Low-temperature interface reaction in aluminium-silicon carbide particulate composites produced by mechanical alloying

An experimental investigation has been carried out on the reaction that takes place between 3 and 20 μm SiC particles and the aluminium alloy 1050 matrix of composite materials prepared by a mechanical alloying process. The work is different from that undertaken by other researchers in that the SiC-Al interface reaction has been studied in the temperature range 853–933 K, i.e., with the matrix initially in the solid state. Differential thermal analysis, X-ray diffraction and scanning electron microscopy all show that the SiC-Al reaction initiates in the solid state at temperatures as low as 883 K. The reaction produces Al4C3 and Si, the latter entering into solid solution in the aluminium matrix. At temperatures exceeding 903 K, the reaction produces a liquid phase and at this stage the speed of the interface reaction increases significantly. The results are discussed in terms of Al-Si-C metastable equilibrium and the kinetics of the reaction. This revised version was published online in November 2006 with corrections to the Cover Date.     

Property Owning and Democracy-Do the Twain Ever Meet?

Starting from the Conservative assertion that home ownership fosters politically active and virtuous citizens, this paper examines two lines of argument in housing theory; (a) Jim Kemeny's thesis that owner occupation is closely linked to increasing privatism, i.e. a growth in lifestyles centred around the home and privacy rather than the workplace or the public affairs in a society, and (b) Peter Saunders' thesis that home owners will organise and mobilise politically in defence of their property interests if and when various government agencies threaten to remove their tax subsidies. To test these propositions empirically, data on the effects of the rapid and comprehensive dismantling of tax privileges to Swedish home owners in the 1980s and early 1990s are confronted with data on political interest, participation and knowledge as well as civic trust and responsibility from the Swedish election surveys of 1979, 1985 and 1991. Contrary to Conservative beliefs, home owners do not stand out as 'democratic examples'; with the exception of political knowledge and party membership, they are no more 'civil' or 'democratic' than other citizens. There is also not much to support Kemeny's 'privatism' or Saunders' 'reaction-to-threat' theses. Although home owners in Sweden saw their tax privileges diminishing rapidly during the 1980s and early 1990s, they do not show the distinctive patterns of change in democratic orientation and spirit predicted by these two housing theorists. To allow for an even more conclusive test of Kemeny's 'privatism' thesis, however, one must overcome the mismatch of income definitions in housing statistics and election survey data.     

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.     

Ein stochastisches,schadensmechanisches Versagensmodell für Komposite

A stochastic damage mechanics failure model of composites This paper focuses on the theoretical simulation of strength and failure of specimens with nonlocal damage. A concept is proposed for quantitative interpretation and prediction of nonlinear. nominal stress-strain curves of damaged materials like fine ceramics or intermetallic alloys. For that reason methods of damage mechanics and of probability theory are combined.     

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.     

Air Filtration and Radon Decay Product Mitigation

Air cleaning as a means of mitigating the risks arising from exposure to indoor radon progeny has been evaluated in a single-family house in the north eastem US. using an automated, semi-continuous activity-weighted size distribution measurement system. The measurements included radon concentration, condensation nuclei count, and activity-weighted size distribution of radon decay products. Measurements were made in the house with and without an operating air filtration system and with various particle sources common to normal indoor activities operating. Aerosols were generated by running water in a shower, candle burning, cigarette smoking, vacuuming, opening doors, and cooking. Using a room model, the changes in attachment rates, average attachment diameters, and deposition rates of the unattached fraction with and without the air cleaning system were calculated. In the presence of active aerosol sources, the air filtration unit typically reduced the concentration of particles within the hour following the end of particle generation. After candle burning, cigarette smoking, and vacuuming in the bedroom, the reductions of PAEC by air filtration are about 60% with the air filtration system operating in the bedroom. During cooking in the kitchen, the reductions of PAEC in the bedroom with the air filtration system were about 40%. However, for all cases the dose reductions were smaller than the particle and PAEC reductions. For those particles that were generated within the bedroom, there was a 20% to 50% reduction in dose. In the case of cooking where the door was open and particles infiltrated from the rest of the house, the dose reduction was only 5% on average and appears to be insignificant. Thus, the dose reductions were h e r than the reductions in activity concentration, but there were no cases where the estimated dose actually increased.     

Die Langzeit-Korrosionsgeschwindigkeit des passiven Eisens in anaeroben alkalischen Lösungen

The long-term corrosion rate of passive iron in anaerobic alcaline solutions Gas generation is an important issue in safety assessments of low and intermediate level radioactive repositories. In this connection the hydrogen production from corrosion of passive iron in saturated calcium hydroxide, in dilute alkali hydroxide and cement porewater solutions has been determined. The measurements were performed manometrically using fusion sealed glass cells, the measurement periods being between 275 and 560 days. In 0.1 M and 0.04 M alkali hydroxide solutions the initial hydrogen generation rate was 12 mmol/m²yr corresponding to a linear corrosion rate of 64 nm/yr. The reaction rate decreases with time. The smallest value obtained after 330 days is 0.3 mmol/m²yr corresponding to 1.5 nm/yr. The influence on iron of the saturated calcium hydroxide solution and the calcic porewater solutions differs from that of the alkali hydroxide solutions. At pH 12.5 the hydrogen generation rate remains practically constant up to breaking off the experiment, the value being about 1 mmol/m²yr corresponding to 5 nm/yr.     

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.