| 1. |
- Andrews, Jennifer E., et al.
(author)
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SN 2017gmr : An Energetic Type II-P Supernova with Asymmetries
- 2019
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 885:1
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Journal article (peer-reviewed)abstract
- We present high-cadence UV, optical, and near-infrared data on the luminous Type II-P supernova SN;2017gmr from hours after discovery through the first 180 days. SN;2017gmr does not show signs of narrow, high-ionization emission lines in the early optical spectra, yet the optical light-curve evolution suggests that an extra energy source from circumstellar medium (CSM) interaction must be present for at least 2 days after explosion. Modeling of the early light curve indicates a ?500 R progenitor radius, consistent with a rather compact red supergiant, and late-time luminosities indicate that up to 0.130;;0.026 M of Ni-56 are present, if the light curve is solely powered by radioactive decay, although the Ni-56 mass may be lower if CSM interaction contributes to the post-plateau luminosity. Prominent multipeaked emission lines of H? and [O i] emerge after day 154, as a result of either an asymmetric explosion or asymmetries in the CSM. The lack of narrow lines within the first 2 days of explosion in the likely presence of CSM interaction may be an example of close, dense, asymmetric CSM that is quickly enveloped by the spherical supernova ejecta.
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| 2. |
- Hao, Zhengming, et al.
(author)
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From n-alkane to polyacetylene on Cu (110): Linkage modulation in chain growth
- 2022
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In: Science in China Series B. - : SCIENCE PRESS. - 1674-7291 .- 1869-1870. ; 65:4, s. 733-739
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Journal article (peer-reviewed)abstract
- Direct coupling or transformation of inert alkanes based on the selective C-H activation is of great importance for both chemistry and chemical engineering. Here, we report the coupling of polyenes that are transformed from n-dotriacontane (n-C32H66) through on-surface cascade dehydrogenation on Cu (110) surface, leading to the formation of polyacetylene (PA). Three distinct linkages have been resolved by scanning tunneling microscope (STM) and noncontact atomic force microscope (nc-AFM). Apart from the alpha-type linkage which is the stemless coupling of the terminal C-C double bond in trans-configuration, beta- and gamma-type linkages appear as knots or defects which are, in fact, the C-C couplings in cis-configurations. Interestingly, the "defects" can be effectively suppressed by adjusting the surface coverage, thus making it of general interest for uniform structure modulation.
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| 3. |
- Liu, Peiji, et al.
(author)
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A generalized method for the inherent energy performance modeling of machine tools
- 2021
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In: Journal of manufacturing systems. - : Elsevier BV. - 0278-6125 .- 1878-6642. ; 61, s. 406-422
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Journal article (peer-reviewed)abstract
- Machine tools (MTs), as the key equipment of manufacturing systems, have enormous quantities and consume a great amount of energy. However, the diversity of both machines and their energy consumption properties make it difficult to transfer the energy-saving knowledge and services among different MT. To facilitate the initialization configuration of energy-saving services, the inherent energy performance (IEP) is investigated to describe the differences in energy consumption among MTs, and a generalized method for modeling the IEP of MT and its electrical subsystems is proposed. Three key enablers, including generalized experimental design rules, automatic coding, and data processing algorithms, are presented and integrated into a supporting system to reduce the modeling efforts and knowledge requirements. Case studies of an offline manufacturing scenario and an Internet of Things (IoT)-enabled manufacturing scenario were carried out to verify the effectiveness and convenience of the proposed method. The results show that the proposed method can provide essential modeling support for large-scale energy-saving service configurations and energy-efficient MT development.
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| 4. |
- Bruce, Louise C, et al.
