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This research aims to provide new information about the mechanical behavior of double-stranded DNA (dsDNA). For this purpose, a series of extended atomic resolution molecular dynamics (MD) simulations of DNA dodecamer is performed. The MD calculations are carried out using Generalized Born solvent-accessible surface area method and Langevin dynamics. The stress-strain curves of DNA obtained under various pulling rates and pulling angles are analyzed, and the role of pulling angle and velocity in determining biomechanical properties of short dsDNA is discussed. The results illustrate that how much the behavior of DNA under action of tensile forces could be complicated. By means of at base pair level analyses of the molecule conformation during the stretching processes, the structural stability of the DNA molecule subjected to the angled pulling with different pulling rates and different pathways to the dsDNA rupture are studied. The structural stability of dsDNA can be dependent on the pulling velocity and pulling angle. Whereas the DNA stability can decrease significantly with the reduction of pulling velocity, stretching the DNA under different angles has different unpredictable effects on its structural stability.

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Objective: Various approaches have been offered for resolution of pain resulting from spinal cord injuries. One approach is the use of herbal and natural products. In the present research, as a preliminary study, we investigate the effect of crocin on chronic pain induced by contusion in the rat spinal cord (SCI). Methods: We randomly divided female Wistar rats into five groups. Groups I and II were contused at the L1 level and immediately treated with crocin (50 mg/kg). These groups were sacrificed after 2 hours and 1 week, respectively. The remaining three groups consisted of group III (control group), group IV (treated with crocin and no contusion), and group V (the contused group that underwent no treatment). Groups III-V were sacrificed after one week. The mechanical behavioral test that used Von Frey hairs; the thermal behavioral test that used a hot-plate and the locomotor recovery test with Basso, Beattie and Bresnahn (BBB) scoring were conducted daily to evaluate the extent of injury and recovery of the rats. The calcitonin-gene related peptide (CGRP) was determined in the animals' plasma by the ELISA kit. Results: The results showed a significant increase in plasma CGRP of contused rats that significantly reduced following crocin treatment. The behavioral tests were not changed significantly due to this treatment. Conclusion: The present study shows the beneficial effects of crocin treatment that may occur by decreasing CGRP on chronic pain induced by SCI. This project is continuing using higher dose of crocin for longer time.

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Due to their accuracy and reliability, atomistic-based methods such as molecular dynamics (MD) simulations have played an essential role in the field of predictive modeling of single layered graphene sheets (SLGSs(. However, due to the computational costs, applications of these methods are limited to small systems. Additionally, according to the discrete nature of SLGSs, conventional continuum-based methods cannot be utilized to study the mechanical characteristics of them. To overcome these issues, here, a new Atomic-scale Finite Element Method (AFEM) based on the Tersoff-Brenner potential has been developed. Efficiency of the proposed method is evaluated through a numerical example analyzed by both of the proposed method and MD simulation. The results show that the computational cost is much reduced (~100 times), while the accuracy of MD simulation is kept. Furthermore, the effects of initial C-C bond length and number of atoms on the speed of the proposed method is investigated. To mimic the MD simulation completely, periodic boundary conditions have been implemented in the extended AFEM. It is demonstrated that there is a noticeable deviation from MD results without considering this type of boundary conditions.

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This paper deals with atomistic modeling of nanomechanical behavior of actin monomer. The major cytoskeletal protein of most cells is actin, which is responsible for the mechanical properties of the cells. Actin also plays critical mechanical roles in many cellular processes which gives structural support to cells and links the interior of the cell with its surroundings. Based on the accuracy of atomistic-based methods such as molecular dynamics simulations, in this paper, we perform a series of steered molecular dynamics simulations on both ATP and ADP single actin monomers to determine their intrinsic molecular strength. The effect of virtual spring of steered molecular dynamics on the mechanical behavior of actin monomer is investigated. The results reveal increasing the virtual spring constant leads to convergence of the stiffness. The stiffness of ADP actin and ATP actin calculated as 215.16 and 228.24 pN/Å, respectively. The results also show higher stiffness and Young’s modulus for ATP G-actin in comparison to ADP G-actin. In order to compare the behavior of ATP and ADP G-actins, the number of hydrogen bonds and nonbonded energies between the nucleotide and the protein is analyzed. The obtained persistent length is 15.61 µm which is in good agreement with the other reported literature values.

