Direct Torque Measurement Research Articles

Insights into the mechanism of ATP-driven rotary motors from direct torque measurement.

Motor proteins are molecular machines that convert chemical energy into mechanical work. In addition to existing studies performed on the linear motors found in eukaryotic cells, researchers in biophysics have also focused on rotary motors such as F1-ATPase. Detailed studies on the rotary F1-ATPase motor have correlated all chemical states to specific mechanical events at the single-molecule level. Recent studies showed that there exists another ATP-driven protein motor in life: the rotary machinery that rotates archaeal flagella (archaella). Rotation speed, stepwise movement, and variable directionality of the motor of Halobacterium salinarum were described in previous studies. Here we review recent experimental work discerning the molecular mechanism underlying how the archaellar motor protein FlaI drives rotation by generation of motor torque. In combination, those studies found that rotation slows as the viscous drag of markers increases, but torque remains constant at 160 pN·nm independent of rotation speed. Unexpectedly, the estimated work done in a single rotation is twice the expected energy that would come from hydrolysis of six ATP molecules in the FlaI hexamer. To reconcile the apparent contradiction, a new and general model for the mechanism of ATP-driven rotary motors is discussed.

КОМПОНУВАННЯ ВИНИЩУВАЧА МАЛОРОЗМІРНИХ БПЛА ДЛЯ ЗАХИСТУ ЛОКАЛЬНО ОБМЕЖЕНОГО ПРОСТОРУ

Стаття присвячена вирішенню актуальної наукової задачі синтезу аеродинамічного компонування винищувача малорозмірних безпілотних літальних апаратів. Проведений аналіз БПЛА який свідчить про посилення ролі безпілотної авіації в світі. Викладена методика проведення експериментальних досліджень компонувань літальних апаратів в аеродинамічних трубах. Представлена розроблена методика визначення аеродинамічних характеристик компонувань, що містить комплексне використання експериментальних методів та числових методів – методу збурених потенціалів. Характерною рисою компонування крила малого подовження з повітряними гвинтами є відсутність елементів, на які не впливають гвинти. Ця особливість істотно ускладнює проведення та автоматизацію експерименту в аеродинамічній трубі, оскільки існують проблеми забезпечення критеріїв подібності для рацюючого повітряного гвинта; складність досягнення ідеального балансування гвинтів з жорстким приводом спричиняє наявність вібрації, рівень якої залежить від неконтрольованих факторів; неможливість знехтувати наявністю впливу тілесних елементів компонування на лопаті повітряних гвинтів; складність безпосереднього виміру тяги та крутного моменту повітряних гвинтів. Такий підхід дозволить поєднати високу достовірність експериментальних при дослідженні фізичної сутності явищ, високу точність визначення аеродинамічних сил при побудові положення вихрової пелени від повітряних гвинтів. Встановлені залежності є основою для розробки рекомендацій з вибору раціональних геометричних параметрів аеродинамічного компонування крила малого подовження з повітряними гвинтами протилежного обертання.

Energy Efficiency Class IE5 Magnet-Free Synchronous Reluctance Motor

Modern synchronous reluctance motors allow improving energy efficiency of many industrial applications. The new standards define five classes of energy efficiency for electric motors, from IE1 to IE5. This paper considers issues related to the mathematical modeling and testing of a magnet-free synchronous reluctance motor of the highest energy efficiency class IE5. The proposed mathematical model allows calculating the efficiency factor, power factor, torque ripple, winding losses in the stator and rotor magnetic cores, and other operating characteristics of the synchronous reluctance motor run in various operation modes. The motor was tested on a test bench, which involved direct torque measurements. Thermocouples were used and measurements made in steady-state thermal mode to find the winding temperature. The body of the prototype synchronous reluctance motor has the same dimensions and rotation axis height as the body of the commercial IE3 induction motor of the same power. The results of a comparative test of the class IE5 prototype magnet-free motor and the class IE4 commercial motor are presented.

