Memorizing and recalling spatial-temporal patterns in an oscillator model of the hippocampus

We describe the model of the hippocampus consisting of interactive oscillators with input from the entorhinal cortex (modulating the main information flow by a theta rhythm) and the septum (a theta rhythm generator). When interconnections between oscillators are allowed to strengthen in an adaptive way, the network can be trained using a series of lessons. This results in a connection matrix that memorizes the temporal sequence of inputs. Presenting one of the lessons to the trained network results in reproduction of the remainder of the sequence. In this paper, we create such a connection matrix, derive from it an appropriate Markov chain and simulate the chain to illustrate its dynamics.     

Mild traumatic brain injury--the Fife perspective

Excretion was studied of catecholamines and diphenilamine (DOPA) in 310 patients with carcinoma of the stomach and large intestine and 43 patients with non-malignant diseases. The oncological patients showed decrease in activity of the mediator link of the sympathoadrenal system (SAS) as well as its reserves but there was no association with sex, age, location or histological structure. Three types of SAS functioning were identified, such as compensation, overstrain and emaciation. Surgical intervention led to activation of the hormonal link and exhaustion of the system's reserves. Two kinds of sympathoadrenal response to stress were described--adequate and inadequate. In the former type, phases of stress remain as they are, unchanged, as are time periods of formation thereof, while under the latter one time periods of the phases formation or formation thereof get disordered.     

Experimental Investigations on Microstructure,Properties and Workability Behavior of Zinc Oxide Reinforced Al–Si–Mg Matrix Composites

Silicon - Al-Si based alloy matrix composites are now broadly utilized by the industrial sectors like automobile, structural, aerospace and more practical industrial applications due to its...     

Reactions of late transition metal complexes with molecular oxygen

Limited natural resources, high energy consumption, economic considerations, and environmental concerns demand that we develop new technologies for the sustainable production of chemicals and fuels. New methods that combine the selective activation of C-H bonds of hydrocarbons with oxidation by a green oxidant such as molecular oxygen would represent huge advances toward this goal. The spectacular selectivity of transition metals in cleaving C-H bonds offers the potential for the direct use of hydrocarbons in the production of value-added organics such as alcohols. However, the use of oxygen, which is abundant, environmentally benign, and inexpensive (particularly from air), has proven challenging, and more expensive and less green oxidants are often employed in transition-metal-catalyzed reactions. Advances in the use of oxygen as an oxidant in transition-metal-catalyzed transformations of hydrocarbons will require a better understanding of how oxygen reacts with transition metal alkyl and hydride complexes. For alkane oxidations, researchers will need to comprehend and predict how metals that have shown particularly high activity and selectivity in C-H bond activation (e.g. Pt, Pd, Rh, Ir) will react with oxygen. In this Account, we present our studies of reactions of late metal alkyls and hydrides with molecular oxygen, emphasizing the mechanistic insights that have emerged from this work. Our studies have unraveled some of the general mechanistic features of how molecular oxygen inserts into late metal hydride and alkyl bonds along with a nascent understanding of the scope and limitations of these reactions. We present examples of the formation of metal hydroperoxide species M-OOH by insertion of dioxygen into Pt(IV)-H and Pd(II)-H bonds and show evidence that these reactions proceed by radical chain and hydrogen abstraction pathways, respectively. Comparisons with recent reports of insertion of oxygen into other Pd(II)-H complexes, and also into Ir(III)-H and Rh(III)-H complexes, point to potentially general mechanisms for this type of reaction. Additionally, we observed oxygen-promoted C-H and H-H reductive elimination reactions from five-coordinate Ir(III) alkyl hydride and dihydride complexes, respectively. Further, when Pd(II)Me(2) and Pt(II)Me(2) complexes were exposed to oxygen, insertion processes generated M-OOMe complexes. Mechanistic studies for these reactions are consistent with radical chain homolytic substitution pathways involving five-coordinate M(III) intermediates. Due to the remarkable ability of Pt(II) and Pd(II) to activate the C-H bonds of hydrocarbons (RH) and form M-R species, this reactivity is especially exciting for the development of partial alkane-oxidation processes that utilize molecular oxygen. Our understanding of how late transition metal alkyls and hydrides react with molecular oxygen is growing rapidly and will soon approach our knowledge of how other small molecules such as olefins and carbon monoxide react with these species. Just as advances in understanding olefin and CO insertion reactions have shaped important industrial processes, key insight into oxygen insertion should lead to significant gains in sustainable commercial selective oxidation catalysis.     

