SEARCH · Search PubMed

Results for “Computer Simulation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources

PubMed1992

Computer simulation of agglomeration in the Wurster process.

A simplified model for computer simulation of agglomeration in the Wurster coating process was constructed using droplet size distribution and the relation between the size of agglomerates and the number of primary particles composing them experimentally determined. Computer simulations were applied to the cases where a 2.5% aqueous solution of hydroxypropyl cellulose (containing sodium carboxymethyl cellulose of 10% on a dry basis) was sprayed on four kinds of sharply fractionized lactose powders between 32 and 75 microns. With cores larger than 53 microns, the agitation exerted on particles strongly suppressed the growth of agglomerates, but the fraction of produced agglomerates reached about 50%. The smallest droplet size that was contributable to agglomeration (critical droplet size) was estimated to be 37.1-49.0 microns, increasing with core size, and the weight fraction of droplets larger than this critical size was only 0.5-2.7%, decreasing with increase in core size. The production of even such a minor amount of coarse droplets could be responsible for significant agglomeration.

Chemistry, Pharmaceutical↗

PubMed2006

Computer simulations of ABC transporter components.

Current computer simulation techniques provide robust tools for studying the detailed structure and functional dynamics of proteins, as well as their interaction with each other and with other biomolecules. In this minireview, we provide an illustration of recent progress and future challenges in computer modeling by discussing computational studies of ATP-binding cassette (ABC) transporters. ABC transporters have multiple components that work in a well coordinated fashion to enable active transport across membranes. The mechanism by which members of this superfamily execute transport remains largely unknown. Molecular dynamics simulations initiated from high-resolution crystal structures of several ABC transporters have proven to be useful in the investigation of the nature of conformational coupling events that may drive transport. In addition, fruitful efforts have been made to predict unknown structures of medically relevant ABC transporters, such as P-glycoprotein, using homology-based computational methods. The various techniques described here are also applicable to gaining an atomically detailed understanding of the functional mechanisms of proteins in general.

ATP-Binding Cassette Transporters↗

PubMedDate not supplied

Validity of computer simulation of blood vessel imaging in angiography.

The computer-simulation technique for imaging of vessels in angiography is being recognized as a useful tool for the study of the effect of physical parameters on the vessel image. We have examined the validity of this technique by comparing the computed image distribution directly with experimental results. The imput x-ray pattern of a blood vessel phantom, the LSF of the focal spot, and the LSF of a screen-film system were measured. From the data obtained, the final image distributions of the phantom were computed and compared with the experimentally determined distributions. A high-precision device for the alignment and positioning of the vessel phantom was employed in the experiments. Results indicate that computer simulation can correctly predict the image distribution of the blood vessel phantom.

Angiography↗

PubMed1985

Effects of normal and pathologic eardrum impedance on sound pressure in the aided ear canal: a computer simulation.

Reported herein are results of computer simulations of aided sound spectra in ears with normal and pathologic eardrum impedance. The computer technique used in this study has been reported elsewhere [D. P. Egolf, D. R. Tree, and L. L. Feth, J. Acoust. Soc. Am. 63, 264-271 (1978)]. Consequently, to develop reader confidence in the computer scheme, its application to real ears was first tested. This was accomplished by (1) comparing computed spectral data with in-the-ear measurements and (2) comparing real ear minus 2-cc coupler data-both computer generated--with an idealized difference curve published elsewhere [R. M. Sachs and M. D. Burkhard, unpublished rep. no. 20022-1, Industrial Research Products, Inc., Elk Grove Village, IL (1972)]. Results indicate that the wide variation in eardrum impedance among normals evidenced in other studies produces a corresponding wide variation in aided spectrum shape. Likewise, simulations utilizing two sets of pathologic eardrum impedance data obtained from the literature show that aided sound spectra in such ears are likely to be significantly different from those occurring in normal ears. These findings suggest, as others have concluded, that there may be a substantial variation in spectrum shape among individuals wearing identically the same hearing aid--even if those individuals have normal hearing. In conclusion, questions are raised about the use of real-ear simulators and the need for a comprehensive computer-based model of an entire hearing aid.

