Characteristic Surface Data for the Eikonal Equation

A method of solving the eikonal equation, in either flat or curved space-times, with arbitrary Cauchy data, is extended to the case of data given on a characteristic surface. We find a beautiful relationship between the Cauchy and characteristic data for the same solution, namely they are related by a Legendre transformation. From the resulting solutions, we study and describe their associated wave-front singularities.Comment: 16 pages, no figures, Scientific Work-Place 2.5, tex, Corrected typo

Stochastic resonance in a suspension of magnetic dipoles under shear flow

We show that a magnetic dipole in a shear flow under the action of an oscillating magnetic field displays stochastic resonance in the linear response regime. To this end, we compute the classical quantifiers of stochastic resonance, i.e. the signal to noise ratio, the escape time distribution, and the mean first passage time. We also discuss limitations and role of the linear response theory in its applications to the theory of stochastic resonance.Comment: 17 pages, 5 figures, approved for publication in PR

Stock assessment of commercially important fishes in Naujan Lake

The study aimed to assess the capture fisheries of Naujan Lake with emphasis on commercially important fish species and to determine the extent of their exploitation. Four major fish landing centers in the municipalities of Socorro, Pola, Victoria and Naujan were surveyed from May 1995 to December 1996. Eight types of fishing gear had been recorded. The most commonly used was gill net or 'pante', followed by fish pot 'bubo', fish corral 'baklad', spear 'salapang', spear gun 'pana', fish trap 'patanga', encircling net 'takilis' and long line 'kitay'. Tilapia comprised 61% of the total fish production of the lake, followed by therapon (16%), goby (4%) and mudfish (2%). The other species caught were 'pla salid', catfish, mullet, carp, milkfish and shrimp, which contributed 17% to the total production. Migratory fishes like the mullet and milkfish, on the other hand, showed a declining trend in production

Periodic Modulation Induced Increase of Reaction Rates in Autocatalytic Systems

We propose a new mechanism to increase the reactions ratesin multistable autocatalytic systems. The mechanism is based upon the possibility for the enhancement of the response of the system due to the cooperative behavior between the noise and an external periodic modulation. In order to illustrate this feature we compute the reaction velocities for the particular case of the Sel'Kov model, showing that they increase significantly when the periodic modulation is introduced. This behavior originates from the existence of a minimum in the mean first passage time, one of the signatures of stochastic resonance.Comment: Submitted to J. Chem. Phy

Temporal Correlations and Persistence in the Kinetic Ising Model: the Role of Temperature

We study the statistical properties of the sum $S_t=\int_{0}^{t}dt' \sigma_{t'}$, that is the difference of time spent positive or negative by the spin $\sigma_{t}$, located at a given site of a $D$-dimensional Ising model evolving under Glauber dynamics from a random initial configuration. We investigate the distribution of $S_{t}$ and the first-passage statistics (persistence) of this quantity. We discuss successively the three regimes of high temperature ($T>T_{c}$), criticality ($T=T_c$), and low temperature ($T<T_{c}$). We discuss in particular the question of the temperature dependence of the persistence exponent $\theta$, as well as that of the spectrum of exponents $\theta(x)$, in the low temperature phase. The probability that the temporal mean $S_t/t$ was always larger than the equilibrium magnetization is found to decay as $t^{-\theta-\frac12}$. This yields a numerical determination of the persistence exponent $\theta$ in the whole low temperature phase, in two dimensions, and above the roughening transition, in the low-temperature phase of the three-dimensional Ising model.Comment: 21 pages, 11 PostScript figures included (1 color figure

Gluino zero-modes for non-trivial holonomy calorons

We couple fermion fields in the adjoint representation (gluinos) to the SU(2) gauge field of unit charge calorons defined on R^3 x S_1. We compute corresponding zero-modes of the Dirac equation. These are relevant in semiclassical studies of N=1 Super-symmetric Yang-Mills theory. Our formulas, show that, up to a term proportional to the vector potential, the modes can be constructed by different linear combinations of two contributions adding up to the total caloron field strength.Comment: 17 pages, 3 Postscript figures, late