64 research outputs found
Schubert calculus of Richardson varieties stable under spherical Levi subgroups
We observe that the expansion in the basis of Schubert cycles for
of the class of a Richardson variety stable under a spherical Levi subgroup is
described by a theorem of Brion. Using this observation, along with a
combinatorial model of the poset of certain symmetric subgroup orbit closures,
we give positive combinatorial descriptions of certain Schubert structure
constants on the full flag variety in type . Namely, we describe
when and are inverse to Grassmannian permutations with unique descents
at and , respectively. We offer some conjectures for similar rules in
types and , associated to Richardson varieties stable under spherical
Levi subgroups of SO(2n+1,\C) and SO(2n,\C), respectively.Comment: Section 4 significantly shortened, and other minor changes made as
suggested by referees. Final version, to appear in Journal of Algebraic
Combinatoric
Cluster structure of 13C probed via the 7Li(9Be,13C*->9Be+alpha) reaction
A study of the 7Li(9Be,4He9Be)3H reaction at E{beam}=70 MeV has been
performed using resonant particle spectroscopy techniques and provides a
measurement of alpha-decaying states in 13C. Excited states are observed at
12.0, 13.4, 14.1, 14.6, 15.2, 16.8, 17.9, 18.7, 21.3 and 23.9 MeV. This study
provides the first measurement of the three highest energy states. Angular
distribution measurements have been performed and have been employed to
indicate the transferred angular momentum for the populated states. These data
are compared with recent speculations of the presence of chain-like structures
in 13C.Comment: accepted for publication in Nuclear Physics
Magnetic Charge Lattices, Moduli Spaces and Fusion Rules
We analyze the set of magnetic charges carried by smooth BPS monopoles in
Yang-Mills-Higgs theory with arbitrary gauge group G spontaneously broken to a
subgroup H. The charges are restricted by a generalized Dirac quantization
condition and by an inequality due to Murray. Geometrically, the set of allowed
charges is a solid cone in the coroot lattice of G, which we call the Murray
cone. We argue that magnetic charge sectors correspond to points in the Murray
cone divided by the Weyl group of H; hence magnetic charge sectors are labelled
by dominant integral weights of the dual group H*. We define generators of the
Murray cone modulo Weyl group, and interpret the monopoles in the associated
magnetic charge sectors as basic; monopoles in sectors with decomposable
charges are interpreted as composite configurations. This interpretation is
supported by the dimensionality of the moduli spaces associated to the magnetic
charges and by classical fusion properties for smooth monopoles in particular
cases. Throughout the paper we compare our findings with corresponding results
for singular monopoles recently obtained by Kapustin and Witten.Comment: 53 pages, 6 figure
alpha-decay of excited states in 11C and 11B
Studies of the 16O(9Be,alpha7Be)14C and 7Li(9Be,alpha7Li)5He reactions at
E{beam}=70 MeV have been performed using resonant particle spectroscopy
techniques. The 11C excited states decaying into alpha+7Be(gs) are observed at
8.65, 9.85, 10.7 and 12.1 MeV as well as possible states at 12.6 and 13.4 MeV.
This result is the first observation of alpha-decay for excited states above 9
MeV. The alpha+7Li(gs) decay of 11B excited states at 9.2, 10.3, 10.55, 11.2,
(11.4), 11.8, 12.5,(13.0), 13.1, (14.0), 14.35, (17.4) and (18.6) MeV is
observed. The decay processes are used to indicate the possible three-centre
2alpha+3He(3H) cluster structure of observed states. Two rotational bands
corresponding to very deformed structures are suggested for the positive-parity
states. Excitations of some observed T=1/2 resonances coincide with the
energies of T=3/2 states which are the isobaric analogs of the lowest 11Be
states. Some of these states may have mixed isospin.Comment: accepted for publication in Nuclear Physics
Whole genome analysis of a schistosomiasis-transmitting freshwater snail
Biomphalaria snails are instrumental in transmission of the human blood fluke Schistosoma mansoni. With the World Health Organization's goal to eliminate schistosomiasis as a global health problem by 2025, there is now renewed emphasis on snail control. Here, we characterize the genome of Biomphalaria glabrata, a lophotrochozoan protostome, and provide timely and important information on snail biology. We describe aspects of phero-perception, stress responses, immune function and regulation of gene expression that support the persistence of B. glabrata in the field and may define this species as a suitable snail host for S. mansoni. We identify several potential targets for developing novel control measures aimed at reducing snail-mediated transmission of schistosomiasis
Bright Opportunities for Atmospheric Characterization of Small Planets: Masses and Radii of K2-3 b, c, and d and GJ3470 b from Radial Velocity Measurements and Spitzer Transits
