5,730 research outputs found
Casimir effect of electromagnetic field in D-dimensional spherically symmetric cavities
Eigenmodes of electromagnetic field with perfectly conducting or infinitely
permeable conditions on the boundary of a D-dimensional spherically symmetric
cavity is derived explicitly. It is shown that there are (D-2) polarizations
for TE modes and one polarization for TM modes, giving rise to a total of (D-1)
polarizations. In case of a D-dimensional ball, the eigenfrequencies of
electromagnetic field with perfectly conducting boundary condition coincides
with the eigenfrequencies of gauge one-forms with relative boundary condition;
whereas the eigenfrequencies of electromagnetic field with infinitely permeable
boundary condition coincides with the eigenfrequencies of gauge one-forms with
absolute boundary condition. Casimir energy for a D-dimensional spherical shell
configuration is computed using both cut-off regularization and zeta
regularization. For a double spherical shell configuration, it is shown that
the Casimir energy can be written as a sum of the single spherical shell
contributions and an interacting term, and the latter is free of divergence.
The interacting term always gives rise to an attractive force between the two
spherical shells. Its leading term is the Casimir force acting between two
parallel plates of the same area, as expected by proximity force approximation.Comment: 28 page
Relationship between macroscopic physical properties and local distortions of low doping La{1-x}Ca{x}MnO3: an EXAFS study
A temperature-dependent EXAFS investigation of La{1-x}Ca{x}MnO3 is presented
for the concentration range that spans the ferromagnetic-insulator (FMI) to
ferromagnetic-metal (FMM) transition region, x = 0.16-0.22. The samples are
insulating for x = 0.16-0.2 and show a metal/insulator transition for x = 0.22.
All samples are ferromagnetic although the saturation magnetization for the 16%
Ca sample is only ~ 70% of the expected value at 0.4T. We find that the FMI
samples have similar correlations between changes in the local Mn-O distortions
and the magnetization as observed previously for the colossal magnetoresistance
(CMR) samples (0.2 < x < 0.5) - except that the FMI samples never become fully
magnetized. The data show that there are at least two distinct types of
distortions. The initial distortions removed as the insulating sample becomes
magnetized are small and provides direct evidence that roughly 50% of the Mn
sites have a small distortion/site and are magnetized first. The large
remaining Mn-O distortions at low T are attributed to a small fraction of
Jahn-Teller-distorted Mn sites that are either antiferromagnetically ordered or
unmagnetized. Thus the insulating samples are very similar to the behavior of
the CMR samples up to the point at which the M/I transition occurs for the CMR
materials. The lack of metallic conductivity for x <= 0.2, when 50% or more of
the sample is magnetic, implies that there must be preferred magnetized Mn
sites and that such sites do not percolate at these concentrations.Comment: 27 pages, 8 figures, to be submitted to Phys. Rev.
Casimir effect of electromagnetic field in Randall-Sundrum spacetime
We study the finite temperature Casimir effect on a pair of parallel
perfectly conducting plates in Randall-Sundrum model without using scalar field
analogy. Two different ways of interpreting perfectly conducting conditions are
discussed. The conventional way that uses perfectly conducting condition
induced from 5D leads to three discrete mode corrections. This is very
different from the result obtained from imposing 4D perfectly conducting
conditions on the 4D massless and massive vector fields obtained by decomposing
the 5D electromagnetic field. The latter only contains two discrete mode
corrections, but it has a continuum mode correction that depends on the
thicknesses of the plates. It is shown that under both boundary conditions, the
corrections to the Casimir force make the Casimir force more attractive. The
correction under 4D perfectly conducting condition is always smaller than the
correction under the 5D induced perfectly conducting condition. These
statements are true at any temperature.Comment: 20 pages, 4 figure
Axially symmetric rotating traversable wormholes
This paper generalizes the static and spherically symmetric traversable
wormhole geometry to a rotating axially symmetric one with a time-dependent
angular velocity by means of an exact solution. It was found that the violation
of the weak energy condition, although unavoidable, is considerably less severe
than in the static spherically symmetric case. The radial tidal constraint is
more easily met due to the rotation. Similar improvements are seen in one of
the lateral tidal constraints. The magnitude of the angular velocity may have
little effect on the weak energy condition violation for an axially symmetric
wormhole. For a spherically symmetric one, however, the violation becomes less
severe with increasing angular velocity. The time rate of change of the angular
velocity, on the other hand, was found to have no effect at all. Finally, the
angular velocity must depend only on the radial coordinate, confirming an
earlier result.Comment: 17 pages, AMSTe
Electronic structure studies of Fe- ZnO nanorods by x-ray absorption fine structure
We report the electronic structure studies of well characterized
polycrystalline Zn_{1-x}Fe_xO (x = 0.0, 0.01, 0.03, and 0.05) nanorods
synthesized by a co-precipitation method through x-ray absorption fine
structure (XAFS). X-ray diffraction (XRD) reveals that Fe doped ZnO
crystallizes in a single phase wurtzite structure without any secondary phase.
