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At least 505 records · Page 28Linked to original sources
PubMed1998

Constrained optimization for neural map formation: a unifying framework for weight growth and normalization.

Computational models of neural map formation can be considered on at least three different levels of abstraction: detailed models including neural activity dynamics, weight dynamics that abstract from the neural activity dynamics by an adiabatic approximation, and constrained optimization from which equations governing weight dynamics can be derived. Constrained optimization uses an objective function, from which a weight growth rule can be derived as a gradient flow, and some constraints, from which normalization rules are derived. In this article, we present an example of how an optimization problem can be derived from detailed nonlinear neural dynamics. A systematic investigation reveals how different weight dynamics introduced previously can be derived from two types of objective function terms and two types of constraints. This includes dynamic link matching as a special case of neural map formation. We focus in particular on the role of coordinate transformations to derive different weight dynamics from the same optimization problem. Several examples illustrate how the constrained optimization framework can help in understanding, generating, and comparing different models of neural map formation. The techniques used in this analysis may also be useful in investigating other types of neural dynamics.

Animals↗
PubMed2005

Proposal for a framework for optimizing artificial environments based on physiological feedback.

We propose and then evaluate a new framework for finding the physical parameters of an artificial environment which give rise to given target physiological characteristics. We assume that a human is a system that takes as inputs the physical parameters of an artificial environment and outputs physiological parameters in response. We define our task as the inverse problem; we must find the best inputs from given target outputs. Our proposed framework solves the inverse problem using evolutionary computation techniques to optimize an artificial environment. We evaluate this framework using a simulation with a vibration environment and verify that it works.

Environment, Controlled↗
PubMed1995

Coevolutionary computation.

This article proposes a general framework for the use of coevolution to boost the performance of genetic search. It combines coevolution with yet another biologically inspired technique, called lifetime fitness evaluation (LTFE). Two unrelated problems--neural net learning and constraint satisfaction--are used to illustrate the approach. Both problems use predator-prey interactions to boost the search. In contrast with traditional "single population" genetic algorithms (GAs), two populations constantly interact and co-evolve. However, the same algorithm can also be used with different types of co-evolutionary interactions. As an example, the symbiotic coevolution of solutions and genetic representations is shown to provide an elegant solution to the problem of finding a suitable genetic representation. The approach presented here greatly profits from the partial and continuous nature of LTFE. Noise tolerance is one advantage. Even more important, LTFE is ideally suited to deal with coupled fitness landscapes typical for coevolution.

Algorithms↗
PubMed2006

Thin double layer approximation to describe streaming current fields in complex geometries: analytical framework and applications to microfluidics.

We set up an analytical framework that allows one to describe and compute streaming effects and electro-osmosis on an equal footing. This framework relies on the thin double layer approximation commonly used for description of electroosmotic flows, but rarely used for streaming problems. Using this framework we quantitatively assess the induction of bulk streaming current patterns by topographic or charge heterogeneities on surfaces. This too also permits analytical computation of all linear electrokinetic effects in complex microfluidic geometries, and we discuss a few immediate applications.

Journal Article↗
PubMedDate not supplied

Consumer informatics in chronic illness.

OBJECTIVE: To explore the informatic requirements in the home care of chronically ill patients. DESIGN: A number of strategies were deployed to help evoke a picture of home care informatics needs: A detailed questionnaire evaluating informational needs and assessing programmable technologies was distributed to a clinic population of parents of children with cancer. Open ended questionnaires were distributed to medical staff and parents soliciting a list of questions asked of medical staff. Parent procedure training was observed to evaluate the training dialog, and parents were observed interacting with a prototype information and education computer offering. RESULTS: Parents' concerns ranged from the details of managing day to day, to conceptual information about disease and treatment, to management of psychosocial problems. They sought information to solve problems and to provide emotional support, which may create conflicts of interest when the material is threatening. Whether they preferred to be informed by a doctor, nurse, or another parent depended on the nature of the information. Live interaction was preferred to video, which was preferred to text for all topics. Respondents used existing technologies in a straightforward way but were enthusiastic about the proposed use of computer technology to support home care. Multimedia solutions appear to complement user needs and preferences. CONCLUSION: Consumers appear positively disposed toward on-line solutions. On-line systems can offer breadth, depth and timeliness currently unattainable. Patients should be involved in the formation and development process in much the same way that users are involved in user-centered computer interface design. A generic framework for patient content is presented that could be applied across multiple disorders.

