Threshold Angle Research Articles

Thresholds for sensing foot dorsi- and plantarflexion during upright stance: effects of age and velocity.

The objective of this study was to determine in healthy young and old adult females the influence of age, rotation direction, angle, and speed on the threshold for sensing foot dorsi- and plantarflexion when standing and bearing weight on the limb. Twelve young (YF, mean age 22 years) and 12 old (OF, 70 years) healthy adult females stood with their dominant foot on a servo-controlled platform and the other foot on a fixed platform. The platform induced either dorsi- or plantarflexion rotations at angular velocities of 0.1, 0.5, or 2.5 degrees/s to angles of 0.05, 0.1, 0.2, 0.4 or 0.8 degree. Subjects performed five trials at each velocity-angle combination and 30 dummy trials in which no platform rotation occurred, for a total of 180 trials. Success rates were determined for detecting both rotation (SRR) and rotation direction (SRD) for each test condition. The angular thresholds required to achieve an SRD of 75% were estimated using logistic regression. Age, rotation angle, and rotation speed significantly affected SRD (repeated measures ANOVA: p < .001). For the YF, DF thresholds were 0.04, 0.09, and 0.41 degree at the fast, moderate, and slow velocities, respectively. Threshold angles were three to four times larger in the OF than in the YF. A 10-fold reduction in the angular threshold was observed upon increasing the speed of rotation from 0.1 to 2.5 degrees/s. Both age and speed significantly affected the thresholds for sensing foot dorsiflexion and plantarflexion in women.

Flux-line lock-in to CuO planes in aLa1.9Sr0.1CuO4single crystal

We report on vector magnetization studies of a ${\mathrm{La}}_{1.9}{\mathrm{Sr}}_{0.1}{\mathrm{CuO}}_{4}$ single crystal, cut in the form of a disk with the anisotropy $(c)$ axis parallel to the disk plane. We observe a sharp threshold in the angular dependences of the isothermal remanent magnetization. When the magnetic field is applied within a threshold angle to the $\mathrm{ab}$ plane, the remanent moment is strictly parallel to $ab,$ and also the $c$-axis component of magnetization is reversible. The threshold angle scales with temperature in the same manner as the lower critical field parallel to the $c$ axis, ${H}_{c1}^{c}.$ These observations give direct support to the presence of a vortex lock-in transition to the CuO planes in our crystal.

Dynamics of kinks in smectic-Cliquid crystals in periodically varying external fields

We have considered the dynamics of kinks in smectic-$C$ liquid crystal in uniformly rotating and oscillating electric or magnetic fields. In tilted oscillating fields our results are at variance with those of earlier investigations which predict chaos in this geometry for a $\ensuremath{\pi}$ kink. On the other hand, we find that the velocity and the structure of a $\ensuremath{\pi}$ kink are oscillatory with the frequency of the varying field. The average velocity as a function of the tilt angle of the field indicates a threshold angle beyond which there is a crossover in velocity selection with the system choosing from a family of solutions. Surprisingly, in a nonoscillating field rotating in a plane normal to the layers, a $\ensuremath{\pi}$ kink has a drift velocity whose direction is dependent upon the sense of rotation. As a result of this, a $2\ensuremath{\pi}$ kink could be in a bound oscillating state or it could split itself into two oppositely drifting oscillating $\ensuremath{\pi}$ kinks. In a nonoscillating tilted field rotating about the layer normal, in the synchronous regime we find an instability of a kink connecting a stable state and a metastable state. In the asynchronous regime, a kink connecting two stable states has aperiodic motion. Interestingly, in the same geometry in oscillating fields, we find that a kink joining a stable state and a metastable state is more stable. In this geometry, periodic and aperiodic fluctuating kink structures are also possible. We have suggested a simple way of understanding the general dynamical features of a kink on the basis of the dynamics of the uniform director state which is found to be very sensitive to parameters of the system.

Metastability and instability in model grain piles: scaling below and at the threshold

We present a careful simulational study of the onset of instabilities in a toy model grain pile as it is tilted through a threshold angle. Our simulations on a system of 1196 grains reveal qualitative differences in the number of grains undergoing translation over extended length scales below and at the threshold angle. The results are consistent with available experimental data and with the mean field treatments of self-organized critical behavior.

