476 research outputs found
THE STRUCTURE OF EMPLOYMENT AND UNEMPLOYMENT IN A DECLINING RURAL COMMUNITY
Labor and Human Capital,
Reconsidering the galactic coordinate system
Initially defined by the IAU in 1958, the galactic coordinate system was
thereafter in 1984 transformed from the B1950.0 FK4-based system to the J2000.0
FK5-based system. In 1994, the IAU recommended that the dynamical reference
system FK5 be replaced by the ICRS, which is a kinematical non-rotating system
defined by a set of remote radio sources. However the definition of the
galactic coordinate system was not updated. We consider that the present
galactic coordinates may be problematic due to the unrigorous transformation
method from the FK4 to the FK5, and due to the non-inertiality of the FK5
system with respect to the ICRS. This has led to some confusions in
applications of the galactic coordinates. We tried to find the transformation
matrix in the framework of the ICRS after carefully investigating the
definition of the galactic coordinate system and transformation procedures,
however we could not find a satisfactory galactic coordinate system that is
connected steadily to the ICRS. To avoid unnecessary misunderstandings, we
suggest to re-consider the definition of the galactic coordinate system which
should be directly connected with the ICRS for high precise observation at
micro-arcsecond level.Comment: 10 pages, 3 figures, accepted for publication in A&
The spatial distribution of O-B5 stars in the solar neighborhood as measured by Hipparcos
We have developed a method to calculate the fundamental parameters of the
vertical structure of the Galaxy in the solar neighborhood from trigonometric
parallaxes alone. The method takes into account Lutz-Kelker-type biases in a
self-consistent way and has been applied to a sample of O-B5 stars obtained
from the Hipparcos catalog. We find that the Sun is located 24.2 +/- 1.7
(random) +/- 0.4 (systematic) pc above the galactic plane and that the disk
O-B5 stellar population is distributed with a scale height of 34.2 +/- 0.8
(random) +/- 2.5 (systematic) pc and an integrated surface density of (1.62 +/-
0.04 (random) +/- 0.14 (systematic)) 10^{-3} stars pc^{-2}. A halo component is
also detected in the distribution and constitutes at least ~5% of the total
O-B5 population. The O-B5 stellar population within ~100 pc of the Sun has an
anomalous spatial distribution, with a less-than-average number density. This
local disturbance is probably associated with the expansion of Gould's belt.Comment: 14 pages, 3 figures, to appear in the May 2001 issue of the
Astronomical Journa
Anxiety Control and Periodontal Practice
Chronic periodontitis is one of the most common diseases in clinical dentistry, which requires various surgical interventions to treat the moderately to severely destructed supporting periodontium. Most patients have anxiety and fear to those surgical procedures and dentists often have problems dealing with those patients. By applying the conscious sedation technique in outpatient units, periodontists have become able to manage their patients successfully with less anxiety or fear. Also, we have experienced the increased level of patients\u27 satisfaction. Generally, periodontal treatments are time consuming procedures and patients are usually reluctant to the periodontal instruments. This study is focused on the sedation procedure with intravenous midazolam infusion performed in Department of Periodontology of Ewha Womans University Hospital. Using questionnaires, we evaluated 80 randomly selected patients for the anxiolytic effect of intravenous midazolam. Anxiety control using IV sedation was very helpful in performing various periodontal reconstructive and advanced surgical procedures in implant dentistry
Kinematics of the Young Stellar Objects associated with the Cometary Globules in the Gum Nebula
An analysis of proper motion measurements of the Young Stellar Objects (YSOs)
associated with the Cometary Globules (CGs) in the Gum Nebula is presented.
While earlier studies based on the radial velocity measurements of the CGs
suggested expansion of the system of the CGs, the observed proper motion of the
YSOs shows no evidence for expansion. In particular the kinematics of two YSOs
embedded in CGs is inconsistent with the supernova explosion of the companion
of Pup about 1.5 Myr ago as the cause of the expansion of the CG
system. YSOs associated with the CGs share the average proper motion of the
member stars of the Vela OB2 association. A few YSOs that have relatively large
proper motions are found to show relatively low infrared excesses.Comment: 19 pages, 6 figures, 4 tables, Accepted for publication in MNRA
Detection of a Corrugated Velocity Pattern in the Spiral Galaxy NGC 5427
Here we report the detection, in Halpha emission, of a radial corrugation in
the velocity field of the spiral galaxy NGC 5427. The central velocity of the
Halpha line displays coherent, wavy-like variations in the vicinity of the
spiral arms. The spectra along three different arm segments show that the
maximum amplitude of the sinusoidal line variations are displaced some 500 pc
from the central part of the spiral arms. The peak blueshifted velocities
appear some 500 pc upstream the arm, whereas the peak redshifted velocities are
located some 500 pc downstream the arm. This kinematical behavior is similar to
the one expected in a galactic bore generated by the interaction of a spiral
density wave with a thick gaseous disk, as recently modeled by Martos & Cox
(1998).Comment: Accepted for publication in Ap
A study of the neglected Galactic HII region NGC 2579 and its companion ESO 370-9
The Galactic HII region NGC 2579 has stayed undeservedly unexplored due to
identification problems which persisted until recently. Both NGC 2579 and its
companion ESO 370-9 have been misclassified as planetary or reflection nebula,
confused with each other and with other objects. Due to its high surface
brightness, high excitation, angular size of few arcminutes and relatively low
interstellar extinction, NGC 2579 is an ideal object for investigations in the
optical range. Located in the outer Galaxy, NGC 2579 is an excellent object for
