Contact Geometry Research Articles

Reply to the discussion by Philippon, Martinie, Vergne on “Scale and contact geometry effects in thermal EHL: Twin-disc versus ball-on-disc” by Liu, Zhang, Bader, Venner and Poll in Tribology International

The authors appreciate the discussion from Philippon, Martinie and Vergne on our paper (Tribol Int 154,2021,106694), in which we reported scale effects in EHL friction, i.e. the reduced coefficient of friction for EHL lubricated contacts with a large radius Rx. This was explained by an increase in film thickness and thus enhanced thermal effects. Philippon et al. found three alternative effects to explain our experimental observation. However, these effects were mainly proposed based on experiments carried out at a fixed Rx, which is largely irrelevant to the main concern in our work dealing with varying Rx. In this reply, the motivation of our work is explained, and the three effects proposed by Philippon et al. are briefly discussed.

DYNAMIC FINITE ELEMENT SIMULATION OF WHEEL–RAIL CONTACT RESPONSE FOR THE CURVED TRACK CASE

The wheel–rail interaction will be intensified on account of the complexity of the wheel–rail contact geometry on a curved track. It also may become more complicated and/or have significant difference as the train speed increases, since the dynamic effects cannot be ignored then. In this study, based on explicit Finite Element (FE) software LS-DYNA 971, a Three-Dimensional (3D) elastic-plastic FE model was built to simulate the dynamic wheel–rail contact behaviour of curve negotiating, where the superelevation and roll angle as well as the strain rate effect were considered. The evolution of contact patch and pressure, wheel–rail contact force, the stress/strain state and the acceleration of the axle were employed to examine the wheel–rail transient dynamic response. Furthermore, the influences of axle load, curve radius and strain rate effect were also discussed. It is found that the maximum vertical contact force, contact pressure, stress and strain on the curved track increase with the decreasing curve radius, and they increase with the increasing axle load except for lateral contact force. The wheel–rail dynamic responses on the curved track are significantly enhanced compared to the straight track. Moreover, the strain rate effect can enhance von-Mises stress and contact pressure, suppress the plastic deformation of the rail and wheel, but it has little effect on the vertical and lateral contact forces and stable acceleration of axle. The Rate-Sensitive Factors (RSF) of the wheel and rail on the curved track are weaker than those on the straight track. These findings will be very helpful to study the competitive relationship between the rolling contact fatigue and wear, as well as the crack initiation and propagation problem.

Highly responsive SnSe/GaN heterostructure-based UVC-SWIR broadband photodetector

Broadband photodetection spans the ultraviolet-C (250 nm) to shortwave-infrared (1250 nm) range is essential and desirable for various applications such as optical communication, spectral switching, and memory storage. We have utilized ultraviolet-responsive gallium nitride (GaN) and Tin selenide (SnSe) as the infrared-activated material to fabricate a broadband heterojunction-based optical detector. Through SnSe/GaN heterostructure, the fabricated detector combines GaN's ultraviolet to visible, with SnSe's visible to shortwave-infrared detectability. The device also possesses great responsiveness and a low dark current due to edge contact geometry, which directly accesses the heterostructure interface for both materials. The fabricated device functions well from the ultraviolet-C to the shortwave-infrared region, exhibiting the highest responsivity of 128 AW-1 and the lowest noise equivalent power of 5.2 × 10−14 WHz−1/2, the quantum efficiency ∼5 × 104% with a response time ∼800 μs for ultraviolet illumination while the highest responsivity of 6.06 AW-1 and noise equivalent power of 1 × 10−12 WHz−1 for the device under infrared illumination. The research will open up new possibilities for optoelectronic applications utilizing heterostructure-based wideband detection.

