549 research outputs found
An original interferometric study of NGC 1068 with VISIR BURST mode images
We present 12.8 microns images of the core of NGC 1068 obtained with the
BURST mode of the VLT/VISIR. We trace structures under the diffraction limit of
one UT and we investigate the link between dust in the vicinity of the central
engine of NGC 1068, recently resolved by interferometry with MIDI, and more
extended structures. This step is mandatory for a multi-scale understanding of
the sources of mid-infrared emission in AGNs. A speckle processing of VISIR
BURST mode images was performed to extract very low spatial-frequency
visibilities, first considering the full field of VISIR BURST mode images and
then limiting it to the mask used for the acquisition of MIDI data. Extracted
visibilities are reproduced with a multi-component model. We identify two major
sources of emission: one compact < 85 mas, associated with the dusty torus, and
an elliptical one, (< 140) mas x 1187 mas at P.A.=-4 degrees from N to E. This
is consistent with previous deconvolution processes. The combination with MIDI
data reveals the close environment of the dusty torus to contribute to about 83
percent of the MIR flux seen by MIDI. This strong contribution has to be
considered in modeling long baseline interferometric data. It must be related
to the NS elongated component which is thought to originate from individually
unresolved dusty clouds and is located inside the ionization cone. Low
temperatures of the dusty torus are not challenged, emphasizing the scenarios
of clumpy torus.Comment: 10 pages, 7 figures, accepted for publication in A&
Classification of symmetric periodic trajectories in ellipsoidal billiards
We classify nonsingular symmetric periodic trajectories (SPTs) of billiards
inside ellipsoids of R^{n+1} without any symmetry of revolution. SPTs are
defined as periodic trajectories passing through some symmetry set. We prove
that there are exactly 2^{2n}(2^{n+1}-1) classes of such trajectories. We have
implemented an algorithm to find minimal SPTs of each of the 12 classes in the
2D case (R^2) and each of the 112 classes in the 3D case (R^3). They have
periods 3, 4 or 6 in the 2D case; and 4, 5, 6, 8 or 10 in the 3D case. We
display a selection of 3D minimal SPTs. Some of them have properties that
cannot take place in the 2D case.Comment: 26 pages, 77 figures, 17 table
Simplifying transformations for nonlinear systems: Part I, an optimisation-based variant of normal form analysis
This paper introduces the idea of a ‘simplifying transformation’ for nonlinear structural dynamic systems. The idea simply stated; is to bring under one heading, those transformations which ‘simplify’ structural dynamic systems or responses in some sense. The equations of motion may be cast in a simpler form or decoupled (and in this sense, nonlinear modal analysis is encompassed) or the responses may be modified in order to isolate and remove certain components. It is the latter sense of simplification which is considered in this paper. One can regard normal form analysis in a way as the removal of superharmonic content from nonlinear system response. In the current paper, this problem is cast in an optimisation form and the differential evolution algorithm is used
On the effective shear speed in 2D phononic crystals
The quasistatic limit of the antiplane shear-wave speed ('effective speed')
in 2D periodic lattices is studied. Two new closed-form estimates of
are derived by employing two different analytical approaches. The first
proceeds from a standard background of the plane wave expansion (PWE). The
second is a new approach, which resides in -space and centers on
the monodromy matrix (MM) introduced in the 2D case as the multiplicative
integral, taken in one coordinate, of a matrix with components being the
operators with respect to the other coordinate. On the numerical side, an
efficient PWE-based scheme for computing is proposed and implemented. The
analytical and numerical findings are applied to several examples of 2D square
lattices with two and three high-contrast components, for which the new PWE and
MM estimates are compared with the numerical data and with some known
approximations. It is demonstrated that the PWE estimate is most efficient in
the case of densely packed stiff inclusions, especially when they form a
symmetric lattice, while in general it is the MM estimate that provides the
best overall fitting accuracy.Comment: 13 pages, 9 figure
Membrane emulsification for the production of uniform poly-N-isopropylacrylamide-coated alginate particles using internal gelation
