Phase diagram of a 2D Ising model within a nonextensive approach

In this work we report Monte Carlo simulations of a 2D Ising model, in which the statistics of the Metropolis algorithm is replaced by the nonextensive one. We compute the magnetization and show that phase transitions are present for $q\neq 1$. A $q -$ phase diagram (critical temperature vs. the entropic parameter $q$) is built and exhibits some interesting features, such as phases which are governed by the value of the entropic index $q$. It is shown that such phases favors some energy levels of magnetization states. It is also showed that the contribution of the Tsallis cutoff is essential to the existence of phase transitions

Strain and order-parameter coupling in Ni-Mn-Ga Heusler alloys from resonant ultrasound spectroscopy

Resonant ultrasound spectroscopy and magnetic susceptibility experiments have been used to characterize strain coupling phenomena associated with structural and magnetic properties of the shape-memory Heusler alloy series Ni$_{50+x}$Mn$_{25-x}$Ga$_{25}$ ($x=0$, 2.5, 5.0, and 7.5). All samples exhibit a martensitic transformation at temperature $T_M$ and ferromagnetic ordering at temperature $T_C$, while the pure end member ($x=0$) also has a premartensitic transition at $T_{PM}$, giving four different scenarios: $T_C>T_{PM}>T_M$, $T_C>T_M$ without premartensitic transition, $T_C\approx T_M$, and $T_C<T_M$. Fundamental differences in elastic properties i.e., stiffening versus softening, are explained in terms of coupling of shear strains with three discrete order parameters relating to magnetic ordering, a soft mode and the electronic instability responsible for the large strains typical of martensitic transitions. Linear-quadratic or biquadratic coupling between these order parameters, either directly or indirectly via the common strains, is then used to explain the stabilities of the different structures. Acoustic losses are attributed to critical slowing down at the premartensite transition, to the mobility of interphases between coexisting phases at the martensitic transition and to mobility of some aspect of the twin walls under applied stress down to the lowest temperatures at which measurements were made.Comment: 9 pages, 5 figure

Developmental perspectives of numerical thinking for the interpretation of physical quantities

This research reveals the perspectives in the teaching of numerical thinking through a documentary review. The representation of physical elements such as functions, vectors and operators, and their subsequent interpretation through numerical thinking gives meaning to the physical quantities that such elements represent. A documentary sample integrated for 40 sources on numerical thinking such as articles published in indexed journals, postgraduate dissertations, and books is considered. A qualitative content analysis method is used. First, an encoding procedure is applied for tagging the extracted information from the source documents. Then, a split and merge procedure is considered in order to establish from the tags the dimensions and categories that allow determining the conceptual relationships that support the developmental perspectives of numerical thinking. The method reveals that the numerical thinking can be developed in the global context from four perspectives, namely, historical, theoretical, curricular, and social perspectives. From these results, an incorporation of the such perspectives can be institutionalized for promoting curricular, didactic and evaluative new proposals for numerical thinking teaching

Modelo de administración de proyectos de electrificación rural en Nicaragua incluyendo la generación en sistemas aislados

The objective of the research described in this article is to contribute to the development of remote rural electrical systems. The study sets out a proposed model for rural electrical project management, with the objective of achieving improved efficiency in operational management within companies or projects. Remote systems which are not connected to the conventional electricity grid, supply electricity to communities in rural areas of Nicaragua. They cover large areas which have, until now, been largely forgotten but which nevertheless have great potential in both natural resources and production. Such is the case in the Northern and Southern Atlantic Regions of Nicaragua. The proposed model for rural electrical project management uses a methodology of project analysis based on outline matrices using instruments of qualitative compilation. Based on the results of this research it is recommended that within projects of thermal power systems (using by-products of petroleum) the form of organization best suited to management needs are those of private companies, in particular the limited liability company. In projects of hydroelectric systems the recommendation is for a form of private organization such as a joint-stock corporation. Finally in projects of photovoltaic systems the recommendation is for a form of private organization such as a business cooperative. Keywords: model of project management; legal and administrative organization.DOI: 10.5377/nexo.v22i1.39Nexo: Revista Cient&iacute;fica Vol.22, No.01, pp.10-14/Agosto 2009Contribuir al desarrollo de los sistemas aislados de generación de energía eléctrica fue el objetivo de la investigación descrita en este artículo. En este estudio se planteó una propuesta de modelo de administración de proyectos de electrificación rural, con el propósito de obtener una mayor eficiencia de la operatividad administrativa de la empresa o proyecto. Los sistemas aislados, no conectados a la red eléctrica convencional, brindan abastecimiento de energía eléctrica a las comunidades de las zonas rurales de Nicaragua; éstos abarcan las zonas más extensas e históricamente olvidadas del país, pero que a su vez poseen grandes potencialidades en recursos naturales y productivos; tal es el caso de las Regiones Atlánticas Norte y Sur. Para la propuesta del modelo de administración de proyectos de electrificación rural se empleó una metodología de análisis de proyectos basada en un esquema matricial con instrumentos de recopilación cualitativa. Basados en los resultados de esta investigación, se recomienda que en los proyectos de sistemas térmicos (usando derivados de petróleo), la forma de organización que mejor se adecua a las necesidades administrativas es del tipo empresa privada, con un enfoque jurídico de sociedad de responsabilidad limitada. En los proyectos de sistemas hidroeléctricos se recomienda una forma de organización privada como una sociedad anónima. Finalmente, en los proyectos de sistemas fotovoltaicos se recomienda una forma de organización privada bajo una empresa cooperativa. Palabras claves: modelo de administración de proyectos; organización jurídica-administrativa.DOI: http://dx.doi.org/10.5377/nexo.v22i1.39Nexo: Revista Científica Vol.22, No.01, pp.10-14/Agosto 200