Upper limits on a stochastic gravitational-wave background using LIGO and Virgo interferometers at 600-1000 Hz
A stochastic background of gravitational waves is expected to arise from a superposition of many incoherent sources of gravitational waves, of either cosmological or astrophysical origin. This background is a target for the current generation of ground-based detectors. In this article we present the first joint search for a stochastic background using data from the LIGO and Virgo interferometers. In a frequency band of 600-1000 Hz, we obtained a 95% upper limit on the amplitude of ΩGW(f)=Ω3(f/900 Hz)3, of Ω3<0.32, assuming a value of the Hubble parameter of h100=0.71. These new limits are a factor of seven better than the previous best in this frequency band.

title: Automatic Alignment for the first science run of the Virgo interferometer
abstract: During the past few years a network of large-scale laser interferometers, including the Virgo detector, has been developed with the aim of detecting gravitational waves. To properly operate the detectors, the longitudinal and angular positions of the suspended detector test masses, the interferometer mirrors, must be kept within a small range from the operating point. The design of the Virgo angular control system, called Automatic Alignment is based on a modified version of the Anderson-Giordano technique, a wave-front sensing scheme which uses the modulation-demodulation technique. This paper will present the theoretical background of the Virgo Automatic Alignment system, the implementation issues and the performances observed during the first Virgo science run (VSR1). A total RMS of 4 × 10−2 to 3 × 10−3 μrad for all angular degrees of freedom has been achieved.

title: Beating the Spin-down Limit on Gravitational Wave Emission from the Vela Pulsar
abstract: We present direct upper limits on gravitational wave emission from the Crab pulsar using data from the first 9 months of the fifth science run of the Laser Interferometer Gravitational-wave Observatory (LIGO). These limits are based on two searches. In the first we assume that the gravitational wave emission follows the observed radio timing, giving an upper limit on gravitational wave emission that beats indirect limits inferred from the spin-down and braking index of the pulsar and the energetics of the nebula. In the second we allow for a small mismatch between the gravitational and radio signal frequencies and interpret our results in the context of two possible gravitational wave emission mechanisms.

title: Automatic Alignment system during the second science run of the Virgo interferometer
abstract: In this paper the performances of the Automatic Alignment sensing and control system in the Virgo gravitational wave detector, during the second scientific run from July 7th 2009 to January 8th 2010, are described. The accuracy of the angular control loops fulfills the original Virgo requirements, reaching the accuracy of a few nano-radians for the most critical angular degrees of freedom, and the control noise is below the Virgo design sensitivity in the whole detection band.

title: Directional limits on persistent gravitational waves using LIGO S5 science data.
abstract: The gravitational-wave (GW) sky may include nearby pointlike sources as well as stochastic backgrounds. We perform two directional searches for persistent GWs using data from the LIGO S5 science run: one optimized for pointlike sources and one for arbitrary extended sources. Finding no evidence to support the detection of GWs, we present 90% confidence level (C.L.) upper-limit maps of GW strain power with typical values between 2-20×10(-50)  strain(2) Hz(-1) and 5-35×10(-49)  strain(2) Hz(-1) sr(-1) for pointlike and extended sources, respectively. The latter result is the first of its kind. We also set 90% C.L. limits on the narrow-band root-mean-square GW strain from interesting targets including Sco X-1, SN 1987A and the Galactic center as low as ≈7×10(-25) in the most sensitive frequency range near 160 Hz.

title: Noise from scattered light in Virgo’s second science run data
abstract: Virgo is one of the large, ground-based interferometers aimed at detecting gravitational waves. One of the technical problems limiting its sensitivity is caused by light in the output beams which is backscattered by seismically excited surfaces and couples back into the main beam of the interferometer. The resulting noise was thoroughly studied, measured and mitigated before Virgo's second science run (VSR2). The residual noise during VSR2, which increases in periods with a large microseism activity, is accurately predicted by the theoretical model. The scattered light has been associated with transient events in the gravitational-wave signal of the interferometer.

title: Collisional excitation of neon-like Ni XIX using the Breit-PauliR-matrix method
abstract: Collision strength for the transition within the first five fine-structure levels in Ni XIX are calculated using the Breit-PauliR-matrix method. Configuration interaction wave functions are used to represent the target states included in theR-matrix expansion. The relativistic effects are incorporated in the Breit-Pauli approximation by including the one-body mass correction, Darwin and spin-orbit interaction terms in scattering equations.

title: Electron scattering in the presence of an intense electromagnetic field
abstract: The general theory of electron scattering in the presence of an external electromagnetic field, provided by an intense laser beam, accompanied by absorption ofn photons, each with energy ħω is discussed. The calculation leads to many summations over intermediate states. A general method for exactly evaluating several sums is described in detail. Numerical results show that the cross-section varies with intensity in a power law fashion.