Toroidal Region Research Articles

Discovery of a nuclear counterjet in NGC 1275: A new way to probe the parsec-scale environment

view Abstract Citations (110) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discovery of a Nuclear Counterjet in NGC 1275: A New Way to Probe the Parsec-Scale Environment Vermeulen, R. C. ; Readhead, A. C. S. ; Backer, D. C. Abstract We present a high dynamic range 22 GHz VLBI image of the core of NGC 1275 (3C 84) and discuss the evolution of some of the features seen in previous 22 GHz images. In addition, our image reveals for the first time a feature which is part of the (northern) counterjet. It is extended, and comparison with an 8 GHz image of Walker, Romney, & Benson (1994), which also shows the northern component, indicates that it has a strongly inverted spectrum, unlike the southern features. A simple explanation is that gas in a roughly toroidal or disklike region obscures the counterjet through free-free absorption. Simultaneous multifrequency VLBI observations may provide a new method of probing the parsec-scale environment in nearby galactic nuclei. Publication: The Astrophysical Journal Pub Date: July 1994 DOI: 10.1086/187433 Bibcode: 1994ApJ...430L..41V Keywords: Active Galactic Nuclei; Counterflow; Radio Jets (Astronomy); Very Long Base Interferometry; Electromagnetic Absorption; Galactic Evolution; Radio Galaxies; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 1275; GALAXIES: ISM; GALAXIES: JETS; GALAXIES: KINEMATICS AND DYNAMICS; GALAXIES: NUCLEI; RADIO CONTINUUM: GALAXIES full text sources ADS | data products SIMBAD (1) NED (1)

Pore Sizes and Filtration Rates from Two Alumina Slips

The relationship between filtration rate and the resultant green body microstructure was examined for aqueous alumina slips cast at two different deflocculation states. The volume loading of both slips was 40%. Slip viscosities of 500 and 60 mPa·s were produced by different tetrasodium pyrophosphate additions. The filtration rate of these slips varied by a factor of 2; however, mercury porosimetry results showed the same average pore size for both samples. Single and multiple small‐angle neutron scattering results showed the specimen cast with the higher‐viscosity slip to possess a bimodal pore size distribution. The body cast with the low‐viscosity slip showed unimodal porosity and, consequently, the filtration is attributed to the toroidal region between the packed particles. These results showed that mercury porosimetry does not provide a pore size that predicts filtration behavior of slips with different degrees of dispersion.

Pressure flux-split viscous solutions for swirl diffusers

A method for predicting flow in diffusers with inlet swirl has been developed. Solutions of the pressure flux-split reduced Navier-Stokes equations are obtained for flows in axisymmetric diffusers. Viscous-inviscid interactions and flow field with toroidal recirculation regions are efficiently captured. The computational model is verified by comparison with experimental data and other computations. The extreme sensitivity to grid, turbulent closure model and inlet profiles is discussed.

Particle Diagnostics and Turbulence Measurements in a Confined Isothermal Liquid Spray

This work reports an experimental study of the behavior and structure of a liquid spray immersed in a strong swirling field. In order to simulate some of the aerodynamic conditions experienced by a spray in a model combustor, an experimental setup using an acrylic chamber, a vane type swirler, and separate air supplies for both the secondary air and the swirl air were integrated to perform the experiments in the wind tunnel. A vane-type swirler exhibiting a high swirl number was used to produce a strong recirculation flow field downstream of a pressure swirl atomizer. Properties of the dispersed phase such as velocity, size distribution, and size-velocity correlation were measured at several locations within the swirling flow field. In addition, mean velocity and turbulence properties were obtained for the gas phase. Flow visualization was performed with a laser sheet to gain further understanding of the formation and influence of the recirculation region on the spray. A two-component PDPA system with a frequency-based Doppler signal analyzer was used throughout the measurements, and proved most valuable in the toroidal vortex region where low SNR conditions and nonuniform concentration of seed particles prevail. The results show that flow reversal of the drops is present at this swirl intensity within the recirculation region at distances up to X/D = 2.0. Small variations of drop size distribution within the recirculation region are observed; however, large variations outside of it are also present. Plots of the normal Reynolds stresses and Reynolds shear stresses show double-peak radial distributions, which indicate regions in the flow where high mean velocity gradients and large shear forces are present. The decay of turbulence velocities in the axial direction was observed to be very fast, an indication of high diffusion and dissipation rates of the kinetic energy of turbulence.

