491 research outputs found
Second-order critical lines of spin-S Ising models in a splitting field with Grassmann techniques
We propose a method to study the second-order critical lines of classical
spin- Ising models on two-dimensional lattices in a crystal or splitting
field, using an exact expression for the bare mass of the underlying field
theory. Introducing a set of anticommuting variables to represent the partition
function, we derive an exact and compact expression for the bare mass of the
model including all local multi-fermions interactions. By extension of the
Ising and Blume-Capel models, we extract the free energy singularities in the
low momentum limit corresponding to a vanishing bare mass. The loci of these
singularities define the critical lines depending on the spin S, in good
agreement with previous numerical estimations. This scheme appears to be
general enough to be applied in a variety of classical Hamiltonians
Dynamics of a thin shell in the Reissner-Nordstrom metric
We describe the dynamics of a thin spherically symmetric gravitating shell in
the Reissner-Nordstrom metric of the electrically charged black hole. The
energy-momentum tensor of electrically neutral shell is modelled by the perfect
fluid with a polytropic equation of state. The motion of a shell is described
fully analytically in the particular case of the dust equation of state. We
construct the Carter-Penrose diagrams for the global geometry of the eternal
black hole, which illustrate all possible types of solutions for moving shell.
It is shown that for some specific range of initial parameters there are
possible the stable oscillating motion of the shell transferring it
consecutively in infinite series of internal universes. We demonstrate also
that this oscillating type of motion is possible for an arbitrary polytropic
equation of state on the shell.Comment: 17 pages, 7 figure
A Generalization of the Bargmann-Fock Representation to Supersymmetry by Holomorphic Differential Geometry
In the Bargmann-Fock representation the coordinates act as bosonic
creation operators while the partial derivatives act as
annihilation operators on holomorphic -forms as states of a -dimensional
bosonic oscillator. Considering also -forms and further geometrical objects
as the exterior derivative and Lie derivatives on a holomorphic , we
end up with an analogous representation for the -dimensional supersymmetric
oscillator. In particular, the supersymmetry multiplet structure of the Hilbert
space corresponds to the cohomology of the exterior derivative. In addition, a
1-complex parameter group emerges naturally and contains both time evolution
and a homotopy related to cohomology. Emphasis is on calculus.Comment: 11 pages, LaTe
On Hubbard-Stratonovich Transformations over Hyperbolic Domains
We discuss and prove validity of the Hubbard-Stratonovich (HS) identities
over hyperbolic domains which are used frequently in the studies on disordered
systems and random matrices. We also introduce a counterpart of the HS identity
arising in disordered systems with "chiral" symmetry. Apart from this we
outline a way of deriving the nonlinear -model from the gauge-invariant
Wegner orbital model avoiding the use of the HS transformations.Comment: More accurate proofs are given; a few misprints are corrected; a
misleading reference and a footnote in the end of section 2.2 are remove
Thermoelectric enhancement in PbTe with K, Na co-doping from tuning the interaction of the light and heavy hole valence bands
The effect of K and K-Na substitution for Pb atoms in the rock salt lattice
of PbTe was investigated to test a hypothesis for development of resonant
states in the valence band that may enhance the thermoelectric power. We
combined high temperature Hall-effect, electrical conductivity and thermal
conductivity measurements to show that K-Na co-doping do not form resonance
states but2 can control the energy difference of the maxima of the two primary
valence sub-bands in PbTe. This leads to an enhanced interband interaction with
rising temperature and a significant rise in the thermoelectric figure of merit
of p-type PbTe. The experimental data can be explained by a combination of a
single and two-band model for the valence band of PbTe depending on hole
density that varies in the range of 1-15 x 10^19 cm^-3.Comment: 8 figure
Toward peripheral nerve mechanical characterization using Brillouin imaging spectroscopy
SIGNIFICANCE: Peripheral nerves are viscoelastic tissues with unique elastic characteristics. Imaging of peripheral nerve elasticity is important in medicine, particularly in the context of nerve injury and repair. Elasticity imaging techniques provide information about the mechanical properties of peripheral nerves, which can be useful in identifying areas of nerve damage or compression, as well as assessing the success of nerve repair procedures.
AIM: We aim to assess the feasibility of Brillouin microspectroscopy for peripheral nerve imaging of elasticity, with the ultimate goal of developing a new diagnostic tool for peripheral nerve injury
APPROACH: Viscoelastic properties of the peripheral nerve were evaluated with Brillouin imaging spectroscopy.
RESULTS: An external stress exerted on the fixed nerve resulted in a Brillouin shift. Quantification of the shift enabled correlation of the Brillouin parameters with nerve elastic properties.
CONCLUSIONS: Brillouin microscopy provides sufficient sensitivity to assess viscoelastic properties of peripheral nerves
The robustness of interdependent clustered networks
It was recently found that cascading failures can cause the abrupt breakdown
of a system of interdependent networks. Using the percolation method developed
for single clustered networks by Newman [Phys. Rev. Lett. {\bf 103}, 058701
(2009)], we develop an analytical method for studying how clustering within the
networks of a system of interdependent networks affects the system's
robustness. We find that clustering significantly increases the vulnerability
of the system, which is represented by the increased value of the percolation
threshold in interdependent networks.Comment: 6 pages, 6 figure
Controlling a resonant transmission across the -potential: the inverse problem
Recently, the non-zero transmission of a quantum particle through the
one-dimensional singular potential given in the form of the derivative of
Dirac's delta function, , with , being a
potential strength constant, has been discussed by several authors. The
transmission occurs at certain discrete values of forming a resonance
set . For
this potential has been shown to be a perfectly reflecting wall. However, this
resonant transmission takes place only in the case when the regularization of
the distribution is constructed in a specific way. Otherwise, the
-potential is fully non-transparent. Moreover, when the transmission
is non-zero, the structure of a resonant set depends on a regularizing sequence
that tends to in the sense of
distributions as . Therefore, from a practical point of
view, it would be interesting to have an inverse solution, i.e. for a given
to construct such a regularizing sequence
that the -potential at this value is
transparent. If such a procedure is possible, then this value
has to belong to a corresponding resonance set. The present paper is devoted to
solving this problem and, as a result, the family of regularizing sequences is
constructed by tuning adjustable parameters in the equations that provide a
resonance transmission across the -potential.Comment: 21 pages, 4 figures. Corrections to the published version added;
http://iopscience.iop.org/1751-8121/44/37/37530
On representations of super coalgebras
The general structure of the representation theory of a -graded
coalgebra is discussed. The result contains the structure of Fourier analysis
on compact supergroups and quantisations thereof as a special case. The general
linear supergroups serve as an explicit illustration and the simplest example
is carried out in detail.Comment: 18 pages, LaTeX, KCL-TH-94-
Stable branches of a solution for a fermion on domain wall
We discuss the case when a fermion occupies an excited non-zero frequency
level in the field of domain wall. We demonstrate that a solution exists for
the coupling constant in the limited interval . We
show that indeed there are different branches of stable solution for in
this interval. The first one corresponds to a fermion located on the domain
wall (). The second branch, which belongs to the interval
, describes a polarized fermion off the domain
wall. The third branch with describes an excited antifermion in
the field of the domain wall.Comment: 15 pages, 7 figures, references adde
- …