Small External Force Research Articles

Reorientation of grain crystal lattices in metals/alloys during electrocrystallisation under the action of force

The purpose of the study was experimental verification of the proposed concept of phase formation in electrocrystallised metals/alloys via the stage of supercooled liquid state. In accordance with the purpose, the task was to reveal the features of formation of the crystallographic texture in metals/alloys during their electrocrystallisation under the action of small force. The effect of the emergence of a new crystallographic texture with lower surface energy in metals/alloys during electrocrystallisation under the action of small external force exerted in the direction opposite to the initial axis of the texture was experimentally established. The obtained result is one more proof of the validity of the concept of phase formation in electrocrystallised metals/alloys via the stage of supercooled liquid state.

Structural and technological allowances, according to changes in the process of operation of dimensional parameters of clothing

The nature of the change in the properties of materials during the operation of clothing is associated with repeated exposure to small external forces that cause the occurrence of reversible and irreversible deformations in materials. The study of the residual deformation of the materials of clothing packages under the action of cyclically changing loads will make it possible to make adjustments to the values of structural allowances, even at the design stage of clothing. The purpose of the work is to determine the relative magnitude of residual deformations of various materials, taking into account operational factors and determining the necessary allowances at the design and manufacture of clothing. The authors have developed an experimental setup that allows cyclic loading and biaxial deformation, and after testing, to measure the value of residual deformation. The work summarizes the experimental experience of research on determining the relative values of residual deformations for various types of materials. To take into account the relative values of residual deformations, formulas are proposed for calculating allowances for materials of a package of products, taking into account relative deformations. These allowances provide freedom of movement, create a comfortable condition for a person. Taking into account the average values of the optimal thickness of the package of materials, the calculation of the increments along the chest line for standard clothing design methods was performed. The results of the research were used in the development of ergonomic clothing for extreme mountain tourism athletes, which received positive feedback from consumers.

Bending performance of the CORC cable with flexible interlocked stainless steel former

The high temperature superconducting cable on round core (CORC) is a kind of cable that could be used in fusion projects. Nevertheless, conventional copper former CORC cables require a large external force to allow the cable to endure plastic deformation and be tightly wound into solenoids. In this case, the superconducting tape will be affected by concentrated stress, resulting in a risk of critical current degradation. Therefore, this paper proposes a new CORC cable with flexible interlocked stainless steel former, which can be wound into a solenoid by applying a small external force. To verify the bending performance of this interlocked former CORC cable, a double-layer and a ten-layer interlocked stainless steel former CORC cable, as well as a double-layer traditional copper former CORC cable, are fabricated. And these three CORC cables are used to wind solenoids of various radius sizes respectively. The experimental results show that the critical bending radius of the double-layer interlocked stainless steel former CORC cable is less than 20 mm, the critical bending radius of the ten-layer interlocked stainless steel former CORC cable is less than 50 mm, and the critical bending radius of the double-layer traditional copper former CORC cable is larger than 55 mm. A self-consistent finite element model for the critical current of the CORC cable solenoid is also established. And the critical current experimental results are in good agreement with the simulation results. The results of this paper verify the excellent bending performance of the interlocked former CORC cable, which provides a good option for the preparation of insert magnets for future fusion projects.

Feasibility of 3D-Printed Locking Compression Plates with Polyether Ether Ketone (PEEK) in Tibial Comminuted Diaphyseal Fractures.

The applicability of a polyether ether ketone locking compression plate (PEEK LCP) fabricated using FDM (fused deposition modeling)-based 3D printing to treat actual patients was studied. Three different tests-bending, axial compression, and axial torsion-were conducted on tibial non-osteoporotic comminuted diaphyseal fracture samples fixed with the commercial titanium alloy LCP and 3D-printed PEEK LCP. Comparing the outcomes of these tests revealed that the commercial titanium alloy LCP underwent plastic deformation in the bending and axial torsion tests, though the LCP did not fail even when an external force greater than the maximum allowable load of the tibia fixture of the LCP was applied. Elastic deformation occurred in the 3D-printed PEEK LCP in the bending and axial torsion tests. However, deformation occurred even under a small external force, and its stiffness was 10% compared to commercial titanium alloy LCP. Thus, 3D-printed PEEK LCP can be applied to the fracture conditions in non-weight-bearing regions. The experimental results reveal detailed insights into the treatment of actual patients by considering the stiffness and high toughness of 3D-printed PEEK LCP.

