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PubMed2003

Computational flow visualization in vibrating flow pump type artificial heart by unstructured grid.

Computational flow visualization in the casing of vibrating flow pump (VFP) was made for various conditions based on the novel techniques of fluid dynamics. VFP type artificial heart can generate the oscillated flow and can be applied to the left ventricular assist device. Flow pattern of blood in an artificial heart is closely connected to mechanical performance and serious biomechanical problems such as hemolysis and blood coagulation. To effectively design the VFP for a left ventricular assist device, the numerical codes for solving Navier-Stokes equations were developed for three-dimensional blood flow based on the finite volume method. Furthermore, the simulation techniques based on the artificial compressibility method and the unstructured grid were also developed here. The numerical calculations were based on the precise configurations and the flow conditions of the prototype device. From the viewpoint of computational fluid dynamics (CFD), the detailed discussion of flow patterns in the casing of VFP, which were closely connected with hemolysis and blood coagulation, was made and the computational results were visualized by the use of the recent technique of computational graphics. Some useful design data of VFP were presented.

Blood Flow Velocity↗
PubMed2006

Assessing the trade-offs between crossover and parallel group designs in sleep research.

Sleep researchers invariably struggle with decisions regarding the optimal design for their studies. Whether such studies involve treatment for insomnia, obstructive sleep apnea, or any other sleep disorder, questions arise regarding the respective trade-offs between a parallel group and a crossover design. This study analyzed the variance structure of commonly measured polysomnographic variables in an effort to describe the statistical impact of these alternate designs. The study examined the effects of opioids on sleep and employed multiple crossovers between placebo, MS-contin, and methadone using a double-blind, randomized crossover design. Thirty-seven healthy subjects were studied. Four of the subjects were unable to complete the protocol for a variety of reasons, and polysomnogram data was unavailable for one subject. Data from 37 subjects provide the basis for this analysis. Despite dropouts, the crossover study was approximately four times as efficient as the parallel group design in terms of being able to recognize differences in deep sleep across these conditions. Other polysomnographic variables also favored the crossover design to varying extents. Despite the operational complexity of a crossover design, the statistical efficiency of this approach makes it a preferable approach for designing intervention studies in sleep research.

Adult↗
PubMed1976

[Curve of labeled mitoses in different kinetic states of cell proliferation. III. Experiments with a mathematical model].

By means of computer simulation, the dynamic structure of labeled mitoses curve (LMC) has been investigated. Experiments using computer demonstrated the dependence of LMC form not only on the values of temporal parameters of the mitotic cycle, but also on the state of cell proliferation kinetics before and after pulse labeling. Of particular interest was a case of a temporal block of cell entry into the S period which has been studied in a greater detail. The results of modelling experiments have shown that the universally accepted graphic procedures for the evaluation of mean durations of S- and G2-periods (using 50%-level of LMC) yield the satisfactory estimates only for systems with stationary age distribution for cells in the mitotic cycle (steady, in the strict sense, and exponential states of cell proliferation kinetics). The paper presents also the kinetic interpretation of certain abnormalities in LMC form arising from some peculiarities of cell population kinetics in the real biological experiment.

Computers↗
PubMed2001

Objective laparoscopic skills assessments of surgical residents using Hidden Markov Models based on haptic information and tool/tissue interactions.

