| 1. |
- Glasbey, JC, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 2. |
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Kunnus, K., et al.
(författare)
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Identification of the dominant photochemical pathways and mechanistic insights to the ultrafast ligand exchange of Fe(CO)(5) to Fe(CO)(4)EtOH
- 2016
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 3:4
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Tidskriftsartikel (refereegranskat)abstract
- We utilized femtosecond time-resolved resonant inelastic X-ray scattering and ab initio theory to study the transient electronic structure and the photoinduced molecular dynamics of a model metal carbonyl photocatalyst Fe(CO)(5) in ethanol solution. We propose mechanistic explanation for the parallel ultrafast intra-molecular spin crossover and ligation of the Fe(CO)(4) which are observed following a charge transfer photoexcitation of Fe(CO)(5) as reported in our previous study [ Wernet et al., Nature 520, 78 (2015)]. We find that branching of the reaction pathway likely happens in the (1)A(1) state of Fe(CO)(4). A sub-picosecond time constant of the spin crossover from B-1(2) to B-3(2) is rationalized by the proposed B-1(2) -> (1)A(1) -> B-3(2) mechanism. Ultrafast ligation of the B-1(2) Fe(CO)(4) state is significantly faster than the spin-forbidden and diffusion limited ligation process occurring from the B-3(2) Fe(CO)(4) ground state that has been observed in the previous studies. We propose that the ultrafast ligation occurs via B-1(2) -> (1)A(1) -> (1)A'Fe(CO)(4)EtOH pathway and the time scale of the (1)A(1) Fe(CO)(4) state ligation is governed by the solute-solvent collision frequency. Our study emphasizes the importance of understanding the interaction of molecular excited states with the surrounding environment to explain the relaxation pathways of photoexcited metal carbonyls in solution.
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| 7. |
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| 8. |
- Kunnus, K., et al.
(författare)
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Quantifying covalent interactions with resonant inelastic soft X-ray scattering : Case study of Ni2+ aqua complex
- 2017
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 669, s. 196-201
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the effects of covalent interactions in Ni 2p3d resonant inelastic X-ray scattering (RIXS) spectra from aqueous Ni2+ ions and find that the relative RIXS intensities of ligand-to-metal charge-transfer final states with respect to the ligand-field final states reflect the covalent mixing between Ni 3d and water orbitals. Specifically, the experimental intensity ratio at the Ni L-3-edge allows to determine that the Ni 3d orbitals have on average 5.5% of water character. We propose that 2p3d RIXS at the Ni L-3-edge can be utilized to quantify covalency in Ni complexes without the use of external references or simulations.
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| 9. |
- Mitzner, Rolf, et al.
(författare)
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L-Edge X-ray Absorption Spectroscopy of Dilute Systems Relevant to Metalloproteins Using an X-ray Free-Electron Laser
- 2013
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:21, s. 3641-3647
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Tidskriftsartikel (refereegranskat)abstract
- L-edge spectroscopy of 3d transition metals provides important electronic structure information and has been used in many fields. However, the use of this method for studying dilute aqueous systems, such as metalloenzymes, has not been prevalent because of severe radiation damage and the lack of suitable detection systems. Here we present spectra from a dilute Mn aqueous solution using a high-transmission zone-plate spectrometer at the Linac Coherent Light Source (LCLS). The spectrometer has been optimized for discriminating the Mn L-edge signal from the overwhelming 0 K-edge background that arises from water and protein itself, and the ultrashort LCLS X-ray pulses can outrun X-ray induced damage. We show that the deviations of the partial-fluorescence yield-detected spectra from the true absorption can be well modeled using the state-dependence of the fluorescence yield, and discuss implications for the application of our concept to biological samples.
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| 10. |
- Padilla, P., et al.