Optical Trapping of a Single Molecule of Length Sub-1 nm in Solution

Optical Trapping of a Single Molecule of Length Sub-1 nm in Solution

On the role of geometry in statistical mechanics and thermodynamics. I. Geometric perspective

This paper contains a fully geometric formulation of the General Equation for Non-Equilibrium Reversible-Irreversible Coupling (GENERIC). Although GENERIC, which is the sum of Hamiltonian mechanics and gradient dynamics, is a framework unifying a vast range of models in non-equilibrium thermodynamics, it has unclear geometric structure due to the diverse geometric origins of Hamiltonian mechanics and gradient dynamics. The difference can be overcome by cotangent lifts of the dynamics, which leads, for instance, to a Hamiltonian form of gradient dynamics. Moreover, the lifted vector fields can be split into their holonomic and vertical representatives, which provides a geometric method of dynamic reduction. The lifted dynamics can be also given physical meaning, here called the rate-GENERIC. Finally, the lifts can be formulated within contact geometry, where the second law of thermodynamics is explicitly contained within the evolution equations.

A numerical study of the contact geometry and pressure distribution along the glenoid track

The glenoid track geometry and the contact forces acting on the glenohumeral joint at static positions of 30°, 60°, 90° and 120° of abduction with 90° of external rotation were evaluated using a finite element model of the shoulder that, differently from most usual approximations, accounts the humeral head translations and the deformable-to-deformable non-spherical joint contact. The model was based on data acquired from clinical exams of a single subject, including the proximal humerus, scapula, their respective cartilages concerning the glenohumeral joint, and the rotator cuff and deltoid muscles. The forces acting on the glenohumeral joint were estimated using a simulation framework consisting of an optimization procedure allied with finite element analysis that seeks the minimum muscle forces that stabilize the joint. The joint reaction force magnitude increases up to 680.25N at 90° of abduction and decreases at further positions. From 60° onward the articular contact remains at the anterior region of the glenoid cartilage and follows an inferior to superior path at the posterior region of the humeral head cartilage. The maximum contact pressure of 3.104MPa occurs at 90° abduction. Although translating inferiorly throughout the movement, the projection of the humeral head center at the glenoid plane remains at the central region of the glenoid surface. The model results qualitatively matched the trends observed in the literature and supports the consideration of the translational degrees of freedom to evaluate the joint contact mechanics.

Dynamic response of vehicle-track interaction at the bolted rail joint in the presence of the polygonal wheel

Rail joints are the weakest link in the railway track structure due to the presence of discontinuities in the track stiffness and wheel-rail contact geometry. This paper presents the dynamic response of vehicle-track interaction at the bolted rail joint (BRJ) in the presence of polygonal wheel wear. A three-dimensional coupled vehicle-track dynamic model was established using the finite element method (FEM) and the multi-body system (MBS) approach, in which the flexibilities of the wheelset and track are taken into account. The proposed dynamic model is validated by the comparisons of field measurement and calculated vertical axle-box acceleration in time and frequency domains. The effects of the flexible wheelset in the presence of polygonal wear on the vehicle-track dynamic interaction at the BRJs are illustrated through comparisons with those obtained using without polygonal wheel model. The results show that the polygonal wheel wear and the rail joint irregularities can induce high-magnitude vertical wheel-rail contact force, and exacerbate the vibration responses of the axle box, the wheelset, and the rails. The simulation results also indicate that the wheelset bending modes, the P2 resonance due to rail joint excitation, and the track vibration modes have significant effects on the vertical vehicle-track dynamic interaction at the supported and suspended BRJs.

Zero Bias Operation: Photodetection Behaviors Obtained by Emerging Materials and Device Structures.

Zero-biased photodetectors have desirable characteristics for potentially next-generation devices, including high efficiency, rapid response, and low power operation. In particular, the detector efficiency can be improved simply by changing the electrode contact geometry or morphological structure of materials, which give unique properties such as energy band bending, photo absorbance and electric field distribution. In addition, several combinations of materials enable or disable the operation of selective wavelengths of light detection. Herein, such recent progresses in photodetector operating at zero-bias voltage are reviewed. Considering the advantages and promises of these low-power photodetectors, this review introduces various zero-bias implementations and reviews the key points.

