Instituto Politécnico Nacional

About: Instituto Politécnico Nacional is a education organization based out in Mexico City, Mexico. It is known for research contribution in the topics: Population & Context (language use). The organization has 43351 authors who have published 63315 publications receiving 938532 citations. The organization is also known as: Instituto Politécnico Nacional & Instituto Politecnico Nacional.

Transverse momentum spectra and nuclear modification factors of charged particles in pp, p-Pb and Pb-Pb collisions at the LHC

Abstract: We report the measured transverse momentum (p$_{T}$) spectra of primary charged particles from pp, p-Pb and Pb-Pb collisions at a center-of-mass energy $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV in the kinematic range of 0.15 < p$_{T}$< 50 GeV/c and |η| < 0.8. A significant improvement of systematic uncertainties motivated the reanalysis of data in pp and Pb-Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=2.76 $ TeV, as well as in p-Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV, which is also presented. Spectra from Pb-Pb collisions are presented in nine centrality intervals and are compared to a reference spectrum from pp collisions scaled by the number of binary nucleon-nucleon collisions. For central collisions, the p$_{T}$ spectra are suppressed by more than a factor of 7 around 6–7 GeV/c with a significant reduction in suppression towards higher momenta up to 30 GeV/c. The nuclear modification factor R$_{pPb}$, constructed from the pp and p-Pb spectra measured at the same collision energy, is consistent with unity above 8 GeV/c. While the spectra in both pp and Pb-Pb collisions are substantially harder at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV compared to 2.76 TeV, the nuclear modification factors show no significant collision energy dependence. The obtained results should provide further constraints on the parton energy loss calculations to determine the transport properties of the hot and dense QCD matter.

Fermi large area telescope observations of the vela pulsar

Abstract: The Vela pulsar is the brightest persistent source in the GeV sky and thus is the traditional first target for new gamma-ray observatories. We report here on initial Fermi Large Area Telescope observations during verification phase pointed exposure and early sky survey scanning. We have used the Vela signal to verify Fermi timing and angular resolution. The high quality pulse profile, with some 32,400 pulsed photons at E>0.03 GeV, shows new features, including pulse structure as fine as 0.3ms and a distinct third peak, which shifts in phase with energy. We examine the high energy behavior of the pulsed emission; initial spectra suggest a phase-averaged power law index of Gamma=1.51{+0.05/-0.04} with an exponential cut-off at E_c=2.9+/-0.1 GeV. Spectral fits with generalized cut-offs of the form e^{-(E/E_c)^b} require b<1, which is inconsistent with magnetic pair attenuation, and thus favor outer magnetosphere emission models. Finally, we report on upper limits to any unpulsed component, as might be associated with a surrounding synchrotron wind nebula (PWN).

Handling constraints using multiobjective optimization concepts

Abstract: In this paper, we propose a new constraint-handling technique for evolutionary algorithms which we call inverted-shrinkable PAES (IS-PAES). This approach combines the use of multiobjective optimization concepts with a mechanism that focuses the search effort onto specific areas of the feasible region by shrinking the constrained search space. IS-PAES also uses an adaptive grid to store the solutions found, but has a more efficient memory-management scheme than its ancestor (the Pareto archived evolution strategy for multiobjective optimization). The proposed approach is validated using several examples taken from the standard evolutionary and engineering optimization literature. Comparisons are provided with respect to the stochastic ranking method (one of the most competitive constraint-handling approaches used with evolutionary algorithms currently available) and with respect to other four multiobjective-based constraint-handling techniques. Copyright© 2004 John Wiley & Sons, Ltd.