(författare)
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Glide Symmetry to Prevent the Lowest Stopband of Printed Corrugated Transmission Lines
- 2018
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Ingår i: IEEE Microwave and Wireless Components Letters. - : Institute of Electrical and Electronics Engineers Inc.. - 1531-1309 .- 1558-1764. ; 28:9, s. 750-752
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, we demonstrate that the dispersion properties of printed double-sided parallel-strip lines can be controlled by using glide symmetry. Glide symmetry is introduced in with corrugations in both strips of a double-sided line. We demonstrate that glide symmetry eliminates the stopband between first and second propagating modes and yields to a higher propagation constant, preserving its linearity, and the broadband nature of the underlying guiding technology. Thus, the glide-symmetric double-sided line can be designed to possess a high equivalent refractive index in an ultrawide range of frequencies. These exceptional properties have been numerically and experimentally validated. Finally, we demonstrate the possibilities of this technology with a specific design, a glide-symmetric double-sided parallel-strip line with filtering properties. Potential applications are low-dispersive leaky-wave antennas and electromechanical tunable phase shifters and filters.
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| 11. |
- Petek, Martin, et al.
(författare)
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Efficient Numerical Computation of Dispersion Diagrams for Glide-Symmetric Periodic Structures with a Hexagonal Lattice
- 2024
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Ingår i: 18th European Conference on Antennas and Propagation, EuCAP 2024. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- In this work, we present a modeling methodology to solve the eigenvalue problem for periodic structures with a hexagonal lattice. The method is based on the previously proposed multi-modal transfer matrix method, which is a hybrid method that takes into account the coupling between the multiple modes of the ports surrounding the single unit cell. Commercial software can be used to obtain the generalized scattering parameters which are subsequently applied to set up and solve the eigenvalue problem of the periodic structure. This approach has the ability to obtain complex solutions and thus makes it possible to analyze the attenuation in the stopbands. Here, we extend the multimodal transfer matrix method to the efficient solution of the resulting eigenvalue problem for the case of a hexagonal lattice, detailing the selection of the appropriate supercells and the appropriate irreducible Brillouin zones. Two types of structures are analyzed: a mirror-symmetric structure and a glide-symmetric structure. Very good agreement is obtained with commercial software, limited to the real part of the dispersion diagrams.
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| 12. |
- Rolles, D., et al.
(författare)
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Femtosecond x-ray photoelectron diffraction on gas-phase dibromobenzene molecules
- 2014
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 47:12
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Tidskriftsartikel (refereegranskat)abstract
- We present time-resolved femtosecond photoelectron momentum images and angular distributions of dissociating, laser-aligned 1,4-dibromobenzene (C6H4Br2) molecules measured in a near-infrared pump, soft-x-ray probe experiment performed at an x-ray free-electron laser. The observed alignment dependence of the bromine 2p photoelectron angular distributions is compared to density functional theory calculations and interpreted in terms of photoelectron diffraction. While no clear time-dependent effects are observed in the angular distribution of the Br(2p) photoelectrons, other, low-energy electrons show a pronounced dependence on the time delay between the near-infrared laser and the x-ray pulse.
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| 13. |
- Wernet, Philippe, 1971-, et al.
(författare)
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Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)5 in solution
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 520:7545, s. 78-81
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Tidskriftsartikel (refereegranskat)abstract
- Transition-metal complexes have long attracted interest for fundamental chemical reactivity studies and possible use in solar energy conversion. Electronic excitation, ligand loss from the metal centre, or a combination of both, creates changes in charge and spin density at the metal site that need to be controlled to optimize complexes for photocatalytic hydrogen production and selective carbon-hydrogen bond activation. An understanding at the molecular level of how transition-metal complexes catalyse reactions, and in particular of the role of the short-lived and reactive intermediate states involved, will be critical for such optimization. However, suitable methods for detailed characterization of electronic excited states have been lacking. Here we show, with the use of X-ray laser-based femtosecond resolution spectroscopy and advanced quantum chemical theory to probe the reaction dynamics of the benchmark transition-metal complex Fe(CO)5 insolution, that the photoinduced removal of CO generates the 16-electron Fe(CO)4 species, a homogeneous catalyst with an electron deficiency at the Fe centre, in a hitherto unreported excited singlet state that either converts to the triplet ground state or combines with a CO or solvent molecule to regenerate a penta-coordinated Fe species on a sub-picosecond timescale. This finding, which resolves the debate about the relative importance of different spin channels in the photochemistry of Fe(CO)5 (refs 4, 16,17,18,19 and 20), was made possible by the ability of femtosecond X-ray spectroscopy to probe frontier-orbital interactions with atom specificity. We expect the method to be broadly applicable in the chemical sciences, and to complement approaches that probe structural dynamics in ultrafast processes.