Highly Efficient Spin-Current Generation by the Spin Hall Effect in Au1−xPtx

We report very efficient spin current generation by the spin Hall effect in the alloy Au0.25Pt0.75, which, as determined by two different direct spin-orbit torque measurements, exhibits a giant internal spin Hall ratio of > 0.58 (anti-damping spin-orbit torque efficiency of ~ 0.35 in bilayers with Co), a relatively low resistivity of ~ 83 uOhm cm, an exceptionally large spin Hall conductivity of > 7.0x10^5 ohm^-1 m^-1, and a spin diffusion length of 1.7 nm. This work establishes Au0.25Pt0.75 as a milestone spin current generator that provides greater energy efficiency than that yet obtained with other heavy metals or with the topological insulators Bi2Se3 and (Bi,Se)2Te3. Our findings should advance spin-orbit torque-based fundamental research and benefit the development of new fast, efficient spin-orbit torque-driven magnetic memories, skyrmion and chiral domain wall devices, and microwave and terahertz emitters.

Polymer Optical Fiber for Angle and Torque Measurements of a Series Elastic Actuator's Spring

Series elastic actuators (SEAs) can provide low output impedance, bandwidth close to the human movement, and direct measurement of torque through the spring deflection. These advantages enable the application of SEAs in human active orthosis and exoskeletons. However, conventional technologies to measure the spring deflection are bulky, inhibit natural pattern of movement or are sensitive to misalignments. This paper presents the application of polymer optical fiber (POF) as a sensor to measure the spring deflection to overcome some of the issues of conventional technologies, since it is compact, lightweight, and have electromagnetic immunity. Furthermore, the spring is employed to validate a torque sensor based on POF stress-optic effects. Results show high linearity of both sensors and mean squared errors below the encoder resolution employed as a reference on dynamic measurements.

A flexoelectricity effect-based sensor for direct torque measurement

In this study, a direct torque sensor based on the flexoelectricity generated by un-polarized polyvinylidene fluoride (PVDF) via electromechanical coupling is developed as a novel torque measurement mechanism that does not require external electric power excitation. The sensing method is developed based on the shear strain gradient and the shear flexoelectric response of PVDF. A theoretical analysis is primarily presented for the design of the sensing structure. Then the structure of the PVDF sensing module is discussed and designed. The radius ratio of the sensing module is defined and then discussed according to the load, the strain gradient, the electrode area and the general electric charge output. The finite element method is used to analyze the mechanical properties of the designed PVDF sensing module. Then the theoretical sensitivity of the sensor is predicated as 0.9441 pC Nm−1. The experiment system setup is developed, and the sensing properties of the measurement mechanism are tested at frequencies of 0.5 Hz, 1 Hz, 1.5 Hz and 2 Hz using identical modules. The measurement range of the designed sensor is 0–1.68 Nm and the average sensitivity is measured as 0.8950 pC Nm−1. The experimental results agree well with the theoretically predicted results. These results prove that the torque sensing method based on un-polarized PVDF is suitable for measurement of dynamic torque loads with a flexoelectricity-based mechanism. When using this method, external electric power excitation of the sensing module is no longer required.

Torque Measurements during the Spontaneous Unbraiding of DNA Molecules Showed Large Fluctuations Attributable to the Formation of Stable DNA-DNA Interactions

