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The present study develops a new topology optimization scheme considering the dynamic instability caused by the unsymmetrical properties of system. From a mathematical point of view, the left and right eigenvectors of asymmetric system are observed with the complex eigenvalues. With the dynamic instability, the magnitudes of structural responses are increasing with respect to time and this phenomenon causes many engineering issues. As the dynamic instability is one of the serious problems, the suppression is desired from an engineering point of view. To systematically reduce this dynamic instability, the present study develops a new topology optimization scheme for the reinforcement design. To overcome the numerical difficulties of the mode conversion and the highly nonlinear behavior, this research proposes the summation of the first several complex eigenvalues. To show the issues of the dynamic instability and the validity of the present approach, several topological reinforcement problems are solved. [ABSTRACT FROM AUTHOR]

Due to the fluidity of the loose medium inside the waste dump slope, the traditional monitoring system cannot fully reflect the misalignment and slip between particles inside the medium, and it is also difficult to capture the precursor information of the slip of the loose accumulation body. To reveal the dynamic evolution process of the slope instability of the waste dump slope, the coupling test system of the slope instability of the waste dump slope was used to carry out the study of the acoustic emission characteristics of the slope instability dynamic response of the dump slope under the action of vibration, and to quantitatively analyse the staged characteristics of the acoustic emission parameter evolution of the dump slope under the action of different vibration frequencies and its instability initiation node. The results show that with the increase of vibration frequency, the damage mode of the slope model gradually changes from sliding of small particles to large-scale landslides, and presents the stage process of "vibration compaction → vibration equilibrium → dynamic instability"; Under the action of low-frequency and high-amplitude, the slope model mainly shows that the tiny particles and the basement gravel slip, which is difficult to capture with the naked eye, while under the action of high-frequency and low-amplitude, the slope surface is damaged in a large area, and the overall model is unstable; The dynamic instability of the waste dump slope is accompanied by obvious acoustic emission activities, and the changes of the characteristic parameters of acoustic emission reveal, to a certain extent, the evolution of the internal state of the slope in the process of dynamic instability of the waste dump slope and its stage characteristics; The amplitude and energy efficiency of acoustic emission in the time domain show obvious fractal characteristics in the dynamic instability of the waste dump slope. When the waste dump slope is close to destruction, the correlation dimensions and NE values of the acoustic emission parameters change significantly, which can be regarded as a precursor to the dynamic instability and failure of the waste dump slope. The research results provide new theoretical and methodological support for the monitoring and prediction of the dynamic instability of the waste dump slope, which is of great significance for improving the safety of the waste dump slope. [ABSTRACT FROM AUTHOR]

During cross‐fault mining, the stress concentration in the surrounding rock of thick coal seam gob‐side entry was prone to dynamic disasters. Based on the in‐site geological conditions of the No. 6305 coal face of the Xinjulong coal mine, a FLAC3D numerical simulation model was established to research the failure and stress staged evolution of coal pillar in the gob‐side entry during cross‐fault mining. By analyzing the relation of surrounding rock structure, the mechanical models of different stages during cross‐fault mining were established. Furthermore, the mechanical mechanism of coal pillars' dynamic instability under the influence of fault activation was revealed, and the mechanical criterion n was given. The control technology of 'asymmetric strengthening support + roof cutting and pressure relief' was proposed and designed. Field practice showed that the maximum roof‐to‐floor and two‐side displacements of the gob‐side entry are 249.3 mm and 150.4 mm, and the force of anchor cable is 184.2 kN. This research provided theoretical guidance and reference for the stability control of roadways within the influence range of fault under deep mining conditions. [ABSTRACT FROM AUTHOR]

A nonlinear finite element dynamic instability analysis of laminated composite stiffened plates subjected to in-plane harmonic edge loading is presented in this article along with the linear and nonlinear dynamic response study. The eight-noded isoparametric degenerated shell element and a compatible three-noded curved beam element are used to model the stiffened plates. Bolotin method is applied to analyze the dynamic instability regions in linear case. Incremental Harmonic Balance (IHB) method is applied to solve the nonlinear frequency response equations and Newmark-β method is used to solve the linear and nonlinear time history response equations. [ABSTRACT FROM AUTHOR]

ABSTRACT During cross‐fault mining, the stress concentration in the surrounding rock of thick coal seam gob‐side entry was prone to dynamic disasters. Based on the in‐site geological conditions of the No. 6305 coal face of the Xinjulong coal mine, a FLAC3D numerical simulation model was established to research the failure and stress staged evolution of coal pillar in the gob‐side entry during cross‐fault mining. By analyzing the relation of surrounding rock structure, the mechanical models of different stages during cross‐fault mining were established. Furthermore, the mechanical mechanism of coal pillars' dynamic instability under the influence of fault activation was revealed, and the mechanical criterion n was given. The control technology of ‘asymmetric strengthening support + roof cutting and pressure relief’ was proposed and designed. Field practice showed that the maximum roof‐to‐floor and two‐side displacements of the gob‐side entry are 249.3 mm and 150.4 mm, and the force of anchor cable is 184.2 kN. This research provided theoretical guidance and reference for the stability control of roadways within the influence range of fault under deep mining conditions.

