Temperature Dependence of the Collisional Removal of O2(A(sup 3)Sigma(sup +)(sub u), upsilon=9 ) with O2 and N2

The temperature dependence of the collisional removal of O2 molecules in the upsilon = 9 level of the A(sup 3)Sigma(sup +)(sub u) electronic state has been studied for the colliders O2 and N2, over the temperature range 150 to 300 K. In a cooled flow cell, the output of a pulsed dye laser excites the O2 to the upsilon = 9 level of the A(sup 3)Sigma(sup +)(sub u) state, and the output of a time-delayed second laser monitors the temporal evolution of this level via a resonance-enhanced ionization. We find the u thermally averaged removal cross section for O2 collisions is constant (approx. 10 A(sup 2)) between room temperature and 200 K, then increases rapidly with decreasing temperature, doubling by 150 K. In contrast, the N2 cross section at 225 K is approx. 8% smaller and gradually increases to a value at 150 K that is approx. 60% larger than the room temperature value. The difference between the temperature dependence of the O2 and N2 collision cross section implies that the removal by oxygen becomes more important at the lower temperatures found in the mesosphere, but removal by N2 still dominates

Valence states and spin structure of spinel FeV2O4 with different orbital degrees of freedom

The electronic structure of spinel FeV2O4, which contains two Jahn-Teller active Fe and V ions, has been investigated by employing soft x-ray absorption spectroscopy (XAS), soft x-ray magnetic circular dichroism (XMCD), and nuclear magnetic resonance (NMR). XAS indicates that V ions are trivalent and Fe ions are nearly divalent. The signs of V and Fe 2p XMCD spectra are opposite to each other. It is found that the effect of the V 3d spin-orbit interaction on the V 2p XMCD spectrum is negligible, indicating that the orbital ordering of V t2g states occurs from the real orbital states and that the orbital moment of a V3+ ion is mostly quenched. NMR shows that V spins are canted to have a Yafet-Kittel-type triangular spin configuration

Interplay between R 4 f and Fe 3d states in charge-ordered RFe2O4 (R = Er, Tm, Lu)

The electronic structures of R 4f and Fe 3d states of RFe2O4 (R = Er, Tm, Lu) have been investigated by employing soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism at the Fe 2p and R 3d absorption edges. It is found that the valence states of Fe and R ions are nearly Fe2.5+ and R3+, and that the net magnetic moments of Fe2+ and Fe3+ ions are antiparallel to each other. Both R 3d and O 1s XAS spectra show that the localized R 4f states do not contribute to the multiferroicity of RFe2O4. On the other hand, the magnetization data for RFe2O4 at low temperature (T) reveal the cluster glass behavior for R = Tm and Lu, but not for R = Er. This work suggests that the T-dependent structural differences among RFe2O4, caused by different R ions, are closely related to the magnetoelectricity at low temperature.112Nsciescopu

Induction of Thioredoxin Is Required for Nodule Development to Reduce Reactive Oxygen Species Levels in Soybean Roots

Nodules are formed on legume roots as a result of signaling between symbiotic partners and in response to the activities of numerous genes. We cloned fragments of differentially expressed genes in spot-inoculated soybean (Glycine max) roots. Many of the induced clones were similar to known genes related to oxidative stress, such as thioredoxin and β-carotene hydroxylase. The deduced amino acid sequences of full-length soybean cDNAs for thioredoxin and β-carotene hydroxylase were similar to those in other species. In situ RNA hybridization revealed that the thioredoxin gene is expressed on the pericycle of 2-d-old nodules and in the infected cells of mature nodules, suggesting that thioredoxin is involved in nodule development. The thioredoxin promoter was found to contain a sequence resembling an antioxidant responsive element. When a thioredoxin mutant of yeast was transformed with the soybean thioredoxin gene it became hydrogen peroxide tolerant. These observations prompted us to measure reactive oxygen species levels. These were decreased by 3- to 5-fold in 7-d-old and 27-d-old nodules, coincident with increases in the expression of thioredoxin and β-carotene hydroxylase genes. Hydrogen peroxide-producing regions identified with cerium chloride were found in uninoculated roots and 2-d-old nodules, but not in 7-d-old and 27-d-old nodules. RNA interference-mediated repression of the thioredoxin gene severely impaired nodule development. These data indicate that antioxidants such as thioredoxin are essential to lower reactive oxygen species levels during nodule development