UNLABELLED: Laparoscopic surgical skills evaluation of surgery residents is usually a subjective process, carried out in the operating room by senior surgeons. By its nature, this process is performed using fuzzy criteria. The objective of the current study was to develop and assess an objective laparoscopic surgical skill scale using Hidden Markov Models (HMM) based on haptic information, tool/tissue interactions and visual task decomposition. METHODS: Eight subjects (six surgical trainees: first year surgical residents 2 x R1, third year surgical residents 2 x R3 fifth year surgical residents 2 x R5; and two expert laparoscopic surgeons: 2 x ES) performed laparoscopic cholecystectomy following a specific 7 steps protocol on a pig. An instrumented laparoscopic grasper equipped with a three-axis force/torque sensor located at the proximal end with an additional force sensor located on the handle, was used to measure the forces and torques. The hand/tool interface force/torque data was synchronized with a video of the tool operative maneuvers. A synthesis of frame-by-frame video analysis was used to define 14 different types of tool/tissue interactions, each one associated with unique force/torque (F/T) signatures. HMMs were developed for each subject representing the surgical skills by defining the various tool/tissue interactions as states and the associated F/T signatures as observations. The statistical distance between the HMMs representing residents at different levels of their training and the HMMs of expert surgeons were calculated in order to generate a learning curve of selected steps during laparoscopic cholecystectomy. RESULTS: Comparison of HMM's between groups showed significant differences between all skill levels, supporting the objective definition of a learning curve. The major differences between skill levels were: (i) magnitudes of F/T applied (ii) types of tool/tissue interactions used and the transition between them and (iii) time intervals spent in each tool/tissue interaction and the overall completion time. The objective HMM analysis showed that the greatest difference in performance was between R1 and R3 groups and then decreased as the level of expertise increased, suggesting that significant laparoscopic surgical capability develops between the first and the third years of their residency training. The power of the methodology using HMM for objective surgical skill assessment arises from the fact that it compiles enormous amount of data regarding different aspects of surgical skill into a very compact model that can be translated into a single number representing the distance from expert performance. Moreover, the methodology is not limited to in-vivo condition as demonstrated in the current study. It can be extended to other modalities such as measuring performance in surgical simulators and robotic systems.

Animals↗
PubMed1995

Glutathione depletion kinetics with acetaminophen. A simulation study.

A tubular-flow model with known published parameters on glutathione (GSH) synthesis, degradation, and transport was developed to examine the distributed-in-space bimolecular reaction of GSH conjugation with acceptor substrates. Simulations were performed to obtain the vascular and intracellular GSH concentrations in the absence and presence of acetaminophen. Zonal localization of GSH was found to be effectively modified upon varying the activities for GSH synthesis and degradation along the sinusoidal flow path. A periportal (zone 1) GSH distribution resulted when GSH synthetic activity was distributed anterior to the degradation activity (models A and D); a perivenous (zone 3) GSH enrichment existed when these activities were reversed (model B), whereas when the synthetic and degradation activities for GSH were homogeneously distributed (model C), GSH concentration was unchanged in all zones. Although the zonation of GSH was model-dependent (models A-D ), only minor differences were found to exist for the length-averaged tissue GSH concentration (5.8-6 mumol/g liver) and the outflow of the liver (approximately 15 microM). With acetaminophen, a substrate known to deplete GSH via its reactive intermediate, N-acetyl-p-quinoneimine (NAPQI), acinar GSH patterns were not greatly perturbed at concentrations < 1 mM. At 10 mM acetaminophen, however, differential patterns of GSH zonal depletion were observed among models, although there was virtually no difference in the length-averaged intracellular GSH concentration (3 mumol/g liver) nor in the formation of the acetaminophen GSH adduct, with the latter being rate-limited by the bioactivation of acetaminophen to NAPQI.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaminophen↗
PubMed1987

Objective evaluation of degree of illness with the weighted Mahalanobis distance. A study for patients suffering from chronic obturative lung disease.

An objective evaluation of the state of patients suffering from chronic obturative lung disease is presented. This evaluation is based on the standardized weighted Mahalanobis distance between a patient and a "centre of health". The method works for both continuous and discrete features. The results of the automatic valuation were compared with the ranked physician's evaluation. This was done by the Spearman rank correlation coefficient, which was statistically significant in all computed variants.

Analysis of Variance↗
PubMed2001

Measurement and modeling of center-surround suppression and enhancement.

