| 1. |
- Abazajian, Kevork, et al.
(författare)
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CMB-S4 : Forecasting Constraints on Primordial Gravitational Waves
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 926:1
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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.
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| 2. |
- Oliveira, Camila, et al.
(författare)
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Surface studies of the chemical environment in gold nanorods supported by X-ray photoelectron spectroscopy (XPS) and ab initio calculations
- 2021
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Ingår i: JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T. - : Elsevier BV. - 2238-7854. ; 15, s. 768-776
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Tidskriftsartikel (refereegranskat)abstract
- In this manuscript, we prepared gold nanorods (Au-NRs) through "silver-assisted seeded methodology" and studied their outermost layer using XPS spectroscopy and ab initio calculations to compare the chemical states of the constituents of the metallic core. Supporting first-principles calculations employing a relativistic, full-potential and all-electron method, with augmented plane waves plus local orbitals as a basis set, ensure proper treatment of the core electron states. Three significant findings can be reported. First, we found that besides Au (0), there are two chemical states for silver, namely Ag (0) and Ag(I), on the Au surface. Our results corroborate with recent results reported in the literature, indicating that Ag monolayer can be oxidized to Ag(I) during the steps of centrifugation and washing with diluted CTAB solution. Second, ab initio simulations showed that Ag atoms have different binding energies, depending on their configuration in Au-NRs (whether silver atoms are found on the surface or if they are spread in bulk as interstitial or substitutional defects). Third, theoretical studies showed that silver atoms located at interstitial sites could distort the crystalline structure, and, therefore, we do not expect interstitial Ag to occur in Au-NRs.
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