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Journal articles on the topic 'Zero velocity curves'
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1
Seow, C. Y., and N. L. Stephens. "Velocity-length-time relations in canine tracheal smooth muscle." Journal of Applied Physiology 64, no. 5 (1988): 2053–57. http://dx.doi.org/10.1152/jappl.1988.64.5.2053.
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Zero-load velocity (V0) as a function of the length of canine tracheal smooth muscle was obtained by applying zero-load clamps to isotonically contracting muscle under various loads. The load clamps were applied at a specific time after onset of contraction. The magnitude of the isotonic load therefore determines the length of the muscle at the moment of release or at the moment the unloaded shortening velocity was measured. A family of such V0-muscle length (L) curves was obtained at 1-s intervals in the time course of contraction. The V0-L curve was fitted by a parabolic function with satisfactory goodness of fit. The maximum shortening velocity at optimum muscle length varied with time, but the minimum length at which V0 diminished to zero was time independent.
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Roman, R., and I. Szücs-Csillik. "A family of zero-velocity curves in the restricted three-body problem." Astrophysics and Space Science 352, no. 2 (2014): 481–91. http://dx.doi.org/10.1007/s10509-014-1988-6.
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Kalvouridis, T. J. "On a property of zero-velocity curves in N-body ring-type systems." Planetary and Space Science 52, no. 10 (2004): 909–14. http://dx.doi.org/10.1016/j.pss.2004.05.001.
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Draudvilienė, Lina, Renaldas Raišutis, Egidijus Žukauskas, and Audrius Jankauskas. "Validation of Dispersion Curve Reconstruction Techniques for the A0 and S0 Modes of Lamb Waves." International Journal of Structural Stability and Dynamics 14, no. 07 (2014): 1450024. http://dx.doi.org/10.1142/s0219455414500242.
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The properties of ultrasonic Lamb waves, such as relatively small attenuation and high sensitivity to structural changes of the object being investigated, allow performing of non-destructive testing of various elongated structures like pipes, cables, etc. Due to the dispersion effect of Lamb waves, a waveform of the received informative signal is usually distorted, elongated and overlapping in the time domain. Therefore, in order to investigate objects using the ultrasonic Lamb waves and to reconstruct the dispersion curves, it is necessary to know the relationship between frequency, phase and group velocities and thickness of the plate. The zero-crossing technique for measurement of phase velocity of Lamb waves (the A0 and S0 modes) has been investigated using modelled dispersed signals and experimental signals obtained for an aluminium plate having thickness of 2 mm. A comparison between two reconstruction methods of Lamb wave phase velocity dispersion curves, namely, the two-dimensional fast Fourier transform (2D-FFT) and zero-crossing technique, along with the theoretical (analytical) dispersion curves is presented. The results indicate that the proposed zero-crossing method is suitable for use in reconstruction of dispersion curves in the regions affected by strong dispersion, especially for the A0 mode.
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Baan, Mirko van der. "Some comments on common-asymptotic-conversion-point (CACP) sorting of converted-wave data in isotropic, laterally inhomogeneous media." GEOPHYSICS 70, no. 3 (2005): U29—U36. http://dx.doi.org/10.1190/1.1925750.
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Common-midpoint (CMP) sorting of pure-mode data in arbitrarily complex isotropic or anisotropic media leads to moveout curves that are symmetric around zero offset. This greatly simplifies velocity determination of pure-mode data. Common-asymptotic-conversion-point (CACP) sorting of converted-wave data, on the other hand, only centers the apexes of all traveltimes around zero offset in arbitrarily complex but isotropic media with a constant P-wave/S-wave velocity ratio everywhere. A depth-varying CACP sorting may therefore be required to position all traveltimes properly around zero offset in structurally complex areas. Moreover, converted-wave moveout is nearly always asymmetric and nonhyperbolic. Thus, positive and negative offsets need to be processed independently in a 2D line, and 3D data volumes are to be divided in common azimuth gathers. All of these factors tend to complicate converted-wave velocity analysis significantly.
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Goudas, C. L., M. leftaki, and E. G. Petsagourakis. "Motions in the field of two rotating magnetic dipoles. III: Zero-velocity curves and surfaces." Celestial Mechanics and Dynamical Astronomy 47, no. 1 (1990): 1–14. http://dx.doi.org/10.1007/bf00052971.
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Lacomba, Ernesto A., and Carles Sim�. "Topology of Jacobi levels with no zero velocity curves in the restricted three-body problem." ZAMP Zeitschrift f�r angewandte Mathematik und Physik 38, no. 1 (1987): 10–20. http://dx.doi.org/10.1007/bf00944918.
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Narayan, A., and Amit Shrivastava. "Pulsating Different Curves of Zero Velocity around Triangular Equilibrium Points in Elliptical Restricted Three-Body Problem." Journal of Mathematics 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/936859.
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The oblateness and the photogravitational effects of both the primaries on the location and the stability of the triangular equilibrium points in the elliptical restricted three-body problem have been discussed. The stability of the triangular points under the photogravitational and oblateness effects of both the primaries around the binary systems Achird, Lyeten, Alpha Cen-AB, Kruger 60, and Xi-Bootis, has been studied using simulation techniques by drawing different curves of zero velocity.
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Papadakis, K. E. "The geometry of the roche coordinates and zero-velocity curves in the photogravitational three-body problem." Astrophysics and Space Science 232, no. 2 (1995): 337–54. http://dx.doi.org/10.1007/bf00658304.
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Singh, Nutan, and A. Narayan. "Pulsating curves of zero velocity for infinitesimal mass around oblate and triaxial rigid body of triangular equilibrium points in elliptical restricted three body problem." International Journal of Advanced Astronomy 5, no. 1 (2017): 29. http://dx.doi.org/10.14419/ijaa.v5i1.7025.
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This paper explore pulsating Curves of zero velocityof the infinitesimal mass around the triangular equilibrium points with oblate and triaxial rigid body in the elliptical restricted three body problem(ER3BP).
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Miller, J. P., G. A. Jacobs, and F. E. Theunissen. "Representation of sensory information in the cricket cercal sensory system. I. Response properties of the primary interneurons." Journal of Neurophysiology 66, no. 5 (1991): 1680–89. http://dx.doi.org/10.1152/jn.1991.66.5.1680.
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1. Six different types of primary wind-sensitive interneurons in the cricket cercal sensory system were tested for their sensitivity to the orientation and peak velocity of unidirectional airflow stimuli. 2. The cells could be grouped into two distinct classes on the basis of their thresholds and static sensitivities to airflow velocity. 3. Four interneurons (the right and left 10–2 cells and the right and left 10–3 cells) made up one of the two distinct velocity sensitivity classes. The mean firing frequencies of these interneurons were proportional to the logarithm of peak stimulus velocity over the range from 0.02 to 2.0 cm/s. 4. The other two interneurons studied (left and right 9-3) had a higher air-current velocity threshold, near the saturation level of the 10–2 and 10–3 interneurons. The slope of the velocity sensitivity curve for the 9–3 interneurons was slightly greater than that for the 10–2 and 10–3 interneurons, extending the sensitivity range of the system as a whole to at least 100 cm/s. 5. All of the interneurons had broad, symmetrical, single-lobed directional sensitivity tuning curves that could be accurately represented as truncated sine waves with 360 degree period. 6. The four low-threshold interneurons (i.e., left and right 10–2 and 10–3) had peak directional sensitivities that were evenly spaced around the horizontal plane, and their overlapping tuning curves covered all possible air-current stimulus orientations. The variance in the cells' responses to identical repeated stimuli varied between approximately 10% at the optimal stimulus orientations and approximately 30% at the zero-crossing orientations. 7. The two higher threshold interneurons (left and right 9-3) had broader directional sensitivity curves and wider spacing, resulting in reduced overlap with respect to the low-threshold class.
