Sliding Velocity Research Articles

The Relative Influence of Actin-Myosin Attachment and Detachment Kinetics on Actin Sliding Velocities is Modulated by Myosin Density

In an in vitro motility assay, actin sliding velocities, V, exhibit a multi-phasic response to increasing myosin densities, N. At low N, V increases with increasing N reaching a peak value before decreasing. The mechanism underlying this biphasic response remains unclear. Here we propose a simple model in which at low myosin numbers, the working step of a myosin head, which occurs upon actin-myosin attachment, is free to displace an actin filament, resulting in a V that is attachment limited. At high myosin numbers, actin-bound myosin heads impose a load against which the working step of a myosin head cannot move, resulting in a detachment limited V. We test this hypothesis by measuring the effects of perturbations to attachment- and detachment-kinetics on the N-dependence of V. The resulting data are accurately fit to our simple model. These results provide insights into the basic mechanism of muscle contraction with implications for how in general multiple motors work together to move cargo. Specifically, these results suggest that V measured in conventional in vitro motility assays is influenced by both attachment and detachment kinetics.

Analysis of bulk temperature field and flash temperature for locomotive traction gear

Sliding velocity variation for gear meshing surface was researched based on theories of gear tribology, heat transfer and Hertz contact, and a model of contact stress considering friction force was derived. The model design process culminated in a comparison of theoretical values and simulated values. Heat flux of friction for different meshing positions and the convective heat transfer coefficient at gear tooth surface and tooth face were initially calculated accurately. The finite element method was then adopted to establish the gear bulk temperature field model and, after the steady state temperature field of the locomotive traction gear was obtained, the distribution law of the steady-state temperature for the gear teeth was analyzed. Transient thermal analysis on the gear was implemented utilizing the steady-state thermal analysis to obtain the transient temperature field of the locomotive traction gear. Applying the Blok flash temperature criterion, theoretical value of the transient temperature rise for the gear tooth surface was calculated. Comparison of the simulation values and the theoretical values for the transient temperature rise indicated that the theoretical values were higher than the simulation values as the Blok flash temperature criterion considers the heat conduction only in the direction vertical to the tooth surface and disregards heat conduction in other directions. The simulation results were then concluded to be superior in practicality and accuracy.

Friction Coefficient Variation with Sliding Velocity in Copper with Copper Contact

In this paper, by applying analytical method and using experimental method data, the effect of sliding velocity on friction coefficient for contact of copper with copper is investigated. Some equations for obtaining friction coefficient as a function of sliding velocity for contact of copper with copper by applying second analytical method and using experimental method data are achieved. The results have shown, for each duration of rubbing, the existence of an exclusive equation for friction coefficient. The friction coefficient functions that are achieved by second analytical method are shown as a curve that indicates specific friction coefficient for each sliding velocity. Friction coefficient can be used to obtain friction force and stress in contact region of materials. In order to have a suitable design, the amounts of stress and friction force in contact region are required.

New Method to Measure Soil-GCL Interaction

The present study presents a new experimental technique to measure friction angle between soil and Geosynthetic Clay Liner (GCL). The method in question avoids some deficiencies observed on the inclined plane and pullout tests. Moreover, the technique allows observing the GCL tensile behaviour. The experimental frame is easy to build in usual geotechnical laboratory. The one employed is made-up in civil engineering Department of Ouargla University (Algeria). It is usable for testing both GCLs and other geosynthetic materials. Also, it permits to apply various experimental conditions (like slide velocity, confining pressure and water content) to the tested materials. The present method highlights that the soil-GCL interaction is, actually, a combination of two loading forces: soil-GCL interface friction and pure traction of the GCL material. The obtained results allow evaluating both soil-GCL angle of friction and intrinsic stiness of the GCL in relation with the confining pressure.

