Theoretical investigation on gas-phase reaction of CF3CH2OCH3 with OH radicals and fate of alkoxy radicals (CF3CH(O)OCH3/CF3CH2OCH2O)

Detailed theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of CF₃CH₂OCH₃ (HFE-263fb2) with OH radicals using ab-initio and DFT methods. Reaction profiles are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels, respectively. Our calculations reveal that hydrogen abstraction from the CH₂ group is thermodynamically and kinetically more facile than that from the CH₃ group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for CF₃CH₂OCH₃ and radicals (CF₃CHOCH₃ and CF₃CH₂OCH₂) are also reported for the first time. The calculated bond dissociation energies for the CH bonds are in good agreement with experimental results. At 298 K, the calculated total rate coefficient for CF₃CH₂OCH₃ + OH reactions is found to be in good agreement with the experimental results. The atmospheric fate of the alkoxy radicals, CF₃CH(O)OCH₃ and CF₃CH₂OCH₂O are also investigated for the first time using the same level of theory. Out of three plausible decomposition channels, our results clearly point out that reaction with O₂ is not the dominant path leading to the formation of CF₃C(O)OCH₃ for the decomposition of CF₃CH(O)OCH₃ radical in the atmosphere. This is in accord with the recent report of Osterstrom et al. [CPL 524 (2012) 32] but found to be in contradiction with experimental finding of Oyaro et al. [JPCA 109 (2005) 337].     

CH3S与CH2SH自由基反应的密度泛函理论研究

用量子化学从头算和密度泛函理论(DFT)对CH3S与CH2SH自由基反应进行了研究。在B3LYP/6-311+G(d,p)水平上优化了反应通道各驻点物种(反应物、中间体、过渡态和产物)的几何构型,用内禀反应坐标(IRC)计算和频率分析的方法对过渡态结构及连接性进行了验证。在QCISD(T)/6-311++G(d,p)水平上计算了各物种的单点能,并对总能量进行了零点能校正。研究结果表明,CH3S与CH2SH反应为多通道反应,有3条可能的反应通道。反应物首先通过C-S键相互作用形成链状碳-硫偶合中间体IM1,再经过裂解和脱氢气机理生成主要产物P1(CH3SH+CH2S)和次要产物P2和P3。根据势能面分析,所有反应均为吸热反应。相对于CH3S与CH2SH,各产物能量分别为(-175.2,335.5和331.5)kJ.mol-1。     

Theoretical studies on kinetics,mechanism and thermochemistry of gas-phase reactions of HFE-449mec-f with OH radicals and Cl atom

A theoretical study on the mechanism and kinetics of the gas phase reactions of CF₃CHFCF₂OCH₂CF₃ (HFE-449mec-f) with the OH radicals and Cl atom have been performed using meta-hybrid modern density functional M06-2X using 6-31+G(d,p) basis set. Two conformers have been identified for CF₃CHFCF₂OCH₂CF₃ and the most stable one is considered for detailed study. Reaction profiles for OH-initiated hydrogen abstraction are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. Our calculations reveal that hydrogen abstraction from the CH₂ group is thermodynamically and kinetically more facile than that from the CHF group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for HFE-449mecf and radicals generated by hydrogen abstraction, are also reported. The calculated bond dissociation energies for CH bonds are in good agreement with experimental results. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250–450 K. The calculated rate constant values are found to be 9.10 × 10⁻¹⁵ and 4.77 × 10⁻¹⁷ cm³ molecule⁻¹ s⁻¹ for reactions with OH radicals and Cl atom, respectively. At 298 K, the total calculated rate coefficient for reactions with OH radical is in good agreement with the experimental results. The atmospheric life time of HFE-449mec-f is estimated to be 0.287 years.     

Mechanism and kinetic study of 3-fluoropropene with hydroxyl radical reaction

Potential energy surface for the reaction of hydroxyl radical (OH) with 3-fluoropropene (CH₂CHCH₂F) has been studied to evaluate the reaction mechanisms, possible products and rate constants. It has been shown that the CH₂CHCH₂F with OH reaction takes place via a barrierless addition/elimination and hydrogen abstraction mechanism. It is revealed for the first time that the initial step for the barrierless additional process involves a pre-reactive loosely bound complex (CR1) that is 1.60 kcal/mol below the energy of the reactants. Subsequently, the reaction bifurcates into two different pathways to form IM1 (CH₂CHOHCH₂F) and IM2 (CH₂OHCHCH₂F), which can decompose or isomerize to various products via complicated mechanisms. Variational transition state model and multichannel RRKM theory are employed to calculate the temperature-, pressure-dependent rate constants and branching ratios. At atmospheric pressure with He as bath gas, IM1 formed by collisional stabilization is dominated at T ≤ 600 K; whereas the direct hydrogen abstraction leading to CH₂CHCHF and H₂O are the major products at temperatures between 600 and 3000 K, with estimated contribution of 72.9% at 1000 K. Furthermore, the predicted rate constants are in good agreement with the available experimental values.     

