A subset solution to the sign problem in random matrix simulations

We present a solution to the sign problem in dynamical random matrix simulations of a two-matrix model at nonzero chemical potential. The sign problem, caused by the complex fermion determinants, is solved by gathering the matrices into subsets, whose sums of determinants are real and positive even though their cardinality only grows linearly with the matrix size. A detailed proof of this positivity theorem is given for an arbitrary number of fermion flavors. We performed importance sampling Monte Carlo simulations to compute the chiral condensate and the quark number density for varying chemical potential and volume. The statistical errors on the results only show a mild dependence on the matrix size and chemical potential, which confirms the absence of sign problem in the subset method. This strongly contrasts with the exponential growth of the statistical error in standard reweighting methods, which was also analyzed quantitatively using the subset method. Finally, we show how the method elegantly resolves the Silver Blaze puzzle in the microscopic limit of the matrix model, where it is equivalent to QCD.Comment: 18 pages, 11 figures, as published in Phys. Rev. D; added references; in Sec. VB: added discussion of model satisfying the Silver Blaze for all N (proof in Appendix E

Interactie tussen menselijke zaadcellen en hamstereicellen

Het in dit proefschrift beschreven onderzoek is er in de eerste plaats op gericht de interactie tussen eicel en zaadcel in laboratoriumomstandigheden (in vitro) te kwantificeren. Een toepassing van een dergelijke diagnostische test wordt belemmerd door een tekort aan menselijke eicellen. Om deze beperkende factor te vermijden, werd niet de menselijke eicel, maar de hamstereicel gebruikt. De interactie tussen speciaal voor dit doel geisoleerde en gemanipuleerde hamstereicellen en humane zaadcellen wordt in paragraaf 1.7 en in hoofdstuk 2 besproken. In de tweede plaats is dit onderzoek gedaan om relaties tussen het sperma-onderzoek en sperma-onderzoek voor concentratie en de de in vitro bevruchting te bestuderen. Omdat een deel berust op subjectieve criteria, werden de beweeglijkheid door middel van een semi-automatische methode objectief bepaald. De beweeglijkheid werd fotografisch vastgelegd (met behulp van meervoudige belichtingsfotografie) en de afbeeldingen werden door middel van computertechnieken verwerkt (1.8 en hoofdstuk 3)

Eficácia da hidroterapia na dor e capacidade funcional em pacientes com espondilite anquilosante: uma revisão bibliográfica

Projeto de Graduação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Licenciado em FisioterapiaIntrodução: Espondilite anquilosante (EA) é uma doença reumática crónica sistémica, sendo um protótipo de espondiloartropatias seronegativas caracterizada por inflamação, afetando predominantemente a coluna vertebral, os métodos de tratamento recomendados são fisioterapia supervisionada recorrendo-se ao tratamento convencional ou à prática de hidroterapia. Objetivo: Determinar os efeitos da hidroterapia na dor e capacidade funcional, nos pacientes com espondilite anquilosante (EA). Metodologia: Pesquisa computorizada nas bases de dados PEDro, Science Direct, EBSCO e PubMed/Medline, para identificar os estudos randomizados controlados que avaliaram os efeitos da hidroterapia na EA. Resultados: Nesta revisão foram incluídos 5 estudos envolvendo 251 indivíduos, com classificação 5,6 metodológica na escala de PEDro. Conclusões: A hidroterapia parece influenciar positivamente no tratamento de pacientes com espondilite anquilosante melhorando parâmetros como a dor e a capacidade funcional. No entanto estes efeitos parecem perder-se com o tempo, e por isso as diferenças entre a hidroterapia e outro tipo de tratamentos parecem esbater-se com o tempo.Introduction: Ankylosing spondylitis (AS) is a chronic systemic rheumatic disease, being a prototype of seronegative spondyloarthropathies characterized by inflammation, affecting predominantly the vertebral column, the recommended treatment methods are supervised physiotherapy using the conventional exercices or the practice of hydrotherapy. Objective: To determine the effects of hydrotherapy on pain and functional capacity in patients with ankylosing spondylitis (AS). Methods: Computerized research in the databases PEDro, Science Direct, EBSCO and PubMed / Medline, to identify randomized controlled trials that evaluated the effects of hydrotherapy in AS. Results This review included 5 studies involving 251 individuals, with a methodological classification of 5.6 on the PEDro scale. Conclusions: Hydrotherapy has shown its effectiveness on pain, stiffness and mobility of the spine, which have a direct impact on patients' functional capacity.N/