Sliding wear behavior of E-glass-epoxy/MWCNT composites: An experimental assessment

This investigation has evaluated the sliding wear properties of E-glass-epoxy/MWCNT (multiwalled carbon nanotube) composite and Epoxy/MWCNT composite. Four different reinforcements (0, 0.5,1 and 1.5 wt %) of MWCNTs are dispersed into an epoxy resin. Design of experiments (DOE) and Analysis of variance (ANOVA) are employed to understand the relationship between control factors (Percentage of reinforcement, Sliding distance, Sliding velocity and Normal load) and response measures (specific wear rate and friction coefficient). The control variables such as sliding distance (300, 600, 900 and 1200 m) and normal loads of 10, 15, 20 and 25 N and at sliding velocities of 1, 2, 3 and 4 m/s are chosen for this study. It is observed that that the specific wear rate and friction coefficient can be reduced by the addition of MWCNTs. Scanning electron microscopy (SEM) is used to observe the worn surfaces of the samples. Compared with neat epoxy, the composites with MWCNTs showed a lower mass loss, friction coefficient and wear rate and these parameters decreased with the increase of MWCNT percentage. Microscopic investigation of worn out sample fracture surface has revealed that fiber debonding happens when the stresses at the fiber matrix interface exceeds the interfacial strength, causing the fiber to debond from the matrix. The optimum control variables have been derived to reduce both wear and friction coefficient of composites.

A Function Generation Synthesis Methodology for All Defect-Free Slider-Crank Solutions for Four Precision Points

The well-established methodology for slider-crank function generation states that five precision points can be achieved without structural error. The resulting designs, however, do not necessarily satisfy all of the kinematic requirements for designing a slider-crank linkage used in common machine applications such as driving the ram of a mechanical press. First, linkage solutions to the five precision point synthesis problem may need to change circuits to reach the precision points. Second, there is no guarantee that the input crank is fully rotatable. This paper presents a modification to the function generation synthesis methodology that reveals a continuum of defect-free, slider-crank solutions for four precision points. Additionally, the methodology allows the specification of velocity or acceleration at the precision points. Although smaller accelerations at a point of zero slide velocity are associated with longer dwell, a point having zero velocity and acceleration is shown not to be possible. Examples are included to illustrate this kinematic synthesis methodology.

Tribological properties of self-assembled monolayers prepared on titanium film

The self-assembled monolayers of octadecyltrichlorosilane (OTS) and 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (FOTS) were prepared on titanium surfaces, irradiated by ultraviolet irradiation device. Contact angle meter, atomic force microscope and Centre for Tribology (CETR) UMT-2 tribometer were used to explore the surface morphology and tribological properties. The influences of function groups, slide velocity, load and ultraviolet irradiation on tribological properties of samples were analysed. From experiments, it was found that OTS and FOTS SAMs (self-assembled monolayers) prepared on titanium films exhibit hydrophobic and tribological properties, especially under 5-minute ultraviolet irradiation. The frictional force of OTS SAMs is lower than that of FOTS SAMs. The wear time of FOTS SAMs is longer than that of OTS SAMs.

Geophysical characterization of the lithological control on the kinematic pattern in a large clayey landslide (Avignonet, French Alps)

Lithology variation is known to have a major control on landslide kinematics, but this effect may remain unnoticed due to low spatial coverage during investigation. The large clayey Avignonet landslide (French Alps) has been widely studied for more than 35 years. Displacement measurements at 38 geodetic stations over the landslide showed that the slide surface velocity dramatically increases below an elevation of about 700 m and that the more active zones are located at the bottom and the south of the landslide. Most of the geotechnical investigation was carried out in the southern part of the landslide where housing development occurred on lacustrine clay layers. In this study, new electrical prospecting all across the unstable area revealed the unexpected presence of a thick resistive layer covering the more elevated area and overlying the laminated clays, which is interpreted as the lower part of moraine deposits. The downslope lithological boundary of this layer was found at around 700 m asl. This boundary coincides with the observed changes in slide velocity and in surface roughness values computed from a LiDAR DTM acquired in 2006. This thick permeable upper layer constitutes a water reservoir, which is likely to influence the hydromechanical mechanism of the landslide. The study suggests a major control of vertical lithological variations on the landslide kinematics, which is highlighted by the relation between slide velocity and electrical resistivity.

