119104483
Relativistic MHD winds from rotating neutron stars
Abstract We review here recent numerical results concerning the acceleration and collimation of relativistic outflows from neutron stars, and we discuss their implications for models of magnetars in their hypothesized initial high rotation states. New results with different injection conditions and extending to much larger distance from the central star are also presented and discussed, showing that, only in the case of weakly magnetized winds, collimated outflows are indeed possible. We finally comment on the possibility that newly born magnetars might trigger GRBs, and we show that numerical results do not support such hypothesis.
119238458
RADIATION PRESSURE FROM MASSIVE STAR CLUSTERS AS A LAUNCHING MECHANISM FOR SUPER-GALACTIC WINDS
Galactic outflows of cool (~104 K) gas are ubiquitous in local starburst galaxies and in most high-redshift galaxies. Hot gas from supernovae has long been suspected as the primary driver, but this mechanism suffers from its tendency to destroy the cool gas. We propose a modification of the supernova scenario that overcomes this difficulty. Star formation is observed to take place in clusters. We show that, for L galaxies, the radiation pressure from clusters with M cl 106 M ☉ is able to expel the surrounding gas at velocities in excess of the circular velocity vc of the disk galaxy. This cool gas travels above the galactic disk before supernovae erupt in the driving cluster. Once above the disk, the cool outflowing gas is exposed to radiation and hot gas outflows from the galactic disk, which in combination drive it to distances of ~50 kpc. Because the radiatively driven clouds grow in size as they travel, and because the hot gas is more dilute at large distance, the clouds are less subject to destruction. Therefore, unlike wind-driven clouds, radiatively driven clouds can give rise to the metal absorbers seen in quasar spectra. We identify these cluster-driven winds with large-scale galactic outflows. The maximum cluster mass in a galaxy is an increasing function of the galaxy's gas surface density, so only starburst galaxies are able to drive cold outflows. We find the critical star formation rate for launching large-scale cool outflows to be , in good agreement with observations.
119108816
Radiation Pressure Feedback in Galaxies
We evaluate radiation pressure from starlight on dust as a feedback mechanism in
 star-forming galaxies by comparing the luminosity and flux of star-forming systems to the
 dust Eddington limit. The linear
 L FIR – \hbox{$L_{\rm HCN}^\prime$}
 L HCN ′ correlation
 provides evidence that galaxies may be regulated by radiation pressure feedback. We show
 that star-forming galaxies approach but do not dramatically exceed Eddington, but many
 systems are significantly below Eddington, perhaps due to the “intermittency” of star
 formation. Better constraints on the dust-to-gas ratio and the CO- and
 HCN-to-H 2 conversion factors are needed to make a definitive assessment of
 radiation pressure as a feedback mechanism.
15632006
Relativistic jets and long-duration gamma-ray bursts from the birth of magnetars
We present time-dependent axisymmetric magnetohydrodynamic simulations of the interaction of a relativistic magnetized wind produced by a proto-magnetar with a surrounding stellar envelope, in the first � 10 seconds after core collapse. We inject a super-magnetosonic wind with u E = 10 51 ergs s 1 into a cavity created by an outgoing supernova shock. A strong toroidal magnetic field builds up in the bubble of plasma and magnetic field that is at first inertially confined by the progenitor star. This drives a jet out along the polar axis of the star, even though the star and the magnetar wind are each spherically symmetric. The jet has the properties needed to produce a longduration gamma-ray burst (GRB). At � 5 s after core bounce, the jet has escaped the host star and the Lorentz factor of the material in the jet at large radii � 10 11 cm is similar to that in the magnetar wind near the source. Most of the spindown power of the central magnetar escapes via the relativistic jet. There are fluctuations in the Lorentz factor and energy flux in the jet on � 0.01 0.1 second timescale. These may contribute to variability in GRB emission (e.g., via internal shocks).
116996486
The Effects of Moore's Law and Slacking on Large Computations
We show that, in the context of Moore's Law, overall productivity can be increased for large enough computations by `slacking' or waiting for some period of time before purchasing a computer and beginning the calculation.
