75,187 research outputs found
Gaussian Effective Potential and the Coleman's normal-ordering Prescription : the Functional Integral Formalism
For a class of system, the potential of whose Bosonic Hamiltonian has a
Fourier representation in the sense of tempered distributions, we calculate the
Gaussian effective potential within the framework of functional integral
formalism. We show that the Coleman's normal-ordering prescription can be
formally generalized to the functional integral formalism.Comment: 6 pages, revtex; With derivation details and an example added. To
appear in J. Phys.
Focusing by Plano-Concave lens using Negative Refraction
We demonstrate focusing of a plane microwave by a plano-concave lens
fabricated from a photonic crystal (PhC) having negative refractive index and
left-handed electromagnetic properties. An inverse experiment, in which a plane
wave is produced from a source placed at the focal point of the lens is also
reported. A frequency dependent negative refractive index, is obtained for the
lens from the experimental data which matches well with that determined from
band structure calculations
An equitriangular integral transform and its applications
Equitriangular integral transform for solving boundary value problems in viscous flow and heat transfe
Domain wall switching: optimizing the energy landscape
It has recently been suggested that exchange spring media offer a way to
increase media density without causing thermal instability
(superparamagnetism), by using a hard and a soft layer coupled by exchange.
Victora has suggested a figure of merit xi = 2 E_b/mu_0 m_s H_sw, the ratio of
the energy barrier to that of a Stoner-Wohlfarth system with the same switching
field, which is 1 for a Stoner-Wohlfarth (coherently switching) particle and 2
for an optimal two-layer composite medium. A number of theoretical approaches
have been used for this problem (e.g., various numbers of coupled
Stoner-Wohlfarth layers and continuum micromagnetics). In this paper we show
that many of these approaches can be regarded as special cases or
approximations to a variational formulation of the problem, in which the energy
is minimized for fixed magnetization. The results can be easily visualized in
terms of a plot of the energy as a function of magnetic moment m_z, in which
both the switching field [the maximum slope of E(m_z)] and the stability
(determined by the energy barrier E_b) are geometrically visible. In this
formulation we can prove a rigorous limit on the figure of merit xi, which can
be no higher than 4. We also show that a quadratic anistropy suggested by Suess
et al comes very close to this limit.Comment: Acccepted for proceedings of Jan. 2007 MMM Meeting, paper BE-0
Negative refraction and plano-concave lens focusing in one-dimensional photonic crystals
Negative refraction is demonstrated in one-dimensional (1D) dielectric
photonic crystals (PCs) at microwave frequencies. Focusing by plano-concave
lens made of 1D PC due to negative refraction is also demonstrated. The
frequency-dependent negative refractive indices, calculated from the
experimental data matches very well with those determined from band structure
calculations. The easy fabrication of one-dimensional photonic crystals may
open the door for new applications.Comment: 3 pages and 5 figure
Fault-tolerant linear optics quantum computation by error-detecting quantum state transfer
A scheme for linear optical implementation of fault-tolerant quantum
computation is proposed, which is based on an error-detecting code. Each
computational step is mediated by transfer of quantum information into an
ancilla system embedding error-detection capability. Photons are assumed to be
subjected to both photon loss and depolarization, and the threshold region of
their strengths for scalable quantum computation is obtained, together with the
amount of physical resources consumed. Compared to currently known results, the
present scheme reduces the resource requirement, while yielding a comparable
threshold region.Comment: 9 pages, 7 figure
The (1+1)-dimensional Massive sine-Gordon Field Theory and the Gaussian Wave-functional Approach
The ground, one- and two-particle states of the (1+1)-dimensional massive
sine-Gordon field theory are investigated within the framework of the Gaussian
wave-functional approach. We demonstrate that for a certain region of the
model-parameter space, the vacuum of the field system is asymmetrical.
Furthermore, it is shown that two-particle bound state can exist upon the
asymmetric vacuum for a part of the aforementioned region. Besides, for the
bosonic equivalent to the massive Schwinger model, the masses of the one boson
and two-boson bound states agree with the recent second-order results of a
fermion-mass perturbation calculation when the fermion mass is small.Comment: Latex, 11 pages, 8 figures (EPS files
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