341 research outputs found
Discovery of molecular gas around HD 131835 in an APEX molecular line survey of bright debris disks
Debris disks are considered to be gas-poor, but recent observations revealed
molecular or atomic gas in several 10-40 Myr old systems. We used the APEX and
IRAM 30m radiotelescopes to search for CO gas in 20 bright debris disks. In one
case, around the 16 Myr old A-type star HD 131835, we discovered a new
gas-bearing debris disk, where the CO 3-2 transition was successfully detected.
No other individual system exhibited a measurable CO signal. Our Herschel Space
Observatory far-infrared images of HD 131835 marginally resolved the disk both
at 70 and 100m, with a characteristic radius of ~170 au. While in stellar
properties HD 131835 resembles Pic, its dust disk properties are
similar to those of the most massive young debris disks. With the detection of
gas in HD 131835 the number of known debris disks with CO content has increased
to four, all of them encircling young (40 Myr) A-type stars. Based on
statistics within 125 pc, we suggest that the presence of detectable amount of
gas in the most massive debris disks around young A-type stars is a common
phenomenon. Our current data cannot conclude on the origin of gas in HD 131835.
If the gas is secondary, arising from the disruption of planetesimals, then HD
131835 is a comparably young and in terms of its disk more massive analogue of
the Pic system. However, it is also possible that this system similarly
to HD 21997 possesses a hybrid disk, where the gas material is predominantly
primordial, while the dust grains are mostly derived from planetesimals.Comment: Accepted for publication in ApJ, 18 pages, 9 figures, 5 table
A Resolved Debris Disk Around the Candidate Planet-hosting Star HD 95086
Recently, a new planet candidate was discovered on direct images around the young (10-17 Myr) A-type star HD 95086. The strong infrared excess of the system indicates that, similar to HR8799, Beta Pic, and Fomalhaut, the star harbors a circumstellar disk. Aiming to study the structure and gas content of the HD 95086 disk, and to investigate its possible interaction with the newly discovered planet, here we present new optical, infrared, and millimeter observations. We detected no CO emission, excluding the possibility of an evolved gaseous primordial disk. Simple blackbody modeling of the spectral energy distribution suggests the presence of two spatially separate dust belts at radial distances of 6 and 64 AU. Our resolved images obtained with the Herschel Space Observatory reveal a characteristic disk size of approx. 6.0 5.4 (540 490 AU) and disk inclination of approx 25 deg. Assuming the same inclination for the planet candidate's orbit, its reprojected radial distance from the star is 62 AU, very close to the blackbody radius of the outer cold dust ring. The structure of the planetary system at HD 95086 resembles the one around HR8799. Both systems harbor a warm inner dust belt and a broad colder outer disk and giant planet(s) between the two dusty regions. Modeling implies that the candidate planet can dynamically excite the motion of planetesimals even out to 270 AU via their secular perturbation if its orbital eccentricity is larger than about 0.4. Our analysis adds a new example to the three known systems where directly imaged planet(s) and debris disks coexist
Relativistic quantum transport theory of hadronic matter: the coupled nucleon, delta and pion system
We derive the relativistic quantum transport equation for the pion
distribution function based on an effective Lagrangian of the QHD-II model. The
closed time-path Green's function technique, the semi-classical, quasi-particle
and Born approximation are employed in the derivation. Both the mean field and
collision term are derived from the same Lagrangian and presented analytically.
The dynamical equation for the pions is consistent with that for the nucleons
and deltas which we developed before. Thus, we obtain a relativistic transport
model which describes the hadronic matter with , and degrees
of freedom simultaneously. Within this approach, we investigate the medium
effects on the pion dispersion relation as well as the pion absorption and pion
production channels in cold nuclear matter. In contrast to the results of the
non-relativistic model, the pion dispersion relation becomes harder at low
momenta and softer at high momenta as compared to the free one, which is mainly
caused by the relativistic kinetics. The theoretically predicted free cross section is in agreement with the experimental data. Medium
effects on the cross section and momentum-dependent
-decay width are shown to be substantial.Comment: 66 pages, Latex, 12 PostScript figures included; replaced by the
revised version, to appear in Phys. Rev.
