803 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
Photometric variability of the LAMOST sample of magnetic chemically peculiar stars as seen by TESS
High-quality light curves from space missions have opened up a new window on
the rotational and pulsational properties of magnetic chemically peculiar (mCP)
stars and have fuelled asteroseismic studies. They allow the internal effects
of surface magnetic fields to be probed and numerous astrophysical parameters
to be derived with great precision. We present an investigation of the
photometric variability of a sample of 1002 mCP stars discovered in the LAMOST
archival spectra with the aims of measuring their rotational periods and
identifying interesting objects for follow-up studies. TESS photometry was
available for 782 mCP stars and was analysed using a Fourier two-term frequency
fit to determine the stars' rotational periods. The rotational signal was then
subtracted from the light curve to identify non-rotational variability. A
pixel-level blending analysis was performed to check whether the variability
originates in the target star or a nearby blended neighbour. We investigated
correlations between the rotational periods, fractional age on the main
sequence, mass, and several other observables. We present rotational periods
and period estimates for 720 mCP stars. In addition, we identified four
eclipsing binary systems that likely host an mCP star, as well as 25 stars with
additional signals consistent with pulsation (12 stars with frequencies above
10 d and 13 stars with frequencies below 10 ). We find that more
evolved stars have longer rotation periods, in agreement with the assumption of
the conservation of angular momentum during main-sequence evolution. With our
work, we increase the sample size of mCP stars with known rotation periods and
identify prime candidates for detailed follow-up studies. This enables two
paths towards future investigations: population studies of even larger samples
of mCP stars and the detailed characterisation of high-value targets.Comment: 30 pages, 9 figures, 1 table. Accepted for publication in the Journal
of Astronomy and Astrophysics (A&A
MOBSTER â III. HDâ62658: a magnetic Bp star in an eclipsing binary with a non-magnetic âidentical twinâ
HDâ62658 (B9pâV) is a little-studied chemically peculiar star. Light curves obtained by the Kilodegree Extremely Little Telescope (KELT) and Transiting Exoplanet Survey Satellite (TESS) show clear eclipses with a period of about 4.75 d, as well as out-of-eclipse brightness modulation with the same 4.75 d period, consistent with synchronized rotational modulation of surface chemical spots. High-resolution ESPaDOnS circular spectropolarimetry shows a clear Zeeman signature in the line profile of the primary; there is no indication of a magnetic field in the secondary. PHOEBE modelling of the light curve and radial velocities indicates that the two components have almost identical masses of about 3 M_â. The primaryâs longitudinal magnetic fieldâ©B_zâȘ varies between about +100 and â250 G, suggesting a surface magnetic dipole strength B_d = 850 G. Bayesian analysis of the Stokes V profiles indicates B_d = 650 G for the primary and B_d < 110 G for the secondary. The primaryâs line profiles are highly variable, consistent with the hypothesis that the out-of-eclipse brightness modulation is a consequence of rotational modulation of that starâs chemical spots. We also detect a residual signal in the light curve after removal of the orbital and rotational modulations, which might be pulsational in origin; this could be consistent with the weak line profile variability of the secondary. This system represents an excellent opportunity to examine the consequences of magnetic fields for stellar structure via comparison of two stars that are essentially identical with the exception that one is magnetic. The existence of such a system furthermore suggests that purely environmental explanations for the origin of fossil magnetic fields are incomplete
The structural and tectonic history of the Mt. Formidable region, North Cascades, Washington
Deformation events associated with crustal thickening are preserved in the Mt. Formidable region of the North Cascades, a Cretaceous orogen and continental arc at the southern end of the Coast Plutonic Complex. The kinematics and timing of deformation in this area during burial, magmatism and metamorphism are the focus of this study. Rocks in the Mt. Formidable region span from at least the Late Triassic to the Early Cretaceous and include supracrustal units and associated metaplutonic rocks that have been interpreted as an island arc sequence. Rocks within the study region include the sub-arc Marblemount Meta-Quartz Diorite, the supra-arc metaclastic and metavolcanic Cascade River unit, interlayered greenschist wallrock and leucogneiss intrusions of the Magic Mountain Gneiss and the ocean-floor Napeequa Schist. Based on new geochronologic data from this study, the name Magic