Thermal Stability and Coefficient of Friction of the Diamond Composites with the Titanium Compound Bonding Phase

In this paper, processes occurring during heat treatment of the diamond-Ti compound composites without Co addition were investigated and compared with commercial PCD. Three types of materials were prepared. The first material was sintered using the mixture containing diamond and 10 mass% of TiC, the second material was prepared using diamond powder and 10 mass% of Ti-Si-C, and the third composite was sintered using the addition of 10 mass% of TiB₂. During the research, it was proved that TiO₂ formation contributes to material swelling and WO₃ (W is present from the milling process) causes a significant increase in coefficient of friction. TiC and Ti-Si-C bonded materials are very susceptible to this process of oxidation; their hardness drops absolutely after wear test at 600 °C. The diamond composite with TiB₂ is the most resistant to oxidation from investigated materials.     

Influence of silicon carbide chills on solidification process and shrinkage porosity of castings made of nickel based superalloys

The paper presents the manufacturing methodology of IN713C castings by application of investment casting method and silicon carbide (SiC) chills.

On the basis of numerical simulation and conducted microstructure analysis, it was established that the application of SiC chills results in significant decrease in shrinkage porosity, in comparison to castings without chills. The temperature measurement was carried out, and the influence of chills on the kinetics of solidification process was established. It was determined that the application of SiC chills causes the increase in cooling rate (～0·1 K s^?1), in comparison to the casting without chills. The authors carried out numerical optimisation with the use of ProCAST software and established which parameters have the largest influence on the solidification process of castings with and without chills. In addition to SiC, the graphite and Al₂O₃ were analysed as chill material in terms of influence on the predicted kinetics of cooling process and the shrinkage porosity of castings. The conditions of solidification process for castings, which are equipped with chills and are free from shrinkage porosity, were determined on the basis of obtained results.     

Power assisted fuel cell

A hybrid fuel cell demonstrated pulse power capability at pulse power load simulations synonymous with electronics and communications equipment. The hybrid consisted of a 25.0 W Proton Exchange Membrane Fuel Cell (PEMFC) stack in parallel with a two-cell lead-acid battery. Performance of the hybrid PEMFC was superior to either the battery or fuel cell stack alone at the 18.0 W load. The hybrid delivered a flat discharge voltage profile of about 4.0 V over a 5 h radio continuous transmit mode of 18.0 W.     

Analytical evaluation of average bit error rate for the land mobile satellite channel

An analytical solution is presented showing the average bit error probability for the land mobile satellite channel. The channel is modelled as Rice and Rayleigh—lognormal fading. Modulation schemes under consideration include differentially detected PSK and non-coherently detected FSK. Results indicate that the receiver performance is highly dominated by the time share of shadowing. The ratio of the BERs in shadowed and unshadowed areas of typical measured channels and an operating point assumed to be at E_s/N_o = 10 dB is of the order of 10^?2.     

Characterization of adsorption sites on aggregate soil samples using synchrotron X-ray computerized microtomography

Synchrotron-source X-ray computerized microtomography (CMT) was used to evaluate the adsorptive properties of aggregate soil samples. A linear relationship between measured mean mass attenuation coefficient (sigma) and mass fraction iron was generated by imaging mineral standards with known iron contents. On the basis of reported stoichiometries of the clay minerals and identifications of iron oxyhydroxides (1), we calculated the mass fraction iron and iron oxyhydroxide in the intergranular material. The mass fractions of iron were estimated to range from 0.17 to 0.22 for measurements made at 18 keV and from 0.18 to 0.21 for measurements made at 26 keV. One aggregate sample also contained regions within the intergranular material with mass fraction iron ranging from 0.29 to 0.31 and from 0.33 to 0.36 for the 18 and 26 keV measurements, respectively. The mass fraction iron oxyhydroxide ranged from 0.18 to 0.35 for the low-iron intergranular material and from 0.40 to 0.59 for the high-iron intergranular material. Using absorption edge difference imaging with CMT, we visualized cesium on the intergranular material, presumably because of adsorption and possible exchange reactions. By characterizing the mass fraction iron, the mass fraction iron oxyhydroxide, and the adsorptive capacity of these soil mineral aggregates, we provide information useful for conceptualization, development, and parametrization of transport models.     

A transcendental approximation for natural convection at small prandtl numbers

An improved method of approximation for natural convection at small Prandtl numbers is described. It involves simple transcendental functions for profile representation. The method utilizes a physically significant model of the velocity distribution in which regions of the thermal boundary layer and viscous boundary layer are distinguished. The shape of the velocity profile is allowed to vary with Prandtl number. The method is checked against known exact results for natural convection on a vertical flat plate and is used to obtain results for a horizontal cylinder.