Direct Torque Measurement Research Articles

Direct Measurement of Torque in an Optical Trap and Its Application to Double-Strand DNA

We present a method that offers the possibility to directly apply and measure torque on particles in an optical trap. It can be used to rotationally manipulate biopolymers attached to appropriate particles. A flat object is trapped and oriented in the focus of a linearly polarized laser light. The direction and power of the orientational trap are controlled by the polarization state of the light. As a demonstration of the capabilities of the method, we examined the torsional stiffness of dsDNA (lambda-DNA) in its linear torsional regime by directly measuring the torque generated by the molecule.

Development of a disc-type torque meter for an automatic transmission vehicle

Torque is one of the key factors in describing engine performance. It is distributed to various parts of the vehicle such as the valvetrain, generator, and water pump. However, the exact torque delivered to each part cannot be determined. The first step to a full understanding of torque distribution is direct measurement of engine output torque. This paper considers the development of a disc-type torque meter that can be installed in a real vehicle. It uses the elastic deformation of a torque sensor which replaces the driveplate. It consists of a strain node, a power node, and a telemetry node, and transmits the torque signal by Bluetooth technology. The developed disc-type torque meter has good linearity and thermostability. It was installed in an in-line four-cylinder engine vehicle, and successfully measured the engine output torque.

Estimating propulsive forces—sink or swim?

The purpose of this study was to investigate the validity of hydrodynamic force estimation in swimming as calculated by the quasi-static approach. To achieve this a full-scale mechanical arm was developed, built and tested. The mechanical arm, covered with a prosthetic shell and driven at the shoulder was used to simulate a single plane underwater rotation at four elbow configurations. A computer program controlled the shoulder movement to achieve a replicable angular velocity profile for each arm movement. A strain gauge system was used to directly measure the generated arm torque. Repeated trials were conducted at fixed elbow angles of 110°, 135°, 160° and 180°. All trials were filmed using a three-dimensional underwater set-up. Each trial was digitised at 25 Hz and the hydrodynamic drag force profile of the hand calculated using the quasi-static procedure. From these data, the estimated shoulder torque was calculated and compared to the direct measurement of shoulder torque from the mechanical arm. The results showed that the arm produced a repeatable movement through the water. The shoulder torque profiles using the direct measure (the arm) and the indirect measures (quasi-static approach) differed considerably. The quasi-static approach appears not to accurately reflect the hydrodynamic force profile generated by the arm movement in swimming. Furthermore, it seems that the swimmer's hand contribution is overstated in up to date studies. It is essential that the propulsive mechanisms in swimming be further investigated if factors underpinning an optimal technique are to be established.

Force and torque measurements using magnetic micro beads for single molecule biophysics

Characterization of optical trapping with laser tweezers of super-paramagnetic beads has been performed for the first time. In particular, we have compared the force action in optical trapping on super-paramagnetic beads with respect to the polystyrene ones. Using a novel magneto-optical manipulator we have developed a direct rotation detection scheme for trapped beads characterized by a high sensitivity and fast time response. Finally a calibration procedure able to directly measure an applied external torque on the trapped bead is shown. This demonstrates the capability of this apparatus to perform direct torque measurement (torsional rigidity) on a single bio-molecule attached to a super-paramagnetic bead.

Experimental Study on the Aerodynamic Performance of a Savonius Rotor

The aerodynamic performance of a Savonius rotor has been studied by measuring the pressure distributions on the blade surfaces at various rotor angles and tip-speed ratios. It is found that the pressure distributions on the rotating rotor differ remarkably from those on the still rotor especially on the convex side of the advancing blade, where a low pressure region is formed by the moving wall effect of the blade. The torque and power performances, evaluated by integrating the pressure, are in close agreement with those by the direct torque measurement. The drag and side force performance is also studied.

Investigation of Pressure Measurements on Blade Surfaces of a Savonius Rotor and its Power Mechanism.

Pressure distributions on the blade surfaces of a Savonius rotor with and without rotation are measured for various rotor angles and tip-speed ratios, and the power mechanism is discussed based on the result. The torque-producing mechanism of the rotating rotor is strongly contributed to by the large negative pressure region formed on the convex side of the advancing blade, suggesting the Coanda-like flow pattern shown in the flow visualization experiment, while that of the still rotor is mainly due to the stagnation effect on the concave side. The torque and the power performances estimated from the present pressure measurement agree approximately with the previous results by direct torque measurement, which shows the approximate two dimensionality of the flow field near the rotor.

