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Transposer operates entirely in analog domain. Input analog signal is serially loaded into analog register at rate determined by voltage-controlled oscillator. At same time, signal is serially unloaded from other register at expanded time rate determined by divider output feeding through switch.
Three experiments on fault tolerant multiprocessors (FTMP) were begun. They are: (1) measurement of fault latency in FTMP; (2) validation and analysis of FTMP synchronization protocols; and investigation of error propagation in FTMP.
A synchronous demodulator includes a switch which is operated in synchronism with an incoming periodic signal and both divides and applies that signal to two signal channels. The two channels each include a network for computing and holding, for a predetermined length of time, the average signal value on that channel and applies those valves, in the form of two other signals, to the inputs of a differential amplifier. The networks may be R-C networks. The output of the differential amplifier may or may not form the output of the synchronous detector and may or may not be filtered. The output will not include a periodic signal due to the presence of a dc offset. Additionally, the output will not contain any substantial ripple due to periodic components in the input signal. In a somewhat more complex version, containing twice the structural components of the above synchronous demodulator with a more complex switching mechanism, essentially all ripple due to periodic components in the input signal are eliminated.
1. Both the timing of behavioural events (activity, sleep and social interactions) and the environmental light-dark cycle have been reported to contribute to entrainment of human circadian rhythms to the 24 h day. Yet, the relative contribution of those putative behavioural synchronizers to that of light exposure remains unclear. 2. To investigate this, we inverted the schedule of rest, sedentary activity and social contact of thirty-two young men either with or without exposure to bright light. 3. On this inverted schedule, the endogenous component of the core temperature rhythm of subjects who were exposed to bright light showed a significant phase shift, demonstrating that they were adapting to the new schedule. In contrast, the core temperature rhythm of subjects who were not exposed to bright light moved on average 0.2 h later per day and after 10 days had not significantly adapted to the new schedule. 4. The direction of phase shift in the groups exposed to bright light was dependent on the time of bright light exposure, while control subjects drifted to a later hour regardless of the timing of their schedule of sleep timing, social contact and meals. 5. These results support the concept that the light-dark cycle is the most important synchronizer of the human circadian system. They suggest that inversion of the sleep-wake, rest-activity and social contact cycles provides relatively minimal drive for resetting the human circadian pacemaker. 6. These data indicate that interventions designed to phase shift human circadian rhythms for adjustment to time zone changes or altered work schedules should focus on properly timed light exposure.
The maximum efficiency of silicon solar cells is calculated and yields a value near 18%. Additionally, the performance of these high efficiency cells in a synchronous orbit radiation field is calculated and indicates that these cells would be superior to present silicon cells at all times. The performance of conventional cells is analyzed and several areas in which performance gains may be achieved are discussed. These areas include improvements in diffused region profile, in reduction of excess forward currents in cells made from low resistivity material and in the theory for describing complex solar cell structures.
A redundant three-axis analog control system was designed and developed to back up a digital fly-by-wire control system for an F-8C airplane. Forty-two flights, involving 58 hours of flight time, were flown by six pilots. The mechanization and operational experience with the backup control system, the problems involved in synchronizing it with the primary system, and the reliability of the system are discussed. The backup control system was dissimilar to the primary system, and it provided satisfactory handling through the flight envelope evaluated. Limited flight tests of a variety of control tasks showed that control was also satisfactory when the backup control system was controlled by a minimum-displacement (force) side stick. The operational reliability of the F-8 digital fly-by-wire control system was satisfactory, with no unintentional downmodes to the backup control system in flight. The ground and flight reliability of the system's components is discussed.
Phase-locked-loop (PLL) bit synchronizers often employ integrate-and-dump type phase detectors that provide phase error information only at discrete points in time. Usually these phase detectors are followed by sample-and-hold circuits to produce a stairstep error voltage as the input to a standard analog circuit loop filter. When the loop is configured in this manner, it is referred to as a hybrid PLL. Sampled-data analysis methods (Z transforms) are used to determine the stability and transient response of this loop.
In the airborne detection system of atmospheric constituents and pollutants described, double-ended differential absorption measurement is accomplished by rapidly current tuning the wavelength of a PbSSe diode laser across a single line of the species under consideration. As the laser wavelength sweeps periodically across the absorption line, the laser beam is amplitude modulated and is then synchronously detected. With this technique, a minimum detectable differential transmission of 0.02 percent is obtained for a 1-sec integration time.
