Two-Dimensional Electrons in a Strong Magnetic Field with Disorder: Divergence of the Localization Length

Electrons on a square lattice with half a flux quantum per plaquette are considered. An effective description for the current loops is given by a two-dimensional Dirac theory with random mass. It is shown that the conductivity and the localization length can be calculated from a product of Dirac Green's functions with the {\it same} frequency. This implies that the delocalization of electrons in a magnetic field is due to a critical point in a phase with a spontaneously broken discrete symmetry. The estimation of the localization length is performed for a generalized model with $N$ fermion levels using a $1/N$--expansion and the Schwarz inequality. An argument for the existence of two Hall transition points is given in terms of percolation theory.Comment: 10 pages, RevTeX, no figure

Floodplain sediment from a 30-year-recurrence flood in 2005 of the Ping River in northern Thailand

International audienceThis paper documents the nature of flood-producing storms and floodplain deposition associated with the 28 September?2 October 2005 30-year-recurrence flood on the Ping River in northern Thailand. The primary purpose of the study is to understand the extent that deposits from summer-monsoon floods can be identified in floodplain stratigraphy A secondary objective is to document the sedimentation processes/patterns associated with a large contemporary flood event on a medium-sized Asian river. Maximum sediment depths of 15 cm were found on the river levee, within 30 m of the main channel, and at 350 m thickness was 4 cm. Sediment depth generally decreased exponentially with distance away from the main channel. The extent of sediment deposition was about 1 km from the river channel. However, 72% of the sediment was deposited within an oval-shaped area 200?400 m from the main channel and centered on a tributary stream, through which sediment-laden water entered the floodplain, in addition to overtopping the levee of the main channel. Sediment concentration during the flood was estimated at 800?1500 mg L?1; and we believe the sediment was delivered by flows of well-mixed flood water occurring over a 1?2 day period. These data suggest that flood-deposited strata related to 30-year recurrence floods is only likely to be preserved in deposits located relatively close to the main river channel where fine sand and clayey coarse silt deposits have thicknesses of at least 5?10 cm. These relatively thick deposits would survive bioturbation, whereas more distal areas with thin clayey silt deposits would not

Thermoregulation of the \u3ci\u3epap\u3c/i\u3e Operon: Evidence for the Involvement of RimJ, the N-terminal Acetylase of Ribosomal Protein S5

Our previous work showed that pap pilin gene transcription is subject to a thermoregulatory control mechanism under which pap pilin is not transcribed at a low temperature (23°C) (L. B. Blyn, B. A. Braaten, C. A. White-Ziegler, D. H. Rolfson, and D. A. Low, EMBO J. 8:613-620, 1989). In order to isolate genes involved in this temperature regulation of gene expression, chromosomal mini-TnlO (mTnlO) mutations that allowed transcription of the pap pilin gene at 23°C were identified, and the locus was designated tcp, for thermoregulatory control of pap (C. A. White-Ziegler, L. B. Blyn, B. A. Braaten, and D. A. Low, J. Bacteriol. 172:1775-1782, 1990). In the present study, quantitative analysis showed that the tcp mutations restore pap pilin transcription at 23°C to levels similar to those measured at 37°C. By in vivo recombination, the tcp mutations were mapped to phage E4H1OS of the Kohara library of the Escherichia coli chromosome (Y. Kohara, K. Akiyama, and K. Isono, Cell 50:495-508, 1987). The tcp locus was cloned by complementation, in which a 1.3-kb DNA fragment, derived from the Kohara phage, was shown to restore thermoregulation to the mTnlO mutants. DNA sequencing revealed two open reading frames (ORFs) encoding proteins with calculated molecular masses of 22.7 and 20.3 kDa. The sequence of the 22.7-kDa ORF was identical to that of rimJ, the N-terminal acetylase of the ribosomal protein S5. The gene encoding the 20.3-kDa ORF, designated g20.3 here, did not display significant homology to any known. DNA or protein sequence. On the basis of Northern (RNA) blot data, rimj and g20.3 are located within the same operon. Two of the mTnlO transposons in the thermoregulatory mutants were inserted within the coding region of rimi, indicating that the RimJ protein plays an important role in the temperature regulation ofpap pilin gene transcription. However, rimj itself is not thermoregulated, since rim. transcripts were detected at both 23 and 37°C. Disruption of the g20.3 gene by insertion and deletion mutagenesis did not affect thermoregulation of the pap operon, suggesting that, although g20.3 lies within the same operon as rimj, it does not play a role in thermoregulation

A snapshot of some pLI score pitfalls

The pLI score reflects the tolerance of a given gene to the loss of function on the basis of the number of protein truncating variants, that is, the frameshift, splice donor, splice acceptor, and stop-gain variants referenced for this gene in control databases weighted by the size of the gene and the sequencing coverage. It is frequently used to prioritize candidate genes when analyzing whole exome or whole genome data. We list here the main pitfalls to consider before using this score. Concrete illustrations are given for each of these pitfalls

Three-dimensional track reconstruction for directional Dark Matter detection

Directional detection of Dark Matter is a promising search strategy. However, to perform such detection, a given set of parameters has to be retrieved from the recoiling tracks : direction, sense and position in the detector volume. In order to optimize the track reconstruction and to fully exploit the data of forthcoming directional detectors, we present a likelihood method dedicated to 3D track reconstruction. This new analysis method is applied to the MIMAC detector. It requires a full simulation of track measurements in order to compare real tracks to simulated ones. We conclude that a good spatial resolution can be achieved, i.e. sub-mm in the anode plane and cm along the drift axis. This opens the possibility to perform a fiducialization of directional detectors. The angular resolution is shown to range between 20$^\circ$ to 80$^\circ$, depending on the recoil energy, which is however enough to achieve a high significance discovery of Dark Matter. On the contrary, we show that sense recognition capability of directional detectors depends strongly on the recoil energy and the drift distance, with small efficiency values (50%-70%). We suggest not to consider this information either for exclusion or discovery of Dark Matter for recoils below 100 keV and then to focus on axial directional data.Comment: 27 pages, 20 figure

Scanning tunneling microscopy and kinetic Monte Carlo investigation of Cesium superlattices on Ag(111)

Cesium adsorption structures on Ag(111) were characterized in a low-temperature scanning tunneling microscopy experiment. At low coverages, atomic resolution of individual Cs atoms is occasionally suppressed in regions of an otherwise hexagonally ordered adsorbate film on terraces. Close to step edges Cs atoms appear as elongated protrusions along the step edge direction. At higher coverages, Cs superstructures with atomically resolved hexagonal lattices are observed. Kinetic Monte Carlo simulations model the observed adsorbate structures on a qualitative level.Comment: 8 pages, 7 figure