Poly(methyl methacrylate) and polyacrylonitrile dispersions stabilized by gelatin

Methyl methacrylate was polymerized in an aqueous medium in the presence of gelatin using potassium persulfate as initiator. The dispersion mode of polymerization, when the monomer is completely miscible with water, was investigated and compared with an emulsion process, which proceeds at higher monomer concentration. Spherical and relatively uniform polymer particles were formed. Macroscopic precipitation of polymer is prevented by combination of the steric stabilization by grafted gelatin and of repulsive electrostatic interactions from the initiator residues attached to the particle surface. Static and dynamic light scattering have been used to determine the molar mass (molar mass of the whole dispersion particle, M_wD ～ 10⁸-10⁹ g mol^?1) and hydrodynamic radius (R_hD ～ 50-120 nm) of the particles. The number of particles per unit volume does not depend on overall monomer concentration, and it is higher, and therefore the particle size is smaller, than that observed for the soapless emulsion polymerization. The addition of gelatin may be thus used to modify the particle size. Acrylonitrile dispersions were prepared under similar conditions. Unlike methyl methacrylate, this monomer does not swell the polymer particles. While poly(methyl methacrylate) particles are spherical and relatively uniform, the polyacrylonitrile dispersions consist of polydisperse aggregates of tiny polymer particles.     

The reduction of Al2O3 to aluminum in a plasma

The reduction of aluminum oxide to aluminum in radio frequency generated plasmas was studied experimentally. Argon with hydrogen, carbon dioxide, and methane were used as plasma gases. Product was collected from the reactor walls and/or cold-finger collectors. Gaseous quenching was also investigated, using hydrogen, methane, and carbon dioxide. Conversions up to 50 pct were determined using wet chemistry. Optical and X-ray methods confirmed the species present during and after reaction. The effects of particle size, flow rates, and power input were determined. Solutions of energy, momentum, and mass balances yield a qualitative explanation of the process. Vaporization rate controls. Formerly at the University of Michigan, Ann Arbor, Mich. Arbor, Mich.     

Effect of reynolds and prandtl number on the frequency response of concentric tube heat exchangers

An analytical and experimental investigation was made of the frequency response of both the shell and tube fluid outlet temperatures of a six foot concentric tube exchanger to disturbances in either flow rate. The fluid Reynolds and Prandtl numbers were varied from 4,000 to 20,000 and 3 to 40 respectively. The effect of increasing either the tube fluid Reynolds or Prandtl number, for both shell and tube flow disturbances, was to increase the attenuation and phase shift of the tube outlet temperature and decrease it for the shell outlet temperature. The “resonance effect”, was observed experimentally.     

Influence of oxygen partial pressure and substrate temperature during vapour deposition on the structural properties of CdSe films

CdSe films prepared in vacuum by sublimation from the compound at oxygen partial pressures in the residual atmosphere from 2.8 × 10^?5 to 3.2 × 10^?4 Torr and at substrate temperatures of 295 and 523 K were subjected to X-ray structural analysis. The results obtained are analysed and discussed in terms of some structures different from those of CdSe, e.g. CdSeO₃ and CdSeO₃.SeO₂.     

Aldehyde functionalization of styrene polymers

Summary Two methods of the introduction of aldehyde group into polystyrene skeleton are described.     

Toxicity increases in ice containing monochlorophenols upon photolysis: environmental consequences

The toxic effects of photoproducts formed upon the photolysis of 2- and 4-chlorophenol (CP) frozen solutions in polycrystalline ice phase were determined with a bacterial luminescence test (Vibrio fisheri), and in vitro biomarker assay for dioxin-like effects (inductions of AhR-dependent luciferase in H4IIE-luc cells) and compared to the toxic effects of products of the same photoreaction in aquatic phase. Coupling photoproducts formed in ice samples (3'-chlorobiphenyl-2,4'-diol and 3-chlorobiphenyl-2,2'-diol from 2-CP photolysis and 5-chlorobiphenyl-2,4'-diol from 4-CP photolysis) were found to be more toxic to V. fisheri than parent CPs and elicited significant inductions of dioxin-like effects (the effective concentrations EC50 approximately 3 x 10(-5) mol L(-1) corresponded to known weaker ligands of AhR, such as nonplanar polychlorinated biphenyls or polycyclic aromatic hydrocarbons). To complete the picture, a photoproduct formed from 4-CP (5-chlorobiphenyl-2,4'-diol) was synthesized, and a detailed toxicity assessment with purified compound confirmed the results obtained with irradiated samples. Our findings support a recently proposed model according to which solar radiation can trigger the formation of new types of organic pollutants in polar ice or tropospheric ice cloud particles, presenting possibly greater risk to the environment than the parent compounds.     

