76,493 research outputs found
Polymer Translocation througha Pore in a Membrane
We construct a new statistical physical model of polymer translocation
through a pore in a membrane treated as the diffusion process across a free
energy barrier. We determine the translocation time in terms of chain
flexibility yielding an entropic barrier, as well as in terms of the driving
mechanisms such as transmembrane chemical potential difference and Brownian
ratchets. It turns out that, while the chemical potential differences induce
pronounced effects on translocation due to the long-chain nature of the
polymer, the ratchets suppress this effect and chain flexibility.Comment: 4 pages, 5 figures, published in Phys. Rev. Lett. 77, 783(1996
The quantization of the chiral Schwinger model based on the BFT-BFV formalism II
We apply an improved version of Batalin-Fradkin-Tyutin (BFT) Hamiltonian
method to the a=1 chiral Schwinger Model, which is much more nontrivial than
the a>1.\delta\xi$ in the measure. As a result, we explicitly
obtain the fully gauge invariant partition function, which includes a new type
of Wess-Zumino (WZ) term irrelevant to the gauge symmetry as well as usual WZ
action.Comment: 17 pages, To be published in J. Phys.
Homologous non-isotopic symplectic tori in a K3-surface
For each member of an infinite family of homology classes in the K3-surface
E(2), we construct infinitely many non-isotopic symplectic tori representing
this homology class. This family has an infinite subset of primitive classes.
We also explain how these tori can be non-isotopically embedded as homologous
symplectic submanifolds in many other symplectic 4-manifolds including the
elliptic surfaces E(n) for n>2.Comment: 15 pages, 9 figures; v2: extended the main theorem, gave a second
construction of symplectic tori, added a figure, added/updated references,
minor changes in figure
Entangled coherent states versus entangled photon pairs for practical quantum information processing
We compare effects of decoherence and detection inefficiency on entangled
coherent states (ECSs) and entangled photon pairs (EPPs), both of which are
known to be particularly useful for quantum information processing (QIP). When
decoherence effects caused by photon losses are heavy, the ECSs outperform the
EPPs as quantum channels for teleportation both in fidelities and in success
probabilities. On the other hand, when inefficient detectors are used, the
teleportation scheme using the ECSs suffers undetected errors that result in
the degradation of fidelity, while this is not the case for the teleportation
scheme using the EPPs. Our study reveals the merits and demerits of the two
types of entangled states in realizing practical QIP under realistic
conditions.Comment: 9 pages, 6 figures, substantially revised version, to be published in
Phys. Rev.
Effect of Applied Orthorhombic Lattice Distortion on the Antiferromagnetic Phase of CeAuSb
We study the response of the antiferromagnetism of CeAuSb to orthorhombic
lattice distortion applied through in-plane uniaxial pressure. The response to
pressure applied along a lattice direction shows a
first-order transition at zero pressure, which shows that the magnetic order
lifts the symmetry of the unstressed lattice. Sufficient
pressure appears to rotate the principal axes of the
order from to . At low pressure, the transition at is weakly first-order, however it
becomes continuous above a threshold pressure. We discuss
the possibility that this behavior is driven by order parameter fluctuations,
with the restoration of a continuous transition a result of reducing the
point-group symmetry of the lattice.Comment: 6 pages, 7 figure
Effects of Foreground Contamination on the Cosmic Microwave Background Anisotropy Measured by MAP
We study the effects of diffuse Galactic, far-infrared extragalactic source,
and radio point source emission on the cosmic microwave background (CMB)
anisotropy data anticipated from the MAP experiment. We focus on the
correlation function and genus statistics measured from mock MAP
foreground-contaminated CMB anisotropy maps generated in a spatially-flat
cosmological constant dominated cosmological model. Analyses of the simulated
MAP data at 90 GHz (0.3 deg FWHM resolution smoothed) show that foreground
effects on the correlation function are small compared with cosmic variance.