拓扑控制对Ad hoc网络能耗及生存期的影响分析

Ad hoc网络的能耗主要与节点的发射功率、数据包转发次数及端到端通过量三者有关。通过建立网络能耗模型分析和实验仿真发现,对负载较低的网络实施拓扑控制技术可以降低网络能耗、延长网络生存期;而对负载较高的网络实施拓扑控制技术,虽不能有效降低网络能耗,但仍然可以延长网络的生存期。     

Theoretical analysis of the lifetime and energy hole in cluster based wireless sensor networks

Cluster based wireless sensor networks have been widely used due to the good performance. However, in so many cluster based protocols, because of the complexity of the problem, theoretical analysis and optimization remain difficult to develop. This paper studies the performance optimization of four protocols theoretically. They are LEACH (Low Energy Adaptive Clustering Hierarchy), MLEACH (Multi-hop LEACH), HEED (Hybrid Energy-Efficient Distributed Clustering Approach), and UCR (Unequal Cluster based Routing). The maximum FIRST node DIED TIME (FDT) and the maximum ALL node DIED TIME (ADT) are obtained for the first time in this paper, as well as the optimal parameters which maximize the network lifetime. Different from previous analysis of network lifetime, this paper analyzes the node energy consumption in different regions through the differential analysis method. Thus, the optimal parameters which maximize the lifetime can be obtained and the detailed energy consumption in different regions at different time can be also obtained. Moreover, we can obtain the time and space evolution of the network, from a steady state (without any death) to a non-steady state (with some death of nodes), and then to the final situation (all nodes die). Therefore, we are fully aware of the network status from spatial and temporal analysis. Additionally, the correctness of the theoretical analysis in this paper is proved by the Omnet++ experiment results. This conclusion can be an effective guideline for the deployment and optimization of cluster based networks.     

The determination of phosphorus in a microfluidic manifold demonstrating long-term reagent lifetime and chemical stability utilising a colorimetric method

The chemical stability of the vanadomolybdophosphoric acid method for phosphate determination in a microfluidic manifold is described. The reagent lifetime has been shown to extend to more than 1 year. A stopped flow regime has been implemented, which enabled a very simple microfluidic manifold design to be employed, and has the added advantages of low reagent consumption coupled with less waste generation and access to the complete reaction profile in the optical cuvette on the microfluidic chip. Optical detection was achieved with an UV-LED, integrated into the microfluidic chip holder, coupled to a portable spectrometer via an optical fibre. The manifold includes integration of reagent and sample introduction inlets, a mixing channel and an optical cuvette of 400 μm path length. Two reagent batches were prepared (December 1999 and April 2001) and were shown to still be highly comparable after 1 year in storage. Multiple calibrations have been performed on the microfluidic system over a 12-month period showing only minimal loss in performance and a standard orthophosphate-containing sample was analysed in the microfluidic manifold on a weekly basis with a relative standard deviation of <2.3%.     

Characteristics of atmospheric divergence and convergence in the Indian Ocean inferred from scatterometer winds

Large-scale surface atmospheric convergence and divergence patterns in the Indian Ocean are mapped using high-spatial resolution, merged scatterometer wind vectors during 1991-2000. The convergence zone evolves to north of 15°S as a result of convection promoted by warm (> 28 °C) equatorial sea surface temperature (SST), and it exhibits strong intensity during boreal summer and winter. A divergence zone evolves to the south of 15°S as a result of subdued convection caused by colder SST (< 24 °C) that reduces outgoing long-wave radiation; it exhibits enhanced intensity in the eastern Indian Ocean during boreal winter. The interannual variability shows that the divergence in the eastern Indian Ocean lags its western counterpart by 5-7 months. The convergence in the eastern Indian Ocean is stronger than its western counterpart during boreal summer. Relationship between Southern Oscillation Index and spatially averaged convergence time series indicate that the latter weakened during strong El Niño years 1994 and 1997. Spatially averaged divergence time series show a near-contemporaneous relationship with all-India rainfall, with a temporal lag of 1∼2 months.     

