Distribution Of Traction Forces Research Articles

Research of the dynamics of the all-wheel-drive tractor-transport machine

The study results of the dynamic and traction-energy performance of an all-wheel drive traction-transport vehicle have been presented. A diagram of a dynamic model of the transmission of an all-wheel drive traction-transport vehicle and a system for calculating the transmission dynamics in the Cauchy form has been compiled. The method makes it possible to determine the distribution of the coil fluids of the transmission elements of a traction-transport vehicle, the distribution of torque moments, and the distribution of additional traction forces on the wheels per hour. The method allows you to determine the optimal transmission parameters, differential design, and transmission numbers to improve the traction and fuel-economic performance of the machine. It has been established that the speed of the front wheels of a traction and transport vehicle is 1.29 rad/s, 1.27 rad/s, and the speed of the rear wheels is 1.24 rad/s, 1.25 rad/s, which should be carried out until kinematic instability and additional energy consumption. The torque values of the front drive wheels are 6972 N m, and the rear drive wheels are 4622 N m. The additional traction forces on the car's front wheels are 5478 N after the car's acceleration is completed, and on the rear wheels, they are 347 3 N. To verify the adequacy of the method for assessing the dynamics of an all-wheel drive transmission, Wheeled traction, and transport vehicles have been developed to simulate the dynamics and energy systems of mobile vehicles—experimental research of the machine on the butt of an all-wheel drive wheeled tractor with an articulated frame. The difference between the values of the heel fluids of the wheel wraps, theoretically and experimentally, is 2%, which indicates a significant loss of the heel fluids by the wheel dynamics sensors. A comprehensive method for assessing the transmission dynamics of an all-wheel drive traction and transport vehicle must be considered adequate. The robotic method can be used to assess the dynamics of wheeled vehicles in motor vehicles. Keywords: cutting speed, torque, traction force, transmission, traction, and transport vehicle.

IMPROVING MANEUVERABILITY OF A WHEELED VEHICLE BY IMPROVING TURN CONTROL METHOD

A large number of scientific works and design developments are devoted to the study and improvement of the properties of maneuverability, which is also a complex (complex) property. At one time, the need to reduce the building volume required the installation of swivel wheels on the front steering axle of the car. However, in this case, additional resistance to the movement of the machine arose, which is due to the discrepancy between the trajectories of the movement of the front outer and inner guide wheels with their trajectories during an ideal turn. The development of the designs of electric vehicles and hybrid vehicles allows for separate control of the front wheels. The analysis of the whole variety of indicators and criteria of maneuverability in general and individual properties was carried out. Unlike other systematization of these indicators and criteria, it is proposed to divide these indicators and criteria into three main groups. All indicators and criteria used to assess the maneuverability of vehicles are also used to assess the maneuverability of wheeled tractors with a center of mass shifted to the rear axle and, therefore, have low controllability. Force and energy criteria can be used in the design of cars and tractors to ensure the ability of the latter to maneuver. In addition, as a result of the study, a combined method for controlling the movement of a two-axle swivel bogie of a wheeled vehicle has been improved due to the fact that its rotation is carried out by two torque control moments. The first of these control torques is generated by the driver through the steering and power cylinder. The second torque control moment is created due to the difference in torques on the wheels of the outer and inner sides of the two-axle swivel bogie. The implementation of these rules for regulating the distribution of traction forces between the sides makes it possible to overcome the resistance to rotation of a two-axle swivel bogie and improve the quality of motion control of the specified bogie and wheeled vehicle. Keywords: maneuverability, separate control, wheeled vehicle, control method, two-axle swivel bogie

Эффективное распределение тяговых сил между роботами при групповой транспортировке груза

The task of collective movement of load by wheeled robots has kinematic redundancy of drives. It allows distributing traction forces without changing the trajectory and velocity of the system. In this way, it is possible to define additional traffic quality criteria which the traction control system should strive to achieve. In addition, efficient distribution will allow the robots to move without wheel slip at a higher speed than classical control methods. Robots and cargo combined into one system mechanically and informationally, form a variable configuration transport cell (VCTC). The following transportation quality criteria are considered: no wheel slippage, maintaining a given speed, no soft bumps, minimizing work in the generator mode, maintaining the desired final charge levels of the robot batteries after transportation. The proposed methods for the efficient distribution of traction forces are based on the finding local minimum and on the Hebbian learning principle. Tests are carried out in the Simulink using the dynamic mathematical model of the VCTC. In the case under consideration, new distribution methods made it possible to increase the maximum allowable turn entry speed by 27% compared with classical control approaches. At a lower speed new method of distribution showed good results on additional transportation quality criteria. The presented material can also be used for multi-wheeled robots with steerable drive wheels.

