Molecular-dynamics simulations were used to calculate the photodissociation yield of F2 in solid Kr as a function of photon energy at 12 K. The calculations used pairwise interactions including empirical gas-phase F(2P3/2)/Kr potentials. Excellent agreement was found with recent experimental data, showing the quantitative accuracy of molecular-dynamics simulations using pairwise reagent/solvent potentials, in describing a chemical condensed-matter reaction.
Recent evidence indicates that under in vitro conditions, superoxide anion and hydrogen peroxide (H2O2) are unstable in the presence of manganese ion (Mn2+). The current studies show that in the presence of Mn2+, H2O2-mediated injury of endothelial cells is greatly attenuated. A source of bicarbonate ion and amino acid is required for Mn2+ to exert its protective effects. Injury by phorbol ester-activated neutrophils is also attenuated under the same conditions. EDTA reverses the protective effects. Acute lung injury produced in vivo in rats by intratracheal instillation of glucose-glucose oxidase is almost completely blocked in rats treated with Mn2+ and glycine. Conversely, treatment of rats with EDTA, a chelator of Mn2+, markedly accentuates lung injury caused by glucose-glucose oxidase. These data are consistent with the findings of others that Mn2+ can facilitate direct oxidation of amino acids with concomitant H2O2 disproportionation. This could form the basis of a new therapeutic approach against oxygen radical-mediated tissue injury.
In Spanish: 'Judíos nuevos en Amsterdam' (1996). In French: 'Les nouveaux-juifs d'Amsterdam' (1999). An earlier Hebrew version appeared in the 'Proceedings of the Israel Academy of Sciences and Humanities' 7 (1986).
He scattering from substitutionally disordered Xe + Kr monolayers is studied theoretically. The angular distribution of the scattered He, and lifetimes of scattering resonances at the surface, are calculated for different Xe:Kr mixing ratios. In addition to Bragg diffraction, new intensity maxima are found. These are interpreted as rainbow effects (disorder rainbows), and may be very useful in characterizing disordered surfaces. Also, trapping resonances are found, which are sharply sensitive to the percolation thresholds for the mixtures. The results show He scattering can be a powerful tool in studying 2D percolation behavior.
It has been remarked that in rational interactions more information to one player, while all others' information remains the same, may reduce his payoff in equilibrium. This classical observation relies on comparing equilibria of two different games. It is argued that this analysis is not tenably performed by comparing equilibria of two different games. Rather, one is compelled to perform the analysis in an interaction without complete information, and to compare equilibria of two interactions that are embedded in some compounded game. It is then shown that the player whose information is unilaterally refined cannot be worse off at equilibrium.
A new method is presented for calculating the quantum dynamics of processes in polyatomic systems. The approach uses the time-dependent self-consistent-field (TDSCF) approximation, which treats each mode as moving in a time-dependent mean field. The new method corrects the TDSCF by a perturbation-theoretic algorithm. The method is tested against numerically exact calculations for vibrationally inelastic He + H-2 collisions, and for reactive H + H-2 scattering. Very good agreement was found with the exact results. Major improvement was obtained over (uncorrected) TDSCF. The method is computationally efficient, practically applicable to systems of many degrees of freedom.
The steady-state bimolecular annihilation reaction A + B –> 0 on two-dimensional surfaces is studied via computer simulations. In the simulations A and B are randomly adsorbed on vacant sites, and reaction takes place whenever A and B reach nearest-neighbor sites, either directly following adsorption or through diffusion. It is found that both with and without diffusion the reactants segregate into separate islands of A's and B's. The islands vary in size and exhibit highly ramified shapes. Moreover, the islands are self-similar with a fractal dimension D = 1.89 (similar to percolation, but also other clusters). D is found to be independent of the diffusion rate K. Other fractal dimensions, e.g., of the ``hull'' differ from those of percolating clusters. The steady-state coverage theta* = theta*A + theta*B decreases with K, as expected (theta*A = theta*B, corresponding to equal fluxes of A and B is the only physical solution). For systems with immobile particles (K = 0) we find theta* congruent-to 0.59 and theta* congruent-to 0.49 for the square and the triangular lattices, respectively, similar to the percolation thresholds on these lattices. The long-time characteristics of the system (D, theta*, etc.) are independent of the initial conditions of the simulation, indicating that the system reaches a stable steady state. Furthermore, for the large systems simulated (typically 500 x 500 lattice sites) it was found that the long-time behavior is independent of the input mode. Namely, the same results are obtained for conserved (i.e., exactly balanced) and nonconserved (statistically balanced) A,B input mechanisms, indicating that on the time scale of the simulations (approximately 10(4) Monte Carlo steps) the apparent steady state (for nonconserved input) is essentially identical with the true steady state (for the conserved input).
