Fluid-phase velocity fluctuations in gas-solid flows

Fluid-phase velocity fluctuations in fixed beds and freely evolving suspensions are quantified using particle-resolved direct numerical simulation (PR-DNS). The flow regime corresponds to homogeneous gas-solid systems typically encountered in fluidized beds, with high solid to fluid density ratios and particle diameters being greater than dissipative length scales. The contribution of turbulent and pseudo-turbulent fluctuations to the level of fluid-phase velocity fluctuations is quantified in flow past fixed particle assemblies. The simulations are then extended to freely evolving suspensions with elastic and inelastic collisions. For the parameter ranges considered here (volume fraction 0.1 and 0.2, particle to fluid density ratio 100 and 1000, coefficient of restitution in the range 0.7-1.0), the level of gas-phase velocity fluctuations in freely evolving suspensions differs by only 10% from the value for a fixed bed at the same solid volume fraction and mean slip Reynolds number. Quantification of the Reynolds stress indicates that the second moments of the gas-phase velocity fluctuations are anisotropic, corresponding to unidirectional axisymmetric velocity fluctuations. The anisotropy increases with Reynolds number to a maximum in the range between 10 to 40, and then decreases. In addition, the anisotropy decreases with increasing solid volume fraction for all cases considered in this study. The Reynolds stress is decomposed into isotropic and deviatoric parts, and their dependence on solid volume fraction and Reynolds number is quantified and explained

Analysis of gas-solid flow using particle-resolved direct numerical simulation: flow physics and modeling

Gas-solid flows are encountered in many industrial processes such as pneumatic conveying, fluid catalytic cracking, CO2 capture and fast pyrolysis process. In spite of several experimental and numerical studies performed to understand the physics governing observed phenomena in gas-solid flows, and to propose accurate closure models for computational fluid dynamics (CFD) simulations using the averaged conservation equations, there are several challenges in gas-solid flows that yet need to be addressed. In many of the industrial processes, the solid-to-fluid density ratio is of the order of 100 to 1000, and the particle diameter ranges from 50 to 500 micron. The interaction of heavy and large particles with the carrier phase leads to the formation of a boundary layer around each particle that in turn gives rise to interphase momentum transfer at the fluid-solid interface. The rate of work done by the carrier flow to sustain the interphase transfer of momentum leads to generation of velocity fluctuations in both the gas phase and the solid phase. Gas-phase velocity fluctuations enhance gas-particle heat transfer and the mixing of chemical species. Additionally, fluctuating motion of solid particles together with microscale hydrodynamic instabilities give rise to formation of mesoscopic particle clusters in gas-solid flows. The particle clusters then modify the hydrodynamic field and then the interconnected phenomena mentioned above dynamically modify the response of the system. Furthermore, if there exists a particle size distribution in the dispersed phase, the differences in the gas-particle and particle-particle drag forces lead to the segregation phenomenon. In this study, particle-resolved direct numerical simulation (PR-DNS) is used to address some aspects of the challenges noted above, and to propose closure models for device-scale CFD calculations. First, the level of gas-phase velocity fluctuations is quantified, and its dependence on flow parameters is explained. An algebraic Reynolds stress model is proposed by decomposing the Reynolds stress into isotropic and deviatoric parts. Also the influence of solid particles with isotropic turbulent flow has been addressed using PR-DNS. In addition, in this study the slip velocity between two particle size classes in a bidisperse mixture is quantified, which is the key signature of segregation of particle size classes. The predictive capability of two-fluid closure models in predicting the slip velocity between particle size classes is also assessed. PR-DNS is used to propose a bidisperse gas-particle drag model that improves the prediction of the mean slip velocity between the two particle size classes. In addition, the mechanism of transfer of kinetic energy from the mean flow to fluid-phase and particle velocity fluctuations in a homogeneous bidisperse suspension is explained. This mechanism of transfer of energy is important because particle velocity fluctuations affect the particle-particle drag, which jointly with the gas-particle drag on each particle class determines the mean slip velocity between the two particle classes. In this study we have also used PR-DNS to quantify the mean drag force on particle clusters that are statistically consistent with those observed in experiments. A clustered particle drag model has been proposed based on our PR-DNS results. To address the effect of filtering the hydrodynamic field on flow statistics, which is used in LES of gas-solid flows, we have shown that the source and sink of kinetic energy in particle velocity fluctuations obtained from the PR-DNS are different from those predicted by the LES approach. These differences lead to a different level of kinetic energy in the solid phase obtained from the two approaches, and thus the flow characteristics that depend on solid-phase kinetic energy, such as formation and evolution of particle clusters, may not be comparable between the PR-DNS and LES approaches. In this study we have also used PR-DNS to quantify the growth rate of mixing length in a particle-laden mixing layer, and the corresponding mechanism is identified by using a scaling analysis

