8,089 research outputs found
The energy partitioning of non-thermal particles in a plasma: or the Coulomb logarithm revisited
The charged particle stopping power in a highly ionized and weakly to
moderately coupled plasma has been calculated to leading and next-to-leading
order by Brown, Preston, and Singleton (BPS). After reviewing the main ideas
behind this calculation, we use a Fokker-Planck equation derived by BPS to
compute the electron-ion energy partitioning of a charged particle traversing a
plasma. The motivation for this application is ignition for inertial
confinement fusion -- more energy delivered to the ions means a better chance
of ignition, and conversely. It is therefore important to calculate the
fractional energy loss to electrons and ions as accurately as possible, as this
could have implications for the Laser Megajoule (LMJ) facility in France and
the National Ignition Facility (NIF) in the United States. The traditional
method by which one calculates the electron-ion energy splitting of a charged
particle traversing a plasma involves integrating the stopping power dE/dx.
However, as the charged particle slows down and becomes thermalized into the
background plasma, this method of calculating the electron-ion energy splitting
breaks down. As a result, the method suffers a systematic error of order T/E0,
where T is the plasma temperature and E0 is the initial energy of the charged
particle. In the case of DT fusion, for example, this can lead to uncertainties
as high as 10% or so. The formalism presented here is designed to account for
the thermalization process, and in contrast, it provides results that are
near-exact.Comment: 10 pages, 3 figures, invited talk at the 35th European Physical
Society meeting on plasma physic
Calculating the Charged Particle Stopping Power Exactly to Leading and Next-to-leading Order
I will discuss a new method for calculating transport quantities, such as the
charged particle stopping power, in a weakly to moderately coupled plasma. This
method, called dimensional continuation, lies within the framework of
convergent kinetic equations, and it is powerful enough to allow for systematic
perturbative expansions in the plasma coupling constant. In particular, it
provides an exact evaluation of the stopping power to leading and
next-to-leading order in the plasma coupling, with the systematic error being
of cubic order. Consequently, the calculation is near-exact for a weakly
coupled plasma, and quite accurate for a moderately coupled plasma. The leading
order term in this expansion has been known since the classic work of Spitzer.
In contrast, the next-to-leading order term has been calculated only recently
by Brown, Preston, and Singleton (BPS), using the aforementioned method, to
account for all short- and long-distance physics accurate to second order in
the plasma coupling, including an exact treatment of the quantum-to-classical
scattering transition. Preliminary numerical studies suggest that the BPS
stopping power increases the ignition threshold, thereby having potential
adverse implications for upcoming high energy density facilities. Since the key
ideas behind the BPS calculation are possibly unfamiliar to plasma physicists,
and the implications might be important, I will use this opportunity to explain
the method in a pedagogical fashion.Comment: 4 pages, proceedings for the 5th International Conference on Inertial
Fusion Science and Applications (IFSA-07), Kobe, Japan, 9-14 September 200
Analysis of dynamic stall using unsteady boundary-layer theory
The unsteady turbulent boundary layer and potential flow about a pitching airfoil are analyzed using numerical methods to determine the effect of pitch rate on the delay in forward movement of the rear flow reversal point. An explicit finite difference scheme is used to integrate the unsteady boundary layer equations, which are coupled at each instant of time to a fully unsteady and nonlinear potential flow analysis. A substantial delay in forward movement of the reversal point is demonstrated with increasing pitch rate, and it is shown that the delay results partly from the alleviation of the gradients in the potential flow, and partly from the effects of unsteadiness in the boundary layer itself. The predicted delay in flow-reversal onset, and its variation with pitch rate, are shown to be in reasonable agreement with experimental data relating to the delay in dynamic stall. From the comparisons it can be concluded (a) that the effects of time-dependence are sufficient to explain the failure of the boundary layer to separate during the dynamic overshoot, and (b) that there may be some link between forward movement of the reversal point and dynamic stall
Ascent from the lunar surface
Ascent from lunar surface problem with solution by variational calculu
Studies of vertical wind profiles at Cape Kennedy, Florida Final report
Vertical wind profiles spectral analysis and numerical wind forecasts at Cape Kenned
THE PROSPECTS AND ASSOCIATED CHALLENGES FOR THE BIOLOGICAL CONTROL OF RODENTS
Biological control using macro- or micro-parasites is a promising research area for control of rodents. The largest impediment to progress is a dearth of high quality research, under field conditions, on wild rodents and their diseases. A major challenge is to identify a candidate control agent which is sufficiently pathogenic, has a high transmission rate and is target specific. Once this has been done, ecological studies of both the host and the disease agent, and of the epidemiology of transmission, are required. Whether the desired pathogenicity is via increased mortality and/or reduced fertility will depend on the agent and on the dynamics of the pest species in particular agricultural systems. Overall, the best prospects for the biological control of rodents lies with agents that reduce fertility rather than increase mortality. The development of immuno-contraception using a virus as a vector is proffered as the most promising generic approach for the biological control of rodent pests
Unocal Corp. v. Mesa Petroleum Co., 493 A.2d 946 (Del. 1985)
Corporate Law-CORPORATIONS MAY EXCLUDE RAIDERS FROM DEFENSIVE SELF-TENDER OFFERS IN WARDING OFF HOSTILE TAKEOVER
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