979 research outputs found
Ground-based Characterization of Hayabusa2 Mission Target Asteroid 162173 Ryugu: Constraining Mineralogical Composition in Preparation for Spacecraft Operations
Asteroids that are targets of spacecraft missions are interesting because
they present us with an opportunity to validate ground-based spectral
observations. One such object is near-Earth asteroid (NEA) (162173) Ryugu,
which is the target of the Japanese Space Agency's (JAXA) Hayabusa2 sample
return mission. We observed Ryugu using the 3-m NASA Infrared Telescope
Facility (IRTF) on Mauna Kea, Hawaii, on July 13, 2016 to constrain the
object's surface composition, meteorite analogs, and link to other asteroids in
the main belt and NEA populations. We also modeled its photometric properties
using archival data. Using the Lommel-Seeliger model we computed the predicted
flux for Ryugu at a wide range of viewing geometries as well as albedo
quantities such as geometric albedo, phase integral, and spherical Bond albedo.
Our computed albedo quantities are consistent with results from Ishiguro et al.
(2014). Our spectral analysis has found a near-perfect match between our
spectrum of Ryugu and those of NEA (85275) 1994 LY and Mars-crossing asteroid
(316720) 1998 BE7, suggesting that their surface regoliths have similar
composition. We compared Ryugu's spectrum with that of main belt asteroid (302)
Clarissa, the largest asteroid in the Clarissa asteroid family, suggested as a
possible source of Ryugu by Campins et al. (2013). We found that the spectrum
of Clarissa shows significant differences with our spectrum of Ryugu, but it is
similar to the spectrum obtained by Moskovitz et al. (2013). The best possible
meteorite analogs for our spectrum of Ryugu are two CM2 carbonaceous
chondrites, Mighei and ALH83100.Comment: 23 pages, 7 figures, 4 tables, accepted in Monthly Notices of the
Royal Astronomical Society Main Journa
Electrospinning of 2-hydroxypropyl-β-cyclodextrin aqueous solutions with added salts
It has been proposed that hydrogen bonding plays a role in promoting the electrospinnability of some materials. In this study, the role of non-covalent interactions in the electrospinnability of 2-hydroxypropyl-β-cyclodextrin (2HP-β-CD) was investigated by varying the physical-chemical properties the solvents. The rheological behaviour of a peroxide-aqueous/acetone-ethanol/NaHCO3 solution and an aqueous urea solution, as a function of aqueous 2HP-β-CD concentration, was compared. The rheological behaviour of 2HP-β-CD solutions was characterized by a frequency-independent stress relaxation plateau such as that observed in cross-linked polymer networks and reversible polymer gels with non-linear viscoelasticity. We conclude that the electrospinnability of 2HP-β-CD is, as evidenced by the changes in the morphology of the electrospun 2HP-β-CD materials, in agreement with other related studies on the electrospinning of Cyclodextrins. Also, the electrospinnability of 2HP-β-CD does appear to be related to the physical-chemical properties of the solvent systems
The contamination of the surface of Vesta by impacts and the delivery of the dark material
The Dawn spacecraft observed the presence of dark material, which in turn
proved to be associated with OH and H-rich material, on the surface of Vesta.
The source of this dark material has been identified with the low albedo
asteroids, but it is still a matter of debate whether the delivery of the dark
material is associated with a few large impact events, to micrometeorites or to
the continuous, secular flux of impactors on Vesta. The continuous flux
scenario predicts that a significant fraction of the exogenous material
accreted by Vesta should be due to non-dark impactors likely analogous to
ordinary chondrites, which instead represent only a minor contaminant in the
HED meteorites. We explored the continuous flux scenario and its implications
for the composition of the vestan regolith, taking advantage of the data from
the Dawn mission and the HED meteorites. We used our model to show that the
stochastic events scenario and the micrometeoritic flux scenario are natural
consequences of the continuous flux scenario. We then used the model to
estimate the amounts of dark and hydroxylate materials delivered on Vesta since
the LHB and we showed how our results match well with the values estimated by
the Dawn mission. We used our model to assess the amount of Fe and siderophile
elements that the continuous flux of impactors would mix in the vestan
regolith: concerning the siderophile elements, we focused our attention on the
role of Ni. The results are in agreement with the data available on the Fe and
Ni content of the HED meteorites and can be used as a reference frame in future
studies of the data from the Dawn mission and of the HED meteorites. Our model
cannot yet provide an answer to the fate of the missing non-carbonaceous
contaminants, but we discuss possible reasons for this discrepancy.Comment: 31 pages, 7 figures, 4 tables. Accepted for publication on the
journal ICARUS, "Dark and Bright Materials on Vesta" special issu
Sublethal dose effects of a neonicotinoid insecticide, clothianidin, on sex pheromone responses in the black cutworm moth
Composition of Near-Earth Asteroid 2008 EV5: Potential target for Robotic and Human Exploration
We observed potentially hazardous asteroid (PHA) 2008 EV5 in the visible
(0.30-0.92 microns) and near-IR (0.75-2.5 microns) wavelengths to determine its
surface composition. This asteroid is especially interesting because it is a
potential target for two sample return mission proposals (Marco Polo-R and
Hayabusa-2) and human exploration due to its low delta-v for rendezvous. The
spectrum of 2008 EV5 is essentially featureless with exception of a weak
0.48-microns spin-forbidden Fe3+ absorption band. The spectrum also has an
overall blue slope. The albedo of 2008 EV5 remains uncertain with a lower limit
at 0.05 and a higher end at 0.20 based on thermal modeling. The Busch et al.