Effect of Rotational Sliding Velocity on Micro Tribological Behaviors of Cu50Zr50 Amorphous Alloy Foils

In this study, the micro tribological behavior of Cu50Zr50 amorphous alloy foils was investigated experimentally at room temperature by pin-on-disc tribological tests. It is found that the friction coefficients are mainly located between 0.15 and 0.45, and increase with the rotational sliding velocity. With the increase of rotational sliding velocity, the wear weight loss also increases. At lower rotational sliding velocity, the wear mechanism tends to a combination action of continuous wear and surface flow. At higher rotational sliding velocity, the wear mechanism tends to a continuous wear. The reported results provide a basis understanding of the tribological behavior of Cu50Zr50 amorphous alloys in micro scale.

Effect of Thompson River elevation on velocity and instability of Ripley Slide

Fourteen large landslides have occurred within a 10 km stretch of the Thompson River Valley south of Ashcroft, British Columbia. The slides have had movements ranging from rapid (metres per hour) to very slow, and the largest slides have volumes approaching 15.0 × 106 m3. Investigations of these slides have been conducted since the early failures of the slopes were noted in the 1860s, and have continued with the periodic reactivations and slope movements since then. This paper focuses on the Ripley Slide, which is one of the slides within the Thompson River Valley. This slide is a very slow-moving landslide, which has recently been reactivated. This landslide is crossed by a major transportation corridor and has therefore been the subject of ongoing geotechnical investigation and instrumentation. The results of this investigation are interpreted in light of the wealth of accumulated knowledge from more than a century of geotechnical investigation within this valley. The data collected from the landslide show that, like other slow-moving landslides in this valley, the seasonal fluctuations of the Thompson River elevation strongly influence the instability and the rate of slope movement. Continuous global positioning system monitoring of the movement of the landslide combined with measurement of the pore pressures within the sliding mass and elevation of the river have allowed for an empirical correlation between the limit equilibrium method modelled factor of safety and the velocity of the landslide.

Comparison of Tribological Properties of Stainless Steel with Hard and Soft DLC Coatings

Stainless steels are widely used in chemical, petrochemical and food-processing industries due to their good anticorrosion properties. However, they generally exhibit poor tribological properties which limit their applications in tribocorrosive conditions. Surface modifications, like diamond-like carbon (DLC) coatings, can be an optimal technological solution to overcome this problem. These films have attracted considerable attention because of their outstanding mechanical and tribological properties, but they have a major drawback that is their high internal stresses and low thermal stability. The internal stresses and film hardness depend on the ratio sp2/sp3, therefore, the film can be classified as hard or soft-DLC coatings depending on this ratio. In this work, different stainless steels (EN14301, EN14435 and EN12316) samples were DLC-coated by plasma assisted chemical vapor deposition. Hard and soft a-C:H:Si films (silicon containing amorphous hydrogenated carbon) were obtained. The films were characterized by wear and adhesion tests; the results show an increase of the practical adhesion at higher film thickness and this improvement would be more effective for harder substrates. Pin-on-disc tests showed that soft-DLC films tend to develop a better tribological behavior than hard-DLC films and it is not influenced by the film thickness or the type of stainless steel substrate. The influence on the tribological behavior of test parameters, such as slide velocity and load, varies with the coating type.