Magnetic tweezers dual-molecule braiding assays provide an adequate framework for studying the mechanical aspects underlying the process of winding two DNA molecules around each other. In its typical implementation however, this technique do not allow direct measurement of torque because the torque exerted by the magnetic traps (∼103 pN nm) is at least one order of magnitude larger than the restoring torque of DNA (∼ 102 pN nm). In previous work, our laboratory showed that enough elastic energy could be stored in a pair of braided DNA molecules to perform mechanical work by rotating a microscopic object in absence of manipulation. Here we have exploited that unique property of DNA to perform a real-time study of braided DNA dynamics. In our experiments, torsionally unconstrained lambda DNA molecules were bound to a surface by one end and to a microscopic dumbbell at the other. A magnetic tweezers apparatus was employed to stretch and braid the molecules. Upon creating the braid, the magnet was removed to trigger the spontaneous unbraiding of DNA. The rotational dynamics of the dumbbell was followed in real-time. Hydrodynamic equations were employed to relate the dynamical information of the dumbbells to torque values. Our most important finding is that the unbraiding process occurs in a discontinuous manner. The estimated magnitudes of torque were found to fluctuate between an upper (∼ 102 pN nm) and a lower bound (∼ 101 pN nm) value along the entire process. The magnitudes of the fluctuations were found to be independent of the amount of times that the molecules crossed each other. No different was found for braids of opposite handedness. We attributed these fluctuations to the formation/rupture of stable DNA interactions.

Combined Magneto-Optical Tweezers and Supperesolution Fluorescence Imaging for Probing Dynamic Single-Molecule Topology of DNA, and Protein Machines that Manipulate DNA Topology

Conventional magnetic tweezers (MT) designs suffer from a few limitations: (i) it is not possible to independently control torque while maintaining the desired force magnitude. The applied torque is orders of magnitude higher than biologically relevant values, precluding direct measurement of torque. (ii) They do not image the biological molecule. Rather, they image the magnetic beads attached to the molecules and infer the transformation of the molecules. This limits experiments to only high-torque processes that result in measurable change of molecular geometry, and even in these experiments the location of events on the molecule cannot be known. (iii) Due to the video-imaging based position detection of the magnetic bead, as opposed to interferometry based tracking typically used in optical tweezers, the low spatial and temporal resolutions prevent the observation of many molecular activities.The above limitations have been overcome individually but there has not been a design that overcomes all the drawbacks. Here we propose magneto-optical tweezers (MOT) to independently apply torques and forces at biologically relevant values while also arranging the DNA molecules in a transverse orientation to allow fluorescence microscopy to be performed and utilising back-focal-plane interferometry for high resolution tracking [1, 2]. We also present preliminary data on DNA topological response to MOT manipulation.1. Miller, H., Zhou, Z., Wollman, A.J., and Leake, M.C. Superresolution imaging of single DNA molecules using stochastic photoblinking of minor groove and intercalating dyes. Methods 2015.2. Zhou, Z., Miller, H., Wollman, A., and Leake, M. Developing a New Biophysical Tool to Combine Magneto-Optical Tweezers with Super-Resolution Fluorescence Microscopy. Photonics 2015. 2, 758.

An Improved Experimental Technique to Characterize Micro-Diameter Copper Wires in Torsion

The experimental technique was improved with direct measurement of small torque and rotation angle to characterize micro-diameter copper wires in torsion. This method allows precise measurement of torque applied to micro-diameter wires as low as 10−8 N · m with reasonably high resolution. The rotation angle is also able to be directly measured such that the shear strain rate on the wire surface can be easily controlled. This experimental design removes the misalignment issue that has affected previous efforts in micro-diameter wire torsion testing. Using this technique, the copper wires with four different diameters (12, 16, 20, and 30 μm) were characterized in torsion. The normalized torque-rotation results showed insignificant size effects for the copper wires investigated in this study.

Evolution of strength and structure during SPD processing of Ti–45Nb alloys: experiments and simulations

A β-phase Ti–45Nb alloy was processed by several severe plastic deformation (SPD) methods as high-pressure torsion, cold rolling and folding, and hydrostatic extrusion to enhance its strength by achieving an ultrafine grained structure without affecting the Young’s modulus being close to that of bone material. Mechanical properties during processing were monitored by direct torque and Vickers hardness measurements, while the micro-/nano-structural evolution was investigated by transmission electron microscopy and X-ray line profile analysis. Simulations of both mechanical and micro-/nano-structural data were performed on the basis of the SPD work-hardening model by Zehetbauer. The simulations not only found a good agreement with the deformation-specific evolution of strength and density of individual dislocations but also well reflected mesoscopic structural quantities such as the sizes of cell/grain interiors and walls without introducing additional fitting parameters.