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| 14. |
- Algaba-Brazalez, A., et al.
(författare)
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Compact Polarization Transformation in a Geodesic Luneburg Lens Antenna
- 2021
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Ingår i: 2021 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting, APS/URSI 2021 - Proceedings. - : Institute of Electrical and Electronics Engineers Inc.. ; , s. 1992-1993
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Konferensbidrag (refereegranskat)abstract
- This paper describes the design of a compact polarizer that rotates the linear polarization of a fully metallic geodesic Luneburg lens antenna for applications requiring polarization diversity. The polarization rotation is achieved by loading the radiating aperture of the antenna with two metallic screens. The integrated antenna operates in the Ka-band, from 25 to 31 GHz, showing around 20% bandwidth with S11 below -10 dB, and a scanning range of 100°.
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| 15. |
- Castillo Tapia, Pilar, et al.
(författare)
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Mode propagation in glide-symmetric dielectric-filled corrugated waveguides
- 2021
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Ingår i: 2021 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting, APS/URSI 2021 - Proceedings. - : Institute of Electrical and Electronics Engineers Inc.. ; , s. 1984-1985
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Konferensbidrag (refereegranskat)abstract
- Glide symmetry in periodic structures introduces several advantages such as low dispersion, wider stopbands, and higher levels of anisotropy. Here, we propose the use of glide symmetry in dielectric-filled corrugated rectangular waveguides. The operation of these filled waveguides is studied by means of a multimodal transfer-matrix approach that carries out a Bloch analysis of the corresponding unit cell to obtain the dispersion diagram of the structure (both the phase shift and the attenuation rate). In this specific configuration, glide symmetry is found to provide a wider backward passband below the cutoff of the non-corrugated housing waveguide.
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| 16. |
- Castillo Tapia, Pilar, et al.
(författare)
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Ray-Tracing Model for the Design and Efficiency Calculation of a Monolithic Geodesic Lens Array Antenna
- 2024
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Ingår i: 18th European Conference on Antennas and Propagation, EuCAP 2024. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- We propose the use of a generalized ray-tracing model to design geodesic lens array antennas. This model is capable of computing the radiation patterns and taking into account losses due to finite conductivity and surface roughness, which are essential when producing prototypes as single monolithic pieces. The ray-tracing model is used to design a modified Rinehart-Luneburg lens that shows very good agreement with simulations while significantly decreasing computation time. The profile of the lens is designed in such a way that it can be vertically stacked in an array and produced as a single piece. The lens array antenna is manufactured as a single monolithic piece using the laser powder-bed fusion technique. The tests of this prototype validate the use of additive manufacturing for geodesic lens antennas operating in V-band.
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| 17. |
- Clendinning, Sarah, et al.
(författare)
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Numerical Aspects of the Application of Ray-Tracing to Geodesic Lenses
- 2022
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Ingår i: 2022 16th European Conference on Antennas and Propagation (EuCAP). - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- This paper presents a model developed to numerically determine the radiation pattern presented by a given geodesic lens. A simplified model describing the trajectory of a TEM-mode wave through the lens was required as a time-efficient alternative to commercial software. Geometrical optics have been used to approximate the ray trajectory from the source to the aperture of the lens. The power conservation in ray tubes is then used to evaluate the amplitude of the electric field in the aperture, knowing the distribution at the source. The Kirchhoff diffraction formula is finally numerically approximated to evaluate the farfield. Three examples have been simulated with our algorithm and compared with full-wave simulations. We demonstrate that our assumptions provide a good agreement with full-wave simulation while reducing significantly the computation time, thus providing an efficient method for design optimization. Most notably, this more general formulation may be extended to non-rotationally symmetric lenses.
