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Bernd GüNTHER 《中国科学B辑(英文版)》2007,50(6)
The interaction between stabilizers and nanoparticles is one of the important factors to prepare stable magnetic fluids. The magnetic nano-size Fe3O4 core with single domain and the average grain size around 8-12 nm were prepared by chemical precipitation method. The O/Fe molar ratio of the particle surface was measured by X-ray photoelectron spectroscopy (XPS). The heat effects of stabilizers ad- sorption on nanoparticles were measured by solution calorimetry. The excess amount of oxygen was possibly the result of the hydroxygen formed on the surface of the nanoparticles. The heat effects showed that compounds containing carboxyl groups can be adsorbed chemically on magnetite by forming chemical bonds. The other stabilizers involving NH-groups, such as polyethylene-imine, can be adsorbed physically. The exothermic value is about half of the former case. 相似文献
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Teng Wang Chi Zhang LiangCai Xu JinHua Wang Shan Jiang ZengWei Zhu ZhaoSheng Wang JiaNan Chu JiaXin Feng LingLing Wang Wei Li Tao Hu XiaoSong Liu Gang Mu 《中国科学:物理学 力学 天文学(英文版)》2020,(2):124-129
Recently, 12442 system of Fe-based superconductors has attracted considerable attention owing to its unique double-Fe As-layer structure. A steep increase in the in-plane upper critical field with cooling has been observed near the superconducting transition temperature, Tc, in KCa2Fe4As4F2 single crystals. Herein, we report a high-field investigation on upper critical field of this material over a wide temperature range, and both out-of-plane(H∥c, Hc2c) and in-plane(H∥ab, Hc2ab ) directions have been measured.A sublinear temperature-dependent behavior is observed for the out-of-plane Hc2c , whereas strong convex curvature with cooling is observed for the in-plane Hc2ab . Such behaviors could not be described by the conventional Werthamer-Helfand-Hohenberg(WHH) model. The data analysis based on the WHH model by considering the spin aspects reveals a large Maki parameter α=9,indicating that the in-plane upper critical field is affected by a very strong Pauli paramagnetic effect. 相似文献
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Wang Teng Chu JiaNan Feng JiaXin Wang LingLing Xu XuGuang Li Wei Wen HaiHu Liu XiaoSong Mu Gang 《中国科学:物理学 力学 天文学(英文版)》2020,63(9):1-5
The Hubble constant H_0 represents the expansion rate of the Universe at present and is closely related to the age of the Universe.The accurate measurement of Hubble constant is crucial for modern cosmology.However,different cosmological observations give diverse values of Hubble constant in literature.Up to now,there are two methods to measure the Hubble constant.One is to directly measure the Hubble constant based on distance ladder estimates of Cepheids and so on.The other is to globally fit the Hubble constant under the assumption of a cosmological model,for example the "standard" ACDM model.Adopting the low-redshift observational datasets,including the Pantheon sample of Type Ⅰa supernovae,baryon acoustic oscillation measurements,and the tomographic Alcock-Paczynski method,we determine the Hubble constant to be 67.95_(-1.03)~(+0.78),69.81_(-2.70)~(+2.22) and66.75_(-4.23)~(+3.42) km s~(-1) Mpc~(-1) at 68% confidence level in the △CDM,wCDM and W_0W_a CDM models,respectively.Compared to the Hubble constant given by Riess et al.in 2019,we conclude that the new physics beyond the standard △CDM model is needed if all of these datasets are reliable. 相似文献
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The interaction between stabilizers and nanoparticles is one of the important factors to prepare stable magnetic fluids. The
magnetic nano-size Fe3O4 core with single domain and the average grain size around 8–12 nm were prepared by chemical precipitation method. The O/Fe
molar ratio of the particle surface was measured by X-ray photoelectron spectroscopy (XPS). The heat effects of stabilizers
adsorption on nanoparticles were measured by solution calorimetry. The excess amount of oxygen was possibly the result of
the hydroxygen formed on the surface of the nanoparticles. The heat effects showed that compounds containing carboxyl groups
can be adsorbed chemically on magnetite by forming chemical bonds. The other stabilizers involving NH-groups, such as polyethylene-imine,
can be adsorbed physically. The exothermic value is about half of the former case.
Supported by the National Natural Science Foundation of China (Grant No. 50476039), and Guangdong Provincial Department of
Science and Technology (Grant No. 2004A10-703001) 相似文献
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