374 research outputs found
A Novel Approach for the Particle-in-Cell Modelling of Gridded Ion Engine Plume Neutralisation
The Particle-in-Cell modelling of gridded ion engine plume neutralisation has been simplified when compared to traditional methods. This results in significantly less computational resources being required. The NSTAR engine was modelled as a reference, where simulated specific impulse values were found to be 5% higher than the real engine. This method will be most suited to rapid prototyping and optimisation studies, where speed of simulations is an important factor
Solar Neutrinos: Where We Are, What We Need
This talk compares standard model predictions with the results of solar
neutrino experiments. Here `standard model' means the combined standard model
of minimal electroweak theory plus a standard solar model. I emphasize the
importance of recent analyses in which the neutrino fluxes are treated as free
parameters, independent of any constraints from solar models, and the stunning
agreement between the predictions of standard solar models and
helioseismological measurements. In order to interpret solar neutrino
experiments more accurately in terms of fundamental physics and astronomy, we
need improved improved nuclear physics data. I describe the five most important
nuclear physics problems whose solution is required for understanding the
precise implications of solar neutrino experiments.Comment: 20 pages, RevTeX file. To appear in the Proceedings of the 15th
International Conference on Few-Body Problems in Physics, Groningen, The
Netherlands, 22--26 July 1997, ed. J. C. S. Bacelar, A. E. L. Dieperink, and
R. A. Malfliet (Amsterdam: Elsevier Science Publishers). Related material at
http://www.sns.ias.edu/~jn
Solar Fluctuations and the MSW Effect
This talk summarizes the results of recent calculations of how fluctuations
within the solar medium can influence resonant neutrino oscillations within the
sun. Although initial calculations pointed to helioseismic waves as possibly
producing detectable effects, recent more careful calculations show this not to
be true. Those features of fluctuations which maximize their influence on
neutrino propagation are identified, and are likely to have implications for
supernovae and the early universe.Comment: 10 pages, LaTeX, talk given at the Erice School on Neutrinos in
Astro, Particle and Nuclear Physic
Biochemical Pharmacology and DNA-Drug Interactions by Cl- 958, a New Antitumor Intercalator Derived from a Series of Substituted 2 H-[1 ]Benzothiopyrano[4 ,3 ,2-cd]indazoles
Radio Frequency Tag Satellite: Backscatter Communication in Low Earth Orbit
Wireless sensor communication can evaluate the structural integrity of a system while reducing the danger and cost of installation and maintenance on satellites. This is needed at the International Space Station as well as other satellites. The objective of this mission is to perform a demonstration using backscatter Radio Frequency Identification (RFID) Tag technology as a method of wireless communication in extremely low earth orbit. While RFID tag communication has been used on earth for many practical applications the technology has yet to be tested in space. A 3U Cubesat was selected as the configuration to house the experiment. This project utilizes an electrical power system, an interface board custom built around a microcontroller, and two radio communication systems to run the RFID experiment to be designed by a Georgia Tech engineering team. The RFID tag will be mounted to a carbon fiber boom that can be extended out one meter to incrementally collect data. This satellite will need to be strong enough to pass a series of vibration and heat tests to be qualified for flight. It will be programmed to maintain its own power, take data, and communicate the data back to earth via the Globalstar Network
Asymptotics for Duration-Driven Long Range Dependent Processes
We consider processes with second order long range dependence resulting from
heavy tailed durations. We refer to this phenomenon as duration-driven long
range dependence (DDLRD), as opposed to the more widely studied linear long
range dependence based on fractional differencing of an process. We
consider in detail two specific processes having DDLRD, originally presented in
Taqqu and Levy (1986), and Parke (1999). For these processes, we obtain the
limiting distribution of suitably standardized discrete Fourier transforms
(DFTs) and sample autocovariances. At low frequencies, the standardized DFTs
converge to a stable law, as do the standardized sample autocovariances at
fixed lags. Finite collections of standardized sample autocovariances at a
fixed set of lags converge to a degenerate distribution. The standardized DFTs
at high frequencies converge to a Gaussian law. Our asymptotic results are
strikingly similar for the two DDLRD processes studied. We calibrate our
asymptotic results with a simulation study which also investigates the
properties of the semiparametric log periodogram regression estimator of the
memory parameter
Z-induced FCNCs and their effects on Neutrino Oscillations
Adding singlet neutrinos to the standard model spectrum in general gives rise
to Z-induced flavor-changing neutral currents. We study the impact of these
currents on matter-induced neutrino oscillations in the sun and in supernovae.
While the effects for solar neutrinos are negligible, dramatic effects are
possible for supernova neutrinos.Comment: 23 pages (including 5 eps-figures), Latex; references [29-34] were
added to the revised versio
Implications of New Gallex Results for the MSW Solution of the Solar Neutrino Problem
We compare the implications for 7Be and pp neutrinos of the two MSW fits to
the new GALLEX solar neutrino measurements . Small mixing angle solutions tend
to suppress the former as electron-neutrinos, but not the latter, and large
angle solutions tend to reduce both by about a factor of 2. The consequences
for BOREXINO and similar solar neutrino--electron scattering experiments are
discussed.Comment: 7 pages (plus 3 figures available upon request) UTAPHY-HEP-
Phenomenology of Neutrino Oscillations
The phenomenology of solar, atmospheric, supernova and laboratory neutrino
oscillations is described. Analytical formulae for matter effects are reviewed.
The results from oscillations are confronted with neutrinoless double beta
decay.Comment: 11 pages, 2 figures, latex, Plenary talk given at Workshop in High
Energy Particle Physics-6, Chennai, Indi
Generating schemes for long memory processes: regimes, aggregation and linearity
This paper analyses a class of nonlinear time series models exhibiting long memory. These processes exhibit short memory fluctuations around a local mean (regime) which switches randomly such that the durations of the regimes follow a power law. We show that if a large number of independent copies of such a process are aggregated, the resulting processes are Gaussian, have a linear representation, and converge after normalisation to fractional Brownian motion. Alternatively, an aggregation scheme with Gaussian common components can yield the same result. However, a non-aggregated regime process is shown to converge to a Levy motion with infinite variance, suitably normalised, emphasising the fact that time aggregation alone fails to yield a FCLT. Two cases arise, a stationary case in which the partial sums of the process converge, and a nonstationary case in which the process itself converges, the Hurst coefficient falling in the ranges () and (), respectively. We comment on the relevance of our results to the interpretation of the long memory phenomenon, and also report some simulations aimed to throw light on the problem of discriminating between the models in practice
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