25,431 research outputs found
OM Theory and V-duality
We show that the (M5, M2, M2, MW) bound state solution of eleven
dimensional supergravity recently constructed in hep-th/0009147 is related to
the (M5, M2) bound state one by a finite Lorentz boost along a M5-brane
direction perpendicular to the M2-brane. Given the (M5, M2) bound state as a
defining system for OM theory and the above relation between this system and
the (M5, M2, M2', MW) bound state, we test the recently proposed V-duality
conjecture in OM theory. Insisting to have a decoupled OM theory, we find that
the allowed Lorentz boost has to be infinitesimally small, therefore resulting
in a family of OM theories related by Galilean boosts. We argue that such
related OM theories are equivalent to each other. In other words, V-duality
holds for OM theory as well. Upon compactification on either an electric or a
`magnetic' circle (plus T-dualities as well), the V-duality for OM theory gives
the known one for either noncommutative open string theories or noncommutative
Yang-Mills theories. This further implies that V-duality holds in general for
the little m-theory without gravity.Comment: 17 pages, typos corrected and references adde
Critical comments on the paper "Crossing by a single scalar field on a Dvali-Gabadadze-Porrati brane" by H Zhang and Z-H Zhu [Phys.Rev.D75,023510(2007)]
It is demonstrated that the claim in the paper "Crossing by a
single scalar field on a Dvali-Gabadadze-Porrati brane" by H Zhang and Z-H Zhu
[Phys.Rev.D75,023510(2007)], about a prove that there do not exist scaling
solutions in a universe with dust in a Dvali-Gabadadze-Porrati (DGP) braneworld
scenario, is incorrect.Comment: 5 pages, 8 eps figure
Phase-reference VLBI Observations of the Compact Steep-Spectrum Source 3C 138
We investigate a phase-reference VLBI observation that was conducted at 15.4
GHz by fast switching VLBA antennas between the compact steep-spectrum radio
source 3C 138 and the quasar PKS 0528+134 which are about 4 away on the
sky. By comparing the phase-reference mapping with the conventional hybrid
mapping, we demonstrate the feasibility of high precision astrometric
measurements for sources separated by 4. VLBI phase-reference mapping
preserves the relative phase information, and thus provides an accurate
relative position between 3C 138 and PKS 0528+134 of
and
(J2000.0) in right ascension and declination, respectively. This gives an
improved position of the nucleus (component A) of 3C 138 in J2000.0 to be
RA= and Dec= under the
assumption that the position of calibrator PKS 0528+134 is correct. We further
made a hybrid map by performing several iterations of CLEAN and
self-calibration on the phase-referenced data with the phase-reference map as
an input model for the first phase self-calibration. Compared with the hybrid
map from the limited visibility data directly obtained from fringe fitting 3C
138 data, this map has a similar dynamic range, but a higher angular
resolution. Therefore, phase-reference technique is not only a means of phase
connection, but also a means of increasing phase coherence time allowing
self-calibration technique to be applied to much weaker sources.Comment: 9 pages plus 2 figures, accepted by PASJ (Vol.58 No.6
Influence of low-level Pr substitution on the superconducting properties of YBa2Cu3O7-delta single crystals
We report on measurements on Y1-xPrxBa2Cu3O7-delta single crystals, with x
varying from 0 to 2.4%. The upper and the lower critical fields, Hc2 and Hc1,
the Ginzburg-Landau parameter and the critical current density, Jc(B), were
determined from magnetization measurements and the effective media approach
scaling method. We present the influence of Pr substitution on the pinning
force density as well as on the trapped field profiles analyzed by Hall probe
scanning.Comment: 4 pages, 5 figures, accepted for publication in J. Phys. Conf. Se
Novel Scaling Behavior for the Multiplicity Distribution under Second-Order Quark-Hadron Phase Transition
Deviation of the multiplicity distribution in small bin from its
Poisson counterpart is studied within the Ginzburg-Landau description for
second-order quark-hadron phase transition. Dynamical factor for the distribution and ratio are defined, and
novel scaling behaviors between are found which can be used to detect the
formation of quark-gluon plasma. The study of and is also very
interesting for other multiparticle production processes without phase
transition.Comment: 4 pages in revtex, 5 figures in eps format, will be appeared in Phys.
Rev.
Cyclic cosmology from Lagrange-multiplier modified gravity
We investigate cyclic and singularity-free evolutions in a universe governed
by Lagrange-multiplier modified gravity, either in scalar-field cosmology, as
well as in one. In the scalar case, cyclicity can be induced by a
suitably reconstructed simple potential, and the matter content of the universe
can be successfully incorporated. In the case of -gravity, cyclicity can
be induced by a suitable reconstructed second function of a very
simple form, however the matter evolution cannot be analytically handled.
Furthermore, we study the evolution of cosmological perturbations for the two
scenarios. For the scalar case the system possesses no wavelike modes due to a
dust-like sound speed, while for the case there exist an oscillation
mode of perturbations which indicates a dynamical degree of freedom. Both
scenarios allow for stable parameter spaces of cosmological perturbations
through the bouncing point.Comment: 8 pages, 3 figures, references added, accepted for publicatio
First-principles study of vibrational and dielectric properties of {\beta}-Si3N4
First-principles calculations have been conducted to study the structural,
vibrational and dielectric properties of {\beta}-Si3N4. Calculations of the
zone-center optical-mode frequencies (including LO-TO splittings), Born
effective charge tensors for each atom, dielectric constants, using density
functional perturbation theory, are reported. The fully relaxed structural
parameters are found to be in good agreement with experimental data. All optic
modes are identified and agreement of theory with experiment is excellent. The
static dielectric tensor is decomposed into contributions arising from
individual infrared-active phonon modes. It is found that high-frequency modes
mainly contribute to the lattice dielectric constant.Comment: 15pages, 1 figure, 5 table
A statistical study of magnetic dipolarization for sawtooth events and isolated substorms at geosynchronous orbit with GOES data
We investigate whether the dipolarization process during sawtooth events is global or not through an examination of the local time distribution of the magnetic tilt angle (i.e. the angle between the <i><b>B</b></i> vector and the equatorial plane in dipole <i>VDH</i> coordinates) at geostationary orbit. From the statistical analysis of 207 individual teeth and 212 isolated substorms, we find that individual teeth follow a dipolarization pattern similar to that observed for isolated substorms. The dipolarization for individual teeth initiates in the sector between 22:00 magnetic local time (MLT) and 00:00 MLT. Then the dipolarization expands both eastward and westward. However, relative to isolated substorms, we find that the nightside magnetosphere is much more stretched prior to the onset, and the change of the tilt angle during the dipolarization process is much larger during individual teeth. The magnetic dipolarization is seen over a wider local time sector during individual teeth than during isolated substorms. However, the magnetic dipolarization is rarely observed near local noon during individual teeth. This suggests that the magnetic dipolarization process during individual teeth is still confined primarily to the nightside
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