Mechanics of aeolian processes: Soil erosion and dust production

Aeolian (wind) processes occur as a result of atmosphere/land-surface system interactions. A thorough understanding of these processes and their physical/mechanical characterization on a global scale is essential to monitoring global change and, hence, is imperative to the fundamental goal of the Earth observing system (Eos) program. Soil erosion and dust production by wind are of consequence mainly in arid and semi arid regions which cover 36 percent of the Earth's land surface. Some recent models of dust production due to wind erosion of agricultural soils and the mechanics of wind erosion in deserts are reviewed and the difficulties of modeling the aeolian transport are discussed

Effects of Chronic Administration of Nickel on Memory Function, Hippocampal Neuronal Morphology and Oxidative Stress Factors in Male Adult Rats

Introduction: Nickel (Ni) is a toxic heavy metal that can damage the brain structure, especially the hippocampus which is an important complex brain structure with a major role in memory and learning. Recent studies showed that heavy metals can alter some brain functions and disrupt hemostasis in central nervous system (CNS). The role of chronic Ni administration on memory and leaning, survival of neurons in CA1 hippocampus and the level of oxidative stress marker in rats. Materials and Methods: In total 24 rats (n=6) were allocated to four groups: Group (I): vehicle received intraperitoneal (IP) normal saline (0.9% NaCl), Group (II, III ,IV): received 0.25 mg/kg, 0.5 mg/kg and 1 mg/kg IP NiCl2 for eight weeks, respectively. During this timespan, the rats were examined in the Morris water maze and novel object recognition test to evaluate memory and learning. Finally, the hippocampus of the rats was extracted and survived neurons were evaluated by Nissl staining; oxidative stress was determined using malondialdehyde (MDA) level and catalase enzyme activity. Results: Results showed that dose-dependent Ni administration decreased memory and leaning in behavioral studies and caused degenerative and morphological changes in neurons by elevating MDA and catalase enzyme activity as the most important oxidative stress markers. Conclusion: Ni induces changes in the structure of hippocampal neurons and disrupts memory and learning function in hippocampus in adult rats by an increase in oxidative markers

Biochemical characterization of digestive amylase of wheat bug, Eurygaster maura (Hemiptera: Scutelleridae)

Biochemical characterization of  -amylase in the midgut and salivary glands of Eurygaster maura was conducted. Results showed that -amylase activities were present in the salivary glands and gut. The activity of -amylase in the midgut and in the salivary glands was 0.098 and 0.057 U/ml, respectively. The pH of salivary glands and the gut was determined to be in the range of 5- 5.5 (for the salivary glands) and in the range of 6-6.5 (for the gut), using staining indicator. The optimum pH and temperature for salivary glands and midgut amylase activity was 6-7 and 35-40ºC, respectively. The stability of amylase was highest in the acidic pH (4-5). Ethylenediamine tetraacetic acid (EDTA), urea, sodium dodecyl sulfate (SDS) and Mg2+ inhibited the enzyme activity but, NaCl and KCl enhanced enzyme activity. Based on linear regression analysis of reciprocal starch concentration versus reciprocal amylase activity Km and Vmax were 0.11% and 0.04 mM maltose/min for midgut amylase and 0.298% and 0.071 mM maltose/min for salivary amylase, respectively. Sodium dodecyl sulfate electrophoresis (SDS-PAGE) showed that both midgut and salivary glands contain isozymes

Investigation of the impact of excavation (reinforced) on the seismic behavior of adjacent steel structures under the influence of near-fault and far-fault earthquakes

