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 & Control theory. 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.

Crystal structure of isotactic polystyrene

Abstract: The crystal structure of isotactic polystyrene is described in this paper. The unit cell as determined from the X-ray diffraction spectra of oriented samples is rhombohedral, and its constants referred to hexagonal axes are: a = 21.9 ± 0.1 A , c = 6.65 ± 0.05 A ( chain axis ) Z = 18 ; Space group R 3 c or R 3 ¯ c .

Impulsive and Long Duration High-Energy Gamma-ray Emission From the Very Bright 2012 March 7 Solar Flares

Abstract: The Fermi Large Area Telescope (LAT) observed two bright X-class solar ares on 2012 March 7, and detected gamma-rays up to 4 GeV. We detected gamma-rays both during the impulsive and temporally-extended emission phases, with emission above 100 MeV lasting for approximately 20 hours. Accurate localization of the gamma-ray production site(s) coincide with the solar active region from which X-ray emissions associated with these ares originated. Our analysis of the > 100 MeV gamma-ray emission shows a relatively rapid monotonic decrease in ux during the rst hour of the impulsive phase, and a much slower, almost monotonic decrease in ux for the next 20 hours. The spectra can be adequately described by a power law with a high energy exponential cuto , or as resulting from the decay of neutral pions produced by accelerated protons and ions with an isotropic power-law energy distribution. The required proton spectrum has a number index 3, with minor variations during the impulsive phase, while during the temporally extended phase the spectrum softens monotonically, starting with index 4. The > 30 MeV proton ux and spectra observed near the Earth by the GOES satellites also show a monotonic ux decrease and spectral softening during the extended phase, but with a harder spectrum, with index 3. Based on the Fermi -LAT and GOES observations of the ux and spectral evolution of these bright ares, we explore the relative merits of prompt and continuous acceleration scenarios, hadronic and leptonic emission processes, and acceleration at the solar corona by the fast Coronal Mass Ejections (CME) as explanations for the observations. We conclude that the most likely scenario is continuous acceleration of protons in the solar corona which penetrate the lower solar atmosphere and produce pions that decay into gamma-rays.

Empirical study of machine learning based approach for opinion mining in tweets

Abstract: Opinion mining deals with determining of the sentiment orientation--positive, negative, or neutral--of a (short) text. Recently, it has attracted great interest both in academia and in industry due to its useful potential applications. One of the most promising applications is analysis of opinions in social networks. In this paper, we examine how classifiers work while doing opinion mining over Spanish Twitter data. We explore how different settings (n-gram size, corpus size, number of sentiment classes, balanced vs. unbalanced corpus, various domains) affect precision of the machine learning algorithms. We experimented with Naive Bayes, Decision Tree, and Support Vector Machines. We describe also language specific preprocessing--in our case, for Spanish language--of tweets. The paper presents best settings of parameters for practical applications of opinion mining in Spanish Twitter. We also present a novel resource for analysis of emotions in texts: a dictionary marked with probabilities to express one of the six basic emotions(Probability Factor of Affective use (PFA)(Spanish Emotion Lexicon that contains 2,036 words.