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This paper deals with studying and developing a proper constitutive model for liver tissue. For this purpose, deformation of liver in uniaxial compression, for two different strain rates, is analytically and numerically studied, based on both hyperelastic and hyperviscoelastic constitutive models. Both of the models are based on a polynomial-form energy function. The stress-strain curves, for uniaxial compression, obtained from these models, have been fitted to the existing experimental data to determine the model coefficients. Moreover the models are examined in uniaxial tension and pure shear loadings. ABAQUS commercial software, in which both of the models are available, has been used for numerical simulations. Then, to evaluate the computational analyses, analytical and numerical results have been compared with each other and also with the existing experimental data. The results show that the presented analytical solution and FE simulation are very close together and also both are accurate enough, compared with the experimental data and an acceptable stability is observed. Furthermore the effect of friction coefficient between the sample and the compressing plate in uniaxial compression test has been investigated. FE simulation results show that the stress will increase with increasing friction coefficient. This implies that friction coefficient must be carefully selected to accurately describe the tissue’s response. Compared with previously published researches on other tissues, the constitutive models adopted here to predict liver behavior is mathematically more complex due to non-zero material constants. Analytical solution of these constitutive models is, in fact, the main challenge and innovation of this paper.

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This paper aims at investigating the effect of heat input in resistance spot welding on microstructure and mechanical behavior of 2304 duplex stainless steel, as a promising candidate for automotive application. The results showed that due to rapid cooling rate inherent to resistance spot welding, the ferrite-austenite phase balance is destroyed and nitride-type precipitates are formed within the ferrite grains. The amount of austenite in the weld nugget was a function of welding current, as the most important factor affecting welding heat input. Increasing welding current increased the austenite volume fraction from 4 to 18%. Moreover, the nitride precipitation was reduced upon using higher welding currents. Investigation of weld mechanical performance during the tensile-shear loading showed that increasing welding current enhances both load bearing capacity and energy absorption capability. The maximum achievable peak load and energy absorption of 2304 duplex stainless steel resistance spot welds were 25 kN and 40 J indicating a superior weldability.

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Powder metallurgy process is commonly used to manufacture nanocomposite products, in which the product quality of this process depends upon Composite of reinforcement nanoparticle and distribution. In this article Metal Matrix Nanocomposite (MMN) by powder metallurgy with a base material stainless steel 316L, a material that is widely used in the industry, and reinforcement particles mixture of Carbide Titanium (TiC) as carbon-based reinforcing particles, and Hexagonal Nitride Boron (hBN) particles as the self-lubricating material is prepared. The reinforcement powders were micro Sized and mixed in high ball milling to reach Nano-sized, after 30 h mixing powders in high ball milling reach to Nano-sized, and then reinforcement Nanoparticles with 2 and 10 Wt.% Mixed with stainless steel 316L for 5 hours and compacted at 400 Mpa and sintered at 1400 C temperature and 3 Hours. Scanning electron microscope (SEM), Energy-dispersive X-ray Spectroscopy (EDX) and X-ray Diffraction (XRD) tests are performed on Powders to identify the nanocomposite microstructure. The Mechanical Properties such as Microhardness, Wear, and Bending Strength Were Analyzed. These results Compare with Results of stainless steel 316L without Reinforcement. Microhardness and abrasion resistance of Nanocomposite material have improved and flexural strength improved at the sample with 2 wt.% reinforcement and reduced at the sample with 10 Wt.%.

