Weak Friction Research Articles

Dynamical evolution of the Uranian satellite system I.: From the 5/3 Ariel–Umbriel mean motion resonance to the present

Mutual gravitational interactions between the five major Uranian satellites raise small quasi-periodic fluctuations on their orbital elements. At the same time, tidal interactions between the satellites and the planet induce a slow outward drift of the orbits, while damping the eccentricities and the inclinations. In this paper, we revisit the current and near past evolution of this system using a N−body integrator, including spin evolution and tidal dissipation with the weak friction model. We update the secular eigenmodes of the system and show that it is unlikely that any of the main satellites were recently captured into a high obliquity Cassini state. We rather expect that the Uranian satellites are in a low obliquity Cassini state and compute their values. We also estimate the current variations in the eccentricities and inclinations, and show that they are not fully damped. We constrain the modified quality factor of Uranus to be QU′=(1.2±0.4)×105, and that of Ariel to be QA′=(7±3)×104. We find that the system most likely encountered the 5/3 mean motion resonance between Ariel and Umbriel in the past, at about (0.7±0.2) Gyr ago. We additionally determine the eccentricities and inclinations of all satellites just after the resonance passage that comply with the current system. We finally show that, from the crossing of the 5/3 MMR to the present, the evolution of the system is mostly peaceful and dominated by tides raised on Uranus by the satellites.

Frictional mechanisms of hydrated montmorillonite under normal loading

The friction behavior of clay particles plays an essential role in controlling its mechanical properties, but remains unclear in microscale. As one of the major clay particles, the nanoscale friction properties of hydrated montmorillonite have been studied using steered molecular dynamics (SMD) simulation method, considering the coupling effect of water content of 0 ∼ 30 % and normal load of 1 atm ∼ 10 GPa. The SMD friction along the y-direction has been performed to investigate the frictional mechanism of hydrated montmorillonite and its structural properties of interlayer water. The evolution of average friction load with water content, friction coefficients, and the distribution of interlayer water molecules were obtained. Furthermore, the SMD pulling along the z-direction was conducted to study the effect of interlayer water molecules on the interaction between montmorillonite layers. All simulation results showed that more energy and a higher friction load were required to slide at a higher normal load. The friction coefficient of 0.058 ∼ 0.17 and internal friction angle of 3.3°∼9.6° for hydrated montmorillonite agreed well with previous studies in microscale, showing the weak friction properties. The evolution of friction coefficient with water content was different at different normal loads, where the friction coefficient of 5 % hydrated montmorillonite was the highest at 3 ∼ 10 GPa. Moreover, the increasing normal load could change the distribution of interlayer water molecules.

Quantifying the energy landscape in weakly and strongly disordered frictional media.

We investigate the "roughness" of the energy landscape of a system that diffuses in a heterogeneous medium with a random position-dependent friction coefficient α(x). This random friction acting on the system stems from spatial inhomogeneity in the surrounding medium and is modeled using the generalized Caldira-Leggett model. For a weakly disordered medium exhibiting a Gaussian random diffusivity D(x) = kBT/α(x) characterized by its average value ⟨D(x)⟩ and a pair-correlation function ⟨D(x1)D(x2)⟩, we find that the renormalized intrinsic diffusion coefficient is lower than the average one due to the fluctuations in diffusivity. The induced weak internal friction leads to increased roughness in the energy landscape. When applying this idea to diffusive motion in liquid water, the dissociation energy for a hydrogen bond gradually approaches experimental findings as fluctuation parameters increase. Conversely, for a strongly disordered medium (i.e., ultrafast-folding proteins), the energy landscape ranges from a few to a few kcal/mol, depending on the strength of the disorder. By fitting protein folding dynamics to the escape process from a metastable potential, the decreased escape rate conceptualizes the role of strong internal friction. Studying the energy landscape in complex systems is helpful because it has implications for the dynamics of biological, soft, and active matter systems.

Quantum-mechanical water-flow enhancement through a sub-nanometer carbon nanotube.

