119946613
Mass production of tile/fiber units for the CDF plug upgrade EM calorimeter
Abstract We have fabricated scintillating tile/fiber units for the CDF plug upgrade electromagnetic calorimeter. The total number of tile/fiber systems amounts to ∼23 000. We describe the quality control tests of scintillator plates, optical fibers, and tile/fiber units which we placed at various stages in the fabrication procedures. We have completed the production retaining the tile/fiber units which satisfy our requirements.
64351367
Consumer server: A UNIX based event distributor in new CDF data acquisition system
Consumer Server is a program to handle event data and consumer trigger requests I/Os among Level 3 farm and consumer processes in CDF new data acquisition system. This program uses standard UNIX libraries and commercial network technologies to obtain higher portability. The authors describe the concept and configuration of the Consumer Server and report its performance.
17908059
0 Numerical simulation of accretion discs in close binary systems and discovery of spiral shocks
The history of hydrodynamic numerical simulations for accretion disks in close binary systems is reviewed, in which emphasis is placed, in particular, on the facts that spiral shock waves were numerically found in 1986 by researchers including one of the present authors and that spiral structure was discovered in IP Pegasi in 1997 by Steeghs et al. The results of our two and three-dimensional numerical simulations in recent years are then summarized, with comparison being made with observations.
18027030
Septum and kicker pulsers for the LNLS 500-MeV booster synchrotron
Brazilian National Synchrotron Light Laboratory (LNLS) has commissioned its new 500-MeV booster synchrotron injector. In this paper we present an overview of the septum and kicker pulse circuits now in operation. Half-sine wave septum current pulses range from 6.1 kA to 7.3 kA with widths around 80 /spl mu/s. Injection and extraction kicker circuits are capable of delivering currents up to 650 A and 1.2 kA, with fall and rise times consistent with the booster revolution period of 112 ns.
119460856
Is Angular Momentum in an Accretion Disk Transported Inwards
The derivation of the viscosity formula of accretion disks appearing in a number of textbooks is based on a mean free path theory of gas particles. However, this procedure, when followed precisely, leads to the incorrect conclusion that the angular momentum of an accretion disk flows from the outer part to the inner part.
5731989
The shape of the gravitational potential in cold dark matter haloes
We use a set of cosmological N-body simulations to investigate the structural shape of galaxysized cold dark matter (CDM) haloes. Unlike most previous work on the subject ‐ which dealt with shapes as measured by the inertia tensor ‐ we focus here on the shape of the gravitational potential, a quantity more directly relevant to comparison with observational probes. A further advantage is that the potential is less sensitive to the effects of substructure and, as a consequence, the isopotential surfaces are typically smooth and well approximated by concentric ellipsoids. Our main result is that the asphericity of the potential increases rapidly towards the centre of the halo. The radial trend is more pronounced than expected from constant flattening in the mass distribution, and reflects a strong tendency for dark matter haloes to become increasingly aspherical inwards. Near the centre the halo potential is approximately prolate on average [(c/a)0 = 0.72 ± 0.04, (b/a)0 = 0.78 ± 0.08], but it becomes less axisymmetric and more spherical in the outer regions. The principal axes of the isopotential surfaces remain well aligned, and in most haloes the angular momentum tends to be parallel to the minor axis and perpendicular to the major axis. This suggests that galactic discs may form in a plane where the potential is elliptical and where its ellipticity varies rapidly with radius. This can result in significant deviations from circular motion in systems such as low surface brightness (LSB) galaxies, even for relatively minor deviations from circular symmetry. Simulated long-slit rotation curves often appear similar to those of LSBs cited as evidence for constant density ‘cores’. This suggests that taking into account the 3D shape of the dark mass distribution might help to reconcile such evidence with the cuspy mass profile of CDM haloes.
14663098
Disk Galaxy Rotation Curves in Triaxial CDM Halos
We use N-body hydrodynamical simulations to study the structure of disks in triaxial potentials resembling CDM halos. Our analysis focuses on the accuracy of the dark mass distribution inferred from rotation curves derived from simulated long-slit spectra. We consider a massless disk embedded in a halo with axis ratios of 0.5:0.6:1.0 and with its rotation axis aligned with the minor axis of the halo. Closed orbits for the gaseous particles deviate from coplanar circular symmetry, resulting in a variety of long-slit rotation curve shapes, depending on the orientation of the disk relative to the line of sight. Rotation curves may thus differ significantly from the spherically-averaged circular velocity profile of the dark matter halo. "Solid-body" rotation curves--typically interpreted as a signature of a constant density core in the dark matter distribution--are obtained about 25% of the time for random orientations although the dark matter follows the cuspy density profile proposed by Navarro, Frenk & White (NFW). We conclude that the discrepancies reported between the shape of the rotation curve of low surface brightness galaxies and the structure of CDM halos may be resolved once the complex effects of halo triaxiality on the dynamics of the gas component is properly taken into account.