Mountain Gneiss is abandoned and the unit is herein referred to as the Magic Mountain Complex. New results indicate that rocks in the Mt. Formidable region experienced at least three generations of ductile deformation and two phases of metamorphism. F1 folds are isoclinal; the axial-planar, regional S1 foliation formed as a result of upper greenschist to lower amphibolite-facies metamorphism (M1). D2 formed tight to isoclinal F2 passive shear folds and a local, incipient crenulation foliation (S2) at greenschist-facies metamorphic conditions (M2). Restored F2 fold orientations are scattered, but suggest that D2 involved sub-vertical shortening and possibly NW or SE sub-horizontal shearing. Open to close F3 folds occur in Type 1, 2 and 3 fold interference patterns with F2 folds. Post-metamorphic D3 is characterized by NE-SW shortening and upright buckling. Variation in foliation, restored S2 surfaces and F3 axial planes suggest post-D3 deformation by a map-scale F4 structure. New dates from the Magic Mountain Complex provide important age constraints for D1 deformation and offer insight into the thermal history of the Mt. Formidable region. Two new 40Ar/39Ar cooling ages, 82.7 ± 2.3 Ma for hornblende and 46 ± 16 Ma for muscovite, are consistent with Late Cretaceous and Eocene cooling ages from the northern Cascades core. A 238U/206Pb zircon age of a foliated, pre-D1 orthogneiss sill is ~155 Ma. A late to post-D1 pegmatite dike, which is folded by F2, yields a 238U/206Pb zircon age of 137.5±5.9 Ma. These ages bracket D1 deformation and regional metamorphism between the latest Jurassic to earliest Cretaceous. Dates from this study are consistent with deformation being older than previously estimated in this portion of the Cascades, which has been inferred as mid to Late Cretaceous. Correlation of rocks in the Mt. Formidable region to similar Triassic arc units and Late Jurassic to Early Cretaceous intrusions in southern British Columbia suggests that D1 may record a major deformational event related to terrane accretion
Rat Dendritic Cells Function as Accessory Cells and Control the Production of a Soluble Factor Required for Mitogenic Responses of T Lymphocytes.
Transformation of T lymphocytes, induced by treatment with periodate or with neuraminidase plus galactose oxidase, requires the participation of accessory cells. Procedures were developed for the fractionation of rat lymph node cells, by which most of the lymphocytes can be recovered as a major population of cells that do not respond to mitogenic stimulation unless accessory cells from a separated minor population are added. Further purification led to a 1000-fold overall increase in accessory activity per cell, with a 50-70% yield. The purest preparations were virtually free of macrophages and contained more than 90% typical dendritic cells. Maximum responses occurred at a ratio of only one dendritic cell per 200 periodate-treated lymphocytes. This evidence thus indicates strongly that in rats, dendritic cells--not macrophages--function as accessory cells. Further, the number of dendritic cells in a preparation governed the magnitude of the mitogenic response and was limiting in the case of unfractionated lymph node cells. In addition, when oxidized with periodate or with neuraminidase plus galactose oxidase, the dendritic cell served as a very potent indirect stimulator of untreated responder lymphocytes. Both functions of the dendritic cell appeared to lack species specificity, since mouse dendritic cells were very active when tested with rat responder lymphocytes. A soluble factor (accessory cell-replacing factor), produced by cultures of lymph node or spleen cells subjected to oxidative mitogenesis, enabled otherwise unresponsive mitogen-treated lymphocytes to respond. Dendritic cells were required for the production of this factor but may not be solely responsible for its production
The significance of sample mass in the analysis of steroid estrogens in sewage sludges and the derivation of partition coefficients in wastewaters
Optimization of an analytical method for determination of steroid estrogens, through minimizing sample size, resulted in recoveries >84%, with relative standard deviations <3% and demonstrated the significance of sample size on method performance. Limits of detection were 2.1â5.3 ng/g. Primary sludges had estrogen concentrations of up to one order of magnitude less than those found in biological sludges (up to 994 ng/g). However, partition coefficients were higher in primary sludges (except estriol), with the most hydrophobic compound (ethinylestradiol) exhibiting the highest Kp value, information which may be of value to those involved in modeling removal during wastewater treatment
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 usersâ
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.; Ălvarez Mendiola, E.; Andreu Ălvarez, 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
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