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• FE modeling of surface effects in Si, Graphene–Silicon and SWCNT-Silicon nanosheet. • Numerical analysis of HACNTs on silicon substrate and its effect on frequency. • Development of analytical model to find frequency of HACNTs arrays on silicon. Silicon-based microelectromechanical system (MEMS) and nanoelectromechanical systems (NEMS) have been used to design and fabricate sensitive sensors and actuators. Recent research trends show that graphene and carbon nanotubes (CNTs) have been used to change the surface properties of silicon-based MEMS and NEMS to improve different mechanical, optical and electrical properties of silicon-based composites. In this paper, we focus on analyzing the vibrational characteristics of silicon-based devices when the surface of silicon is coated with single-layer graphene and horizontally aligned carbon nanotubes (HACNTs). To perform the analysis, we use multi-scale finite element approach for developing graphene–silicon nanocomposites (GSNCs) and carbon nanotube-silicon nanocomposites (CSNC) composites in which interface layer of silicon with graphene or CNT is modeled using bonded contact element. Subsequently, we performed modal analysis to find the first transverse mode frequency of GSNC and CSNC composites for beam with smaller as well as longer lengths. The numerical model is compared with classical beam theory with and without surface effect. For GSNCs composites, we take a fixed-free case with lengths in the range of (20 Å–120 Å) and (400 Å–2000 Å), respectively. For CSNC composites, CNT diameter is varied from (5 Å–30 Å) for single walled nanotube. Subsequently, we analyze the influence of HACNTs-on-silicon on its vibrational characteristics. The analysis presented in the paper demonstrate that GSNCs offer a higher bending stiffness compared to single layer graphene (SLGs) and isolated silicon nanosheet which lead to higher natural frequency. A similar trend is found in the case of HACNTs on silicon NS when the number of tubes increases. [ABSTRACT FROM AUTHOR]

The paper experimentally investigates the frictional behaviour of bolted joints with varying preload, inclined bolt head interface, and varying contact area between plates subjected to tangential loading. Experimental result shows a reduction macroslip force and energy dissipation with decrease in bolt preload. Similarly, increase in inclination of bolt bearing surface reduces macroslip force and energy dissipation. The reduction in contact area does not affect the tangential stiffness or frictional energy dissipation when contact pressure profile on plate interface is fully developed. For truncated pressure profile, the reduction in contact area reduces both the tangential stiffness and the energy dissipation. The experiments are conducted to determine the energy dissipation during pinning reveals differential pinning for lower displacements. At higher displacements, the crack initiates into the bolt shank which reduces the energy dissipation. [ABSTRACT FROM AUTHOR]

A simple and efficient methodology is proposed for computing the nonlinear stress-strain behavior and fracture strength under tensile loading of graphene-silicon nanosheet composites. A nonlinear finite-element model (FEM) is developed to obtain the stress-strain relationships, which in general are computed using the computationally expensive procedure of molecular dynamics (MD) simulations. The modelling method, based on the interconnection of continuum micro-mechanics approaches, incorporates bonded contact at the graphene-silicon interface with the graphene being modelled as the multilinear elastic and the silicon assumed as an isotropic material is fed into an atomistic progressive fracture model. Using this model, we get the nonlinear behaviour of graphene, silicon and its composites, as a nonlinear stress-strain curve with their critical stress at inflection point leading to failure. The obtained results of the stress-strain curves, the elastic modulus and the critical stresses of single layer graphene (SLG), silicon nanosheet and their composites (GSNC) with different thickness of silicon nanosheet are in good agreement with the MD results available in the literature. These results elucidate that the tensile strength and Young’s modulus of the silicon nanosheet increase enormously by putting the graphene layer on the top and bottom surface of the silicon nanosheet. This model is then employed to study the non-linear stress behaviour for the different orientations of silicon with varying thickness and their corresponding composites with graphene and the effect of various chirality of SLGs are also considered. Thus, we try to establish FEM as a reliable numerical method to obtain the mechanical behaviour of graphene-silicon nanosheet composites which for long-time has been solved using the classical approach of MD. The parametric study which is done using the developed FEM model shows that the GSNC helps to enhance the mechanical properties of silicon nanosheet, which in turn is helpful for the silicon-based semiconductor industry. This fact correlates well with the other methods, well-established in the literature. [ABSTRACT FROM AUTHOR]