The Influence of Sliding Velocity on the Wear Intensity in Case of Polymeric Composite Materials Reinforced with Short Carbon Fibers

This paper presents a study of the tribological properties of polymeric composite materials reinforced with short carbon fibers. Reinforces carbon fibers materials are more effective if refer to specific properties per unit volume compared to conventional isotropic materials. Potential benefits of carbon fibers composite materials are: high resistance to breakage and high value ratios strength/density; resistance to high temperatures; low density and high resistance to wear; low or high friction coefficient. The composites are complex and versatile materials; their versatility it is given by the multitude of choice variety of the constituent materials that can be combined to obtain the desired properties of otherwise unobtainable from conventional materials. The composite materials used in this research work are obtained combining epoxy with short carbon fibers with titanium carbide and tantalum carbide in order to investigate the variation of the friction coefficient for three different sliding velocities. Varying the percent of epoxy from 29,35% to 43,92% and the percent of short carbon fibers from 35,43% to 53,70%, nine different composite materials are obtained and tested. Friction tests are carried out, at room temperature, in dry conditions, on a pin-on-disc machine. The friction coefficient was measured maintaining constant the pressing force (8 daN) and sliding time (120 sec), and varying the sliding velocity to 8, 14 and 23 m/sec. The main objective of this research work it was to identify a composite material with higher friction coefficient.

Studies on Tribological Behavior of Polyamide Filled Jute Fiber-Nano-ZnO Hybrid Composites

In this study, the tribological performance of Polyamide (PA) based hybrid composites have filled with short jute fibers (JF) and nano ZnO particles, which are fabricated with different volume fractions, and it was machined (test specimens) as per ASTM-G99 standard. Wear tests were conducted by pin-on-disc (POD) test rig, is a new test setup for online measuring of wear rate (WR) and friction coefficient (COF). Experiments were conducted based on central composite rotatable design (CCD), with the input parameters like normal force (NF), sliding velocity (SV) and reinforcements (RF) on wear rate and friction coefficient. The mathematical models were developed by using response surface methodology (RSM). Analysis of variance (ANOVA) test also carried out to check the adequacy of the developed empirical models. The debris and the worn out surfaces were observed through scanning electron microscope (SEM). Despite extensive research on composites, determining the desirable operating conditions in industrial setting still relies on the skill of the operators and trial-and-error methods. The main intension of this work is to optimize the tribological variables for minimum wear and friction based on multi-objective optimization techniques (MOOT). This was probably due to the fact that PA has good flexibility and for the incorporation of reinforcements, it is believed that a continuous thin coherent transfer films and tribo chemical reactions were involved by hybrid composites on the steel counterface, which contributes a lower friction and wear. This debris was re-adhered on the mating surfaces which improves the wear resistance and prevent the oxidation and degradation behavior more effectively, which might be one of the anti-wear mechanisms of nano ZnO fillers. Both wear rate and friction coefficient of the hybrid composites were significantly lower than those of the pure polyamide.

Effects of Contact Pressure, Plastic Strain and Sliding Velocity on Sticking in Cold Forging of Aluminium Billet

Hot rolling of stainless steel is one of the most important steps in manufacturing process regarding surface quality of the product. Stabilised ferritic stainless steels are widely used in automotive and cosmetic appliances but are also concerned by sticking phenomenon. These grades, having high dry corrosion and creep resistance, are enriched in specific chemical elements such as Cr, Nb or Ti, limiting also slab oxidation during hot rolling. Nevertheless, the mastered oxidation of slab surface is a way to protect metal surface from direct contact with rolls. In order to better understand initiation of sticking, a first campaign was based on topography and rolls surface state wear analysis. This study revealed that sticking initiation is not due to the presence of roll scratches which depth is higher than oxide layer thickness. Indeed, the probability that roll scratches are deeper than oxide layer thickness is very low. In a second time, a pilot was designed, reproducing tribological conditions of a roll bite, to better understand mechanisms that initiate sticking. Keeping in mind the importance of rolls and slab surface state, this pilot is able to use specimen taking from industrial products, having the original oxide layer surface. This second study highlighted the major role of silicon oxides on scale adherence and the high heterogeneity of this scale layer in thickness and in chemical composition.

