196,450 research outputs found
Nasal disinfection for the prevention and control of COVID-19: A scoping review on potential chemo-preventive agents
No full textBackground: Neither pre-exposure nor post-exposure chemo-prophylaxis agents are currently available to prevent COVID-19. On the other hand, high loads of SARS-CoV-2 are shed from the nasal cavity before and after symptoms onset. Objective: To conduct a scoping review on the available evidence on tolerable nasal disinfectants with encouraging health outcomes against SARS-CoV-2, i.e., agents effective against at least two different viruses beyond SARS-CoV-2. Methods: Online databases were searched to identify papers published during 2010–2020. Publications were selected if they were relevant to the scoping review. The review was narrative, describing for each treatment the mechanism(s) of action, tolerability, in vitro and in vivo evidence of the effects against SARS-CoV-2 and whether the product had been marketed. Results: Eight treatments were scrutinized: hypothiocyanite, lactoferrin, N-chlorotaurine, interferon-alpha, povidone-iodine, quaternary ammonium compounds, alcohol-based nasal antiseptics and hydroxychloroquine. In vitro viricidal effect against SARS-CoV-2 was reported for ethanol, alcohol-based hand sanitizers and povidone-iodine. Inhibition of other coronaviruses was described for lactoferrin, hydroxychloroquine and quaternary ammonium compound. No treatment has been tested against SARS-CoV-2 in randomized controlled clinical trials thus far. However, interferon-alpha, lactoferrin and hydroxychloroquine were tested in one-arm open label uncontrolled clinical trial. Oxidant activity (hypothiocyanite, N-chlorotaurine and povidone-iodine), enhancement of endocytic and lysosomal pH (quaternary ammonium compounds and hydroxychloroquine) and destruction of the viral capsid (quaternary ammonium compounds, alcohol-based nasal antiseptics) were the main mechanisms of action. Lactoferrin and interferon-alpha have subtle biological mechanisms. With the exception of N-chlorotaurine, all other products available on the market. Conclusions: Effective and safe chemo-prophylactic drugs against SARS-CoV-2 do not exist yet but most eligible candidates are already in the market. Whilst the human nasal cavity is the port of entry for SARS-CoV-2, the mouth is involved as exit site through emission of respiratory droplets. The well-known hand-to-nose-to-hand cycle of contamination requires appropriate additional strategies for infection control. To narrow down the subsequent laboratory and clinical investigations, a case-control approach could be employed to compare the use of candidate drugs among individuals testing positive and negative to COVID-19 swabs
Investigating the effect of nanovoid inelastic surface stress and the austenite–martensite interface inelastic stress on the martensitic growth at the nanovoid surface
No full textIn this paper, the effect of nanovoid inelastic surface stress and austenite (A)–martensite (M) interface inelastic stress on the martensitic growth at the nanovoid surface is investigated. Within the phase field approach (PFA), the coupled Cahn–Hilliard and elasticity equations involving the nanovoid inelastic surface stress are solved to generate a nanovoid. Then, the coupled Ginzburg–Landau and elasticity equations involving both the A-M interface and nanovoid inelastic surface stresses are solved to capture the evolution of martensite in the presence of the nanovoid. A nanovoid concentration-dependent phase transformation (PT) kinetic coefficient is introduced which, in contrast to previous works, removes the unphysical transformation inside the nanovoid. The FEM implemented in the commercial software COMSOL is used to solve the system of equations. It is found that the nanovoid changes the PT morphology and decreases the transformation rate. Both the A-M interface and nanovoid inelastic surface stresses decrease the transformation rate which amount depends on initial and boundary conditions. The effect of the A-M inelastic interface stress on the total stress is more pronounced in the presence of nanovoid. Nevertheless, the nanovoid inelastic surface stress shows no significant effect on the PT critical stress. Moreover, the study of the PT critical temperature versus the gradient energy coefficient also revealed that both the A-M interface and nanovoid inelastic surface stresses have no significant effect on the PT critical temperature
The effect of a pre-existing nanovoid on martensite formation and interface propagation: a phase field study
