1,295 research outputs found
Spectral Energy Distributions of Young Stars in IC 348: The Role of Disks in Angular Momentum Evolution of Young, Low-Mass Stars
Theoretical work suggests that a young star's angular momentum and rotation
rate may be strongly influenced by magnetic interactions with its circumstellar
disk. A generic prediction of these 'disk-locking' (DL) theories is that a
disk-locked star will be forced to co-rotate with the Keplerian angular
velocity of the inner edge of the disk. These theories have also been
interpreted to suggest a correlation between young stars' rotation periods and
the structural properties of their disks, such that slowly rotating stars
possess close-in disks that enforce the star's slow rotation, whereas rapidly
rotating stars possess anemic or evacuated inner disks that are unable to brake
the stars and they spin up as they contract. To test these expectations, we
model the SEDs of 33 young stars in IC 348 with known rotation periods and
infrared excesses indicating the presence of disks. For each star, we match the
observed spectral energy distribution, typically sampling 0.6-8.0 \mum, to a
grid of 200,000 pre-computed star+disk radiative transfer models, from which we
infer the disk's inner-truncation radius (R_trunc). We then compare this
R_trunc to the disk's co-rotation radius (R_co), calculated from the star's
rotation period. We do not find obvious differences in the disk R_trunc of slow
vs. rapid rotators. This holds true both at the level of whether close-in disk
material is present at all, and in analyzing the precise location of the inner
disk edge relative to the R_co amongst the subset of stars with close-in disk
material. One interpretation is that DL is unimportant for the IC 348 stars in
our sample. Alternatively, if DL does operate, then it must operate on both the
slow and rapid rotators, potentially producing both spin-up and spin-down
torques, and the transition from the disk-locked state to the disk-released
state must occur more rapidly than the stellar contraction timescale.Comment: 52 pages, 37 figures, 2 tables Accepted by Astronomical Journal, 02
June, 201
Background Light in Potential Sites for the ANTARES Undersea Neutrino Telescope
The ANTARES collaboration has performed a series of {\em in situ}
measurements to study the background light for a planned undersea neutrino
telescope. Such background can be caused by K decays or by biological
activity. We report on measurements at two sites in the Mediterranean Sea at
depths of 2400~m and 2700~m, respectively. Three photomultiplier tubes were
used to measure single counting rates and coincidence rates for pairs of tubes
at various distances. The background rate is seen to consist of three
components: a constant rate due to K decays, a continuum rate that
varies on a time scale of several hours simultaneously over distances up to at
least 40~m, and random bursts a few seconds long that are only correlated in
time over distances of the order of a meter. A trigger requiring coincidences
between nearby photomultiplier tubes should reduce the trigger rate for a
neutrino telescope to a manageable level with only a small loss in efficiency.Comment: 18 pages, 8 figures, accepted for publication in Astroparticle
Physic
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Toward an improved representation of middle atmospheric dynamics thanks to the ARISE project
This paper reviews recent progress toward understanding the dynamics of the middle atmosphere in the framework of the Atmospheric Dynamics Research InfraStructure in Europe (ARISE) initiative. The middle atmosphere, integrating the stratosphere and mesosphere, is a crucial region which influences tropospheric weather and climate. Enhancing the understanding of middle atmosphere dynamics requires improved measurement of the propagation and breaking of planetary and gravity waves originating in the lowest levels of the atmosphere. Inter-comparison studies have shown large discrepancies between observations and models, especially during unresolved disturbances such as sudden stratospheric warmings for which model accuracy is poorer due to a lack of observational constraints. Correctly predicting the variability of the middle atmosphere can lead to improvements in tropospheric weather forecasts on timescales of weeks to season. The ARISE project integrates different station networks providing observations from ground to the lower thermosphere, including the infrasound system developed for the Comprehensive Nuclear-Test-Ban Treaty verification, the Lidar Network for the Detection of Atmospheric Composition Change, complementary meteor radars, wind radiometers, ionospheric sounders and satellites. This paper presents several examples which show how multi-instrument observations can provide a better description of the vertical dynamics structure of the middle atmosphere, especially during large disturbances such as gravity waves activity and stratospheric warming events. The paper then demonstrates the interest of ARISE data in data assimilation for weather forecasting and re-analyzes the determination of dynamics evolution with climate change and the monitoring of atmospheric extreme events which have an atmospheric signature, such as thunderstorms or volcanic eruptions
Measurement of the quasi-elastic axial vector mass in neutrino-oxygen interactions