The straight-line stability analysis of the vehicle with the electronic stability control

BACKGROUND: At present time, branches of industry have been increasingly filled with electronics, capable of controlling different processes in order to achieve demanded paremeters values. Automotive industry, safety issues of which such as vehicle stability and handling are paid much attention, have not become an exclusion. Vehicle safety improvement is one of the areas of development of modern auto-motive industry. Manufacturers permanentally increase the number of control systems and raise the level of control on wheeled vehicle motion parameters in order to achieve the highest possible level of stability and handling. Using of various all-wheel-drive systems becomes more relevant and reasonable. Traction force distribution between all wheels improves dynamic performance indicators, makes cross-country ability better in similar road conditions and allows using algorithms, improving handling and course-keeping ability of a vehicle.
 AIMS: Determination of variation range of the control parameter in order to ensure stable straight-line motion of a vehicle with controlled transmission.
 MATERIALS AND METHODS: The two-axled vehicle, which transmission has an ability of torque distribution between front and rear axles, is considered in the article. The system of diiferential equations in terms of middle wheels side slip angles was made up in the study. The LinardChipart algebraic cri-terion was used to define variation ranges of the control parameter in order to ensure stable straight-line motion of the vehicle.
 RESULTS: The obtained variation ranges of the control parameter are included in the adjustment range of modern torque distribution mechanisms, consequently, it is possible to speak about ability to ensure stability of straight-line motion of a full-wheel-driven vehicle with currently existing mechanisms. The scientific novelty of the study lies in analytical determination of variation range of the control parameter for the case of straight-line motion of a vehicle equipped with the electronic stability control.
 CONCLUSIONS: Practical value of the study lies in establishment of ability to ensure stability of straight-line motion of a full-wheel-driven vehicle with currently existing mechanisms.

Curvilinear motion control laws for a semi-trailer caterpillar train for off-road cargo transportation

BACKGROUND: For transport accessibility in areas with an undeveloped road network, the use of tracked trains that provide low ground pressure is a rational solution. To ensure the mobility of a semi-trailed, unmanned caterpillar train, which can be controlled remotely by a driver-operator or by an automatic unmanned driving system, traffic control laws are needed.
 AIMS: Ensuring energy efficiency in curve control of a unmanned semi-trailer tracked train for off-road freight transport.
 METHODS: The methods of simulation mathematical modelling and analytical methods based on the consideration of the quasi-stationary motion of the caterpillar train links are used to derive energy-efficient control laws and determine the mobility performance that can be achieved.
 RESULTS: Control laws are obtained for two variants of tracked trains: a tracked train with independent drive control of driving wheels and a tracked train with a differential drive scheme of a semi-trailer link. The control laws are designed to improve the energy efficiency of travel which is achieved by rational distribution of traction forces on the driving wheels of the tracked train and use of the regulator which ensures adjustment of the traction on the semi-trailer driving wheels accord-ing to the sign and magnitude of force in the fifth-wheel coupling of the tractor.
 A block diagram of a governing system of a caterpillar train and a mathematical description of its basic structural components (blocks) are given. Using the developed control laws the theoretical research of curvilinear movement by simulation mathematical modelling is carried out; the comparative analysis of the considered control laws of the semitrailer caterpillar train movement with two transmission variants is given.
 CONCLUSIONS: The application of the developed caterpillar train motion control laws will enable the vehicle to move unmanned or follow the lead vehicle along a set path with high accuracy of turning manoeuvres and, consequently, will improve the safety of freight transportation.

