Compression set in gas-blown condensation-cured polysiloxane elastomers

Accelerated thermal ageing studies on foamed condensation cured polysiloxane materials have been performed in support of life assessment and material replacement programmes. Two different types of filled hydrogen-blown and condensation cured polysiloxane foams were tested; commercial (RTV S5370), and an in-house formulated polysiloxane elastomer (Silfoam). Compression set properties were investigated using Thermomechanical (TMA) studies and compared against two separate longer term ageing trials carried out in air and in dry inert gas atmospheres using compression jigs. Isotherms measured from these studies were assessed using time-temperature (T/t) superposition. Acceleration factors were determined and fitted to Arrhenius kinetics. For both materials, the thermo-mechanical results were found to closely follow the longer term accelerated ageing trials. Comparison of the accelerated ageing data in dry nitrogen atmospheres against field trial results showed the accelerated ageing trends over predict, however the comparison is difficult as the field data suffer from significant component to component variability. Of the long term ageing trials reported here, those carried out in air deviate more significantly from field trials data compared to those carried out in dry nitrogen atmospheres. For field return samples, there is evidence for residual post-curing reactions influencing mechanical performance, which would accelerate compression set. Multiple quantum-NMR studies suggest that compression set is not associated with significant changes in net crosslink density, but that some degree of network rearrangement has occurred due to viscoelastic relaxation as well as bond breaking and forming processes, with possible post-curing reactions at early times.     

Extremal Polyomino Chains on k-matchings and k-independent Sets

Denote by the set of polyomino chains with n squares. For any , let m _k (T _n ) and i _k (T _n ) be the number of k-matchings and k-independent sets of T _n , respectively. In this paper, we show that for any polyomino chain and any , and , with the left equalities holding for all k only if T _n =L _n , and the right equalities holding for all k only if T _n =Z _n , where L _n and Z _n are the linear chain and the zig-zag chain, respectively. This work is supported by NNSFC (10371102).     

Adaptation of one‐electron basis sets to spatial confinements

A method that generates out of a given orbital basis set its analog appropriate for describing the effects of a spatial confinement is presented. The method is based on the requirement that the one‐particle model spaces for the confined and for the unconfined systems are equivalent in the sense of a criterion derived from the basis‐set‐generating eigenvalue equations. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 341–347, 1999     

On the Dirac equation in the algebraic approximation

It is shown that the restrictive conditions of Wood et al. [1] are not necessary to reach the conclusion that the Dirac hamiltonian, projected onto the space of the large component, exhibits variational properties. The eigenvalue spectrum of matrix approximations to the partitioned hamiltonian (obtained by matrix partitioning) converges to the exact spectrum in the limit of infinite order (assuming completeness) but not necessarily from above as for true matrix representations (obtained from operator partitioning). Optimization of non-linear parameters is shown not to cause variational instabilities.Control Data Corporation PACER fellow 1984–1986     

An experimental and theoretical study of vibrational spectra of picolinamide, nicotinamide, and isonicotinamide

The molecular structures and vibrational spectra of the three isomers of pyridinecarboxamide (picolinamide, nicotinamide, isonicotinamide) were calculated with the Density Functional Theory (DFT) method using the B3LYP function and the 6-31++G(d,p), Z2PolX, Z3PolX basis sets. The calculations were performed by using the Gaussian98W packet program set. The total energy distributions (TED) of the vibrational modes of these molecules were calculated by using the Scale 2.0 program and the vibrational modes of the molecules were determined. The Scaled Quantum Mechanical (SQM) method was used in the scaling procedure. In the experimental part of the study, the solid phase FT-IR and Micro Raman spectra of the three isomers of pyridinecarboxamide have been recorded in the range of 4000-650 and 1200-100 cm⁻¹, respectively. The calculated wavenumbers were compared to the corresponding experimental values. As a result, the observed bands of the three isomers of pyridinecarboxamide were assigned with good accuracy.     

Irregular 1-sets on the graphs of continuous functions

One can define in a natural way irregular 1-sets on the graphs of several fractal functions, like Takagi’s function, Weierstrass-Cellerier type functions and the typical continuous function. These irregular 1-sets can be useful during the investigation of level-sets and occupation measures of these functions. For example, we see that for Takagi’s function and for certain Weierstrass-Cellerier functions the occupation measure is singular with respect to the Lebesgue measure and for almost every level the level set is finite.     

Critically prime interval orders

We prove that a prime interval order, not necessarily finite, has no prime upper cover if and only if it has width two. On the other hand, we prove that every finite prime N-free order has at least one prime upper cover.     

RESERVOIR DESCRIPTION BY USING A PIECEWISE CONSTANT LEVEL SET METHOD

We consider the permeability estimation problem in two-phase porous media flow. We try to identify the permeability field by utilizing both the production data from wells as well as inverted seismic data. The permeability field is assumed to be piecewise constant, or can be approximated well by a piecewise constant function. A variant of the level set method, called Piecewise Constant Level Set Method is used to represent the interfaces between the regions with different permeability levels. The inverse problem is solved by minimizing a functional, and TV norm regularization is used to deal with the ill-posedness. We also use the operator-splitting technique to decompose the constraint term from the fidelity term. This gives us more flexibility to deal with the constraint and helps to stabilize the algorithm.     

Operators on Soft Inner Product Spaces

In the present paper, self-adjoint operator and completely continuous operator on soft inner product spaces have been introduced and some basic properties of such operators are studied.