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为了揭示CO2驱替过程中沥青质沉积对致密储层的伤害机理,文中基于岩心核磁共振T2谱测试原理,开展了CO2注入压力下的岩心驱替实验,研究了沥青质在岩心中的沉积特征,评价了沥青质沉积对储层的伤害程度。实验结果表明:沥青质沉积量和渗透率伤害率随着CO2注入压力的升高呈现先快速上升后趋于平缓的趋势;在CO2注入过程中,沥青质主要沉积在弛豫时间大于10 ms的大、中孔隙,导致大、中孔隙占比下降,微细、小孔隙占比增加,且随着CO2注入压力的升高,大、中孔隙占比下降幅度增大,微细、小孔隙占比上升幅度增大;此外,沥青质沉积会引起润湿性发生反转,随着沥青质沉积量的增加,润湿反转指数增大,岩心润湿性不断向强油湿方向转变。 相似文献
44.
Dr. Kresimir Rupnik Dr. Kazuki Tanifuji Lee Rettberg Prof. Dr. Markus W. Ribbe Prof. Dr. Yilin Hu Prof. Dr. Brian J. Hales 《Chembiochem : a European journal of chemical biology》2020,21(12):1767-1772
The active site of the nitrogen-fixing enzyme Mo-nitrogenase is the M cluster ([MoFe7S9C ⋅ R-homocitrate]), also known as the FeMo cofactor or FeMoco. The biosynthesis of this highly complex metallocluster involves a series of proteins. Among them, NifB, a radical-SAM enzyme, is instrumental in the assembly of the L cluster ([Fe8S9C]), a precursor and all-iron core of the M cluster. In the absence of sulfite, NifB assembles a precursor form of the L cluster called the L* cluster ([Fe8S8C]), which lacks the final ninth sulfur. EPR and MCD spectroscopies are used to probe the electronic structures of the paramagnetic, oxidized forms of both the L and L* clusters, labeled LOx and [ L* ] Ox . This study shows that both LOx and [ L* ] Ox have nearly identical EPR and MCD spectra, thus suggesting that the two clusters have identical structures upon oxidation; in other words, a sulfur migrates away from LOx following oxidation, thereby rendering the cluster identical to [ L* ] Ox . It is proposed that a similar migration could occur to the M cluster upon oxidation, and that this is an instrumental part of both M cluster formation and nitrogenase substrate/inhibitor binding. 相似文献
45.
为了研究电磁诱导透明效应在拓扑单向波导中的表现,设计了一种基于磁性光子晶体的耦合谐振腔波导。通过对谐振腔位置的调控实现了具有单向性质的电磁诱导透明效应,并利用有限时域差分仿真证明了电磁诱导透明效应在单向拓扑波导中的相关特性。该研究可为拓扑波导中实现光延迟、光开关等提供参考。 相似文献
46.
AbstractThe knowledge of moisture content (MC) and drying stress are crucial parameters to control the drying process and maintain the quality of dried wood. Herein, we investigated the pattern of moisture transfer and stress development in Chinese fir during the high-temperature drying process. The MC in each layer of lumber was separated into bound water and free water via nuclear magnetic resonance (NMR), and the drying and residual stress were measured using prong test method. There was different MC in each layer along the thickness, resulting in an MC gradient that initially increased and then decreased, which is consistent with the trend of drying stress. The T21 peak indicating bound water shifted to the left especially when MC was below the fiber saturation point, signifying that the discharge of moisture became difficult with prolonged drying time. The ratio of bound water to free water was different in each layer, indicating that the moisture transfer was different along the thickness. Furthermore, the residual stress was greater than the corresponding drying stress though the disparity reduced gradually, which suggests that the MC gradient was the largest affecting factor for drying stress at high MC stages but decreased to some extent as the drying process continued. 相似文献
47.