(author)
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A multi-lake comparative analysis of the General Lake Model (GLM) : Stress-testing across a global observatory network
- 2018
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In: Environmental Modelling & Software. - : Elsevier BV. - 1364-8152 .- 1873-6726. ; 102, s. 274-291
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Journal article (peer-reviewed)abstract
- The modelling community has identified challenges for the integration and assessment of lake models due to the diversity of modelling approaches and lakes. In this study, we develop and assess a one-dimensional lake model and apply it to 32 lakes from a global observatory network. The data set included lakes over broad ranges in latitude, climatic zones, size, residence time, mixing regime and trophic level. Model performance was evaluated using several error assessment metrics, and a sensitivity analysis was conducted for nine parameters that governed the surface heat exchange and mixing efficiency. There was low correlation between input data uncertainty and model performance and predictions of temperature were less sensitive to model parameters than prediction of thermocline depth and Schmidt stability. The study provides guidance to where the general model approach and associated assumptions work, and cases where adjustments to model parameterisations and/or structure are required.
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| 5. |
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| 6. |
- Song, Luying, et al.
(author)
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Intra- and Inter-Self-Assembly of Identical Supramolecules on Silver Surfaces
- 2022
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In: The Journal of Physical Chemistry Letters. - : AMER CHEMICAL SOC. - 1948-7185. ; 13:38, s. 8902-8907
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Journal article (peer-reviewed)abstract
- Self-assembly of identical organometallic supra -molecules into ordered superstructures is of great interest in both chemical science and nanotechnology due to its potential to generate neoteric properties through collective effects. In this work, we demonstrate that large-scale self-organization of atomically precise organometallic supramolecules can be achieved through cascaded on-surface chemical reactions, by the combination of intra-and inter-supramolecular interactions. Supramolecules with defined size and shape are first built through intramolecular reaction and intermolecular metal coordination, followed by the formation of well-ordered two-dimensional arrays with the assistance of Br atoms by-C-HmiddotmiddotmiddotBr interactions. The mechanism of this process has been investigated from the perspectives of thermodynamics and kinetics.
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| 7. |
- Song, Luying, et al.
(author)
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Synthesis of Two-Dimensional Metal-Organic Frameworks via Dehydrogenation Reactions on a Cu(111) Surface
- 2020
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In: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:23, s. 12390-12396
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Journal article (peer-reviewed)abstract
- Metal-organic frameworks prepared on surfaces (SMOFs) have been considered to have potential applications in various research fields. Traditionally, the SMOFs are prepared by coadsorbing organic ligands and metal atoms on surfaces. In this article, we successfully construct the SMOFs via the dehydrogenation reactions of aromatic amines on the Cu(111) surfaces. The dehydrogenated nitrogen radicals interact with the copper adatoms, forming the N-Cu-N bonds. Combining with the scanning tunneling microscopy and the density functional theory calculations, we obtain the structural models of the SMOFs.
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| 8. |
- Wang, Junbo, et al.
(author)
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Influence of Molecular Configurations on the Desulfonylation Reactions on Metal Surfaces
- 2022
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In: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 144:47, s. 21596-21605
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Journal article (peer-reviewed)abstract
- On-surface synthesis is a powerful methodology for the fabrication of low-dimensional functional materials. The precursor molecules usually anchor on different metal surfaces via similar configurations. The activation energies are therefore solely determined by the chemical activity of the respective metal surfaces. Here, we studied the influence of the detailed adsorption configuration on the activation energy on different metal surfaces. We systematically studied the desulfonylation homocoupling for a molecular precursor on Au(111) and Ag(111) and found that the activation energy is lower on inert Au(111) than on Ag(111). Combining scanning tunneling microscopy observations, synchrotron radiation photoemission spectroscopy measurements, and density functional theory calculations, we elucidate that the phenomenon arises from different molecule-substrate interactions. The molecular precursors anchor on Au(111) via Au-S interactions, which lead to weakening of the phenyl-S bonds. On the other hand, the molecular precursors anchor on Ag(111) via Ag-O interactions, resulting in the lifting of the S atoms. As a consequence, the activation barrier of the desulfonylation reactions is higher on Ag(111), although silver is generally more chemically active than gold. Our study not only reports a new type of on-surface chemical reaction but also clarifies the influence of detailed adsorption configurations on specific on-surface chemical reactions.
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| 9. |
- Wang, Junbo, et al.
