Optical guiding in meter-scale plasma waveguides

We demonstrate a new highly tunable technique for generating meter-scale low density plasma waveguides. Such guides can enable electron acceleration to tens of GeV in a single stage. Plasma waveguides are imprinted in hydrogen gas by optical field ionization induced by two time-separated Bessel beam pulses: The first pulse, a J_0 beam, generates the core of the waveguide, while the delayed second pulse, here a J_8 or J_16 beam, generates the waveguide cladding. We demonstrate guiding of intense laser pulses over hundreds of Rayleigh lengths with on axis plasma densities as low as N_e0=5x10^16 cm^-3

Monitoring of water fluxes by self-potential and TDR probes in the unsaturated vadoze zone during an intense cyclone

Réunion is an island located 700 km east of Madagascar in the southern Indian Ocean region. The Colimaçons research station is located on the western slope of Piton des Neiges at 800 m ASL (21°07'47 S and 55°18'19 E). The soil studied at the Colimaçons research station was located in the middle of a toposequence in which Andosols prevail. It was classified as an andic Cambisol, which included: (i) a surface A horizon (0-40 cm) altered to a shallow depth (<50 cm) by anthropedogenic processes, and (ii) an andic B horizon (40-200 cm). A pit dug down to 9 m showed that the subsoil is constituted by altered fissured and fractured rocks. The subsoil is composed of three types of rock levels. The first type of rock is hard and very compact, very little altered but cracked. Mineralogy was determined by optical microscopy and polarized light and natural XRD: 65% plagioclase (labrador), 15% Augite, Olivine 10% and 10% oxides (Illmenite, Magnetite and Hematite). They correspond to plagioclase basalts. The pit dug down to 9 m was equipped and protected against weather. The pit was equipped ca. each meter from the floor to the surface (-9, -8, -7... -1 and -0.4 m) with instruments to monitor water contents and fluxes. Time Domain Reflectometry (TDR) probes (CS616, Campbell Scientific) and Self-Potential (SP) probes were connected to a datalogger (CR10X-2M, Campbell Scientific) that recorded measurements on a 10-min basis from January 2007 to the end of March 2007 (day 1 to 80). This study was aimed at assessing whether (i) a continuous measurement with time of self potential and humidity allows us to follow water fluxes in the unsaturated zone and, (ii) which internal and external phenomenon could explain these variations of self potential and humidity during a cyclone period. The strategy adopted was, at first, to analyse simultaneously humidity signal from TDR probes and self-potential signals recorded before and after a cyclone (360 mm in 3 days). During the cyclone Gamède and during the following two weeks, the humidity measurements deducted from TDR probes have all increased. The more they are close to the surface, the more moisture measurements increased earlier and quickly. During this same period, the signals of SP probes showed a coherent and different dynamic. No major signal was observed despite a water flux of 360 mm in three days. The minima of the signals from sensors SP 2 to 10 are offset in time. As the depth increases, the signals of SP probes reach their minimum later. However, these fluctuations have remained low over the entire signal (a few mV to ten mV) throughout the period. (Texte intégal

Turbulent-like fluctuations in quasistatic flow of granular media

We analyze particle velocity fluctuations in a simulated granular system subjected to homogeneous quasistatic shearing. We show that these fluctuations share the following scaling characteristics of fluid turbulence in spite of their different physical origins: 1) Scale-dependent probability distribution with non-Guassian broadening at small time scales; 2) Power-law spectrum, reflecting long-range correlations and the self-affine nature of the fluctuations; 3) Superdiffusion with respect to the mean background flow

New universality class for the three-dimensional XY model with correlated impurities: Application to 4^4He in aerogels

Encouraged by experiments on $^4$He in aerogels, we confine planar spins in the pores of simulated aerogels (diffusion limited cluster-cluster aggregation) in order to study the effect of quenched disorder on the critical behavior of the three-dimensional XY model. Monte Carlo simulations and finite-size scaling are used to determine critical couplings $K_c$ and exponents. In agreement with experiments, clear evidence of change in the thermal critical exponents $\nu$ and $\alpha$ is found at nonzero volume fractions of impurities. These changes are explained in terms of {\it hidden} long-range correlations within disorder distributions.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let

Extended microsatellite analysis in microsatellite stable, MSH2 and MLH1 mutation-negative HNPCC patients: Genetic reclassification and correlation with clinical features

Background: Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant disorder predisposing to predominantly colorectal cancer (CRC) and endometrial cancer frequently due to germline mutations in DNA mismatch repair (MMR) genes, mainly MLH1, MSH2 and also MSH6 in families seen to demonstrate an excess of endometrial cancer. As a consequence, tumors in HNPCC reveal alterations in the length of simple repetitive genomic sequences like poly-A, poly-T, CA or GT repeats (microsatellites) in at least 90% of the cases. Aim of the Study: The study cohort consisted of 25 HNPCC index patients ( 19 Amsterdam positive, 6 Bethesda positive) who revealed a microsatellite stable (MSS) - or low instable (MSI-L) - tumor phenotype with negative mutation analysis for the MMR genes MLH1 and MSH2. An extended marker panel (BAT40, D10S197, D13S153, D18S58, MYCL1) was analyzed for the tumors of these patients with regard to three aspects. First, to reconfirm the MSI-L phenotype found by the standard panel; second, to find minor MSIs which might point towards an MSH6 mutation, and third, to reconfirm the MSS status of hereditary tumors. The reconfirmation of the MSS status of tumors not caused by mutations in the MMR genes should allow one to define another entity of hereditary CRC. Their clinical features were compared with those of 150 patients with sporadic CRCs. Results: In this way, 17 MSS and 8 MSI-L tumors were reclassified as 5 MSS, 18 MSI-L and even 2 MSI-H ( high instability) tumors, the last being seen to demonstrate at least 4 instable markers out of 10. Among all family members, 87 malignancies were documented. The mean age of onset for CRCs was the lowest in the MSI-H-phenotyped patients with 40.5 +/- 4.9 years (vs. 47.0 +/- 14.6 and 49.8 +/- 11.9 years in MSI-L- and MSS-phenotyped patients, respectively). The percentage of CRC was the highest in families with MSS-phenotyped tumors (88%), followed by MSI-L-phenotyped ( 78%) and then by MSI-H-phenotyped (67%) tumors. MSS tumors were preferentially localized in the distal colon supposing a similar biologic behavior like sporadic CRC. MSH6 mutation analysis for the MSI-L and MSI-H patients revealed one truncating mutation for a patient initially with an MSS tumor, which was reclassified as MSI-L by analyzing the extended marker panel. Conclusion: Extended microsatellite analysis serves to evaluate the sensitivity of the reference panel for HNPCC detection and permits phenotype confirmation or upgrading. Additionally, it confirms the MSS status of hereditary CRCs not caused by the common mutations in the MMR genes and provides hints to another entity of hereditary CRC. Copyright (C) 2004 S. Karger AG, Basel

Optimal box-covering algorithm for fractal dimension of complex networks

The self-similarity of complex networks is typically investigated through computational algorithms the primary task of which is to cover the structure with a minimal number of boxes. Here we introduce a box-covering algorithm that not only outperforms previous ones, but also finds optimal solutions. For the two benchmark cases tested, namely, the E. Coli and the WWW networks, our results show that the improvement can be rather substantial, reaching up to 15% in the case of the WWW network.Comment: 5 pages, 6 figure