Geometry-dependent defect merging induces bifurcated dynamics in active networks

Cytoskeletal networks can repair defects to maintain structural integrity.However, the mechanisms and dynamics of defect merging remain poorlyunderstood. Here we report a geometry-tunable merging mechanism inmicrotubule-motor networks initiated by active crosslinking. We directlygenerate defects using a light-controlled microtubule-motor system in O-shapedand V-shaped networks, and observe that the defects can self-close. Combiningtheory and experiment, we find that the V-shaped networks must overcomeinternal elastic resistance in order to zip up cracks, giving rise to abifurcation of dynamics dependent on the initial opening angle of the crack:the crack merges below a critical angle and opens up at larger angles.Simulation of a continuum model reproduces the bifurcation dynamics, revealingthe importance of overlapping boundary layers where free motors andmicrotubules can actively crosslink and thereby merge the defects. We alsoformulate a simple elastic-rod model that can qualitatively predict thecritical angle, which is tunable by the network geometry.

Biological systems control ambient fluids through the self-organization of active protein structures, including flagella, cilia, and cytoskeletal networks. Self-organization of protein components enables the control and modulation of fluid flow fields on micron scales, however, the physical principles underlying the organization and control of active-matter-driven fluid flows are poorly understood. Here, we use an optically-controlled active-matter system composed of microtubule filaments and light-switchable kinesin motor proteins to analyze the emergence of persistent flow fields. Using light, we form contractile microtubule networks of varying size and shape, and demonstrate that the geometry of microtubule flux at the corners of contracting microtubule networks predicts the architecture of fluid flow fields across network geometries through a simple point force model. Our work provides a foundation for programming microscopic fluid flows with controllable active matter and could enable the engineering of versatile and dynamic microfluidic devices.

Synopsis To solve the support stability control problem for a coal face with large angles along both strike and dip (CLSD), the ’support-surrounding rock’ mechanical model has been developed, which takes into account the impact of the dip angle of the seam on the stability of the support in the strike direction. The mechanical relationships of the critical topple angle and critical slip angle of the support along the strike of the coal face with large dip angle and the support height, support resistance, friction coefficient, and other factors have been derived through the mechanical analysis of support stability in the strike direction of CLSDs in the free state, the operating state, and the special state. The research findings were applied to a fully mechanized CLSD in Xinji Coal Mine. The maximum underhand angle and overhand angle in strike are 42° and 25° respectively, and the maximum dip is 39°. It is calculated that during underhand mining and overhand mining, the critical support resistances for avoiding support toppling are 3723 kN and 1714 kN respectively, and the critical support resistances for avoiding slipping of the support are 7405 kN and 6606 kN respectively. Thus, the selection of type ZZ7600/18/38 hydraulic roof support for the coal face is justified. Measures to prevent sliding of the support and the installation of a limiting stop maintain the support runs in good condition and ensure safe and efficient mining of CLSD.

Myosin motor proteins drive vigorous steady-state fluctuations in the actin cytoskeleton of cells. Endogenous embedded semiflexible filaments such as microtubules, or added filaments such as single-walled carbon nanotubes are used as novel tools to noninvasively track equilibrium and nonequilibrium fluctuations in such biopolymer networks. Here, we analytically calculate shape fluctuations of semiflexible probe filaments in a viscoelastic environment, driven out of equilibrium by motor activity. Transverse bending fluctuations of the probe filaments can be decomposed into dynamic normal modes. We find that these modes no longer evolve independently under nonequilibrium driving. This effective mode coupling results in nonzero circulatory currents in a conformational phase space, reflecting a violation of detailed balance. We present predictions for the characteristic frequencies associated with these currents and investigate how the temporal signatures of motor activity determine mode correlations, which we find to be consistent with recent experiments on microtubules embedded in cytoskeletal networks.

The replicator-mutator equations from evolutionary dynamics serve as a model for the evolution of language, behavioral dynamics in social networks, and decision-making dynamics in networked multiagent systems. Analysis of the stable equilibria of these dynamics has been a focus in the literature, where symmetry in fitness functions is typically assumed. We explore asymmetry in fitness and show that the replicator-mutator equations exhibit Hopf bifurcations and limit cycles. We prove conditions for the existence of stable limit cycles arising from multiple distinct Hopf bifurcations of the dynamics in the case of circulant fitness matrices. In the noncirculant case we illustrate how stable limit cycles of the dynamics are coupled to embedded directed cycles in the payoff graph. The limit cycles correspond to oscillations of grammar dominance in language evolution and to oscillations in behavioral preferences in social networks; for decision-making systems, the limit cycles correspond to sustained oscillati...

