156 resultados para 894.541


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The synthesis of a new aryl ether ketone polymer with an advantageous ratio of glass transition temperature to melting temperature is reported.

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Manipulation of electroosmotic flow in capillary electrophoresis is an important step for separation of inorganic anions. The type. and concentration of electroosmotic flow modifier (OFM) exert a tremendous influence on the electroosmotic mobility. In the presence of CTAB as buffer solutions' pH values increase, the electroosmotic mobility becomes lower. At the same ionic strength, the buffer type affects the electroosmotic velocity and the migration order for iodide and iodate.

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2,2'-Bis(3,4-dicarboxyphenoxy)-1,1'-binaphthyl dianhydride was used as a new monomer with various aromatic diamines to obtain polyimides by the usual two-step method. The bis(ether anhydride) was prepared by a nucleophilic substitution of I,1'-bi-2-naphthol with N-phenyl-4-chlorophthalimide, N-methyl-4-nitrophthalimide or 4-nitrophthalonitrile in aprotic polar solvent, and subsequent hydrolysis of the resulting bis(ether imide)s or bis(ether dinitrile), and then dehydration of the corresponding tetracarboxylic acid to afford the dianhydride. Most of the obtained polyimides were soluble in chloroform, pyridine, DMF, etc. The polyimide prepared from p-phenylene diamine was partial crystalline, whereas the others showed amorphous patterns in a WAXD study. These polymers have glass transition temperatures between 255-294 degrees C and 5% weight loss temperatures in the range of 502-541 degrees C in nitrogen and 473-537 degrees C in air. (C) 1997 Elsevier Science Ltd.

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An effort has been made to modify the mechanical behaviour of our previously reported gel-type gamma-radiation crosslinked polyethylene oxide (PEO)-LiClO4 polymer electrolyte. A highly polar and gamma-radiation crosslinkable crystalline polymer, polyvinylidene fluoride (PVDF), was selected to blend with PEO and then subjected to gamma-irradiation in order to make an simultaneous interpenetrating network (SIN), which was used as a polymer host to impart stiffness to the plasticized system. Experimental results have shown that the presence of PVDF in the system, through gamma-radiation induced SIN formation, could not only give a rather high mechanical modulus of 10(7) Pa at ambient temperature, but also maintain the room temperature ionic conductivity at a high level (greater than 10(-4) S/cm). DSC, DMA and conductivity measurement techniques were used to examine the effects of blending, gamma-irradiation and plasticization on the variations of glass transition and melting endotherm, on the appearance of high elastic plateau and on the temperature dependence of ionic conductivity: In addition, it was found that, in contrast with the unplasticized system, the ionic conductivity mechanism of this gel-type electrolyte seems to conform to the Arrhenius model, suggesting that, as a result of the high degree of plasticization, the polymer chains act mainly as the skeleton of the networks or polymer cages to immobilize the liquid electrolyte solution, whereas the ionic species migrate as if they were in a liquid medium. (C) 1997 Elsevier Science Ltd.

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The compounds O(CH2CH2C5H4)(2)Ln(THF)(2) [Ln = Sm(1), Yb(2)] were synthesized by the reduction of O(CH2CH2C5H4)(2)LnCl with sodium metal in tetrahydrofuran (THF) at room temperature. Recrystallization of 2 from dimethoxyethane (DME) produced the single-crystal O(CH2CH2C5H4)(2)Yb(DME) (3) whose structure has been determined by an X-ray diffraction study. The crystals are orthorhombic, space group Pcab, with a = 14.168(4), b = 13.541(6), c = 19.314(8) Angstrom, Z = 8, D-calc. = 1.66 g cm(-3).

