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PubMedDate not supplied

The effects of wheelchair-seating stiffness and energy absorption on occupant frontal impact kinematics and submarining risk using computer simulation.

Many wheelchair users must travel in motor vehicles while seated in their wheelchairs. The safety features of seat assemblies are key to motor vehicle occupant crash protection. Seating system properties such as strength, stiffness, and energy absorbance have been shown to have significant influence on risk of submarining. This study investigated the effects of wheelchair seat stiffness and energy absorption properties on occupant risk of submarining during a frontal motor vehicle 20 g/30 mph impact using a validated computer crash simulation model. The results indicate that wheelchair-seating stiffness and energy absorption characteristics influence occupant kinematics associated with the risk of submarining. Softer seat surfaces and relatively high energy absorption/permanent deformation were found to produce pelvis excursion trajectories associated with increased submarining risk. Findings also suggest that the current American National Standards Institute/Rehabilitation Engineering and Assistive Technology Society of North America (ANSI/RESNA) WC-19 seating integrity may not adequately assess submarining risk.

Accidents, Traffic↗
PubMed1988

Effects of continuous low dose-rate irradiation: computer simulations.

The effects of continuous low dose-rate irradiation are studied with a computer model that incorporates cell kinetics and the accumulation and repair of radiation damage. This theoretical approach independently explores the effects on survival curves of a phase block, inherited damage and proliferation by dying cells. The computer model is a Monte Carlo simulation which follows the evolution in time of the family trees of a growing cell population under continuous irradiation. The model uses as input the measured phase-specific survival curves for acute exposures and the cell kinetic parameters to generate survival curves for continuous low dose-rate irradiations. Cell survival curves for Chinese hamster lung cells (V79) for dose rates ranging from 15 to 500 cGy/h have been generated using various model assumptions. The model shows that for these cells a G2 block will maximize cell killing for an optimum dose rate near 75 cGy/h. The effect on survival curves of inherited damage, as well as that of the proliferation by dying cells, is shown to increase monotonically with decreasing dose rates, and to be quite large at low dose rates.

Animals↗
PubMed1972

Computer simulation of fluorescence depolarization due to brownian motion.

A computer program has been written to simulate the Brownian motion of rigid fluorescent molecules. The time dependence of the fluorescence polarization anisotropy as generated by this simulation is in agreement with that predicted by the recent theoretical treatment of Belford, Belford, and Weber (Proc. Nat. Acad. Sci. USA (1972) 69, 1392-1393). The program thus serves as a verification of their equation. It is being generalized to cover the case of nonrigid molecules.

Journal Article↗
PubMed1997

A beginner's guide to computer simulation of voltage-gated ion conductances.

This article provides a simple introduction to the simulation of voltage-dependent ion conductances in both macroscopic and single-channel modes. Only Markovian (time-independent) systems are considered. The programmes listed are written in Microsoft QBasic or QuickBASIC but versions in other languages are available. The Hodgkin-Huxley Na+ current is used as a starting system for which an explicit macroscopic solution may be obtained and compared with the results of numerical simulations employing 4th order Runge-Kutta integration. Non-Hodgkin-Huxley behaviour such as voltage-independent inactivation and double exponential current decay are discussed and simulated. A stochastic programme is used to simulate single channel behaviour. The problems and methodologies involved in fitting experimental data using complex kinetic schemes are briefly discussed, as are alternative sources of simulation software.

Animals↗
PubMed2002

[The computer simulation of magnetic resonance imaging].

Based on the Bloch equation, we can describe the working principle of the magnetic resonance imaging system with mathematic model, the inputs are the three templates of appropriate rho, T1 and T2. In this paper, the simulation process is illustrated by spin echo examples of the signal exciting, phase coding, reading-out and image reconstruction. The satisfactory results show that this method can be widely used in simulation researches.

Algorithms↗
PubMed1990

Computer simulation of ciprofloxacin pharmacokinetics in patients on CAPD.

Continuous ambulatory peritoneal dialysis (CAPD) has become an accepted alternative to chronic hemodialysis in the treatment of end-stage renal disease. The method utilizes the diffusion of drugs from the blood through the peritoneal membrane to the peritoneal cavity if administered intravenously (IV) and perorally (PO) and in the opposite direction if applied intraperitoneally (IP). The present work uses an open, two-compartment pharmacokinetic model reversibly linked with the compartment representing the peritoneal cavity and an analog-hybrid computer to simulate drug levels in sampled and unsampled compartments under conditions of various routes of administration (IV, IP and sequential IV, IP and PO) and different clinical status (presence and absence of peritonitis). The drug chosen for simulation was ciprofloxacin (CIP), a new synthetic antibacterial agent of the 4-quinolone group. Eight patients were included in the study, and CIP concentrations in plasma and dialysate were obtained by HPLC analysis to assess the reliability of the model and the efficiency of the sequential dosing scheme. CIP plasma and dialysate levels were adequate for the majority of microbes causing CAPD peritonitis. The proposed regimen was efficient in 85% of cases.

