"Got a Revolution, got to revolution": Student Activism and the Anti-war Movement. An Historical Assessment

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"Got a Revolution, got to revolution": Student Activism and the Anti-war Movement. An Historical Assessment

no abstrac

Particle Acceleration at Ultra-Relativistic Shocks and the Spectra of Relativistic Fireballs

We examine Fermi-type acceleration at relativistic shocks, and distinguish between the initial boost of the first shock crossing cycle, where the energy gain per particle can be very large, and the Fermi process proper with repeated shock crossings, in which the typical energy gain is of order unity. We calculate by means of numerical simulations the spectrum and angular distribution of particles accelerated by this Fermi process, in particular in the case where particle dynamics can be approximated as small-angle scattering. We show that synchrotron emission from electrons or positrons accelerated by this process can account remarkably well for the observed power-law spectra of GRB afterglows and Crab-like supernova remnants. In the context of a decelerating relativistic fireball, we calculate the maximum particle energy attainable by acceleration at the external blast wave, and discuss the minimum energy for this acceleration process and its consequences for the observed spectrum.Comment: To appear in Proceedings of the 5th Huntsville Gamma-Ray Burst Symposium. LaTeX, 6 pages, 2 figures, uses aipproc.sty and epsfi

An eigenfunction method for particle acceleration at ultra-relativistic shocks

We adapt and modify the eigenfunction method of computing the power-law spectrum of particles accelerated at a relativistic shock front via the first-order Fermi process (Kirk, J.G., Schneider, P., Astrophysical Journal 315, 425 (1987)) to apply to shocks of arbitrarily high Lorentz factor. The power-law index of accelerated particles undergoing isotropic small-angle scattering at an ultrarelativistic, unmagnetized shock is found to be s=4.23 +/- 0.2 (where s=d\ln f/ d\ln p, with f the Lorentz-invariant phase-space density and p the momentum), in agreement with the results of Monte-Carlo simulations. We present results for shocks in plasmas with different equations of state and for Lorentz factors ranging from 5 to infinity.Comment: 4 pages, 2 figures, contribution to the Proceedings of the 5th Huntsville GRB Symposiu

Puzzles of the Past: Silences, Omissions and Unexplored Topics in History

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Rate-dependent morphology of Li2O2 growth in Li-O2 batteries

Compact solid discharge products enable energy storage devices with high gravimetric and volumetric energy densities, but solid deposits on active surfaces can disturb charge transport and induce mechanical stress. In this Letter we develop a nanoscale continuum model for the growth of Li2O2 crystals in lithium-oxygen batteries with organic electrolytes, based on a theory of electrochemical non-equilibrium thermodynamics originally applied to Li-ion batteries. As in the case of lithium insertion in phase-separating LiFePO4 nanoparticles, the theory predicts a transition from complex to uniform morphologies of Li2O2 with increasing current. Discrete particle growth at low discharge rates becomes suppressed at high rates, resulting in a film of electronically insulating Li2O2 that limits cell performance. We predict that the transition between these surface growth modes occurs at current densities close to the exchange current density of the cathode reaction, consistent with experimental observations.Comment: 8 pages, 6 fig

Levene (Mark) and Roberts (Penny), (Eds.), The Massacre in History

Massacres are everywhere. At least that is the impression one could get from recent newspaper headlines like : « Massacre at Columbine High School ». « Jaguars massacre Dolphins ». « Massacre in Yugoslavia ». From a shooting by some disgruntled teenagers to sports, like the devastating defeat meted out to the Miami Dolphins by the Jacksonville Jaguars, to the annihilation of a village in the Balkans, massacres seem to be all around us. A search of the word « massacre » on the Internet produce..