The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform
Wassim M. Haddad - One of the best experts on this subject based on the ideXlab platform.
-
Robust stabilization of axial Flow compressors with uncertain Pressure-Flow maps
IEEE Transactions on Control Systems Technology, 2000Co-Authors: Alexander Leonessa, Vijaysekhar Chellaboina, Wassim M. HaddadAbstract:We develop globally robustly stabilizing controllers for rotating stall and surge in multimode axial Flow compressor models with uncertain Pressure-Flow compressor performance characteristic maps. Specifically, using Lyapunov stability theory, a switching nonlinear globally robustly stabilizing control law based on equilibria-dependent Lyapunov functions with converging domains of attraction is developed. The locus of the equilibrium points on which the equilibria-dependent Lyapunov functions are predicated is characterized by the axisymmetric stable Pressure-Flow equilibrium branch of the nominal compression system. The proposed robust nonlinear control framework is directly applicable to uncertain compression systems with actuator amplitude and rate saturation constraints while providing a guaranteed domain of attraction. An application to a two-mode axial Flow compressor with an uncertain Pressure-Flow map and rate saturation control constraints is presented.
-
Robust stabilization of axial Flow compressors with uncertain Pressure-Flow maps
Proceedings of the 1997 IEEE International Conference on Control Applications, 1Co-Authors: Alexander Leonessa, Vijaysekhar Chellaboina, Wassim M. HaddadAbstract:We develop globally robustly stabilizing controllers for rotating stall and surge in multi-mode axial Flow compressor models with uncertain Pressure-Flow compressor performance characteristic maps. Specifically using Lyapunov stability theory, a novel nonlinear globally robustly stabilizing control law based on equilibria-dependent Lyapunov functions with converging domains of attraction is developed. The locus of the equilibrium points on which equilibria-dependent Lyapunov functions are predicted is characterized by the axisymmetric stable Pressure-Flow equilibrium branch of the nominal compression system. The proposed robust nonlinear control framework is applied to a two-mode axial Flow compressor with an uncertain Pressure-Flow map.
Anders Spangberg - One of the best experts on this subject based on the ideXlab platform.
-
standardization of terminology of lower urinary tract function Pressure Flow studies of voiding urethral resistance and urethral obstruction
Neurourology and Urodynamics, 1997Co-Authors: Derek Griffiths, Kai Hofner, Ron Van Mastrigt, Harm J Rollema, Anders Spangberg, Donald M GleasonAbstract:textabstractThe 1988 version of the collated reports on standardisation of terminology, which appeared in Neurourology and Urodynamics, vol. 7, pp. 403–427, contains material relevant to Pressure Flow studies in many different sections. This report is a revision and expansion of Sections 4.2 and 4.3 and parts of Sections 6.2 and 7 of the 1988 report. It contains a recommendation for a provisional standard method for defining obstruction on the basis of Pressure-Flow data. 2. Evaluation of Micturition 2.1. Pressure-Flow Studies At present, the best method of analysing voiding function quantitatively is the Pressure-Flow study of micturition, with simultaneous recording of abdominal, intravesical and detrusor Pressures and Flow rate (Fig. A.1.6.1). Direct inspection of the raw Pressure and Flow data before, during and at the end of micturition is essential, because it allows artefacts and untrustworthy data to be recognised and eliminated. More detailed analyses of Pressure-Flow relationships, described below, are advisable to aid diagnosis and to quantify data for research studies. The Flow pattern in a Pressure-Flow study should be representative of free Flow studies in the same patient. It is important to eliminate artefacts and unrepresentative studies before applying more detailed analyses. Pressure-Flow studies contain information about the behaviour of the urethra and the behaviour of the detrusor.