In this paper, we developed two dimensional and three dimensional boundary element method (BEM) to compute hydrodynamic forces due to the oscillation of non-uniform beam (NUB) in a quiescent incompressible fluid with linear and quartic varying widths. To model the fluid flow under small amplitude oscillation of thin NUB in its first mode, the linearized unsteady Stokes equation is solved using BEM. After finding the converged structural and fluid nodes in all the cases, we compute real and imaginary components of hydrodynamic function. Subsequently, damping ratio or quality factor is found from energy dissipation due to drag forces mainly because of stress jumps across the thin beam thickness. Similarly, the frequency shift is found due to virtual added mass obtained from the mean hydrodynamic thrust force. The results are validated with existing literature and further analysis is done in terms of tapering parameter and index of non-uniform beam, and the corresponding aspect ratio and frequency parameters. Based on the analysis presented, it is found that quartic converging beam provides better quality factor and least added mass effect and it can be explored to design a cantilever based resonator operating in fluid with improved performance such as AFM probes. Thus, the new model developed for non-uniform beam can be useful to drag forces in other types of 2D and 3D beams. [Display omitted] • Development of 3D-Boundary Element Method for the non-uniform beams • Hydrodynamic forces in linear and quartic non-uniform flexible beams. • Comparison between 3D BEM and 3D FEM using ANSYS. • Reduction in drag for non-uniform beam with quartic varying width. [ABSTRACT FROM AUTHOR]

The perfect alignment of holes cannot be guaranteed while assembling the parts using the bolted joint. The misalignment of plates affects the contact pressure distribution at the bolted plate interface. In addition, the varying contact area at the bolted joint interface affects both the friction and the contact pressure distribution. The variation in the contact pressure and friction at the interface affects the dynamic behavior of the bolted structure. Accuracy of frictional energy dissipation is a prerequisite in predicting the dynamics of the bolted structure. Driven by this demand, we have developed an analytical model to predict the effect of hole misalignment and varying plate interface area on the frictional energy dissipated by the bolted structure. For misaligned bolted plates, we observed an asymmetric hysteresis loop with different maximum and minimum force magnitude. In addition, the bending of the bolt shank for misaligned holes is also observed. The contact area between plates does not affect the energy dissipation when contact pressure drops to zero at the plate interface. However, when the contact pressure does not drop to zero, the contact area between plates affects the energy dissipation and the tangential stiffness of the bolted joint. All these phenomena are modeled using the Iwan-based analytical models developed using the pressure profile obtained from the FEM simulation result. The developed analytical model is validated using the hysteresis loop obtained from FEM simulation results. It is observed that the developed analytical model can predict all the phenomena discussed above and can capture the hysteresis loop with reasonable accuracy for all the cases considered. [Display omitted] • Analytical models to predict plate misalignment and varying contact area effects on a bolted joint is developed. • The bending in the bolt shank is observed for misaligned bolted joint. • The misalignment of the plate results in an asymmetric hysteresis loop. • When the contact pressure at the bolted joint interface does not drop to zero, the energy dissipation and tangential stiffness reduces. [ABSTRACT FROM AUTHOR]

Abstract: Recently it was reported that 3μg/ml of recombinant YopJ induced apoptosis in murine peritoneal macrophages in vitro. However, in this study, we report the activation of murine peritoneal macrophages in vitro on treatment with sub-apoptotic dose of recombinant YopJ protein (1μg/ml). The activation involves enhanced production of nitric oxide (NO), tumor necrosis factor-α (TNF-α), IL-12, and IL-6. Production of NO and IL-6 was found to peak at 24h of rYopJ treatment, whereas IL-12 and IFN-γ production peaked at 18h of rYopJ treatment. Increased mRNAs expression of nitric oxide, IL-12, IL-6 and IFN-γ molecules, was also observed in rYopJ-treated macrophages by RT-PCR. rYopJ induced the enhanced activity of protein tyrosine kinases which was inhibited by pharmacological inhibitor genestein, wortmanin and H-7 suggesting the role of tyrosine kinases, PI3K and PKC in the above process. rYopJ also induced increased enhanced production chemokines MIP-1α, MCP-1, and RANTES in macrophages. Significantly, increased expression of TLR-2, TLR-6, MyD 88 and IRAK-1 was also observed by immunoblotting in rYopJ-treated macrophages. rYopJ induced production of NO, TNF-α and IL-6 was significantly inhibited in macrophages pretreated with pharmacological inhibitor wortmanin, genestein and H-7 demonstrating the probable involvement of protein tyrosine kinases in the above process. [Copyright &y& Elsevier]