Every year, as a result of earthquake, abundant losses may be created as result of roof motion and sliding and rupture. Under normal conditions, the ground and soils forming the ground tolerate and transfer the existing stresses and any kind of action like excavation and release of trench and applying dynamic load could distort the balance of stresses and endanger stability of roof. In this study, behavior of a steel building in adjacency of excavation is studied. The pit is stabled using hybrid system of pinching and anchoring and is studied before and after excavation under the effect of far and near-fault earthquakes with regard to soil-structure interaction. The results obtained from nonlinear dynamic analysis of time history of two said spectrums showed that the momentum of floor in the structure after excavation is increased compared to the time before excavation. The momentum of floor in the desired structure in near-fault earthquake has been increased compared to far-fault earthquake before excavation compared to the time after excavation. However, the overall drift of floors in the structure before excavation in near-fault earthquakes has been increased more than far-fault earthquakes.Keywords: excavation, earthquake, far and near-fault zone, dynamic behavior, soil-structure interaction, steel structur

Effect of Curcumin on Beta-Amyloid Plasma Level in Alzheimer Disease: A Systematic Review and Meta-analysis

Alzheimer’s disease is known as a most common dementia disorder in the world. The famous hypothesis about the cause of this disease is beta-amyloid (Aβ ) accumulation in the brain. There is a widespread neuroinflammation in the patient’s brain, leading to neuronal apoptosis and brain atrophy. Curcumin is a well-known anti-inflammation and anti-oxidant ingredient. It can easily cross the blood-brain barrier. There are controversial results about the effects of curcumin on Aβ clearance and metabolism in Alzheimer’s disease and the elderly. The aim of this meta-analysis and systematic review was to review the effect of curcumin on Aβ clearance in clinical studies. We performed a systematic review and meta-analysis on the three randomized clinical trials (RCTs) and one pilot study that assessed the effect of curcumin on Aβ plasma level in Alzheimer’s disease. For this purpose, we searched PubMed and Scopus databases up to December 2020. Our result showed there was no significant change in serum Aβ level (weighted mean difference [WMD]: 5.3, 95% CI: 0.78-9.97) following curcumin consumption in patients with Alzheimer’s disease. Further clinical trials should be done to evaluate the effects of curcumin in Aβ level in Alzheimer’s disease

Regulation of cytotoxic drug-induced apoptosis by death receptor 5 in human colon cancer cells

5-Fluorouracil(5-FU)is a cytotoxic drug that is widely used for the treatment of colon cancer. However, 5-FU-resistance is still a common issue which needs to be overcome. Understanding the molecular pathway of 5-FU-induced apoptosis will help designing more effective cancer treatments. Chemotherapeutic drugs such as 5-FU are thought to trigger cell death via the intrinsic apoptosis pathway which involves caspase-9 activation as one of the initiating molecular events. However, our group recently found the new apoptotic pathways which are involved in 5-FU-induced apoptosisin which caspase-8 is an essential factor for 5-FU-induced cell death with caspase-9 being dispensable for this process. Aside from caspase-8, the death receptor TRAIL-R2 (DR5), which is usually involved in the extrinsic pathway of apoptosis, was found to be required for the execution of 5-FU-triggered cell death. Moreover,following 5-FU treatment, DR5 is not responsible for caspase-8 activation, but for the activation of c-Jun N-terminal kinases (JNK) without the involvement of its natural ligand TRAIL. In the current study, factors associated with DR5 that are involved in JNK activation are identified. Also, the involvement ofTRAF2, FADD, caspase-8, caspase-10 and RIP1 in JNK activation were examined. It was found that JNK is activated in HCT116, but not in DR5, caspase-8 and FADD knockdown cells after 5-FU treatment. Moreover, the absence of caspase-10, TRAF2 and RIP1 does not affect JNK activation.Also it was discovered that similar to 5-FU, when cells are treated with etoposide,another cytotoxic drug, JNK is also activated and initiated by DR5 and mediated by FADD and caspase-8. Thus, in the present study, the factors that are involved in activating JNK after 5-FU and etoposide treatment have been identified. The obtained results further clarify the mechanism of cell death in colon cancer cells after 5-FU and etoposide treatment which constitutes a novel regulating pathway of apoptosis