222 research outputs found
Method, System And Device For Transmitting Lighting Device Data
It is presented a method for transmitting lighting device data. The method comprises the steps of obtaining, in a lighting device, a subset of lighting device data, the lighting device data containg information of the lighting device, transmitting, from the lighting device, using light, the subset of lighting device data, and repeating the above steps until all subsets jointly corresponding to the complete lighting device data have been transmitted. A corresponding lighting device and lighting system are also presented.<br/
Porosity measurements of interstellar ice mixtures using optical laser interference and extended effective medium approximations
Aims. This article aims to provide an alternative method of measuring the
porosity of multi-phase composite ices from their refractive indices and of
characterising how the abundance of a premixed contaminant (e.g., CO2) affects
the porosity of water-rich ice mixtures during omni-directional deposition.
Methods. We combine optical laser interference and extended effective medium
approximations (EMAs) to measure the porosity of three astrophysically relevant
ice mixtures: H2O:CO2=10:1, 4:1, and 2:1. Infrared spectroscopy is used as a
benchmarking test of this new laboratory-based method. Results. By
independently monitoring the O-H dangling modes of the different water-rich ice
mixtures, we confirm the porosities predicted by the extended EMAs. We also
demonstrate that CO2 premixed with water in the gas phase does not
significantly affect the ice morphology during omni-directional deposition, as
long as the physical conditions favourable to segregation are not reached. We
propose a mechanism in which CO2 molecules diffuse on the surface of the
growing ice sample prior to being incorporated into the bulk and then fill the
pores partly or completely, depending on the relative abundance and the growth
temperature.Comment: 9 pages, 6 figures, 1 table. Accepted for publication in A&
Photoinduced polycyclic aromatic hydrocarbon dehydrogenation: The competition between H- and H2-loss
PAHs constitute a major component of the interstellar medium carbon budget,
locking up to 10--20% of the elemental carbon. Sequential fragmentation induced
by energetic photons leads to the formation of new species, including
fullerenes. However, the exact chemical routes involved in this process remain
largely unexplored. In this work, we focus on the first photofragmentation
steps, which involve the dehydrogenation of these molecules. For this, we
consider a multidisciplinary approach, taking into account the results from
experiments, DFT calculations, and modeling using dedicated Monte-Carlo
simulations. By considering the simplest isomerization pathways --- i.e.,
hydrogen roaming along the edges of the molecule --- we are able to
characterize the most likely photodissociation pathways for the molecules
studied here. These comprise nine PAHs with clearly different structural
properties. The formation of aliphatic-like side groups is found to be critical
in the first fragmentation step and, furthermore, sets the balance of the
competition between H- and H2-loss. We show that the presence of trio
hydrogens, especially in combination with bay regions in small PAHs plays an
important part in the experimentally established variations in the odd-to-even
H-atom loss ratios. In addition, we find that, as PAH size increases, H2
formation becomes dominant, and sequential hydrogen loss only plays a marginal
role. We also find disagreements between experiments and calculations for
large, solo containing PAHs, which need to be accounted for. In order to match
theoretical and experimental results, we have modified the energy barriers and
restricted the H-hopping to tertiary atoms. The formation of H2 in large PAHs
upon irradiation appears to be the dominant fragmentation channel, suggesting
an efficient formation path for molecular hydrogen in PDRs.Comment: 17 pages, 13 figures, accepted for publication in A&
Reaction Networks For Interstellar Chemical Modelling: Improvements and Challenges
We survey the current situation regarding chemical modelling of the synthesis
of molecules in the interstellar medium. The present state of knowledge
concerning the rate coefficients and their uncertainties for the major
gas-phase processes -- ion-neutral reactions, neutral-neutral reactions,
radiative association, and dissociative recombination -- is reviewed. Emphasis
is placed on those reactions that have been identified, by sensitivity
analyses, as 'crucial' in determining the predicted abundances of the species
observed in the interstellar medium. These sensitivity analyses have been
carried out for gas-phase models of three representative, molecule-rich,
astronomical sources: the cold dense molecular clouds TMC-1 and L134N, and the
expanding circumstellar envelope IRC +10216. Our review has led to the proposal
of new values and uncertainties for the rate coefficients of many of the key
reactions. The impact of these new data on the predicted abundances in TMC-1
and L134N is reported. Interstellar dust particles also influence the observed
abundances of molecules in the interstellar medium. Their role is included in
gas-grain, as distinct from gas-phase only, models. We review the methods for
incorporating both accretion onto, and reactions on, the surfaces of grains in
such models, as well as describing some recent experimental efforts to simulate
and examine relevant processes in the laboratory. These efforts include
experiments on the surface-catalysed recombination of hydrogen atoms, on
chemical processing on and in the ices that are known to exist on the surface
of interstellar grains, and on desorption processes, which may enable species
formed on grains to return to the gas-phase.Comment: Accepted for publication in Space Science Review
High resolution electronic spectroscopy of a non-linear carbon chain radical C6H4+.