Impedance control and test of an automatic rotational orthosis for walking with arm swing

Neurological damage after stroke and spinal cord injury often results in walking impairments. The theory of interlimb neural coupling implies that synchronized arm swing should be included during gait training to improve rehabilitation outcomes. We previously developed an automatic rotational orthosis for walking with arm swing (aROWAS), which produced coordinated interlimb movement when running in passive mode. The current case-series study had three aims: to develop impedance control algorithms for generating flexible movement in the aROWAS system, to validate its technical feasibility, and to investigate interlimb muscle activity when using it. A force-free controller was developed to compensate for gravity and friction, and an impedance controller was developed to produce a flexible movement pattern. Experiments were performed on three able-bodied volunteers to evaluate the feasibility of the flexible aROWAS system and muscle activity in their upper and lower limbs was recorded. In force-free mode, the leg rig was static but easily moved by small external forces, and the subjects reported very little resistance when attempting to walk synchronously in the aROWAS system. In impedance mode, the leg rig performed the pre-defined gait pattern, but the joint trajectories were adaptable to external forces. All participants produced earlier hip extension and greater knee flexion during active walking than during passive walking. Furthermore, the arm and lower limb muscles simultaneously produced higher electromyography activity. The control algorithms enabled the aROWAS system to produce walking-like coordinated joint performance in the upper and lower limbs, and also allowed for some degree of adjustment in response to voluntary input from the users. Stronger interlimb muscle activity was produced when participants walked actively in the system. This aROWAS system has the technical potential to serve as an effective tool for investigating interlimb neural coupling and as a novel testbed for walking rehabilitation with synchronized arm swing.

Statistical analysis of the thickness and biomechanical properties of Japanese children’s skulls

ObjectiveThe structure and strength of a child's skull are important in accurately determining what and how external forces were applied when examining head injuries. The aims of this study were to measure skull thickness and strength in children, evaluate sex differences, and investigate the correlation between skull thickness and strength and age. Materials and methodsSkulls were obtained from 42 Japanese dead bodies under 20 years of age. During the autopsies, bone samples were taken from each skull. The length, width, and central thickness of the skulls were measured using calipers. Three-point bending tests were conducted, and bending load and displacement were recorded. Bending stress and bending strain were calculated, and Young's modulus, 0.2% proof stress, and maximum stress were obtained. ResultsIn cases under 1.5 years old, 14 out of 46 male samples and 20 out of 40 female samples did not fracture during the three-point bending test, though no significant sex differences were detected. No significant differences in age, sample thickness, Young's modulus, 0.2% proof stress, or maximum stress were detected between the sexes. The sample thickness, Young's modulus, 0.2% proof stress, and maximum stress increased significantly and logarithmically with age (R2 = 0.761–0.899). Although age correlated with thickness, Young's modulus, and maximum stress more in females than in males, 0.2% proof stress correlated slightly better in males than in females. ConclusionThe skulls of preschool children, in particular, are thin, have low strength, and are at high risk of fracturing even with relatively small external forces. Unlike adults, no significant sex differences in skull thickness or strength were observed in children.

Multiway Softness Polyurethane Elastomeric Composite with Enhanced Thermal Conductivity and Application as Thermal Interface Materials

AbstractThe ever‐increasing computing power in modern electronics comes with significant heat waste that can't be ignored. For microchips to dissipate heat efficiently, thermal interface materials (TIMs) are the most critical components in semiconductor packaging. Soft elastomer composites are often used as TIMs due to their large‐strain reversible deformability with a small external force. For TIMs to cushion between the microchip and heat spreader, they must have high thermal conductivity and temperature‐tunable softness to reduce thermal resistance and relieve the warpage failure caused by thermal stress. However, thermal conductivity and softness are interrelated and restrict each other. To address this challenge, a radical strategy of introducing dynamic covalent bonds in the polyurethane/aluminum composite is used. The reversible and low energy of dynamic imine bonds along with the lengthening of the Khun segment in the crosslinking network imbues the material with temperature‐tunable softness function while maintaining high thermal conductivity. The resulting polyurethane elastomer (PUE) composite exhibits remarkable thermal conductivity (6.90 W m−1 K−1), low thermal resistance (0.13 K cm2 W−1), and excellent softness (elastic modulus 759.50 kPa, and stretchability 140.30%). This work provides a practical method to design thermally conductive and temperature‐tunable soft elastomer composites as TIMs in semiconductor packaging.

