4,025 research outputs found
New and Old Results in Resultant Theory
Resultants are getting increasingly important in modern theoretical physics:
they appear whenever one deals with non-linear (polynomial) equations, with
non-quadratic forms or with non-Gaussian integrals. Being a subject of more
than three-hundred-year research, resultants are of course rather well studied:
a lot of explicit formulas, beautiful properties and intriguing relationships
are known in this field. We present a brief overview of these results,
including both recent and already classical. Emphasis is made on explicit
formulas for resultants, which could be practically useful in a future physics
research.Comment: 50 pages, 15 figure
SDiff(2) and uniqueness of the Pleba\'{n}ski equation
The group of area preserving diffeomorphisms showed importance in the
problems of self-dual gravity and integrability theory. We discuss how
representations of this infinite-dimensional Lie group can arise in
mathematical physics from pure local considerations. Then using Lie algebra
extensions and cohomology we derive the second Pleba\'{n}ski equation and its
geometry. We do not use K\"ahler or other additional structures but obtain the
equation solely from the geometry of area preserving transformations group. We
conclude that the Pleba\'{n}ski equation is Lie remarkable
Anomalous Diffusion at Edge and Core of a Magnetized Cold Plasma
Progress in the theory of anomalous diffusion in weakly turbulent cold
magnetized plasmas is explained. Several proposed models advanced in the
literature are discussed. Emphasis is put on a new proposed mechanism for
anomalous diffusion transport mechanism based on the coupled action of
conductive walls (excluding electrodes) bounding the plasma drain current (edge
diffusion) together with the magnetic field flux "cutting" the area traced by
the charged particles in their orbital motion. The same reasoning is shown to
apply to the plasma core anomalous diffusion. The proposed mechanism is
expected to be valid in regimes when plasma diffusion scales as Bohm diffusion
and at high , when collisions are of secondary importance.Comment: 9 pages, 4 figure
Effect of Anode Dielectric Coating on Hall Thruster Operation
An interesting phenomenon observed in the near-anode region of a Hall
thruster is that the anode fall changes from positive to negative upon removal
of the dielectric coating, which is produced on the anode surface during the
normal course of Hall thruster operation. The anode fall might affect the
thruster lifetime and acceleration efficiency. The effect of the anode coating
on the anode fall is studied experimentally using both biased and emissive
probes. Measurements of discharge current oscillations indicate that thruster
operation is more stable with the coated anode
Resistivity and Hall effect of LiFeAs: Evidence for electron-electron scattering
LiFeAs is unique among the broad family of FeAs-based superconductors,
because it is superconducting with a rather large K under
ambient conditions although it is a stoichiometric compound. We studied the
electrical transport on a high-quality single crystal. The resistivity shows
quadratic temperature dependence at low temperature giving evidence for strong
electron-electron scattering and a tendency towards saturation around room
temperature. The Hall constant is negative and changes with temperature, what
most probably arises from a van Hove singularity close to the Fermi energy in
one of the hole-like bands. Using band structure calculations based on angular
resolved photoemission spectra we are able to reproduce all the basic features
of both the resistivity as well as the Hall effect data.Comment: 6 pages, 3 figures included; V2 has been considerably revised and
contain a more detailed analysis of the Hall effect dat
The superconducting gaps in LiFeAs: Joint study of specific heat and ARPES
We present specific heat, c_P, and ARPES data on single crystals of the
stoichiometric superconductor LiFeAs. A pronounced anomaly is found in c_P at
the superconducting transition. The electronic contribution can be described by
two s-type energy gaps with magnitudes of approximately Delta1 = 1.2 meV and
Delta2 = 2.6 meV and a normal-state gamma coefficient of 10 mJ/mol K^2. All
these values are in remarkable agreement with ARPES results.Comment: 4 pages, 3 figure
On the interrelation between monopoles, vortices, topological charge and chiral symmetry breaking: an analysis using overlap fermions for SU(2)
We study the properties of configurations from which P-vortices on one hand
or Abelian monopoles on the other hand have been removed. We find that the zero
modes and the band of non-zero modes close to zero disappear from the spectrum
of the overlap Dirac operator, confirming the absence of topological charge and
quark condensate. The different behavior of the modified ensembles under
smearing compared to the unmodified Monte Carlo ensemble corroborates these
findings. The gluonic topological susceptibility rapidly approaches zero in
accordance with Q_{index}=0. The remaining (ultraviolet) monopoles without
vortices and -- to a less extent -- the remaining vortices without monopoles
are unstable under smearing whereas smearing of the unmodified Monte Carlo
ensemble effects the monopoles and vortices only by smoothing, reducing the
density only slightly.Comment: 13 pages, 5 figures, strongly revised, results added, one figure
added, accepted for publication, title changed
Theoretical model for the superconducting and magnetically ordered borocarbides
We present a theory of superconductivity in presence of a general magnetic
structure in a form suitable for the description of complex magnetic phases
encountered in borocarbides. The theory, complemented with some details of the
band structure and with the magnetic phase diagram, may explain the nearly
reentrant behaviour and the anisotropy of the upper critical field of HoNi2B2C.
The onset of the helical magnetic order depresses superconductivity via the
reduction of the interaction between phonons and electrons caused by the
formation of magnetic Bloch states. At mean field level, no additional
suppression of superconductivity is introduced by the incommensurability of the
helical phase.Comment: 8 pages, 2 figures. Published version, one important reference adde
- …