Oblate Symmetry Research Articles

Integrated performance of large HDC-capsule implosions on the National Ignition Facility

We report on eight, indirect-drive, deuterium–tritium-layered, inertial-confinement-fusion experiments at the National Ignition Facility to determine the largest capsule that can be driven symmetrically without relying on cross-beam energy transfer or advanced Hohlraum designs. Targets with inner radii of up to 1050 μm exhibited controllable P2 symmetry, while larger capsules suffered from diminished equatorial drive. Reducing the Hohlraum gas-fill-density from 0.45 mg/cm3 to 0.3 mg/cm3 did not result in a favorable shift of P2 amplitude as observed in preceding tuning experiments. Reducing the laser-entrance-hole diameter from 4 mm to 3.64 mm decreased polar radiation losses as expected, resulting in an oblate symmetry. The experiments exhibited the expected performance benefit from increased experimental scale, with yields at a fixed implosion velocity roughly following the predicted 1D dependence. With an inner radius of 1050 μm and a case-to-capsule-ratio of 3.0, experiment N181104 is the lowest implosion-velocity experiment to exceed a total neutron yield of 1016.

Using AMS combined with mineral shape preferred orientation analysis to understand the emplacement fabrics of the Apiaí gabbro-norite (Ribeira Belt, SE Brazil)

The Apiaigabbro-norite is a massive fine- grained Neoproterozoic intrusion emplaced in a core of synformal structure that deforms low-grade marine metasedimentary rocks of the Ribeira Belt of south-eastern Brazil. The lack of visible magmatic layering or any internal fabric has been a major limitation in deciding whether the emplacement occurred before or after the regional folding. To assist in the tectonic interpretations, we combine low-field anisotropy of magnetic susceptibility (AMS) and silicate shape preferred orientation (SPO) to reveal the internal structure of the mafic intrusion. Mag- netic data indicate a mean susceptibility of about 10 -2 SI and a mean anisotropy degree (P) of about 1.08, essentially yielded by titanomagnetite. The magnetic and silicate foliations for P C 1.10 are parallel to each other, while the lineations tend to scatter on the foliation plane, in agree- ment with the dominant oblate symmetry of the AMS and SPO ellipsoids. For lower P values, the magnetic and silicate fabrics vary from coaxial to oblique, and for P B 1.05, their shapes and orientations can be quite distinct. The crystal size distribution (CSD) of plagioclase for P ( 1.05 is log linear, in agreement with a bulk simple crystallisation history. These results combined show that for a strong SPO, corresponding to a magnetic anisotropy above 1.10, AMS is a reliable indicator of the magmatic fabric. They indicate that the Apiaigabbro-norite consists of sill-like body that was inclined gently to the north by the regional folding.

Inferential statistics of electron backscatter diffraction data from within individual crystalline grains

Highly concentrated distributed crystallographic orientation measurements within individual crystalline grains are analysed by means of ordinary statistics neglecting their spatial reference. Since crystallographic orientations are modelled as left cosets of a given subgroup of SO(3), the non-spatial statistical analysis adapts ideas borrowed from the Bingham quaternion distribution on {\bb S}^3. Special emphasis is put on the mathematical definition and the numerical determination of a `mean orientation' characterizing the crystallographic grain as well as on distinguishing several types of symmetry of the orientation distribution with respect to the mean orientation, like spherical, prolate or oblate symmetry. Applications to simulated as well as to experimental data are presented. All computations have been done with the free and open-source texture toolboxMTEX.

Magnetic fabric and zircon U–Pb geochronology of the Itaoca pluton: Implications for the Brasiliano deformation of the southern Ribeira Belt (SE Brazil)

The Itaoca pluton consists of porphyritic monzogranite that intruded the upper crust into low-grade metasedimentary rocks of the Apiaí Domain (Ribeira Belt). Anisotropy of magnetic susceptibility and zircon U–Pb (Shrimp) geochronology were combined to determine pluton emplacement mechanisms and its chronology relative to the collision structures of the Paranapiacaba (Brasiliano II) orogenic system. Magnetic susceptibility ranges between 4 and 38 × 10 −3 SI, and thermomagnetic measurements indicate multidomain magnetite is the main carrier of anisotropy. The pluton shows an “onion-skin” structure roughly elongated to the northeast with its hinge zone including kilometer-wide roof-pendants. Magnetic lineations are variable in orientation in consistency with the dominant oblate symmetry of the magnetic fabric. A distinct NE-trending point-maxima, however, indicates the mean lineation is parallel to the stretching direction of the transpressive deformation that affected the regional host rocks. Prismatic zircon from the monzogranite, both in the core and in the finely-zoned margins, yielded an age of 623 ± 10 Ma. These results suggest the magmatic fabric recorded the earlier strain increments of the regional shear deformation. It may correspond to the transition from continental arc to collision tectonics of the southern Ribeira Belt.