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Dagys, R., A. Pauliukonis, D. Kazlauskas, M. Mankevicius, and R. Simutis. "Determination of initial velocities of enzymic reactions from progress curves." Biochemical Journal 237, no. 3 (1986): 821–25. http://dx.doi.org/10.1042/bj2370821.
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The present communication describes a novel method for estimating initial velocities (v) of enzyme-catalysed reactions. It is based on an approximation of experimental data obtained by the cubic spline function. The initial velocity of a reaction is calculated as a derivative of the approximating function at a time value equal to zero. The proposed method is usable on a computer with a FORTRAN IV program. The method can be successfully used in such cases as substantial extents of substrate conversion, the inactivation of an enzyme in the course of a reaction, the existence of large experimental error or when the reaction mechanism is unknown.
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Butler, J., B. Haack, and M. Tomizuka. "Reference Input Generation for High Speed Coordinated Motion of a Two Axis System." Journal of Dynamic Systems, Measurement, and Control 113, no. 1 (1991): 67–74. http://dx.doi.org/10.1115/1.2896361.
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A method for generating two-dimensional reference trajectories to be followed by a linear second-order system under feedforward/feedback control is proposed. A differential equation is derived which assigns tracking velocity and tangential tracking acceleration as functions of time in such a way to allow high speed motion through an arbitrary smooth curve while guaranteeing the absence of actuator saturation. A method for using preview information for motion along curves with corners is also presented. The results are verified by simulation of a two axis cartesian positioning system under discrete time zero phase error tracking control.
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Duggleby, R. G. "Estimation of the initial velocity of enzyme-catalysed reactions by non-linear regression analysis of progress curves." Biochemical Journal 228, no. 1 (1985): 55–60. http://dx.doi.org/10.1042/bj2280055.
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Most methods for studying the kinetic properties of an enzyme involve the determination of initial velocities. When the reaction progress curve shows significant curvature due to depletion of the substrate, accumulation of inhibitory products or instability of the enzyme, estimation of the initial velocity is a subjective and inexact process. Two methods have been suggested [Cornish-Bowden (1975) Biochem. J. 144, 305-312; Boeker (1982) Biochem J. 203, 117-123] that attempt to eliminate this subjective element. The present study offers a third alternative, which is based on fitting a reparameterized form of the integrated Michaelis-Menten equation to the progress curves by non-linear regression. This method yields estimates and standard errors of the initial velocity and of the time to reach 50% reaction. No prior knowledge of the apparent product concentration at zero time or infinite time is required, since both of these quantities are also estimated from the data. It is shown that this method yields reliable estimates of the initial velocity under a wide range of circumstances, including those where the two previously published methods perform poorly.
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Deshmukh, Sharief, Patrik Peska, and Nasser Bin Turki. "Geodesic Vector Fields on a Riemannian Manifold." Mathematics 8, no. 1 (2020): 137. http://dx.doi.org/10.3390/math8010137.
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A unit geodesic vector field on a Riemannian manifold is a vector field whose integral curves are geodesics, or in other worlds have zero acceleration. A geodesic vector field on a Riemannian manifold is a smooth vector field with acceleration of each of its integral curves is proportional to velocity. In this paper, we show that the presence of a geodesic vector field on a Riemannian manifold influences its geometry. We find characterizations of n-spheres as well as Euclidean spaces using geodesic vector fields.
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Zagrouba, Mouldi, and Mohamed Shili Bouhdima. "Numerical study of S1 zero group velocity Lamb modes for nonlinear functionally graded materials." Canadian Journal of Physics 94, no. 11 (2016): 1189–94. http://dx.doi.org/10.1139/cjp-2016-0042.
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This paper presents detailed theoretical investigation of the first-order symmetric zero group velocity (S1-ZGV) modes propagating in functionally graded material (FGM) plates. Governing equations for the Lamb waves are derived and the power series technique (PST) is employed to solve the recursive equations associated with any power law and its gradient coefficient. The convergence criteria relative to PST have been discussed. Then, the dispersion curves are obtained on the basis of PST. Additionally, the impact of the FGM base materials and the gradient coefficient on S1-ZGV frequency is investigated. Numerical results show that S1-ZGV frequency is comparatively more sensitive to the shear modulus than to the Lamé parameter λ. Additionally, the variations of S1-ZGV frequency as a function of the Poisson ratio of various FGM plates are clarified.
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Maeland, Einar. "Focusing aspects of the parabolic Radon transform." GEOPHYSICS 63, no. 5 (1998): 1708–15. http://dx.doi.org/10.1190/1.1444466.
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From a geometrical point of view, the parabolic Radon transform of a common shotpoint gather is a focusing technique where the “focal length” is determined by the velocity field. When the traveltime curves at small offset are approximated by hyperbolas, the reciprocal of the curvature of an “image” is related to the square of the curvature at zero offset of the corresponding traveltime curve. Each event on a common‐shotpoint gather will be separated by the parabolic Radon transform, and the position of the foci associated with peg‐leg multiples can be predicted. Examples on synthetic common‐shotpoint gathers illustrate the merits of the analysis.
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Ding, Yuanyuan. "An improvement of the Lagrangian analysis method based on particle velocity profiles." EPJ Web of Conferences 183 (2018): 01023. http://dx.doi.org/10.1051/epjconf/201818301023.
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In general, techniques used in studies on dynamic behaviour of materials could be classified into two categories, namely the split Hopkinson pressure bar technique (SHPB) and the wave propagation technique (WPT). Lagrangian analysis method is one of the most famous methods in WPT. The traditional Lagrangian analysis based on the particle velocity wave-profiles measurements should consider a boundary condition, because it involves integral operations. However, the boundary stress data in some cases cannot be detected or determined by the experimental measures. To tackle this situation, this paper presents a modified Lagrangian analysis method which does not involve the boundary stress computation. Starting from the path-lines method and utilizing the zero-initial condition, the material constitutive stress-strain curves under high strain-rates is deduced from only observing the particle velocity curve measurements. The dynamic stress/strain wave-profiles of the PMMA material, as a paradigm, are numerically studied using the proposed method, which are well in agreement with the theoretical result using the method of characteristics, which confirms the reliability and validity of the presented method.
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Reiche, Sönke, and Benjamin Berkels. "Automated stacking of seismic reflection data based on nonrigid image matching." GEOPHYSICS 83, no. 3 (2018): V171—V183. http://dx.doi.org/10.1190/geo2017-0189.1.
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Stacking of multichannel seismic reflection data is a crucial step in seismic data processing, usually leading to the first interpretable seismic image. Stacking is preceded by traveltime correction, in which all events contained in a common-midpoint (CMP) gather are corrected for their offset-dependent traveltime increase. Such corrections are often based on the assumption of hyperbolic traveltime curves, and a best fit hyperbola is usually sought for each reflection by careful determination of stacking velocities. However, assuming hyperbolic traveltime curves is not accurate in many situations, e.g., in the case of strongly curved reflectors, large offset-to-target-ratios, or strong anisotropy. Here, we found that an underlying model parameterizing the shape of the traveltime curve is not a strict necessity for producing high-quality stacks. Based on nonrigid image-matching techniques, we developed an alternative way of stacking, both independent of a reference velocity model and any prior assumptions regarding the shape of the traveltime curve. Mathematically, our stacking operator is based on a variational approach that transforms a series of seismic traces contained within a CMP gather into a common reference frame. Based on the normalized crosscorrelation and regularized by penalizing irregular displacements, time shifts are sought for each sample to minimize the discrepancy between a zero-offset trace and traces with larger offsets. Time shifts are subsequently exported as a data attribute and can easily be converted to stacking velocities. To demonstrate the feasibility of this approach, we apply it to simple and complex synthetic data and finally to a real seismic line. We find that our new method produces stacks of equal quality and velocity models of slightly better quality compared with an automated, hyperbolic traveltime correction and stacking approach for complex synthetic and real data cases.
