Velocity Of Deflection Research Articles

Visco-Elastic Plate Motion after Its Breaking into Parts

Mathematical modelling of visco-elastic plate breaking and consequent deflection of the plate are studied using the simplified formulation. The plate is modelled as a thin visco-elastic plate of constant thickness. The edges of the plate are clamped. The plate deflection is caused by a uniform aerodynamic pressure, which slowly increases in time. The plate deflection before breaking is approximated as quasi-static. The plate breaks instantly then and there, when and where the modified fracture criterion by Petrov and Morozov is achieved. Both the deflections and velocities of the plate before and after breaking are assumed equal.The motion of the plate parts after breaking are highly unsteady and dependent on the viscous properties of the plate. If the viscosity of the plate material is negligible compared with the elastic characteristics of the plate, then the velocity of the plate deflection is discontinuous at the time instant of the plate breaking. This feature of the plate motion after its breaking should be taken into account in interpretation of the numerical results within the linearised model of plate deflection with sudden breaking. It is shown that the plate can break in a cascade way. Each part after the first breaking breaks again. The configuration studied in this paper is specially tailored to highlight the behaviour of the numerical solutions of the plate breaking problems in applications.

The velocity of roof deflection as an indicator of underground workings stability – Case study from polish deep copper mines

The paper presents the research results of a study concerning the recognition of roof instability mechanism in the conditions of the Legnica-Głogów Copper Belt (LGCB), in which the final mining phase encompasses roof collapse. Due to the high potential risk of this type of phenomenon to the health and safety of mine operators it was decided to launch a roof stability assessment study in order to identify timely preventive measures adequate for this hazard.The approach is based on taking measurements of the changes of roof angles of inclination near the sidewalls of the mine working using high-sensitivity inclinometers fixed to the end of rock anchors in the roof. In this paper, it is shown that this method works well as it captures the natural bending phenomena of the roof prior to its collapse. It is found that the observed roof bending deformation is predominantly the result of combined gravity force and in-situ horizontal stress, regardless of the presence of other factors.Field measurements indicate that the roof collapse is preceded by a characteristic process covering three specific phases of development: these are described in detail. A new criterion for the recognition of imminent roof destabilization was developed based on the analysis of collected field measurements.

Effects of Adaptation on Discrimination of Whisker Deflection Velocity and Angular Direction in a Model of the Barrel Cortex.

Two important stimulus features represented within the rodent barrel cortex are velocity and angular direction of whisker deflection. Each cortical barrel receives information from thalamocortical (TC) cells that relay information from a single whisker, and TC input is decoded by barrel regular-spiking (RS) cells through a feedforward inhibitory architecture (with inhibition delivered by cortical fast-spiking or FS cells). TC cells encode deflection velocity through population synchrony, while deflection direction is encoded through the distribution of spike counts across the TC population. Barrel RS cells encode both deflection direction and velocity with spike rate, and are divided into functional domains by direction preference. Following repetitive whisker stimulation, system adaptation causes a weakening of synaptic inputs to RS cells and diminishes RS cell spike responses, though evidence suggests that stimulus discrimination may improve following adaptation. In this work, I construct a model of the TC, FS, and RS cells comprising a single barrel system—the model incorporates realistic synaptic connectivity and dynamics and simulates both angular direction (through the spatial pattern of TC activation) and velocity (through synchrony of the TC population spikes) of a deflection of the primary whisker, and I use the model to examine direction and velocity selectivity of barrel RS cells before and after adaptation. I find that velocity and direction selectivity of individual RS cells (measured over multiple trials) sharpens following adaptation, but stimulus discrimination using a simple linear classifier by the RS population response during a single trial (a more biologically meaningful measure than single cell discrimination over multiple trials) exhibits strikingly different behavior—velocity discrimination is similar both before and after adaptation, while direction classification improves substantially following adaptation. This is the first model, to my knowledge, that simulates both whisker deflection velocity and angular direction and examines the ability of the RS population response to pinpoint both stimulus features within the context of adaptation.

Role of die structures on metal flow balance in multi-output porthole extrusion of thin-walled profile

A novel multi-output porthole extrusion die for thin-walled aluminum alloy profile is introduced and its thermo-mechanical modeling for the analyses of metal flow and elasto-plastic deformation is developed. In order to explore the sources of undesirable deformations, two key deformation behaviors (non-uniform relative exit velocity of profile and mandrel deflection of extrusion die) which play considerable effects on the metal flow balance are analyzed based on the developed numerical model. Finally, the optimization design of the multi-output porthole extrusion die structure is performed for the improvement of extruded profile quality.

