Contact Form Research Articles

Mechanical behavior of entangled metallic wire mesh–silicone rubber interpenetrating phase composites under quasistatic compression

Interpenetrating phase composites (IPCs) with porous metal materials as the matrix and polymer materials as the reinforcement, which have a broad application prospect, have both the high strength of metal materials and the high energy absorption capacity of polymer materials. Entangled metallic wire materials are a new type of porous material with damping characteristics, which is an excellent choice for use as the matrix of IPCs. In the present work, a novel entangled metallic wire material–silicone rubber IPC is developed through the vacuum infiltration method with the entangled wire material as the matrix and silicone rubber as the reinforcing element. The mechanical properties (loss factor and tangent modulus) of the as-synthesized composites are characterized through compression tests. More specifically, the effects of key experimental parameters (strain) and material properties (matrix density, wire diameter, and anisotropy) on the mechanical properties of the composites are analyzed in detail. It is found that with the introduction of interfacial friction, the loss factor of the composites becomes higher than those of the pure entangled metallic wire material and silicone rubber; in particular, the tangent modulus is significantly enhanced. The complex structural characteristics of the proposed composite enable the loss factor and tangent modulus to exhibit a nonlinear relationship with the density over a range of displacement values. Moreover, the smaller the wire diameter is, the greater the loss factor of the composites is, while the tangent modulus exhibits the opposite trend. The unique wire contact form and preparation process endow the composites with nonlinear properties in the molding direction as well as pronounced anisotropy characteristics. HIGHLIGHT A novel interpenetrating phase composite is proposed. The composite quasistatic curve is nonlinear with excellent mechanical properties. The improved energy consumption properties are due to the interfacial friction. The increase in wire density greatly improves the elastic modulus of the composite. The composite is anisotropic with a better bearing capacity in the molding direction.

Normal form for pseudo-Einstein contact forms and intrinsic CR normal coordinates

We give a normal form for pseudo-Einstein contact forms and apply it to construct intrinsic CR normal coordinates parametrized by the structure group of CR geometry. The proof is based on the construction of parabolic normal coordinates by Jerison and Lee.

Kinematic Characteristics Analysis of Orbiting Scroll and Structural Optimization of Oldham’s Coupling in Scroll Compression

The contact form of the orbiting scroll and Oldham’s coupling plays an important role in improving the operation stability of the scroll compressor. In this study, the kinematic simulation of key moving parts such as the orbiting scroll and Oldham’s coupling was carried out under the condition of low speed, and the reason for the impact between Oldham’s coupling and the orbiting scroll was revealed. Results showed that the clearance between the moving pairs causes the orbiting scroll to have a slight rotation tendency and causes the impact between Oldham’s coupling and the orbiting scroll. The angular velocity of the orbiting scroll in the x-axis direction can effectively characterize this impact. The impact of the Oldham’s coupling convex key on the mainframe keyway is more severe than that on the keyway of the orbiting scroll. By optimizing the structure of the convex key of Oldham’s coupling, the contact form between Oldham’s coupling and the orbiting scroll is improved, and the starting acceleration of the orbiting scroll is reduced by 53%, which greatly improved the working stability of the scroll compressor.

Research on bearing capacity and sealing contact characteristics of the subsea wellhead connector

This paper analyzed the bearing capacity of a subsea wellhead connector when exposed to external pressure and the bending moment in different operational modes and load conditions to determine the possible areas prone to failure. The contact between certain parts during the pre-tightening process impacts other areas, affecting the sealing performance. A symmetrical, three-dimensional periodic contact model was established via Finite Element Method (FEM) to simulate and analyze the sealing performance of the subsea wellhead connector. Furthermore, this study examined the variation laws governing contact form, preload, contact width, radial compression, and internal pressure, as well as their influence on the contact stress of the metal sealing ring. The results indicated that effective sealing was achieved at radial compression levels ranging from 0.1045 to 0.2089 mm. The preload contact stress was directly proportional to the preload and radial compression and inversely proportional to the contact width. The operational contact stress initially decreased, then increased at a higher internal pressure.

