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561.
562.
通过构建一个简单的模型分析了普遍服务约束下的垄断产业在引入竞争后的市场竞争,模型很好地展现了垄断产业引入竞争后所出现的“撇脂现象”.通过分析得出:引入竞争后,在位者的盈利和亏损同时减少,但盈利减少得更多;竞争对消费者总体上是有利的,但竞争的好处更多地被低成本的城市消费者所获得,高成本的农村消费者则没有分享到改革的成果;... 相似文献
563.
Dr. Feng Liang Dr. Shengqing Li Prof. Stuart Lindsay Prof. Peiming Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(19):5998-6007
We have developed a chemical reagent that recognizes all naturally occurring DNA bases, a so called universal reader, for DNA sequencing by recognition tunneling in nanopores. 1 The primary requirements for this type of molecules are the ability to form non‐covalent complexes with individual DNA bases and to generate recognizable electronic signatures under an electrical bias. 1‐H‐imidazole‐2‐carboxamide was designed as such a recognition moiety to interact with the DNA bases through hydrogen bonding. In the present study, we first furnished a synthetic route to 1‐H‐imidazole‐2‐carboxamide containing a short ω‐functionalized alkyl chain at its 4(5) position for its attachment to metal and carbon electrodes. The acid dissociation constants of the imidazole‐2‐carboxamide were then determined by UV spectroscopy. The data show that the 1‐H‐imidazole‐2‐carboxamide exists in a neutral form between pH 6–10. Density functional theory (DFT) and NMR studies indicate that the imidazole ring exists in prototropic tautomers. We propose an intramolecular mechanism for tautomerization of 1‐H‐imidazole‐2‐carboxamide. In addition, the imidazole‐2‐carboxamide can self‐associate to form hydrogen bonded dimers. NMR titration found that naturally occurring nucleosides interacted with 1‐H‐imidazole‐2‐carboxamide through hydrogen bonding in a tendency of dG>dC?dT>dA. These studies are indispensable to assisting us in understanding the molecular recognition that takes place in the nanopore where routinely used analytical tools such as NMR and FTIR cannot be conveniently applied. 相似文献
564.
《Analytical letters》2012,45(8):1171-1192
Abstract The response of polycyclic aromatic hydrocarbons (PAH) at different UV wavelengths was measured using high performance liquid chromatography with spectrophotometric diode-array detection. By utilizing the total UV absorption bandwidth (200-400 nm), it was found that a narrow distribution of normalized response factors (area/g) could be obtained for 16 PAH in a reference mixture of frequently-occurring species, even though the PAH represented a wide variety of different chromophores. Using the mean response factor for the 16 PAH, a universal calibration factor was obtained that formed the basis of a method for the determination of PAH for which calibration data cannot otherwise be obtained. It utilized normal phase high performance liquid chromatography (HPLC) with a cyanopropyl column and a hexane-dichloromethane mobile phase. The HPLC conditions were optimized for the separation of PAH according to their aromatic ring number. The method was developed for the characterization of complex mixtures of fossil fuels-derived PAH that cannot be analyzed by traditional methods. It is applicable to PAH having from 1 to 10 or more fused aromatic rings. 相似文献
565.
We consider a finite dimensional representation of the dihedral group D2p over a field of characteristic two where p is an odd integer and study the corresponding Hilbert ideal IH. We show that IH has a universal Gröbner basis consisting of invariants and monomials only. We provide sharp bounds for the degree of an element in this basis and in a minimal generating set for IH. We also compute the top degree of coinvariants when p is prime. 相似文献
566.
Let be a countable and locally finite CW complex. Suppose that the class of all metrizable compacta of extension dimension contains a universal element which is an absolute extensor in dimension . Our main result shows that is quasi-finite.
567.
Chong Wu 《中国科学 数学(英文版)》2012,55(3):625-632
Let QS* (S 1) be the space of quasisymmetric homeomorphisms of the unit circle such that the corresponding subspace of the universal Teichmu¨ller space has Weil-Petersson metric.In this paper we give a necessary condition for a quasisymmetric homeomorphism to belong to QS *(S 1) from the aspect of cross-ratio distortion. 相似文献
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为了有效处理试验数据欠缺情况下结构可靠性问题,提出了一种新的结构非概率可靠性分析方法.该方法考虑了结构非概率可靠性计算中非线性系统区间运算带来的不确定性,利用泛灰数代替参数不确定区间变量参与可靠性运算,成功克服了区间运算不确定对结构可靠性结果的影响.通过三个数值算例表明,当存在区间运算不确定时,文中方法得到结构非概率可靠度要小于基于区间的非概率可靠性模型得到的结果,这是由于后者未考虑区间运算的不确定所致.在缺少试验数据的情况下,文中所提方法可以得到较保守的结构可靠性结果,能够更加客观、真实地反映结构的实际安全状况,更加适于实际工程应用. 相似文献