From the XRD pattern, it is observed that peak positions shift towards lower
2\theta value with Fe doping. The change in the peak positions with increase in
Fe contents clearly indicates that Fe ions are replacing Zn ions in the ZnO
matrix. Linear combination fittings (LCF) at Fe K-edge demonstrate that Fe is
in mixed valent state (Fe3+/Fe2+) with a ratio of ~ 7:3 (Fe3+:Fe2+). XAFS data
is successfully fitted to wurtzite structure using IFEFFIT and Artemis. The
results indicate that Fe substitutes Zn site in the ZnO matrix in tetrahedral
symmetry.Comment: 7 pages, 5 figures, 2 tables, regular articl
Topological Defects and Gapless Modes in Insulators and Superconductors
We develop a unified framework to classify topological defects in insulators
and superconductors described by spatially modulated Bloch and Bogoliubov de
Gennes Hamiltonians. We consider Hamiltonians H(k,r) that vary slowly with
adiabatic parameters r surrounding the defect and belong to any of the ten
symmetry classes defined by time reversal symmetry and particle-hole symmetry.
The topological classes for such defects are identified, and explicit formulas
for the topological invariants are presented. We introduce a generalization of
the bulk-boundary correspondence that relates the topological classes to defect
Hamiltonians to the presence of protected gapless modes at the defect. Many
examples of line and point defects in three dimensional systems will be
discussed. These can host one dimensional chiral Dirac fermions, helical Dirac
fermions, chiral Majorana fermions and helical Majorana fermions, as well as
zero dimensional chiral and Majorana zero modes. This approach can also be used
to classify temporal pumping cycles, such as the Thouless charge pump, as well
as a fermion parity pump, which is related to the Ising non-Abelian statistics
of defects that support Majorana zero modes.Comment: 27 pages, 15 figures, Published versio
Lanthanides: Applications in Cancer Diagnosis and Therapy
Lanthanide complexes are of increasing importance in cancer diagnosis and therapy, owing to the versatile chemical and magnetic properties of the lanthanide-ion 4f electronic configuration. Following the first implementation of gadolinium(III)-based contrast agents in magnetic resonance imaging in the 1980s, lanthanide-based small molecules and nanomaterials have been investigated as cytotoxic agents and inhibitors, in photodynamic therapy, radiation therapy, drug/gene delivery, biosensing, and bioimaging. As the potential utility of lanthanides in these areas continues to increase, this timely review of current applications will be useful to medicinal chemists and other investigators interested in the latest developments and trends in this emerging field
Computational predictions of corroles as a class of Hsp90 inhibitors
Corroles have been shown experimentally to cause cell cycle arrest, and there is some evidence that this might be attributed to an inhibitory effect of corroles on Heat shock protein 90 (Hsp90), which is known to play a vital role in cancer cell proliferation. In this study, we used molecular dynamics to examine the interaction of gallium corroles with Hsp90, and found that they can bind preferentially to the ATP-binding N-terminal site. We also found that structural variations of the corrole ring can influence the binding energies and affinities of the corrole to Hsp90. We predict that both the biscarboxylated corrole (4-Ga) and a proposed 3,17-bis-sulfonated corrole (7-Ga) are promising alternatives to Ga(III) 5,10,15-tris(pentafluorophenyl)-2,17-bis(sulfonic acid)-corrole (1-Ga) as anti-cancer agents
Rotating traversable wormholes
The general form of a stationary, axially symmetric traversable wormhole is
discussed. This provides an explicit class of rotating wormholes that
generalize the static, spherically symmetric ones first considered by Morris
and Thorne. In agreement with general analyses, it is verified that such a
wormhole generically violates the null energy condition at the throat. However,
for suitable model wormholes, there can be classes of geodesics falling through
it which do not encounter any energy-condition-violating matter. The possible
presence of an ergoregion surrounding the throat is also noted.Comment: 15 pages, harvmac; 1 figure in PicTeX; minor changes; to appear in
Phys. Rev.
SIC~POVMs and Clifford groups in prime dimensions
We show that in prime dimensions not equal to three, each group covariant
symmetric informationally complete positive operator valued measure (SIC~POVM)
is covariant with respect to a unique Heisenberg--Weyl (HW) group. Moreover,
the symmetry group of the SIC~POVM is a subgroup of the Clifford group. Hence,
two SIC~POVMs covariant with respect to the HW group are unitarily or
antiunitarily equivalent if and only if they are on the same orbit of the
extended Clifford group. In dimension three, each group covariant SIC~POVM may
be covariant with respect to three or nine HW groups, and the symmetry group of
the SIC~POVM is a subgroup of at least one of the Clifford groups of these HW
groups respectively. There may exist two or three orbits of equivalent
SIC~POVMs for each group covariant SIC~POVM, depending on the order of its
symmetry group. We then establish a complete equivalence relation among group
covariant SIC~POVMs in dimension three, and classify inequivalent ones
according to the geometric phases associated with fiducial vectors. Finally, we
uncover additional SIC~POVMs by regrouping of the fiducial vectors from
different SIC~POVMs which may or may not be on the same orbit of the extended
Clifford group.Comment: 30 pages, 1 figure, section 4 revised and extended, published in J.
Phys. A: Math. Theor. 43, 305305 (2010
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