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  • 1
    Electronic Resource
    Electronic Resource
    Algorithms, Visualization, and Mental Models: High School Students' Interactions with a Relative Motion Simulation (2000)
    Springer
    Journal of science education and technology 9 (2000), S. 311-325 
    Details
    ISSN: 1573-1839
    Keywords: Computer simulation ; visualization ; imagery ; conceptual change ; physics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Natural Sciences in General , Technology
    Notes: Abstract Galileo's contemporaries as well as today's students have difficulty understanding relative motion. We hypothesize that the construction of visual models, resolution of these visual models with numeric models, and, in many cases, rejection of commitments such as the belief in one “true” velocity, are necessary for students to form integrated mental models of relative motion events. To investigate students' relative motion problem solving, high school science students were videotaped in classroom and laboratory settings as they performed collaborative predict-observe-explain activities with relative motion computer simulations. Half of the students interacted with simulations that provided animated feedback; the other half received numeric feedback. Learning, as measured by a diagnostic test, occurred following both conditions. There is evidence that many numeric condition students used faulty mechanical algorithms to solve problems, while many animation condition students used mental imagery to solve problems. In this paper, interactions in which student involvement was visual model based will be contrasted with interactions in which involvement was algorithm based. Implications for pedagogy and educational uses of computer simulations will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009480425377
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  • 2
    Electronic Resource
    Electronic Resource
    Model Study of Vector-Loop Morphology During Electrical Mapping of Microscopic Conduction in Cardiac Tissue (2000)
    Springer
    Annals of biomedical engineering 28 (2000), S. 1244-1252 
    Details
    ISSN: 1573-9686
    Keywords: Potential gradient ; Volume conductor ; Local conduction velocity ; Four-element electrode array ; Unipolar–bipolar ; Continuous conduction ; Computer simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The large variety in loop morphology of potential differences recorded at the cardiac surface has been generally attributed to structural discontinuities of the tissue. The aim of this work was to examine if the diversity of vector loops of the electric field E found experimentally may also arise during continuous anisotrope conduction. For this purpose a monodomain computer model was used, consisting of a two-dimensional sheet of excitable tissue surrounded with an unbounded volume conductor. Close to the tissue surface our computations predicted a narrow biphasic course of Φe with peak-to-peak separation of less than 400 μm. We examined how accurately E could be reconstructed from measurements recorded with four-element electrode arrays and how activation sequence, interelectrode spacing, and probe orientation affects the results. We found “closed” vector loops of E in planar, and at the apex of elliptical wave fronts, whereas outside of these regions vector loops were “open.” Varying probe orientation and size resulted in substantial changes of vector-loop morphology. We concluded that close to the cardiac current sources accurate measurement of E would require interelectrode distances of less than 100 μm. © 2000 Biomedical Engineering Society. PAC00: 8719Nn, 8719Hh
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.1320841
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  • 3
    Electronic Resource
    Electronic Resource
    Ectopic Activity in Ventricular Cells Induced by Early Afterdepolarizations Developed in Purkinje Cells (2000)
    Springer
    Annals of biomedical engineering 28 (2000), S. 1343-1351 
    Details
    ISSN: 1573-9686
    Keywords: EAD propagation ; Purkinje-ventricular junction ; Computer simulation ; Two-dimensional model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The development of early afterdepolarizations (EADs) in Purkinje fibers and their propagation to ventricular muscle cells are studied by computer modeling. The Purkinje-ventricular system has been simulated by a two-dimensional model of a Purkinje fiber (PF) connected to a thin sheet of ventricular muscle tissue (VMT). EADs are induced in the PF by enhancing the fast second inward current, i Ca,f and blocking the delayed K+ current, i K while the VMT is kept under physiological conditions. Different phenomena are observed depending on the EAD conditions applied. For 70% i K blockade and i Ca,f enhancement greater than 60%, a single phase 3 EAD developed in the PF propagates to the VMT generating an ectopic beat. For 80% i K blockade and i Ca,f enhancement in the range from 0% to 70%, multiple ectopic beats appear in the VMT. However, for i K blockades over 80%, action potentials in PF cells do not repolarize and the ectopic activity in the VMT disappears. In our simulations, the ionic mechanism underlying phase 3 EAD development is the reactivation of the fast sodium current in the PF. Our results demonstrate that there exists a critical range of EAD conditions that favor the development of EADs in the PF and their propagation to the VMT as ectopic activity. This phenomenon could underlie the genesis of some triggered arrhythmias. © 2000 Biomedical Engineering Society. PAC00: 8719Nn, 8716Uv, 8719Hh, 8719Ff, 8717Nn
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.1326032
