Experimental and theoretical studies of the reaction between cationic vanadium oxide clusters and acetylene

The time of flight mass spectrometer coupled with a laser ablation/supersonic expansion cluster source and a fast flow reactor was adopted to study the reactivity of cationic vanadium oxide clusters （VinOS,） toward acetylene （C2H2） molecules under gas phase （P, - 1.14 kPa）, under near room temperature （T, - 350 K） conditions. Association products, VmOnC2H2^＋ （m,n = 2,4; 2,6; 3,7-8; 4,9-11; 5,12-13; 6,13-16, and 7,17）, are observed. The oxidation of C2H2 by （V2Os）n^＋ （n = 1 -3） is experimentally identified. The reactivity of （V2O5）n^＋ decreases as n increases. Density functional theory （DFT） calculations were carried out to interpret the reaction mechanisms. The DFT results indicate that a terminal oxygen atom from V2O5^＋ can transfer overall barrierlessly to C2H2 at room temperature, which is in agreement with the experimental observation. Other experimental results such as the observation of V206C2H2^＋ and nonobservation of V2O7,8C2H2^＋ in the experiments are also well interpreted based on the DFT calculations. The reactivity of vanadium oxide clusters toward acetylene and other hydrocarbons may be considered in identifying molecular level mechanisms for related heterogeneous catalysis.     

具有Markov延迟的网络化控制系统控制与通信协同设计

由于网络化控制系统分析与设计的复杂性,其控制与通信协同设计问题一直没有得到解决.该文讨论了一类离散线性时不变网络化控制系统在服从介质访问约束和传感器-控制器端存在Markov随机延迟的情况下控制与通信协同设计问题,提出了系统均方稳定的条件.采用静态通信序列,使通信序列和控制器可以分别设计,应用V-K迭代算法设计最优周期控制增益.仿真算例验证了系统在所设计的最优控制器下达到均方稳定.     

Meiyu in the middle and lower reaches of the Yangtze River since 1736

＂Yu Xue Fen Cun＂ records during the Qing Dynasty are used to identify the starting and ending dates of Meiyu at the period of 1736-1911. These results, along with the instrumental meteorological records, are used to reconstruct the series of length and precipitation of Meiyu during 1736-2000 over the middle and lower reaches of the Yangtze River. The characteristics of Meiyu are analyzed since 1736. Moreover, the strength of East Asian Summer Monsoon and locations of rainband are discussed, based on the relationship between the length of Meiyu and the Index of East Asian Summer Monsoon. It is found that the starting and ending dates and the length of Meiyu have significant interannual and interdecadal variations. Apart from 7-8 years, 20-30 years and 40 years cycles for the lengths of Meiyu, the centennial oscillation is also presented. The length of Meiyu, monsoon rainband movement over eastern China, and the strength of East Asian Summer Monsoon （EASM） have a very good correlation, which can be expressed in the following： during the periods of 1736-1770, 1821-1870 and 1921-1970, the EASM was stronger, and the monsoon rainband was located in North China and South China easily, corresponding to the decreased length of Meiyu. Whereas during the periods of 1771-1820, 1871-1920 and 1971-2000, the EASM was weaker and monsoon rainband usually stopped at the middle and lower reaches of the Yangtze River, corresponding to the increased length of Meiyu.     

Rate constants for the reaction of ozone with <Emphasis Type="Italic">n</Emphasis>-butyl, <Emphasis Type="Italic">s</Emphasis>-butyl and <Emphasis Type="Italic">t</Emphasis>-butyl methyl sulfides

The rate constants for the ozone reactions with n-butyl methyl sulfide （n-BMS, CHaCH2CH2CH2SCH3）, sec-butyl methyl sulfide （s-BMS, CH3CH2（CH3）CHSCHa） and tert-butyl methyl sulfide （t-BMS, （CH3）3CSCH3） were measured using our smog chamber under supposedly pseudo-first-order conditions at 30002 K and 760 Torr. The experimental determined rate constants for n-butyl, s-butyl and t-butyl methyl sulfide are （1.23 ± 0.06）×10-19, （5.08 ± 0.19）×10-20 and （2.26 ± 0.14）×10-20 cm3 molecule-1· s-1, respectively. The reactivity-structure relationship of the reactions was discussed and used to illustrate the mechanism of the ozone reaction with thioethers. The results enrich the kinetics data of atmospheric chemistry.     

一种有限波长转换能力OBS网络的信令协议

提出一种基于竞争限制的信令协议.该信令协议融合了按需波长重分配(WAoD)和按需延迟(DoD)两种竞争处理策略,不仅在当次突发包传送过程中实现了数据传送时隙的可修改性,而且还支持对数据承载波长的重置操作,有效地从资源竞争中挽救数据突发包.仿真结果表明,在有限波长转换能力的OBS网络结构中,与DoD和以往传统信令机制相比,所提出的信令协议可明显降低全网丢包率,提高了网络性能.     

太原地区冰雹气候特征及防雹减灾对策

采用1979年—2001年太原市6个县(市、区)气象局的历史资料,分析了降雹的空间分布和年变化、日变化及持续时间。根据当地情况,提出了加强预测预报、植树造林和改良土壤等减轻冰雹灾害的对策。     

Channel estimation for MIMO-OFDM systems in wireless mobile channels

New training sequences and frame structure are proposed to estimate time-varying channel for multipie-input multiple-output and orthogonal frequency division multiplexing （MIMO-OFDM） systems. The training sequences are modulatable orthogonal polyphase sequences, which have both good autocorrelations and cross-correlations. The channel impulse response （CIR） can be obtained by measuring the correlation between the received training sequence and the locally generated training sequence. The training sequences are used as guard interval instead of cyclic prefix, which not only improve the transmission efficiency but also enable the channel estimator to track time-varying channel. The simulation results show that the proposed method has about 2dB SNR gain over conventional methods in fast time-varying channel.     

Implementation of generic AHP evaluation system and its application to impact factors of on-line consumption behavior

To implement the computation of AHP （Analytic Hierarchy Process） automatically, make the implementation independence on the platform, and to convenient the service composition and service computation, this study implemented AHP model as a Web service and stored the evaluation information as XML form. This paper introduces the overall demands of AHP evaluation system firstly, and then presents some key technologies to implement AHP evaluation system, including mainly AHP evaluation index architecture based on XML, the class of AHP model, the Web service encapsulation of AHP, the publication and invocation of AHP and the client application. At last, the system is used to analyze the impact factors of online consumption behavior.     

基于权重的可视分存方案研究

视密码学的可视分存方案仅关注权重相同的参与者,忽略了原图主次信息的区别,造成了方案应用的局限性．为解决该问题,构建更具适用性、一般性的可视分存方案,提出了一种基于一般存取结构的可视分存方案,并进行扩展,进一步提出了基于权重的可视分存方案．该方案生成的图像与原图相比几乎没有任何失真,适用于黑白、灰度、彩色等各类图像的秘密共享．     

论言内语境对“吃＋宾（补）”结构的语义彰显作用

“吃＋宾”结构是现代汉语中讨论得比较多的问题,本文结合语境理论对其作了综合述评,着重探讨其言内语境;对学者们研究较少的“吃＋补”结构着重从语义指向角度分析其言内语境对语义的彰显作用。指出“吃＋宾（补）”结构生成发展的深层因素是汉民族的文化、心理、语言习惯。