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Purpose: This research paper explores the dynamic instability behaviour of laminated curved shell composite structures under in-plane loading conditions. Methods: Two higher-order theories (nine and ten degrees of freedom at each node) are adopted to develop the composite mathematical model considering the in-plane loading conditions to compute the parametric instability based on the finite element (FE) discretization technique. The system's differential equations of motion are converted into a set of ordinary differential equations and addressed as an ordinary eigenvalue solution utilizing the Bolotin approach. Results: The precision and adaptability of the current model are confirmed by comparing the current outcomes with the existing solutions. The influence of numerous constraints of the laminated curved shell composite structure is investigated, such as different structural forms, thickness and aspect ratio, diversity in end condition, and static and dynamic load factors. Additionally, the compared outcomes (excitation frequency) between two different models (Model I and Model II) are varying from 0.93 to 34% under the static load factors (low to high range). Conclusion: The outcomes of the developed numerical models are carefully examined, compared and discussed. Model II responses are showing a higher side excitation frequency when compared to Model I due to the presence of stretching term in displacement kinematics. The excitation frequency increases due to a decrease in static load factor and an increase in curvature and aspect ratio. [ABSTRACT FROM AUTHOR]

In this article, the nonlinear dynamic instability of stiffened laminated composite plates is studied in the finite element (FE) framework subjected to uniform in-plane harmonic patch loading. The harmonic load is applied to the two opposite sides of the stiffened plate. The linear and nonlinear time-history response analysis is also studied. The skin and the stiffener are modeled using an eight-node isoparametric degenerated shell element and a three-node curved beam element, respectively. A system of matrices is developed by considering the Green–Langrange strain–displacement relationship. In the linear case, the Bolotin method is used to analyze the dynamic instability region (DIR). The nonlinear instability behavior of the laminated composite stiffened plate is studied by applying the Incremental Harmonic Balance Method (IHB). The Newmark-β method is used to solve the linear and nonlinear time-history response equations to understand the instability behavior of the stiffened plates. The effect of the parameters such as the length of the in-plane loading patch, varying number of stiffeners in x -direction and the position of the patch on the nonlinear vibrations and nonlinear dynamic response is examined. [ABSTRACT FROM AUTHOR]

The gas–phase flow field within a cyclone plays a critical role in the particle separation process. While previous research has primarily focused on the steady–state, time–averaged characteristics of this flow field, there has been limited investigation into its dynamic instability. This study seeks to address this gap by examining the dynamic instability of gas swirling flows in cyclones, offering new insights into their spatial and temporal dimensions. Numerical simulations were performed via large eddy simulation (LES) for the gas swirling flow in a reverse cyclone and tangential velocity was measured with a hot–wire anemometer (HWA). The model's accuracy was validated against experimental data. The results demonstrate that the distributions of instantaneous tangential velocity and pressure exhibit spatial asymmetry and temporal instability across different sections of the cyclone. The dynamic instability of the gas swirling flow in the cyclone is the superposition of the spatial asymmetry and the temporal instability. These instabilities are more pronounced in the internal regions than the outer regions. Dynamic instability arises from the combined effects of rotational dynamics and wall curvature, leading to an eccentric rotation of the swirling center, particularly evident in the lower sections of the cyclone cone. This instability increases fluctuations in the instantaneous parameters, enhancing turbulence intensity and fine particle diffusion, and ultimately impairing both separation efficiency and particle size efficiency. [ABSTRACT FROM AUTHOR]

Featured Application: The first-order asymptotic method (FOAM) is used to analyze the dynamic instability in the area of principal parametric resonance (APPR) for the automotive driveshaft's (AD) forced torsional vibration (ADFTV). This paper aims to investigate using FOAM to analyze the dynamic instability in the APPR for ADFTV based on a dynamic model (DMADFTV). The DMADFTV considers the following aspects: AD kinematic nonuniformity (ADKN), AD geometric nonuniformity (ADGN) of inertial characteristics for the spinning movements (ICSM) of the AD elements (ADE), and the excitations induced by the gearbox–internal combustion engine modulations. The DMADFTV is considered the already-designed dynamic model developed by the first author of the ADFTV in a previous publication. This DMADFTV was used to compute the stationary frontiers of instability and the nonstationary spectral velocity amplitude (NSVA) versus nonstationary spectral amplitude (NSA) in the configuration space in transition through APPR, using the FOAM. The use of FOAM is much more versatile, from the analytical point of view, than the method of multiple scales and allows the computation of the NSA and the NSVA in the APPR. In contrast, these computations cannot be performed using the harmonic balance method. MATLAB Software R 2017 was developed based on DMADFTV and used the FOAM to compute the stationary frontiers of instability and the NSVA versus the NSA in transition through APPR for the ADFTV. The numerical results were compared with the experimental and numerical data published in the literature, finding agreements. The computation of the NSVA versus NSA in the configuration space using FOAM represents a method of detection of the chaotic manifestation of ADFTV. [ABSTRACT FROM AUTHOR]

The libration motion of conductive tether in the electrodynamic tether system has been demonstrated to be inherently unstable. However, the relationship between the instability of libration motion and the tether current, orbital inclination and attitude of libration motion has not been thoroughly investigated. The novelty of this paper lies in the determination of the critical ranges of attitude and ε that lead to rapid tumbling of libration motion, and the study of how the instability of libration motion varies with attitude and ε , where ε accounts for the effects of tether current and orbital inclination. Some numerical simulations were conducted to demonstrate that, as attitude and ε increase, the instability of libration motion gradually becomes more pronounced, especially when the attitude angle or ε exceeds the respective critical range, in which case the libration will become unstable even with implementation of control strategy. The critical range of tether current, which leads to rapid tumbling of the libration motion, can be determined based on the range of ε , and this range of current can serve as a basis for designing the current regulation range, thereby preventing rapid tumbling that may result from improperly designed or regulated current values. The critical range of attitude angle can be utilized to monitor attitude motion and to avoid quick tumbling caused by excessive attitude angle. [ABSTRACT FROM AUTHOR]

Observations of coherent scatter from patchy sporadic E layers in the subauroral zone made with a 30‐MHz coherent scatter radar imager are presented. The quasiperiodic (QP) echoes are similar to what has been observed at middle latitudes but with some differences. The echoes arise from bands of scatterers aligned mainly northwest to southeast and propagating to the southwest. A notable difference from observations at middle latitudes is the appearance of secondary irregularities or braids oriented obliquely to the primary bands and propagating mainly northward along them. We present a spectral simulation of the patchy layers that describes neutral atmospheric dynamics with the incompressible Navier Stokes equations and plasma dynamics with an extended MHD model. The simulation is initialized with turning shears in the form of an Ekman spiral. Ekman‐type instability deforms the sporadic E layer through compressible and incompressible motion. The layer ultimately exhibits both the QP bands and the braids, consequences mainly of primary and secondary neutral dynamic instability. Vorticity due to dynamic instability is an important source of structuring in the sporadic E layer. Key Points: Radar observations and theory of subauroral sporadic E layer irregularities are presentedCoherent scatter from the layers presents as primary bands of irreguarities with secondary, oblique, braided structureSimulations of neutral dynamic instability associated with turning shears in Es layers consistent with observations [ABSTRACT FROM AUTHOR]

