Oxidative stress is considered the main cause of cellular damage in a number of neurodegenerative disorders. One suitable ways to prevent cell damage is the use of the exogenous antioxidant capacity ...of natural products, such as microalgae. In the present study, four microalgae extracts, isolated from the Persian Gulf, were screened to analyze their potential antioxidant activity and free radical scavenging using ABTS, DPPH, and FRAP methods. The methanolic extracts (D1M) of green microalgae derived from Chlorella sp. exhibited potent free radical scavenging activity. In order to characterize microalgae species, microscopic observations and analysis of the expression of 18S rRNA were performed. The antioxidant and neuroprotective effects of D1M on H2O2-induced toxicity in PC12 cells were investigated. The results demonstrated that D1M significantly decreased the release of nitric oxide (NO), formation of intracellular reactive oxygen species (ROS), and the level of malondialdehyde (MDA), whereas it enhanced the content of glutathione (GSH), and activity of heme oxygenase 1 (HO-1), NAD(P)H: quinone oxidoreductase 1 (NQO1), and catalase (CAT) in PC12 cells exposed to H2O2. The pretreatment of D1M improved cell viability as measured by the MTT assay and invert microscopy, reduced cell apoptosis as examined by flow cytometry analysis, increased mitochondrial membrane potential (MMP), and diminished caspase-3 activity. The GC/MS analysis revealed that D1M ingredients have powerful antioxidant and anti-inflammatory compounds, such as butylated hydroxytoluene (BHT), 2,4-di-tert-butyl-phenol (2,4-DTBP), and phytol. These results suggested that Chlorella sp. extracts have strong potential to be applied as neuroprotective agents, for the treatment of neurodegenerative disorders.
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A simple semi-hyperbolic state-dependent constitutive model for sand-structure interfaces is proposed. The model formulation is consistent with critical state soil mechanics since void ratio evolves ...continuously with shear strain from initial state towards asymptotic critical state at extremely large shear strains. The model takes into account influence of normal stiffness on volume change and stress path. The proposed interface model is implemented in a pile segment analysis scheme for simulation of shaft resistance mobilization in non-displacement piles. Results reveal that the proposed pile segment analysis can well predict shaft resistance of model piles embedded in different sands.
Experimental findings have revealed that up to a certain transitional threshold, adding non-plastic silt to coarse soils like sands leads to the increase in susceptibility of liquefaction. In silty ...sands, silt grains fill voids between the coarse constituent, but do not actively participate in stress transmitting microstructure. To consider the partial participation of fines in load bearing structure, an equivalent intergranular void ratio is suggested. The proposed empirical relationship, takes into account the combined influence of fines content, soil gradation, and the average shape of coarse and fine constituents. An equivalent intergranular state parameter is employed in the model formulation to define soil state uniquely. Moreover, recent experimental studies indicate that the consequences of initial anisotropy on the mechanical behavior of silty sands are mitigated with the increase in fines content. To consider this phenomenon, vector magnitude, a measurable index of anisotropy, is related to fines content. Then, proper constitutive equations are introduced to modify plastic hardening modulus and critical state line in loading paths involving rotation of principal stress axes. The simulative capability of the model is evaluated by direct comparison of its predictions with experimental data of triaxial and hollow cylindrical cells reported by four research teams.
•The mechanical behavior of silty sands is extensively reviewed.•An intergranular void ratio as an index of the density of load carrying structure of silty sands is introduced.•An existing constitutive model for clean sands is modified to cover both clean and silty sands.
Adding a small amount of non-plastic silt to clean sands may lead to dramatic loss of shear strength and a noteworthy tendency toward contraction when the mechanical behavior of the mixture is ...compared with that of the clean host sand. Thus, simulation of the behavior of silty sands with varying fines content is still a challenging subject in geomechanics. A unified constitutive model for clean and silty sands is presented in this paper. To eliminate the factitious decrease of void ratio associated with inactive silt particles in various silty sand mixtures, the concept of equivalent void ratio is used in the model formulation instead of the global void ratio. In addition, the instantaneous soil state is expressed in terms of intergranular state parameter taking into account the combined influence of intergranular void ratio, mean principal effective stress and fines content. Then, dilatancy and plastic hardening modulus are directly linked to the intergranular state parameter. To improve the model capacity in simulation of cyclic tests, new features are added to the plastic hardening modulus. It is shown that the proposed model can reasonably reproduce the mechanical behavior as well as the onset of flow liquefaction instability of clean and silty sands using a unique set of parameters.
