Rotational Velocity Field Research Articles

Travelling air vortex rings as potential communication signals in a cricket

1. Crickets of the non-stridulating speciesPhaeophilacris spectrum (Phalangopsidae) generate travelling air vortex rings, which might serve as a hitherto unknown method of non-acoustic communication involving air particle movements. 2. The males produce a series of forward wing flicks during courtship and single wing flicks during aggressive encounters (Figs. 1, 2). In simulation experiments with moving wing pairs (Fig. 3) travelling vortex rings were visualized by using TiCl4 smoke or tracer particles in the air flow field (Fig. 4). 3. The vortex rings have an initial diameter of about 2 cm, increasing to 5 cm, and travel a maximum distance of 15 cm, depending on wing size and wing flick duration. Both wing size and flick duration determine the Reynolds number (Fig. 6). 4. Generally the velocity of propagation of vortex rings (from an initial velocity of about 40 cm/s) decays exponentially with distance (Fig. 5B). 5. The internal structure of the vortex rings, as visualized with tracer particles (Fig. 8), reveals a typical rotational velocity field. Particle velocities approach 15 cm/s (Fig. 9). 6. The physical basis of vortex ring generation by wing flicks and their possible communication role are discussed.

The Upper Bound Approach to Plane Strain Problems Using Linear and Rotational Velocity Fields—Part I: Basic Concepts

This paper investigates an upper bound approach to plane strain deformation of a rigid, perfectly plastic material. In this approach the deformation region is divided into a finite number of rigid triangular bodies that slide with respect to one another. Neighboring rigid body zones are analyzed in specific cases where the zones are (1) both in rotational motion, (2) one in linear, the other in rotational motion and (3) both in linear motion. Specific equations are presented that describe surfaces of velocity discontinuity (shear boundaries) between the moving bodies, and the velocity discontinuities and shear power losses for each of the three cases. The shape of the surface of velocity discontinuity is uniquely determined by the velocity ratios of neighboring bodies, their relative directions of motion and, where applicable, the positions of their centers of rotation. Where one or both neighboring bodies exhibit rotational motion, the surface of velocity discontinuity is found to be a cylindrical surface. In the case of two neighboring bodies, each with linear motion, the surface of velocity discontinuity is found to be planar. The velocity discontinuity is found to be constant along the entire surface of velocity discontinuity. The characteristics of the surfaces of velocity discontinuity in plane strain deformation are investigated. The upper-bound approach to plane strain problems can be successfully adapted to real metal forming processes, including sheet and strip drawing, extrusion, forging, rolling, leveling, ironing, and machining.

The Upper Bound Approach to Plane Strain Problems Using Linear and Rotational Velocity Fields—Part II: Applications

Following Part I which investigated an upper bound approach to plane strain deformation of a rigid, perfectly plastic material, this Part II considers the same approach as applied to actual forming operations. The processes of drawing and extrusion, of metal cutting and of rolling are analyzed, and explicit equations are developed to calculate the surfaces of velocity discontinuity (shear boundaries), velocity discontinuities, and the upper bound on power for these processes. Both the simple, unielement velocity fields as well as the more complex multielement fields are explored. The upper bound solution is shown to be a function of the independent (input) and pseudoindependent (assumed) process parameters as minimized by an optimization procedure. Rules concerning the assumption of pseudoindependent parameters are presented and the optimization procedure is discussed. Final conclusions lead the way for the application of upper bound analyses to such industrial processes as sheet and strip drawing, extrusion, forging, rolling, leveling, ironing and machining, and to the investigation of such flow failure modes as central bursting, piping and end splitting (alligatoring).

An Experimental Study of Baroclinic Flows with and without Two-Wave Bottom Topography

Abstract A series of laboratory experiments was performed in a thermally-driven rotating annulus of fluid with and without two-wave bottom topography. Velocity measurements were made by illuminating a thin layer of fluid at mid-depth and photographing successive positions of tracer particles suspended in the fluid. Streamfunctions were determined from the calculated vorticity. Comparison of the rotational velocity field with the measured velocity field revealed negligible differences, indicating that the flow was horizontally quasi-nondivergent. A detailed analysis was made of one experiment with and one without topography at the same point in dimensionless parameter space. The results indicate that the effect of topography is 1) to modulate the synoptic-scale waves in both space and time, 2) to suppress the odd modes and 3) to force a “planetary” scale mode which oscillates about a climatological mean position (with high pressure centers located in this experiment approximately 22° upstream of the mounta...

