排序方式: 共有43条查询结果,搜索用时 453 毫秒
31.
Silica nanosheets (SiO2NSs)were successfully assembled on titanium (Ti)wires by sol-gel method. TiO2 nanosheets (TiO2NSs)were grown in situ on Ti wires using anodic oxidation in a fluoride-containing electrolyte to obtain Ti@TiO2NSs. The Ti@TiO2NSs@SiO2NSs fibers were obtained by coating Ti@TiO2NSs with SiO2NSs. It was characterized by scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). The fibers were used for solid-phase microextraction of ultraviolet absorbers (UVFs). Under the optimized conditions, six UVFs presented good linearity with the correlation coefficients (R2) greater than 0.999, and the limits of detection (LODs)ranged from 9 to 59 ng/L. The intra-day and inter-day relative standard deviations (RSDs) were from 4.3% to 5.1% and 4.6% to 5.8% for a single fiber at the spiked level of 25 μg/L, respectively. The developed method was successfully applied to the selective enrichment and determination of target UVFs in environmental water samples with recoveries from 93.2% to 108.1% and RSDs from 4.5% to 7.1%. Moreover, the fiber can be fabricated in a precisely controllable manner and is stable for at least 200 extraction and desorption cycles. © 2023, Youke Publishing Co.,Ltd. All rights reserved. 相似文献
32.
The poor electronic conductivity restricts the wide applications of Li4Ti5O12 as anode materials in Li‐ion batteries. We report a facile approach to fabricate nitrogen‐doped carbon‐coated Li4Ti5O12 through carbonizing pyrrole and pyridine at different temperatures. Comparative experiments demonstrated that the carbon content plays a key role in governing the cycling performance and rate capability of Li4Ti5O12. The composites with higher carbon content exhibited superior cycling performance, and the composite prepared at 600 °C using pyridine as the carbon source gave the best cycling and rate performance. 相似文献
33.
Xinzhen Xiang Shenheng Guan Alan G. Marshal 《Journal of the American Society for Mass Spectrometry》1994,5(4):238-249
We present a numerical method for computation of electrostatic (trapping) and time-varying (excitation) electric fields and the resulting ion trajectory and detected time-domain-induced voltage signal in a rectangular (or cubic) ion cyclotron resonance (ICR) ion trap. The electric potential is calculated by use of the superposition principle and relaxation method with a large number of grid points (e.g., 100 × 100 × 100 for a cubic trap). Complex ICR experiments and spectra may now be simulated with high accuracy. Ion trajectories may be obtained for any combination of trapping and excitation modes, including quadrupolar or cubic trapping in static or dynamic mode; and dipolar, quadrupolar, or parametric excitation with single-frequency, frequency-sweep (chirp), or stored waveform inverse Fourier transform waveforms. The resulting ion trajectory may be represented either as its three dimensional spatial path or as two-dimensional plots of x-, y-, or z-position, velocity, or kinetic energy versus time in the absence or presence of excitation. Induced current is calculated by use of the reciprocity principle, and simulated ICR mass spectra are generated by Fourier transform of the corresponding time-domain voltage signal. 相似文献
34.
Biocompatible amphiphilic conetwork based on crosslinked star copolymers: A potential drug carrier
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Haiye Wang Aiwen Qin Xiang Li Xinzhen Zhao Dapeng Liu Chunju He 《Journal of polymer science. Part A, Polymer chemistry》2015,53(21):2537-2545
A series of amphiphilic conetworks (APCNs) is synthesized through crosslinking of well‐defined tri‐arm star diblock copolymers via atom transfer radical polymerization. A new three‐arm initiator is synthesized to initiate the polymerization of 2‐hydroxyethyl methacrylate (HEMA) via “core‐first” method. The resulting star HEMA homopolymers with well‐defined molecular weight and narrow polydispersity are used as macroinitiator to incorporate allyl methacrylate to get the star diblock copolymers. Then, the precursors with allyl pendant groups are fully crosslinked with polyhydrosiloxanes through hydrosilylation. The so‐prepared APCNs exhibit unique properties of microphase separation of hydrophilic (HI) and hydrophobic (HO) phases with small channel size, a variable swelling capacity, excellent biocompatibility, and outstanding mechanical strength (2 ± 0.5 MPa). The properties of APCNs depend on the ratio of HI to HO, which can be regulated via precise synthesis of the star diblock copolymers. The APCNs show well‐controlled drug release to choline theophyllinate, suggesting a promising intelligent drug carrier for controlled release. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2537–2545 相似文献
35.
