Approximating curves and their offsets using biarcs and Pythagorean hodograph quintics

This paper compares two techniques for the approximation of the offsets to a given planar curve. The two methods are based on approximate conversion of the planar curve into circular splines and Pythagorean hodograph (PH) splines, respectively. The circular splines are obtained using a novel variant of biarc interpolation, while the PH splines are constructed via Hermite interpolation of C¹ boundary data.We analyze the approximation order of both conversion procedures. As a new result, the C¹ Hermite interpolation with PH quintics is shown to have approximation order 4 with respect to the original curve, and 3 with respect to its offsets. In addition, we study the resulting data volume, both for the original curve and for its offsets. It is shown that PH splines outperform the circular splines for increasing accuracy, due to the higher approximation order.     

Stabilization of New Phases in Ion-Conducting Nanocomposites

Physical properies of ion-conducting nanocomposites are reviewed. Special attention is paid to the change of the bulk characteristics of ionic salts in the nanocomposites due to the formation of the interface phases. The main thermodynamic reason of the formation of the nanocomposite as well as the stabilization of the interface phases is the adhesion energy _a. At sufficiently high _a values, the ionic salt tends to spread along the oxide surface, which leads to the formation of the nanocomposite on sintering. The adhesion is the result of the interface interaction and incorporates the stage of the specific adsorption of the interface ions. It leads to the formation of the double layer formed by the point defects in the interface region of the ionic salt. In the case of the strong adhesion, the structural reconstruction or the formation of the metastable interface phase takes place. Analysis of the experimental data shows that interface phases exist in composites AgI–Al₂O₃, MeNO₃–Al₂O₃ (Me = Li, Na, K, Rb, and Cs), CsHSO₄–SiO₂, RbNO₃–SiO₂ and CsCl–Al₂O₃. Their structure may be either epitaxial crystalline, or amorphous. The thickness of the interface phase as estimated on the basis of the brick-wall model is about 3–4 nm.     

Spectroscopic characterization of 1,5-diphenyl-3,7-dihydroxy-1,5-diazacyclooctane — (8C ring compound) formed in N,N-diglycidylanaline/aniline curing systems

Summary A NMR and infrared analysis of the cyclic product formed by the reaction of N,N-diglycidylaniline with aniline confirms the structure of an eight-membered ring (I). The conformational structure of this compound is discussed.     

The crystal structure of the processive endocellulase CelF of Clostridium cellulolyticum in complex with a thiooligosaccharide inhibitor at 2.0 A resolution

The mesophilic bacterium Clostridium cellulolyticum exports multienzyme complexes called cellulosomes to digest cellulose. One of the three major components of the cellulosome is the processive endocellulase CelF. The crystal structure of the catalytic domain of CelF in complex with two molecules of a thiooligosaccharide inhibitor was determined at 2.0 A resolution. This is the first three-dimensional structure to be solved of a member of the family 48 glycosyl hydrolases. The structure consists of an (alpha alpha)6-helix barrel with long loops on the N-terminal side of the inner helices, which form a tunnel, and an open cleft region covering one side of the barrel. One inhibitor molecule is enclosed in the tunnel, the other exposed in the open cleft. The active centre is located in a depression at the junction of the cleft and tunnel regions. Glu55 is the proposed proton donor in the cleavage reaction, while the corresponding base is proposed to be either Glu44 or Asp230. The orientation of the reducing ends of the inhibitor molecules together with the chain translation through the tunnel in the direction of the active centre indicates that CelF cleaves processively cellobiose from the reducing to the non-reducing end of the cellulose chain.     

Influence of oxygen partial pressure and substrate temperature during vapour deposition on the structural properties of CdSe films

CdSe films prepared in vacuum by sublimation from the compound at oxygen partial pressures in the residual atmosphere from 2.8 × 10^?5 to 3.2 × 10^?4 Torr and at substrate temperatures of 295 and 523 K were subjected to X-ray structural analysis. The results obtained are analysed and discussed in terms of some structures different from those of CdSe, e.g. CdSeO₃ and CdSeO₃.SeO₂.     

Chemical oxygen demand of some nitrogenous heterocyclic compounds

Chemical oxygen demands of fourteen nitrogenous compounds were determined by the dichromate method. Only pyridine and its derivatives were resistant to oxidation. Heterocyclic compounds containing one atom of nitrogen in a molecule, e.g. quinoline, pyrrole, proline, and indole were 90–100 per cent oxidized. Nitrogen is split off these compounds as NH₃. Heterocyclic compounds containing two or more atoms of nitrogen in a molecule are also easily oxidized. However, only a part of the nitrogen is split off as NH₃. On the basis of the results obtained it is possible to make the following generalization: nitrogen in amino groups is split off mostly as NH₃; quinoline, pyrrole, pyrrolidine, and indole nitrogen is split off as NH₃; from imidazole and pyrimidine rings, one atom of nitrogen is split off as NH₃ and one as N₂; from the purine configuration, two atoms of nitrogen are split off as NH₃ and two atoms as N₂; from isoalloxazine, three atoms of nitrogen are split off as NH₃ and one as N₂.     

Experimental activation energies for evolution of oxygen and chlorine on oxide electrodes

The chlorine and oxygen overpotential in dependence on the current density i (A cm^?2) and on the temperature in the range of 15–75°C was measured at γ-MnO₂ and β-PbO₂ electrodes in concentrated water solutions of sodium chloride and perchlorate. From the measured values the experimental activation energy in dependence on overpotential was calculated and, for the temperature of 25°C, the constants of Tafel's equation (a,b) (α, i_o respectively) were evaluated.     

The absence of the Isw2p-Itc1p chromatin-remodelling complex induces mating type-specific and Flo11p-independent invasive growth of Saccharomyces cerevisiae

The Isw2p-Itc1p chromatin remodelling complex of Saccharomyces cerevisiae is a member of the ISWI class of ATPases with a nucleosome spacing activity, involved in regulation of expression of a broad spectrum of genes. Its absence causes derepression of a-specific genes and aberrant morphology in alpha-mating type cells. We report here that the deletion of the ISW2 gene in the originally non-invasive BY strain induces mating type-specific invasive growth strongly affected by nitrogen starvation. Although the Flo11 protein was postulated to be critical for haploid invasive growth, we showed that the invasive growth caused by the isw2 and itc1 deletions in alpha-mating type cells was Flo11p-independent. This type of invasive growth was proved to be a consequence of the activation of the pheromone response pathway. Our results suggest that Isw2 and Itc1 proteins do not have the same impact on the described phenomenon.     

Separation of H(2)SO(4) + CuSO(4) mixture by diffusion dialysis

Diffusion dialysis of aqueous solution of H(2)SO(4) + CuSO(4) has been investigated in a two-compartment cell with an anion-exchange membrane Neosepta-AFN. The experiments have proved that sulfuric acid permeates well through the membrane used, while cupric sulfate is efficiently rejected. This operation is very effective at high acid concentrations and low concentrations of cupric sulfate. Furthermore, it has been found that even at the highest concentration of CuSO(4), the rejection coefficient is higher than 0.965. The flux of CuSO(4) calculated from the time dependences of the CuSO(4) concentration is negatively influenced by increasing acid concentration.