1,072 research outputs found
Polarization imaging reflectometry in the wild
We present a novel approach for on-site acquisition of surface reflectance for planar, spatially varying, isotropic materials in uncontrolled outdoor environments. Our method exploits the naturally occuring linear polarization of incident illumination: by rotating a linear polarizing filter in front of a camera at 3 different orientations, we measure the linear polarization reflected off the sample and combine this information with multiview analysis and inverse rendering in order to recover per-pixel, high resolution reflectance maps. We exploit polarization both for diffuse/specular separation and surface normals estimation by combining polarization measurements from at least two near orthogonal views close to Brewster angle of incidence. We then use our estimates of surface normals and albedos in an inverse rendering framework to recover specular roughness. To the best of our knowledge, our method is the first to successfully extract a complete set of reflectance parameters with passive capture in completely uncontrolled outdoor environments
Human Food Safety Implications of Variation in Food Animal Drug Metabolism
Citation: Lin, Z., Vahl, C. I., & Riviere, J. E. (2016). Human Food Safety Implications of Variation in Food Animal Drug Metabolism. Scientific Reports, 6. doi:10.1038/srep27907Violative drug residues in animal-derived foods are a global food safety concern. The use of a fixed main metabolite to parent drug (M/D) ratio determined in healthy animals to establish drug tolerances and withdrawal times in diseased animals results in frequent residue violations in food-producing animals. We created a general physiologically based pharmacokinetic model for representative drugs (ceftiofur, enrofloxacin, flunixin, and sulfamethazine) in cattle and swine based on extensive published literature. Simulation results showed that the M/D ratio was not a fixed value, but a time-dependent range. Disease changed M/D ratios substantially and extended withdrawal times; these effects exhibited drug-and species-specificity. These results challenge the interpretation of violative residues based on the use of the M/D ratio to establish tolerances for metabolized drugs
Herschel GASPS spectral observations of T Tauri stars in Taurus: unraveling far-infrared line emission from jets and discs
At early stages of stellar evolution young stars show powerful jets and/or
outflows that interact with protoplanetary discs and their surroundings.
Despite the scarce knowledge about the interaction of jets and/or outflows with
discs, spectroscopic studies based on Herschel and ISO data suggests that gas
shocked by jets and/or outflows can be traced by far-IR (FIR) emission in
certain sources. We want to provide a consistent catalogue of selected atomic
([OI] and [CII]) and molecular (CO, OH, and HO) line fluxes observed in
the FIR, separate and characterize the contribution from the jet and the disc
to the observed line emission, and place the observations in an evolutionary
picture. The atomic and molecular FIR (60-190 ) line emission of
protoplanetary discs around 76 T Tauri stars located in Taurus are analysed.
The observations were carried out within the Herschel key programme Gas in
Protoplanetary Systems (GASPS). The spectra were obtained with the
Photodetector Array Camera and Spectrometer (PACS). The sample is first divided
in outflow and non-outflow sources according to literature tabulations. With
the aid of archival stellar/disc and jet/outflow tracers and model predictions
(PDRs and shocks), correlations are explored to constrain the physical
mechanisms behind the observed line emission. The much higher detection rate of
emission lines in outflow sources and the compatibility of line ratios with
shock model predictions supports the idea of a dominant contribution from the
jet/outflow to the line emission, in particular at earlier stages of the
stellar evolution as the brightness of FIR lines depends in large part on the
specific evolutionary stage. [Abridged Abstract]Comment: 37 pages, 27 figures, accepted for publication in A&
Gas and dust in the Beta Pictoris Moving Group as seen by the Herschel Space Observatory
Context. Debris discs are thought to be formed through the collisional
grinding of planetesimals, and can be considered as the outcome of planet
formation. Understanding the properties of gas and dust in debris discs can
help us to comprehend the architecture of extrasolar planetary systems.
Herschel Space Observatory far-infrared (IR) photometry and spectroscopy have
provided a valuable dataset for the study of debris discs gas and dust
composition. This paper is part of a series of papers devoted to the study of
Herschel PACS observations of young stellar associations.
Aims. This work aims at studying the properties of discs in the Beta Pictoris
Moving Group (BPMG) through far-IR PACS observations of dust and gas.
Methods. We obtained Herschel-PACS far-IR photometric observations at 70, 100
and 160 microns of 19 BPMG members, together with spectroscopic observations of
four of them. Spectroscopic observations were centred at 63.18 microns and 157
microns, aiming to detect [OI] and [CII] emission. We incorporated the new
far-IR observations in the SED of BPMG members and fitted modified blackbody
models to better characterise the dust content.
Results. We have detected far-IR excess emission toward nine BPMG members,
including the first detection of an IR excess toward HD 29391.The star HD
172555, shows [OI] emission, while HD 181296, shows [CII] emission, expanding
the short list of debris discs with a gas detection. No debris disc in BPMG is
detected in both [OI] and [CII]. The discs show dust temperatures in the range
55 to 264 K, with low dust masses (6.6*10^{-5} MEarth to 0.2 MEarth) and radii
from blackbody models in the range 3 to 82 AU. All the objects with a gas
detection are early spectral type stars with a hot dust component.Comment: 12 pages, 7 figures, 6 table
The Transiting Exocomets in the HD 172555 System
The Earth is thought to have formed dry, in a part of the Solar Nebula deficient in organic material, and to have acquired its organics and water through bombardment by minor bodies. Observations of this process in well-dated systems can provide insight into the probable origin and composition of the bombarding parent bodies. Transiting cometary activity has previously been reported in Ca II for the late-A member of the 241 Myr old Pictoris Moving Group member, HD 172555(Kiefer et al. 2014). We present HST STIS and COS spectra of HD 172555 demonstrating that the star has chromospheric emission and variable in falling gas features in transitions of silicon and carbon ions at times when no Fe II absorption is seen in the UV data, and no Ca II absorption is seen in contemporary optical spectra. The lack of CO absorption and stable gas absorption at the system velocity is consistent with the absence of a cold Kuiper belt analog (Riviere-Marichalar et al. 2012) in this system. The presence of infall in some species at one epoch and others at different epochs suggests that, like Pictoris, there may be more than one family of exocomets. If perturbed into star-grazing orbits by the same mechanism as for Pic, these data suggest that the wide planet frequency among A-early F stars in the PMG is at least 37.5, well above the frequency estimated for young moving groups independent of host star spectral type
Partialization losses of ON/OFF operation of waterto- water refrigeration/heat-pump units
[EN] This paper presents the results of an experimental campaign for the characterization of the dynamic behavior of a water-to-water refrigeration/heat-pump unit under ON/OFF operation.