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Raj, Anant, and Jacob Eapen. "Computing Phonon Dispersion using Fast Zero-Point Correlations of Conjugate Variables." MRS Advances 3, no. 10 (2018): 531–36. http://dx.doi.org/10.1557/adv.2018.288.
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ABSTRACTTime correlations of dynamic variables in the reciprocal space offer a rich theoretical setting for computing the phonon dispersion curves, particularly for systems with marked anharmonic interactions. Present techniques primarily rely either on the equipartition of energy between the phonon modes or on the oscillation of the time correlation of the normal mode projections. The former can lead to numerical errors due to deviation from equipartition while the latter usually requires long simulations for computing the time correlations. We investigate a different approach using the ratio of the normal mode expectation value of two conjugate variables – velocity and acceleration. Since only the correlations at the initial time (t=0) are needed, this approach is computationally attractive. In this work, we employ this method to extract the full Brillouin zone phonon dispersion for graphene.
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Li, Ke, Shuangxi Jing, Jiangong Yu, Xiaoming Zhang, and Bo Zhang. "The Complex Rayleigh Waves in a Functionally Graded Piezoelectric Half-Space: An Improvement of the Laguerre Polynomial Approach." Materials 13, no. 10 (2020): 2320. http://dx.doi.org/10.3390/ma13102320.
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The research on the propagation of surface waves has received considerable attention in order to improve the efficiency and natural life of the surface acoustic wave devices, but the investigation on complex Rayleigh waves in functionally graded piezoelectric material (FGPM) is quite limited. In this paper, an improved Laguerre orthogonal function technique is presented to solve the problem of the complex Rayleigh waves in an FGPM half-space, which can obtain not only the solution of purely real values but also that of purely imaginary and complex values. The three-dimensional dispersion curves are generated in complex space to explore the influence of the gradient coefficients. The displacement amplitude distributions are plotted to investigate the conversion process from complex wave mode to propagating wave mode. Finally, the curves of phase velocity to the ratio of wave loss decrements are illustrated, which offers extra convenience for finding the high phase velocity points where the complex wave loss is near zero.
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Schleicher, Jörg, Peter Hubral, German Höcht, and Frank Liptow. "Seismic constant‐velocity remigration." GEOPHYSICS 62, no. 2 (1997): 589–97. http://dx.doi.org/10.1190/1.1444168.
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When a seismic common midpoint (CMP) stack or zero‐offset (ZO) section is depth or time migrated with different (constant) migration velocities, different reflector images of the subsurface are obtained. If the migration velocity is changed continuously, the (kinematically) migrated image of a single point on the reflector, constructed for one particular seismic ZO reflection signal, moves along a circle at depth, which we call the Thales circle. It degenerates to a vertical line for a nondipping event. For all other dips, the dislocation as a function of migration velocity depends on the reflector dip. In particular for reflectors with dips larger than 45°, the reflection point moves upward for increasing velocity. The corresponding curves in a Time‐migrated section are parabolas. These formulas will provide the seismic interpreter with a better understanding of where a reflector image might move when the velocity model is changed. Moreover, in that case, the reflector image as a whole behaves to some extent like an ensemble of body waves, which we therefore call remigration image waves. In the same way as physical waves propagate as a function of time, these image waves propagate as a function of migration velocity. Different migrated images can thus be considered as snapshots of image waves at different instants of migration velocity. By some simple plane‐wave considerations, image‐wave equations can be derived that describe the propagation of image waves as a function of the migration velocity. The Thales circles and parabolas then turn out to be the characteristics or ray trajectories for these image‐wave equations.
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El-Zahar, Essam R., Ahmed M. Rashad, and Laila F. Seddek. "Impacts of Viscous Dissipation and Brownian motion on Jeffrey Nanofluid Flow over an Unsteady Stretching Surface with Thermophoresis." Symmetry 12, no. 9 (2020): 1450. http://dx.doi.org/10.3390/sym12091450.
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The goal of this investigation is to explore the influence of viscous dissipation and Brownian motion on Jeffrey nanofluid flow over an unsteady moving surface with thermophoresis and mixed convection. Zero mass flux is also addressed at the surface such that the nanoparticles fraction of maintains itself on huge obstruction. An aiding transformation is adopted to renovate the governing equations into a set of partial differential equations which is solved using a new fourth-order finite difference continuation method and various graphical outcomes are discussed in detail with several employed parameters. The spectacular influence of pertinent constraints on velocity and thermal curves are inspected through various plots. Computational data for the heat transfer rate and skin-friction coefficient are also reported graphically. Graphical outcomes indicate that an augmentation in buoyance ratio and thermophoretic parameter leads to diminish the velocity curves and increase the temperature curves. Furthermore, it is inspected that escalating Deborah number exhibits increasing in the skin friction and salient decreasing heat transmission. Increasing magnetic strength leads to a reduction in the skin friction and enhancement in the Nusselt number, whilst a reverse reaction is manifested with mixed convection aspects.
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Kresan, T. A., S. F. Pylypaka, V. M. Babka, and Ya S. Kremets. "Moving and fixed axoids of frenet thrihedral of directing curve on example of cylindrical line." Naukovij žurnal «Tehnìka ta energetika» 11, no. 3 (2020): 41–48. http://dx.doi.org/10.31548/machenergy2020.03.041.
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If the solid body makes a spatial motion, then at any point in time this motion can be decomposed into rotational at angular velocity and translational at linear velocity. The direction of the axis of rotation and the magnitude of the angular velocity, that is the vector of rotational motion at a given time does not change regardless of the point of the solid body (pole), relative to which the decomposition of velocities. For linear velocity translational motion is the opposite: the magnitude and direction of the vector depend on the choice of the pole. In a solid body, you can find a point, that is, a pole with respect to which both vectors of rotational and translational motions have the same direction. The common line given by these two vectors is called the instantaneous axis of rotation and sliding, or the kinematic screw. It is characterized by the direction and parameter - the ratio of linear and angular velocity. If the linear velocity is zero and the angular velocity is not, then at this point in time the body performs only rotational motion. If it is the other way around, then the body moves in translational manner without rotating motion. The accompanying trihedral moves along the directing curve, it makes a spatial motion, that is, at any given time it is possible to find the position of the axis of the kinematic screw. Its location in the trihedral, as in a solid body, is well defined and depends entirely on the differential characteristics of the curve at the point of location of the trihedral – its curvature and torsion. Since, in the general case, the curvature and torsion change as the trihedral moves along the curve, then the position of the axis of the kinematic screw will also change. Multitude of these positions form a linear surface - an axoid. At the same time distinguish the fixed axoid relative to the fixed coordinate system, and the moving - which is formed in the system of the trihedral and moves with it. The shape of the moving and fixed axoids depends on the curve. The curve itself can be reproduced by rolling a moving axoid over a fixed one, while sliding along a common touch line at a linear velocity, which is also determined by the curvature and torsion of the curve at a particular point. For flat curves, there is no sliding, that is, the movable axoid is rolling over a stationary one without sliding. There is a set of curves for which the angular velocity of the rotation of the trihedral is constant. These include the helical line too. The article deals with axoids of cylindrical lines and some of them are constructed.
