2,862 research outputs found
A RE-EXAMINATION OF EVENT STUDIES APPLIED TO CHALLENGED HORIZONTAL MERGERS
A growing body of empirical studies have been interpreted as support for a laissez-faire policy towards mergers. These "event studies" examine the reaction of stock market prices of firms that announce an agreement to merge. The type ~f reaction reveals whether a merger is motivated by a desire for market power or purely to improve market efficiency. In this paper, a version of the capital asset pricing model (CAPM) is applied to determine if abnormal returns are earned by rivals of 22 pairs of firms whose attempted horizontal mergers were challenged by the federal antitrust agencies. At most eight, and possibly only five, of the cases were found to be motivated by efficiency in seeking merger, and at most six, and possibly only one, were motivated by market power; the rest were inconclusive. The event-study technique is highly flawed for the study of business-regulation effects. Numerous unrealistic assumptions, inappropriate data constraints, and questionable interpretations hamper .the application of this technique to policy analysis.Industrial Organization,
Measurement of teicoplanin by liquid chromatography-tandem mass spectrometry:development of a novel method
Teicoplanin is an antibiotic used for the treatment of endocarditis, osteomyelitis, septic arthritis and methicillin-resistant Staphylococcus aureus. Teicoplanin is emerging as a suitable alternative antibiotic to vancomycin, where their trough serum levels are monitored by immunoassay routinely. This is the first report detailing the development of a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for measuring teicoplanin in patients' serum
The Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS): survey design, data catalogue and GAMA/WiggleZ spectroscopy
© 2016 The Authors. We present the Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS), a spectroscopic catalogue of radio sources designed to include the full range of radio AGN populations out to redshift z ~ 0.8. The catalogue covers ~800 deg 2 of sky, and provides optical identifications for 19 179 radio sources from the 1.4 GHz Faint Images of the Radio Sky at Twenty-cm (FIRST) survey down to an optical magnitude limit of i mod < 20.5 in Sloan Digital Sky Survey (SDSS) images. Both galaxies and point-like objects are included, and no colour cuts are applied. In collaboration with the WiggleZ and Galaxy And Mass Assembly (GAMA) spectroscopic survey teams, we have obtained new spectra for over 5000 objects in the LARGESS sample. Combining these new spectra with data from earlier surveys provides spectroscopic data for 12 329 radio sources in the survey area, of which 10 856 have reliable redshifts. 85 per cent of the LARGESS spectroscopic sample are radio AGN (median redshift z = 0.44), and 15 per cent are nearby star-forming galaxies (median z = 0.08). Low-excitation radio galaxies (LERGs) comprise the majority (83 per cent) of LARGESS radio AGN at z < 0.8, with 12 per cent being high-excitation radio galaxies (HERGs) and 5 per cent radioloud QSOs. Unlike the more homogeneous LERG and QSO sub-populations, HERGs are a heterogeneous class of objects with relatively blue optical colours and a wide dispersion in mid-infrared colours. This is consistent with a picture in which most HERGs are hosted by galaxies with recent or ongoing star formation as well as a classical accretion disc
Revealing the High-Redshift Star Formation Rate with Gamma-Ray Bursts
While the high-z frontier of star formation rate (SFR) studies has advanced
rapidly, direct measurements beyond z ~ 4 remain difficult, as shown by
significant disagreements among different results. Gamma-ray bursts, owing to
their brightness and association with massive stars, offer hope of clarifying
this situation, provided that the GRB rate can be properly related to the SFR.
