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Multiscale-linking simulation of irreversible colloidal deposition in the presence of DLVO interactions.

An efficient multiscale-linking algorithm, based on the self-consistent integration of Brownian dynamics simulation of particle trajectories with the solution of the continuum-level conservation equation for particle concentration subject to an adaptive Neumann boundary condition that accounts for the blocking effect of deposition, is developed. The algorithm has been already validated in the case of deposition of noninteracting hard spheres [R.V. Magan, R. Sureshkumar, Multiscale Model. Simul. 2 (2004) 475]. In this study, the above algorithm is extended to incorporate particle interactions modeled by the DLVO theory. The simulations are used to identify a time scale at which the deposition process transitions from a power-law to an asymptotic regime. Detailed characterization of the two regimes is provided for a wide range of ionic strength, particle surface charge density, bulk volume fraction, and substrate potential values. The radial distribution functions obtained for various ionic strengths can be collapsed into a master curve when the radial distance is normalized with respect to a characteristic length scale of inter-particle repulsion. Moreover, simulation results suggest a rescaled, uniformly valid soft random sequential adsorption (RSA) model. Simulation results for the kinetics and monolayers structure compare favorably with experimental data, without the use of adjustable parameters. Comparison with other dynamic simulation techniques shows that while their predictions are qualitatively similar, notable quantitative differences exist especially for small ionic strengths.

Adsorption↗

Low-dimensional manifolds in tropospheric chemical systems.

Ordinary differential equations derived from large nonlinear systems of chemical reactions are computationally expensive to solve because of the large number of coupled species and the large range of time-scales present. The range of time-scales often spans several orders of magnitude leading to stiff systems of equations requiring implicit numerical techniques. The use of slow manifolds for the description of long time-scale chemical processes has two advantages in that it reduces the number of variables required and also the stiffness of the chemical system by assuming that the fast time-scales are in local equilibrium with respect to the slower ones. The method exploits the existence of a low-dimensional manifold within a large-dimensional species phase space onto which the system quickly collapses. This paper investigates the existence of slow manifolds for nonlinear tropospheric chemical systems and presents a simple method for estimating the local dimension of the manifold using linear perturbation theory. The method is demonstrated for several tropospheric mechanisms over diurnal simulations including a subset of the Master Chemical Mechanism describing butane oxidation and the formation of ozone in the troposphere. It is shown that the intrinsic dimension of the slow manifold varies diurnally and depends on photolytic processes and the relative concentrations of major pollutants.

Journal Article↗

Calibration of STUD+ parameters to achieve optimally efficient broadband adiabatic decoupling in a single transient

To provide the most efficient conditions for spin decoupling with least RF power, master calibration curves are provided for the maximum centerband amplitude, and the minimum amplitude for the largest cycling sideband, resulting from STUD+ adiabatic decoupling applied during a single free induction decay. The principal curve is defined as a function of the four most critical experimental input parameters: the maximum amplitude of the RF field, RFmax, the length of the sech/tanh pulse, Tp, the extent of the frequency sweep, bwdth, and the coupling constant, Jo. Less critical parameters, the effective (or actual) decoupled bandwidth, bweff, and the sech/tanh truncation factor, beta, which become more important as bwdth is decreased, are calibrated in separate curves. The relative importance of nine additional factors in determining optimal decoupling performance in a single transient are considered. Specific parameters for efficient adiabatic decoupling can be determined via a set of four equations which will be most useful for 13C decoupling, covering the range of one-bond 13C1H coupling constants from 125 to 225 Hz, and decoupled bandwidths of 7 to 100 kHz, with a bandwidth of 100 kHz being the requirement for a 2 GHz spectrometer. The four equations are derived from a recent vector model of adiabatic decoupling, and experiment, supported by computer simulations. The vector model predicts an inverse linear relation between the centerband and maximum sideband amplitudes, and it predicts a simple parabolic relationship between maximum sideband amplitude and the product JoTp. The ratio bwdth/(RFmax)2 can be viewed as a characteristic time scale, tauc, affecting sideband levels, with tauc approximately Tp giving the most efficient STUD+ decoupling, as suggested by the adiabatic condition. Functional relationships between bwdth and less critical parameters, bweff and beta, for efficient decoupling can be derived from Bloch-equation calculations of the inversion profile for a single sech/tanh pulse. Residual splitting of the centerband, normally associated with incomplete or inefficient decoupling, is not seen in sech/tanh decoupling and therefore cannot be used as a measure of adiabatic decoupling efficiency. The calibrated experimental performance levels achieved in this study are within 20% of theoretical performance levels derived previously for ideal sech/tanh decoupling at high power, indicating a small scope for further improvement at practical RF power levels. The optimization procedures employed here will be generally applicable to any good combination of adiabatic inversion pulse and phase cycle. Copyright 1998 Academic Press.

Journal Article↗

The equation of state of isotropic fluids of hard convex bodies from a high-level virial expansion.

