Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “computational frameworks”

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.

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

At least 577 records · Page 32Linked to original sources
PubMed2003

Development and evaluation of a computer-animated tutor for vocabulary and language learning in children with autism.

Using our theoretical framework of multimodal processing, we developed and evaluated a computer-animated tutor, Baldi, to teach vocabulary and grammar for children with autism. Baldi was implemented in a Language Wizard/Player, which allows easy creation and presentation of a language lesson involving the association of pictures and spoken words. The lesson plan includes both the identification of pictures and the production of spoken words. In Experiment 1, eight children were given initial assessment tests, tutorials, and reassessment tests 30 days following mastery of the vocabulary items. All of the students learned a significant number of new words and grammar. A second within-subject design with six children followed a multiple baseline design and documented that the program was responsible for the learning and generalization of new words. The research indicates that children with autism are capable of learning new language within an automated program centered around a computer-animated agent, multimedia, and active participation and can transfer and use the language in a natural, untrained environment.

Autistic Disorder↗
PubMed1994

A computational model for shape from texture.

Shape from texture is best analysed in a two-stage framework analogous to stereopsis and structure from motion: (a) computing the 'texture distortion' from the image; and (b) interpreting the 'texture distortion' to infer the orientation and shape of the scene surface in 3D. We model the texture distortion at a point in any particular direction on the image plane as an affine transformation and derive the relationship between the parameters of the affine transformation and the surface shape and orientation. We have developed a technique for estimating affine transforms between nearby image patches which is based on solving a system of linear constraints derived from a differential analysis. It is not necessary explicitly to identify texels or make restrictive assumptions about the nature of the image texture like isotropy. We have developed two different models for recovering surface orientation (slant and tilt) and shape (principal curvatures and directions) based on the estimated affine transforms in a number of directions. Experimental results are presented on images of planar and curved surfaces under perspective projection.

Animals↗
PubMed2003

A computational basis to object?

To use an object, we must be able to perceive the spatial relationship between the object's parts. The accepted view of how the brain coherently encodes an object is that some neurons in the frontal cortex employ an object-centered coordinate frame. A new computational model challenges this view, using the rich conceptual framework of neural basis functions.

Computational Biology↗
PubMedDate not supplied

Stress distribution on the metal framework of the implant-supported fixed prosthesis using different veneering materials.

PURPOSE: This study evaluated stress distribution in metal frameworks constructed on implants under masticatory forces using computer simulations. MATERIALS AND METHODS: Three-dimensional finite element analysis was used to study four different veneering materials-metal framework combinations using Calcitek implants. The veneering materials used in the study were porcelain, heat-polymerized poly(methyl methacrylate) resin, microfilled composite resin, and glass-modified composite resin. All computations were conducted for different levels on the buccal and lingual sides. RESULTS: Changing the veneering material on the prosthesis produced significant effects on stress levels and stress distribution on the metal frameworks. Stresses were concentrated along the marginal area of the prosthesis. Acrylic resin showed greater displacement than porcelain, probably because of its lower modulus of elasticity. CONCLUSION: In comparison to porcelain, more stress is borne by the acrylic resin-veneered metal framework under static loading.

Acrylic Resins↗
PubMed2003

Spectroscopic and computational characterization of the nickel-containing F430 cofactor of methyl-coenzyme M reductase.

Methyl-coenzyme M reductase (MCR) catalyzes the terminal reaction in methanogenesis, the formation of methane from methyl-coenzyme M and coenzyme B. The active site of MCR binds the prosthetic group F(430), a unique nickel hydrocorphin cofactor. Here, spectroscopy and computations are employed in developing detailed electronic descriptions of the Ni(II) and Ni(I) forms of the free cofactor. Absorption, magnetic circular dichroism (MCD), and variable-temperature variable-field MCD data are analyzed within the framework of time-dependent DFT computations to assign key electronic transitions. DFT calculations are further employed to evaluate possible reduced F(430) models-a one-electron reduced Ni(I)F(430) model and a three-electron reduced Ni(I)F(red430) model (possessing a reduced hydrocorphin ligand)-on the basis of excited-state spectra and published EPR/ENDOR parameters. While calculations on both models yield spectroscopic parameters that are consistent with most experimental data, overall better agreement is achieved using the Ni(I)F(430) model, particularly with respect to electronic absorption and (1)H ENDOR. The experimentally validated bonding descriptions generated herein show that in Ni(II)F(430) the occupied Ni 3d orbitals are too low in energy to significantly perturb the dominant electronic transition involving the pi and pi* frontier MOs of the macrocycle (i.e., the HOMO-->LUMO transition). Upon one-electron reduction of the Ni(II) ion, the occupied Ni 3d orbitals are raised in energy, shifting between the HOMO and the LUMO of the oxidized cofactor. These ground-state changes have a dramatic effect on the excited-state structure, causing a blue shift of the dominant pi-->pi* transition and the appearance of numerous Ni 3d-->hydrocorphin pi* charge-transfer features in the vis/near-IR region.

