Gary Wallace

First Surface-resolved Results with the Infrared Optical Telescope Array Imaging Interferometer: Detection of Asymmetries in Asymptotic Giant Branch Stars

We have measured non-zero closure phases for about 29% of our sample of 56 nearby Asymptotic Giant Branch (AGB) stars, using the 3-telescope Infrared Optical Telescope Array (IOTA) interferometer at near-infrared wavelengths (H band) and with angular resolutions in the range 5-10 milliarcseconds. These nonzero closure phases can only be generated by asymmetric brightness distributions of the target stars or their surroundings. We discuss how these results were obtained, and how they might be interpreted in terms of structures on or near the target stars. We also report measured angular sizes and hypothesize that most Mira stars would show detectable asymmetry if observed with adequate angular resolution.We have measured nonzero closure phases for about 29% of our sample of 56 nearby asymptotic giant branch (AGB) stars, using the three-telescope Infrared Optical Telescope Array (IOTA) interferometer at near-infrared wavelengths (H band) and with angular resolutions in the range 5-10 mas. These nonzero closure phases can only be generated by asymmetric brightness distributions of the target stars or their surroundings. We discuss how these results were obtained and how they might be interpreted in terms of structures on or near the target stars. We also report measured angular sizes and hypothesize that most Mira stars would show detectable asymmetry if observed with adequate angular resolution.

First Results with the IOTA3 Imaging Interferometer: The Spectroscopic Binaries λ Virginis and WR 140

We report the first spatially resolved observations of the spectroscopic binaries λ Vir and WR 140, including the debut of aperture-synthesis imaging with the upgraded three-telescope IOTA interferometer. Using IONIC-3, a new integrated optics beam combiner capable of a precise closure phase measurement, short observations were sufficient to extract the angular separation and orientation of each binary system and the component brightness ratio. Most notably, the underlying binary in the prototypical colliding-wind source WR 140 (WC7 + O4/O5) was found to have a separation of ~13 mas with a position angle of 152°, consistent with previous interpretations of the 2001 dust shell ejection only if the Wolf-Rayet star is fainter than the O star at 1.65 μm. We also highlight λ Vir, whose peculiar stellar properties of the Am star components will permit direct testing of current theories of tidal evolution when the full orbit is determined.

The Spring System: Integrated Support for Complex Real-TimeSystems

The Spring system is a highly integrated collection of software and hardware that synergistically operates to provide end-to-end support in building complex real-time applications. In this paper, we show how Springs specification language, programming language, software generation system, and operating system kernel are applied to build a flexible manufacturing testbed. The same ingredients have also been used to realize a predictable version of a robot pick and place application used in industry. These applications are good examples of complex real-time systems that require flexibility. The goal of this paper is to demonstrate the integrated nature of the system and the benefits of integration; in particular, the use of reflective information and the value of function and time composition. The lessons learned from these applications and the project as a whole are also presented.

The spring scheduling co-processor: a scheduling accelerator

We present a novel co-processor for multiprocessor scheduling in the Spring real-time operating system. Since most dynamic scheduling problems are NP-complete, we use a heuristic algorithm which uses a smart searching scheme to find a feasible schedule for a set of specified tasks and hard deadlines. A parallel VLSI architecture for scheduling is developed that can be scaled for different numbers of tasks, numbers of resources, internal wordlengths, and future IC technologies. The scheduling architecture is implemented in a 0.8/spl mu/ CMOS technology and uses an advanced clocking scheme to allow further scaling to future technologies. With an internal clock rate of 100 MHz, a speed increase of two orders of magnitude is expected for scheduling tasks, thus removing a major bottleneck in real-time systems.<<ETX>>

The spring scheduling coprocessor: a scheduling accelerator

The spring scheduling coprocessor is a novel very large scale integration (VLSI) accelerator for multiprocessor real-time systems. The coprocessor can be used for static as well as online scheduling. Many different policies and their combinations can be used (e.g., earliest deadline first, highest value first, or resource-oriented policies such as earliest available time first). In this paper, we describe a coprocessor architecture, a CMOS implementation, an implementation of the host/coprocessor interface and a study of the overall performance improvement. We show that the current VLSI chip speeds up the main portion of the scheduling operation by over three orders of magnitude. We also present an overall system improvement analysis by accounting for the operating system overheads and identify the next set of bottlenecks to improve. The scheduling coprocessor includes several novel VLSI features. It is implemented as a parallel architecture for scheduling that is parameterized for different numbers of tasks, numbers of resources, and internal wordlengths. The architecture was implemented using a single-phase clocking style in several novel ways. The 328 000 transistor custom 2-/spl mu/m VLSI accelerator running with a 100-MHz clock, combined with careful hardware/software co-design results in a considerable performance improvement, thus removing a major bottleneck in real-time systems.

