L\'evy flights of photons in hot atomic vapours

Properties of random and fluctuating systems are often studied through the use of Gaussian distributions. However, in a number of situations, rare events have drastic consequences, which can not be explained by Gaussian statistics. Considerable efforts have thus been devoted to the study of non Gaussian fluctuations such as L\'evy statistics, generalizing the standard description of random walks. Unfortunately only macroscopic signatures, obtained by averaging over many random steps, are usually observed in physical systems. We present experimental results investigating the elementary process of anomalous diffusion of photons in hot atomic vapours. We measure the step size distribution of the random walk and show that it follows a power law characteristic of L\'evy flights.Comment: This final version is identical to the one published in Nature Physic

Hypergravity effects on glide arc plasma

The behaviour of a special type of electric discharge – the gliding arc plasma – has been investigated in hypergravity (1g –18g) using the Large Diameter Centrifuge (LDC) at ESA/ESTEC. The discharge voltage and current together with the videosignal from a fast camera have been recorded during the experiment. The gliding of the arc is governed by hot gas buoyancy and by consequence, gravity. Increasing the centrifugal acceleration makes the glide arc movement substantially faster. Whereas at 1g the discharge was stationary, at 6g it glided with 7 Hz frequency and at 18g the gliding frequency was 11 Hz. We describe a simple model for the glide arc movement assuming low gas flow velocities, which is compared to our experimental results

Production of XeO * in a CW microwave discharge

A low-power CW microwave discharge at 2.45 GHz was used to produce XeO * excimer molecules. It was found that a total gas pressure between 5 and 20 Torr, absorbed power of about 20–100 W, and an oxygen-to-xenon ratio of 1∶100 maximized the XeO( 1 S− 1 D) green emission at 5200 to 5600 Å. The XeO * emission appeared in the cooler parts of the discharge near the containment tube walls and in the electric field nodes of the TM 012 resonant mode.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45480/1/11090_2005_Article_BF01023916.pd

Relaxed DM requirements during class II peptide loading and CD4+ T cell maturation in BALB/c mice.

Current ideas about DM actions have been strongly influenced by studies of mutant strains expressing the H-2(b) haplotype. To evaluate DM contributions to class II activities in BALB/c mice, we generated a novel mutation at the DMa locus via embryonic stem cell technology. Unlike long-lived A(b)/class II-associated invariant chain-derived peptide (CLIP) complexes, mature A(d) and E(d) molecules are loosely occupied by class II-associated invariant chain-derived peptide and are SDS unstable. BALB/c DM mutants weakly express BP107 conformational epitopes and toxic shock syndrome toxin-1 superantigen-binding capabilities, consistent with partial occupancy by wild-type ligands. Near normal numbers of mature CD4(+) T cells fail to undergo superantigen-mediated negative selection, as judged by TCR Vbeta usage. Ag presentation assays reveal consistent differences for A(d)- and E(d)-restricted T cells. Indeed, the mutation leads to decreased peptide capture by A(d) molecules, and in striking contrast causes enhanced peptide loading by E(d) molecules. Thus, DM requirements differ for class II structural variants coexpressed under physiological conditions in the intact animal