| 1. |
- Abazajian, Kevork, et al.
(författare)
-
CMB-S4 : Forecasting Constraints on Primordial Gravitational Waves
- 2022
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 926:1
-
Tidskriftsartikel (refereegranskat)abstract
- CMB-S4—the next-generation ground-based cosmic microwave background (CMB) experiment—is set to significantly advance the sensitivity of CMB measurements and enhance our understanding of the origin and evolution of the universe. Among the science cases pursued with CMB-S4, the quest for detecting primordial gravitational waves is a central driver of the experimental design. This work details the development of a forecasting framework that includes a power-spectrum-based semianalytic projection tool, targeted explicitly toward optimizing constraints on the tensor-to-scalar ratio, r, in the presence of Galactic foregrounds and gravitational lensing of the CMB. This framework is unique in its direct use of information from the achieved performance of current Stage 2–3 CMB experiments to robustly forecast the science reach of upcoming CMB-polarization endeavors. The methodology allows for rapid iteration over experimental configurations and offers a flexible way to optimize the design of future experiments, given a desired scientific goal. To form a closed-loop process, we couple this semianalytic tool with map-based validation studies, which allow for the injection of additional complexity and verification of our forecasts with several independent analysis methods. We document multiple rounds of forecasts for CMB-S4 using this process and the resulting establishment of the current reference design of the primordial gravitational-wave component of the Stage-4 experiment, optimized to achieve our science goals of detecting primordial gravitational waves for r > 0.003 at greater than 5σ, or in the absence of a detection, of reaching an upper limit of r < 0.001 at 95% CL.
|
|
| 2. |
- Kunnus, Kristjan, et al.
(författare)
-
Chemical control of competing electron transfer pathways in iron tetracyano-polypyridyl photosensitizers
- 2020
-
Ingår i: Chemical Science. - : ROYAL SOC CHEMISTRY. - 2041-6520 .- 2041-6539. ; 11:17, s. 4360-4373
-
Tidskriftsartikel (refereegranskat)abstract
- Photoinduced intramolecular electron transfer dynamics following metal-to-ligand charge-transfer (MLCT) excitation of [Fe(CN)(4)(2,2 '-bipyridine)](2-) (1), [Fe(CN)(4)(2,3-bis(2-pyridyl)pyrazine)](2-) (2) and [Fe(CN)(4)(2,2 '-bipyrimidine)](2-) (3) were investigated in various solvents with static and time-resolved UV-Visible absorption spectroscopy and Fe 2p3d resonant inelastic X-ray scattering (RIXS). This series of polypyridyl ligands, combined with the strong solvatochromism of the complexes, enables the (MLCT)-M-1 vertical energy to be varied from 1.64 eV to 2.64 eV and the (MLCT)-M-3 lifetime to range from 180 fs to 67 ps. The (MLCT)-M-3 lifetimes in 1 and 2 decrease exponentially as the MLCT energy increases, consistent with electron transfer to the lowest energy triplet metal-centred ((MC)-M-3) excited state, as established by the Tanabe-Sugano analysis of the Fe 2p3d RIXS data. In contrast, the (MLCT)-M-3 lifetime in 3 changes non-monotonically with MLCT energy, exhibiting a maximum. This qualitatively distinct behaviour results from a competing (MLCT)-M-3 -> ground state (GS) electron transfer pathway that exhibits energy gap law behaviour. The (MLCT)-M-3 -> GS pathway involves nuclear tunnelling for the high-frequency polypyridyl breathing mode (h nu = 1530 cm(-1)), which is most displaced for complex 3, making this pathway significantly more efficient. Our study demonstrates that the excited state relaxation mechanism of Fe polypyridyl photosensitizers can be readily tuned by ligand and solvent environment. Furthermore, our study reveals that extending charge transfer lifetimes requires control of the relative energies of the (MLCT)-M-3 and the (MC)-M-3 states and suppression of the intramolecular distortion of the acceptor ligand in the (MLCT)-M-3 excited state.
|
|