Measurement and analysis of instantaneous torque and angular velocity variations of a low speed two stroke diesel engine

This paper presents an investigation into the potential of using direct measurement of engine torque for diagnostic purposes in large engines – in this case applied to power generation. The procedures for measuring and analyzing the instantaneous torque, the angular displacement on the generator output end and the angular displacement on its free end for a ten-cylinder, low speed two stroke diesel engine are presented. Angular speed oscillations are frequently used for combustion engine diagnostics although they cannot be used to measure engine power directly. In addition, and for engines with huge inertia generators such as those used in power plants, speed oscillations are very low and this reduces the signal to noise ratio and makes the evaluation of the instantaneous angular speed very noisy. In the work described here, torque and angular displacement measurements carried out at the same point and with the same engine conditions are compared and the superior performance of torque is demonstrated. Harmonic analysis of instantaneous torque allowed the identification of the dynamic characteristics of the power train of the diesel group and clearly suggests that this signal can be used as a diagnostic tool for excitation, combustion malfunctions, or for the mechanical characteristics of the system and crankshaft stiffness. The torque distortion introduced by the generator due to the discontinuity imposed by the pole pairs is also observed in the torque signal, suggesting that the torque signal can be used to identify generator malfunction.

Fabrication and Surface Functionalization of Highly Birefringent Particles for Optical Torque Wrench

Conventional optical tweezers are limited by the ability to apply only translational manipulation to probe the diverse biological systems. The recent extension of optical tweezers, i.e., the optical torque wrench (OTW), allows the direct application and measurement of torque. The OTW provides a platform to measure rotational dynamics of biomolecules and motors including the torque-dependence of DNA or DNA-protein interactions, and of powerful machines such as F0F1-ATP-synthase or bacterial flagellar motor.The applicable torque of the OTW is largely dependent on the birefringence of the trapped particle. Quartz (SiO2) is widely used due to its facile fabrication and stability in biological environments. However, the birefringence of quartz is limited to fully investigate the torque-speed relationships of diverse biological systems so we explored more highly birefringent crystals such as rutile (TiO2) and vanadate (YVO4). Developing novel fabrication protocol is required because the particle fabrication from these alternative crystals is not as straightforward as quartz. For example, Cr was used as a mask for dry etching cylinders from rutile with SF6/CH4 processing gases and it resulted in etching selectivity of 1:28 which is higher than electron beam resist mask with selectivity of 1:1.3.To promote the selective attachment of the particle to target biological system, a submicron-sized protrusion can be fabricated on one end of a cylindrical particle and functionalized with specific ligand biomolecules. Alkoxysilane based surface crosslinkers, such as APTES, that are commonly used to bind biomolecules to solid supports, tend to polymerize and result in inhomogeneous surface coatings. To obtain uniform, dense, and reproducible surface coating for nanoscale structures, we explored the use of cyclic aza-silanes as alternative crosslinkers for biomolecule attachment.

Contactless Shaft Torque Detection for Wide Range Performance Measurement of Exhaust Gas Turbocharger Turbines

Turbochargers develop away from an auxiliary component—being “off the shelve”—towards an integrated component of the internal combustion engine. Hence, increased attention is paid to the accuracy of the measured turbine and compressor maps. Especially turbine efficiency measurement under engine-relevant operating conditions (pulsed flow) is recently receiving increased attention in the respective research community. Despite various turbine map extrapolation methods, sufficient accuracy of the input test data is indispensable. Accurate experimental data are necessary to achieve high quality extrapolation results, enabling a wide range and precise prediction of turbine behavior under unsteady flow conditions, determined by intermittent operation of the internal combustion engine. The present work describes the first application of a contactless shaft torque measurement technique—based on magnetostriction—to a small automotive turbocharger. The contactless torque measuring system is presented in detail and sensor principle as well as sensor calibration are illustrated. A sensitivity study regarding sensor position influences onto sensor signal proves the robustness and very good repeatability of the system. In the second part of the paper, steady state experimental results from operation on a conventional hot gas test stand over a wide map range are presented. These results are validated against full turbine stage (adiabatic as well as diabatic) CFD results as well as against “cold” efficiency measurements, based on measured inlet and outlet temperatures. The influence and relevance of bearing friction for such measurements is underlined and the improvements on this matter—achieved by direct torque measurement—are demonstrated.

