1,310 research outputs found
The CNGS Neutrino Beam
The CERN to Gran Sasso Neutrino beam (CNGS) was commissioned at CERN in early
August 2006 and was first sent at low intensity to Gran Sasso on August 17,
2006. The Borexino, LVD and OPERA experiments continued the commissioning of
their detectors and started taking data with practically no dead time. The CNGS
collected several hundred events with clean time distributions.Comment: 11 pages, 14 EPS figures. Lecture given at the 2nd Latin American
School on Cosmic Rays and Astrophysics, Puebla, Mexico, 30th August - 8th
September 200
A Flare of AE Aquarii Observed with XMM-Newton
We present the results of analyzing the XMM-Newton data obtained in 2001
November 7 - 8. A flare is observed simultaneously in X-ray and UV together
with a quiescence. We find that during the flare event X-ray flux varies with
UV with no significant time lag, indicating a close correlation of flux
variation for X-ray and UV flares. An upper limit of the lag is estimated to be
\~1 min. From a timing analysis for X-ray data, we find that both pulsed and
unpulsed flux increase clearly as the flare advances in the entire energy band
0.15 - 10 keV. The net increase of pulsed flux to the quiescence is, however,
small and corresponds to about 3 - 4% of the increase in unpulsed flux,
confirming that a flux variation of flare in AE Aqr is dominated by unpulsed
X-rays. A spectral analysis reveals that the energy spectrum is similar to that
of the quiescence at the beginning of the flare, but the spectrum becomes
harder as the flare advances. Based on these results, we discuss the current
issues that need to be clarified, e.g., the possible flaring site and the mass
accretion problem of the white dwarf. We also discuss the flare properties
obtained in this study.Comment: 15 pages, 3 tables, 9 figures, accepted for publication in Ap
Lithium Abundances in the Young Open Cluster IC 2602
We have obtained high-resolution spectra for 28 candidate late-type stars in the 30 Myr old cluster IC 2602. NLTE Li abundances have been derived from measured equivalent widths. The log n(Li) - T(sub eff) and log n(Li) - mass distributions for our sample stars have been compared with those of the Pleiades and alpha Persei. Our data show that F stars in the three clusters have the same lithium content, which corresponds to the initial content for Pop. I stars. G and early-K IC 2602 stars are, on average, somewhat more Li-rich than their counterparts in the two slightly older clusters. Finally, the latest-type IC 2602 stars are heavily Li depleted, with their Li content being as low as the lowest measured among the Pleiades. As in the Pleiades and alpha Per, a star-to-star scatter in lithium is observed among 30 Myr old late-K/early-K dwarfs in IC 2602, indicating that this spread develops in the pre-main sequence phases
Some Like it Hot: The X-Ray Emission of The Giant Star YY Mensae
(Abridged abstract) We present an analysis of the X-ray emission of the
rapidly rotating giant star YY Mensae observed by Chandra HETGS and XMM-Newton.
Although no obvious flare was detected, the X-ray luminosity changed by a
factor of two between the XMM-Newton and Chandra observations taken 4 months
apart. The coronal abundances and the emission measure distribution have been
derived from three different methods using optically thin collisional
ionization equilibrium models. The abundances show an inverse first ionization
potential (FIP) effect. We further find a high N abundance which we interpret
as a signature of material processed in the CNO cycle. The corona is dominated
by a very high temperature (20-40 MK) plasma, which places YY Men among the
magnetically active stars with the hottest coronae. Lower temperature plasma
also coexists, albeit with much lower emission measure. Line broadening is
reported, which we interpret as Doppler thermal broadening, although rotational
broadening due to X-ray emitting material high above the surface could be
present as well. We use two different formalisms to discuss the shape of the
emission measure distribution. The first one infers the properties of coronal
loops, whereas the second formalism uses flares as a statistical ensemble. We
find that most of the loops in the corona of YY Men have their maximum
temperature equal to or slightly larger than about 30 MK. We also find that
small flares could contribute significantly to the coronal heating in YY Men.
Although there is no evidence of flare variability in the X-ray light curves,
we argue that YY Men's distance and X-ray brightness does not allow us to
detect flares with peak luminosities Lx <= 10^{31} erg/s with current
detectors.Comment: Accepted paper to appear in Astrophysical Journal, issue Nov 10, 2004
(v615). This a revised version. Small typos are corrected. Figure 7 and its
caption and some related text in Sct 7.2 are changed, without incidence for
the conclusion
Fast X-ray Transients and Their Connection to Gamma-Ray Bursts
Fast X-ray transients (FXTs) with timescales from seconds to hours have been
seen by numerous space instruments. We have assembled archival data from
Ariel-5, HEAO-1 (A-1 and A-2), WATCH, ROSAT, and Einstein to produce a global
fluence-frequency relationship for these events. Fitting the log N-log S
distribution over several orders of magnitude to simple power law we find a
slope of -1.0. The sources of FXTs are undoubtedly heterogeneous, the -1 power
law is an approximate result of the summation of these multiple sources. Two
major contributions come from gamma-ray bursts and stellar flares.
