Modeling the movement of smoke and the effect of ventilation systems in mine shaft fires

Physical principles governing mine ventilation systems and state of the art ventilation modeling are initially outlined. Several computer programs for modeling the mine ventilation-mine fire interaction, which were developed during the last decade, are then described. An older program considers fires and ventilation systems as going through a sequence of steady state conditions. Airflow rates, pressure losses, temperatures, fume and methane concentrations can be determined. Newer programs allow transient state fume concentration calculations under the assumption of constant airflow rates as well as the determination of fume exposures of escaping miners. Recent work attempts the complete transient state simulation of fires and all ventilation properties.     

Electroluminescence spectroscopy for reliability investigations of 1.55 μm bulk semiconductor optical amplifier

This paper demonstrates the complementary relation between functional parameters and electroluminescence spectroscopy for reliability investigations of 1550 nm Semiconductor Optical Amplifiers of 700 μm length active region. Ageing tests have been set to 270 mA-100 °C-1500 h and realized on two different wafers showing more impact on wafer 1 than on wafer 2. Our investigations are particularly focused on interpretation of electroluminescence spectra, from reference and aged SOAs of wafer 1, leading to an improvement of degradation mechanisms understanding. The shift rate to lower energies of the recombination energy peak at 1550 nm, as reported by electroluminescence spectra between reference and aged SOAs in relation with the decrease of optical power measured at 200 mA for the degraded SOA and completed by I(V) characterizations, suggest occurrence of non radiative deep centers near the buried ridge structure in relation with the cleaning process uniformity of interfaces before epitaxial overgrowth. These defects mainly trap majority injected carriers instead of minority carriers reducing the luminescence in the active zone. By monitoring the most sensitive failure indicator (pseudo-threshold current), lifetime distributions are also calculated to determine failure rate, between 150 and 200 FITs over 15 years for operating conditions (25 °C-200 mA) using experimental degradation laws and statistic computations, demonstrating the overall robustness of this technology.     

A basis for the design of a multiattribute heuristic for single resource project scheduling

Two important characteristics of a project network are the network's topology and the amount of resources available. Most published project scheduling procedures take one or both of these two characteristics into account. Project scheduling procedures that are robust over variations of network characteristics are desirable. The degree of robustness is generally gauged by one or more measures of performance.

The objective of this paper is to compare a set of priority rules that are useful for a single resource project scheduling problem. The set of networks suggested by Patterson (1973) is used along with the set of performance measures proposed by Khattab and Choobineh 1991. The result of this comparison allows one to design a multiattribute heuristic for a single resource project scheduling problem.     

A tool shelf for tracking design decisions

An extensible conceptual model for recording design decisions and other supporting information is described along with the tool shell OSC in which it is embedded. The OSC shell consists of a design database and a family of query, manipulation, and extension facilities. The design database maintains a record of the design process. The extension facilities can be used to enrich the design database scheme incrementally and create new query or manipulation facilities. The core model provides a base language for describing the design process. Extension facilities augment this basis with more powerful, customized facilities. The implementation of the OSC shell using ESSAIM, an expert-system shell based on Smalltalk, is discussed     

The 'Conceptual Change In Science' project

Abstract This paper outlines the work of the Conceptual Change in Science project, funded as part of the ESRC InTER programme. The aims of this research project are to clarify and describe the process of change in learners' conceptual understandings of natural phenomena. The domain of reasoning selected for study is that of mechanics. Computer software which may be useful in exploring and developing pupils' reasoning and promoting conceptual change in this domain is being developed and evaluated. The group that is carrying out the research is based at the Universities of Leeds, Glasgow and the Open University.     

A Narrowband Pulse-Echo Technique for In Vivo Ultrasonic Attenuation Estimation

The principles of a narrowband technique for pulse echo attenuation measurements are presented. Experiments are described which compare the attenuation in tissue-mimicking phantoms, measured by known methods, to the attenuation measured by the present technique. The effects of various experimental parameters on the results are investigated. The attenuation in spleens of canine models and in livers of human volunteers is presented.     

Satellite-to-Satellite Range-Rate Measurement

The measurement of range rate between two low-orbiting spacecraft with a precision of better than 1 ?m/s provides a means for sensing global gravity variability. An analysis is given to show the conditions under which this precision can be realized, with emphasis on the requirements of NASA's Geopotential Research Mission. Experimental results obtained with a millimeter-wave demonstration system are presented along with a proposed design for a spaceborne instrument.