38,837 research outputs found
Reproducible and User-Controlled Software Environments in HPC with Guix
Support teams of high-performance computing (HPC) systems often find
themselves between a rock and a hard place: on one hand, they understandably
administrate these large systems in a conservative way, but on the other hand,
they try to satisfy their users by deploying up-to-date tool chains as well as
libraries and scientific software. HPC system users often have no guarantee
that they will be able to reproduce results at a later point in time, even on
the same system-software may have been upgraded, removed, or recompiled under
their feet, and they have little hope of being able to reproduce the same
software environment elsewhere. We present GNU Guix and the functional package
management paradigm and show how it can improve reproducibility and sharing
among researchers with representative use cases.Comment: 2nd International Workshop on Reproducibility in Parallel Computing
(RepPar), Aug 2015, Vienne, Austria. http://reppar.org
Probabilistic Inference from Arbitrary Uncertainty using Mixtures of Factorized Generalized Gaussians
This paper presents a general and efficient framework for probabilistic
inference and learning from arbitrary uncertain information. It exploits the
calculation properties of finite mixture models, conjugate families and
factorization. Both the joint probability density of the variables and the
likelihood function of the (objective or subjective) observation are
approximated by a special mixture model, in such a way that any desired
conditional distribution can be directly obtained without numerical
integration. We have developed an extended version of the expectation
maximization (EM) algorithm to estimate the parameters of mixture models from
uncertain training examples (indirect observations). As a consequence, any
piece of exact or uncertain information about both input and output values is
consistently handled in the inference and learning stages. This ability,
extremely useful in certain situations, is not found in most alternative
methods. The proposed framework is formally justified from standard
probabilistic principles and illustrative examples are provided in the fields
of nonparametric pattern classification, nonlinear regression and pattern
completion. Finally, experiments on a real application and comparative results
over standard databases provide empirical evidence of the utility of the method
in a wide range of applications
PBO Fibres: from saliling design towards architectural performance
p. 3013-3023PBO fibres, also called "high-performance" polymer fibres, are a group of materials known as "rigid rods". Through this work it is pretended to make some considerations about the use of these new generation fibres. Poly (p-phenylene-2.6-benzobisoxazole)(PBO) is rigid-rod isotropic crystal polymer. PBO fibre is a high performance fibre developed by TOYOBO (Japan) PBO fibre is quite flexible and has very soft handling, in spite of its extremely high mechanical properties. Over the past ten years Future Fibres Company has pioneered the use of PBO for yacht rigging and has proven it to provide remarkable performance and longevity. Their method of producing these PBO cables delivers the lightest, smallest cables available on the market today. The PBO cable is formed by combining the incredible properties of PBO (poly(p-phenylene-2,6- benzobisoxazole)) fibre with the simple yet undeniably reliable process of continuous winding.
A PBO cable is dry fibre tightly compacted and does not rely on a resin matrix that, if impacted, can be compromised. The cover of the cable is a vital component and whilst PBO is an excellent material for yacht rigging purposes, due to its extreme strength, low elongation and general robustness it must be protected from sunlight and seawater. Future Fibres has perfected its cover design that comprises a consolidating film, environmental protection layer and a customizable braided cover that can be tailored to suit any specific application. PBO has great potential to be used in construction or rehabilitation applications. At the same time the fibres, following further testing, would open up several design opportunities for high quality architectural projects.Gough, CE.; Pobo Blasco, M.; Ruiz Checa, JR. (2009). PBO Fibres: from saliling design towards architectural performance. Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/670
Polyakov loop in chiral quark models at finite temperature
We describe how the inclusion of the gluonic Polyakov loop incorporates large
gauge invariance and drastically modifies finite temperature calculations in
chiral quark models after color neutral states are singled out. This generates
an effective theory of quarks and Polyakov loops as basic degrees of freedom.
We find a strong suppression of finite temperature effects in hadronic
observables triggered by approximate triality conservation (Polyakov cooling),
so that while the center symmetry breaking is exponentially small with the
constituent quark mass, chiral symmetry restoration is exponentially small with
the pion mass. To illustrate the point we compute some low energy observables
at finite temperature and show that the finite temperature corrections to the
low energy coefficients are suppressed due to color average of the
Polyakov loop. Our analysis also shows how the phenomenology of chiral quark
models at finite temperature can be made compatible with the expectations of
chiral perturbation theory. The implications for the simultaneous center
symmetry breaking-chiral symmetry restoration phase transition are also
discussed.Comment: 24 pages, 8 ps figures. Figure and appendix added. To appear in
Physical Review
Chiral Symmetry and s-wave Low-Lying Meson-Baryon Resonances
The wave meson-baryon scattering is analyzed for the isospin-strangeness
and sectors, in a Bethe-Salpeter coupled channel
formalism incorporating Chiral Symmetry. For both sectors, four channels have
been considered: , , , and ,
, , , respectively. The needed two particle
irreducible matrix amplitudes are taken from lowest order Chiral Perturbation
Theory in a relativistic formalism. There appear undetermined low energy
constants, as a consequence of the renormalization of the amplitudes, which are
obtained from fits to the available data: elastic phase-shifts, and cross sections and to
mass-spectrum, the elastic and
--matrices and to the
cross section data. The position and residues of the complex poles in the
second Riemann sheet of the scattering amplitude determine masses, widths and
branching ratios of the (1535) and (1650) and
(1405) and (1670) resonances, in reasonable agreement with
experiment. A good overall description of data, from threshold up to around 2
GeV is achieved despite the fact that three-body channels have not been
explicitly included.Comment: 5 Pages, 2 figures, invited contribution to Focus Session on Nature
of Threshold N*, to be published in Proceedings of Nstar 2002, Pittsburgh,
USA, October 9-12, 2002 (World Scientific
Dynamical magnetic anisotropy and quantum phase transitions in a vibrating spin-1 molecular junction
We study the electronic transport through a spin-1 molecule in which
mechanical stretching produces a magnetic anisotropy. In this type of device, a
vibron mode along the stretching axis will couple naturally to the molecular
spin. We consider a single molecular vibrational mode and find that the
electron-vibron interaction induces an effective correction to the magnetic
anisotropy that shifts the ground state of the device toward a non-Fermi liquid
phase. A transition into a Fermi liquid phase could then be achieved, by means
of mechanical stretching, passing through an underscreened spin-1 Kondo regime.
We present numerical renormalization group results for the differential
conductance, the spectral density, and the magnetic susceptibility across the
transition.Comment: 7 pages, 7 figure
- …