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Cho, Hana,Strader, Matthew L.,Hong, Kiryong,Jamula, Lindsey,Gullikson, Eric M.,Kim, Tae Kyu,de Groot, Frank M. F.,McCusker, James K.,Schoenlein, Robert W.,Huse, Nils The Royal Society of Chemistry 2012 Faraday discussions Vol.157 No.-
<P>Ultrafast excited-state evolution in polypyridyl Fe(<SMALL>II</SMALL>) complexes is of fundamental interest for understanding the origins of the sub-ps spin-state changes that occur upon photoexcitation of this class of compounds as well as for the potential impact such ultrafast dynamics have on incorporation of these compounds in solar energy conversion schemes or switchable optical storage technologies. We have demonstrated that ground-state and, more importantly, ultrafast time-resolved X-ray absorption methods can offer unique insights into the interplay between electronic and geometric structure that underpins the photo-induced dynamics of this class of compounds. The present contribution examines in greater detail how the symmetry of the ligand field surrounding the metal ion can be probed using these X-ray techniques. In particular, we show that steady-state K-edge spectroscopy of the nearest-neighbour nitrogen atoms reveals the characteristic chemical environment of the respective ligands and suggests an interesting target for future charge-transfer femtosecond and attosecond spectroscopy in the X-ray water window.</P>
윤정석,Anne Strader,Jian Zhou,Onno Dijkstra,Ramon Secanell,민기복 한국암반공학회 2023 터널과지하공간 Vol.33 No.1
In this study, we simulated induced seismicity in the Groningen natural gas reservoir using 2D hydro-mechanical coupled discrete element modelling (DEM). The code used is PFC2D (Particle Flow Code 2D), a commercial software developed by Itasca, and in order to apply to this study we further developed 1)initialization of inhomogeneous reservoir pressure distribution, 2)a non-linear pressure-time history boundary condition, 3)local stress field monitoring logic. We generated a 2D reservoir model with a size of 40 × 50 km2 and a complex fault system, and simulated years of pressure depletion with a time range between 1960 and 2020. We simulated fault system failure induced by pressure depletion and reproduced the spatio- temporal distribution of induced seismicity and assessed its failure mechanism. Also, we estimated the ground subsidence distribution and confirmed its similarity to the field mea- surements in the Groningen region. Through this study, we confirm the feasibility of the presented 2D hydro-mechanical coupled DEM in simulating the deformation of a complex fault system by hydro-mechanical coupled processes.
Cho, Hana,Hong, Kiryong,Strader, Matthew L.,Lee, Jae Hyuk,Schoenlein, Robert W.,Huse, Nils,Kim, Tae Kyu American Chemical Society 2016 Inorganic Chemistry Vol.55 No.12
<P>We present a time-resolved X-ray spectroscopic study of the structural and electronic rearrangements of the photocatalyst Mn-2(CO)(10) upon photodeavage of the metal-metal bond. Our study of the manganese K-edge fine structure reveals details of both the molecular structure and valence charge distribution of the photodissociated radical product. Transient X-ray absorption spectra of the formation of the Mn(CO)(5) radical demonstrate surprisingly small structural modifications between the parent molecule and the resulting two identical manganese monomers. Small modifications of the local valence charge distribution are decisive for the catalytic activity of the radical product. The spectral changes reflect altered hybridization of metal-3d, metal-4p, and ligand-2p orbitals, particularly loss of interligand interaction, accompanied by the necessary spin transition due to radical formation. The spectral changes in the manganese pre- and main-edge region are well-reproduced by time-dependent density functional theory and ab initio multiple scattering calculations.</P>