Changes in glutathione and xanthophyll cycle pigments in the high light-stressed lichens Umbilicaria antarctica and Lasallia pustulata

Hydrated thalli of two lichen species--Umbilicaria antarctica and Lasallia pustulata--were exposed to high light (1800 micromol m-2s-1) for 30 min. High light exposure led to a decrease of total glutathione in both species, while de-epoxidation state of xanthophyll cycle pigments and non-photochemical quenching increased. In the subsequent recovery, the values of de-epoxidation state of xanthophyll cycle pigments decreased towards initial values. Glutathione (GSH) was resynthetised slowly. In conclusion, zeaxanthin-related protection is probably more involved than GSH-related protection in short-term response to high light stress in U. antarctica and L. pustulata. Faster recovery from photoinhibition in L. pustulata than U. antarctica is mainly due to faster conversion of zeaxanthin to violaxanthin and larger GSH pool of former species.     

Partial photoionization cross sections and angular distributions for double excitation of helium up to the N = 13 threshold

Partial photoionization cross sections sigmaN(Egamma) and photoelectron angular distributions betaN(Egamma) were measured for the final ionic states He+ (N > 4) in the region between the N = 8 and N = 13 thresholds (Egamma > 78.155 eV) using the cold target recoil ion momentum spectroscopy technique (COLTRIMS). Comparison of the experimental data with two independent sets of theoretical predictions reveals disagreement for the branching ratios to the various HeN(+) states. The angular distributions just below the double ionization threshold suggest an excitation process for highly excited N states similar to the Wannier mechanism for double ionization.     

Unified picture of polariton propagation in bulk GaAs semiconductors

High-resolution amplitude and phase linear spectroscopy of high-quality bulk GaAs are reported. The detailed structure of the observed full complex transmission is consistently explained by polariton effects on the basis of microscopic calculations. The coupled equations for the excitonic polarization and the light field in the slab configuration are evaluated using appropriate boundary conditions for the electromagnetic field and the excitonic wave function without reference to additional boundary conditions for the macroscopic polarization.     

Buchbesprechungen

Ohne Zusammenfassung     

The Transformation Groups Whose C*-Algebras are Fell Algebras

Let (G, X) be a locally compact transformation group in whichG acts freely on X. We show that the associated transformation-groupC*-algebra C₀(X) G is a Fell algebra if and only if X is aCartan G-space.     

Improving solid-state NMR dipolar recoupling by optimal control

We present the first solid-state NMR experiments developed using optimal control theory. Taking heteronuclear dipolar recoupling in magic-angle-spinning NMR as an example, it proves possible to significantly improve the efficiency of the experiments while introducing robustness toward instrumental imperfections such as radio frequency inhomogeneity. The improvements are demonstrated by numerical simulations as well as practical experiments on a 13Calpha,15N-labeled powder of glycine. The experiments demonstrate a gain of 53% in the efficiency for 15N to 13Calpha coherence transfer relative to the typically double-cross-polarization experiments.     

Advanced method using microwaves and solid-phase microextraction coupled with gas chromatography-mass spectrometry for the determination of pyrethroid residues in strawberries

A microwave-assisted desorption method was developed and coupled with solid-phase microextraction and GC-MS for the analysis of pyrethroid residues in strawberries. In the first step, pyrethroid analytes were desorbed from the whole fruits in an aqueous acetonitrile solution at 50% under microwave assistance, so preventing these compounds to be captured with strong matrix effects by endogenous constituents. Then, the 100 microm poly(dimethylsiloxane)-coated fibre was exposed for 30 min in the obtained extracting solution. Calibration curves, realised from blank strawberries spiked at different concentrations with standards, showed a linear range between 1 microg/kg and 250 microg/kg with r2 > 0.992 and variation coefficients below 15%. Limits of detection and quantitation were found lower than 14 microg/kg and 40 microg/kg, respectively. Observed analysis results by using this method and relative to field incurred strawberry samples were also compared to those obtained by two accredited trading laboratories using traditional methods.     

Twisted actions and the obstruction to extending unitary representations of subgroups

Suppose that G is a locally compact group and π is a (not necessarily irreducible) unitary representation of a closed normal subgroup N of G on a Hilbert space . We extend results of Clifford and Mackey to determine when π extends to a unitary representation of G on the same space in terms of a cohomological obstruction.