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Search Results: 1 - 10 of 484029 matches for " Samanta Hernández-García "
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Purification, Immobilization and Characterization of Lipase Isoenzyme from Aspergillus niger with C8 Magnetic Particles  [PDF]
Samanta Hernández-García, María Inmaculada García-García, Francisco García-Carmona
Advances in Bioscience and Biotechnology (ABB) , 2014, DOI: 10.4236/abb.2014.57075

The purification of a lipase isoenzyme from an Aspergillus niger lipase A is reported in this manuscript. Purification was carried out in a simple adsorption step, in which the lipase was offered at low ionic strength to the commercially available C8 modified magnetic particles, MaKProt C8. When the isoenzyme was desorbed with a 0.2% solution of Triton X-100, the SDS-PAGE gel showed a single pure band with a molecular weight of 35 KDa. The purified fraction showed 66.75-fold purification compared with the crude extract. The pure fraction was characterized along with the crude extract and the lipase adsorbed on the MaKProt C8. The purified and the adsorbed lipase showed better activity for the tested substrates (p-nitrophenyl acetate, decanoate, myristate and palmitate) than the crude extract, the preferred substrates being myristate (26.7 μmol·min-1·mg-1) and decanoate (17.4 μmol·min-1·mg-1), respectively. The temperature and pH profiles showed no change for the three enzymes, the optimum temperature being 37°C and the best pH 7.0.

Hydrolysis of Trivalent Holmium in Aqueous Solutions of 2 M Ionic Strength by Spectrophotometric and Potentiometric Methods  [PDF]
Miguel Angel Hernández-García, Hilario López-González, Alberto Rojas-Hernández
Advances in Materials Physics and Chemistry (AMPC) , 2015, DOI: 10.4236/ampc.2015.55017
Abstract: The first hydrolysis constants of trivalent holmium in 2 M NaClO4 and 2 M NaCl at 303 K and in CO2 free conditions were determined. The pCH borderlines of precipitation and first hydrolysis were determined by means of a spectrophotometric method and last one with the program SQUAD. Independently, the stability constant for the first hydrolytic species was determined, by means of potentiometric pH titrations whose data were treated with the program SUPERQUAD. The hydrolysis constants obtained were: \"\"?and \"\". These values attained by both methods are the same. The log10β1,Cl constants for the species HoCl2+ was also calculated for 2 M ionic strength and 303 K from the hydrolysis constant obtained in both perchlorate and chloride media. This value was logβ1,Cl = -0.56.
Seasonal and regional characterization of horizontal stirring in the global ocean
I. Hernández-Carrasco,C. López,E. Hernández-García,A. Turiel
Physics , 2011, DOI: 10.1029/2012JC008222
Abstract: Recent work on Lagrangian descriptors has shown that Lyapunov Exponents can be applied to observed or simulated data to characterize the horizontal stirring and transport properties of the oceanic flow. However, a more detailed analysis of regional dependence and seasonal variability was still lacking. In this paper, we analyze the near-surface velocity field obtained from the Ocean general circulation model For the Earth Simulator (OFES) using Finite-Size Lyapunov Exponents (FSLE). We have characterized regional and seasonal variability. Our results show that horizontal stirring, as measured by FSLEs, is seasonally-varying, with maximum values in Summer time. FSLEs also strongly vary depending on the region: we have first characterized the stirring properties of Northern and Southern Hemispheres, then the main oceanic basins and currents. We have finally studied the relation between averages of FSLE and some Eulerian descriptors such as Eddy Kinetic Energy (EKE) and vorticity (w) over the different regions.
