The role of onium salts in the oxidation of hydrocarbons by O2 catalysed by cationic phase-transfer reagents

Experimental and theoretical evidence is presented that cationic phase-transfer catalysts promote the homolytic decomposition of hydroperoxide initiators into radicals, this being a fundamental step in the catalysis of the oxidation of hydrocarbons by O-2. Such decomposition of the model substance tert-butyl hydroperoxide (t-BHP) results in O-2, tert-butanol (90-95%) di-tert-butyl peroxide (5-10%) and traces of CO2. The stoichiometric ratio Delta[t-BHP]/Delta O-2 was found to have a value of 2, independently of the nature of the counteranion present. It is assumed that the interaction between hydroperoxide and onium cation is mainly electrostatic in nature and that its effectivity depends on the positive charge density on the onium cation, which is controlled by the nature and dimensions of the counteranion. The role of water in the decomposition of t-BHP is also elucidated

A Rule-Based Consultant for Accelerator Beam Scheduling Used in the CERN PS Complex

The CERN PS accelerator complex consists of nine interacting accelerators which work together to produce particle beams for different end users, varying in particle type, energy, time structure, and geometry. The beam production schedule is time sliced and depends on the current operational requirements and dynamically on the accelerator status, so that production schedule changes occur in real time. Many potential schedules are not valid due to various system constraints and these constraints vary over time as new operational modes are introduced. In order to ensure that only valid schedules are given to the complex, an automated tool has been developed to indicate whether a potential schedule is valid or not. This presentation describes the method by which the validity of a beam schedule is determined and how this method was implemented using a rule-based approach based on SQL, avoiding the use of an expert system shell. Both the data to instantiate the rules and the rules themselves are kept in an Oracle data base. The SQL interpreter provides the inference engine for this knowledge-based system. A few examples are presented and the running experience with the tool is discussed

Onium salts as catalysts in the liquid-phase oxidation of cyclohexene or tetraline by N2O

The liquid-phase oxidation of cyclohexene or tetraline with N2O was studied in various solvents in the presence of onium salts or without them. The onium salts exerted significant promoting effect on the reactions. The activation of the oxidant was studied by IR spectroscopy. It was found that the interactions of the ions in the onium salts and the polarised N–O bond further enhanced polarisation leading to an activation of the oxidant, thus, increasing the rate of oxidation

Excess Electron Localization Sites in Neutral Water Clusters

We present approximate pseudopotential quantum mechanical calculations of the excess electron states of equilibrated neutral water clusters sampled by classical molecular dynamics simulations. The internal energy of the clusters are representative of those present at temperatures of 200 K and 300 K. Correlated electronic structure calculations are used to validate the pseudopotential for this purpose. We find that the neutral clusters support localized, bound excess electron ground states in about 50 % of the configurations for the smallest cluster size studied (n=20), and in almost all configurations for larger clusters (n>66). The state is always exterior to the molecular frame, forming typically a diffuse surface state. Both cluster size and temperature dependence of energetic and structural properties of the clusters and the electron distribution are explored. We show that the stabilization of the electron is strongly correlated with the pre-existing instantaneous dipole moment of the neutral clusters, and its ground state energy is reflected in the electronic radius. The findings are consistent with electron attachment via an initial surface state. The hypothetical spectral dynamics following such attachment is also discussed

Faceting and branching in 2D crystal growth

The official published version of the Article can be accessed from the link below - Copyright @ 2011 APSUsing atomic scale time-dependent density functional calculations we confirm that both diffusion-controlled and diffusionless crystallization modes exist in simple 2D systems. We provide theoretical evidence that a faceted to nonfaceted transition is coupled to these crystallization modes, and faceting is governed by the local supersaturation at the fluid-crystalline interface. We also show that competing modes of crystallization have a major influence on mesopattern formation. Irregularly branched and porous structures are emerging at the crossover of the crystallization modes. The proposed branching mechanism differs essentially from dendritic fingering driven by diffusive instability.This work has been supported by the EU FP7 Collaborative Project ENSEMBLE under Grant Agreement NMP4-SL-2008-213669 and by the Hungarian Academy of Sciences under Contract No. OTKA-K-62588

