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At least 19 recordsLinked to original sources
PubMed1994

Energy deposition and ionization fluctuations induced by ions in small sites--an analytical approach.

A concise, analytical approach is developed for calculating energy deposition and ionization fluctuations in volumes within ion-irradiated media which have dimensions as small as 1 nm. The method accounts for both direct ion interactions with the site and interactions of secondary electrons which are produced by ions in the surrounding medium. Particular attention is given to the way the contributions of the two types of events are combined. Since energy deposition fluctuations are simply related to the fundamental quantities ZD and yD employed in microdosimetry theory, this new approach provides a convenient means to obtain these parameters. Results obtained with the analytical method show good agreement with Monte Carlo charged-particle track-structure calculations of yD for 0.5 to 20 MeV protons incident on spherical sites of water vapor with diameters ranging from 1 nm to 10 microns. In contrast to Monte Carlo techniques, the analytical method does not depend on knowing the intricacies of single ion and electron interactions with the target and can therefore be adapted to calculations with heavier incident ions and different target materials, including those of the condensed state.

Electrons↗
PubMed1976

Age differences in personality structure: a cluster analytic approach.

A cluster analytic approach was used to determine possible age differences in the structure of personality as measured by the Cattell Sixteen Personality Factor Questionnaire. Subjects were 969 adult male volunteers, originally divided into three groups: 25 to 34, 35 to 54, and 55 to 82. Two familiar dimensions of personality, Anxiety-Adjustment and Introversion-Extraversion, were found to be cross sectionally stable. A third cluster dimension, interpreted as openness to experience, showed age-related differences. Young subjects showed openness to feelings; middle-aged subjects showed openness to ideas; and old subjects showed a balanced openness to both feelings and ideas. Repartitioning of the sample into two groups (ages 25 to 43 and 44 to 82), and three groups (25 to 39, 40 to 47, and 48 to 82) confirmed these age differences in the third cluster. The interpretation of the third cluster is discussed in terms of Jung's concepts of psychological functions.

Age Factors↗
PubMed1999

The bits and bytes of computer/Internet addiction: a factor analytic approach.

A factor analytic approach was used to explore possible constructs underlying so-called computer/Internet addiction. A 94-item survey was developed, from which two major and two minor factors were derived. Factor 1 focused on problematic computer-related behaviors in heavy users of the Internet, whereas Factor 2 focused on the usefulness and general purpose nature of computers and the Internet. Factor 3 isolated a combination of use of the Internet for sexual gratification and shyness/introversion, and Factor 4 focused on an absence of problems related to Internet use that were coupled with a mild aversion or a disinterest in this technology. These data support the notion that some individuals have a mixture of obsessive-like characteristics related specifically to their computer/Internet use but that, not surprisingly, they also exhibit a preference for on-line, rather than in-person, interactions.

Adolescent↗
PubMed2004

Vectorial two-beam coupling with arbitrary shifted photorefractive gratings: an analytical approach.

An analytical solution is presented to the vectorial coupled wave equations for the steady state amplitudes of two waves interacting in cubic photorefractive crystals. The solution accounts for pump depletion as well as an arbitrary phase shift between the interference pattern and photorefractive grating. It is shown that bidirectional vectorial amplification and polarization orthogonalization of the interacting beams take place in photorefractive crystal with diffusion, drift or mixed mechanism of space-charge formation.

Journal Article↗
PubMed1994

Photon propagation and detection in single-photon emission computed tomography--an analytical approach.

An analytical theory of photon propagation and detection in single-photon emission computed tomography (SPECT) for collimated detectors is developed from first principles. The total photon detection kernel is expressed as a sum of terms due to the primary and the Compton scattered photons. The primary as well as contributions due to every order of Compton scattering are calculated separately. The model accounts for the three-dimensional depth dependence of the collimator holes as well as for nonhomogeneous attenuation. No specific assumptions about the boundary or the homogeneity of the attenuating medium are made. The energy response of the detector is also modeled by the theory. Analytical expressions are obtained for various contributions to the photon detection kernel, and the multidimensional integrals involved are calculated using standard numerical integration methods. Theoretically calculated projections and scatter fractions for the primary and the first through second scattering orders are compared with our own experimental results for a small cylindrical primary radiation source immersed at various positions in a uniform cylindrical phantom. Also, theoretically calculated scatter fractions for a small spherical (pointlike) source in a uniform elliptic phantom are compared with experimental and Monte Carlo simulation results taken from the recent literature. The results from the analytical method are essentially exact and are free from the inaccuracies inherent in the numerical simulation methods used to deal with the photon propagation and detection problem in SPECT so far. The method developed here is unique in the sense that it provides accurate theoretical predictions of results averaged over an infinite number of simulations or experiments. We believe that our theory enhances an intuitive understanding of the complex image formation process in SPECT and is an important step toward solving the inverse problem, that of reconstructing the primary radiation source distribution from the measured gamma camera projections.

