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PubMed2002

Cholangiocyte biology.

Due in part to the recent development of new experimental models, cholangiocytes--the epithelial cells that line the bile ducts--are increasingly recognized as important transporting epithelia actively involved in the absorption and secretion of water, ions, and solutes. New biologic concepts have emerged including the identification and topography of receptors and flux proteins involved in the molecular mechanisms of ductal bile secretion. Individually isolated or perfused bile duct units from livers of rats and mice serve as new, physiologically relevant in vitro models to study cholangiocyte transport. Biliary tree dimensions and novel insights into anatomic remodeling of proliferating bile ducts have emerged from three-dimensional reconstruction using computed tomographic scanning and sophisticated software. Moreover, new pathologic concepts have arisen regarding the interaction of cholangiocytes with pathogens. These concepts may provide the framework for new therapies for the cholangiopathies, a group of important hepatobiliary diseases in which cholangiocytes are the target cell.

Journal Article↗
PubMed1980

Optimal investigation policies under selected PSRO procedures.

This article presents a methodology for utilization review which aids the local Professional Standards Review Organization (PSRO) in selecting optimal timing of Concurrent Stay certification by diagnosis. This procedure is accomplished by modeling patients' admissions, inpatients stays and discharges for each diagnosis as a stochastic process which is audited under the PSRO by three utilization review techniques: preadmission, concurrent and retrospective review. The timing of concurrent stay certification is determined so that the maximum benefits are derived for the utilization review cost expanded. The methodology presented here is a tool to aid local PSRO management in determining the most cost-beneficial utilization review process to utilized in their jurisdiction. It is not an attempt to demonstrate the effectiveness of our utilization review policy over another in general. On the contrary, while the model is generalizable to every PSRO, the utilization review policies resulting from any application are situation-specific. The major contributions of this article are new insight into modeling the utilization review process and the provision of a methodology for which computer programs exist and are readily available to any PSRO that should desire to determine its utilization review procedure in this cost-benefit framework. In order to apply the model it is necessary that certain parameters specific to the application site be estimated or assumed. Exact procedures to aid the PSRO in parameter estimation is the subject of current investigation.

Concurrent Review↗
PubMedDate not supplied

Computerized documentation systems: blessings or curse?

This article considers the possibility that computerized documentation systems will negatively impact knowledge development in nursing. Ideas from three vantage points is presented. First, systems are being developed from theoretical frameworks that are not necessarily grounded in nursing, and these systems, in turn, influence the nurses's ability to process and conceptualize information. Second, computer systems may support the retrieval of empirical data to the elimination of other types of data necessary to the development of nursing knowledge. Third, computers may decrease opportunities for collegial dialogue. These factors together create an atmosphere of "technologic determinism" (Robinson & Robinson, 1990), which can inhibit the development of new ideas in nursing.

Decision Support Techniques↗
PubMed2003

Spatio-temporal synchronization of recurrent epidemics.

Long-term spatio-temporal datasets of disease incidences have made it clear that many recurring epidemics, especially childhood infections, tend to synchronize in-phase across suburbs. In some special cases, epidemics between suburbs have been found to oscillate in an out-of-phase ('antiphase') relationship for lengthy periods. Here, we use modelling techniques to help explain the presence of in-phase and antiphase synchronization. The nonlinearity of the epidemic dynamics is often such that the intensity of the outbreak influences the phase of the oscillation thereby introducing 'shear', a factor that is found to be important for generating antiphase synchronization. By contrast, the coupling between suburbs via the immigration of infectives tends to enhance in-phase synchronization. The emerging synchronization depends delicately on these opposite factors. We use theoretical results from continuous time models to provide a framework for understanding the relationship between synchronization patterns for different model structures.

Computer Simulation↗
PubMed2004

Stresses in isostatic granular systems and emergence of force chains.

Progress is reported on several questions that bedevil understanding of granular systems: (i) Are the stress equations elliptic, parabolic, or hyperbolic? (ii) How can the often-observed force chains be predicted from a first-principles continuous theory? (iii) How do we relate insight from isostatic systems to general packings? Explicit equations are derived for the stress components in two dimensions including the dependence on the local structure. The equations are shown to be hyperbolic and their general solutions, as well as the Green function, are found. It is shown that the solutions give rise to force chains, and the explicit dependence of the force chains trajectories and magnitudes on the local geometry is predicted. Direct experimental tests of the predictions are proposed. Finally, a framework is proposed to relate the analysis to nonisostatic and more realistic granular assemblies.

Computer Simulation↗
PubMed1980

The thermodynamic-buffer enzymes.

