Oval Distortion Research Articles

Unveiling a Hidden Bar-like Structure in NGC 1087: Kinematic and Photometric Evidence Using MUSE/VLT, ALMA, and JWST

We report a faint nonaxisymmetric structure in NGC 1087 through the use of James Webb Space Telescope Near Infrared Camera, with an associated kinematic counterpart observed as an oval distortion in the stellar velocity map, Hα, and CO J = 2 → 1 velocity fields. This structure is not evident in the MUSE optical continuum images but only revealed in the near-IR with the F200W and F300M band filters at 2 μm and 3 μm, respectively. Due to its elongation, this structure resembles a stellar bar although with remarkable differences with respect to conventional stellar bars. Most of the near-IR emission is concentrated within 6″∼500 pc with a maximum extension up to 1.2 kpc. The spatial extension of the large-scale noncircular motions is coincident with the bar, which undoubtedly confirms the presence of a nonaxisymmetric perturbation in the potential of NGC 1087. The oval distortion is enhanced in CO due to its dynamically cold nature rather than in Hα. We found that the kinematics in all phases, including stellar, ionized, and molecular, can be described simultaneously by a model containing a bisymmetric perturbation; however, we find that an inflow model of gas along the bar major axis is also likely. Furthermore, the molecular mass inflow rate associated can explain the observed star-formation rate in the bar. This reinforces the idea that bars are mechanisms for transporting gas and triggering star formation. This work contributes to our understanding of nonaxisymmetry in galaxies using the most sophisticated data so far.

Exploring Stellar and Ionized Gas Noncircular Motions in Barred Galaxies with MUSE

We present Multi Unit Spectroscopic Explorer (MUSE) integral-field stellar and ionized velocity maps for a sample of 14 barred galaxies. Most of these objects exhibit “S”-shape isovelocities in the bar region indicative of the presence of streaming motions in the velocity fields. By applying circular rotation models we observe that bars leave symmetric structures in the residual maps of the stellar velocity. We built noncircular rotation models using the XookSuut tool to characterize the observed velocity fields; in particular we adopt bisymmetric models and a harmonic decomposition for a bar potential for describing the nonaxisymmetric velocities. We find that both models are able to reproduce the oval distortion observed in the velocity maps. Furthermore, the position angle of the oval distortion estimated from the bisymmetric model correlates with the photometric bar position angle (ρ pearson = 0.95), which suggests that noncircular velocities are caused by the bar. Because of the weak detection of Hα in our objects we are not able to compare gas to stellar noncircular motions in our sample, although we show that when galaxies are gas-rich, oval distortion is also observed but with larger amplitudes. Finally, we do not find evidence that the amplitude of the noncircular motions is dependent on the bar size, stellar mass, or global star formation rate.

Linear and Helical Cesium Iodide Atomic Chains in Ultranarrow Single-Walled Carbon Nanotubes: Impact on Optical Properties.

One-dimensional (1D) atomic chains of CsI were previously reported in double-walled carbon nanotubes with ∼0.8 nm inner diameter. Here, we demonstrate that, while 1D CsI chains form within narrow ∼0.73 nm diameter single-walled carbon nanotubes (SWCNTs), wider SWCNT tubules (∼0.8-1.1 nm) promote the formation of helical chains of CsI 2 × 1 atoms in cross-section. These CsI helices create complementary oval distortions in encapsulating SWCNTs with highly strained helices formed from strained Cs2I2 parallelogram units in narrow tubes to lower strain Cs2I2 units in wider tubes. The observed structural changes and charge distribution were analyzed by density-functional theory and Bader analysis. CsI chains also produce conformation-selective changes to the electronic structure and optical properties of the encapsulating tubules. The observed defects are an interesting variation from defects commonly observed in alkali halides as these are normally associated with the Schottky and Frenkel type. The energetics of CsI 2 × 1 helix formation in SWCNTs suggests how these could be controllably formed.

