Magnetic Monopole in Noncommutative Space-Time and Wu-Yang Singularity-Free Gauge Transformations

We investigate the validity of the Dirac Quantization Condition (DQC) for magnetic monopoles in noncommutative space-time. We use an approach which is based on an extension of the method introduced by Wu and Yang. To study the effects of noncommutativity of space-time, we consider the gauge transformations of $U_\star(1)$ gauge fields and use the corresponding deformed Maxwell's equations. Using a perturbation expansion in the noncommutativity parameter $\theta$, we show that the DQC remains unmodified up to the first order in the expansion parameter. The result is obtained for a class of noncommutative source terms, which reduce to the Dirac delta function in the commutative limit.Comment: 18 pages. Relation to relevant literature clarified in the conclusions, 6 references adde

The Forum of European Geological Surveys Geochemistry Task Group 1994-1996 inventory

The Forum of European Geological Surveys (FOREGS) includes representatives from 33 European countries and is responsible for co-ordinating Geological Survey activities in Europe. The FOREGS Geochemistry Task Group was established in 1994 to develop a strategy for the preparation of European geochemical maps following the recommendations of the International Geological Correlation Programme (IGCP) Project 259 ‘International Geochemical Mapping’ (now the International Union of Geological Sciences (IUGS) /International Association of Geochemistry and Cosmochemistry (IAGC) Working Group on Global Geochemical Baselines). The FOREGS geochemistry programme is aimed at preparing a standardised European geochemical baseline to IGCP-259 standards. The principal aims of this dataset will be for environmental purposes, as a baseline for the assessment of the extent and distribution of contaminated land in the context of variations in the natural geochemical background, but it will also have applications in resource assessment and for the development of policy for the sustainable management of metalliferous mineral and other resources. The first phase of the programme was the compilation of an inventory of geochemical data based on the results of a questionnaire completed by Geological Surveys and related organisations throughout the FOREGS community. The results show that the sample types which have been used most extensively are stream sediment (26% coverage), surface water (19% coverage) and soil (11% coverage). Stream sediments have been collected using a narrow range of mesh sizes (< 150–< 200 μm), but soil samples have been collected according to two different conventions: some surveys used a similar mesh size range to that used for stream sediments while others employed the < 1000 or < 2000 μm fractions traditionally used by soil surveys. Sample densities range from 1 sample per 0.5 km2 to 1 per 3500 km2. Various analytical methods have been used, but most of the available data have been calibrated using international reference materials, and data for the most important of the potentially harmful elements (PHEs) are available for most datasets. Systematic radiometric data are available for only a small proportion of Europe, a situation which compares very unfavourably with that in Australia, North America, the former Soviet Union and many developing countries. Recommendations are made for increasing the compatibility of geochemical methods between national geochemical surveys as a basis for the preparation of a series of European geochemical maps. The next stage of the FOREGS Geochemistry Task Group will be the collection of the Global Reference Network of samples against which to standardise national datasets according to the methods recommended in the final report of the IGCP 259 programme

Superconducting Coil Compression by Scissor Laminations

A new system of coil compression has been designed which uses iron laminations to transfer the pressure from an outer shrink ring to the coil. The laminations are simple circular discs around the coil with the peculiarity that the rim is slightly eccentric as compared to the coil. Successive laminations are mounted with different angular orientations to oppose their eccentricities. The shrink ring pushed these discs inwards against the coil creating compression by a scissor movement. Tests on mechanical models of single as well as multiple aperture magnets have shown it to work as expected. The system has already successfully been applied to several corrector magnets for LHC. The advantages are low cost (suppression of the usual collars), increased coil compression in particular from cooling down, and field enhancement from having the iron close to the coil

On inversions and Doob hh-transforms of linear diffusions

Let $X$ be a regular linear diffusion whose state space is an open interval $E\subseteq\mathbb{R}$. We consider a diffusion $X^*$ which probability law is obtained as a Doob $h$-transform of the law of $X$, where $h$ is a positive harmonic function for the infinitesimal generator of $X$ on $E$. This is the dual of $X$ with respect to $h(x)m(dx)$ where $m(dx)$ is the speed measure of $X$. Examples include the case where $X^*$ is $X$ conditioned to stay above some fixed level. We provide a construction of $X^*$ as a deterministic inversion of $X$, time changed with some random clock. The study involves the construction of some inversions which generalize the Euclidean inversions. Brownian motion with drift and Bessel processes are considered in details.Comment: 19 page

Roughening of Fracture Surfaces: the Role of Plastic Deformations

Post mortem analysis of fracture surfaces of ductile and brittle materials on the $\mu$m-mm and the nm scales respectively, reveal self affine graphs with an anomalous scaling exponent $\zeta\approx 0.8$. Attempts to use elasticity theory to explain this result failed, yielding exponent $\zeta\approx 0.5$ up to logarithms. We show that when the cracks propagate via plastic void formations in front of the tip, followed by void coalescence, the voids positions are positively correlated to yield exponents higher than 0.5.Comment: 4 pages, 6 figure

Superconducting Sextupole Corrector Magnet for the LHC Main Dipoles

Each LHC main dipole will be equipped with small sextupole corrector ma g nets with a field strength of 1970 x2 T/m2 and a magnetic length of 100 mm designed to correct the sextupole field errors. The paper presents a cosine-q type of design where much emphasis has been put on the cost reduction because these magnets have to be made in large series of some 2500 pieces. We describe the design of a two-layer coil which can be wound automatically. The winding starts in the middle of the wire with the only joggle, the layer jump, which is housed in a corresponding groove in the end of the central island. The two layers are wound simultaneously turning in opposite directions to find their position without the need of local tooling. The coil ends are closely packed and need no end spacers. The 18 pole perturbation introduced by the ends is corrected by the position of the coil block in the straight part. The yoke is made of iron laminations of the "Scissors type" which transmit the pre-stress from the outer aluminium shrink ring to the coil. This allows the iron to be close to the coil for field enhancement and also boosts the pre-stress in the coil due to the cool down contractions. The paper describes the experience with the magnet construction and gives the first test results