We have calculated virial coefficients up to seventh order for the isotropic phases of a variety of fluids composed of hard aspherical particles. The models studied were hard spheroids, hard spherocylinders, and truncated hard spheres, and results are obtained for a variety of length-to-width ratios. We compare the predicted virial equations of state with those determined by simulation. We also use our data to calculate the coefficients of the y expansion [B. Barboy and W. M. Gelbart, J. Chem. Phys. 71, 3053 (1979)] and to study its convergence properties. Finally, we use our data to estimate the radius of convergence of the virial series for these aspherical particles. For fairly spherical particles, we estimate the radius of convergence to be similar to that of the density of closest packing. For more anisotropic particles, however, the radius of convergence decreases with increased anisotropy and is considerably less than the close-packed density.

Journal Article↗

Determination of plasma bicarbonate of neonates in intensive care.

Most modern blood-gas analyzers are programmed to use the Henderson-Hasselbalch equation to calculate a value for plasma bicarbonate. It has been suggested, however, that among acutely ill patients, including newborns, these calculated values may be at variance with measured total CO2. To assess the clinical significance of such errors, we compared calculated bicarbonate with measured total CO2 in 79 blood samples from 40 babies in intensive care. The calculated bicarbonate values consistently exceeded the measured values by about 1.5 mmol/L. Of the errors, 94% were within the range -10% to +20%. When the systematic bias was removed, calculated and measured bicarbonate values agreed within +/- 3.30 mmol/L in 95% of cases. Because calculated values can be obtained much more quickly and frequently than laboratory measurements, we believe that these limits are clinically acceptable.

Bicarbonates↗

Psychological characteristics of women with sexual inhibition (frigidity) in six clinics.

Traditional psychiatric thought has equated the inability of a female to obtain an orgasm (particularly a vaginal orgasm during intercourse) with psychological maladjustment. The research literature generally does not support this position. The present paper describes the psychological characteristics of 44 frigid women who applied for treatment of their sexual problem at two university hospital sex clinics and 26 women selected for treatment by the same criterion, but treated in private practice. Presented for comparison are 53 female neurotics from a Temple University Hospital psychotherapy study, a sample of 65 consecutive female walk-ins of mixed psychiatric diagnosis from the Psychiatric Outpatient Clinic of Temple Hospital, and a group of 35 female college student sophomores from Temple University who comprised the normal sample. A battery of psychological tests including the MMPI, the Institute for Personality and Ability Testing--Self-Evaluation Form (IPAT), the Symptom Check List, and the Eysenck Personality Inventory were given to each group. The data indicate that female patients who apply to a sex dysfunction clinic, complaining primarily of sexual inhibition, appear as a group identical to a normal control group in terms of their psychological profile and less neurotic than psychiatric outpatients, with the exception that the normals were less depressed. When women with primary orgasmic dysfunction from the above three samples were combined and compared to those with secondary orgasmic dysfunction (using Masters and Johnson's criterion), the groups were identical, at least from a global psychological perspective. We suggest that little else can be gained by assessing global personality characteristics. Without discarding the primary and secondary classifications a potentially more fruitful approach would be to develop instruments that would measure specific dimensions, such as sexual misinformation, specific sexual anxiety or guilt, or resentment or hostility directed toward the immediate sexual partner. A scale to measure specific phobic-like sexual anxiety, in addition, would have treatment implications because of the recently demonstrated effectiveness of specific anxiety-reducing techniques, such as systematic desensitization. Specific scales can also be useful in the assessment and prediction of outcome in psychotherapy.

Adolescent↗

The association of perceived health, clinical status, and initiation of HAART (highly active antiretroviral therapy) in adolescents.

PURPOSE: To examine factors associated with the initiation of highly active antiretroviral therapy (HAART) in adolescents to understand better how current National Institutes of Health (NIH) Guidelines are being used in practice. METHODS: HIV infected and HAART-naive adolescents seen at 15 REACH clinical sites were selected. Repeated measures methodology using generalized estimating equations was applied to identify associations between subject demographic characteristics, risk behaviors, perceived health, and clinical status with the outcome measure of HAART initiation during the first 24 study months. RESULTS: A total of 219 subjects were eligible for analysis; HAART was prescribed in 115 (53%). Significant univariate associations with HAART prescription included lower CD4(+) T cell counts (OR = 1.7, 95% CI: 1.1-2.6), higher viral loads (OR = 2.7, 95% CI: 1.5-5.0), and calendar year of HAART prescription (OR as high as 2.4, 95% CI: 1.1-5.2). Multivariate results showed that after controlling for CD4(+) T cell counts below 500 cells/mm(3), higher plasma HIV-1 RNA (<or=10,000 copies per ml), and temporal factors, having a high school diploma/GED but no further education (OR = 2.7, 95% CI: 1.3-5.5) and subject's perception of poor health status (OR = .987; 95% CI: .975- .999) were independently associated with prescription of HAART. HAART was most likely to be prescribed during the first half of 1998 in this cohort (OR = 10.8; 95% CI: 4.0-29.0). CONCLUSIONS: In this first ever study of HAART prescription in adolescents infected with HIV, perception of poor health status and having a high school diploma/GED were independently associated with prescription of HAART suggesting that the personal decision to accept therapy is related to the belief that one's health is deteriorating and that the decision to prescribe therapy may be linked in some fashion to the prescriber's assessment of the patient's ability to master the regimen as well as clinical status.