Humans↗
PubMed1990

Current analytical approaches to measuring blood analytes.

In recent years, laboratory testing in the critical-care setting has increased, a trend due, in part, to the evolution of electrochemical sensors. Various innovations have extended sensor lifetimes, reduced sensor maintenance, and led to the development of single-use and unit-use disposable sensors. These sensor technologies allow the accurate and precise determination, either at or near the bedside, of several analytes including pO2, pCO2, pH, Na, K, Cl, ionized calcium, hematocrit, total hemoglobin, and glucose. Use of these new systems, however, has raised new issues regarding sensor calibration and sample handling and collection. The number of direct-reading analyzers for electrolyte determinations has also increased dramatically. Issues regarding calibration of ion-selective electrodes (ISEs) for Na/K have also been raised after demonstrations of between-instrument variation. Recently, collaborative efforts between eight ISE instrument manufacturers and the National Institute of Standards and Technology resulted in the development of a Standard Reference Material, SRM 956, for the purpose of standardizing direct-reading Na/K ISEs to the flame photometer. Other widely used technologies that provide noninvasive, continuous monitoring include pulse oximetry and transcutaneous gas electrodes. These trends are expected to continue and to produce a new generation of electrochemical and optical sensors.

Autoanalysis↗
PubMed1994

Climate change impact on distribution and abundance of wildlife species: an analytical approach using GIS.

An analytical approach to modelling the likely impact of climate change on the distribution and abundance of wildlife species is described using examples from Scotland. Data for present day distribution of wildlife and habitat are analysed using map data describing geographic variation in climatic factors. Climate data for the present day and under specified scenarios of change are themselves modelled within a GIS; climate modelling uses meteorological station data, climate change scenarios developed from GCMs and a variety of spatial interpolation techniques. The analytical procedure generates hypotheses defining ecological relationships between species distribution and climatic factors (monthly, seasonal and annual data). These relationships are then used to model the distribution of the species directly from climate and predict impacts of climate change. The analysis takes account of both direct impacts of climate on wildlife and indirect effects manifested through habitat response to climate change. The analytical procedure is implemented as a generic tool for inductive spatial analysis in GIS.

Journal Article↗
PubMedDate not supplied

Toward an analytical approach to health sector reform.

An analytical approach to health sector reform requires definition of the objectives of the health sector. Although a multiplicity of objectives may be appealing, there are compelling analytical reasons for simplicity. It is argued that a health status maximization objective is a widely acceptable choice, which captures most of the important aspects of utility maximization of relevance for health sector reform. Equity can be addressed in the process of aggregating individual outcomes. The widely recognized need for health sector reform in developing countries constitutes, in itself, evidence of the market failures in the health sector. If the market worked, why would we need reform? Given an objective and a justification for reform, analysis should proceed to address measurement questions and intervention strategies. The disability-adjusted life year lost is proposed as a consistent and feasible measure of health. Based on an optimization model of health sector performance in Africa, the paper discusses interventions to improve allocative and technical efficiency. These are broadly characterized as interventions dealing with lack of knowledge and interventions dealing with institutional shortcomings. They lead to different approaches to health sector reform. The paper concludes that we now have a systematic analytical approach to reform, in which tools and methods for addressing information gaps are well developed and need to be more widely applied, while those addressing institutional failures still need further development and application.

Developing Countries↗
PubMed2000

A meta-analytic approach to growth curve analysis.