Administration, Oral↗
PubMed1994

A modeling and computer simulation approach to determine optimal lower extremity joint angular velocities based on a criterion to maximize individual muscle power.

A computer program was developed in conjunction with a musculoskeletal modeling scheme to determine lower extremity joint angular velocity profiles which allow specific muscles, if activated tetanically, to generate their greatest power. As input the program requires subject anthropometric and joint configuration data. Muscle-tendon (MT) attachment location data and a straight line MT model are used to calculate MT lengths for each joint configuration. The shortening velocity which allows an active muscle to generate its greatest power is calculated based on muscle architecture and a relationship between power and shortening velocity. A finite difference technique is used to calculate the time between sequential joint configurations which will produce the optimal muscle shortening velocity. This time is then used to calculate optimal joint angular velocities for each muscle and and for each joint configuration. The utility of this program is demonstrated by calculating optimal joint angular velocities for fifteen muscles and comparing calculated knee extension velocities with experimental results cited in the literature.

Anthropometry↗
PubMed2005

Pudendal nerve stretch during vaginal birth: a 3D computer simulation.

OBJECTIVE: The purpose of this study was to determine the increase in pudendal nerve branch lengths using a 3D computer model of vaginal delivery. STUDY DESIGN: The main inferior rectal and perineal branches of the pudendal nerve were dissected in 12 hemi-pelves from 6 adult female cadavers. Their 3D courses were digitized in the 4 specimens with the most characteristic nerve branching pattern, and the data were imported into a published 3D computer model of the pelvic floor. Each nerve branch was then represented by a stretchable cord with a fixation point at the ischial spine. The length change in each branch was then quantified as the fetal head descended through the pelvic floor. The maximum nerve strains ([final length minus original length/original length] x 100) were calculated for 5 degrees of perineal descent: reference descent from the literature, 1.25 cm and 2.5 cm caudal and cephalad. The effect of alternative fixation points on resultant nerve strain was also studied. RESULTS: The inferior rectal branch exhibited the maximum strain, 35%, and this strain varied by 15% from the scenario with the least perineal descent to that with the most perineal descent. The strain in the perineal nerve branch innervating the anal sphincter reached 33%, while the branches innervating the posterior labia and urethral sphincter reached values of 15% and 13%, respectively. The more proximal the nerve fixation point, the greater the nerve strain. CONCLUSION: During the second stage: (1) nerves innervating the anal sphincter are stretched beyond the 15% strain threshold known to cause permanent damage in appendicular peripheral nerve, and (2) the degree of perineal descent is shown to influence pudendal nerve strain.

Aged↗
PubMed1997

Computer simulation study on the conversion of spirolactone to enones over H-Y zeolite.

We report here the results of computer modeling studies and quantum chemical calculations on the spirolactone-to-enone conversion reaction over the zeolite catalysts, especially H-Y zeolite. We studied the adsorption mode of the molecules inside the supercage of H-Y and the mechanism of electron transfer between organic molecules and the framework of zeolite H-Y by density functional theory (DFT) calculations. Because the organic molecules considered in the present study are less symmetrical we docked the molecule inside the supercage of H-Y and energy minimization was then applied to these docked structures to yield representative low-energy binding sites for the molecules within the host structure. The interaction energy results show that the major interaction is between the methylene hydrogen of the molecule and the oxygen of the framework. The molecular electrostatic potential maps show that the ketonic oxygen of the reactant molecules abstract proton from Brönsted acid site. Thus the mechanism proposed by DFT calculation matches well with the experimental observations.

Computer Simulation↗
PubMed1992

Computer simulation of human tympanic membrane.

Because of the difficulties in studying the mechanical properties of the human tympanic membrane in situ, structural data from the cadaveric tympanic membrane samples is used for simulation of the surface structure of the tympanic membrane with the help of a computer. The hitherto poorly understood contour of the tympanic membrane is available for the development of a tympanic membrane and middle ear model.

Computer Simulation↗
PubMed2005

Computational simulation of the blood separation process.

The aim of this work is to construct a computational fluid dynamics model capable of simulating the quasitransient process of apheresis. To this end a Lagrangian-Eulerian model has been developed which tracks the blood particles within a delineated two-dimensional flow domain. Within the Eulerian method, the fluid flow conservation equations within the separator are solved. Taking the calculated values of the flow field and using a Lagrangian method, the displacement of the blood particles is calculated. Thus, the local blood density within the separator at a given time step is known. Subsequently, the flow field in the separator is recalculated. This process continues until a quasisteady behavior is reached. The simulations show good agreement with experimental results. They shows a complete separation of plasma and red blood cells, as well as nearly complete separation of red blood cells and platelets. The white blood cells build clusters in the low concentrate cell bed.

Animals↗