6,025 research outputs found
Hostile Share Acquisitions and Corporate Governance: A Framework for Evaluating Antitakeover Activities
In recent years, there has been a significant increase in the number of hostile share acquisitions of American businesses. The authors examine the validity of the various defensive measures employed by target companies to defeat or deter a hostile takeover bid. They argue that antitakeover activity should not be viewed as a separate subset of legal analysis; rather, it should be analyzed according to four traditional principles of corporate governance: (1) the discretion afforded corporate management by the business judgment rule; (2) the prohibition against discriminating between members of the same class of shareholders; (3) the prohibition against shifting control from the shareholders to the board of directors for actions reserved by statute to the shareholders; and (4) the prohibition against shifting control from a majority to a minority of shareholders for decisions reserved by statute to the majority. Moreover, the authors assert that even if a court uses these principles of corporate goverance as the basis for its decision, the court\u27s analysis is still incomplete if it focuses only on the target board\u27s initial decision to resist a hostile share acquisition. Rather, a court must undertake a two-step analysis, whereby it looks first at the target board\u27s initial decision to resist the hostile takeover, and second, to the means employed by the target board to effectuate that decision
Massive molecular outflows at high spatial resolution
We present high-spatial resolution Plateau de Bure Interferometer CO(2-1) and
SiO(2-1) observations of one intermediate-mass and one high-mass star-forming
region. The intermediate-mass region IRAS20293+3952 exhibits four molecular
outflows, one being as collimated as the highly collimated jet-like outflows
observed in low-mass star formation sources. Furthermore, comparing the data
with additional infrared H2 and cm observations we see indications that the
nearby ultracompact HII region triggers a shock wave interacting with the
outflow. The high-mass region IRAS19217+1651 exhibits a bipolar outflow as well
and the region is dominated by the central driving source. Adding two more
sources from the literature, we compare position-velocity diagrams of the
intermediate- to high-mass sources with previous studies in the low-mass
regime. We find similar kinematic signatures, some sources can be explained by
jet-driven outflows whereas other are better constrained by wind-driven models.
The data also allow to estimate accretion rates varying from a few times
10^{-5}Msun/yr for the intermediate-mass sources to a few times 10^{-4}Msun/yr
for the high-mass source, consistent with models explaining star formation of
all masses via accretion processes.Comment: 14 pages text, 4 tables, 8 figures, accepted for Ap
Void Statistics in Large Galaxy Redshift Surveys: Does Halo Occupation of Field Galaxies Depend on Environment?
We use measurements of the projected galaxy correlation function w_p and
galaxy void statistics to test whether the galaxy content of halos of fixed
mass is systematically different in low density environments. We present new
measurements of the void probability function (VPF) and underdensity
probability function (UPF) from Data Release Four of the Sloan Digital Sky
Survey, as well as new measurements of the VPF from the full data release of
the Two-Degree Field Galaxy Redshift Survey. We compare these measurements to
predictions calculated from models of the Halo Occupation Distribution (HOD)
that are constrained to match both w_p and the space density of galaxies. The
standard implementation of the HOD assumes that galaxy occupation depends on
halo mass only, and is independent of local environment. For luminosity-defined
samples, we find that the standard HOD prediction is a good match to the
observations, and the data exclude models in which galaxy formation efficiency
is reduced in low-density environments. More remarkably, we find that the void
statistics of red and blue galaxies (at L ~ 0.4L_*) are perfectly predicted by
standard HOD models matched to the correlation function of these samples,
ruling out "assembly bias" models in which galaxy color is correlated with
large-scale environment at fixed halo mass. We conclude that the luminosity and
color of field galaxies are determined predominantly by the mass of the halo in
which they reside and have little direct dependence on the environment in which
the host halo formed. In broader terms, our results show that the sizes and
emptiness of voids found in the distribution of L > 0.2L_* galaxies are in
excellent agreement with the predictions of a standard cosmological model with
a simple connection between galaxies and dark matter halos. (abridged)Comment: 20 emulateapj pages, 9 figures. submitted to Ap
Observations on the Formation of Massive Stars by Accretion
Observations of the H66a recombination line from the ionized gas in the
cluster of newly formed massive stars, G10.6-0.4, show that most of the
continuum emission derives from the dense gas in an ionized accretion flow that
forms an ionized disk or torus around a group of stars in the center of the
cluster. The inward motion observed in the accretion flow suggests that despite
the equivalent luminosity and ionizing radiation of several O stars, neither
radiation pressure nor thermal pressure has reversed the accretion flow. The
observations indicate why the radiation pressure of the stars and the thermal
pressure of the HII region are not effective in reversing the accretion flow.
