40,239 research outputs found
VAMDC as a Resource for Atomic and Molecular Data and the New Release of VALD
The Virtual Atomic and Molecular Data Centre (VAMDC) (M.L. Dubernet et al.
2010, JQSRT 111, 2151) is an EU-FP7 e-infrastructure project devoted to
building a common electronic infrastructure for the exchange and distribution
of atomic and molecular data. It involves two dozen teams from six EU member
states (Austria, France, Germany, Italy, Sweden, United Kingdom) as well as
Russia, Serbia, and Venezuela. Within VAMDC scientists from many different
disciplines in atomic and molecular physics collaborate with users of their
data and also with scientists and engineers from the information and
communication technology community. In this presentation an overview of the
current status of VAMDC and its capabilities will be provided. In the second
part of the presentation I will focus on one of the databases which have become
part of the VAMDC platform, the Vienna Atomic Line Data Base (VALD). VALD has
developed into a well-known resource of atomic data for spectroscopy
particularly in astrophysics. A new release, VALD-3, will provide numerous
improvements over its predecessor. This particularly relates to the data
contents where new sets of atomic data for both precision spectroscopy (i.e.,
with data for observed energy levels) as well as opacity calculations (i.e.,
with data involving predicted energy levels) have been included. Data for
selected diatomic molecules have been added and a new system for data
distribution and data referencing provides for more convenience in using the
upcoming third release of VALD.Comment: 8 pages, 1 tabl
Reflectance spectroscopy in planetary science: Review and strategy for the future
Reflectance spectroscopy is a remote sensing technique used to study the surfaces and atmospheres of solar system bodies. It provides first-order information on the presence and amounts of certain ions, molecules, and minerals on a surface or in an atmosphere. Reflectance spectroscopy has become one of the most important investigations conducted on most current and planned NASA Solar System Exploration Program space missions. This book reviews the field of reflectance spectroscopy, including information on the scientific technique, contributions, present conditions, and future directions and needs
Synthesising, using, and correcting for telluric features in high-resolution astronomical spectra
We present a technique to synthesise telluric absorption and emission
features both for in-situ wavelength calibration and for their removal from
astronomical spectra. While the presented technique is applicable for a wide
variety of optical and infrared spectra, we concentrate in this paper on
selected high-resolution near-infrared spectra obtained with the CRIRES
spectrograph to demonstrate its performance and limitation. We find that
synthetic spectra reproduce telluric absorption features to about 2%, even
close to saturated line cores. Thus, synthetic telluric spectra could be used
to replace the observation of telluric standard stars, saving valuable
observing time. This technique also provides a precise in-situ wavelength
calibration, especially useful for high-resolution near-infrared spectra in the
absence of other calibration sources.Comment: 11 pages, 11 figures, accepted for publication in A&A (updated
version
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Using Nanoparticle X-ray Spectroscopy to Probe the Formation of Reactive Chemical Gradients in Diffusion-Limited Aerosols.
For aerosol particles that exist in highly viscous, diffusion-limited states, steep chemical gradients are expected to form during photochemical aging in the atmosphere. Under these conditions, species at the aerosol surface are more rapidly transformed than molecules residing in the particle interior. To examine the formation and evolution of chemical gradients at aerosol interfaces, the heterogeneous reaction of hydroxyl radicals (OH) on ∼200 nm particles of pure squalane (a branched, liquid hydrocarbon) and octacosane (a linear, solid hydrocarbon) and binary mixtures of the two are used to understand how diffusion limitations and phase separation impact the particle reactivity. Aerosol mass spectrometry is used to measure the effective heterogeneous OH uptake coefficient (γeff) and oxidation kinetics in the bulk, which are compared with the elemental composition of the surface obtained using X-ray photoemission. When diffusion rates are fast relative to the reaction frequency, as is the case for squalane and low-viscosity squalane-octacosane mixtures, the reaction is efficient (γeff ∼ 0.3) and only limited by the arrival of OH to the interface. However, for cases, where the diffusion rates are slower than reaction rates, as in pure octacosane and higher-viscosity squalane-octacosane mixtures, the heterogeneous reaction occurs in a mixing-limited regime and is ∼10× slower (γeff ∼ 0.03). This is in contrast to carbon and oxygen K edge X-ray absorption measurements that show that the octacosane interface is oxidized much more rapidly than that of pure squalane particles. The O/C ratio of the surface (estimated to be the top 6-8 nm of the interface) is measured to change with rate constants of (3.0 ± 0.9) × 10-13 and (8.6 ± 1.2) × 10-13 cm3 molecule-1 s-1 for squalane and octacosane particles, respectively. The differences in surface oxidation rates are analyzed using a previously published reaction-diffusion model, which suggests that a 1-2 nm highly oxidized crust forms on octacosane particles, whereas in pure squalane, the reaction products are homogeneously mixed within the aerosol. This work illustrates how diffusion limitations can form particles with highly oxidized surfaces even at relatively low oxidant exposures, which is in turn expected to influence their microphysics in the atmosphere
Radio astronomy
The following subject areas are covered: (1) scientific opportunities (millimeter and sub-millimeter wavelength astronomy; meter to hectometer astronomy; the Sun, stars, pulsars, interstellar masers, and extrasolar planets; the planets, asteroids, and comets; radio galaxies, quasars, and cosmology; and challenges for radio astronomy in the 1990's); (2) recommendations for new facilities (the millimeter arrays, medium scale instruments, and small-scale projects); (3) continuing activities and maintenance, upgrading of telescopes and instrumentation; (4) long range programs and technology development; and (5) social, political, and organizational considerations
The NASA program on upper atmospheric research
The purpose of the NASA Upper Atmospheric Research Program is to develop a better understanding of the physical and chemical processes that occur in the earth's upper atmosphere with emphasis on the stratosphere
Analysis of the C (d-a) Swan bands as a thermometric probe in CO microwave plasmas
The optical emission spectra of high pressure CO microwave plasmas are
usually dominated by the C Swan bands. In this paper, the use of the C
Swan bands for estimating the gas temperature in CO microwave plasmas is
assessed. State by state fitting is employed to check the correctness of
assuming a Boltzmann distribution for the rotational and vibrational
distribution functions and, within statistical and systematic uncertainties,
the C Swan band can be fitted accurately with a single temperature for
rotational and vibrational levels. The processes leading to the production of
the C molecule and particularly its d state are briefly reviewed
as well as collisional relaxation times of the latter. It is concluded that its
rotational temperature can be associated to the gas temperature of the CO
microwave plasma and the results are moreover cross-checked by adding a small
amount of N in the discharge and measuring the CN violet band system. The
2.45~GHz plasma source is analyzed in the pressure range 180-925~mbar, for
input microwave powers ranging from 0.9 - 3 kW and with gas flow rates of
5-100~L/min. An intense C Swan bands emission spectrum can be measured only
when the plasma is operated in contracted regime. A unique temperature of about
6000 500 K is obtained for all investigated conditions. A spectroscopic
database is constructed using the recent compilation and calculations by Brooke
et al. \cite{BROOKE201311} of the line strengths and molecular constants for
the C (d-a) Swan bands system and made available as
Supplementary Material in a format compatible with the open source MassiveOES
software
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