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901.
Since the 1960s, many rivers have been destroyed as a consequence of the process of rapid urbanization. As accurate figures are important to repair rivers, there have been many research reports on methods to obtain the exact river slope and elevation. Until now, many research efforts have analyzed the river using measured river topographic factors, but when the flow velocity changes rapidly, such as during a flood, surveying is not easy; and due to cost, frequent measurements are difficult. Previous research has focused on the cross section of the river, so the information on the river longitudinal profile is insufficient. In this research, using informational entropy theory, equations are presented that can calculate the average river slope, river slope, and river longitudinal elevation for a river basin in real time. The applicability was analyzed through a comparison with the measured data of river characteristic factors obtained from the river plan. The parameters were calculated using informational entropy theory and nonlinear regression analysis using actual data, and then the longitudinal elevation entropy equation for each river and the average river slope were calculated. As a result of analyzing the applicability of the equations presented in this study by R2 and Root Mean Square Error, all R2 values were over 0.80, while RMSE values were analyzed to be between 0.54 and 2.79. Valid results can be obtained by calculating river characteristic factors. 相似文献
902.
Yaoxiao Zhao Weixing Chen Mengyang Li Kun Yuan Meng An 《International journal of quantum chemistry》2024,124(1):e27269
The search for good nonlinear optical (NLO) materials is of utmost importance in laser technology and optical information science, making it a popular research topic in materials science. It is reported that the introduction of alkali metal Li can enhance the NLO properties of nanocarbon materials. Here, metal Al, which exhibits similar electron transfer characteristics to Li, was used for the first time to enhance the NLO properties of nanocarbon cluster C60, which possesses a large delocalized π structure and the highest yield in the fullerene family. Density functional theory calculations in combination with Boltzmann distribution showed that the most thermodynamically stable Al@Ih(1812)-C60 exhibited good second-order NLO properties, which originated from the noncentrosymmetry geometry and one extra delocalized electron on Ih(1812)-C60 from the 3p shell of inner Al. Density of state analysis indicated that the molecular orbitals of Al@Ih(1812)-C60 were primarily formed by Ih(1812)-C60 with minimal Al participation, and the presence of Al always resulted in an antibonding orbital effect. Bond critical point and electron localization function analyses indicated almost no covalent interaction between Al and Ih(1812)-C60. Exohedral functionalization was employed to further stabilize Al@Ih(1812)-C60 with radical character, and the infrared spectrum was also analyzed in detail. This study has promising implications for expanding the potential applications of fullerenes in optical devices. 相似文献
903.
Dong Zhu Zhao Yi Miao Rui Xiang YangHong Mei Wen Wei LiJun Chen An KangChen-Xiao Shan Sheng YuYue Hu 《Analytica chimica acta》2016
The current widely utilized polymer or C8, C18 end-capped material-based sorbents for solid-phase extraction could not capture alkaloids well only based on “like dissolves like” principle. In this paper, a layer-by-layer functionalized porous Zinc sulfide nanospheres-based solid-phase extraction (SPE) combined with liquid chromatography time-of-flight/mass spectrometry (LC-TOF/MS) and gas chromatography-mass spectrometry (GC-MS) was developed for the specific enrichment and identification of alkaloids from complex matrixes, Crinum asiaticum var. sinicum crude extracts. The functionalized porous Zinc sulfide nanospheres were prepared by the amidation reaction of poly-(acrylic acid) (PAA) homopolymer with amino groups onto the porous ZnS nanospheres. Tandem LC-TOF/MS spectrometry presented that the almost all of the twenty-three main peaks in elution fraction from the SPE could be inferred as alkaloids with ion of mass according to the nitrogen rule and hit formula with Peak View1.2@software from AB SCIEX, and seven alkaloids including two new found chemical entities were directly identified from their GC-MS spectra and retention indices. We believe that this SPE protocol can also be utilized in the future to selectively enrich alkaloids from extracts of other plant species. 相似文献
904.