Spallation reactions. A successful interplay between modeling and applications
The spallation reactions are a type of nuclear reaction which occur in space
by interaction of the cosmic rays with interstellar bodies. The first
spallation reactions induced with an accelerator took place in 1947 at the
Berkeley cyclotron (University of California) with 200 MeV deuterons and 400
MeV alpha beams. They highlighted the multiple emission of neutrons and charged
particles and the production of a large number of residual nuclei far different
from the target nuclei. The same year R. Serber describes the reaction in two
steps: a first and fast one with high-energy particle emission leading to an
excited remnant nucleus, and a second one, much slower, the de-excitation of
the remnant. In 2010 IAEA organized a worskhop to present the results of the
most widely used spallation codes within a benchmark of spallation models. If
one of the goals was to understand the deficiencies, if any, in each code, one
remarkable outcome points out the overall high-quality level of some models and
so the great improvements achieved since Serber. Particle transport codes can
then rely on such spallation models to treat the reactions between a light
particle and an atomic nucleus with energies spanning from few tens of MeV up
to some GeV. An overview of the spallation reactions modeling is presented in
order to point out the incomparable contribution of models based on basic
physics to numerous applications where such reactions occur. Validations or
benchmarks, which are necessary steps in the improvement process, are also
addressed, as well as the potential future domains of development. Spallation
reactions modeling is a representative case of continuous studies aiming at
understanding a reaction mechanism and which end up in a powerful tool.Comment: 59 pages, 54 figures, Revie
Reduced Physiological Complexity in Robust Elderly Adults with the APOE ε4 Allele
BACKGROUND:It is unclear whether the loss of physiological complexity during the aging process is due to genetic variations. The APOE gene has been studied extensively in regard to its relationship with aging-associated medical illness. We hypothesize that diminished physiological complexity, as measured by heart rate variability, is influenced by polymorphisms in the APOE allele among elderly individuals. METHODOLOGY/PRINCIPAL FINDINGS:A total of 102 robust, non-demented, elderly subjects with normal functions of daily activities participated in this study (97 males and 5 females, aged 79.2+/-4.4 years, range 72-92 years). Among these individuals, the following two APOE genotypes were represented: epsilon4 non-carriers (n = 87, 85.3%) and epsilon4 carriers (n = 15, 14.7%). Multi-scale entropy (MSE), an analysis used in quantifying complexity for nonlinear time series, was employed to analyze heart-rate dynamics. Reduced physiological complexity, as measured by MSE, was significantly associated with the presence of the APOE epsilon4 allele in healthy elderly subjects, as compared to APOE epsilon4 allele non-carriers (24.6+/-5.5 versus 28.9+/-5.2, F = 9.429, p = 0.003, respectively). CONCLUSIONS/SIGNIFICANCE:This finding suggests a role for the APOE gene in the diminished physiological complexity seen in elderly populations
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
The inclusive and dijet production cross-sections have been measured for jets
containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass
energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The
measurements use data corresponding to an integrated luminosity of 34 pb^-1.
The b-jets are identified using either a lifetime-based method, where secondary
decay vertices of b-hadrons in jets are reconstructed using information from
the tracking detectors, or a muon-based method where the presence of a muon is
used to identify semileptonic decays of b-hadrons inside jets. The inclusive
b-jet cross-section is measured as a function of transverse momentum in the
range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet
cross-section is measured as a function of the dijet invariant mass in the
range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets
and the angular variable chi in two dijet mass regions. The results are
compared with next-to-leading-order QCD predictions. Good agreement is observed
between the measured cross-sections and the predictions obtained using POWHEG +
Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet
cross-section. However, it does not reproduce the measured inclusive
cross-section well, particularly for central b-jets with large transverse
momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final
version published in European Physical Journal
Relativistic transport theory of N, \Delta and N^{*}(1440) interacting through , and mesons
A self-consistent relativistic integral-differential equation of the
Boltzmann-Uehling-Uhlenbeck-type for the (1440) resonance is developed
based on an effective Lagrangian of baryons interacting through mesons. The
closed time-path Green's function technique and semi-classical, quasi-particle
and Born approximations are employed in the derivation. The non-equilibrium
RBUU-type equation for the (1440) is consistent with that of nucleon's
and delta's which we derived before. Thus, we obtain a set of coupled equations
for the , and (1440) distribution functions.
