Workshop scheduling using practical (inaccurate) data Part 2: An investigation of the robustness of scheduling rules in a dynamic and stochastic environment

In research on generating a predictive schedule, the scheduling problem is often viewed as a deterministic problem. However, the real-life job shop environment is stochastic in that information on job attributes and shop floor status is not precisely known in advance. In this situation, in order to increase the effectiveness of a predictive schedule in practice, the focus should be on creating a robust schedule. The purpose of this paper is to investigate the robustness of a number of scheduling rules in a dynamic and stochastic environment using the rolling time horizon approach. A cost-based performance measure is used to evaluate the scheduling rules. The simulation results, under various conditions in a balanced and unbalanced shop, are presented and the effects of the rescheduling interval and operational factors including shop load conditions and a bottleneck on the robustness of the schedule are studied. From the results the key factors that influence the robustness of a scheduling system are identified and, consequently, general guidelines for creating robust schedules are proposed.     

Steady-state performance and chemical efficiency of Microbial Electrolysis Cells

The objective of this paper was to study MEC performance at steady-state conditions in continuous mode and to analyse MEC performance in terms of chemical efficiency. At steady-state operation, a current density of 10.2 A m⁻² (applied voltage 1.0 V) for a set-up with an AEM was produced, compared to 7.2 A m⁻² for a set-up with a CEM. For all applied voltages, total internal resistance for the AEM configuration was lower than or the CEM configuration. Therefore, energy input for the AEM configuration is lower than for the CEM configuration. In case a CEM is used, the conductivity in the cathode reaches high values: >130 mS cm⁻¹. This conductivity is mainly caused by the presence of Na⁺ (7.8 g L⁻¹), K⁺ (12.2 g L⁻¹) and OH⁻ (8.3 g L⁻¹). Furthermore, MECs perform better at high buffer and electrolyte concentrations. However, as current density does not increase proportionally with increase in chemicals, the effectiveness of chemical addition decreases when more chemicals are added. Therefore, addition of chemicals and buffer does not necessarily enhance performance but increases operational costs.     

Cooperative mechanisms between leg joints of Carausius morosus I. Nonspiking interneurons that contribute to interjoint coordination

Three nonspiking interneurons are described in this paper that influence the activity of the motor neurons of three muscles of the proximal leg joints of the stick insect. Interneurons were recorded and stained intracellularly by glass microelectrodes; motor neurons were recorded extracellularly with oil-hook electrodes. The motor neurons innervate the two subcoxal muscles, the protractor and retractor coxae, and the thoracic part of the depressor trochanteris muscle. The latter spans the subcoxal joint before inserting the trochanter, thus coupling the two proximal joints mechanically. The three interneurons are briefly described here. First, interneuron NS 1 was known to become more excited during the swing phase of the rear and the stance phase of the middle leg. When depolarized it excited several motor neurons of the retractor coxae. This investigation revealed that it inhibits the activity of protractor and thoracic depressor motor neurons when depolarized as well. In a pilocarpine-activated animal, the membrane potential showed oscillations in phase with the activity of protractor motor neurons, suggesting that NS 1 might contribute to the transition from swing to stance movement. Second, interneuron NS 2 inhibits motor neurons of protractor and thoracic depressor when depolarized. In both a quiescent and a pilocarpine-activated animal, hyperpolarizing stimuli excite motor neurons of both muscles via disinhibition. In one active animal the disinhibiting stimuli were sufficient to generate swing-like movements of the leg. In pilocarpine-activated preparations the membrane potential oscillated in correlation with the motor neuronal activity of the protractor coxae and thoracic depressor muscle. Hyperpolarizing stimuli induced or reinforced the protractor and thoracic depressor bursts and inhibited the activity of the motor neurons of the retractor coxae muscle, the antagonistic muscle of the protractor. Therefore interneuron NS 2 can be regarded as an important premotor interneuron for the switching from stance to swing and from swing to stance. Finally, interneuron NS 3 inhibits the spontaneously active motor neurons of both motor neuron pools in the quiescent animal. During pilocarpine-induced protractor bursts, depolarizing stimuli applied to the interneuron excited several protractor motor neurons with large action potentials and one motor neuron of the thoracic depressor. No oscillations of the membrane potentials were observed. Therefore this interneuron might contribute to the generation of rapid leg movements. The results demonstrated that the two proximal joints are coupled not only mechanically but also neurally and that the thoracic part of the depressor appears to function as a part of the swing-generating system.     