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of the Electric Axis of Stimulation on the Induced Transmembrane Potentials in Ellipsoidal Bidomain Heart (2000)
    Springer
    Annals of biomedical engineering 28 (2000), S. 244-252 
    Details
    ISSN: 1573-9686
    Keywords: Anisotropy ; Cardiac ; Computer simulation ; Defibrillation ; Fiber curvature ; Fiber rotation ; Finite element method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract This theoretical study was provoked by and designed to interpret, complement and extend the implications of recent experimental observations by Wikswo and Lin (PACE, 21:940, 1998) on the epicardial surface of rabbit hearts. Using a macroscopic bidomain representation of the cardiac structure and the finite element method, we model the response of the heart to uniform electric fields applied under different angles. To overcome intra- and interspecies differences in the geometric and structural characteristics of the cardiac muscle, the analysis is conducted for an idealized ellipsoidal heart. Although idealized, this heart model incorporates important structural features, i.e., fiber curvature, transmural fiber rotation, and unequal anisotropy for the intra- and extracellular domains. This study shows that regions of maximum polarization of opposite sign may develop along an axis, significantly deviating from the axis of the applied electric field. The polarization evoked inside the ventricular wall seems to be a major contributor to this phenomenon. Nonperiodic structural inhomogeneities on multicellular level (endocardial “trabeculation” in our model) result in local unaligned polarization dipoles weakening the magnitude of the global polarization dipole and reducing its deviation from the axis of stimulation. Our results might be helpful in improving current understanding of defibrillation mechanisms. © 2000 Biomedical Engineering Society. PAC00: 8719Nn, 8719Hh, 8750Rr
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.264
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  • 5
    Electronic Resource
    Electronic Resource
    Staged Growth of Optimized Arterial Model Trees (2000)
    Springer
    Annals of biomedical engineering 28 (2000), S. 495-511 
    Details
    ISSN: 1573-9686
    Keywords: Heart ; Epicardial and endocardial differences ; Vascular growth model ; Mathematical model ; Computer simulation ; Constrained constructive optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract There is a marked difference in the structure of the arterial tree between epi- and endocardial layers of the human heart. To model these structural variations, we developed an extension to the computational method of constrained constructive optimization (CCO). Within the framework of CCO, a model tree is represented as a dichotomously branching network of straight cylindrical tubes, with flow conditions governed by Poiseuille's law. The tree is grown by successively adding new terminal segments from randomly selected points within the perfusion volume while optimizing the geometric location and topological site of each new connection with respect to minimum intravascular volume. The proposed method of “staged growth” guides the generation of new terminal sites by means of an additional time-dependent boundary condition, thereby inducing a sequence of domains of vascular growth within the given perfusion volume. Model trees generated in this way are very similar to reality in their visual appearance and predict diameter ratios of parent and daughter segments, the distribution of symmetry, the transmural distribution of flow, the volume of large arteries, as well as the ratio of small arterial volume in subendocardial and subepicardial layers in good agreement with experimental data. From this study we conclude that the method of CCO combined with staged growth reproduces many characteristics of the different arterial branching patterns in the subendocardium and the subepicardium, which could not be obtained by applying the principle of minimum volume alone. © 2000 Biomedical Engineering Society. PAC00: 8719Uv, 8719Hh, 4760+i
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.290
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  • 6
    Electronic Resource
    Electronic Resource
    ARTMEM—An interactive graphical program simulating membrane potential measurements across artificial membranes (1994)
    Springer
    Annals of biomedical engineering 22 (1994), S. 218-225 
    Details
    ISSN: 1573-9686
    Keywords: Physiology teaching ; Computer simulation ; Membrane potentials ; Computer programs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract This paper describes ARTMEM, an interactive graphical simulation program, and its use for teaching students the concept of membrane potentials and the measurement of electrical potentials across an ion-selective membrane. The program, written in Borland C++, and specifically designed for IBM-PC-compatible equipment, can also run on fast Macintosh computers using SoftPC emulation software. It demonstrates how an ion-selective membrane separating two different salt solutions automaticallygenerates a potential across the membrane, as well as how such electrical potentials can be measured simply and the underlying permeability ratio determined. The program was developed to replace a previous experiment with actual artificial resin membranes; virtually every feature of the experiment has been simulated (e.g., unstirred-layer effects, solutionmixing contamination, liquid junction potential effects). In addition, a number of these features and the procedure for data fitting are more clearly demonstrated using the computer simulation. The efficacy of such a simulation is discussed in comparison with the real experiment and other types of simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02390380
