Arteriosclerosis Research Using Vascular Flow Models: From 2-D Branches to Compliant Replicas

1993 ◽  
Vol 115 (4B) ◽  
pp. 595-601 ◽  
Author(s):  
Morton H. Friedman
Keyword(s):  
Fluid Dynamics ◽  
Flow Field ◽  
Large Body ◽  
Disease Process ◽  
The United States ◽  
Specific Flow ◽  
Flow Models ◽  
Hemodynamic Variables ◽  
Vascular Flow ◽  
Flow Through

A large body of evidence implicates fluid dynamic forces in the genesis and progression of atherosclerosis, the leading cause of death in the United States. To understand the mechanism by which hemodynamics influences the disease process, and to identify the specific flow variable(s) responsible for its localization, it is essential to know the distribution of hemodynamic variables in susceptible regions of the vasculature. Vascular flow models have been used more than any other means to gain insight into the details of arterial hemodynamics. The first flow models were not very realistic. Our first attempt, reported at an early Biomechanics Symposium, was probably the most unrealistic of all: a “2-D branch” that was constructed to validate a 2-D computed flow field. Most of the first models were made of cylindrical tubes, and their geometry too only approximated that of real arteries. Much was learned about the fluid dynamics in branches and bends using such models, but measurements in them could be related only generally to the fluid dynamics in living vessels. Accordingly, we began to make flow field measurements in replicas prepared from human arteries. Others challenged their glassblowers and shops to make models more representative of real vessels. These flow-through casts and fabricated models were initially rigid and perfused with Newtonian fluids. Using these more realistic systems, we and others were able to demonstrate relationships between specific hemodynamic variables and localized arterial pathology. The fidelity of flow simulations today exceeds that of only a few years ago. We now perfuse compliant replicas as small as coronary diagonal branches with fluids whose rheology mimics blood. This level of fidelity is harder to justify for the present application than the switch from tubes to flow-through casts. There is no evidence that the disease has kept secrets from the rigid casts that will be exposed in compliant ones. Nonetheless, there is comfort in simulating the real world as faithfully as possible, and one never knows until one tries whether the next increment of reality will yield unexpected new insights.

A Review of Nonsteady Flow Models for Compressor Stability

1994 ◽  
Vol 116 (2) ◽  
pp. 202-215 ◽  
Author(s):  
J. P. Longley
Keyword(s):  
Fluid Dynamics ◽  
Flow Field ◽  
Rotating Stall ◽  
Time Development ◽  
Mathematical Treatment ◽  
Two Dimensional ◽  
Nonsteady Flow ◽  
Physical Processes ◽  
Flow Models ◽  
Modeling Techniques

This paper presents a review of the different approaches to modeling the nonsteady fluid dynamics associated with two-dimensional compressor flow fields. These models are used to predict the time development of flow field disturbances and have been found useful in both the study of rotating stall and the development of active control. The opportunity to digest the earlier investigations has now made it possible to express the modeling ideas using only a very simple mathematical treatment. Here, the emphasis is on the underlying physical processes that the models simulate and how the assumptions within the models affect predictions. The purpose of this work is to produce, in a single document, a description of compressor modeling techniques, so that prospective users can assess which model is the most suitable for their application.

Influence of Shroud Cavity Jet and Steam Admission Through a Circumferential Slot on the Flow Field in a Steam Turbine

2012 ◽  
Author(s):  
David Engelmann ◽  
Tobias J. Kalkkuhl ◽  
Thomas Polklas ◽  
Ronald Mailach
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Steam Turbine ◽  
Test Facility ◽  
Incoming Flow ◽  
Specific Flow ◽  
Intermediate Pressure ◽  
Steam Admission ◽  
Flow Through ◽  
Pressure Part

Steam turbines for industrial application are often constructed according to modular design concepts. This allows interchangeable combinations of modules including steam admission and extraction. Prior to field tests the flow in a typical stage configuration of such a steam turbine is predicted numerically. Focus of the current work is the axial gap between high pressure and intermediate pressure part containing a circumferential slot. Mass flow used for axial thrust balancing re-enters the blade channel through this slot. Another exceptional feature appears at the high pressure vane carrier: For manufacturing reasons the last rotor shroud next to and upstream of the gap is not fully enclosed by the vane carrier. This results in a turbulent jet at the exit of the rotor shroud cavity mixing with both the blade channel flow as well as the incoming flow from the slot. A commercial 3D RANS CFD-solver (ANSYS CFX 12) is used to predict the mixing of the different flow partitions within the stage gap. Therefore, the last stage of the high pressure part, the gap with the slot and the first stage of the intermediate pressure part are modeled and solved numerically. The amount of flow through the circumferential slot is varied to discern the influences of the specific flow partitions. Additionally, a modification of the vane carrier helps to analyze radial distribution of incoming flow for the downstream vane row as well as scoring global loss characteristics. As the simulation results indicate, flow parameters up- and downstream and also fluctuations crossing the gap are affected by flow through the slot. Furthermore, the computed flow field shows locations appropriate for a traversing probe system to be used in the test facility.