-
Pressure/Flow studies preoperatively and postoperatively in patients with benign prostatic hypertrophy: Estimation of the urethral Pressure/Flow relation and urethral elasticity
Neurourology and Urodynamics, 1991Co-Authors: Anders Spangberg, Heikki Teriö, Per Ask, Anders Engberg, D. J. GriffithsAbstract:Pressure/Flow studies were performed in 28 men with benign prostatic hypertrophy. Twenty-three of the men were also studied postoperatively. Urethral function during micturition was quantified by the urethral Pressure/Flow relation, P(det) = P(mo) + L(m) Q(m), where P(det) is detrusor Pressure, P(mo) is minimal opening Pressure, Q is Flow rate, and m and L(m) are parameters. Using this method to quantify urethral function, three urodynamically different types of obstruction can be defined. In the first of these, P(mo) is elevated corresponding to Schafer’s compressive obstruction. The second is a constrictive type of obstruction in which m greater-than-or-equal-to 4/3 and L(m) is elevated and the third is a low-compliant type of obstruction in which m less-than-or-equal-to 1 and L(m) is elevated. The two latter types of obstruction may be combined with a compressive obstruction. The preoperative Pressure/Flow relations were mostly characterized by a very high P(mo), a moderately elevated L(m), and a low m. Thus the majority of patients had a combination of compressive and low-compliant obstruction. Postoperatively, micturitions were much improved and the Pressure/Flow relations often had an even lower P(mo) than normal, a normal L(m), and a high m. From the Pressure/Flow relations, the elasticity of the Flow-controlling zone can be estimated and described by the urethral Pressure/area relation, p(A) = P(mo) + K(n) A(n), where p(A) is the intrinsic urethral Pressure, A is the cross-sectional area of the Flow-controlling zone and K(n) and n are parameters describing the distensibility of the Flow-controlling zone. Preoperatively, the Flow-controlling zone had a low distensibility. The shape of the curve suggested that the urethra could have been distended further by higher Pressure. Postoperatively, the urethra was distended to larger cross-sectional areas, but in many cases the shape of the curve suggested that distension was restricted by fibrosis. Median and range values for the model parameters as well as discriminating limits between the preoperative micturitions and micturitions in elderly men without voiding problems are presented. The exponent m is not perfectly reproducible but tends to be the same if a person performs several micturitions. The residual sum of squares is often increased more than 100% if an exponent m value other than the optimal one is used for curve fitting. Results when the micturitions were analysed with Schafer’s model and classified using the maximum Flow/Pressure at maximum Flow diagram recommended by the International Continence Society are also shown.
Donald M Gleason - One of the best experts on this subject based on the ideXlab platform.
-
standardization of terminology of lower urinary tract function Pressure Flow studies of voiding urethral resistance and urethral obstruction
Neurourology and Urodynamics, 1997Co-Authors: Derek Griffiths, Kai Hofner, Ron Van Mastrigt, Harm J Rollema, Anders Spangberg, Donald M GleasonAbstract:textabstractThe 1988 version of the collated reports on standardisation of terminology, which appeared in Neurourology and Urodynamics, vol. 7, pp. 403–427, contains material relevant to Pressure Flow studies in many different sections. This report is a revision and expansion of Sections 4.2 and 4.3 and parts of Sections 6.2 and 7 of the 1988 report. It contains a recommendation for a provisional standard method for defining obstruction on the basis of Pressure-Flow data. 2. Evaluation of Micturition 2.1. Pressure-Flow Studies At present, the best method of analysing voiding function quantitatively is the Pressure-Flow study of micturition, with simultaneous recording of abdominal, intravesical and detrusor Pressures and Flow rate (Fig. A.1.6.1). Direct inspection of the raw Pressure and Flow data before, during and at the end of micturition is essential, because it allows artefacts and untrustworthy data to be recognised and eliminated. More detailed analyses of Pressure-Flow relationships, described below, are advisable to aid diagnosis and to quantify data for research studies. The Flow pattern in a Pressure-Flow study should be representative of free Flow studies in the same patient. It is important to eliminate artefacts and unrepresentative studies before applying more detailed analyses. Pressure-Flow studies contain information about the behaviour of the urethra and the behaviour of the detrusor.
Alexander Leonessa - One of the best experts on this subject based on the ideXlab platform.
