The Experts below are selected from a list of 114 Experts worldwide ranked by ideXlab platform

Pei Fu-jun - One of the best experts on this subject based on the ideXlab platform.

  • A New Method for Modeling the Hydraulic Servo System
    Computer Simulation, 2002
    Co-Authors: Pei Fu-jun
    Abstract:

    It is difficult to measure the flow of the Valve of the hydraulic servo system, and so we are difficult to model the non-Linear Valve by measuring. we design an identifier with an artificial neural network, in this identifier we use the priori knowledge of this hydraulic system and use a RBF neural network to instead the model of the non-Linear dead zone. A standard recursive least-squares algorithm is used to estimate the parameters of the identifier. The identifier is fulfilled by programming S_Function module in the Matlab/simulink at last. The simulation shows that the identifier can overcome the problem of modeling the hydraulic system.

Charles S. White - One of the best experts on this subject based on the ideXlab platform.

  • high prevalence of a Linear Valve like structure on ct at the pulmonary artery terminus of patent ductus arteriosus in adult patients mimicking endarteritis
    Surgical and Radiologic Anatomy, 2021
    Co-Authors: Min Ji Son, Eun Ju Chun, Seung Min Yoo, Hwa Yeon Lee, In Sup Song, Charles S. White
    Abstract:

    A Linear Valve-like structure at the pulmonary artery terminus is identified on CT in some patients with patent ductus arteriosus (PDA) and can potentially be mistaken for endarteritis. The purpose of this study was to evaluate the differences in CT features between adult patients with PDA and a Linear structure and those without. We retrospectively evaluated ECG-gated cardiac CT of 38 patients with PDA dividing them into two groups [patients with Linear symmetrical Valve-like structure (group1, n = 16), and those without (group 2, n = 22)]. We analyzed CT findings of the PDA including length, minimal and maximal diameter, presence of calcification, and PDA type, comparing the two subgroups. The authors also investigated the prevalence of endarteritis. There was no difference in CT findings between the two groups in the prevalence of calcification and length, and minimal and maximal diameter of PDA. Notably the Linear Valve-like structure was only identified in type 1 PDA (cone-shaped PDA) (p = 0.04), while there were variable types of PDA in group 2. There was only one case of endarteritis as a complication of PDA in group 1. In contrast to a Linear Valve-like structure, asymmetrical nodular thickening was noted in the patient with endarteritis on CT overlying the pre-existing Linear Valve-like structure at the pulmonary end of PDA. A Linear Valve-like structure is frequently identified at the pulmonary end in type 1 PDA. This CT finding should not be mistaken for endarteritis in the absence of other clinical evidence.

  • High prevalence of a Linear Valve-like structure on CT at the pulmonary artery terminus of patent ductus arteriosus in adult patients, mimicking endarteritis
    Surgical and Radiologic Anatomy, 2020
    Co-Authors: Min Ji Son, Eun Ju Chun, Seung Min Yoo, Hwa Yeon Lee, In Sup Song, Charles S. White
    Abstract:

    Purpose A Linear Valve-like structure at the pulmonary artery terminus is identified on CT in some patients with patent ductus arteriosus (PDA) and can potentially be mistaken for endarteritis. The purpose of this study was to evaluate the differences in CT features between adult patients with PDA and a Linear structure and those without. Materials and methods We retrospectively evaluated ECG-gated cardiac CT of 38 patients with PDA dividing them into two groups [patients with Linear symmetrical Valve-like structure (group1, n  = 16), and those without (group 2, n  = 22)]. We analyzed CT findings of the PDA including length, minimal and maximal diameter, presence of calcification, and PDA type, comparing the two subgroups. The authors also investigated the prevalence of endarteritis. Results There was no difference in CT findings between the two groups in the prevalence of calcification and length, and minimal and maximal diameter of PDA. Notably the Linear Valve-like structure was only identified in type 1 PDA (cone-shaped PDA) ( p  = 0.04), while there were variable types of PDA in group 2. There was only one case of endarteritis as a complication of PDA in group 1. In contrast to a Linear Valve-like structure, asymmetrical nodular thickening was noted in the patient with endarteritis on CT overlying the pre-existing Linear Valve-like structure at the pulmonary end of PDA. Conclusion A Linear Valve-like structure is frequently identified at the pulmonary end in type 1 PDA. This CT finding should not be mistaken for endarteritis in the absence of other clinical evidence.

