Statistical Mechanics Characterization of Neuronal Mosaics

The spatial distribution of neuronal cells is an important requirement for achieving proper neuronal function in several parts of the nervous system of most animals. For instance, specific distribution of photoreceptors and related neuronal cells, particularly the ganglion cells, in mammal's retina is required in order to properly sample the projected scene. This work presents how two concepts from the areas of statistical mechanics and complex systems, namely the \emph{lacunarity} and the \emph{multiscale entropy} (i.e. the entropy calculated over progressively diffused representations of the cell mosaic), have allowed effective characterization of the spatial distribution of retinal cells.Comment: 3 pages, 1 figure, The following article has been submitted to Applied Physics Letters. If it is published, it will be found online at http://apl.aip.org

Effects of Random Biquadratic Couplings in a Spin-1 Spin-Glass Model

A spin-1 model, appropriated to study the competition between bilinear (J_{ij}S_{i}S_{j}) and biquadratic (K_{ij}S_{i}^{2}S_{j}^{2}) random interactions, both of them with zero mean, is investigated. The interactions are infinite-ranged and the replica method is employed. Within the replica-symmetric assumption, the system presents two phases, namely, paramagnetic and spin-glass, separated by a continuous transition line. The stability analysis of the replica-symmetric solution yields, besides the usual instability associated with the spin-glass ordering, a new phase due to the random biquadratic couplings between the spins.Comment: 16 pages plus 2 ps figure

Metastable Markov chains: from the convergence of the trace to the convergence of the finite-dimensional distributions

We consider continuous-time Markov chains which display a family of wells at the same depth. We provide sufficient conditions which entail the convergence of the finite-dimensional distributions of the order parameter to the ones of a finite state Markov chain. We also show that the state of the process can be represented as a time-dependent convex combination of metastable states, each of which is supported on one well

Effective restoration of chiral and axial symmetries at finite temperature and density

The effective restoration of chiral and axial symmetries is investigated within the framework of the SU(3) Nambu-Jona-Lasinio model. The topological susceptibility, modeled from lattice data at finite temperature, is used to extract the temperature dependence of the coupling strength of the anomaly. The study of the scalar and pseudoscalar mixing angles is performed in order to discuss the evolution of the flavor combinations of $q \bar q$ pairs and its consequences for the degeneracy of chiral partners. A similar study at zero temperature and finite density is also realized.Comment: 5 pages, 1 figure. Talk given at Strange Quark Matter 2004, Cape Town, South Africa, 15-20 September, 200

Effects of levels of potassium and nitrogen on yields and post-harvest conservation of onions in winter.

Os elementos presentes, em maior percentagem, na matéria seca da cebola são potássio e nitrogênio. Com o objetivo de avaliar a produtividade e conservação pós-colheita do cultivar de cebola Vale Ouro IPA-11, em função de doses de nitrogênio e potássio, foi conduzido experimento, de junho a dezembro de 2009, em Petrolina-PE. O delineamento experimental foi o de blocos ao acaso, no esquema fatorial 4x3, compreendendo quatro doses de nitrogênio (0; 60; 120 e 180 kg ha-1) e três doses de potássio (0; 90 e 180 kg ha-1), com três repetições. A maior produtividade comercial de bulbos foi estimada com a dose de 172,6 kg ha-1 de N. A menor produção de refugos foi obtida com a dose de 147,0 kg ha-1 de N. Menor percentual de bulbos menores (classe 2) foram obtidos com o aumento das doses de N e K, ocorrendo, para a dose de 90 kg ha-1 de K2O, efeito quadrático, com ponto de mínima produção com 127,6 kg ha-1 de N (20,3%). Com relação a bulbos de maior calibre (classe 4), foram obtidos efeitos lineares, tanto na ausência quanto com a dose de 90 kg ha-1 de K2O, com o incremento das doses de N. Quando se aplicou a dose maior, de 180 kg ha-1 de K2O, estimou-se a dose de 92,8 kg ha-1 de N como a que promoveria a maior produção de bulbos dessa classe (35,4%), verificando-se 5,3%, com a ausência da adubação potássica