Role of fabrication route and sintering on wear and mechanical properties of liquid-phase-sintered alumina

Liquid-phase-sintered Al₂O₃ (LPS) fabricated by slip casting, tape casting, isopressing, uniaxial pressing, piston and auger extrusion showed substantial differences in wear due to differences in morphology as observed in image analyses of SEM micrographs. The abrasive wear was low in the case of uniaxial pressing and high in the case of tape casting in the ‘dry sand and rubber wheel’ test. The wear surface of the tape cast specimen exhibited extensive microcracking possibly due to orientation of Al₂O₃ platelet (major face) parallel to the abraded surface whereas some degree of perpendicular orientation in extruded surface resulted in lower wear loss. In wet-milling wear test, the isopressed balls of a 95–97 wt% LPS derived from reactive powder (<1 μm) showed 25% lower wear loss than that of the extruded balls of a 91–94 wt% LPS derived from coarse powder (70–100 μm). Sintering at a lower temperature with longer duration and batch milling of the composition in between 12 and 16 h resulted in low wear loss. Flexural strength also improved by longer sintering time but did not show any improvement by increasing milling time. However, the variation in flexural strength was minimized by isopressing the extruded specimen. A high indentation fracture toughness at 49.03 N test load was associated with (i) large elongated reinforcement grains in a fine-grained microstructure with overall elongated morphology and (ii) with an intergranular fracture.     

Simple Scheduling Algorithms for Use with a Waveguide Grating Multiplexer Based Local Optical Network

As the need for greater bandwidth in local-area networks grows, wavelength-division multiplexing (WDM) is gathering attention as a viable successor to Gigabit Ethernet technologies. In this paper we introduce a new WDM optical LAN architecture based on the waveguide grating multiplexer (WGM) rather than the traditional passive star coupler (PSC). An N-port WGM allows N ² × N ² connectivity via only N physical wavelengths, due to its inherent space-division multiplexing property. Wavelength-routed networks based on the WGM promise to be significant components of future LAN and WAN technologies not only because of their efficient use of wavelengths, but also because they have been implemented as integrated devices. We propose simple, low-complexity TDM schedules for interconnecting MN nodes (M nodes per port) with a WGM in a local environment. Each node is equipped with a single tunable transmitter and a single tunable receiver (both of which can access all N wavelengths). Various transmitter and receiver tuning latencies are considered. We show that, for negligible tuning latencies, aggregate network throughput approaching min(MN, N ²) can be achieved, and for tuning latencies on the order of a packet length or more, throughput on the order of N can be achieved. Since these performance metrics are vastly superior to that of an equivalent PSC-based system (whose maximum throughput is limited by the number of wavelengths, N), we propose that the WGM be considered as an alternative to the PSC for enabling WDM LANs and multiprocessor interconnects.     

Formation of Fiber-Like Amorphous Silica Structures by Externally Applied Shear

The structure of amorphous silica determines its properties and governs its applications. Here we report the synthesis of elongated silica chains/rods on the nanometer size scale formed by the orientation of a growing silica sol. We have utilized a cationically charged synthetic organic polymer as a catalyst/template and perturbed the system by externally applied shear. It is proposed that the polymer orientation plays an important role in the formation of such morphologies.     

A Simple Heuristic for Assignment of Cells to Switches in a PCS Network

This work deals with a design problem for a network of Personal Communication Services (PCS). The goal is to assign cells to switches in a PCS Network (PCSN) in an optimum manner so as to minimize the total cost which includes two types of cost, namely handoff cost between two adjacent cells, and cable cost between cells and switches. The design is to be optimized subject to the constraint that the call volume of each switch must not exceed its call handling capacity. In the literature, this problem has been conventionally formulated as an integer programming problem. However, because of the time complexity of the problem, the solution procedures are usually heuristic when the number of cells and switches are more. In this paper, we have proposed an assignment heuristic which is faster and much simpler than the existing algorithms. Despite its simplicity, experimental results show that it performs equally well in terms of solution quality, and, at the same time, it is faster than its predecessors. We present the algorithm as well as comparative results to justify our claim.     

Online connection provisioning in metro optical WDM networks using reconfigurable OADMs

Optical add/drop multiplexers (OADMs) can significantly reduce the cost of metro optical wavelength-division multiplexing (WDM) ring networks by allowing traffic to bypass intermediate nodes without expensive opto-electro-opto (O-E-O) conversion. Some traditional OADMs, called fixed OADMs (FOADMs), can only add/drop traffic on a specific wavelength. Reconfigurable OADMs (ROADMs) are emerging, which can add/drop traffic onto/from different wavelengths at different time. ROADMs provide desirable flexibility, enable fast provisioning of dynamic traffic, and save capital expenditure (CapEx) and operational expenditure (OpEx). In order to be cost effective, some ROADMs employ architectures that tune the ROADM continuously from one wavelength to another, crossing through all the wavelengths in between, which may cause interference to the connections, if any, on those wavelengths being crossed. In order to prevent existing connections from being interrupted, a constraint needs to be imposed that ROADMs cannot cross working wavelengths when tuning. In this paper, the design and the benefits of metro optical WDM network architectures using ROADMs and the impact of this tuning constraint on the performance of the network are investigated. The dynamic traffic provisioning problem is analyzed and divided into two subproblems: 1) a traditional one on resource allocation; and 2) a new subproblem on tuning-head positioning (TP). Several heuristics for each subproblem are developed to combat the tuning constraint. Results from our simulation experiments show that the tuning constraint can significantly affect the network performance in terms of overall connection blocking probability, and good heuristics for network control and management are needed to overcome this tuning constraint.     

Optimization of HV electrode systems by neural networks using a newlearning method

To avoid a large number of iterations, optimization of electrode shapes has been done by artificial neural networks (NN). Two practical examples have been considered, an axisymmetric single-phase GIS bus termination and an axisymmetric transformer shield ring. The shape of the electrodes has been taken as quarter-ellipse or half-ellipse because an ellipse has more flexibility than a circle. For NN, the so-called resilient propagation algorithm, learning faster than the standard back-propagation algorithm, has been employed. The training sets as well as the test sets of NN have been prepared by charge simulation method     

Grain boundary sliding in nanomaterials at elevated temperatures

The unique deformation behavior of nanocrystalline materials is considered to be caused by suppression of conventional lattice dislocation slip (which dominates in coarse-grained materials) and effective action of alternative deformation mechanisms occurring through motion of grain boundary defects. A significant role of grain boundary sliding in deformation processes in nanocrystalline materials was shown in models and was revealed experimentally.     

Isothermalin situ reduction kinetic analysis of NiCl2-containing gel

Isothermalin situ reduction kinetic study of NiCl₂-containing gel was carried out. The detailed statistical as well as reduced time analysis show that contracting geometry and nucleation and growth type of mixed mechanisms are operative. The activation energy for reduction is in the range 158–193 kJ/mol. Thermal analysis on NiCl₂-containing gel was carried out in the temperature range 800°C to 900°C.