3,142 research outputs found
Effective coupling between two Brownian particles
We use the system-plus-reservoir approach to study the dynamics of a system
composed of two independent Brownian particles. We present an extension of the
well-known model of a bath of oscillators which is capable of inducing an
effective coupling between the two particles depending on the choice made for
the spectral function of the bath oscillators. The coupling is non-linear in
the variables of interest and an exponential dependence on these variables is
imposed in order to guarantee the translational invariance of the model if the
two particles are not subject to any external potential. The effective
equations of motion for the particles are obtained by the Laplace transform
method and besides recovering all the local dynamical properties for each
particle we end up with an effective interaction potential between them. We
explicitly analyze one of its possible forms.Comment: 4 pages, 1 figur
Quantum boundary currents for nonsimply-laced Toda theories
We study the quantum integrability of nonsimply--laced affine Toda theories
defined on the half--plane and explicitly construct the first nontrivial
higher--spin charges in specific examples. We find that, in contradistinction
to the classical case, addition of total derivative terms to the "bulk" current
plays a relevant role for the quantum boundary conservation.Comment: 11 pages, latex, no figure
Majorana Fermions Signatures in Macroscopic Quantum Tunneling
Thermodynamic measurements of magnetic fluxes and I-V characteristics in
SQUIDs offer promising paths to the characterization of topological
superconducting phases. We consider the problem of macroscopic quantum
tunneling in an rf-SQUID in a topological superconducting phase. We show that
the topological order shifts the tunneling rates and quantum levels, both in
the parity conserving and fluctuating cases. The latter case is argued to
actually enhance the signatures in the slowly fluctuating limit, which is
expected to take place in the quantum regime of the circuit. In view of recent
advances, we also discuss how our results affect a -junction loop.Comment: 10 pages, 11 figure
Relic Abundances and the Boltzmann Equation
I discuss the validity of the quantum Boltzmann equation for the calculation
of WIMP relic densities.Comment: 5 pages, no figures; talk given at Dark Matter 2000; an important
reference is added in the revised versio
Single-Spin Measurement and Decoherence in Magnetic Resonance Force Microscopy
We consider a simple version of a cyclic adiabatic inversion (CAI) technique
in magnetic resonance force microscopy (MRFM). We study the problem: What
component of the spin is measured in the CAI MRFM? We show that the
non-destructive detection of the cantilever vibrations provides a measurement
of the spin component along the effective magnetic field. This result is based
on numerical simulations of the Hamiltonian dynamics (the Schrodinger equation)
and the numerical solution of the master equation.Comment: 5 pages + 5 figures (PNG format
Covariant approach to equilibration in effective field theories
The equilibration of two coupled reservoirs is studied using a Green function
approach which is suitable for future development with the closed time path
method. The problem is solved in two parameterizations, in order to demonstrate
the non-trivial issues of parameterization in both the intermediate steps and
the interpretation of physical quantities. We use a covariant approach to find
self-consistent solutions for the statistical distributions as functions of
time. We show that by formally introducing covariant connections, one can
rescale a slowly varying non-equilibrium theory so that it appears to be an
equilibrium one, for the purposes of calculation. We emphasize the importance
of properly tracking variable redefinitions in order to correctly interpret
physical quantities.Comment: 11 pages, Late
Photoluminescence spectrum of an interacting two-dimensional electron gas at \nu=1
We report on the theoretical photoluminescence spectrum of the interacting
two-dimensional electron gas at filling factor one (\nu=1). We considered a
model similar to the one adopted to study the X-ray spectra of metals and
solved it analytically using the bosonization method previously developed for
the two-dimensional electron gas at \nu=1. We calculated the emission spectra
of the right and the left circularly polarized radiations for the situations
where the distance between the two-dimensional electron gas and the valence
band hole are smaller and greater than the magnetic length. For the former, we
showed that the polarized photoluminescence spectra can be understood as the
recombination of the so-called excitonic state with the valence band hole
whereas, for the latter, the observed emission spectra can be related to the
recombination of a state formed by a spin down electron bound to n spin waves.
This state seems to be a good description for the quantum Hall skyrmion.Comment: Revised version, 10 pages, 5 figures, accepted to Phys. Rev.
Thermal Stability of RNA Phage Virus-Like Particles Displaying Foreign Peptides
<p>Abstract</p> <p>Background</p> <p>To be useful for genetic display of foreign peptides a viral coat protein must tolerate peptide insertions without major disruption of subunit folding and capsid assembly. The folding of the coat protein of RNA phage MS2 does not normally tolerate insertions in its AB-loop, but an engineered single-chain dimer readily accepts them as long as they are restricted to one of its two halves.</p> <p>Results</p> <p>Here we characterize the effects of peptide insertions on the thermal stabilities of MS2 virus-like particles (VLPs) displaying a variety of different peptides in one AB-loop of the coat protein single-chain dimer. These particles typically denature at temperatures around 5-10°C lower than unmodified VLPs. Even so, they are generally stable up to about 50°C. VLPs of the related RNA phage PP7 are cross-linked with intersubunit disulfide bonds and are therefore significantly more stable. An AB-loop insertion also reduces the stability of PP7 VLPs, but they only begin to denature above about 70°C.</p> <p>Conclusions</p> <p>VLPs assembled from MS2 single-chain dimer coat proteins with peptide insertions in one of their AB-loops are somewhat less stable than the wild-type particle, but still resist heating up to about 50°C. Because they possess disulfide cross-links, PP7-derived VLPs provide an alternate platform with even higher stability.</p
Effective Coupling Between Two Brownian Particles.
We use the system-plus-reservoir approach to study the dynamics of a system composed of two independent Brownian particles. We present an extension of the well-known model of a bath of oscillators which is capable of inducing an effective coupling between the two particles depending on the choice made for the spectral function of the bath oscillators. The coupling is nonlinear in the variables of interest, and an exponential dependence on these variables is imposed in order to guarantee the translational invariance of the model if the two particles are not subject to any external potential. The effective equations of motion for the particles are obtained by the Laplace transform method, and, besides recovering all the local dynamical properties for each particle, we end up with an effective interaction potential between them. We explicitly analyze one of its possible forms.9725060
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