Non-Gaussianities due to Relativistic Corrections to the Observed Galaxy Bispectrum

High-precision constraints on primordial non-Gaussianity (PNG) will significantly improve our understanding of the physics of the early universe. Among all the subtleties in using large scale structure observables to constrain PNG, accounting for relativistic corrections to the clustering statistics is particularly important for the upcoming galaxy surveys covering progressively larger fraction of the sky. We focus on relativistic projection effects due to the fact that we observe the galaxies through the light that reaches the telescope on perturbed geodesics. These projection effects can give rise to an effective $f_{\rm NL}$ that can be misinterpreted as the primordial non-Gaussianity signal and hence is a systematic to be carefully computed and accounted for in modelling of the bispectrum. We develop the technique to properly account for relativistic effects in terms of purely observable quantities, namely angles and redshifts. We give some examples by applying this approach to a subset of the contributions to the tree-level bispectrum of the observed galaxy number counts calculated within perturbation theory and estimate the corresponding non-Gaussianity parameter, $f_{\rm NL}$, for the local, equilateral and orthogonal shapes. For the local shape, we also compute the local non-Gaussianity resulting from terms obtained using the consistency relation for observed number counts. Our goal here is not to give a precise estimate of $f_{\rm NL}$ for each shape but rather we aim to provide a scheme to compute the non-Gaussian contamination due to relativistic projection effects. For the terms considered in this work, we obtain contamination of $f_{\rm NL}^{\rm loc} \sim {\mathcal O}(1)$.Comment: 31 pages, 6 figures, Typos corrected to match the published version in JCA

Models of the water retention curve for soils with a fractal pore size distribution

The relationship between water content and water potential for a soil is termed its water retention curve. This basic hydraulic property is closely related to the soil pore size distribution, for which it serves as a conventional method of measurement. In this paper a general model of the water retention curve is derived for soil whose pore size distribution is fractal in the sense of the Mandelbrot number-size distribution. This model, which contains two adjustable parameters (the fractal dimension and the upper limiting value of the fractal porosity) is shown to include other fractal approaches to the water retention curve as special cases. Application of the general model to a number of published data sets covering a broad range of soil texture indicated that unique, independent values of the two adjustable parameters may be difficult to obtain by statistical analysis of water retention data for a given soil. Discrimination among different fractal approaches thus will require water retention data of high density and precision. (Résumé d'auteur

No planet for HD 166435

The G0V star HD166435 has been observed by the fiber-fed spectrograph ELODIE as one of the targets in the large extra-solar planet survey that we are conducting at the Observatory of Haute-Provence. We detected coherent, low-amplitude, radial-velocity variations with a period of 3.7987days, suggesting a possible close-in planetary companion. Subsequently, we initiated a series of high-precision photometric observations to search for possible planetary transits and an additional series of CaII H and K observations to measure the level of surface magnetic activity and to look for possible rotational modulation. Surprisingly, we found the star to be photometrically variable and magnetically active. A detailed study of the phase stability of the radial-velocity signal revealed that the radial-velocity variability remains coherent only for durations of about 30days. Analysis of the time variation of the spectroscopic line profiles using line bisectors revealed a correlation between radial velocity and line-bisector orientation. All of these observations, along with a one-quarter cycle phase shift between the photometric and the radial-velocity variationss, are well explained by the presence of dark photospheric spots on HD166435. We conclude that the radial-velocity variations are not due to gravitational interaction with an orbiting planet but, instead, originate from line-profile changes stemming from star spots on the surface of the star. The quasi-coherence of the radial-velocity signal over more than two years, which allowed a fair fit with a binary model, makes the stability of this star unusual among other active stars. It suggests a stable magnetic field orientation where spots are always generated at about the same location on the surface of the star.Comment: 9 pages, 8 figures, Accepted for publication in A&

Antimicrobial polymers : mimicking amino acid functionality, sequence control and three-dimensional structure of host-defense peptides

Peptides and proteins control and direct all aspects of cellular function and communication. Having been honed by nature for millions of years, they also typically display an unsurpassed specificity for their biological targets. This underlies the continued focus on peptides as promising drug candidates. However, the development of peptides into viable drugs is hampered by their lack of chemical and pharmacokinetic stability and the cost of large scale production. One method to overcome such hindrances is to develop polymer systems that are able to retain the important structural features of these biologically active peptides, while being cheaper and easier to produce and manipulate chemically. This review illustrates these principles using examples of polymers designed to mimic antimicrobial host-defence peptides. The host-defence peptides have been identified as some of the most important leads for the next generation of antibiotics as they typically exhibit broad spectrum antimicrobial ability, low toxicity toward human cells and little susceptibility to currently known mechanisms of bacterial resistance. Their movement from the bench to clinic is yet to be realised, however, due to the limitations of these peptides as drugs. The literature provides a number of examples of polymers that have been able to mimic these peptides through all levels of structure, starting from specific amino acid sidechains, through to more global features such as overall charge, molecular weight and three-dimensional structure (e.g. α-helical). The resulting optimised polymers are able retain the activity profile of the peptides, but within a synthetic macromolecular construct that may be better suited to the development of a new generation of antimicrobial therapeutics. Such work has not only produced important new leads to combat the growing threat of antibiotic resistance, but may also open up new ways for polymers to mimic other important classes of biologically active peptides

