Sticking Time Research Articles

Explicit frictional stick–slip dynamics of elastic contact problem incorporating the LuGre model

Dynamical contact problem with friction is of continuous concern and have been investigated over the years. The effective and accurate description of the development of the friction force is the key to this problem. However, the stick–slip phenomenon, as typical dynamical behaviour, has rarely been considered when developing contact algorithms for frictional contact problems of elastic bodies. The conventionally used Coulomb’s model, with differentiating the static and kinetic coefficient of friction, can lead to inaccurate results due to errors generated when switch between the stick or slip states. In this work, a three-dimensional mortar-based frictional contact algorithm is proposed in an explicit scheme. The proposed algorithm incorporates the LuGre model to account for dynamical frictional behaviours such as stick–slip. The effectiveness and accuracy of the proposed algorithm are validated through several simplified two-dimensional cases. The sticking time ratio and the evolution of the global coefficient of friction with time of a three-dimensional contact problem with a randomly rough contact interface are investigated as an application.

Sticky islands in stochastic webs and anomalous chaotic cross-field particle transport by E×B electron drift instability

The ExB electron drift instability, present in many plasma devices, is an important agent in cross-field particle transport. In presence of a resulting low frequency electrostatic wave, the motion of a charged particle becomes chaotic and generates a stochastic web in phase space. We define a scaling exponent to characterise transport in phase space and we show that the transport is anomalous, of super-diffusive type. Given the values of the model parameters, the trajectories stick to different kinds of islands in phase space, and their different sticking time power-law statistics generate successive regimes of the super-diffusive transport.

Experimental Design, Instrumentation, and Testing of a Laboratory-Scale Test Rig for Torsional Vibrations—The Next Generation

Drilling technology and specially drilling equipment has dramatically changed in the last 10 years through intensive and innovative technologies, both in terms of hardware and software. While engineers are focusing on safer, faster, and more reliable than ever technologies, big data and automation are currently considered the way forward to achieve these goals. Especially when automation concepts are proposed, the prior testing and qualification under a laboratory-controlled environment are mandatory. Drilling simulators have been hugely successful in training industry personnel and academic professionals. A big reason for its success lies in the seamless integration of hardware and software to include an interactive user interface. Physical experimental simulators have the advantage of exposing the user with visual and auditive aids to better understand the real process. This paper provides an insight into the construction and results obtained using a dedicated laboratory setup, which is also configured to various levels of automation. The setup is capable of safely recreating drilling vibrations that occur in wells, including stick-slip vibrations, which are detrimental in nature. With advanced sensor capabilities, the impact of proper sampling rates on the diagnosis of stick-slip vibrations has been analyzed in the paper. The results show that these vibrations are not only dependent on drilling parameters, such as rotational speed (RPM), torque, and weight on bit, but also on stick-slip parameters, such as bit sticking time period and frequency.

Quasiclassical method for calculating the density of states of ultracold collision complexes

We derive a quasiclassical expression for the density of states (DOS) of an arbitrary, ultracold, $N$-atom collision complex, for a general potential energy surface (PES). We establish the accuracy of our quasiclassical method by comparing to exact quantum results for the K$_2$-Rb and NaK-NaK systems, with isotropic model PESs. Next, we calculate the DOS for an accurate NaK-NaK PES to be 0.124~$\mu$K$^{-1}$, with an associated Rice-Ramsperger-Kassel-Marcus (RRKM) sticking time of 6.0~$\mu$s. We extrapolate the DOS and sticking times to all other polar bialkali-bialkali collision complexes by scaling with atomic masses, equilibrium bond lengths, dissociation energies, and dispersion coefficients. The sticking times calculated here are two to three orders of magnitude shorter than those reported by Mayle et al. [Phys. Rev. A 85, 062712 (2012)]. We estimate dispersion coefficients and collision rates between molecules and complexes. We find that the sticking-amplified three-body loss mechanism is not likely the cause of the losses observed in the experiments.

Nuclear Spin Relaxation, Conversion, and Polarization of Molecular Hydrogen in Paramagnetic Solvents

Recent NMR experiments have measured the conversion rate of hydrogen molecules dissolved in paramagnetic organic solvents. The registered proton signals display negative peaks during an initial period. The present interpretation describes a polarization effect: the transient behavior of the nuclear spins directed on the average along the magnetic electronic spins. It relies on a nonequilibrium ortho drift and gives access to numerous parameter functions of the sample magnetic concentration. The most important ones are related to the negative transient nuclear magnetization: its building, maximum, and lifetime. Important ratios are deduced: conversion versus relaxation characteristic times and collision versus sticking time intervals. The contact interaction is found to be stronger than the long-range and fluctuating dipolar one for magnetically concentrated samples during the short sticking of the colliding partners but weaker for diluted ones. Some information on the viscosity of the organic solvent is d...

