Showing papers by "Wrocław University of Technology published in 1995"

Asymptotic distributions of continuous-time random walks: A probabilistic approach

Abstract: We provide a systematic analysis of the possible asymptotic distributions o one-dimensional continuous-time random walks (CTRWs) by applying the limit theorems of probability theory. Biased and unbiased walks of coupled and decoupled memory are considered. In contrast to previous work concerning decoupled memory and Levy walks, we deal also with arbitrary coupled memory and with jump densities asymmetric about its mean, obtaining asymmetric Levy-stable limits. Suprisingly, it is found that in most cases coupled memory has no essential influence on the form of the limiting distribution. We discuss interesting properties of walks with an infinite mean waiting time between successive jumps.

Computer simulation of Lévy α-stable variables and processes

Abstract: The aim of this paper is to demonstrate how the appropriate numerical, statistical and computer techniques can be successfully applied to the modeling of some physical systems. We propose to use a fast and accurate method of computer generation of Levy α-stable random variates.

Herbicidal activity of phosphonic, phosphinic, and phosphonous acid analogues of phenylglycine and phenylalanine

Abstract: A series of phosphonic, phosphinic, and phosphonous acid analogues of phenylglycine and phenylalanine was synthesized and tested as herbicides against Lepidium sativum and Cucumis sativus. Aminobenzylphosphonic acids exhibited notable herbicidal activity and thus represent a group of the most active herbicides found among aminophosphonic acids.

Coupled‐Cluster approaches with an approximate account of triply and quadruply excited clusters: Implementation of the orthogonally spin‐adapted CCD + ST(CCD), CCSD + T(CCSD), and ACPQ + ST(ACPQ) formalisms

Abstract: The orthogonally spin-adapted (OSA) coupled-pair (CCD) methods with an approximate account of triply and quadruply excited clusters are considered. We focus on the CCD + ST(CCD) perturbative estimate of the singly and triply excited clusters due to Raghavachari [J. Chem. Phys. 82, 4607 (1985)] and its ACPQ + ST(ACPQ) analog proposed by Paldus and Piecuch [Int. J. Quantum Chem. 42, 135 (1992)]. The latter approach combines the perturbative treatment of singles and triples with an approximate CCD theory corrected for connected quadruply excited clusters (ACPQ). We also consider the OSA version of the CCSD + T(CCSD) method (coupled-cluster [CC] approach with singly and doubly excited clusters and noniterative perturbative account of triply excited clusters) introduced by Urban et al. {J. Chem. Phys. 83, 4041 (1985)}. The explicit OSA expressions for the previously neglected {P. Piecuch and J. Paldus, Theor. Chim. Acta 78, 65 (1990)} S(CCD) and S(ACPQ) terms are derived using diagrammatic methods of many-body perturbation theory and graphical methods of spin algebras. The CCD + ST(CCD), CCSD + T(CCSD), and ACPQ + ST(ACPQ) formalisms have been implemented and the general purpose ab initio programs have been written using a newly developed procedure for improving the convergence of the reduced linear equation method {P. Piecuch and L. Adamowicz, J. Chem. Phys. 100, 5857 (1994)}. Results of the pilot calculations for few nondegenerate and quasi-degenerate systems are presented and compared with the full configuration interaction data. © 1995 John Wiley & Sons, Inc.

Storage stabilization of enzyme activity by poly(ethyleneimine)

Abstract: The effect of mixing penicillin acylase with poly(ethyleneimine) is discussed. The properties of the polymer-enzyme system were evaluated for a wide range of enzyme concentrations (0.3–45.5 mg/cm3) and poly(ethyleneimine) concentrations (0.0001–10% wt). It was shown that addition of poly(ethyleneimine) to crude enzyme preparation caused precipitation of ballast protein and stabilization of the enzyme fraction remaining in the supernatant. The soluble fraction had stable activity for 21 days storage at 37 °C while the native enzyme lost about 80% of its initial activity. Additionally, it was ascertained that the polymer very slightly affected the properties of penicillin acylase in the PEI-enzyme preparations. Finally, possible ways of using the polymer-enzyme preparations in a membrane reactor are suggested.