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| 18. |
- Clendinning, Sarah, et al.
(författare)
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Ray Tracing Model for Non-Rotationally Symmetric Geodesic Lens Antennas with Full Beam Scanning Range in the Azimuthal Plane
- 2023
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Ingår i: The 13th International Conference on Metamaterials, Photonic Crystals and Plasmonics, META 2023. - : META Conference. ; , s. 1050-1051
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Konferensbidrag (refereegranskat)abstract
- This presentation discusses a ray tracing model developed to determine the radiation pattern of geodesic lens antennas with non-rotationally symmetric footprints, where the geometry of the lens is defined using spline functions. The shape of this footprint and lens height profile can be modified by changing parameters in the defined functions. The code features a significant modification to work previously published by the authors to account for the non-rotationally symmetric design. The model runs significantly faster than commercially available software.
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| 19. |
- Clendinning, Sarah, et al.
(författare)
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Reducing the Refractive Index Range of GRIN Lenses Through the Integration of a Reflectarray
- 2023
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Ingår i: 2023 17TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION, EUCAP. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- This paper presents a half-lens antenna integrated with a reflectarray. The combination of the half-lens and the reflectarray provides additional design freedom. In this work, this design freedom is used to reduce the refractive index range required to produce a planar wavefront using a half-lens, as compared to the half-Luneburg lens. Specifically, we demonstrate that the properties of a half-Luneburg lens can be mimicked with a lens that has reduced the maximum refractive index by 30% by integrating the reflectarray with the lens.
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| 20. |
- Clendinning, Sarah, et al.
(författare)
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Tailoring the Performance of Geodesic Lens Antennas By Defining their Footprint
- 2024
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Ingår i: 18th European Conference on Antennas and Propagation, EuCAP 2024. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses non-rotationally symmetric geodesic lens antennas. By defining the shape of the lens footprint, additional degrees of freedom are introduced into the design process, allowing for further tailoring of the electromagnetic performance of the lens while simultaneously reducing the volume occupied by the lens. An in-house ray-tracing model for geodesic lenses has been modified to analyze this class of lenses. Examples showing the effect of modifying the lens profile are presented, with a more detailed discussion on profile presenting improved side-lobe levels at the extreme ports. The examples presented operate at 30 GHz.
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| 21. |
- Ebrahimpouri, Mahsa, et al.
(författare)
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Wide Angle Impedance Matching Using Glide-symmetric Metasurfaces
-
Annan publikation (populärvet., debatt m.m.)abstract
- This letter demonstrates that glide symmetry can be used to match the impedance of highly dense dielectric profiles in wide angle and broad bandwidth. Using glidesymmetric metasurfaces permits tuning the magnetic properties of materials, so high values of permittivity can be matched to free space in wide band. This matching is achieved without disturbing the performance of the device since the refractive index remains fixed. The performance of the proposed matching method is validated through measurements for normal incidence. For oblique incidence, a hyperbolic dielectric lens is matched with glide-symmetric structures in simulations. These simulations demonstrate a smooth transmission of the fields manifesting a well-matched profile of the lens.
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| 22. |
- Ebrahimpouri, Mahsa, et al.
(författare)
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Wide-Angle Impedance Matching Using Glide-Symmetric Metasurfaces
- 2020
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Ingår i: IEEE Microwave and Wireless Components Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1531-1309 .- 1558-1764. ; 30:1, s. 8-11
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Tidskriftsartikel (refereegranskat)abstract
- This letter demonstrates that glide symmetry can be used to match the impedance of highly dense dielectric profiles in wide angle and broad bandwidth. Using glide-symmetric metasurfaces permits tuning the magnetic properties of materials, so high values of permittivity can be matched to free space in wideband. This matching is achieved without disturbing the performance of the device, since the refractive index remains fixed. The performance of the proposed matching method is validated through measurements for normal incidence. For oblique incidence, a hyperbolic dielectric lens is matched with glide-symmetric structures in simulations. These simulations demonstrate a smooth transmission of the fields, manifesting a well-matched profile of the lens.
