3,049 research outputs found
Evaluating Trade Developments in Dairy Products
Replaced with revised version of paper 02/11/04.International Relations/Trade,
Inverse Bremsstrahlung in Shocked Astrophysical Plasmas
There has recently been interest in the role of inverse bremsstrahlung, the
emission of photons by fast suprathermal ions in collisions with ambient
electrons possessing relatively low velocities, in tenuous plasmas in various
astrophysical contexts. This follows a long hiatus in the application of
suprathermal ion bremsstrahlung to astrophysical models since the early 1970s.
The potential importance of inverse bremsstrahlung relative to normal
bremsstrahlung, i.e. where ions are at rest, hinges upon the underlying
velocity distributions of the interacting species. In this paper, we identify
the conditions under which the inverse bremsstrahlung emissivity is significant
relative to that for normal bremsstrahlung in shocked astrophysical plasmas. We
determine that, since both observational and theoretical evidence favors
electron temperatures almost comparable to, and certainly not very deficient
relative to proton temperatures in shocked plasmas, these environments
generally render inverse bremsstrahlung at best a minor contributor to the
overall emission. Hence inverse bremsstrahlung can be safely neglected in most
models invoking shock acceleration in discrete sources such as supernova
remnants. However, on scales > 100pc distant from these sources, Coulomb
collisional losses can deplete the cosmic ray electrons, rendering inverse
bremsstrahlung, and perhaps bremsstrahlung from knock-on electrons, possibly
detectable.Comment: 13 pages, including 2 figures, using apjgalley format; to appear in
the January 10, 2000 issue, of the Astrophysical Journa
What\u27s on First?: Organizing the Casebook and Molding the Mind
This study empirically tests the proposition that law students adopt different conceptions of the judge’s role in adjudication based on whether they first study intentional torts, negligence, or strict liability. The authors conducted an anonymous survey of more than 450 students enrolled in eight law schools at the beginning, mid-point, and end of the first semester of law school. The students were prompted to indicate to what extent they believed the judge’s role to be one of rule application and, conversely, to what extent it was one of considering social, economic, and ideological factors. The survey found that while all three groups of students shifted toward a belief that judges consider social, economic, and ideological factors, the degree of the shift differed in a statistically significant way depending on which torts their professors taught first. These differences persisted throughout the semester, even after they studied other torts. Further, these differences were observed even when the analysis controlled for law school ranking and were more pronounced among students attending the highest ranked schools.
In interpreting the survey results, the authors employ sociologist Erving Goffman’s theory of “frame analysis” and the work of cognitive psychologists including Amos Tversky and Daniel Kahneman on “anchoring.” The Article concludes that the category of tort liability to which students are first exposed affects the “frame” or “lens” through which they view the judicial process. This frame becomes anchored and persists throughout the study of other tort categories. The lessons about the nature of the judging process learned implicitly through the professor’s choice of topic sequence may be even more important than the substantive topics themselves
Keeping Cases from Black Juries: An Empirical Analysis of How Race, Income Inequality, and Regional History Affect Tort Law
This Article presents an empirical analysis of how race, income inequality, the regional history of the South, and state politics affect the development of tort law. Beginning in the mid-1960s, most state appellate courts rejected doctrines such as contributory negligence that traditionally prevented plaintiffs’ cases from reaching the jury. We examine why some, mostly Southern states did not join this trend.
To enable cross-state comparisons, we design an innovative Jury Access Denial Index (JADI) that quantifies the extent to which each state’s tort doctrines enable judges to dismiss cases before they reach the jury. We then conduct a multivariate analysis that finds strong correlations between a state’s JADI and two factors: (1) the percentage of African Americans in its largest cities, and (2) its history as a former slave-holding state.
These findings suggest that some appellate courts, particularly those in the South, afraid that juries with substantial African-American representation would redistribute wealth or retaliate for grievances, struck preemptively to prevent cases from reaching them. Surprisingly, we do not find a consistent association between a state’s JADI and either income inequality or its political leanings. In other words, race and region, rather than economic class or politics, explain the failure to embrace pro-plaintiff changes that occurred elsewhere.
