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At least 145 records · Page 8Linked to original sources
PubMedDate not supplied

BoneMorphing versus freehand localization of anatomical landmarks: consequences for the reproducibility of implant positioning in total knee arthroplasty.

OBJECTIVE: This study analyzed the influence of the acquisition method in image-free computer-assisted total knee arthroplasty (CAS-TKA), and the reproducibility of implant planning using BoneMorphing, a 3D morphometric model obtained by a 3D-to-3D elastic registration of statistical models to sparse point clouds acquired directly on the bone surface with a pointer. MATERIALS AND METHODS: Five surgeons (one expert, four trainees) each performed a CAS-TKA hybrid protocol based on morphometric models and landmarks on a cadaveric knee 10 times. In addition, several additional landmarks were digitized during each acquisition. The reproducibility of the implant positioning and sizing, as determined by an implant planning algorithm with morphometric models, was compared to direct digitization accuracy. RESULTS: Femoral and tibial implant positioning parameters with the hybrid protocol resulted in intra-surgeon standard deviations (SDs) of less than+/-1.4 degrees for rotation and 1.9 mm for translation for all surgeons in all directions except for tibial axial rotation (the only parameter determined by a digitized landmark and not recomputed in the 3D model). The variability in individual landmark digitization varied from 2 to 5 mm SD for certain landmarks, with ranges of 15-25 mm across all surgeons. The comparison study showed an improvement in femoral rotation reproducibility with the morphometric model when using the posterior condylar axis. Tibial implant reproducibility for each method was comparable, with the morphometric model giving better results in well-digitized areas such as the tibial plateau. CONCLUSION: A CAS-TKA protocol based on a deformed statistical model offers reproducible implant positioning. Some landmarks, such as distal condyles, show sufficient reproducibility in the direction of interest, while others, such as the anterior tibial tubercle, can lead to hazardous implant positioning. This should be taken into consideration when designing a CAS-TKA system with bony landmarks. In areas where a sufficient number of points have been digitized with good coverage, such as on the distal and posterior femoral condyles or the tibial plateau areas, the information derived from the 3D model is more accurate and reproducible than that derived from digitization. Good training and a guiding user interface are essential to guarantee coverage quality.

Arthroplasty, Replacement, Knee↗
PubMed1994

Size effects in Kauffman type evolution for rugged fitness landscapes.

Millions of sites are simulated in an NK fitness model of evolution and coevolution. We find a logarithmic size dependence of the number of hill-climbing iterations needed to reach a local fitness optimum (Nash equilibrium). We also check for chaotic behavior and determine the size of the damage clouds or avalanches. Random noise (simulated annealing) is shown to increase appreciably the fitness.

Algorithms↗
PubMedDate not supplied

Advanced practice geriatric nursing education. New options in Kansas.

Knowledgeable practitioners with the skills needed to serve in a variety of clinical settings are the primary objective of the Adult-Geriatric Advanced Nursing Program and the FNP elective, Advanced Practice Nursing Care of the Frail Elderly. The continued blending of long term and acute care settings will further cloud and challenge the school responsible for educating APNs in the care of older adults, particularly the frail elderly. Education needs to provide flexibility for students through new service designs such as interactive computer courses. Nurses with an orientation to the future should consider geriatric nursing education.

Aged↗
PubMed2000

Head-tail instability caused by electron clouds in positron storage rings

In positron or proton storage rings with many closely spaced bunches, an electron cloud can build up in the vacuum chamber due to photoemission or secondary emission. We discuss the possibility of a single-bunch two-stream instability driven by this electron cloud. Depending on the strength of the beam-electron interaction, the chromaticity and the synchrotron oscillation frequency, this instability either resembles a linac beam breakup or a head-tail instability. We present computer simulations of the instabilities, and compare the simulation results with analytical estimates.

Journal Article↗
PubMed1981

Child health--a time for better understanding?

The importance of community and preventive child health services is generally recognized, but the questions raised about the delivery of these services are jeopardizing their development. The sequelae to the Court report have clouded the future for clinical medical officers; there are arguments about the relationship between general practitioners and the community services, whose management in turn may be reduced by NHS restructuring; while the debate about computer systems has caused further acrimony. However, an analysis of basic objectives and methods shows no valid ground for conflict, and instead all that is needed is agreement on how to implement the most efficient pattern of prevention for the benefit of all children.

