Observation of Exceptional Points in Electronic Circuits

Two damped coupled oscillators have been used to demonstrate the occurrence of exceptional points in a purely classical system. The implementation was achieved with electronic circuits in the kHz-range. The experimental results perfectly match the mathematical predictions at the exceptional point. A discussion about the universal occurrence of exceptional points -- connecting dissipation with spatial orientation -- concludes the paper.Comment: 4 pages, latex, 3 postscript figures, submitted for publicatio

Autonomous power system brassboard

The Autonomous Power System (APS) brassboard is a 20 kHz power distribution system which has been developed at NASA Lewis Research Center, Cleveland, Ohio. The brassboard exists to provide a realistic hardware platform capable of testing artificially intelligent (AI) software. The brassboard's power circuit topology is based upon a Power Distribution Control Unit (PDCU), which is a subset of an advanced development 20 kHz electrical power system (EPS) testbed, originally designed for Space Station Freedom (SSF). The APS program is designed to demonstrate the application of intelligent software as a fault detection, isolation, and recovery methodology for space power systems. This report discusses both the hardware and software elements used to construct the present configuration of the brassboard. The brassboard power components are described. These include the solid-state switches (herein referred to as switchgear), transformers, sources, and loads. Closely linked to this power portion of the brassboard is the first level of embedded control. Hardware used to implement this control and its associated software is discussed. An Ada software program, developed by Lewis Research Center's Space Station Freedom Directorate for their 20 kHz testbed, is used to control the brassboard's switchgear, as well as monitor key brassboard parameters through sensors located within these switches. The Ada code is downloaded from a PC/AT, and is resident within the 8086 microprocessor-based embedded controllers. The PC/AT is also used for smart terminal emulation, capable of controlling the switchgear as well as displaying data from them. Intelligent control is provided through use of a T1 Explorer and the Autonomous Power Expert (APEX) LISP software. Real-time load scheduling is implemented through use of a 'C' program-based scheduling engine. The methods of communication between these computers and the brassboard are explored. In order to evaluate the features of both the brassboard hardware and intelligent controlling software, fault circuits have been developed and integrated as part of the brassboard. A description of these fault circuits and their function is included. The brassboard has become an extremely useful test facility, promoting artificial intelligence (AI) applications for power distribution systems. However, there are elements of the brassboard which could be enhanced, thus improving system performance. Modifications and enhancements to improve the brassboard's operation are discussed

Firm Capabilities, Competition and Industrial Policies in a History-Friendly Model of the Computer Industry

In this paper, we explore some problems that industrial policy faces in industries characterized by dynamic increasing returns on the basis of a 'history friendly model' of the evolution of the computer industry. How does policy affect industry structure over the course of industry evolution? Is the timing of the intervention important? Do policy interventions have indirect and perhaps unintended consequences on different markets at different times? We focus on two sets of policies: antitrust and interventions aiming at supporting the entry of new forms in the industry. The results of our simulations show that, if strong dynamic increasing returns are operative, both through technological capabilities and through customer tendency to stick with a brand, there is little that antitrust and entry policy could have done to avert the rise of a dominant firm in mainframes. On the other hand, if the customer lock in effect had been smaller, either by chance or through policies that discouraged efforts of firms to lock in their customers, the situation might have been somewhat different. In the first place, even in the absence of antitrust or entry encouraging policies, market concentration would have been lower, albeit a dominant firm would emerge anyhow. Second, antitrust and entry encouraging policies would have been more effective in assuring that concentration would decrease. The leading firm would continue to dominate the market, but its relative power would be reduced. © Elsevier Science B.V

Automated mixed traffic transit vehicle microprocessor controller

An improved Automated Mixed Traffic Vehicle (AMTV) speed control system employing a microprocessor and transistor chopper motor current controller is described and its performance is presented in terms of velocity versus time curves. The on board computer hardware and software systems are described as is the software development system. All of the programming used in this controller was implemented using FORTRAN. This microprocessor controller made possible a number of safety features and improved the comfort associated with starting and shopping. In addition, most of the vehicle's performance characteristics can be altered by simple program parameter changes. A failure analysis of the microprocessor controller was generated and the results are included. Flow diagrams for the speed control algorithms and complete FORTRAN code listings are also included

Versatile, low-cost, computer-controlled, sample positioning system for vacuum applications

A versatile, low-cost, easy to implement, microprocessor-based motorized positioning system (MPS) suitable for accurate sample manipulation in a Second Ion Mass Spectrometry (SIMS) system, and for other ultra-high vacuum (UHV) applications was designed and built at NASA LeRC. The system can be operated manually or under computer control. In the latter case, local, as well as remote operation is possible via the IEEE-488 bus. The position of the sample can be controlled in three linear orthogonal and one angular coordinates

Exploration and exploitation in the presence of network externalities

This paper examines the conditions under which exploration of a new, incompatible technologyis conducive to firm growth in the presence of network externalities. In particular, this studyis motivated bythe divergent evolutions of the PC and the workstation markets in response to a new technology: reduced instruction set computing (RISC). In the PC market, Intel has developed new microprocessors bymaintaining compatibilitywith the established architecture, whereas it was radicallyr eplaced byRISC in the workstation market. History indicates that unlike the PC market, the workstation market consisted of a large number of power users, who are less sensitive to compatibilitythan ordinaryusers. Our numerical analysis indicates that the exploration of a new, incompatible technologyis more likelyto increase the chance of firm growth when there are a substantial number of power users or when a new technologyis introduced before an established technologytakes off. (; ; ;

TMS communications hardware. Volume 2: Bus interface unit

A prototype coaxial cable bus communication system used in the Trend Monitoring System to interconnect intelligent graphics terminals to a host minicomputer is described. The terminals and host are connected to the bus through a microprocessor-based RF modem termed a Bus Interface Unit (BIU). The BIU hardware and the Carrier Sense Multiple Access Listen-While-Talk protocol used on the network are described

Design of a microprocessor-based Control, Interface and Monitoring (CIM unit for turbine engine controls research

High speed minicomputers were used in the past to implement advanced digital control algorithms for turbine engines. These minicomputers are typically large and expensive. It is desirable for a number of reasons to use microprocessor-based systems for future controls research. They are relatively compact, inexpensive, and are representative of the hardware that would be used for actual engine-mounted controls. The Control, Interface, and Monitoring Unit (CIM) contains a microprocessor-based controls computer, necessary interface hardware and a system to monitor while it is running an engine. It is presently being used to evaluate an advanced turbofan engine control algorithm

Conceptual design study for Infrared Limb Experiment (IRLE)

The phase A engineering design study for the Infrared Limb Experiment (IRLE) instrument, the infrared portion of the Mesosphere-Lower Thermosphere Explorer (MELTER) satellite payload is given. The IRLE instrument is a satellite instrument, based on the heritage of the Limb Infrared Monitor of the Stratosphere (LIMS) program, that will make global measurements of O3, CO2, NO, NO2, H2O, and OH from earth limb emissions. These measurements will be used to provide improved understanding of the photochemistry, radiation, dynamics, energetics, and transport phenomena in the lower thermosphere, mesosphere, and stratosphere. The IRLE instrument is the infrared portion of the MELTER satellite payload. MELTER is being proposed to NASA Goddard by a consortium consisting of the University of Michigan, University of Colorado and NASA Langley. It is proposed that the Space Dynamics Laboratory at Utah State University (SDL/USU) build the IRLE instrument for NASA Langley. MELTER is scheduled for launch in November 1994 into a sun-synchronous, 650-km circular orbit with an inclination angle of 97.8 deg and an ascending node at 3:00 p.m. local time