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排序方式: 共有219条查询结果,搜索用时 31 毫秒
1.
Nitrogen desorption scanning hysteresis loops (DSHLs) for large-pore MCM-41 silicas (pore diameter from 4.0 to 6.5 nm) are reported for the first time. DSHLs for MCM-41 were compared with those of conventional mesoporous silicas and no appreciable differences were found, although hysteresis loops and DSHLs for the latter were usually broader. Since desorption behavior of conventional porous silicas is appreciably influenced by pore connectivity, the observed similarity in hysteresis behavior suggests single-pore blocking effects for MCM-41 due to variation of pore diameter along its nonintersecting channels. It was also shown that the steepness of nitrogen desorption branches at relative pressures close to 0.4 often results from proximity of the lower pressure limit of adsorption-desorption irreversibility and consequently it is not justified to consider it as an indication of narrow pore size distribution. Thus, application of desorption data in calculations of pore size distributions may be grossly misleading. 相似文献
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Abstract Thermoluminescence induced in CaF2 powder by fission fragments emanating from a uranium foil bombarded by fast neutrons has been measured as a function of neutron fluence. A linear relationship between the glow produced and the fast neutron fluence between 5 × 1010 and 6.5 × 1011 n/cm2 has been obtained, thus establishing the feasibility of the use of this method for fast-neutron dosimetry. A limitation of the method is that, if the fissile foil is not separated from the phosphor after irradiation, the TL produced by the α-disintegration of 238U may eventually mask the fission-induced TL. 相似文献
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For self-interstitial atom (SIA) clusters in various concentrated alloys, one-dimensional (1D) migration is induced by electron irradiation around 300 K. But at elevated temperatures, the 1D migration frequency decreases to less than one-tenth of that around 300 K in iron-based bcc alloys. In this study, we examined mechanisms of 1D migration at elevated temperatures using in situ observation of SUS316L and its model alloys with high-voltage electron microscopy. First, for elevated temperatures, we examined the effects of annealing and short-term electron irradiation of SIA clusters on their subsequent 1D migration. In annealed SUS316L, 1D migration was suppressed and then recovered by prolonged irradiation at 300 K. In high-purity model alloy Fe-18Cr-13Ni, annealing or irradiation had no effect. Addition of carbon or oxygen to the model alloy suppressed 1D migration after annealing. Manganese and silicon did not suppress 1D migration after annealing but after short-term electron irradiation. The suppression was attributable to the pinning of SIA clusters by segregated solute elements, and the recovery was to the dissolution of the segregation by interatomic mixing under electron irradiation. Next, we examined 1D migration of SIA clusters in SUS316L under continuous electron irradiation at elevated temperatures. The 1D migration frequency at 673 K was proportional to the irradiation intensity. It was as high as half of that at 300 K. We proposed that 1D migration is controlled by the competition of two effects: induction of 1D migration by interatomic mixing and suppression by solute segregation. 相似文献
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Yu Sherry Jiang Dr. Sanchita Bhadra Bingling Li Andrew D. Ellington 《Angewandte Chemie (International ed. in English)》2014,53(7):1845-1848
Catalytic hairpin assembly (CHA) has previously proven useful as a transduction and amplification method for nucleic acid detection. However, the two hairpin substrates in a CHA circuit can potentially react non‐specifically even in the absence of a single‐stranded catalyst, and this non‐specific background degrades the signal‐to‐noise ratio. The introduction of mismatched base pairs that impede uncatalyzed strand exchange reactions led to a significant decrease of the background signal, while only partially damping the signal in the presence of a catalyst. Various types and lengths of mismatches were assayed by fluorimetry, and in many instances, our MismatCHA designs yielded 100‐fold increased signal‐to‐background ratios compared to a ratio of 4:1 with the perfectly matched substrates. These observations could be of general utility for the design of non‐enzymatic nucleic acid circuits. 相似文献
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The class of local analyitic Bruck loops (or equivalently K-loops) is strongly related to locally symmetric spaces. In particular, both have Lie triple systems as their tangent algebra. In this paper, we consider the existence and some properties of the Campbell-Hausdorff series of local analytic Bruck loops (K-loops). This formula can be used to determine the local symmetries of the associated symmetric space. 相似文献
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The Brownian loop soup 总被引:6,自引:0,他引:6
Gregory F.?Lawler Wendelin?WernerEmail author 《Probability Theory and Related Fields》2004,128(4):565-588
We define a natural conformally invariant measure on unrooted Brownian loops in the plane and study some of its properties. We relate this measure to a measure on loops rooted at a boundary point of a domain and show how this relation gives a way to chronologically add Brownian loops to simple curves in the plane.Cornell University; Research supported in part by the National Science FoundationUniversité Paris-Sud and IUFMathematics Subject Classification (2000):60J65, 81T40 相似文献
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We study systematically the natural generalization of Schreier’s extension theory to obtain proper loops and show that this construction gives a rich family of examples of loops in all traditional common, important loop classes. 相似文献