Experimental observations unambiguously reveal quasi-frictionless water flow through nanometer-scale carbon nanotubes (CNTs). Classical fluid mechanics is deemed unfit to describe this enhanced flow, and recent investigations indicated that quantum mechanics is required to interpret the extremely weak water-CNT friction. In fact, by quantum scattering, water can only release discrete energy upon excitation of electronic and phononic modes in the CNT. Here, we analyze in detail how a traveling water molecule couples to both plasmon and phonon excitations within a sub-nanometer, periodic CNT. We find that the water molecule needs to exceed a minimum speed threshold of ∼50 m/s in order to scatter against CNT electronic and vibrational modes. Below this threshold, scattering is suppressed, as in standard superfluidity mechanisms. The scattering rates, relevant for faster water molecules, are also estimated.

Analogue modelling of the Ainsa oblique zone in the Southern Central Pyrenees, Spain

The Pyrenees are a collisional orogen striking WNW-ESE. However, in the Ainsa oblique zone in the south-central part of the Pyrenees, faults and folds rotate to ∼N–S over a westward thinning evaporitic layer. The influence of lateral change in basal friction due to declining evaporitic layer thickness in a fold-and-thrust belt is studied by analogue modelling simulating the Ainsa oblique zone. In the experiments the transition zone is simulated by a viscous silicone mixture sheet that laterally changes in thickness adjacent to frictional-plastic quartz-sand. The models confirm that a transition between weak and strong basal friction causes oblique structures to develop. Weak detachment zones are prone to fault propagation whereas strong detachment zones are prone to imbrication. At the transition zone those structural styles are combined, resulting in a complex domain. The differences in deformation style cause dextral shear and clockwise rotation in the transition zone and larger horizontal deformation propagation in the weak basal friction zone. Structures produced in the analogue models are compared to structures in the Ainsa oblique zone and found to be representative. Therefore, this study shows that transition between weak and strong detachment layers can explain the regional structural deformation style in the Ainsa oblique zone.

Effects of friction properties and rheological structures on the deformation patterns and evolution of fold-and-thrust belts—New insights from analogue modelling

Studying fold-and-thrust belts is crucial in geoscience; fold-and-thrust belts are rich in petroleum and natural gas. However, the effects of friction properties and rheological structures on the deformation patterns and evolution of fold-and-thrust belts with two detachment layers are less frequently discussed. Therefore, using models with a basal silicone layer, a middle silicone layer and overlying quartz sand layers, this study conducted an analogue modelling analysis of the effects of friction conditions, rheological structures and compressional velocity on the deformation and evolution of fold-and-thrust belts. The results show the following. 1) The weak layer or low friction strength of the basement forms complex deformations of the structural style, forming forward thrust, backward thrust, symmetrical pop-up structure and frontward–backward oscillating structural characteristics. 2) The friction strength ratio between the lateral and basement layers does not determine the structural style of a fold-and-thrust belt; moreover, it is closely related to the construction of strata or rheological structures. 3) The deformation of double detachment layers complicates the structural style of fold-and-thrust belts. 4) The analogue modelling results are similar to the structural style of the simple fold belt of the Zagros fold-and-thrust belt (ZFTB), indicating that deep and middle detachment layers control the current deformation of the ZFTB.

A highly sensitive friction-imaging device based on cascading stimuli responsiveness.

Imaging and measurement of friction forces are required in a variety of fields. If the friction forces originating from the motions of professionals are quantitatively analyzed, the data can be applied to a motion-copying system by a robot. However, weak friction forces have not been visualized and quantified using conventional sensing materials and devices because of their low sensitivity. Here we present a highly sensitive friction-imaging device based on the cascading responses of stimuli-responsive materials, namely polydiacetylene (PDA) and dry liquid (DL). Weak friction forces disrupt the DL, which is composed of liquid droplets surrounded by solid particles. The outflowing liquid under chemical stress changes the color of PDA. The cascading responses enable colorimetric imaging and measurement of weak friction forces in the range of 0.006-0.080 N. Furthermore, the device visualizes the force distribution of handwriting in calligraphy depending on the individual characteristics of an expert, a practician, and a beginner. A high-sensitivity friction-imaging device can be used to understand various motions.

