Effects Of Contact Interactions Research Articles

Normal contact stress analysis of large-deflection compliant mechanisms using a CPRBM-based method

The contact interaction between compliant mechanisms and external objects is a common occurrence in the field of grasping and manipulation. However, accurately modeling the large deformation and contact force/stress remains a challenging task. This paper presents a contact analysis method to evaluate the deformation and normal contact force/stress of compliant mechanisms with general-shape beams. The general beams are modeled by using the chained pseudo-rigid-body model (CPRBM). On basis of CPRBM framework, linear and distributed contact springs are introduced at the interface to represent the contact force. A numerical method is established to fast calculate the boundary penetrations, and a contact stiffness formulation is proposed based on the theory of elasticity. Then, the effect of contact interaction can be evaluated by the contact potential energy of contact springs, which is part of the system’s total potential energy. By minimizing the potential energy function of the compliant system, the static equilibrium configuration and contact force/stress can be obtained easily. Numerical examples are used to verify the feasibility and accuracy of the proposed method.

Dispersion forces and equilibrium distance between deposited rough films in contact

The average distance ${h}_{0}$ separating two contacting bodies is a critical parameter for many problems, for example, for control of unwanted stiction in micro/nanoelectromechanical systems. Here this problem is analyzed in relation to precise determination of the dispersion forces in a difficult for measurement range of $5\ensuremath{-}30\phantom{\rule{0.222222em}{0ex}}\mathrm{nm}$. The unloaded contact between two deposited rough films characterized by a relatively large number of high asperities is considered. The equilibrium distance ${h}_{0}$ can be found from the balance of attractive dispersion forces and repulsive forces acting in the spots of real contact. A simple columnar model associated with AFM images of rough surfaces is used to describe the balance. The numerical analysis, which treats the high asperities as elastoplastic semispheroids, demonstrates that the columnar model describes the contact adequately. It is shown that in contrast with the value of ${h}_{0}$ the adhesion energy between the surfaces is nearly entirely defined by the dispersion interaction, but the effects of contact interaction and plastic deformations can be neglected. This property is proposed to use for more precise determination of the equilibrium distance.

Weak adhesion between deposited rough films: Relation to dispersion forces

Although the contact theory between rough surfaces is designed for adhesion energies $\ensuremath{\gtrsim}100\phantom{\rule{4pt}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$, microsystems are controlled by much weaker adhesion $\ensuremath{\lesssim}100\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{J}/{\mathrm{m}}^{2}$, which is critical for their operation. The weakest adhesion is related to the omnipresent fluctuation-induced dispersion forces. We develop a theory for such a weak adhesion emphasizing that the adhesion energy as a function of the average distance separating the bodies is almost entirely defined by the dispersion interaction. This dependence can be evaluated using the Lifshitz theory, but the effects of contact interaction or plastic deformations give only small contribution to the adhesion. Such a behavior is explained by a specific roughness of the deposited thin films used in microtechnologies. The films deposited on cold substrates have a much larger number of high asperities than is predicted by the Gaussian distribution and the contact occurs over a few asperities with heights much larger than the root-mean-square roughness. Finally, we discuss application of the effect for more precise determination of the distance upon contact, which is crucial for precise measurements of the dispersion forces especially at short separations in the range $5<h<50\phantom{\rule{4pt}{0ex}}\mathrm{nm}$.

Simulation of the seismic-stability problem for buried constructions

A procedure for the numerical simulation of seismic effects on a buried construction on a transversely isotropic multilayer base is proposed subject to the effects of contact interactions and the gravity field with an accelerogram at the day surface. The effects of the location of the earthquake hypocenter on the horizontal and vertical displacements of construction walls and the adjacent ground are estimated. The great significance of the consideration of the mechanical characteristics of the ground depending on the depth and the gravity field is shown for loose bases.

Fragility of the fractional quantum spin Hall effect in quantum gases

We consider the effect of contact interaction in a prototypical quantum spin Hall system of pseudo-spin-1/2 particles. A strong effective magnetic field with opposite directions for the two spin states restricts two-dimensional particle motion to the lowest Landau level. While interaction between same-spin particles leads to incompressible correlated states at fractional filling factors as known from the fractional quantum Hall effect, these states are destabilized by interactions between opposite spin particles. Exact results for two particles with opposite spin reveal a quasi-continuous spectrum of extended states with a large density of states at low energy. This has implications for the prospects of realizing the fractional quantum spin Hall effect in electronic or ultra-cold atom systems. Numerical diagonalization is used to extend the two-particle results to many bosonic particles and trapped systems. The interplay between an external trapping potential and spin-dependent interactions is shown to open up new possibilities for engineering exotic correlated many-particle states with ultra-cold atoms.

