A fractional-order model for the novel coronavirus (COVID-19) outbreak

Nonlinear Dynamics - The outbreak of the novel coronavirus (COVID-19), which was firstly reported in China, has affected many countries worldwide. To understand and predict the transmission...     

Curing Kinetics Modeling of Epoxy Modified by Fully Vulcanized Elastomer Nanoparticles Using Rheometry Method

In this study, the curing kinetics of epoxy nanocomposites containing ultra-fine full-vulcanized acrylonitrile butadiene rubber nanoparticles (UFNBRP) at different concentrations of 0, 0.5, 1 and 1.5 wt.% was investigated. In addition, the effect of curing temperatures was studied based on the rheological method under isothermal conditions. The epoxy resin/UFNBRP nanocomposites were characterized via Fourier transform infrared spectroscopy (FTIR). FTIR analysis exhibited the successful preparation of epoxy resin/UFNBRP, due to the existence of the UFNBRP characteristic peaks in the final product spectrum. The morphological structure of the epoxy resin/UFNBRP nanocomposites was investigated by both field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) studies. The FESEM and TEM studies showed UFNBRP had a spherical structure and was well dispersed in epoxy resin. The chemorheological analysis showed that due to the interactions between UFNBRP and epoxy resin, by increasing UFNBRP concentration at a constant temperature (65, 70 and 75 °C), the curing rate decreases at the gel point. Furthermore, both the curing kinetics modeling and chemorheological analysis demonstrated that the incorporation of 0.5% UFNBRP in epoxy resin matrix reduces the activation energy. The curing kinetic of epoxy resin/UFNBRP nanocomposite was best fitted with the Sestak–Berggren autocatalytic model.     

The 2 × 1 reconstruction of the rutile TiO2(0 1 1) surface: A combined density functional theory, X-ray diffraction, and scanning tunneling microscopy study

An extensive search for possible structural models of the (2 × 1)-reconstructed rutile TiO₂(0 1 1) surface was carried out by means of density functional theory (DFT) calculations. A number of models were identified that have much lower surface energies than the previously-proposed ‘titanyl’ and ‘microfaceting’ models. These new structures were tested with surface X-ray diffraction (SXRD) and voltage-dependent STM measurements. The model that is (by far) energetically most stable shows also the best agreement with SXRD data. Calculated STM images agree with the experimental ones for appropriate tunneling conditions. In contrast to previously-proposed models, this structure is not of missing-row type; because of its similarity to the fully optimized brookite TiO₂(0 0 1) surface, we call it the ‘brookite (0 0 1)-like’ model. The new surface structure exhibits two different types of undercoordinated oxygen and titanium atoms, and is, in its stoichiometric form, predicted to be rather inert towards the adsorption of probe molecules.     

Spatial Prediction of Current and Future Flood Susceptibility: Examining the Implications of Changing Climates on Flood Susceptibility Using Machine Learning Models

The main aim of this study was to predict current and future flood susceptibility under three climate change scenarios of RCP2.6 (i.e., optimistic), RCP4.5 (i.e., business as usual), and RCP8.5 (i.e., pessimistic) employing four machine learning models, including Gradient Boosting Machine (GBM), Random Forest (RF), Multilayer Perceptron Neural Network (MLP-NN), and Naïve Bayes (NB). The study was conducted for two watersheds in Canada, namely Lower Nicola River, BC and Loup, QC. Three statistical metrics were used to validate the models: Receiver Operating Characteristic Curve, Figure of Merit, and F1-score. Findings indicated that the RF model had the highest accuracy in providing the flood susceptibility maps (FSMs). Moreover, the provided FSMs indicated that flooding is more likely to occur in the Lower Nicola River watershed than the Loup watershed. Following the RCP4.5 scenario, the area percentages of the flood susceptibility classes in the Loup watershed in 2050 and 2080 have changed by the following percentages from the year 2020 and 2050, respectively: Very Low = −1.68%, Low = −5.82%, Moderate = +6.19%, High = +0.71%, and Very High = +0.6% and Very Low = −1.61%, Low = +2.98%, Moderate = −3.49%, High = +1.29%, and Very High = +0.83%. Likewise, in the Lower Nicola River watershed, the changes between the years 2020 and 2050 and between the years 2050 and 2080 were: Very Low = −0.38%, Low = −0.81%, Moderate = −0.95%, High = +1.72%, and Very High = +0.42% and Very Low = −1.31%, Low = −1.35%, Moderate = −1.81%, High = +2.37%, and Very High = +2.1%, respectively. The impact of climate changes on future flood-prone places revealed that the regions designated as highly and very highly susceptible to flooding, grow in the forecasts for both watersheds. The main contribution of this study lies in the novel insights it provides concerning the flood susceptibility of watersheds in British Columbia and Quebec over time and under various climate change scenarios.     