We report improved masses, radii, and densities for four planets in two bright M-dwarf systems, K2-3 and GJ3470, derived from a combination of new radial velocity and transit observations. Supplementing K2 photometry with follow-up Spitzer transit observations refined the transit ephemerides of K2-3 b, c, and d by over a factor of 10. We analyze ground-based photometry from the Evryscope and Fairborn Observatory to determine the characteristic stellar activity timescales for our Gaussian Process fit, including the stellar rotation period and activity region decay timescale. The stellar rotation signals for both stars are evident in the radial velocity data and is included in our fit using a Gaussian process trained on the photometry. We find the masses of K2-3 b, K2-3 c, and GJ3470 b to be 6.48, 2.14, and 12.58 M ⊕, respectively. K2-3 d was not significantly detected and has a 3σ upper limit of 2.80 M ⊕ . These two systems are training cases for future TESS systems; due to the low planet densities (ρ < 3.7 g cm -3 ) and bright host stars (K < 9 mag), they are among the best candidates for transmission spectroscopy in order to characterize the atmospheric compositions of small planets
TESS Spots a Compact System of Super-Earths around the Naked-eye Star HR 858
Transiting Exoplanet Survey Satellite (TESS) observations have revealed a compact multiplanet system around the sixth-magnitude star HR 858 (TIC 178155732, TOI 396), located 32 pc away. Three planets, each about twice the size of Earth, transit this slightly evolved, late F-type star, which is also a member of a visual binary. Two of the planets may be in mean motion resonance. We analyze the TESS observations, using novel methods to model and remove instrumental systematic errors, and combine these data with follow-up observations taken from a suite of ground-based telescopes to characterize the planetary system. The HR 858 planets are enticing targets for precise radial velocity observations, secondary eclipse spectroscopy, and measurements of the Rossiter-McLaughlin effect
Hipersensibilidade e necrose sistêmica em Nicotiana benthamiana transformada com o gene de resistência Sw-5 de tomateiro
TOI-481 b and TOI-892 b: Two Long-period Hot Jupiters from the Transiting Exoplanet Survey Satellite
We present the discovery of two new 10 day period giant planets from the Transiting Exoplanet Survey Satellite mission, whose masses were precisely determined using a wide diversity of ground-based facilities. TOI-481 b and TOI-892 b have similar radii (0.99 0.01 and 1.07 0.02, respectively), and orbital periods (10.3311 days and 10.6266 days, respectively), but significantly different masses (1.53 0.03, respectively). Both planets orbit metal-rich stars ( = dex and = for TOI-481 and TOI-892, respectively) but at different evolutionary stages. TOI-481 is a = 1.14 0.02 = 1.66 0.02 G-type star (=K), that with an age of 6.7 Gyr, is in the turn-off point of the main sequence. TOI-892 on the other hand, is a F-type dwarf star (=K), which has a mass of = 1.28 0.03 and a radius of = 1.39 0.02. TOI-481 b and TOI-892 b join the scarcely populated region of transiting gas giants with orbital periods longer than 10 days, which is important to constrain theories of the formation and structure of hot Jupiters
The western painted turtle genome, a model for the evolution of extreme physiological adaptations in a slowly evolving lineage
Background: We describe the genome of the western painted turtle, Chrysemys picta bellii, one of the most widespread, abundant, and well-studied turtles. We place the genome into a comparative evolutionary context, and focus on genomic features associated with tooth loss, immune function, longevity, sex differentiation and determination, and the species' physiological capacities to withstand extreme anoxia and tissue freezing.Results: Our phylogenetic analyses confirm that turtles are the sister group to living archosaurs, and demonstrate an extraordinarily slow rate of sequence evolution in the painted turtle. The ability of the painted turtle to withstand complete anoxia and partial freezing appears to be associated with common vertebrate gene networks, and we identify candidate genes for future functional analyses. Tooth loss shares a common pattern of pseudogenization and degradation of tooth-specific genes with birds, although the rate of accumulation of mutations is much slower in the painted turtle. Genes associated with sex differentiation generally reflect phylogeny rather than convergence in sex determination functionality. Among gene families that demonstrate exceptional expansions or show signatures of strong natural selection, immune function and musculoskeletal patterning genes are consistently over-represented.Conclusions: Our comparative genomic analyses indicate that common vertebrate regulatory networks, some of which have analogs in human diseases, are often involved in the western painted turtle's extraordinary physiological capacities. As these regulatory pathways are analyzed at the functional level, the painted turtle may offer important insights into the management of a number of human health disorders
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