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At least 1,063 records · Page 59Linked to original sources
PubMed1992

A miniaturised force-torque sensor with six degrees of freedom for dental measurements.

Force-torque sensor systems capable of simultaneously measuring all six spatial degrees of freedom on solid bodies are not very widespread in the medical field, particularly because of the hitherto unacceptably large external dimensions. A sensor based on the strain gauge technique has been developed with a diameter of only 32.5 mm and height of 29 mm. The miniaturised supporting framework for the strain gauges has been cast in a single piece from a wax-plastic model by the one-way mould principle. A sensitivity of 10 mN with an upper limit of 50 N is attained.

Crowns↗
PubMed1988

Effect of stabilization on maximal isokinetic torque of the quadriceps femoris muscle during concentric and eccentric contractions.

The purpose of this study was to investigate the effect of stabilization on the maximal isokinetic torque generated by the quadriceps femoris muscle during concentric and eccentric contractions at different velocities using the KIN/COM isokinetic dynamometer. Fifteen female volunteers between the ages of 18 and 32 years were trained to perform maximal isokinetic concentric and eccentric contractions. Each subject participated in two testing sessions. In one testing session, subjects were stabilized maximally, and in the other testing session, subjects were stabilized minimally. Subjects were tested both concentrically and eccentrically at velocities of 30 degrees, 60 degrees, 90 degrees, 120 degrees, 150 degrees, 180 degrees, and 200 degrees/sec. The velocity sequence and stabilization procedure used were randomly assigned. Two nested model analyses of variance followed by post hoc comparisons were used to analyze the data. Results revealed no significant difference between the maximal stabilization procedure and the minimal stabilization procedure for concentric and eccentric contractions. The results of this study should aid rehabilitation specialists in the development of testing and rehabilitation procedures when using the KIN/COM.

Adult↗
PubMed1992

A new method for the determination of the characteristic shape of an isokinetic quadriceps femoris muscle torque curve.

It has been suggested that visual analysis of isokinetic quadriceps femoris muscle torque curve (TC) shapes may have potential use in the diagnosis and prognosis of knee pathologies. The primary purpose of this pilot study was to develop a method for analyzing the shape of an isokinetic TC. Our method normalizes and averages the TC, and then uses curvilinear analysis of the TC shape to aid in diagnosis and prognosis. For demonstration, the method was applied to isokinetic quadriceps femoris muscle TC data collected using a LIDO digital dynamometer from 25 healthy volunteer subjects and retrospectively acquired from the uninvolved limbs of 37 patients with unilateral knee pathologies. The preliminary results revealed (1) that a common quadriceps femoris muscle TC shape existed for the volunteer group at 60 degrees and 180 degrees/s; (2) that the uninvolved limbs of the patient group exhibited the same shape at 60 degrees/s, but not at 180 degrees/s; and (3) that the quadriceps femoris muscle TC shape demonstrated no significant differences with respect to limb dominance or gender for either group. Further testing of this quantitative method on a larger sample is needed to determine its usefulness in the analysis and implications of TC shape concerning pathology and diagnosis.

Adult↗
PubMed2003

A comparison of a left-sided Broncho-Cath with the torque control blocker univent and the wire-guided blocker.

UNLABELLED: Lung isolation can be accomplished in two ways: the first, a double-lumen endotracheal tube (DLT) and the second, a bronchial blocker (Univent or Arndt blocker). Previous studies have found that the DLT and the Univent are comparable when providing lung isolation. A new bronchial blocker, the wire-guided endobronchial blocker (Arndt blocker), has been introduced. However, there is no study to report its effectiveness with lung isolation during elective thoracic surgical cases. Therefore, we designed a prospective, randomized trial to compare the effectiveness of lung isolation among the 3 endotracheal tubes: the left-sided DLT Broncho-Cath Group A (n = 16 patients), the torque control blocker Univent Group B (n = 16 patients), and the wire-guided Arndt blocker Group C (n = 32 patients). The following variables were recorded: 1) time to initially position the assigned tube, 2) frequency of malpositions, 3) frequency of use of fiberoptic bronchoscope, 4) overall surgical exposure, and 5) tube acquisition cost. The Arndt blocker took longer to place (3:34 min/s) compared with the other 2 groups: the DLT group (2:08 min/s) or the Univent group (2:38 min/s) (P < 0.0004). There was no statistical difference in tube malpositions among the three groups: two for the DLT group, four for the Univent group, and nine in the Arndt group. Excluding the time for tube placement, the Arndt group also took longer for the lung to collapse (26:02 min/s), compared with the DLT group (17:54 min/s) or Univent group (19:28 min/s) (P < 0.0060). Furthermore, unlike the other two groups, the majority of the Arndt patients required suction to achieve lung collapse. Once lung isolation was achieved, overall surgical exposure was rated excellent for the three groups. Acquisition cost for the DLT group was $1663.20 (21 tubes opened), $2329.00 for the Univent group (17 tubes opened), and $3567.00 for the Arndt group (33 wire-guided blockers opened). This study demonstrates that the Arndt blocker takes longer to position and longer to deflate the isolated lung. For elective thoracic surgical cases, once the lung was isolated, the management seemed to be similar for all three tube groups. IMPLICATIONS: We compared the latest design of double-lumen tubes Broncho-Cath, Univent, and Arndt blockers during lung isolation. Our results show that the Arndt blocker takes longer to position and longer to deflate the isolated lung. Once the lung was isolated, the management seemed to be similar for all three devices.

