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Search Results: 1 - 10 of 15480 matches for " Manuel Sparta "
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How Metal Substitution Affects the Enzymatic Activity of Catechol-O-Methyltransferase
Manuel Sparta, Anastassia N. Alexandrova
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0047172
Abstract: Catechol-O-methyltransferase (COMT) degrades catecholamines, such as dopamine and epinephrine, by methylating them in the presence of a divalent metal cation (usually Mg(II)), and S-adenosyl-L-methionine. The enzymatic activity of COMT is known to be vitally dependent on the nature of the bound metal: replacement of Mg(II) with Ca(II) leads to a complete deactivation of COMT; Fe(II) is slightly less than potent Mg(II), and Fe(III) is again an inhibitor. Considering the fairly modest role that the metal plays in the catalyzed reaction, this dependence is puzzling, and to date remains an enigma. Using a quantum mechanical / molecular mechanical dynamics method for extensive sampling of protein structure, and first principle quantum mechanical calculations for the subsequent mechanistic study, we explicate the effect of metal substitution on the rate determining step in the catalytic cycle of COMT, the methyl transfer. In full accord with experimental data, Mg(II) bound to COMT is the most potent of the studied cations and it is closely followed by Fe(II), whereas Fe(III) is unable to promote catalysis. In the case of Ca(II), a repacking of the protein binding site is observed, leading to a significant increase in the activation barrier and higher energy of reaction. Importantly, the origin of the effect of metal substitution is different for different metals: for Fe(III) it is the electronic effect, whereas in the case of Ca(II) it is instead the effect of suboptimal protein structure.
Photo-driven Molecular Wankel Engine B$_{13}^+$
Jin Zhang,Alina P. Sergeeva,Manuel Sparta,Anastassia N. Alexandrova
Physics , 2012,
Abstract: We report a molecular Wankel motor, the dual-ring structure B13+, driven by circularly-polarized infrared electromagnetic radiation, under which a guided uni-directional rotation of the outer ring is achieved with rotational frequency of the order of 300 MHz.
Distúrbio de Percep??o Temporal e sua Influência na Memória: Estudo de Caso de Paciente com Les?o Frontal
Parente, Maria Alice de Mattos Pimenta;Sparta, M?nica;Palmini, André Luiz;
Psicologia: Reflex?o e Crítica , 2001, DOI: 10.1590/S0102-79722001000200009
Abstract: the cognitive mechanisms of the episodic memory allow a person to travel through time. these mechanisms that are related to the future compose the so-called prospective memory. the main objective of this work was to verify whether it is possible to dissociate neurocognitive mechanisms of the working memory from those of the prospective memory by using a case study with frontal lesion, presenting failures in time perception and memory disorders. based on the ellis model, the patient was tested using both a frontal lobe battery and an einstein and daniel's task. the results showed that the failures did not affect attentional resources required for the execution of complex actions, but decreased the self-driven mechanisms such as the notion of time, intentionality and decision making. following the model, the patient had specific failures in the activation of intentions and in the supervision process. these failures suggest that both the working memory and the prospective memory may have different neuropsychological attributes.
Distúrbio de Percep o Temporal e sua Influência na Memória: Estudo de Caso de Paciente com Les o Frontal
Parente Maria Alice de Mattos Pimenta,Sparta M?nica,Palmini André Luiz
Psicologia: Reflex?o e Crítica , 2001,
Abstract: Os mecanismos da memória episódica possibilitam uma pessoa "viajar" pelo tempo, e quando relacionados ao tempo futuro, comp em a memória prospectiva. O objetivo desse trabalho é verificar, através de um estudo de caso de uma paciente com les o cerebral no lobo frontal, apresentando distúrbio de percep o temporal e falhas de memória, se é possível diferenciar os mecanismos neurocognitivos de memória operacional dos da memória prospectiva. Tomando por base o modelo de Ellis, a paciente foi submetida a uma bateria de lobo frontal e à prova experimental proposta por Einstein e Daniel. Os resultados mostraram que suas falhas n o afetam recursos atencionais necessários na execu o de a es complexas, mas o controle de mecanismos internos (self-driven), como a no o do tempo, ativa o de inten es e tomada de decis es. De acordo com o modelo adotado, a paciente apresenta falha específica na ativa o de inten es e no processo de supervis o. Esses achados indicam que memória operacional e memória prospectiva podem ter correlatos neuropsicológicos diversos.
Molecular Beam Depletion: A New Approach  [PDF]
Manuel Dorado
Journal of Modern Physics (JMP) , 2014, DOI: 10.4236/jmp.2014.512116
Abstract:

