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TiC、TiC1-x、(Ti1-xNbx)C电子结构的计算 总被引:2,自引:0,他引:2
采用离散变分x_α法(DV-X_α法)对TiC理想晶体、空位和掺杂缺陷结构中的电子结构进行了计算.通过选取分子簇模型,模拟了理想晶体、空位和掺杂缺陷情况.采用多重散射离散变分X_α法,通过自治迭代来求解局域密度泛函方程,得到了各个分子簇模型的电子结构.分析计算结果发现,在理想TiC结构的态密度图中,费米能级位于两峰之间.但在费米能级处的电子态密度不为零,这提供了TiC导电性的来源.在空位模型中,发现电子态密度在费米能级处有较大的值,说明空位的存在有利于提高TiC的导电能力.对于Nb掺杂后的电子结构,在费米能级处存在一个电子态密度峰,因而也有利于提高其导电性.在计算的过程中考虑到了分子簇模型边界条件带来的电行转移效应对电子结构的影响,通过提供适当的环境势,得到了较精确的计算结果.与已有的计算结果进行了对比,有较好的一致性. 相似文献
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以对二硝基苯为实例,介绍一种与伊滕法和柯亨法不同的单斜晶系粉晶X射线衍射圈的指标化方法.此法无需通过倒易晶格进行指标化、再通过还原晶胞得到正晶胞的指标化和晶格常数,也不需要衍射峰的不缺少,只需将分组,取d测与d计重叠数量最多的一组中误差最小的d测进行计算处理;可较简便地得到结果. 相似文献
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本从色谱峰的EMG模型出发,通过对重叠色谱峰的模拟和回归分析,提出了一种三元重叠色谱峰的面积的定量方法,三元重叠色谱峰的每一个峰面积可以由峰面积比和总面积求得,此法所需的数据都由实验色谱图上测得,峰面积计算结果的相对误差小于±5%,适用于相对峰谷为50%-95%的三元重叠色谱峰面积的定量。 相似文献
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丙烯气相一步氧化制环氧丙烷用Ag-Mo催化剂的研究 总被引:2,自引:0,他引:2
用浸渍法和溶胶-凝胶法制备了一系列以银及氧化钼为活性组分,负载于不同载体上的催化剂.在以分子氧为氧化剂,且原料气中不添加任何抑制剂的情况下,采用微反-色谱联合装置考察了催化剂对丙烯气相一步氧化制环氧丙烷的催化性能.结果表明,载体和助剂对催化剂上丙烯环氧化性能产生明显的影响.以TiO2-ZrO2为载体,CsNO3-NaCl为助剂的Ag-MoO3催化剂具有较好的催化性能,在400℃下,氧的转化率和环氧丙烷的选择性可分别达到11.3%和34.8%;在450℃下,氧的转化率和环氧丙烷的选择性可分别提高到33.0%和35.3%.采用溶胶-凝胶法制备的MoO3/SiO2催化剂对丙烯气相一步环氧化反应也具有一定的催化活性. 相似文献
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质量作用定律适用于所有的基元过程。基元过程是只被一个能峰隔开的两个相邻的有一定稳定性的状态之间的变化。能峰可高可低,最低时为0。基元过程既可以是发生化学变化的基元反应,也可以是简单的物理变化。 相似文献
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聚丙烯/层状硅酸盐纳米复合材料的制备、结构和性能 总被引:10,自引:0,他引:10
聚丙烯/层状硅酸盐纳米复合材料可通过丙烯单体插层聚合、聚丙烯溶液插层和聚丙烯熔融插层等方法制备,得到插层型或剥离型纳米复合材料,形成了与传统填充型聚合物复合材料不同的微观结构,其机械性能,热性能,阻隔性能和流变性能等明显提高,由于聚丙烯的非极性及层状硅酸盐纳米复合材料制备方法的特殊性,该研究具有一定的理论价值。 相似文献
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尿毒症患者血清及正常人尿液内中分子物质的分离分析 总被引:5,自引:2,他引:3
采用凝胶色谱法,以206nm处的紫外吸收为检测手段,分别从尿毒症患者血 清及正常人尿液内分离出A,B两个中分子峰,而从正常人血清中分离出来的A峰远低 于尿毒症患者血清的A峰;在B峰的位置正常人血清未出现明显的吸收.运用该方法 不仅提高了凝胶色谱的分离效果,且能方便地得到中分子级分的纯品.对清除了淋洗 液组分的中分子级分进行紫外和红外扫描,结果发现来源于尿毒症患者血清及正常人 尿液的A峰物质具有相同的紫外吸收且红外吸收光谱极其相似,而不同来源的B峰物 质虽然紫外吸收相同,但它们的红外吸收却存在一定的差异.采用离子交换色谱法对B 峰物质进行进一步的分离,以230nm处的紫外吸收为检测手段,正常人尿液的B峰物 质被分离成17个亚峰,尿毒症血清的B峰物质被分离成13个亚峰.其中绝大部分亚峰 的出峰位置(洗脱体积)相同. 相似文献
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热处理对Nylon—11结构的影响 总被引:2,自引:0,他引:2
对不同温度热处理过的Nylon-11样品,采用广角X射线衍射(WAXD),根据X射线衍射强度理论,用多重峰图解分峰方法研究了Nylon-11结构的变化,并导出了计算Nylon-11结晶度的公式.所得结果与密度法、DSC法进行了比较.同时也给出了Nylon-11的有关热力学参数, 相似文献
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Summary The paper deals with composite peaks in which the resolution is not sufficient to allow simple area determinations with conventional
integrator procedures. It is proposed to use the second derivatives of composite peaks, since the derivatives accentuate envelope
perturbations due to overlapped peaks. In particular, when there are two solutes in the composite, and when the peak separation
is between 2 and 4σ, the second derivative of the composite has two minima and three maxima. The second maximum is indicative
of the cross point of the two solutes. This point can be used to initiate and/or terminate the integration of the components
in the composite. Similarly, the second minimum occurs at a point close to the true maximum of the second peak in the composite.
This point can also be used for the quantitative determination of the second component in the composite. The second derivative
traces can also be integrated, but their utility in quantitative analysis of the peaks is questionable. An inversion procedure
is given in which the second derivative trace is inverted to yield a trace similar to the conventional chromatograms but with
better apparent resolution. In special circumstances, the inverted derivatives can be used for integration purposes. 相似文献
14.
H. N. Cheng 《Macromolecular theory and simulations》1994,3(6):979-1004
