Electrochemical scanning tunneling microscopy was used to study the structural evolution of adsorbed CO during preoxidation on Pt(111) modified with spontaneously deposited Ru. During the preoxidation process, a phase transition was observed from (2 × 2)-3CO-α to (√19 × √19)R23.4°-13CO via the transient structures (2 × 2)-3CO-β and (1 × 1)-CO. A comparison of these structural changes with those that occur on unmodified Pt(111) revealed that the presence of Ru resulted in higher populations of transient structures at lower potentials and a cathodic shift in the potential at which preoxidation is complete. These observations are discussed in terms of increased mobility of adsorbed CO in the presence of Ru. 相似文献
Low levels of water (limit of detection 2-5 mg kg1?)can be determined in a non-polar organic solvents such as benzene, 1,2-dichloroethane (DCE) and n-hexane by utilizing the reaction of water with SnCl4 or SbCl5. The reaction results of hydrolysis in halide and is accompanied by a decrease in optical absorption. With SnSl4, the reaction is monitored near 300 nm and with SbCl5 it is monitored at lower wavelengths (350-420). Niether reactons proceeds well in media containing only DCE and n-hexane. For this reason, the arrangemens involves a halide reagent dissolved in benzene which is merged with a benzene/n-hexane/DCE carrier stream into which samlpe is injected. A configuration in which only 2μl of a concentrated halide reagent solution is injected into the flowing sample stream is also shown to be viable for the determination of water in benzene. A membrane-permeation-based calibration method for preparing trace water standards is described. 相似文献
The physical dimensions of ensemble structures formed by adsorbed Bi on Pt(111) were estimated and correlations were established between ensemble size and oxidation activity. Measurements were made by examining electrochemical scanning tunneling microscopy (EC-STM) images of Bi irreversibly adsorbed on Pt(111). Percentage coverages of Bi, CO, poison, and ensemble were determined by both EC-STM and cyclic voltammetry. As the fractional Bi coverage increased, from 0.03 to 0.21, the ensemble size decreased, from approximately 9 to 1 nm. Poison formation was inhibited at ensemble sizes less than 2 nm and the turnover frequency of formic acid was enhanced by a factor of 100–200. Bi is hypothesized to not only physically produce the ensembles, but may also chemically alter their electronic properties. 相似文献
A Raman laser based on a bulk silicon single crystal with 1.127 μm emission wavelength is demonstrated. The Si crystal with 30 mm length was placed into an external cavity and pumped by a Q-switched Nd:YAG master oscillator power amplifier system. Strong defocusing of the pump and Raman laser beam by free carriers was compensated by an intracavity lens. Raman laser operation with a pulse duration of 2.5 ns was identified by a Raman laser threshold significantly lower than the single-pass stimulated Raman-scattering threshold. Linear absorption losses of the 1.06415 μm pump radiation are strongly reduced by cooling the Si crystal to a temperature of 10 K. 相似文献
To study the evolution of segregation in social networks across systems embedded in different institutional environments, we develop an identity-based learning model where segregation is stochastically conditioned by the initial distribution of the actor’s attention to identity and the updating of this distribution over time. The updating process, which we call the process of mutual learning multiplier, is based on an actor’s success and failure experiences in tying with the same-subgroup and cross-subgroup actors. Results from a Monte Carlo simulation of the model show that the mutual learning multiplier produces disproportional relationships between the initial distribution of identity attention and the level of segregation in social networks. We also find that those relationships are affected by the actors’ attention to structural holes, rate of learning from experience, system size, and the identity heterogeneity of the system. Overall, the model provides insights into various dynamics of network structuration across time and space. 相似文献
We examine returns policy in a Newsboy framework. Unlike the prior literature, however, we assume that both supplier and retailer have limited and stochastic salvage capacities. We first analyze the case of integrated supply chain in which the agents’ decisions are fully coordinated for the joint profits. The result prescribes a partial returns policy, in which the retailer returns a part of the leftovers to the supplier and liquidates the remainder through its clearance sale. In a decentralized system, the supplier should motivate the retailer to duplicate the outcome of the integrated system in choosing order and returns quantities. We propose three coordination contracts, of which each uses two benefit transfer schemes as an incentive to the retailer, instead of using a single benefit scheme as in the prior literature. All three effectively coordinate the supply chain. The supplier, as a Stakelberg leader, chooses the most profitable one since each contract yields the different shares of the agents’ profits. 相似文献
Hexagonal Ca5(PO4)3F, known as natural crystal fluorapatite and oldest host‐crystal for Ln3+‐lasant ions, is presented as a Raman‐active material. High‐order Raman‐induced χ(3)‐nonlinear processes are discovered in natural crystals of fluorapatite under picosecond pumping at 1.064 μm and 0.532 μm wavelength. A multitude of Stokes and anti‐Stokes components is generated in the ultraviolet, visible and near‐infrared spectral region by stimulated Raman scattering (SRS) and Raman four‐wave mixing (FWHM), resulting in a frequency comb with a width of 520 THz. The spectral lines are identified and attributed to the ν1(Ag) vibration mode of the tetrahedral [PO4] units which is related to a Raman shift of ωSRS ≈ 965 cm−1. The first Stokes steady‐state Raman gain coefficient in the near‐infrared spectral range is estimated to be >0.38 cm·GW−1. Finally, a short review of SRS‐promoting vibration modes and observed χ(3)‐ nonlinear interactions in all known SRS‐active natural crystals (minerals) is given.