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At least 919 records · Page 51Linked to original sources
PubMed1990

A theory of visual attention.

A unified theory of visual recognition and attentional selection is developed by integrating the biased-choice model for single-stimulus recognition (Luce, 1963; Shepard, 1957) with a choice model for selection from multielement displays (Bundesen, Pedersen, & Larsen, 1984) in a race model framework. Mathematically, the theory is tractable, and it specifies the computations necessary for selection. The theory is applied to extant findings from a broad range of experimental paradigms. The findings include effects of object integrality in selective report, number and spatial position of targets in divided-attention paradigms, selection criterion and number of distracters in focused-attention paradigms, delay of selection cue in partial report, and consistent practice in search. On the whole, the quantitative fits are encouraging.

Attention↗
PubMed1998

A framework to identify learning needs for continuing nurse education using information technology.

This paper concerns one of the main problems facing continuing nurse education, that of matching the learning needs of the individual nurse with the needs of the care setting. This endeavour is inescapable because of the necessity for giving high quality care within financial restraint. Modern information technology, it is suggested, can be helpful in fulfilling the task more easily. A theoretical framework is introduced as a possible solution for developing a computer program which, it is the hope of the author, will be available in the not so far future.

Computers↗
PubMed2006

Finite-element implementation for electron transport in nanostructures.

We have modeled transport properties of nanostructures using Green's-function method within the framework of the density-functional theory. The scheme is computationally demanding, so numerical methods have to be chosen carefully. A typical solution to the numerical burden is to use a special basis-function set, which is tailored to the problem in question, for example, the atomic-orbital basis. In this paper we present our solution to the problem. We have used the finite-element method with a hierarchical high-order polynomial basis, the so-called p elements. This method allows the discretation error to be controlled in a systematic way. The p elements work so efficiently that they can be used to solve interesting nanosystems described by nonlocal pseudopotentials. We demonstrate the potential of the implementation with two different systems. As a test system a simple Na-atom chain between two leads is modeled and the results are compared with several previous calculations. Secondly, we consider a thin hafnium dioxide (HfO2) layer on a silicon surface as a model for a gate structure of the next generation of microelectronics.

Journal Article↗
PubMed2006

A novel algorithm to model the influence of host lattice flexibility in molecular dynamics simulations: loading dependence of self-diffusion in carbon nanotubes.

We describe a novel algorithm that includes the effect of host lattice flexibility into molecular dynamics simulations that use rigid lattices. It uses a Lowe-Andersen thermostat for interface-fluid collisions to take the most important aspects of flexibility into account. The same diffusivities and other properties of the flexible framework system are reproduced at a small fraction of the computational cost of an explicit simulation. We study the influence of flexibility on the self-diffusion of simple gases inside single walled carbon nanotubes. Results are shown for different guest molecules (methane, helium, and sulfur hexafluoride), temperatures, and types of carbon nanotubes. We show, surprisingly, that at low loadings flexibility is always relevant. Notably, it has a crucial influence on the diffusive dynamics of the guest molecules.

Journal Article↗
PubMed2004

A phylogenetic mixture model for detecting pattern-heterogeneity in gene sequence or character-state data.

We describe a general likelihood-based 'mixture model' for inferring phylogenetic trees from gene-sequence or other character-state data. The model accommodates cases in which different sites in the alignment evolve in qualitatively distinct ways, but does not require prior knowledge of these patterns or partitioning of the data. We call this qualitative variability in the pattern of evolution across sites "pattern-heterogeneity" to distinguish it from both a homogenous process of evolution and from one characterized principally by differences in rates of evolution. We present studies to show that the model correctly retrieves the signals of pattern-heterogeneity from simulated gene-sequence data, and we apply the method to protein-coding genes and to a ribosomal 12S data set. The mixture model outperforms conventional partitioning in both these data sets. We implement the mixture model such that it can simultaneously detect rate- and pattern-heterogeneity. The model simplifies to a homogeneous model or a rate-variability model as special cases, and therefore always performs at least as well as these two approaches, and often considerably improves upon them. We make the model available within a Bayesian Markov-chain Monte Carlo framework for phylogenetic inference, as an easy-to-use computer program.

Base Sequence↗
PubMed2004

Optical tomographic mapping of cerebral haemodynamics by means of time-domain detection: methodology and phantom validation.

