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Searching for faint companions to nearby stars with the Hubble Space Telescope

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC 1996年第724期108卷 510-519页

作者： Schroeder, DJ Golimowski, DA JOHNS HOPKINS UNIV DEPT PHYS & ASTRONCTR ASTROPHYS SCIBALTIMOREMD 21218

A search for faint companions (FCs) to selected stars within 5 pc of the Sun using the Hubble Space Telescope's Planetary Camera (PC) has been initiated. To assess the PC's ability to detect FCs, we have constructed both model and laboratory-simulated images and compared them to actual PC images. We find that the PC's point-spread function (PSF) is 3-4 times brighter over the angular range 2 ''-5 '' than the PSF expected for a perfect optical system. Azimuthal variations of the PC's PSF are 10-20 times larger than expected for a perfect PSF. These variations suggest that light is scattered nonuniformly from the surface of the detector. Because the anomalies in the PC's PSF cannot be precisely simulated, subtracting a reference PSF from the PC image is problematic. We have developed a computer algorithm that identifies local brightness anomalies within the PSF as potential FCs. We find that this search algorithm will successfully locate FCs anywhere within the circumstellar field provided that the average pixel signal from the FC is at least 10 sigma above the local background. This detection limit suggests that a comprehensive search for extrasolar Jovian planets with the PC is impractical. However, the PC is useful for detecting other types of substellar objects, With a stellar signal of 10(9) e(-), for example, we may detect brown dwarfs as faint as M(l)=16.7 separated by 1 '' from a Cen A.

关键词： Hubble Space Telescope Micro computer Syncope Searches Point spread function Fluorocarbons NEARBY STARS SEARCHING ALGORITHM Companions Jovian planet Anomalies computer algorithms

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Analysis of one-way reservation algorithms

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JOURNAL OF HIGH SPEED NETWORKS 1996年第4期5卷 347-363页

作者： Cidon, I Rom, R Shavitt, Y SUN MICROSYST INC MT VIEWCA 94043 TECHNION ISRAEL INST TECHNOL DEPT ELECT ENGNIL-32000 HAIFAISRAEL

Modem high speed networks (and ATM networks in particular) use resource reservation as a basic means of establishing communications. One-way on-the-fly reservation is a method for allocating resources for short bursts of data when regular reservation is too costly. The first of such algorithms were recently suggested by Turner. We investigate two examples that are characteristic to the way traffic streams interact in virtual circuit networks: a three node subnetwork that also acts as a 4X2 switch and a ring. For both systems we compute system throughput under homogeneous load, and compare it with the throughput when fast reservation protocols (FRP) are used. For the three node subnetwork we give an explicit expression for an upper bound.

关键词： Real-time computing computer algorithms Virtual machine systems

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A fully distributed power control algorithm for cellular mobile systems

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 1996年第4期14卷 692-697页

作者： Lee, TH Lin, JC NATL SCI COUNCIL NATL SPACE PROGRAM OFFHSINCHU 300TAIWAN

Several distributed power control algorithms that can achieve carrier-to-interference ratio (CIR) balancing with probability one have been proposed recently for cellular mobile systems [5]-[8], In these algorithms, only local information is used to adjust transmitting power, However, a normalization procedure is required in each iteration to determine transmitting power and, thus, these algorithms are not fully distributed, In this paper, we present a distributed power control algorithm which does not need the normalization procedure, We show that the proposed algorithm can achieve CIR balancing with probability one, Moreover, numerical results reveal our proposed scheme performs better than the algorithm presented in [7], which has the best performance among the distributed power control algorithms studied in [5]-[8], The excellent performance and the fully distributed property make our proposed algorithm a good choice for cellular mobile systems.

关键词： cellular mobile system Power control Cells algorithms Transmitter power Distribute Mobile computer algorithms

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Soft-handling gripper driven by piezoceramic bimorph strips

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SMART MATERIALS AND STRUCTURES 1996年第4期5卷 407-414页

作者： Chonan, S Jiang, ZW Kosekl, M TOHOKU UNIV DEPT MECHATRON & PRECIS ENGN SENDAI MIYAGI 98077 JAPAN TOSHIBA CO LTD DEPT SYST ENGN HINO TOKYO 191 JAPAN

This paper is a study on the hybrid position/force control of a two-fingered miniature gripper driven by piezoelectric bimoph cells. The system is composed of the flexible cantilevers and a compact force sensor attached to the tip of one finger. Control action is applied by two piezoelectric bimorph strips placed at the base of each finger. The theoretical model of the electro-mechanical system is developed and applied to the study of a control problem where the gripper is commanded to grasp its object with a time-constant force 0.01 N at a prescribed commanded fingertip position. The PID control algorithm is introduced to drive the gripper. The system control behaviour is examined both theoretically and experimentally.