No full textIn the present work, the effect of a pre-existing nanovoid on martensitic phase transformation (PT) is investigated using the phase field approach. The nanovoid is created as a solution of the coupled Cahn–Hilliard and elasticity equations. The coupled Ginzburg–Landau and elasticity equations are solved to capture the martensitic nanostructure. The above systems of equations are solved using the finite element method and COMSOL code. The austenite (A)–martensite (M) interface propagation is investigated without the nanovoid and with it for different nanovoid misfit strains and different temperatures. With the nanovoid, the evolution of the moving interface is changed even before it reaches the nanovoid surface due to the nanovoid stress concentration. It is also found that for small misfit strains, pre-transformation occurs near the nanovoid. For larger misfit strains, martensite nucleates and grows near the nanovoid surface and coalesces with the moving interface. The nanovoid shows a promotive effect on the PT with an increase in the rate of transformation, which is discussed based on the transformation work distribution. The effect of the nanovoid is more pronounced on a curved interface. The nanovoid-induced martensitic growth is mainly dependent on the transformation strain tensor. Examples for different transformation strains are presented where a stable non-complete transformed sample with no void becomes unstable in the presence of the nanovoid. The presented model and results will help to develop an interaction model between nanovoids and multiphase structures at the nanoscale
Surface layer effect on high pressure phase growth in a bicrystal: phase field model and simulations
No full textEffect of the external surface layer on the phase transition (PT) between the low pressure phase and high pressure phase (HPP) in a NiAl bicrystal is investigated. Using a phase field model, the external surface layer is included, within which the elastic properties and surface energy are properly distributed. After resolving a stationary layer, the coupled phase field and elasticity equations are solved to capture the HPP evolution. Residual stress concentrator is included as a shear band representing an inelastic shear strain. Due to the small grain size, the surface layer can influence the stress distribution and consequently, the critical inelastic shear strain γcr for the HPP growth. Above a certain applied pressure, the surface layer width Δξ shows no effect on γcr, e.g., P=10 GPa for the grain size of L = 20 nm. For lower pressures, γcr increases as pressure reduces. Due to the interplay of size addition by the surface layer and size reduction by the transformation strain, γcr reduces versus Δξ and then increases for larger Δξ. For smaller grain sizes, the surface layer effect is promoted as it is imposed to a larger transformation work. The lowest γcr is obtained for P=19 GPa, in good agreement with the theoretical pressure of 20 GPa. Combining the external shear on pressure adds an extra shear term to the transformation work, which allows for the relaxation of the shear band and results in a nonlinear reduction of the PT pressure versus applied shear
Interaction of Phase Transformations and Plasticity at the Nanoscale: Phase Field Approach
No full textPhase field approach (PFA) to the interaction between phase transformations (PTs) and dislocations is developed at large strains as a nontrivial combination of our recent advanced PFAs to martensitic PTs and dislocation evolution. Finite element method (FEM) simulations are performed to solve the coupled phase-field and elasticity equations and are applied to study of the growth and arrest of martensitic plate for temperature-induced PTs, the evolution of dislocations and high pressure phase in a nanograined material under pressure and shear, and the dislocation inheritance for stress-induced PT.This article is published as Levitas, V. I., and M. Javanbakht. "Interaction of phase transformations and plasticity at the nanoscale: phase field approach." Materials Today: Proceedings, 2 (2015): S493-S498. 10.1016/j.matpr.2015.07.334. Posted with permission.</p
Phase field approach to interaction of phase transformations and plasticity at large strains
