10,679 research outputs found
Theoretical study of X-ray absorption of three-dimensional topological insulator
X-ray absorption edge singularity which is usually relevant for metals is
studied for the prototype topological insulator .
The generalized integral equation of Nozi\`eres and Dominicis type for X-ray
edge singularity is derived and solved. The spin texture of surfaces states
causes a component of singularity dependent on the helicity of the spin
texture. It also yields another component for which the singularity from
excitonic processes is absent.Comment: RevTeX 4.1. 4 pages, no figur
Similarity of Operators in the Bergman Space Setting
We give a necessary and sufficient condition for an n-hypercontraction to be
similar to the backward shift operator in a weighted Bergman space. This
characterization serves as a generalization of the description given in the
Hardy space setting, where the geometry of the eigenvector bundles of the
operators is used
Nanoscale Heat Transfer from Magnetic Nanoparticles and Ferritin in an Alternating Magnetic Field
Recent suggestions of nanoscale heat confinement on the surface of synthetic and biogenic magnetic nanoparticles during heating by radio frequency-alternating magnetic fields have generated intense interest because of the potential utility of this phenomenon for noninvasive control of biomolecular and cellular function. However, such confinement would represent a significant departure from the classical heat transfer theory. Here, we report an experimental investigation of nanoscale heat confinement on the surface of several types of iron oxide nanoparticles commonly used in biological research, using an all-optical method devoid of the potential artifacts present in previous studies. By simultaneously measuring the fluorescence of distinct thermochromic dyes attached to the particle surface or dissolved in the surrounding fluid during radio frequency magnetic stimulation, we found no measurable difference between the nanoparticle surface temperature and that of the surrounding fluid for three distinct nanoparticle types. Furthermore, the metalloprotein ferritin produced no temperature increase on the protein surface nor in the surrounding fluid. Experiments mimicking the designs of previous studies revealed potential sources of the artifacts. These findings inform the use of magnetic nanoparticle hyperthermia in engineered cellular and molecular systems
X-ray edge singularity of bilayer graphene
The X-ray edge singularity of bilayer graphene is studied by generalizing the
path integral approach based on local action which was employed for monolayer
graphene. In sharp contrast to the case of monolayer graphene, the bilayer
graphene is found to exhibit the edge singularity even at half-filling and its
characteristics are determined by interlayer coupling. At finite bias the
singular behaviors sensitively depend on the relative magnitude of fermi energy
and applied bias, which is due to the peculiar shape of energy band at finite
bias.Comment: RevTeX 4.1, 4 pages. No figur
Super Weyl Anomalies in the AdS/CFT Correspondence
Anomalies of N = (4,4) superconformal field theories coupled to a conformal
supergravity background in two dimensions are computed by using the AdS/CFT
correspondence. We find that Weyl, axial gauge and super Weyl transformations
are anomalous, while general coordinate, local Lorentz, vector gauge and local
super transformations are not. The coefficients of the anomalies show that the
superconformal field theories have the central charge expected in the AdS/CFT
correspondence.Comment: 16 pages, LaTeX, references added and typos correcte
Limits on the evolution of galaxies from the statistics of gravitational lenses
We use gravitational lenses from the Cosmic Lens All-Sky Survey (CLASS) to
constrain the evolution of galaxies since redshift in the current
\LCDM cosmology. This constraint is unique as it is based on a mass-selected
lens sample of galaxies. Our method of statistical analysis is the same as in
Chae (2003). We parametrise the early-type number density evolution in the form
of and the velocity dispersion as . We find that
() if we assume , implying
that the number density of early-type galaxies is within 50% to 164% of the
present-day value at redshift . Allowing the velocity dispersion to
evolve, we find that (), indicating that
the velocity dispersion must be within 57% and 107% of the present-day value at
. These results are consistent with the early formation and passive
evolution of early-type galaxies. More stringent limits from lensing can be
obtained from future large lens surveys and by using very high-redshift quasars
(z \ga 5) such as those found from the Sloan Digital Sky Survey.Comment: 10 pages (preprint format), 2 figures, ApJL in press (December 20th
issue
Blandford-Znajek process as a gamma ray burst central engine
We investigate the possibility that gamma-ray bursts are powered by a central
engine consisting of a black hole with an external magnetic field supported by
a surrounding disk or torus. The rotational energy of the black hole can be
extracted electromagnetically as a Poynting flux, a mechanism proposed by
Blandford and Znajek(1977). Recently observed magnetars indicate that some
compact objects have very high magnetic fields, up to G, which is
required to extract the energy within the duration of a GRB, i.e., in 1000 s or
less. We demonstrate also that the Poynting flux need not be substantially
dominated by the disk.Comment: 7 pages, no figure, paspconf.sty, to appear in Proceedings " Gamma
Ray Bursts: The First Three Minutes", Gr\"aft{\aa}vallen, Sweden, Feb. 6 -
11, 199
Parity-violating nucleon-nucleon interaction from different approaches
Two-pion exchange parity-violating nucleon-nucleon interactions from recent
effective field theories and earlier fully covariant approaches are
investigated. The potentials are compared with the idea to obtain better
insight on the role of low-energy constants appearing in the effective field
theory approach and the convergence of this one in terms of a perturbative
series. The results are illustrated by considering the longitudinal asymmetry
of polarized protons scattering off protons, , and the
asymmetry of the photon emission in radiative capture of polarized neutrons by
protons, .Comment: 31 page
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