4,386 research outputs found
The lithium isotope ratio in the metal-poor halo star G271-162 from VLT/UVES observations
A high resolution (R = 110.000), very high S/N (>600) spectrum of the
metal-poor turnoff star G271-162 has been obtained in connection with the
commissioning of UVES at VLT/Kueyen. Using both 1D hydrostatic and 3D
hydrodynamical model atmospheres, the lithium isotope ratio has been estimated
from the LiI 670.8 nm line by means of spectral synthesis. The necessary
stellar line broadening (1D: macroturbulence + rotation, 3D: rotation) has been
determined from unblended KI, CaI and FeI lines. The 3D line profiles agree
very well with the observed profiles, including the characteristic line
asymmetries. Both the 1D and 3D analyses reveal a possible detection of 6Li in
G271-162, 6Li/7Li = 0.02 +-0.01 (one sigma). It is discussed if the smaller
amount of 6Li in G271-162 than in the similar halo star HD84937 could be due to
differences in stellar mass and/or metallicity or whether it may reflect an
intrinsic scatter of the Li isotope ratio in the ISM at a given metallicity.Comment: 5 pages with 6 figures. Accepted as a letter in A&
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
Beyond electronic disintermediation through multi-agent systems
Supply chain management represents a critical competency
in today's global business environment and has been the
focus of considerable, but mixed, information systems
research. The research described in this paper builds on
work in multi-agent systems to argue that intelligent agents
offer excellent potential and capability for supply chain
management, and contributes to discussion and theory
pertaining to electronic markets and supply chain
disintermediation. Argues that the knowledge associated
with intermediation work represents a key mediating
variable between disintermediating technology and supply
chain efficacy and discusses how intelligent agent
technology can be employed to both intermediate and
disintermediate the supply chain, attaining the cost and
cycle-time benefits of disintermediation without the
attendant loss of human knowledge and expertise. The
paper outlines a number of implications for theory and
practice in information systems, and it formalizes some
important research questions through a contingency
framework to help stimulate and guide future work along
these lines
Toward enterprise process engineering: configuration measurement and analysis
The enterprise process has become a central unit of analysis in management. But a dearth of theory and methods to predict process performance is available to the enterprise manager. With the proposition that enterprise process design represents an engineering problem as much as a managerial one, we focus on the process configuration and measurement to overcome design limitations that currently confront the enterprise manager. Building on seminal work for process description and comparison, and employing Graph Theory and Measurement Theory, we integrate this work and demonstrate useful analytical properties associated with the kinds of measures proposed (e.g., ratio scales). This represents a new result, which extends the prior research on enterprise process design and makes a contribution to our understanding in management science. Further, with parallels to the predictive capability enjoyed by engineers who design physical artifacts, we indicate how enterprise process configuration measures can be used to hypothesize relations with respect to enterprise performance. And we suggest how enterprise managers may design processes in a deductive manner-working backward from performance requirements to determine configuration parameters required for designs to meet performance goals. These represent new ca abilities not previously available to the enterprise manager as well as another contribution of the resent research.Approved for public release; distribution is unlimited
O/Fe in metal-poor main sequence and subgiant stars
A study of the O/Fe ratio in metal-poor main sequence and subgiant stars is
presented using the [OI] 6300A line, the OI 7774A triplet, and a selection of
weak FeII lines observed on high-resolution spectra acquired with the VLT UVES
spectrograph. The [OI] line is detected in the spectra of 18 stars with -0.5 <
[Fe/H] < -2.4, and the triplet is observed for 15 stars with [Fe/H] ranging
from -1.0 to -2.7. The abundance analysis was made first using standard model
atmospheres taking into account non-LTE effects on the triplet: the [OI] line
and the triplet give consistent results with [O/Fe] increasing quasi-linearly
with decreasing [Fe/H] reaching [O/Fe] ~ +0.7 at [Fe/H] = -2.5. When
hydrodynamical model atmospheres representing stellar granulation in dwarf and
subgiant stars replace standard models, the [O/Fe] from the [OI] and FeII lines
is decreased by an amount which increases with decreasing [Fe/H]. The [O/Fe] vs
[Fe/H] relation remains quasi-linear extending to [O/Fe] ~ +0.5 at [Fe/H] =
-2.5, but with a tendency of a plateau with [O/Fe] ~ +0.3 for -2.0 < [Fe/H] <
-1.0, and a hint of cosmic scatter in [O/Fe] at [Fe/H] ~ -1.0. Use of the
hydrodynamical models disturbs the broad agreement between the oxygen
abundances from the [OI], OI, and OH lines, but 3D non-LTE effects may serve to
erase these differences.Comment: ps file, 18 pages (including 10 figures) - Accepted for publication
in A&
Toward an Operational Proxy for Acquisition Workforce Quality: Measuring Dynamic Knowledge and Performance at the Tactical Edges of Organizations
Naval Postgraduate School Acquisition Research Progra
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
Manned-Unmanned Teaming in Distributed Maritime Operations
NPS NRP Project PosterManned-Unmanned Teaming in Distributed Maritime OperationsN9 - Warfare SystemsThis research is supported by funding from the Naval Postgraduate School, Naval Research Program (PE 0605853N/2098). https://nps.edu/nrpChief of Naval Operations (CNO)Approved for public release. Distribution is unlimited.
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