Sites of copper binding in Streptomyces pilosus

Abstract: Copper abstraction from aqueous solutions by Streptomyces pilosus was studied. Comparison of the amount of metal accumulated by living and killed cells as well as by isolated cell wall preparations, indicated that the cell interiors of the organism play an important role in the Cu (II) ions biosorption process. This was confirmed by electron microscope and EPR examinations. The EPR spectra showed that accumulated copper formed complexes with CuO4 and CuO2N2 or CuO3N chromophores. These complexes were found in the whole cells (live and dead). However, in the case of isolated cell walls, the complex with CuCuO2N2 or CuO3N chromophore was absent.

On the reversibility of hydroxyphosphonate formation in the kabachnik-fields reaction

Abstract: The reversibility of hydroxyphosphonate synthesis in the Kabachnik-Fields synthesis was studied. It was found that in all studies cases which included aliphatic and aromatic aldehydes or ketones the hydroxyphosphonates decompose to the starting ketone and dialkyl phosphite in the presence of aliphatic amines as determined by 1H-, 13C-, 31P-NMR.

An efficient synthesis of 1-aminophosphonic acids and esters bearing heterocyclic moiety

Abstract: New α-aminophosphonic esters and acids derived from furan, thiophene and pyrazole were prepared in high yield, in the reactions of benzylamine, benzhydrylaraine or benzyl carbamate with heterocyclic aldehydes and diethyl or diphenyl phosphonates. The protecting groups at amine (benzyl or benzhydryl) were removed by hydrogenolysis or hydrolysis, respectively. The N-benzyloxycarbonyl (Z-group) was removed by treatment with 45% HBr in acetic acid.

Sulfonated polysulfone membranes with antifouling activity

Abstract: The protein fouling phenomenon was investigated on modified polysulfone ultrafiltration membranes. The sulfonation degree was correlated to the extent of deposition of bovine serum albumin. It was shown that membranes prepared from modified polysulfone were less fouled than their off-charge analogues. The fouling phenomenon was also investigated for membranes prepared from co-cast blends. It was demonstrated that blends containing more than 50 wt.-% of sulfonated derivative behaved like a membrane from pure sulfonated polysulfone. The effect was attributed to surface separation of polymers and formation of surfaces enriched with sulfonic groups.

Photoreflectance characterisation of GaAs and GaAs/GaAIAs structures grown by MOCVD

Abstract: Epitaxial undoped and doped (Si and Zn) GaAs and GaAIAs layers as well as heterostructures of GaAs/GaAIAs have been grown in an atmospheric pressure, vertical MOCVD system. Room temperature photoreflectance (PR) has been applied to characterise the layers and heterostructures as well as multiple quantum wells. The surface- and interface-related PR has been studied by application of Kramers–Kronig analysis. A decomposition of the PR spectrum into spectra connected with the surface region and with the interface has been proposed.

A criterion for Toeplitz flows to be topologically isomorphic and applications

Abstract: A dynamical system is said to be coalescent if its only endomorphisms are automorphisms. The question whether there exist coalescent ergodic dynamical systems with positive entropy has not been solved so far and it seems to be difficult. The analogous problem in topological dynamics has been solved by Walters ([W]). His example, however, is not minimal. In [B-K2], a class of strictly ergodic (hence minimal) Toeplitz flows is presented, which have positive entropy and trivial topological centralizers (the last condition implies coalescence). The entropy, however, is only estimated from below. Also the class is obtained in a not completely constructive way. The basic idea of this paper is contained in Section 2, in a criterion which describes homomorphisms (isomorphisms) between Toeplitz flows in terms of a block code simplified to a function sending blocks of a given length to blocks of the same length. This idea is then applied in Section 3 to effectively construct an uncountable family of pairwise nonisomorphic Toeplitz flows with topological entropy equal to a common arbitrarily preset value. Furthermore, all the Toeplitz flows have the same maximal uniformly continuous factor. In Section 4 we obtain conditions sufficient for coalescence of a Toeplitz flow. In particular, all Toeplitz flows of Section 3 turn out to be coalescent. We are grateful to Professor P. Liardet for several helpful conversations and valuable remarks.

Influence of additional ligands on the two-phase epoxidation with sodium hypochlorite catalyzed by (salen)managanese(III) complexes

Abstract: The two-phase epoxidation of olefins with sodium hypochlorite catalyzed by the salen-type Mn(III) complex 1 was examined in the presence of various additional ligands and 4-dodecyloxypyridine 1-oxide (3) was found as the most effective one. The system 1–3 was studied by conductometry and UV-Vis spectra. The results support the hypothesis that the disproportionation of the dimeric μ-oxo Mn(IV) complex producing an active oxidant is strongly favoured by the presence of 3.