1,337 research outputs found
Is our Sun a Singleton?
Most stars are formed in a cluster or association, where the number density
of stars can be high. This means that a large fraction of initially-single
stars will undergo close encounters with other stars and/or exchange into
binaries. We describe how such close encounters and exchange encounters can
affect the properties of a planetary system around a single star. We define a
singleton as a single star which has never suffered close encounters with other
stars or spent time within a binary system. It may be that planetary systems
similar to our own solar system can only survive around singletons. Close
encounters or the presence of a stellar companion will perturb the planetary
system, often leaving planets on tighter and more eccentric orbits. Thus
planetary systems which initially resembled our own solar system may later more
closely resemble some of the observed exoplanet systems.Comment: 2 pages, 1 figure. To be published in the proceedings of IAUS246
"Dynamical Evolution of Dense Stellar Systems". Editors: E. Vesperini (Chief
Editor), M. Giersz, A. Sill
Internal calibration of Gaia BP/RP low-resolution spectra
The full third Gaia data release will provide the calibrated spectra obtained
with the blue and red Gaia slit-less spectrophotometers. The main challenge
when facing Gaia spectral calibration is that no lamp spectra or flat fields
are available during the mission. Also, the significant size of the line spread
function with respect to the dispersion of the prisms produces alien photons
contaminating neighbouring positions of the spectra. This makes the calibration
special and different from standard approaches.
This work gives a detailed description of the internal calibration model to
obtain the spectrophotometric data in the Gaia catalogue. The main purpose of
the internal calibration is to bring all the epoch spectra onto a common flux
and pixel (pseudo-wavelength) scale, taking into account variations over the
focal plane and with time, producing a mean spectrum from all the observations
of the same source.
In order to describe all observations in a common mean flux and
pseudo-wavelength scale, we construct a suitable representation of the
internally calibrated mean spectra via basis functions and we describe the
transformation between non calibrated epoch spectra and calibrated mean spectra
via a discrete convolution, parametrising the convolution kernel to recover the
relevant coefficients.
The model proposed here is able to combine all observations into a mean
instrument to allow the comparison of different sources and observations
obtained with different instrumental conditions along the mission and the
generation of mean spectra from a number of observations of the same source.
The output of this model provides the internal mean spectra, not as a sampled
function (flux and wavelength), but as a linear combination of basis functions,
although sampled spectra can easily be derived from them.Comment: 20 pages, 22 figure
The MODEST questions: challenges and future directions in stellar cluster research
We present a review of some of the current major challenges in stellar cluster research, including young clusters, globular clusters, and galactic nuclei. Topics considered include: primordial mass segregation and runaway mergers, expulsion of gas from clusters, the production of stellar exotica seen in some clusters (eg blue stragglers and extreme horizontal--branch stars), binary populations within clusters, the black--hole population within stellar clusters, the final parsec problem, stellar dynamics around a massive black hole, and stellar collisions. The Modest Questions posed here are the outcome of discussions which took place at the Modest-6A workshop held in Lund, Sweden, in December, 2005. Modest-6A was organised as part of the activities of the Modest Collaboration (see www.manybody.org for further details
Persistent Scatterer Interferometry (PSI) technique for landslide characterization and monitoring
: The measurement of landslide superficial displacement often represents the most effective method for defining its behavior, allowing one to observe the relationship with triggering factors and to assess the effectiveness of the mitigation measures. Persistent Scatterer Interferometry (PSI) represents a powerful tool to measure landslide displacement, as it offers a synoptic view that can be repeated at different time intervals and at various scales. In many cases, PSI data are integrated with in situ monitoring instrumentation, since the joint use of satellite and ground-based data facilitates the geological interpretation of a landslide and allows a better understanding of landslide geometry and kinematics. In this work, PSI interferometry and conventional ground-based monitoring techniques have been used to characterize and to monitor the Santo Stefano d’Aveto landslide located in the Northern Apennines, Italy. This landslide can be defined as an earth rotational slide. PSI analysis has contributed to a more in-depth investigation of the phenomenon. In particular, PSI measurements have allowed better redefining of the boundaries of the landslide and the state of activity, while the time series analysis has permitted better understanding of the deformation pattern and its relation with the causes of the landslide itself. The integration of ground-based monitoring data and PSI data have provided sound results for landslide characterization. The punctual information deriving from inclinometers can help in defining the actual location of the sliding surface and the involved volumes, while the measuring of pore water pressure conditions or water table level can suggest a correlation between the deformation patterns and the triggering factors
Garvey-Kelson Relations for Nuclear Charge Radii
The Garvey-Kelson relations (GKRs) are algebraic expressions originally
developed to predict nuclear masses. In this letter we show that the GKRs
provide a fruitful framework for the prediction of other physical observables
that also display a slowly-varying dynamics. Based on this concept, we extend
the GKRs to the study of nuclear charge radii. The GKRs are tested on 455 out
of the approximately 800 nuclei whose charge radius is experimentally known. We
find a rms deviation between the GK predictions and the experimental values of
only 0.01 fm. This should be contrasted against some of the most successful
microscopic models that yield rms deviations almost three times as large.