S1$S^1$‐equivariant contact homology for hypertight contact forms

In a previous paper, we showed that the original definition of cylindrical contact homology, with rational coefficients, is valid on a closed three-manifold with a dynamically convex contact form. However, we did not show that this cylindrical contact homology is an invariant of the contact structure. In the present paper, we define ‘nonequivariant contact homology’ and ‘ S 1 $S^1$ -equivariant contact homology’, both with integer coefficients, for a contact form on a closed manifold in any dimension with no contractible Reeb orbits. We prove that these contact homologies depend only on the contact structure. Our construction uses Morse–Bott theory and is related to the positive S 1 $S^1$ -equivariant symplectic homology of Bourgeois-Oancea. However, instead of working with Hamiltonian Floer homology, we work directly in contact geometry, using families of almost complex structures. When cylindrical contact homology can also be defined, it agrees with the tensor product of the S 1 $S^1$ -equivariant contact homology with Q ${\mathbb {Q}}$ . We also present examples showing that the S 1 $S^1$ -equivariant contact homology contains interesting torsion information. In a subsequent paper, we will use obstruction bundle gluing to extend the above story to closed three-manifolds with dynamically convex contact forms, which in particular will prove that their cylindrical contact homology has a lift to integer coefficients which depends only on the contact structure.

The Progress of Research into Flexible Sensors in the Field of Smart Wearables.

In modern society, technology associated with smart sensors made from flexible materials is rapidly evolving. As a core component in the field of wearable smart devices (or ‘smart wearables’), flexible sensors have the advantages of excellent flexibility, ductility, free folding properties, and more. When choosing materials for the development of sensors, reduced weight, elasticity, and wearer’s convenience are considered as advantages, and are suitable for electronic skin, monitoring of health-related issues, biomedicine, human–computer interactions, and other fields of biotechnology. The idea behind wearable sensory devices is to enable their easy integration into everyday life. This review discusses the concepts of sensory mechanism, detected object, and contact form of flexible sensors, and expounds the preparation materials and their applicability. This is with the purpose of providing a reference for the further development of flexible sensors suitable for wearable devices.

Effect of wall slip on the viscoelastic particle ordering in a microfluidic channel.

The formation of a line of equally spaced particles at the centerline of a microchannel, referred as "particle ordering," is desired in several microfluidic applications. Recent experiments and simulations highlighted the capability of viscoelastic fluids to form a row of particles characterized by a preferential spacing. When dealing with non-Newtonian fluids in microfluidics, the adherence condition of the liquid at the channel wall may be violated and the liquid can slip over the surface, possibly affecting the orderingefficiency. In this work, we investigate the effect of wall slip on the ordering of particles suspended in a viscoelastic liquid by numerical simulations. The dynamics of a triplet of particles in an infinite cylindrical channel is first addressed by solving the fluid and particle governing equations. The relative velocities computed for the three-particle system are used to predict the dynamics of a train of particles flowing in a long microchannel. The distributions of the interparticle spacing evaluated at different slip coefficients, linear particle concentrations, and distances from the channel inlet show that wall slip slows down the self-assembly mechanism. For strong slipping surfaces, no significant change of the initial microstructure is observed at low particle concentrations, whereas strings of particles in contact form at higher concentrations. The detrimental effect of wall slip on viscoelastic ordering suggests care when designing microdevices, especially in case of hydrophobic surfaces that may enhance the slippingphenomenon.

Analysis of Contact Stress Distribution between Rolling Element and Variable Diameter Raceway of Cageless Bearing

The change in contact state between the rolling elements and raceway of a cageless bearing with a variable diameter raceway affect the wear of the bearing, which leads to discrete motion failure of the rolling elements. For this purpose, the contact characteristics as contact form and contact stress between the rolling elements and raceway were determined. A numerical method is proposed to determine the three-dimensional contact stress of a cageless bearing. First, combined with the variable diameter raceway structure characteristics and the motion of rolling elements, the rolling elements and raceway contact stress model was established, and the influence factors of contact stress and the maximum stress distribution were determined. Based on the rolling contact theory, the relative position of the stick-slip region and the tangential stress distribution of the contact area were analyzed. The stress equations for the three-dimensional between rolling elements and variable diameter raceway were obtained by the principle of superposition, and the stress component characteristics of the contact area were numerically simulated. The results show that the main influencing factors of contact stress are: load, structure of variable diameter raceway, spindle speed, friction coefficient µ and the ratio of the stick region and the slip region k. Taking a cageless bearing as an example, the influence of the contact curvature Ri on the contact stress is smaller than that of ri. Increasing ri to make it larger than 1.5 mm and controlling the speed to be lower than 13,950 r/min, the maximum stress appears in the conventional raceway, which is beneficial to alleviate the failure of the variable diameter raceway. There are a slip region and a stick region in the contact area, reducing the friction coefficient µ and increasing the stick-slip coefficient k appropriately can ensure the discrete movement of the rolling elements and reduce the wear of the variable diameter raceway. The error of the stress distribution model is less than 15%, which can predict and characterize the contact stress distribution between the rolling elements and the variable diameter raceway. The theoretical guidance for the development and application of cageless bearings is provided.