《Ceramics International》2020,46(11):19121-19126
We examined the magnetic, structural, and chemical properties of CoFe2O4 films deposited on Al2O3 substrates using RF-magnetron sputtering under Ar and Ar + O2 environments. Perpendicular magnetic anisotropy with large magnetization was observed in the case of the film deposited under the Ar + O2 environment. However, no significant anisotropy appeared in the film deposited under the Ar environment. Interestingly, depth-dependent X-ray photoelectron spectra showed nearly identical stoichiometric ratios of Co/Fe and oxygen vacancies regardless of the deposition environment. Structurally, high-quality crystallinity with in-plane compressive strain, and lower surface and interfacial roughness were induced in the film deposited under the Ar + O2 environment. Cross-sectional transmission electron microscopy and X-ray reflectivity measurements showed that oxygen not only suppressed the deposition rate but also increased the electron density of the film, resulting in better crystallinity. Hence, the presence of oxygen during deposition should be considered as one of the essential parameters for improving the structural and magnetic properties of ferrite films. 相似文献
48.
磁性纳米材料具有较强的化学稳定性、可再生回收、良好的吸附性能和易于分离等优点,在去除水溶液中的铀酰离子方面有广泛的应用前景。然而,磁性纳米材料也存在易团聚、易氧化等不足,通过表面修饰或改性等方法可改善其不足,提高其对废水中铀酰离子的去除能力,改善其吸附效果。本文通过总结近年来的相关研究资料,概括了磁性纳米材料的种类,归纳总结并比较了不同种类磁性纳米材料对含铀废水的去除能力及优势与不足,探讨了磁性纳米材料在含铀废水处理中的应用并对其机理进行了分析,阐述了磁性纳米材料去除溶液中铀酰离子的影响因素,简述了目前磁性纳米材料在处理含铀废水中有待解决的问题,并对其在分离放射性元素方面的应用前景进行了展望。 相似文献
49.
《Ceramics International》2020,46(4):4410-4415
Spinel Mg ferrites Mg1-xCdxCo0.05Fe1.95O4 (x=0.0, 0.2, 0.3 and 0.4) as potential agents for the miniaturization of high frequency antennas are presented. All the synthesized compositions were experimentally revealed to possess pure spinel phase. Dual-equivalent permeability and permittivity (μ'≈26, ε'≈25, x=0.3 and μ'≈29, ε'≈28, x=0.4) from 5 to 100 MHz can be achieved by introducing Cd2+ ions, yielding large miniaturization factors of up to 25 and 28. To figure out the effects of Cd2+ ions substitution on magnetic and dielectric properties, the change in microstructure is mainly investigated. Meanwhile, enhanced magnetic properties including upward saturation magnetization (Ms) (approximately 47.60 emu/g) and reduced coercivity (approximately 54.22 Oe) are obtained due to increased grain size and denser microstructure arrangements reflected from scanning electron microscopy images. With low magnitude order of magnetic and dielectric losses factors (tanδε reaches 10-4, tanδμ reaches 10-2), the composites can potentially exhibit high operating efficiencies at high frequencies. 相似文献
50.
针对矿用带式输送机启动过程易出现打滑、淤带和断带等问题,基于永磁涡流传动技术,将双盘式磁力耦合器作为带式输送机的驱动装置,建立双盘式磁力耦合器动态数学模型,运用AMEsim软件搭建带式输送机系统仿真模型,设置启动时间分别为60、80和100 s,采用Harrison控制曲线启动时,研究带式输送机满载启动时机头、机尾部输送带的速度特性和张力特性,张紧装置位移特性以及双盘式磁力耦合器调速气隙特性,仿真结果表明:当启动时间为60 s时,带式输送机输送带速度波动大,动张力明显,尾部输送带最大张力达到29 kN,启动过程不平稳;双盘式磁力耦合器调速时,气隙变化与带式输送机启动速度变化趋势相反,启动过程气隙从22 mm减小到4 mm;当启动时间为80 s和100 s时,带式输送机启动过程相对平稳,速度和张紧装置位移波动小,尾部输送带张力波动幅度分别为5 kN和3 kN;带式输送机启动过程存在最佳启动时间,继续延长时间,对带式输送机启动特性影响越来越小,80 s可作为合理启动时间。 相似文献