Spectroscopy of CP Stars in the Groups of Different Age

AbstractThe observational results for 108 stars, members of 10 galactic groups at the age range of lg t = 6,4 - 8,7 (years), are briefly described. It is shown that the peculiarity index, rotational velocity and magnetic field strength of all the types of CP stars do not vary during their evolution across the main sequence stripe.

Rotational Field and Velocity Dispersion in Globular Clusters: ω CEN and 47 TUC

Thanks to numerous and accurate radial velocity measurements obtained with CORAVEL, the rotational velocity fields, the spatial velocity dispersions from the centre to the edge and the ordered to random motions ratios are deduced for two globular clusters: ω Cen and 47 Tuc. Masses through virial theorem and M/L ratios are also given. A more comprehensive study will be published in Astron. & Astrophys.

Rotational motion at finite temperature

Moments of inertia and rotational velocity fields are calculated in the cranking model for the harmonic oscillator and the Nilsson potential for even-even rare earth nuclei. By means of a temperature-averaging procedure these quantities are decomposed into a smooth and a shell-structure-dominated part. The results are in good agreement with the corresponding Strutinsky-averaged results. The velocity fields are analyzed in terms of vector spherical harmonics and compared to rigid flow. The smooth velocity fields reveal rigid flow in the nuclear interior; in the surface region a deviation from rigid flow occurs, giving rise to a backflow in the inner system. The temperature dependence of the smooth moments of inertia is approximated by a quadratic function.

A Powerful Method for Deriving Mass-Loss Rates from Planetary Nebulae and Other Objects: The First Order Moment W1 of Unsaturated P Cygni Line Profiles

For the case of optically thin lines, we show that the relation existing between the first order moment of a P Cygni line profile and the quantity n (level) (cf. Castor, Lutz and Seaton, 1981), where is the mass-loss rate of the central star and n (level) the fractional abundance of the relevant ion, is in fact independent of any Sobolev-type approximations used for the transfer of line radiation. Consequently, all results established in the context of “very rapidly” expanding atmospheres (see Surdej, 1982) and mainly referring to the non-dependence of W1 on various physical (underlying photospheric absorption line, limb darkening, collisions, multiplet line transitions, etc.) and geometrical (radial and rotational velocity fields, size of the atmosphere, etc) effects remain unchanged for arbitrary (e.g. non-Sobolev type) outward-accelerating velocity laws.

High resolution line profiles in the Seyfert galaxy NGC 3783: The structure of the emitting regions

We present the analysis of emission line profiles in the Seyfert nucleus of NGC 3783. The lines, covering a wide range of ionization from O0 up to Fe9+, are analysed from IPCS or electronographic data obtained with resolutions from 0.03 to 0.12 nm. When the signal-to-noise ratio allowed it, a precise analysis generally showed a broad, blueshifted component in the line under consideration. The main results of this study are the following: (1) There appears to be a relationship between the FWHI of the main component within a line and the ionization potential of the corresponding ion. (2) For all the forbidden lines, there is a relationship between the FWHI of any component and its emission shift, with broad components and high ionization species being more blueshifted: for example, the main broad component in the [Fe X] line is blueshifted by 400 km s−1 with respect to the [O I], [O II] and [N II] emission velocity. (3) The Balmer lines show components corresponding to these forbidden line regions but their main contribution is from a very broad (3000 km s−1) redshifted (+ 200 km s−1) component. The results are most plausibly interpreted in the framework of a central massive object surrounded by an accretion disc (AD), for which we derive an inclination of 15° and a mean radius of 103RS. Arguments are then presented that only the high-density region (⁠|$N_\text e\gt 10^{10} \text {cm}^{-3}$|⁠) is concerned with the AD itself, while the forbidden-line region is dominated by a radial rather than a rotational velocity field whose magnitude increases towards the centre where the photo-ionizing source lies. Consideration of the ionization equilibrium together with the observed radial velocities, assumed to be from infalling matter, favour the picture of filaments clustering towards the centre and decelerated by frictional mechanisms which also increase the turbulence of the medium.

