The Internet Addiction Test: Factor structure, measurement invariance, and psychometric properties of a six-item version among Spanish women with eating disorders

Background: Eating disorders and internet addiction are widespread conditions that have considerably increased because of the current lockdown. Their comorbidity is frequently undiscovered, which may increase patients’ distress and hamper recovery. Identifying the constructs of internet addiction may facilitate its detection and management. The Internet Addiction Test is widely used to evaluate internet addiction among students and healthy adults, with less agreement on its dimensional structure.Objectives: To examine the structure of the Internet Addiction Test and its invariance among patients with eating disorders.Methods: In this cross-sectional study, exploratory and confirmatory factor analyses evaluated the structure of the Internet Addiction Test among 123 women with eating disorders (59 women with anorexia nervosa (group 1) and 64 women with other eating disorders (group 2)) recruited from the General University Hospital of Ciudad Real between February and November 2018. Multigroup analysis examined invariance of the Internet Addiction Test across eating disorder groups, and correlation with the Bergen Facebook Addiction Scale examined its criterion validity.Results: One factor explained 83.4%, 74.4%, and 87.4% of the variances in the whole sample, group 1, and group 2, with excellent reliability (coefficient alpha = 0.99, 0.98, and 0.99, respectively). In confirmatory factor analysis, two- and bifactor structures (a general factor with two specific factors: Emotional and cognitive preoccupation; Loss of control and interference with daily life) expressed some satisfactory fit in all groups, but they displayed metric and scalar variance—less tendency of women with anorexia nervosa to endorse items 14, 15, and 16. A 12-item version expressed a better fit. However, the six-item Internet Addiction Test expressed the best fit, along with configural and metric invariance across groups, and excellent reliability (coefficient alpha = 0.97, 0.95, and 0.98, respectively). The criterion validity of the Internet Addiction Test, the12-item version, and our six-item version was confirmed by strong positive correlations with the Bergen Facebook Addiction Scale (r = 0.906, 0.883, and 0.878, respectively).Conclusion: The Internet Addiction Test is a unidimensional or bidimensional measure. The six-item version expresses better fit, less variance, and comparable reliability and criterion validity to the Internet Addiction Test and the 12-item version. Its brevity allows test batteries to include several measures. Scalar variance implies that differences in the properties of the Internet Addiction Test across eating disorder groups may cause statistical differences in group means, which should be considered when conducting interventional studies. Further investigations are intensely needed.

Push-pull flows reveal the scalar signature of chaos in porous media

<p>Recent works have shown that laminar flows through porous media generate Lagrangian chaos at pore scale, with strong implications for a range of transport, reactive, and biological processes in the subsurface. The characterization and understanding of mixing dynamics in these opaque environments remains an outstanding challenge. We present a novel experimental technique based upon high-resolution imaging of the scalar signature produced by push-pull flows through various porous materials (beads, gravels, sandstones) at high Péclet number. We show that this method provides a direct image (see below) of the invariant unstable manifold of the chaotic flow, while allowing a precise quantification of the incompleteness of mixing at pore scale. In the limit of large Péclet numbers, we demonstrate that the decay rate of the scalar variance is directly related to the Lyapunov exponent of the chaotic flow. Thus, this new push-pull method has the potential to provide a complete characterization of chaotic mixing dynamics in a large class of opaque porous materials.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.2deb367885ff54776299061/sdaolpUECMynit/12UGE&app=m&a=0&c=2dcb0848f87d632804dd684b486c506f&ct=x&pn=gepj.elif&d=1" alt=""></p><p> </p>

Simple solutions for the concentration fluctuations of a passive scalar

<p>The dispersion dynamics of a contaminant released in the atmosphere is crucial for risk assessments and environmental analyses. Yet, because of the unsolved problem of turbulence, analytical solutions physically-derived are currently limited to the Gaussian models for the mean concentration field. In this work, we have obtained simple solutions for the concentration statistics of a passive scalar released from a punctual source. The main result is a novel analytical solution for the passive scalar variance, which is obtained from the contaminant transport equation. We have verified this solution against wind-tunnel data, and further adopted it in a simple stochastic model to provide closed relationships for the temporal statistics of concentration (e.g., the mean duration and occurrence of the peak events). These results may serve as a rapid and practical way to estimate the intensity and duration of the concentration fluctuations of a pollutant released in the atmosphere.</p>

Turbulent shear-layer mixing: initial conditions, and direct-numerical and large-eddy simulations

Aspects of turbulent shear-layer mixing are investigated over a range of shear-layer Reynolds numbers, $Re_{\unicode[STIX]{x1D6FF}}=\unicode[STIX]{x0394}U\unicode[STIX]{x1D6FF}/\unicode[STIX]{x1D708}$, based on the shear-layer free-stream velocity difference, $\unicode[STIX]{x0394}U$, and mixing-zone thickness, $\unicode[STIX]{x1D6FF}$, to probe the role of initial conditions in mixing stages and the evolution of the scalar-field probability density function (p.d.f.) and variance. Scalar transport is calculated for unity Schmidt numbers, approximating gas-phase diffusion. The study is based on direct-numerical simulation (DNS) and large-eddy simulation (LES), comparing different subgrid-scale (SGS) models for incompressible, uniform-density, temporally evolving forced shear-layer flows. Moderate-Reynolds-number DNS results help assess and validate LES SGS models in terms of scalar-spectrum and mixing estimates, as well as other metrics, to $Re_{\unicode[STIX]{x1D6FF}}\lesssim 3.3\times 10^{4}$. High-Reynolds-number LES investigations to $Re_{\unicode[STIX]{x1D6FF}}\lesssim 5\times 10^{5}$ help identify flow parameters and conditions that influence the evolution of scalar variance and p.d.f., e.g. marching versus non-marching. Initial conditions that generate shear flows with different mixing behaviour elucidate flow characteristics in each flow regime and identify elements that induce p.d.f. transition and scalar-variance behaviour. P.d.f. transition is found to be largely insensitive to local flow parameters, such as $Re_{\unicode[STIX]{x1D6FF}}$, or a previously proposed vortex-pairing parameter based on downstream distance, or other equivalent criteria. The present study also allows a quantitative comparison of LES SGS models in moderate- and high-$Re_{\unicode[STIX]{x1D6FF}}$ forced shear-layer flows.

The turbulent Prandtl number in a pure plume is 3/5

We derive a new expression for the entrainment coefficient in a turbulent plume using an equation for the squared mean buoyancy. Consistency of the resulting expression with previous relations for the entrainment coefficient implies that the turbulent Prandtl number in a pure plume is equal to 3/5 when the mean profiles of velocity and buoyancy have a Gaussian form of equal width. Entrainment can be understood in terms of the volume flux, the production of turbulence kinetic energy or the production of scalar variance for either active or passive variables. The equivalence of these points of view indicates how the entrainment coefficient and the turbulent Prandtl and Schmidt numbers depend on the Richardson number of the flow, the ambient stratification and the relative widths of the velocity and scalar profiles. The general framework is valid for self-similar plumes, which are characterised by a power-law scaling. For jets and pure plumes it is shown that the derived relations are in reasonably good agreement with results from direct numerical simulations and experiments.