More about excited bottomonium radiative decays

Radiative decays of bottomonium are revisited, focusing on contributions from higher-order relativistic effects. The leading relativistic correction to the magnetic spin-flip operator at the photon vertex is found to be particularly important. The combination of O(v^6) effects in the nonrelativistic QCD action and in the transition operator moves previous lattice results for excited Upsilon decays into agreement with experiment.Comment: 4 pages, 3 figures, published versio

Skyrme and Wigner crystals in graphene

At low-energy, the band structure of graphene can be approximated by two degenerate valleys $(K,K^{\prime})$ about which the electronic spectra of the valence and conduction bands have linear dispersion relations. An electronic state in this band spectrum is a linear superposition of states from the $A$ and $B$ sublattices of the honeycomb lattice of graphene. In a quantizing magnetic field, the band spectrum is split into Landau levels with level N=0 having zero weight on the $B(A)$ sublattice for the $$ valley. Treating the valley index as a pseudospin and assuming the real spins to be fully polarized, we compute the energy of Wigner and Skyrme crystals in the Hartree-Fock approximation. We show that Skyrme crystals have lower energy than Wigner crystals \textit{i.e.} crystals with no pseudospin texture in some range of filling factor $\nu$ around integer fillings. The collective mode spectrum of the valley-skyrmion crystal has three linearly-dispersing Goldstone modes in addition to the usual phonon mode while a Wigner crystal has only one extra Goldstone mode with a quadratic dispersion. We comment on how these modes should be affected by disorder and how, in principle, a microwave absorption experiment could distinguish between Wigner and Skyrme crystals.Comment: 14 pages with 11 figure

Strange-quark Current in the Nucleon from Lattice QCD

The contribution of the strange-quark current to the electromagnetic form factors of the nucleon is studied using lattice QCD. The strange current matrix elements from our lattice calculation are analyzed in two different ways, the differential method used in an earlier work by Wilcox and a cumulative method which sums over all current insertion times. The preliminary results of our simulation indicate the importance of high statistics, and that consistent results between the varying analysis methods can be achieved. Although this simulation does not yet yield a number that can be compared to experiment, several criteria useful in assessing the robustness of a signal extracted from a noisy background are presented.Comment: 12 pages, 9 figures, Presented at EMI 200

Dynamical matrix of two-dimensional electron crystals

In a quantizing magnetic field, the two-dimensional electron (2DEG) gas has a rich phase diagram with broken translational symmetry phases such as Wigner, bubble, and stripe crystals. In this paper, we derive a method to get the dynamical matrix of these crystals from a calculation of the density response function performed in the Generalized Random Phase Approximation (GRPA). We discuss the validity of our method by comparing the dynamical matrix calculated from the GRPA with that obtained from standard elasticity theory with the elastic coefficients obtained from a calculation of the deformation energy of the crystal.Comment: Revised version published in Phys. Rev. B. 12 pages with 11 postscripts figure

Intellectual Property Topics in Open University Distance-Taught Courses

Patents lie at the heart of engineering as a permanent and ongoing record of invention. We have taught the subject for about 5 years in both UG and PG courses, written from scratch owing to the absence of textbooks aimed specifically at engineers. Most practising engineers develop patent skills on the job rather than through conventional courses. But there is a need to present such courses as early as possible in the engineering curriculum, so that graduates have a flying start in their first employment

Portable electron beam weld chamber

Development and characteristics of portable vacuum chamber for skate type electron beam welding are discussed. Construction and operational details of equipment are presented. Illustrations of equipment are provided

Investigating the Martian atmosphere using the ExoMars 2016 lander

Accurate modelling of the Martian atmosphere is essential both for planning and completing future missions to the Martian surface, and for accurate analysis and interpretation of the data that they return. Large dust storms and local wind patterns can affect spacecraft landing profiles, and the level of dust present in the atmosphere may impact lander performance. The ExoMars 2016 Mission will carry an Entry, Descent and Landing Demonstrator Module (EDM), primarily designed to test the ability of ESA’s lander technology to carry a science package to the surface [1]. The Atmospheric Mars Entry and Landing Investigations and Analysis (AMELIA) team [2] will use the module’s entry and descent trajectory to characterise the structure of the atmosphere along the travelled landing profile, and to determine properties of the atmosphere, such as density and wind speed, over a wide altitude range from the upper atmosphere to the surface. Aerosol abundances, including atmospheric dust, will also be characterised. These combined datasets will enable more accurate predictions of the atmospheric environment that future landers will encounter. EDM’s surface science package, DREAMS (Dust characterisation, Risk assessment, and Environment Analyser on the Martian Surface), includes sensors to measure wind speed and direction, surface temperature, pressure, and the amount of atmospheric dust present near the surface [3]. We will use the descent and surface profile data collected by EDM to verify and improve current Martian atmospheric modelling completed at The Open University, using both the global circulation and mesoscale models. [1] Forget et al. (2011) Fourth International Workshop on the Mars Atmosphere: Modeling and Observations, Paris. [2] Ferri et al. (2012) 9th International Planetary Probe Workshop (IPPW9), Toulouse. [3] Esposito et al. (2013) EPSC Abstracts Vol. 8, EPSC2013-815

Atmospheric modelling for NOMAD-UVIS on board the ExoMars Trace Gas Orbiter mission

The Ultraviolet and Visible Spectrometer (UVIS) instrument development process requires the construction of an atmospheric model to provide synthetic UV transmission spectra. We discuss the requirements of the model to enable observational limits to be found, and the potential for certain atmospheric parameters to be further constrained