5,879 research outputs found
Common learning
Consider two agents who learn the value of an unknown parameter by observing a sequence of private signals. The signals are independent and identically distributed across time but not necessarily across agents. We show that when each agent's signal space is finite, the agents will commonly learn the value of the parameter, that is, that the true value of the parameter will become approximate common knowledge. The essential step in this argument is to express the expectation of one agent's signals, conditional on those of the other agent, in terms of a Markov chain. This allows us to invoke a contraction mapping principle ensuring that if one agent's signals are close to those expected under a particular value of the parameter, then that agent expects the other agent's signals to be even closer to those expected under the parameter value. In contrast, if the agents' observations come from a countably infinite signal space, then this contraction mapping property fails. We show by example that common learning can fail in this case
Is Creep Feeding Lambs a Profitable Undertaking?
Creep feeding is a technique of providing feed to nursing lambs to supplement the milk they consume. Creep-fed lambs grow faster than noncreep-feds and are more aggressive in nursing ewes. This aggression stimulates greater ewe milk production which, in turn, increases creep feed intake because these lambs will be bigger at a given age
An Introduction to Sheep
The information in this fact sheet was developed to provide a quick reference to the most frequently asked questions about sheep and sheep production
Just how hot are the Centauri extreme horizontal branch pulsators?
Past studies based on optical spectroscopy suggest that the five Cen
pulsators form a rather homogeneous group of hydrogen-rich subdwarf O stars
with effective temperatures of around 50 000 K. This places the stars below the
red edge of the theoretical instability strip in the log Teff diagram,
where no pulsation modes are predicted to be excited. Our goal is to determine
whether this temperature discrepancy is real, or whether the stars' effective
temperatures were simply underestimated. We present a spectral analysis of two
rapidly pulsating extreme horizontal branch (EHB) stars found in Cen.
We obtained Hubble Space Telescope/COS UV spectra of two Cen
pulsators, V1 and V5, and used the ionisation equilibrium of UV metallic lines
to better constrain their effective temperatures. As a by-product we also
obtained FUV lightcurves of the two pulsators. Using the relative strength of
the N IV and N V lines as a temperature indicator yields Teff values close to
60 000 K, significantly hotter than the temperatures previously derived. From
the FUV light curves we were able to confirm the main pulsation periods known
from optical data. With the UV spectra indicating higher effective temperatures
than previously assumed, the sdO stars would now be found within the predicted
instability strip. Such higher temperatures also provide consistent
spectroscopic masses for both the cool and hot EHB stars of our previously
studied sample.Comment: 9 pages, accepted for publication in Astronomy and Astrophysic
The rise of an ionized wind in the Narrow Line Seyfert 1 Galaxy Mrk 335 observed by XMM-Newton and HST
We present the discovery of an outflowing ionized wind in the Seyfert 1
Galaxy Mrk 335. Despite having been extensively observed by most of the largest
X-ray observatories in the last decade, this bright source was not known to
host warm absorber gas until recent XMM-Newton observations in combination with
a long-term Swift monitoring program have shown extreme flux and spectral
variability. High resolution spectra obtained by the XMM-Newton RGS detector
reveal that the wind consists of three distinct ionization components, all
outflowing at a velocity of 5000 km/s. This wind is clearly revealed when the
source is observed at an intermediate flux state (2-5e-12 ergs cm^-2 s^-1). The
analysis of multi-epoch RGS spectra allowed us to compare the absorber
properties at three very different flux states of the source. No correlation
between the warm absorber variability and the X-ray flux has been determined.
The two higher ionization components of the gas may be consistent with
photoionization equilibrium, but we can exclude this for the only ionization
component that is consistently present in all flux states (log(xi)~1.8). We
have included archival, non-simultaneous UV data from HST (FOS, STIS, COS) with
the aim of searching for any signature of absorption in this source that so far
was known for being absorption-free in the UV band. In the COS spectra obtained
a few months after the X-ray observations we found broad absorption in CIV
lines intrinsic to the AGN and blueshifted by a velocity roughly comparable to
the X-ray outflow. The global behavior of the gas in both bands can be
explained by variation of the covering factor and/or column density, possibly
due to transverse motion of absorbing clouds moving out of the line of sight at
Broad Line Region scale.Comment: 24 pages, 12 figures, ApJ accepte
Did LIGO detect dark matter?