The distinction between multifragmentation and sequential binary decay

Following the idea of López and Randrup, the influence of the Coulomb interaction on trajectories of fragments emitted from a hot nuclear system is investigated. The fragments are allowed to decay in flight with decay constants depending upon their mass and excitation energy. It is found that the Coulomb field of the two heaviest fragments focuses velocities of the other fragments into some toroidal region, when the hot system breaks up simultaneously, while in the case of the sequential binary decay these velocities exhibit a nearly isotropic distribution. The sensitivity of this effect and its limitations are discussed.

Current collection by probes and electrodes in space magnetoplasmas: A review

We present a survey of a very incomplete subject. The best‐developed and simplest theories for current collection in magnetic fields are steady‐state collisionless theories, and these must be understood before departures from them can be analyzed usefully, so we begin with a review of them. Recent numerical results indicate that steady‐state collisionless Laplace‐limit currents remain substantially below the Parker‐Murphy (1967) canonical upper bound out to very large electrode potentials and approach it as a limit only very slowly if at all. Attempts to correct this theory for space‐charge effects lead to potential disturbances which extend to infinite distance along the electrode's magnetic shadow, unless collisional effects are also taken into account. However, even a small amount of relative plasma drift motion, such as that involved in a typical rocket experiment, can change this conclusion fundamentally. It is widely believed that time‐averaged current collection may be increased by effects of plasma turbulence, and we review the available evidence for and against this contention. Steady‐state collisionless particle dynamics predicts the existence of a toroidal region of trapped orbits which surrounds the electrode. Light emissions from this region have been photographed, indicating that collisional ionization may also occur there, and this, and/or scattering by collisions or possibly turbulent fluctuations in this region, may also increase current collection by the electrode. We also discuss effects on particle motions near the electrode, associated with “breakdown of magnetic insulation” in the region of large electric fields near it.

Flow between eccentric rotating cylinders: Bifurcation and stability

The effect of cylinder eccentricity on Couette-Taylor transition is investigated here for flow between infinite rotating cylinders. The method of analysis is Fourier expansion of the conservation equations in the axial direction, followed by projection onto a polynomial subspace. Critical points of the solution, which are characterized by singularity of the Jacobian matrix, are located via parametric continuation. This computational scheme permits an extension of the DiPrima and Stuart results to higher values of the eccentricity ratio; it also makes it possible to move far from the critical point into the supercritical Reynolds number regime. The first bifurcation from Couette flow is found to be supercritical, while supercritical flow is shown to consist of regions of plane motion with recirculation, separating toroidal vortex regions. The domain of recirculating flow is asymmetric with respect to the line of centers, and on increasing the supercritical Reynolds number its axial dimension decreases while its radial dimension, in the plane separating the vortex cells, increases. The results established here for critical Reynolds number agree well with those of DiPrima and Stuart at eccentricities where their small perturbation solution is applicable, and there is good agreement with the experimental data of Vohr. The torque calculations compare favorably with the experimental data of Donnelly and Simon for the concentric case and with the data of Castle and Mobbs for non-zero eccentricity.

BNL volume H− source

The volume H− ion source under development at Brookhaven is unique in that it has a toroidal plasma region, which feeds ions into the central extraction region through a conically shaped filter field. In pulsed operation, it produces 25 mA of H− in a 1 cm2 aperture, with an electron-to-H− ratio of ≊3. At 19 mA, a normalized, 90% emittance of 0.44 π mm mrad has been measured. Up to 50 mA has been extracted through a 1.87 cm2 aperture. Although not designed for steady state operation, up to 6 mA has been extracted dc. The addition of xenon to the discharge was found to improve the source output by 20%–70%. The circular magnetic cusp field geometry was found to be more favorable than radial cusp fields.

