Technology choice and capacity expansion with two product families: tradeoffs between scale and scope

Recent developments in modern technologies such as CIM, FMS and CAD provide a great degree of operational flexibility and permit production of a variety of products with little or no changeover costs. In contrast, dedicated technologies with specialized equipment are designed to produce a limited range of products more efficiently. In this paper, we examire the tradeoffs between scale and scope economies in a two-product environment with general, dynamic demand patterns. We use a discrete period, finite horizon mathematical program to determine the optimal mix of dedicated and flexible technologies. Since the problem is difficult to solve optimally, we develop a two-phased heuristic procedure to obtain good expansion plans that determine type of technologies and amount of capacity additions. These procedures are based on easily solvable subproblems derived from the planning problem. Our computational results suggest that the methods work well and provide acceptable solutions with reasonable effort.     

Experimental Investigations of Colloidal Silica Grouting in Porous Media

This paper presents the results of an experimental investigation performed to understand the processes influencing the injection of colloidal silica grout into porous media. Based on the combined analysis of grout injection pressures and the visually observed grout distribution patterns, three major processes, gelation, shear, and viscous fingering, have been identified to occur during grout injection. The results demonstrate the dynamic interplay between grout viscosity variations and the resulting flow instabilities.     

The use of slow releasing nanoparticle encapsulated Azadirachtin formulations for the management of Caryedon serratus O. (groundnut bruchid)

Nanobiotechnology is one of the emerging fields and its interventions in agriculture is been attracting the scientific community. Herein, the authors first to report on control of groundnut bruchid (Caryedon serratus O.) using nanoscale zinc oxide (ZnONPs) particles and nanoscale chitosan (CNPs) particles‐based Azadirachtin formulations. ZnONPs and CNPs were prepared using sol–gel and ion tropic gelation techniques, respectively. Neem seed kernel extract (NSKE) 5% and Neem oil (3000 and 1000 ppm) were encapsulated using the prepared nanoscale materials and characterised using the techniques such as dynamic light scattering, high‐resolution transmission electron microscopy. Spherical‐shaped nanoparticles were formed after encapsulation with the required bio‐materials (ZnONPs 33.1 nm; CNPs 78.8 nm; neem oil encapsulated (3000 ppm) ZnONPs 182.9 nm; NSKE encapsulated ZnONPs 84.9 nm) and observed that the particles are stable (52.3 mV for ZnONPs, −36.2 mV for CNPs, −43.0 mV for neem oil encapsulated (3000 ppm) ZnONPs and −39.4 mV for NSKE encapsulated ZnONPs). NSKE encapsulated CNPs were able to contain groundnut bruchid up to 180 days with 54.61% weight loss compared to other formulations tested. Thus biomaterial encapsulated nanoscale material formulations are proved to be effective in controlling stored grain pests to reduce huge economic losses.Inspec keywords: nanobiotechnology, agricultural products, toxicology, agrochemicals, food safety, sol‐gel processing, food preservation, agriculture, II‐VI semiconductors, storage, nanoparticles, transmission electron microscopy, encapsulation, nanofabrication, zinc compounds, wide band gap semiconductors, food processing industry, light scattering, materials preparation, pest control, nanocompositesOther keywords: voltage ‐36.2 mV, voltage ‐43.0 mV, voltage ‐39.4 mV, voltage 52.3 mV, size 84.9 nm, size 182.9 nm, size 78.8 nm, size 33.1 nm, NSKE, neem seed kernel extract, caryedon serratus O., CNPs, bio‐materials, nanoscale materials, nanoparticle, encapsulation, spherical‐shaped nanoparticles, high‐resolution transmission electron microscopy, neem oil, ion tropic gelation techniques, sol–gel, nanoscale chitosan particles, nanoscale zinc oxide particles, scientific community, groundnut bruchid, Azadirachtin formulations, biomaterial encapsulated nanoscale material formulations     

Permutation flow shop scheduling with earliness and tardiness penalties

We consider the permutation flow shop scheduling problem with earliness and tardiness penalties (E/T) and common due date for jobs. We show that the problem can be sub-divided into three cases: (i) the due date is such that all jobs are necessarily tardy; (ii) the due date is unrestricted; and (iii) the due date is between the two. Based on analytical results we provide partial characterisation of the optimal solution and develop a comprehensive approach for solving the problem over the entire range of due dates. Our approach, which draws upon the existing literature and results for the single machine problem, successfully exploits the properties of the optimal solution. Limited computational results indicate that the performance of the heuristic is reasonable and has the potential to significantly improve performance. This approach has been incorporated as part of the scheduling module of the production planning and scheduling system we developed for a medium-sized bulk drug manufacturer.     