The electronic spectrum of a member of a so-far-unstudied class of carbon chain radicals was observed:a nonlinear and noncyclic species. The spectrum was observed more or less accidentally around 604 nm when scanning for coincidences with diffuse interstellar band features in a hydrocarbon plasma. The observed spectrum has a clear rotational and K-type structure. Simulation of the spectrum allowed an accurate determination of the molecular constants of the carrier
A coincidence between a hydrocarbon plasma absorption spectrum and the lambda 5450 DIB
The aim of this work is to link the broad lambda 5450 diffuse interstellar
band (DIB) to a laboratory spectrum recorded through an expanding acetylene
plasma. Cavity ring-down direct absorption spectra and astronomical
observations of HD 183143 with the HERMES spectrograph on the Mercator
Telescope in La Palma and the McKellar spectrograph on the DAO 1.2 m Telescope
are compared. In the 543-547 nm region a broad band is measured with a band
maximum at 545 nm and FWHM of 1.03(0.1) nm coinciding with a well-known diffuse
interstellar band at lambda 5450 with FWHM of 0.953 nm. A coincidence is found
between the laboratory and the two independent observational studies obtained
at higher spectral resolution. This result is important, as a match between a
laboratory spectrum and a - potentially lifetime broadened - DIB is found. A
series of additional experiments has been performed in order to unambiguously
identify the laboratory carrier of this band. This has not been possible. The
laboratory results, however, restrict the carrier to a molecular transient,
consisting of carbon and hydrogen.Comment: 6 pages, 3 figures, accepted for publication in A&
SURFRESIDE2: An ultrahigh vacuum system for the investigation of surface reaction routes of interstellar interest
A new ultrahigh vacuum experiment is described to study atom and radical addition reactions in interstellar ice analogues for astronomically relevant temperatures. The new setup – SURFace REaction SImulation DEvice (SURFRESIDE2) – allows a systematic investigation of solid state pathways resulting in the formation of molecules of astrophysical interest. The implementation of a double beam line makes it possible to expose deposited ice molecules to different atoms and/or radicals sequentially or at the same time. Special efforts are made to perform experiments under fully controlled laboratory conditions, including precise atom flux determinations, in order to characterize reaction channels quantitatively. In this way, we can compare and combine different surface reaction channels with the aim to unravel the solid state processes at play in space. Results are constrained in situ by means of a Fourier transform infrared spectrometer and a quadrupole mass spectrometer using reflection absorption infrared spectroscopy and temperature programmed desorption, respectively. The performance of the new setup is demonstrated on the example of carbon dioxide formation by comparing the efficiency through two different solid state channels (CO + OH → CO_2 + H and CO + O → CO_2) for which different addition products are needed. The potential of SURFRESIDE2 to study complex molecule formation, including nitrogen containing (prebiotic) compounds, is discussed
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