Stability of the Ni sites across the pressure-induced metallization in YNiO3

The local environment of nickel atoms in Y NiO3 across the pressure- induced insulator to metal (IM) transition was studied using X-ray absorption spectroscopy (XAS) supported by ab initio calculations. The monotonic contraction of the NiO6 units under applied pressure observed up to 13 GPa, stops in a limited pressure domain around 14 GPa, before resuming above 16 GPa. In this narrow pressure range, crystallographic modifications basically occur in the medium/long range, not in the NiO6 octahedron, whereas the evolution of the near-edge XAS features can be associated to metallization. Ab initio calculations show that these features are related to medium range order, provided that the Ni-O-Ni angle enables a proper overlap of the Ni eg and O 2p orbitals. Metallization is then not directly related to modifications in the average local geometry of the NiO6 units but more likely to an inter-octahedra rearrangement. These outcomes provides evidences of the bandwidth driven nature of the IM transition.Comment: 6 pages with figure

Patterns of oocyte development in natural habitat and captive Salminus hilarii Valenciennes, 1850 (Teleostei: Characidae)

Fecundity and oocyte development in Salminus hilarii female brood stock were analyzed with the aim of investigating the impact of migration impediment on oogenesis. Histological analyses of the ovaries were performed in adult females caught in two different environments-the TietA(a) River (natural) and captivity-and the gonadossomatic index, oocyte diameter and fecundity determined. Five germ cell development stages (oogonium, perinucleolar, cortical alveoli, vitellogenic, ripe) and two other structures (postovulatory follicles and atretic oocytes) were observed in females caught in the river. Captive animals lacked the ripe oocytes and postovulatory follicles and had a relatively higher number of atretic oocytes. Females in captivity are known to produce larger oocytes, and they release fewer eggs in each spawn (absolute fecundity) when compared with animals that are able to migrate. Our results suggest that the TietA(a) River is undergoing alterations which are being reflected in the reproductive performance of S. hilarii, mainly due to the presence of atretic oocytes in females caught in the river. The lack of postovulatory follicles and ripe oocytes in captive animals reveals that migratory impediment negatively impacts final oocyte maturation. However, the stage of maturation reached is adequate for ovulation induction with hormone manipulation.FAPESP[01/10483-1]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Master`s student fellowship CNPq[134451/2005-8]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Temperature and high-pressure dependent x-ray absorption of SmNiO3 at the Ni K and Sm L3 edges

Wereport on x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) measurements of SmNiO from 20 K to 600 K and up to 38 GPa at the Ni K and SmL edges. A multiple component pre-NiKedge tail is understood, originating from 1 s transitions to 3d-4p states while a post-edge shoulder increases distinctively smoothly, at about the insulator to metal phase transition (T), due to the reduction of electron-phonon interactions as the Ni 3d and O 2p b and overlap triggers the metallic phase. This effect is concomitant with pressure-induced Ni-O-Ni angle increments toward more symmetric Ni octahedra of the rhombohedral R3c space group. Room temperature pressure-dependent Ni white line peak energies have an abrupt∼3.10 ± 0.04 GPa valence discontinuity from non-equivalent Ni + Ni charge disproportionate net unresolved absorber turning at ∼T into Ni of the orthorhombic Pbnm metal oxide phase. At 20 Kthe overall white line response, still distinctive at T∼8.1 ± 0.6 GPa is much smoother due to localization. Octahedral bond contraction up to 38 GPa and at 300 K and 20 K show breaks in its monotonic increase at the different structural changes. The SmL edge does not show distinctive behaviors either at 300 K or 20 K up to about 35 GPa but the perovskite Smcage, coordinated to eight oxygen atoms, undergoes strong uneven bond contractions at intermediate pressures where we found the coexistence of octahedral and rhombohedral superexchange angle distortions.Wefound that the white line pressure-dependent anomaly may be used as an accurate alternative for delineating pressure-temperature phase diagrams

Involvement of pituitary gonadotropins, gonadal steroids and breeding season in sex change of protogynous dusky grouper, Epinephelus marginatus (Teleostei: Serranidae), induced by a non-steroidal aromatase inhibitor

Two experiments were performed using the aromatase inhibitor (AI) letrozole (100mg/kg) to promote sex change, from female-to-male, in protogynous dusky grouper. One experiment was performed during the breeding season (spring) and the other at the end of the breeding season (summer). During the spring, AI promoted sex change after 9weeks and the sperm produced was able to fertilize grouper oocytes. During the summer, the sex change was incomplete; intersex individuals were present and sperm was not released by any of the animals. Sex changed gonads had a lamellar architecture; cysts of spermatocytes and spermatozoa in the lumen of the germinal compartment. In the spring, after 4weeks, 11ketotestosterone (11KT) levels were higher in the AI than in control fish, and after 9weeks, coincident with semen release, testosterone levels increased in the AI group, while 11KT returned to the initial levels. Estradiol (E2) levels remained unchanged during the experimental period. Instead of decreasing throughout the period, as in control group, 17 α-OH progesterone levels did not change in the AI-treated fish, resulting in higher values after 9weeks when compared with control fish. fshβ and lhβ gene expression in the AI animals were lower compared with control fish after 9weeks. The use of AI was effective to obtain functional males during the breeding season. The increase in androgens, modulated by gonadotropins, triggered the sex change, enabling the development of male germ cells, whereas a decrease in E2 levels was not required to change sex in dusky grouper. © 2013 Elsevier Inc