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Angella, Giuliano. "Flow Curve Modelling of an Austenitic Stainless Steel at High Temperatures Starting from the One-Parameter Model of Strain Hardening." Materials Science Forum 706-709 (January 2012): 1361–66. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.1361.
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The flow curves of an austenitic stainless steel deformed at temperatures 700-1000°C with strain rates 10-5-10-2s-1were modelled with the Voce equation. The parameters needed to draw the Voce equation, are the saturation stressσVthat defines the height of the flow curve, the critical strainεCthat defines the velocity to achieveσV, and the stressσo, namely the back-extrapolated flow stress to zero strain. A modified strain hardening analysis based on the one-parameter model was used to analyze the strain hardening rate dσ/dεvs. the flow stressσin order to obtainσVandεC. The modified approach was based on the assumption that the dislocation multiplication component of strain hardening was temperature and strain rate dependent through the thermal activation termsof flow stress. A parameters’ proportional toswas obtained from the strain hardening analysis and a relationship betweens’ and temperature and strain rate was found. Relationships betweenσV,σo,εCands’ were finally established and at this stage the Voce equation could reproduce the experimental flow curves at any imposed deformation conditions of temperature and strain rate.
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A. Ansari, Abdullah, Ashraf Ali, Kumari Shalini, and Mehtab Alam. "Heterogeneous primaries in CR4BP." International Journal of Advanced Astronomy 7, no. 2 (2019): 49. http://dx.doi.org/10.14419/ijaa.v7i2.29648.
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This paper investigates the motion of the massless body moving under the influence of the gravitational forces of the three equal heterogeneous oblate spheroids placed at Lagrangian configuration. After determining the equations of motion and the Jacobian constant of the massless body, we have illustrated the numerical work (Stationary points, zero-velocity curves, regions of motion, Poincare surfaces of section and basins of attraction). And then we have checked the linear stability of the stationary points and found that all the stationary points are unstable.
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Stephens, N. L., A. Fust, H. Jiang, W. Li, and X. Ma. "Isotonic relaxation of control and sensitized airway smooth muscle." Canadian Journal of Physiology and Pharmacology 83, no. 10 (2005): 941–51. http://dx.doi.org/10.1139/y05-103.
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Smooth muscle relaxation has most often been studied in isometric mode. However, this only tells us about the stiffness properties of the bronchial wall and thus only about wall capacitative properties. It tells us little about airflow. To study the latter, which of course is the meaningful parameter in regulation of ventilation and in asthma, we studied isotonic shortening of bronchial smooth muscle (BSM) strips. Failure of BSM to relax could be another important factor in maintaining high airway resistance. To analyze relaxation curves, we developed an index of isotonic relaxation, t1/2(P, lCE), which is the half-time for relaxation that is independent of muscle load (P) and of initial contractile element length (lCE). This index was measured in curves of relaxation initiated at 2 s (normally cycling crossbridges) and at 10 s (latch-bridges). At 10 s no difference was seen for adjusted t1/2(P, lCE) between curves obtained from control and sensitized BSM, (8.38 ± 0.92 s vs. 7.78 ± 0.93 s, respectively). At 2 s the half-time was almost doubled in the sensitized BSM (6.98 ± 0.01 s (control) vs. 12.74 ± 2.5 s (sensitized)). Thus, changes in isotonic relaxation are only seen during early contraction. Using zero load clamps, we monitored the time course of velocity during relaxation and noted that it varied according to 3 phases. The first phase (phase i) immediately followed cessation of electrical field stimulation (EFS) at 10 s and showed almost the same velocity as during the latter 1/3 of shortening; the second phase (phase ii) was linear in shape and is associated with zero load velocity, we speculate it could stem from elastic recoil of the cells' internal resistor; and the third phase (phase iii) was convex downwards. The zero load velocities in phase iii showed a surprising spontaneous increase suggesting reactivation of the muscle. Measurements of intracellular calcium (Fura-2 study) and of phosphorylation of the 20 kDa myosin light chain showed simultaneous increments, indicating phase iii represented an active process. Studies are under way to determine what changes occur in these 3 phases in a sensitized muscle. And of course, in the context of this conference, just what role the plastic properties of the muscle play in relaxation requires serious consideration.Key words: airway smooth muscle, sensitized smooth muscle, isotonic relaxation, intracellular calcium transients, myosin light chain (20 kDa) phosphorylation.
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Amarante, A., and O. C. Winter. "Surface dynamics, equilibrium points and individual lobes of the Kuiper Belt object (486958) Arrokoth." Monthly Notices of the Royal Astronomical Society 496, no. 4 (2020): 4154–73. http://dx.doi.org/10.1093/mnras/staa1732.
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ABSTRACT The New Horizons space probe led the first close flyby of one of the most primordial and distant objects left over from the formation of the Solar system, the contact binary Kuiper Belt object (486958) Arrokoth. This is composed of two progenitors, the lobes called Ultima and Thule. In the current work, we investigate Arrokoth’s surface in detail to identify the location of equilibrium points and also we explore each lobe’s individual dynamic features. We assume that Arrokoth’s irregular shape is a homogeneous polyhedra contact binary. We explore its dynamic characteristics numerically by computing its irregular binary geopotential in order to study its quantities, such as geometric height, oblateness, ellipticity and zero-power curves. The stability of Arrokoth Hill was also explored through zero-velocity curves. Arrokoth’s external equilibrium points have no radial symmetry due to its highly irregular shape. We identified even equilibrium points concerning its shape and spin rate: i.e. four unstable external equilibrium points and three inner equilibrium points, where two points are linearly stable, with an unstable central point that has a slight offset from its centroid. Moreover, the large and small lobes each have five equilibrium points with different topological structures from those found in Arrokoth. Our results also indicate that the equatorial region of Arrokoth’s lobes is an unstable area due to the high rotation period, while its polar locations are stable resting sites for surface particles. Finally, the zero-power curves indicate the locations around Arrokoth where massless particles experience enhancing and receding orbital energy.
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Nedlin, G. "t-x reflection curves for arbitrary three‐dimensional media in terms of geometry of a reflector and a near‐reflector wavefront." GEOPHYSICS 51, no. 10 (1986): 1912–22. http://dx.doi.org/10.1190/1.1442048.
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A general relation between a normal‐moveout velocity (NMOV) for t-x (time‐offset) reflection curves and the geometrical properties of a reflector and a wavefront in the vicinity of the reflector has been found. Furthermore, by considering the reflector as a set of zero‐offset reflecting points for different shot locations on the earth’s surface, a new formulation of the special “seismic” parametric description of a reflecting surface allows the arrival times to be related directly to the wavefront equation, without introducing any earth model above the reflector. The NMOV is expressed in terms of the local velocity near the reflector and the curvatures of the reflector and of the near‐reflector wavefront. New equations for geometrical migration make it possible to do direct wavefront modeling without earth modeling (above the reflector). If t-x curves are approximated by hyperbolas (i.e., terms higher than those quadratic in the offsets are neglected), all rays in a common‐midpoint (CMP) panel with a fixed midpoint have the same reflecting point, for any earth model.
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Sarvandani, Mohamadhasan Mohamadian, Emanuel Kästle, Lapo Boschi, Sylvie Leroy, and Mathilde Cannat. "Seismic Ambient Noise Imaging of a Quasi-Amagmatic Ultra-Slow Spreading Ridge." Remote Sensing 13, no. 14 (2021): 2811. http://dx.doi.org/10.3390/rs13142811.
