检索结果-内蒙古大学图书馆

Simulation of the microstructure formation in hardening self-compacting cement paste containing limestone powder as filler via computer-based model

引用

MATERIALS AND STRUCTURES 2013年第11期46卷 1861-1879页

作者： Liu, Xian Ye, Guang De Schutter, Geert Yuan, Yong Tongji Univ Key Lab Geotech & Underground Engn Minist Educ Shanghai 200092 Peoples R China Tongji Univ Dept Geotech Engn Shanghai 200092 Peoples R China Univ Ghent Dept Struct Engn Magnel Lab Concrete Res B-9000 Ghent Belgium Delft Univ Technol Fac Civil Engn & Geosci Microlab Delft Netherlands

With the development of concrete technology, fillers are widely used in high performance concrete to improve its properties. Among them, limestone powder is popularly added in self-compacting concrete to gain good flowability. However, by lack of experimental data, several materials properties after the addition of limestone powder are still not sure, which actually yield some uncertainty for the further use of limestone powder in cement-based materials. In this study, by employing computer-based model, the microstructure of self-compacting cement paste containing limestone as filler is simulated and further used to investigate the role of limestone in hardening materials. To gain this goal, thermometric isothermal conduction calorimetry, thermal analysis and backscattered electron image acquisition were applied to understand the hydration kinetics with the addition of limestone filler. After that, a computational materials model based on HYMOSTRUC was developed to simulate the formation of microstructure in materials containing limestone powder. The predictive ability of the model was validated with the experimental test results. Then the developed model was employed to investigate the influence of several variables, such as water to cement ratio, limestone filler content and fineness, on the microstructure formation in hardening materials. The numerical experiments show that the addition of limestone filler could result in a denser microstructure at the initial hydration stage. With the proceeding of hydration, the limestone powder has a decreasing influence on the microstructure, and could obstruct somewhat the formation of a denser microstructure at later hydration stage. And it is found that computer-based modelling is an effective method to provide insights into the material behaviour, by relieving researchers from numerous repeated experiments.

关键词： Limestone powder Self-compacting material Microstructure computer-based model

来源：评论

学校读者我要写书评

暂无评论

modelling water systems in an introductory undergraduate course: students' use and evaluation of data-driven, computer-based models

引用

INTERNATIONAL JOURNAL OF SCIENCE EDUCATION 2019年第14期41卷 1999-2023页

作者： Lally, Diane Forbes, Cory Univ Nebraska Sch Nat Resources Hardin Hall3310 Holdrege St Lincoln NE 68583 USA

Introductory undergraduate courses present an opportunity to use disciplinary concepts in solving authentic problems. Making complex natural systems accessible to students through computer-based models allows them to practice making evidence-based predictions and communicate understanding. Despite the importance of modelling tools in formal classrooms, gaps exist in our understanding of how post-secondary students engage in computer-based modelling. Introductory courses, particularly in the hydrosciences, typically do not use these tools. This mixed methods study examines students' model-based reasoning about a water-related issue over two years in response to a flipped course model. Students in an introductory water course learned basic hydrologic content and used a computer-based water model to complete a project. Data came from a pre-/post-course assessment, student assignments, and student interviews. Results of quantitative and qualitative data analyses show that students in the revised version of the course (Year 2, n = 53) increased their understanding of core hydrology concepts and performed better on their evaluation of a computer-based water model, than students in the initial course (Year 1, n = 38). We tentatively attribute these observed changes to increased active learning opportunities surrounding computer-based modelling of water systems. Findings contribute to science literacy development, undergraduate science learning environment design, and undergraduate scientific modelling.

关键词： Undergraduate water computer-based model geoscience

来源：评论

学校读者我要写书评

暂无评论

An in silico simulation of flow-mediated dilation reveals that blood pressure and other factors may influence the response independent of endothelial function

引用

AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY 2020年第5期318卷 H1337-H1345页

作者： Jin, Weiwei Chowienczyk, Philip Alastruey, Jordi Kings Coll London Sch Biomed Engn & Imaging Sci Dept Biomed Engn London England Kings Coll London British Heart Fdn Ctr St Thomas Hosp Dept Clin Pharmacol London England Sechenov Univ Inst Personalized Med Moscow Russia

