30,430 research outputs found
Gauge-invariant Green function in 3+1 dimensional QED (QCD) and 2+1 dimensional Abelian (Non-Abelian) Chern-Simon theory
By applying the simple and effective method developed to study the the
gauge-invariant fermion Green function in dimensional non-compact QED,
we study the gauge-invariant Green function in dimensional QED and dimensional non-compact Chern-Simon theory. We also extend our results to
the corresponding non-Abelian gauge theories. Implications for
Fractional Quantum Hall effect are briefly discussed.Comment: 8 pages, 4 figures, published versio
Abelian bosonization approach to quantum impurity problems
Using Abelian Bosonization, we develop a simple and powerful method to
calculate the correlation functions of the two channel Kondo model and its
variants. The method can also be used to identify all the possible boundary
fixed points and their maximum symmetry, to calculate straightforwardly the
finite size spectra, to demonstrate the physical picture at the boundary
explicitly. Comparisons with Non-Abelian Bosonization method are made. Some
fixed points corresponding to 4 pieces of bulk fermions coupled to s=1/2
impurity are listed.Comment: 12 pages, REVTEX, 1 Table, no figures. To appear in Phys. Rev. Letts.
July 21, 199
On gauge-invariant Green function in 2+1 dimensional QED
Both the gauge-invariant fermion Green function and gauge-dependent
conventional Green function in dimensional QED are studied in the large
limit. In temporal gauge, the infra-red divergence of gauge-dependent
Green function is found to be regulariable, the anomalous dimension is found to
be . This anomalous dimension was argued to be
the same as that of gauge-invariant Green function. However, in Coulomb gauge,
the infra-red divergence of the gauge-dependent Green function is found to be
un-regulariable, anomalous dimension is even not defined, but the infra-red
divergence is shown to be cancelled in any gauge-invariant physical quantities.
The gauge-invariant Green function is also studied directly in Lorentz
covariant gauge and the anomalous dimension is found to be the same as that
calculated in temporal gauge.Comment: 8 pages, 6 figures, to appear in Phys. Rev.
An experimental approach to quantify strain transfer efficiency of fibre bragg grating sensors to host structures
This paper developed a method to evaluate the strain transfer efficiency of
fibre Bragg grating sensors to host structures. Various coatings were applied to
fibre Bragg grating sensors after being fabricated. They were epoxy, silane
agent and polypropylene, representing different surface properties. A neat epoxy
resin plate was used as the host in which the coated fibre sensors were embedded
in the central layer. The tensile strain output from the FBGs was compared with
that obtained from electrical strain gauges which were attached on the surface
of the specimen. A calculating method based on the measured strains was
developed to quantify the strain transfer function of different surface
coatings. The strain transfer coefficient obtained from the proposed method
provided a direct indicator to evaluate the strain transfer efficiency of
different coatings used on the FBG sensors, under either short or long-term
loading. The results demonstrated that the fibre sensor without any coating
possessed the best strain transfer, whereas, the worst strain transfer was
created by polypropylene coating. Coatings play a most influential role in
strain measurements using FBG sensors
Acoustic Attenuation by Two-dimensional Arrays of Rigid Cylinders
In this Letter, we present a theoretical analysis of the acoustic
transmission through two-dimensional arrays of straight rigid cylinders placed
parallelly in the air. Both periodic and completely random arrangements of the
cylinders are considered. The results for the sound attenuation through the
periodic arrays are shown to be in a remarkable agreement with the reported
experimental data. As the arrangement of the cylinders is randomized, the
transmission is significantly reduced for a wider range of frequencies. For the
periodic arrays, the acoustic band structures are computed by the plane-wave
expansion method and are also shown to agree with previous results.Comment: 4 pages, 3 figure
Phase transitions for random states and a semi-circle law for the partial transpose
