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Results for “Compaction simulator”

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At least 127 records · Page 7Linked to original sources
PubMed2003

Engineering requirements for a haptic simulator for knee arthroscopy training.

This paper describes the initial development of an innovative haptic device that will be integrated into an existing virtual reality training system for knee arthroscopy. The resulting system will be called WISHKATS (Warwick, Imperial, Sheffield Knee Arthroscopy Training System). This haptic device will enable the trainee to feel realistic forces on the probing tool and will work together with software, which will simulate tissue deformation. The proposed haptic system is a compact, multi-degree of freedom, motorised mechanism with force sensors, and will be used to simulate the diagnostic aspects of knee arthroscopy. There are a number of problems associated with the development of a suitable haptic system and this paper explores the engineering requirements of such a device.

Arthroscopy↗
PubMed1998

Molecular modeling of HIV-1 coreceptor CCR5 and exploring of conformational space of its extracellular domain in molecular dynamics simulation.

The chemokine receptor CCR5 functions as a major fusion coreceptor for macrophage-tropic human immunodeficiency virus entry into cell. Here we report a three-dimensional model of CCR5 built using molecular modeling approach. Because the virus binds to extracellular domain of the receptor, special attention was given to conformational flexibility, hydrogen bonding, and environmental polarity properties of this protein part. Such data were obtained in the result of molecular dynamics study of the extracellular domain. It was shown that during the simulation the extracellular segments form a compact globular domain with numerous long-range hydrogen bonds between them. First loop of the receptor stays quite rigid while N-terminal region and loops 2, 3 are rather flexible. A number of amino acid residues disposed in unfavourable environment and, therefore, potentially involved in binding of CCR5 to viral glycoproteins and chemokines, was delineated. Comparison of the results with available experimental data permits a proposal that such residues in loop-1 and N-terminal part of the receptor are important for HIV-1 entry, while those in loops 2 and 3 participate in ligand binding. Perspectives of rational alteration of virus-binding activity of CCR5 are discussed.

Amino Acid Sequence↗
PubMed1995

Performance of computer-controlled infusion of propofol: an evaluation of five pharmacokinetic parameter sets.

Computer-controlled infusion of propofol is used with increasing frequency for the induction and maintenance of anesthesia. The performance of computer-controlled infusion devices is highly dependent on how well the implemented pharmacokinetic parameter set matches the pharmacokinetics of the patient. This study examined the performance of a computer-controlled infusion device when provided with five different pharmacokinetic parameter sets of propofol in female patients. The infusion rate-time data that had been stored on a disk from 19 female patients who had been given propofol by computer-controlled infusion, using the pharmacokinetic parameter set from Gepts et al. (Anesth Analg 1987;66:1256-63), were entered into a computer simulation program to recalculate predicted propofol concentrations that would have been obtained with four other pharmacokinetic parameter (Shafer et al., Anesthesiology 1988;69:348-56; Kirkpatrick et al., Br J Anesth 1988;60:146-50; Cockshott et al., Br J Anesth 1987;59:941P; Tackley et al., Br J Anesth, 1989;62:46-53) sets of propofol, had these been implemented. The performance error (PE) was determined for each measured blood propofol concentration, on the basis of each of the five pharmacokinetic parameter sets. Then, for each of the five pharmacokinetic parameter sets, the performance in the population was determined by the median absolute performance error (MDAPE), the median performance error (MDPE), the wobble (the median absolute deviation of each PE from the MDPE), and the divergence (the percentage change of the absolute PE with time). The MDPE and MDAPE were compared between the parameter sets by the multisample median test. The initially used pharmacokinetic parameter set from Gepts et al. resulted in a MDPE of 24% and MDAPE of 26%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2005

Hydrodynamic simulation (computational fluid dynamics) of asymmetrically positioned tablets in the paddle dissolution apparatus: impact on dissolution rate and variability.

The aim of this work was to investigate the dissolution rate from both the curved and planar surfaces of cylindrical compacts of benzoic acid, which were placed centrally and non-centrally at the base of the vessel of the paddle dissolution apparatus. The effect of fixing the compacts to a particular position on the variability of dissolution results was also examined. In addition, computational fluid dynamics (CFD) was used to simulate fluid flow around compacts in the different positions in the vessel, and the relationship between the local hydrodynamics in the region of the compacts and the dissolution rate determined. The dissolution rate was found to increase from the centre position to the off-centre positions for each surface examined. There was a corresponding increase in maximum fluid velocities calculated from the CFD fluid flow simulations at a fixed distance from the compact. There was less variability in dissolution from compacts fixed to any of the positions compared with those that were not fixed. Fluid flow around compacts in different positions could be successfully modelled, and hydrodynamic variability examined, using CFD. The effect of asymmetric fluid flow was evident visually from the change in shape of the eroded compacts.