Non-Markovian dynamics of black hole phase transition

We provide a comprehensive study on the non-Markovian dynamics of the black hole phase transitions based on the underlying free energy landscape. By assuming that the transition processes between different black hole states are stochastic, the non-Markovian dynamics of the black hole phase transition is governed by the generalized Langevin equation with the time-dependent friction that represents the memory effect from the effective thermal bath when the timescale of the system is comparable or shorter than the timescale of the effective thermal bath. We consider the first passage problem associated with the black hole phase transitions and derive the analytical expressions of the mean first passage time in the weak, intermediate, and large friction regimes. As the concrete examples, we study the effects of three types of time dependent friction kernel (delta function friction, exponentially decayed friction, and oscillatory friction) on the dynamics of Hawking-Page phase transition and the small/large RNAdS black hole phase transition. we found that there is a kinetic turnover point for each type of friction kernel when the friction strength varies. For the exponentially decayed friction kernel, it is shown that the non-Markovian effect slows down the phase transition dynamics in the weak friction regime and speeds up the transition process in the strong friction regime. For the oscillating decayed friction kernel, we found kinetic resonances when the oscillating frequency of the effective thermal bath is equal to the oscillating frequency of the black hole state in the initial potential well on the free energy landscape.

The frictional layer in the observed momentum budget of the trades.

Profiles of eddy momentum flux divergence are calculated as the residual in the momentum budget constructed from airborne circular dropsonde arrays ( 220 km) for 13 days during the EUREC A/ATOMIC field campaign. The observed dynamical forcing averaged over all flights agrees broadly with European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS) forecasts. In the direction of the flow, a mean flux divergence (friction) exists over a 1.5-km deep Ekman layer, and a mean flux convergence (acceleration) is present near cloud tops. The friction is countergradient between 1 and 1.5 km, where vertical wind shear exceeds the observed thermal wind. From the frictional profile, a 10-m momentum flux of 0.1 N m is derived, in line with Saildrone turbulence measurements. A momentum flux divergence in the cross-wind direction is pronounced near the surface and acts to veer the wind, opposing the friction-induced cross-isobaric wind turning. Weaker friction and upper-level acceleration of easterly flow are observed when stronger winds and more vigorous convection prevail. Turbulence measurements on board the SAFIRE ATR-42 aircraft and the Uncrewed Aircraft System (UAS) RAAVEN reveal pronounced spatial variability of momentum fluxes, with a non-negligible contribution of mesoscales (5-30 km). The findings highlight the nontrivial impact of turbulence, convection, and mesoscale flows in the presence of diverse cloud fields on the depth and strength of the frictional layer.

Chemical Reactions in Imperfect Cavities: Enhancement, Suppression, and Resonance

The use of optical cavities to control chemical reactions has been of great interest recently, following demonstrations of enhancement, suppression, and negligible effects on chemical reaction rates depending on the specific reaction and cavity frequency. In this work, we study the reaction rate inside imperfect cavities, where we introduce a broadening parameter in the spectral density to mimic Fabry-P\'erot cavities. We investigate cavity modifications to reaction rates using non-Markovian Langevin dynamics with frictional and random forces to account for the presence of imperfect optical cavities. We demonstrate that in the regime of weak solvent and cavity friction, the cavity can enhance chemical reaction rates. On the other hand, in the high friction regime, cavities can suppress chemical reactions. Furthermore, we find that the broadening of the cavity spectral density gives rise to blue shifts of the resonance conditions and, surprisingly, increases the sharpness of the resonance effect.

Resonant Cavity Modification of Ground-State Chemical Kinetics.

Recent experiments have suggested that ground-state chemical kinetics can be suppressed or enhanced by coupling molecular vibrations with a cavity radiation mode. Here, we develop an analytical rate theory for cavity-modified chemical kinetics based on the Pollak-Grabert-Hänggi theory. Unlike previous work, our theory covers the complete range of solvent friction values, from the energy-diffusion-limited to the spatial-diffusion-limited regimes. We show that chemical kinetics is enhanced when bath friction is weak and suppressed when bath friction is strong. For weak bath friction, the resonant photon frequency (at which the maximum modification of the chemical rate is achieved) is close to the reactant well. In the strong friction limit, the resonant photon frequency is instead close to the barrier frequency. Finally, we observe that rate changes as a function of the photon frequency are much sharper and more sizable in the weak friction limit than in the strong friction limit.

