4,310 research outputs found
Relativistic Quasilinear Diffusion in Axisymmetric Magnetic Geometry for Arbitrary-Frequency Electromagnetic Fluctuations
A relativistic bounce-averaged quasilinear diffusion equation is derived to
describe stochastic particle transport associated with arbitrary-frequency
electromagnetic fluctuations in a nonuniform magnetized plasma. Expressions for
the elements of a relativistic quasilinear diffusion tensor are calculated
explicitly for magnetically-trapped particle distributions in axisymmetric
magnetic geometry in terms of gyro-drift-bounce wave-particle resonances. The
resonances can destroy any one of the three invariants of the unperturbed
guiding-center Hamiltonian dynamics.Comment: 22 pages, Latex, to appear in Physics of Plasma
High spectral resolution time-resolved optical spectroscopy of V893 Sco
We present high resolution time-resolved optical spectra of the high
inclination short orbital period dwarf nova V893 Sco. We performed spectral
analysis through radial velocity measurements, Doppler mapping, and ratioed
Doppler maps. Our results indicate that V893 Sco's accretion disk is dissimilar
to WZ Sge's accretion disk, and does not fit any of the current accretion disk
models. We derive the system parameters M1 and i, and present evidence for V893
Sco as a very young cataclysmic variable and an ER UMa star. We advance the
hypothesis that all ER UMa stars may be newly formed cataclysmic variables.Comment: 23 pages (total), 8 figures, accepted by Ap
Compressed natural gas (CNG) transit bus experience survey: April 2009âApril 2010
The U.S. Department of Energy (DOE) and the National Renewable Energy Laboratory (NREL) commissioned this survey to collect and analyze experiential data from U.S. transit agencies with varying degrees of compressed natural gas (CNG) bus and station experience. This information helps DOE and NREL determine areas of CNG transit bus success and priority areas for which further technical or other assistance might be required to enable success.
Clean Vehicle Education Foundation (CVEF) staff and subcontractors developed a battery of questions and identified 10 transit agencies to represent all U.S. transit agencies that use CNG buses, accounting for the diversity in characteristics such as fleet size, management system, station ownership and operation, and geographic location. The survey was conducted onsite.
The study found that the average fuel economy in CNG buses is approximately 20% lower than in diesel buses, although there is reason to believe that this gap will be narrower for new CNG and diesel engines. Based on a recent 12-month periodâand after adjusting for energy content, bus fuel efficiency, station maintenance and power costs, and fuel-cost subsidiesâthe average CNG cost was $1.06 per diesel gallon equivalent
Preliminary test results of the joint FAA-USAF-NASA runway research program. Part 1: Traction measurements of several runways under wet and dry conditions with a Boeing 727, a diagonal-braked vehicle, and a mu-meter
The stopping distance, brake application velocity, and time of brake application were measured for two modern jet transports, along with the NASA diagonal-braked vehicle and the British Mu-Meter on several runways, which when wetted, cover the range of slipperiness likely to be encountered in the United States. Tests were designed to determine if correlation between the aircraft and friction measuring vehicles exists. The test procedure, data reduction techniques, and preliminary test results obtained with the Boeing 727, the Douglas DC-9, and the ground vehicles are given. Time histories of the aircraft test run parameters are included
Negative magnetoresistance and phase slip process in superconducting nanowires
We argue that the negative magnetoresistance of superconducting nanowires,
which was observed in recent experiments, can be explained by the influence of
the external magnetic field on the critical current of the phase slip process.
We show that the suppression of the order parameter in the bulk superconductors
made by an external magnetic field can lead to an enhancement of both the first
and the second critical currents of the phase slip process in
nanowires. Another mechanism of an enhancement of can come from
decreasing the decay length of the charge imbalance at weak
magnetic fields because is inversely proportional to . The
enhancement of the first critical current leads to a larger intrinsic
dissipation of the phase slip process. It suppresses the rate of both the
thermo-activated and/or quantum fluctuated phase slips and results in
decreasing the fluctuated resistance.Comment: 7 pages, 4 figure
Chorus acceleration of radiation belt relativistic electrons during March 2013 geomagnetic storm
Abstract The recent launching of Van Allen probes provides an unprecedent opportunity to investigate variations of the radiation belt relativistic electrons. During the 17-19 March 2013 storm, the Van Allen probes simultaneously detected strong chorus waves and substantial increases in fluxes of relativistic (2 - 4.5 MeV) electrons around L = 4.5. Chorus waves occurred within the lower band 0.1-0.5fce (theelectron equatorial gyrofrequency), with a peak spectral density âŒ10-4 nT 2/Hz. Correspondingly, relativistic electron fluxes increased by a factor of 102-103 during the recovery phase compared to the main phase levels. By means of a Gaussian fit to the observed chorus spectra, the drift and bounce-averaged diffusion coefficients are calculated and then used to solve a 2-D Fokker-Planck diffusion equation. Numerical simulations demonstrate that the lower-band chorus waves indeed produce such huge enhancements in relativistic electron fluxes within 15 h, fitting well with the observation. Key Points Initial RBSP correlated data of chorus waves and relativistic electron fluxes A realistic simulation to examine effect of chorus on relativistic electron flux Chorus yields huge increases inelectron flux rapidly, consistent with data
Perturbations in the Kerr-Newman Dilatonic Black Hole Background: Maxwell Waves, the Dilaton Background and Gravitational Lensing
In this paper we continue the analysis of our previous papers and study the
affect of the existence of a non-trivial dilaton background on the propagation
of electromagnetic waves in the Kerr-Newman dilatonic black hole space-time.
