522 research outputs found
Spectral properties of the largest asteroids associated with Taurid Complex
We obtained spectra of six of the largest asteroids (2201, 4183, 4486, 5143,
6063, and 269690) associated with Taurid complex. The observations were made
with the IRTF telescope equipped with the spectro-imager SpeX. Their taxonomic
classification is made using Bus-DeMeo taxonomy. The asteroid spectra are
compared with the meteorite spectra from the Relab database. Mineralogical
models were applied to determine their surface composition. All the spectral
analysis is made in the context of the already published physical data.
Five of the objects studied in this paper present spectral characteristics
similar to the S taxonomic complex. The spectra of ordinary chondrites
(spanning H, L, and LL subtypes) are the best matches for these asteroid
spectra. {\bf The asteroid} (269690) 1996 RG3 presents a flat featureless
spectrum which could be associated to a primitive C-type object. The increased
reflectance above 2.1 microns constrains its geometrical albedo to a value
around 0.03.
While there is an important dynamical grouping among the Taurid Complex
asteroids, the spectral data of the largest objects do not support a common
cometary origin. Furthermore, there are significant variations between the
spectra acquired until now.Comment: Accepted for publication in A&
Activation characteristics of the fusion power plant coolants He, water, Pb-li and aspects of tritium extraction techniques
Power Control for Target Tracking in Sensor Networks
We consider the problem of a sensor network tracking a moving target that exhibits a Markov model of mobility. The sensor nodes have adjustable power levels and the precision of the measurement of the target location depends on both the relative distance from the target to the measuring sensor, and on the sensing power level used by that sensor. An important issue in sensor networks is the power effi- ciency, thus we consider the optimization of a family of cost functions that include both the accuracy of a measurement and the power used to do that measurement. We define our problem as a control policy optimization for a partially observed Markov chain. For such scenarios, we derive optimal power control policies based only on partial observations of the target location, and propose hand-off techniques based on this policies
Taxonomic classification of asteroids based on MOVIS near-infrared colors
We aim to provide a taxonomic classification for asteroids observed by
VISTA-VHS survey. We derive a method for assigning a compositional type to an
object based on its (Y-J), (J-Ks), and (H-Ks) colors. We present a taxonomic
classification for 18\,265 asteroids from the MOVIS catalog, using a
probabilistic method and the k-nearest neighbors algorithm. Because our
taxonomy is based only on NIR colors, several classes from Bus-DeMeo were
clustered into groups and a slightly different notation was used (i.e. the
superscript indicates that the classification was obtained based on the NIR
colors and the subscript indicates possible miss-identifications with other
types). Our results are compared with the information provided by the Sloan
Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE). The
two algorithms used in this study give a taxonomic type for all objects having
at least (Y-J) and (J-Ks) observed colors. A final classification is reported
for a set of 6\,496 asteroids based on the criteria that KNN and probabilistic
algorithms gave the same result, (Y-J) 0.118 and
(J-Ks)0.136. This set includes 144 bodies classified as ,
613 as , 197 as , 91 as , 440 as , 665
as , 233 as , 3\,315 as , and 798 as . We
report the albedo distribution for each taxonomic group and we compute new
median values for the main types. We found that V-type and A-type candidates
have identical size frequency distributions, but the V-types are five times
more common than the A-types. Several particular cases, such as the A-type
asteroid (11616) 1996 BQ2 and the S-type (3675) Kematsch, both in the Cybele
population, are discussed. Files and codes available at:
https://github.com/marcelpopescu/MOVIS-TaxonomyComment: 18 pages, 10 figures, accepted for publication in Astronomy &
Astrophysics (A&A
Towards discovery of gravitationally lensed explosive transients: the brightest galaxies in massive galaxy clusters from Planck-SZ2
We combine the Planck-SZ2 galaxy cluster catalogue with near-infrared
photometry of galaxies from the VISTA Hemisphere Survey to identify candidate
brightest cluster galaxies (BCGs) in 306 massive clusters in the Southern skies
at redshifts of . We find that 91% of these clusters have at least one
candidate BCG within the 95% confidence interval on the cluster centers quoted
by the Planck collaboration, providing reassurance that our analyses are
statistically compatible, and find 92% to be reasonable candidates following a
manual inspection. We make our catalog publicly available to assist colleagues
interested in multi-wavelength studies of cluster cores, and the search for
gravitationally lensed explosive transients in upcoming surveys including the
Legacy Survey of Space and Time by the Vera C. Rubin Observatory.Comment: Published in RNAAS in March 2023. 3 pages, 1 figur
Evolutionary factors affecting Lactate dehydrogenase A and B variation in the Daphnia pulex species complex
Background: Evidence for historical, demographic and selective factors affecting enzyme evolution can be
obtained by examining nucleotide sequence variation in candidate genes such as Lactate dehydrogenase (Ldh). Two
closely related Daphnia species can be distinguished by their electrophoretic Ldh genotype and habitat. Daphnia
pulex populations are fixed for the S allele and inhabit temporary ponds, while D. pulicaria populations are fixed for
the F allele and inhabit large stratified lakes. One locus is detected in most allozyme surveys, but genome
sequencing has revealed two genes, LdhA and LdhB.
