1,643 research outputs found
Other People\u27s Money: The Effects of Ownership on Compensation Strategy and Executive Pay
In this paper we develop and test hypotheses based on agency theory and managerial capitalism to address the question of whether firms\u27 compensation strategies are designed to motivate actions in the interests of equity holders or those of management. We examined differences in the organizational incentive structure of lower-level executives in management-controlled, owner controlled, and owner-managed firms. We found that when managers controlled the firm, there was pervasively weak incentive alignment for managers within the hierarchy and that, beyond base pay, they were able to extract compensation premiums through bonuses and long-term incentives, in spite of the fact that their firms did not demonstrate better economic performance than other types of firms. We were also able to demonstrate that equity holders pay substantial agency costs in management-controlled firms compared with owner-controlled firms. We end with a discussion of the organizational context for rationalizing executive compensation and the role of compensation consultants
HII Region Metallicity Distribution in the Milky Way Disk
The distribution of metals in the Galaxy provides important information about
galaxy formation and evolution. HII regions are the most luminous objects in
the Milky Way at mid-infrared to radio wavelengths and can be seen across the
entire Galactic disk. We used the NRAO Green Bank Telescope (GBT) to measure
radio recombination line and continuum emission in 81 Galactic HII regions. We
calculated LTE electron temperatures using these data. In thermal equilibrium
metal abundances are expected to set the nebular electron temperature with high
abundances producing low temperatures. Our HII region distribution covers a
large range of Galactocentric radius (5 to 22 kpc) and samples the Galactic
azimuth range 330 degree to 60 degree. Using our highest quality data (72
objects) we derived an O/H Galactocentric radial gradient of -0.0383 +/- 0.0074
dex/kpc. Combining these data with a similar survey made with the NRAO 140 Foot
telescope we get a radial gradient of -0.0446 +/- 0.0049 dex/kpc for this
larger sample of 133 nebulae. The data are well fit by a linear model and no
discontinuities are detected. Dividing our sample into three Galactic azimuth
regions produced significantly different radial gradients that range from -0.03
to -0.07 dex/kpc. These inhomogeneities suggest that metals are not well mixed
at a given radius. We stress the importance of homogeneous samples to reduce
the confusion of comparing data sets with different systematics. Galactic
chemical evolution models typically derive chemical evolution along only the
radial dimension with time. Future models should consider azimuthal evolution
as well.Comment: Accepted for publication in Ap
The chemistry of planetary nebulae and HII regions in the dwarf galaxies Sextans A and B from deep VLT spectra
Spectroscopic observations obtained with the VLT of one planetary nebula (PN)
in Sextans A and of five PNe in Sextans B and of several HII regions (HII) in
these two dwarf irregular galaxies are presented. The extended spectral
coverage, from 320.0 to 1000.0nm, and the large telescope aperture allowed us
to detect a number of emission lines, covering more than one ionization stage
for several elements (He, O, S, Ar). The electron temperature (Te) diagnostic
[OIII] line at 436.3 nm was measured in all six PNe and in several HII allowing
for an accurate determination of the ionic and total chemical abundances by
means of the Ionization Correction Factors method. For the time being, these
PNe are the farthest ones where such a direct measurement of the Te is
obtained. In addition, all PNe and HII were also modelled using the
photoionization code CLOUDY. The physico-chemical properties of PNe and HII are
presented and discussed. A small dispersion in the oxygen abundance of HII was
found in both galaxies: 12 + (O/H)=7.60.2 in SextansA, and
7.80.2 in SextansB. For the five PNe of SextansA, we find that 12 +
(O/H)=8.00.3, with a mean abundance consistent with that of HII. The
only PN known in SextansA appears to have been produced by a quite massive
progenitor, and has a significant nitrogen overabundance. In addition, its
oxygen abundance is 0.4 dex larger than the mean abundance of HII, possibly
indicating an efficient third dredge-up for massive, low-metallicity PN
progenitors. The metal enrichment of both galaxies is analyzed using these new