No full textThermodynamically consistent phase field approach (PFA) for multivariant martensitic phase transformations (PTs) and twinning for large strains is developed [1, 2]. Thermodynamic potential in hyperspherical order parameters is introduced, which allowed us to describe each martensite‑martensite (i.e., twin) interface with a single order parameter [3]. These theories are utilized for finite element simulation of various important problems [1‑4]. Phase field approach to dislocation evolution was developed during the last decade and it is widely used for the simulation of plasticity at the nanoscale. Despite significant success, there are still a number of points for essential improvement. In our study [5], a new PFA to dislocation evolution is developed. It leads to a well-posed formulation and mesh-independent solutions and is based on fully large-strain formulation. Our local potential is designed to eliminate stress-dependence of the Burgers vector and to reproduce desired local stress–strain curve, as well as to obtain the mesh-independent dislocation height H for any dislocation orientation. The gradient energy contains an additional term, which excludes localization of dislocation within height smaller than H but disappears at the boundary of dislocation and the rest of the crystal; thus, it does not produce interface energy and does not lead to a dislocation widening. Problems for nucleation and evolution of multiple dislocations along the multiple slip systems are studied. The interaction between PT and dislocations is the most basic problem in the study of martensite nucleation and growth. Here, a PFA is developed to a coupled evolution of martensitic PTs and dislocations [6], including inheritance of dislocation during direct and reverse PTs. A complete system of equations, including Ginzburg–Landau equations is presented. It is applied to studying the hysteretic behavior and propagation of an austenite‑martensite interface with incoherency dislocations, the growth and arrest of martensitic plate for temperature-induced PTs, the evolution of phase and dislocation structures for stress-induced PTs, and the evolution of dislocations and high pressure phase in a nanograined material under pressure and shear [6, 7]. REFERENCES [1] Levitas, V.I., Levin, V.A., Zingerman, K.M., Freiman, E.I. Phys. Rev. Lett. 2009, 103, 025702. [2] Levitas, V.I. Int. J. Plasticity. 2013, 49, 85‑118. [3] Levitas, V.I., Roy, A.M., Preston, D.L. Phys. Rev. B. 2013, 88, 054113. [4] Levin, V.A., Levitas, V.I., Zingerman, K.M., Freiman, E.I. Int. J. Solids & Struct. 2013, 50, 2914‑2928. [5] Levitas, V.I., Javanbakht, M. Phys. Rev. B., Rapid Commun. 2012, 86, 140101. [6] Levitas, V.I., Javanbakht, M. Appl. Phys. Lett. 2013, 102, 251904. [7] Levitas, V.I., Javanbakht, M. Nanoscale. 2014, 6, 162‑166
Economic evaluation of the climate changes on food security in Iran: application of CGE model
No full textThe present study aims to examine the economic impact of changing climate variables on two components of food security
in Iran: availability and access to food. Wheat and rice, the two most important foods in the country, were considered representatives
of food security. A CGE model was developed to achieve the research goals. In this context, a stochastic model
based on Monte Carlo simulation was used to provide three scenarios (best, average, and worst) indicating probable changes
in climate variables. It is important to model the problem of changing climatic variables for irrigated crops, as groundwater
resource depletion and restrictions on extraction from Iranian aquifers reduce planted areas and yields. Therefore, this study
applies this model to both rain-fed and irrigated crops, whereas studies in the literature only evaluate rain-fed crops. Food
security will face serious challenges as food supplies, and consumption of goods and services are declining in average and
worst scenarios, according to findings. Consequently, the negative impact of climate change on food security and people’s
livelihoods requires a review of the policies implemented within the country. Effective solutions include research and development
to introduce drought-tolerant varieties and adopt appropriate strategies to adapt to climate change. Improving the
incomes of farmers is one solution to mitigating the impacts of climate change
Nonlinear buckling analysis of double-layered graphene nanoribbons based on molecular mechanics
No full textDouble-layer graphene nanoribbons promise potential application in nanoelectromechanical systems and optoelectronic devices, and knowledge about mechanical stability is a crucial parameter to flourish the application of these materials at the next generation of nanodevices. In this paper, molecular mechanics is utilized to investigate nonlinear buckling behavior, critical buckling stress, and lateral deflection of double-layered graphene nanoribbons under various configurations of stacking mode and chirality. The implicit arc-length iterative method (modified Riks method) with Ramm’s algorithm is utilized to analyze the nonlinear structural stability problem. The covalent bonds are modeled using three-dimensional beam elements in which elastic moduli are calculated