Accurate measurement of pavement deflection velocity under dynamic loads

Abstract Bearing capacity is one of the most important indices that reflects the condition of road pavements. For high-speed and non-destructive measurement of bearing-capacity values, advanced dynamic deflectometers have been developed in the past decade. The deflection range is typically computed based on the Euler-Bernoulli elastic equation with a number of deflection velocity values. The deflection velocity refers to the vertical velocity of pavement deflection under a force action; it can be captured by a number of positions in the deflection basin by laser Doppler sensors. Thus, the accurate measurement of deflection velocity is of vital importance to the performance of a deflectometer system. In this paper, we consider the problem of accurately measuring the deflection velocity based on dynamic posture and calibration. Both methods build the relationship between the measured values and the relative postures of the sensors and targets. We first validate the effectiveness of the static calibration that determines the relative postures of the sensors with indoor settings. Second, with respect to self-correlation of the velocity values, the dynamic-posture-based method and the calibration-based method are compared. Third, the impact of traffic speed on the measuring results is investigated. Last, we further validate the accuracy of the measured velocity by computing deflection ranges and comparing them to ground-truth values. Experiments in real measuring tasks demonstrated that both the calibration-based method and the dynamic-posture-based method can produce accurate and effective results.

Spider joint hair sensilla: adaptation to proprioreceptive stimulation.

Adding to previous efforts towards a better understanding of the remarkable diversity of spider mechanosensitive hair sensilla, this study examines hairs of Cupiennius salei most likely serving a proprioreceptive function. At the tibia-metatarsus joint of all walking legs, there are two opposing groups of hairs ventrally on the tibia (20 hairs) and metatarsus (75 hairs), respectively. These hairs deflect each other when the joint flexes during locomotion, reversibly interlocking by microtrichs on their hair shafts. The torque resisting the hair deflection into the direction of natural stimulation is smaller by up to two powers of ten than that for the other directions. The torsional restoring constant S of the hair suspension is about 10(-10)Nmrad(-1) in the preferred direction, up to a hair deflection angle of 30° (mean of natural deflection angles). Joint movements were imposed in ranges and at rates measured in walking spiders and sensory action potentials recorded. Within the natural step frequencies (0.3-3Hz) the rate of action potentials follows the velocity of hair deflection. All findings point to the morphological, mechanical, and physiological adaptedness of the joint hair sensilla to their proprioreceptive stimulation during locomotion.

Localized and chaotic folding: the role of axial plane structures

Most natural fold systems are not sinusoidal in profile. A widely held view is that such irregularity derives solely from inherited initial geometrical perturbations. Although, undoubtedly, initial perturbations can contribute to irregularity, we explore a different (but complementary) view in which the irregular geometry results from some material or system softening process. This arises because the buckling response of a layer (or layers) embedded in a weaker matrix is controlled in a sensitive manner by the nature of the reaction forces exerted by the deforming matrix on the layer. In many theoretical treatments of the folding problem, this reaction force is assumed to be a linear function of some measure of the deformation or deformation rate. This paper is concerned with the influence of nonlinear reaction forces such as arise from nonlinear elasticity or viscosity. Localized folds arising from nonlinearity form in a fundamentally different way than the Biot wavelength selection process. As a particular example of nonlinear behaviour, we examine the influence of axial plane structures made up of layers of different mineralogy formed by chemical differentiation processes accompanying the deformation; they are referred to as metamorphic layering. The alternating mineralogical composition in the metamorphic layers means that the embedding matrix exerts a reaction force on the folded layers that varies not only with the deflection or the velocity of deflection of the layer, but also in a periodic manner along the length of the folded layers. The influence of this spatially periodic reaction force on the development of localized and chaotic folding is explored numerically.

Acceleration and Force Reveal Different Mechanisms of Electromechanical Delay

Electromechanical delay (EMD) represents a series of complex processes of converting an electrical stimulus to a mechanical response. To quantify the contribution of electrochemical and mechanical processes of EMD in the human biceps brachii muscle over a wide range of elbow joint angles, we determined the onset of muscle contraction and the beginning of force development by recording acceleration of skin surface over the muscle and elbow flexion force, respectively. Ten healthy male volunteers underwent two experimental sessions, in which submaximal paired-pulse stimuli were applied percutaneously to the resting biceps brachii muscle at 10 different elbow joint angles from 40° to 130° (0° represents full extension). The electrical stimulation induced repeatable contractions, in which the test-retest reliability of time parameters was sufficiently high (intraclass correlation coefficient=0.84-0.88). The time for electrochemical process ranged between 3.1±0.8 and 3.6±0.9 ms and was independent of elbow joint angle (P=0.64). The time for mechanical process and the total duration of EMD, however, were significantly greater at elbow flexion positions than at 40°, the most extended position in this study (P<0.05). Regression analysis revealed that at elbow flexion positions, the time for mechanical process increased significantly with decreasing the muscle-tendon length of the biceps brachii calculated from a musculoskeletal model (R=0.54, P<0.001). These results suggest that, in the human biceps brachii muscle, the prolongation of EMD at short muscle-tendon length is not attributed to the impairment of the electrochemical process of muscle contraction but to the increased slack within the muscle-tendon unit.

