A methodology for evaluating and selecting processes for natural gas conditioning

The aim of this work was to develop a generic methodology for evaluating and selecting, at the conceptual design phase of a project, the best process technology for Natural Gas conditioning. A generic approach would be simple and require less time and would give a better understanding of why one process is to be preferred over another. This will lead to a better understanding of the problem. Such a methodology would be useful in evaluating existing, novel and hybrid technologies. However, to date no information is available in the published literature on such a generic approach to gas processing. It is believed that the generic methodology presented here is the first available for choosing the best or cheapest method of separation for natural gas dew-point control. Process cost data are derived from evaluations carried out by the vendors. These evaluations are then modelled using a steady-state simulation package. From the results of the modelling the cost data received are correlated and defined with respect to the design or sizing parameters. This allows comparisons between different process systems to be made in terms of the overall process. The generic methodology is based on the concept of a Comparative Separation Cost. This takes into account the efficiency of each process, the value of its products, and the associated costs. To illustrate the general applicability of the methodology, three different cases suggested by BP Exploration are evaluated. This work has shown that it is possible to identify the most competitive process operations at the conceptual design phase and illustrate why one process has an advantage over another. Furthermore, the same methodology has been used to identify and evaluate hybrid processes. It has been determined here that in some cases they offer substantial advantages over the separate process techniques.

Mechanisms of ion channel activation in primary cultured and clonal cell lines

The effects of hypotonic shock upon membrane C1 permeability of ROS 17/2.8 osteoblast-like cells was investigated using the patch-clamp technique. Hypotonic shock produced cell swelling that was accompanied by large amplitude, outwardly rectifying, currents that were active across the entire physiological range of membrane potentials (-80 to +100 mV). At strong depolarisations (> +50 mV) the currents exhibited time-dependent inactivation that followed a monoexponential time course. The currents were anion selective and exhibited a selectivity sequence of SCN- > I > Br- > Cl- > F- > gluconate. Current activation was unaffected by inhibitors of protein kinase (A (H-89) and tyrosine kinase (tyrphostin A25), and could not be mimicked by elevation of intracellular Ca2+ or activation of protein kinase C. Similarly, disruption of actin filaments by dihydrocytochalsin B, or generation of membrane tension by dipyridamole failed to elicit significant increases in cell chloride permeability. The mechanism of current activation is as yet undetermined. The currents were effectively inhibited by the chloride channel inhibitors NPPB and DIDS but resistant to DPC. A Cl- conductance with similar characteristics was found to be present in mouse primary cultured calvarial osteoblasts. The volume-sensitive Cl- current in ROS 17/2.8 cells was inhibited by arachidonic acid in two distinct phases. A rapid block that developed within 10 s, preceding a slower developing inhibitory phase that occurred approximately 90 s after onset of arachidonate superfusion. Arachidonic acid also induced kinetic modifications of the current which were evident as an acceleration of the time-dependent· inactivation exhibited at depolarised potentials. Inhibitors of cyclo-oxygenases, lipoxygenases and cytochrome P-4S0 were ineffectual against arachidonic acid's effects sugtgesting that arachidonic acid may elicit it's effects directly. Measurements of cell volume under hypotonic conditions showed that ROS 17/2,8 cells could effectively regulate their volume, However, effective inhibitors of the volume-sensitive CI" current drastically impaired this response suggesting that physiologically this current may have a vital role in cell volume regulation, In L6 skeletal myocytes, vasopressin was found to rapidiy hyperpolarise cells. This appears to occur as the result of activation of Ca2+ -sensitive K+ channels in a process dependent upon the presence of extracellular Ca2+.

Task classification and decision processes in monitoring behaviour

Task classification is introduced as a method for the evaluation of monitoring behaviour in different task situations. On the basis of an analysis of different monitoring tasks, a task classification system comprising four task 'dimensions' is proposed. The perceptual speed and flexibility of closure categories, which are identified with signal discrimination type, comprise the principal dimension in this taxonomy, the others being sense modality, the time course of events, and source complexity. It is also proposed that decision theory provides the most complete method for the analysis of performance in monitoring tasks. Several different aspects of decision theory in relation to monitoring behaviour are described. A method is also outlined whereby both accuracy and latency measures of performance may be analysed within the same decision theory framework. Eight experiments and an organizational study are reported. The results show that a distinction can be made between the perceptual efficiency (sensitivity) of a monitor and his criterial level of response, and that in most monitoring situations, there is no decrement in efficiency over the work period, but an increase in the strictness of the response criterion. The range of tasks exhibiting either or both of these performance trends can be specified within the task classification system. In particular, it is shown that a sensitivity decrement is only obtained for 'speed' tasks with a high stimulation rate. A distinctive feature of 'speed' tasks is that target detection requires the discrimination of a change in a stimulus relative to preceding stimuli, whereas in 'closure' tasks, the information required for the discrimination of targets is presented at the same point In time. In the final study, the specification of tasks yielding sensitivity decrements is shown to be consistent with a task classification analysis of the monitoring literature. It is also demonstrated that the signal type dimension has a major influence on the consistency of individual differences in performance in different tasks. The results provide an empirical validation for the 'speed' and 'closure' categories, and suggest that individual differences are not completely task specific but are dependent on the demands common to different tasks. Task classification is therefore shovn to enable improved generalizations to be made of the factors affecting 1) performance trends over time, and 2) the consistencv of performance in different tasks. A decision theory analysis of response latencies is shown to support the view that criterion shifts are obtained in some tasks, while sensitivity shifts are obtained in others. The results of a psychophysiological study also suggest that evoked potential latency measures may provide temporal correlates of criterion shifts in monitoring tasks. Among other results, the finding that the latencies of negative responses do not increase over time is taken to invalidate arousal-based theories of performance trends over a work period. An interpretation in terms of expectancy, however, provides a more reliable explanation of criterion shifts. Although the mechanisms underlying the sensitivity decrement are not completely clear, the results rule out 'unitary' theories such as observing response and coupling theory. It is suggested that an interpretation in terms of the memory data limitations on information processing provides the most parsimonious explanation of all the results in the literature relating to sensitivity decrement. Task classification therefore enables the refinement and selection of theories of monitoring behaviour in terms of their reliability in generalizing predictions to a wide range of tasks. It is thus concluded that task classification and decision theory provide a reliable basis for the assessment and analysis of monitoring behaviour in different task situations.

A unified classification of manufacturing strategies and design processes

This article categorises manufacturing strategy design processes and presents the characteristics of resulting strategies. This work will therefore assist practitioners to appreciate the implications of planning activities. The article presents a framework for classifying manufacturing strategy processes and the resulting strategies. Each process and respective strategy is then considered in detail. In this consideration the preferred approach is presented for formulating a world class manufacturing strategy. Finally, conclusions and recommendations for further work are given.