分光光度法测量铝镓氮外延片中的铝含量

采用熔融的氢氧化钠刻蚀在蓝宝石衬底上生长的铝镓氮外延层,用深紫外光致发光光谱仪测量铝镓氮的荧光光谱来控制铝镓氮层的刻蚀深度,用盐酸将含铝氢氧化钠中和并调节至酸性(pH1~2)后转移至250 mL的容量瓶内定容,用铬天青S络合显色,用分光光度计在546 nm处测定吸光度来确定铝的浓度。该法测量结果的相对标准偏差为1.1%(n=5),加铝标准溶液做回收试验,回收率为96%~103%。该法可用于铝镓氮外延片中铝含量的准确测量。     

Preparation and characterization of cellulose nanocrystals via ultrasonication-assisted FeCl3-catalyzed hydrolysis

Cellulose nanocrystals (CNC) was obtained from bamboo pulp via ultrasonication-assisted FeCl₃-catalyzed hydrolysis process, with parameters optimized by response surface methodology. The optimal parameters were reaction temperature: 107 °C, reaction time: 58 min, ultrasonication time: 186 min. The morphological, crystal structural, chemical structural and thermal features of the prepared cellulose nanocrystals were analyzed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), Fourier transfer infrared (FTIR) and thermogravimetric analysis. The results showed that the cellulose nanocrystals formed an interconnected network structure and CNC was rod-like with the length of 100–200 nm and the width of 10–20 nm. XRD result revealed that, compared with cellulose pulp, the crystallinity index of CNC increased from 69.5 to 79.4 %, while the cellulose I crystal structure remained. FTIR analysis demonstrated that CNC had the similar chemical structures to that of cellulose pulp, which indicated that the chemical structures of CNC remained unchanged in the presence of FeCl₃-catalyzed hydrolysis process and ultrasonication treatment. Thermogravimetric analysis revealed that the resulting CNC exhibited relatively high thermal stability. The research shows that ultrasonication-assisted FeCl₃-catalyzed hydrolysis could be a highly efficient method for preparing CNC.     

Covalent Immobilization of Cellulases onto a Water-Soluble–Insoluble Reversible Polymer

The covalent immobilization of a commercial preparation of cellulase on a reversibly soluble–insoluble enteric polymer Eudragit S-100 by carbodiimide coupling was carried out. The characteristics of covalent Eudragit cellulase were evaluated using Fourier transform infrared (FTIR) spectra, circular dichroism (CD) spectra, and fluorescence spectra. FTIR, CD, and fluorescence measurements also revealed that the cellulases were covalently bonded to the supports. Covalent Eudragit cellulase had binding efficiency of 81.08% which was higher than the noncovalent Eudragit cellulase 56.83%. The relative activity of the native cellulase and covalent Eudragit cellulase increased and reached the maximum (at pH 5.0, 50°C) and then decreased with further increases in pH and temperature. The covalent Eudragit cellulase shows higher stability especially at higher pH and temperature. The K _m value of covalent Eudragit cellulase (4.78 g·L⁻¹) was decreased compared to that of the native cellulase (2.89 g·L⁻¹). The affinity of the cellulase to its substrate was increased when it was immobilized on Eudragit S-100.     

关于分块矩阵的群逆

本文讨论了形如M=[A B C D]分块矩阵的群逆,在一定条件下给出了其具体表达式,所得结果与文[1～3]的结果没有互相包含关系。     

圈平方图复杂性的一个简捷证明

本文给出了圈平方图支撑树数目公式的一个简捷证明。从而也获得它的渐近性质．     

Robust chaos synchronization of four-dimensional energy resource system via adaptive feedback control

This paper investigates the robust chaos synchronization problem for the four-dimensional energy resource systems with mismatched parameters. Based on the Lyapunov stability theory, the sufficient conditions for the synchronization are obtained analytically and an adaptive feedback control law is derived to make the states of two slightly mismatched chaotic systems asymptotically synchronized. Finally, some numerical simulations are performed to verify the proposed results.     