The Lynden-Bell bar formation mechanism in simple and realistic galactic models

ABSTRACT Using the canonical Hamilton–Jacobi approach we study the Lynden-Bell concept of bar formation based on the idea of orbital trapping parallel to the long or short axes of the oval potential distortion. The concept considered a single parameter – a sign of the derivative of the precession rate over angular momentum, determining the orientation of the trapped orbits. We derived a perturbation Hamiltonian that includes two more parameters characterizing the background disc and the perturbation, which are just as important as the earlier known one. This allows us to link the concept with the matrix approach in linear perturbation theory, the theory of weak bars, and explain some features of the non-linear secular evolution observed in N-body simulations.

Full-scale finite element analysis of deformation and contact of a wire-wrapped fuel bundle subject to realistic thermal and irradiation conditions

The fuel bundle in a fast breeder reactor (FBR) is wrapped with wires for guiding the flow of liquid metal. Under operation condition with irradiation and high temperature, the wrapped bundle undergoes complex contact so that the flow channel of liquid will be affected. There are mainly four factors involved: radiation swelling, thermal expansion, radiation creep and thermal creep. In the present study, a full-scale finite element model (FEM) is established to consider the effect of these factors on the complex contact during operation. The established model can capture the contact separation, spacer wire’s dispersion, oval distortion and bowing details of fuel pins. The results show that the local contact dispersion caused by the wire slip can alleviate the severe transverse bending deformation of the bundle. What is more important, we find out that the dispersion of contact points in the peripheral direction of the bundle is another key factor for alleviating the severe deformation of the bundle during operation, this new mechanism – peripheral dispersion of contact – has not been achieved in previous studies.

The Net Radial Flow Velocity of the Neutral Hydrogen in the Oval Distortion of NGC 4736

Abstract The net radial flow velocity of gas is an important parameter for understanding galaxy evolution. It is difficult to measure in the presence of the elliptical orbits of an oval distortion because the mathematical model describing the observed velocity is degenerate in the unknown velocity components. A method is developed in this paper that breaks the degeneracy using additional information about the angular frequency of the oval distortion. The method is applied to the neutral hydrogen in the oval distortion of NGC 4736. The neutral hydrogen is flowing inward at a mean rate of −6.1 ± 1.9 km s−1. At this rate, it takes 400 Myr, or 1.7 rotations of the oval distortion, for the neutral hydrogen to travel the 2.5 kpc from the end to the beginning of the oval distortion. The mean mass flow rate of the neutral hydrogen in this region is −0.25 ± 0.11 M ⊙ yr−1, which is similar to estimates for the star formation rate reported in the literature.

Piercing of Continuous-Cast Billet on Two-Roller Screw Mills with Liners

In billet piercing on two-roller screw mills, the influence of the shape and position of the liner (guide piece) on the ratio of the transverse and longitudinal deformation is analyzed. The quality of the sleeve obtained from the continuous-cast billet is ensured by simulating the parameters of the deformation region so as to increase the proportion of transverse deformation. In the piercing mill, the rollers consist of two conical sections, with a gorge between the cones. A piercing mandrel is mounted between the rollers. The tip of the mandrel projects from the gorge toward the input to the deformation region. Liners (guide pieces) limit the transverse motion. The liners consist of a conical input section, an output section, and an intermediate collar. The proportion of transverse deformation is increased by adjusting the distribution of oval distortion of the blank over the length of the deformation region.