Benzoic Acid↗
PubMed1997

Modelling of the void space of tablets compacted over a range of pressures.

A previously developed computer model, named Pore-Cor, has been used to simulate the changes in the void-space dimensions which occur during the compaction of tablets over a range of pressures. The tablets were made by mixing pharmaceutical grade crystalline lactose and an anti-inflammatory compound in the proportion 4:1. Compacts were made by placing a weighed amount of the mixed powder into a stainless-steel die and applying pressure with a hand-operated calibrated hydraulic press. Compacts were prepared at eight pressures over the hydraulic pressure range 1 to 8 ton in-2 (15.4-123.2 MPa) in 1 ton in-2 increments. Mercury-intrusion curves were measured for the eight samples by use of a porosimeter and the Pore-Cor package was then used to simulate the mercury-intrusion curves and generate void-space models of the correct porosity. The experimental and simulated characteristic throat diameter, the experimental and simulated porosity, and the simulated permeability of the tablets have all been shown to follow expected trends. The successful modelling of void-structure parameters, which are difficult or impossible to measure experimentally, opens the way to an improved understanding of the strength of compacts.

Anti-Inflammatory Agents↗
PubMed2001

Effectiveness of different obturation techniques in the filling of simulated lateral canals.

The purpose of this in vitro study was to evaluate the ability of lateral compaction of gutta-percha and of five thermoplasticized gutta-percha filling techniques to obturate simulated lateral canals. Sixty extracted single-rooted human teeth were instrumented at the working length to a #35 file before creating three simulated lateral canals on the mesial and distal surfaces of the root, one in each third, using a #15 engine reamer. After enlarging root canals to a #45 file, the teeth were randomly divided into six equal groups of 10 and obturated according to the following techniques: lateral compaction of gutta-percha (group A), hybrid technique (group B), Ultrafil (group C), Obtura II (group D), System B + Obtura II (group E), and Thermafil (group F). AH26 was used as the sealer. A greater number of simulated lateral canals were obturated when Ultrafil, Thermafil, and System B + Obtura II were used, in comparison with canals obturated with the hybrid technique, Obtura II, or lateral compaction of gutta-percha. This difference was statistically significant (p < 0.05). No statistically significant differences were found between results obtained in the obturation of simulated lateral canals in the different thirds of the root (p > 0.05).

Gutta-Percha↗
PubMed1991

Protein folding. Effect of packing density on chain conformation.

Recent lattice polymer simulations by Chan & Dill suggest that compactness may be a significant driving force in the formation of secondary structure. We have addressed the robustness of this conclusion for non-lattice polymers using a rotational isomeric model of proteins. Boundary conditions are used to enforce compactness and excluded volume effects are explicitly incorporated. As in the cubic lattice studies, compactness is seen to influence secondary structure content. This effect is modest for densities comparable to native proteins but dramatic for chains that are approximately 30% more dense than native proteins. alpha-Helical structure is common but beta-sheet structure is rare. It appears that lattices impart to compact chains an organizational bias that favors beta-sheet structure. The strengths and weakness of various simplified representations of polypeptide chains are also discussed.

Crystallography↗
PubMed2000

Development of pectin matrix tablets for colonic delivery of model drug ropivacaine.

The objective of this work was to develop pectin-based matrix tablets for colonic delivery of the model drug ropivacaine, with the future perspective of radiolabelling the system by neutron activation technique for a gamma-scintigraphic study. The aim was to investigate some formulation factors that could reduce the release of the drug in the simulated gastric and intestinal fluids, increase the release in the simulated cecal fluid (with pectinolytic enzymes) and improve the poor compactibility of pectins. For dissolution studies, the flow-through apparatus with sequential dissolution liquids simulating the mouth-to-colon conditions was used. The effect of two pectin types, the incorporation of ethylcellulose as a dry matrix-additive and water or ethanol as granulation liquids were investigated in a study designed as a D-optimal mixture. Amidated pectin (Am.P) produced harder tablets than the calcium salt of pectin (Ca.P) and was more susceptible to enzymatic degradation. Addition of ethylcellulose increased the tablet strength and the dissolution rate. Furthermore, directly compressed Am.P tablets were produced by addition of coarse or micronised qualities of ethylcellulose. The latter improved the crushing strength markedly imposing a marginal release-reducing effect. Coating this formulation with Eudragit((R)) L 100 reduced the release in the simulated upper GI conditions without interference with the subsequent enzymatic activity.