A Novel Method for the Synthesis of Newfangled Asymmetric Schiff Bases from α‐amino Acids under Ultrasonic Conditions and in Aqueous Medium 下载免费PDF全文
Kıvılcım Şendil Turgay Tekin Haydar Göksu Mehmet Oğuz Barış Anıl Mehmet Serdar Gültekin 《中国化学会会志》2016,63(9):808-817
Chiral Schiff bases were obtained at high yields via a novel technique. Aryl aldehydes and chiral α‐amino acids were treated (1) in the presence of H3PO4 in ethanol at 80°C for 24 h, and (2) in the presence of K2CO3 under ultrasonic conditions in an aqueous ethanol medium within 5 min with yields reaching up to 96%. The results showed that the presented methodology under ultrasonic conditions was effective, practical, and eco‐friendly compared to that using an acidic medium. The corresponding asymmetric Schiff bases were synthesized for the first time, and were characterized by 1H and 13C nuclear magnetic resonance and infrared spectroscopy and high‐resolution mass spectrometry. 相似文献
905.
906.
Pentaerythritol/butane tetracarboxylic acid/polyethylene glycol (PBPEG) crosslinking copolymers as a novel solid-solid phase change material (SSPCM) were successfully synthesized through the reaction mechanism and conditions of hydroxyl-carboxyl condensation reaction. The composition and chemical structure, crystalline properties, phase change behaviors, thermal reliability and chemical stability of PBPEG crosslinking copolymers were investigated by Fourier transform infrared spectroscopy (FT-IR), wide-angle X-ray diffraction (WAXD), polarization optical microscopy (POM), differential scanning calorimetry (DSC), and thermogravimetry (TGA), respectively. The results show that PBPEG crosslinking copolymers have typical solid-solid phase transition temperatures in the range of 10.31~53.27°C and high latent heat enthalpy in the range of 89.6~102.8 J/g, the synthesized SSPCMs have good thermal reliability and chemical stability after 300 thermal cycles, and PBPEG crosslinking copolymers have good thermal stability before 364°C. In summary, the synthesized PBPEG crosslinking copolymers could be potentially used for thermal energy storage. 相似文献
907.
908.
Model-based predictive controller design for a class of nonlinear networked systems with communication delays and data loss 下载免费PDF全文
This paper discusses the model-based predictive controller design of networked nonlinear systems with communication delay and data loss. Based on the analysis of the closed-loop networked predictive control systems, the model-based networked predictive control strategy can compensate for communication delay and data loss in an active way. The designed model-based predictive controller can also guarantee the stability of the closed-loop networked system. The simulation results demonstrate the feasibility and efficacy of the proposed model-based predictive controller design scheme. 相似文献
909.
Ferromagnetic barrier-induced negative differential conductance on the surface of a topological insulator 下载免费PDF全文
The effect of the negative differential conductance of a ferromagnetic barrier on the surface of a topological insulat( is theoretically investigated. Due to the changes of the shape and position of the Fermi surfaces in the ferromagnetic barrie the transport processes can be divided into three kinds: the total, partial, and blockade transmission mechanisms. The bias voltage can give rise to the transition of the transport processes from partial to blockade transmission mechanisms, which results in a considerable effect of negative differential conductance. With appropriate structural parameters, the currenl voltage characteristics show that the minimum value of the current can reach to zero in a wide range of the bias voltag and then a large peak-to-valley current ratio can be obtained. 相似文献
910.
Designing of a polarization beam splitter for the wavelength of 1310 nm on dual-core photonic crystal fiber with high birefringence and double-zero dispersion 下载免费PDF全文
We have proposed a novel kind of photonic crystal fiber which contains two asymmetric cores. The bireti'ingence and the dispersion are numerically analyzed based on finite element method when the size of the air holes and the pitch of two adjacent air holes are changed. It is shown that the proposed photonic crystal fiber has high birefringence up to the order of 10-2 and double-zero dispersion points are at the wavelengths of 1310 nm and 800 rim, simultaneously. At the same time, the normalized power and the extinction ratios of the proposed photonic crystal fiber have been simulated. It is demonstrated that, at the wavelength of 1310 rim, the x-polarized mode and the y-polarized mode are separated when the propagation distance is 2.481 ram. 相似文献