The Normal Force Characteristic of a Novel Magnetorheological Elastomer Based on Butadiene Rubber Matrix Compounded with the Self-Fabricated Silly Putty

In this paper, a novel magnetorheological elastomer (MRE) was prepared by dispersing carbonyl iron particles (CIPs) into a composite matrix compounded by butadiene rubber (BR) and self-fabricated Silly Putty. The rate-sensitive and magneto-induced characteristics of normal force were experimental investigated to discuss the working mechanism. The results demonstrated that the normal force increased with the compression rate and the mass fraction of boron-silicon copolymer added to the composite matrix due to the formation of the more and more B-O cross bonds which could be blocked in the C-C cross-linked network of BR. Meanwhile, the magneto-induced normal force was positively correlated with the applied magnetic field strength and the compression strain due to the decreased gap between the centers of soft magnetic particles and the increased particle intensity of magnetization. Moreover, the magneto-induced normal force continued to enhance with the increase of compression strain because the CIP chains fixed in the C-C cross-linked network could bend to a radian and CIP chains in B-O cross-linked network could rupture to form more stable and intensive short-chain structures. Besides, a simplified model was deduced to characterize the mechanism of the generation of the magneto-induced normal force. Furthermore, the normal force varied stably with the oscillatory shear strain (less than 9%) at different magnetic induction intensities and suddenly reduced when the applied oscillatory shear strain was more than 9%.

Determination of the force characteristic of head car’s passive safety system – large road vehicle interaction in a collision

One of the priorities of the National Economic Strategy of Ukraine for the Period up to 2030 is the development of the transport sector, in particular railway vehicle renewal, the introduction of high-speed railway passenger transport, and railway traffic safety improvement. The home motor-car trains must be renewed in compliance with new home standards harmonized with European ones, among which one should mention the Ukrainian State Standard DSTU EN 15227, which specifies the passive safety of a passenger train in its emergency collisions with different obstacles. New car designs must provide not only effective up-to-date braking systems to prevent emergency collisions, but also passive safety systems with energy-absorbing devices. The main purpose of these devices is to reduce the longitudinal forces in the intercar connections and the car accelerations to an acceptable level for the three collision scenarios specified in the DSTU EN 15227. The Department of Statistical Dynamics and Multidimensional Mechanical Systems Dynamics, Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine, developed a passive protection concept for home high-speed passenger trains in emergency collisions by the DSTU EN 15227 scenarios, proposals on the passive protection of a motor-car train head car, and honeycomb designs of lower- and upper-level energy-absorbing devices (EAD 1 and UL EAD, respectively), which are integrated into the head car front part and serve to damp the major part of the impact energy in front collisions with obstacles. This paper considers DSTU EN 15227 Scenario 3: a collision of a reference motor-car train at a speed of 110 km/h at a railway crossing with a large 15 t road vehicle, which is simulated as a large-size deformable obstacle (LSDO). The aim of the paper is to determine the force characteristic of the interaction of energy-absorbing devices mounted on the head car front part with a large road vehicle in a collision to assess the compliance of the proposed passive protection with the normative requirements. Finite-element models were constructed to analyze the plastic deformation of the elements of the EAD 1 – LSDO, UL EAD – LSDO, and EAD 1 – UL EAD –LSDO systems in a collision with account for geometric and physical nonlinearities, steel dynamic hardening as a function of the impact speed, and varying contact interaction between the elements of the systems considered. The studies conducted made it possible to determine the force characteristics of energy-absorbing device – obstacle interaction and the total characteristic of the contact force between two lower-level devices and two upper-level ones as a function of the obstacle center of mass displacement in a collision. The proposed mathematical models and the calculated force characteristics may be used in the study of the dynamics of a reference motor-car train – large road vehicle collision with the aim to assess the compliance of the passive protection of the home head car under design with the DSTU EN 15227 requirements.

Recanalization Treatment of Acute Ischemic Stroke Caused by Large-Artery Occlusion in the Elderly: A Comparative Analysis of “the Elderly” and “the Very Elderly”

