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Search Results: 1 - 10 of 410335 matches for " M. GARCIA "
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Letter to the Editor  [PDF]
Victor M. Bolanos-Garcia
Advances in Enzyme Research (AER) , 2013, DOI: 10.4236/aer.2013.13004
Abstract: Letter to Advances in Enzyme Research
Seminavis atlantica Garcia, a new psammic diatom (Bacillariophyceae) from southern Brazilian sandy beaches
Garcia, M;
Brazilian Journal of Biology , 2007, DOI: 10.1590/S1519-69842007000400026
Abstract: the paper presents the description of seminavis atlantica garcia, a psammic marine diatom from dissipative sandy beaches from southern brazil. it is characterized by its convex linear dorsal margin (37 to 50% of its length is in a straight line), linear ventral margin and raphe located very close to the ventral margin. its morphology is compared to similar species such as amphora clevei grunow, amphora angusta (greg.) cleve var. orientalis allem, amphora ventricosa gregory and amphora eulesteinii grunow.
Integrative Control of Energy Balance and Reproduction in Females
R. M. Garcia-Garcia
ISRN Veterinary Science , 2012, DOI: 10.5402/2012/121389
Abstract:
Integrative Control of Energy Balance and Reproduction in Females
R. M. Garcia-Garcia
ISRN Veterinary Science , 2012, DOI: 10.5402/2012/121389
Abstract: There is a strong association between nutrition and reproduction. Chronic dietary energy deficits as well as energy surpluses can impair reproductive capacity. Metabolic status impacts reproductive function at systemic level, modulating the hypothalamic GnRH neuronal network and/or the pituitary gonadotropin secretion through several hormones and neuropeptides, and at the ovarian level, acting through the regulation of follicle growth and steroidogenesis by means of the growth hormone-IGF-insulin system and local ovarian mediators. In the past years, several hormones and neuropeptides have been emerging as important mediators between energy balance and reproduction. The present review goes over the main sites implicated in the control of energy balance linked to reproductive success and summarizes the most important metabolic and neuroendocrine signals that participate in reproductive events with special emphasis on the role of recently discovered neuroendocrine peptides. Also, a little overview about the effects of maternal nutrition, affecting offspring reproduction, has been presented. 1. Introduction The relationship between energy balance and reproduction is well known. Nutrition has a significant impact on numerous reproductive functions including hormone production, folliculogenesis, fertilization, and early embryonic development [1–3]. This intimate association is because reproductive processes are energetically expensive, and the brain must temper the fertility of individuals to match nutritional availability [4, 5]. Reproduction function in mammals can be inhibited when food availability is low or when increased energy demands are not met by compensatory food intake such as in short-term and chronic withdrawal of nutrients [6–8]. This very close alignment with the food supply is more important in females, where pregnancy and lactation are linked to considerable energetic expenses, needed for the nurture of embryos and newborns [9]. In fact, her reproductive outcome can be seriously altered and even life threatening to both the mother and offspring when nutritional imbalance occurs [4]. The link between nutrition and reproduction is mainly through the energy balance [1, 4], apart from the effect of specific nutrients that act independently of such energy balance [10]. Energy balance is usually measured as energy input, considered as feed intake, minus energy output that includes milk, maintenance, activity, growth, and pregnancy expenses [9, 11]. In order to keep constant body energy stores, in mammals, a series of homeostatic events leading to
Classical singularities and Semi-Poisson statistics in quantum chaos and disordered systems
A. M. Garcia-Garcia
Physics , 2005, DOI: 10.1103/PhysRevE.72.066210
Abstract: We investigate a 1D disordered Hamiltonian with a non analytical step-like dispersion relation whose level statistics is exactly described by Semi-Poisson statistics(SP). It is shown that this result is robust, namely, does not depend neither on the microscopic details of the potential nor on a magnetic flux but only on the type of non-analyticity. We also argue that a deterministic kicked rotator with a non-analytical step-like potential has the same spectral properties. Semi-Poisson statistics (SP), typical of pseudo-integrable billiards, has been frequently claimed to describe critical statistics, namely, the level statistics of a disordered system at the Anderson transition (AT). However we provide convincing evidence they are indeed different: each of them has its origin in a different type of classical singularities.