Child↗
PubMed2006

Adsorption equilibria of hydrocarbons in the structure of the reforming catalyst: molecular modeling.

Molecular modeling was used to analyze the phenomena involved in the sorption of hydrocarbons by the Pt/Al2O3 reforming catalyst. The interactions between the atoms of the catalyst structure and the molecules of the model reforming compounds were described in terms of the universal forcefield. Making use of the GCMC algorithms, the adsorption isotherms for the reagents in the catalytic system and the temperature dependence of the Henry constant were determined. The research has produced the following major findings: the amount of the hydrocarbon molecules adsorbed rises with increasing pressure and decreasing temperature, and the adsorption isotherm for toluene has a characteristic plot as compared to the isotherms of the other hydrocarbons studied. Mass cloud analysis has revealed a favorable effect of platinum on adsorption in the catalyst model.

Adsorption↗
PubMed1991

Observation of DNA molecules undergoing capillary electrophoresis.

This paper presents a method to observe the motions and configurations of large DNA molecules undergoing capillary electrophoresis (CE). A simple device to perform CE horizontally under microscopic observation is designed and images of single DNA molecules inside the capillary are obtained using an epi-fluorescence microscope. DNA molecules moved towards the negative electrode when an electric field was applied. The mobilities of three types of DNA (T4 and lambda bacteriophage DNA and PBR322 plasmid DNA) were measured at different electric field strength. The mobility vs. electric field strength curves of these three large DNAs showed that the mobility remained constant at high electric field strength (200-600 Volt/cm) and increased significantly at low electric field strength (less than or equal to 50 Volt/cm.). The apparent mobilities of the large DNA molecules were independent of molecular weight. At electric field strengths greater than or equal to 400 Volt/cm., big aggregates (snowballs) of DNA molecules formed and moved upstream towards the positive electrode. When the field was turned off, the aggregates dissociated into a cloud of single DNA molecules, and diffused into the solution.

DNA↗
PubMed2004

Characterization of atmospheric aerosols from infrared measurements: simulations, testing, and applications.

An inversion method for the characterization of atmospheric condensed phases from infrared (IR) spectra is described. The method is tested with both synthetic IR spectra and the spectra of particles that flow in a cryogenic flow tube. The method is applied to the IR spectra recorded by the Atmospheric Trace Molecule Spectroscopy instrument carried by the Space Shuttle during three missions in 1992, 1993, and 1994. The volume density and particle size distribution for sulfate aerosol are obtained as a function of altitude. The density and size distribution of ice particles in several cirrus clouds are also retrieved. The probable radius of the ice particles in the high-altitude (10-15-km) cirrus clouds is found to be approximately 6-7 microm.

Aerosols↗
PubMed1990

The development of new radiopharmaceuticals.

The development of new radiopharmaceuticals is the basis of the continuing growth of nuclear medicine. Chemical interactions of electron clouds in their three-dimensional conformations bring together, in the process of molecular recognition, the reaction of antibody and antigen, receptor and ligand, enzyme and substrate, hormone and response site. This convergence enables the computer design of molecules such as ligands to fit computer-displayed conformational models showing active centres, positive and negative charges and other interactions. Indeed, given a particular molecule, a complementary binding structure can be devised. The hybridoma approach to monoclonal antibody production is being superceded by the bacterial bioengineer. The gene for the hypervariable region from the spleen cells of immunized mouse can be coupled with the myeloma gene. The polymerase chain reaction can duplicate the DNA a million times over in 20 min and the result transfected into a bacterial plasmid to produce the antibody. These scientific problems are soluble in principle and are being solved. However, so much damage to this developing biological field is being done by regulatory authorities that one must ask who should or can regulate the regulators. These problems have to be overcome in order to provide the new radiopharmaceuticals that are the food and wine of nuclear medicine.

Animals↗
PubMed2006

Homogeneous freezing of water starts in the subsurface.

Molecular dynamics simulations of homogeneous ice nucleation in extended aqueous slabs show that freezing preferentially starts in the subsurface. The top surface layer remains disordered during the freezing process. The subsurface accommodates better than the bulk the increase of volume connected with freezing. It also experiences strong electric fields caused by oriented surface water molecules, which can enhance ice nucleation. Our computational results shed new light on the experimental controversy concerning the bulk vs surface origin of homogeneous ice nucleation in water droplets. This has important atmospheric implications for the microphysics of formation of high altitude clouds.