Geoffrey M. Shaw - One of the best experts on this subject based on the ideXlab platform.

  • Unique parameter identification of a cardiovascular system model using feedback control
    2009 IEEE International Conference on Control and Automation, 2009
    Co-Authors: Christopher E. Hann, J. Geoffrey Chase, Thomas Desaive, C. Froissart, James A. Revie, D Stevenson, Geoffrey M. Shaw
    Abstract:

    Lumped parameter differential equation models are a common approach to modeling the cardiovascular system. However, there are highly non-Linear Valve dynamics inherent in these models which makes parameter identification difficult. Standard methods for parameter identification rely on gradient descent, which can often converge to wrong solutions, particularly as the number of parameters increases. This paper presents a new concept of parameter identification, applied to a 2 chamber model of the left ventricle systemic system. The changes in the parameters are treated as an actuation force into a feed back control system, where the reference output is taken to be steady state values of measured volume and pressure. The major advantage of the method is that when it converges, it must be at the global minimum, so that the correct solution is always found. The method is validated in both simulation and on a porcine model of pulmonary embolism. Very accurate matches to clinically measured left ventricle volume/pressure and aortic pressure waveforms are achieved, and the method gives considerable flexibility in capturing any required geometrical feature in the waveforms.

  • Efficient implementation of non-Linear Valve law and ventricular interaction dynamics in the minimal cardiac model
    Computer methods and programs in biomedicine, 2005
    Co-Authors: Christopher E. Hann, James Geoffrey Chase, Geoffrey M. Shaw
    Abstract:

    A minimal model of the cardio-vascular system (CVS) with ventricular interaction and inertial effects that accurately captures the physiological trends of a variety of disease states has been developed. However, the physiologically accurate open on pressure, close on flow Valve law is computationally heavy to implement, reducing the model's potential clinical benefit. A significantly simpler representation of the Valve law using Heaviside functions is derived and the ventricular interaction equations are reformulated to obtain a unique closed form analytical solution. The new formulation is tested and compared with the previous formulation for a healthy human and four clinically significant disease states: mitral and aortic stenosis, pulmonary embolism and septic shock. The new model formulation matches the previous model definition, differing by a mean model response error of no more than 0.2%. Computationally, it is 24x faster than the previous method. More specifically, a short 20-beat simulation that took [email protected]?s now requires [email protected]?s, significantly improving the model's potential for practical use in a diagnostic and/or decision support role in the intensive care unit.

Panagiotis D. Christofides - One of the best experts on this subject based on the ideXlab platform.

  • Elucidating and handling effects of Valve-induced nonLinearities in industrial feedback control loops
    Computers & Chemical Engineering, 2018
    Co-Authors: Helen Durand, Robert L. Parker, Anas Alanqar, Panagiotis D. Christofides
    Abstract:

    Abstract In this work, we investigate the effects of various types of Valve behavior (e.g., Linear Valve dynamics and stiction) on the effectiveness of process control in a unified framework based on systems of nonLinear ordinary differential equations that characterize the dynamics of closed-loop systems including the process, Valve, and controller dynamics. By analyzing the resulting dynamic models, we demonstrate that the responses of the Valve output and process states when Valve behavior cannot be neglected (e.g., stiction-induced oscillations in measured process outputs) are closed-loop effects that can be difficult to predict a priori due to the coupled and typically nonLinear dynamics of the process-Valve model. Subsequently, we discuss the implications of this closed-loop perspective on the effects of Valve dynamics in closed-loop systems for understanding Valve behavior compensation techniques and developing new ones. We conclude that model-based feedback control designs that can account for process and Valve constraints and dynamics provide a systematic method for handling the multivariable interactions in a process-Valve system, where the models in such control designs can come either from first-principles or empirical modeling techniques. The analysis also demonstrates the necessity of accounting for Valve behavior when designing a control system due to the potentially different consequences under various control methodologies of having different types of Valve behavior in the loop. Throughout the work, a level control example and a continuous stirred tank reactor example are used to illustrate the developments.

