Treatment of the infrared contribution: NLO QED evolution as a pedagogic example

We show that the conventional prescription used for DGLAP parton evolution at NLO has an inconsistent treatment of the contribution from the infrared (IR) region. We illustrate the problem by studying the simple example of QED evolution, treating the electron and photon as partons. The deficiency is not present in a physical approach which removes the IR divergency and allows calculation in the normal 4-dimensional space.Comment: 15 pages, 2 figures, erratum at the end of the articl

The LHC can probe small x PDFs; the treatment of the infrared region

First, we show how to reduce the sensitivity of the NLO predictions of the Drell-Yan production of low-mass, lepton-pairs, at high rapidity, to the choice of factorization scale. In this way, observations of this process at the LHC can make direct measurements of parton distribution functions in the low x domain; x < 10^{-4}. Second, we find an inconsistency in the conventional NLO treatment of the infrared region. We illustrate the problem using the NLO coefficient function of Drell-Yan production.Comment: 5 pages, 1 figure, contribution to the Proceedings of "Diffraction2012", Puerto del Carmen, Lanzarote, Spain, Sept. 10-15th, 201

Treatment of heavy quarks in QCD

We show that to correctly describe the effects of the heavy-quark mass, m_h, in DGLAP evolution, it is necessary to work in the so-called `physical' scheme. In this way, we automatically obtain a smooth transition through the heavy-quark thresholds. Moreover, we show that to obtain NLO accuracy, it is sufficient to account for the heavy-quark mass, m_h, just in the LO (one-loop) splitting function. The use of the MS-bar factorisation scheme is not appropriate, since at NLO we deal with a mixture of quarks and gluon (that is, the mass of the heavy parton is not well-defined). The formulae for the explicit m_h dependence of the splitting functions, and for alpha_s, are presented.Comment: 14 pages, 3 figures, references updated, version to be published in EPJ

Data analysis with ordinal and interval dependent variables: examples from a study of real estate salespeople

This paper re-examines the problems of estimating the parameters of an underlying linear model using survey response data in which the dependent variables are in discrete categories of ascending order (ordinal, as distinct from numerical) or, where they are observed to fall into certain groups on a continuous scale (interval), where the actual values remain unobserved. An ordered probit model is discussed as an appropriate framework for statistical analysis for ordinal dependent variables. Next, a maximum likelihood estimator (MLE) derived from grouped data regression for interval dependent variable is discussed. Using LIMDEP, a packaged statistical program, survey data from an earlier manuscript are analyzed and the findings presented.

Models for the Effects of G-seat Cuing on Roll-axis Tracking Performance

Including whole-body motion in a flight simulator improves performance for a variety of tasks requiring a pilot to compensate for the effects of unexpected disturbances. A possible mechanism for this improvement is that whole-body motion provides high derivative vehicle state information whic allows the pilot to generate more lead in responding to the external disturbances. During development of motion simulating algorithms for an advanced g-cuing system it was discovered that an algorithm based on aircraft roll acceleration producted little or no performance improvement. On the other hand, algorithms based on roll position or roll velocity produced performance equivalent to whole-body motion. The analysis and modeling conducted at both the sensory system and manual control performance levels to explain the above results are described

Alignment and Precession of a Black Hole with a Warped Accretion Disc

We consider the shape of an accretion disc whose outer regions are misaligned with the spin axis of a central black hole and calculate the steady state form of the warped disc in the case where the viscosity and surface densities are power laws in the distance from the central black hole. We discuss the shape of the resulting disc in both the frame of the black hole and that of the outer disc. We note that some parts of the disc and also any companion star maybe shadowed from the central regions by the warp. We compute the torque on the black hole caused by the Lense-Thirring precession and hence compute the alignment and precession timescales. We generalise the case with viscosity and hence surface density independent of radius to more realistic density distributions for which the surface density is a decreasing function of radius. We find that the alignment timescale does not change greatly but the precession timescale is more sensitive. We also determine the effect on this timescale if we truncate the disc. For a given truncation radius, the the timescales are less affected for more sharply falling density distributions.Comment: Accepted for publication in MNRA

Voyager electronic parts radiation program, volume 1

The Voyager spacecraft is subject to radiation from external natural space, from radioisotope thermoelectric generators and heater units, and from the internal environment where penetrating electrons generate surface ionization effects in semiconductor devices. Methods for radiation hardening and tests for radiation sensitivity are described. Results of characterization testing and sample screening of over 200 semiconductor devices in a radiation environment are summarized

Cryogenic seal remains leaktight during thermal displacement

Cryogenic seals protect the surfaces of a plastic member in a low-pressure system subjected to extreme temperature changes. The outer seal is an aluminum expansion ring bonded to the lens outer surface and the inner seal consists of a resin-filled aluminum U-ring bonded to the inner surface

Phase behaviour of attractive and repulsive ramp fluids: integral equation and computer simulation studies

Using computer simulations and a thermodynamically self consistent integral equation we investigate the phase behaviour and thermodynamic anomalies of a fluid composed of spherical particles interacting via a two-scale ramp potential (a hard core plus a repulsive and an attractive ramp) and the corresponding purely repulsive model. Both simulation and integral equation results predict a liquid-liquid de-mixing when attractive forces are present, in addition to a gas-liquid transition. Furthermore, a fluid-solid transition emerges in the neighbourhood of the liquid-liquid transition region, leading to a phase diagram with a somewhat complicated topology. This solidification at moderate densities is also present in the repulsive ramp fluid, thus preventing fluid-fluid separation.Comment: 29 pages, 10 figure