Design of maximum thrust plug nozzles with variable inlet geometry

An optimization analysis is presented for axisymmetric plug nozzles with varible inlet geometry. The analysis is based on the governing gas dynamic relations for a rotational flow of a frozen or equilibrium gas mixture. The problem is formulated to maximize the axial thrust produced by the plug nozzle for a general isoperimetric constraint, such as constant nozzle length or constant nozzle surface area. The effects of base pressure and ambient pressure are included in the thrust expression to be maximized. The governing gas dynamic equations and the differential and integral constraints that the solution must satisfy are incorporated into the formulation by means of Lagrange multiples. The formalism of the calculus of variations is applied to the resulting functional to be maximized. The results of the optimization analysis are a set of partial differential equations for determining the Lagrange multipliers in the region of interest and a set of equations for determining the necessary boundary conditions for the solution. The complete set of equations for the gas dynamic properties and the Lagrange multipliers are system of first order, quasi-linear, non-homogeneous partial differential equations of the hyperbolic type, which can be treated by the method of charac- teristics. The characteristic and compatibility equations for the system are presented. A numerical solution procedure is presented to determine wether or not a given plug nozzle geometry is an optimal solution. An iteration technique is developed which systematically adjusts the plug nozzle geometry until the optimal solution is obtained. Selected parametric studies are presented. These studies illustrate the effect of the specific heat ratio, the design pressure ratio and the base pressure model on the thrust peformance and nozzle geometry of optimal, fixed length, plug nozzles.     

Photoionization cross-sections and energy levels of gold,iron, platinum,silver, and titanium in silicon

The photoionization cross-sections of various deep impurities of interest in solar-grade silicon for photovoltaic cells, and the corresponding energy levels, have been determined by steady state photo-induced currents in pn junctions or Schottky barrier junctions irradiated simultaneously with two wavelengths of light. Light of about half the band-gap energy controls the occupancy of the deep impurity level and the spectral dependence of the photocurrent on a higher photon energy light source then provides, via the Lucovsky model, the photo-cross-section and the impurity energy level. The results obtained for Au and Pt in Si are in agreement with those of Braun and Grimmeiss and the energy levels for Fe, Ti, and Ag obtained optically are in agreement with those obtained by other methods.     

Nova Scotia moose mystery--a moose sickness related to cobalt- and vitamin B12 deficiency

A wasting, debilitating disease with uncertain aetiology affecting moose (Alces alces americana) in Eastern North America has been reported repeatedly ever since the 1910s. Despite the intensive studies during 1930-1960s the cause of the sickness could not be established. In the 1960s a parasitic nematode (Parelaphostrongylus tenuis) was reported as constituting a probable explanation for the sickness, although several clinical and pathological signs remained unexplained. In Sweden, a moose disease with similar signs, has been shown to be caused by molybdenosis resulting from a nutritional imbalance. The findings of this investigation were applied in Nova Scotia to determine trace element concentrations in tissues from indigenous moose. Co deficiency was found in about half of the cases and the investigation was complemented by determining the vitamin B12 level, which proved nutritional Co/vitamin B12 deficiency, further verified by an increased MMA (methylmalonic acid) level in plasma. Deficiencies were found mainly in the Tobeatic and Cape Breton Highland regions. No indications of molybdenosis or other trace element disturbances were found in Nova Scotia. Otherwise, extremely high Cd levels (148 mg Cd/kg kidney wet wt., maximum) were found, though probably not contributing to the moose sickness. The Cd burden of moose on mainland Nova Scotia was more than 50% higher than that of moose in Huntville and Alonquin (Ontario, Canada) and five- to six-fold is higher than the highest Cd levels found in Sweden. To counteract the bio-geochemical effects of Co deficiency in the moose environment, provision of Co-containing salt licks is suggested.     

Economic growth and energy consumption in the UK, 1700–1975

This paper attempts to trace the development of energy consumption in the UK during the process of industrialization. First a quantitative overview of the relationship between energy consumption and economic growth for the period 1700–1975 is presented. An examination of the factors affecting relations between economic growth and energy consumption is then presented. This is divided into two main periods: pre-1800 and 1800–1975. The discussion of pre-1800 energy consumption is mainly concerned with coal use, while a more detailed account is given of developments in the later period.     

Mesure du Débit d’Absorption Spécifique (das) des téléphones mobiles — contribution du projetcomobio à la normalisation internationale

Human exposure to electromagnetic fields emitted by mobile phones is characterised by the Specific Absorption Rate (sar). This value corresponds to therf power absorbed by unitary mass of the equivalent tissue. It represents the basic restriction used to define limit of human exposure torf electromagnetic fields. Academic and industrial labs have contributed through thecomobio project to define international standards for mobile phones certification.     

Statistical Models for Data Mining

We review the background to the papers presented in this special issue and give a short introduction to each. We also briefly describe the workshop on Statistical models for data mining, held in Pavia (Italy), in October 2000, where the papers were presented.     

Agent-based simulation of electricity markets: a survey of tools

Agent-based simulation has been a popular technique in modeling and analyzing electricity markets in recent years. The main objective of this paper is to study existing agent-based simulation packages for electricity markets. We first provide an overview of electricity markets and briefly introduce the agent-based simulation technique. We then investigate several general-purpose agent-based simulation tools. Next, we review four popular agent-based simulation packages developed for electricity markets and several agent-based simulation models reported in the literature. We compare all the reviewed packages and models and identify their common features and design issues. Based on the study, we describe an agent-based simulation framework for electricity markets to facilitate the development of future models for electricity markets.     

Embracing and Extending 20th-Century Instruction Set Architectures

A vector case study shows how new functionality can be added to extend the 80times86 and PowerPC architectures to support a full vector architecture, primarily by enhancing their multimedia extensions to provide a better model for compilers and an easier-to-understand model for programmers     

Fundamental Thermal Noise in Distributed Feedback Fiber Lasers

A detailed analysis of fundamental thermal frequency noise in distributed feedback fiber lasers (DFB FL) is presented. An expression relating the laser frequency noise spectrum to the spectrum of thermal (temperature) fluctuations in the fiber, accounting for the nontrivial DFB FL mode shape, is derived. A new expression for the thermal fluctuation spectrum of single-mode optical fiber is derived which predicts high-frequency thermal noise 3 dB higher than previously published results. Theoretical predictions are compared against experimental measurements for a well characterized DFB FL. Anomalous 1/f noise at low frequency is discussed     

A stochastic optimization model for real-time ambulance redeployment

When ambulances are engaged in responding to emergency calls, the ability to respond quickly to future calls is considerably compromised. The available ambulances are typically relocated to reestablish maximal coverage. We present a two-stage stochastic optimization model for the ambulance redeployment problem that minimizes the number of relocations over a planning horizon while maintaining an acceptable service level. We conduct computational testing based on the real historical data from the Region of Waterloo Emergency Medical Services. The results show that the optimal relocation strategies can be computed within 40 s of computational time for a desired service level of 90%.