Dynamische Systeme

This workshop continued a biannual series of workshops at Oberwolfach on dynamical systems that started with a meeting organized by Moser and Zehnder in 1981. Workshops in this series focus on new results and developments in dynamical systems and related areas of mathematics, with symplectic geometry playing an important role in recent years in connection with Hamiltonian dynamics. In this year special emphasis was placed on various kinds of spectra (in contact geometry, in Riemannian geometry, in dynamical systems and in symplectic topology) and their applications to dynamics.

Fast and Stable Iterative Algorithm for Searching Wheel–Rail Contact Point Based on Geometry Constraint Equations

Abstract This paper proposes a fast and stable iterative algorithm for wheel–rail contact geometry based on constraint equations, which can be implemented in dynamic wear simulations that real-time profile updating is needed. Further, critical factors that determine convergence and iteration stability are analyzed. A B-spline is adopted for wheel–rail profile modeling because it does not contribute to changes in the global shape of curves. It is found that the smoothness of the first and second derivative curves significantly affects the numerical stability of the Jacobian matrix, which determines the increments in iterations. Moreover, a damped Newton's iteration formula with a scaling factor of 0.5 is proposed considering the convergence rate and out-of-bound issues for the updated step. The influence of the initial iteration parameters on the convergence is studied using Newton fractals. The range within ±3 mm, centered on the target contact point, is found to be an unconditionally stable domain. The proposed method could achieve convergence within 10 and 30 steps under thread and flange contact conditions, respectively.

On roughness attenuation in elastohydrodynamic lubricated line and circular contacts

The commonly accepted “roughness attenuation” theory offers a description of the deformation of surface features as they travel through elastohydrodynamic lubricated contacts, based on the Boussinesq half-space approximation. Through a finite element model, incorporating surface features into the contact geometry (which cannot be done with the half-space approach), this work reveals three shortcomings in the theory. First, contact pressures are assumed normal to the substrate rather than the surface features lying on it. Second, it uses reduced solid properties that are invalid in the presence of surface features. Third, it does not account for the deformation of the features themselves. A correction procedure is devised, allowing for the theory to be rectified, without the need to incorporate surface features into the contact geometry, which can be computationally prohibitive.

2D InSe Self‐Powered Schottky Photodetector with the Same Metal in Asymmetric Contacts

AbstractSelf‐powered photodetectors (SPPDs) are generally carried out in multilayered heterostructures with different semiconductors or in Schottky junctions with different metal electrodes. It is interesting to build an SPPD using metal–semiconductor–metal (MSM) structures with the same type of metal electrodes. Here, an SPPD is fabricated facilely by stacking a piece of irregular InSe nanosheet on a pair of Au electrodes with asymmetric van der Waals contacts. The SPPD performs a high responsivity of 0.103 A W−1, a high on‐off current ratio over 104, a high detectivity of 1.83 × 1010 Jones, a fast response time of 1 ms and a broadband sensing spectrum ranging from 300 to 1000 nm under zero bias. A series of characterization and working mechanism analysis demonstrate the contribution of the asymmetric Schottky barrier heights and contact geometries in Au–InSe junctions to the self‐powered performance of the detector. This work offers an effective scheme to construct high‐performance SPPDs in simple architecture and processing for potential optoelectronic device applications.

Structural, Theoretical Analysis, and Molecular Docking of Two Benzamide Isomers. Halogen Bonding and Its Role in the Diverse Ways of Coupling with Protein Residues.