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  • 7
    Electronic Resource
    Electronic Resource
    Simple and accurate way for estimating total and segmental arterial compliance: The pulse pressure method (1994)
    Springer
    Annals of biomedical engineering 22 (1994), S. 392-397 
    Details
    ISSN: 1573-9686
    Keywords: Windkessel model ; Computer simulation ; Nonlinear arterial system ; Input impedance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract We derived and tested a new, simple, and accurate method to estimate the compliance of the entire arterial tree and parts thereof. The method requires the measurements of pressure and flow and is based on fitting the pulse pressure (systolic minus diastolic pressure) predicted by the two-element windkessel model to the measured pulse pressure. We show that the two-element windkessel model accurately describes the modulus of the input impedance at low harmonics (0–4th) of the heart rate so that the gross features of the arterial pressure wave, including pulse pressure, are accounted for. The method was tested using a distributed nonlinear model of the human systemic arterial tree. Pressure and flow were calculated in the ascending aorta, thoracic aorta, common carotid, and iliac artery. In a linear version of the systemic model the estimated compliance was within 1% of the compliance at the first three locations. In the iliac artery an error of 7% was found. In a nonlinear version, we compared the estimates of compliance with the average compliance over the cardiac cycle and the compliance at the mean working pressure. At the first three locations we found the estimated and “actual” compliance to be within 12% of each other. In the iliac artery the error was larger. We also investigated an increase and decrease in heart rate, a decrease in wall elasticity and exercise conditions. In all cases the estimated total arterial compliance was within 10% of mean compliance. Thus, the errors result mainly from the nonlinearity of the arterial system. Segmental compliance can be obtained by subtraction of compliance determined at two locations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368245
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  • 8
    Electronic Resource
    Electronic Resource
    A study of optimal configuration and control of a multi-chamber balloon for intraaortic balloon pumping (1994)
    Springer
    Annals of biomedical engineering 22 (1994), S. 524-531 
    Details
    ISSN: 1573-9686
    Keywords: Mathematical modeling ; Cardiovascular system ; Computer simulation ; Cardiac assist device
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Balloon configuration and control scheme are important for the optimization of assistance of the failing heart with an intraaortic balloon pumping device. In this work, the configuration of a multi-chamber balloon and control schemes have been investigated by using a hemodynamic model and computer simulation methods. Following the simulation study, physical testing and animal experiments were performed to demonstrate the simulation results. Results show that the optimal configuration and controlled multi-chamber balloon can provide better assistance to the failing heart. Based on the simulation and experimental results, it was found that the shape of the rear chamber of a multi-chamber balloon is critical. The optimal control scheme was to inflate the rear chamber first and deflate it last.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02367088
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  • 9
    Electronic Resource
    Electronic Resource
    “Thermal layer” effect in MHD: Interaction of a parallel shock with a layer of decreased density (1993)
    Springer
    Shock waves 3 (1993), S. 73-78 
    Details
    ISSN: 1432-2153
    Keywords: Computer simulation ; MHD ; “Thermal layer” effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Interaction of a parallel fast MHD shock with a layer of decreased density is discussed using ideal MHD approach. This is an extrapolation of gas dynamic “thermal layer” effect on ideal MHD. Computer simulations show that a magnetic field of a moderate intensity (β ∼ 1) may change the character of the flow for intermediate Mach numbers (M ≤ 5) and a new “raking” regime may occur which is not observed in the absence of a magnetic field. Self similar precursor analogous to that in gas dynamics may develop in the case of highM and low density in the layer but magnetic forces essentially decrease its growth rate. This problem appears in connection with cosmical shock propagation where planetary magnetic tails play the role of the “thermal layer”, and it may also be observed in the laboratory when the shock is strong enough to heat the walls ahead of it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02115886
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  • 10
    Electronic Resource
    Electronic Resource
    Computer simulation of geometry and hemodynamics of canine pulmonary arteries (1993)
    Springer
    Annals of biomedical engineering 21 (1993), S. 107-115 
    Details
    ISSN: 1573-9686
