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991.
Liu J Kharitonova EP Duan CG Mei WN Smith RW Hardy JR 《The Journal of chemical physics》2005,122(14):144503
We studied temperature dependence of complex capacitance, impedance, and polarized Raman spectra of single crystal Cs2Nb4O11. First, we observed a sharp lambda-shaped peak at 165 degrees C in the complex capacitance, then found drastic changes in the Raman spectra in the same temperature range. Utilizing the pseudosymmetry search of structure space group, we attributed the observed anomalies to a structural change from the room temperature orthorhombic Pnn2 to another orthorhombic Imm2. We also measured room temperature polarized Raman spectra in different symmetries of normal vibrations and assigned high wavenumber Raman bands to the internal vibrations of NbO6 octahedra and NbO4 tetrahedra. 相似文献
992.
The covalent binding of acrylonitrile (CH(2)=CH-C triple bond N) and the formation of a C=C-C=N structure on Si(100) have been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional theory (DFT) calculations. For chemisorbed acrylonitrile, the absence of nu(C triple bond N) at 2245 cm(-1) and the appearance of nu(C=N) at 1669 cm(-1) demonstrate that the cyano group directly participates in the interaction with Si(100), which is further supported by XPS and UPS observations. Our experimental results and DFT calculations unambiguously demonstrate a [2 + 2] cycloaddition mechanism for acrylonitrile chemisorption on Si(100) through the binding of C triple bond N to Si dimers. The resulting chemisorbed monolayer with a C=C-C=N skeleton can serve as a precursor for further chemical syntheses of multilayer organic thin films in a vacuum and surface functionalization for in situ device fabrication. 相似文献
993.
Li Mingdong Deng Weiwei Fan Yousan Yang Jiyuan Liu Xiaolei 《Plasma Chemistry and Plasma Processing》2004,24(1):73-84
In order to prolong cathode lifetime of hollow electrode plasma generators, a method of impressed double magnetic fields with an alternating frequency is presented in this paper. The alternating frequency of the double magnetic fields is an important factor that influences the erosion rate on the area between the two coils' central planes. By analyzing the arc movement in the hollow cathode with a simplified theoretical model, the spiral curve shape of the radial arc and the relationship between the optimal alternating frequency and the intensity of magnetic fields are obtained. A photoelectric method is employed to measure the arc root rotation speed in the hollow cathode, and then the optimal alternating frequency is calculated as 319 Hz for the experimental conditions. The life testing with this alternating frequency showed that the cathode lifetime could be prolonged significantly. 相似文献
994.
Preparation of Mn3O4 nanocrystallites by low-temperature solvothermal treatment of γ-MnOOH nanowires
The preparation of trimanganese tetroxide (Mn3O4) nanocrystallites from γ-MnOOH nanowires under mild conditions has been achieved by two steps: first, γ-MnOOH nanowires with a mean diameter of about 12 nm and lengths of up to several micrometers were directly prepared via hydrothermal reaction between KMnO4 and toluene in water at 180°C for 24 h; then, pure Mn3O4 nanocrystallites could be obtained by solvothermal treatment of the γ-MnOOH nanowires in ethylenediamine (EDA) and ethylene glycol (EG) at 150°C for 24 h. It was found that the Mn3O4 product obtained in EDA comprised well-defined nanocrystallites with the size in the range of 15-35 nm, while the one obtained in EG consisted of aggregated nanoparticles with the size of less than 18 nm.The possible formation mechanism of nanocrystalline Mn3O4 in EDA and EG and reasons for the different effects of various solvents on the products were also proposed. 相似文献
995.
Magnetic field-induced orientation of a chiral side chain liquid crystalline polyacrylate(P-11) was studied by using IR dichroism. For the investigated P-11, it has been shown thatthe magnetic alignment takes place over the entire temperature range between its meltingpoint and clearing point and the orientation level is strongly temperature-dependent, thedevelopment with time of the magnetic orieatation follows an exponeotial-type relation,and the smectic phase state influences the thermal relaxation process in the absence of themagnetic field. 相似文献
996.
997.
Controlled drug delivery remains a research focus for public health to enhance patient compliance, drug efficiency and reduce
the side effects of drugs. Pectin, an edible plant polysaccharide, has been shown to be useful for the construction of drug
delivery systems for specific drug delivery. Several pectin derived formulations have been developed in our laboratory and
tested in vitro, ex vivo, and in vivo for the ability to deliver bioactive substances for therapeutic purposes in the context of interactions with living tissues.