(author)
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Universal inter-molecular radical transfer reactions on metal surfaces
- 2024
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In: Nature Communications. - : NATURE PORTFOLIO. - 2041-1723. ; 15:1
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Journal article (peer-reviewed)abstract
- On-surface synthesis provides tools to prepare low-dimensional supramolecular structures. Traditionally, reactive radicals are a class of single-electron species, serving as exceptional electron-withdrawing groups. On metal surfaces, however, such species are affected by conduction band screening effects that may even quench their unpaired electron characteristics. As a result, radicals are expected to be less active, and reactions catalyzed by surface-stabilized radicals are rarely reported. Herein, we describe a class of inter-molecular radical transfer reactions on metal surfaces. With the assistance of aryl halide precursors, the coupling of terminal alkynes is steered from non-dehydrogenated to dehydrogenated products, resulting in alkynyl-Ag-alkynyl bonds. Dehalogenated molecules are fully passivated by detached hydrogen atoms. The reaction mechanism is unraveled by various surface-sensitive technologies and density functional theory calculations. Moreover, we reveal the universality of this mechanism on metal surfaces. Our studies enrich the on-surface synthesis toolbox and develop a pathway for producing low-dimensional organic materials. Radicals are expected to be inactive on metal surfaces. Here the authors describe general intermolecular radical transfer reactions on Ag and Cu surfaces and confirm the reaction mechanism by extensive control experiments.
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| 10. |
- Wang, Mengwei, et al.
(author)
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Different or the same? exploring the physicochemical properties and molecular mobility of celecoxib amorphous forms
- 2024
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In: International Journal of Pharmaceutics. - 0378-5173. ; 661
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Journal article (peer-reviewed)abstract
- The influence of different preparation methods on the physicochemical properties of amorphous solid forms have gained considerable attention, especially with recent publications on pharmaceutical polyamorphism. In the present study, we have investigated the possible occurrence of polyamorphism in the drug celecoxib (CEL) by investigating the thermal behavior, morphology, structure, molecular mobility and physical stability of amorphous CEL obtained by quench-cooling (QC), ball milling (BM) and spray drying (SD). Similar glass transition temperatures but different recrystallization behaviors were observed for CEL-QC, CEL-BM and CEL-SD using modulated differential scanning calorimetry analysis. A correlation between the different recrystallization behaviors of the three CEL amorphous forms and the respective distinct powder morphologies, was also found. Molecular dynamics simulations however, reveal that CEL presents similar molecular conformational distributions when subjected to QC and SD. Moreover, the obtained molecular conformational distributions of CEL are different from the ones found in its crystal structure and also from the ones found in the lowest-energy structure obtained by quantum mechanical calculations. The type and strength of CEL hydrogen bond interactions found in CEL-QC and CEL-SD systems are almost identical, though different from the ones presented in the crystal structure. Pair distribution function analyses and isothermal microcalorimetry show similar local structures and structural relaxation times, respectively, for CEL-QC, CEL-BM and CEL-SD. The present work shows that not only similar physicochemical properties (glass transition temperature, and structural relaxation time), but also similar molecular conformational distributions were observed for all prepared CEL amorphous systems. Hence, despite their different recrystallization behaviors, the three amorphous forms of CEL did not show any signs of polyamorphism.
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| 11. |
- Wang, Xiaodi, et al.
