Thermal properties of MgB2: the effect of disorder on gap amplitudes and relaxation times of p and s bands

We present thermal conductivity and specific heat measurements on MgB2 and Mg-AlB2 samples. Thermal properties have been analysed by using a two-gap model in order to estimate the gap amplitudes, D(0)p and D(0)s and the intra-band scattering rates, Gss and Gpp. As a function of Al doping and disorder D(0)s rapidly decreases, while D(0)p is rather constant. Gss and Gpp are increased by the disorder, being Gpp more affected than Gss.Comment: 2 pages, 3 figures, presented to the conference M2S-HTSC, 25-30 May 2003, Rio de Janeir

Modeling Shallow Water Flows on General Terrains

A formulation of the shallow water equations adapted to general complex terrains is proposed. Its derivation starts from the observation that the typical approach of depth integrating the Navier-Stokes equations along the direction of gravity forces is not exact in the general case of a tilted curved bottom. We claim that an integration path that better adapts to the shallow water hypotheses follows the "cross-flow" surface, i.e., a surface that is normal to the velocity field at any point of the domain. Because of the implicitness of this definition, we approximate this "cross-flow" path by performing depth integration along a local direction normal to the bottom surface, and propose a rigorous derivation of this approximation and its numerical solution as an essential step for the future development of the full "cross-flow" integration procedure. We start by defining a local coordinate system, anchored on the bottom surface to derive a covariant form of the Navier-Stokes equations. Depth integration along the local normals yields a covariant version of the shallow water equations, which is characterized by flux functions and source terms that vary in space because of the surface metric coefficients and related derivatives. The proposed model is discretized with a first order FORCE-type Godunov Finite Volume scheme that allows implementation of spatially variable fluxes. We investigate the validity of our SW model and the effects of the bottom geometry by means of three synthetic test cases that exhibit non negligible slopes and surface curvatures. The results show the importance of taking into consideration bottom geometry even for relatively mild and slowly varying curvatures

Examination of the seepage face boundary condition in subsurface and coupled surface/subsurface hydrological models

A seepage face is a nonlinear dynamic boundary that strongly affects pressure head distributions, water table fluctuations, and flow patterns. Its handling in hydrological models, especially under complex conditions such as heterogeneity and coupled surface/subsurface flow, has not been extensively studied. In this paper, we compare the treatment of the seepage face as a static (Dirichlet) versus dynamic boundary condition, we assess its resolution under conditions of layered heterogeneity, we examine its interaction with a catchment outlet boundary, and we investigate the effects of surface/subsurface exchanges on seepage faces forming at the land surface. The analyses are carried out with an integrated catchment hydrological model. Numerical simulations are performed for a synthetic rectangular sloping aquifer and for an experimental hillslope from the Landscape Evolution Observatory. The results show that the static boundary condition is not always an adequate stand-in for a dynamic seepage face boundary condition, especially under conditions of high rainfall, steep slope, or heterogeneity; that hillslopes with layered heterogeneity give rise to multiple seepage faces that can be highly dynamic; that seepage face and outlet boundaries can coexist in an integrated hydrological model and both play an important role; and that seepage faces at the land surface are not always controlled by subsurface flow. The paper also presents a generalized algorithm for resolving seepage face outflow that handles heterogeneity in a simple way, is applicable to unstructured grids, and is shown experimentally to be equivalent to the treatment of atmospheric boundary conditions in subsurface flow models

O imaginário visual do pós-humano: uma leitura antropológica entre cinema e arte contemporânea

The first step was to define the posthuman. This study is particularly focused on some art works and movies to try to recognize what are their implications on the weaving of the collective imagination, referring to the visual dimension of a coming future. The report continues with the analyses of the film Gattaca (1997), directed by New Zealander Andrew M. Niccol, and of artworks by  Cypher (2009), which contain an explicit reference to  Niccol’s film and GFP Bunny/Alba (2000), both created by the artist Eduardo Kac. The works of these two authors and  the relations between them become the main  referential axis for examination of the construction of  an imaginary of transformations in the parental relationship and, more generally, in social relationships associated with artificial genetic revolution.O imaginário visual do pós-humano: uma leitura antropológica entre cinema e arte contemporânea. A primeira etapa dessa relação é a definição de pós-humano; isto se concentra particularmente em alguns trabalhos de arte e cinema, tentando reconhecer quais as implicações destes na trama da imaginação coletiva, com referência à dimensão visual de um futuro próximo. O estudo prossegue com uma análise do filme Gattaca (1997), dirigido pelo neozelandês Andrew M. Niccol, e os trabalhos de arte Cypher (2009), que contém uma referência explícita ao filme de Niccol, e GFP Bunny/Alba (2000), ambos criados pelo artista Eduardo Kac. Os trabalhos desses dois autores e sua relação entre si tornam-se o principal eixo de referência para a análise da construção de um imaginário das transformações na relação parental e, de maneira mais ampla, nas relações sociais ligadas à revolução genética artificial