Results: We sequenced both Ldh genes from 70 isolates of these two species from North America to determine if
the association between Ldh genotype and habitat shows evidence for selection, and to elucidate the evolutionary
history of the two genes. We found that alleles in the pond-dwelling D. pulex and in the lake-dwelling D. pulicaria
form distinct groups at both loci, and the substitution of Glutamine (S) for Glutamic acid (F) at amino acid 229
likely causes the electrophoretic mobility shift in the LDHA protein. Nucleotide diversity in both Ldh genes is much
lower in D. pulicaria than in D. pulex. Moreover, the lack of spatial structuring of the variation in both genes over a
wide geographic area is consistent with a recent demographic expansion of lake populations. Neutrality tests
indicate that both genes are under purifying selection, but the intensity is much stronger on LdhA.
Conclusions: Although lake-dwelling D. pulicaria hybridizes with the other lineages in the pulex species complex,
it remains distinct ecologically and genetically. This ecological divergence, coupled with the intensity of purifying
selection on LdhA and the strong association between its genotype and habitat, suggests that experimental
studies would be useful to determine if variation in molecular function provides evidence that LDHA variants are
adaptive
Continuous wave optical parametric oscillator for quartz-enhanced photoacoustic trace gas sensing
A continuous wave optical parametric oscillator, generating up to 300 mW idler output in the 3–4 μm wavelength region, and pumped by a fiber-amplified DBR diode laser is used for trace gas detection by means of quartz-enhanced photoacoustic spectroscopy (QEPAS). Mode-hop-free tuning of the OPO output over 5.2 cm-1 and continuous spectral coverage exceeding 16.5 cm-1 were achieved via electronic pump source tuning alone. Online monitoring of the idler wavelength, with feedback to the DBR diode laser, provided an automated closed-loop control allowing arbitrary idler wavelength selection within the pump tuning range and locking of the idler wavelength with a stability of 1.7×10-3 cm-1 over at least 30 min.\ud
\ud
Using this approach, we locked the idler wavelength at an ethane absorption peak and obtained QEPAS data to verify the linear response of the QEPAS signal at different ethane concentrations (100 ppbv-20 ppmv) and different power levels. The detection limit for ethane was determined to be 13 ppbv (20 s averaging), corresponding to a normalized noise equivalent absorption coefficient of 4.4×10-7 cm-1 W/Hz1/2
Status of maturation of critical technologies and systems design: Breeding blanket
The scope of the EUFOfusion Work Package Breeding Blanket is to develop a blanket concept for the EU DEMO reactor; this includes the blanket segments inside the Vacuum Vessel and the related Tritium Extraction/Removal Systems. In the Pre-Concept Design (PCD) Phase, two concepts have been selected as candidates; a solid and a liquid breeder blanket cooled with helium and water, respectively. The design of these two blanket systems has been adapted to the DEMO plant design developed in the PCD Phase and performances assessed. A large R&D programme has been implemented with the scope to evaluate different technologies for these blankets; including the development of breeders, tritium extraction and cooling technologies, and the manufacturing of the blanket system. A major milestone in the subsequent Concept Design Phase is the final selection of the blanket concept for DEMO
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