Low frequency acoustics in solid 4^4He at low temperature

The elastic properties of hcp $^4$He samples have been investigated using low frequency (20 Hz to 20 kHz) high sensitivity sound transducers. In agreement with the findings of other workers, most samples studied grew very significantly stiffer at low temperature; Poisson's ratio $\nu$ was observed to increase from 0.28 below 20 mK to $\sim 0.35$ at 0.7 K. The span of the variation of $\nu$ varies from sample to sample according to their thermal and mechanical history. Crystals carefully grown at the melting curve show a different behavior, the change in $\nu$ taking place at lower $T$ and being more abrupt

How to estimate the differential acceleration in a two-species atom interferometer to test the equivalence principle

We propose a scheme for testing the weak equivalence principle (Universality of Free Fall) using an atom-interferometric measurement of the local differential acceleration between two atomic species with a large mass ratio as test masses. A apparatus in free fall can be used to track atomic free-fall trajectories over large distances. We show how the differential acceleration can be extracted from the interferometric signal using Bayesian statistical estimation, even in the case of a large mass and laser wavelength difference. We show that this statistical estimation method does not suffer from acceleration noise of the platform and does not require repeatable experimental conditions. We specialize our discussion to a dual potassium/rubidium interferometer and extend our protocol with other atomic mixtures. Finally, we discuss the performances of the UFF test developed for the free-fall (0-g) airplane in the ICE project (\verb"http://www.ice-space.fr"

A group model for stable multi-subject ICA on fMRI datasets

Spatial Independent Component Analysis (ICA) is an increasingly used data-driven method to analyze functional Magnetic Resonance Imaging (fMRI) data. To date, it has been used to extract sets of mutually correlated brain regions without prior information on the time course of these regions. Some of these sets of regions, interpreted as functional networks, have recently been used to provide markers of brain diseases and open the road to paradigm-free population comparisons. Such group studies raise the question of modeling subject variability within ICA: how can the patterns representative of a group be modeled and estimated via ICA for reliable inter-group comparisons? In this paper, we propose a hierarchical model for patterns in multi-subject fMRI datasets, akin to mixed-effect group models used in linear-model-based analysis. We introduce an estimation procedure, CanICA (Canonical ICA), based on i) probabilistic dimension reduction of the individual data, ii) canonical correlation analysis to identify a data subspace common to the group iii) ICA-based pattern extraction. In addition, we introduce a procedure based on cross-validation to quantify the stability of ICA patterns at the level of the group. We compare our method with state-of-the-art multi-subject fMRI ICA methods and show that the features extracted using our procedure are more reproducible at the group level on two datasets of 12 healthy controls: a resting-state and a functional localizer study

Tapered-amplified AR-coated laser diodes for Potassium and Rubidium atomic-physics experiments

We present a system of room-temperature extended-cavity grating-diode lasers (ECDL) for production of light in the range 760-790nm. The extension of the tuning range towards the blue is permitted by the weak feedback in the cavity: the diodes are anti-reflection coated, and the grating has just 10% reflectance. The light is then amplified using semiconductor tapered amplifiers to give more than 400mW of power. The outputs are shown to be suitable for atomic physics experiments with potassium (767nm), rubidium (780nm) or both, of particular relevance to doubly-degenerate boson-fermion mixtures

Thermodynamic inequalities in superfluid

We investigate general thermodynamic stability conditions for the superfluid. This analysis is performed in an extended space of thermodynamic variables containing (along with the usual thermodynamic coordinates such as pressure and temperature) superfluid velocity and momentum density. The stability conditions lead to thermodynamic inequalities which replace the Landau superfluidity criterion at finite temperatures.Comment: 7 pages, 1 figur

Propriétés osmotiques et magnétiques des solutions d'hélium-3 dans l'hélium-4 superfluide

