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

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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

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COST ACCOUNTING IN RADIATION ONCOLOGY - A computer-based model FOR REIMBURSEMENT

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INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 1993年第5期25卷 895-906页

作者： PEREZ, CA KOBEISSI, B SMITH, BD FOX, S GRIGSBY, PW PURDY, JA PROCTER, HD WASSERMAN, TH WASHINGTON UNIV ST LOUISMO 63130

Purpose: The skyrocketing cost of medical care in the United States has resulted in multiple efforts in cost containment. The present work offers a rational computer-based cost accounting approach to determine the actual use of resources in providing a specific service in a radiation oncology center. Methods and Materials: A procedure-level cost accounting system was developed by using recorded information on actual time and effort spent by individual staff members performing various radiation oncology procedures, and analyzing direct and indirect costs related to staffing (labor), facilities and equipment, supplies, etc. Expenditures were classified as direct or indirect and fixed or variable. A relative value unit was generated to allocate specific cost factors to each procedure. Results: Different costs per procedure were identified according to complexity. Whereas there was no significant difference in the treatment time between low-energy (4 and 6 MV) or high-energy (18 MV) accelerators, there were significantly higher costs identified in the operation of a high-energy linear accelerator, a reflection of initial equipment investment, quality assurance and calibration procedures, maintenance costs, service contract, and replacement parts. Utilization of resources was related to the complexity of the procedures performed and whether the treatments were delivered to inpatients or outpatients. In analyzing time motion for physicians and other staff, it was apparent that a greater effort must be made to train the staff to accurately record all times involved in a given procedure, and it is strongly recommended that each institution perform its own time motion studies to more accurately determine operating costs. Sixty-six percent of our facility's global costs were for labor, 20% for other operating expenses, 10% for space, and 4% for equipment. Significant differences were noted in the cost allocation for professional or technical functions, as tabor, space, and eq

关键词： COST ACCOUNTING REIMBURSEMENT RADIATION THERAPY COST ANALYSIS computer-based model

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

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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

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A hemicord locomotor network of excitatory interneurons: a simulation study

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BIOLOGICAL CYBERNETICS 2007年第2期96卷 229-243页

作者： Kozlov, A. K. Lansner, A. Grillner, S. Kotaleski, J. Hellgren Royal Inst Technol Sch Comp Sci & Commun S-10044 Stockholm Sweden Karolinska Inst Nobel Inst Neurophysiol Dept Neurosci S-17177 Stockholm Sweden

Locomotor burst generation is simulated using a full-scale network model of the unilateral excitatory interneuronal population. Earlier small-scale models predicted that a population of excitatory neurons would be sufficient to produce burst activity, and this has recently been experimentally confirmed. Here we simulate the hemicord activity induced under various experimental conditions, including pharmacological activation by NMDA and AMPA as well as electrical stimulation. The model network comprises a realistic number of cells and synaptic connectivity patterns. Using similar distributions of cellular and synaptic parameters, as have been estimated experimentally, a large variation in dynamic characteristics like firing rates, burst, and cycle durations were seen in single cells. On the network level an overall rhythm was generated because the synaptic interactions cause partial synchronization within the population. This network rhythm not only emerged despite the distributed cellular parameters but relied on this variability, in particular, in reproducing variations of the activity during the cycle and showing recruitment in interneuronal populations. A slow rhythm (0.4-2 Hz) can be induced by tonic activation of NMDA-sensitive channels, which are voltage dependent and generate depolarizing plateaus. The rhythm emerges through a synchronization of bursts of the individual neurons. A fast rhythm (4-12 Hz), induced by AMPA, relies on spike synchronization within the population, and each burst is composed of single spikes produced by different neurons. The dynamic range of the fast rhythm is limited by the ability of the network to synchronize oscillations and depends on the strength of synaptic connections and the duration of the slow after hyperpolarization. The model network also produces prolonged bouts of rhythmic activity in response to brief electrical activations, as seen experimentally. The mutual excitation can sustain long-lasting activity for a realist

关键词： LAMPREY SPINAL-CORD AMINO-ACID RECEPTORS INTERSEGMENTAL PHASE-LAG computer-based model RHYTHM GENERATION XENOPUS-EMBRYOS RETICULOSPINAL NEURONS REALISTICSIMULATIONS FICTIVE LOCOMOTION NEURAL NETWORKS

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A GENERALIZED NEURONAL ACTIVATION FUNCTION DERIVED FROM ION-CHANNEL CHARACTERISTICS

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NETWORK-COMPUTATION IN NEURAL SYSTEMS 1995年第3期6卷 389-401页

作者： CARTLING, B Department of Theoretical Physics The Royal Institute of Technology S-100 44 Stockholm Sweden

An abstract model neuron, simple enough to be used in analytical studies of neural networks, is defined. It incorporates neuronal adaptation, i.e. the coupling between neuronal activity and excitability, which can control the complexity of neural network dynamics. A generalized neuronal activation function is defined as the output activity, i.e. the firing rate of action potentials, as a function of an input and an excitability variable. For a biological neuron, the intracellular concentration of Ca ions is shown to be a useful excitability variable. The principal features of the generalized activation function are derived by means of a multicompartment model neuron with ionic currents described by Hodgkin-Huxley-type equations. As a relevant neuron type for investigations of cortical associative memory, a neocortical pyramidal cell of the regularly-spiking type is selected. An approximate analytical consideration suggests a simple form of independent variable of the generalized activation function. The complete numerical treatment verifies this form and displays a threshold character of the activation function. The derivation thereby provides an interpretation of dynamic threshold models of neuronal adaptation in terms of ionic mechanisms. The threshold with respect to the input has well-defined dynamics directly given by the intracellular Ca dynamics. A comparison of the response of the Hodgkin-Huxley-type and reduced-model neurons to a varying input variable indicates that the reduced model is a useful approximation even for the detailed behaviour of the firing rate. The generalized activation function also accounts for the dependence on neuromodulation via an adaptability parameter. An abstract model neural network of units thus defined has the capacity to describe complex network dynamics and the simplicity to allow elucidation of mechanisms and applications to large-scale systems.

