Open Spirals Research Articles

Effects of axial electric and transverse magnetic fields on a rotating electro-osmotic flow in micro-parallel plates

This paper explores the combined influence of an axial electric field and a perpendicular magnetic field imposed on rotating micro-parallel plates immersed in an electrolyte solution. A specialized computer program was developed to solve the velocity as well as the EDL potential fields using the finite difference method, employing the Debye-Hückel (DH) approximation to linearization the EDL potential. The study examines the influence of various non-dimensional parameters, including rotational speed (ω), Hartmann number (Ha), Debye-Hückel parameter (κ), and the non-dimensional parameter ‘S’, on axial, and transverse velocities, wall shear stress, and net flow rate. Results demonstrate that, both velocity components decrease with increased rotational speed and Hartmann number, while the net flow rate increases with the Debye-Hückel parameter for both rotating and non-rotating systems. The impact of these parameters on shear stress was also analyzed. Analysis of Ekmann spirals in the velocity plane revealed closed spirals at a higher rotational speed and open spirals at lower speeds, with spiral size reducing as rotational speed increases.

Bottom’s Dream and the Amplification of Filamentary Gas Structures and Stellar Spiral Arms

Abstract Theories of spiral structure traditionally separate into tight-winding Lin–Shu spiral density waves and the swing-amplified material patterns of Goldreich & Lynden-Bell and Julian & Toomre. In this paper we consolidate these two types of spirals into a unified description, treating density waves beyond the tight-winding limit, in the regime of shearing and nonsteady open spirals. This shearing wave scenario novelly captures swing amplification that enables structure formation above conventional Q thresholds. However, it also highlights the fundamental role of spiral forcing on the amplification process in general, whether the wave is shearing or not. Thus it captures resonant and nonresonant mode growth through the donkey effect described by Lynden-Bell & Kalnajs and, critically, the cessation of growth when donkey behavior is no longer permitted. Our calculations predict growth exclusive to trailing spirals above the Jeans length, the prominence of spirals across a range of orientations that increases with decreasing arm multiplicity, and a critical orientation where growth is fastest that is the same for both modes and material patterns. Predicted structures are consistent with highly regular, high-multiplicity gaseous spur features and long filaments spaced close to the Jeans scale in spirals and bars. Applied to stellar disks, conditions favor low multiplicity (m < 5) open trailing spirals with pitch angles in the observed range 10° < i p < 50°. The results of this work serve as a basis for describing spirals as a unified class of transient waves, abundantly stimulated but narrowly selected for growth depending on local conditions.

Dynamics of Thick, Open Spirals in PERLAS Potentials∗

Abstract The PERLAS potential has been successfully used in many studies related to the dynamics of the spiral arms on the equatorial plane of normal (nonbarred) spiral galaxies. In the present work, we extend these studies by investigating the three-dimensional (3D) dynamics of the spiral arms in the same type of potential. We consider a typical open, logarithmic, spiral pattern of pitch angle 25° and we examine the stellar orbits that can support it as the ratio of the masses of the spiral over the disk component (M s /M d ) varies. We indicate the families of 3D periodic orbits that act as the backbone of the spiral structure and we discuss their stability in the models we present. We study further the quasiperiodic and nonperiodic orbits in general that follow spiral-supporting orbits as the M s /M d ratio increases. We find that a bisymmetric spiral with 25° pitch angle is better supported by orbits in models with . In these cases, a strong spiral pattern is supported between the radial 2:1 and 4:1 resonances, whereas local enhancements of the imposed spirals are encountered in some models between 4:1 and corotation. A characteristic barlike structure is observed in all models at radii smaller than the radius of the 2:1 resonance.

