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.
55404585
STATUS OF THE 476 MHz 50 kW SOLID STATE AMPLIFIER FOR THE LNLS STORAGE RING
In November 2010, LNLS plans to replace the two 50 kW UHF klystron system which currently provides power to the RF cavities installed in the storage ring. To replace this system, two 50 kW solid state amplifiers have been built and are now under commissioning. Thanks to a close collaboration with the Synchrotron SOLEIL started in 1999, LNLS adapted the characteristics of the French project to 476 MHz. A short description of the amplifiers is presented, as well as the power tests performed with one of them using a resistive load.
16747752
Comments on “Angular Momentum Transport in Quasi-Keplerian Accretion Disks”
Subramanian, Pujari and Becker (2004) claim that the correct expression for the angular momentum transport in an accretion disc, which is proportional to dΩ/dR, can be derived on the basis of the analysis of the epicyclic motion of gas parcels in adjacent eddies in the disc. We study their argument and show that their derivation contains several fundamental errors: 1) the biased choice of the desired formula from an infinite number of formulae; 2) the biased choice of parcel trajectories; and 3) confusion regarding the reference frames. Following 1) we could derive, for example, a (invalid) formula in which the angular momentum transport is proportional to dv Φ /dR, and from 2) we could even prove that the angular momentum transport is either inward or null. We present the correct approach to the problem of angular momentum transport in an accretion disc in terms of mean free path theory.
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.
14631759
Hiding cusps in cores: kinematics of disc galaxies in triaxial dark matter haloes
We study the kinematics of gaseous discs in triaxial dark matter haloes using the closed-loop orbit solutions in non-axisymmetric potentials. The orbits are in general non-circular and, for a given triaxiality, their ellipticity depends on the ratio of escape to circular velocities, V 2 esc /V 2 c . This ratio increases steeply towards the centre for cold dark matter (CDM) halo density profiles, implying that even minor deviations from spherical symmetry may induce large deviations from circular orbits in the velocity field of a gaseous disc, especially near the centre. This result suggests that caution should be exercised when interpreting constraints on the presence of density cusps in the dark halo derived from the innermost velocity profile. Simulated long-slit rotation curves vary greatly in shape, depending primarily on the viewing angle of the disc and on its orientation relative to the principal axes of the potential. 'Solid-body' rotation curves - typically interpreted as a signature of a constant density core in the dark matter distribution - are often obtained when the slit samples velocities near the major axis of the closed-loop orbits. Triaxial potentials imprint specific symmetries in 2D velocity fields, generally inducing 'twists' in the isovelocity contours and antisymmetric patterns in opposite quadrants. We suggest that triaxial haloes may be responsible for the variety of shapes of long-slit rotation curves of low surface brightness (LSB) galaxies, as well as for the complex central kinematics of LSBs, which are sometimes ascribed to the presence of 'radial motions' in the gas. We argue that LSB rotation curves might be reconciled with the structure of CDM haloes once the effects of halo triaxiality on the dynamics of gaseous discs are properly taken into account.
16684392
How rare is the bullet cluster
The galaxy cluster 1E 0657−56 has a bullet-like subcluster that is moving away from the centre of the main cluster at high speed. Markevitch et al. (2004) recently estimated a relative velocity of Vbullet= 4500+1100−800  km s−1, based on observations of the bow shock in front of the subcluster. The weak lensing analysis of Clowe, Gonzalez & Markevitch (2004) indicates that a substantial secondary mass peak is associated with this subcluster. We estimate the likelihood of such a configuration by examining the distribution of subhalo velocities for clusters in the Millennium Run, a large Λ cold dark matter (ΛCDM) cosmological simulation. We find that the most massive subhalo has a velocity as high as that of the bullet subcluster in only about one out of every 100 cluster-sized haloes. This estimate is strongly dependent on the precise velocity adopted for the bullet. One of the 10 most massive subhaloes has such a high velocity about 40 per cent of the time. We conclude that the velocity of the bullet subcluster is not exceptionally high for a cluster substructure, and can be accommodated within the currently favoured ΛCDM cosmogony.