Self-consistent calculation of electric potentials in Hall devices

Using a first-principles classical many-body simulation of a Hall bar, we study the necessary conditions for the formation of the Hall potential: (i) Ohmic contacts with metallic reservoirs, (ii) electron-electron interactions, and (iii) confinement to a finite system. By propagating thousands of interacting electrons over million time-steps we capture the build-up of the self-consistent potential, which resembles results obtained by conformal-mapping methods. As shown by a microscopic model of the current injection, the Hall effect is linked to specific boundary conditions at the particle reservoirs.Comment: 6 pages, 7 figure

Theory of the quantum Hall effect in graphene

We study the quantum Hall effect (QHE) in graphene based on the current injection model. In our model, the presence of disorder, the edge-state picture, extended states and localized states, which are believed to be indispensable ingredients in describing the QHE, do not play an important role. Instead the boundary conditions during the injection into the graphene sheet, which are enforced by the presence of the Ohmic contacts, determine the current-voltage characteristics.Comment: 4 pages, 3 figures, rewritten, role of contacts for boundary conditions in small device

Revivals of quantum wave-packets in graphene

We investigate the propagation of wave-packets on graphene in a perpendicular magnetic field and the appearance of collapses and revivals in the time-evolution of an initially localised wave-packet. The wave-packet evolution in graphene differs drastically from the one in an electron gas and shows a rich revival structure similar to the dynamics of highly excited Rydberg states. We present a novel numerical wave-packet propagation scheme in order to solve the effective single-particle Dirac-Hamiltonian of graphene and show how the collapse and revival dynamics is affected by the presence of disorder. Our effective numerical method is of general interest for the solution of the Dirac equation in the presence of potentials and magnetic fields.Comment: 22 pages, 10 figures, 3 movies, to appear in New Journal of Physic

Lattice thermal conductivity of freestanding gallium nitride nanowires

aip Publishers Publications Topics | Librarians Authors Your access is provided by: Eastern Illinois University Register to create your user account, or sign in if you have an existing account Additional sign in Sign in via Shibboleth/Athens My cart Export citations Add to my favorites Recommend to library Subscribe to email alerts Submit an article Reprints & Permissions Subscribe to RSS Access Key Free Content Open Access Content Subscribed Content Free Trial Content Home \u3e Publishers \u3e AIP Publishing \u3e Journal of Applied Physics \u3e Volume 108, Issue 3 \u3e Article banner image F Lattice thermal conductivity of freestanding gallium nitride nanowires Download PDF Jie Zou1,a) + View Affiliations a) Electronic mail: [email protected]. J. Appl. Phys. 108, 034324 (2010); http://dx.doi.org/10.1063/1.3463358 Previous Article Table of Contents Next Article Back to Search Results facebook twitter Share this page separator email print this page Abstract Full Text References (28) Cited By (8) Data & Media Metrics Related We report detailed calculations of the lattice thermal conductivity of freestanding gallium nitride(GaN)nanowires with diameters ranging from 20 to 140 nm. Results are compared with experimental data on GaNnanowires grown by thermal chemical vapor deposition(CVD). Calculations are based on the Boltzmann transport equation and take into account the change in the nonequilibrium phonon distribution in the case of diffuse scattering at the surfaces. Phonon dispersion relation is obtained in the elastic continuum approximation for each given nanowire. For valid comparisons with the experimental data, simulations are performed with a dopant concentration and impurity profile characteristic of thermal CVDGaNnanowires. Our results show that the room-temperature thermal conductivity of the nanowires has very low values, ranging from 6.74 W/m K at 20 nm to 16.4 W/m K at 140 nm. The obtained results are in excellent agreement with the experimental data. We have also demonstrated that in addition to impurity scattering, boundary scattering, and phonon confinement, the change in the nonequilibrium phonon distribution leads to a further reduction in the thermal conductivity of the nanowires and has to be taken into account in the calculations. Our conclusion is different from that of an earlier study which attributed the very low thermal conductivity to the unusually large mass-difference scattering in the nanowires

The AMSC mobile satellite system

The American Mobile Satellite Consortium (AMSC) Mobile Satellite Service (MSS) system is described. AMSC will use three multi-beam satellites to provide L-band MSS coverage to the United States, Canada and Mexico. The AMSC MSS system will have several noteworthy features, including a priority assignment processor that will ensure preemptive access to emergency services, a flexible SCPC channel scheme that will support a wide diversity of services, enlarged system capacity through frequency and orbit reuse, and high effective satellite transmitted power. Each AMSC satellite will make use of 14 MHz (bi-directional) of L-band spectrum. The Ku-band will be used for feeder links

Mobile satellite service in the United States

Mobile satellite service (MSS) has been under development in the United States for more than two decades. The service will soon be provided on a commercial basis by a consortium of eight U.S. companies called the American Mobile Satellite Consortium (AMSC). AMSC will build a three-satellite MSS system that will offer superior performance, reliability and cost effectiveness for organizations requiring mobile communications across the U.S. The development and operation of MSS in North America is being coordinated with Telesat Canada and Mexico. AMSC expects NASA to provide launch services in exchange for capacity on the first AMSC satellite for MSAT-X activities and for government demonstrations

The structure and mechanistic impact of carbon deposits in dehydrogenation reactions

The catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes is widely studied as a route to the formation of alkenes and di-alkenes, important precursor molecules for synthetic rubbers, plastics and a variety of other products [1-4]. Recent studies have focused on the non-oxidative DH of butane over alumina-supported vanadia catalysts [5-7]. In the present work, we provide a detailed understanding of both the role and structure of coke deposited on VOx/Al2O3 during reaction. A range of characterisation techniques have been employed including the first application of terahertz time domain spectroscopy (THz-TDS) to the study of coke. Complementary THz-TDS characterisation of carbonaceous materials including carbon nanofibres (CNFs) has also been conducted