Novel sodalite stabilized zero-valent iron for super stable and outstanding efficiency in activating persulfate for organic pollutants fast removal

In this study, novel porous sodalite (SOD) was synthesized through Reactive Oxidation Species (ROS) route from industrial waste lithium silicon fume (LSF) to stabilize nZVI (SOD@nZVI), and used as an outstanding persulfate (PS) activator for efficient organic degradation. Characterization results revealed nZVI evenly distributed on SOD via ion-exchange, and the fabricated SOD@nZVI exhibited high stability and superior reactivity over a wide pH range of 2–12 during oxidation reaction. The mechanism responsible for fast organic degradation in the SOD@nZVI+PS system was carefully investigated, and weak magnetic field (WMF) and friction were found to contribute to improved SOD@nZVI performance. The fast redox cycle of Fe2+/Fe3+ on SOD@nZVI can be stimulated by changing the mixing condition and altering the friction layer to harvest mechanical energy during the reaction, which can maximum persulfate activation to generate more reactive radicals for organic fast degradation. This study is of great significance, as it offers a practical route turning waste into excellent PS activator for in-situ organic pollution remediation, as well as proposing a new idea to maximum PS activation performance by manipulating the inner lining of reactor.

Controls of the Foreland Deformation Pattern in the Orogen‐Foreland Shortening System: Constraints From High‐Resolution Geodynamic Models

AbstractControls on the deformation pattern (shortening mode and tectonic style) of orogenic forelands during lithospheric shortening remain poorly understood. Here, we use high‐resolution 2D thermomechanical models to demonstrate that orogenic crustal thickness and foreland lithospheric thickness significantly control the shortening mode in the foreland. Pure‐shear shortening occurs when the orogenic crust is not thicker than the foreland crust or thick, but the foreland lithosphere is thin (<70–80 km, as in the Puna foreland case). Conversely, simple‐shear shortening, characterized by foreland underthrusting beneath the orogen, arises when the orogenic crust is much thicker. This thickened crust results in high gravitational potential energy in the orogen, which triggers the migration of deformation to the foreland under further shortening. Our models present fully thick‐skinned, fully thin‐skinned, and intermediate tectonic styles in the foreland. The first tectonics forms in a pure‐shear shortening mode whereas the others require a simple‐shear mode and the presence of thick (>∼4 km) sediments that are mechanically weak (friction coefficient <∼0.05) or weakened rapidly during deformation. The formation of fully thin‐skinned tectonics in thick and weak foreland sediments, as in the Subandean Ranges, requires the strength of the orogenic upper lithosphere to be less than one‐third as strong as that of the foreland upper lithosphere. Our models successfully reproduce foreland deformation patterns in the Central and Southern Andes and the Laramide province.

Improved Stable Drag Reduction of Controllable Laser-Patterned Superwetting Surfaces Containing Bioinspired Micro/Nanostructured Arrays.

Superwetting surfaces are widely used in many engineering fields for reducing energy and resistance loss. A facile and efficient method using laser etching has been used to fabricate and control superwettable drag reduction surfaces. Inspired by the self-cleaning theory of lotus leaves, we propose controllable patterned bionic superhydrophobic surfaces (BSSs) simulating the uneven micro/nanostructures of lotus leaves. The superhydrophobicity and drag reduction ratios at low velocities are highly improved using a laser ablation method on metal substrates. However, unstable air layers trapped on superhydrophobic surfaces are usually cut away by a high-velocity flow, which greatly reduces the drag reduction performance. The fabricated bionic superhydrophobic/hydrophilic surfaces (BSHSs) with alternated hydrophilic strips can build a large surface energy barrier to bind the three-phase contact line. It maintains the stable drag reduction by capturing the air bubbles attached to the hydrophilic strips at a high velocity. Three-dimensional simulation analysis and equipment to measure the weak friction of a self-assembled solid–liquid interface are used to explain the drag reduction mechanism and measure the drag reduction ratios at different flow speeds. BSSs achieve an improved drag reduction effect (maximum 52.76%) at a low velocity (maximum 1.5568 m/s). BSHSs maintain an improved and steady drag reduction effect at high speed. The drag reduction ratios can be maintained at about 30% at high speed, with a maximum value of 4.448 m/s. This research has broad application prospects in energy saving, liquid directional transportation, and shipping due to their robust superhydrophobic properties and stable drag reduction effect.

