422 research outputs found
Infrared and sub-mm observations of outbursting young stars with Herschel and Spitzer
Episodic accretion plays an important role in the evolution of young stars.
Although it has been under investigation for a long time, the origin of such
episodic accretion events is not yet understood. We investigate the dust and
gas emission of a sample of young outbursting sources in the infrared to get a
better understanding of their properties and circumstellar material, and we use
the results in a further work to model the objects. We used Herschel data, from
our PI program of 12 objects and complemented with archival observations to
obtain the spectral energy distributions (SEDs) and spectra of our targets. We
report here the main characteristics of our sample, focussing on the SED
properties and on the gas emission lines detected in the PACS and SPIRE
spectra. The SEDs of our sample show the diversity of the outbursting sources,
with several targets showing strong emission in the far-infrared from the
embedded objects. Most of our targets reside in a complex environment, which we
discuss in detail. We detected several atomic and molecular lines, in
particular rotational CO emission from several transitions from J=38-37 to
J=4-3. We constructed rotational diagrams for the CO lines, and derived in
three domains of assumed local thermodynamic equilibrium (LTE) temperatures and
column densities, ranging mainly between 0-100 K and 400-500K. We confirm
correlation in our sample between intense CO emission and the column
density of the warm domain of CO, N(warm). We notice a strong increase in
luminosity of HH 381 IRS and a weaker increase for PP 13 S, which shows the
beginning of an outburst.Comment: 23 pages, 17 figures, A&A accepte
Self-consistent modelling of the dust component in protoplanetary and circumplanetary disks: the case of PDS 70
Direct observations of young stellar objects are important to test
established theories of planet formation. PDS 70 is one of the few cases where
robust evidence favours the presence of two planetary mass companions inside
the gap of the transition disk. Those planets are believed to be going through
the last stages of accretion from the protoplanetary disk, a process likely
mediated by a circumplanetary disk (CPD). We aim to develop a three dimensional
radiative transfer model for the dust component of the PDS 70 system which
reproduces the system's global features observed at two different wavelengths:
855 with ALMA and 1.25 with VLT/SPHERE.
We use this model to investigate the physical properties of the planetary
companion PDS 70 c and its potential circumplanetary disk. We select initial
values for the physical properties of the planet and CPD through appropriate
assumptions about the nature and evolutionary stage of the object. We modify
iteratively the properties of the protoplanetary disk until the predictions
retrieved from the model are consistent with both data sets. We provide a model
that jointly explains the global features of the PDS 70 system seen in
submillimeter and polarised-scattered light. Our model suggests that spatial
segregation of dust grains is present in the protoplanetary disk. The
submillimeter modelling of the PDS 70 c source favours the presence of an
optically thick CPD and places an upper limit to its dust mass of 0.7
. Furthermore, analysis of the thermal structure of the CPD
demonstrates that the planet luminosity is the dominant heating mechanism of
dust grains inside 0.6 au from the planet while heating by stellar photons
dominates at larger planetocentric distances.Comment: accepted for publication in A&
Science with an ngVLA: Resolving the Radio Complexity of EXor and FUor-type Systems with the ngVLA
Episodic accretion may be a common occurrence in the evolution of young
pre-main sequence stars and has important implications for our understanding of
star and planet formation. Many fundamental aspects of what drives the
accretion physics, however, are still unknown. The ngVLA will be a key tool in
understanding the nature of these events. The high spatial resolution, broad
spectral coverage, and unprecedented sensitivity will allow for the detailed
analysis of outburst systems. The proposed frequency range of the ngVLA allows
for observations of the gas, dust, and non-thermal emission from the star and
disk.Comment: 8 pages, 1 figure, To be published in the ASP Monograph Series,
"Science with a Next-Generation VLA", ed. E. J. Murphy (ASP, San Francisco,
CA
European Guideline on Achalasia - UEG and ESNM recommendations
Altres ajuts: These guidelines have been developed and funded within the United European Gastroenterology.Achalasia is a primary motor disorder of the oesophagus characterised by absence of peristalsis and insufficient lower oesophageal sphincter relaxation. With new advances and developments in achalasia management, there is an increasing demand for comprehensive evidence-based guidelines to assist clinicians in achalasia patient care. Guidelines were established by a working group of representatives from United European Gastroenterology, European Society of Neurogastroenterology and Motility, European Society of Gastrointestinal and Abdominal Radiology, and the European Association of Endoscopic Surgery in accordance with the Appraisal of Guidelines for Research and Evaluation (AGREE) II instrument. A systematic review of the literature was performed and the certainty of the evidence was assessed using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) methodology. Recommendations were voted upon using a nominal group technique. These guidelines focus on the definition of achalasia, treatment aims, diagnostic tests, medical, endoscopic and surgical therapy, management of treatment failure, follow-up and oesophageal cancer risk. These multidisciplinary guidelines provide a comprehensive evidence-based framework with recommendations on the diagnosis, treatment and follow-up of adult achalasia patients
