513 research outputs found
Picard groups and strongly graded coalgebras
AbstractIn this paper we study strongly graded coalgebras and its relation to the Picard group. A classification theorem for this kind of coalgebras is given via the second Doi's cohomology group. The strong Picard group of a coalgebra is introduced in order to characterize those graded coalgebras with strongly graded dual ring. Finally, for a Hopf algebra H we also characterize the H∗-Galois coextensions with dual H-Galois extension solving the question proposed in Dăscălescu et al., J. Algebra 178 (1995) 400–413
Optical and Infrared Photometry of the Unusual Type Ia Supernova 2000cx
We present optical and infrared photometry of the unusual Type Ia supernova
2000cx. With the data of Li et al. (2001) and Jha (2002), this comprises the
largest dataset ever assembled for a Type Ia SN, more than 600 points in
UBVRIJHK. We confirm the finding of Li et al. regarding the unusually blue B-V
colors as SN 2000cx entered the nebular phase. Its I-band secondary hump was
extremely weak given its B-band decline rate. The V minus near infrared colors
likewise do not match loci based on other slowly declining Type Ia SNe, though
V-K is the least ``abnormal''. In several ways SN 2000cx resembles other slow
decliners, given its B-band decline rate (Delta m_15(B) = 0.93), the appearance
of Fe III lines and weakness of Si II in its pre-maximum spectrum, the V-K
colors and post-maximum V-H colors. If the distance modulus derived from
Surface Brightness Fluctuations of the host galaxy is correct, we find that the
rate of light increase prior to maximum, the characteristics of the bolometric
light curve, and the implied absolute magnitude at maximum are all consistent
with a sub-luminous object with Delta m_15(B) ~ 1.6-1.7 having a higher than
normal kinetic energy.Comment: 46 pages, 17 figures, to be published in Publications of the
Astronomical Society of the Pacifi
Visualizing plasmon-exciton polaritons at the nanoscale using electron microscopy
Polaritons are compositional light-matter quasiparticles that have recently
enabled remarkable breakthroughs in quantum and nonlinear optics, as well as in
material science. Despite the enormous progress, however, a direct
nanometer-scale visualization of polaritons has remained an open challenge.
Here, we demonstrate that plasmon-exciton polaritons, or plexcitons, generated
by a hybrid system composed of an individual silver nanoparticle and a
few-layer transition metal dichalcogenide can be spectroscopically mapped with
nanometer spatial resolution using electron energy loss spectroscopy in a
scanning transmission electron microscope. Our experiments reveal important
insights about the coupling process, which have not been reported so far. These
include nanoscale variation of Rabi splitting and plasmon-exciton detuning, as
well as absorption-dominated extinction signals, which in turn provide the
ultimate evidence for the plasmon-exciton hybridization in the strong coupling
regime. These findings pioneer new possibilities for in-depth studies of
polariton-related phenomena with nanometer spatial resolution
Hydrologic responses to deforestation in southwestern amazon sub-basins corroborated by hydrologic simulations.
Calibração do modelo CERES-rice para cultivares de arroz irrigado no Rio Grande do Sul.
No presente trabalho são apresentados os resultados referentes a calibração do modelo CERES-Rice/DSSAT para quatro cultivares cobrindo os principais grupos de maturação utilizados comercialmente no Estado do Rio Grande do Sul, maior estado produtor do Brasil
Water demand prospects for the irrigation in São Francisco River.
Abstract: This study analyzed how the irrigation expansion in São Francisco Hydrographic Region (SFRH) would affect the water availability in four specifics physiographic regions into SFRH (Upper, Middle, sub-Middle, and Lower). The TERM-BR model was used to simulate expansion scenarios in irrigated areas aiming to verify the impact in the water use for 2025 and 2035 according to with National Water Resources Plan (PNRH), and Water Resources Plan for the São Francisco River (SFP). The simulations were carried out for areas deemed potentially suitable for irrigation based on the Ministry of National Integration report (MI). The Climatic Water Balance (CWB) was estimated for São Francisco hydrographic region (SFRH) in order to compare regional water supply and demand. Results suggest that cities located in Upper and Middle São Francisco region would present greater irrigation potential due to the water availability and the proximity to neighborhoods that also irrigate. The comparative result of the CWB and the TERM-BR model shown water availability problems in the states of Alagoas and Pernambuco in particular and cities located in São Francisco Lower.GTAP Resource #5725
Yield and morphophysiological indices of irrigated rice genotypes in contrasting ecosystems.
Rice phenology and development are events controlled by environmental and genetic factors, and the yield potential of the crop is defined by their interaction. This study aimed at analyzing the performance of irrigated rice genotypes in contrasting ecosystems and their effects on morphophysiological characteristics. Two ecosystems (tropical and subtropical) were analyzed, as well as cultivars recommended for tropical (BRS Catiana and BRS Jaçanã) and subtropical (BRS Pampa, BRS 7 Taim and IRGA 424) regions. The experiments were arranged in a complete randomized block design, with four replicates, being the factors the genotypes, sowing times and sites. The phenological development, biomass dynamics, radiation use efficiency and grain yield were evaluated. The accumulated degree-days demand for flowering decreased faster in the tropical ecosystem than in the subtropical ecosystem for late sowing. The radiation use efficiency values were similar in the subtropical ecosystem and yield was high for all sowing dates. On the other hand, the tropical ecosystem showed a high variation for radiation use efficiency values and yield. The higher accumulation of degree-days and solar radiation during the reproductive and grain-filling phases contributed to increase yield in both ecosystems
Dissecting X-ray-emitting Gas around the Center of our Galaxy
Most supermassive black holes (SMBHs) are accreting at very low levels and
are difficult to distinguish from the galaxy centers where they reside. Our own
Galaxy's SMBH provides a uniquely instructive exception, and we present a
close-up view of its quiescent X-ray emission based on 3 mega-second of Chandra
observations. Although the X-ray emission is elongated and aligns well with a
surrounding disk of massive stars, we can rule out a concentration of low-mass
coronally active stars as the origin of the emission based on the lack of
predicted Fe Kalpha emission. The extremely weak H-like Fe Kalpha line further
suggests the presence of an outflow from the accretion flow onto the SMBH.
These results provide important constraints for models of the prevalent
radiatively inefficient accretion state.Comment: 18 pages, 5 PDF figures, pdflatex format; Final version, published in
Scienc
On the efficiency of the Blandford-Znajek mechanism for low angular momentum relativistic accretion
Blandford-Znajek (BZ) mechanism has usually been studied in the literature
for accretion with considerably high angular momentum leading either to the
formation of a cold Keplerian disc, or a hot and geometrically thick
sub-Keplerian flow as described within the framework of ADAF/RIAF. However, in
nearby elliptical galaxies, as well as for our own Galactic centre, accretion
with very low angular momentum is prevalent. Such quasi-spherical strongly
sub-Keplerian accretion has complex dynamical features and can accommodate
stationary shocks. In this letter, we present our calculation for the maximum
efficiency obtainable through the BZ mechanism for complete general
relativistic weakly rotating axisymmetric flow in the Kerr metric. Both shocked
and shock free flow has been studied in detail for rotating and counter
rotating accretion. Such study has never been done in the literature before. We
find that the energy extraction efficiency is low, about 0.1%, and increases by
a factor 15 if the ram pressure is included. Such an efficiency is still much
higher than the radiative efficiency of such optically thin flows. For BZ
mechanism, shocked flow produces higher efficiency than the shock free
solutions and retrograde flow provides a slightly larger value of the
efficiency than that for the prograde flow.Comment: Substantially revised final version to appear in MNRAS Letters. Three
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