8,912 research outputs found
Anomalous Chiral Fermi Surface
We provide a geometrical argument for the emergence of a Wess-Zumino-Witten
(WZW) term for a Fermi surface threaded by a Berry curvature. In the presence
of external fields, the gauged WZW term yields a chiral (triangle) anomaly for
the fermionic current at the edge of the Fermi surface. Fermion number is
conserved though since the Berry curvatures occur always in pairs with opposite
(monopole) charge. The anomalous vector and axial currents for a a fermionic
fluid at low temperature threaded by pairs of Berry curvatures are discussed.
The leading temperature correction to the chiral vortical effect in a slowly
rotating Fermi surface threaded by a Berry curvature maybe tied to the
gravitational anomaly.Comment: 4 pages; version to appear in PR
0+ states in the large boson number limit of the Interacting Boson Approximation model
Studies of the Interacting Boson Approximation (IBA) model for large boson
numbers have been triggered by the discovery of shape/phase transitions between
different limiting symmetries of the model. These transitions become sharper in
the large boson number limit, revealing previously unnoticed regularities,
which also survive to a large extent for finite boson numbers, corresponding to
valence nucleon pairs in collective nuclei. It is shown that energies of 0_n^+
states grow linearly with their ordinal number n in all three limiting
symmetries of IBA [U(5), SU(3), and O(6)]. Furthermore, it is proved that the
narrow transition region separating the symmetry triangle of the IBA into a
spherical and a deformed region is described quite well by the degeneracies
E(0_2^+)=E(6_1^+), E(0_3^+)=E(10_1^+), E(0_4^+)=E(14_1^+), while the energy
ratio E(6_1^+) /E(0_2^+) turns out to be a simple, empirical, easy-to-measure
effective order parameter, distinguishing between first- and second-order
transitions. The energies of 0_n^+ states near the point of the first order
shape/phase transition between U(5) and SU(3) are shown to grow as n(n+3), in
agreement with the rule dictated by the relevant critical point symmetries
resulting in the framework of special solutions of the Bohr Hamiltonian. The
underlying partial dynamical symmetries and quasi-dynamical symmetries are also
discussed.Comment: 6 pages, 4 postscript figures, LaTeX. To appear in the Proceedings of
the International Conference on Nuclear Physics and Astrophysics: From Stable
Beams to Exotic Nuclei (Cappadocia, 2008
Dimensionless scaling of heat-release-induced planar shock waves in near-critical CO2
We performed highly resolved one-dimensional fully compressible Navier-Stokes
simulations of heat-release-induced compression waves in near-critical CO2. The
computational setup, inspired by the experimental setup of Miura et al., Phys.
Rev. E, 2006, is composed of a closed inviscid (one-dimensional) duct with
adiabatic hard ends filled with CO2 at three supercritical pressures. The
corresponding initial temperature values are taken along the pseudo-boiling
line. Thermodynamic and transport properties of CO2 in near-critical conditions
are modeled via the Peng-Robinson equation of state and Chung's Method. A heat
source is applied at a distance from one end, with heat release intensities
spanning the range 10^3-10^11 W/m^2, generating isentropic compression waves
for values < 10^9 W/m^2. For higher heat-release rates such compressions are
coalescent with distinct shock-like features (e.g. non-isentropicity and
propagation Mach numbers measurably greater than unity) and a non-uniform
post-shock state is present due to the strong thermodynamic nonlinearities. The
resulting compression wave intensities have been collapsed via the thermal
expansion coefficient, highly variable in near-critical fluids, used as one of
the scaling parameters for the reference energy. The proposed scaling applies
to isentropic thermoacoustic waves as well as shock waves up to shock strength
2. Long-term time integration reveals resonance behavior of the compression
waves, raising the mean pressure and temperature at every resonance cycle. When
the heat injection is halted, expansion waves are generated, which counteract
the compression waves leaving conduction as the only thermal relaxation
process. In the long term evolution, the decay in amplitude of the resonating
waves observed in the experiments is qualitatively reproduced by using
isothermal boundary conditions.Comment: As submitted to AIAA SciTech 2017, available at
http://arc.aiaa.org/doi/pdf/10.2514/6.2017-008
Multiresolution analysis in statistical mechanics. I. Using wavelets to calculate thermodynamic properties
The wavelet transform, a family of orthonormal bases, is introduced as a
technique for performing multiresolution analysis in statistical mechanics. The
wavelet transform is a hierarchical technique designed to separate data sets
into sets representing local averages and local differences. Although