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Passive seismic interferometry has become very popular in recent years in exploration geophysics. However, it has not been widely applied in marine exploration. The purpose of this study is to investigate the internal structure of a quasi-amagmatic portion of the Southwest Indian Ridge by interferometry and to examine the performance and reliability of interferometry in marine explorations. To reach this goal, continuous vertical component recordings from 43 ocean bottom seismometers were analyzed. The recorded signals from 200 station pairs were cross-correlated in the frequency domain. The Bessel function method was applied to extract phase–velocity dispersion curves from the zero crossings of the cross-correlations. An average of all the dispersion curves was estimated in a period band 1–10 s and inverted through a conditional neighborhood algorithm which led to the final 1D S-wave velocity model of the crust and upper mantle. The obtained S-wave velocity model is in good agreement with previous geological and geophysical studies in the region and also in similar areas. We find an average crustal thickness of 7 km with a shallow layer of low shear velocities and high Vp/Vs ratio. We infer that the uppermost 2 km are highly porous and may be strongly serpentinized.
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Hindsley, Robert, and R. A. Bell. "An Adjustment to Cepheid Distances Calculated Using Model Atmospheres." International Astronomical Union Colloquium 139 (1993): 94. http://dx.doi.org/10.1017/s0252921100116987.
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Hindsley and Bell (1989, Ap. J., 341, 1004) determined distances for 23 Cepheids using the surface brightness method. The color V – IC on the Cousins system or V – RJ on the Johnson system was used to measure visual surface brightness. Combined with the observed visual magnitudes, angular diameters were then calculated. Comparison of angular diameters with radius differences in linear units, obtained by integrating the radial velocity curve, yielded each Cepheid's distance.Hindsley and Bell calibrated the relationship between color and surface brightness using model atmospheres. The zero point of the relationship was found using observations of Vega and an appropriate model. More recently the spectral scans of Gunn and Strycker (1983, Ap. J. Suppl., 52, 121) and the Cousins filter response curves of Hindsley and Bell were used to calculate colors and these were compared to the corresponding observed colors.
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Lou, Di Ming, Yi Zhou Zhao, Yuan Hu Zhi, Pi Qiang Tan, and Yan Juan Zhu. "Characteristics of Particulate Matter Emissions on Diesel Passenger Vehicles Fueled with GTL Based on Real-Road Operating Parameters." Advanced Materials Research 534 (June 2012): 253–60. http://dx.doi.org/10.4028/www.scientific.net/amr.534.253.
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An on-board experimental research was made on diesel passenger vehicles fueled with national IV diesel, gas-to-liquid (GTL) fuel and three other different volume ratio of mixed fuel (G10D90, G20D80, G50D50) about the regularity of Particulate Matter (PM) emission characteristics changing with velocity, acceleration and vehicle specific power (VSP). The experimental results show that: PM emission rate increases gradually with higher velocity; acceleration leads to the deterioration of emissions; curves concave at the point when VSP value equals zero. Moreover, the emission rate of particle number decreases 50% to 60% while that of particle mass decreases 30% to 45% when the volumetric mixture ratio of GTL fuel improves. It is obvious that GTL fuel improves the characteristics of PM emission significantly, making it one of the promising clean alternative fuel.
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Kohr, Mirela. "A Direct Boundary Integral Method for a Mobility Problem." Georgian Mathematical Journal 7, no. 1 (2000): 73–84. http://dx.doi.org/10.1515/gmj.2000.73.
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Abstract The problem of a Stokes flow in the presence of a solid particle, a rigid wall and a viscous cell is formulated as a system of Fredholm integral equations of the second kind, with the surface force on the boundary of the solid particle and the velocity on the interface as unknowns. The particularity of the problem consists in the fact that the total force and the total torque of the flow on the solid particle are zero. The existence and the uniqueness result of solution is obtained when the boundaries are curves of the class C 2.
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Abduljabar Ansari, Abdullah, and Mehtab Alam. "Dynamics in the circular restricted three body problem with perturbations." International Journal of Advanced Astronomy 5, no. 1 (2017): 19. http://dx.doi.org/10.14419/ijaa.v5i1.7102.
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This paper presents the dynamics in the restricted problem with perturbations i.e. the circular restricted three body problem by considering one of the primaries as oblate and other one having the solar radiation pressure and all the masses are variable (primaries and infinitesimal body). For finding the autonomized equations of motion, we have used the Meshcherskii transformation. We have drawn the libration points, the time series, the zero velocity curves and Poincare surface of sections for the different values of the oblateness and solar radiation pressure. Finally, we have examined the stability and found that all the libration points are unstable.
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Ansari, Abdullah A., Prashant Kumar, and Mehtab Alam. "Heterogeneous Oblate Primaries in Photo-gravitational CR5BP with Kite Configuration." Journal of Nepal Mathematical Society 2, no. 1 (2019): 1–14. http://dx.doi.org/10.3126/jnms.v2i1.33012.
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This paper presents the investigation of the motion of infinitesimal body in the circular restricted five-body problem in which four bodies are taken as heterogeneous oblate spheroid with different densities in three layers and sources of radiation pressure. These four primaries are moving on the circumference of a circle and form a kite configuration. After evaluating the equations of motion and Jacobi-integral, we study the numerical part of the paper such as equilibria, zero-velocity curves and regions of motion. Finally, we examine the stability of the equilibria and observed that all the equilibria are unstable.
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Ahmadov, T. "FORM OF SEISMIC HORIZON ON TIME SECTION AND REFLECTED WAVE COMMON SHOT POINT TRAVEL TIME CURVE IN TRANSITION ZONE FOR THE CASE OF COMPLICATION OF TARGET HORIZON COVER BY FAULT." Visnyk of Taras Shevchenko National University of Kyiv. Geology, no. 3 (90) (2020): 44–48. http://dx.doi.org/10.17721/1728-2713.90.06.
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The paper is devoted to study of reflection pattern (seismic horizon) and CSP travel time curve of reflected wave when the base of seismic oscillations receivers is within transition zone, i.e. the portion of base is in one flank while the other part is already in the next flank. The equation has been derived for travel time curve of zero-offset survey, i.e. reflection pattern) for the case when target horizon cover is complicated by fault. The other equation derived is the equation of traveltime curve of CSP of reflected wave, which upgoing rays are refracted on the fault line. For this, we have used the equation of traveltime curve of normal reflections refracted on the fault line. Based on derived formulae we have calculated traveltime curves of CSP for various models of environment. Analysis of these models has shown that while passing through seismic waves receiver base over the faulted zone the travel time curve is divided into two cuts with differing curvature and various time offsets relative to each other depending on velocity section difference from the fault line leading to the impression that these two cuts are not the sections of the same travel time curve.
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Kozyreva, Alexandra, Petr Baklanov, Samuel Jones, Georg Stockinger, and Hans-Thomas Janka. "Synthetic observables for electron-capture supernovae and low-mass core collapse supernovae." Monthly Notices of the Royal Astronomical Society 503, no. 1 (2021): 797–814. http://dx.doi.org/10.1093/mnras/stab350.
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ABSTRACT Stars in the mass range from 8 M⊙ to 10 M⊙ are expected to produce one of two types of supernovae (SNe), either electron-capture supernovae (ECSNe) or core-collapse supernovae (CCSNe), depending on their previous evolution. Either of the associated progenitors retain extended and massive hydrogen-rich envelopes and the observables of these SNe are, therefore, expected to be similar. In this study, we explore the differences in these two types of SNe. Specifically, we investigate three different progenitor models: a solar-metallicity ECSN progenitor with an initial mass of 8.8 M⊙, a zero-metallicity progenitor with 9.6 M⊙, and a solar-metallicity progenitor with 9 M⊙, carrying out radiative transfer simulations for these progenitors. We present the resulting light curves for these models. The models exhibit very low photospheric velocity variations of about 2000 km s−1; therefore, this may serve as a convenient indicator of low-mass SNe. The ECSN has very unique light curves in broad-bands, especially the U band, and does not resemble any currently observed SN. This ECSN progenitor being part of a binary will lose its envelope for which reason the light curve becomes short and undetectable. The SN from the 9.6 M⊙ progenitor exhibits also quite an unusual light curve, explained by the absence of metals in the initial composition. The artificially iron-polluted 9.6 M⊙ model demonstrates light curves closer to normal SNe IIP. The SN from the 9 M⊙ progenitor remains the best candidate for so-called low-luminosity SNe IIP like SN 1999br and SN 2005cs.