A meta-analytic approach to growth curve analysis is described and illustrated by applying it to the evaluation of the Arizona Pilot Project, an experimental project for financing the treatment of the severely mentally ill. In this approach to longitudinal data analysis, each individual subject for which repeated measures are obtained is initially treated as a separate case study for analysis. This approach has at least two distinct advantages. First, it does not assume a balanced design (equal numbers of repeated observations) across all subjects; to accommodate a variable number of observations for each subject, individual growth curve parameters are differentially weighted by the number of repeated measures on which they are based. Second, it does not assume homogeneity of treatment effects (equal slopes) across all subjects. Individual differences in growth curve parameters representing potentially unequal developmental rates through time are explicitly modeled. A meta-analytic approach to growth curve analysis may be the optimal analytical strategy for longitudinal studies where either (1) a balanced design is not feasible or (2) an assumption of homogeneity of treatment effects across all individuals is theoretically indefensible. In our evaluation of the Arizona Pilot Project, individual growth curve parameters were obtained for each of the 13 rationally derived subscales of the New York Functional Assessment Survey, over time, by linear regression analysis. The slopes, intercepts, and residuals obtained for each individual were then subjected to meta-analytic causal modeling. Using factor analytic models and then general linear models for the latent constructs, the growth curve parameters of all individuals were systematically related to each other via common factors and predicted based on hypothesized exogenous causal factors. The same two highly correlated common factors were found for all three growth curve parameters analyzed, a general psychological factor and a general functional factor. The factor patterns were found to be nearly identical across the separate analyses of individual intercepts, slopes, and residuals. Direct effects on the unique factors of each subscale of the New York Functional Assessment Survey were tested for each growth curve parameter by including the common factors as hierarchically prior predictors in the structural model for each of the indicator variables, thus statistically controlling for any indirect effect produced on the indicator through the common factors. The exogenous predictors modeled were theoretically specified orthogonal contrasts for Method of Payment (comparing Arizona Pilot Project treatment or "capitation" to traditional or "fee-for-service" care as a control), Treatment Administration Site (comparing various locations within treatment or control groups), Pretreatment Assessment (comparing general functional level at intake as assigned by an Outside Assessment Team), and various interactions among these main effects. The intercepts, representing the initial status of individual subjects on both the two common factors and the 13 unique factors of the subscales of the New York Functional Assessment Survey, were found to vary significantly across many of the various different treatment conditions, treatment administration sites, and pretreatment functional levels. This indicated a severe threat to the validity of the originally intended design of the Arizona Pilot Project as a randomized experiment. When the systematic variations were statistically controlled by including intercepts as hierarchically prior predictors in the structural models for slopes, recasting the experiment as a nonequivalent groups design, the effects of the intercepts on the slopes were found to be both statistically significant and substantial in magnitude. (ABSTRACT TRUNCATED)

Capitation Fee↗
PubMed2000

Dynamics of proteins predicted by molecular dynamics simulations and analytical approaches: application to alpha-amylase inhibitor.

The dynamics of alpha-amylase inhibitors has been investigated using molecular dynamics (MD) simulations and two analytical approaches, the Gaussian network model (GNM) and anisotropic network model (ANM). MD simulations use a full atomic approach with empirical force fields, while the analytical approaches are based on a coarse-grained single-site-per-residue model with a single-parameter harmonic potential between sufficiently close (r </= 7 A) residue pairs. The major difference between the GNM and the ANM is that no directional preferences can be obtained in the GNM, all residue fluctuations being theoretically isotropic, while ANM does incorporate directional preferences. The dominant modes of motions are identified by (i) the singular value decomposition (SVD) of the MD trajectory matrices, and (ii) the similarity transformation of the Kirchhoff matrices of inter-residue contacts in the GNM or ANM. The mean-square fluctuations of individual residues and the cross-correlations between domain movements retain the same characteristics, in all approaches-although the dispersion of modes and detailed amplitudes of motion obtained in the ANM conform more closely with MD results. The major weakness of the analytical approaches appears, on the other hand, to be their inadequacy to account for the anharmonic motions or multimeric transitions driven by the slowest collective mode observed in MD. Such motions usually suffer, however, from MD sampling inefficiencies, and multiple independent runs should be tested before making conclusions about their validity and detailed mechanisms. Overall this study invites attention to (i) the robustness of the average properties (mean-square fluctuations, cross-correlations) controlled by the low frequency motions, which are invariably reproduced in all approaches, and (ii) the utility and efficiency of the ANM, the computational time cost of which is of the order of "minutes" (real time), as opposed to "days" for MD simulations. Proteins 2000;40:512-524.

Computer Simulation↗
PubMed1999

An analytical approach to determine the in situ forces in the glenohumeral ligaments.