Honghong Rao Yaya Ma Zhonghua Xue Xinzhen Du Guohu Zhao Shenyin Li 《Analytical letters》2017,50(9):1435-1447
A sensitive and selective amperometric method for maltol is reported based on a nanostructural Co3O4-assembled Mobil composite material (MCM-41). The amperometric sensor was characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, cyclic voltammetry, electrochemical impedance spectroscopy, and ultraviolet–visible absorption spectroscopy. The obtained calibration curve showed that the oxidative peaks increased linearly with the maltol concentration from 1.66?×?10?6?M to 1.15?×?10?4?M with a detection limit of 0.42?µM. Furthermore, the mechanism of oxidation of the analyte on the modified electrode surface was investigated using electrochemical techniques. The modified electrode was used for the determination of maltol using the method of standard addition with satisfactory results. 相似文献
36.
Xinzhen Zhang Guanglu Zhou Louis Caccetta Mohammed Alqahtani 《Frontiers of Mathematics in China》2017,12(6):1409-1426
We consider approximation algorithms for nonnegative polynomial optimization problems over unit spheres. These optimization problems have wide applications e.g., in signal and image processing, high order statistics, and computer vision. Since these problems are NP-hard, we are interested in studying on approximation algorithms. In particular, we propose some polynomial-time approximation algorithms with new approximation bounds. In addition, based on these approximation algorithms, some efficient algorithms are presented and numerical results are reported to show the efficiency of our proposed algorithms. 相似文献
37.
3‐D graphene‐supported mesoporous SiO2@Fe3O4 composites for the analysis of pesticides in aqueous samples by magnetic solid‐phase extraction with high‐performance liquid chromatography
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Xuemei Wang Huan Wang Muxin Lu Xiaomin Ma Pengfei Huang Xiaoquan Lu Xinzhen Du 《Journal of separation science》2016,39(9):1734-1741
Three‐dimensional graphene‐supported mesoporous silica@Fe3O4 composites (mSiO2@Fe3O4‐G) were prepared by modifying mesoporous SiO2‐coated Fe3O4 onto hydrophobic graphene nanosheets through a simple adsorption co‐condensation method. The obtained composites possess unique properties of large surface area (332.9 m2/g), pore volume (0.68 cm3/g), highly open pore structure with uniform pore size (31.1 nm), as well as good magnetic separation properties. The adsorbent (mSiO2@Fe3O4‐G) was used for the magnetic solid‐phase extraction of seven pesticides with benzene rings in different aqueous samples before high‐performance liquid chromatography. The main parameters affecting the extraction such as adsorbent amount, volume of elution solvent, time of extraction and desorption, salt effect, oscillation rate were investigated. Under the optimal conditions, this method provided low limits of detection (S/N = 3, 0.525–3.30 μg/L) and good linearity (5.0–1000 μg/L, R2 > 0.9954). Method validation proved the feasibility of the developed adsorbent, which has a high extraction efficiency and excellent enhancement performance for pesticides in this study. The proposed method was successfully applied to real aqueous samples, and satisfactory recoveries ranging from 77.5 to 113.6% with relative standard deviations within 9.7% were obtained. 相似文献
38.
In this paper, we consider a bi‐quadratic homogeneous polynomial optimization problem over two unit spheres arising in nonlinear elastic material analysis and in entanglement studies in quantum physics. The problem is equivalent to computing the largest M‐eigenvalue of a fourth‐order tensor. To solve the problem, we propose a practical method whose validity is guaranteed theoretically. To make the sequence generated by the method converge to a good solution of the problem, we also develop an initialization scheme. The given numerical experiments show the effectiveness of the proposed method. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
39.
Two kinds of mesoporous cellular foams (MCFs), including mesoporous silica materials (MCF-1) and phenyl modified mesoporous materials (Ph-MCF-1), were synthesized and for the first time used as fiber-coating materials for solid-phase microextraction (SPME). By using stainless steel wire as the supporting core, four types of fibers were prepared by sol–gel method and immobilized by epoxy-resin method. To evaluate the performance of the home-made fibers for SPME, seven brominated flame retardants (BFRs), including tetrabromobisphenol A (TBBPA), tetrabromobisphenol S (TBBPS) and related compounds were selected as analytes. The main parameters that affect the extraction and desorption efficiencies, such as extraction temperature, extraction time, desorption time, stirring rate and ionic strength of samples were investigated and optimized. The optimized SPME coupled with high performance liquid chromatography (HPLC) was successfully applied to the determination of the seven BFRs in water samples. The linearity range was from 5.0 to 1000 μg L−1 for each compound except TBBPS (from 1.0 to 1000 μg L−1), with the correlation coefficients (r2) ranging from 0.9993 to 0.9999. The limits of detection of the method were 0.4–0.9 μg L−1. The relative standard deviations varied from 1.2 to 5.1% (n = 5). The repeatability of fiber-to-fiber and batch-to-batch was 2.5–6.5% and 3.2–6.7%. The recoveries of the BFRs from aqueous samples were in the range between 86.5 and 103.6%. Compared with three commercial fibers (100 μm PDMS, 85 μm PA and 65 μm PDMS/DVB), the MCFs-coated fiber showed about 3.5-fold higher extraction efficiency. 相似文献
40.