1,783 research outputs found
Phase diagram and magnetic properties of LaCaMnO compound for
In this article a detailed study of LaCaMnO () phase diagram using powder x-ray diffraction and magnetization
measurements is presented. Unfortunately, in the related literature no properly
characterized samples have been used, with consequence the smearing of the real
physics in this complicated system. As the present results reveal, there are
two families of samples. The first family concerns samples prepared in
atmosphere ( Atm) which are all ferromagnetic with Curie
temperature rising with . The second family concerns samples, where a post
annealing in nearly zero oxygen partial pressure is applied. These samples show
a canted antiferromagnetic structure for below , while
for an unconventional ferromagnetic insulated phase is
present below . The most important difference between nonstoichiometric
and stoichiometric samples concerning the magnetic behavior, is the anisotropy
in the exchange interactions, in the stoichiometric samples putting forward the
idea that a new orbital ordered phase is responsible for the ferromagnetic
insulating regime in the LaCaMnO compound
Inhibition of DNA damage response at telomeres improves the detrimental phenotypes of Hutchinson–Gilford Progeria Syndrome
Hutchinson–Gilford progeria syndrome (HGPS) is a genetic disorder characterized by premature aging features. Cells from HGPS patients express progerin, a truncated form of Lamin A, which perturbs cellular homeostasis leading to nuclear shape alterations, genome instability, heterochromatin loss, telomere dysfunction and premature entry into cellular senescence. Recently, we reported that telomere dysfunction induces the transcription of telomeric non-coding RNAs (tncRNAs) which control the DNA damage response (DDR) at dysfunctional telomeres. Here we show that progerin-induced telomere dysfunction induces the transcription of tncRNAs. Their functional inhibition by sequence-specific telomeric antisense oligonucleotides (tASOs) prevents full DDR activation and premature cellular senescence in various HGPS cell systems, including HGPS patient fibroblasts. We also show in vivo that tASO treatment significantly enhances skin homeostasis and lifespan in a transgenic HGPS mouse model. In summary, our results demonstrate an important role for telomeric DDR activation in HGPS progeroid detrimental phenotypes in vitro and in vivo
Crystal structure and high-field magnetism of La2CuO4
Neutron diffraction was used to determine the crystal structure and magnetic
ordering pattern of a La2CuO4 single crystal, with and without applied magnetic
field. A previously unreported, subtle monoclinic distortion of the crystal
structure away from the orthorhombic space group Bmab was detected. The
distortion is also present in lightly Sr-doped crystals. A refinement of the
crystal structure shows that the deviation from orthorhombic symmetry is
predominantly determined by displacements of the apical oxygen atoms. An
in-plane magnetic field is observed to drive a continuous reorientation of the
copper spins from the orthorhombic b-axis to the c-axis, directly confirming
predictions based on prior magnetoresistance and Raman scattering experiments.
A spin-flop transition induced by a c-axis oriented field previously reported
for non-stoichiometric La2CuO4 is also observed, but the transition field (11.5
T) is significantly larger than that in the previous work
High-Temperature Transport Properties of Yb4−xSmxSb3
Polycrystalline L4Sb3 (L = La, Ce, Sm, and Yb) and Yb4−x Sm x Sb3, which crystallizes in the anti-Th3P4 structure type (I-43d no. 220), were synthesized via high-temperature reaction. Structural and chemical characterization were performed by x-ray diffraction and electronic microscopy with energy-dispersive x-ray analysis. Pucks were densified by spark plasma sintering. Transport property measurements showed that these compounds are n-type with low Seebeck coefficients, except for Yb4Sb3, which shows semimetallic behavior with hole conduction above 523 K. By partially substituting Yb by a trivalent rare earth we successfully improved the thermoelectric figure of merit of Yb4Sb3 up to 0.7 at 1273 K
Approach of Passive Filters using NSGA II in industrial installations: Part I