Adult↗
PubMed2004

Critical adsorption and Casimir torque in wedges and at ridges.

Geometrical structures of confining surfaces profoundly influence the adsorption of fluids upon approaching a critical point T(c) in their bulk phase diagram, i.e., for t= (T- T(c) ) / T(c) -->+/-0 . Guided by general scaling considerations, we calculate, within the mean-field theory, the temperature dependence of the order parameter profile in a wedge with opening angle gamma pi) for T>< T(c) and in the presence of surface fields. For a suitably defined reduced excess adsorption Gamma (+/-) (gamma,t-->+/-0) approximately Gamma (+/-) (gamma) mid R:tmid R:(beta-2nu) we compute the universal amplitudes Gamma (+/-) (gamma) , which diverge as Gamma (+/-) (gamma-->0) approximately 1/gamma for small opening angles, vary linearly close to gamma=pi for gamma 2pi . There is evidence that, within the mean-field theory, the ratio Gamma (+) (gamma) / Gamma (-) (gamma) is independent of gamma . We also discuss the critical Casimir torque acting on the sides of the wedge as a function of the opening angle and temperature.

Journal Article↗
PubMed2005

Torque-balanced high-density steady states of single-component plasmas.

Electron plasmas in a Penning-Malmberg trap are compressed radially using a rotating electric field (the "rotating-wall technique"). For large electric fields, plasmas can be compressed over a broad range of frequencies. This permits access to a novel high-density regime in which outward transport is insensitive to plasma density. The limiting density occurs when the plasma rotation frequency equals the rotating-wall frequency. Characteristics of the resulting torque-balanced steady states are described, and implications for high-density electron and positron plasma confinement are discussed.

Journal Article↗
PubMed2005

Theory of magnetodynamics induced by spin torque in perpendicularly magnetized thin films.

A nonlinear model of spin-wave excitation using a point contact in a thin ferromagnetic film is introduced. Large-amplitude magnetic solitary waves are computed, which help explain recent spin-torque experiments. Numerical simulations of the fully nonlinear model predict excitation frequencies in excess of 0.2 THz for contact diameters smaller than 6 nm. Simulations also predict a saturation and redshift of the frequency at currents large enough to invert the magnetization under the point contact. The theory is approximated by a cubic complex Ginzburg-Landau type equation. The mode's nonlinear frequency shift is found by use of perturbation techniques, whose results agree with those of direct numerical simulations.

Journal Article↗
PubMed2006

Enhanced magnetoresistance induced by spin transfer torque in granular films with a magnetic field.

Spin-transfer torques (STT) provide a mechanism to alter the magnetic configurations of magnetic heterostructures, a result previously only achieved by an external magnetic field. In granular solids, we demonstrate a new form of STT effect that can be exploited to induce a large spin disorder when combined with a large magnetic field. We have obtained a very large magnetoresistance effect in excess of 400% at 4.2 K in a large magnetic field, the largest ever reported in any metallic systems. The STT characteristics of granular solids differ significantly from those of multilayers, showing no STT effect at low magnetic fields but prominent STT effects at high fields.

Journal Article↗
PubMed2006

Temperature dependence of the spin torque effect in current-induced domain wall motion.