An asymptotic approach to heat recirculation in diffusion flames fueled by organic particles

Journal of Thermal Analysis and Calorimetry - Owing to their safety, stability and controllability, diffusion flames have found extensive applications in medicine and power generation. Regarding...     

Irreversibility of nanomaterial due to MHD via numerical approach

Journal of Thermal Analysis and Calorimetry - In current research, MAPLE software was utilized to scrutinize the heat transfer of copper–H2O nanomaterial migration over a sheet. Entropy...     

Extraction of nanofibers from polymer blends: A brief review

This review is about the naturally formed and intentionally produced nanofibrils or nanofibers (NFs) that have been extracted and utilized or expected to be used for special applications. The diameter of NFs ranges between a few to a few hundred nanometers. Methods to arrange synthetic NFs assembly in yarns or pads forms have been examined. High throughput productions, versatility of various thermoplastics, and less environmental pollution are the advantages of the methods of extraction, which seems to make it as an economical process. It can also be used for the polymers that are difficult to be converted to NFs by electrospinning. The process is challenging and scientifically fascinating to attract the investigators. There are many more polymers to be considered, and there are many more envisioned applications that have to be practiced in the future. A theoretical base is needed for the evaluation of the effects of polymer flow parameters on the extracted NFs properties.     

Eccentricity effect of micropatterned surface on contact angle

This article experimentally shows that the wetting property of a micropatterned surface is a function of the center-to-center offset distance between successive pillars in a column, referred to here as eccentricity. Studies were conducted on square micropatterns which were fabricated on a silicon wafer with pillar eccentricity ranging from 0 to 6 μm for two different pillar diameters and spacing. Measurement results of the static as well as the dynamic contact angles on these surfaces revealed that the contact angle decreases with increasing eccentricity and increasing relative spacing between the pillars. Furthermore, quantification of the contact angle hysteresis (CAH) shows that, for the case of lower pillar spacing, CAH could increase up to 41%, whereas for the case of higher pillar spacing, this increment was up to 35%, both corresponding to the maximum eccentricity of 6 μm. In general, the maximum obtainable hydrophobicity corresponds to micropillars with zero eccentricity. As the pillar relative spacing decreases, the effect of eccentricity on hydrophobicity becomes more pronounced. The dependence of the wettability conditions of the micropatterned surface on the pillar eccentricity is attributed to the contact line deformation resulting from the changed orientation of the pillars. This finding provides additional insights in design and fabrication of efficient micropatterned surfaces with controlled wetting properties.     

Computational approaches to aspect-ratio-dependent upper bounds and heat flux in porous medium convection

Direct numerical simulation (DNS) has shown that Rayleigh–Bénard convection in a fluid-saturated porous medium self-organizes into narrowly spaced plumes at (ostensibly) asymptotically high values of the Rayleigh number Ra. In this Letter a combination of DNS and upper bound theory is used to investigate the dependence of the Nusselt number Nu on the domain aspect ratio L at large Ra  . A novel algorithm is introduced to solve the optimization problems arising from the upper bound analysis, allowing for the best available bounds to be extended up to Ra≈2.65×10⁴$\mathit{Ra}\approx 2.65\times {10}^4$. The dependence of the bounds on L(Ra)$L(\mathit{Ra})$ is explored and a “minimal flow unit” is identified.     

Modeling of aerosol spray characteristics for synthesis of sensor thin film from solution

A model is developed of aerosol spray for synthesis of sensor film from solution. The synthesis technique considered involves atomization of a solution of mixed salts in methanol, spraying of solution droplets, droplet deposition on a heated substrate, evaporation and chemical reaction to produce mixed oxides, and subsequent film growth. The precise control of oxide nanoparticle size distribution and inter-particle spacing in the film is crucial to achieving high sensitivity. These in turn largely depend on the droplet characteristics prior to impingement on the substrate. This paper focuses on the development of a model to describe the atomization and spray processes prior to the film growth. Specifically, a mathematical model is developed utilizing computational fluid dynamics solution of the equations governing the transport of atomized droplets from the nozzle to the substrate in order to predict droplet characteristics in flight. The predictions include spatial distribution of droplet size and concentration, and the effect on these characteristics of swirling inlet flow at the spray nozzle.