663 research outputs found
Technology challenges for space interferometry: the option of mid-infrared integrated optics
Nulling interferometry is a technique providing high angular resolution which
is the core of the space missions Darwin and the Terrestrail Planet Finder. The
first objective is to reach a deep degree of starlight cancelation in the range
6 -- 20 microns, in order to observe and to characterize the signal from an
Earth-like planet. Among the numerous technological challenges involved in
these missions, the question of the beam combination and wavefront filtering
has an important place. A single-mode integrated optics (IO) beam combiner
could support both the functions of filtering and the interferometric
combination, simplifying the instrumental design. Such a perspective has been
explored in this work within the project Integrated Optics for Darwin (IODA),
which aims at developing a first IO combiner in the mid-infrared. The solutions
reviewed here to manufacture the combiner are based on infrared dielectric
materials on one side, and on metallic conductive waveguides on the other side.
With this work, additional inputs are offered to pursue the investigation on
mid-infrared photonics devices.Comment: Accepted in Adv. in Space Researc
Mid-infrared laser light nulling experiment using single-mode conductive waveguides
Aims: In the context of space interferometry missions devoted to the search
of exo-Earths, this paper investigates the capabilities of new single mode
conductive waveguides at providing modal filtering in an infrared and
monochromatic nulling experiment; Methods: A Michelson laser interferometer
with a co-axial beam combination scheme at 10.6 microns is used. After
introducing a Pi phase shift using a translating mirror, dynamic and static
measurements of the nulling ratio are performed in the two cases where modal
filtering is implemented and suppressed. No additional active control of the
wavefront errors is involved. Results: We achieve on average a statistical
nulling ratio of 2.5e-4 with a 1-sigma upper limit of 6e-4, while a best null
of 5.6e-5 is obtained in static mode. At the moment, the impact of external
vibrations limits our ability to maintain the null to 10 to 20 seconds.;
Conclusions: A positive effect of SM conductive waveguide on modal filtering
has been observed in this study. Further improvement of the null should be
possible with proper mechanical isolation of the setup.Comment: Accepted in A&A, 7 pages, 5 figure
Transmission measurement at 10.6 microns of Te2As3Se5 rib-waveguides on As2S3 substrate
The feasibility of chalcogenide rib waveguides working at lambda = 10.6
microns has been demonstrated. The waveguides comprised a several microns thick
Te2As3Se5 film deposited by thermal evaporation on a polished As2S3 glass
substrate and further etched by physical etching in Ar or CF4/O2 atmosphere.
Output images at 10.6 microns and some propagation losses roughly estimated at
10dB/cm proved that the obtained structures behaved as channel waveguides with
a good lateral confinement of the light. The work opens the doors to the
realisation of components able to work in the mid and thermal infrared up to 20
microns and even more.Comment: The following article appeared in Vigreux-Bercovici et al., Appl.
Phys. Lett. 90, 011110 (2007) and may be found at
http://link.aip.org/link/?apl/90/01111
A new study of the spectroscopic binary 7 Vul with a Be star primary
We confirmed the binary nature of the Be star 7~Vul, derived a~more accurate
spectroscopic orbit with an orbital period of (69.4212+/-0.0034) d, and
improved the knowledge of the basic physical elements of the system. Analyzing
available photometry and the strength of the \ha emission, we also document the
long-term spectral variations of the Be primary. In addition, we confirmed
rapid light changes with a~period of 0.5592 d, which is comparable to the
expected rotational period of the Be primary, but note that its amplitude and
possibly its period vary with time. We were able to disentangle only the He I
6678 A line of the secondary, which could support our tentative conclusion that
the secondary appears to be a hot subdwarf. A search for this object in
high-dispersion far-UV spectra could provide confirmation. Probable masses of
the binary components are ()~Mnom \ and ()~Mnom. If the
presence of a hot subdwarf is firmly confirmed, 7 Vul might be identified as a
rare object with a B4-B5 primary; all Be + hot subdwarf systems found so far
contain B0-B3 primaries.Comment: 17 pages, 23 figures, accepted for publication in Astronomy and
Astrophysic
Planet Formation Imager (PFI): Introduction and Technical Considerations
Complex non-linear and dynamic processes lie at the heart of the planet
formation process. Through numerical simulation and basic observational
constraints, the basics of planet formation are now coming into focus. High
resolution imaging at a range of wavelengths will give us a glimpse into the
past of our own solar system and enable a robust theoretical framework for
predicting planetary system architectures around a range of stars surrounded by
disks with a diversity of initial conditions. Only long-baseline interferometry
can provide the needed angular resolution and wavelength coverage to reach
these goals and from here we launch our planning efforts. The aim of the
"Planet Formation Imager" (PFI) project is to develop the roadmap for the
construction of a new near-/mid-infrared interferometric facility that will be
optimized to unmask all the major stages of planet formation, from initial dust
coagulation, gap formation, evolution of transition disks, mass accretion onto
planetary embryos, and eventual disk dispersal. PFI will be able to detect the
emission of the cooling, newly-formed planets themselves over the first 100
Myrs, opening up both spectral investigations and also providing a vibrant look
into the early dynamical histories of planetary architectures. Here we
introduce the Planet Formation Imager (PFI) Project
(www.planetformationimager.org) and give initial thoughts on possible facility
architectures and technical advances that will be needed to meet the