The purpose of this study was to use an analytical approach to determine the forces in the glenohumeral ligaments during joint motion. Predictions from the analytical approach were validated by comparing them to experimental data. Using a geometric model, the lengths of the four glenohumeral ligaments were determined during anterior-posterior loading simulations and forward flexion-extension. The corresponding force in each structure was subsequently calculated based on length data via load-elongation curves obtained experimentally. During the anterior loading simulation at 0 deg of abduction, the superior glenohumeral ligament carried up to 71 N at the maximally translated position. At 90 deg of abduction, the anterior band of the inferior glenohumeral ligament had the highest force of 45 N during anterior loading. These results correlated well with those found in previous experimental studies. We believe that this validated analytical approach can be used to predict the forces in the glenohumeral ligaments during more complex joint motion as well as assist surgeons during shoulder repair procedures.

Aged↗
PubMed2002

Analytical approach for the Lucas-Washburn equation.

Porous media can be characterized by studying the kinetics of liquid rise within the pore spaces. Although porous media generally have a complex structure, they can be modeled as a single, vertical capillary or as an assembly of such capillaries. The main difficulties lie in separately estimating the effective mean radius of the capillaries and the contact angle between the liquid and the pore. In this paper we circumvent these obstacles by exploring another approach and suggest an analytical approach of the classical Lucas-Washburn equation (LWE). Specifically, we consider that the contact angle between the liquid meniscus and the inner surface of the capillary becomes a dynamic contact angle when the liquid front is in movement. It has previously been demonstrated that the resulting time dependence is due to frictional dissipation at the moving wetting front.

Journal Article↗
PubMed1994

An analytical approach to quantitative reconstruction of non-uniform attenuated brain SPECT.

An analytical approach to quantitative brain SPECT (single-photon-emission computed tomography) with non-uniform attenuation is developed. The approach formulates accurately the projection-transform equation as a summation of primary- and scatter-photon contributions. The scatter contribution can be estimated using the multiple-energy-window samples and removed from the primary-energy-window data by subtraction. The approach models the primary contribution as a convolution of the attenuated source and the detector-response kernel at a constant depth from the detector with the central-ray approximation. The attenuated Radon transform of the source can be efficiently deconvolved using the depth-frequency relation. The approach inverts exactly the attenuated Radon transform by Fourier transforms and series expansions. The performance of the analytical approach was studied for both uniform- and non-uniform-attenuation cases, and compared to the conventional FBP (filtered-backprojection) method by computer simulations. A patient brain X-ray image was acquired by a CT (computed-tomography) scanner and converted to the object-specific attenuation map for 140 keV energy. The mathematical Hoffman brain phantom was used to simulate the emission source and was resized such that it was completely surrounded by the skull of the CT attenuation map. The detector-response kernel was obtained from measurements of a point source at several depths in air from a parallel-hole collimator of a SPECT camera. The projection data were simulated from the object-specific attenuating source including the depth-dependent detector response. Quantitative improvement (>5%) in reconstructing the data was demonstrated with the nonuniform attenuation compensation, as compared to the uniform attenuation correction and the conventional FBP reconstruction. The commuting time was less than 5 min on an HP/730 desktop computer for an image array of 1282*32 from 128 projections of 128*32 size.

Brain↗
PubMed2004

Determination of dioxin and dioxin-like compounds in sediments from UK estuaries using a bio-analytical approach: chemical-activated luciferase expression (CALUX) assay.

The DR-CALUX assay has been utilised for the bio-analytical screening of a number of estuarine sediments for dioxin-like activity. Total sediment extracts (samples containing all extracted compounds) and cleaned-up extracts (samples with the most stable compounds isolated from the total extracts) were screened. The concentration of the stable dioxin-like compounds in the cleaned-up sediment extracts was between 1.0 and 106 pgTEQCALUX g(-1) dry weight. The majority of sediments contained levels of dioxin-like compounds that were above concentrations that are considered to be a low risk to aquatic organisms. The CALUX bio-analytical approach showed some disparity with the traditional analytical approach. The reasons for these differences have been identified tentatively: firstly, the DR-CALUX assay responds to all dioxin-like compounds, and secondly, it measures non-additive effects. The dioxin-like activity of compounds in sediment total extracts, which contain both labile and stable compounds, were also assessed and were six orders of magnitude higher than the cleaned-up samples. This suggests the vast majority of the total dioxin-like activity is attributable to labile compounds. Overall, the DR-CALUX assay is shown to be a useful tool in the assessment of dioxin-like activity in estuarine sediments.