Preparation and properties of surfactant-bacillolysin ion-pair in organic solvents

The transesterification-active enzyme bacillolysin was extracted into organic solvents such as isooctane by enzyme-AOT (bis (2-ethylhexyl) sulfosuccinate) ion-pairing preserving its natural second structure and catalytic activity. Extraction efficiency was affected by the interaction mode of the two phases, ionic strength, and pH of aqueous phase, surfactant and enzyme concentration. Magnetic stirring with phase mixing was favorable for the enzyme extraction. Optimal ionic strength and pH were 8 mM CaCl₂ and 5.0, respectively. Critical number of AOT molecule for an enzyme molecule to be extracted into isooctane was 89. Optimal initial enzyme concentration in the aqueous phase was 7 mg mL⁻¹ while the initial AOT concentration in isooctane was 3 mM. Within CMC (critical micellar concentration) of AOT in isooctane, the increase of initial AOT concentration enhanced the extraction efficiency.     

Magnetic field effects on the open circuit potential of ferromagnetic electrodes in corroding solutions

Magnetic fields shift the open circuit potential (OCP) of ferromagnetic electrodes (Fe, Co, and Ni) in corroding solutions. The OCP changes we observe (a) follow the series Fe>Co>Ni; (b) increase with the magnetic flux density; (c) reach a maximum with disk electrodes approximately 1 mm in diameter; and (d) depend on the orientation of the electrode. We report that when the surface of the electrode is oriented parallel (theta = 90 degrees) or perpendicular (theta = 0 degrees) to the magnetic field, the open circuit potential moves in opposite directions (positive and negative, respectively) with the largest changes occurring when the electrode surface is parallel to the magnetic field. Nonconvective sleeve electrodes produce the same behavior. The overall experimental evidence suggests that the magnetic field changes the OCP by modifying the surface concentrations of the paramagnetic participants in the corrosion process of the ferromagnetic electrode by species in solution; this in turn is accomplished by imposing a field-gradient driven mode of mass transfer upon paramagnetic species in solution (magnetophoresis). Simulations of the magnetic field around the ferromagnetic electrode at the two extreme orientations considered here show that in one case (theta = 90 degrees) field gradients actually repel, while in the other case (theta = 0 degrees) they attract paramagnetic species in the vicinity of the electrode.     

Nd-Fe-B permanent magnet electrodes. Theoretical evaluation and experimental demonstration of the paramagnetic body forces

Cyclic voltammetry with Nd-Fe-B disk magnet electrodes (3.2 mm diameter) at slow sweep rates (< or = 0.01 V s(-1)) in relatively concentrated solutions (e.g., 80 mM) of diamagnetic redox-active species (e.g., TMPD) is controlled by diffusion. Under similar conditions, cyclic voltammetry with conventional noble metal disk millielectrodes is characterized by the absence of diffusion waves and the presence of density gradient driven natural convection. Although the magnetic field in the vicinity of Nd-Fe-B electrodes is relatively strong (approximately 0.5 T at the surface of the magnet electrode), the absence of magnetohydrodynamic stirring effects is attributed to the fact that the i and B vectors are almost parallel, and therefore the magnetohydrodynamic force F(B) (=i x B) is very small. On the other hand, the absence of natural convection is attributed to the two possible paramagnetic body forces, F(inverted Delta B) and F(inverted Delta C), exerted by the magnet electrode on the diffusion layer. Of those two forces, the former depends on field gradients (F(inverted Delta B) approximately B x inverted Delta B), while the latter depends on concentration gradients (F(inverted Delta C) approximately inverted Delta C(j)) and is directed toward areas with higher concentration of paramagnetic j. Through thorough analysis of the magnetic field and its gradients, it is found that the average F(inverted Delta C) force acting upon the entire diffusion layer is approximately 1.75 times stronger than F(inverted Delta B). Nevertheless, it is calculated that either force independently is strong enough and would have been able to hold the diffusion layer by itself. Further evidence suggests that, integrated over the entire solution, F(inverted Delta B) is the dominant paramagnetic force when the redox-active species is paramagnetic, e.g., [Co(bipy)(3)](ClO(4))(2) (bipy = 2,2'-bipyridine). Finally, convective behavior with diamagnetic redox-active species and magnet millielectrodes can be observed by holding closely (2-3 mm away) a repelling second magnet that bends the induction B to the point that the i x B product is not equal to 0. with Nd-Fe-B disk ma