Dynamic scheduling of hard real-time tasks and real-time threads

The authors investigate the dynamic scheduling of tasks with well-defined timing constraints. They present a dynamic uniprocessor scheduling algorithm with an O(n log n) worst-case complexity. The preemptive scheduling performed by the algorithm is shown to be of higher efficiency than that of other known algorithms. Furthermore, tasks may be related by precedence constraints, and they may have arbitrary deadlines and start times (which need not equal their arrival times). An experimental evaluation of the algorithm compares its average case behavior to the worst case. An analytic model used for explanation of the experimental results is validated with actual system measurements. The dynamic scheduling algorithm is the basis of a real-time multiprocessor operating system kernel developed in conjunction with this research. Specifically, this algorithm is used at the lowest, threads-based layer of the kernel whenever threads are created     

Closed-loop class E transcutaneous power and data link for microimplants.

Magnetic transcutaneous coupling is frequently used for power and data transfer to implanted electronic devices. The proposed development of MicroImplants, small enough to be injected through a hypodermic needle suggest the need for a high-efficiency magnetic transcutaneous link. This paper describes the use of a multifrequency transmitter coil driver based upon the Class E topology. The development of a "high-Q approximation" which simplifies the design procedure is presented. A closed-loop controller to compensate for transmitter and receiver variations, and a method of data modulation, using synchronous frequency shifting are described. The closed-loop Class E circuit shows great promise, especially for circuits with unusually low coefficients of coupling. Currents of several amperes, at radio frequencies, can easily and efficiently be obtained.     

Native data representation: An efficient wire format for high-performance distributed computing

New trends in high-performance software development such as tool- and component-based approaches have increased the need for flexible and high-performance communication systems. When trying to reap the well-known benefits of these approaches, the question of what communication infrastructure should be used to link the various components arises. In this context, flexibility and high-performance seem to be incompatible goals. Traditional HPC-style communication libraries, such as MPI, offer good performance, but are not intended for loosely-coupled systems. Object- and metadata-based approaches like XML offer the needed plug-and-play flexibility, but with significantly lower performance. We observe that the flexibility and baseline performance of data exchange systems are strongly determined by their wire formats, or by how they represent data for transmission in heterogeneous environments. After examining the performance implications of using a number of different wire formats, we propose an alternative approach for flexible high-performance data exchange, Native Data Representation, and evaluate its current implementation in the portable binary I/O library.     

Publish-subscribe for high-performance computing

High-performance computing could significantly benefit from publish-subscribe communication, but current systems don't deliver the kind of performance required by applications in that domain. In response, the authors developed Echo, a high-performance event-delivery middleware designed to scale to the data rates typically found in grid environments. This article provides an overview of Echo, the infrastructure on which it's built, and the techniques used to implement it.     

Distribution and molecular analysis of Lyme disease spirochetes, Borrelia burgdorferi, isolated from ticks throughout California

Previous studies describing the occurrence and molecular characteristics of Lyme disease spirochetes, Borrelia burgdorferi, from California have been restricted primarily to isolates obtained from the north coastal region of this large and ecologically diverse state. Our objective was to look for and examine B. burdorferi organisms isolated from Ixodes pacificus ticks collected from numerous regions spanning most parts of California where this tick is found. Thirty-one isolates of B. burgdorferi were examined from individual or pooled I. pacificus ticks collected from 25 counties throughout the state. One isolate was obtained from ticks collected at Wawona Campground in Yosemite National Park, documenting the occurrence of the Lyme disease spirochete in an area of intensive human recreational use. One isolate from an Ixodes neotomae tick from an additional county was also examined. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblot analysis, agarose gel electrophoresis, Southern blot analysis, and the polymerase chain reaction were used to examine the molecular and genetic determinants of these uncloned, low-passage-number isolates. All of the isolates were identified as B. burgdorferi by their protein profiles and reactivities with monoclonal and polyclonal antibodies, and all the isolates were typed by the polymerase chain reaction as North American-type spirochetes (B. burgdorferi sensu stricto). Although products of the ospAB locus were identified in protein analyses in all of the isolates, several isolates contained deleted forms of this locus that would result in the expression of chimeric OspA-OspB proteins. The analysis of OspC demonstrated that this protein was widely conserved among the isolates but was also quite variable in its molecular mass and the amount of it that was expressed.     