Amides↗
PubMed1986

Equilibrium and kinetic measurements of the conformational transition of thioredoxin in urea.

Addition of urea to solutions of Escherichia coli thioredoxin results in a cooperative unfolding of the protein centered at 6.7 M urea at 25 degrees C and 5.1 M urea at 2 degrees C and neutral pH as judged by changes in tryptophan fluorescence emission, far-ultraviolet circular dichroism, and exclusion chromatography. Kinetic profiles of changes in tryptophan fluorescence emission intensity were analyzed following either manual or stopped-flow mixing to initiate unfolding or refolding. Unfolding of the native protein occurs in a single kinetic phase whose time constant is markedly dependent on urea concentration. Refolding of the urea-denatured protein occurs in a multiplicity of kinetic phases whose time constants and fractional amplitudes are also dependent upon urea concentration. Urea gradient gel electrophoretic and exclusion chromatographic measurements suggest the transient accumulation of at least one and likely two compact nativelike intermediate conformations during refolding. Simulations of both electrophoretic and chromatographic results suggest that the intermediate conformations are generated by the concerted action of the middle and fast refolding phases.

Bacterial Proteins↗
PubMed2006

Electroosmotic flow patterning using microfluidic delay loops.

A theoretical and experimental investigation of alternating electroosmotic flow patterns by means of specially designed delay loops is presented. Using elementary methods of compact network modeling and detailed FEM simulations the flow behavior and, in particular, the rearrangement of sample plugs is modeled. The proposed designs rely on flow splitting in combination with electroosmotic delay loops leading to a runtime difference or phase shift between two sub-streams. Due to this phase shift, a new fluid interface is generated at the merging point. The approach is experimentally validated by injection of a Rhodamine 6G solution into an aqueous sodium tetraborate buffer.

Borates↗
PubMed2003

Acoustic detection of manatee vocalizations.

The West Indian manatee (trichechus manatus latirostris) has become endangered partly because of a growing number of collisions with boats. A system to warn boaters of the presence of manatees, that can signal to boaters that manatees are present in the immediate vicinity, could potentially reduce these boat collisions. In order to identify the presence of manatees, acoustic methods are employed. Within this paper, three different detection algorithms are used to detect the calls of the West Indian manatee. The detection systems are tested in the laboratory using simulated manatee vocalizations from an audio compact disk. The detection method that provides the best overall performance is able to correctly identify approximately 96% of the manatee vocalizations. However, the system also results in a false alarm rate of approximately 16%. The results of this work may ultimately lead to the development of a manatee warning system that can warn boaters of the presence of manatees.

Algorithms↗
PubMedDate not supplied

Converting laserdisc video to digital video: a demonstration project using brain animations.

Interactive laserdiscs are of limited value in large group learning situations due to the expense of establishing multiple workstations. The authors implemented an alternative to laserdisc video by using indexed digital video combined with an expert system. High-quality video was captured from a laserdisc player and combined with waveform audio into an audio-video-interleave (AVI) file format in the Microsoft Video-for-Windows environment (Microsoft Corp., Seattle, WA). With the use of an expert system, a knowledge-based computer program provided random access to these indexed AVI files. The program can be played on any multimedia computer without the need for laserdiscs. This system offers a high level of interactive video without the overhead and cost of a laserdisc player.

Audiovisual Aids↗
PubMed2005

Translational-entropy gain of solvent upon protein folding.

We show that even in the complete absence of potential energies among the atoms in a protein-aqueous solution system, there is a physical factor that favors the folded state of the protein. It is a gain in the translational entropy (TE) of water originating from the translational movement of water molecules. An elaborate statistical-mechanical theory is employed to analyze the TE of water in which a protein or peptide with a prescribed conformation is immersed. It is shown that if the number of residues is sufficiently large, the TE gain is powerful enough to compete with the conformational-entropy loss upon folding. For protein G we have tested over 100 compact conformations generated by a computer simulation with the all-atom potentials as well as the native structure. A significant finding is that the largest TE is attained in the native structure. The translational movement of water molecules is quite effective in achieving the tight packing in the interior of a natural protein. These results are true only when the solvent is water whose molecular size is the smallest among the ordinary liquids in nature.

Computer Simulation↗
PubMed1998

Molecular dynamics simulations of hydrophobic collapse of ubiquitin.

