A stochastic network with mobile users in heavy traffic

We consider a stochastic network with mobile users in a heavy-traffic regime. We derive the scaling limit of the multi-dimensional queue length process and prove a form of spatial state space collapse. The proof exploits a recent result by Lambert and Simatos which provides a general principle to establish scaling limits of regenerative processes based on the convergence of their excursions. We also prove weak convergence of the sequences of stationary joint queue length distributions and stationary sojourn times.Comment: Final version accepted for publication in Queueing Systems, Theory and Application

Anisotropic splitting of intersubband spin plasmons in quantum wells with bulk and structural inversion asymmetry

In semiconductor heterostructures, bulk and structural inversion asymmetry and spin-orbit coupling induce a k-dependent spin splitting of valence and conduction subbands, which can be viewed as being caused by momentum-dependent crystal magnetic fields. This paper studies the influence of these effective magnetic fields on the intersubband spin dynamics in an asymmetric n-type GaAs/AlGaAs quantum well. We calculate the dispersions of intersubband spin plasmons using linear response theory. The so-called D'yakonov-Perel' decoherence mechanism is inactive for collective intersubband excitations, i.e., crystal magnetic fields do not lead to decoherence of spin plasmons. Instead, we predict that the main signature of bulk and structural inversion asymmetry in intersubband spin dynamics is a three-fold, anisotropic splitting of the spin plasmon dispersion. The importance of many-body effects is pointed out, and conditions for experimental observation with inelastic light scattering are discussed.Comment: 8 pages, 6 figure

Nasal Carriage of Staphylococcus aureus and Associated Risk Factors among Food Handlers in a Nigerian University

Staphylococcal foodborne illness, caused by the ingestion of contaminated foods by induced Staphylococcus aureus enterotoxins, is one of the most recurrent foodborne diseases worldwide. Food handlers working in food-service establishments who carry enterotoxigenic isolates represent a reservoir for potential contamination leading to staphylococcal food intoxication. The aim of this research was to investigate the prevalence of nasal transmission of S. aureus among food handlers in a University community. A total of 100 nasal swab specimens were obtained from the food handlers and analyzed by standard laboratory techniques for isolation and identification. Questionnaires were administered to ascertain the risk determinants associated with nasal carriage of S. aureus. Antibiotic susceptibility testing of the isolates was done by disk diffusion method. Thirty-two food handlers were found to be carriers of S. aureus. Majority were females (63%), and 30% had been certified for food safety and handling. There were however no significant association between the nasal distribution of S. aureus together with established risk factors. Among the isolates, 93.75% were found to be resistant to penicillin, 50% to gentamicin and 50% to oxacillin. These findings indicate the need for training of food handlers on food safety, as well as the knowledge of antibiotic resistance

Analysis of Harvesting Energy from Mistuned Multiple Harvesters with and without Coupling

AbstractEnergy harvesting has received a lot of attention in the recent past. At present a single device does not harvested energy enough to power up an electronic sensors. In order to increase the power output multiple identical harvesters are used. When multiple harvesters are used, they bring in non-uniformity in their physical parameters due to variability during manufacturing or even during deployment. Therefore, ‘n’ numbers of harvesters do not necessary produce ‘n’ times the harvested power of a single device. The variability in parameters is less enough to be coined as mistuning. In this paper, an analysis of multiple energy harvesters is studied. The harvesters are assumed to show mistuning. The study is further extended to understand the effect of mechanical coupling between the harvesters. For simplification, pendulums are considered as the harvesters, with magnetic tip masses for the electromagnetic energy harvesting. Mistuning is achieved by varying the length of the pendulums. A generalized mathematical model for n coupled harvesters with mistuning is developed. Simulations are performed with the number of harvesters varying from 2 to 6 with ±1% non-repetitive mistuning in the lengths of the harvesters, and a comparison of the power harvested between mechanically coupled and uncoupled harvesters is presented

Intersubband spin-density excitations in quantum wells with Rashba spin splitting

