3,451 research outputs found
Quasar 3C 298: a test-case for meteoritic nanodiamond 3.5 ”m emission
Aims. We calculate the dust emission expected at 3.43 and 3.53 ”m if meteoritic (i.e. hydrogenated) nanodiamonds are responsible for most of the far-UV break observed in quasars.
Methods. We integrate the UV flux that hydrogenated nanodiamonds must absorb to reproduce the far-UV break. Based on laboratory spectra of H-terminated diamond surfaces, we analyse the radiative energy budget and derive theoretically the IR emission profiles expected for possible C-H surface stretch modes of the diamonds.
Results. Using as test case a spectrum of 3C 298 provided by the Spitzer Observatory, we do not find evidence of these emission bands.
Conclusions. While diamonds without surface adsorbates remain a viable candidate for explaining the far-UV break observed in quasars, hydrogenated nanodiamonds appear to be ruled out, as they would give rise to IR emission bands, which have not been observed so far
Multigenome DNA sequence conservation identifies Hox cis-regulatory elements
To learn how well ungapped sequence comparisons of multiple species can predict cis-regulatory elements in Caenorhabditis elegans, we made such predictions across the large, complex ceh-13/lin-39 locus and tested them transgenically. We also examined how prediction quality varied with different genomes and parameters in our comparisons. Specifically, we sequenced âŒ0.5% of the C. brenneri and C. sp. 3 PS1010 genomes, and compared five Caenorhabditis genomes (C. elegans, C. briggsae, C. brenneri, C. remanei, and C. sp. 3 PS1010) to find regulatory elements in 22.8 kb of noncoding sequence from the ceh-13/lin-39 Hox subcluster. We developed the MUSSA program to find ungapped DNA sequences with N-way transitive conservation, applied it to the ceh-13/lin-39 locus, and transgenically assayed 21 regions with both high and low degrees of conservation. This identified 10 functional regulatory elements whose activities matched known ceh-13/lin-39 expression, with 100% specificity and a 77% recovery rate. One element was so well conserved that a similar mouse Hox cluster sequence recapitulated the native nematode expression pattern when tested in worms. Our findings suggest that ungapped sequence comparisons can predict regulatory elements genome-wide
Alternative global Cretaceous paleogeography
Plate tectonic reconstructions for the Cretaceous have assumed that the major
continental blocksâEurasia, Greenland, North America, South America, Africa, India,
Australia, and Antarcticaâhad separated from one another by the end of the Early
Cretaceous, and that deep ocean passages connected the Pacific, Tethyan, Atlantic, and
Indian Ocean basins. North America, Eurasia, and Africa were crossed by shallow
meridional seaways. This classic view of Cretaceous paleogeography may be incorrect.
The revised view of the Early Cretaceous is one of three large continental blocksâ
North AmericaâEurasia, South AmericaâAntarctica-India-Madagascar-Australia;
and Africaâwith large contiguous land areas surrounded by shallow epicontinental
seas. There was a large open Pacific basin, a wide eastern Tethys, and a circum-
African Seaway extending from the western Tethys (âMediterraneanâ) region
through the North and South Atlantic into the juvenile Indian Ocean between
Madagascar-India and Africa. During the Early Cretaceous the deep passage from
the Central Atlantic to the Pacific was blocked by blocks of northern Central America
and by the Caribbean plate. There were no deep-water passages to the Arctic. Until
the Late Cretaceous the Atlantic-Indian Ocean complex was a long, narrow, sinuous
ocean basin extending off the Tethys and around Africa.
