6,230 research outputs found
Casimir effect across a layered medium
Using nonstandard recursion relations for Fresnel coefficients involving
successive stacks of layers, we extend the Lifshitz formula to configurations
with an inhomogeneous, n-layered, medium separating two planar objects. The
force on each object is the sum of a Lifshitz like force and a force arising
from the inhomogeneity of the medium. The theory correctly reproduces very
recently obtained results for the Casimir force/energy in some simple systems
of this kind. As a by product, we obtain a formula for the force on an
(unspecified) stack of layers between two planar objects which generalizes our
previous result for the force on a slab in a planar cavity.Comment: 5 pages, 1 figure, presented at QFEXT1
The Catastrophic Effects of Natural Disasters on Insurance Markets
Natural catastrophes often have catastrophic risks on insurance companies as well as on the insured. Using a very large dataset on homeowners%u2019 insurance coverage by state, by firm, and by year for the 1984 to 2004 period, this paper documents the positive effect on losses and loss ratios of both unexpected catastrophes as well as large events that the authors term %u201Cblockbuster catastrophes.%u201D Insurers adapt to these catastrophic risks by raising insurance rates, leading to lower loss ratios after the catastrophic event. There is a widespread event of unexpected catastrophes and blockbuster catastrophes that reduces total premiums earned in the state, reduces the total number writing insurance coverage in the state, and leads to the exit of firms from the state. Firms with low levels of homeowners%u2019 premiums are most adversely affected by the catastrophes.
Nonlinear Maxwell Equations
A new relativistic invariant version of nonlinear Maxwell equations is
offerred. Some properties of these equations are considered.Comment: 6 pages, LaTe
Self-Interacting Electromagnetic Fields and a Classical Discussion on the Stability of the Electric Charge
The present work proposes a discussion on the self-energy of charged
particles in the framework of nonlinear electrodynamics. We seek magnet- ically
stable solutions generated by purely electric charges whose electric and
magnetic fields are computed as solutions to the Born-Infeld equa- tions. The
approach yields rich internal structures that can be described in terms of the
physical fields with explicit analytic solutions. This suggests that the
anomalous field probably originates from a magnetic excitation in the vacuum
due to the presence of the very intense electric field. In addition, the
magnetic contribution has been found to exert a negative pressure on the
charge. This, in turn, balances the electric repulsion, in such a way that the
self-interaction of the field appears as a simple and natural classical
mechanism that is able to account for the stability of the electron charge.Comment: 8 pages, 1 figur
Selfduality of non-linear electrodynamics with derivative corrections
In this paper we investigate how electromagnetic duality survives derivative
corrections to classical non-linear electrodynamics. In particular, we
establish that electromagnetic selfduality is satisfied to all orders in
for the four-point function sector of the four dimensional open
string effective action.Comment: 8 page
Rapport ta' l-eżaminaturi fuq il-konkors ta’ essays dwar Malta u l-inkoronazzjoni tal-maestà tagħha r-Reġina Eliżabetta II
Dan hu rapport tal-eżaminaturi fuq il-konkors ta’ esejs dwar Malta u l-inkurunazzjoni tal-maestà tagħha r-Reġina Eliżabetta II.N/
Ab initio Wannier-function-based many-body approach to Born charge of crystalline insulators
In this paper we present an approach aimed at performing many-body
calculations of Born-effective charges of crystalline insulators, by including
the electron-correlation effects. The scheme is implemented entirely in the
real space, using Wannier-functions as single-particle orbitals. Correlation
effects are computed by including virtual excitations from the Hartree-Fock
mean field, and the excitations are organized as per a Bethe-Goldstone-like
many-body hierarchy. The results of our calculations suggest that the approach
presented here is promising.Comment: 5 pages, to appear in Phys. Rev. B. (Rapid Comm., Dec 15, 2004
Singularity-Free Electrodynamics for Point Charges and Dipoles: Classical Model for Electron Self-Energy and Spin
It is shown how point charges and point dipoles with finite self-energies can
be accomodated into classical electrodynamics. The key idea is the introduction
of constitutive relations for the electromagnetic vacuum, which actually
mirrors the physical reality of vacuum polarization. Our results reduce to
conventional electrodynamics for scales large compared to the classical
electron radius cm. A classical simulation for a
structureless electron is proposed, with the appropriate values of mass, spin
and magnetic moment.Comment: 3 page
Nonperturbative calculation of Born-Infeld effects on the Schroedinger spectrum of the hydrogen atom
We present the first nonperturbative numerical calculations of the
nonrelativistic hydrogen spectrum as predicted by first-quantized
electrodynamics with nonlinear Maxwell-Born-Infeld field equations. We also
show rigorous upper and lower bounds on the ground state.
When judged against empirical data our results significantly restrict the
range of viable values of the new electromagnetic constant which is introduced
by the Born-Infeld theory.
We assess Born's own proposal for the value of his constant.Comment: 4p., 2 figs, 1 table; submitted for publicatio
Dirac-Kronig-Penney model for strain-engineered graphene
Motivated by recent proposals on strain-engineering of graphene electronic
circuits we calculate conductivity, shot-noise and the density of states in
periodically deformed graphene. We provide the solution to the
Dirac-Kronig-Penney model, which describes the phase-coherent transport in
clean monolayer samples with an one-dimensional modulation of the strain and
the electrostatic potentials. We compare the exact results to a qualitative
band-structure analysis. We find that periodic strains induce large pseudo-gaps
and suppress charge transport in the direction of strain modulation. The
strain-induced minima in the gate-voltage dependence of the conductivity
characterize the quality of graphene superstructures. The effect is especially
strong if the variation of inter-atomic distance exceeds the value a^2/l, where
a is the lattice spacing of free graphene and l is the period of the
superlattice. A similar effect induced by a periodic electrostatic potential is
weakened due to Klein tunnelling.Comment: 11 pages, 8 figure
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