11,763 research outputs found
Phase Coexistence Near a Morphotropic Phase Boundary in Sm-doped BiFeO3 Films
We have investigated heteroepitaxial films of Sm-doped BiFeO3 with a
Sm-concentration near a morphotropic phase boundary. Our high-resolution
synchrotron X-ray diffraction, carried out in a temperature range of 25C to
700C, reveals substantial phase coexistence as one changes temperature to
crossover from a low-temperature PbZrO3-like phase to a high-temperature
orthorhombic phase. We also examine changes due to strain for films greater or
less than the critical thickness for misfit dislocation formation.
Particularly, we note that thicker films exhibit a substantial volume collapse
associated with the structural transition that is suppressed in strained thin
films
Hartree-Fock-Bogoliubov Calculations in Coordinate Space: Neutron-Rich Sulfur, Zirconium, Cerium, and Samarium Isotopes
Using the Hartree-Fock-Bogoliubov (HFB) mean field theory in coordinate
space, we investigate ground state properties of the sulfur isotopes from the
line of stability up to the two-neutron dripline (). In particular,
we calculate two-neutron separation energies, quadrupole moments, and rms-radii
for protons and neutrons. Evidence for shape coexistence is found in the very
neutron-rich sulfur isotopes. We compare our calculations with results from
relativistic mean field theory and with available experimental data. We also
study the properties of neutron-rich zirconium (), cerium
(), and samarium () isotopes which exhibit very large
prolate quadrupole deformations.Comment: 7 pages, 6 figures, 2 tables submitted to Phys. Rev.
Cmah-dystrophin deficient mdx mice display an accelerated cardiac phenotype that is improved following peptide-PMO exon skipping treatment
Duchenne muscular dystrophy (DMD) is caused by loss of dystrophin protein, leading to progressive muscle weakness and premature death due to respiratory and/or cardiac complications. Cardiac involvement is characterized by progressive dilated cardiomyopathy, decreased fractional shortening and metabolic dysfunction involving reduced metabolism of fatty acids—the major cardiac metabolic substrate. Several mouse models have been developed to study molecular and pathological consequences of dystrophin deficiency, but do not recapitulate all aspects of human disease pathology and exhibit a mild cardiac phenotype. Here we demonstrate that Cmah (cytidine monophosphate-sialic acid hydroxylase)-deficient mdx mice (Cmah−/−;mdx) have an accelerated cardiac phenotype compared to the established mdx model. Cmah−/−;mdx mice display earlier functional deterioration, specifically a reduction in right ventricle (RV) ejection fraction and stroke volume (SV) at 12 weeks of age and decreased left ventricle diastolic volume with subsequent reduced SV compared to mdx mice by 24 weeks. They further show earlier elevation of cardiac damage markers for fibrosis (Ctgf), oxidative damage (Nox4) and haemodynamic load (Nppa). Cardiac metabolic substrate requirement was assessed using hyperpolarized magnetic resonance spectroscopy indicating increased in vivo glycolytic flux in Cmah−/−;mdx mice. Early upregulation of mitochondrial genes (Ucp3 and Cpt1) and downregulation of key glycolytic genes (Pdk1, Pdk4, Ppara), also denote disturbed cardiac metabolism and shift towards glucose utilization in Cmah−/−;mdx mice. Moreover, we show long-term treatment with peptide-conjugated exon skipping antisense oligonucleotides (20-week regimen), resulted in 20% cardiac dystrophin protein restoration and significantly improved RV cardiac function. Therefore, Cmah−/−;mdx mice represent an appropriate model for evaluating cardiac benefit of novel DMD therapeutics
Illuminating dark matter and primordial black holes with interstellar antiprotons
Interstellar antiproton fluxes can arise from dark matter annihilating or
decaying into quarks or gluons that subsequently fragment into antiprotons.
Evaporation of primordial black holes also can produce a significant antiproton
cosmic-ray flux. Since the background of secondary antiprotons from spallation
has an interstellar energy spectrum that peaks at \sim 2\gev and falls
rapidly for energies below this, low-energy measurements of cosmic antiprotons
are useful in the search for exotic antiproton sources. However, measurement of
the flux near the earth is challenged by significant uncertainties from the
effects of the solar wind. We suggest evading this problem and more effectively
probing dark-matter signals by placing an antiproton spectrometer aboard an
interstellar probe currently under discussion. We address the experimental
challenges of a light, low-power-consuming detector, and present an initial
design of such an instrument. This experimental effort could significantly
increase our ability to detect, and have confidence in, a signal of exotic,
nonstandard antiproton sources. Furthermore, solar modulation effects in the
heliosphere would be better quantified and understood by comparing results to
inverse modulated data derived from existing balloon and space-based detectors
near the earth.Comment: 18 pages, 3 figure
ARPES Study of the Metal-Insulator Transition in Bismuth Cobaltates
We present an angle-resolved photoemission spectroscopy (ARPES) study of a
Mott-Hubbard-type bismuth cobaltate system across a metal-insulator transition.
By varying the amount of Pb substitution, and by doping with Sr or Ba cation, a
range of insulating to metallic properties is obtained. We observe a systematic
change in the spectral weight of the coherent and incoherent parts, accompanied
by an energy shift of the incoherent part. The band dispersion also shows the
emergence of a weakly dispersing state at the Fermi energy with increasing
conductivity. These changes correspond with the changes in the
temperature-dependent resistivity behavior. We address the nature of the
coherent-incoherent parts in relation to the peak-dip-hump feature seen in
cuprates superconductors
Positronium oscillations to Mirror World revisited
We present a calculation of the branching ratio of orthopositronium decay
into an invisible mode, which is done in the context of Mirror World models,
where ordinary positronium can disappear from our world due to oscillation into
its mirror twin. In this revision we clarify some formulas and approximations
used previously, correct them at some places, add new effects relevant for a
feasible experiment and finally perform a combined analysis. We include into
consideration various effects due to external magnetic and electric fields,
collisions with cavity walls and scattering off gas atoms in the cavity.
Oscillations of the Rydberg positroniums are also considered. To perform a
numerical estimates in a realistic case we wrote computer code, which can be
adopted in any experimental setup. Its work is illustrated with an example of a
planned positronium experiment within the AEgIS project.Comment: 23 pages, 4 figures, typos corrected, references added, published
versio
Staging superstructures in high- Sr/O co-doped LaSrCuO
We present high energy X-ray diffraction studies on the structural phases of
an optimal high- superconductor LaSrCuO tailored by
co-hole-doping. This is specifically done by varying the content of two very
different chemical species, Sr and O, respectively, in order to study the
influence of each. A superstructure known as staging is observed in all
samples, with the staging number increasing for higher Sr dopings . We
find that the staging phases emerge abruptly with temperature, and can be
described as a second order phase transition with transition temperatures
slightly depending on the Sr doping. The Sr appears to correlate the
interstitial oxygen in a way that stabilises the reproducibility of the staging
phase both in terms of staging period and volume fraction in a specific sample.
The structural details as investigated in this letter appear to have no direct
bearing on the electronic phase separation previously observed in the same
samples. This provides new evidence that the electronic phase separation is
determined by the overall hole concentration rather than specific Sr/O content
and concommittant structural details.Comment: 8 pages, incl. 4 figure
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