16,064 research outputs found
Dual Formulation of the Lie Algebra S-expansion Procedure
The expansion of a Lie algebra entails finding a new, bigger algebra G,
through a series of well-defined steps, from an original Lie algebra g. One
incarnation of the method, the so-called S-expansion, involves the use of a
finite abelian semigroup S to accomplish this task. In this paper we put
forward a dual formulation of the S-expansion method which is based on the dual
picture of a Lie algebra given by the Maurer-Cartan forms. The dual version of
the method is useful in finding a generalization to the case of a gauge free
differential algebra, which in turn is relevant for physical applications in,
e.g., Supergravity. It also sheds new light on the puzzling relation between
two Chern-Simons Lagrangians for gravity in 2+1 dimensions, namely the
Einstein-Hilbert Lagrangian and the one for the so-called "exotic gravity".Comment: 12 pages, no figure
Problematic areas of host university support services for short-term mobility students
The growing numbers of mobile students over the years made the provision of student services a key topic of interest for higher education institutions. In order to offer a better experience for international students, it is important to be aware of and assess their needs in relation to different sets of support services. The data used in this paper were gathered through the ESNsurvey 2016 project, a research venture focused on the experiences of participants in short-term student mobility in Europe. Responses were collected from 12,365 international students, who have participated in a short-term (3-12 months) study period abroad mostly through Europe’s most promoted mobility program called ERASMUS+. For the purpose of this paper, the focus was only on the aspect of host university support services. The comments of 2,012 students about their experiences were analyzed using a probabilistic methodology known as Latent Dirichlet Allocation (LDA)
Practical study of optical stellar interferometry
In this work we present an observational technique and a detailed analysis of
the stellar interferograms produced by three bright stars: Betelgeuse, Rigel
and Sirius. It is shown that the atmospheric turbulence is responsible for the
reduction of the long-exposure fringe visibility of the obtained interference
patterns. By using different baselines in our interferometer, we are able to
distinguish the decay of the visibility with the baseline, how different
parameters such us the diameter of the holes in our interferometer or their
distribution affects the pattern, and to measure the turbulence with the
estimation of the Fried parameter r0. The work and methodology are presented as
a method for postgraduate students that targets practical learning of optical
interferometry in astronomy and how it is affected by several causes, such as
the atmospheric turbulence.Comment: 11 pages, 6 figures, paper submitted and accepted to AJ
Dominant negative phenotype of Bacillus thuringiensis Cry1Ab, Cry11Aa and Cry4Ba mutants suggest hetero-oligomer formation among different Cry toxins.
Background - Bacillus thuringiensis Cry toxins are used worldwide in the control of different insect pests important in agriculture or in human health. The Cry proteins are pore-forming toxins that affect the midgut cell of target insects. It was shown that non-toxic Cry1Ab helix a-4 mutants had a dominant negative (DN) phenotype inhibiting the toxicity of wildtype Cry1Ab when used in equimolar or sub-stoichiometric ratios (1:1, 0.5:1, mutant:wt) indicating that oligomer formation is a key step in toxicity of Cry toxins. Methodology/Principal Findings - The DN Cry1Ab-D136N/T143D mutant that is able to block toxicity of Cry1Ab toxin, was used to analyze its capacity to block the activity against Manduca sexta larvae of other Cry1 toxins, such as Cry1Aa, Cry1Ac, Cry1Ca, Cry1Da, Cry1Ea and Cry1Fa. Cry1Ab-DN mutant inhibited toxicity of Cry1Aa, Cry1Ac and Cry1Fa. In addition, we isolated mutants in helix a-4 of Cry4Ba and Cry11Aa, and demonstrate that Cry4Ba-E159K and Cry11Aa-V142D are inactive and completely block the toxicity against Aedes aegypti of both wildtype toxins, when used at sub-stoichiometric ratios, confirming a DN phenotype. As controls we analyzed Cry1Ab-R99A or Cry11Aa-E97A mutants that are located in helix a-3 and are affected in toxin oligomerization. These mutants do not show a DN phenotype but were able to block toxicity when used in 10:1 or 100:1 ratios (mutant:wt) probably by competition of binding with toxin receptors. Conclusions/Significance - We show that DN phenotype can be observed among different Cry toxins suggesting that may interact in vivo forming hetero-oligomers. The DN phenotype cannot be observed in mutants affected in oligomerization, suggesting that this step is important to inhibit toxicity of other toxin
