Charged Particle Motion in a Highly Ionized Plasma

A recently introduced method utilizing dimensional continuation is employed to compute the energy loss rate for a non-relativistic particle moving through a highly ionized plasma. No restriction is made on the charge, mass, or speed of this particle. It is, however, assumed that the plasma is not strongly coupled in the sense that the dimensionless plasma coupling parameter g=e^2\kappa_D/ 4\pi T is small, where \kappa_D is the Debye wave number of the plasma. To leading and next-to-leading order in this coupling, dE/dx is of the generic form g^2 \ln[C g^2]. The precise numerical coefficient out in front of the logarithm is well known. We compute the constant C under the logarithm exactly for arbitrary particle speeds. Our exact results differ from approximations given in the literature. The differences are in the range of 20% for cases relevant to inertial confinement fusion experiments. The same method is also employed to compute the rate of momentum loss for a projectile moving in a plasma, and the rate at which two plasmas at different temperatures come into thermal equilibrium. Again these calculations are done precisely to the order given above. The loss rates of energy and momentum uniquely define a Fokker-Planck equation that describes particle motion in the plasma. The coefficients determined in this way are thus well-defined, contain no arbitrary parameters or cutoffs, and are accurate to the order described. This Fokker-Planck equation describes the longitudinal straggling and the transverse diffusion of a beam of particles. It should be emphasized that our work does not involve a model, but rather it is a precisely defined evaluation of the leading terms in a well-defined perturbation theory.Comment: Comments: Published in Phys. Rep. 410/4 (2005) 237; RevTeX, 111 Pages, 17 Figures; Transcription error corrected in temperature equilibration rate (3.61) and (12.44) which replaces \gamma-2 by \gamma-

Kinetics of solid-solid phase transformations in shock waves

This research is focused on the development of a microstructural model for phase transformation kinetics in shock waves. It is assumed that the Hugoniot state lies in the region of metastability around an equilibrium solid‑solid phase boundary, hence this model applies to transformations occurring through nucleation and growth. The model accounts for both homogeneous (thermally driven) and heterogeneous (catalyzed by crystal defects) nucleation in the shock front, the subsequent growth of the nuclei, and their eventual coalescence. The spatiotemporal dependence of the volume fraction is calculated using KJMA kinetic theory. An explicit expression for the interphase interface speed, which appears in the Avrami equation, is provided by a phase field model [1]; the thermodynamic driving force for interface propagation includes the free energy difference of the phases, the transformation work, and an athermal threshold associated with crystal defects [2]. The transformation work accounts for shear stresses due to the shock wave as well as residuals associated with the two-phase microstructure. The plastic constitutive relation of the two-phase material, which is computed using the KJMA-based volume fraction and now standard results from the literature (Crisfield, Eshelby, and Hill), and the heat transport equation are coupled to the thermoelastic equations. The solution of this coupled set of equations yields a nonsteady, two-wave shock profile. We relate the evolution of this shock profile to the nucleation rate and interface speed. Several examples of shock-induced microstructure evolution are presented. REFERENCES [1] Levitas, V.I., Preston, D.L. Phys. Rev. B. 2002, 66, 134206, 134207. [2] Levitas, V.I., Lee, D.-W., Preston, D.L. 2010. Int. J. Plasticity. 2010, 26, 395

Identification of Three Required Positive Cis-Regulated Inputs of the Sea Urchin Pigment Cell Gene Polyketide Synthase 1

Sea urchin pigment cells are single cells of mesodermal origin embedded in the aboral ectoderm. Strongylocentrotus purpuratus polyketide synthase 1 (Sp-PKS1) is required for the biosynthesis of the echinochrome pigment. Evidence suggests that pigment cells are immune cells. In order to reconstruct the gene regulatory network of pigment cells a bottom-up approach combined with comparative genomics has been used in this study. We compared the cis-regulatory regions of five pigment cell genes, Sp-Pks1, flavin monooxygenase 1, 2, and 3 (Sp-Fmo) and sulfotransferase (Sp-Sult), across three different species, Strongylocentrotus purpuratus, Mesocentrotus franciscanus, and Strongylocentrotus fragilis. The computational tool used was multiple expectation maximization motif elicitation analysis. Thirty cis-regulatory motif candidates were identified, three of which were considered for further analysis. The functionality of these motifs was tested by injecting embryos with a -2KbPks-Gfp DNA construct having one of the three motifs mutagenized. All three motifs resulted to be functional cis-regulatory sequences. Specifically, they contained DNA-binding sites for transcriptional activators of Sp-Pks1

Rigorous theory of nuclear fusion rates in a plasma

Real-time thermal field theory is used to reveal the structure of plasma corrections to nuclear reactions. Previous results are recovered in a fashion that clarifies their nature, and new extensions are made. Brown and Yaffe have introduced the methods of effective quantum field theory into plasma physics. They are used here to treat the interesting limiting case of dilute but very highly charged particles reacting in a dilute, one-component plasma. The highly charged particles are very strongly coupled to this background plasma. The effective field theory proves that this mean field solution plus the one-loop term dominate; higher loop corrections are negligible even though the problem involves strong coupling. Such analytic results for very strong coupling are rarely available, and they can serve as benchmarks for testing computer models.Comment: 4 pages and 2 figures, presented at SCCS 2005, June 20-25, Moscow, Russi

Shell model Monte Carlo calculations for Dy-170

We present the first auxiliary field Monte Carlo calculations for a rare earth nucleus, Dy-170. A pairing plus quadrupole Hamiltonian is used to demonstrate the physical properties that can be studied in this region. We calculate various static observables for both uncranked and cranked systems and show how the shape distribution evolves with temperature. We also introduce a discretization of the path integral that allows a more efficient Monte Carlo sampling.Comment: 11 pages, figures available upon request, Caltech Preprint No. MAP-16