Power spectrum for critical statistics: A novel spectral characterization of the Anderson transition
Antonio M. Garcia-Garcia
Physics , 2005, DOI: 10.1103/PhysRevE.73.026213
Abstract: We examine the power spectrum of the energy level fluctuations of a family of critical power-law random banded matrices with properties similar to those of a disordered conductor at the Anderson transition. It is shown both analytically and numerically that the Anderson transition is characterized by a power spectrum which presents $1/f^2$ noise for small frequencies but $1/f$ noise for larger frequencies. The analysis of the transition region between these two power-law limits gives an accurate estimation of the Thouless energy of the system. Finally we discuss under what circumstances these findings may be relevant in the context of non-random Hamiltonians.
Classical intermittency and quantum Anderson transition
Antonio M. Garcia-Garcia
Physics , 2003, DOI: 10.1103/PhysRevE.69.066216
Abstract: We investigate the quantum properties of 1D quantum systems whose classical counterpart presents intermittency. The spectral correlations are expressed in terms of the eigenvalues of an anomalous diffusion operator by using recent semiclassical techniques. For certain values of the parameters the spectral properties of our model show similarities with those of a disordered system at the Anderson transition. In Hamiltonian systems, intermittency is closely related to the presence of cantori in the classical phase space. We suggest, based on this relation, that our findings may be relevant for the description of the spectral correlations of (non-KAM) Hamiltonians with a classical phase space filled by cantori. Finally we discuss the extension of our results to higher dimensions and their relation to Anderson models with long range hopping.
Spectral properties of a generalized chGUE
Antonio M. Garcia-Garcia
Physics , 2001, DOI: 10.1103/PhysRevE.64.066121
Abstract: We consider a generalized chiral Gaussian Unitary Ensemble (chGUE) based on a weak confining potential. We study the spectral correlations close to the origin in the thermodynamic limit. We show that for eigenvalues separated up to the mean level spacing the spectral correlations coincide with those of chGUE. Beyond this point, the spectrum is described by an oscillating number variance centered around a constant value. We argue that the origin of such a rigid spectrum is due to the breakdown of the translational invariance of the spectral kernel in the bulk of the spectrum. Finally, we compare our results with the ones obtained from a critical chGUE recently reported in the literature. We conclude that our generalized chGUE does not belong to the same class of universality as the above mentioned model.
A semiclassical theory of the Anderson transition
Antonio M. Garcia-Garcia
Physics , 2007, DOI: 10.1103/PhysRevLett.100.076404
Abstract: We study analytically the metal-insulator transition in a disordered conductor by combining the self-consistent theory of localization with the one parameter scaling theory. We provide explicit expressions of the critical exponents and the critical disorder as a function of the spatial dimensionality, $d$. The critical exponent $\nu$ controlling the divergence of the localization length at the transition is found to be $\nu = {1 \over 2}+ {1 \over {d-2}}$. This result confirms that the upper critical dimension is infinity. Level statistics are investigated in detail. We show that the two level correlation function decays exponentially and the number variance is linear with a slope which is an increasing function of the spatial dimensionality.
Effect of a magnetic flux on the critical behavior of a system with long range hopping
Antonio M. Garcia-Garcia
Physics , 2003, DOI: 10.1103/PhysRevB.69.245121
Abstract: We study the effect of a magnetic flux in a 1D disordered wire with long range hopping. It is shown that this model is at the metal-insulator transition (MIT) for all disorder values and the spectral correlations are given by critical statistics. In the weak disorder regime a smooth transition between orthogonal and unitary symmetry is observed as the flux strength increases. By contrast, in the strong disorder regime the spectral correlations are almost flux independent. It is also conjectured that the two level correlation function for arbitrary flux is given by the dynamical density-density correlations of the Calogero-Sutherland (CS) model at finite temperature. Finally we describe the classical dynamics of the model and its relevance to quantum chaos.
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