Resonant demagnetization of a dipolar BEC in a 3D optical lattice

We study dipolar relaxation of a chromium BEC loaded into a 3D optical lattice. We observe dipolar relaxation resonances when the magnetic energy released during the inelastic collision matches an excitation towards higher energy bands. A spectroscopy of these resonances for two orientations of the magnetic field provides a 3D band spectroscopy of the lattice. The narrowest resonance is registered for the lowest excitation energy. Its line-shape is sensitive to the on-site interaction energy. We use such sensitivity to probe number squeezing in a Mott insulator, and we reveal the production of three-body states with entangled spin and orbital degrees of freedom.Comment: 5 pages, 3 Figures, Supplemental Materia

Dipolar atomic spin ensembles in a double-well potential

We experimentally study the spin dynamics of mesoscopic ensembles of ultracold magnetic spin-3 atoms located in two separated wells of an optical dipole trap. We use a radio-frequency sweep to selectively flip the spin of the atoms in one of the wells, which produces two separated spin domains of opposite polarization. We observe that these engineered spin domains are metastable with respect to the long-range magnetic dipolar interactions between the two ensembles. The absence of inter-cloud dipolar spin-exchange processes reveals a classical behavior, in contrast to previous results with atoms loaded in an optical lattice. When we merge the two subsystems, we observe spin-exchange dynamics due to contact interactions which enable the first determination of the s-wave scattering length of 52Cr atoms in the S=0 molecular channel a_0=13.5^{+11}_{-10.5}a_B (where a_B is the Bohr radius).Comment: 9 pages, 7 figure

Accumulation and thermalization of cold atoms in a finite-depth magnetic trap

We experimentally and theoretically study the continuous accumulation of cold atoms from a magneto-optical trap (MOT) into a finite depth trap, consisting in a magnetic quadrupole trap dressed by a radiofrequency (RF) field. Chromium atoms (52 isotope) in a MOT are continuously optically pumped by the MOT lasers to metastable dark states. In presence of a RF field, the temperature of the metastable atoms that remain magnetically trapped can be as low as 25 microK, with a density of 10^17 atoms.m-3, resulting in an increase of the phase-space density, still limited to 7.10^-6 by inelastic collisions. To investigate the thermalization issues in the truncated trap, we measure the free evaporation rate in the RF-truncated magnetic trap, and deduce the average elastic cross section for atoms in the 5D4 metastable states, equal to 7.0 10^-16m2.Comment: 9 pages, 10 Figure

TRIDENT: an Infrared Differential Imaging Camera Optimized for the Detection of Methanated Substellar Companions

A near-infrared camera in use at the Canada-France-Hawaii Telescope (CFHT) and at the 1.6-m telescope of the Observatoire du Mont-Megantic is described. The camera is based on a Hawaii-1 1024x1024 HgCdTe array detector. Its main feature is to acquire three simultaneous images at three wavelengths across the methane absorption bandhead at 1.6 microns, enabling, in theory, an accurate subtraction of the stellar point spread function (PSF) and the detection of faint close methanated companions. The instrument has no coronagraph and features fast data acquisition, yielding high observing efficiency on bright stars. The performance of the instrument is described, and it is illustrated by laboratory tests and CFHT observations of the nearby stars GL526, Ups And and Chi And. TRIDENT can detect (6 sigma) a methanated companion with delta H = 9.5 at 0.5" separation from the star in one hour of observing time. Non-common path aberrations and amplitude modulation differences between the three optical paths are likely to be the limiting factors preventing further PSF attenuation. Instrument rotation and reference star subtraction improve the detection limit by a factor of 2 and 4 respectively. A PSF noise attenuation model is presented to estimate the non-common path wavefront difference effect on PSF subtraction performance.Comment: 41 pages, 16 figures, accepted for publication in PAS

Modelling of anal sphincter tone based on pneumatic and cable-driven mechanisms

Motivated by the need for improving a haptics-based simulation tool for learning and training digital rectal examinations, a sphincter tone model and its actuation is conceived and developed. Two approaches are presented: One based on pneumatics actuation and the other using cable-driven mechanical actuation using servo motors. Clinical scenarios are modelled as profiles based on studies of anorectal manometry and adapted with clinical input. Both designed mechanisms and scenarios were experimentally evaluated by six experts, Nurse Practitioners in Continence and Colorectal Surgeons. Results show that both mechanisms produce enough pressure on examining finger and profiles are able to generate a wide range of healthy and abnormal cases. Either approach could be used to provide a more realistic experience during training of sphincter tone assessment

Purely entropic self-assembly of the bicontinuous Ia3̅d gyroid phase in equilibrium hard-pear systems