Experimental Analysis about Heat Treatment Distortion in Bearing Race

It’s well known that the vehicle fuel economy is improved by reducing the weight of their structural and mechanical components. Therefore, there is a demand of bearing race with thin thickness for weight reduction. But, this thickness reduction also causes a large oval distortion in bearings after Heat Treatment (HT). The factors affecting the HT distortion are extremely complicated, which makes it difficult to do rectification only by experimental analysis. There is also a limitation in numerical analysis due to the lack of workable model for HT distortion. Therefore, the aim of this study is to identify the effective factors of HT distortion by experimental approach in order to build suitable numerical simulation model that can estimate HT distortion. The material used in this study is a conventional case-hardened steel (Fe-0.4mass%C-Cr-Mn). The ring with the diameter of 100mm is heat treated and quenched. The resulting HT distortion is evaluated by measurement of maximum and minimum diameter of the race. A jig was developed to correct the ring shape during heat treatment, which helped in identifying that the quenching affects more than 50% of HT distortion. From these results, we developed a cooling equipment to reproduce inhomogeneous cooling rate by controlling oil flow toward the exterior of the ring. The quenching with this equipment reveals that inhomogeneous flow with opposite side (0 degree and 180 degree) reproduces a large oval distortion. The data obtained from the experimental analysis is suitable for developing the numerical model for HT distortion.

SDSS-IV MaNGA: characterizing non-axisymmetric motions in galaxy velocity fields using the Radon transform

We show how the Radon transform (defined as a series of line integrals through an image at different orientations and offsets from the origin) can be used as a simple, non-parametric tool to characterize galaxy velocity fields, specifically their global kinematic position angles (PA_k) and any radial variation or asymmetry in PA_k. This method is fast and easily automated, making it particularly beneficial in an era where IFU and interferometric surveys are yielding samples of thousands of galaxies. We demonstrate the Radon transform by applying it to gas and stellar velocity fields from the first ~2800 galaxies of the SDSS-IV MaNGA IFU survey. We separately classify gas and stellar velocity fields into five categories based on the shape of their radial PA_k profiles. At least half of stellar velocity fields and two-thirds of gas velocity fields are found to show detectable deviations from uniform coplanar circular motion, although most of these variations are symmetric about the center of the galaxy. The behavior of gas and stellar velocity fields is largely independent, even when PA_k profiles for both components are measured over the same radii. We present evidence that one class of symmetric PA_k variations is likely associated with bars and/or oval distortions, while another class is more consistent with warped disks. This analysis sets the stage for more in-depth future studies which explore the origin of diverse kinematic behavior in the galaxy population.

Orbits in elementary, power-law galaxy bars – 1. Occurrence and role of single loops

Orbits in galaxy bars are generally complex, but simple closed loop orbits play an important role in our conceptual understanding of bars. Such orbits are found in some well-studied potentials, provide a simple model of the bar in themselves, and may generate complex orbit families. The precessing, power ellipse (p-ellipse) orbit approximation provides accurate analytic orbit orbits in symmetric galaxy potentials. It remains useful for finding and fitting simple loop orbits in the frame of a rotating bar with bar-like and symmetric power-law potentials. Second order perturbation theory yields two or fewer simple loop solutions in these potentials. Numerical integrations in the parameter space neighborhood of perturbation solutions reveal zero or one ac- tual loops in a range of such potentials with rising rotation curves. These loops are embedded in a small parameter region of similar, but librating orbits, which have a subharmonic frequency superimposed on the basic loop. These loops and their librat- ing companions support annular bars. Solid bars can be produced in more complex potentials, as shown by an example with power-law indices varying with radius. The power-law potentials can be viewed as the elementary constituents of more complex potentials. Numerical integrations also reveal interesting classes of orbits with multiple loops. In two-dimensional, self-gravitating bars, with power-law potentials, single loop orbits are very rare. This result suggests that gas bars or oval distortions are unlikely to be long-lived, and that complex orbits or three-dimensional structure must support self-gravitating stellar bars.

Expansion of large-diameter welded pipe

The expansion of large-diameter welded pipe is modeled by the finite-element method. The dependence of the oval distortion of the pipe on that of the pipe blank is studied. The equivalent stress is changed by the first expansion step.

