Thermodynamic and conformational properties of partially butyralized poly(vinyl alcohol) in aqueous solution

Phase separation behavior has been studied in aqueous solutions of partially butyralized poly(vinyl alcohol) (BuPVA) with various degrees of butyralization x_Bu and various molecular weights. It is found that these systems exhibit both upper and lower critical solution temperatures. The theta temperatures θ_LCST, evaluated by means of Shultz–Flory plots, are found to be 25.1, 23.3, and 14.4°C for BuPVAs with x_Bu of 7.5, 9.9, and 12.7 mol %, respectively. The unperturbed dimension 〈R²〉₀/M is evaluated as ca. 1.2 × 10^?16 Ų in the above range of x_Bu from viscosity measurement at θ_LCST. Properties of the BuPVA solutions are compared with those of other PVA copolymers.     

An optimal stopping problem for a geometric Brownian motion with poissonian jumps

This paper examines an optimal stopping problem for a geometric Brownian motion with random jumps. It is assumed that jumps occur according to a time-homogeneous Poisson process and the proportions of these sizes are independent and identically distributed nonpositive random variables. The objective is to find an optimal stopping time of maximizing the expected discounted terminal reward which is defined as a nondecreasing power function of the stopped state. By applying the “smooth pasting technique” [1,2], we derive almost explicitly an optimal stopping rule of a threshold type and the optimal value function of the initial state. That is, we express the critical state of the optimal stopping region and the optimal value function by formulae which include only given problem parameters except an unknown to be uniquely determined by a nonlinear equation.     

Development of a novel vertical high shear kneader and its performance in wet kneading of pharmaceutical powders

A novel multi-functional vertical high shear kneader has been developed. Wet kneading of pharmaceutical powders was conducted under various blade components and operating conditions. Compression properties of wet kneaded mass was analyzed and dispersion of hinder liquid (water) among the mass was investigated by assaying tracer aqueous pigment. Pellets were produced through a dome type extrusion granulator with continuous extrusion pressure measurement device and a fluidized bed drier, and then the physical properties were measured. Quantitative relationship between the pellet's physical properties and the binder dispersion condition as well as the compression properties could be obtained. It was found that the newly developed kneader was very effective to uniformly disperse binder as well as impart high shear stress to the wet mass without generating obvious adhesion onto the vessel wall. It was also pointed out that the extrusion pressure could determine the physical strength of pellet. This method proposes a new methodology for continuous monitoring of kneading condition as well as predicting pellet's physical properties.     

A novel water-soluble Hantzsch 1,4-dihydropyridine compound that functions in biological processes through NADH regeneration

A novel Hantzsch 1,4-dihydropyridine derivative could function in an organic solvent-free solution, and thus it could function in biological systems. These functions can be accomplished through regeneration of the reduced form of nicotinamine adenine dinucleotide (NADH), an essential compound for living organisms. The results obtained here demonstrate the usefulness of a water-soluble Hantzsch 1,4-dihydropyridine derivative and its wide applicability as a chemical energy source, which drives various biological processes efficiently.     

The yield of color center formation in KBr doped with KI

Measurements have been made of F and H centre production rates in KBr doped with KI, when electron irradiated at 5°K. Significant concentrations of I⁻ reduce the production rates of both centres. In the mixed crystals complex H bands are formed and the thermal annealing behaviour of these bands has been measured.     

Effect of Mass Diffusion on Nitration Rates of Moderately Reactive Aromatic Substrates

Competitive nitrations of two pairs of aromatic substrates were carried out in order to clarify the effect of several methods of mixing on the observed relative rates. The experimental results indicate that a commercially available four-jet mixer for rapid reaction could not achieve homogeneous mixing in the competitive nitration of aromatic substrates in aqueous sulfuric acid.