Min Ji Son - One of the best experts on this subject based on the ideXlab platform.

  • high prevalence of a Linear Valve like structure on ct at the pulmonary artery terminus of patent ductus arteriosus in adult patients mimicking endarteritis
    Surgical and Radiologic Anatomy, 2021
    Co-Authors: Min Ji Son, Eun Ju Chun, Seung Min Yoo, Hwa Yeon Lee, In Sup Song, Charles S. White
    Abstract:

    A Linear Valve-like structure at the pulmonary artery terminus is identified on CT in some patients with patent ductus arteriosus (PDA) and can potentially be mistaken for endarteritis. The purpose of this study was to evaluate the differences in CT features between adult patients with PDA and a Linear structure and those without. We retrospectively evaluated ECG-gated cardiac CT of 38 patients with PDA dividing them into two groups [patients with Linear symmetrical Valve-like structure (group1, n = 16), and those without (group 2, n = 22)]. We analyzed CT findings of the PDA including length, minimal and maximal diameter, presence of calcification, and PDA type, comparing the two subgroups. The authors also investigated the prevalence of endarteritis. There was no difference in CT findings between the two groups in the prevalence of calcification and length, and minimal and maximal diameter of PDA. Notably the Linear Valve-like structure was only identified in type 1 PDA (cone-shaped PDA) (p = 0.04), while there were variable types of PDA in group 2. There was only one case of endarteritis as a complication of PDA in group 1. In contrast to a Linear Valve-like structure, asymmetrical nodular thickening was noted in the patient with endarteritis on CT overlying the pre-existing Linear Valve-like structure at the pulmonary end of PDA. A Linear Valve-like structure is frequently identified at the pulmonary end in type 1 PDA. This CT finding should not be mistaken for endarteritis in the absence of other clinical evidence.

  • High prevalence of a Linear Valve-like structure on CT at the pulmonary artery terminus of patent ductus arteriosus in adult patients, mimicking endarteritis
    Surgical and Radiologic Anatomy, 2020
    Co-Authors: Min Ji Son, Eun Ju Chun, Seung Min Yoo, Hwa Yeon Lee, In Sup Song, Charles S. White
    Abstract:

    Purpose A Linear Valve-like structure at the pulmonary artery terminus is identified on CT in some patients with patent ductus arteriosus (PDA) and can potentially be mistaken for endarteritis. The purpose of this study was to evaluate the differences in CT features between adult patients with PDA and a Linear structure and those without. Materials and methods We retrospectively evaluated ECG-gated cardiac CT of 38 patients with PDA dividing them into two groups [patients with Linear symmetrical Valve-like structure (group1, n  = 16), and those without (group 2, n  = 22)]. We analyzed CT findings of the PDA including length, minimal and maximal diameter, presence of calcification, and PDA type, comparing the two subgroups. The authors also investigated the prevalence of endarteritis. Results There was no difference in CT findings between the two groups in the prevalence of calcification and length, and minimal and maximal diameter of PDA. Notably the Linear Valve-like structure was only identified in type 1 PDA (cone-shaped PDA) ( p  = 0.04), while there were variable types of PDA in group 2. There was only one case of endarteritis as a complication of PDA in group 1. In contrast to a Linear Valve-like structure, asymmetrical nodular thickening was noted in the patient with endarteritis on CT overlying the pre-existing Linear Valve-like structure at the pulmonary end of PDA. Conclusion A Linear Valve-like structure is frequently identified at the pulmonary end in type 1 PDA. This CT finding should not be mistaken for endarteritis in the absence of other clinical evidence.