Verification of the FBR fuel bundle–duct interaction analysis code BAMBOO by the out-of-pile bundle compression test with large diameter pins

The BAMBOO computer code was verified by results for the out-of-pile bundle compression test with large diameter pin bundle deformation under the bundle–duct interaction (BDI) condition. The pin diameters of the examined test bundles were 8.5mm and 10.4mm, which are targeted as preliminary fuel pin diameters for the upgraded core of the prototype fast breeder reactor (FBR) and for demonstration and commercial FBRs studied in the FaCT project. In the bundle compression test, bundle cross-sectional views were obtained from X-ray computer tomography (CT) images and local parameters of bundle deformation such as pin-to-duct and pin-to-pin clearances were measured by CT image analyses. In the verification, calculation results of bundle deformation obtained by the BAMBOO code analyses were compared with the experimental results from the CT image analyses. The comparison showed that the BAMBOO code reasonably predicts deformation of large diameter pin bundles under the BDI condition by assuming that pin bowing and cladding oval distortion are the major deformation mechanisms, the same as in the case of small diameter pin bundles. In addition, the BAMBOO analysis results confirmed that cladding oval distortion effectively suppresses BDI in large diameter pin bundles as well as in small diameter pin bundles.

Evolution induced by dry minor mergers onto fast-rotator S0 galaxies

We analysed collisionless N-body simulations of intermediate and minor dry mergers onto S0s to test whether these mergers can generate S0 galaxies with kinematics intermediate between fast and slow rotators. We find that minor mergers induce a lower decrease of the global rotational support than encounters of lower mass ratios, which results in S0s with properties intermediate between fast and slow rotators. The resulting remnants are intrinsically more triaxial, less flattened, and span the whole range of apparent ellipticities up to $\epsilon_\mathrm{e} \sim 0.8$. They do not show lower apparent ellipticities in random projections than initially; on the contrary, the formation of oval distortions and the disc thickening increase the percentage of projections at $0.4 < \epsilon_\mathrm{e} < 0.7$. In the experiments with S0b progenitor galaxies, minor mergers tend to spin up the bulge and to decrease slightly its intrinsic ellipticity, whereas in the cases of primary S0c galaxies they keep the rotational support of the bulge nearly constant and decrease significantly its intrinsic ellipticity. The remnant bulges remain nearly spherical ($B/A \sim C/A > 0.9$), but exhibit a wide range of triaxialities ($0.20 < T < 1.00$). In the plane of global anisotropy of velocities ($\delta$) vs. intrinsic ellipticity ($\epsilon_\mathrm{e,intr}$), some of our models extend the linear trend found in previous major merger simulations towards higher $\epsilon_\mathrm{e,intr}$ values, while others depart from it. This is consistent with the wide dispersion exhibited by real S0s in this diagram compared with ellipticals, which follow the linear trend drawn by major merger simulations. The different trends exhibited by ellipticals and S0 galaxies in the $\delta$ - $\epsilon_\mathrm{e}$ diagram may be pointing to the different role played by major mergers in the build-up of each morphological type.

Star formation in bulgeless late-type galaxies: clues to their evolution

We present GMRT 1280 MHz radio continuum observations and follow-up optical studies of the disk and nuclear star formation in a sample of low luminosity bulgeless galaxies. The main aim is to understand bulge formation and overall disk evolution in these late type galaxies. We detected radio continuum from five of the twelve galaxies in our sample; the emission is mainly associated with disk star formation. Only two of the detected galaxies had extended radio emission; the others had patchy disk emission. In the former two galaxies, NGC3445 and NGC4027, the radio continuum is associated with star formation triggered by tidal interactions with nearby companion galaxies. We did follow-up Halpha imaging and nuclear spectroscopy of both galaxies using the Himalayan Chandra Telescope (HCT). The Halpha emission is mainly associated with the strong spiral arms. The nuclear spectra indicate ongoing nuclear star formation in NGC3445 and NGC4027 which maybe associated with nuclear star clusters. No obvious signs of AGN activity were detected. Although nearly bulgeless, both galaxies appear to have central oval distortions in the R band images; these could represent pseudobulges that may later evolve into large bulges. We thus conclude that tidal interactions are an important means of bulge formation and disk evolution in bulgeless galaxies; without such triggers these galaxies appear to be low in star formation and overall disk evolution.

