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SOLVING RECURRENCE RELATIONS INVOLVING FLOOR AND CEILING FUNCTIONS

ELECTRONICS LETTERS 1994年第17期30卷 1391-1393页

作者： THOMPSON, BC Dept. of Comput. Sci. Univ. Coll. of Swansea

A rounding lemma is presented which has applications in the field of discrete mathematics. The lemma can be used to simplify complex terms and analyse certain recurrence relations.

关键词： ALGORITHM THEORY computer algorithms

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ACCOMMODATION OF TIME-DELAY VARIATIONS IN AUTOMATIC INFUSION OF SODIUM-NITROPRUSSIDE

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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING 1994年第11期41卷 1083-1091页

作者： DELAPASSE, JS BEHBEHANI, K TSUI, KC KLEIN, KW UNIV TEXAS DEPT BIOMED ENGNARLINGTONTX 76019 LEE MED SYST INC KERMERSVILLENC 27284 UNIV TEXAS SW MED CTRDEPT ANESTHESIOLDALLASTX 75235

A new self-tuning regulator for control of mean arterial blood pressure using sodium nitroprusside is presented. In addition to adapting to various patient response gains and time constants, the controller can accommodate variations in pure time delays, a problem that has not been addressed fully in previously proposed controllers. The control algorithm derivation is based on incorporating a self-tuning controller with an adaptive discrete time delay compensator. The derivation, however, is general and can potentially be applied to other pharmacological agents in addition to sodium nitroprusside. The a priori information required for implementation of the controller is the estimate of the order of the patient response transfer function and the range of the pure time delay. An attractive feature of the controller is its capability to optimize the level of the infused drug during the transient phase of the control without creating an output offset. This feature tends to reduce the overall level of the infused drug. Hence, it may be useful when the cost of a drug or its long-term administration side effects is of concern, such as in the case of sodium nitroprusside.

关键词： biocontrol biomedical equipment controllers haemodynamics patient treatment pressure control a priori information automatic infusion blood pressure control control algorithm infused drug output offset patient response gains patient response transfer func Sodium Nitroprusside Medical device Controllers Nitroprusside patient treatment Pressure control computer algorithms Hemodynamics

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GRAPHICAL FISHEYE VIEWS

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COMMUNICATIONS OF THE ACM 1994年第12期37卷 73-84页

作者： SARKAR, M BROWN, MH DIGITAL EQUIPMENT CORP SYST RES CTRPALO ALTOCA 94301

This article explores a fisheye lens approach to viewing and browsing graphs. A fisheye view of a graph shows an area of interest quite large and with detail and shows other areas successively smaller and in less detail. A fisheye lens seems to have all advantages of the other approaches for viewing and browsing a graph without any of drawbacks. Graphs with hundreds of vertices and edges are common in many application areas of computer science, such as network topology, and graph theory. There are literally hundreds of algorithms for positioning nodes to produce an aesthetic and informative display. Displaying all the information associated with the vertices and edges shows the global structure of the graph but has the drawback that details are typically too small to be seen. Alternatively, zooming into a part of the graph and panning to other parts does show local details but loses the overall structure of the graph. Using two or more views, one of the entire graph and the other of a zoomed portion, gives one the advantage of seeing both local detail and overall structure but has drawbacks of requiring extra screen space and forcing the viewer to mentally integrate the views.

关键词： computer algorithms Graphic methods Charts, diagrams, etc. computer science computer networks computer graphics Topology

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CRYPTANALYSIS AND PROTOCOL FAILURES

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COMMUNICATIONS OF THE ACM 1994年第11期37卷 56-65页

作者： SIMMONS, GJ P.O. Box 365 Sandia Park NM

This article presents examples of protocol failures in cryptographic operations. In many protocols, the security of the cryptographic portion is progressively weakened as a result of the protocol being exercised, for example, by reducing the size of the key space that one would have to search to identify an active cryptographic key but these are not considered examples of true protocol failures, even though they are clearly examples of potential sources of failure in the intended security function of a protocol. Finding and fixing failures of the latter type is the function of conventional analysis of cryptoalgorithms. An algorithm or protocol can be unconditionally secure, computationally secure, provably secure, or, of course, insecure. A scheme is said to be unconditionally secure if the probability of breaking it is independent of the computing resources and time an opponent is able or willing to spend. A scheme is said to be computationally secure if breaking it requires an attacker to carry out some computation that is possible in principle but for which all known methods of execution require an infeasible amount of computation.

关键词： CRYPTOGRAPHY computer network protocols computer security computer algorithms CRYPTOGRAMS COMPUTATIONAL complexity computer science

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BOTTOM-UP DESIGN OF SOFTWARE AGENTS

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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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