One of the primary applications of diffuse optical imaging is to localize and quantify the changes in the cerebral oxygenation during functional brain activation. Up to now, data from an optical imager are simply presented as a two-dimensional (2D) topographic map using the modified Beer-Lambert law that assumes homogeneous optical properties beneath each optode. Due to the highly heterogeneous nature of the optical properties in the brain, the assumption is evidently invalid, leading to both low spatial resolution and inaccurate quantification in the assessment of haemodynamic changes. To cope with these difficulties, we propose a nonlinear tomographic image reconstruction algorithm for a two-layered slab geometry that uses time-resolved reflected light. The algorithm is based on the previously developed generalized pulse spectrum technique, and implemented within a semi-three-dimensional (3D) framework to conform to the topographic visualization and to reduce computational load. We demonstrate the advantages of the algorithm in quantifying simulated changes in haemoglobin concentrations and investigate its robustness to the uncertainties in the cortical structure and optical properties, as well as the effects of random noises on image quality. The methodology is also validated by experiments using a solid layered phantom.

Algorithms↗
PubMed2002

A model-based method for identifying species hybrids using multilocus genetic data.

We present a statistical method for identifying species hybrids using data on multiple, unlinked markers. The method does not require that allele frequencies be known in the parental species nor that separate, pure samples of the parental species be available. The method is suitable for both markers with fixed allelic differences between the species and markers without fixed differences. The probability model used is one in which parentals and various classes of hybrids (F(1)'s, F(2)'s, and various backcrosses) form a mixture from which the sample is drawn. Using the framework of Bayesian model-based clustering allows us to compute, by Markov chain Monte Carlo, the posterior probability that each individual belongs to each of the distinct hybrid classes. We demonstrate the method on allozyme data from two species of hybridizing trout, as well as on two simulated data sets.

Animals↗
PubMedDate not supplied

Patient flow based allocation of hospital resources.

The current practice of allocating resources within a hospital introduces peaks and troughs in the workloads of departments and leads therefore to loss of capacity. This happens when requirements for capacity coordination are not adequately taken into account in the decision making process of allocating resources to specialties. The first part of this research involved an analysis of the hospital's production system on dependencies between resources, resulting in a number of capacity coordination requirements that need to be fulfilled for optimized resource utilization. The second, modelling, part of the study involved the development of a framework for resource management decision making, of a set of computer models to support hospital managerial decision making on resource allocation issues in various parts of the hospital, and of an implementation strategy for the application of the models to concrete hospital settings. The third part of the study was devoted to a number of case-studies, illustrating the use of the models when applied in various resource management projects, such as a reorganization of an operating theatre timetable, or the development of a master plan for activities of a group of general surgeons serving two locations of a merged hospital system. The paper summarizes the main findings of the study and concludes with a discussion of results obtained with the new allocation procedure and with recommendations for future research.

Bed Occupancy↗
PubMed2003

Regional musculoskeletal examination: what the students say.

Confusion exists over which musculoskeletal examination skills medical students should learn. This study aimed to explore the views of third-year medical students. This was a qualitative study to allow in-depth exploration of beliefs and attitudes. Twenty students were randomly assigned to 1 of 2 focus groups. Their attitudes towards musculoskeletal examination were explored and discussed. The groups' discussions were recorded, transcribed, and framework analysis was undertaken with the aid of NUD*IST computer software. The following themes were identified: students dislike eponymous names for clinical tests; students felt there is a need for a more structured approach to musculoskeletal examination; students appeared unaware that many clinical tests were not based on evidence; students complained of a lack of confidence in the use of musculoskeletal clinical tests. Student's confidence in their musculoskeletal examination skills may be improved by the development of an agreed set of so-called core examination skills.

Journal Article↗
PubMed2006

Improved performance of bayesian solutions for inverse electrocardiography using multiple information sources.