关键词： terminal interface processor force sensors Electro-Mechanical Systems bimorph Ribbon Device Component Automobile driving Fingers computer algorithms

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Applying continuous chaotic modeling to cardiac signal analysis

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IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE 1996年第5期15卷 97-102页

作者： Cohen, ME Hudson, DL Deedwania, PC UNIV CALIF SAN FRANCISCO SAN FRANCISCO CA 94143 USA VET AFFAIRS MED CTR FRESNO CA USA

In the last decade, chaos theory has become a popular method for approaching the analysis of nonlinear data for which most mathematical models produce intractable solutions. The concept of chaos was first introduced with applications in meteorology. Since then, considerable work has been done in the theoretical aspects of chaos. Applications have abounded, especially in medicine and biology. A particularly active area for the application of chaos theory has been cardiology. Many aspects of heart disease have been addressed, including whether chaos represents the healthy or diseased state. Most approaches to chaotic modeling rely on discrete models of continuous problems, which are represented by computer algorithms. Due to the nature of chaotic models, both the discretization and the computer simulation can lead to propagation of errors that may overtake the actual solution. This article describes an approach to chaotic modeling in which a continuous model is developed based on a conjectured solution to the logistic equation. As a result of this approach, two practical methods for quantifying variability in data sets have been derived. The first is a graphical representation obtained by using second-order difference plots of time series data. The second is a central tendency measure (CTM) that quantifies this degree of variability. The CTM can then be used as a parameter in decision models, such as neural networks. It appears that measuring the degree of variability is a more useful measure of chaos, as demonstrated by the application of this work to the analysis of congestive heart failure patients as compared to normal controls.

关键词： Cataract, zonular Congestive Heart Failure Signal analysis time series data Chaos theory Meteorology chaos computer algorithms Modeling

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A hybrid-type active vibration isolation system using neural networks

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JOURNAL OF SOUND AND VIBRATION 1996年第4期192卷 793-805页

作者： Ahn, KG Pahk, HJ Jung, MY Cho, DW SEOUL NATL UNIV DEPT MECH DESIGN & PROD ENGNSEOULSOUTH KOREA POHANG UNIV SCI & TECHNOL DEPT IND ENGNPOHANG 790784SOUTH KOREA

Vibration isolation of mechanical systems is achieved through either passive or active vibration control systems. Although a passive vibration isolation system offers simple and reliable means to protect mechanical systems from a vibration environment, it has inherent performance limitations, that is, its controllable frequency range is limited and the shape of its transmissibility does not change. Recently, in some applications, such as active suspensions or precise vibration systems, active vibration isolation systems have been employed to overcome the limitations of the passive systems. In this paper, a hybrid-type active vibration isolation system that uses electromagnetic and pneumatic force is developed, and a new control algorithm adopting neural networks is proposed. The characteristics of the hybrid system proposed in the paper were investigated via computer simulation and experiments. It was shown that the transmissibility of the vibration isolation system could be kept below 0.63 over the entire frequency range, including the resonance frequency. (C) 1996 Academic Press Limited

关键词： Mechanical systems Vibration isolation hybrid systems isolation system active vibration isolation active suspension frequency ranges ELECTROMAGNETIC computer algorithms

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MIMO and SISO self-tuning hybrid position/force control of robotic manipulators

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JOURNAL OF ROBOTIC SYSTEMS 1996年第1期13卷 41-51页

作者： Ozsoy, C Sisman, T SELCUK UNIV FAC ENGNDEPT MECH ENGNKONYATURKEY

This article presents a new approach for the hybrid position/force control of a manipulator by using self-tuning regulators (STR). For this purpose, the discrete-time stochastic multi-input multi-output (MIMO) and single-input single-output (SISO) models are introduced. The MIMO model's output vector has the positions and velocities of the gripper expressed in the world (xyz) coordinate system as the components. The SISO model outputs are the hybrid errors consisting of the derivatives of the position and force errors at the joints. The inputs of both models are the joint torques. The unknown parameters of those models can be calculated recursively on-line by the square-root estimation algorithm (SQR). An adaptive MIMO and SISO self-tuning type controllers are then designed by minimizing the expected value of a quadratic criterion. This performance index penalizes the deviations of the actual position and force path of the gripper from the desired values expressed in the Cartesian coordinate system. An integrating effect is also included in the performance index to remove the steady-state errors. Digital simulation results using the parameter estimation and the control algorithms are presented and the performances of those two controllers are discussed. (C) 1996 John Wiley & Sons, Inc.

