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At least 1,405 records · Page 78Linked to original sources
PubMed2006

Dynamics of polymer translocation through nanopores: theory meets experiment.

The dynamics of translocation of polymer molecules through nanopores is investigated via molecular dynamics. We find that an off-lattice minimalist model of the system is sufficient to reproduce quantitatively all the experimentally observed trends and scaling behavior. Specifically, simulations show (i) two translocation regimes depending on the ratio of pore and polymer length, (ii) two different regimes for the probability of translocation depending on applied voltage, (iii) an exponential dependence of translocation velocity upon applied voltage, and (iv) an exponential decrease of the translocation time with temperature. We also propose a simple theoretical explanation of each of the observed trends within a free energy landscape framework.

Computer Simulation↗
PubMed2005

Optimal block boundary pre/postfiltering for wavelet-based image and video compression.

This paper presents a pre/postfiltering framework to reduce the reconstruction errors near block boundaries in wavelet-based image and video compression. Two algorithms are developed to obtain the optimal filter, based on boundary filter bank and polyphase structure, respectively. A low-complexity structure is employed to approximate the optimal solution. Performances of the proposed method in the removal of JPEG 2000 tiling artifact and the jittering artifact of three-dimensional wavelet video coding are reported. Comparisons with other methods demonstrate the advantages of our pre/postfiltering framework.

Algorithms↗
PubMed2005

Screw preloads and measurements of surface roughness in screw joints: an in vitro study on implant frameworks.

BACKGROUND: With the development of milled titanium implant frameworks, new surfaces that have not previously been studied are now being used in screw joints. PURPOSE: The aims of the present study were to compare the preload produced in screw-retained titanium and gold alloy frameworks and the preload for titanium frameworks before and after the application of veneers. Another aim was to try to relate the surface roughness of the screw joints to variations in preload. MATERIALS AND METHODS: Ten identical titanium and five gold alloy frameworks were fabricated. The gold screws were tightened to 10 Ncm. Preload measurements were made for the gold alloy frameworks and before and after the porcelain or acrylic resin veneers had been applied to the titanium frameworks. Surface roughness measurements were made after preload measurements on the screw joint surfaces of the titanium frameworks and corresponding gold screws. RESULTS: The preloads for the titanium and gold alloy frameworks were similar. Preload in both types of frameworks decreased after repeated torques (p<.05-.01) but was unaffected by the application of veneering materials to the titanium frameworks (p>.05). No relationship (p>.05) between preload and surface roughness characteristics was observed. Loaded titanium framework screw sites, however, had lower mean S(a) values than unloaded sites (p<.001), whereas the surfaces of loaded gold screws had higher mean S(a) values compared with the surfaces of control gold screws (p<.05-.001). CONCLUSION: When using gold screws, milled titanium frameworks have preloads similar to those of gold alloy frameworks and preloads for both decrease after repeated tightening. The preload was similar before and after the veneering of the titanium frameworks. Unloaded milled titanium screw sites had rougher surfaces than loaded, and loaded gold screws had rougher surfaces than unloaded. However, no correlation between screw joint surface and preload was observed for veneered titanium frameworks.

Computer-Aided Design↗
PubMed2003

A deformable finite element derived finite difference method for cardiac activation problems.

We present a finite element (FE) derived finite difference (FD) technique for solving cardiac activation problems over deforming geometries using a bidomain framework. The geometry of the solution domain is defined by a FE mesh and over these FEs a high resolution FD mesh is generated. The difference points are located at regular intervals in the normalized material space within each of the FEs. The bidomain equations are then transformed to the embedded FD mesh which provides a solution space that is both regular and orthogonal. The solution points move in physical space with any deformation of the solution domain, but the equations are set up in such a way that the solution is invariant as it is constructed in material space. The derivation of this new solution technique is presented along with a series of examples that demonstrate the accuracy of this bidomain framework.

Action Potentials↗
PubMed2005

Interpretation of proton relative biological effectiveness using lesion induction, lesion repair, and cellular dose distribution.

Phenomenological biophysical models have been successfully used to estimate the relative biological effectiveness (RBE) of ions. The predictive power of these models is limited because they require measured dose-response data that are not necessarily available for all clinically relevant end points. Furthermore, input parameters often lack mechanistic interpretation. In order to link RBE to more fundamental biological parameters we combine the concepts of two well-established biophysical models, i.e., the phenomenological "track structure" model and the more mechanistic "lethal lesion/potentially lethal lesion" (LPL) model. We parametrize a relation between RBE, dose homogeneity in the cell nucleus and induction rates for different lesion types. The macroscopic dose-response relationship is described in the LPL model and the microscopic, subcellular, relationship is determined by the local dose deposition pattern. The formalism provides a framework for a mechanistic interpretation of RBE values.