All the (1440)-relevant in-medium two-body scattering cross sections
within the , and (1440) system are derived from the same
effective Lagrangian in addition to the mean field and presented analytically,
which can be directly used in the study of relativistic heavy-ion collisions.
The theoretical prediction of the free cross section is
in good agreement with the experimental data. We calculate the in-medium , and cross
sections in cold nuclear matter up to twice the nuclear matter density. The
influence of different choices of the coupling strengths, which
can not be obtained through fitting certain experimental data, are discussed.
The results show that the density dependence of predicted in-medium cross
sections are sensitive to the coupling strengths used. An evident
density dependence will appear when a large scalar coupling strength of
is assumed.Comment: 64 pages, Latex, 13 PostScript figures include
The Insulin Receptor Substrate 1 (Irs1) in Intestinal Epithelial Differentiation and in Colorectal Cancer
Colorectal cancer (CRC) is associated with lifestyle factors that affect insulin/IGF signaling, of which the insulin receptor substrate 1 (IRS1) is a key transducer. We investigated expression, localization and pathologic correlations of IRS1 in cancer-uninvolved colonic epithelium, primary CRCs with paired liver metastases and in vitro polarizing Caco2 and HT29 cells. IRS1 mRNA and protein resulted higher, relative to paired mucosa, in adenomas of familial adenomatous polyposis patients and in CRCs that overexpressed c-MYC, ß-catenin, InsRß, and IGF1R. Analysis of IRS1 immunostaining in 24 cases of primary CRC with paired colonic epithelium and hepatic metastasis showed that staining intensity was significantly higher in metastases relative to both primary CRC (P<0.01) and colonic epithelium (P<0.01). Primary and metastatic CRCs, compared to colonic epithelium, contained significantly higher numbers of IRS1-positive cells (P = 0.013 and P = 0.014, respectively). Pathologic correlations in 163 primary CRCs revealed that diffuse IRS1 staining was associated with tumors combining differentiated phenotype and aggressive markers (high Ki67, p53, and ß-catenin). In Caco 2 IRS1 and InsR were maximally expressed after polarization, while IGF1R was highest in pre-polarized cells. No nuclear IRS1 was detected, while, with polarization, phosphorylated IRS1 (pIRS1) shifted from the lateral to the apical plasma membrane and was expressed in surface cells only. In HT29, that carry mutations constitutively activating survival signaling, IRS1 and IGF1R decreased with polarization, while pIRS1 localized in nuclear spots throughout the course. Overall, these data provide evidence that IRS1 is modulated according to CRC differentiation, and support a role of IRS1 in CRC progression and liver metastatization
Neurodegeneration of the retina in mouse models of Alzheimer’s disease: what can we learn from the retina?
Alzheimer’s disease (AD) is an age-related progressive neurodegenerative disease commonly found among elderly. In addition to cognitive and behavioral deficits, vision abnormalities are prevalent in AD patients. Recent studies investigating retinal changes in AD double-transgenic mice have shown altered processing of amyloid precursor protein and accumulation of β-amyloid peptides in neurons of retinal ganglion cell layer (RGCL) and inner nuclear layer (INL). Apoptotic cells were also detected in the RGCL. Thus, the pathophysiological changes of retinas in AD patients are possibly resembled by AD transgenic models. The retina is a simple model of the brain in the sense that some pathological changes and therapeutic strategies from the retina may be observed or applicable to the brain. Furthermore, it is also possible to advance our understanding of pathological mechanisms in other retinal degenerative diseases. Therefore, studying AD-related retinal degeneration is a promising way for the investigation on (1) AD pathologies and therapies that would eventually benefit the brain and (2) cellular mechanisms in other retinal degenerations such as glaucoma and age-related macular degeneration. This review will highlight the efforts on retinal degenerative research using AD transgenic mouse models
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