氧化铟纳米线的水热-退火合成及其NO2气敏性能研究

以InCl3·4H2O、草酸和氢氧化钠为原料,采用水热-退火路径,合成出了In2O3纳米线.X射线粉末衍射(XRD)和扫描电子显微镜(SEM)表征结果表明:合成产物为立方相的In2O3纳米线,其直径约为30-50 nm,长径比超过40.气敏性能测试结果表明,以该法合成的In2O3纳米线对NO2灵敏度高,选择性好,响应恢复快,可以检测1 ppm(i.e.×10-6)的NO2,是一种应用前景良好的NO2敏感材料.     

聚3—己基噻吩及其掺杂TiO2材料对NO2的气敏特性

制作了一种工作于室温下的NO2气体传感器。该传感器以有机聚合物聚3—己基噻吩(P3HT)为敏感材料,以聚对苯二甲酸乙二醇酯(PET)薄膜为柔性衬底。对敏感膜进行了SEM表征。室温下,对不同体积分数的NO2进行了测试,对器件尺寸的影响进行了分析,并对响应规律进行了总结。经实验,对NO2测试下限可达到0.2×10-6。为提高敏感性、减小恢复时间,尝试对敏感膜掺杂TiO2,并同未掺杂的敏感膜进行实验比较,发现对体积分数1.5×10-6的NO2,掺杂TiO2可将敏感性提高8%,恢复性也有明显改善,对周期为1060 s的循环测试表明:掺杂TiO2下阻值基本能完全恢复。     

尿素施用对土壤pH值和模拟温室箱内NH3和NO2浓度的影响

在模拟条件下测定尿素引起土壤的pH变化及其对氨挥发的影响,同时利用被动采样法测定模拟温室箱中施用尿素所造成的NO2和NH3浓度变化趋势。实验表明:在短期内施用尿素能明显升高土壤pH,并增加土壤氨挥发。用1%柠檬酸作为NH3的吸收剂,测得NH3浓度在6～18μgm-3之间,用25%TEA作为NO2的吸收剂,测得NO2的浓度在12～35μgm-3之间。施用氮肥的模拟温室箱中NH3、NO2浓度明显高于不使用氮肥的状况及背景环境。     

用于化学热泵的氯化钙/甲醇络合反应动力学的研究

CaCl2／CH3OH的络合反应动力学是设计该体系化学热泵装置，选定合格工艺条件的重要基础。本文采用变温热重分析法，在真空状态下，通过改变氯化钙粒度，反应温度及系统压力，利用Marquart非线性优化方法进行实验数据模拟计算，对气固相化学热泵系统中的工质对CaCl2／CH3OH的络合反应动力学进行了实验研究，获取了具有一定机理、关联众多影响因素的络合反应动力学模型。结果表明：氯化钙同甲醇的络合反应符合收缩园柱形表面化学反应的机理；甲醇蒸发器温度及氯化钙样品的预络合度在不同条件下对其络合反应动力学的影响程度不同；在本实验条件下，氯化钙粒度对络合反应特性影响相对较小。该模型弥补了前人实验域较小，关联因素少等不足。对氯化钙／甲醇体系化学热泵的设计和开发有着十分重要的理论和实际意义。     

大气环境中先进与实用NH3测量技术进展

NH3是大气的重要组成部分,对于中和酸性气体和维持生态平衡起着重要作用。但同时作为大气污染物,NH3严重地影响着人类生存环境。而且气态NH3可以与硫酸、硝酸和盐酸发生化学反应而形成的铵盐,进而增加大气污染物PM2．5颗粒物的浓度。因此,大气环境中NH3体积分数精确测量越来越受到人们的重视。介绍了近年来6种先进大气NH3体积分数检测技术（TDLAS,PAS,CRDS,DOAS,TDLAS和纳米材料传感器）的研究方法与研究进展,总结并归纳了这些技术的特点,同时,选择有代表性的测量实验结果进行分析对比。简要介绍了4种实用大气NH3检测技术（湿化学、CIMS,IMS和金属半导体传感器）的特点与研究现状。     

Mechanism,kinetics and atmospheric fate of CF3CHCH2, CF3CFCH2, and CF3CFCF2 by its reaction with OH-radicals: CVT/SCT/ISPE and hybrid meta-DFT methods

The dual level direct dynamic study is carried out for the reactions of CF₃CHCH₂, CF₃CFCH₂ and CF₃CFCF₂ with hydroxyl radicals. The dynamic calculations are performed using the variational transition state theory (VTST) with interpolated single-point energies (ISPE) method at M06-2X/MG3S//M06-2X/6-31+G(d,p) level of theory. All the possible reactions such as abstraction and addition–elimination pathways are explored for the title reactions. The temperature dependent rate coefficients using canonical variational transition state theory with small curvature tunneling for the reaction of OH radicals with test molecules over the temperature range of 200–3000 K are computed. The predicted rate coefficients (in 10⁻¹² cm³ molecule⁻¹ s⁻¹) using CVT/SCT/ISPE methodology for the reaction of CF₃CHCH₂, CF₃CFCH₂ and CF₃CFCF₂ with OH radicals are 1.48, 1.02 and 1.77, respectively, are in good agreement with reported ones at 298 K. The atmospheric lifetimes for the test molecules CF₃CHCH₂, CF₃CFCH₂ and CF₃CFCF₂ are calculated at 277 K to be 8, 11 and 6 days, respectively. Global warming potentials are also reported for the different time horizon of 20, 100 and 500 years.     

