1,720,967 research outputs found
Developing a reduced order model for pulsatile blood flow simulations using minimal three-dimensional simulation data
No full textBackground and Objective: Pulsatile blood flow simulations are essential for understanding cardiovascular physiology but are often constrained by the computational cost of full 3D modeling. While reduced-order models (ROMs) offer efficiency, many depend on empirical parameters, limiting their accuracy in complex subject-specific geometries. This study introduces a 1D ROM that minimizes empirical assumptions by deriving parameters directly from 3D simulation data. Methods: The proposed ROM estimates pressure-flow relationships by fitting parameters of a simplified 1D blood flow equation to results from three 3D simulations under distinct flow conditions. Validation was performed against full 3D Computational Fluid Dynamics (CFD) simulations for three cases: an idealized stenotic cylinder, a patient-specific coarcted aorta, and a coronary artery model with serial lesions. The model was also compared with a widely used empirical stenosis model. Results: The ROM achieved mean relative errors below 2.0 % in all cases and under 1.0 % in the coronary model with multiple lesions. It significantly outperformed the empirical model in complex geometries and delivered up to 3000 times faster computation on a desktop compared to 3D simulations performed on a 64-core high-performance computing system. Conclusions: By leveraging 3D simulation data, the proposed 1D ROM combines high accuracy with exceptional computational efficiency across various geometries. Its robustness and speed make it well suited for clinical applications, optimization tasks, and uncertainty quantification.
Sensitivity of Pulsatile Parameters of Computed Fractional Flow Reserve using a Reduced-order Model
No full textFractional flow reserve (FFR) is the clinical gold standard for diagnosing coronary artery disease, yet many computational methods rely on steady flow assumptions even though clinical FFR values are measured under pulsatile flow conditions. To address the computational cost and uncertainty associated with pulsatile blood flow simulations, we present a reduced-order model combined with a polynomial chaos expansion (PCE) method. The coronary geometry is represented by thin slabs defined by consecutive centerline points and radius, while a polynomial function approximates pressure differences as a function of flow and its time derivative based on minimal three-dimensional simulations. Diverse pulsatile flow conditions are modeled using lumped parameter models which approximate a wide range of pulsatile flow conditions. Uncertainties in pulsatile parameters, including cardiac output, heart rate, and pulse pressure, are modeled using a third-order Chebyshev PCE to maintain a mean relative error below 1.0%. Validation was conducted using a cylindrical model across stenosis severities from 40% to 90%, as well as a patient-specific model with diverse disease conditions. In both cases, the computed FFR distributions agreed with clinical observations. Sensitivity analysis showed that myocardial compression, distal aortic resistance, and contractility are the primary factors influencing FFR variability, with FFR variation exhibiting a linear correlation with its value. This reduced-order approach enables efficient pulsatile FFR simulations and provides valuable insights into key parameters affecting FFR
SENSITIVITY OF PULSATILE PARAMETERS OF COMPUTED FRACTIONAL FLOW RESERVE USING A REDUCED ORDER MODEL
No full textFractional flow reserve (FFR) has been recognized as a gold standard in diagnosing coronary artery disease and many endeavors have been conducted to compute FFR using computational methods. The majority of them, however, have utilized steady flow analysis but FFR in reality is measured by averaging pulsatile pressure quantities. Pulsatile blood flow simulations are often avoided due to the computational expense and the uncertainties in approximating pulsatile blood flow conditions.To address these two limitations, we develop a reduced-order model to efficiently approximate three-dimensional pulsatile blood flow simulations and integrate with a non-invasive polynomial chaos expansion (PCE) method for the uncertainty quantification of the pulsatile parameters, such as cardiac outputs and heart rates. A three-dimensional coronary