Czech results at criticality dosimetry intercomparison 2002

Two criticality dosimetry systems were tested by Czech participants during the intercomparison held in Valduc, France, June 2002. The first consisted of the thermoluminescent detectors (TLDs) (Al-P glasses) and Si-diodes as passive neutron dosemeters. Second, it was studied to what extent the individual dosemeters used in the Czech routine personal dosimetry service can give a reliable estimation of criticality accident exposure. It was found that the first system furnishes quite reliable estimation of accidental doses. For routine individual dosimetry system, no important problems were encountered in the case of photon dosemeters (TLDs, film badge). For etched track detectors in contact with the 232Th or 235U-Al alloy, the track density saturation for the spark counting method limits the upper dose at approximately 1 Gy for neutrons with the energy >1 MeV.     

Effective diffusivity and optimum apparent density of vanadia catalysts for sulfur dioxide oxidation

The effective diffusivities of air and SO₂ in four industrial vanadium pentoxide catalysts were measured at steady-state using helium as the counter diffusing gas. An improved catalyst mounting technique and diffusion cell were employed. The nonsurface component of diffusion was successfully correlated using Bruggeman's model for tortuosity. and ¯a based on pore size distribution data or calculated from specific pore volume and surface. However, it was necessary to use flow porosity in place of open porosity. Since the same pore model can be used for the catalytic oxidation So₂, non-reacting flow measurements can be employed to predict effective diffusivities under reaction conditions in this case.With models for the effective diffusivity and the kinetics of the catalytic oxidation of SO₂, an optimum apparent density of the catalyst may be determined which gives the maximum rate of reaction per unit volume of catalyst. Calculations are given for the SVD catalyst.     

Static load balancing applied to Schur complement method

A finite element method often leads to large sparse symmetric and positive definite systems of linear equations. We consider parallel solvers based on the Schur complement method on homogeneous parallel machines with distributed memory. A finite element mesh is partitioned by graph partitioning. Such partitioning results in submeshes with similar numbers of elements and, consequently, submatrices of similar sizes. The submatrices are partially factorised. The time spent on the partial factorisation can be different, i.e., disbalanced, because methods exploiting the sparsity of submatrices are used. This paper proposes a Quality Balancing heuristic that modifies classic mesh partitioning so that the partial factorisation times are balanced, which saves overall computation time, especially for time dependent mechanical and nonstationary transport problems.     

Variation in fatty acid composition of ewes' milk during continuous transition from dry winter to natural pasture diet

The profile variations of approximately 70 fatty acids (FAs) in milk of ewes consuming total mixed rations (TMR) and grazing natural pasture were determined. Milk of ewes grazing pasture in May and September in the Slovak Republic contained 3-times more conjugated linoleic acid (CLA) (P < 0.001) and trans-vaccenic acid (TVA) (P < 0.001), and 2-times more α-linolenic acid (ALA) (P < 0.001) than that of ewes fed TMR. A doubling of the CLA and TVA contents of milk of ewes fed with TMR was achieved by changing to meadow hay containing a higher ALA content. Less availability of vegetation and lower ALA pasture content in summer (P < 0.001) caused a 2-fold decrease (P < 0.001) of CLA and TVA contents when compared with data obtained in May. With grass re-growth and an increase in pasture ALA content in September, the CLA and TVA contents rose to values similar to those obtained in May (P > 0.05). No significant differences in the FA composition in milk of ewes grazing on summer pasture at higher altitude were observed.