Rotational Studies of Lower Main Sequence Stars

This review summarizes the techniques and limitations involved in determining small rotational velocities in late-type stars. Recent results from photoelectric line profiles of field main sequence G stars will also be presented.Historically three techniques have been used to measure stellar rotational velocities: (1.) calibration of a “clean” line width in terms of computed profile models, (2.) use of the Fourier transform frequency domain (dissection of rotation and turbulent velocity fields from the thermal profile), and (3.) monitoring of the rotational modulation of a chromospherically active or spotted star. The results discussed below concern technique (2.). Technique (3.) has not been exploited much yet but holds considerable promise for the future, in particular for the measurement of ultra-slow rotation.

Independent particle Schrödinger fluid: Moments of inertia

The philosophy of the single particle Schrödinger fluid, especially as regards the velocity fields which find such a natural role therein, is applied to the study of the moments of inertia of independent fermion system. It is shown that three simplified systems exhibit the rigid-body rotational velocity field in the limit of large A, and that the leading deviations, both on the average and fluctuating, from this large- A limit can be described analytically, and verified numerically. For a single particle in a Hill-Wheeler box the moments are studied numerically, and their large fluctuations identified with the specific energy level degeneracies of its parallelepiped shape. The full assemblage of these new and old results is addressed to the question of the necessary and sufficient condition that the moment has the rigid value. Counter examples are utilized to reject some conditions, and the conjecture is argued that unconstrained shape equilibrium might be the necessary and sufficient condition. The spheroidal square-well problem is identified as a promising test case.

The motion of a small sphere in a rotating velocity field: A possible mechanism for suspending particles in turbulence

The diffusion and transport of particles suspended in turbulent flows depend on the interaction between the particles and the turbulence. To investigate a possible particle-turbulence interaction, we observed particle trajectories in a rotating fluid with a solid body velocity profile, as might occur in the core of a vortex or an eddy. The experiments were conducted with a series of single small spheres (with low particle Reynolds numbers) sinking or rising in a horizontal cylinder rotating about its central axis at a constant speed. Each sphere was found to follow a nearly circular orbit in a vertical plane perpendicular to the cylinder axis. The orbit center lay very near the horizontal plane through the axis of the cylinder and was at the point in the fluid where the velocity of the fluid was equal and opposite to the terminal velocity of the particle. The particle trajectories also evolved slowly, spiraling either inward or outward. A theoretical description of the particle motion shows that the two principal forces on the particle, fluid drag and gravity-buoyancy, account for the circular motion. A force due to particle inertia (a centrifugal force from the center of its orbit), a small position-dependent wall effect on drag, a very small force (also affected by the walls), and a very small centrifugal buoyancy force account for the long-term inward or outward spirals. This kind of systematic interaction in which particles seek and remain in fluid closely opposing their own motion could have a role in the suspension of small particles in some turbulent flows.

Nuclear rotational current and velocity fields, the cranking model, and transverse electroexcitation of the first excited state ofC12

We examine current and velocity fields of rotating deformed nuclei. Although the harmonic oscillator cranking model gives rigid moments of inertia, the velocity field is not a rigid rotation in the examples studied. Such fields are partially observable via electroexcitation, and we compare $^{12}\mathrm{C}$ to experiment. A slight improvement in experimental precision would allow different models to be distinguished.NUCLEAR REACTIONS Inelastic electron scattering, deformed nuclei; transverse electroexcitation probability, rotational model; $^{12}\mathrm{C}(e,{e}^{\ensuremath{'}})^{12}\mathrm{C}^{*}$ (4.4 MeV).