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| 23. |
- Eckert, Sebastian, et al.
(författare)
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Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering
- 2017
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 56:22, s. 6088-6092
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Tidskriftsartikel (refereegranskat)abstract
- The femtosecond excited-state dynamics following resonant photoexcitation enable the selective deformation of N-H and N-C chemical bonds in 2-thiopyridone in aqueous solution with optical or X-ray pulses. In combination with multiconfigurational quantum-chemical calculations, the orbital-specific electronic structure and its ultrafast dynamics accessed with resonant inelastic X-ray scattering at the N 1s level using synchrotron radiation and the soft X-ray free-electron laser LCLS provide direct evidence for this controlled photoinduced molecular deformation and its ultrashort time-scale.
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| 24. |
- Escobar, Ana C., et al.
(författare)
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Homogenization of Densely Packed Wire Media Using Transfer Matrix Methods
- 2023
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Ingår i: 17th International Congress on Artificial Materials for Novel Wave Phenomena, Metamaterials 2023. - : Institute of Electrical and Electronics Engineers Inc.. ; , s. 25-27
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Konferensbidrag (refereegranskat)abstract
- Multimodal Transfer Matrix Method is a powerful technique that can be used in the study of periodical structures. It allows for accurate calculation of the dispersion relation and effective constitutive parameters even for very densely packed structures. In this work, we calculate effective constitutive parameters of artificial plasmas and compare them with a theoretical model based on a cascade of surface admittances.
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| 25. |
- Escobar, A. C., et al.
(författare)
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Retrieval of the Constitutive Parameters and Dispersion Relation of Glide-Symmetric Metamaterials via the Multimodal Transfer Matrix Method
- 2020
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Ingår i: 2020 FOURTEENTH INTERNATIONAL CONGRESS ON ARTIFICIAL MATERIALS FOR NOVEL WAVE PHENOMENA (METAMATERIALS). - : IEEE.
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Konferensbidrag (refereegranskat)abstract
- We have implemented a method to retrieve the dispersion relation and the effective material constitutive parameters of a densely arranged periodic structure by solving an eigenvalue problem associated with the multimodal transfer matrix of the corresponding unit cell. The material parameters and the dispersion relation of a metasurface made of glide-symmetric square patches are here obtained with this method.
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| 26. |
- Flores-Espinosa, Núria, et al.
(författare)
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Design of a Dielectric Lens Using a Ray-Tracing Model for Satellite Communications
- 2024
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Ingår i: 18th European Conference on Antennas and Propagation, EuCAP 2024. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- In millimeter-wave applications, it is essential to use highly directional and steerable antennas. Phased array antennas are the most common choice, but they have restricted scanning coverage because of their effective aperture. To enhance the scanning coverage, a dielectric lens can be placed on top of the array. However, full-wave simulations require a lot of computing time to simulate this type of structure. In this work, a two-dimensional ray-tracing model has been adapted and improved to efficiently compute the radiation pattern of arrays combined with multilayered dielectric radomes for satellite communications applications. Moreover, this model can also calculate the absorption and reflection losses and the transmitted power required to comply with the regulatory mask. This model has been used to design a lens that increases the scanning range of an array while maintaining a maximum height and ensuring that it complies with the regulatory masks for satellite communications.
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| 27. |
- Giusti, Federico, et al.
(författare)
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Multimodal Transfer Matrix Method Applied to 3-D Periodic Structures
- 2021
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Ingår i: 2021 International Symposium on Antennas and Propagation, ISAP 2021. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- In this work, we discuss the application of the multimodal transfer matrix method (MMTMM) to compute the dispersion diagram of 3-D periodic structures. The problem of finding the complex wavenumber (both the phase and/or attenuation constants) of the different modes is posed as a standard linear eigenvalue problem in terms of the transfer matrix of the unit cell. The numerical drawbacks associated with the search of complex solutions in the complex plane are then avoided, thus making the MMTMM a useful tool to analyze and design periodic structures.
