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Sándor J. Kovács - One of the best experts on this subject based on the ideXlab platform.

  • The E-Wave Delayed Relaxation Pattern to LV Pressure Contour Relation: Model-Based Prediction With in vivo Validation
    Ultrasound in medicine & biology, 2010
    Co-Authors: Wei Zhang, Leonid Shmuylovich, Sándor J. Kovács
    Abstract:

    The transmitral Doppler E-wave “delayed relaxation” (DR) pattern is an established sign of diastolic dysfunction (DD). Furthermore, chambers exhibiting a DR filling pattern are also expected to have a prolonged time-constant of isovolumic relaxation (τ). The simultaneous observation of a DR pattern and normal τ in the same heart is not uncommon, however. The simultaneous hemodynamic equivalent of the DR pattern has not been proposed. To determine the feature of the left ventricular (LV) Pressure Contour during the E-wave that is causally related to its DR pattern we applied kinematic and fluid mechanics based arguments to derive the Pressure recovery ratio (PRR). The PRR is dimensionless and is defined by the left ventricular Pressure difference between diastasis and minimum Pressure, normalized to the Pressure difference between a fiducial diastolic filling Pressure and minimum Pressure [PRR=(PDiastasis-PMin)/(PFiducial-PMin)]. We analyzed 354 cardiac cycles from 40 normal sinus rhythm (NSR) subjects and 113 beats from nine atrial fibrillation (AF) subjects from our database of simultaneous transmitral flow-micromanometric LV Pressure recordings. The fiducial Pressure is defined by the end diastolic Pressure in NSR and by the Pressure at dP/dtMIN in the setting of AF. Consistent with derivation, PRR was linearly related to a DR pattern related, model-based relaxation parameter (R2 = 0.77, 0.83 in NSR and AF, respectively). Furthermore, the PRR successfully differentiated subjects with a DR pattern from subjects with partial DR or normal E-wave pattern (p < 0.05). We conclude that the PRR may differentiate between subjects having a DR pattern and subjects with normal E-waves, even when τ cannot. (E-mail: sjk@wuphys.wustl.edu)

  • Automated method for calculation of a load-independent index of isovolumic Pressure decay from left ventricular Pressure data
    Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Inte, 2009
    Co-Authors: Leonid Shmuylovich, Sándor J. Kovács
    Abstract:

    Diastolic heart failure (DHF) is present in over 50% of hospitalized heart failure patients, and diastolic dysfunction is known to play a critical pathophysiologic role. Measurement of left-ventricular Pressure (LVP) via catheterization is the gold standard for diastolic function (DF) evaluation, but current methods fail to fully capitalize on the complete information content of the Pressure Contour. We have previously demonstrated that a kinematic model of isovolumic Pressure decay (IVPD), which accounts for restoring force (stiffness) and resistance (viscoelasticity/relaxation), provides mechanistic insight into IVPD physiology and provides an accurate fit to the recorded Contour. Recently we derived a novel load-independent index of isovolumic Pressure decay (LIIIVPD) involving IVPD kinematic model stiffness and resistance parameters. In this work we detail methods and provide guidelines by which LIIIVPD computation may be achieved in real-time from the Pressure Contour recorded during cardiac catheterization.

  • Phase plane analysis of left ventricular hemodynamics.
    Journal of applied physiology (Bethesda Md. : 1985), 2001
    Co-Authors: Stephanie A. Eucker, Jennifer B. Lisauskas, Jasvindar Singh, Sándor J. Kovács
    Abstract:

    We sought to extract additional physiological information from the time-dependent left ventricular (LV) Pressure Contour and thereby gain new insights into ventricular function. We used phase plane analysis to characterize high-fidelity Pressure data in selected subjects undergoing elective cardiac catheterization. The standard hemodynamic indexes of LV systolic and diastolic function derived from the time-dependent LV Pressure Contour could be easily obtained using the phase plane method. Additional novel attributes of the phase plane Pressure loop, such as phase plane Pressure loop area, graphical representation of the isovolumic relaxation time constant, and quantitative measures of beat-to-beat systolic-diastolic coupling were characterized. The asymmetry between the Pressures at which maximum isovolumic Pressure rise and Pressure fall occur, as well as their load dependence, were also easily quantitated. These results indicate that the phase plane method provides a novel window for physiological discovery and has theoretical and applied advantages in quantitative ventricular function characterization.

Zack Kertzman - One of the best experts on this subject based on the ideXlab platform.

  • Sound Pressure mapping with a hand held sound level meter/real time analyzer
    Journal of the Acoustical Society of America, 2005
    Co-Authors: Roger J. Anderson, Zack Kertzman
    Abstract:

    For the past twenty years or so we have been using acoustic intensity to map out the surface of an object in order to have a visual representation of that noise source. More recently the trend has been to use large microphone arrays and acoustic holography. Acoustic intensity is reasonably easy to do but requires an intensity probe, a two channel analyzer some training and special software. In total the system cost can easily exceed $20,000. Acoustic holography systems provide more information but are much more expensive and need trained personnel. However, a low cost single channel SLM/RTA can be used to generate very good sound Pressure Contour maps that help noise control engineers understand noise sources. The other advantage is that it is simple to use requiring only an hour or less of training. Several example Pressure maps will be presented and compared to acoustic intensity maps.