Epithelial cell cluster size affects force distribution in response to EGF-induced collective contractility

Several factors present in the extracellular environment regulate epithelial cell adhesion and dynamics. Among them, growth factors such as EGF, upon binding to their receptors at the cell surface, get internalized and directly activate the acto-myosin machinery. In this study we present the effects of EGF on the contractility of epithelial cancer cell colonies in confined geometry of different sizes. We show that the extent to which EGF triggers contractility scales with the cluster size and thus the number of cells. Moreover, the collective contractility results in a radial distribution of traction forces, which are dependent on integrin β1 peripheral adhesions and transmitted to neighboring cells through adherens junctions. Taken together, EGF-induced contractility acts on the mechanical crosstalk and linkage between the cell-cell and cell-matrix compartments, regulating collective responses.

РАСПРЕДЕЛЕНИЕ КРУТЯЩИХ МОМЕНТОВ ПО КОЛЕСАМ ТРАКТОРА

The regularities of the distribution of torques on axles and tractor wheels have been studied. An energy-saturated universal tractor of class 2 integrated circuit LTZ-155 with all driving and steered twin wheels of the same size with tires of size 9.5-42 was chosen as the object of research. The studies were carried out under the following layout options and driving conditions: 1) rectilinear movement of a separate tractor - idling; 2) execution of the technological process during operation of the machine-tractor unit in row spacing of row crops - cultivation; 3) rectilinear movement of a machinetractor unit with guns in the transport position - idling. It was found that the total values of torques on tractor wheels under relatively constant driving conditions for all experimental races with an increase in translational speed of movement slightly, by about 5... 18%, increase due to an increase in the frequency of the dynamic impact of the microprofile from the side of the bearing surface on the wheels and fluctuations in the traction load. At the same time, the mean square deviation of the wheel moments does not exceed 18... 25% of their average value, which is constant for a stationary ergodic process. With the considered variants of operation of the machine-tractor unit, the redistribution of torques, both on the axles and on the wheels of each axle, even if we assume that a constant total torque is supplied to the driving wheels, is very complex and dynamic, due to the inaccuracy of landings due to the tolerances of the coupling in the coupling device between the tractor and the cultivator from- due to the inability to comply with the alignment of the covered and encompassing connecting elements of the connecting triangles, this leads to an asymmetry of the normal weight load of the wheels from the mounted guns and the corresponding non-proportional distribution of traction forces on the wheels.

Single Cell Micro-Pillar-Based Characterization of Endothelial and Fibroblast Cell Mechanics

Mechanotransduction, the ability of cells to sense and respond to the mechanical cues from their microenvironment, plays an important role in numerous cellular processes, ranging from cell migration to differentiation. Several techniques have been developed to investigate the underlying mechanisms of mechanotransduction, in particular, force measurement-based techniques. However, we still lack basic single cell quantitative comparison on the mechanical properties of commonly used cell types, such as endothelial and fibroblast cells. Such information is critical to provide a precedent for studying complex tissues and organs that consist of various cell types. In this short communication, we report on the mechanical characterization of the commonly used endothelial and fibroblast cells at the single cell level. Using a micropillar-based assay, we measured the traction force profiles of these cells. Our study showcases differences between the two cell types in their traction force distribution and morphology. The results reported can be used as a reference and to lay the groundwork for future analysis of numerous disease models involving these cells.

Subcellular Force Quantification of Endothelial Cells Using Silicone Pillar Arrays.

Micropillar arrays are one of the tools that quantify the mechanical forces exerted by endothelial cells and any other adherent cell types. This chapter describes the fabrication and usage of the micropillars that reports spatial distribution of traction forces by endothelial cells. The fabrication begins with making a "master" pillar substrate using photolithography, followed by softlithography of the master with polydimethylsiloxane. The pillars can then be printed with an extracellular matrix protein in specific shape using stamp-off technique. Lastly, imaging of the micropillars with cells and the analysis of the traction force using Matlab-based software are described.

Компоновка электропривода вагона метрополитена

Objective: Analysis of various layouts of the electric drive of wheelsets and the control traction con- verter on transistor modules. Methods: The assessment and comparison of the layout solutions of asynchronous electric drives with one inverter supplying two or four traction motors is carried out. A mathematical analysis of the influence of the difference in the diameters of wheelsets leading to an inequality of traction forces and causing sliding has been carried out. Results: It was revealed that the use of the layout one inverter — four asynchronous motors is the least efficient and leads to a greater extent to negative consequences during the operation of wheelsets. Practical importance: The use of an electric drive scheme for subway cars with one inverter feeding two traction motors is substantiated, which leads to a more even distribution of traction and braking forces and significantly reduces the risk of slipping and skidding. Thus, the wear of wheelsets and the rest of the kinematic chain is reduced and the resource of their nodes and elements increases to a large extent

