一种可溶性多氯取代的聚芳醚酮酮的合成

聚芳醚酮具有优异的机械性能、耐热性、耐化学腐蚀性等优点因而被广泛应用于航空航天、电子器件、机械仪表等领域．传统的聚芳醚酮由于其主链的规整性和刚性,使其难溶难熔,给加工和应用带来一定的困难．近20年来,人们不断开发新的品种,通过在聚合物分子主链中引入柔性的醚键、取代侧基(苯基、三氟甲基、甲基等)或者     

Resin impregnation of cellulose nanofibril films facilitated by water swelling

Flexible composite films were produced by impregnating aqueous phenol formaldehyde (PF) resin into water-swollen cellulose nanofibril (CNF) films. CNF films were prepared using a pressurized filtration method in combination with freeze drying. The freeze-dried films were swollen with water then impregnated with PF resin by soaking in aqueous resin solutions of varying concentrations. Small amounts of PF slightly enhanced the tensile properties of CNF films. The formulation with the best mechanical properties was CNF/PF films with 8 wt % resin exhibiting tensile stress and toughness of 248 MPa and 26 MJ/m³, respectively. Resin concentrations higher than about 8 % resulted in composites with decreased tensile properties as compared to neat CNF films. The wet strength of the composite films was significantly higher than that of the neat CNF films. The resulting composites showed greater resistance to moisture absorption accompanied by reduced thickness swelling when soaked in water as compared to neat CNF films. The composites also showed decreased oxygen permeability at low humidity compared to neat films, but the composites did not show improved barrier properties at high humidity.     

Study of the cation distributions in Eu doped Sr2Y8(SiO4)6O2 by X-ray diffraction and photoluminescent spectra

The crystal structure and photoluminescent properties of europium doped silicate Sr₂Y₈(SiO₄)₆O₂:Eu³⁺ are reported. The Sr₂Y_8−xEu_x(SiO₄)₆O₂ compounds have typical apatite crystal structures with the P6₃/m space group. The distributions of Eu³⁺ between the two crystallographic sites 4f and 6h in the apatite structure are investigated by the powder X-ray diffraction and Rietveld refinement. Results show that Eu³⁺ ions only occupy the 4f sites when the Eu doping concentration is low (x=0-0.5 in Sr₂Y_8−xEu_x(SiO₄)₆O₂). However, in higher concentrations, Eu³⁺ ions begin to enter the 6h sites as well. The distributions of the Eu³⁺ are also reflected in photoluminescent spectra. The CIE coordinates for Sr₂Y₆Eu₂(SiO₄)₆O₂ are (0.63, 0.37), which is close to the pure red color.     

CrSi(2) hexagonal nanowebs

Single-crystalline CrSi(2) nanostructures with a unique hexagonal nanoweb morphology have been successfully synthesized for the first time. These nanowebs span 150-200 nm and are composed of <112?0> nanowire segments with a thickness of 10-30 nm. It is proposed that surface charges on the {101?0} sidewalls and the minimization of electrostatic energy induce the nanoweb formation. Calculations of the electrostatic energies were used to predict the transitions between different modes of bending, which agreed well with the experimental observations.     

Microparticle HZSM-5 zeolite as highly active catalyst for the hydration of cyclohexene to cyclohexanol

Microparticle HZSM-5 zeolite (MPZ) has been prepared without employing any organic templates, and used as a catalyst for the hydration of cyclohexene to synthesize cyclohexanol. MPZ exhibits better catalytic performance and superior settlement separation property than those of commercial HZSM-5 prepared by the traditional method using an organic template. The stability of MPZ has been investigated for a 1200-h test, and the regenerated performance of MPZ has also been investigated. The results show that although MPZ was reused for five recycles, the high cyclohexene conversion of 9.6 % and the high cyclohexanol selectivity of 96.8 % are still attained after the fifth regeneration. FT-IR, XRD and N₂ adsorption–desorption characterizations show that coke deposit on the surface and in the channels of MPZ is the main reason for the deactivation. ICP-AES, SEM–EDS and NH₃-TPD characterizations indicate that hydrothermal dealumination reduces the strong acidity and accelerates the catalyst deactivation. The spent catalyst by regeneration with H₂O₂ could be recovered to its initial high catalytic activity, due to the restored appropriate channels and exposed active sites.

     

提高验证牛顿第二定律实验精度的创新和改进

在验证牛顿第二定律实验中,除了教会学生动手操作、数据采集与处理外,还要向学生传授物理实验思想、实验设计方案、数学模型建立、误差分析与误差纠正等方面的内容。笔者撰写此论文,意在通过挖掘该实验创新知识点,以便达到培养学生创新思维和创造力的目的。     

The sloshing effects on distribution characteristics of gas–liquid mixture in spiral-wound heat exchanger

Journal of Thermal Analysis and Calorimetry - Spiral-wound heat exchanger (SWHE) is important equipment for industry, and it is suitable for floating production storage off-loading (FPSO). However,...     

Tensor product varieties,perverse sheaves,and stability conditions

The space spanned by the class of simple perverse sheaves in Zheng (2008) without localization is isomorphic to the tensor product of a Verma module with a tensor product of irreducible integrable highest weight modules of the quantum enveloping algebra associated with a graph. Under the isomorphism, the simple perverse sheaves get identified with the canonical basis elements of the tensor product module. The two stability conditions coincide with the localization process in Zheng (2008), by using supports and singular supports of complexes of sheaves, respectively.     

Derivations and right ideals of algebras

Let R be a K-algebra acting densely on V_D, where K is a commutative ring with unity and V is a right vector space over a division K-algebra D. Let ρ be a nonzero right ideal of R and let f(X₁,…,X_t) be a nonzero polynomial over K with constant term 0 such that μR≠0 for some coefficient μ of f(X₁,…,X_t). Suppose that d:R→R is a nonzero derivation. It is proved that if rankd(f(x₁,…,x_t))?m for all x₁,…,x_t∈ρ and for some positive integer m, then either ρ is generated by an idempotent of finite rank or d=ad(b) for some b∈End(V_D) of finite rank. In addition, if f(X₁,…,X_t) is multilinear, then b can be chosen such that rank(b)?2(6t+13)m+2.