Preparation of Poly(D,L-Lactide/Glycolide) Nanoparticles of Controlled Particle Size Distribution: Application of Experimental Designs

This study investigates the use of the solvent evaporation method for preparing acid and glycolic acid-based copolymer nanoparticles. Initially, appropriate technological and formulation factors for elaboration of polymeric particles were selected by screening. Most favourable results were obtained using polyvinyl alcohol as a dispersing agent and a high pressure homogenizer to reduce the droplet size of the emulsion initially formed. On the basis of the conclusion thus drawn, a composite rotational experimental design was employed to evaluate the joint influence of three formulation variables (phase volume ratio of the emulsion formed, polymer concentration and homogenization pressure) on the micromeritic properties of the suspension finally obtained (mean particle size, coefficient of variation and polydispersity of the particle size distribution). Analysis of variance corresponding to the experimental design, showed a significant influence of the volume phase ratio and the polymer concentration on the mean particle size and the coefficient of variation, whereas the polydispersity is also affected by the homogenization pressure. Considering this information, a 3² experimental factorial design was then selected to investigate the possible interaction between the phase volume ratio and the concentration of polyvinyl alcohol in the aqueous phase. Analysis of variance and subsequent sequencial regression analysis evidenced last hypothesis providing the way to determine the experimental conditions required to achieve a specific particle size distribution.     

A mathematical model for the prediction of temperature in a dry snow layer

A mathematical model for predicting the temperature in a homogeneous layer of dry snow is presented. The model, which is physically based, is capable of predicting diurnal temperature behaviour at the snow surface and at any depth within a snow layer given the variation in a limited set of meteorological parameters over that period. A sensitivity analysis is performed to determine the important parameters in the prediction of snow surface temperatures. These are found to be consistent with simple physical reasoning.     

Mikrobielle Werkstoffzerstörung – Schadensfälle und Gegenmaßnahmen für Kunst- und Naturstoffe: Mikrobielle Zerstörung von Kunststoffen

Microbial deterioration of materials – case histories and countermeasures for plastics and organic and natural materials: Microbial deterioration of plastics Large-scale production of synthetic plastics began in the thirties. The versatility of the new materials was enhanced by new processing technologies and above all by designing special formulations tailored to the different fields of applications. Their increasing universal application was, however, also accompanied by growing records of documented microbial attack. The mechanisms of attack have largely been identified. Damage is commonly caused by surface growth, discolourations and changes of mechanical and electrical properties. National and international test standards have been developed to predict the service life of certain plastics or to evaluate the protection afforded by certain biocides. Several standard methods of test are presented and the criteria for evaluation are critically examined. Finally, the activities of the Plastics Project Group are represented, wich has carried out several international co-operative tests to evaluate the reproducibility of the results of different test methods and has worked out recommendations and improvements.     

Synthesis of fine composite particles for hydrogen storage, starting from Mg-YNi2 mixture

We synthesized new composite particles for hydrogen storage on the basis of an idea of “particle designing”. As starting materials, powders of Mg and YNi₂ were selected. Fine composite particles containing mainly Mg₂Ni could be designed by repetitive hydriding and dehydriding cycles at 673 K. In the synthesis process of the composite particles, the following two points were found to be essential for this technique. The first point is that, after being activated by the sequential processes of hydrogenation, amorphization and disproportionation, YNi₂ reacts effectively with Mg. The second point is that evaporated Mg, which occurs during dehydriding, adheres to the surface of the activated YNi₂ and accelerates a diffusion reaction to form Mg₂Ni at the interface. In these composite particles, Mg₂NiH₄ is formed, even at 373 K, under a hydrogen pressure of 5 MPa.     

Evolution of BET internal surface area in glassy carbon powder during thermal oxidation

It is demonstrated that glassy carbon powder can be thermochemically activated. During activation, a film with open pores is created on the glassy carbon particles. This film has a large internal surface area, which is accessible to liquids and gases. A simple model for the evolution of the internal surface area in glassy carbon powder during thermochemical gas-phase oxidation is also presented and compared with experimental data. Experimental results are in qualitative agreement with the model. We found that a sharp particle size distribution is desirable with regard to potential technical applications.     

A problem of pursuit and evasion

A trajectory problem of pursuit and evasion on a plane is considered for the case of equal absolute velocities of the players. Exact solutions are obtained for fixed initial conditions.Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 138–143, May–June, 1992.     

Bisensors for amino acids

Two kinds of biosensors for amino acids (one with nonspecific enzyme as bioelement, the other with specific enzyme(s) as bioelement), including their principles, applications, recent researches and future trends were discussed in detail. 61 references were given. A part of work for gaining Ph. D in chemical and biochemical application at FPMs (Mons, Belgique) Synopsis of the first author Xia Jinlan, Male, born in 1963, now at Facult’e Polytechnique de Mons, Belgique     

The Principles of Calculus of Behavior Scenarios of Complex Systems in the ECS

Theoretical results of the development of the principles of scenario calculus are presented, which are obtained in the framework of the design of an emergency control system (ECS). Relying on the suggested system concept of the formation of a scenario system, consideration is given to the principles of the construction of operations in scenario spaces, which account for specific features of the scenario analysis and the process of the decision-making in the ECS. Principal problems of the development of scenario calculus on the basis of a system approach are treated, the classification of operations on scenarios is given, and a number of operations on elements of the basic metacollection are formalized.