20,143 research outputs found
Magnetism and Electronic Correlations in Quasi-One-Dimensional Compounds
In this contribution on the celebration of the 80th birthday anniversary of
Prof. Ricardo Ferreira, we present a brief survey on the magnetism of
quasi-one-dimensional compounds. This has been a research area of intense
activity particularly since the first experimental announcements of magnetism
in organic and organometallic polymers in the mid 80s. We review experimental
and theoretical achievements on the field, featuring chain systems of
correlated electrons in a special AB2 unit cell structure present in inorganic
and organic compounds
Quantum Properties of a Which-Way Detector
We explore quantum properties of a which-way detector using three versions of
an idealized two slit arrangements. Firstly we derive complementarity relations
for the detector; secondly we show how the "experiment" may be altered in such
a way that using single position measurement on the screen we can obtain
quantum erasure. Finally we show how to construct a superposition of "wave" and
"particle" components
Dependence of the Black-body Force on Spacetime Geometry and Topology
In this paper we compute the corrections to the black-body force (BBF)
potential due to spacetime geometry and topology. This recently discovered
attractive force on neutral atoms is caused by the thermal radiation emitted
from black bodies and here we investigate it in relativistic gravitational
systems with spherical and cylindrical symmetries. For some astrophysical
objects we find that the corrected black-body potential is greater than the
flat case, showing that this kind of correction can be quite relevant when
curved spaces are considered. Then we consider four cases: The Schwarzschild
spacetime, the global monopole, the non-relativistic infinity cylinder and the
static cosmic string. For the spherically symmetric case of a massive body, we
find that two corrections appear: One due to the gravitational modification of
the temperature and the other due to the modification of the solid angle
subtended by the atom. We apply the found results to a typical neutron star and
to the Sun. For the global monopole, the modification in the black-body
potential is of topological nature and it is due to the central solid angle
deficit that occurs in the spacetime generated by that object. In the
cylindrical case, which is locally flat, no gravitational correction to the
temperature exists, as in the global monopole case. However, we find the
curious fact that the BBF depends on the topology of the spacetime through the
modification of the azimuthal angle and therefore of the solid angle. For the
static cosmic string we find that the force is null for the zero thickness
case.Comment: 8 pages, 5 figures. Revised versio
Quantum phase transitions in alternating spin-(1/2, 5/2) Heisenberg chains
The ground state spin-wave excitations and thermodynamic properties of two
types of ferrimagnetic chains are investigated: the alternating spin-1/2
spin-5/2 chain and a similar chain with a spin-1/2 pendant attached to the
spin-5/2 site. Results for magnetic susceptibility, magnetization and specific
heat are obtained through the finite-temperature Lanczos method with the aim in
describing available experimental data, as well as comparison with theoretical
results from the semiclassical approximation and the low-temperature
susceptibility expansion derived from Takahashi's modified spin-wave theory. In
particular, we study in detail the temperature vs. magnetic field phase diagram
of the spin-1/2 spin-5/2 chain, in which several low-temperature quantum phases
are identified: the Luttinger Liquid phase, the ferrimagnetic plateau and the
fully polarized one, and the respective quantum critical points and crossover
lines
Avaliação da atividade antibacteriana de filmes finos de quitosana/nanopartículas de próprolis contra staphylococcus aureus.
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