1,713 research outputs found
Dissecting a hot molecular core: The case of G31.41+0.31
We made a detailed observational analysis of a well known hot molecular core
lying in the high-mass star-forming region G31.41+0.31. This core is believed
to contain deeply embedded massive stars and presents a velocity gradient that
has been interpreted either as rotation or as expansion, depending on the
authors. Our aim was to shed light on this question and possibly prepare the
ground for higher resolution ALMA observations which could directly detect
circumstellar disks around the embedded massive stars. Observations at
sub-arcsecond resolution were performed with the Submillimeter Array in methyl
cyanide, a typical hot molecular core tracer, and 12CO and 13CO, well known
outflow tracers. We also obtained sensitive continuum maps at 1.3 mm. Our
findings confirm the existence of a sharp velocity gradient across the core,
but cannot confirm the existence of a bipolar outflow perpendicular to it. The
improved angular resolution and sampling of the uv plane allow us to attain
higher quality channel maps of the CH3CN lines with respect to previous studies
and thus significantly improve our knowledge of the structure and kinematics of
the hot molecular core. While no conclusive argument can rule out any of the
two interpretations (rotation or expansion) proposed to explain the velocity
gradient observed in the core, in our opinion the observational evidence
collected so far indicates the rotating toroid as the most likely scenario. The
outflow hypothesis appears less plausible, because the dynamical time scale is
too short compared to that needed to form species such as CH3CN, and the mass
loss and momentum rates estimated from our measurements appear too high.Comment: Astronomy and Astrophysics, in pres
Effects of biasing on the galaxy power spectrum at large scales
n this paper we study the effect of biasing on the power spectrum at large
scales. We show that even though non-linear biasing does introduce a white
noise contribution on large scales, the behavior of the
matter power spectrum on large scales may still be visible and above the white
noise for about one decade. We show, that the Kaiser biasing scheme which leads
to linear bias of the correlation function on {\em large} scales, also
generates a linear bias of the {\rm power spectrum} on rather small scales.
This is a consequence of the divergence on small scales of the pure
Harrison-Zeldovich spectrum. However, biasing becomes k-dependent when we damp
the underlying power spectrum on small scales. We also discuss the effect of
biasing on the baryon acoustic oscillations.Comment: 9 pages, 4 figures. One figure and comments clarifying the linear
biasing on small scales and references added. V3 version accepted in PR
Infall, outflow, and rotation in the G19.61-0.23 hot molecular core
Aims: The main goal of this study is to perform a sub-arcsecond resolution
analysis of the high-mass star formation region G19.61-0.23, both in the
continuum and molecular line emission. While the centimeter continuum images
will be discussed in detail in a forthcoming paper, here we focus on the
(sub)mm emission, devoting special attention to the hot molecular core.
Results: Our observations resolve the HMC into three cores whose masses are on
the order of 10^1-10^3 Msun. No submm core presents detectable free-free
emission in the centimeter regime, but they appear to be associated with masers
and thermal line emission from complex organic molecules. Towards the most
massive core, SMA1, the CH3CN (18_K-17_K) lines reveal hints of rotation about
the axis of a jet/outflow traced by H2O maser and H13CO+ (1--0) line emission.