16087297
Assessing Millisecond Proto-Magnetars as GRB Central Engines
Los magnetares representan una clase importante dentro de las estrellas de neutrones. Sus intensos campos magn eticos son probablemente una consecuencia de los cortos periodos de rotaci on (algunos milisegundos) en las estrellas de neutrones producidas en supernovas por colapso del n ucleo. Durante los primeros segundos de sus vidas, los magnetares pasan de ser objetos calientes y extendidos, a cuerpos fr os, dominados por campos magn eticos que identicamos unos 10,000 a~ m as tarde como Repetidores de Rayos Gama Suaves y Pulsares An omalos de rayos X. Del mismo modo, los vientos emitidos por el proto-magnetar durante la fase de enfriamiento pasan de ser no relativistas y dominados por efectos t ermicos, a magneto-centr fugos y nalmen te a relativistas, y dominados por el ujo de Poynting. Damos aqu una revisi on de las consideraciones b asicas asociadas con esta transici on. En especial, discutimos el aumento en periodo de rotaci on de los protomagnetares de milisegundo durante la epoca de enfriamiento de Kelvin-Helmholtz. Dada su enorme reserva de energ a rotacional, su asociaci on con supernovas y el hecho de que sus vientos probablemente se vuelven relativistas unos cuantos segundos despu es de su formaci on, estos objetos han sido propuestos como fuentes de destellos de rayos gama de larga duraci on. Discutimos algunas de las preguntas y problemas por resolver, relacionados con este fen omeno.
30927596
Measurement of the W boson mass using electrons at large rapidities
We report a measurement of the W boson mass based on an integrated luminosity of 82 pb(-1) from p&pmacr; collisions at sqrt[s] = 1.8 TeV recorded in 1994-1995 by the D0 detector at the Fermilab Tevatron. We identify W bosons by their decays to enu, where the electron is detected in the forward calorimeters. We extract the mass by fitting the transverse mass and the electron and neutrino transverse momentum spectra of 11 089 W boson candidates. We measure M(W) = 80.691+/-0.227 GeV. By combining this measurement with our previously published central calorimeter results from data taken in 1992-1993 and 1994-1995, we obtain M(W) = 80.482+/-0.091 GeV.
44554792
Optical model approach for heavy ion fusion.
The differences between optical model (OM) and the barrier transmission approaches for fusion are studied in detail at low energy. In the heavy ion case at deep subbarrier energies, the absorption mean square spin of an optical model calculation using a short ranged imaginary potential differs significantly from the results of the WKB transmission method. This discrepancy of OM results is shown to be due to absorption occurring beyond the barrier position. The coupled reaction channel calculations for fusion based on OM approach are shown to be sensitive to the choice of imaginary fusion potentials, whereas the coupling effects on fusion are dominant for energies only around the barrier. {copyright} {ital 1996 The American Physical Society.}
11342486
Radii of halo nuclei from cross section measurements.
The root mean square matter radii of halo nuclei provide a basic measure in constructing, constraining, and assessing theoretical models of halo structures. We consider corrections to static density (optical limit) Glauber model calculations of reaction cross sections of such nuclei at high energy giving careful consideration to their intrinsic few-body structure and the adiabatic nature of the halo nucleus-target interaction. We take as important examples the loosely bound two- and three-body systems {sup 11}Be, {sup 6}He, {sup 11}Li, and {sup 14}Be. The contribution of the valence particles to the calculated reaction cross sections are shown to be significantly reduced, requiring increased halo radii to reproduce experimental data. The implications of these changes for structure models of extended two- and three-body systems are discussed. {copyright} {ital 1996 The American Physical Society.}
18221234
Quasielastic scattering of 11Li using realistic three-body wave functions.
The quasielastic scattering of Li from C at 60 MeV/nucleon is calculated in a four-body Glauber approximation. Different Li ground-state wave functions are used, including those calculated using Faddeev three-body models. The calculated quasielastic cross sections, including the 2 and 3 states of C in a distorted wave Born approximation, reproduce the experimental data over most of the angular range, the dHFerences between theoretical models being less than the quoted statistical errors on the available data. PACS number(s): 25.70.Bc, 27.20.+n
30604611
Existence of proton halos near the drip line.
The proton drip-line nucleus $^{17}\mathrm{Ne}$ is studied in a three-body model of $^{15}\mathrm{O}$ plus two protons. The $^{17}\mathrm{Ne}$ nucleus has a Borromean binding structure, and calculations show a rms matter radius of 2.77\char21{}2.81 fm, in agreement with experiment. The model gives a proton radius excess about 0.26\char21{}0.32 fm over the neutron radius, showing that a proton skin is present. The 73% probability of a valence proton being outside the rms core radius is sufficiently large, however, to indicate a halo. Predictions for the momentum distributions of $^{15}\mathrm{O}$ fragments are given, and these, if verified, would also suggest a two-proton halo structure for $^{17}\mathrm{Ne}$. This would be the first identification of a two-proton halo nucleus.