A Gaseous Divertor for High Field Reactors

A novel gaseous divertor concept is proposed consisting of gas chamber and pumping at high pressure or by reionizing the neutrals. The concept results in substantial reductions of the plasma temperature and heat flux at the target and the pumping requirement. Fluid model simulations of the scrape-off region of the Aries Reactor design by feeding the gas at the target at a flux of 1 × 1023m−2/s at 0.5 eV has shown that the electron and ion temperatures can be cooled to 20 eV. The heat flux to the target can be reduced from 80 MW/m2 to 6 MW/m2. The plasma temperature and heat flux at the divertor target are monotonically decreasing functions of the neutral incident flux. Interestingly the temperature and the heat flux also decrease with decreasing neutral gas initial flowing speed removing the need of gas jets. The backflow problem can be minimized by including a baffle plate to form a gaseous chamber. Monte-Carlo simulations using test particles have showed that the throat of the gaseous chamber can be practically plugged by the incident plasma to prevent backflow of neutrals into plasma core. The pumping can be facilitated by either operating the divertor chamber at high pressure on the order of 30 torr or reionizing the neutrals traveling to a weak toroidal field region.

Plasma distribution models in a rotating magnetic dipole and refilling of plasmaspheric flux tubes

Rotating stars or planets like Earth are sometimes surrounded by a dipolar magnetic field distribution. The thermal plasma forming a corona or an ionosphere around these astrophysical objects diffuses upward along the magnetic field lines and forms a toroidal region filled with this thermal plasma, like the terrestrial plasmasphere. The field-aligned distribution of this thermal ionospheric plasma is controlled by the gravitational and pseudocentrifugal potential distribution. One can distinguish two extreme types of plasma distribution in this field-aligned potential: the diffusive equilibrium distribution and the exospheric equilibrium distribution corresponding, respectively, (i) to a saturated, and (ii) to an almost depleted, magnetic flux tube. As a result of pitch angle scattering by Coulomb collisions, an increasing number of ions escaping from the ionosphere are stored in trapped orbits. These trapped particles have magnetic mirror points at high altitudes, i.e., in the low-density exospheric region. Also as a result of collisions, the field-aligned density distributions irreversibly evolve from exospheric equilibrium with a highly anisotropic pitch angle (cigarlike) distribution to a diffusive equilibrium distribution characterized by an isotropic pitch angle distribution. It is shown that the suprathermal ions become anisotropic much more slowly than ions of energies smaller than 1 eV.

Characteristics of dump combustor flows

Turbulent flows through dump combustors with different inlet geometries and flow conditions were investigated. The combustors was simulated by an axisymmetric tube with a sudden expansion geometry. Specifically two different inlet geometries were studied; one resembled an actual inlet, another a well-designed convergent nozzle. Furthermore two different step heights were examined. Finally, the effects of rotation on the flow behavior were also studied. The results show that of all the geometric and flow parameters investigated, inlet turbulene and rotation have the greatest effect on the flow inside the combustor, in particular, the characteristics of the toroidal recirculating flow. Both parameters act to decrease the toroidal recirculation region and hence the reattachement length. The limited data available tend to show that the effects due to these two parameters are additive. On the other hand, inlet geometry only has as indirect effect on the combustor flow. It influences the flow characteristics because it creates different inlet turbulence at the sudden expansion.

Vortex Rings with Swirl: Axisymmetric Solutions of the Euler Equations with Nonzero Helicity

This work introduces a new class of steady solutions of the axisymmetric Euler equations for an incompressible inviscid fluid. Each solution represents a three-dimensional vortex flow whose azimuthal components of vorticity and velocity are nonzero inside a toroidal region determined by the solution. The governing free-boundary problem is solved by variational techniques. The underlying variational principle is formulated from the natural invariants associated with the evolution equations for axisymmetric flows, and involves a family of invariants that generalizes the standard angular impulse and helicity integrals. A direct method is employed to prove the existence of steady solutions in a bounded domain and steadily translating solutions in space. Qualitative properties of these vortices are discussed and concentrated vortex rings with large swirl are shown to constitute a desingularization of the classical circular vortex filament.

Atomization of Organic Compounds in the Inductively Coupled Plasma

The problem of incomplete atomization when nonmetals are being determined in aspirated organic solutions was studied. Abel inverted spatial profiles of C2, CN, C(I) and S(I) emission were acquired at several heights. It was found that molecular emission caused by the analyte is restricted to the lower aerosol channel. Nonmetal atomic emission is found in the toroidal region and higher up in the aerosol channel. Compounds that contained nonmetals comprised of either oxygen, nitrogen, or sulfur, which were dissolved in xylene, exhibited nonmetal emission intensities independent of the structure of the compound.

