Geometric properties of crumpled wires and the condensed non-solid packing state of very long molecular chains
Journal of the Brazilian Chemical Society
Geometric aspects associated with the hierarchical and heterogeneous packing of crumpled wires ar... more Geometric aspects associated with the hierarchical and heterogeneous packing of crumpled wires are reviewed. The recently discovered phenomenon of condensation of elastic energy of curvature in these structures is discussed, and new results are presented with emphasis on robust scaling laws. It is examined the possible relevance of these laws in the conformational properties of long molecular chains densely packaged in a non-solid state, as e.g. in the packing of DNA strands in chromosomes, or in virus capsids. In particular, mean field arguments are used to estimate the dependence of the number of loops in the dense non-solid packed three-dimensional configurations of a very long polymer strand as a function of the number of monomers or the chain length.
On the game of life: population and its diversity
Physica A: Statistical Mechanics and its Applications, 1993
ABSTRACT One of the most important features of biological life in all levels is its astounding di... more ABSTRACT One of the most important features of biological life in all levels is its astounding diversity. In this work we study the well-known game ``Life'' due to Conway analysing the statistics of cluster population, N(t), and cluster diversity, D(t). We have performed simulations on ``Life'' for dimensions d = 1 and 2 starting with an uncorrelated distribution of live and dead sites at t = 0. For d = 2 we study the effect of different neighbourhood relations in identifying and counting clusters. An interesting scaling relation connecting the maxima of N(t) and D(t) is found.
In a 4D four-fermion model we study the dynamical restoration of Lorentz and CPT symmetries at fi... more In a 4D four-fermion model we study the dynamical restoration of Lorentz and CPT symmetries at finite temperature. We evaluate the gap equation both at zero and at finite temperature and observe that, depending on the parameters of the theory, there is a critical temperature at which the Lorentz and CPT symmetries are restored.
We use a model whose rules were inspired by population genetics, the random capability growth mod... more We use a model whose rules were inspired by population genetics, the random capability growth model, to describe the statistical details observed in experiments of fragmentation of brittle platelike objects, and in particular the existence of (i) composite scaling laws, (ii) small critical exponents τ associated with the power-law fragment-size distribution, and (iii) the typical pattern of cracks.
Physical review D: Particles and fields, Jan 15, 1988
Mass perturbation in the Thirring model
Physical review D: Particles and fields, Jan 15, 1986
ABSTRACT Using the equivalence with a derivative-coupling model, mass perturbation in the Thirrin... more ABSTRACT Using the equivalence with a derivative-coupling model, mass perturbation in the Thirring model is investigated. We show that, for 4π(2- √3 )<β2<8π all ultraviolet divergences cancel. Finite composite operators are constructed in this range. Ward identities and equations of motion are discussed.
Dynamical mass generation in the Gross-Neveu model at finite temperature and density
Physical review D: Particles and fields, Jan 15, 1989
Equivalence between the Thirring model and a derivative-coupling model
Physical review D: Particles and fields, Jan 15, 1986
We investigate the occurrence of ambiguities for Lorentz-violating gravitational Chern-Simons ter... more We investigate the occurrence of ambiguities for Lorentz-violating gravitational Chern-Simons term. It turns out that this term is accompanied by a coefficient depending on an undetermined parameter, due to an arbitrariness in the choice of the conserved current. * Electronic address: mgomes,ajsilva,tmariz,[email protected]
Extinction debt and the role of static and dynamical fragmentation on biodiversity
Ecological Complexity, 2015
ABSTRACT The mass-extinction events caused by human-driven habitat loss is a current concern in c... more ABSTRACT The mass-extinction events caused by human-driven habitat loss is a current concern in conservation science. However, the observed number of extinctions is consider- ably smaller than predicted. The overestimation of extinction rates comes from the time-delay which depends on the species sensitivity to habitat changes. The standard method of predicting the effect of habitat loss on biodiversity is to use the species-area relationship and progressively following it backwards to smaller areas. The difference between the actual number of species and the one provided by the backwards species-area relationship is dubbed extinction debt. Previous studies in general adopt a static view for the spatial distribution of species. Nonetheless, a precise understanding of the problem urges us to adopt a dynamic framework to this issue since the time between disturbances of the landscape plays an active role in influencing the strength of the extinction debt. In this context, here we address two distinct approaches for this question: a static and a dynamic view of fragmentation. In the former we quantify the extinction debt in a quenched spatial distribution of species, whereas in the latter the community is let to evolve between disturbance events of the landscape. Here we show that the size of the extinction debt depends on the pattern of the fragmentation. It is found that random distributions of destroyed habitats provide larger extinction debts than those obtained for contiguous areas of fragmentation. Furthermore, in the dynamic approach it is observed that dispersal can lead to unexpected outcomes such as lower biodiversity levels than ones inferred from the backwards species-area relationship.
The model of the position-dependent noncommutativety in quantum mechanics is proposed. We start w... more The model of the position-dependent noncommutativety in quantum mechanics is proposed. We start with a given commutation relations between the operators of coordinates x i ,x j = ω ij (x), and construct the complete algebra of commutation relations, including the operators of momenta. The constructed algebra is a deformation of a standard Heisenberg algebra and obey the Jacobi identity. The key point of our construction is a proposed first-order Lagrangian, which after quantization reproduces the desired commutation relations. Also we study the possibility to localize the
Using the superfield formalism, we study the dynamical breaking of gauge symmetry and superconfor... more Using the superfield formalism, we study the dynamical breaking of gauge symmetry and superconformal invariance in the N = 1 three-dimensional supersymmetric Chern-Simons model, coupled to a complex scalar superfield with a quartic self-coupling. This is an analogue of the conformally invariant Coleman-Weinberg model in four spacetime dimensions. We show that a mass for the gauge and matter superfields are dynamically generated after twoloop corrections to the effective superpotential. We also discuss the N = 2 extension of our work, showing that the Coleman-Weinberg mechanism in such model is not feasible, because it is incompatible with perturbation theory.
Recently, it has been proposed a spacetime noncommutativity that involves spin degrees of freedom... more Recently, it has been proposed a spacetime noncommutativity that involves spin degrees of freedom, here called "spin noncommutativity". One of the motivations for such a construction is that it preserves Lorentz invariance, which is deformed or simply broken in other approaches to spacetime noncommutativity. In this work, we gain further insight in the physical aspects of the spin noncommutativity. The noncommutative Dirac equation is derived from an action principle, and it is found to lead to the conservation of a modified current, which involves the background electromagnetic field. Finally, we study the Landau problem in the presence of spin noncommutativity. For this scenario of a constant magnetic field, we are able to derive a simple Hermitean non-commutative correction to the Hamiltonian operator, and show that the degeneracy of the excited states is lifted by the noncommutativity at the second order or perturbation theory.
Within the superfield formalism, we study the ultraviolet properties of the threedimensional supe... more Within the superfield formalism, we study the ultraviolet properties of the threedimensional supersymmetric quantum electrodynamics. The theory is shown to be finite at all loops orders in a particular gauge.
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Papers by Marcelo Gomes