The unit was previously tested at different water inlet temperatures under steady
state conditions, and a very good agreement was found between the instantaneous dynamic performance of the heat pump and the corresponding quasi-steady state operation.
In parallel, a series of tests were carried out to quantify the coefficient of performance
(COP) degradation as a function of the load ratio, and a simple formula for the Part Load
Factor is presented. Results lead to the conclusion that the only non-negligible factor in the COP degradation is the stand-by electrical consumption during the OFF period, especially at low load ratios. Finally, it is concluded that the minimization of the stand-by consumption is a key point for the future improvement of the seasonal performance of water-to-water systems.This research has been partially funded by the European FP7 framework project "Advanced ground source heat pump systems for heating and cooling in Mediterranean climate" (GROUND-MED) and the Spanish Ministry of Economy and Competitiveness (MINECO) through the project "Estudio de evaporadores y condensadores basados en tecnologia de minicanales para su aplicaciOn en equipos de aire acondicionado, refrigeraciOn y bomba de calor estacionarios" with reference DPI2011-26771-C02-01. The authors gratefully acknowledge their financial support.Corberán, JM.; D.Donadello; Martínez Galván, IO.; Montagud, C. (2013). Partialization losses of ON/OFF operation of waterto- water refrigeration/heat-pump units. International Journal of Refrigeration. 36(8):2251-2261. https://doi.org/10.1016/j.ijrefrig.2013.07.002S2251226136
DZ Cha: a bona fide photoevaporating disc
DZ Cha is a weak-lined T Tauri star (WTTS) surrounded by a bright
protoplanetary disc with evidence of inner disc clearing. Its narrow \Ha line
and infrared spectral energy distribution suggest that DZ Cha may be a
photoevaporating disc. We aim to analyse the DZ Cha star + disc system to
identify the mechanism driving the evolution of this object. We have analysed
three epochs of high resolution optical spectroscopy, photometry from the UV up
to the sub-mm regime, infrared spectroscopy, and J-band imaging polarimetry
observations of DZ Cha. Combining our analysis with previous studies we find no
signatures of accretion in the \Ha line profile in nine epochs covering a
time baseline of years. The optical spectra are dominated by
chromospheric emission lines, but they also show emission from the forbidden
lines [SII] 4068 and [OI] 6300 that indicate a disc outflow. The
polarized images reveal a dust depleted cavity of au in radius and two
spiral-like features, and we derive a disc dust mass limit of
M_\mathrm{dust}
80 \MJup) companions are detected down to 0\farcs07 ( au,
projected). The negligible accretion rate, small cavity, and forbidden line
emission strongly suggests that DZ Cha is currently at the initial stages of
disc clearing by photoevaporation. At this point the inner disc has drained and
the inner wall of the truncated outer disc is directly exposed to the stellar
radiation. We argue that other mechanisms like planet formation or binarity
cannot explain the observed properties of DZ Cha. The scarcity of objects like
this one is in line with the dispersal timescale ( yr) predicted
by this theory. DZ Cha is therefore an ideal target to study the initial stages
of photoevaporation.Comment: A&A in press, language corrections include
Exocomet signatures around the A-shell star Leo?
We present an intensive monitoring of high-resolution spectra of the Ca {\sc
ii} K line in the A7IV shell star Leo at very short (minutes, hours),
short (night to night), and medium (weeks, months) timescales. The spectra show
remarkable variable absorptions on timescales of hours, days, and months. The
characteristics of these sporadic events are very similar to most that are
observed toward the debris disk host star Pic, which are commonly
interpreted as signs of the evaporation of solid, comet-like bodies grazing or
falling onto the star. Therefore, our results suggest the presence of solid
bodies around Leo. To our knowledge, with the exception of Pic,
our monitoring has the best time resolution at the mentioned timescales for a
star with events attributed to exocomets. Assuming the cometary scenario and
considering the timescales of our monitoring, our results indicate that
Leo presents the richest environment with comet-like events known to date,
second only to Pic.Comment: A&A letters, proof-correcte
Polar Smectic Films
We report on a new experimental procedure for forming and studying polar
smectic liquid crystal films. A free standing smectic film is put in contact
with a liquid drop, so that the film has one liquid crystal/liquid interface
and one liquid crystal/air interface. This polar environment results in changes
in the textures observed in the film, including a boojum texture and a
previously unobserved spiral texture in which the winding direction of the
spiral reverses at a finite radius from its center. Some aspects of these
textures are explained by the presence of a Ksb term in the bulk elastic free
energy density that favors a combination of splay and bend deformations.Comment: 4 pages, REVTeX, 3 figures, submitted to PR
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