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COMMUNICATIONS OF THE ACM 1994年第7期37卷 143-146页

作者： KAUTZ, HA SELMAN, B COEN, M MIT ARTIFICIAL INTELLIGENCE LABCAMBRIDGEMA 02139

The creation of software agents has generated much recent interest. A variety of approaches and projects use the term 'agents,' ranging from adaptive user interfaces to systems that use planning algorithms to generate shell scripts. Generally, agents assist users in a range of daily, mundane activities like setting up meetings, sending out papers, locating information in multiple databases, tracking the whereabouts of people, and so on. The objective is to design agents that blend transparently into normal work environments, while relieving users of low-level administrative and clerical tasks. The practical aspects of software agents are taken seriously. Users should be able to assume the agents are reliable and predictable and the human user remains in ultimate control. One of the most difficult aspects of agent design is to define specific tasks that are both feasible using current technology, and are truly useful to the everyday user. Agents must provide solutions to real problems that are important to real users.

关键词： INTELLIGENT agents (computer software) USER interfaces (computer systems) computer algorithms computer users HUMAN-computer interaction computer software

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CRYPTOGRAPHY POLICY

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COMMUNICATIONS OF THE ACM 1994年第9期37卷 109-117页

作者： HOFFMAN, LJ ALI, FA HECKLER, SL HUYBRECHTS, A GEORGE WASHINGTON UNIV INST COMP & TELECOMMWASHINGTONDC 20052 STANFORD UNIV STANFORDCA 94305 BANNER BLUE SOFTWARE FREMONTCA 94539

During the past five years, encryption technology has become easily available to both individuals and businesses, affording them a level of security formerly available to only military, national security, and law enforcement agencies. This article analyzes trends in encryption technology. It is divided into four primary sections: technology, market analysis, export controls,and public policy issues. The current trends in encryption technology include increasing miniaturization, increasing use of public and private key cryptography, and the continued development of increasingly secure algorithms. The National Security Agency (NSA) is likely to continue protecting its 'turf' by advocating continued restrictions on encryption technology. It may attempt to expand its domain within the government. Commercial encryption technologies described in the article are Data Encryption Standard, RSA ( named after Rivest, Shamir, and Adelman) algorithms. RSA is a public key algorithm that is widely used for data security.

关键词： DATA encryption (computer science) PUBLIC key cryptography MINIATURE electronic equipment computer algorithms NATIONAL security computer network security

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MEASUREMENT OF AORTIC INPUT IMPEDANCE IN RATS

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AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY 1994年第5期267卷 H1907-H1915页

作者： MITCHELL, GF PFEFFER, MA WESTERHOF, N PFEFFER, JM FREE UNIV AMSTERDAM PHYSIOL LAB 1081 BT AMSTERDAM NETHERLANDS

Measurement of aortic input impedance in the rat is complicated by a high basal heart rate but is possible if appropriate compensation is made for frequency-dependent errors in modulus and phase resulting from analog filters in the equipment and from nonalignment of pressure and flow sensors. Because input impedance is a complex quantity, accurate values for both phase and modulus are required before meaningful interpretation of the data can be made. We measured aortic pressure and electromagnetic ascending aortic blood flow in mature, ether-anesthetized, open-chest male Wistar rats. Pressure and flow waveforms were averaged in the time domain and converted to Fourier series. Flow moduli were corrected for the measured frequency response of the flowmeter. Phase spectra were corrected by the classic frequency-domain and two new time-domain methods. Compensation for instrumentation errors was assessed at two different flowmeter filter settings in five animals. Reproducibility, variability, and the effects of vasoconstriction were assessed in 43 animals. Three methods of estimating characteristic impedance from the impedance spectra were evaluated and found to produce comparable results at baseline and following pharmacological elevation of blood pressure with graded methexamine infusion. Physiologically equivalent values for phase, as assessed by comparing oscillatory power calculated from the impedance spectra, were obtained with each of the phase-correction techniques. The new time-domain methods facilitate the assessment of aortic input impedance in this small animal model because they do not require measurement of the spatial separation between pressure and flow transducers and pulse wave velocity in the proximal aorta.

关键词： CHARACTERISTIC IMPEDANCE computer algorithms FOURIER ANALYSIS IMPULSE TRAIN RESPONSE

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AN EFFICIENT computer ALGORITHM FOR THE CALCULATION OF THE WALSH TRANSFORM FOR INCOMPLETELY SPECIFIED MULTIPLE-VALUED BINARY FUNCTIONS

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INTERNATIONAL JOURNAL OF ELECTRONICS 1993年第2期75卷 163-175页

作者： FALKOWSKI, BJ SCHAFER, I PERKOWSKI, MA LATTICE SEMICOND SANTA CLARACA 95051 PORTLAND STATE UNIV DEPT ELECT ENGNPORTLANDOR 97207

An efficient computer implementation of an originally developed spectral representation of multiple-valued input binary functions is presented. In such a representation, the spectrum for each multiple-valued input binary function is composed of a vector of Walsh transforms, each of them defined for one pair of input variables of the function. By that approach, the number of spectral coefficients describing a given multiple-valued input binary function is a minimal one. The implementation of the algorithm allows for the calculation of the spectra of binary functions having an arbitrary number of literals;each of them can have up to 32 different logical values. The algorithm is interactive so users can manually determine the generation of a partial or whole spectrum.

