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At least 1,099 records · Page 61Linked to original sources
PubMed1984

The solvation contribution to the binding energy of DNA with non-intercalating antibiotics.

The influence of the solvent on the binding energies to DNA of six non-intercalating antibiotics - netropsin, distamycin-3, distamycin-2, SN 18071, berenil and stilbamidine - is evaluated by combining the effect of the first hydration shell with that of bulk water. The first effect is computed by a methodology based on a spherical/point dipole model of water and limited to electrostatic interaction energies. Hydration shells are obtained which are energy optimized with respect to both water-solute and water-water interactions for the complexes and for the isolated DNA oligomers and ligands. The method allows even very large complexes to be studied in reasonable computation times. The second effect is introduced via a cavity treatment. It is shown that if the vacuum interaction energies already predict correctly the preference of the ligands for the minor groove of AT sequences of B-DNA, the introduction of the solvation effect is indispensable for reproducing the order of affinity of the ligands and for bringing the values of the complexation energies into close agreement with experimental data.

Anti-Bacterial Agents↗
PubMedDate not supplied

Head-holder interfacing computed tomography with Talairach stereotactic frame.

A device is described which allows employ of CT data in conjunction to the Talairach frame for biopsy and other fine localization procedures. A series of new accessory parts allows reversible exact placement of the patient head in the same relative position to the reference system both in the stereotactic frame and the CT machine. No modification has been introduced in the standard Talairach head-holder, preserving its features of simplicity and versatility without need for introduction of new stereotactic methodologies or new computer programs.

Biopsy↗
PubMed1989

Assessing the impact of computer workload on operator stress: the role of system controllability.

This paper considers the impact of working with computer-based systems in terms of mental workload and the well-being of operators. In particular, the paper focuses on issues of controllability in human-computer systems as they relate to operator stress. Through the adoption of a state control model of stress regulation, it becomes apparent that while general usability criteria are necessary for the design of controllable systems, they may not be sufficient to guarantee controllability. The implications for research and system design are discussed, with reference to the assessment of operator workload, controllability and stress. A methodology for assessing computer stress is described, based on the analysis of stressful computer-related episodes and their accompanying affective and cognitive states. This technique allows the relationship between workload and controllability to be studied in particular computer work environments, in relation to individual work goals and coping strategies.

Attitude to Computers↗
PubMed2002

A Bayesian analysis of bivariate ordinal data: Wisconsin epidemiologic study of diabetic retinopathy revisited.

In many biomedical experiments one may often encounter bivariate data which are component-wise ordinal. The data set of the ophthalmologic experiment of the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) is an example of such data. Several authors considered the analysis of such data from different viewpoints. The present work reviews the existing literature based on the WESDR data and on the basis of some latent variables provide the technique for analysing such data more easily in a Bayesian framework. Computation supports the methodology to a great extent. A comparison between our approach and the likelihood based approach considered by Kim has also been made.

Adult↗
PubMed2004

Comparison between the geometric and electronic structures and reactivities of [FeNO]7 and [FeO2]8 complexes: a density functional theory study.