Inverse P-Cygni profiles of the 13CO (3--2) and C18O (3--2) lines seen towards
SMA1 indicate that the central high-mass (proto)star(s) is (are) still gaining
mass with an accretion rate Msun/yr. Due to the linear scales
and the large values of the accretion rate, we hypothesize that we are
observing an accretion flow towards a cluster in the making, rather than
towards a single massive star.Comment: A&A accepted; 18 pages; Preprint with full-resolution figures is
available at http://subarutelescope.org/staff/rsf/publication.htm
Pandemic Considerations on Essential Oral Health Care
The coronavirus disease 2019 (COVID-19) pandemic revealed a lack of consensus on the concept of essential oral health care. We propose a definition of essential oral health care that includes urgent and basic oral health care to initiate a broader debate and stakeholder alignment. We argue that oral health care must be part of essential health care provided by any health system. Essential oral health care covers the most prevalent oral health problems through an agreed-on set of safe, quality, and cost-effective interventions at the individual and community level to promote and protect oral health, as well as prevent and treat common oral diseases, including appropriate rehabilitative services, thereby maintaining health, productivity, and quality of life. By default, essential oral health care does not include the full spectrum of possible interventions that contemporary dentistry can provide. On the basis of this definition, we conceptualize a layered model of essential oral health care that integrates urgent and basic oral health care, as well as advanced/specialist oral health care. Finally, we present 3 key reflections on the essentiality of oral health care. First, oral health care must be an integral component of a health care system's essential services, and by implication, oral health care personnel are part of the essential health care workforce. Second, not all dental care is essential oral health care, and not all essential care is also urgent, particularly under the specific risk conditions of the pandemic. Third, there is a need for criteria, evidence, and consensus-building processes to define which dental interventions are to be included in which category of essential oral health care. All stakeholders, including the research, academic, and clinical communities, as well as professional organizations and civil society, need to tackle this aspect in a concerted effort. Such consensus will be crucial for dentistry in view of the Sustainable Development Goal's push for universal health coverage, which must cover essential oral health care
Valuing spectrum at mm wavelengths for cellular networks
This paper investigates the economic value of spectrum at mm wavelengths. The analysis uses four techniques to value spectrum, namely a benchmarking comparison, a discounted cash flow analysis, a real options approach and a deprival method. The methods to calculate spectrum value presented in this paper can be used for any spectrum band and in any country. However, to determine the value of mm wavelengths for cellular networks, we have used data from New Zealand, specifically for the existing 700 MHz LTE network and for a hypothetical 28 GHz LTE network. These models are based on geographic data, population, cellular traffic analysis and LTE network design from this country. The results from the modelling analysis show that the value of spectrum in this case is bounded by the low value presented by the deprival valuation method and by the high value presented in the real options approach. All results show that as the demand for network capacity increases then mm wavelength spectrum becomes more valuable. This work will be useful to both regulators and operators. To regulators it offers insights into the economic value of mm wavelength spectrum which helps sets fees for spectrum licenses and to set reserve price and expected budgets for future spectrum auctions. To operators this paper offers insights into spectrum valuation techniques and presents data on the value of mm wavelengths for cellular networks
Compositional analysis of InAs-GaAs-GaSb heterostructures by low-loss electron energy loss spectroscopy
As an alternative to Core-Loss Electron Energy Loss Spectroscopy, Low-Loss EELS is suitable for compositional analysis of complex heterostructures, such as the InAs-GaAs-GaSb system, since in this energy range the edges corresponding to these elements are better defined than in Core-Loss. Furthermore, the analysis of the bulk plasmon peak, which is present in this energy range, also provides information about the composition. In this work, compositional information in an InAs-GaAs-GaSb heterostructure has been obtained from Low-Loss EEL spectra
Three-dimensional quasi-conformal transformation optics through numerical optimization
In this paper we demonstrate the possibility to achieve 3-dimensional quasi-conformal transformation optics through parametrization and numerical optimization without using sliding boundary conditions. The proposed technique, which uses a quasi-Newton method, is validated in two cylindrical waveguide bends as design examples. Our results indicate an arbitrarily small average anisotropy can be achieved in 3D transformation optics as the number of degrees of freedom provided by the parametrization was increased. The waveguide simulations confirm modal preservation when the residual anisotropy is neglected24151646516470CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFINANCIADORA DE ESTUDOS E PROJETOS - FINEPFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIGFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPnão temnão temnão temnão temnão te
Infall of gas as the formation mechanism of stars up to 20 times more massive than the Sun
Theory predicts and observations confirm that low-mass stars (like the Sun)
in their early life grow by accreting gas from the surrounding material. But
for stars ~ 10 times more massive than the Sun (~10 M_sun), the powerful
stellar radiation is expected to inhibit accretion and thus limit the growth of
their mass. Clearly, stars with masses >10 M_sun exist, so there must be a way
for them to form. The problem may be solved by non-spherical accretion, which
allows some of the stellar photons to escape along the symmetry axis where the
density is lower. The recent detection of rotating disks and toroids around
very young massive stars has lent support to the idea that high-mass (> 8
M_sun) stars could form in this way. Here we report observations of an ammonia
line towards a high-mass star forming region. We conclude from the data that
the gas is falling inwards towards a very young star of ~20 M_sun, in line with
theoretical predictions of non-spherical accretion.Comment: 11 pages, 2 figure
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