4,769 research outputs found
Identifying the outflow driving sources in Orion-KL
The enigmatic outflows of the Orion-KL region have raised discussions about
their potential driving sources for several decades. Here, we present C18O(2-1)
observations combined from the Submillimeter Array and the IRAM30m telescope.
The molecular gas is associated on large scales with the famous
northwest-southeast high-velocity outflow whereas the high-velocity gas on
small spatial scales traces back to the recently identified submm source SMA1.
Therefore, we infer that SMA1 may host the driving source of this outflow.
Based on the previously published thermal and maser SiO data, source I is the
prime candidate to drive the northeast-southwest low-velocity outflow. The
source SMA1 is peculiar because it is only detected in several submm wavelength
bands but neither in the infrared nor cm regime. We discuss that it may be a
very young intermediate- to high-mass protostar. The estimated outflow masses
are high whereas the dynamical time-scale of the outflow is short of the order
10^3yrs.Comment: 4 pages, 3 figures, Astrophysical Journal Letters in press, a
high-resolution version is available at
http://www.mpia.de/homes/beuther/papers.htm
The Effects of Relaxin on The Composition of Bovine Milk
Protoplasm is a fragile substance keeping its homeostatic properties by many physiochemical phenomena. Much is known about the properties of protoplasm; but it is, perhaps, only meager when compared to what is yet to be learned. Such physical changes as electrical impulses, diffusion, and oxidation – to mention a few – are necessary for protoplasm to retain its integrity. In higher animals, particularity, for our purpose, mammals, protoplasm is sustained by different body system working harmoniously together to supply raw materials that remove waste, and govern all endeavors. One should not infer that single called animals have a more simple type of protoplasm than multicellular animals, for the composition of all protoplasm is essentially the same. Single called animals differ from multicellular animals in their methods of attaining protoplasmic precursors to the cell proper and removal of waste. The major system of the body that help maintain homeostasis are: circulatory, respiratory, nervous muscle, urinary, and endocrine. The endocrine system supplies hormones which are chemicals that function as an indispensable link in the chain of events that occur in the dynamics of protoplasm and hence, the whole organism. Some of the hormones have been vaguely identified, their properties understood, and their function know. Some are a complete mystery; others are just in the infancy of scientific study. The major work presented in this thesis is an investigation into the mysteries of one such hormone, relaxin
Non-LTE analysis of copper abundances for the two distinct halo populations in the solar neighborhood
Two distinct halo populations were found in the solar neighborhood by a
series of works. They can be clearly separated by [alpha\Fe] and several other
elemental abundance ratios including [Cu/Fe]. Very recently, a non-local
thermodynamic equilibrium (non-LTE) study revealed that relatively large
departures exist between LTE and non-LTE results in copper abundance analysis.
We aim to derive the copper abundances for the stars from the sample of Nissen
et al (2010) with both LTE and non-LTE calculations. Based on our results, we
study the non-LTE effects of copper and investigate whether the high-alpha
population can still be distinguished from the low-alpha population in the
non-LTE [Cu/Fe] results. Our differential abundance ratios are derived from the
high-resolution spectra collected from VLT/UVES and NOT/FIES spectrographs.
Applying the MAFAGS opacity sampling atmospheric models and spectrum synthesis
method, we derive the non-LTE copper abundances based on the new atomic model
with current atomic data obtained from both laboratory and theoretical
calculations. The copper abundances determined from non-LTE calculations are
increased by 0.01 to 0.2 dex depending on the stellar parameters compared with
the LTE results. The non-LTE [Cu/Fe] trend is much flatter than the LTE one in
the metallicity range -1.6<[Fe/H]<-0.8. Taking non-LTE effects into
consideration, the high- and low-alpha stars still show distinguishable copper
abundances, which appear even more clear in a diagram of non-LTE [Cu/Fe] versus
[Fe/H]. The non-LTE effects are strong for copper, especially in metal-poor
stars. Our results confirmed that there are two distinct halo populations in
the solar neighborhood. The dichotomy in copper abundance is a peculiar feature
of each population, suggesting that they formed in different environments and
evolved obeying diverse scenarios.Comment: 9 pages, 7 figures, 2 table
Chemical composition of 90 F and G disk dwarfs
High resolution, high S/N spectra have been obtained for a sample of 90 F and
G main-sequence disk stars covering the metallicity range -1.0 < [Fe/H] < +0.1,
and have been analysed in a parallel way to the work of Edvardsson et al.