Magnetic anisotropy of some heavy rare-earth metals

Abstract The first order axial anisotropy coefficient, K2, has been evaluated for terbium at constant magnetic fields from torque measurements in its paramagnetic region. In this region K2 can also be calculated at constant magnetization from the known anisotropy in susceptibility between the basal plane and c axis. From the latter results, an extrapolation to 0 K has been made on the basis of the validity of the single-ion theory for the anisotropy of the heavy rare earths. This yields the following values in erg/cm3 for K2(0): Tb, 2.7 × 108; Dy, 3.1 × 108; Ho, 1.0 × 108; Er, −1.9 × 108. The basal-plane anistropy coefficient K66 of terbium has been determined at different temperatures and fields by direct torque measurements. It obeys the single-ion magnetization dependence with a value at 0 K of 2.9 × 106 erg/cm3.

Nuclear Magnetic Resonance Studies in Antiferromagnetic CrCl3

We have investigated the metamagnetic properties of CrCl3 by studying the temperature and magnetic field dependences of the Cr53 nuclear magnetic resonance in the temperature range 0.39°–11.5°K. Below 238°K the crystal structure of CrCl3 is isomorphous with that of CrBr3 (space group R3̄). A specific heat anomaly occurs at T=16.8°K1 due to a transition to a magnetically ordered structure in which ferromagnetic (001) sheets alternate in direction along the hexagonal c axis.2 The large field-dependent perpendicular susceptibility arises from the small value of the antiferromagnetic interlayer exchange energy compared to the much larger ferromagnetic intralayer exchange energy. The measured susceptibility below 4°K3 gives an antiferromagnetic exchange field HE=1450 Oe corresponding to an exchange constant JLzL/k=−0.065°K. From the observed Tc, simple molecular field theory gives an intralayer exchange constant JTzT/k=6.7°K, where zL and zT are the number of exchange-coupled nearest neighbors along the c axis and in the basal plane, respectively. It is apparent from the magnitude of JT/JL that the low-temperature magnetic properties of CrCl3 should closely approximate those of a two-dimensional Heisenberg ferromagnet. Among the unusual properties expected for such a system are a nearly linear M(T)/M(0) relation at sufficiently high temperatures and a large parallel magnetic susceptibility. These predictions are in good agreement with our experimental results. We have analyzed the temperature dependence of the Cr53 zero-field resonance by means of the following isotropic exchange Hamiltonian: H=−JT ∑ i,j Si·Sj−gβHA ∑ i Siz,where HA is an effective anisotropy field which includes HE. We have compared our data with several approximate solutions of (1): (a) simple spin-wave, long wave (k2) limit; (b) simple spin-wave, exact calculation of M(T)/M(0) from the dispersion relation; (c) spin-wave model with approximate treatment of spin-wave interactions. [The effective anisotropy field was given a temperature dependence HA(T) = HA(0)M(T)χ⊥(0)/M(0)χ⊥ (T) and the intralayer interactions were treated by renormalization techniques.] Approximations (a) and (b) were applied to the data below 4°K and (c) to the whole range 0.39°–8.2°K. Agreement within the experimental uncertainty is found in all three cases and the results are: (a) JTZT/k=11.85∘K, HA =2700 Oe,(b) JTZT/k=13.35∘K, HA =2000 Oe,(c) JTZT/k=15.03∘K, HA(0)=1525 Oe.The effect of the intralayer renormalization in (c) is only important above 4°K; the effect of the temperature dependence of HA, however, is very noticeable even below 4°K as can be seen from the differences in JT, HA obtained from (b) and (c). The magnitude of JT derived from spin-wave theory is considerably larger than that obtained from the molecular field model. The spin-wave value, however, is consistent with values derived for two-dimensional lattices from Tc by the Kramers-Opechowski method.4 The anisotropy in CrCl3 is very small since HA(0)≈HE. One expects a large negative axial dipolar anisotropy; however this anisotropy is almost cancelled by a positive single-ion term arising from spin-orbit interactions. This conclusion is in agreement with results of spin-wave calculations which include these interactions explicitly, as well as direct torque measurements of the anisotropy.5 We have investigated the intensity enhancement of the Cr53 resonance in zero field and in weak external fields. In both cases the resonance is driven by the appropriate antiferromagnetic resonance mode. We have compared the measured intensities with calculations based on the measured static susceptibilities and have obtained a value of K3≈150 erg/cm3 for the weak sixfold anisotropy in the (001) plane. The weak-field enhancement leads to selective excitations in polycrystalline samples resulting in observable splittings of the nuclear resonance when the driving field is parallel to the steady field. These splittings are a result of the expected strong field dependence of the sublattice magnetizations. We have determined χ∥ at several temperatures from these observations. At 4.00°K we find χ∥=0.28 emu/mole which compares with values of 0.227 and 0.289 calculated from spin-wave models (b) and (c), respectively. A complete account of this work appears elsewhere.6