The optimization of passive filters in industrial systems has been presented by different computational methods. The objective of this paper is to develop a computational algorithm with NSGA II to select the configuration and design parameters of a set of passive filters for industrial installations. As a methodology, the optimization problem was addressed using three independent objective functions of innovative character for compensation of harmonics through passive filters as a multiobjective problem. The results were the computational solution to this problem that determines a set of Pareto optimal solutions (Frontier). In addition, the computational tool has several new features such as: calculates the parameters that characterize the filters, but also selects the type of configuration and the number of branches of the filter in each candidate bar according to a set of pre-established configurations according to PRODIST-M8 (Brazilian Standard) and IEEE 519-2014. Also determine solutions with good power quality indicators (THD, TDD and NPV) for several characteristic and non-characteristic scenarios of the system that allow to represent: daily variations of the load, and variations of system parameters and filters. It evaluates the cost of energy bills in an industrial power grid that has different operating conditions (characteristic scenarios) and evaluates the economic effect of harmonic filters as reactive power compensators
Exchange Bias in BiFe_{0.8}Mn_{0.2}O_3 Nanoparticles with an Antiferromagnetic Core and a Diluted Antiferromagnetic Shell
We have observed conventional signature of exchange bias (EB), in form of
shift in field-cooled (FC) hysteresis loop, and training effect, in
BiFe0.8Mn0.2O3 nanoparticles. From neutron diffraction, thermoremanent
magnetization and isothermoremanent magnetization measurements, the
nanoparticles are found to be core-shell in nature, consisting of an
antiferromagnetic (AFM) core, and a 2-dimensional diluted AFM (DAFF) shell with
a net magnetization under a field. The analysis of the training effect data
using the Binek's model shows that the observed loop shift arises entirely due
to an interface exchange coupling between core and shell, and the intrinsic
contribution of the DAFF shell to the total loop shift is zero. A significantly
high value of EB field has been observed at room temperature. The present study
is useful to understand the origin of EB in other DAFF-based systems as well.Comment: 20 pages, 7 figures, Phys. Rev. B 2011 (accepted
Approach to the metal-insulator transition in La(1-x)CaxMnO3 (0<x<.2): magnetic inhomogeneity and spin wave anomaly
We describe the evolution of the static and dynamic spin correlations of
LaCaMnO, for x=0.1, 0.125 and 0.2, where the system evolves
from the canted magnetic state towards the insulating ferromagnetic state,
approaching the metallic transition (x=0.22).
In the x=0.1 sample, the observation of two spin wave branches typical of two
distinct types of magnetic coupling, and of a modulation in the elastic diffuse
scattering characteristic of ferromagnetic inhomogeneities, confirms the static
and dynamic inhomogeneous features previously observed at x0.1. The
anisotropic q-dependence of the intensity of the low-energy spin wave suggests
a bidimensionnal character for the static inhomogeneities. At x=0.125, which
corresponds to the occurence of a ferromagnetic and insulating state, the two
spin wave branches reduce to a single one, but anisotropic. At this
concentration, an anomaly appears at {\bf q}=(1.25,1.25,0), that could be
related to an underlying periodicity, as arising from (1.5,1.5,0)
superstructures.
At x=0.2, the spin-wave branch is isotropic. In addition to the anomaly
observed at q, extra magnetic excitations are observed at larger q, forming
an optical branch. The two dispersion curves suggest an anti-crossing behavior
at some {\bf q'} value, which could be explained by a folding due to an
underlying perodicity involving four cubic lattice spacings
Measurement of the local Jahn-Teller distortion in LaMnO_3.006
The atomic pair distribution function (PDF) of stoichiometric LaMnO_3 has
been measured. This has been fit with a structural model to extract the local
Jahn-Teller distortion for an ideal Mn(3+)O_6 octahedron. These results are
compared to Rietveld refinements of the same data which give the average
structure. Since the local structure is being measured in the PDF there is no
assumption of long-range orbital order and the real, local, Jahn-Teller
distortion is measured directly. We find good agreement both with published
crystallographic results and our own Rietveld refinements suggesting that in an
accurately stoichiometric material there is long range orbital order as
expected. The local Jahn-Teller distortion has 2 short, 2 medium and 2 long
bonds.Comment: 5 pages, 3 postscript figures, minor change
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