We present an experimental study of domain wall motion induced by current pulses as well as by conventional magnetic fields at temperatures between 2 and 300 K in a 110 nm wide and 34 nm thick Ni80Fe20 ring. We observe that, in contrast with field-induced domain wall motion, which is a thermally activated process, the critical current density for current-induced domain wall motion increases with increasing temperature, which implies a reduction of the spin torque efficiency. The effect of Joule heating due to the current pulses is measured and taken into account to obtain critical fields and current densities at constant sample temperatures. This allows for a comparison of our results with theory.

Journal Article↗
PubMed1995

Estimating net joint torques from kinesiological data using optimal linear system theory.

Net joint torques (NJT) are frequently computed to provide insights into the motor control of dynamic biomechanical systems. An inverse dynamics approach is almost always used, whereby the NJT are computed from 1) kinematic measurements (e.g., position of the segments), 2) kinetic measurements (e.g., ground reaction forces) that are, in effect, constraints defining unmeasured kinematic quantities based on a dynamic segmental model, and 3) numerical differentiation of the measured kinematics to estimate velocities and accelerations that are, in effect, additional constraints. Due to errors in the measurements, the segmental model, and the differentiation process, estimated NJT rarely produce the observed movement in a forward simulation when the dynamics of the segmental system are inherently unstable (e.g., human walking). Forward dynamic simulations are, however, essential to studies of muscle coordination. We have developed an alternative approach, using the linear quadratic follower (LQF) algorithm, which computes the NJT such that a stable simulation of the observed movement is produced and the measurements are replicated as well as possible. The LQF algorithm does not employ constraints depending on explicit differentiation of the kinematic data, but rather employs those depending on specification of a cost function, based on quantitative assumptions about data confidence. We illustrate the usefulness of the LQF approach by using it to estimate NJT exerted by standing humans perturbed by support-surface movements. We show that unless the number of kinematic and force variables recorded is sufficiently high, the confidence that can be placed in the estimates of the NJT, obtained by any method (e.g., LQF, or the inverse dynamics approach), may be unsatisfactorily low.

Algorithms↗
PubMed2006

Dynamic modeling and torque estimation of FES-assisted arm-free standing for paraplegics.

This paper presents an application of recent findings in the field of redundant robotic systems' control, toward investigating the feasibility of functional electrical stimulation (FES) assisted arm-free standing for paraplegics. Twelve degrees-of-freedom (DOF) forward and inverse dynamic models of quiet standing have been developed. These models were used to investigate the minimum number of DOF that would need to be actuated in order to generate stable quiet standing in paraplegics despite internal and external disturbances. The results presented herein suggest that the proposed nonlinear dynamic model could achieve guaranteed asymptotic stability with only six active DOF, assuming that the remaining six DOF are passive, i.e., there is no active or passive torques applied to those DOF. The stability analyses were performed using a proportional and derivative (PD) controller coupled with gravity compensation. The results of this analysis suggest that if only six particular DOF are actively controlled in a paraplegic subject, this individual should be able to achieve stable quiet standing despite disturbances. This result has both clinical and system-design implications for the development of a device that will facilitate FES-assisted arm-free quiet standing. The clinical implication is, if a paraplegic patient can exert voluntary control over specified six DOF in the lower limbs, that patient, after intensive physiotherapy, will have the potential to perform quiet standing unassisted. The system-design implication is that FES-assisted arm-free standing for paraplegics is theoretically plausible if one would actively control only six out of 12 DOF in the lower limbs. The proposed solution does not require the locking of joints in the lower limbs (commonly applied in the field) or voluntary control of the upper body to compensate for the internal and external disturbances. Another important finding of this study is the existence of six different combinations of six active DOF able to facilitate stable quiet standing. This dynamic redundancy of the biological bipedal stance allows the selection of an ideal subset of six DOF in designing a neuroprosthesis for standing. This further implies that a considerably less complex FES system than previously anticipated needs to be developed for FES-assisted standing.

Algorithms↗
PubMed1995

Knee extensor performance of dominant and non-dominant limb throughout repeated isokinetic contractions, with special reference to peak torque and mean frequency of the EMG.

The aim of this study was to investigate whether significant differences in peak torque (PT), mean power frequency of EMG (fmean) and perceived fatigue exist between the dominant and non-dominant knee extensors throughout repeated contractions. The present study forms part of a research project aimed at developing tests for the determination of the degree of motor control in patients with sequelae after CNS injury. A total of 22 clinically healthy subjects (14 males and eight females) took part in the investigation. The subjects performed endurance tests of the lower limbs, consisting of 100 repeated knee extensions using a Cybex dynamometer at 1.57 rad s-1. The patterns of PT, fmean and perception of fatigue throughout the endurance test were investigated. The endurance curves of PT and fmean showed, in common with other studies, an initial steep decrease followed by a stable phase. No significant differences existed between dominant and non-dominant knee extensors with regard to PT, fmean or perception of fatigue. The results indicate that it may be possible to use the contralateral knee extensors as an indicator of motor recovery in hemiplegia in patients with a high degree of recovery.