geometry is approximated as a collection of thin slabs comprising two consecutive centerline points and the corresponding radius values. The relationship between the flow and pressure difference for each slab is approximated by conducting three-dimensional simulations at three different flow conditions and fitting to a polynomial function of flow and flow time derivative. A lumped parameter model is coupled to the boundaries of the geometry as a boundary condition and the parameter values are chosen to span a wide, physiologically realistic pressure and flow values. For the PCE method, the Chebyshev polynomial order of three is chosen to maintain the mean relative error of the PCE results within 1.0%.The methodology was validated using both a simple cylindrical geometry with degrees of stenosis ranging from 40% to 90% and a patient-specific coronary model with a randomly generated degree of stenosis between 40% and 90% and varying numbers of serial lesions between one and three. In both cases, the variations in the computed FFR values were comparable to those of the clinical data. The sensitivity analysis revealed that among the pulsatile parameters, myocardial pressure effect, aortic distal resistance, and heart contractility significantly influence the pulsatile FFR computation. Further, the variation in FFR was found to exhibit a linear correlation with its value. We show that the developed methodology can simulate FFR with uncertainties in pulsatile parameters at a reasonable computational expense, while also providing insights into the key factors affecting FFR
Tissue-growth-based synthetic tree generation and perfusion simulation
No full textBiological tissues receive oxygen and nutrients from blood vessels by developing an indispensable supply and demand relationship with the blood vessels. We implemented a synthetic tree generation algorithm by considering the interactions between the tissues and blood vessels. We first segment major arteries using medical image data and synthetic trees are generated originating from these segmented arteries. They grow into extensive networks of small vessels to fill the supplied tissues and satisfy the metabolic demand of them. Further, the algorithm is optimized to be executed in parallel without affecting the generated tree volumes. The generated vascular trees are used to simulate blood perfusion in the tissues by performing multiscale blood flow simulations. One-dimensional blood flow equations were used to solve for blood flow and pressure in the generated vascular trees and Darcy flow equations were solved for blood perfusion in the tissues using a porous model assumption. Both equations are coupled at terminal segments explicitly. The proposed methods were applied to idealized models with different tree resolutions and metabolic demands for validation. The methods demonstrated that realistic synthetic trees were generated with significantly less computational expense compared to that of a constrained constructive optimization method. The methods were then applied to cerebrovascular arteries supplying a human brain and coronary arteries supplying the left and right ventricles to demonstrate the capabilities of the proposed methods. The proposed methods can be utilized to quantify tissue perfusion and predict areas prone to ischemia in patient-specific geometries.
Multiscale Computational Methods for Heat Transfer Simulation between Body Tissue and Blood Flow
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
TRENDS TOWARD UNIVERSAL BANKING IN KOREA
No full text세계의 금융산업이 빠르게 변하고 있다. 정보산업의 발달과 인터넷의 확산, 그리고 세계화의 기운이 더해져 전세계의 금융 기관들이 서로 경쟁하게 되었다. 이와 같은 변화는 1990년대 들어 각 나라의 시장이 차츰 개방되기 시작하면서 가속도가 붙기 시작했으며, 각 나라 금융기관의 사업방식 자체를 바꾸게도 하였다.
기본적인 예금이나 투자 업무만을 다루던 은행들이 보험업에 까지 뛰어들게 되었고, 다국적 은행이나 투자회사와의 인수 · 합병을 통해 은행의 규모를 확장하게 되었다. 한국에서도 은행의 보험업무를 둘러싸고 다양한 의견이 있으나, 세계화의 흐름을 타고 점점 금융시장도 개방되고 있는 추세이며, 이에 따라 정부차원에서의 규범이나 원칙의 재정립이 요구되고 있다.
미국에서는, 은행업무를 증권, 보험업무와 구분하기 위하여 1933년에 제정한 글래스-스티걸 법과 상반되는 법안이 1999년에 통과됨으로써 금융기관의 겸업화가 더욱 활발히 진행돼가고 있으며, 한국도 1997년 IMF 외환위기를 시작으로 금융 제도를 전면적으로 정비하고, 세계 금융시장에서 살아 남기 위한 경쟁력 제고의 한 방안으로 금융기관의 겸업화가 시작되었다. 무조건적으로 은행, 증권회사, 보험회사의 업무를 한 곳에 모아 놓는 것이 아니라 상호 보완적인 측면에서 소비자에게 종합적인 맞춤 서비스를 제공하기 위한 노력의 결과인 것이다.
본 논문은 금융기관의 겸업화가 가져올 수 있는 이익과 비용을 은행, 기업, 가계의 입장에서 설명하고, 이 중 특히 중요한 개념들은 보다 상세히 설명하고 있다. 또한 한국이 금융 겸업화를 허용하게 된 계기와 그 역사적 과정을 우리종합금융과 신한종합금융의 예를 들어 설명함으로써 한국 금융의 겸업화로의 자연스러운 귀결을 얻어내고자 하였다.