Journal Article↗
PubMed2000

A model of human heading judgement in forward motion.

We developed a new computational model of human heading judgement from retinal flow. The model uses two assumptions: a large number of sampling points in the flow field and a symmetric sampling region around the origin. The algorithm estimates self-rotation parameters by calculating statistics whose expectations correspond to the rotation parameters. After the rotational components are removed from the retinal flow, the heading direction is recovered from the flow field. Performance of the model was compared with human data in three psychophysical experiments. In the first experiment, we generated stimuli which simulated self-motion toward the ground, a cloud or a frontoparallel plane and found that the simulation results of the model were consistent with human performance. In the second and third experiment, we measured the slope of the perceived versus simulated heading function when a perturbation velocity weighted according to the distance relative to the fixation distance was added to the vertical velocity component under the cloud condition. It was found that as the magnitude of the perturbation was increased, the slope of the function increased. The characteristics observed in the experiments can be explained well by the proposed model.

Computer Simulation↗
PubMed1982

[Zoster encephalitis without rash: report of two cases (author's transl)].

Two previously healthy men, aged 54 and 41 years, fell ill with headaches and increased fatiguability, one also with vomiting, the other with fever, transitory visual disturbances and slight weakness of the left hand. Both of them had a stiff neck and clouded consciousness. The EEG had moderate to severe dysrhythmia, predominantly over the temporal area, CSF showed an increased cell count of 1000/3, predominantly lymphocytes, and increased protein. The younger patient also had global aphasia and the computed tomography indicated an area of decreased density in the left temporal region. In the CSF there were locally produced IgG. The clinical findings were similar to those of herpes encephalitis, but were milder and regressed more quickly. Severe months later only a few minor organic behavioural changes were present. Antibody findings in CSF and serum suggest varicella-zoster virus as the causative agent, although in both instances no rash was observed throughout the entire period of observation.

Adult↗
PubMed2004

Range image segmentation into planar and quadric surfaces using an improved robust estimator and genetic algorithm.

This paper presents a novel range image segmentation method employing an improved robust estimator to iteratively detect and extract distinct planar and quadric surfaces. Our robust estimator extends M-estimator Sample Consensus/Random Sample Consensus (MSAC/RANSAC) to use local surface orientation information, enhancing the accuracy of inlier/outlier classification when processing noisy range data describing multiple structures. An efficient approximation to the true geometric distance between a point and a quadric surface also contributes to effectively reject weak surface hypotheses and avoid the extraction of false surface components. Additionally, a genetic algorithm was specifically designed to accelerate the optimization process of surface extraction, while avoiding premature convergence. We present thorough experimental results with quantitative evaluation against ground truth. The segmentation algorithm was applied to three real range image databases and competes favorably against eleven other segmenters using the most popular evaluation framework in the literature. Our approach lends itself naturally to parallel implementation and application in real-time tasks. The method fits well, into several of today's applications in man-made environments, such as target detection and autonomous navigation, for which obstacle detection, but not description or reconstruction, is required. It can also be extended to process point clouds resulting from range image registration.

Algorithms↗
PubMed2001

[The application of wavelet analysis of remote detection of pollution clouds].

The discrete wavelet transform (DWT) is used to analyse the spectra of pollution clouds in complicated environment and extract the small-features. The DWT is a time-frequency analysis technology, which detects the subtle small changes in the target spectrum. The results show that the DWT is a quite effective method to extract features of target-cloud and improve the reliability of monitoring alarm system.

Air Pollutants↗
PubMed2003

A new method for the computer-aided evaluation of three-dimensional changes in gypsum materials.