The crystal structures of two methoxyphenylbenzamide isomers are described, (Ph2Br) and (Ph3Br), with the general formula C14H12BrNO2. This structural study revealed the presence of N-H-O and C-H-O hydrogen bonds, Br-Br halogen bonds, C-H-π, and C-Br-π molecular contacts, showing in both compounds, a central C1-C7(O1)-N1(H1)-C8 amide segment, to be almost linear. The close proximity between the Br1 and O1 in Ph2Br showed that its interatomic distance was less than the sum of their VDW radii, generating an increase in the electrostatic potential in the O1 region, making possible the appearance of the so-called σ and π-holes on bromine. These specific conditions give rise to the formation of the Br-Br halogens bonds, which are united in a very interesting way, allowing the bond to extend by joining halogen atoms between different molecules forming an isosceles triangle with Br-Br distances equal to 3.5403(4) Å and 5.085 Å as its base. The presence of the carbonyl group in Ph2Br, an excellent acceptor of hydrogen and halogen bonds, led to competition between these bonds to organize crystal growth. The analysis of the compounds as pharmacophores showed that the bromine atom plays a key role in interactions with protein residues, reaching good ligand-protein interaction values comparable to the values presented by the parent inhibitor, Asciminib. In contact with the ALA356 residue, the bromine of Ph2Br participates with a higher contact geometry using the σ-hole, whereas the bromine of Ph3Br employs a more efficient contact geometry by taking advantage of its π-hole.

A review on foot-ground contact modeling strategies for human motion analysis

• Foot-ground contact modeling strategies for human motion analysis were reviewed. • A total of 30 contact models were included in this review. • Most studies used points, circles and 3D scanning to define the contact geometry. • Over 75% of studies used contact force approaches for foot-ground interaction. This review discusses the methodologies available in the literature, usually utilized to study the foot-ground interaction in the human locomotion. For this purpose, PubMed, Web of Science and Scopus databases were considered to identify publications focusing on foot-ground contact modeling strategies. As the consequence of a critical reading of those publications, some additional papers were identified and included in the present review. A total of 30 papers were analyzed, in which different contact geometries were established with the goal of defining the foot and ground surfaces. The most common geometries were based on points, circles, ellipses, spheres, ellipsoids, rectangular contact elements and surfaces obtained from 3D scanning procedures. Regarding the resolution of the foot-ground interaction, the formulations based on contact force approaches were preferred to the methods based on geometrical constraints. Several studies considered both computational and experimental approaches. One of the main limitations reported in the analyzed papers dealt with the restriction of the motion to the sagittal plane. It was observed that a standard and general procedure to formulate the human foot-ground contact is still lacking.

A geometric approach to contact Hamiltonians and contact Hamilton–Jacobi theory

We propose a novel approach to contact Hamiltonian mechanics which, in contrast to the one dominating in the literature, serves also for non-trivial contact structures. In this approach Hamiltonians are no longer functions on the contact manifold M itself but sections of a line bundle over M or, equivalently, 1-homogeneous functions on a certain -principal bundle , which is equipped with a homogeneous symplectic form ω. In other words, our understanding of contact geometry is that it is not an ‘odd-dimensional cousin’ of symplectic geometry but rather a part of the latter, namely ‘homogeneous symplectic geometry’. This understanding of contact structures is much simpler than the traditional one and very effective in applications, reducing the contact Hamiltonian formalism to the standard symplectic picture. We develop in this language contact Hamiltonian mechanics in the autonomous, as well as the time-dependent case, and the corresponding Hamilton–Jacobi theory. Fundamental examples are based on canonical contact structures on the first jet bundles of sections of line bundles L, which play in contact geometry a fundamental rôle, similar to that played by cotangent bundles in symplectic geometry.

Switching in Nanoscale Molecular Junctions due to Contact Reconfiguration

Switching effects are key elements in the design and characterization of nanoscale molecular electronics systems. They are used to achieve functionality through the transition between different conducting states. In this study, we analyze the presence of switching events in reference molecular systems, which are not designed to have switching behavior, such as oligo(phenylene ethynylene)s and alkanes, using the mechanically controllable break junction technique. These events can be classified in two groups, depending on whether the breaking trace shows exponential decay or plateau-like features before the switch happens. We argue that the former correspond to junctions forming after rupture of the gold atomic point contact, while the latter can be related to a change in the contact geometry of the junction. These results highlight how a proper choice of anchoring group and careful comparison with reference compounds are essential to understanding the origin of switching in molecular break junctions.

