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1. The missing base molecules in atmospheric acid–base nucleation

   https://doi.org/10.1093/nsr/nwac137  

   Cai, Runlong; Yin, Rujing; Yan, Chao; Yang, Dongsen; Deng, Chenjuan; Dada, Lubna; Kangasluoma, Juha; Kontkanen, Jenni; Halonen, Roope; Ma, Yan; et al (July 2022, National Science Review)

   Abstract Transformation of low-volatility gaseous precursors to new particles affects aerosol number concentration, cloud formation and hence the climate. The clustering of acid and base molecules is a major mechanism driving fast nucleation and initial growth of new particles in the atmosphere. However, the acid–base cluster composition, measured using state-of-the-art mass spectrometers, cannot explain the measured high formation rate of new particles. Here we present strong evidence for the existence of base molecules such as amines in the smallest atmospheric sulfuric acid clusters prior to their detection by mass spectrometers. We demonstrate that forming (H2SO4)1(amine)1 is the rate-limiting step in atmospheric H2SO4-amine nucleation and the uptake of (H2SO4)1(amine)1 is a major pathway for the initial growth of H2SO4 clusters. The proposed mechanism is very consistent with measured new particle formation in urban Beijing, in which dimethylamine is the key base for H2SO4 nucleation while other bases such as ammonia may contribute to the growth of larger clusters. Our findings further underline the fact that strong amines, even at low concentrations and when undetected in the smallest clusters, can be crucial to particle formation in the planetary boundary layer. 

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2. Solvable base change

   https://doi.org/10.1515/crelle-2020-0023  

   Clozel, Laurent; Rajan, Conjeeveram S. (August 2020, Journal für die reine und angewandte Mathematik (Crelles Journal))

   Abstract We determine the image and the fibers for solvable base change. 

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3. Photodynamics of alternative DNA base isoguanine

   https://doi.org/10.1039/c9cp01622h  

   Gate, Gregory; Szabla, Rafał; Haggmark, Michael R.; Šponer, Jiří; Sobolewski, Andrzej L.; de Vries, Mattanjah S. (January 2019, Physical Chemistry Chemical Physics)

   Isoguanine is an alternative nucleobase that has been proposed as a component of expanded genetic codes. It has also been considered as a molecule with potential relevance to primordial informational polymers. Here, we scrutinize the photodynamics of isoguanine, because photostability has been proposed as a critical criterion for the prebiotic selection of biomolecular building blocks on an early Earth. We discuss resonance-enhanced multiphoton ionization, IR-UV double resonance spectroscopy and pump–probe measurements performed for this molecule to track the excited-state behaviour of its different tautomeric forms in the gas phase. These experiments, when confronted with highly accurate quantum chemical calculations and nonadiabatic dynamics simulations provide a complete mechanistic picture of the tautomer-specific photodynamics of isoguanine. Our results indicate that UV-excited enol tautomers of isoguanine are relatively short lived and therefore photostable. In contrast, the biologically more relevant keto forms are trapped in dark nπ* states which are sufficiently long lived to participate in destructive photochemistry. The resulting lower photostability compared to canonical nucleobases may have been one of the reasons why isoguanine was not incorporated into DNA and RNA. 

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4. Stability of organic permeable base transistors

   https://doi.org/10.1063/1.5125233  

   Subedi, Kashi; Al-Shadeedi, Akram; Lussem, Bjorn (November 2019, Applied physics letters)

   Organic Permeable Base Transistors (OPBTs) reach a very high transit frequency and large on-state currents. However, for a later commercial application of this technology, a high operational stability is essential as well. Here, the stability of OPBTs during continuous cycling and during base bias stress is discussed. It is observed that the threshold voltage of these transistors shifts toward more positive base voltages if stressed by applying a constant potential to the base electrode for prolonged times. With the help of a 2D device simulation, it is proposed that the observed instabilities are due to charges that are trapped on top of an oxide layer formed around the base electrode. These charges are thermally released after removing the stress, and the device reaches its initial performance after around 24–48 h. 

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5. Influence of biaxial interaction of hysteretic restoring base forces on wind-induced inelastic response of base-isolated tall buildings

   https://doi.org/10.1177/13694332221130794  

   Tian, Jingying; Chen, Xinzhong (October 2022, Advances in Structural Engineering)

   This study addresses the influence of biaxial interaction of hysteretic restoring forces of base isolation system on wind-induced response of base-isolated tall buildings. Both buildings with and without eccentricity in center of resistance are considered. Response history analysis is carried out to characterize the coupled responses of a square-shaped base-isolated tall building. A comprehensive parameter study is presented which covers a wide range of yielding level, response ratio and correlation of alongwind and crosswind base displacements. The results demonstrate that the biaxial interaction leads to increase in low-frequency component and decrease in resonant component of lower inelastic base displacement. However, the increase of low-frequency component of base displacement does not affect the upper building response relative to base isolation system. As a result, the upper building response is reduced by the influence of biaxial interaction. The biaxal interaction also results in fast growth of time-varying mean alongwind base displacement. The increase of low-frequency component can be significant when the yielding level of higher response is significant and two translational base displacements are quite different in magnitude. The correlation of two translational base displacements enhances the influence of biaxial interaction. For the base-isolated building with eccentricity, the alongwind and crosswind base responses are closer in magnitudes thus are less influenced by the biaxial interaction. 

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