one-to-one transformations of data sets are possible, the advantage of the
wavelet transform is as an approximation scheme for the efficient calculation
of thermodynamic and ensemble properties. Even under the most drastic of
approximations, the resulting errors in the values obtained for average
absolute magnetization, free energy, and heat capacity are on the order of 10%,
with a corresponding computational efficiency gain of two orders of magnitude
for a system such as a Ising lattice. In addition, the errors in
the results tend toward zero in the neighborhood of fixed points, as determined
by renormalization group theory.Comment: 13 pages plus 7 figures (PNG
Holographic Pomeron: Saturation and DIS
We briefly review the approach to dipole-dipole scattering in holographic QCD
developed in ARXIV:1202.0831. The Pomeron is modeled by exchanging closed
strings between the dipoles and yields Regge behavior for the elastic
amplitude. We calculate curvature corrections to this amplitude in both a
conformal and confining background, identifying the holographic direction with
the virtuality of the dipoles. The it wee-dipole density is related to the
string tachyon diffusion in both virtuality and the transverse directions. We
give an explicit derivation of the dipole saturation momentum both in the
conformal and confining metric. Our holographic result for the dipole-dipole
cross section and the it wee-dipole density in the conformal limit are shown to
be identical in form to the BFKL pomeron result when the non-critical string
transverse dimension is . The total dipole-dipole cross section is
compared to DIS data from HERA
Two-dimensional hybrid Monte Carlo-fluid modelling of dc glow discharges: Comparison with fluid models, reliability, and accuracy
Two-dimensional hybrid Monte Carlo-fluid numerical code is developed and applied to model the dc glow discharge. The model is based on the separation of electrons into two parts: the low energetic (slow) and high energetic (fast) electron groups. Ions and slow electrons are described within the fluid model using the drift-diffusion approximation for particle fluxes. Fast electrons, represented by suitable number of super particles emitted from the cathode, are responsible for ionization processes in the discharge volume, which are simulated by the Monte Carlo collision method. Electrostatic field is obtained from the solution of Poisson equation. The test calculations were carried out for an argon plasma. Main properties of the glow discharge are considered. Current-voltage curves, electric field reversal phenomenon, and the vortex current formation are developed and discussed. The results are compared to those obtained from the simple and extended fluid models. Contrary to reports in the literature, the analysis does not reveal significant advantages of existing hybrid methods over the extended fluid model. (C) 2015 AIP Publishing LLC
Some Orthogonal Polynomials Arising from Coherent States
We explore in this paper some orthogonal polynomials which are naturally
associated to certain families of coherent states, often referred to as
nonlinear coherent states in the quantum optics literature. Some examples turn
out to be known orthogonal polynomials but in many cases we encounter a general
class of new orthogonal polynomials for which we establish several qualitative
results.Comment: 21 page
Foreign and U.S Educated Faculty Members’ Views on What Constitutes Excellent Teaching: Effects of Gender and Discipline
This study identifies views of foreign-educated faculty who teach in American universities on what constitutes excellence in teaching based on different demographics using the online version of the Teacher Behavior Checklist. Faculty from 14 institutions within the Southern Regional Educational Board (SREB) were asked to rank the top 10 of 28 teacher qualities of excellent teaching. The final faculty sample consisted of 448 participants, of which 309 were United States-educated (US-educated), and 139 were foreign-educated. The majority of the foreign-educated faculty were from Asia and Europe. Results showed that both US- and foreign-educated faculty agreed on eight qualities as the most important for excellent teaching, although in different order. “Knowledgeable” and “enthusiastic” were generally ranked the number 1 and 2 top qualities. Foreign-educated faculty tended to rank “confident,” “effective communicator,” and “encourages and cares” significantly higher than US-educated faculty. There was a statistically significant difference between US- and foreign-educated faculty in ranking the top qualities between and within demographic characteristics (that is, gender and discipline). This study provides a significant contribution to the literature on perceived qualities of excellent teaching between foreign- and US-educated faculty as well as important information for higher education administrators responsible for educational development
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