Acoustic Impedance Tests↗

PubMed1980

Computer simulation: a diagnostic method in comparative studies of valve prostheses.

Computer simulation was used to compare flow characteristics through Starr-Edwards and Björk-Shiley valves in the mitral and aortic positions. Pressure and velocity determinations were mathematically computed with the use of a model based on the recognition that blood is a non-Newtonian fluid. The results were displayed in two-dimensional graphic form. In both the mitral and aortic positions the Björk-Shiley prosthesis showed a more favorable laminar flow pattern, producing fewer eddies and smaller pressure and velocity gradients through the occluder. Computer simulation is a valuable adjunct in the comparative testing of the hemodynamic properties of artificial heart valves and offers several advantages over physical simulators.

Aortic Valve↗

PubMed2000

Modeling access, cost, and perceived quality: computer simulation benefits orthodontic clinic staffing decisions.

Given limited financial resources, simulation permits a financial analysis of the optimum staffing levels for orthodontists and dental assistants in an orthodontic clinic. A computer simulation provides the information for managerial review. This study, by building a computer simulation of an orthodontic service, set out to determine the most efficient mix between providers and support staff to maximize access, maximize perceived quality, and minimize expenditures. Six combinations of providers and support staff were compared during an animated, computer-generated what-if analysis. Based on the clinic workload and size, on the cost per patient, and on the cost per quality point, the research team recommended a staffing mix of one orthodontist and three assistants. This study shows that computer simulation is an enormous asset as a decision support tool for management.

Ambulatory Care↗

PubMed1990

Randomness in the heparin polymer: computer simulations of alternative action patterns of heparin lyase.

Heparin is a mixture of linear polysaccharides of undetermined sequence. Both biosynthetic data and computer simulation studies have established that each heparin polymer chain is comprised of oligosaccharides of defined sequence, representing ordered domains. One such ordered domian is a pentasaccharide corresponding to heparin's antithrombin III binding site. Previous computer simulation studies, performed under the assumption that heparin lyase (heparinase, EC 4.2.2.7), has a random endolytic action pattern, suggested that certain of these ordered oligosaccharide domains may themselves be nonrandomly arranged in the heparin polymer. The present work presents computer simulations of alternative action patterns for heparin lyase while assuming a random distribution of these oligosaccharide units within the heparin polymer. We consider action patterns that are determined solely by the primary structure of the substrate molecules. Results of the simulations are compared to (1) the experimental measurements of product chains formed throughout the reaction and (2) the change in weight average molecular weight Mw as a function of reaction completion as determined by absorbance at 232 nm. From the simulation of 60 action patterns for heparin lyase, we infer that one of the following statements concerning heparin and heparin lyase is true: (1) Heparin is a random arrangement of a small number of structurally defined oligosaccharide units. Heparin lyase changes its action pattern during the depolymerization of heparin (perhaps influenced by the secondary structure of substrate). (2) Heparin contain clusters of oligosaccharide sequences that are present in low concentrations (overall) in the polymer. Heparin lyase has a specificity for cleaving glycosidic linkages either exolytically at the nonreducing terminus of a chain or (endolytically) at the reducing side of these rare oligosaccharide sequence.

Carbohydrate Conformation↗

PubMed1993

Application of physicians' predictions of meal and exercise effects on blood glucose control to a computer simulation.

Our aim was to develop a computer simulator program that allows patients to practise insulin dose and dietary adjustment on a day of planned exercise, and shows the resulting blood glucose response in an average diabetic patient. The degree of blood glucose change predicted by the program was determined from changes predicted by five local specialists in seven hypothetical scenarios involving exercise +/- dietary or insulin dose adjustments. The program was then tested against 18 outside specialists' responses in 7 different scenarios. The program simulates the 24 h glycaemic response after 45 min mild or moderate exercise starting 2 h after meals, as well as changes to this response induced by alterations in dietary carbohydrate and/or insulin dose. Coefficients of variation of specialists' blood glucose predictions were greater for exercise (35% local, 31% outside specialists) than dietary change (7% local, 10% outside specialists; p = 0.002-0.04). The program's predicted change in blood glucose levels in the seven scenarios correlated well with the outside specialists' corresponding mean predictions (r = 0.97; p = 0.0001). We conclude that specialists are less consistent in predicting glycaemic change with exercise than with dietary alteration. Nevertheless it is possible to represent their predictions in a computerized simulator for diabetic patient education.