Mercury porosimetry of fine particles: Particle interaction and compression effects

By using a simplified ‘random packing of uniform spheres’ model to simulate the process of fine powder compaction during mercury porosimetry, we have been able to ascertain the relative magnitudes of the pore volume distribution curve corresponding to interparticle void filling, sample compression and pore filling. The filling of the toroidal region in the vicinity of particle contacts and particle near-neighbors is calculated from the exact solution of the Young—Laplace equation. Sample compression is assumed to be described by a linear model and the Washburn equation is assumed to describe pore filling. Inter-particle void filling is not complete until dimensionless pressures, PR/γ, of ⋍50 are attained. The largest pore size which can be accurately measured is approximately 4% of the particle size. However, if sample compression is significant, accurate density and pore size analysis may not be possible.

An integral equation technique for the exterior and interior neumann problem in toroidal regions

An integral equation technique for the Neumann problem of finding a function Φ satisfying ΔΦ = 0 with prescribed values of ∂Φ∂n on the boundary is described. Fourier representation of the potential Φ on the boundary with respect to two angle-like variables transforms the integral equation to an infinite set of linear equations for the Fourier coefficients of Φ. The singularity of the Green's function is treated by a regularization method: a function with the same singularity is subtracted and its analytically calculated Fourier-transform is added to the Fourier transformed integral equation. A computer code named NESTOR is developed. Applications include studies of toroidal magnetic vacuum fields and calculation of the vacuum field contribution for the 3D free-boundary equilibrium problem.

Mercury porosimetry: Theoretical and experimental characterization of random microsphere packings

A new analysis for the application of mercury porosimetry to porous solids comprised of random packings of uniform spheres (ϵ ∼- 0.36–0.39) is presented. The filling of pore volume in the region where two spheres are near neighbors (distance of separation ⪡ sphere size) is modeled by solving the Young-Laplace equation to determine the degree of curvature of the meniscus as a function of sphere spacing, contact angle, and filling angle. The correct meniscus shape for mercury intrusion into the toroidal void is a nonoid. From the known distribution of sphere spacings in a random packing and the calculated pressure-volume relationship, the unfilled void fraction as a function of dimensionless pressure ( PR/γ) and contact angle is determined. Mercury porosimetry experiments have been conducted using porous solids fabricated from monodisperse, nonporous silica spheres (radius = 51, 125, 165,226 nm). Agreement between the toroidal void filling theory and all four experiments was excellent when the measured mercury contact angle of 138.7° was used in the theory. It is demonstrated that very large values of PR/γ (∼-100) are necessary to completely fill the toroidal void region and therefore, determine the total sample porosity.

On the existence of an exterior toroidal region in the nonaligned pulsar magnetosphere

On the existence of an exterior toroidal region in the nonaligned pulsar magnetosphere

Persistent Currents in SuperfluidHe3-B

Observations of persistent currents in superfluid $^{3}\mathrm{He}$-$B$ have been made with use of a recently developed ac gyroscope technique. The persistent currents are generated in a toroidal region filled with a fibrous material with average pore size of ${10}^{\ensuremath{-}2}$ cm. In this geometry, a mean critical velocity of 7 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}2}$ cm/sec was observed. To within experimental error, no decay of the currents was observed for periods of over one hour.

On the essential spectrum of MHD plasma in toroidal region

On the essential spectrum of MHD plasma in toroidal region

Formation of magnetic islands and ergodic magnetic layers in wall-lapping plasma as a non-divertor concept for a reactor-relevant tokamak

The formation of resonant islands and the ergodization of magnetic field lines in the tokamak boundary due to the subsidiary helical coils are numerically analyzed for the wall-lapping plasma concept as a non-divertor scenario for a reactor-relevant tokamak. The parameters are taken referring to the R-tokamak, a reacting plasma project in IPP-Nagoya. We have verified that this concept could be realized using the rotating islands produced by three sets of helical coils carrying alternating currents with shifted phases. It is also shown that this is possible by using local helical coils which span limited toroidal regions of the torus.