Product mix determination in the presence of alternate process plans and stochastic demand

The product mix problem in the presence of alternate process plans under uncertain demand is formulated as a non-linear programming model. A heuristic solution procedure based on lagrangean relaxation technique is also presented.     

Cell formation in flexible manufacturing systems under resource constraints

In this paper, the cell formation problem in Flexible Manufacturing Systems under resource constraints is discussed. A 0–1 integer programming model is developed to form the machine-part groups and to decide on the number of machines and the number of copies of tools required to achieve minimum overall system cost. The model takes into account the processing time available on any machine, tool lives and the processing requirements of the parts. The model is illustrated using a numerical example.     

Focusing properties of small lenses

The potential use of small substrate lenses for coupling to antennas at millimeter wave frequencies is investigated by analyzing the focusing properties of dielectric spheres with quarter-wave matching layers. The fields and the power density are calculated at various points within the sphere to learn how the focusing deteriorates as the lens is made smaller. The absorption loss of the lens is also calculated. The calculations show that quartz spheres with quarter-wave matching layers, can exhibit good focusing properties down to a radius of about half a free space wavelength. This minimum radius was found to increase almost linearly with the refractive index of the lens. The calculations also indicate that at 94GHz the absorption losses of fused quartz, silicon and gallium arsenide lenses, with radii of one free space wavelength or less, are less than 0.2 dB. As the minimum diameter of a quartz lens is comparable with the spot size in free space, it should be possible to build an imaging lens array in which each lens will act as a separate imaging element.     

Vehicle requirements model for automated guided vehicle systems

A simulation-based cost model is presented for determining the number of automated guided vehicles (AGVs) needed to meet the material handling requirements in a manufacturing system. The estimation of the number of vehicles is based on the sum of the idle-time costs of vehicles and machines, and the cost of waiting time of parts. While an increase in the number of vehicles reduces the waiting time of parts and the idle time of machines, it increases the idle time of vehicles. The application is illustrated using a hypothetical manufacturing system.     

MoO(3-x) nanowire arrays as stable and high-capacity anodes for lithium ion batteries

In this study, vertical nanowire arrays of MoO(3-x) grown on metallic substrates with diameters of ~90 nm show high-capacity retention of ~630 mAhg(-1) for up to 20 cycles at 50 mAg(-1) current density. Particularly, they exhibit a capacity retention of ~500 mAhg(-1) in the voltage window of 0.7-0.1 V, much higher than the theoretical capacity of graphite. In addition, 10 nm Si-coated MoO(3-x) nanowire arrays have shown a capacity retention of ~780 mAhg(-1), indicating that hybrid materials are the next generation materials for lithium ion batteries.     

Resource-requirements planning in flexible manufacturing systems

In this paper, we address the problem of planning the requirements of some of the important resources in flexible manufacturing systems. Specifically, we model the problem of estimating the required numbers and types of machines and tools in the context of a cellular layout. A two-stage procedure is developed which first forms the part families, using the complete-linkage clustering method based on a new similarity index defined in terms of the tooling requirements, and then subsequently estimates the resource requirements to manufacture the part families using an integer programming model. Several variations of the model are discussed and a numerical example is given.     

Thermal Microstructural Multiscale Simulation of Solidification and Eutectoid Transformation of Hypereutectic Gray Cast Iron

Although the gray cast iron solidification process has been the subject of several modeling studies, almost all available models appear to deal with only the more widely used hypoeutectic compositions. Models related to hypereutectic gray iron compositions with lamellar (or flake) graphite, and in particular for the proeutectic and eutectoid zones, are hard to find in the open literature. Hence, in the present work, a thermal microstructural multiscale model is proposed to describe the solidification and eutectoid transformation of a slightly hypereutectic composition leading to lamellar graphite gray iron morphology. The main predictions were: (a) temperature evolutions; (b) fractions of graphite, ferrite, and pearlite; (c) density; and (d) size of ferrite, pearlite, and gray eutectic grains; (e) average interlamellar graphite spacing; and (f) its thickness. The predicted cooling curves and fractions for castings with two different compositions and two different pouring temperatures were validated using experimental data. The differences between this model and existing models for hypoeutectic compositions are discussed.     

Performance analysis of machine cell configurations using simulation

The objective of this research is to develop a generalized model that can analyze the performance of any cellular manufacturing system under various combinations of dispatching and loading policies. Early stages of the research along this line before generalization of the model is presented in this paper. A menu-driven SIMAN based simulation model is developed to analyze the performance of a particular cellular manufacturing system in terms of machine utilization, tool utilization, transporter (AGV) utilization, part waiting time, etc.     

Surface roughness and slope measurements using polarimetric SARdata

In this paper, the circular polarization coherence, ρ_RRLL , is investigated as a potential estimator of terrain surface roughness and small-scale slopes. The studies utilize microwave backscatter collected from 1) dielectric surfaces in an anechoic chamber and 2) a desert test site using P-, L-, and C-band NASA/JPL AIRSAR data. These experimental studies and supporting theory, indicate a sensitive decrease of |ρ_RRLL| with increasing surface roughness ks over a range 0 ⩽ ks ⩽ 1. For the present studies this decrease is caused largely by the depolarizing effects of small-scale surface slopes in the azimuth direction rather than by volume, or multiple scatter. For cases when the scatter is reflection symmetric, the value of |ρ_RRLL| depends on the surface roughness and on the local incidence angle. The dependence of |ρ_PRRLL| on the local incidence angle is supported by theory and experimental results. For these same scattering cases, however, |ρ_PRRLL| is independent of the surface dielectric constant. Estimation of the functional dependency of |ρ_PRRLL| versus ks, for a mid-range incidence angle, has been carried out using roughness estimates derived from an empirical model