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排序方式: 共有10000条查询结果,搜索用时 62 毫秒
61.
Minh Nguyen Vo Jonathan P. Ruffley J. Karl Johnson 《American Institute of Chemical Engineers》2021,67(3):e17156
Metal organic frameworks (MOFs) containing zirconium secondary building units (SBUs) in UiO-67 and related MOFs, are highly active for neutralizing both the chemical warfare agents and simulants, such as dimethyl methylphosphonate (DMMP). However, two recent publications gave conflicting reports of DMMP reaction with UiO-67 under ultra high vacuum (UHV) conditions, with one reporting chemisorption and reaction (Wang et al., J Phys Chem C, 2017, 121, 11261–11272) and the other reporting only physisorption and reversible desorption (Ruffley et al., J Phys Chem C, 2019, 123, 19748–19758) from very similar temperature programmed desorption experiments. We show that the discrepancy between these experiments may be explained by different levels of missing linker defects in the UiO-67 samples. We present density functional theory calculations showing that SBU sites having two-adjacent missing linkers exhibit reaction barriers that are about 30 kJ/mol lower than SBU sites having a single missing linker. We also show that topology of the undercoordinated sites plays an important role in the reaction barrier under UHV conditions. 相似文献
62.
Alison Willette Benjamin Fallen Hem Bhandari Carl Sams Feng Chen Virginia Sykes Chris Smallwood Kristin Bilyeu Zenglu Li Vincent Pantalone 《Journal of the American Oil Chemists' Society》2021,98(8):861-869
Soybean oil hydrogenation alters the linolenic acid molecule to prevent the oil from becoming rancid, however, health reports have indicated trans-fat caused by hydrogenation, is not generally regarded as safe. Typical soybeans contain approximately 80 g kg−1 to 120 g kg−1 linolenic acid and 240 g kg−1 of oleic acid. In an effort to accommodate the need for high-quality oil, the United Soybean Board introduced an industry standard for a high oleic acid greater than 750 g kg−1 and linolenic acid less than 30 g kg−1 oil. By combing mutations in the soybean plant at four loci, FAD2-1A and FAD2-1B, oleate desaturase genes and FAD3A and FAD3C, linoleate desaturase genes, and seed oil will not require hydrogenation to prevent oxidation and produce high-quality oil. In 2017 and 2018, a study comparing four near-isogenic lines across multiple Tennessee locations was performed to identify agronomic traits associated with mutations in FAD3A and FAD3C loci, while holding FAD2-1A and FAD2-1B constant in the mutant (high oleic) state. Soybean lines were assessed for yield and oil quality based on mutations at FAD2-1 and FAD3 loci. Variations of wild-type and mutant genotypes were compared at FAD3A and FAD3C loci. Analysis using a generalized linear mixed model in SAS 9.4, indicated no yield drag or other negative agronomic traits associated with the high oleic and low linolenic acid genotype. All four mutations of fad2-1A, fad2-1B, fad3A, and fad3C were determined as necessary to produce a soybean with the new industry standard (>750 g kg−1 oleic and <30 g kg−1 linolenic acid) in a maturity group-IV-Late cultivar for Tennessee growers. 相似文献
63.
Haiyue Xu Ji Zou Weimin Wang Hao Wang Wei Ji Zhengyi Fu 《Journal of the European Ceramic Society》2021,41(1):635-645
Fully dense ceramics with retarded grain growth can be attained effectively at relatively low temperatures using a high-pressure sintering method. However, there is a paucity of in-depth research on the densification mechanism, grain growth process, grain boundary characterization, and residual stress. Using a strong, reliable die made from a carbon-fiber-reinforced carbon (Cf/C) composite for spark plasma sintering, two kinds of commercially pure α-Al2O3 powders, with average particle sizes of 220 nm and 3 μm, were sintered at relatively low temperatures and under high pressures of up to 200 MPa. The sintering densification temperature and the starting threshold temperature of grain growth (Tsg) were determined by the applied pressure and the surface energy relative to grain size, as they were both observed to increase with grain size and to decrease with applied pressure. Densification with limited grain coarsening occurred under an applied pressure of 200 MPa at 1050 °C for the 220 nm Al2O3 powder and 1400 °C for the 3 μm Al2O3 powder. The grain boundary energy, residual stress, and dislocation density of the ceramics sintered under high pressure and low temperature were higher than those of the samples sintered without additional pressure. Plastic deformation occurring at the contact area of the adjacent particles was proved to be the dominant mechanism for sintering under high pressure, and a mathematical model based on the plasticity mechanics and close packing of equal spheres was established. Based on the mathematical model, the predicted relative density of an Al2O3 compact can reach ~80 % via the plastic deformation mechanism, which fits well with experimental observations. The densification kinetics were investigated from the sintering parameters, i.e., the holding temperature, dwell time, and applied pressure. Diffusion, grain boundary sliding, and dislocation motion were assistant mechanisms in the final stage of sintering, as indicated by the stress exponent and the microstructural evolution. During the sintering of the 220 nm alumina at 1125 °C and 100 MPa, the deformation tends to increase defects and vacancies generation, both of which accelerate lattice diffusion and thus enhance grain growth. 相似文献
64.
Kun Yang Yachun Wang Penghui Lei Tiankai Yao Dong Zhao Jie Lian 《Journal of the European Ceramic Society》2021,41(12):6018-6028
Chemical durability of lanthanide zirconates (A2Zr2O7) (A = La-Yb) under near-field environments is important for evaluating their application as potential nuclear waste forms. In this work, A2Zr2O7 (A = La-Yb) are synthesized by spark plasma sintering with controlled microstructure and their chemical durability are evaluated in a nitric acid solution (pH = 1). Scanning transmission electron microscopy analysis reveals an amorphous passivation film either enriched with Zr or lanthanide. The complex chemistry of the passivation films can be correlated with a transition in corrosion mechanisms from a preferential release of lanthanide in La2Zr2O7 to a preferential release of Zr in Er2Zr2O7 and Yb2Zr2O7. These results suggest a dominant mechanism of incongruent dissolution and surface reorganization for the formation of passivation films. Strong correlations are identified between the leaching rates and cation ionic size, ionic potential, electronegativity differences between A-site cation and Zr, and bonding valence sum of oxygen, suggesting important impacts of structural and bonding characteristics in controlling chemical durability of lanthanide zirconates. 相似文献
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Gao Qian Zhong Chuanrong Han Peihui Cao Ruibo 《Chemistry and Technology of Fuels and Oils》2021,57(2):368-375
Chemistry and Technology of Fuels and Oils - When a reservoir is subjected to long-term water and polymer flooding, the formed preferential flow paths are widely distributed in the formation, and... 相似文献
69.
70.
Cell encapsulation within hydrogel droplets is transforming what is feasible in multiple fields of biomedical science such as tissue engineering and regenerative medicine, in vitro modeling, and cell-based therapies. Recent advances have allowed researchers to miniaturize material encapsulation complexes down to single-cell scales, where each complex, termed a single-cell microgel, contains only one cell surrounded by a hydrogel matrix while remaining <100 μm in size. With this achievement, studies requiring single-cell resolution are now possible, similar to those done using liquid droplet encapsulation. Of particular note, applications involving long-term in vitro cultures, modular bioinks, high-throughput screenings, and formation of 3D cellular microenvironments can be tuned independently to suit the needs of individual cells and experimental goals. In this progress report, an overview of established materials and techniques used to fabricate single-cell microgels, as well as insight into potential alternatives is provided. This focused review is concluded by discussing applications that have already benefited from single-cell microgel technologies, as well as prospective applications on the cusp of achieving important new capabilities. 相似文献