Mechanism of stereospecific alcohol elimination from cyclohexane trans-1,3-dicarboxylates under electron impact ionization

Diesters of cyclohexane trans-1,3-dicarboxylic acid give rise to major [M ? ROH]^+·. ions under electron impact ionization. A mass spectral study of the isomeric mixed methyl ethyl esters of the diacid, substituted by a methyl group at position 1 and deuterium labelled at position 3, indicates a stepwise mechanism for this alcohol elimination; the 3-hydrogen (or deuterium) is transferred to the carbonyl of the 1-ester group in the initial step. Subsequent migration of that hydrogen (or deuterium) to the alkoxyl of position 3 results in the highly site- and stereospecific alcohol elimination. CID spectra of the [M ? ROH]^+. ions obtained from the stereoisomeric diesters clearly show that they have different structures (or are different mixtures of structures).     

The effect of configuration of gas phase protonated ethenedicarboxylates on their low energy collision induced dissociation behaviour

Low energy collision induced dissociation (CID) spectra were measured by a triple stage quadrupole mass spectrometer for the [MH]⁺ ions of diethyl and dimethyl esters of maleic, fumaric, citraconic and mesaconic acids. A very high degree of stereospecificity was observed for the geometrically isomeric diethyl esters. The cis esters give rise to very abundant [MH? EtOH]⁺ and [MH? EtOH? C₂H₄]⁺ ions, while the trans isomers exhibit very abundant [MH? C₂H₄]⁺ and [MH? 2 C₂H₄]⁺ ions. The highly stereospecific processes indicate that the double bond configuration is retained in the protonated species under the conditions of the experiment.     

Fusion cross section at sub-Coulomb energies

The effective barrier at low energies is approximated by a Coulomb and parabolic barriers. A simple closed formula is obtained for the total reaction cross section which is the natural extension of Wong's results into the low energy domain. Theoretical predictions of averaged energy behaviour agree fairly well with various experimental results. The relation?ω ₀≧π(2kh ²Z₁Z₂ e ²/μ)^1/2 R ₀ ^?3/2 between the curvature and the extremum point of the nucleus-nucleus potential is suggested, based on low energy fusion experiments. By assuming equality sign, it is possible to extract the parameters of the barrier directly from experiment. Incidentally it is found that?ω ₀ remains persistently arround 4.5 MeV for all the reactions which have been investigated.     

Atrazine degradation by Pseudomonas strain ADP entrapped in sol-gel glass

Sol-gel entrapment was evaluated as a method for immobilization of an atrazine degrading Pseudomonas. It was found that the bacterium lost much of its atrazine degrading activity upon immobilization. However, partial activity could have been restored by amendment of nutrients. Bacteria immobilized using a prehydrolysis technique for the preparation of the sol-gel, retained better activity in comparison to bacteria immobilized using a composite calcium alginate/sol-gel procedure. Further study is underway to improve the activity of sol-gel entrapped bacteria.     

Heavy Traffic Limits for Queues with Many Deterministic Servers

Queueing Systems - Consider a sequence of stationary GI/D/Nqueues indexed by N↑∞, with servers' utilization $1 - \beta /\sqrt N ,\beta &;gt;0$ . For such queues we show that...     

Unifying model for several classes of two-dimensional phase transition

A relatively simple and physically transparent model based on quantum percolation and dephasing is employed to construct a global phase diagram which encodes and unifies the critical physics of the quantum Hall, "two-dimensional metal-insulator," classical percolation and, to some extent, superconductor-insulator transitions. Using real-space renormalization group techniques, crossover functions between critical points are calculated. The critical behavior around each fixed point is analyzed and some experimentally relevant puzzles are addressed.     

Theory of elastic π3He scattering

The pion-three-nucleon system is investigated using coupled Schrödinger equations. The coupling between the four-body (πNNN) and three-body (NNN) systems is explicitly implemented by operators for emission and absorption of the pion by each nucleon. The only simplifying assumption is the separable form for amplitudes pertaining to pure potential scattering. A set of Amado-Lovelace type equations is derived, from which the amplitude for the reaction π + ³He→ π + ³He can be evaluated. The integral equations involve intermediate integration over single relative momenta so that subsequent numerical solution is within reach.