Formation of S0 galaxies through mergers. Morphological properties: tidal relics, lenses, ovals, and other inner components
Major mergers are popularly considered too destructive to produce the relaxed
regular structures and the morphological inner components (ICs) usually
observed in lenticular (S0) galaxies. We aim to test if major mergers can
produce remnants with realistic S0 morphologies. We have selected a sample of
relaxed discy remnants resulting from the dissipative merger simulations of the
GalMer database and derived their properties mimicking the typical conditions
of current observational data. We compare their global morphologies, visual
components, and merger relics in mock photometric images with their real
counterparts. Only 1-2 Gyr after the full merger, we find that: 1) many
remnants (67 major and 29 minor events) present relaxed structures and typical
S0 or E/S0 morphologies, for a wide variety of orbits and even in gas-poor
cases. 2) Contrary to popular expectations, most of them do not exhibit any
morphological traces of their past merger origin under typical observing
conditions and at distances as nearby as 30 Mpc. 3) The merger relics are more
persistent in minor mergers than in major ones for similar relaxing time
periods. 4) No major-merger S0-like remnant develops a significant bar. 5)
Nearly 58% of the major-merger S0 remnants host visually detectable ICs, such
as embedded inner discs, rings, pseudo-rings, inner spirals, nuclear bars, and
compact sources, very frequent in real S0s too. 6) All remnants contain a lens
or oval, identically ubiquitous in local S0s. 7) These lenses and ovals do not
come from bar dilution in major merger cases, but are associated with stellar
halos or embedded inner discs instead (thick or thin). We conclude that the
relaxed morphologies, lenses, ovals, and other ICs of real S0s do not
necessarily come from internal secular evolution, gas infall or environmental
mechanisms, as traditionally assumed, but they can result from major mergers as
well.Comment: Accepted for publication in A&A, 37 pages, 21 figures, 9 tables.
Version with better resolution and language edited. A version with full
Appendices is available at:
https://www.researchgate.net/publication/325905181_Formation_of_S0_galaxies_through_mergers_Morphological_properties_tidal_relics_lenses_ovals_and_other_inner_components_-_Version_of_the_corresponding_AA_paper_with_full_Appendice
Glass transition of semi-crystalline PLLA with different morphologies as studied by dynamic mechanical analysis
Poly(L-lactic acid) was crystallized from the
glassy state at different temperatures to produce fully
transformed semi-crystalline specimens exhibiting different
lamellar morphologies. The materials were tested by
dynamic mechanical analysis, where a Tg decrease was
found with an increasing crystallization temperature. Considering
a three-phase model, this tendency was related to
the corresponding increase in the thickness of the rigid
amorphous phase. It is suggested that this phase could, in
some extent, accommodate through local translational/
rotational motions the cooperative motions taking place
within the mobile amorphous phase. This could be due to
the non-compact structure of the cooperatively rearranging
regions, which can present a string-like or fractal structure
in their edges. The width of the loss factor peak associated
to the glass transition increases with increasing crystallization
temperature, suggesting an increase in the broadness of
the distribution of relaxation times. The drop in the storage
modulus across Tg varies systematically with the crystallization
temperature in the different materials and could be
correlated with the crystalline content. Above Tg, the loss
factor exhibits a plateau-like behaviour at significantly high
values, which seems to be a rather general behaviour in
semi-crystalline systems that could be related to the
contribution of pure irreversible flow in the overall
viscoelastic behaviour
Surgical treatment of theintersex condition in the dog
Intersexuality is a rare congenital condition that leads to the development of an ambiguous urogenital tract. Removal of the reproductive tract is recommended to avoid genital diseases; however there is scant information about the procedure. The objective of this report is to describe the surgical procedure used to treat the canine intersex condition. Surgical corrections were performed on four intersex dogs: three 78 XX SRY-negative (one bilateral ovotestis, two sertolicell-only syndrome) and one 78 XX SRY-positive (sertolicell-only syndrome). Despite the different genetic and histological features, the anatomical characteristics were similar. The patients presented a vulva that lacked of dorsal fold placed ventrocranially to its anatomically normal position, a hypertrophied os clitoris protruding from the vulva and a urinary opening near to its normal position in the bitch..
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