The observational data for the 124 cataclysmic and low-mass X-ray binaries of known orbital period are compiled. It is found that the eruption properties are very well correlated with the orbital periods, in a manner that suggests that the mass transfer is the all-important determinant of evolution and of the eruptive behavior. Transfer rates of 10 to the -11th to 10 to the -7th solar mass/year are found, which are well correlated with orbital period. It is concluded that the mechanism which drives these systems is the magnetic braking of the secondary's rotation by its own stellar wind, coupled with the enforcement of synchronous rotation by tidal friction. This permits CVs to lose sufficient angular momentum to begin mass transfer in a reasonable time and drives the mass transfer at a high rate once it begins. An account of the long-lived phases of CV evolution is given.
The workload effects on computer performance are addressed first for a highly reliable unibus multiprocessor used in real-time control. As an approach to studing these effects, a modified Stochastic Petri Net (SPN) is used to describe the synchronous operation of the multiprocessor system. From this model the vital components affecting performance can be determined. However, because of the complexity in solving the modified SPN, a simpler model, i.e., a closed priority queuing network, is constructed that represents the same critical aspects. The use of this model for a specific application requires the partitioning of the workload into job classes. It is shown that the steady state solution of the queuing model directly produces useful results. The use of this model in evaluating an existing system, the Fault Tolerant Multiprocessor (FTMP) at the NASA AIRLAB, is outlined with some experimental results. Also addressed is the technique of measuring fault latency, an important microscopic system parameter. Most related works have assumed no or a negligible fault latency and then performed approximate analyses. To eliminate this deficiency, a new methodology for indirectly measuring fault latency is presented.
Hurricane cloud and precipitation structure have been studied by means of IR and stereoscopic visual satellite data from synchronized scanning GOES-East and -West, in combination with ground-based radar data for Hurricane Frederico and time-composited airborne radar data for Hurricane Allen. It is noted that stereoscopically measured cloudtop height in these hurricanes is not as closely correlated to radar reflectivity at lower levels as it is in intense thunderstorms over land. This and other results obtained imply that satellite precipitation estimation techniques for tropical cyclones that are based on cloudtop measurements will not be accurate with respect to time and place scales that are less than several hours and a few hundred km, respectively.
The communication and synchronization overhead inherent in parallel processing can lead to situations where adding processors to the solution method actually increases execution time. Problem type, problem size, and architecture type all affect the optimal number of processors to employ. The numerical solution of an elliptic partial differential equation is examined in order to study the relationship between problem size and architecture. The equation's domain is discretized into n sup 2 grid points which are divided into partitions and mapped onto the individual processor memories. The relationships between grid size, stencil type, partitioning strategy, processor execution time, and communication network type are analytically quantified. In so doing, the optimal number of processors was determined to assign to the solution, and identified (1) the smallest grid size which fully benefits from using all available processors, (2) the leverage on performance given by increasing processor speed or communication network speed, and (3) the suitability of various architectures for large numerical problems.
The communication and synchronization overhead inherent in parallel processing can lead to situations where adding processors to the solution method actually increases execution time. Problem type, problem size, and architecture type all affect the optimal number of processors to employ. The numerical solution of an elliptic partial differential equation is examined in order to study the relationship between problem size and architecture. The equation's domain is discretized into n sup 2 grid points which are divided into partitions and mapped onto the individual processor memories. The relationships between grid size, stencil type, partitioning strategy, processor execution time, and communication network type are analytically quantified. In so doing, the optimal number of processors was determined to assign to the solution, and identified (1) the smallest grid size which fully benefits from using all available processors, (2) the leverage on performance given by increasing processor speed or communication network speed, and (3) the suitability of various architectures for large numerical problems.