We suggest, therefore, that states that declined to discard antiquated anti-jury substantive doctrines between the mid-1960s and the mid-1980s should acknowledge that these precedents were tainted by their predecessors’ efforts to keep tort cases from African-American jurors and refuse to accord them deference
Direct Acceleration of Pickup Ions at The Solar Wind Termination Shock: The Production of Anomalous Cosmic Rays
We have modeled the injection and acceleration of pickup ions at the solar wind termination shock and investigated the parameters needed to produce the observed Anomalous Cosmic Ray (ACR) fluxes. A non-linear Monte Carlo technique was employed, which in effect solves the Boltzmann equation and is not restricted to near-isotropic particle distribution functions. This technique models the injection of thermal and pickup ions, the acceleration of these ions, and the determination of the shock structure under the influence of the accelerated ions. The essential effects of injection are treated in a mostly self-consistent manner, including effects from shock obliquity, cross- field diffusion, and pitch-angle scattering. Using recent determinations of pickup ion densities, we are able to match the absolute flux of hydrogen in the ACRs by assuming that pickup ion scattering mean free paths, at the termination shock, are much less than an AU and that modestly strong cross-field diffusion occurs. Simultaneously, we match the flux ratios He(+)/H(+) or O(+)/H(+) to within a factor approx. 5. If the conditions of strong scattering apply, no pre-termination-shock injection phase is required and the injection and acceleration of pickup ions at the termination shock is totally analogous to the injection and acceleration of ions at highly oblique interplanetary shocks recently observed by the Ulysses spacecraft. The fact that ACR fluxes can be modeled with standard shock assumptions suggests that the much-discussed "injection problem" for highly oblique shocks stems from incomplete (either mathematical or computer) modeling of these shocks rather than from any actual difficulty shocks may have in injecting and accelerating thermal or quasi-thermal particles
Non-linear Particle Acceleration in Oblique Shocks
We have developed a Monte Carlo technique for self-consistently calculating
the hydrodynamic structure of oblique, steady-state shocks, together with the
first-order Fermi acceleration process and associated non-thermal particle
distributions. This is the first internally consistent treatment of modified
shocks that includes cross-field diffusion of particles. Our method overcomes
the injection problem faced by analytic descriptions of shock acceleration, and
the lack of adequate dynamic range and artificial suppression of cross-field
diffusion faced by plasma simulations; it currently provides the most broad and
versatile description of collisionless shocks undergoing efficient particle
acceleration. We present solutions for plasma quantities and particle
distributions upstream and downstream of shocks, illustrating the strong
differences observed between non-linear and test-particle cases. It is found
that there are only marginal differences in the injection efficiency and
resultant spectra for two extreme scattering modes, namely large-angle
scattering and pitch-angle diffusion, for a wide range of shock parameters,
i.e., for subluminal shocks with field obliquities less than or equal to 75
degrees and de Hoffmann-Teller frame speeds much less than the speed of light.Comment: 38 pages, 15 figures, AASTeX format, to appear in the Astrophysical
Journal, December 20, 199
Magnetohydrodynamic Jump Conditions for Oblique Relativistic Shocks with Gyrotropic Pressure
Shock jump conditions are obtained for steady-state, plane shocks with
oblique magnetic fields and arbitrary flow speeds. For ultrarelativistic and
nonrelativistic shocks, the jump conditions may be solved analytically. For
mildly relativistic shocks, analytic solutions are obtained for isotropic
pressure using an approximation for the adiabatic index that is valid in high
sonic Mach number cases. In the more general case of gyrotropic pressure, the
jump conditions cannot be solved analytically without additional assumptions,
and the effects of gyrotropic pressure are investigated by parameterizing the
distribution of pressure parallel and perpendicular to the magnetic field. Our
numerical solutions reveal that relatively small departures from isotropy
(e.g., about 20%) produce significant changes in the shock compression ratio,
r, at all shock Lorentz factors, including ultrarelativistic ones, where an
analytic solution with gyrotropic pressure is obtained. In particular, either
dynamically important fields or significant pressure anisotropies can incur
marked departures from the canonical gas dynamic value of r=3 for a shocked
ultrarelativistic flow and this may impact models of particle acceleration in
gamma-ray bursts and other environments where relativistic shocks are inferred.
The jump conditions presented apply directly to test-particle acceleration, and
will facilitate future self-consistent numerical modeling of particle
acceleration at oblique, relativistic shocks.Comment: 26 pages with 7 figures, submitted to Ap. J. April 200
Ozone Response to Aircraft Emissions: Sensitivity Studies with Two-dimensional Models
Our first intercomparison/assessment of the effects of a proposed high-speed civil transport (HSCT) fleet on the stratosphere is presented. These model calculations should be considered more as sensitivity studies, primarily designed to serve the following purposes: (1) to allow for intercomparison of model predictions; (2) to focus on the range of fleet operations and engine specifications giving minimal environmental impact; and (3) to provide the basis for future assessment studies. The basic scenarios were chosen to be as realistic as possible, using the information available on anticipated developments in technology. They are not to be interpreted as a commitment or goal for environmental acceptability
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