Well controlled gas phase experiments of the size and dopant dependent reactivity of gold clusters can shed light on the surprising discovery that nanometer sized gold particles are catalytically active. Most studies that investigate the reactivity of gold clusters in the gas phase focused on charged, small sized clusters. Here, reactivity measurements in a low-pressure reaction cell were performed to investigate carbon monoxide adsorption on neutral bare and silver doped gold clusters (Au(n)Ag(m); n = 10-45; m = 0, 1, 2) at 140 K. The size dependence of the reaction probabilities reflects the role of the electronic shells for the carbon monoxide adsorption, with closed electronic shell systems being the most reactive. In addition, the cluster's reaction probability is reduced upon substitution of gold atoms for silver. Inclusion of a single silver atom causes significant changes in the reactivity only for a few cluster sizes, whereas there is a more general reduction in the reactivity with two silver atoms in the cluster. The experimental observations are qualitatively explained on the basis of a Blyholder model, which includes dopant induced features such as electron transfer from silver to gold, reduced s-d hybrization, and changes in the cluster geometry. 相似文献
The purpose of this study was to determine the objective vocal quality in 36 prelingually deaf children using cochlear implant (CI) with a mean age of 9 years. An additional purpose was to compare the objective vocal quality of these 36 CI users with 25 age-matched children with prelingual severe hearing loss using conventional hearing aids (HAs) and 25 normal hearing (NH) children.
Study Design
The design for this cross-sectional study was a multigroup posttest-only design.
Methods
The objective vocal quality was measured by means of the dysphonia severity index (DSI). Moreover, perceptual voice assessment using the GRBASI scale was performed.
Results
CI children have a vocal quality by means of the DSI of +1.8, corresponding with a DSI% of 68%, indicating a borderline vocal quality situated 2% above the limit of normality. The voice was perceptually characterized by the presence of a very slight grade of hoarseness, roughness, strained phonation, and higher pitch and intensity levels. No significant objective vocal quality differences were measured between the voices of the CI children, HA users, and NH children.
Conclusions
According to the results, one aspect of the vocal approach in children with CI and using HAs must be focused on the improvement of the strained vocal characteristic and the use of a lower pitch and intensity level. 相似文献
This paper deals with axially and biaxial monogenic functions that are derived using two fundamental methods of Clifford analysis, namely the Cauchy-Kowalevski extension and monogenic plane waves. 相似文献
Size matters! The electronic structure and size‐dependent stability of neutral and cationic scandium‐doped copper clusters have been investigated by mass spectrometric studies (for the cations) and also quantum chemical computations. The proposed reaction paths ultimately lead to the most stable Frank–Kasper‐shaped Cu16Sc+ cluster (shown here), which could be the germ of a new crystallization process.
Finding the shortest addition chain for a given exponent is a significant problem in cryptography. In this work, we present a genetic algorithm with a novel encoding of solutions and new crossover and mutation operators to minimize the length of the addition chains corresponding to a given exponent. We also develop a repair strategy that significantly enhances the performance of our approach. The results are compared with respect to those generated by other metaheuristics for exponents of moderate size, but we also investigate values up to \(2^{255} - 21\). For numbers of such size, we were unable to find any results produced by other metaheuristics which could be used for comparison purposes. Therefore, we decided to add three additional strategies to serve as benchmarks. Our results indicate that the proposed approach is a very promising alternative to deal with this problem. We also consider a more practical perspective by taking into account the implementation cost of the chains: we optimize the addition chains with regards to the type of operations as well as the number of instructions required for the implementation. 相似文献
The reaction of the organometallic diarsene complex [Cp2Mo2(CO)4(η2-As2)] ( 1 ) with Ag[Al{OC(CF3)3}4] (Ag[TEF]) yielded the AgI monomer [Ag(η2- 1 )3][TEF] ( 2 ). This compound exhibits dynamic behavior in solution, which allows directed selective synthesis of unprecedented organometallic–organic hybrid assemblies upon its reaction with N-donor organic molecules by a stepwise pathway, which is supported by DFT calculations. Accordingly, the reaction of 2 with 2,2′-bipyrimidine ( L1 ) yielded the dicationic molecular compound [{(η2- 1 )2Ag}2(μ- L1 )][TEF]2 ( 3 ) or the 1D polymer [{(η2- 1 )Ag}(μ- L1 )]n[TEF]n ( 4 ) depending on the ratio of the reactants. However, its reactions with the pyridine-based linkers 4,4′-bipyridine ( L2 ), 1,2-bis(4-pyridyl)ethylene ( L3 ) and 1,2-bis(4-pyridyl)ethyne ( L4 ) allowed the formation of the 2D polymers [{(η2- 1 )Ag}2(μ- Lx )3]n[TEF]2n [ Lx=L2 ( 5 ), L3 ( 6 ), L4 ( 7 ), respectively]. Additionally, this concept was extended to step-by-step one-pot reactions of 1 , [Ag(CH3CN)3][Al{OC(CF3)2(CCl3)}4] ([Ag(CH3CN)3][TEFCl]) and linkers L2 – L4 to produce the 2D polymers [{(η2- 1 )Ag}2(μ, Lx )3]n[TEFCl]2n [ Lx = L2 ( 8 ), L3 ( 9 ), L4 ( 10 ), respectively]. 相似文献