Positive Displacements Research Articles

A Family of Transients Suitable for Reproduction on a Shaker Based on the cosm(x) Window

A family of transients with the property that the initial and final acceleration, velocity, and displacement are all zero is derived. The transients are based on a relatively arbitrary function multiplied by window of the form cosm(x). Several special cases are discussed which result in odd acceleration and displacement functions. This is desirable for shaker reproduction because the required positive and negative peak accelerations and displacements will be balanced. Another special case is discussed which will permit the development of transients with the first five (0-4) temporal moments specified. The transients are defined with three or four parameters that will allow sums of components to be found which will match a variety of shock response spectra.

Effect of Variations in Morphological Data on Calculated Mechanical Energy Cost in Equine Gait

During transport, horses are subjected to acceleration in three dimensions, rapid braking, turning, noise, and other stressors. The animal's ability to make postural corrections may be insufficient to prevent injury or distress, and so knowledge of the compensatory motion patterns of the horse in the trailer is a necessary precondition for smart design of transport systems. A custom two-horse trailer was built for this project. It had a horse compartment 1.85 m wide by 3.95 m long, with adjustable bulkheads and a centre divider separating the horses. The floor was instrumented with 24 shearbeam load cells to measure the vertical load imposed by each horse and its horizontal motion. Two horses were driven on a 56 km trip on both rural and urban roads. Load data were collected at 100 Hz for the 58-minute trip and were filtered with a cut-off frequency of 5 Hz using a Butterworth low-pass filter and then vertical acceleration computed. A pivot table counted sign reversals in the vertical acceleration signal, and vertical displacement was calculated using the fundamental frequency of the resulting acceleration data. Total vertical motion was calculated by making the negative displacements absolute and summing these with the positive displacements, and vertical work done was calculated by multiplying the force by the displacement measures. Horizontal motion was calculated by averaging the transverse and cranio-caudal position of the centre of pressure every second and adding the resultant displacements. Absolute vertical displacement of the two horses was 69.55 m and 97.56 m. In addition to the work done by standing, vertical work done in response to vibration was 322.4 kJ and 443.2 kJ. Horizontal excursion was 227.1 m and 243.0 m. This is a first effort to quantify the additional workload imposed on animals during transport, which will aid in the design of smart transport vehicles that will minimize the stress to horses.

Interaction between normal faults and fractures and fault scarp morphology

Fault slip and geomorphic surface processes create and modify bedrock normal fault scarps. Our field studies and numerical models show that mechanical interaction between near‐surface fractures and active faults may diminish scarp slopes and broaden deformation near the surface. In our models, increasing fracture density and depth reduces and complicates the scarp's topographic expression. Fracture depth and density, and orientation of the structures control the location and magnitude of zones of positive and negative shear displacements along the fractures. Our field studies of the interaction of active graben bounding normal faults and fractures in Northern Arizona illustrate the mechanical analysis. Reduction in scarp slopes and broadening of the deformation field may cause incorrect interpretations of shallow bedrock scarp morphologies as old, rather than as the result of slip along fractures around the fault.

Path-integral theory of an axially confined worm-like chain

A path-integral formulation is developed for the thermodynamic properties of a worm-like chain moving on a surface and laterally confined by a harmonic potential. The free energy of the chain is calculated as a function of its length and boundary conditions at each end. Distribution functions for chain displacements can be constructed by utilizing the Markov property as a function of displacement (s) and its derivative d(s)/ds along the path. These quantities are also calculated in the presence of pinning sites which impose fixed positive or negative displacements, foreshadowing their application to a model for the regulation of striated muscle.

Electrostatic interaction between stereocilia: II. Influence on the mechanical properties of the hair bundle

This paper is based on our model [Dolgobrodov et al., 2000. Hear. Res., submitted for publication] in which we examine the significance of the polyanionic surface layers of stereocilia for electrostatic interaction between them. We analyse how electrostatic forces modify the mechanical properties of the sensory hair bundle. Different charge distribution profiles within the glycocalyx are considered. When modelling a typical experiment on bundle stiffness measurements, applying an external force to the tallest row of stereocilia shows that the asymptotic stiffness of the hair bundle for negative displacements is always larger than the asymptotic stiffness for positive displacements. This increase in stiffness is monotonic for even charge distribution and shows local minima when the negative charge is concentrated in a thinner layer within the cell coat. The minima can also originate from the co-operative effect of electrostatic repulsion and inter-ciliary links with non-linear mechanical properties. Existing experimental observations are compared with the predictions of the model. We conclude that the forces of electrostatic interaction between stereocilia may influence the mechanical properties of the hair bundle and, being strongly non-linear, contribute to the non-linear phenomena, which have been recorded from the auditory periphery.