Mosquito and Tick-borne Illnesses in the United States. Guidelines for the Recognition and Empiric Treatment of Zoonotic Diseases in the Wilderness.

2019 ◽  
Vol 19 (3) ◽  
pp. 238-257
Author(s):  
Suresh Antony
Keyword(s):  
United States ◽  
Lyme Disease ◽  
Spotted Fever ◽  
Disease Process ◽  
Rocky Mountain ◽  
The United States ◽  
Health Care Facilities ◽  
Diagnostic Tools ◽  
Rocky Mountain Spotted Fever ◽  
Number Of Patients

Background:In the United States, tick-borne illnesses account for a significant number of patients that have been seen and treated by health care facilities. This in turn, has resulted in a significant morbidity and mortality and economic costs to the country.Methods:The distribution of these illnesses is geographically variable and is related to the climate as well. Many of these illnesses can be diagnosed and treated successfully, if recognized and started on appropriate antimicrobial therapy early in the disease process. Patient with illnesses such as Lyme disease, Wet Nile illness can result in chronic debilitating diseases if not recognized early and treated.Conclusion:This paper covers illnesses such as Lyme disease, West Nile illness, Rocky Mountain Spotted fever, Ehrlichia, Tularemia, typhus, mosquito borne illnesses such as enteroviruses, arboviruses as well as arthropod and rodent borne virus infections as well. It covers the epidemiology, clinical features and diagnostic tools needed to make the diagnosis and treat these patients as well.

Telemedicine for Patients with Inflammatory Bowel Disease (TELE-IBD) Clinical Trial: Qualitative Assessment of Participants’ Perceptions of the TELE-IBD Intervention (Preprint)

2019 ◽  
Author(s):  
Charlene C Quinn ◽  
Sarah Chard ◽  
Erin G Roth ◽  
J. Kevin Eckert ◽  
Katharine M Russman ◽  
...  
Keyword(s):  
Clinical Trial ◽  
Disease Activity ◽  
Remote Monitoring ◽  
Standard Care ◽  
Disease Process ◽  
The United States ◽  
Qualitative Assessment ◽  
Structured Interviews ◽  
Treatment Groups ◽  
Inflammatory Bowel

BACKGROUND Inflammatory bowel diseases (IBD), comprising Crohn’s disease and ulcerative colitis, affects 1 to 3 million people in the United States. Telemedicine has shown promise in IBD. The objective of the parent study, TELE-IBD, was to compare disease activity and quality of life (QoL) in a one-year randomized clinical trial of IBD patients receiving telemedicine versus standard care. Treatment groups experienced improvements in disease activity and QoL but there was not significant differences between groups. Study adherence to the text-based intervention was less than the 80% of the targeted goal. OBJECTIVE To understand adherence to remote monitoring, the goal of this qualitative assessment was to obtain TELE-IBD trial participants’ perceptions of the TELE-IBD system, including their recommendations for future TELE-IBD monitoring. METHODS In the parent study, patients attending three tertiary referral centers with worsening IBD symptoms in the previous two years were eligible for randomization to remote monitoring via texts every other week (EOW), weekly (W) or standard care. Participants (n=348) were evenly enrolled in the treatment groups and 259 (74.4%) completed the study. For this study, a purposive sample of adherent (N=15) and non-adherent (N=14) patients was drawn from the TELE-IBD trial population. Adherence was defined as the completion of 80% or more of the W or EOW self-assessments. Semi-structured interviews conducted by phone surveyed 1) the strengths and benefits of TELE-IBD; 2) challenges associated with using TELE-IBD; and 3) how to improve the TELE-IBD intervention. Interviews were recorded, professionally transcribed, and coded based on a priori concepts and emergent themes with the aid of ATLAS.ti qualitative data analysis software. RESULTS Participants' discussions centered on three elements of the intervention: 1) self-assessment questions, 2) action plans, and 3) educational messages. Participants also commented on: text-based platform, depression and adherence, TELE-IBD system in place of office visit, and their recommendations for future TELE-IBD systems. Adherent and non-adherent participants prefer a flexible system that is personalized, including targeted education messages, and they perceive TELE-IBD as effective in facilitating IBD self-management. CONCLUSIONS Participants identified clear benefits to the TELE-IBD system, including obtaining a better understanding of the disease process, monitoring their symptoms, and feeling connected to their health care provider. Participants' perceptions obtained in this qualitative study will assist in improving the TELE-IBD system to be more responsive to patients with IBD. CLINICALTRIAL NCT01692743