각각의 이익 집단 즉, 은행, 기업, 가계가 금융 겸업화를 통해 상이한 이익을 얻고, 상이한 비용을 치뤄야 하기 때문에 금융 겸업화에 대해 서로 다른 입장을 갖게 되지만, 한국 경제가 국제 금융시장에서 경쟁력을 키워 나가기 위해서는 세계경제의 추세에 맞추어 금융 겸업화를 확산해 나가는 것이 선행될 수 밖에 없는 것이다. 따라서 한국 정부는 이러한 금융 겸업화가 소수의 이익 집단에 의해 좌절되지 않고, 또한 한국의 경제 현실에 맞게 발전해 나갈 수 있도록 충분한 법적 · 제도적 뒷받침을 마련해 나가야 할 것이다.;The banking industry has been dramatically changed since 1990s driven by forces including information technological developments, globalization of financial services competition and regulatory changes in international financial market environment. This drastic changes pushed banks to reconsider their positioning in a changing circumstance and to reform their systems to survive.
In order to prevent further deterioration generated by increased competition and to improve the competitive position, banks have tried to transform into universal banks and achieve lager scale, diversify to non-bank or non-financial activities and internationalize their activities. In Korea, there also has been considerable debate on undertaking a universal set of activities, and the global financial liberalization mood and Korea’s governmental regulatory policy are pulling banks toward universal banking system.
Through the universalized banking system, banks could gain or lose in terms of their profit making, customer relations, firm soundness and so on. Moreover, research on the effects of universal banking has been inconclusive as there is no clear-cut evidence in favor of or against it anywhere. Nevertheless, the U.S. has started moving cautiously toward universal banking through the Gramm-Leach-Bliley Act of 1999, which rolled back from many of the earlier restrictions like the 1933 Glass-Steagall Act. In addition to this, growing competition among financial organizations caused by liberalization of capital movements and the entry of new competitors into the financial services industry is prevalent almost all the industrialized countries. Because of this situation, more than ever before, the banking industry is facing fierce competition in many countries.
This paper first defines the meaning of universal banking, describes the trends toward universal banking, and analyzes the costs and benefits of universal banking in the perspective of banks, firms, and households. Then, it describes the development process of Korean universal banking, focusing on the background of financial reform and the governmental economic policies with first two financial holding groups, which are Woori Financial Group and Shinhan Financial Group, since the 1997 IMF crisis.
Universal banking system will continue to play an important role in Korean financial market exploiting economies of scale and scope and the universality of banking will be achieved in various ways other than just one single type of it. Also, small specialized financial institutions will not disappear but coexist with large universal banks. Although specialized banks and universal banking institutions would be in different position with different businesses, the government should prepare proper regulations and laws for sound banking infrastructure. After that, Korean universal banking system could be able to grow further in a stable environment and to compete with world’s universal banks.Ⅰ. INTRODUCTION 1
Ⅱ. TRENDS TOWARD UNIVERSAL BANKING 5
A. Technological Developments Affecting Financial Services 6
B. The Internationalization of Financial Services Competition 7
C. Regulatory Adaptation 9
Ⅲ. THE COSTS AND BENEFITS OF UNIVERSAL BANKING 10
A. Cost and Benefits: Banks 10
1. Cost (1): Greater Market Concentration 11
2. Cost (2): Conflicts of Interest 12
3. Benefit (1) & (2): Economies of Scale and Economies of Scope 13
B. Cost and Benefits: Firms 14
C. Cost and Benefits: Households 15
1. Costs (1): Financial Instability - Higher Risk 15
2. Benefit (1): One-Stop Supplier for Various Financial Services 17
Ⅳ. UNIVERSAL BANKING IN KOREA 18
A. The Development Process of Korean Universal Banking 18
B. What is a Financial Holding Company? 23
1. Case 1: Woori Financial Group 25
2. Case 2: Shinhan Financial Group 27
C. Expected Results of Universal Banking 32
1. Banks: Emergence of More Universal Banks 33
2. Securities Firms: Fierce Competition in the Stock Market 33
3. Insurance Companies: Transformation into Universal Banks 34
D. The Future of Universal Banking in Korea 35
Ⅴ. Summary and Conclusion 37
REFERENCES 42
국문요약 4
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