184 research outputs found
The collapse of the local, Spitzer-Haerm formulation and a global-local generalization for heat flow in an inhomogeneous, fully ionized plasma
The breakdown of the classical (CBES) field aligned transport relations for electrons in an inhomogeneous, fully ionized plasma as a mathematical issue of radius of convergence is addressed, the finite Knudsen number conditions when CBES results are accurate is presented and a global-local (GL) way to describe the results of Coulomb physics moderated conduction that is more nearly appropriate for astrophysical plasmas are defined. This paper shows the relationship to and points of departure of the present work from the CBES approach. The CBES heat law in current use is shown to be an especially restrictive special case of the new, more general GL result. A preliminary evaluation of the dimensionless heat function, using analytic formulas, shows that the dimensionless heat function profiles versus density of the type necessary for a conduction supported high speed solar wind appear possible
Stellar winds driven by Alfven waves
Models of stellar winds were considered in which the dynamic expansion of a corona is driven by Alfven waves propagating outward along radial magnetic field lines. In the presence of Alfven waves, a coronal expansion can exist for a broad range of reference conditions which would, in the absence of waves, lead to static configurations. Wind models in which the acceleration mechanism is due to Alfven waves alone and exhibit lower mass fluxes and higher energies per particle are compared to wind models in which the acceleration is due to thermal processes. For example, winds driven by Alfven waves exhibit streaming velocities at infinity which may vary between the escape velocity at the coronal base and the geometrical mean of the escape velocity and the speed of light. Upper and lower limits were derived for the allowed energy fluxes and mass fluxes associated with these winds
A theory of local and global processes which affect solar wind electrons. 2: Experimental support
The microscopic characteristics of the Coulomb cross section show that there are three natural subpopulations for plasma electrons: the subthermals with local kinetic energy E kT sub c; the transthermals with kT sub c E 7 kT sub c and the extrathermals E 7 kT sub c. Data from three experimental groups on three different spacecraft in the interplanetary medium over a radial range are presented to support the five interrelations projected between solar wind electron properties and changes in the interplanetary medium: (1) subthermals respond primarily to local changes (compression and rarefactions) in stream dynamics; (2) the extrathermal fraction of the ambient electron density should be anti-correlated with the asymptotic bulk speed; (3) the extrathermal "temperature" should be anti-correlated with the local wind speed at 1 AU; (4) the heat flux carried by electrons should be anti-correlated with the local bulk speed; and (5) the extrathermal differential 'temperature' should be nearly independent of radius within 1 AU
The Creation and Propagation of Radiation: Fields Inside and Outside of Sources
We present a new algorithm for computing the electromagnetic fields of
currents inside and outside of finite current sources, for arbitrary time
variations in the currents. Unexpectedly, we find that our solutions for these
fields are free of the concepts of differential calculus, in that our solutions
only involve the currents and their time integrals, and do not involve the time
derivatives of the currents. As examples, we give the solutions for two
configurations of current: a planar solenoid and a rotating spherical shell
carrying a uniform charge density. For slow time variations in the currents, we
show that our general solutions reduce to the standard expressions for the
fields in classic magnetic dipole radiation. In the limit of extremely fast
turn-on of the currents, we show that for our general solutions the amount of
energy radiated is exactly equal to the magnetic energy stored in the static
fields a long time after current creation. We give three associated problem
statements which can be used in courses at the undergraduate level, and one
problem statement suitable for courses at the graduate level. These problems
are of physical interest because: (1) they show that current systems of finite
extent can radiate even during time intervals when the currents are constant;
(2) they explicitly display transit time delays across a source associated with
its finite dimensions; and (3) they allow students to see directly the origin
of the reaction forces for time-varying systemsComment: 25 pages, 5 figure
How does private firm disclosure affect demand for public firm equity? Evidence from the global equity market
We investigate the relationship between private firms’ disclosures and the demand for the equity of their publicly traded peers. Using data on the global movement of portfolio investments in public equity, we find that a 10% increase in private firm disclosure transparency – proxied by the number of disclosed private firms’ financial statement line items – reduces global investors’ demand for public equity by 4.3% or $358 million per investee country-industry. These findings are consistent with private firm disclosures generating negative pecuniary externalities – global investors reallocate their capital away from public firms to more transparent private firms – and less consistent with these disclosures creating positive information externalities that would benefit public firms. Consistent with this interpretation, we find that the reduction in demand for public equity is offset by a comparable increase in capital allocation to more transparent private firms. Using a simulated instruments approach and the staggered implementations of electronic business registers in investee countries in Europe as plausibly exogenous shocks to private firm transparency, we conclude that the negative relationship between private firm disclosures and public equity demand is likely causa
TOT Approach in stress urinary incontinence (SUI) – outcome in obese female
BACKGROUND: Only limited data are available on the outcome of tension-free obturator tape (TOT) procedures in overweight and obese women. We would like to verify the objective and subjective outcomes of TOT in women with a higher body mass index (BMI). METHODS: We evaluated the records of 116 patients who had undergone TOT, stratifying by BMI into normal weight (n = 31), overweight (n = 56), and obese (n = 29) groups. We compared pre- and postoperative evaluations, including subjective and objective outcome of TOT, complications, and quality of life assessed by validated questionnaires (ICIQ-SF and KHQ). RESULTS: The median follow-up was 21 months. There were no significant differences between different groups in terms of objective cure rate and subjective success, quality of life scores and postoperative complications. CONCLUSIONS: Our data demonstrate that TOT procedure is safe and effective. BMI did not influence the outcome of TOT procedures at a median of 21 months after surgery and represents no contraindication for continence surgery. The success of the outcome of TOT procedure in females and the occurrence of complications are not negatively affected by obesity
Librational motion of CO in solid Ar: Raman and IR spectra and quantum simulations
Rovibrational Raman spectra of CO molecules isolated in solid Ar were measured for the 9–30 K temperature
range and compared to past and present IR spectra. The fundamental band appears as a triplet-split structure,
where the center peak shows completely different response to temperature in the Raman and IR spectroscopies.