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Yousuf, Saleem, and Ram Kishor. "Effects of the albedo and disc on the zero velocity curves and linear stability of equilibrium points in the generalized restricted three-body problem." Monthly Notices of the Royal Astronomical Society 488, no. 2 (2019): 1894–907. http://dx.doi.org/10.1093/mnras/stz1668.
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ABSTRACT The important aspects of a dynamical system are its stability and the factors that affect its stability. In this paper, we present an analysis of the effects of the albedo and the disc on the zero velocity curves, the existence of equilibrium points and their linear stability in a generalized restricted three-body problem (RTBP). The proposed problem consists of the motion of an infinitesimal mass under the gravitational field of a radiating-oblate primary, an oblate secondary and a disc that is rotating about the common centre of mass of the system. Significant effects of the albedo and the disc are observed on the zero velocity curves, on the positions of equilibrium points and on the stability region. A linear stability analysis of collinear equilibrium points L1, 2, 3 is performed with respect to the mass parameter μ and albedo parameter QA of the secondary, separately. It is found that L1, 2, 3 are unstable in both cases. However, the non-collinear equilibrium points L4, 5 are stable in a finite range of mass ratio μ. After analysing the individual as well as combined effects of the radiation pressure force of the primary, the albedo force of the secondary, the oblateness of both the primary and secondary and the disc, it is found that these perturbations play a significant role in the design of the trajectories in the vicinity of equilibrium points and in the analysis of their stability property. In the future, the results obtained will improve existing results and will help in the analysis of different space missions. These results are limited to the regular symmetric disc and radiation pressure, which can be extended later.
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Anashkina, Elena A., and Alexey V. Andrianov. "Design and Dispersion Control of Microstructured Multicore Tellurite Glass Fibers with In-Phase and Out-of-Phase Supermodes." Photonics 8, no. 4 (2021): 113. http://dx.doi.org/10.3390/photonics8040113.
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High nonlinearity and transparency in the 1–5 μm spectral range make tellurite glass fibers highly interesting for the development of nonlinear optical devices. For nonlinear optical fibers, group velocity dispersion that can be controlled by microstructuring is also of great importance. In this work, we present a comprehensive numerical analysis of dispersion and nonlinear properties of microstructured two-, four-, six-, and eight-core tellurite glass fibers for in-phase and out-of-phase supermodes and compare them with the results for one-core fibers in the near- and mid-infrared ranges. Out-of-phase supermodes in tellurite multicore fibers are studied for the first time, to the best of our knowledge. The dispersion curves for in-phase and out-of-phase supermodes are shifted from the dispersion curve for one-core fiber in opposite directions; the effect is stronger for large coupling between the fields in individual cores. The zero dispersion wavelengths of in-phase and out-of-phase supermodes shift to opposite sides with respect to the zero-dispersion wavelength of a one-core fiber. For out-of-phase supermodes, the dispersion can be anomalous even at 1.55 μm, corresponding to the operating wavelength of Er-doped fiber lasers.
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Hai, C. M., and R. A. Murphy. "Regulation of shortening velocity by cross-bridge phosphorylation in smooth muscle." American Journal of Physiology-Cell Physiology 255, no. 1 (1988): C86—C94. http://dx.doi.org/10.1152/ajpcell.1988.255.1.c86.
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We have proposed a model that incorporates a dephosphorylated "latch bridge" to explain the mechanics and energetics of smooth muscle. Cross-bridge phosphorylation is proposed as a prerequisite for cross-bridge attachment and rapid cycling. Features of the model are 1) myosin light chain kinase and phosphatase can act on both free and attached cross bridges, 2) dephosphorylation of an attached phosphorylated cross bridge produces a noncycling "latch bridge," and 3) latch bridges have a slow detachment rate. This model quantitatively predicts the latch state: stress maintenance with reduced phosphorylation, cross-bridge cycling rates, and ATP consumption. In this study, we adapted A. F. Huxley's formulation of crossbridge cycling (A. F. Huxley, Progr. Biophys. Mol. Biol. 7: 255-318, 1957) to the latch-bridge model to predict the relationship between isotonic shortening velocity and phosphorylation. The model successfully predicted the linear dependence of maximum shortening velocity at zero external load (V0) on phosphorylation, as well as the family of stress-velocity curves determined at different times during a contraction when phosphorylation values varied. The model implies that it is unnecessary to invoke an internal load or multiple regulatory mechanisms to explain regulation of V0 in smooth muscle.
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Tweed, D., M. Fetter, D. Sievering, H. Misslisch, and E. Koenig. "Rotational kinematics of the human vestibuloocular reflex. II. Velocity steps." Journal of Neurophysiology 72, no. 5 (1994): 2480–89. http://dx.doi.org/10.1152/jn.1994.72.5.2480.
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1. Gain matrices were used to quantify the three-dimensional vestibuloocular reflex (VOR) in five human subjects who were accelerated over 1 s and then spun at a constant 150 degrees/s for 29 s in darkness. Rotations were torsional, vertical and horizontal, about earth-vertical and earth-horizontal axes. 2. Elements on the main diagonal of the gain matrices were much smaller than the optimal value of -1, and torsional gain was weaker than vertical or horizontal. Off-diagonal elements, indicating cross talk, were minimal except for a small but consistent horizontal response to torsional head rotation. 3. Downward slow phases were more than twice as fast as upward at the start of rotation about both earth-vertical and earth-horizontal axes, but the asymmetry vanished later in the rotation. 4. During earth-vertical-axis rotation, all matrix elements decayed to zero. The main-diagonal torsional and vertical gains waned with time constants close to that of the cupula (6.7 and 7.3 s). Velocity storage prolonged the horizontal response to horizontal head rotation (time constant 14.2 s) but not the horizontal response to torsion (7.7 s). A simple explanation is that velocity storage acts on a central estimate of head motion that accurately distinguishes horizontal from torsional and that the inappropriate horizontal eye velocity response to torsion occurs because of cross talk downstream from velocity storage. 5. During earth-horizontal-axis rotation, the torsional, vertical, and horizontal main-diagonal elements declined, with time constants of 7.6, 8.2, and 7.9 s, to maintained nonzero values, all equal to about -0.1. Off-diagonal elements, including the horizontal response to torsion, decayed to zero, so that the otolith-driven reflex, late in the rotation, was equally strong in all dimensions and almost free of detectable cross talk. 6. The difference between gain curves over the course of earth-vertical- and earth-horizontal-axis rotations was not constant but increased with time, suggesting that the VOR response to earth-horizontal-axis rotation is not a simple sum of canal and otolith reflexes.
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Cacciari, Carla, Gisella Clementini1, Fiorella Castelli, and Fabrizio Melandri. "Revised Baade–Wesselink Analysis of RR Lyrae Stars." International Astronomical Union Colloquium 176 (2000): 176–81. http://dx.doi.org/10.1017/s0252921100057493.
