187,038 research outputs found
CFD simulations of segregating fluidized bidisperse mixtures of particles differing in size
No full textIn this work, we use a multifluid model to investigate numerically the dynamics of segregating fluidized
bidisperse mixtures. The model uses the default multifluid equations of commercial computational fluid
dynamics (CFD) codes, except for the fluid–particle drag force closure, which Mazzei and Lettieri [1]
recently developed and extended to polydisperse systems. The study also comprises some preliminary
simulations of collapsing monodisperse beds, focusing on the role of the plastic solid stress. This work
tests whether the model is able to correctly predict not only the axial segregation profiles through the bed,
but also the minimum fluid velocities at which a) the mixture, being no longer fixed, starts segregating
and transient fluidization takes place, and b) the mixture becomes steadily fluidized and fully mixed. To
validate the model predictions, we use the experimental findings of Marzocchella et al. [2]. The plastic
stress results to play an important role, rendering the simulations more stable and allowing for larger
time steps. The model well predicts the stationary axial segregation profiles, and for short computational
times estimates correctly the onset of transient fluidization; for longer computational times, however,
the system evolves towards a new steady state where, even if the powder is at maximum packing, it
partly segregates. The model overestimates the velocity required to fully mix the suspension, probably
because the simulated bubbling is not as vigorous as it is experimentally
Nonresonant Kerr effect in microporous silicon: Nonbulk dispersive behavior of below band gap χ (3)(ω)
No full textAlthough in recent years resonant optical nonlinearities in quantum confined silicon generated significant interest, no experimental work has been dedicated to the nonresonant regime, which is the range of interest for optical switching applications. In this article we report a systematic investigation on the different types of optical nonlinearities which can be activated in quantum-sized silicon. In particular, original measurements of nonresonant nonlinear refraction (Kerr effect) are reported at different wavelengths, spanning the infrared middle-gap range. The dispersive scaling rule and values of the nonlinear refractive index are clearly incompatible with those of three-dimensional semiconductors. Hence the quantum confined density of states plays a key role in determining the frequency dispersion of the nonresonant third-order susceptivity χ (3)(ω). Also, this suggests the need of further investigation of the influence of quantum-size effects (and related density of states modifications) on below-gap χ (3). © 2002 American Institute of Physics
The measurement of powder flow properties with a mechanically stirred aerated bed
No full textThis paper re-examines a set of experimental data published by Bruni et al. (2007a, 2007b) [Bruni, G., Barletta, D., Poletto, M., Lettieri, P., 2007a. A rheological model for the flowability of aerated fine powders. Chem. Eng. Sci. 62, 397–407; Bruni, G., Lettieri, P., Newton, D., Barletta, D., 2007b. An investigation of the effect of the interparticle forces on the fluidization behaviour of fine powders linked with rheological studies. Chem. Eng. Sci. 62, 387–396] carried out on a mechanically stirred fluid-bed rheometer (msFBR), which was developed to study the rheology of aerated and fluidized powders. The use of aeration below fluidization allowed to carry out experiments with powders at very low consolidation levels. Two mathematical models, based on the Janssen approach to evaluate stresses in powder containers, were developed in order to relate the torque measurements in the Fluidized Bed Rheometer to the flow properties of the powders measured with standard powder flow testers. Results indicate that the models were able to satisfactorily predict the torque measured by the msFBR. The larger complexity of the Walker (1966) [Walker, D.M., 1966. An approximate theory for pressures and arching in hoppers, Chem. Eng. Sci. 21, 975–997] and Walters (1973) [Walters, J.K., 1973. A theoretical analysis of stresses in silos with vertical walls, Chem. Eng. Sci. 28, 13–21] stress analysis adopted in one of the two models did not introduce significant improvements in the evaluation of the stress distribution to justify its use. A procedure for the inverse application of the model was developed and applied to estimate the powder flow properties starting from msFBR data. The application of this procedure provided good results in terms of effective angle of internal friction and is promising for the ability of the system to explore powder flow at very low consolidation states
CFD SIMULATIONS OF THE MIXING OF INERT POLYDISPERSE FLUIDIZED SUSPENSIONS USING QMOM & DQMOM
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Direct Quadrature Method of Moments for the Mixing of Inert Polydisperse Fluidized Powders and the Role of Numerical Diffusion
No full textUse of health apps and wearable devices : Survey among Italian associations for patient advocacy
No full textBackground: Technological tools such as Web-based social networks, telemedicine, apps, or wearable devices are becoming more widespread in health care like elsewhere. Although patients are the main users, for example, to monitor symptoms and clinical parameters or to communicate with the doctor, their perspective is seldom analyzed, and to the best of our knowledge, no one has focused on the patients’ health care advocacy associations’ point of view. Objective: The objective of this study was to assess patients’ health care advocacy associations’ opinions about the use, usefulness, obstacles, negative aspects, and impact of health apps and wearable devices through a Web-based survey. Methods: We conducted a Web-based survey through SurveyMonkey over nearly 3 months. Participants were contacted via an email explaining the aims of the survey and providing a link to complete the Web-based questionnaire. All the 20 items were mandatory, and the anonymized data were collected automatically into a database. Only fully completed questionnaires were considered for analysis. Results: We contacted 1998 patients’ health care advocacy associations; a total of 258 questionnaires were received back (response rate 12.91%), and 227 of the received questionnaires were fully completed (completion rate 88.0%). Informative apps, hospital apps for viewing medical reports or booking visits, and those for monitoring physical activity are the most used. They are considered especially useful to improve patients’ engagement and compliance with treatment. Wearable devices to check physical activity and glycemia are the most widespread considering, again, their benefits in increasing patients’ involvement and treatment compliance. For health apps and wearable devices, the main obstacles to their use are personal and technical reasons; the risk of overmedicalization is considered the most negative aspect of their constant use, while privacy and confidentiality of data are not rated a limitation. No statistical difference was found on stratifying the answers by responders’ technological level (P=.30), age (P=.10), and the composition of the association’s advisory board (P=.15). Conclusions: According to responders, health apps and wearable devices are sufficiently known and used and are considered potential supports for greater involvement in health management. However, there are still obstacles to their adoption, and the developers need to work to make them more accessible and more useful. The involvement of patients and their associations in planning services and products based on these technologies (as well as others) would be desirable to overcome these barriers and boost awareness about privacy and the confidentiality of data
Boolean dominated MV-algebras
No full textIn this paper the authors study an obvious generalization of the hyperarchimedian MV-algebras: boolean dominated MV-algebras. Particularly they point out the wide difference between the class of the hyperarchimedian MV-algebras and the class of the Boolean dominated MV-algebras
Influence of doping concentration on the photoluminescence of silicon nanocrystals
No full textPhotoluminescent silicon films have been fabricated starting from p-type silicon powders, by means of a purely wet-chemical process at different doping concentrations. Their light emission properties have been investigated by means of continuous wave and time-resolved photoluminescence measurements. In all the samples Auger saturation has been observed, showing that light emission from quantum confined Si nanocrystals occurs. The doping level influences the spectra, the decay times and the reactivity towards oxidizing environment. The same features are observed in samples obtained from simultaneously processing p- and n-type silicon powders. Hence, our results support the hypothesis that, during the chemical reaction, merging of p- and n-type silicon nanocrystals and subsequent doping neutralization occurs
Della patologia del pensiero: note su Plotino e gli gnostici
No full textIl saggio intende ricostruire il rapporto di analogia, ma pure di irriducibile differenza tra lo gnosticimo (irriducibilmente caratterizzato da una forma cristiana) e il neoplatonismo di Plotino
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