We investigate a model of hard pear-shaped particles which forms the bicontinuous Ia3d structure by entropic self-assembly, extending the previous observations of Barmes et al. (2003 Phys. Rev. E 68, 021708. (doi:10.1103/PhysRevE.68.021708)) and Ellison et al. (2006 Phys. Rev. Lett. 97, 237801. (doi:10.1103/PhysRevLett.97.237801)). We specifically provide the complete phase diagram of this system, with global density and particle shape as the two variable parameters, incorporating the gyroid phase as well as disordered isotropic, smectic and nematic phases. The phase diagram is obtained by two methods, one being a compression–decompression study and the other being a continuous change of the particle shape parameter at constant density. Additionally, we probe the mechanism by which interdigitating sheets of pears in these systems create surfaces with negative Gauss curvature, which is needed to form the gyroid minimal surface. This is achieved by the use of Voronoi tessellation, whereby both the shape and volume of Voronoi cells can be assessed in regard to the local Gauss curvature of the gyroid minimal surface. Through this, we show that the mechanisms prevalent in this entropy-driven system differ from those found in systems which form gyroid structures in nature (lipid bilayers) and from synthesized materials (di-block copolymers) and where the formation of the gyroid is enthalpically driven. We further argue that the gyroid phase formed in these systems is a realization of a modulated splay-bend phase in which the conventional nematic has been predicted to be destabilized at the mesoscale due to molecular-scale coupling of polar and orientational degrees of freedo

Fine Structure of the N=1 (1s3p)3Πu State of the Hydrogen Molecule Determined by Magnetic Resonance

International audienceIn the preceding paper some of our results on the magnetic-resonance experiments performed at 64 MHz indicated a beginning of N.S decoupling on the N=1 (1s3p)3Πu state of H2 excited by electron impact. In the present paper we present further results on the resonance experiments performed at higher frequencies in order to determine the fine structure of this level. Our findings indicate that the energy separation between J=1 and J=2 levels is 160+/-5 MHz and between J=1 and J=0 levels it is 2100+/-600 MHz, and in addition the former exhibits a small dependence on the vibrational number. The relative order of these levels is J=1, 2, 0 instead of the theoretically predicted 2, 1, 0. The Landé g factor is 1.249+/-0.010, which corresponds to a pure Hund's-coupling case (b)

Brownian Dynamics Simulation of Polydisperse Hard Spheres

Standard algorithms for the numerical integration of the Langevin equation require that interactions are slowly varying during to the integration timestep. This in not the case for hard-body systems, where there is no clearcut between the correlation time of the noise and the timescale of the interactions. Starting from a short time approximation of the Smoluchowsky equation, we introduce an algorithm for the simulation of the overdamped Brownian dynamics of polydisperse hard-spheres in absence of hydrodynamics interactions and briefly discuss the extension to the case of external drifts

Lifetimes, g Factors, and Collision Cross Sections of Hydrogen Molecules in the (1s3p)3Πu Level

International audienceExperimental results obtained by Hanle and Bitter-Brossel effects on the N=1 and N=2 (v=0, 1, 2, and 3) levels of the (1s3p)3Πu state of the parahydrogen molecule excited by electron impact are presented. Resonances are found at the experimentally lowest possible frequencies (21-64 MHz) in a region where the N. S decoupling is nonexistent for the N=2 level [the measured Landé g factors are 0.77 +/- 0.01 and 0.48 +/- 0.02 corresponding to a pure Hund's-coupling case (b)] and just beginning for the N=1 level (at 21 MHz the apparent measured g is 1.235 +/- 0.01). These results together with the calculations carried out in the case of complete N.S coupling lead to lifetimes τ=(3.10+/-0.3)×10-8 see (N=1) and τ=(3.15+/-0.3)×10-8 sec (N=2) and H2* - H2 cross sections τ=232+/-30 Å2 (N=1) and σ=240+/-30 Å2 (N=2). The quantities g, τ, and σ were all found to be independent on the vibrational number. Risk of cascade was eliminated

The role of surface free energy in the early in vivo formation of dental plaque on human enamel and polymeric substrata

Strips of teflon and cellulose acetate were glued to the upper lateral incisors of human volunteers in a split mouth, double blind study on the influence of the substratum surface free energy (s.f.e.) on supragingival dental plaque accumulation during a three day period of no oral hygiene. Plaque accumulation, microbial composition of the plaque and s.f.e. of the microorganisms were determined and compared to plaque developed on natural enamel surfaces. Significantly less microorganisms colonised the polymer surfaces (p &lt; 0.002). Streptococcus sanguis I was the predominant microorganism found in enamel samples, comprising about one-third of the total microflora, whereas it was recovered infrequently and in lower numbers from the polymeric surfaces, which predominantly contained Streptococcus sanguis II. Only on cellulose acetate sometimes high numbers of Streptococcus mitis and Streptococcus morbillorum were detected. The mean s.f.e. of the total plaque flora was lowest on teflon (84.5 mJ m-2) followed by cellulose acetate (86.0 mJm-2), whereas enamel harboured a microflora with a significantly higher mean s.f.e. (930 mJ m-2; p &lt; 0.05). Also within the same bacterial species lower s.f.e. strains were isolated from the polymer surfaces compared to enamel. The results conform to a previously postulated model in which the interfacial free energy is the driving force for adhesion of microorganisms to solid surfaces.</p