Benchmarking GEANT4 nuclear models for hadron therapy with 95 MeV/nucleon carbon ions

In carbon-therapy, the interaction of the incoming beam with human tissues may lead to the production of a large amount of nuclear fragments and secondary light particles. An accurate estimation of the biological dose deposited into the tumor and the surrounding healthy tissues thus requires sophisticated simulation tools based on nuclear reaction models. The validity of such models requires intensive comparisons with as many sets of experimental data as possible. Up to now, a rather limited set of double di erential carbon fragmentation cross sections have been measured in the energy range used in hadrontherapy (up to 400 MeV/A). However, new data have been recently obtained at intermediate energy (95 MeV/A). The aim of this work is to compare the reaction models embedded in the GEANT4 Monte Carlo toolkit with these new data. The strengths and weaknesses of each tested model, i.e. G4BinaryLightIonReaction, G4QMDReaction and INCL++, coupled to two di fferent de-excitation models, i.e. the generalized evaporation model and the Fermi break-up are discussed

General and partial equilibrium analysis of the impact of the Central America Free Trade Agreement on the U.S. rice sector

The market conditions proposed by CAFTA are likely to positively impact the U.S. rice sector. Despite the differences in the impact of the agreement, both analytical approaches, namely, partial and general equilibrium modeling, yield results in the same direction. The small difference in the results from both approaches suggests low income and cross-sectoral effects between the U.S. rice sector and other segments of the economy. U.S. rice production is likely to expand to meet an increasing international demand for this commodity. The U.S. rice milling industry should also expect benefits from CAFTA, expanding by 1 percent in the general equilibrium model and up to 8 percent in the partial equilibrium framework.International Relations/Trade,

Detection of an anomalous cluster in a network

We consider the problem of detecting whether or not, in a given sensor network, there is a cluster of sensors which exhibit an "unusual behavior." Formally, suppose we are given a set of nodes and attach a random variable to each node. We observe a realization of this process and want to decide between the following two hypotheses: under the null, the variables are i.i.d. standard normal; under the alternative, there is a cluster of variables that are i.i.d. normal with positive mean and unit variance, while the rest are i.i.d. standard normal. We also address surveillance settings where each sensor in the network collects information over time. The resulting model is similar, now with a time series attached to each node. We again observe the process over time and want to decide between the null, where all the variables are i.i.d. standard normal, and the alternative, where there is an emerging cluster of i.i.d. normal variables with positive mean and unit variance. The growth models used to represent the emerging cluster are quite general and, in particular, include cellular automata used in modeling epidemics. In both settings, we consider classes of clusters that are quite general, for which we obtain a lower bound on their respective minimax detection rate and show that some form of scan statistic, by far the most popular method in practice, achieves that same rate to within a logarithmic factor. Our results are not limited to the normal location model, but generalize to any one-parameter exponential family when the anomalous clusters are large enough.Comment: Published in at http://dx.doi.org/10.1214/10-AOS839 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Rice Trade Policies and Their Implications for Food Security

There is a strong linkage between the behavior of the rice market and the state of food security in many regions around the world, particularly in Asia, as made evident in the 2007-08 commodity crisis. Rice is a staple for the majority of the population in Asia, where roughly 60% of the close to one billion undernourished people live (FAO, 2010). As Timmer (2010) states, “it is impossible to improve food security in the short run or long run without providing adequate supplies of rice that are accessible to the poor” (p. 2). The rice crisis of 2007-08 showed the crucial role of export and import policies on the behavior of the rice market and its consequences for price stability and food security. Market fundamentals could only explain a minimal part of the skyrocketing increase in rice prices observed (Dawe, 2010). The overarching objective of this study is to assess the impact of international rice trade policies on the patterns of production, consumption, trade, and prices, from an ex-post and ex-ante perspective, and analyze the implications of these policies from a food-security point of view. The RICEFLOW model (Durand-Morat and Wailes, 2010) is used for the assessment. RICEFLOW is a spatial partial equilibrium model of the global rice economy in which the behavior of producers and consumers are specified according to neoclassical economic theory (profit and utility maximizers, respectively). Domestic production and imports are specified as imperfect substitutes following Armington (1969). The model is calibrated to calendar year 2008, the latest available year for which the RICEFLOW database is available. The 2008 RICEFLOW database is disaggregated into 65 country/regions, including the largest producers and traders of rice, and 9 rice commodities defined on two dimensions, (1) milling degrees (paddy, brown, and milled), and (2) type (long grain, medium & short grain, and fragrant). Given the crucial importance of the Armington elasticities and the lack of good estimates on these parameters, systematic sensitivity analysis is conducted on the best available estimates to generate stochastic distributions of the endogenous variables with respect to these behavioral parameters. Results are decomposed in two dimensions, namely, (1) trade policy groups, and (2) countries, to obtain a better idea of the partial effect of policies and or countries applying them. Achieving food security implies guaranteeing access (physical availability and affordability) to safe and nutritious food to the entire population. Improving food security is the key goal of the World Food Summit of 1996 and the first Millennium Development Goal. Food security assessments have traditionally been done either at the macro level (market stability) or micro level (household access). Although the methodology used in this study constrains us to focus on the macro level, it can contribute to an improved understanding of trade policy for regional and global rice supply and, thus, for improved market stability.rice, trade, policies, food security, Agricultural and Food Policy, Food Security and Poverty, International Relations/Trade, F13, Q17, Q18,