H I ASYMMETRIES IN THE ISOLATED GALAXY CIG 292

We present Expanded Very Large Array (EVLA) D-array observations in the 21-cm line of neutral hydrogen (HI) of CIG 292, an isolated SA(s)b galaxy at a distance of ~ 24.3Mpc. From previous HI single dish observations the galaxy was known to have a mildly asymmetric HI profile (A_flux =1.23 {\pm}0.3). Our EVLA observations show there is ~ 12% more HI projected South of the optical centre (approaching velocities) than in the North (receding velocities), despite the HI extending ~ 16% further to the North than the South. The HI projected within the optical disk must have been perturbed within the HI relaxation time (~ 10^8 yr) which implies that this can not have been caused by any of the three nearest companions, as their distance (~ 0.5Mpc) is too large. Neither HI-rich companions nor tidal tails were found within our field of view and velocity range covered. Our kinematical data suggest that the inner part harbors an oval distortion whereas the outer regions show signs of a modest warp. The mild asymmetry in the HI global profile thus actually masks stronger asymmetries in the two-dimensional distributions of gas and star forming regions in this galaxy. Since the galaxy is isolated, this must predominantly be due to processes related to its formation and secular evolution.

KK 246: A DWARF GALAXY WITH AN EXTENDED H I DISK IN THE LOCAL VOID

We have found that KK 246, the only confirmed galaxy located within the nearby Tully Void, is a dwarf galaxy with an extremely extended H I disk and signs of an H I cloud with anomalous velocity. It also exhibits clear misalignment between the kinematical major and minor axes, indicative of an oval distortion, and a general misalignment between the H I and optical major axes. We measure a H I mass of 1.05 +- 0.08 x 10^8 M_sun, and a H I extent 5 times that of the stellar disk, one of the most extended H I disks known. We estimate a dynamical mass of 4.1 x 10^9 M_sun, making this also one of the darkest galaxies known, with a mass-to-light ratio of 89. The relative isolation and extreme underdense environment make this an interesting case for examining the role of gas accretion in galaxy evolution.

More precise superfinishing by means of statistical modeling

Superfinishing is the final stage in the manufacture highprecision parts that take the form of solids of rev� olution. The main goal of superfinishing is the increase the precision of the part's crosssectional profile. It is assessed in terms of noncircularity—in particular, oval distortion, faceting, and undulation of the surface. Pro� duction experience shows that faceting and undulation may be effectively reduced in most cases, whereas it is much more difficult to reduce oval distortion. In centerless superfinishing, stable reduction of oval distortion is impossible for the following reasons. (1) Centerless basing tends to retain the shape of the blank from preceding operations. Therefore, much of the resultant error consists of basing error, with par� tial copying of the initial shape errors and the forma� tion of new errors. (2) In a batch of blanks, the shape fluctuations are stochastic, and it is not always possible to identify one or two dominant harmonics of the profile. Therefore, setup of the machine tool on the basis of determinate models only ensures precision in the first approxima� tion. Thus, further improvement in the precision of cen� terless superfinishing entails creating statistical models of shaping for batches of blanks and developing meth� ods of machinetool setup on that basis. The mathematical model of basing in centerless superfinishing was considered in (1). However, certain simplifications in the formulation of the problem introduced considerable error in the calculation. In addition, random initial phases and correlations between the amplitudes of the harmonics significantly complicate the problem and call for other methods of solution. In the present work, we adopt a statistical modeling method—the MonteCarlo method (2). In machine� tool setup so as to minimize the basing error, this method involves simulation of the stochastic input data (the shape fluctuations of the blanks); repeated implementation of the analytical basing model; and the derivation of probabilistic characteristics whose numerical values agree with the results of determinate solution. In the end, we obtain a series of particular values of the basing error, whose statistical analysis reveals the influence of machinetool setup on the machining precision for the batch of blanks. The precision of the crosssectional profile is assessed in terms of the noncircularity, which indicates how much the actual profile differs from some basic circle. Most often, the basic circle adopted is the mean circle corresponding to the periphery of the part's cross section according to the leastsquares method (3). Then the blank's cross section with shape fluctua� tions may be described by a trigonometric polynomial in polar coordinates (4)

