Spectroscopic Evidences for the Hyperconjugative Interaction in 2-Bromosubstituted Acetophenones

Several 2-bromo-4′-substituted acetophenomes were investigated by vibrational and electronic spectroscopies. The solvent effect on the bands assigned to μ_CO and μ_C-Br together with the comparison between the fundamental and overtone μ_CO frequencies indicate a cis/gauche rotational isomerism. The progressive.     

The gelation of PVC: Characterization and control

Poly(vinyl chloride), PVC, can be gelled from 10% (w/w) solutions in a number of solvents so as to give model networks where the junctions are directly accessible by crystallographic techniques, and where the extent and properties of the network can be correlated with the nature of these junctions. The resulting network structure has been studied as a function of polymer crystallinity and polymer-solvent interaction, and a correlation between gel-forming ability and solubility parameters was found. As in previous and accompanying work [1, 2], the gel system was found to consist of two crystal populations, the gel-forming micellar (B) and the better-developed, presumably lamellar (A) crystals incorporated in the gel. The thermal behavior of wet and dried gels was followed by DSC and by high-temperature x-ray diffraction, in the course of which the distinctness of the two crystal classes became apparent also as regards thermal stability.

The gelation behavior of PVC is discussed in the wider perspective of polymer crystallization and in relation to plasticization and the stereochemistry of PVC. The explicit connections between industrial plasticization and the present gelation behavior are being pointed out, hopefully with benefit for the understanding and control of the former. The crystallization effects themselves raise further questions as regards the necessity of long syndiotactic runs in the chain (as opposed to the usually envisaged random distribution of stereoisomers) or alternatively the incorporation of substantial amounts of isomeric defects into the syndiotactic lattice. Arguments for and against these obviously fundamental alternatives are invoked.     

Singular Optimal Control for a Transport-Diffusion Equation

In this paper we consider a transport-diffusion equation with coefficient of diffusion ε > 0 small and coefficient of transport M(x, t). We study the asymptotic behavior of the cost of the null controllability of such a system when ε 0⁺.

If at least one trajectory associated to M(x, t) does not enter the control zone, we prove that this cost explodes exponentially as ε 0⁺. On the other hand, as long as trajectories reach the control region and the controllability time is sufficiently large, we prove that the cost is bounded as ε 0⁺, and moreover decays exponentially as ε 0⁺ as soon as all trajectories cross the boundary.     

Improved resolution in the acidic and basic region of 2‐DE of insect antennae proteins using hydroxyethyl disulfide

Olfaction is essential for processing chemical signals in insects, but characterizing the proteins implicated in this process has proved challenging. We optimized 2‐DE gel resolution of insect proteins by using a buffer containing two reducing agents, DTT and hydroxyethyl disulfide. This buffer clearly improved resolution and decreased spot streaking and spot trains of 2‐DE in comparison to DTT alone. We described for the first time that the buffer with DTT and hydroxyethyl disulfide further to reducing streaking in the basic part of the gel eliminates false spots in the acidic gel regions that appeared when only DTT was used as reducing agent.     

SIMS-Tiefenverteilungsanalyse in Nichtleitern mit hoher Massenaufl?sung: P in SiO2/Si

Summary The problems of SIMS-distribution analysis in insulators are discussed for P in the system SiO₂/Si. Quantitative depth profiles are measured by the use of autocontrolled adjustment of the magnetic analyzer and the accelerating voltage of the secondary ions and bombardment with electrons during measurement.     

Study of crystal texture in pvc gels by x-ray diffraction and infrared dichroism

An enquiry is presented into the nature and origin of thermoreversible gelation of poly(vinyl chloride) (PVC). In line with a previous paper it is demonstrated by direct x-ray diffraction evidence that the origin of the gelation is crystallization, and that this crystallinity can be conspicuously apparent even for the usual technological polymer. In addition some unusual diffraction effects become apparent such as do not obviously follow from existing notions of the PVC structure. Combined infrared dichroism and x-ray studies revealed that these new effects are attributable to a two-component nature of the crystallinity where the components are distinguished by their orientation behavior, lateral extension, and possibly morphology of the crystallites. Some of the crystals orient with their a axes (type A crystals) and some with their c axes (type B crystals) along the stretch direction. Other more complex orientability differences are also manifest during film formation. Crystals B are smaller, and are believed to correspond to the network forming junctions, hence to fringed micellar crystals. Crystals A have a less evident connection with the network and are hypothesized to be of lamellar character, the behavior of which is closely simulated by lamellar crystal additives (stabilizer crystals). High-temperature x-ray work revealed no melting of crystals even in the temperature range where endotherms appear in the thermograms.     

Integral transform solution for the lid-driven cavity flow problem in streamfunction-only formulation

The basic ideas in the generalized integral transform technique are further advanced to allow for the hybrid numerical-analytical solution of the two-dimensional steady Navier-Stokes equations in streamfunction-only formulation. The classical lid-driven square cavity problem is selected for illustration of the approach. The corresponding biharmonic-type non-linear partial differential equation for the streamfunction is integral transformed in one of the co-ordinates and an infinite system of coupled non-linear ODEs for the transformed potential results in the other independent variable. Upon truncation to an appropriate finite order, the ODE system is numerically solved by well-established algorithms with automatic error control devices. The convergence behaviour of the eigenfunction expansion is demonstrated and reference results are provided for typical values of Reynolds number.     

The effect of electrostatic interactions on hot electron transport in n-GaAs

Hot electron transport in bulk n-GaAs is investigated in a three dimensional numerical simulation. An emphasis is placed on understanding the effect of the electrostatic interaction and, in particular, that of the ionized impurity scattering on drift velocity vs electric field characteristics. In order to account for the spatial correlations between electrons and scattering centers, the numerical model combines molecular dynamics and Monte Carlo techniques. A major result is that the impurities enhance the drift velocity of hot electrons. This emphasizes the inappropriateness of the concept of a phenomenological mean free flight time when the interaction potential is long range. An explanation of the effect is proposed which applies to a general multi-valley semiconductor; and the model is compared to the traditional Brooks-Herring treatment of electron-ionized impurity scattering.     

L?sungspolymerisation von 1,3,5-Trioxan und 1,3,5,7-Tetroxocan. 1. Mitt. Polymerisationsgeschwindigkeit, Charakterisierung und Schmelzverhalten des so erhaltenen Polyoxymethylens

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