Estimating Model on Torque for Alternating Current Electric Dynamometer Based on the Support Vector Machine Combined with the Fuzzy System

In order to solve the problems such as high cost and complicated measurement system existing in the process of direct torque measurement for an alternating current electric dynamometer, the indirect measurement of support vector machine combined with the fuzzy system was adopted. Fuzzy rules were obtained by training the support vector machine and at the same time the genetic algorithm was brought to optimize parameters of the support vector machine and thus could obtain the most optimum fuzzy rule base. Moreover, torque of the alternating current electric dynamometer was estimated. The result shows that the precision of estimation with the support vector machine combined with the fuzzy system is high. So the direct torque measurement could be replaced by the indirect one and the support vector machine combined with the fuzzy system could be a method of cost reduction at present.

Direct shaft torque measurements in a transient turbine facility

This paper describes the development and implementation of a shaft torque measurement system for the Oxford Turbine Research Facility (formerly the Turbine Test Facility (TTF) at QinetiQ, Farnborough), or OTRF. As part of the recent EU TATEF II programme, the facility was upgraded to allow turbine efficiency measurements to be performed. A shaft torque measurement system was developed as part of this upgrade. The system is unique in that, to the authors’ knowledge, it provided the first direct measurement of shaft torque in a transient turbine facility although the system has wider applicability to rotating test facilities in which power measurement is a requirement. The adopted approach removes the requirement to quantify bearing friction, which can be difficult to accurately calibrate under representative operating conditions. The OTRF is a short duration (approximately 0.4 s run time) isentropic light-piston facility capable of matching all of the non-dimensional parameters important for aerodynamic and heat studies, namely Mach number, Reynolds number, non-dimensional speed, stage pressure ratio and gas-to-wall temperature ratio. The single-stage MT1 turbine used for this study is a highly loaded unshrouded design, and as such is relevant to modern military, or future civil aero-engine design. Shaft torque was measured directly using a custom-built strain gauge-based torque measurement system in the rotating frame of reference. This paper describes the development of this measurement system. The system was calibrated, including the effects of temperature, to a traceable primary standard using a purpose-built facility. The bias and precision uncertainties of the measured torque were ±0.117% and ±0.183%, respectively. To accurately determine the shaft torque developed by a turbine in the OTRF, small corrections due to inertial torque (associated with changes in the rotational speed) and aerodynamic drag (windage) are required. The methods for performing these corrections are described.

Magnetic Torque Tweezers and Their Application in Probing the Torsional Properties of DNA, RNA, and DNA Filaments

