Measurements of the Top Quark Pair-Production Cross Section

Measurements of the inclusive and differential cross section for the production of top quark pairs in proton-(anti)proton collision at center-of-mass energies of 1.96, 7.0 and 8.0 TeV are presented and compared with the latest theory predictions and Monte-Carlo models. In addition, first measurements of the production of top quark pairs in association with additional jets or with a boson are highlighted. All measurements are in good agreement with the Standard Model.Comment: 6 pages, 11 figures, proceedings of HCP2012, Kyoto (Japan

Diffractive Final States with the H1 Detector at HERA

Recent measurements of diffractive dijet and charm quark production in electron-proton collisions using the H1 detector at HERA are presented, where the exchanged photon is either almost real or highly virtual. The data are compared with leading and next-to-leading order QCD calculations based on the diffractive parton distributions obtained from a recent DGLAP QCD analysis of H1 inclusive diffractive deep-inelastic scattering data, thus testing QCD factorization in diffractive ep interactions.Comment: 3 pages, 6 figures, to appear in the proceedings of the Intl. Europhysics Conference on High Energy Physics EPS 2003, Aachen, July 200

Exterior and Symmetric Powers of Modules for Cyclic 2-Groups

We prove a recursive formula for the exterior and symmetric powers of modules for a cyclic 2-group. This makes computation straightforward. Previously, a complete description was only known for cyclic groups of prime order

Particle Acceleration in Gamma-Ray Burst Jets

Gradual shear acceleration of energetic particles in gamma-ray burst (GRB) jets is considered. Special emphasis is given to the analysis of universal structured jets, and characteristic acceleration timescales are determined for a power-law and a Gaussian evolution of the bulk flow Lorentz factor $\gamma_b$ with angle $\phi$ from the jet axis. The results suggest that local power-law particle distributions may be generated and that higher energy particles are generally concentrated closer to the jet axis. Taking several constraints into account we show that efficient electron acceleration in gradual shear flows, with maximum particle energy successively decreasing with time, may be possible on scales larger than $r \sim 10^{15}$ cm, provided the jet magnetic field becomes sufficiently weak and/or decreases rapidly enough with distance, while efficient acceleration of protons to ultra-high energies $> 10^{20}$ eV may be possible under a wide range of conditions.Comment: 11 pages, 3 figures; ApJ Letters accepted; final version: small typos corrected in order to match published versio

Learning flexibility: the environment and a case study

This paper outlines the flexible student learning environment in the Faculty of Engineering and Surveying, before concentrating on evaluating one online learning option. This Faculty provides a variety of high quality on-campus, distance education and on-line academic programmes and various learning strategies for the heterogeneous student cohort (national and international). By accessing appropriate flexible learning and different learning experiences, students are empowered to determine learning opportunities and methodologies to suit their personal needs. The off-campus mode study may disadvantage students since they don’t have the benefit of face-to-face instructions or to participate in formative assessments delivered informally in lectures. This may lead to feelings of remoteness and isolation leading to poorer learning, lower results in assessments, and may also contribute to drop-out rates, particularly in first year courses. To overcome this inequity, the usual training materials presented for a first year course in 2005 were supplemented with PowerPoint lectures, enhanced with synchronous audio, and a series of quizzes to be used as formative assessments. The lectures and quizzes were presented online via a course web site and were designed to become an integral part of the learning experience. An evaluation of the effectiveness of these strategy demonstrated improved students' learning, a positive contribution to the learning experience, increased enjoyment of the course, and a strong learning motivator. Students reported feeling less disenfranchised with the university and having a greater affinity with the lecturer

HERA Diffractive Structure Function Data and Parton Distributions

Recent diffractive structure function measurements by the H1 and ZEUS experiments at HERA are reviewed. Various data sets, obtained using systematically different selection and reconstruction methods, are compared. NLO DGLAP QCD fits are performed to the most precise H1 and ZEUS data and diffractive parton densities are obtained in each case. Differences between the Q^2 dependences of the H1 and ZEUS data are reflected as differences between the diffractive gluon densities.Comment: Contributed to the Proceedings of the Workshop on HERA and the LHC, DESY and CERN, 2004-200