Viscoelastic Properties of Aorta From Oscillatory Pressure Tests

2011 ◽  
Author(s):  
Vasily Romanov ◽  
Mobin Rastgar Agah ◽  
Kurosh Darvish
Keyword(s):  
Blood Vessels ◽  
Material Properties ◽  
Large Deformations ◽  
Aortic Rupture ◽  
Viscoelastic Model ◽  
The Body ◽  
Time Dependency ◽  
Linear Viscoelastic ◽  
Almost All ◽  
The Relationship

Aorta is the largest and most important artery in the body due to its role in conveying all of the oxygenated blood to smaller branches and ultimately to all of the organs in the body. Knowing its mechanical characteristics and material properties is a basic stage in almost all studies on aorta e.g. evaluating the effect of aging and disease, design and manufacturing of compatible stents and traumatic aortic rupture. Since blood vessels are non-homogeneous, non-linear viscoelastic materials and can experience large deformations, a unique formulation that can describe their mechanical behavior under various loading conditions has not been developed yet. Several previous studies looked into modeling of the blood vessels at large deformation, but the models developed did not include the time dependency of the material [1,2]. In this work, we characterized the material properties of aorta under biaxial oscillatory loading at large deformations taking into account its time dependency. A viscoelastic model was developed to describe the relationship between the inflation and pressure.

Application of a Viscoelastic Model for Polyester Mooring

2010 ◽  
Author(s):  
J. W. Kim ◽  
J. H. Kyoung ◽  
A. Sablok
Keyword(s):  
Material Properties ◽  
Viscoelastic Model ◽  
Practical Method ◽  
Time Dependent ◽  
Mooring Line ◽  
New Model ◽  
Global Performance ◽  
Excitation Period ◽  
Linear Viscoelastic ◽  
Floating Platforms

A new practical method to simulate time-dependent material properties of polyester mooring line is proposed. The time-dependent material properties of polyester rope are modeled with a standard linear solid (SLS) model, which is one of the simplest forms of a linear viscoelastic model. The viscoelastic model simulates most of the mechanical properties of polyester rope such as creep, strain-stress hysteresis and excitation period-dependent stiffness. The strain rate-stress relation of the SLS model has been re-formulated to a stretch-tension relation, which is more suitable for implementation into global performance and mooring analyses tools for floating platforms. The new model has been implemented to a time-domain global performance analysis software and applied to simulate motion of a spar platform with chain-polyester-chain mooring system. The new model provides accurate platform offset without any approximation on the mean environmental load and can simulate the transient effect due to the loss of a mooring line during storm conditions, which has not been possible to simulate using existing dual-stiffness models.

scholarly journals Mechanics of the small punch test: a review and qualification of additive manufacturing materials

2021 ◽  
Vol 56 (18) ◽  
pp. 10707-10744
Author(s):  
Jonathan Torres ◽  
Ali P. Gordon
Keyword(s):  
Additive Manufacturing ◽  
Material Properties ◽  
Materials Science ◽  
Contemporary Literature ◽  
The Body ◽  
Small Punch Test ◽  
Small Punch ◽  
Punch Test ◽  
Testing Data ◽  
The Relationship

AbstractThe small punch test (SPT) was developed for situations where source material is scarce, costly or otherwise difficult to acquire, and has been used for assessing components with variable, location-dependent material properties. Although lacking standardization, the SPT has been employed to assess material properties and verified using traditional testing. Several methods exist for equating SPT results with traditional stress–strain data. There are, however, areas of weakness, such as fracture and fatigue approaches. This document outlines the history and methodologies of SPT, reviewing the body of contemporary literature and presenting relevant findings and formulations for correlating SPT results with conventional tests. Analysis of literature is extended to evaluating the suitability of the SPT for use with additively manufactured (AM) materials. The suitability of this approach is shown through a parametric study using an approximation of the SPT via FEA, varying material properties as would be seen with varying AM process parameters. Equations describing the relationship between SPT results and conventional testing data are presented. Correlation constants dictating these relationships are determined using an accumulation of data from the literature reviewed here, along with novel experimental data. This includes AM materials to assess the fit of these and provide context for a wider view of the methodology and its interest to materials science and additive manufacturing. A case is made for the continued development of the small punch test, identifying strengths and knowledge gaps, showing need for standardization of this simple yet highly versatile method for expediting studies of material properties and optimization.