Deep passages connecting the western Tethys with the Central Atlantic, the
Central Atlantic with the Pacific, and the South Atlantic with the developing Indian
Ocean appeared in the Late Cretaceous. There were many island land areas surrounded
by shallow epicontinental seas at high sea-level stands
Verification of real-time WSA-ENLIL+Cone simulations of CME arrival-time at the CCMC from 2010-2016
The Wang-Sheeley-Arge (WSA)-ENLIL+Cone model is used extensively in space
weather operations world-wide to model CME propagation. As such, it is
important to assess its performance. We present validation results of the
WSA-ENLIL+Cone model installed at the Community Coordinated Modeling Center
(CCMC) and executed in real-time by the CCMC space weather team. CCMC uses the
WSA-ENLIL+Cone model to predict CME arrivals at NASA missions throughout the
inner heliosphere. In this work we compare model predicted CME arrival-times to
in-situ ICME leading edge measurements at STEREO-A, STEREO-B, and Earth (Wind
and ACE) for simulations completed between March 2010-December 2016 (over 1,800
CMEs). We report hit, miss, false alarm, and correct rejection statistics for
all three locations. For all predicted CME arrivals, the hit rate is 0.5, and
the false alarm rate is 0.1. For the 273 events where the CME was predicted to
arrive at Earth, STEREO-A, or STEREO-B, and was actually observed (hit event),
the mean absolute arrival-time prediction error was 10.4 +/- 0.9 hours, with a
tendency to early prediction error of -4.0 hours. We show the dependence of the
arrival-time error on CME input parameters. We also explore the impact of the
multi-spacecraft observations used to initialize the model CME inputs by
comparing model verification results before and after the STEREO-B
communication loss (since September 2014) and STEREO-A sidelobe operations
(August 2014-December 2015). There is an increase of 1.7 hours in the CME
arrival time error during single, or limited two-viewpoint periods, compared to
the three-spacecraft viewpoint period. This trend would apply to a future space
weather mission at L5 or L4 as another coronagraph viewpoint to reduce CME
arrival time errors compared to a single L1 viewpoint
Bandt-Pompe symbolization dynamics for time series with tied values: A data-driven approach
In 2002, Bandt and Pompe [Phys. Rev. Lett. 88, 174102 (2002)] introduced a successfully symbolic encoding scheme based on the ordinal relation between the amplitude of neighboring values of a given data sequence, from which the permutation entropy can be evaluated. Equalities in the analyzed sequence, for example, repeated equal values, deserve special attention and treatment as was shown recently by Zunino and co-workers [Phys. Lett. A 381, 1883 (2017)]. A significant number of equal values can give rise to false conclusions regarding the underlying temporal structures in practical contexts. In the present contribution, we review the different existing methodologies for treating time series with tied values by classifying them according to their different strategies. In addition, a novel data-driven imputation is presented that proves to outperform the existing methodologies and avoid the false conclusions pointed by Zunino and co-workers.Fil: Traversaro Varela, Francisco. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional de LanĂșs; ArgentinaFil: Redelico, Francisco Oscar. Hospital Italiano; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Risk, Marcelo. Hospital Italiano; Argentina. Instituto TecnolĂłgico de Buenos Aires; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Frery, Alejandro CĂ©sar. Universidade Federal de Alagoas; BrasilFil: Rosso, Osvaldo AnĂbal. Hospital Italiano; Argentina. Universidade Federal de Alagoas; Brasil. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Los Andes; Chil
An approach towards rapid optical measurements of antioxidant activity in blueberry cultivars
Blueberries are well known for their high antioxidant levels. Compared to bilberries (V. myrtillus) with higher antioxidant activity and more intensive blue colour throughout the whole berry, highbush blueberries have the blue pigments concentrated in the skin. Highbush blueberry skin is found to contain a very high content of phenolic compounds. To measure the total antioxidant activity in blueberries, several methods, mostly destructive, including the FRAP assay, have been used. This work is an initial approach towards a simple and rapid method, combining optical and antioxidant activity measurements. Highbush blueberry (V. corymbosum) cultivars âBluecropâ, âHardyblueâ, âPatriotâ, and lowbush cultivars âPutteâ (a hybrid originated from V. angustifolium) and âAronâ (V. corymbosum x V. uliginosum) were grown at the Norwegian University of Life Sciences (59Âș 40âN). Berries were harvested at commercial blue-ripe stage of maturity. Fresh berries were cut horizontally and placed on a scanner in order to examine berry size and skin thickness. Berries were weighed, and analysed for antioxidant activity using the FRAP (Ferric Reducing Ability of Plasma) assay. The FRAP assay is a non-specific method based on absorption changes following a reduction of a ferric- to a ferrous-complex in the presence of antioxidants.Own previous results have shown that antioxidant activity and berry weight varied between cultivars (REMBERG et al., 2003). Small berries had higher antioxidant activity compared to larger berries. In this follow-up project, skin thickness and berry diameter were measured by using an image- processing program. Berry and skin cross-section areas were correlated with the antioxidant activity
XMM-Newton Surveys of the Canada-France Redshift Survey Fields - III: The Environments of X-ray Selected AGN at 0.4<z<0.6
The environmental properties of a sample of 31 hard X-ray selected AGN are
investigated, from scales of 500 kpc down to 30 kpc, and are compared to a
control sample of inactive galaxies. The AGN all lie in the redshift range
0.4<z<0.6. The accretion luminosity-density of the Universe peaks close to this
redshift range, and the AGN in the sample have X-ray luminosities close to the
knee in the hard X-ray luminosity function, making them representative of the
population which dominated this important phase of energy conversion.