关键词： Unknown parameter performance indicators multiple input multiple output systems Robot Manipulator physical location EXPECTATION VALUE single input single output systems Parameter estimation Controllers Cartesian coordinate system Manipulators computer algorithms

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Control effort weighting in feedforward adaptive control systems

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JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 1996年第5期99卷 2955-2964页

作者： Rossetti, DJ Jolly, MR Southward, SC Lord Corporation 405 Gregson Drive Cary North Carolina 27540

Active control of noise and vibration in large dimensional complex systems is generally accomplished with adaptive feedforward control algorithms based on the steepest descent optimization approach. This paper examines the effects of incorporating control effort weighting into the cost function that is minimized by an adaptive control algorithm. When the plant matrix is rank-deficient, the least-squares solution to which the control algorithm converges is nonunique. In such situations, the control signals can drift with no change in performance. Small amounts of uniform control effort weighting can enforce a unique solution at the expense of decreased performance. A nonuniform form of control effort weighting is introduced that yields a unique solution without a performance penalty. With ill-conditioned systems, small amounts of effort weighting can provide significant reductions in the control signals with only a very small increase in residual error. A form of effort weighting is introduced for ill-conditioned systems based on the results for the rank-deficient case. Stability and robustness issues are examined for each form of weighting. It is shown that the nonuniform forms of control effort weighting can significantly diminish the trade-off between performance and robustness in the presence of plant model error. (C) 1996 Acoustical Society of America.

关键词： control systems Adaptive control systems active control CONTROL SIGNAL Fishing power Noise control computer algorithms Robustness

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Experimental study of a rapidly convergent adaptive controller applied to suppression of random noise transmission

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JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 1996年第5期99卷 3236-3239页

作者： Koshigoe, S Gordon, AA Ndefo, ED Tsay, CH Teagle, A CALIF STATE UNIV LONG BEACH LONG BEACHCA 90840

In this letter, an efficient, rapid-convergent, control algorithm will be developed and compared with finite impulse response (FIR), filtered-x, LMS [Widrow et al., Proc. IEEE 63, 1692-1711 (1975)], and a modified version of Godard's algorithm [D. Godard, IBM J. Res. Develop., pp. 267-273 (1974)]. The experiments will be performed on an active noise control (ANC) system. Comparisons of the random noise attenuation capability, transient and convergence performance, and computational requirements of each algorithm will be made as the order of the controller and relevant convergence parameters are varied. The ANC system used for these experiments is a test bed of noise suppression technology for expendable launch vehicles, It consists of a flexible plate backed by a rigid cavity. Piezoelectric actuators are mounted on the plate and polyvinylidene fluoride (PVDF) microphones are used to sense the reference and error signals. The plate is bombarded with an amplified random noise signal, and the control system is used to suppress the cavity noise generated by the sound source. (C) 1995 Acoustical Society of America.

关键词： noise propagation polyvinylidene fluoride control systems random noise test bed disposable vehicle IMPULSE RESPONSE adaptive controller Acid neutralising capacity flexible sheet acoustic radiators computer algorithms

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Robust throttle control of automotive engines: Theory and experiment

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JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME 1996年第1期118卷 92-98页

作者： Choi, SB Hedrick, JK Department of Mechanical Engineering University of California Berkeley CA 94720

An adaptive, sliding control algorithm is developed for automated throttle control of an I.C. engine to be used in drive-by-H ire applications such as coordinated engine/transmission gear shiftings, traction control and autonomous vehicle control (NHS). The paper presents a new sliding control formulation that includes combustion transport delays and a simplified adapation law to account for slowly varying engine parameters. The new technique is evaluated by computer simulation and laboratory dynamometer tests.

关键词： throttle controls Sliding control Engines AUTOMOTIVE ENGINES computer algorithms

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