Adaptation, Psychological↗
PubMed2002

[The 3D PACS image system based on pipeline framework].

We put forward an image rendering system based on pipeline framework for processing and displaying medical images. Compared to original computer graphics algorithms divided into volume rendering and surface rendering, this framework can effectively comprehend methods of computer graphics and image processing, import some new concepts such as vertex buffer, pixel buffer and texture buffer. We implement Shaded Surface Display, Maximum Intensity Projection, Digitally Reconstructed Radiography, Multi planar Reformation, Curved Planar Reformation and Interactive Virtual Endoscopy in our new developed PACS image system.

Algorithms↗
PubMed2005

A user-centered framework for redesigning health care interfaces.

Numerous health care systems are designed without consideration of user-centered design guidelines. Consequently, systems are created ad hoc, users are dissatisfied and often systems are abandoned. This is not only a waste of human resources, but economic resources as well. In order to salvage such systems, we have combined different methods from the area of computer science, cognitive science, psychology, and human-computer interaction to formulate a framework for guiding the redesign process. The paper provides a review of the different methods involved in this process and presents a life cycle of our redesign approach. Following the description of the methods, we present a case study, which shows a successfully applied example of the use of this framework. A comparison between the original and redesigned interfaces showed improvements in system usefulness, information quality, and interface quality.

Artificial Intelligence↗
PubMed2005

Algorithmic approaches for computing elementary modes in large biochemical reaction networks.

The concept of elementary (flux) modes provides a rigorous description of pathways in metabolic networks and proved to be valuable in a number of applications. However, the computation of elementary modes is a hard computational task that gave rise to several variants of algorithms during the last years. This work brings substantial progresses to this issue. The authors start with a brief review of results obtained from previous work regarding (a) a unified framework for elementary-mode computation, (b) network compression and redundancy removal and (c) the binary approach by which elementary modes are determined as binary patterns reducing the memory demand drastically without loss of speed. Then the authors will address herein further issues. First, a new way to perform the elementarity tests required during the computation of elementary modes which empirically improves significantly the computation time in large networks is proposed. Second, a method to compute only those elementary modes where certain reactions are involved is derived. Relying on this method, a promising approach for computing EMs in a completely distributed manner by decomposing the full problem in arbitrarity many sub-tasks is presented. The new methods have been implemented in the freely available software tools FluxAnalyzer and Metatool and benchmark tests in realistic networks emphasise the potential of our proposed algorithms.

Algorithms↗
PubMed1999

A framework and tools for authoring, editing, documenting, sharing, searching, navigating, and executing computer-based clinical guidelines.

With the spread of managed care and integrated delivery networks, an increased emphasis has been placed on the cost-effectiveness of clinical practices. The need has been recognized to use guidelines to support education, and to integrate them into clinical practice. A specification for guideline representation that would facilitate computer-based clinical guideline sharing has been developed by the InterMed Collaboratory. Called GLIF (GuideLine Interchange Format), this specification and its proposed extensions have been the basis for our implementation of a framework and suite of integrated software tools for guideline authoring and editing, packaging in XML, Internet distribution, navigation, eligibility determination, and automatic execution.

Eligibility Determination↗
PubMed2006

Application of a two-length-scale field theory to the solvation of neutral and charged molecules.

We develop a continuous self-consistent theory of solute-water interactions that allows determination of the hydrophobic layer around a solute molecule of any geometry, with an explicit account of solvent structure described by its correlation function. We compute the mean solvent density profile n(r) surrounding the solute molecule as well as its solvation free energy deltaG. We compare the two-length-scale field theory to the numerical data of Monte Carlo simulations found in the literature for spherical molecules and discuss the possibility of self-consistent adjustment of the free parameters of the theory. In the framework of this approach, we compute the solvation free energies of alkane molecules and the free energy of interaction of two spheres of radius R separated by the distance D. We describe the general setting of the self-consistent account of electrostatic interactions in the framework of our model where the water is considered not as a continuous medium but as a gas of dipoles. We analyze the limiting cases where the proposed theory coincides with the electrostatics of a continuous medium.

