3,494 research outputs found
Computation of Madelung Energies for Ionic Crystals of Variable Stoichiometries and Mixed Valencies and their application in Lithium-ion battery voltage modelling
Electrostatic energy (Madelung energy) is a major constituent of the cohesive
energy of ionic crystals. Several physicochemical properties of these materials
depend on the response of their electrostatic energy to a variety of applied
thermal, electrical and mechanical stresses. In the present study, a method has
been developed based on Ewalds technique, to compute the electrostatic energy
arising from ion-ion interactions in ionic crystals like LixMn2O4 with variable
stoichiometries and mixed valencies. An interesting application of this method
in computing the voltages of lithium ion batteries employing spinel cathodes is
presented for the first time. The advantages of the present method of
computation over existing methods are also discussed.Comment: 15 page
Properties of AGN coronae in the NuSTAR era
The focussing optics of NuSTAR have enabled high signal-to-noise spectra to
be obtained from many X-ray bright Active Galactic Nuclei (AGN) and Galactic
Black Hole Binaries (BHB). Spectral modelling then allows robust
characterization of the spectral index and upper energy cutoff of the coronal
power-law continuum, after accounting for reflection and absorption effects.
Spectral-timing studies, such as reverberation and broad iron line fitting, of
these sources yield coronal sizes, often showing them to be small and in the
range of 3 to 10 gravitational radii in size. Our results indicate that coronae
are hot and radiatively compact, lying close to the boundary of the region in
the compactness - temperature diagram which is forbidden due to runaway pair
production. The coincidence suggests that pair production and annihilation are
essential ingredients in the coronae of AGN and BHB and that they control the
shape of the observed spectra.Comment: 11 pages, 8 figures, accepted for publication in MNRA
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