The apparent contrast of a central stimulus is affected by the presence of surrounding stimuli. For some stimulus conditions, the apparent contrast is suppressed and for other conditions the apparent contrast is enhanced. This report is intended to offer a coherent description of the stimulus factors that influence suppression and enhancement. Using a contrast-matching protocol, we measured the contrast dependence of center-surround interactions by systematically varying the suprathreshold contrasts of the central and surround gratings. Different spatial configurations of the surround stimuli were studied. Our results confirmed previous findings that (1) a surround stimulus could produce either contrast enhancement or contrast suppression depending on the balance of the central and surround contrasts; (2) suppression varied with the width of the surround stimulus and was strongly orientation-specific; and (3) enhancement was less sensitive to changes in surround configurations (in particular, enhancement did not depend on the colinearity of the central and surround gratings). Based on the experimental data, we developed a computational model to account for center-surround suppression and enhancement.

Contrast Sensitivity↗
PubMed2001

New approaches to missing data in psychological research: introduction to the special section.

Traditional approaches to missing data (e.g., listwise deletion) can lead to less than optimal results in terms of bias, statistical power, or both. This article introduces the 3 articles in the special section of Psychological Methods, which consider multiple imputation and maximum-likelihood methods, new approaches to missing data that can often yield improved results. Computer software is now available to implement these new methods.

Bias↗
PubMed1999

A highly automated heavy-atom search procedure for macromolecular structures.

A new highly automated heavy-atom search procedure combines a fast Fourier transform translation function, Patterson superposition functions and Patterson correlation refinement. The search procedure can be applied to various native and difference Patterson maps and their statistically weighted averages. The procedure was tested with diffraction data for several crystal structures with up to 30 heavy-atom sites in the asymmetric unit and with minimum Bragg spacings ranging from 3 to 4 A. In all cases, the correct sites were found with modest computing time.

Algorithms↗
PubMed1997

Incremental learning of probabilistic rules from clinical databases based on rough set theory.

Several rule induction methods have been introduced in order to discover meaningful knowledge from databases, including medical domain. However, most of the approaches induce rules from all the data in databases and cannot induce incrementally when new samples are derived. In this paper, a new approach to knowledge acquisition, which induce probabilistic rules incrementally by using rough set technique, is introduced and was evaluated on two clinical databases. The results show that this method induces the same rules as those induced by ordinary non-incremental learning methods, which extract rules from all the datasets, but that the former method requires more computational resources than the latter approach.

Algorithms↗
PubMed1997

Heat transfer and lethality considerations in aseptic processing of liquid/particle mixtures: a review.

Consumer awareness and demand for nutritious yet inexpensive food products call for innovative processing techniques that have both safety and quality as primary objectives. These challenges appear to have been met by aseptic processing techniques, especially for liquid and high-acid foods. However, the extension of aseptic processing principles to low-acid foods containing discrete particles in viscous sauces has not been approved by regulatory agencies, particularly in North America. This apparent limitation is due primarily to the lack of adequate temperature monitoring devices to keep track of particles in dynamic motion, as well as to the residence time distribution of particles flowing in the continuous heat-hold-cool sections of the aseptic processing system. These problems have prompted active research to describe the phenomenal behavior of particulates through sound mathematical modeling and computer simulators. The accuracy of mathematical models depends heavily on how accurate input parametric values are. These parameters include the thermophysical properties of the carrier fluid and particles, as well as the aseptic processing system characteristics in relation to residence time distribution and the fluid-to-particle interfacial heat transfer coefficient. Apparently, several contradictory findings have been reported in the literature with respect to the effect of various processing parameters on the above-mentioned input parametric values. The need therefore arises for more collaborative studies involving the industry and academia. This review brings to perspective, the current status on the aseptic processing of particulate foods with respect to the critical processing parameters which affect the fluid-to-particle convective heat transfer coefficient associated with particulate laden products.

Computer Simulation↗
PubMed1990

[Possibilities of predicting the outcome of diseases after cardiosurgical interventions].

