In eukaryotic cells, organelles and the cytoskeleton undergo highly dynamic yet organized interactions capable of orchestrating complex cellular functions. Visualizing these interactions requires ...noninvasive, long-duration imaging of the intracellular environment at high spatiotemporal resolution and low background. To achieve these normally opposing goals, we developed grazing incidence structured illumination microscopy (GI-SIM) that is capable of imaging dynamic events near the basal cell cortex at 97-nm resolution and 266 frames/s over thousands of time points. We employed multi-color GI-SIM to characterize the fast dynamic interactions of diverse organelles and the cytoskeleton, shedding new light on the complex behaviors of these structures. Precise measurements of microtubule growth or shrinkage events helped distinguish among models of microtubule dynamic instability. Analysis of endoplasmic reticulum (ER) interactions with other organelles or microtubules uncovered new ER remodeling mechanisms, such as hitchhiking of the ER on motile organelles. Finally, ER-mitochondria contact sites were found to promote both mitochondrial fission and fusion.
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•Super-resolution live-cell imaging up to 266 fps at 97-nm resolution•Hitchhiking interactions among organelles remodel ER and mitochondrial networks•ER-mitochondrion contacts promote coalescence of mitochondrial membranes•Collision of late endosomes or lysosomes carried along microtubules split ER tubules
A new approach for visualizing dynamic processes within cells offers insight into membrane-membrane contact interactions and microtubule function.
Over the last few years, some novel researches in the field of medical science made a tendency to have a therapy without any complications or side-effects of the disease with the aid of prognosis ...about the behaviors of the substructure living biological cell. Regarding this issue, nonlinear frequency characteristics of substructure living biological cell in axons with attention to different size effect parameters based on generalized differential quadrature method is presented. Supporting the effects of surrounding cytoplasm and MAP Tau proteins are considered as nonlinear elastic foundation. The Substructure living biological cell are modeled as a moderately thick curved cylindrical nanoshell. The displacement- strain of nonlinearity via Von Karman nonlinear shell theory is obtained. Extended Hamilton's principle is used for obtaining nonlinear equations of the living biological cells and finally, GDQM and PA are presented to obtain large amplitude and nonlinear frequency information of the substructure living biological cell. Based on presented numerical results, increasing the nonlinear MAP tau protein parameter causes to improve the hardening behavior and increase the maximum amplitudes of resonant vibration of the microtubule. The crucial consequence is when the fixed boundary conditions in the microstructure switch to cantilevered, the living part of the cells could manage to have irrational feedback at the broad field of the excitation frequency. The current study has been made into the influences of the NSG parameters, geometrical and physical parameters on the instability of the curved microtubule employing continuum mechanics model.
Communicated by Ramaswamy H. Sarma
This paper investigates the dynamic instability of a functionally graded porous arch reinforced with uniformly distributed graphene platelets (GPLs) under the combined action of a static force and a ...dynamic uniform pressure in the radial direction. The relationship between the elastic modulus and mass density of the material is determined by the closed-cell cellular solids under Gaussian Random Field scheme. The governing equation is derived based on classical Euler-Bernoulli theory. Galerkin approach is used to derive the Mathieu-Hill equation from which the dynamic unstable region is obtained using Bolotin method. A comprehensive parametric study is conducted to examine the effects of GPL weight fraction and dimensions, porosity distribution, pore size, static force, and arch geometry and size on the dynamic stability characteristics of the arch. Numerical results show that the porous arch's resistance against dynamic instability can be considerably improved by using symmetrically non-uniform porosity distribution and the addition of a small amount of GPLs.
•Dynamic stability of arch is greatly influenced by porosity distribution and graphene platelets.•An arch with symmetric porosity distribution has the best resistance against dynamic instability.•Addition of graphene platelets effectively improves arch's dynamic stability characteristics.•Dynamic stability of the arch is very sensitive to its geometry and size.
This paper studies the dynamic instability of functionally graded multilayer nanocomposite beams reinforced with a low content of graphene nanoplatelets (GPLs) and subjected to a combined action of a ...periodic axial force and a temperature change. The weight fraction of GPL nanofillers is assumed to be constant in each individual GPL-reinforced composite (GPLRC) layer but follows a layerwise variation across the beam thickness. The Halpin-Tsai micromechanics model is used to estimate the effective Young’s modulus of GPLRC layers. The differential quadrature method is employed to convert the partial differential governing equations into a linear system of Mathieu-Hill equations, from which the principle unstable region of functionally graded multilayer GPLRC beams is determined by Bolotin’s method. Special attention is given to the effects of GPL distribution pattern, weight fraction, geometry and dimension on the dynamic instability behaviour. The thermal buckling and free vibration are also discussed as subset problems. Numerical results show that distributing more GPLs near the top and bottom surfaces can effectively increase the natural frequency and reduce the size of the unstable region. The influences of GPL geometry and dimension tend to be insignificant when the GPL width-to-thickness ratio is larger than 103.
