Handling Scheme Research Articles

Signal amplification by means of cavity solitons in semiconductor microcavities

Cavity solitons were recently predicted in semiconductor microresonators grown with a vertical geometry. By exploiting a previously introduced model valid for both passive and active configurations of a multiple-quantum-well device, we studied the response in the time domain offered by such self-organized structures in the device, when a small modulated optical signal is applied. Using appropriate symmetry considerations, the (2+1)-dimensional problem is reduced to a tractable form, by means of a semianalytical method. We demonstrated that large differential-gain factors, competitive with those of other all-optical and some opto-electronic devices, are attainable, when the output signal is collected at the peak of the cavity soliton. This fact, in connection with the reconfigurability properties already established for cavity soliton arrays, allows to conceive different schemes for optical information handling: feasible arrangements for parallel amplification and for signal commutation are proposed.

Sensor‐referenced multiple robot cooperation for material handling

In this paper, a new cooperation control scheme for multiple robot material handling is presented. First, the event‐based planning and control method is introduced, which lays down the foundation for sensor‐referenced cooperation of multiple robot systems. The key step is the development of event‐based action reference. Based on the real‐time sensory information, the event‐based action reference drives the system to achieve the best possible coordination. The event‐based cooperation control scheme can easily be implemented in a distributed computer system. A real‐time control and computing architecture is proposed to implement this scheme in a parallel computation. The new multiple robot cooperation scheme has been experimentally implemented and tested on two 6‐DOF PUMA 560 robots. The experimental results have demonstrated the advantages of the scheme.

Legislation in Action: Must We Lift?

<h2>Summary</h2> A special handling scheme carried out over a six-month period in 1988 illustrates the thrust of the 1993 EC legislation in action in a psychiatric hospital. An ergonomic approach to the severe handling problems of patients suffering from dementia was aimed at eliminating unnecessary lifting. Changes made in the ward layout, some reorganisation of seating, and the introduction of handling which gave the patients an opportunity to take weight through their feet while being assisted to transfer, resulted in two previously immobile patients regaining their ability to walk. The failure of training over many years to oust the hazardous ‘lug/drag' method of transfer is set against success after a nurse training officer was appointed. The training sessions, augmented by the monitoring role of the nurse training officer and the willingness of the ward staff to make changes combined to bring success.

Interrupt handling for out-of-order execution processors

Processors with multiple functional units, including the superscalars, achieve significant performance enhancement through low-level execution concurrency. In such processors, multiple instructions are often issued and definitely executed concurrently and out-of-order. Consequently, interrupt and exception handling becomes a vexing problem. The authors identify latency, cost, and performance degradation as factors that must be considered in evaluating the effectiveness of interrupt and exception handling schemes. They then briefly enumerate proposals and implementations for interrupt and exception handling on out-of-order execution processors. An efficient hardware mechanism, the instruction window (IW), and an approach which allows for precise, responsive, and flexible interrupt and exception handling are presented. The implementation of the IW is discussed. The design of an eight-cell IW has been carried out; it can work with a very short machine cycle time. A comparison of all interrupt and exception handling schemes for out-of-order execution processors is also presented. >

PREHARVEST FACTORS INFLUENCING POSTHARVEST QUALITY OF TROPICAL AND SUBTROPICAL FRUIT

Although postharvest handling schemes have improved during recent years, it is still possible to observe considerable variability in fruit quality between individual lots. Preharvest factors such as irrigation, nutrition and pest management practices, as well as rootstock and environmental variables, may greatly influence quality after harvest and may well account for some of the differences between individual lots. The influence of preharvest factors on postharvest quality of tropical and subtropical fruit will be discussed using pertinent examples from the literature. Emphasis will be given to those factors which can be manipulated to improve quality.

Development of Heavy-Oil Reservoirs

Although complex categorizations are in vogue, ''heavy oils'' can be defined simply in terms of their flow properties in the reservoir-e.g., a 100-cp (100-mPa.s) or greater viscosity. Such heavy oils are major world hydrocarbon resource that is exploited where indigenous demand exists. Efficient methods of production require enthalpy input to the reservoir by hot-fluid injection or by creation of heat in the reservoir. Heat losses must be minimized to achieve maximum production efficiency. The widely used cyclic-steam-injection process is examined analytically to indicate which parameters govern successful exploitation. Steamflood and in-situ combustion techniques are discussed with reference to recent developments. Heavy-oil recovery from the more difficult carbonate reservoirs, such as those of the Middle East, is reviewed and potential production mechanism are examined. Production techniques are described together with export handling schemes.

Finite Element Algorithms for Simulating Three‐Dimensional Groundwater Flow and Solute Transport in Multilayer Systems

A finite element formulation is developed for the simulation of groundwater flow and solute transport in multilayer systems of several aquifers and aquitards. This formulation is general, flexibile, and capable of taking full advantage of the nature of flow in such multilayer systems. A fully three‐dimensional spatial representation can be performed for certain aquifers or for the entire flow system if needed. Those parts of the system that require three‐dimensional spatial discretization are handled effectively by combining two‐dimensional basis functions in the x‐y space and one‐dimensional basis functions in the z space. Furthermore, the formulation has a desirable option to perform one‐dimensional representation of flow and transport in aquitards and areal representation of flow and transport in certain aquifers that do not require the fully three‐dimensional discretization. When the one‐dimensional representation of an aquitard is used, coupling of adjacent aquifer and aquitard layers is handled using a convolution integral approach. A general solution strategy is also developed to allow systematic time stepping and cost‐effective matrix handling schemes. For those parts of the system that require three‐dimensional discretization, an algorithm referred to as the alternate sublayer and line sweep procedure is presented for decomposing three‐dimensional matrix equations. This algorithm can accomodate several thousand nodal unknowns without requiring excessive core storage and CPU time. Four examples of transient flow and transport problems are provided. These examples show verification of numerical results and demonstrate that the present finite element models are far more cost‐effective than earlier three‐dimensional models that are based on the conventional Galerkin approach and direct matrix solution algorithms.