Nine nonnative conformations of ubiquitin, generated during two different thermal denaturation trajectories, were simulated under nearly native conditions (62 degrees C). The simulations included all protein and solvent atoms explicitly, and simulation times ranged from 1-2.4 ns. The starting structures had alpha-carbon root-mean-square deviations (RMSDs) from the crystal structure of 4-12 A and radii of gyration as high as 1.3 times that of the native state. In all but one case, the protein collapsed when the temperature was lowered and sampled conformations as compact as those reached in a control simulation beginning from the crystal structure. In contrast, the protein did not collapse when simulated in a 60% methanol:water mixture. The behavior of the protein depended on the starting structure: during simulation of the most native-like starting structures (<5 A RMSD to the crystal structure) the RMSD decreased, the number of native hydrogen bonds increased, and the secondary and tertiary structure increased. Intermediate starting structures (5-10 A RMSD) collapsed to the radius of gyration of the control simulation, hydrophobic residues were preferentially buried, and the protein acquired some native contacts. However, the protein did not refold. The least native starting structures (10-12 A RMSD) did not collapse as completely as the more native-like structures; instead, they experienced large fluctuations in radius of gyration and went through cycles of expansion and collapse, with improved burial of hydrophobic residues in successive collapsed states.

Computer Simulation↗
PubMed2005

Bioactive calcium pyrophosphate glasses and glass-ceramics.

Calcium phosphate glass-based materials in the pyrophosphate region are briefly reviewed. Calcium pyrophosphate glasses can be prepared by including a small amount of TiO(2) (<or=10mol%). Bonelike apatite forms on some of the glasses in simulated body fluid. By heating powder-compacts of the glasses, they are crystallized and subsequently are sintered, resulting in fabrication of high-strength glass-ceramics with machinability; they are easier to be machined using conventional tools in comparison with conventional calcium phosphate ceramics. beta-Ca(2)P(2)O(7) crystal formed in the glass-ceramics plays an important role in the machinability. Their apatite-forming ability in simulated body fluid is drastically enhanced after autoclaving in distilled water. The glass-ceramics can be easily coated on a new beta-type titanium alloy using a conventional glazing technique.

Alloys↗
PubMed2001

Numerical model for granular compaction under vertical tapping.

A simple numerical model is used to simulate the effect of vertical taps on a packing of monodisperse hard spheres. Our results are in good agreement with an experimental work done in Chicago and with other previous models, especially concerning the dynamics of the compaction, the influence of the excitation strength on the compaction efficiency, and some aging effects. The principal asset of the model is that it allows a local analysis of the packings. Vertical and transverse density profiles are used, as well as size and volume distributions of the pores. An interesting result concerns the appearance of a vertical gradient in the density profiles during compaction. Furthermore, the volume distribution of the pores suggests that the smallest pores, ranging in size between tetrahedral and octahedral sites, are not strongly affected by the tapping process, in contrast to the largest pores which are more sensitive to the compaction of the packing.

Journal Article↗
PubMed2006

Modelling the biomechanical properties of DNA using computer simulation.

Duplex DNA must remain stable when not in use to protect the genetic material. However, the two strands must be separated whenever genes are copied or expressed to expose the coding strand for synthesis of complementary RNA or DNA bases. Therefore, the double stranded structure must be relatively easy to take apart when required. These conflicting biological requirements have important implications for the mechanical properties of duplex DNA. Considerable insight into the forces required to denature DNA has been provided by nanomanipulation experiments, which measure the mechanical properties of single molecules in the laboratory. This paper describes recent computer simulation methods that have been developed to mimic nanomanipulation experiments and which, quite literally, 'destruction test' duplex DNA in silico. The method is verified by comparison with single molecule stretching experiments that measure the force required to unbind the two DNA strands. The model is then extended to investigate the thermodynamics of DNA bending and twisting. This is of biological importance as the DNA must be very tightly packaged to fit within the nucleus, and is therefore usually found in a highly twisted or supercoiled state (in bacteria) or wrapped tightly around histone proteins into a densely compacted structure (in animals). In particular, these simulations highlight the importance of thermal fluctuations and entropy in determining the biomechanical properties of DNA. This has implications for the action of DNA processing molecular motors, and also for nanotechnology. Biological machines are able to manipulate single molecules reliably on an energy scale comparable to that of thermal noise. The hope is that understanding the statistical mechanisms that a cell uses to achieve this will be invaluable for the future design of 'nanoengines' engineered to perform new technological functions at the nanoscale.

Biomechanical Phenomena↗