Endothelial dysfunction is thought to underpin atherosclerotic cardiovascular disease. The most widely used in vivo test of endothelial function is flow-mediated dilation (FMD). However, the results of FMD may be subject to some confounding factors that are not fully understood. We investigated potential biophysical confounding factors that could cause a disassociation between FMD and true endothelial cell shear stress response (the release of endothelium-dependent relaxing factors in response to wall shear stress). Arterial hemodynamics during FMD was simulated using a novel computational modeling approach. The model included an endothelial response function relating changes in wall shear stress to changes in local vascular stiffness in the arm arteries and accounted for vascular stiffening with increasing blood pressure. The hemodynamic effects of cuff inflation and deflation were modeled by prescribing intraluminal arterial pressure changes and peripheral vasodilation. Evolution of arterial diameter and flow velocity during FMD was assessed by comparison against in vivo data. Our model revealed that vasoconstriction occurring immediately after cuff deflation is independent of endothelial response function and entirely caused by the change in transmural pressure along conduit arteries. Moreover, for the same endothelial response function model, FMD values increased exponentially with increasing peak flow velocity, decreased linearly with increasing arterial stiffness at a rate of 0.95%/MPa, and increased linearly with increasing central blood pressure at a rate of 0.22%/mmHg. Dependence of FMD on confounding factors, such as arterial stiffness and blood pressure, suggests that the current FMD test may not reflect the true endothelial cell response. NEW & NOTEWORTHY First, a novel computational model simulating arterial hemodynamics during flow-mediated dilation (FMD) was proposed. Second. the model was used to explain why FMD may be influenced by endothelium-indep

关键词： computer-based model endothelial function flow-induced dilation hemodynamics

来源：评论

学校读者我要写书评

暂无评论

Computational modeling for Cardiac Resynchronization Therapy

引用

JOURNAL OF CARDIOVASCULAR TRANSLATIONAL RESEARCH 2018年第2期11卷 92-108页

作者： Lee, Angela W. C. Costa, Caroline Mendonca Strocchi, Marina Rinaldi, Christopher A. Niederer, Steven A. Kings Coll London Sch Biomed Engn & Imaging Sci London England Guys & St Thomas Hosp Dept Cardiol London England

Cardiac resynchronization therapy (CRT) is an effective treatment for heart failure (HF) patients with an electrical substrate pathology causing ventricular dyssynchrony. However 40-50% of patients do not respond to treatment. Cardiac modeling of the electrophysiology, electromechanics, and hemodynamics of the heart has been used to study mechanisms behind HF pathology and CRT response. Recently, multi-scale dyssynchronous HF models have been used to study optimal device settings and optimal lead locations, investigate the underlying cardiac pathophysiology, as well as investigate emerging technologies proposed to treat cardiac dyssynchrony. However the breadth of patient and experimental data required to create and parameterize these models and the computational resources required currently limits the use of these models to small patient numbers. In the future, once these technical challenges are overcome, biophysically based models of the heart have the potential to become a clinical tool to aid in the diagnosis and treatment of HF.

关键词： Cardiac resynchronisation therapy Left bundle branch block Electrophysiology modeling Electromechanical modeling Hemodynamic modeling computer-based model

来源：评论

学校读者我要写书评

暂无评论

Optogenetic manipulation of anatomical re-entry by light-guided generation of a reversible local conduction block

引用

CARDIOVASCULAR RESEARCH 2017年第3期113卷 354-366页

作者： Watanabe, Masaya Feola, Iolanda Majumder, Rupamanjari Jangsangthong, Wanchana Teplenin, Alexander S. Ypey, Dirk L. Schalij, Martin J. Zeppenfeld, Katja de Vries, Antoine A. F. Pijnappels, Daniel A. Heart Lung Ctr Leiden Dept Cardiol Lab Expt Cardiol Albinusdreef 2 NL-2300 RC Leiden Netherlands

Aims Anatomical re-entry is an important mechanism of ventricular tachycardia, characterized by circular electrical propagation in a fixed pathway. It's current investigative and therapeutic approaches are non-biological, rather unspecific (drugs), traumatizing (electrical shocks), or irreversible (ablation). Optogenetics is a new biological technique that allows reversible modulation of electrical function with unmatched spatiotemporal precision using light-gated ion channels. We therefore investigated optogenetic manipulation of anatomical re-entry in ventricular cardiac tissue. Methods and results Transverse, 150-mu m-thick ventricular slices, obtained from neonatal rat hearts, were genetically modified with lentiviral vectors encoding Ca2+-translocating channelrhodopsin (CatCh), a light-gated depolarizing ion channel, or enhanced yellow fluorescent protein (eYFP) as control. Stable anatomical re-entry was induced in both experimental groups. Activation of CatCh was precisely controlled by 470-nm patterned illumination, while the effects on anatomical re-entry were studied by optical voltage mapping. Regional illumination in the pathway of anatomical re-entry resulted in termination of arrhythmic activity only in CatCh-expressing slices by establishing a local and reversible, depolarization-induced conduction block in the illuminated area. Systematic adjustment of the size of the lightexposed area in the re-entrant pathway revealed that re-entry could be terminated by either wave collision or extinction, depending on the depth (transmurality) of illumination. In silico studies implicated source-sink mismatches at the site of subtransmural conduction block as an important factor in re-entry termination. Conclusions Anatomical re-entry in ventricular tissue can be manipulated by optogenetic induction of a local and reversible conduction block in the re-entrant pathway, allowing effective re-entry termination. These results provide distinctively new mechanistic insi

