Some Insights into MIMO Mutual Information: The High SNR Case

We consider mutual information of multiple-input multiple-output (MIMO) wireless channels with complex isotropic Gaussian input in the case where the receiver has perfect channel, knowledge. For arbitrary fading statistics, a mutual information lower bound is decomposed in a sum of three terms involving: a) average SNR; b) channel fading; and c) a term characterizing the "effective rank", or eigenvalue dispersion, of the channel matrix. The decomposition suggests that spatial multiplexing efficiency of a MIMO channel can be characterized by the so-called ellipticity statistic. Distribution functions, means and variances of the random terms in the decomposition for the case of Rayleigh fading are also derived     

Development of crumb rubber reinforced bituminous binder under laboratory conditions

Bituminous binders are widely used in the construction of flexible pavements. However, in some applications, the performance of conventional binders is not considered to be satisfactory. Reinforcing these binders with selected polymers prevents premature failure of a pavement by improving the properties of the binder. Another source of reinforcement comes from crumb (ground) rubber produced from waste tyres. After they have been worn-out during their limited service life, millions of used tyres are discarded every year and are hauled to a dump. The fatigue resistance at temperatures below normal service temperatures (25°C), one of the key engineering properties of crumb rubber reinforced binders, has been found to be lower than that of neat binders. This paper is concerned with the development of a rubber reinforced binder. It was shown that the binder has the potential to be used as an all-weather wearing course in flexible roads, whilst at the same time recycling a considerable amount of waste rubber.     

Solutions to a combined problem of excessive hydrogen sulfide in biogas and struvite scaling.

The Woodman Point Wastewater Treatment Plant (WWTP) in Western Australia has experienced two separate problems causing avoidable maintenance costs: the build-up of massive struvite (MgNH4PO4. 6H2O) scaling downstream of the anaerobic digester and the formation of hydrogen sulfide (H2S) levels in the digester gas to levels that compromised gas engine operation and caused high operating costs on the gas scrubber. As both problems hang together with a chemical imbalance in the anaerobic digester, we decided to investigate whether both problems could be (feasibly and economically) addressed by a common solution (such as dosing of iron solutions to precipitate both sulfide and phosphate), or by using separate approaches. Laboratory results showed that, the hydrogen sulfide emission in digesters could be effectively and economically controlled by the addition of iron dosing. Slightly higher than the theoretical value of 1.5 mol of FeCl3 was required to precipitate 1 mol of dissolved sulfide inside the digester. Due to the high concentration of PO4(3-) in the digested sludge liquor, significantly higher iron is required for struvite precipitation. Iron dosing did not appear an economic solution for struvite control via iron phosphate formation. By taking advantage of the natural tendency of struvite formation in the digester liquid, it is possible to reduce the risk of struvite precipitation in and around the sludge-dewatering centrifuge by increasing the pH to precipitate struvite out before passing through the centrifuge. However, as the Mg2+/PO4(3-) molar ratio in digested sludge was low, by increasing the pH alone (using NaOH) the precipitation of PO4(3-) was limited by the amount of cations (Ca2+ and Mg2+) available in the sludge. Although this would reduce struvite precipitation in the centrifuge, it could not significantly reduce PO4(3-) recycling back to the plant. For long-term operation, maximum PO4(3-) reduction should be the ultimate aim to minimise PO4(3-) accumulation in the plant. Magnesium hydroxide liquid (MHL) was found to be the most cost-effective chemical to achieve this goal. It enhanced struvite precipitation from both, digested sludge and centrate to the point where more than 95% PO4(3-) reduction in the digested sludge was achieved.     