Mixed-mode I and II fatigue threshold and crack deflection angle in [formula omitted] composite

Liu, PL (reprint author), ACAD SINICA,INST MET RES,STATE KEY LAB FATIGUE & FRACTURE MAT,SHENYANG 110015,PEOPLES R CHINA

Long-lasting reductions of spasticity induced by skin electrical stimulation.

We studied the effects of electrical stimulation of the skin on upper extremity spasticity in nine hemiparetic stroke subjects. The effects were quantified by comparing reflex torque responses elicited during ramp and hold angular perturbations of the elbow recorded before and after low-intensity skin stimulation. Electrical stimulation was applied to skin over the biceps muscle for a period of ten minutes at a 20 Hz frequency, pulse duration 0.1 ms, with an intensity level below motor threshold but above sensory threshold. In seven of the nine subjects, stimulation of skin over spastic muscle reduced peak torque responses in both flexors and extensors for at least 30 min. In these seven subjects there were significant increases in mean threshold angle for the onset of reflex torque so that a greater angular rotation was required to initiate the stretch reflex response. This shift occurred without change in reflex impedance. The origins of these long-term changes in reflex torque are unclear, but may reflect synaptic plasticity of spinal circuitry outside the stretch reflex loop.

A Simple and Rapid Test of Sensorimotor Function in the Aged Rat

A total of 107 Fischer 344 rats (male and female, 2 to 29 months old) were tested on three tasks designed to measure sensorimotor function. In the first task, a new test of sensorimotor function, animals were required to maintain their balance on a stationary inclined Plexiglas plane for 5 s. Performance was evaluated with a series of increasing angles ranging from 25° to 50° in 1° increments (four trials/angle). The animals were also evaluated on two common tests of sensorimotor function: suspension from a wire by the forepaws and traversing a narrow, horizontal bar (three trials each). Age effects were significant ( p < .043 to p < .0001) for each of the 11 dependent measures (first fall angle, threshold angle, and total falls for the inclined plane, and first, best, mean, and median latencies to fall for the remaining two tests). No relationship was observed between performance, sex, and body weight. Coefficients of variation differed between tests, with the inclined plane being the least variable and the horizontal bar the most. Importantly, the inclined plane was least likely to violate the ANOVA assumption of homogeneity of variance, a problem often encountered when measuring age-related variables. Since the inclined plane test has a relatively low degree of variability, and since the between-group variation is homogeneous, it should serve as both a useful and robust test for sensorimotor function in the aged rat.

The role of stretch reflex threshold regulation in normal and impaired motor control

Some hypotheses suggest that stretch reflex threshold regulation may be an essential element of motor control. Disturbances in this mechanism may lead to motor dysfunction. We investigated this possibility by comparing stretch reflex threshold regulation in 11 spastic hemiparetic and 6 normal subjects. Subjects sat with their arms fully supported in a forearm and hand mold attached to a manipulandum mounted on and controlled by a torque motor. They remained completely passive while their elbow was extended from 30° flexion through an arc of 100°. Displacement and velocity of the forearm were measured as well as EMG signals from 2 elbow flexors and 2 elbow entensors, when the elbow flexors were stretched at each of 7 velocities. Velocities ranged from 8 to 160°/s for hemipharetic subjects and from 32 to 300°/s for normal subjects. Phase diagrams (velocity verus angle) were plotted and the threshold angles ( λ ∗ ) for muscle activation at each velocity of stretch were used to determine the static stretch reflex threshold (λ) and the slope (μ) of the relationship between the λ ∗s and velocity. Our main findings were that static and dynamic stretch reflex threshold were decreased in spastic hemiparetic compared to normal subjects and that the thresholds depended on velocity. The static threshold value correlated with the severity of clinically measured spasticity. In addition, the range of regulation of λ was decreased in the patients compared to normal. This may explain some of the problems of force and position regulation as well as hypertonus (and weakness) common to these patients.