The Oxford Handbook of IPOs

2018 ◽  
Keyword(s):  
United States ◽  
Initial Public Offerings ◽  
Financial Regulation ◽  
Large Body ◽  
Public Information ◽  
The United States ◽  
Minimum Size ◽  
Stock Exchanges ◽  
Public Offerings ◽  
Firm’S Life Cycle

Firms generally begin as privately owned entities. When they grow large enough, the decision to go public and its consequences are among the most crucial times in a firm’s life cycle. The first time a firm is a reporting issuer gives rise to tremendous responsibilities about disclosing public information and accountability to a wide array of retail shareholders and institutional investors. Initial public offerings (IPOs) offer tremendous opportunities to raise capital. The economic and legal landscape for IPOs has been rapidly evolving across countries. There have been fewer IPOs in the United States in the aftermath of the 2007–2009 financial crisis and associated regulatory reforms that began in 2002. In 1980–2000, an average of 310 firms went public every year, while in 2001–2014 an average of 110 firms went public every year. At the same time, there are so many firms that seek an IPO in China that there has been a massive waiting list of hundreds of firms in recent years. Some countries are promoting small junior stock exchanges to go public early, and even crowdfunding to avoid any prospectus disclosure. Financial regulation of analysts and investment banks has been evolving in ways that drastically impact the economics of going public—in some countries, such as the United States, drastically increasing the minimum size of a company before it can expect to go public. This Handbook not only systematically and comprehensively consolidates a large body of literature on IPOs, but provides a foundation for future debates and inquiry.

Vascular Fluid Mechanics, the Arterial Wall, and Atherosclerosis

1992 ◽  
Vol 114 (3) ◽  
pp. 274-282 ◽  
Author(s):  
R. M. Nerem
Keyword(s):  
Cell Culture ◽  
Blood Flow ◽  
Fluid Mechanics ◽  
Arterial Wall ◽  
Disease Process ◽  
The United States ◽  
Structure And Function ◽  
Medium Size ◽  
Important Relationship ◽  
And Function

Atherosclerosis, a disease of large- and medium-size arteries, is the chief cause of death in the United States and in most of the western world. Severe atherosclerosis interferes with blood flow; however, even in the early stages of the disease, i.e. during atherogenesis, there is believed to be an important relationship between the disease processes and the characteristics of the blood flow in the arteries. Atherogenesis involves complex cascades of interactions among many factors. Included in this are fluid mechanical factors which are believed to be a cause of the highly focal nature of the disease. From in vivo studies, there is evidence of hemodynamic influences on the endothelium, on intimal thickening, and on monocyte recruitment. In addition, cell culture studies have demonstrated the important effect of a cell’s mechanical environment on structure and function. Most of this evidence is for the endothelial cell, which is believed to be a key mediator of any hemodynamic effect, and it is now well documented that cultured endothelial monolayers, in response to a fluid flow-imposed laminar shear stress, undergo a variety of changes in structure and function. In spite of the progress in recent years, there are many areas in which further work will provide important new information. One of these is in the engineering of the cell culture environment so as to make it more physiologic. Animal studies also are essential in our efforts to understand atherogenesis, and it is clear that we need better information on the pattern of the disease and its temporal development in humans and animal models, as well as the specific underlying biologic events. Complementary to this will be in vitro model studies of arterial fluid mechanics. In addition, one can foresee an increasing role for computer modelling in our efforts to understand the pathophysiology of the atherogenic process. This includes not only computational fluid mechanics, but also modelling the pathobiologic processes taking place within the arterial wall. A key to the atherogenic process may reside in understanding how hemodynamics influences not only intimal smooth muscle cell proliferation, but also the recruitment of the monocyte/macrophage and the formation of foam cells. Finally, it will be necessary to begin to integrate our knowledge of cellular phenomena into a description of the biologic processes within the arterial wall and then to integrate this into a picture of the disease process itself.

scholarly journals A Simple Transient Poiseuille-Based Approach to Mimic the Womersley Function and to Model Pulsatile Blood Flow

Dynamics ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 9-17
Author(s):  
Andrea Natale Impiombato ◽  
Giorgio La Civita ◽  
Francesco Orlandi ◽  
Flavia Schwarz Franceschini Zinani ◽  
Luiz Alberto Oliveira Rocha ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Blood Flow ◽  
Boundary Conditions ◽  
Quadratic Function ◽  
Pulsatile Blood Flow ◽  
Flow Through ◽  
Simplified Analysis ◽  
Function Models ◽  
Flow Reversals