A general analytical approach is devised to treat the NMR data of stereoirregular and regioirregular homopolymers. The methodology is based on the four-component copolymerization model, treating normal and inverted monomer and the levo and dextro configurations as “comonomers”. In this way, the effects of monomer inversion and tacticity can be separately deduced. The analytical approach has been computerized. From the conditional probabilities, information on propagation mechanism (chain-end or catalytic-site control) can be obtained. The model has been used to analyze the NMR data of poly(propylene) samples made with titanium, vanadium and group IV metallocene catalysts. Comparisons have been made between model parameters and polymer microstructure. 相似文献
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Saeid Rajabzadeh Masaaki Teramoto Mohamed H. Al-Marzouqi Eiji Kamio Yoshikage Ohmukai Tatsuo Maruyama Hideto Matsuyama 《Journal of membrane science》2010,346(1):38
Five kinds of asymmetric poly(vinylidene fluoride) (PVDF) hollow fiber membranes with considerable different porosities at the inner and outer surfaces of the membrane were prepared via thermally induced phase separation (TIPS) method and applied for propylene absorption as gas–liquid membrane contactors. A commercial microporous poly(tetrafluoroethylene) (PTFE) hollow fiber membrane was also used as a highly hydrophobic membrane. Experiments on the absorption of pure propylene into silver nitrate solutions were performed and the effects of membrane structure, inner diameter, silver nitrate concentration and absorbent liquid flow rate were investigated at 298 K. PVDF membranes prepared by using nitrogen as bore fluid had lower inner surface porosity than the membranes prepared with solvent as bore fluid. Except the membrane with a skin layer at the outer surface, propylene absorption flux was inversely proportional to the inner diameter of the hollow fiber membrane, and propylene absorption rate per fiber was almost the same. Propylene flux increased with increasing the silver nitrate concentration and also with increasing the absorbent flow rate.A mathematical model for pure propylene absorption in a membrane contactor, which assumes that the membrane resistance is negligibly small and the total membrane area is effective for gas absorption, was proposed to simulate propylene absorption rates. Experimental results were satisfactorily simulated by the model except for the membrane having a skin layer. The model also suggested that propylene is absorbed in silver nitrate solutions accompanied by the instantaneous reversible reaction. This paper may be the first experimental and theoretical study on propylene absorption in membrane contactors. 相似文献
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Junting Xu Linxian Feng Shilin Yang Yinan Wu Yiqing Yang Xiangming Kong 《Macromolecular rapid communications》1996,17(9):645-651
Poly(propylene) samples produced by heterogeneous Ziegler-Natta catalysts containing different internal electron donors were fractionated by using temperature rising elution fractionation; some key fractions were analyzed with 13C NMR. It was found that internal electron donors with different structures can convert aspecific active sites into different isospectrific ones. The employment of bis(2-ethylhexyl) phthalate as internal electron donor leads to chemically inverted structures in the atactic fraction. This suggests that an internal electron donor may also exist in the environment of aspecific active sites. 相似文献