The anisotropy of the irreversible magnetizations of YBCO and LaSrCuO: Evidence for a transition from Abrikosov to Josephson vortices in LaSrCuO

The anisotropy of the magnetization and the critical current density of the high temperature superconductors YBa 2Cu 3O 7 − δ and La 1.85Sr 0.15CuO 4 are investigated as a function of the orientation θ of the applied field with respect to the crystallographic c-axis. The results are analyzed in the framework of the recent model by Bulaevskii et al. In agreement with this model, there is a threshold angle θ 0(∼ 50°) beyond which the vortex line lattice enters the sample parallel to the ab planes and then undergoes a lock-unlock transition at a field H 1 of the order of H c1, c /cos θ. In addition, at high fields the vortex lattice of La 1.85Sr 0.15CuO 4 exhibits a sharp change in a narrow angle of less than one degree around the ab basal planes. No anomalous behavior of this kind is seen in YBa 2Cu 3O 7 − δ . In this angular domain the critical density of La 1.85Sr 0.15CuO 4 increases slightly with temperature while that of YBa 2Cu 3O 7 − δ drops sharply in the same reduced temperature range. These data are hard to interpret with existing pinning theories and are tentatively ascribed to a gradual transformation from Josephson-like to Abrikosov-like vortices in the LaSr based compound which is much more anisotropic than YBCO material.

Model for experimental extraction of the charmed-quark mass(es).

A simple charm-production model is presented which approximates the running of the charmed-quark mass by identifying the mass in the quark propagators with the bare and/or current mass arising from electroweak symmetry breakdown and identifying the mass in Dirac spinors with the QCD renormalized long-distance and/or constituent mass. The model offers the possibility of (i) understanding the differing charmed-quark mass values extracted from different experiments, (ii) determining the bare charmed-quark mass relevant to quark mass matrix and mixing angle studies, and (iii) determining the renormalized charmed-quark mass, which determines the charmed-quark threshold, which in turn sensitively affects the extraction of ${sin}^{2}{\ensuremath{\theta}}_{W}$. We point out that the threshold and forward angle production offer the best possibilities to test the model and extract meaningful charmed-quark masses. The model may also be used to extract $b$-quark masses.

Slope—a real-time ECG data compressor

An ECG sampled at a rate of 250 samples s-1 or more produces a large amount of redundant data that are difficult to store and transmit. In the paper, a real-time ECG data compressor, SLOPE, is presented. SLOPE considers some adjacent samples as a vector, and this vector is extended if the coming sample falls in a fan spanned by this vector and a threshold angle; otherwise, it is delimited as a linear segment. By this means SLOPE repeatedly delimits linear segments of different lengths and different slopes. The Huffman codes for the parameters to describe this linear segment are transmitted for that linear segment. SLOPEa, which is a slightly modified version of SLOPE, is used to compress ambulatory ECG data. All the operations used by SLOPE and SLOPEa are simple integer operations, both SLOPE and SLOPEa being real-time compressors. Experimental results show that an average of 192 bits per channel per second (bpcs) for each ECG signal is obtained by SLOPE and an average of 148 bpcs for each ECG signal is obtained by SLOPEa.

へき開ファセット破面領域の3次元解析アルゴリズムの開発とその鉄鋼材料のぜい性破面解析への応用

Computer image processing technology was applied to cleavage fracture surface analysis and an algorithm for the estimation of 3-dimensional cleavage facet boundaries and 3-dimensional facet areas were developed. An angle αi, j between relative normal vectors of a mesh plane Mi, j and the adjacent mesh plane Mi+1, j along X axis was calculated and αi, j was compared to α threshold angle αth. If αi, j is larger than αth and αi+1, j is smaller than αth, the mesh plane Mi+1, j was decided to be the facet boundary. The same calculation was continued along both X- and Y-axes to obtain facet numbers contained in the analyzed area. After the estimation of facet boundaries, 3-dimensional facet areas were calculated from the 2-dimensional facet areas divided by cosβi, j, which is the angle between average normal vector of α facet and vertical vector. The algorithm developed in this study was applied to analyze the cleavage fracture surfaces of mild steel and HT80 steel and the effect of the threshold angle on the estimated facet numbers, distribution of the values of α and the 3-dimensional facet areas were discussed. The developed method is very useful for analyzing the cleavage facet size and for discussing a relationship between cleavage fracture and microstructures of steels, such as ferrite and the prior austenite grain sizes.