Computational Biology↗
PubMed2006

Computational principles of working memory in sentence comprehension.

Understanding a sentence requires a working memory of the partial products of comprehension, so that linguistic relations between temporally distal parts of the sentence can be rapidly computed. We describe an emerging theoretical framework for this working memory system that incorporates several independently motivated principles of memory: a sharply limited attentional focus, rapid retrieval of item (but not order) information subject to interference from similar items, and activation decay (forgetting over time). A computational model embodying these principles provides an explanation of the functional capacities and severe limitations of human processing, as well as accounts of reading times. The broad implication is that the detailed nature of cross-linguistic sentence processing emerges from the interaction of general principles of human memory with the specialized task of language comprehension.

Attention↗
PubMed2004

Collision handling of deformable anatomical models for real-time surgery simulation.

Efficient collision handling of dynamically deforming anatomical models is a very challenging problem in real-time surgery simulation. In this paper, we present a new, efficient approach that detects collisions and self-collisions of deformable models. Our algorithm is integrated in a simulation framework for multiple interacting objects. This framework consists of three components. The first one computes the dynamic behavior of deformable structures using an efficient and robust approach with distance- and volume-preserving constraints. The second component detects collisions and self-collisions of deformable models. A novel image-space technique is employed that detects volumetric intersections. This allows to compute the penetration depth which is used to resolve collisions in the third component of our framework. Our system handles volumetric deformable models of up to several thousand surface triangles and tetrahedra in real-time and can be used in surgical training systems.

Algorithms↗
PubMed2006

The place of white in a world of grays: a double-anchoring theory of lightness perception.

The specific gray shades in a visual scene can be derived from relative luminance values only when an anchoring rule is followed. The double-anchoring theory I propose in this article, as a development of the anchoring theory of Gilchrist et al. (1999), assumes that any given region (a) belongs to one or more frameworks, created by Gestalt grouping principles, and (b) is independently anchored, within each framework, to both the highest luminance and the surround luminance. The region's final lightness is a weighted average of the values computed, relative to both anchors, in all frameworks. The new model accounts not only for all lightness illusions that are qualitatively explained by the anchoring theory but also for a number of additional effects, and it does so quantitatively, with the support of mathematical simulations.

Attention↗
PubMed2006

Finger synergies during multi-finger cyclic production of moment of force.

We investigated multi-finger synergies stabilizing the total moment of force and the total force when the subjects produced a quick cyclic change in the total moment of force. The seated subjects performed the task with the fingers of the dominant arm while paced by the metronome at 1.33 Hz. They were required to produce a rhythmic, sine-like change in the total pronation-supination moment of force computed with respect to the midpoint between the middle and ring fingers. The framework of the uncontrolled manifold hypothesis was used to compute indices of stabilization of the total moment and of the total force across 20 cycles. Variance of the total moment showed a cyclic pattern with peaks close to the peak rate of the moment change. Variance of the total force was maximal close to peak moment into supination. Higher magnitudes of the moment directed against the required moment direction (antagonist moment) were produced by individual fingers during supination efforts as compared to pronation efforts. Indices of multi-finger synergies showed across-trials stabilization of the total moment over the whole cycle but not of the total force. These indices were smaller during supination efforts. We conclude that the central nervous system facilitates multi-finger synergies stabilizing the total rotational action across a variety of tasks. Synergies stabilizing the total force are not seen in tasks that do not explicitly require accurate force control. Pronation efforts are performed more efficiently and with better stabilization of the action.

