Theory of Lattice and Electronic Fluctuations in Weakly Localized Spin-Peierls Systems

A theoretical approach to the influence of one-dimensional lattice fluctuations on electronic properties in weakly localized spin-Peierls systems is proposed using the renormalization group and the functional integral techniques. The interplay between the renormalization group flow of correlated electrons and one-dimensional lattice fluctuations is taken into account by the one-dimensional functional integral method in the adiabatic limit. Calculations of spin-Peierls precursor effects on response functions are carried out explicitely and the prediction for the temperature dependent magnetic susceptibility and nuclear relaxation is compared with available experimental data for (TMTTF)$_{2}$PF$_{6}$.Comment: 15 pages, 7 Encapsulated Postscript figure

High-impedence NbSi TES sensors for studying the cosmic microwave background radiation

Precise measurements of the cosmic microwave background (CMB) are crucial in cosmology, because any proposed model of the universe must account for the features of this radiation. Of all CMB measurements that the scientific community has not yet been able to perform, the CMB B-mode polarization is probably the most challenging from the instrumental point of view. The signature of primordial gravitational waves, which give rise to a B-type polarization, is one of the goals in cosmology today and amongst the first objectives in the field. For this purpose, high-performance low-temperature bolometric cameras, made of thousands of pixels, are currently being developed by many groups, which will improve the sensitivity to B-mode CMB polarization by one or two orders of magnitude compared to the Planck satellite HFI detectors. We present here a new bolometer structure that is able to increase the pixel sensitivities and to simplify the fabrication procedure. This innovative device replaces delicate membrane-based structures and eliminates the mediation of phonons: the incoming energy is directly captured and measured in the electron bath of an appropriate sensor and the thermal decoupling is achieved via the intrinsic electron-phonon decoupling of the sensor at very low temperature. Reported results come from a 204-pixel array of Nb$_{x}$Si$_{1-x}$ transition edge sensors with a meander structure fabricated on a 2-inch silicon wafer using electron-beam co-evaporation and a cleanroom lithography process. To validate the application of this device to CMB measurements, we have performed an optical calibration of our sample in the focal plane of a dilution cryostat test bench. We have demonstrated a light absorption close to 20% and an NEP of about 7$\times10^{-16}$ W/$\sqrt{Hz}$, which is highly encouraging given the scope for improvement in this type of detectors.Comment: 6 pages, 10 figures. arXiv admin note: text overlap with arXiv:1005.0555 by other author

Zuid-West-Vlaanderen Energieneutraal in 2050: naar een regionale energiestrategie

Dit cahier bevat een voorstel voor een regionale energiestrategie voor Zuid-West-Vlaanderen: Zuid-West-Vlaanderen energieneutraal in 2050. Het biedt een denkkader over hoe Zuid-West-Vlaanderen de komende decennia met energie moet omgaan. Het cahier formuleert een visie, plus een aantal concrete acties om de visie op korte termijn in de praktijk te brengen. Het is de neerslag van een uitgebreid proces dat Leiedal opstartte, in samenwerking met de regionale energiestuurgroep en thematisch verdiept aan de hand van verschillende expertenworkshops en regionale energiefora

Restauration myope d'images pour l'inspection des ouvrages d'art par un système de vision embarqué sur drône

- Cet article présente les premiers résultats d'une étude de faisabilité du développement d'un système aérien de vision pour l'inspection des structures de génie civil telles que des ponts, tunnels. L'objectif final est d'effectuer l'inspection à l'aide d'un dispositif de vision embarqué sur un drône évoluant à l'extérieur, ou même à l'intérieur des ouvrages d'art. Les images acquises par un tel système de vision embarqué sont inévitablement dégradées. Les dégradations sont dues au comportement dynamique du drône ou aux conditions opérationnelles pendant l'inspection de la structure. Ils se traduisent essentiellement par un flou de mouvement qui peut être combiné avec un flou de défocalisation sur les images acquises. Dans la pratique, ils sont tous les deux inconnus. Nous simulons expérimentalement les dégradations qui peuvent affecter la qualité des images acquises par un tel système de vision embarqué sur drône. Nous considérons ensuite leur restauration numérique. La restauration est réalisée au moyen d'un système de traitement myope. Elle inclut deux modules de traitement, un pour identifier la PSF et un autre pour la restauration de l'image. L'identification et l'évaluation de la PSF est réalisée en utilisant le critère de la validation croisée généralisée et une contrainte de douceur sur l'image. L'étape de restauration utilise une régularisation de type Tikhonov-Miller. Les premiers résultats prouvent que ce système donne des résultats plutôt bons sur les diverses configurations (statique, dynamique) d'acquisition des images. Il est tout à fait efficace sur les images flouées et bruitées, sans connaissance a priori des caractéristiques de bruit ou de l'image

