4,356 research outputs found
Explicit Solution of the Time Domain Volume Integral Equation Using a Stable Predictor-Corrector Scheme
An explicit marching-on-in-time (MOT) scheme for solving the time domain volume integral equation is presented. The proposed method achieves its stability by employing, at each time step, a corrector scheme, which updates/corrects fields computed by the explicit predictor scheme. The proposedmethod is computationally more efficient when compared to the existing filtering techniques used for the stabilization of explicit MOT schemes. Numerical results presented in this paper demonstrate that the proposed method maintains its stability even when applied to the analysis of electromagnetic wave interactions with electrically large structures meshed using approximately half a million discretization elements
Progress in Measurements of the Gravitational Bending of Radio Waves Using the VLBA
We have used the Very Long Baseline Array (VLBA) at 43, 23 and 15 GHz to
measure the solar gravitational deflection of radio waves among four radio
sources during an 18-day period in October 2005. Using phase-referenced radio
interferometry to fit the measured phase delay to the propagation equation of
the parameterized post-Newtonian (PPN) formalism, we have determined the
deflection parameter gamma = 0.9998 +/- 0.0003$ (68% confidence level), in
agreement with General Relativity. The results come mainly from 43 GHz
observations where the refraction effects of the solar corona were negligible
beyond 3 degrees from the sun. The purpose of this experiment is three-fold: to
improve on the previous results in the gravitational bending experiments near
the solar limb; to examine and evaluate the accuracy limits of terrestrial VLBI
techniques; and to determine the prospects and outcomes of future experiments.
Our conclusion is that a series of improved designed experiments with the VLBA
could increase the presented accuracy by at least a factor of 4.Comment: 22 pages, 3 figure
Characterizations of hemirings by their -ideals
In this paper we characterize hemirings in which all -ideals or all fuzzy
-ideals are idempotent. It is proved, among other results, that every
-ideal of a hemiring is idempotent if and only if the lattice of fuzzy
-ideals of is distributive under the sum and -intrinsic product of
fuzzy -ideals or, equivalently, if and only if each fuzzy -ideal of
is intersection of those prime fuzzy -ideals of which contain it. We
also define two types of prime fuzzy -ideals of and prove that, a
non-constant -ideal of is prime in the second sense if and only if each
of its proper level set is a prime -ideal of
Brownian dynamics studies of DNA internal motions
Earlier studies by Chow and Skolnick suggest that the internal motions of bacterial DNA may be governed by strong forces arising from being crowded into the small space of the nucleoid, and that these internal motions affect the diffusion of intranuclear protein through the dense matrix of the nucleoid. These findings open new questions regarding the biological consequences of DNA internal motions, and the ability of internal motions to influence protein diffusion in response to different environment factors. The results of diffusion studies of DNA based on coarse-grained simulations are presented. Here, our goals are to investigate the internal motions of DNA with respect to external factors, namely salt concentration of the solvent and intranuclear protein size, and to understand the mechanisms by which proteins dif- fuse through the dense matrix of bacterial DNA. First, a novel coarse-grained model of the DNA chain was developed and shown to maintain the fractal property of in vivo DNA. Next, diffusion studies using this model were performed through Brownian dynamics simulations. Our results suggest that DNA internal motions may be substantially affected by ion concentrations near physiological ion concentration ranges, with the diffusion activity increasing to a limit with increases in ion concentration. Furthermore, it was found that, for a fixed protein volume fraction, the motions of proteins in a DNA-protein system are substantially affected by the size of the proteins, with the diffusion activity increasing to a limit with decreasing protein radii, but the internal motions of DNA within the same system do not appear to change with changes to protein sizes.M.S
Higher Order Power Corrections in Inclusive B Decays
We discuss order 1/m_b^4 and 1/m_b^5 corrections in inclusive semileptonic
decay of a meson. We identify relevant hadronic matrix elements of
dimension seven and eight and estimate them using the ground-state saturation
approximation. Within this approach the effects on the integrated rate and on
kinematic moments are estimated. The overall relative shift in V_{cb} turns out
about +0.4% as applied to the existing fits. Similar estimates are presented
for B -> X_s+\gamma decays.Comment: 30 pages, 16 figure
Computational Modelling of Cardiac Electrophysiological Changes in Malarial Fever
Cardiac function is impaired in severe malarial fever, and ECGs show changes associated with repolarization. These could contribute to mortality via ventricular arrhythmia. The cardiac effects could be due to the malarial parasite load in the heart, specific cardio-toxic effects of the parasite or cardio-toxic effects of antimalarial agents. We construct a simple 1-dimensional electrophysiological model for the physico-chemical changes clinically observed during malarial fever: with temperature, pH and [ionic]plasma changes. The model can quantitatively reproduce the tachycardia and QTc prolongation seen in the adult, and shortening seen in the child during malarial fever
Measuring the dark flow with public X-ray cluster data
We present new results on the "dark flow" from a measurement of the dipole in
the distribution of peculiar velocities of galaxy clusters, applying the
methodology proposed and developed by us earlier. Our latest measurement is
conducted using new, low-noise 7-yr WMAP data as well as an all-sky sample of
X-ray selected galaxy clusters compiled exclusively from published catalogs.