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| 28. |
- Jay, Raphael M., et al.
(författare)
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Disentangling Transient Charge Density and Metal-Ligand Covalency in Photoexcited Ferricyanide with Femtosecond Resonant Inelastic Soft X-ray Scattering
- 2018
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:12, s. 3538-3543
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Tidskriftsartikel (refereegranskat)abstract
- Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal-ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. pi-Back-donation is found to be mainly determined by the metal site occupation, whereas the ligand hole instead influences sigma-donation. Our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.
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| 29. |
- Kunnus, Kristjan, et al.
(författare)
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A setup for resonant inelastic soft x-ray scattering on liquids at free electron laser light sources
- 2012
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 83:12
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Tidskriftsartikel (refereegranskat)abstract
- We present a flexible and compact experimental setup that combines an in vacuum liquid jet with an x-ray emission spectrometer to enable static and femtosecond time-resolved resonant inelastic soft x-ray scattering (RIXS) measurements from liquids at free electron laser (FEL) light sources. We demonstrate the feasibility of this type of experiments with the measurements performed at the Linac Coherent Light Source FEL facility. At the FEL we observed changes in the RIXS spectra at high peak fluences which currently sets a limit to maximum attainable count rate at FELs. The setup presented here opens up new possibilities to study the structure and dynamics in liquids. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4772685]
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| 30. |
- Kunnus, Kristjan, et al.
(författare)
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Anti-Stokes resonant x-ray Raman scattering for atom specific and excited state selective dynamics
- 2016
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 18
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrafast electronic and structural dynamics of matter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functional materials. Since x-rays determine electronic and structural properties with elemental, chemical, orbital and magnetic selectivity, short pulse x-ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x-rays have been poor at picking up excited state moieties from the unexcited ones. With time-resolved anti-Stokes resonant x-ray Raman scattering (AS-RXRS) performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital and magnetic selectivity of x-rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe(CO)(5) in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics with AS-RXRS with transform-limited x-ray pulses is given-which will be covered experimentally by upcoming transform-limited x-ray sources.
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| 31. |
- Kunnus, Kristjan, et al.
(författare)
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From Ligand Fields to Molecular Orbitals : Probing the Local Valence Electronic Structure of Ni2+ in Aqueous Solutions with Resonant Inelastic X-ray Scattering
- 2013
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 117, s. 16512-16521
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Tidskriftsartikel (refereegranskat)abstract
- Bonding of the Ni2+(aq) complex is investigated with an unprecedented combination of resonant inelastic X-ray scattering (RIXS) measurements and ab initio calculations at the Ni L absorption edge. The spectra directly reflect the relative energies of the ligand-field and charge-transfer valence-excited states. They give element-specific access with atomic resolution to the ground-state electronic structure of the complex and allow quantification of ligand-field strength and 3d–3d electron correlation interactions in the Ni2+(aq) complex. The experimentally determined ligand-field strength is 10Dq = 1.1 eV. This and the Racah parameters characterizing 3d–3d Coulomb interactions B = 0.13 eV and C = 0.42 eV as readily derived from the measured energies match very well with the results from UV–vis spectroscopy. Our results demonstrate how L-edge RIXS can be used to complement existing spectroscopic tools for the investigation of bonding in 3d transition-metal coordination compounds in solution. The ab initio RASPT2 calculation is successfully used to simulate the L-edge RIXS spectra.
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| 32. |
- Li, Y, et al.
(författare)
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Power control of an energy harvesting sensor for remote state estimation
- 2017
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Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 62:1, s. 277-290
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Tidskriftsartikel (refereegranskat)abstract
- We investigate sensor transmission power control for remote state estimation. Instead of using a conventional sensor, a sensor equipped with an energy harvester which can obtain energy from the external environment is utilized. We formulate power control of the energy harvesting sensor into an infinite time-horizon Markov decision process (MDP). To deal with the computation complexity associated with this multi-dimensional MDP, a continuous-time approach and perturbation analysis are used and a closed-form approximate value function is derived. Based on the approximation, we obtain a closed-form optimal power control solution which has a threshold-based structure. A numerical example is provided to evaluate the estimation performance of the optimal solution compared with other power scheduling schemes.