Non-Steady wall-bounded flows of viscoelastic fluids under periodic forcing
Anier Hernández-García,Antonio Fernández-Barbero,Oscar Sotolongo-Costa
Physics , 2013, DOI: 10.1007/s13538-014-0211-0
Abstract: The problem of oscillating flows inside pipes under periodic forcing of viscoelastic fluids is addressed here. Starting from the linear Oldroyd-B model, a generalized Darcy's law is obtained in frequency domain and an explicit expression for the dependence of the dynamic permeability on fluid parameters and forcing frequency is derived. Previous results in both viscoelastic and Newtonian fluids are here shown to be particular cases of our results. On the basis of our calculations, a possible explanation for the observed damping of local dynamic response as the forcing frequency increases is given. Good fitting with recent experimental studies of wave propagation in viscoelastic media is here exhibited. Sound wave propagation in viscoelastic media flowing inside straight pipes is investigated. In particular, we obtain the local dynamic response for weakly compressible flows.
Extracting directed information flow networks: an application to genetics and semantics
A. P. Masucci,A. Kalampokis,V. M. Eguíluz,E. Hernández-García
Physics , 2010, DOI: 10.1103/PhysRevE.83.026103
Abstract: We introduce a general method to infer the directional information flow between populations whose elements are described by n-dimensional vectors of symbolic attributes. The method is based on the Jensen-Shannon divergence and on the Shannon entropy and has a wide range of application. We show here the results of two applications: first extracting the network of genetic flow between the meadows of the seagrass Poseidonia Oceanica, where the meadow elements are specified by sets of microsatellite markers, then we extract the semantic flow network from a set of Wikipedia pages, showing the semantic channels between different areas of knowledge.
Diversity and Noise Effects in a Model of Homeostatic Regulation of the Sleep-Wake Cycle
Marco Patriarca ,Svetlana Postnova,Hans A. Braun,Emilio Hernández-García,Raúl Toral
PLOS Computational Biology , 2012, DOI: 10.1371/journal.pcbi.1002650
Abstract: Recent advances in sleep neurobiology have allowed development of physiologically based mathematical models of sleep regulation that account for the neuronal dynamics responsible for the regulation of sleep-wake cycles and allow detailed examination of the underlying mechanisms. Neuronal systems in general, and those involved in sleep regulation in particular, are noisy and heterogeneous by their nature. It has been shown in various systems that certain levels of noise and diversity can significantly improve signal encoding. However, these phenomena, especially the effects of diversity, are rarely considered in the models of sleep regulation. The present paper is focused on a neuron-based physiologically motivated model of sleep-wake cycles that proposes a novel mechanism of the homeostatic regulation of sleep based on the dynamics of a wake-promoting neuropeptide orexin. Here this model is generalized by the introduction of intrinsic diversity and noise in the orexin-producing neurons, in order to study the effect of their presence on the sleep-wake cycle. A simple quantitative measure of the quality of a sleep-wake cycle is introduced and used to systematically study the generalized model for different levels of noise and diversity. The model is shown to exhibit a clear diversity-induced resonance: that is, the best wake-sleep cycle turns out to correspond to an intermediate level of diversity at the synapses of the orexin-producing neurons. On the other hand, only a mild evidence of stochastic resonance is found, when the level of noise is varied. These results show that disorder, especially in the form of quenched diversity, can be a key-element for an efficient or optimal functioning of the homeostatic regulation of the sleep-wake cycle. Furthermore, this study provides an example of a constructive role of diversity in a neuronal system that can be extended beyond the system studied here.
Radiación solar y supervivencia en una plantación de vara de perlilla (Symphoricarpos microphyllus H.B.K.)
Hernández-García, J. D.;Rodríguez-Trejo, D. A.;
Revista Chapingo. Serie ciencias forestales y del ambiente , 2008,
Abstract: a "vara de perlilla" (symphoricarpos microphyllus h.b.k.) plantation was established in the forest nursery of the división de ciencias forestales, universidad autónoma chapingo. the objective was to study survival and growth under different solar radiation condi-tions. the shrubs were planted under a pine forest plantation in different light conditions. with a digital camera with hemispheric lens and the hemiview program?, were measured direct and diffuse solar radiation, and visible sky. from the shrubs was recorded survival, number and length of branches, shoot and root biomass and total biomass. the probability of mortality was obtained with a logistic model, using as explanatory variable direct solar radiation. also was employed linear regression. the logistic model was significant (p= 0.0970), with higher mortality at higher light levels. the lineal regressions were not significant or had a verly low r2.