Neural network modelling of eye compensation during off-vertical-axis rotation

Compensatory eye motion during off-vertical axis rotation of the head in darkness (OVAR), has been modelled with a neural network. The three layered nework was trained with back-propagation to simulate the estimation of head velocity during OVAR. The network produced good estimates within its training range and predicted the eye velocity versus head velocity characteristics in the monkey. Invariance of the compensation to changes in tilt angle, not fully addressed in previous models, was demonstrated by the network, along with a smooth decline in velocity estimate below a threshold angle. This also agreed well with data from the monkey. Study of the internal units of the network provided insight into the manner in which pattern comparison produced the estimates. In addition, the behavior of the network's units suggests types of behavior that might be looked for through unit recordings in the central nervous system during OVAR.

Algorithm for three-dimensional analysis of cleavage facet and its application for brittle fracture surface of steels.

Computer image processing technology has been applied to cleavage fracture surface analysis and the algorithm for the estimation of 3-dimensional cleavage facet boundaries and 3-dimensional facet areas has been developed. An angle αi, j between relative normal vectors of one mesh Pi, j and adjacent mesh plane Pi+1, j was calculated and the αi, j was compared to the threshold one αth. If αi, j is larger than αth and the αi+1, j calculated between the mesh planes Pi+1, j and Pi+2, j along X axis is smaller than αth, the Pi+1, j mesh plane was decided to be the facet boundary. The same calculation was continued along both X- and Y-axes and facet numbers being contained in the analyzed area were obtained. After the estimation of facet boundaries, 3-dimensional facet areas were calculated dividing by the 2-dimensional facet areas by cos βk which is the angle between average normal vector of facet and vertical vector. By this algorithm, the cleavage fracture surfaces were analyzed of JIS SS41 and HT80 steels and the effect of the threshold angles αth was discussed on the facet numbers estimated, the distribution of the values of α and the 3-dimensional facet areas. The method developed is very useful to analyze the cleavage facet size and to discuss the relationship between the cleavage fracture and microstructures of steels, such as ferritic grain size and prior austenitic grain.

Energetics of piscivorous predator-prey interactions

Information on fish swimming mechanics and feeding behaviour are combined in an energetic model of the feeding efficiency of a simple piscivorous predator-prey interaction. The intent is to make quantitative assessments of actual energies expended and gained in the interaction, and to determine the optimal prey size for a piscivorous predator. Feeding efficiency is defined here as “the energy input through feeding divided by the energy output required to catch and consume the prey”. This is also referred to as the relative energetic benefit. The variables in the model include the size of the prey relative to the predator, length of predator, its fineness ratio (length/maximum depth of section), a visual threshold angle at which the predator initiates an interaction, and a variable that reflects prey experience. The prey size that maximizes feeding efficiency is the largest available. Feeding efficiency is also high when predator length and threshold angle are small, fineness ratio is high, and the prey is naive. The model focuses on a three-stage interaction involving an approach chase, and strike. When the size of the prey is small relative to the size of the predator, the accelerative energy of the strike dominates the energy output. When this term is large, the drag force during the approach is important. Other predatory strategies (ambush, constant-velocity foraging, and high speed attacks on schools) are discussed with respect to optimal prey size and feeding efficiency. Constant-velocity foraging provides the greatest relative energetic benefit, but is restricted to small prey. The relative energetic benefit for the ambush strategy exceeds that for high speed attacks when the size of the prey relative to the predator is greater than about 0·4.

Ecdysial growth of the filiform hairs and sensitivity of the cercal sensory system of the cricket,Gryllus bimaculatus