Animals↗
PubMed1997

Informational Capacity and Recall Quality in Sparsely Encoded Hopfield-like Neural Network: Analytical Approaches and Computer Simulation.

A sparsely encoded Hopfield-like attractor neural network is investigated analytically and by computer simulation. Informational capacity and recall quality are evaluated. Three analytical approaches are used: replica method (RM); method of statistical neurodynamics (SN); and single-step approximation (SS). Computer simulation confirmed the good accuracy of RM and SN for all levels of network activity. SS is accurate only for large sparseness. It is shown that informational capacity monotonically increases when sparseness increases, while recall quality changes nonmonotonically: initially it decreases and then increases. Computer simulation revealed the main features of network behaviour near the saturation which are not predicted by the used analytical approaches. Copyright 1997 Elsevier Science Ltd.

Journal Article↗
PubMed2006

Noninvasive methods for the investigation of ancient Chinese jades: an integrated analytical approach.

This paper reports on an integrated analytical approach for the noninvasive characterization of Chinese nephrite samples, encompassing both geological reference specimens and museum objects. Natural variations induced by cationic substitutions, as well as human-induced alterations such as heating, which both affect color, are the focus of this contribution. Totally noninvasive methods of analysis were used, including X-ray fluorescence spectroscopy, Raman microspectroscopy, visible reflectance spectroscopy and X-ray diffraction; moreover, the feasibility of using a portable Raman spectrometer for the in-field identification of jades has been demonstrated. Fe/Fe+Mg (% p.f.u.) ratios of the jades have been calculated based on hydroxyl stretching Raman bands, which will provide an important addition to similar data that are being collected at major museums in the Western and Eastern hemispheres.

Journal Article↗
PubMedDate not supplied

Meta-analytic approaches to dose-response relationships, with application in studies of lung cancer and exposure to environmental tobacco smoke.

This paper outlines several meta-analytic approaches to the assessment of quantal dose-response relationships; that is, to the evaluation of an increase in the level of exposure to an agent and the associated relative risk of a disease when this is investigated over a number of different studies. Analysis is developed at two levels: first, a consistent method of evaluating the dose-response relationship is applied to each study, and second, an overall picture is obtained by comparing and combining these relationships. At the first stage, for an individual study, dose-response assessment involves choices of model and appropriate tests for trend, which are influenced by such issues as dose measurement and use of the unexposed group. At the second stage, different methods for pooling results across studies must be considered. These depend on the choices made in the first stage of analysis, with additional attention paid to heterogeneity, and possible bias due to studies included in meta-analysis. We describe these meta-analytic approaches for three methods of evaluating dose response. The approaches are illustrated by evaluating the relationship between lung cancer and levels of exposure to environmental tobacco smoke (ETS). The strength of this relationship has been a point of debate in recent assessment of evidence for an overall carcinogenic effect of ETS exposure. We find little indication of a consistent dose response, a result explained in terms of recent models for cancer and passive smoking developed by Darby and Pike, the current meta-analysis results of overall risk-ratios of current studies in Tweedie and Mengersen, and misclassification models developed by the United States Environmental Protection Agency (EPA).

Case-Control Studies↗
PubMed2004

Coronary artery calcification and cardiovascular risk factors: impact of the analytic approach.

Coronary artery calcification (CAC) may help identify novel risk factors for coronary atherosclerosis. However, analysis of CAC is challenging because of the distribution of CAC in the population. This has resulted in difficulty in interpreting and comparing results across studies. We applied several analytic approaches to CAC data in order to determine the impact of analytic methods on the association with established cardiovascular risk factors in 914 asymptomatic subjects in the Study of Inherited Risk Factors for Coronary Atherosclerosis. Multivariable analyses included: (1) linear regression of different transformations of CAC scores; (2) tobit regression of the log of (CAC + 1); (3) logistic regression using CAC zero as a cut-point; and (4) ordinal logistic regression using CAC categories. Linear regression of the log CAC scores and logistic regression of CAC zero cut-point failed to detect associations with some risk factors. In contrast, linear and tobit regression of the log (CAC + 1) and ordinal regression of CAC categories identified more associations and provided consistent results. Commonly applied methods of CAC analysis may fail to detect associations with cardiovascular risk factors. We present analytic approaches that are likely to provide consistent results and recommend the use of at least two distinct multivariable methods.

Adult↗