Scavenging of "dry" electrons prior to hydration by azide ions: Effect on the formation of H2 in the radiolysis of water by 60Co γ-rays and tritium β-electrons.

In this study, we use Monte Carlo track chemistry simulations to show that "dry" secondary electrons, precursors of the "hydrated" electron (e^-_aq), can be scavenged on the sub-picosecond time scale prior to hydration, by a high concentration (>0.1-1 M) of azide ions (N₃^-) in water irradiated with ⁶⁰Co γ-rays and ³H β-electrons at 25 °C. This is a striking result, as N₃^- is known to react very slowly with e^-_aq. These processes tend to significantly reduce the yields of H₂ as observed experimentally. For both energetic Compton electrons ("linear energy transfer", LET ∼ 0.3 keV/μm), which are generated by the cobalt-60 γ-rays, and ³H β-electrons (LET ∼ 6 keV/μm), our H₂ yield results confirm previous Monte Carlo simulations, which indicated the necessity of including the capture of the precursors to e^-_aq. Interestingly, our calculations show no significant changes in the scavenging of "dry" electrons at high azide concentrations in passing from γ-radiolysis to tritium β-radiolysis (<i>i.e.</i>, with LET). This led us to the conclusion that the higher H₂ yield observed experimentally for ³H β-electrons compared to ⁶⁰Co γ-rays is explained mainly by the difference in the radiation track structures during the chemical stage (>1 ps). The higher LET of tritium β-electrons leads to more molecular products (H₂ in this case) in tritium radiolysis than in γ-radiolysis. Finally, a value of 0.5 nm was derived for the reaction distance between N₃^- and the “dry” electron from the H₂ yields observed in ⁶⁰Co γ-radiolysis at high N₃^- concentrations.

Dynamic 15N{1H} NOE measurements: a tool for studying protein dynamics

Intramolecular motions in proteins are one of the important factors that determine their biological activity and interactions with molecules of biological importance. Magnetic relaxation of 15N amide nuclei allows one to monitor motions of protein backbone over a wide range of time scales. 15N{1H} nuclear Overhauser effect is essential for the identification of fast backbone motions in proteins. Therefore, exact measurements of NOE values and their accuracies are critical for determining the picosecond time scale of protein backbone. Measurement of dynamic NOE allows for the determination of NOE values and their probable errors defined by any sound criterion of nonlinear regression methods. The dynamic NOE measurements can be readily applied for non-deuterated or deuterated proteins in both HSQC and TROSY-type experiments. Comparison of the dynamic NOE method with commonly implied steady-state NOE is presented in measurements performed at three magnetic field strengths. It is also shown that improperly set NOE measurement cannot be restored with correction factors reported in the literature.

Terahertz Time-Domain Spectroscopy

Time-Domain terahertz spectroscopy (THz TDS) has attracted attention from many scientific disciplines as it enables accessing the gap between electronic and optical techniques. One application is to probe spintronic dynamics in sub-picosecond time scale. Here, we discuss principles and technical aspects of a typical THz TDS setup. We also show an example of terahertz time-domain data obtained from a Co/Pt thin film calibrant, which is a well-studied spintronic structure emitting strong THz radiation. See video at https://youtu.be/X7vrvQcmy8c.

Unipolar magnetic field pulses as an advantageous tool for ultrafast operations in superconducting Josephson “atoms”

A theoretical approach to the consistent full quantum description of the ultrafast population transfer and magnetization reversal in superconducting meta-atoms induced by picosecond unipolar pulses of a magnetic field is developed. A promising scheme based on the regime of stimulated Raman Λ-type transitions between qubit states via upper-lying levels is suggested in order to provide ultrafast quantum operations on the picosecond time scale. The experimental realization of a circuit-on-chip for the discussed ultrafast control is presented.

Unipolar magnetic field pulses as an advantageous tool for ultrafast spin-flip in superconducting Josephson “atoms”

The theoretical approach to the consistent fully quantum description of the ultrafast population transfer and magnetization reversal in superconducting meta-atoms induced by picosecond unipolar pulses of the magnetic field is developed. A promising scheme based on the regime of stimulated Raman Λ-type transitions between qubit spin states via upper-lying levels is suggested in order to provide an ultrafast spin-flip on the picosecond time scale. The experimental realization of the ultrafast control of circuit -on -chip is presented.