Niobium Silicon alloys for Kinetic Inductance Detectors

We are studying the properties of Niobium Silicon amorphous alloys as a candidate material for the fabrication of highly sensitive Kinetic Inductance Detectors (KID), optimized for very low optical loads. As in the case of other composite materials, the NbSi properties can be changed by varying the relative amounts of its components. Using a NbSi film with T_c around 1 K we have been able to obtain the first NbSi resonators, observe an optical response and acquire a spectrum in the band 50 to 300 GHz. The data taken show that this material has very high kinetic inductance and normal state surface resistivity. These properties are ideal for the development of KID. More measurements are planned to further characterize the NbSi alloy and fully investigate its potential.Comment: Accepted for publication on Journal of Low Temperature Physics. Proceedings of the LTD15 conference (Caltech 2013

Bi-layer Kinetic Inductance Detectors for space observations between 80-120 GHz

We have developed Lumped Element Kinetic Inductance Detectors (LEKID) sensitive in the frequency band from 80 to 120~GHz. In this work, we take advantage of the so-called proximity effect to reduce the superconducting gap of Aluminium, otherwise strongly suppressing the LEKID response for frequencies smaller than 100~GHz. We have designed, produced and optically tested various fully multiplexed arrays based on multi-layers combinations of Aluminium (Al) and Titanium (Ti). Their sensitivities have been measured using a dedicated closed-circle 100 mK dilution cryostat and a sky simulator allowing to reproduce realistic observation conditions. The spectral response has been characterised with a Martin-Puplett interferometer up to THz frequencies, and with a resolution of 3~GHz. We demonstrate that Ti-Al LEKID can reach an optical sensitivity of about $1.4$ $10^{-17}$~$W/Hz^{0.5}$ (best pixel), or $2.2$ $10^{-17}$~$W/Hz^{0.5}$ when averaged over the whole array. The optical background was set to roughly 0.4~pW per pixel, typical for future space observatories in this particular band. The performance is close to a sensitivity of twice the CMB photon noise limit at 100~GHz which drove the design of the Planck HFI instrument. This figure remains the baseline for the next generation of millimetre-wave space satellites.Comment: 7 pages, 9 figures, submitted to A&

SICANE: a Detector Array for the Measurement of Nuclear Recoil Quenching Factors using Monoenergetic Neutron Beam

SICANE is a neutron scattering multidetector facility for the determination of the quenching factor (ratio of the response to nuclear recoils and to electrons) of cryogenic detectors used in direct WIMP searches. Well collimated monoenergetic neutron beams are obtained with inverse (p,n) reactions. The facility is described, and results obtained for the quenching factors of scintillation in NaI(Tl) and of heat and ionization in Ge are presented.Comment: 30 pages, Latex, 11 figures. Submitted to NIM

Le risque : un modèle conceptuel d'intégration

The following project report is the first of a sequence which will focus on integrated risk management. This report presents a conceptual model which goal is to define the concept of risk. This conceptual model integrates the definitions of multiple domains having an interest in risk management. With the model, a terminology is proposed. This conceptual model is a foundation upon which it will be possible to exchange methods and measures of risk between domains. Ce rapport de projet est le premier d'une série qui s'intéressera à la gestion intégrée du risque. Dans l'objectif de répondre à la question « qu'est-ce que le risque? », un modèle conceptuel définissant le concept du risque est proposé. Ce modèle conceptuel intègre les définitions du risque de différentes disciplines. Une terminologie a été élaborée pour accompagner le modèle. Ce modèle conceptuel tente d'élaborer une base à partir de laquelle pourra se faire l'échange de méthodes et de mesures entre les domaines s'intéressant au risque.Risk, integrated risk management, definition, integration, Risque, gestion intégrée du risque, définition, intégration

Critical revision of the ZEPLIN-I sensitivity to WIMP interactions

The ZEPLIN collaboration has recently published its first result presenting a maximum sensitivity of $1.1 \times 10^{-6}$ picobarn for a WIMP mass of $\approx$ 60 GeV. The analysis is based on a discrimination method using the different time distribution of scintillation light generated in electron recoil and nuclear recoil interactions. We show that the methodology followed both for the calibration of the ZEPLIN-I detector response and for the estimation of the discrimination power is not reliable enough to claim any background discrimination at the present stage. The ZEPLIN-I sensitivity appears then to be in the order of 10$^{-3}$ picobarn, three orders of magnitude above the claimed 1.1 10$^{-6}$ picobarn.Comment: 8 pages, 4 figures, minor corrections, two references updated, final version accepted in Physics Letters