data.Comment: 19 pages, 11 figures, Accepted by A&
The metallicity gradient of M 33: chemical abundances of HII regions
We present spectroscopic observations of a sample of 72 emission-line
objects, including mainly HII regions, in the spiral galaxy M 33. Spectra were
obtained with the multi-object, wide field spectrograph AF2/WYFFOS at the 4.2m
WHT telescope. Line intensities, extinction, and electron density were
determined for the whole sample of objects. The aim of the present work was to
derive chemical and physical parameters of a set of HII regions, and from them
the metallicity gradient. Electron temperatures and chemical abundances were
derived for the 14 HII regions where both [OII] and [OIII] emission line fluxes
were measured, including the electron temperature sensitive emission line
[OIII] 436.3 nm and in a few cases [NII] 575.5 nm. The ionization correction
factor (ICF) method was used to derive the total chemical abundances. The
presence of abundance gradients was inferred from the radial behaviour of
several emission-line ratios, and accurately measured from chemical abundances
directly derived in 14 HII regions. The oxygen abundances of our HII regions,
located in the radial region from ~2 to ~7.2 kpc, gave an oxygen gradient
-0.054+/-0.011 dex/kpc The overall oxygen gradient for M 33 obtained using ours
and previous oxygen determinations in a large number of HII regions with direct
electron temperature determination as well as abundance in young stars
presented a two slope shape: -0.19 dex/kpc for the central regions (R<3kpc),
and -0.038dex/kpc for the outer regions (R>=3kpc).Comment: 16 pages, 14 figures, A&A accepted 10/05/200
The building up of the disk galaxy M33 and the evolution of the metallicity gradient
The evolution of radial gradients of metallicity in disk galaxies and its
relation with the disk formation are not well understood. Theoretical models of
galactic chemical evolution make contrasting predictions about the time
evolution of metallicity gradients. To test chemical evolution models and trace
the star formation and accretion history of low luminosity disk galaxies we
focus on the Local Group galaxy M33. We analyze O/H and S/H abundances in
planetary nebulae, H{\sc ii} regions, and young stars, together with known
[Fe/H] abundances in the old stellar population of M33. With a theoretical
model, we follow the time evolution of gas (diffuse and condensed in clouds),
stars, and chemical abundances in the disk of M33, assuming that the galaxy is
accreting gas from an external reservoir. Our model is able to reproduce the
available observational constraints on the distribution of gas and stars in M33
and to predict the time evolution of several chemical abundances. In
particular, we find that a model characterized by a continuous infall of gas on
the disk, at a rate of yr, almost
constant with time, can also account for the relatively high rate of star
formation and for the shallow chemical gradients. Supported by a large sample
of high resolution observations for this nearby galaxy, we conclude that the
metallicity in the disk of M33 has increased with time at all radii, with a
continuous flattening of the gradient over the last Gyr.Comment: 16 pages, 11 figures, A&A accepte
The evolution of the Galactic metallicity gradient from high-resolution spectroscopy of open clusters
Open clusters offer a unique possibility to study the time evolution of the
radial metallicity gradients of several elements in our Galaxy, because they
span large intervals in age and Galactocentric distance, and both quantities
can be more accurately derived than for field stars. We re-address the issue of
the Galactic metallicity gradient and its time evolution by comparing the
empirical gradients traced by a sample of 45 open clusters with a chemical
evolution model of the Galaxy. At variance with previous similar studies, we
have collected from the literature only abundances derived from
high--resolution spectra. The clusters have distances kpc and ages
from Myr to 11 Gyr. We also consider the -elements Si, Ca,
Ti, and the iron-peak elements Cr and Ni. The data for iron-peak and
-elements indicate a steep metallicity gradient for R_GC<12R_{\rm GC}\lesssim 12$ kpc (that we associate with an
early phase of disk formation from the collapse of the halo) and in a slow
inflow of material per unit area in the outer regions at a constant rate with
time.Comment: 16 pages, 18 figures, A&A accepte
Dynamical and chemical evolution of NGC1569
