A closed form solution for the G/M/r machine interference model

This paper solves the machine interference problem in which N different machines are looked after by a team of r operatives. The run time of each machine is assumed to have a general distribution, different for each machine and the repair times are assumed to have a negative exponential distribution with different means for the different machines. An explicit expression for the probability that a particular group of machines is found running in the steady state is derived. From this other useful measures for the system can be obtained. It is shown that these depend on the run time distributions only through the means of those distributions.     

Two-dimensional analysis of a negative differential conductance gate transistor as a THz emitter

We investigate plasma modes in a transistor including a negative differential conductance in the gate.The analytical results show that the plasma wave generation is substantially influenced by the lateral direction (width of the transistor),gate leakage current and viscosity.The injection from the gate (opposed to the gate leakage current) can improve the plasma oscillations and their amplitude with respect to ordinary transistors.We also estimate,which to our best knowledge has been derived for the first time,the total power emitted by the transistor and the emitted pattern which qualitatively gives reasonable agreement with the experimental data.The results show that the radiated power depends on various parameters such as drift velocity,momentum relaxation time,gate leakage current and especially the lateral direction.A negative gate current enhances the power while the gate leakage current decreases the power.     

A comparison of SPOT and Landsat-TM data for use in conducting inventories of forest resources

Abstract

SPOT multispectral (XS) and Landsat Thematic Mapper (TM) digital data were studied in an attempt to evaluate the use of this data in detailed assessments of forest conditions. Forest type, basal area, and age class information were collected from 256 sample sites within an intensively managed 80000acre experimental forest in North Carolina, U.S.A. A comparison of the SPOT and TM data with the sample site information showed that XS3, the near-infrared waveband, and TM bands 2, 3, 4, 5, and 7 were significantly correlated with basal area. Age class was not found to be significantly correlated with any of the three SPOT XS wavebands. TM bands 2, 3, 4, 5, and 7 were, however, shown to be significantly correlated with age class. Although significant, the correlation coefficients between the TM or SPOT waveband data and basal area or age class were low (<0.65).

Six forest cover types, and an additional water category, were selected as the basis of a land cover classification system for use with the TM and SPOT data. Verification of the classification of the seven cover types using the SPOT XS waveband data resulted in an estimated accuracy of 74.4 per cent. Classification accuracy was slightly reduced (70.8 per cent) when the TM wavebands corresponding to the SPOT XS bands were used as inputs to the classifier. When each of the six visible and reflective infrared TM wavebands were included in the classification process overall accuracy increased to 885 per cent.     

Remote sensing of tidal chlorophyll-a variations in estuaries

Simultaneous acquisition of surface chlorophyll-a concentrations for 39 samples from boats and Daedalus 1260 Multispectral Scanner data from a U-2 aircraft was conducted in the northern reaches of San Francisco Bay on 28 August 1980. These data were used to develop regression models for predicting surface chlorophyll-a concentrations over the study area for ebb-tide (8.40 a.m. P.D.T. (Pacific Daylight Time)) and flood-tide (3.10 p.m. P.D.T.) conditions. After selection of a single ‘best fitting’ model for both morning and afternoon data sets, the chlorophyll-a concentration was predicted for ebb and flood tide for the entire study area at approximately 40m × 40m resolution. The predicted spatial display of chlorophyll-a revealed a localized area of high phytoplankton biomass that has been inferred from field surveys and appears to be a common summer phenomenon.

Knowledge of the distribution of phytoplankton and the location of this zone of high biomass is valuable in establishing management policies for this ecologically important estuary. Furthermore, the techniques used here may provide an alternative cost-effective method for assessing water-quality conditions and they may prove useful for studying spatial variations (patchiness) and seasonal variations in phytoplankton biomass in other estuaries and coastal waters.     

Water quality mapping from Landsat digital data

Landsat multispectral scanner (MSS) data, and U-2 colour and colour infrared photographs were combined with in situ data for the assessment of water quality parameters within the San Francisco Bay-Delta. The water quality parameters of interest included turbidity and suspended solids. The U-2 photography and water quality samples were obtained simultaneously and coincidently with Landsat overpass. Regression models were developed between each of the water quality parameter measurements and Landsat digital data for 29 pre-selected sample sites. These regression models were then extended to the entire study area for mapping the water quality parameters of interest. The results included a series of colour-coded maps, each pertaining to one of the water quality parameters, and the statistical summaries. Areas of relatively high biological activity were clearly discernible on digitally enhanced Landsat MSS data.     

Logistics Decisions Following Urban Disasters

This work describes the development and functions of an IBM-compatible real-time microcomputer software to be used as a decision tool in coordinating and carrying out transportation-related activities in the aftermath of urban disasters such as earthquakes. The package incorporates the needs and experiences of response organizations involved in the postearthquake transportation-related operations in Mexico City. A number of transportation needs recognized as vital in operations related to emergency preparedness, response, and return to normalcy have been addressed. The software is named the "Transportation Emergency Decision Support System" (TEDSS) and includes the following features: 1) A graphical network-editing capability to modify the street network in terms of geometric and operational changes which could take place, including closed street links, changes in number of lanes, changes in travel direction of streets, cordoned off areas, parking-regulation changes, changes in transit routes, etc. 2) An emergency vehicle-dispatch algorithm to determine the best route to be taken from an origin to an incident point, considering all the changes which have taken place in the street system geometry and operational conditions. 3) A street clean-up prioritization scheme to assign priorities for the clean up of closed street links in terms of the amount of resources needed for the cleanup of a closed link as well as the degree of importance of each closed link in search and rescue operations and return to normalcy.