In this study, the instability and bifurcation diagrams of a functionally graded (FG) porous sandwich beam on an elastic, viscous foundation which is influenced by an axial load, are investigated with an analytical attitude. To do so, the Timoshenko beam theory is utilized to take the shear deformations into account, and the nonlinear Von-Karman approach is adopted to acquire the equations of motion. Then, to turn the partial differential equations (PDEs) into ordinary differential equations (ODEs) in the case of equations of motion, the method of Galerkin is employed, followed by the multiple time scale method to solve the resulting equations. The impact of parameters affecting the response of the beam, including the porosity distribution, porosity coefficient, temperature increments, slenderness, thickness, and damping ratios, are explicitly discussed. It is found that the parameters mentioned above affect the bifurcation points and instability of the sandwich porous beams, some of which, including the effect of temperature and porosity distribution, are less noticeable. [ABSTRACT FROM AUTHOR]

Ring-shaped structures are widely used in engineering. However, their rotation axes are typically not coincident with the geometric axes, thus resulting in a rotational centrifugal force and significant vibration. This study focuses on the dynamic instability caused by constant and time-varying eccentricities. An analytical model is established using Hamilton's principle and the Galerkin method, in which the rotational centrifugal forces resulting from constant and time-varying eccentricities are incorporated. Based on this model, the effects of rotation, revolution, eccentricity ratio, and damping on instability behaviors are examined. The instabilities caused by constant eccentricity are predicted using eigensolutions, whereas those caused by time-varying eccentricity with single- and multifrequency components are estimated by applying the Floquét theory. The results show that the instability domains from the multifrequency eccentricity are not a simple superposition of those from the single-frequency eccentricity but contain more instability domains originating from their combinations. The instability suppressions imposed by damping and gyroscopic effects are compared. Finally, the instability domains from constant and time-varying eccentricities are verified via numerical calculations. [ABSTRACT FROM AUTHOR]

Objective: Clinical-standard MRI is the imaging modality of choice for the wrist, yet limited to static evaluation, thereby potentially missing dynamic instability patterns. We aimed to investigate the clinical benefit of (dynamic) real-time MRI, complemented by automatic analysis, in patients with complete or partial scapholunate ligament (SLL) tears. Material and methods: Both wrists of ten patients with unilateral SLL tears (six partial, four complete tears) as diagnosed by clinical-standard MRI were imaged during continuous active radioulnar motion using a 1.5-T MRI scanner in combination with a custom-made motion device. Following automatic segmentation of the wrist, the scapholunate and lunotriquetral joint widths were analyzed across the entire range of motion (ROM). Mixed-effects model analysis of variance (ANOVA) followed by Tukey's posthoc test and two-way ANOVA were used for statistical analysis. Results: With the increasing extent of SLL tear, the scapholunate joint widths in injured wrists were significantly larger over the entire ROM compared to those of the contralateral healthy wrists (p<0.001). Differences between partial and complete tears were most pronounced at 5°–15° ulnar abduction (p<0.001). Motion patterns and trajectories were altered. Complete SLL deficiency resulted in complex alterations of the lunotriquetral joint widths. Conclusion: Real-time MRI may improve the functional diagnosis of SLL insufficiency and aid therapeutic decision-making by revealing dynamic forms of dissociative instability within the proximal carpus. Static MRI best differentiates SLL-injured wrists at 5°–15° of ulnar abduction. [ABSTRACT FROM AUTHOR]

The dynamic stability/parametric stability characteristics of rotating truncated conical shells under periodic axial loads is investigated. The partial differential equations of rotating conical shells are transformed into Mathieu-Hill ordinary differential equations based on Haar wavelet discretization method. In general, Bolotin method can be used to analyze the stability of parametrically excited systems. This method is a boundary tracing method, and the stability boundary can be easily obtained. However, Bolotin method is not suitable for analyzing the stability of gyroscopic system under parametric excitation, because this method is not satisfied with the hypothesis of the Floquet multiplier for gyroscopic system. In this article, Floquet exponent method, which is widely used in parametric excitation system, is used to analyze the parametric stability of rotating conical shells. The correctness of the proposed model and stability analysis method is verified by comparing with the results of the other literature. The results show that due to the rotational effect, only the combination instability zone exists in the rotating shell, but no principal instability zone is found. When the circumferential wave number is 1 and other wave numbers are compared, it is found that the rotational speed has different effects on the stability under the two circumferential wave numbers. Communicated by Francesco Tornabene. [ABSTRACT FROM AUTHOR]

Objective: To determine sensitivity and specificity for anterior-inferior tibiofibular ligament (AiTFL) integrity and tibiofibular clearspace (TFCS) cut-off points for dynamic evaluation using ultrasound (US) in a pediatric population. Design: Prospective cohort study. Setting: Tertiary care university-affiliated pediatric hospital patients between the ages of 12 and 18 sustaining acute ankle trauma with syndesmotic injury. Interventions: Participants were assigned to the syndesmotic injury protocol that included a standardized MRI and US. Main Outcome Measures: Anterior-inferior tibiofibular ligament integrity for static assessment and TFCS measurements for dynamic assessment on US. For dynamic assessment, the distance between the distal tibia and fibula was first measured in neutral position and then in external rotation for each ankle. The US results on AiTFL integrity were compared with MRI, considered as our gold standard. Optimal cut-off points of TFCS values were determined with receiver operating characteristics curve analysis. Results: Twenty-six participants were included. Mean age was 14.8 years (SD = 1.3 years). Sensitivity and specificity for AiTFL integrity were 79% and 100%, respectively (4 false negatives on partial tears). For dynamic assessment, the cut-off points for the differences in tibiofibular distance between the 2 ankles in 1) neutral position (TFCS NI-U) and 2) external rotation (TFCS ERI-U) were 0.2 mm (sensitivity = 83% and specificity = 80%) and 0.1 mm (sensitivity 5 83% and specificity = 80%), respectively. Conclusions: Static US could be used in a triage context as a diagnostic tool for AiTFL integrity in a pediatric population as it shows good sensitivity and excellent specificity. [ABSTRACT FROM AUTHOR]