Blood Glucose↗

PubMed1992

Tumor-cell motility and invasion within tumors determined by applying computer simulation to histologic patterns.

Proliferation and motility are crucial prerequisites for tumor-cell invasion in vivo. While proliferation can be assessed in situ by a variety of methods, the measurement of motility is largely restricted to in vitro models. In previous studies, computer simulations of tumor growth strongly indicated that a close relationship exists between tumor-cell motility on the one hand and the resulting morphological pattern on the other. Moreover, estimates of motility parameters can be based on image analysis of the particular pattern. The objective of the present study was to examine whether tumor-cell populations differing in their in vitro motility produce particular patterns in vivo similar to those predicted by the computer simulations, and whether the motility estimates derived from these patterns are consistent with the in vitro motility results. This was done using murine fibrosarcomas grown in syngeneic animals from various cell lines which had been selected for and confirmed to show greatly increased speeds of motility in vitro relative to the unselected parent cell population. Computer simulations coupled with image analysis of the various variant tumors showed that the calculated motility of tumor cells within the different tumors agreed well with the relative levels of tumor-cell motility observed in vitro. Our results thus show that the computer simulation method, along with histological analysis, produced reliable estimates of tumor-cell motility within tumors.

Animals↗

PubMed1999

Effect of partition coefficient, permeability surface product, and radioisotope on the signal-to-noise ratio in PET functional brain mapping: a computer simulation.

In this work we use a computer simulation to estimate the magnitude of improvement in the signal-to-noise ratio of PET functional brain mapping studies as a function of partition coefficient and permeability surface product for O-14, F-17, and O-15 labeled flow tracers. A model for signal-to-noise ratio is derived from the Kety model for inert diffusible blood flow tracers. The results of the simulation suggest that moderate increases in partition coefficient and permeability surface product compared with water would lead to an increase in signal-to-noise ratio of a factor of about 3.

Artifacts↗

PubMed1991

A computer simulation of muscle-tendon mechanics.

A computer simulation program was developed to study and illustrate the complex interactions that exist between muscle structure, neural activation, and mechanical characteristics. The software incorporates equations inherent in a comprehensive muscle-tendon model. The software provides a multi-menu interface allowing the user to easily alter quantities related to muscle architecture, kinematics, and activation level. Five different simulations may be performed and graphically displayed including: force-length, force-velocity, force-activation, force-time, and muscle vs tendon length. Up to three different muscle design/contraction condition combinations can be displayed simultaneously for each simulation. Sample simulation results illustrating the mechanical behavior of muscles with different structures are presented.

Biomechanical Phenomena↗

PubMed1999

A computer simulation of wavelet noise reduction in computed tomography.

We describe the use of a graphical mathematical spreadsheet programming environment which can be used to simulate the acquisition and reconstruction processes of an x-ray computed tomography (CT) machine. The simulation is used to study the effect of photon counting statistics on the noise in the reconstructed image. Finally we describe and evaluate a novel technique for noise reduction using a nonlinear wavelet filter in which the filter thresholds are calculated individually from the "measured" projection data. This filter is shown to compare favorably to threshold filters based on global estimates of noise variance.

Biophysical Phenomena↗

PubMed1989

Hydration forces between parallel DNA double helices: computer simulations.

We have performed two molecular dynamics computer simulations of two 10-base-pair segments of DNA molecules immersed in water. The goal of these simulations is to study the structural and dynamical properties of water between the DNA molecules. We have observed water ordering next to DNA surfaces. Existence of such ordering was proposed earlier by Marcelja and Radic [Marcelja, S. & Radic, N. (1976) Chem. Phys. Lett. 42, 129-130] to explain strong hydration forces between macromolecular surfaces.

