2,344 research outputs found
Coherent States for Particle Beams in the Thermal Wave Model
In this paper, by using an analogy among {\it quantum mechanics}, {\it
electromagnetic beam optics in optical fibers}, and {\it charge particle beam
dynamics}, we introduce the concept of {\it coherent states} for charged
particle beams in the framework of the {\it Thermal Wave Model} (TWM). We give
a physical meaning of the Gaussian-like coherent structures of charged particle
distribution that are both naturally and artificially produced in an
accelerating machine in terms of the concept of coherent states widely used in
quantum mechanics and in quantum optics. According to TWM, this can be done by
using a Schr\"{o}dinger-like equation for a complex function, the so-called
{\it beam wave function} (BWF), whose squared modulus is proportional to the
transverse beam density profile, where Planck's constant and the time are
replaced by the transverse beam emittance and by the propagation coordinate,
respectively. The evolution of the particle beam, whose initial BWF is assumed
to be the simplest coherent state (ground-like state) associated with the beam,
in an infinite 1-D quadrupole-like device with small sextupole and octupole
aberrations, is analytically and numerically investigated.Comment: 21 pages, Late
Measuring elemental abundance ratios in protoplanetary disks at millimeter wavelengths
During the million years of evolution, gas dust and ice in protoplanetary
disks can be chemically reprocessed. There are evidences that the gas-phase
carbon and oxygen abundances are sub-solar in disks belonging to nearby star
forming regions. These findings have a major impact on the composition of the
primary atmosphere of giant planets (but it may also be valid for super-Earths
and sub-Neptunes) as they accrete their gaseous envelopes from the surrounding
material in the disk. In this study, we performed a thermo-chemical modelling
analysis with the aim at testing how reliable and robust are the estimates of
elemental abundance ratios based on (sub-)millimeter observations of molecular
lines. We created a grid of disk models for the following different elemental
abundance ratios: C/O, N/O and S/O, and, we computed the line flux of a set of
carbon-, nitrogen and sulphur-bearing species, namely CN, HCN, NO, CH,
c--CH, HCO, HCN, CHCN, CS, SO, HS and
HCS, that have been detected with present (sub-)millimeter facilities
such as ALMA and NOEMA. We find that the line fluxes, once normalized to the
flux of the CO line, are sensitive to the elemental abundance
ratios. On the other hand, the stellar and disk physical parameters have only a
minor effect of the line flux ratios. Our results demonstrate that a
simultaneous analysis of multiple molecular transitions is a valid approach to
constrain the elemental abundance ratio in protoplanetary disks.Comment: Accepted for publication to A&
Connection between jets, winds and accretion in T Tauri stars: the X-shooter view
We have analysed the [OI]6300 A line in a sample of 131 young stars with
discs in the Lupus, Chamaeleon and signa Orionis star forming regions, observed
with the X-shooter spectrograph at VLT. The stars have mass accretion rates
spanning from 10^{-12} to 10^{-7} Mo/yr. The line profile was deconvolved into
a low velocity component (LVC,
40 km/s ), originating from slow winds and high velocity jets, respectively.
The LVC is by far the most frequent component, with a detection rate of 77%,
while only 30% of sources have a HVC. The [OI]6300 luminosity of both the LVC
and HVC, when detected, correlates with stellar and accretion parameters of the
central sources (i.e. Lstar , Mstar , Lacc , Macc), with similar slopes for the
two components. The line luminosity correlates better with the accretion
luminosity than with the stellar luminosity or stellar mass. We suggest that
accretion is the main drivers for the line excitation and that MHD disc-winds
are at the origin of both components. In the sub-sample of Lupus sources
observed with ALMA a relationship is found between the HVC peak velocity and
the outer disc inclination angle, as expected if the HVC traces jets ejected
perpendicularly to the disc plane. Mass loss rates measured from the HVC span
from ~ 10^{-13} to ~10^{-7} Mo/yr. The corresponding Mloss/Macc ratio ranges
from ~0.01 to ~0.5, with an average value of 0.07. However, considering the
upper limits on the HVC, we infer a ratio < 0.03 in more than 40% of sources.
We argue that most of these sources might lack the physical conditions needed
for an efficient magneto-centrifugal acceleration in the star-disc interaction
region. Systematic observations of populations of younger stars, that is, class
0/I, are needed to explore how the frequency and role of jets evolve during the
pre-main sequence phase.Comment: 15 pages, 14 figures, Accepted for publication in A&
ALMA 870 m continuum observations of HD 100546. Evidence of a giant planet on a wide orbit
This paper reports on a new analysis of archival ALMA m dust
continuum observations. Along with the previously observed bright inner ring
(au), two addition substructures are evident in the new
continuum image: a wide dust gap, au, and a faint outer ring
ranging from au to au and whose presence was
formerly postulated in low-angular-resolution ALMA cycle 0 observations but
never before observed. Notably, the dust emission of the outer ring is not
homogeneous, and it shows two prominent azimuthal asymmetries that resemble an
eccentric ring with eccentricity . The characteristic double-ring
dust structure of HD 100546 is likely produced by the interaction of the disk
with multiple giant protoplanets. This paper includes new
smoothed-particle-hydrodynamic simulations with two giant protoplanets, one
inside of the inner dust cavity and one in the dust gap. The simulations
qualitatively reproduce the observations, and the final masses and orbital
distances of the two planets in the simulations are 3.1 at 15 au and
8.5 at 110 au, respectively. The massive outer protoplanet
substantially perturbs the disk surface density distribution and gas dynamics,
producing multiple spiral arms both inward and outward of its orbit. This can
explain the observed perturbed gas dynamics inward of 100 au as revealed by
ALMA observations of CO.