This work develops a three-dimensional (3D) weak formulation, based on the consistent couple stress theory (CCST), for analyzing the size-dependent dynamic instability behavior of simply-supported, functionally graded (FG) cylindrical microshells that are subjected to combinations of periodic axial compression and external pressure. In our formulation, the microshells are artificially divided into nl layers. The displacement components of each individual layer are selected as the primary variables, which are expanded as a double Fourier series in the in-plane domain and are interpolated with Hermitian C2 polynomials in the thickness direction. Incorporating the layer-wise displacement models into our weak formulation, we develop a Hermitian C2 finite layer method (FLM) for addressing the current issue. The accuracy and the convergence rate of our Hermitian C2 FLM are validated by comparing the solutions it produces with the accurate two-dimensional solutions of critical loads and critical pressures of FG cylindrical macroshells and single-walled carbon nanotubes, which were reported in the literature. The numerical results show the effects of the material length-scale parameter, the inhomogeneity index, the radius-to-thickness and length-to-radius ratios, the load magnitude ratio, and the static and dynamic load factors on the first principal and first secondary instability regions of parametric resonance of simply-supported FG cylindrical microshells are significant. [ABSTRACT FROM AUTHOR]

Inelastic displacement demand is an important part of the performance-based design and it should be estimated realistically to determine a reliable seismic performance of a structure. In this context, the coefficient method is an easy and practical method for this estimation. The coefficient method is a method that is used to estimate inelastic displacement demand by the multiplication of the elastic displacement demand and inelastic displacement ratio. Thus, it is clear that a reliable estimation of inelastic displacement demand depends on a reliable inelastic displacement ratio. After a reliable estimation of the inelastic displacement ratio, it is essential to propose an equation for the usage of engineering practice. Although nonlinear regression analysis is preferred in the literature as a classical method to estimate an equation, the Artificial Neural Network method is a new and modern way that can be used in the estimation of inelastic displacement ratio. In this study, Artificial Neural Network models have been proposed by using data of inelastic displacement ratios of Single Degree of Freedom systems with stiffness and strength degrading peak-oriented hysteretic model and collapse potential by performing nonlinear time history analyses. Firstly, a large number of trials have been conducted to obtain an optimum Artificial Neural Network model. The results of Artificial Neural Network models have been compared to the results of equation estimated by using nonlinear regression analysis and given in the previous studies. According to the results, Artificial Neural Network models give closer values to the inelastic displacement ratios of time history analysis than nonlinear regression analysis. Especially, the Bayesian Regularization Backpropagation model of the Artificial Neural Network method with two hidden layers achieved the best performance among the other Artificial Neural Network models. It can be said that Artificial Neural Network methods can be used to estimate inelastic displacement ratio since it yields better accuracy than previous techniques for different parameters. [ABSTRACT FROM AUTHOR]

This paper aims to investigate using FOAM to analyze the dynamic instability in the APPR for ADFTV based on a dynamic model (DMADFTV). The DMADFTV considers the following aspects: AD kinematic nonuniformity (ADKN), AD geometric nonuniformity (ADGN) of inertial characteristics for the spinning movements (ICSM) of the AD elements (ADE), and the excitations induced by the gearbox–internal combustion engine modulations. The DMADFTV is considered the already-designed dynamic model developed by the first author of the ADFTV in a previous publication. This DMADFTV was used to compute the stationary frontiers of instability and the nonstationary spectral velocity amplitude (NSVA) versus nonstationary spectral amplitude (NSA) in the configuration space in transition through APPR, using the FOAM. The use of FOAM is much more versatile, from the analytical point of view, than the method of multiple scales and allows the computation of the NSA and the NSVA in the APPR. In contrast, these computations cannot be performed using the harmonic balance method. MATLAB Software R 2017 was developed based on DMADFTV and used the FOAM to compute the stationary frontiers of instability and the NSVA versus the NSA in transition through APPR for the ADFTV. The numerical results were compared with the experimental and numerical data published in the literature, finding agreements. The computation of the NSVA versus NSA in the configuration space using FOAM represents a method of detection of the chaotic manifestation of ADFTV.

Microtubules (MTs) are polymers of αβ-tubulin heterodimers that stochastically switch between growth and shrinkage phases. This dynamic instability is critically important for MT function. It is believed that GTP hydrolysis within the MT lattice is accompanied by destabilizing conformational changes and that MT stability depends on a transiently existing GTP cap at the growing MT end. Here, we use cryo-electron microscopy and total internal reflection fluorescence microscopy of GTP hydrolysis-deficient MTs assembled from mutant recombinant human tubulin to investigate the structure of a GTP-bound MT lattice. We find that the GTP-MT lattice of two mutants in which the catalytically active glutamate in α-tubulin was substituted by inactive amino acids (E254A and E254N) is remarkably plastic. Undecorated E254A and E254N MTs with 13 protofilaments both have an expanded lattice but display opposite protofilament twists, making these lattices distinct from the compacted lattice of wild-type GDP-MTs. End-binding proteins of the EB family have the ability to compact both mutant GTP lattices and to stabilize a negative twist, suggesting that they promote this transition also in the GTP cap of wild-type MTs, thereby contributing to the maturation of the MT structure. We also find that the MT seam appears to be stabilized in mutant GTP-MTs and destabilized in GDP-MTs, supporting the proposal that the seam plays an important role in MT stability. Together, these structures of catalytically inactive MTs add mechanistic insight into the GTP state of MTs, the stability of the GTP- and GDP-bound lattice, and our overall understanding of MT dynamic instability.