Experimental modelling of mechanisms causing occurrence of seismic oscillation sources in case of interactions of uneven surfaces in faults

Field experiments were carried out using TRIBO, a specially designed testing stand including a concrete plate that can be moved at different rates. In our experiment, the plate served as an artificial allochtonous wing placed at the uneven surface of the segment of the Angarsky fault in Pribaikalie. Tribological effects of contact interaction of the uneven surfaces in the zone of sliding movements of the plate were recorded by strain gauges, linear displacement gauges and four Baikal-7HR seismic stations; such stations are commonly used for earthquake recording. The effect of shocks in initiation of seismic oscillation sources was studied with changes of the regimes of destruction of the uneven surfaces (underneath the base of the plate) which differ in size and strength. The study was focused on stages in the process of friction at preparation to transition from quasi-regular decelerated sliding movement of the plate to its breakaway and occurrence of a high-energy seismic impulse. The applied method of large-scale modelling at natural objects in field provides new data that may prove useful for stu­dies of mechanisms causing seismicity, identification of stages in occurrence of earthquakes in fault zones and interpretation of seismic monitoring data. Results of such physical tests can contribute to the development of methods aimed at forecasting of rock shocks and earthquakes and also for the development of new physical models showing formation of earthquake foci of various scales in tectonic faults.

Long-time behavior of many-particle quantum decay

While exponential decay is ubiquitous in Nature, deviations at both short and long times are dictated by quantum mechanics. Non-exponential decay is known to arise due to the possibility of reconstructing the initial state from the decaying products. We discuss the quantum decay dynamics by tunneling of a many-particle system, characterizing the long-time non-exponential behavior of the non-escape and survival probabilities. The effects of contact interactions and quantum statistics are described. It is found that whereas for non-interacting bosons the long-time decay follows a power-law with an exponent linear in the number of particles $\N$, the exponent becomes quadratic in $\N$ in the fermionic case. The same results apply to strongly interacting many-body systems related by the generalized Bose-Fermi duality. The faster fermionic decay can be traced back to the effective hard-core interactions between particles, which are as well the decaying products, and exhibit spatial anti-bunching which hinders the reconstruction of the initial unstable state. The results are illustrated with a paradigmatic model of quantum decay from a trap allowing leaks by tunneling, whose dynamics is described exactly by means of an expansion in resonant states.

Local cell metrics: a novel method for analysis of cell-cell interactions

BackgroundThe regulation of many cell functions is inherently linked to cell-cell contact interactions. However, effects of contact interactions among adherent cells can be difficult to detect with global summary statistics due to the localized nature and noise inherent to cell-cell interactions. The lack of informatics approaches specific for detecting cell-cell interactions is a limitation in the analysis of large sets of cell image data, including traditional and combinatorial or high-throughput studies. Here we introduce a novel histogram-based data analysis strategy, termed local cell metrics (LCMs), which addresses this shortcoming.ResultsThe new LCM method is demonstrated via a study of contact inhibition of proliferation of MC3T3-E1 osteoblasts. We describe how LCMs can be used to quantify the local environment of cells and how LCMs are decomposed mathematically into metrics specific to each cell type in a culture, e.g., differently-labelled cells in fluorescence imaging. Using this approach, a quantitative, probabilistic description of the contact inhibition effects in MC3T3-E1 cultures has been achieved. We also show how LCMs are related to the naïve Bayes model. Namely, LCMs are Bayes class-conditional probability functions, suggesting their use for data mining and classification.ConclusionLCMs are successful in robust detection of cell contact inhibition in situations where conventional global statistics fail to do so. The noise due to the random features of cell behavior was suppressed significantly as a result of the focus on local distances, providing sensitive detection of cell-cell contact effects. The methodology can be extended to any quantifiable feature that can be obtained from imaging of cell cultures or tissue samples, including optical, fluorescent, and confocal microscopy. This approach may prove useful in interpreting culture and histological data in fields where cell-cell interactions play a critical role in determining cell fate, e.g., cancer, developmental biology, and tissue regeneration.

