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Selected AbstractsSoman-induced seizures: limbic activity, oxidative stress and neuroprotective proteins,,JOURNAL OF APPLIED TOXICOLOGY, Issue S1 2001T. L. Pazdernik Abstract Soman, a potent acetylcholinesterase inhibitor, induces status epilepticus in rats followed by conspicuous neuropathology, most prominent in piriform cortex and the CA3 region of the hippocampus. Cholinergic seizures originate in striatal,nigral pathways and with fast-acting agents (soman) rapidly spread to limbic related areas and finally culminate in a full-blown status epilepticus. This leads to neurochemical changes, some of which may be neuroprotective whereas others may cause brain damage. Pretreatment with lithium sensitizes the brain to cholinergic seizures. Likewise, other agents that increase limbic hyperactivity may sensitize the brain to cholinergic agents. The hyperactivity associated with the seizure state leads to an increase in intracellular calcium, cellular edema and metal delocalization producing an oxidative stress. These changes induce the synthesis of stress-related proteins such as heat shock proteins, metallothioneins and heme oxygenases. We show that soman-induced seizures cause a depletion in tissue glutathione and an increase in tissue ,catalytic' iron, metallothioneins and heme oxygenase-1. The oxidative stress induces the synthesis of stress-related proteins, which are indicators of ,stress' and possibly provide neuroprotection. These findings suggest that delocalization of iron may catalyze Fenton-like reactions, causing progressive cellular damage via free radical products. Copyright © 2001 John Wiley & Sons, Ltd. [source] A critical look at the kinematic-wave theory for sedimentation,consolidation processes in closed vesselsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 16 2001R. Bürger Abstract The two-phase flow of a flocculated suspension in a closed settling vessel with inclined walls is investigated within a consistent extension of the kinematic wave theory to sedimentation processes with compression. Wall boundary conditions are used to spatially derive one-dimensional field equations for planar flows and flows which are symmetric with respect to the vertical axis. We analyse the special cases of a conical vessel and a roof-shaped vessel. The case of a small initial time and a large time for the final consolidation state leads to explicit expressions for the flow fields, which constitute an important test of the theory. The resulting initial-boundary value problems are well posed and can be solved numerically by a simple adaptation of one of the newly developed numerical schemes for strongly degenerate convection-diffusion problems. However, from a physical point of view, both the analytical and numerical results reveal a deficiency of the general field equations. In particular, the strongly reduced form of the linear momentum balance turns out to be an oversimplification. Included in our discussion as a special case are the Kynch theory and the well-known analyses of sedimentation in vessels with inclined walls within the framework of kinematic waves, which exhibit the same shortcomings. In order to formulate consistent boundary conditions for both phases in a closed vessel and in order to predict boundary layers in the presence of inclined walls, viscosity terms should be taken into account. Copyright © 2001 John Wiley & Sons, Ltd. [source] Electron beam,specimen interactions and their effect on high-angle annular dark-field imaging of dopant atoms within a crystalACTA CRYSTALLOGRAPHICA SECTION A, Issue 3 2010B. G. Mendis A Bloch wave model based on perturbation theory is used to analyse high-angle annular dark-field (HAADF) imaging of a substitutional and interstitial W atom in [111]-oriented body-centred-cubic Fe. For the substitutional atom the 1s Bloch state is scattered to high angles thereby producing HAADF dopant atom contrast. Intraband scattering of the 1s state is the strongest individual Bloch wave transition but collective interband scattering of the non-1s states to the 1s state leads to variations in the high-angle scattering with depth of the dopant atom. The non-1s states are Coulomb attracted towards the W atom thereby giving rise to an `atom focusing' effect similar to channelling. For the interstitial atom, which in the [111] orientation does not overlap with an atom column of the host lattice, high-angle scattering and Coulomb attraction takes place through the non-1s states. Scattering of the 1s state is, however, negligible. [source] Synthesis of sub-micrometer core,shell rubber particles with 1,2-azobisisobutyronitrile as initiator and deformation mechanisms of modified polystyrene under various conditionsPOLYMER INTERNATIONAL, Issue 10 2009Rujun Dai Abstract BACKGROUND: Sub-micrometer core-shell polybutadiene- graft -polystyrene (PB- g -PS) copolymers with various ratios of polybutadiene (PB) core to polystyrene (PS) shell were synthesized by emulsion grafting polymerization with 1,2-azobisisobutyronitrile (AIBN) as initiator. These graft copolymers were blended with PS to prepare PS/PB- g -PS with a rubber content of 20 wt%. The mechanical properties, morphologies of the core-shell rubber particles and deformation mechanisms under various conditions were investigated. RESULTS: Infrared spectroscopic analysis confirmed that PS could be grafted onto the PB rubber particles. The experimental results showed that a specimen with a ,cluster' dispersion state of rubber particles in the PS matrix displayed better mechanical properties. Transmission electron micrographs suggested that crazing only occurred from rubber particles and extended in a bridge-like manner to neighboring rubber particles parallel to the equatorial plane at a high speed for failure specimens, while the interaction between crazing and shear yielding stabilized the growing crazes at a low speed in tensile tests. CONCLUSION: AIBN can be used as an initiator in the graft polymerization of styrene onto PB. The dispersion of rubber particles in a ,cluster' state leads to better impact resistance. The deformation mechanism in impact tests was multi-crazing, and crazing and shear yielding absorbed the energy in tensile experiments. Copyright © 2009 Society of Chemical Industry [source] | ||||||||||