1,329 research outputs found
Lattice dynamical probe of charge order and antipolar bilayer stacking in LuFe2O4
We investigated the infrared response of LuFe2O4 through the series of charge, magnetic, and structural transitions. All vibrational modes couple strongly to the charge order, whereas the LuO zone-folding modes are also sensitive to magnetic order and structural distortion. The dramatic splitting of the LuO2 layer mode is attributed to charge-rich/poor proximity effects and its temperature dependence reveals the antipolar nature of the W layer pattern
Exploring skewed parton distributions with two body models on the light front II: covariant Bethe-Salpeter approach
We explore skewed parton distributions for two-body, light-front wave
functions. In order to access all kinematical regimes, we adopt a covariant
Bethe-Salpeter approach, which makes use of the underlying equation of motion
(here the Weinberg equation) and its Green's function. Such an approach allows
for the consistent treatment of the non-wave function vertex (but rules out the
case of phenomenological wave functions derived from ad hoc potentials). Our
investigation centers around checking internal consistency by demonstrating
time-reversal invariance and continuity between valence and non-valence
regimes. We derive our expressions by assuming the effective qq potential is
independent of the mass squared, and verify the sum rule in a non-relativistic
approximation in which the potential is energy independent. We consider
bare-coupling as well as interacting skewed parton distributions and develop
approximations for the Green's function which preserve the general properties
of these distributions. Lastly we apply our approach to time-like form factors
and find similar expressions for the related generalized distribution
amplitudes.Comment: 25 pages, 12 figures, revised (minor changes but essential to
consistency
Bohmian mechanics, the quantum-classical correspondence and the classical limit: the case of the square billiard
Square billiards are quantum systems complying with the dynamical
quantum-classical correspondence. Hence an initially localized wavefunction
launched along a classical periodic orbit evolves along that orbit, the
spreading of the quantum amplitude being controlled by the spread of the
corresponding classical statistical distribution. We investigate wavepacket
dynamics and compute the corresponding de Broglie-Bohm trajectories in the
quantum square billiard. We also determine the trajectories and statistical
distribution dynamics for the equivalent classical billiard. Individual Bohmian
trajectories follow the streamlines of the probability flow and are generically
non-classical. This can also hold even for short times, when the wavepacket is
still localized along a classical trajectory. This generic feature of Bohmian
trajectories is expected to hold in the classical limit. We further argue that
in this context decoherence cannot constitute a viable solution in order to
recover classicality.Comment: Figures downgraded to low resolution; To be published in Found. Phys.
(2009)
Study of calcium-phosphate films obtained by pulsed laser deposition
We investigated the infrared response of LuFe2O4 through the series of charge, magnetic, and structural transitions. All vibrational modes couple strongly to the charge order, whereas the LuO zone-folding modes are also sensitive to magnetic order and structural distortion. The dramatic splitting of the LuO2 layer mode is attributed to charge-rich/poor proximity effects and its temperature dependence reveals the antipolar nature of the W layer pattern
Thin Film Growth and Device Fabrication of Iron-Based Superconductors
Iron-based superconductors have received much attention as a new family of
high-temperature superconductors owing to their unique properties and distinct
differences from cuprates and conventional superconductors. This paper reviews
progress in thin film research on iron-based superconductors since their
discovery for each of five material systems with an emphasis on growth,
physical properties, device fabrication, and relevant bulk material properties.Comment: To appear in J. Phys. Soc. Jp
Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors
In the first three years since the discovery of Fe-based high Tc
superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed
light on three important questions. First, STM has demonstrated the complexity
of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle
interference (QPI) imaging and low temperature spectroscopy have shown that the
pairing order parameter varies from nodal to nodeless s\pm within a single
family, FeTe1-xSex. Second, STM has imaged C4 -> C2 symmetry breaking in the
electronic states of both parent and superconducting materials. As a local
probe, STM is in a strong position to understand the interactions between these