Adolescent↗

[Multidimensional assessment of coping: validation of the Brief COPE among French population].

This Article aims to introduce the translation and the validation of a multidimensional measure of coping strategies: the Brief COPE, in a French population. The coping concept comes from psychological studies that were conducted on stress. In the conceptual analysis of stress by Lazarus and Folkman, coping works with two cognitive appraisals performed by the person concerning the perception of a threatening situation and his or her available resources to deal with it. Coping is defined as "cognitive and behavioural efforts to master, reduce, or tolerate the internal and/or external demands that are created by the stressful transaction". The Brief COPE is the abridged version of the COPE inventory and presents fourteen scales all assessing different coping dimensions: 1) active coping, 2) planning, 3) using instrumental support, 4) using emotional support, 5) venting, 6) behavioural disengagement, 7) self-distraction, 8) self-blame, 9) positive reframing, 10) humor, 11) denial, 12) acceptance, 13) religion, and 14) substance use. Each scale contains two items (28 altogether). This inventory has the advantage of being built from acknowledged theoretical models (Lazarus' transactional model of stress, 1984; behavioral self-regulation model, Carver and Scheier, 1981, 1998). It can be used to assess trait coping (the usual way people cope with stress in everyday life) and state coping (the particular way people cope with a specific stressful situation). As is the COPE inventory, the Brief COPE is a measure used for many health-relevant studies: drugs addiction, ageing, breast cancer, depression, AIDS. Both measures are widely used in Anglophone countries and translated in many Languages. Today, the COPE inventory has been validated among Estonian, Croatian, Chinese, and Italian populations and the Brief COPE is also validated among Spanish people. Thus, the worldwide use of this coping inventory should allow a broad comparison of medical and psychological research for coping strategies regarding every kind of pathologies. Thus, we were led to present the translation and the validation of this measure in a French population. Two studies are presented in this Article: the first one describes the validation of the inventory in a dispositional format (trait coping) and the second one the validation of the inventory in a situational format (state coping). The French version of Brief COPE, which was used for both studies, was back-translated and analysed by the Brief COPE Author: Charles S. Carver. For study 1, 834 first Year university students answered the Brief COPE in its dispositional format. To study the factor structure of the Brief COPE, we used structural equation modeling and the LISREL software. Results show that the expected theoretical structure and the observed one fit adequately (c2=606, p<0,05, RMSEA=0,04, GFI>0,95, AGFI>0,92, RMR<0,03). In order to study convergent and discriminant validity of Brief COPE, self-esteem (SEI, Rosenberg, 1979), perceived stress (PSS, Cohen et al., 1983), and psychological distress (GHQ-12, Goldberg, 1972) measures were used. Results show that functional coping strategies (eg, active coping) are linked to good self-esteem, to lower perceived stress, and to lower psychological distress, whereas less functional strategies (eg, denial or self-blame) are widely linked to poor self-esteem, to a high perceived stress, and to psychological distress. Study 1 shows also several significant gender differences. Study 2 describes the Brief COPE validation in its situational format. 178 additional students answered this version. The method that was used is the same the one developed by Lazarus and his colleagues for the WCC validation. Participants were asked to recall and think about the most stressful event they had experienced during the past two Months. They were also to give an account of how much that situation mattered to them. They had to evaluate their capacity to control the situation and indicated whether they felt the situation was amenable to change. The study includes only peoples only people who labeled an event as "important" or "very important". Here again LISREL was used to study the factor structure of the Brief COPE. The results emphasise - as in study 1 - that the expected theoretical structure and the observed one fit adequately (c2=391, p<0,05, RMSEA<0,05, GFI=0,87, AGFI=0,80, RMR<0,06). Differences among means showed how the perceived control of the situation and how the perception of its favourable evolution influenced the coping strategies used (eg, humour or denial). Results in both studies indicate good psychometric properties for the Brief COPE in its French version, whatever the format (ie, dispositional or situational). Thus French searchers have a relevant tool on hand to measure as accurately as possible the coping strategies someone used in everyday life (strategies interfering on health, on a long scale), or in distressful situations (eg, serious illness, traumas). The fact that this easy-to-use coping measure is worldwide spread among medical and psychological studies allows a better broadcast and comparison of results whatever the pathology.

Adaptation, Psychological↗