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At least 1,207 records · Page 67Linked to original sources
PubMed1986

Computer simulation of single-file transport.

A stochastic model of single-file transport was developed as the Markov process in continuous time technique. The model was constructed using an EC-1060 computer. Unidirectional fluxes were investigated and populations of channels were correlated with flux fluctuations. The profiles of channel populations were shown to have nonlinear shapes even with the transport of nonelectrolyte (the classical diffusion approach gives linear profiles). The relationship between the paired correlation function F(AB) and the concentration of transported particles was examined. The F(AB) profile was shown to become flattened (or exponential for asymmetrical cases) at high concentrations. The concentration dependence jA/jA0 ratio were analyzed, where jA is a single-file unidirectional flux, jA0 is unidirectional flux for the case of free diffusion. An interesting "stack" phenomenon was observed for abnormal time correlations of single-file fluxes.

Biological Transport↗
PubMed1989

Evaluation of stopping rules for audiological ascending test procedures using computer simulations.

Stopping rules for ascending audiological test procedures were evaluated by Monte Carlo simulation. The stopping rules differed in the minimum number of responses required at a level, whether these responses occurred on half or a majority of the ascending series, and whether all or only the most recent ascending series were considered. For all procedures, shallow psychometric function slopes yielded estimated thresholds closer to the level giving 50% detection than did steeper slopes, which yielded estimated thresholds roughly 2.5 dB above the level corresponding to 50% on the psychometric function. Shallow slopes also resulted in decreased reliability across threshold measurements, an increased number of trials required for threshold estimates, and a higher proportion of measurements that had to be repeated. Stopping rules using a two-response criterion were faster than those using a three-response criterion, with only a small decrease in reliability. Among stopping rules using the same number of responses for criterion, differences were seen primarily in efficiency for shallow slopes, particularly for procedures using a three-response rather than a two-response criterion for stopping. Results from these simulations should be useful to standards groups.

Audiometry↗
PubMedDate not supplied

Computer simulation of fluid resuscitation in trauma. First pragmatic validation in thermal injury.

A comprehensive pathophysiologic model has been designed to describe the fluid shifts and hemodynamics in connection with fluid therapy for patients who have had trauma. The model is used to simulate treatment of a patient with burn injury, and these results are compared with measured physiologic and biochemical variables. Various formulas for resuscitation of patients with thermal injuries are also simulated to illustrate the potential use of the "patient simulator" for designing fluid resuscitation programs.

Burns↗
PubMed1997

Computational simulation of turbulent signal loss in 2D time-of-flight magnetic resonance angiograms.

Time-of-flight magnetic resonance (MR) angiography is currently limited in the evaluation of arterial stenoses by flow-induced signal loss. This signal loss has been attributed to phase dispersion and to phase misregistration. We have developed a fluid mechanics model of 2D time-of-flight MR angiograms to study the amount of signal loss caused by random turbulence. The simulations were created by stochastic analysis of particle pathlines determined by computational fluid dynamics for turbulent flow. The images obtained by the model compare well to actual MR images of flow in stenoses. By selectively removing the random turbulent motion in the simulation, it can be seen that random phase dispersion is the dominant mechanism of signal loss. Phase misregistration and mean flow phase dispersion act as secondary effects. The MR simulation model recreates accurately the variation of signal loss over a range of echo times. The model can be used further to explore and design new pulse sequences. For example, the current study showed that high slew rate gradient waveforms can significantly reduce poststenotic signal loss. In conclusion, computational modeling of MR angiography can be a useful approach for the analysis of MRA signal loss and the design of improved pulse sequences.

Blood Flow Velocity↗
PubMed1994

Cardiovascular physiology teaching: computer simulations vs. animal demonstrations.

The roots of physiology lie in laboratory observation, and physiology courses continue to rely on laboratory observation to provide students with practical information to correlate with their developing base of conceptual knowledge. To this end, animal laboratories provide a functioning example of interactions among organ systems and a source of data for student analysis. However, there are continuing objections to using animals for teaching, and animal labs are costly in time and effort. As an alternative laboratory tool, computer software can simulate the operation of multiple organ systems: responses to interventions illustrate intrinsic organ behavior and integrated systems physiology. Advantages of software over animal studies include alteration of variables that are not easily changed in vivo, repeated interventions, and cost-effective hands-on student access. Nevertheless, simulations miss intangible aspects of experimental physiology, and results depend critically on the assumptions of the model. We used both computer and animal demonstrations in teaching cardiovascular physiology to first-year medical students. The students rated both highly, but the computer-based session received a higher rating. We believe that both forms of teaching have educational merit. At the introductory level, the computer appears to provide an effective alternative.

Animals↗
PubMed1996

The Frank Stinchfield Award. 3-Dimensional sliding/contact computational simulation of total hip wear.

Polyethylene wear in total hip replacements is a complex, multifactorial process. A tribologically grounded finite element formulation was developed to make quantitative estimates of polyethylene wear in total hip arthroplasty, incorporating the combined influences of contact stress, sliding distance, and a surface specific wear coefficient. For loading and sliding distance inputs taken directly from human gait data, the computational model showed a strong direct proportionality between femoral head size and volumetric wear rate. Other factors being equal, reducing the thickness of the polyethylene liner led to increases in the computed wear rates, but the effect was far less pronounced than the strong increases in wear rate that accompanied head size increases. Compared with human gait inputs, the load and sliding distance inputs for a 23 degrees biaxial rocking hip simulator led to computed wear rates that were 1.7 times as large, and in which the direction of wear was near the cup apex rather than within the posterosuperolateral quadrant. In general, the finite element model's results emphasize the importance of articulation kinematics, especially sliding distance, in the complex process of polyethylene wear in total hip arthroplasty.

Computer Simulation↗
PubMed1989

[Computer simulation of the stable climate on the PC in veterinary practice].

The wide distribution of personal computers allows the application of programs which enable veterinary surgeons to assist in the management of live stock. A simulation model is made for the field of indoor climates of stables which makes a full-year calculation of temperature and humidity of the indoor climate and the quality of the air in stables. The calculation is based on a steady-state balance model of energy (heat and humidity) and matter. Using the example of a pig fattening sty, all the necessary system parameters are stated that are needed to totally present the model. The results of the simulation are then interpreted. Furthermore the assertions and conclusions will be shown which result thereby.

Animals↗
PubMed1984

Computer simulation to predict patient responses to alterations in the ventilation regime.

We have developed a technique for simulating artificially ventilated patients using a computer model of the respiratory system and have investigated its ability to predict the patient's response to alterations in the ventilation regime. The majority of those studied were in a stable condition following cardiac surgery. Predictions for PaO2 showed a reasonable correlation with measured values (r = 0.94), although individual predictions could differ appreciably (SEE = +/- 17.3 mmHg). Predictions for PaCO2 correlated less well (r = 0.89, SEE = +/- 2.0 mmHg) and there was a consistent tendency to overestimate this variable. The least accurate predictions were those for PvO2 (r = 0.61, SEE = +/- 3.8 mmHg). Errors in prediction were attributable to deficiencies in the model (most importantly the three-compartment lung and the modelling of CO2 production, storage and excretion), compounded by unpredictable alterations in the patient's physiology (mainly Vo2, Vco2 and Qt). However, allowing for accepted clinical variability and routine measurement accuracy, the predictions are generally reasonable. This suggests that, with some further modifications, computer modelling of this, and other, systems may prove to be a clinically and educationally useful technique.

Adult↗