Mechano-Triboelectric Analysis of Surface Charge Generation on Replica-Molded Elastomeric Nanodomes.

Replica molding-based triboelectrification has emerged as a new and facile technique to generate nanopatterned tribocharge on elastomer surfaces. The “mechano-triboelectric charging model” has been developed to explain the mechanism of the charge formation and patterning process. However, this model has not been validated to cover the full variety of nanotexture shapes. Moreover, the experimental estimation of the tribocharge’s surface density is still challenging due to the thick and insulating nature of the elastomeric substrate. In this work, we perform experiments in combination with numerical analysis to complete the mechano-triboelectrification charging model. By utilizing Kelvin probe force microscopy (KPFM) and finite element analysis, we reveal that the mechano-triboelectric charging model works for replica molding of both recessed and protruding nanotextures. In addition, by combining KPFM with numerical electrostatic modeling, we improve the accuracy of the surface charge density estimation and cross-calibrate the result against that of electrostatic force microscopy. Overall, the regions which underwent strong interfacial friction during the replica molding exhibited high surface potential and charge density, while those suffering from weak interfacial friction exhibited low values on both. These multi-physical approaches provide useful and important tools for comprehensive analysis of triboelectrification and generation of nanopatterned tribocharge. The results will widen our fundamental understanding of nanoscale triboelectricity and advance the nanopatterned charge generation process for future applications.

Effect of tides on the orbital evolution of the redback system PSR 1723–2837

ABSTRACT The standard model of stellar evolution in close binary systems assumes that during mass transfer episodes, the system is in a synchronized and circularized state. Remarkably, the redback system PSR J1723–2837 has an orbital period derivative $\dot{P}_{\rm orb}$ too large to be explained by this model. Motivated by this fact, we investigate the action of tidal forces in between two consecutive mass transfer episodes for a system under irradiation feedback, which is a plausible progenitor for PSR J1723–2837. We base our analysis on Hut’s treatment of equilibrium tidal evolution, generalized by considering the donor as a two layers object that may not rotate as a rigid body. We also analyse three different relations for the viscosity with the tidal forcing frequency. We found that the large value measured for $\dot{P}_{\rm orb}$ can be reached by systems where the donor star rotates slower (by few per cent) than the orbit just after mass transfer episodes. Van Staden & Antoniadis have observed this object and reported a lack of synchronism, opposite to that required by the Hut’s theory to account for the observed $\dot{P}_{\rm orb}$. Motivated by this discrepancy, we analyse photometric data obtained by the spacecraft Kepler second mission K2, with the purpose of identifying the periods present in PSR J1723–2837. We notice several periods close to those of the orbit and the rotation. The obtained periods pattern reveals the presence of a more complex phenomenology, which would not be well described in the frame of the weak friction model of equilibrium tides.

Rheological behavior, internal stress and structural changes of ultra-high-filled wood-flour/high-density polyethylene composite in shear flow field

