551 research outputs found
Spin Degree of Freedom in a Two-Dimensional Electron Liquid
We have investigated correlation between spin polarization and
magnetotransport in a high mobility silicon inversion layer which shows the
metal-insulator transition. Increase in the resistivity in a parallel magnetic
field reaches saturation at the critical field for the full polarization
evaluated from an analysis of low-field Shubnikov-de Haas oscillations. By
rotating the sample at various total strength of the magnetic field, we found
that the normal component of the magnetic field at minima in the diagonal
resistivity increases linearly with the concentration of ``spin-up'' electrons.Comment: 4 pages, RevTeX, 6 eps-figures, to appear in PR
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
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
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 artÃculo 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 indÃgenas 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
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
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Mast cell clones: a model for the analysis of cellular maturation.
Cloned mouse mast cells resemble, by ultrastructure, immature mast cells observed in vivo. These mast cell clones can be grown in the absence of any other cells, facilitating direct investigations of their biochemistry and function. We find that cloned mast cells express plasma membrane receptors (Fc epsilon R) that bind mouse IgE with an equilibrium constant (KA) similar to that of normal mouse peritoneal mast cells. In addition, cloned mast cells do not display detectable la antigens and cannot enhance lg secretion when added to lymphocyte cultures or mediate natural killer lysis. In the presence of 1 mM sodium butyrate, cloned mast cells stop dividing and acquire abundant electron-dense cytoplasmic granules similar to those of mature mast cells. Their histamine content increases concomitant with cytoplasmic granule maturation and may exceed that of untreated mast cells by 50-fold. Unlike peritoneal mast cells, cloned mast cells incorporate 35SO4 into chondroitin sulfates rather than heparin. These findings demonstrate that, unlike fully differentiated mouse peritoneal mast cells, cloned immature mouse mast cells contain no heparin and low levels of histamine. In addition, they establish that high-affinity Fc epsilon R are expressed early in mast cell maturation, well before completion of cytoplasmic granule synthesis and mediator storage
Spin Polarization of Two-Dimensional Electrons Determined from Shubnikov-de Haas Oscillations as a Function of Angle
Recent experiments in the two dimensional electron systems in silicon MOSFETs
have shown that the in-plane magnetic field required to saturate the
conductivity to its high-field value and the magnetic field needed to
completely align the spins of the electrons are comparable. By small-angle
Shubnikov-de Haas oscillation measurements that allow separate determinations
of the spin-up and spin-down subband populations, we show that to
an accuracy of 5% for electron densities cm.Comment: 4 pages, 3 figures; minor changes, references updated and adde
Universality at integer quantum Hall transitions
We report in this paper results of experimental and theoretical studies of
transitions between different integer quantum Hall phases, as well as
transition between the insulating phase and quantum Hall phases at high
magnetic fields. We focus mainly on universal properties of the transitions. We
demonstrate that properly defined conductivity tensor is universal at the
transitions. We also present numerical results of a non-interacting electron
model, which suggest that the Thouless conductance is universal at integer
quantum Hall transitions, just like the conductivity tensor. Finite temperature
and system size effects near the transition point are also studied.Comment: 20 pages, 15 figure
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