Constant Pulling Speed Research Articles

In vitro quantification of the resistance force properties of a hydraulic resistance device designed for sprinting

The hydraulic resistance device (HRD), a state-of-the-art device developed primarily for resisted sprint training, lacks exploration of its force-generating properties. This technical note aims to evaluate these properties in vitro. In a laboratory experiment, the HRD was pulled with a motorised winch at four speeds (1–4 m s−1) and 12 different HRD resistance levels (low, medium and high). The resistance force induced by the HRD was measured using a force plate mounted under the device, and calculated as mean horizontal force produced at a constant pulling speed. Resistance force repeatability between pulling speeds at specific resistance levels was assessed using the coefficient of variation (CV) whereas the intraclass correlation coefficient (ICC3,1) was calculated to determine the consistency. A linear regression model quantified resistance force as a function of HRD resistance level. Accuracy of the model was assessed using root mean square error (RMSE). Across 12 resistance levels, the HRD produced resistance forces ranging from 22.57 ± 4.84 to 164.57 ± 4.84 N. The CV decreased from 21.5% at the lowest resistance to 0.4% at the highest. The HRD produced resistance force with high consistency (ICC3,1 CI = 0.990–0.999). The linear regression model showed a near-perfect fit ( R2 = 0.99) and predicted resistance force more accurately at medium and high resistance (RMSE range = 0.97–4.57 N). The HRD provides favourable force-generating properties for resisted sprint training and testing, warranting further studies on its exploration in vivo.

Mechanical response of polyprotein revealed by single-molecule optical tweezers

We researched the mechanical unfolding of protein domains in monomeric protein NuG2 and the tandem polyproteins (NuG2)8 and (NuG2)16 using a dual-trap optical tweezers system. By stretching NuG2 and its polyproteins, (NuG2)8 and (NuG2)16 at the constant pulling speed of 500 nm s−1, we achieved the mechanical unfolding force of each domain in these proteins. Besides, we calculated the energy dissipation of NuG2, (NuG2)8 and (NuG2)16 by measuring the area enclosed by stretching and relaxation traces. Our results represent a key step towards engineering artificial polyproteins with controllable mechanical force and energy dissipation properties for force-buffering and energy dissipator applications.

Nonlinear Generalized Predictive Control of the Crystal Diameter in CZ-Si Crystal Growth Process Based on Stacked Sparse Autoencoder

A new control structure with constant pulling speed for growing high-quality crystal in the Czochralski (CZ) method is presented in this brief. In this control structure, the pulling speed is not involved in the controlling of crystal diameter and only the temperature is used as the control quantity. Due to the time delay and the nonlinearity relationship are commonly involved between the temperature and crystal diameter, which make the diameter control difficult and complicated, a generalized predictive controller (GPC) based on the stacked sparse autoencoder (SSAE) is proposed under the new control structure. The time delay is obtained by using the correlation identification algorithm, the input order and output order are determined by the Lipchitz quotients algorithm, and the prediction model is trained by SSAE. Combining the SSAE with the nonlinear GPC algorithm, the control law of the temperature is calculated for diameter control. The simulation result verifies the correctness of the proposed control algorithm. The experimental result indicates that the new control structure with constant pulling speed is more conducive to growing high-quality crystal, avoiding the fluctuation of pulling speed. The proposed SSAE-based GPC algorithm can accurately track the reference diameter. The studies in this brief provide a feasible strategy for growing large size and high-quality crystal in the CZ method.

Study on design and experiments of extrusion die for polypropylene single-lumen micro tubes

The extrusion die is one of the most important parts in extrusion processing. It is difficult to design and manufacture to the land length of the die for polypropylene single-lumen micro tubes. In the paper, the land length was designed by rheological properties of polypropylene. For single-lumen micro tubes, the land length with a small air hole was so small that it was easily to be broken, especially in the processing. Therefore, the land length was manufactured by micro-EDM. Then, the experimental results showed that the designed and manufactured die was reasonable and could meet the using requirements. According to the further extrusion experiments, the relationships between tube sizes and extrusion processing parameters were explored. The results indicated that the die temperature had little effect on the tube sizes. That was because the increasing temperature reduced the viscosity and the pressure drop in the die simultaneously. With the given temperature and the constant screw speed, the macromolecules of the polymers with the increasing pulling speeds were straightened to the limit and slipped among the macromolecules, which caused the diameters and wall thicknesses of the micro tubes to decrease in the nonlinear curves. Meanwhile, in the given temperature and the constant pulling speed, the higher the screw speeds got, because of the shear thinning, the smaller the shear viscosity was. However, the increasing amplitudes of the pressure in the die were getting small. So the volume flow rates were also reduced accordingly. Thus the change rates of the diameters and wall thicknesses were also getting small. In the other word, the relations between the micro tube sizes and the screw speeds were not linear, but nonlinear. These results were very valuable for the extrusion die designs of multi-lumen micro tubes and the extrusion processing.