Wood plastic composite (WPC) is a green material with an excellent performance, environmental protection and recyclability, and potential in the field of green construction materials. A rheological study of WPC provides a key theoretical basis for mold design, equipment upgrade, production efficiency and quality improvement. In this study, an innovative approach was proposed to analyze the characters of a wood-flour/high-density polyethylene composite with an ultra-high wood-flour content (70 wt%–90 wt%, UWPC) in a shear flow field, including (1) a redesigned shear rheometer that can seal heat and (2) an analysis of the interactions between components in the UWPC by decomposing and calculating the stress during the rheological process. The stress that was generated by the UWPC melt during shearing originated mainly from wood particles and weak interfacial friction, whereas the stress that was generated by the polymer matrix could be ignored. Therefore, the polymer matrix served only to connect the wood particles and transfer stresses. Maleic-anhydride-grafted polyethylene (MAPE) enhanced the UWPC melt system interface, made the system structure more uniform and increased its fluidity. The enhancement effect of MAPE on the weak interface of UWPC melt was calculated quantitatively by calculating and analyzing the weak interfacial friction stress. The MAPE strengthening rate for the weak interface was 72.3%, 81.1% and 91.9% at 130 °C, 150 °C and 170 °C, respectively. These findings can be applied to improve WPC processing and equipment manufacture.

Tribological performance and scuffing behaviors of several automobile piston rings mating with chrome-plated cylinder liner

The friction and wear properties, as well as the scuffing resistance, of different piston-ring coatings mating with a chrome-plated cylinder liner were investigated. Interrupted wear tests under the lubricant starvation condition were conducted to examine the wear behavior of Cr-diamond coating (GDC) and diamond-like coating (DLC). The results indicated that the DLC coating had outstanding tribological properties (small coefficient of friction and wear loss) at 150 °C, while the GDC coating exhibited better performance at an elevated temperature (240 °C). The DLC coating had a better scuffing resistance; no material adhesion occurred for 70 min under the unlubricated condition. The interrupted wear behaviors revealed that the scuffing process of the GDC coating involved the consumption of lubricant oil with relatively stable wear, a reduction in the friction force, and the occurrence of scuffing, in sequence. In contrast, although the friction force also increased after a short period of weak friction, no scuffing was observed. This is attributed to the formation of a mixed oxide and graphitic C tribolayer.

Counter-Gradient Momentum Transport Through Subtropical Shallow Convection in ICON-LEM Simulations.

It is well known that subtropical shallow convection transports heat and water vapor upwards from the surface. It is less clear if it also transports horizontal momentum upwards to significantly affect the trade winds in which it is embedded. We utilize unique multiday large‐eddy simulations run over the tropical Atlantic with ICON‐LEM to investigate the character of shallow convective momentum transport (CMT). For a typical trade‐wind profile during boreal winter, CMT acts as an apparent friction to decelerate the north‐easterly flow. This effect maximizes below the cloud base while in the cloud layer, friction is very small, although present over a relatively deep layer. In the cloud layer, the zonal component of the momentum flux is counter‐gradient and penetrates deeper than reported in traditional shallow cumulus LES cases. The transport through conditionally sampled convective updrafts and downdrafts explains a weak friction effect, but not the counter‐gradient flux near the cloud tops. The analysis of the momentum flux budget reveals that, in the cloud layer, the counter‐gradient flux is driven by convectively triggered nonhydrostatic pressure‐gradients and horizontal circulations surrounding the clouds. A model set‐up with large domain size and realistic boundary conditions is necessary to resolve these effects.

Effect of silane coupling agents on flowability and compressibility of compound for bonded NdFeB magnet

Based on the difference of the Y-terminal functional group of the silane coupling agent (Y–Si(X)3), four different silane coupling agents were employed to pretreat the surface of the NdFeB powders. The effects of silane coupling agents on the flowability and compressibility of compounds for preparing bonded NdFeB magnets were studied. It is indicated that compounds pretreated by silane coupling agents have weaker friction and meshing force. The apparent density is increased by 0.3 g/cm3 compared with the compound without silane coupling agent, and the radial crushing strength is significantly increased by about 3–4 times. In addition, the epoxy resin is more evenly distributed on the surface of the compounds treated by silane coupling agents observed by scanning electron microscopy, and some agglomerated particles are produced. Also, the compressibility of compounds with silane coupling agents is significantly improved due to the fact that hardening exponents are reduced. However, the addition of silane coupling agents has almost no effect on the magnetic properties of bonded magnets. The special energy was used to manifest the flowability of magnetic powder particles representing the macroscopic performance of the force between powder particles, providing a new direction for the study of the interface compatibility of two-phase or multiphase composite materials.