Isolation of gravitational waves from displacement noise and utility of a time-delay device

Interferometers with kilometer-scale arms have been built for gravitational-wave detections on the ground; ones with much longer arms are being planned for space-based detection. One fundamental motivation for long baseline interferometry is from displacement noise. In general, the longer the arm length L, the larger the motion the gravitational-wave induces on the test masses, until L becomes comparable to the gravitational wavelength. Recently, schemes have been invented, in which displacement noises can be evaded by employing differences between the influence of test-mass motions and that of gravitational waves on light propagation. However, in these schemes, such differences only becomes significant when L approaches the gravitational wavelength, and shot-noise limited sensitivity becomes worse than that of conventional configurations by a factor of at least (f L/c)^(-2), for f<c/L. Such a factor, although can be overcome theoretically by employing high optical powers, makes these schemes quite impractical. In this paper, we explore the use of time delay in displacement-noise-free interferometers, which can improve their shot-noise-limited sensitivity at low frequencies, to a factor of (f L/c)^(-1) of the shot-noise-limited sensitivity of conventional configurations.Comment: 10 pages, 12 figures, a proceeding for the Spanish Relativity Meeting ERE 200

The Mitotic Checkpoint Complex Requires an Evolutionary Conserved Cassette to Bind and Inhibit Active APC/C

The Spindle Assembly Checkpoint (SAC) ensures genomic stability by preventing sister chromatid separation until all chromosomes are attached to the spindle. It catalyzes the production of the Mitotic Checkpoint Complex (MCC), which inhibits Cdc20 to inactivate the Anaphase Promoting Complex/Cyclosome (APC/C). Here we show that two Cdc20-binding motifs in BubR1 of the recently identified ABBA motif class are crucial for the MCC to recognize active APC/C-Cdc20. Mutating these motifs eliminates MCC binding to the APC/C, thereby abolishing the SAC and preventing cells from arresting in response to microtubule poisons. These ABBA motifs flank a KEN box to form a cassette that is highly conserved through evolution, both in the arrangement and spacing of the ABBA-KEN-ABBA motifs, and association with the amino-terminal KEN box required to form the MCC. We propose that the ABBA-KEN-ABBA cassette holds the MCC onto the APC/C by binding the two Cdc20 molecules in the MCC-APC/C complex.This work was supported by an SFI Starting Investigator Research Grant (13/SIRG/2193) to N.E.D. and a CR UK Programme grant C29/A13678 to J.P. J.P. acknowledges the financial support of Wellcome Trust Grant 092096 and CR UK Grant C6946/A14492 core support to the Gurdon Institute

Variation in grouping patterns, mating systems and social structure: what socio-ecological models attempt to explain

Socio-ecological models aim to predict the variation in social systems based on a limited number of ecological parameters. Since the 1960s, the original model has taken two paths: one relating to grouping patterns and mating systems and one relating to grouping patterns and female social structure. Here, we review the basic ideas specifically with regard to non-human primates, present new results and point to open questions. While most primates live in permanent groups and exhibit female defence polygyny, recent studies indicate more flexibility with cooperative male resource defence occurring repeatedly in all radiations. In contrast to other animals, the potential link between ecology and these mating systems remains, however, largely unexplored. The model of the ecology of female social structure has often been deemed successful, but has recently been criticized. We show that the predicted association of agonistic rates and despotism (directional consistency of relationships) was not supported in a comparative test. The overall variation in despotism is probably due to phylogenetic grade shifts. At the same time, it varies within clades more or less in the direction predicted by the model. This suggests that the model's utility may lie in predicting social variation within but not across clades

Measurement of the neutron detection efficiency of a 80% absorber - 20% scintillating fibers calorimeter

The neutron detection efficiency of a sampling calorimeter made of 1 mm diameter scintillating fibers embedded in a lead/bismuth structure has been measured at the neutron beam of the The Svedberg Laboratory at Uppsala. A significant enhancement of the detection efficiency with respect to a bulk organic scintillator detector with the same thickness is observed.Comment: 10 pages, 7 figure

Performance of a 1200m long suspended Fabry-Perot cavity

Using one arm of the Michelson interferometer and the power recycling mirror of the interferometric gravitational wave detector GEO600, we created a Fabry-Perot cavity with a length of 1200 m. The main purpose of this experiment was to gather first experience with the main optics, its suspensions and the corresponding control systems. The residual displacement of a main mirror is about 150 nm rms. By stabilising the length of the 1200 m long cavity to the pre-stabilised laser beam we achieved an error point frequency noise of 0.1 mHz/sqrt(Hz) at 100 Hz Fourier frequency. In addition we demonstrated the reliable performance of all included subsystems by several 10-hour-periods of continuous stable operation. Thus the full frequency stabilisation scheme for GEO600 was successfully tested.Comment: Amaldi 4 (Perth 2001) conference proceedings, 10 pages, 8 figure

Critical behavior of 3D SU(2) gauge theory at finite temperature: exact results from universality

We show that universality arguments, namely the Svetitsky-Yaffe conjecture, allow one to obtain exact results on the critical behavior of 3D SU(2) gauge theory at the finite temperature deconfinement transition,through a mapping into the 2D Ising model. In particular, we consider the finite-size scaling behavior of the plaquette operator, which can be mapped into the energy operator of the 2D Ising model. We obtain exact predictions for the dependence of the plaquette expectation value on the size and shape of the lattice and we compare them to Monte Carlo results, finding complete agreement. We discuss the application of this method to the computation of more general correlators of the plaquette operator at criticality, and its relevance to the study of the color flux tube structure.Comment: 10 pages, LaTeX file + 3 eps figure