A multifactorial correlation and regression analysis with the use of a pack of applied programs "SAND" in the computer SM-4 was performed for prognosis of the outcome of the disease in 38 patients with acquired heart diseases operated upon under conditions of extracorporeal circulation. A linear mathematical model was obtained which allowed predicting the course of the postoperative period and outcome of the disease of cardio-surgical patients with 70-80% probability.

Adolescent↗
PubMed1998

A simple method of sample size calculation for linear and logistic regression.

A sample size calculation for logistic regression involves complicated formulae. This paper suggests use of sample size formulae for comparing means or for comparing proportions in order to calculate the required sample size for a simple logistic regression model. One can then adjust the required sample size for a multiple logistic regression model by a variance inflation factor. This method requires no assumption of low response probability in the logistic model as in a previous publication. One can similarly calculate the sample size for linear regression models. This paper also compares the accuracy of some existing sample-size software for logistic regression with computer power simulations. An example illustrates the methods.

Humans↗
PubMed2006

Psychopathy in adolescent female offenders: an item response theory analysis of the psychopathy checklist: youth version.

The present study examined the applicability of the PCL:YV items to a sample of detained adolescent girls. Item response theory (IRT) was used to analyze test and item functioning of the PCL:YV. Examination of IRT trace lines indicated that the items most discriminating of the underlying construct of psychopathy included "callousness and a lack of empathy", "conning and manipulation", and "a grandiose sense of self-worth". Results from the analyses also demonstrated that the items least discriminating in this sample, or least useful for identifying psychopathy, included "poor anger control", "shallow affect", or engaging in a "serious violation of conditional release". Consistent with previous research (Cooke & Michie, 1997; Hare, 2003), interpersonal and affective components of psychopathy provided more information than behavioral features. Moreover, although previous research has also found affective features to provide the most information in past studies, it was interpersonal features of psychopathy in this case, followed by affective features, that provided greater levels of information. Implications of these results are discussed.

Adolescent↗
PubMed1991

The analysis of categorical data from cross-over trials using a latent variable model.

A latent variable model for categorical data is described. The nuisance parameters in the model can be eliminated from the analysis through the use of a conditional likelihood and this leads to an analysis based on a log-linear model. It is shown how the structure of a cross-over trial allows considerable simplification in the formulation of this model and routine application of well-known statistical packages. The method is illustrated by data from a three-period cross-over trial on the relief of primary dysmenorrhea using the GLIM and SAS packages.

Analysis of Variance↗
PubMed2001

Predicting the functional consequences of non-synonymous single nucleotide polymorphisms: structure-based assessment of amino acid variation.

We have developed a formalism and a computational method for analyzing the potential functional consequences of non-synonymous single nucleotide polymorphisms. Our approach uses a structural model and phylogenetic information to derive a selection of structure and sequence-based features serving as indicators of an amino acid polymorphim's effect on function. The feature values can be integrated into a probabilistic assessment of whether an amino acid polymorphism will affect the function or stability of a target protein. The method has been validated with data sets of unbiased mutations in the lac repressor and lysoyzyme. Applying our methodology to recent surveys of genetic variation in the coding regions of clinically important genes, we estimate that approximately 26-32 % of the natural non-synonymous single nucleotide polymorphisms have effects on function. This estimate suggests that a typical person will have about 6240-12,800 heterozygous loci that encode proteins with functional variation due to natural amino acid polymorphism.

Amino Acids↗
PubMed1996

Estimation of the size of the media necessary to construct a medical image database.

To estimate the size of the media necessary to construct a medical image database, a statistical analysis was made of the radiological data in our hospital information system database. The distribution of the total radiological image data storage required during one working day can be regarded as a normal distribution, and the distribution per patient was different from a normal one. Therefore, the mean amount required for the data storage of radiological images during one working day is very useful in estimating the data storage required for radiological images during a given number of working days.

Computer Systems↗