Simultaneous recording of evoked potentials and T2*-weighted MR images during somatosensory stimulation of rat

Somatosensory evoked potentials (SEP) and T2*-weighted nuclear magnetic resonance (NMR) images were recorded simultaneously during somatosensory stimulation of rat to investigate the relationship between electrical activation of the brain tissue and the signal intensity change in functional NMR imaging. Electrical forepaw stimulation was performed in Wistar rats anesthetized with -chloralose. SEPs were recorded with calomel electrodes at stimulation frequencies of 1.5, 3, 4.5, and 6 Hz. At the same time, T2*-weighted imaging was performed, and the signal intensity increase during stimulation was correlated with the mean amplitude of the SEP. Both the stimulation-evoked signal intensity increase in T2*-weighted images and the amplitude of SEPs were dependent on the stimulation frequency, with the largest signals at a stimulation frequency of 1.5 Hz and decreasing activations with increasing frequencies. The feasibility of simultaneous, artifact-free recordings of T2*-weighted NMR images and of evoked potentials is proved. Furthermore, the study demonstrates - in the intact brain - the validity of functional magnetic resonance imaging for estimating the intensity of electrocortical activation

Time course of circulatory and metabolic recovery of cat brain after cardiac arrest assessed by perfusion- and diffusion-weighted imaging and MR-spectroscopy

Copyright 2003 ELSEVIER SCI IRELAND LT

Exploring the Chemistry of Low-Temperature Ignition by Pressure-Accelerated Dynamics

O trabalho discute, numa abordagem filosófica, a formação ética, a partir das possibilidades da arte de viver. Explicita que a arte de viver tem uma dimensão estética em que própria obra da vida tem a arte como modelo, por meio da criação de diferentes estratégias (desde as interativas até as literárias), articuladas com princípios universais. Esta ética, com seu apelo às condições concretas da vida e aos sentimentos, não exclui o reconhecimento de uma normatividade que ultrapassa as regras criadas pelo próprio sujeito, ou seja, universalidade e particularidade não se excluem. O texto apresenta (1) a contribuição helenística para a arte de viver, por meio do modelo terapêutico de filosofar, e (2) o papel das emoções e da phronesis na articulação entre o universal e o particular, para apontar que (3) uma educação ético-estética se constitui pelo reconhecimento da tensão entre o eu singular e o nós (ethos comum)

Automatic potential energy surface exploration by accelerated reactive MD simulations: from pyrolysis to oxidation chemistry

Automatic potential energy surface (PES) exploration is important to better understand reaction mechanisms. Existing automatic PES mapping tools usually rely on predefined knowledge or on computationally expensive on-the-fly quantum-chemical calculations. In this work, we have developed a method for discovering novel reaction pathways and automatically mapping out the PES when only being given a starting species. We have therefore extended the reactive molecular dynamics simulation tool ChemTraYzer2.0 (Chemical Trajectory Analyzer, CTY) for this PES-mapping algorithm. To explore PESs with low-temperature reactions, we applied the acceleration method Collective Variable-driven Hyperdynamics (CVHD). This involved the development of tailored collective variable (CV) templates, which are discussed in this study. The PES mapping algorithm can generate new seed species, automatically start replica simulations for new pathways, and stop the simulation when a reaction has been found, reducing the computational cost of the algorithm. It is validated for known pathways in various pyrolysis and oxidation systems: hydrocarbon isomerization and dissociation (C4H7 and C8H7 PES), mostly dominant at high temperatures, low-temperature oxidation of n-butane (C4H9O2 PES) and cyclohexane (C6H11O2 PES). As a result, in addition to new pathways showing up in the simulations, common isomerization and dissociation pathways were found very fast: for example, 44 reactions of butenyl radicals including major isomerizations and decompositions within about 30 minutes wall time and low-temperature chemistry such as the internal H-shift of RO2 → QO2H within one day wall time. Furthermore, since CTY keeps track of all found geometries of the reactants, transition states, and products, PES mapping facilitates automated higher-level calculations without a priori knowledge. Lastly, we applied PES mapping to the oxidation of the recently proposed bio-hybrid fuel 1,3-dioxane and validated that the tool could be used to discover new reaction pathways of larger molecules that are of practical use

A reactive molecular dynamics study of chlorinated organic compounds, part I : force field development

This work presents a novel parametrization for the ReaxFF formalism as a means to investigate reaction processes of chlorinated organic compounds. Force field parameters cover the chemical elements C, H, O, Cl and were obtained using a novel optimization approach involving relaxed potential energy surface scans as training targets. The resulting ReaxFF parametrization shows good transferability, as demonstrated on two independent ab initio validation sets. While this first part of our two-paper series focuses on force field parametrization, we apply our parameters to the simulation of chlorinated dibenzofuran formation and decomposition processes in Part II