Blue Compact Dwarf and Dwarf Irregular galaxies are generally believed to be
unevolved objects, due to their blue colors, compact appearance and large gas
fractions. Many of these objects show an ongoing intense burst of star
formation or have experienced it in the recent past. By means of 2-D
hydrodynamical simulations, coupled with detailed chemical yields originating
from SNeII, SNeIa, and intermediate-mass stars, we study the dynamical and
chemical evolution of model galaxies with structural parameters similar to
NGC1569, a prototypical starburst galaxy. A burst of star formation with short
duration is not able to account for the chemical and morphological properties
of this galaxy. The best way to reproduce the chemical composition of this
object is by assuming long-lasting episodes of star formation and a more recent
burst, separated from the previous episodes by a short quiescent period. The
last burst of star formation, in most of the explored cases, does not affect
the chemical composition of the galaxy, since the enriched gas produced by
young stars is in a too hot phase to be detectable with the optical
spectroscopy. Models assuming the infall of a big cloud towards the center of
the galaxy reproduce the chemical composition of the NGC1569, but the pressure
exercised by the cloud hampers the expansion of the galactic wind, at variance
with what observed in NGC1569.Comment: 16 pages, 10 figures, A&A accepte
Planetary nebulae: abundances and abundance gradients
In this work, a review is given of some recent results and problems involved in the determination of chemical abundances of galactic planetary nebulae, particularly regarding disk and bulge objects
Variations on a theme: diversification of cuticular hydrocarbons in a clade of cactophilic Drosophila
<p>Abstract</p> <p>Background</p> <p>We characterized variation and chemical composition of epicuticular hydrocarbons (CHCs) in the seven species of the <it>Drosophila buzzatii </it>cluster with gas chromatography/mass spectrometry. Despite the critical role of CHCs in providing resistance to desiccation and involvement in communication, such as courtship behavior, mating, and aggregation, few studies have investigated how CHC profiles evolve within and between species in a phylogenetic context. We analyzed quantitative differences in CHC profiles in populations of the <it>D. buzzatii </it>species cluster in order to assess the concordance of CHC differentiation with species divergence.</p> <p>Results</p> <p>Thirty-six CHC components were scored in single fly extracts with carbon chain lengths ranging from C<sub>29 </sub>to C<sub>39</sub>, including methyl-branched alkanes, <it>n</it>-alkenes, and alkadienes. Multivariate analysis of variance revealed that CHC amounts were significantly different among all species and canonical discriminant function (CDF) analysis resolved all species into distinct, non-overlapping groups. Significant intraspecific variation was found in different populations of <it>D. serido </it>suggesting that this taxon is comprised of at least two species. We summarized CHC variation using CDF analysis and mapped the first five CHC canonical variates (CVs) onto an independently derived <it>period </it>(<it>per</it>) gene + chromosome inversion + mtDNA COI gene for each sex. We found that the COI sequences were not phylogenetically informative due to introgression between some species, so only <it>per </it>+ inversion data were used. Positive phylogenetic signal was observed mainly for CV1 when parsimony methods and the test for serial independence (TFSI) were used. These results changed when no outgroup species were included in the analysis and phylogenetic signal was then observed for female CV3 and/or CV4 and male CV4 and CV5. Finally, removal of divergent populations of <it>D. serido </it>significantly increased the amount of phylogenetic signal as up to four out of five CVs then displayed positive phylogenetic signal.</p> <p>Conclusions</p> <p>CHCs were conserved among species while quantitative differences in CHC profiles between populations and species were statistically significant. Most CHCs were species-, population-, and sex-specific. Mapping CHCs onto an independently derived phylogeny revealed that a significant portion of CHC variation was explained by species' systematic affinities indicating phylogenetic conservatism in the evolution of these hydrocarbon arrays, presumptive waterproofing compounds and courtship signals as in many other drosophilid species.</p
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