For linear combinations of Bernstein-Kantorovich operators Kn, r(f, x), we give an equivalent theorem with ω2r?λ(f, t). The theorem unites the corresponding results of classical and Ditzian-Totik moduli of smoothness. 相似文献
In this paper, poly(acrylate-g-siloxane) with novel comb-like structure was designed and prepared so as to create a strongly hydrophobic polymer surface. In order to achieve this goal, a series of organic-siloxane oligomers with different chain lengths and a double bond were firstly synthesized through the catalytic reforming and hydrosilylation reaction. Then, poly(acrylate-g-siloxane) was prepared by the copolymerization of the resulting oligomers with acrylate via emulsion polymerization. The as-synthesized oligomers were characterized by 1H NMR and UV spectrometry, and the morphologies and surface chemical compositions of the dried membrane were investigated by FT-IR, XPS, as well as AFM. XPS analysis result shows that the chemical composition of the membrane's surface was rich in polysiloxane segments, which could be responsible for an increase of surface water repellency (the contact angle could reach 115° at a lower content of polysiloxane). A further investigation suggest that the side chain length of siloxane in the poly(acrylate-g-siloxane) was the dominant factor in influencing the hydrophobicity of the membrane’ surface. When the siloxane chain length reaches to eight, the membrane's surface could exhibit the strongest hydrophobicity. 相似文献
The purpose of this paper is to derive the pointwise estimate for three general exponential-type operators by using new Ditzian-Totik modulus.AMS Subject Classification (2000): 41A27, 41A36Supported by the National Science Foundation, Hebei, China. 相似文献
A copper(II) acetate complex with a urea-functionalized pyridyl ligand, [CuL(OAc)2]2 · 2AcOH ( 1 ) [L = N-(3-chlorophenyl)-N'-(3-pyridyl) urea], was synthesized by the reaction of L with Cu(OAc)2 in methanol. A zigzag-shaped hydrogen bond chain of L is obtained via urea N–H ··· Npyridyl interactions, and a two-dimensional hydrogen bond network structure is further formed through the C–H ··· O interaction. In the complex 1 , a paddle-wheel structure is generated by Cu ··· Oacetate interactions and Cu ··· Npyridyl interactions. Furthermore, hydrogen bonding chain structure is extended through weak C–H ··· O hydrogen bond interactions. Through ultraviolet-visible (UV/Vis) spectroscopy, the acetate binding properties of L in solution were also evaluated. Variable temperature magnetic susceptibility measurement indicates that the metal complex 1 displays antiferromagnetic coupling property. 相似文献
A novel nitrogen doped and surface functionalized fluorescent CDs (T1) was synthesized by one-step and green hydrothermal method, which exhibits a satisfactory fluorescence quantum yield and a series of admirable features such as good aqueous solubility, narrow particle size distribution, resistance to photobleaching as well as excitation-dependent behavior. Benefitting from above merits, T1 can be employed to serve as an outstanding sensing platform for sensitive and accurate detection of ClO– by remarkable fluorescence “on–off” process with rapid and anti-interference. More notably, the good biocompatibility and photostability can ensure enormous bioimaging potential and successful application of T1 in monitoring of exogenous ClO– in MG-63 cells. Meanwhile, T1 can also be regarded as a filter paper sensor providing a convenient and efficient analyzing technology for monitoring of free residual chlorine in practical environmental samples. All these results demonstrate that there exists promising possibility for practical applications of T1 in bioimaging systems and environmental monitoring.
It is crucial for the wavefront sensor to reduce the influence of noise and enhance the detection accuracy of the centroid, which is also an important step for improving the performances of adaptive optics. In this paper, based on the theoretical analysis and by utilizing the Monte-Carlo simulation (MCS) technology, the results obtained by using the centroid algorithms have been compared in detail for the case, in which centroid of the signal is not at the center of the detection area and it also has a relatively large area. It is shown that the size of the signal spot and its centroid position have considerable influences on the centroid detection accuracy. The numerical results agree well with the theoretical predictions and the optimized parameters for each algorithm have been found. The study will be helpful for further optimizing the optical system and improving the centroid measurement accuracy of the wavefront sensor. 相似文献