Oxidative phosphorylation operates at optimal efficiency if and only if the condition of conductance matching L33/L11 = square root 1-q2 is fulfilled. In this relation L11 is the phenomenological conductance of phosphorylation, L33 the phenomenological conductance of the load, i.e. the irreversible ATP-utilizing processes in the cell, and q the degree of coupling of oxidative phosphorylation driven by respiration. Since during short time intervals L11 and q are constant whereas L33 fluctuates in the cell, oxidative phosphorylation would only rarely operate at optimal efficiency due to violation of conductance matching. This paper demonstrates that the reversible ATP-utilizing reaction catalyzed by adenylate kinase can effectively compensate deviations from conductance matching in the presence of a fluctuating L33 and hence allows oxidative phosphorylation to operate at optimal efficiency in the cell. Since the adenylate kinase reaction was found to buffer a thermodynamic potential, i.e. the phosphate potential, this finding was generalized to the concept of thermodynamic buffering. The thermodynamic buffering ability of the adenylate kinase reaction was demonstrated by experiments with incubated rat-liver mitochondria. Considerations of changes introduced in the entropy production by the adenylate kinase reaction allowed to establish the theoretical framework for thermodynamic buffering. The ability of thermodynamic buffering to compensate deviations from conductance matching in the presence of fluctuating loads was demonstrated by computer simulations. The possibility of other reversible ATP-utilizing reactions, like the ones catalyzed by creatine kinase and arginine kinase, to contribute to thermodynamic buffering is discussed. Finally, the comparison of the theoretically calculated steady-stae cytosolic adenine nucleotide concentrations with experimental data from perfused livers demonstrated that in livers from fed rats conductance matching is fulfilled on a time average and that the degree of coupling corresponded to qpec = 0.97 permitting the most economic maintenance of a maximal output power of oxidative phosphorylation. For the case of livers from starved rats this analysis suggested that the degree of coupling corresponded to qfec = 0.95, permitting the most economic maintenance of a maximal net rate of ATP synthesis at optimal efficiency of oxidative phosphorylation.

Adenine Nucleotides↗
PubMed2000

Fast analysis of transient acoustic wave scattering from rigid bodies using the multilevel plane wave time domain algorithm

The analysis of transient wave scattering from rigid bodies using integral equation-based techniques is computationally intensive: if carried out using classical schemes, the evaluation of the velocity potential on the surface of a three-dimensional scatterer, represented in terms of Ns spatial basis functions for Nt time steps, requires O(NtNs2) operations. The recently developed plane wave time domain (PWTD) algorithm permits the rapid evaluation of transient fields that are generated by bandlimited source distributions. It has been shown that incorporation of the PWTD algorithm into integral equation-based solvers in a two-level setting reduces the computational complexity of a transient analysis to O(NtNs1.5 logNs). In this paper, it is shown that casting the PWTD scheme into a multilevel framework permits the analysis of transient acoustic surface scattering phenomena in O(NtNslog2Ns) operations using O(NtNs) memory. Numerical examples that demonstrate the efficacy of the multilevel implementation are also presented.

Journal Article↗
PubMed1977

Toward the automation of echocardiography.

Schemes applicable to the automated classification of disease states identifiable through echocardiography are being studied. Initial success has been achieved in the classification of anterior mitral leaflet wave forms associated with mitral stenosis and mitral valve prolapse. These two categories were found to be readily distinguished from the normal state in a Fourier analysis framework.

Automation↗
PubMed1999

Representing contrast detection as an eigenvalue problem.

Contrast detection can be formulated as an eigenvalue problem. One of the simplest resulting models has only two parameters. The model is space variant and employs the Hermite functions as eigenfunctions. Computing the response to a sinusoidal acuity grating yields the observer's contrast response. The model itself, however, is developed within an abstract mathematical framework which is general enough to include Fourier analysis as a special case. Consequently, the methods of Fourier analysis are generalized to those of eigenfunction expansion and the spectral theory of linear operators.

Contrast Sensitivity↗
PubMed1982

A corporate strategy for the control of information processing.

Although the use of information processing has become widespread, many organizations have developed systems that are basically independent of the firm's strategy. However, the authors in this article argue that the greatest benefits come when information technology is merged with strategy formulation. The article includes examples of how this has been done and presents a framework for top management direction and control of information processing.

Computers↗
PubMed1999

Authorization & security aspects in the middleware-based healthcare information system.

The integration and evolution of existing systems represents one of the most urgent priorities of health care information systems in order to allow the whole organisation to meet the increasing clinical organisational and managerial needs. The CEN ENV 12967-1 'Healthcare Information Systems Architecture'(HISA) standard defines an architectural approach based on a middleware of business-specific common services, enabling all parts of the local and geographical system to operate on the common information heritage of the organisation and on exploiting a set of common business-oriented functionality. After an overview on the key aspects of HISA, this paper discusses the positioning of the authorization and security aspects in the overall architecture. A global security framework is finally proposed.

Computer Communication Networks↗
PubMed2003

A domain combination based probabilistic framework for protein-protein interaction prediction.