Cell Survival↗
PubMed2003

A taxonomy for spatiotemporal connectionist networks revisited: the unsupervised case.

Spatiotemporal connectionist networks (STCNs) comprise an important class of neural models that can deal with patterns distributed in both time and space. In this article, we widen the application domain of the taxonomy for supervised STCNs recently proposed by Kremer (2001) to the unsupervised case. This is possible through a reinterpretation of the state vector as a vector of latent (hidden) variables, as proposed by Meinicke (2000). The goal of this generalized taxonomy is then to provide a nonlinear generative framework for describing unsupervised spatiotemporal networks, making it easier to compare and contrast their representational and operational characteristics. Computational properties, representational issues, and learning are also discussed, and a number of references to the relevant source publications are provided. It is argued that the proposed approach is simple and more powerful than the previous attempts from a descriptive and predictive viewpoint. We also discuss the relation of this taxonomy with automata theory and state-space modeling and suggest directions for further work.

Classification↗
PubMed2005

Inference of demographic history from genealogical trees using reversible jump Markov chain Monte Carlo.

BACKGROUND: Coalescent theory is a general framework to model genetic variation in a population. Specifically, it allows inference about population parameters from sampled DNA sequences. However, most currently employed variants of coalescent theory only consider very simple demographic scenarios of population size changes, such as exponential growth. RESULTS: Here we develop a coalescent approach that allows Bayesian non-parametric estimation of the demographic history using genealogies reconstructed from sampled DNA sequences. In this framework inference and model selection is done using reversible jump Markov chain Monte Carlo (MCMC). This method is computationally efficient and overcomes the limitations of related non-parametric approaches such as the skyline plot. We validate the approach using simulated data. Subsequently, we reanalyze HIV-1 sequence data from Central Africa and Hepatitis C virus (HCV) data from Egypt. CONCLUSIONS: The new method provides a Bayesian procedure for non-parametric estimation of the demographic history. By construction it additionally provides confidence limits and may be used jointly with other MCMC-based coalescent approaches.

Algorithms↗
PubMed2005

Decentralized formation flying control in a multiple-team hierarchy.

In recent years, formation flying has been recognized as an enabling technology for a variety of mission concepts in both the scientific and defense arenas. Examples of developing missions at NASA include magnetospheric multiscale (MMS), solar imaging radio array (SIRA), and terrestrial planet finder (TPF). For each of these missions, a multiple satellite approach is required in order to accomplish the large-scale geometries imposed by the science objectives. In addition, the paradigm shift of using a multiple satellite cluster rather than a large, monolithic spacecraft has also been motivated by the expected benefits of increased robustness, greater flexibility, and reduced cost. However, the operational costs of monitoring and commanding a fleet of close-orbiting satellites is likely to be unreasonable unless the onboard software is sufficiently autonomous, robust, and scalable to large clusters. This paper presents the prototype of a system that addresses these objectives-a decentralized guidance and control system that is distributed across spacecraft using a multiple team framework. The objective is to divide large clusters into teams of "manageable" size, so that the communication and computation demands driven by N decentralized units are related to the number of satellites in a team rather than the entire cluster. The system is designed to provide a high level of autonomy, to support clusters with large numbers of satellites, to enable the number of spacecraft in the cluster to change post-launch, and to provide for on-orbit software modification. The distributed guidance and control system will be implemented in an object-oriented style using a messaging architecture for networking and threaded applications (MANTA). In this architecture, tasks may be remotely added, removed, or replaced post launch to increase mission flexibility and robustness. This built-in adaptability will allow software modifications to be made on-orbit in a robust manner. The prototype system, which is implemented in Matlab, emulates the object-oriented and message-passing features of the MANTA software. In this paper, the multiple team organization of the cluster is described, and the modular software architecture is presented. The relative dynamics in eccentric reference orbits is reviewed, and families of periodic, relative trajectories are identified, expressed as sets of static geometric parameters. The guidance law design is presented, and an example reconfiguration scenario is used to illustrate the distributed process of assigning geometric goals to the cluster. Next, a decentralized maneuver planning approach is presented that utilizes linear-programming methods to enact reconfiguration and coarse formation keeping maneuvers. Finally, a method for performing online collision avoidance is discussed, and an example is provided to gauge its performance.

Journal Article↗
PubMed2000

Professional codes for electronic HC record protection: ethical, legal, economic and structural issues.

Guidelines for the protection of electronic health care data frequently stipulate that national laws should be followed. This stipulation is subjected to analysis and critique. It is argued that it commits the fallacy of nationality, and suggests that appropriately constructed ethical guidelines for the protection of electronic health care data must focus solely on fundamental ethical principles as these are applied to the types of situations in which such electronic data are generated, used and ultimately disposed of. The relevance of economic considerations is also be addressed. An attempt is made to sketch a general ethical framework within which data protection guidelines could be situated.

