29,440 research outputs found
The Behaviour of the Green Function for the BFKL Pomeron with Running Coupling
We analyse here in LO the physical properties of the Green function solution
for the BFKL equation. We show that the solution obeys the orthonormality
conditions in the physical region and fulfills the completeness requirements.
The unintegrated gluon density is shown to consists of a set of few poles with
parameters which could be determined by comparison with the DIS data of high
precision
Indirect Evidence for New Physics at the 10 TeV Scale
We show that the supersymmetric extension of the Standard Model modifies the
structure of the low lying BFKL discrete pomeron states (DPS) which give a
sizable contribution to the gluon structure function in the HERA x and Q2
region. The comparison of the gluon density, determined within DPS with N=1
SUSY, with data favours a supersymmetry scale of the order of 10 TeV. The DPS
method described here could open a new window to the physics beyond the
Standard Model.Comment: 14 pages, 6 figure
Effect of disorder studied with ferromagnetic resonance for arrays of tangentially magnetized sub-micron Permalloy discs fabricated by nanosphere lithography
Tangentially magnetized trigonal arrays of sub-micron Permalloy discs are
characterized with ferromagnetic resonance to determine the possible
contributions to frequency and linewidth from array disorder. Each array is
fabricated by a water-surface self-assembly lithographic technique, and
consists of a large trigonal array of 700 nm diameter magnetic discs. Each
array is characterized by a different degree of ordering. Two modes are present
in the ferromagnetic resonance spectra: a large amplitude, `fundamental' mode
and a lower amplitude mode at higher field. Angular dependence of the resonance
field in a very well ordered array is found to be negligible for both modes.
The relationship between resonance frequency and applied magnetic field is
found to be uncorrelated with array disorder. Linewidth is found to increase
with increasing array disorder
H{\alpha} Imaging of Nearby Seyfert Host Galaxies
We used narrowband interference filters with the CCD imaging camera on the
Nickel 1.0 meter telescope at Lick Observatory to observe 31 nearby (z < 0.03)
Seyfert galaxies in the 12 {\mu}m Active Galaxy Sample. We obtained pure
emission line images of each galaxy in order to separate H{\alpha} emission
from the nucleus from that of the host galaxy. The extended H{\alpha} emission
is expected to be powered by newly formed hot stars, and correlates well with
other indicators of current star formation in these galaxies: 7.7 {\mu}m PAH,
far-infrared, and radio luminosity. Relative to what would be expected from
recent star formation, there is a 0.8 dex excess of radio emission in our
Seyfert galaxies. The nuclear H{\alpha} luminosity is dominated by the AGN, and
is correlated with the hard X-ray luminosity. There is an upward offset of 1
dex in this correlation for the Seyfert 1s due to a strong contribution from
the Broad Line Region. We found a correlation between star formation rate and
AGN luminosity. In spite of selection effects, we concluded that the absence of
bright Seyfert nuclei in galaxies with low SFRs is real, albeit only weakly
significant. We used our measured spatial distributions of H{\alpha} emission
to determine what these Seyfert galaxies would look like when observed through
fixed apertures at high redshifts. Although all would be detectable emission
line galaxies at any redshift, most would appear dominated by HII region
emission. Only the most luminous AGN would still be identified at z~0.3.Comment: 13 pages, 11 figures, accepted for publication in Ap
Fast Mesh Refinement in Pseudospectral Optimal Control
Mesh refinement in pseudospectral (PS) optimal control is embarrassingly easy
--- simply increase the order of the Lagrange interpolating polynomial and
the mathematics of convergence automates the distribution of the grid points.
Unfortunately, as increases, the condition number of the resulting linear
algebra increases as ; hence, spectral efficiency and accuracy are lost in
practice. In this paper, we advance Birkhoff interpolation concepts over an
arbitrary grid to generate well-conditioned PS optimal control discretizations.
We show that the condition number increases only as in general, but
is independent of for the special case of one of the boundary points being
fixed. Hence, spectral accuracy and efficiency are maintained as increases.
The effectiveness of the resulting fast mesh refinement strategy is
demonstrated by using \underline{polynomials of over a thousandth order} to
solve a low-thrust, long-duration orbit transfer problem.Comment: 27 pages, 12 figures, JGCD April 201
Quasiharmonic elastic constants corrected for deviatoric thermal stresses
The quasiharmonic approximation (QHA), in its simplest form also called the
statically constrained (SC) QHA, has been shown to be a straightforward method
to compute thermoelastic properties of crystals. Recently we showed that for
non-cubic solids SC-QHA calculations develop deviatoric thermal stresses at
high temperatures. Relaxation of these stresses leads to a series of
corrections to the free energy that may be taken to any desired order, up to
self-consistency. Here we show how to correct the elastic constants obtained
using the SC-QHA. We exemplify the procedure by correcting to first order the
elastic constants of MgSiO-perovskite and MgSiO-post-perovskite, the
major phases of the Earth's lower mantle. We show that this first order
correction is quite satisfactory for obtaining the aggregated elastic averages
of these minerals and their velocities in the lower mantle. This type of
correction is also shown to be applicable to experimental measurements of
elastic constants in situations where deviatoric stresses can develop, such as
in diamond anvil cells.Comment: 4 figures, 1 table, submitted to Phys. Rev. B, July 200
Classification of Standard Model Particles in Orbifold Grand Unified Theories
We classify the standard model fermions, which originate from bulk fields of
the or representation after orbifold breaking, in
grand unified theories on 5 or 6-dimensional space-time, under the
condition that , and survive as zero modes.Comment: 24 pages, typos corrected, to appear in IJMP
Magnetization pinning in conducting films demonstrated using broadband ferromagnetic resonance
The broadband microstrip ferromagnetic resonance technique has been applied
for detection and characterization of a magnetic inhomogeneity in a film
sample. In the case of a 100nm thick Permalloy film an additional magnetically
depleted top sub-layer, practically unidentifiable by the conventional
ferromagnetic resonance setup, has been detected and characterized. These
results have been confirmed by Brillouin light scattering spectroscopy
revealing the fact that the optical properties of the additional sub-layer do
not differ much from those of the bulk of the film. Subsequent characterization
of a large number of other presumably single-layer films with thicknesses in
the range 30-100nm using the same ferromagnetic resonance technique also
revealed the same effect
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