Coupler force reduction method for multiple-unit trains using a new hierarchical control system

During traction and braking of multiple-unit trains, substantial longitudinal dynamic forces might occur in couplers due to the non-optimal distribution of traction and braking forces generated by self-propelled carriages. These dynamic forces might create shocks affecting the reduction of endurance of the weakest train structural components primarily. Thus, the overall operational safety of the train is also lowered. The purpose of the paper is to develop a new control system to supervise the activities related to the longitudinal dynamics of each train carriage in a multiple-unit train to reduce the longitudinal coupler forces acting during train traction and braking. The hierarchical structure of the control system consists of two levels. The first master level of control works like standard cruise control. However, the reduction of longitudinal coupler forces is achieved by applying a second level of slave control systems with a control configuration of feedback compensation.

Study on the Expansion Dynamics of MDCK Epithelium by Interstitial Flow Using a Traction Force-Measurable Microfluidic Chip.

The movement of collective cells is affected through changes in physical interactions of cells in response to external mechanical stimuli, including fluid flow. Most tissues are affected by fluid flow at the interstitial level, but few studies have investigated the physical effects in collective cells affected by a low flow rate. In this study, collective cell migration of Madin–Darby canine kidney (MDCK) epithelial cells was investigated under static or interstitial flow (0, 0.1, and 1 μL/min) using a traction microfluidic device. The optimization of calculation of cellular traction forces was first achieved by changing interrogation window size from the fluorescent bead images. Migration analysis of cell collectives patterned with a 700 μm circular shape reveals that cells under the slow flow (0.1 and 1 μL/min) showed the inhibitory migration by decreasing cell island size and cellular speed compared to that of static condition. Analysis of cellular forces shows that level of traction forces was lower in the slow flow condition (~20 Pa) compared to that of static condition (~50 Pa). Interestingly, the standard deviation of traction force of cells was dramatically decreased as the flow rate increased from 0 to 1 μL/min, which indicates that flow affects the distribution of cellular traction forces among cell collectives. Cellular tension was increased by 50% in the cells under the fluid flow rate of 1 μL/min. Treatment of calcium blocker increased the migratory speed of cells under the flow condition, whereas there is little change of cellular forces. In conclusion, it has been shown that the interstitial flow inhibited the collective movement of epithelial cells by decreasing and re-distributing cellular forces. These findings provide insights into the study of the effect of interstitial flow on cellular behavior, such as development, regeneration, and morphogenesis.

Інформаційно-розрахунковий комплекс «Тягові розрахунки» та математичні методи пошуку основних параметрів руху поїзда як основи оптимізації витрат ресурсів на тягу

The article deals with the issues of determining the main parameters of traction calculations and presents formulas for the mathematical apparatus of their search. A method for finding the distribution of specific traction forces and intervals of their action at selected calculation polygons and rationalizing the application of the driver's controller position relative to the locomotive speed is presented. The necessity of applying algorithmization based on the fuel efficiency of traction rolling stock is economically proved by comparative characteristics of rationing fuel consumption by a diesel locomotive, on a selected shoulder with a train of the appropriate weight, with values obtained as a result of the operation of the software package. The software product "traction calculations" in the programming language "C#"is presented. The calculation algorithm and its description are given with logically corresponding examples of the essence of the automated system. The basis of this software product is the law of conservation of mechanical energy, as an expression that takes into account all the factors of influence of external and internal circumstances on the train and its equations of motion. Graphically, the parameters of the movement of a freight train are interpreted in the form of curves of the dependence of time, speed, current of traction electric motors on the distance traveled and the conversion of calculations to the Microsoft Office Excel format as the basis for the optimization calculation of engineering and management apparatus.

Stress fibres are embedded in a contractile cortical network.

Contractile actomyosin networks are responsible for the production of intracellular forces. There is increasing evidence that bundles of actin filaments form interconnected and interconvertible structures with the rest of the network. In this study, we explored the mechanical impact of these interconnections on the production and distribution of traction forces throughout the cell. By using a combination of hydrogel micropatterning, traction-force microscopy and laser photoablation, we measured the relaxation of traction forces in response to local photoablations. Our experimental results and modeling of the mechanical response of the network revealed that bundles were fully embedded along their entire length in a continuous and contractile network of cortical filaments. Moreover, the propagation of the contraction of these bundles throughout the entire cell was dependent on this embedding. In addition, these bundles appeared to originate from the alignement and coalescence of thin and unattached cortical actin filaments from the surrounding mesh.