Concentration dependence of the magnetic properties in amorphous Fe-P-B alloys

The concentration dependence of the magnetic properties of amorphous Fe-P-B alloys obtained by splat-cooling is discussed. For a given Fe concentration, the magnetic moment μ averaged over all atoms of material and the Curie temperature Tcboth increase with the substitution of B for P. We observed for the variation of μ and T_c as a function of the B content the same discontinuity as that occurring between the two phases\varepsilonand\varepsilon_{1}of the crystalline Fe_3P_(1-x)B_x compounds. We studied also the variation of μ and T_c when one metalloid (P or B) substitutes for Fe, the other metalloid remaining constant. μ was found to decrease when the P (or B) content is increased, as expected from a rigid band model. For the same concentrations, T_c increases. The different behaviours of μ and T_c are tentatively explained by assuming that the amorphous Fe has two magnetic states (ferro and antiferromagnetic) as already suggested for crystalline Fe in a fcc environment

Sensitive Product Treatment in Agricultural Trade Negotiations

The fact that trade, and especially agricultural trade, remains far from free is puzzling, since the superiority of free trade receives overwhelming support among economists (Gawande and Krishna, 2003; Rodrik, 1994). International trade scholars have devoted significant resources to forecasting the impact of trade policy reforms (for a survey of these studies see Congressional Budget Office, 2005), and their findings are relevant inputs for officials negotiating a trade agreement as well as for politicians in charge of ratifying it. The perceived gains and losses attached to different outcomes have been identified as a significant factor shifting the outcome of a trade agreement negotiation (McMillan, 1990). Less well-known are the factors that would impact the result of a negotiation round involving agriculture. While political scientists have devoted significant resources and developed numerous theories to explain the pattern of bargaining outcomes, the number of empirical assessments remains limited. Among the factors to blame for the low number of empirical evaluations is the scarcity of information regarding negotiation strategies and outcomes (Odell, 2002). The lack of research in this area is puzzling, since countries negotiating regionally and multilaterally have many times struggled to satisfactorily conclude negotiations due to a lack of consensus on agriculture. The potential gains that a reduction in agricultural protection worldwide could generate, and the limited knowledge on the ways negotiation outcomes can be affected, are the main motivations for this study. As stated by Hoekman and Anderson (1999) in reference to reaching an agreement on agriculture in the current WTO Doha Round of negotiations, “The potential gains from liberalization are large”, but “Getting there is another matter” (p. 175). This study focuses on U.S. trade negotiations with Western Hemisphere countries, with particular attention to sensitive agricultural products, about which the most heated bargaining occurs. Arguably as a consequence of the lack of progress at the multilateral arena, the U.S. has embarked on bilateral trade negotiations with several countries, but with a particular emphasis with Western Hemisphere partners. Thus, over the last 10 years it has ratified trade agreements with Chile, Peru, Costa Rica, Dominican Republic, El Salvador, Guatemala, Honduras, and Nicaragua (the last six as part of the DR-CAFTA Agreement), and signed but not yet ratified agreements with Colombia and Panama. Following Trefler (1993), a simultaneous equation model is developed to estimate the correlation between the change in market access (ΔMA) as a result of free trade negotiations, and a number of political economy (PA) and negotiation context (NC) variables suggested by the endogenous tariff theory to be associated with the level of protection granted to a sector. The change in market access in the context of this study is represented by changes in import tariffs and tariff-rate-quotas negotiated as part of the preferential trade agreements (PTAs). While we acknowledge the increasing importance of non-tariff barriers (other than TRQs) as a way to afford protection from imports, PTAs usually do not include specific outcomes on NTBs, and therefore gauging the change in NTBs resulting from a PTA is not possible. Negotiation process variables (NP) primarily bargaining strategies, are seen by many scholars as important intervening variables to explain the pattern of market access achieved in bargaining. By focusing on sensitive agricultural products, this study controls for (NP) variables, since negotiations on sensitive agricultural products between the U.S. and its developing Western Hemisphere partners are assumed to have entailed the use of strong bargaining strategies on both sides. Political economy variables subject to be used are economic size, concentration ratios, import penetration ratios and their change, capital/labor ratios, and sectoral to total labor ratios, all argued to be positively related to the level of protection granted to a sector. Among feasible negotiation context variables are relative power of nations, foreign direct investment in the partner’s economy, unemployment rate, and tax structure (dependence on import policies as a source of revenues). The level of imports (IMP) is modeled to be a function of comparative advantage variables (CA) and the change in market access ΔMA. ΔMA = f(PA, NC NP) IMP = f(CA, ΔMA) The findings from the quantitative assessment are to be complemented with findings from selected case studies, thus expanding our understanding of the factors affecting the outcome of the bargaining activity over sensitive agricultural products in the context of preferential trade agreements.trade negotiations, agricultural trade, free trade agreements, political economy, Agricultural and Food Policy, International Relations/Trade, Political Economy, F59, Q17,

Aperiodic tilings and entropy

In this paper we present a construction of Kari-Culik aperiodic tile set - the smallest known until now. With the help of this construction, we prove that this tileset has positive entropy. We also explain why this result was not expected