Objective. To assess whether the effectiveness and safety of recanalization therapy for acute ischemic stroke (AIS) caused by large-artery occlusion (LAO) differ between patients aged 60–79 years and patients aged ≥80 years. Methods. We analyzed prospective data of patients with LAO (≥60 years) who underwent recanalization therapy at the Department of Vascular Neurosurgery, New Era Stroke Care and Research Institute, PLA Rocket Force Characteristic Medical Center, from November 2013 to July 2017. The data were compared between elderly patients (60–79 years) and very elderly patients (≥80 years). The effectiveness of recanalization therapy was evaluated using the 90-day modified Rankin scale (mRS) score, while safety was assessed by the rates of symptomatic intracranial hemorrhage (SICH) and mortality within 30 days. Results. A total of 151 patients with AIS induced by LAO were included in this study. Seventy-three patients (48.3% [73/151]) had an overall favorable outcome (mRS score 0–2) after treatment. A higher proportion of patients in the elderly group showed a favorable outcome compared with the very elderly group (58.6% [34/58] vs. 41.6% [39/93], respectively; P = 0.046 ). The incidence of SICH (12.7% vs. 16.13%, respectively; P = 0.561 ) and mortality (10.3% vs. 7.5%, respectively; P = 0.548 ) within 30 days was not significantly different between the two groups. Conclusion. Recanalization treatment of LAO is more effective in elderly patients compared with very elderly patients, while the safety of recanalization treatment is comparable between these two groups.

Study on cutting force of reaming porcine bone and substitute bone

Accurate mechanical feedback systems are critical to the successful implementation of virtual and robotic surgical assistant systems. Experimental measurements of reaming force could further our understanding of the cancellous bone reaming process during hip arthroplasty to help develop surgical simulators with realistic force effects and improve the protection mechanism of robot-assisted surgical systems. In this study, reaming experiments with natural bone (porcine femur) and a bone substitute (polyurethane blocks) were performed on a CNC lathe. This paper proposes using the maximum reaming force of the steady reaming stage to represent the force characteristic. The reaming force is biased to one side in the overlap direction and the maximum reaming force will vary when the reamer is not coincident with the long axis of the bone. The diameter of the reamer has the greatest influence on reaming force, which clearly increases with increasing reamer diameter. During operation, a medium rotation speed and high feed speed can reduce the reaming force. After cutting, the morphology of the cut surface is not flat, but arc-shaped, which will have a significant impact on implantation of the femoral prosthesis. In in vitro cutting experiments, polyurethane blocks can be used as a substitute for cancellous bone.

The Super-Relaxed State and Length Dependent Activation in Porcine Myocardium

Rationale: Myofilament length dependent activation (LDA) is the key underlying mechanism of cardiac heterometric autoregulation, commonly referred as the Frank-Starling law of the heart. Although alterations in LDA are common in cardiomyopathic states, the precise structural and biochemical mechanisms underlying LDA remain unknown. Objective: Here, we examine the role of structural changes in the thick filament during diastole, in particular changes in the availability of myosin heads, in determining both calcium sensitivity and maximum contractile force during systole in permeabilized porcine cardiac fibers. Methods and Results: Permeabilized porcine fibers from ventricular myocardium were studied under relaxing conditions at short and long sarcomere length (SL) using muscle mechanics, biochemical measurements, and X-ray diffraction. Upon stretch, porcine myocardium showed the increased calcium sensitivity and maximum calcium activated force characteristic of LDA. Stretch increased diastolic ATP turnover, recruiting reserve myosin heads from the super-relaxed state (SRX) at longer SL. Structurally, X-ray diffraction studies in the relaxed-muscle confirmed a departure from the helical ordering of the thick-filament upon stretch which occurred concomitantly with a displacement of myosin heads towards actin, facilitating cross-bridge formation upon systolic activation. Mavacamten, a selective myosin-motor inhibitor known to weaken the transition to actin-bound power-generating states and to enrich the ordered SRX myosin population, reversed the structural effects of stretch on the thick-filament, blunting the mechanical consequences of stretch; mavacamten did not, however, prevent other structural changes associated with LDA in the sarcomere, such as decreased lattice spacing or troponin-displacement. Conclusions: Our findings strongly indicate that in ventricular muscle, LDA and its systolic consequences are dependent on the population of myosin heads competent to form cross-bridges and involves the recruitment of myosin heads from the reserve SRX pool during diastole.