Inspired by the reversible adhesion behaviors of geckos, the effects of pre-tension in a bio-inspired nano-film and a hierarchical structure on adhesion are studied theoretically. In the case with a uniformly distributing pre-tension in a spatula-like nano-film under peeling, a closed-form solution to a critical peeling angle is derived, below or above which the peel-off force is enhanced or reduced, respectively, compared with the case without pre-tension. The effects of a non-uniformly distributing pre-tension on adhesion are further investigated for both a spatula-like nano-film and a hierarchical structure-like gecko's seta. Compared with the case without pre-tension, the pre-tension, no matter uniform or non-uniform, can increase the adhesion force not only for the spatula-like nano-film but also for the hierarchical structure at a small peeling angle, while decrease it at a relatively large peeling angle. Furthermore, if the pre-tension is large enough, the effective adhesion energy of a hierarchical structure tends to vanish at a critical peeling angle, which results in spontaneous detachment of the hierarchical structure from the substrate. The present theoretical predictions can not only give some explanations on the existing experimental observation that gecko's seta always detaches at a specific angle and no apparent adhesion force can be detected above the critical angle but also provide a deep understanding for the reversible adhesion mechanism of geckos and be helpful to the design of biomimetic reversible adhesives.

Flow visualization tests and fluid force measurements were conducted in a water tunnel to investigate flow around and fluid forces on a cross-shaped tube (CST) in a cross-flow. The following results were obtained. Flow around a CST is classified into two patterns. One is perfect-separation flow for small incidence angle and the other is reattached flow for large incidence angle. The critical incidence angle where the flow pattern changes from the former to the latter is about 7.5°∼15°. At the critical angle, the mean drag and lift coefficients reach their minimum while the Strouhal number attains to the maximum. The amplitude of the fluctuating lift decreases as the incidence angle increases. These features of flow around and fluid forces on a CST are quite similar to those of a square prism. These results imply that one-degree-of-freedom galloping and vortex-induced vibration possibly occur for small incidence angle while ILEV (impingement of leading edge vortices) vibration might be caused for large incidence angle when a CST is elastically supported in a cross-flow.

The stagnant region often appears in front of the tool cutting edge, which is caused by mechanical inlay and excessive pressing in plastic metal cutting with large negative rake angle tools at a low speed. It results in the change of the effective negative rake angle which can affect the flow characteristics of material, the quality of machined surface and the abrasion loss of cutting tools. However, the critical negative rake angle model based on the existence of the stagnant region has not been reported yet. Therefore, in order to investigate the critical negative rake angle value considering the stagnant region, a critical negative rake angle model based on the principle of minimum required energy is established, and the correctness of the theoretical model is verified by orthogonal cutting experiments. At the same time, the influence of the critical value of the large negative rake angle tool on the machined surface quality is studied through different cutting experiments. These experimental results show that the deviations of both experimental and theoretical critical negative rake angle are less than 5% during the orthogonally cutting of the aluminium (AL1060) and copper (T2) materials by the negative rake angle tool. Meanwhile, the critical negative rake angle is related to the adhesive friction coefficient of tool–workpiece contact surface. The analysis of friction characteristics shows that the deviation values of both theoretical and experimental critical negative rake angle are proportional to the coefficient of adhesive friction and the thickness of the stagnant region. Critical negative rake angle has a significant effect on roughness and residual stress of the machined surface.

In order to solve the problems of low compensation accuracy and long compensation time in traditional time delay compensation methods for active distribution network distributed generation system, a new time delay compensation method for active distribution network distributed generation system is proposed. Firstly, the cause of time delay in active distribution network distributed generation system is determined, and then the global characteristics of time delay in active distribution network distributed generation system are extracted by frequency domain method. On this basis, the time delay characteristics of active distribution network distributed generation system are discretized, and the time delay characteristics set of active distribution network distributed generation system is obtained. The continuous function in Banach space is determined by the element method. On this basis, it is discretized, and the time delay compensation model of distributed generation system in active distribution network is constructed. The Lagrange coefficient is used to correct the model to complete the time delay compensation of distributed generation system in active distribution network. The experimental results show that the proposed method has the highest accuracy of 98% and the shortest compensation time of 0.1 s.

A key early objective of Active Networking (AN) was to support on-the-fly network evolution. Although AN has been used relatively extensively to build application-customized protocols and even whole networking systems, demonstrations of evolution have been limited.This paper examines three AN mechanisms and how they enable evolution: active packets and plug-in extensions, well-known to the AN community, and update extensions, which are novel to AN. We devote our presentation to a series of demonstrations of how each type of evolution can be applied to the problem of adding support for mobility to a network. This represents the most large-scale demonstration of AN evolution to date. These demonstrations show what previous AN research has not: that AN technology can, in fact, support very significant changes to the network, even while the network is operational.

