A Higher-Order Asymptotic Theory for Fully Developed Turbulent Flow in Smooth Pipes

A complete second-order asymptotic theory for fully developed turbulent flow in smooth pipes at high turbulent Reynolds numbers is presented in the paper. The theory is based on Prandtl's mixing-length hypothesis involving a fourth-order polynomial representation for the mixing length and taking into account its dependence on the Reynolds number. Two main contributions with respect to the existing literature have been achieved:(a) the friction law is obtained by asymptotic evaluation of an integral, completely independently of the velocity field, and(b) an axis layer (in addition to the wall layer and the outer layer) has to be included in the analysis in order to remove a nonuniformity appearing in the second-order solution for the velocity fieldClosed-form analytic expressions for all constants and wake functions appearing up to the second-order solution in both the friction law and the velocity field are obtained. The results are in a very good agreement with experiments.     

Modified self-propagating high-temperature synthesis of nanosized La0.7Ca0.3MnO3

A modified solid-state combustion route was developed for the preparation of nanocrystalline manganite La_0.7Ca_0.3MnO₃ in a single-step process, using metal nitrates and glucose/KNO₃ redox mixture. The obtained sample was found to crystallize within O′ type of orthorhombic perovskite structure (space group Pnma), without the presence of other structural phases or impurities. Nanoparticles are found to have particle size in the range 12–35 nm, and to be highly crystalline without the presence of amorphous surface layer. Magnetic measurements show that nanoparticles display bulk-like magnetic properties, with ferromagnetic phase transition at 125 K and the absence of superparamagnetic or spin-glass behavior.     

Refractory coating based on cordierite for application in new evaporate pattern casting process

Standard raw materials, kaolin, talc, MgO, alumina, feldspar and sepiolite, were used in synthesis of four different cordierite type ceramics. Sintered cordierite was used as refractory filler in the ceramic coating for evaporative polystyrene patterns in the EPC process. The cordierite samples were tested by the following methods: roentgen diffraction analysis, diffraction thermal analysis and polarized microscope. The shape and grain size were analyzed by the program package OZARIA 2.5. In order to evaluate the possible application of cordierite as the refractory filler, four different coating processes were investigated.     

Effect of multipath propagation on the forward link of a CDMA cellular system

In this paper we study the effect of multipath propagation on the performance of the forward link of a CDMA cellular system. We assume that RAKE receivers are used by the mobile terminals to receive the multipath signals and derive signal-to-noise ratios (SNR) for the RAKE receiver output for both orthogonal and non-orthogonal spreading sequences. These SNR expressions are evaluated using real impulse response measurement data obtained in the city of Toronto and comparisons are made between urban and suburban environments. We have found that even though multipath propagation tends to destroy the orthogonality of signals in an orthogonal CDMA system, the system with orthogonal CDMA codes still performs significantly better than a system utilizing random spreading codes in realistic multipath propagation environments.This work was supported in part by Bell Mobility Cellular and in part by the Information Technology Research Center of Ontario (ITRC).     

Multi-layer atom chips for atom tunneling experiments near the chip surface

This paper describes the design and fabrication of an atom chip to be used in ultra-high-vacuum cells for cold-atom tunneling experiments. A fabrication process was developed to pattern micrometer- and nanometer-scale copper wires onto a single chip. The wires, with fabricated widths down to 200 nm, can sustain current densities of more than 7.5 × 10⁷ A/cm². Partially suspended wires, developed in order to reduce the Casimir–Polder force between atoms and surface, were also fabricated and tested. Extensive measurements for variable wire width show that the sustainable currents are sufficiently large to allow chip-based atom tunneling experiments. Such chips may allow the realization of an atom transistor.     

Adopting Software Engineering Trends in AI

Designing and developing reliable, robust, well-architected, and easy-to-extend software applications or tools in any field requires conformance to sound principles and rules of software engineering. Intelligent systems, especially AI development tools, are no exception. Although AI has always been a wellspring of ideas that software engineering has later adopted, most of its gems remain buried in laboratories, available only to a few AI practitioners. This paper believes that AI tools should be integrated with mainstream SE tools and thus become more widely known and used. To that end, this paper presents the development of Air, an integrated AI development environment based on model-driven-architecture concepts. Using the philosophy of MDA in Air, familiar and mainstream software technologies are used and expanded with new functionalities     

Control of the Electrical Properties in Spinel Oxides by Manipulating the Cation Disorder

In this work, the impact of cation disorder on the electrical properties of biaxially textured Co₂ZnO₄ and Co₂NiO₄ thin films grown by pulsed laser deposition are investigated using a combination of experiment and theory. Resonant elastic X‐ray diffraction along with conductivity measurements both before and after post‐deposition annealing show that Co₂ZnO₄ and Co₂NiO₄ exhibit opposite changes of the conductivity with cation disorder, which can be traced back to their different ground‐state atomic structures, being normal and inverse spinel, respectively. Electronic structure calculations identify a self‐doping mechanism as the origin of conductivity. A novel thermodynamic model describes the non‐equilibrium cation disorder in terms of an effective temperature. This work offers a way of controlling the conductivity in spinels in a quantitative manner by controlling the cation disorder and a new design principle whereby non‐equilibrium growth can be used to create beneficial disorder.     

Anomalous behaviour of the magnetic hysteresis loop in the α-Fe2O3/SiO2 nanocomposite

The α-Fe₂O₃/SiO₂ nanocomposite containing 45 wt.% of hematite was prepared by the sol-gel method and characterized by using X-ray diffractometer (XRD), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometer. TEM microscopy showed spherical particles with average size about 10 nm, whereas XRD diffraction confirmed the formation of the hematite phase. The magnetic measurements showed anomalous behavior of the hysteresis loops including decrease of high field isothermal magnetization and overlap of initial, remagnetization and magnetization curves. This anomalous behavior represents a novel effect for α-Fe₂O₃/SiO₂ nanocomposites. We conjecture that a field-induced antiferromagnetic coupling between nanoparticles may produce this effect.