In this paper, we propose a probabilistic framework to predict the interaction probability of proteins. The notion of domain combination and domain combination pair is newly introduced and the prediction model in the framework takes domain combination pair as a basic unit of protein interactions to overcome the limitations of the conventional domain pair based prediction systems. The framework largely consists of prediction preparation and service stages. In the prediction preparation stage, two appearance probability matrices are constructed. Each matrix holds information on appearance frequencies of domain combination pairs in the interacting and non-interacting sets of protein pairs, respectively. Based on the appearance probability matrix, a probability equation is devised. The equation maps a protein pair to a real number in the range of 0 to 1. Two distributions of interacting and non-interacting sets of protein pairs are obtained using the equation. In the prediction service stage, the interaction probability of a protein pair is predicted using the distributions and the equation. The validity of the prediction model is evaluated for the interacting set of protein pairs in a Yeast organism and artificially generated non-interacting set of protein pairs. When 80% of the set of interacting protein pairs in DIP (Database of Interacting Proteins) is used as a learning set of interacting protein pairs, very high sensitivity (86%) and moderate specificity (56%) are achieved within our framework.

Amino Acid Sequence↗
PubMed2004

Use of the ISO/IEC 17799 framework in healthcare information security management.

Shared care implies sharing information. This requires a common concept of information security among healthcare providers and a system to maintain compliance to the security requirements within the healthcare community. This paper describes the use of the Code of Practice for Information Security Management ISO/IEC 17799 as a general framework for establishing a set of controls for information security in a particular organisation and as a framework for standards on information security in healthcare and their implementation.

Access to Information↗
PubMed2002

Phi-LOG: a domain specific language for solving phylogenetic inference problems.

Domain experts think and reason at a high level of abstraction when they solve problems in their domain of expertise. We present the design and motivation behind a domain specific language called Phi-LOG to enable biologists (domain experts) to program solutions to phylogenetic inference problems at a very high level of abstraction. The implementation infrastructure (interpreter, compiler, debugger) for the DSL is automatically obtained through a software engineering framework based on Denotational Semantics and Logic Programming.

Computer Simulation↗
PubMed1991

[Genetic determination of rheumatoid arthritis].

The study on the nature of genetic determination of the definite rheumatoid arthritis (RA) and its forms was carried out, based on the material comprising clinical data on 189 probands and their 1st and 2nd degree relatives (713 subjects) which is contained in the computer Family Data Bank at the Department of Epidemiology and Genetics of this institute. The heritability coefficient "in narrow sense" (80%) obtained within the framework of the multifactorial threshold model confirmed once more important role of genetic factors in the appearance of the disease. The study of genetic heterogeneity within the framework of the Ch. Smith's and T. Reich's models failed to reveal any independent genetically RA forms. An assumption of the essential role of the genes localized in the X chromosome, based on diverse susceptibility of sexes, received no conformation. It has been shown that the RA distribution in the population and families may well be described by means of a variant of the single autosomal two-allele locus model with incomplete and differentiated for two sexes penetrance. The model parameters obtained, a particular penetrance of the mutant homozygote in both sexes equalling 100%, and penetrance of the normal homozygote equalling 0 in men and reaching 0 (0.028%) in women testify to a very essential influence of the major gene on determination of RA.

Arthritis, Rheumatoid↗
PubMed1990

Idiotope structure and genetic diversity in anti-streptococcal group A carbohydrate antibodies.

Three cross-reactive idiotopes(Id), termed IdX, IdI-1, and Id5, that are present on free L chains from murine anti-group A streptococcal carbohydrate antibodies have been mapped; these Id distinguish between products of three homologous V kappa genes. For each determinant, sequence analysis of anti-streptococcal group A carbohydrate antibody V domains yielded small numbers of amino acids invariably associated with Id expression. Flow micro-fluorimetry was used to isolate three IdI-1- spontaneous mutants of the IdI-1+ hybridoma GAC 39; all had single amino acid changes in the L chain at position 60 and 77, all retained other Id, and all bound group A carbohydrate. Computer modeling was used to examine spatial relationships between Id. A number of the conserved Id5 and IdX residues cluster in the L chain framework region 1 around the first back loop connecting strands of the beta pleated sheets, and overlap at residue 15 (Id5, proline; IdX, leucine). This overlap accords with the mutually exclusive expression of Id5 and IdX. The IdI-1 loss variants have mutations of residues 60 or 77 on adjacent back loops, approximately 7.5 and 14 A from residue 15. Competitive inhibition of anti-IdX and anti-IdI-1 binding to antibodies expressing both Id can be attributed to steric hindrance. The framework back loops may be favored sites for cross-reactive Id expressed by products of a single V region gene. IdI-3a, an individual Id not associated with use of a particular gene segment, has been localized in part to residue 31 (hypervariable region 1) of the H chain.

Amino Acid Sequence↗