Cotton rats and other small mammals as hosts for immature Dermacentor variabilis (Acari: Ixodidae) in central Oklahoma

Eight species of small mammals were evaluated as potential hosts for American dog ticks, Dermacentor variabilis (Say), in an upland, tallgrass prairie study site in central Oklahoma. Only hispid cotton rats, Sigmodon hispidus, and deer mice, Peromyscus maniculatus, were found to be important hosts for immature D. variabilis. Although D. varibilis larvae and nymphs frequently infested both cotton rats and deer mice, cotton rats were the most important host species for both immature stages in the study area. Cotton rats constituted 63.2% of the total 530 small mammals captured and were hosts to 85.2% of all larvae and 88.7% of all nymphs. Deer mice accounted for 19.8% of all small mammals captured and were hosts for 14.5% of the larvae and 10.8% of the nymphs recovered. The remaining small mammal species were hosts for less than 1% of the immature ticks collected. Larval infestations peaked during summer, whereas summer and spring peaks were noted for the nymphal infestations. The relative importance of cotton rats and deer mice as hosts for immature ticks could be largely, but not completely, explained by cotton rats being more than three times as abundant as deer mice. Attachment site data indicated that differences in grooming behavior also might be partially responsible for the larger infestations observed on cotton rats. Other possible ecological and behavioral explanations of the heavy infestations observed on cotton rats are discussed.     

System-Level Resource Monitoring in High-Performance Computing Environments

Low-overhead resource monitoring is key to the successful management of distributed high-performance computing environments, particularly when applications have well-defined quality of service (QoS) requirements. The dproc system-level monitoring mechanisms provide tools both for efficiently monitoring system-level events and for notifying remote hosts of events relevant to their operation. Implemented as extension to the Linux kernel, dproc provides several key functions. First, utilizing the familiar /proc virtual filesystem, dproc extends this interface with resource information collected from both local and remote hosts. Second, to predictably capture and distribute monitoring information, dproc uses a kernel-level group communication facility, termed KECho, which implements events and event channels. Third, and the focus of this paper, is dproc's run-time customizability for resource monitoring, which includes the generation and deployment of monitoring functionality within remote operating system kernels. Using dproc, we show that (a) data streams can be customized according to a client's resource availabilities (dynamic stream management), (b) by dynamically varying distributed monitoring (dynamic filtering of monitoring information), an appropriate balance can be maintained between monitoring overheads and application quality, and (c) by performing monitoring at kernel-level, the information captured enables decision making that takes into account the multiple resources used by applications.     

Effect of surface cooling and blood flow on the microwave heating of tissue

The one-dimensional heat transport equation has been solved for a semi-infinite plane of tissue irradiated by microwave radiation, to determine the effects of thermal convection due to blood flow and transfer of heat from the tissue surface into space on the steady-state temperature distribution in the tissue. For microwaves in the 1 to 10-GHz range, the effective heating depth is 1 to 2 cm, and can be much deeper than the penetration depth of the radiation in the tissue. The position of the maximum tissue temperature can be varied by a centimeter or so by cooling the surface. The results suggest that microwave irradiation of simulated biomaterials is not likely to provide accurate estimates of the actual microwave-induced temperature distribution in tissue.     

Reliability of power transits

Contents One of the key measures in establishing competitive electricity markets are power transits. Existing network planning tools must be adapted for the consideration of such transits. The research project presented here assessed especially supply reliability with consideration of power transits. The modifications necessary to include power transits in the probabilistic reliability calculation tool ZUBER are presented. The supply reliability is assessed using the insurance model. Finally, the presented aspects are demonstrated in the analysis of an example power system. Received: 30 April 2001/Accepted: 8 June 2001