126 research outputs found
Colossal Spin-Phonon Anomalies and the Ferroelectric Phase Transition in the Model Multiferroic Bifeo3
We report a temperature-dependent Raman and neutron scattering investigation
of the multiferroic material bismuth ferrite BiFeO3 (BFO).Comment: submitted to PRL (July 2005
Non-collinear magnetism in Al-Mn topologically disordered systems
We have performed the first ab-initio calculations of a possible complex
non-collinear magnetic structure in aluminium-rich Al-Mn liquids within the
real-space tight-binding LMTO method. In our previous work we predicted the
existence of large magnetic moments in Al-Mn liquids [A.M. Bratkovsky, A.V.
Smirnov, D. N. Manh, and A. Pasturel, \prb {\bf 52}, 3056 (1995)] which has
been very recently confirmed experimentally. Our present calculations show that
there is a strong tendency for the moments on Mn to have a non-collinear
(random) order retaining their large value of about 3~. The d-electrons
on Mn demonstrate a pronounced non-rigid band behaviour which cannot be
reproduced within a simple Stoner picture. The origin of the magnetism in these
systems is a topological disorder which drives the moments formation and
frustrates their directions in the liquid phase.Comment: 10 pages, RevTex 3.0, 24kb. 3 PS figures available on request from
[email protected] The work has been presented at ERC
``Electronic Structire of Solids'' (Lunteren, The Netherlands, 9-14 September
1995
EXAFS study of lead-free relaxor ferroelectric BaTi(1-x)Zr(x)O3 at the Zr K-edge
Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge
were carried out on perovskite relaxor ferroelectrics BaTi(1-x)Zr(x)O3 (BTZ) (x
= 0.25, 0.30, 0.35), and on BaZrO3 for comparison. Structural information up to
4.5 A around the Zr atoms is obtained, revealing that the local structure
differs notably from the average Pm-3m cubic structure deduced from X-ray
diffraction. In particular, our results show that the distance between Zr atoms
and their first oxygen neighbors is independent of the Zr substitution rate x
and equal to that measured in BaZrO3, while the X-ray cubic cell parameter
increases linearly with x. Furthermore, we show that the Zr atoms tend to
segregate in Zr-rich regions. We propose that the relaxor behavior in BTZ is
linked to random elastic fields generated by this particular chemical
arrangement, rather than to random electric fields as is the case in most
relaxors.Comment: 13 pages, 12 figures, 4 tables. Submitted to Phys. Rev.
Hidden magnetic frustration by quantum relaxation in anisotropic Nd-langasite
The static and dynamic magnetic properties of the NdGaSiO
compound, which appears as the first materialization of a rare-earth
kagome-type lattice, were re-examined, owing to contradictory results in the
previous studies. Neutron scattering, magnetization and specific heat
measurements were performed and analyzed, in particular by fully taking account
of the crystal electric field effects on the Nd ions. One of the novel
findings is that the peculiar temperature independent spin dynamics observed
below 10 K expresses single-ion quantum processes. This would short-circuit the
frustration induced cooperative dynamics, which would emerge only at very low
temperature
Corneal Transduction by Intra-Stromal Injection of AAV Vectors In Vivo in the Mouse and Ex Vivo in Human Explants
The cornea is a transparent, avascular tissue that acts as the major refractive surface of the eye. Corneal transparency, assured by the inner stroma, is vital for this role. Disruption in stromal transparency can occur in some inherited or acquired diseases. As a consequence, light entering the eye is blocked or distorted, leading to decreased visual acuity. Possible treatment for restoring transparency could be via viral-based gene therapy. The stroma is particularly amenable to this strategy due to its immunoprivileged nature and low turnover rate. We assayed the potential of AAV vectors to transduce keratocytes following intra-stromal injection in vivo in the mouse cornea and ex vivo in human explants. In murine and human corneas, we transduced the entire stroma using a single injection, preferentially targeted keratocytes and achieved long-term gene transfer (up to 17 months in vivo in mice). Of the serotypes tested, AAV2/8 was the most promising for gene transfer in both mouse and man. Furthermore, transgene expression could be transiently increased following aggression to the cornea
Long Range Plan: Dense matter theory for heavy-ion collisions and neutron stars
Since the release of the 2015 Long Range Plan in Nuclear Physics, major
events have occurred that reshaped our understanding of quantum chromodynamics
(QCD) and nuclear matter at large densities, in and out of equilibrium. The US
nuclear community has an opportunity to capitalize on advances in astrophysical
observations and nuclear experiments and engage in an interdisciplinary effort
in the theory of dense baryonic matter that connects low- and high-energy
nuclear physics, astrophysics, gravitational waves physics, and data scienceComment: 70 pages, 3 figures, White Paper for the Long Range Plan for Nuclear
Scienc
Optimization methods for electric power systems: An overview
Power systems optimization problems are very difficult to solve because power systems are very large, complex, geographically widely distributed and are influenced by many unexpected events. It is therefore necessary to employ most efficient optimization methods to take full advantages in simplifying the formulation and implementation of the problem. This article presents an overview of important mathematical optimization and artificial intelligence (AI) techniques used in power optimization problems. Applications of hybrid AI techniques have also been discussed in this article
NMR and NQR study of the electronic and structural properties of Al-Cu-Fe and Al-Cu-Ru quasicrystals
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