In inversion-asymmetric semiconductors, spin-orbit coupling induces a k-dependent spin splitting of valence and conduction bands, which is a well-known cause for spin decoherence in bulk and heterostructures. Manipulating nonequilibrium spin coherence in device applications thus requires understanding how valence and conduction band spin splitting affects carrier spin dynamics. This paper studies the relevance of this decoherence mechanism for collective intersubband spin-density excitations (SDEs) in quantum wells. A density-functional formalism for the linear spin-density matrix response is presented that describes SDEs in the conduction band of quantum wells with subbands that may be non-parabolic and spin-split due to bulk or structural inversion asymmetry (Rashba effect). As an example, we consider a 40 nm GaAs/AlGaAs quantum well, including Rashba spin splitting of the conduction subbands. We find a coupling and wavevector-dependent splitting of the longitudinal and transverse SDEs. However, decoherence of the SDEs is not determined by subband spin splitting, due to collective effects arising from dynamical exchange and correlation.Comment: 10 pages, 4 figure

A low power photoemission source for electrons on liquid helium

Electrons on the surface of liquid helium are a widely studied system that may also provide a promising method to implement a quantum computer. One experimental challenge in these studies is to generate electrons on the helium surface in a reliable manner without heating the cryo-system. An electron source relying on photoemission from a zinc film has been previously described using a high power continuous light source that heated the low temperature system. This work has been reproduced more compactly by using a low power pulsed lamp that avoids any heating. About 5e3 electrons are collected on 1 cm^2 of helium surface for every pulse of light. A time-resolved experiment suggests that electrons are either emitted over or tunnel through the 1eV barrier formed by the thin superfluid helium film on the zinc surface. No evidence of trapping or bubble formation is seen.Comment: 9 pages, 3 figures, submitted to J. Low Temp. Phy

Anatomy of the lattice magnetic monopoles

We study the Abelian and non-Abelian action densitynear the monopole in the maximal Abelian gauge of SU(2) lattice gauge theory. We find that the non-Abelian action density near the monopoles belonging to the percolating cluster decreases when we approach the monopole center. Our estimate of the monopole radius is R_mon ~ 0.04 fm.Comment: 9 pp., Latex2e, 2 figure (epsfig), published versio

Influence of the crystallization process on the luminescence of multilayers of SiGe nanocrystals embedded in SiO2

Multilayers of SiGe nanocrystals embedded in an oxide matrix have been fabricated by low-pressure chemical vapor deposition SiO2 onto Si wafers (in a single run at 390 ◦C and 50mTorr, using GeH4, Si2 H6 and O2) followed by a rapid thermal annealing crystallize the SiGe nanoparticles. The main emission band is located at 400 nm in both cathodoluminescence and photoluminescence at 80K and also at room temperature. The annealing conditions (temperatures ranging from 700 to 1000 ◦C and for times of 30 investigated in samples with different diameter of the nanoparticles (from ≈3 to ≥5 nm) and oxide interlayer thickness (15 and establish a correlation between the crystallization of the nanoparticles, the degradation of their composition by Ge diffusion the luminescence emission band. Structures with small nanoparticles (3–4.5 nm) separated by thick oxide barriers (≈35 nm) annealed 60 s yield the maximum intensity of the luminescence. An additional treatment at 450 ◦C in forming gas for dangling-bond the intensity of the luminescence band by 25–30%

Klein tunneling in graphene: optics with massless electrons

This article provides a pedagogical review on Klein tunneling in graphene, i.e. the peculiar tunneling properties of two-dimensional massless Dirac electrons. We consider two simple situations in detail: a massless Dirac electron incident either on a potential step or on a potential barrier and use elementary quantum wave mechanics to obtain the transmission probability. We emphasize the connection to related phenomena in optics, such as the Snell-Descartes law of refraction, total internal reflection, Fabry-P\'erot resonances, negative refraction index materials (the so called meta-materials), etc. We also stress that Klein tunneling is not a genuine quantum tunneling effect as it does not necessarily involve passing through a classically forbidden region via evanescent waves. A crucial role in Klein tunneling is played by the conservation of (sublattice) pseudo-spin, which is discussed in detail. A major consequence is the absence of backscattering at normal incidence, of which we give a new shorten proof. The current experimental status is also thoroughly reviewed. The appendix contains the discussion of a one-dimensional toy model that clearly illustrates the difference in Klein tunneling between mono- and bi-layer graphene.Comment: short review article, 18 pages, 14 figures; v3: references added, several figures slightly modifie

PLOS Genetics Data Sharing Policy: In Pursuit of Functional Utility

About a year ago, PLOS implemented a new process intended to further the overarching principle that data used in the work we publish should be accessible and reusable. The motivation goes hand-in-hand with both our open access ethos and the scientific method itself: the validity of a conclusion depends on the ability to reproduce the underlying results