Analytic expression for the pull-or-jerk experiment

This work focuses on a theoretical analysis of a well-known inertia demonstration, which uses a weight suspended by a string with an extra string that hangs below the weight. The point in question is which string, the upper or lower, will break when pulling down on the bottom edge of the lower string at a constant pulling speed. An analytic solution for the equation of motion allows us to identify the critical value of the pulling speed, beyond which the string breaking varies from one to the other. The analysis also provides us with a phase diagram that illustrates the interplay between the pulling speed and the stringʼs elasticity in the pull-or-jerk experiment.

An Improved Device to MeasureCottonseed Strength

<abstract><title><italic>Abstract. </italic></title> During processing, seeds of cotton cultivars with fragile seeds often break and produce seed coat fragments that can cause processing problems at textile mills. A previously developed cottonseed shear tester was modified with enhancements to the drive system to provide a constant pulling speed to the shearing mechanism which measured cottonseed strength. Evaluation of the modified tester showed that placing a cottonseed in the shear mechanism with the chalazal end of the cottonseed flush with the face of the mechanism produced a truer double shear than an alternative position. This flush position also resulted in less variable cottonseed shear force measurements. The shear device provides a useful tool for cotton breeders to rapidly quantify the seed strength of prospective cotton cultivars.

Molecular Dynamics of Pectin Extension

AbstractSummary: A pectin 10mer under constant pulling speed and constant force was studied using the atomistic simulations. Molecular dynamics (MD) with the Amber99 and Amber‐Glycam04 forcefields were performed. The main result of the present Amber‐based MD simulations is that the two plateaux of the experimental force‐ extension dependence for pectin can be explained by transitions between three conformational states of pectin monomer ring (first from a chair (4C1) to boat conformation and second from boat to an inverted chair (1C4) conformation). A multi‐state dynamical model of single biopolymer extension under external force was elaborated and applied to extension of polymers with three‐state monomers relevant to pectin.

Kinetics of a semiflexible chain under external force

The kinetic properties of a semiflexible chain subject to an external force are investigated using scaling arguments and computer simulations. By monitoring the mean square displacements in principal axes, the authors found that the anisotropic dynamic fluctuations go through several distinct kinetic regimes characterized by two different exponents corresponding to transverse and longitudinal fluctuations. When a force is applied at one chain end, the tension propagates gradually to the other end, leading to nonuniform tension profiles. At short times, they observe sublinear relaxation of the mean square fluctuations in both longitudinal and transverse directions. At intermediate times, the kinetics is dominated by tension driven straightening with smaller kinetic exponents. Nonuniform tension profiles lead to the superlinear dependence of the longitudinal mean square displacement. In contrast, the late stage relaxation is diffusive again once the tension profile becomes uniform. The detailed tension profiles are reported for constant force measurement as well as constant pulling speed measurement.

Intrinsic Rates and Activation Free Energies from Single-Molecule Pulling Experiments

We present a unified framework for extracting kinetic information from single-molecule pulling experiments at constant force or constant pulling speed. Our procedure provides estimates of not only (i) the intrinsic rate coefficient and (ii) the location of the transition state but also (iii) the free energy of activation. By analyzing simulated data, we show that the resulting rates of force-induced rupture are significantly more reliable than those obtained by the widely used approach based on Bell's formula. We consider the uniqueness of the extracted kinetic information and suggest guidelines to avoid over-interpretation of experiments.