Sensorimotor synchronization: the impact of temporally displaced auditory feedback

When subjects are asked to tap in synchrony to a regular sequence of stimulus events (e.g., clicks), performance is not perfect in that, usually, an anticipation of the tap is observed. The present study examines the influence of temporally displaced auditory feedback on the size of this anticipatory error. Whereas earlier studies have shown that this asynchrony exhibits a linear increase in size as a function of an increasing delay in such additional auditory feedback, this study compared the impact of shifting feedback forward in time (i.e., feedback presented before the tap) with that of delayed auditory feedback. Results showed that the impact of feedback displacement on the amount of asynchrony differed for positive and negative displacements. Delayed feedback led to an increase in asynchrony, whereas negative displacements had (almost) no effect. This finding is related to a model assuming that the various feedback components arising from the tap (tactile, kinesthetic, auditory) are integrated to form one central representation, and that the timing of this central representation arises from a linear combination of the components involved.

Two components of transducer adaptation in auditory hair cells.

Mechanoelectrical transducer currents in turtle auditory hair cells adapted to maintained stimuli via a Ca(2+)-dependent mechanism characterized by two time constants of approximately 1 and 15 ms. The time course of adaptation slowed as the stimulus intensity was raised because of an increased prominence of the second component. The fast component of adaptation had a similar time constant for both positive and negative displacements and was unaffected by the myosin ATPase inhibitors, vanadate and butanedione monoxime. Adaptation was modeled by a scheme in which Ca(2+) ions, entering through open transducer channels, bind at two intracellular sites to trigger independent processes leading to channel closure. It was assumed that the second site activates a modulator with 10-fold slower kinetics than the first site. The model was implemented by computing Ca(2+) diffusion within a single stereocilium, incorporating intracellular calcium buffers and extrusion via a plasma membrane CaATPase. The theoretical results reproduced several features of the experimental responses, including sensitivity to the concentration of external Ca(2+) and intracellular calcium buffer and a dependence on the onset speed of the stimulus. The model also generated damped oscillatory transducer responses at a frequency dependent on the rate constant for the fast adaptive process. The properties of fast adaptation make it unlikely to be mediated by a myosin motor, and we suggest that it may result from Ca(2+) binding to the transducer channel or a nearby cytoskeletal element.

Critical Displacement of Neural Injuries in Supracondylar Humeral Fractures in Children

To investigate a relation between the degree of initial fracture displacement and nerve complication, 53 consecutive acute extension-type supracondylar humeral fractures in children during 10 years were analyzed. From the initial roentgenographs, the direction and degree of displacement of each fracture were plotted on the coronal two-dimensional coordinates at the fracture site. The degree of displacement was represented by a diameter of the humeral shaft. Of 53 fractures, 42 were displaced. Six patients had nerve injuries, representing an 11.3% incidence of neurologic complication. Their displacements were >90% of the diameter of the shaft. Predictive negative and positive displacements of the median nerve were <90% of the diameter and >150% of that in posterolaterally displaced fractures, respectively. Those of radial nerve were <130% and >190% in posteromedially displaced fractures, respectively.

Shifts of cortical d.c. potential induced by application of gamma-aminobutyric acid in rats in vivo.

Generally, increases in cortical activity go in parallel with negative shifts and decreases with positive shifts of cortical d.c. potentials. The aim of the present investigation was to test the effects of the inhibitory transmitter gamma-aminobutyric acid (GABA) and of GABA receptor agonists on cortical d.c. potentials. Concomitant changes of local pH were measured to get first insights as to the mechanisms of the evoked d.c. changes. The experiments were carried out on anesthetized and artificially ventilated rats. d.c. potentials were recorded at a cortical depth of about 1000 microm by glass microelectrodes. Extracellular pH was measured by ion-selective microelectrodes. GABA (0.1 mol/l), the GABA(A) receptor agonist muscimol (0.1 mmol/l) and the GABA(B) receptor agonist baclofen (0.1 mmol/l) were microejected by pressure pulses at a distance of 20-40 microm from the recording electrode. GABA evoked positive d.c. shifts with low pressure ejection and long application times. With increasing pressure the positive d.c. shifts were initially superimposed by negative ones. The GABA(A) receptor agonist muscimol elicited negative and the GABA(B) receptor agonist baclofen positive displacements of the d.c. potential independent of application time or pressure. The negative d.c. shifts induced by GABA and muscimol were associated with an extracellular alkalization of up to 0.1 pH units. The findings led one to assume (1) that the negative d.c. shift after GABA application was due to a neuronal depolarization and to an increase in excitation via local alkalization and (2) that the positive d.c. shift mirrored neuronal hyperpolarization.