Using both the spatial clustering amplitude and near neighbour counts it is
found that the AGN have environments that are indistinguishable from normal,
inactive galaxies over the same redshift range and with similar optical
properties. Typically, the environments are of sub-cluster richness, in
contrast to similar studies of high-z quasars, which are often found in
clusters with comparable richness to the Abell R>=0 clusters.
It is suggested that minor mergers with low mass companions is a likely
candidate for the mechanism by which these modest luminosity AGN are fuelled.Comment: 12 pages, 6 figures, accepted by MNRA
Globally sparse PLS regression
Volume 56 ; Print ISBN : 978-1-4614-8282-6Partial least squares (PLS) regression combines dimensionality reduction and prediction using a latent variable model. It provides better predictive ability than principle component analysis by taking into account both the independent and re- sponse variables in the dimension reduction procedure. However, PLS suffers from over-fitting problems for few samples but many variables. We formulate a new criterion for sparse PLS by adding a structured sparsity constraint to the global SIMPLS optimization. The constraint is a sparsity-inducing norm, which is useful for selecting the important variables shared among all the components. The optimization is solved by an augmented Lagrangian method to obtain the PLS components and to perform variable selection simultaneously. We propose a novel greedy algorithm to overcome the computation difficulties. Experiments demonstrate that our approach to PLS regression attains better performance with fewer selected predictor
JHK Observations of Faint Standard Stars in the Mauna Kea Near-Infrared Photometric System
JHK photometry in the Mauna Kea Observatory (MKO) near-IR system is presented
for 115 stars. Of these, 79 are UKIRT standards and 42 are LCO standards. The
average brightness is 11.5 mag, with a range of 10 to 15. The average number of
nights each star was observed is 4, and the average of the internal error of
the final results is 0.011 mag. These JHK data agree with those reported by
other groups to 0.02 mag. The measurements are used to derive transformations
between the MKO JHK photometric system and the UKIRT, LCO and 2MASS systems.
The 2MASS-MKO data scatter by 0.05 mag for redder stars: 2MASS-J includes H2O
features in dwarfs and MKO-K includes CO features in giants. Transformations
derived for stars whose spectra contain only weak features cannot give accurate
transformations for objects with strong absorption features within a filter
bandpasses. We find evidence of systematic effects at the 0.02 mag level in the
photometry of stars with J<11 and H,K<10.5. This is due to an underestimate of
the linearity correction for stars observed with the shortest exposure times;
very accurate photometry of stars approaching the saturation limits of infrared
detectors which are operated in double-read mode is difficult to obtain. Four
stars in the sample, GSPC S705-D, FS 116 (B216-b7), FS 144 (Ser-EC84) and FS 32
(Feige 108), may be variable. 84 stars in the sample have 11< J< 15 and
10.5<H,K<15, are not suspected to be variable, and have magnitudes with an
estimated error <0.027 mag; 79 of these have an error of <0.020 mag. These
represent the first published high-accuracy JHK stellar photometry in the MKO
photometric system; we recommend these objects be employed as primary standards
for that system [abridged].Comment: Accepted for publication in MNRAS, 14 pages, 5 Figure
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