Extrapolating from the BATSE catalog of GRBs, we find that the fraction of
X-ray flashes that can be the X-ray counterparts of gamma-ray bursts is a
function of fluence. Certainly most FXTs are not counterparts of standard
gamma-ray bursts. The fraction of FXTs from non-GRB sources, such as magnetic
stars, is greatest for the faintest FXTs. Our understanding of the FXT
phenomenon remains limited and would greatly benefit from a large, homogeneous
data set, which requires a wide-field, sensitive instrument.Comment: 36 pages, 8 figure
Myticalins: A novel multigenic family of linear, cationic antimicrobial peptides from marine mussels (Mytilus spp.)
The application of high-throughput sequencing technologies to non-model organisms has brought new opportunities for the identification of bioactive peptides from genomes and transcriptomes. From this point of view, marine invertebrates represent a potentially rich, yet largely unexplored resource for de novo discovery due to their adaptation to diverse challenging habitats. Bioinformatics analyses of available genomic and transcriptomic data allowed us to identify myticalins, a novel family of antimicrobial peptides (AMPs) from the mussel Mytilus galloprovincialis, and a similar family of AMPs from Modiolus spp., named modiocalins. Their coding sequence encompasses two conserved N-terminal (signal peptide) and C-terminal (propeptide) regions and a hypervariable central cationic region corresponding to the mature peptide. Myticalins are taxonomically restricted to Mytiloida and they can be classified into four subfamilies. These AMPs are subject to considerable interindividual sequence variability and possibly to presence/absence variation. Functional assays performed on selected members of this family indicate a remarkable tissue-specific expression (in gills) and broad spectrum of activity against both Gram-positive and Gram-negative bacteria. Overall, we present the first linear AMPs ever described in marine mussels and confirm the great potential of bioinformatics tools for the de novo discovery of bioactive peptides in non-model organisms
Fabrication of photothermally active poly(vinyl alcohol) films with gold nanostars for antibacterial applications.
The unique photothermal properties of non-spherical gold nanoparticles under near-infrared (NIR) irradiation find broad application in nanotechnology and nanomedicine. The combination of their plasmonic features with widely used biocompatible poly(vinyl alcohol) (PVA) films can lead to novel hybrid polymeric materials with tunable photothermal properties and a wide range of applications. In this study, thin PVA films containing highly photothermally efficient gold nanostars (GNSs) were fabricated and their properties were studied. The resulting films displayed good mechanical properties and a pronounced photothermal effect under NIR irradiation. The local photothermal effect triggered by NIR irradiation of the PVA-GNS films is highly efficient at killing bacteria, therefore providing an opportunity to develop new types of protective antibacterial films and coatings
Solar neutrino detection in a large volume double-phase liquid argon experiment
Precision measurements of solar neutrinos emitted by specific nuclear
reaction chains in the Sun are of great interest for developing an improved
understanding of star formation and evolution. Given the expected neutrino
fluxes and known detection reactions, such measurements require detectors
capable of collecting neutrino-electron scattering data in exposures on the
order of 1 ktonne yr, with good energy resolution and extremely low background.
Two-phase liquid argon time projection chambers (LAr TPCs) are under
development for direct Dark Matter WIMP searches, which possess very large
sensitive mass, high scintillation light yield, good energy resolution, and
good spatial resolution in all three cartesian directions. While enabling Dark
Matter searches with sensitivity extending to the "neutrino floor" (given by
the rate of nuclear recoil events from solar neutrino coherent scattering),
such detectors could also enable precision measurements of solar neutrino
fluxes using the neutrino-electron elastic scattering events. Modeling results
are presented for the cosmogenic and radiogenic backgrounds affecting solar
neutrino detection in a 300 tonne (100 tonne fiducial) LAr TPC operating at
LNGS depth (3,800 meters of water equivalent). The results show that such a
detector could measure the CNO neutrino rate with ~15% precision, and
significantly improve the precision of the 7Be and pep neutrino rates compared
to the currently available results from the Borexino organic liquid
scintillator detector.Comment: 21 pages, 7 figures, 6 table
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