关键词： algorithms computer algorithms BINARY forms QUADRATIC forms ELECTRONICS ELECTRICAL engineering

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OPTIMAL FLOW-CONTROL ALLOCATION POLICIES IN COMMUNICATION-NETWORKS WITH MULTIPLE MESSAGE CLASSES

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IEEE TRANSACTIONS ON AUTOMATIC CONTROL 1993年第3期38卷 390-403页

作者： BOURNAS, RM BEUTLER, FJ TENEKETZIS, D UNIV MICHIGAN DEPT ELECT ENGN & COMP SCIANN ARBORMI 48109

We consider M (greater-than-or-equal-to 2) transmitting stations sending packets to a single receiver over a slotted time-multiplexed link. For each phase consisting of T consecutive slots, the receiver dynamically allocates these slots among the M transmitters. The cost per slot for holding a packet may vary among the transmitters, and may be interpreted in terms of multiple classes of messages. Our objective is to characterize policies that minimize the discounted and long-term average costs due to holding packets at the M stations, based on delayed information on the numbers of packets being held at the respective transmitters. We derive properties of optimal (discounted) policies that reduce the computational complexity of the optimal How control algorithm. For M = 2, we show that the minimal total cost is convex and submodular in the state, and we prove the following properties of optimal policies: 1) when the state at transmitter i increases by unity while the state at the other transmitter j is fixed, the optimal allocation is either unchanged, or increases by one at transmitter i and decreases hy one at transmitter j;and 2) the optimal policy is of the threshold type. We use these properties to show that the optimization reduces to the calculation of optimal allocations for a finite number of states. In addition, for each such state (excluding the origin), property 1) implies a significant reduction in the computation of optimal allocations. As an application, we further characterize optimal policies when the message generation at the transmitter of higher priority is stochastically larger than the message generation at the other. Under additional restrictions on the average arrival rate and the second moment of the number of arrivals per slot, similar results are derived for optimal policies with time-average costs.

关键词： flow control optimal allocation Packet complexity classes networks(communications) Optimization algorithms Optimal Policies computer algorithms

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METHODOLOGY FOR 3-DIMENSIONAL RECONSTRUCTION OF THE LEFT-VENTRICLE FROM TRANSESOPHAGEAL ECHOCARDIOGRAMS

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ULTRASOUND IN MEDICINE AND BIOLOGY 1993年第1期19卷 27-38页

作者： MARTIN, RW BASHEIN, G NESSLY, ML SHEEHAN, FH UNIV WASHINGTON CTR BIOENGNSEATTLEWA 98195 UNIV WASHINGTON DEPT MEDDIV CARDIOLSEATTLEWA 98195

A technique is presented for three-dimensional (3-D) reconstruction of the left-ventricular endocardial surface from multiplanar transesophageal echocardiograms, using both commercial software and investigator written Fortran programs for Intel 80286 and 80386 microcomputers. The approach provides quantitative global and regional cardiac performance measures and allows viewing the endocardial surface, at end-diastole and end-systole, from chosen perspectives. Anatomical landmarks are incorporated to aid in orientation. For regional calculation, the surface is divided into equal angular elements with each conceptually connected to the left-ventricular end-diastole centroid, forming a pyramidal volume element. This angular division automatically normalizes for heart size. The fractional change of these elements over the cardiac cycle provides a regional ejection fraction measure which is color-coded on the reconstructed endocardial surface. Composite perspective views, regional ejection fraction histograms and calculations of global end-diastolic, end-systolic, and stroke volumes, are all performed by the method.