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| 33. |
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| 34. |
- Padilla, Pablo, et al.
(författare)
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Glide-symmetric printed corrugated transmission lines with controlable stopband
- 2019
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Ingår i: 13th European Conference on Antennas and Propagation, EuCAP 2019. - : Institute of Electrical and Electronics Engineers (IEEE). - 9788890701887
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Konferensbidrag (refereegranskat)abstract
- Here, we demonstrate that the dispersion properties of printed lines can be controlled by using glide symmetry. Glide symmetry is introduced by means of corrugations in the printed lines. The glide-symmetric configuration provides a more linear propagation constant, avoiding the presence of stopband between first and second propagating modes. Additionally, the breakage of the glide-symmetric geometry introduces a tunable stopband that can be used for filtering.
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| 35. |
- Petek, M., et al.
(författare)
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An Integral-Equation Kernel for Glide Symmetric Structures
- 2023
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Ingår i: 2023 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, AP-S/URSI 2023 - Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 555-556
-
Konferensbidrag (refereegranskat)abstract
- Glide-symmetric structures can improve properties of periodic structures for a wide variety of applications, such as lenses, filters and gap waveguides. Therefore, fast and accurate tools are needed to facilitate their use. In this work, we present a modelling approach based on a method of moments with a novel Green's function. The solutions are found as singularities of the impedance matrix. The results are shown to be in good agreement with a well-established method.
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| 36. |
- Petek, M., et al.
(författare)
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Efficient Integral Equation Approach for the Modelling of Glide-Symmetric Structures
- 2023
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Ingår i: 2023 17th European Conference on Antennas and Propagation (EuCAP). - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- For the design of advanced microwave and antenna components, efficient and accurate electromagnetic methods are required. In this work, we present a technique to fast simulate mirror- and glide-symmetric periodic structures. More concretely, a novel Green's function is proposed which allows to reduce the computational domain to one half of the unit cell. Full dispersion diagrams are computed for metallic glide- and mirror-symmetric structures with three stages of mesh refinement. The results converge with the meshing and agree well with conventional eigenmode analyses.
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| 37. |
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| 38. |
- Wernet, Philippe, et al.
(författare)
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Dissecting Local Atomic and Intermolecular Interactions of Transition-Metal Ions in Solution with Selective X-ray Spectroscopy
- 2012
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 3:23, s. 3448-3453
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Tidskriftsartikel (refereegranskat)abstract
- Determining covalent and charge-transfer contributions to bonding in solution has remained an experimental challenge. Here, the quenching of fluorescence decay channels as expressed in dips in the L-edge X-ray spectra of solvated 3d transition-metal ions and complexes was reported as a probe. With a full set of experimental and theoretical ab initio L-edge X-ray spectra of aqueous Cr3+, including resonant inelastic X-ray scattering, we address covalency and charge transfer for this prototypical transition-metal ion in solution. We dissect local atomic effects from intermolecular interactions and quantify X-ray optical effects. We find no evidence for the asserted ultrafast charge transfer to the solvent and show that the dips are readily explained by X-ray optical effects and local atomic state dependence of the fluorescence yield. Instead, we find, besides ionic interactions, a covalent contribution to the bonding in the aqueous complex of ligand-to-metal charge-transfer character
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| 39. |
- Wernet, Philippe, et al.
(författare)
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Mapping chemical bonding of reaction intermediates with femtosecond X-ray laser spectroscopy
- 2013
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Ingår i: XVIIIth International Conference on Ultrafast Phenomena. - : EDP Sciences. - 9782759809561 ; , s. 05025-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We determine the pathways in the photo-dissociation reactions of Fe(CO)5 both in the gas phase and in solution by mapping the valence electronic structure of the reaction intermediates with femtosecond X-ray laser spectroscopy.
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