International audienceWe review in this paper recent (prior to 1978) theoretical and experimental work done at Orsay and elsewhere on 3He-4He mixtures. We start by showing that the set of thermodynamic variables (T,n,n_3,\mu_4) is a privileged set for the description of a superfluid solution and we derive basic formulae of the statistical mechanics of boson-fermion mixtures. We insert in the formalism the equation of state, assumed to be known at the start, and the fact that 3He and 4He are isotopes. This simple approach leads in the dilute 3He limit to the well-known theory of Bardeen-Baym-Pines that we summarize with its more recent developments. To go beyond this straight-forward construction, we parametrize the scattering amplitude V(p,p',q) of two scattering 3He quasi-particles with momenta p and p' to lowest order in q=p'-p, p and p'. We proceed to compute all the equilibrium properties of the mixtures. We then extract `best values'' of the model parameters from experimental results.Nous donnons, dans cet article de revue, une synthèse de travaux récents effectués à Orsay et ailleurs, tant sur le plan théorique qu'expérimental sur les mélanges d'3He dans l'4He. Nous commençons par montrer que le jeu de variables thermodynamiques (T, n, n_3, \mu_4) fournit une description privilégiée de la solution superfluide et nous rappelons quelques formules fondsmentales de la mécanique statistique des mélanges fermions-bosons. A ce formalisme, nous ajoutons la connaissance de l'équation d'état d'une part, et d'autre part le fait qu'3He et 4He sont isotopes. Cette démarche directe mène, pour les solutions diluées, à la théorie bien connue de Bardeen-Baym-Pines dont nous donnons un condensé, ainsi que de ses développements récents. Pour aller au-delà de cette construction sans complication, nous introduisons une forme paramétrée de l'amplitude de collision de deux quasi-particules 3He en interaction. Nous évaluons ensuite les propriétés thermodynamiques correspondantes. Nous extrayons ensuite les valeurs des paramètres de ce modèle des données expérimentales

Nasal cavity lobular capillary hemangioma due to insect sting

SummaryIntroductionLobular capillary hemangioma is a frequent benign vascular inflammatory lesion of the skin tissue. It rarely reaches the mucous membrane, and the nasal fossa involvement is exceptional.Case reportA 68-year-old woman presented with an ulcerous hemorrhagic mass blocking the left nasal fossa, which had appeared a few weeks after a wasp sting in the nose. The insect was evacuated only three weeks after the sting. The clinical and radiological data suggested malignancy. Biopsy under local anesthesia proved non-contributory and was complicated by 1 week's hospitalization for severe nosebleed. Surgical excision under video-endoscopy confirmed diagnosis. At 31 months’ follow-up, the patient was free of recurrence.Discussion/conclusionThe pathogeny of lobular capillary hemangioma is uncertain. No previous cases affecting the mucous membrane after insect sting have been reported. Except in the typical contexts of long-term packing or pregnancy, diagnosis can be difficult and misleading. It can mimic a malignant pathology. Its rich vascularization requires caution during biopsy, and the risk of recurrence requires excision to be complete

I.C.E.: a Transportable Atomic Inertial Sensor for Test in Microgravity

We present our the construction of an atom interferometer for inertial sensing in microgravity, as part of the I.C.E. (\textit{Interf\'{e}rom\'{e}trie Coh\'{e}rente pour l'Espace}) collaboration. On-board laser systems have been developed based on fibre-optic components, which are insensitive to mechanical vibrations and acoustic noise, have sub-MHz linewidth, and remain frequency stabilised for weeks at a time. A compact, transportable vacuum system has been built, and used for laser cooling and magneto-optical trapping. We will use a mixture of quantum degenerate gases, bosonic $^{87}$Rb and fermionic $^{40}$K, in order to find the optimal conditions for precision and sensitivity of inertial measurements. Microgravity will be realised in parabolic flights lasting up to 20s in an Airbus. We show that the factors limiting the sensitivity of a long-interrogation-time atomic inertial sensor are the phase noise in reference frequency generation for Raman-pulse atomic beam-splitters and acceleration fluctuations during free fall

I.C.E.: An Ultra-Cold Atom Source for Long-Baseline Interferometric Inertial Sensors in Reduced Gravity

The accuracy and precision of current atom-interferometric inertialsensors rival state-of-the-art conventional devices using artifact-based test masses . Atomic sensors are well suited for fundamental measurements of gravito-inertial fields. The sensitivity required to test gravitational theories can be achieved by extending the baseline of the interferometer. The I.C.E. (Interf\'erom\'etrie Coh\'erente pour l'Espace) interferometer aims to achieve long interrogation times in compact apparatus via reduced gravity. We have tested a cold-atom source during airplane parabolic flights. We show that this environment is compatible with free-fall interferometric measurements using up to 4 second interrogation time. We present the next-generation apparatus using degenerate gases for low release-velocity atomic sources in space-borne experiments