During the last years some interesting experimental results have been reported for experiments in N2O, NO, NO dimer, H2, Toluene and BaFCH3 cluster. The main result consists in the observation of molecular beam depletion when the molecules of a pulsed beam interact with a static electric or magnetic field and an oscillating field (RF). In these cases, and as a main difference, instead of using four fields as in the original technique developed by I.I. Rabi and others, only two fields, those which configure the resonant unit, are used. That is, without using the nonhomogeneous magnetic fields. The depletion explanation for I.I. Rabi and others is based in the interaction between the molecular electric or magnetic dipole moment and the non-homogeneous fields. But, obviously, the change in the molecules trajectories observed on these new experiments has to be explained without considering the force provided by the field gradient because it happens without using non-homogeneous fields. In this paper a theoretical way for the explanation of these new experimental results is presented. One important point emerges as a result of this development, namely, the existence of an, until now unknown, spin-dependent force which would be responsible of the aforementioned deviation of the molecules.

On Simple Completely Reducible Binary-Lie Superalgebras over sl2(F)  [PDF]
Manuel Arenas
Advances in Pure Mathematics (APM) , 2015, DOI: 10.4236/apm.2015.55030
Abstract:

In this article, we prove that if B is a simple binary-Lie superalgebra whose even part is isomorphic to sl2(F) ?and whose odd part is a completely reducible binary-Lie-module over the even part, then B is a Lie superalgebra. We introduce also a binary-Lie module over which is sl2(F) not completely reducible.

Magnetic properties of single-crystalline CeCuGa3
Devang A. Joshi,P. Burger,P. Adelmann,D. Ernst,T. Wolf,K. Sparta,G. Roth,K. Grube,C. Meingast,H. v. L?hneysen
Physics , 2012, DOI: 10.1103/PhysRevB.86.035144
Abstract: The magnetic behavior of single-crystalline CeCuGa3 has been investigated. The compound forms in a tetragonal BaAl4-type structure consisting of rare-earth planes separated by Cu-Ga layers. If the Cu-Ga site disorder is reduced, CeCuGa3 adopts the related, likewise tetragonal BaNiSn3-type structure, in which the Ce ion are surrounded by different Cu and Ga layers and the inversion symmetry is lost. In the literature conflicting reports about the magnetic order of CeCuGa3 have been published. Single crystals with the centrosymmetric structure variant exhibit ferromagnetic order below approx. 4 K with a strong planar anisotropy. The magnetic behavior above the transition temperature can be well understood by the crystal-field splitting of the 4f Hund's rule ground-state multiplet of the Ce ions.
Big Bang nucleosynthesis revisited via Trojan Horse Method measurements
R. G. Pizzone,R. Sparta,C. A. Bertulani,C. Spitaleri,M. La Cognata,J. Lalmansingh,L. Lamia,A. Mukhamedzhanov,A. Tumino
Physics , 2014, DOI: 10.1088/0004-637X/786/2/112
Abstract: Nuclear reaction rates are among the most important input for understanding the primordial nucleosynthesis and therefore for a quantitative description of the early Universe. An up-to-date compilation of direct cross sections of 2H(d,p)3H, 2H(d,n)3He, 7Li(p,alpha)4He and 3He(d,p)4He reactions is given. These are among the most uncertain cross sections used and input for Big Bang nucleosynthesis calculations. Their measurements through the Trojan Horse Method (THM) are also reviewed and compared with direct data. The reaction rates and the corresponding recommended errors in this work were used as input for primordial nucleosynthesis calculations to evaluate their impact on the 2H, 3,4He and 7Li primordial abundances, which are then compared with observations.
Origin and Evolution of Life Constraints on the Solar Model  [PDF]
K Michaelian, O Manuel
Journal of Modern Physics (JMP) , 2011, DOI: 10.4236/jmp.2011.226068
Abstract: Life arose as a non-equilibrium thermodynamic process to dissipate the photon potential generated by the hot Sun and cold outer space. Evidence from the geochemical record of the evolutionary history of life on Earth suggests that life originated in a hot aqueous environment dissipating UV light and evolved later to dissipate visible light. This evidence places constraints on models of solar origin and evolution. The standard solar model seems less compatible with the data than does the pulsar centered solar model.
Increasing the Efficiency of Transboundary Water Management: A Regionalization Approach  [PDF]
Dirk Huchtemann, Manuel Frondel
Journal of Water Resource and Protection (JWARP) , 2010, DOI: 10.4236/jwarp.2010.26057
Abstract: In this paper, we develop a methodological approach to increase the efficiency of watershed management approaches that focuses on the reduction of diffuse water pollution. The basic idea is that the efficiency may be improved by identifying and constituting homogenous groups of contiguous administrative units of a watershed, which jointly implement water pollution reduction measures. Homogeneity means similarity of group members with respect to a set of local and environmental characteristics, such as the degree of pollution and abatement costs. We empirically apply our methodology to the watershed of the German river Ems and identify homogenous groups of contiguous administrative units using cluster analysis methods implemented in a Geographical Information System.
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