21,807 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
Identifying Sneutrino Dark Matter: Interplay between the LHC and Direct Search
Under R-parity, the lightest supersymmetric particle (LSP) is stable and may
serve as a good dark matter candidate. The R-parity can be naturally introduced
with a gauge origin at TeV scale. We go over why a TeV scale B-L gauge
extension of the minimal supersymmetric standard model (MSSM) is one of the
most natural, if not demanded, low energy supersymmetric models. In the
presence of a TeV scale Abelian gauge symmetry, the (predominantly)
right-handed sneutrino LSP can be a good dark matter candidate. Its
identification at the LHC is challenging because it does not carry any standard
model charge. We show how we can use the correlation between the LHC
experiments (dilepton resonance signals) and the direct dark matter search
experiments (such as CDMS and XENON) to identify the right-handed sneutrino LSP
dark matter in the B-L extended MSSM.Comment: 5 pages, 3 figure
DEVS-based intelligent control of space adapted fluid mixing
The development is described of event-based intelligent control system for a space-adapted mixing process by employing the DEVS (Discrete Event System Specification) formalism. In this control paradigm, the controller expects to receive confirming sensor responses to its control commands within definite time windows determined by its DEVS model of the system under control. The DEVS-based intelligent control paradigm was applied in a space-adapted mixing system capable of supporting the laboratory automation aboard a Space Station
ADE Singularities and Coset Models
We consider the compactification of the IIA string to (1+1) dimensions on
non-compact 4-folds that are ALE fibrations. Supersymmetry requires that the
compactification include 4-form fluxes, and a particular class of these models
has been argued by Gukov, Vafa and Witten to give rise to a set of perturbed
superconformal coset models that also have a Landau-Ginzburg description. We
examine all these ADE models in detail, including the exceptional cosets. We
identify which perturbations are induced by the deformation of the singularity,
and compute the Landau-Ginzburg potentials exactly. We also show how the the
Landau-Ginzburg fields and their superpotentials arise from the geometric data
of the singularity, and we find that this is most naturally described in terms
of non-compact, holomorphic 4-cycles.Comment: 41 pages; harvma
AdS/QHE: Towards a Holographic Description of Quantum Hall Experiments
Transitions among quantum Hall plateaux share a suite of remarkable
experimental features, such as semi-circle laws and duality relations, whose
accuracy and robustness are difficult to explain directly in terms of the
detailed dynamics of the microscopic electrons. They would naturally follow if
the low-energy transport properties were governed by an emergent discrete
duality group relating the different plateaux, but no explicit examples of
interacting systems having such a group are known. Recent progress using the
AdS/CFT correspondence has identified examples with similar duality groups, but
without the DC ohmic conductivity characteristic of quantum Hall experiments.
We use this to propose a simple holographic model for low-energy quantum Hall
systems, with a nonzero DC conductivity that automatically exhibits all of the
observed consequences of duality, including the existence of the plateaux and
the semi-circle transitions between them. The model can be regarded as a
strongly coupled analog of the old `composite boson' picture of quantum Hall
systems. Non-universal features of the model can be used to test whether it
describes actual materials, and we comment on some of these in our proposed
model.Comment: LaTex 52 pages 11 figures. Repost improves the discussion of the
probe approximation; corrects minor errors; adds references. Second repost
generalizes charged solution and improves scaling discussio
Splitting of Surface Plasmon Frequencies of Metal Particles in a Nematic Liquid Crystal
We calculate the effective dielectric function for a suspension of small
metallic particles immersed in a nematic liquid crystal (NLC) host. For a
random suspension of such particles in the dilute limit, we calculate the
effective dielectric tensor exactly and show that the surface plasmon
(SP)resonance of such particles splits into two resonances, polarized parallel
and perpendicular to the NLC director. At higher concentrations, we calculate
this splitting using a generalized Maxwell-Garnett approximation, which can
also be applied to a small metal particle coated with NLC. To confirm the
accuracy of the MGA for NLC-coated spheres, we also use the Discrete Dipole
Approximation. The calculated splitting is comparable to that observed in
recent experiments on NLC-coated small metal particlesComment: 11 pages, 2 figures. To be published in Appl. Phys. Let
Low energy effective theory of Fermi surface coupled with U(1) gauge field in 2+1 dimensions
We study the low energy effective theory for a non-Fermi liquid state in 2+1
dimensions, where a transverse U(1) gauge field is coupled with a patch of
Fermi surface with N flavors of fermion in the large N limit. In the low energy
limit, quantum corrections are classified according to the genus of the 2d
surface on which Feynman diagrams can be drawn without a crossing in a double
line representation, and all planar diagrams are important in the leading
order. The emerging theory has the similar structure to the four dimensional
SU(N) gauge theory in the large N limit. Because of strong quantum fluctuations
caused by the abundant low energy excitations near the Fermi surface, low
energy fermions remain strongly coupled even in the large N limit. As a result,
there are infinitely many quantum corrections that contribute to the leading
frequency dependence of the Green's function of fermion on the Fermi surface.
On the contrary, the boson self energy is not modified beyond the one-loop
level and the theory is stable in the large N limit. The non-perturbative
nature of the theory also shows up in correlation functions of gauge invariant
operators.Comment: 14 pages, 20 figures; v2) Sec. V on correlation function of gauge
invariant operators added; v3) typos corrected, minor changes (to appear in
PRB
U(1) Gauge Theory of the Hubbard Model : Spin Liquid States and Possible Application to k-(BEDT-TTF)_2 Cu_2 (CN)_3
We formulate a U(1) gauge theory of the Hubbard model in the slave-rotor
representation. From this formalism it is argued that spin liquid phases may
exist near the Mott transition in the Hubbard model on triangular and honeycomb
lattices at half filling. The organic compound k-(BEDT-TTF)_2 Cu_2 (CN)_3 is a
good candidate for the spin liquid state on a triangular lattice. We predict a
highly unusual temperature dependence for the thermal conductivity of this
material.Comment: 5 pages, 2 figures; paper shortened and the phase diagram of
anisotropic triangular lattice correcte
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