challenging top-level science requirements.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2014, Paper ID 9146-35, 10 pages, 2 Figure
Bioaccumulation of perfluoroalkyl compounds in midge (Chironomus riparius) larvae exposed to sediment
Midge larvae (Chironomus riparius) were exposed to sediments from a deposition sampled at a site along the Rhône River (France) downstream of an industrial site releasing various perfluorinated chemicals. This sediment is characterized by high concentrations of perfluoroundecanoic acid (PFUnA) and perfluorotridecanoic acid (PFTrDA) and a low perfluorooctane sulfonate (PFOS) concentration. Concentrations of 23 perfluoroalkyl compounds, including C4eC14 carboxylate acids, C4eC10 sulfonates, and seven precursors, were analyzed in overlying and pore water, sediment, and larvae. Midge larvae accumulated carboxylate acids (C11eC14), PFOS, and two precursors (perfluorooctane sulfonamide: FOSA and 6:2 fluorotelomer sulfonic acid, 6:2 FTSA). These substances accumulated mainly during the fourth instar larvae exponential growth phase. Accumulation of 6:2 FTSA, PFUnA, and PFOS occured via trophic and tegumentary routes. Other compounds mainly accumulated from food. Kinetics followed a partition model, from which uptake and elimination constants were derived
Design of Efficient Water Pricing Policies Integrating Basinwide Resource Opportunity Costs
By ignoring the opportunity cost of water use, water is undervalued, which can lead to significant errors in investments and water
allocation decisions. The marginal resource opportunity cost (MROC) varies in time and space, as resource availability, demands, and users’
WTP vary. This spatial and temporal variability can only be captured by basinwide hydro-economic models integrating water demands and
environmental requirements, resources, infrastructure, and operational and institutional restrictions. This paper presents a method for the
simulation of water pricing policies linked to water availability, and the design of efficient pricing policies that incorporate the basinwide
marginal value of water. Two approaches were applied: priority-based simulation and economic optimization. The improvement in economic
efficiency was assessed by comparing the results from simulation of the current system operation and the pricing schedule. The difference
between the benefits for the simulated current management and the upper bound benefits from optimization indicates the maximum gap that
could be bridged with pricing. In the application to a synthetic case, a storage-dependent step pricing schedule derived from average MROC
values led to benefits that capture 80% of the gap of net benefits between management without pricing and the economically optimal management.
Different pricing policies were tested, depending not only on reservoir storage but also on previous inflows. The results show that
the method is useful for designing pricing policies that enhance the economic benefits, leading to more efficient resource allocations over time
and across the competing uses.This study has been partially funded by the EU 6th FP project AQUAMONEY (SSPI-022723), the 7th FP GENESIS project (226536), and SAWARES (Plan Nacional I+D+i 2008-2011, CGL2009-13238-C02-01 and C02-02) and SCARCE (Consolider-Ingenio 2010 CSD2009-00065) of the Spanish Ministry of Economy and Competitiveness.Pulido-Velazquez, M.; Álvarez Mendiola, E.; Andreu Álvarez, J. (2013). Design of Efficient Water Pricing Policies Integrating Basinwide Resource Opportunity Costs. Journal of Water Resources Planning and Management. 139(5):583-592. https://doi.org/10.1061/(ASCE)WR.1943-5452.0000262S583592139
Modal Filtering for Nulling Interferometry-First Single-Mode Conductive Waveguides in the Mid-Infrared
This paper presents the work achieved for the manufacturing and
characterization of first single-mode waveguides to be used as modal filters
for nulling interferometry in the mid-infrared range [4-20 um]. As very high
dynamic range is mandatory for detection of Earth-like planets, modal filtering
is one of the most stringent instrumental aspects. The hollow metallic
waveguides (HMW) presented here are manufactured using micro-machining
techniques. Single-mode behavior has been investigated in laboratory through a
technique of polarization analysis while transmission features have been
measured using flux relative comparison. The single-mode behavior have been
assessed at lambda=10.6 um for rectangular waveguides with dimensions a=10 um
and b<5.3 um with an accuracy of ~2.5 %. The tests have shown that a
single-polarization state can be maintained in the waveguide. A comparison with
results on multi-mode HMW is proposed. Excess losses of 2.4 dB (~ 58 %
transmission) have been measured for a single-mode waveguide. In particular,
the importance of coupling conditions into the waveguide is emphasized here.
The goal of manufacturing and characterizing the first single-mode HMW for the
mid-infrared has been achieved. This opens the road to the use of integrated
optics for interferometry in the mentioned spectral range.Comment: 10 pages, 6 figures, accepted in A&
Ultraviolet Spectropolarimetry with Polstar: on the origin of rapidly rotating B stars
The proposed MIDEX mission, Polstar, will provide high resolution UV
spectroscopy and spectropolarimetry and offers a unique opportunity to study
massive stars in this wavelength range with unprecedented detail. We
demonstrate that these observations will provide critical new knowledge of
several types of massive stars (specifically the B-emission stars and the Bn
stars). We will determine accurate stellar parameters including their rotation
rates and variation of surface temperature associated with stellar oblateness.
Our work will allow us to detect binary companions and determine binary orbital
properties. Binary population synthesis predictions will allow us to determine
the fraction of these stars that are spun up due to binary interaction compared
to single star evolution. These rapidly rotating stars have the potential to
probe mass loss and the mixing of chemical elements which affects their
evolution and ultimately the evolution of their surroundings.Comment: white paper, 24 page
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