Decoding of the light changes in eclipsing Wolf-Rayet binaries I. A non-classical approach to the solution of light curves

We present a technique to determine the orbital and physical parameters of eclipsing eccentric Wolf-Rayet + O-star binaries, where one eclipse is produced by the absorption of the O-star light by the stellar wind of the W-R star. Our method is based on the use of the empirical moments of the light curve that are integral transforms evaluated from the observed light curves. The optical depth along the line of sight and the limb darkening of the W-R star are modelled by simple mathematical functions, and we derive analytical expressions for the moments of the light curve as a function of the orbital parameters and the key parameters of the transparency and limb-darkening functions. These analytical expressions are then inverted in order to derive the values of the orbital inclination, the stellar radii, the fractional luminosities, and the parameters of the wind transparency and limb-darkening laws. The method is applied to the SMC W-R eclipsing binary HD 5980, a remarkable object that underwent an LBV-like event in August 1994. The analysis refers to the pre-outburst observational data. A synthetic light curve based on the elements derived for the system allows a quality assessment of the results obtained.Comment: Accepted for publication in Astronomy & Astrophysic

Statistical investigation of the full concentration range of fasted and fed simulated intestinal fluid on the equilibrium solubility of oral drugs

Upon oral administration the solubility of a drug in intestinal fluid is a key property influencing bioavailability. It is also recognised that simple aqueous solubility does not reflect intestinal solubility and to optimise in vitro investigations simulated intestinal media systems have been developed. Simulated intestinal media which can mimic either the fasted or fed state consists of multiple components each of which either singly or in combination may influence drug solubility, a property that can be investigated by a statistical design of experiment technique. In this study a design of experiment covering the full range from the lower limit of fasted to the upper limit of fed parameters and using a small number of experiments has been performed. The measured equilibrium solubility values are comparable with literature values for simulated fasted and fed intestinal fluids as well as human fasted and fed intestinal fluids. The equilibrium solubility data range is statistically equivalent to a combination of published fasted and fed design of experiment data in six (indomethacin, phenytoin, zafirlukast, carvedilol, fenofibrate and probucol) drugs with three (aprepitant, tadalafil and felodipine) drugs not equivalent. In addition the measured equilibrium solubility data sets were not normally distributed. Further studies will be required to determine the reasons for these results however it implies that a single solubility measurement without knowledge of the solubility distribution will be of limited value. The statistically significant media factors which promote equilibrium solubility (pH, sodium oleate and bile salt) were in agreement with published results but the number of determined significant factors and factor interactions was fewer in this study, lecithin for example did not influence solubility. This may be due to the reduction in statistical sensitivity from the lower number of experimental data points or the fact that using the full range will examine media parameters ratios that are not biorelevant. Overall the approach will provide an estimate of the solubility range and the most important media factors but will not be equivalent to larger scale focussed studies. Further investigations will be required to determine why some drugs do not produce equivalent DoE solubility distributions, for example combined fasted and fed DoE, but this simply may be due to the complexity and individuality of the interactions between a drug and the media components

Étude comparée de deux rythmes de reproduction chez le lapin de chair

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Active optical decoupling circuit for radio frequency endoluminal coil

International audienceDespite the enhanced image provided by multiple-channels array coils, an accurate exploration of bowel diseases and detailed information about the gastrointestinal wall layers are still not available. The use of endoluminal RF coil located in the region of interest could potentially allow good evaluation of tumor invasion or depth of inflammatory processes [1]. However, since metallic coaxial cables are used, patient safety is threatened due to local electric field concentration that can happen and the associated local high Specific Absorption Rate (SAR) [2]. Moreover, in this case, cable isolation and traps cannot be straightforwardly employed due to limited dimension. Signal transmission based onoptical fiber is an alternative to coaxial cables to solve definitively the electromagnetic issues. On a receiver coil, both signal transmission and decoupling have to be insured. For MR signal transmission, the electro-optical conversion has been partially validated based on electro-optic effect of some crystals [3]. In this work, an active optical decoupling circuit for endoluminal coil is presented and compared to a reference coil with regular decoupling using bias signal though coaxial cable