For this purpose we again employ the double expansion in both the background
electric charge and the wave parameters of the relevant quantities in the
Newman-Penrose formalism and then identify the first order at which the dilaton
background enters the Maxwell equations. We then assume that gravitational and
dilatonic waves are negligible (at that order in the charge parameter) with
respect to electromagnetic waves and argue that this condition is consistent
with the solutions already found in the previous paper. Explicit expressions
are given for the asymptotic behavior of scattered waves, and a simple physical
model is proposed in order to test the effects. An expression for the relative
intensity is obtained for Reissner-Nordstrom dilaton black holes using
geometrical optics. A comparison with the approximation of geometrical optics
for Kerr-Newman dilaton black holes shows that at the order to which the
calculations are carried out gravitational lensing of optical images cannot
probe the dilaton background.Comment: 9 pages, 1 figur
Third Best Brief, 2007 ABA National Appellate Advocacy Competition
The ABA Law Student Division\u27s National Appellate Advocacy Competition (NAAC) emphasizes the development of oral advocacy skills through a realistic appellate advocacy experience. Competitors participate in a hypothetical appeal to the United States Supreme Court. The competition involves writing a 40-page brief as either respondent or petitioner and then arguing the case in front of the mock court. This year the teams argued the case McCarthy v. United States, a fictional appeal, to the Supreme Court.
Second-year students Shunta R. Harmon, Leslie B. Horne and Rebecca captured the regional championship and third best brief. Third-year student Stephen A. Shea and second-year students Jennifer S. Blakely and Ellen H. Persons were regional finalists. Serving as coaches were third-year students Cristine L. Patterson and Phillip R. Green, and Holly A. Pierson, Esq., served as advisor.
The ABA competition routinely features approximately 180 teams from across the country participating in regional competitions with only 20 teams advancing to the national tier of the competition each spring. Over the past 10 years, Georgia Law has captured eight ABA regional championships
Using the <i>aa</i> index over the last 14 solar cycles to characterize extreme geomagnetic activity
Geomagnetic indices are routinely used to characterize space weather event intensity. The DST index is well resolved, but is only available over 5 solar cycles. The aa index extends over 14 cycles but is highly discretized with poorly resolved extremes. We parameterize extreme aa activity by the annual averaged top few % of observed values, show these are exponentially distributed and they track annual DST index minima. This gives a 14 cycle average of ~ 4% chance of at least one great (DST nT) storm and ~ 28% chance of at least one severe (DST nT) storm per year. At least one DST=â809 [â663,â955] nT event in a given year would be a 1:151 year event. Carrington event estimate DST ~ â850 nT is within the same distribution as other extreme activity seen in aa since 1868 so that its likelihood can be deduced from that of more moderate events. Events with DST âČ â1000 nT are in a distinct class, requiring special conditions
Estimating Be Star Disk Radii using H-alpha Emission Equivalent Widths
We present numerical models of the circumstellar disks of Be stars, and we
describe the resulting synthetic H-alpha emission lines and maps of the
wavelength-integrated emission flux projected onto the sky. We demonstrate that
there are monotonic relationships between the emission line equivalent width
and the ratio of the angular half-width at half maximum of the projected disk
major axis to the radius of the star. These relationships depend mainly upon
the temperatures of the disk and star, the inclination of the disk normal to
the line of sight, and the adopted outer boundary for the disk radius. We show
that the predicted H-alpha disk radii are consistent with those observed
directly through long baseline interferometry of nearby Be stars (especially
once allowance is made for disk truncation in binaries and for dilution of the
observed H-alpha equivalent width by continuum disk flux in the V-band).Comment: 12 pages, 2 figures, ApJL in pres
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