We have investigated the effect of the Ni substitution on the local structure and the valence electronic states of the SrFe2−xNixAs2 (x = 0.00, 0.16, and 0.23) superconductor with a multi-edge ...extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy. The As K-edge and Fe K-edge EXAFS measurements in the two polarizations (E‖ab and E‖c) show a clear change in the local structure with Ni concentration. The near-neighbor bondlengths and the related mean-square relative displacements (MSRDs) decrease as the Ni content increases. The polarized XANES spectra at the As, Fe and Ni K edges reveal a systematic change in the anisotropy of the valence electronic structure. The results suggest that the quasi 2D electronic structure of this system tends to become more isotropic as the Ni content increases. The local structure and the valence electronic states are discussed in the frame of the evolving electronic transport of the SrFe2−xNixAs2 system.
Anthracnose, caused by the fungus Colletotrichum acutatum is one of the most important diseases in strawberry crop. Due to environmental pollution and resistance produced by chemical fungicides, ...nowadays biological control is considered a good alternative for crop protection. Among biocontrol agents, there are plant growth-promoting bacteria, such as members of the genus Azospirillum. In this work, we demonstrate that under iron limiting conditions different strains of A. brasilense produce siderophores, exhibiting different yields and rates of production according to their origin. Chemical assays revealed that strains REC2 and REC3 secrete catechol type siderophores, including salicylic acid, detected by thin layer chromatography coupled with fluorescence spectroscopy and gas chromatography-mass spectrometry analysis. Siderophores produced by them showed in vitro antifungal activity against C. acutatum M11. Furthermore, this latter coincided with results obtained from phytopathological tests performed in planta, where a reduction of anthracnose symptoms on strawberry plants previously inoculated with A. brasilense was observed. These outcomes suggest that some strains of A. brasilense could act as biocontrol agent preventing anthracnose disease in strawberry.
We have combined the extended X-ray absorption fine structure (EXAFS) and X-ray emission spectroscopy (XES) to investigate the local structure and the local iron magnetic moments of (Li
1−
x
Fe
x
...)OHFeSe (
x
∼0.2) superconductors. The local structure, studied by Fe K-edge EXAFS measurements, is found to be inhomogeneous that is characterized by different Fe-Se bond lengths. The inhomogeneous phase exhibits a peculiar temperature dependence with lattice anomalies in the local structural parameters at the critical temperature
T
c
(36 K) and at the spin density wave (SDW) transition temperature
T
N
(130 K). Fe Kβ XES shows iron to be in a low spin state with the local Fe magnetic moment evolving anomalously as a function of temperature. Apart from a quantitative measurement of the local structure of (Li
1−
x
Fe
x
)OHFeSe, providing direct evidence of nanoscale inhomogeneity, the results provide further evidence of the vital role that the coupled electronic, lattice and magnetic degrees of freedom play in the iron-based superconductors.
Anomalous local structure and magnetic moment of an inhomogeneous FeSe based superconductor indicating importance of the structure and magnetic correlations in these materials.
Temperature-dependent Fe K-edge extended X-ray absorption fine structure (EXAFS) and Fe Kβ X-ray emission spectroscopy (XES) measurements are used to study the local structure and local Fe magnetic ...moment in the self-doped CaKFe4As4 superconductor. The local Fe–As and Fe–Fe bond lengths show thermal expansion similar to the one found in other iron-based superconductors. The arsenic height from the Fe–Fe plane changes anomalously with a sharp decrease in the vicinity of the superconducting transition temperature. The Fe Kβ XES reveals that Fe in CaKFe4As4 is in the low spin state, and the local magnetic moment decreases sharply while the sample is cooled across the transition temperature. The results indicate importance of the magnetoelastic coupling in the superconductivity with a key role of interlayer atomic correlations in these materials.
