Mirroring within the Fokker-Planck formulation of cosmic ray pitch angle scattering in homogeneous magnetic turbulence

The Fokker-Planck coefficient for pitch angle scattering, appropriate for cosmic rays in homogeneous, stationary, magnetic turbulence, is computed from first principles. No assumptions are made concerning any special statistical symmetries the random field may have. This result can be used to compute the parallel diffusion coefficient for high energy cosmic rays moving in strong turbulence, or low energy cosmic rays moving in weak turbulence. Becuase of the generality of the magnetic turbulence which is allowed in this calculation, special interplanetary magnetic field features such as discontinuities, or particular wave modes, can be included rigorously. The reduction of this results to previously available expressions for the pitch angle scattering coefficient in random field models with special symmetries is discussed. The general existance of a Dirac delta function in the pitch angle scattering coefficient is demonstrated. It is proved that this delta function is the Fokker-Planck prediction for pitch angle scattering due to mirroring in the magnetic field

The Fokker-Planck coefficient for pitch-angle scattering of cosmic rays

For the case of homogeneous, isotropic magnetic field fluctuations, it is shown that most theories which are based on the quasi-linear and adiabatic approximation yield the same integral for the Fokker-Planck coefficient for the pitch angle scattering of cosmic rays. For example, despite apparent differences, the theories due to Jokipii and to Klimas and Sandri yield the same integral. It is also shown, however, that this integral in most cases has been evaluated incorrectly in the past. For large pitch angles these errors become significant, and for pitch angles of 90 deg the actual Fokker-Planck coefficient contains a delta function. The implications for these corrections relating cosmic ray diffusion coefficients to observed properties of the interplanetary magnetic field are discussed

Agricultural Distortion Patterns Since the 1950s: What Needs Explaining?

This paper summarizes a new database that sheds light on the impact of trade-related policy developments over the past half century on distortions to agricultural incentives and thus also to consumer prices for food in 75 countries spanning the per capita income spectrum. Price-support policies of advanced economies hurt not only domestic consumers and exporters of other products but also foreign producers and traders of farm products, and they reduce national and global economic welfare. On the other hand, the governments of many developing countries have directly taxed their farmers over the past half-century, both directly (e.g., export taxes) and also indirectly via overvaluing their currency and restricting imports of manufactures. Thus the price incentives facing farmers in many developing countries have been depressed by both own-country and other countries’ agricultural price and international trade policies. We summarize these and related stylized facts that can be drawn from a new World Bank database that is worthy of the attention of political economy theorists, historians and econometricians. These indicators can be helpful in addressing such questions as the following: Where is there still a policy bias against agricultural production? To what extent has there been overshooting in the sense that some developing-country food producers are now being protected from import competition along the lines of the examples of earlier-industrializing Europe and Japan? What are the political economy forces behind the more-successful reformers, and how do they compare with those in less-successful countries where major distortions in agricultural incentives remain? And what explains the pattern of distortions across not only countries but also industries and in the choice of support or tax instruments within the agricultural sector of each country?Distorted incentives, agricultural and trade policy reforms, national agricultural development, Political economy, agricultural price and trade policies, Agricultural and Food Policy, International Relations/Trade, F13, F14, Q17, Q18, F59, H20, N50, O13,

Improving education for refugee background students: research findings

This research aimed to understand the experiences of refugee background students (RBS) in secondary schools and colleges in order to support their progression to Higher Education. The research focused on the refugee students’ experiences of arriving in, and moving through, the education system. Additionally, the research looked at the aspirations of young refugees, how these are being met and their perceptions of the difficulties and challenges they face in moving through the education system. The project worked in partnership with The Hummingbird Project, a charity supporting young refugees and unaccompanied asylum-seeking children in Brighton, and Sanctuary on Sea, part of the national network, City of Sanctuary, whose objective is to make cities more welcoming for refugees and migrants. The project also worked in collaboration with an Advisory Group of partners from schools, colleges, the University of Brighton and the University of Sussex, Brighton and Hove City Council and representatives of refugee communities (See Annex 1). The group met three times over the course of the project. Alongside general oversight of the research, the group contributed their invaluable professional and practice-based perspectives, these have helped to shape the findings presented here. Two peer researchers with refugee backgrounds were recruited to help with data collection. They were trained in a two-day workshop on research methods at the University of Sussex led by the principal investigator. Peer researchers also contributed to the Advisory Group with their own experiences of education in the UK