Predictions - with reliable uncertainties - are provided for 116 nuclei whose
charge radius is presently unknown.Comment: 4 pages and 3 figure
Gaia data release 1: Principles of the photometric calibration of the G band
Context. Gaia is an ESA cornerstone mission launched on 19 December 2013
aiming to obtain the most complete and precise 3D map of our Galaxy by
observing more than one billion sources. This paper is part of a series of
documents explaining the data processing and its results for Gaia Data Release
1, focussing on the G band photometry. Aims. This paper describes the
calibration model of the Gaia photometric passband for Gaia Data Release 1.
Methods. The overall principle of splitting the process into internal and
external calibrations is outlined. In the internal calibration, a
self-consistent photometric system is generated. Then, the external calibration
provides the link to the absolute photometric flux scales. Results. The Gaia
photometric calibration pipeline explained here was applied to the first data
release with good results. Details are given of the various calibration
elements including the mathematical formulation of the models used and of the
extraction and preparation of the required input parameters (e.g. colour
terms). The external calibration in this first release provides the absolute
zero point and photometric transformations from the Gaia G passband to other
common photometric systems. Conclusions. This paper describes the photometric
calibration implemented for the first Gaia data release and the instrumental
effects taken into account. For this first release no aperture losses,
radiation damage, and other second-order effects have not yet been implemented
in the calibration.Comment: 15 pages, 16 figures, Gaia data release 1 documentation special
volum
Relativistic transition wavelenghts and probabilities for spectral lines of Ne II
Transition wavelengths and probabilities for several 2p4 3p - 2p4 3s and 2p4
3d - 2p4 3p lines in fuorine-like neon ion (NeII) have been calculated within
the multiconfiguration Dirac-Fock (MCDF) method with quantum electrodynamics
(QED) corrections. The results are compared with all existing experimental and
theoretical data
Untargeted lipidomics uncovers lipid signatures distinguishing severe versus moderate forms of acutely decompensated cirrhosis
BACKGROUND AND AIM: Acutely decompensated of cirrhosis is a heterogeneous clinical entity associated with moderate mortality. In some patients, this condition develops quickly into a more often deadly acute-on-chronic liver failure (ACLF), in which other organs such as the kidneys or brain fail. The aim of this study was to characterize the blood lipidome in a large series of patients with cirrhosis and identify specific signatures associated with acute decompensation and ACLF development. METHODS: Serum untargeted lipidomics was performed in 561 patients with acutely decompensated (AD) cirrhosis (518 without and 43 with ACLF) (discovery cohort) and in 265 AD patients (128 without and 137 with ACLF) in whom serum samples were available to perform repeated measurements during the 28-day follow-up (validation cohort). Analyses were also performed in 78 AD patients included in a therapeutic albumin trial, 43 patients with compensated cirrhosis and 29 healthy subjects. RESULTS: The circulating lipid landscape associated with cirrhosis was characterized by a generalized suppression, which was more manifest during acute decompensation and in non-surviving patients. By computing discriminating accuracy and the variable importance projection score for each of the 223 annotated lipids, we identified a sphingomyelin fingerprint specific for AD cirrhosis and a distinct cholesteryl ester and lysophosphatidylcholine fingerprint for ACLF. Liver dysfunction, mainly, and infections were the principal net contributors to these fingerprints, which were dynamic and interchangeable between AD patients whose condition worsened to ACLF and those who improved. Notably, blood lysophosphatidylcholine levels increased in these patients after albumin therapy. CONCLUSIONS: Our findings provide insights into the lipid landscape associated with decompensation of cirrhosis and ACLF progression and identify unique noninvasive diagnostic biomarkers of advanced cirrhosis. LAY SUMMARY: Analysis of lipids in blood from patients with advanced cirrhosis reveals a general suppression of their levels in the circulation of these patients. A specific group of lipids known as sphingomyelins are useful to distinguish compensated from decompensated patients with cirrhosis. Another group of lipids designated cholesteryl esters further distinguish patients with decompensated patients who are at risk of developing organ failures
Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors
In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime
Underground operation of the ICARUS T600 LAr-TPC: first results
Open questions are still present in fundamental Physics and Cosmology, like
the nature of Dark Matter, the matter-antimatter asymmetry and the validity of
the particle interaction Standard Model. Addressing these questions requires a
new generation of massive particle detectors exploring the subatomic and
astrophysical worlds. ICARUS T600 is the first large mass (760 ton) example of
a novel detector generation able to combine the imaging capabilities of the old
famous "bubble chamber" with an excellent energy measurement in huge electronic
detectors. ICARUS T600 now operates at the Gran Sasso underground laboratory,
studying cosmic rays, neutrino oscillation and proton decay. Physical
potentialities of this novel telescope are presented through few examples of
neutrino interactions reconstructed with unprecedented details. Detector design
and early operation are also reported.Comment: 14 pages, 8 figures, 2 tables. Submitted to Jins
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