Tetragonal to orthorhombic phase transition in SmFeAsO: a synchrotron powder diffraction investigation

The crystal structure of SmFeAsO has been investigated by means of Rietveld refinement of high resolution synchrotron powder diffraction data collected at 300 K and 100 K. The compound crystallizes in the tetragonal P4/nmm space group at 300 K and in the orthorhombic Cmma space group at 100 K; attempts to refine the low temperature data in the monoclinic P112/n space group diverged. On the basis of both resistive and magnetic analyses the tetragonal to orthorhombic phase transition can be located at T about 140 K.Comment: Submitted to: Superconductor Science and Technology PACS: 61.05.cp, 61.66.Fn, 74.10.+v, 74.62.Dh, 74.70.D

PENINGKATAN KEMAMPUAN REPRESENTASI MATEMATIS SISWA MELALUI PEMBELAJARAN MODEL QUANTUM TEACHING

Penelitian ini bertujuan untuk mengkaji peningkatan kemampuan representasi matematis siswa SMP yang memperoleh pembelajaran dengan model Quantum Teaching dibandingkan dengan siswa yang memperoleh pembelajaran dengan model konvensional dan respon siswa terhadap pembelajaran matematika yang menggunakan model Quantum Teaching. Metode penelitian yang digunakan adalah kuasi eksperimen dengan desain penelitian kelompok control non ekuivalen. Populasi penelitian adalah seluruh siswa kelas VIII di salah satu SMP Negeri di Kota Bandung dengan sampel penelitian adalah dua buah kelas yang berperan sebagai kelas eksperimen dan kelas control. Data penelitian yang diperoleh adalah tes kemampuan representasi matematis, angket respon, dan lembar observasi. Hasil penelitian menunjukkan bahwa: (1) peningkatan kemampuan representasi matematis siswa yang memperoleh pembelajaran dengan model Quantum Teaching lebih baik dari siswa yang memperoleh pembelajaran dengan model konvensional; (2) Siswa memberikan respon positif terhadap pembelajaran matematika dengan model Quantum Teaching.----------The purpose of this study were reviewed the enhancement of mathematical representation ability in Junior High School students who obtained teaching under Quantum Teaching model compared to students who obtained teaching under conventional model and student’s response against learning mathematics using Quantum Teaching model. The method in this study was quasi-experimental with nonequivalent control group design. The population in this study was the eighth grades of a junior high school in Bandung with sample of this study were two classes that contribute as experiment class and control class. The research data was obtained from mathematical representation ability test, questionnaires, and observation sheet. The result showed that: (1) the enhancement of student’s mathematical representation ability who obtained teaching under Quantum Teaching model was better than students who obtained teaching under conventional model; (2) students give a positive response against learning mathematics using Quantum Teaching model

Consequences of the peculiar intrinsic properties of MgB2 on its macroscopic current flow

The influence of two important features of magnesium diboride on the macroscopic transport properties of polycrystalline MgB2 is discussed in the framework of a percolation model. While two band superconductivity does not have significant consequences in the field and temperature range of possible power applications, the opposite is true for the anisotropy of the upper critical field. The field dependence of the critical current densities strongly increases and the macroscopic supercurrents disappear well below the apparent upper critical field. The common scaling laws for the field dependence of the volume pinning force are altered and Kramer's plot is no longer linear, although grain boundary pinning dominates in nearly all polycrystalline MgB2 conductors. In contrast to the conventional superconductors NbTi and Nb3Sn, a significant critical current anisotropy can be induced by the preparation technique of MgB2 tapes