A first-principles investigation of the thermodynamic and mechanical properties of Ni-Ti-Sn Heusler and half-Heusler materials

First principles calculations of the vibrational, thermodynamic and mechanical properties of the Ni-Ti-Sn Heusler and half-Heusler compounds have been performed. First, we have calculated the Raman and infrared spectra of NiTiSn, providing benchmark theoretical data directly useful for the assignments of its experimental spectra and clarifying the debate reported in the literature on the assignment of its modes. Then, we have discussed the significant vibrational density-of-states of Ni2TiSn at low-frequencies. These states are at the origin of (i) its smaller free energy, (ii) its higher entropy, and (iii) its lower Debye temperature, with respect to NiTiSn. Finally, we have reported the mechanical properties of the two compounds. In particular, we have found that the half-Heusler compound has the largest stiffness. Paradoxically, its bulk modulus is also the smallest. This unusual behavior has been related to the Ni-vacancies that weaken the structure under isostatic compression. Both compounds show a ductile behavior.Comment: 22 pages, 7 figure

Ciudadanía y nacionalidad en América Latina

No existe democracia sin ciudadanos, como tampoco ciudadanía que no se funde en la condición previa de una nacionalidad concebida como identidad solidaria. La afirmación es obvia en el caso de las democracias ya consolidadas. En cambio, resulta problemática en los países que afrontan el reto de una transición democrática. Ante todo, ¿cuál es la sustancia que vivifica ambas nociones? Y, en segundo lugar, ¿cómo puede resolverse la paradoja en virtud de la cual los dos elementos son necesarios para la eclosión de la democracia, y sin embargo no adquieren su plenitud más que en un marco democrático ya creado? Respecto de esos dos planos indisociables de la ciudadanía y la nacionalidad, ¿muestran los latinoamericanos filiación con Europa? ¿O se sitúan más bien en un particular Tercer Mundo que, si bien latino, sólo desde un punto de vista topográfico sería occidental

CURRENCY CRISIS AND BALANCE SHEET CHANNEL EFFECT. The Korean Experience

Some theoretical crisis models of third generation incorporate the "balance sheet effect" emphasized by Bernanke and Gertler (1989) and many papers since. In a crisis context this mechanism, based on asymmetric information in the credit market, describes how a currency depreciation affects domestic firms' investment. This paper proposes an empirical validation of this theoretical prediction. To this end, we study the investment behaviour of 477 Korean manufacturing firms, particularly during the 1997 Asian crisis. However, contrary to many studies in which cash flow account variable is used as proxy for entrepreneurs'' net worth, our analysis focuses on a more relevant variable, the cash stock, to measure these internal funds. The preliminary results stipulate that firms'' balance sheets in the aftermath of the Asian crisis, are more robust in explaining investment than before the crisis. It is further shown that this relationship is more relevant for small firms.

Individuals tell a fascinating story: using unsupervised text mining methods to cluster policyholders based on their medical history

Background and objective: Classifying people according to their health profile is crucial in order to propose appropriate treatment. However, the medical diagnosis is sometimes not available. This is for example the case in health insurance, making the proposal of custom prevention plans difficult. When this is the case, an unsupervised clustering method is needed. This article aims to compare three different methods by adapting some text mining methods to the field of health insurance. Also, a new clustering stability measure is proposed in order to compare the stability of the tested processes. Methods : Nonnegative Matrix Factorization, the word2vec method, and marginalized Stacked Denoising Autoencoders are used and compared in order to create a high-quality input for a clustering method. A self-organizing map is then used to obtain the final clustering. A real health insurance database is used in order to test the methods. Results: the marginalized Stacked Denoising Autoencoder outperforms the other methods both in stability and result quality with our data. Conclusions: The use of text mining methods offers several possibilities to understand the context of any medical act. On a medical database, the process could reveal unexpected correlation between treatment, and thus, pathology. Moreover, this kind of method could exploit the refund dates contained in the data, but the tested method using temporality, word2vec, still needs to be improved since the results, even if satisfying, are not as better as the one offered by other methods

Symbolic assessment of free text answers in a second-language tutoring system

We present an approach to Computer-Assisted Assessment of free-text material based on symbolic analysis of student input. The theory that underlies this approach arises from previous work on DidaLect, a tutoring system for second-language reading skill enhancement. The theory enables the processing of free-text segments for assessment to operate without preencoded reference material. A study based on a corpus of 48 student answers to several types of questions has justified our approach, helped define a methodology and design a prototype