1,402 research outputs found
Reconstruction of Objects by Direct Demodulation
High resolution reconstruction of complicated objects from incomplete and
noisy data can be achieved by solving modulation equations iteratively under
physical constraints. This direct demodulation method is a powerful technique
for dealing with inverse problem in general case. Spectral and image
restorations and computerized tomography are only particular cases of general
demodulation. It is possible to reconstruct an object in higher dimensional
space from observations by a simple lower dimensional instrument through direct
demodulation. Our simulations show that wide field and high resolution images
of space hard X-rays and soft gamma rays can be obtained by a collimated
non-position-sensitive detector without coded aperture masks.Comment: 11 pages, 6 figure
Sources of CP Violation in the Two-Higgs Doublet Model
Assuming CP violation arises solely through the Higgs potential, we develop
the most general two-Higgs doublet model. There is no discrete symmetry that
distinguishes the two Higgs bosons. It is assumed that an approximate global
family symmetry sufficiently suppresses flavor-changing neutral scalar
interactions. In addition to a CKM phase, neutral boson mixing, and superweak
effects, there can be significant CP violation due to charged Higgs boson
exchange. The value of due to this last effect could be as
large as in the standard model.Comment: 8 pages, RevTex, (appear in Phys. Rev. Lett. 73, (1994) 1762 ),
CMU-HEP94-1
Response, relaxation and transport in unconventional superconductors
We investigate the collision-limited electronic Raman response and the
attenuation of ultrasound in spin-singlet d-wave superconductors at low
temperatures. The dominating elastic collisions are treated within a t-matrix
approximation, which combines the description of weak (Born) and strong
(unitary) impurity scattering. In the long wavelength limit a two-fluid
description of both response and transport emerges. Collisions are here seen to
exclusively dominate the relaxational dynamics of the (Bogoliubov)
quasiparticle system and the analysis allows for a clear connection of response
and transport phenomena. When applied to quasi-2-d superconductors like the
cuprates, it turns out that the transport parameter associated with the Raman
scattering intensity for B1g and B2g photon polarization is closely related to
the corresponding components of the shear viscosity tensor, which dominates the
attenuation of ultrasound. At low temperatures we present analytic solutions of
the transport equations, resulting in a non-power-law behavior of the transport
parameters on temperature.Comment: 22 pages, 3 figure
A Compact Linear Programming Relaxation for Binary Sub-modular MRF
We propose a novel compact linear programming (LP) relaxation for binary
sub-modular MRF in the context of object segmentation. Our model is obtained by
linearizing an -norm derived from the quadratic programming (QP) form of
the MRF energy. The resultant LP model contains significantly fewer variables
and constraints compared to the conventional LP relaxation of the MRF energy.
In addition, unlike QP which can produce ambiguous labels, our model can be
viewed as a quasi-total-variation minimization problem, and it can therefore
preserve the discontinuities in the labels. We further establish a relaxation
bound between our LP model and the conventional LP model. In the experiments,
we demonstrate our method for the task of interactive object segmentation. Our
LP model outperforms QP when converting the continuous labels to binary labels
using different threshold values on the entire Oxford interactive segmentation
dataset. The computational complexity of our LP is of the same order as that of
the QP, and it is significantly lower than the conventional LP relaxation
Constraints on scalar-tensor theories of gravity from observations
In spite of their original discrepancy, both dark energy and modified theory
of gravity can be parameterized by the effective equation of state (EOS)
for the expansion history of the Universe. A useful model independent
approach to the EOS of them can be given by so-called
Chevallier-Polarski-Linder (CPL) parametrization where two parameters of it
( and ) can be constrained by the geometrical
observations which suffer from degeneracies between models. The linear growth
of large scale structure is usually used to remove these degeneracies. This
growth can be described by the growth index parameter and it can be
parameterized by in general. We use the
scalar-tensor theories of gravity (STG) and show that the discernment between
models is possible only when is not negligible. We show that the
linear density perturbation of the matter component as a function of redshift
severely constrains the viable subclasses of STG in terms of and
. From this method, we can rule out or prove the viable STG in future
observations. When we use , shows the convex shape of evolution
in a viable STG model. The viable STG models with are not
distinguishable from dark energy models when we strongly limit the solar system
constraint.Comment: 19 pages, 20 figures, 2 tables, submitted to JCA
Magneto-transport in a quantum network: Evidence of a mesoscopic switch
We investigate magneto-transport properties of a shaped three-arm
mesoscopic ring where the upper and lower sub-rings are threaded by
Aharonov-Bohm fluxes and , respectively, within a
non-interacting electron picture. A discrete lattice model is used to describe
the quantum network in which two outer arms are subjected to binary alloy
lattices while the middle arm contains identical atomic sites. It is observed
that the presence of the middle arm provides localized states within the band
of extended regions and lead to the possibility of switching action from a high
conducting state to a low conducting one and vice versa. This behavior is
justified by studying persistent current in the network. Both the total current
and individual currents in three separate branches are computed by using
second-quantized formalism and our idea can be utilized to study magnetic
response in any complicated quantum network. The nature of localized
eigenstates are also investigated from probability amplitudes at different
sites of the quantum device.Comment: 7 pages, 9 figure
Novel CP-violating Effects in B decays from Charged-Higgs in a Two-Higgs Doublet Model for the Top Quark
We explore charged-Higgs cp-violating effects in a specific type III
two-Higgs doublet model which is theoretically attractive as it accommodates
the large mass of the top quark in a natural fashion. Two new CP-violating
phases arise from the right-handed up quark sector. We consider CP violation in
both neutral and charged B decays. Some of the important findings are as
follows. 1) Large direct-CP asymmetry is found to be possible for B+- to psi/J
K+-. 2) Sizable D-anti-D mixing effect at the percent level is found to be
admissible despite the stringent constraints from the data on K-anti-K mixing,
b to s gamma and B to tau nu decays. 3) A simple but distinctive CP asymmetry
pattern emerges in decays of B_d and B_s mesons, including B_d to psi/J K_S, D+
D-, and B_s to D_s+ D_s-, psi eta/eta^prime, psi/J K_S. 4) The effect of
D-anti-D mixing on the CP asymmetry in B+- to D/anti-D K+- and on the
extraction of the angle gamma of the unitarity triangle from such decays can be
significant.Comment: 32 pages, 5 figures, section V.A revised, version to appear in PR
Accelerating universe from F(T) gravity
It is shown that the acceleration of the universe can be understood by
considering a F(T) gravity models. For these F(T) gravity models, a variant of
the accelerating cosmology reconstruction program is developed. Some explicit
examples of F(T) are reconstructed from the background FRW expansion history.Comment: 13 pages, references adde
Temperature enhanced persistent currents and " periodicity"
We predict a non-monotonous temperature dependence of the persistent currents
in a ballistic ring coupled strongly to a stub in the grand canonical as well
as in the canonical case. We also show that such a non-monotonous temperature
dependence can naturally lead to a periodicity of the persistent
currents, where =h/e. There is a crossover temperature , below
which persistent currents increase in amplitude with temperature while they
decrease above this temperature. This is in contrast to persistent currents in
rings being monotonously affected by temperature. is parameter-dependent
but of the order of , where is the level spacing
of the isolated ring. For the grand-canonical case is half of that for
the canonical case.Comment: some typos correcte
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