The two‐dimensional stationary Navier–Stokes equations in toroidal Besov spaces

AbstractWe consider the stationary Navier–Stokes equations in the two‐dimensional torus . For any , we show the existence, uniqueness, and continuous dependence of solutions in homogeneous toroidal Besov spaces for given small external forces in when . These spaces become closer to the scaling invariant ones if the difference ε becomes smaller. This well‐posedness is proved by using the embedding property and the para‐product estimate in homogeneous Besov spaces. In addition, for the case , we can show the ill‐posedness, even in the scaling invariant spaces. Actually in such cases of p and q, we can prove that ill‐posedness by showing the discontinuity of a certain solution map from to .

Existence of the stationary Navier-Stokes flow in [formula omitted] around a radial flow

We consider the stationary Navier-Stokes equations on the whole plane R2. We show that for a given small and smooth external force around a radial flow, there exists a classical solution decaying like |x|−1. In our result, it is not necessary to impose any symmetric conditions on external forces.

Some recurrent motions of Navier-Stokes equations with Coriolis force

In this paper, we consider the problems of recurrence (almost automorphy, Birkhoff recurrence, Poisson stability) for Navier-Stokes equations with a small external force in the rotational framework. We prove that these fluid equations admit a unique solution which possesses the same character of recurrence as the external force.

Interfacial Coordination Interaction Enables Soft Elastomer Composites High Thermal Conductivity and High Toughness.

Soft elastomers have attracted wide applications, such as soft electronic devices and soft robotics, due to their ability to undergo large deformation with a small external force. Most elastomers suffer from poor toughness and thermal conductivity, which limits their use. The addition of inorganic fillers can enhance the thermal conductivity and toughness, but it deteriorates the softness (low Young's modulus and high stretchability). Integrating thermal conductivity, toughness, and softness into one elastomer is still a challenge. Here, we report a strategy of interfacial coordination interaction to achieve soft elastomer composites with high thermal conductivity and high toughness. We demonstrate the strategy by using poly(lipoic acid) elastomer and silver-coated aluminum filler as model, where silver-sulfur coordination cross-links are formed at the interface. The resultant elastomer composite shows high streachability (450%), high thermal conductivity (2.35 W m-1 K-1), low modulus (321 kPa), and high toughness (3496 J m-2), which cannot be achieve in existing elastomers. The time domain thermoreflectance technique demonstrates that the silver-sulfur coordination interaction lowers the interfacial thermal resistance, resulting in enhanced thermal conductivity of the elastomer composites. The excellent softness stems from lower bonding energy of the silver-sulfur coordination cross-links compared with covalent chemical cross-links. The high toughness also benefits from the interfacial silver-sulfur coordination interaction that can dissipate more energy upon deformation. We further demonstrate the potential application of the thermally conductive, tough, and soft elastomer composites for thermal management of chip and soft electronic devices.

High Dynamic Range Force Sensing of a Robot Hand Combining Signals on Tip and Wrist

When a robot grasps a tool, the force at the tip of the tool needs to be determined. However, the vibration noise caused by the inertial force of the hand is a major factor that degrades the force-sensing performance. In this study, we develop a gripper force sensor that uses the structure of the fingertip as a flexure element and integrates the response with that of a wrist force sensor to ensure high force-sensing performance. It can measure small external forces and has high load capacity. The measurement range of the gripper force sensor is 0.005 N to 10 N, and the overload capacity exceeds 50 N. We experimentally demonstrate that hand vibration does not degrade the force detection performance, and that the dynamic range of the force can be extended. In addition, we show through a drawing demonstration that a fine adjustment of the force can be achieved.