An evaluation of postural stability and the effects of middle-ear drainage on vestibulo-spinal reflexes of children with chronic otitis media with effusion

Objective: Many authors agree that chronic otitis media with effusion (OME) are the main causes of vertigo and balance disturbances in children.The aim of this work was the stabilometric evaluation of postural stability and the influence of middle ear drainage on vestibulo-spinal reflexes in children with OME. Methods: Fifteen children with OME (5–14 years old, 13 males and two females) were selected for bilateral drainage of the middle ear after conservative treatment proved ineffective. The control group consisted of 15 healthy children of an analogous age range. Static and quasi-dynamic posturography was performed to evaluate balance. The tests were performed three times: 1 day before drainage, 1 day after drainage and 4 weeks after drainage. Parameters including the field of the developed area and the average velocity of body deflection were analysed. Results: There was statistically significant elevation of stabilogram parameters in almost all the tests in children with OME as compared to the control group. The changes in the stabilogram parameters were analysed with reference to the timing of the evaluation. Significant improvement was noted after the fluid was removed from the ear, although recovery was not complete after 4 weeks. Conclusions: The presence of fluid in the middle ear impairs the functioning of the balance system in children. Postural stability and the quantity of vestibulo-spinal reflexes seem to depend on the functional condition of the middle ear. Prolonged cases of OME could potentially handicap a child’s motor development.

From crack deflection to lattice vibrations—macro to atomistic examination of dynamic cleavage fracture

A set of cleavage experiments with strip-shaped single-crystal silicon specimens subjected to three-point bending is reported. The experiments enabled examination of the relationships between the dynamic energy release rate, the velocity, the orientation-dependent cleavage energy, and the cleavage plane of propagation. Dynamic crack propagation experiments show that when a [0 0 1] silicon single crystal is fractured under three-point bending at ‘parallel’ velocity (directly measured at the bottom surface of the specimen) of up to 1500 m/ s , it prefers to cleave along the vertical (1 1 0) plane, while when the specimen is fractured under the same conditions but at a velocity higher than 2900 m/ s , it cleaves along the inclined (1 1 1) plane. At intermediate velocities, the crack will deflect from the (1 1 0) plane to the (1 1 1) plane. Crack velocity was determined by the initial notch length. The local (calculated) velocity of deflection between the cleavage planes ranges from 2900 m/ s , for a crack propagating on the (1 1 0) plane in the [1 1 ̄ 0] direction, to about 30 m/ s , for a crack on the (1 1 0) plane, but in the [0 0 1] direction. It is suggested that the cause of the deflection phenomenon is the anisotropic, velocity-dependent cleavage energy, resulted phonon radiation caused by anisotropic, velocity-dependent lattice vibrations. We have studied the effect of material properties and propose selection criteria to explain the deflection phenomenon: the crack will deflect to the plane of least-energy, for which G− Γ i ( V)=max, or to the plane with maximum crack tip velocity, V i ( Γ)=max.

반능동 현가시스템용 자기동조 게인조절형 스카이훅 제어기의 구현 및 실험

In this paper, a self-tuning gain-scheduled skyhook control for semi-active suspension systems is investigated. The dynamic characteristics of a continuously variable damper including electro-hydraulic pressure control valves is analyzed. A 2-d.o.f. time-varying quarter-car model that permits variations in sprung mass and suspension spring coefficient is considered. The self-tuning skyhook control algorithm proposed in this paper requires only the measurement of body acceleration. The absolute velocity of the sprung mass and the relative velocity of the suspension deflection are estimated by using integral filters. The skyhook gains are gain-scheduled in such a way that the body acceleration and the dynamic tire force are optimized. An ECU prototype is discussed. Experimental results using a 1/4-ear simulator are discussed. Also, a suspension ECU prototype targeting real implementation is provided.

Circuit dynamics and coding strategies in rodent somatosensory cortex.