Molecular Dynamics Simulation of Dextran Extension at Constant Pulling Speed

AbstractSummary: A dextran monomer and a 10mer under constant pulling speed were studied using the atomistic simulations. Molecular dynamics (MD) with the new Amber‐Glycam04 forcefield were performed. The main result of the present Amber‐based MD simulations is that the experimental plateau of the force‐extension dependence for dextran can be explained by a transition of the glucopyranose rings in the dextran monomers from a chair (4C1) to a inverted chair (1C4) conformation whereas chair to boat transitions occur at higher forces. Density functional (DFT) calculations of monomer were also performed for a monomer at different fixed end‐to‐end distances (lengths) to clarify the molecular mechanism of dextran extension. These DFT calculations confirm the existence of an inverted chair (1C4) conformation at intermediate extensions and its possible important contribution to the plateau in the experimental force‐extension dependence of dextran.

Morphological Transitions of Shallow Cells during Thin-Film Solidification of an Alloy: Phase Field Modeling & Experimental Observation

The morphological transitions of shallow cells near the onset of Mullins-Sekerka instability during the thin-film directional solidification of a succinonitrile/acetone alloy have been simulated quantitatively by means of phase field modeling for the first time. Long time/length scale experiments at a constant pulling speed were performed for the purpose of comparison. The simulation results show good agreement with classic theories in the planar and λ(subscript c)↔λ(subscript c)/2 cellular bifurcation regions, where λ(subscript c) is the critical wavelength. At a higher pulling speed, V, an anti-trapping current was introduced to maintain the local equilibrium, and the region for Vλ^2~constant was found. Finally, multiplets appeared when λ was close to λ(subscript c)/4. In the experiments, due to slow solute accumulation in the molten zone, morphological transitions were also revealed. Some interesting nonlinear phenomena, such as tip splitting, coarsening, pinch-off, and asymmetric cells, were also confirmed through both simulations and experiments.

Nano- to Microscale Dynamics of P-Selectin Detachment from Leukocyte Interfaces. II. Tether Flow Terminated by P-Selectin Dissociation from PSGL-1

We have used a biomembrane force probe decorated with P-selectin to form point attachments with PSGL-1 receptors on a human neutrophil (PMN) in a calcium-containing medium and then to quantify the forces experienced by the attachment during retraction of the PMN at fixed speed. From first touch to final detachment, the typical force history exhibited the following sequence of events: i), an initial linear-elastic displacement of the PMN surface, ii), an abrupt crossover to viscoplastic flow that signaled membrane separation from the interior cytoskeleton and the beginning of a membrane tether, and iii), the final detachment from the probe tip most often by one precipitous step of P-selectin:PSGL-1 dissociation. Analyzing the initial elastic response and membrane unbinding from the cytoskeleton in our companion article I, we focus in this article on the regime of tether extrusion that nearly always occurred before release of the extracellular adhesion bond at pulling speeds ≥1μm/s. The force during tether growth appeared to approach a plateau at long times. Examined over a large range of pulling speeds up to 150μm/s, the plateau force exhibited a significant shear thinning as indicated by a weak power-law dependence on pulling speed, f∞=60 pN(νpull/μm/s)0.25. Using this shear-thinning response to describe the viscous element in a nonlinear Maxwell-like fluid model, we show that a weak serial-elastic component with a stiffness of ∼0.07 pN/nm provides good agreement with the time course of the tether force approach to the plateau under constant pulling speed.

THE EFFECT OF ANISOTROPIC THERMAL CONDUCTIVITY ON THE PULTRUSION PROCESS SIMULATION

The composite materials have been used in a large set of commercial products (space and aeronautical structures, automotive panels, tennis rackets, among others). One of the lower-cost processes for manufacturing bars of composite materials with constant cross-section is the pultrusion. In this process, a fiber creel is impregnated in a resin bath and passes through a heated die with a constant pulling speed, where the high die temperature induces the resin cure exothermic reaction. At the present study, the energy and the kinetics of cure equations are discretized by the finite element method with an unstructured triangular mesh. The obtained algebraic equations system is iteratively solved. Usually, the pultrusion process simulation is performed supposing isotropic thermal properties, that is, equal thermal conductivity in the composite material bar axial and transversal directions. This work reports the effect of the anisotropic thermal conductivity on the degree of cure and temperature profiles. Three cases are studied: in the first one, the axial conduction is neglected (parabolic approach); in the second case, isotropic thermal conductivity is assumed (first elliptic approach). In the last one, the carbon fiber anisotropic property is carried on the solution (second elliptic approach). The influence of the convective to diffusive transport terms ratio on the obtained results for the composite bar curing process is also analyzed. It is shown that in convective-dominant problems (high pulling speed) the fiber thermal conductivity anisotropy influence is less significant.

