Nonperturbative renormalization group approach to frustrated magnets

This article is devoted to the study of the critical properties of classical XY and Heisenberg frustrated magnets in three dimensions. We first analyze the experimental and numerical situations. We show that the unusual behaviors encountered in these systems, typically nonuniversal scaling, are hardly compatible with the hypothesis of a second order phase transition. We then review the various perturbative and early nonperturbative approaches used to investigate these systems. We argue that none of them provides a completely satisfactory description of the three-dimensional critical behavior. We then recall the principles of the nonperturbative approach - the effective average action method - that we have used to investigate the physics of frustrated magnets. First, we recall the treatment of the unfrustrated - O(N) - case with this method. This allows to introduce its technical aspects. Then, we show how this method unables to clarify most of the problems encountered in the previous theoretical descriptions of frustrated magnets. Firstly, we get an explanation of the long-standing mismatch between different perturbative approaches which consists in a nonperturbative mechanism of annihilation of fixed points between two and three dimensions. Secondly, we get a coherent picture of the physics of frustrated magnets in qualitative and (semi-) quantitative agreement with the numerical and experimental results. The central feature that emerges from our approach is the existence of scaling behaviors without fixed or pseudo-fixed point and that relies on a slowing-down of the renormalization group flow in a whole region in the coupling constants space. This phenomenon allows to explain the occurence of generic weak first order behaviors and to understand the absence of universality in the critical behavior of frustrated magnets.Comment: 58 pages, 15 PS figure

An Observational Overview of Solar Flares

We present an overview of solar flares and associated phenomena, drawing upon a wide range of observational data primarily from the RHESSI era. Following an introductory discussion and overview of the status of observational capabilities, the article is split into topical sections which deal with different areas of flare phenomena (footpoints and ribbons, coronal sources, relationship to coronal mass ejections) and their interconnections. We also discuss flare soft X-ray spectroscopy and the energetics of the process. The emphasis is to describe the observations from multiple points of view, while bearing in mind the models that link them to each other and to theory. The present theoretical and observational understanding of solar flares is far from complete, so we conclude with a brief discussion of models, and a list of missing but important observations.Comment: This is an article for a monograph on the physics of solar flares, inspired by RHESSI observations. The individual articles are to appear in Space Science Reviews (2011

Measurements of daily urinary uranium excretion by German KFOR personnel and residents of Kosovo to assess potential intakes of Depleted Uranium (DU).

Following the end of the Kosovo conflict, in June 1999, an investigation was instigated to evaluate the size of the health risk, if any, presented by depleted uranium (DU) to German KFOR personnel serving in the Balkans. In addition, the investigations were extended to residents of Kosovo, who had been living in areas where DU munitions were deployed. In order to assess a possible DU intake both the urinary uranium excretion of volunteer residents and environmental samples were collected and analysed using ICP-MS. Measurements by ICP-MS require only small sample volumes of a few ml. Urine sampling, transport and storage until measurement, etc. would be much easier if cumulative, 24-hours collections were not required. For that reason, in the first part of the study, the urine sampling method was analysed in order to evaluate the suitability of spot collections for urinary uranium excretion determination. However, it was concluded that 24-hr urine sampling should be performed to avoid large uncertainties in the quantitation of daily urinary excretion values. In the second part of the study, the uranium excretion by German KFOR personnel serving on the Balkans was investigated. In total, more than 1300 urine samples from soldiers, civil servants and unexposed controls of different genders and age were analysed to determine uranium excretion parameters. The volunteers, aged from 3 to 92 years, were grouped into 10-year age groups for evaluation. For all 1199 male subjects, the arithmetic mean of the uranium excretion rate was 19.96 ± 19.13 ng/d (mean ± SD), equivalent to 247.5 ± 237.2 mBq/d. For 118 female volunteers, an average uranium excretion rate of 16.65 ± 17.57 ng/d (mean ± SD)) was measured, corresponding to 206.5 ± 217.9 mBq/d. Inter-subject variation in uranium excretion was high and no significant age-specific differences were found. Most significantly, the levels of uranium excretion by KFOR personnel and unexposed individuals were similar. It can be concluded that KFOR personnel were not exposed to biologically relevant amounts of DU intake during their stay in Kosovo. The third part of the study monitored 24-hour urine samples provided by selected residents of Kosovo, adjacent regions of Serbia and controls from Munich, Germany. The urine samples collected were split and analysed in the frame of an inter-comparison study. Total uranium and isotope ratios were measured in order to determine DU content. 238U/235U ratios were within ±0.3% of the natural value, and 236U/238U was less than 0.0000002, indicating no significant DU in any of the urine samples provided, despite total uranium excretion being sometimes very high.&nbsp

The solid speciation of 90Sr, 137Cs, 226Ra, 238U and 239,240Pu in surface soils from sites of special radiological interest in Kazakhstan

The solid speciation of some radiologically important radioelements has been examined in soils sampled at the former Semipalatinsk (Nuclear) Test Site (STS) and at Kurdai, the site of a former major uranium mining operation - both situated in Kazakhstan. Specifically, the partitioning of radiostrontium, radiocaesium and plutonium has been examined using sequential extraction on selected soils from the test site, while the partitioning of radium and uranium has been evaluated in soils at Kurdai. The data show that at the STS, in general, little (if any) of the radiostrontium, radiocaesium and plutonium is in an exchangeable form, with the great bulk of the radiostrontium and radiocaesium in a strongly bound or refractory form. In the case of plutonium, the proportion in a strongly bound or refractory form varies from 40% to 95% depending on site and appears to be a function of the explosive yield involved. At the Kurdai ore deposit, less than 5% of the uranium and radium is in an exchangeable form, with some 35-60% of the uranium and the bulk of the radium in a strongly bound or residual form. © 2009 al-Farabi Kazakh National University

The solid speciation of 90Sr, 137Cs, 226Ra, 238U and 239,240Pu in surface soils from sites of special radiological interest in Kazakhstan

The solid speciation of some radiologically important radioelements has been examined in soils sampled at the former Semipalatinsk (Nuclear) Test Site (STS) and at Kurdai, the site of a former major uranium mining operation - both situated in Kazakhstan. Specifically, the partitioning of radiostrontium, radiocaesium and plutonium has been examined using sequential extraction on selected soils from the test site, while the partitioning of radium and uranium has been evaluated in soils at Kurdai. The data show that at the STS, in general, little (if any) of the radiostrontium, radiocaesium and plutonium is in an exchangeable form, with the great bulk of the radiostrontium and radiocaesium in a strongly bound or refractory form. In the case of plutonium, the proportion in a strongly bound or refractory form varies from 40% to 95% depending on site and appears to be a function of the explosive yield involved. At the Kurdai ore deposit, less than 5% of the uranium and radium is in an exchangeable form, with some 35-60% of the uranium and the bulk of the radium in a strongly bound or residual form. © 2009 al-Farabi Kazakh National University

An infinity of super-Belnap logics

We look at extensions (i.e., stronger logics in the same language) of the Belnap–Dunn four-valued logic. We prove the existence of a countable chain of logics that extend the Belnap–Dunn and do not coincide with any of the known extensions (Kleene’s logics, Priest’s logic of paradox). We characterise the reduced algebraic models of these new log- ics and prove a completeness result for the first and last element of the chain stating that both logics are determined by a single finite logical matrix. We show that the last logic of the chain is not finitely axiomatisable