Computer Security↗
PubMed2001

['Millennium Project' of MHLW].

Human Genome Project (information and technology) provides insights so profound that it has the ability to change the way we understand, predict, prevent, diagnose, and treat disease. Because SNPs, single nucleotide polymorphisms, are the most common type of polymorphism, they can have significant effects on both susceptibility to disease as well as drug response. In Japan, 'Millennium Project' based on SNPs has started in 2000, and National Research Centers of MHLW are performing genome-wide association study on five common diseases (dementia, cancer, diabetes mellitus, hypertension, and asthma/allergy). National Children's Hospital group studies asthma/allergy and its drug therapy. Here the overview of 'Millennium Project' and the actual research framework of National Children's Hospital group is reviewed.

Asthma↗
PubMed2000

Separating predictive genetic testing from snake oil: regulation, liabilities, and lost opportunities.

This article explores the extent to which completion of maps of the human genome, coupled with the introduction of technology that will accelerate the identification of gene and protein function, have introduced immeasurable potential to advance life science and health care through genetic profiling. In light of definitional uncertainty, the regulatory and legal environment surrounding predictive genetic testing threatens to impede clinical utilization of genetic profiling technologies that could significantly improve human health. Especially given that genetic testing technologies have been stigmatized in the public and medical community, they must enter the marketplace with a regulatory framework that assures safety, efficacy, and market responsibility.

Biotechnology↗
PubMed2006

A secure semantic interoperability infrastructure for inter-enterprise sharing of electronic healthcare records.

Healthcare professionals need access to accurate and complete healthcare records for effective assessment, diagnosis and treatment of patients. The non-interoperability of healthcare information systems means that interenterprise access to a patient's history over many distributed encounters is difficult to achieve. The ARTEMIS project has developed a secure semantic web service infrastructure for the interoperability of healthcare information systems. Healthcare professionals share services and medical information using a web service annotation and mediation environment based on functional and clinical semantics derived from healthcare standards. Healthcare professionals discover medical information about individuals using a patient identification protocol based on pseudonymous information. The management of care pathways and access to medical information is based on a well-defined business process allowing healthcare providers to negotiate collaboration and data access agreements within the context of strict legislative frameworks.

Computer Security↗
PubMed1984

A new approach to the design of information systems for foodservice management in health care facilities.

An organizational framework for integrating foodservice data into an information system for management decision making is presented. The framework involves the application to foodservice of principles developed by the disciplines of managerial economics and accounting, mathematics, computer science, and information systems. The first step is to conceptualize a foodservice system from an input-output perspective, in which inputs are units of resources available to managers and outputs are servings of menu items. Next, methods of full cost accounting, from the management accounting literature, are suggested as a mechanism for developing and assigning costs of using resources within a foodservice operation. Then matrix multiplication is used to illustrate types of information that matrix data structures could make available for management planning and control when combined with a conversational mode of computer programming.

Accounting↗
PubMed1996

Morphometric descriptors and cable modelling of dendritic arborizations based on 3-dimensional reconstructions.

The main goal of this paper is twofold. First, to classify some of the quantitative morphological descriptors within a common theoretical framework and to illustrate their use in the neurobiological research. The second aim is to describe how the computer modelling of dendritic impulse propagation could be related to those high-fidelity morphological databases of dendritic arborizations that we had obtained by three-dimensional reconstructions. Most of the illustrative examples cited here were chosen from morphological and computer simulation studies published by our institute in the past few years. The selection of different morphological parameters in reliability tests of our newly developed 3DARBOR three-dimensional neuronal tree reconstruction system was also cited as an example. The advantages of the parallelled morphological and computational approach in the study of dendritic arborizations were discussed. A full flow chart that gives an outline of the methods we followed in setting up a morphologically accurate cable model was also presented.

Animals↗
PubMed2004

User acceptance of clinical information systems: a methodological approach to identify the key dimensions allowing a reliable evaluation framework.

The introduction of Computerized Information Systems (CIS) in clinical settings encountered difficulties. These difficulties highlight the lack of understanding of factors and mechanisms influencing user acceptance. The existing tools and research obtained contradictory results that point out the existence of neglected aspects, such as impacts of CIS, in computer science developments in complex settings. This paper proposes to identify key dimensions which make up user acceptance in clinical settings through the union of three methods. They define five main dimensions which require a concrete evaluation to validate the underlying proposed framework and to complete the description of the acceptance phenomenon. Identifying key dimensions opens the gate to comparative evaluation of many CIS and adds new indicators to evaluate the highlighted dimensions. A long-term aim is the development of longitudinal studies and to state priorities and guidelines for new CIS designs.

Attitude to Computers↗