Recent Developments in Mems-Based Micro Fuel Cells

Micro fuel cells ($\mu$-FC) represent promising power sources for portable applications. Today, one of the technological ways to make $\mu$-FC is to have recourse to standard microfabrication techniques used in the fabrication of micro electromechanical systems (MEMS). This paper shows an overview on the applications of MEMS techniques on miniature FC by presenting several solutions developed throughout the world. It also describes the latest developments of a new porous silicon-based miniature fuel cell. Using a silane grafted on an inorganic porous media as the proton-exchange membrane instead of a common ionomer such as Nafion, the fuel cell achieved a maximum power density of 58 mW cm-2 at room temperature with hydrogen as fuel.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

On large deviation regimes for random media models

The focus of this article is on the different behavior of large deviations of random subadditive functionals above the mean versus large deviations below the mean in two random media models. We consider the point-to-point first passage percolation time $a_n$ on $\mathbb{Z}^d$ and a last passage percolation time $Z_n$. For these functionals, we have $\lim_{n\to\infty}\frac{a_n}{n}=\nu$ and $\lim_{n\to\infty}\frac{Z_n}{n}=\mu$. Typically, the large deviations for such functionals exhibits a strong asymmetry, large deviations above the limiting value are radically different from large deviations below this quantity. We develop robust techniques to quantify and explain the differences.Comment: Published in at http://dx.doi.org/10.1214/08-AAP535 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

A theoretical analysis of the electromagnetic environment of the AS330 super Puma helicopter external and internal coupling

Numerical techniques such as Finite Difference Time Domain (FDTD) computer programs, which were first developed to analyze the external electromagnetic environment of an aircraft during a wave illumination, a lightning event, or any kind of current injection, are now very powerful investigative tools. The program called GORFF-VE, was extended to compute the inner electromagnetic fields that are generated by the penetration of the outer fields through large apertures made in the all metallic body. Then, the internal fields can drive the electrical response of a cable network. The coupling between the inside and the outside of the helicopter is implemented using Huygen's principle. Moreover, the spectacular increase of computer resources, as calculations speed and memory capacity, allows the modellization structures as complex as these of helicopters with accuracy. This numerical model was exploited, first, to analyze the electromagnetic environment of an in-flight helicopter for several injection configurations, and second, to design a coaxial return path to simulate the lightning aircraft interaction with a strong current injection. The E field and current mappings are the result of these calculations

Competition between Electromagnetically Induced Transparency and Raman Processes

We present a theoretical formulation of competition among electromagnetically induced transparency (EIT) and Raman processes. The latter become important when the medium can no longer be considered to be dilute. Unlike the standard formulation of EIT, we consider all fields applied and generated as interacting with both the transitions of the $\Lambda$ scheme. We solve Maxwell equations for the net generated field using a fast-Fourier-transform technique and obtain predictions for the probe, control and Raman fields. We show how the intensity of the probe field is depleted at higher atomic number densities due to the build up of multiple Raman fields.Comment: 3.5 pages, 7 figure

Pathobiology of mycobacteria in striped bass (Morone saxatilis)

Striped bass (Morone saxatilis) in Chesapeake Bay, USA, are experiencing an epizootic of mycobacteriosis. This disease, caused by bacteria in the genus Mycobacterium, causes granulomatous lesions of the skin and viscera. Diseased fish are often emaciated, and fish with skin lesions may be significantly disfigured. The overall goal of this work was to examine aspects of the pathobiology of mycobacteria in striped bass via laboratory exposure studies and cellular assays. Striped bass were injected intraperitoneally with a sublethal dose of Mycobacterium marinum, M. shottsii, or M. gordonae and sampled for histology and bacteriology at regular intervals to 45 weeks post-injection (p.i.). Fish injected with M. marinum developed granulomas in the mesenteries, spleen and anterior kidney. Acid-fast bacilli (AFB) were rare in initial stages of disease whereas granulomas at 8 weeks p.i. and later frequently contained large numbers of AFB. Secondary disease was observed in some fish between 26 and 45 weeks p.i., with granuloma disintegration, severe inflammation, and elevated splenic bacterial densities. Relative to fish injected with M. marinum, fish injected with M. shottsii or M. gordonae did not develop severe pathology. Granulomas were observed in the mesenteries, but were not observed in the spleen or, with one exception, anterior kidney. M. shottsii and M. gordonae both established persistent splenic infections. The ultrastructure of developing M. marinum granulomas in experimentally infected bass was examined. Formation of large macrophage aggregations containing intracellular bacilli was observed within the peritoneal cavity shortly after injection. M. marinum were always contained within phagosomes, and apparent phagolysosomal fusion was frequently observed. Epithelioid transformation of macrophages was observed. Ultrastructural observation of bacilli within granulomas agreed with histologic findings. The in vitro interaction between macrophages and intracellular M. marinum was examined ultrastructurally and with a quantitative bactericidal assay. Phagosomes containing M. marinum were fused at high rates by pre-labeled lysosomes. No differences in lysosomal fusion rates were observed between phagosomes containing live or heat-killed M. marinum. Intracellular M. marinum remained largely viable for the duration of the assay (72 hours). Heat-killed M marinum were resistant to lysis within phagolysosomes

