Heavy Quark Thermalization in Classical Lattice Gauge Theory: Lessons for Strongly-Coupled QCD

Thermalization of a heavy quark near rest is controlled by the correlator of two electric fields along a temporal Wilson line. We address this correlator within real-time, classical lattice Yang-Mills theory, and elaborate on the analogies that exist with the dynamics of hot QCD. In the weak-coupling limit, it can be shown analytically that the dynamics on the two sides are closely related to each other. For intermediate couplings, we carry out non-perturbative simulations within the classical theory, showing that the leading term in the weak-coupling expansion significantly underestimates the heavy quark thermalization rate. Our analytic and numerical results also yield a general understanding concerning the overall shape of the spectral function corresponding to the electric field correlator, which may be helpful in subsequent efforts to reconstruct it from Euclidean lattice Monte Carlo simulations.Comment: 22 pages. v2: a reference and clarifications added; published versio

On the Hierarchy of Block Deterministic Languages

A regular language is $k$-lookahead deterministic (resp. $k$-block deterministic) if it is specified by a $k$-lookahead deterministic (resp. $k$-block deterministic) regular expression. These two subclasses of regular languages have been respectively introduced by Han and Wood ($k$-lookahead determinism) and by Giammarresi et al. ($k$-block determinism) as a possible extension of one-unambiguous languages defined and characterized by Br\"uggemann-Klein and Wood. In this paper, we study the hierarchy and the inclusion links of these families. We first show that each $k$-block deterministic language is the alphabetic image of some one-unambiguous language. Moreover, we show that the conversion from a minimal DFA of a $k$-block deterministic regular language to a $k$-block deterministic automaton not only requires state elimination, and that the proof given by Han and Wood of a proper hierarchy in $k$-block deterministic languages based on this result is erroneous. Despite these results, we show by giving a parameterized family that there is a proper hierarchy in $k$-block deterministic regular languages. We also prove that there is a proper hierarchy in $k$-lookahead deterministic regular languages by studying particular properties of unary regular expressions. Finally, using our valid results, we confirm that the family of $k$-block deterministic regular languages is strictly included into the one of $k$-lookahead deterministic regular languages by showing that any $k$-block deterministic unary language is one-unambiguous

Data analysis strategies for the detection of gravitational waves in non-Gaussian noise

In order to analyze data produced by the kilometer-scale gravitational wave detectors that will begin operation early next century, one needs to develop robust statistical tools capable of extracting weak signals from the detector noise. This noise will likely have non-stationary and non-Gaussian components. To facilitate the construction of robust detection techniques, I present a simple two-component noise model that consists of a background of Gaussian noise as well as stochastic noise bursts. The optimal detection statistic obtained for such a noise model incorporates a natural veto which suppresses spurious events that would be caused by the noise bursts. When two detectors are present, I show that the optimal statistic for the non-Gaussian noise model can be approximated by a simple coincidence detection strategy. For simulated detector noise containing noise bursts, I compare the operating characteristics of (i) a locally optimal detection statistic (which has nearly-optimal behavior for small signal amplitudes) for the non-Gaussian noise model, (ii) a standard coincidence-style detection strategy, and (iii) the optimal statistic for Gaussian noise.Comment: 5 pages RevTeX, 4 figure

Iron Displacements and Magnetoelastic Coupling in the Spin-Ladder Compound BaFe2Se3

We report long-range ordered antiferromagnetism concomitant with local iron displacements in the spin-ladder compound BaFe$_2$Se$_3$. Short-range magnetic correlations, present at room temperature, develop into long-range antiferromagnetic order below T$_N$ = 256 K, with no superconductivity down to 1.8 K. Built of ferromagnetic Fe$_4$ plaquettes, the magnetic ground state correlates with local displacements of the Fe atoms. These iron displacements imply significant magnetoelastic coupling in FeX$_4$-based materials, an ingredient hypothesized to be important in the emergence of superconductivity. This result also suggests that knowledge of these local displacements is essential for properly understanding the electronic structure of these systems. As with the copper oxide superconductors two decades ago, our results highlight the importance of reduced dimensionality spin ladder compounds in the study of the coupling of spin, charge, and atom positions in superconducting materials

Qualidade e diferenciação em torno do café: modelos em concorrência.

O objetivo deste trabalho consiste em discutir dois enfoques divergentes em torno da cafeicultura com vistas a fornecer elementos de análise para uma pesquisa acerca das dinâmicas territoriais, agricultura e sociedade. Cada vez mais, oportunidades se desenham para uma revalorização da cafeicultura, particularmente em sintonia com as idéias de fortalecer a agricultura familiar, de promover as dinâmicas territoriais e de preservar o meio ambiente. Porém, estas oportunidades concorrem com um modelo dominante de conceber os sistemas agro-alimentares no Brasil, no qual a agricultura consiste apenas em suporte para a produção de commodities indiferenciadas, baratas e abundantes

Kinetics pathway of precipitation in model Co-Al-W superalloy

International audienc

A First Step Towards Automatically Building Network Representations

To fully harness Grids, users or middlewares must have some knowledge on the topology of the platform interconnection network. As such knowledge is usually not available, one must uses tools which automatically build a topological network model through some measurements. In this article, we define a methodology to assess the quality of these network model building tools, and we apply this methodology to representatives of the main classes of model builders and to two new algorithms. We show that none of the main existing techniques build models that enable to accurately predict the running time of simple application kernels for actual platforms. However some of the new algorithms we propose give excellent results in a wide range of situations

Identificação de dinâmicas sociais e econômicas na construção territorial de cafés de qualidade diferenciada no Sul de Minas.

O Sul de Minas é a maior região produtora de café do país e o espaço geográfico de Machado, Poço Fundo e Campestre, aí localizado, compreende um dos mais destacados conjuntos de municípios sob o ponto de vista do cultivo. A base técnica e social sob a qual a cultura do café destas três áreas se desenvolveu historicamente é caracterizada por numerosas e pequenas explorações familiares. O café é de toda evidência responsável por uma identidade territorial aí existente, o que torna pertinente uma pesquisa nestes municípios do Sul de Minas Gerais, com ênfase nos conhecimentos, práticas e representações utilizadas na produção, usos, difusão e conservação de recursos do território. O objetivo da pesquisa é buscar respostas aos problemas do desenvolvimento territorial sustentável e, para tal, destacou inicialmente o município de Poço Fundo, dentre os três mencionados. A partir da conclusão do mapeamento de projetos coletivos, atores sociais e programas públicos, esta fase da pesquisa, aqui em destaque, buscou identificar as dinâmicas sociais e econômicas capazes de caracterizar o processo de construção de território junto a gestores públicos e atores representativos dos projetos coletivos, por intermédio do uso de entrevistas apoiadas em um roteiro único semi-estruturado