Displacement noise from back scattering and specular reflection of input optics in advanced gravitational wave detectors

The second generation of ground-based interferometric gravitational wave detectors are currently being built and installed. They are designed to be better in strain sensitivity by about a factor 10 with respect to the first generation. Light originating from the laser and following unintended paths, called stray light, has been a major problem during the commissioning of all of the first generation detectors. Indeed, stray light carries information about the phase of the emitting object. Therefore, in the next generation all the optics will be suspended in the vacuum in order to mitigate their associated stray light displacement noise. Despite this additional precaution, the challenging target sensitivity at low frequency which is partially limited by quantum radiation pressure combined with up-conversion effects, requires more detailed investigation. In this paper, we turn our attention to stray light originating from auxiliary optical benches. We use a dedicated formalism to compute the re-coupling of back-reflected and back-scattered light. We show, in particular, how much care should be taken in designing and setting requirements for the input bench optics

Inhibitors of nuclear factor kappa B cause apoptosis in cultured macrophages

The precise role of the transcription factor nuclear factor kappa B (NF- κB) in the regulation of cell survival and cell death is still unresolved and may depend on cell type and position in the cell cycle. The aim of this study was to determine if three pharmacologic inhibitors of NF-κB, pyrrolidine dithiocarbamate, N-tosyl-L-lysl chloromethyl ketone and calpain I inhibitor, induce apoptosis in a murine macrophage cell line (RAW 264.7) at doses similar to those required for NF-κB inhibition. We found that each of the three inhibitors resulted in a dose- and time-dependent increase in morphologic indices of apoptosis in unstimulated, LPS-stimulated and TNF-stimulated cells. Lethal doses were consistent with those required for NF- κB inhibition. We conclude that nuclear NF-κB activation may represent an important survival mechanism in macrophages

Utilisation des contours actifs ou « snake » pour l'extraction des arêtes de représentations temps-fréquences : Application à l'analyse des contractions utérines

L'analyse et la caractérisation des représentations temps-fréquences d'un signal réel est souvent complexe. Pour simplifier ces représentations, on utilise généralement leurs arêtes ou chaînes de maxima énergétiques locaux. Nous proposons dans ce travail, une approche originale pour l'extraction des arêtes basée sur une méthode de traitement d'image : les contours actifs ou « snakes » associée à la méthode Gradient Vector Flow ou méthode du flux du vecteur de gradient, comme force d'attraction du contour actif. La méthode GVF-snake, appliquée sur différentes représentations temps-fréquences et pour des signaux diversement bruités, est robuste comparée à une méthode classique de traitement du signal. Le temps d'exécution est principalement fonction de la taille du contour actif. De plus, les erreurs d'extraction sont relativement faibles, quelle que soit la situation étudiée. Cette nouvelle approche a aussi été testée sur des représentations temps-fréquences de contractions utérines enregistrées chez le singe pendant la grossesse. Les erreurs d'extraction obtenues sur ces signaux réels se sont aussi révélées meilleures que celles obtenues avec la méthode classique

Short Term Effects of Hurricane Irma on the Phytoplankton of Lake Louise, Georgia, USA

Natural disturbances such as fires and severe storms can have profound impacts on the hydrology and ecology of inland waters, potentially altering the structure and function of the ecosystem for extended periods of time. Studies of the initial impacts are, however, uncommon. Here we report on the short-term impacts of Hurricane Irma in the structure of the phytoplankton association in Lake Louise, a small blackwater lake in southern Georgia. Irma hit the region on September 11, 2017, with tropical storm force winds. The event corresponded to a period during which we were conducting routine weekly monitoring of environmental conditions in the lake. Parameters monitored included temperature, dissolved oxygen, conductivity, and light from the surface to a depth of 6 m. Chlorophyll concentrations and the structure of the phytoplankton were also determined at 1 m intervals from the surface to a depth of 5 m. An increase in the overall abundance of phytoplankton in the upper meter of the lake and a decrease in the abundance of phytoplankton deeper in the water column were observed immediately after Hurricane Irma. These decreases were followed by a bloom involving several species of cyanobacteria beginning about four weeks after the passage of the hurricane. Signatures of the passage of the hurricane were erased in early December as cooler temperatures created isothermal conditions in the lake