The usual goal in inverse electrocardiography (ECG) is to reconstruct cardiac electrical sources from body surface potentials and a mathematical model that relates the sources to the measurements. Due to attenuation and smoothing that occurs in the thorax, the inverse ECG problem is ill-posed and imposition of a priori constraints is needed to combat this ill-posedness. When the problem is posed in terms of reconstructing heart surface potentials, solutions have not yet achieved clinical utility; limitations include the limited availability of good a priori information about the solution and the lack of a "good" error metric. We describe an approach that combines body surface measurements and standard forward models with two additional information sources: statistical prior information about epicardial potential distributions and sparse simultaneous measurements of epicardial potentials made with multielectrode coronary venous catheters. We employ a Bayesian methodology which offers a general way to incorporate these information sources and additionally provides statistical performance analysis tools. In a simulation study, we first compare solutions using one or more of these information sources. Then, we study the effects of varying the number of sparse epicardial potential measurements on reconstruction accuracy. To evaluate accuracy, we used the Bayesian error covariance as well as traditional error metrics such as relative error. Our results show that including even sparsely sampled information from coronary venous catheters can substantially improve the reconstruction of epicardial potential distributions and that a Bayesian framework provides a feasible approach to using this information. Moreover, computing the Bayesian error standard deviations offers a means to indicate confidence in the results even in the absence of validation data.

Action Potentials↗
PubMed2005

Inverse method predicting spinning modes radiated by a ducted fan from free-field measurements.

In the study the inverse problem of deducing the modal structure of the acoustic field generated by a ducted turbofan is addressed using conventional farfield directivity measurements. The final objective is to make input data available for predicting noise radiation in other configurations that would not have been tested. The present paper is devoted to the analytical part of that study. The proposed method is based on the equations governing ducted sound propagation and free-field radiation. It leads to fast computations checked on Rolls-Royce tests made in the framework of previous European projects. Results seem to be reliable although the system of equations to be solved is generally underdetermined (more propagating modes than acoustic measurements). A limited number of modes are thus selected according to any a priori knowledge of the sources. A first guess of the source amplitudes is obtained by adjusting the calculated maximum of radiation of each mode to the measured sound pressure level at the same angle. A least squares fitting gives the final solution. A simple correction can be made to take account of the mean flow velocity inside the nacelle which shifts the directivity patterns. It consists of modifying the actual frequency to keep the cut-off ratios unchanged.

Journal Article↗
PubMed1999

Effects of macromolecular transport and stochastic fluctuations on dynamics of genetic regulatory systems.

To predict the dynamics of genetic regulation, it may be necessary to consider macromolecular transport and stochastic fluctuations in macromolecule numbers. Transport can be diffusive or active, and in some cases a time delay might suffice to model active transport. We characterize major differences in the dynamics of model genetic systems when diffusive transport of mRNA and protein was compared with transport modeled as a time delay. Delays allow for history-dependent, non-Markovian responses to stimuli (i.e., "molecular memory"). Diffusion suppresses oscillations, whereas delays tend to create oscillations. When simulating essential elements of circadian oscillators, we found the delay between transcription and translation necessary for oscillations. Stochastic fluctuations tend to destabilize and thereby mask steady states with few molecules. This computational approach, combined with experiments, should provide a fruitful conceptual framework for investigating the function and dynamic properties of genetic regulatory systems.

Animals↗
PubMed2026

Leveraging bioinformatics approaches for drug repositioning in space radiation protection.

The health effects of space radiation, primarily Galactic Cosmic Rays (GCRs), on humans remain largely unknown, with potential cardiovascular consequences posing a significant threat to astronauts on long-duration spaceflight missions. Currently, there are no established pharmacological countermeasures for GCR exposure. Drug repositioning offers a promising strategy to accelerate pharmaceutical research in space medicine. This study leverages existing bioinformatics techniques to identify and prioritize potential drug candidates associated with proteomic perturbations following simulated GCR exposure using previously published murine cardiac proteomic data. A protein-protein interaction (PPI) network was constructed using the top differentially expressed proteins (DEPs) from murine heart tissue following exposure to 5-ion GCRs as seed nodes, focusing on experimentally supported interactions. Network topology, Markov clustering, and functional enrichment analyses were used to characterize biologically relevant proteins and pathways. Drug-protein interactions were predicted using Drugst.One and mapped to PPI clusters of interest to identify candidate drugs. Selected drug-macromolecule interactions were further explored using CB-Dock2 molecular docking and short-duration molecular dynamics simulations as hypothesis-generating structural assessments. Analysis of a key PPI network cluster consisting of several ATP synthase proteins identified 23 unique drug candidates. These analyses demonstrate a systematic approach for leveraging bioinformatics techniques to identify candidate molecular targets and generate pharmacological hypotheses in the context of space radiation countermeasures. Ultimately, this strategy introduces a hypothesis-generating framework for the prioritization of potential drug candidates for future computational characterization and experimental investigation against spaceflight stressors.

