Rotational dynamics of a soft filament: wrapping transition and propulsive forces

We analyze experimentally the shape of a long elastic filament rotating in a viscous liquid. We identify a continuous but sharp transition from a straight to an helical shape, resulting from the competition between viscous stresses and elastic forces. This induced helicity generates a propulsive force along the axis of rotation. In addition, we show that the shape transition is associated with an unstable branch in the force-torque relation. A linearized model of the fluid-structure interaction is proposed to account for all the features of the non-linear filament dynamics

On the transverse mode of an atom laser

The transverse mode of an atom laser beam that is outcoupled from a Bose-Einstein condensate is investigated and is found to be strongly determined by the mean--field interaction of the laser beam with the condensate. Since for repulsive interactions the geometry of the coupling scheme resembles an interferometer in momentum space, the beam is found show filamentation. Observation of this effect would prove the transverse coherence of an atom laser beam.Comment: 4 pages, 4 figure

A slow gravity compensated Atom Laser

We report on a slow guided atom laser beam outcoupled from a Bose-Einstein condensate of 87Rb atoms in a hybrid trap. The acceleration of the atom laser beam can be controlled by compensating the gravitational acceleration and we reach residual accelerations as low as 0.0027 g. The outcoupling mechanism allows for the production of a constant flux of 4.5x10^6 atoms per second and due to transverse guiding we obtain an upper limit for the mean beam width of 4.6 \mu\m. The transverse velocity spread is only 0.2 mm/s and thus an upper limit for the beam quality parameter is M^2=2.5. We demonstrate the potential of the long interrogation times available with this atom laser beam by measuring the trap frequency in a single measurement. The small beam width together with the long evolution and interrogation time makes this atom laser beam a promising tool for continuous interferometric measurements.Comment: 7 pages, 8 figures, to be published in Applied Physics

Atom laser coherence and its control via feedback

We present a quantum-mechanical treatment of the coherence properties of a single-mode atom laser. Specifically, we focus on the quantum phase noise of the atomic field as expressed by the first-order coherence function, for which we derive analytical expressions in various regimes. The decay of this function is characterized by the coherence time, or its reciprocal, the linewidth. A crucial contributor to the linewidth is the collisional interaction of the atoms. We find four distinct regimes for the linewidth with increasing interaction strength. These range from the standard laser linewidth, through quadratic and linear regimes, to another constant regime due to quantum revivals of the coherence function. The laser output is only coherent (Bose degenerate) up to the linear regime. However, we show that application of a quantum nondemolition measurement and feedback scheme will increase, by many orders of magnitude, the range of interaction strengths for which it remains coherent.Comment: 15 pages, 6 figures, revtex

A clock network for geodesy and fundamental science

Leveraging the unrivaled performance of optical clocks in applications in fundamental physics beyond the standard model, in geo-sciences, and in astronomy requires comparing the frequency of distant optical clocks truthfully. Meeting this requirement, we report on the first comparison and agreement of fully independent optical clocks separated by 700 km being only limited by the uncertainties of the clocks themselves. This is achieved by a phase-coherent optical frequency transfer via a 1415 km long telecom fiber link that enables substantially better precision than classical means of frequency transfer. The fractional precision in comparing the optical clocks of three parts in $10^{17}$ was reached after only 1000 s averaging time, which is already 10 times better and more than four orders of magnitude faster than with any other existing frequency transfer method. The capability of performing high resolution international clock comparisons paves the way for a redefinition of the unit of time and an all-optical dissemination of the SI-second.Comment: 14 pages, 3 figures, 1 tabl

Coherent matter wave inertial sensors for precision measurements in space

We analyze the advantages of using ultra-cold coherent sources of atoms for matter-wave interferometry in space. We present a proof-of-principle experiment that is based on an analysis of the results previously published in [Richard et al., Phys. Rev. Lett., 91, 010405 (2003)] from which we extract the ratio h/m for 87Rb. This measurement shows that a limitation in accuracy arises due to atomic interactions within the Bose-Einstein condensate

Liaison sans fils à 60 GHz et réseau domestique multi-gigabit/s basé sur une infrastructure radio sur fibre bas coût

National audienceLe projet FUI8 ORIGIN (Optical Radio Infrastructure for Gigabit/s Indoor Network) s'adresse au marché du Réseau Local Domestique (RLD) en proposant une infrastructure bas coût qui combine l'efficacité de la fibre optique pour la diffusion radio avec les avantages d'une transmission sans fils. Les premières réalisations et les tests réussis sont présentés dans ce papier

Back to the Future – In support of a renewed emphasis on generic agility training within sports-specific developmental pathways

Perhaps as a consequence of increased specialism in training and support, the focus on engendering and maintaining agility as a generic quality has diminished within many contemporary sports performance programmes. Reflecting this, we outline a rationale suggesting that such a decreased focus represents an oversight which may be detrimental to maximising the potential of performers. We present an evidence-based argument that both generic and specific elements of agility performance should be consistently emphasised within long-term performance-training programmes. We contend that prematurely early specialisation in athlete development models can diminish focus on generic movement skill development with a subsequent detriment in adult performance. Especially when this is coupled with poor primary physical education and limited movement experiences. More speculatively, we propose that generic agility can play a role in operationalising movement development through facilitating skill transfer: thereby enabling the learning of new skills, reduce incidence of injury and facilitating re-learning of old skills during rehabilitation and Return-to-Play processes

Quantum cascade laser frequency stabilisation at the sub-Hz level

Quantum Cascade Lasers (QCL) are increasingly being used to probe the mid-infrared "molecular fingerprint" region. This prompted efforts towards improving their spectral performance, in order to reach ever-higher resolution and precision. Here, we report the stabilisation of a QCL onto an optical frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and 10-14, respectively. The comb is stabilised to a remote near-infrared ultra-stable laser referenced to frequency primary standards, whose signal is transferred via an optical fibre link. The stability and frequency traceability of our QCL exceed those demonstrated so far by two orders of magnitude. As a demonstration of its capability, we then use it to perform high-resolution molecular spectroscopy. We measure absorption frequencies with an 8x10-13 relative uncertainty. This confirms the potential of this setup for ultra-high precision measurements with molecules, such as our ongoing effort towards testing the parity symmetry by probing chiral species

Differential Effects of Aging on Fore– and Hindpaw Maps of Rat Somatosensory Cortex

Getting older is associated with a decline of cognitive and sensorimotor abilities, but it remains elusive whether age-related changes are due to accumulating degenerational processes, rendering them largely irreversible, or whether they reflect plastic, adaptational and presumably compensatory changes. Using aged rats as a model we studied how aging affects neural processing in somatosensory cortex. By multi-unit recordings in the fore- and hindpaw cortical maps we compared the effects of aging on receptive field size and response latencies. While in aged animals response latencies of neurons of both cortical representations were lengthened by approximately the same amount, only RFs of hindpaw neurons showed severe expansion with only little changes of forepaw RFs. To obtain insight into parallel changes of walking behavior, we recorded footprints in young and old animals which revealed a general age-related impairment of walking. In addition we found evidence for a limb-specific deterioration of the hindlimbs that was not observed in the forelimbs. Our results show that age-related changes of somatosensory cortical neurons display a complex pattern of regional specificity and parameter-dependence indicating that aging acts rather selectively on cortical processing of sensory information. The fact that RFs of the fore- and hindpaws do not co-vary in aged animals argues against degenerational processes on a global scale. We therefore conclude that age-related alterations are composed of plastic-adaptive alterations in response to modified use and degenerational changes developing with age. As a consequence, age-related changes need not be irreversible but can be subject to amelioration through training and stimulation