Modified Intravital Microscopy to Assess Vascular Health and T-Cell Motility.

The ability to study the microcirculation in real time is key to elucidating how the immune system and the associated microvasculature interact and influence one another within the lymph node (LN). Here, we present a method for near in-situ imaging of the inguinal LN. In particular, this method is ideal for the assessment of overall vascular health that influences immune functions and for the evaluation of T-cell motility. We focus on imaging of the microvasculature of the LN, paying particular attention to methods that ensure the study of healthy vessels, the ability to maintain imaging of viable vessels over a number of hours, quantification of vessel magnitude and vessel integrity. Modified intravital microscopy (M-IVM) of the LNs allows direct evaluation of microvascular functions as well as real-time imaging of the direct interface between immune cells, the LN, and the microcirculation. Importantly, M-IVM technique can be readily combined with many other vascular and immunological techniques such as fluorescent cell labeling and assessment of sticking and rolling time as descripted. Furthermore, it can be adapted to study vasculature of other than the inguinal LN. Overall, this chapter provides a dependable method for fundamental vascular immunological assessment of LNs that is decidedly useful in a diverse range of investigations.

Study on viscoelastic friction and wear between friction linings and wire rope

The purpose of this paper is to establish the relationship between dynamic viscoelastic friction and wear. Friction and wear mechanisms were analysed by dynamically monitoring the viscoelastic slippage and temperature of the friction interface. The results show that the friction coefficient was positively correlated with the loss factor. Friction and wear both decreased with the increase of the interfacial friction temperature. The wear increased exponentially with the increase of the loss factor. Friction and wear properties of three types of friction linings were compared; the loss factor of K25 lining was the largest (0.21); the sticking time of the K25 lining was the longest (0.27 s), and its friction coefficient was the largest (0.67) in the early stage of the friction experiment. As the friction experiment progressed, the temperature of the interface increased. The loss factor and the friction coefficient decreased noticeably with the increase of temperature. This resulted in less friction, less surface damage and fewer cracks and debris. The wear of the K25 lining was the smallest (0.32 g).

Fusion and quasifission studies for the Ca40+W186,Os192 reactions

Background: All elements above atomic number 113 have been synthesized using hot fusion reactions with calcium beams on statically deformed actinide target nuclei. Quasifission and fusion-fission are the two major mechanisms responsible for the very low production cross sections of superheavy elements.Purpose: To achieve a quantitative measurement of capture and quasifission characteristics as a function of beam energy in reactions forming heavy compound systems using calcium beams as projectiles.Methods: Fission fragment mass-angle distributions were measured for the two reactions $^{40}\mathrm{Ca}+^{186}\mathrm{W}$ and $^{40}\mathrm{C}+^{192}\mathrm{Os}$, populating $^{226}\mathrm{Pu}$ and $^{232}\mathrm{Cm}$ compound nuclei, respectively, using the Heavy Ion Accelerator Facility and CUBE spectrometer at the Australian National University. Mass ratio distributions, angular distributions, and total fission cross sections were obtained from the experimental data. Simulations to match the features of the experimental mass-angle distributions were performed using a classical phenomenological approach.Results: Both $^{40}\mathrm{Ca}+^{186}\mathrm{W}$ and $^{40}\mathrm{C}+^{192}\mathrm{Os}$ reactions show strong mass-angle correlations at all energies measured. A maximum fusion probability of $60\ensuremath{-}70%$ is estimated for the two reactions in the energy range of the present study. Coupled-channels calculations assuming standard Woods-Saxon potential parameters overpredict the capture cross sections. Large nuclear potential diffuseness parameters $\ensuremath{\sim}1.5$ fm are required to fit the total capture cross sections. The presence of a weak mass-asymmetric quasifission component attributed to the higher angular momentum events can be reproduced with a shorter average sticking time but longer mass-equilibration time constant.Conclusions: The deduced above-barrier capture cross sections suggest that the dissipative processes are already occurring outside the capture barrier. The mass-angle correlations indicate that a compact shape is not achieved for deformation aligned collisions with lower capture barriers. The average sticking time of fast quasifission events is ${10}^{\ensuremath{-}20}$ s.