Journal Article↗
PubMed1999

Merging multiple institutions: information architecture problems and solutions.

Amalgamating organizations face great challenges when trying to merge their formerly separate information systems. An architectural approach is essential in order to understand the business process and data implications of the new organization's business decisions and application choices. HL7 is useful as a common messaging standard, but does not help to reconcile conflicting local identifier coding systems. The Information Services department has an important role in catalyzing decisions about inconsistent business processes and conflicting universal coding systems within an enterprise framework.

Computer Systems↗
PubMed2001

End-user support: a necessary issue in the implementation and use of EPR systems.

A successful integration of an IT-system is dependent not only of the quality of the information and the user interface features of the system but also of the organizations ability to support the users learning process. As IT is becoming more and more pervasive in the Health Care sector as such there is a need for a systematic approach to the question on how to support end-users. Based on an empirical study of an implementation process in a Danish Primary Health Care Services the concept of end-user support is discussed and it is argued that there is a need for a distinction between different kinds of support depending of the type of activity involved. First the organizations strategy for learning when the system was implemented is described. The evaluation of the learning strategy revealed that there was a need for different kinds of knowledge involving qualitatively different kinds of learning. Second the area of end-user support is discussed and it is argued that the common understanding of end-user support as something provided by DP staff, vendors or manuals are to narrow. Third a more differentiated way of thinking of support that link the need for different kind of knowledge and learning processes to different kinds of support is proposed. Finally Activity Theory is put forward as a possible basis that provide the opportunity of discussing issues belonging to different kinds of end-user support within an integrated framework.

Computer User Training↗
PubMed2005

Theoretical predictions of chemical degradation reaction mechanisms of RDX and other cyclic nitramines derived from their molecular structures.

Analysis of environmental degradation pathways of contaminants is aided by predictions of likely reaction mechanisms and intermediate products derived from computational models of molecular structure. Quantum mechanical methods and force-field molecular mechanics were used to characterize cyclic nitramines. Likely degradation mechanisms for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) include hydroxylation utilizing addition of hydroxide ions to initiate proton abstraction via 2nd order rate elimination (E2) or via nucleophilic substitution of nitro groups, reductive chemical and biochemical degradation, and free radical oxidation. Due to structural similarities, it is predicted that, under homologous circumstances, certain RDX environmental degradation pathways should also be effective for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and similar cyclic nitramines. Computational models provided a theoretical framework whereby likely transformation mechanisms and transformation products of cyclic nitramines were predicted and used to elucidate in situ degradation pathways.

Azocines↗
PubMed2003

Neural representation of probabilistic information.

It has been proposed that populations of neurons process information in terms of probability density functions (PDFs) of analog variables. Such analog variables range, for example, from target luminance and depth on the sensory interface to eye position and joint angles on the motor output side. The requirement that analog variables must be processed leads inevitably to a probabilistic description, while the limited precision and lifetime of the neuronal processing units lead naturally to a population representation of information. We show how a time-dependent probability density rho(x; t) over variable x, residing in a specified function space of dimension D, may be decoded from the neuronal activities in a population as a linear combination of certain decoding functions phi(i)(x), with coefficients given by the N firing rates a(i)(t) (generally with D << N). We show how the neuronal encoding process may be described by projecting a set of complementary encoding functions phi;(i)(x) on the probability density rho(x; t), and passing the result through a rectifying nonlinear activation function. We show how both encoders phi;(i)(x) and decoders phi(i)(x) may be determined by minimizing cost functions that quantify the inaccuracy of the representation. Expressing a given computation in terms of manipulation and transformation of probabilities, we show how this representation leads to a neural circuit that can carry out the required computation within a consistent Bayesian framework, with the synaptic weights being explicitly generated in terms of encoders, decoders, conditional probabilities, and priors.

Models, Neurological↗
PubMedDate not supplied

Medical informatics and the science of cognition.