The peak is sharp and stable in Raman but reversibly broadens beyond recognition in IR upon annealing. The
red-shifted, intense line of the triplet is found thermally inert similarly in both spectroscopies. The third line is
the weakest, and as concentration dependent, it is assigned to a dimer as before. The CO–H₂O impurity complex
is identified as a side band. We employ crystal field and quantum chemical modeling to interpret the disparity
between the spectroscopies. The stable and broadening lines are given assignments to double- and singlesubstitution
sites, respectively. Thermal excitations are not effective in the former case of angularly tightconfined,
deep potential well. In the single-substitutional case, the librational level structure shows up in discriminating
between the Raman and IR selection rules. An effectively ΔJ = 0 totally symmetric transition is found
for Raman that is uncoupled from lattice phonons and corresponding broadening mechanisms. The low-temperature
limit necessitates the use of a fixed lattice approach while the warmer end of the range is best described
with an adiabatic, pseudorotating lattice approach
A Bow Shock Nebula Around a Compact X-Ray Source in the Supernova Remnant IC443
We present spectra and high resolution images of the hard X-ray feature along
the southern edge of the supernova remnant IC443. Data from the Chandra X-ray
Observatory reveal a comet-shaped nebula of hard emission, which contains a
softer point source at its apex. We also present 20cm, 6cm, and 3.5cm images
from the Very Large Array that clearly show the cometary nebula. Based on the
radio and X-ray morphology and spectrum, and the radio polarization properties,
we argue that this object is a synchrotron nebula powered by the compact source
that is physically associated with IC443. The spectrum of the soft point source
is adequately but not uniquely fit by a black body model (kT=0.71 +/- 0.08 keV,
L=(6.5 +/- 0.9) * 10^31 erg/s). The cometary morphology of the nebula is the
result of the supersonic motion of the neutron star (V_NS=250 +/- 50 km/s),
which causes the relativistic wind of the pulsar to terminate in a bow shock
and trail behind as a synchrotron tail. This velocity is consistent with an age
of 30,000 years for the SNR and its associated neutron star.Comment: 9 pages, 5 figures, accepted for publication in the ApJ Letter
Non-Maxwellian electron distributions in clusters of galaxies
Thermal X-ray spectra of clusters of galaxies and other sources are commonly
calculated assuming Maxwellian electron distributions. There are situations
where this approximation is not valid, for instance near interfaces of hot and
cold gas and near shocks. The presence of non-thermal electrons affects the
X-ray spectrum. To study the role of these electrons in clusters and other
environments, an efficient algorithm to calculate the X-ray spectra is needed.
We approximate an arbitrary electron distribution by the sum of Maxwellian
components. The decomposition is done using either a genetic algorithm or an
analytical approximation. The X-ray spectrum is then evaluated using a linear
combination of those Maxwellian components. Our method is fast and leads to an
accurate evaluation of the spectrum. The use of Maxwellian components allows to
use the standard collisional rates that are available in plasma codes such as
SPEX. We give an example of a spectrum for the supra-thermal electron
distribution behind a shock in a cluster of galaxies. The relative intensities
of the satellite lines in such a spectrum are sensitive to the presence of the
supra-thermal electrons. These lines can only be investigated with high
spectral resolution. We show that the instruments on future missions like
Astro-H and IXO will be able to demonstrate the presence or absence of these
supra-thermal electrons.Comment: 6 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics, main journa
Mixed-Morphology Supernova Remnants in X-rays: Isothermal Plasma in HB21 and Probable Oxygen-Rich Ejecta in CTB 1
(Abridged) We present an analysis of X-ray observations made of the Galactic
supernova remnants (SNRs) HB21 (G89.0+4.7) and CTB 1 (G116.9+0.2), two
well-known mixed-morphology (MM) SNRs. We find a marked contrast between the
X-ray properties of these SNRs: for HB21, the extracted ASCA spectra of the
northwest and southeast regions of the X-ray emitting plasma can be fit with a
single thermal model with marginally enhanced silicon and sulfur abundances.
For both of these regions, the derived column density and temperature are
N_H~0.3x10^22 cm^-2 and kT~0.7 keV, respectively. No significant spatial
differences in temperature or elemental abundances between the two regions are
detected and the X-ray-emitting plasma in both regions is close to ionization
equilibrium. Our Chandra spectral analysis of CTB 1 reveals that this source is
likely an oxygen-rich SNR with enhanced abundances of oxygen and neon. The
extracted ASCA spectra for the southwestern and northeastern regions of CTB 1
cannot be fit with a single thermal component. Based on our fits to these
spectra, we derive a column density N_H~0.6x10^22 cm^-2 and a temperature for
the soft thermal component of kT_soft~0.28 keV. The hard emission from the
southwest may be modeled with either a thermal component (kT_hard~3 keV) or by
a power law component (Gamma~2-3) while the hard emission from the northeast
may be modeled with a power law component (Gamma~1.4). We have also extracted
ASCA GIS spectra of the discrete X-ray source 1WGA J0001.4+6229 which is seen
in projection toward CTB 1. These spectra are best fit using a power-law model
with a photon index Gamma=2.2^{+0.5}_{-1.2} which is typical for featureless
power-law continua produced by rotation-powered pulsars. This source may be a
neutron star associated with CTB 1.Comment: 46 pages, 16 figures, accepted for publication in the Astronomical
Journa
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