552 research outputs found
Structure and Stability of the Iodide Elpasolite, Cs2AgBiI6
Iodide elpasolites (or double perovskites, A2B'B"I6, B' = M+, B" = M3+) are
predicted to be promising alternatives to lead-based perovskite semiconductors
for photovoltaic and optoelectronic applications, but no iodide elpasolite has
ever been definitively prepared or structurally characterized. Iodide
elpasolites are widely predicted to be unstable due to favorable decomposition
to the competing A3B2I9 (B = M3+) phase. Here, we report the results of
synchrotron XRD and X-ray total scattering measurements on putative Cs2AgBiI6
nanocrystals made via anion exchange from parent Cs2AgBiBr6 nanocrystals.
Rietveld refinement of XRD and PDF data shows that these nanocrystals indeed
exhibit a tetragonal (I4-m) elpasolite structure, making them the first example
of a structurally characterized iodide elpasolite. A series of experiments
probing structural relaxation and the effects of surface ligation or grain size
all point to the critical role of surface free energy in stabilizing the iodide
elpasolite phase in these nanocrystals.Comment: 7 figures, 1 scheme, plus supporting information fil
Validity of the Polar V800 heart rate monitor to measure RR intervals at rest
Purpose To assess the validity of RR intervals and short-term heart rate variability (HRV) data obtained from the Polar V800 heart rate monitor, in comparison to an electrocardiograph (ECG). Method Twenty participants completed an active orthostatic test using the V800 and ECG. An improved method for the identification and correction of RR intervals was employed prior to HRV analysis. Agreement of the data was assessed using intra-class correlation coefficients (ICC), Bland–Altman limits of agreement (LoA), and effect size (ES). Results A small number of errors were detected between ECG and Polar RR signal, with a combined error rate of 0.086 %. The RR intervals from ECG to V800 were significantly different, but with small ES for both supine corrected and standing corrected data (ES 0.999 for both supine and standing corrected intervals. When analysed with the same HRV software no significant differences were observed in any HRV parameters, for either supine or standing; the data displayed small bias and tight LoA, strong ICC (>0.99) and small ES (≤0.029). Conclusions The V800 improves over previous Polar models, with narrower LoA, stronger ICC and smaller ES for both the RR intervals and HRV parameters. The findings support the validity of the Polar V800 and its ability to produce RR interval recordings consistent with an ECG. In addition, HRV parameters derived from these recordings are also highly comparable
Extension and approximation of -subharmonic functions
Let be a bounded domain, and let be a
real-valued function defined on the whole topological boundary . The aim of this paper is to find a characterization of the functions
which can be extended to the inside to a -subharmonic function under
suitable assumptions on . We shall do so by using a function algebraic
approach with focus on -subharmonic functions defined on compact sets. We
end this note with some remarks on approximation of -subharmonic functions
Effect of Reducing Atmosphere on the Magnetism of Zn1-xCoxO Nanoparticles
We report the crystal structure and magnetic properties of Zn1-xCoxO
nanoparticles synthesized by heating metal acetates in organic solvent. The
nanoparticles were crystallized in wurtzite ZnO structure after annealing in
air and in a forming gas (Ar95%+H5%). The X-ray diffraction and X-ray
photoemission spectroscopy (XPS) data for different Co content show clear
evidence for the Co+2 ions in tetrahedral symmetry, indicating the substitution
of Co+2 in ZnO lattice. However samples with x=0.08 and higher cobalt content
also indicate the presence of Co metal clusters. Only those samples annealed in
the reducing atmosphere of the forming gas, and that showed the presence of
oxygen vacancies, exhibited ferromagnetism at room temperature. The air
annealed samples remained non-magnetic down to 77K. The essential ingredient in
achieving room temperature ferromagnetism in these Zn1-xCoxO nanoparticles was
found to be the presence of additional carriers generated by the presence of
the oxygen vacancies.Comment: 11 pages, 6 figures, submitted to Nanotechnology IO
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