关键词： Optogenetics Anatomical re-entry Tissue culture Optical mapping computer-based model

来源：评论

学校读者我要写书评

暂无评论

A Computable Phenotype Improves Cohort Ascertainment in a Pediatric Pulmonary Hypertension Registry

引用

JOURNAL OF PEDIATRICS 2017年 188卷 224-+页

作者： Geva, Alon Gronsbell, Jessica L. Cai, Tianxi Cai, Tianrun Murphy, Shawn N. Lyons, Jessica C. Heinz, Michelle M. Natter, Marc D. Patibandla, Nandan Bickel, Jonathan Mullen, Mary P. Mandl, Kenneth D. Boston Childrens Hosp Computat Hlth Informat Program 300 Longwood Ave1 Autumn 535Mail Stop BCH3187 Boston MA 02115 USA Boston Childrens Hosp Dept Anesthesiol Perioperat & Pain Med Div Crit Care Med Boston MA USA Harvard Med Sch Dept Anesthesia Boston MA USA Harvard TH Chan Sch Publ Hlth Dept Biostat Boston MA USA Brigham & Womens Hosp Div Rheumatol Immunol & Allergy 75 Francis St Boston MA 02115 USA Partners Healthcare Dept Res Informat Serv & Comp Boston MA 02114 USA Massachusetts Gen Hosp Dept Neurol Boston MA 02114 USA Harvard Med Sch Dept Biomed Informat Boston MA USA Harvard Med Sch Dept Pediat Boston MA USA Boston Childrens Hosp Informat Serv Dept Boston MA USA Boston Childrens Hosp Dept Cardiol Boston MA USA

Objectives To compare registry and electronic health record (EHR) data mining approaches for cohort ascertainment in patients with pediatric pulmonary hypertension (PH) in an effort to overcome some of the limitations of registry enrollment alone in identifying patients with particular disease phenotypes. Study design This study was a single-center retrospective analysis of EHR and registry data at Boston Children's Hospital. The local Informatics for Integrating Biology and the Bedside (i2b2) data warehouse was queried for billing codes, prescriptions, and narrative data related to pediatric PH. Computable phenotype algorithms were developed by fitting penalized logistic regression models to a physician-annotated training set. Algorithms were applied to a candidate patient cohort, and performance was evaluated using a separate set of 136 records and 179 registry patients. We compared clinical and demographic characteristics of patients identified by computable phenotype and the registry. Results The computable phenotype had an area under the receiver operating characteristics curve of 90% (95% CI, 85%-95%), a positive predictive value of 85% (95% CI, 77%-93%), and identified 413 patients (an additional 231%) with pediatric PH who were not enrolled in the registry. Patients identified by the computable phenotype were clinically distinct from registry patients, with a greater prevalence of diagnoses related to perinatal distress and left heart disease. Conclusions Mining of EHRs using computable phenotypes identified a large cohort of patients not recruited using a classic registry. Fusion of EHR and registry data can improve cohort ascertainment for the study of rare diseases.

关键词： pulmonary hypertension pediatrics registry computer-based model bioinformatics

来源：评论

学校读者我要写书评

暂无评论

Development and Assessment of a computer Algorithm for Stroke Vascular Localization Using Components of the National Institutes of Health Stroke Scale

引用

JOURNAL OF STROKE & CEREBROVASCULAR DISEASES 2016年第2期25卷 281-287页

作者： Lerner, David P. Tseng, Bertrand P. Goldstein, Larry B. Massachusetts Gen Hosp 55 Fruit StWACC 720 Boston MA 02114 USA Duke Univ Med Ctr Durham NC USA Univ Kentucky KY Clin Lexington KY USA