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Reduction of hydrogen peroxide at a glassy carbon (GC) electrode modified with sigma-bonded pyrrole iron(III) octaethylporphyrin complex, (OEP)Fe(Pyr), was studied by cyclic voltammetry and a rotating disk electrode. In 0.1N NaOH solution, it is shown that such an (OEP)Fe(Pyr)/GC electrode has a significant catalytic activity towards hydrogen peroxide reduction (E(D) = -0.80 V, k = 0.066 cm s(-1)); however, the electrode stability is low. The deactivation is observed when the reaction charge (Q) is passing through the (OEP)Fe(Pyr)/GC disk electrode. A linear rotation scan method is applied to study the kinetic process by determining the disk electrochemical response (i(D)) to rotation rate (omega) at a definite disk potential (E(D)). Considering that the number of adsorbed electroreduced catalyst molecules (Red) varies according to the disk potential, a factor theta(= Gamma(Red)/(Gamma(Red) + Gamma(Ox))) is introduced to describe the electrode surface area fraction for electroreduced species. The obtained Koutecky-Levich equation is applicable whatever the potential is.

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用欠焦电子显微术和电子衍射技术研究了降温速率对高密度聚乙烯(HDPE)在全同立构聚丙烯(iPP)上附生结晶的影响.HDPE在高取向iPP基质膜上的附生生长仅发生在HDPE与iPP的直接接触面上,存在一临界附生层厚度,超出这一厚度的HDPE与iPP无取向附生关系.降温速率不影响附生层内的HDPE与iPP的附生结构关系,但对iPP基质膜上附生生长的HDPE的厚度,即HDPE的临界附生层厚度有明显影响.在缓慢降温(0.5℃/min)条件下,HDPE在iPP上的附生层厚度约为100nm.而室温空气降温条件下,HDPE在iPP上的附生层厚度则为250nm.

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本文首次提出了Eu~(3+)-TTA-N_(263)-异辛基苯氧基聚乙氧基乙醇(Triton X-100)体系的荧光分光光度法测定铕。在此最佳条件下铕的测定下限可达0.9ng/ml,并可允许存在一定量的其它共存稀土离子。该法用于测定包头混合稀土氧化物中的痕量铕,获得较满意的结果。

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式中A_(ij)是E_i向E_j的跃迁几率,分母是对E_i向不同下能级E_k的所有可能的跃迁几率求和。假定有N_i个原子处于高能级E_j中,则从E_i至E_j发射的荧光强度I_(ij)可用公式

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对于不同晶体结构类型和不同Ln的差热分析结果表明,随着从稀土元素的原子序数增加、无论是a-KLnP_4O_(12)还是β-KLnP_4O_(12)晶体的吸热峰温度均降低。如a-KLaP_4O_(12)的吸热峰温度为894℃、a-KSmP_4O_(12)为887℃、a-KEuP_4O_(12)为878℃、a-KGdP_4O_(12)为870℃、

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用丙酮作溶剂,提取糖甜菜中含有的丰富酪氨酸氧化酶,将所得丙酮粉浆固定于氧电极,制成的酪氨酸电极,在0.05~0.5mmol/L浓度范围内与输出信号值有线性关系。研究了电极的制备及操作条件,电极寿命可达30天。

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合成了钐与磷酸二甲酯的配合物,该配合物的组成为Sm〔(CH_3O)_2PO_2〕_3,测定了该配合物的红外和拉曼光谱。x射线单晶衍射法测定配合物的晶体属单斜晶系,P2_(1/c)空间群,α=10.434(4)A,b=16.541(3)A,c=10.804(4)A,β=111.75(3)°,V=1731.7(9)A~3,Z=4。钐与6个氧原子配位,每2个相邻的钐原子通过双“O—P—O”桥相连接,形成奇特的“双桥24元环”的环套环网状结构。钐氧配位多面体为稍微扭曲的正八面体。

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Year-round induction of sporogenesis of Laminaria saccharina was performed by mechanically blocking the transport of the putative sporulation inhibitors produced by the blade meristem and culturing the plants in constant short days. Sporogenesis was successfully induced by removal of the blade meristem, either by cultivating distal blade fragments or by performing a transverse cut in the frond. The earliest sorus formation after artificial induction was 10 days. The age of the sporophytes used for induction was 6-11 months or 2 years in tank-grown or field-collected sporophytes, respectively. Zoospores were successfully released in all cases. Thus, by year-round artificial induction of sporogenesis, (1) sporeling production of L. saccharina and thereafter sporophyte cultivation could be achieved without seasonal limitation, and (2) the life cycle of L. saccharina (from spore to spore) could be completed within 8 months under controlled conditions. (C) 2004 Elsevier B.V. All rights reserved.