studying the Galactic chemical abundance gradients. In this paper we present
the first comprehensive observational study on the nebular and stellar
properties of NGC 2579 and ESO 370-9, including the determination of electron
temperature, density structure, chemical composition, kinematics, distance, and
the identification and spectral classification of the ionizing stars, and
discuss the nature of ESO 370-9. Long slit spectrophotometric data in the
optical range were used to derive the nebular electron temperature, density and
chemical abundances and for the spectral classification of the ionizing star
candidates. Halpha and UBV CCD photometry was carried out to derive stellar
distances from spectroscopic parallax and to measure the ionizing photon flux.Comment: To be published in Astronomy & Astrophysic
Genetic differentiation of European grayling (Thymallus thymallus) populations in Serbia, based on mitochondrial and nuclear DNA analyses
<p>Abstract</p> <p>Background</p> <p>The structure and diversity of grayling (<it>Thymallus thymallus</it>) populations have been well studied in most of its native habitat; however the southernmost populations of the Balkan Peninsula remain largely unexplored. The purpose of this study was to assess the genetic diversity of Serbian grayling populations, detect the impact of stocking and provide guidelines for conservation and management.</p> <p>Methods</p> <p>Eighty grayling individuals were collected from four rivers (Ibar, Lim, Drina and Rzav). The mitochondrial DNA control region (CR; 595 bp of the 3'end and 74 bp of flanking tRNA) and the ATP6 gene (630 bp fragment) were sequenced for 20 individuals (five from each locality). In addition, all individuals were genotyped with 12 microsatellite loci. The diversity and structure of the populations as well as the recent and ancient population declines were studied using specialized software.</p> <p>Results</p> <p>We detected three new haplotypes in the mtDNA CR and four haplotypes in the ATP6 gene of which three had not been described before. Previously, one CR haplotype and two ATP6 gene haplotypes had been identified as allochthonous, originating from Slovenia. Reconstruction of phylogenetic relations placed the remaining two CR haplotypes from the River Danube drainage of Serbia into a new clade, which is related to the previously described sister Slovenian clade. These two clades form a new Balkan clade. Microsatellite marker analysis showed that all four populations are genetically distinct from each other without any sign of intra-population structure, although stocking of the most diverse population (Drina River) was confirmed by mtDNA analysis. Recent and historical population declines of Serbian grayling do not differ from those of other European populations.</p> <p>Conclusions</p> <p>Our study shows that (1) the Ibar, Lim and Drina Rivers grayling populations are genetically distinct from populations outside of Serbia and thus should be managed as native populations in spite of some introgression in the Drina River population and (2) the Rzav River population is not appropriate for further stocking activities since it originates from stocked Slovenian grayling. However, the Rzav River population does not represent an immediate danger to other populations because it is physically isolated from these.</p
A high-resolution radio survey of the Vela supernova remnant
This paper presents a high-resolution radio continuum (843 MHz) survey of the
Vela supernova remnant. The contrast between the structures in the central
pulsar-powered nebula of the remnant and the synchrotron radiation shell allows
the remnant to be identified morphologically as a member of the composite
class. The data are the first of a composite remnant at spatial scales
comparable with those available for the Cygnus Loop and the Crab Nebula, and
make possible a comparison of radio, optical and soft X-ray emission from the
resolved shell filaments. The survey, made with the Molonglo Observatory
Synthesis Telescope, covers an area of 50 square degrees at a resolution of
43'' x 60'', while imaging structures on scales up to 30'.Comment: 18 pages, 7 jpg figures (version with ps figures at
http://astro.berkeley.edu/~dbock/papers/); AJ, in pres
Sequential Star Formation in RCW 34: A Spectroscopic Census of the Stellar Content of High-mass Star-forming Regions
We present VLT/SINFONI integral field spectroscopy of RCW 34 along with
Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different
regions. A large bubble has been detected on the IRAC images in which a cluster
of intermediate- and low-mass class II objects is found. At the northern edge
of this bubble, an HII region is located, ionized by 3 OB stars. Intermediate
mass stars (2 - 3 Msun) are detected of G- and K- spectral type. These stars
are still in the pre-main sequence (PMS) phase. North of the HII region, a
photon-dominated region is present, marking the edge of a dense molecular cloud
traced by H2 emission. Several class 0/I objects are associated with this
cloud, indicating that star formation is still taking place. The distance to
RCW 34 is revised to 2.5 +- 0.2 kpc and an age estimate of 2 - 1 Myrs is
derived from the properties of the PMS stars inside the HII region. The most
likely scenario for the formation of the three regions is that star formation
propagates from South to North. First the bubble is formed, produced by
intermediate- and low-mass stars only, after that, the HII region is formed
from a dense core at the edge of the molecular cloud, resulting in the
expansion as a champagne flow. More recently, star formation occurred in the
rest of the molecular cloud. Two different formation scenarios are possible:
(a) The bubble with the cluster of low- and intermediate mass stars triggered
the formation of the O star at the edge of the molecular cloud which in turn
induces the current star-formation in the molecular cloud. (b) An external
triggering is responsible for the star-formation propagating from South to
North. [abridged]Comment: 19 pages, 11 figures, accepted by Ap
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