Recent developments in medical informatics research have afforded possibilities for great advances in health care delivery. These exciting opportunities also present formidable challenges to the implementation and integration of technologies in the workplace. As in most domains, there is a gulf between technologic artifacts and end users. Since medical practice is a human endeavor, there is a need for bridging disciplines to enable clinicians to benefit from rapid technologic advances. This is turn necessitates a broadening of disciplinary boundaries to consider cognitive and social factors pertaining to the design and use of technology. The authors argue for a place of prominence for cognitive science. Cognitive science provides a framework for the analysis and modeling of complex human performance and has considerable applicability to a range of issues in informatics. Its methods have been employed to illuminate different facets of design and implementation. This approach has also yielded insights into the mechanisms and processes involved in collaborative design. Cognitive scientific methods and theories are illustrated in the context of two examples that examine human-computer interaction in medical contexts and computer-mediated collaborative processes. The framework outlined in this paper can be used to refine the process of iterative design, end-user training, and productive practice.

Cognitive Science↗
PubMed1992

[Acute abdominal pain--standardized findings as diagnostic support. Results of a prospective multicenter intervention study and testing of a computer-assisted diagnosis system].

Despite powerful diagnostic tools (e.g. ultrasound, special laboratory investigations), the diagnosis of acute abdominal pain is still a considerable problem. Several studies in the UK have shown that the diagnostic accuracy can be improved by structured and standardized history taking and clinical examination and by computer-aided diagnosis. In the framework of a concerted action of the European Community we have conducted a prospective multicenter interventional trial comparing two consecutive phases: a) a baseline phase in clinical routine without additional intervention, b) a test phase with structured and standardized history and clinical examination (questionnaire, documentation programme). In addition, a computer-aided diagnostic system developed in the UK was applied to the cases in the test phase. Outcome criteria were the diagnostic accuracy of the initial and the final examiner, the perforated appendix rate, the negative appendectomy rate, the negative laparotomy rate and the rates of diagnostic errors with missing indication to operation and of delayed urgent operations. No differences could be found between the phases with respect to the outcome criteria. In the baseline phase (test phase) diagnostic accuracy was 59% (59%), diagnostic accuracy after investigation (senior examiner) was 77% (78%), perforated appendix rate was 11% (16%), negative appendectomy rate was 13% (15%), negative laparotomy rate was 7% (8%), the rate of missed urgent indications to operation was 1.1% (1.9%) and the rate of delayed urgent operations was 3.4% (2.4%). Major differences between the centers were recorded. Computer-aided diagnosis resulted in a diagnostic accuracy of 51%. The introduction of structured and standardized history taking and clinical examination has not brought any improvement of the good results in clinical routine. It is doubtful, whether existing systems of computer-aided diagnosis are able to significantly decrease the still remaining error rate of 20%.

Abdomen, Acute↗
PubMed2005

Computational and in vitro studies of persistent activity: edging towards cellular and synaptic mechanisms of working memory.

Persistent neural activity selective to features of an extinct stimulus has been identified as the neural correlate of working memory processes. The precise nature of the physiological substrate for this self-sustained activity is still unknown. In the last few years, this problem has gathered experimental together with computational neuroscientists in a quest to identify the cellular and network mechanisms involved. I introduce here the attractor theory framework within which current persistent activity computational models are built, and I then review the main physiological mechanisms that have been linked thereby to persistent activity and working memory. Open computational and physiological issues with these models are discussed, together with their potential experimental validation in current in vitro models of persistent activity.

Action Potentials↗
PubMed2006

Design of stereoselective Ziegler-Natta propene polymerization catalysts.

After five decades of largely serendipitous (albeit formidable) progress, catalyst design in Ziegler-Natta olefin polymerization, i.e., the rational implementation of new active species to target predetermined polyolefin architectures, has ultimately become a realistic ambition, thanks to a much deeper fundamental understanding and major advances in the tools of computational chemistry. In this article, we discuss, as a case history, a unique class of stereorigid C2-symmetric bis(phenoxy-amine)Zr(IV) catalysts with controlled kinetic behavior. A large variety of polypropylene microstructures have been obtained with these catalysts by modulating the steric demand of one key substituent, without altering the nature and symmetry of the ancillary ligand framework, under the guidance of computer modeling. This unusual achievement is relevant per se and for the perspective implications in catalyst discovery.

Journal Article↗