Lot sizing under (Q, R) policy in a capcity constrained manufacturing facility

Traditional approaches to lot sizing and inventory control consider uncertainties in either the demand or manufacturing process but not both. In these models it is usually assumed that the lead times are independent and identically distributed, but this is not realistic in many practical instances. In this paper we consider the lot sizing problem for items with stochastic demands and manufacturing lead times. It is assumed that the inventory of the finished product is controlled by continuous review policy of Q,R type—order quantity, order point system—and the problem is to determine optimal Q and R. We examine the decision parameters under a variety of conditions using exact and approximate methods.     

An optimization approach to capacity expansion in semiconductor manufacturing facilities

For a given demand and planning horizon, the general facility design problem faced by semiconductor manufacturers is to decide how much capacity to build into their systems. When the technology is known and only a small number of products is to be manufactured, the specific problem is to find a tool-set configuration that minimizes the average cycle time within a prescribed budget. In this paper, it is shown that this version of the capacity expansion problem can be modelled as a nonlinear integer program in which the decision variables correspond to the number of tools at a workstation. The major difficulty encountered in trying to find solutions is that no closed form expressions exist for the waiting time, primarily due to the presence of re-entrant flow. This means that it has to be approximated. At the outset, it was observed that previously proposed approximation methods based on parametric decomposition provided extremely poor results. In response, a new set of expressions, in the form of simultaneous equations, has been devised for approximating the average waiting time in a multiserver batch queuing system. When the number of batch servers is fixed, these equations become linear and are easy to solve. This fact is exploited in the development of a series of algorithms. The first two are greedy in nature, the third is based on simulated annealing, and the fourth is an exact method centring on implicit enumeration. Each is used to solve a large sample of test problems generated from data (complied by Sematech) reflecting current technology, costs, and process routings. The results indicate that high quality solutions can be obtained with little computational effort.     

Liquid phase residence time distribution for gas–liquid flow in Kenics static mixer

The residence time distribution (RTD) of the liquid phase for co-current gas–liquid upflow in a Kenics static mixer (KSM) with air/water and air/non-Newtonian fluid systems was investigated. The effect of liquid and gas superficial velocities on liquid holdup and Peclet number was studied. Experiments were conducted in three KSMs of diameter 2.54 cm with 16 elements and 5.08 cm diameter with 8 and 16 elements, respectively, of constant L_e/D_e = 1.5 for different liquid and gas velocities. A correlation was developed for Peclet number, in terms of generalized liquid Reynolds number, gas Froude number and liquid Galileo number, where as for liquid holdup, a correlation was developed as a function of gas Reynolds number. The axial dispersion model was found to be in good agreement with the experimental data.     

Spreading of liquid droplets on proton exchange membrane of a direct alcohol fuel cell

Spreading of liquid droplets over solid surfaces is a fundamental process with a number of applications including electro-chemical reactions on catalyst surface in membrane electrode assembly of proton exchange membrane (PEM) fuel cell and direct alcohol fuel cell. The spreading process of droplet on the PEM porous substrate consists of two phenomena, e.g., spreading of droplet on PEM surface and imbibition of droplet into PEM porous substrate. The shrinkage of the droplet base occurs due to the suction of the liquid from the droplet into the PEM porous substrate. As a result of these two competing processes, the radius of the drop base goes through a maximum with time. The variation of droplet base and front diameter with time on the PEM porous substrate is monitored using microscope fitted with CCD camera and a PC. It is seen that the droplet base diameter goes through a maximum with time, whereas the front diameter increases continuously with time. Further, methanol droplet spreading and wetting front movement was faster than that for ethanol and deionized water. As the PEM porous substrate is wetted and imbibed well by the methanol compared to ethanol, it is expected that the cross over of methanol would be higher than that of ethanol in direct alcohol fuel cell. It should be noted that cross over of alcohol from anode side to cathode side through membrane is detrimental to the fuel cell operation. The experimental data on the variation of droplet base and wetting front diameter with time is predicted by the model available in the literature.