The plant cytoskeleton is a highly dynamic component of plant cells and mainly based on microtubules (MTs), and actin filaments (AFs). The important functions of dynamic cytoskeletal networks have been indicated for almost every intracellular activity, from cell division to cell movement, cell morphogenesis and cell signal transduction. Recent studies have also indicated a close relationship between the plant cytoskeleton and plant salt stress tolerance. Salt stress is a significant factor that adversely affects crop productivity and quality of agricultural fields worldwide. The complicated regulatory mechanisms of plant salt tolerance have been the subject of intense research for decades. It is well accepted that cellular changes are very important in plant responses to salt stress. Because the organization and dynamics of cytoskeleton may play an important role in enhancing plant tolerance through various cell activities, study on salt stress-induced cytoskeletal network has been a vital topic in the subject of plant salt stress tolerance mechanisms. In this article, we introduce our recent work and review some current information on the dynamic changes and functions of cytoskeletal organization in response to salt stress. The accumulated data point to the existence of highly dynamic cytoskeletal arrays and the activation of complex cytoskeletal regulatory networks in response to salt stresses. The important role played by cytoskeleton in mediating the plant cell’s response to salt stresses is particularly emphasized.

Control during alpine skiing is achieved principally through the mechanical interaction between the ski and the snow. In that the nature of this interaction is basically a cutting or machining process, it is proposed that the complex physical and mechanical properties of the snow responsible for its skiability can be related to its machinability. A simple testing device is presented, which can machine the snow while keeping the ratio of the thrust (vertical) to cutting (horizontal) forces equal to the tangent of the edge angle. The edge angle is varied to find a critical angle such that skidding occurs at large angles and holding at smaller angles. Using traditional machining theory, it is shown that this critical angle should be a function of the shear-strength-to-hardness ratio of the snow. A plot of critical angles versus shear-strength-to-hardness ratios is presented, which divides the surface into carving or holding and skidding regions. Critical angles have been measured between about 40 and 70°. These angles correspond to shear-strength-to-hardness ratios between 0.24 and 3.84. The difficulty of relating this critical angle to some function of maximum skiable slope steepness is discussed relative to ski technique and forces on the ski.

For the distribution network with high permeability distributed energy access, distribution network fault current distribution network operation mode, the influence of the distributed power control strategy, and the existing in ring network cabinet configuration does not meet the high sensitivity and high reliability requirements of the active power of fuse protection, in this paper, an adaptive protection system for active distribution network is proposed by using the passive protection terminal installed in the ring network cabinet and the protection host configured at the dispatching end. The protection host receives SCADA data of distribution network scheduling to obtain the topology of active distribution network, uses distributed power supply voltage and grid voltage to adaptively calculate the passive protection setting value, and sends the setting value to the passive protection terminal through communication to realize the adaptive protection function of active distribution network. Finally, the simulation model is established, and the fuse protection of active distribution network and the adaptive protection system with passive protection terminals are compared, and the sensitivity and reliability of the adaptive protection scheme are verified.

acute respiratory distress syndrome (ARDS) is a clinical condition characterized by impaired gas exchange as a result of the accumulation of edema in the alveolar space. The clinical management of ARDS patients includes mechanical ventilation with high oxygen concentrations. Mechanical

Transcranial ultrasound imaging and therapy depend on the efficient transmission of acoustic energy through the skull. Multiple previous studies have concluded that a large incidence angle should be avoided during transcranial-focused ultrasound therapy to ensure transmission through the skull. Alternatively, some other studies have shown that longitudinal-to-shear wave mode conversion might improve transmission through the skull when the incidence angle is increased above the critical angle (i.e., 25° to 30°). The effect of skull porosity on the transmission of ultrasound through the skull at varying incidence angles was investigated for the first time to elucidate why transmission through the skull at large angles of incidence is decreased in some cases but improved in other cases. Transcranial ultrasound transmission at varying incidence angles (0°-50°) was investigated in phantoms and ex vivo skull samples with varying bone porosity (0% to 28.54%±3.36%) using both numerical and experimental methods. First, the elastic acoustic wave transmission through the skull was simulated using micro-computed tomography data of ex vivo skull samples. The trans-skull pressure was compared between skull segments having three levels of porosity, that is, low porosity (2.65%±0.03%), medium porosity (13.41%±0.12%), and high porosity (26.9%). Next, transmission through two 3D-printed resin skull phantoms (compact vs. porous phantoms) was experimentally measured to test the effect of porous microstructure alone on ultrasound transmission through flat plates. Finally, the effect of skull porosity on ultrasound transmission was investigated experimentally by comparing transmission through two ex vivo human skull segments having similar thicknesses but different porosities (13.78%±2.05% vs. 28.54%±3.36%). Numerical simulations indicated that an increase in transmission pressure occurs at large incidence angles for skull segments having low porosities but not for those with high porosity. In experimental studies, a similar phenomenon was observed. Specifically, for the low porosity skull sample (13.78%±2.05%), the normalized pressure was 0.25 when the incidence angle increased to 35°. However, for the high porosity sample (28.54%±3.36%), the pressure was no more than 0.1 at large incidence angles. These results indicate that the skull porosity has an evident effect on the transmission of ultrasound at large incidence angles. The wave mode conversion at large, oblique incidence angles could enhance the transmission of ultrasound through parts of the skull having lower porosity in the trabecular layer. However, for transcranial ultrasound therapy in the presence of highly porous trabecular bone, transmission at a normal incidence angle is preferable relative to oblique incidence angles due to the higher transmission efficiency.