A study of the changes in performance of quayside container cranes

The learning effect, whereby performance improves with experience, is well documented for manufacturing situations. This article applies these learning concepts to quayside container cranes, in order to determine the relationship between number of containers moved and unloading time. The results show that crane performance has improved with time, and that the learning effect is essentially the same for four ports. Container vessel operators are looking for consistency in port operations. An analysis of variability for one port shows that this consistency is not always achieved and that crane performance does not appear to be related to vessel size.     

An Optimal Continuous Time Control Strategy for Active Suspensions with Preview

A continuous time control strategy for an active suspension with preview, based on optimal control theory, is presented. No approximation is needed to model the time delay between the excitation of the front and the rear wheels. The suspension is applied to a two DOF model of the rear side of the tractor of a tractor-semitrailer. The purpose of the suspension is to reduce either the required suspension working space or the maximum absolute acceleration of the sprung mass, without an increase of the dynamic tire force variation. For a step function as road input, reductions of 65% and 55%, respectively, are possible compared with a passive suspension.     

Energy savings due to land transportation management in Singapore

Singapore has been actively engaged in implementing various land transportation policies and traffic management schemes since the early 1970s to reduce traffic congestion. This paper examines the benefits in energy savings arising from the following five major schemes: (a) the Area Licensing Scheme, (b) the computerised Area Traffic control System, (c) the adaptive traffic control system, (d) the exclusive bus lane scheme, and (e) the island-wide expressway system. The analyses are made based on the findings of a two-year study that developed vehicle fuel consumption models for Singapore traffic. The Area Licensing Scheme that restricts traffic flow into the Central Business District (CBD) is found to have the greatest energy impact, followed by the island-wide expressway system and the traffic-signals control systems within the CBD.     

A Comparison of Adaptive LQG and Nonlinear Controllers for Vehicle Suspension Systems

A design feature of many computer-controlled suspension systems, is their ability to adapt control law parameters to suit prevailing road conditions. Here, for systems employing high bandwidth actuators and state variable feedback control, the benefits of such adaptation are shown to be at best marginal. An optimal adaptive LQG system is compared with a fixed structure nonlinear feedback controller in the context of a simple quarter-vehicle suspension model. Performance comparisons are made, and trends considered under more realistic conditions. In consequence the overall usefulness of this type of adaptation is called into question.     

THE EFFECT OF RT-PA ALONE AND IN COMBINATION WITH THROMBIN INHIBITORS IN A MODEL OF CEREBROVASCULAR THROMBOSIS IN THE RABBIT

Occlusivevasculardisorders,bothvenousandarterial,aresomeofthemostcommoncausesofmorbidityandmortalityindevelopedcountries.Theaimoftherapyinsuchconditionsis,firstly,torestoreandmaintainbloodflowtotheaffectedtissueororgan,andsecondly,torestorethesystemtothenormalhaemostaticstatewithoutovercompensatingandproducingcomplicationssuchashaemorrhage.Thrombolyticagents,suchasrecombinanttissueplasminogenactivator(rt-PA),arewidelyusedinthetreatmentofpatientswithacutemyocardialinfarction.However,successful…     

Factors influencing job satisfaction among merchant seamen

This paper explores the occupational and extra-occupational sources of job satisfaction in merchant seamen. Data were collected using a survey instrument from a sample of 302 seamen, both officers and crew. Factors determining variance in levels of job satisfaction are examined using a multiple regression technique. Several factors were found to have a significant impact on the degree of job satisfaction, particularly shipboard status and marital status. Collectively, the independent variables predicted over 63% of the variance.     

Pollution history of a tropical estuary revealed by combined hydrodynamic modelling and sediment geochemistry

Hydrodynamic modelling of water movement in Hunts Bay, a protected part of Kingston Harbour, Jamaica, shows that depth averaged tidal flows are very low. In the northeast corner of Hunts Bay, water is essentially stagnant. Even under high flow conditions, much of the Bay bottom water is ‘bypassed' by buoyant, lower salinity surface flows. The muddy sediments of Hunts Bay reflect these sluggish to stagnant conditions; sediment cores from the northeast corner of the Bay contain progressively higher amounts of organic matter in their upper parts (last 15–20 years sedimentation). Combined C/N ratios and stable carbon isotope compositions of this organic matter imply a sewage origin. Both lead and chromium metal concentrations and enrichment factors relative to average crustal shales show geographically related patterns that reflect hydrodynamic circulation predicted by modelling. In particular, metal concentrations and enrichment factors are highest at the northern end of the bay, especially in the northeast corner. Modelling confirms that stagnant conditions would occur in the northeast part of the bay even without the presence of a major causeway. The causeway may contribute to low flow conditions, but is not the principal cause of organic contamination, which is simply an excessive input of sewage.