4,969 research outputs found
Crystal chemistry and electron localization in Sn‐doped Fe3O4
For Fe3−xSnxO4 at 300 K and x≳0.1, a paramagnetic quadrupole doublet pattern, in addition to the usual two magnetic patterns, is observed in the 57Fe NGR spectra. This doublet is due to A site Fe2+ whose concentration for 0.1?x?0.5 is such that approximately equal amounts of Fe2+ and Fe3+ are on the B site. The 200 kG field at the Sn4+ site at 300 K is smaller than that in NiFe2O4. At 80 K a paramagnetic quadrupole doublet is observed in the 119Sn NGR spectrum and is due to Sn2+.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87558/2/390_1.pd
Regional Differences in Heat Shock Protein 25 Expression in Brain and Spinal Cord Astrocytes of Wild-Type and SOD1 (G93A) Mice
Heterogeneity of glia in different CNS regions may contribute to the selective vulnerability of neuronal populations in neurodegenerative conditions such as amyotrophic lateral sclerosis (ALS). Here, we explored regional variations in the expression of heat shock protein 25 in glia under conditions of acute and chronic stress. Hsp27 (Hsp27; murine orthologue: Hsp25) fulfils a number of cytoprotective functions and may therefore be a possible therapeutic target in ALS. We identified a subpopulation of astrocytes in primary murine mixed glial cultures that expressed Hsp25. Under basal conditions, the proportion of Hsp25-positive astrocytes was twice as high in spinal cord cultures than in cortical cultures. To explore the physiological role of the elevated Hsp25 expression in spinal cord astrocytes, we exposed cortical and spinal cord glia to acute stress, using heat stress and pro-inflammatory stimuli. Surprisingly, we observed no stress-induced increase in Hsp25 expression in either cortical or spinal cord astrocytes. Similarly, exposure to endogenous stress, as modelled in glial cultures from SOD1 G93A-ALS mice, did not increase Hsp25 expression above that observed in astrocytes from wild-type mice. In vivo, Hsp25 expression was greater under conditions of chronic stress present in the spinal cord of SOD1 G93A mice than in wild-type mice, although this increase in expression is likely to be due to the extensive gliosis that occurs in this model. Together, these results show that there are differences in the expression of Hsp25 in astrocytes in different regions of the central nervous system, but Hsp25 expression is not upregulated under acute or chronic stress conditions
Spatiotemporal Chaos, Localized Structures and Synchronization in the Vector Complex Ginzburg-Landau Equation
We study the spatiotemporal dynamics, in one and two spatial dimensions, of
two complex fields which are the two components of a vector field satisfying a
vector form of the complex Ginzburg-Landau equation. We find synchronization
and generalized synchronization of the spatiotemporally chaotic dynamics. The
two kinds of synchronization can coexist simultaneously in different regions of
the space, and they are mediated by localized structures. A quantitative
characterization of the degree of synchronization is given in terms of mutual
information measures.Comment: 6 pages, using bifchaos.sty (included). 7 figures. Related material,
including higher quality figures, could be found at
http://www.imedea.uib.es/PhysDept/publicationsDB/date.html . To appear in
International Journal of Bifurcation and Chaos (1999
Novel effects of strains in graphene and other two dimensional materials
The analysis of the electronic properties of strained or lattice deformed
graphene combines ideas from classical condensed matter physics, soft matter,
and geometrical aspects of quantum field theory (QFT) in curved spaces. Recent
theoretical and experimental work shows the influence of strains in many
properties of graphene not considered before, such as electronic transport,
spin-orbit coupling, the formation of Moir\'e patterns, optics, ... There is
also significant evidence of anharmonic effects, which can modify the
structural properties of graphene. These phenomena are not restricted to
graphene, and they are being intensively studied in other two dimensional
materials, such as the metallic dichalcogenides. We review here recent
developments related to the role of strains in the structural and electronic
properties of graphene and other two dimensional compounds.Comment: 75 pages, 15 figures, review articl
Vanishing Twist near Focus-Focus Points
We show that near a focus-focus point in a Liouville integrable Hamiltonian
system with two degrees of freedom lines of locally constant rotation number in
the image of the energy-momentum map are spirals determined by the eigenvalue
of the equilibrium. From this representation of the rotation number we derive
that the twist condition for the isoenergetic KAM condition vanishes on a curve
in the image of the energy-momentum map that is transversal to the line of
constant energy. In contrast to this we also show that the frequency map is
non-degenerate for every point in a neighborhood of a focus-focus point.Comment: 13 page
Winding number instability in the phase-turbulence regime of the Complex Ginzburg-Landau Equation
We give a statistical characterization of states with nonzero winding number
