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排序方式: 共有1093条查询结果,搜索用时 15 毫秒
1.
Philomena Schlexer Anton Bay Andersen Bela Sebok Ib Chorkendorff Jakob Schitz Thomas W. Hansen 《Particle & Particle Systems Characterization》2019,36(3)
Nanoparticles have an immense importance in various fields, such as medicine, catalysis, and various technological applications. Nanoparticles exhibit a significant depression in melting point as their size goes below ≈10 nm. However, nanoparticles are frequently used in high temperature applications such as catalysis where temperatures often exceed several 100 degrees which makes it interesting to study not only the melting temperature depression, but also how the melting progresses through the particle. Using high‐resolution transmission electron microscopy, the melting process of gold nanoparticles in the size range of 2–20 nm Au nanoparticles combined with molecular dynamics studies is investigated. A linear dependence of the melting temperature on the inverse particle size is confirmed; electron microscopy imaging reveals that the particles start melting at the surface and the liquid shell formed then rapidly expands to the particle core. 相似文献
2.
Rebeca P. Medina Angela R. Araujo Raymond J. Andersen Marcos A. Soares Fabio de A. Silva 《Natural product research》2019,33(3):443-446
Endophytic fungi were isolated from red alga Asparagopsis taxiformis - Falkenbergia stage, collected from the Brazilian coast, and were identified as Annulohypoxylon stygium (AT-03) and A. yungensis (AT-06) based on their macro/micromorphological and molecular features. Bioassay-guided fractionation of the EtOAc extract from laboratory cultures of both strains yielded known compounds pyrogallol from A. stygium, (3R)-scytalone and (3R,4R)-4-hydroxy-scytalone from A. yungensis. Pyrogallol was active against methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli strains. An inactive fraction from A. stygium afforded two additional compounds, (3R,4R)-3,4,5-trihydroxy-1-tetralone and tyrosol. Optically active compounds had their stereochemistry determined by circular dichroism (CD) spectroscopy. 相似文献
3.
Transport in Porous Media - A numerical model is investigated representing counter-current spontaneous imbibition of water to displace oil or gas from a core plug. The model is based on mass and... 相似文献
4.
Graphitic‐Carbon Layers on Oxides: Toward Stable Heterogeneous Catalysts for Biomass Conversion Reactions 下载免费PDF全文
Dr. Haifeng Xiong Thomas J. Schwartz Nalin I. Andersen Prof. James A. Dumesic Prof. Abhaya K. Datye 《Angewandte Chemie (International ed. in English)》2015,54(27):7939-7943
Conversion of biomass‐derived molecules involves catalytic reactions under harsh conditions in the liquid phase (e.g., temperatures of 250 °C and possibly under either acidic or basic conditions). Conventional oxide‐supported catalysts undergo pore structure collapse and surface area reduction leading to deactivation under these conditions. Here we demonstrate an approach to deposit graphitic carbon to protect the oxide surface. The heterogeneous catalysts supported on the graphitic carbon/oxide composite exhibit excellent stability (even under acidic conditions) for biomass conversion reactions. 相似文献
5.
Fourier transform infrared (FTIR) smog chamber techniques were used to investigate the atmospheric chemistry of the isotopologues of methane. Relative rate measurements were performed to determine the kinetics of the reaction of the isotopologues of methane with OH radicals in cm3 molecule−1 s−1 units: k(CH3D + OH) = (5.19 ± 0.90) × 10−15, k(CH2D2 + OH) = (4.11 ± 0.74) × 10−15, k(CHD3 + OH) = (2.14 ± 0.43) × 10−15, and k(CD4 + OH) = (1.17 ± 0.19) × 10−15 in 700 Torr of air diluent at 296 ± 2 K. Using the determined OH rate coefficients, the atmospheric lifetimes for CH4–xDx (x = 1–4) were estimated to be 6.1, 7.7, 14.8, and 27.0 years, respectively. The results are discussed in relation to previous measurements of these rate coefficients. 相似文献
6.