Sediment disturbance by Ediacaran bulldozers and the roots of the Cambrian explosion

Trace fossils of sediment bulldozers are documented from terminal Ediacaran strata of the Nama Group in Namibia, where they occur in the Spitskop Member of the Urusis Formation (Schwarzrand Subgroup). They consist of unilobate to bilobate horizontal to subhorizontal trace fossils describing scribbles, circles and, more rarely, open spirals and meanders, and displaying an internal structure indicative of active fill. Their presence suggests that exploitation of the shallow infaunal ecospace by relatively large bilaterians was already well underway at the dawn of the Phanerozoic. Efficient burrowing suggests coelom development most likely linked to metazoan body-size increase. These trace fossils are the earliest clear representatives so far recorded of sediment bulldozing, an activity that may have had a negative impact on suspension-feeding and/or osmotroph communities, as well as on matgrounds, representing early examples of ecosystem engineering and trophic-group amensalism. The occurrence of sediment bulldozers may have promoted the establishment of gradients in horizontal and vertical distribution of organic material in connection with spatially heterogeneous environments on the sea floor at a critical time in Earth evolution.

Rings and spirals in barred galaxies – II. Ring and spiral morphology

In this series of papers, we propose a theory to explain the formation and properties of rings and spirals in barred galaxies. The building blocks of these structures are orbits guided by the manifolds emanating from the unstable Lagrangian points located near the ends of the bar. In this paper we focus on a comparison of the morphology of observed and of theoretical spirals and rings and we also give some predictions for further comparisons. Our theory can account for spirals as well as both inner and outer rings. The model outer rings have the observed $R_1$, $R_1'$, $R_2$, $R_2'$ and $R_1R_2$ morphologies, including the dimples near the direction of the bar major axis. We explain why the vast majority of spirals in barred galaxies are two armed and trailing, and discuss what it would take for higher multiplicity arms to form. We show that the shapes of observed and theoretical spirals agree and we predict that stronger non-axisymmetric forcings at and somewhat beyond corotation will drive more open spirals. We compare the ratio of ring diameters in theory and in observations and predict that more elliptical rings will correspond to stronger forcings. We find that the model potential may influence strongly the numerical values of these ratios.

Effects of alkali pre-treatment on dye exhaustion, color values, color fastness, tensile and surface properties of lyocell yarns

The effects of alkali (aqueous NaOH and KOH solutions) pre-treatment on dye exhaustion, color values, color fastness, tensile and surface properties of lyocell yarns were investigated. Dye exhaustion and color yield of lyocell yarns increased by increasing alkali concentrations. The lyocell yarns showed weight loss due to the decrease in carboxyl groups during alkali pre-treatment. The tensile strengths of lyocell yarns decreased with the increase of alkali concentrations because of the decrement of yarn diameter by weight loss the open twist spirals, and the increased volume of lyocell yarns after alkali pre-treatment. The washing and perspiration fastness results of untreated lyocell yarns were better than alkali pre-treated lyocell yarns, while the light fastness results of untreated and alkali pre-treated samples were similar.

Order and chaos in spiral galaxies

Spiral galaxies contain both ordered and chaotic orbits. In normal spirals the perturbations are weak (of order 2–10%) and most orbits are ordered. The density wave theory refers mainly to linear perturbations. Nonlinear effects appear in the outer parts of the open spirals (S_b, S_c) and produce the termination of these spirals near the 4/1 resonance. On the other hand in barred spirals the perturbations are relatively strong (of order 100%). Then the outer spirals and the envelope of the bar are composed mainly of chaotic orbits, while the main body of the bar is composed of ordered orbits. The chaotic orbits of the spiral arms of strong barred galaxies are sticky, i.e. they do not escape from the galaxy for at least a Hubble time. The forms of these spirals are delineated by the unstable manifolds of the unstable periodic orbits L_1, L_2 near the ends of the bar and of other unstable periodic orbits inside and outside corotation.