A new technique for differentiating between diffusion and flow in granular media using magnetic resonance imaging

We have shown that a simple nuclear magnetic resonance spin-tagging sequence for spatial encoding of the longitudinal magnetization, combined with an imaging sequence, can be used to measure flow and diffusion in granular materials. Using this technique, experiments have been performed to study flow and diffusion profiles during convection induced by the vertical shaking of a container (39 mm diameter) filled with a granular medium. We have shown that maximum diffusion and displacements occur in a thin boundary layer near the container’s walls. The observed flow profiles are predominantly flat with relatively small positive displacements across the container with the exception of the boundary layer, where increasingly negative displacements are observed as the container’s edges are approached.

Intracellular calcium variations evoked by mechanical stimulation of mammalian isolated vestibular type I hair cells

The variations of intracellular free calcium concentration ([Ca2+]i) were recorded on-line from guinea-pig isolated vestibular sensory cells using a fura-2 fast fluorescent photometry system, during mechanical displacements of the hair bundle. Repetitive displacements of the hair bundle towards the kinocilium (positive stimulation 7 degrees, 300 ms, 2Hz for 10 s), revealed [Ca2+]i variations detectable only in the cuticular plate. [Ca2+]i increased from 105 to 145 nM. Single mechanical displacements of the hair bundle (7 degrees, 200 ms, 0.5 Hz) evoked increases of [Ca2+]i from 50 +/- 23 nM to 139 +/- 79 (n = 12). In the opposite direction, the mechanical stimulations (8 degrees, 400 ms, 0.5 Hz) evoked a decrease of [Ca2+]i from 68 +/- 17 nM to 37 +/- 12 nM (n = 8). The variations of [Ca2+]i detected in the cuticular plate during positive displacements of the hair bundle were reversibly abolished in the presence of 100 microM gentamicin and they could not be evoked in 0.1 mM calcium in the external medium. From these experiments, it has been concluded that the [Ca2+]i variations recorded in the cuticular plate were due to a limited entry of calcium ions through transduction channels localized in the hair bundle. The typical kinetics of variations of [Ca2+]i evoked during positive displacements of the hair bundle should account for the presence of strong calcium regulation systems in the hair bundle and cuticular plate.

Seismic Durability of Retrofitted Reinforced‐Concrete Columns

The seismic performances of four (three retrofitted and one control) half‐scale, circular, reinforced‐concrete columns were studied. The columns were 10‐ft high, 18‐in. diameter cantilevers. The longitudinal flexural steel was spliced to the foundation dowels just above the fixed base. A concentric axial load of 0.20 f′cAg was continually applied during testing. The free ends of the cantilevers were translated to produce a maximum displacement of four times that necessary to produce yield in the longitudinal reinforcing steel. This loading was repeated with both positive and negative displacements in a quasistatic manner until the lateral forces required to produce these displacements approached zero. The measure of seismic durability used was the number of such cycles that a column sustained before losing structural integrity. The laboratory arrangement was intended to model the arrangement of bridge columns constructed in the 1950 to mid‐1970 era. Three columns were retrofitted with prestressed, externally located circular hoops at intervals along the lower 4 ft. The spacing and size of these ties varied from column to column. The control column sustained less than two cycles before losing structural integrity; the retrofitted columns sustained a minimum of 12 cycles.

Determination of certain energetic parameters of laser radiation from the results of frequency and time interval measurements

takes place with movement of the FLG. The algorithm worked out facilitated optimization of the FLG for producing its best image. This, in turn, gives a maximum permissible range of FLG displacement with minimization of the size of the aberrated image. The dispersed field image is formed on the focal plane of the lens which collects the dispersed radiation and is, thereafter, projected on the FPZS rule in a reduced form. The optical system made it possible to obtain approximately 85% of the maximum permissible displacement and distortion equivalent to error of the order of • in measuring the geometrical characteristics. Since distortion exists in the same direction for both positive and negative displacements, this error can be of the order of •

15N NMR of nitranions: Opposite shift effects of σ and π charge

AbstractNitranions of pyrrole, aromatic and heteroaromatic amines, carboxamides and pyridyl carbanions are generated by deprotonation either of NH or CH acids. The positive or negative displacements undergone by the 15N nucleus relative to the neutral precursor depend on whether a σ or π charge is increased. They are associated with the symmetry of the nitrogen orbital in which the electron pair is either generated or that to which it is delocalized.

