3,657 research outputs found
Chiral Dynamics and Nuclear Matter
We calculate the equation of state of isospin-symmetric nuclear matter in the
three-loop approximation of chiral perturbation theory. The contributions to
the energy per particle from one- and two-pion exchange diagrams
are ordered in powers of the Fermi momentum (modulo functions of ). It is demonstrated that, already at order , two-pion
exchange produces realistic nuclear binding. The underlying saturation
mechanism is surprisingly simple (in the chiral limit), namely the combination
of an attractive -term and a repulsive -term. The empirical
saturation point and the nuclear compressibility MeV are well
reproduced at order with a momentum cut-off of GeV which parametrizes short-range dynamics. No further
short-distance terms are required in our calculation of nuclear matter. In the
same framework we calculate the density-dependent asymmetry energy and find
MeV at the saturation point, in good agreement with the
empirical value. The pure neutron matter equation of state is also in fair
qualitative agreement with sophisticated many-body calculations and a
resummation result of effective field theory, but only for low neutron
densities fm.Comment: 18 pages, 8 figure
Recent progress on the calculation of three-loop heavy flavor Wilson coefficients in deep-inelastic scattering
We report on our latest results in the calculation of the three-loop heavy
flavor contributions to the Wilson coefficients in deep-inelastic scattering in
the asymptotic region . We discuss the different methods used to
compute the required operator matrix elements and the corresponding Feynman
integrals. These methods very recently allowed us to obtain a series of new
operator matrix elements and Wilson coefficients like the flavor non-singlet
and pure singlet Wilson coefficients.Comment: 11 pages Latex, 2 Figures, Proc. of Loops and Legs in Quantum Field
Theory, April 2014, Weimar, German
Structural Alignment of RNAs Using Profile-csHMMs and Its Application to RNA Homology Search: Overview and New Results
Systematic research on noncoding RNAs (ncRNAs) has revealed that many ncRNAs are actively involved in various biological networks. Therefore, in order to fully understand the mechanisms of these networks, it is crucial to understand the roles of ncRNAs. Unfortunately, the annotation of ncRNA genes that give rise to functional RNA molecules has begun only recently, and it is far from being complete. Considering the huge amount of genome sequence data, we need efficient computational methods for finding ncRNA genes. One effective way of finding ncRNA genes is to look for regions that are similar to known ncRNA genes. As many ncRNAs have well-conserved secondary structures, we need statistical models that can represent such structures for this purpose. In this paper, we propose a new method for representing RNA sequence profiles and finding structural alignment of RNAs based on profile context-sensitive hidden Markov models (profile-csHMMs). Unlike existing models, the proposed approach can handle any kind of RNA secondary structures, including pseudoknots. We show that profile-csHMMs can provide an effective framework for the computational analysis of RNAs and the identification of ncRNA genes
A Seeded Genetic Algorithm for RNA Secondary Structural Prediction with Pseudoknots
This work explores a new approach in using genetic algorithm to predict RNA secondary structures with pseudoknots. Since only a small portion of most RNA structures is comprised of pseudoknots, the majority of structural elements from an optimal pseudoknot-free structure are likely to be part of the true structure. Thus seeding the genetic algorithm with optimal pseudoknot-free structures will more likely lead it to the true structure than a randomly generated population. The genetic algorithm uses the known energy models with an additional augmentation to allow complex pseudoknots. The nearest-neighbor energy model is used in conjunction with Turner’s thermodynamic parameters for pseudoknot-free structures, and the H-type pseudoknot energy estimation for simple pseudoknots. Testing with known pseudoknot sequences from PseudoBase shows that it out performs some of the current popular algorithms
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Fully dynamic maintenance of euclidean minimum spanning trees
We maintain the minimum spanning tree of a point set in the plane, subject to point insertions and deletions, in time O(n^5/6 log1^2/2 n) per update operation. No nontrivial dynamic geometric minimum spanning tree algorithm was previously known. We reduce the problem to maintaining bichromatic closest pairs, which we also solve in the same time bounds. Our algorithm uses a novel construction, the ordered nearest neighbors of a sequence of points. Any point set or bichromatic point set can be ordered so that this graph is a simple path
On hyperlogarithms and Feynman integrals with divergences and many scales
It was observed that hyperlogarithms provide a tool to carry out Feynman
integrals. So far, this method has been applied successfully to finite
single-scale processes. However, it can be employed in more general situations.
We give examples of integrations of three- and four-point integrals in
Schwinger parameters with non-trivial kinematic dependence, involving setups
with off-shell external momenta and differently massive internal propagators.
The full set of Feynman graphs admissible to parametric integration is not yet
understood and we discuss some counterexamples to the crucial property of
linear reducibility. Furthermore we clarify how divergent integrals can be
approached in dimensional regularization with this algorithm.Comment: 26 pages, 11 figures, 2 tables, explicit results in ancillary file
"results" and on http://www.math.hu-berlin.de/~panzer/ (version as in JHEP;
link corrected
Iterated-greedy-based algorithms with beam search initialization for the permutation flowshop to minimize total tardiness
The permutation flow shop scheduling problem is one of the most studied operations research related problems. Literally, hundreds of exact and approximate algorithms have been proposed to optimise several objective functions. In this paper we address the total tardiness criterion, which is aimed towards the satisfaction of customers in a make-to-order scenario. Although several approximate algorithms have been proposed for this problem in the literature, recent contributions for related problems suggest that there is room for improving the current available algorithms. Thus, our contribution is twofold: First, we propose a fast beam-search-based constructive heuristic that estimates the quality of partial sequences without a complete evaluation of their objective function. Second, using this constructive heuristic as initial solution, eight variations of an iterated-greedy-based algorithm are proposed. A comprehensive computational evaluation is performed to establish the efficiency of our proposals against the existing heuristics and metaheuristics for the problem.Ministerio de Ciencia e Innovación DPI2013-44461-PMinisterio de Ciencia e Innovación DPI2016-80750-
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