2,305 research outputs found
A Search for Biomolecules in Sagittarius B2 (LMH) with the ATCA
We have used the Australia Telescope Compact Array to conduct a search for
the simplest amino acid, glycine (conformers I and II), and the simple chiral
molecule propylene oxide at 3-mm in the Sgr B2 LMH. We searched 15 portions of
spectrum between 85 and 91 GHz, each of 64 MHz bandwidth, and detected 58
emission features and 21 absorption features, giving a line density of 75
emission lines and 25 absorption lines per GHz stronger than the 5 sigma level
of 110 mJy. Of these, 19 are transitions previously detected in the
interstellar medium, and we have made tentative assignments of a further 23
features to molecular transitions. However, as many of these involve molecules
not previously detected in the ISM, these assignments cannot be regarded with
confidence. Given the median line width of 6.5 km/s in Sgr B2 LMH, we find that
the spectra have reached a level where there is line confusion, with about 1/5
of the band being covered with lines. Although we did not confidently detect
either glycine or propylene oxide, we can set 3 sigma upper limits for most
transitions searched. We also show that if glycine is present in the Sgr B2 LMH
at the level of N = 4 x 10^{14} cm^{-2} found by Kuan et al. (2003) in their
reported detection of glycine, it should have been easily detected with the
ATCA synthesized beam size of 17.0 x 3.4 arcsec^{2}, if it were confined to the
scale of the LMH continuum source (< 5 arcsec). This thus puts a strong upper
limit on any small-scale glycine emission in Sgr B2, for both of conformers I
and II.Comment: 12 pages, 2 figures, 5 tables, accepted by MNRA
Communication satisfaction, job satisfaction, organisational commitment and intention to leave
The retention of highly motivated, skilled and committed employees is a major concern by organisations to achieve a competitive advantage. The turnover intentions of human capital are of interest to managers, employees, and organisations today. This study explores a theoretical model of turnover intentions that included three proximal variables, job satisfaction, affective and continuance commitment, the distal variables of subordinate communication, horizontal communication, personal feedback, media quality, communication climate, supervisor communication, job-related communication, and management communication, with turnover intentions. A questionnaire was completed by 101 participants of a rental firm in New Zealand. Job satisfaction, affective commitment, continuance commitment, subordinate communication, horizontal communication, personal feedback, media quality, communication climate, supervisor communication, job-related communication, and management communication correlated with turnover intentions. The results of the mediated regression analysis indicated that job satisfaction, affective commitment, and continuance commitment are significant mediators between the eight distal (organisational communication) variables, with turnover intentions.
This study highlights the necessity for managers to develop good quality relationships with their employees to improve the quality of their communication, to foster job satisfaction, affective commitment, and continuance commitment to reduce turnover intentions. The conclusion of this study discusses the practical implications for managers, and organisations and the direction for future research
Multi-transition study and new detections of class II methanol masers
We have used the ATNF Mopra antenna and the SEST antenna to search in the
directions of several class II methanol maser sources for emission from six
methanol transitions in the frequency range 85-115 GHz. The transitions were
selected from excitation studies as potential maser candidates. Methanol
emission at one or more frequencies was detected from five of the maser
sources, as well as from Orion KL. Although the lines are weak, we find
evidence of maser origin for three new lines in G345.01+1.79, and possibly one
new line in G9.62+0.20.
The observations, together with published maser observations at other
frequencies, are compared with methanol maser modelling for G345.01+1.79 and
NGC6334F. We find that the majority of observations in both sources are
consistent with a warm dust (175 K) pumping model at hydrogen density ~10^6
cm^-3 and methanol column density ~5 x 10^17 cm^-2. The substantial differences
between the maser spectra in the two sources can be attributed to the geometry
of the maser region.Comment: 13 pages, 6 figures, Accepted for publication in MNRA
Class I and Class II methanol masers in high-mass star forming regions
Among the tracers of the earliest phases in the massive star formation
process, methanol masers have gained increasing importance. The
phenomenological distinction between Class I and II methanol masers is based on
their spatial association with objects such as jets, cores, and ultracompact
HII regions, but is also believed to correspond to different pumping
mechanisms: radiation for Class II masers, collisions for Class I masers. In
this work, we have surveyed a large sample of massive star forming regions -
296 objects divided into two groups named 'High' and 'Low' according to their
[25-12] and [60-12] IRAS colours - in Class I and II methanol masers. Previous
studies indicate that the High sources are likely more evolved. Therefore, the
sample can be used to assess the existence of a sequence for the occurrence of
Class I and II methanol masers during the evolution of a massive star forming
region. We observed the 6 GHz (Class II) CH3OH maser with the Effelsberg 100-m
telescope, and the 44 GHz and 95 GHz (Class I) CH3OH masers with the Nobeyama
45-m telescope. We have detected: 55 sources in the Class II line (12 new
detections); 27 sources in the 44 GHz Class I line (17 new detections); 11
sources in the 95 GHz Class I line (all except one are new detections). Our
statistical analysis shows that the ratio between the detection rates of Class
II and Class I methanol masers is basically the same in High and Low sources.