Projektieren der zykloidenverzahnungen hydraulischer verdrängermaschinen

Cycloidal gears are of great importance in the design of positive displacements machines. They are frequently called gerotor gears, without the design technique, gearing type or gear profile being differentiated. There are, however, different types of these gears with different gear profiles. Thus general design techniques for these types of gears may be determined. There are two methods of cycloidal gear design: the external envelope technique and the internal enveloped technique, with the first one usually being applied. With this technique, the external gearing of the base gear first and then according to it, the internal gearing of the mating gear are determined. The most beneficial solution is the one shown in Fig. 5, where the external gearing of the base gear is designed on the basis of being equidistant to the curtailed epicycloid and the internal mating gearing has the form of circles (rollers). This type of gear is employed, by Danfoss among others in orbit motors (low-speed orbitrary motors) and control modules for the steering systems of traction vehicles. The internal envelope technique is, as a matter of fact, the inversion of the external envelope technique. First, the internal basic gearing and then, the external mating are formed. This technique is used rarely and is regarded as the complementary one except for a special case of the hypocycloidal gears in which the internal base gear is formed in accordance with the curtailed hypocycloid and the external mating gearing has the form of circles (rollers). This special case is shown in Fig. 9. This type of gearing is applied by Rexroth in its MZ type low-speed motors.

The structure of Cu3Au above the critical temperature

The diffuse x-ray scattering intensity from a single crystal of Cu3Au was measured in a volume of reciprocal space at a temperature of 703 K, approximately 35 K above the transition temperature for ordering in this alloy. Intensity was measured in absolute units and was separated into components due to short-range order (SRO) and atomic displacements. The SRO parameters determined agree qualitatively with previous experimenters but agree best in magnitude with the original study by Cowley [J. Appl. Phys. 21, 24 (1950)]. Computer simulations of the structure, based on the SRO parameters, show that atoms with ordered environments tend to cluster into small domains that have dimensions of 1–10 unit cells in length and are surrounded by a disordered matrix. The average displacements of near-neighbor pairs were found to be contrary to what has previously been assumed: Au-Au neighbors were found to have negative displacements on average and Au-Cu pairs positive displacements, compared to the average interatomic displacements.

Non‐linear boundary value problems for the annular membrane: New results on existence of positive solutions

AbstractThe Föppl‐Hencky theory of small finite deflections has been applied to the study of axisymmetric deformations of annular membranes by various authors. The mathematical problem of uniqueness of tensile solutions for the corresponding non‐linear boundary value problems in the full range of physically meaningful boundary data was solved only recently.3, 4 In this paper, a new integral equation technique of solution is developed which yields the existence of tensile solutions for a parameter range of the boundary data where previous investigations on this matter had not been successful. It is shown that tensile solutions no longer exist, when sufficiently large positive radial displacements are prescribed at the inner edge of the annulus.

Aperture intensity ratio fiber-optic displacement sensor

A displacement sensor based on the ratio of fiber-optic light emitted from two fixed position optical fibers into a third, movable fiber connected to a photodetector is described. Square-wave modulated light of opposite phases produces a corresponding square wave at the detector which has zero ac amplitude at the center position and an amplitude proportional to displacement on either side of the detection fiber. A phase-sensitive detector produces a positive dc output voltage for positive displacements and negative for negative displacements.

Theoretical and Experimental Determination of the Dynamic Characteristics of a Hydrodynamic Journal Bearing

This paper describes a theoretical and experimental investigation into the nonlinear characteristics of the eight coefficients which specify the lateral flexibility of a hydrodynamic journal bearing. Coefficient calculations allowed viscosity to vary with temperature, and pressure, and examined a range of positive and negative displacements and velocities. Experimental techniques have been developed in which coefficients were deduced from specially chosen, imposed vibration orbits arising from two mutually perpendicular external oscillating forces of variable relative magnitude and phase. Journal centre displacement and velocity were measured using high speed data logging equipment. Coefficients are defined in terms of a “zero” value and linear gradient. Using realistic criteria, measured coefficient non-linearity was found to be significant at eccentricity ratios greater than 0.78. Theory adequately predicted some “zero” values but not gradients. An improvement in the coefficient prediction may depend on the inclusion of some previous history dependent factors.

Isotopieverschiebung der nat�rlichen geraden und ungeraden Sm- und Nd-Isotope

The isotope shift of the natural isotopes of Sm and Nd was investigated by a digital recording Fabry-Perot spectrometer using highly enriched samples. By the accuracy achieved in the measurements it was possible to verify earlier results indicating different relative isotope shifts for lines with positive and negative displacements, and to show that also lines with the same sign of the displacement may have different relative isotope shifts. It is shown that these non-constant relative isotope shifts can be explained for the even isotopes by the different contributions of the mass and volume effect to the isotope shifts in the different lines, but this explanation seems only to be partly valid for some distances between even and odd isotopes. The size of the mass effect is estimated and its influence especially on the results of the odd-even staggering is considered. The odd-even staggering is compared to earlier results for Hg. The estimation of the mass effect shows that the results forδ〈r 2〉 determined from the measured isotope shifts without correcting for the mass effect may be considerably wrong. Nevertheless it is possible by a suitable combination of the measured distances to calculate a quantity which only depends on nuclear properties and which therefore enables to check the known theories of the volume dependent isotope shift also without calculating the probability density of thes-electrons at the nucleus.