We consider the possibility that the black-hole (BH) binary detected by LIGO
may be a signature of dark matter. Interestingly enough, there remains a window
for masses where
primordial black holes (PBHs) may constitute the dark matter. If two BHs in a
galactic halo pass sufficiently close, they radiate enough energy in
gravitational waves to become gravitationally bound. The bound BHs will rapidly
spiral inward due to emission of gravitational radiation and ultimately merge.
Uncertainties in the rate for such events arise from our imprecise knowledge of
the phase-space structure of galactic halos on the smallest scales. Still,
reasonable estimates span a range that overlaps the Gpc yr
rate estimated from GW150914, thus raising the possibility that LIGO has
detected PBH dark matter. PBH mergers are likely to be distributed spatially
more like dark matter than luminous matter and have no optical nor neutrino
counterparts. They may be distinguished from mergers of BHs from more
traditional astrophysical sources through the observed mass spectrum, their
high ellipticities, or their stochastic gravitational wave background. Next
generation experiments will be invaluable in performing these tests.Comment: 5 pages, 2 figures, updated to match version published in PR
Discriminating active from latent tuberculosis in patients presenting to community clinics.
BACKGROUND: Because of the high global prevalence of latent TB infection (LTBI), a key challenge in endemic settings is distinguishing patients with active TB from patients with overlapping clinical symptoms without active TB but with co-existing LTBI. Current methods are insufficiently accurate. Plasma proteomic fingerprinting can resolve this difficulty by providing a molecular snapshot defining disease state that can be used to develop point-of-care diagnostics. METHODS: Plasma and clinical data were obtained prospectively from patients attending community TB clinics in Peru and from household contacts. Plasma was subjected to high-throughput proteomic profiling by mass spectrometry. Statistical pattern recognition methods were used to define mass spectral patterns that distinguished patients with active TB from symptomatic controls with or without LTBI. RESULTS: 156 patients with active TB and 110 symptomatic controls (patients with respiratory symptoms without active TB) were investigated. Active TB patients were distinguishable from undifferentiated symptomatic controls with accuracy of 87% (sensitivity 84%, specificity 90%), from symptomatic controls with LTBI (accuracy of 87%, sensitivity 89%, specificity 82%) and from symptomatic controls without LTBI (accuracy 90%, sensitivity 90%, specificity 92%). CONCLUSIONS: We show that active TB can be distinguished accurately from LTBI in symptomatic clinic attenders using a plasma proteomic fingerprint. Translation of biomarkers derived from this study into a robust and affordable point-of-care format will have significant implications for recognition and control of active TB in high prevalence settings
Physician Willingness to Withhold Tube Feeding after Cruzan: An Empirical Study
In Cruzan v. Hannon, the Missouri Supreme Court declined to let Nancy Cruzan\u27s father discontinue her tube feedings. The court insisted on clear and convincing evidence of her wishes and was unsatisfied that proof of this kind had been presented in her case.\u27 In addition, it refused to defer to her family or to consider her quality of life. On June 25, 1990, the United States Supreme Court affirmed the Missouri Supreme Court\u27s decision. Since Cruzan, public demand for living wills has exploded
Sry delivery to the adrenal medulla increases blood pressure and adrenal medullary tyrosine hydroxylase of normotensive WKY rats
BACKGROUND: Our laboratory has shown that a locus on the SHR Y chromosome increases blood pressure (BP) in the SHR rat and in WKY rats that had the SHR Y chromosome locus crossed into their genome (SHR/y rat). A potential candidate for this Y chromosome hypertension locus is Sry, a gene that encodes a transcription factor that is responsible for testes development and the Sry protein may affect other target genes. METHODS: The following study examined if exogenous Sry would elevate adrenal Th, adrenal catecholamines, plasma catecholamines and blood pressure. We delivered 10 μg of either the expression construct, Sry1/pcDNA 3.1, or control vector into the adrenal medulla of WKY rats by electroporation. Blood pressure was measured by the tail cuff technique and Th and catecholamines by HPLC with electrochemical detection. RESULTS: In the animals receiving Sry there were significant increases after 3 weeks in resting plasma NE (57%) and adrenal Th content (49%) compared to vector controls. BP was 30 mmHg higher in Sry injected animals (160 mmHg, p < .05) compared to vector controls (130 mmHg) after 2–3 weeks. Histological analysis showed that the electroporation procedure did not produce morphological damage. CONCLUSION: These results provide continued support that Sry is a candidate gene for hypertension. Also, these results are consistent with a role for Sry in increasing BP by directly or indirectly activating sympathetic nervous system activity
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