Therefore, both masers are equally associated with each evolutionary phase. In
contrast, all maser species have about 3 times higher detection rates in High
than in Low sources. This might indicate that the phenomena that originate all
masers become progressively more active with time, during the earliest
evolutionary phases of a high-mass star forming region.Comment: 30 pages including Appendices, 11 figures, accepted for publication
in Astronomy & Astrophysic
VLBI study of maser kinematics in high-mass SFRs. II. G23.01-0.41
The present paper focuses on the high-mass star-forming region G23.01-0.41.
Methods: Using the VLBA and the EVN arrays, we conducted phase-referenced
observations of the three most powerful maser species in G23.01-0.41: H2O at
22.2 GHz (4 epochs), CH3OH at 6.7 GHz (3 epochs), and OH at 1.665 GHz (1
epoch). In addition, we performed high-resolution (> 0".1), high-sensitivity (<
0.1 mJy) VLA observations of the radio continuum emission from the HMC at 1.3
and 3.6 cm. Results: We have detected H2O, CH3OH, and OH maser emission
clustered within 2000 AU from the center of a flattened HMC, oriented SE-NW,
from which emerges a massive 12CO outflow, elongated NE-SW, extended up to the
pc-scale. Although the three maser species show a clearly different spatial and
velocity distribution and sample distinct environments around the massive YSO,
the spatial symmetry and velocity field of each maser specie can be explained
in terms of expansion from a common center, which possibly denotes the position
of the YSO driving the maser motion. Water masers trace both a fast shock (up
to 50 km/s) closer to the YSO, powered by a wide-angle wind, and a slower (20
km/s) bipolar jet, at the base of the large-scale outflow. Since the compact
free-free emission is found offset from the putative location of the YSO along
a direction consistent with that of the maser jet axis, we interpret the radio
continuum in terms of a thermal jet. The velocity field of methanol masers can
be explained in terms of a composition of slow (4 km/s in amplitude) motions of
radial expansion and rotation about an axis approximately parallel to the maser
jet. Finally, the distribution of line of sight velocities of the hydroxyl
masers suggests that they can trace gas less dense (n(H2) < 10^6 cm^-3) and
more distant from the YSO than that traced by the water and methanol masers,
which is expanding toward the observer. (Abridged)Comment: 23 pages, 8 figures, 4 tables, accepted by Astronomy and Astrophysic
Selforganized 3-band structure of the doped fermionic Ising spin glass
The fermionic Ising spin glass is analyzed for arbitrary filling and for all
temperatures. A selforganized 3-band structure of the model is obtained in the
magnetically ordered phase. Deviation from half filling generates a central
nonmagnetic band, which becomes sharply separated at T=0 by (pseudo)gaps from
upper and lower magnetic bands. Replica symmetry breaking effects are derived
for several observables and correlations. They determine the shape of the
3-band DoS, and, for given chemical potential, influence the fermion filling
strongly in the low temperature regime.Comment: 13 page
A search for 4750- and 4765-MHz OH masers in Southern Star Forming Regions
We have used the Australia Telescope Compact Array (ATCA) to make a sensitive
(5- 100 mJy) search for maser emission from the 4765-MHz
F=10 transition of OH. Fifty five star formation regions
were searched and maser emission with a peak flux density in excess of 100 mJy
was detected toward fourteen sites, with ten of these being new discoveries. In
addition we observed the 4750-MHz F=11 transition towards a
sample of star formation regions known to contain 1720-MHz OH masers, detecting
marginal maser emission from G348.550-0.979. If confirmed this would be only
the second maser discovered from this transition. The occurrence of 4765-MHz OH
maser emission accompanying 1720-MHz OH masers in a small number of well
studied star formation regions has lead to a general perception in the
literature that the two transitions favour similar physical conditions. Our
search has found that the presence of the excited-state 6035-MHz OH transition
is a much better predictor of 4765-MHz OH maser emission from the same region
than is 1720-MHz OH maser emission. Combining our results with those of
previous high resolution observations of other OH transitions we have examined
the published theoretical models of OH masers and find that none of them
predict any conditions in which the 1665-, 6035- and 4765-MHz transitions are
simultaneously inverted.
Erratum abstract:
Dodson & Ellingsen (2002) included several observations with significant
pointing errors, invalidating the upper limits found in these directions. These
have now been reobserved or recalculated. A new table of upper limits has been
generated, and two more masers that would have been seen have been found.Comment: Included an Erratum with Max as another author. This erratum was
rejected by MNRAS (Feb 04) as it contained too much data. Resubmitted as a
paper (Jun 04). Rejected (Sep 04) it had too little data. Resubmitted as
reduced erratum (Apr 05). Still waitin
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