This paper presents a continuation of our efforts to numerically study accretion disks that are misaligned (tilted) with respect to the rotation axis of a Kerr black hole. Here we present results of a global numerical simulation which fully incorporates the effects of the black hole spacetime as well as magnetorotational turbulence that is the primary source of angular momentum transport in the flow. This simulation shows dramatic differences from comparable simulations of untilted disks. Accretion onto the hole occurs predominantly through two opposing plunging streams that start from high latitudes with respect to both the black-hole and disk midplanes. This is due to the aspherical nature of the gravitational spacetime around the rotating black hole. These plunging streams start from a larger radius than would be expected for an untilted disk. In this regard the tilted black hole effectively acts like an untilted black hole of lesser spin. Throughout the duration of the simulation, the main body of the disk remains tilted with respect to the symmetry plane of the black hole; thus there is no indication of a Bardeen-Petterson effect in the disk at large. The torque of the black hole instead principally causes a global precession of the main disk body. In this simulation the precession has a frequency of 3(M ⊙ /M ) Hz, a value consistent with many observed low-frequency quasi-periodic oscillations. However, this value is strongly dependent on the size of the disk, so this frequency may be expected to vary over a large range.

Ignition is needed to make fusion energy a viable alternative energy source, but has yet to be achieved. A key step on the way to ignition is to have the energy generated through fusion reactions in an inertially confined fusion plasma exceed the amount of energy deposited into the deuterium-tritium fusion fuel and hotspot during the implosion process, resulting in a fuel gain greater than unity. Here we report the achievement of fusion fuel gains exceeding unity on the US National Ignition Facility using a 'high-foot' implosion method, which is a manipulation of the laser pulse shape in a way that reduces instability in the implosion. These experiments show an order-of-magnitude improvement in yield performance over past deuterium-tritium implosion experiments. We also see a significant contribution to the yield from α-particle self-heating and evidence for the 'bootstrapping' required to accelerate the deuterium-tritium fusion burn to eventually 'run away' and ignite.

Point design targets have been specified for the initial ignition campaign on the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 443, 2841 (2004)]. The targets contain D-T fusion fuel in an ablator of either CH with Ge doping, or Be with Cu. These shells are imploded in a U or Au hohlraum with a peak radiation temperature set between 270 and 300 eV. Considerations determining the point design include laser-plasma interactions, hydrodynamic instabilities, laser operations, and target fabrication. Simulations were used to evaluate choices, and to define requirements and specifications. Simulation techniques and their experimental validation are summarized. Simulations were used to estimate the sensitivity of target performance to uncertainties and variations in experimental conditions. A formalism is described that evaluates margin for ignition, summarized in a parameter the Ignition Threshold Factor (ITF). Uncertainty and shot-to-shot variability in ITF are evaluated, and sensitivity of the margin to characteristics of the experiment. The formalism is used to estimate probability of ignition. The ignition experiment will be preceded with an experimental campaign that determines features of the design that cannot be defined with simulations alone. The requirements for this campaign are summarized. Requirements are summarized for the laser and target fabrication.

Abstract. Using hydrodynamic computer codes, we study the possible patterns of relativistic expansion of an enormous pair-electromagnetic-pulse (P.E.M. pulse); a hot, high density plasma composed of photons, electronpositron pairs and baryons deposited near a charged black hole (EMBH). On the bases of baryon-loading and energy conservation, we study the bulk Lorentz factor of expansion of the P.E.M. pulse by both numerical and analytical methods.Key words: black hole physics -gamma-ray bursts, theory, observationsIn the paper by Preparata et al. (1998), the "dyadosphere" is defined as the region outside the horizon of a EMBH where the electric field exceeds the critical value for e + e − pair production. In Reissner-Nordstrom EMBHs, the horizon radius is expressed asThe outer limit of the dyadosphere is defined as the radius r ds at which the electric field of the EMBH equals this critical fieldThe total energy of pairs, converted from the static electric energy, deposited within a dyadosphere is thenIn Wilson (1975Wilson ( , 1977 a black hole charge of the order 10% was formed. Thus, we henceforth assume a black hole charge Q = 0.1Q max , Q max = √ GM for our detailed numerical calculations. The range of energy is of interest as a possible gamma-ray burst source. In order to model the radially resolved evolution of the energy deposited within the e + e − -pair and photon plasma fluid created in the dyadosphere of EMBH, we need to discuss the relativistic hydrodynamic equations describing such evolution.The metric for a Reissner-Nordstrom black hole iswhereWe assume the plasma fluid of e + e − -pairs, photons and baryons to be a simple perfect fluid in the curved spacetime (Eq. (4)). The stress-energy tensor describing such a fluid is given by (Misner et al. 1975)where ρ and p are respectively the total proper energy density and pressure in the comoving frame. The U µ is the four-velocity of the plasma fluid. The baryon-number and energy-momentum conservation laws arewhere n B is the baryon-number density. The radial component of Eq. (7) reduces to ∂p ∂rThe component of the energy-momentum conservation Eq. (7) Equations (6) and (9) give rise to the relativistic hydrodynamic equations.

We numerically compute light and polarization curves of γ‐ray burst (GRB) afterglows for various configurations of the jet luminosity structure and for different dynamical evolutions. We especially consider the standard homogeneous ‘top hat’ jet and the ‘universal structured jet’ with power‐law wings. We also investigate a possible, more physical variation of the ‘top hat’ model: the ‘Gaussian jet’. The polarization curves for the last two jet types are shown here for the first time together with the computation of X‐ray and radio polarized fluxes. We show that the light curves of the total flux from these configurations are very similar to each other, and therefore only very high quality data could allow us to pin down the underlying jet structure. We demonstrate instead that polarization curves are a powerful means to solve the jet structure, since the predicted behaviour of polarization and its position angle at times around the jet break are very different, if not opposite. We conclude that the afterglow polarization measurements provide clear footprints of any outflow energy distribution (unlike the light curves of the total flux) and the joint analysis of the total and polarized flux should reveal the jet structure of GRBs.