Critical Transitions in Lake Ecosystem State May Be Driven by Coupled Feedback Mechanisms: A Case Study from Lake Erhai, China

Critical transitions between ecosystem states can be triggered by relatively small external forces or internal perturbations and may show time-lagged or hysteretic recovery. Understanding the precise mechanisms of a transition is important for ecosystem management, but it is hampered by a lack of information about the preceding interactions and associated feedback between different components in an ecosystem. This paper employs a range of data, including paleolimnological, environmental monitoring and documentary sources from lake Erhai and its catchment, to investigate the ecosystem structure and dynamics across multiple trophic levels through the process of eutrophication. A long-term perspective shows the growth and decline of two distinct, but coupled, positive feedback loops: a macrophyte-loop and a phosphorus-recycling-loop. The macrophyte-loop became weaker, and the phosphorus-recycling-loop became stronger during the process of lake eutrophication, indicating that the critical transition was propelled by the interaction of two positive feedback loops with different strengths. For lake restoration, future weakening of the phosphorus-recycling loop or a reduction in external pressures is expected to trigger macrophyte growth and eventually produce clear water conditions, but the speed of recovery will probably depend on the rates of feedback loops and the strength of their coupling.

Compression and Stretching of Confined Linear and Ring Polymers by Applying Force.

We use Langevin dynamics to study the deformations of linear and ring polymers in different confinements by applying compression and stretching forces on their two sides. Our results show that the compression deformations are the results of an interplay among of polymer rigidity, degree of confinement, and force applied. When the applied force is beyond the threshold required for the buckling transition, the semiflexible chain under the strong confinement firstly buckles; then comes helical deformation. However, under the same force loading, the semiflexible chain under the weaker confinement exhibits buckling instability and shrinks from the folded ends/sides until it becomes three-folded structures. This happens because the strong confinement not only strongly reduces the buckling wavelength, but also increases the critical buckling force threshold. For the weakly confined polymers, in compression process, the flexible linear polymer collapses into condensed states under a small external force, whereas the ring polymer only shows slight shrinkage, due to the excluded volume interactions of two strands in the crowded states. These results are essential for understanding the deformations of the ring biomacromolecules and polymer chains in mechanical compression or driven transport.

How can cultural conditions affect society’s decisions?

Recently, the evolution of people cooperation in the context of evolutionary games has attracted noticeable attention. In this regard, people’s assessment of their neighbor’s payoff affects the cooperation or defection decisions. Different decisions of each person can be a function of environment (e.g. cultural, climatic, and physical conditions). Thus, the individuals’ decisions and their values can change under the influence of these factors. In the present study, the effect of cultural, climatic, and physical conditions is considered as a chaotic dynamic (here Lorenz system). Using different initial conditions, the Lorenz time-series is unique to each individual in calculating her/his payoff. In other words, society members are considered as agents or nodes within a complex network. Here, the mechanism of applying Lorenz dynamics and external force in the context of the iterated prisoner’s dilemma game is applied. Using large-scale Monte Carlo simulations, we can see that the cooperation of the whole network is significantly improved even in the presence of a small external force. It is concluded that applying a chaotic dynamic on valuations and coupling between agents is an effective way to increase network cooperation, even in severely tempted situations of the evolutionary game. It is stated that the impact of cultural, climatic, educational conditions and the coupling between agents in the cooperation of social networks, can be modeled by the help of chaotic signals.

Research of release characteristics of ship attached fouling

Marine fouling increases navigation resistance and restricts the performance of hulls. Based on the fluid-structure coupling theory, the release characteristics of fouling barnacles attached to the silicone coating were studied by a numerical analysis method according to the antifouling performance parameters, such as coating thickness and elastic modulus. The simulation results show that the influence of coating thickness and elastic modulus on barnacle release is far less than that of composite variable (E/T)0.5. For the hull coating with a small (E/T)0.5 value, the barnacle more easily peels off under small external forces. This provides a reference for the selection of silicone antifouling coatings for ships.

On the Forced Surface Quasi-Geostrophic Equation: Existence of Steady States and Sharp Relaxation Rates

We consider the asymptotic behavior of the surface quasi-geostrophic equation, subject to a small external force. Under suitable assumptions on the forcing, we first construct the steady states and we provide a number of useful a posteriori estimates for them. Importantly, to do so, we only impose minimal cancellation conditions on the forcing function. Our main result is that all $L^1\cap L^\infty$ localized initial data produces global solutions of the forced SQG, which converge to the steady states in $L^p(\mathbf R^2), 1<p\leq 2$ as time goes to infinity. This establishes that the steady states serve as one point attracting set. Moreover, by employing the method of scaling variables, we compute the sharp relaxation rates, by requiring slightly more localized initial data.