The Swift GRB data reveal an increasing evolution in the GRB rate relative to
the SFR at intermediate z; taking this into account, we use the highest-z GRB
data to make a new determination of the SFR at z = 4-7. Our results exceed the
lowest direct SFR measurements, and imply that no steep drop exists in the SFR
up to at least z ~ 6.5. We discuss the implications of our result for cosmic
reionization, the efficiency of the universe in producing stellar-mass black
holes, and ``GRB feedback'' in star-forming hosts.Comment: 4 pages, 2 figures; ApJ Letters, in pres
Differential cytokine gene expression profiles in the three pathological forms of sheep paratuberculosis
<p>Abstract</p> <p>Background</p> <p>Johne's disease is a chronic inflammatory disease of the gut caused by infection with <it>Mycobacterium avium </it>subspecies <it>paratuberculosis </it>(MAP). Symptoms include wasting, diarrhoea, loss of condition and eventual death. Three forms of Johne's disease have been described in sheep – paucibacillary, multibacillary and asymptomatic. The paucibacillary form is characterized by an inflammatory, Th1-type immune response. The multibacillary form of the disease, which disseminates the infection, is characterized by macrophage infiltration mediated by a Th2-type immune response, and asymptomatic animals have no clinical symptoms or pathology but are infected with MAP. What determines these three forms of the disease is unknown. To further understand these differences, we used real-time RT-PCR to compare the expression of thirteen cytokine and cytokine-related genes in ileal tissue from sheep with the three forms of the disease.</p> <p>Results</p> <p>Three pathological forms of sheep paratuberculosis were defined on the basis of histopathology, cytochemistry (Zeihl-Neelsen) and IS900 PCR. Paucibacillary lesions have largely T cell and eosinophil infiltration and are ZN negative; multibacillary lesions have macrophage infiltration and large numbers of acid-fast bacteria. The pauci- and multibacillary forms are linked to the differential expression of IFNγ and IL-10 respectively. In addition the increased levels of the proinflammatory cytokines (IL-1β and TNFα), IL-8, IL-18 and TRAF-1 in both diseased forms is indicative of persistent inflammatory lesions. No changes were seen in IL-1α in any sheep ileum tissues. Asymptomatic animals are IS900+ with normal histology but have significantly decreased levels of IL-18 and increased levels TNFα.</p> <p>Conclusion</p> <p>We have quantified the expression levels of thirteen cytokine and cytokine related genes in three forms of ovine paratuberculosis using real-time PCR analyses and confirm that sheep pauci- and multibacillary disease are linked to type 1 and type 2 T cell responses respectively. The expression patterns of other cytokines shows that both disease forms have an inflammatory aetiology but that the central role for IL-1α in bovine paratuberculosis is not seen in the sheep infection. Asymptomatic animals are infected and show no pathology but can be distinguished, in terms of cytokine expression pattern, from uninfected controls.</p
The Star Formation Rate in the Reionization Era as Indicated by Gamma-ray Bursts
High-redshift gamma-ray bursts (GRBs) offer an extraordinary opportunity to
study aspects of the early Universe, including the cosmic star formation rate
(SFR). Motivated by the two recent highest-z GRBs, GRB 080913 at z = 6.7 and
GRB 090423 at z = 8.1, and more than four years of Swift observations, we first
confirm that the GRB rate does not trace the SFR in an unbiased way. Correcting
for this, we find that the implied SFR to beyond z = 8 is consistent with
LBG-based measurements after accounting for unseen galaxies at the faint end of
the UV luminosity function. We show that this provides support for the
integrated star formation in the range 6 < z < 8 to have been alone sufficient
to reionize the Universe.Comment: 4 pages, 4 figures; modified to match version accepted for
publication in ApJ Letter
Using GAMA to probe the impact of small-scale galaxy physics on nonlinear redshift-space distortions
We present improved modelling of the redshift-space distortions of galaxy
clustering that arise from peculiar velocities. We create mock galaxy
catalogues in the framework of the halo model, using data from the Bolshoi
project. These mock galaxy populations are inserted into the haloes with
additional degrees of freedom that govern spatial and kinematical biases of the
galaxy populations relative to the dark matter. We explore this generalised
halo model with an MCMC algorithm, comparing the predictions to data from the
Galaxy And Mass Assembly (GAMA) survey, and thus derive one of the first
constraints on the detailed kinematic degrees of freedom for satellite galaxies
within haloes. With this approach, the distortions of the redshift-space galaxy
autocorrelations can be accounted for down to spatial separations close to 10
kpc, opening the prospect of improved RSD measurements of the perturbation
growth rate by the inclusion of data from nonlinear scales.Comment: 19 pages, 10 figures, comments are welcom
A Direct Measurement of the IGM Opacity to HI Ionizing Photons
We present a new method to directly measure the opacity from HI Lyman limit
(LL) absorption k_LL along quasar sightlines by the intergalactic medium (IGM).
The approach analyzes the average (``stacked'') spectrum of an ensemble of
quasars at a common redshift to infer the mean free path (MFP) to ionizing
radiation. We apply this technique to 1800 quasars at z=3.50-4.34 drawn from
the Sloan Digital Sky Survey (SDSS), giving the most precise measurements on
k_LL at any redshift. From z=3.6 to 4.3, the opacity increases steadily as
expected and is well parameterized by MFP = (48.4 +/- 2.1) - (38.0 +/-
5.3)*(z-3.6) h^-1 Mpc (proper distance). The relatively high MFP values
indicate that the incidence of systems which dominate k_LL evolves less
strongly at z>3 than that of the Lya forest. We infer a mean free path three
times higher than some previous estimates, a result which has important
implications for the photo-ionization rate derived from the emissivity of star
forming galaxies and quasars. Finally, our analysis reveals a previously
unreported, systematic bias in the SDSS quasar sample related to the survey's
color targeting criteria. This bias potentially affects all z~3 IGM studies
using the SDSS database.Comment: 7 pages, 4 figures; Accepted to ApJ
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