Several abrupt changes in conodont biofacies are documented to occur synchronously at six primary control sections across the Frasnian-Famennian boundary in Euramerica. These changes occurred within a time-span of only about 100,000 years near the end of the latest Frasnian linguiformis Zone, which is formally named to replace the Uppermost gigas Zone. The conodont-biofacies changes are interpreted to reflect a eustatic rise followed by an abrupt eustatic fall immediately preceding the late Frasnian mass extinction. Two new conodont species are named and described. Ancyrognathus ubiquitus n.sp. is recorded only just below and above the level of late Frasnian extinction and hence is a global marker for that event. Palmatolepispraetriangularis n.sp. is the long-sought Frasnian ancestor of the formerly cryptogenic species, Pa. triangularis, indicator of the earliest Famennian Lower triangularis Zone. The actual extinction event occurred entirely within the Frasnian and is interpreted to have been of brief duration-from as long as 20,000 years to as short as several days. The eustatic rise-and-fall couplet associated with the late Frasnian mass extinction is similar to eustatic couplets associated with the demise of most Frasnian (F2h) reefs worldwide about 1 m.y. earlier and with a latest Famennian mass extinction about 9.5 m.y. later. All these events may be directly or indirectly attributable to extraterrestrial triggering mechanisms. An impact of a small bolide or a near miss of a larger bolide may have caused the earlier demise of Frasnian reefs. An impact of possibly the same larger bolide in the Southern Hemisphere would explain the late Frasnian mass extinction. Global regression during the Famennian probably resulted from Southern-Hemisphere glaciation triggered by the latest Frasnian impact. Glaciation probably was the indirect cause of the latest Famennian mass extinction.
During a 9-hour period following a storm-sudden commencement, six spacecraft near geosynchronous orbit, one over the pole, and three in the mgnetotail, monitored a complex sequence of magnetospheric variations. Magnetic field compressions associated with the sudden commencement were seen first by the near-earth spacecraft and subsequently by the three down-tail spacecraft with increasing time delays that were consistent with the tailward movement of an interplanetary-shock-associated pressure enhancement. Ground magnetograms and synchronous orbit data are used to identify 7 substorm intensifications during this geomagnetically active period. Six of these intensifications are clearly associated with tail lobe field decreases about 18 R sub E behind the earth. Four of these intensifications are followed by both Bz field increases in the tail lobes at about 18 and about 30 R sub E and by the subsequent observation of rapidly flowing plasma sheet plasma at ISEE 3 about 110 R sub E down the tail. During two substorms where DE 1 was optically observing the auroral oval, the area of the polar cap was observed to decrease as the tail lobe field decreased at 18 R sub E. All these observations are consistent with the substorm associated release of a plasmoid at a neutral line near 20 R sub E.
From the perspective of scheduling, some medical consultations can have asynchronous and synchronous components. Consultations frequently involve the compilation of patient data, its analysis, a consultant's report, and a real-time conference between the referring physician and the consultant. The bandwidth of the Internet with Moscow and advances in the hardware and software of personal computing now make possible telemedicine events with store-and-forward components and real-time components. These are hybrid telemedicine and this paper describes such a case.
In the present paper we examine the control problem for a class of composite hybrid machines (CHMs) that consist of concurrent operation (employing synchronous composition) of elementary hybrid machines (EHMs), that allows both signal sharing and event synchronization. A controller can then be coupled with the plant by means of synchronous composition. We confine our attention to controllers that interact with the system only through event synchronization. We present an initial investigation of synthesis of liveness controllers for hybrid machines. To this end we define open hybrid machines as systems that can interact with the environment through event synchronization and can be therefor be "driven" to their marked configuration by user (controller). Liveness specifications must be associated with timing constraints. We may require that for a specified time limit, every run reach a marked configuration within that time limit. Alternatively, a more relaxed specification may be that, for some (unspecified) global time bound, every run of the system reach a marked configuration within that time bound. Finally, the least restrictive liveness requirement is that every run reach a marked configuration within a finite time limit (but we do not insist on the existence of a global time bound for all runs).
This paper presents a reusable design of a data distribution framework for data parallel high performance applications. We are implementing the design in the context of the Chapel high productivity programming language. Distributions in Chapel are a means to express locality in systems composed of large numbers of processor and memory components connected by a network. Since distributions have a great effect on,the performance of applications, it is important that the distribution strategy can be chosen by a user. At the same time, high productivity concerns require that the user is shielded from error-prone, tedious details such as communication and synchronization. We propose an approach to distributions that enables the user to refine a language-provided distribution type and adjust it to optimize the performance of the application. Additionally, we conceal from the user low-level communication and synchronization details to increase productivity. To emphasize the generality of our distribution machinery, we present its abstract design in the form of a design pattern, which is independent of a concrete implementation. To illustrate the applicability of our distribution framework design, we outline the implementation of data distributions in terms of the Chapel language.