Long-range adiabatic quantum state transfer through a linear array of quantum dots
We introduce an adiabatic long-range quantum communication proposal based on
a quantum dot array. By adiabatically varying the external gate voltage applied
on the system, the quantum information encoded in the electron can be
transported from one end dot to another. We numerically solve the Schr\"odinger
equation for a system with a given number of quantum dots. It is shown that
this scheme is a simple and efficient protocol to coherently manipulate the
population transfer under suitable gate pulses. The dependence of the energy
gap and the transfer time on system parameters is analyzed and shown
numerically. We also investigate the adiabatic passage in a more realistic
system in the presence of inevitable fabrication imperfections. This method
provides guidance for future realizations of adiabatic quantum state transfer
in experiments.Comment: 7 pages, 7 figure
Tunneling dynamics in exactly-solvable models with triple-well potentials
Inspired by new trends in atomtronics, cold atoms devices and Bose-Einstein
condensate dynamics, we apply a general technique of N=4 extended
Supersymmetric Quantum Mechanics to isospectral Hamiltonians with triple-well
potentials, i.e. symmetric and asymmetric. Expressions of quantum-mechanical
propagators, which take into account all states of the spectrum, are obtained,
within the N = 4 SQM approach, in the closed form. For the initial Hamiltonian
of a harmonic oscillator, we obtain the explicit expressions of potentials,
wavefunctions and propagators. The obtained results are applied to tunneling
dynamics of localized states in triple-well potentials and for studying its
features. In particular, we observe a Josephson-type tunneling transition of a
wave packet, the effect of its partial trapping and a non-monotonic dependence
of tunneling dynamics on the shape of a three-well potential. We investigate,
among others, the possibility of controlling tunneling transport by changing
parameters of the central well, and we briefly discuss potential applications
of this aspect to atomtronic devices.Comment: Latex, 28 pages, 7 Figs, 2 Tables; minor presentation changes,
journal versio
Bonn Potential and Shell-Model Calculations for 206,205,204Pb
The structure of the nuclei 206,205,204Pb is studied interms of shell model
employing a realistic effective interaction derived from the Bonn A
nucleon-nucleon potential. The energy spectra, binding energies and
electromagnetic properties are calculated and compared with experiment. A very
good overall agreement is obtained. This evidences the reliability of our
realistic effective interaction and encourages use of modern realistic
potentials in shell-model calculations for heavy-mass nuclei.Comment: 4 pages, 4 figures, submitted to Physical Review
The Adiabatic Transport of Bose-Einstein Condensates in a Double-Well Trap: Case a Small Nonlinearity
A complete adiabatic transport of Bose-Einstein condensate in a double-well
trap is investigated within the Landau-Zener (LZ) and Gaussian Landau-Zener
(GLZ) schemes for the case of a small nonlinearity, when the atomic interaction
is weaker than the coupling. The schemes use the constant (LZ) and
time-dependent Gaussian (GLZ) couplings. The mean field calculations show that
LZ and GLZ suggest essentially different transport dynamics. Significant
deviations from the case of a strong coupling are discussed.Comment: 6 pages, 3 figures, to be published in Laser Physic
Effect of Cell Age and Membrane Rigidity on Red Blood Cell Shape in Capillary Flow
Blood flow in the microcirculatory system is crucially affected by intrinsic red blood cell
(RBC) properties, such as their deformability. In the smallest vessels of this network, RBCs adapt
their shapes to the flow conditions. Although it is known that the age of RBCs modifies their physical
properties, such as increased cytosol viscosity and altered viscoelastic membrane properties, the
evolution of their shape-adapting abilities during senescence remains unclear. In this study, we
investigated the effect of RBC properties on the microcapillary in vitro flow behavior and their
characteristic shapes in microfluidic channels. For this, we fractioned RBCs from healthy donors
according to their age. Moreover, the membranes of fresh RBCs were chemically rigidified using
diamide to study the effect of isolated graded-membrane rigidity. Our results show that a fraction
of stable, asymmetric, off-centered slipper-like cells at high velocities decreases with increasing age
or diamide concentration. However, while old cells form an enhanced number of stable symmetric
croissants at the channel centerline, this shape class is suppressed for purely rigidified cells with
diamide. Our study provides further knowledge about the distinct effects of age-related changes of
intrinsic cell properties on the single-cell flow behavior of RBCs in confined flows due to inter-cellular
age-related cell heterogeneity
Conditions for Vanishing Central-well Population in Triple-well Adiabatic Transport
Analytical expressions are derived for coherent tunneling via adiabatic
passage (CTAP) in a triple well system with negligible central-well population
at all times during the transfer. It is shown that a manipulation of the depths
of the extreme-wells, correlated with the time variation of the
\emph{non-adjacent} barriers is essential for maintaining vanishing population
of the central well. The validity of our conditions are demonstrated with a
numerical solution of the time-dependent Schr\"{o}dinger equation. The transfer
process is interpreted in terms of a current through the central well.Comment: 7 pages; 3 figure
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