Actin-Activated Atpase and Actin Sliding Velocities are Similarly Influenced by Actin-Myosin Binding Kinetics

Detachment-limited models of muscle shortening assume that with increasing myosin densities maximal velocities are achieved when at least one myosin head is bound to a given actin filament. However, numerous studies suggest that actin sliding velocities, V, are influenced by actin-myosin attachment kinetics, suggesting that V should saturate - along with actin-activated myosin ATPase activity, v - when myosin heads saturate binding sites on actin. Here we used an in vitro motility assay to measure both V and v in the same flow cell. We observed that both V and v exhibited similar saturation kinetics with increasing myosin densities and that increasing ionic strength similarly decreased the Km for both activation curves. Using the same in vitro assay, we measured the calcium-dependence of V for regulated thin filaments (actin filaments reconstituted with tropomyosin and troponin) and observed that the myosin-dependence of calcium sensitivity (pCa50) exhibited saturation kinetics similar to that of V and v. These results suggest that saturation of V, v, and pCa50 all occur when myosin saturates binding sites on actin. This is consistent with estimates showing that saturating myosin densities in a motility assay correspond to a linear spacing of myosin along an actin filament that is similar to the repeat of myosin binding sites along one side of the filament.

Comparison of Mechanical Properties and Effect of Sliding Velocity on Wear Properties of Al 6061, Mg 4%, Fly Ash and Al 6061, Mg 4%, Graphite 4%, Fly Ash Hybrid Metal Matrix Composite.

This Metal matrix composites (MMCs) are of great interest in industrial applications for its lighter weight with high specific strength, stiffness and heat resistance. The processing of MMCs by casting process is an effective way of manufacturing. In this paper the effect of rpm on specific wear rate and comparison of mechanical properties of two metal matrix composites have been investigated. In first case AL6061, 4%MG chosen as a base metal and varying composition of Fly ash i.e. 10%, 15% and20% was taken as reinforcement in second case AL6061, 4%MG, 4%Graphite was taken as base material and varying composition of Fly ash i.e. 10%, 15% and20% as reinforcement. It was found that tensile strength increase with addition of fly ash. Similarly when graphite was added then a decrease in tensile and hardness was observed. The composite with 4%Mg, 15%Fly ash found to be maximum tensile whereas composite of 4%Mg, 20%Fly ash was found to be of maximum hardness. Specific wear rate decreases with addition of fly ash up to a certain volume whereas with graphite addition it also decreases.

Frictional Properties and Microstructure of Calcite-Rich Fault Gouges Sheared at Sub-Seismic Sliding Velocities

We report an experimental and microstructural study of the frictional properties of simulated fault gouges prepared from natural limestone (96 % CaCO3) and pure calcite. Our experiments consisted of direct shear tests performed, under dry and wet conditions, at an effective normal stress of 50 MPa, at 18–150 °C and sliding velocities of 0.1–10 μm/s. Wet experiments used a pore water pressure of 10 MPa. Wet gouges typically showed a lower steady-state frictional strength (μ = 0.6) than dry gouges (μ = 0.7–0.8), particularly in the case of the pure calcite samples. All runs showed a transition from stable velocity strengthening to (potentially) unstable velocity weakening slip above 80–100 °C. All recovered samples showed patchy, mirror-like surfaces marking boundary shear planes. Optical study of sections cut normal to the shear plane and parallel to the shear direction showed both boundary and inclined shear bands, characterized by extreme grain comminution and a crystallographic preferred orientation. Cross-sections of boundary shears, cut normal to the shear direction using focused ion beam—SEM, from pure calcite gouges sheared at 18 and 150 °C, revealed dense arrays of rounded, ~0.3 μm-sized particles in the shear band core. Transmission electron microscopy showed that these particles consist of 5–20 nm sized calcite nanocrystals. All samples showed evidence for cataclasis and crystal plasticity. Comparing our results with previous models for gouge friction, we suggest that frictional behaviour was controlled by competition between crystal plastic and granular flow processes active in the shear bands, with water facilitating pressure solution, subcritical cracking and intergranular lubrication. Our data have important implications for the depth of the seismogenic zone in tectonically active limestone terrains. Contrary to recent claims, our data also demonstrate that nanocrystalline mirror-like slip surfaces in calcite(-rich) faults are not necessarily indicative of seismic slip rates.