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It is seldom possible that rock engineering structures found without joints, cracks, or discontinuities. On the other hand, the application range of these structures are steadily increasing in recent years and includes bridges, tunnels, slopes, underground gas storage. Thereby, their impact is to be considered in the rock structure design. In the present study, it is intended to evaluate the effect of induced micro-cracks on the mechanical behavior of rock specimens. For this purpose, 24 cylindrical specimens of Granit were prepared and some of them heated up to 1000 degrees Celsius to induce micro-crack in the specimens. In the next, Uniaxial compression test for determination of stress-strain curve of heated and unheated specimens were performed based on International Society for Rock Mechanics (ISRM) suggested methods on a cylindrical specimen with 110 mm and 54 mm in length and diameter, respectively. The tests were conducted using a load controlled testing machine and the loading rate was kept at 0.5 MPa/Sec. Results of experimental tests indicated that mechanical properties of heated specimens decrease with increasing the temperature. In the heated specimens, some fractures induced that influence on the failure pattern of specimens. The failure pattern of unheated specimen is axial splitting mode, while the failure pattern of heated specimen up to 1000 degree Celsius changes to shear mode failure. It is seldom possible that rock engineering structures found without joints, cracks, or discontinuities. On the other hand, the application range of these structures are steadily increasing in recent years and includes bridges, tunnels, slopes, underground gas storage. Thereby, their impact is to be considered in the rock structure design. In the present study, it is intended to evaluate the effect of induced micro-cracks on the mechanical behavior of rock specimens. For this purpose, 24 cylindrical specimens of Granit were prepared and some of them heated up to 1000 degrees Celsius to induce micro-crack in the specimens. In the next, Uniaxial compression test for determination of stress-strain curve of heated and unheated specimens were performed based on International Society for Rock Mechanics (ISRM) suggested methods on a cylindrical specimen with 110 mm and 54 mm in length and diameter, respectively. The tests were conducted using a load controlled testing machine and the loading rate was kept at 0.5 MPa/Sec. Results of experimental tests indicated that mechanical properties of heated specimens decrease with increasing the temperature. In the heated specimens, some fractures induced that influence on the failure pattern of specimens. The failure pattern of unheated specimen is axial splitting mode, while the failure pattern of heated specimen up to 1000 degree Celsius changes to shear mode failure. It is seldom possible that rock engineering structures found without joints, cracks, or discontinuities. On the other hand, the application range of these structures are steadily increasing in recent years and includes bridges, tunnels, slopes, underground gas storage. Thereby, their impact is to be considered in the rock structure design. In the present study, it is intended to evaluate the effect of induced micro-cracks on the mechanical behavior of rock specimens. For this purpose, 24 cylindrical specimens of Granit were prepared and some of them heated up to 1000 degrees Celsius to induce micro-crack in the specimens. In the next, Uniaxial compression test for determination of stress-strain curve of heated and unheated specimens were performed based on International Society for Rock Mechanics (ISRM) suggested methods on a cylindrical specimen with 110 mm and 54 mm in length and diameter, respectively. The tests were conducted using a load controlled testing machine and the loading rate was kept at 0.5 MPa/Sec. Results of experimental tests indicated that mechanical properties of heated specimens decrease with increasing the temperature. In the heated specimens, some fractures induced that influence on the failure pattern of specimens. The failure pattern of unheated specimen is axial splitting mode, while the failure pattern of heated specimen up to 1000 degree Celsius changes to shear mode failure.

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The temperature-dependent nonlinear mechanical behaviors of functionally graded rectangular plates in the thickness direction resting on Winkler–Pasternak elastic foundation are investigated using the three-dimensional theory of elasticity. The material properties are temperature-dependent and varied in the thickness direction based on a power-law. Considering the nonlinear Green-Lagrange strain relation, the geometric nonlinearity is taken into account. After obtaining the potential strain, kinetic energies, taking into account the effects of the temperature and the elastic foundation, the Hamilton’s principle is used to derive the nonlinear three-dimensional governing equations and corresponding boundary conditions. To solve the nonlinear free vibration problem, first, the generalized differential quadrature (GDQ) method is used to discretize the nonlinear coupled governing equations in the space domain. Then, the obtained equations are converted to the time-dependent ordinary differential equations using the numerical-based Galerkin scheme and the time periodic discretization (TPD) are used to discretize them in the time domain. Finally, the arc-length method is employed to find the frequency-response of system. Also, to solve the nonlinear bending problem, by neglecting the effect of inertia and using the arc length algorithm, the maximum deflection versus the applied load is obtained. The effects of different parameters such as length-to-thickness ratio, Winkler–Pasternak elastic foundation coefficients, uniform and linear temperature rises and volume fraction index on the frequency response and maximum deflection of functionally graded plates with various edge conditions are studied.

