2,315 research outputs found
Identity and distribution of southern African sciaenid fish species of the genus Umbrina
Two Umbrina species, U. canariensis Valenciennes 1843 and U. robinsoni Gilchrist and Thompson 1908, are recognised from southern Africa. The latter species was hitherto believed to be a synonym of Umbrina ronchus Valenciennes 1843 (type locality Canary Islands). U. canariensis is distributed along the South Africa eastern seaboard from Cape Point to Sodwana Bay and U. robinsoni is known from False Bay to Madagascar and Oman. African Umbrina taxonomy has, however, been hindered by geographic samples that were either too few or consisted of specimens of disparate length; and as a result the identification and distribution of South African Umbrina species was confused. Morphological comparison of a large number of South African Umbrina with specimens from the type locality (Canary Islands) confirmed the identity of South African U. canariensis and allowed for an expanded description of the species. However, differences between specimens of U. ronchus and those of the second South African species (n = 251) led us to resurrect U. robinsoni (Gilchrist and Thompson 1908) as a valid name for this species. U. robinsoni differs from U. ronchus in having a smaller supraoccipital crest and thus a less steep pre-dorsal profile; a shallower preorbital bone (13–21% head length [HL] vs 21% HL); and a shorter nostril-orbit distance (2.4–6.9% HL vs 7.8–8.5% HL). Colour patterns also differ between the two species, with U. ronchus lacking the oblique, wavy, white stripes evident on the flanks of U. robinsoni. U. ronchus does not occur in South African waters, and is an eastern Atlantic species occurring from Gibraltar to Angola. Specimens from the east coast of Africa (Moçambique to Gulf of Oman) that were previously identified as U. ronchus are U. robinsoni. Differences between U. robinsoni and U. canariensis include: a lower modal number of soft dorsal fin rays, (22–27 vs 24–30); less deep body depth, (26–36% standard length [SL] vs 33–39% SL); shorter pectoral fin length (15–21% SL vs 20–25% SL); longer caudal peduncle length (26–34% SL vs 21–28% SL) and snout length (27–38% HL vs 23–32% HL); and smaller orbit diameter (14–33% HL vs 23–34% HL). Otoliths of U. robinsoni differ from those of U. canariensis in being smaller, less elongate, lacking a massive post-central umbo and having a post-dorsal spine remnant. The body colour and nature of the striping pattern on the flanks differs markedly between the species: in U. robinsoni the oblique stripes are thin, wavy, white lines; in U. canariensis the oblique stripes are thicker, nearly straight and brown; U. robinsoni also lacks the triangleshaped mark on the outer operculum and the dark pigmentation of the inner operculum that is found on U. canariensis. Spatial analysis of South African specimens collected with a variety of gear revealed U. robinsoni to be a shallow-water species found from the surf-zone to 40m, whereas U. canariensis occurs predominantly from 40 to 100m depth. Although both species occur throughout the South African eastern seaboard, U. canariensis is most common west of the Kei River, where the shelf is wider. Examination of three specimens of U. steindachneri Cadenat 1950 confirmed the presence of a fourth sub-Saharan Umbrina species that is limited to tropical West African waters from Senegal to Angola. U. steindachneri differs from the other African Umbrina in having a high number of soft dorsal rays (28–29), a greater 3rd dorsal spine length (25–27% SL) and a very pronounced and convoluted striping pattern on the flanks
Magnetic Anisotropy in Single Crystalline CeAuIn
We have grown the single crystals of LaAuIn and
CeAuIn by high temperature solution method and report on the
anisotropic magnetic behavior of CeAuIn . The compounds crystallize
in an orthorhombic structure with space group \textit {Pnma}.
LaAuIn shows a Pauli-paramagnetic behavior. CeAuIn do
not order down to 1.8 K. The easy axis of magnetization for CeAuIn
is along [010] direction. The magnetization data is analyzed on the basis of
crystalline electric field (CEF) model.Comment: 7 figures 4 page
Interplay of crystal field structures with configuration to heavy fermions
We examine a relevance between characteristic of crystal field structures and
heavily renormalized quasiparticle states in the -- Anderson
lattice model. Using a slave-boson mean-field approximation, we find that for
configurations two or three quasiparticle bands are formed near the Fermi
level depending on the number of the relevant orbitals in the
crystal field ground state. The inter-orbital correlations characterizing the
crystal field ground state closely reflect in inter-band residual interactions
among quasiparticles. Particularly in the case of a singlet crystal field
ground state, resulting residual antiferromagnetic exchange interactions among
the quasiparticles lead to an anomalous suppression of the quasiparticle
contribution of the spin susceptibility, even though the quasiparticle mass is
strongly enhanced.Comment: 8 pages, 7 color figures, in JPSJ styl
Bott periodicity and stable quantum classes
We use Bott periodicity to relate previously defined quantum classes to
certain "exotic Chern classes" on . This provides an interesting
computational and theoretical framework for some Gromov-Witten invariants
connected with cohomological field theories. This framework has applications to
study of higher dimensional, Hamiltonian rigidity aspects of Hofer geometry of
, one of which we discuss here.Comment: prepublication versio
Lattice Distortion and Resonant X-Ray Scattering in DyB2C2
We study the resonant x-ray scattering (RXS) spectra at the Dy
absorption edge in the quadrupole ordering phase of DyBC. Analyzing the
buckling of sheets of B and C atoms, we construct an effective model that the