This study examined the dynamic instability of a drum brake induced by the rigid modes of the brake shoe. The brake shoe was modeled as a rigid curved plate subject to frictional contact with a rotating drum. In the presence of a negatively sloped friction curve, dynamic instability was numerically analyzed with respect to variation in the system parameters. The results showed that mode-coupling instability did not occur, but dynamic instability was induced by negative damping in a specific rigid mode, and its propensity varied with the operating conditions and geometric changes. [ABSTRACT FROM AUTHOR]

The focus of this paper is to examine the static and dynamic instabilities of functionally graded beam that contains multiple inclined cracks under the influence of an axial force comprising both static and time-varying harmonic components. The elasticity modulus and mass density of the functionally graded beam are assumed to vary exponentially along its thickness direction. Local stiffness matrix model-based finite element analysis (FEA) is conducted to determine the bending stiffness and tensile stiffness of the section with a crack, and the coupled effect of tensile and bending loadings. Two-node beam elements with three degrees-of-freedom per node are utilized. By combining the Euler–Bernoulli beam theory with Lagrange method, we derive the governing equations that describe the static and dynamic instabilities of a functionally graded beam with multiple inclined cracks. These equations can be solved as eigenvalue problems to obtain the natural frequency and static critical buckling load of the beam. Furthermore, to investigate the dynamic instability of the system, we use the Bolotin method to determine the boundary between the regions of instability and stability based on the same governing equations. By adopting this approach, the study comprehensively investigates the impacts of crack position, inclination angle, and length, as well as elasticity modulus ratio, static and dynamic load factors on both static and dynamic stabilities of a cracked functionally graded beam to gain valuable insights into the stability and performance of cracked functionally graded structures. [ABSTRACT FROM AUTHOR]

During mitosis, kinetochore-attached microtubules form bundles (k-fibers) in which many filaments grow and shorten in near-perfect unison to align and segregate each chromosome. However, individual microtubules grow at intrinsically variable rates, which must be tightly regulated for a k-fiber to behave as a single unit. This exquisite coordination might be achieved biochemically, via selective binding of polymerases and depolymerases, or mechanically, because k-fiber microtubules are coupled through a shared load that influences their growth. Here, we use a novel dual laser trap assay to show that microtubule pairs growing in vitro are coordinated by mechanical coupling. Kinetic analyses show that microtubule growth is interrupted by stochastic, force-dependent pauses and indicate persistent heterogeneity in growth speed during non-pauses. A simple model incorporating both force-dependent pausing and persistent growth speed heterogeneity explains the measured coordination of microtubule pairs without any free fit parameters. Our findings illustrate how microtubule growth may be synchronized during mitosis and provide a basis for modeling k-fiber bundles with three or more microtubules, as found in many eukaryotes.

ABSTRACTAcross the domains of life, actin homologs are integral components of many essential processes, such as DNA segregation, cell division, and cell shape determination. Archaeal genomes, like those of bacteria and eukaryotes, also encode actin homologs, but much less is known about these proteins’ in vivo dynamics and cellular functions. We identified and characterized the function and dynamics of Salactin, an actin homolog in the hypersaline archaeon Halobacterium salinarum. Live-cell time-lapse imaging revealed that Salactin forms dynamically unstable filaments that grow and shrink out of the cell poles. Like other dynamically unstable polymers, Salactin monomers are added at the growing filament end, and its ATP-bound critical concentration is substantially lower than the ADP-bound form. When H. salinarum’s chromosomal copy number becomes limiting under low-phosphate growth conditions, cells lacking Salactin show perturbed DNA distributions. Taken together, we propose that Salactin is part of a previously unknown chromosomal segregation apparatus required during low-ploidy conditions.IMPORTANCEProtein filaments play important roles in many biological processes. We discovered an actin homolog in halophilic archaea, which we call Salactin. Just like the filaments that segregate DNA in eukaryotes, Salactin grows out of the cell poles towards the middle, and then quickly depolymerizes, a behavior known as dynamic instability. Furthermore, we see that Salactin affects the distribution of DNA in daughter cells when cells are grown in low-phosphate media, suggesting Salactin filaments might be involved in segregating DNA when the cell has only a few copies of the chromosome.

The presented work examines the stability of general rotors subject to harmonic follower force. The examined rotor consists of asymmetric Timoshenko shaft carrying asymmetric rigid disk and supported by anisotropic flexible bearings. The assumed modes method is combined with Lagrange's equation to derive the governing equations of motion with the help of symbolic computation. The employed approach resulted in equations of motion with multi-frequency periodic coefficients, and Floquet's method was used to determine stability boundaries of the considered rotors. After validation of the proposed mathematical model, it was employed to examine the combined effect of rotor asymmetry, support anisotropy, and rotor speed on its stability in the presence of harmonic follower force. The presented results show that the considered general rotor exhibits both subharmonic and combination instabilities, which were completely identified and investigated. Additional higher order subharmonic and combination instabilities are observed for general rotors only. [ABSTRACT FROM AUTHOR]

In the present study, by using a higher-order shear deformation plate theory (HSDT) and considering the second model proposed by Frostig and Thomsen, Dynamic instability, static buckling, and free vibration of the Magneto-Rheological (MR) fluid sandwich plates subjected to an axial periodic force is investigated. MR fluids are a group of smart materials whose rheological properties change rapidly with the application of a magnetic field. The upper and lower layers of the core (face layers) are selected from two different types. In the first group, they are made of functionally graded materials (FGMs), and the second group, consists of a matrix phase reinforced with carbon nanotubes (CNTs). The mechanical properties of the nanocomposite are considered in accordance with the extended rule of mixtures. The governing equations are derived using Hamilton's principle and discretized by the finite strip method. The results obtained from the finite strip method are compared with the results of available literature. The impact of various parameters such as magnetic field intensity, core thickness, static and dynamic load factors, different boundary conditions, and the CNT distribution on the critical static buckling, natural frequency, and instability zone of the structure are investigated. The results show that increasing the MR fluid thickness has a stabilizing effect on the dynamic instability of the MR fluid sandwich plates. [ABSTRACT FROM AUTHOR]