The local structure of the filled tetragonal tungsten bronze (TTB) niobate Ba3Nb5−xTixO15 (x = 0, 0.1, 0.7, 1.0), showing a metal-insulator transition with Ti substitution, has been studied by Nb ...K-edge extended X-ray absorption fine structure (EXAFS) measurements as a function of temperature. The Ti substitution has been found to have a substantial effect on the local structure, that remains largely temperature independent in the studied temperature range of 80–400 K. The Nb-O bonds distribution shows an increased octahedral distortion induced by Ti substitution, while Nb-Ba distances are marginally affected. The Nb-O bonds are stiffer in the Ti substituted samples, which is revealed by the temperature dependent mean square relative displacements (MSRDs). Furthermore, there is an overall increase in the configurational disorder while the system with Nb 4d electrons turns insulating. The results underline a clear relationship between the local structure and the electronic transport properties suggesting that the metal-insulator transition and possible thermoelectric properties of TTB structured niobates can be tuned by disorder.
Background and aims Azospirillum brasilense REC3 is a plant growth-promoting and siderophore-producing bacterium isolated from strawberry. Colletotrichum acutatum M11 is the causal agent of ...anthracnose, an important disease in strawberry crop. The aim of this study was to characterize at the biochemical and molecular level, the systemic resistance induced by A. brasilense on pathogen-challenged strawberry plants. Methods Phytopathological tests were performed; the content of phenolic compounds was determined spectrophotometrically; callose depositions in leaves by aniline blue staining; salicylic acid (SA) content in leaves by HPLC; and defense-related gene expression pathogenesis-related proteins (FaPR1), chitinases (FaChi2-1; FaChi2-2) and glucanase (FaBG2-2) by RT-PCR. Results A. brasilense REC3 reduced anthracnose symptoms on pathogen-challenged plants, and the effect became greater as the elapsed time between bacterial inoculation and fungal infection increased. Biochemical and transcriptional studies revealed a transient accumulation of SA and the induction of defense-related genes, suggesting further that this response is related to structural cell wall modifications as consequence of the observed increase in phenolic compounds and callose deposition. Conclusions The plant growth-promoting bacterium A. brasilense REC3 participates actively in the induction of systemic protection on strawberry plants against anthracnose disease caused by C. acutatum M11.
In this work, an innovative analytical approach focused on the use of advanced imaging techniques for the chemical mapping of degradation and/or restoration products is proposed. A representative ...cross-section showing a very complex stratigraphy from the
Saint Wilgefortis Triptych
(Hieronymus Bosch), exhibited in the
Galleria dell'Accademia di Venezia
, was investigated. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) experiments were performed using a time-of-flight detector operating in the so-called delayed extraction mode. The time delay applied during the extraction of the secondary ions permitted mass spectra to be obtained with an excellent mass resolution and chemical maps with nanometer scale spatial resolution. The painting's cross-section was also analysed at the micrometer scale by micro-Fourier transform infrared spectroscopy (micro-FTIR). The combined analytical approaches highlighted the colocalization of lead chloride, oxychloride, and hydroxychloride ions, suggesting the transformation of lead white ((PbCO
3
)
2
Pb(OH)
2
) into laurionite (PbClOH). Furthermore, chlorine appears evenly diffused in the cinnabar (HgS) layer, inducing the alteration of its more external part into calomel (Hg
2
Cl
2
). In fact, from the chemical maps the presence in the sample of an unaltered portion of the cinnabar layer is evident. Such degradation products were probably due to the exposure of the painting to a chloride-rich atmosphere for a long time. This led to a global blackening of the painting. To protect the painting from aggressive chemical species, siloxane compounds were probably used as a modern restorative treatment. ToF-SIMS chemical maps revealed permeation of the silicon-based consolidants within the sample's cracks and no interaction products with the other constitutive materials of the painting were found. Finally, the presence of different lead soaps was detected in correspondence with the lead white layer.
In this work, an innovative analytical approach focused on the use of advanced imaging techniques for the chemical mapping of degradation and/or restoration products is proposed.
We give a semantic account of the execution time (i.e. the number of cut elimination steps leading to the normal form) of an untyped MELL net. We first prove that: (1) a net is head-normalizable ...(i.e. normalizable at depth 0) if and only if its interpretation in the multiset based relational semantics is not empty and (2) a net is normalizable if and only if its exhaustive interpretation (a suitable restriction of its interpretation) is not empty. We then give a semantic measure of execution time: we prove that we can compute the number of cut elimination steps leading to a cut free normal form of the net obtained by connecting two cut free nets by means of a cut-link, from the interpretations of the two cut free nets. These results are inspired by similar ones obtained by the first author for the untyped lambda-calculus.
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