Airborne bacterial populations above desert soils of the McMurdo Dry Valleys, Antarctica

Bacteria are assumed to disperse widely via aerosolized transport due to their small size and resilience. The question of microbial endemicity in isolated populations is directly related to the level of airborne exogenous inputs, yet this has proven hard to identify. The ice-free terrestrial ecosystem of Antarctica, a geographically and climatically isolated continent, was used to interrogate microbial bio-aerosols in relation to the surrounding ecology and climate. High-throughput sequencing of bacterial ribosomal RNA (rRNA) genes was combined with analyses of climate patterns during an austral summer. In general terms, the aerosols were dominated by Firmicutes, whereas surrounding soils supported Actinobacteria-dominated communities. The most abundant taxa were also common to aerosols from other continents, suggesting that a distinct bio-aerosol community is widely dispersed. No evidence for significant marine input to bio-aerosols was found at this maritime valley site, instead local influence was largely from nearby volcanic sources. Back trajectory analysis revealed transport of incoming regional air masses across the Antarctic Plateau, and this is envisaged as a strong selective force. It is postulated that local soil microbial dispersal occurs largely via stochastic mobilization of mineral soil particulates

Scaling laws for the photo-ionisation cross section of two-electron atoms

The cross sections for single-electron photo-ionisation in two-electron atoms show fluctuations which decrease in amplitude when approaching the double-ionisation threshold. Based on semiclassical closed orbit theory, we show that the algebraic decay of the fluctuations can be characterised in terms of a threshold law $\sigma \propto |E|^{\mu}$ as $E \to 0_-$ with exponent $\mu$ obtained as a combination of stability exponents of the triple-collision singularity. It differs from Wannier's exponent dominating double ionisation processes. The details of the fluctuations are linked to a set of infinitely unstable classical orbits starting and ending in the non-regularisable triple collision. The findings are compared with quantum calculations for a model system, namely collinear helium.Comment: 4 pages, 1 figur

Charge states and magnetic ordering in LaMnO3/SrTiO3 superlattices

We investigated the magnetic and optical properties of [(LaMnO3)n/(SrTiO3)8]20 (n = 1, 2, and 8) superlattices grown by pulsed laser deposition. We found a weak ferromagnetic and semiconducting state developed in all superlattices. An analysis of the optical conductivity showed that the LaMnO3 layers in the superlattices were slightly doped. The amount of doping was almost identical regardless of the LaMnO3 layer thickness up to eight unit cells, suggesting that the effect is not limited to the interface. On the other hand, the magnetic ordering became less stable as the LaMnO3 layer thickness decreased, probably due to a dimensional effect.Comment: 17 pages including 4 figures, accepted for publication in Phys. Rev.

Electrical Switching in Metallic Carbon Nanotubes

We present first-principles calculations of quantum transport which show that the resistance of metallic carbon nanotubes can be changed dramatically with homogeneous transverse electric fields if the nanotubes have impurities or defects. The change of the resistance is predicted to range over more than two orders of magnitude with experimentally attainable electric fields. This novel property has its origin that backscattering of conduction electrons by impurities or defects in the nanotubes is strongly dependent on the strength and/or direction of the applied electric fields. We expect this property to open a path to new device applications of metallic carbon nanotubes.Comment: 4 pages and 4 figure

Influence of dietary pattern on the development of overweight in a Chinese population

Objective: To examine dietary factors predisposing to overweight and obesity, taking into account age, gender, education level and physical activity. Design: Longitudinal population study. Setting: Community living subjects in Hong Kong. Subjects: One thousand and ten Chinese subjects participating in a territory wide dietary and cardiovascular risk factor prevalence survey in 1995-1996 were followed up for 5-9 years. Measurements: Body mass index (BMI) was measured. Information was collected on factors predisposing to development of overweight and obesity (age, gender, education level, physical activity, macronutrient intake, Mediterranean diet score and food variety), and the predisposing dietary factors examined, adjusted for other confounding factors, using logistic regression. Results: The 5-9-year incidence of overweight is 22.6% (BMI ≥ 23 kg/ m 2, 95% confidence interval (CI) = 15.0-30.1%) or 11.5% (BMI ≥ 25 kg/m 2, 95% CI = 7.3-15.7%), and for obesity (BMI ≥ 30 kg/m 2) is 0.6% (95% CI = -0.2-1.4%). The corresponding figures for women were 14.1% (95% CI = 8.8-19.5%), 9.7% (95% CI = 6.0-13.4%) and 3% (95% CI = 1.3-4.8%). After adjusting for confounding factors (age, sex, education and physical activity), increased variety of snack consumption was associated with increased risk of developing overweight (BMI ≥ 23 kg/m 2) in the Hong Kong Chinese population over a 5-9-year period. Conclusion: Increased variety of snack consumption may predispose to weight gain over a 5-9-year period.postprin

Irreversible Deposition of Line Segment Mixtures on a Square Lattice: Monte Carlo Study

We have studied kinetics of random sequential adsorption of mixtures on a square lattice using Monte Carlo method. Mixtures of linear short segments and long segments were deposited with the probability $p$ and $1-p$, respectively. For fixed lengths of each segment in the mixture, the jamming limits decrease when $p$ increases. The jamming limits of mixtures always are greater than those of the pure short- or long-segment deposition. For fixed $p$ and fixed length of the short segments, the jamming limits have a maximum when the length of the long segment increases. We conjectured a kinetic equation for the jamming coverage based on the data fitting.Comment: 7 pages, latex, 5 postscript figure

Effects of pressure on the ferromagnetic state of the CDW compound SmNiC2

We report the pressure response of charge-density-wave (CDW) and ferromagnetic (FM) phases of the rare-earth intermetallic SmNiC2 up to 5.5 GPa. The CDW transition temperature (T_{CDW}), which is reflected as a sharp inflection in the electrical resistivity, is almost independent of pressure up to 2.18 GPa but is strongly enhanced at higher pressures, increasing from 155.7 K at 2.2 GPa to 279.3 K at 5.5 GPa. Commensurate with the sharp increase in T_{CDW}, the first-order FM phase transition, which decreases with applied pressure, bifurcates into the upper (T_{M1}) and lower (T_c) phase transitions and the lower transition changes its nature to second order above 2.18 GPa. Enhancement both in the residual resistivity and the Fermi-liquid T^2 coefficient A near 3.8 GPa suggests abundant magnetic quantum fluctuations that arise from the possible presence of a FM quantum critical point.Comment: 5 pages, 5 figure