Surface-edge state and half quantized Hall conductance in topological insulators

We propose a surface-edge state theory for half quantized Hall conductance of surface states in topological insulators. The gap opening of a single Dirac cone for the surface states in a weak magnetic field is demonstrated. We find a new surface state resides on the surface edges and carries chiral edge current, resulting in a half-quantized Hall conductance in a four-terminal setup. We also give a physical interpretation of the half quantized conductance by showing that this state is the product of splitting of a boundary bound state of massive Dirac fermions which carries a conductance quantum

American ginseng improves neurocognitive function in senescence-accelerated mice: Possible role of the upregulated insulin and choline acetyltransferase gene expression

信州大学博士（医学）・学位論文・平成23年3月31日授与（甲第905号）・史峻Aim: To investigate the effects of American ginseng on neurocognitive function and glucose regulation in senescence-accelerated mice. Methods: Male senescence-resistant inbred strains (SAMR1) and senescence-prone inbred strains (SAMP10) mice were divided into five groups and fed either a control diet or an American ginseng-supplemented diet (1% or 2% g/g) from 6 weeks to 10 months of age. Bodyweight, levels of fasting plasma glucose (FPG) and grading scores were monitored every month and neurocognitive functions were evaluated at 9 months of age with a KUROBOX apparatus using a stress-free positive cue task. Gene expressions of peroxisome proliferator-activated receptor delta (PPAR-d), insulin, choline acetyltransferase (ChAT) and amyloid precursor protein (APP) in the brain were measured by real-time quantitative reverse transcription polymerase chain reaction assays. Results: American ginseng decreased FPG in SAMR1 mice, but increased FPG in SAMP10 mice. Correct visit ratios were higher in both SAMR1 and SAMP10 strains consuming an American ginseng-supplemented diet. Gene upregulation of insulin and ChAT in the brain, but not of PPAR-d or APP, was evident in American ginseng-fed groups. Conclusion: Daily consumption of American ginseng induced an enhancement in neurocognitive function in senescence-accelerated mice, which could be related to the upregulation of insulin and ChAT gene expression in the brain. Geriatr Gerontol Int 2012; 12: 123-130.ArticleGERIATRICS & GERONTOLOGY INTERNATIONAL. 12(1):123-130 (2012)journal articl

Parallel Algorithms for Hierarchical Nucleus Decomposition

Nucleus decompositions have been shown to be a useful tool for finding dense subgraphs. The coreness value of a clique represents its density based on the number of other cliques it is adjacent to. One useful output of nucleus decomposition is to generate a hierarchy among dense subgraphs at different resolutions. However, existing parallel algorithms for nucleus decomposition do not generate this hierarchy, and only compute the coreness values. This paper presents a scalable parallel algorithm for hierarchy construction, with practical optimizations, such as interleaving the coreness computation with hierarchy construction and using a concurrent union-find data structure in an innovative way to generate the hierarchy. We also introduce a parallel approximation algorithm for nucleus decomposition, which achieves much lower span in theory and better performance in practice. We prove strong theoretical bounds on the work and span (parallel time) of our algorithms. On a 30-core machine with two-way hyper-threading on real-world graphs, our parallel hierarchy construction algorithm achieves up to a 58.84x speedup over the state-of-the-art sequential hierarchy construction algorithm by Sariyuce et al. and up to a 30.96x self-relative parallel speedup. On the same machine, our approximation algorithm achieves a 3.3x speedup over our exact algorithm, while generating coreness estimates with a multiplicative error of 1.33x on average

Parallel Five-Cycle Counting Algorithms

Counting the frequency of subgraphs in large networks is a classic research question that reveals the underlying substructures of these networks for important applications. However, subgraph counting is a challenging problem, even for subgraph sizes as small as five, due to the combinatorial explosion in the number of possible occurrences. This paper focuses on the five-cycle, which is an important special case of five-vertex subgraph counting and one of the most difficult to count efficiently. We design two new parallel five-cycle counting algorithms and prove that they are work-efficient and achieve polylogarithmic span. Both algorithms are based on computing low out-degree orientations, which enables the efficient computation of directed two-paths and three-paths, and the algorithms differ in the ways in which they use this orientation to eliminate double-counting. We develop fast multicore implementations of the algorithms and propose a work scheduling optimization to improve their performance. Our experiments on a variety of real-world graphs using a 36-core machine with two-way hyper-threading show that our algorithms achieves 10-46x self-relative speed-up, outperform our serial benchmarks by 10-32x, and outperform the previous state-of-the-art serial algorithm by up to 818x

Compressive behavior of FRP-confined concrete-encased steel columns

FRP-confined concrete-encased steel I-section columns (FCSCs) are an emerging form of hybrid columns. An FCSC consists of an outer FRP tube, an encased steel section and a concrete infill. The FCSCs possess many advantages over conventional reinforced concrete columns, including the excellent corrosion resistance, excellent ductility and ease for construction. Existing studies on FCSCs, however, have been rather limited. This paper presents a combined experimental and theoretical study on the behavior of FCSCs under concentric and eccentric compression. The experimental program included the testing of a total of 14 specimens, with the main variables being the section configuration, the thickness of the FRP tube and the loading scheme. The theoretical part included the development of a model for section analysis based on the so-called fiber element approach. The test results showed that the buckling of steel section was well constrained and the concrete was effectively confined in FCSCs, leading to a very ductile response under both concentric and eccentric compression. The theoretical model was shown to provide reasonably accurate predictions of the test results

Competition between weak localization and antilocalization in topological surface states

A magnetoconductivity formula is presented for the surface states of a magnetically doped topological insulator. It reveals a competing effect of weak localization and weak antilocalization in quantum transport when an energy gap is opened at the Dirac point by magnetic doping. It is found that, while random magnetic scattering always drives the system from the symplectic to the unitary class, the gap could induce a crossover from weak antilocalization to weak localization, tunable by the Fermi energy or the gap. This crossover presents a unique feature characterizing the surface states of a topological insulator with the gap opened at the Dirac point in the quantum diffusion regime.Comment: 5 pages, 4 figure