On periodic solutions for one-phase and two-phase problems of the Navier\u2013Stokes equations

This paper is devoted to proving the existence of time-periodic solutions of one-phase or two-phase problems for the Navier–Stokes equations with small periodic external forces when the reference domain is close to a ball. Since our problems are formulated in time-dependent unknown domains, the problems are reduced to quasilinear systems of parabolic equations with non-homogeneous boundary conditions or transmission conditions in fixed domains by using the so-called Hanzawa transform. We separate solutions into the stationary part and the oscillatory part. The linearized equations for the stationary part have eigen-value 0, which is avoided by changing the equations with the help of the necessary conditions for the existence of solutions to the original problems. To treat the oscillatory part, we establish the maximal L_p–L_q regularity theorem of the periodic solutions for the system of parabolic equations with non-homogeneous boundary conditions or transmission conditions, which is obtained by the systematic use of {mathcal R}-solvers developed in Shibata (Diff Int Eqns 27(3–4):313–368, 2014; On the {{mathcal {R}}}-bounded solution operators in the study of free boundary problem for the Navier–Stokes equations. In: Shibata Y, Suzuki Y (eds) Springer proceedings in mathematics & statistics, vol. 183, Mathematical Fluid Dynamics, Present and Future, Tokyo, Japan, November 2014, pp 203–285, 2016; Comm Pure Appl Anal 17(4): 1681–1721. https://doi.org/10.3934/cpaa.2018081, 2018; {{mathcal {R}}} boundedness, maximal regularity and free boundary problems for the Navier Stokes equations, Preprint 1905.12900v1 [math.AP] 30 May 2019) to the resolvent problem for the linearized equations and the transference theorem obtained in Eiter et al. ({{mathcal {R}}}-solvers and their application to periodic L_p estimates, Preprint in 2019) for the L_p boundedness of operator-valued Fourier multipliers. These approaches are the novelty of this paper.

Electron-acoustic supernonlinear waves and their multistability in the framework of the nonlinear Schrödinger equation

Finite-amplitude supernonlinear electron-acoustic waves (EAWs) are investigated under the nonlinear Schrödinger (NLS) equation in a plasma system that is composed of cold electron fluid, immobile ions and q-nonextensive hot electrons. Using the wave transfiguration, the NLS equation is deduced in a dynamical system. The presence of finite-amplitude nonlinear and supernonlinear EAWs is shown by phase plane analysis. The effects of the nonextensive parameter (q) and the speed of waves (v) on different traveling wave solutions of EAWs are presented. Furthermore, by introducing a small external periodic force in the dynamical system, multistability behaviors of EAWs under the NLS equation are shown for the first time in classical plasmas.

Particle dynamics and transport enhancement in a confined channel with position-dependent diffusivity

This work focuses on the dynamics of particles in a confined geometry with position-dependent diffusivity, where the confinement is modelled by a periodic channel consisting of unit cells connected by narrow passage ways. We consider three functional forms for the diffusivity, corresponding to the scenarios of a constant (D0), as well as a low (Dm) and a high (Dd) mobility diffusion in cell centre of the longitudinally symmetric cells. Due to the interaction among the diffusivity, channel shape and external force, the system exhibits complex and interesting phenomena. By calculating the probability density function, mean velocity and mean first exit time with the Itô calculus form, we find that in the absence of external forces the diffusivity Dd will redistribute particles near the channel wall, while the diffusivity Dm will trap them near the cell centre. The superposition of external forces will break their static distributions. Besides, our results demonstrate that for the diffusivity Dd, a high dependence on the x coordinate (parallel with the central channel line) will improve the mean velocity of the particles. In contrast, for the diffusivity Dm, a weak dependence on the x coordinate will dramatically accelerate the moving speed. In addition, it shows that a large external force can weaken the influences of different diffusivities; inversely, for a small external force, the types of diffusivity affect significantly the particle dynamics. In practice, one can apply these results to achieve a prominent enhancement of the particle transport in two- or three-dimensional channels by modulating the local tracer diffusivity via an engineered gel of varying porosity or by adding a cold tube to cool down the diffusivity along the central line, which may be a relevant effect in engineering applications. Effects of different stochastic calculi in the evaluation of the underlying multiplicative stochastic equation for different physical scenarios are discussed.