Moduli spaces of hyperbolic 3-manifolds and dynamics on character varieties

The space AH(M) of marked hyperbolic 3-manifold homotopy equivalent to a compact 3-manifold with boundary M sits inside the PSL_2(C)-character variety X(M) of \pi_1(M). We study the dynamics of the action of Out(\pi_1(M)) on both AH(M) and X(M). The nature of the dynamics reflects the topology of M. The quotient AI(M)=AH(M)/Out(\pi_1(M)) may naturally be thought of as the moduli space of unmarked hyperbolic 3-manifolds homotopy equivalent to M and its topology reflects the dynamics of the action

Absolute Determination of the 22Na(p,g) Reaction Rate in Novae

Gamma-ray telescopes in orbit around the Earth are searching for evidence of the elusive radionuclide 22Na produced in novae. Previously published uncertainties in the dominant destructive reaction, 22Na(p,g)23Mg, indicated new measurements in the proton energy range of 150 to 300 keV were needed to constrain predictions. We have measured the resonance strengths, energies, and branches directly and absolutely by using protons from the University of Washington accelerator with a specially designed beamline, which included beam rastering and cold vacuum protection of the 22Na implanted targets. The targets, fabricated at TRIUMF-ISAC, displayed minimal degradation over a ~ 20 C bombardment as a result of protective layers. We avoided the need to know the stopping power, and hence the target composition, by extracting resonance strengths from excitation functions integrated over proton energy. Our measurements revealed that resonance strengths for E_p = 213, 288, 454, and 610 keV are stronger by factors of 2.4 to 3.2 than previously reported. Upper limits have been placed on proposed resonances at 198-, 209-, and 232-keV. We have re-evaluated the 22Na(p,g) reaction rate, and our measurements indicate the resonance at 213 keV makes the most significant contribution to 22Na destruction in novae. Hydrodynamic simulations including our rate indicate that the expected abundance of 22Na ejecta from a classical nova is reduced by factors between 1.5 and 2, depending on the mass of the white-dwarf star hosting the nova explosion.Comment: 20 pages, 18 figures; shortened paper, accepted in Phys. Rev.

InAs nanowire transistors with multiple, independent wrap-gate segments

We report a method for making horizontal wrap-gate nanowire transistors with up to four independently controllable wrap-gated segments. While the step up to two independent wrap-gates requires a major change in fabrication methodology, a key advantage to this new approach, and the horizontal orientation more generally, is that achieving more than two wrap-gate segments then requires no extra fabrication steps. This is in contrast to the vertical orientation, where a significant subset of the fabrication steps needs to be repeated for each additional gate. We show that cross-talk between adjacent wrap-gate segments is negligible despite separations less than 200 nm. We also demonstrate the ability to make multiple wrap-gate transistors on a single nanowire using the exact same process. The excellent scalability potential of horizontal wrap-gate nanowire transistors makes them highly favourable for the development of advanced nanowire devices and possible integration with vertical wrap-gate nanowire transistors in 3D nanowire network architectures.Comment: 18 pages, 5 figures, In press for Nano Letters (DOI below

The Baade-Wesselink p-factor applicable to LMC Cepheids

Context. Recent observations of LMC Cepheids bring new constraints on the slope of the period-projection factor relation (hereafter Pp relation) that is currently used in the Baade-Wesselink (hereafter BW) method of distance determination. The discrepancy between observations and theoretical analysis is particularly significant for short period Cepheids Aims. We investigate three physical effects that might possibly explain this discrepancy: (1) the spectroscopic S/N that is systematically lower for LMC Cepheids (around 10) compared to Galactic ones (up to 300), (2) the impact of the metallicity on the dynamical structure of LMC Cepheids, and (3) the combination of infrared photometry/interferometry with optical spectroscopy. Methods. To study the S/N we use a very simple toy model of Cepheids. The impact of metallicity on the projection factor is based on the hydrodynamical model of delta Cep already described in previous studies. This model is also used to derive the position of the optical versus infrared photospheric layers. Results. We find no significant effect of S/N, metallicity, and optical-versus-infrared observations on the Pp relation. Conclusions. The Pp relation of Cepheids in the LMC does not differ from the Galactic relation. This allows its universal application to determine distances to extragalactic Cepheids via BW analysis.Comment: accepted in A&A LETTER