关键词： TRANSESOPHAGEAL ECHOCARDIOGRAPHY TRANSGASTRIC 3-DIMENSIONAL RECONSTRUCTION ULTRASONIC IMAGING 3-DIMENSIONAL ULTRASOUND REGIONAL AND GLOBAL VENTRICULAR PERFORMANCE computer algorithms

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PARAMETER DRIFT INSTABILITY IN DISTURBANCE-FREE ADAPTIVE SYSTEMS

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IEEE TRANSACTIONS ON AUTOMATIC CONTROL 1993年第4期38卷 584-587页

作者： LAWRENCE, DA SETHARES, WA REN, W UNIV WISCONSIN DEPT ELECT & COMP ENGNMADISONWI 53706 UNIV CALIF BERKELEY DEPT ELECT ENGN & COMP SCIBERKELEYCA 94720

Adaptive identification and control algorithms can exhibit local instability when certain ideal assumptions, such as satisfaction of SPR conditions, are violated. However, recent conjectures suggest that due to a ''self-stabilization'' mechanism, global boundedness may still hold despite local instabilities. We present counterexamples to these conjectures, showing that self stabilization is bypassed via ''hidden'' unbounded parameter drift. Although parameter drift instability is known to occur in adaptive systems with disturbances, concrete examples are given to show that unbounded drift can also occur in the disturbance-free case when SPR conditions are violated.

关键词： drift instability SELF-STABILIZING strictly positive real Satisfaction Local buckling Strategic petroleum reserve Adaptive systems computer algorithms

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A STUDY ON INSERTION LOSS IMPROVEMENT FOR AN OPTICAL CONNECTOR USING THE ANALYSIS OF TRANSMITTED OPTICAL-INTENSITY

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IEEE TRANSACTIONS ON COMPONENTS HYBRIDS AND MANUFACTURING TECHNOLOGY 1993年第8期16卷 768-777页

作者： CHUN, OG AHN, SH JEONG, MY CHOY, TG Component Technology Section Electronics and Telecommunications Research Institute Daejeon South Korea

In the butt-joint couPling using cylindrical ferrules and sleeve, the insertion loss of the single-mode optical connector depends on the accuracies of components that consist of optical connector (i.e., sleeve, ferrule, fiber, etc.). It is also difficult to achieve both cost reduction and performance improvement simultaneously in optical connectors because higher accuracies give better performance but cause higher cost. For single-mode fiber connection, the dimensional accuracies of currently available ferrules and optical fibers are not sufficiently high to ensure a low insertion loss with reasonable cost. Many efforts have been made to have low insertion loss without any higher order of accuracies of components. In one of the proposed methods the technique of stepwise orientation of the ferrule is used to reduce the transverse offset between butt-joint fiber cores by achieving the minimizing loss region (MLR). This method requires several stepwise rotations to make the fiber core within the MLR, which was determined by the optimal trade-off between insertion loss and working dme. In this method the insertion loss severely depends on the size of the predetermined MLR. In this paper, a new assembling method through which a very small MLR can be achieved in a short time, is proposed.

关键词： Connector Device Component Coating fiber core insertion loss Ferrule Device Component Working time optical Optical connectors assembly method computer algorithms

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A ROBUST INDIRECT ADAPTIVE REGULATION ALGORITHM WITH SELF-EXCITATION CAPABILITY

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IEEE TRANSACTIONS ON AUTOMATIC CONTROL 1993年第2期38卷 271-276页

作者： PENG, HJ CHEN, BS Department of Electrical Engineering TsingHua University Hsinchu Taiwan

In this note, we present a robust version of the adaptive control algorithm established by Kreisselmeier [1]. We know that if the conventional dead-zone adaptive law is used in the adaptive system, it is troubleseome that the size of the unmodeled dynamics, denoted by epsilon, must be within the chosen dead-zone size for robustness. In this robust version, by introducing a positive design parameter epsilonBAR, the robust stability can be achieved without this constraint. It is also shown that the plant output and control input will converge asymptotically within a bound proportional to max {cepsilon, epsilonBAR} := epsilon(m), where c is a finite positive constant. Moreover, in the ideal case (i.e., epsilon = 0), the plant output and control input will converge to zero under some condition.

关键词： Converge design parameter control input self excitation asymptotic Dead band unmodeled dynamics Adaptive systems computer algorithms Robustness Self tuning

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THE EFFECT OF EXTENDED PAYMENT TERMS ON PURCHASING DECISIONS

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computerS IN INDUSTRY 1993年第3期22卷 311-318页

作者： BREGMAN, RL TEXAS A&M UNIV SYST COLL BUSINESS ADMDEPT BUSINESS ANAL & RESCOLL STNTX 77843 GRAD SCH BUSINESS COLL STNTX 77843

In this paper, computer algorithms are developed for determining optimal purchasing strategies for firms that receive extended payment terms from vendors. The resultant models are particularly attractive in high-volume environments with extended payment terms, a high opportunity cost of capital, and relatively large inventory-related costs. It is shown that purchases of quantities smaller than the traditional Economic Order Quantity may be appropriate in these environments and other situations where vendors offer either all-units or incremental purchase price discounts. The resultant algorithms are solved in this study using a spreadsheet-based search procedure implemented on a personal computer.

关键词： computer algorithms INVENTORY LOT SIZING PURCHASING

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