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.     

Neutron diffraction studies of the incommensurate modulation structure in SrxBa1-xNb2O6 mixed crystals of various compositions

Using time-of-flight technique between 100 K and 700 K a nearly constant IC modulation parameter is found. It depends only weakly on crystal composition. The intensity of the first-and second-order satellites decreases with temperature and at 700 K it is nearly disappeared. These facts are discussed with a view to the anti-phase domain model.     

From categorial to dimensional diagnosis

The concepts of categorical and dimensional assessment approaches and their specific advantages--and disadvantages are described. A combination of both concepts within the framework of Multiple Assessment of Psychiatric Disturbances is proposed. This includes the different levels of behavioural and emotional disturbances, different assessment methods, the situational specificity of behavioural and emotional disturbances and individually tailored and treatment related assessment procedures. Thereby two phases are distinguished. In the first phase basic procedures of the Multiple Assessment of Psychiatric Disturbances are accomplished, which cover a broad spectrum of behavioural and emotional problems. In the second phase a differentiated picture of the-specific disturbance is assessed by using symptom-specific instruments of the Multiple Assessment of Psychiatric Disturbances. In a case report the diagnostic procedure is explained.     

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.     

The probability density and autocorrelation of short-term global and beam irradiance

For individual hours, a characteristic bimodal pattern of short-term global and beam irradiance is frequently observed, with modes at high and low irradiances and with low probabilities near the hourly averages. For such hours, averaging over the hour will imply smoothing of quite significant variations within the hour. Models for the probability density distributions of short-term (5 min or less) irradiances are presented in this paper. These distributions are not unique functions of the hourly averages, but depend heavily also on the irradiance variability within the hour. This intrahour variability is found to depend on the averaging time and also on the interhour variability among three hourly averages, namely, the hour in question, the preceding and the deceding hour. The distribution differences between 5 min averages and instantaneous values are, however, negligible for most practical purposes. The lag one autocorrelation is evaluated as a function of averaging time, and a first order autoregressive model is presented. With hourly averages as the only input the probability density and autoregressive model in combination produce time series of short-term intrahour averages having realistic distributions and autocorrelation structure.     

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.     

Evaluation of a commercial process for collection and cooling of beef offals by a temperature function integration technique.

The hygienic adequacy of a commercial process for the collection and cooling of beef offals was assessed by a temperature function integration technique. The diverse operations for collection of offals were inspected. The rates of product movement through those operations, and the temperatures of products at the time of their being packed, were determined. From that information, four of the nine product types were selected for examination of their temperature histories during the assembly and cooling of the cartoned products. The products selected encompassed product at near-body and near-air-ambient temperatures at the time of packaging, product in the largest and smallest cartons used in the process, and product with relatively short and long residence times in an unchilled carton stack assembly area. Twenty-one temperature histories were collected for each of the products, and the possible proliferation of an indicator organism, Escherichia coli, calculated for each temperature history. The results were assessed against a temperature function integration criterion derived from studies of beef carcass and cartoned meat cooling processes. Products packaged at near-ambient temperature readily met with the criterion, but products packed at near-body temperatures did not comply. The latter non-compliance was extreme for product packaged in large cartons. However, the principal cause of non-compliance was identified as highly variable cooling conditions in the carton freezing facility. A brief survey of air speeds and temperatures within that facility indicated means by which product cooling could be better controlled.