Conformational aspects of segmented poly(ester-urethanes)

Segmented poly(ester-urethanes) containing hard and soft segments, were obtained from aromatic diisocyanates with thiodiglycol or diethylene glycol as chain extenders, and poly(ethylene glycol)adipate usig a multistep polyaddition process. Transition temperatures by differential scanning calorimetry and thermo-optical analysis were employed to characterize polyurethane materials. Changes in the conformation of these polyurethanes were analyzed also, by viscometer measurements in N,N-dimethyl-formamide. The obtained data revealed that the thermal curves are influenced by the soft and hard segment structures in the temperature range studied.     

Nanoscale patterning of functional perovskite-type complex oxides by pulsed laser deposition through a nanostencil

We present studies on parallel nanoscale patterning of piezoelectrics/ferroelectrics via deposition through a nanostencil. Unlike other processes reported for oxide nanostructuring, we selectively deposit the material, directly, by interposing a nanosieve between the substrate and the deposition source. We show that this selective deposition can be realized even with materials as complex as perovskite oxides, both at room temperature and at high temperature. We elaborate on and analyze the performance of the nanostenciling approach for the growth of barium titanate BaTiO₃ on strontium titanate SrTiO₃(1 0 0). The patterned structures of ferroelectric materials are characterized by X-ray diffraction and imaged locally by scanning probe microscopy in piezoresponse mode to individually probe their functionality.     

Defects responsuble for electrical property changes in irradiated oxides

Abstract

A comparison is made between the activation energies for post-irradiation thermal recovery of electrical properties of NiO, Cr₂O₂ and UO₂-SiO₂ which were determined from previously published data, and the activation energies found in the literature for volume diffusion of the component atoms. It is shown that oxygen vacancies are most probably responsible for irradiation-induced changes in electrical properties of NiO and Cr₂O₂. Oxygen defects contribute also to the changes in electrical properties observed at UO₂-SiO₂.     

Green's functions on finite lattices and their connection to the infinite lattice limit

It is shown that the Green's function on a finite lattice in arbitrary space dimension can be obtained from that of an infinite lattice by means of a translation operator. Explicit examples are given for one- and two-dimensional lattices.     

Monotonicity and existence of periodic orbits for projected dynamical systems on Hilbert spaces

We present here results about the existence of periodic orbits for projected dynamical systems (PDS) under Minty-Browder monotonicity conditions. The results are formulated in the general context of a Hilbert space of arbitrary (finite or infinite) dimension. The existence of periodic orbits for such PDS is deduced by means of nonlinear analysis, using a fixed point approach. It is also shown how occurrence of periodic orbits is intimately related to that of critical points (equilibria) of a PDS in certain cases.

     

Dynamics Analysis of Ground Contact Pressure of English Pointer Dogs

In this study force sensing resistors were used to determine thepressure on the central area of each of the weight bearing pads of thefore and hind paws of dogs at the walk. Six adult normal healthy EnglishPointer dogs were used in this project. Pressure data were collected byaffixing a force sensing resistor to the central area of the groundcontact surface of each weight bearing paw pad of the right fore andhind limbs. Pressure signal data from stance phase during walking wereanalyzed. Within paw pads, the pressure graphs were consistent in formand magnitude. Within paws, there were significant pressure differencesamong pads on both fore and hind limbs. The coefficient of restitution,the embedding dimension, and the Lyapunov exponents were calculated. Theability to measure and analyze pressure on individual paw pads providesinsight into soft tissue stresses on the palmar/plantar surface of thepaw. Pressure at a wound site on the pads has a detrimental effect onwound healing and a better understanding these stresses will be ofbenefit when suturing and bandaging pad wounds. Such information isespecially important in athletic and working dogs, e.g. search andrescue dogs.     

Dual‐emissive polydiphenylsilane nanocomposite: effect of N,N′‐bis(4‐hydroxysalicylidene)‐1,2‐phenylenediamine‐Zn complex

The fluorescence properties of polysilane can be strongly influenced by creating new excited states that involve electronic transitions and the relaxation to the ground state. This work presents the optical effects obtained by doping a specially designed polydiphenylsilane copolymer with Zn complex of N,N′‐bis(4‐hydroxysalicylidene)‐1,2‐phenylenediamine. The nanocomposites have been prepared in solution by mixing the polymer with low amounts of Zn–salophen and using tetrahydrofuran as solvent. The ultraviolet–visible spectrum has shown the occurrence of an intermolecular charge transfer between polysilane and the metal complex. Photoluminescence studies have revealed an interesting dual emission profile of nanocomposite. The origin of this phenomenon has been evidenced by molecular modeling and simulation of the electronic transitions. The modeling results have unveiled a new low‐lying excited state due to intermolecular interactions. The thin films of nanocomposites have been drop‐casted from solutions. The obtained films have been studied by Transmission Electron Microscopy (TEM)‐Scanning Transmission Electron Microscopy (STEM)‐Energy Dispersive X‐ray analysis (EDX) to gain information on the film‐forming capacity and surface morphology. The results have revealed a high potential of such materials for fluorescence sensing applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation of carbon nitride fine powder by laser induced gas-phase reactions

3 N₄ structure, with an α-C₃N₄-like form being prevalent. The powders were found to be slightly contaminated by SF₆ sensitizer products. Our results suggest that by improving the experimental parameters this contamination might be reduced and that the laser pyrolysis method offers possibilities for production of C_xN_y materials, with controlled composition. Received: 4 February 1997/Accepted: 7 April 1997     

Synthesis and structure of novel heterocyclic aminotelluranes

A series of novel 6-alkoxy-12H, 14H-[1,2,3]benzoxatellurazino[2,3-b]-[1,2,3]benzoxatellurazines 3 was synthesized from tetraalkoxytelluranes and bis(2-hydroxybenzyl)amines. ¹H, ¹³C and ¹²⁵Te NMR studies suggest that these aminotelluranes, unlike their orthoamidoester analogs, have a rigid trans-fused conformation. A preferential trans-fused conformation was also deduced from ab initio MO calculations of a model oxatellurazinooxatellurazine 7, using the STO-3G and SBK basis sets, and the Gaussian-92 program, which imply that the trans-fused aminotellurane is more stable than the corresponding cis isomer by 10.3 kcal/mol.     

Cyclicity of elliptic curves modulo <Emphasis Type="Italic">p</Emphasis> and elliptic curve analogues of Linnik’s problem

Let E be an elliptic curve defined over and of conductor N. For a prime we denote by the reduction of E modulo p. We obtain an asymptotic formula for the number of primes p x for which is cyclic, assuming a certain generalized Riemann hypothesis. The error terms that we get are substantial improvements of earlier work of J-P. Serre and M. Ram Murty. We also consider the problem of finding the size of the smallest prime p = p_E for which the group is cyclic and we show that, under the generalized Riemann hypothesis, p_E = ((log N)^{4 +} ) if E is without complex multiplication, and p_E = ((log N)^{2 +} ) if E is with complex multiplication, for any 0 < < 1.Mathematics Subject Classification (2001):11G05, 11N36, 11R45Research supported in part by an Ontario Graduate Scholarship.Research supported in part by an NSERC grant.Revised version: 11 April 2004