  • sound Pressure mapping with a hand held sound level meter real time analyzer
    Journal of the Acoustical Society of America, 2005
    Co-Authors: Roger J. Anderson, Zack Kertzman
    Abstract:

    For the past twenty years or so we have been using acoustic intensity to map out the surface of an object in order to have a visual representation of that noise source. More recently the trend has been to use large microphone arrays and acoustic holography. Acoustic intensity is reasonably easy to do but requires an intensity probe, a two channel analyzer some training and special software. In total the system cost can easily exceed $20,000. Acoustic holography systems provide more information but are much more expensive and need trained personnel. However, a low cost single channel SLM/RTA can be used to generate very good sound Pressure Contour maps that help noise control engineers understand noise sources. The other advantage is that it is simple to use requiring only an hour or less of training. Several example Pressure maps will be presented and compared to acoustic intensity maps.

R. Balendra - One of the best experts on this subject based on the ideXlab platform.

  • Pressure Contours on forming dies
    Journal of Materials Processing Technology, 2001
    Co-Authors: R. Balendra
    Abstract:

    Abstract The assessment of the Pressure Contour on the die-cavity was conducted using physical modelling techniques; regardless, FE simulation was performed with a view to compare the two approaches. Two particular Pressure Contours were of interest in the programme of research; the first was that which prevailed at the end of the forming operation and the second was that which present when the punch Pressure had been removed. These Pressures were evaluated for a number of industrial components which had been provided to validate the proposed technique. The simulation required development of software which enabled the extraction of relevant data from the FE databases created during the simulation for comparison with the results from physical modelling experiments. The comparison indicated that the Pressure Contours were of sufficient accuracy for use in the analysis of die-elasticity: further refinements would be necessary to match the Contours which were derived using physical modelling.

  • Evaluation of FE models for the calculation of die-cavity compensation
    Journal of Materials Processing Technology, 1996
    Co-Authors: R. Balendra
    Abstract:

    Abstract Engineering components which are defined by complex surfaces and those which are manufactured in high-strength materials are often forged to net-form to eliminate the need for subsequent machining. The design of the dies for such forgings has to take into account the elastic behaviour of the die and the work material during the forging cycle. Several numerical approaches for the definition of compensation requirements are possible. The most comprehensive approach available is based on an interactive, elastic—plastic, FE model which regards the die and the workpiece as elastic and elastic/plastic bodies, respectively. An alternative is to regard the die as perfectly rigid whilst the workpiece is subjected to an elastic-plastic analysis over the forging cycle. A further approach is to create linear elastic models of both the die and the workpiece and to subject these to the derived contact Pressures. These three approaches are compared in this paper by analysing a forging example. A simplified linear elastic model which uses an experimentally-defined Pressure Contour is able to predict the compensation requirements with sufficient accuracy to discount the need for more complex considerations. An alternative to using experimentally-defined Pressure Contours is to derive these using the 'rigid die, elastic/plastic workpiece' and the 'elastic die, elastic workpiece' analyses.

Dong-hoon Choi - One of the best experts on this subject based on the ideXlab platform.

  • An Optimum Design of the Transverse Pressure Contour Slider for Enhanced Flying Characteristics
    Journal of Tribology, 1997
    Co-Authors: Sang-joon Yoon, Dong-hoon Choi
    Abstract:

    This paper proposes a design method for determining the configuration of a TPC slider by using an optimization technique in order to meet the desired flying characteristics over the entire recording band. The desired flying characteristics considered in this study are to minimize the variation in flying height from a target value, to maintain the pitch angle as large as possible, to keep the roll angle as small as possible. and to keep the outside rail to fly, lower than the inside rail. The design variables selected are left-side step width, pad width, right-side step width, side step depth, front taper height, and pivot offset in the transverse direction of the slider. The sequential quadratic programming (SQP) method in Automated Design Synthesis (ADS) is used to efficiently find the optimum design variables which simultaneously meet all the desired flying characteristics. To validate the suggested design method, a computer program is developed and applied to the configuration design of two TPC slider models positioned by a rotary actuator. The optimum configurations of each slider model are automatically obtained for three different target flying heights with the same predefined skew angle range without any difficulty. This shows the effectiveness of the proposed design method in comparison with the conventional one based on the parametric study.

Shahram Attarian - One of the best experts on this subject based on the ideXlab platform.

  • Surface Pressure Contour Prediction Using a GRNN Algorithm
    International Journal of Engineering, 2014
    Co-Authors: Ali R. Davari, Mohammad Reza Soltani, Shahram Attarian
    Abstract:

    A new approach based on a Generalized Regression Neural Network (GRNN) has been proposed to predict the planform surface Pressure field on a wing-tail combination in low subsonic flow. Extensive wind tunnel results were used for training the network and verification of the values predicted by this approach. GRNN has been trained by the aforementioned experimental data and subsequently was used as a prediction tool to determine the surface Pressure. Most of the previous applications of the GRNN in prediction problems were restricted to single or limited outputs, while in the present method the entire planform surface Pressure was predicted at once. This highly decreases the calculation time while preserving a remarkable degree of accuracy. The wind tunnel results verify the accuracy of the data offered by the GRNN, which indicates that the present prediction and optimization tool provides sufficient accuracy with modest amount of experimental data.