Numerical modelling of the sticking process of a S. aureus bacterium

The investigation of the dynamics of a single bacterium may help to understand the behaviour of a system of bacteria (e.g. biofilm formation) as well as the transmission of infections in the air. One of the important factors influencing the stability of a bacterial structure but also important in the context of an infection is the adhesion force.In order to model the sticking process over time, two theoretical models for bacteria are presented. These models allow to simulate the sticking process numerically. As the model complexity, may affect the calculation time, in this paper we derive two theoretical models of different complexity. One is a simple, adhesive viscous elastic, the other a more complex adhesive viscous elastic-plastic model. Both models can be applied to the simulation of the dynamics of bacteria. Thereby forces act when the bacterium is at a distance to a surface as well as during its contact. The attractive force is described by the van der Waals force by applying an adhesive-dissipative model. For the description of the bacterium within a liquid medium electrostatic double-layer and steric force models are additionally considered. In the attractive-dissipative sticking process viscous damping forces were considered, which results in the theoretically expected load-unload behaviour. The sticking process of a bacterium on a substrate is solved by applying the discrete element method.The bacterium addressed is S. aureus; while as substrate glass is considered. The parameters needed for the numerical simulation of this bacterium are taken from published physical experiments performed with atomic force measurements. Detailed results on the sticking process of the bacterium are presented. A characterisation of the influence of repulsive and attractive forces on the bacterium is given. Obtained results are shown in terms of force displacement diagrams as well as a function of the sticking time history.

Exploring quasifission characteristics forS34+Th232formingSg266

Background: Fission fragments from heavy ion collisions with actinide nuclei show mass-asymmetric and mass-symmetric components. The relative probabilities of these two components vary rapidly with beam energy with respect to the capture barrier, indicating a strong dependence on the alignment of the deformed nucleus with the partner in the collisions.Purpose: To study the characteristics of the mass-asymmetric quasifission component by reproducing the experimental mass-angle distributions to investigate mass evolution and sticking times.Methods: Fission fragment mass-angle distributions were measured for the $^{34}\text{S}+^{232}\text{Th}$ reaction. Simulations to match the measurements were made by using a classical phenomenological approach. Mass ratio distributions and angular distributions of the mass-asymmetric quasifission component were simultaneously fit to constrain the free parameters used in the simulation.Results: The mass-asymmetric quasifission component---predominantly originating from tip (axial) collisions with the prolate deformed $^{232}\text{Th}$---is found to be peaked near $A=200$ at all energies and center-of-mass angles. A Monte Carlo model using the standard mass equilibration time constant of $5.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}$ s predicts more symmetric mass splits. Three different hypotheses assuming (i) a mass halt at $A=200$, (ii) a slower mass equilibration time, or (iii) a Fermi-type mass drift function reproduced the main experimental features.Conclusions: In tip collisions for the $^{34}\text{S}+^{232}\text{Th}$ reaction, mass-asymmetric fission with $A\ensuremath{\sim}200$ is the dominant outcome. The average sticking time is found to be $\ensuremath{\sim}7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}$ s, independent of the scenario used for mass evolution.

Fission fragment mass and angular distributions: Probes to study non-equilibrium fission

Synthesis of heavy and superheavy elements is severely hindered by fission and fission-like processes. The probability of these fission-like, non-equilibrium processes strongly depends on the entrance channel parameters. This article attempts to summarize the recent experimental findings and classify the signatures of these non-equilibrium processes based on macroscopic variables. The importance of the sticking time of the dinuclear complex with respect to the equilibration times of various degrees of freedom is emphasized.

Accurate measurement of the sticking time and sticking probability of Rb atoms on a polydimethylsiloxane coating

We present the results of a systematic study of Knudsen’s flow of Rb atoms in cylindrical capillary cells coated with a polydimethylsiloxane (PDMS) compound. The purpose of the investigation is to determine the characterization of the coating in terms of the sticking probability and sticking time of Rb on the two types of coating of high and medium viscosities. We report the measurement of the sticking probability of a Rb atom to the coating equal to 4.3 × 10−5, which corresponds to the number of bounces 2.3 × 104 at room temperature. These parameters are the same for the two kinds of PDMS used. We find that at room temperature, the respective sticking times for high-viscosity and medium-viscosity PDMS are 22 ± 3 μs and 49 ± 6 μs. These sticking times are about million times larger than the sticking time derived from the surface Rb atom adsorption energy and temperature of the coating. A tentative explanation of this surprising result is proposed based on the bulk diffusion of the atoms that collide with the surface and penetrate inside the coating. The results can be important in many resonance cell experiments, such as the efficient magnetooptical trapping of rare elements or radioactive isotopes and in experiments on the light-induced drift effect.

Severe slowing-down and universality of the dynamics in disordered interacting many-body systems: ageing and ultraslow diffusion

Low-dimensional, many-body systems are often characterized by ultraslow dynamics. We study a labelled particle in a generic system of identical particles with hard-core interactions in a strongly disordered environment. The disorder is manifested through intermittent motion with scale-free sticking times at the single particle level. While for a non-interacting particle we find anomalous diffusion of the power-law form of the mean squared displacement with , we demonstrate here that the combination of the disordered environment with the many-body interactions leads to an ultraslow, logarithmic dynamics with a universal exponent. Even when a characteristic sticking time exists but the fluctuations of sticking times diverge we observe the mean squared displacement with , that is slower than the famed Harris law without disorder. We rationalize the results in terms of a subordination to a counting process, in which each transition is dominated by the forward waiting time of an ageing continuous time process.

