Towards gauge theories in four dimensions

The abundance of infrared singularities in gauge theories due to unresolved emission of massless particles (soft and collinear) represents the main difficulty in perturbative calculations. They are typically regularized in dimensional regularization, and their subtraction is usually achieved independently for virtual and real corrections. In this paper, we introduce a new method based on the loop-tree duality (LTD) theorem to accomplish the summation over degenerate infrared states directly at the integrand level such that the cancellation of the infrared divergences is achieved simultaneously, and apply it to reference examples as a proof of concept. Ultraviolet divergences, which are the consequence of the point-like nature of the theory, are also reinterpreted physically in this framework. The proposed method opens the intriguing possibility of carrying out purely four-dimensional implementations of higher-order perturbative calculations at next-to-leading order (NLO) and beyond free of soft and final-state collinear subtractions.Comment: Final version to appear in JHE

Beyond the happy sheets! Evaluating learning in information skills teaching

This paper reviews three years of data measuring students' immediate reactions to a computer-assisted learning package in information skills and reports on work in progress to establish a more comprehensive programme of evaluation which will assess the longer term impact on learning of both the courseware itself and the way the courseware is delivered to students. The GAELS courseware was developed in the late 1990s as part of a collaborative project between the Universities of Glasgow and Strathclyde, with funding from the Scottish Higher Education Funding Council. The courseware was designed to teach higher level information skills and was initially developed for use with postgraduate engineering students; it has subsequently been adapted for use with students in other subject areas, including biological and physical sciences, and has been embedded for several years now in workshop sessions undertaken with postgraduate and undergraduate students across the Faculties of Science and Engineering at the University of Strathclyde. The courseware is introduced at the start of the academic session and made available on the Web so that students can use it as needed during their course and project work. During the first year, the courseware was used in isolation from other teaching methods (although a librarian was present to support students), whilst in the second and third years it was integrated into more traditional workshop-style teaching sessions (led by a librarian). Following work described in Joint (2003), library staff now wish to assess the longer term impact on learning of both the courseware itself and the way the courseware is delivered to students. However, the existing evaluation data does not adequately support this type of assessment. Teaching sessions are routinely evaluated by means of simple feedback forms, with four questions answered using a five-point Likert scale, collected at the conclusion of each session. According to Fitzpatrick (1998), such feedback forms measure students' reactions and represent but the first level of evaluation. Learning, which can be defined as the extent to which a student changes attitudes, improves knowledge and/or increases skill as a result of exposure to the training, is the second level and is not being measured with these forms. A more comprehensive programme of evaluation, including logging usage of the courseware outside teaching sessions and follow-up of students several months after their introduction to the courseware, is now being established to support a more meaningful assessment of impact of the courseware on student learning

Development of allergy in children. I. Association with virus infections.

Children born into allergic families, with two allergic parents, are at high risk of developing allergy within the first 5 years of life. In order to observe possible external factors in the sensitization process, a prospective study of 13 such children was done, in which serial clinical and immunologic observations were made at 3- to 6-month intervals over a period of 1 to 4 yr. Eleven of these children are now clinically allergic; 5 have asthma. Immunologic evidence for allergic sensitization was observed in these 11 children by RAST, antigen-induced leukocyte histamine release, lymphoblastogenesis, and rise in serum IgE. Upper respiratory infections (URI) occurred in these 11 allergic children 1 to 2 months prior to the onset of allergic sensitization. In 10 of these 11 URI children, complement-fixing antibodies to viruses (parainfluenza, RSV, CMV) increased in the same blood samples in which immunologic allergic sensitization was first evidenced. This coincidence suggests that certain viruses may contribute to the allergic sensitization process

Equilibrium States of Liquid, Solid, and Vapor and the Configurations for Copper, Tungsten, and Pores in Liquid-Phase Sintering

The equilibrium state of the liquid-solid structure during liquid-phase sintering (LPS) is pondered with respect to minimum energy geometries. Besides the solid-liquid ratio, several interfacial energies determine the most stable geometric configuration. In this study, we rely on the attributes of the copper or nickel as the liquid, tungsten as the solid, and vapor to solve for terminal configurations that include liquid pools inside the solid grains. Surface evolution is enabled using a stepwise computer program[1] to rearrange and reshape small grain clusters reflective of LPS based on a preset combination of wetting and dihedral angles. The findings show how different interfacial energies, as a result of oxidation or impurity segregation, play a role in determining the final geometry. The specific concern is identification of situations in which a liquid is stable inside the solid, as observed in some LPS materials.open112Nsciescopu

The effect of Fe atoms on the adsorption of a W atom on W(100) surface

We report a first-principles calculation that models the effect of iron (Fe) atoms on the adsorption of a tungsten (W) atom on W(100) surfaces. The adsorption of a W atom on a clean W(100) surface is compared with that of a W atom on a W(100) surface covered with a monolayer of Fe atoms. The total energy of the system is computed as the function of the height of the W adatom. Our result shows that the W atom first adsorbs on top of the Fe monolayer. Then the W atom can replace one of the Fe atoms through a path with a moderate energy barrier and reduce its energy further. This intermediate site makes the adsorption (and desorption) of W atoms a two-step process in the presence of Fe atoms and lowers the overall adsorption energy by nearly 2.4 eV. The Fe atoms also provide a surface for W atoms to adsorb facilitating the diffusion of W atoms. The combination of these two effects result in a much more efficient desorption and diffusion of W atoms in the presence of Fe atoms. Our result provides a fundamental mechanism that can explain the activated sintering of tungsten by Fe atoms.Comment: 9 pages, 2 figure