Alginate particles, crosslinked by calcium ions, have a number of potential biopharmaceutical industry applications due to the biocompatibility of the materials used and formed. One such use is as microcarriers for cell attachment,growth and then detachment without the use of proteolytic enzymes. A straightforward and reproducible method for producing uniform calcium alginate particles with controllable median diameters which employs membrane emulsification and internal gelation (solid particles contained in the dispersed phase) is demonstrated, as well as functionalisation of the resulting beads with amine terminated poly N-isopropylacrylamide (pNIPAM) to form temperature responsive particles, by taking advantage of the electrostatic interaction between the carboxyl groups of the alginate and amino groups of the modified pNIPAM. Cell attachment, growth and detachment capabilities of these core–shell structures were assessed and successfully demonstrated by using phase contrast microscopy and fluorescent staining with calcein-AM and ethidium homodimer-1.The formulation used for the alginate particles avoided non-GRAS chemicals by only using food grade and pharmaceutical grade reagents. The median particle size was controllable within the range between 55 m and 690 m and the size distributions produced were very narrow: ‘span’ values as low as 0.2. When using a membrane pore sizeof 20 m no membrane blockage by the suspended calcium carbonate necessary for internal gelation of the alginate particles was observed. Membrane pore openings with diameters of 5 and 10 m were also tested, but blocked with the 2.3 m median diameter calcium carbonate solids
Marker-Assisted Pyramiding of Blast-Resistance Genes in a japonica Elite Rice Cultivar through Forward and Background Selection
Rice blast, caused by Pyricularia oryzae, is one of the main rice diseases worldwide. The
pyramiding of blast-resistance (Pi) genes, coupled to Marker-Assisted BackCrossing (MABC), provides
broad-spectrum and potentially durable resistance while limiting the donor genome in the
background of an elite cultivar. In this work, MABC coupled to foreground and background selections
based on KASP marker assays has been applied to introgress four Pi genes (Piz, Pib, Pita, and
Pik) in a renowned japonica Italian rice variety, highly susceptible to blast. Molecular analyses on the
backcross (BC) lines highlighted the presence of an additional blast-resistance gene, the Pita-linked
Pita2/Ptr gene, therefore increasing the number of blast-resistance introgressed genes to five. The
recurrent genome was recovered up to 95.65%. Several lines carrying four (including Pita2) Pi genes
with high recovery percentage levels were also obtained. Phenotypic evaluations confirmed the
effectiveness of the pyramided lines against multivirulent strains, which also had broad patterns
of resistance in comparison to those expected based on the pyramided Pi genes. The developed
blast-resistant japonica lines represent useful donors of multiple blast-resistance genes for future
rice-breeding programs related to the japonica group
Resolving the complex structure of the dust torus in the active nucleus of the Circinus galaxy
To test the dust torus model for active galactic nuclei directly, we study
the extent and morphology of the nuclear dust distribution in the Circinus
galaxy using high resolution interferometric observations in the mid-infrared
with the MIDI instrument at the Very Large Telescope Interferometer. We find
that the dust distribution in the nucleus of Circinus can be explained by two
components, a dense and warm disk-like component of 0.4 pc size and a slightly
cooler, geometrically thick torus component with a size of 2.0 pc. The disk
component is oriented perpendicular to the ionisation cone and outflow and
seems to show the silicate feature at 10 micron in emission. It coincides with
a nuclear maser disk in orientation and size. From the energy needed to heat
the dust, we infer a luminosity of the accretion disk corresponding to 20% of
the Eddington luminosity of the nuclear black hole. We find that the
interferometric data are inconsistent with a simple, smooth and axisymmetric
dust emission. The irregular behaviour of the visibilities and the shallow
decrease of the dust temperature with radius provide strong evidence for a
clumpy or filamentary dust structure. We see no evidence for dust reprocessing,
as the silicate absorption profile is consistent with that of standard galactic
dust. We argue that the collimation of the ionising radiation must originate in
the geometrically thick torus component. Our findings confirm the presence of a
geometrically thick, torus-like dust distribution in the nucleus of Circinus,
as required in unified schemes of Seyfert galaxies. Several aspects of our data
require that this torus is irregular, or "clumpy".Comment: 20 pages, 16 figures, accepted for publication by A&
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