Abstract We have studied the convective (or static) and dynamic instabilities between 80 and 100 km above Tromsø (69.6° N, 19.2° E) using temperature and wind data of 6 min and 1 km resolutions primarily almost over a solar cycle obtained with the sodium lidar at Tromsø. First, we have calculated Brunt–Väisälä frequency (N) for 339 nights obtained from October 2010 to December 2019, and the Richardson number (Ri) for 210 nights obtained between October 2012 to December 2019. Second, using those values (N and Ri), we have calculated probabilities of the convective instability (N 2

A finite element modeling combined with the strain gradient theory (SGT) and the refined higher-order shear deformation beam theory is developed to study the dynamic instability of magnetically embedded functionally graded porous (FGP) nanobeams. Nanobeams with elastic foundation (EF) subjected to an axially oscillating load are analyzed. Nanobeams are made of functionally graded material (FGM) with an uneven porosity distribution. A three-node beam element with 8 degrees of freedom (DOFs) for two outer nodes and 2 DOFs for the middle node, which has the C1 and C2 continuous Hermite shape functions, is used to simulate nanobeams. Besides, Bolotin’s method is employed to determine the instability region of FGP nanobeams. The accuracy of the proposed method is tested by comparing it with other published works. In addition, the influences of various parameters such as magnetic potential, small-scale parameter, porosity coefficient, stiffness foundation, boundary conditions (BCs) on the dynamic instability of nanobeams are studied in detail.

To ascertain the unexpected departure of traditional statistical seismic laws with largest labquakes on model granular materials, we enlarge the behaviour of stick-slip motions in triaxial compression under drained and quasi-static shearing conditions. We estimate the effectiveness of these extended seismic laws (Gutenberg-Richter, inter-event times, and productivity) against more widespread laboratory conditions approaching real-world cases. Regardless of the saturation (dry, water-wet, and water-saturated) of the granular assembly, the initial density (very loose to medium dense), and the effective initial confining pressure up to 500 kPa, large and repeated spontaneous stick-slip frictional failures under uncontrolled triggering stress suggest the universality of these extended empirical seismic relations on laboratory shear experiments with model granular materials. These laboratory extended seismic laws can help to understand qualitatively natural earthquakes of potentially largest magnitude. [ABSTRACT FROM AUTHOR]

Dynamic stability is an important mechanical behavior of nanobeams, which has been studied extensively using the Euler–Bernoulli and Timoshenko beam theories, while the Levinson-beam-theory-based dynamic instability analysis of nanobeams has not been investigated yet. Shear deformation is not or is not suitably considered in the Euler–Bernoulli and Timoshenko theories, so it is very important to introduce the Levinson beam theory in the dynamic stability analysis of nanobeams, which correctly models the combined action of bending and shear in nanobeams with smaller length/height ratios. In this work, the equation of the transverse vibration of a Levinson beam embedded in an elastic foundation is firstly formulated based on the displacement field of Levinson beam theory, and the nonlocal theory is further applied to the Levinson nanobeam. Then, the governing equation of the dynamic stability of the Levinson nanobeam is derived using Bolotin's method to achieve a generalized eigenvalue problem corresponding to the boundaries of regions of dynamic instability. The principal instability region (PIR) is the most important among all regions, so the boundary of the PIR is focused on in this work to investigate the dynamic stability of the Levinson nanobeam. When the width, length/height ratio, density, Young's modulus, Poisson's ratio, size scale parameter, and medium stiffness increase by about 1.5 times, the width of the PIR changes by about 19%, −57%, −20%, 65%, 0, −9%, and −11%, respectively. If a smaller critical excitation frequency and narrower width of the PIR correspond to the better performance of dynamic stability, the study shows that the dynamic stability of the Levinson nanobeam embedded in an elastic medium improves under a larger length and density and a smaller width, height, and Young's modulus, since these factors are related to the natural frequency of the nanobeam which controls the width of the PIR. Additionally, the local model would overestimate the dynamic stability behavior of the Levinson nanobeam. [ABSTRACT FROM AUTHOR]

This work presents an analytical study of the parametric instability of cylindrical panels containing functionally graded porous exposed to static and dynamic periodic axial loads under simply supported boundary conditions. Based on Hamilton’s principle, the governing equation of motion by using first-order shear deformation theory (FSDT) has been obtained. By applying the Galerkin technique, an excitation frequency expression is derived, which helps identify areas of instability of functionally graded porous cylindrical panels. Numerical simulations are used to validate the analytical results. Eventually, the impacts of the porosity coefficient, porosity distribution method, static and dynamic periodic axial loads, panel angle, circumferential wave number, and cylindrical panel characteristics on the region of instability are displayed in the section of results and discussions. The findings show that when the porosity is further from the surface, the more stable the structure is. Furthermore, a small angle of the cylindrical panels gives a better dynamic response than a large angle. In addition, increased static and dynamic loads lead to an expansion of areas of instability.