The effect of chirality on the existence of backward waves in metamaterials made from resonance planar chiral elements

Artificial media made from lattices of resonance planar chiral elements (RPCEs), such as planar double open rings and plane spirals, are considered. The effect of chirality on the electromagnetic properties of such media is investigated theoretically. It is shown that, when RPCEs are identically oriented, backward waves do not propagate in the medium, although there is a region where permittivity ɛ and permeability μ are negative simultaneously. However, such a metamaterial exhibits chirality and, hence, the refractive index turns out to be imaginary even when energy dissipation is disregarded. It is found that a medium with the opposite orientation of neighboring RPCEs is nonchiral; in such a medium, the resonance property of ɛ and μ is retained; the refractive index is real; and backward waves are present at frequencies at which both ɛ and μ are negative. For these media, it is found that there are regions where the directions of propagation of the wave energy and phase coincide (right-handed passbands), a region where these directions are opposite (left-handed passbands), and regions of evanescent waves.

Nuclear Spirals as Signatures of Supermassive Black Holes

Recent high resolution images of spiral galaxies show wide varieties of features including nuclear spirals in the central parts. Some of the galaxies show grand-design nuclear spirals. The morphology of grand-design spirals can be further divided by the openness of the arms: tightly wound ones with winding angle of around 3$\pi$ radian and open spirals with winding angle of around $\pi$ radian. Based on hydrodynamical simulations, we have investigated the mechanism responsible for the openness of nuclear spirals. Since the gas flow in the nuclear region is mainly governed by the central mass concentration near the nuclei and the sound speed of the gas, we have examined various models with different mass concentration represented by the mass of the central black hole and different sound speeds. We found that the tightly wound spirals can be formed when the mass of the black hole is large enough to remove the inner-inner Lindblad resonances and sound speeds lie between 15 - 20 km/sec. Thus, the presence of the tightly wound nuclear spiral could imply the presence of relatively massive black hole in the center.

Gravitational Bar and Spiral Arm Torques fromKs-band Observations and Implications for the Pattern Speeds

We have obtained deep near-infrared Ks-band William Herschel Telescope observations of a sample of 15 nearby spiral galaxies having a range of Hubble types and apparent bar strengths. The near-infrared light distributions are converted into gravitational potentials, and the maximum relative gravitational torques due to the bars and the spirals are estimated. We find that spiral strength, Qs, and bar strength, Qb, correlate well with other measures of spiral arm and bar amplitudes and that spiral and bar strengths also correlate well with each other. We also find a correlation between the position angle of the end of the bar and the position angle of the inner spiral. These correlations suggest that the bars and spirals grow together with the same rates and pattern speeds. We also show that the strongest bars tend to have the most open spiral patterns. Because open spirals imply high disk-to-halo mass ratios, bars and spirals most likely grow together as a combined disk instability. They stop growing for different reasons, however, giving the observed variation in bar-spiral morphologies. Bar growth stops because of saturation when most of the inner disk is in the bar, and spiral growth stops because of increased stability as the gas leaves and the outer disk heats up.

Resonantly Excited Waves in Gaseous Disks: Asymptotic Theory versus Numerical Hydrodynamics

The nonlinear asymptotic theory of bar-driven spiral density waves, developed by Yuan & Kuo, is tested by numerical hydrodynamical calculations using a relaxation scheme proposed by Jin & Xin. The scheme is of second-order accuracy and uses a local relaxation approximation. We have shown that the asymptotic theory, which is based on the assumption of tightly wound spirals, is valid even for relatively open spirals. We present two numerical results, one for waves excited at the outer Lindblad resonance (tightly wound spirals) and one for waves excited at the inner Lindblad resonance (relatively open spirals). Both are in good agreement with the asymptotic theory.