(2011) albedo estimate of 0.12 is consistent with our thermal modeling results.
The albedo and composition of 2008 EV5 are also consistent with a C-type
taxonomic classification (Somers et al. 2008). The best spectral match is with
CI carbonaceous chondrites similar to Orgueil, which also have a weak
0.48-microns feature and an overall blue slope. This 0.48-microns feature is
also seen in the spectrum of magnetite. The albedo of CI chondrites is at the
lower limit of our estimated range for the albedo of 2008 EV5.Comment: Pages: 19 Figures: 6 Tables:
Understanding Dark Current-Voltage Characteristics in Metal-Halide Perovskite Single Crystals
Hybrid halide perovskites have great potential for application in optoelectronic devices. However, an understanding of some basic properties, such as charge-carrier transport, remains inconclusive, mainly due to the mixed ionic and electronic nature of these materials. Here, we perform temperature-dependent pulsed-voltage space-charge-limited current measurements to provide a detailed look into the electronic properties of methylammonium lead tribromide (MAPbBr(3)) and methylammonium lead triiodide (MAPbI(3)) single crystals. We show that the background carrier density in these crystals is orders of magnitude higher than that expected from thermally excited carriers from the valence band. We highlight the complexity of the system via a combination of experiments and drift-diffusion simulations and show that different factors, such as thermal injection from the electrodes, temperature-dependent mobility, and trap and ion density, influence the free-carrier concentration. We experimentally determine effective activation energies for conductivity of (349 +/- 10) meV for MAPbBr3 and (193 +/- 12) meV for MAPbI(3), which includes the sum of all of these factors. We point out that fitting the dark current density-voltage curve with a drift-diffusion model allows for the extraction of intrinsic parameters, such as mobility and trap and ion density. From simulations, we determine a charge-carrier mobility of 12.9 cm(2)/Vs, a trap density of 1.52 x 10(13) cm(-3), and an ion density of 3.19 x 10(12) cm(-3) for MAPbBr(3) single crystals. Insights into charge-carrier transport in metal-halide perovskite single crystals will be beneficial for device optimization in various optoelectronic applications
Low doses of a neonicotinoid insecticide modify pheromone response thresholds of central but not peripheral olfactory neurons in a pest insect
Insect pest management relies mainly on neurotoxic insecticides, including neonicotinoids, leaving residues in the environment. There is now evidence that low doses of insecticides can have positive effects on pest insects by enhancing various life traits. Because pest insects often rely on sex pheromones for reproduction, and olfactory synaptic transmission is cholinergic, neonicotinoid residues could modify chemical communication. We recently showed that treatments with different sublethal doses of clothianidin could either enhance or decrease behavioural sex pheromone responses in the male moth, Agrotis ipsilon. We investigated now effects of the behaviourally active clothianidin doses on the sensitivity of the peripheral and central olfactory system. We show with extracellular recordings that both tested clothianidin doses do not influence pheromone responses in olfactory receptor neurons. Similarly, in vivo optical imaging does not reveal any changes in glomerular response intensities to the sex pheromone after clothianidin treatments. The sensitivity of intracellularly recorded antennal lobe output neurons, however, is upregulated by a lethal dose 20 times and downregulated by a dose 10 times lower than the lethal dose 0. This correlates with the changes of behavioural responses after clothianidin treatment and suggests the antennal lobe as neural substrate involved in clothianidin-induced behavioural changes
Données récentes sur les caractéristiques morphologiques et biologiques de la population d'Alose feinte du Rhône (Alosa fallax rhodanensis Roule, 1924)
- …