Carrier transport in 2D graphene layers

Carrier transport in gated 2D graphene monolayers is theoretically considered in the presence of scattering by random charged impurity centers with density $n_i$. Excellent quantitative agreement is obtained (for carrier density $n > 10^{12} \rm{cm}^{-2}$) with existing experimental data (Ref. \onlinecite{kn:novoselov2004, kn:novoselov2005, kn:zhang2005, kn:kim2006, kn:fuhrer2006}). The conductivity scales linearly with $n/n_i$ in the theory, and shows extremely weak temperature dependence. The experimentally observed asymmetry between electron and hole conductivities is explained by the asymmetry in the charged impurity configuration in the presence of the gate voltage, while the high-density saturation of conductivity for the highest mobility samples is explained as a crossover between the long-range and the point scattering dominated regimes. We argue that the experimentally observed saturation of conductivity at low density arises from the charged impurity induced inhomogeneity in the graphene carrier density which becomes severe for $n \lesssim n_i \sim 10^{12} \rm{cm}^{-2}$.Comment: 5 pages, 4 figures, published in Phys. Rev. Let

Crossover from Endogenous to Exogenous Activity in Open-Source Software Development

We have investigated the origin of fluctuations in the aggregated behaviour of an open-source software community. In a recent series of papers, de Menezes and co-workers have shown how to separate internal dynamics from external fluctuations by capturing the simultaneous activity of many system's components. In spite of software development being a planned activity, the analysis of fluctuations reveals how external driving forces can be only observed at weekly and higher time scales. Hourly and higher change frequencies mostly relate to internal maintenance activities. There is a crossover from endogenous to exogenous activity depending on the average number of file changes. This new evidence suggests that software development is a non-homogeneous design activity where stronger efforts focus in a few project files. The crossover can be explained with a Langevin equation associated to the cascading process, where changes to any file trigger additional changes to its neighbours in the software network. In addition, analysis of fluctuations enables us to detect whether a software system can be decomposed in several subsystems with different development dynamics.Comment: 7 pages, 4 figures, submitted to Europhysics Letter

Birth of a Closed Universe of Negative Spatial Curvature

We propose a modified form of the spontaneous birth of the universe by quantum tunneling. It proceeds through topology change and inflation, to eventually become a universe with closed spatial sections of negative curvature and nontrivial global topology.Comment: 10 pages, 1 figure. Revised version with better comments on assumed topology chang

Potential of Lactic Acid Bacteria Isolated From Dangke and Indonesian Beef as Hypocholesterolaemic Agent

Lactobacillus fermentum strains were successfully isolated from dangke which was a fresh cheese-like product originating from Enrekang, South Sulawesi Province, Indonesia. In addition, Lactobacillus plantarum and Lactobacillus acidophillus were isolated from beef. This study aimed to investigate the ability of those 8 LAB strains from dangke and beef in lowering cholesterol level by using in vitro study. Strain of Lactic acid bacteria used were L. fermentum strains (A323L, B111K, B323K, C113L, C212L), L. plantarum strains (IIA-1A5 and IIA-2C12), and L. acidophillus IIA-2B4. Variables observed were identification of Bile Salt Hydrolase (BSH) gene by Polymerase Chain Reaction (PCR), BSH activity and cholesterol assimilation. Phylogenetic tree indicated homology of L. plantarum IIA-IA5 was 98% to BSH gene of L. plantarum Lp529 with access code of FJ439771 and FJ439775 obtained from GenBank. The results demonstrated that eight strains of LAB isolated from dangke and beef that potentially showed cholesterol-lowering effects were L. fermentum B111K and L. plantarum IIA-1A5. L. fermentum B111K was able to assimilate cholesterol by 4.10% with assimilated cholesterol of 0.13 mg in 1010 cells. In addition, L. plantarum IIA-1A5 had BSH gene and BSH activity, as well as the ability to assimilate cholesterol by 8.10% with assimilated cholesterol of 0.06 mg in 1010 cells. It is concluded that L. fermentum B111K and L. plantarum IIA-1A5 were strains that showed cholesterol-lowering effects

Apparatus for use in the production of ribbon-shaped crystals from a silicon melt

A susceptor for facilitating induction heating of silicon melt is described. The susceptor comprises a pair of susceptor halves of a thickness less than two skin depths, each being the mirror image of the other, disposed in mutually opposed, electrically insulated relation. The crucible comprises a quartz body supported by the graphite susceptor, whereby the R-F coil is electrically coupled with the melt

Thermodynamic analysis of topological black holes in Gauss-Bonnet gravity with nonlinear source

Employing two classes of nonlinear electrodynamics, we obtain topological black hole solutions of Gauss-Bonnet gravity. We investigate geometric properties of the solutions and find that there is an intrinsic singularity at the origin. We investigate the thermodynamic properties of the asymptotically flat black holes and also asymptotically adS solutions. Using suitable local transformation, we generalize static horizon-flat solutions to rotating ones. We discuss their conserved and thermodynamic quantities as well as the first law of thermodynamics. Finally, we calculate the heat capacity of the solutions to obtain a constraint on the horizon radius of stable solutions.Comment: accepted in Eur. Phys. J. C (DOI: 10.1140/epjc/s10052-014-3079-9