OBJECTIVES: The quantitative evaluation of the time- or process-dependent three-dimensional stability of dental materials is a common question in dentistry. An investigation procedure has been developed based on a CAD-surface model of a prepared upper canine, as well as a high-precision physical copy (metal master die). The specific aim of this study was to test this method's reliability. Additionally, the ability of the developed procedure to determine the three-dimensional stability of resin-reinforced gypsum master casts over time was investigated. METHODS: Ten duplicate dies of improved dental stone (esthetic-rock, dentona, Germany) were manufactured, and digitized 1, 3, 7, 28 and 56 days after pouring. A three-coordinate optical measuring device was used for the data acquisition. The three-dimensional accuracy of stone dies was determined by comparing the digitized data of the stone dies made from the metal master die to its CAD-surface model (Surfacer) Version 9.0. Imageware Inc., Ann Arbor Michigan, USA). To assess the procedure, test surfaces were created from the digitized data and compared with a reference. RESULTS: The mean deviation between the digitized point cloud and the test surface was less than 3 microm. During the 56 day examination period no significant three-dimensional changes in dimensional stability were found. SIGNIFICANCE: The procedure for the quantitative three-dimensional evaluation was shown to be suitable. Best-fit registration enabled a reliable alignment of the point cloud to the CAD-surface model. Alteration of three-dimensional accuracy over 6 weeks was insignificant and without clinical relevance.

Calcium Sulfate↗
PubMed1995

Reflection-polarization patterns at flat water surfaces and their relevance for insect polarization vision

It has recently been shown that horizontally polarized ultraviolet light reflected from the surface of water is the main optical cue for habitat finding by insects living in, on, or near water. What are the polarization properties that make the skylight reflected by water attractive to flying water insects in nature? In this paper, as an approach to this problem, the patterns of the degree and direction of polarization of skylight visible over a flat water surface are computed for unpolarized light from an overcast sky and for partially polarized skylight as a function of the zenith distance of the sun. These patterns are compared with the corresponding celestial polarization patterns. The effect of depolarizing clouds on these reflection-polarization patterns is demonstrated. Reflectivity patterns of a flat water surface are also calculated for clear and overcast skies. The polarization of the blue sky is described by the semi-empirical Rayleigh model. It is assumed that the reflection polarization of skylight at the water surface is governed by the Fresnel formulae. The effect of some modifying factors on the reflection-polarization field is briefly discussed. The adaptations of the visual system of insects living in, on, or near water to reflection-polarization patterns at water surfaces are briefly reviewed and discussed by means of three representative species: the waterstrider (Gerris lacustris), the backswimmer (Notonecta glauca), and the dragonfly (Hemicordulia tau). Copyright 1995 Academic Press Limited

Journal Article↗
PubMedDate not supplied

The medical effects of postulated accidental release of radioactive material from Heysham Nuclear Power Station.

The effects of a postulated reactor accident at one of the four AGRs at Heysham, NW England, have been studied, assuming a 10% release of the radioactive core. Methods used are a computer program TIRION, analysis of the radiation doses from the Chernobyl release of 1986 and the Windscale fire of 1957. Fatal cases predicted are 200 on-site, 3000 within 30 km and 250,000 in the cloud paths over Northern England. The results would suggest the incidence of fatal cancer would increase from roughly 20% to 27% in the postulated exposed population of 3.6 million.

Accidents, Occupational↗
PubMed2002

A model based upon pseudo regular spacing of cells combined with the randomisation of the nuclei can explain the significant changes in high-frequency ultrasound signals during apoptosis.

Recent ultrasound (US) experiments on packed myeloid leukaemia cells have shown that, at frequencies from 32 to 40 MHz, significant increases of signal amplitude were observed during apoptosis. This paper is an attempt to explain these signal increases based upon a simulation of the backscattered signals from the cells nuclei. The simulation is an expansion of work in which a condensed sample of cells, with fairly regular sizes, could be considered as an imperfect crystal. Thus, destructive interference could occur and this would be observed as a large reduced value of backscattered signals compared with the values obtained from a similar, but random, scattering source. This current paper explores the possibility that simple changes in the nuclei, such as their observed condensation or the small loss of nuclei scatterers from cells, could cause a significant increase in the observed backscattered signals. This model indicates that the greater backscattered signals can be explained by further randomisation of the average positions of the scattering sources in each cell. When these "microechoes" are added together, so that the destructive interference is reduced, a large increase in the signal is predicted. The simplified model strongly suggests that much of observed large increases of the backscattered signals could be simply explained by the randomisation of the position of the condensed nuclei during apoptosis, and the destruction of the nuclei could produce further signal amplitude changes due to disruption of the cloud of backscattered waves.

Apoptosis↗