Respiratory Rate Estimation Using U-Net-Based Cascaded Framework From Electrocardiogram and Seismocardiogram Signals.

At-home monitoring of respiration is of critical urgency especially in the era of the global pandemic due to COVID-19. Electrocardiogram (ECG) and seismocardiogram (SCG) signals-measured in less cumbersome contact form factors than the conventional sealed mask that measures respiratory air flow-are promising solutions for respiratory monitoring. In particular, respiratory rates (RR) can be estimated from ECG-derived respiratory (EDR) and SCG-derived respiratory (SDR) signals. Yet, non-respiratory artifacts might still be present in these surrogates of respiratory signals, hindering the accuracy of the RRs estimated. In this paper, we propose a novel U-Net-based cascaded framework to address this problem. The EDR and SDR signals were transformed to the spectro-temporal domain and subsequently denoised by a 2D U-Net to reduce the non-respiratory artifacts. We have shown that the U-Net that fused an EDR input and an SDR input achieved a low mean absolute error of 0.82 breaths per minute (bpm) and a coefficient of determination (R2) of 0.89 using data collected from our chest-worn wearable patch. We also qualitatively provided insights on the complementariness between EDR and SDR signals and demonstrated the generalizability of the proposed framework. ECG and SCG collected from a chest-worn wearable patch can complement each other and yield reliable RR estimation using the proposed cascaded framework. We anticipate that convenient and comfortable ECG and SCG measurement systems can be augmented with this framework to facilitate pervasive and accurate RR measurement.

Higher systolic inequalities for 3-dimensional contact manifolds

A contact form is called Besse when the associated Reeb flow is periodic. We prove that Besse contact forms on closed connected 3-manifolds are the local maximizers of suitable higher systolic ratios. Our result extends earlier ones for Zoll contact forms, that is, contact forms whose Reeb flow defines a free circle action.

Mechanism of shear strength deterioration of soil-rock mixture after freeze–thaw cycles

The growth and melting of internal ice crystals reorganizing the pore structure and internal skeleton of soil-rock mixture (S-RM), which leads to the deterioration of the S-RM shear strength after freeze–thaw cycles and its strength characteristics after the cycles are different from the normal temperature one. Due to unclear S-RM strength deterioration mechanism after freeze–thaw cycles, stability of S-RM cutting slopes in cold regions cannot be effectively evaluated. In this paper, particle flow code (PFC) simulation as well as direct shear and nuclear magnetic resonance (NMR) tests were carried to study strength degradation behaviors and pore structure changes of S-RMs containing various amounts of rock after freeze–thaw cycles. The results show that the shear strength and internal friction angle of S-RM are no longer positively correlated with the rock content after the cycles, and the strength parameters will decrease at rock contents of above 45%. Based on the simulation test, shear band thickness variation after the cycles was quantitatively evaluated, and an innovative method to obtain the fluctuation value of shear failure surface was proposed. It is found that the change laws of shear band thickness and failure surface fluctuation value with rock content after the cycles are consistent with that of shear strength, and they all reach the maximum value when the rock content is 45%. Fractal theory was introduced for quantitative evaluation of changes in S-RM pore structure after the cycles, and combined with the strength parameter attenuation, the strength deterioration mechanism of S-RM was revealed: The deterioration of shear strength in samples containing low rock content is mainly due to changes in the contact form between particles caused by internal inclusion structure formation after the cycles. The deterioration of S-RM with rock content of 55% and 65% is mainly due to attenuation of the internal skeleton effect caused by the appearance of overhead structures. The internal pores and skeleton structure of the sample with 45% rock content have little change, so the attenuation changes of the strength parameters and the undulation value of the failure surface are minimal.

Dynamical implications of convexity beyond dynamical convexity

We establish sharp dynamical implications of convexity on symmetric spheres that do not follow from dynamical convexity. It allows us to show the existence of elliptic and non-hyperbolic periodic orbits and to furnish new examples of dynamically convex contact forms, in any dimension, that are not equivalent to convex ones via contactomorphisms that preserve the symmetry. Moreover, these examples are $$C^1$$ -stable in the sense that they are actually not equivalent to convex ones via contactomorphisms that are $$C^1$$ -close to those preserving the symmetry. We also show the multiplicity of symmetric non-hyperbolic and symmetric (not necessarily non-hyperbolic) closed Reeb orbits under suitable pinching conditions.