Spectroscopic evidence for a higher rotation rate of magnetized plasma at the solar photosphere

Simultaneous observations of the photospheric rotation velocity and magnetic field are made with 5'' spatial resolution. The results show a significant increase in plasma rotation velocity with absolute magnetic intensity. The difference in rotation velocity between the highest and lowest magnetic fields, in areas of quiet photosphere, is 41 +- 6 m s/sup -1/ in 1975 and 46 +- 11 m s/sup -1/ in 1974, measured in the lambda5250 line of Fe i. A less significant increase is found in the lambda5233 line. These results indicate that the magnetic network rotates at least 2 percent faster than the general photosphere, and the flux tubes accelerate the local plasma of the network boundaries. (AIP)

Differential Rotation and Global-Scale Velocity Fields

A review is given of the observational and theoretical background of global-scale velocity fields on the solar surface. A newly-developed method of reduction of the Mount Wilson velocity data is described, and the results from this new method are compared with the results of the old method. A preliminary analysis is made of the new results over a short time interval. Small-scale latitude irregularities in the differential rotation are shown to exist. Variations in time which occur in the rotation rate are broadly distributed in latitude and longitude. Although a non-solar (instrumental) cause cannot be found for these variations, such a cause cannot be ruled out at this time. Global-scale non-axisymmetric velocity field patterns intermediate between solar diameter and super-granular scale are shown to exist on the solar surface as predicted by theory.

Beyond the hartree-liquid model of superfluid bosons

A model of interacting superfluid bosons is proposed which is intended to extend the usual Hartree-liquid model in the case of the stationary state. The result id a coupled set of three differential equations relating the order parameter, a purely rotational velocity field, and a depletion scalar field. The latter two fields play a role similar to that of the vector and scalar potentials coupled to a complex matter field and the formulation thus closely resembles the Landau-Ginzberg equation of superconductivity coupled to the electromagnetic field.

Flow in heterogeneous porous mediums: 1. Darcian‐type description of two‐phase systems

Theoretical work leading to the description of fluid flow in a heterogeneous porous medium has developed slowly and somewhat sporadically, even though the areas of engineering applications predominantly involve flow in a nonhomogeneous medium. In providing a theoretically consistent basis for analysis, the special characteristics of macroscopically heterogeneous materials are discussed to provide accurate definitions. The definitions establish the functional dependence and make mathematical representation possible. The special implications of heterogeneity in Darcian‐type dynamic relationships for each of the fluid phases are considered, and the rotational velocity field resulting from nonhomogeneity is shown as a contrast to the classical irrotational case for flow in a homogeneous medium. The velocity field is also shown to be the classical complex lamellar type; hence considerable insight into the flow fields in heterogeneous mediums is immediately available. The end result of the discussion and derivation is a set of rather general Eulerian equations describing two‐phase flow in a macroscopically heterogeneous medium. These equations and their reduced forms include descriptions of some forty different flow systems. Such a variety of flow conditions is categorized through the use of a special tabular scheme, which makes it possible to write the appropriate equations efficiently. (Key words: Flow; heterogeneous porous mediums; equations)

A Note on the Spin of Sub-condensations Forming in a Differentially Rotating Medium

In many studies on the origin of the solar system, the planets are supposed to form as sub-condensations in a differentially-rotating, disk-like medium. Each proto-planet will have an angular momentum of orbital motion about the centre of the disk, and also an angular momentum of spin about its own mass–centre. In this note we emphasize that the spin angular momentum depends, in magnitude and sign, on both the law of rotation in the disk and the geometry of the condensation. It is incorrect, for example, to assert that if the rotational velocity in the disk decreases outwards (as in a Keplerian disk), then the spin of the sub-condensation is necessarily retrograde. Equally, one cannot argue that because the rotational velocity field in any realistic disk has a vorticity with the same sign as the angular velocity, then retrograde spin by a sub-condensation is ruled out.

Motions in the Sun at the Photospheric Level IV. The Equatorial Rotation and Possible Velocity Fields in the Photosphere

Motions in the Sun at the Photospheric Level IV. The Equatorial Rotation and Possible Velocity Fields in the Photosphere