Performance of a thermally deformable mirror for correction of low-order aberrations in laser beams

The thermally deformable mirror is a device aiming at correcting beam-wavefront distortions for applications where classical mechanical methods are precluded by noise considerations, as in advanced gravitational wave interferometric detectors. This moderately low-cost technology can be easily implemented and controlled thanks to the good reproducibility of the actuation. By using a flexible printed circuit board technology, we demonstrate experimentally that a device of 61 actuators in thermal contact with the back surface of a high-reflective mirror is able to correct the low-order aberrations of a laser beam at 1064 nm and could be used to optimize the mode matching into Fabry-Perot cavities

Monitoring and lifetime prediction of pvc cables: methodology by multiscale and multidisciplinary approach

Monitoring of the PVC cables as well as the prediction of their residual lifetime are important issues for the maintenance of the French nuclear power plants (NPPs). To date, the unanimously end of life criterion admitted for these cables is a 50% value of elongation at break and, to our knowledge, only destructive tests give access to this parameter. This study reports a relationship between elongation at break of the PVC and their plasticizer content. This correlation opens the door to a monitoring directly on site or by micro sampling since all classic laboratory techniques able to measure this content become ways to judge the condition of the PVC sheaths and insulators. In addition, this study demonstrates the feasibility of prediction of industrial PVC behavior changes. This model, adapted to the case of thin films, involved tools of chemical kinetics and the implementation of a constitutive model

DC-readout of a signal-recycled gravitational wave detector

All first-generation large-scale gravitational wave detectors are operated at the dark fringe and use a heterodyne readout employing radio frequency (RF) modulation-demodulation techniques. However, the experience in the currently running interferometers reveals several problems connected with a heterodyne readout, of which phase noise of the RF modulation is the most serious one. A homodyne detection scheme (DC-readout), using the highly stabilized and filtered carrier light as local oscillator for the readout, is considered to be a favourable alternative. Recently a DC-readout scheme was implemented on the GEO 600 detector. We describe the results of first measurements and give a comparison of the performance achieved with homodyne and heterodyne readout. The implications of the combined use of DC-readout and signal-recycling are considered.Comment: 11 page

LOFAR observations of the quiet solar corona

The quiet solar corona emits meter-wave thermal bremsstrahlung. Coronal radio emission can only propagate above that radius, $R_\omega$, where the local plasma frequency eqals the observing frequency. The radio interferometer LOw Frequency ARray (LOFAR) observes in its low band (10 -- 90 MHz) solar radio emission originating from the middle and upper corona. We present the first solar aperture synthesis imaging observations in the low band of LOFAR in 12 frequencies each separated by 5 MHz. From each of these radio maps we infer $R_\omega$, and a scale height temperature, $T$. These results can be combined into coronal density and temperature profiles. We derived radial intensity profiles from the radio images. We focus on polar directions with simpler, radial magnetic field structure. Intensity profiles were modeled by ray-tracing simulations, following wave paths through the refractive solar corona, and including free-free emission and absorption. We fitted model profiles to observations with $R_\omega$ and $T$ as fitting parameters. In the low corona, $R_\omega < 1.5$ solar radii, we find high scale height temperatures up to 2.2e6 K, much more than the brightness temperatures usually found there. But if all $R_\omega$ values are combined into a density profile, this profile can be fitted by a hydrostatic model with the same temperature, thereby confirming this with two independent methods. The density profile deviates from the hydrostatic model above 1.5 solar radii, indicating the transition into the solar wind. These results demonstrate what information can be gleaned from solar low-frequency radio images. The scale height temperatures we find are not only higher than brightness temperatures, but also than temperatures derived from coronograph or EUV data. Future observations will provide continuous frequency coverage, eliminating the need for local hydrostatic density models