Cepheid variables in the LMC cluster NGC 1866. I. New BVRI CCD photometry

We report BV(RI)c CCD photometric data for a group of seven Cepheid variables in the young, rich cluster NGC 1866 in the Large Magellanic Cloud. The photometry was obtained as part of a program to determine accurate distances to these Cepheids by means of the infrared surface brightness technique, and to improve the LMC Cepheid database for constructing Cepheid PL and PLC relations. Using the new data together with data from the literature, we have determined improved periods for all variables. For five fundamental mode pulsators, the light curves are now of excellent quality and will lead to accurate distance and radius determinations once complete infrared light curves and radial velocity curves for these variables become available.Comment: To appear in ApJ Supp., AASTeX, 24 pages, 8 tables, 8 figure

Laboratory surveillance of Shigella dysenteriae type 1 in Kwazulu-natal

Objective. To collect data on the antimicrobial susceptibility of Shigella dysenteriae type 1 in KwaZulu-Natal, including the testing of newer therapeutic agents, and to evaluate the ability of laboratories to participate in a provincial surveillance programme.Design. Prospective descriptive study.Setting. Hospital laboratories in KwaZulu-Natal, including peripheral laboratories and the medical microbiology laboratory of the University of Natal.Main outcome measures. Antimicrobial susceptibility pattern of surveillance strains and evaluation of the ability of provincial laboratories to isolate Shigella.Results. All 354 strains tested were resistant to ampicillin, chloramphenicol and tetracycline. Co-trimoxazole resistance was found in 99.2% of strains, and 0.8% of strains were resistant to nalidixic acid. All strains were susceptible to ceftriaxone, ciprofloxacin, ofloxacin, pivmecillinam, azithromycin, loracarbef and fosfomycin. Of the 29 laboratories surveyed, 18 (62.1%) were able to isolate and identify S, dysenteriae correctly, and 9 (32%) were able to serotype it further to S, dysenteriae type 1. Twenty-seven (93.1%) had appropriate culture media and 26 (89.7%) had antisera for Shigella identification.Conclusions. There is little variation among strains of S. dysenteriae type 1 in KwaZulu-Natal with regard to their antimicrobial susceptibility pattern. Nalidixic acid should remain the antimicrobial of choice for treatment of dysentery in our region as resistance to it is low. The majority of KwaZulu-Natallaboratories.have the expertise and equipment to perform the isolation and identification of Shigella species

MODELING STREAMBANK EROSION ON COMPOSITE STREAMBANKS ON A WATERSHED SCALE

Streambanks can be a significant source of sediment and phosphorus to aquatic ecosystems. Although the streambank-erosion routine in the Soil and Water Assessment Tool (SWAT) has improved in recent versions, the recently developed routine in SWAT 2012 has undergone limited testing, and the lack of site or watershed specific streambank data increases the uncertainty in the streambank-erosion predictions. There were two primary objectives of this research: (1) modify and test the 2012 SWAT streambank-erosion routine on composite streambanks, and (2) compare SWAT default and field-measured channel parameters and assess their influence on predicted streambank erosion. Three modifications were made to the SWAT 2012 streambank-erosion routine: (1) replacing the empirical effective shear stress equation with a process-based equation, (2) replacing bankfull width and depth measurements with top width and streambank height, and (3) incorporating an area-adjustment factor to account for non-trapezoidal cross-sections. The proposed streambank-erosion routine was tested on gravel-dominated streambanks on the Barren Fork Creek in northeastern Oklahoma. The study used data from 28 cross-sectional surveys, including streambank height and top width, side slope, thickness and texture of streambank layers, and an area-adjustment factor. Gravel d50 and kd- ô c relationships were used to estimate the critical shear stress ( ô c) and the erodibility coefficient (kd), respectively. Incorporating the process-based shear stress equation, areaadjustment factor, or the top width and streambank height increased predicted streambank erosion by 85%, 31%, and - 30%, respectively. Incorporating the process-based effective shear stress equation, sinuosity, radius of curvature, and measured bed slope improved the predicted versus observed streambank erosion Nash-Sutcliffe efficiency from -0.33 to 0.49 and the coefficient of determination (R2) from 0.02 to 0.65 at the ten study sites. Although the process-based effective shear stress equation was the most influential modification, incorporating the top width, streambank height, and area-adjustment factor more accurately represented the measured irregular cross-sections