Wear and Creep Characteristics of a Carbon‐Derived Si3N4/SiC Micro/Nanocomposite

In the presented work some properties of a recently developed Si₃N₄/SiC micro/nanocomposite have been investigated. The material was tested using a pin on disc configuration. Under unlubricated sliding conditions using Si₃N₄ pin at 50 % humidity, the friction coefficient was in the range of 0,6 ‐ 0,7. The reduction of humidity resulted in a lower coefficient of friction, in vacuum the coefficient of friction had a value of about 0,6. The wear resistance in vacuum was significantly lower then that in air. The wear patterns on the Si₃N₄+SiC disc revealed that mechanical fracture was the wear controlling mechanism. Creep tests were realized in four point bending configuration in the temperature interval 1200‐1400 °C at stresses 50,100 and 150 MPa and the minimal creep deformation rate was established for each stress level. The activation energy, established from the minimal creep deformation had a value of about 360 kJ/mol and the stress exponent values were in the range of 0.8‐1.28. From the achieved stress exponents it can be assumed that under the studied load/temperature conditions the diffusion creep was the most probable creep controlling mechanism.     

Colloidal processing of polymer ceramic nanocomposite integral capacitors

Polymer ceramic composites form a suitable material system for low temperature fabrication of embedded capacitors appropriate for the MCM-L technology. Improved electrical properties such as permittivity can be achieved by efficient filling of polymers with high dielectric constant ceramic powders such as lead magnesium niobate-lead titanate (PMN-PT) and barium titanate (BT). Photodefinable epoxies as the matrix polymer allow fine feature definition of the capacitor elements by conventional lithography techniques. The optimum weight percent of dispersant is tuned by monitoring the viscosity of the suspension. The dispersion mechanism (steric and electrostatic contribution) in a slightly polar solvent such as propylene glycol methyl ether acetate (PGMEA) is investigated from electrophoretic measurements. A high positive zeta potential is observed in the suspension, which suggests a strong contribution of electrostatic stabilization. By optimizing the particle packing using a bimodal distribution and modified processing methodology, a dielectric constant greater than 135 was achieved in PMN-PT/epoxy system. Suspensions are made with the lowest PGMEA content to ensure the efficiency of the dispersion and efficient particle packing in the dried film. Improved colloidal processing of nanoparticle-filled epoxy is a promising method to obtain ultra-thin capacitor films (<2/spl mu/m) with high capacitance density and improved yield. Capacitance of 35 nF/cm/sup 2/ was achieved with the thinnest films (2.5-3.0 /spl mu/m).     

Development of a Continuous Segmented Flow Tubular Reactor and the “Scale‐out” Concept – In Search of Perfect Powders

The synthesis of powders with controlled shape and narrow particle size distributions is still a major challenge for many industries. A continuous Segmented Flow Tubular Reactor (SFTR) has been developed to overcome homogeneity and scale‐up problems encountered when using batch reactors. Supersaturation is created by mixing the co‐reactants in a micromixer inducing precipitation; the suspension is then segmented into identical micro‐volumes by a non‐miscible fluid and sent through a tube. These micro‐volumes are more homogeneous when compared to large batch reactors leading to narrower size distributions, better particle morphology, polymorph selectivity and stoichiometry. All these features have been demonstrated on single tube SFTR for different chemical systems. To increase productivity for commercial application the SFTR is being “scaled‐out” by multiplying the number of tubes running in parallel instead of scaling‐up by increasing their size. The versatility of the multi‐tube unit will allow changes in type of precipitate with a minimum of new investment as new chemistry can be researched, developed and optimised in a single tube SFTR and then transferred to the multi‐tube unit for powder production.     

Reliability investigation of 0.07-/spl mu/m InGaAs-InAlAs-InP HEMT MMICs with pseudomorphic In/sub 0.75/Ga/sub 0.25/As channel

