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.     

Oscillatory behavior of interface exchange coupling caused by finite caps of variable thickness

The effect of non-magnetic cap-layers on the periods and the amplitudes of the oscillations of interlayer exchange coupling (IEC) is studied theoretically using an ab initio spin-polarized surface Green function technique within a tight-binding linear muffin-tin orbital method and the Lloyd formulation of the IEC. Applications are made to the free-electron like model as well as to Co/Cu/Co (0 0 1) trilayers with a cap interfacing vacuum through the dipole barrier. The results are analyzed in terms of a discrete two-dimensional Fourier transformation which confirms a pronounced oscillatory behavior of the IEC with respect to the thickness of the cap- and the spacer-layers. The results are in agreement with available experimental data as well as with predictions of the electron confinement model of the IEC.     

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.     

Fracture behaviour of single crystal silicon microstructures

The fracture behaviour of single crystal silicon (SCSi) microstructures is analysed based on microme-chanical torsional and tensile experiments. The uniaxial testpieces are characterised by the presence of sharp not-ches at the gauge length extremities. The critical loading conditions are reproduced in a finite element model in order to identify the analogies of the failure conditions in tension and torsion. The stress field in the vicinity of the notch tip (were cracks originate) is analyzed, and fracture mechanics parameters are determined. In the finite element model a crack, reproducing the failure process observed in the experiments, is included. The crack area is incrementally increased and the energy release rate for the critical loading conditions in tension and torsion is calculated. Based on these results a failure criterion is formulated along with a procedure for the mechanical integrity analysis of SCSi microstructures of arbitrary shape and loading conditions.