Our analysis of the CMB signature of the kinematic Sunyaev-Zeldovich (SZ)
effect finds a statistically significant dipole at the location of galaxy
clusters. The residual dipole outside the cluster regions is small, rendering
our overall measurement 3-4 sigma significant. The amplitude of the dipole
correlates with cluster properties, being larger for the most X-ray luminous
clusters, as required if the signal is produced by the SZ effect. Since it is
measured at zero monopole, the dipole can not be due to the thermal SZ effect.
Our results are consistent with those obtained earlier by us from 5-yr WMAP
data and using a proprietary cluster catalog. In addition, they are robust to
quadrupole removal, demonstrating that quadrupole leakage contributes
negligibly to the signal. The lower noise of the 7-yr WMAP also allows us, for
the first time, to obtain tentative empirical confirmation of our earlier
conjecture that the adopted filtering flips the sign of the KSZ effect for
realistic clusters and thus of the deduced direction of the flow. The latter is
consistent with our earlier measurement in both the amplitude and direction.
Assuming the filtering indeed flips the sign of the KSZ effect from the
clusters, the direction agrees well also with the results of independent work
using galaxies as tracers at lower distances. We make all maps and cluster
templates derived by us from public data available to the scientific community
to allow independent tests of our method and findings.Comment: ApJ, in press. Replaced with accepted version. The data needed for
these results are at http://www.kashlinsky.info/bulkflows/data_publi
The Imperial IRAS-FSC Redshift Catalogue: luminosity functions, evolution and galaxy bias
We present the luminosity function and selection function of 60 micron
galaxies selected from the Imperial IRAS-FSC Redshift Catalogue (IIFSCz). Three
methods, including the 1/Vmax} and the parametric and non-parametric maximum
likelihood estimator, are used and results agree well with each other. A
density evolution proportional to (1+z)^3.4 or a luminosity evolution exp(1.7
t_L / \tau)$ where t_L is the look-back time is detected in the full sample in
the redshift range [0.02, 0.1], consistent with previous analyses. Of the four
infrared subpopulations, cirrus-type galaxies and M82-type starbursts show
similar evolutionary trends, galaxies with significant AGN contributions show
stronger positive evolution and Arp 220-type starbursts exhibit strong negative
evolution. The dominant subpopulation changes from cirrus-type galaxies to
M82-type starbursts at log (L_60 / L_Sun) ~ 10.3.
In the second half of the paper, we derive the projected two-point spatial
correlation function for galaxies of different infrared template type. The mean
relative bias between cirrus-type galaxies and M82-type starbursts, which
correspond to quiescent galaxies with optically thin interstellar dust and
actively star-forming galaxies respectively, is calculated to be around 1.25.
The relation between current star formation rate (SFR) in star-forming galaxies
and environment is investigated by looking at the the dependence of clustering
on infrared luminosity. We found that M82-type actively star-forming galaxies
show stronger clustering as infrared luminosity / SFR increases. The
correlation between clustering strength and SFR in the local Universe seems to
echo the basic trend seen in star-forming galaxies in the Great Observatories
Origins Deep Survey (GOODS) fields at z ~ 1.Comment: 15 pages, 11 figures, accepted for publication in MNRA
On the effects of using CO2 and F2 lasers to modify the wettability of a polymeric biomaterial.
Enhancement of the surface properties of a material by means of laser radiation has been amply demonstrated previously. In this work a comparative study for the surface modification of nylon 6,6 has been conducted in order to vary the wettability characteristics using CO2 and excimer lasers. This was done by producing 50 μm spaced (with depths between 1 and 10 μm) trench-like patterns using various laser parameters such as varying the laser power for the CO2 laser and number of pulses for the excimer laser. Topographical changes were analysed using optical microscopy and white light interferometry which indicated that both laser systems can be implemented for modifying the topography of nylon 6,6. Variations in the surface chemistry were evaluated using energy-dispersive X-ray spectroscopy and x-ray photoelectron spectroscopy analysis and showed that the O2 increased by up to 1.5% At. and decreased by up to 1.6% At. for the CO2 and F2 laser patterned samples, respectively. Modification of the wettability characteristics was quantified by measuring the advancing contact angle, which was found to increase in all instances for both laser systems. Emery paper roughened samples were also analysed in the same manner to determine that the topographical pattern played a major role in the wettability characteristics of nylon 6,6. From this, it is proposed that the increase in contact angle for the laser processed samples is due to a mixed intermediate state wetting regime owed to the periodic surface roughness brought about by the laser induced trench-like topographical patterns
- …