Background: The National Institutes of Health Stroke Scale (NIHSS) was not intended to be used to determine the stroke's vascular distribution. The aim of this study was to develop, assess the reliability, and validate a computer algorithm based on the NIHSS for this purpose. Methods: Two cohorts of patients with ischemic stroke having similar distributions of Oxfordshire localizations (total anterior, partial anterior, lacunar, and posterior circulation) based on neuroimaging were identified. The first cohort (n = 40) was used to develop a computer algorithm for vascular localization using a modified version of the NIHSS (NIHSSLocalization [NIHSS-Loc]) that included the laterality of selected deficits;the second (n = 20) was used to assess the reliability of algorithm-based localizations compared to those of 2 vascular neurologists. The validity of the algorithm-based localizations was assessed in comparison to neuroimaging. Agreement was assessed using the unweighted kappa (kappa) statistic. Results: Agreement between the 2 raters using the standard NIHSS was slight to moderate (kappa =.36, 95% confidence interval [CI] .10-.61). Inter-rater agreement significantly improved to the substantial to almost perfect range using the NIHSS-Loc (kappa=.88, 95% CI .73-1.00). Agreement was perfect when the 2 raters entered the data into the NIHSS-Loc computer algorithm (kappa = 1.00, 95% CI 1.00-1.00). Agreement between the algorithm localization and neuroimaging results was fair to moderate (kappa = .59,95% CI .35-.84) and not significantly different from the localizations of either rater using the NIHSS-Loc. Conclusion: A computerized, modified version of the standard NIHSS can be used to reliably and validly assign the vascular distribution of an acute ischemic stroke.

关键词： Ischemic stroke computer-based model acute stroke localization

来源：评论

学校读者我要写书评

暂无评论

Early afterdepolarizations promote transmural reentry in ischemic human ventricles with reduced repolarization reserve

引用

PROGRESS IN BIOPHYSICS & MOLECULAR BIOLOGY 2016年第1-3期120卷 236-248页

作者： Dutta, Sara Minchole, Ana Zacur, Ernesto Quinn, T. Alexander Taggart, Peter Rodriguez, Blanca Univ Oxford Dept Comp Sci BHF Ctr Res Excellence Oxford England Univ Oxford Inst Biomed Engn Oxford England Dalhousie Univ Dept Physiol & Biophys Halifax NS B3H 3J5 Canada UCL Bars Heart Ctr Inst Cardiovasc Sci London WC1E 6BT England

Aims: Acute ischemia is a major cause of sudden arrhythmic death, further promoted by potassium current blockers. Macro-reentry around the ischemic region and early afterdepolarizations (EADs) caused by electrotonic current have been suggested as potential mechanisms in animal and isolated cell studies. However, ventricular and human-specific arrhythmia mechanisms and their modulation by repolarization reserve remain unclear. The goal of this paper is to unravel multiscale mechanisms underlying the modulation of arrhythmic risk by potassium current (I-Kr) block in human ventricles with acute regional ischemia. Methods and results: A human ventricular biophysically-detailed model, with acute regional ischemia is constructed by integrating experimental knowledge on the electrophysiological ionic alterations caused by coronary occlusion. Arrhythmic risk is evaluated by determining the vulnerable window (VW) for reentry following ectopy at the ischemic border zone. Macro-reentry around the ischemic region is the main reentrant mechanism in the ischemic human ventricle with increased repolarization reserve due to the ATP-sensitive potassium current (I-K(ATP)) activation. Prolongation of refractoriness by 4% caused by 30% I-Kr reduction counteracts the establishment of macro-reentry and reduces the VW for reentry (by 23.5%). However, a further decrease in repolarization reserve (50% I-Kr reduction) is less anti-arrhythmic despite further prolongation of refractoriness. This is due to the establishment of transmural reentry enabled by electrotonically-triggered EADs in the ischemic border zone. EADs are produced by L-type calcium current (I-caL) reactivation due to prolonged low amplitude electrotonic current injected during the repolarization phase. Conclusions: Electrotonically-triggered EADs are identified as a potential mechanism facilitating intramural reentry in a regionally-ischemic human ventricles model with reduced repolarization reserve. (C) 2016 The Authors. Pu

关键词： lschemic heart disease computer-based model Ventricular arrhythmia Potassium channels Repolarization

来源：评论

学校读者我要写书评

暂无评论

Stochastic spontaneous calcium release events trigger premature ventricular complexes by overcoming electrotonic load

引用

CARDIOVASCULAR RESEARCH 2015年第1期107卷 175-183页

作者： Campos, Fernando O. Shiferaw, Yohannes Prassl, Anton J. Boyle, Patrick M. Vigmond, Edward J. Plank, Gernot Med Univ Graz Inst Biophys Graz Austria Calif State Univ Northridge Dept Phys Northridge CA 91330 USA Johns Hopkins Univ Inst Computat Med Baltimore MD USA Univ Bordeaux LIRYC Inst Bordeaux France Univ Calgary Dept Elect & Comp Engn Calgary AB Canada