Pectin derivatives carrying primary amine groups were more mucoadhesive and have shown potential in nasal drug delivery and
other mucosal drug delivery. Pectin derivatives with highly esterified galacturonic acid residues are more hydrophobic and
able to sustain the release of incorporated fragrances for a prolonged duration. Less esterified pectin derivatives are able
to penetrate deeper into the skin and may be useful in aromatherapy formulations. Pectin, in combination with zein, a corn
protein, forms hydrogel beads. The bound zein restricts bead swelling and retains the porosity of the beads; the pectin networks
shield the zein from protease attack. The complex beads are ideal vehicles for colon-specific drug delivery. Studies presented
in this paper indicate the flexibility and possibility to tailor pectin macromolecules into a variety of drug delivery systems
to meet different clinical requirements.
Mention of trade names or commercial products in this article is solely for the purpose of providing specific information
and does not imply recommendation or endorsement by the US Department of Agriculture. 相似文献
998.
纳米TiO2膜用于光催化氧化测定化学需氧量的研究 总被引:4,自引:0,他引:4
A photocatalytic oxidation method for determination of chemical oxygen demand (COD) using nano-TiO2 film, based on the use of a nano-TiO2-Ce(SO4)2 system and electrochemical detection, was proposed. The technique was originated from the direct determination of the Ce(Ⅲ) concentration change resulting from photocatalytic oxidation of organic compounds. Ce(Ⅲ), which was produced by photocatalytic reduction of Ce(SO4)2, could be measured at a multi-walled carbon nanotubes (MWNT) chemically modified electrode (CME). The COD values by this method were calculated from the differential pulse voltammetry (DPV) current of Ce(Ⅲ) at the CME. Under the optimal operation conditions, the detection limit of 0.5 mg·L^-1 COD with the linear range of 1-600 mg·L^-1 was achieved. This method was also applied to determination of various COD of ground water and wastewater samples. The resuits were in good agreement with those from the conventional COD methods, i.e., permanganate and dichromate ones. 相似文献
999.
Dong L Liu YC Tong YH Xiao ZY Zhang JY Lu YM Shen DZ Fan XW 《Journal of colloid and interface science》2005,283(2):380-384
Colloidal ZnO particles with narrow size distribution were prepared via a sol-gel process by base-catalyzed hydrolysis of zinc acetate. The morphology of ordered arrays of the particles was recorded by SEM. SEM also reveals that these uniform particles were composed of tiny ZnO subunits (singlets) sized of several nanometers. The size of the singlets, which is confirmed by X-ray diffraction and UV-vis absorption spectra, increases as the aging time is prolonged. The size-selective formation of colloids by aggregation of nanosized subunits is proposed to consist of two-stage growth by nucleation of nanosized crystalline primary particles and their subsequent aggregation into polycrystalline secondary colloids. The aggregates are all spherical because the internal rearrangement processes are fast enough. The ZnO colloids, i.e., the aggregates, tend to self-assemble into well-ordered hexagonal close-packed structures. Room-temperature photoluminescence was characterized for green and aged ZnO. 相似文献
1000.
A strategy for design of bioimprinted proteins with glutathione peroxidase (GPX) activity has been proposed. The proteins imprinted with a glutathione derivative were converted into selenium-containing proteins by chemical modifying the reactive hydroxyl groups of serines followed by sodium hydrogen selenide displacement. These selenium-containing proteins exhibited remarkable GPX activities and the GPX activities of reduction of H2O2 by glutathione (GSH) were found to be 101-817 U μmol−1, which approaches the activity of a selenium-containing catalytic antibody elicited by a hapten similar to our template. The steady state kinetic study for imprinted protein catalysis revealed Michaelis-Menten kinetics for both H2O2 and GSH, e.g. the pesudo-first-order rate constant kcat (H2O2) and the apparent Michaelis constant Km (H2O2) at 1 mM GSH were calculated to be 784 min−1 and 1.24×10−3 M, respectively, and the apparent second-order rate constant kcat (H2O2)/Km (H2O2) was determined to be 6.33×105 (M min)−1. The kinetics and the template inhibition showed that the strategy might be a remarkably efficient one for generating artificial enzyme with GPX activity. 相似文献