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For the first time in this paper, by using semi-analytical scaled boundary finite element method (SBFM), a perfect nano garphene sheet or defected ones were simulated and their mechanical behavior had been investigated. In this analysis, the atomic carbon bonds were modeled by simple bar elements with circular cross- sections and then the scaled boundary finite element relations were formulated based on the geometry of the model. The obtained results from SBFM were compared to those obtained from molecular dynamic method which showed that the SBFM can be used as a continuum mechanics model with high accuracy in mechanical analysis of both perfect and defected nano graphene sheets. Existence of structural defects in nano grapheme sheets decrease the strength as well as fracture strain in a considerable manner. It can be noted that in a defected nano grapheme sheet, the fracture stress decreases more than 34% while fracture strain decreases more than 50%. In the cases that instead of using bar elements, whole area is considered as a continuum sheet and in order to obtain a similar geometry to those problems have bar elements, no material zone be modeled by zero elastic properties, the results show considerable errors.

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Soil pH is a measure of the acidity and alkalinity in soils, ranging from 0 to 14 that measured in a slurry of soil mixed with water. Soil pH normally falls between 3 and 10, with 7 being neutral, acid soils have a pH below 7 and alkaline soils have a pH above 7. Ultra-acidic soils have pH value less than 3.5 and very strongly alkaline soils have pH value more than 9 which are rare. Extremes in acidity or alkalinity may affect mechanical behaviour physical properties of soil. Recently, the rapid development of cities and the industrial revolution have caused enormous environmental impacts and become a serious environmental problem. About 80% of the pollutants in the atmosphere, including suspended particles and gases, result from vehicular traffic and industrial activities. Precipitation acts as a significant natural cycle to clean up atmospheric pollutants such as gases and particles in the air. The major sources of acid water are strong presence of SO₂ and NO_x gases in the atmosphere. One of the most important effects of acid water is its effect on soil, including washing nutrient cations, releasing toxic elements, and acidifying the soil. Also, acid mine drainage and the contaminants associated with it, is a common occurrence in waste dumps of mining sites results in acidic conditions with a pH of less than 4 develop over time. On the other hand, mineral deposits, over liming in some parts of the land and the use of limestone to improve the different soil natural and control the pH in waste dumps leads to alkaline conditions (pH more than 7) at mine sites. One of the most important effects of air pollution is acid rain. The increasing expansion of cities, the rapid growth of urbanization and the industrial revolution have caused enormous environmental impacts in and around cities. Industrial activities, production of energy and fuel, the use of fertilizers and pesticides cause significant amounts of contaminants to the atmosphere. The entry of metal contaminants and acidifying compounds such as sulfur, nitrogen compounds or their reaction to the atmosphere in the rain will increase the acidity of the rain which can change the quality of atmospheric precipitation. In general, it can be stated that the meaning of acid rain is a rain that has a pH of less than 5.5 which is a lower natural pH. In the current study, the effect of acid rain on the mechanical behavior and physical properties of lime stabilized sand with respect to the eastern regions of Isfahan has been investigated. At first, the various lime content was added to the soil and the specimens were tested after treatment and saturation under various pH values. The results show that adding lime increased the optimum moisture content, shear strength of the specimens, the cohesion and the friction angle of the soil. On the other hand, reducing the pH value results in continuously decreasing the shear strength parameters of the soil specimens. Finally, based on the scanning electron microscopy (SEM) image from the specimens, the effect of pH and lime content on the bonds between the sand grains was investigated.

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One of the new approaches to produce nanoscale metals with ultera fine grains is applying severe plastic deformation on initial sample with coarse grains. In this method, by applying intense strain to the sample in several steps, the size of the grain decreases to a nanoscale, which results in the improvement of the mechanical and physical properties of the metals. One of the most important methods for this purpose is the constrained groove pressing (CGP) method. Due to the need for a small weight of space structures, sheets of aluminum alloys, aluminum7075-T6, and steel 4130 were selected. The mechanical behavior of the sheets was studied experimentally. The simulation of the interaction between the fluid and the structure was performed for a curved fin model with three different alloys and the deformation of the flying rocket was compared. The results show that the size of the aluminum7075-T6 block decreases from 60 microns to 270 nm with increasing the stages of the process, while the yield strength in the fourth pass increases compared to the annealed sample by 38%. The tensile strength increased by 34%, and the length elongation in the fourth passes reduced by 40%. The total deformation in the fin of the aluminum 7075-T6 improved to 99.9% with the CGP process. However, the amount of deformation in the steel 4130 fin compared to the CGPed aluminum7075-T6 is less than 0.1% of the total deformation.

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