broken symmetry states and superconductivity. Finally, STM has been used to
image the vortex state, giving insights into the technical problem of vortex
pinning, and the fundamental problem of the competing states introduced when
superconductivity is locally quenched by a magnetic field. Here we give a
pedagogical introduction to STM and QPI imaging, discuss the specific
challenges associated with extracting bulk properties from the study of
surfaces, and report on progress made in understanding Fe-based superconductors
using STM techniques.Comment: 36 pages, 23 figures, 229 reference
Application of Chinese Jun-Cao technique for the production of Brazilian Ganoderma lucidum strains
Ganoderma lucidum is a medicinal mushroom traditionally used in China against a wide range of diseases such as cancer and also for its prevention. In this work, commercial Chinese strains G. lucidum were compared to wild Brazilian strains aiming to determine the cultivation potential through the use of Jun-Cao. Six formulations were tested and the strains presented good response to the applied method. In general, the mixture between the grass and wood was well suited for the basidiomycetes, contributing to the preparation of substrates that generated better results in Jun Cao
The Zoning of Semi-Enclosed Bodies of Water According to the Sediment Pollution: The Bay of Algeciras as a Case Example
This paper reports a study of the occurrence and
levels of polycyclic aromatic hydrocarbons (PAHs) in a bay
characterised by a chronic persistent impact. A total of 55
sediment samples were taken at different depths up to
111 m in two sampling campaigns. Chemical analyses were
carried out by gas chromatography-mass spectroscopy. The
results indicate that: (1) significant spatial variations exist,
(2) levels of PAHs are related more strongly to the spatial
distribution of sediments than to mineralogy/granulometry,
(3) the sediments are slightly-to-moderately contaminated
by PAHs, and (4) these PAHs derive from pyrolytic and
petrogenic sources. Through use of an innovative data
classification system (proposed according to depth and
spatial location of sampling points), and using factorial and
cluster techniques, five zones have been differentiated
depending on the contamination level and source
The stellar halo of the Galaxy
Stellar halos may hold some of the best preserved fossils of the formation
history of galaxies. They are a natural product of the merging processes that
probably take place during the assembly of a galaxy, and hence may well be the
most ubiquitous component of galaxies, independently of their Hubble type. This
review focuses on our current understanding of the spatial structure, the
kinematics and chemistry of halo stars in the Milky Way. In recent years, we
have experienced a change in paradigm thanks to the discovery of large amounts
of substructure, especially in the outer halo. I discuss the implications of
the currently available observational constraints and fold them into several
possible formation scenarios. Unraveling the formation of the Galactic halo
will be possible in the near future through a combination of large wide field
photometric and spectroscopic surveys, and especially in the era of Gaia.Comment: 46 pages, 16 figures. References updated and some minor changes.
Full-resolution version available at
http://www.astro.rug.nl/~ahelmi/stellar-halo-review.pd
Bioativos em frutos de mandacaru colhidos no sertão paraibano: Bioactive in mandacaru fruits harvested in sertão paraibano
O mandacaru - Cereus jamacaru - é uma cactácea de frutos com elevado potencial ao consumo in natura/industrial. Assim, objetivou-se quantificar os compostos bioativos em frutos de mandacaru colhidos na zona rural de Pombal, Sertão Paraibano. O experimento foi realizado no Laboratório de Química, Bioquímica e Análise de Alimentos, Centro de Ciências e Tecnologia Agroalimentar, da Universidade Federal de Campina Grande, Campus Pombal-PB. Após a colheita, os frutos foram selecionados e classificados em estádios de maturação conforme a cor da casca (maduro, casca totalmente vermelha e no estádio de transição, casca verde com manchas vermelhas). O delineamento experimental utilizado foi inteiramente ao acaso, em um fatorial 2 x 2 (fator 1: estádios de maturação, transição e maduro; fator 2: porção do fruto, casca e polpa), com 4 repetições. Os parâmetros estudados compreenderam o pH, íons H+, sólidos solúveis, acidez titulável, ratio, ácido ascórbico, clorofilas (a, b e total), carotenoides e compostos fenólicos. Os frutos em transição obtiveram teores significativos de clorofilas, carotenoides e compostos fenólicos, principalmente na casca. Isto evidencia o potencial bioativo do mandacaru, valorizando o fruto in natura e sua aplicabilidade na agroindústria
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