crystal field is acting on the and states with the principal axes
different for different sublattices. Treating the states as a band and the
states as localized states, we calculate the spectra within the dipole
transition. We take account of processes that (1) the lattice distortion
directly modulates the states and (2) the charge anisotropy of the
quadrupole ordering states modulates the states through the -
Coulomb interaction. Both processes give rise to the RXS intensities on
and spots. Both give similar
photon-energy dependences and the same azimuthal-angle dependences for the main
peak, in agreement with the experiment. The first process is found to give the
intensities much larger than the second one in a wide parameter range of
crystal field. This suggests that the main-peak of the RXS spectra is not a
direct reflection of the quadrupole order but mainly controlled by the lattice
distortion.Comment: 8 pages, 8 figures, Latex, To be published in J. Phys. Soc. Jp
High Velocity Line Emission in the NLR of NGC 4151
Narrow-band imaging of the nuclear region of NGC 4151 with the Hubble Space
Telescope is presented. The filter bandpasses isolate line emission in various
high velocity ranges in several ions. Slitless and long-slit spectra of the
region with the Space Telescope Imaging Spectrograph also indicate the
locations of high velocity gas. These emission regions are faint and are
interspersed among the bright emission clouds seen in direct images. They have
radial velocities up to 1400 km/s relative to the nucleus, and are found in
both approach and recession on both sides of the nucleus. This contrasts
strongly with the bright emission line clouds which have been discussed
previously as showing bidirectional outflow with velocities within 400 km/s of
the nucleus. We discuss the possible connections of the high velocity material
with the radio jet and the nuclear radiation.Comment: 12 pages plus 6 figures, to be published in A
STIS Longslit Spectroscopy Of The Narrow Line Region Of NGC 4151. I. Kinematics and Emission Line Ratios
Longslit spectra of the Seyfert galaxy NGC 4151 from the UV to near infrared
have been obtained with STIS to study the kinematics and physical conditions in
the NLR. The kinematics show evidence for three components, a low velocity
system in normal disk rotation, a high velocity system in radial outflow at a
few hundred km/s relative to the systemic velocity and an additional high
velocity system also in outflow with velocities up to 1400 km/s, in agreement
with results from STIS slitless spectroscopy (Hutchings et al., 1998, Kaiser et
al., 1999, Hutchings et al., 1999) We have explored two simple kinematic models
and suggest that radial outflow in the form of a wind is the most likely
explanation. We also present evidence indicating that the wind may be
decelerating with distance from the nucleus.
We find that the emission line ratios along our slits are all entirely
consistent with photoionization from the nuclear continuum source. A decrease
in the [OIII]5007/H-beta and [OIII]5007/[OII]3727 ratios suggests that the
density decreases with distance from the nucleus. This trend is borne out by
the [SII] ratios as well. We find no strong evidence for interaction between
the radio jet and the NLR gas in either the kinematics or the emission line
ratios in agreement with the results of Kaiser et al. (1999) who find no
spatial coincidence of NLR clouds and knots in the radio jet. These results are
in contrast to other recent studies of nearby AGN which find evidence for
significant interaction between the radio source and the NLR gas.Comment: 32 pages, 13 figures, accepted for publication in The Astrophysical
Journa
Mapping the Kinematics of the Narrow-Line Region in the Seyfert Galaxy NGC 4151
Using The Hubble Space Telescope's Space Telescope Imaging Spectrograph HST's
STIS, observations of the OIII emission from the narrow-line region (NLR) of
NGC 4151 were obtained and radial velocities determined. Five orbits of HST
time were used to obtain spectra at five parallel slit configurations, at a
position angle of 58 degrees, with spatial resolution 0.2 arcseconds across and
0.1 arcseconds along each slit. A spectral resolving power of ~ 9,000 with the
G430M grating gave velocity measurements accurate to ~ 34 km/s. A kinematic
model was generated to match the radial velocities, for comparison to previous
kinematic models of biconical radial outflow developed for low-dispersion
spectra at two slit positions. The new high-resolution spectra permit the
measurement of accurate velocity dispersions for each radial-velocity
component. The full-width at half-maximum (FWHM) reaches a maximum of 1000 km/s
near the nucleus, and generally decreases with increasing distance to about 100
km/s in the extended narrow-line region (ENLR), starting at about 6 arcseconds
from the nucleus. In addition to the bright emission knots, which generally fit
our model, there are faint high velocity clouds which do not fit the biconical
outflow pattern of our kinematic model. These faint clouds occur at the
turnover points of the outflowing bright clouds. We suggest possible scenarios
that could explain these rogue clouds: (1) backflow resulting from shocks and
(2) outflow outside of the bicones, although the latter does not explain how
the knots are ionized and accelerated. A comparison of our observations with a
high-resolution radio map shows that there is no evidence that the kinematics
of the NLR clouds are affected by the radio lobes that comprise the inner jet.Comment: 30 pages, 15 figures (some color), accepted for publication in the
Astronomical Journal. Downloadable versions of the paper with high resolution
figures/images are available here:
http://www.chara.gsu.edu/~crenshaw/NGC4151_kinematics.pdf <--PDF Version
http://www.chara.gsu.edu/~crenshaw/NGC4151_kinematics.ps <--PS Versio
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