Adult↗
PubMed1997

Cost-effective management of high-risk patients: a case-map approach.

BACKGROUND: The case-management approach to patient care used by most cardiac surgical practices frequently highlights patients designated as high-risk. Increased risk might be because of advanced age, the need for complex reoperations, high risk of bleeding, and renal failure, all of which may be superimposed on poor ventricular performance. METHODS: A small consensus panel of cardiac surgeons, anesthesiologists, perfusionists, cardiac-care nurse managers, and coagulation experts met to assess the potential for development of case-management pathways targeted towards high-risk coronary artery bypass graft patients. The process comprised review of the literature to identify risk factors and strategies most cost-effective in reducing risk. RESULTS: A series of management strategies driven by data from the literature--or by consensus when such information was not available--were developed to cost-effectively manage the high-risk patient. The process was then converted to a multidimensional computer program. This personal computer-driven program served as a framework upon which any institution could impose its own practice style and modify recommendations. The program was designed to be interactive and to allow easy transition from patient-management strategies to support data. A facilitator generally coordinates the interaction between the local patient-care group and the computer information base to evolve a case-management map. CONCLUSIONS: By using stored information based on current literature and easily updated, the system is both educational and product oriented, and provides a case-map approach to the cost-effective management of patients during the preoperative, intraoperative, and postoperative phases of hospital care.

Case Management↗
PubMed1995

A generalizable framework for information systems for physician recruitment/referral.

Hospital information systems have evolved from data processing systems for patient billing and payroll to decision-support systems which support decision making at the middle and upper management levels. With the advancements in the areas of database management, expert systems and networks, important hospital functions such as physician recruitment and referral which historically were performed using traditional procedures, are now performed using these computer-based technologies. Develops a generalizable framework for information systems for physician recruitment and referral using technologies of database management, expert systems and networks. This GIS-PRR system may be used by hospitals and other health-care providers to improve the efficiency and effectiveness of the physician recruitment/referral process.

Database Management Systems↗
PubMed2005

Optimized stereo reconstruction of free-form space curves based on a nonuniform rational B-spline model.

Analytical reconstruction of 3D curves from their stereo images is an important issue in computer vision. We present an optimization framework for such a problem based on a nonuniform rational B-spline (NURBS) curve model that converts reconstruction of a 3D curve into reconstruction of control points and weights of a NURBS representation of the curve, accordingly bypassing the error-prone point-to-point correspondence matching. Perspective invariance of NURBS curves and constraints deduced on stereo NURBS curves are employed to formulate the 3D curve reconstruction problem into a constrained nonlinear optimization. A parallel rectification technique is then adopted to simplify the constraints, and the Levenberg-Marquardt algorithm is applied to search for the optimal solution of the simplified problem. The results from our experiments show that the proposed framework works stably in the presence of different data samplings, randomly posed noise, and partial loss of data and is potentially suitable for real scenes.

Algorithms↗
PubMed2003

LOGOS: a modular Bayesian model for de novo motif detection.

The complexity of the global organization and internal structures of motifs in higher eukaryotic organisms raises significant challenges for motif detection techniques. To achieve successful de novo motif detection it is necessary to model the complex dependencies within and among motifs and incorporate biological prior knowledge. In this paper, we present LOGOS, an integrated LOcal and GlObal motif Sequence model for biopolymer sequences, which provides a principled framework for developing, modularizing, extending and computing expressive motif models for complex biopolymer sequence analysis. LOGOS consists of two interacting submodels: HMDM, a local alignment model capturing biological prior knowledge and positional dependence within the motif local structure; and HMM, a global motif distribution model modeling frequencies and dependencies of motif occurrences. Model parameters can be fit using training motifs within an empirical Bayesian framework. A variational EM algorithm is developed for de novo motif detection. LOGOS improves over existing models that ignore biological priors and dependencies in motif structures and motif occurrences, and demonstrates superior performance on both semi-realistic test data and cis-regulatory sequences from yeast and Drosophila sequences with regard to sensitivity, specificity, flexibility and extensibility.

Algorithms↗
PubMed1995

Stereopsis, vertical disparity and relief transformations.