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AbstractWe have applied the Baade–Wesselink method to two field RR Lyrae stars, i.e. SW And and RR Cet, and derived their distances and physical parameters. With respect to previous B–W analyses we have applied the following improvements: i) use of all sets of available data, after proper comparison for homogeneity and compatibility; ii) use of the most recent and accurate model atmospheres, with turbulent velocity Vturb = 4 km s−1 and the no-overshooting approximation, and comparison with other treatments of convection; iii) use of the instantaneous gravity along the pulsation cycle rather than the mean value; iv) comparison with modified radial velocity curves according to various assumptions on radial velocity gradients in the atmosphere; and v) careful reanalysis of the temperature scale. The main aim of this study is to evaluate the effect of the above items on the B–W results and verify whether any (or a combination) of them can possibly account for the discrepancy of the absolute magnitude zero-point with respect to other independent determinations.
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Sanmiguel Vila, C., R. Vinuesa, S. Discetti, A. Ianiro, P. Schlatter, and R. Örlü. "On the identification of well-behaved turbulent boundary layers." Journal of Fluid Mechanics 822 (May 31, 2017): 109–38. http://dx.doi.org/10.1017/jfm.2017.258.
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This paper introduces a new method based on the diagnostic plot (Alfredsson et al., Phys. Fluids, vol. 23, 2011, 041702) to assess the convergence towards a well-behaved zero-pressure-gradient (ZPG) turbulent boundary layer (TBL). The most popular and well-understood methods to assess the convergence towards a well-behaved state rely on empirical skin-friction curves (requiring accurate skin-friction measurements), shape-factor curves (requiring full velocity profile measurements with an accurate wall position determination) or wake-parameter curves (requiring both of the previous quantities). On the other hand, the proposed diagnostic-plot method only needs measurements of mean and fluctuating velocities in the outer region of the boundary layer at arbitrary wall-normal positions. To test the method, six tripping configurations, including optimal set-ups as well as both under- and overtripped cases, are used to quantify the convergence of ZPG TBLs towards well-behaved conditions in the Reynolds-number range covered by recent high-fidelity direct numerical simulation data up to a Reynolds number based on the momentum thickness and free-stream velocity $Re_{\unicode[STIX]{x1D703}}$ of approximately 4000 (corresponding to 2.5 m from the leading edge) in a wind-tunnel experiment. Additionally, recent high-Reynolds-number data sets have been employed to validate the method. The results show that weak tripping configurations lead to deviations in the mean flow and the velocity fluctuations within the logarithmic region with respect to optimally tripped boundary layers. On the other hand, a strong trip leads to a more energized outer region, manifested in the emergence of an outer peak in the velocity-fluctuation profile and in a more prominent wake region. While established criteria based on skin-friction and shape-factor correlations yield generally equivalent results with the diagnostic-plot method in terms of convergence towards a well-behaved state, the proposed method has the advantage of being a practical surrogate that is a more efficient tool when designing the set-up for TBL experiments, since it diagnoses the state of the boundary layer without the need to perform extensive velocity profile measurements.
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Půst, Ladislav, Luděk Pešek, and Alena Radolfová. "Dynamics of Simple Gearing Model with Flexible Planetary Pins." Applied Mechanics and Materials 821 (January 2016): 274–81. http://dx.doi.org/10.4028/www.scientific.net/amm.821.274.
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The influence of flexible pins of planet gears on the dynamic properties of planetary gearing box is investigated by means of a general analysis with some alternative values of parameters. For discovering of basic dynamic behaviour of planetary gear system the simplest planetary gear set with neglected compliance of teeth contacts, fixed axes of central sun wheel and fixed planetary carrier, etc is used One mode of free vibration with eigenfrequency Ω proportional to and zero frequency mode Ω→0 corresponding to the rotation with constant angular velocity were analysed. Forced vibrations, analysed by means of response curves, were oriented on ascertaining of influence of driving aggregate characteristic on frequency spectrum of the whole set.
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Barone, Ilaria, Emanuel Kästle, Claudio Strobbia, and Giorgio Cassiani. "Surface wave tomography using 3D active-source seismic data." GEOPHYSICS 86, no. 1 (2021): EN13—EN26. http://dx.doi.org/10.1190/geo2020-0068.1.
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Surface wave tomography (SWT) is a powerful and well-established technique to retrieve 3D shear-wave (S-wave) velocity models at the regional scale from earthquakes and seismic noise measurements. We have applied SWT to 3D active-source data, in which higher modes and heterogeneous spatial sampling make phase extraction challenging. First, synthetic traveltimes calculated on a dense, regular-spaced station array are used to test the performance of three different tomography algorithms (linearized inversion, Markov chain Monte Carlo [MCMC], and eikonal tomography). The tests suggest that the lowest misfit to the input model is achieved with the MCMC algorithm, at the cost of a much longer computational time. Then, real phases were extracted from a 3D exploration data set at different frequencies. This operation included an automated procedure to isolate the fundamental mode from higher order modes, phase unwrapping in two dimensions, and the estimation of the zero-offset phase. These phases are used to compute traveltimes between each source-receiver couple, which are input into the previously tested tomography algorithms. The resulting phase-velocity maps show good correspondence, highlighting the same geologic structures for all three methods. Finally, individual dispersion curves obtained by the superposition of phase-velocity maps at different frequencies are depth inverted to retrieve a 3D S-wave velocity model.
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FABRE, DAVID, and STÉPHANE LE DIZÈS. "Viscous and inviscid centre modes in the linear stability of vortices: the vicinity of the neutral curves." Journal of Fluid Mechanics 603 (April 30, 2008): 1–38. http://dx.doi.org/10.1017/s0022112008000578.
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In a previous paper, We have recently that if the Reynolds number is sufficiently large, all trailing vortices with non-zero rotation rate and non-constant axial velocity become linearly unstable with respect to a class of viscous centre modes. We provided an asymptotic description of these modes which applies away from the neutral curves in the (q, k)-plane, where q is the swirl number which compares the azimuthal and axial velocities, and k is the axial wavenumber. In this paper, we complete the asymptotic description of these modes for general vortex flows by considering the vicinity of the neutral curves. Five different regions of the neutral curves are successively considered. In each region, the stability equations are reduced to a generic form which is solved numerically. The study permits us to predict the location of all branches of the neutral curve (except for a portion of the upper neutral curve where it is shown that near-neutral modes are not centre modes). We also show that four other families of centre modes exist in the vicinity of the neutral curves. Two of them are viscous damped modes and were also previously described. The third family corresponds to stable modes of an inviscid nature which exist outside of the unstable region. The modes of the fourth family are also of an inviscid nature, but their structure is singular owing to the presence of a critical point. These modes are unstable, but much less amplified than unstable viscous centre modes. It is observed that in all the regions of the neutral curve, the five families of centre modes exchange their identity in a very intricate way. For the q vortex model, the asymptotic results are compared to numerical results, and a good agreement is demonstrated for all the regions of the neutral curve. Finally, the case of ‘pure vortices’ without axial flow is also considered in a similar way. In this case, centre modes exist only in the long-wave limit, and are always stable. A comparison with numerical results is performed for the Lamb–Oseen vortex.
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Zinchenko, I. A., L. S. Pilyugin, F. Sakhibov, et al. "Peculiar motions of the gas at the centre of the barred galaxy UGC 4056." Astronomy & Astrophysics 628 (August 2019): A55. http://dx.doi.org/10.1051/0004-6361/201935897.