Attosecond XUV vortices from high-order harmonic generation
C. Hernández-García,A. Picón,J. San Román,L. Plaja
Physics , 2015, DOI: 10.1103/PhysRevLett.111.083602
Abstract: We present a theoretical study of high-order harmonic generation (HHG) and propagation driven by an infrared field carrying orbital angular momentum (OAM). Our calculations unveil the following relevant phenomena: extreme-ultraviolet harmonic vortices are generated and survive to the propagation effects, vortices transport high-OAM multiple of the corresponding OAM of the driving field and, finally, the different harmonic vortices are emitted with similar divergence. We also show the possibility of combining OAM and HHG phase-locking to produce attosecond pulses with helical pulse structure.
Wikipedia Information Flow Analysis Reveals the Scale-Free Architecture of the Semantic Space
Adolfo Paolo Masucci,Alkiviadis Kalampokis,Victor Martínez Eguíluz,Emilio Hernández-García
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0017333
Abstract: In this paper we extract the topology of the semantic space in its encyclopedic acception, measuring the semantic flow between the different entries of the largest modern encyclopedia, Wikipedia, and thus creating a directed complex network of semantic flows. Notably at the percolation threshold the semantic space is characterised by scale-free behaviour at different levels of complexity and this relates the semantic space to a wide range of biological, social and linguistics phenomena. In particular we find that the cluster size distribution, representing the size of different semantic areas, is scale-free. Moreover the topology of the resulting semantic space is scale-free in the connectivity distribution and displays small-world properties. However its statistical properties do not allow a classical interpretation via a generative model based on a simple multiplicative process. After giving a detailed description and interpretation of the topological properties of the semantic space, we introduce a stochastic model of content-based network, based on a copy and mutation algorithm and on the Heaps' law, that is able to capture the main statistical properties of the analysed semantic space, including the Zipf's law for the word frequency distribution.
Scaling properties of protein family phylogenies
Alejandro Herrada, Víctor M Eguíluz, Emilio Hernández-García, Carlos M Duarte
BMC Evolutionary Biology , 2011, DOI: 10.1186/1471-2148-11-155
Abstract: The comparative analysis between protein and species phylogenies shows that both sets of phylogenies share a remarkably similar scaling behavior, suggesting the universality of branching rules and of the evolutionary processes that drive biological diversification from gene to species level. In order to explain such generality, we propose a simple model which allows us to estimate the proportion of evolvability/robustness needed to approximate the scaling behavior observed in the phylogenies, highlighting the relevance of the robustness of a biological system (species or protein) in the scaling properties of the phylogenetic trees.The invariance of the scaling properties at levels spanning from genes to species suggests that rules that govern the incapability of a biological system to diversify are equally relevant both at the gene and at the species level.During the last century, an important effort has been devoted to the understanding of diversification patterns and processes in terms of branching evolutionary trees [1-7]. Tempo and mode of genetic change, and their connections with tempo and mode of speciation is an important issue in this context. In that sense, we address the question of whether similar forces act across the gene level and species-level evolution [8-10], through a comparative analysis of the topological behavior of protein and species phylogenies.Previous analyses of the topological properties of phylogenies have revealed universal patterns of phylogenetic differentiation [3,6,7,11,12]. This means that the impact of evolutionary forces shaping the diversity of life on Earth on the shape of phylogenetic trees is, at least to the level of detail captured by the descriptors used, similar across a broad range of scales, from macro-evolution to speciation and population differentiation, and across diverse organisms such as eukaryotes, eubacteria, archaea or viruses, thereby. This together with the fact that evolutionary forces work at molecular lev
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