3D convex contact forms and the Ruelle invariant

Let \(X \subset {\mathbb {R}}^4\) be a convex domain with smooth boundary Y. We use a relation between the extrinsic curvature of Y and the Ruelle invariant of the Reeb flow on Y to prove that there are constants \(C> c > 0\) independent of Y such that $$\begin{aligned} c \leqslant {\text {ru}}(Y) \cdot {\text {sys}}(Y)^{1/2} \leqslant C \end{aligned}$$Here \({\text {sys}}(Y)\) is the systolic ratio of Y, i.e. the square of the minimal period of a closed Reeb orbit of Y divided by twice the volume of X, and \({\text {ru}}(Y)\) is the volume-normalized Ruelle invariant. We then construct dynamically convex contact forms on \(S^3\) that violate this bound using methods of Abbondandolo–Bramham–Hryniewicz–Salomão. These are the first examples of dynamically convex contact 3-spheres that are not strictly contactomorphic to a convex boundary Y.

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Improvement and metallurgy of current-related heating problem of circuit breakers made of AgSnO2 and AgCdO

Abstract Recent developments in technology increase the application area of electronic systems used in cars and commercial vehicles day by day. Along with the increase in the features expected from the vehicles, the battery capacities required to meet the desired features also increase. Especially in commercial vehicles, high-capacity battery systems are used depending on the function of the vehicle. Circuit breaker systems providing high voltage and current are used to intervene in the event of a possible problem from the batteries. During the operation of the vehicle, heat is generated due to the high current passing through the circuit breakers. In this study, different materials and surface contact forms were examined to solve the heating problem of circuit breakers operating at high voltage and current values. AgSnO2 and AgCdO coating materials were used for surface coatings of rivets used in circuit breakers. Moreover, rivet groups with various surface contact geometries such as flat–flat and curved–flat were used for each material. After applying 24 V–250 A values to the different materials and rivets of different surface shape geometries, thermal and metallographic analyses were performed. The experimental study showed that the best thermal results under resistive load are formed by the curved–flat contact geometry of the AgSnO2 coating material.

The practice of applying the norms on responsibility for sexual crimes (Articles 131-135 of the Criminal Code of the Russian Federation) and ways to improve it

The subject. The article reflects the progress and results of the study of the practice of applying the norms on responsibility for crimes against sexual inviolability and sexual freedom of the individual (Chapter 18 of the Criminal Code of the Russian Federation). There are a large number of general and specific law enforcement problems that do not allow us to effectively counteract such crimes.Purpose of the study. The purpose of the study is to confirm the scientific hypothesis about the presence of systemic problems in the practice of applying the norms of Chapter 18 of the Criminal Code of the Russian Federation, as well as to develop proposals for improving law enforcement.Methodology. The identification of law enforcement problems was carried out by analyzing published and unpublished materials of judicial practice and comparing them with the main categories and principles of criminal law. Access to the published materials was carried out through the legal reference systems and the State Automated System "Justice". Unpublished materials were obtained in the course of their own professional activities, as well as when studying the scientific works of other authors. The use of previously obtained results of their own scientific activities, the results of scientific research of modern criminologists and criminologists, as well as the study of the experience of foreign countries allowed us to formulate proposals for solving the identified problems.The main results. In the course of the study, the following systemic problems of law enforcement were identified. (1) The uncertainty of the content of other sexual actions. (2) The ambiguity of the legal assessment of the multiplicity of crimes against sexual inviolability and sexual freedom of the individual. (3) The blurring of the content and methods of committing depraved actions.These problems characterize the current state of the practice of applying the norms of Chapter 18 of the Criminal Code of the Russian Federation.To solve these problems and improve law enforcement, the following proposals are justified and formulated.At the level of the resolution of the Plenum, it should be clarified that other actions of a sexual nature are contact forms of the perpetrator's influence on the victim's body that can satisfy sexual needs, with the exception of sexual intercourse, sodomy and lesbianism (for example, masturbation, fellatio, forced kisses, manual influence on the mammary glands or genitals and other ways of stimulating sexual arousal).On the issue of the qualification of continuing crimes, the Plenum of the Supreme Court should indicate that repeated sexual acts that form the objective side of one corpus delicti should be considered as a single continuing crime, if their commission was covered by a single intent. At the same time, such intent may be evidenced by the behavior of the perpetrator, in which he does not stop the violation of sexual freedom or sexual inviolability of a particular victim.The provisions of the resolution of the Plenum of the Supreme Court concerning the qualification of depraved acts should be changed, indicating that depraved acts are other sexual acts that are not covered by the dispositions of Article 134 of the Criminal Code of the Russian Federation, and actually depraved acts committed without direct physical contact in order to satisfy sexual needs or arouse the victim's interest in sexual acts. It is also important to emphasize that the acts provided for in the note to Article 131 of the Criminal Code of the Russian Federation should include only other actions of a sexual nature.Conclusions. In conclusion, it should be noted that the proposals formulated to solve the identified problems of law enforcement cannot completely eliminate them. The solution to these problems should be found through legislative changes. In this activity, it seems correct to focus on the positive experience of European legislators, which provides for a more detailed differentiation of responsibility depending on the features that objectively affect the nature and degree of public danger of the act.

