We study here some linear recurrence relations in the algebra of square matrices. With the aid of the Cayley–Hamilton Theorem, we derive some explicit formulas for An (nr) and etA for every r×r matrix A, in terms of the coefficients of its characteristic polynomial and matrices Aj, where 0jr−1. 相似文献
The bioisosteres of 1,3,4-oxadiazoles and 1,3,4-thiadiazoles are well-known pharmacophores for many medicinally important drugs. Throughout the past 10 years, 1,3,4-oxa-/thiadiazole nuclei have been very attractive to researchers for drug design, synthesis, and the study of their potential activity towards a variety of diseases, including microbial and viral infections, cancer, diabetes, pain, and inflammation. This work is an up-to-date comparative study that identifies the differences between 1,3,4-thiadiazoles and 1,3,4-oxadiazoles concerning their methods of synthesis from different classes of starting compounds under various reaction conditions, as well as their biological activities and structure–activity relationship. 相似文献
Nanocomposite biopolymer materials containing colorimetric pH-responsive indicators were prepared from gelatin and chitosan nanofibers. Plant-based extracts from barberry and saffron, which both contained anthocyanins, were used as pH indicators. Incorporation of the anthocyanins into the biopolymer films increased their mechanical, water-barrier, and light-screening properties. Infrared spectroscopy and scanning electron microscopy analysis indicated that a uniform biopolymer matrix was formed, with the anthocyanins distributed evenly throughout them. The anthocyanins in the composite films changed color in response to alterations in pH or ammonia gas levels, which was used to monitor changes in the freshness of packaged fish during storage. The anthocyanins also exhibited antioxidant and antimicrobial activity, which meant that they could also be used to slow down the degradation of the fish. Thus, natural anthocyanins could be used as both freshness indicators and preservatives in biopolymer-based nanocomposite packaging materials. These novel materials may therefore be useful alternatives to synthetic plastics for some food packaging applications, thereby improving the environmental friendliness and sustainability of the food supply. 相似文献
MoS2 has been commonly used as a catalyst in hydrodesulfurization (HDS) of petroleum cuts in crude oil refineries. In this study, the synthesis of unsupported MoS2 and Co-promoted MoS2 nanosheets produced from molybdenum oxide and thiourea is reported. The synthesized samples were characterized by using x-ray fluorescence, x-ray diffraction, Brunauer–Emmett–Teller (BET), temperature-programmed reduction, thermal gravimetric analysis, and transmission electron microscopy methods, and then they were utilized for HDS of diesel through a fixed-bed catalytic reactor. Results indicated that a cobalt promoter affected both the number and the performance of active sites of the molybdenum sulfides, and the activity of the promoted MoS2 catalyst was consistently higher than that of the MoS2 catalyst. More significantly, the activity of the promoted catalyst was slightly declined during 48 h continuous HDS reaction, which indicated the stability of this catalyst. Additionally, during 12 h of test run, the HDS activity of the promoted catalyst was about 60% higher than MoS2 one. 相似文献
Large signal analysis of the serially cascaded electroabsorption modulator driven by a multisinusoidal RF signal is presented. The special case of a two-tone equal-amplitude RF signal is considered in detail, and the results are compared with previously published results. 相似文献
Large signal analysis of the multiple-quantum-well electroabsorption modulators driven by a mutisinusoidal RF signal is presented. The special case of a two-tone equal-amplitude RF signal is considered in detail and the results are compared with previously published results. 相似文献
We study Basic algebra, the algebraic structure associated with basic propositional calculus, and some of its natural extensions. Among other things, we prove the amalgamation property for the class of Basic algebras, faithful Basic algebras and linear faithful Basic algebras. We also show that a faithful theory has the interpolation property if and only if its correspondence class of algebras has the amalgamation property. 相似文献
A one-pot three-component condensation reaction of 3-amino-5-methylisoxazole, aryl aldehyde and 2-naphthol to afford the corresponding 3-amino isoxazolmethylnaphthols in good to excellent yields. The remarkable features of this new procedure are high conversions, clean reaction condition, short reaction time, nonhazardous and environmentally friendly reaction condition, inexpensive and easily commercially availability of the catalyst and simple work-up procedures. 相似文献
Novel composites were obtained via direct assembly of polysulfides (Sx2?, X?=?3, 4, 6) on the surface of a metal organic framework (MOF; type benzene-1,3,5-tricarboxylic/Cu(II). They are referred to as Sx-MOFs and were used for highly selective and efficient extraction of ultra-trace amounts of heavy metal ions from aqueous solutions. The structure of the Sx-MOFs was characterized by Raman spectroscopy, FT-IR, X-ray diffraction, and scanning electron microscopy. The Raman spectra of Sx-MOF is similar to the bare MOF and shows the MOFs structure to be well retained after Sx functionalization. The selective interaction of Sx with soft metal ions and the high surface area of MOFs resulted in excellent affinity and selectivity for ions such as Hg(II). The Sx-MOFs of type S4-MOF had the highest distribution coefficient Kd value (~107) and best extraction recovery (~100%) for Hg(II). The S4-MOF also has high selectivity in the following order: Hg(II) >?>?Pb(II)?>?Zn(II)?>?Ni(II)?>?Co(II). The binding process of the metals occurs via M–S bonding. The ions were quantified by inductively coupled plasma optical emission spectrometry (ICP-OES). The detection limit for Hg(II) is 0.13 μg L?1. The S4-MOF was applied to the extraction of trace metal ions from natural and contaminated waters and data were compared with other sorbets. The results revealed that S4-MOF is an excellent adsorbent for sorption of heavy metal ions even in the presence of the relatively high concentration of other ions.
Graphical abstract A composite was synthesized via direct assembly of polysulfides (Sx2?, X?=?3, 4, 6) on surface of the metal organic framework (Sx-MOF) and was used for selective and efficient extraction of ultra-trace amounts of heavy metal ions from aqueous solutions.