Effects of Electron Impact on Ionization of Short-Lived Isotopes in a Hot Cavity

A Monte Carlo method based numerical model of hot cavity surface ion source that takes into account radioactive decay and the delay due to the sticking of particles to ionizer surface is considered. The in uence of electron impact ionization by thermionic electrons accelerated by the extraction eld is investigated. It is shown that the contribution from that process rises with decreasing half-life period and cannot be neglected, especially for substances of small surface ionization coe cient. The changes of relative yields from electron impact and surface processes with the length of the average sticking time are also studied.

Surface Ionization of Radioactive Nuclides - Numerical Simulations

The Monte Carlo method based model of the ionization in the hot cavity taking into account radioactive decay of nuclides is presented. The code upgraded compared to the previous version enables calculation of the ion source ionization e ciency not only for di erent geometries and temperatures of the ionizer, extraction voltages etc. but also gives opportunity of setting di erent values of the nuclide half-life and its sticking time, which may be considered as the main factor determining the time that a particle spends in the ion source. The results of calculations are presented together with the discussion of the radioactive decay on the ion source performance.

A comparative study of influence of fluidized conditions on sticking time during reduction of Fe2O3 particles with CO

The Fe2O3 particles were reduced with CO in a fluidized bed and the sticking time as a process parameter was defined based on the pressure drop to describe the sticking. Influences of fluidized conditions (CO concentration, reduction potential, gas velocity and temperature) on the sticking time were compared. The order is temperature>CO concentration>reduction potential>gas velocity. On account of increasing iron–iron contact area when particles collided together, which resulted from increase of the metallization ratio and the specific surface area of particles, the sticking time decreased with increasing CO concentration and reduction potential. On the other hand, the sticking time increased with gas velocity for enhancing momentum of particles. Due to increase of the surface energy of precipitated iron, as a dominant source of driving force for sticking, the sticking time decreased with increasing temperature.

Improvement of Display Performance for PSVA-LCD Based on Novel RM Monomer with Short Alkyl Spacer

We proposed a novel UV curable reactive mesogen monomer for VA-LCD with Polymer-Sustained (Stabilized) Vertical Alignment (PSVA) which shows a high display performance. The experimental results reveal that the PSVA by the novel-monomer realizes less image sticking and better response time.

Light-induced atomic desorption and diffusion of Rb from porous alumina

We present a study of light-induced atom desorption (LIAD) of an alkali-metal atom (Rb) in porous alumina. We observe the variation due to LIAD of the rubidium density in a vapor cell as a function of illumination time, intensity, and wavelength. The simple and regular structure of the alumina pores allows a description of the atomic diffusion in the porous medium in which the diffusion constant only depends on the known pore geometry and the atomic sticking time to the pore wall. A simple one-dimensional theoretical model is presented which reproduces the essential features of the observed signals. Fitting of the model to the experimental data gives access to the diffusion constant and consequently the atom-wall sticking time and its dependence on light intensity and wavelength. The nonmonotonic dependence of the LIAD yield on the illumination light frequency is indicative of the existence of Rb clusters in the porous medium.

Calculation of electron-positron production in supercritical uranium-uranium collisions near the Coulomb barrier

The time-dependent Dirac equation was solved for zero-impact-parameter bare U-U collisions in the monopole approximation using a mapped Fourier grid matrix representation. A total of 2048 states including bound, as well as positive- and negative-energy states for an $N=1024$ spatial grid were propagated to generate occupation amplitudes as a function of internuclear separation. From these amplitudes spectra were calculated for total inclusive positron and electron production, and also the correlated spectra for $({e}^{+},{e}^{\ensuremath{-}})$ pair production. These were analyzed as a function of nuclear sticking time in order to establish signatures of spontaneous pair creation, i.e., QED vacuum decay. Subcritical Fr-Fr and highly supercritical Db-Db collisions both at the Coulomb barrier were also studied and contrasted with the U-U results.

Oxidation of aluminum studied by secondary electron emission

The electron emission yield is measured for impact of 3 keV electrons on polycrystalline aluminum, which is exposed to oxygen. At different oxygen gas pressures the yield is measured as a function of time. The oxygen pressure is in the range between 2×10 −9 and 3×10 −6 mbar. It is found that the yield depends not only on oxygen exposure but also on the oxygen pressure. In the begin of oxygen exposure the yield decreases due to chemisorption of oxygen, but then the yield increases due to oxide formation. A model based on rate equations with adjustable parameters is proposed, which describes the oxidation process and electron emission yield. The parameters are fitted to give best agreement with the measured yield curves. The parameters include sticking coefficients and time constants of oxidation. Whenever possible, evaluated parameters were compared with published data and reasonable agreement is found.