in slot coating in both the slot over roll and tensioned web modes. The minimum film thickness here is defined with respect to the onset of air entrainment rather than rivulets, the reason being that rivulets are an extreme form of instabilities occurring at much higher speeds. The gas viscosity effects are simulated experimentally by encasing the coaters in a sealed gas chamber in which various gases can be admitted. An appropriate choice of two gases was used to compare performances: air at atmospheric pressure and helium at sub-ambient pressure (25mbar), which we establish has a significantly lower âthin filmâ viscosity than atmospheric air. A capacitance sensor was used to continuously measure the film thickness on the web, which was ramped up in speed at a fixed acceleration whilst visualizations of the film stability were recorded through a viewing port in the chamber. The data collected show clearly that by coating in rarefied helium rather that atmospheric air we can reduce the minimum film thickness or air/gas entrainment low-flow limit. We attribute this widening of the stable coating window to the enhancement of dynamic wetting that results when the thin film gas viscosity is reduced. These results have evident practical significance for slot coating, the coating method of choice in many new technological applications, but it is their fundamental merit which is new and one that should be followed with further data and theoretical underpinning
Theory of Two-Dimensional Quantum Heisenberg Antiferromagnets with a Nearly Critical Ground State
We present the general theory of clean, two-dimensional, quantum Heisenberg
antiferromagnets which are close to the zero-temperature quantum transition
between ground states with and without long-range N\'{e}el order. For
N\'{e}el-ordered states, `nearly-critical' means that the ground state
spin-stiffness, , satisfies , where is the
nearest-neighbor exchange constant, while `nearly-critical' quantum-disordered
ground states have a energy-gap, , towards excitations with spin-1,
which satisfies . Under these circumstances, we show that the
wavevector/frequency-dependent uniform and staggered spin susceptibilities, and
the specific heat, are completely universal functions of just three
thermodynamic parameters. Explicit results for the universal scaling functions
are obtained by a expansion on the quantum non-linear sigma model,
and by Monte Carlo simulations. These calculations lead to a variety of
testable predictions for neutron scattering, NMR, and magnetization
measurements. Our results are in good agreement with a number of numerical
simulations and experiments on undoped and lightly-doped .Comment: 81 pages, REVTEX 3.0, smaller updated version, YCTP-xxx
Stripes, Pseudogaps, and Van Hove Nesting in the Three-band tJ Model
Slave boson calculations have been carried out in the three-band tJ model for
the high-T_c cuprates, with the inclusion of coupling to oxygen breathing mode
phonons. Phonon-induced Van Hove nesting leads to a phase separation between a
hole-doped domain and a (magnetic) domain near half filling, with long-range
Coulomb forces limiting the separation to a nanoscopic scale. Strong
correlation effects pin the Fermi level close to, but not precisely at the Van
Hove singularity (VHS), which can enhance the tendency to phase separation. The
resulting dispersions have been calculated, both in the uniform phases and in
the phase separated regime. In the latter case, distinctly different
dispersions are found for large, random domains and for regular (static)
striped arrays, and a hypothetical form is presented for dynamic striped
arrays. The doping dependence of the latter is found to provide an excellent
description of photoemission and thermodynamic experiments on pseudogap
formation in underdoped cuprates. In particular, the multiplicity of observed
gaps is explained as a combination of flux phase plus charge density wave (CDW)
gaps along with a superconducting gap. The largest gap is associated with VHS
nesting. The apparent smooth evolution of this gap with doping masks a
crossover from CDW-like effects near optimal doping to magnetic effects (flux
phase) near half filling. A crossover from large Fermi surface to hole pockets
with increased underdoping is found. In the weakly overdoped regime, the CDW
undergoes a quantum phase transition (), which could be obscured
by phase separation.Comment: 15 pages, Latex, 18 PS figures Corrects a sign error: major changes,
esp. in Sect. 3, Figs 1-4,6 replace
Transport Properties of the Quark-Gluon Plasma -- A Lattice QCD Perspective
Transport properties of a thermal medium determine how its conserved charge
densities (for instance the electric charge, energy or momentum) evolve as a
function of time and eventually relax back to their equilibrium values. Here
the transport properties of the quark-gluon plasma are reviewed from a
theoretical perspective. The latter play a key role in the description of
heavy-ion collisions, and are an important ingredient in constraining particle
production processes in the early universe. We place particular emphasis on
lattice QCD calculations of conserved current correlators. These Euclidean
correlators are related by an integral transform to spectral functions, whose
small-frequency form determines the transport properties via Kubo formulae. The
universal hydrodynamic predictions for the small-frequency pole structure of
spectral functions are summarized. The viability of a quasiparticle description
implies the presence of additional characteristic features in the spectral
functions. These features are in stark contrast with the functional form that
is found in strongly coupled plasmas via the gauge/gravity duality. A central
goal is therefore to determine which of these dynamical regimes the quark-gluon
plasma is qualitatively closer to as a function of temperature. We review the
analysis of lattice correlators in relation to transport properties, and
tentatively estimate what computational effort is required to make decisive
progress in this field.Comment: 54 pages, 37 figures, review written for EPJA and APPN; one parag.
added end of section 3.4, and one at the end of section 3.2.2; some Refs.
added, and some other minor change
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