Cosmic Masks Still Dance

The Hubble classification scheme of galaxies is based on their optical appearance or ‘masks’. As one goes from early to late type spirals, both barred and unbarred, the optical appearance will be dominated more and more by the young Population I, i.e., blue stars and dust. Atlases reveal the rich variety of responses of the Population I component of gas and dust (the mask) to the underlying, older, stellar population. However, the gaseous Population I component, may only constitute 5 percent of the dynamical mass of the galaxy. Masks of negligible mass may conceal the human face — and that of galaxy. In the near-infrared, the morphology of older star-dominated disk indicates a simple classification scheme: the dominant Fourier m-mode in the dust penetrated regime, and the associated pitch angle. A ubiquity of low m=1 and m=2 modes is confirmed. On the basis of deprojectcd H (1.65µm) and K’ (2.1µm) images, we propose that the evolved stellar disks may be grouped into three principal dust penetrated archetypes: those with tightly wound stellar arms characterised by pitch angles at K’ of ∼ 10° (the α class), an intermediate group with pitch angles of ∼25° (the β class) and thirdly, those with open spirals demarcated by pitch angles at K’ of ∼ 40° (the γ bin). Flat or falling rotation curves give rise to the tightly wound γ class; rising rotation curves are associated with the open y class. The observed dust penetrated classes are inextricably related to the rate of shear in the stellar disk, as determined by \(\tfrac{A}{\omega }\). Here A is the first Oort constant and w denotes the angular velocity. There is no correlation between our dust penetrated classes and optical Hubble binning: the Hubble tuning fork does not constrain the morphology of the old stellar Population II disks. NGC 3223 and NGC 7083 (both SbI-II and almost the same absolute blue magnitude) have identical Hubble types and identical luminosity classes; the dust penetrated disk of NGC 3223 has tightly wrapped arms of class a, whereas the near-infrared disk of NGC 7083 has open arms of class y. This is in turn associated with their very different rotation curve shapes yielding different rates of shear \(\tfrac{A}{\omega }\). in their stellar disks. Any specific dust penetrated archetype may be the resident disk of both an early or late type galaxy. The number of arms and the pitch angle of the arms at K’ of the early-type ‘a’ spiral NGC 718 are almost identical to those for the late-type ‘c’ spiral NGC 309. We demonstrate that galaxies on opposite ends of the tuning fork can display remarkably similar evolved disk morphologies and belong to the same dust penetrated class. In this sense, there is no differentiation between an early and late type galaxy: the Hubble tuning fork becomes a circle. Furthermore, a prototypically flocculent galaxy such as NGC 5055 (Elmegreen arm class 3) can have an evolved disk morphology almost identical to that of NGC 5861, characterised in the optical as having one of Permanent address: Instituto Nacional de Astrofisica, Optica y Electronica, Calle Luis Enrique Erro 1, 72840 Tonantzintla, Puebla, Mexico the most regular spiral patterns known and of Elmegreen class 12. Both optically flocculent or grand design galaxies can reside within the same dust penetrated morphological hin. As was suggested by Block et al. (1994a), it is the gas dominated Population I component which determines the optical types (a, b, c). This may be partially or even fully decoupled from the Population II disk. Those L=lopsided galaxies (where m=1 is a dominant mode) are designated La, Ls and Ly according to the dust penetrated pitch angle; E=evensided galaxies (where m=2 is the dominant Fourier mode) are classified into classes Eα, Eβ and Eγ, according to our three principal dust penetrated archetypes. The L and E modes arc the most common morphologies in our sample, which spans a range of Hubble types from early (a) to late (irregular).

Spiral Structure in the Central Disks of NGC 1068 and M100

The nonlinear asymptotic theory of bar-driven spiral density waves developed by Yuan & Kuo is applied to the spiral structure in the gas-dominated central disk of NGC 1068 and M100. Comparison with radio interferometric observations confirms the predictions that a pair of tightly wound spirals in the central region can be regarded as the signature of a rapidly rotating bar (in the case of NGC 1068) and that a pair of relatively open spirals as the signature of a slowly rotating bar (in the case of M100). Furthermore, consistent with the theory, we find that streaming motions along the spiral arms are radially outward for the tightly wound spiral arms and radially inward for the relatively open spirals. Associated with the spiral density waves is the angular momentum transport between the bar and the disk, which eventually results in redistribution of the gas in the disk in slow long-term inflows or outflows. We discuss the implications of such flows in, for example, fueling AGNs or in starburst ring activities.

