1,723 research outputs found
Multiwavelength Raman spectroscopy analysis of a large sampling of disordered carbons extracted from the Tore Supra tokamak
Disordered carbon often exhibit a complex Raman spectrum, with four to six
components. Here, a large variety of disordered carbons, forming a collection
of samples with a great variety of structures, are analysed using
multi-wavelength Raman microscopy (325.0, 514.5, 785.0 nm). They allow us to
extend Raman behaviour known for nano-crystalline graphite to amorphous
carbons, (dependence with the excitation wavelength) and other known for
amorphous carbons to nano-crystalline graphite, (differentiation of the
smallest cluster size probed using different excitation wavelengths).
Experimental spectra were compared to simulated spectra, built using known
laws, to evidence a new source of broadening
Renormalization of myoglobin-ligand binding energetics by quantum many-body effects
We carry out a first-principles atomistic study of the electronic mechanisms
of ligand binding and discrimination in the myoglobin protein. Electronic
correlation effects are taken into account using one of the most advanced
methods currently available, namely a linear-scaling density functional theory
(DFT) approach wherein the treatment of localized iron 3d electrons is further
refined using dynamical mean-field theory (DMFT). This combination of methods
explicitly accounts for dynamical and multi-reference quantum physics, such as
valence and spin fluctuations, of the 3d electrons, whilst treating a
significant proportion of the protein (more than 1000 atoms) with density
functional theory. The computed electronic structure of the myoglobin complexes
and the nature of the Fe-O2 bonding are validated against experimental
spectroscopic observables. We elucidate and solve a long standing problem
related to the quantum-mechanical description of the respiration process,
namely that DFT calculations predict a strong imbalance between O2 and CO
binding, favoring the latter to an unphysically large extent. We show that the
explicit inclusion of many body-effects induced by the Hund's coupling
mechanism results in the correct prediction of similar binding energies for
oxy- and carbonmonoxymyoglobin.Comment: 7 pages, 5 figures. Accepted for publication in the Proceedings of
the National Academy of Sciences of the United States of America (2014). For
the published article see
http://www.pnas.org/content/early/2014/04/09/1322966111.abstrac
Entropy of stationary nonequilibrium measures of boundary driven symmetric simple exclusion processes: Entropy of nonequilibrium stationary measures
International audienceWe examine the entropy of stationary nonequilibrium measures of boundary driven symmetric simple exclusion processes. In contrast with the Gibbs--Shannon entropy \cite{B, DLS2}, the entropy of nonequilibrium stationary states differs from the entropy of local equilibrium states
The chromising process: a novel development
The industrial application of the chromising process
started in about 1935. It enjoyed a steady growth until
about 1975 but has since declined in importance, being
replaced by novel CVD and PVD processes. Its use for
corrosion and oxidisation resistance is very small but
there are some applications for wear resistance which
exploit the high hardness of chromium carbide.
A chance observation in the wear pattern and performance of chromised automotive timing chain link-pins, led to the
identification of a diffusion coating structure which had
not been previously recognised as having enhanced wear
resistance. It was the purpose of this research to examine
the nature of this novel structure, to determine how it was
occurring in practice and to develop a chromising process
which could consistently reproduce the desired end product. [Continues.
Understanding the Siphon: An Example of the Development of Pedagogical Content Knowledge Using Textbooks and the Writings of Early Scientists
A general explanatory principle for determining whether fluid will flow or will not flow from a siphon is developed and discussed after a consideration of the explanations provided by textbooks and the writings of Blaise Pascal
The Distance and Median Problems in the Single-Cut-Or-Join Model with Single-Gene Duplications
Background.
In the field of genome rearrangement algorithms, models accounting for gene duplication lead often to hard problems. For example, while computing the pairwise distance is tractable in most duplication-free models, the problem is NP-complete for most extensions of these models accounting for duplicated genes. Moreover, problems involving more than two genomes, such as the genome median and the Small Parsimony problem, are intractable for most duplication-free models, with some exceptions, for example the Single-Cut-or-Join (SCJ) model.
Results.
We introduce a variant of the SCJ distance that accounts for duplicated genes, in the context of directed evolution from an ancestral genome to a descendant genome where orthology relations between ancestral genes and their descendant are known. Our model includes two duplication mechanisms: single-gene tandem duplication and the creation of single-gene circular chromosomes. We prove that in this model, computing the directed distance and a parsimonious evolutionary scenario in terms of SCJ and single-gene duplication events can be done in linear time. We also show that the directed median problem is tractable for this distance, while the rooted median problem, where we assume that one of the given genomes is ancestral to the median, is NP-complete. We also describe an Integer Linear Program for solving this problem. We evaluate the directed distance and rooted median algorithms on simulated data.
Conclusion.
Our results provide a simple genome rearrangement model, extending the SCJ model to account for single-gene duplications, for which we prove a mix of tractability and hardness results. For the NP-complete rooted median problem, we design a simple Integer Linear Program. Our publicly available implementation of these algorithms for the directed distance and median problems allow to solve efficiently these problems on large instances
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