Corrections to Finite Size Scaling in Percolation

A 1/L-expansion for percolation problems is proposed, where L is the lattice finite length. The square lattice with 27 different sizes L = 18, 22 ... 1594 is considered. Certain spanning probabilities were determined by Monte Carlo simulations, as continuous functions of the site occupation probability p. We estimate the critical threshold pc by applying the quoted expansion to these data. Also, the universal spanning probability at pc for an annulus with aspect ratio r=1/2 is estimated as C = 0.876657(45)

Optimization of hierarchical structures of information flow

The efficiency of a large hierarchical organisation is simulated on Barabasi-Albert networks, when each needed link leads to a loss of information. The optimum is found at a finite network size, corresponding to about five hierarchical layers, provided a cost for building the network is included in our optimization.Comment: Draft of 6 pages including all figure

Comportamento mandioca de mesa sob adubação, em área dependente de chuva, em Petrolina-PE.

Com objetivo de comparar comportamento das variedades de mandioca de mesa sob adubação, em área dependente de chuva, foi realizado o presente trabalho entre fevereiro de 2010 e novembro de 2011, nas comunidades Pereiros, Caiçara e Mudubim, pertencentes ao município de Petrolina/PE. A adubação constou de 2,0 t ha -1 de calcário dolomítico, em área total, e nos sulcos, 60 kg ha-1 de P22OO55, na forma de superfosfato simples, além da imersão das manivas cortadas numa solução de sulfato de zinco 2%. As variedades utilizadas foram Brasília e Gema de Ovo e o experimento foi realizado em delineamento inteiramente casualizado, com dois tratamentos e 4 repetições. Na ausência da adubação as variedades Brasília e Gema de Ovo não apresentaram diferenças significativas em produção de raízes e da planta inteira, porém na presença da calagem e fósforo a variedade Gema de Ovo supera a variedade Brasília em todos os aspectos de produtividade, seja da parte aérea, da raiz ou da planta inteira, apresentando respectivamente 18,7, 36,7 e 59,2 t.ha-1. A variedade Gema de Ovo destaca-se sobre as demais na produção de parte aérea nas comunidades dos Pereiros (19,85 t.ha-1) e Caiçara (13,87 t.ha-1), indicando ser uma variedade adequada, também para uso da parte aérea fenada na alimentação animal

Optimizing the ensemble for equilibration in broad-histogram Monte Carlo simulations

We present an adaptive algorithm which optimizes the statistical-mechanical ensemble in a generalized broad-histogram Monte Carlo simulation to maximize the system's rate of round trips in total energy. The scaling of the mean round-trip time from the ground state to the maximum entropy state for this local-update method is found to be O([N log N]^2) for both the ferromagnetic and the fully frustrated 2D Ising model with N spins. Our new algorithm thereby substantially outperforms flat-histogram methods such as the Wang-Landau algorithm.Comment: 6 pages, 5 figure

Produção da parte aérea de variedades de mandioca em Petrolina-PE.

Com objetivo de avaliar a produção da parte aérea de variedades de mandioca, em área dependente de chuva, foi realizado o presente trabalho nas comunidades Pereiros, Caiçara e Mudubim, pertencentes ao município de Petrolina/PE no período de fevereiro de 2010 e setembro de 2011. O delineamento experimental usado foi blocos casualizados em esquema fatorial 4x2, compreendendo quatro variedades de mandioca (Engana Ladrão, Brasília, Gema de Ovo e Curvelinha) e dois tipos de adubação (com e sem), com quatro repetições. Os teores de fósforo aumentaram 23,9% na comunidade dos Pereiros, chegando a 87,2% na comunidade Mudubim, o que representa ganho real do elemento no solo com a adubação realizada. A variedade Gema de Ovo destacou-se sobre as demais na produção de parte aérea nas comunidades dos Pereiros (19,85 t.ha-1) e Caiçara (13,87 t.ha-1), indicando ser uma variedade com potencial para uso da parte aérea na alimentação animal

Turbulence and Chaos in Anti-de-Sitter Gravity

Due to the AdS/CFT correspondence the question of instability of Anti-de-Sitter spacetimes sits in the intersection of mathematical and numerical relativity, string theory, field theory and condensed matter physics. In this essay we revisit that important question emphasizing the power of spectral methods and highlighting the effectiveness of standard techniques for studying nonlinear dynamical systems. In particular we display explicitly how the problem can be modeled as a system on nonlinearly coupled harmonic oscillators. We highlight some of the many open questions that stem from this result and point out that a full understanding will necessarily required the interdisciplinary cooperation of various communities.Comment: 6 pages, 12 figures. Essay awarded honorable mention in the Gravity Research Foundation essay competition 201

Does Good Mutation Help You Live Longer?

We study the dynamics of an age-structured population in which the life expectancy of an offspring may be mutated with respect to that of its parent. When advantageous mutation is favored, the average fitness of the population grows linearly with time $t$, while in the opposite case the average fitness is constant. For no mutational bias, the average fitness grows as t^{2/3}. The average age of the population remains finite in all cases and paradoxically is a decreasing function of the overall population fitness.Comment: 4 pages, 2 figures, RevTeX revised version, to appear in Phys. Rev. Let

Speeding Up Computer Simulations: The Transition Observable Method

A method is presented which allows for a tremendous speed-up of computer simulations of statistical systems by orders of magnitude. This speed-up is achieved by means of a new observable, while the algorithm of the simulation remains unchanged.Comment: 20 pages, 6 figures Submitted to Phys.Rev.E (August 1999) Replacement due to some minor change

Projected single-spin flip dynamics in the Ising Model

We study transition matrices for projected dynamics in the energy-magnetization space, magnetization space and energy space. Several single spin flip dynamics are considered such as the Glauber and Metropolis canonical ensemble dynamics and the Metropolis dynamics for three multicanonical ensembles: the flat energy-magnetization histogram, the flat energy histogram and the flat magnetization histogram. From the numerical diagonalization of the matrices for the projected dynamics we obtain the sub-dominant eigenvalue and the largest relaxation times for systems of varying size. Although, the projected dynamics is an approximation to the full state space dynamics comparison with some available results, obtained by other authors, shows that projection in the magnetization space is a reasonably accurate method to study the scaling of relaxation times with system size. The transition matrices for arbitrary single-spin flip dynamics are obtained from a single Monte-Carlo estimate of the infinite temperature transition-matrix, for each system size, which makes the method an efficient tool to evaluate the relative performance of any arbitrary local spin-flip dynamics. We also present new results for appropriately defined average tunnelling times of magnetization and compute their finite-size scaling exponents that we compare with results of energy tunnelling exponents available for the flat energy histogram multicanonical ensemble.Comment: 23 pages and 6 figure