The dehydrobromination of PhCH2CH2Br to give styrene under phase-transfer catalytic conditions was sharply accelerated if a 3-liq.-phase system could be engineered. Bu4NBr promoted such a system at >38° and at high concn., the 3rd phase being rich in catalyst. Excessively concd. NaOH (>42%) caused a drop in the reaction rate by nearly 1 order of magnitude, as did a small change in temp. Such effects were due to destabilization of the 3rd phase and pptn. of the catalyst. Neither Pr4NBr nor the tetrapentyl analog showed such behavior. The data were explained by ref. to anomalous phys. and surface chem. properties of Bu4NBr. [on SciFinder(R)]
Angel Sáenz Badillos. 1991. “Sobre el autor de las Tešubot ʿal Se'adyah..” In Exile and diaspora: studies in the history of the Jewish people presented to Professor Haim Beinart. [Ed. Aharon Mirsky, Abraham Grossman, Yosef Kaplan], Pp. 26 - 43. Ben-Zvi Institute & The Hebrew University. Publisher's Version
Carnosine, anserine and homocarnosine are natural compounds which are present in high concentrations (2-20 mM) in skeletal muscles and brain of many vertebrates. We have demonstrated in a previous work that these compounds can act as antioxidants, a result of their ability to scavenge peroxyl radicals, singlet oxygen and hydroxyl radicals. Carnosine and its analogues have been shown to be efficient chelating agents for copper and other transition metals. Since human skeletal muscle contains one-third of the total copper in the body (20-47 mmol/kg) and the concentration of carnosine in this tissue is relatively high, the complex of carnosine:copper may be of biological importance. We have studied the ability of the copper:carnosine (and other carnosine derivatives) complexes to act as superoxide dismutase. The results indicate that the complex of copper:carnosine can dismute superoxide radicals released by neutrophils treated with PMA in an analogous mechanism to other amino acids and copper complexes. Copper:anserine failed to dismute superoxide radicals and copper:homocarnosine complex was efficient when the cells were treated with PMA or with histone-opsonized streptococci and cytochalasine B. The possible role of these compounds to act as physiological antioxidants that possess superoxide dismutase activity is discussed.
A mean field theory of chain packing in amphiphilic aggregates is used to calculate conformational and thermodynamic properties of the inverse hexagonal phase. These properties are compared with those for planar bilayers and curved monolayers. Calculated bond order parameters reveal that chains packed in the hexagonal arrangement have more conformational freedom than chains packed in a bilayer. The calculated order parameters are in good agreement with recent experimental results. Free energy calculations are also presented. It is found that for small areas per head group the packing free energy of amphiphiles in a bilayer is considerably higher than in the hexagonal phase.
We present a statistical-thermodynamic theory that associates fracture of a solid with the approach of a spinodal upon increasing stress. This formulation is illustrated by a one-dimensional model, and the temperature dependence of the nonlinear stress-strain relation and fracture stress is obtained. A two-dimensional network model is treated by both effective-medium theory and Monte Carlo simulations, showing metastability and the nucleation of microcracks.
A patient who developed severe metabolic bone disease is presented. He had received long-term home parenteral nutrition (HPN) following extensive small bowel resection after mesenteric vein thrombosis. Bone disease caused by aluminum intoxication had components of osteomalacia and low-turnover osteoporosis. Aluminum was detected at the surface of mineralized bone and was elevated in the serum, resulting in a positive deferoxamine infusion test. One year of treatment with high doses of calcium (up to 24 mEq per day) significantly diminished the patient's bone pain, increased the serum levels of calcium, abolished aluminum deposits in the mineralized trabecula, improved bone formation, and increased trabecular bone volume as assessed by repeated histomorphometric analysis.