关键词： computer-based model Neural networks Associative memory Realistic simulations Hippocampal-neurons Olfactory cortex Modulation Receptors Conductances Excitation Olfactory Cortex Associative memory Action Potentials Activation Neural network Conductance computer based modeling Excitability Receptor Excitation Neurons realistic simulation

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

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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

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Three-dimensional sensitivity assessment of thoracic aortic aneurysm wall stress: a probabilistic finite-element study

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EUROPEAN JOURNAL OF CARDIO-THORACIC SURGERY 2014年第3期45卷 467-475页

作者： Celi, Simona Berti, Sergio Heart Hosp G Pasquinucci Scuola Super St Anna Massa Italy Heart Hosp G Pasquinucci CNR Reg Toscana Fdn G Monasterio Dept Adult Cardiol Massa Italy

OBJECTIVES: In clinical practice, maximum diameter is used as a criterion to estimate aneurysm-rupture risk;however, it is only a general indicator and its value becomes difficult to estimate in the thoracic segment. Improved understanding of aortic aneurysm complexity and biomechanics is needed to achieve advancements in surgical repair techniques. The objective of this study was to determine the maximum wall stress by using imaging-derived data and a specific probabilistic design integrated into finite element (FE) analysis. METHODS: Computed tomography images of thoracic aortic aneurysms from our database were analysed and the main morphological features were identified by means of a specific automatic routine. Morphological data were used to develop an idealized finite element library of thoracic aortic arch models. Sensitivity analyses were performed by using the geometrical parameters as input variables for a statistical wall stress assessment. Numerical results were compared with those obtained from deterministic analysis on patient-specific three-dimensional reconstructions. RESULTS: The results showed that in small aneurysms, wall stress values similar to those of large aneurysms can be obtained if a significant eccentricity is achieved. In small aneurysms, the peak stress is primarily affected by the eccentricity of the bulge [correlation coefficient (CC) = 0.86], while for diameters in the range of 50-60 mm, the CC is 0.43 for the eccentricity and 0.72 for the maximum diameter. CONCLUSIONS: The stress distribution in small aneurysms may contribute to the pathogenesis of aortic rupture and dissections. Our method can provide a novel and efficient procedure for generating computational models to estimate the wall stress in a comparative multivariate manner.

关键词： Thoracic aorta Aneurysm Biomechanics Imaging computer-based model

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

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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

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

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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

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Virtual Electrophysiological Study in a 3-Dimensional Cardiac Magnetic Resonance Imaging model of Porcine Myocardial Infarction

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JOURNAL OF THE AMERICAN COLLEGE OF CARDIOLOGY 2012年第5期60卷 423-430页

作者： Ng, Jason Jacobson, Jason T. Ng, Justin K. Gordon, David Lee, Daniel C. Carr, James C. Goldberger, Jeffrey J. Northwestern Univ Div Cardiac Electrophysiol Feinberg Sch Med Bluhm Cardiovasc Inst Chicago IL 60611 USA Northwestern Univ Div Cardiol Feinberg Sch Med Chicago IL 60611 USA Northwestern Univ Dept Radiol Feinberg Sch Med Chicago IL 60611 USA

Objectives This study sought to test the hypothesis that "virtual" electrophysiological studies (EPS) on an anatomic platform generated by 3-dimensional magnetic resonance imaging reconstruction of the left ventricle can reproduce the reentrant circuits of induced ventricular tachycardia (VT) in a porcine model of myocardial infarction. Background Delayed-enhancement magnetic resonance imaging has been used to characterize myocardial infarction and "gray zones," which are thought to reflect heterogeneous regions of viable and nonviable myocytes. Methods Myocardial infarction by coronary artery occlusion was induced in 8 pigs. After a recovery period, 3-dimensional cardiac magnetic resonance images were obtained from each pig in vivo. Normal areas, gray zones, and infarct cores were classified based on voxel intensity. In the computer model, gray zones were assigned slower conduction and longer action potential durations than those for normal myocardium. Virtual EPS was performed and compared with results of actual in vivo programmed stimulation and noncontact mapping. Results The left ventricular volumes ranged from 97.8 to 166.2 cm(3), with 4.9% to 17.5% of voxels classified as infarct zones. Six of the 7 pigs in which VT developed during actual EPS were also inducible with virtual EPS. Four of the 6 pigs that had simulated VT had reentrant circuits that approximated the circuits seen with noncontact mapping, whereas the remaining 2 had similar circuits but propagating in opposite directions. Conclusions This initial study demonstrates the feasibility of applying a mathematical model to magnetic resonance imaging reconstructions of the left ventricle to predict VT circuits. Virtual EPS may be helpful to plan catheter ablation strategies or to identify patients who are at risk of future episodes of VT. (J Am Coll Cardiol 2012;60:423-30) (C) 2012 by the American College of Cardiology Foundation

关键词： computer-based model magnetic resonance imaging myocardial infarction ventricular tachycardia 3D 3-dimensional EPS electrophysiological study LV left ventricle MI myocardial infarction MRI magnetic resonance imaging SCD sudden cardiac death VEPS virtual electrophysiological study VT ventricular tachycardia

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