Sr7N2Sn3: a layered antiperovskite-type nitride stannide containing zigzag chains of Sn4 polyanions

Metallic black platelet single crystals of a new ternary compound, Sr7N2Sn3, were obtained by heating Sr and Sn in a Na flux together with NaN3 as a nitrogen source at 1073 K, followed by slow cooling. Single-crystal X-ray analysis revealed that this compound crystallizes in an orthorhombic cell with the cell parameters a = 10.4082(2), b = 18.0737(4), and c = 7.43390(10) Å (space group Pmna, Z = 2), and has a layered (modular) antiperovskite-type structure which could be related to the inverse structure of Ca2Nb2O7 ((Ca2)[Ca2Nb4O14]). Four-membered zigzag [Sn4] chains are situated between slabs comprising four antiperovskite layers cut by the (110) plane of the ideal anitiperovskite structure, and Sr7N2Sn3 can be expressed as [Sn4][Sn2N4Sr14]. Although an electron-precise valence electron distribution according to the formula (Sr2+)14(N3−)4(Sn4−)2([Sn4]8−) is proposed for this ternary compound, yet, there are certain structural peculiarities which cannot be explained by this idealized picture. Therefore, first principles-based means were employed to account for the aforementioned structural features.

All twist and no bend makes raft edges splay: Spontaneous curvature of domain edges in colloidal membranes

Using theory and experiments, we study the interface between two immiscible domains in a colloidal membrane composed of rigid rods of different lengths. Geometric considerations of rigid rod packing imply that a domain of sufficiently short rods in a background membrane of long rods is more susceptible to twist than the inverse structure, a long-rod domain in a short-rod membrane. The midplane tilt at the interdomain edge forces splay, which, in turn, manifests as spontaneous edge curvature with energetics controlled by the length asymmetry of constituent rods. A thermodynamic model of such tilt-curvature coupling at interdomain edges explains a number of experimental observations, including annularly shaped long-rod domains, and a nonmonotonic dependence of edge twist on domain radius. Our work shows how coupling between orientational and compositional degrees of freedom in two-dimensional fluids gives rise to complex shapes of fluid domains, analogous to shape transitions in 3D fluid vesicles.

The conclusive impact of aerosols vertical structure on low-atmosphere stability and its critical role in aerosol–PBL interaction

Aerosol-planetary boundary layer (PBL) interaction was proposed as an important mechanism to stabilize atmosphere and exacerbate surface air pollution. Despite the tremendous progress made in understanding this process, its magnitude and significance still bear large uncertainties and vary largely with aerosol distribution and meteorological conditions. In this study, we particularly focus on the role of aerosol vertical distribution on thermodynamic stability and PBL development by jointly using the micropulse lidar, sun-photometer, and radiosonde measurements over Beijing. Despite complex aerosol vertical distributions, the cloud-free aerosol structures can be classified into three types: well-mixed, decreasing with height, and the inversed. Under these different aerosol vertical structures, the aerosol-PBL relationships and the diurnal cycles of the PBLH and PM2.5 show distinct characters. The vertical distribution of aerosol radiative forcing differs drastically with strong heating in the lower, mid, and upper PBL respectively. Such a discrepancy in heating rate affects the atmospheric buoyancy and stability differently in the three distinct aerosol structures. Absorbing aerosol have a weak effect of stabilizing the low-atmosphere under the decreasing structure than under the inverse structure. As a result, the aerosol–PBL interaction can be strengthened by the inverse aerosol structure and can be potentially neutralized by the decreasing structure. Moreover, aerosols can both enhance and suppress the PBL stability, leading to both positive and negative feedback loops. This study attempts to improve our understanding of aerosol–PBL interaction, which shows the importance of the observation constraint of aerosol vertical distribution for simulating the interaction and consequent feedbacks.

Role of direct and inverted undoped spiro-OMeTAD–perovskite architectures in determining solar cells performances: an investigation via electrical impedance spectroscopy

Spiro-OMeTAD/perovskite direct and inverse structure architectures’ influence on the performance of solar cells are elucidated via the analysis of the structure impedance response.

The structure and homogeneity of Psalm 32

Psalm 32 is widely regarded as a psalm of thanksgiving with elements of wisdom poetry intermingled into it. The wisdom elements are variously explained as having been present from the beginning, or as having been added to a foundational composition. Such views of the Gattung have had a decisive influence on the interpretation of the psalm. This article argues, on the basis of a structural analysis, that Psalm 32 should be understood as a homogeneous wisdom composition. The parallel and inverse structure of its two stanzas demonstrate that the aim of its author was to encourage the upright to foster an open, intimate relationship with Yahweh in which transgressions are confessed and Yahweh’s benevolent guidance on the way of life is wisely accepted.