Nowadays, sandwich plates with cellular core structures are gaining the attention of researchers owing to their outstanding features. For a better insight into auxetic structures, in this study, we ...propose an excellent computational approach based on polygonal meshes to comprehensively examine the free vibration, buckling and dynamic instability behaviors of the auxetic honeycomb sandwich plate structures. A generalized C0-type higher-order shear deformation theory (C0-HSDT) in conjunction with both Laplace and quadratic serendipity shape functions is employed to approximate the strain fields for polygonal plate elements. The sandwich plate structures are constituted by an auxetic honeycomb core layer with negative Poisson’s ratio and two skin layers reinforced by graphene nanoplatelets (GNPs). Ultra-light features of the plate structures can be obtained by using the auxetic honeycomb cells with negative Poisson’s ratio while the GNPs are embedded into skin layers to enhance the structural stiffness. In order to determine the dynamic instability region of the sandwich plate, Bolotin’s approach is utilized in the current research. Several numerical examples are carried out to investigate the influences of geometrical parameters of auxetic cell and GNPs reinforcement on the structural behaviors. The results obtained in the current research can be considered as benchmark ones to investigate auxetic sandwich plate structures.
Dynamic instability of viscoelastic porous functionally graded (FG) nanobeam embedded on visco-Pasternak medium subjected to an axially oscillating loading as well as magnetic field is presented in ...this research. Porosity-dependent material properties of the porous nanobeam are described via a modified power-law function. Viscoelasticity of the nanostructure is considered based on the Kelvin–Voigt model. Employing Eringen's differential law in conjunction with Timoshenko beam theory (TBT), the motion equations are derived via Hamilton's variational principle. Navier's solution as well as Bolotin's approach are utilized to obtain the dynamic instability region of viscoelastic porous FG nanobeam. Some benchmark results related to the effects of structural damping, length to thickness ratio, foundation type, nonlocal parameter (NP), static load factor, power-law index, porosity volume index and magnetic field on the instability region of porous FG nanobeam are evaluated. The results reveal that with increasing power-law index and structural damping, the pulsation frequency decreases and so, instability region shifts to left side while as magnetic field magnifies, the dynamic instability moves to right side. Also, it is represented that the porosity effect on the dynamic stability of FG nanobeam depends significantly on the values of power-low index and magnetic field.
•Dynamic instability of temperature-dependent FG nanobeam subjected to an axially oscillating loading as well as magnetic field in thermal environment is explored.•The governing equilibrium equations ...are obtained according to the nonlocal strain gradient theory (NSGT) in conjunction with Timoshenko beam theory (TBT).•Navier in conjunction with bolotin methods are applied for obtaining dynamic instability region (DIR) of the FG nanobeam.•The influences of various noticeable factors such as temperature variation, length to thickness ratio, nonlocal parameter (NP), static load factor, length scale parameter (LSP), power-law index as well as magnetic field on the dynamic instability behavior of FG nanobeam are carefully examined.
Dynamic instability of temperature-dependent TIMOSHENKO functionally graded (TFG) nanobeam exposed to an axial excitation load and magnetic field in thermal environment is carried out in the present work. The power-law model is utilized to represent the material variations across the nanobeam thickness. In accordance with nonlocal strain gradient theory (NSGT), the equations of motion are derived through Hamilton's principle. Navier and Bolotin's approaches are here employed in order to specify the dynamic instability region of the FG nanoscale beam. The effects of different factors like length to thickness ratio, temperature variation, nonlocal parameter (NP), power-law index, static load factor, magnetic field as well as length scale parameter (LSP) on the dynamic instability boundary are scrutinized through some parametric studies. Based on the outcomes, with increasing temperature change, power-law index and NP, the instability region will be happened at lower pulsation frequencies whereas LSP and magnetic field effects are on the contrary. The obtained results can be useful as reference solutions for future dynamic stability analysis of FG nanobeams reinforced nanocomposites under thermal and magnetic effects.
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•Analytical descriptions are provided for damping axial and buckling waves in elastic bars.•We address concerns about the reliability of MD simulations using ultra-high strain rates.•We offer a ...criterion for distinguishing quasistatic and dynamic loading in MD simulations.•It is found that increasing impact velocity does not always lead to a larger impact force.
Elastic bars serve as primary mechanical members, spanning from atomic to macroscopic scales. The development of theoretical frameworks for elastic bars is crucial for guiding a wide array of industrial and everyday applications. In this study, we comprehensively investigate wave propagation in elastic bars subjected to tension and compression under constant velocity loading conditions. First, axial waves were studied by analytically solving the axial wave equation with damping. Subsequently, we employed this theoretical framework in atomistic simulations to measure loading-rate effects and thus determine the conditions for distinguishing quasi-static and dynamic loading. Given the coupled compressive axial waves, deflection waves were analyzed to predict dynamic instability. Our findings revealed that a continuous increase in impact velocity may not necessarily result in a larger impact force. This study offers fresh insights into the mechanical theory on the dynamic behaviour of bars across diverse scales (atomic to macroscopic). These insights are invaluable for determining suitable loadings in atomistic simulations, and provide guidelines for engineering impact applications.
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Dynamic instability behavior of functionally graded carbon nanotube reinforced hybrid composite plates subjected to periodic loadings is studied. The governing equations of motion of Mathieu-type are ...established by using the Galerkin method with reduced eigenfunctions transforms. With the Mathieu equations, the dynamic instability regions of hybrid nanocomposite plates are determined by using the Bolotin’s method. Results reveal that the dynamic instability is significantly affected by the carbon nanotube volume fraction, layer thickness ratio, bending stress, static and dynamic load parameters. The effects of important parameters on the instability region and dynamic instability index of hybrid nanocomposite plates are discussed.
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