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1.
In this paper we design a fast new algorithm for reducing an N × N quasiseparable matrix to upper Hessenberg form via a sequence of N − 2 unitary transformations. The new reduction is especially useful when it is followed by the QR algorithm to obtain a complete set of eigenvalues of the original matrix. In particular, it is shown that in a number of cases some recently devised fast adaptations of the QR method for quasiseparable matrices can benefit from using the proposed reduction as a preprocessing step, yielding lower cost and a simplification of implementation. 相似文献
2.
James E. Keesling Yuli B. Rudyak 《Proceedings of the American Mathematical Society》2007,135(8):2629-2631
We discuss which groups can be realized as the fundamental groups of compact Hausdorff spaces. In particular, we prove that the claim ``every group can be realized as the fundamental group of a compact Hausdorff space' is consistent with the Zermelo-Fraenkel-Choice set theory.
3.
Bakhtar Ullah Yuli Zhou Jingwen Chen Zongbi Bao Yiwen Yang Qiwei Yang Qilong Ren Zhiguo Zhang 《Tetrahedron letters》2019,60(4):348-351
Thiourea itself has been introduced as a mild and efficient organocatalyst for the oxidative α -cyanation of N-aryltetrahydroisoquinolines (THIQs) with trimethylsilyl cyanide (TMSCN), giving the corresponding products in good to excellent yields. Experimental investigations demonstrated that thiourea acts as a radical initiator by abstracting hydroxyl radical (OH) from tert-butyl hydroperoxide (TBHP) directly instead of non-covalent hydrogen bondings (H-bondings) activation. The use of thiourea as a radical initiator offers a new avenue for innovative chemical transformations in organocatalyzed radical chemistry. 相似文献
4.
以H2S和CS2作硫化剂,用PPS和TPDS方法研究了水煤气变换催化剂CoMoK/γ-Al2O3的硫化及反硫化过程。用H2S/H2硫化时,只发现H2S的消耗和H2O的生成,用CS2/H2硫化时,只发现H2S的消耗和H2O的生成。用CS2/H2硫化时,首先生成CO2,然后是CH4,H2O和H2S,TPG实验表明催化剂表面上积炭,造成催化剂和活性降低,但积炭在水煤变换反应进行了逐渐除法。TPDS实验表 相似文献
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基于双功能单体的磁性双酚A印迹聚合物的制备及应用 总被引:1,自引:0,他引:1
以二氧化硅包覆的四氧化三铁为载体,双酚A(BPA)为模板分子,β-环糊精和4-乙烯基吡啶为二元功能单体,采用热聚合方法制备了对双酚A具有特异吸附性能的磁性印迹复合材料(mag-MIPs).采用透射电子显微镜(TEM)、傅里叶变换红外光谱(FTIR)和振动样品磁强计(VSM)对该印迹复合材料进行了表征,并结合磁固相萃取(M-SPE)技术和高效液相色谱(HPLC)研究了其对双酚A的吸附行为,结果表明该印迹复合材料对双酚A具有良好的选择吸附能力.液相色谱检测结果表明,该磁性印迹复合材料可用于环境水样中双酚A的快速分离富集,回收率为90.51%~98.21%. 相似文献
7.
Preparation of novel curcumin‐imprinted polymers based on magnetic multi‐walled carbon nanotubes for the rapid extraction of curcumin from ginger powder and kiwi fruit root 下载免费PDF全文
Zhaohui Zhang Xing Chen Wei Rao Fang Long Liang Yan Yuli Yin 《Journal of separation science》2015,38(1):108-114
A novel molecularly imprinted polymer based on magnetic phenyl‐modified multi‐walled carbon nanotubes was synthesized using curcumin as the template molecule, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross‐linker. The phenyl groups contained in the magnetic imprinted polymers acted as the assisting functional monomer. The magnetic imprinted polymers were characterized by scanning electron microscopy, Fourier‐transform infrared spectroscopy and vibrating sample magnetometry. Adsorption studies demonstrated that the magnetic imprinted polymers possessed excellent selectivity toward curcumin with a maximum capacity of 16.80 mg/g. Combining magnetic extraction and high‐performance liquid chromatography technology, the magnetic imprinted polymer based on magnetic phenyl‐modified multi‐walled carbon nanotubes was applied for the rapid separation and enrichment of curcumin from ginger powder and kiwi fruit root successfully. 相似文献
8.
Mechanically Adaptive and Shape‐Memory Behaviour of Chitosan‐Modified Cellulose Whisker/Elastomer Composites in Different pH Environments 下载免费PDF全文
Biomimetic polymer composites with water‐active mechanically adaptive and shape‐memory behaviour in different pH environments are synthesised by using chitosan‐modified cellulose whiskers (CS‐CWs) as the stimulus‐responsive phase and thermoplastic polyurethane (TPU) as the resilient matrix. The effect of surface modification on the mechanically adaptive behaviour of CS‐CW/TPU composites is investigated by using three representative solutions with various pH values. The results show that surface modification significantly enhances the modulus contrast under wet and dry conditions with the acidic solution as the stimulus, while maintaining the high modulus contrast with the basic solution as the stimulus. CS‐CW/TPU composites also exhibit excellent shape‐memory effects in all three solutions that are comparable to those pristine CW/TPU composites. Furthermore, activation of force generation in the stretched CS‐CW/TPU composites by water absorption/desorption was observed. 相似文献
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10.
Structural modifications of 3-OH in the glucose moiety of dapagliflozin(1), an approved potent sodium-dependent glucose transporter 2(SGLT2) inhibitor, led to 3-oxodapagliflozin(16), a highly potent and more selective SGLT2 inhibitor[IC50(hSGLT1)/IC50(hSGLT2)=2851 for compound 16 vs. 843 for compound 1]. 3-Oxodapagliflozin(16) exhibited in vitro(IC50=1.0nmol/L against hSGLT2 for compound 16 vs. 1.3 nmol/L for compound 1) and in vivo activities comparable to those of dapagliflozin(1). The bioactivities of 3-oxodapagliflozin (16) warrant its further evaluation as a promising SGLT2 inhibitor for the treatment of type 2 diabetes. 相似文献