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We have found that the application of a weak radio frequency (rf) pulse to a spin system with indirect spin-spin (J) couplings can produce a narrow inverted peak in spectral regions where there are many overlapping peaks. Examples of three compounds with (1)H-(1)H J couplings and one with (1)H-(13)C J couplings are given. The dependences of the signals on the frequency, duration, and amplitude of the weak rf irradiation have been studied. For an rf power of gammaB(1)/2pi=1.0 Hz, pulse widths longer than 0.25 s consistently produce inverted narrow peaks in spectral regions with unresolved peaks. An interpretation of the origin of this unusual result of selective excitation in spin systems with homogeneous broadening is given: the inverted signal observed can be considered as a cumulative effect of the weak rf irradiation acting on many uncorrelated transitions that are slightly off resonance on both sides of the irradiating frequency; the only role of the J couplings (or dipolar couplings in liquid crystals) is to produce a large number of closely spaced peaks that overlap with each other. Computer simulations of both coupled and noninteracting spin systems have been carried out, and the results support this interpretation. 相似文献
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Wendell V. Smith 《Journal of Polymer Science.Polymer Physics》1980,18(7):1587-1597
Monad, dyad, and triad populations have been derived from the 13C NMR spectra of eight ethylene-propylene copolymers. Using these values, Kinetic parameters of the polymerization have been calculated, including conditional probabilities, and reactivity ratios. The fraction of propylene entering in an inverted order has been found to be about 20%. The copolymerization is dominated by the relatively large reactivity of ethylene. There is an alternating tendency for the two monomers which is evident both in the normal addition of propylene and the inverted addition. Penultimate effects do not play a significant role. 相似文献
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H. N. Cheng 《Macromolecular Symposia》1994,86(1):77-102
Propylene can be polymerized using a variety of catalysts under different reaction conditions. In the general case, the polymer may exhibit both stereochemistry (tacticity) and regiochemistry (normal and inverted propylene enchainment). When the molecular weight is low, chain ends also become important. The NMR spectra of the resulting polymers can be very complex. In this work, the spectra are studied with the help of analytical (model fitting) and synthetic (computer simulation) approaches in conjunction with a tetrapolymerization model. The approaches described herein are applied to regioirregular polypropylene, particularly low-molecular-weight irregular polypropylene samples (polypropylene oils) made with homogeneous catalysts. Complete spectral assignments and analyses are provided for these oils. Studies of polymer main chain structure provide information on polymer chain propagation; analyses of chain ends provide information on initiation, chain transfer, and termination. 相似文献
20.
Toshiyuki Tsunetsugu Junji Furukawa Takayuki Fueno 《Journal of polymer science. Part A, Polymer chemistry》1971,9(12):3541-3546
Optically active propylene sulfide was polymerized in the presence of potassium hydroxide as catalyst to give optically active poly(propylene sulfide). Rotatory dispersion curves of the polymer thus obtained were measured in benzene and chloroform media. In both cases, the curves were anomalous in shape with the same sign, having troughs at 290 and 275 mμ, respectively. (–)-1,2-Diethylthiopropane was prepared as an optically active model compound of poly(propylene sulfide) in optical rotatory properties. It was found that the model compound also shows anomalous rotatory dispersion both in benzene and chloroform with the same sign. Thus it may be concluded that the anomalous dispersion of poly(propylene sulfide) must be attributed to an additional Cotton effect caused by the absorption of sulfide bonds, which are generally admitted to have absorptions at 200 and 230 mμ (shoulder). 相似文献