Strength of a Weak Bond Connecting Flexible Polymer Chains

Bond dissociation under steadily rising force occurs most frequently at a time governed by the rate of loading (Evans and Ritchie, 1997 Biophys. J. 72:1541–1555). Multiplied by the loading rate, the breakage time specifies the force for most frequent failure (called bond strength) that obeys the same dependence on loading rate. The spectrum of bond strength versus log(loading rate) provides an image of the energy landscape traversed in the course of unbonding. However, when a weak bond is connected to very compliant elements like long polymers, the load applied to the bond does not rise steadily under constant pulling speed. Because of nonsteady loading, the most frequent breakage force can differ significantly from that of a bond loaded at constant rate through stiff linkages. Using generic models for wormlike and freely jointed chains, we have analyzed the kinetic process of failure for a bond loaded by pulling the polymer linkages at constant speed. We find that when linked by either type of polymer chain, a bond is likely to fail at lower force under steady separation than through stiff linkages. Quite unexpectedly, a discontinuous jump can occur in bond strength at slow separation speed in the case of long polymer linkages. We demonstrate that the predictions of strength versus log(loading rate) can rationalize conflicting results obtained recently for unfolding Ig domains along muscle titin with different force techniques.

Nonisothermal Elongational Flow of Polymeric Fluids According to the Leonov Model

The time‐dependent nonisothermal elongational flows of polymeric fluids have been modeled using the Leonov constitutive theory. The stress growth at a constant elongational strain rate or constant pulling speed and stress relaxation after elongation have been considered under various thermal histories including constant cooling rate and a sudden jump or a drop in temperature. Following the concept of thermorheological simplicity, the nonisothermal effects have been conveniently incorporated into the theory via experimentally determined temperature shift factors together with the effect of nonzero cooling rates on glass transition temperature. The predicted results have been compared with the available experimental data of Bogue and co‐workers. In general, the agreement between theory and experiment is found to be good and comparable to the available results of other theories.

Nonlinear relaxation behavior of amorphous polymers in the rubbery state (T &gt; Tg): A new analysis of the data according to the “double-shift” procedure

Abstract Reliable data published in the literature on the nonlinear relaxational behavior of amorphous polymers in the rubbery range (T > Tg) are reanalyzed according to the “double-shift” procedure. The purpose of this study is to investigate the existence of a low strain-middle strain transition at around 40—50% of strain when an amorphous polymer is pulled in the rubbery state. This critical strain transition separating two distinct regimes of deformational behavior has already been reported in tensile experiments at constant pulling speed. In the work which is reanalyzed here, cross-linked or un-cross-linked amorphous elastomers are suddenly deformed at a constant temperature to a certain finite strain level and then allowed to relax. We replot the original relaxation data in a manner which is compatible with the double-shift superposition technique. Then we determine the best value of the horizontal and vertical shift factors so the curves obtained at different relaxational strains can superimpose. The analysis of the strain dependence of the shift factors confirms the existence, for the elastomers studied (PDMS, PBD, PIB), of a critical strain transition at around 40—50% of strain.

Nonequilibrium tensile deformation of amorphous polymers in the rubbery state: Temperature, strain rate, and strain effects. I

Abstract We analyze nonequilibrium tensile deformational behavior of an amorphous uncrosslinked random copolymer of styrene and acrylonitrile stretched above its Tg at various temperatures and constant strain rates. The variable investigated is the force required to pull the specimen to a certain strain level. Our results suggest the deformational behavior in the rubbery state can be incorporated in a universal scheme where strain, strain rate, and temperature effects are all superposed, e.g., the effect of strain is identical to the effect of temperature and strain rate. This unexpected result is true within two contiguous but distinct regimes of strain, on both sides of ca. 40% strain, suggesting that non-equilibrium extension at constant pulling speed in the rubbery state occurs by at least two successive mechanisms. Our results also reveal that the physical parameter which should be used to achieve a true superposition of strain rate and temperature data is not as simple as has long been commonly prop...