Underwater Landslide Characteristics from 2D Laboratory Modeling

Landslide-generated impulse waves are considered a severe danger for humans and infrastructure. Design formulas following intensive laboratory research allow for a quick assessment of potential slide-event wave features. Unfortunately, prototype data are rare except for underwater slide deposits often corresponding to the only traces of a past event. If past events could be back-analyzed based on in situ scanned underwater slide deposits, the existing assessment approaches could be supported. Video recordings of 41 slide-generated impulse wave tests in a two-dimensional (2D) wave channel were analyzed regarding the underwater slide dynamics and their final deposition patterns. The underwater slide propagation process is described for three specifically selected tests. Correlation equations are presented for underwater slide front propagation and velocity, which are also useful for numerical modeling purposes. In addition, correlation equations are given for slide deposit features, including length and thickness, allowing for their estimation based on initial slide parameters.

Friction Resistance between Valve Made of TiAl Alloy and its Guide Made of Phosphor Bronze

A lightweight valve is often made of TiAl alloys and its stem can be solid or hollow. Such valves can mate with guides made of cast iron or of phosphor bronze at different conditions in their contact zone valve/quide. The aim of the research was to measure the friction force in the sliding contact between the valve stem made of TiAl alloy and its guide made of phosphor bronze, in the absence of oil. The experiment was conducted at room temperature and in static air under normal pressure. The investigations were conducted with use of the tester, which is presented in this article. The loading of contact zone has varied periodically during series. The displacement and acceleration of valve and the force during its impact into seat insert have been measured during tests. Additionally the sound level has been measured, either. Tests have been provided for different frequency of driving force. Additionally, researches on the tribotester pin-on-disc, presented in the article, have been provided, with the pin made of Ti6Al4V alloy and the disc made of phosphor bronze. The model of research stand has been elaborated for the simulation of dynamics for the material sample rotating plate assembly. The aim of such researches has been to obtain values of coefficient of friction for such tribological pair and to simulate dynamics of the material sample rotating plate assembly, characteristic for used research stand. The obtained courses of coefficient of friction vs. loading, slide velocity, duration of motion of material sample in respect to the rotating plate have been presented in the article. On the base of simulation results the values of damping coefficient have been estimated, which allow to obtain the value for the amplitude of the modeled motion for the material sample in respect to the rotating plate near to the value of the amplitude for the real motion. Such estimation allows forecasting the dynamics of the mentioned assembly for other values of velocity and loading.

Friction and Wear Behavior of Carbon/PEEK Composites according to Sliding Velocity

This study was to correctly estimate the friction and wear behavior of carbon fiber and PEEK sheet composites, and the validity of using them as alternatives to the metal-based materials used for artificial hip joints. Moreover, this work evaluated the friction coefficient according to the fiber ply orientation, along with the fractured surfaces of the carbon/PEEK composites. The unidirectional composites had higher friction coefficients than those multidirectional composites. This was caused by the debonding between the carbon fiber and the PEEK sheet, which was proportional to the contact area between the sliding surface and the carbon fiber. The friction test results showed that there was no significant differences in relation to the fiber ply orientation. However, in a case where the speed was 2.5 m/s, the friction coefficient was relatively large for configuration I. The friction surface of the specimen was analyzed using an electron microscope. In all cases, the debonding of the fiber and PEEK could be confirmed.