Previous experimental studies of both cortical barrel and thalamic barreloid neuron responses in rodent somatosensory cortex have indicated an active role for barrel circuitry in processing thalamic signals. Previous modeling studies of the same system have suggested that a major function of the barrel circuit is to render the response magnitude of barrel neurons particularly sensitive to the temporal distribution of thalamic input. Specifically, thalamic inputs that are initially synchronous strongly engage recurrent excitatory connections in the barrel and generate a response that briefly withstands the strong damping effects of inhibitory circuitry. To test this experimentally, we recorded responses from 40 cortical barrel neurons and 63 thalamic barreloid neurons evoked by whisker deflections varying in velocity and amplitude. This stimulus evoked thalamic response profiles that varied in terms of both their magnitude and timing. The magnitude of the thalamic population response, measured as the average number of evoked spikes per stimulus, increased with both deflection velocity and amplitude. On the other hand, the degree of initial synchrony, measured from population peristimulus time histograms, was highly correlated with the velocity of whisker deflection, deflection amplitude having little or no effect on thalamic synchrony. Consistent with the predictions of the model, the cortical population response was determined largely by whisker velocity and was highly correlated with the degree of initial synchrony among thalamic neurons (R(2) = 0.91), as compared with the average number of evoked thalamic spikes (R(2) = 0.38). Individually, the response of nearly all cortical cells displayed a positive correlation with deflection velocity; this homogeneity is consistent with the dependence of the cortical response on local circuit interactions as proposed by the model. By contrast, the response of individual thalamic neurons varied widely. These findings validate the predictions of the modeling studies and, more importantly, demonstrate that the mechanism by which the cortex processes an afferent signal is inextricably linked with, and in fact determines, the saliency of neural codes embedded in the thalamic response.

Processing of vibrissa sensory information within the rat neocortex.

Neuronal response properties were compared among different layers of the urethan-anesthetized rat vibrissa cortex. Measurements were made of the receptive-field (RF) size, the degree of directional selectivity, the latency of driving, the velocity threshold, and the tuning-curve slope. The RF size was defined by the number of whiskers that, when deflected individually, activated a neurons. For the center whisker of the RF (usually whisker C3), the response to deflection in the most preferred direction was compared with that in the opposite direction to classify the neuron as either strongly directional, weakly directional, or nondirectional. For the most preferred direction of the center whisker, the minimum velocity of deflection required to drive the unit was defined as the velocity threshold, the latency of driven response to a standard supramaximal velocity was measured, and finally, using exponential ramp-and-hold deflection, the threshold amplitude was determined at different values of time constant to construct a tuning-curve slope. Cortical layer IV neurons, as a whole, have the lowest threshold velocity. Layer Vb neurons stand on the opposite extreme in having the highest mean velocity threshold value. Although this difference is consistent with the generally held view that the "barrels" in layer IV represent the input stage of cortical information processing, the lack of laminar differences in latency and RF size support the idea that neurons of other cortical layers also receive direct thalamocortical inputs. The population of cortical neurons thus appears quite homogeneous across different layers as far as the results of examination with short-pulsed stimulation are concerned. Correlation of pairs of parameters (RF, directionality, velocity threshold, and latency) was tested in the two layers (layer IV and layer Vb). The latency and velocity threshold are highly correlated within both layers. Also, most of correlation coefficients of the corresponding pairs of the two layers are similar. However, the use of exponential ramp-and-hold deflection of whiskers revealed a difference in tuning-curve slope between layer IV and layer Vb (also layers II-III); layer IV neurons show flatter tuning-curve slopes (more oriented for detection of the amplitude component of whisker deflection) than neurons of layer Vb and layers II-III, which are more oriented for velocity detection. During the hold phase of whisker deflection, layer IV neurons tend to show sustained discharges, whereas layer Vb (also layers II-III) neurons mainly exhibit transient responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantitative studies of stimulus coding in first-order vibrissa afferents of rats. 2. Adaptation and coding of stimulus parameters.

Mechanosensory neurons are often classified as either rapidly adapting or slowly adapting. We examined response decay (adaptation) during constant deflection of the vibrissae with quantitative, repeatable, ad hoc measures. We found that first-order vibrissa-activated neurons of the fifth ganglion exhibit a variety of adaptation rates that appear to be distributed continuously between the rapidly and slowly adapting extremes. Also, adaptation rate is influenced markedly by stimulus magnitude. We found no evidence for a dichotomy within the more slowly adapting neurons on the basis of discharge regularity. Threshold tuning curves were used to evaluate vibration sensitivity. Both the best frequencies and 1:1 discharge thresholds for sinusoidal stimulation ranged over two orders of magnitude and were continuously distributed. First-order vibrissa-activated afferents exhibit a broad variety of response patterns to constant-velocity stimulation. The pattern of discharge varied both as a function of time during constant-velocity (ramp) deflection and as a function of stimulus velocity. Although information about the parameters of a stimulus may be conveyed by any of several features of the response pattern, it appears that few if any neurons function as "pure" encoders of any particular stimulus parameter. We examined quantitatively the relationship between discharge rate and both velocity and amplitude of vibrissa deflection with the aid of a computer-based curve-fitting procedure. We found that about half the observed rate-level functions were best described by a power function; the remainder were best fit by a logarithmic function. The parameters of the best-fitting functions varied widely and continuously, emphasizing further the diversity of coding properties of the rat's vibrissa afferents. Rate-level curves for stimulus magnitude generally exhibited saturation; some were nonmonotonic. None were described adequately by either a logarithmic function or a power function.