1,208 research outputs found
IRAS04325+2402C: A very low mass object with an edge-on disk
IRAS04325+2402C is a low luminosity object located near a protostar in
Taurus. We present new spatially-resolved mm observations, near-infrared
spectroscopy, and Spitzer photometry that improve the constraints on the nature
of this source. The object is clearly detected in our 1.3 mm interferometry
map, allowing us to estimate the mass in a localized disk+envelope around it to
be in the range of 0.001 to 0.01Ms. Thus IRAS04325C is unlikely to accrete
significantly more mass. The near-infrared spectrum cannot be explained with an
extincted photosphere alone, but is consistent with a 0.03-0.1Ms central source
plus moderate veiling, seen in scattered light, confirming the edge-on nature
of the disk. Based on K-band flux and spectral slope we conclude that a central
object mass >~0.1Ms is unlikely. Our comparison of the full spectral energy
distribution, including new Spitzer photometry, with radiative transfer models
confirms the high inclination of the disk (>~80deg), the very low mass of the
central source, and the small amount of circumstellar material. IRAS04325C is
one of the lowest mass objects with a resolved edge-on disk known to date,
possibly a young brown dwarf, and a likely wide companion to a more massive
star. With these combined properties, it represents a unique case to study the
formation and early evolution of very low mass objects.Comment: 5 pages, 3 figures, Astrophysical Journal Letters, in pres
The Next Influenza Pandemic: Lessons from Hong Kong, 1997
The 1997 Hong Kong outbreak of an avian influenzalike virus, with 18 proven human cases, many severe or fatal, highlighted the challenges of novel influenza viruses. Lessons from this episode can improve international and national planning for influenza pandemics in seven areas: expanded international commitment to first responses to pandemic threats; surveillance for influenza in key densely populated areas with large live-animal markets; new, economical diagnostic tests not based on eggs; contingency procedures for diagnostic work with highly pathogenic viruses where biocontainment laboratories do not exist; ability of health facilities in developing nations to communicate electronically, nationally and internationally; licenses for new vaccine production methods; and improved equity in supply of pharmaceutical products, as well as availability of basic health services, during a global influenza crisis. The Hong Kong epidemic also underscores the need for national committees and country-specific pandemic plans.publishedVersio
Mechanical rotation via optical pumping of paramagnetic impurities
Hybrid quantum systems exhibiting coupled optical, spin, and mechanical degrees of freedom can serve as a platform for sensing, or as a bus to mediate interactions between qubits with disparate energy scales. These systems are also creating opportunities to test foundational ideas in quantum mechanics, including direct observations of the quantum regime in macroscopic objects. Here, we make use of angular momentum conservation to study the dynamics of a pair of paramagnetic centers featuring different spin numbers in the presence of a properly tuned external magnetic field. We examine the interplay between optical excitation, spin evolution, and mechanical motion, and theoretically show that in the presence of continuous optical illumination, interspin cross relaxation must induce rigid rotation of the host crystal. The system dynamics is robust to scattering of spin-polarized phonons, a result we build on to show this form of angular momentum transfer should be observable using state-of-the-art torsional oscillators or trapped nanoparticles.Fil: Zangara, Pablo RenĂ©. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de FĂsica Enrique Gaviola. Universidad Nacional de CĂłrdoba. Instituto de FĂsica Enrique Gaviola; Argentina. City College of New York; Estados UnidosFil: Wood, Alexander. University of Melbourne; AustraliaFil: Doherty, Marcus W.. Australian National University; AustraliaFil: Meriles, Carlos A.. City College of New York; Estados Unido
Extension of the composite CBS-QB3 method to singlet diradical calculations
The composite CBS-QB3 method is widely used to obtain accurate energies of
molecules and radicals although its use in the case of singlet diradicals gives
rise to some difficulties. The problem is related to the parameterized
correction this method introduces to account for spin-contamination. We report
a new term specifically designed to describe singlet diradicals separated by at
least one CH2 unit. As a test case, we have computed the formation enthalpy of
a series of diradicals that includes hydrocarbons as well as systems involving
heteroatoms (nitrogen, oxygen). The resulting CBS-QB3 energies are very close
to experiment
Forests for the New Millennium - MAKING FORESTS WORK FOR PEOPLE AND NATURE
THE WAYS IN WHICH FORESTS ARE PERCEIVED AND USED HAVE CHANGED DRAMATICALLY OVER RECENT YEARS. FORESTS ARE NO LONGER SEEN SIMPLY AS A SOURCE OF TIMBER, BUT AS COMPLEX ECOSYSTEMS WHICH SUSTAIN LIVELIHOODS AND PROVIDE A RANGE OF PRODUCTS AND ENVIRONMENTAL SERVICES. IT IS NOW WIDELY RECOGNISED THAT FORESTS CAN CONTRIBUTE TO RURAL DEVELOPMENT AND POVERTY ALLEVIATION.Forest, economics, livelihoods
Occurrence of whale barnacles in Nerja Cave (MaÌlaga, southern Spain): Indirect evidence of whale consumption by humans in the Upper Magdalenian
A total of 167 plates of two whale barnacle species (Tubicinella majorLamarck, 1802 and Cetopirus complanatusMörch, 1853) have been found in the Upper Magdalenian layers of Nerja Cave, Mina Chamber (Maro, Målaga, southern Spain). This is the first occurrence of these species in a prehistoric site. Both species are specific to the southern right whale Eubalena australis, today endemic in the Southern Hemisphere. Because of Antarctic sea-ice expansion during the Last Glacial Period, these whales could have migrated to the Northern Hemisphere, and reached southern Spain. Whale barnacles indicate that maritime-oriented forager human groups found stranded whales on the coast and, because of the size and weight of the large bones, transported only certain pieces (skin, blubber and meat) to the caves where they were consumed
Probing the circumstellar structure of Herbig Ae/Be stars
We present Halpha spectropolarimetry observations of a sample of 23 Herbig
Ae/Be stars. A change in the linear polarisation across Halpha is detected in a
large fraction of the objects, which indicates that the regions around Herbig
stars are flattened (disc-like) on small scales. A second outcome of our study
is that the spectropolarimetric signatures for the Ae stars differ from those
of the Herbig Be stars, with characteristics changing from depolarisation
across Halpha in the Herbig Be stars, to line polarisations in the Ae group.