1. The ecdysial growth of cercal filiform hairs was investigated in the cricketGryllus bimaculatus. The length of hairs varied from 40 to 500 μm in the 1st, from 40 to 650 μm in the 3rd and from 30 to 800 μm in the 5th instar nymphs (Fig. 1). Hemimetabolous development causes both hair growth and the appearance of new hairs at each ecdysis (Figs. 2, 3). The newly acquired hairs were shorter than 200 μm in every case (Fig. 4). 2. Velocity thresholds of cercal sensory interneurons (CSIs) to sinusoidal air-currents were measured in 3rd instar nymphs (Fig. 5 A, B, C). CSIs 8-1 (medial giant interneuron: MGI) and 9-1 (lateral giant interneuron: LGI) showed threshold curves of acceleration sensitivity similar to those in adults. The thresholds for CSIs 8-1 and 9-1 were on the average higher in nymphs than in adults. The threshold curves for the two velocity-sensitive CSIs 10-2 and 10-3 were similar for nymphs and adults. 3. Velocity thresholds of cercal filiform sensilla were measured in 3rd instar nymphs (Fig. 6). In spite of the small size of nymphal hairs, the most sensitive ones showed the same sensitivity as did the long 1000 μm hairs of the adult. 4. The filiform hairs in 3rd instar nymphs were supported by a weaker spring than in adults (Fig. 7). Relative stiffness was about 50% of that in the long hairs in adults, but not much different than that in the short hairs. 5. Based on a theoretical estimation of hair motion, the threshold angle of a filiform sensillum in the 3rd instar nymph was calculated (Fig. 9). Threshold angles of the long sensilla seemed to be unchanged throughout hemimetabolous development.

Response of hip joint afferent fibers to pressure and vibration in the cat

Mechanical properties of 33 slowly adapting and 8 quickly adapting capsule receptors of the hip joint were investigated. All the slowly adapting receptors identified were of a limited range, discharging only when the femur was rotated to its limit of movement. They behaved as single-spot high-threshold pressure receptors as shown by the von Frey's hairs. In addition they showed a low sensitivity to vibratory stimuli applied perpendicularly to their receptive field. Only 14 out of 33 units were found to discharge following vibration; 11 could be driven 1:1 at different frequencies. There was a general trend to be entrained at lower amplitudes for higher frequencies of vibration. A positive correlation between the pressure threshold and both activation angle and vibration threshold was found. The mechanical properties of all the quickly adapting capsule receptors were found to be similar to those described in other tissues. Finally, unlike joint receptors, slowly adapting muscle afferents travelling in the same hip articular nerve were highly sensitive to pressure and vibratory stimuli.

Anomalous reflected images of objects on crystal surfaces in reflection electron microscopy

A gap observed sometimes between the direct and reflected images of foreign objects lying on atomically flat crystal surfaces is interpreted as taking place by an anomalous displacement of the reflected image, resulting from the displacement of electron trajectories at reflection. This displacement is shown to be of the same kind as those which have been observed in acoustics and optics at the threshold angle of total reflection, and have been interpreted as the result of rapid variation of the phase of the reflection coefficient with the angle of incidence. It is shown that the same kind of rapid phase variation occurs at Bragg reflection of the electron beam, and that the displacement estimated by using the dynamical theory of electron diffraction is of the same order of magnitude as the observed ones.

Three‐component recordings: Interest for land seismic source study

Three‐component recordings provide access to the particle trajectory due to seismic events. This three‐dimensional picture shows successions of complex phenomena. Nevertheless, this trajectory has predominant directions of polarization. A method of spatial directional filtering is described to calculate the polarization direction of parts of the trajectory. The application of this method provides means to reject trajectory parts for which the angular gap between their polarization axis and a reference direction, for example X, Y, or Z, is greater than a given threshold angle. Real data are submitted to this method, leading to a color‐coded display showing the direction of polarization of each wave train. The same noise spread, used in conjunction with two different seismic sources, was recorded with triphone groups. The two sources were an SH‐wave vibrator and Marthor®. Using spatial directional filterings with threshold angles varying from 0 to 90 degrees, the corresponding quantities of energy emitted in each principal direction X, Y, and Z were evaluated. A set of diagrams was plotted for comparing the behavior of both sources and to calculate the part of the received energies along X, Y, and Z directions as a function of (1) the emitted energies, and (2) the local propagation effects. ® SH‐wave weight‐drop source, IFP trademark.

Cross polarization from dual mode horn antennas

The cross polarization from dual mode horn antennas supporting the TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> and TM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> -modes has been analyzed both theoretically and experimentally. The cross polarization has been shown to be strongly dependent on the length and flare angle of the horn. When the flare angle for a given horn length becomes larger than a certain threshold angle, the cross-polar sidelobes increase rapidly. Simple formulas for this threshold angle are presented. This cross-polar degradation will not occur if a plane phase front is provided over the horn aperture, either by profiling the horn or by applying a lens in the aperture.