in the Phase Turbulence (PT) regime of the one-dimensional Complex
Ginzburg-Landau equation. We find that states with winding number larger than a
critical one are unstable, in the sense that they decay to states with smaller
winding number. The transition from Phase to Defect Turbulence is interpreted
as an ergodicity breaking transition which occurs when the range of stable
winding numbers vanishes. Asymptotically stable states which are not
spatio-temporally chaotic are described within the PT regime of nonzero winding
number.Comment: 4 pages,REVTeX, including 4 Figures. Latex (or postscript) version
with figures available at http://formentor.uib.es/~montagne/textos/nupt
The Quasi-Molecular Stage of Ternary Fission
We developed a three-center phenomenological model,able to explain
qualitatively the recently obtained experimental results concerning the
quasimolecular stage of a light-particle accompanied fission process. It was
derived from the liquid drop model under the assumption that the aligned
configuration, with the emitted particle between the light and heavy fragment,
is reached by increasing continuously the separation distance, while the radii
of the heavy fragment and of the light particle are kept constant. In such a
way,a new minimum of a short-lived molecular state appears in the deformation
energy at a separation distance very close to the touching point. This minimum
allows the existence of a short-lived quasi-molecular state, decaying into the
three final fragments.The influence of the shell effects is discussed. The
half-lives of some quasimolecular states which could be formed in the Be
and C accompanied fission of Cf are roughly estimated to be the
order of 1 ns, and 1 ms, respectively.Comment: 12 pages, 6 epsf, uses ws-p8-50x6-00.cl
Production of low formaldehyde emission particleboard by using new formulated formaldehyde based resin
In order to preserve the global market competitiveness, the particleboard industry was affronted with challenges to reduce formaldehyde emission while maintaining the quality strength properties of particleboard. To counter the issue, particleboards with five different surface-to-core ratio were fabricated by applying newly formulated UF and MUF resins which were 30% surface: 70% core (3:7); 40% surface: 60% core (4:6); 50% surface: 50% core (5:5); 60% surface: 40% core (6:4) and 70% surface: 30% core (7:3) based on dry particle weight respectively. Formaldehyde emission and strength properties of the fabricated particleboard were investigated based on Japanese Industrial Standard, which are JIS A 1460 and JIS A 5908, respectively. All the MUF-bonded particleboard complied with the type 18 standard, whereas all the UF-bonded particleboard produced complied with type 13 except thickness swelling of the UF-bonded particleboard. The surface-to-core ratio applied in three layered particleboard for both resins exerted considerable influence on the strength properties and formaldehyde emission of particleboards produced from both resins. MUF-bonded particleboard with 40% surface and 60% core recorded the lowest formaldehyde emission (0.09 mg L-1) and highest strength properties. For UF-bonded particleboard, the ratio of 60% surface and 40% core showed the lowest formaldehyde emission (0.28 mg L-1) with better strength properties. This study highlighted the potential of MUF resin to replace UF resin due to its ability to produce F**** particleboard with better strength properties and lower formaldehyde emission according to JIS A 5908
Analytical method for perturbed frozen orbit around an Asteroid in highly inhomogeneous gravitational fields : A first approach
This article provides a method for nding initial conditions for perturbed frozen orbits around inhomogeneous fast rotating asteroids. These orbits can be used as reference trajectories in missions that require close inspection of any rigid body. The generalized perturbative procedure followed exploits the analytical methods of relegation of the argument of node and Delaunay normalisation to arbitrary order. These analytical methods are extremely powerful but highly computational. The gravitational potential of the heterogeneous body is rstly stated, in polar-nodal coordinates, which takes into account the coecients of the spherical harmonics up to an arbitrary order. Through the relegation of the argument of node and the Delaunay normalization, a series of canonical transformations of coordinates is found, which reduces the Hamiltonian describing the system to a integrable, two degrees of freedom Hamiltonian plus a truncated reminder of higher order. Setting eccentricity, argument of pericenter and inclination of the orbit of the truncated system to be constant, initial conditions are found, which evolve into frozen orbits for the truncated system. Using the same initial conditions yields perturbed frozen orbits for the full system, whose perturbation decreases with the consideration of arbitrary homologic equations in the relegation and normalization procedures. Such procedure can be automated for the first homologic equation up to the consideration of any arbitrary number of spherical harmonics coefficients. The project has been developed in collaboration with the European Space Agency (ESA)
- …