198 research outputs found
The sl(2n|2n)^(1) Super-Toda Lattices and the Heavenly Equations as Continuum Limit
The continuum limit of super-Toda models associated with the
affine (super)algebra series produces -dimensional
integrable equations in the spacetimes. The
equations of motion of the (super)Toda hierarchies depend not only on the
chosen (super)algebras but also on the specific presentation of their Cartan
matrices. Four distinct series of integrable hierarchies in relation with
symmetric-versus-antisymmetric, null-versus-nonnull presentations of the
corresponding Cartan matrices are investigated. In the continuum limit we
derive four classes of integrable equations of heavenly type, generalizing the
results previously obtained in the literature. The systems are manifestly N=1
supersymmetric and, for specific choices of the Cartan matrix preserving the
complex structure, admit a hidden N=2 supersymmetry. The coset reduction of the
(super)-heavenly equation to the spacetime (with a line segment) is
illustrated. Finally, integrable supersymmetrically extended models in
dimensions are constructed through dimensional reduction of the
previous systems.Comment: 12 page
Differential-Algebraic Integrability Analysis of the Generalized Riemann Type and Korteweg-de Vries Hydrodynamical Equations
A differential-algebraic approach to studying the Lax type integrability of
the generalized Riemann type hydrodynamic equations at N = 3; 4 is devised. The
approach is also applied to studying the Lax type integrability of the well
known Korteweg-de Vries dynamical system.Comment: 11 page
Massive pulsating stars observed by BRITE-Constellation. I. The triple system Beta Centauri (Agena)
This paper aims to precisely determine the masses and detect pulsation modes
in the two massive components of Beta Cen with BRITE-Constellation photometry.
In addition, seismic models for the components are considered and the effects
of fast rotation are discussed. This is done to test the limitations of seismic
modeling for this very difficult case. A simultaneous fit of visual and
spectroscopic orbits is used to self-consistently derive the orbital
parameters, and subsequently the masses, of the components. The derived masses
are equal to 12.02 +/- 0.13 and 10.58 +/- 0.18 M_Sun. The parameters of the
wider, A - B system, presently approaching periastron passage, are constrained.
Analysis of the combined blue- and red-filter BRITE-Constellation photometric
data of the system revealed the presence of 19 periodic terms, of which eight
are likely g modes, nine are p modes, and the remaining two are combination
terms. It cannot be excluded that one or two low-frequency terms are rotational
frequencies. It is possible that both components of Beta Cen are Beta Cep/SPB
hybrids. An attempt to use the apparent changes of frequency to distinguish
which modes originate in which component did not succeed, but there is
potential for using this method when more BRITE data become available. Agena
seems to be one of very few rapidly rotating massive objects with rich p- and
g-mode spectra, and precisely known masses. It can therefore be used to gain a
better understanding of the excitation of pulsations in relatively rapidly
rotating stars and their seismic modeling. Finally, this case illustrates the
potential of BRITE-Constellation data for the detection of rich-frequency
spectra of small-amplitude modes in massive pulsating stars.Comment: 17 pages (with Appendix), 15 figures, accepted for publication in A&
Interaction patterns of methoprene-tolerant and germ cell-expressed Drosophila JH receptors suggest significant differences in their functioning
Methoprene-tolerant (Met) and germ cell-expressed (Gce) proteins were shown to be juvenile hormone (JH) receptors of Drosophila melanogaster with partially redundant functions. We raised the question of where the functional differentiation of paralogs comes from. Therefore, we tested Met and Gce interaction patterns with selected partners. In this study, we showed the ability of Gce and its C-terminus (GceC) to interact with 14-3-3 in the absence of JH. In contrast, Met or Met C-terminus (MetC) interactions with 14-3-3 were not observed. We also performed a detailed structural analysis of Met/Gce interactions with the nuclear receptor fushi tarazu factor-1 (Ftz-F1) ligand-binding domain. We showed that GceC comprising an Ftz-F1-binding site and full-length protein interacts with Ftz-F1. In contrast to Gce, only MetC (not full-length Met) can interact with Ftz-F1 in the absence of JH. We propose that the described differences result from the distinct tertiary structure and accessibility of binding sites in the full-length Met/Gce. Moreover, we hypothesize that each interacting partner can force disordered MetC and GceC to change the structure in a partner-specific manner. The observed interactions seem to determine the subcellular localization of Met/Gce by forcing their translocation between the nucleus and the cytoplasm, which may affect the activity of the proteins. The presented differences between Met and Gce can be crucial for their functional differentiation during D. melanogaster development and indicate Gce as a more universal and more active paralog. It is consistent with the theory indicating gce as an ancestor gene
Studying the photometric and spectroscopic variability of the magnetic hot supergiant Orionis Aa
Massive stars play a significant role in the chemical and dynamical evolution
of galaxies. However, much of their variability, particularly during their
evolved supergiant stage, is poorly understood. To understand the variability
of evolved massive stars in more detail, we present a study of the O9.2Ib
supergiant Ori Aa, the only currently confirmed supergiant to host a
magnetic field. We have obtained two-color space-based BRIght Target Explorer
photometry (BRITE) for Ori Aa during two observing campaigns, as well
as simultaneous ground-based, high-resolution optical CHIRON spectroscopy. We
perform a detailed frequency analysis to detect and characterize the star's
periodic variability. We detect two significant, independent frequencies, their
higher harmonics, and combination frequencies: the stellar rotation period
d, most likely related to the presence of the
stable magnetic poles, and a variation with a period of d
attributed to circumstellar environment, also detected in the H and
several He I lines, yet absent in the purely photospheric lines. We confirm the
variability with /4, likely caused by surface
inhomogeneities, being the possible photospheric drivers of the discrete
absorption components. No stellar pulsations were detected in the data. The
level of circumstellar activity clearly differs between the two BRITE observing
campaigns. We demonstrate that Ori Aa is a highly variable star with
both periodic and non-periodic variations, as well as episodic events. The
rotation period we determined agrees well with the spectropolarimetric value
from the literature. The changing activity level observed with BRITE could
explain why the rotational modulation of the magnetic measurements was not
clearly detected at all epochs.Comment: 20 pages, 5 tables, 12 figures, accepted for publication in A&
The BRITE-Constellation Nanosatellite Space Mission And Its First Scientific Results
The BRIght Target Explorer (BRITE) Constellation is the first nanosatellite
mission applied to astrophysical research. Five satellites in low-Earth orbits
perform precise optical two-colour photometry of the brightest stars in the
night sky. BRITE is naturally well suited for variability studies of hot stars.
This contribution describes the basic outline of the mission and some initial
problems that needed to be overcome. Some information on BRITE data products,
how to access them, and how to join their scientific exploration is provided.
Finally, a brief summary of the first scientific results obtained by BRITE is
given.Comment: 5 pages, 1 figure, to appear in the proceedings of "Seismology of the
Sun and the Distant Stars 2016. Using Today's Successes to Prepare the
Future. Joint TASC2/KASC9 Workshop - SPACEINN/HELAS8 Conference", ed. M. J.
P. F. G. Monteir
Supersymmetry for integrable hierarchies on loop superalgebras
The algebraic approach is employed to formulate N=2 supersymmetry
transformations in the context of integrable systems based on loop
superalgebras with homogeneous gradation. We
work with extended integrable hierarchies, which contain supersymmetric AKNS
and Lund-Regge sectors.
We derive the one-soliton solution for which solves positive and
negative evolution equations of the N=2 supersymmetric model.Comment: Latex, 21 page
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