    Keywords: Computer simulation ; Pulmonary arteries ; Branching patterns ; Hemodynamics studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Assuming that along the pulmonary arteries, mathematical expectations of branching are equal to matrix (E i,j; i: parent branch class, j: daughter branch class number), we made computer drafts of patterns of pulmonary arterial branching trees from the published data of canine pulmonary arterial casts with the “Monte Carlo methods” by FORTRAN, calculating from these data, the numbers of branches, size and resistance of the trees. We also analyzed blood flow distribution in a pulmonary branch according to the pathlength from the entrance of the tree. The graphics of the trees were similar to the original arterial casts, and numbers of the branches were nearly the same as the previous reported values. Calculated resistance was reasonable. The rate of blood flow per unit vessel in the short pathlength group was calculated as 1.5 times that of the long pathlength group of the same diameter. We believe that our method of describing the branching pattern matrix (E i,j) provides a reasonable simulation of complex branching patterns such as pulmonary arteries and a useful means to analyze local hemodynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02367606
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  • 11
    Electronic Resource
    Electronic Resource
    A microcomputer oxygen control system for ventilatory therapy (1992)
    Springer
    Annals of biomedical engineering 20 (1992), S. 547-558 
    Details
    ISSN: 1573-9686
    Keywords: Feedback control ; Artificial ventilation ; Computer simulation ; Arterial oxygen saturation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A computer-based feedback system has been developed to adjust the concentration of oxygen in the inspired gas of a patient under artificial respiration. The system uses a proportional plus integral controller and feedback of arterial oxygen saturation to adjust the inspired oxygen fraction. The effectiveness of the controller has been tested using a dynamic, mathematical model of the human respiratory system. This relatively sophisticated model has been developed and examined in the past, and it has been shown that it can realistically describe the human respiratory system for a wide variety of test conditions. The performance of the oxygen control system has been evaluated using the simulation model. The response of the controller to different disturbances is always stable, with arterial pressure of oxygen returning to normal in less than 12 minutes. Some of the simulation results are presented to illustrate the dynamic behavior and robustness of the controller.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368173
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  • 12
    Electronic Resource
    Electronic Resource
    Temporal aggregate size distributions from simulation of platelet aggregation and disaggregation (1990)
    Springer
    Annals of biomedical engineering 18 (1990), S. 427-444 
    Details
    ISSN: 1573-9686
    Keywords: Computer simulation ; Platelet aggregation ; Platelet disaggregation ; Platelet size distributions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A modification of the Smoluchowski collision theory for platelet aggregation is proposed with additional kinetic terms to accommodate observed disaggregation behavior. This model, consisting of a set of coupled, nonlinear, first-order differential equations, approximates size distributions with time for normal human platelets in plasma after the addition of a stimulus. Parameters controlling the kinetics of the formation and breakup of aggregates are numerically investigated. The aggregation coefficient, predominant during the aggregation phase, is strongly dependent on both time and aggregating agent doses. For the disaggregation phase, the disaggregation rate constants are a function of aggregate size, with a time-dependent disaggregation coefficient. Numerical results generated by the model are compared with experimental volume-size distribution curves from the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02364158
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  • 13
    Electronic Resource
    Electronic Resource
    A compartmental model for oxygen transport in brain microcirculation (1989)
    Springer
    Annals of biomedical engineering 17 (1989), S. 13-38 
    Details
    ISSN: 1573-9686
    Keywords: Oxygen transport ; Microcirculation ; Cerebral circulation ; Carbon monoxide ; Mathematical model ; Computer simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A compartmental model is formulated for oxygen transport in the cerebrovascular bed of the brain. The model considers the arteriolar, capillary and venular vessels. The vascular bed is represented as a series of compartments on the basis of blood vessel diameter. The formulation takes into account such parameters as hematocrit, vascular diameter, blood viscosity, blood flow, metabolic rate, the nonlinear oxygen dissociation curve, arterial PO2, P50 (oxygen tension at 50% hemoglobin saturation with O2) and carbon monoxide concentration. The countercurrent diffusional exchange between paired arterioles and venules is incorporated into the model. The model predicts significant longitudinal PO2 gradients in the precapillary vessels. However, gradients of hemoglobin saturation with oxygen remain fairly small. The longitudinal PO2 gradients in the postcapillary vessels are found to be very small. The effect of the following variables on tissue PO2 is studied: blood flow, PO2 in the arterial blood, hematocrit, P50, concentration of carbon monoxide, metabolic rate, arterial diameter, and the number of perfused capillaries. The qualitative features of PO2 distrbution in the vascular network are not altered with moderate variation of these parameters. Finally, the various types of hypoxia, namely hypoxic, anemic and carbon monoxide hypoxia, are discussed in light of the above sensitivity analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02364271
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