Abstract: Bacterial species evolved evasive maneuvers to bypass their recognition by the receptors primarily TLRs of the innate immune cells. We have reported that 3μg/ml of recombinant YopJ when provided extracellularly induced apoptosis in murine peritoneal macrophages in vitro. The present investigations demonstrate the role of TLR2 in apoptotic signals induced by rYopJ protein in murine peritoneal macrophages. The role of TLR2 in rYopJ induced macrophage apoptosis was shown by neutralization experiments and its co-immunoprecipitation with downstream molecule MyD88. The observed functional consequence of TLR2 neutralization were the inhibition of caspase-8 and caspase-3 activation, change in mitochondrial membrane potential (Δψm) and DNA fragmentation induced by rYopJ in macrophages. Further, rYopJ induced enhanced expression of IRAK-4, FADD, phosphorylation of IκB and p38 MAP kinase in macrophages. Pharmacological inhibitor of p38 MAP kinase and neutralization of TLR2 with neutralizing antibodies significantly inhibited the rYopJ induced caspases activation and DNA fragmentation, suggesting the possible involvement of TLR2 and p38 MAP kinase in rYopJ induced macrophages apoptosis. [ABSTRACT FROM AUTHOR]

Abstract: The squeeze-film damping in perforated structures is modelled using a modified Reynolds equation that includes compressibility and rarefaction effect. This equation is linearized and transformed to the standard two-dimensional diffusion equation using a simple mapping function. The analytical solution is then obtained using Green’s function. The solution thus obtained adds an additional term to the damping and spring force expressions derived by Blech for compressible squeeze flow through non-perforated plates. This additional term contains several parameters related to perforations and rarefaction. Setting , one recovers Blech’s formulae. We compute the squeeze film forces using these new formulae and compare the computed forces with the solution of 3D Navier–Stokes equation solved using ANSYS for different perforation ratios (ratio of hole to cell dimensions). The results match very well. The approximate limit of maximum frequencies under which the formulae give reasonable results is also discussed. Although the main result is derived for a rigid plate under transverse motion, we discuss the effect of flexibility of the structure by deriving results for a flexible plate under a specified set of boundary conditions and comparing the results with that of a suitably modified rigid plate result. For small amplitude motion, the results show that a suitably modified rigid plate model can capture the effect of flexibility through a simple scaling factor. [Copyright &y& Elsevier]

Clearance between bolt and hole in the bolted joint allows the slipping of jointed beams when subjected to vibratory/shock loading. When this jointed beam slips the distance equal to the clearance of bolted joints, the pinning initiates. The pinning phenomena result in the compression and restitution phase in the bolted joint, which results in energy dissipation. This work proposes an improved Winkler elastic foundation based model referred as edge effect model to obtain the pinning force. The proposed model considers the stress concentration at edges during the pinning and is found to give satisfactory results in both conforming as well as non-conforming contact cases. Moreover, the hysteresis loop due to compression and restitution is also obtained using instantaneous contact stiffness based on pinning force obtained from the edge effect model. Finally, the proposed hysteresis loop during pinning is integrated into the Iwan model to have a better understanding of the response of the bolted joint subjected to vibratory/shock loading. • Eight parameter Iwan model is described to capture pinning. • Hertzian model based on cylindrical contact is compared with spherical contact for pinning. • New Winkler model under conforming and nonconforming contact with end effects is developed. • Energy dissipation in pinning due to impact incorporated in Winkler model. • New pinning model is incorporated in six parameter Iwan model. [ABSTRACT FROM AUTHOR]

The paper deals with the effect of different parameters on the frictional energy dissipated by 3D-printed bolted joints of different configurations. A test rig is developed using the accelerometers and shaker to perform this task. The shaker provides the force that induces a relative displacement between plates. The induced relative displacement is measured using the accelerometer. The bolted plate samples are 3D printed with polylactic acid (PLA) fibre using fused deposition modelling (FDM) and joined together using a metal bolt. The four different configurations of bolted joints are developed. A single bolt flat contact, a double bolt flat contact (90°orientation), a single bolt slanted contact (1°angle on both surfaces), and a single bolt flat and curved contact. The effect of bolt preload, excitation frequency, and excitation amplitude on the experimental frictional energy dissipation of the bolted joint is studied. The energy dissipation increases with the increase in excitation amplitude and the bolt preload. However, with increasing excitation frequency, the energy dissipation decreases. The type of contact between bolted plates also seems to affect the frictional energy dissipation. [ABSTRACT FROM AUTHOR]