The Lynden-Bell slow bar as a determinant of the spiral-ring structure in barred galaxies

It is demonstrated that the Lynden-Bell slow bar provides a consistent understanding of some typical features in barred galaxies. The responses of the disc surface density to a slow-bar forcing are analysed and displayed. Different values of the bar angular velocity and growth rate give rise to a variety of forms occurring in the disc: inner and outer rings, more or less open half-turn spirals, and some other resonance features. Bar-enveloping inner rings become linked to the inner Lindblad resonance (ILR) with the m=2, dominant bar mode, and the outer rings become linked to the m=4 ILR, next in both importance and location. Remarkably, the resonance radial ratio is r 4 /r 2 ≃2.2, which falls within the observed peak of the outer-to-inner ring axial ratio R/r

Cable guide for multiple accessory cords on the operating microscope.

It has been three decades since the operating microscope for otologic surgery was introduced into the United States. Today's surgical microscope is used not only for surgery but also for still photography, motion pictures, and videotape recordings. The needs of photography are such that additional fiberoptic light sources or strobe flash units are often attached to the operating microscope for illumination during photography. Each accessory uses a cord or cable to its electrical source, causing a myriad of cords to be serried alongside the extension arms of the microscope. Multiple cables frequently become entangled and create drag, which restricts the mobility of the microscope. A cable-carrying guide system of stainless steel rods shaped into open spirals of approximately one and one-half turns is described. The system contains the accessory cords while permitting full mobility of the microscope during surgical procedures.

Stellar Dynamics in Thin Disk Galaxies. II. Stellar Hydrodynamic Equations

A set of closed moment equations of hydrodynamic form is presented. These equations were derived from the collisionless Boltzmann equation and should be useful for nonlinear simulations of open spirals and barlike disturbances in galaxies. Tests also show that these equations can describe the physics of short spiral waves. Important nonlinear effects such as particle trapping at the corotation region are also within the scope of these stellar hydrodynamic equations.

Local Density-Potential Relation for Spiral Density Waves in Galaxies

A local relation between the surface density and the gravitational potential for a disk distribution of mass is derived. The solution is explicitly evaluated and discussed in view of its relevance to recent developments in the density wave theory of the spiral structure in galactic dynamics. This formal asymptotic solution has been tested numerically and found to be rather accurate even when the radial wavelengths are no longer so short (i.e., relatively open spirals).

The Non-Linear Theory of Spiral Structure

AbstractThe main steps of the non-linear theory of spiral structure are described. Near each of the main resonances the basic periodic orbits are calculated, and the sets of non-periodic orbits that follow them are found. A different integral of motion is applicable for each set, besides the Jacobi integral. Then the initial distribution function, f, is expressed as a function of the two integrals and the corresponding angles. The final distribution function is found by averaging over the angles:Then by integratingover all velocities we find the response density σresp. In order that σrespshould be equal to the imposed density, σimpwe must adjust the parameters of the imposed spiral field. The form of σrespaway from resonances can be derived explicitely for tight ana open spirals or bars; however near the resonances σrespcan be only calculated numerically. If the imposed field has almost constant amplitude, then the amplitude of the response is very large near the Inner Lindblad Resonance. In the case of a tight spiral the azimuth of the response density maximum with respect to the imposed density maximum tends to zero outside the ILR, while it tends to -90° inside the ILR. One possible self-consistent solution has zero amplitude inside the ILR both in the case of tight spirals and of bars. Finally an important quadrupole term was found near the ILR.

Taxonomic characteristic of the strain ETH 7437 producing granaticin.

The streptomycete strain ETH 7437, producing granaticin, was characterized according to present taxonomic standards and compared with the strainsStreptomyces olivaceus (Waksman) Waksman and Henrici,Streptomyces coelicolor (Muller) andStreptomyces violaceruber (Waksman & Curtis). The strain ETH 7437 formed gray aerial mycelium, straight and flexuos sporophores, even single hooks and open spirals. Normally the amount of spores in chains was over 50, the surface of spores being smooth. The strain utilizedd-glucose,d-arabinose,d-xylose andd-fructose. The strain was capable of forming antibiotic pigment stably. For the strain ETH 7437 the termStreptomyces granaticolor was proposed.