Universal transport properties of three-dimensional topological insulator nanowires

We report theoretical calculations of electronic and transport properties mediated by topological helical states on the walls of three-dimensional topological insulator (TI) nanowires. A universal regime of quantized conductance and fluctuations is found that is induced by disorder. The average conductance of the disordered nanowire scales as a function of the number of transmission channels N in a universal form = independent of the system details. For instance, for Bi2Se3 nanowires cleaved along the x or y direction with the quintuple layers along the z direction =(5/12)N+1/2. The universal and quantized behavior is due to the topological physics happening on the walls of the nanowire under the influence of disorder. © 2014 American Physical Society.published_or_final_versio

Dynamic response and breakage of trees subject to a landslide-induced air blast

Landslides have been known to generate powerful air blasts capable of causing destruction and casualties far beyond the runout of sliding mass. The extent of tree damage provides valuable information on air blast intensity and impact region. However, little attention has been paid to the air blast–tree interaction. In this study, we proposed a framework to assess the tree destruction caused by powerful air blasts, including the eigenfrequency prediction method, tree motion equations and the breakage conditions. The tree is modeled as a flexible beam with variable cross-sections, and the anchorage stiffness is introduced to describe the tilt of the tree base. Large tree deflection is regarded when calculating the air blast loading, and two failure modes (bending and overturning) and the associated failure criteria are defined. Modeling results indicate that although the anchorage properties are of importance to the tree eigenfrequency, tree eigenfrequency is always close to the air blast frequency, causing a dynamic magnification effect for the tree deformation. This magnification effect is significant in cases with a low air blast velocity, while the large tree deflection caused by strong air blast loading would weaken this effect. Furthermore, failure modes of a specific forest subject to a powerful air blast depend heavily on the trunk bending strength and anchorage characteristics. The large variation in biometric and mechanical properties of trees necessitates the establishment of a regional database of tree parameters. Our work and the proposed method are expected to provide a better understanding of air blast power and to be of great use for air blast risk assessment in mountainous regions worldwide.</p

AIDS epidemic at age 25 and control efforts in China

In the first 10 years of AIDS epidemic in China, intravenous drug users (IDUs) and Former Plasma Donors (FPDs) were hardly hit in the late 1980s and mid 1990s respectively. In the last 10 years, while IDU epidemic keeps at a fast pace, sexual transmitted cases of HIV have been steadily increasing. All signs indicate that the HIV epidemic in China is at a turning point, spreading from high risk groups to the general population. Learning from the SARS epidemic, China has recently launched an impressive AIDS campaign by making serious political commitments, and by strengthening the public health system and implementing an aggressive Four Free One Care Policy. There remains huge challenges both at the societal level which form the roots of the AIDS epidemic and at increasing the capabilities of the implementation teams. In addition to other needed efforts, enhancing AIDS research through international collaborations will strengthen China's ability to conduct her huge control program efficiently. Only with a scientific approach and evidence-based strategy, can China seize the opportunity to stop AIDS at an early stage

A new measurement of antineutrino oscillation with the full detector configuration at Daya Bay

We report a new measurement of electron antineutrino disappearance using the fully-constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9$\times$10$^5$ GW$_{\rm th}$-ton-days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six $^{241}$Am-$^{13}$C radioactive calibration sources reduced the background by a factor of two for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of $\sin^{2}2\theta_{13}$ and $|\Delta m^2_{ee}|$ were halved as a result of these improvements. Analysis of the relative antineutrino rates and energy spectra between detectors gave $\sin^{2}2\theta_{13} = 0.084\pm0.005$ and $|\Delta m^{2}_{ee}|= (2.42\pm0.11) \times 10^{-3}$ eV$^2$ in the three-neutrino framework.Comment: Updated to match final published versio