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

Perturbative quantum analysis and classical limit of the electron scattering by a solenoidal magnetic field

A well known example in quantum electrodynamics (QED) shows that Coulomb scattering of unpolarized electrons, calculated to lowest order in perturbation theory, yields a results that exactly coincides (in the non-relativistic limit) with the Rutherford formula. We examine an analogous example, the classical and perturbative quantum scattering of an electron by a magnetic field confined in an infinite solenoid of finite radius. The results obtained for the classical and the quantum differential cross sections display marked differences. While this may not be a complete surprise, one should expect to recover the classical expression by applying the classical limit to the quantum result. This turn not to be the case. Surprisingly enough, it is shown that the classical result can not be recuperated even if higher order corrections are included. To recover the classic correspondence of the quantum scattering problem a suitable non-perturbative methodology should be applied.Comment: To appear in the proceedings of 13th Mexican School of Particles and Fields (MSPF 2008), San Carlos, Sonora, Mexico, 2-11 Oct 2008. 6 pages, 2 Postscript figure

FRAGILE STATES: DEFINING DIFFICULT ENVIRONMENTS FOR POVERTY REDUCTION

Food Security and Poverty,

DRIVERS OF FRAGILITY: WHAT MAKES STATES FRAGILE?

Food Security and Poverty,

UNIFORM OUTPUT SUBSIDIES IN AN ECONOMIC UNION WITH FIRMS HETEROGENEITY

In this paper we show the importance of cost asymmetry and demand curvature in the effect of a uniform output subsidy policy in an economic union. We consider an economic union formed by two countries each with a single firm producing a homogeneous good. We find that when firms have different cost, the optimal level of the uniform subsidy can be negative if the demand is concave enough. The low cost firm expands its market share if the demand function is sufficiently convex whereas in the case of a concave demand function it is the higher cost firm which gains market share. This implies that a uniform output subsidy policy may cause a change in production e¢ciency. Finally, we consider how a divergence between private and social costs of public funds may a¤ect the desirability of such a subsidy policy.Uniform output subsidy policy, economic union, social welfare, cost differences