The economics of garbage collection

This paper argues that economic theory can improve our understanding of memory management. We introduce the allocation curve, as an analogue of the demand curve from microeconomics. An allocation curve for a program characterises how the amount of garbage collection activity required during its execution varies in relation to the heap size associated with that program. The standard treatment of microeconomic demand curves (shifts and elasticity) can be applied directly and intuitively to our new allocation curves. As an application of this new theory, we show how allocation elasticity can be used to control the heap growth rate for variable sized heaps in Jikes RVM

Cross-entropy optimisation of importance sampling parameters for statistical model checking

Statistical model checking avoids the exponential growth of states associated with probabilistic model checking by estimating properties from multiple executions of a system and by giving results within confidence bounds. Rare properties are often very important but pose a particular challenge for simulation-based approaches, hence a key objective under these circumstances is to reduce the number and length of simulations necessary to produce a given level of confidence. Importance sampling is a well-established technique that achieves this, however to maintain the advantages of statistical model checking it is necessary to find good importance sampling distributions without considering the entire state space. Motivated by the above, we present a simple algorithm that uses the notion of cross-entropy to find the optimal parameters for an importance sampling distribution. In contrast to previous work, our algorithm uses a low dimensional vector of parameters to define this distribution and thus avoids the often intractable explicit representation of a transition matrix. We show that our parametrisation leads to a unique optimum and can produce many orders of magnitude improvement in simulation efficiency. We demonstrate the efficacy of our methodology by applying it to models from reliability engineering and biochemistry.Comment: 16 pages, 8 figures, LNCS styl

Unintended Consequences of Cigarette Prohibition, Regulation, and Taxation

Abstract Laws that prohibit, regulate, or tax cigarettes can generate illicit markets for tobacco products. Illicit markets both reduce the efficacy of policies intended to improve public health and create harms of their own. Enforcement can reduce evasion but creates additional harms, including incarceration and violence. There is strong evidence that more enforcement in illicit drug markets can spur violence. The presence of licit substitutes, such as electronic cigarettes, has the potential to greatly reduce the size of illicit markets. We present a model demonstrating why enforcement can increase violence, show that states with higher tobacco taxes have larger illicit markets, and apply the findings to discussion of public policy toward a potential ban on menthol cigarettes. The social calculus involved in determining public policy toward tobacco cigarettes should include the harms from both consumption and control. We conclude by highlighting areas where more research is needed for effective policymaking

A new proposal for the design of confined masonry buildings

Confined masonry has been efficiently used for buildings in Latin-America, Northern-Africa and Asia, even in seismic areas. However, despite all the research on the seismic behaviour of this structural typology, mainly in Latin-America, the lack of clear criteria for confined masonry design limits its application in Europe. In this work, a semi-empirical strength criterion for confined masonry, based on the diagonal shear failure of confined walls, is proposed. For this purpose, data mining is applied to a database of confined walls under cyclic loading tests, in order to clarify the variables that influence the shear strength. This study showed that the shear strength can be acceptably predicted by a multiple regression of the normal stress, diagonal shear strength, slenderness and masonry cross-section ratio of the walls. The relevance of longitudinal reinforcement of the confinement columns is low, with a significant contribution only in the post-cracking stage

Monte Carlo simulator project for neutron transport with continuous energy : shielding, criticality and spectral angular neutron flux analysis

This thesis reports on the project developed during the author’s doctorate. This encompasses the development of an open license Monte Carlo simulation software for neutron transport in reactor core materials. This tool consists of a C++ program following recent paradigms of advanced power computing, and takes into account the continuous physical dimensions (position, direction of motion and energy) of the neutron transport phase space. Two scattering models are implemented and discussed. These are based on the target at rest hypothesis and the free gas model, and the difference between models is shown. Also, the simulated spectral angular neutron flux is tested as a solution of the seven-dimensional Boltzmann transport equation. In this work a shielding scenario, a criticality benchmark from the International Handbook of Evaluated Criticality Safety Benchmark Experiments book, and two simulations in a multiplicative medium, each with a different scattering model, were simulated in order to portray the software capabilities. The simulator shows itself versatile in the different kind of results that can be obtained, e.g. neutron flux, neutron density, reaction rates, criticality, among others. Lastly the spectral neutron fluxes are parametrized (in the range of [10−14; 101]MeV ) and these functions are verified as possible solutions of the Boltzmann transport equation.Esta tese relata o projeto desenvolvido durante o doutorado do autor. Isso engloba o desenvolvimento de um software de simulação de Monte Carlo de licença aberta para o transporte de nêutrons em materiais de núcleo de reatores. Esta ferramenta consiste em um programa C ++ seguindo os paradigmas recentes em computação de alto desempenho, e leva em consideração as dimensões físicas contínuas (posição, direção de movimento e energia) do espaço de fase do transporte de nêutrons. Dois modelos de espalhamento são implementados e discutidos. Estes são baseados na hipótese de alvo em repouso e no modelo de gás livre, e a diferença entre os modelos é apresentada. Além disso, o fluxo de nêutrons angular espectral simulado é testado como uma solução da equação de transporte de Boltzmann nas suas sete dimensões. Neste trabalho, um cenário de blindagem, um benchmark de criticidade do livro International Handbook of Evaluated Criticality Safety Benchmark Experiments e duas simulações em meio multiplicativo, cada uma com um modelo de espalhamento diferente, foram simulados para apresentar as capacidades do software. O simulador mostra-se versátil nos diferentes tipos de resultados que podem ser obtidos, e.g. fluxo de nêutrons, densidade de nêutrons, taxas de reação, criticidade, entre outros. Por último, os fluxos espectrais de nêutrons são parametrizados (na faixa de [10−14; 101]MeV ) e essas funções são verificadas como possíveis soluções da equação de transporte de Boltzmann

A Simulation for Determining the Relation between Position of the Center Mass and the Impact of the Accident's Fatality on the Car Driver.

The most dangerous type of collision between two cars is a head on collisions, which can be fatal to either or both drivers. The data collected on that suggest the risk of fatality to driver is less if that driver has a passenger or passengers in that car. The main objective of this study is to show with a help of simulation the relation between position of the center mass and the impact of the accident's fatality on the drivers. Moreover, this report starts with the statement of the problem and the theoretical knowledge of the project. Then on the way the software used for simulation is included with the results. As a result many figures can be seen and the various relations between accident concepts can be found. Later the calculation part justifies the obtained results as a proof. Following the discussion part explains about the problem faced during preparation of this project. Through discussions the report moves to conclusion and recommendations