Infrared response of ordered polarons in layered perovskites

We report on the infrared absorption spectra of three oxides where charged superlattices have been recently observed in diffraction experiments. In La$_{1.67}$Sr$_{0.33}$NiO$_4$, polaron localization is found to suppress the low-energy conductivity through the opening of a gap and to split the $E_{2u}$-$A_{2u}$ vibrational manifold of the oxygen octahedra. Similar effects are detected in Sr$_{1.5}$La$_{0.5}$MnO$_4$ and in La$_2$NiO$_{4+y}$, with peculiar differences related to the type of charge ordering.Comment: File latex, 11 p. + 3 Figures, to appear on Phys. Rev. B (Rapid Commun.), 1 Oct. 1996. The figures will be faxed upon request. E-mail:[email protected] Fax: +39-6-446315

Auxin signaling and vascular cambium formation enables storage metabolism in cassava tuberous roots

Open Access Article; Published online: 13 Mar 2021Cassava storage roots are among the most important root crops worldwide and represent one of the most consumed staple foods in Sub-Saharan Africa. The vegetatively propagated tropical shrub can form many starchy tuberous roots from its stem. These storage roots are formed through the activation of secondary root growth processes. However, the underlying genetic regulation of storage root development is largely unknown. Here we report on distinct structural and transcriptional changes occurring during the early phases of storage root development. A pronounced increase in auxin-related transcripts and the transcriptional activation of secondary growth factors, as well as a decrease in gibberellin-related transcripts was observed during the early stages of secondary root growth. This was accompanied by increased cell wall biosynthesis, increased most notably during the initial xylem expansion within the root vasculature. Starch storage metabolism was activated only after the formation of the vascular cambium. The formation of nonlignified xylem parenchyma cells and the activation of starch storage metabolism coincided with increased expression of the KNOX/BEL genes KNAT1, PENNYWISE and POUND-FOOLISH, indicating their importance for proper xylem parenchyma function

Elucidating electrochemical nitrate and nitrite reduction over atomically-dispersed transition metal sites

Abstract Electrocatalytic reduction of waste nitrates (NO3 −) enables the synthesis of ammonia (NH3) in a carbon neutral and decentralized manner. Atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts demonstrate a high catalytic activity and uniquely favor mono-nitrogen products. However, the reaction fundamentals remain largely underexplored. Herein, we report a set of 14; 3d-, 4d-, 5d- and f-block M-N-C catalysts. The selectivity and activity of NO3 − reduction to NH3 in neutral media, with a specific focus on deciphering the role of the NO2 − intermediate in the reaction cascade, reveals strong correlations (R=0.9) between the NO2 − reduction activity and NO3 − reduction selectivity for NH3. Moreover, theoretical computations reveal the associative/dissociative adsorption pathways for NO2 − evolution, over the normal M-N4 sites and their oxo-form (O-M-N4) for oxyphilic metals. This work provides a platform for designing multi-element NO3RR cascades with single-atom sites or their hybridization with extended catalytic surfaces