Analysis of a service center in a multiline factory

Abstract It has been demonstrated that several performance measures (e.g., expected delay and number in the system) improve when n servers take customers from a single queue rather than from n separate queues dedicated to individual servers. In this paper, we discuss the application of this concept in a manufacturing environment. In a multiple factory, common machines from individual lines were pooled to form a service center. The expected benefits, however, were not realized and we were called in to identify the cause of the poor performance. To analyze the service center, a Σ Gl/G/1 queueing model (the superposition of independent renewal arrival streams offered to a general single server) was used. We found that the material handling scheme in place significantly degraded the system performance. Using the model, alternative schemes were proposed to improve the performance of the facility.

GEMS: A generalized manufacturing simulator

The purpose of this paper is to describe a Generalized Manufacturing Simulator (GEMS) which can be used in the analysis of complex discrete part manufacturing systems. GEMS is a FORTRAN based analysis program which has been developed to study assembly line or job shop manufacturing environments. However, the current capabilities of GEMS enable a user to model a wide range of industrial, social, and operational problems. Conceptualization of manufacturing environments to the GEMS program is executed via a box/node arc network representation of the manufacturing system. GEMS is an activity-on box (node) simulation program composed of standardized simulation input via specialized boxes and arcs. A box (node)/arc structure can be developed to represent complex material flow patterns, probabilistics branching, routing based on attribute values, resource constraints, cost considerations, and complex queueing characteristics. GEMS can be used to study product flow rates, manufacturing capabilities, and queueing phenomena; assess in-process inventories and raw material storage requirements; determine the effects of alternate sequencing and scheduling rules; different routing and material handling schemes; and the impact of limited resources and increased/decreased production rates. An analysis package has been constructed which normally requires only a representation of the simulated system in terms of a network diagram, and transmission of this diagram to the GEMS program structure through FORTRAN NAMELIST data inputs.

The Physical-Chemical Treatment of Sour Gas Plant Process Waste Waters

Abstract The feasibility of physical-chemical treatment of sour gas plant aqueous wastes was studied on a laboratory scale. Experimental data on (a) the adsorption of organic pollutants on Culligan 1627-00 activated carbon, (b) the removal of sulphides from sulphur plant aqueous waste and (c) the chemical clarification of two aqueous waste streams are presented. Initially, the adsorption by the carbon of major organic chemicals used in treating sour gas was studied. The concentrations of the dilute aqueous solutions of those chemicals were measured by a Beckman Total Carbon Analyzer, A four-hour contact period was found to be sufficient for equilibrium adsorption of the organics. The adsorption data are well represented by Freundlich isotherms, Experimental data on the treatment of sour gas plant waste waters by physical-chemical methods indicate the need for (a) segregation of various waste streams and (b) a combination of inclination, steam stripping, clarification and activated carbon adsorption for the treatment and disposal of different streams. The data indicate that the incorporation of a proposed aqueous waste handling and treatment scheme, for a typical sour gas plant, will produce an aqueous effluent containing less than 10 mg/L of total organic carbon and less than 100 mg/L of chemical oxygen demand. Treatment of the sour gas plant waste water samples by chlorine-ultraviolet oxidation and by ozonation does not appear to be capable of meeting the current waste quality standards. Introduction Sour gas treatments plants in Alberta are able to meet the recently established waste water quality standards largely because they are allowed to inject the process waste waters into subsurface strata(1). However, concern about the long-term risks of waste water injection is growing and various governmental agencies in North America are weighing these long-term risks with the short-term gains(2, 3). It may become necessary for sour gas plants to demonstrate that the subsurface injection of aqueous wastes is the best disposal method in terms of over-all environmental protection. The EPA in the United States already has regulations of this type for industrial aqueous waste injection(2). To determine that subsurface injection of aqueous wastes would be least damaging environmentally, alternate aqueous waste treatment processes should be evaluated and the costs compared. A recent study by Milne and Tollefson(4), in which various alternative methods for the disposal or treatment of aqueous wastes from sour gas plants were evaluated, indicated that the necessary experimental data were not available in the literature and that any comparison of treatment methods had to be based on "guesstimates". Recently, research has been undertaken in these laboratories to investigate the feasibility of "physical-chemical treatment" of aqueous wastes from sour gas plants. Synthetic systems were employed in the early phases of this research to generate equilibrium and kinetic data for the adsorption by activated carbon of some of the major organic compounds used in sour gas treating service in Alberta, Subsequently, waste water samples obtained from three sour gas treatment plants were used to determine the extent of adsorption of the organic components by activated carbon.

Bonding and Grounding in Aerospace Vehicles and Ground Equipment

Safety and reliability in aerospace vehicles and associated ground equipment are directly affected by basic design concepts in power system grounding and bonding practice. The three major objectives covered in this paper are; avoidance of static charges, protection from lightning, and safe containment of power system faults. Effective measures are outlined which hold static charges to insignificant levels incapable of sparking. Basic precautions which improve safety from lightning are specified. A number of alternate schemes for safe handling of power system faults are discussed. In addition, some simple and effective methods of obtaining effective electric bonding of equipment and structure are described and illustrated.