On Reciprocal Equivalence of Stäckel Systems

In this paper we investigate Stäckel transforms between different classes of parameter‐dependent Stäckel separable systems of the same dimension. We show that the set of all Stäckel systems of the same dimension splits to equivalence classes so that all members within the same class can be connected by a single Stäckel transform. We also give an explicit formula relating solutions of two Stäckel‐related systems. These results show in particular that any two geodesic Stäckel systems are Stäckel equivalent in the sense that it is possible to transform one into another by a single Stäckel transform. We also simplify proofs of some known statements about multiparameter Stäckel transform.     

Optimal design of bars under nonuniform tension with respect to mixed creep rupture time

The first attempt of finding of optimal shape for bars in presence of body forces with respect to mixed creep rupture is made. For given volume of the bar, distribution of initial cross-section, ensuring the longest life-time to mixed rupture is sought. The finite strain theory and physical law in form of Norton's law generalized for true stresses and logarithmic strains are applied. Using the method of parametric optimization, the best of linear and quadratic functions describing the initial shape of the bar are found. The shape of initial strength is corrected in a way leading to longer life-time. Results of both approaches are compared.     

The influence of electron–phonon interaction on the OSL decay curve shape

The significance of the electron–phonon interaction for optically stimulated luminescence (OSL) process in quartz is demonstrated. OSL variation with temperature has been investigated for four samples of natural quartz. Changes of the OSL decay rate have been observed for all components of the OSL signal. The scale and tendency of these changes are comparable with outcomes of computer simulations carried out for the model composed of two deep electron traps, one shallow trap and one recombination centre, taking into account the electron–phonon interactions.     

Thermal,Raman and dielectric study of 0.5K0.5Bi0.5TiO3–0.5PbTiO3 ceramics

The 0.5K_0.5Bi_0.5TiO₃–0.5PbTiO₃ ceramics were prepared by following a standard solid-state method. The Raman, thermal and dielectric properties of these ceramics were investigated. The X-ray measurements showed that samples have single perovskite-type structure with tetragonal symmetry. Dielectric study revealed that the dielectric behaviour of the investigated ceramics is rather of normal ferroelectrics with large thermal hysteresis. The transition temperature observed by means of differential scanning calorimetry measurements is in good agreement with that obtained from dielectric study.     

Quinazoline Antifolate Thymidylate Synthase Inhibitors: Replacement of Glutamic Acid by Aminophosphonic Acids

The synthesis of six analogues of the potent thymidylate synthase (TS) inhibitor N -[4-[ N -[(3,4-dihydro-2-methyl-4-oxo-6-quinazolinoyl)-methyl]- N -prop-2-ynylamino]benzoyl]- L -glutamic acid 2 is described in which the glutamic acid residue has been replaced by DL -aminophosphonic acids. New antifolates were tested as inhibitors of TS isolated from mouse L1210 leukemic cells as well as inhibitors of growth mouse leukemic L5178Y cells. In general these modifications result in compounds that are considerably less potent than 2 as TS inhibitors with K i 's 0.17-1.10 w M. Very poor solubility in water limited their proper assay of growth cells inhibition.     

Mechanistic and Synthetic Aspects of Atom Transfer Radical Polymerization

Abstract

Mechanistic and synthetic aspects of atom transfer radical polymerization (ATRP) are reviewed. This controlled/“living” system polymerizes many monomers including styrenes, (meth)acrylates, acrylonitrile and dienes. The halogen end groups can be converted to other functional groups such as amines and azides. In addition to producing well-defined linear homopolymers, statistical copolymers, block copolymers, and gradient copolymers, ATRP can be used to synthesize graft and hyperbranched copolymers through copolymerization with functionalized monomers. Selection of appropriate conditions for ATRP depends on targeted molecular weight and degree of polymer chain end-functionality and includes considering the monomer(s) to be polymerized, initiator structure/reactivity, amount of catalyst/deactivator used, halogen end-group used, and temperature.     

The effect of carbon nanotubes on epoxy matrix nanocomposites

The paper concerns thermal properties of epoxy/nanotubes composites for aircraft application. In this work, influence of carbon nanotubes on thermal stability, thermal conductivity, and crosslinking density of epoxy matrix was determined. Three kinds of nanotubes were used: non-modified with 1- and 1.5-μm length, and 1-μm length modified with amino groups. Scanning electron microscopy observations were done for examining dispersion of nanotubes in the epoxy matrix. Glass transition temperature (T _g) was readout from differential scanning calorimetry. From dynamic mechanical analysis, crosslinking density was calculated for epoxy and its composites. Also, thermogravimetric analysis was done to determine influence of nanotubes addition on thermal stability and decomposition process of composites. Activation energy was calculated from TGA curves by Flynn–Wall–Ozawa method. Thermal diffusivity was also measured. SEM images proved the uniform dispersion of carbon nanotubes without any agglomerates. It was found that nanotubes modified with amino groups lead to the increase of epoxy matrix crosslinking density. The significant increase in T _g was also observed. On the other hand, addition of carbon nanotubes leads to the decrease of thermal stability of polymer due to the increase of thermal diffusivity.