Sampling Procedures for Risk Simulation

Risk simulation has become a standard alternative to the utilization of single estimates for input data to investment appraisal models. Under the risk simulation approach managers define probability distributions for relevant input factors. During this process management may consciously or subconsciously assume certain relationships between the input variables. These interdependencies are often omitted from the models, however, under the justification that they are accounted for implicitly in the values attributed to the variables by management. It is demonstrated in this paper that such omissions may lead to significant errors in the observed distributions of the selected appraisal criteria. Various forms of discriminate sampling are introduced and an example is cited for which certain discriminate schemes are shown to be more accurate than traditional independent sampling.     

Structure and Phase Behavior of the Expanded‐Metal Compound 7Li(ND3)4

Metal lite : High‐resolution neutron powder diffraction data reveals that the body‐centered cubic crystal structure of lithium(0)tetraamine transforms to a simple cubic structure below 22 K. The detailed structure determinations will allow new insights into the coupled structural and electronic properties of the lightest metal.

     

Acid–base complexes of polymers

The physical interactions of polymers with neighboring molecules are determined by only two kinds of interactions: London dispersion forces and Lewis acid–base interactions. These two kinds of attractive energies (together with certain steric restrictions) determine solubility, solvent retention, plasticizer action, wettability, adsorption, adhesion, reinforcement, crystallinity, and mechanical properties. The London dispersion force interaction energies of polymers have been quantified by the dispersion force contribution to cohesive energy density (δ²_d) and the dispersion force contribution to surface energy (δ^d). The Lewis acid–base interactions, often referred to as “polar” interactions, can be best quantified by Drago's C_A and E_A constants for acid sites and C_B and E_B constants for basic sites. In this article infrared spectral shifts are featured as a method of determining enthalpies of acid–base interaction, and the C and E constants for polymers, plasticizers, and solvents. Examples are given where acid–base complexation of polymers with solvents dominate solubility and swelling phenomena. Enthalpies of acid–base complexation in polymer blends are determined from spectral shifts.     

Acid-base properties of glass surfaces

The adhesion of polymers to inorganic oxides such as glass is very dependent on acid-base interactions between the acidic or basic surface sites of the glass and the basic or acidic functional sites of the polymer. This paper reviews the principles of such interactions, methods of measuring the acidity or basicity of surface sites, and the enhanced mechanical properties of glass-reinforced polymer composites resulting from interfacial acid-base complexation. A new study is presented of the acid-base properties of fiberglass and of surface treatments with silane coupling agents and polyvinyl acetate. It illustrates calorimetric titration methods for assessing surface acidity and basicity, and correlates these findings with angular-dependent X-ray photoelectron spectroscopy (ADXPS).     

A branch and bound algorithm for the global optimization of Hessian Lipschitz continuous functions

We present a branch and bound algorithm for the global optimization of a twice differentiable nonconvex objective function with a Lipschitz continuous Hessian over a compact, convex set. The algorithm is based on applying cubic regularisation techniques to the objective function within an overlapping branch and bound algorithm for convex constrained global optimization. Unlike other branch and bound algorithms, lower bounds are obtained via nonconvex underestimators of the function. For a numerical example, we apply the proposed branch and bound algorithm to radial basis function approximations.     

Electron donor–acceptor properties of thin polymer films on silicon. II. Tetrafluoroethylene polymerized by RF glow discharge techniques

Metal–insulator–semiconductor (MIS) techniques were used to show that 86–210 nm thick plasma-polymerized tetrafluoroethylene films on silicon stored only negative charge (electron acceptors). This property persisted at a reduced level when a 7 nm thick inner layer of hydrolyzed γ-aminopropyltriethoxysilane was combined with an outer layer of plasma-polymerized tetrafluoroethylene. The dispersion force contribution to the surface energy, γ^d_s, for the fluorocarbon films was found to be 6 mJ/m² (erg/cm²) which is comparable with the lowest values found in the literature. X-ray photoelectron spectroscopy (XPS) revealed a substantial content of ? CF₃ groups in the fluorocarbon films. This finding coupled with the reported effects of noncrystallinity, crosslinking, and branching on the surface energies of fluorocarbon systems were used to explain the low surface energy and electrophilicity of the plasma-deposited poly(tetrafluoroethylene)s.     

Crack repair using an elastic filler

The effect of repairing a crack in an elastic body using an elastic filler is examined in terms of the stress intensity levels generated at the crack tip. The effect of the filler is to change the stress field singularity from order 1/r^1/2 to 1/r^(1-λ) where r is the distance from the crack tip, and λ is the solution to a simple transcendental equation. The singularity power (1-λ) varies from (the unfilled crack limit) to 1 (the fully repaired crack), depending primarily on the scaled shear modulus ratio γ_r defined by G₂/G₁=γ_rε, where 2πε is the (small) crack angle, and the indices (1, 2) refer to base and filler material properties, respectively. The fully repaired limit is effectively reached for γ_r≈10, so that fillers with surprisingly small shear modulus ratios can be effectively used to repair cracks. This fits in with observations in the mining industry, where materials with G₂/G₁ of the order of 10^-3 have been found to be effective for stabilizing the walls of tunnels. The results are also relevant for the repair of cracks in thin elastic sheets.