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Proceedings of the IEEE

Issue 6 • Date June 1988

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Displaying Results 1 - 10 of 10
  • Gyrotron oscillators

    Page(s): 644 - 656
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    The history of gyrotron development, the principles of gyrotron operation, and possible ways to enhance the power level to increase the operating frequency of gyrotrons are outlined. The state of the art of gyrotrons, their present and possible applications, and perspectives on gyrotrons are considered.<> View full abstract»

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  • Lightning and the heart: fractal behavior in cardiac function

    Page(s): 693 - 699
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    The basic concepts of fractals are briefly reviewed and are then shown to apply cardiac functions. It is demonstrated that some of the same principles govern both lightning discharge and cardiac flow; fractal expressions are provided for each. Fractal behavior in other biological phenomena, including transport (practical kinetics), population growth cycles, and turbulence, is touched on View full abstract»

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  • Cardiovascular responses to acceleration stress: a computer simulation

    Page(s): 700 - 707
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    Engineering methodology was used to develop a mathematical model of the cardiovascular system which is capable of predicting the effects of acceleration stress on peripheral and central vision. The basic model, previously reported, has been extended to include a simulation of the venous system and a number of additional refinements. It includes simulations of the heart, arterial, and venous system, physiologic compensatory mechanisms, and the effects of protective devices and maneuvers. Information derived from the model is important to understanding of cardiovascular responses to acceleration stress, mechanisms which determine tolerance, and factors which limit a pilot's performance. The model has been used to study the relative effectiveness of several acceleration protection methods and devices, including an anti-G suit design. Results from simulations using the model correlate well with reports in the literature View full abstract»

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  • Three-dimensional computer model of electric fields in internal defibrillation

    Page(s): 720 - 730
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    The automatic internal defibrillator delivers a low-energy shock directly to the heart. Optimal strategies for these shock deliveries are determined by studying a three-dimensional computer model of the electric fields produced by initial defibillation electrodes. A finite-element analysis technique is used to calculate energy and current density distributions in three commonly used electrode configurations: (1) patch-patch (PP), (2) catheter-patch (CP), and (3) catheter-catheter (CC). analysis of these simulations indicates that : (1) the PP and CP configurations are more effective at channeling energy to the myocardium than the CC configuration; (2) small electrodes and the edges of the electrodes give rise to high local current densities which might cause damage to the myocardium: (3) energy delivered to the myocardium is not significantly altered for different electrode placements tested; (4) electrode size influences current density distribution, especially near the electrodes; and (5) energy distribution is sensitive to the relative conductances of the myocardial tissue and blood View full abstract»

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  • Performance of the `smaller of' and `greater of' detectors integrating M pulses

    Page(s): 731 - 733
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    In previous studies by V.G. Hansen (1973) and by Hansen and J.H. Sawyers (1980), performance models were developed for the smaller of (SO) and greater of (GO) constant false alarm rate (CFAR) detectors processing a single sweep (or single pulse). Here, performances of the SO and GO detectors are derived when M pulses are incoherently integrated in a homogeneous environment. This situation is fitted to the case of a radar system processing M sweeps per range bin View full abstract»

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  • Interference rejection techniques in spread spectrum communications

    Page(s): 657 - 671
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    It is argued that the ability of a spread-spectrum system to withstand interference, both intentional and unintentional, is probably its greatest asset. Any spread spectrum receiver can only suppress a given amount of interference; if the level of interference becomes too great, the system will not function properly. Even under these latter circumstances, however, other techniques, which enhance the performance of the system over and above the performance improvement that comes automatically to systems from using spread spectrum, are available for use. These techniques typically involve some type of additional signal processing and are examined here. Two general types of narrowband interference suppression schemes are discussed and an overview is presented for several other techniques. The two classes of rejection schemes emphasized are (1) those based on least-mean-square estimation techniques, and (2) those based on transform-domain processing structures View full abstract»

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  • Three-dimensional computer simulation of the cardiac system

    Page(s): 708 - 719
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    An integrated approach to modeling the cardiac system is described and related to physiological measurements and other model approaches. The model is composed of a number of parts that will ultimately be used as a tool to study the various functions of the cardiac system. The 3-D geometry of the LV is reconstructed by using a helical coordinate system which provides a quantitative tool for shape description and analysis. Analysis of the regular geometry may be achieved using either the analytical helical system or a finite element technique. A simplified geometry is used to study the physiological interrelationship between the global ventricular function and the transmural temporal distribution of parameters which relate to mechanics, perfusion, energetics, and temperature in the myocardium. Transmural electrical activation maps are calculated based on analytical as well as a finite-element approach, eventually to be used in combination with the mechanical model to study LV contraction View full abstract»

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  • Self-processing networks and their biomedical implications

    Page(s): 680 - 692
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    Self-processing networks (connectionist models, neural networks, marker-passing systems, etc.) represent information as a network of interconnected nodes and process that information through the controlled spread of activation throughout the network. Properties characterized as manifestations of intelligence, such as associative recall of stored memories, pattern classification, and learning, are emergent properties; they are global system properties that arise from the concurrent local interactions between the numerous network components. The authors characterize the nature of self-processing networks developed as models of intelligent systems in neuroscience, cognitive science, and artificial intelligence, and contrast them with more traditional information processing models View full abstract»

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  • Refinement and extension of Belevitch's criterion through perturbation techniques

    Page(s): 733 - 734
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    A nonredundant derivation of V. Belevitch's (1959) stability criterion for negative-conductance quasisinusoidal quasistatic oscillators is presented. The key stop step of the analysis is the definition of the asymptotic baseband impedance operator associated with the tank circuit of concern. An extension of the criterion to oscillators with both resistive and capacitive nonlinearity is provided View full abstract»

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  • The chronic disease data bank-the ARAMIS experience

    Page(s): 672 - 679
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    The authors provide an overview of the American Rheumatism Association Medical Information System (ARAMIS), a national database and database management system containing parallel longitudinal clinical data sets from 17 rheumatic disease centers. 22 000 patients and 183000 observation time points are represented. The database contains measures of five dimensions-death, disability, discomfort, iatrogenic, and economic-and subdivisions of each dimension that provide a measure of the impact of the disease. The database management system is the MEDLOG time oriented database statistical software system. It runs on MOS-DOS-compatible microcomputers MEDLOG's file limits and abilities are described, and future directions for ARAMIS and MEDLOG are briefly covered View full abstract»

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North Carolina State University