For a system of N identical particles in a random pure state, there is a
threshold k_0 = k_0(N) ~ N/5 such that two subsystems of k particles each
typically share entanglement if k > k_0, and typically do not share
entanglement if k < k_0. By "random" we mean here "uniformly distributed on the
sphere of the corresponding Hilbert space." The analogous phase transition for
the positive partial transpose (PPT) property can be described even more
precisely. For example, for N qubits the two subsystems of size k are typically
in a PPT state if k
k_1. Since, for a given state of the entire system, the induced state of a
subsystem is given by the partial trace, the above facts can be rephrased as
properties of random induced states. An important step in the analysis depends
on identifying the asymptotic spectral density of the partial transposes of
such random induced states, a result which is interesting in its own right.Comment: 5 pages, 2 figures. This short note contains a high-level overview of
two long and technical papers, arXiv:1011.0275 and arXiv:1106.2264. Version
2: unchanged results, editorial changes, added reference, close to the
published articl
Hofstadter-type energy spectra in lateral superlattices defined by periodic magnetic and electrostatic fields
We calculate the energy spectrum of an electron moving in a two-dimensional
lattice which is defined by an electric potential and an applied perpendicular
magnetic field modulated by a periodic surface magnetization. The spatial
direction of this magnetization introduces complex phases into the Fourier
coefficients of the magnetic field. We investigate the effect of the relative
phases between electric and magnetic modulation on band width and internal
structure of the Landau levels.Comment: 5 LaTeX pages with one gif figure to appear in Phys. Rev.
Systematic study of Optical Feshbach Resonances in an ideal gas
Using a narrow intercombination line in alkaline earth atoms to mitigate
large inelastic losses, we explore the Optical Feshbach Resonance (OFR) effect
in an ultracold gas of bosonic Sr. A systematic measurement of three
resonances allows precise determinations of the OFR strength and scaling law,
in agreement with coupled-channels theory. Resonant enhancement of the complex
scattering length leads to thermalization mediated by elastic and inelastic
collisions in an otherwise ideal gas. OFR could be used to control atomic
interactions with high spatial and temporal resolution.Comment: Significant changes to text and figure presentation to improve
clarity. Extended supplementary material. 4 pages, 4 figures; includes
supplementary material 8 pages, 4 figures. Submitted to Physical Review
Letter
Interaction of HIV protease inhibitors with OATP1B1, 1B3, and 2B1
The effects of human immunodeficiency virus (HIV) protease inhibitors (PI) on the accumulation of the fluorescent bile salt analogue cholyl-glycylamido-fluorescein (CGamF) were determined in organic anion transporting polypeptide (OATP)-1B1 and -1B3-expressing Chinese hamster ovary (CHO) cells. In addition, interaction studies in Caco-2 monolayers, known only to express the OATP2B1 isoform, were conducted using the established OATP substrate estrone 3-sulfate (E3S), since no CGamF accumulation was observed in Caco-2 monolayers. CGamF appeared an excellent substrate for the OATP1B subfamily, with net accumulation clearance values of 7.8 and 142 microl min(-1) mg(-1) protein in OATP1B1 and OATP1B3-transfected cells, respectively. K(i)-values reflecting inhibition of CGamF accumulation by HIV PI correlated well between OATP1B1 and OATP1B3-expressing cells. Lopinavir was the most potent inhibitor (K(i) = 0.5-1.4 microM) of OATP1B-mediated CGamF accumulation compared with atazanavir, darunavir, ritonavir, and saquinavir (K(i) between 1.4 and 3.3 microM). Inhibitory profiles towards OATP2B1-mediated E3S accumulation were different with only indinavir, saquinavir, and ritonavir showing substantial effects. In conclusion, OATP1B3 appears to be a major transport mechanism mediating sodium-independent CGamF accumulation in human liver, and CGamF could be used as a probe substrate for in vitro drug interaction studies. The remarkably potent inhibition of OATP1B1 by lopinavir may explain some clinically relevant drug interactions between lopinavir and OATP1B substrates such as fexofenadine
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