As it is known, the Womersley function models velocity as a function of radius and time. It has been widely used to simulate the pulsatile blood flow through circular ducts. In this context, the present study is focused on the introduction of a simple function as an approximation of the Womersley function in order to evaluate its accuracy. This approximation consists of a simple quadratic function, suitable to be implemented in most commercial and non-commercial computational fluid dynamics codes, without the aid of external mathematical libraries. The Womersley function and the new function have been implemented here as boundary conditions in OpenFOAM ESI software (v.1906). The discrepancy between the obtained results proved to be within 0.7%, which fully validates the calculation approach implemented here. This approach is valid when a simplified analysis of the system is pointed out, in which flow reversals are not contemplated.

scholarly journals Retinal Redox Stress and Remodeling in Cardiometabolic Syndrome and Diabetes

2010 ◽  
Vol 3 (6) ◽  
pp. 392-403 ◽  
Author(s):  
Ying Yang ◽  
Melvin R. Hayden ◽  
Susan Sowers ◽  
Sarika V. Bagree ◽  
James R. Sowers
Keyword(s):  
Metabolic Pathways ◽  
Tissue Injury ◽  
Disease Process ◽  
Polyol Pathway ◽  
The United States ◽  
Redox Stress ◽  
Blood Retinal Barrier ◽  
Cardiometabolic Syndrome ◽  
Hexosamine Pathway ◽  
Pathway Flux

Diabetic retinopathy (DR) is a significant cause of global blindness; a major cause of blindness in the United States in people aged between 20–74. There is emerging evidence that retinopathy is initiated and propagated by multiple metabolic toxicities associated with excess production of reactive oxygen species (ROS). The four traditional metabolic pathways involved in the development of DR include: increased polyol pathway flux, advanced glycation end-product formation, activation of protein kinase Cisoforms and hexosamine pathway flux. These pathways individually and synergisticallycontribute to redox stress with excess ROS resulting in retinal tissue injury resulting in significant microvascular blood retinal barrier remodeling. The toxicity of hyperinsulinemia, hyperglycemia, hypertension, dyslipidemia, increased cytokines and growth factors, in conjunction with redox stress, contribute to the development and progression of DR. Redox stress contributes to the development and progression of abnormalities of endothelial cells and pericytes in DR. This review focuses on the ultrastructural observations of the blood retinal barrier including the relationship between the endothelial cell and pericyte remodeling in young nine week old Zucker obese (fa/ fa) rat model of obesity; cardiometabolic syndrome, and the 20 week old alloxan induced diabetic porcine model. Preventing or delaying the blindness associated with these intersecting abnormal metabolic pathways may be approached through strategies targeted to reduction of tissue inflammation and oxidative—redox stress. Understanding these abnormal metabolic pathways and the accompanying redox stress and remodeling mayprovide both the clinician and researcher a new concept of approaching this complicated disease process

Construction Ventilation Scheme Optimization of Underground Main Powerhouse Based on CFD

2013 ◽  
Vol 368-370 ◽  
pp. 619-623
Author(s):  
Zhen Liu ◽  
Xiao Ling Wang ◽  
Ai Li Zhang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Field ◽  
Air Flow ◽  
Scheme Optimization ◽  
Pressure Distributions ◽  
Air Volume ◽  
Computational Fluid Dynamics Cfd ◽  
Traditional Construction ◽  
Ventilation Scheme

For the purpose of avoiding the deficiency of the traditional construction ventilation, the ventilation of the underground main powerhouse is simulated by the computational fluid dynamics (CFD) to optimize ventilation parameters. A 3D unsteady RNG k-ε model is performed for construction ventilation in the underground main powerhouse. The air-flow field and CO diffusion in the main powerhouse are simulated and analyzed. The two construction ventilation schemes are modelled for the main powerhouse. The optimized ventilation scheme is obtained by comparing the air volume and pressure distributions of the different ventilation schemes.

scholarly journals Effect of Doppler flow meter position on discharge measurement in surcharged manholes

2017 ◽  
Vol 77 (3) ◽  
pp. 647-654 ◽  
Author(s):  
Haoming Yang ◽  
David Z. Zhu ◽  
Yanchen Liu
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Field ◽  
Flow Regimes ◽  
Flow Meter ◽  
Flow Meters ◽  
Flow Discharge ◽  
Doppler Flow ◽  
Sewer Systems ◽  
Computational Fluid Dynamics Cfd

Abstract Determining the proper installation location of flow meters is important for accurate measurement of discharge in sewer systems. In this study, flow field and flow regimes in two types of manholes under surcharged flow were investigated using a commercial computational fluid dynamics (CFD) code. The error in measuring the flow discharge using a Doppler flow meter (based on the velocity in a Doppler beam) was then estimated. The values of the corrective coefficient were obtained for the Doppler flow meter at different locations under various conditions. Suggestions for selecting installation positions are provided.

Sign in / Sign up

Export Citation Format

Share Document