In this article, the dynamic instability of the hybrid fiber/nanocomposite-reinforced toroidal shells is investigated. By using the approximation of Fourier series and applying the Galerkin method, a semi-analytical solution is achieved. The proposed method provides an accurate assessment of the dynamic stability of the shell with no computational costs in comparison to the numerical methods. By comparing the obtained results for some examples with those available in the present literature, the accuracy of present formulation is approved. In order to evaluate the effects of geometrical and mechanical specifications on the dynamic instability of the proposed shells, a comprehensive parametric study is performed, as well. [ABSTRACT FROM AUTHOR]

This study aims to investigate the predictability of a friction-induced nonlinear dynamic behavior on a simplified yet controlled laboratory experiment through the fuzzy logic approach. First, a mass-sliding belt experiment is built to observe the effects of several operating parameters on the occurrence of nonlinear dynamic behavior. Second, experiments are performed at various levels of these operating parameter, and the data are recorded. Third, fuzzy logic model architectures with different membership functions are built, where these operating parameters are assumed as the input parameters. The output of the fuzzy logic model architecture is defined as a new parameter called squeal index. Finally, a fuzzy logic model with a 96.97% prediction accuracy is obtained. Hence, it is shown that the proposed model can provide insight about the dynamic behavior of the system of interest without solving the nonlinear governing equations. Furthermore, the proposed model allows the prediction of the system state at operating conditions where experimentation is not possible, and it can be used for the determination of the critical operating parameters at which the system behavior switches from one state to another. [ABSTRACT FROM AUTHOR]

The parametrically excited instability of the spatially periodic visco-elastomer sandwich plate with supported masses under quadrilateral longitudinal temporal harmonic excitations is studied. The improvability of the parametrically excited instability by periodic distribution parameters is explored. The direct eigenvalue analysis approach for solving the parametrically excited stability problem of the periodic sandwich plate system under longitudinal harmonic excitations is proposed. The spatial periodic distribution of facial layer thickness and core layer modulus of the sandwich plate is considered. The non-linear partial differential equations of longitudinal and transverse coupling motions of the periodic visco-elastomer sandwich plate with supported masses under biaxial longitudinal boundary excitations are derived. The longitudinal displacements of the sandwich plate are separated into two parts and the longitudinal boundary excitations relevant to symmetric part are incorporated into the sandwich plate system. Then the partial differential equations with boundary excitations are converted into parametrically excited system equations and further converted into ordinary differential equations with time-varying parameters, which describe the parametrically excited vibration with multi-mode coupling of the periodic sandwich plate system. The fundamental perturbation solution to the equations is expressed as the product of periodic and exponential parts based on the Floquet theorem. The ordinary differential equations with harmonic parameters are converted into a set of algebraic equations using the harmonic balance method. Then the parametrically excited instability of the periodic sandwich plate system is determined directly by matrix eigenvalues. The overall instability characteristics of parametrically excited vibration with multi-mode coupling of the system under longitudinal harmonic excitations are illustrated by numerical results on unstable regions. The parametrically excited instability can be improved by the spatially periodic distribution of geometrical and physical parameters. The proposed approach is applicable to general sandwich structures with spatial distribution parameters in multi-mode-coupling parametrically excited vibrations for overall instability analysis on continuous frequency band. [ABSTRACT FROM AUTHOR]

Les atteintes ligamentaires peuvent être sources méconnues de douleur chronique du poignet. Après un traumatisme initial parfois oublié, les patients développent des douleurs mécaniques avec plus rarement des claquements ou des sensations d'instabilité et de lâchage d'objets. Les antécédents traumatiques et la clinique peuvent évoquer le diagnostic mais en cas d'instabilité dynamique, les clichés standard vont rester normaux. Dans ce contexte clinique, il sera donc important de compléter par des clichés dynamiques qui peuvent être réalisés de face, de profil ou poing fermé. Cet article s'intéresse aux modalités de réalisation de ces clichés dynamiques, leur intérêt et valeur diagnostique. Ligament damage can be an unrecognized source of chronic wrist pain. After an initial trauma that is sometimes forgotten, patients develop mechanical pain with, more rarely, snapping or sensations of instability and dropping of objects. The history of trauma and the clinical examination can make the diagnosis likely but in case of dynamic instability the standard X-ray will remain normal. In this clinical context, it is important to add dynamic X-ray which is comprised of a postero-anterior, lateral and clenched fist projections. This article focuses on the modalities of realization of these dynamic films, their interest and diagnostic value. [ABSTRACT FROM AUTHOR]

The dynamic stability of nanobeams has been investigated by the Euler-Bernoulli and Timoshenko beam theories in the literature, but the higher-order Reddy beam theory has not been applied in the dynamic stability evaluation of nanobeams. In this work, the governing equations of the motion and dynamic stability of a nanobeam embedded in elastic medium are derived based on the nonlocal theory and the Reddy's beam theory. The parametric studies indicate that the principal instability region (PIR) moves to a lower frequency zone when length, sectional height, nonlocal parameter, Young's modulus and mass density of the Reddy nanobeam increase. The PIR shifts to a higher frequency zone only under increasing shear modulus. Increase in length makes the width of the PIR shrink obviously, while increase in height and Young's modulus makes the width of the PIR enlarge. The sectional width and foundation modulus have few effects on PIR. [ABSTRACT FROM AUTHOR]

We have studied the convective (or static) and dynamic instabilities between 80 and 100 km above Tromsø (69.6° N, 19.2° E) using temperature and wind data of 6 min and 1 km resolutions primarily almost over a solar cycle obtained with the sodium lidar at Tromsø. First, we have calculated Brunt–Väisälä frequency (N) for 339 nights obtained from October 2010 to December 2019, and the Richardson number (Ri) for 210 nights obtained between October 2012 to December 2019. Second, using those values (N and Ri), we have calculated probabilities of the convective instability (N2 < 0) and the dynamic instability (0 ≤ Ri < 0.25) that can be used for proxies for evaluating the atmospheric stability. The probability of the convective instability varies from about 1% to 24% with a mean value of 9%, and that of the dynamic instability varies from 4 to 20% with a mean value of 10%. Third, we have compared these probabilities with the F10.7 index and local K-index. The probability of the convective instability shows a dependence (its correlation coefficient of 0.45) of the geomagnetic activity (local K-index) between 94 and 100 km, suggesting an auroral influence on the atmospheric stability. The probability of the dynamic instability shows a solar cycle dependence (its correlation coefficient being 0.54). The probability of the dynamic instability shows the dependence of the 12 h wave amplitude (meridional and zonal wind components) (C.C. = 0.52). The averaged potential energy of gravity waves shows decrease with height between 81 and 89 km, suggesting that dissipation of gravity waves plays an important role (at least partly) in causing the convective instability below 89 km. The probability of the convective instability at Tromsø appears to be higher than that at middle/low latitudes, while the probability of the dynamic instability is similar to that at middle/low latitudes. [ABSTRACT FROM AUTHOR]

