Electroconvective flow propagation and defect formation in MBBA

A new type of highly organized, large scale propagation of vortical flow has been observed in MBBA subject to a transverse electric field. This is a transient phenomenon associated with the transformation, occurring at elevated voltages, between electrically distorted homeotropic and planar states. The convective flows generate an array of linear defects which persist even after removal of the field.     

Alternating copolymerization of N-benzylidine aniline (NBA) with α-haloacrylic acids (XAA). IV. Synthesis,characterization, and kinetics

This article describes a new, spontaneous, 1:1 alternating copolymerization between a Schiff base, N-benzylidine aniline (NBA), and α-haloacrylic acids (XAA) such as α-chloroacrylic acid (ClAA) and α-bromoacrylic acid (BrAA). The structure of the copolymers was identified by nuclear magnetic resonance (NMR) and infrared (IR) spectra. By using the isolation method we determined the order of each monomer. On the basis of kinetic studies, a mechanism that involves initiation, propagation, and termination by zwitterion is proposed. The effects of copolymerization under various conditions were studied and the intrinsic viscosity and number-average molecular weight were measured. The overall energy of activation, E_Rp, for the copolymerization was determined and thermal degradation studies were made.     

On a new computing technique in optimal control and its application to minimal-time flight profile optimization

A new constructive approach to optimization problems for dynamic systems that avoids having to solve dynamic equations and has both computational and theoretical advantages is presented. On the theoretical level, it yields a simple direct method for the Hamiltonian and the maximum principle and a constructive derivation of the Lagrange parameters. The computational aspects are illustrated by results obtained for a minimal-time flight profile optimization problem.This research was supported in part by the Applied Mathematics Division, Office of Scientific Research, Office of Aerospace Research, United States Air Force, under Grant No. 69-1408. All the calculations presented in this paper were carried out under the direction of Mr. L. W. Taylor, NASA Flight Research Center, Edwards, California, who also contributed many essential ideas throughout this work. This paper was presented at the Colloquium on Optimization held in Novosibirsk, USSR, 1968.     

Tensammetric studies on corrosion inhibitors

The study of adsorption by the alternating current polarographic method is known as ‘tensammetry’. This technique has been extended to the study of the adsorption characteristics of organic corrosion inhibitors with a view to elucidate the mechanism of inhibition by such compounds. The usefulness of such studies in elucidating the mechanism of inhibition by dicyclohexylamine nitrite, which is now widely used as a vapour phase corrosion inhibitor, is brought out. For this purpose, results obtained by tensammetric studies have been compared with potential measurements on the one hand and direct corrosion tests on the other and discussed.     

On abstract stochastic bilinear equations with white noise inputs

We study the response of a class of stochastic bilinear hyperbolic (oscillatory) systems to multiplicative noise inputs. We formulate them as bilinear abstract Cauchy problems in the framework of (finitely additive) white noise theory. We show that the solution can be expressed in terms of the integral of the noise, which enables us to study relevant stochastic properties of the solution.     

Equilibrium concentration of oxygen rich and deficient defect centers in germanosilicate glasses

Equilibrium concentrations of oxygen rich and deficient defect centers are calculated as a function of temperature and glass redox condition for germanosilicate glasses. We have here used the approach of Silin and Lace [J. Non-Cryst. Solids 149 (1992) 54-61] but extended it to include the case of binary system of germanosilicate glasses. A set of 23 reactions is identified as the possible pathway for formation of different defect centers. Each of these reactions are represented by forward and backward steps with Arrhenius kinetics and their activation energies are estimated based on the relevant bond energies of the involved species. Equilibrium concentrations are determined by setting rates of each of these reactions equal to zero. Typical results are presented for glasses which are: (i) stoichiometric, (ii) glasses with excess oxygen levels of 10¹⁶ to 10²⁰ cm⁻³, and (iii) glasses which are oxygen deficient by 10¹⁶ to 10¹⁸ cm⁻³.     

Nickel(II) complexes of β-N-alkylimme arylhydrazones

Summary -N-alkylimine arylhydrazone ligand complexes of nickel(II) have been synthesised by metal template reactions. The azomethine nitrogen and the a-nitrogen of the arylhydrazone coordinate to the metal with square-planar geometry around the nickel(II) ion. Structures have been proposed based on the spectral properties of the complexes.Reprints of this article are not available.     

Solvent effects on the NMR spectra of heterocyclics

The NMR spectra of pyridine, pyrazine and imidazole are examined in acetone-d₆. The differential shifts of the ring protons are accounted for in terms of an interaction between the lone pair on the ring nitrogen atom and the carbonyl group of acetone.     

Fluctuations and viscoelasticity

Viscoelasticity is exhibited by polymers, metals undergoing diffusion creep, etc. The strain is a linear functional of the stress, but there is no unique equilibrium relationship between them. Under a constant stress, the strain does not saturate to an equilibrium value. This divergence is the main difficulty facing a first-principles theory of viscoelasticity, in contrast to anelasticity which has already been understood as a relaxation process in terms of response theory, fluctuations and related concepts. We now present such a theory, based on the recognition that viscoelasticity occurs whenever the spontaneous fluctuations of the strainrate, butnot of the strain, form a stationary random process. We give fundamental formulas for the creep function and the complex compliance, in terms of the spontaneous fluctuations of the strain rate, that apply to both viscoelasticity and anelasticity. A detailed stochastic analysis of the basic viscoelastic network equation corroborates and complements these results. The unphysical instantaneous response of the network is eliminated, and the network parameters are related to internal fluctuations. A certain functional form of the creep function is derived that is common to several physical situations, a few of which are mentioned. Detailed applications will be taken up elsewhere.