A Missão numa Perspectiva Antropológica

This article is a study about religious missions it discusses anthropological publications related to this theme, found within the analyses of various authors of the anthropology of religion. The author analyses academic publications from the middle of the last century to understand the relations between missionaries and anthropologists. The article relates how anthropologists view missions and gives a large theoretical revision about the anthropological interpretations of the missions.Este artigo apresenta um estudo sobre as missões religiosas discutindo as produções antropológicas referentes a este tema, presentes na análise de diversos autores da antropologia da religião. A autora faz uma análise das produções acadêmicas desde meados do século passado para compreender as relações travadas entre missionários e antropólogos. Relata como os antropólogos pensam as missões e faz uma farta revisão teórica sobre as interpretações antropológicas em torno das missões

Mujeres y conocimientos ancestrales en la Amazonia, Brasil.

En este artículo se discute la importancia de la mujer en la actividad productiva y en la producción de los respectivos conocimientos, en esta medida el material utilizado en este documento proviene de la experiencia a lo largo de años de investigación en la Amazonia Brasileña tanto entre indígenas como entre poblaciones caboclas, campesinas, cimarronas entre otros grupos sociales que viven en el medio rural. En este sentido se presenta una reflexión conceptual y una caracterización de la importancia de las mujeres amazónicas. Finalmente, se revela la centralidad de las mujeres en la producción del conocimiento ancestral.This article discusses the importance of women in the productive activity and the production of the respective knowledge, to this extent the material used in this document comes through years of research experience in the Brazilian Amazon among indigenous as populations caboclas, peasant, maroon among other social groups living in rural areas. In this sense is presented a conceptual reflection and characterization the importance of the amazon women. Finally, it is revealed the centrality of women in the production of the ancestral knowledge

A New Liquid Phase and Metal-Insulator Transition in Si MOSFETs

We argue that there is a new liquid phase in the two-dimensional electron system in Si MOSFETs at low enough electron densities. The recently observed metal-insulator transition results as a crossover from the percolation transition of the liquid phase through the disorder landscape in the system below the liquid-gas critical temperature. The consequences of our theory are discussed for variety of physical properties relevant to the recent experiments.Comment: 12 pages of RevTeX with 3 postscript figure

Magnetoresistance and electronic structure of asymmetric GaAs/AlGaAs double quantum wells in the in-plane/tilted magnetic field

Bilayer two-dimensional electron systems formed by a thin barrier in the GaAs buffer of a standard heterostructure were investigated by magnetotransport measurements. In magnetic fields oriented parallel to the electron layers, the magnetoresistance exhibits an oscillation associated with the depopulation of the higher occupied subband and the field-induced transition into a decoupled bilayer. Shubnikov-de Haas oscillations in slightly tilted magnetic fields allow to reconstruct the evolution of the electron concentration in the individual subbands as a function of the in-plane magnetic field. The characteristics of the system derived experimentally are in quantitative agreement with numerical self-consistent-field calculations of the electronic structure.Comment: 6 pages, 5 figure

Universality in an integer Quantum Hall transition

An integer Quantum Hall effect transition is studied in a modulation doped p-SiGe sample. In contrast to most examples of such transitions the longitudinal and Hall conductivities at the critical point are close to 0.5 and 1.5 (e^2/h), the theoretically expected values. This allows the extraction of a scattering parameter, describing both conductivity components, which depends exponentially on filling factor. The strong similarity of this functional form to those observed for transitions into the Hall insulating state and for the B=0 metal- insulator transition implies a universal quantum critical behaviour for the transitions. The observation of this behaviour in the integer Quantum Hall effect, for this particular sample, is attributed to the short-ranged character of the potential associated with the dominant scatterers

Indication of the ferromagnetic instability in a dilute two-dimensional electron system

The magnetic field B_c, in which the electrons become fully spin-polarized, is found to be proportional to the deviation of the electron density from the zero-field metal-insulator transition in a two-dimensional electron system in silicon. The tendency of B_c to vanish at a finite electron density suggests a ferromagnetic instability in this strongly correlated electron system.Comment: 4 pages, postscript figures included. Revised versio

On the Theory of Metal-Insulator Transitions in Gated Semiconductors

It is shown that recent experiments indicating a metal-insulator transition in 2D electron systems can be interpreted in terms of a simple model, in which the resistivity is controlled by scattering at charged hole traps located in the oxide layer. The gate voltage changes the number of charged traps which results in a sharp change in the resistivity. The observed exponential temperature dependence of the resistivity in the metallic phase of the transition follows from the temperature dependence of the trap occupation number. The model naturally describes the experimentally observed scaling properties of the transition and effects of magnetic and electric fields.Comment: 4 two-column pages, 4 figures (included in the text

Possible triplet superconductivity in MOSFETs

A theory that predicts a spin-triplet, even-parity superconducting ground state in two-dimensional electron systems is re-analyzed in the light of recent experiments showing a possible insulator-to-conductor transition in such systems. It is shown that the observations are consistent with such an exotic superconductivity mechanism, and predictions are made for experiments that would further corroborate or refute this proposal.Comment: 4 pp., REVTeX, psfig, 1 eps fig, final version as publishe

Interactions and Scaling in a Disordered Two-Dimensional Metal

We show that a non-Fermi liquid state of interacting electrons in two dimensions is stable in the presence of disorder and is a perfect conductor, provided the interactions are sufficiently strong. Otherwise, the disorder leads to localization as in the case of non-interacting electrons. This conclusion is established by examining the replica field theory in the weak disorder limit, but in the presence of arbitrary electron-electron interaction. Thus, a disordered two-dimensional metal is a perfect metal, but not a Fermi liquid.Comment: 4 pages, RevTe

Coexistence of Weak Localization and a Metallic Phase in Si/SiGe Quantum Wells

Magnetoresistivity measurements on p-type Si/SiGe quantum wells reveal the coexistence of a metallic behavior and weak localization. Deep in the metallic regime, pronounced weak localization reduces the metallic behavior around zero magnetic field without destroying it. In the insulating phase, a positive magnetoresistivity emerges close to B=0, possibly related to spin-orbit interactions.Comment: 4 pages, 3 figure