The authors have investigated the reliability performance of G-band (183 GHz) monolithic microwave integrated circuit (MMIC) amplifiers fabricated using 0.07-/spl mu/m T-gate InGaAs-InAlAs-InP HEMTs with pseudomorphic In/sub 0.75/Ga/sub 0.25/As channel on 3-in wafers. Life test was performed at two temperatures (T/sub 1/ = 200 /spl deg/C and T/sub 2/ = 215 /spl deg/C), and the amplifiers were stressed at V/sub ds/ of 1 V and I/sub ds/ of 250 mA/mm in a N/sub 2/ ambient. The activation energy is as high as 1.7 eV, achieving a projected median-time-to-failure (MTTF) /spl ap/ 2 /spl times/ 10/sup 6/ h at a junction temperature of 125 /spl deg/C. MTTF was determined by 2-temperature constant current stress using /spl Delta/G/sub mp/ = -20% as the failure criteria. The difference of reliability performance between 0.07-/spl mu/m InGaAs-InAlAs-InP HEMT MMICs with pseudomorphic In/sub 0.75/Ga/sub 0.25/As channel and 0.1-/spl mu/m InGaAs-InAlAs-InP HEMT MMICs with In/sub 0.6/Ga/sub 0.4/As channel is also discussed. The achieved high-reliability result demonstrates a robust 0.07-/spl mu/m pseudomorphic InGaAs-InAlAs-InP HEMT MMICs production technology for G-band applications.     

Effect of thermal annealing on optical and photoelectric properties of microcrystalline hydrogenated silicon films

The effect of thermal annealing in the temperature range T _a=300–600°C of films of microcrystal-line hydrogenated silicon (μc-Si:H) lightly doped with boron on the spectral dependences of the absorption coefficient (α) at photon energies hν=0.8–2.0 eV, dark conductivity (σ_d), and photoconductivity (Δσ_ph) was studied at room temperature. With increasing annealing temperature, a nonmonotonic variation of α (at hν<1.2 eV), σ_d, and Δσ_ph was observed. The data obtained are attributed to a change in the concentration of electrically active impurities and formation of defects, caused by hydrogen effusion and bond restructuring at high annealing temperatures.     

The hot compaction behaviour of woven oriented polypropylene fibres and tapes. I. Mechanical properties

The aim of this work was to establish the important parameters that control the hot compaction behaviour of woven oriented polypropylene. Five commercial woven cloths, based on four different polypropylene polymers, were selected so that the perceived important variables could be studied. These include the mechanical properties of the original oriented tapes or fibres, the geometry of the oriented reinforcement (fibres or tapes), the mechanical properties of the base polymer (which are crucially dependant on the molecular weight and morphology), and the weave style. The five cloths were chosen so as to explore the boundaries of these various parameters, i.e. low and high molecular weight: circular or rectangular reinforcement (fibres or tapes): low or high tape initial orientation: coarse or fine weave.A vital aspect of this study was the realisation that hot compacted polypropylene could be envisaged as a composite, comprising an oriented ‘reinforcement’ bound together by a matrix phase, formed by melting and recrystallisation of the original oriented material. We have established the crucial importance of the properties of the melted and recrystallised matrix phase, especially the level of ductility, in controlling the properties of the hot compacted composite.     

Thermal conductivity of doped PbTe-based solid solutions with off-center impurities

The coefficients of thermopower and electrical and thermal conductivity in the PbTe_0.8Se_0.1 S _0.1 solid solution with electron concentration (4.6–54) × 10¹⁸ cm^?3 are studied in the range of 85–300 K (and in some cases up to 700 K). The temperature dependences of electrical and thermal conductivity indicate that the low-temperature electron and phonon scattering initiated by the off-center impurity of sulfur exists. The temperature dependences of the electronic and lattice components of thermal conductivity are calculated in the approximation of a parabolic spectrum and electron scattering by acoustic phonons and neutral substitutional impurities. The lattice thermal conductivity is found to have a feature in the form of a shallow minimum in the range of 85–250 K. A similar feature, while not so clearly pronounced, is found to exist also in Pb_1?x Sn_xTe_1?x Se_x alloys (x≥0.15) with an off-center tin impurity. An analysis of the possible origins of this effect suggests that, at low temperatures, the Lorentz numbers L of the materials under study are smaller than the L₀ numbers employed which correspond to the above scattering mechanisms. The cause of the decrease in L is related to electron scattering at two-level systems, a mechanism whose effect grows with increasing electron energy. An analysis of experimental data obtained at high temperatures, as well as on undoped samples with the lowest possible carrier concentrations, yields the values of L for samples with different electron densities. The minimum value L/L₀ = 0.75 is obtained for a lightly doped sample at ～130 K.