基于OMI数据的兰州及附近地区大气边界层SO2量值变化初步分析

环境遥感是遥感技术应用的重要领域。随着高光谱遥感技术和定量遥感理论的发展,利用OMI、MODIS等数据开展大气SO²分布的研究得到关注。OMI是新一代大气成分探测传感器,其痕量数据产品OMSO²在反演大气SO²量值中有较好的效果。选取2005年2、5、8、11月及2005~2008年各年2月每日的OMI Level-2痕量数据,采用遥感和GIS方法,对兰州及附近地区大气边界层SO²空间分布、季节变化和冬季年际变化进行了分析。结果表明:研究区内SO²量值呈离散面状分布,兰州-白银、金昌是两个明显的高值区;冬季SO²量值明显高于其他季节,年际变化波动比较明显。研究表明,利用OMI Level\|2痕量数据产品,能够对较大尺度范围人类活动排放SO²状况进行检测和评估。     

The behaviour of the multi-layer perceptron and the support vector regression learning methods in the prediction of NO and NO2 concentrations in Szeged, Hungary

The main aim of this paper is to predict NO and NO₂ concentrations 4 days in advance by comparing two artificial intelligence learning methods, namely, multi-layer perceptron and support vector machines, on two kinds of spatial embedding of the temporal time series. Hourly values of NO and NO₂ concentrations, as well as meteorological variables were recorded in a cross-road monitoring station with heavy traffic in Szeged, in order to build a model for predicting NO and NO₂ concentrations several hours in advance. The prediction of NO and NO₂ concentrations was performed partly on the basis of their past values, and partly on the basis of temperature, humidity and wind speed data. Since NO can be predicted more accurately, its values were considered primarily when forecasting NO₂. Time series prediction can be interpreted in a way that is suitable for artificial intelligence learning. Two effective learning methods, namely, multi-layer perceptron and support vector regression are used to provide efficient non-linear models for NO and NO₂ time series predictions. Multi-layer perceptron is widely used to predict these time series, but support vector regression has not yet been applied for predicting NO and NO₂ concentrations. Three commonly used linear algorithms were considered as references: 1-day persistence, average of several day persistence and linear regression. Based on the good results of the average of several day persistence, a prediction scheme was introduced, which forms weighted averages instead of simple ones. The optimization of these weights was performed with linear regression in linear case and with the learning methods mentioned in non-linear case. Concerning the NO predictions, the non-linear learning methods give significantly better predictions than the reference linear methods. In the case of NO₂, the improvement of the prediction is considerable, however, it is less notable than for NO.     

乙基甲基咪唑磷酸二乙酯+水/乙醇/甲醇二元溶液混合热及比热容的测量与关联

离子液体是一类新型绿色溶剂,具有蒸汽压极低,不挥发,不易燃,宽液程和良好的热稳定性,对许多有机物和无机物有良好的溶解性。前期的研究发现,离子液体乙基甲基咪唑磷酸二乙酯[EMIM][DEP]与H_2O、C_2H_5OH和CH_3OH有良好的溶解性,所构成的二元溶液表现出对拉乌尔定律显著的负偏差,这些性质使得离子液体[EMIM][DEP]有可能成为吸收制冷/热泵循环的新型吸收剂。二元工质溶液[EMIM][DEP]+H_2O/C_2H_OH/CH_3OH的混合热以及比热容是分析吸收制冷/热泵性能重要的热力学基础数据之一。本文采用绝热量热法对[EMIM][DEP]分别与水,乙醇和甲醇所构成的3个二元溶液体系,在25℃以及不同浓度下的混合热进行了测量,并采用Redlich-Kister方程对数据进行了关联。实验结果表明,[EMIM][DEP]与水,乙醇和甲醇的混合过程均为放热过程,混合热大小次序是H_2O>CH_3OH>C_2H_5OH。对3个二元溶液体系在不同温度和浓度下的比热容进行了测量,并采用浓度的多项式函数对其进行关联。结果发现,离子液体溶液的比热容随温度的增加而线性增加,随离子液体的含量增加而降低。