The Spring scheduling co-processor: Design, use, and performance

We present a novel VLSI co-processor for real-time multiprocessor scheduling. The co-processor can be used for sophisticated static scheduling as well as for online scheduling using many different algorithms such as earliest deadline first, highest value first, or the Spring scheduling algorithm. When such an algorithm is used online it is important to assess the performance impact of the interface of the co-processor to the host system, in this case, the Spring kernel. We focus on the interface and its implications for overall scheduling performance. We show that the current VLSI chip speeds up the main portion of the scheduling operation by over three orders of magnitude and speeds up the overall scheduling operation 30 fold. The parallel VLSI architecture for scheduling is briefly presented. This architecture can be scaled for different numbers of tasks, resources, and internal word lengths. The implementation uses an advanced clocking scheme to allow further scaling using future IC technologies.<<ETX>>

IOTA: Recent Technology and Science ⁄

The Sydney University Stellar Interferometer (SUSI) is a long-baseline optical interferometer operating at an observatory near Narrabri in Australia. SUSI features a 640 m long North-South array with 11 fixed siderostat stations. New science from the Blue (400-500 nm) and from the recently commissioned Red (500-950 nm) fringe detectors will be presented. Recent technological developments, mainly associated with the new Red detection system, encompassing wavefront correction, fringe encoding, wavelength switching and data analysis strategies, are described.Closure-phase science and technology are dominant features of the recent activity at IOTA. Our science projects include imaging several spectroscopic binary stars, imaging YSOs including Herbig AeBe stars, detecting asymmetries in a large sample of Mira stars, and measuring water shells around Miras. Many technology projects were pursued in order to make these science observations possible. These include installation of a third-generation integrated-optics 3-beam combiner (IONIC), completion of the real-time control system software, installation of fringe-packet tracking software, use of narrow sub-H band filters, validation of the phase-closure operation, development of CPLD control of the science camera (PICNIC) and star-tracker camera (LLiST), installation of a new star-tracker camera, expansion of the observing facility, and installation of new semi-automated optical alignment tools.

Kernel-level threads for dynamic, hard real-time environments

The design of a kernel-level thread package for dynamic, hard real-time environments is presented. A highly integrated design is used to ensure predictability. A system description language and real-time programming language are used to specify key properties of threads and thread groups. For a thread, this includes whether or not the thread spawns other threads at run-time, the type of performance guarantee the thread requires, how the thread interacts with other threads, and what processors the thread may execute on. A predictable kernel uses this information along with on-line dynamic guarantees to ensure predictable execution of threads. The first phase of the thread package has been implemented and performance measurements have indicated a 66% improvement in context switching costs.

IOTA: Recent science and technology

We present a brief review of recent scientific and technical advances at the Infrared Optical Telescope Array (IOTA). IOTA is a long-baseline interferometer located atop Mount Hopkins, Arizona. Recent work has emphasized the use of the three-telescope interferometer completed in 2002. We report on results obtained on a range of scientific targets, including AGB stars, Herbig AeBe Stars, binary stars, and the recent outburst of the recurrent nova RS Oph. We report the completion of a new spectrometer which allows visibility measurements at several high spectral resolution channels simultaneously. Finally, it is our sad duty to report that IOTA will be closed this year.

A robotic assembly application on the Spring real-time system

The Spring real-time system and environment provides methods for program representation and corresponding run-time system support that allow programs to meet the predictability demands of complex real-time applications. The primary objective of the work described in this paper is to present the experiences gained and the lessons learned from porting a real-world, real-time application to make it predictable and flexible. The exercise has also provided a test case which helps to answer questions about the completeness and ease of use of software development tools that have been developed to provide for flexibility while achieving real-time guarantees. This test case is derived from an existing real-time application in industry-a robotic work-cell that is currently in use for the assembly of circuit boards. From our experience with this reengineering exercise, we believe that a user must possess a good understanding of the following: (1) the general properties of the target hardware-for effective process and resource layout, and (2) the shared resource usage and interprocess communication, and, more generally, the statements that cause processes to suspend-for efficient run-time representation of the tasks. Tools that help the user obtain this understanding and perform detailed timing analysis are essential. Although the algorithms and tools used in the reimplementation were developed in the context of the Spring real-time environment, we believe that the lessons learned from this experiment will be useful not only to potential users of Spring, but also to real-time practitioners at large.