Insight on Hole-Hole Interaction and Magnetic Order from Dichroic Auger-Photoelectron Coincidence Spectra

The absence of sharp structures in the core-valence-valence Auger line shapes of partially filled bands has severely limited the use of electron spectroscopy in magnetic crystals and other correlated materials. Here by a novel interplay of experimental and theoretical techniques we achieve a combined understanding of the Photoelectron, Auger %$M_{23}M_{45}M_{45}$ and Auger-Photoelectron Coincidence Spectra (APECS) of CoO. This is a prototype antiferromagnetic material in which the recently discovered Dichroic Effect in Angle Resolved (DEAR) APECS reveals a complex pattern in the strongly correlated Auger line shape. A calculation of the \textit{unrelaxed} spectral features explains the pattern in detail, labeling the final states by the total spin. The present theoretical analysis shows that the dichroic effect arises from a spin-dependence of the angular distribution of the photoelectron-Auger electron pair detected in coincidence, and from the selective power of the dichroic technique in assigning different weights to the various spin components. Since the spin-dependence of the angular distribution exists in the antiferromagnetic state but vanishes at the N\'eel temperature, the DEAR-APECS technique detects the phase transition from its local effects, thus providing a unique tool to observe and understand magnetic correlations in such circumstances, where the usual methods (neutron diffraction, specific heat measurements) are not applicable.Comment: Accepted by: Physical Review Letter

THE EISENBUD-GREEN-HARRIS CONJECTURE

We survey most of the known results concerning the Eisenbud-Green-Harris Conjecture. Our presentation includes new proofs of several theorems, as well as a unified treatment of many results which are otherwise scattered in the literature. We include a final section with some applications, and examples

Voltage-Dependent Proton Transport by the Voltage Sensor of the ShakerK+ Channel

AbstractIn voltage-dependent ion channels, pore opening is initiated by electrically driven movements of charged residues, and this movement generates a gating current. To examine structural rearrangements in the Shaker K+ channel, basic residues R365 and R368 in the S4 segment were replaced with histidine, and gating currents were recorded. Changes in gating charge displacement with solvent pH reveal voltage-dependent changes in exposure of the histidine to solvent protons. This technique directly monitors accessibility changes during gating, probes the environment even in confined locations, and introduces minimal interference of gating charge motion. The results indicate that charges 365 and 368 traverse the entire electric field during gating. The remarkable implication of the successive exposure of histidine to each side of the membrane is that in a pH gradient, the voltage sensor transports protons

Molecular determinants of external barium block in Shaker potassium channels

AbstractMutations in the outer pore region of Shaker K+ channels (T449 and D447) can influence external Ba2+ block. Substitution of T449 by A, V or Y differentially reduced Ba2+ block primarily by decreasing the blocking rate. Substitution of D447 by N resulted in a non-conducting channel with apparently normal gating currents. External Ba2+ can speed the OFF gating current of a different non-conducting mutant, W434F; this effect was markedly attenuated by the D447N substitution. These results suggest that D447 contributes to an external Ba2+ binding site while T449 imposes a barrier to the access of that site

Tomato and Pepper Seeds as Pathways for the Dissemination of Phytopathogenic Bacteria: A Constant Challenge for the Seed Industry and the Sustainability of Crop Production

The seed industry plays a crucial role in global food production but it faces a persistent challenge in ensuring the health and quality of seeds, particularly those of tomato and pepper seeds, which represent key seed commodities on the global market. Seeds can serve as potential pathways for the introduction and dissemination of seed-borne bacteria, which may have devastating effects on crop yield, farmers’ remunerability, and food security. Therefore, fungicides and other antimicrobial compounds are extensively used to disinfect the seeds, thus increasing the input of chemicals in the agri-environment. In this review, we address aspects that connect disease epidemiology with seed infection and health, including seed contamination, endophytic colonization, and seedborne infections. We focused on the main bacterial diseases affecting tomato and pepper seeds by discussing their official seed testing methods as requirements supporting a smooth seed trade. Moreover, we present a survey on the past and recent innovations for seed treatments, focusing on sustainable disinfection methods. Therefore, this review will be a short but indispensable guide for seed technologists and pathologists involved in the production of high-quality seeds, providing indications and suggestions to contrast seed-borne pathogen dissemination and avoid international controversies and complaints by phytosanitary authorities, extension services, and farmers