7.
Graeme W. Carlile Robert A. Keyzers Katrina A. Teske Renaud Robert David E. Williams Roger G. Linington Christopher A. Gray Ryan M. Centko Luping Yan Suzana M. Anjos Heidi M. Sampson Donglei Zhang Jie Liao John W. Hanrahan Raymond J. Andersen David Y. Thomas 《Chemistry & biology》2012,19(10):1288-1299
8.
Louis Nilsson Mie Andersen Jacob Bjerre Richard Balog Bjørk Hammer Liv Hornekær Ivan Stensgaard 《Surface science》2012,606(3-4):464-469
Scanning tunneling microscopy shows that a layer of graphene can be grown on the hex-reconstructed Pt(100) surface and that the reconstruction is preserved after growth. A continuous sheet of graphene can be grown across domain boundaries and step edges without loss of periodicity or change in direction. Density functional theory calculations on a simple model system support the observation that the graphene can have different rotation angles relative to the hex-reconstructed Pt surface. The graphene sheet direction can be changed by incorporating pentagon-heptagon defects giving rise to accommodation of edge dislocations. The defect formation energy and the induced buckling of the graphene have been characterized by DFT calculations. 相似文献
9.
Eva C. Sonnenschein Marc Stierhof Stephan Goralczyk Floriane M. Vabre Leonie Pellissier Kine Østnes Hanssen Mercedes de la Cruz Caridad Díaz Peter de Witte Daniëlle Copmans Jeanette Hammer Andersen Espen Hansen Venke Kristoffersen José R. Tormo Rainer Ebel Bruce F. Milne Hai Deng Lone Gram Jioji N. Tabudravu 《Tetrahedron》2017,73(18):2633-2637
A new siderophore containing a 4,5-dihydroimidazole moiety was isolated from Pseudoalteromonas piscicida S2040 together with myxochelins A and B, alteramide A and its cycloaddition product, and bromo- and dibromoalterochromides. The structure of pseudochelin A was established by spectroscopic techniques including 2D NMR and MS/MS fragmentation data. In bioassays selected fractions of the crude extract of S2040 inhibited the opportunistic pathogen Pseudomonas aeruginosa. Pseudochelin A displayed siderophore activity in the chrome azurol S assay at concentrations higher than 50 μM, and showed weak activity against the fungus Aspergillus fumigatus, but did not display antibacterial, anti-inflammatory or anticonvulsant activity. 相似文献
10.
Andreas Klitgaard Anita Iversen Mikael R. Andersen Thomas O. Larsen Jens Christian Frisvad Kristian Fog Nielsen 《Analytical and bioanalytical chemistry》2014,406(7):1933-1943
In natural-product drug discovery, finding new compounds is the main task, and thus fast dereplication of known compounds is essential. This is usually performed by manual liquid chromatography-ultraviolet (LC-UV) or visible light-mass spectroscopy (Vis-MS) interpretation of detected peaks, often assisted by automated identification of previously identified compounds. We used a 15 min high-performance liquid chromatography–diode array detection (UHPLC–DAD)–high-resolution MS method (electrospray ionization (ESI)+ or ESI?), followed by 10–60 s of automated data analysis for up to 3000 relevant elemental compositions. By overlaying automatically generated extracted-ion chromatograms from detected compounds on the base peak chromatogram, all major potentially novel peaks could be visualized. Peaks corresponding to compounds available as reference standards, previously identified compounds, and major contaminants from solvents, media, filters etc. were labeled to differentiate these from compounds only identified by elemental composition. This enabled fast manual evaluation of both known peaks and potential novel-compound peaks, by manual verification of: the adduct pattern, UV–Vis, retention time compared with log D, co-identified biosynthetic related compounds, and elution order. System performance, including adduct patterns, in-source fragmentation, and ion-cooler bias, was investigated on reference standards, and the overall method was used on extracts of Aspergillus carbonarius and Penicillium melanoconidium, revealing new nitrogen-containing biomarkers for both species. 相似文献