An Application of CLP: Checking the Correctness of Theorems in Geometry

International audienceConstraint Logic Programming can be advantageously used to deal with quadratic constraints stemming from the verification of planar geometry theorems. A hybrid symbolic--numeric representation involving radicals and multiple precision rationals is used to denote the results of quadratic equations. A unification--like algorithm tests for the equality of two expressions using that representation. The proposed approach also utilizes geometric transformations to reduce the number of quadratic equations defining geometric constructions involving circles and straight lines. A large number (512) of geometry theorems has been verified using the proposed approach. Those theorems had been proven correct using a significantly more complex (exponential) approach in a treatise authored by Chou in 1988. Even though the proposed approach is based on verification -rather than strict correctness utilized by Chou- the efficiency attained is polynomial thus making the approach useful in classroom situations where a construction attempted by student has to be quickly validated or refuted

An algorithm for linear constraint solving: its incorporation in a prolog meta-interpreter for CLP

AbstractThe paper presents an incremental and efficient algorithm for testing the satisfiability of systems of linear equalities, inequalities (strict or unrestricted), and disequalities. In addition, it describes the incorporation of that algorithm into a metalevel interpreter capable of processing both tree constraints and the mentioned linear constraints in the domain of rationals. Important characteristics of the described algorithm are (1) detection of fixed variables within the context of Gaussian elimination, including the simplex method. (2) efficient dereferencing by considering subclasses of solved forms, and (3) efficient testing of inconsistencies between equality and disequality subclasses. The metalevel interpreter is written in Prolog. Examples of its usage are provided. Finally, the paper outlines how the approach may be generalized to consider the efficient and incremental testing of constraint satisfiability in various domains

A comparative study between kriging and adaptive sparse tensor-product methods for multi-dimensional approximation problems in aerodynamics design

International audienceThe performances of two multivariate interpolation procedures are compared using functions that are either synthetic or coming from a shape optimization problem in aerodynamics. The aim is to evaluate the efficiency of adaptive sparse interpolation algorithms [2] and compare them with the kriging approach developed for the design and analysis of computer experiment (DACE) [21]. The accuracy and computational time of the two methods are examined as the number N of samples used in the interpolation increases. It appears in our test cases that both methods perform equivalently, in terms of precision. However, as the dimension d increases, the computational time involved in the enrichement of the kriging sample becomes intractable for large values of N. This problem is circumvented in the case of the sparse interpolation procedure for which the computational time scales linearly with N and d.Nous comparons les performances de deux méthodes d'interpolation en grande dimension, aussi bien sur des fonctions synthétiques que pour celles issues d'un problème d'optimisation de forme en aérodynamique. L'objectif est d'évaluer l'efficacité d'algorithmes adaptatifs d'interpolation parcimonieuse [2], et de les comparer avec l'approche du kriging développée dans le cadre design and analysis of computer experiment (DACE) [21]. La précision et le temps de calcul des deux méthodes sont étudiés lorsque le nombre N d'échantillons utilisés pour l'interpolation augmente. Les cas tests montrent que les deux méthodes sont comparables en terme de précision. Cependant, lorsque la dimension d augmente, le temps de calcul associé a l'enrichissement de l'échantillon pour le kriging devient prohibitif pour les grandes valeurs de N. Ce problème est contourné dans le cas de l'interpolation parcimonieuse pour lequel le temps de calcul est linéaire en N et d

Regularity and identification of Generalized Multifractional Gaussian Processes

International audienceIn this article a class of multifractal processes is introduced, called Generalized Multifractional Gaussian Process (GMGP). For such multifractional models, the Hurst exponent on the celebrated Fractional Brownian Motion is replaced by a function, called the multifractional function, which may be irregular. The main aim of thi paper is to show how to identify irregular multifractional functions in the setting of GMGP. Examples of discontinuous multiractional functions are also given

Women asylum seekers and refugees: Opportunities, constraints and the role of agency

This article is based on the findings of research undertaken towards a doctoral thesis funded by the University of Leeds. The research focuses upon the actions and experiences of women asylum seekers and refugees living inWest Yorkshire. While acknowledging that the context in which women find themselves can present a number of barriers, this paper looks at their actions and practices at the individual and collective levels. It illustrates that some women are able to draw on the resources available, and are engaged in activities that not only assist their own settlement in the host society but also assist the development of support structures for future arrivals of asylum seekers and refugees