Quantifying non-circular streaming motions in disc galaxies

High-quality velocity maps of galaxies frequently exhibit signatures of non-circular streaming motions. We here apply the software tool, "velfit" recently proposed by Spekkens & Sellwood, to five representative galaxies from the THINGS sample. We describe the strengths and weaknesses of the tool, and show that it is both more powerful and yields results that are more easily interpreted than the commonly used procedure. We demonstrate that it can estimate the magnitudes of forced non-circular motions over a broad range of bar strengths from a strongly barred galaxy, through cases of mild bar-like distortions to placing bounds on the shapes of halos in galaxies having extended rotation curves. We identify mild oval distortions in the inner parts of two dwarf galaxies, NGC 2976 and NGC 7793, and show that the true strength of the non-axisymmetric gas flow in the strongly barred galaxy NGC 2903 is revealed more clearly in our fit to an optical Halpha map than to the neutral hydrogen data. The method can also yield a direct estimate of the ellipticity of a slowly-rotating potential distortion in the flat part of a rotation curve, and we use our results to place tight bounds on the possible ellipticity of the outer halos of NGC 3198 and NGC 2403.

UNVEILING THE NATURE OF M94's (NGC4736) OUTER REGION: A PANCHROMATIC PERSPECTIVE

We have conducted a deep multiwavelength analysis (0.15–160 μm) to study the outer region of the nearby galaxy M94. We show that the non-optical data support the idea that the outskirts of this galaxy are not formed by a closed stellar ring (as traditionally claimed in the literature) but by a spiral arm structure. In this sense, M94 is a good example of a Type III (anti-truncated) disk galaxy having a very bright outer disk. The outer disk of this galaxy contains ∼23% of the total stellar mass budget of the galaxy and contributes ∼10% of the new stars created showing that this region of the galaxy is active. In fact, the specific star formation rate (SFR) of the outer disk (∼0.012 Gyr−1) is a factor of ∼2 larger (i.e., the star formation is more efficient per unit stellar mass) than in the inner disk. We have explored different scenarios to explain the enhanced star formation in the outer disk. We find that the inner disk (if considered as an oval distortion) can dynamically create a spiral arm structure in the outer disk which triggers the observed relatively high SFR as well as an inner ring similar to what is found in this galaxy.

Irradiation Performance of Fast Reactor MOX Fuel Assemblies Irradiated to High Burnups

Mixed oxide fuel assemblies (MFA-1 and MFA-2 assemblies) were irradiated in the fast flux test facility to evaluate the irradiation performance of fast reactor core fuels at high burnups and high fast neutron fluences. The MFA-1 and MFA-2 assemblies achieved respective peak pellet burnups of 147 and 162GWd/t, and resisted to respective peak fast neutron fluences (E > 0:1 MeV) of 21:4 _ 1026 and 23:8 _ 1026 n/m2, without any indication of fuel pin breaching. Structural components of these assemblies were made of modified type 316 stainless steel and 15Cr-20Ni base advanced austenitic stainless steel. Postirradiation examinations of these assemblies revealed dimensional changes of fuel pins and assembly ducts due to irradiation-induced void swelling and irradiation creep, and fuel cladding local oval distortions due to bundle-duct interaction (BDI). The swelling resistance of 15Cr-20Ni base advanced austenitic stainless steel fuel pin cladding was almost the same as that of the modified type 316 stainless steel cladding, while the assembly duct of the former material had a slightly higher swelling resistance than that of the latter material. Analyses of fuel pin bundle deformations indicated that these assemblies likely mitigate BDI mainly by fuel pin bowings and cladding oval distortions.