This paper presents the results of an extensive series of direct shear tests covering a broad spectrum of bedding plane inclination angles with respect to the shearing plane to study the outcome of ...inherent anisotropy on the mechanical behavior of sand-steel interfaces. As a part of the research, it is shown that the peak friction and the maximum dilation angles of the tested inherently anisotropic sand are highly influenced by the bedding plane inclination angle. However, for smooth, intermediate, rough, and very rough sand-steel interfaces, the test results indicate that the variation in peak friction angle with the bedding plane inclination angle is meaningfully less than that for the same sand. Moreover, it is observed that the extrema of peak friction and maximum dilation angles in sand-steel interface tests are attained at bedding plane inclination angles that are significantly different from those obtained from direct shear tests on sand samples.
Central nervous system (CNS) infection is a global health problem with high rate of mortality and associated morbidities. Viruses, bacteria, fungi, and protozoa parasites are the main cause of CNS ...infection. Various medications are currently used for treatment of brain infections, but most of them do not have enough efficiency because the majority of conventional drugs cannot pass the blood–brain barrier (BBB) to combat the pathogens. Nanotechnology has provided promising approaches to solve this issue, since nanoparticles (NPs) can facilitate the drugs entrance through the BBB. Herein, we systematically reviewed all available literature to provide evidences for practicality of NPs in treatment of CNS infection. A systematic literature search was performed on January 29, 2021, in Web of Science, PubMed, Scopus, Science Direct, Embase, Ovid, and Google Scholar using “CNS infections” and “NPs/nanoformulation” including all their equivalent terms as keyword. Due to lack of human studies, no strict inclusion criteria were defined, and all relevant documents were included. After several steps of article selection, a total of 29 documents were collected and used for data synthesis. The results showed that drug-loaded NPs is fairly safe and can be a promising approach in developing anti-infective agents for treatment of CNS infection, since nanoformulated drugs could act up to tenfold more efficient that drug alone. Findings of this review indicate the importance of NPs and nanoformulation of drugs to enhance the efficiency of treatment and warrant the safety of treatment in human studies; however, clinical trials are required to confirm such efficiency and safety in clinical practice.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sparked a global pandemic that continues to affect various facets of human existence. Many sources reported virus-induced acute ...cerebrovascular disorders. Systematically, this paper reviews the case studies of COVID-19-related acute cerebrovascular diseases such as ischaemic stroke, intracerebral hemorrhage, and cerebral sinus thrombosis. We also spoke about how SARS-CoV-2 can infect the brain and trigger the aforementioned disorders. We stated that SARS-CoV-2 neuroinvasion and BBB dysfunction could cause the observed disorders; however, further research is required to specify the mechanisms and pathogenesis of the virus.
Lashkari responds to the discussion on "A simple critical state interface model and its application in prediction of shaft resistance of non-displacement piles in sand" by R F Feng, Q Q Zhang, S W ...Liu and X M Li. Details on how the mobilized shear stress in the proposed interface model is calculated are presented.
Soil elastic moduli are highly pressure-dependent. Experimental findings have indicated that the elastic shear modulus of sands depends on pχ, where p is mean principal effective stress and χ is a ...non-dimensional parameter. χ practically remains unchanged for shear strains less than 10−5 where the mechanical behavior is purely elastic. However, experiments have revealed that the emergence of plasticity for shear strains larger than 10−5 provokes a gradual increase in χ. Technically, this observation is an elastic–plastic coupling effect in which plasticity causes to change the elastic characteristics. Here, this issue is considered in hyper-elasticity framework in conjunction with a critical state compatible bounding surface plasticity platform for granular soils. To this aim, constitutive equations linking χ to a proper kinematic hardening parameter are presented. Then, using the proposed approach, a hyper-elastic theory is modified to consider the mentioned elastic–plastic coupling effect in the whole domain of the elastoplastic behavior. Adopting the improved hyper-elasticity necessitates the modification of a number of basic plasticity platform elements. In this regard, dilatancy and plastic hardening modulus of the bounding surface platform are modified. Successful performance of the modified constitutive model is presented against experimental data of loading/unloading triaxial tests.
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