-
Robust stabilization of axial Flow compressors with uncertain Pressure-Flow maps
IEEE Transactions on Control Systems Technology, 2000Co-Authors: Alexander Leonessa, Vijaysekhar Chellaboina, Wassim M. HaddadAbstract:We develop globally robustly stabilizing controllers for rotating stall and surge in multimode axial Flow compressor models with uncertain Pressure-Flow compressor performance characteristic maps. Specifically, using Lyapunov stability theory, a switching nonlinear globally robustly stabilizing control law based on equilibria-dependent Lyapunov functions with converging domains of attraction is developed. The locus of the equilibrium points on which the equilibria-dependent Lyapunov functions are predicated is characterized by the axisymmetric stable Pressure-Flow equilibrium branch of the nominal compression system. The proposed robust nonlinear control framework is directly applicable to uncertain compression systems with actuator amplitude and rate saturation constraints while providing a guaranteed domain of attraction. An application to a two-mode axial Flow compressor with an uncertain Pressure-Flow map and rate saturation control constraints is presented.
-
Robust stabilization of axial Flow compressors with uncertain Pressure-Flow maps
Proceedings of the 1997 IEEE International Conference on Control Applications, 1Co-Authors: Alexander Leonessa, Vijaysekhar Chellaboina, Wassim M. HaddadAbstract:We develop globally robustly stabilizing controllers for rotating stall and surge in multi-mode axial Flow compressor models with uncertain Pressure-Flow compressor performance characteristic maps. Specifically using Lyapunov stability theory, a novel nonlinear globally robustly stabilizing control law based on equilibria-dependent Lyapunov functions with converging domains of attraction is developed. The locus of the equilibrium points on which equilibria-dependent Lyapunov functions are predicted is characterized by the axisymmetric stable Pressure-Flow equilibrium branch of the nominal compression system. The proposed robust nonlinear control framework is applied to a two-mode axial Flow compressor with an uncertain Pressure-Flow map.
Jørgen Nordling - One of the best experts on this subject based on the ideXlab platform.
-
Pressure-Flow studies: short-time repeatability.
Neurourology and urodynamics, 1999Co-Authors: Frank Hansen, Lene Irene Olsen, Ali Atan, Jørgen NordlingAbstract:The within and between examination variation in selected test parameters and test results in repeated Pressure-Flow studies was determined in a prospective study of consecutive Pressure-Flow examinations in 22 patients. The patients were Pressure-Flow tested twice within a month. Furthermore, it was evaluated whether there was a systematic change in the measured parameters during retesting. By using the Abrams-Griffiths nomogram, patients were classified as obstructed, equivocal, or unobstructed. Within and between examination variations in classification were evaluated. We found a systematic variation in P(det.Qmax) during testing, which in the absence of statistically significant systematic variations in P(det.Close) and Qmax, indicates a physiological effect of repeated Pressure-Flow studies, resulting in a less-obstructed second voiding. Supporting this, we found that all patients who changed group of classification of bladder outlet obstruction in the first examination shifted to a group of less obstruction, as did 66% of the patients who changed group of classification of bladder outlet obstruction in the second examination. Still, 80, respectively 85%, of the patients remained in the same group of classification of bladder outlet obstruction during retesting in the first and second examinations, respectively. Classifying the degree of bladder outlet obstruction by Qmax, P(det.Qmax), and P(det.Close) 85% of the patients reproduced their test results accurately in both examinations and taking only the first voiding in both examinations into account 95% reproduced their test results.
-
A clinical view of Pressure-Flow studies
World journal of urology, 1995Co-Authors: Jørgen NordlingAbstract:Lower-urinary-tract symptoms might be due to bladder dysfunction, infravesical obstruction, or both, and these conditions give rise to the same type of symptoms. Classification of symptomatic benign prostatic hyperplasia (BPH) patients into obstructed or unobstructed cases can be done only by Pressure-Flow studies. This classification has been demonstrated to be of predictive value for the outcome of surgical treatment, both symptomatically and urodynamically. Pressure-Flow studies are therefore helpful in the pretreatment workup of patients in regard to both diagnosing the underlying pathophysiology and, consequently, stratifying patients for different treatments or watchful waiting. Different methods of interpreting Pressure-Flow investigations share the same theoretical foundation and therefore have only minor differences in classifying patients into obstructed or unobstructed cases. The more advanced methods make a more differentiated classification possible, but these are currently mostly of theoretical value in research.