Kondo screening cloud in a one dimensional wire: Numerical renormalization group study

We study the Kondo model --a magnetic impurity coupled to a one dimensional wire via exchange coupling-- by using Wilson's numerical renormalization group (NRG) technique. By applying an approach similar to which was used to compute the two impurity problem we managed to improve the bad spatial resolution of the numerical renormalization group method. In this way we have calculated the impurity spin - conduction electron spin correlation function which is a measure of the Kondo compensation cloud whose existence has been a long standing problem in solid state physics. We also present results on the temperature dependence of the Kondo correlations.Comment: published versio

Interior- and Surface-Bound Excess Electron States in Large Water Cluster Anions

We present the results of mixed quantum/classical simulations on relaxed thermal nanoscale water cluster anions,(H_2O)^-_n, with n=200, 500, 1000 and 8000. By using initial equilibration with constraints, we investigate stable/metastable negatively charged water clusters with both surface-bound and interior-bound excess electron states. Characterization of these states is performed in terms of geometrical parameters, energetics, and optical absorption spectroscopy of the clusters. The calculations provide data characterizing these states in the gap between previously published calculations, and experiments, on smaller clusters and the limiting cases of either an excess electron in bulk water, or an excess electron at an infinite water/air interface. The present results are in general agreement with previous simulations and provide a consistent picture of the evolution of the physical properties of water cluster anions with size over the entire size range, including results for vertical detachment energies and absorption spectra that would signify their presence. In particular, the difference in size dependence between surface-bound and interior-bound state absorption spectra is dramatic, while for detachment energies the dependence is qualitatively the same

Excess Electron Relaxation Dynamics at Water/Air Interfaces

We have performed mixed quantum-classical molecular dynamics simulations of the relaxation of a ground state excess electron at interfaces of different phases of water with air. The investigated systems included ambient water/air, supercooled water/air, Ih ice/air and an amorphous solid water/air interfaces. The present work explores the possible connections of the examined interfacial systems to finite size cluster anions, and the three-dimensional infinite, fully hydrated electron. Localization site analyses indicate that in the absence of nuclear relaxation the electron localizes in a shallow potential trap on the interface in all examined systems in a diffuse, surface-bound (SB) state. With relaxation, the weakly bound electron undergoes an ultrafast localization and stabilization on the surface with the concomitant collapse of its radius. In the case of the ambient liquid interface the electron slowly (on the 10 ps timescale) diffuses into the bulk to form an interior-bound (IB) state. In each other case, the excess electron persists on the interface in surface-bound (SB) states. The relaxation dynamics occur through distinct SB structures which are easily distinguishable by their energetics, geometries, and interactions with the surrounding water bath. The systems exhibiting the most stable SB excess electron states (supercooled water/air and Ih ice/air interfaces) are identified by their characteristic hydrogen-bonding motifs which are found to contain double acceptor type water molecules in the close vicinity of the electron. These surface states correlate reasonably with those extrapolated to infinite size from simulated water cluster anions

Is Quantum Mechanics Compatible with a Deterministic Universe? Two Interpretations of Quantum Probabilities

Two problems will be considered: the question of hidden parameters and the problem of Kolmogorovity of quantum probabilities. Both of them will be analyzed from the point of view of two distinct understandings of quantum mechanical probabilities. Our analysis will be focused, as a particular example, on the Aspect-type EPR experiment. It will be shown that the quantum mechanical probabilities appearing in this experiment can be consistently understood as conditional probabilities without any paradoxical consequences. Therefore, nothing implies in the Aspect experiment that quantum theory is incompatible with a deterministic universe.Comment: REVISED VERSION! ONLY SMALL CHANGES IN THE TEXT! compressed and uuencoded postscript, a uuencoded version of a demo program file (epr.exe for DOS) is attached as a "Figure