3,850 research outputs found
Confined spin waves reveal an assembly of nanosize domains in ferromagnetic La(1-x)CaxMnO3 (x=0.17,0.2)
We report a study of spin-waves in ferromagnetic LaCaMnO,
at concentrations x=0.17 and x=0.2 very close to the metallic transition
(x=0.225). Below T, in the quasi-metallic state (T=150K), nearly
q-independent energy levels are observed. They are characteristic of standing
spin waves confined into finite-size ferromagnetic domains, defined in {\bf a,
b) plane for x=0.17 and in all q-directions for x=0.2. They allow an estimation
of the domain size, a few lattice spacings, and of the magnetic coupling
constants inside the domains. These constants, anisotropic, are typical of an
orbital-ordered state, allowing to characterize the domains as "hole-poor". The
precursor state of the CMR metallic phase appears, therefore, as an assembly of
small orbital-ordered domains.Comment: 4 pages, 5 figure
Diversity and conservation status of Peruvian palms
Indigenous palm species of Peru are listed with data on their distribution patterns, ecology, frequency. density in the ecosystems, and conservation status. Peruvian palm flora includes 140 native species in 34 genera with the following distribution patterns: strictly Andean (17), Andean and Subandean (3), strictly Subandean (19), Subandean and Amazonian (20), strictly Amazonian (7&), Amazonian and South peripheral (2) , South peripheral (1). About 43 % of the species occur at very low or low frequency in the country and about 9 % are insufficiently known in situ for their conservation status to be defined. There are no Extinct species. Sixteen of the 17 strictly Andean palms are threatened species; 3 of them are Endangered, while only 5 strictly Subandean, 3 Subandean-Amazonian, and 4 strictly Amazonian palms are in these categories
The ideal relativistic spinning gas: polarization and spectra
We study the physics of the ideal relativistic rotating gas at
thermodynamical equilibrium and provide analytical expressions of the momentum
spectra and polarization vector for the case of massive particles with spin 1/2
and 1. We show that the finite angular momentum J entails an anisotropy in
momentum spectra, with particles emitted orthogonally to J having, on average,
a larger momentum than along its direction. Unlike in the non-relativistic
case, the proper polarization vector turns out not to be aligned with the total
angular momentum with a non-trivial momentum dependence.Comment: Final published version. Minor corrections to formula
Thirty Femtograms Detection of Iron in Mammalian Cells
Inorganic nanomaterials and particles with enhanced optical, mechanical or
magnetic attributes are currently being developed for a wide range of
applications. Safety issues have been formulated however concerning their
potential cyto- and genotoxicity. For in vivo and in vitro experimentations,
recent developments have heightened the need of simple and facile methods to
measure the amount of nanoparticles taken up by cells or tissues. In this work,
we present a rapid and highly sensitive method for quantifying the uptake of
iron oxide nanoparticles in mammalian cells. Our approach exploits the
digestion of incubated cells with concentrated hydrochloric acid reactant and a
colorimetric based UV-Visible absorption technique. The technique allows the
detection of iron in cells over 4 decades in masses, from 0.03 to 300 picograms
per cell. Applied on particles of different surface chemistry and sizes, the
protocol demonstrates that the coating is the key parameter in the
nanoparticle/cell interactions. The data are corroborated by scanning and
transmission electron microscopy and stress the importance of resiliently
adsorbed nanoparticles at the plasma membrane.Comment: 18 pages, 6 figure
Bilinear and quadratic Hamiltonians in two-mode cavity quantum electrodynamics
In this work we show how to engineer bilinear and quadratic Hamiltonians in
cavity quantum electrodynamics (QED) through the interaction of a single driven
two-level atom with cavity modes. The validity of the engineered Hamiltonians
is numerically analyzed even considering the effects of both dissipative
mechanisms, the cavity field and the atom. The present scheme can be used, in
both optical and microwave regimes, for quantum state preparation, the
implementation of quantum logical operations, and fundamental tests of quantum
theory.Comment: 11 pages, 3 figure
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