In a previous study, we analyzed the electronic structure of S = 3/2 [FeNO](7) model complexes [Brown et al. J. Am. Chem. Soc. 1995, 117, 715-732]. The combined spectroscopic data and SCF-X alpha-SW electronic structure calculations are best described in terms of Fe(III) (S = 5/2) antiferromagnetically coupled to NO(-) (S = 1). Many nitrosyl derivatives of non-heme iron enzymes have spectroscopic properties similar to those of these model complexes. These NO derivatives can serve as stable analogues of highly labile oxygen intermediates. It is thus essential to establish a reliable density functional theory (DFT) methodology for the geometry and energetics of [FeNO](7) complexes, based on detailed experimental data. This methodology can then be extended to the study of [FeO(2)](8) complexes, followed by investigations into the reaction mechanisms of non-heme iron enzymes. Here, we have used the model complex Fe(Me(3)TACN)(NO)(N(3))(2) as an experimental marker and determined that a pure density functional BP86 with 10% hybrid character and a mixed triple-zeta/double-zeta basis set lead to agreement between experimental and computational data. This methodology is then applied to optimize the hypothetical Fe(Me(3)TACN)(O(2))(N(3))(2) complex, where the NO moiety is replaced by O(2). The main geometric differences are an elongated Fe[bond]O(2) and a steeper Fe[bond]O[bond]O angle in the [FeO(2)](8) complex. The electronic structure of [FeO(2)](8) corresponds to Fe(III) (S = 5/2) antiferromagnetically coupled to O(2)(-) (S = 1/2), and, consistent with the extended bond length, the [FeO(2)](8) unit has only one Fe(III)-O(2)(-) bonding interaction, while the [FeNO](7) unit has both sigma and pi type Fe(III)-NO(-) bonds. This is in agreement with experiment as NO forms a more stable Fe(III)-NO(-) adduct relative to O(2)(-). Although NO is, in fact, harder to reduce, the resultant NO(-) species forms a more stable bond to Fe(III) relative to O(2)(-) due to the different bonding interactions.

Ferric Compounds↗
PubMed2002

Specific force field parameters determination for the hybrid ab initio QM/MM LSCF method.

The pure quantum mechanics method, called Local Self-Consistent Field (LSCF), that allows to optimize a wave function within the constraint that some predefined spinorbitals are kept frozen, is discussed. These spinorbitals can be of any shape, and their occupation numbers can be 0 or 1. Any post-Hartree-Fock method, based on the restricted or unrestricted Hartree-Fock Slater determinant, and Kohn-Sham-based DFT method are available. The LSCF method is easily applied to hybrid quantum mechanics/molecular mechanics (QM/MM) procedure where the quantum and the classical parts are covalently bonded. The complete methodology of our hybrid QM/MM scheme is detailed for studies of macromolecular systems. Not only the energy but also the gradients are derived; thus, the full geometry optimization of the whole system is feasible. We show that only specific force field parameters are needed for a correct description of the molecule, they are given for some general chemical bonds. A careful analysis of the errors induced by the use of molecular mechanics in hybrid computation show that a general procedure can be derived to obtain accurate results at low computation effort. The methodology is applied to the structure determination of the crambin protein and to Menshutkin reactions between primary amines and chloromethane.

Journal Article↗
PubMed1992

Correlation between computer-assisted femoral arteriography and physiological tests in hypercholesterolaemic patients: a methodological study with special reference to clinical trials.

The validity of computer-assisted femoral arteriography, for the study of regression/progression of atherosclerosis in follow-up clinical trials, was investigated by comparison with routine physiological estimates of peripheral circulatory function. Thus, in 114 hypercholesterolaemic patients, the results of aorto-femoral arteriography were compared with those of leg segmental blood pressure measurement, oscillometry, digital pulse plethysmography, and bicycle and treadmill exercise tests. In 107 patients, 18 with symptoms of peripheral vascular disease (PVD) and 89 asymptomatic, magnification arteriograms of a 20 cm segment of the right or left superficial femoral artery were obtained. These arteriograms were digitized and the following variables were calculated: arterial lumen volume (corrected for body size), per cent stenosis, and edge roughness. The correlation between arteriographic and physiological variables was investigated with a linear regression model, taking into account the possible interaction with sex, and presence or absence of symptoms of PVD. Lumen volume correlated significantly with all five physiological variables, and per cent stenosis correlated significantly with four of the physiological variables. For the roughness measure, however a significant correlation was found only with plethysmography. By using logistic multiple regression analysis linear functions of physiological variables were constructed to detect ilio-femoral arterial occlusion. The sensitivity/specificity for detection of right-sided, left-sided, and bilateral occlusion was 0.83/0.98, 0.78/0.98, and 0.60/1.00 respectively (N = 108-111). Systolic blood pressure (ankle-arm ratio) was the single variable most closely correlated to the likelihood of arterial occlusions. It is concluded that arterial lumen volume and per cent stenosis, measured for the digitized femoral arteriogram, correlate well with physiological variables, which reflect the state of atherosclerosis both in the femoral arteries and in other arterial beds including the heart, and that routine physiological tests can be used to identify patients with arterial occlusions in the iliac and femoral arteries.

