38 research outputs found
Generalised analytical method unravels framework-dependent kinetics of adsorption-induced structural transition in flexible metal–organic frameworks
ゲート型吸着剤はガス分子をどう取り込む? --サブ秒でのX線回折測定が動的過程を紐解く--. 京都大学プレスリリース. 2023-11-08.Flexible metal–organic frameworks (MOFs) exhibiting adsorption-induced structural transition can revolutionise adsorption separation processes, including CO₂ separation, which has become increasingly important in recent years. However, the kinetics of this structural transition remains poorly understood despite being crucial to process design. Here, the CO₂-induced gate opening of ELM-11 ([Cu(BF₄)₂(4, 4’-bipyridine)₂]n) is investigated by time-resolved in situ X-ray powder diffraction, and a theoretical kinetic model of this process is developed to gain atomistic insight into the transition dynamics. The thus-developed model consists of the differential pressure from the gate opening (indicating the ease of structural transition) and reaction model terms (indicating the transition propagation within the crystal). The reaction model of ELM-11 is an autocatalytic reaction with two pathways for CO₂ penetration of the framework. Moreover, gas adsorption analyses of two other flexible MOFs with different flexibilities indicate that the kinetics of the adsorption-induced structural transition is highly dependent on framework structure
Acute inflammation at a mandibular solitary horizontal incompletely impacted molar
Acute inflammation is frequently seen in the elderly around incompletely impacted molars located apart from molars or premolars. To identify the factors causing acute inflammation in the solitary molars without second molars or without second and first molars, ages of patients and rates of acute inflammation in 75 horizontal incompletely impacted mandibular molars in contact or not in contact with molars in subjects 41 years old or older were studied using orthopantomographs. Acute inflammation was seen in nine third molars out of 48 third molars in contact with second molars (18.8%), whereas acute inflammation was seen in 11 molars out of 19 solitary molars without second molars or without first and second molars (57.9%) (p < 0.01). The mean age of 48 subjects with third molars in contact with the second molar was 50.42 ± 7.62 years, and the mean age of 19 subjects with isolated molars was 65.16 ± 10.41 years (p < 0.0001). These indicate that a solitary horizontal incompletely impacted molar leads more frequently to acute inflammation along with aging due to possible bone resorption resulting from teeth loss
Enhanced Si and B diffusion in semiconductor-grade SiO 2 and the effect of strain on diffusion
Abstract We present experimental and simulation results of Si self-diffusion and B diffusion in SiO 2 formed directly on Si substrates by thermal oxidation. We show that both Si and B diffusion in SiO 2 are enhanced by SiO generated at the Si/SiO 2 interface and diffusing into SiO 2 . We also show that the existence of high-concentration B in SiO 2 enhances SiO diffusion, which enhances both Si self-diffusion and B diffusion. This correlated diffusion of Si and B in SiO 2 is consistent with the first-principles calculation results, which show that B diffuses via a complex of BSiO with frequent bond exchanges in the SiO 2 network. Furthermore, based on the results, the enhancement of Si self-diffusion and B diffusion in SiO 2 by compressive strain and their retardation by tensile strain are suggested.