(1993). Effective temperatures are based on the Alonso et al. (1996)
calibration of color indices and surface gravities are calculated from
Hipparcos parallaxes, which also allow more accurate ages to be calculated. In
addition, more reliable kinematical parameters are derived from Hipparcos
distances and proper motions. Finally, a larger spectral coverage, 5600 - 8800
A, makes it possible to improve the abundance accuracy by studying more lines
and to discuss several elements not included in the work of Edvardsson et al.
The present paper provides the data and discusses some general results of the
abundance survey. A group of stars in the metallicity range of -1.0 < [Fe/H] <
-0.6 having a small mean Galactocentric distance in the stellar orbits, Rm < 7
kpc, are shown to be older than the other disk stars and probably belong to the
thick disk. Excluding these stars, a slight decreasing trend of [Fe/H] with
increasing Rm and age is found, but a large scatter in [Fe/H] (up to 0.5 dex)
is present at a given age and Rm. The derived trends of O, Mg, Si, Ca, Ti, Ni
and Ba as a function of [Fe/H] agree rather well with those of Edvardsson et
al., but the overabundance of Na and Al for metal-poor stars found in their
work is not confirmed. Furthermore, the Galactic evolution of elements not
included in Edvardsson et al., K, V and Cr, is studied.Comment: 16 pages with 10 figures. Accepted for publication in A&A
Observations of spatial and velocity structure in the Orion Molecular Cloud
Observations are reported of H2 IR emission in the S(1) v=1-0 line at 2.121
microns in the Orion Molecular Cloud, OMC1, using the GriF instrument on the
Canada-France-Hawaii Telescope. GriF is a combination of adaptive optics and
Fabry-Perot interferometry, yielding a spatial resolution of 0.15" to 0.18" and
a velocity discrimination as high as 1 km/s. Thanks to the high spatial and
velocity resolution of the GriF data, 193 bright H2 emission regions can be
identified in OMC1. The general characteristics of these features are described
in terms of radial velocities, brightness and spatial displacement of maxima of
velocity and brightness, the latter to yield the orientation of flows in the
plane of the sky. Strong spatial correlation between velocity and bright H2
emission is found and serves to identify many features as shocks. Important
results are: (i) velocities of the excited gas illustrate the presence of a
zone to the south of BN-IRc2 and Peak 1, and the west of Peak 2, where there is
a powerful blue-shifted outflow with an average velocity of -18 km/s. This is
shown to be the NIR counterpart of an outflow identified in the radio from
source I, a very young O-star. (ii) There is a band of weak velocity features
(<5 km/s) in Peak 1 which may share a common origin through an explosive event,
in the BN-IRc2 region, with the fast-moving fingers (or bullets) to the NW of
OMC1. (iii) A proportion of the flows are likely to represent sites of low mass
star formation and several regions show multiple outflows, probably indicative
of multiple star formation within OMC1. The high spatial and velocity
resolution of the GriF data show these and other features in more detail than
has previously been possible.Comment: 27 pages, 19 figures, submitted to A&A Version 2: Several additions,
including a section on protostellar candidates in OMC1, have been made based
on the referee's suggestions v3: corrected typograph
Cosmological Cosmic Rays and the observed Li6 plateau in metal poor halo stars
Very recent observations of the Li6 isotope in halo stars reveal a Li6
plateau about 1000 times above the predicted BBN abundance. We calculate the
evolution of Li6 versus redshift generated from an initial burst of
cosmological cosmic rays (CCRs) up to the formation of the Galaxy. We show that
the pregalactic production of the Li6 isotope can account for the Li6 plateau
observed in metal poor halo stars without additional over-production of Li7.
The derived relation between the amplitude of the CCR energy spectra and the
redshift of the initial CCR production puts constraints on the physics and
history of the objects, such as pop III stars, responsible for these early
cosmic rays. Consequently, we consider the evolution of Li6 in the Galaxy.
Since Li6 is also produced in Galactic cosmic ray nucleosynthesis, we argue
that halo stars with metallicities between [Fe/H] = -2 and -1, must be somewhat
depleted in Li6.Comment: 8 pages, 6 figures, version accepted for publication in Ap
Trust-mistrust as a design contingency: laboratory experimentation in a counterterrorism context
Trust research assumes organizational managers ought to establish high levels of trust. Research also suggests trust is decreasing and therefor raises an important management dilemma. We study trust from a contingency theory framework and hypothesize that trust levels may vary depending on different organizational designs. Using the ELICIT multiplayer intelligence game we conduct laboratory experiments to examine the effect of trust levels and organizational design on performance. Results are mixed: trust and organizational design have strong interactions, and high levels of trust do not necessarily equate to good performance.recommended for Best Paper Award
Augmented cerebral mitochondrial function and hippocampal ketone body metabolism in Db/db mice
- …