Diffractive production of high pt photons at HERA

We study the diffractive production of high pt photons at HERA. We have implemented the process as a new hard sub-process in the HERWIG event generator in order to prepare the ground for a future measurement.Comment: 4 pages, 4 figures. Contribution to the 1999 UK Phenomenology Workshop on Collider Physics, Durham, U

Large Interstellar Polarisation Survey II. UV/optical study of cloud-to-cloud variations of dust in the diffuse ISM

It is well known that the dust properties of the diffuse interstellar medium exhibit variations towards different sight-lines on a large scale. We have investigated the variability of the dust characteristics on a small scale, and from cloud-to-cloud. We use low-resolution spectro-polarimetric data obtained in the context of the Large Interstellar Polarisation Survey (LIPS) towards 59 sight-lines in the Southern Hemisphere, and we fit these data using a dust model composed of silicate and carbon particles with sizes from the molecular to the sub-micrometre domain. Large (> 6 nm) silicates of prolate shape account for the observed polarisation. For 32 sight-lines we complement our data set with UVES archive high-resolution spectra, which enable us to establish the presence of single-cloud or multiple-clouds towards individual sight-lines. We find that the majority of these 35 sight-lines intersect two or more clouds, while eight of them are dominated by a single absorbing cloud. We confirm several correlations between extinction and parameters of the Serkowski law with dust parameters, but we also find previously undetected correlations between these parameters that are valid only in single-cloud sight-lines. We find that interstellar polarisation from multiple-clouds is smaller than from single-cloud sight-lines, showing that the presence of a second or more clouds depolarises the incoming radiation. We find large variations of the dust characteristics from cloud-to-cloud. However, when we average a sufficiently large number of clouds in single-cloud or multiple-cloud sight-lines, we always retrieve similar mean dust parameters. The typical dust abundances of the single-cloud cases are [C]/[H] = 92 ppm and [Si]/[H] = 20 ppm.Comment: A&A accepte

The contrasting physiological and subjective effects of chewing gum on social stress

Uncertainty exists with respect to the extent to which chewing gum may attenuate stress-induced rises in cortisol secretion (Scholey et al., 2009; Smith, 2010; Johnson et al., 2011). The present study used the Trier Social Stress Task (TSST: Kirschbaum et al., 1993), a task known to elevate cortisol secretion (Kudielka et al., 2004), in order to examine the moderating physiological and subjective effects of chewing gum on social stress. Forty participants completed the TSST either with or without chewing gum. As expected, completion of the TSST elevated both cortisol and subjective stress levels, whilst impairing mood. Although gum moderated the perception of stress, cortisol concentrations were higher following the chewing of gum. The findings are consistent with Smith (2010) who argued that elevations in cortisol following the chewing of gum reflect heightened arousal. The findings suggest that chewing gum only benefits subjective measures of stress. The mechanism remains unclear; however, this may reflect increased cerebral blood flow, cognitive distraction, and/or effects secondary to task facilitation

Blind estimation of reverberation time in classrooms and hospital wards

This paper investigates blind Reverberation Time (RT) estimation in occupied classrooms and hospital wards. Measurements are usually made while these spaces are unoccupied for logistical reasons. However, occupancy can have a significant impact on the rate of reverberant decay. Recent work has developed a Maximum Likelihood Estimation (MLE) method which utilises only passively recorded speech and music signals, this enables measurements to be made while the room is in use. In this paper the MLE method is applied to recordings made in classrooms during lessons. Classroom occupancy levels differ for each lesson, therefore a model is developed using blind estimates to predict the RT for any occupancy level to within ±0.07s for the mid-frequency octave bands. The model is also able to predict the effective room and per person absorption area. Ambient sound recordings were also carried out in a number of rooms in two hospitals for a week. Hospital measurements are more challenging as the occurrence of free reverberant decay is rarer than in schools and the acoustic conditions may be non-stationary. However, by gaining recordings over a period of a week, estimates can be gained within ±0.07 s. These estimates are representative of the times when the room contains the highest acoustic absorption. In other words when curtains are drawn, there are many visitors or perhaps a window may be open

Threshold corrections in bottom and charm quark hadroproduction at next-to-next-to-leading order.

We calculate threshold soft-gluon corrections to total cross sections and transverse momentum distributions for bottom and charm quark production in fixed-target experiments, considering both pp and −p interactions. We investigate the quality of the near threshold soft-gluon approximation at next-to-leading order (NLO) and calculate next-to-nextto- leading order (NNLO) corrections through next-to-next-to-next-to-leading-logarithmic (NNNLL) accuracy, including some virtual terms. We find that the NNLO threshold corrections reduce the factorization and renormalization scale dependence of the cross sections

Research on solar pumped liquid lasers

A solar pumped liquid laser that can be scaled up to high power (10Mw CW) for space applications was developed. Liquid lasers have the inherent advantage over gases in that they provide much higher lasant densities and thus high power densities. Liquids also have inherent advantages over solids in that they have much higher damage thresholds and are much cheaper to produce for large scale applications. Among the liquid laser media that are potential candidates for solar pumping, the POC13:Nd(3+):ZrC14 liquid was chosen for its high intrinsic efficiency as well as its relatively good stability against decomposition due to protic contamination. The development and testing of the laser liquid and the development of a large solar concentrator to pump the laser was emphasized. The procedure to manufacture the laser liquid must include diagnostic tests of the solvent purity (from protic contamination) at various stages in the production process

First-principles study of the energetics of charge and cation mixing in U_{1-x} Ce_x O_2

The formalism of electronic density-functional-theory, with Hubbard-U corrections (DFT+U), is employed in a computational study of the energetics of U_{1-x} Ce_x O_2 mixtures. The computational approach makes use of a procedure which facilitates convergence of the calculations to multiple self-consistent DFT+U solutions for a given cation arrangement, corresponding to different charge states for the U and Ce ions in several prototypical cation arrangements. Results indicate a significant dependence of the structural and energetic properties on the nature of both charge and cation ordering. With the effective Hubbard-U parameters that reproduce well the measured oxidation-reduction energies for urania and ceria, we find that charge transfer between U(IV) and Ce(IV) ions, leading to the formation of U(V) and Ce(III), gives rise to an increase in the mixing energy in the range of 4-14 kJ/mol of formula unit, depending on the nature of the cation ordering. The results suggest that although charge transfer between uranium and cerium ions is disfavored energetically, it is likely to be entropically stabilized at the high temperatures relevant to the processing and service of urania-based solid solutions.Comment: 8 pages, 6 figure