Aims Premature ventricular complexes (PVCs) due to spontaneous calcium (Ca) release (SCR) events at the cell level can precipitate ventricular arrhythmias. However, the mechanistic link between SCRs and PVC formation remains incompletely understood. The aim of this study was to investigate the conditions under which delayed afterdepolarizations resulting from stochastic subcellular SCR events can overcome electrotonic source-sink mismatch, leading to PVC initiation. Methods and results A stochastic subcellular-scale mathematical model of SCR was incorporated in a realistic model of the rabbit ventricles and Purkinje system (PS). Elevated levels of diastolic sarcoplasmic reticulum Ca2+ (Ca-SR) were imposed until triggered activity was observed, allowing us to compile statistics on probability, timing, and location of PVCs. At Ca-SR >= 1500 mu mol/L PVCs originated in the PS. When SCR was incapacitated in the PS, PVCs also emerged in the ventricles, but at a higher Ca-SR (>= 1550 mu mol/L) and with longer waiting times. For each model configuration tested, the probability of PVC occurrence increased from 0 to 100% within a well-defined critical Ca-SR range;this transition was much more abrupt in organ-scale models (similar to 50 mu mol/L Ca-SR range) than in the tissue strand (similar to 100 mu mol/L) or single-cell (similar to 450 mu mol/L) models. Among PVCs originating in the PS, similar to 68% were located near Purkinje-ventricular junctions (<1 mm). Conclusion SCR events overcome source-sink mismatch to trigger PVCs at a critical Ca-SR threshold. Above this threshold, PVCs emerge due to increased probability and reduced variability in timing of SCR events, leading to significant diastolic depolarization. Sites of lower electronic load, such as the PS, are preferential locations for triggering.

关键词： Delayed afterdepolarization Triggered activity computer-based model Purkinje system Arrhythmia

来源：评论

学校读者我要写书评

暂无评论

A Novel Strategy to Translate the Biomechanical Rupture Risk of Abdominal Aortic Aneurysms to their Equivalent Diameter Risk: Method and Retrospective Validation

引用

EUROPEAN JOURNAL OF VASCULAR AND ENDOVASCULAR SURGERY 2014年第3期47卷 288-295页

作者： Gasser, T. C. Nchimi, A. Swedenborg, J. Roy, J. Sakalihasan, N. Boeckler, D. Hyhlik-Duerr, A. Royal Inst Technol KTH Dept Solid Mech Stockholm Sweden Univ Hosp Liege Dept Vasc Surg Liege Belgium Karolinska Univ Hosp & Inst Dept Vasc Surg Stockholm Sweden St Joseph Hosp Dept Med Imaging Liege Belgium Heidelberg Univ Dept Vasc Surg Heidelberg Germany

Objective: To translate the individual abdominal aortic aneurysm (AAA) patient's biomechanical rupture risk profile to risk-equivalent diameters, and to retrospectively test their predictability in ruptured and non-ruptured aneurysms. Methods: Biomechanical parameters of ruptured and non-ruptured AAAs were retrospectively evaluated in a multicenter study. General patient data and high resolution computer tomography angiography (CTA) images from 203 non-ruptured and 40 ruptured aneurysmal infrarenal aortas. Three-dimensional AAA geometries were semi-automatically derived from CTA images. Finite element (FE) models were used to predict peak wall stress (PWS) and peak wall rupture index (PWRI) according to the individual anatomy, gender, blood pressure, intraluminal thrombus (ILT) morphology, and relative aneurysm expansion. Average PWS diameter and PWRI diameter responses were evaluated, which allowed for the PWS equivalent and PWRI equivalent diameters for any individual aneurysm to be defined. Results: PWS increased linearly and PWRI exponentially with respect to maximum AAA diameter. A size-adjusted analysis showed that PWS equivalent and PWRI equivalent diameters were increased by 7.5 mm (p = .013) and 14.0 mm (p < .001) in ruptured cases when compared to non-ruptured controls, respectively. In non-ruptured cases the PWRI equivalent diameters were increased by 13.2 mm (p < .001) in females when compared with males. Conclusions: Biomechanical parameters like PWS and PWRI allow for a highly individualized analysis by integrating factors that influence the risk of AAA rupture like geometry (degree of asymmetry, ILT morphology, etc.) and patient characteristics (gender, family history, blood pressure, etc.). PWRI and the reported annual risk of rupture increase similarly with the diameter. PWRI equivalent diameter expresses the PWRI through the diameter of the average AAA that has the same PWRI, i.e. is at the same biomechanical risk of rupture. Consequently, PWRI equ

关键词： Aneurysms rupture Biomechanical analysis Aneurysm repair indication computer-based model Risk assessment

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：