The frequency of depolarisations detected in the Herbig Be stars (7/12) is
particularly interesting as, by analogy to classical Be stars, it may be the
best evidence to date that the higher mass Herbig stars are surrounded by
flattened structures. For the Herbig Ae stars, 9 out of 11 show a line
polarisation effect that can be understood in terms of a compact Halpha
emission that is itself polarised by a rotating disc-like circumstellar medium.
The spectropolarimetric difference between the Herbig Be and Ae stars may be
the first indication that there is a transition in the Hertzsprung-Russell
Diagram from magnetic accretion at spectral type A to disc accretion at
spectral type B. Alternatively, the interior polarised line emission apparent
in the Ae stars may be masked in the Herbig Be stars due to their higher levels
of Halpha emission.Comment: 14 pages, MNRAS accepte
Differential limit on the extremely-high-energy cosmic neutrino flux in the presence of astrophysical background from nine years of IceCube data
We report a quasi-differential upper limit on the extremely-high-energy (EHE)
neutrino flux above GeV based on an analysis of nine years of
IceCube data. The astrophysical neutrino flux measured by IceCube extends to
PeV energies, and it is a background flux when searching for an independent
signal flux at higher energies, such as the cosmogenic neutrino signal. We have
developed a new method to place robust limits on the EHE neutrino flux in the
presence of an astrophysical background, whose spectrum has yet to be
understood with high precision at PeV energies. A distinct event with a
deposited energy above GeV was found in the new two-year sample, in
addition to the one event previously found in the seven-year EHE neutrino
search. These two events represent a neutrino flux that is incompatible with
predictions for a cosmogenic neutrino flux and are considered to be an
astrophysical background in the current study. The obtained limit is the most
stringent to date in the energy range between and GeV. This result constrains neutrino models predicting a three-flavor
neutrino flux of $E_\nu^2\phi_{\nu_e+\nu_\mu+\nu_\tau}\simeq2\times 10^{-8}\
{\rm GeV}/{\rm cm}^2\ \sec\ {\rm sr}10^9\ {\rm GeV}$. A significant part
of the parameter-space for EHE neutrino production scenarios assuming a
proton-dominated composition of ultra-high-energy cosmic rays is excluded.Comment: The version accepted for publication in Physical Review
Relationship between haemagglutination-inhibiting antibody titres and clinical protection against influenza: development and application of a bayesian random-effects model
<p>Abstract</p> <p>Background</p> <p>Antibodies directed against haemagglutinin, measured by the haemagglutination inhibition (HI) assay are essential to protective immunity against influenza infection. An HI titre of 1:40 is generally accepted to correspond to a 50% reduction in the risk of contracting influenza in a susceptible population, but limited attempts have been made to further quantify the association between HI titre and protective efficacy.</p> <p>Methods</p> <p>We present a model, using a meta-analytical approach, that estimates the level of clinical protection against influenza at any HI titre level. Source data were derived from a systematic literature review that identified 15 studies, representing a total of 5899 adult subjects and 1304 influenza cases with interval-censored information on HI titre. The parameters of the relationship between HI titre and clinical protection were estimated using Bayesian inference with a consideration of random effects and censorship in the available information.</p> <p>Results</p> <p>A significant and positive relationship between HI titre and clinical protection against influenza was observed in all tested models. This relationship was found to be similar irrespective of the type of viral strain (A or B) and the vaccination status of the individuals.</p> <p>Conclusion</p> <p>Although limitations in the data used should not be overlooked, the relationship derived in this analysis provides a means to predict the efficacy of inactivated influenza vaccines when only immunogenicity data are available. This relationship can also be useful for comparing the efficacy of different influenza vaccines based on their immunological profile.</p
Observation of High-Energy Astrophysical Neutrinos in Three Years of IceCube Data
A search for high-energy neutrinos interacting within the IceCube detector
between 2010 and 2012 provided the first evidence for a high-energy neutrino
flux of extraterrestrial origin. Results from an analysis using the same
methods with a third year (2012-2013) of data from the complete IceCube
detector are consistent with the previously reported astrophysical flux in the
100 TeV - PeV range at the level of per flavor and reject a
purely atmospheric explanation for the combined 3-year data at .
The data are consistent with expectations for equal fluxes of all three
neutrino flavors and with isotropic arrival directions, suggesting either
numerous or spatially extended sources. The three-year dataset, with a livetime
of 988 days, contains a total of 37 neutrino candidate events with deposited
energies ranging from 30 to 2000 TeV. The 2000 TeV event is the highest-energy
neutrino interaction ever observed.Comment: 8 pages, 5 figures. Accepted by PRL. The event catalog, event
displays, and other data tables are included after the final page of the
article. Changed from the initial submission to reflect referee comments,
expanding the section on atmospheric backgrounds, and fixes offsets of up to
0.9 seconds in reported event times. Address correspondence to: J. Feintzeig,
C. Kopper, N. Whitehor
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