排序方式: 共有41条查询结果,搜索用时 15 毫秒
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Two novel 25,27-dihydroxy-26,28-bis(3-phenylthiapropxy)-calix[4]arene(3) and 25,27-dihydroxy-26,28-bis(3-phenylthiapropoxy)-5,11,17,23-tetra-tert-butylcalix[4] arene (4) were synthesized for the evaluation of their ion-selectivity in ion-selective electrodes(ISEs).ISEs based on 3 and 4 as neutral ionophores were prepared,and their selectivity coefficients for Ag^ (lg KAg,M^pot)were investigated against other alkali metal,alkaline-earth metal,aluminum,thallium(Ⅰ),Lead and some transition metal ions using the separate solution method (SSM).These ISEs showed excellent Ag^ seletivity over most of the interfering cations examined,except for Hg^2 and Fe^2 having relative smaller interference(lg KAg,M^pot≤-2.1). 相似文献
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Hydroxyl (OH) is identified and characterized on the Ni(111) surface by high‐resolution electron energy loss spectroscopy. We find clear evidence of stretching, bending, and translational modes that differ significantly from modes observed for H2O and O on Ni(111). Hydroxyl may be produced from water by two different methods. Annealing of water co‐adsorbed with atomic oxygen at 85 K to above 170 K leads to the formation of OH with simultaneous desorption of excess water. Pure water layers treated in the same fashion show no dissociation. However, the exposure of pure water to 20 eV electrons at temperatures below 120 K produces OH in the presence of adsorbed H2O. In combination with temperature‐programmed desorption studies, we show that the OH groups recombine between 180 and 240 K to form O and immediately desorbing H2O. The lack of influence of co‐adsorbed H2O at 85 K on the O? H stretching mode indicates that OH does not participate in a hydrogen‐bonding network. 相似文献
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Takahashi K Kodama R Tanaka KA Hashimoto H Kato Y Mima K Weber FA Barbee TW Da Silva LB 《Physical review letters》2000,84(11):2405-2408
A laser self-focused channel formation into overdense plasmas was observed using a soft x-ray laser probe system with a grid image refractometry (GIR) technique. 1.053 &mgr;m laser light with a 100 ps pulse duration was focused onto a preformed plasma at an intensity of 2x10(17) W/cm (2). Cross sections of the channel were obtained which show a 30 &mgr;m diameter in overdense plasmas. The channel width in the overdense region was kept narrow as a result of self-focusing. Conically diverging density ridges were also observed along the channel, indicating a Mach cone created by a shock wave due to the supersonic propagation of the channel front. 相似文献
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Stepped platinum surfaces can become hydrophobic when they are hydrogenated. Even though the Pt(533) and Pt(553) surfaces have similar geometries, the hydrophobicity on the deuterated surface is surprisingly different: on Pt(533) the surface is hydrophobic with water clustering at steps, whereas the entire surface is wet on Pt(553). 相似文献
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Ben Juurlink Petr Kolman Friedhelm Meyer auf der Heide Ingo Rieping 《Journal of Discrete Algorithms》2003,1(2):151
In this paper matching upper and lower bounds for broadcast on general purpose parallel computation models that exploit network locality are proven. These models try to capture both the general purpose properties of models like the PRAM or BSP on the one hand, and to exploit network locality of special purpose models like meshes, hypercubes, etc., on the other hand. They do so by charging a cost l(|i−j|) for a communication between processors i and j, where l is a suitably chosen latency function.An upper bound T(p)=∑i=0loglogp2i·l(p1/2i) on the runtime of a broadcast on a p processor H-PRAM is given, for an arbitrary latency function l(k).The main contribution of the paper is a matching lower bound, holding for all latency functions in the range from l(k)=Ω(logk/loglogk) to l(k)=O(log2k). This is not a severe restriction since for latency functions l(k)=O(logk/log1+log(k)) with arbitrary >0, the runtime of the algorithm matches the trivial lower bound Ω(logp) and for l(k)=Θ(log1+k) or l(k)=Θ(k), the runtime matches the other trivial lower bound Ω(l(p)). Both upper and lower bounds apply for other parallel locality models like Y-PRAM, D-BSP and E-BSP, too. 相似文献
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A new generation of experimental techniques quantifies the gas–surface reactivity of polyatomic reactants prepared in a single quantum state. These experiments eliminate internal state averaging and permit reactivity measurements on molecules with well-defined internal and translational energy. Varying the identity of the selected vibrational and rotational state and the molecule’s translational energy reveals how energy in specific energetic coordinates promotes reaction. When applied to methane’s dissociative chemisorption, which is rate-limiting in the industrial steam reforming reaction, these experiments reveal the molecular basis for activation, and they provide detailed insight into energy flow dynamics prior to reaction. This review will focus on experiments that quantify the reactivity of methane prepared in select rovibrational quantum states via optical excitation in a supersonic molecular beam. An overview will provide context, and a survey of experimental methods will emphasize features unique to these experiments. A presentation and discussion of state-resolved beam-surface scattering studies of methane activation on Ni(1 1 1), Ni(1 0 0), and Pt(1 1 1) will highlight the mechanistic and dynamical insights that such studies can provide. For example, while C–H stretching excitation best promotes transition state access on Ni(1 1 1) and Ni(1 0 0), bending excitation also activates dissociation, suggesting that many different energetic coordinates contribute to reactivity. Among those states studied, non-statistical behavior, including vibrational mode-specific and even bond-selective chemistry, is widespread, which indicates that the assumptions underlying statistical rate theories do not apply to this reaction. We examine the relevant timescales for energy exchange and reaction to provide a plausible explanation for the observation of non-statistical behavior. Finally, we suggest how these methods, and the results they have produced, might guide future work in the field. 相似文献
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ThetheoryofnonlinearpolymerizationwasinitiatedbyFlory[1]andStockmayer[2].Forsimplifyingtheevaluationofaveragepolymerquantities,manyotherstatisticalmethodssuchastheprobabilityofgeneratingfunctionmethod[3],thelawoftotalprobabilitymethod[4,5]andtheothermethods[6… 相似文献