The seaworthiness of a ship plays a critical role in ensuring the safety of life and property and the prevention of marine pollution. One meaning of seaworthiness is the fundamental ability to sail safely to a destination, as well as being fit and ready for cargo. The parameters of seaworthiness have been expanded with the introduction of new maritime regulations. The entry of the 2019 amendments to the IMSBC Code into force has brought significant changes to bulk carriers with cargo that may liquefy at sea. Using examples from history, as well as an understanding of the environmental conditions of the oceans that ships are subject to, the seaworthiness of bauxite carriers was examined critically. First, the concept and doctrine of seaworthiness were clarified considering the existing transportation technology. Then, the spirit of the 2019 amendments to the IMSBC Code was applied to the seaworthiness of a bauxite carrier, showing that it demonstrated dynamic instability. Beyond that, from a transportability performance perspective, an extensive discussion was provided concerning the major correlation related to seaworthiness. Finally, practical recommendations were given on keeping a ship seaworthy before and during the process of bauxite transportation. [ABSTRACT FROM AUTHOR]

Purpose. The work is aimed to determine the real location in space and conduct possible measurement of the true geometric dimensions of the NPP cooling pond dam, especially its underwater part and to detect the additional and previously unaccounted factors that could affect these parameters, as well as the state of the entire structure in general. Methodology. A comprehensive analysis of all available materials about engineering surveys and geotechnical studies was carried out at the dam of the cooling pond of the Zaporizhzhia NPP. Due to this, a more comprehensive look at the results of engineering and geological surveys was obtained. Findings. The state of soils in the body of the earth dam can be influenced by weakened and poorly studied zones of the dam. These zones were determined based on the analysis of the soil studies data of the dam’s ground. Previously uncovered issues on the operation of the facility were raised and considered. The ways and methods for additional study of the earth dam of the cooling pond were selected, the conditions for their use were substantiated. A numerical relationship between the thickness of loose soils and the amount of surface subsidence were determined for the first time. A generalized geological section of the dam body was compiled for further modeling of geotechnical processes. Originality. For the first time since construction, a comprehensive program was developed for assessing the technical condition of the cooling pond dam using innovative methods from the Laboratory of Research of Nuclear and Thermal Power Plants in Prydniprovska State Academy of Civil Engineering and Architecture (PSACEA). In particular, combined hydrographic-geodetic and aerovisual methods were proposed using specially designed universal leading signs that have no analogues in world practice. Practical value. The application of the developed comprehensive program using innovative methods allows assessing the technical condition of the cooling pond dam of the NPP.

This paper presents experimental tests on a free-hanging aspirating pipe used for cold-water pipe (CWP) in Ocean Thermal Energy Conversion (OTEC). The focus is on the dynamic instability induced by internal flow in a cantilevered aspirating pipe, and the vortex-induced vibration (VIV) response under the combined action of internal and external flows. Results indicate that near-periodic motion in the pipe model arises from first bending mode instability induced by internal flow. Although the internal flow does not significantly affect the dominant mode and frequency of the VIV response, it does impact the strain response magnitude and mode transition. Furthermore, variations in top connection types, bottom clump weight, and submersion depth may induce mode transitions in cross-flow vibrations. Moreover, the impact of bottom counterweights on the strain response is also closely related to the dominant vibration mode, with potential reversals in influence patterns as the dominant mode changes. The findings offer valuable insights into the dynamic response of large-scale flexible pipelines in deep-sea environments, considering both internal and external flow conditions. This aids in the development and refinement of predictive models, as well as guiding the design of OTEC systems in the industry. • A model experiment for the cold-water pipe of a floating OTEC system was conducted. • Dynamic response of the pipe under internal and external flows was analysed for basic instability insights. • Studied the dynamic response of cantilevered aspirating pipes influenced by internal and external flows. • Investigated effects of key parameters like top constraint, mass ratio, clump weight, and submersion length on pipe vibrations. [ABSTRACT FROM AUTHOR]

This study examined the dynamic instability of a drum brake induced by the rigid modes of the brake shoe. The brake shoe was modeled as a rigid curved plate subject to frictional contact with a rotating drum. In the presence of a negatively sloped friction curve, dynamic instability was numerically analyzed with respect to variation in the system parameters. The results showed that mode-coupling instability did not occur, but dynamic instability was induced by negative damping in a specific rigid mode, and its propensity varied with the operating conditions and geometric changes.

Microtubules (MTs) are polymers assembled from αβ-tubulin heterodimers that display the hallmark behavior of dynamic instability. MT dynamics are driven by GTP hydrolysis within the MT lattice, and are highly regulated by a number of MT-associated proteins (MAPs). How MAPs affect MTs is still not fully understood, partly due to a lack of high-resolution structural data on undecorated MTs, which need to serve as a baseline for further comparisons. Here we report three structures of MTs in different nucleotide states (GMPCPP, GDP, and GTPγS) at near-atomic resolution and in the absence of any binding proteins. These structures allowed us to differentiate the effects of nucleotide state versus MAP binding on MT structure. Kinesin binding has a small effect on the extended, GMPCPP-bound lattice, but hardly affects the compacted GDP-MT lattice, while binding of end-binding (EB) proteins can induce lattice compaction (together with lattice twist) in MTs that were initially in an extended and more stable state. We propose a MT lattice-centric model in which the MT lattice serves as a platform that integrates internal tubulin signals, such as nucleotide state, with outside signals, such as binding of MAPs or mechanical forces, resulting in global lattice rearrangements that in turn affect the affinity of other MT partners and result in the exquisite regulation of MT dynamics.