Animals↗
PubMedDate not supplied

[Neurophysiological mechanisms of acquisition of fear-resistance habit controlled by biological feedback displayed by skin galvanic response].

The aim of the study was to reveal a probable structural-functional basis of emotional self-regulation processes within the framework of cortex--basal ganglia interaction using on-line computer analysis of the EEG. The tested subjects were unable to overcome the emotional stress increasing in the process of decision making under conditions of high responsibility for the results of task solving. Striving to hold their social positions these subjects created a stable psychological set to keep their high responsibility and resist the relaxation tendency. Such a set facilitated the acceptance of the task for volitional effort to resist fear controlled by a biofeedback displayed in skin galvanic reaction.

Adult↗
PubMed1987

The implementation of nursing diagnoses. The Iowa Veterans Home experience.

This article has reviewed the process of implementing nursing diagnoses in one long-term care agency. Nursing diagnoses improved nursing process skills, made problem identification more accurate, and aided the identification of nursing interventions and desired outcomes. Nursing diagnoses have become the organizing framework for quality assurance, staff development, specialization and consultation, and computer applications. The presence of a professional model of nursing practice facilitated the use of nursing diagnoses. Prior to implementing nursing diagnoses, IVH nurses had defined the scope of nursing practice and formed a committee structure for decision-making by all RNs. The structure included mechanisms for collective and individual accountability. All nurses participated in the decision to use nursing diagnoses in their practice. Each nurse had the opportunity to influence the process of change. The process of implementing nursing diagnoses at IVH continues. Nurses recognize the need to establish the validity of each diagnostic statement. Skill with the diagnostic process is expected to improve. Nurses also recognize the need to test interventions for specific diagnoses. The standard nomenclature will continue to be used for the improvement of nursing practice and for nursing department programming. The use of nursing diagnoses is the basis of the continued development of a professional model of nursing practice.

Adult↗
PubMedDate not supplied

The generalized geometry of eye plaque therapy.

A calculation is described that enables the rapid assessment of dose rate at various points of interest within the eye (lens, optic nerve, etc.) for the treatment of choroidal melanoma by plaque therapy. 125I seeds are used as the radiation source. The location of the plaque and its associated seeds relative to the eye (in a Cartesian coordinate system) is determined from the description of the tumor, as drawn and dimensioned on a fundus-view diagram by the ophthalmologist. This requires a computer to numerically solve an equation, which is derived in the framework of spherical geometry. Further results of this calculation yield data files that serve as the input to a conventional brachytherapy treatment planning program. This enables the visualization of the dose distribution within a plane that contains the major axis of the tumor in order to assess the adequacy of the treated volume.

Brachytherapy↗
PubMed1998

Gibbs sampler for the logistic model in the analysis of longitudinal binary data.

Logistic mixed-effects models constitute a natural framework to study longitudinal binary response variables when the question addressed with the data is related to covariate effects within persons. However, the computations of the likelihoods are generally tedious and require the resolution of integrals which have no analytical solution. In this paper, we study a logistic mixed-effects model in a Bayesian framework and use the Gibbs sampler to overcome the current computational limitations. From a study of side-effects occurring during plasma exchanges, we explore the issues of bayesian formulation, model parametrization, choice of the prior distributions, diagnosing convergence, comparison between models and model adequacy. Finally, we show that a Bayesian random-effects model is useful to facilitate prediction.

Bayes Theorem↗
PubMedDate not supplied

Addressing organizational issues into the evaluation of medical systems.

New system design and evaluation methodologies are being developed to address social, organizational, political, and other non-technological issues in medical informatics. This paper describes a social interactionist framework for researching these kinds of organizational issues, based on research within medical informatics and other disciplines over the past 20 years. It discusses how effective evaluation strategies may be undertaken to address organizational issues concerning computer information systems in medicine and health care. The paper begins with a theoretical framework for evaluation. It then describes the 4Cs of evaluation: communication, care, control, and context. Five methodological guidelines are given for conducting comprehensive evaluations that address these 4Cs. An example of an evaluation research design that fits the guidelines and was used in an evaluation of an on-line clinical imaging system is discussed. Results of the evaluation study illustrate how this approach addresses organizational concerns and the 4Cs.

Communication↗