Einfluß der Unterbrechergeometrie auf die Arbeitsübertragung und den Wirkungsgrad von Seitenkanalverdichtern

Zusammenfassung Zur Trennung von Druck- und Saugseite des Seitenkanals ist ein Unterbrecher erforderlich, der das direkte überstr?men des verdichteten Gases verhindert. Der Unterbrecher bewirkt aber nicht nur die Abdichtung, sondern er beeinflu?t auch wesentlich den Expansionsvorgang des überstr?menden Unterbrechermassestromes und damit wiederum den Verdichtungsvorgang im Seitenkanal. Um den Einflu? der Unterbrechergeometrie auf diese Vorg?nge zu ermitteln, wurden unterschiedliche Unterbrechermodule in einem Seitenkanalverdichter bei Druck- und Vakuumbetrieb untersucht. Der Umfangswinkel des Unterbrechers und die Oberfl?chengeometrie beeinflussen den Expansionsvorgang und den polytropen Kupplungswirkungsgrad unterschiedlich im Bereich von η=0,41 bis 0,49. Damit ist aufgezeigt, da? eine Optimierung des Unterbrechers notwendig ist, um m?glichst adiabate Zustands?nderungen im Seitenkanalverdichter zu erreichen. Der relative Unterbrecherwinkel soll für Schaufelzahlen von 40 bis 60 α_U/2π=0,115 bis 0,135 betragen.     

Polychlorierte Biphenyle (PCB) in Fischen aus Teichwirtschaften und Nachklärteichen

European Food Research and Technology - Das Muskelgewebe von 58 Fischen aus Teichwirtschaften und 17 Fischen aus Nachklärteichen wurde auf seinen Gehalt an den sechs in der...     

Season of birth and schizophrenia: A response to the Lewis and Griffin critique.

A number of studies have suggested that schizophrenics are particularly likely to have been born in the winter months. M. S. Lewis and T. A. Griffin (1981) have argued that this "seasonality" effect may be an artifact resulting from (a) the use of inappropriate expected values in calculating chi-squares; (b) the age–incidence effect—the tendency of risk to increase with time in disorders whose incidence increases with age; and (c) the age–prevalence effect—the fact that people born early in a reporting period have been at risk for any disease longer than those born later in that period. The birth months of 3,556 schizophrenics at a Minnesota VA hospital were studied before and after instituting corrections in expected values for year-to-year across-month variations in birthrates and for the age-prevalence bias toward the January–March seasonality effect. Data on a subset of patients in whom the age–incidence effect should be minimal were reanalyzed. Even after these corrections, results support the contention that the winter birthrate for schizophrenics is excessive, at least in severe climates. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alcohol production through volatile fatty acids reduction with hydrogen as electron donor by mixed cultures

In this research we demonstrated a new method to produce alcohols. It was experimentally feasible to produce ethanol, propanol and butanol from solely volatile fatty acids (VFAs) with hydrogen as electron donor. In batch tests, VFAs such as acetic, propionic and butyric acids were reduced by mixed microbial cultures with a headspace of 1.5 bar of hydrogen. Observed alcohol concentrations were 3.69 ± 0.25 mM of ethanol, 8.08 ± 0.85 mM of propanol and 3.66 ± 0.05 mM of n-butanol. The conversion efficiency based on the electron balance was 55.1 ± 5.6% with acetate as substrate, 50.3 ± 4.7% with propionate and 46.7 ± 2.2% with n-butyrate. Methane was the most predominant by-product in each batch experiment, 33.6 ± 9.6% of VFA and hydrogen was converted to methane with acetate as substrate; which was 27.1 ± 7.1% with propionate and 36.6 ± 2.2% with n-butyrate. This VFAs reducing renewable fuel production process does not require carbohydrates like fermentable sugars, but uses biomass with high water content or low sugar content that is unsuitable as feedstock for current fermentation processes. This so-called low-grade biomass is abundantly present in many agricultural areas and is economically very attractive feedstock for the production of biofuels.     

Workshop scheduling using practical (inaccurate) data Part 1: The performance of heuristic scheduling rules in a dynamic job shop environment using a rolling time horizon approach

This paper is a report on a simulation study to investigate the performance of a number of scheduling rules on the basis of a rolling time horizon approach for a dynamic job shop environment. The performance measure considered is an economic objective which includes the main costs involved in a scheduling decision. The first purpose of the study was to find the best scheduling rule and the second to investigate the effects of the rescheduling interval on performance and examine whether there is a policy that can always improve performance. The simulation study, which is part of a larger project on practical workshop scheduling, has been carried out under widely varying conditions in terms of due date tightness, shop load level, and shop load balance level. The results show that a recently developed scheduling rule, SPT-C/R, is the most appropriate scheduling rule in minimizing overall cost and that the relationship between performance and rescheduling interval can be shown.