based on molecular structural mechanics technique, and the interlayer van der Waals (vdW) interactions are modeled with nonlinear truss elements. An analytical expression for Young’s modulus of nonlinear truss elements is derived based on the Lennard–Jones potential function and implemented in numerical simulation with a UMAT subroutine based on FORTRAN code to capture the nonlinearity of the vdW interactions during the buckling analysis. The results indicate that the highest critical buckling stress and the minimum lateral deflection occur for armchair and zigzag chirality, both with AB stacking mode, respectively. Moreover, the critical buckling stress is found to be directly dependent on the mode shape number regardless of in-phase or anti-phase deflection direction of layers. Lateral deflection exhibits a similar trend with mode shape in anti-phase mode; however, it is decreasing by increasing mode shape number in in-phase mode
Economy-wide impact of food processing industry exports in Iran
No full textThis paper aims to analyze the economy-wide impact of an increase in the export of food processing industry in Iran and to compare it to the same increase in oil and gas exports as the main economic sector. It uses both demand-driven and supply-driven mixed Input-Output models referred to as 2011 SAM framework purposely designed by authors. The results show that an increase in the food processing industry promotes the production of other sectors and, increases factor employment and household income. The significance of this impact is comparable to a similar shock in the oil and gas sector
Coupled phase field and nonlocal integral elasticity analysis of stress-induced martensitic transformations at the nanoscale: boundary effects, limitations and contradictions
No full textIn this paper, the coupled phase field and local/nonlocal integral elasticity theories are used for stress-induced martensitic phase transformations (MPTs) at the nanoscale to investigate the limitations and contradictions of the nonlocal integral elasticity, which are due to the fact that the support of the nonlocal kernel exceeds the integration domain, i.e., the boundary effect. Different functions for the nonlocal kernel are compared. In order to compensate the boundary effect, a new nonlocal kernel, i.e., the compensated two-phase kernel, is introduced, in which a local part is added to the nonlocal part of the two-phase kernel to account for the boundary effect. In contrast to the previously introduced modified kernel, the compensated two-phase kernel does not lead to a purely nonlocal behavior in the core region, and hence no singular behavior, and consequently, no computational convergence issue is observed. The nonlinear finite element approach and the COMSOL code are used to solve the coupled system of Ginzburg–Landau and local/nonlocal integral elasticity equations. The numerical implementation of the phase field-local elasticity equations and the 2D nonlocal integral elasticity are verified. Boundary effect is investigated for MPT with both homogeneous and nonhomogeneous stress distributions. For the former, in contrast to the local elasticity, a nonhomogeneous phase transformation (PT) occurs in the nonlocal case with the two-phase kernel. Using the compensated two-phase kernel results in a homogeneous PT similar to the local elasticity. For the latter, the sample transforms to martensite except the adjacent region to the boundary for the local elasticity, while for the two-phase kernel, the entire sample transforms to martensite. The solution of the compensated two-phase kernel, however, is very similar to that of the local elasticity. The applicability of boundary symmetry in phase field problems is also investigated, which shows that it leads to incorrect results within the nonlocal integral elasticity. This is because when the symmetric portions of a sample are removed, the corresponding nonlocal effects on the remaining portion are neglected and the symmetric boundaries violate the normalization condition. An example is presented in which the results of a complete model with the two-phase kernel are different from those of its one-fourth model. In contrast, the compensated two-phase kernel can generate similar solutions for both the complete and one-fourth models. However, in general, none of the nonlocal kernels can overcome this issue. Therefore, the symmetrical models are not recommended for nonlocal integral elasticity based phase field simulations of MPTs. The current study helps for a better study of nonlocal elasticity based phase field problems for various phenomena such as various PTs
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