Highlights • FEM based model with and without van der Waals interaction is developed and validated for SWCNTs and DWCNTs. • FEM modeling of VACNTs with and without van der Waals forces are presented. • Influence of arrays size of VACNTs on elastic modulus is studied. • Influence of arrays size, intertube spacing and tube diameter on buckling strength of VACNTs is studied. Graphical abstract Image, graphical abstract Abstract Vertically aligned carbon nanotubes (VACNTs) have been explored widely in various applications due to their unique anisotropic properties. However, its application is limited due to large aspect ratio of nanotubes which lead to buckling phenomena. In this paper, we perform a finite element analysis to predict the variation of elastic modulus and critical buckling load of VACNTs. While elastic modulus is obtained from the slope of stress–strain variation of tubes when one end is fixed and another end is subjected to longitudinal loading, critical buckling load is found using eigenvalue analysis corresponding to first buckling mode. We also perform study to show size dependence of elastic modulus and buckling load of single walled carbon nanotubes (SWCNTs) using FEM approach and compare the results with MD results found in the literature. After validating FEM approach with available results of single-walled and double-walled carbon nanotubes, we apply the same method to arrays of VACNTs. It is found that elastic modulus of VACNTs increases from 1.18 TPa to 2.02 TPa when the size increases from 4 to 36 tubes and then it becomes nearly size independent. The variations of critical buckling load versus other parameters such as tube diameter, intertube spacing, etc., are also obtained. It is found that with the increase in diameter, there is a steep rise in the buckling load for the case of VACNTs arrays. In order to show the influence of non-linear van der Waals force in VACNTs, we compare the above results with and without the presence of van der Waals force and discuss its significance. The modelling and analysis presented in the paper can be used to optimise the number density of VACNTs for different applications. [ABSTRACT FROM AUTHOR]

Nonlocal and surface effects become important for nanoscale devices. To model these effects on frequency response of linear and nonlinear nanobeam subjected to electrostatic excitation, we use Eringen’s nonlocal elastic theory and surface elastic theory proposed by Gurtin and Murdoch to modify the governing equation. Subsequently, we apply Galerkin’s method with exact mode shape including nonlocal and surface effects to get static and dynamic modal equations. After validating the procedure with the available results, we analyze the variation of pull-in voltage and frequency resonance by varying surface and nonlocal parameters. To do frequency analysis of nonlinear system, we solve nonlinear dynamic equation using the method of multiple scale. We found that the frequency response of nonlinear system reduces for fixed excitation as the surface and nonlocal effects increase. Also, we found that the nature of nonlinearity can be tuned from hardening to softening by increasing the nonlocal effects. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Site-selective nitration of 7-azaindoles. • Use of inexpensive organic nitrating agent (t BuNO 2) • Gram-scale synthesis and reductive transformation of nitro group. • Mechanistic investigation for catalytic cycle. Abstract The site-selective C–H nitration reaction of 7-azaindoles with t -butyl nitrite under palladium catalysis is described. This protocol provides an efficient method for the construction of ortho -nitrated N -aryl-7-azaindoles with excellent site-selectivity and functional group compatibility. The formed 7-azaindole derivatives can be readily transformed into 7-azaindoles containing an aniline functional group under palladium-catalyzed hydrogenation conditions. [ABSTRACT FROM AUTHOR]

Uniform cantilever microbeam has been at the helm of affair since the advent of micromechanical system (MEMS) technology to develop sensitive MEMS based sensors and actuators. Since then, several improved designs were incorporated to improve their sensitivity and bandwidth. In the work described in this paper, we focus on improving the frequency bandwidth by utilizing unique characteristics of non-uniform beams. To do the study, we first fabricated single non-uniform diverging and converging beams and characterize them to find their resonance frequency variation with respect to uniform beams under ambient and vacuum conditions. Subsequently, we took two mechanically coupled beams with different combinations of uniform and non-uniform beams. We measured their first in-phase and out-of-phase modes. We found that a combination of diverging and converging beam can tune the difference between these frequencies from 278 Hz to 8.8 kHz with respect to the frequency difference of 316 Hz for a combination of two uniform beams. A frequency tuning of about 2685% signifies the importance of non-uniform beams. After showing the coupling effect of arrays of mechanically coupled three, four and five uniform beams, we numerically demonstrated the tuning for a specific combination of uniform beam, diverging beam and converging beam in five beams array. The obtained results can be applied to increase the frequency band of various MEMS resonators based on the combinations of uniform and non-uniform coupled beams. [ABSTRACT FROM AUTHOR]