(author)
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Surrogate model enabled deep reinforcement learning for hybrid energy community operation
- 2021
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In: Applied Energy. - : ELSEVIER SCI LTD. - 0306-2619 .- 1872-9118. ; 289
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Journal article (peer-reviewed)abstract
- Local peer-to-peer (P2P) transactions in a community are becoming a trend for energy integration and man-agement. The introduction of P2P trading scheme requires comprehensive consideration on various aspects, such as peer privacy, computational efficiency, network security and operational economics. This paper provides a novel hybrid community P2P market framework for multi-energy systems, where a data-driven market surrogate model-enabled deep reinforcement learning (DRL) method is proposed to facilitate P2P transaction within technical constraints of the community delivery networks. Specifically, to achieve privacy protection, a market surrogate model based on deep belief network (DBN) is developed to characterize P2P transaction behaviors of peers in the community without disclosing their private data. Since the energy inputs and outputs of peers are highly correlated with real time signals of retail energy prices, the data-driven market surrogate model is further integrated into the DRL-enabled optimization model of a community agent (CA) for on-line retail energy price generation. Particularly, by integrating network constraints into DRL reward function, the P2P transaction scheme among community peers under specific retail energy price is guaranteed to proceed within a feasible region of community networks. Numerical results indicate that the proposed market framework can achieve 7.6% energy cost saving for community peers over none P2P transaction scheme while increase 284.4$ economic benefits for CA in one day over other comparison algorithms. This study provides an effective prototype to supplement existing P2P markets.
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| 12. |
- Yang, Bernard, et al.
(author)
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A New Thermal Categorization of Ice-Covered Lakes
- 2021
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:3
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Journal article (peer-reviewed)abstract
- Lakes are traditionally classified based on their thermal regime and trophic status. While this classification adequately captures many lakes, it is not sufficient to understand seasonally ice‐covered lakes, the most common lake type on Earth. We describe the inverse thermal stratification in 19 highly varying lakes and derive a model that predicts the temperature profile as a function of wind stress, area, and depth. The results suggest an additional subdivision of seasonally ice‐covered lakes to differentiate underice stratification. When ice forms in smaller and deeper lakes, inverse stratification will form with a thin buoyant layer of cold water (near 0°C) below the ice, which remains above a deeper 4°C layer. In contrast, the entire water column can cool to ∼0°C in larger and shallower lakes. We suggest these alternative conditions for dimictic lakes be termed “cryostratified” and “cryomictic.”
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| 13. |
- Zhu, Liping, et al.
(author)
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A similar to 30,000-year record of environmental changes inferred from Lake Chen Co, Southern Tibet
- 2009
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In: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 42:3, s. 343-358
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Journal article (peer-reviewed)abstract
- Climatic and environmental changes since the last glacial period are important to our understanding of global environmental change. There are few records from Southern Tibet, one of the most climatically sensitive areas on earth. Here we present a study of the lake sediments (TC1 core) from Lake Chen Co, Southern Tibet. Two sediment cores were drilled using a hydraulic borer in Terrace 1 of Lake Chen Co. AMS C-14 dating of the sediments showed that the sequence spanned > 30,000 years. Analyses of present lake hydrology indicated that glacier melt water is very important to maintaining the lake level. Sediment variables such as grain size, TOC, TN, C/N, Fe/Mn, CaCO3, and pollen were analyzed. Warm and moderately humid conditions dominated during the interval 30,000-26,500 cal year BP. From 26,500 to 20,000 cal year BP, chemical variables and pollen assemblages indicate a cold/dry environment, and pollen amounts and assemblages suggest a decline in vegetation. From 20,000 to 18,000 cal year BP, the environment shifted from cold/dry to warm/humid and vegetation rebounded. The environment transitioned to cold/humid during 16,500-10,500 cal year BP, with a cold/dry event around 14,500 cal year BP. After 10,500 cal year BP, the environment in this region tended to be warm/dry, but exhibited three stages. From 10,500 to 9,000 cal year BP, there was a short warm/humid period, but a shift to cold/dry conditions occurred around 9,000 cal year BP. Thereafter, from 9,000 to 6,000 cal year BP, there was a change from cold/dry to warm/humid conditions, with the warmest period around 6,000 cal year BP. After 6,000 cal year BP, the environment cooled rapidly, but then displayed a warming trend. Chemical variables indicate that a relatively warm/dry event occurred around 5,500-5,000 cal year BP, which is supported by time-lagged pollen assemblages around 4,800 cal year BP. Our lake sediment sequence exhibits environmental changes since 30,000 cal year BP, and most features agree with records from the Greenland GISP2 ice core and with other sequences from the Tibetan Plateau. This indicates that environmental changes inferred from Lake Chen Co, Southern Tibet were globally significant.
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