Bayesian inference on earthquake size distribu- tion: a case study in Italy

This paper is focused on the study of earthquake size statistical distribution by using Bayesian inference. The strategy consists in the definition of an a priori distribution based on instrumental seismicity, and modeled as a power law distribution. By using the observed historical data, the power law is then modified in order to obtain the posterior distribution. The aim of this paper is to define the earthquake size distribution using all the seismic database available (i.e., instrumental and historical catalogs) and a robust statistical technique. We apply this methodology to the Italian seismicity, dividing the territory in source zones as done for the seismic hazard assessment, taken here as a reference model. The results suggest that each area has its own peculiar trend: while the power law is able to capture the mean aspect of the earthquake size distribution, the posterior emphasizes different slopes in different areas. Our results are in general agreement with the ones used in the seismic hazard assessment in Italy. However, there are areas in which a flattening in the curve is shown, meaning a significant departure from the power law behavior and implying that there are some local aspects that a power law distribution is not able to capture

Calidad de las matérias primas em la elaboración de raciones: bases para el êxito.

Projeto: 03.11.09.008

The GRAAL high resolution BGO calorimeter and its energy calibration and monitoring system

We describe the electromagnetic calorimeter built for the GRAAL apparatus at the ESRF. Its monitoring system is presented in detail. Results from tests and the performance obtained during the first GRAAL experiments are given. The energy calibration accuracy and stability reached is a small fraction of the intrinsic detector resolution.Comment: 19 pages, 14 figures, submitted to Nuclear Instruments and Method

A review and new insights on the estimation of the b-valueand its uncertainty

The estimation of the b-value of the Gutenberg-Richter Law and its uncertainty is crucial in seismic hazard studies, as well as in verifying theoretical assertions, such as, for example, the universality of the Gutenberg-Richter Law. In spite of the importance of this issue, many scientific papers still adopt formulas that lead to different estimations. The aim of this paper is to review the main concepts relative to the estimation of the b-value and its uncertainty, and to provide some new analytical and numerical insights on the biases introduced by the unavoidable use of binned magnitudes, and by the measurement errors on the magnitude. It is remarked that, although corrections for binned magnitudes were suggested in the past, they are still very often neglected in the estimation of the b-value, implicitly by assuming that the magnitude is a continuous random variable. In particular, we show that: i) the assumption of continuous magnitude can lead to strong bias in the b-value estimation, and to a significant underestimation of its uncertainty, also for binning of ?M = 0.1; ii) a simple correction applied to the continuous formula causes a drastic reduction of both biases; iii) very simple formulas, until now mostly ignored, provide estimations without significant biases; iv) the effect on the bias due to the measurement errors is negligible compared to the use of binned magnitudes

A technical note on the bias in the estimation of the b-value and its uncertainty through the Least Squares technique

We investigate conceptually, analytically, and numerically the biases in the estimation of the b-value of the Gutenberg-Richter Law and of its uncertainty made through the least squares technique. The biases are introduced by the cumulation operation for the cumulative form of the Gutenberg-Richter Law, by the logarithmic transformation, and by the measurement errors on the magnitude. We find that the least squares technique, applied to the cumulative and binned form of the Gutenberg-Richter Law, produces strong bias in the b-value and its uncertainty, whose amplitudes depend on the size of the sample. Furthermore, the logarithmic transformation produces two different endemic bends in the Log(N) versus M curve. This means that this plot might produce fake significant departures from the Gutenberg-Richter Law. The effect of the measurement errors is negligible compared to those of cumulation operation and logarithmic transformation. The results obtained show that the least squares technique should never be used to determine the slope of the Gutenberg-Richter Law and its uncertainty