Local procrustes for manifold embedding: a measure of embedding quality and embedding algorithms

We present the Procrustes measure, a novel measure based on Procrustes rotation that enables quantitative comparison of the output of manifold-based embedding algorithms such as LLE (Roweis and Saul, Science 290(5500), 2323–2326, 2000) and Isomap (Tenenbaum et al., Science 290(5500), 2319–2323, 2000). The measure also serves as a natural tool when choosing dimension-reduction parameters. We also present two novel dimension-reduction techniques that attempt to minimize the suggested measure, and compare the results of these techniques to the results of existing algorithms. Finally, we suggest a simple iterative method that can be used to improve the output of existing algorithms.     

Isomerization Dynamics of Dicyanine A in n-Alcoholic Solution

The radiationless relaxation of dicyanine A molecules in n-alcohols methanol to butanol has been studied by picosecond fluorescence spectroscopy and time-resolved nonlinear spectroscopy. The fluorescence decay rates have been measured as a function of viscosity, temperature, and fluorescence wavelength. It is shown that the wavelength dependence can be explained by coexistence of two ground-state conformers. The intrinsic activation barrier for the nonradiative decay from the excited surface is very small, much less than 1 kcal/mol. In a particular solvent the time constants of the nonradiative relaxation show a linear dependence on the variation of viscosity. The experimental data are discussed in relation to the BFO theory (Bagchi, B.; Fleming, G.R.; Oxtoby, D.W. J. Chem. Phys. 1983, 78: 7375).     

Energy Trapping in Dications

The energy interaction curves of a number of diatomic and polyatomic dication systems were calculated in order to study their energy-trapping properties. Generally, the ab initio complete active space multiconfiguration self-consistent field method was used in an extended valence + polarization basis set, with compact effective potentials replacing the core electrons. The diatomic dications include all ten possible binary combinations of oxygen, sulphur, selenium, and tellurium. O₂²⁺ shows the largest exothermicity, measured from equilibrium to the monocation combination asymptote, and highest barrier to dissociation. The calculated equilibrium bond length and harmonic vibrational frequency agree very well with experiment. The O₂²⁺, SO²⁺, SeO²⁺, and TeO²⁺ series show progressively decreasing exothermicities but similar barrier heights. The non-oxides, in contrast, show similar exothermicities but decreasing barriers with increasing size of the atom constituents. These trends are interpreted in terms of both valence bond curve-crossing and molecular orbital bonding models. The ozone dication, O₃²⁺, is found to have a number of low-lying singlet and triplet stationary state structures spanning near-linear to D_3h2+ symmetries. Although the calculated exothermicity is even larger than for O₂²⁺, the barrier to O₂⁺ + O⁺ dissociation is predicted to be low in each case. O₂²⁺ surrounded by six argon atoms to model an isolating environment shows increased equilibrium O–O bond length, decreased exothermicity, and increased barrier to dissociation, relative to the bare dication. O₂²⁺ flanked at each end by a perpendicularly oriented H₂ molecule in a staggered conformation is obstructed from direct conversion to the water dimer dication by a high barrier. However, [(H₂O)₂]²⁺ dissociates smoothly from equilibrium to two water monocations with a large exothermicity but a small barrier.     

Simple automatic initiator for microwave induced plasmas

A simple circuit is described which is used to maintain continuity of a radio-frequency or microwave induced plasma. The microwave power reflected from the discharge is monitored. Upon an increase of the reflected power which indicates that the plasma has become extinguished, a high-voltage pulse is applied to a coil wrapped around the discharge region. The repetition rate, voltage of the pulse, and threshold of reflected power are adjustible. This circuit is applicable to resonance fluorescence, atomic absorption and emission, and kinetic determinations.     

Attenuation of cocaine-induced locomotor activity by butyrylcholinesterase.

A primary enzyme for the metabolism of cocaine is butyrylcholinesterase (BChE). To determine whether the systemic administration of BChE can increase the metabolism of cocaine sufficiently to alter a behavioral effect, rats were tested in a locomotor activity chamber after receiving 17 mg of cocaine per kg intraperitoneally. In rats pretreated intravenously with 5,000 IU of horse serum-derived BChE, the locomotor activity effect was significantly attenuated. BChE pretreatment increased plasma BChE levels approximately 400-fold. When added to rat plasma, this amount of BChE reduced the cocaine half-life from over 5 hr to less than 5 min. BChE altered the cocaine metabolic pattern such that the relatively nontoxic metabolite ecgonine methyl ester was produced, rather than benzoylecgonine. These results suggest that systemic administration of BChE can increase the metabolism of cocaine sufficiently to alter a behavioral effect of cocaine and thus should be investigated as a potential treatment for cocaine abuse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)