970 research outputs found
Magnetodielectric coupling in Mn3O4
We have investigated the dielectric anomalies associated with spin ordering
transitions in the tetragonal spinel MnO, using thermodynamic,
magnetic, and dielectric measurements. We find that two of the three magnetic
ordering transitions in MnO lead to decreases in the temperature
dependent dielectric constant at zero applied field. Applying a magnetic field
to the polycrystalline sample leaves these two dielectric anomalies practically
unchanged, but leads to an increase in the dielectric constant at the
intermediate spin-ordering transition. We discuss possible origins for this
magnetodielectric behavior in terms of spin-phonon coupling. Band structure
calculations suggest that in its ferrimagnetic state, MnO corresponds
to a semiconductor with no orbital degeneracy due to strong Jahn-Teller
distortion.Comment: 6 pages, 7 figure
The radio counter-jet of the QSO 3C~48
We present multi--frequency radio observational results of the quasar 3C~48.
The observations were carried out with the Very Large Array (VLA) at five
frequencies of 0.33, 1.5, 4.8, 8.4, and 22.5 GHz, and with the Multi--Element
Radio Linked Interferometer Network (MERLIN) at the two frequencies of 1.6 and
5 GHz. The source shows a one--sided jet to the north within 1\arcsec, which
then extends to the northeast and becomes diffuse. Two bright components (N2
and N3), containing most of the flux density are present in the northern jet.
The spectral index of the two components is and
(). Our images show the
presence of an extended structure surrounding component N2, suggestive of
strong interaction between the jet and the interstellar medium (ISM) of the
host galaxy. A steep--spectrum component, labelled as S, located 0.25 ardsec
southwest to the flat--spectrum component which could be the core of 3C 48, is
detected at a significance of . Both the location and the steepness
of the spectrum of component S suggest the presence of a counter--jet in 3C 48.Comment: 7 pages, 6 figures, accepted by A&
Breaking the Disk/Halo Degeneracy with Gravitational Lensing
The degeneracy between the disk and the dark matter contribution to galaxy
rotation curves remains an important uncertainty in our understanding of disk
galaxies. Here we discuss a new method for breaking this degeneracy using
gravitational lensing by spiral galaxies, and apply this method to the spiral
lens B1600+434 as an example. The combined image and lens photometry
constraints allow models for B1600+434 with either a nearly singular dark
matter halo, or a halo with a sizable core. A maximum disk model is ruled out
with high confidence. Further information, such as the circular velocity of
this galaxy, will help break the degeneracies. Future studies of spiral galaxy
lenses will be able to determine the relative contribution of disk, bulge, and
halo to the mass in the inner parts of galaxies.Comment: Replaced with minor revisions, a typo fixed, and reference added; 21
pages, 8 figures, ApJ accepte
Estimating the incidence of equine viral arteritis and the sensitivity of its surveillance in the French breeding stock
Equine viral arteritis (EVA) may have serious economic impact on the equine industry. For this reason, it is monitored in many countries, especially in breeding stock, to avoid its spread during breeding activities. In France, surveillance is mainly based on serological tests, since mares are not vaccinated, but difficulties in interpreting certain series of results may impair the estimation of the number of outbreaks. In this study, we propose specific rules for identifying seroconversion in order to estimate the number of outbreaks that were detected by the breeding stock surveillance component (BSSC) in France between 2006 and 2013. A consensus among multidisciplinary experts was reached to consider seroconversion as a change in antibody titer from negative to at least 32, or as an eight-fold or greater increase in antibody level. Using these rules, 239 cases and 177 outbreaks were identified. Subsequently, we calculated the BSSC's sensitivity as the ratio of the number of detected outbreaks to the total number of outbreaks that occurred in breeding stock (including unreported outbreaks) estimated using a capture-recapture model. The total number of outbreaks was estimated at 215 (95% credible interval 195-249) and the surveillance sensitivity at 82% (CrI95% 71-91). Our results confirm EVA circulation in French breeding stock, show that neutralizing antibodies can persist up to eight years in naturally infected mares and suggest that certain mares have been reinfected. This study shows that the sensitivity of the BSSC is relatively high and supports its relevance to prevent the disease spreading through mating
The Nature of Composite LINER/HII Galaxies, As Revealed from High-Resolution VLA Observations
A sample of 37 nearby galaxies displaying composite LINER/HII and pure HII
spectra was observed with the VLA in an investigation of the nature of their
weak radio emission. The resulting radio contour maps overlaid on optical
galaxy images are presented here, together with an extensive literature list
and discussion of the individual galaxies. Radio morphological data permit
assessment of the ``classical AGN'' contribution to the global activity
observed in these ``transition'' LINER galaxies. One in five of the latter
objects display clear AGN characteristics: these occur exclusively in
bulge-dominated hosts.Comment: 31 pages, 27 figures, accepted by ApJ
CMB quenching of high-redshift radio-loud AGNs
The very existence of more than a dozen of high-redshift (z 73 4) blazars indicates that a much larger population of misaligned powerful jetted active galactic nucleus (AGN) was already in place when the Universe was 721.5 Gyr old. Such parent population proved to be very elusive, and escaped direct detection in radio surveys so far. High-redshift blazars themselves seem to be failing in producing extended radio lobes, raising questions about the connection between such class and the vaster population of radio galaxies. We show that the interaction of the jet electrons with the intense cosmic microwave background (CMB) radiation explains the lack of extended radio emission in high-redshift blazars and in their parent population, helping to explain the apparently missing misaligned counterparts of high-redshift blazars. On the other hand, the emission from the more compact and more magnetized hotspots are less affected by the enhanced CMB energy density. By modelling the spectral energy distribution of blazar lobes and hotspots, we find that most of them should be detectable by low-frequency deep radio observations, e.g. by LOw-Frequency ARray for radio astronomy and by relatively deep X-ray observations with good angular resolution, e.g. by the Chandra satellite. At high redshifts, the emission of a misaligned relativistic jet, being debeamed, is missed by current large sky area surveys. The isotropic flux produced in the hotspots can be below \u2dc1 mJy and the isotropic lobe radio emission is quenched by the CMB cooling. Consequently, even sources with very powerful jets can go undetected in current radio surveys, and misclassified as radio-quiet AGNs
Cosmic-ray strangelets in the Earth's atmosphere
If strange quark matter is stable in small lumps, we expect to find such
lumps, called ``strangelets'', on Earth due to a steady flux in cosmic rays.
