Sign patterns that allow diagonalizability revisited

Characterization of sign patterns that allow diagonalizability has been a long-standing open problem. In this article, necessary and sufficient conditions for a sign pattern to allow diagonalizability are obtained, in terms of allowing related properties. Some properties of normal sign patterns are considered. In particular, it is shown that normal sign patterns of order up to 3 allow diagonalizability. Two combinatorial necessary conditions for a sign pattern to allow diagonalizability are also presented.     

Thermosensitive t‐PLA‐b‐PNIPAAm tri‐armed star block copolymer nanoscale micelles for camptothecin drug release

Thermosensitive polylactide‐block‐poly(N‐isopropylacrylamide) (t‐PLA‐b‐PNIPAAm) tri‐armed star block copolymers were synthesized by atom transfer radical polymerization (ATRP) of monomer NIPAAm using t‐PLA‐Cl as macroinitiator. The synthesis of t‐PLA‐Cl was accomplished by esterification of star polylactides (t‐PLA) with 2‐chloropropionyl chloride using trimethylolpropane as a center molecule. FT‐IR, ¹H NMR, and GPC analyses confirmed that the t‐PLA‐b‐PNIPAAm star block copolymers had well‐defined structure and controlled molecular weights. The block copolymers could form core‐shell micelle nanoparticles due to their hydrophilic‐hydrophobic trait in aqueous media, and the critical micelle concentrations (CMC) were from 6.7 to 32.9 mg L^?1, depending on the system composition. The as‐prepared micelle nanoparticles showed reversible phase changes in transmittance with temperature: transparent below low critical solution temperature (LCST) and opaque above the LCST. Transmission electron microscopy (TEM) observations revealed that the micelle nanoparticles were spherical in shape with core‐shell structure. The hydrodynamic diameters of the micelle nanoparticles depended on copolymer compositions, micelle concentrations and media. MTT assays were conducted to evaluate cytotoxicity of the camptothecin‐loaded copolymer micelles. Camptothecin drug release studies showed that the copolymer micelles exhibited thermo‐triggered targeting drug release behavior, and thus had potential application values in drug controlled delivery. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4429–4439     

Simultaneous determination of seven lignans in Justicia procumbens by high performance liquid chromatography–photodiode array detection using relative response factors

A simple and sensitive HPLC coupled with photodiode array (HPLC–PDA) method was developed for simultaneous determination of seven lignans in Justicia procumbens using relative response factors (RRFs). The chromatographic separation was performed on a Shiseido Capcell Pak C₁₈ column (250 × 4.6 mm id, 5 μm), a gradient elution of acetonitrile/water, and a photodiode array detector. The column temperature was maintained at 35°C and the detection wavelength was set at 256 nm. Chinensinaphthol methyl ether was selected as the reference compound for calculating the relative response factors of the lignans. It has shown that the RRFs for lignans are quite similar at 256 nm of detection under different analytical conditions (different columns and HPLC instruments). Using RRFs, not every lignan is needed as a reference standard, making the method ideal for rapid, routine analysis, especially for those laboratories where lignans standards are not readily available. An economic and practicable HPLC method using RRFs was established for the determination of seven lignans in J. procumbens. This method not only can determine multiple indexes in traditional Chinese medicines (TCMs) simultaneously, but also resolve the problem of lacking of chemical standards. It will be a good quality evaluation method and pattern for TCMs.     

Thermal stability of functionalized carbon nanotubes studied by in-situ transmission electron microscopy

The thermal stability of funtionalized carbon nanotubes (CNTs) has been studied experimentally by direct in-situ observations using a heating stage in a transmission electron microscope, from room temperature (RT) to about 1000 °C. It was found that the thermal stability of the functionalized CNTs was significantly reduced during the in-situ heating process. Their average diameter dramatically expanded from RT to about 500 °C, and then tended to be stable until about 1000 °C. The X-ray energy dispersive spectroscopy analysis suggested that the diameter expansion was associated with coalescence of the carbon structure instead of deposition with additional foreign elements during the heating process.     

Catalytic pyrolysis of Pubescens to phenols over Ni/C catalyst

The pyrolysis of Pubescens over Ni/C catalyst was studied at 350 °C in H₂ flow. The presence of Ni/C catalyst efficiently improved the degradation of raw materials, and produced bio-oil with high content of phenols but low contents of acetic acid, furfural and water. In the reaction, Ni/C catalyst plays the role of catalytic decomposition and catalytic hydrogenation. The existence of the carbon carrier favors the formation of active Ni in small sizes with more defects, which results in high catalytic activity of Ni in biomass decomposition and selective production of phenols.     

Capacitive position measurement for high-precision space inertial sensor

Low noise position measurement is fundamental for space inertial sensors, and at present the capacitive position sensor is widely employed for space inertial sensors. The design for the possible suppression of the front-end electric noises for a capacitive sensor is presented. A prototype capacitive sensor with 2×10⁻⁶pF/Hz1/2 at frequency above 0.04 Hz is achieved and further improvements are discussed.      

红外光谱法测定尿素生产中脱氢催化剂的 S(Ⅵ)含量

本文介绍一个用红外光谱法测定尿素生产装置内使用过的脱氢催化剂中S(Ⅵ)的含量(以SO_4~-形式存在)。取Al_2(SO_4)_3作标样,溴化钾压片法制备13mm样片,用补偿法测定1120cm~(-1)SO_4~(2-)吸收峰的光密度,绘制A_(1120)～S(Ⅵ)标准曲线。样片中SO_4~(2-)含量在1mg以内符合朗伯—比尔定律。当脱氢催化剂中S(Ⅵ)含量在20％以内,方法准确度为3％,平均偏差最大为0.20。文中并介绍了操作误差的来源及克服办法。