Scaling in a continuous time model for biological aging

In this paper we consider a generalization to the asexual version of the Penna model for biological aging, where we take a continuous time limit. The genotype associated to each individual is an interval of real numbers over which Dirac $\delta$--functions are defined, representing genetically programmed diseases to be switched on at defined ages of the individual life. We discuss two different continuous limits for the evolution equation and two different mutation protocols, to be implemented during reproduction. Exact stationary solutions are obtained and scaling properties are discussed.Comment: 10 pages, 6 figure

Three-dimensional Ca2+ imaging advances understanding of astrocyte biology.

Astrocyte communication is typically studied by two-dimensional calcium ion (Ca2+) imaging, but this method has not yielded conclusive data on the role of astrocytes in synaptic and vascular function. We developed a three-dimensional two-photon imaging approach and studied Ca2+ dynamics in entire astrocyte volumes, including during axon-astrocyte interactions. In both awake mice and brain slices, we found that Ca2+ activity in an individual astrocyte is scattered throughout the cell, largely compartmented between regions, preponderantly local within regions, and heterogeneously distributed regionally and locally. Processes and endfeet displayed frequent fast activity, whereas the soma was infrequently active. In awake mice, activity was higher than in brain slices, particularly in endfeet and processes, and displayed occasional multifocal cellwide events. Astrocytes responded locally to minimal axonal firing with time-correlated Ca2+ spots

Gestures and words in naming: Evidence from cross-linguistic and cross-cultural comparison

We report on an analysis of spontaneous gesture production in 2-year-old children who come from three countries (Italy, UK and Australia) and whom speak two languages (Italian and English), in an attempt to tease apart the influence of language and culture when comparing children from different cultural and linguistic environments. Eighty-seven monolingual children aged 24-30 months completed an experimental task measuring their comprehension and production of nouns and predicates. The Italian children scored significantly higher than the other groups on all lexical measures. With regards to gestures, British children produced significantly fewer pointing and speech combinations compared to the Italian and Australian children, who did not differ from each other. In contrast, Italian children produced significantly more representational gestures than the two other groups. We conclude that spoken language development is primarily influenced by the input language over gesture production, whereas the combination of cultural and language environments affects gesture productions

On the compatibility of causality and symmetry (Comments on "Analysis of causality in time-dependent density functional theory")

It is argued that there exists the only one inverse of the linear response function $\chi$, i.e. $\chi^{-1}$, which depends symmetrically of its spatial-times variables, see M.K. Harbola, and A. Banerjee, Phys. Rev. A {\bf 60}, 5101 (1999). Some brief comments on this consideration are presented. We show instead, that it is possible to construct the causal inverse also. At the same time we confirm the main statement of M.K. Harbola and A. Banerjee that in fact there is no contradiction between the symmetry and causality.Comment: 4 pages, LaTe

Emergent spatial correlations in stochastically evolving populations

We study the spatial pattern formation and emerging long range correlations in a model of three species coevolving in space and time according to stochastic contact rules. Analytical results for the pair correlation functions, based on a truncation approximation and supported by computer simulations, reveal emergent strategies of survival for minority agents based on selection of patterns. Minority agents exhibit defensive clustering and cooperative behavior close to phase transitions.Comment: 11 pages, 4 figures, Adobe PDF forma

Worldline Casting of the Stochastic Vacuum Model and Non-Perturbative Properties of QCD: General Formalism and Applications

The Stochastic Vacuum Model for QCD, proposed by Dosch and Simonov, is fused with a Worldline casting of the underlying theory, i.e. QCD. Important, non-perturbative features of the model are studied. In particular, contributions associated with the spin-field interaction are calculated and both the validity of the loop equations and of the Bianchi identity are explicitly demonstrated. As an application, a simulated meson-meson scattering problem is studied in the Regge kinematical regime. The process is modeled in terms of the "helicoidal" Wilson contour along the lines introduced by Janik and Peschanski in a related study based on a AdS/CFT-type approach. Working strictly in the framework of the Stochastic Vacuum Model and in a semiclassical approximation scheme the Regge behavior for the Scattering amplitude is demonstrated. Going beyond this approximation, the contribution resulting from boundary fluctuation of the Wilson loop contour is also estimated.Comment: 37 pages, 1 figure. Final version to appear in Phys.Rev.

Orthorhombic Electron Spin Resonance Spectrum of U3+ in CaF2

An orthorhombic spectrum of U3+ in CaF2 was measured. The orthorhombic X, Y axes are found to lie in the (110) plane and the Z axis perpendicular to these axes. The X axes are at ±(19±1)° with the [11̅0] direction. There are, in general, twelve inequivalent magnetic sites. The g factors corresponding to one set of axes are gx=1.38±0.01, gy=2.85±0.02, and gz=2.94±0.01. Various models explaining this spectrum are discussed. The most likely model is that of an interstitial F- in the second-nearest neighbor position

On the Influence of Noise on the Critical and Oscillatory Behavior of a Predator-Prey Model: Coherent Stochastic Resonance at the Proper Frequency

Noise induced changes in the critical and oscillatory behavior of a Prey-Predator system are studied using power spectrum density and Spectral Amplification Factor (SAF) analysis. In the absence of external noise, the population densities exhibit three kinds of asymptotic behavior, namely: Absorbing State, Fixed Point (FP) and an Oscillatory Regime (OR) with a well defined proper (natural) frequency. The addition of noise destabilizes the FP phase inducing a transition to a new OR. Surprisingly, it is found that when a periodic signal is added to the control parameter, the system responds robustly, without relevant changes in its behavior. Nevertheless, the "Coherent Stochastic Resonance" phenomenon is found only at the proper frequency. Also, a method based on SAF allows us to locate very accurately the transition points between the different regimes.Comment: RevTex, 18 pgs, 6 figures. Submitted to Physics Letters A (2000

Nonlocal Electrodynamics of Rotating Systems

The nonlocal electrodynamics of uniformly rotating systems is presented and its predictions are discussed. In this case, due to paucity of experimental data, the nonlocal theory cannot be directly confronted with observation at present. The approach adopted here is therefore based on the correspondence principle: the nonrelativistic quantum physics of electrons in circular "orbits" is studied. The helicity dependence of the photoeffect from the circular states of atomic hydrogen is explored as well as the resonant absorption of a photon by an electron in a circular "orbit" about a uniform magnetic field. Qualitative agreement of the predictions of the classical nonlocal electrodynamics with quantum-mechanical results is demonstrated in the correspondence regime.Comment: 23 pages, no figures, submitted for publicatio

Coexistence and Survival in Conservative Lotka-Volterra Networks

Analyzing coexistence and survival scenarios of Lotka-Volterra (LV) networks in which the total biomass is conserved is of vital importance for the characterization of long-term dynamics of ecological communities. Here, we introduce a classification scheme for coexistence scenarios in these conservative LV models and quantify the extinction process by employing the Pfaffian of the network's interaction matrix. We illustrate our findings on global stability properties for general systems of four and five species and find a generalized scaling law for the extinction time