Chemical Phenomena↗

PubMed1992

Computer simulations of ultrasonic heating for ocular therapy.

Computer simulations are being performed to model the temperature patterns produced during ultrasonically induced hyperthermia of ocular tumours. The software package for these simulations incorporates operator interaction and uses tissue geometry obtained from B-mode data. Previous studies used geometric approximations for the incident beams used for hyperthermia. In the current study, these beams were computed using diffraction analysis to obtain more realistic simulations of clinical exposures.

Body Temperature↗

PubMed2002

Computer simulation of affinity capillary electrophoresis.

A computer-simulated model of affinity capillary electrophoresis is developed. Unlike existing models, it is able to describe the situation where the concentrations of sample molecules and ligand molecules are commensurable, or even the situation where the zones occupied by these molecules are not mixed initially. The model permits to study the dependence of the spatial and temporal distributions of sample molecules on various parameters such as reaction rate constants, concentrations of sample and reagent, electromigration velocities of sample and reagent and sample injection volume. A collection of peak shapes for different values of parameters is presented. The dependence of peak variance on the ratio of the time of analysis to the characteristic time of reaction is studied.

Computer Simulation↗

PubMed2006

Microscopic and thermodynamic properties of the HFA134a-water interface: atomistic computer simulations and tensiometry under pressure.

A combined computational and experimental approach is used to determine the interfacial thermodynamic and structural properties of the liquid 1,1,1,2-tetrafluoroethane (HFA134a)-vapor and liquid HFA134a-water (HFA134a|W) interfaces at 298 K and saturation pressure. Molecular dynamics (MD) computer simulations reveal a stable interface between HFA134a and water. The "10-90" interfacial thickness is comparable with those typically reported for organic-water systems. The interfacial tension of the HFA134a|W interface obtained from the pressure tensor analysis of the MD trajectory is in good agreement with the experimental value determined using in situ high-pressure tensiometry. These results indicate that the potential models utilized are capable of describing the intermolecular interactions between these two fluids. The tension of the HFA134a|W interface is significantly lower than those typically observed for conventional oil-water interfaces and similar to that of the compressed CO(2)-water interface, observed at moderate CO(2) pressures. The MD and tensiometric results are also compared and contrasted with the HFA134a|W and chlorofluorocarbon-water tension values estimated from a parametric relationship. This represents the first report of the interfacial and microscopic properties of the (propellant) hydrofluoroalkanes (HFA)|W interface. The results presented here are of relevance in the design of surfactants capable of forming and stabilizing water-in-HFA microemulsions. Reverse aqueous microemulsions in HFA-based pressurized metered-dose inhalers are candidate formulations for the systemic delivery of biomolecules to and through the lungs.

Computer Simulation↗

PubMed1980

Computer-simulated laboratory experiments in food science. II. Evaluation of the model in use.

Evidence obtained in this study indicates that computer simulations can be a successful method of teaching foods or can replace laboratory experiences. For nine of eleven attitudinal test items, students' attitudes became more positive concerning the value of the course in which computer simulations were used. On the achievement test, seventeen of the twenty-five questions revealed that significant learning (p of less than or equal to 0.05) occurred when the simulations were integrated into a foods course. These students seemed to do well and to like this method of instruction. The advantages of these computer simulations are that students can be motivated to learn and solve problems.

Computer-Assisted Instruction↗

PubMedDate not supplied

Computer simulation helps predict cerebral aneurysms.

Researchers have recently proven the ability of computer simulation to predict the behaviour of cerebral aneurysms. Accurately simulating the flow of blood within the aneurysm helps researchers to predict the growth pattern of the aneurysm and the danger of rupturing. As this tool is further developed into a practical diagnostic tool, it is expected to dramatically improve the ability of surgeons to weigh the results of alternate treatment methods. The simulation method used, computational fluid dynamics (CFD), provides much more information than current diagnostic tools, including particularly shear stress levels at various stages of the cardiac cycle, which help to pinpoint areas of aneurysm formation and growth.

Animals↗