Magnesium oxide microspheres as a packing material for the separation of basic compounds in normal-phase liquid chromatography

Uniform monodisperse magnesium oxide microspheres with a high surface area have been prepared by a facile seed-induced precipitation. By characterizing these particles with scanning electron microscopy and N(2) physisorption techniques, the results demonstrate that these magnesium oxide microspheres have an average particle diameter of 9.5 microm, a specific surface area of 211.7 m(2)g(-1), a total pore volume of 0.76 mL g(-1), and an average pore diameter of 143 A. The chromatographic properties of these microspheres have been investigated in normal-phase mode for the separation of various basic compounds including aniline, quinoline, and pyridine derivatives. In contrast to conventional silica, the magnesium oxide particles exhibit unique selectivity and retention property for the separation of the tested basic compounds, and these microspheres are promising as an alternative new packing material for high-performance liquid chromatography.     

Kinetic analysis of sequential multistep reactions

Many processes in biology and chemistry involve multistep reactions or transitions. The kinetic data associated with these reactions are manifested by superpositions of exponential decays that are often difficult to dissect. Two major challenges have hampered the kinetic analysis of multistep chemical reactions: (1) reliable and unbiased determination of the number of reaction steps, and (2) stable reconstruction of the distribution of kinetic rate constants. Here, we introduce two numerically stable integral transformations to solve these two challenges. The first transformation enables us to deduce the number of rate-limiting steps from kinetic measurements, even when each step has arbitrarily distributed rate constants. The second transformation allows us to reconstruct the distribution of rate constants in the multistep reaction using the phase function approach, without fitting the data. We demonstrate the stability of the two integral transformations by both analytic proofs and numerical tests. These new methods will help provide robust and unbiased kinetic analysis for many complex chemical and biochemical reactions.     

Dual-fluorescent donor-acceptor dyad with tercarbazole donor and switchable imide acceptor: promising structure for an integrated logic gate

A dual-fluorescent donor-acceptor (D-A) dyad with tercarbazole (donor) and 2,3-dithienylmaleimide (acceptor) was synthesized and characterized. The emission intensity of long wavelength could be regulated by either bistable structures of the dyad or the polarities of solvents. By mimicking the function of an integrated logic gate, a 2-input AND logic operation is established. [reaction: see text].     

枣疯病植原体PCR检测方法的建立及16SrDNA序列分析

以新郑灰枣枣疯病叶片为试验材料,先提取枣疯病病株叶片的DNA,经过巢式PCR扩增后对枣疯病植原体16SrDNA进行测序和分析.获得枣疯病植原体的16SrDNA基因片段为1125bp,通过序列同源性比较,表明枣疯病样品中检测到的植原体与EY(AY197655)同源性高达99％,应属于16SrV组,确定了枣疯病植原体的分类...     

Gauss曲率具下界的Ricci流

证明了一个2维流形上,如果初始Riemann度量的Gauss曲率有下界,则不论度量是否完备,它的Ricci流存在.     

Effect of bases with different solubility on the release behavior of risperidone loaded PLGA microspheres

Poly (D, L-lactide-co-glycolide) (PLGA) microspheres are attractive delivery vehicles due to their excellent sustained release capabilities. One major problem with PLGA microspheres is that the hydrophobic properties of PLGA generally cause a lag period in the process of drug release, leading to fluctuation of drug concentration in the blood and various resulting adverse reactions. Herein, Mg(OH)?, an inorganic base, and arginine, an organic base, were separately co-encapsulated into risperidone-loaded PLGA microspheres at varying concentration using the solvent evaporation method to improve release profiles from the microspheres. High encapsulation efficiencies were obtained in all formulations. The surface of base-free microspheres was smooth, whereas a few pores formed in base co-encapsulated microspheres. After 7-days degradation, many inter-connecting pores were formed in the interior of the microspheres containing 10 mg Mg(OH)?. The final pH in the microspheres with Mg(OH)? was higher than in those with arginine after 28-days degradation. The initial release of risperidone from microspheres containing Mg(OH)? was higher than from those containing arginine, and the latter release exhibited a more uniform pattern. Microspheres with 5mg and 10mg arginine exhibited zero-order release kinetics. However, both bases eliminated the lag phase of release. These results indicate that the incorporation of bases has potential in addressing the problem of the lag period in drug release from PLGA microspheres, and improving release behavior toward an ideal model.     

Optimization architecture for joint multi-path routing and scheduling in wireless mesh networks

In Wireless Mesh Networks (WMN), the optimal routing of data depends on the link capacities which are determined by link scheduling. The optimal performance of the network, therefore, can only be achieved by joint routing and scheduling optimization. Although the joint single-path routing and scheduling optimization problem has been extensively studied, its multi-path counterpart within wireless mesh networks has not yet been fully investigated. In this paper, we present an optimization architecture for joint multi-path QoS routing and the underlying wireless link scheduling in wireless mesh networks. By employing the contention matrix to represent the wireless link interference, we formulate a utility maximization problem for the joint multi-path routing and MAC scheduling and resolve it using the primal–dual method. Since the multi-path routing usually results in the non-strict concavity of the primal objective function, we first introduce the Proximal Optimization Algorithm to get around such difficulty. We then propose an algorithm to solve the routing subproblem and the scheduling subproblem via the dual decomposition. Simulations demonstrate the efficiency and correctness of our algorithm.     

Error analysis of dual wavelength quadrature phase demodulation for low-finesse Fabry-Pérot cavity based fibre optic sensor

An analysis of the errors in the dual wavelength quadrature phase demodulation technique for low-finesse Fabry-Pérot cavity based fibre optic sensor is presented. A simple numeric model for calculating the error is established. For sensors that experience only small cavity length changes during measurement, a simplified analytical expression of relative error is also derived. Errors for various sets of interrogation wavelengths are calculated and analyzed. The results show that two wavelengths with very slight difference should be chosen to avoid significant errors.     

Poly(N‐vinylpyrrolidone)‐Modified Surfaces for Biomedical Applications

Poly(N‐vinylpyrrolidone) (PVP), an important water soluble synthetic polymer, has many desirable properties including low toxicity, chemical stability, and good biocompatibility. Since PVP is hemocompatible and physiologically inactive, it has been used as a blood plasma substitute. Surface modification with PVP has been investigated extensively over the past few years as a means of preventing nonspecific protein adsorption. PVP may therefore be seen as a promising antifouling surface modifier comparable to poly(ethylene glycol) (PEG). In this review, various approaches for the design and preparation of PVP‐modified surfaces are summarized and potential biomedical applications of these PVP‐modified materials are indicated. Finally, some perspectives on future research on PVP for surface modification are discussed.

     

超宽带匹配馈电结构的设计与实验

设计研制了一种低阻抗传输线向高阻抗超宽带天线馈电的馈电结构,理想情况下,该馈电方法可实现特性阻抗为50Ω的同轴传输线向特性阻抗为200Ω的超宽带天线匹配馈电。分别用TEM喇叭天线和抛物反射面天线进行了实验验证,结果表明,与同轴线直接馈电相比,采用该匹配馈电结构后,TEM喇叭天线的辐射场强提高了15%,反射面天线的辐射场强提高了27%。