Symmetric periodic orbits and invariant disk-like global surfaces of section on the three-sphere

We study Reeb dynamics on the three-sphere equipped with a tight contact form and an anti-contact involution. We prove the existence of a symmetric periodic orbit and provide necessary and sufficient conditions for it to bound an invariant disk-like global surface of section. We also study the same questions under the presence of additional symmetry and obtain similar results in this case. The proofs make use of pseudoholomorphic curves in symplectizations. As applications, we study Birkhoff’s conjecture on disk-like global surfaces of section in the planar circular restricted three-body problem and the existence of symmetric closed Finsler geodesics on the two-sphere. We also present applications to some classical Hamiltonian systems.

Lorentzian distance functions in contact geometry

An important tool to analyse the causal structure of a Lorentzian manifold is given by the Lorentzian distance function. We define a class of Lorentzian distance functions on the group of contactomorphisms of a closed contact manifold depending on the choice of a contact form. These distance functions are continuous with respect to the Hofer norm for contactomorphisms defined by Shelukhin [The Hofer norm of a contactomorphism, J. Symplectic Geom. 15 (2017) 1173–1208] and finite if and only if the group of contactomorphisms is orderable. To prove this, we show that intervals defined by the positivity relation are open with respect to the topology induced by the Hofer norm. For orderable Legendrian isotopy classes we show that the Chekanov-type metric defined in [D. Rosen and J. Zhang, Chekanov’s dichotomy in contact topology, Math. Res. Lett. 27 (2020) 1165–1194] is nondegenerate. In this case, similar results hold for a Lorentzian distance functions on Legendrian isotopy classes. This leads to a natural class of metrics associated to a globally hyperbolic Lorentzian manifold such that its Cauchy hypersurface has a unit co-tangent bundle with orderable isotopy class of the fibres.

On the singular Weinstein conjecture and the existence of escape orbits for b-Beltrami fields

Motivated by Poincaré’s orbits going to infinity in the (restricted) three-body problem [see H. Poincaré, Les Méthodes Nouvelles de la Mécanique Céleste, Vol. 3 (Gauthier-Villars, 1899) and A. Chenciner, Poincaré and the three-body problem, in Henri Poincaré, 1912–2012 (Birkhäuser, Basel, 2015), pp. 51–149], we investigate the generic existence of heteroclinic-like orbits in a neighborhood of the critical set of a [Formula: see text]-contact form. This is done by using a singular counterpart [R. Cardona, E. Miranda and D. Peralta-Salas, Euler flows and singular geometric structures, Philos. Trans. R. Soc. A 377(2158) (2019) 20190034] of Etnyre–Ghrist’s contact/Beltrami correspondence [J. Etnyre and R. Ghrist, Contact topology and hydrodynamics: I. Beltrami fields and the Seifert conjecture, Nonlinearity 13(2) (2000) 441–458], and genericity results concerning eigenfunctions of the Laplacian established by Uhlenbeck [Generic properties of eigenfunctions, Amer. J. Math. 98(4) (1976) 1059–1078]. Specifically, we analyze the [Formula: see text]-Beltrami vector fields on [Formula: see text]-manifolds of dimension [Formula: see text] and prove that for a generic asymptotically exact [Formula: see text]-metric they exhibit escape orbits. We also show that a generic asymptotically symmetric [Formula: see text]-Beltrami vector field on an asymptotically flat [Formula: see text]-manifold has a generalized singular periodic orbit and at least four escape orbits. Generalized singular periodic orbits are trajectories of the vector field whose [Formula: see text]- and [Formula: see text]-limit sets intersect the critical surface. These results are a first step towards proving the singular Weinstein conjecture.

Geometric integration by parts and Lepage equivalents

We compare the integration by parts of contact forms – leading to the definition of the interior Euler operator – with the so-called canonical splittings of variational morphisms. In particular, we discuss the possibility of a generalization of the first method to contact forms of lower degree. We define a suitable Residual operator for this case and, working out an original conjecture by Olga Rossi, we recover the Krupka–Betounes equivalent for first order field theories. A generalization to the second order case is discussed.