Following recent astrophysical models, we predict the strangelet flux at the
top of the atmosphere, and trace the strangelets' behavior in atmospheric
chemistry and circulation. We show that several strangelet species may have
large abundances in the atmosphere; that they should respond favorably to
laboratory-scale preconcentration techniques; and that they present promising
targets for mass spectroscopy experiments.Comment: 28 pages, 4 figures, revtex
Star Formation Activities of Galaxies in the Large-Scale Structures at z=1.2
Recent wide-field imaging observations of the X-ray luminous cluster
RDCSJ1252.9-2927 at z=1.24 uncovered several galaxy groups that appear to be
embedded in filamentary structure extending from the cluster core. We make a
spectroscopic study of the galaxies in these groups using GMOS on Gemini-South
and FORS2 on VLT with the aim of determining if these galaxies are physically
associated to the cluster. We find that three groups contain galaxies at the
cluster redshift and that they are probably bound to the cluster. This is the
first confirmation of filamentary structure as traced by galaxy groups at z>1.
We then use several spectral features in the FORS2 spectra to determine the
star formation histories of group galaxies. We find a population of relatively
red star-forming galaxies in the groups that are absent from the cluster core.
While similarly red star forming galaxies can also be found in the field, the
average strength of the hd line is systematically weaker in group galaxies.
Interestingly, these groups at z=1.2 are in an environment in which the
on-going build-up of red sequence is happening. The unusual line strengths can
be explained by star formation that is heavily obscured by dust. We hypothesize
that galaxy-galaxy interactions, which is more efficient in the group
environment, is the mechanism that drives these dust obscured star formation.
The hypothesis can be tested by obtaining spectral observations in the near-IR,
high resolution imaging observations and observations in the mid-IR.Comment: 12 pages, 12 figures. Accepted for publication in A&
The VMC Survey - VI. Quasars behind the Magellanic system
The number and spatial distribution of confirmed quasi-stellar objects (QSOs)
behind the Magellanic system is limited. This undermines their use as
astrometric reference objects for different types of studies. We have searched
for criteria to identify candidate QSOs using observations from the VISTA
survey of the Magellanic Clouds system (VMC) that provides photometry in the
YJKs bands and 12 epochs in the Ks band. The (Y-J) versus (J-Ks) diagram has
been used to distinguish QSO candidates from Milky Way stars and stars of the
Magellanic Clouds. Then, the slope of variation in the Ks band has been used to
identify a sample of high confidence candidates. These criteria were developed
based on the properties of 117 known QSOs presently observed by the VMC survey.
VMC YJKs magnitudes and Ks light-curves of known QSOs behind the Magellanic
system are presented. About 75% of them show a slope of variation in Ks>10^-4
mag/day and the shape of the light-curve is in general irregular and without
any clear periodicity. The number of QSO candidates found in tiles including
the South Ecliptic Pole and the 30 Doradus regions is 22 and 26, respectively,
with a ~20% contamination by young stellar objects, planetary nebulae, stars
and normal galaxies. By extrapolating the number of QSO candidates to the
entire VMC survey area we expect to find about 1200 QSOs behind the LMC, 400
behind the SMC, 200 behind the Bridge and 30 behind the Stream areas, but not
all will be suitable for astrometry. Further, the Ks band light-curves can help
support investigations of the mechanism responsible for the variations.Comment: 17 pages, 15 figures, replaced with accepted version by Astronomy &
Astrophysic
Drug Inhibition Profile Prediction for NFκB Pathway in Multiple Myeloma
Nuclear factor κB (NFκB) activation plays a crucial role in anti-apoptotic responses in response to the apoptotic signaling during tumor necrosis factor (TNFα) stimulation in Multiple Myeloma (MM). Although several drugs have been found effective for the treatment of MM by mainly inhibiting NFκB pathway, there are not any quantitative or qualitative results of comparison assessment on inhibition effect between different drugs either used alone or in combinations. Computational modeling is becoming increasingly indispensable for applied biological research mainly because it can provide strong quantitative predicting power. In this study, a novel computational pathway modeling approach is employed to comparably assess the inhibition effects of specific drugs used alone or in combinations on the NFκB pathway in MM and to predict the potential synergistic drug combinations
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