| 1. |
- Gregoire, Luc-Andre, et al.
(författare)
-
Modular Multilevel Converters Overvoltage Diagnosis and Remedial Strategy During Blocking Sequences
- 2015
-
Ingår i: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107. ; 30:5, s. 2777-2785
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the authors first highlight an existing overvoltage phenomenon that is inherent to the modular multilevel converter (MMC) topology. The latter occurs during the blocking sequences of semiconductor devices if the converter needs to be stopped due to circulating current, loss of control, or unexpected faults. An analysis based on time-domain expressions describing each operating sequence during normal and faulty blocking conditions is used to demonstrate the origin of this overvoltage. Thereafter, system behaviour is obtained when devices gating signals are withheld as well as the exact overvoltage cause. Real-time simulation, with submicrosecond time steps, and experimental results validate the overvoltage phenomena and the proposed remedial strategy to avoid uncontrolled faulty conditions.
|
|
| 2. |
- Ho, Phay J., et al.
(författare)
-
The role of transient resonances for ultra-fast imaging of single sucrose nanoclusters
- 2020
-
Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 11
-
Tidskriftsartikel (refereegranskat)abstract
- Intense x-ray free-electron laser (XFEL) pulses hold great promise for imaging function in nanoscale and biological systems with atomic resolution. So far, however, the spatial resolution obtained from single shot experiments lags averaging static experiments. Here we report on a combined computational and experimental study about ultrafast diffractive imaging of sucrose clusters which are benchmark organic samples. Our theoretical model matches the experimental data from the water window to the keV x-ray regime. The large-scale dynamic scattering calculations reveal that transient phenomena driven by non-linear x-ray interaction are decisive for ultrafast imaging applications. Our study illuminates the complex interplay of the imaging process with the rapidly changing transient electronic structures in XFEL experiments and shows how computational models allow optimization of the parameters for ultrafast imaging experiments. X-ray free electron lasers provide high photon flux to explore single particle diffraction imaging of biological samples. Here the authors present dynamic electronic structure calculations and benchmark them to single-particle XFEL diffraction data of sucrose clusters to predict optimal single-shot imaging conditions.
|
|
| 3. |
- March, Anne Marie, et al.
(författare)
-
Elucidation of the photoaquation reaction mechanism in ferrous hexacyanide using synchrotron x-rays with sub-pulse-duration sensitivity
- 2019
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151:14
-
Tidskriftsartikel (refereegranskat)abstract
- Ligand substitution reactions are common in solvated transition metal complexes, and harnessing them through initiation with light promises interesting practical applications, driving interest in new means of probing their mechanisms. Using a combination of time-resolved x-ray absorption spectroscopy and hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations and x-ray absorption near-edge spectroscopy calculations, we elucidate the mechanism of photoaquation in the model system iron(ii) hexacyanide, where UV excitation results in the exchange of a CN- ligand with a water molecule from the solvent. We take advantage of the high flux and stability of synchrotron x-rays to capture high precision x-ray absorption spectra that allow us to overcome the usual limitation of the relatively long x-ray pulses and extract the spectrum of the short-lived intermediate pentacoordinated species. Additionally, we determine its lifetime to be 19 (±5) ps. The QM/MM simulations support our experimental findings and explain the ∼20 ps time scale for aquation as involving interconversion between the square pyramidal (SP) and trigonal bipyramidal pentacoordinated geometries, with aquation being only active in the SP configuration.
|
|