Potential vorticity mixing by marginally unstable baroclinic disturbances

The weakly nonlinear dynamics of a baroclinic wave in a two-layer model near minimum critical shear is described in terms of a nonlinear critical layer problem which is completely integrable in the absence of dissipation. Sufficiently small amplitude supercritical inviscid disturbances are found to equilibrate to leading order, even though the absolute potential enstrophy of the lowest layer is always transient and transferred irreversibly to smaller and smaller scales. The inviscid equilibrium amplitude of the fundamental is found to be larger by a factor of 2 than the weakly dissipative value found by Pedlosky, implying that the limits t [RIGHTWARDS ARROW] ∞ and vanishing dissipation are not interchangeable. The fundamental equilibrates when the mixing in the lowest layer results in the streamwise homogenization of the coarse-grained potential vorticity. It is also noted that coarse-grain homogenization can be established on faster time scales than the fine-grain versions discussed by Rhines and Young. With weak or vanishing supercriticality or larger initial disturbance amplitudes, the fundamental may either equilibrate or oscillate periodically, depending on the form and strength of the initial disturbance. In the oscillating case, the baroclinic vortex reversibly wraps up and un-wraps and there is no tendency to mix potential vorticity. Finally, the possibility of further instabilities similar to those discussed by Killworth and McIntyre, and Haynes for the Rossby wave critical layer problem is also noted

Security of high-dimensional quantum key distribution protocols using Franson interferometers

Franson interferometers are increasingly being proposed as a means of securing high-dimensional energy-time entanglement-based quantum key distribution (QKD) systems. Heuristic arguments have been proposed that purport to demonstrate the security of these schemes. We show, however, that such systems are vulnerable to attacks that localize the photons to several temporally separate locations. This demonstrates that a single pair of Franson interferometers is not a practical approach to securing high-dimensional energy-time entanglement based QKD. This observations leads us to investigate the security of modified Franson-based-protocols, where Alice and Bob have two or more Franson interferometers. We show that such setups can improve the sensitivity against attacks that localize the photons to multiple temporal locations. While our results do not constituting a full security proof, they do show that a single pair of Franson interferometers is not secure and that multiple such interferometers could be a promising candidate for experimentally realizable high-dimensional QKD.Comment: 14 pages (single column format

Direct imaging of a digital-micromirror device for configurable microscopic optical potentials

Programable spatial light modulators (SLMs) have significantly advanced the configurable optical trapping of particles. Typically, these devices are utilized in the Fourier plane of an optical system, but direct imaging of an amplitude pattern can potentially result in increased simplicity and computational speed. Here we demonstrate high-resolution direct imaging of a digital micromirror device (DMD) at high numerical apertures (NA), which we apply to the optical trapping of a Bose-Einstein condensate (BEC). We utilise a (1200 x 1920) pixel DMD and commercially available 0.45 NA microscope objectives, finding that atoms confined in a hybrid optical/magnetic or all-optical potential can be patterned using repulsive blue-detuned (532 nm) light with 630(10) nm full-width at half-maximum (FWHM) resolution, within 5% of the diffraction limit. The result is near arbitrary control of the density the BEC without the need for expensive custom optics. We also introduce the technique of time-averaged DMD potentials, demonstrating the ability to produce multiple grayscale levels with minimal heating of the atomic cloud, by utilising the high switching speed (20 kHz maximum) of the DMD. These techniques will enable the realization and control of diverse optical potentials for superfluid dynamics and atomtronics applications with quantum gases. The performance of this system in a direct imaging configuration has wider application for optical trapping at non-trivial NAs.Comment: 9 page

On large deviations for the parabolic Anderson model

The focus of this article is on the different behavior of large deviations of random functionals associated with the parabolic Anderson model above the mean versus large deviations below the mean. The functionals we treat are the solution u(x, t) to the spatially discrete parabolic Anderson model and a functional A n which is used in analyzing the a.s. Lyapunov exponent for u(x, t). Both satisfy a “law of large numbers”, with $${\lim_{t\to \infty} \frac{1}{t} \log u(x,t)=\lambda (\kappa)}$$ and $${\lim_{n\to \infty} \frac{A_n}{n}=\alpha}$$ . We then think of αn and λ(κ)t as being the mean of the respective quantities A n and log u(t, x). Typically, the large deviations for such functionals exhibits a strong asymmetry; large deviations above the mean take on a different order of magnitude from large deviations below the mean. We develop robust techniques to quantify and explain the differences