Unveiling the Mechanotransduction Mechanism of Substrate Stiffness‐modulated Cancer Cell Motility via ROCK1 and ROCK2 Differentially Regulated Manner

In addition to soluble factors and stromal cells, the mechanical properties of extracellular matrix (ECM) are considered to be an important component of tumor microenvironment. In particular, substrate stiffness is a mechanical characteristic of the ECM by which certain anchorage cells sense and respond to a variety of cellular behaviors. At the same time, clinical studies have observed that substrate stiffness was increased during tumorigenesis, which could promote tumor malignant transformation and metastasis. However, the biomechanical behavior of tumor cells and the underlying mechanotransduction pathways remain unclear. Here, using stiffness‐regulable polyacrylamide (PAA) substrates to simulate the tissue stiffness at different progress stages of breast cancer in vitro, we found that moderate substrate stiffness induced the emergence of malignant phenotypes and further unregulated breast cancer cell motility. Subcellular structure observation showed that moderate substrate stiffness promote the formation of leading‐edge protrusion by accelerating focal adhesion maturation and polarizing intracellular traction force distribution. Moreover, the substrate stiffness directly activated integrin β1 and focal adhesion kinase (FAK), which accelerate focal adhesion (FA) maturation and induce the downstream cascades of intracellular signals of the RhoA/ROCK pathway. Interestingly, the differential regulatory mechanism between two ROCK isoforms (ROCK1 and ROCK2) in cell motility and mechanotransduction was clearly identified. ROCK1 phosphorylated the myosin‐regulatory light chain (MRLC) and facilitated the generation of traction force, while ROCK2 phosphorylated cofilin and regulated the cytoskeletal remodeling by suppressing F‐actin depolymerization. The ROCK isoforms differentially regulated the pathways of RhoA/ROCK1/p‐MLC and RhoA/ROCK2/p‐cofilin in a coordinate fashion to modulate breast cancer cell motility in a substrate stiffness‐dependent manner via integrin β1‐activated FAK signaling. Our findings provide new insights into the mechanisms of matrix mechanical property‐induced cancer cell migration and malignant behaviors. Taming these physical forces by implanting scaffolds with specific stiffness or by inhibiting specific ROCK isoforms could have potential implications for improving therapeutic outcomes in cancer.Support or Funding InformationThis work was supported, in part or in whole, by the National Natural Science Foundation of China (11772088, 31470906, 31700811, 11802056, and 31800780).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Direct Yaw Moment Control for Enhancing Handling Quality of Lightweight Electric Vehicles with Large Load-To-Curb Weight Ratio

In this paper a vehicle dynamics control system is designed to compensate the change in vehicle handling dynamics of lightweight vehicles due to variation in loading conditions and the effectiveness of the proposed design is verified by simulations and an experimental study using a fixed-base driving simulator. Considering the electrification of future mobility, the target vehicle of this research is a lightweight vehicle equipped with in-wheel motors that can generate an additional direct yaw moment by transverse distribution of traction forces to control vehicle yawing as well as side slip motions. Previously, the change in vehicle handling dynamics for various loading conditions have been analyzed by using a linear two-wheel vehicle model in planar motion and a control law of the DYC system based on feed-forward of front steering angular velocity and feedback of vehicle yaw rate. The feed-forward controller is derived based on the model following control with approximation of the vehicle dynamics to 1st-order transfer function. To make the determination of the yaw rate feedback gain model-based and adaptable to various vehicle velocity conditions, this paper selects a method where the yaw rate feedback gain in the DYC system is determined in a way that the steady-state yaw rate gain of the controlled loaded vehicle matches the gain of the unloaded vehicle. The DYC system is simulated in a single lane change maneuver to confirm the improved responsiveness of the vehicle while simulations of a double-lane change maneuver with a driver steering model confirms the effectiveness of the DYC system to support tracking control. Finally, the effectiveness of the proposed DYC system is also verified in an experimental study with ten human drivers using a fix-based driving simulator.