Adult↗
PubMed2002

Occlusal loading of EBA and MTA root-end fillings in a computer-controlled masticator: a scanning electron microscopic study.

AIM: The aim of this investigation was to assess the marginal adaptation of Super-EBA (EBA) and Pro Root MTA (MTA) root-end fillings and the occurrence of microcracks in resected root-ends of extracted teeth before and after occlusal loading for a five-year equivalent period in a computer-controlled masticator. METHODOLOGY: Twenty-four molar teeth were root-filled using lateral condensation and their root-ends resected. Root-end cavities were prepared and either EBA or MTA root-end fillings were placed. All surgical procedures were completed in vitro under an operating microscope. Replicas taken of the root-end fillings and resected root-ends were examined using an SEM before and after they were subjected to in vitro chewing cycles in a computer-controlled chewing simulator for the equivalent of 5 years. Marginal adaptation and integrity of the two root-end filling materials were evaluated and the presence of microcracks recorded. RESULTS: Before loading, a continuous margin was observed with 99.4 +/- 2.4% of EBA and 99.2 +/- 1.6% of MTA root-end fillings. After loading, the percentage of continuous margin decreased to 93.1 +/- 6.6% and 98.9 +/- 3.2% for EBA and MTA, respectively. After occlusal loading, 39.5% of the EBA root-end fillings were overfilled, whilst 52.6% of the MTA root-end fillings were underfilled. In total, 12.5% of the resected root-end surfaces showed microcracking before loading and 25% after occlusal loading. CONCLUSIONS: Both EBA and MTA displayed excellent marginal adaptation before masticatory loading. After loading, the amount of continuous margin for both root-end filling materials decreased slightly but was still high.

Aluminum Compounds↗
PubMed1990

[Computerized audiometry. Analysis and modeling of brain stem evoked auditory potentials].

The use of microcomputer for the Brain-Stem Response Audiometry was discussed. The obtained results using the computer system, the methodology and technique of hearing examination were presented. Special attention was called to modelling aspects of the components of the registered signal and the instability of generators in the neuronal structures of the acoustic pathway.

Audiometry, Evoked Response↗
PubMed2003

Peptide backbone folding induced by the C(alpha)-tetrasubstituted cyclic alpha-amino acids 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) and 1-aminocyclopentane-1-carboxylic acid (Ac5c). A joint computational and experimental study.

The conformational study of a new group of synthetic peptides containing 4-amino-1,2-dithiolane-4-carboxylic acid (Adt), a cysteine-related achiral residue, has been carried out through a joint application of computational and experimental methodologies. Molecular Dynamics simulations clearly suggest the tendency of this molecule to adopt a gamma-turn conformation in vacuum and help in analyzing the complex and crucial conformational behaviour of the dithiolane ring which appears to preferentially adopt a C(S)-like structure. Electronic structure calculations carried out in solution using the Density Functional Theory also indicate the preservation of the gamma-like folding in apolar solvents and the helix-like one in more polar solvents. A comparison with the achiral 1-aminocycloalkane-1-carboxylic acid (Ac5c) has been carried out using the same computational tools. NMR and IR data on dipeptide derivatives containing the Adt or Ac5c residue show that in chloroform solution all the models prefer a gamma-turn structure, centered at the cyclic residue, stabilized by an intramolecular H-bond, whereas in a more polar solvent, i.e. dimethyl sulfoxide, this folding is not maintained. The experimental conformational studies, extended to N-Boc protected tripeptides, clearly indicate the remarkable tendency of both the five-membered C(alpha)-tetrasubstituted cyclic amino acids Adt and Ac5c to induce the gamma-turn structure also in models able to adopt the beta-bend conformation.

Amino Acids↗
PubMed2006

[The cost of complications: implications for the measurement of the cost of type II diabetes mellitus].