Effect of Contact Interaction on the Stress Intensity Factors for a Crack under Harmonic Loading

This paper concerns fracture dynamic problems for elastic cracked solids with allowance for crack faces contact interaction. The contact problem for a penny-shaped crack with an initial opening under normally incident tension-compression wave is solved by the method of boundary integral equations. The solution is compared with those obtained without allowance for crack faces contact interaction for various values of the initial opening.

Transition form factors and probabilities of the semileptonic decays of B and D mesons within covariant light-front dynamics

Electroweak form factors for the decays of heavy B and D mesons are considered within the covariant formulation of light-front dynamics. With the aid of this approach, it is possible to separate the physical and unphysical contributions to the form factors. An analytic expression is obtained for gluon corrections to the electroweak vertex of the vector and the vector-axial quark current, and it is shown that, for constructing a quantitative description of available experimental data, it is important to take into account such corrections to the decay widths of heavy hadrons. The effect of contact interaction on the transition form factors is analyzed, and the importance of taking into account contact interaction for 0− → 1− transitions is demonstrated numerically. The elements |Vbc|, |Vbu|, |Vcs|, and |tVcd| of the Cabibbo-Kobayashi-Maskawa matrix are determined from an analysis of the entire body of data on 0− → 0− and 0− → 1− semileptonic decays. Within the experimental errors, the results obtained in this way are intrinsically consistent and comply with world-averaged data.

Effect of contact interactions on Higgs production at an e+e− collider

New interactions appearing at a scale $\Lambda$ larger than the weak interaction scale v can affect physical processes at energies below $\Lambda$ through non-renormalizable $SU(3)\times SU(2)\times U(1)_y$ invariant operators added to the standard model Lagrangian. In this article we investigate the effect of flavor conserving contact interactions on the total cross-section for the process $e^+e^-\to HZ$ at $\sqs =500$ Gev. We find that for $\Lambda\approx 2.5 $ Tev, which is consistent with LEP and SLD asymmetry measurements on Z peak as well as theoretical estimates, these operators can increase the total cross-section by a factor of 3 relative to the SM for intermediate mass higgs boson.

Effect of the contact of crack lips under variable loads

We formulate a contact problem of the theory of elasticity with unilateral constraints for cracked bodies under random variable loading and consider a special case of harmonic loads very important for practical applications. The problem is solved by the method of boundary integral equations of the elastodynamic theory of cracked bodies. We also analyze typical singularities of the kernels of potentials of these equations and develop an algorithm for the solution of unilateral contact problems of the dynamics of cracked bodies based on the determination of the saddle point of a subdifferential boundary functional. We solve dynamical problems of propagation of plane harmonic compression-dilatation waves in a plane with cracks of finite lengths under the assumption of unilateral contact of the crack lips. We present numerical results and investigate the effect of contact interaction of the crack lips both quantitatively and qualitatively.

Numerical modeling of the strength and longevity of structures with allowance for scale effect. Report 3. Investigation of the stress state, strength, and longevity of cylindrical-type high-pressure apparatus

The stress-strain state of one of the promising high-pressure apparatuses (HPA) after the assembly process and in the operating mode is investigated by the finite-element method. The stress state of plastically deformable container with a reactive mixture is calculated, and the effect of contact interaction and the elastoplastic deformations of equipment components is defined more precisely. The static and fatigue strengths of hard-alloy HPA components are estimated using previously developed criteria. The dependence of the strength and longevity of geometrically similar dies and punches on their effective volume is established. An interpretation of the most characteristic forms of HPA is given on the basis of computational results, and several means of improving their designs are indicated.

Test of compositeness: Zγ processes at the [formula omitted]p TeV colliders

Some exotic sources of the Zγ processes due to composite or technicolour particles are studied at Tevatron and SSC ( p p TeV colliders. We conclude that light composite spinless weak bosons having technicolour-type coupling to gluon-gluon or a weak universal coupling to fermion pairs should be seen at the Tevatron. The SSC should be a good place to see heavy composite bosons with higher spins (e.g., spin two) and to see the effects of contact interactions. The absence of the above signals will provide additional constraints on the spectra and underlying structure of models based on dynamical electroweak breaking.