Results of cone and piston pull-out tests for evaluation of clay-soil adhesion

Adhesion between metal surfaces and soil can have significant effects on soil-tool interaction. The cone pull-out test (CPT) and piston pull-out test (PPT) for adhesion assessment were used in this study on smectite, illite and kaolinite clays at different water contents. In the CPT, the tangential adhesion stress (TAS) and cone adhesion (CA) were measured. In the PPT, the normal adhesion stress (NAS) and piston adhesion (PA) were measured. The results showed that the NAS and TAS depended on the type of clay. The ratios of NAS to TAS for smectite and kaolinite had the largest and smallest values, respectively. For all three types, NAS and TAS decreased as the water content (W) decreased. An increase in the thickness of the water film at the soil-metal contact surface reduced the stress required to separate the metal from the soil. The relationship between CA-W and PA-W for the three clay types differed. For smectite, a change in water content had no effect on CA or PA. For illite, an increase in water content decreased the CA and PA. For kaolinite, a bell-shaped curve formed such that, as water content increased, where W<liquid limit (LL), CA and PA increased and, where W>LL, CA and PA decreased. For all three clay soil types, NAS and PA were higher than TAS and CA at a specific water content. This demonstrated the effect of the metal-to-soil contact geometry on the adhesion parameters. The NAS and TAS values were classified in terms of clogging potential. Clogging potential is the adhesion of soil to the cutting tools or conveying system. The selection of the use of the CPT or PPT for adhesion assessment depended on the phenomenon being studied.

A three-dimensional model to describe complete human corneal oxygenation during contact lens wear.

We perform a novel 3D study to quantify the corneal oxygen consumption and diffusion in each part of the cornea with different contact lens materials. The oxygen profile is calculated as a function of oxygen tension at the cornea-tear interface and the oxygen transmissibility of the lens, with values used in previous studies. We aim to determine the influence of a detailed geometry of the cornea in their modeling compared to previous low dimensional models used in the literature. To this end, a 3-D study based on an axisymmetric volume element analysis model was applied to different contact lenses currently on the market. We have obtained that the model provides a valuable tool for understanding the flux and cornea oxygen profiles through the epithelium, stroma, and endothelium. The most important results are related to the dependence of the oxygen flux through the cornea-lens system on the contact lens thickness and geometry. Both parameters play an important role in the corneal flux and oxygen tension distribution. The decline in oxygen consumption experienced by the cornea takes place just inside the epithelium, where the oxygen tension falls to between 95 and 16 mmHg under open eye conditions, and 30 to 0.3 mmHg under closed eye conditions, depending on the contact lens worn. This helps to understand the physiological response of the corneal tissue under conditions of daily and overnight contact lens wear, and the importance of detailed geometry of the cornea in the modeling of diffusion for oxygen and other species.

Selective control of conductance modes in multi-terminal Josephson junctions

The Andreev bound state spectra of multi-terminal Josephson junctions form an artificial band structure, which is predicted to host tunable topological phases under certain conditions. However, the number of conductance modes between the terminals of a multi-terminal Josephson junction must be few in order for this spectrum to be experimentally accessible. In this work, we employ a quantum point contact geometry in three-terminal Josephson devices to demonstrate independent control of conductance modes between each pair of terminals and access to the single-mode regime coexistent with the presence of superconducting coupling. These results establish a full platform on which to realize tunable Andreev bound state spectra in multi-terminal Josephson junctions.

Hamiltonian perturbations in contact Floer homology

We study the contact Floer homology \(\mathrm{HF}_*(W, h)\) introduced by Merry–Uljarević in [21], which associates a Floer-type homology theory with a Liouville domain W and a contact Hamiltonian h on its boundary. The main results investigate the behavior of \(\mathrm{HF}_*(W, h)\) under the perturbations of the input contact Hamiltonian h. In particular, we provide sufficient conditions that guarantee \(\mathrm{HF}_*(W, h)\) to be invariant under the perturbations. This can be regarded as a contact geometry analog of the continuation and bifurcation maps along the Hamiltonian perturbations of Hamiltonian Floer homology in symplectic geometry. As an application, we give an algebraic proof of a rigidity result concerning the positive loops of contactomorphisms for a wide class of contact manifolds.