BACKGROUND: A well-known methodology used to compute the macroeconomic cost of risk factors is the etiologic cost ratio, leading to estimates based on data on the prevalence of the risk factor in the general population, the relative risk of complications associated to it and the cost of the complications. A major problem of this method is that it is in some extent inconsistent with recent findings showing an increase in the per capita cost of some complications in presence of type II diabetes mellitus. The aim of the paper is to reconcile the approach with most recent economic studies and to overview the consequences of such an attempt in terms of methodological framework. METHODS: We developed a methodological framework introducing heterogeneity in the cost of treating complications according to the presence of diabetes. We estimated the macroeconomic cost of type II diabetes mellitus based on selected complications (stroke, myocardial infarction, nephropathy and peripheral arterial obstructive disease) from French representative data in two situations: a situation in which the heterogeneity is not taken into account, another situation in which heterogeneity is introduced. RESULTS: Our results point out that the assumption of homogeneity in the cost of complications is associated to an underestimation of the cost of diabetes by about 30%. CONCLUSION: Our results present an attempt to reconcile the economic modeling of the cost of type II diabetes mellitus with the "real world". We conclude that the introduction of heterogeneity is necessary to capture the whole extent of the economic burden of the disease and that it places significant constraints on the data and the methodological framework to be used in such attempts.

Costs and Cost Analysis↗
PubMed2004

Innovative technologies for the assessment of cardiovascular medical devices: state-of-the-art techniques for artificial heart valve testing.

Prosthetic heart valves (PHVs) are engineered devices used for replacing diseased natural cardiac valves. This article presents several investigational techniques for the evaluation of the performance of these clinical devices, whose implantation is not completely free of drawbacks. The state-of-the-art in the technological approach for PHV testing is addressed. As the fluid dynamics of PHVs are particularly complex, the main focus will be on experimental velocimetric techniques and computational analysis. A methodology for the analysis of the valve's signature, in terms of its characteristic sound in the opening and closing phases, is also presented. The aforementioned techniques are necessary to guarantee an operational life of the implanted device as free as possible from clinical complications. It can be realistically expected that this characterization will help designers in improving PHV performance.

Biotechnology↗
PubMed1999

[Assessment of educational performance of different teaching methodologies applied to medical students in the area of arterial hypertension].

BACKGROUND: Modernization of medical teaching includes the use of new teaching methodologies and among these, computer assisted tutorials. Previous experience has shown that this type of methodology is associated with better student performances. AIM: To assess the cognitive performance of fourth year medical students using different teaching methodologies. MATERIAL AND METHODS: During the hypertension course, medical students were allowed to choose to receive a printed booklet (group A), to receive the booklet and attend lectures (group B), to receive the booklet and use a multimedial educational program (group C) and to use all three methodologies (group D). Cognitive performance was evaluated with a multiple choice test scored from 0 to 100. RESULTS: The mean scores obtained by students were 84.5 in group A, 82.4 in group B, 88.9 in group C and 84.4 in group D. This overall score of 83.6 in hypertension was significantly better than the mean score of 72.5 obtained in the cardiology test. CONCLUSIONS: Allowing students to choose the most suitable method to learn according to their personal preferences, results in a better cognitive performance.

Education, Medical↗
PubMedDate not supplied

A computer-based neurobehavioral evaluation system for occupational and environmental epidemiology: methodology and validation studies.

To facilitate the evaluation of populations at risk for nervous system dysfunction due to environmental agents, we have developed a computer-administered neurobehavioral evaluation system (NES). The system includes a set of testing programs, designed to run on a microcomputer, and questionnaires which are used to record symptoms, obtain exposure history, and characterize potential confounding variables. Standard tasks evaluating memory, visual/motor function, vocabulary ability, and mood were selected and adapted for computer presentation following the recommendation of a World Health Organization (WHO)-National Institute for Occupational Safety and Health (NIOSH) expert committee. After the performance of several pilot studies designed to refine our methodology, validation studies were initiated to assess comparability of selected computer tasks to existing standard ones administered and scored by an interviewer. A different aspect of validity, score stability, was addressed by repeated administration of tests to a small unexposed group. Comparability to existing tests was good (r = .42 to .76). Score stability was excellent over a 150 day interval, particularly for the digit span and continuous performance tests. From our experience, this approach appears to be a feasible, efficient, acceptable, and sensitive approach to evaluating central nervous system function in populations.

