Studies on the mechanism of the fluorescence decline induced by strong actinic light in PS II particles under different redox conditions

AbstractFluorescence changes induced by strong actinic light at room temperature were measured in isolated photosystem II (PS II) particles under different redox conditions. Comparative measurements of the absorption changes accompanying the light-induced fluorescence decay show that in the absence of Na2S2O4 the formation of a chlorophyll cation radical (probably together with oxidized carotenoid) causes a quenching while in the presence of Na2S2O4 photoaccumulation of the pheophytin anion radical (Pheo.−) takes place. The 695 nm band of the 77 K emission spectrum becomes specifically reduced if Pheo.− accumulates in the reaction center, whereas in the case of quenching by the cation radicals the ratio of the emission peaks at 685 nm and 695 nm remains constant. The present data favor the hypothesis that F-695 originates from the PS II reaction center [FEBS Lett. (1982) 147, 16–20]. If the primary plastoquinone acceptor (PQA) stayed oxidized in the dark before the onset of the illumination. Pheo.− photoaccumulation was not observed. This effect is explained by the existence of at least one further redox component which is able to accept electrons efficiently from Pheo.−. The proposed model also explains the differences in the redox titration curves of the electrochromic bandshift and the inital fluorescence, respectively

Bias and angular dependence of spin-transfer torque in magnetic tunnel junctions

We use spin-transfer-driven ferromagnetic resonance (ST-FMR) to measure the spin-transfer torque vector T in MgO-based magnetic tunnel junctions as a function of the offset angle between the magnetic moments of the electrodes and as a function of bias, V. We explain the conflicting conclusions of two previous experiments by accounting for additional terms that contribute to the ST-FMR signal at large |V|. Including the additional terms gives us improved precision in the determination of T(V), allowing us to distinguish among competing predictions. We determine that the in-plane component of has a weak but non-zero dependence on bias, varying by 30-35% over the bias range where the measurements are accurate, and that the perpendicular component can be large enough to be technologically significant. We also make comparisons to other experimental techniques that have been used to try to measure T(V).Comment: 30 pages, 8 figures. Expanded with additional data and discussion. In press at PR

RF amplification property of the MgO-based magnetic tunnel junction using field-induced ferromagnetic resonance

The radio-frequency (RF) voltage amplification property of a tunnel magnetoresistance device driven by an RF external-magnetic-field-induced ferromagnetic resonance was studied. The proposed device consists of a magnetic tunnel junction (MTJ) and an electrically isolated coplanar waveguide. The input RF voltage applied to the waveguide can excite the resonant dynamics in the free layer magnetization, leading to the generation of an output RF voltage under a DC bias current. The dependences of the RF voltage gain on the static external magnetic field strength and angle were systematically investigated. The design principles for the enhancement of the gain factor are also discussed.Comment: 12 pages, 3 figure

Automatic Computation of Cross Sections in HEP

For the study of reactions in High Energy Physics (HEP) automatic computation systems have been developed and are widely used nowadays. GRACE is one of such systems and it has achieved much success in analyzing experimental data. Since we deal with the cross section whose value can be given by calculating hundreds of Feynman diagrams, we manage the large scale calculation, so that effective symbolic manipulation, the treat of singularity in the numerical integration are required. The talk will describe the software design of GRACE system and computational techniques in the GRACE.Comment: 6 pages, Latex, ICCP