Beyond Stemming and Lemmatization: Ultra-stemming to Improve Automatic Text Summarization

In Automatic Text Summarization, preprocessing is an important phase to reduce the space of textual representation. Classically, stemming and lemmatization have been widely used for normalizing words. However, even using normalization on large texts, the curse of dimensionality can disturb the performance of summarizers. This paper describes a new method for normalization of words to further reduce the space of representation. We propose to reduce each word to its initial letters, as a form of Ultra-stemming. The results show that Ultra-stemming not only preserve the content of summaries produced by this representation, but often the performances of the systems can be dramatically improved. Summaries on trilingual corpora were evaluated automatically with Fresa. Results confirm an increase in the performance, regardless of summarizer system used.Comment: 22 pages, 12 figures, 9 table

Chiral transport equation from the quantum Dirac Hamiltonian and the on-shell effective field theory

We derive the relativistic chiral transport equation for massless fermions and antifermions by performing a semiclassical Foldy-Wouthuysen diagonalization of the quantum Dirac Hamiltonian. The Berry connection naturally emerges in the diagonalization process to modify the classical equations of motion of a fermion in an electromagnetic field. We also see that the fermion and antifermion dispersion relations are corrected at first order in the Planck constant by the Berry curvature, as previously derived by Son and Yamamoto for the particular case of vanishing temperature. Our approach does not require knowledge of the state of the system, and thus it can also be applied at high temperature. We provide support for our result by an alternative computation using an effective field theory for fermions and antifermions: the on-shell effective field theory. In this formalism, the off-shell fermionic modes are integrated out to generate an effective Lagrangian for the quasi-on-shell fermions/antifermions. The dispersion relation at leading order exactly matches the result from the semiclassical diagonalization. From the transport equation, we explicitly show how the axial and gauge anomalies are not modified at finite temperature and density despite the incorporation of the new dispersion relation into the distribution function.Comment: 9 pages, no figures. v2: Some comments and more details added, typos fixed and reference list updated. Final version matching the published articl

Dynamical evolution of the chiral magnetic effect: Applications to the quark-gluon plasma

We study the dynamical evolution of the so-called chiral magnetic effect in an electromagnetic conductor. To this end, we consider the coupled set of corresponding Maxwell and chiral anomaly equations, and we prove that these can be derived from chiral kinetic theory. After integrating the chiral anomaly equation over space in a closed volume, it leads to a quantum conservation law of the total helicity of the system. A change in the magnetic helicity density comes together with a modification of the chiral fermion density. We study in Fourier space the coupled set of anomalous equations and we obtain the dynamical evolution of the magnetic fields, magnetic helicity density, and chiral fermion imbalance. Depending on the initial conditions we observe how the helicity might be transferred from the fermions to the magnetic fields, or vice versa, and find that the rate of this transfer also depends on the scale of wavelengths of the gauge fields in consideration. We then focus our attention on the quark-gluon plasma phase, and analyze the dynamical evolution of the chiral magnetic effect in a very simple toy model. We conclude that an existing chiral fermion imbalance in peripheral heavy ion collisions would affect the magnetic field dynamics, and consequently, the charge dependent correlations measured in these experiments.Comment: 41 pages, 14 figures, 3 appendices. Version 2: new global structure (appendix added), more explanations and additional references. Version accepted for publication in Physical Review D journa

¿Existe una la ley propia de la evolución biológica?

Comenzamos nuestra exposición distinguiendo entre leyes de la naturaleza y leyes científicas. Si existieran las primeras -probablemente descendientes de la visión onto-teológica de Descartes y Newton-, ellas serían un reflejo especular de la realidad. A pesar de que se debe reconocer que son continuamente invocadas en la práctica científica por los mismos científicos, es dudoso que tales leyes están o que, en presencia de ellas, podamos justificar que son tales. Las leyes naturales serían de valor irrestricto pata el dominio que se les atribuye y eso es algo que nunca estaríamos en condiciones de demostrar Específicamente, asegurar que no existen contraejemplos y que la ley se cumple universal y necesariamente. El análisis hecho por R. Grere (1999, 85-96) sobre la pretendida ley natural de la gravitación universal brida buenos argumentos en este sentido, sobre todo porque le muestra que no se pueden recrear las condiciones ideales bajo las cuales se cumplirían estrictamente las leyes de la mecánica. Además y como es conocido, siempre subsiste el problema del cumplimiento efectivo de la cláusula "ceteris paribus", que hoy con razón,es denominada "ceteris ausentibus" .Finalmente, la historia de la ciencia da buenos argumentos para dejar de lado la temeraria afirmación que estamos frente a leyes de inexorable cumplimiento

Antecedentes históricos y conceptuales de una tesis central de The Selfish Gene

Comenzamos citando una tesis que ganó gran aceptación en la comunidad científica y filosófica en los últimos años: "It is now evident that man was invented to provide DNA with the opportunity to explore extraterrestrial possib!lities for replication". En realidad, esta tesis - que es casi necesario decir que está formulada ex professo de modo antropomorfico y finalistlco - es una consecuencia lógica de otra más general que afirma que los genes son lo que es seleccionado - la unidad de selección - en el proceso evolutivo, mientras que los organismos son aquello de lo que se valen para subsistir, multíplicatse y progresar Como es conocido, esta úl!ima es la tesis más conspicua de uno de los fundadores de la sociobiología. Nos referimos a R. Dawkins (1976, 1987