Finally, the reduced dust surface density in the au dust gap
can nicely clarify the origin of the previously detected HO gas and ice
emission.Comment: Accepted for publicatio
Long-lived Dust Rings around HD 169142
Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations of the protoplanetary disk around HD 169142 reveal a peculiar structure made of concentric dusty rings: a main ring at similar to 20 au, a triple system of rings at similar to 55-75 au in millimetric continuum emission, and a perturbed gas surface density from the (CO)-C-12,(CO)-C-13, and (CO)-O-18 (J = 2-1) surface brightness profile. In this Letter, we perform 3D numerical simulations and radiative transfer modeling exploring the possibility that two giant planets interacting with the disk and orbiting in resonant locking can be responsible for the origin of the observed dust inner rings structure. We find that in this configuration the dust structure is actually long lived while the gas mass of the disk is accreted onto the star and the giant planets, emptying the inner region. In addition, we also find that the innermost planet is located at the inner edge of the dust ring, and can accrete mass from the disk, generating a signature in the dust ring shape that can be observed in mm ALMA observations
Organic molecules in the protoplanetary disk of DG Tau revealed by ALMA
Planets form in protoplanetary disks and inherit their chemical compositions.
It is thus crucial to map the distribution and investigate the formation of
simple organics, such as formaldehyde and methanol, in protoplanetary disks. We
analyze ALMA observations of the nearby disk-jet system around the T Tauri star
DG Tau in the o-HCO and CHOH E,
A transitions at an unprecedented resolution of ,
i.e., au at a distance of 121 pc. The HCO emission originates from
a rotating ring extending from au with a peak at au, i.e., at
the edge of the 1.3mm dust continuum. CHOH emission is not detected down to
an r.m.s. of 3 mJy/beam in the 0.162 km/s channel. Assuming an ortho-to-para
ratio of 1.8-2.8 the ring- and disk-height-averaged HCO column density is
cm, while that of CHOH is
cm. In the inner au no o-HCO emission
is detected with an upper limit on its beam-averaged column density of
cm. The HCO ring in the disk of DG Tau is
located beyond the CO iceline (R au). This suggests that the
HCO abundance is enhanced in the outer disk due to formation on grain
surfaces by the hydrogenation of CO ice. The emission peak at the edge of the
mm dust continuum may be due to enhanced desorption of HCO in the gas phase
caused by increased UV penetration and/or temperature inversion. The
CHOH/HCO abundance ratio is , in agreement with disk chemistry
models. The inner edge of the HCO ring coincides with the radius where the
polarization of the dust continuum changes orientation, hinting at a tight link
between the HCO chemistry and the dust properties in the outer disk and at
the possible presence of substructures in the dust distribution.Comment: 8 pages, 6 figures, accepted for publication on A&A Letter
The bubble heart'. an unusual natural history told by multimodality imaging- a case report
Background Intracardiac thrombosis is a relatively common pathological condition. Often, it is diagnosed at echocardiography during the subacute or chronic phase. In the very acute phase, tissue composition can make thrombus appearance very different from that usually seen. Fresh thrombosis has been previously found also in peripartum cardiomyopathy (PPC), but with imaging features different from our case.
Case summary A 27-year-old woman was referred to our hospital for PPC, with echocardiographic finding of intraventricular masses, resembling big bubbles. Cardiac magnetic resonance (CMR) allowed definitively diagnosing intracardiac 'very acute' thrombosis, which is rarely detected.
Discussion Our case provides a practical lesson about management of an unusual presentation of a common problem. When early echocardiography does not allow making a certain diagnosis, CMR can be helpful and decisive, due to its unique ability to provide characterization of intracardiac masses
In vitro 3D tissue modelling: Insights into ameloblastoma pathogenesis
Ameloblastoma is a rare, benign oral tumour. Tumours develop within the jaw bone and are highly destructive and invasive, with cells migrating into the jaw and surrounding soft tissue. This is a little-understood disease which if left untreated causes dramatic bone destruction and maxillofacial disfigurement. Current treatment is radical surgery, often resulting in extensive loss of function and tissue. An ameloblastoma-derived cell line, AM-1, has been established [1]. Cells were isolated from a human tumour and immortalised by the addition of HPV-16 DNA. This study aims to (i) make a 3D in vitro ameloblastoma disease model, using plastic-compressed collagen gel [2] seeded with AM-1 cells, and (ii) use this bone construct to characterise tissue remodelling, cell growth and invasiveness
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