2,537 research outputs found
Noncommutative Quantum Field Theory: A Confrontation of Symmetries
The concept of a noncommutative field is formulated based on the interplay
between twisted Poincar\'e symmetry and residual symmetry of the Lorentz group.
Various general dynamical results supporting this construction, such as the
light-wedge causality condition and the integrability condition for
Tomonaga-Schwinger equation, are presented. Based on this analysis, the claim
of the identity between commutative QFT and noncommutative QFT with twisted
Poincar\'e symmetry is refuted.Comment: 20 page
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 âInternational Geochemical Mappingâ (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 (< 150â< 200 ÎŒm), 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 ÎŒm 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
On inversions and Doob -transforms of linear diffusions
Let be a regular linear diffusion whose state space is an open interval
. We consider a diffusion which probability law is
obtained as a Doob -transform of the law of , where is a positive
harmonic function for the infinitesimal generator of on . This is the
dual of with respect to where is the speed measure of
. Examples include the case where is conditioned to stay above
some fixed level. We provide a construction of as a deterministic
inversion of , 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
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On -transforms of one-dimensional diffusions stopped upon hitting zero
For a one-dimensional diffusion on an interval for which 0 is the
regular-reflecting left boundary, three kinds of conditionings to avoid zero
are studied. The limit processes are -transforms of the process stopped
upon hitting zero, where 's are the ground state, the scale function, and
the renormalized zero-resolvent. Several properties of the -transforms are
investigated
Implementation of improved postoperative care decreases the mortality rate of operated mice after an abundant 6-hydroxydopamine lesion of nigrostriatal dopaminergic neurons
A mouse model of Parkinsonâs disease with an abundant lesion of nigrostriatal dopaminergic neurons can be achieved by stereotactic injection of 6-hydroxydopamine into the medial forebrain bundle. However, postoperative mortality can be excessively high without intensive postoperative care. Here, we show that improvements in stereotactic operations and postoperative care result in significant benefits for both animal well-being and research efficiency. Adopting a wide combination of mostly previously described improvements resulted in a decrease of postoperative mortality from 71% to 14% and an increase in successful abundant dopaminergic lesions from 46% to 81%. The techniques adopted are described in detail. In addition, we describe a simple protocol for gradual preoperative handling which can be utilized to decrease animal stress, aggressive and aversive behaviors, and to facilitate postoperative care and other subsequent handling. We propose that the implementation of these improvements greatly decreases the risk of animal suffering and that the improvements are worth adopting in any research group utilizing abundant 6-hydroxydopamine-induced dopaminergic lesions in mice. Suggestions for further improvement are also presented
Roughness and multiscaling of planar crack fronts
We consider numerically the roughness of a planar crack front within the
long-range elastic string model, with a tunable disorder correlation length
. The problem is shown to have two important length scales, and the
Larkin length . Multiscaling of the crack front is observed for scales
below , provided that the disorder is strong enough. The asymptotic
scaling with a roughness exponent is recovered for scales
larger than both and . If , these regimes are separated
by a third regime characterized by the Larkin exponent .
We discuss the experimental implications of our results.Comment: 8 pages, two figure
Predictors of blood pressure and hypertension long-term after treatment of isolated coarctation of the aorta in children-a population-based study
OBJECTIVES The aim of this study was to assess predictors of BP and hypertension and relations between BP and LV mass in a population-based retrospective study of repaired isolated coarctation of aorta. METHODS We collected follow-up data until 2018 of 284/304 (93%) patients with coarctation treated by surgery (n = 235) or balloon angioplasty/stent (n = 37/12) in our unit 2000-2012. Systolic hypertension was defined as systolic BP (SBP) z-score >=+2 standard deviation (SD) or regular use of BP medication. LV hypertrophy was defined as LV mass z-score >=+2 SD or LV mass index g/m(2.7) >= 95th percentile. RESULTS The median (25-75th percentiles) follow-up time and age at follow-up were 9.7 years (6.9-13.2) and 11.8 years (7.9-16.0), respectively. Age at first procedure (P = 0.011) and systolic arm-leg-gradient (P = 0.007) were positively and transverse arch (P = 0.007) and isthmus diameter (P = 0.001) z-scores at follow-up were negatively associated with SBP z-score adjusted for age at follow-up and need for reintervention for coarctation. Systolic hypertension was present in 53/284 (18.7%) and related with increasing age at first procedure (median 33.2 vs 0.6 months; P < 0.001) and arm-leg-gradient at follow-up (mean +/- SD, -0.3 +/- 14.6 vs -6.4 +/- 11.6 mmHg; P = 0.047) adjusted for reintervention for coarctation and age at follow-up. LV hypertrophy was present in 20/227 (9.3%) and related with SBP z-score. CONCLUSIONS Higher SBP and hypertension in repaired coarctation of aorta are related with increasing age at first procedure and arm-leg-gradient at follow-up. Transverse arch and isthmus diameters at follow-up are inversely related with SBP.Peer reviewe
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