4,391 research outputs found
nbodykit: an open-source, massively parallel toolkit for large-scale structure
We present nbodykit, an open-source, massively parallel Python toolkit for
analyzing large-scale structure (LSS) data. Using Python bindings of the
Message Passing Interface (MPI), we provide parallel implementations of many
commonly used algorithms in LSS. nbodykit is both an interactive and scalable
piece of scientific software, performing well in a supercomputing environment
while still taking advantage of the interactive tools provided by the Python
ecosystem. Existing functionality includes estimators of the power spectrum, 2
and 3-point correlation functions, a Friends-of-Friends grouping algorithm,
mock catalog creation via the halo occupation distribution technique, and
approximate N-body simulations via the FastPM scheme. The package also provides
a set of distributed data containers, insulated from the algorithms themselves,
that enable nbodykit to provide a unified treatment of both simulation and
observational data sets. nbodykit can be easily deployed in a high performance
computing environment, overcoming some of the traditional difficulties of using
Python on supercomputers. We provide performance benchmarks illustrating the
scalability of the software. The modular, component-based approach of nbodykit
allows researchers to easily build complex applications using its tools. The
package is extensively documented at http://nbodykit.readthedocs.io, which also
includes an interactive set of example recipes for new users to explore. As
open-source software, we hope nbodykit provides a common framework for the
community to use and develop in confronting the analysis challenges of future
LSS surveys.Comment: 18 pages, 7 figures. Feedback very welcome. Code available at
https://github.com/bccp/nbodykit and for documentation, see
http://nbodykit.readthedocs.i
A kinematic classification of the cosmic web
A new approach for the classification of the cosmic web is presented. In
extension of the previous work of Hahn et al. (2007) and Forero-Romero et al.
(2009) the new algorithm is based on the analysis of the velocity shear tensor
rather than the gravitational tidal tensor. The procedure consists of the
construction of the the shear tensor at each (grid) point in space and the
evaluation of its three eigenvectors. A given point is classified to be either
a void, sheet, filament or a knot according to the number of eigenvalues above
a certain threshold, 0, 1, 2, or 3 respectively. The threshold is treated as a
free parameter that defines the web. The algorithm has been applied to a dark
matter only, high resolution simulation of a box of side-length 64Mpc
and N = particles with the framework of the WMAP5/LCDM model. The
resulting velocity based cosmic web resolves structures down to <0.1Mpc
scales, as opposed to the ~1Mpc scale of the tidal based web. The
under-dense regions are made of extended voids bisected by planar sheets, whose
density is also below the mean. The over-dense regions are vastly dominated by
the linear filaments and knots. The resolution achieved by the velocity based
cosmic web provides a platform for studying the formation of halos and galaxies
within the framework of the cosmic web.Comment: 8 pages, 4 Figures, MNRAS Accepted 2012 June 19. Received 2012 May
10; in original form 2011 August 2
Bayesian models and algorithms for protein beta-sheet prediction
Prediction of the three-dimensional structure greatly benefits from the information related to secondary structure, solvent accessibility, and non-local contacts that stabilize a protein's structure. Prediction of such components is vital to our understanding of the structure and function of a protein. In this paper, we address the problem of beta-sheet prediction. We introduce a Bayesian approach for proteins with six or less beta-strands, in which we model the conformational features in a probabilistic framework. To select the optimum architecture, we analyze the space of possible conformations by efficient heuristics. Furthermore, we employ an algorithm that finds the optimum pairwise alignment between beta-strands using dynamic programming. Allowing any number of gaps in an alignment enables us to model beta-bulges more effectively. Though our main focus is proteins with six or less beta-strands, we are also able to perform predictions for proteins with more than six beta-strands by combining the predictions of BetaPro with the gapped alignment algorithm. We evaluated the accuracy of our method and BetaPro. We performed a 10-fold cross validation experiment on the BetaSheet916 set and we obtained significant improvements in the prediction accuracy
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