3,746 research outputs found
Structural and ultrametric properties of twenty(L-alanine)
We study local energy minima of twenty(L-alanine). The minima are generated
using high-temperature Molecular Dynamics and Chain-Growth Monte Carlo
simulations, with subsequent minimization. We find that the lower-energy
configurations are -helices for a wide range of dielectric constant
values and that there is no noticeable difference
between the distribution of energy minima in space for different
values of Ultrametricity tests show that lower-energy -helical) configurations form a set which is ultrametric to a
certain degree, providing evidence for the presence of fine structure among
those minima. We put forward a heuristic argument for this fine structure. We
also find evidence for ultrametricity of a different kind among and energy minima. We analyze the distribution of lengths of
-helical portions among the minimized configurations and find a
persistence phenomenon for the ones, in qualitative agreement
with previous studies of critical lengths. Email contact:
[email protected]: Saclay-T93/025 Email: [email protected]
BLOCK: Bilinear Superdiagonal Fusion for Visual Question Answering and Visual Relationship Detection
Multimodal representation learning is gaining more and more interest within
the deep learning community. While bilinear models provide an interesting
framework to find subtle combination of modalities, their number of parameters
grows quadratically with the input dimensions, making their practical
implementation within classical deep learning pipelines challenging. In this
paper, we introduce BLOCK, a new multimodal fusion based on the
block-superdiagonal tensor decomposition. It leverages the notion of block-term
ranks, which generalizes both concepts of rank and mode ranks for tensors,
already used for multimodal fusion. It allows to define new ways for optimizing
the tradeoff between the expressiveness and complexity of the fusion model, and
is able to represent very fine interactions between modalities while
maintaining powerful mono-modal representations. We demonstrate the practical
interest of our fusion model by using BLOCK for two challenging tasks: Visual
Question Answering (VQA) and Visual Relationship Detection (VRD), where we
design end-to-end learnable architectures for representing relevant
interactions between modalities. Through extensive experiments, we show that
BLOCK compares favorably with respect to state-of-the-art multimodal fusion
models for both VQA and VRD tasks. Our code is available at
https://github.com/Cadene/block.bootstrap.pytorch
KIC 1718290: A Helium-rich V1093-Her-like Pulsator on the Blue Horizontal Branch
We introduce the first g-mode pulsator found to reside on the classical blue
horizontal branch. One year of Kepler observations of KIC 1718290 reveals a
rich spectrum of low-amplitude modes with periods between one and twelve hours,
most of which follow a regular spacing of 276.3 s. This mode structure strongly
resembles that of the V1093Her pulsators, with only a slight shift towards
longer periods. Our spectroscopy, however, reveals KIC 1718290 to be quite
distinct from the sdB stars that show V1093Her pulsations, which all have
surface gravities higher than log g = 5.1 and helium abundances depleted by at
least an order of magnitude relative to the solar composition. We find that
KIC1718290 has T_eff = 22 100K, log g = 4.72, and a super-solar helium
abundance (log N(He)/N(H) = -0.45). This places it well above the extreme
horizontal branch, and rather on the very blue end of the classical horizontal
branch, where shell hydrogen burning is present. We conclude that KIC 1718290
must have suffered extreme mass loss during its first giant stage, but not
sufficient to reach the extreme horizontal branch.Comment: Accepted for publication in ApJ
The VIMOS Public Extragalactic Redshift Survey (VIPERS). Exploring the dependence of the three-point correlation function on stellar mass and luminosity at 0.5<z<1.1
The three-point correlation function (3PCF) is a powerful probe to
investigate the clustering of matter in the Universe in a complementary way
with respect to lower-order statistics, providing additional information with
respect to the two-point correlation function and allowing us to shed light on
biasing, nonlinear processes, and deviations from Gaussian statistics. In this
paper, we analyse the first data release of the VIMOS Public Extragalactic
Redshift Survey (VIPERS), determining the dependence of the three-point
correlation function on luminosity and stellar mass at . We
exploit the VIPERS Public Data Release 1, consisting of more than 50,000
galaxies with B-band magnitudes in the range and stellar masses in the range
. We measure both the
connected 3PCF and the reduced 3PCF in redshift space, probing different
configurations and scales, in the range [Mpc/h]. We find a
significant dependence of the reduced 3PCF on scales and triangle shapes, with
stronger anisotropy at larger scales ( Mpc/h) and an almost flat trend
at smaller scales, Mpc/h. Massive and luminous galaxies present a
larger connected 3PCF, while the reduced 3PCF is remarkably insensitive to
magnitude and stellar masses in the range we explored. These trends, already
observed at low redshifts, are confirmed for the first time to be still valid
up to , providing support to the hierarchical scenario for which massive
and bright systems are expected to be more clustered. The possibility of using
the measured 3PCF to provide independent constraints on the linear galaxy bias
has also been explored, showing promising results in agreement with other
probes.Comment: 12 pages, 11 figures, 2 tables, accepted for publication in A&
The study of the physics of cometary nuclei
A semiannual progress report describing the work completed during the period 1 September 1975 to 29 February 1976 on the physics of cometary nuclei was given. The following items were discussed: (1) a paper entitled ""A speculation about comets and the earth'', (2) a chapter entitled"" The physics of comets'' for ""Reviews of Astronomy and Astrophysics'', (3) continuing work on split comets, and (4) results dealing with a new application of nongravitational solar-radial forces as a measure of comet nucleus dimensions and activity
RecA and DNA recombination: a review of molecular mechanisms
International audienceRecombinases are responsible for homologous recombination and maintenance of genome integrity. In Escherichia coli, the recombinase RecA forms a nucleoprotein filament with the ssDNA present at a DNA break and searches for a homologous dsDNA to use as a template for break repair. During the first step of this process, the ssDNA is bound to RecA and stretched into a Watson-Crick base-paired triplet conformation. The RecA nucleoprotein filament also contains ATP and Mg 2+ , two cofactors required for RecA activity. Then, the complex starts a homology search by interacting with and stretching dsDNA. Thanks to supercoiling, intersegment sampling and RecA clustering, a genome-wide homology search takes place at a relevant metabolic timescale. When a region of homology 8 to 20 base pairs in length is found and stabilized, DNA strand exchange proceeds, forming a heteroduplex complex that is resolved through a combination of DNA synthesis, ligation and resolution. RecA activities can take place without ATP hydrolysis, but this latter activity is necessary to improve and accelerate the process. Protein flexibility and monomer-monomer interactions are fundamental for RecA activity, which functions cooperatively. A structure/function relationship analysis suggests that the recombinogenic activity can be improved and that recombinases have an inherently large recombination potential. Understanding this relationship is essential for designing RecA derivatives with enhanced activity for biotechnology applications. For example, this protein is a major actor in the recombinase polymerase isothermal amplification (RPA) used in point-of-care diagnostics
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