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We derive the circular velocity curves of the gaseous and stellar discs of UGC 4056, a giant barred galaxy with an active galactic nucleus (AGN). We analyse UGC 4056 using the 2D spectroscopy obtained within the framework of the Mapping Nearby Galaxies at APO (MaNGA) survey. Using images and the colour index g − r from the Sloan Digital Sky Survey (SDSS), we determined the tilt of the galaxy, which allows us to conclude that the galaxy rotates clockwise with trailing spiral arms. We found that the gas motion at the central part of the UGC 4056 shows peculiar features. The rotation velocity of the gaseous disc shows a bump within around three kiloparsecs while the rotation velocity of the stellar disc falls smoothly to zero with decreasing galactocentric distance. We demonstrate that the peculiar radial velocities in the central part of the galaxy may be caused by the inflow of the gas towards the nucleus of the galaxy. The unusual motion of the gas takes place at the region with the AGN-like radiation and can be explained by the gas response to the bar potential.
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Al-Fadhli, AbdulAziz, and Emad Khorshid. "A smooth optimized input shaping method for two-dimensional crane systems using Bezier curves." Transactions of the Institute of Measurement and Control 43, no. 11 (2021): 2512–24. http://dx.doi.org/10.1177/0142331221995305.
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Conventional input shaping commands have been successfully employed to suppress residual vibration in the payload rest-to-rest transportation process. Most of these methods introduce an impractical large and sudden variation on the acceleration profile. This paper presents a new smooth command input with adjustable time length and limited jerks. The command input is generated from the trolley displacement using a Bezier curve function by adjusting the position of the control points, which were divided into boundary and intermedium points. The boundary control points are selected to accurately move the trolley to its desired position with zero velocity and acceleration at the closing motion. The positions of the intermedium points were optimized using a particle swarm scheme for reducing maneuvering time while suppressing the payload oscillations at the end of the process and satisfying physical system constraints. Several cases were discussed for fixed cable length, variable cable involving single and multi-hoisting mechanisms, and different maneuver times. Simulated results were validated experimentally on a laboratory size crane. The results demonstrated that the proposed input Bezier-curve shaper provides an effective, reliable, and practical technique to be used for the payload transportation process. Moreover, the proposed method can generate asymmetrical acceleration and deceleration motions, which cannot be achieved using existing smoother commands.
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Cunningham, R. G. "Liquid Jet Pumps for Two-Phase Flows." Journal of Fluids Engineering 117, no. 2 (1995): 309–16. http://dx.doi.org/10.1115/1.2817147.
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Isothermal compression of a bubbly secondary fluid in a mixing-throat and diffuser is described by a one-dimensional flow model of a liquid-jet pump. Friction-loss coefficients used in the four equations may be determined experimentally, or taken from the literature. The model reduces to the liquid-jet gas compressor case if the secondary liquid is zero. Conversely, a zero secondary-gas flow reduces the liquid-jet gas and liquid (LJGL) model to that of the familiar liquid-jet liquid pump. A “jet loss” occurs in liquid-jet pumps if the nozzle tip is withdrawn from the entrance plane of the throat, and jet loss is included in the efficiency equations. Comparisons are made with published test data for liquid-jet liquid pumps and for liquid-jet gas compressors. The LJGL model is used to explore jet pump responses to two-phase secondary flows, nozzle-to-throat area ratio, and primary-jet velocity. The results are shown in terms of performance curves versus flow ratios. Predicted peak efficiencies are approximately 50 percent. Under severe operating conditions, LJGL pump performance curves exhibit maximum-flow ratios or cut-offs. Cut-off occurs when two-phase secondary-flow streams attain sonic values at the entry of the mixing throat. A dimensionless number correlates flow-ratio cut-offs with pump geometry and operating conditions. Throat-entry choking of the secondary flow can be predicted, hence avoided, in designing jet pumps to handle two-phase fluids.
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Corchete, V. "Shear-wave Velocity Structure of Greenland from Rayleigh-wave Analysis." Earth Sciences Research Journal 20, no. 1 (2016): 1–11. http://dx.doi.org/10.15446/esrj.v20n1.41079.
Full textAbstract:
<p>The elastic structure beneath Greenland is shown by means of S-velocity maps for depths ranging from zero to 350 km, determined by the regionalization and inversion of Rayleigh-wave dispersion. The traces of 50 earthquakes, occurring from 1990 to 2011, have been used to obtain Rayleigh-wave dispersion data. These earthquakes were registered by 21 seismic station located in Greenland and the surrounding area. The dispersion curves were obtained for periods between 5 and 200 s, by digital filtering with a combination of MFT (Multiple Filter Technique) and TVF (Time Variable Filtering). Later, all seismic events (and some stations) were grouped to obtain a dispersion curve for each source-station path. These dispersion curves were regionalized and inverted according to the generalized inversion theory, to obtain shear-wave velocity models for a rectangular grid of 16x20 points. The shear-velocity structure obtained through this procedure is shown in the S-velocity maps plotted for several depths. These results agree well with the geology and other geophysical results previously obtained. The obtained S-velocity models suggest the existence of lateral and vertical heterogeneity. The zones with consolidated and old structures present greater S-velocity values than the other zones, although this difference can be very little or negligible in some case. Nevertheless, in the depth range of 15 to 45 km, the different Moho depths present in the study area generate the principal variation of S-velocity. A similar behaviour is found for the depth range from 80 to 230 km, in which the lithosphere-asthenosphere boundary (LAB) generates the principal variations of S-velocity. Finally, the new and interesting feature obtained in this study: the definition of the base of the asthenosphere (for the whole study area and for depths ranging from 130 to 280 km, respectively) should be highlighted.</p><p> </p><p><strong>Estructura de velocidad de cizalla de Groenlandia obtenida de análisis de onda Rayleigh</strong></p><p><strong><br /></strong></p><p><strong>Resumen</strong></p><p>La estructura elástica bajo Groenlandia es mostrada por medio de mapas de velocidad de onda para profundidades variando desde cero a 350 km, determinada por la regionalización e inversión de la dispersión de onda Rayleigh. Las trazas de 50 terremotos, ocurridos desde 1990 hasta 2011, han sido usados para obtener datos de dispersión de onda Rayleigh. Estos terremotos fueron registrados por 21 estaciones sísmicas localizadas en Groenlandia y el área circundante. Las curvas de dispersión fueron obtenidas para periodos entre 5 y 200 s, por filtrado digital con una combinación de MFT (Técnica de Filtrado Múltiple) y TVF (Filtrado en Tiempo Variable). Después, todos los eventos sísmicos (y algunas estaciones) fueron agrupados para obtener una curva de dispersión para cada trayecto fuente-estación. Estas curvas de dispersión fueron regionalizadas e invertidas de acuerdo con la teoría de la inversión generalizada, para obtener modelos de velocidad de cizalla para una rejilla rectangular de 16x20 puntos. La estructura de velocidad de cizalla obtenida a través de este procedimiento es mostrada in los mapas de velocidad de onda S representados para varias profundidades. Estos resultados muestran buen acuerdo con la geología y con otros resultados geofísicos obtenidos previamente. Los modelos de velocidad de onda S obtenidos sugieren la existencia de heterogeneidad lateral y vertical. Las zonas con estructuras antiguas y consolidadas presentan mayores valores de velocidad de onda S que las otras zonas, aunque esta diferencia puede ser muy pequeña o despreciable en algún caso. No obstante, en el rango de profundidad de 15 a 45 km, las diferentes profundidades del Moho presentes en el área de estudio generan la principal variación de velocidad de onda S. Un comportamiento similar es encontrado para el rango de profundidad desde 80 a 230 km, en el cual la frontera litosfera-astenosfera (LAB) genera las principales variaciones de velocidad de onda S. Finalmente, debería ser destacada la nueva e interesante característica obtenida en este estudio: la definición de la base de la astenosfera (para el área de estudio completa y para profundidades variando desde 130 a 280 km, respectivamente).</p>