The double-stranded nature of DNA links processes such as replication, transcription, and repair, to rotational motion and torsional strains. Magnetic tweezers (MT) are a powerful single-molecule technique to apply both forces and torques to individual molecules. However, while the forces applied in conventional MT can be calibrated from thermal fluctuations or computed from first principles [1], direct measurement of the torque is challenging.Here we present the magnetic torque tweezers (MTT), which enable the direct measurement of torque [2] based on a tracking protocol that monitors x, y, z, and angle and on a redesigned magnet configuration. We have applied the MTT to dsDNA, dsRNA, and RecA-DNA heteroduplex filaments. Our measurements of the effective torsional stiffness C of dsDNA indicate a significant force dependence, with C ≈ 40 nm at low forces up to C ≈ 100 nm at high forces, reconciling previous partially conflicting measurements. Torque measurements on RecA-DNA heteroduplex filaments reveal an initial torsional stiffness about two-fold higher than that of DNA. However, at relatively moderate torques further build-up of torsional strain is prevented by partial RecA disassembly and structural transitions in the filament. Preliminary results on the torsional properties of fully dsRNA indicate static properties overall similar to dsDNA, but significantly different dynamics of supercoil formation.Finally, we compare the MTT configuration with recently developed strategies to measure torque using optical tweezers [3] and with a related MT approach that allows straight-forward measurements of free rotation termed freely-orbiting magnetic tweezers [4].[1] Lipfert, Hao & Dekker, Biophys. J. (2009).[2] Lipfert, Kerssemakers, Jager & Dekker, Nature Methods, in press (2010).[3] Forth, et al. Phys. Rev. Lett. (2008).[4] Lipfert, Wiggin, Kerssemakers & Dekker, submitted (2010).

Passive Torque Wrench and Angular Position Detection Using a Single Beam Optical Trap

The recent advent of angular optical trapping techniques has allowed for rotational control and direct torque measurement on biological substrates. Here we present a novel method that increases the versatility and flexibility of these techniques. We demonstrate that a single beam with a rapidly rotating linear polarization can be utilized to apply a constant controllable torque to a trapped particle without active feedback while simultaneously measuring the particle's angular position. In addition, this device can rapidly switch between a torque wrench and an angular trap. These features should make possible torsional measurements across a wide range of biological systems.

Passive torque wrench and angular position detection using a single-beam optical trap

The recent advent of angular optical trapping techniques has allowed for rotational control and direct torque measurement on biological substrates. Here we present a method that increases the versatility and flexibility of these techniques. We demonstrate that a single beam with a rapidly rotating linear polarization can be utilized to apply a constant controllable torque to a trapped particle without active feedback, while simultaneously measuring the particle angular position. In addition, this device can rapidly switch between a torque wrench and an angular trap. These features should make possible torsional measurements across a wide range of biological systems.

Turbine Efficiency Measurement System for the QinetiQ Turbine Test Facility

Abstract A turbine efficiency measurement system has been developed and installed on the turbine test facility (TTF) at QinetiQ Farnborough. The TTF is an engine-scale short-duration (0.5s run time) rotating transonic facility, which can operate as either single stage (HP vane and rotor) or 112 stage (HP stage with IP or LP vane). The current MT1 HP stage is highly loaded and unshrouded and is therefore relevant to current design trends. Implementation of the efficiency measurement system forms part of the EU Turbine Aero-Thermal External Flows (TATEF II) program. The following aspects of the efficiency measurement system are discussed in this paper: mass-flow rate measurement, power measurement by direct torque measurement, turbine inlet and exit area traverse measurement systems, computation of efficiency by mass weighting, and uncertainty analysis of the experimentally determined turbine efficiency. The calibration of the mass-flow rate and torque measurement systems are also discussed. Emphasis was placed on the need for a low efficiency precision uncertainty, so that changes in efficiency associated with turbine inlet temperature distortion and swirl can be resolved with good accuracy. Measurements with inlet flow distortion form part of the TATEF II program and will be the subject of forthcoming publications.

Direct measurement of current-induced fieldlike torque in magnetic tunnel junctions

We present a direct and quantitative method to measure the current-induced fieldlike torques in current perpendicular to plane magnetic multilayers. We illustrate this method on nanopillars patterned from MgO-based magnetic tunnel junctions. By measuring how the Stoner astroids are displaced, shrinked, and distorted under the influence of a bias current, we separate the contributions of the current-induced fieldlike torque, the current-induced heating, and the current-induced spin torque. In contrast to high frequency based measurement methods that are better suited to analyze the spin torque than the fieldlike term, our measurement is direct and quantitative for the current-induced fieldlike term and the heating induced reduction in shape anisotropy, while only qualitative for the spin torque.