However, the Galactic emission, even just from the region with |b| > 20 deg,
significantly affects the topology of CMB anisotropy, causing a negative genus
shift non-Gaussianity signal. Given the expected level of cosmic variance, this
effect can be effectively reduced by subtracting existing Galactic foreground
emission models from the observed data. IRAS and DIRBE far-infrared
extragalactic sources have little effect on the CMB anisotropy. Radio point
sources raise the amplitude of the correlation function considerably on scales
below 0.5 deg. Removal of bright radio sources above a 5 \sigma detection limit
effectively eliminates this effect. Radio sources also result in a positive
genus curve asymmetry (significant at 2 \sigma) on 0.5 deg scales. Accurate
radio point source data is essential for an unambiguous detection of CMB
anisotropy non-Gaussianity on these scales. Non-Gaussianity of cosmological
origin can be detected from the foreground-subtracted CMB anisotropy map at the
2 \sigma level if the measured genus shift parameter |\Delta\nu| >= 0.02 (0.04)
or if the measured genus asymmetry parameter |\Delta g| >= 0.03 (0.08) on a 0.3
(1.0) deg FWHM scale.Comment: 26 pages, 7 figures, Accepted for Publication in Astrophysical
Journal (Some sentences and figures modified
Generalized BFT Formalism of Electroweak Theory in the Unitary Gauge
We systematically embed the SU(2)U(1) Higgs model in the unitary
gauge into a fully gauge-invariant theory by following the generalized BFT
formalism. We also suggest a novel path to get a first-class Lagrangian
directly from the original second-class one using the BFT fields.Comment: 14 pages, Latex, no figure
Design and construction of a point-contact spectroscopy rig with lateral scanning capability
The design and realization of a cryogenic rig for point-contact spectroscopy
measurements in the needle-anvil configuration is presented. Thanks to the use
of two piezoelectric nano-positioners, the tip can move along the vertical
() and horizontal () direction and thus the rig is suitable to probe
different regions of a sample \textit{in situ}. Moreover, it can also form
double point-contacts on different facets of a single crystal for achieving,
e.g., an interferometer configuration for phase-sensitive measurements. For the
latter purpose, the sample holder can also host a Helmholtz coil for applying a
small transverse magnetic field to the junction. A semi-rigid coaxial cable can
be easily added for studying the behavior of Josephson junctions under
microwave irradiation. The rig can be detached from the probe and thus used
with different cryostats. The performance of this new probe has been tested in
a Quantum Design PPMS system by conducting point-contact Andreev reflection
measurements on Nb thin films over large areas as a function of temperature and
magnetic field.Comment: 7 pages, 7 figures, published in Rev. Sci. Instru
ENVIRONMENTAL POLICY INFLUENCES ON LIVESTOCK STOCKING AND LOCATION DECISIONS
This paper explores the relationship between state level environmental regulations and stocking and location decisions in the U.S livestock and poultry industry (beef, chicken, dairy and hogs). Rather than conduct this analysis on a species-by-species basis, we choose to focus upon the overall size of the livestock industry (expressed in animal units) and the size of industry found on large, medium and small operations by state (48) and over time (28 yrs). Results indicate that industry may drive policy rather than the converse. However, since we also find that existing policy rules have differential impacts on the industry by operation size, we conclude that structural change in the industry may be driven in part by size or legal structure discriminating regulations.Demand and Price Analysis, Livestock Production/Industries,
Experimental program for real gas flow code validation at NASA Ames Research Center
The experimental program for validating real gas hypersonic flow codes at NASA Ames Rsearch Center is described. Ground-based test facilities used include ballistic ranges, shock tubes and shock tunnels, arc jet facilities and heated-air hypersonic wind tunnels. Also included are large-scale computer systems for kinetic theory simulations and benchmark code solutions. Flight tests consist of the Aeroassist Flight Experiment, the Space Shuttle, Project Fire 2, and planetary probes such as Galileo, Pioneer Venus, and PAET
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