Magnetic properties of ZnFe2O4 nanoparticles

Fine particles of ZnFe₂O₄ were synthesized by a wet chemical method in the (80 wt.% Fe₂O₃ + 20 wt.% ZnO) system. The morphological and structural properties of the mixed system were investigated by scanning electron microscopy, X-ray diffraction, inductively coupled plasma atomic emission, and X-ray photoelectron spectroscopy. The major phase was determined to be the ZnFe₂O₄ spinel with particle size of 11 nm. The magnetic properties of the material were investigated by ferromagnetic resonance (FMR) in the temperature range from liquid helium to room temperature. A very intense, asymmetric FMR signal from ZnFe₂O₄ nanoparticles was recorded, which has been analyzed in terms of two Callen-lineshape lines. Temperature dependence of the FMR parameters was obtained from fitting the experimental lines with two component lines. Analysis of the FMR spectra in terms of two separate components indicates the presence of strongly anisotropic magnetic interactions.     

C-Acylation of Electron-Excess Heterocycles by Isocyanatophosphoric Acid Dichlorides

Abstract

Isocyanatophosphoric acid dichlondes was used for introduction of phosphorus-containing groups at electron-excess heterocycles. Hetaryl containing dichlorophosphates, convenient starting material for synthesis for wide set of derivatives, were prepared by C-acylation with this reagent.     

Determination of thallium and lead in cadmium salts by anodic stripping voltammetry with addition of surfactants to suppress the cadmium peaks

Conditions have been found which make possible the determination of thallium and/or lead in cadmium and its salts without preliminary separation. The electrochemical activity of the cadmium, which usually interferes in the determination of thallium, is inhibited by the addition of 0.01% of polyethylene glycol of M.W. 4000. Thallium is determined by electrolysis at ?0.74 V vs. SCE, in 0.1M EDTA solution: 10^?1M thallium can be determined in the presence of 0.1M cadmium, while copper and lead at 10^?2M and 10^?5M respectively do not interfere. Lead is determined in 0.1M acetic acid containing 0.1% cetyltrimethylammonium bromide (CTAB). The addition of CTAB shifts the cadmium peak, as well as the optimum deposition potential for cadmium, to more negative values, making it possible to determine lead in the presence of cadmium as long as the deposition potential lies in the range between ?0.50 and ?0.56 V vs. SCE. Lead can be determined in the presence of ten times as much thallium.     

The acid-catalysed reaction of thiols with alkyl 2,3-dideoxy-glyc-2-enopyranosides or glycals

The acid-catalysed (HCl or SnCl₄) reaction of alkyl 2,3 dideoxy-glyc-2-enopyranosides or 3,4,6-tri-O-acetyl-D-glycals with thiols leads to mixtures of alkyl 2,3-dideoxy-1-thio-glyc-2-enopyranosides and 3-S-alkyl-3-thioglycals. Under equilibrium conditions the latter are the preponderant products of the reaction. Cross experiments have confirmed the intermediacy of the allylic carbocation in the reaction. A rationalization of the substitution reactions of 1,2- and 2,3-unsaturated sugars based on HSAB principle has been proposed.     

Periodic solutions of nonlinear hyperbolic evolution systems

We shall deal with the periodic problem for nonlinear perturbations of abstract hyperbolic evolution equations generating an evolution system of contractions. We prove an averaging principle for the translation operator associated with the nonlinear evolution system, expressed in terms of the topological degree. The abstract results shall be applied to the damped hyperbolic partial differential equation.     

On the exponential exponents of discrete linear systems

In this paper we introduce the concepts of exponential exponents of discrete linear time varying systems. It is shown that these exponents describe the possible changes in the Lyapunov exponents under perturbation decreasing at infinity at exponential rate. Finally we present formulas for the exponential exponents in terms of the transition matrix of the system.     

Anomalous diffusion approach to dielectric spectroscopy data with independent low- and high-frequency exponents

We advance a perspective outcome of tempered α-stable processes used in modeling of anomalous diffusion, a physical mechanism underlying the non-Debye relaxations. The tempered processes are characterized by a heavy tail truncation in time and have finite moments, but they also save some useful features of a purely skewed α-stable process. Due to these features, the relaxation phenomena get a transient character being shown in their asymptotic behavior. From the stochastic subordination scenario of the tempered anomalous diffusion we derive relaxation functions with independent low- and high-frequency exponents falling in the range (0, 1]. Those functions can be used to model all types of experimentally observed two-power-law relaxation patterns.     

A census of semisymmetric cubic graphs on up to 768 vertices

A list is given of all semisymmetric (edge- but not vertex-transitive) connected finite cubic graphs of order up to 768. This list was determined by the authors using Goldschmidt's classification of finite primitive amalgams of index (3,3), and a computer algorithm for finding all normal subgroups of up to a given index in a finitely-presented group. The list includes several previously undiscovered graphs. For each graph in the list, a significant amount of information is provided, including its girth and diameter, the order of its automorphism group, the order and structure of a minimal edge-transitive group of automorphisms, its Goldschmidt type, stabiliser partitions, and other details about its quotients and covers. A summary of all known infinite families of semisymmetric cubic graphs is also given, together with explicit rules for their construction, and members of the list are identified with these. The special case of those graphs having K_1,3 as a normal quotient is investigated in detail. Supported in part by N.Z. Marsden Fund (grant no. UOA 124) and N.Z. Centres of Research Excellence Fund (grant no. UOA 201) Supported in part by “Ministrstvo za šolstvo, znanost in šport Slovenije”, research program no. 101-506. Supported in part by research projects no. Z1-4186-0101 and no. Z1-3124-0101. The fourth author would like to thank the University of Auckland for hospitality during his visit there in 2003.