Increasing the safery of railway passenger and freight traffic

In 2020, the Ukrainian Government conducted an audit of the Ukrainian economy for nearly 30 years of independence and decided on the vectors of economic development aimed at European and Euro-Atlantic integration. The audit of the Ukrainian railways showed that most of the railway assets are critically worn. The audit and the vectors became a starting point for the development of the National Economic Strategy of Ukraine up to 2030, which was approved on March 3, 2021. One of the priorities of this strategy is the development of the transport sector by a succession of steps, including railway track and vehicle renewal, the introduction of high-speed passenger transport, and increasing railway traffic safety and environment safety on the Urrainian railways. The aim of this paper is to work out recommendations on increasing the safety of passenger and freight traffic in Ukraine. The paper generalizes the experience gained over the years of Ukrainian independence in the fundamental and applied transport-oriented reseach conducted at the Department of Sttistical Dynamics and Multidimensional Mechanical Systems, Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine. This experience may be useful in the implementation of the above steps on the way to the sustainable development of the Ukrainian railway transport. In the paper, emphasis is on new investigations into the passive propection of the cars of a motor car train in emergency collisions whose scenarios are specified by Ukrainian State Standard DSTU EN 15227. Based on a mathematical model of a collision of identical motor car trains, a mathematical model was developed to simulate a collision of a motor car train with a large vehicle at a crossing with account for a specified force characteristic of interaction of the leading car equipped with a passive safety system with a deformable obstacle. The model developed was used in analyzing dynamic loads on the cars of a motor car train with a passive safety system in its collision at 110 km/h with a 15 t large vehicle at a railway crossing. With consideration for the results of previous investigations into the dynamics of emergency collisions of a motor car train with an identical train and a fright car, recommendations were worked out on the passive protection of a home-made leading car in accordance with the requirements of normative documents. The proposed mathematical models and designs of energy-absorbing devices, the research results, and the practical recommendations worked out may be used in designing new motor car train vehicles for the Ukrainian railways in accordance with the DSTU EN 15227 requirements for passive protection in emergency collisions.

Application of the parallelogram mechanism with the effect of quasi-zero stiffness in the vibration protection systems of the operator’s chair of a road construction machine

For vibration protection of operators of construction and road machines, a promising direction is the use of passive vibration protection systems based on mechanisms with quasi-zero rigidity. Passive vibration isolation systems, being less complex than active ones, require less frequent maintenance, are cheaper to manufacture and more reliable than active ones. The problem of selecting the optimal, most reliable and simple design of the mechanism with the effect of quasi-zero rigidity remains urgent. In this case, the most widespread use of elements that create negative stiffness. This requires elements with positive stiffness in the mechanism, which complicates the design. More promising structures of mechanisms, where elements with negative stiffness are not separated into a separate structure. In mechanisms such as the parallelogram, studied in this work, a section with quasi-zero stiffness can be provided with just one tension spring, which simplifies the design and reduces the cost of the entire vibration protection system. By the method of direct analytical inference for the presented diagram of a parallelogram mechanism with one spring, analytical expressions are obtained for the tensile force of the spring necessary to compensate for the force of gravity of the chair with the operator on the height of the chair and the length of the spring. As an example, the graphical dependences of the spring tensile force on the chair lift and on the spring’s own length are given as an example. It was found that the static force characteristic of the spring is a straight line passing through the origin. That is, the zero force corresponds to the zero spring length, which is not technically feasible. It is proposed to use a mechanism that replaces the tension spring, which will provide a given power characteristic.

OSCILLATION OF PULSE-LOADED OSCILLATOR WITH DEGREE POSITIONAL FRICTION

Nonstationary oscillations of the oscillator with nonlinear positional friction caused by an instantaneous force pulse are described. The power dependence of the positional friction force on the displacement of the system, which generalizes the known models, is accepted. The corresponding dynamics problems were solved precisely by the method of adding and approximated by the method of energy balance. In the study, using periodic Ateb-functions, an exact analytical solution of the nonlinear differential equation of motion was constructed. Compact formulas for calculating oscillation ranges and half-cycle durations are derived. It is shown that the decrease in the amplitude of oscillations, as well as under the action of the force of linear viscous resistance, follows the law of geometric progression. The denominator of the progression is less than one and depends on the positional friction constants, in particular on the nonlinearity index. Thus, we have not only a decrease in the amplitude of oscillations, but also an increase in the durations of half-cycles, which is characteristic of nonlinear systems with a rigid force characteristic. Approximate displacement calculations use Pade-type approximations for periodic Ateb-functions. The error of these approximations is less than one percent. From the obtained analytical relations, as separate cases, the known dependences covered in the theory of oscillations for linear positional friction follow. It is shown that even in the case of nonlinear positional friction the process of oscillations caused by an instantaneous momentum has many oscillations and is not limited in time. In the case of power positional friction, the oscillation ranges of the pulse-loaded oscillator can be calculated by elementary formulas. The calculation of displacements in time is associated with the use of periodic Ateb-functions, the values of which are not difficult to determine by known asymptotic formulas. Calculations confirm that the obtained approximate formula does not give large errors. In order to verify the adequacy of the obtained analytical solutions, numerical computer integration of the original nonlinear differential equation of motion was performed. The results of the calculation, which lead to analytical and numerical solutions of the Cauchy problem, are well matched.