ChandraEvidence of a Flattened, Triaxial Dark Matter Halo in the Elliptical Galaxy NGC 720

We present an analysis of a Chandra ACIS-S observation of the elliptical galaxy NGC 720, to verify the existence of a dark matter halo and to measure its ellipticity. The ACIS-S3 image reveals over 60 point sources distributed throughout the field, most of which were undetected and therefore unaccounted for in previous X-ray studies. For semimajor axes a ≲ 150'' (18.2 h kpc), the ellipticity of the diffuse X-ray emission is consistent with a constant value, X ≈ 0.15, which is systematically less than the values of 0.2-0.3 obtained from previous ROSAT PSPC and HRI observations because of the unresolved point sources contaminating the ROSAT values. The Chandra data confirm the magnitude of the ~20° position angle (P.A.) twist discovered by ROSAT over this region. However, the twist in the Chandra data is more gradual and occurs at smaller a, also because of the point sources contaminating the ROSAT values. For a ≳ 150'' out to a = 185'' (22.4 h kpc), which is near the edge of the S3 CCD, X and P.A. diverge from their values at smaller a. Possible origins of this behavior at the largest a are discussed. Overall, the ellipticities and P.A. twist for a ≲ 150'' can be explained by the triaxial mass model of NGC 720 published by Romanowsky & Kochanek (which could not produce the abrupt P.A. twist in the ROSAT HRI data). Since the optical image displays no substantial isophote twisting, the X-ray P.A. twist requires a massive dark matter halo if the hot gas is in hydrostatic equilibrium. Furthermore, the values of X obtained by Chandra are too large to be explained if the gravitating mass follows the optical light (M ∝ L*), irrespective of the P.A. twist. The M ∝ L* hypothesis is inconsistent with the Chandra ellipticities at the 96% confidence level, assuming oblate symmetry, and at the 98% confidence level for prolate symmetry. Thus, both the P.A. twist and the ellipticities of the Chandra image imply the existence of dark matter, independent of the temperature profile of the gas. This geometric evidence for dark matter cannot be explained by alternative gravity theories, such as the modification of Newtonian dynamics (MOND). To constrain the ellipticity of the dark matter halo, we considered both oblate and prolate spheroidal mass models to bracket the full range of (projected) ellipticities of a triaxial ellipsoid. The dark matter density model, ρ ∝ (a + a2)-1, provides the best fit to the data and gives ellipticities and 1 σ errors of = 0.37 ± 0.03 for oblate and = 0.36 ± 0.02 for prolate models. Navarro-Frenk-White (NFW) and Hernquist models give similar ellipticities for the dark matter. These moderate ellipticities for the dark halo are inconsistent with both the nearly spherical halos predicted if the dark matter is self-interacting and the highly flattened halos predicted if the dark matter is cold molecular gas. These ellipticities may also be too large to be explained by warm dark matter, but they are consistent with galaxy-sized halos formed in the currently popular ΛCDM paradigm.

Evidence From Intrinsic Shapes for Two Families of Elliptical Galaxies

Bright elliptical galaxies have a markedly different distribution of Hubble types than faint ellipticals; the division occurs near M_B=-20 and bright ellipticals are rounder on average. The Hubble types of galaxies in both groups are narrowly clustered, around E1.5 in the case of the bright galaxies and around E3 for the fainter ones. The Hubble-type distribution of the faint ellipticals is consistent with oblate symmetry, but the oblate hypothesis fails for the bright ellipticals. However a distribution of triaxial intrinsic shapes can successfully reproduce the apparent shape data for either group. The distribution of intrinsic, short-to-long axis ratios is peaked around 0.75 for bright galaxies and 0.65 for faint galaxies. Our results provide further evidence that elliptical galaxies should be divided into two, morphologically distinct families.

General calculations of rotational effects on spectral lines

view Abstract Citations (10) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS General calculations of rotational effects on spectral lines. Clark, F. O. ; Martin, H. M. ; Biretta, J. A. Abstract The paper presents a family of spectral-line profiles (flux profiles) in velocity space for rotating objects with spherical and oblate symmetry. Calculations are given which include the range of theoretically expected density laws as currently reported in the literature, and the range of rotational-velocity laws which extend from rigid body rotation to conservation of angular momentum. In addition, calculations are presented for objects which are uniformly sampled, as well as for Gaussian sampling which may occur with a radio telescope beam power pattern. The latter Gaussian convolved results include effects of offsets in the equatorial plane. Finally, results are compared to observational examples from the literature. Publication: The Astrophysical Journal Pub Date: September 1979 DOI: 10.1086/157321 Bibcode: 1979ApJ...232..624C Keywords: Galactic Radiation; Galactic Rotation; Interstellar Gas; Line Shape; Nebulae; Angular Momentum; Cosmic Dust; Radio Sources (Astronomy); Spectral Line Width; Astrophysics; Line Profiles:Radio Lines; Line Profiles:Rotating Gas full text sources ADS |

Rotation of nuclei around a prolate symmetry axis at very high spin states

Classically one expects that nuclei rotate at very high spins (30≦I≦80) around an oblate symmetry axis. It is shown that strong shell correction energies yield for some nuclei at the end of the rare earth region and in the Pb-region yrast states for a rotation around a prolate symmetry axis. Like for the rotation around an oblate symmetry axis one expects also here yrast traps. The deformation energy surfaces for very high spin states are calculated by the Strutinsky method using a Saxon-Woods potential and by a microscopic method built on constraint Nilsson functions. Both methods agree qualitatively. Yrast traps are studied for these nuclei. It is shown that the MONA (Maximisation of theOverlap ofNuclear wave functions byAlignment) effect prefers at high spin rotation around the symmetry axis of a negative deformed shape at the beginning of the shell and of positive deformation at the end of the shell.