The observed rate of the accretion flow, 0.001 solar masses/yr, is sufficient
to form massive stars within the time scale imposed by their short main
sequence lifetimes. A simple model of disk accretion relates quenched HII
regions, trapped hypercompact HII regions, and photo-evaporating disks in an
evolutionary sequence
Probing dark matter haloes with satellite kinematics
Using detailed mock galaxy redshift surveys (MGRSs) we investigate to what extent the kinematics of large samples of satellite galaxies extracted from flux-limited surveys can be used to constrain halo masses. Unlike previous studies, which focused only on satellites around relatively isolated host galaxies, we try to recover the average velocity dispersion of satellite galaxies in all haloes, as a function of the luminosity of the host galaxy. We show that previous host-satellite selection criteria (SC) yield relatively large fractions of interlopers and with a velocity distribution that, contrary to what has been assumed in the past, differs strongly from uniform. We show that with an iterative, adaptive selection criterion one can obtain large samples of hosts and satellites, with strongly reduced interloper fractions, that allow an accurate measurement of σsat(Lhost) over 2.5 orders of magnitude in host luminosity. We use the conditional luminosity function (CLF) to make predictions and show that satellite weighting, which occurs naturally when stacking many host-satellite pairs to increase the signal-to-noise ratio, introduces a bias towards higher σsat(Lhost) compared to the true, host-averaged mean. A further bias, in the same direction, is introduced when using flux-limited, rather than volume-limited, surveys. We apply our adaptive selection criterion to the Two Degree Field Galaxy Redshift Survey (2dFGRS) and obtain a sample of 12 569 satellite galaxies and 8132 host galaxies. We show that the kinematics of these satellite galaxies are in excellent agreement with the predictions based on the CLF, after taking account of the various biases. We thus conclude that there is independent dynamical evidence to support the mass-to-light ratios predicted by the CLF formalis
The abundance and radial distribution of satellite galaxies
Using detailed mock galaxy redshift surveys (MGRSs) we investigate the abundance and radial distribution of satellite galaxies. The mock surveys are constructed using large numerical simulations and the conditional luminosity function (CLF), and are compared against data from the Two Degree Field Galaxy Redshift Survey (2dFGRS). We use Monte Carlo Markov chains to explore the full posterior distribution of the CLF parameter space, and show that the average relation between light and mass is tightly constrained and in excellent agreement with our previous models and with that of Vale & Ostriker. The radial number density distribution of satellite galaxies in the 2dFGRS reveals a pronounced absence of satellites at small projected separations from their host galaxies. This is (at least partly) owing to the overlap and merging of galaxy images in the 2dFGRS parent catalogue. Owing to the resulting close-pair incompleteness we are unfortunately unable to put meaningful constraints on the radial distribution of satellite galaxies; the data are consistent with a radial number density distribution that follows that of the dark matter particles, but we cannot rule out alternatives with a constant number density core. Marginalizing over the full CLF parameter space, we show that in a ΛCDM concordance cosmology the observed abundances of host and satellite galaxies in the 2dFGRS indicate a power spectrum normalization of σ8 ⋍ 0.7. The same cosmology but with σ8= 0.9 is unable to match simultaneously the abundances of host and satellite galaxies. This confirms our previous conclusions based on the pairwise peculiar velocity dispersions and the group multiplicity functio
Prevalência e formas clínicas de Trypanosoma cruzi em candidatos a doadores de sangue no Brasil
A prevalência e a manifestação das formas clinicas de Trypanosoma cruzi foram avaliadas em candidatos a doadores de sangue atendidos em um hospital geral de Nova Iguaçu, Rio de Janeiro, Brasil, no período de janeiro de 1997 a abril de 1999. A pesquisa sorológica foi realizada por meio do teste de hemaglutinação indireta e confirmada pelo ELISA. Os dados foram coletados considerando os exames clínicos, eletrocardiograma convencional, radiografia de tórax e ecocardiografia. Os resultados demonstraram que, apesar da prevalência ser de 1,17% (128 pacientes), principalmente entre homens com idade igual ou superior a 40 anos, 70,8%, principalmente de homens entre 19 e 39 anos, demonstraram alterações que permitiram o diagnóstico de cardiopatias e/ou esofagopatias, ratificando mais uma vez sua importância nos centros urbanos.The prevalence and clinical forms of Trypanosoma cruzi were evaluated among blood donor candidates attended at a general hospital in Rio de Janeiro, Brazil, from January 1997 to April 1999. The investigation was done by means of the indirect hemagglutination test and was confirmed via ELISA. Data were collected from clinical examinations, conventional electrocardiogram, chest radiography and echocar-diography. The results showed that despite Trypanosoma cruzi prevalence of 1.17% (128 patients), mainly in males aged 40 years or over, 70.8% of these patients, mainly males aged 19 to 39 years, demonstrated abnormalities that allowed the diagnosis of cardiopathy and/or esophagopathy. This once again corroborates the importance of Trypanosoma cruzi infection in urban centers
Dense ion clouds of 0.1 ? 2 keV ions inside the CPS-region observed by Astrid-2
International audienceData from the Astrid-2 satellite taken between April and July 1999 show several examples of dense ion clouds in the 0.1?2 keV energy range inside the inner mag-netosphere, both in the northern and southern hemispheres. These inner magnetospheric ion clouds are found predomi-nantly in the early morning sector, suggesting that they could have originated from substorm-related ion injections on the night side. However, their location and density show no cor-relation with Kp, and their energy-latitude dispersion is not easily reproduced by a simple particle drift model. There-fore, these ion clouds are not necessarily caused by substorm-related ion injections. Alternative explanations for the ion clouds are the direct solar wind injections and up-welling ions from the other hemisphere. These explanations do not, however, account for all of the observations
Multiple outflows in IRAS 19410+2336
PdBI high-spatial resolution CO observations combined with near-infrared H2
data disentangle at least 7 (maybe even 9) molecular outflows in the massive
star-forming region IRAS19410+2336. Position-velocity diagrams of the outflows
reveal Hubble-like relationships similar to outflows driven by low-mass
objects. Estimated accretion rates are of the order 10^-4 Msun/yr, sufficiently
high to overcome the radiation pressure and form massive stars via
disk-mediated accretion processes. The single-dish large-scale mm continuum
cores fragment into several compact condensations at the higher spatial
resolution of the PdBI which is expected due to the clustering in massive star
formation. While single-dish data give a simplified picture of the source,
sufficiently high spatial resolution resolves the structures into outflows
resembling those of low-mass star-forming cores. We interpret this as further
support for the hypothesis that massive stars do form via disk-accretion
processes similar to low-mass stars.Comment: 10 pages, 4 figures, higher resolution version of images at
http://cfa-www.harvard.edu/~hbeuther/. A&A, accepte
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