Pulsed EPR Dipolar Spectroscopy under the Breakdown of the High-Field Approximation: The High-Spin Iron(III) Case

Pulsed EPR dipolar spectroscopy (PDS) offers several methods for measuring dipolar coupling and thus the distance between electron-spin centers. To date, PDS measurements to metal centers were limited to ions that adhere to the high-field approximation. Here, the PDS methodology is extended to cases where the high-field approximation breaks down on the example of the high-spin Fe³⁺/nitroxide spin-pair. First, the theory developed by Maryasov et al. (Appl. Magn. Reson. 2006 , 30, 683–702) was adapted to derive equations for the dipolar coupling constant, which revealed that the dipolar spectrum does not only depend on the length and orientation of the interspin distance vector with respect to the applied magnetic field but also on its orientation to the effective g-tensor of the Fe³⁺ ion. Then, it is shown on a model system and a heme protein that a PDS method called relaxation-induced dipolar modulation enhancement (RIDME) is well-suited to measuring such spectra and that the experimentally obtained dipolar spectra are in full agreement with the derived equations. Finally, a RIDME data analysis procedure was developed, which facilitates the determination of distance and angular distributions from the RIDME data. Thus, this study enables the application of PDS to for example, the highly relevant class of high-spin Fe³⁺ heme proteins.     

Parametric model of the BAW resonator phase-noise

Excepted for the very short terms the frequency stability of ultra-stable oscillators is mainly limited by the resonator noise. In this work we proposed a parametric model of the bulk acoustic wave (BAW) resonator phase noise based on an equivalent circuit. This model explains phase noise generated by a BAW crystal from a point of view of parametric fluctuations and proves the f⁻¹ dependences of the crystal noise. The model performance is verified with simulation. Simulation results are compared to experimental data and discussed. Comparison of three existing models is made.     

Aharonov-Bohm effect as a probe of interaction between magnetic impurities

We study the effects of the RKKY interaction between magnetic impurities on the mesoscopic conductance fluctuations of a metal ring with dilute magnetic impurities. At sufficiently low temperatures and strong magnetic fields, the loss of electron coherence occurs mainly due to the scattering off rare pairs of strongly coupled magnetic impurities. We establish a relation between the dephasing rate and the distribution function of the exchange interaction within such pairs. In the case of the RKKY exchange interaction, this rate exhibits 1/B(2) behavior in strong magnetic fields. We demonstrate that the Aharonov-Bohm conductance oscillations may be used as a probe of the distribution function of the exchange interaction between magnetic impurities in metals.     

Working group report: Collider Physics

This is summary of the activities of the working group on collider physics in the IXth Workshop on High Energy Physics Phenomenology (WHEPP-9) held at the Institute of Physics, Bhubaneswar, India in January 2006. Some of the work subsequently done on these problems by the subgroups formed during the workshop is included in this report.     

Velocity–vorticity–helicity formulation and a solver for the Navier–Stokes equations

For the three-dimensional incompressible Navier–Stokes equations, we present a formulation featuring velocity, vorticity and helical density as independent variables. We find the helical density can be observed as a Lagrange multiplier corresponding to the divergence-free constraint on the vorticity variable, similar to the pressure in the case of the incompressibility condition for velocity. As one possible practical application of this new formulation, we consider a time-splitting numerical scheme based on an alternating procedure between vorticity–helical density and velocity–Bernoulli pressure systems of equations. Results of numerical experiments include a comparison with some well-known schemes based on pressure–velocity formulation and illustrate the competitiveness on the new scheme as well as the soundness of the new formulation.     

Open‐chain unsaturated selanyl sulfides: stereochemical structure and stereochemical behavior of their 77Se–1H spin–spin coupling constants

Stereochemical structure of nine Z‐2‐(vinylsulfanyl)ethenylselanyl organyl sulfides has been investigated by means of experimental measurements and second‐order polarization propagator approach calculations of their ¹H–¹H, ¹³C–¹H, and ⁷⁷Se–¹H spin–spin coupling constants together with a theoretical conformational analysis performed at the MP2/6‐311G** level. All nine compounds were shown to adopt the preferable skewed s‐cis conformation of their terminal vinylsulfanyl group, whereas the favorable rotational conformations with respect to the internal rotations around the C–S and C–Se bonds of the internal ethenyl group are both skewed s‐trans. Stereochemical trends of ⁷⁷Se–¹H spin–spin coupling constants originating in the geometry of their coupling pathways and the selenium lone pair effect were rationalized in terms of the natural J‐coupling analysis within the framework of the natural bond orbital approach. Copyright © 2012 John Wiley & Sons, Ltd.