Weak Localization and Transport Gap in Graphene Antidot Lattices

We fabricated and measured antidot lattices in single layer graphene with lattice periods down to 90 nm. In large-period lattices, a well-defined quantum Hall effect is observed. Going to smaller antidot spacings the quantum Hall effect gradually disappears, following a geometric size effect. Lattices with narrow constrictions between the antidots behave as networks of nanoribbons, showing a high-resistance state and a transport gap of a few mV around the Dirac point. We observe pronounced weak localization in the magnetoresistance, indicating strong intervalley scattering at the antidot edges. The area of phase-coherent paths is bounded by the unit cell size at low temperatures, so each unit cell of the lattice acts as a ballistic cavity.Comment: some revisions, to appear in New Journal of Physics, Special Issue Graphen

Pulsation models for the roAp star HD 134214

Precise time-series photometry with the MOST satellite has led to identification of 10 pulsation frequencies in the rapidly oscillating Ap (roAp) star HD 134214. We have fitted the observed frequencies with theoretical frequencies of axisymmetric modes in a grid of stellar models with dipole magnetic fields. We find that, among models with a standard composition of $(X,Z) = (0.70,0.02)$ and with suppressed convection, eigenfrequencies of a $1.65\,{\rm M}_\odot$ model with $\log T_{\rm eff} = 3.858$ and a polar magnetic field strength of 4.1kG agree best with the observed frequencies. We identify the observed pulsation frequency with the largest amplitude as a deformed dipole ($\ell = 1$) mode, and the four next-largest-amplitude frequencies as deformed $\ell = 2$ modes. These modes have a radial quasi-node in the outermost atmospheric layers ($\tau \sim 10^{-3}$). Although the model frequencies agree roughly with observed ones, they are all above the acoustic cut-off frequency for the model atmosphere and hence are predicted to be damped. The excitation mechanism for the pulsations of HD 134214 is not clear, but further investigation of these modes may be a probe of the atmospheric structure in this magnetic chemically peculiar star.Comment: 9 pages, 6 figures; accepted for publication in MNRA

Automated NLO QCD Corrections with WHIZARD

We briefly discuss the current status of NLO QCD automation in the Monte Carlo event generator WHIZARD. The functionality is presented for the explicit study of off-shell top quark production with associated backgrounds at a lepton collider.Comment: 9 pages, 5 figures, to appear in the proceedings of the European Physical Society Conference on High Energy Physics 2015 (EPS-HEP 2015), Vienna, Austria, 22nd to 29th of July 201

Matching NLO QCD Corrections in WHIZARD with the POWHEG scheme

Building on the new automatic subtraction of NLO amplitudes in WHIZARD, we present our implementation of the POWHEG scheme to match radiative corrections consistently with the parton shower. We apply this general framework to two linear collider processes, $e^+e^-\,\to\,t\bar{t}$ and $e^+e^-\,\to\,t\bar{t}H$.Comment: 7 pages, 4 figures, to appear in the proceedings of the European Physical Society Conference on High Energy Physics 2015 (EPS-HEP 2015), Vienna, Austria, 22nd to 29th of July 201

Topological partition relations to the form omega^*-> (Y)^1_2

Theorem: The topological partition relation omega^{*}-> (Y)^{1}_{2} (a) fails for every space Y with |Y| >= 2^c ; (b) holds for Y discrete if and only if |Y| <= c; (c) holds for certain non-discrete P-spaces Y ; (d) fails for Y= omega cup {p} with p in omega^{*} ; (e) fails for Y infinite and countably compact

Non-classical symmetries and the singular manifold method: A further two examples

This paper discusses two equations with the conditional Painleve property. The usefulness of the singular manifold method as a tool for determining the non-classical symmetries that reduce the equations to ordinary differential equations with the Painleve property is confirmed once moreComment: 9 pages (latex), to appear in Journal of Physics

Integrability of a Generalized Ito System: the Painleve Test

It is shown that a generalized Ito system of four coupled nonlinear evolution equations passes the Painleve test for integrability in five distinct cases, of which two were introduced recently by Tam, Hu and Wang. A conjecture is formulated on integrability of a vector generalization of the Ito system.Comment: LaTeX, 5 page

Digital Signal Processing Education: Technology and Tradition

In this paper we discuss a DSP course presented to both University students and to participants on industrial short courses. The "traditional" DSP course will typically run over one to two semesters and usually cover the fundamental mathematics of z-, Laplace and Fourier transforms, followed by the algorithm and application detail. In the course we will discuss, the use of advanced DSP software and integrated support software allow the presentation time to be greatly shortened and more focussed algorithm and application learning to be introduced. By combining the traditional lecture with the use of advanced DSP software, all harnessed by the web, we report on the objectives, syllabus, and mode of teaching