Adult↗
PubMed1996

Influence of the parameters of a human triceps surae muscle model on the isometric torque-angle relationship.

This study investigates the influence of parameter values of the human triceps surae muscle on the torque-angle relationship. The model used consisted of three units, each containing a contractile, a series elastic and a parallel elastic element. Parameter values were based on morphological characteristics, which made it possible to model individual units. However, for a number of parameters the values reported in the literature vary considerably. It was investigated how sensitive model results were for variation of these parameters. Slack length of the series elastic element, mean moment arm, maximum force, and length of the contractile element appeared to be the most important determinants of the behavior. For mean moment arm and contractile element length, morphology-based methods of estimation could be recommended. Slack length and maximum force were obtained through optimization. It was concluded that the model does not contain parameters on which its output depends strongly and which are difficult to estimate as well, with two exceptions: slack length of the series elastic element and maximum force.

Ankle↗
PubMed2005

Time-domain measurements of nanomagnet dynamics driven by spin-transfer torques.

We present time-resolved measurements of gigahertz-scale magnetic dynamics caused by torque from a spin-polarized current. By working in the time domain, we determined the motion of the magnetic moment throughout the process of spin-transfer-driven switching, and we measured turn-on times of steady-state precessional modes. Time-resolved studies of magnetic relaxation allow for the direct measurement of magnetic damping in a nanomagnet and prove that this damping can be controlled electrically using spin-polarized currents.

Journal Article↗
PubMed1986

Distribution of joint mobility in a normal population: results of the use of fixed torque measuring devices.

Fixed torque measuring devices were used to measure the range of movement at three sites in 364 normal adolescents and young adults. The results confirm the findings of less reproducible measurement techniques that joint mobility at a particular site follows a Gaussian distribution with a wide range in a normal population. In addition, apart from very few individuals, mobility at one site could not predict mobility elsewhere. It seems likely that the degree of connective tissue laxity generally is of lesser importance than local factors in determining the range of joint mobility at a given site in normal individuals.

Adolescent↗
PubMed2004

Reduction of ocular muscle torque by splitting of the rectus muscle II: technique and results.

AIM: To present the results of a new technique that the authors have developed to weaken the extraocular muscles. The biomechanics of this technique, which is termed "Y-split recession," are given in the companion paper. METHODS: A retrospective study, testing the effects of a new surgical technique on strabismus, nystagmus, and visual acuity. 228 patients (aged 6.8 (SD 6.0) years) with variable angle strabismus and nystagmus were treated by splitting and detaching two rectus muscles, and re-attaching the two halves at an angle of about 65 degrees to each other. Subjects were examined with the usual orthoptic tests immediately after the operation, and up to 96 months later. RESULTS: The operation reduced the strabismus, eliminated or weakened the nystagmus in primary position, and improved binocular vision and the development of visual acuity. Only minor side effects were observed. CONCLUSIONS: The Y-split recession can be used to reduce the torque for extraocular rectus muscles, and provides an alternative to "Cuppers Fadenoperation," recession, and similar procedures.

Adolescent↗
PubMed1974

'Pugnatron'-like reaction in a patient with familial dystonia: torque induced motion analysis.

A patient is described who suffered from an unusual extrapyramidal syndrome involving both legs and one arm. In the affected parts there was an extreme degree of rigidity. Measurements have been made of the motion that occurred as a result of applying force to the left foot. The torque was provided by a printed motor. The effect of a maintained plantar flexing force was anomalous for the foot moved to a dorsiflexed position. A model illustrating possible principles of feedback control-the Pugnatron-is described.

Action Potentials↗
PubMed1984

Action of tizanidine on responses of forearm flexors and extensors to torque disturbances.

The effects of tizanidine on the electromyographic responses of forearm flexors and extensors to torque disturbances were studied in normal subjects. Tizanidine had a strong depressive action on all the reflex responses, and on muscle background activity. It is concluded that the action on reflexes is not specific, but secondary to decreased spinal cord excitability.

Adult↗