Optimization of a Viscoelastic Structure: The Seat-Belt Problem

1969 ◽  
Vol 36 (3) ◽  
pp. 565-572 ◽  
Author(s):  
W. Nachbar ◽  
J. B. Schipmo¨lder
Keyword(s):  
Seat Belt ◽  
Viscoelastic Model ◽  
Small Strain ◽  
The Body ◽  
Strain Rates ◽  
Maximum Displacement ◽  
Critical Displacement ◽  
Viscoelastic Models ◽  
Maximum Value ◽  
Linear Viscoelastic

Optimization of the parameters of elementary linear viscoelastic models is considered for the design of a lap seat belt in automobiles. The vehicle is assumed to stop abruptly on impact. The parameters are optimized to allow the speed of the vehicle before impact to have the largest permissible value consistent with constraints imposed for the safety of the user of the belt. The constraints chosen here are: (a) the maximum displacement of the body after impact is equal to or less than a prescribed critical displacement; (b) the forward speed of the body at the critical displacement does not exceed a prescribed maximum value; (c) the force exerted by the belt on the body during the motion following impact does not exceed a prescribed maximum value. It is found that the optimized Kelvin-Voigt viscoelastic model is nearly 40 percent more effective than the purely elastic material. It is nearly as effective as constant deceleration. An additional and advantageous property is proposed, moreover, for belts of viscoelastic materials. This is that the material should have a relatively low spring rate at relatively small strain rates. The optimized belts for the elementary viscoelastic models are shown to be quite stiff at low strain rates, however.

Viscoelasticity reduces the dynamic stresses and strains in the vessel wall: implications for vessel fatigue

2007 ◽  
Vol 293 (4) ◽  
pp. H2355-H2360 ◽  
Author(s):  
Wei Zhang ◽  
Yi Liu ◽  
Ghassan S. Kassab
Keyword(s):  
Fatigue Life ◽  
Blood Vessels ◽  
Relaxation Function ◽  
Vessel Wall ◽  
Circumferential Stress ◽  
Viscoelastic Model ◽  
Temporal Variations ◽  
Elastic Response ◽  
Wall Movement ◽  
Linear Viscoelastic

The mechanical behavior of blood vessels is known to be viscoelastic rather than elastic. The functional role of viscoelasticity, however, has remained largely unclear. The hypothesis of this study is that viscoelasticity reduces the stresses and strains in the vessel wall, which may have a significant impact on the fatigue life of the blood vessel wall. To verify the hypothesis, the pulsatile stress in rabbit thoracic artery at physiological loading condition was investigated with a quasi-linear viscoelastic model, where the normalized stress relaxation function is assumed to be isotropic, while the stress-strain relationship is anisotropic and nonlinear. The artery was subjected to the same boundary condition, and the mechanical equilibrium equation was solved for both the viscoelastic and an elastic (which has a constant relaxation function) model. Numerical results show that, compared with purely elastic response, the viscoelastic property of arteries reduces the magnitudes and temporal variations of circumferential stress and strain. The radial wall movement is also reduced due to viscoelasticity. These findings imply that viscoelasticity may be beneficial for the fatigue life of blood vessels, which undergo millions of cyclic mechanical loadings each year of life.

scholarly journals Tobacco Smoking and Cancer Types: A Review

2018 ◽  
Vol 5 (4) ◽  
pp. 2142-2159 ◽  
Author(s):  
Yousef Khani ◽  
Nima Pourgholam-Amiji ◽  
Mohammad Afshar ◽  
Omid Otroshi ◽  
Mehran Sharifi-Esfahani ◽  
...  
Keyword(s):  
Tobacco Smoke ◽  
Tobacco Smoking ◽  
Hematologic Malignancies ◽  
Protective Role ◽  
The Body ◽  
Upper Aerodigestive Tract ◽  
Increased Risk ◽  
Incidence And Mortality ◽  
Almost All ◽  
The Relationship

Objective: Tobacco smoking is one of the causes of the incidence and mortality of cancer in the world. This study aimed to review the relationship between TS and especially the use of cigarettes with common cancers of various organs of the body. Methods: This study was  conducted  in  English by November 2017 through a search in databases of the PubMed, Scopus and Web of Science. The search strategy included the key words "cancer", "tobacco smoke", "tobacco smoke", and "smoking." Articles that looked at the relationship between each type of cancer and smoking were entered into the study and summarized in Review. Results: Tobacco smoking is associated with an increased risk of lung cancer, Upper aerodigestive tract, esophagus, stomach, bladder, kidneys, colorectal, prostate, and pancreas. However, further studies are needed to confirm the association between Tobacco smoking and liver, cervical, brain, gallbladder, Hodgkin’s disease, non-Hodgkin’s lymphoma and hematologic malignancies. However, Tobacco smoking plays a protective role in the development of thyroid cancers, skin and Kaposi’s sarcoma. Conclusions: Given that almost all of the risk factors for most cancers are Tobacco smoking, increasing the public’s awareness of the harmful effects of smoking, implementing programs and policies to  reduce smoking, can lead to a reduction in smoking and consequently reduce  the  resulting  harmful  consequences.

COMPARISON OF ANTIHYPERTENSIVE EFFECT OF MOXONIDINE VERSUS CLONIDINE IN RENAL FAILURE PATIENTS.