The pattern of retinal binocular disparities acquired by a fixating visual system depends on both the depth structure of the scene and the viewing geometry. This paper treats the problem of interpreting the disparity pattern in terms of scene structure without relying on estimates of fixation position from eye movement control and proprioception mechanisms. We propose a sequential decomposition of this interpretation process into disparity correction, which is used to compute three-dimensional structure up to a relief transformation, and disparity normalization, which is used to resolve the relief ambiguity to obtain metric structure. We point out that the disparity normalization stage can often be omitted, since relief transformations preserve important properties such as depth ordering and coplanarity. Based on this framework we analyse three previously proposed computational models of disparity processing; the Mayhew and Longuet-Higgins model, the deformation model and the polar angle disparity model. We show how these models are related, and argue that none of them can account satisfactorily for available psychophysical data. We therefore propose an alternative model, regional disparity correction. Using this model we derive predictions for a number of experiments based on vertical disparity manipulations, and compare them to available experimental data. The paper is concluded with a summary and a discussion of the possible architectures and mechanisms underling stereopsis in the human visual system.

Convergence, Ocular↗
PubMed1985

[Value of computer tomographic determination of spleen size for the elucidation of splenic involvement within the framework of primary lymph node neoplasms].

The splenic index was determined in 155 persons, without evidence of splenic disease, in order to obtain a simple measure of splenic size. Subsequently 36 patients with malignant lymphomas and who then had their spleens removed were examined by CT. A comparison of the CT and pathological-anatomical findings showed that it is a valuable non-invasive method for diagnosing splenic involvement, having a specificity of 86%, sensitivity of 77% and accuracy of 83%.

Adolescent↗
PubMed2005

Performance evaluation of image processing algorithms in CADe.

One of the key limitations of existing image processing algorithms for computer-aided detection (CADe) is that they are often designed and evaluated in an ad hoc manner. This paper characterizes some of the issues and shortcomings in existing performance evaluation paradigms for image processing algorithms in breast cancer screening, particularly in the context of computer aided detection. We present the framework for establishing a performance evaluation process using standardized criteria. We conclude with some specific recommendations to improve the infrastructure for evaluation the performance of image processing algorithms.

Algorithms↗
PubMed2004

Logos: a modular bayesian model for de novo motif detection.

The complexity of the global organization and internal structure of motifs in higher eukaryotic organisms raises significant challenges for motif detection techniques. To achieve successful de novo motif detection, it is necessary to model the complex dependencies within and among motifs and to incorporate biological prior knowledge. In this paper, we present LOGOS, an integrated LOcal and GlObal motif Sequence model for biopolymer sequences, which provides a principled framework for developing, modularizing, extending and computing expressive motif models for complex biopolymer sequence analysis. LOGOS consists of two interacting submodels: HMDM, a local alignment model capturing biological prior knowledge and positional dependency within the motif local structure; and HMM, a global motif distribution model modeling frequencies and dependencies of motif occurrences. Model parameters can be fit using training motifs within an empirical Bayesian framework. A variational EM algorithm is developed for de novo motif detection. LOGOS improves over existing models that ignore biological priors and dependencies in motif structures and motif occurrences, and demonstrates superior performance on both semi-realistic test data and cis-regulatory sequences from yeast and Drosophila genomes with regard to sensitivity, specificity, flexibility and extensibility.

Algorithms↗
PubMed1996

Neuronal-based synaptic compensation: a computational study in Alzheimer's disease.

In the framework of an associative memory model, we study the interplay between synaptic deletion and compensation, and memory deterioration, a clinical hallmark of Alzheimer's disease. Our study is motivated by experimental evidence that there are regulatory mechanisms that take part in the homeostasis of neuronal activity and act on the neuronal level. We show that following synaptic deletion, synaptic compensation can be carried out efficiently by a local, dynamic mechanism, where each neuron maintains the profile of its incoming post-synaptic current. Our results open up the possibility that the primary factor in the pathogenesis of cognitive deficiencies in Alzheimer's disease (AD) is the failure of local neuronal regulatory mechanisms. Allowing for neuronal death, we observe two pathological routes in AD, leading to different correlations between the levels of structural damage and functional decline.

Alzheimer Disease↗