Neighbouring group participation in formation of condensed azines. Formation of pyrazolo(3,4-b)pyrazines,isoxazolo(4,5-b)pyrazines and isothiazolo(5,4-b)pyridine

Pyrazine- and pyridinecarboxamidoximes with an amino, potentially tautomeric hydroxy or mercapto group inortho position could be transformed in the appropriate condensed azines. In this manner, representatives of pyrazolo(3,4-b)pyrazine, isoxazolo(4,5-b)pyrazine and isothiazolo(5,4-b)pyridine ring system were synthesized and some transformations investigated.Presented in part at the 8th International Congress of Heterocyclic Chemistry, Graz, 1981.     

Defect Analysis of Ionically Compensated Quadruple and Quintuple Perovskite Layered Cuprates with Ti Blocking Layers

This work presents a modified defect model for pure and chemically substituted quadruple and quintuple pure perovskite layered cuprates, using data from the Jonker (thermopower vs ln conductivity) and Brouwer (log conductivity vs log pO₂) analyses. The closely matched in-plane bond lengths of the blocking and the active layers in these structures promote ionic compensation rather than electronic compensation upon aliovalent p-type doping. A comprehensive defect model that takes into account all the major defect species in an ionically compensated quadruple or quintuple perovskite provides a better means for understanding the electrical behavior of these novel materials. The presented model allows for the calculation of effective dopant and the oxygen interstitial concentrations in these materials.     

A high statistics measurement of the Lambda(+)(c) lifetime

A high statistics measurement of the Lambda(+)(c) lifetime from the Fermilab fixed-target FOCUS photoproduction experiment is presented. We describe the analysis technique with particular attention to the determination of the systematic uncertainty. The measured value of 204.6 +/- 3.4 (stat) +/- 2.5 (syst) fs from 8034 +/- 122 Lambda(+)(c)-->pK(-)pi(+) decays represents a significant improvement over the present world average.     

Dynamic aspects of phase decomposition in reactive blends of polycarbonate and syndiotactic polymethyl methacrylate

Dynamics of phase separation in bisphenol-A polycarbonate (PC)/syndiotactic polymethyl methacrylate (sPMMA) blends has been investigated by means of time-resolved light scattering. Solvent-cast films of the PC/sPMMA blends were transparent, suggestive of miscible character. Several temperature jumps were carried out at a 50/50 PC/sPMMA composition from a homogeneous state (room temperature) into a two-phase regime. The process of phase separation first occurred for some considerable period, then it was followed by phase dissolution driven by chemical reaction. The thermodegradative reaction of sPMMA triggered the dissolution process by probably forming PC/sPMMA graft or random copolymers at the interface, which eventually resulted in a single phase. However, annealing at elevated temperatures for an extended period could lead to cross-linking, and thus a two-phase structure could be fixed permanently. The early stage of spinodal decomposition was interpreted in terms of the linearized Cahn-Hilliard theory. In the late stages of spinodal decomposition, the relationship between scattering peak wavenumber and time was found to obey a power law, but the exponents showed a strong dependence on temperature jumps. The temporal universal scaling failed due to the influence of the chemical reaction. © 1995 John Wiley & Sons, Inc.     

A new device for in-situ movement detection and measurement

A new device for movement detection in joints is designed using the moiré technique. Archimedean spiral grids are used. A space displacement may be evaluated in two planes by vectors of known magnitudes and directions. An extremely simple design is proposed to provide stability for the system being installedin situ over long periods of time.     

A one-dimensional statistical model of friction in deeply inelastic heavy ion collisions

We use the semiclassical approximation for the relative motion (which is simplified and taken to be one-dimensional), neglect other collective degrees of freedom, and describe the coupling between relative motion and intrinsic degrees of freedom by a random-matrix model. This leads to an explicit expression for the friction coefficient. Numerical calculations show qualitative agreement with the data.     

A facile access to α-phenylselenenyl carbonyl compounds by electrochemical oxidation

A novel α-phenylselenenylation of carbonyl compounds has been performed by electrolysis of a solution of ketones, diphenyl diselenide, tetraethylammonium bromide, and magnesium bromide in polar solvents (MeOH, AcOH, MeCN). The electrolysis enables us to prepare the desired seleno-carbonyl compounds without employing strong bases and the activated selenenyl reagents PhSeX.     

Coherent structures in subsonic coaxial jets

This paper describes a detailed study of the initial region of coaxial jets and the large scale coherent structures within this region. The coaxial jets investigated have an area ratio of 2·67 and were run at three different velocity ratios. A simple model in terms of two arrays of vortex-rings in the mixing region of the coaxial jet is proposed, and its use verified by comparisons with experimental results. Overall and spectral results of hot wire and microphone signals, obtained in the flow, support the model proposed. Evidence supporting the concept of a preferred mode, which governs the growth or decay of the vortices in the intermediate zone, is also presented.