33,352 research outputs found
On a Classical, Geometric Origin of Magnetic Moments, Spin-Angular Momentum and the Dirac Gyromagnetic Ratio
By treating the real Maxwell Field and real linearized Einstein equations as
being imbedded in complex Minkowski space, one can interpret magnetic moments
and spin-angular momentum as arising from a charge and mass monopole source
moving along a complex world line in the complex Minkowski space. In the
circumstances where the complex center of mass world-line coincides with the
complex center of charge world-line, the gyromagnetic ratio is that of the
Dirac electron.Comment: 17 page
Thermal Photons and Lepton Pairs from Quark Gluon Plasma and Hot Hadronic Matter
The formulation of the real and virtual photon production rate from strongly
interacting matter is presented in the framework of finite temperature field
theory. The changes in the hadronic spectral function induced by temperature
are discussed within the ambit of the Walecka type model, gauged linear and
non-linear sigma models, hidden local symmetry approach and QCD sum rule
approach. Possibility of observing the direct thermal photon and lepton pair
from quark gluon plasma has been contrasted with those from hot hadronic matter
with and without medium effects for various mass variation scenarios. At SPS
energies, in-medium effects of different magnitude on the hadronic properties
for the Walecka model, Brown-Rho scaling and Nambu scaling scenarios are
conspicuously visible through the low invariant mass distribution of dilepton
and transverse momentum spectra of photon. However, at RHIC energies the
thermal photon (dilepton) spectra originating from Quark Gluon Plasma
overshines those from hadronic matter for large transverse momentum (invariant
mass) irrespective of the models used for evaluating the finite temperature
effects on the hadronic properties. It is thus expected that both at RHIC and
LHC energies the formation of Quark Gluon Plasma in the initial stages may
indeed turn out to be a realistic scenario.Comment: Text revised, 3 figures adde
Microelectromechanical systems vibration powered electromagnetic generator for wireless sensor applications
This paper presents a silicon microgenerator, fabricated using standard silicon micromachining techniques, which converts external ambient vibrations into electrical energy. Power is generated by an electromagnetic transduction mechanism with static magnets positioned on either side of a moving coil, which is located on a silicon structure designed to resonate laterally in the plane of the chip. The volume of this device is approximately 100 mm3. ANSYS finite element analysis (FEA) has been used to determine the optimum geometry for the microgenerator. Electromagnetic FEA simulations using Ansoft’s Maxwell 3D software have been performed to determine the voltage generated from a single beam generator design. The predicted voltage levels of 0.7–4.15 V can be generated for a two-pole arrangement by tuning the damping factor to achieve maximum displacement for a given input excitation. Experimental results from the microgenerator demonstrate a maximum power output of 104 nW for 0.4g (g=9.81 m s1) input acceleration at 1.615 kHz. Other frequencies can be achieved by employing different geometries or material
Revisiting the double-binary-pulsar probe of non-dynamical Chern-Simons gravity
One of the popular modifications to the theory of general relativity is
non-dynamical Chern-Simons (CS) gravity, in which the metric is coupled to an
externally prescribed scalar field. Setting accurate constraints to the
parameters of the theory is important owing to their implications for the
scalar field and/or the underlying fundamental theory. The current best
constraints rely on measurements of the periastron precession rate in the
double-binary-pulsar system and place a very tight bound on the characteristic
CS lengthscale k_cs^{-1} <~ 3*10^{-9} km. This paper considers several effects
that were not accounted for when deriving this bound and lead to a substantial
suppression of the predicted rate of periastron precession. It is shown, in
particular, that the point mass approximation for extended test bodies does not
apply in this case. The constraint to the characteristic CS lengthscale is
revised to k_cs^{-1} <~ 0.4 km, eight orders of magnitude weaker than what was
previously found.Comment: 12 pages, 4 figures, to be submitted to PRD. Comments are welcom
Photons from Nucleus-Nucleus Collisions at Ultra-Relativistic Energies
We compare the photon emission rates from hot hadronic matter with in-medium
mass shift and Quark Gluon Plasma (QGP). It is observed that the WA98 data can
be well reproduced by hadronic initial state with initial temperature MeV if the universal scaling of temperature dependent hadronic masses are
assumed and the evolution of temperature with time is taken from transport
model or (3+1) dimensional hydrodynamics. The data can also be reproduced by
QGP initial state with similar initial temperature and non-zero initial radial
velocity.Comment: Talk given in the International Nuclear Physics Conference, at the
University of California, Berkeley, USA, during July 30 - August 3, 200
How effective is school-based deworming for the community-wide control of soil-transmitted helminths?
Background: The London Declaration on neglected tropical diseases was based in part on a new World Health Organization roadmap to “sustain, expand and extend drug access programmes to ensure the necessary supply of drugs and other interventions to help control by 2020”. Large drug donations from the pharmaceutical industry form the backbone to this aim, especially for soil-transmitted helminths (STHs) raising the question of how best to use these resources. Deworming for STHs is often targeted at school children because they are at greatest risk of morbidity and because it is remarkably cost-effective. However, the impact of school-based deworming on transmission in the wider community remains unclear.
Methods: We first estimate the proportion of parasites targeted by school-based deworming using demography, school enrolment, and data from a small number of example settings where age-specific intensity of infection (either worms or eggs) has been measured for all ages. We also use transmission models to investigate the potential impact of this coverage on transmission for different mixing scenarios.
Principal Findings: In the example settings <30% of the population are 5 to <15 years old. Combining this demography with the infection age-intensity profile we estimate that in one setting school children output as little as 15% of hookworm eggs, whereas in another setting they harbour up to 50% of Ascaris lumbricoides worms (the highest proportion of parasites for our examples). In addition, it is estimated that from 40–70% of these children are enrolled at school.
Conclusions: These estimates suggest that, whilst school-based programmes have many important benefits, the proportion of infective stages targeted by school-based deworming may be limited, particularly where hookworm predominates. We discuss the consequences for transmission for a range of scenarios, including when infective stages deposited by children are more likely to contribute to transmission than those from adults
Higher Resolution VLBI Imaging with Fast Frequency Switching
Millimetre-VLBI is an important tool in AGN astrophysics, but it is limited
by short atmospheric coherence times and poor receiver and antenna performance.
We demonstrate a new kind of phase referencing for the VLBA, enabling us to
increase the sensitivity in mm-VLBI by an order of magnitude. If a source is
observed in short cycles between the target frequency, nu_t, and a reference
frequency, nu_ref, the nu_t data can be calibrated using scaled-up phase
solutions from self-calibration at nu_ref. We have demonstrated the phase
transfer on 3C 279, where we were able to make an 86 GHz image with 90 %
coherence compared to self-calibration at nu_t. We have detected M81, our
science target in this project, at 86 GHz using the same technique. We describe
scheduling strategy and data reduction. The main impacts of fast frequency
switching are the ability to image some of the nearest, but relatively weak AGN
cores with unprecedented high angular resolution and to phase-reference the
nu_t data to the nu_ref core position, enabling the detection of possible core
shifts in jets due to optical depth effects. This ability will yield important
constraints on jet properties and might be able to discriminate between the two
competing emission models of Blandford-Konigl jets and spherical
advection-dominated accretion flows (ADAFs) in low-luminosity AGNs.Comment: 4 pages, 6 figures, appears in: Proceedings of the 6th European VLBI
Network Symposium held on June 25th-28th in Bonn, Germany. Edited by: E. Ros,
R.W. Porcas, A.P. Lobanov, and J.A. Zensu
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