Cost-efficient Maintenance Research Articles

WEB-BASED TEST AND ASSESSMENT SYSTEM: DESIGN PRINCIPLES AND CASE STUDY

Courseware engineering targets towards the cost-efficient production and maintenance of educational material. We propose a separation of courseware into content parts, presentation parts, and pedagogic and didactic parts as a major step in order to strengthen reusability and adaptability of e-learning contents. This separation should guarantee that specialists can focus on their field and define questions without concerning about presentation or design the look and feel without going into details of the question content. As a case study, we present tetrodo, a framework for web-based education and show its application for the development of test and assessment purposes. Our system supports computer-correctable questions at higher taxonomy levels compared to the multiple-choice and fill-in type supported by commercial e-learning systems. In order to show a flavour what is possible, we give examples from a recent course on Algorithms and Data Structures. We sketch the hierarchy of question patterns built up and report on the authoring tool developed. Finally we describe a new approach in students involvement in questioning and summarize practical experiences so far.

Model-based condition monitoring of an actuator system driven by a brushless DC motor

Air pressure in passenger aircrafts is controlled by opening and closing an outflow valve, which serves to release air from the cabin. Early identification of potential malfunctions in the underlying actuator-driven system is important both from the point of view of cost-efficient maintenance as well as overall safety. This paper presents a system for diagnosing faults in a valve actuator driven by a brushless DC motor during off-line pre-flight tests. First, a simple mathematical model of the drive is developed. Based on this, parity relations are derived with the aim of fault detection. Fault isolation is realised by means of an approximate reasoning technique referred to as transferable belief model (TBM). The problem of distinguishing between faults with the same fault signatures is addressed. It is shown that additional improvements in terms of diagnostic resolution can be achieved by applying parameter estimation. The proposed FDI scheme is tested on the actual drive under various faults. The achieved performance features high diagnostic resolution, diagnostic stability and accuracy.

A new cryofixation device (CF 100)

The aim of this project was to develop an ultrarapid cooling device which optimized the parameters of metal mirror cryofixation, minimized operator dependence and was configured for cost efficient and low maintenance operation.Cooling of the cryogenic surface is accomplished by flow through of liquid nitrogen at 20 PSI to allow attachment directly to a standard liquid nitrogen tank. Cooling time +25 to -185°C is 45 seconds measured with thermocouple bonded to the upper cryogenic surface.Atmospheric contamination of the cryogenic surface during cooling is prevented by a surrounding vacuum. Precooling of the sample is avoided by reversal of surrounding vacuum by room temperature ultrapure nitrogen gas at the time of sample application. Atmospheric contamination of the cryogenic surface during application of the sample is prevented by the nitrogen atmosphere and functional interaction of shutter retraction and plunger activation.Bounce of sample is eliminated by sample holder design and use of a pneumatic plunger at selectable PSI to ensure linear force of application.