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841.
A subset U of a group G is called k-universal if U contains a translate of every k-element subset of G. We give several nearly optimal constructions of small k-universal sets, and use them to resolve an old question of Erdős and Newman on bases for sets of integers, and to obtain
several extensions for other groups. 相似文献
842.
Eric Ofosu Kissi Robin Nilsson Liebert Parreiras Nogueira Anette Larsson Ingunn Tho 《Molecules (Basel, Switzerland)》2021,26(15)
Fused deposition modelling-based 3D printing of pharmaceutical products is facing challenges like brittleness and printability of the drug-loaded hot-melt extruded filament feedstock and stabilization of the solid-state form of the drug in the final product. The aim of this study was to investigate the influence of the drug load on printability and physical stability. The poor glass former naproxen (NAP) was hot-melt extruded with Kollidon® VA 64 at 10–30% w/w drug load. The extrudates (filaments) were characterised using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). It was confirmed that an amorphous solid dispersion was formed. A temperature profile was developed based on the results from TGA, DSC, and DMA and temperatures used for 3D printing were selected from the profile. The 3D-printed tablets were characterised using DSC, X-ray computer microtomography (XµCT), and X-ray powder diffraction (XRPD). From the DSC and XRPD analysis, it was found that the drug in the 3D-printed tablets (20 and 30% NAP) was amorphous and remained amorphous after 23 weeks of storage (room temperature (RT), 37% relative humidity (RH)). This shows that adjusting the drug ratio can modulate the brittleness and improve printability without compromising the physical stability of the amorphous solid dispersion. 相似文献
843.
844.
Dr. Laura M. McCaslin Dr. Andreas W. Götz Prof. Mark A. Johnson Prof. R. Benny Gerber 《Chemphyschem》2023,24(5):e202300085
The reaction of N2O5 at atmospheric interfaces has recently received considerable attention due to its importance in atmospheric chemistry. N2O5 reacts preferentially with Cl− to form ClNO2/NO3− (Cl− substitution), but can also react with H2O to form 2HNO3 (hydrolysis). In this paper, we explore these competing reactions in a theoretical study of the clusters N2O5/Cl−/nH2O (n=2–5), resulting in the identification of three reaction motifs. First, we uncovered an SN2-type Cl− substitution reaction of N2O5 that occurs very quickly due to low barriers to reaction. Second, we found a low-lying pathway to hydrolysis via a ClNO2 intermediate (two-step hydrolysis). Finally, we found a direct hydrolysis pathway where H2O attacks N2O5 (one-step hydrolysis). We find that Cl− substitution is the fastest reaction in every cluster. Between one-step and two-step hydrolysis, we find that one-step hydrolysis barriers are lower, making two-step hydrolysis (via ClNO2 intermediate) likely only when concentrations of Cl− are high. 相似文献