An AWID and AWIS X-By-Wire UGV: Design and Hierarchical Chassis Dynamics Control

In this paper, an all-wheel independently driven and all-wheel independently steered unmanned ground vehicle (UGV) is described. This paper investigates the hierarchical chassis yaw dynamics control (CYDC) and the tyre force control of the UGV in the remote control mode (RCM). The hierarchical CYDC scheme in RCM is proposed. As the key part in the control scheme, a yaw moment controller is proposed to deal with the oversteer problem of the UGV. Through the robust-based pole placement technique, the ideal poles’ zones of the lateral UGV dynamics system are able to be tuned to meet different dynamics behavior requirements in different UGV tasks. The robust state feedback yaw dynamics controller is investigated based on the linear matrix inequalities approach. It considers the unavoidable parametric disturbance and uncertainty, such as the variation of the UGV’s mass, yaw inertia, and tyre-road characteristics. In addition, in order to improve its performance in off-road conditions, the tyre traction force distribution algorithm and sliding mode wheel slip controller are designed to negotiate uneven terrains. The experiments in paved and off-road conditions are conducted to demonstrate the performance of the proposed controller.

Effect of sanguinarine on biomechanics of rat airway smooth muscle cells

This study aimed to evaluate the effect of sanguinarine on biomechanical properties of rat airway smooth muscle cells (rASMCs) including stiffness, traction force and cytoskeletal stress fiber organization. To do so, rASMCs cultured in vitro were treated with sanguinarine solution at different concentrations (0.005~5 μmol/L) for 12 h, 24 h, 36 h, and 48 h, respectively. Subsequently, the cells were tested for their viability, stiffness, traction force, migration and microfilament distribution by using methylthiazolyldiphenyl-tetrazolium bromide assay, optical magnetic twisting cytometry, Fourier transform traction microscopy, scratch wound healing method, and immunofluorescence microscopy, respectively. The results showed that at concentration below 0.5 μmol/L sanguinarine had no effect on cell viability, but caused dose and time dependent effect on cell biomechanics. Specifically, rASMCs treated with sanguinarine at 0.05 μmol/L and 0.5 μmol/L for 12 and 24 h exhibited significant reduction in stiffness, traction force and migration speed, together with disorganization of the cytoskeletal stress fibers. Considering the essential role of airway smooth muscle cells (ASMCs) biomechanics in the airway hyperresponsiveness (AHR) of asthma, these findings suggest that sanguinarine may ameliorate AHR via alteration of ASMCs biomechanical properties, thus providing a novel approach for asthma drug development.

3081 - Geometrical Control of Stem Cell Fate by Self-Organization of Cytoskeleton

The commitment of mesenchymal stem cells (MSCs) differentiation lineage can be controlled by physical signals, such as geometric cues of extracellular matrix (ECM). It is well known that the physical stimuli drive focal adhesions (FAs) maturation, actin polymerization and stress fiber formation, yet how cell shape controls MSC differentiation through the FA-mediated signals or FA-cytoskeleton organization remains largely unknown. To determine how geometric cues direct MSC lineage commitment, a technique of microcontact printing is performed to shape MSCs. We find that the geometric cues control osteogenic-adipogenic switch in MSC lineage commitment through regulating the organization of FAs, actin filaments, intermediate filaments, microtubules and nucleus, which further influences the distribution of cellular visco-elasticity and traction forces. Our data demonstrate a role for FA signaling in dictating MSC differentiation regulated by geometric cues.

Model of Cell Crawling Controlled by Mechanosensitive Adhesion.

We study the motility of model cells and biomimetic soft objects crawling over a substrate covered with adhesive linkers. The cell exerts traction forces on the substrate through the active periodic motion of molecular complexes to which the linkers bind and unbind stochastically. We first show that the diffusion coefficient of a force dipole (unable by symmetry to perform directed motion) is maximal for a finite ratio of the unbinding to binding rates, highlighting the role of adhesion kinetics on cell translocation. We next show that cells exerting more complex traction force distributions may exhibit directed motion only if the linkers are mechanosensitive, i.e., if the bonds' lifetime decreases (slip bonds) or increases (catch bonds) under stress. The average migration speed is higher in the catch-bond regime but so are the fluctuations, yielding a biased diffusive motion characterized by a Peclet number smaller than in the slip-bond regime.