2018 ◽  
Vol 6 (9) ◽  
Author(s):  
DR.MATHEW GEORGE ◽  
DR.LINCY JOSEPH ◽  
MRS.DEEPTHI MATHEW ◽  
ALISHA MARIA SHAJI ◽  
BIJI JOSEPH ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Renal Failure ◽  
Blood Flow ◽  
Blood Vessel ◽  
Blood Vessels ◽  
High Blood Pressure ◽  
Antihypertensive Effect ◽  
The Body ◽  
Ability To Work ◽  
Blood Flows

Blood pressure is the force of blood pushing against blood vessel walls as the heart pumps out blood, and high blood pressure, also called hypertension, is an increase in the amount of force that blood places on blood vessels as it moves through the body. Factors that can increase this force include higher blood volume due to extra fluid in the blood and blood vessels that are narrow, stiff, or clogged(1). High blood pressure can damage blood vessels in the kidneys, reducing their ability to work properly. When the force of blood flow is high, blood vessels stretch so blood flows more easily. Eventually, this stretching scars and weakens blood vessels throughout the body, including those in the kidneys.

The use of Body Surface Index as a Better Clinical Health indicators Compare to Body Mass Index and Body Surface Area for Clinical Application

2018 ◽  
pp. 131-136
Author(s):  
Shirazu I. ◽  
Theophilus. A. Sackey ◽  
Elvis K. Tiburu ◽  
Mensah Y. B. ◽  
Forson A.
Keyword(s):  
Surface Area ◽  
Body Surface Area ◽  
Clinical Application ◽  
Body Surface ◽  
Body Height ◽  
Health Indicators ◽  
The Body ◽  
Body Parameters ◽  
The Relationship ◽  
Individual Body

The relationship between body height and body weight has been described by using various terms. Notable among them is the body mass index, body surface area, body shape index and body surface index. In clinical setting the first descriptive parameter is the BMI scale, which provides information about whether an individual body weight is proportionate to the body height. Since the development of BMI, two other body parameters have been developed in an attempt to determine the relationship between body height and weight. These are the body surface area (BSA) and body surface index (BSI). Generally, these body parameters are described as clinical health indicators that described how healthy an individual body response to the other internal organs. The aim of the study is to discuss the use of BSI as a better clinical health indicator for preclinical assessment of body-organ/tissue relationship. Hence organ health condition as against other body composition. In addition the study is `also to determine the best body parameter the best predict other parameters for clinical application. The model parameters are presented as; modeled height and weight; modelled BSI and BSA, BSI and BMI and modeled BSA and BMI. The models are presented as clinical application software for comfortable working process and designed as GUI and CAD for use in clinical application.

Contemporary Qur'anic Studies in Iran and its Relationship with Qur'anic Studies in the West

2012 ◽  
Vol 14 (1) ◽  
pp. 45-72
Author(s):  
Morteza Karimi-Nia
Keyword(s):  
Islamic Law ◽  
Human Sciences ◽  
The West ◽  
Communications Technologies ◽  
Religious Learning ◽  
The Status ◽  
Islamic Republic Of Iran ◽  
Almost All ◽  
The Impact ◽  
The Relationship

The status of tafsīr and Qur'anic studies in the Islamic Republic of Iran has changed significantly during recent decades. The essay provides an overview of the state of Qur'anic studies in Iran today, aiming to examine the extent of the impact of studies by Western scholars on Iranian academic circles during the last three decades and the relationship between them. As in most Islamic countries, the major bulk of academic activity in Iran in this field used to be undertaken by the traditional ʿulamāʾ; however, since the beginning of the twentieth century and the establishment of universities and other academic institutions in the Islamic world, there has been increasing diversity and development. After the Islamic Revolution, many gradual changes in the structure and approach of centres of religious learning and universities have occurred. Contemporary advancements in modern sciences and communications technologies have gradually brought the institutions engaged in the study of human sciences to confront the new context. As a result, the traditional Shīʿī centres of learning, which until 50 years ago devoted themselves exclusively to the study of Islamic law and jurisprudence, today pay attention to the teaching of foreign languages, Qur'anic sciences and exegesis, including Western studies about the Qur'an, to a certain extent, and recognise the importance of almost all of the human sciences of the West.

CONCEPTUALISING RISK CULTURE ON ERM IMPLEMENTATION IN CONSTRUCTION COMPANIES

2020 ◽  
Vol 17 (1) ◽  
pp. 59
Author(s):  
Ching Ching Wong
Keyword(s):  
Risk Management ◽  
Risk Identification ◽  
The Body ◽  
Risk Indicators ◽  
Construction Companies ◽  
Risk Appetite ◽  
Risk Culture ◽  
Risk Treatment ◽  
Managing Risk ◽  
The Relationship

Enterprise Risk Management (ERM) is an effective technique in managing risk within an organization strategically and holistically. Risk culture relates to the general awareness, attitudes and behaviours towards risk management in an organisation. This paper presents a conceptual model that shows the relationship between risk culture and ERM implementation. The dependent variable is ERM implementation, which is measured by the four processes namely risk identification and risk assessment; risk treatment; monitor and consult; communicate and consult. The independent variables under risk culture are risk policy and risk appetite; key risk indicators; accountability; incentives; risk language and internal relationships. This study aims to empirically test the relationship between risk culture and ERM implementation among Malaysian construction public listed companies. Risk culture is expected to have direct effects and significantly influence ERM. This study contributes to enhance the body of knowledge in ERM especially in understanding significant of risk culture that influence its’ implementation from Malaysian perspective.

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