Epidemiologic Methods↗
PubMedDate not supplied

The bootstrap and identification of prognostic factors via Cox's proportional hazards regression model.

This paper describes the use of the bootstrap, a new computer-based statistical methodology, to help validate a regression model resulting from the fitting of Cox's proportional hazards model to a set of censored survival data. As an example, we define a prognostic model for outcome in childhood acute lymphocytic leukemia with the Cox model and use of a training set of 224 patients. To validate the accuracy of the model, we use a bootstrap resampling technique to mimic the population under study in two stages. First, we select the important prognostic factors via a stepwise regression procedure with 100 bootstrap samples. Secondly we estimate the corresponding regression parameters for these important factors with 400 bootstrap samples. The bootstrap result suggests that the model constructed from the training set is reasonable.

Child↗
PubMed1998

Using theory and simulation to understand permeation and selectivity in ion channels.

It is clear that the function of ion channels must flow from their structure. With recent advances in computational power and methodology, it appears feasible to correlate structure to ion channel permeation at an atomistically detailed level of description. The overall strategy is to structure the calculations in a hierarchy, ranging from coarse-grained thermodynamic and kinetic descriptions to fine-grained molecular dynamics descriptions with atomic detail. Each level of description is connected to the others by appropriate statistical mechanical theory. The coarse-grained descriptions can be correlated directly with electrophysiological experiment. The fine-grained descriptions are used to parameterize the coarse-grained descriptions and to describe the permeation process at the most detailed level. This strategy has so far had varying degrees of success. It has successfully described water permeation through lipid bilayers and gramicidin channels. It has revealed the essential events of ion permeation through gramicidin channels at an atomistically detailed level. The role of channel protein motions in permeation has been elucidated. However, it appears that force fields used to describe molecular dynamics must be refined further to achieve completely accurate predictions of the permeation of such small ions as sodium. Channels with more complex structure and more multiion occupancy than gramicidin pose major computational challenges with respect to sampling protein conformations and ion distributions involved in the permeation process. Possible approaches to meeting these challenges are discussed.

Diffusion↗
PubMed1995

Multispiral three-dimensional computed tomography in the investigation of craniosynostosis: technique optimization.

21 infants with craniosynostosis were studied with a new three-dimensional (3D) computed tomography (CT) methodology. We describe technique optimization using multiple spiral data acquisitions with low dose (85 mAs) technique. One caudal volume of 3 mm slice thickness was obtained with a further two volumes of 1 mm slice thickness at the vertex. Image reconstruction of spiral raw data allowed overlapping 3 mm sections to be generated without the dose increase that would result from conventional axial CT scanning. We illustrate common technical artefacts of 3D CT and explain their cause and solution. A dramatic dose reduction to the lens was achieved with no loss in 3D image quality. Lens dose was 8.91 mSv compared with 24.6 mSv using the standard paediatric head technique.

Craniosynostoses↗
PubMed1984

A taxonomy: hospital information systems evaluation methodologies.

During the past decade, computers and information systems and their resultant products have pervaded hospitals. Not only have the number of and investments in computers and their associated systems increased, but the types of hospital systems and affected functions have also multiplied. Unfortunately, methodologies to measure impacts of these systems have not evolved at the same pace. There have been few developments of new techniques. Existing techniques have not been adapted for use in hospitals. As a result, evaluations are not performed or are based upon generalizations, often with users minimally involved, if at all. Most techniques emphasize the cost-benefit approach, but this should not be the only tool used. This paper presents a taxonomy of methodologies for the evaluation of hospital information systems. The analyses of methodologies and systems are accomplished from user's perspectives. Effectiveness of system products is emphasized. Users are provided with an additional tool to plan, organize, control, and direct the information resources and achieve the hospital's goals and objectives.

Classification↗