The weak nucleon axial-vector form factor for quasi-elastic interactions is
determined using neutrino interaction data from the K2K Scintillating Fiber
detector in the neutrino beam at KEK. More than 12,000 events are analyzed, of
which half are charged-current quasi-elastic interactions nu-mu n to mu- p
occurring primarily in oxygen nuclei. We use a relativistic Fermi gas model for
oxygen and assume the form factor is approximately a dipole with one parameter,
the axial vector mass M_A, and fit to the shape of the distribution of the
square of the momentum transfer from the nucleon to the nucleus. Our best fit
result for M_A = 1.20 \pm 0.12 GeV. Furthermore, this analysis includes updated
vector form factors from recent electron scattering experiments and a
discussion of the effects of the nucleon momentum on the shape of the fitted
distributions.Comment: 14 pages, 10 figures, 6 table
Measurement of the B+ --> p pbar K+ Branching Fraction and Study of the Decay Dynamics
With a sample of 232x10^6 Upsilon(4S) --> BBbar events collected with the
BaBar detector, we study the decay B+ --> p pbar K+ excluding charmonium decays
to ppbar. We measure a branching fraction Br(B+ --> p pbar
K+)=(6.7+/-0.5+/-0.4)x10^{-6}. An enhancement at low ppbar mass is observed and
the Dalitz plot asymmetry suggests dominance of the penguin amplitude in this B
decay. We search for a pentaquark candidate Theta*++ decaying into pK+ in the
mass range 1.43 to 2.00 GeV/c2 and set limits on Br(B+ -->
Theta*++pbar)xBr(Theta*++ --> pK+) at the 10^{-7} level.Comment: 8 pages, 7 postscript figures, submitted to Phys. Rev. D (Rapid
Communications
Search for the W-exchange decays B0 --> Ds(*)- Ds(*)+
We report a search for the decays , , in a sample of 232
million decays to \BBb ~pairs collected with the \babar detector
at the PEP-II asymmetric-energy storage ring. We find no significant
signal and set upper bounds for the branching fractions: and at 90% confidence level.Comment: 8 pages, 2 figures, submitted to PRD-R
Whole Genomes of Chandipura Virus Isolates and Comparative Analysis with Other Rhabdoviruses
The Chandipura virus (CHPV) belonging to the Vesiculovirus genus and Rhabdoviridae family, has recently been associated with a number of encephalitis epidemics, with high mortality in children, in different parts of India. No full length genome sequences of CHPV isolates were available in GenBank and little is known about the molecular markers for pathogenesis. In the present study, we provide the complete genomic sequences of four isolates from epidemics during 2003–2007. These sequences along with the deduced sequence of the prototype isolate of 1965 were analysed using phylogeny, motif search, homology modeling and epitope prediction methods. Comparison with other rhaboviruses was also done for functional extrapolations. All CHPV isolates clustered with the Isfahan virus and maintained several functional motifs of other rhabdoviruses. A notable difference with the prototype vesiculovirus, Vesicular Stomatitis Virus was in the L-domain flanking sequences of the M protein that are known to be crucial for interaction with host proteins. With respect to the prototype isolate, significant additional mutations were acquired in the 2003–2007 isolates. Several mutations in G mapped onto probable antigenic sites. A mutation in N mapped onto regions crucial for N-N interaction and a putative T-cell epitope. A mutation in the Casein kinase II phosphorylation site in P may attribute to increased rates of phosphorylation. Gene junction comparison revealed changes in the M-G junction of all the epidemic isolates that may have implications on read-through and gene transcription levels. The study can form the basis for further experimental verification and provide additional insights into the virulence determinants of the CHPV
Study of large hemispherical photomultiplier tubes for the ANTARES neutrino telescope
The ANTARES neutrino telescope, to be immersed depth in the Mediterranean Sea, will consist of a 3 dimensional matrix of 900 large area photomultiplier tubes housed in pressure resistant glass spheres. The selection of the optimal photomultiplier was a critical step for the project and required an intensive phase of tests and developments carried out in close collaboration with the main manufacturers worldwide. This paper provides an overview of the tests performed by the collaboration and describes in detail the features of the PMT chosen for ANTARES
Status of the Horizon 2020 EuPRAXIA conceptual design study
The Horizon 2020 project EuPRAXIA (European Plasma Research Accelerator with eXcellence In Applications) is producing a conceptual design report for a highly compact and cost-effective European facility with multi-GeV electron beams accelerated using plasmas. EuPRAXIA will be set up as a distributed Open Innovation platform with two construction sites, one with a focus on beam-driven plasma acceleration (PWFA) and another site with a focus on laser-driven plasma acceleration (LWFA). User areas at both sites will provide access to free-electron laser pilot experiments, positron generation and acceleration, compact radiation sources, and test beams for high-energy physics detector development. Support centres in four different countries will complement the pan-European implementation of this infrastructure
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